Late Quaternary glacial history of the Pennell Coast region, Antarctica, with implications for sea-level change and controls on ice sheet behavior; and, Late Quaternary statigraphic evolution of the west Louisiana continental shelf.

摘要

The Pennell Coast continental shelf is isolated from West Antarctic Ice Sheet drainage; for an ice sheet to ground in this region it must flow over the Transantarctic Mountains from East Antarctica. Features observed indicate that ice grounded on the Pennell shelf. Cores from the shelf sampled till, a pelletized unit, glacial-marine sediments, contourite deposits, and diatomaceous muds. The timing of ice sheet grounding is revealed by radiocarbon dates that indicate the ice sheet was grounded on the shelf during the Last Glacial Maximum and has a retreat history that differs from nearby drainage areas. Comparison to sea-level curves suggests that melting ice from the region contributed to the Holocene sea-level rise and that formation of that ice contributed to the fall in sea level immediately prior to the Last Glacial Maximum.; Comparison between the Pennell Coast and drainage outlets of the West Antarctic Ice Sheet allows examination of controls on ice sheet behavior. There is a consistent pattern of erosional features on the crystalline bedrock of the inner shelf, mega-scale glacial lineations on the sedimentary strata of the outer shelf, and drumlins between the two. The troughs in the areas of sedimentary substrate are interpreted to have been occupied by fast-flowing ice and those in the areas of crystalline substrate by slower-moving ice. The Pennell shelf differs in that it has both crystalline and sedimentary substrates but no drumlins or lineations. Possible reasons for this difference include the size of the drainage basin, the narrow continental shelf, and the high sand content of the tills.; Core and seismic data were used to conduct an analysis of the west Louisiana outer shelf depositional systems formed during the last glacial-eustatic cycle. Differences in deltaic deposition in the area illustrate the complex relationship between depositional patterns and sea-level change. Particularly salient is the difference between the two primary sequence boundaries. The oldest sequence boundary is a major erosional surface. The youngest sequence boundary is characterized by much smaller channels and is primarily an interfluve feature. The observed variations in each system can be used to refine sequence-stratigraphic models.