Polskie badania paleontologiczne w Antarktyce Zachodniej (1986)

Abstract

POLISH PALEONTOLOGICAL INVESTIGATIONS IN WEST ANTARCTICA IN 1986 Summary Paleontological studies carried out in the austral summer 1985-1986 in King George Island, South Shetland Islands (West Antarctica) dealt with the fossiliferous glacio-marine sediments cropping-out in the Melville Peninsula and Low Head area (Fig. 1 ). The sequence of glacio-marine sediments of the Melville Glaciation represented by the Cape Melville Formation ( 4-5) is best exposed in cliffs slopes of the Melville Peninsula (Fig. 1, see also cover photos): The sediments of the Cape Melville Formation contain abundant marine fossils, some of them in live position (22-23, 8, 4, 15, 10, 17-18, 24-25, 29-30, 32). Microfossils comprise frequent benthic foraminifers: Cyclammina (Fig. 5a), Globobulimina (Figs 5b, 6g), Haplophragmoides (Fig. 6e), Uvigerinella (Fig. 6f), planktonic foraminifers (Globigerinidae, Heterohelicidae), numerous diatoms; Actinoptychus, Asteromphalus, Coscinodiscus, Triceratium (Fig. 6c), Trinacria; sponge spicules "hexactin" (Fig. 6b), radiolarians, ostracods (Cytheridae), polychaete jaws: Drilonereis, Glycera, Lumbrineris, Ophryotrocha (Fig. 6d), as well as problematic microfossil Bolboforma (Fig. 6a). This Tertiary fossils is an autochtonous biota. The recycled forms included Cretaceous coccoliths (15) and belemnites (10). The K-Ar data (around 20 Ma) obtained from the andesite dykes cutting through glacio-marine sediments of the Cape Melville Formation allow to estimate the age of the formation as no younger than the Early Miocene (9). Numerous samples for micropaleontological and radiometrical studies have been taken. The earliest skeletal fossils are recorded for the first time from the Antarctic limestones which occurring as erratic boulders (dropstones) in the sediments of the Cape Melville Formation. The limestones are dated as Early Cambrian (Atdabanian) on the basis of the co-occurrence of small shelly fossils such as Camenella (Fig. 7e), Lapworthella, Chancelloria (Fig. 7a, b), Halkieria (Fig. 7h) and Mongolitubulus. The limestones yielding this fossil assemblage remain unknown from Antarctic continent but it is possible that their outcrops are completely covered by ice. However, general lithological composition of the whole spectrum of erratics from the Cape Melville Formation and its similarity to that of erratics brought to King Georg Island in times of the Polonez Glaciation (3, 5-7, 27) suggest that outcrops of the Lower Cambrian rocks stretching around the Weddell Sea (Ellsworth Mts, Pensacola Mts and northern Transantarctic Mts) acted as source areas of the boulders. The sequence of glacio-marine sediments of the Polonez Glaciation represented by the Polonez Cove Formation (3, 5) is best exposed in the steep cliff-face near Low Head (Fig. 1). The sediments of the Polonez Cove Formation are also rich in invertebrate fossils (12, 20-22). The Chlamys coquinas are the most fossiliferous and contain mixed biota of shallow- to deep-marine environments (20). The formation was dated as Pliocene by the occurrence of the bivalve Chlamys anderssoni (Hennig, 1911) analogous to that of the Pecten Conglomerate on the Cockburn Island (3). Recently recognized coccoliths indicate Oligocene age of the formation (19). The K-Ar dating of lavas overlying the studied sequence shows that rocks of the Polonez Cove Formation are older than 23 Ma (6). A number of samples for further micropaleontological study have been collected. The collections of fossils (mainly invertebrate fauna and flora), gathered in the course of the Polish Antarctic Expeditions have been studied by Polish and foreign paleontologists. The results of the studies were presented in over 25 papers. Results of current studies on the Antarctic collections will be presented in a new series of Palaeontologia Polonica - "Palaeontological Results of the Polish Antarctic Expeditions" and will be printed in vol. 49 scheduled for 1987.