site data date occupied: •j '•-• date departed1973/08/18 · site 303 42 153 154 155...

2. SITE 303: JAPANESE MAGNETIC LINEATIONS

The Shipboard Scientific Party1

SITE DATA

Date Occupied: 18 August 1973 (2351)

Date Departed: 24 August 1973 (0800)

Time on Site: 128 hours

Position: 40°48.50'N, 154°27.07'E

Water Depth: 5609 corrected meters (echo sounding)

Bottom Felt With Drill Pipe At: 5625 meters below rig floor

Penetration: 293 meters

Number of Holes: 2

Number of Cores: 16

Total Length of Cored Section: 136.0 meters

Total Core Recovered: 31.7 meters

•JHAKODATE V\

y ' • - •

303

3?4

306 #

P A C

305

I F I C

309#308

0 C E A

• 310

• 311

#312

313

HAWAIIAN ISLANDS

HONOLULU £

150° 160° 170° 180° -170° -160° -150°

BACKGROUND AND OBJECTIVES

The evolution of the northwestern Pacific Ocean hasbeen modeled by Larson and Chase (1972), based oncorrelations of three sets of linear magnetic anomaliesand consideration of their geometry. These anomalieshave been numbered M-l (youngest) through M-22. Aneast-striking set near the Phoenix Islands was drilled onLeg 17, where the lowest sediment over basalt wasHauterivian in age between M-7 and M-8. In thewestern North Atlantic, the north-striking Keathleylinear anomalies have been correlated with M-2 throughM-22, and Oxfordian-Callovian(?) sediments cored onLeg 11 lie on basalt immediately west of M-22.

Site 303 (Figure 1) lies on the Japanese lineationpattern, an east-striking set of anomalies (M-4 to M-10,also possibly M-ll and M-l2) that are located east ofthe Japanese Islands. Site 303 is located on anomaly M-4, the northernmost of these extremely linear features.The main goal at Site 303 is to drill to basement anddetermine its age, either from the overlying sediments orradiometric dating of the basalt itself. This will establishor deny the contention of Larson and Chase (1972) thatthe Japanese lineations correlate with the Phoenix linea-tions as features that result from sea-floor spreading and

'Roger L. Larson, Lamont-Doherty Geological Observatory,Palisades, New York (Co-chief scientist); Ralph Moberly, HawaiiInstitute of Geophysics, Honolulu, Hawaii (Co-chief scientist); DavidBukry, U.S. Geological Survey, La Jolla, California; Helen P. Fore-man, Oberlin College, Oberlin, Ohio; James V. Gardner, Scripps Insti-tution of Oceanography, La Jolla, California; John B. Keene, ScrippsInstitution of Oceanography, La Jolla, California; Yves Lancelot,Lamont-Doherty Geological Observatory, Palisades, New York;Hanspeter Luterbacher, Esso Production Research—European,Begles, France; Monte C. Marshall, U. S. Geological Survey, MenloPark, California; Albert Matter, Universitat Bern, Bern, Switzerland.

magnetic field reversals during the Early Cretaceous.Site 303 will also test and further calibrate the lateMesozoic reversal time scale of Larson and Pitman(1972) that predicts a Barremian or possibly Hau-terivian age for anomaly M-4.

Besides the intrinsic interest of correlating the anoma-ly sets and establishing a well-founded time scale forMesozoic magnetic field reversals, this study will alsotest the hypothesis of Larson and Pitman (1972) that theLate Cretaceous period between the "Cenozoic" andMesozoic reversals was the time of a worldwide increasein sea-floor-spreading rates. Larson and Pitman haverelated this spreading "pulse" to a simultaneous pulse inbatholith emplacement around the Pacific Basin andHays and Pitman (1973) have postulated the spreadingpulse as the cause of the worldwide transgression of epi-continental seas during the Late Cretaceous. BecauseM-4 lies close to the top of the late Mesozoic reversalsequence, its basement age will have a significant bear-ing on the reality of this hypothesis of increased spread-ing rates during the Late Cretaceous.

The sediments at Site 303 should contain carbonatematerial that is a record of the early deposition on thenewly formed crust and also a record of the equatorialcrossing of this part of the Pacific plate, as it is proposedthat this site was formed very close to, or at the equator.Determination of the age and nature of these "ridgecrest" and "equatorial" carbonate sequences should addconsiderable information to the evolution of this areasince its formation.

It may also be possible to compare cherts at Site 303with those of the same age recovered from shallow-water sites, with an attempt to sort out other factors inchertification, such as percentage of carbonate, etc.Diagenetic studies of zeolitic, pelagic clays will also beundertaken.

SITE 303

42

153 154° 155°

Figure 1. Bathymetry in the region of Site 303 (after Chaseet al., 1971). Contour interval 200 fm uncorrected.

At Site 303 the anticipated basement is ridge-crest-type tholeiite (commonly olivine-normative and verylow in alkalies) with pillows and hyaloclastites whichtypify many previous DSDP basaltic sites. However,these rocks will be older than those previously en-countered, and by projection of the physical measure-ments of Christensen (Salisbury and Christensen, 1972)and the mineralogical determinations of Bass (Bass etal., 1973) on marine basalts of various ages, these shouldbe severely altered. Their study will provide an endmember to the spectrum of basalt alteration and will beuseful to geophysicists in refraction seismology, to geo-chemists postulating the composition of subductedcrust, and perhaps to geochemists interested in thetransfer of transition elements from volcanic rocks tooverlying sediments.

The magnetic properties of the basement rocks thatare presumably oceanic tholeiite should be of con-siderable interest. We are especially concerned with theremnant magnetic inclination, which should be low ornearly horizontal if the rocks were emplaced and thusmagnetized at the equator. Recent studies by Lowrie etal. (1973) have demonstrated a marginal correspondencebetween measured inclinations and values that werepredicted from tectonic reconstruction and/or skew-nesses of the marine magnetic anomalies. We are also in-terested in the magnetic mineral content of the basaltsand the stability and intensity of remnant mag-netization.

OPERATIONS

With the intention of holding our survey time to aminimum, we intersected the Conrad-\405 track, ourreference profile, immediately north of the intended site(Figure 2). After turning to run parallel with the Conradtrack, we slowed in order to retrieve one of the hydro-phone streamers and maintained 5 knots until the pro-files of the magnetometer and airgun showed a suitablesite on magnetic anomaly M-4. The seismic profile(Figure 3) suggested the section above the deepest re-flector would be about 30 meters thinner than the sec-tion shown on the Conrad profile, but otherwise it was

\\\\\

'°56/!8 AUG Ve 1248/18 AUG - ^

\ \ SITE 303-\Λ 40°48.50'N

^Λ \ \ 1 5 4 ° 2 7 ' 0 7

\ \ 2324/23 AUG>T\SATELLITE NAVIGATION

^ ç ^ V 0324/24 AUGV VN

0410/24 AUG\ ^155°E

Figure 2. Track chart in the vicinity of Site 303. Solid trackis Leg 32 Glomar Challenger, short dashed track is fromConrad 1405, and long dashed lines mark identified mag-netic anomalies. Navigation points marked with opencircles and annotated time/day-month.

comparable. No beacon had been presoaked to bedropped "on the run," so a lighted spar buoy was jet-tisoned to mark the site while the ship was turned aboutand the remaining geophysical gear was retrieved. Anacoustic beacon was dropped at 2351, 18 August 1973 ina water depth of 5609 meters (corrected by Matthews'Tables from the echo sounder).

A seismic record from a sonobuoy was attempted onstation, but it was terminated early when a momentaryloss of propulsion allowed the ship to be blown backover the buoyed airguns, with potential damage to thepackings of the propeller shafts. The direct water wavehad become impossible to detect in the propeller andthruster noise by that time anyway, and so the principalvalue of the sonobuoy record was to be its indication ofno strong reflectors in the upper part of the section. Wewere thereby assured that the drill collars could beburied to support them laterally before any hard drillingcommenced.

An excursion northward to stream geophysical gear,and then a turn to cross over the beacon on course toSite 304 sufficed for a postsite survey (Figure 2).

Nearly 35 hr elapsed between the initial occupation ofSite 303 and the initial recovery of sediment. The partdue to the depth of water had been expected. A weatherfront with winds gusting above 40 knots while rapidlyshifting direction was compounded with the site's loca-tion in the Kuroshio Extension Current, and the re-

18

SITE 303

SITE 303

- 6 SEC

I—SITE303

I I I ! I I I I I I I I I I I I I2 24 Aug 00 23 Aug 73 13 10

Speed M O Kts 6 Kts| Speed •̂ 10 Kts165°| 170°|092°

Figure 3. Seismic profiler section approaching and leaving Site 303.

I I I I I I18 Aug 73 7

092°I 098°

g

suiting positioning problems caused a few hours of de-lay. The first beacon had a very weak signal and had tobe replaced with a second beacon after 12 hr. Severalstands of old drill pipe had been replaced by new pipe,but the new pipe was not exactly the same length as theold lengths and had not been measured. Two coringtrips that turned out to be in the water over the bottom,and additional time for speculation, were expendedwhile attempting to find the sea floor with the drillstring, due to the unknown length of the drill string andthe absence onboard of any in-pipe or expendablepinger.

Between the surface and 211 meters we cored at inter-vals of approximately 50 meters, with little or no rota-tion or circulation, and generally good recovery. Below211 meters we intended to core continuously. Whileretrieving Core 5, the inner barrel jammed at 500 metersabove the bit and the safety pin in the overshot latchsheared while attempting to pull it free. The barrel waspumped down with mud, the overshot latched on, andthe barrel pulled slowly to the surface. However, Core 6jammed solidly in the lowermost drill collar, and afterbreaking two more safety pins and running a magnetdown the pipe, the drill string had to be pulled out of thehole to clean the obstruction. A piece of a steel snap-hook that had fallen into the drill pipe had wedged thebarrel firmly.

The absence of chert in the moderately thick Miocenesiliceous ooze intensified our belief that this site af-forded an excellent opportunity to reach basement inthis part of the northwestern Pacific, and so we con-tinued by drilling Hole 3O3A. The upper section waswashed and drilled to 211 meters, and we again com-menced a program of coring continuously. Recovery inthe interbedded chert and zeolitic mud was poor,however, and on two occasions slugs of mud werepumped in attempts to lift the abundant chert cuttingsand chips out of the hole. Basalt was encountered in

Core 9A. We had planned next to take a full 9-metercore of basalt, followed by a partial core, using theSperry-Sun orienting device. However, only 5 meters ofCore 10A had been penetrated when the bit stuck,presumably from chert chips that continued to cave intothe hole, and that core was pulled as soon as the bitcould be freed. There was, therefore, no attempt to cutan oriented core, as the orientation process requires in-tervals when circulation and rotation must be stopped.

Fossiliferous sediment had been recovered within ameter or two of extrusive basement, and so although thetime on station was lengthy and we were plagued withminor operational difficulties in addition to those listedabove, our primary objective of dating magnetic anoma-ly M-4 was fulfilled. The site was abandoned after Core10A at a total depth of 293 meters. We were underway at0800, 24 August 1973).

The intervals drilled and cored in Holes 303 and 303Aare listed in Table 1.

LITHOLOGIC SUMMARYMost of the section present at Site 303 has been sam-

pled in two consecutive holes. The section sampled canbe considered as a single record of the sediment presentat the site because coring in Hole 3O3A overlapped thelowermost level reached in Hole 303. Coring was ter-minated in basaltic rocks at the bottom of Hole 303A.Table 2 shows a summary of the smear slide data.

The upper part of the section was sampled discon-tinuously from 0 to 211 meters subbottom and con-tinuously from 211 meters to the bottom of Hole 3O3A(293 m). Recovery was relatively good in the upper 183meters and very poor in the lower part due to the oc-currence of abundant interbedded chert.

The section can be divided into four units as follows:Unit 1—Diatom-rich radiolarian ooze, commonly

rich in volcanic ash and grading down to radiolarian-bearing pelagic clay (Cores 1 through 4).

19

SITE 303

TABLE 1Coring Summary

Core

Date(Aug.1973)

Hole 303

123456

Total

202020202122

Hole 3O3A

123456789

10

Total

22222222232323232323

Site Total

Time

100013301550184504300015

1725192021202325025505100720093012001640

Depth FromDrill Floor

(m)

5625.0-5637.05687.0-5696.05742.0-5751.05799.0-5808.05836.0-5845.05845.0-5854.0

5836.00-5845.005845.00-5854.255854.25-5863.505863.50-5872.755872.75-5882.005882.00-5891.255891.25-5900.505900.50-5909.755909.75-5913.005913.00-5918.00

Depth BelowSea Floor

(m)

0.0-12.062.0-71.0

117.0-126.0174.0-183.0211.0-220.0220.0-229.0

211.00-220.00220.00-229.25229.25-238.50238.50-247.75247.75-257.00257.00-266.25266.25-275.50275.50-284.75284.75-288.00288.00-293.00

LengthCored(m)

9.09.09.09.09.09.0

54.0

9.009.259.259.259.259.259.259.253.255.00

82.00

136.0

LengthRecovered

(m)

0.59.08.08.3tr0.0

25.8

trtr0.20.41.50.40.50.41.51.0

5.9

31.7

Recovery(%)

5100

8992< l

0

47.8

<l< l

24

16454

46207.3

23.3

Unit 2—Zeolitic pelagic clay and chert (Core 5 andCores 1A through 5A).

Unit 3—Clayey nanno ooze and chert (Cores 7A and8A).

Unit 4—Basalt (Cores 9A and 10A).

Unit 1—Diatom-radiolarian Ooze andRadiolarian-bearing Pelagic Clay (Cores 1 through 4)

The upper part of this unit (Core 1) consists of well-preserved siliceous fossil remains and volcanic glassshards in roughly equal amounts. The siliceous micro-fossils are predominantly diatoms, generally very wellpreserved, with lesser amounts of radiolarians andsilicoflagellates.

The volcanic components are predominantly light-colored glass shards with rare colored glass and oc-casional feldspar fragments.

Some small angular quartz grains (possibly windtransported) are also found in smear slides from the firsttwo cores. X-ray diffraction analysis (Zemmels, John-son, and Cook, this volume) shows relatively abundantquartz throughout this interval. Below Core 1 the sedi-ment composition shows a very noticeable decrease inthe amount of volcanogenic components except in thinlayers and mottles. The sediment consists predominant-ly of diatoms and radiolarians in nearly equal amounts,with some silicoflagellates and minor amounts of light-colored volcanic glass shards. Clay minerals are general-ly absent in the smear slides except in a small green hardnodule in Core 2, Section 1. However, relatively abun-dant mica and montmorillonite are reported in the X-ray analysis results. The occurrence of both theseminerals in roughly comparable amounts suggests aduality in the sources. The relatively abundant quartz

and mica indicate significant terrigenous contribution tothe sediment.

Core 4 shows a gradual transition between this unitand the underlying one. It consists of zeolitic pelagicclay with upward increasing amounts of radiolariansand diatoms. The radiolarian fragments show evidenceof dissolution yet some diatom fragments appear to re-main well preserved.

Unit 2—Zeolitic Pelagic Clay and Chert(Core 5 and Cores 1A through 5A)

Core 5 recovered only a smear of slightly zeoliticbrown pelagic clay with small angular chert fragments.The top of the chert-bearing section is not preciselyknown and might be between Cores 4 and 5. The dis-solution of radiolarian fragments at the base of Core 4suggests that the youngest chert in the section might lierather close to the base of Unit 1 although the drillingrecord shows that the first hard layer was encountered at217 meters while cutting Core 5.

The relative amounts of chert and clay in this unit areunknown due to the poor recovery in this kind of sedi-ment. The clay is generally very zeolitic, especially insome light-colored layers where zeolites and clayminerals appear to occur in equal amounts. The zeolitesare predominantly clinoptilolite with rare occurrences ofphillipsite. Amorphous iron oxide, finely dispersed orconcentrated in microscopic aggregates or in micro-nodules, is present throughout but hematite is very rare.Volcanic glass is present in minor amounts.

Radiolarian remains are common; they are generallychalcedony-filled molds similar to those observed in thechert.

20

SITE 303

TABLE 2Smear Slide Summary, Holes 303, 303A

CHoo

T

2

2^

2

2

3

3

3

3

4

44

4

T]1A

1A

2A

3Al4A5A5A

5A

7A8A

9A

Rl

SECTION

1

2

4

CC

1

2

5

5

CC

2

2

3

CC

CC

CCCC

CC

CC

CC

CC

1

2

CC1

1

INTERVAL cm

5866

88

98

110

147

67

138

147

EXOGENIC

Detrital

QUARTZ

|

75 190 1

65

8C66

10

110

130

135

FELDSPARS

1r

Li i

1 j

>

HEAVY

MINERALS

\\1π

LIGHT GLASS

DARK GLASS

• l

|

1

\π

||

11π1

,V

πNf11

j

U11π

H.Ill III

-

CLAY MINER

!

mLImt11

AUTHIGENIC-DIAGENETIC

PALAGONITE

11

11I

Lir

Llr

IMM

i•

T̂ 1II I!

ZEOLITES

J

1j

1J

1 1!

HEMATITE

I

amorphous

IRON OXIDE

11

IITN••Tiii

1

1

oO

ö

L ^

i

1πLft•Esir

-j-

-BASALT-

PYRITE

recrystal1 .

SILICA

j

1i1T

iT i.

recrystal1.

CALCITE

<

rhombs

BI0GENIC

FORAMINIFERS

ö

<

RADIOLARIA

DIATOMS

mirm

i

SPONGE

SPICULES

•+Duu••

I-•mL

111

1II III

L1t1

• •

:

FISH

DEBRIS

j

LA

11|r

-

P

.7

SILIC0FLAG-

ELLATES

Il

1

•

P

r

21

SITE 303

Chert nodules (or possibly layers) are dark brown toyellowish-brown and display well-preserved sedimen-tary structures such as discrete layering and micro-faulting. They contain inclusions of partially silicifiedsediment. Abundant radiolarian molds filled with chal-cedony are also found in the cherts. The chert at 252meters was the layer most resistant to drilling for the en-tire site.

Unit 3—Clayey Nanno Ooze and Chert(Cores 7A and 8A)

Although coring was continuous, poor recoverycaused by the combined occurrence of chert and softsediments precludes any precise estimate of the actualcomposition of this section. Only very disturbed andsmall sections were recovered which contain abundantchert fragments and watery sediment. Part of the chertfragments may have fallen from upper parts of the hole,but some of them are clearly associated with the nanno-fossil ooze since they contain some carbonate inclusions.

The sediment consists of clayey nanno ooze but it isnot clear whether the occurrence of clay is due tothorough mixing during recovery or it corresponds tothe actual composition of the sediments.

Nannofossils are abundant to dominant and the restof the sediment consists of clay minerals, zeolites, glassshards, chert fragments, and amorphous iron oxide, asin the unit above.

The base of this unit lies at the contact with extrusivebasalt. This contact was not actually sampled althoughCore 8A bottomed no more than 2 meters above base-ment and is probably within 1 meter of the contact. It isprobable that the soft calcareous sediments overlyingthe basalt were washed away during the cutting of Core9A.

Unit 4—Fine-grained, Extrusive Basalt(Cores 9A and 10A)

This unit consists of fine- to very fine-grained basalt.Although no glassy selvage survived drilling, thepresence of varioles 22 cm below the top of the basalt aswell as alternating darker, more finely crystalline, andlighter, less finely crystalline, intervals show the basaltconsists of several cooling units and is most likely an ex-trusive, pillow basalt. The contact between the basaltand the overlying sediment was not recovered. Thebasalt is highly fractured, the average fracture spacingbeing about 2-3 cm. The fractures are filled with calciteand a green occasionally red) clayey material (cela-donite and montmorillonite). The deepest piece re-covered is a 4-cm-diameter, rounded piece of limestone,well abraded from coring. It may be sediment that wassqueezed between, or was deposited between, pillows.

In thin section, the basalt is seen to consist of plagio-clase laths with interstitial pyroxene, magnetite, il-menite, and patches of green-orange alteration (cela-donite and montmorillonite, the color depending on theamount of admixed goethite [?]). The irregular patchesare possibly altered interstitial glass, while the more"euhedral" ones are altered olivine (?) phenocrysts. Apoint count (200 pts) gives the following mode: plagio-clase 54%, pyroxene 34%, magnetite and ilmenite 7%,

alteration 5%. The Plagioclase laths and pyroxene grainsappear to be largely unaltered, which is remarkable con-sidering the age of this basalt.

The degree of weathering of the basalt is not uniformthroughout the section. In several of the core segmentsthe basalt adjacent to fractures is green, whereas thebasalt 1-2 cm distant is gray and apparently unaltered.

ConclusionsMost of the section consists of sediments deposited

below the carbonate compensation depth except for thelowermost layers recovered immediately above base-ment. The relatively high rates of sedimentation ob-served in the upper part (see below, SedimentationRates) probably result from a combination of highproductivity related to the Kuroshio-Oyashio currentsystem as well as contributions from volcanogenic com-ponents.

A major unsampled hiatus is probably present at thebase of the Tertiary and top of the Cretaceous, and theupper Mesozoic section appears to be very thin. This in-terval was probably deposited in areas of rather lowproductivity north of the equatorial zone. The car-bonate-rich layers recovered at the base of the sectionappear too thin to account for accumulation of "ridgeflank" and "equatorial" types of sedimentation. Thissuggests that the crust at this site was not generated un-der the equatorial zone of high productivity.

It is probable that the crust was generated south of theequator and that the equatorial crossing is recorded bylarge amounts of siliceous deposits after the area hadsubsided beneath the carbonate compensation depth(CCD) (see discussion in Lancelot and Larson, this vol-ume).

GEOCHEMICAL MEASUREMENTSAlkalinity, pH, and salinity measurements are sum-

marized in Table 3 and presented graphically in Figure4. The core samples were squeezed at 4°C to obtain theinterstitial water. Techniques used were those routinelyperformed during previous legs and are described in thefollowing pages.

AlkalinitySurface seawater and three cored samples were

analyzed. More samples could not be taken because ofdrilling disturbance in the sediment. The maximumalkalinity of 4.83 meq/kg was obtained from Unit 1 at124.5 meters subbottom. This unit is a diatom-radio-larian ooze. The lowest value for the interstitial waterwas 2.85 meq/kg from the deepest sample (181.5 m) in aradiolarian-bearing clay of Unit 1. The surface wateralkalinity was 2.43. The values obtained in these samplesare reasonable for this type of sediment.

pHThe two pH values obtained by the punch-in method

were both below that of seawater at the site, which isnormal for marine sediments. The sample from Core 4was too stiff to use the punch-in method. The increase inpH to 8.43 in Core 3, using the combination electrode,seems high and is probably incorrect; however, there is

22

SITE 303

TABLE 3Summary of Shipboard (Geochemical Data

Sample(Intervalin cm)

Depth BelowSea Floor (m)

Surface Seawater2-5, 144-1503-5, 144-1504-5, 144-150

pH

8

52-71117-126174-183

9 0

pH

Punch- Flow-in through

8.197.537.18

-

Alkalinity (

1 2 3

Alkalinity(meq/kg)

2.434.674.832.85

; meq/kg)

4 5

Salinity(%o)

34.635.235.235.2

6 30

Remarks(Combinationelectrode pH)

8.297.968.437.44

Sal i n i t

31 32

50

100

Q 150

200

Punch-in

Combination

Figure 4. Graphic summary of geochemical data taken at Site 303.

no obvious explanation for this result. The equipmentfor the flow-through method was broken during the siteanalyses.

Salinity

The three salinity measurements made were all similarto the surface seawater value.

PHYSICAL PROPERTIES

Wet Bulk Density and Porosity of Soft Sediments

The wet bulk density of most of the soft to stiff andmoderately to intensely disturbed sediments recoveredfrom Hole 303 was measured continuously using thegamma-ray attenuation porosity evaluator (GRAPE).These data are summarized in Figure 6. The density isconstant through most of each cored interval and in-creases from about 1.25 g/cc in the radiolarian diatomooze of Core 2 to 1.33 g/cc in the clayey ooze and radio-larian-bearing pelagic clay of Cores 3 and 4. A syringesample was taken from each core as an independentmeasure of bulk density and porosity. The density of theclayey ooze and radiolarian-bearing pelagic clay, 1.36

g/cc, agrees with the GRAPE value, whereas the valuemeasured in the ooze of Core 2, 1.18 g/cc, is about 5%lower than the GRAPE value and suggests that thesyringe sample is not entirely representative of the coredinterval. The porosity, combining the GRAPE andsyringe data, is about 85% in the radiolarian diatomooze and 80% in the lower, clayey sediments.

Velocity MeasurementsThe compressional wave velocity, Vp , of the soft

sediments and rocks was measured with a Hamiltonframe. Vp of the soft sediments was measured on thesplit cores, and that of the cherts and basalt wasmeasured on fragments and small cores, respectively.

The Vp of the soft to stiff, moderately to intensely dis-turbed siliceous ooze and pelagic clay cluster closelyaround 1.50 km/sec. The Vp of the cherts is much higherand ranges from 3.7 to 5.2 km/sec. Some of the chertsamples show a large anisotropy—Vp parallel to bed-ding is between 4 and 5 km/sec, whereas the velocityperpendicular to bedding is about 3.0 km/sec. Thisdirectional dependence results from the interlayering of

23

SITE 303

earthy, relatively unsilicified (Porcellanite) layers withmuch harder layers. Measured parallel to bedding, thefirst arrival of the sound wave is that transmitted by thewell-indurated layers. Perpendicular to bedding, thesound velocity is an average of the soft, slow layers andthe fast, hard layers. As expected, even the horizontalvelocity of Porcellanite samples containing no chertlaminae is quite low (about 2 km/sec).

Since the Vp of well-silicified chert is considerablyhigher than that of unconsolidated sediments andporcellanites, such a chert layer should return much ofthe incident energy from the ship's sonic profiler. Thisexplains why, upon drilling, the deepest reflector("basement") shown on the profiler coincided with themost massive chert zone and not with the underlyingbasalt.

The Vp of the basalt samples group around 4.5km/sec. This velocity is probably a maximum for thepillow basalt layer, since the somewhat rubbly contactsbetween pillows as well as the poorly cemented fracturesreduce the average velocity.

CORRELATION OF SEISMIC REFLECTIONPROFILES WITH DRILLING RESULTS

The seismic reflection profiles recorded while ap-proaching and leaving (Figure 3) Site 303 show a faintlystratified layer, approximately 0.31 sec thick, overlying ahighly reflective acoustic basement. Examination ofprofiles in the area suggests that this acoustic basementis probably composed of two reflective layers too closelyspaced to be separated on the record at Site 303. Atransparent interval can indeed be observed at and southof Site 304. It becomes undiscernible around Site 304and disappears gradually toward the north as it becomesfilled with reverberation from the uppermost of the tworeflectors.

The upper faintly stratified interval correlates wellwith the diatom-radiolarian ooze and clayey radiolarianooze recovered from Cores 1-5 of Hole 303 and thezeolitic pelagic clay and chert recovered from Cores 1-5of Hole 3O3A. Although some scattered chert was en-countered in this latter interval, the first massive chertwas recovered in Core 6A and corresponds to a majordecrease in the drilling rate at a subbottom depth of 253meters. This major discontinuity corresponds probablyto the uppermost part of the acoustic basement observedon the profile. This results in a calculated average inter-val velocity of 1.63 km/sec for the upper interval. Thesound velocity measurements performed on opened coresections (see Physical Properties, Appendix I) yieldedvelocities ranging from 1.5 km/sec in the diatom-radio-larian oozes, and in the zeolitic pelagic clays, to 2.0 to5.0 km/sec in the chert nodules. If a 1.5 km/sec velocityis attributed to the upper 217 meters, a velocity of about2.8 is obtained for the lower zeolitic and chert-rich 36meters of this upper interval.

No interval velocity can be computed from the lowerinterval beneath the main reflector because of thepresence of heavy reverberation masking the possiblepresence of a lowermost reflector corresponding to thetop of the basaltic basement. If we assume a soundvelocity of about 3.0 for this lower interval, the top of

the basalt would produce a reflector at about 0.02 secbelow the top of the acoustic basement and is undis-cernible on the seismic profile. A summary of the cor-relation between the lithology and the seismic profile isgiven in Figure 5.

SEDIMENTATION RATESThe sparse recovery from Site 303 provides only a

general indication of rates of sediment accumulation.The average rate for the Neogene from middle Mioceneto late Pleistocene (Cores 1 to 4) is 16 m/m.y. Thismoderately high rate reflects a substantial amount ofbiogenic and volcanogenic siliceous material.

An uncored interval of 28 meters between NeogeneCore 4 and Cretaceous Cores 5 and 1A to 8A represents,at least, 65 m.y. Erosion is implied by the resultant smallsedimentation rate (0.4 m/m.y.) for such a long period.

Sediment accumulation rates for the Cretaceous areuncertain because of the small amounts of sediment ac-tually recovered and because of the broad age deter-minations. Implied rates could vary from 1 to 16 m/m.y.if accumulation were continuous. But chert formationand a possible unconformity between Cores 4A and 5Awould make any calculations suspect.

BIOSTRATIGRAPHIC SUMMARY

CenozoicOnly Neogene siliceous microfossils are present in

samples from Cores 1 to 4 (0-182 m). Well-preserveddiatoms predominate. Radiolaria and silicoflagellatesare also well preserved and common. In Core 4 a dis-solution sequence is present; preservation in the core-catcher sample is poor, Sections 4 to 6 is moderate, andSections 1 to 3 is moderate to good.

MesozoicRadiolaria provide much of the biostratigraphic con-

trol for the Mesozoic section of Cores 5 and 1A to 8A(210-284 m). The age assignments have been determinedby correlating the Radiolaria with those from Sites 305and 306 where ages are controlled by calcareous fossils.In the Neocomian there is approximately a one-stagedifference between the age assignments based onforaminifer and those based on nannoplankton. Be-cause no value judgments can be made, the completeranges given for both the foraminifera and the nanno-plankton are used in assigning ages to the correspondingcores with Radiolaria only in Hole 303. Therefore somerather long ranges result. Cores 5 and 1A and 2A areconsidered to be late Albian; 3A, Albian; 4A, Aptian toBarremian; and 5A, Barremian to Hauterivian. A dis-tinct change in the fauna between Cores 4A and 5Amarks the transition from the Acaeniotyle umbilicataZone to the Eucyrtis tenuis Zone. Core 6A is consideredto be Aptian or Barremian, and Cores 7A and 8A areconsidered to be Aptian to Barremian or Hauterivian.

Coccoliths and foraminifers occur only in Cores 7A to8A (266-284 m) at the base of the sediment section.Benthonic foraminifer faunules from Cores 7A and 8Aare Early Cretaceous (probably Hauterivian to Bar-remian). Dorothia hauteriviana is relatively frequent

24

SITE 303

LITHOLOGY(km/sec)

GRADING DOWN

POLITIC P £ M G I C

INTERVALSOUND SUBBOTTOM

VELOCITY DEPTHMETERS

o-

50-

1.5

2.8

4.5** MEASURED ONROCK SAMPLES

1 0 0 -

150 -

2 0 0 -

2 5 0 -

300-20

2 4 6 8 10 12DRILLING RATE MIN/METER

Figure 5. Correlation of seismic reflection profiles with drilling results at Site 303.

among the arenaceous foraminifers. Coccolith assem-blages are most diverse and abundant in Core 8A, butare dominated by long-ranged, diagenetically resistantspecies such as Parhabdolithus embergeri and Watz-naueria bamesae. The assemblage is probably Valangi-nian to Hauterivian based on rare Tubodiscus sp. cf. T.verenae.

ForaminiferaCores 1 to 5 and 1A to 6A are carbonate free. The

washed residues from the core catchers contain only afew Radiolaria, diatoms, and sponge spicules. Frag-ments of "Rhabdammina" are observed in Core 4.

The core-catcher sample of Core 7A contains a verypoor and badly preserved faunule with Glomospira spp.,Astacolus spp., Pseudonodosaria humilis and Ramulinasp. The core-catcher sample of Core 8A has a poormicrofauna characterized by lagenids and Dorothia spp.The presence of Dorothia hauteriviana, Dorothia sp. cf.D. praeoxycona and Corothia sp. df. D. zedlerae allowsthis sample to be placed into the "Interval with Dorothiahauteriviana" which is attributed to the Hauterivian orBarremian.

CoccolithsCoccoliths are present only in the lowest two sediment

cores (266 to 284 m). Although they are common toabundant, preservation is poor. The assemblages areEarly Cretaceous, however, many stratigraphically diag-nostic species are missing. Identification of rare Tubo-

discus sp. cf. T. verenae indicates a probable Valangin-ian or Hauterivian age (124 ±9 m.y.).

Diatoms and SilicoflagellatesWell-preserved, warm- and temperate-water diatom

assemblages are abundant in the four discontinuouslycut shallow cores between 0 and 182 meters. Silico-flagellates are meager to common in these same coresand, together with the diatoms, reflect the enduring in-fluence of the Kuroshio Extension Current in this area.The tropical Dictyocha epidon Zone of silicoflagellatesand the Roperia tessellata Zone of diatoms occur inCore 1 (0-12 m). Core 2 contains temperate-waterassemblages of the Dictyocha fibula Zone of silico-flagellates. A count of 300 specimens from Sample 303-2-5, 90-92 cm (69 m) includes 50% Distephanus speculumspeculum, 13% Dictyocha fibula, 9% D. rhombica, 9%Mesocena elliptica, 4% Distephanus boliviensis, 3% D.speculum pentagonus, 2% Mesocena diodon, 1% Dic-tyocha aspera, 2% Distephanus speculum binoculus, 4%Mesocena circulus, 2% Distephanus crux, and less than1% D. speculum quintus. The high proportion ofDistephanus specimens in the assemblage indicatestemperate water conditions.

Late Miocene diatoms and silicoflagellates in Core 3(117-126 m) are excellently preserved. The presence ofThalassiosira convexa and the predominance of Dic-tyocha aspera and D. rhombica over D. fibula indicatesthe upper Dictyocha aspera Zone. A high proportion ofDictyocha to Distephanus specimens indicates warm-

SITE 303

water deposition. A count of 303 silicoflagellate speci-mens in Sample 303-3-5, 30-32 cm (123 m) includes 34%Dictyocha aspera, 20% D. rhombica, 19% Distephanusspeculum speculum, 16% Dictyocha fibula, 10%Naviculopsis quadratus, and less than 1% eachDistephanus boliviensis and D. speculum quintus.

In Core 4 (173-182 m) Dictyocha aspera is alsopredominant, however, the occurrence of the diatomsAsteromphalus moroensis and Coscinodiscus plicatussuggest the lower part of Dictyocha aspera Zone which isearly late Miocene or middle Miocene in age.

Diatoms and silicoflagellates are absent in deepercores from this site.

RadiolariaUnless otherwise stated, only core-catcher samples

were examined for this report.

NeogeneOnly siliceous fossils are present in the Neogene Cores

1-4 recovered from Hole 303. Radiolaria are commonand well preserved in all of them.

Core 1, at a depth of 0-12 meters below the sedimentsurface, is late Quaternary Artostrobium tumidulumZone. Core 2, at a depth of 62-71 meters early Pliocene,Stichocorys peregrina. Cores 3 and 4, at a depth of 117-126 meters and 173-182 meters, respectively, are belowthe range of Hays'(1970)zonation for the North Pacific,and the age determination is made on the basis of theRiedel and Sanfilippo (1971) equatorial zonation: Core3, late Miocene, Stichocorys peregrina Zone and Core 5,late Miocene, Ommatartus antepenultimus Zone.

MesozoicSamples of both clay and chert were examined. In

general, the Radiolaria are better preserved in the chertand unless otherwise stated, age assignments have beenmade from these samples.

Radiolaria were recovered from Core 5 in Hole 303and Cores 1A-8A in Hole 303A and age assignments aremade on the basis of correlations with radiolarian eventsin Holes 305 and 306 which have calcareous fossil con-trol (see Foreman, fig. 1, this volume). No other sili-ceous fossils were observed.

Cores 5 and 1A at depths of 211-220 meters, and Core2A at 220-229 meters, contain few poorly preserved tomoderate Radiolaria which are considered to beCenomanian or late Albian, and late Albian, respective-ly. All belong to the Dictyomitra somphedia Zone. Cores3A (229-238 m) with few, poor Radiolaria, and 4A (238-247 m) with common, moderate Radiolaria, are Albian,and Aptian or Barremian, and are assigned to theAcaeniotyle umbilicata Zone. An abrupt change in thefauna from Cores 4A to 5A marks the transition to theEucyrtis tenuis Zone. The remaining Cores 6A to 8A allbelong to this zone. Cores 5A (247-257 m) with commonpoor and 6A (257-266 m) with common moderateRadiolaria are Aptian to Barremian and Aptian toBarremian or Hauterivian, respectively. Cores 7 A (266-275 m) and 8A (275-284 m) contain a fauna similar to,but sparser and more poorly preserved than that in Core6A. Table 4 summarizes the biostratigraphic data.

SUMMARY AND CONCLUSIONSFigure 6 shows a summary of the coring, lithology,

biostratigraphy, and physical properties of Site 303. Themost significant discovery at Site 303 is the EarlyCretaceous age of the sediments overlying basement.The east-northeast-striking Japanese linear magneticanomalies therefore cannot be any part of the latestCretaceous to present-day magnetic reversal sequencethat has been reported in all the major oceans. Rather,as predicted, the Japanese lineations correlate with thePhoenix lineations (Site 166).

There was little recovery of fossiliferous sediment inthe lower part of Hole 3O3A, and this combined withmultistage microfossil range determinations make it dif-ficult to establish age limits more exactly than Valangi-nian to Barremian. The calcareous microfossil rangesoverlap in the Hauterivian so this is the most likely agein the average sense. This is very close to the agepredicted (early Barremian) for anomaly M-4, but thelack of precise age determination indicates that drillingof additional sites, or refinement of biostratigraphic cor-relations between Europe and the Pacific will benecessary for calibration of the Larson and Pitmanmodel of Cretaceous spreading rates.

The actual contact of sediment on basalt was notrecovered, but as it is known within 2 meters, it seemsunlikely that the missing sediment (which is more than10 m thick) can be significantly older than what wasrecovered. Even though the contact could not be ex-amined, there can be little doubt that the basalt is of ex-trusive origin. The uppermost core is very fine grainedand variolitic, and that texture is repeated at several in-tervals through the basalt cores, indicating several cool-ing units of pillows or successive flows.

Very little amorphous ferromanganese-rich mud andno hyaloclastite was recovered in the lower part of thesection of generally poor recovery, and so the questionremains whether processes that have formed thosesediments so commonly in the central and easternPacific were active at Site 303.

The poor recovery also restricts the value of this sitefor interpreting paleodepths and the passage of thePacific plate under the equator; however, good remnantmagnetic inclination measurements on the basalts (Lar-son and Lowrie, this volume) indicate that this site wasformed at about 6° south latitude. This was probablyjust south of the equatorial zone of productivity presentat that time. While very little is known about the depres-sion of the CCD beneath the Cretaceous equator, it isreasonable to assume that the ridge had subsidedenough before its subsequent transit under the equatorthat carbonate was dissolved, and radiolarians, nowchert, were deposited.

Chert is a component of all cores below 211 metersand is especially massive at 253 meters where it formsthe lowermost seismic reflector at the site. There may besome relationship between the possible mid-Cretaceousstratigraphic break based on radiolarians and the de-velopment of chert.

The greatly compressed section or unconformitybetween the Cenomanian and the Miocene is the mostimportant break in the stratigraphic history of the site.

26

SITE 303

TABLE 4Distribution, Age, and Frequency of Investigated Microfossils

Cor

e

1

2

3

4

5

6

1A

2A

3A

4A

5A

6A

7A

8A

9A

10A

Depth (m)

0.0-12.0

62.0-71.0117.0-126.0174.0-183.0

211.0-220.0

220.0-229.0

211.0-220.0

220.0-229.25229.25-238.50238.50-247.75

247.75-257.0

257.0-266.25

266.25-275.50

275.50-284.75

284.75-288.0288.0-293.0

β>>n<DOo<D

5

100

89

92

< l

0

< l

< l

24

16

4

5

4

46

20

Foraminifera

Pla

nkt.

-

-

-

-

-

-

-

-

-

-

-

-

-

-

Ben

th.

-

-

-

+

-

-

-

-

-

-

-

-

+

+

-

---

-

-

-

--

-

-

-

-

Barremian/Hauterivian

CalcareousNannoplankton

-

-

-

-

-

-

-

-

-

-

-

-

o

•

-

-

-

-

-

-

-

-

-

-

-

-

Hauterivian/Valanginian

Hauterivian/Valanginian

Radiolaria

o

0

o

*

+

-

***

o

o

*

*

LatePleistoceneEarly PlioceneLate MioceneLate MioceneCenomanianor late Albian

-

Cenomanianor late AlbianLate AlbianAlbianAptian/BarremianBarremian/HauterivianAptian toBarremian/Hauterivian

Aptian toBarremian/HauterivianAptian toBarremian/Hauterivian

BASALT

Note: abundant; o common; * frequent; + rare; - absent.

There is no indication on the airgun records, either of a"hard ground" reflector, or of thickening or thinning inthat part of the section in adjacent areas that might helpone to decide whether an actual erosional unconformityis present.

The Neogene section is rich in siliceous fossils. Unfor-tunately, time did not allow us to take more than a fewcores in the upper part of Hole 303 and none there inHole 303A. The great abundance of diatoms, radio-larians, and silicoflagellates suggests that the mixingboundary between the Kuroshio and Oyashio currentshas been in the vicinity of Site 303 for the past 15 m.y.

Several of the topics considered above are also dis-cussed in the Site 304 chapter that follows, along with acomparison of the two sites and an illustration of thefossil ranges involved.

REFERENCES

Bass, M. N., Moberly, R., Rhodes, J. M., Shih, C, andChurch, S. E., 1973. Volcanic rocks cored in the CentralPacific, Leg 17, Deep Sea Drilling Project. In Winterer, E.L., Ewing, J. I., et al., Initial Reports of the Deep Sea Drill-ing Project, Volume 17: Washington (U. S. GovernmentPrinting Office), p. 429-503.

Chase, T. E., Menard, H. W., and Mammerickx, J., 1971.Topography of the North Pacific. Institute of MarineResources, University of California, San Diego.

Hays, J. D., 1970. Stratigraphy and evolutionary trends ofRadiolaria in North Pacific sediments: Geol. Soc. Am.,Mem. 126, p. 185-218.

Hays, J. D. and Pitman, W. C, III, 1973. Lithospheric platemotion, sea level changes and climatic and ecological con-sequences: Nature, v. 246, p. 18-22.

Larson, R. L. and Chase, C. G., 1972. Late Mesozoic evolu-tion of the Western Pacific: Geol. Soc. Am. Bull., v. 83, p.3627-3644.

Larson, R. L. and Pitman, W. C, III, 1972. Worldwide cor-relation of Mesozoic magnetic anomalies, and its im-plications: Geol. Soc. Am. Bull., v. 83, p. 3645-3662.

Lowrie, W., Opdyke, N. O., and Lovlie, R., 1973. Magneticproperties of DSDP basalts from the Pacific Ocean(abstract): E.O.S. (Am. Geophys. Union Trans.), v. 54, p.256.

Riedel, W.R. and Sanfilippo, A., 1971. Cenozoic Radiolariafrom the western tropical Pacific, Leg 7. In Winterer, E.L.,Riedel, W.R., et al., Initial Reports of the Deep Sea Drill-ing Project, Vol. 2: Washington (U.S. Government Prin-ting Office), p. 1529-1672.

Salisbury, M. H. and Christensen, N. I., 1972. Velocity-densitysystematics for JOIDES basalts (abstract): Geol. Soc. Am.,Abstracts with programs, v. 4, p. 228.

27

SITE 303

CORESNO. DEPTH LITHOLOGY AGE

BIOSTRATIGRAPHIC ZONATIONFORAMINIFERA NANNOPLANKTON RADIOLARIA

POROSITY | SONIC VEL. |(GRAPE) %1.4 KM/SEC 5.4

50

100

-3

1 50 —

117

126

Diatom volcanic ash

Radiolarian diatom ooze

Clayey diatom

radiolarian ooze

R. teεsellata

Zone (D)

D. epiodon

Zone(S)

"D. fibula

Zone."

(S)

Up. D. aspera

Zone (S)

Artostrobium

tumidulum

Zone

Stiahooorys

peregrina

Zone

Figure 6. Summary of coring, lithology, biostratigraphy, and physical properties at Site 303.

150

CORESNO. DEPTH LITHOLOGY AGE

BIOSTRATIGRAPHIC ZONATIONFORAMINIFERA NANNOPLANKTON RADIOLARIA

POROSITY SONIC VEL.(GRAPE) %i .4 (KM/SEC) 5.4

200 r

250

5&

JA6&

2A

3A

-4A

r5A

-6A

. 7A

9A

10A

174

183

211

220

229

238

247

257

266

275

284

293

300-T.D.

;i

Basalt

Diatom and radiolarian-

bearing pelagic clay

Zeolitic pelagic clay

and chert

Chert and zeolitic

pelagic clay

Chert and zeolitic

pelagic clay

Chert and zeolitic

pelagic clay

Chert and zeolitic

pelagic clay

(253: Hard drilling

on chert that probably

is main reflector)

Chert

Nanno pelagic clay

and chert

Nanno ooze and chert

"(286: Hard drilling:

probably top of base-

ment)

BARREMIAN OR

HAUTERIVIAN

Late Miocene:

Lo. D. aspera

Zone (S)

C. pliaatus

Zone (D)

Ommatartus

antepenultimut

Zone

Diatyomitra

somphedia

Aoaeniotyle

umbilicata

DiσtyomitraC?

laorimula

Tubodiseus

jurapelag-

icus*** ' Se thoaapsa

traahyostraaa

*Turonian to

Cenomanian

**Albian

***Probable Valanginian to

Hauterivian (124 +9 m.y.)

V

50 85

Figure 6. (Continued).

28

Site 303

LATE

PL

EIST

OCEN

E

ZONE

NANN

OSFORAMS

RADS

Rope

ria

tessellata and Di

chty

oca

epio

don

zone

Artostrobium

tumidulum zone

Hole

FOSSIL

CHARACTER

FOSS

IL

FRSDN

ABUND.

CRA

PRES

.

GGG

Core 1

SECT

ION

0

1

METE

RS1

1 1

1 1 1

I

I 1 1

1

1 1

1

Core

Catcher

Cored I

LITHOLOGY

NOT

OPENEC

*•{=) 5 "Cv

iter

DEFO

RMAT

ION

val

LITHO.SAMPLE

*CC

0.0-12.0 m

LITHOLOGIC DESCRIPTION

Section 1 not opened: watery anddisturbed.

DIATOM VOLCANIC ASH, dark greenishgray, soupy, no primary structurespreserved.

Smear Slide at CCCompositionLight glass ADiatoms A

— 1 Rads C,.„ .., Quartz R5 G Y 4/1 Feldspars R

_ 1 Hark qlass R' Palagonite R

Amorphous ironoxide R

Micronodules RSilicoflagellates R

Site 303 Hole Cored Interval:62.0-71.0 m


5G 4/1

5G 5/1

5G 6/1to10YR 4/2

Core is mostly dark greenish gray(5G 4/1, 5GY 5/1, 5GY 6/1) to grayisholive (10Y 4/2) with spots and layersof brownish gray (5YR 4/1) and oliveblack (5Y 2/1) color in the upper partof the core. Most of the core is softto stiff and intensely disturbed.

Dominant lithology RADIOLARIAN DIATOMOOZE.

Smear Slide at 1-66CompositionRads ADiatoms ASilicoflagellates CLight glass C

Smear Slide at 2-147CompositionRads ADiatoms ASilicoflagellates CDark glass C

Grain Size3-20 (2.6-47.2-50.1) silty clay

Chlo 5.2%Calc 4.6%Amor 94.5%

Minor lithology at 4-67 white spot ofVOLCANIC ASH.

Slide at 4-67CompositionLight glassHeavy mineralsRads

Explanatory notes in Chapter 1

oSite 303 Hole Core 3 Cored Interval:117.0-126.0 m Core 4 Cored Interval:174.0-183.0 m

ZONEFOSSIL

CHARACTER

T


Most of the core is stiff to very stiffand moderately to intensely disturbedthroughout.

Major lithology CLAYEY DIATOM RADIO-LARIAN OOZE mainly greenish gray withvarious shades of grayish black anddark greenish gray toward the base ofthe core.

Smear

Grain5-135

X-rayQuarMicaPlag

Slide

Size7571-'

5-13537.3%27.3%18.7%

at 1-138CompositionRadsDiatomsSilicoflagellatesClay mineralsLight glassDark glassFish debris

18.6-45.9) clayey silt

Mont 7.2% ChloK-Fe 4.4% AmorKaol 3.3%

AAC

ccRR

1.87.

Minor lithology at 5-75 thin layer ofVOLCANIC ASH.

Smear Slide at 5-75CompositionLight glass DFeldspar CHeavy minerals RPalagonite RRads RDiatoms R

The lower part of Section 6 and the corecatcher sample show an increase in theamount of VOLCANIC ASH in the sediment.

Smear Slide at CCCompositionRads ADiatoms ALight glass ASilicoflagellates CClay minerals CDetrital quartz RDark glass R

FOSSILCHARACTER

CoreCatcher


Core is mostly light brown, stiff, withsemiiithified layers and nodules. RADIO-LARIAN PELAGIC CLAY, with occasional smallspecks of pumice and ferro-manganesemicronodules (micronodules especiallyabundant in the middle of Section 2).

5YR 6/4

Smear Slide at 2-80CompositionClay mineralsRadsDiatomsSilicoflagellatesLight glassMicronodules

Grain Size2-83 (1.0-18.7-80.3) clay

Smear Slide at CCCompositionClay mineralsRadsAmorphous iron

oxideLight and dark

glassZeolitesDiatoms

AACC.-:R

0C

c

RRR

At 5-0 to 5-3 manganese nodule (Φ 3 cm).


Site

AGE

TE AL

BIAN

1 CEN

OMAN

IAN TO LA

303

ZONE

NANN

OSFORAMS

RADS

somp

hedi

aDictyomitra

Hole

FOSSILCHARACTER

FOSS

IL

RFSDN

ABUN

D.

R

_

PRES

.

P

_

Core 5

SECT

ION

0

METE

RS

CoreCatcher

Cored In te rva l :

LITHOLOGY

HU

DEFO

RMAT

ION

LITH

O.SA

MPLE

CC

211.0-220.0 m


ZEOLITIC PELAGIC CLAY and small chips oflnYR o RIO CHERT. Clay is dusky yel lowish brown.I U ' Chert is brown to l i gh t tan.

CompositionClay minerals DZeolites CAmorphous iron

oxide CMicronodules CRecrystall ized

s i l i c a RFish debris R

Site 303 Hole A Core 3 Cored Interval:229.0-238.0 m

Site 303 Hole A Corel Cored Interval:211.0-220.0 m

AGE

[ CE

NOMA

NIAN TO LA

TE A

LBIA

N

ZONE

NANN

OSFORAMS

RADS

Dict

yomi

tra

somp

hedi

a

FOSSILCHARACTER

FOSS

IL

RFSDN

ABUN

D.

R

PRES

.

a. 1 1

1 1 |

SECT

ION

j

0

METE

RS

CoreCatcher

LITHOLOGY

II^^I =

DEFO

RMAT

ION

LITH

O.SA

MPLE

*CC*CC


ZEOLITIC PELAGIC CLAY, predominantlydusky ye l l ow ish brown w i th ra re l i g h t tanspots and fragments of tan CHERT.

10YR 2/2Smear S l ide a t CC

CompositionClay minerals AZeo l i t es ARecrystallized

silica CRads CLight glass RDiatoms R

Radiolarian molds are f i l led withchalcedony.

Site 303 Hole A Core 2 Cored Interval:22O.0-229.0 m

FOSSILCHARACTER

CoreCatcher


10YR 2/2 (clay)and10YR 4/2to5YR 5/6 (chert)

Banded CHERT, dusky yellowish brownwith discontinuous laminae of lightbrown color, showing microfaulting.

Very small amount of brown ZEOLITICPELAGIC CLAY mixed with the smallchert fragments.

Smear Slide at CC (in clay)CompositionClay mineralsZeolitesRecrystallized

silicaRadsLight glass

AA

CCR

FOSSILCHARACTER

CoreCatcher


CHERT, dusky yellowish brown and smallamounts of brown ZEOLITIC PELAGIC CLAY.

10YR 2/2to10YR 4/2

Smear Slide at CC (in clay)CompositionClay mineralsZeolitesMicronodulesLight glassHematite

AACRR


a

1 AP

TIAN TO BAR

REMI

AN

ZONE

NANN

OSFORAMS

RADS

Acae

niot

yle

umbi

lica

ta

FOSSILCHARACTER

FOSS

IL

RNDS

ABUN

D.

C

PRES.

M

SECT

ION

0

METE

RS

CoreCatcher

LITHOLOGY

IB

DEFO

RMAT

ION

LITH

O.SA

MPLE

"cc


CHERT, dusky yellowish brown with small10YR 2/2 amounts of brown ZEOLITIC PELAGIC CLAY.

lnvp 4/9 Smear Slide at CC ( in clay)' Composition

Clay minerals AZeolites AAmorphous iron

oxide CMicronodules CLight glass RRads RFish debris R


FOSSIL

explanatory notes in Chapter 1


10YR 2/2 to5Y 7/3and10YR 6/6

Large pieces and small ctiips of CHERT,dusky yellowish brown to yellowish grayand yellowish brown, sometimes laminatedand showing microfaulting, and smallamounts of ZEOLITIC PELAGIC CLAY ofsame colors.Smear Slide at 1-120 (in clay)

CompositionClay minerals AZeolites ALight glass CAmorphous iron

oxide CPalagonite RFish debris R

Large pieces of light olive gray andyellowish brown CHERT with thin whitelayers, and small amounts of PELAGICCLAY of same colors.

Smear Slide at CC (in clay)CompositionClay mineralsZeolitesRecrystallized

silicaRadsLight glass

AA

CCR

X-ray 2-118Mont 31.9% Mica 10.5* Ban" 4.4*Cl in 26.9% Plag 6.3% C a l c 1.7S6Quar 13.5% K-Fe 4.8% Amor 77.1%


AGE

1| APTIAN TO BARREMIAN OR HAUTERIVIAN

ZONE

NANNOS

FORAMS

RADS

Eucyrtis

tenu

is

FOSSILCHARACTER

FOSSIL

RNDS

ABUND.

PRES

.Mil

SECT

ION

1

0

1

METERS

—'

CD

1 1

1 1

1 1

1 1

1 1

1 1

II

CoreCatcher

LITHOLOGY

"JVOID

DEFORMATION

|

LITHO. SAMPLE!


Strongly fractured CHERT, light brownto dusky yellowish brown. Fracturesare healed with clear chalcedony which is

5un j., found in botryoidal shape in cavities.

\°B ,., Upper pieces of chert have a dull aspectlurK ùl and are laminated with tan thin layers.

Site 303

AGE

R VALANGINIAN

HAUTERI

o

<c

α.

ZONE

NANNOS

FORAMS

RADS

» jurapelagicus

is tenuis

scu

Tubo

Hole A

FOSSILCHARACTER

FOSSIL

R

F

N

ABUND.

F

R

C

PRES.

M

P

P

Core 7

SECTIC

0

1

METERS

0.5-

1.0-

CoreCatcher

Cored Inter

LITHOLOGY

VOID

DEFORMAT

val:

IPLE

LITHO.SAI

130

«CC

266.0-275.0 m

~~1 10YR 3/2

—1

10YR 2/2to10YR 6/6


Soupy NANNO PELAGIC CLAY with smallCHERT fragments; very dark grayishbrown.

Smear Slide at 1-130CompositionClay minerals ANannos A

Recrystallizedsilica C

Rads (chalcedonyfilled) C

Amorphous ironoxide C

Palagonite RMicronodules R

Base of Section 1 and core catcher aremainly CHERT fragments, dusky yellowishbrown to yellow brown with some sus-pended soupy mud rich in Nannofossils.

Site

AGE

n

|

APTIAN TO H

AUTERIVIAN OR VALANGIN

303

ZONE

NANNOS

FORAMS

RADS

Tubodiscus jurapelagicus

Eucyrtis tenuis

Hole A

FOSSILCHARACTER

FOSSIL

N

RFDSN

ABUND.

A

F

F

A

PRES.

M

P

P

p

Core 8

SECTION

0

1

METERS

11

1 1 1

1 1 1

1

1 1

:

CoreCatcher

Cored I

LITHOLOGY

VOID

iter

DEFORMATION

i/al:

LITHO.SAMPLE

*35

275.0-284.8 m


Broken CHERT, dusky yellowish brownto brownish black, and NANNO OOZE,dusky yellowish brown and light brown.

Smear Slide at 1-135CompositionNannos AAmorphous iron

10YR 2/2 Clay minerals Cto (chert) Light glass R5YR 2/1 Zeolites R1 0 Y R 2 / 2

(ooze)5YR 5/6

l o o z e )

Site

AGE

303

ZONE

NANNOS

FORAMS

RADS

Hole A

FOSSILCHARACTER

FOSSIL

ABUND.

PRES.

Core 9

SECTION

0

1

METERS

1 1

1 1 1

1 1 1

1 1 1

1 1

1

Cored I

LITHOLOGY

nterval:

DEFORMATION

LITHO.SAMPLE

*TS

284.8-288.0 m


Segments of aphanitic BASALT. Grayish

black (N2) - greenish black (5G 2/1)

when wet, medium light gray-light green-

averages 2 to 3 cm. Fractures filled

J0 with calcite, montmorillonite, and

5 G ''' celadonite. Varioles seen at 22 cm,

but not glassy selvages. Sparse, 0.5 mm

vesicles. TS at 66 cm. Very fine grained

(<0.5mm), intersertal basalt.

Plagioclase 542!Pyroxene 3UMagnetite and

ilmenite 7%Alteration 5%

Celadonite and montmorillonite occur asvesicle fillings, replacing olivine(?)phenocrysts, and patches (after glass?)in the groundmass. The Plagioclase lathsand pyroxene grains appear to be fairlyunaltered.

Hole A CorelO Cored Interval : 288.0-293.0

AGE

ZONE

NANNOS

FORAMS

RADS

FOSSILCHARACTER

FOSSIL

ABUND.

PRES.

SECTION

0

1

METERS

J 1

1 1 1

1 1 1

1 1

1 1 1

1

LITHOLOGY

VOIC

DEFORMATION

LITHO.SAMPLE

*C

*TS


Aphanitic BASALT as above. SparsePlagioclase phenocrysts (1 mm). Basaltis darker and finer grained at 48, 76,87, 108, and 126 cm - probably coolingunit margins. No glass selvages seen.TS at 136 cm. Basalt finer grained thanin TS above. Patches of light brownglass. Central area of TS appears tobe totally unaltered.

The alteration in several of the coresegments appears to be greater in azone 1 to 2 cm thick bordering fractures.Here the basalt is green whereas it isgray in the interior of the segment.

C • chemistry sample


CORE 303-2

= GRAPE WET-BULK DENSITY, g/cc

® Syringe porosity, % COMPRESSIONAL SOUND VELOCITY

1 2 3

CORE 303-3

100 50 0

DEPTH POROSITY, %IN

HOLE 2(m) *rg-

O-r- 3

1 -

2-

3 —- —

4-

5-

7-

8-

"WET"WATER

CONTENT B% wt

© = PerpendicularTo Bedding

A = Parallel ToBeddingkm/sec

75 25 2 3 4 51 r • • i • • • • i • • • • i • ' " " ' i -

*rg = grain density, g/cc. i . . . , ....I l••••i•.••l I... .i.... I.


® Syringe porosity, COMPRESSIONAL SOUND VELOCITY

1

DEPTH POROSITY,

HOLE 2

1 -

2-

4-

5-

7-

8-

9

"WET"WATER

CONTENT Swt

® = PerpendicularTo Bedding


*rg = grain density, g/cc

3 4 5

• l • • • . i . • • • l I . . . . I

•P>•CORE 303-4



1 2 3

1 -

2 _Z

4-

5-

7-

9-1-

"WET"WATERCONTENT H

wt



25 2 4I • • • • I • • • • I • • • • I | " • • | . . | . " • | - • " | • " I • • • • I .


CORE 303A-2



1 2 3DEPTHIN

HOLE

POROSITY, %,100 50 0

(m) *rg-i

0-r- 3

1 -

4-

5-

7-

8-

75

"WET"WATER

CONTENT H% wt

25



r • • i • • • • i • • • • i p

O A A A

i i i I...,I....I...•I•••.I•.••I i....I,...i....I.


CORE 3O3A-3

= GRAPE WET-BULK DENSITY, g/cc .


1 2 3

DEPTH POROSITY, %

HOLE 2

1 -

2-

3--

5 _I

7-

"WET"WATERCONTENT B% wt



75 25 2 3 4• • • • i i• ••i I • • • I • - I i " " ! 1 1 " 1 " " ! 1 1 " ! 1 " 1 ! 1 1 1 1 ' " " ! " " 1 -

.1 1..••i


CORE 303A-4

= GRAPE WET-BULK DENSITY, g/cc.

© Syringe porosity, % COMPRESSIONAL SOUND VELOCITY

1 2 3

DEPTH POROSITY,IN

HOLEJOO 50

1 H

2-

4-

5-

7-

"WET"WATER

CONTENT Hwt

25



'""I"" I'1"1 -

krq = grain density, g/cc.I....!....!....!....! I....I•...I.•.•L.••I.•.•I••••I•...I• tn

CORE 3O3A-5



1 2 3

DEPTH POROSITY, %

HOLE 210° 5° °

1 -

2-

4-

5-

7-

9 -J-

"WET"WATER

CONTENT H% wt




|.••T•"|—i

CORE 303A-6



1 2 3

DEPTH POROSITY, %

HαE 210°

5° °

8-

"WET"WATER

CONTENT B% wt




CORE 3O3A-7


® Syringe p o r o s i t y , % COMPRESSIONAL SOUND VELOCITY

1 2 3

DEPTH POROSITY,IN

HOLE 2

"WET"WATER

CONTENT Bwt




CORE 303A-8


© Syringe porosity, % COMPRESSIONAL SOUND VELOCITY

1 2 3DEPTH POROSITY,

HOLE 210° 50

0-r- 3

1 -

4-

5-

7-

"WET"WATER

CONTENT Hwt


A = Parallel ToBedd i ngkm/sec

25 2'•"T1"'""!""1""!

l • • • • i . • • • l I I

= gra in dens i t y , g/cc

00 CORE 303A-9



1 2 3

DEPTH POROSITY, %IN

HOLE 2100 50 0

(m) *rg-

1 -

2-

3 —- —

4-

5-

7-

8-

"WET"WATER

CONTENT (3% wt



75 25 2 3 4T-| ,...,,....,....,....,...., , , ,.... ,....,..,.,.

©A

*rg = grain density, g/cc.I....I..,,;....! i• . l • • • • l • • • • l • . • • i • • • • l l • • • • i

CORE 303A-10



1 2 3

7-

8-

"WET"WATER

CONTENT Bwt



1....1....L...1....1 I..UL,ÜI....L,,.I..,.I.•..I...,I


SITE 303

i—Ocm

1-25

1—50

1—75

1—100

1—125

1—150303-2-1 303-2-2 303-2-3 303-2-4 303-2-5 303-2-6

SITE 303

—25

—50

75

— 1Q0

— 125

150303-3-1 303-3-2 303-3-3 303-3-4 303-3-5 303-3-6

40

SITE 303

r-- 0cm

—25

—50

•—75

— 100

— 125

L—150303-4-1 303-4-2 303-4-3 303-4-4 303-4-5 303-4-6

41

SITE 303

0cm

h-25

\— 50

h-75

h-ioo

h-125

1—150303A-5-1 303A-5-2 303A-6-1 303A-7-1 303A-8-1 303A-9-1

42

I—Ocm

h-75

—100

SITE 303

\—]25 4ß

303A-10-1

43

site data date occupied: •j '•-• date departed1973/08/18 · site 303 42 153 154 155...

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