HR: 14:25h
AN: H53I-03 INVITED     [Abstracts]
TI: Sediment Yields Of Quaternary Advancing and Retreating Temperate Tidewater Glaciers with an Example of how these may Constrain Continental Landscape Evolution
AU: * Powell, R D
EM: ross@geol.niu.edu
AF: Department of Geology and Environmental Geosciences, Northern Illinois University, DeKalb, IL 60115 United States
AB: About 25 years ago a conceptual model was developed to describe key architectural elements of temperate fjord glacimarine systems. The model has been further positively tested on continental shelf successions. Data are presented here synthesizing sedimentation rates, sediment accumulation rates, and inferred sediment yields from these temperate glacimarine systems in southern and southeastern Alaska. The data show that: (i) sediment yields from these glaciers are similar whether they are advancing or retreating, and (ii) short-term yields from modern process studies are of similar magnitude to those estimated from slightly longer term yields over decades to centuries, and also to those of continental shelf packages over thousands of years, during both advance to and retreat from the LGM. When combined with a global database, these data show sediment yields of Quaternary glaciers are dependent on glacial regime and often independent of drainage basin size. Average erosion rates inferred from the sediment yields are ca. 1mm/a (temperate), 0.3 mm/a (polythermal), and 0.05mm/a (polar). These data are used with climate and glacial regime histories determined from geological cores and proxy records of global temperature trends based on Mg/Ca and terrestrial data for Antarctica to provide general estimates of landscape evolution of that continent. From glacial initiation through to late Eocene-early Oligocene, glaciers were temperate and often not extensive. Erosion rates may have been quite high locally to create topographic relief and local depocenters. Early to late Oligocene the ice sheet was often extensive, and temperate (or at least warm polythermal). This period was likely one of maximum erosion of large areas and high sediment yields. Relief generated earlier may not have increased, but erosion was possibly significant in enhancing uplift rates. Late Oligocene to mid Miocene probably saw smaller, colder (polythermal) glaciers for much of the time, leading to decreased erosion rates, but a significant increase in topographic relief. Local depocenters fed by valley or outlet glaciers may have had high sediment yields. Mid Miocene to today experienced increasing ice volumes, finally reaching maximum size again, but now were mainly cold (polar) regimes These conditions would have led to a gradual but ultimately significant decrease in sediment yields. Initially, differential erosion may have enhanced relief, but as the ice sheet expanded, that would have decreased. Erosion rates were at their Cenozoic minimum and were least likely to enhance uplift.
DE: 0720 Glaciers
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 1815 Erosion
DE: 4558 Sediment transport (1862)
DE: 4863 Sedimentation (1861)
SC: Hydrology [H]
MN: Fall Meeting 2005