The History of Glacial Retreat in a Temperate Paraglacial Turbid Outwash Fjord: Simpson Bay, Prince William Sound, Alaska

J. C. Noll and T. M. Dellapenna
Texas A&M University at Galveston

Seismic profiles and sediment cores have been used to investigate at the distribution of sedimentary strata and to develop a chronology of glacial retreat in a small turbid outwash fjord, Simpson Bay, Alaska. An approximately 2800 year record of punctuated changes in strata is evidence of changing modes of sedimentation as the system evolved from a glaciated basin to a non-glaciated fjord. Within stratal units, reflectors are found indicative of short term changes in sediment distribution. In Simpson Bay, immediately above a basal surface of glacial diamicton is a unit of thick high amplitude reflectors with transparent and chaotic units as well as truncated reflectors indicative of proglacial debris flows. This unit marks the beginning of glacial retreat in Simpson Bay about 2800 years before present. Sedimentation rates during this stage were rapid due to large input of sediment from the glacier. The next unit is composed of homogenous, ponded sediment indicating that glaciers were grounded in the drainage basin where coarse grain material was entrained in rivers, flood plains, and fjord head deltas. A unit of fine scale low amplitude reflectors is at the top of the sequence records neoglacial climate changes that affect sediment discharge and has captured approximately the last 1100 years of sediment accumulation. In general calculated dates correlate well with global events, but the presence of additional layers points to the effectiveness of fjords at preserving fine scale sedimentary records and the importance of small local scale shifts in basin evolution.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas