Tertiary Stratigraphy and Petroleum Potential of Cold Bay-False Pass Area, Alaska Peninsula: GEOLOGIC NOTES

Recent mapping clarifies the age, distribution, and environments of deposition of Tertiary sedimentary rocks along the outer part of the Alaska Peninsula and on Unimak Island. Marine and leaf-fossil assemblages indicate that the Belkofski Formation is of Oligocene age, and comprises interfingering marine and nonmarine volcaniclastic rocks. The Bear Lake Formation of Miocene age is not present in the Cold Bay area as previously mapped; and in a previously unmapped area, the Tachilni Formation of late Miocene and early Pliocene age extends from Cold Bay to False Pass. Pre-Tertiary rocks do not crop out along the shoreline of Unimak Island. The petroleum potential of Tertiary and Mesozoic rocks in the Cold Bay area is minimized by sandstone with poor reservoir properties, absence of organic-rich source rocks, and weakly developed folds.