A NEW EOCENE SEDIMENTARY SEQUENCE FROM ANTARCTICA AND ITS PALYNOLOGIC CHARACTER

Eocene stratigraphic sections are rare in Antarctica, and are limited to units from Seymour Island (Antarctic Peninsula, AP) and Prydz Bay (PB), and to fossiliferous glacial erratics retrieved from McMurdo Sound (MS). In 2014, the first geological and geophysical study of the Sabrina Coast (SC) of East Antarctica was conducted in order to understand the past and modern glacial dynamics of the region seaward of the Aurora Subglacial Basin (ASB) in central Wilkes Land. Two organic-rich sediment cores, collected from an eroded trough on the inner shelf, contain abundant palynomorphs and based on the sedimentology and seismic stratigraphy, reveal a transitional deltaic environment during the mid-late Eocene.

Both jumbo piston cores (JPC), JPC-54 and 55, contain Late Pleistocene-Holocene glacial marine sediment overlying non-glacial muddy sands, separated by a sharp contact. This contact is also illustrated by an abrupt decrease in water content (40-25%), magnetic susceptibility (150-25 SI) and δ¹³C_org (^-25-^-26‰), and an increase in density (1.8-2.1g/cm³) and %TOC (0.30-0.75%) below the contact. JPC-55 contains a large (freshwater?) gastropod and a large spherical concretion formed around a presumed fossilized flower bud, further supporting its non-glacial origin, while JPC-54 contains angular ice-rafted cobbles of crystalline character, supporting its syn-glacial origin.

These cores contain at least 30 new and previously identified pollen and spore morphospecies. Some key morphospecies include Proteacidites recavus, Nothofagidities asperus, and Proteacidites bremerensis, which allow us to assign a late middle Eocene to early late Eocene age to these units. The assemblage is dominated by Gambierina spp. which is believed to be limited to the late Cretaceous based on AP units. This new Eocene section therefore suggests that Gambierina spp. and associated floristic elements experienced extirpation on the AP while surviving through the Eocene near the SC, which is supported by previous interpretations from PB sedimentary sequences and by their complete absence in Eocene rocks from MS. Thus, the paleobotanical environments of the Antarctic and Australian segments of Gondwana were spatially and temporally complex as evidenced by the palynological and stratigraphic analyses of this new mid-late Eocene unit.