TERRIGENOUS, BIOGENIC, AND VOLCANOCLASTIC SEDIMENTATION PATTERNS OF THE BRANSFIELD STRAIT AND BAYS OF THE NORTHERN ANTARCTIC PENINSULA: IMPLICATIONS FOR QUATERNARY GLACIAL HISTORY

Abstract

A marine sedimentologic investigation was conducted on the northern Antarctic Peninsula continental margin. The data base included piston cores, surficial sediments, and high resolution seismic reflection profiles. The objectives of this study were three-fold: examine sedimentation patterns in the Bransfield Basin, a high-latitude, actively spreading back-arc basin; relate sedimentation processes to lithofacies patterns in bays and fjords of the South Shetland Islands, Palmer Archipelago, and Danco Coast; and interpret the recent glacial-climatic history of this region. As a back-arc basin in a polar latitude, the Bransfield Basin represents a unique sedimentary environment. Fluvial discharge systems are lacking and the Bransfield Basin receives only minor amounts of continentally-derived sediment. The South Shetland arc is inactive, and the locus of recent volcanic activity is the axis of back-arc spreading. The sediments accumulating in the Bransfield Basin represent the input of terrigenous, biogenic, and volcaniclastic phases. Sediment distribution reflects the interplay of marine currents, primary production, and volcanic activity. At water depths $<$250 m, marine currents actively redistribute sediment, and residual deposits blanket the shelf between the northern tip of the Antarctic Peninsula and Tower Island. A transition from residual deposits to deposits with increased mud content west of Tower Island indicates a decrease in the intensity of marine currents as they flow east to west along the shelf. Lower energy conditions characterize the Bransfield Basin, permitting the suspension settling of fine terrigenous and biogenic phases. These predominantly fine-grained deposits record episodic pulses of increased volcaniclastic input. The normally graded volcanic ash layers represent both air fall deposits and sediment gravity flow deposits (turbidites). The distribution and composition of lithofacies recovered in bays and fjords appear to be regulated by the proximity to ice margins and to discharging meltwater systems. Where terrigenous sediment input is less pronounced, a biogenic lithofacies is present. Seismic records show that the thickness of the meltwater facies increases from south to north in the study area. It appears that initiation of meltwater production occurred relatively recently in bays of the Danco Coast. In contrast, sedimentation in bays of the Palmer Archipelago and South Shetland Islands is meltwater-dominated, and terrigenous sediments are rapidly accumulating. (Abstract shortened with permission of author.)