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Roof, S.R., 1995

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Bibliographic Reference

Roof, S.R., 1995, Sedimentology, stratigraphy, and paleoclimatic significance of middle Pleistocene marine, glaciomarine, and glacial deposits in the Kotzebue Sound region, northwestern Alaska: University of Massachusetts, Amherst, Ph.D. dissertation, 169 p., illust., maps.

Abstract

Coastal bluffs of Baldwin Peninsula, NW Alaska, provide excellent exposures of middle Pleistocene nonglacial marine sediment overlain by prodeltaic glaciomarine sediment, indicating that glaciers reached Kotzebue Sound while the shallow Beringian continental shelf was submerged. Because the thin valley glaciers could not have significantly depressed the crust, this glacial advance must have occurred during a global high sea level, most likely during marine oxygen isotope stages 11, 9, or 7. The glacier limit can be traced through the region based on contrasting surface morphology of drift-covered and driftless areas. Simple numerical modeling of valley glaciers in the Noatak and Kobuk river valleys suggests that glaciers flowed over easily deformable sediments, at least in the lower reaches of the valleys. The extent of epimerization of the amino acid isoleucine in fossil molluscs was used to estimate the age of the marine and glaciomarine sediments. The preferred molluscan genera were not abundant, but shells of the genus Astarte were. Laboratory pyrolysis experiments reveal that Astarte and Macoma epimerize at similar rates and both are faster than Mya. Epimerization measured in the free fraction of pyrolyzed shells is surprisingly low compared to fossil shells with similar extents of epimerization measured in the total hydrolysate. The pyrolyzed shells show evidence of lower rates of hydrolysis relative to epimerization compared to fossil shells, suggesting that the energy of activation for hydrolysis and epimerization may not be constant over the wide temperature range separating natural burial conditions and laboratory pyrolysis experiments. Overall, Astarte showed greater potential to lose amino acids by leaching, therefore this genus is less preferred for amino acid geochronology. The extent of glaciers in the Beringian Arctic appears to be controlled primarily by moisture availability. The strength of atmospheric circulation, and therefore moisture transport to high latitudes, is largely controlled by the difference in insolation between low and high latitudes. Periods with both high autumn latitudinal insolation gradients (the difference between 0 degrees and 60 degrees N Sept insolation) and decreasing summer insolation that occur during submergence of the Bering/Chukchi continental shelf appear most conducive to glacier growth in northwestern Alaska.

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