Recent deep-sea benthic foraminiferal distributions in ...

Coarse Fraction +100 Mesh, % 10 15 20 25

Sr ppm 110

Rb ppm

120 130

110

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CaO

120

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Si0 1.3 72

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2 78

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Strat, Units

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Figure 2. Depth variation of chemical parameters on the basis of which unit lB is subdivided as indicated. Analytical data are explained briefly In the table.

This research was supported by National Science Foundation grant DPP 72-00459. The Deep Sea Drilling Project provided the sediment samples.

Recent deep-sea benthic foraminiferal distributions in the southeast Indian Ocean

References

BRUCE H. CoRLIss Graduate School of Oceanography University of Rhode Island Kingston, Rhode Island 02881

Faure, G., and J . L. Bannigan. 1975. Geochemistry and mineralogy of DSDP core 270, Ross Sea. Antarctic Journal of the U.S., X(5): 256-257. The distribution of deep-sea benthic foraminiHayes, D. E., et al. 1975. Initial Reports of the Deep Sea Drilling fera has been examined from Recent surface sediProject, 28. Washington, D.C., U.S. Government Printing Ofments from USNS Eltanin trigger cores in the fice. 10 17p. Reynolds, R. C. 1963. Matrix corrections in trace element analy- southeast Indian Ocean between 250 to 50°S. and sis by X-ray fluorescence. American Mineralogy, 48: 1133- 80° to 120°E. to evaluate possible relationships 1143. with water masses. Two abyssal water masses are Shaffer, N. R., and G. Faure. In press. Regional variation of 87 Sr/ 86 Sr ratios and mineral compositions of sediment from present in the area with Antarctic Bottom Water the Ross Sea, Antarctica. Geological Society of America Bulle- (AABW) found south of the Southeast Indian Ridge tin, 87(10). and Indian Bottom Water found astride the west-

September 1976

165

Map of the southeast Indian Ocean showing the location of USNS Eltanin trigger core tops used to determine the distribution of benthic foraminifera. The factor loadings for factor 2 are shown at each sample location. High values reflect dominance of C. wuel-

lerstorfi, E. umbonifera, G. subglobosa, and 0. toner,

and are inferred to be areas of Antarctic Bottom Water activity. Low values represent areas of high dominance of E. exlgua and Uvlgerina app. and are areas where Indian Bottom Water is inferred to be present. Bathymetric contours, shown at 2,000, 3,000, and 4,000 meters, are from Heezen at al. (1972).

ern ridge crest. Previous work by Streeter (1973) and Schnitker (1974) in the Atlantic demonstrated an association between abyssal water masses and benthic foraminiferal assemblages, with small environmental changes having a large effect upon the distribution of benthic foraminifera. The observed relationships were used to infer paleoceanographic changes during the Quaternary. Factor analysis of species frequencies in the southeast Indian Ocean reveals two faunal assemblages with distinct water mass preferences. The first faunal assemblage is marked by a strong dominance of Epictominella exigua (Brady) and Uvigerina spp. and is associated with Indian Bottom Water. The second assemblage is marked by several dominant species, the most important of which are Cibicides wuellerstorfi (Schwager), Epistominella umbonfera (Cushman), Globocassidulina subglobosa (Brady), and Oridorsalis tener (Brady). These fauna are found in waters with low bottom temperatures and salinities and with high dissolved oxygen content interpreted to be AABW. Distribution of the second faunal assemblage associated with AABW (figure) suggests that the AABW flows across the Southeast Indian Ridge at 166

120°E. and then turns westward forming a narrow western boundary undercurrent along the base of the ridge. This direction of bottom water is expected from coriolis forces. The presence of a contour current is supported by the existence of hiatuses and/or very low sedimentation rates in the Eltanin piston cores in the region of the inferred current (Kennett and Watkins, 1976; Williams, 1976). Temperature, salinity, and dissolved oxygen content of the bottom waters do not fully explain the observed faunal patterns and other environmental factors must influence the fauna! distributions. A factor that may play an important role as an environmental stress is calcium carbonate undersaturation of the bottom waters. Edmonds (1974) suggested that bottom current activity may enhance the corrosiveness of bottom waters. Hence, the corrosiveness of the waters in the region would be enhanced not only by the cold temperatures of AABW, but also by the current effect. Biometric analysis of one of the dominant species in the region, G. subglobosa, revealed size variation trends that may be associated with water mass distributions. The greatest variation in size is found in ANTARCTIC JOURNAL

areas of high dissolved oxygen content and low salinity associated with AABW. Two possible explanations are offered for this association. First, winflowing and/or carbonate dissolution related to AABW activity may preferentially dissolve or remove the smaller tests and increase the relative number of large tests within a sample. This concentration of large tests would be reflected by increases in mean size and variability in size. Second, the observed size distribution may result from phenotypic variation in this species with larger test sizes related to high dissolved oxygen and low salinity conditions. This research was supported by National Science Foundation grant DPI' 75-15511. References Edmonds, J . M. 1974. On the dissolution of carbonate and silicate in the deep ocean. Deep-Sea Research, 21: 455-480. Gordon, A. L., and E. Molinelli. 1975. USNS Eltanin Southern Ocean Oceanographic Atlas. Palisades, Lamont-Doherty. 91p. Heezen, B. C., M. Tharp, and C. R. Bentley. 1972. Morphology of the earth in the Antarctic and Subantarctic. Antarctic Map Folio Series, 16. Kennett, J . P., and N. D. Watkins. 1976. Regional deep-sea dynamic processes recorded by late Cenozoic sediments of the southeastern Indian Ocean. Geological Society of America Bulletin, 87: 321-339. Schnitker, D. 1973. West Atlantic abyssal circulation during the past 120,000 years. Nature, 248: 385-387. Streeter, S. S. 1973. Bottom water and benthonic foraminifera in the North Atlantic—glacial-interglacial contrasts. Quaternary Research, 3: 131-141. Williams, D. F. 1976. Planktonic foraminiferal paleoecology in deep-sea sediments of the Indian Ocean. Ph.D. thesis. Kingston, University of Rhode Island.

Oxfordian onychites and a possible decapod microappendage from the Falkland (Malvinas) Plateau FRANK

H.

WIND, MENNO G. DINKELMAN, SHERWOOD W. WISE, JR.

and

Department of Geology Florida State University Tallahassee, Florida 32306

Falkland (Malvinas) Plateau coring over the past 2 years during ARA Islas Orcadas cruise 7 and GbSeptember 1976

mar Challenger leg 36 recovered a variety of sedi-

ment types ranging from fluvial deltaic and shallow-water continental shelf facies to open marine pelagic, hemipelagic, and glacial marine deposits (Warnke et al., 1976; Barker et al., in press). Most of these units yielded abundant and diverse microfaunas and floras consisting primarily of palynomorphs, foraminifera, coccoliths, radiolarians, silicoflagellates, or diatoms. One unusual microfossil assemblage consisted of tooth and claw-like objects that resemble, superficially, annelid jaw apparatuses (scolecodonts). Over 150 specimens of scolecodont-like microfossils were recovered from 42 samples taken from a Jurassic sapropelic clay cored at Deep Sea Drilling Project site 330 (50019S. 46°53'W.; DSDP cores 330-5 to 330-10, 300 to 414 meters subbottom depth). All samples were determined to be Oxfordian in age using calcareous nannofossils (Wise and Wind, in press) and palynomorphs (Harris, in press). Several of the 10- to 15-milligram samples contained as many as 10 to 12 complete or nearly complete scolecodont-like objects. Complete specimens range in size from less than 0.5 millimeter to nearly 5 millimeters in length. The microfossils are dark brown to black in color, with a dull lustre. Specimens were generally well preserved when taken from the organic-rich sediment. On drying, surfaces of many became crazed and, in time, developed large fissures. The fauna. Most specimens sufficiently complete for identification can be placed in Paraglycerites and Longuncus, two genera identified by Kulicki and Szaniawski (1972) as cephalopod arm hooks (onychites). Paraglycerites Eisenack (1939) is characterized by a straight to arcuate, long shaft, with spur and uncinus well-developed. Longuncus Kulicki and Szaniawski (1972) includes forms described as hooks with long, thin shafts, and a small uncinus and spur. Additional specimens represent the genus Accoluncus defined as small, gently arcuate forms bearing a small spur situated very close to an equally small uncinus. Other specimens appear to represent species of Deinuncus Kulicki and Szaniawski (1972) and Urbanekuncus Kulicki and Szaniawski (1972). The onychite fauna is described, and new taxa are illustrated in Wind, Dinkelman, and Wise (in press). One large, well-preserved specimen, illustrated in the figure, bears no similarity to other specimens recovered in these samples, and is unlike all scolecodonts and onychites previously described and illustrated. Although the specimen was originally described by Wind et al. (in press) under Incertae sedis, it has since been suggested to us (L. G. Abele, 1976, personal communication) that the object is possibly the subchela (distal extremity of a limb 167