Offshore Evidence of Glaciations in Lower Cook Inlet, Alaska: ABSTRACT

Abstract

The Lower Cook Inlet is a northeast-trending tidal embayment of the North Pacific Ocean located in south-central Alaska between the Alaska-Aleutian Ranges on the west and the Chugach and Kenai Mountains on the east. Five major Pleistocene glaciations have been documented for the region. The first three glaciations completely filled the Cook Inlet trough, truncating Tertiary strata and creating an inlet-wide angular unconformity. In the last two glaciations, ice coalesced across the southern part of the inlet only, impounding fresh water from the north in a large proglacial lake. High-resolution seismic-reflection records reveal many glacial and related features on the sea bottom and buried beneath Holocene marine sediments. Sea bottom features identified include sand waves, megaripples, sand ribbons, lag gravels, and ice-rafted boulders with associated comet marks. Subbottom features include terminal, lateral, and ground moraines; glacio-fluvial, glacio-marine, and lacustrine deposits; drainage channels and tunnel valleys; and eskers, outwash fans, and sand waves. The sea floor may be divided into four morphological provinces separated by the 60-, 120-, and 190-m isobaths. The two deeper provinces are expressions of ice-erosional morphology, whereas the shallower provinces are dominantly expressions of ice-depositional morphology. These buried features and the present sea-floor configuration reflect deposition and erosion during the last two glaciations and subsequent modification by tidal currents and marine deposition. End_of_Article - Last_Page 681------------