--> Abstract: Stratigraphic Architecture of the Bear Lake Formation, Bristol Bay Basin, Alaska Peninsula, by Kenneth D. Ridgway, Rocky R. Reifenstuhl, and Emily S. Finzel; #90039 (2005)

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Stratigraphic Architecture of the Bear Lake Formation, Bristol Bay Basin, Alaska Peninsula

Kenneth D. Ridgway1, Rocky R. Reifenstuhl2, and Emily S. Finzel2
1 Purdue University, West Lafayette, IN
2 Alaska Division of Geological & Geophysical Surveys, Fairbanks, AK

The Miocene Bear Lake Formation (BLF) forms spectacular exposures along the coast and mountains of the central Alaska Peninsula. This formation is ~ 1000 m thick onshore and up to 2360 m thick in offshore boreholes. The BLF has produced oil shows in offshore exploration wells and is considered to be one of the primary potential reservoirs in this frontier basin. Ongoing stratigraphic analysis of the BLF indicates that it consists of three main facies associations. The lower part of the formation contains fine-grained sandstone within broad channels. Internal stratification in these channels mimics the channel geometry. Tabular conglomerate beds (~50 cm thick) containing disarticulated oyster fossils are interbedded with the sandstone. We interpret this facies association to have been deposited in subtidal and shelf environments of a sand-dominated estuarine system. The middle part of the formation is characterized by medium-grained sandstone with well developed lateral accretion surfaces. This facies forms large channel complexes with lengths of 100's of meters. Interbedded with the channel sandstone are flaser bedded sandstone and siltstone, and fossilized oyster banks. We interpret this facies association to represent intertidal and subtidal channel and tidal flat environments. The upper part of the section contains trough cross stratified sandstone and conglomerate. Ripple-laminated siltstone and coal are interbedded with the sandstone. We interpret this facies association to have been deposited in the fluvial-dominated part of the estuarine system. Ongoing palynological, porosity/permeability, and TOC analyses are being conducted to evaluate the reservoir potential of each of these facies associations.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005