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Hartbauer, C.L., 2010

Provenance and diagenesis of the Miocene Bear Lake Formation, Bristol Bay basin, Alaska

Bibliographic Reference

Hartbauer, C.L., 2010, Provenance and diagenesis of the Miocene Bear Lake Formation, Bristol Bay basin, Alaska: University of Alaska Fairbanks, M.S. thesis, xiii, 213 p., illust., maps.


The Miocene Bear Lake Formation (BLF) is a prospective hydrocarbon reservoir exposed on the southwestern Alaska Peninsula, extending into the subsurface to the northwest (reaching 2,360 m maximum thickness). This study comprehensively characterizes composition of BLF sandstones, and develops important implications for varying reservoir quality. Unique integration of standard petrographic methods, electron microprobe analysis (EMPA), and 40Ar/39Ar dating of detrital hornblende strengthens interpretations by providing multiple lines of evidence and a more complete picture of composition, source units and terrane, and diagenetic history than possible with petrography alone. EMPA provides superior classification of volcanic rock fragments and identification of diagenetic minerals. Results indicate a pressure-controlled diagenetic system, and a provenance more complicated than recycling of older strata, as currently interpreted. Simultaneous derivation from the Meshik Volcanics and recycling of Tolstoi, Chignik, and Naknek formations suggests erosion of a structurally deformed source terrain (e.g., reverse-faulted anticlines). Abundance patterns of pore-filling zeolites, calcite, albite, and kaolinite likely represent variations in Pco2 caused by variations in burial depth. Optimal reservoir quality is likely present in the subsurface upper BLF along the northwestern coast (and deeper in the basin), where sandstone composition is presumably more quartz-rich, less volcaniclastic, and has experienced higher Pco2 fluid migration.

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