SHELF, COASTAL AND SUBGLACIAL POLAR CARBONATES, EAST ANTARCTICA

Modem and Pleistocene polar carbonates occur in East Antarctica in she lf, coast, lakes and marginal to underneath glaciers, associated mainl y with glacigene muds, boulder tills and diamictites. Shelf carbonates (in Prydz Bay) are calcitic and unlithified, and consist mainly of sp onges, bryozoans, echinoderms, bivalves and diatoms. Coastal carbonate s (in the Vestfold Hills) are calcitic and contain faunal assemblages similar to those on the shelf, with calcareous algae, microbial mats, minor peloids and cements. Lake carbonates are aragonitic micrites and peloids. Carbonates close to glaciers (the Loken Moraines) are aragon itic and contain abundant ooids with intragranular fibrous cements. Su bglacial carbonates are aragonitic micrites and peloids. Carbonate min eralogy changes from mainly low-Mg calcite in marine shelf to aragonit e in brackish to freshwater dominated inland regions. Antarctic carbon ate delta(18)O values (4.5 to -47 parts per thousand PDB) vary markedl y due to frigid temperatures (0 to -2 degrees C) and salinity (0 to 35 parts per thousand) changes, as a result of meltwater dilution from a djacent glaciers. Their delta(13)C values (-9 to 8 parts per thousand PDB) also vary markedly due to exposure to atmospheric CO2, the circul ation of water masses and reaction of carbonate with CO2 trapped in gl acial ice. The regional distribution of carbonate sediments and their sedimentology, mineralogy, and delta(18)O and delta(13)C compositions indicate three types of glacial environments of formation. The first c orresponds to a glacial stage and the formation of subglacial and bank carbonates, when the Antarctic ice sheet expanded onto the inner shel ves. The second corresponds to interglacial stages and the formation o f ice-marginal carbonates, during the retreat of the ice sheet from th e inner shelf grounding line and accompanying the discharge of appreci able meltwater. The third corresponds to an interglacial oasis and the formation of coastal carbonates, proximal to distal lacustrine carbon ates, and distal subglacial carbonates.