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Victoria University Antarctic Research Expedition Science and Logistics Reports 1979-80: VUWAE 24

Foraminiferal Assemblages

Foraminiferal Assemblages

There are two foraminiferal assemblages evident in the samples we collected from the MSSTS 1 drill core. The upper fauna was found in cores 2, 10, 11, 15 and 16. It consists of twelve species, as follows: Trochammina sp., Pyrgo sp., one other species from the Miliolidae family, Fissurina sp., Rosalina globularis, Epistominella exigua, Spirillina sp., Globocassidulina subglobosa, Globocassidulina crassa, Nonion sp. (possibly Elphidium sp.), and a planktonic from the Globigerinidae family (see Table 6). The sub-bottom depths from which this fauna was extracted range from 9.72m to 32.15m. The assemblage consists of several species which are long-ranging in time, making it very difficult to determine an age for the sediments of this upper sequence.

This fauna exhibits some similarities to Pleistocene faunas from the DVDP holes 10 and 11 in Taylor Valley and also to that of the elevated marine deposits of the Cape Barne-Royds area of Ross Island (Wrenn, 1977, Ward, 1979). Rosalina globularis, Epistominella exigua (?vitrea), Globocassidulina crassa and G. subglobosa are found in all three of these sites. Species of Pyrgo, Trochammina, Fissurina, and Trifarina are also found at all three locations, though all those present in MSSTS 1 drill core have not been specifically identified to the species level. None of these taxa are particularly definitive as to time range, but the comparisons of the MSSTS 1 material with the known Pleistocene collections seen to indicate a similar age for the upper fauna of MSSTS 1.

The lower foraminiferal assemblage is also characterized by sparse faunal occurrences. The largest populations are confined to the interval from 118m to 127m sub-bottom (Cores 36 through 39), although scattered tests are found between 63m (Core 29) and 186m (Core 59). The interval from 186m to the bottom of MSSTS 1 (229m) appears to be barren of Foraminifera. Fifteen species are recognized in this lower assemblage: ?Verneuilina sp., Fissurina cf. annectens, Cassidulinoides parkerianus, C. ?porrectus, Epistominella exigua, Rosalina globularis, Elphidium Sp., Trochoelphidiella sp., Cribrononion cf. magellanicum, Globigerina quinqueloba, ?Candeina sp., Eponides tumidulus, Ehrenbergina sp., Nonionella bradii, and Anomalinoides sp. Two of these species are also present in the upper assemblage.

The small size of the lower foraminiferal assemblage and its sparse occurrences put some constraints on age determination. This fauna has strong similarities to the early and mid-Miocene assemblages from DSDP Sites 270, 272 and 273 in the Ross Sea (Leckie, Koch, D'Agostino, these in progress). The planktonic foraminiferid Globigerina quinqueloba has a New Zealand range of Otaian (early Miocene) to Recent (Jenkins, 1971). A potentially useful bioseries in the genus Trochoelphidiella Webb has been recognized in the early Miocene sequence of DSDP Stie 270 (Leckie, in progress). Continued investigations of Trochoelphidiella sp. from MSSTS 1 using the scanning electron microscope may permit better age resolution and correlation.

The preservation of the Foraminifera from MSSTS 1 is generally moderate to good. The tests have a characteristic yellowish color, differing from the clean white forms found on the floor of McMurdo Sound today. The presence of fragmented diatoms, sponge spicules, and other macrofossil debris as well as stratification of the sediments, suggests some reworking. There is no clear evidence for mixing of foraminiferal faunas of different ages. This observation, along with the quality of preservation, argues against extensive recycling of sediments. The very low abundance of Foraminifera may, in part, be explained by the small sample sizes. Oceanographic conditions page 25 influenced by the glacial regime prevalent at the time of deposition on an unstable sea floor may also be important factors inhibiting benthic productivity.

TABLE 6: Samples and processing techniques for foraminifera for MSSTS 1

TABLE 6: Samples and processing techniques for foraminifera for MSSTS 1

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TABLE 7 Foraminifera and other biogenic material recovered from MSSTS 1 cores.

TABLE 7 Foraminifera and other biogenic material recovered from MSSTS 1 cores.