Alaskan Peninsula Cenozoic Stratigraphy: Stratigraphic Sequences and Current Research: ABSTRACT

Abstract

Geology of the Alaska Peninsula-Island Arc and Continental Margin, by C. A. Burk, is the principal reference for stratigraphic studies on the Alaska Peninsula. Burk mapped the Phanerozoic stratigraphy and provided a geologic history and structural interpretation of the area between Wide Bay and Unimak Island. Cenozoic rocks were mapped as three unconformity-bounded sequences. Recognition of specific formations was difficult due to similarity of lithofacies, isolated outcrops, rapid facies changes, and alteration and burial by young volcanics. Consequently, megafossil assemblages were relied upon to facilitate correlations between study areas. The three unconformity-bounded Cenozoic sequences are: 1. The Paleogene Beaver Bay Group consisting of three formations: the dominantly nonmarine Tolstoi Formation, the dominantly marine Stepovak Formation, and the volcanic Meshik Formation. Current work suggests these units are at least in part coeval facies of late Paleocene through Oligocene age. 2. The Neogene Bear Lake Formation consisting of the lower Unga Conglomerate Member and an unnamed upper member. Rapid facies changes and incorrect reports of fossil occurrence have resulted in confusion of stratigraphic relationships within this sequence of middle to late Miocene age. 3. A late Neogene informally defined upper sequence consisting of interbedded marginal marine, coastal-plain, and volcanic facies. Current work suggests this sequence is Pliocene through Pleistocene in age. The ongoing research presented in this symposium focuses on the refinement of Burk's work using an interdisciplinary approach involving revised biostratigraphic frameworks, sedimentologic models, radiometric dating, and paleomagnetic studies. While much progress has been made, many problems remain unresolved. End_of_Article - Last_Page 655------------