Pre-glacial sedimentary facies of the Point Thomas Formation (Eocene) at Cytadela, Admiralty Bay, King George Island, West Antarctica

Abstract

New evidence of Eocene preglacial environments has been found on the southern coast of Ezcurra Inlet on King George Island, South Shetland Islands, West Antarctica. Plant remains (trunks, leaves, detritus) and carbonaceous seams and beds occur in sedimen− tary strata in a 4 km long Cytadela outcrop of the Point Thomas Formation. They are an evi− dence for the presence and diversity of terrestrial vegetation in the northern Antarctic Penin− sula region. The forests were composed mostly of Podocarpaceae-Araucaria-Nothofagus, with an undergrowth of hygrophilous and thermophilous ferns, and grew on volcanic slopes and surrounding lowland areas of King George Island during breaks in volcanic activity. The succession that crops out at Cytadela provides a record of changing climatic conditions from a warm and wet climate with extensive vegetation to a much drier climate with limited vegetation and ubiquitous weathering of volcanic bedrock. The geochemical indices of weathering (CIA, PIA and CIW) have narrow and relatively high value ranges (76-88), sug− gesting moderate to high chemical weathering under warm and humid climate conditions. The decrease in humidity and the decline in plant life through the succession can be related to the gradually cooling climate preceding development of the Oligocene ice cover across the Antarctic continent.

Eocene sedimentary facies in a volcanogenic succession on King George Island, South Shetland Islands: a record of pre-ice sheet terrestrial environments in West Antarctica

“…Among the ferns, a Blechnum-re lated form is re corded. Poorly pre served fragments of Podocarpaceae are also pres ent (Birkenmajer and Zastawniak, 1989a;Mozer, 2012). This plant fos sil as sem blage is sim i lar to those de scribed by Askin (1992) and Fran cis et al (2009) from other lo cal i ties of plant beds on KGI.…”

“…A Mid dle Eocene age for the Mount Wawel For ma tion was pro posed by Nawrocki et al (2011) as a re sult of U-Pb and 40 Ar-39 Ar anal y ses. Tak ing into ac count that sim i lar plant beds were found in the Fildes For ma tion on Fildes Pen insula and dated to be Eocene in age (Poole et al, 2001;Fontes and Dutra, 2010), a sim i lar age of the Point Thomas For ma tion in Ezcurra In let is highly prob a ble (Mozer, 2012). A Mid dle Eocene age was sug gested for the Lions Cove For ma tion (Z. Pécskay, pers.…”

“…The ex po sure is com posed of two mem bers and dem on strate dis tinct in for mal units. The lower mem ber is com posed of a com plex of andesitic lavas, con glomer ates and volcanoclastic sed i ments with abun dant fos sil plants, whereas the up per mem ber is com posed mainly of andesitic lavas and con glom er ates (Mozer, 2012;Fig. 5A).…”

Eocene age of the Baranowski Glacier Group at Red Hill, King George Island, West Antarctica

“…Similar fossil plant assemblages have been found in the Ezcurra Inlet Group (Arctowski Cove and Point Thomas formations) in Ezcurra Inlet, in the Mount Wawel Formation at Wawel and in the Lions Cove Formation in King George Bay (Mozer 2012(Mozer , 2013. The K−Ar ages of volcanic intercalations in these preglacial successions fall in the range between 47-40 Ma (Lutetian and early Bartonian), which confirm an Middle Eocene age of the fossil flora.…”

“…Our new geochronology data indi− cate that this flora is of Eocene age, and similar to Eocene floras described from other parts of KGI, e.g. from the Ezcurra Inlet Group in Ezcurra Inlet, the Point Hennequin Group at Wawel in Admiralty Bay, and the Lions Cove Formation in King George Bay (Mozer 2012(Mozer , 2013.…”