KRZYSZTOF BIRKENMAJER OLIGOCENE-MIOCENE GLACIO-MARINE SEQUENCES OF KING

• Main Author: George Islano (south Shetland Islands
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Antarctic; Antarctic Peninsula; Birkenmajer; Cape Melville; Chopin Ridge; Cockburn; Cockburn Island; Destruction Bay; Hennequin; King George Island; Legru Bay; Polonez Cove; West Antarctica; Antarc*; Antarctica; Ice Sheet; Iceberg*
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.470.9658; http://www.palaeontologia.pan.pl/Archive/1987-49_9-36_1-4.pdf

evidence for three Tertiary glaciations, post-dating Late Oligocene plant-bearing beds (po int Hennequin Group) intercalated in andesite lavas K-Ar-dated at about 24.5 Ma. The onset of continental glaciation (ice-sheet at sea level) in King George Island area was close to the Oligocene-Miocene boundary. There are two separate glacigenic successions, the Polonez Cove Formation (Chopin Ridge Group), and the Cape Melville Formation (Moby Dick Group) which contain material of Antarctic continent provenance, and a third one (Legru Bay Group) with locally derived tillites. The Polonez Cove Formation includes lodgement till at the base followed by glacio-marine strata with numerous iceberg-rafted debris, rich in invertebrate fauna of the Chlamys anderssoniassociation. By comparison with the "Pecten Conglomerate" of Cockburn Island, NE Antarctic Peninsula, this fauna has been attributed to the Pliocene. The glacial event, termed the Polonez Glaciation, is considered to be the largest Cenozoic glaciation in West Antarctica. K·Ar dating of acidic lavas overlying glacio-marine strata yielded dates of more than 22.4 Ma and more than 23.6 Ma. Thus the Polonez Glaciation and its deposits pre-date the Oligocene-Miocene boun-dary. The geological age of this glaciation which post-dates the youngest non-glacial climate plant-beds of late Oligocene age, 24.5 Ma, appears thus to be latest Oligo-cene. In the Moby Dick Group, shallow-marine deposits (Destruction Bay Formation) with pieces of carbonized wood (driftwood1), brachiopods of Early Miocene character, and recycled Cretaceous fossils, are followed by fossiliferous glacio-marine strata (Cape Melville Formation). These are crowded with ice-rafted debris, an evidence for the Melville Glaciation. A greater part of the fauna is Tertiary, there is moreover a considerable share of recycled Cretaceous fossils. Andesite dykes which cut through these strata yielded K-Ar ages of about 20 Ma. This, together with palaeontological dating of the underlying Destruct ion Bay Formation (Lower ...