Admiralty Bay, which is the largest embayment on King George Island (South Shetland Islands, West Antarctica) has been geologically mapped by the present author between 1977 and 1979. The following rock-complexes have been distinguished: 1) evoic stratiform complex of andesitic and rhyolitic lavas and sediments (Martel Inlet Group and Cardozo Cove Group: probably Upper Jurassic); 2) Andean intrusions represented by gabbroic and dioritic dykes with associated pyrite-mineralization (Wegger Peak Group: approximately Cretaceous-Tertiery boundary); 3) Tertiary stratiform complex of basaltic and andesitic lavas and interstratified sediments, altogether more than 2700 m thick (King Island Supergroup: probably Eocene — Middle Miocene); 4) late Tertiary intrusive complex of basaltic and andesitic dykes and plugs (Admiralty Bay Group: probably boundary of Miocene and Pliocene); 5) late Tertiary effusives: olivine basalts, andesites etc., and sediments, about 600 m thick (Kraków Icefield Supergroup: Pliocene and ?earfy Pleistocene), with well preserved traces of two subsequent glaciations; 6) Quaternary intrusions (Cape Syrezol Group), Pleistocene) and effusives (Penguin Island Group: Holocene), mainly olivine basalts, related to opening of the Bransfield rift. An outline of structural history of King George Island is also presented.
The area of NW Wedel Jarlsberg Land south of Bellsund (Spitsbergen), between Dunderbukta in the west and the Berzeliustinden mountain group in the east, consists of five fault-bounded blocks: (1) the Renardbreen Block (Middle–Late Proterozoic basement rocks), (2) the Chamberlindalen Block (Late Proterozoic basement rocks), (3) the Martinfjella Block (Late Proterozoic through Early Ordovician basement rocks), (4) the Berzeliustinden Block (Late Proterozoic and Early Ordovician basement rocks covered by Late Palaeozoic–Tertiary platform deposits), (5) the Reinodden Block (Late Palaeozoic and Mesozoic rocks). The paper presents an outline of lithostratigraphy (Middle/Upper Proterozoic–Lower Ordovician: Hecla Hoek Succession) and architecture of the Caledonian basement in which several thrust-sheets and thrust-folds have been recognized. It also discusses some aspects of Tertiary overthrusting, faulting and rotation with affected the basement rocks and remodelled its Caledonian architecture.
There are two important unconformities in the Calypsostranda Group (late Palaeogene) at Bellsund, Spitsbergen. The first one is the basal angular unconformity of the Skilvika Formation against folded and planated Proterozoic metasediments: the author provides evidence for its primary sedimentary character. The second one is an intraformational erosional disconformity/discontinuity expressed by rapid replacement of coal-bearing terrestrial strata (Skilvika Formation) by shallow-marine strata (Renarddodden Formation).
Shallow−marine deposits of the Krabbedalen Formation (Kap Dalton Group) from Kap Brewster, central East Greenland, yielded rich dinoflagellate cyst and pollen− −spore assemblages. Previously, this formation yielded also rich mollusc and foraminifer age−diagnostic assemblages. A Lower Oligocene age of the Krabbedalen Formation seems to be supported by the dinoflagellate cyst assemblage analysis, while the pollen−spore as− semblages point to a wider stratigraphic age range within Oligocene–Middle Miocene.
Thin coal seams found in the Lions Cove Formation, Polonia Glacier Group (Middle Eocene, upper part) at King George Bay, King George Island (South Shetland Islands, West Antarctica), represent lustrous (vitrine) brown-coal metaphase. The coal from the lower seam represents carbonized wood, probably angiosperm, that from the upper ones originated due to accumulation of branches or larger wood fragments and leaf remains. These coals are slightly older than metaxylite brown coal previously described from Admiralty Bay on King George Island, and dated at Eocene-Oligocene boundary. Both coal occurrences are evidences for a warm climate which prevailed in the Antarctic Peninsula sector during the Arctowski Interglacial (ca 50—32 Ma).
Anthracite coal matter fills irregular voids in dolostones of the Upper Proterozoic Höferpynten Formation in the Hornsund area, south Spitsbergen. The coals are of organic origin, as indicated by a variety of coal-petrographic studies, and by association with algal structures. They probably derived from bitumina accumulated in voids of dolostone at an early diagenelic stage. The degree of coalification (graphitization) is high but diversified, suggesting several coalification stages, probably related t o successive metamorphic events. The oldest changes may correspond to initial stage of t h e greenschist-amphibolite phase of regional metamorphism, with temperatures of over 500°C and pressure of over 20,000 MPa . Multiphase graphite crystallites which occur in t h e coal are mainly fibrous. There are also crystallites which precipitated from gaseous phase, and pyrolitic graphite; they may have originated due to action of mesothermal solutions which had produced ore-bearing veins.
Nine samples of basic (dolerite, gabbro) intrusions collected at Bellsund, South Spitsbergen, have been K−Ar dated. Three dates, between 87.8 and 102.9 Ma, obtained from dolerite sills which intrude Carboniferous and Permian deposits in Van Keulenfjorden point to a Cretaceous age of intrusive activity (Diabasodden Suite). The K−Ar dates obtained from dolerite and gabbro which intrude Upper Proterozoic metasedimentary terrane of Chamber− lindalen form two groups: the dates between 97.1 and 178.6 Ma point to a Mesozoic age of the intrusions (Diabasodden Suite); the dates from a tectonized gabbroid (280.9–402.0 Ma) might point to a Late Palaeozoic age of the intrusion. No K−Ar dates which would indicate a Proterozoic age of the basic intrusions were obtained
The lithospheric transect South Shetland Islands (SSI) — Antarctic Peninsula (AP) includes: the Shetland Trench (subductional) and the adjacent portion of the SE Pacific oceanic crust; the South Shetland Microplate (younger magmatic arc superimposed on continental crust); the Bransfield Rift and Platform (younger back-arc basin); the Trinity Horst (older magmatic arc superimposed on continental crust); the Gustav Rift (Late Cenozoic) and James Ross Platform (older back-arc basin). Deep seismic sounding allowed to trace the Moho discontinuity at about 30 km under South Shetlands and at 38—42 km in the northern part of Antarctic Peninsula (Trinity Horst), under typical continental crust. Modified crust was recognized under Bransfield Strait. Geological interpretation based on deep seismic refraction and multichannel reflection soundings, and surface geological data, is presented.
One of the most significant global climatic events in the Cenozoic was the transition from greenhouse to icehouse conditions in Antarctica. Tectonic evolution of the region and gradual cooling at the end of Eocene led to the first appearance of ice sheets at the Eocene/Oligocene boundary (ca. 34 Ma). Here we report geological record of mountain glaciers that preceded major ice sheet formation in Antarctica. A terrestrial, valley-type tillite up to 65 metres thick was revealed between two basaltic lava sequences in the Eocene– Oligocene Point Thomas Formation at Hervé Cove – Breccia Crag in Admiralty Bay, King George Island, South Shetland Islands. K-Ar dating of the lavas suggests the age of the glaciation at 45–41 Ma (Middle Eocene). It is the oldest Cenozoic record of alpine glaciers in West Antarctica, providing insight into the onset of glaciation of the Antarctic Peninsula and South Shetland Islands.