Sedimentologic Facies in Modern Glacial-Marine Environment: ABSTRACT

Studies of recent Antarctic glacial-marine sediments have enabled us to delineate facies associations that reflect the influence of fundamental glaciologic and glacio-isostatic processes on continental-margin deposition. Glacial-marine deposits can be broadly categorized as representing three sedimentary provinces. These are (1) the grounded shelf province--that portion of the continental shelf where sediments have been deposited by grounded ice at some time during glaciation; (2) the nongrounded shelf-upper-slope province; and (3) the middle to lower slope-rise province. Sediments in the grounded shelf province consist predominantly of orthotills deposited by grounded ice, related till-flow deposits, and paratills deposited from floating ice. Glacial erosion and deposition by subglacial streams are also important processes. Seaward of the maximum grounding line, on the nongrounded shelf and upper slope, deposition is primarily by floating ice. However, substantial sediment reworking occurs, forming coarse residual deposits and sediments enriched in fine-grained material. From a sedimentologic standpoint, distinction between the outer shelf and upper slope is problematic. The middle to lower slope and continental rise may be dissected by submarine canyons or may be nonchannelized. Gravity-flow deposits are commonplace. Laminated muds, perhaps deposited by contour currents, are also widespread. The boundary separating the two slope provinces is related to a zone of glacio-isostatically induced slumping where sediment gravity flows are generated, and perhaps to the shallowest depth at which contour currents occur. These facies associations are useful in characterizing older sequences; they have been used to interpret several ancient glacial-marine sequences. End_of_Article - Last_Page 483------------