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Jaeger, J.M., 1998

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Bibliographic Reference

Jaeger, J.M., 1998, Modern sedimentary processes on a glacially impacted, mountainous coastline, south-central Alaska: Stony Brook, New York, State University of New York, Ph.D. dissertation, 296 p.

Abstract

Although continental margin sedimentary deposits represent the bulk of the sedimentary record, little research has been accomplished on tectonically active margins. The purpose of this dissertation was to investigate strata formation in the marine environment along the glaciated, mountainous (> 5,000 m elevation) coastline of south-central Alaska between the Alsek River and Prince William Sound. Sediment accumulation rates in the eastern half of the study area are highest (~10 mm/yr-1) at mid-shelf depths and near rivers draining the Bering Glacier (~20 mm/yr-1). On the Copper River Delta, rates are highest for the delta front (>20 mm/yr-1) decreasing westward. Total annual accumulation is 93-137 x 106 tons/yr-1 on the shelf. Similar spatial patterns in sediment accumulation between centennial and Holocene timescales reflect the dominance of the Copper River and Bering and Malaspina glaciers as sediment sources. Temporal variability in accumulation rates between centennial and Holocene timescales exists for portions of the study area near fjords and demonstrates the considerable changes that occur in sediment supply during glacial advances and retreats. The formation on lithofacies was investigated using short-lived tracers (234Th and chlorophyll-a) and x-radiography. Given the high rates of biologic mixing (101 cm2/yr) the extensive surface mixed layer (10-20 cm), and the sediment accumulation rates (10 cm/y), a thoroughly bioturbated lithofacies is predicted and observed. Five lithofacies can be identified for the study area: an inner shelf sand facies, a sandy mud facies, a bioturbated mud facies, a gravelly mud facies, and a tertiary bedrock facies. The bioturbated mud facies is dominant, representing more than 75 percent of the shelf area. During the months May-July 1995, deposition of sediment in a temperate glacial fjord, Icy Bay Alaska, varied from highly non-steady state at ice-proximal stations to steady-state at a mid-fjord station. Deposition rates exponentially decrease down fjord from 0.6-0.02 cm/d-1. Laminated muds were deposited at proximal stations during the period of observation. Diamicton beds, containing biogenic structures, were found near the seabed surface and were formed during the winter. To contrast point- and multiple-source depositional systems on the shelf, along-shelf trends in grain size, sediment accumulation rates, sedimentary structures, and Holocene stratal thickness were measured along a point-source coastline (Copper River Delta-CRD) and a multiple-source coastline (Bering-Malaspina shelf-BMS). The presence of both types of depositional systems was best demonstrated by trends in sediment accumulation rates and stratal geometries.

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