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Admiralty Bay, King George Island (Soth Shetland Islands, West Antarctica): A geological monograph

Birkenmajer K.

Studia Geologica Polonica

2003

Vol. 120

5-73

Admiralty Bay is the largest fjord system on King George Island, South Shetland Islands (West Antarctica). Exposures along its coasts, and on nunataks, give a good insight into geological history of the area, spanning more than 90 Ma, from Late Cretaceous to Recent. King George Island is located in the middle of the South Shetland Islands arc. To the north, it borders on the South Shetland subduction trench, part of Drake Passage, to the south - it is divided from crustal block of Antarctic Peninsula by a young rift and basin of Bransfield Strait. The island consists of four tectonic blocks/terranes bounded by longitudinal strike-slip faults of Tertiary age. Three of these blocks, the Barton Horst (axial), the Warszawa Block (southern, downthrown with respect to the Barton Horst), and the Kraków Block (southernmost, downthrown with respect to the Warszawa Block, bordering on Bransfield Rift) are present at Admiralty Bay. Geological successions of stratiform volcanic/sedimentary and intrusive (hypabyssal and plutonic) rocks markedly differ between these tectonic blocks/terranes, suggesting considerable horizontal displacements between them along longitudinal strike-slip faults. Geological age of stratiform and intrusive magmatic successions is there generally well established on radiometric dating. Terrestrial strata yielded numerous fossil plant assemblages of Late Cretaceous and Early Tertiary ages. In the Admiralty Bay area, there occur also the westernmost exposures of Oligocene marine/glaciomarine strata, whose principal outcrops are located further east. The paper is a monograph of the Admiralty Bay area, the geological map of which, 1:50,000 scale (Pl. I), and geological cross-sections (Pl. II), are attached under a separate jacket. The monograph gives an outline of geological research on King George Island since its beginnings in the 19th century, a concise description of the Upper Cretaceous through Lower Oligocene rock successions within each tectonic block/terrane, and of Quaternary strata, forms and events.