10. pliocene and quaternary benthic foraminifers from site 910
TRANSCRIPT
Thiede, J., Myhre, A.M., Firth, J.V., Johnson, G.L., and Ruddiman, W.F. (Eds.), 1996Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 151
10. PLIOCENE AND QUATERNARY BENTHIC FORAMINIFERSFROM SITE 910, YERMAK PLATEAU1
Lisa E. Osterman2
ABSTRACT
The benthic foraminiferal record of Ocean Drilling Program (ODP) Site 910 can be divided into four assemblage zones,from oldest to youngest: the Cassidulina spp. zone, the Elphidium spp. zone, the Elphidium albiumbilicatum zone and theElphidium excavata forma clavata zone. The Pliocene benthic foraminifers in the three lower zones of Site 910C, 102.8-504.7meters below sea floor (mbsf), indicate warm conditions that cool progressively from 2.7 to 1.6 Ma. Based on the number anddiversity of planktonic foraminifers and the high benthic foraminiferal abundances, the lowermost Cassidulina spp. zone indi-cates the warmest water conditions within the Pliocene at this locality. The Elphidium spp. zone of Site 910C indicates warmbut cooling conditions with decreasing foraminiferal diversities and abundances, which end with the initiation of glacial drop-stones at 208.7 mbsf. The presence of species described from Pacific deposits in both lower zones suggests a Pacific Oceaninfluence during the late Pliocene at this site. However, climatic conditions change when Atlantic species begin to dominate theuppermost Pliocene sediments. The uppermost Pliocene sediments of the E. albiumbilicatum zone indicate glacial-marine con-ditions with warm episodes.
The uppermost E. excavatum f. clavata zone (0-102.8 mbsf), of Quaternary age, records glacial and interglacial climaticfluctuations, including one or more instances of grounded glacial ice (or episodes of severe ice-rafting) and ice-free interglacialdeposits.
It appears to be possible to correlate the Pliocene benthic foraminiferal assemblages in Hole 910C with the isolated pocketsof Arctic Pliocene sediment that have been previously described (Brouwers et al., 1991; Brigham-Grette and Carter, 1992; Fey-ling-Hanssen, 1990; Feyling-Hanssen et al., 1982).
INTRODUCTION
Ocean Drilling Program Site 910 was cored to provide a high res-olution Late Neogene record of the interaction between the North At-lantic and the Arctic Oceans; it is the shallowest site in a transectalong the Yermak Plateau. Approximately 504.7 m of nearly homo-geneous silty clays were recovered at this site. This site provides anexcellent record of calcareous benthic foraminifers from the longestcontinuous record of pre-glacial Pliocene sediment in the Arctic.
Because of eustatic and glacio-eustatic sea level fluctuations, nu-merous outcrops of shallow-water Pliocene marine deposits occurthroughout the Arctic (e.g., Brouwers et al., 1991; Brigham-Gretteand Carter, 1992; Feyling-Hanssen, 1976,1980,1990; Feyling-Hans-sen etal , 1982,Funderetal., 1985; Todd, 1957; Vincent etal., 1984).Most of these sections indicate that the Pliocene was an interval of in-creased temperatures, compared to today, which has a direct bearingon the climatic history and ice cover of the Arctic Ocean. The prob-lems with these terrestrial sites are threefold. First, most of thesePliocene sections lack any definitive age control. They are correlatedeither by the use of amino-acid racemization values, or by macro- ormicrofaunal assemblages. Second, the calcareous marine biota(benthic foraminifers, ostracodes, and molluscs) found in these shal-low marine sections are strongly controlled by local environmentalconditions and can be subject to loss by post-depositional dissolution(e.g., Feyling-Hanssen, 1976). Third, most of the Arctic terrestrial lo-calities represent isolated sections of the Pliocene, which may or maynot be correlative events throughout the entire Arctic.
'Thiede, J., Myhre, A.M., Firth, J.V., Johnson, G.L., and Ruddiman, W.F. (Eds.),1996. Proc. ODP, Sci. Results, 151: College Station, TX (Ocean Drilling Program).
department of Paleobiology, NHB-121, Smithsonian Institution, Washington,D.C. 20560, U.S.A. [email protected]
Hole 910C is the first continuous upper Pliocene marine sectionin the Arctic that is dated by calcareous nannofossils and planktonicforaminifers. Therefore, Site 910 should help to resolve some of theconfusion that exists among the widely scattered and discontinuousArctic Pliocene records. This paper will discuss the Pliocene andPleistocene benthic foraminifer record of Hole 9 IOC.
MODERN OCEANOGRAPHY
ODP Hole 910C is located in 556.4 m of water on the Yermak Pla-teau, northwest Svalbard continental shelf (80°15.896'N,6°35.430'E), in a hydrographically unstable area of the North Atlan-tic-Arctic Gateway (Fig. 1). This site is located in the zone of mixingbetween the northward-flowing, relatively warmer West SpitsbergenCurrent and the colder, lower-salinity, southward-flowing waters ofthe East Greenland Current (Aagaard et al., 1985). The Yermak Pla-teau is also located at the edge of the Arctic pack ice and is coveredby sea ice for most of the year, although it may have open water inlate summer and early autumn during some years. Site 910 was cho-sen to study the interaction between water masses and climatic histo-ry within the North Atlantic-Arctic Gateway.
METHODS
Sediment in 20-cm3 samples was disaggregated with the use of avibrating hot plate, without the use of any chemicals. Samples weresoaked overnight and then mechanically agitated for up to 1 hr beforewashing over a 63-µm sieve. Samples were dried overnight in anoven at less than 60°C. Samples from Hole 910C were picked at >63µm. Samples were split to obtain between 100 to 300 benthic fora-minifers. If fewer foraminifers were present the sample was usually
187
L.E. OSTERMAN
ièo°
Figure 1. Location of Site 910 in comparison to other Pliocene sections, KapK0benhavn, Lodin Elv, and the Alaskan Coastal Plain.
not analyzed. Shipboard core-catcher samples processed on board theJOIDES Resolution were measured volumetrically and subjected toCalgon solution as well as sonic vibration (Shipboard Scientific Par-ty, 1995).
AGE CONTROL
The upper 100 m of Hole 9IOC is identified as Quaternary, but isplagued with poor recovery and the presence of one or more intervalsof overconsolidated sediment (see Rack et al., this volume, chapter21; Flower, this volume). The uppermost overconsolidated zone oc-curs at 19 mbsf in Hole 910A, and can be assumed to be close to thatdepth in Hole 9IOC. The Quaternary/Pliocene boundary is poorlyconstrained within the interval of no recovery from Sample 151-910C-8R-CC (73.8 mbsf) to Sample 151-910C-11R-CC (102.8 mbsf;Fig. 2). Calcareous nannofossils, as well as benthic and planktonicforaminifers all suggest an age near the Quaternary/Pliocene bound-ary (1.6 Ma) for Sample 151-910C-11R-CC (102.8 mbsf; ShipboardScientific Party, 1995). New nannofossil data place the boundary at67 mbsf, slightly above Sample 910C-8R-CC (73.8 mbsf; Hull et al.,this volume; Sato and Kameo, this volume).
All microfossil groups indicate that the interval from Sample 151-910C-12R-CC (112.4 mbsf) to the base of the hole (504.7 mbsf) isclearly of Late Pliocene age (NN15-18). Cronin (this volume) reportsthe presence of the ostracode Pterygocythereis vannieuwenhuisei inSamples 151-910C-45R-CC (429.3 mbsf) to 151-910C-43R-CC(410.78 mbsf). This indicates an age of >2.5 Ma for these samples.Assuming a uniform sedimentation rate (between 102.8 and 429.3
mbsf), an age of 2.7 Ma is extrapolated for the base (507.4 mbsf).This age is in agreement with the recognition of Pacific benthic fora-minifers, including Paracassidulina neocarinata, Globocassidulinagrooviapeture, and Paracassidulina sagamenensis in Sample 151-910C-53R-CC (507.4 mbsf), indicating that it must have been depos-ited after the opening of the Bering Straits at approximately 3.0 Ma(Shipboard Scientific Party, 1995).
The magnetic record shows normally magnetized sedimentsthroughout Hole 910A (24.71 mbsf). Poor recovery and strong con-centrations of iron sulfides limited the magnetic stratigraphy in Hole910C (Shipboard Scientific Party, 1995; Cande and Kent, 1992).
RESULTS
The benthic foraminifers of Hole 910C can be divided into fourassemblage zones (Fig. 2). The upper two (the Elphidium excavatumf. clavata and Elphidium albiumbilicatum) zones indicate glacialconditions, while the lower two (the Elphidium spp. and Cassidulinaspp.) zones show evidence of a more ameliorated pre-glacial environ-ment.
The uppermost zone occurs from Sample 151-910C-1R-1, 1 cm(0.01 mbsf) to Sample 151-910C-8R-CC (73.8 mbsf) and containsforaminifers indicating both glacial and interglacial climatic condi-tions, including the highest percentages of E. excavatum f. clavata.Elphidium excavatum f. clavata is common in Pleistocene glacial-marine sediments in the Arctic (Osterman, 1984; Osterman et al.,1985). Samples indicative of glacial stages contain lower diversities(number of species, S, = 5-9). Samples indicative of interglacial stag-es contain higher diversities (S = 13-19).
The E. excavatum f. clavata zone includes the overconsolidatedinterval at 19 mbsf that was identified by physical properties (Ship-board Scientific Party, 1995). The cause of the overconsolidated in-terval was reported to be overcompacted due to excessive glacialdropstones or the grounding of glacial ice on the Yermak Plateau(Shipboard Scientific Party, 1995; Rack et al., this volume). Whatev-er the cause of the overconsolidated layer it certainly represents a ma-jor climatic event on the Yermak Plateau, and, as might be expected,the foraminifers differ somewhat above and below the uppermostoverconsolidated layer, mainly in overall foraminiferal abundances.Sediments above the uppermost overconsolidated interval are be-lieved to be younger than Oxygen Isotope Stage 15 (Flower, this vol-ume). Modern oceanographic conditions are represented by the up-permost Samples 151-91OC-1R,1 cm (0.01 mbsf) and 151-910C-1R,3-7 cm (0.03 mbsf), which contains a benthic foraminifer assem-blage dominated by branching and tubular agglutinated foraminifersincluding Bathysiphon major, Bathysiphon rufus, Rhabdamina abys-sorum, Astrorhiza limnicola, Saccorhiza ramosa, and Reophax scor-piurus; rare calcareous species include Cassidulina teretis, Cassid-ulina reniforme, Cibicides lobatulus, and Nonion barleeanum. Be-neath this uppermost agglutinated-foraminifer-rich sediment theremaining glacial-marine sediments of this upper interval from Sam-ple 151-910C1R-1, 83-87 cm (0.83 mbsf) to the overconsolidated in-terval at 19 mbsf contains a fairly consistent assemblage of predom-inately calcareous benthic foraminifers including additional calcare-ous species Epistominella vitrea, Stainforthia concava, andStainforthia feylingi.
Beneath the overconsolidated interval, from 19 to 102.8 mbsf (in-cluding Samples 151-910C-4R-3, 104-109 cm to 8R-CC), the lowerpart of the E. excavatum f. clavata zone occurs. Owing to both theovercompacted nature of the sediment and the abundance of drop-stones, recovery was poor in the interval from 19 to 73.8 mbsf. Mostof the samples below 19 mbsf contain only rare foraminifers with afew exceptions seen in Table 1. Samples 151-910C-4R-3, 104-109cm (30.44 mbsf), 151-910C-5R-1, 103-108 cm (36.9 mbsf), and151-910C-8R-2, 20-23 cm (65.9 mbsf) contain higher diversity for-
188
PLIOCENE AND QUATERNARY BENTHIC FORAMINIFERS
Elphidiume×cavatumf. clavata
zone
Elphidiumalbiumbil-
icatumzone
Figure 2. Biostratigraphic summary of Hole 9IOC including from left to right:depth (mbsf), core numbers, recovery, nannofossil zones, planktonic foramin-iferal zones, benthic foraminiferal zones discussed in this paper, and age.Quaterary/Pliocene boundary now placed at 67 mbsf.
aminiferal assemblages indicating Pleistocene interglacial condi-tions. In addition, there was good recovery of Cores 151-910C-4R,5R, and 8R, when compared to the other cores between 19 and 102.8mbsf. This suggests that there might have been several episodes of se-vere glaciation, evidenced by poor recovery, as well as climatic ame-lioration, evidenced by good recovery, on the Yermak Shelf duringthe Quaternary ice ages.
The Quaternary E. excαvαtum f. clαvαtα zone also includes in-creased numbers of reworked benthic foraminiferal specimens. InQuaternary sediments on Arctic continental shelves reworked speci-mens represent a problem. Often the reworked specimens can beidentified by a worn or abraded texture or by a different color or bro-ken test, in which case they are counted as reworked and not included
in the foraminiferal percentages of Table 1. However, not all re-worked specimens can be easily identified by their appearance; someare identified as reworked by ecological or temporal displacement.Species of Elphidium are usually restricted to shallow water and arecommon in proximal glacial-marine environments (Osterman, 1984),so it is possible that a majority of the Elphidium specimens in this up-permost zone of Hole 9IOC are ice-rafted into this water depth. Thenature of other specimens is not so clear. In the Arctic, Cibicidesgrossα has been traditionally used to identify Pliocene deposits(King, 1983; McNeil, 1989; Knudsen and Asbj0rnsdöttir, 1991).Therefore, the presence of Cibicides grossα in the Quaternary sedi-ments of Hole 9IOC is assumed to have been due to reworking andice rafting. However, the well-preserved nature of C. grossα in theQuaternary sediments suggests caution in the use of this species as aPliocene marker at this latitude.
The second benthic foraminifer zone, the Elphidium αlbiumbili-cαtum zone, occurs from Sample 151-910C-11R-CC (102.8 mbsf) to151-910C-20R-3, 133-136 cm (184.13 mbsf) and has been deter-mined to be of latest Pliocene based on calcareous nannofossils andplanktonic foraminifers (Shipboard Scientific Party, 1995). This zoneis characterized by the presence of E. αlbiumbilicαtum in most sam-ples. Also characteristic of this zone is high percentages of Cαssiduli-nα reniforme and lower percentages of C. teretis. Cibicides grossα isalso found in this zone. The number of species in this zone rangesfrom 2 to 23 (avg. S = 10) and the number of foraminifers per cm3
ranges from 2 to 68 (avg. = 21 per cm3).Elphidium αlbiumbilicαtum is an Atlantic Ocean boreal water in-
dicator, first recorded in the Sangamon deposits of Long Island, NY(Weiss, 1954). On the other hand, Cαssidulihα reniforme is a polarspecies and indicative of proximal glacial-marine environments (Sej-rup and Guilbault, 1980; Osterman, 1984; Elverhoi et al., 1980).Therefore, the benthic foraminifers of this zone indicate both arcticand boreal conditions (i.e., glacial intervals, with episodes of warmerinterglacials). This is also consistent with the interpretation of bothpollen (Willard, 1995, this volume), ostracodes (Cronin, 1995, thisvolume), and sediments (Shipboard Scientific Party, 1995) over thesame interval. This foraminifer zone occurs below the interval ofpoor recovery and slightly above the first dropstone occurrence at208.7 mbsf. It appears as though the environmental change in thebenthic foraminiferal assemblages occurred somewhat later than thesedimentological indicators for increased glaciation. This suggeststhat there is a lag between the time of ice build up, reflected by thedropstones, and the time of oceanic cooling, reflected by the foramin-iferal change.
Reworking of the foraminiferal fauna appears to be less commonin the E. αlbiumbilicαtum zone than in the uppermost zone, but ice-rafting of benthic foraminifers, as well as other fossil groups, certain-ly occurred. Evidence is seen in the interval from Sample 151-910C-17R-CC (161.15 mbsf) to Sample 151-910C-20R-CC (187.84 mbsf)which contains reworked Miocene diatoms and radiolarians (Ship-board Scientific Party, 1995).
The third benthic foraminiferal zone occurs from Sample 151-910C-21R-1, 27-30 cm (189.67 mbsf) to 151-910C-43R-6, 80-83cm (409.5 mbsf). The benthic foraminifer assemblage is character-ized by the occurrence of large-sized elphidium including Elphidiumexcαvαtum, Elphidium groenlαndicus, Elphidiellα hαnni, and Elphi-diellα hughesi. Elphidiellα hughesi and E. hαnni were originally de-scribed from the Pliocene of California (Cushman and Grant, 1927).Nonion mαtchigαricus, originally described from the Miocene depos-its of Sakhalin, Russia in the North Pacific (Volshinova, 1952) wasalso observed in this zone. Epistominellα vitreα is also common inthis zone. There is a wide range of diversity and abundance values inthis zone which includes a benthic foraminiferal low-diversity zone,recognized by the Shipboard Scientific Party (1995), from Samples151-910C-33R-CC to 38R-CC (314.8 to 362.9 mbsf). The number ofspecies ranges from 2 to 18 (avg. S = 8) and the number of foramin-
189
L.E. OSTERMAN
Table 1. Most abundant species percentages, Hole 910C.
Core, section,interval (cm)
151-910C-1R-1, 1lR-1,3-91R-1, 83-871R-CC, 7-112R-1,76-802R-CC3R-1,40-444R-3, 104-1095R-1,103-1086R-1,20-238R-1, 18-228R-2, 20-238R-CC11R-CC13R-1, 85-8813R-2, 45-4814R-1, 130-13415R-1, 68-7217R-1, 37-4117R-2, 37-4117R-3, 37-4119R-1, 34-3819R-2, 34-3820R-2, 46-4920R-3, 133-13621R-1, 27-3022R-1,27-3022R-1, 136-13822R-4, 28-3122R-5, 35-3823R-3, 34-3623R-5, 34-3624R-1, 129-13225R-2, 61-6725R-CC26R-2, 80-8327R-4, 79-8528R-2, 78-8229R-2, 77-8229R-4, 77-8232R-2, 80-8332R-4, 80-8332R-5, 80-8332R-6, 80-8333R-2, 76-8034R-2, 83-8735R-4, 82-8636R-5, 78-8237R-3, 96-10037R-5, 96-10039R-2, 79-8340R-2, 77-8340R-5, 77-8340R-6, 77-8341R-2, 74-7741R-4, 62-6641R-6, 73-7942R-2, 80-8342R-4, 80-8342R-6, 80-8343R-2, 80-8343R-4, 80-8343R-6, 80-8346R-4, 110-11447R-4, 80-8448R-2, 86-9049R-1, 74-7849R-2, 74-7850R-4, 80-8350R-6, 80-8351R-2, 79-8551R-4, 79-8552R-2, 80-8352R-4, 80-8352R-6, 80-8353R-2, 77-8153R-4, 77-81
Depth(mbsf)
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190
PLIOCENE AND QUATERNARY BENTHIC FORAMINIFERS
ifers per cm3 ranges from 2-108 (avg. = 26 per cm3). Wood and plantfragments are found in the interval from Samples 151-910C-25R-CC(236.54 mbsf) to 151-910C-39R-CC (386.9 mbsf) (Shipboard Scien-tific Party, 1995) suggesting warm forested conditions within theArctic. There does not appear to be any strong glacial influence inthis assemblage, and no dropstones were recognized (Shipboard Sci-entific Party, 1995).
The lowest zone is designated the Cassidulina spp. zone and oc-curs from Sample 151-910C-46R-4, 110-114 (435.5 mbsf) to thebase of the hole at 504.7 mbsf. The foraminiferal diversity and abun-dance of this zone is the highest in the Pliocene. The number of spe-cies ranges from 4 to 16 (avg. S = 10) and the number of foraminifersper cm3 ranges from 2-143 (avg. = 56 per cm3). The oldest sedimentsin Hole 9IOC show increased benthic foraminiferal diversity of theCassidulinid species, in particular the carinate forms including Cas-sidulina pliocarinata and Paracassidulina neocarinata. Several spe-cies show Pacific affinities including Globocassidulina grooviape-ture, Paracassidulina neocarinata, and Paracassidulina sagamenen-sis (Nomura, 1983a, 1983b; Matoba et al., 1990). Nonion erucopsis,originally described from Carter Creek, Alaska (Todd, 1957), is alsofound in this zone. It is most important to recognize that this assem-blage zone has an increase in the number and diversity of planktonicforaminifers. Sample 151-910C-51R-4, 79-85 cm (483.69 mbsf)contains the largest number of planktonic foraminifers in all Pliocenesamples, which indicates the warmest water during the deposition ofthese sediments. Planktonic species Neogloboquadrina atlanticaboth dextral and sinistral are found throughout this interval, as wellas sporadically in the other zones. Other planktonic species, includ-ing Globigerina quinqueloba (Sample 151-910C-49R-1, 74-78 cm[459.74 mbsf]), and Globigerina bulloides (Sample 151-910C-51R-4, 79-85 cm [483.69 mbsf]), are found only in this lowermost zone.
DISCUSSION
The purpose of this paper is to provide a benthic foraminiferal zo-nation that will allow comparison to other Pliocene marine sedimentsof the Arctic. Preliminary analysis suggests that there are several sim-ilarities between the Pliocene section of Hole 910C and otherPliocene-aged sediments in the Arctic, in particular the Lodin Elv andKap K0benhavn Formations of Greenland and the Pliocene marinetransgressions of the Alaskan Arctic Coastal Plain (Feyling-Hanssenet al., 1982; Feyling-Hanssen, 1990; Brigham-Grette and Carter,1992). All of these sites contain evidence for several Pliocene eventswhich I believe can be correlated based on the benthic foraminifers.
Three warm Pliocene marine transgressions have been reportedfrom the Alaskan Coastal Plain (Brigham-Grette and Carter, 1992).These are tentatively dated as the Covillian Transgression (2.7 to 2.48Ma), the Bigbendian Transgression (around 2.48 Ma), and the Fish-creekian Transgression (2.48 to 2.14 Ma) (Brigham-Grette and Cart-er, 1992). Macrofaunal evidence suggests that these were warm watertransgressions that became progressively cooler from oldest toyoungest. The timing of these transgressions is important to Arcticstratigraphy. Unfortunately, most Alaskan samples contain very fewbenthic foraminifers; however, samples of the youngest Plioceneunit, the Fishcreekian Transgression, do contain large Elphidium in-cluding E. hughesi (Osterman, unpubl. data). This correlates stronglywith the Elphidium spp. zone of Site 910.
In eastern Greenland, Pliocene benthic foraminifers from the Lo-din Elv Formation (71°10'N, 24°24'W) have been reported by Fey-ling-Hanssen et al., (1982). The Lodin Elv Formation represents aninner shelf environment and is believed to straddle the Pliocene/Qua-ternary boundary (Feyling-Hanssen, 1985, 1990; Feyling-Hanssen etal., 1982). The benthic foraminiferal assemblages are divided into alower Zone I with C. grossa, C. reniforme, and E. vitrea, and the up-per Zone II without C. grossa. Placing the Pliocene/Quaternaryboundary between Zones I and II is based on the presence/absence of
C. grossa at Lodin Elv. The study of Site 910 has shown that thestratigraphic use of C. grossa alone may be suspect. I would proposethat the entire Lodin Elv formation appears to correlate to the upper-most Pliocene deposits of Site 910C with increased percentages of C.reniforme and E. vitrea.
The Kap K0benhavn Formation (82°30'N, 21 °W) is also believedto have been deposited in an inner shelf environment during the latePliocene to early Quaternary. Both ostracodes (Brouwers et al., 1991)and benthic foraminifers (Feyling-Hanssen, 1990) have been studied.The Kap K0benhavn Formation is subdivided into four members,from bottom to top, A, Bl, B2, and B3 (Funder et al., 1985). Mem-bers B2 and B3 contain glacial dropstones along with abundant woodfragments, which suggests a warm, forested Arctic with nearbymountain glaciers. Funder et al., (1985) believe that the climate ofNorthern Greenland during the deposition of the Kap K0benhavn for-mation was similar to present-day Labrador.
Benthic foraminifers are found in Kap K0benhavn members Aand B2. Member A contains N. erucopsis, C. reniforme, C. teretis,and C. laevigata (which Feyling-Hanssen [1990] reports as beingvery close to C. pliocarinata). Feyling-Hanssen (1990) also reportsthat Kap K0benhavn has numerous similarities to Japanese faunas,including P. sagminensis (Asano and Nakamura, 1937) found inmember A. The foraminiferal assemblage of Member A is very sim-ilar to the Cassidulina spp. zone of Site 910C, which also includes N.erucopsis, C. pliocarinata, and P. sagmenensis.
The lower part of Kap K0benhavn member B2 contains variouslarge elphidium including Elphidium rolfi, E. hanni, and E. hughesi,as well as Nonion niveum (= N. tallahattensis of Feyling-Hanssen[1976] and reported to be similar to Nonion akitaensis Asano,[1950]). The upper part of member B2 contains increased E. albium-bilaticum, C. reniforme, and E. vitrea. Member B has similarities toboth the Elphidium spp. and E. albiumbilicatum zones of Site 9IOC.
The age and stratigraphy of the Kap K0benhavn Formation is stilldisputed. Feyling-Hanssen (1990) reports that member B2 of the KapK0benhavn Formation straddles the Pliocene/Quaternary boundary( 2? Ma) which agrees with Brigham-Grette and Carter's (1992) cor-relation of Kap K0benhavn member B to the Fishcreekian transgres-sion of the Alaskan Coastal Plain (2.14 to 2.48 Ma). This correlationalso agrees with the occurrence of the large Elphidium in deposits ofthe Fishcreekian transgression, in member B of Kap K0benhavn andin the Elphidium spp. zone of Hole 910C. Brigham-Grette and Carter(1992) correlate Kap K0benhavn member A to the either the Covil-lian Transgression (2.7 to 2.48 Ma) or the Bigbendian Transgression(-2.48 Ma).
On the other hand, the ostracode fauna (Brouwers et al., 1991) ofmember B2 contains P. vannieuwenhuisei, which corresponds to theolder Covillian Transgression (2.48 and 2.7 Ma) on the North Slopeof Alaska. Regardless of the age, ostracodes from the Kap K0ben-havn Formation suggest that winter temperatures were 1-2° C warm-er and summer temperatures were 7° to 8° C warmer than presentduring this interval (Brouwers et al., 1991).
SUMMARY
It appears to be possible to correlate 400 m of Pliocene-aged con-tinental shelf sediment in Hole 910C with the isolated pockets of Arc-tic Pliocene sediment that have been previously described. Somestrong similarities exist. Hole 910C contains three separate Pliocenebenthic foraminiferal zones that appear to have been deposited be-tween 2.7 to 1.6 Ma. This agrees with the time span discussed bymost of the previous researchers (Feyling-Hanssen, 1985,1990; Fey-ling-Hansen et al., 1982; Brigham-Grette and Carter, 1992; Brouwersetal., 1991).
The benthic foraminifers in the three Pliocene zones of Site 910Cindicate increasingly cooler conditions from Pliocene to Quaternary.Based on the numbers of planktonic foraminifers and benthic fora-
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miniferal abundances, the lowermost Cassidulina spp. zone indicatesthe warmest water conditions within the Pliocene at this locality. TheCassidulina spp. zone also shows an increased number of specieswith Pacific affinities. These include G. grooviapeture, P. neocarina-ta, and P. sagmenensis. These species do not occur at this location to-day. The Cassidulina spp. zone appears to correlate to Member A ofKap K0benhavn and either the Covillian Transgression (2.7 to 2.48Ma) or the Bigbendian Transgression of the Alaskan Coastal Plain.The occurrence of the ostracode Pterygocythereis vannieuwenhuiseiin Samples 151-910C-45R-CC (429.3 mbsf) to 151-910C-43R-CC(410.78 mbsf) suggests a correlation to the Covillian Transgression.
The Elphidium spp. zone of Site 9IOC indicates warm, but cool-ing, conditions with decreasing foraminiferal diversities and abun-dances ending with the initiation of glacial dropstones at 208.7 mbsf.This zone can be correlated to the lower part of Kap K0benhavnMember B and the Fishcreekian transgression based on the occur-rence of large Elphidium including E. hughesi at all three localities.The presence of Pacific species E. hughesi, E. hanni, and N. matchi-garicus indicate a continuing Pacific influence at this site.
Climatic conditions changed during the latest Pliocene when At-lantic species began to dominate the sediments. Glacial-marine con-ditions with warm episodes are indicated in the upper Pliocene E. al-biumbilicatum zone. A similar foraminiferal assemblage with in-creased E. albiumbilaticum, C. reniforme, and E. vitrea is recognizedin the upper part of Kap K0benhavn Member B as well as Zones I andII of Lodin Elv.
The uppermost Quaternary E. excavatum f. clavata zone (0 to102.8 mbsf) records glacial and interglacial climatic fluctuations in-cluding one or more episodes of grounded glacial ice (or severe epi-sodes of ice-rafting) and ice-free interglacial deposits. Poor recoveryof these youngest sediments in Hole 9 IOC limit further interpretation.
ACKNOWLEDGMENTS
I would like to thank co-chief scientists Annik Myhre and JörnThiede and the fellow shipboard scientists of Leg 151.1 wish to thankTom Ribbens, the crew and staff of the JOIDES Resolution. TheSmithsonian Institution and the United States Geological Survey(Reston) are thanked for providing space to complete this research. Ithank Detmar Schnitker for reviewing this manuscript.
FAUNAL REFERENCE LIST
Astrononion gallowayi Loeblich and TappanAstrorhiza limnicola SandahlBathysiphon major de Folin 1886Bathysiphon rufus de Folin 1886Buccella arctica (Volshinova 1960)Buccella frigida (Cushman)Bulimina aculeata (d'Orbigny)Cassidulina reniforme N0rvingCassidulina teretis TappanCassidulina pliocarinata van VorthuysenCibicides grossa (Dam and Walker)Cibicides lobatulus (Walker and Jacob)Elphidium albiumbilicatum (Weiss)Elphidium excavatum (Terquem) forma clavata CushmanElphidium groenlandicum CushmanElphidiella hanni Cushman and GrantElphidiella hughesi Cushman and GrantEpistominella vitrea ParkerGuttulina yamazaki Cushman and OzawaGlandulina laevigata d'OrbignyGlobocassidulina grooviapeture (Nomura) = Cassidulina gemmaIslandiella algida (Cushman) = Islandiella islandicaIslandiella helenae Feyling-Hanssen and BuzasIslandiella norcrossi (Cushman)Miliolinella subrotunda (Montagu)Nonion barleeanum (Williamson)
Nonion labradoricum (Dawson)Nonion erucopsis ToddNonion matchigaricus VolshinovaParacassidulina neocarinata (Nomura)Paracassidulina sagminensis (Asano and Nakamura)Pullina bulloides (d'Orbigny)Pyrgo williamsoni (Silvestri)Quinquloculina arctica CushmanQuinquloculina stalkeri Loeblich and TappanReophax scorpiurus de MontfortRhabdammina abssorum M. SarsSaccorhiza ramosa (Brady)Scutularis tegminis Loeblich and TappanStainforthia concava (Höglund)Stainforthia feylingi (Knudsen and Seidenkrantz)Triloculina trihedra Loeblich and Tappan
TAXONOMIC NOTES
Cibicides grossaThis research seems to show that there may be two forms of Cibicides
grossa. The broadly rounded and coarsely perforate form is found in the uppertwo zones of Hole 9IOC. Another form with a convex umbilical side and asomewhat keeled periphery is found in older sediments. Both forms appear tobe figured by Dam and Reinhold (1941). More work is needed to understandthe relationship of these two forms. In addition, caution is urged in the use ofthis species as a Pliocene indicator. Very fresh looking specimens of C. grossa(up to 4%) occur in clearly Quaternary sediments.
Cassidulina teretisIn this study it was often difficult to determine the identification of the
cassidulinids. Most specimens had broken apertures, making positive identi-fication impossible, and were sufficiently frosted to make the recognition ofbosses impossible. In these counts Cassidulina teretis includes all formswhich could not be positively identified as /. helenae and /. norcrossi.
REFERENCES
Aagaard, K., Swift, J.H., and Carmack, E.C., 1985. Thermohaline circulationin the Arctic Mediterranean seas. J. Geophys. Res., 90:4833-4846.
Asano, K., 1950. Part 1: Nonionidae. In Stach, L.W. (Ed.), Illustrated Cata-logue of Japanese Tertiary Smaller Foraminifer a: Tokyo (Hosokawa).
Asano, K., and Nakamura, M., 1937. On the Japanese species of Cassidulina.Jpn. J. Geol. Geogr. Trans. Abstr., 14:147.
Brigham-Grette, J., and Carter, L.D., 1992. Pliocene marine transgressions ofnorthern Alaska: circumarctic correlations and paleoclimate interpreta-tions. Arctic, 45:74-89.
Brouwers, E.M., J0rgensen, N.O., and Cronin, T.M., 1991. Climatic signifi-cance of the ostracode fauna from the Pliocene Kap K0benhavn Forma-tion, north Greenland.Micropaleontology, 37:245-267.
Cande, S.C., and Kent, D.V., 1992. A new geomagnetic polarity time scalefor the Late Cretaceous and Cenozoic. J. Geophys. Res., 97:13917—13951.
Cronin, T., 1995. Microfaunal evidence for late Pliocene warm oceanicAtlantic water on the Yermak Plateau, eastern Arctic Ocean, from ODPLeg 151, Site 910. AGU Abstr., S167.
Cushman, J.A., and Grant, U.S., IV, 1927. Late Tertiary and QuaternaryElphidiums of the West Coast of North America. Trans. San Diego Soc.Nat. Hist., 4:69-82.
Dam, A.T., and Reinhold, T., 1941. Die stratigraphische Gliederung desniederlandischen Plio-Pleistozans nach Foraminiferen. Meded. Geol.Sticht., Ser. C-V.
Elverhoi, A., Liestol, O., and Nagy, J., 1980. Glacial erosion, sedimentation,and microfauna in the inner part of the Kongfjorden, Spitsbergen. Saertr.Norsk Polarinst.
Feyling-Hanssen, R.W., 1976. The Clyde Foreland formation: a micropale-ontological study of Quaternary stratigraphy. 1st. Int. Symp. on Ben-thonic Foraminifera of Continental Margins (Pt. B): Paleoecology andBiostratigraphy. Mark. Sed., Spec. Publ., 1:315-377.
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, 1985. Late Cenozoic marine deposits East Baffin Island and EastGreenland, microbiostratigraphy-correlation-age. In Andrews, J.T. (Ed.),Quaternary Environments: Eastern Canadian Arctic, Baffin Bay, andWestern Greenland: Boston (Allen and Unwin), 354-393.
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Feyling-Hanssen, R.W., Funder, S., and Petersen, K.S., 1982. The Lodin Elvformation: a Plio-Pleistocene occurrence in Greenland. Bull. Geol. Soc.Den., 31:81-106.
Funder, S., Abrahamsen, N., Bennike, O., and Feyling-Hanssen, R.W., 1985.Forested Arctic: evidence from North Greenland. Geology, 13:542-546.
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Sejrup, H.-P, and Guilbault, J.-P., 1980. Cassidulina reniforme and C. obtusa(foraminifera) taxonomy, distribution and ecology. Sarsia, 65:79-85.
Shipboard Scientific Party, 1995. Site 910. In Myhre, A.M., Thiede, J., Firth,J.V., et al., Proc. ODP, Init. Repts., 151: College Station, TX (OceanDrilling Program), 221-270.
Todd, R., 1957. Foraminifera from Carter Creek Northeastern Alaska. Geol.Surv. Prof. Pap. U.S., 294-F:260-277.
Vincent, J.S., Morris, W.A., and Occheitti, S., 1984. Glacial and nonglacialsediments of Matuyama paleomagnetic age on Banks Island, CanadianArctic Archipelago. Geology, 12:139-142.
Volshinova, N.A., 1952. Fossil foraminifera of the U.S.S.R.: Nonionidae,Cassidulinidae, and Chilostomellidae. In Voloshinova, N.A., and Dain, L.(Eds.), VNIGRI, 63. (in Russian)
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Date of initial receipt: 1 July 1995Date of acceptance: 12 December 1995Ms 151SR-107
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Plate 1. Quaternary and Pliocene foraminifers from Site 910. 1. Elphidicum excavatum, Sample 151-910A-3H-1, 113-117 cm (170×). 2. Elphidium albiumbili-catum, Sample 151-910A-3H-1, 113-117 cm (130×). 3. Elphidicum excavatum forma clavata, Sample 151-910A-3H-1, 113-117 cm (130×). 4. Stainforthiaconcava, Sample 151-910A-3H-1, 113-117 cm (200×). 5. Buccella arctica, Sample 151-910C-25R-CC (200×). 6. Elphidiella hughesi Sample 151-910D-8R-CC (70×). 7. Elphidium groenlandicum, Sample 151-910C-25R-CC (80×). 8. Stainforthia feylingi, Sample 151-910C-1R-1, 3-9 (250×). 9. Cibicides grossa,Sample 151-910C-49R-CC (lOO×). 10. Cibicides grossa, Sample 151-910C-49R-CC (80×). 11. Cibicides grossa, Sample 151-910C-25R-CC (120×). 12. Non-ion labradoricum, Sample 151-910C-1R-1, 3-9 cm (120×).
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Plate 2. Quaternary and Pliocene foraminifers from Site 910. 1. Bulimina aculeata, Sample 151-910A-3H-1, 113-117 cm (120×). 2. hlandiella norcrossi, Sam-ple 151-910A-3H-1, 113-117cm (150×). 3. hlandiella helenae, Sample 151-910C-1R-1, 3-9 cm (150×). 4. Cassidulina teretis, Sample 151-910A-3H-1, 113-117 cm (150×). 5. Cassidulina reniforme, Sample 151-910A-3H-1, 113-117 cm (170×). 6. hlandiella algida, Sample 151-910A-2H-CC (250×). 7. Glandulinalaevigata, Sample 151-910C-25R-CC (120×). 8. Nonion barleeanum, Sample 151-910A-3H-1, 113-117 cm (130×). 9. Brizalina sp., Sample 151-910C-1R-1,3-9 cm (250×). 10. Nonion matchigaricus, Sample 151-910C-25R-CC (170×). 11. Globocassidulina sp., Sample 151-910C-49R-CC (130×). 12. Pullina bul-loides, Sample 151-910C-52R-CC (120×). 13. Cassidulina pliocarinata, Sample 151-910C-51R-CC (170×). 14. Paracassidulina sagminensis, Sample 151-910C-51R-CC (170×). 15. Globocassidulina grooviapeture, Sample 151-910C-51R-CC (lOO×).
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