4. site 872 - €¦ · water depth (drill-pipe measurement from sea level, m): 1082.1 total depth...

Premoli Silva, L, Haggerty, J., Rack, F., et al., 1993Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 144

4. SITE 872

Shipboard Scientific Party

HOLE 872A

Date occupied: 2 June 1992

Date departed: 3 June 1992

Time on hole: 1 day

Position: lO<mδSOK 162°51.960'E

Bottom felt (rig floor, m; drill-pipe measurement): 1094.5

Distance between rig floor and sea level (m): 10.9

Water depth (drill-pipe measurement from sea level, m): 1083.6

Total depth (rig floor, m): 1238.5

Penetration (m): 144.0

Number of cores (including cores with no recovery): 18

Total length of cored section (m): 144.00

Total core recovered (m): 123.63

Core recovery (%): 86

Oldest sediment cored:Depth (mbsf): 143.7Nature: phosphatized chalkAge: middle Eocene

Hard rock:Depth (mbsf): 144.0Nature: basalt

HOLE 872B



Time on hole: 1 day, 20 hr, 30 min

Position: 10°05.808'N, 162°51.996^









Core recovery (%): 30

Oldest sediment cored:Depth (mbsf): 136.0Nature: pelagic sediment infilling fractures in basaltAge: early Santonian

1 Premoli Silva, I., Haggerty, J., Rack, F., et al., 1993. Proc. ODP, Init. Repts.,144: College Station, TX (Ocean Drilling Program).

Shipboard Scientific Party is as given in the list of participants preceding thecontents.

Hard rock:Depth (mbsf): 136.0Nature: basalt

HOLE 872C



Time on hole: 23 hr, 45 min

Position: 10°05.62'N, 162°52.002'E









Core recovery (%): 98.5

Oldest sediment cored:Depth (mbsf): 141.7Nature: foraminifer oozeAge: late Oligocene

Hard rock:

Depth (mbsf): 141.7Nature: basalt

Principal results: Site 872 is located at 10°05.85'N, 162°51.96'E at 1084 mwater depth, on the central portion of Lo-En Guyot, approximately 148.2km from Anewetak Atoll in the northern Marshall Islands. Lo-En Guyotand the living atoll Anewetak, located to the northwest, are bathymetricfeatures that share the same volcanic pedestal. In the Marshall Islands area,the association of atolls with adjacent guyots is prevalent (Fig. 1).

The guyots in the Marshall Islands region have pelagic caps thatrange in thickness from virtually 0 to 150 m. The thickness of anindividual pelagic cap appears to be strongly correlated with both thedepth of the guyot (related to the length of the depositional history) andthe size of the guyot (less erosion near the perimeter of the summit). Ofthe guyots surveyed on the 1988 cruise of the Moana Wave(MW8805), the pelagic cap atop Lo-En Guyot appears to be the mostcomplete in the region. Recovering the pelagic cap sediments was akey objective of drilling on this guyot; therefore, on the basis of the3.5-kHz echo-sounder records, the position of Site 872 was selectedin the thickest portion of the pelagic cap on Lo-En Guyot.

The objectives at this location were (1) to recover pelagic sedi-ments for high-resolution stratigraphy and for reconstructing thepaleoceanography in this sector of the Pacific; (2) to relate the acous-tic stratigraphy of the pelagic cap to its depositional and diagenetichistory and correlate seismic reflectors with those seen in othersettings; (3) to date the interface between the pelagic cap and theunderlying platform, and to infer the age and cause of platformdrowning; (4) to establish the characteristics of platform carbonatefacies and facies changes with time; (5) to compare the stratigraphyand facies of Lo-En Guyot with Anewetak; and (6) to establish theage of the basement.

Three holes were drilled at Site 872. Hole 872A is located 150 mnorthwest of Hole 872B, and Hole 872C is located 106 m north of

105

SITE 872

Hole 872B; all three holes were offset 75 m from the acoustic beacondeployed at this site. The unusual distance between the three holeswas chosen to prevent or diminish the chance that drilling disturbancein the vicinity of one drill hole would disrupt the physical propertiesof the ooze within another drill hole in the pelagic cap. Experiencewith the exceptionally soupy, winnowed foraminifer ooze from Site871 on Limalok Guyot guided this decision.

Holes 872A and 872C were cored with the advanced hydraulicpiston cores (APC) to 143.7 and 139.5 mbsf, respectively, whererefusal occurred at the boundary between late Oligocene and middleEocene sediments. These holes were continued by extended corebarrel (XCB) coring to 144 mbsf with a total recovery of 85.9% (Hole872A) and 148 mbsf with a total recovery of 98.5% (Hole 872C),respectively. Hole 872B was spudded using the rotary core barrel(RCB) system. After spot coring the pelagic cap, cores were recoveredfrom 135.2 to 192.5 mbsf total depth (TD), for a total recovery of30.1% inHole872B.

The APC cores recovered from Hole 872A were winnowed andvery soupy, similar to the material recovered from the pelagic cap atLimalok Guyot (Site 871). The lack of cohesion in these sedimentswhen they are drilled, and the subsequent handling of these water-laden cores on deck, result in cores that are poor candidates forhigh-resolution stratigraphy. To salvage Site 872 for the high-resolu-tion stratigraphy objective, we implemented a different method ofhandling cores upon arrival on the rig floor when drilling Hole 872C.Excess water at the top of a core was removed with a device, nameda piglet, that was inserted into the core liner while the core was uprightwithin the core barrel on the rig floor. Additional excess water wasremoved after the core was cut into sections. Each section was turnedupright to permit water to rise to the top for removal and the core linerwas then trimmed at the top of the ooze. In this manner, we were ableto recover cores in which the details of mottling, sharp changes incolor and lithology, and sedimentary structures could be observed.

Four lithologic units were recognized at Site 872 using a combi-nation of visual core descriptions, augmented with smear slide andthin-section data. Age identification of these units is based on calcare-ous nannofossils and planktonic foraminifers studied in smear slides,washed residues, and thin-section samples. The units identified are,from top to bottom, as follows:

Unit I (Hole 872A, 0-143.6 mbsf; Hole 872C, 0-141.7 mbsf)consists of white to pale brown nannofossil foraminifer ooze interca-lated with foraminifer ooze of Pleistocene to late Oligocene age.Sediment composition allowed the division of Unit I in two subunits.The calcium carbonate content of Unit I is almost 100%, and intersti-tial water analysis indicates minimal diagenesis. Subunit IA (Hole872A, 0-30.2 mbsf; Hole 872C, 0-32.9 mbsf) is comprised of whiteto very pale brown nannofossil foraminifer ooze and intercalatedforaminifer ooze of Pleistocene to late Miocene age. Subunit IB (Hole872A, 30.2-143.6 mbsf; Hole 872C, 32.9-141.7 mbsf) is comprisedof very pale brown homogeneous foraminifer ooze with a mediumsand texture that is well sorted, winnowed, and of late Miocene to lateOligocene age. The transition between the two subunits is marked byan interval of sediment characterized by a mixture of nannofloras andfaunas of different zones followed by a disconformity. This mixed andincomplete interval spans the late middle to early late Miocene.Within the lower Miocene, another disconformity, representing ahiatus of approximately 5 m.y., was observed in Subunit IB at about100 mbsf in both holes. The sedimentary succession across the Oligo-cene/Miocene boundary appears to be complete.

Unit II (Hole 872A, 143.6-143.7 mbsf; Hole 872B, 135.2-135.36mbsf) includes three subunits. Subunit IIA is composed of phospha-tized middle Eocene chalk containing pebbles of basalt, conglomer-ates, and volcaniclastics (Hole 872A, 143.6-143.7 mbsf). Subunit HBconsists of phosphatized volcaniclastic sandstone of indeterminateage (Hole 872B, 135.2-135.3 mbsf). Subunit HC is comprised of aconglomerate, coated by a shiny dark brown to black veneer thatencloses phosphatized lithoclasts, <l to 3 cm in diameter (Hole 872B,135.3-135.36 mbsf). The phosphatized lithoclasts contain volcani-clastic debris set in a pelagic limestone matrix of latest Santonian toearly Campanian age. The lithoclasts are redeposited in pelagic sedi-ment of late Paleocene age.

Unit III (Hole 872B, 135.36-135.41 mbsf) consists of subangularbasalt clasts, 0.5 to 4 cm in size, in a pelagic limestone matrix of lateearly Santonian age in contact with slightly altered basalt.

Unit IV (Hole 872A, 143.7-144.0 mbsf; Hole 872B, 135.41-192.5mbsf; Hole 872C, 141.7-148.0 mbsf, 872C) is composed of differen-tiated alkali olivine basalt as massive flows and flow-top breccias.The uppermost 71 cm of Unit IV in Hole 872B has a few fracturesinfilled with pelagic sediments of early Santonian age. These pelagicsediments are increasingly phosphatized with depth and contain somereworked planktonic foraminifers of late Turonian age. A sparselyolivine-phyric basalt identifies the uppermost flow in Holes 872A and872B; in Hole 872C, the upper volcanic flow is a highly altered olivinebasalt (142.75-143.10 mbsf) that belongs to a different flow.3 Thebrecciated flow tops in several flow units in Hole 872B suggest thatthese flows were erupted subaerially in a short time, which precludedsoil development on top of the flows. In Hole 872C, the basalt unit isoverlain by a 10-cm-thick dark gray clay that appears to be analteration product of the basalt. Basalt samples display natural rema-nent magnetization (NRM) intensities of <IO A/m and usually have anearly univectorial magnetization. Inclinations of the characteristicremanent magnetization are negative and range from -41° to -61°.

Logging in Hole 872B was initially planned (1) to gain definitiveinformation about the presence or absence of additional sedimentintervals in the basalt, and (2) to obtain a clearer understanding of theunconformity between the upper Oligocene foraminifer ooze and theunderlying hardground. The condition of the hole was less thanfavorable; however, with difficulty, it was cleaned to total depth inpreparation for logging. However, logging proved to be unsuccessful,as both of the geochemical tools onboard the ship would not properlycalibrate during in-pipe checks, and a tool run encountered a bridgeonly 4 m beneath the pipe. The prospects of obtaining any loggingresults did not justify additional logging time.

BACKGROUND AND OBJECTIVESSite 872 (proposed Site Pel-3) is located at 10°05.85'N,

162°51.96'E, in a water depth of 1084 m, on the central summitregion of Lo-En Guyot in the northern Marshall Islands. Lo-EnGuyot is the sibling edifice of the living atoll Anewetak, locatedto the northwest; both bathymetric features share the same vol-canic pedestal. In the Marshall Islands area, the association ofatolls with adjacent guyots is prevalent (Fig. 1).

The guyots in the Marshall Islands region have pelagic capsthat range in thickness from virtually 0 to 150 m. The thicknessof an individual pelagic cap appears to be strongly correlated withboth the depth of the guyot (related to the length of the deposi-tional history) and the size of the guyot (less erosion near theperimeter of the summit). Of the guyots surveyed on the 1988cruise of the Moana Wave (MW8805), the pelagic cap atop Lo-EnGuyot appears to be the most complete in the region and was akey objective, therefore, of drilling on this guyot.

Rock dredges, obtained during Cruise MW8805 from thesouthern side of Lo-En Guyot, contain breccia composed ofangular fragments of vesicular basalt floating in a calcareousmatrix of shallow-water debris and planktonic foraminifers (Lin-coln et al., in press). The most abundant planktonic foraminifersare specimens belonging to Favusella washitensis and possiblyother species of favusellids. Associated in these rocks are alsocommon specimens of the calpionellid species Colomiella recta.The stratigraphic distribution of Favusella is from early Albianto Cenomanian; the distribution of Colomiella is from late Aptianto early Albian. Both of these species, although planktonic, gen-erally occur in a near-shore environment and are missing in the

3 In Hole 872C, the basement contact at the top of Lithologic Unit IV is placedat 141.7 mbsf within Section 144-872C-17X-CC. The actual depth of this contact isthought to be at 142.5 to 142.75 mbsf based on a change in drilling parameters.

106

SITE 872

14°N

1OC

North Wod-EnGuyot

( 8 6 M a )

5 n ^ r

σ %•ε?

t$$\/^ v Woden-KopakiA

Lobbadθde ~~u s

Gtvyof(82,Ma)

0

®"ùWo θjebato Guyof\ nn3 (138 Ma)

Sites 873-877Ma)

Anewetak -«• Atoll

U 7 6 M a >1 Lo-En Guyot

Site 872

P160°E 164° 1 6 8 C 172 C

Figure 1. Bathymetry around the Marshall Islands. Contour interval is 1000 m, and the ages shown in parentheses are radiometric dates of basalts collectedover a number of different surveys. Radiometric ages from Davis et al. (1989) and Pringle (1992). Figure revised from Hein et al. (1990). The locations ofLo-En Guyot and Site 872 are indicated.

open-ocean, deep-water deposits. Their occurrence indicates thata shallow-marine environment existed at least in the early tomiddle Albian on Lo-En Guyot. This interpretation of age andenvironment is supported by the presence of poorly preservedspecimens of the planktonic foraminifer Prαeglobotruncαnαstephαni, which demonstrates that Lo-En Guyot was already in apelagic regime by latest Albian time.

The shallow-water debris contained within the matrix of thisbreccia are abundant bryozoan fragments, echinoid debris, spongespicules, and possibly mdist fragments. Numerous agglutinatedforaminifer specimens related to Vercorsellα and/or Sαbαudiα alsooccur; their presence suggests that a carbonate platform was aliveon Lo-En Guyot by Aptian-Albian time. The dredged rocks wereprobably deposited in an outer slope environment, as indicated bythe mixture of basalt fragments, shallow-water debris, and open-marine planktonic foraminifers (Lincoln et al., in press).

The same dredge haul on Lo-En Guyot includes a manganese-encrusted foraminifer limestone that is conceivably Coniacian inage. The planktonic foraminifer assemblage contains whiteinel-lids and marginotruncanids, as well as one specimen of Dicαrinellα

concαvαtα; this may identify the assemblage, therefore, as belong-ing to the Dicarinella concavata Zone. Another breccia from thisdredge haul is composed of angular basalt pebbles floating in aplanktonic foraminifer-rich matrix attributable to the Globotrun-canita elevata Zone of early Campanian age (Lincoln et al., inpress).

All the dredge haul data demonstrate that Lo-En Guyot (1)erupted before early Albian time, (2) supported a shallow-watercarbonate environment during most of the Albian, and (3) sub-sided into the pelagic realm by latest Albian time. No evidenceexists that this guyot returned to sea level during the Late Creta-ceous, although the Campanian age of volcanic breccias recov-ered from the flanks of this guyot could indicate an erosionalevent potentially caused by uplift that coincides with the eruptionof adjacent Anewetak Atoll. The radiometric age of 75.9 ± 0.6 Mafor Anewetak basalt indicates that Lo-En's sibling erupted duringpassage over either the Rurutu or Rarotonga hotspots in the LateCretaceous (Lincoln et al., in press); this coincides with the LateCretaceous uplift events at nearby Wodejebato and Ruwituntun.The SeaMARC II side-scan imagery of Lo-En Guyot shows two

107

SITE 872

volcanic cones that breach the surface of the pelagic cap along thecentral, southwestern region of the summit of the guyot (see"Underway and Site Geophysics" section, this chapter). Thesevolcanic cones have not been radiometrically dated and may berelated to Late Cretaceous or younger volcanism.

The primary objectives planned for Site 872 (Pel-3) were (1)to recover pelagic sediments for high-resolution stratigraphy andfor reconstruction of the paleoceanography of this sector of thePacific; (2) to relate the acoustic stratigraphy of the pelagic capto its depositional and diagenetic history and correlate reflectorswith those seen in other settings; (3) to date the interface betweenthe pelagic cap and the underlying platform, and to infer the ageand cause of platform drowning; (4) to establish the charac-teristics of the shallow-water facies and changes with time; (5) tocompare the stratigraphy and facies of Lo-En Guyot with its livingsibling Anewetak; and (6) to establish the age of the basement.

Drilling at Site 872, in the central portion of Lo-En Guyot, didnot recover a carbonate platform; therefore, the carbonate plat-form objectives cannot be addressed directly. Cores from thepelagic cap, as well as the igneous edifice, were recovered, butthe anticipated carbonate platform was absent. The remainder ofthe primary objectives can be addressed with the preliminaryshipboard studies and additional shore-based studies.

OPERATIONS

Site 871 to Site 872The ship track to the second drill site led to the northwest

between Jaluit and Ailinglapalap atolls, then passed south of UjaeAtoll, in the Republic of the Marshall Islands. An average transitspeed of 11.8 kt was maintained. A 200-in.3 water gun wasstreamed, and the approach survey began about 10 nmi southeastof proposed Site Pel-3. The seismic line was shot along a south-east-northwest transect over only the southern portion of Lo-EnGuyot; a sonobuoy experiment was simultaneously conductedduring the seismic profiling. When proposed Site Pel-3 wascrossed, the profile continued about 6 nmi before the ship re-versed course and recrossed the site. A positioning beacon wasdropped at 1352L (L = local time) on 2 June 1992 to beginoperations at Site 872. The total distance traveled, includingsurveys, was 644 nmi.

Site 872 (Pel-3)—Lo-En GuyotSite 872 (proposed Site Pel-3) is centrally located on Lo-En

Guyot, a sibling guyot adjacent to Anewetak Atoll and on thesame volcanic pedestal. The setting, geology, and operationalplan were virtually identical to those of Site 871, except that thelimestone section was expected to be older and better indurated.The site location was chosen to obtain the maximum thickness ofthe pelagic cap on top of the guyot.

Hole 872A

The seismic gear was recovered following the beacon launch;the vessel took station on the beacon and the pipe trip began. Thetrip was faster than at Hole 871A because of the shallower waterdepth and because it was not necessary to drift and measure thedrill string. A "geoset" drag-type outer bit was used with theAPC/XCB bottom-hole assembly (BHA), primarily to providesmoother drilling and greater compatibility with the XCB shoe inthe limestone section. Special subs were added to the BHA toprovide the option of using the motor-driven core barrel (MDCB)to core limestone at the bottom of the planned APC/XCB holes.Again, a "pig" was pumped through the drill string to dislodgeany loose rust before APC operations began.

The initial spud attempt was at 1730L on 2 June 1992, but theAPC assembly apparently did not seat at the landing sub becausepressure did not build up with pump circulation. The APC wasrecovered, inspected, and found to be still pinned together. It wasrun back to the BHA and landed about 15 m too high. The pig hadonly traveled down the drill string to the MDCB latch sub, whereit became lodged when circulation could bypass it through theslots in the inner wall of the sub. The pig eventually was dislodgedthrough vigorous "spudding" with the APC and using high pumpcirculation rates with the wireline blowout preventer (BOP)closed. A successful spud was accomplished at 1800L. The recov-ery of a mud-line core indicated a seafloor depth of 1094.5 mbelow the dual-elevator stool (DES) or 1083.6 m below sea level.

Further delays were experienced as coring continued. A shear-pin stub jammed the APC after Core 144-872A-2H; it was disas-sembled and rescoped. Core 144-872A-3H had no recovery be-cause the core-catcher flapper had stuck open. After Core144-872A-8H, a fuse blew on the coring winch control and anadditional half hour of downtime ensued. As soon as mechanicalproblems abated, hole trouble began. Below about 70 mbsf, soupyforaminifer ooze flowed into the hole and accumulated aroundand above the BHA. The drill string became stuck while Core144-872A-11H was being retrieved from 100 mbsf and an over-pull of 130,000 lb was required to free it.

Cores 144-872A-5H to -12H were magnetically oriented; heat-flow data were collected during recovery of Cores 144-872A-4H,-7H, and -10H using the Adara shoe. The orientation and heat-flow programs had to be discontinued because of adverse holeconditions. Coring continued with the liberal use of mud flushes,and the hole seemed to stabilize below 120 mbsf. Incompletestrokes of the core barrel on Cores 144-872A-11H and -12Happear to coincide with a reflector on the 3.5-kHz echo sounderrecord, but no hard strata were noted in the cores or by drillingparameters. Full stroke then was regained until Core 144-872A-17H (to 143.7 mbsf), when the core barrel struck middle Eocenephosphatized foraminifer limestone that contained fragments ofbasalt and a reworked, phosphatized Santonian pebbly conglom-erate.

Coring then switched to the XCB mode. Core 144-872A-18Xencountered hard drilling with an extremely low rate of penetra-tion (ROP). The core barrel was pulled after only 30 cm ofpenetration; it contained 24 cm of basalt core.

Plans to attempt MDCB cores of limestone were abandonedbecause of the unexpected occurrence of basalt. A second APChole was postponed until another method of handling the highlyfluid sediment cores could be initiated. Operational plans wereconfused further because we had intended to protect a deep RCBpenetration against the unstable pelagic section by emplacing adrill-in casing (DIC) string through the soft upper sediments. Notknowing whether more sediments existed below the basalt unit,we decided to take a maximum positioning offset from Hole 872Aand drill at least 50 m into hard rock. If only basalt was encoun-tered, the site would be abandoned. If more sediments were found,the hole would continue toward the original objectives and holeconditions would be dealt with as conditions dictated.

Hole 872B

During the round trip of the drill string, the vessel was offsetto a point 75 m southeast of the beacon (and 150 m southeast ofHole 872A). A backup beacon was launched at the new locationwhile the pipe trip was in progress. Hole 872B was spudded at1900L on 3 June 1992 and washed to 77 mbsf. Coring with theRCB began at 77 mbsf in an attempt to recover ooze associatedwith the approximate sub-bottom depth of the seismic reflector

108

SITE 872

and also the interval not recovered by the APC in Hole 872A.After three successive cores, to 106 mbsf, only a few lumps offirm foraminifer ooze were recovered and hole problems returned.The hole was drilled ahead from 106 to 135 mbsf, the "washbarrel" was recovered, and continuous coring began.

Fragments of a hardground, as well as a phosphatized lime-stone conglomerate in contact with the underlying basalt, wererecovered from Hole 872B at 135.4 mbsf. The basalt was quitehard and dense; coring ROP averaged only about 3 m/hr. Holeconditions stabilized by the time hard-rock coring began, andoperations proceeded smoothly with an average ROP of about 2.8m/hr and a core recovery rate of over 50% (Table 1).

The drill string unexpectedly became stuck just after the corebarrel for Core 144-872B-9R was dropped, apparently the resultof loose rocks in the hole beside the BHA. The bit was about 13m above total depth, so circulation continued at a slightly elevatedpressure; however, the pipe could not be rotated or moved verti-cally. After several minutes of "working" the pipe to free it (asmuch as 150,000 lb up and 60,000 lb down), multiple attemptswere made to jar the BHA loose with the drilling jars. Unfortu-

Table 1. Coring summary, Site 872.

Date(June

Core no. 1992)Time(Z)

Depth Cored Recovered Recovery(mbsf) (m) (m) (%)

144-872A-1H2H3H4H5H6H7H8H9H10HUH12H13H14H15H16H17H18X

Coring totals

144-872B-1R2R3R4R5R6R7R8R9R

Coring totals

144-872C-1H2H3H4H5H6H7H8H9H10HI I H12H13H14H15H16H17X18X

071507500845094010051035113512101340143515101650174518101845192020102305

080008450930122516352020231504550945

035504150445050505300600063007050755083009050940102011051135121014501700

0-7.57.5-17.017.0-26.526.5-36.036.0-45.545.5-55.055.0-64.564.5-74.074.0-83.583.5-93.093.0-100.0100.0-102.0102.0-111.5111.5-121.0121.0-130.5130.5-140.0140.0-143.7143.7-144.0

77.3-87.087.0-96.696.6-106.3135.2-144.8144.8-154.5154.5-164.0164.0-173.1173.1-182.6182.6-192.5

0.0-9.09.0-18.518.5-28.028.0-37.537.5^7.047.0-56.556.5-66.066.0-75.575.5-85.085.0-94.594.5-104.0104.0-106.0106.0-115.5115.5-125.0125.0-130.0130.0-139.5139.5-146.0146.0-148.0

7.59.59.59.59.59.59.59.59.59.57.02.09.59.59.59.53.70.3

7.698.570.007.688.168.768.729.419.219.057.240.008.518.218.799.004.390.24

102.090.20.080.885.992.291.899.096.995.2103.00.089.686.492.594.7118.080.0

144.0 123.63

9.79.69.79.69.79.59.19.59.9

0.080.050.050.744.370.878.074.507.23

85.9

0.80.50.57.7

45.09.2

88.747.373.0

86.3

9.09.59.59.59.59.59.59.59.59.59.52.09.59.55.09.56.52.0

25.96

8.849.299.819.148.738.999.079.429.449.768.753.089.499.507.829.153.731.71

30.1

98.297.8103.096.291.994.695.599.199.3103.092.1154.099.9100.0156.096.357.485.5

Coring totals 148.0 145.72 98.5

nately, the jars could not be cocked for either up or down blowsby introducing left-hand torque. After left-hand torque had beenput into the string several times, about 14,000 ft-lb was appliedand the pipe suddenly spun to the left and came free in the hole.The weight indicator showed a loss of about 34,000 lb, indicatingthat a BHA connection had backed off! The free upper portion ofthe drill string was kept just above the backed-off connectionwhile the motion compensator was activated; the string was low-ered carefully with slow rotation and moderate circulation. Anabrupt rise in circulating pressure, followed by weight and torqueindications, showed that the connection reengaged successfully.When only moderate right-hand torque was applied, the stuckBHA suddenly broke free and normal parameters were regained.

Only one core remained to fulfill the drilling objectives of thehole; the operation was completed with the undertorqued connec-tion. A mud flush was circulated and the final core was cut andrecovered without incident.

The contact of the pelagic cap with the hardground, the contactof the conglomerate with the basalt, and the presence or absenceof sediments in the basalt, were of particular scientific interest sopreparations were made to log the hole. A wiper trip was made toprepare the hole for logging. The condition of the hole was foundto be less favorable than anticipated; the string encountered about30,000 lb drag as it was lowered from 90 mbsf to the basalt contactat 145 mbsf. Considerable difficulty was experienced in workingthe bit past a ledge at the contact, but the hole eventually wascleaned out to total depth. Another viscous mud flush then wascirculated and the bit was released with the rotary shifting tool(RST). The end of the drill string was pulled to just below thebasalt contact for logging, with the intention of raising the stringpast the contact as the logging tool approached from below.

Logging proved to be unsuccessful because both geochemicaltools on board the ship would not calibrate properly during in-pipechecks. When the second backup tool also failed to calibrate inthe pipe, an attempt was made to record a log anyway. Only 4 mbeneath the pipe, the tool encountered a bridge that had formedduring the elapsed 4 hr from the wiper trip. The prospects ofobtaining any logging results did not justify additional loggingtime. The logging tools were recovered and rigged down.

The drill string was recovered; the BHA was changed to theAPC/XCB configuration. All BHA connections were checked fortorque, and the connection between the body and the lower sub ofthe drilling jar was identified as the back-off culprit.

Hole 872C

On 5 June 1992, the first APC core found the seafloor at 1093m from driller's datum. The soft pelagic section was cored in aneffort to duplicate Hole 87 2A and fill in unrecovered gaps in thesection. To salvage Site 872 for the high-resolution stratigraphyobjective, we implemented a different method of handling coresupon arrival on the rig floor.

Excess water at the top of a core was removed with a device(named a "piglet") that was inserted into the core liner while thecore was upright within the core barrel on the rig floor. Thesurficial water flowed through the central portion of the pigletuntil the piglet contacted the upper surface of the sediment. Thecore barrel was then placed horizontally for removal of the coreliner and draining of excess water. The piglet inside the core linerprevented the sediment from sloshing during the removal of theliner from the horizontally placed core barrel and during thetransport of the core to the catwalk for subsequent labeling andcutting into sections. After the core was cut into sections, eachsection was turned upright to permit additional excess water torise to the top for removal, and the resulting void was removedby trimming the core liner to prevent the resuspension and distur-bance of the sediment. In this manner, we were able to achieve

109

SITE 872

recovery of cores in which details of mottling, sharp changes incolor and lithology, and sedimentary structures could be ob-served.

Magnetic orientation was attempted for all APC cores startingwith Core 144-872C-4H. An incomplete stroke was indicated onCore 144-872C-12H from 104 mbsf, but full stroke was regainedon Cores 144-872C-13H and -14H. Cores 144-872C-15H and-16H had incomplete stroke in upper Oligocene foraminifer ooze.

The XCB system was used to core from 139.5 mbsf. A hardcontact was encountered in Core 144-872C-17X, where upperOligocene foraminifer ooze was found to overlie clay and basalt;the contact was noted by changes in the drilling parameters at142.5 mbsf.4 Core 144-872C-17X became jammed immediatelyupon encountering the harder material. The ROP through theunrecovered 4.5 m seemed high for the XCB in basalt; an addi-tional core was attempted in an effort to recover more transitionalmaterial from the contact zone. A higher circulation rate was usedfor Core 144-872C-18X, which penetrated 2 m in 1 hr. The corebarrel recovered 1.71 m of nicely trimmed core of altered basalt.

As sedimentary strata were not located within the 50 m drilledbeneath the basalt contact, the achievable objectives of the sitewere considered fulfilled and the drill string and beacons wererecovered. JOIDES Resolution departed the site at 0800L on 6June 1992.

UNDERWAY AND SITE GEOPHYSICS

Introduction

West of the Ralik Chain, over a 1000 km northwest of LimalokGuyot, a cluster of volcanoes marks the westernmost extent of thesouthern Marshall Islands (Fig. 1). This volcanic cluster consistsof two atolls flanked by a number of guyots. Ujlan Atoll lies onthe western edge of the cluster, Anewetak Atoll (formerly Eniwe-tok Atoll) marks the northern perimeter, and Lo-En Guyot formsthe eastern edge.

Information on the reefs and volcanoes within this clustercomes primarily from drilling on Anewetak Atoll during Opera-tion Crossroads in the late 1940s. Two holes drilled on Anewetakduring Operation Crossroads reached volcanic basement. HoleF-l, located on Elugelab Island in the northwest, struck volcanicbasement at 1405 m; Hole E-l, located on Parry Island in thesoutheast, encountered basalt cuttings at 1267 m and solid basaltat 1282 m (Schlanger, 1963). Shallow-water carbonate sedimentsof Eocene age lie directly over the basalt. Seismic refractionstudies at Anewetak (Raitt, 1957) showed that the upper surfaceof the atoll's volcanic foundation slopes gently to the northwest,and that basement was shallower beneath Anewetak Atoll andParry Island than beneath Elugelab Island. The basalt, originallydated by K/Ar methods as being in the range of 51.4 to 61.4 Ma,has subsequently been dated by 4 0Ar/3 9Ar methods to obtain atotal fusion age of-77 Ma (M.S. Pringle, unpubl. data).

Lo-En Guyot, centered about 10°10'N and 163°52'E, lies -150km south-southeast of Anewetak Atoll. Before the site surveywork conducted in 1988, little was known about the detailedmorphology of Lo-En Guyot. A ridge extending from the southflank of Anewetak Atoll connects the edifice with that of Lo-EnGuyot. In plan-view, Lo-En's edifice resembles a square with amaximum width slightly >50 km. A small seamount lies north ofthis edifice, straddling the ridge between Lo-En Guyot andAnewetak Atoll. Two more small seamounts with diameters <14km lie west-southwest of Lo-En Guyot.

See Footnote 3.

Site Survey—Moα/iα Wave Cruises MW8805and MW9009

As mentioned above, little was known about Lo-En Guyotbefore the site survey work of Moana Wave Cruises MW8805 andMW9009. Cruise MW8805 conducted the original site survey ofthis guyot, collecting a suite of geophysical data that includedSeaMARC II side-scan sonar images and swath-map bathymetry,digital single-channel seismic data, 3.5-kHz echo-sounderbathymetry, and gravity and magnetics measurements. In additionto the geophysical data, basalt and limestone were recovered inthree dredges from various depths along the flanks of Lo-EnGuyot. Cruise MW9009 returned to Lo-En Guyot to collect six-channel seismic data over the summit and to dredge a cone-shapedfeature identified in the Cruise MW88O5 data.

Lincoln et al. (in press), as part of a regional overview on themid-Cretaceous and Late Cretaceous volcanic and tectonic his-tory of the Marshall Islands, cite the contents of Cruise MW8805rock dredge (RD) 33 as evidence for the existence of a shallow-water carbonate bank on top of Lo-En Guyot during the mid-Cre-taceous. Sample RD33, taken from the southwest flank of Lo-Enat -2400 m depth, contained breccia consisting of angular frag-ments of vesicular basalt floating in a calcareous matrix of shal-low-water debris and planktonic foraminifers. The planktonicforaminifers suggest a middle to late Albian age for these rocks.Two other dredges across this guyot (RD34 and RD35) sampledshallower portions of the slope. Samples RD34 and RD35 recov-ered rocks of similar lithology from depths of -1900 and -1775m, respectively. These rocks consisted of rounded basalt cobblesand basalt pebbles in a matrix containing planktonic foraminifersof Paleogene age. Although no direct evidence existed in theCruise MW8805 data for Late Cretaceous volcanism or reefgrowth on Lo-En Guyot, Lincoln et al. (in press) postulated thatuplift and subaerial exposure of this edifice was likely around thetime of volcanic activity on Anewetak Atoll (-77 Ma).

SeaMARC II bathymetry over Lo-En shows the gross mor-phology of the edifice (Fig. 2). The summit approaches a maxi-mum diameter of -40 km in a north-south direction. In general,the 1400-m contour marks the first break in slope down from thesummit. In the side-scan images, a high-backscatter band marksthe edge of the summit (Fig. 3). The flanks of the guyot maintaina fairly uniform gradient of 15°, except in areas where shelvesextend away from the summit. These shelves are most prominentalong the north and south flanks of the guyot, and they commonlyhave slopes of <6° across their tops (Fig. 2). The southern shelfis -6 km wide, whereas the northern shelf merges with the ridgeconnecting Lo-En Guyot and Anewetak Atoll. Along the westflank of Lo-En Guyot, low-backscatter terraces -0.5 km wide liedownslope from the summit edge (Fig. 3).

A thick layer of pelagic sediments covers the central portionof Lo-En's summit (Fig. 4). Cropping out from these pelagicsediments are a number of high-backscatter cones and lobes (Fig.3). These features are especially prominent across the southernshelf. It is impossible to determine the origin of the cones (eitherigneous or sedimentary) from the side-scan and bathymetric dataalone. During Cruise MW8805, the ship fortuitously crossed oneof the summit cones (Figs. 3-4). This particular cone exhibited ahigh magnetic signature, which suggests a volcanic origin. At-tempts to sample this feature during Cruise MW9009 were unsuc-cessful.

Two profiles representative of the single-channel seismic datacollected during Cruise MW8805 are shown in Figure 4. ProfileA-A' crosses the summit in a north-south direction. Along thisprofile the presumed volcanic cone crops out from the pelagicsediments. Profile B-B' is an east-west crossing of the summitthat was used to pick the location of proposed Site Pel-3. The

110

SITE 872

10°30'N

10°00

Small-seamount

162°40'E 163°00'

Figure 2. Contoured SeaMARC II bathymetry of Lo-En Guyot. Contourinterval is 200 m. The ship tracks shown in this figure represent the seismiccoverage across this guyot. Profiles A-A' and B-B' were collected during a1988 Moana Wave cruise (MW8805), and Profile C-C' was collected duringLeg 144.

reflectors annotated in this profile mark the boundaries of thepresumed sedimentary units overlying the volcanic basement. Theinterpretation of this profile (at Pel-3) placed a sequence ofpelagic sediments 0.18 s two-way traveltime (TWT) over a rela-tively thin (<0.2 s) carbonate platform. The primary focus ofdrilling on Lo-En Guyot was the sampling of this thick sequenceof pelagic sediments and the associated internal reflectors. Unfor-tunately, Figure 4 does not clearly show the individual reflectorpackets within the pelagic sequence. Beneath the pelagic se-quence, a carbonate platform 0.14 s TWT thick presumably over-lies volcanic basement, and the "deep reflector" annotated inFigure 4 represents some sort of structure within the volcaniccomplex.

Site Survey—Leg 144

Magnetics data in addition to 3.5- and 12-kHz echo-sounderbathymetric data were collected during the transit from Site 871to Lo-En Guyot. The site survey over Lo-En Guyot consisted ofa northwest-oriented line intersecting the Cruise MW8805 single-channel line at the location of Site Pel-3 (Fig. 2). We deployedthe seismic gear at 2230Z on Julian Day (JD) 153, with a ship'sheading of 305° and a ship speed of ~6 kt. We initially used a200-in.3 water gun as a source, but the gun began to malfunctionaround 2245Z and was recovered shortly thereafter. An 80-in.3

water gun was deployed in its place. A quick repair of the 200-in.3

gun allowed us to deploy it again near the edge of the summit, at2340Z. Upon cresting the summit edge, we launched a sonobuoyat 2357Z and received a strong signal and some possible refrac-tions for ~l hr. Site Pel-3 was crossed on JD 154 at 0059Z, andwe turned shortly after to a heading of ~l 15°. The beacon marking

Site 872 was dropped on the return line at 0252Z. By 0300Z theseismic gear was recovered, and by 0315Z the ship was on station.

The purpose of running the survey line across the southeastslope of Lo-En Guyot was to collect data along its flank overwhich no previous coverage existed. Both echo-sounder and seis-mic profiles show a topographic high along the perimeter of thesummit (Figs. 5-6). The height of this feature above the first slopebreak is 98 m. Behind this perimeter high, and beneath the accu-mulated pelagic sediments, the topography remains hummockyfor ~1.5 km. The pelagic sediments thicken toward the center ofthe summit, reaching a maximum thickness of 0.18 s TWT at thelocation of Site 872. A packet of strong reflectors 0.04 s TWTthick forms the uppermost sequence of these pelagic sediments.Deeper within the section, two reflectors spaced -0.02 s TWTapart appear to shallow toward the margin of the summit inrelation to the relatively flat platform reflector. The platformreflector itself exhibits relief of <O.Ol s TWT, except directlybehind the perimeter high. The seismic data collected during Leg144 does not show much structure beneath the pelagic-platforminterface (Fig. 6).

LITHOSTRATIGRAPHY

Drilling results from the three holes on Lo-En Guyot aresummarized in a single lithostratigraphic framework (Fig. 7 andTable 2). Lithologic units are identified by color, carbonate andclay content, fossil and particle constituents, lithification, andsedimentary structures. Four major units were recognized (Fig.7): Unit I, nannofossil and foraminifer oozes; Unit II, fragmentsof an iron manganese crust, phosphatized chalk that containspebbles of the underlying unit, phosphatized volcaniclastic sand-stone, and pieces of phosphatized conglomerate consisting ofvolcaniclastic pebbles in planktonic foraminifer limestone ma-trix; Unit III, subangular basalt clasts within a planktonicforaminifer limestone; and Unit IV, basalt. In Hole 872B, cre-vasses and fractures in the upper flows of the basalt are infiltratedby planktonic foraminifer limestone from the overlying unit; inHole 872C, a thin clay layer encloses a few basalt clasts (Interval144-872C-17X-CC, 28-38 cm).

Unit IIntervals: Hole 872A, Core 144-872A-1H through Section 144-872A-

17H-3; Hole 872B, Core 144-872B- IR through to -3R; Hole 872C,Core 144-872C-1H through Section 144-872C-17X-CC, 20 cm

Depth: Hole 872A, 0-143.6 mbsf; Hole 872B, 77.3-106.3 mbsf; Hole872C, 0-141.7 mbsf

Age: Hole 872A, Pleistocene to late Oligocene; Hole 872B, middle toearly Miocene; and Hole 872C, Pleistocene to late Oligocene

Unit I consists of white (10YR 8/2) to pale brown (10YR 7/3)nannofossil foraminifer ooze intercalated with foraminifer ooze,which grades downhole into foraminifer ooze. A small amount ofterrigenous clay is dispersed within the ooze. The calcium carbon-ate content averages 96.9% (see "Organic Geochemistry" section,this chapter). Unit I is divided into two subunits based on adownhole decrease in nannofossil abundance, a correspondingcoarsening of the sediment texture, and a minor change in color.

Subunit IAIntervals: Hole 872A, Core 144-872A-1H to Section 144-872A-4H-3,

72 cm; Hole 872C, Core 144-872C-1H to Section 144-872C-4H-3Depth: Hole 872A, 0-30.2 mbsf; Hole 872C, 0-32.9 mbsfAge: Holes 872A and 872C, Pleistocene to late Miocene

Subunit IA consists mainly of white (10YR 8/2) foraminiferooze, which is interbedded with subordinate, very pale brown(10YR 8/3) nannofossil foraminifer ooze in vague layers andbands several centimeters to tens of centimeters thick. In Hole872C, several beds of foraminifer ooze 5 to 22 cm thick are

111

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9°45'N 10°00' 10°15• 10°30' 10°45'Figure 3. Side-scan images over Lo-En Guyot. In this image, dark tones represent high backscatter features, and light-gray to white tones represent low backscatter features. The dark band represents the edgeof the summit.

SITE 872

Data gap

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Proposed sitePel-3

0430ZTime (Z)

0530Z

1.3

1.8

2.3

2.6

Base of pelagic sedimentsBT

Basement reflector

Deep reflector

Figure 4. Single-channel seismic Profiles A-A' and B-B' collected during Cruise MW8805 across Lo-En Guyot. Profile A-A' shows the presumed volcaniccone that crops out from the pelagic sediments, whereas Profile B-B' is the seismic line from which Site 872 was selected. An arrow marks the location of thesite directly above the thickest sequence of the pelagic sediments. The basement reflector marked on this profile represents the bottom of the presumed carbonatecomplex. The deep reflector suggests a change in the character of the basement.

intercalated within the nannofossil foraminifer ooze. The bounda-ries between beds are sharp. Locally, gray, circular spots, about1 cm in diameter, are found in the ooze; they are probablyburrows.

The ooze in Hole 872A is strongly disturbed by drilling and issoupy, which precludes recognition of any sedimentary struc-tures. This problem was addressed by changes in core handlingfor Hole 872C; cores were stored vertically, then water wasdrained from the top of the core and from each core section andthe resulting void was removed by trimming the core liner beforethe cores were split. This resulted in somewhat improved preser-vation of sedimentary structures in the upper cores; toward thelower part of the unit, however, no significant difference in

drilling disturbance was detected between the different core han-dling techniques.

At the top of Subunit IA (Cores 144-872 A-1H and -2H andCores 144-872C-1H and -2H), the ooze contains light yellowishbrown (10YR 6/4) specks. The specks are either limonite orphosphatic stains on the tests of planktonic foraminifers. Pinkishgray (5YR 6/2) laminae that are 1 cm thick are present in Core144-872A-2H-6.

Subunit IBIntervals: Hole 872A, Sections 144-872A-4H-3,72 cm, through -17H-

3; Hole 872B, Cores 144-872B-1R to -3R; Hole 872C, Sections144-872C-4H-4 to -17X-CC, 20 cm

113

SITE 872

Site 872

0130Z 0115Z 0100Z 0045Z

Time (Z)

Figure 5. Profile C-C' of 3.5-kHz echo sounder collected during Leg 144 over Lo-En Guyot.

0030Z 0015Z 0000Z

Site 872

^^mM&vsmmaBBmβBSSBSSawfàm

2.2

0130Z 0100Z 0030ZTime (Z)

Figure 6. Single-channel seismic Profile C-C' collected during Leg 144 over Lo-En Guyot with the location of Site 872.

0000Z

Depth: Hole 872A, 30.2-143.6 mbsf; Hole 872B, 77.3-106.3 mbsf;Hole 872C, 32.9-141.7 mbsf;

Age: Hole 872A, late Miocene to late Oligocene; Hole 872B, middleto early Miocene; Hole 872C, late Miocene to late Oligocene

The boundary between Subunits IA and IB is placed at thedisappearance downhole of color banding. Subunit IB consists ofvery pale brown (10YR 7/3), homogenous foraminifer ooze. The

ooze is soupy and is comprised of fine to medium sand-sizedforaminifer tests. Nannofossils are a minor component in thesesediments (<5%); clay minerals, zeolites, sponge spicules, andradiolarians occur as traces. Lumps of slightly consolidated ooze,up to 1 cm in diameter, were recovered from Core 144-872A-7H-6to the base of Core 144-872A-11H, and in Cores 144-872C-8H to-UH. These lumps are friable and crumble easily. The occurrenceof these lumps may indicate the initial stages of sediment consoli-

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Unit discriptions:

IA: Nannofossil foraminifer ooze

IB: Foraminifer oozeII: Chalk-basalt pebble conglomerateIII: Limestone-basalt pebble

conglomerateIV: Basalt with planktonic foraminifer

limestone filling fractures

Figure 7. Lithostratigraphic summary of Site 872. TD total depth.

115

SITE 872

Table 2. Summary of lithostratigraphic units, Site 872.

Unit/subunit

Core, section,interval (cm)

Depth(mbsf) Age Description

1A 144-872A-1H to -4H-3, 72 cm

144-872C-lHto-4H-3

IB 144-872A-4H-3, 72 cm, to -17H

144-872B-lRto-3R

144-872C-4H-4to-17X

IIA 144-872A-17H-CC, 0-10 cm

HB 144-872B-4R-l,0-10cm

HC 144-872B-4R-1, 10-16 cm

III 144-872B-4R-1, 16-21 cm

IV 144-872A-18X

144-872B-4R-1, 21 cm, to -9R

144-872C-17X-CC, 20 cm, to -18X

Pleistocene to late Miocene Intercalated nannofossil foraminifer and foraminifer ooze.0.0-30.2

0.0-32.9

30.2-143.6

77.3-106.3

32.9-141.7

143.6-143.7

135.2-135.30

135.30-135.36

135.36-135.40

143.7-144.0

135.41-192.5

141.7-148.0

Pleistocene to late Mioc

late Miocene to late Olij

middle Eocene9

late Paleocene

late early Santonian

early Santonian or older9

Phosphatized chalk that contains pebbles of the underlying unit.

Phosphatized volcaniclastic sandstone; age relationship with adjacent subunits uncertain.

Pieces of phosphatized conglomerate consisting of volcaniclastic pebbles in pelagic limestoneof latest Santonian to early Campanian age. These conglomerate pieces are redeposited in

pelagic sediment of late Paleocene age.

Subangular basalt clasts in a pelagic limestone matrix.

Basalt with fractures filled by planktonic foraminifer limestone in upper 71 cm.

Basalt.

dation occurring from about 66 to 100 mbsf. The pelagic oozefound below Cores 144-872A-8H and 144-872C-8H is white(10YR 8/2). In Core 144-872A-12R, the ooze contains yellowishbrown foraminifer tests possibly stained by iron (Fe) or manga-nese (Mn). Specks of very pale brown color (10YR 8/3) areabundant in Cores 144-872A-15H to -17H. They are most com-mon in Section 144-872A-17H-3, which gives a "salt and pepper"appearance to the sediment. In Core 144-872A-17H, at the baseof Subunit IB, the nannofossil content increases to 20%-65%.Minor phosphate impregnation within a thin bed of foraminiferooze was noted in Interval 144-872C-17X-CC, 20-28 cm; it maydelineate a brief period of slow deposition.

Unit IIIntervals: Hole 872A, Interval 144-872A-17H-CC; 0-10 cm; Hole

872B, Interval 144-872B-4R-1, 0-16 cm;Depth: Hole 872A, 143.6-143.7 mbsf; Hole 872B, 135.2-135.4 mbsfAge: Hole 872A, middle Eocene; Hole 872B, indeterminate

Unit II consists of numerous fragments of several differentlithologies: phosphatized chalk and limestone, manganese crusts,volcaniclastic sandstones, and reworked pieces of Unit HI. UnitII is divided into three subunits based on variations in lithologyand its position in the recovered core. However, all pieces withinUnit II are small enough (the largest is 4 cm) to have caved fromthe walls of the above hole or to have been displaced inside thecore during drilling and recovery.

Subunit IIAIntervals: Interval 144-872A-17H-CC, 0-10 cmDepth: 143.6-143.7Age: middle Eocene

Subunit IIA consists of chalk fragments, a fragment of phos-phatic and manganiferous crust; loose basalt and volcaniclasticpebbles with shiny, polished surfaces; and fragments of basalt-pebble conglomerate with pelagic limestone matrix (late San-tonian in age) that have been reworked from the underlying unit.Some of the smaller pebbles are cemented within the chalk, butmost are loose. Some of the larger pebbles have chalk cementedto surfaces. We assume that the larger pebbles broke loose fromthe chalk as it disintegrated during drilling. The uppermost sev-eral millimeters of a 1-cm-thick fragment of phosphatic crust islaminated with Fe/Mn dendrites at the top. Below the phosphatelaminae, the crust is a lithified, yellow foraminifer chalk withseveral small pebbles intercalated within the chalk. Near thesurface of the crust are several cemented pebbles, a few millime-ters in size, with soft foraminifer ooze trapped around them.

Another fragment of a yellowish chalk has a burrow infilled withsoft foraminifer ooze and several pebbles up to 5 mm in size,including a fragment of volcanic glass (Fig. 8). The sediment inthe burrow fill has been assigned an Oligocene age based on theidentification of foraminifers, but the chalk has been assigned amiddle Eocene age (see "Biostratigraphy" section, this chapter).

The loose pebbles that co-occur with chalk fragments in Sec-tion 144-872A-17H-CC are polished, somewhat rounded or flat-tened in shape, and dark brown to blackish in color. One of thepebbles is a fragment of a conglomerate that is about 2 cm across;it is rounded and coated by phosphate. This lithoclast is composedof two rounded pebbles of highly altered volcaniclastic sandstoneand one pebble of vesicular basalt, all of which are cemented byphosphatized foraminifer limestone matrix (Fig. 9). Poorly pre-

1 cm

Figure 8. Close-up core photograph of a fragment of chalk from Subunit IIA,with a filled boring (Interval 144-872A-17H-CC, 0-5 cm).

116

SITE 872

Figure 9. Close-up photograph of a thin section made from pebble conglomer-ate reworked from Unit HI into Subunit HA (from Interval 144-872A-17H-CC,0-10 cm).

served tests of planktonic foraminifers occur in the matrix; theyhave been assigned a late Santonian age (see "Biostratigraphy"section, this chapter). This pebble is a reworked fragment of UnitIII (see description below). These larger pebbles have middleEocene foraminifer chalk cemented to some surfaces; we assumethey were originally incorporated within the chalk and were laterfreed during the drilling process.

Subunit HB

Interval: Interval 144-872B-4R-1, 0-10 cmDepth: 135.2-135.3 mbsfAge: indeterminate

Subunit HB consists of several pieces of highly altered vol-caniclastic sandstones that have oxidized, dark brown upper sur-faces. The sandstone is composed of fine-grained, highly alteredvolcanic grains; one piece has trace amounts of very fine micriticcarbonate grains. One clast in this unit has traces of carbonatecement on its surface. It is uncertain whether these volcaniclasticcobbles are part of a distinct volcaniclastic bed or are clastsbroken from a friable chalky matrix. The position of this subunitrelative to adjacent subunits is uncertain; the largest piece ofSubunit HB is only 4 cm long, and all pieces of adjacent subunitsare smaller still. Any or all of these fragments could have cavedfrom previously drilled intervals or could have been displaced inthe core during drilling or recovery. The age of Subunit HB isindeterminate.

Subunit HC

Interval: Interval 144-872B-4R-1, 10-16 cmDepth: 135.3-135.36 mbsfAge: late Paleocene

Several pebbles of conglomerate and altered basalt, up to 2 cmin diameter and coated by a thin, phosphate film, compriseSubunit HC. Several pebbles are brown in color, have a shinysurface, and are partially covered by a sandy carbonate cement,indicating that they were broken from their matrix during drilling(Fig. 10). At least one of these pebbles is a two-generationconglomerate (Fig. 10). Thin-section examination showed thatsmall pebbles of basalt and highly altered carbonate rock werecemented by a foraminifer-rich packstone during early Cam-panian time. This matrix contains some volcanic glass shards.After lithification the rock was phosphatized and partly coated byiron manganese crust. The conglomerate was then fractured andthe pieces reworked and cemented by a planktonic foraminiferlimestone matrix of late Paleocene age. The late Paleocene matrixcontains small volcaniclastic pebbles.

Unit IIIInterval: Interval 144-872B-4R-1, 16-21 cmDepth: 135.36-135.41 mbsfAge: late Santonian

The phosphatic pebbles in Interval 144-872B-4R-1, 0-16 cm,are underlain by a limestone with basalt clasts (Fig. 11). The lowercontact between the limestone and the basalt is irregular but sharpand welded. Clasts within the limestone are subangular and 0.5-5cm in diameter; they have a basaltic composition. The basalt isfinely crystalline, with trachytic texture and dark-rimmed feld-spar laths. The clasts are probably derived from a basalt flow. Oneof the clasts is triangular in shape and oriented with the sharp edgedownward, which may indicate that the clasts fell into the carbon-ate mud or were carried downslope in a gravity flow. It could alsobe interpreted that the carbonate layer is the fill of a wider fractureand not a continuous planktonic limestone conglomerate bed. Thepelagic foraminifer limestone contains about 40% planktonicforaminifers, l%-2% ostracodes, and traces of volcanic grains;these are surrounded by a clotted, micritic matrix. Noticeablyabsent are any benthic or shallow-water fossils in the limestone.The phosphatized pebble conglomerates with limestone matrix

Manganesecrust

latePaleocene

matrix \ , earlyCampanian

matrix

Manganesecrust

Figure 10. Close-up photograph of a thin section made from pebble conglom-erate reworked from Unit III into Subunit UC (from Interval 144-872B-4R-1,13-16 cm).

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cm13—I

1 5 -

1 7 -

1 9 -

21 —

23—

2 5 -

Figure 11. Close-up core photograph of pebbles in Subunit HC and of theunderlying pebbly limestone of Unit III (Interval 144-872B-4R-1, 13-26 cm).Note the sharp, welded boundary between the basalt and Unit III, and theangular shape of basalt clasts incorporated into it.

described from Subunits IIA and HC are thought to be reworkedfrom Unit III.

Unit IVInterval: Hole 872A, Core 144-872A-18X; Hole 872B, Section 144-

872B-4R-1, 21 cm, to Core 144-872B-9R; Hole 872C, Section144-872C-17X-CC, 20 cm, through Core 144-872C-18X

Depth: Hole 872A, 143.7-144.0 mbsf; Hole 872B, 135.4-192.5 mbsf;Hole 872C 141.7-148.0 mbsf

Age: Hole 872A, indeterminate; Hole 872B, early Santonian or older;Hole 872C, indeterminate

Unit IV is composed of basalt. Detailed descriptions of theserocks are given in the "Igneous Petrography" section (this chap-ter). However, two aspects of the volcanic basement are sedimen-tologically significant and need to be mentioned here. Five cre-vasses or fractures within the upper 71 cm of the basalt are filledby foraminifer limestone (Core 144-872B-4R; Fig. 12). The in-fillings of these fractures are 1 mm to >l cm thick, white to palered (10R 6/3), phosphatized, foraminifer limestone. Foraminifersare mostly planktonic and poorly preserved; few benthicforaminifers are present. Additional components of the limestoneare ostracodes, pellets, probably crustacean fecal pellets (Favre-ina), a fish tooth, a fragment of a sponge or a coral, and sand-sizeddebris of weathered basalt. The matrix is clotted and pelleted limemud, which is locally bioturbated. The fracture fill is early San-tonian (see "Biostratigraphy" section, this chapter).

A very different lithologic development was found in Core144-872C-17X, where the top of a highly altered, greenish, mi-crocrystalline, vesicular basalt is overlain by 10 cm of a dark-grayclay with several basalt fragments. The clay is overlain by aforaminifer ooze of Oligocene age (see "Biostratigraphy" section,this chapter). The contact between the clay and overlying oozewas not recovered.

Preliminary Interpretation of Depositional HistoryAn important lesson to be learned from the drilling at Lo-En

Guyot is that, even in holes drilled 75 m apart, stratigraphicsequences may differ significantly. In Hole 872C, altered basalticbasement is overlain by a veneer of unfossiliferous dark clay,which in turn is overlain by upper Oligocene foraminifer ooze (forall stratigraphic age data, see "Biostratigraphy" section, this chap-ter). However, in Hole 872B, cracks in the basalt are filled bylower Santonian limestone. The microfossil assemblage in thelimestone suggests that the basalt surface was submerged in innerto middle neritic depths at the time of deposition. Why no indica-

Figure 12. Close-up photograph of a fracture within the basalt infilled bypelagic carbonate (Interval 144-872B-4R-1, 60-67 cm).

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SITE 872

tion of this submergence is recorded in Hole 872C, located 75 mdistant from Hole 872B, remains unexplained.

The presence of a foraminifer packstone within fractures at thetop of the subaerially(?) formed basalt (see "Igneous Petrology"section, this chapter) in Core 144-872B-4R indicates possibleflooding of the basaltic basement during early Santonian time.Pelagic sediments rained down into basalt fractures and filledintergranular space between volcanic pebbles on the surface ofthe guyot. Based on ages of the pebble conglomerate matrixes,this pelagic sedimentation lasted at least through early Cam-panian. Volcanic glass shards in the matrix of one conglomeratewith a Campanian matrix may suggest nearby volcanic activity.It is uncertain whether the volcaniclastic sands of Subunit HB maybe related to the volcanic fragments in the pelagic limestone ofLate Cretaceous age.

Apparently, a period of nondeposition occurred between theearly Campanian and the late Paleocene; many of the pebbleswithin chalks of late Paleocene and middle Eocene age werecoated with phosphatic deposits and thin manganese crusts beforeredeposition. Evidence also exists that the conglomerate of UnitIII was eroded following lithification; at least one conglomeratepebble (Interval 144-872B-4R-1, 13-16 cm; Fig. 11) was frac-tured across both clasts and matrix before redeposition into ayounger pelagic matrix during late Paleocene time.

The phosphatized crust fragments within the Subunit IIA chalksuggest a period of post-middle Eocene nondeposition that lasteduntil the late Oligocene, when deposition of the foraminifer ooze ofSubunit IB began. Deposition of the ooze continued with severalshort breaks into the Pleistocene. Manganese, or iron-stainedforaminifer tests, which give a speckled appearance to the oozein Holes 872A and 872C (Cores 144-872A-1H and -2H, and Cores144-872C-1H and -2H), may indicate slowed or interrupted depo-sition at these levels. However, no paleontologic hiatus was notedin either Core 144-872A-2H or Core 144-872C-2H. This mayindicate that the observed stained tests are caused by contamina-tion from the surface. The Oligocene to Miocene foraminifer oozewas winnowed by bottom currents. The depositional conditionschanged slightly during the Pliocene to Pleistocene, when in-creases in the nannofossil content within the ooze point to adecreased intensity of the current activity.

Lo-En Guyot is morphologically a classic guyot with a flatupper surface. Drilling on the guyot did not recover any platformlimestone, or any indication of a carbonate platform near the site.All the drilling evidence points to persistent pelagic depositionover the center of the guyot. However, as Site 872 was locatednear the center of the guyot where the pelagic cap is thickest, thisresult does not exclude the possibility of a fringing carbonateplatform closer to the seaward edge of the guyot.

The flat upper surface of Lo-En Guyot cannot be explained bya continuous carbonate platform cap. However, based on thedrilling results, we cannot say whether the flat surface of the guyotwas produced by erosion of the entire volcano to a peneplain orby a fringing reef buildup combined with erosion of the centralcone. The erosional setting could have been subaerial or subma-rine, by wave planation. The time of earliest erosion is lessspeculative than the mechanism. It must have been before theearly Santonian, the age of pelagic sediments overlying and fillingthe cracks of the eroded basalt surface. Evidence is also presentfor later periods of erosion before or during the late Paleoceneand perhaps in the middle Eocene.

Lo-En Guyot thus stands in sharp contrast to other guyots (e.g.,Limalok Guyot; see "Site 871" chapter, this volume) in that itlacks a continuous cover of platform carbonate over its top. Sucha finding documents significant differences in the geologic histo-ries of individual guyots in this region.

BIOSTRATIGRAPHY

Introduction

Three holes were drilled at Site 872. Holes 872A and 872Cwere drilled with the APC and APC/XCB, respectively, for thepurpose of coring the pelagic cap of Lo-En Guyot; Hole 872B wasrotary drilled to penetrate and core horizons below the pelagiccap. Sediments spanning the Santonian through the Pleistocenewere recovered. Age dating and paleoenvironmental interpreta-tions were based on calcareous microplankton fossils, with addi-tional paleoecologic information provided by benthic foraminif-ers, palynomorphs, and diatoms.

Calcareous NannofossilsHoles 872A and 872C

Time constraints limited nannofossil analysis largely to core-catcher samples, although some detailed work was done on se-lected cores from Hole 872A. The following discussion is re-stricted to the record in Hole 872A except in the few cases whereresults from Hole 872C differ significantly from those of Hole872A.

The interval from Samples 144-872A-1H-1, 25-26 cm, through-1H-1, 85-86 cm, contains Emiliania huxleyi and Pontosphaeraindooceanica, indicating the Emiliania huxleyi Zone of late Pleis-tocene age. The assemblages are dominated by Gephyrocapsaspp. This dominance, as well as the presence of P. indooceanica,indicate that the uppermost Pleistocene zone {Emiliania huxleyiAcme Zone) is either contained in the upper 24 cm of the hole oris absent. The underlying Gephyrocapsa oceanica Zone occurs inSamples 144-872A-1H-1, 135-136 cm, and -1H-2, 25-26 cm(1.35-1.75 mbsf), based on the absence of both E. huxleyi andPseudo emiliania lacunosa. The interval from Samples 144-872A-1H-2, 85-86 cm, through -1H-4, 25-26 cm (2.35-4.75 mbsf)contains P. lacunosa but lacks Helicosphaera sellii. Samples inthis interval are dominated by the larger gephyrocapsids such asG. oceanica. The association of these species, in combinationwith the dominance of the G. oceanica group, indicates the P.lacunosa Zone of middle to early Pleistocene age. Samples 144-872A-1H-5, 85-86 cm, through -1H-5, 25-26 cm, also contain P.lacunosa and lack H. sellii, but they are dominated by the smallgephyrocapsids. This association indicates the small Gephyro-capsa Zone of early Pleistocene age. Samples 144-872A- 1H-4, 5,85-86 cm, and -1H-CC have been assigned to the Helicosphaerasellii Zone of early Pleistocene age. Sample 144-872A-2H-1, 0-1cm, is assigned to the Calcidiscus macintyrei Zone based on theoccurrence of C. macintyrei and the absence of discoasters. Thepresence of rare Gephyrocapsa oceanica indicates an early Pleis-tocene age, although planktonic foraminifers suggest that thissample is late Pliocene in age (Zone N21, see below).

Core 144-872A-2H contains upper Pliocene nannofossilforaminifer ooze in which at least two subzones are represented.Sample 144-872A-2H-2, 25-26 cm (9.25 mbsf), contains Dis-coaster brouweri and Discoaster triradiatus without Discoasterpentaradiatus or Discoaster surculus, indicating Subzone CN12dof late Pliocene age. Sample 144-872A-2H-CC (17.0 mbsf) con-tains a more abundant discoaster assemblage, including D.brouweri, D. pentaradiatus, D. asymmetricus, D. blackstockae,and D. tristellifer but lacking Discoaster tamalis. This associationindicates Subzone CN12b of late Pliocene age.

Sediment was not recovered in Core 144-872A-3H. Sample144-872C-3H-CC (28.0 mbsf) contains a lower Pliocene assem-blage that includes Reticulofenestra pseudoumbilica, Spheno-lithus abies, Amaurolithus delicatus, and Ceratolithus rugosusbut lacks Pseudoemiliania lacunosa and Discoaster asymmet-

119

SITE 872

ricus. This assemblage indicates Subzone CNlOc of early Plio-cene age.

The interval from Samples 144-872A-4H-1, 50-51 cm, through-4H-3, 50-51 cm (27.0-30.5 mbsf), contains well-preservednannofossils, including Discoaster quinqueramus, Discoasterberggrenii, and Amaurolithus primus, which indicates SubzoneCN9b of late Miocene age. Sample 144-872A-4H-5, 50-51 cm(33.0 mbsf), is assigned to Zone CN8 of late Miocene age basedon the presence of Discoaster neohamatus and the absence of D.quinqueramus, D. berggrenii, Discoaster hamatus, and Catinas-ter spp.

Age determinations in the interval from Sections 144-872A-4H-CC through -5H-2 (36.0-39.0 mbsf) are difficult because ofpervasive assemblage mixing. Samples within this interval con-tain Discoaster hamatus, Discoaster quinqueramus, Discoasterberggrenii, Catinaster coalitus, and Catinaster calyculus. Theassociation of these species is most easily explained by the mixingof taxa from Subzones CN7b and CN9b (both of late Mioceneage). In addition, rare Discoaster tamalis, representative of latePliocene Subzone CN12a, occur in some samples within thisinterval. Although it is impossible to determine whether thismixing is the result of reworking or downhole contamination, thepresence of the upper Pliocene D. tamalis suggests the latterinterpretation. Planktonic foraminifer data also indicate signifi-cant downhole contamination within this interval (see below). Ifthe interpretation of downhole contamination is accepted, thenthis interval may be assigned to Subzone CN7b of early lateMiocene age. This is in concert with the unmixed Subzone CN7bassemblages that immediately underlie the mixed interval.

The interval from Samples 144-872A-5H-3, 50-51 cm,through -5H-CC (39.5-44.16 mbsf) contains Discoaster hamatus,Catinaster coalitus, and Catinaster calyculus, indicating SubzoneCN7b of early late Miocene age. Sample 144-872A-6H-1, 50-51cm (50.0 mbsf), contains a slightly older assemblage (Zone CN6)that includes Catinaster coalitus but lacks Discoaster hamatusand Catinaster calyculus. The apparent absence of Subzone CN7asuggests a small disconformity at the core break between Cores144-872A-5H and -6H.

Samples 144-872A-6H-CC through -8H-3, 50-51 cm (54.26-68 mbsf), contain Discoaster exilis but lack Catinaster coalitusand Sphenolithus heteromorphus, indicating Zone CN5 of middleMiocene age. The presence of Discoaster kugleri in samples fromSample 144-872A-6H-CC through Core 144-872A-7H indicatesSubzone CN5b. This species is apparently absent in Samples144-872A-8H-1, 50-51 cm, through -8H-3, 50-51 cm (66.50-68.0 mbsf), suggesting Subzone CN5a, although this may be anartifact of relatively poorer preservation and insufficient observa-tion.

The interval from Sample 144-872A-8H-4, 50-51 cm, throughCore 144-872A-11H (66.5-100 mbsf) is assigned to the combinedZone CN3/4 based on the occurrence of Sphenolithus heteromor-phus. Separation of these zones is normally based on the presenceor absence of Helicosphaera ampliaperta. This species, however,is known to favor areas near continental margins and is notori-ously rare or absent in remote oceanic locations. Thus, it is notuseful for zonal division at the Lo-En Guyot site.

Lower Miocene Zone CN2, identified by the presence ofSphenolithus belemnos, occurs within Core 144-872A-12H (100-102 mbsf). The thinness of this zone (2 m) is probably caused bythe existence of a hiatus, as suggested by the planktonic foraminif-ers (see below). However, it might be attributable, at least in part,to the short APC stroke of this core. An incomplete stroke of 2 moccurred at a similar stratigraphic level in Hole 872C. Cores144-872A-13H and -14H (102.0-121.0 mbsf) contain Cyclicar-golithus abisectus, Cyclicargolithus floridanus, and Sphenolithus

delphix but lack Sphenolithus belemnos, Dictyococcites bisectus,Zygrhablithus bijugatus, and Sphenolithus ciperoensis, indicatingZone CN1 of early Miocene age. The abundance of Tri-quetrorhabdulus carinatus in Sample 144-872A-14H-CC indi-cates Subzones CNla and CNlb of earliest Miocene age.

Core 144-872A-15H (121.0-130.5 mbsf) contains assem-blages of Subzone CP 19b of latest Oligocene age. Species presentinclude Sphenolithus ciperoensis, Dictyococcites bisectus, Zy-grhablithus bijugatus, Cyclicargolithus abisectus, and Trique-trorhabdulus carinatus. Samples 144-872A-17H-3, 50-51 cm,through -17H-CC (143.5-143.7 mbsf) contain Sphenolithus dis-tentus and S. ciperoensis, indicating Subzone CP 19a of late Oli-gocene age.

Section 144-872A-17H-CC contains material of three distinctages. The soft, white foraminifer ooze of Subzone CP19a (lateOligocene age) is intermixed with tan, pebble-bearing foraminiferchalk. This tan chalk contains Dictyococcites bisectus, Toweiusmagnicrassus, and Chiasmolithus gigas, indicating SubzoneCPI3b of middle Eocene age. The white Oligocene ooze fillsburrows within some pieces of the middle Eocene chalk.

In addition to the Paleogene material, nannofossils occur in thepelagic limestone matrix of a conglomeratic clast. Nannofossilsfrom this matrix were identified in thin section. Small patches(burrows?) within the matrix contain well-preserved nannofossilsindicative of the Fasciculithus tympaniformis Zone (CP4) of earlylate Paleocene age. The bulk of the matrix contains several bios-tratigraphically restricted forms that suggest a Santonian age. Thepresence of Micula concava and Reinhardtites anthophorus indi-cate a maximum age of late early Santonian (CC15). The presenceof Stoverius coronatus, Stoverius biarcus, Gephyrorhabdus coro-nadventis, and common Aspidolithus parcus expansus and Ark-hangelskiella specillata without Aspidolithus parcus parcus orAspidolithus parcus constrictus restricts the minimum age of thisassemblage to the latest Santonian (CC17). This age assignmentcorroborates the late Santonian age provided from planktonicforaminifer evidence (Fig. 13).

Hole 872B

Hole 872B was washed down to a depth of 77.3 mbsf. Cores144-872B-1R through -3R recovered part of the Neogene pelagiccap from 77.3 to 106.3 mbsf. Samples 144-872B-1R-CC and-2R-CC (77.38 and 87.05 mbsf, respectively) contain nannofossilassemblages with Sphenolithus heteromorphus, Reticulofenestrapseudoumbilica, and rare Calcidiscus macintyrei, indicating theSphenolithus heteromorphus Zone (CN4) of middle Miocene age.Sample 144-872B-3R-CC (96.65 mbsf) contains Sphenolithusbelemnos, Sphenolithus conicus, Cyclicargolithus abisectus, andCyclicargolithus floridanus, indicating the Sphenolithus belem-nos Zone (CN2) of early Miocene age (Fig. 14).

The underlying 28.9 m were washed and coring resumed at adepth of 135.2 mbsf. Core 144-872B-4R recovered basalts withthin sediment layers (Fig. 15). The nannofossil content was inves-tigated both in smear slides and thin sections prepared from allthe sediment layers. Sample 144-872B-4R-1, 20-22 cm, containscommon, moderately preserved nannofloras, including Lithas-trinus septenarius, Eiffellithus eximius, Reinhardtites anthopho-rus, and Micula decussata, indicating Zone CC15 of early San-tonian age. Sample 144-872B-4R-1, 61-62 cm, contains very rareand poorly preserved specimens of Eiffellithus eximius andMarthasterites furcatus, indicating an age no older than the lateTuronian. Only a few specimens of Eiffellithus eximius wereobserved in Sample 144-872B-4R-1, 68-70 cm, which cannot beolder than early Turonian. Planktonic foraminifer assemblagesfrom this interval are more diagnostic (see below) and indicate aSantonian age.

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SITE 872

Hole 872 A Hole 872 C

100

144

100-

Upper Neogene nannofossil zones

6 = E. huxleyi 3 = small Gephyrocapsa

5 = G. oceanica 2 = H. sellii

4 = P. lacunosa 1 = C. macintyrei

Figure 13. Biostratigraphy of Holes 872A and 872C, Lo-En Guyot.

Planktonic Foraminifers

Holes 872A and 872C

Planktonic foraminifers are very abundant throughout the pe-lagic sequence at Site 872 (Lo-En Guyot). Core-catcher samplesfrom Holes 872A and 872C were examined. Further sampling wasconducted on cores from Hole 872A to constrain the zonalboundaries more tightly. Figure 13 shows the planktonicforaminifer biostratigraphy obtained from these holes.

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Processes such as dissolution, current winnowing, erosion, andredeposition of sediment on the guyot have contributed to thevariable preservation observed at this site. For much of the se-quence, relatively well-preserved individuals are accompanied bybroken, peeled, or dissolved specimens. The fine fraction (45-150µm) is often dominated by broken and etched fragments. Rework-ing of older material is encountered at various levels in thesequence. Downhole contamination causes additional problemsand is in some cases severe, particularly in the top one or twosections of cores. Downhole contaminants are usually Pleistocene

121

SITE 872

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in age, often being discolored by iron staining. These occurthrough much of the sequence to the level of Core 144-872A-9H.

The following discussion is centered on the faunal sequenceobserved in Hole 872A. The record from Hole 872C was foundto be comparable. Reference is made to Hole 872C only at thoselevels where additional information is available from that hole.

Sample 144-872A-1H-3, 59-61 cm (3.59 mbsf), contains Trun-corotαliα truncαtulinoides, Globorotαliα tumidα, and Pulleniαtinαobliquiloculαtα and is Pleistocene in age (Zone N22). Samples144-872A-1H-CC, -2H-3, 59-61 cm, and 144-872A-2H-CC yieldan upper Pliocene (Zone N21) assemblage containing Truncorotaliatosaensis, Globigerinoides fistulosus, Globorotalia tumida, and G.tumida ßexuosa. Material from Core 144-872A-3H was not re-covered, but an upper Miocene (Zone NI 8) assemblage was foundat a comparable depth in Hole 872C (Sample 144-872C-3H-CC),which includes frequent Sphaeroidinellopsis (but no Sphaeroidi-nella) associated with Globigerina nepenthes and Globorotaliatumida. In Sample 144-872A-4H-CC, a slightly older assemblageof late Miocene age (Subzone NI7a) was found, including Glo-boquadrina dehiscens, Globigerinoides obliquus, and a fewSphaeroidinellopsis seminulina, but no Pulleniatina or Globoro-talia tumida.

One sample was taken from each section of Cores 144-872 A-5H and -6H. This interval is problematic for several reasons,

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100Figure 15. Biostratigraphy and microfacies of sediments recovered in Section144-872B-4R-1, Lo-En Guyot.

which include variable preservation, severe downhole contamina-tion, extensive reworking, and the scarcity of important markerspecies of the upper middle and upper Miocene, such as Neoglo-boquαdrinα αcostαensis and Paragloborotalia siakensis. This in-terval has not been zoned by planktonic foraminifers, although anannofossil zonation is available (Fig. 13). Reworked taxa in-clude Oligocene and lower Miocene species.

A less mixed fauna was found in Sample 144-872A-6H-CC,containing G. praemenardii and a few Paragloborotalia siakensisbut no Globigerina nepenthes. This assemblage is representativeof Zone NI3 of middle Miocene age. The boundary betweenZones NI3 and NI2 is placed between Samples 144-872A-7H-2,59-61 cm (57.09 mbsf), and -7H-3, 59-61 cm (57.72 mbsf), thelatter containing the index species Globorotalia fohsi robusta andG.fohsi lobata. These advanced members of the G. fohsi lineage,which are definitive of Zone NI2, occur throughout the lower partof Core 144-872A-7H to Sample 144-872A-7H-CC.

Sample 144-872A-8H-5, 59-61 cm (71.09 mbsf), contains Glo-borotalia praefohsi (sensu Blow, 1969) and G. peripheroacuta butlacks fully keeled individuals of G.fohsi; this sample belongs toZone N i l of middle Miocene age. Sample 144-872A-8H-CCcontains Globorotalia peripheroacuta and Orbulina universa, butit lacks the more advanced representatives of the G. fohsi groupand is consequently assigned to Zone N10. Samples 144-872A-9H-CC, -10H-CC, and -11H-CC contain Globigerinoides bisphericus,

SITE 872

Praeorbulina sicana, P. transitoria, and P. glomerosa curva, butthey lack Orbulina spp. This assemblage is assigned to Zone N8of late early Miocene age.

Sample 144-872A-12H-CC lacks Praeorbulina spp. but doescontain forms transitional from Globigerinoides trilobus to G.bisphericus; for this reason it is assigned to Zone N7. Samples144-872A-13H-3, 59-61 cm, and -13H-CC contain Globigeri-noides spp. and Globoquadrina dehiscens in conjunction withmembers of the "Globigerina" ciperoensis group and commonParagloborotalia kugleri. The occurrence of P. kugleri in abun-dance is taken as good evidence of Subzone N4b (earliest Mioceneage), even though the species does occur sporadically throughsome higher parts of the sequence as a result of reworking. Thedisconformity separating Zone N7 and Subzone N4b occurs be-tween Cores 144-872A-12H and -13H. This disconformity wasalso detected at a similar stratigraphic depth in Hole 872C. Theshort APC stroke of both Cores 144-872A-12H and 144-872C-12H may be related to this disconformity.

Sample 144-872A-14H-CC is also assigned to Subzone N4b.Rare, well-preserved, middle Eocene planktonic foraminifers{Truncorotaloides topilensis and Morozovella crassata) werefound reworked in Samples 144-872A-13H-CC and -14H-CC.

An upper Oligocene (Zone P22) fauna lacking typically Mio-cene forms such as Globigerinoides spp. and Globoquadrinadehiscens but containing common "Globigerina" ciperoensis and"G." angulisuturalis was found in Samples 144-872A-15H-3,58-60 cm, -15H-CC, -16H-3, 58-60 cm, and -16H-CC. The lattertwo samples, in particular, show a distinctly mixed preservationstyle. A high proportion (30%-40%) of the fauna in the >150-µmsize fraction is strongly discolored to an orange-brown color fromiron staining and/or phosphatization. These specimens are wellsorted with respect to their size, occurring only rarely as frag-ments in the 45-150 µm fraction. Samples 144-872A-17H-3,58-60 cm, and 144-872C-17X-CC contain common Paraglo-borotalia opima associated with members of the "Globigerina"ciperoensis lineage, including the important marker species "G."angulisuturalis. This assemblage indicates Zone P21 of late Oli-gocene age.

Section 144-872A-17H-CC consists of several lithified frag-ments, in which rounded phosphatic clasts are set in a matrix ofindurated foraminifer chalk. In this chalk, planktonic foraminifersare recrystallized, iron stained, and phosphatized. The markerspecies Globigerinatheka index, Hantkenina mexicana, Claviger-inella eocanica, Morozovella aragonensis, and Truncorotaloidestopilensis were identified. This assemblage is attributed to ZonePI 1 of middle Eocene age. Burrows, occurring in a few fragments,contain concentrations of small phosphatized clasts and well-pre-served, white, Oligocene planktonic foraminifers. A superficialdusting of Oligocene (Zone P21-P22) ooze occurs on severalfragments.

The phosphatized pebbles in this section belong to a conglom-erate consisting of altered volcanic elements cemented by par-tially phosphatized chalk that is rich in planktonic foraminifers.Tests of planktonic foraminifers, observed in thin section, arepartially or totally phosphatized; this has not modified the char-acteristic profiles of the various species, however. The assem-blage includes Dicarinella concavata gr., Marginotruncana si-gali, M. pseudolinneiana, Contusotruncana fornicata, Heterohelixglobulosa, H. reussi, Globigerinelloides prairiehillensis, G. bol-lii, and Ventilabrella glabrata associated with rare Globotrun-canita elevata and G. stuartiformis. This assemblage is charac-teristic of the upper part of the Dicarinella asymetrica Zone oflate Santonian age.

Hole 872B

The first three cores of Hole 872B recovered pelagic oozecontaining abundant planktonic foraminifers. Sample 144-872B-1R-CC contains Globorotalia praefohsi but no advanced repre-sentatives of the G. fohsi lineage; it is assigned to Zone N i l ofmiddle Miocene age. Sample 144-872B-2R-CC contains Globig-erinoides bisphericus and Praeorbulina sicana but lacks Orbu-lina; it is assigned to Zone N8 of early to middle Miocene age.Sample 144-872B-3R-CC lacks Praeorbulina sicana but containsforms transitional from Globigerinoides trilobus to G. bisphericus,indicating the higher part of Zone N7 of early Miocene age.

Core 144-872B-4R recovered pelagic sediments cementingvolcanic rock fragments, infilling cracks in the basalt, or asinterbedded layers between lava flows (Figs. 14-15). A pebble,belonging to Subunit HC (Sample 144-872B-4R-1, 13-16 cm) isa conglomerate with two generations of matrix (Fig. 10). Theolder matrix contains a rich planktonic fauna attributable to theGlobotruncanita elevata Zone of early Campanian age. Theyounger matrix is barren of planktonic foraminifers. Sample 144-872B-4R-1, 18-22 cm, yields common to abundant, rather well-preserved planktonic foraminifers. The assemblage includes com-mon marginotruncanids (e.g., M. sigali, M. schneegansi, M.pseudolinneiana, M. coronata), several Dicarinella concavata,Globigerinelloides bollii, Heterohelix reussi, rare Contusotrun-cana fornicata, Archaeoglobigerina cretacea, Globotruncanalinneiana, Ventilabrella eggeri, and V. glabrata. This assemblageis indicative of the Dicarinella asymetrica Zone (even in theabsence of the nominate species) and is Santonian in age (possiblyearly Santonian).

In the lower samples (Samples 144-872B-4R-1, 46-48 cm,-4R-1, 60-62 cm, and -4R-1, 68-71 cm; Fig. 15), planktonicforaminifer assemblages are substantially similar to those in theprevious sample, although they seem to display a slightly oldercharacter. The abundant marginotruncanids and Heterohelixreussi and common Dicarinella concavata are associated withrare whiteinellids and Dicarinella primitiva along with rare, pos-sibly older forms attributable to Dicarinella hagni and Margi-notruncana marianosiin Sample 144-872B-4R-1, 68-71 cm. Thebulk of the planktonic faunas in all three layers are indicative ofthe Dicarinella concavata Zone of early Santonian age, but thesupposed older forms are known to become extinct in the lateTuronian. Poor recovery and the discontinuous record make itdifficult to determine whether the older aspect of the assemblageis related to reworking or to preservation. There is evidence infavor of both hypotheses. On the one hand, the occurrence ofshallow-water foraminifers and other skeletal organisms withinthe faunal-rich pelagic sediments would support the possibility ofsome transport and reworking. On the other hand, the decrease instate of preservation and increase of degree of phosphatizationdownhole may account for the apparent older aspect of the fauna.Other notable features of this sequence are the occurrence ofseveral medium-sized, perfectly preserved fish teeth, the sharpdownhole increase in the abundance of fecal pellets (Favreinasp.), and the occurrence of a few benthic foraminifers indicativeof shallow-water environment (see below; Fig. 15).

Benthic ForaminifersTwo species of benthic foraminifers were found in the sedi-

ments infilling the basalt cracks in Core 144-872B-4R (Fig. 15):Dictyopselloides sp. (Samples 144-872B-4R-1, 46-48 cm, -4R-1,60-62 cm, and -4R-1, 68-71 cm) and Dorothia sp. cf. D. bulletta(Sample 144-872B-4R-1, 68-71 cm). The latter species is known

123

SITE 872

from the Upper Cretaceous; the genus Dictyopselloides is knownfrom the Santonian of France and Spain.

These benthic foraminifers are usually reported from the innerto middle neritic deposits ("circalittoral" of French authors) at apaleodepth of 10 to 100 m, with a maximum paleodepth ofapproximately 200 m. The association of these species in thecrack infillings suggests a relatively shallow paleodepth, althoughthe possibility of post-mortem transport or reworking cannot beeliminated.

PalynologyPalynomorphs

Palynologic analyses were performed on 15 core-catcher sam-ples (Samples 144-872A-1H-CC through -11H-CC and Samples144-872A-13H-CC through -16H-CC) through the entire thick-ness of the pelagic cap in Hole 872A. Samples vary from nanno-fossil foraminifer ooze to foraminifer ooze. Treatment with 20%HC1 alone was sufficient to concentrate the organic fraction forvisual analysis. For each sample two microscope slides wereprepared: one containing unsieved residue for total kerogen andpalynofacies analysis, the other containing residue sieved at 20µm for biostratigraphic analysis.

Dinoflagellates occur only in the three uppermost core catch-ers (Samples 144-872A-1H-CC, -2H-CC, and -4H-CC; Sample144-872A-3H-CC was not recovered). For each of these samples(ages from calcareous plankton fossils in parenthesis), the follow-ing taxa were recognized:

1. Sample 144-872A-1H-CC (early Pleistocene): Impagidiniumaculeatum, I. japonicum, I. strialatum, Impagidinium sp. cf. /. patu-lum, Operculodinium israelianum, and Spiniferites sp.

2. Sample 144-872A-2H-CC (early late Pliocene): Impagid-inium aculeatum, I. japonicum, I. patulum, I. strialatum, Opercu-lodinium centrocarpum (s.l.), Polysphaeridium sp., and Incertaesedis sp. 1 of Edwards (1985).

3. Sample 144-872A-4H-CC (late Miocene): Impagidiniumaculeatum, Impagidinium sp. cf. /. paradoxum?, and Impagidiniumsp. cf. /. strialatum.

Of all the taxa found in these core-catcher samples, onlyone—Incertae sedis sp. 1 of Edwards (1985)—has a restrictedrange within the upper Cenozoic. Incertae sedis sp. 1 of Edwards(1985), recorded here for the first time from Pacific Ocean sedi-ments, is confined to the Neogene in the North Atlantic (see Headet al., 1989, p. 441, for a discussion of occurrences) where itoccurs as high as the lower upper Pliocene (MJ. Head, unpubl.data).

Neither embryophyte spores nor pollen were found, althoughspores(?) of probable algal origin were found in Samples 144-872A-3H-CC and -4H-CC, and possible copepod eggs were re-covered from Sample 144-872A-2H-CC.

Palynofacies

Several categories of organic remains were recognized atlOOO× magnification within the >20-µm organic residue fraction.The most commonly represented categoiy consists of rounded andsubrounded clasts of granular amorphogen, up to about 150 µmin diameter and enclosing numerous fine, colorless mineral parti-cles. The larger, rounded, and somewhat elongated clasts areinterpreted to be fecal pellets, and the smaller clasts to be frag-ments of them. A second category comprises the organic infillingof foraminifer chambers. As with the fecal pellets, theseforaminifer infillings generally appear as rounded clasts of granu-lar amorphogen, but they have a denser, finer texture and sharp,rather than diffuse, margins. Other categories recorded are dinoflag-

ellates, woody tissues (from higher plants), and foraminifer lin-ings that are thick walled and of amber color.

Visual kerogen analysis of the >20-µm fraction permits recog-nition of three palynofacies units (Fig. 16), as follows:

Palynofacies Unit 1 (Samples 144-872A- 1H-CC through -4H-CC) is defined by the presence of dinoflagellates, these occurringin trace amounts. Well-preserved fecal pellets dominate, and rareforaminifer infillings, trace amounts of woody tissues, and occa-sional trace amounts of foraminifer linings also occur. Organicremains generally have excellent preservation.

Palynofacies Unit 2 is recognized in Samples 144-872A-5H-CC through -13H-CC. Its top is defined by the downhole disap-pearance of dinoflagellates and its base by the top of PalynofaciesUnit 3. It is characterized by dominant to abundant amounts ofmoderately to well-preserved fecal pellets, rare to commonforaminifer infillings, trace amounts of woody tissues, and occa-sional trace amounts of foraminifer linings. Organic remains aregenerally moderately to well preserved so that the absence ofdinoflagellates—which are much more resistant to degradationthan are fecal pellets—cannot be attributed to preservational loss.

Palynofacies Unit 3 is recognized in Samples 144-872A-14H-CC through -16H-CC. Its top is defined by a downhole decreasein both the preservation and relative abundance of fecal pellets,and a relative increase in foraminifer linings. In addition, rare tocommon foraminifer infillings and occasional trace amounts ofwoody tissues are present. Organic remains are generally moder-ately to rather poorly preserved. Commonly present are transpar-ent membranous tissues, with pyrite impregnation implying somedegree of anaerobic decomposition within the lower sediments ofthe pelagic cap at this site.

Differences between Palynofacies Units 2 and 3 are interpretedas being largely taphonomic. The uphole appearance of dinoflag-ellates, marking the base of Palynofacies Unit 1, seems to be aprimary feature and is discussed in detail below.

Paleoenvironmental Interpretation Based onDinoflagellate Assemblages

The presence of dinoflagellate cysts in the upper 40 m (Palyn-ofacies Unit 1) of the pelagic cap at Site 872 represents the firstdiscovery of dinoflagellates as a result of drilling on westernPacific guyots and atolls. The scarcity of sporopollenin dinoflag-ellate cysts in the oceanic Pacific region is indicated by theirabsence in palynologically examined sediments recovered duringODP Leg 129 (Lancelot, Larson, et al., 1990) and ODP Leg 143(Sager, Winterer, et al., in press) as well as their absence fromSite 871 sediments (see "Biostratigraphy" section, "Site 871"chapter, this volume).

The dinoflagellate assemblages at Site 872 are dominated bythe genus Impagidinium and are thus oceanic in character, al-though a single specimen of Operculodinium israelianum sug-gests some inner neritic influence. In view of the recorded absenceof dinoflagellate cysts elsewhere in this part of the Pacific, theirpresence at Site 872 is intriguing. Perhaps they flourished aroundemergent islands to the east and were swept in suspension bysurface or subsurface currents to Lo-En Guyot. Their absencefrom Palynologic Unit 2 (and possibly Unit 3) might be causedby winnowing but it is not a preservational bias: the presence ofrelatively fragile fecal pellets in these sediments argues againstthe preservational loss of dinoflagellates cysts by oxidation.

Inspection of unsieved residues of samples from Hole 872Arevealed an increase in silt-sized (up to about 10 µm) quartz grainswithin those samples containing dinoflagellate cysts. The siltgrains are angular to subrounded and probably represent eoliandeposition. It is hypothesized that the apparent link between

124

SITE 872

increased silt and dinoflagellate occurrence is related to a sus-tained shift in atmospheric and oceanic circulation beginningduring the late Miocene.

Siliceous Microfossilsand Their Diagenetic Products

The acid-insoluble silt and sand fraction of the sediments fromthe pelagic cap at this site contain authigenic silicates, such as thezeolites: phillipsite and clinoptilolite (Fig. 16). Trace remains ofsiliceous microfossils, such as the dissolution-resistant spongespicules and radiolarians, occur sporadically, generally where theabundance of zeolites decreases. This association may indicatethe presence of a relict assemblage derived from more abundantsiliceous microfossils, the majority of which were dissolved andprovided silica for zeolite formation.

A special situation was encountered in a sample from the topof Core 144-872A-13H. Here, the HCl-insoluble residue wasdominated by light, slightly vesicular ash and by iron oxides. Inaddition, isolated diatoms were found. None of the species en-countered yields significant stratigraphic information. Most of thevalves belong to marine planktonic diatoms. These, and the pres-ence of a resting spore, imply a shelf or slope environment. Inaddition, one valve of the freshwater diatom Aulacosira granulatawas found. The unique presence of diatoms in this sample, whichis also rich in silicic ash, suggests that the silica dissolved fromthis ash protected the diatom shells from dissolution.

SummaryThe oldest sediment preserved on Lo-En Guyot consists of

Santonian pelagic limestone occurring as crack fillings and avolcanic pebble conglomeratic matrix lying atop basaltic base-ment in Core 144-872B-4R. Planktonic foraminifers and, to alesser extent, calcareous nannofossils constrain the age of thismaterial as early Santonian, although there are indications that thelowermost pelagic limestone may be slightly older than that at thetop of the sequence. The presence of middle neritic benthicforaminifers in the lowest material may indicate either a relativelyshallow pelagic paleoenvironment or transport of shallow-watermaterial into a deeper site of deposition. The Santonian fossils areextensively phosphatized, indicating an extended period of expo-sure at the seafloor. The presence of middle Eocene sedimentsdirectly overlying the Santonian limestones indicates a substantialdisconformity with a hiatus of approximately 35 m.y.

The Santonian limestones are mantled by a thin conglomeraticchalk with recrystallized, iron-stained, and/or phosphatized mid-dle Eocene (Zone PU) planktonic foraminifers and partially orwholly replaced (phosphatized?) calcareous nannofossils. A peb-ble from this interval is a conglomerate with a lower Campanianmatrix that was subsequently bored and filled with ooze duringthe early late Paleocene. The middle Eocene mantle of conglom-eratic chalk is, in turn, overlain by upper Oligocene and Neogenepelagic carbonates. Prolonged exposure at the seafloor is indi-cated also for the middle Eocene conglomeratic chalk by theextensive recrystallization and phosphatization of the microfos-sils. The hiatus of the disconformity overlying the middle Eocenesediment suggests seafloor exposure may have been as long asapproximately 15 m.y.

A 140-m-thick sequence of upper Oligocene through Pleisto-cene foraminifer ooze was deposited atop the middle Eoceneexposure surface. Calcareous microplankton stratigraphy indi-cates that sedimentation was relatively continuous from the lateOligocene (Zone P21/Subzone CPI9a) through the Pleistocene,with only minor periods of nondeposition and/or erosion duringthe early Miocene (Zone N7 overlying Subzone N4b; hiatus =approximately 5 m.y.), middle Miocene (Subzone CN7a missing;

hiatus = <l m.y.), and late Miocene (Subzone CN9a missing;hiatus = approximately 2 m.y.). An additional break in sedimentpreservation may occur in the lower Pliocene, although this inter-val may be represented by a relatively condensed sequence inCores 144-872C-3H and -4H (which have not been investigatedin detail as a result of time constraints). The abnormally high ratioof planktonic foraminifers to nannofossils throughout most of theOligocene and Miocene sequence indicates significant winnow-ing of the sediment. This current activity apparently waned duringthe Pliocene and Pleistocene, as evidenced by the relative increasein the volume of nannofossils in the oozes.

PALEOMAGNETISMInitial magnetic susceptibility was measured at an interval of

5 cm on most whole-round cores from the pelagic sediment andon the archive half of split cores containing basalt at Site 872 (Fig.17). The susceptibility in the pelagic sediments is generally lowor negative, with larger values (typically at the tops of cores)probably the result of rust contamination. A downcore decreasein susceptibility, similar to the reduction noted at Site 871, occursat approximately 30 mbsf. Susceptibility values in the basalt aremuch higher (ca. I0"4 to 10~3 cgs). Low values of susceptibilityfrom about 186 to 190 mbsf in Hole 872B correspond to an alteredvesicular ankaramite flow (Unit 18; see "Igneous Petrology"section, this chapter), which is also characterized by an order ofmagnitude lower magnetization than the remaining lavas fromSite 872.

The pelagic sediment at Hole 872A was too soupy and dis-turbed to yield reliable magnetic results. At Hole 872C, an attemptwas made to improve the quality of the cores containing pelagicsediment. The 1.5-m-long core sections were stored in a verticalposition for 2-3 hr, the excess water was drained from eachsection, and the resulting void was removed to prevent the resus-pension and disturbance of the sediment. We measured Cores144-872C-1H through -4H as a test of whether this proceduremight preserve the magnetic signal better. The resulting magneticdata (Fig. 18) have exclusively positive inclinations, presumablyrelated to reorientation during the coring process. Thus, no mag-netostratigraphic data were obtained from the pelagic sediment.We will measure discrete samples in detail on land to examinewhether the pelagic sediment has any reliable remanent magneti-zation.

Thirteen discrete samples of basalt were measured with thepass-through cryogenic magnetometer after alternating-field(AF) demagnetization (Table 3). The majority of the basalt sam-ples have nearly univectorial magnetization and a characteristicdirection that is well defined by AF demagnetization (Figs. 19-20). The NRM intensity of the basalt is <IO A/m. In addition to alow NRM intensity (0.23 A/m), the ankaramite flow mentionedabove (Sample 144-872B-9R-5, 131-133 cm) also exhibits adifferent demagnetization behavior, with little reduction in inten-sity after AF demagnetization in a field of 90 mT (Fig. 21).

The inclinations of the characteristic remanent magnetizationare negative, except for Sample 144-872B-8R-4, 6-8 cm, whichshowed a positive inclination. Subsequent measurement of asample from lower in the same section (Sample 144-872B-8R-4,43-45 cm) and two samples from higher in the same flow unit(Samples 144-872B-8R-1, 70-72 cm, and -8R-2, 89-91 cm)yielded negative inclinations. Thus, the positive inclination of thissingle sample seems to be the result of a section of core that hasbeen inverted.

Basement inclinations range from -41° to -61°, which issteeper than that of the basalts at Site 871 (+2° to -32°). Thesimplest interpretation of the data from Lo-En Guyot is that thedirection represents a normal polarity magnetization acquired at

125

SITE 872

Hole 872A

50.0-

α>Q

100.0.

144.0

Upper Neogene nannofossil zones

6 = E. huxleyi 3 = small Gephyrocapsa R = Very rare radiolarian fragments

5 = G. oceanica 2 = H. sellii D = Single diatoms associated with ash

4 = P. lacunosa 1 = C. maciπtyrei S = Single sponge spicules

Figure 16. Palynofacies units and siliceous microfossil and zeolite abundances for Hole 872A.

a paleolatitude of approximately 30°S. The present latitude of theLo-En Guyot is about 10°N, so the guyot may have moved northabout 40° in latitude after its formation.

SEDIMENTATION RATES

Pelagic Cap

Pelagic sediment accumulation rates for Site 872 (Lo-EnGuyot) are estimated using micropaleontologic data from Hole

872A, the hole in which the greatest biostratigraphic resolutionwas achieved (see "Biostratigraphy" section, this chapter). Paleo-magnetic data are not available because of the disturbed nature ofpelagic sediments at this site (see "Paleomagnetism" section, thischapter). Age assignments for calcareous nannofossils and plank-tonic foraminifers, as shown in Table 4, are taken from Berggren,Kent, and Flynn (1985) and Berggren, Kent, and Van Couvering(1985). Sediment accumulation is plotted graphically in Figure22.

126

SITE 872

Magneticsusceptibility(x 10"6cgs)0 4 8

Magneticsusceptibility(x 10"6 cgs)0 4 8

Magneticsusceptibility(x 10~6cgs)

10 100 1000

20 -

40 J

60

80 -

100 -

120 -

140

i • * -

< * — -

f'f. :Å Hole 872A .

1 : . . : •

-ti.VJT

- I Hole872C-o

200

Figure 17. Magnetic susceptibility variations at Site 872. Note change of scalefor Hole 872C.

0

Declination Inclination(degrees) (degrees)

0 90 180 270360-90 -30 30 90 10"* 1 10' 10

Intensity(mA/m)

. . 2 . . 4

10

Q.

a20

30

Table 3. Results of demagnetization of basaltsfrom Cores 144-872B-5R to -9R and Core 144-872C-18X.


144-872B-5R-1,47-495R-3, 102-1046R-1,40-427R-1,31-337R-4, 67-697R-7, 74_768R-1, 70-728R-2, 89-91*8R-4, 6-88R-4, 4 3 ^ 59R-2, 92-949R-5, 131-133

144-872C-18X-2, 26-28

Inclination(degrees)

-50.2-41.6-48.0-43.3-55.8^ 8 . 7-51.3-43.9

54.4-52.2-61.0-42.5

^ 7 . 5

*Section apparently inverted.

Sample 144-872B-6R-1, 40 cm

W, up

Figure 18. Declination, inclination, and intensity variations for Cores 144-872C-lHto-4H.

Div. = 5.0 x 10

30 50 70mT

Figure 19. Alternating-field (AF) demagnetization results for basalt Sample144-872B-6R-1,40 cm. Demagnetization fields are 0,2.5, 5,7.5,10,12.5, 15,20, 29, 40, 50, 60, and 70 mT. A. Orthogonal vector plot of progressive AFdemagnetization. Closed circles represent horizontal component of the mag-netization, and open circles represent vertical component. B. Stereonet plot ofvector end-points after progressive demagnetization. C. Variation of intensityafter progressive AF demagnetization.

Following a long hiatus that extended from the middle Eocene(nannofossil Subzone CP13b-Zone CP 14, planktonic foraminiferZone PU) through the late Oligocene (nannofossil SubzoneCPI 9a, planktonic foraminifer Zone P21), foraminifer ooze beganto accumulate on the guyot at a rate of approximately 7 m/m.y.Sediment accumulation continued at a similar rate through theOligocene/Miocene boundary interval to the early Miocene. Asignificant part of the lower Miocene interval is missing. There-after, sediment accumulated at an accelerated rate of 15-16m/m.y. A condensed interval of middle Miocene age, spanningplanktonic foraminifer Zones N10-N12 is present in Core 144-872A-8H. After this, for most of the later part of the middleMiocene, sediment once again accumulated at a relatively rapidrate (10—20 m/m.y.). Sediment accumulation rates for the remain-ing part of the sequence (i.e., the upper Miocene, Pliocene, andPleistocene) are difficult to estimate given the existence of several

127

SITE 872

Sample 144-872B-7R-1, 31 cm

W, up

Table 4. Biohorizons used to compute sediment accumulationrates for the pelagic cap of Hole 872A.

E, down

Div. = 5.0x 10'

Figure 20. Alternating-field (AF) demagnetization results for basalt Sample144-872B-7R-1, 31 cm. Demagnetization fields are 0, 2.5,5,7.5,10, 12.5, 15,20, 25, 30, 40, 50, and 70 mT. Other plot conventions are identical to Figure19.

B

Sample 144-872B-9R-5, 131 cm

W, up

IE, down

Div.=δ.Ox 10C

1.0

0.5

J/Jn = 2 . 3 x 1 0 '

10 30 50 70 90mT

Figure 21. Alternating-field (AF) demagnetization results for basalt Sample144-872B-9R-5, 131 cm. Demagnetization fields are 0, 2.5, 5, 7.5, 10, 12.5,15,20,29,40,50,70, and 90 mT. Other plot conventions are identical to Figure19.

short disconformities, but they appear to be on the order of 5m/m.y.

A hiatus in the lower Miocene, spanning planktonicforaminifer Zones N5 and N6, is inferred between Cores 144-872A-12H and -13H. A similar hiatus is noted at approximatelythe same sub-bottom depth in Hole 872C. The hiatus representsapproximately 5 m.y. of missing time. It should be noted that forthe twelfth core of both holes an incomplete stroke of the APCwas recorded, which may indicate some physical change at thislevel. Higher in the sequence, in Cores 144-872A-4H and -5H,reworking of Oligocene and middle Miocene planktonicforaminifers suggests the presence of one or more disconformi-ties, although these approach the limit of biostratigraphic resolu-

Code Datum

Calcareous nannofossils:ClC2C3C4C5C6C7C8C9CIO

enC12C13CHC15C16

FAD E. huxleyiLAD P. lacunosaLAD H. selliiLAD C. macintyreiLAD D. brouweriLAD D. quinqueramusLAD D. hamatusLAD C. coalitusFAD D. hamatusFAD C. coalitusLAD S. heteromorphusFAD S. heteromorphusLAD S. belemnosFAD S. belemnosLAD S. ciperoensisLAD S. distentus

Planktonic foraminifers:FIF2F3F4F5F6F7F8F9F10FUF12F13F14F15

FAD T. truncatulinoidesFAD T. tosaensisFAD S. dehiscensFAD G. tumidaFAD P. primalisLAD G. fohsi robustaFAD G.fohsi lobataFAD G. praefohsiFAD G. peripheroacutaFAD OrbulinaFAD P. sicanaLAD P. kugleriFAD G. dehiscensFAD Globigerinoides spp.LAD P. opima

Age(Ma)

0.280.471.371.451.905.608.859.00

10.0010.8014.4017.1017.4021.5025.2028.20

1.903.105.105.205.80

11.5013.1013.9014.9015.2016.6021.8023.2024.3028.20

Topdepth(mbsf)

0.851.755.857.507.50

17.0036.0036.0045.5047.0068.00

100.00100.00102.00121.00130.50

3.5917.0017.0017.0030.0957.0969.5971.0974.0074.00

100.00102.50111.50121.00140.00

Basedepth(mbsf)

1.352.356.257.507.75

26.5045.5045.5046.0047.5070.00

102.00102.00111.50130.50140.00

7.5030.0930.0930.0936.0057.7271.0972.5983.5083.50

102.00105.59115.08124.58143.58

Notes: Ages given are those from Berggren et al. (1985a, 1985b). "Topdepth" denotes the lowest sample above a biohorizon; "Base depth"denotes the highest sample below the biohorizon. FAD first appear-ance datum, and LAD = last appearance datum.

tion. The absence of nannofossil Subzone CN7a in Core 144-872A-5H is probably because of a short hiatus. Also, nannofossilZone CN8 (0.65 m.y.) was not found in Core 144-872A-4H,suggesting another minor gap in the record, although the assem-blage is very mixed at this level. An additional hiatus is possiblein the unrecovered interval represented by Core 144-872A-3H,although if it does occur, it cannot be a major break because anearly Pliocene assemblage of planktonic foraminifers and nanno-fossils was found in the core catcher of Core 144-872C-3H.

Sediment accumulation rates on Lo-En Guyot are generallycomparable with those observed on Limalok (see "SedimentationRates" section, "Site 871" chapter, this volume). However, accu-mulation on Lo-En was significantly slower through the middleMiocene and Pleistocene.

INORGANIC GEOCHEMISTRY

Interstitial Waters

Interstitial waters were taken from 12 core samples in Hole872A and analyzed according to the methods outlined in the"Explanatory Notes" chapter (this volume). All of these samplescame from calcareous oozes comprising the pelagic cap in theupper 143 m. No interstitial water samples were taken from theunderlying units. Shipboard interstitial water data from Site 872are presented in Table 5.

Salinity and Chlorinity

Pore-water salinity values of samples from Hole 872A areindicative of normal seawater (consistently 35.5 ppt). Chlorinity

128

SITE 872

144

Figure 22. Sediment accumulation rates for the pelagic cap of Hole 872A. Barsrepresent the upper and lower limits of a biohorizon as constrained by sampling.Foraminifer biohorizons are indicated by filled bars, and calcareous nannofos-sils by open bars. Codes for biohorizons are keyed to Table 4.

measurements of these samples are also in the range of normalseawater (555-565 mM) and show no significant depth trend (Fig.23).

Alkalinity, pH, Calcium, Magnesium, Sodium, Potassium,Rubidium, and Lithium

Calcium, magnesium, sodium, potassium, rubidium, and lith-ium concentrations remain constant with depth and are similar toseawater, with pore waters moderately enriched (-1-1.5 mM)with respect to seawater calcium concentrations (Fig. 23). The pHand alkalinity values that were measured have mean values of 7.63and 2.42, respectively, and show no depth trend.

Silica

Silica concentrations of the interstitial water samples fromHole 872A range from 116.93 to 132.13 µM, show no depth trend,and reflect deep-sea concentrations.

Sulfate and Ammonium

Ammonium concentrations in the interstitial water samplesfrom Hole 872A vary from 5.43 to 125.76 µM but show nosystematic depth trend (Fig. 23). Sulfate pore-water concentra-tions are generally invariant with depth and indicative of normalseawater. The maximum ammonium pore-water concentration(125.76 µM) coincides with the minimum sulfate pore-waterconcentration (27.52 mM) in Sample 144-872A-2H-5, 145-150cm, indicating some localized sulfate reduction and organic-mat-ter decomposition at 6 m (Fig. 23).

Fluoride and Strontium

Fluoride and strontium concentrations in interstitial watersamples from Hole 872A vary from 79 to 90 µM and from 104 to115 µM, respectively, and are consistently enriched with respectto normal seawater (Table 5). Although the depth trends forfluoride and strontium are not simple, some covariation is presentbetween these constituents (Fig. 23).

ORGANIC GEOCHEMISTRYAt Site 872, in addition to safety monitoring for hydrocarbon

gases, 23 samples were analyzed to determine the content ofinorganic carbon (IC). No determinations were made of totalorganic carbon, nitrogen, sulfur, and hydrogen because of mal-functioning instruments. The procedures used for the analyticalprogram are described in the "Organic Geochemistry" section,"Explanatory Notes" chapter (this volume).

Volatile HydrocarbonsThe shipboard safety and pollution monitoring program re-

quires regular measurements of light hydrocarbon gases (Ci toC3) in cores immediately after retrieval onto the core deck. Fifteenheadspace gas samples were obtained from the pelagic carbonateooze in Hole 872A. The results of the headspace gas analyses aregiven in Table 6. Very low concentrations of volatile hydrocarbongases were detected. Methane concentrations varied from 2 to 3ppm. The concentrations are only slightly higher than the generalbackground of methane in the laboratory and on the core deck,which was found to vary from 1.8 to 2.1 ppm. Traces of ethaneand propane were found in two of the samples. The very low

Table 5. Surface seawater and interstitial water geochemical data, Site 872.


Surface seawater

144-872A-1H-4, 145-1502H-5, 145-1504H-4, 145-1505H-5, 145-1506H-5, 140-1507H-5, 140-1508H-5, 143-1509H-5, 143-15010H-5, 140-15011H-4, 143-15014H-5, 143-15017H-2, 143-150

Depth(mbsf)

0

5.9514.9532.4543.4552.9062.4071.9381.4390.9098.93

118.93142.93

PH

8.01

7.867.617.327.607.667.637.547.637.567.677.727.76

Alkalinity(mM)

2.30

2.622.312.252.272.332.312.402.382.352.462.742.63

Salinity(g/kg)

35.0

35.535.535.535.535.535.535.535.535.535.535.535.5

er(mM)

555

555556556560565562555559562563563564

Mg2+

(mM)

53.34

53.0653.7053.7853.9552.8654.0654.0254.0152.2453.3953.5453.80

Ca2+

(mM)

10.65

11.7412.1412.3111.9712.1812.1812.2211.9911.9912.0611.6611.64

so -̂(mM)

28.9

27.528.528.628.828.728.629.028.928.728.728.928.7

NHJ(µM)

7

12511155

17137

4016172239

SiO2

(µM)

11

117126132115117128136132126126123128

KT(mM)

10.00

9.479.869.529.189.339.239.479.529.389.479.529.57

Rb(µM)

1.40

1.631.55

:

:

.56

.58

.53

.57

.58

.53

.53

.571.591.61

(µM)

91

109109115105106109111105106104106107

Na+

(mM)

498

482491501502497497505505493502502501

F(µM)

70

879084868888798581857982

Li(µM)

26

272726272626272726272726

129

SITE 872

Alkalinity K + SiO2 Na + Cl" Ca 2 + Li(mM) pH (mM) (µM) (mM) (mM) (mM) (µM)

2 4 6 8 10 100 300 500 10 30

Salinity

50 -

Q .CD

Q

100

(mM)50

150

I 1 1 . 1 ,

D 0 0

D 0 C

D O 0

D O 0

D 0 O~

D 0 0

D 0 O

D 0 0

D 0 0

XI 0 0_

D 0 0

D 0 01 , 1 , 1 ,

1 ' 1D O 0

D O O

D O O

D O O

D O O

D 0 O

D O O

D O O

D O O

XI O O_

D O O

D O 01 , 1

1X D O O

X D O O

X D O O

X D O O

X D O O

X D O O

_× D O o

X D O O

X D O O

X D O O _

X D O O

X D O O1 , 1

0

F Sr2+ SO4" NH4 Rb(µM) (µM) (mM) (µM) (µM)

70 80 90 100 110 1200 20 40 60 80 100 120 140 1.54 1.56 1.58 1.60 1.62 1.64

50 -

Q .CD

Q

100 -

D O

D O

D O

D O

D O

D O

D O

D O

D O

D O _

D O

D O1 I > I 1 I 1 I 1

, | , | 1 | • | . | . | •

O D

D O

D O

D O

D O

D O

_D O

O D

D O

_ D O _

DO

O D, 1 , 1 , ,

O

O

O

O

~O

O

O

0

0

0

0

0

1 , 1 . 1 , 1 , 1 ,150

Figure 23. Concentrations of interstitial pore-water parameters vs. depth, Hole 872A. Concentration values remain constant at nearseawater values throughout the 143 m of the pelagic cap, with the exception of minor elevations in calcium, fluoride, and strontium andlocalized sulfate depletion together with ammonium enrichment (see text for details).

130

SITE 872

Table 6. Results of headspace gas analyses, Hole872A.


144-872 A-1H-5, 0-52H-6, 0-54H-6, 0-55H-6, 0-56H-6, 0-57H-6, 0-58H-6, 0-59H-6, 0-510H-6, 0-5llH-5,0-513H-6, 0-514H-6, 0-515H-6, 0-516H-5, 0-517H-3.0-5

Laboratory backgroundCore deck background

Methane(ppm)

2.22.72.02.62.02.02.32.52.02.01.92.02.02.52.82.11.9

Ethane(ppm)

TrNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNone

TrNoneNone

Propane(ppm)

TrTr

NoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNoneNone

Notes: Tr = trace, and None = no gas detected.

volatile gas concentration in the pelagic cap can be ascribed tolow concentrations of organic carbon in these sediments (TOCbelow 0.5%; see paragraph on organic carbon).

Carbonate Carbon

Inorganic carbon content (IC) was measured in 23 samplesfrom Holes 872A and 872B with the Coulometrics carbon dioxidecoulometer. No carbonate determinations were performed onsamples from Hole 872C. In Hole 872A, one sample from eachcore of the pelagic cap was analyzed for IC. Most of the sampleswere obtained from the material squeezed for pore-water analysis,as described in the "Inorganic Geochemistry" section, "Explana-tory Notes" chapter (this volume). By using this approach, sam-ples should be virtually free of pore water before drying and nopore-water precipitates are expected. Nevertheless, a few samplesdesalted before coulometer analysis were found to be signifi-cantly higher in IC than the squeeze-cake samples (see Fig. 24),probably reflecting minor amounts of pore-water salts precipi-tated during sample handling. Thus, the most accurate carbonatedeterminations are obtained from desalted samples. This proce-dure should be applied for precise carbonate determinations ofpelagic oozes in the future. In Hole 872B, which contained indu-rated limestones, three microsamples (approximately 100 mg)were collected by hand drilling, using a standard 5-mm drill bit.

The IC and calcium carbonate values for Holes 872A and 872Bare given in Table 7. Calcium carbonate content was very high inall samples from the pelagic cap, ranging from 94% to 99%(average = 96.9%, standard deviation = 1.39). The minor fluctua-tions with depth seen in Hole 872A (Fig. 24) can probably beascribed to analytical error (see above) and are not consideredsignificant except for the shift toward lower calcium carbonatevalues in the bottom of the hole (Core 144-872A-17H). Thecarbonate content of the limestone matrix of the basalt brecciasin Core 144-872B-4R-1 was between 91% and 97%.

Organic Carbon and Total Sulfur

Because of malfunctioning analytical instruments, no determi-nations were made of organic carbon and total sulfur.

Organic Matter Typeand Thermal Maturation Level

Shipboard geochemical characterizations of organic matter arenormally performed by Rock-Eval (RE) and pyrolysis gas chro-

,60

Carbonate (wt %)70 80 90 100

50 -

Q.

Q

100 -_

•

i • i

•

DesaltedSqueeze cake

i '

•

•

•

•

•

•

•

•π -

B

a

D

IA

IB

Figure 24. Carbonate content of sediments in Holes 872A and 872B, calculatedas calcium carbonate. Also shown are the major lithologic units, as given inthe "Lithostratigraphy" section (this chapter).

Table 7. Results of geochemical analyses, Holes 872A and 872B.


144-872A-1H-4, 145-1502H-5, 145-1504H-4, 145-1505H-5, 145-1506H-5, 145-1507H-5, 145-1508H-5, 143-1459H-5, 143-14510H-5, 140-15011H-4, 69-7111H-5, 69-7113H-5, 69-7113H-6, 69-7114H-5, 143-15015H-5, 69-7116H-5, 69-7117H-1,69-7117H-2, 69-7117H-2, 143-15017H-3, 69-71

144-872B-4R-1, 19-214R-1, 51-524R-1, 68-71

Lithology

Calcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous oozeCalcareous ooze

LimestoneLimestoneLimestone

Depth(mbsf)

5.9514.9532.4543.4552.9062.4071.9381.4390.9098.1999.69

108.69110.19118.93127.69137.19140.69142.19142.93143.69

135.39135.71135.88

IC(wt%)

11.668.59

11.5511.7111.6811.5411.6411.4711.4211.3511.5911.8011.8211.2911.8311.8311.8011.7811.5911.50

10.9511.2911.55

CaCO3

(wt%)

97.1571.5796.2397.5797.3296.1596.9895.5795.1594.5796.5798.3298.4894.0798.5798.5798.3298.1596.5795.82

91.2494.0796.23

Notes: IC = inorganic carbon. CaCCb = carbonate carbon calculated as calciumcarbonate.

131

SITE 872

matographic (Py-GC) analyses. During the time spent at Site 872,neither the Rock-Eval system nor the Geofina Py-GC were oper-ating properly; therefore, no results are reported here. Visualinspection by light microscopy shows organic matter to be ther-mally immature, as judged from the light brown to yellow colorof the particles.

ConclusionsThe following conclusions can be made regarding the organic

geochemistry at Site 872: (1) no volatile hydrocarbons wereencountered at Site 872; (2) the pelagic cap sediments (LithologicUnit I) have a calcium carbonate content of almost 100%; and (3)organic matter at this site is thermally immature with regard tohydrocarbon formation.

IGNEOUS PETROLOGY

IntroductionThree holes were drilled at Site 872 on Lo-En Guyot. Basalt

was recovered in the bottom of each hole, although only smallamounts were recovered from Holes 872A and 872C. Hole 872Bpenetrated 57.3 m into basalt, starting at 135.4 mbsf, with 41%recovery. Basalt was reached at 143.7 and 142.75 mbsf, with 0.29and 2.06 m of recovery in Holes 872A and 872C, respectively. Theinterval and a description of each unit are in Table 8.

The uppermost basalt unit in each hole is an alkali olivinebasalt. On the basis of petrographically determined texture, min-eralogy, and alteration, Unit 1 in Hole 872A and Unit 5 in Hole872B (the first basalt flow; Units 1-4 are conglomerates andfracture fill) appear to be from the same flow. Unit 1 in Hole 872Cis quite different in texture and mineralogy from any unit in Hole872B and is likely to have been from a different flow. Beginningin Section 144-872B-4R-1, 21 cm, Units 5-18 are a series of

differentiated basalt and hawaiite flows. Unit 11 may be amugearite. Thick, brecciated flow tops occur in Unit 10 (Section144-872B-5R-4, 24 cm) and several units downsection, suggest-ing that these flows were erupted subaerially. Below Unit 14(Section 144-872B-7R-2,0 cm), recovery is sufficiently completeto establish that the time interval between flows was short enoughto preclude soil development on top of the flows.

This sequence of flows appears to represent the very latestshield stage or the alkalic-cap stage of hotspot volcanism.

Hole 872ATwenty-nine centimeters of a severely altered, aphyric basalt

were recovered in Hole 872A. The matrix is light brownish grayand has been altered to clay minerals. Abundant veins and vesiclesfilled with calcite, zeolites, and brown clays are also present. Muchof the groundmass has been obscured by green and brown clays. Theidentifiable groundmass mineralogy is 8% iddingsite and greenclay pseudomorphs after olivine; 56% Plagioclase laths, mostpseudomorphed by speckled brown clays; and 15% subhedraltitanomagnetite grains and trace ilmenite needles, most pseudo-morphed by hematite. This mineralogy is consistent with the unitbeing a differentiated alkali olivine basalt.

Hole 872BUnits 1-6

Units 1-6 include volcanic and biogenic materials recoveredin Core 144-872B-4R-1. Only Unit 6 is large enough and freshenough to be useful for igneous petrology and geochemistry, butthe intercalated sediments are of particular interest in view of theirCretaceous faunas (see "Biostratigraphy" section, this chapter)and because they provide a minimum age for the underlyingbasalt.

Table 8. Summary of igneous units, Site 872.

Unit Core, section, interval (cm) Description

Hole 872A:1

Hole 872B:123456789

144-872A-18X-l,0-29cm

144-872B-4R-l,0-13cm144-872B-4R-1, 13-16 cm144-872B-4R-1, 17-21 cm144-872B-4R-1, at 28, 34, 50, 60, and 67 cm144-872B-4R-1, 21-31144-872B-4R-1, 33 cm, to -5R-2, 6 cm144-872B-5R-2, 6 - l l cm144-872B-5R-2, 11^*3 cm144-872B-5R-2, 43 cm, to -5R-4, 23 cm

10 144-872B-5R-4, 24 cm, to -6R-1, 67 cm

11121314

15

16

17

18

19Hole 872C:

1

144-872B-6R-1, 74-100 cm144-872B-6R-1, 101-126 cm144-872B-7R-l,0-65cm144-872B-7R-2, 0 cm, to -7R-6, 43 cm

144-872B-7R-6, 43 cm, to -7R-7, 83 cm

144-872B-7R-7, 83 cm, to -9R-1, 5 cm

144-872B-9R-1, 6 cm, to -9R-3, 90 cm

144-872B-9R-3, 91 cm, to -9R-6, 60 cm

144-872B-9R-6, 60-72 cm

144-872C-17X-CC, 48 cm, to -18X-2, 60 cm

Clinopyroxene basalt

Volcanogenic sandstonePhosphatic pebble conglomerate with foraminifer limestone matrixBasalt pebble conglomerate with foraminifer limestone matrixForaminifer limestone fracture filling in Units 5 and 6Olivine basaltClinopyroxene basaltAphyric basaltAphyric basaltClinopyroxene basalt

Subunit 9A flow-top brecciaSubunit 9B massive flow

Aphyric basaltSubunit 10A flow-top brecciaSubunit 10B massive flow

Clinopyroxene basaltAphyric basaltClinopyroxene basaltClinopyroxene-olivine basalt

Subunit 14A flow-top brecciaSubunit 14B massive flow

Clinopyroxene basaltSubunit 15A flow-top breccia.Subunit 15B massive flow

Clinopyroxene basaltSubunit 16A flow-top breccia.Subunit 16B massive flow.

Aphyric basaltSubunit 17A flow-top brecciaSubunit 17B massive flow

Olivine-clinopyroxene basaltSubunit 18A flow-top brecciaSubunit 18B massive flow

Very altered basalt

Olivine basalt

132

SITE 872

Unit 1 (Interval 144-872B-4R-1, 0-13 cm) is a pale yellow tolight yellowish brown volcanogenic sandstone. Unit 2 (Interval144-872B-4R-1, 13-16 cm) is aphosphatic pebble conglomerate.Dark brown phosphatic pebbles and occasional angular basaltclasts with 1-2 cm diameters are in a friable foraminifer limestonematrix. Unit 3 (Interval 144-872B-4R-1,17-21 cm) is a conglom-erate with subrounded to subangular, 0.5-5 cm basalt clasts in awhite foraminifer limestone matrix. Unit 4 includes several frac-ture fillings of foraminifer limestone within the basalts of Units5 and 6 (see "Biostratigraphy" section, this chapter).

Unit 5 (Interval 144-872B-4R-1, 21-31 cm) is a sparselyolivine-phyric basalt. Patches of brown clay obscure 30% of thegroundmass. What remains is 10% iddingsite and green claypseudomorphs after olivine, 15% hematite pseudomorphs aftereuhedral titanomagnetite, and 45% Plagioclase laths, mostlypseudomorphed by brown speckled clays. This mineralogy isconsistent with the unit being a differentiated alkali olivine basalt,indistinguishable from the basalt of Hole 872A, Unit 1.

Unit 6 (from Sections 144-872B-4R-1, 31 cm, to -5R-1, 150cm) contains sparse, dark green phenocrysts. The matrix is yel-lowish brown and appears quite altered, but less so in the lowerpart of the unit where its color is grayer. It contains fewer than1 % olivine phenocrysts, which are unaltered and have anhedral,resorbed shapes subsequently rimmed with optically continuousskeletal overgrowths and 7% euhedral Plagioclase phenocrysts.The groundmass consists of Plagioclase microlites (An35-45) ar-ranged in a pilotaxitic texture, and 20% euhedral to subhedraltitanomagnetite microphenocrysts. The texture and Plagioclasecomposition of this lava suggest that it is an hawaiite.

Units 7-9 and 11-13

Units 7-13, excluding Unit 10, are six distinct lava flows withrecovered thicknesses between 26 cm and 2.61 m. Flow bounda-ries were not recovered.

All these flows are aphyric or sparsely clinopyroxene-phyricbasalts with microcrystalline groundmasses. Groundmass colorsrange from dusky reds and yellowish browns, indicative of oxi-dation and severe alteration to clay and zeolite minerals, respec-tively, to shades of medium and dark gray indicative of lessalteration. Units 9 and 13 have mottled red and gray ground-masses.

Round to irregular vesicles occur in Units 8, 9, and 13. Theabundances of vesicles are widely variable within each flow(5%-40%, with an average of about 20%), and they range in sizefrom 0.25 mm to 1 cm. A small number of vesicles are lined withblue and green clay, but most are filled with calcite and white orpinkish orange zeolites. Larger vesicles typically have a 2-mmrim of the pinkish orange zeolite and a calcite-filled center. AnX-ray diffraction (XRD) analysis of the pinkish orange zeoliteindicated that it is the mineral chabazite.

Subhorizontal sparry calcite and zeolite veins are uniformlydistributed throughout each flow. They are <l to 7 mm in widthand are spaced about 10—12 cm apart.

Unit 9 has been divided into Subunits 9A and 9B, separated bya gradational boundary between a more altered and oxidizedupper zone (A), and a less altered and oxidized lower zone (B).In thin section, there are 5%-10%, subhedral, slightly pink (ti-taniferous?) augite phenocrysts, traces of titanomagnetite and<5% ilmenite microphenocrysts, and 80% Plagioclase phe-nocrysts and microlites. This mineralogy suggests that this flowis a differentiated alkalic basalt or perhaps an hawaiite.

Unit 11 has 3% pseudomorphs after olivine, 55% euhedralPlagioclase phenocrysts and microlites, subequal (about 5% each)abundances of euhedral titanomagnetite and ilmenite needles,both of which appear in reflected light to be fresh, trace, anhedral

potassic feldspar, biotite, and hornblende. The flow has beenextensively altered to very bright green phyllosilicates (chlorite?)and brown speckled clays, which cover 25% of the groundmassin irregular 0.25-1 mm patches. The "chloritization" of the sam-ple, which is a common characteristic of equivalent Samoan lavas,and the presence of biotite, hornblende, and potassic feldsparsuggest that the flow is a mugearite.

Unit 13 is pervasively altered, with both phenocrysts andgroundmass replaced by phyllosilicates. Pseudomorphs of plagio-clase (47%), olivine (1%), titanomagnetite (7%), and accessoryilmenite can still be distinguished. Despite the alteration, 2% ofunaltered olivine and clinopyroxene xenocrysts persist. The se-verity of alteration makes identification very difficult, but themineralogy that can be discerned suggests that the flow was adifferentiated alkali olivine basalt.

Unüs 10 and 14-18

Unit 10 and Units 14 through 18 are single flows, each with arelatively thick flow-top breccia above a massive base. Recoveredthicknesses of brecciated flow tops vary from 19 cm to 3.28 m,whereas recovered thicknesses of massive flows vary from 91 cmto 3.39 m.

Clasts in the flow-top breccias are typically subangular and1-10 cm across; occasional larger clasts, up to 30 cm, are present.They are aphyric (smaller clasts) to sparsely clinopyroxene-phyric (larger clasts). Colors vary within each flow top; usuallyclasts of both dark red and medium to dark gray are present. TheUnit 16 flow top has very indistinct clast-matrix boundaries; allother flow tops have very distinct clast-matrix boundaries.

Except for Unit 18, in which all the clasts are nonvesicular, theclasts of the flow-top breccias have vesicle abundances varyingfrom 0% to 50%. The vesicles are 0.5-10 mm in size, irregular toround in shape, and either filled with calcite and the pinkishorange zeolite (chabazite?) or lined with blue and green clays. Afew are filled with dark green clay. Figure 25 is a photo of a typicalportion of flow-top breccia.

The matrix around the clasts consists of sand- and granule-sized (2—4 mm), subrounded volcaniclastic grains. These arecemented by calcite and chabazite. Units 10 and 18 also havepatches of dark green phyllosilicates in the flow-top matrix.

The massive portions of the flows are aphyric to sparselyclinopyroxene and olivine-phyric with microcrystalline ground-masses. Groundmass colors are medium gray where fresh, andyellowish, reddish, and greenish gray where more alteration hasoccurred. The massive portions of Units 14 and 16 have a morealtered yellowish gray zone with dark iron staining along fracturesin the lower halves, returning to fresher material about 30 cmabove the top of the next unit.

All massive portions of the units are vesicular. Vesicles tendto be concentrated in subhorizontal bands on a scale of roughly10-30 cm, with abundances ranging from 2% to 50%. As in theflow tops, vesicle centers are filled with calcite and a whitezeolite, often inside a 2-mm rim of the pinkish orange zeolite; afew are empty and lined with blue and green clays.

Veins constitute l%-4% of all these flows, increasing to 10%in the massive portion of Unit 18. They are 0.25-7 mm thick,filled with sparry calcite and zeolites, and are often subhorizontal.In Unit 18 the veins occur in subhorizontal anastomosing bands,5-20 mm in width, spaced roughly every 5 cm (see Fig. 26). Theseveins give a strong impression of shearing, but no evidence fordeformation of the intervening lavas exists.

Several of the contacts between the brecciated flow tops andmassive bottoms were recovered within a single piece of core. Thecontact between the massive bottom of Unit 14 and the brecciatedtop of Unit 15 was also recovered. No evidence of soil develop-

133

SITE 872

cm

56-i

5 8 -

6 0 -

6 2 -

6 4 -

6 6 -

6 8 -

7 0 -

7 2 -

7 4 -

7 6 -

7 8 -

Figure 25. Interval 144-872B-7R-3, 55-80 cm, part of Igneous Subunit 14A.Flow-top breccia of 1-10 cm, subangular clasts in a volcanogenic sand matrixcemented by calcite (white) and the zeolite chabazite (light gray in photo, withvery visible saw marks). Typical of the flow-top breccias in Hole 872B.

cm9 2 -

9 4 -

9 6 -

9 8 -

100-

102-

104-

106-

108-

110—

112-

114-i

116-

118-

Figure 26. Interval 144-872B-9R-4, 92-119 cm, part of Igneous Subunit 18B.Vesicular, massive flow portion of Unit 18 with anastomosing veins of calcite.Vesicles are filled with calcite and chabazite.

134

SITE 872

ment at this contact or anywhere else in these flows is present;they appear to have been erupted subaerially in a short period oftime.

In thin section, Units 10, 14, 15, 16, and 17 have 45%-70%Plagioclase phenocrysts and microlites, often forming a slightlyfelty texture, and 8%-25% euhedral titanomagnetite microphe-nocrysts. Ilmenite is present in some of the flows. Mafic phe-nocrysts and microphenocrysts are present in small amounts inmost of the flows. Many are now pseudomorphs after phyllosili-cates, and much of the groundmass of each flow has been ob-scured by green and brown clays. The low abundances of olivineand clinopyroxene, the lack of orthopyroxene, and the preponder-ance of Plagioclase and titanomagnetite suggest that these lavasbelong to a differentiated alkalic series. Units 14, 15, and 16appear to be differentiated alkalic basalts. Unit 17, which lacksmafic phenocrysts, is probably an hawaiite.

Unit 18 has a groundmass very similar to the overlying flows;it is probably an hawaiite, based on the composition of the pla-gioclase (An30-35) and on the low abundances (5% total) of oxideminerals. However, the lava contains 17% fibrous, subhedralpseudomorphs after olivine and 3% fresh, cracked, anhedralaugites. These are unlikely to have been in equilibrium with thegroundmass and are interpreted as xenocrysts.

Hole 872CThe basalt pieces recovered from Hole 872C appear to be from

a single flow. They are aphyric, with a medium gray groundmassthat consists of 15% iddingsite and green clay pseudomorphs afterolivine; 4% ilmenite needles and 1 % titanomagnetite grains, bothreplaced by hematite; 5% slightly pink (titaniferous), fresh augite;and 70% slightly altered (to clay) microlites of Plagioclase. Themineralogy suggests that the sample is a differentiated alkaliolivine basalt. However, the unit differs, by the presence ofclinopyroxene microphenocrysts and a distinct subophitic tex-ture, from the flow(s) sampled at the top of the basaltic units inHoles 872A and 872B, and thus is probably not the same flow.

PHYSICAL PROPERTIES

IntroductionThe objectives of the physical properties measurement pro-

gram at Site 872 were (1) to measure the standard shipboardphysical properties and (2) to identify geotechnical units fordownhole and cross-hole correlations. The standard shipboardphysical properties program included (1) nondestructive meas-urements of bulk density, acoustic compressional velocity, andmagnetic susceptibility, made using sensors mounted on the mul-tisensor track (MST); and (2) discrete measurements of indexproperties, vane shear strength, compressional wave velocity, andthermal conductivity (see "Explanatory Notes" chapter, this vol-ume). Shear strength was measured on the pelagic sedimentsusing the Wykeham-Farrance vane shear device. Thermal conduc-tivity measurements were made using the needle-probe method inunlithified sediments (von Herzen and Maxwell, 1959); the slabmethod was used in basalts (Vacquier, 1985). Compressionalwave velocities were measured using the digital sound velocime-ter (DSV) in the pelagic sediments and the Hamilton Frame (HF)on sample cubes of the basalts. All whole-round sections werepassed through the MST-mounted sensors before being split;shipboard and shore-based whole-round samples were cut firstfrom either end of the section.

Sediments recovered at Site 872 consist of unlithified nanno-fossil foraminifer ooze (Hole 872A, 0-30 mbsf; Hole 872C, 0-18mbsf) and foraminifer ooze (Hole 872A, 30-144 mbsf; Hole872C, 18-148 mbsf) forming the pelagic cap on the guyot. Thepelagic sediments are very similar lithologically to those from

Site 871. Pelagic sediments from Holes 872A and 872C weresampled at intervals of 1.5 to 4.0 m. Basalt, altered and/or weath-ered to various degrees, underlies the pelagic sediments. The onlylimestone at this site was observed as infillings of lithified car-bonate in the basalt. Core recovery in the pelagic cap varied from0% to 100%; however, the average recovery of pelagic cap sedi-ments was 85%. In contrast, core recovery in the basalts averagedonly 25% (range of 0%-88% recovery). Basalts were sampled ateach lithologic change where recovery permitted. As was the casewith Site 871, samples were shared with other shipboard labora-tories where appropriate.

The pelagic oozes from Hole 872A suffered considerabledisturbance from both drilling, handling, and splitting operations(see "Physical Properties" section, "Site 871" chapter, this vol-ume). To reduce disturbance to the pelagic sediments, specialhandling procedures were used for cores from Hole 872C. Theliners were cut into sections and stored upright on the catwalkbefore making whole-round measurements and splitting the core.After allowing time for settlement, free water was drained off, thecore liner was trimmed to the upper level of the sediments, andthe core sections were capped. This process was generally suc-cessful in reducing the proportion of free water in each sectionand, hence, in improving the quality of whole-core measurements.

The results from physical properties measurements on thepelagic sediments and basalts are similar to those obtained at Site871. Bulk density profiles for Hole 872C show a characteristicuniformity, with the exception of the uppermost 35 m of sediment,where some variation is observed (also seen at Site 871). Therewere two peaks in bulk density in the upper pelagic cap: one near8 mbsf and the other near 28 mbsf. Physical properties data fromSite 872 are presented in Tables 9 (index properties), 10 (thermalconductivity), 11 (DSV velocities), 12 (HF velocities), and 13(vane shear strength).

Geotechnical and Properties UnitsPelagic Cap

Geotechnical Subunits 1A and IB were defined through anexamination of discrete measurements of physical properties(Figs. 27-29 and Table 9), and using the GRAPE density profiles(Fig. 30). At Holes 872A and 872C, Geotechnical Subunit 1A(Hole 872A, 0-30 mbsf, and Hole 872C, 0-32 mbsf) coincideswith Lithologic Subunit IA. The lack of core recovery in Core144-872A-3H at Hole 872A resulted in a gap in the density profileat an important point downhole, thus making the correlationbetween holes in the lower portion of Geotechnical Unit IAuncertain.

The discrete density profile for Hole 872C shows two well-de-fined peaks at approximately 14 and 28 mbsf. Below 35 mbsf inHoles 872A and 872B, the measured bulk density of discretesamples of pelagic sediment is fairly uniform; dry-bulk densitiesare between 0.6 and 0.7 g/cm3 and wet-bulk densities are between1.4 and 1.5 g/cm3.

The water content data reveal a trend toward a peak in watercontent at 50 mbsf in both Holes 872A and 872C (Figs. 27 and29), despite moderate scatter. A second peak is also suggested ata depth of 85 mbsf in both holes. Below 50 mbsf, a gradualreduction in water content takes place. Errors in the determinationof water content and wet-bulk density are introduced by the rapiddraining of the foraminifer oozes on the workbench. Samplestaken from the deepest part of the split core contain more waterthan those taken from the cut surface.

The GRAPE profiles, from 0 to 35 mbsf in Holes 872A and872C, are in good agreement with each other when allowance ismade for the shortened section lengths in Hole 872C. A series oflarge density peaks observed just above 30 mbsf in Hole 872 A arefound just below 30 mbsf in Hole 872C. A low-density interval

135

SITE 872

Table 9. Index properties data, Site 872.


Depth(mbsf)

Wet-bulkdensity(g/cm3)

Dry-bulkdensity(g/cmJ)

Graindensity(g/cm*)

PorosityWatercontent

(% dry wt)

144-872A-1H-1,4(M21H-1, 130-1321H-2, 100-1021H-3, 100-1021H-4, 100-1021H-5, 100-1022H-1, 100-1022H-2, 100-1022H-3, 100-1022H-4, 60-622H-5,120-1222H-6, 20-224H-1,30-324H-2, 30-324H-3, 30-324H-4, 30-324H-5, 30-325H-1, 80-825H-2, 80-825H-3, 80-825H-4, 80-825H-5, 80-826H-2, 130-1326H-4, 125-1276H-6, 80-827H-2, 35-377H-4, 100-1027H-6, 50-528H-1, 100-1028H-3, 100-1028H-5, 80-828H-7, 7-99H-2, 80-829H-4, 63-659H-6,47-4910H-2, 50-5210H-4, 50-5210H-6, 50-5211H-2, 66-6811H-4, 50-5213H-2, 116-11813H-4, 70-7213H-6, 39-4114H-2, 60-6214H-4, 50-5214H-6, 25-2715H-1, 110-11215H-2, 110-11215H-3, 110-11215H-4, 110-11215H-6, 110-11216H-2, 100-10216H-4, 100-10216H-6, 100-10217H-1,80-8217H-2, 80-8217H-3, 135-137

144-872B-5R-1,47^95R-3, 102-1046R-1,40-427R-1,31-337R4, 67-69

0.401.302.504.005.507.008.50

10.0011.5012.6014.7015.2026.8028.3029.8031.3032.8036.8038.3039.8041.3042.8048.3051.2553.8056.8560.5063.0065.5068.5071.3073.5776.3079.1381.9785.5088.5091.5095.1698.00

104.66107.20109.89113.60116.50119.25122.10123.60125.10126.60129.40133.00136.00139.00140.80142.30144.30

145.27148.64154.90164.31168.09

1.501.451.461.521.521.491.481.491.511.501.531.481.511.631.561.431.451.451.441.421.441.421.381.411.431.391.421.401.441.421.401.441.391.431.391.401.491.401.441.491.481.431.431.481.521.531.451.441.431.441.441.521.511.471.521.541.55

2.712.732.432.452.69

0.760.690.690.760.760.740.730.740.760.750.810.700.780.960.860.650.670.670.650.630.620.630.580.610.620.590.630.610.670.630.620.650.600.660.600.590.730.620.660.750.730.650.650.730.800.790.670.660.640.660.650.770.770.710.770.800.83

2.662.602.182.232.57

2.812.612.692.782.702.802.732.702.752.742.822.792.662.742.782.832.782.802.752.752.752.822.662.702.712.722.782.712.592.752.672.682.732.752.742.722.732.712.752.672.692.652.812.692,862.772.712.782.732.812.722.732.782.722.802.752.75

2.812.922.842.822.82

75.0076.5077.6076.7076.7075.4075.8075.6075.2075.0073.6078.3073.8068.4070.5078.7078.1079.0079.5079.7082.4080.0081.4080.6081.4081.2079.4079.6077.6079.6079.5079.5080.5078.5079.7081.2076.0079.6078.7075.8076.2078.2078.5075.8073.6074.5079.0079.2079.8079.2079.8076.1075.4077.1075.4075.2072.70

4.9012.4024.5022.5011.70

104.30118.40119.50107.00107.00107.80110.10107.90104.70105.7096.70

119.00100.9075.3086.30

128.60123.90127.10130.80134.80142.00137.20152.20141.00140.50147.80134.50139.10123.50135.30137.90131.00144.50127.90142.00147.30110.30138.80127.30108.20111.40128.50129.00109.8098.00

100.00125.50128.30132.80128.90130.60105.70104.50115.70103.8099.7092.30

1.904.90

11.5010.404.70


Depth(mbsf)

Wet-bulkdensity(g/cm*)

Dry-bulkdensity(g/cmJ)

Graindensity(g/cm5)

PorosityWater

content(% dry wt)

144-872B-(Cont.)7R-7, 74-768R-1,70-728R-2, 89-918R-4, 6-89R-1,46-489R-2, 92-949R4, 14-169R-5, 131-133

144-872C-1H-6,66-682H-2,61-632H-3, 61-632H-4, 61-632H-5, 61-632H-6, 61-633H-2, 70-723H-3, 70-723H-4, 70-723H-5, 70-723H-6, 70-723H-7, 20-224H-1, 80-824H-2, 80-824H-3, 80-824H-4, 80-824H-5, 80-824H-6, 80-825H-2, 70-725H-3, 70-725H4, 70-725H-5, 70-725H-6, 70-726H-2, 72-746H-4, 72-746H-6, 72-747H-1,63-657H-3, 70-727H-5, 30-328H-2, 70-728H-4, 70-728H-6, 70-729H-2, 70-729H4, 70-729H-6, 70-7210H-2, 70-7210H-5, 70-7210H-6, 125-12711H-2, 70-7211H4, 70-7211H-6, 70-7212H-2, 70-7213H-2, 70-7213H-5, 70-7214H-3, 70-7214H-5, 70-7214H-7,29-3115H-1, 50-5215H-3, 50-5215H-5, 50-5216H-2, 100-10216H-4, 100-10216H-6, 100-10217X-2, 25-27

172.37173.80175.35177.48183.06184.90186.72189.29

7.1410.5711.9313.3114.6316.0020.2621.4722.7724.0825.4026.3028.8029.8231.0832.4133.7134.9239.0640.2141.4742.6643.8648.6151.1653.7257.1359.5161.7867.7170.3172.9777.5380.1682.8386.8490.9892.9896.4099.07

101.66106.20107.88111.84118.59121.19123.52125.50127.84130.06131.78134.23136.52140.30

2.422.512.822.872.352.852.432.44

1.581.521.541.511.421.471.511.441.501.491.571.591.611.571.531.561.481.421.471.421.411.421.451.391.391.401.471.431.431.431.431.421.401.391.401.391.391.381.421.411.481.471.441.451.491.531.581.461.431.461.431.511.561.63

2.182.312.732.792.012.752.132.14

0.870.800.820.780.650.7!0.760.650.760.700.830.900.880.870.810.810.690.630.710.630.620.620.650.590.590.620.690.620.640.660.670.650.610.600.640.600.610.590.640.630.730.720.690.700.760.750.850.710.670.710.670.770.820.93

2.912.722.852.882.742.952.782.91

2.692.662.652.612.642.682.722.722.802.732.722.732.682.842.722.642.572.662.742.702.682.542.562.692.722.692.462.752.632.612.732.692.592.682.522.622.592.542.682.582.662.682.592.662.572.722.702.662.672.582.522.672.712.68

24.6020.60

9.407.70

34.4010.2030.8030.70

71.3072.5072.9073.7078.1076.3076.1079.6074.8080.4074.6070.4073.6070.7072.9075.2080.1080.5077.1079.8079.5080.7081.3081.0081.6079.5079.6082.5080.4077.9077.7078.2079.7080.0077.2080.1079.0079.8078.6078.9075.4075.8076.0075.1073.6078.9074.0075.4077.2076.4076.9074.3075.2071.00

11.609.203.502.80

17.703.80

14.9014.80

86.3095.6094.20

100.70128.20114.30106.60131.30104.40123.4094.8082.6088.0085.7095.3097.90

124.20138.30116.00135.60137.40139.00134.10149.20150.10138.10123.80144.30135.60126.50124.60129.60140.60143.60129.80143.50138.10144.50131.20134.80109.80112.50117.30113.50102.10111.9091.70

112.80123.50114.90122.30101.8097.2080.50

separating the two largest density peaks is noted at -29 mbsf inHole 872A and at -31.5 mbsf in Hole 872C. This density low isassociated with a peak in magnetic susceptibility values at thesesame depths in each hole (Fig. 31).

Magnetic susceptibility data plotted vs. depth (Fig. 31) showa "core" effect in which values are higher in the first section ofeach core. Values of magnetic susceptibility in pelagic carbonateswithin the core generally lie below zero, with the exception of theinterval between 0 and 20 mbsf. No clear trend can be discernedwith depth. Unusually high susceptibility values may be a func-tion of drilling contamination, which was sometimes indicated inthe white pelagic sediments by dark patches, probably derivedfrom pipe dope.

Figure 32 shows the DSV velocity profile for Holes 872A and872C (see Table 11). Both profiles show considerable scatter withno clear trend apparent. The velocity values, as was the case atSite 871, cluster around the value for seawater. The P-wave logger(PWL) data are generally poor as a result of the lack of signalstrength and inadequate sediment-to-liner contact, despite the

improvements in core handling described earlier. Velocity valuesappeared to switch at random between 1400-1500 m/s and 2400-2500 m/s. It seems more likely that the lower values are "correct"as they agree with those (discrete) obtained by the DSV apparatus;these lower values were obtained at those points where signalstrength was higher.

It was possible, using an empty liner, to demonstrate conclu-sively that the PWL has a bimodal characteristic when used withsediments that have poor contact with the liner. Compressionalwave transmission through the sediment produced values of1400-1500 m/s, whereas the higher values commonly obtained(2400-2500 m/s) were caused by compressional wave transmis-sion around the inside of the liner. These higher values wereassociated with lower signal strengths and presumably poorersediment-liner contact. In the case of the DSV apparatus, insertionof the transducers into the sediment usually caused cracking ofthe half-round core and hence poor contact between sediment andtransducer. The experimental factors discussed above applyequally to the Site 871 results.

136

SITE 872

Table 10. Thermal conductivity data, Site 872.


144-872A-1H-2, 501H-3, 501H-5, 502H-1,412H-2, 1002H-3, 1002H-5, 1004H-2, 1004H-3, 1004H-5, 1005H-2, 1005H-3, 1005H-5, 1005H-6, 306H-2, 506H-3, 506H-5, 506H-6, 507H-3, 507H-5, 508H-2, 508H-3, 508H-5, 508H-6, 509H-2, 509H-3, 509H-5, 509H-6, 5010H-2, 5010H-3; 5010H-5, 5010H-6, 50HH-2,5011H-3,5O11H-4, 5011H-5.5013H-2, 5013H-3, 5013H-5, 5013H-6, 5014H-2, 5014H-3, 5014H-5, 5014H-6, 2515H-2, 5015H-5, 5015H-6, 5016H-2, 5016H-3, 5016H-5, 5016H-6, 5017H-1.5017H-2, 5017H-3, 5017H-3, 10

144-872B-4R-1, 684R-1.835R-1, 725R-2, 885R-3, 195R-4, 256R-1,67R-1.77R-4, 717R-5.1178R-1.298R-1.298R-3, 398R-3, 399R-1, 439R-2, 809R-3, 129R-4, 19R-5, 139R-6, 1

144-872C-4H-2, 504H-3, 504H-5, 504H-6, 5012H-1, 5012H-2, 50

Depth(mbsf)

2.003.506.507.9110.0011.5014.5029.0030.5033.5038.5040.0043.0043.8047.5049.0052.0053.5058.5061.5066.5068.0071.0072.5076.0077.5080.5082.0085.5087.0090.0091.5095.0096.5098.0099.50104.00105.50108.50110.00113.50115.00118.00119.30123.00127.50129.00132.50134.00137.00138.50140.50142.00143.50144.10

135.90136.00145.50147.20148.70149.40154.60164.10168.10169.90173.40173.40176.40176.40183.00184.80185.60186.60188.10189.40

29.5030.8033.4034.60105.00106.00

Thermalconductivity(W/[m K])

1.491.421.221.421.231.121.091.411.481.361.330.671.031.021.531.530.961.030.810.961.381.311.061.031.211.381.211.041.201.581.011.031.260.991.060.962.211.711.431.031.581.431.391.031.371.121.071.401.371.301.221.661.931.341.27

1.200.720.870.911.280.830.771.171.220.841.160.970.941.020.881.651.630.871.140.79

1.741.611.211.041.411.33

Error range(W/[m • K])

0.0070.0050.0040.0160.0060.0060.0030.0040.0040.0050.0050.0040.0040.0030.0020.0050.0050.0020.0100.0030.0060.0030.0040.0030.0060.0040.0040.0030.0030.0030.0030.0050.0040.0060.0040.0040.0040.0020.0050.0030.0040.0050.0670.0030.0050.0030.0020.0020.0060.0030.0030.0050.0030.0060.002

0.0120.0160.0040.0140.0150.0730.0020.0800.0040.0030.0080.0040.0110.0030.0020.0120.0150.0020.0070.004

0.0020.0030.0040.0020.0050.004

Drift(K/min)

-0.010-0.001-0.013-0.025-0.0370.000

-0.002-0.0140.002

-0.024-0.009-0.007-0.014-0.0030.0180.0110.0270.0060.006

-0.028-0.010-0.001-0.012-0.0010.0000.027

-0.0150.0080.0310.032

-0.0740.004

-0.006-O.020-0.075-0.0330.0200.003

-0.004-0.0020.015

-0.0480.0310.005

-0.024-0.016-0.003-0.041-0.008-0.0010.0200.0310.046

-0.0090.025

-0.023-0.029-0.128-0.056-0.031-fl.009-0.0780.038

-0.037-0.1000.009

-0.018-0.077-0.091-0.0990.0030.044

-0.080-0.016-0.188

0.0110.0000.0020.000

-0.028-0.010

Thermal conductivity profiles are given in Figure 33 and Table10. These show moderate scatter, but an underlying uniformitywithin the pelagic sediments of Hole 872A. Values range from0.9 to 1.6 W/(m K). These values agree well with those from Site871, although they lack the slightly higher trend above 40 mbsfseen in Hole 871A ("Physical Properties" section, "Site 871"chapter, this volume). Unfortunately, a software malfunction re-sulted in the loss of thermal conductivity data for Hole 872C.

Shear strength data from Holes 872A and 872C are given inFigure 34 and Table 13. These data suggest a strength "peak" ata depth of 70 mbsf in Hole 872A, but considerable scatter ispresent in the data, and the peak is not matched in Hole 872C. Ageneral strength increase does occur, however, below 60 mbsf inHole 872C. Values of shear strength generally range from 0 to 15kPa. The test is described as undrained, but in these materials itis at least partially drained, even at the high deformation rateemployed by the modified Wykeham-Farrance vane apparatus(see "Explanatory Notes" chapter, this volume). The majority ofvane tests in the pelagic sediments did not feature a clear failurepeak, and strength values may be considered as fully or partially"remolded" values. Because of the particle size (coarse silt to finesand) of the pelagic ooze, the Torvane is considered an inappro-priate technique.

CarbonateCarbonate rock was recovered in very small amounts in Holes

872A and 872B, primarily infilling basalt fractures. The recov-ery did not permit any physical properties measurements tobe conducted; thus, a separate physical property unit was notappropriate.

BasaltSignificant quantities of basalt were recovered only in Hole

872B between 135 and 193 mbsf. No major weathering profilewas found. However, both basalt with vein fillings and brecciatedbasalt tended to crack and spall on drying, thus creating problemsfor the Hamilton Frame compressional wave velocity measure-ments. Basalts from Site 872 were less susceptible to crackingthan basalts measured at Site 871 ("Physical Properties" section,"Site 871" chapter, this volume). Porosity was between 5% and35% (Fig. 28). Hamilton Frame compressional wave velocitiesrange from 3500 to 5600 m/s (Table 12). Velocity determinationswere conducted out on orthogonal faces of the cube sample.Anisotropy coefficients are grouped around zero and the resultsgenerally show little anisotropy. What anisotropy was recordedwas probably the result of micro-fissuring and veining in thesample. Samples were soaked for several hours before beingtested. It was found, by experiment, that oven drying times neededto be extended beyond the usual 24 hr for the basalts if consistentresults were to be obtained.

DOWNHOLE MEASUREMENTSAND SEISMIC STRATIGRAPHY

Logging OperationsLogging was attempted at Hole 872B by placing the bottom of

the drill pipe at 151 mbsf, 14 m below the contact with basalticbasement, and lowering the geochemical tool string to calibrationdepth. Neither the primary geochemical tool string or its sparewould calibrate properly, but the Shipboard Scientific Party fi-nally decided to attempt the logging run anyway. Although thetool string could be lowered below the bottom of the drill pipe, ithung up only a few meters below that level, probably on a ledgewithin basement that we could not pass. Because the hole wasshallow, the tool string was uncalibrated, and hole conditions

137

SITE 872

Table 11. DSV compressional wave velocity measure-ments, Holes 872A and 872C.


144-872A-4H-2, 69-764H-2, 105-1054H-3, 80-876H-2, 53-608H-2, 77-849H-4, 71-789H-6, 63-7010H-2, 66-7310H-4, 60-6710H-6, 62-6911H-4, 32-3913H-2, 62-6913H-4, 59-6613H-6, 21-2814H-2, 34-4116H-6, 23-3011H-6, 32-3912H-2, 50-5713H-2, 35^213H-5, 41-4814H-2, 70-7714H-3, 94-10114H4, 74-8114H-5, 106-11314H-6, 73-8016H-2, 94-101

144-872C-1H-2, 4 1 ^ 81H-3,41^81H4, 42^91H-5, 30-371H-6, 36-433H-5, 60-674H-3, 45-526H-2, 40-477H-3, 34-418H-2, 43-509H-2, 40-479H-4, 43-501 OH-1,43-5010H-5, 45-5210H-7, 22-2911H-2, 52-5911H-4, 38^511H-6, 32-3912H-2, 50-5713H-2, 35-4213H-5, 41^*814H-2, 70-7714H-3, 94-10114H-4, 74-8114H-5, 106-11314H-6, 73-8016H-2, 94-101

Depth(mbsf)

28.7029.1030.3047.5066.8079.2082.1085.7088.6091.6097.80

104.00107.00110.00113.00138.00101.30106.00107.50111.60117.30118.80120.00121.60122.60131.70

1.412.714.135.406.84

23.9830.7348.2959.1567.4477.2379.8985.4390.7393.3796.2298.75

101.30106.00107.50111.60117.30118.80120.00121.60122.60131.70

Temperature(°C)

21.4020.3019.9021.7020.3021.9020.9021.8020.8021.3021.3021.6021.1021.8022.1021.3021.0021.0021.0021.0021.0021.0021.0021.0021.0020.00

22.0022.0021.0021.0021.0021.0021.0022.0022.0021.0021.0020.0022.0022.0021.0022.0021.0021.0021.0021.0021.0021.0021.0021.0021.0021.0020.00

Velocity(m/s)

1552.001512.901488.401477.201514.501504.601498.101562.601501.301499.701470.901511.201566.101514.501499.701457.801500.601507.201454.701451.601570.701581.501560.001423.201565.301577.90

1551.201500.601502.201505.501453.201540.801542.601503.901539.101513.801454.701572.501492.501495.701515.401512.101513.801500.601507.201454.701451.601570.701581.501560.001423.201565.301577.90

Note: DSV = digital sound velocimeter.

were bad, logging operations ended at that point and no loginformation was obtained.

Seismic Stratigraphy

An excellent single-channel seismic profile was obtained ontwo crossings of Hole 872B using a 200-in.3 water gun as a soundsource. These data were recorded on a Masscomp computer,refiltered, and displayed (Fig. 35). The base of the foraminiferooze (pelagic cap) is easily identified at 143 mbsf, where drill pipepenetration abruptly slowed, and at 1.62 s TWT on the seismicrecord. This reflector is easily substantiated by the 3.5-kHz recordthat also shows a pronounced "hardground" reflector at the sameTWT. Below this horizon are other coherent reflections, the mostprominent being at about 2.12 s TWT. These may be reflectionsfrom within basement, or possibly reflections from older sedi-mentary horizons covered by the lava flows sampled at Hole872B.

Because no logging information was obtained at this site, theformation velocity of the foraminifer ooze was calculated fromthe interval traveltime to the basement reflection and the depthbelow seafloor was obtained from the drill-pipe penetration re-cord. By this method, the 0.187 s, 143-m-thick section offoraminifer ooze has a formation velocity of 1.5 km/s, essentiallythe same as seawater.

SUMMARY AND CONCLUSIONS

Initial interpretation of the cores obtained at Site 872 indicatethat a series of subaerial eruptions of differentiated alkali olivinebasalt, possibly hawaiites and mugearite, form the upper portionof the igneous basement at Lo-En Guyot. They appear to representthe very latest shield stage or the alkalic-cap stage of hotspotvolcanism. Magnetic measurements demonstrate that the basalt isnormally magnetized with the magnetization probably acquiredat a paleolatitude of about 30°S.

Planktonic foraminifers and possibly calcareous nannofossilsof late Turonian age are reworked into lower Santonian sedimentsfilling the fractures in the basalt. On the basis of the biostrati-graphic age of these organisms and other benthic organisms, itwas determined that volcanism occurred before the late Turonian.Moreover, the association of middle neritic benthic foraminiferswith planktonic organisms demonstrates that by early Santoniantime, a relatively shallow pelagic environment was present onLo-En Guyot, or, alternatively, transport of shallow-water mate-rial into a deeper site of deposition occurred at that time. Thehypothesis that the Lo-En volcanic edifice existed and was sub-merged before late Turonian time is further supported by theoccurrence of near-shore marine organisms of early Albian agerecovered in dredges along the southern slope of this guyot. Thebacktracked location of Lo-En Guyot and other volcanic edificesthat erupted during the mid Cretaceous (Lincoln et al., in press),agrees with the interpretation that Lo-En Guyot existed before thelate Turonian and was located at a paleolatitude of 30°S.

The overall paucity of pelagic sediments, and the occurrenceof highly phosphatized, manganese-oxide-encrusted lithoclasts ofdifferent origin and age (late Santonian, early Campanian, andlate Paleocene) above the basalt in Holes 872A and 872B, suggestthat for several millions of years the guyot experienced prevailingnondepositional conditions in an active current regime. A some-what higher energy environment may have existed at the locationof Hole 872C where only the youngest, slightly phosphatizedchalk of middle Eocene age and one pebble with a Santonianmatrix were recovered; alternatively, this may be a function ofpoor core recovery.

Continuous pelagic sedimentation was established on Lo-EnGuyot only by late Oligocene time. The middle Eocene sedimentthinly blanketing the conglomeratic chalk is overlain by a 140-m-thick sequence of upper Oligocene and Neogene pelagic carbon-ates. The hiatus associated with this middle Eocene to late Oligo-cene disconformity suggests that the seafloor may have beenexposed for as long as 15 m.y. Calcareous microplankton strati-graphy indicates that sedimentation was relatively continuousfrom the late Oligocene through the Pleistocene, with only minorperiods of nondeposition and/or erosion during the Miocene andpossibly during the early Pliocene. The abnormally high ratio ofplanktonic foraminifers to nannofossils throughout most of theOligocene and Miocene pelagic sequence suggests significantwinnowing of the sediment. This current activity apparentlywaned during the Pliocene and Pleistocene, as indicated by therelative increase in the volume of nannofossils in the uppermostoozes.

An indirect relationship with Anewetak Atoll is confined to afew volcanic glass shards in a single pebble with a Campanianpelagic matrix from Hole 872B. These shards may be interpreted

138

SITE 872

Table 12. Hamilton Frame measurements of compressional wave velocity, Hole 872.


144-872B-5R-1,47-495R-1, 47^95R-1, 47-495R-3, 102-1045R-3, 102-1045R-3, 102-1046R-1,40-426R-1, 40-426R-1, 40-427R-1, 31-337R-1, 31-337R-1, 31-337R4, 67-697R4, 67-697R4, 67-697R-7, 74-767R-7, 74-767R-7, 74-768R-1, 70-728R-1, 70-728R-1, 70-728R-2, 5-78R-2, 5-78R-2, 5-78R4, 46-488R4, 46-488R4, 4^489R-1, 59-619R-1, 59-619R-1,59-619R-2, 90-929R-2, 90-929R-2, 90-929R4, 130-1329R4, 130-1329R4, 130-1329R-5, 19-219R-5, 19-219R-5, 19-21

Depth(mbsf)

145.27145.27145.27148.64148.64148.64154.90154.90154.90164.31164.31164.31168.09168.09168.09172.37172.37172.37173.80173.80173.80175.39175.39175.39177.48177.48177.48183.07183.07183.07184.90184.90184.90186.72186.72186.72189.31189.31189.31

Distance(mm)

24.0521.3921.3923.6121.5021.3525.6221.4921.4025.9821.4621.4425.5821.2721.4022.2521.5021.3920.5121.5021.4025.0221.4821.3524.0321.4621.3321.9821.6521.5123.0721.4421.3620.8921.8321.4923.6921.5921.48

Axes ofmeasurement

abcabcabcabcabcabcabcabcabcabcabcabcaab

Traveltime(µs)

7.897.347.288.027.417.45

10.359.018.74

10.238.978.758.137.507.539.168.849.118.117.797.837.836.726.727.336.766.71

10.299.949.947.936.966.968.518.488.869.378.849.11

Correctedtraveltime

(µs)

4.894.344.285.024.414.457.356.015.747.235.975.755.134.504.536.165.846.115.114.794.834.833.723.724.333.763.717.296.946.944.933.963.965.515.485.866.375.846.11

Measuredvelocity

(m/s)

4918.204928.574997.664703.194875.284797.753485.713575.713728.223593.363594.643728.704986.364726.674724.063612.013681.513500.824013.704488.524430.645180.125774.195739.255549.655707.455749.333015.093119.603099.424679.515414.145393.943791.293983.583667.243719.003696.923515.55

Velocityanisotropy

index

-O.01

0.00

-0.05

-0.04

0.03

0.04

-0.04

-0.05

-0.02

-0.01

-0.07

0.06

0.05

Notes: a = direction perpendicular to split core plane, b = direction transverse to split core plane, and c = coreaxis; all axes orthogonal.

as evidence of the Campanian volcanic event that was responsiblefor the eruption of the basalts recovered by drilling in AnewetakAtoll.

REFERENCES*

Berggren, W.A., Kent, D.V., and Flynn, J.J., 1985. Jurassic to Paleogene:Part 2. Paleogene geochronology and chronostratigraphy. In Snelling,NJ. (Ed.), The Chronology of the Geological Record. Geol. Soc.London Mem., 10:141-195.

Berggren, W.A., Kent, D.V., and Van Couvering, J.A., 1985. The Neo-gene: Part 2. Neogene geochronology and chronostratigraphy. InSnelling, NJ . (Ed.), The Chronology of the Geological Record. Geol.Soc. London Mem., 10:211-260.

Blow, W.H., 1969. Late middle Eocene to Recent planktonic foraminif-eral biostratigraphy. In Brönniman, P., and Renz, H.H. (Eds.), Proc.First Int. Conf. Planktonic Microfossils, Geneva, 1967: Leiden (EJ.Brill), 1:199-422.

* Abbreviations for names of organizations and publication titles in ODP referencelists follow the style given in Chemical Abstracts Service Source Index (publish-ed by American Chemical Society).

Davis, A.S., Pringle, M.S., Pickthorn, L.B.G., Clague, D.A., and Schwab,W.C., 1989. Petrology and age of alkalic lava from the Ratak chain ofthe Marshall Islands. J. Geophys. Res., 94:5757-5774.

Edwards, L.E., 1985. Miocene dinocysts from Deep Sea Drilling ProjectLeg 81, Rockall Plateau, Eastern North Atlantic Ocean. In Roberts,D.G., Schnitker, D., et al., Init. Repts. DSDP, 81: Washington (U.S.Govt. Printing Office), 581-594.

Head, MJ., Norris, G., and Mudie, PJ. , 1989. Palynology and dinocyststratigraphy of the Upper Miocene and Lowermost Pliocene, ODP Leg105, Site 646, Labrador Sea. In Srivastava, S.P., Arthur, M., Clement,B., et al., Proc. ODP, Sci. Results, 105: College Station, TX (OceanDrilling Program), 423-451.

Hein, J.R., Kang, J.K., et al., 1990. Geological, geochemical, geophysi-cal, and Oceanographic data and interpretations of seamounts andC-rich ferromanganese crusts from the Marshall Islands, KORDI-USGS R.V. Faranella Cruise F10-S9-CP. Open-File Rep .—U.S. Geol.Surv., 90-407.

Lancelot, Y., Larson, R., et al., 1990. Proc. ODP, Init. Repts., 129:College Station, TX (Ocean Drilling Program).

Lincoln, J.M., Pringle, M.S., and Premoli Silva, I., in press. Early andLate Cretaceous volcanism and reef-building in the Marshall Islands.In Pringle, M.S., Sager, W.W., Sliter, W.V., and Stein, S. (Eds.),The Mesozoic Pacific. Am. Geophys. Union, Geophys. Monogr.Ser.

139

SITE 872

Pringle, M.S., Jr., 1992. Geochronology and petrology of the MusiciansSeamounts, and the search for hot spot volcanism in the CretaceousPacific [Ph.D. dissert.]. Univ. of Hawaii, Honolulu.

Raitt, R.W., 1957. Seismic refraction studies of Eniwetok Atoll. Geol.Surv. Prof. Pap. U.S., 260-S:685-698.

Sager, W.W., Winterer, E.L., Firth, J.V., et al., in press. Proc. ODP,Init. Repts., 143: College Station, TX (Ocean Drilling Program).

Schlanger, S.O., 1963. Subsurface geology of Eniwetok Atoll. Geol.Surv. Prof. Pap. U.S., 260-BB:991-1066.

Vacquier, V., 1985. The measurement of thermal conductivity of solidswith a transient linear heat source on the plane surface of a poorlyconducting body. Earth Planet. Sci. Lett., 74:275-279.

Von Herzen, R.P., and Maxwell, A.E., 1959. The measurement of thermalconductivity of deep-sea sediments by a needle probe method. / .Geophys. Res., 65:1557-1563.

Ms 144IR-105

NOTE: For all sites drilled, core-description forms ("barrel sheets") and core photographs canbe found in Section 3, beginning on page 453. Forms containing smear-slide data can be foundin Section 4, beginning on page 1017. Thin-section data are given in Section 5, beginning on page1037.

Table 13. Wykeham-Farrance shear sthength data, Holes 872A and 872C.


144-872 A-1H-2, 140-1411H-3, 100-1011H-5, 90-912H-2, 92-932H-5, 116-1174H-2, 115-1164H-3, 20-215H-4, 112-1136H-2, 125-1268H-2, 102-1038H-3, 104-1059H-2, 124-1259H-4, 128-1299H-6, 119-12010H-2, 120-12110H-4, 110-11110H-6, 118-11911H-2, 129-13011H-4, 88-8913H-2, 110-11113H-4, 115-11613H-6, 118-11914H-2, 20-2115H-3, 80-8116H-4, 105-106

144-872C-1H-2, 96-971H-3, 97-981H-4, 98-991H-5, 87-881H-6, 92-933H-5, 117-1184H-3, 103-1045H-3, 95-966H-2, 96-977H-3, 92-938H-2, 98-998H-6,100-1019H-2, 96-979H-4, 99-1009H-6, 85-8610H-2, 99-10010H-5, 102-10310H-7, 32-3311H-2, 91-9211H-4, 92-9311H-6, 43-^412H-2, 104-10513H-2, 91-9213H-5, 98-9914H-1, 70-7114H-2, 70-7114H-3, 94-9514H-4, 74-7514H-5, 106-10714H-6, 73-7415H-1, 100-10116H-1, 12-1316H-2, 105-10617X-2, 47^1817X-2, 38-39

Depth(mbsf)

2.904.006.909.92

14.6629.1529.7041.6248.2567.0268.5476.7479.7882.6986.2089.1092.1895.7998.38

104.60107.70110.73113.20124.80136.10

1.963.274.695.977.40

24.5531.3140.4648.8559.7367.9973.2777.7980.4582.9887.1391.3093.4796.6199.29

101.40106.50108.10112.10116.20117.30118.80120.00121.60122.60126.00130.10131.80140.50140.40

Testtype

WFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWF

WFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWFWF

Springconstant

31.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.27

31.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.2731.27

Vaneconstant

0.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.23

0.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.230.23

Tensionangle

(degree)

1.001.000.500.000.003.001.003.000.00

25.0014.0014.006.00

14.0012.0012.0012.004.000.004.001.00

12.001.002.001.00

0.000.004.004.005.502.004.001.000.00

12.005.003.00

11.006.003.005.007.007.002.00

14.002.003.005.002.006.001.002.00

10.002.000.00

43.006.00

14.0065.0060.00

Undrainedshear strength

(kPa)

0.700.700.350.000.002.090.702.090.00

17.429.769.764.189.768.368.368.362.790.002.790.708.360.701.390.70

0.000.002.792.793.831.392.790.700.008.363.482.097.674.182.093.484.884.881.399.761.392.093.481.394.180.701.396.971.390.00

29.964.189.76

45.2941.81

Note: WF = Wykeham-Farrance vane.

140

SITE 872

Wet- and dry-bulkdensity (g/cm3)

1.0 2.0 2.0

Grain density(g/cm3)

2.5

Water content

3.0 50 100 150

Porosity

50 70 90

50

E

Q.

Q

100

150

DBD

WBD

Figure 27. Measurements of index properties (wet- and dry-bulk density, grain density, water content, and porosity) vs. depth,Hole 872A.

Wet- and dry-bulk Grain densitydensity (g/cm3) (g/cm3)

1.0 2.0 3.0 2.0 2.5 3.0 3.5 0

Water content

80 160 0

Porosity

40 80

50

100CDQ

150

200

DBD

WBD

Figure 28. Measurements of index properties (wet- and dry-bulk density, grain density, water content, and porosity) vs. depth,Holes 872A and 872B.

141

SITE 872

Wet- and dry-bulkdensity (g/cm3)

1.0 2.0 2.0

Grain density(g/cm3)

2.5 3.0 50

Water content(%)

100 150 50

Porosity(%)

70 90

50

Q.03

Q

100

150

• DBD°WBD

Figure 29. Measurements of index properties (wet- and dry-bulk density, grain density, water content, and porosity) vs. depth,Hole 872C.

GRAPE bulk density GRAPE bulk density(g/cm3) (g/cm3)

1.4 1.5 1.6 1.7 1.4 1.5 1.6 1.7 1.1

Magnetic susceptibility Magnetic susceptibility^ (x10~6cgs)

- 1 0 1 2 3 4 5 6 - 1 1 3 5 7 9

* •

• i.

i'j••

fX'

•j

'f 1

f • 1 . 4 • • l '

. * Hole872C

y • .

*

_

-I •

-

< .

. 1 . 1 . 1 .

Figure 30. GRAPE bulk density vs. depth, Holes 872A and 872C. Figure 31. Magnetic susceptibility vs. depth, Holes 872A and 872C.

142

SITE 872

P-wave velocity, DSV P-wave velocity, HF P-wave velocity, DSV

(m/s) (m/s) (m/s)1000 1200 1400 2000 4000 6000 1200 1400 16000

50

Q.

Φ

a

100 "

150 "

Hole872A

.•

•••••••• •••«•

•

i , i ,

Hole872B

• ••*•• . S "

" .r * *i

i • i i

Hole '872C

••

••

••

••• •

•••••••

•

I . I .

200

Figure 32. Digital sound velocimeter (DSV) and Hamilton Frame (HF) measurements of compres-

sional wave velocity vs. depth, Holes 872A, 872B, and 872C.

0

Thermal conductivity(W/[m K])

0 1 2

Thermal conductivity(W/[m K])

0 1 2

50 -

100 "Q.CD

Q

150 "

200

Hole j£872A ^ "

i . i

• i • i

Hole872B

i . i

0

20 -

Vane shear strength Vane shear strength

(kPa) (kPa)20 40 0 20 40

60 -

S 80

100 -

120 -

140 -

! Hole872A

•

••

•- -•••

•1

1 . 1

K Hole872C

•

••

•— ~•••••••*••(•• •- •- -

i . i

Figure 33. Thermal conductivity vs. depth for pelagic sediments in Hole 872A Figure 34. Vane shear strength vs. depth, Holes 872A and 872C.and basalts in Hole 872B.

143

SITE 872

1.4 -

1.6 -

Litholo

143-

Lithology

/ / / * / * /S \ S S s \ \

Foraminifer ooze;Oligocene-Neogene1.5 km/s

Basaltic edifice

1BH

Figure 35. Lithostratigraphic correlations to the seismic stratigraphy section at Site 872. The major reflector corresponds to thebasement/pelagic cap interface. Depth to basement is based on the drill-pipe penetration record. Formation velocity for the pelagiccap is based on that depth, and on the interval traveltime to the basement reflection from the seismic records.

144

4. site 872 - €¦ · water depth (drill-pipe measurement from sea level, m): 1082.1 total depth...

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