Nearshore Glacial-Marine Sedimentation; Preliminary Modeling Based on Pliocene-Pleistocene Deposits of Puget Lowlands: ABSTRACT

Abstract

Environmental interpretations based on combined sedimentologic and micropaleontologic analyses together with field relations have enabled preliminary modeling of processes of nearshore glacial-marine sedimentation in the Puget Sound region (Washington and British Columbia). Although these processes are active today in the Arctic and Antarctic, ice cover makes direct observations of them difficult. Therefore, uplifted Pliocene-Pleistocene deposits were examined, using various criteria for the recognition of similar deposits in the ancient record. Forty-six whole or partial sections from the Puget Lowlands have been measured, described, and sampled, and over 200 samples have been analyzed for foraminiferal content. These data, in conjunction with detailed textural (settling tube) analyses and available radiocarbon dates from the area, have enabled the delineation of sedimentary environments and their associated facies. Modeling is based on the interaction of such parameters as thermal regime of the ice sheet, eustatic sea-level fluctuations, circulation patterns as delineated by the microfaunas, and changes in bathymetry resulting from isostatic loading and rebound and from regional tectonics. Thermal regime of the ice appears to be the major controlling factor, determining both the kinds of sediments deposited and the extent to which marine processes are able to act on them. Microfaunas show strong evidence of the mixing of a restricted shallow-water ice-shelf fauna with mid-shelf and outer-shelf forms which must be explained by any subsequent models. Glaciotectonic structures appear to be an important consideration for interpreting these sequences and may possibly be used to explain some of the pr sent problems with regional stratigraphic correlations. End_of_Article - Last_Page 434------------