Applied Depositional Geosystems of the Coos Bay Basin, Oregon: Organic Geochemistry, Maturation, Paleoenvironmental Reconstruction and Biostratigraphy of the Coaledo Delta during the Middle Eocene Climatic Optimum (MECO)

Author

Allison K. Barbato, Louisiana State University and Agricultural and Mechanical CollegeFollow

Degree

Doctor of Philosophy (PhD)

Department

Geology

Document Type

Dissertation

Abstract

The Coos Bay Basin on the southwestern coast of Oregon is a forearc basin that contains exceptionally preserved Eocene to Miocene, tidal to wave-dominated, shallow deltaic to deep marine sediments of the Coaledo Delta. Coastal depositional environments are known to host source, reservoir, and seal rocks. Climate, topographic relief, and geographical position all play an important role in regional vegetation development and oceanic setting. This study assesses 84 outcrop and 12 core samples from Coos Bay for their organic geochemical characteristics and microfossil assemblage to provide source rock characterization information, organofacies descriptions, environmental reconstructions, and age control.

Results indicate the lower and upper Coaledo contain organic-rich coal seams and siltstone that are the most prospective gas-prone source rock units, with kerogen sources ranging from terrigenous to marine, and are dominated by the huminite maceral. Samples are generally immature, potentially suggesting gas migration from deeper sources, however palynomorph analyses of core samples exhibit maturation at depth. Variations within %R_o plots may preserve evidence corresponding to the evolution of the basin. This study highlights a hierarchical approach to filtering S2 data when determining T_max by evaluating S2 peak morphology using statistical descriptors in combination with an S2 > 0.15 mgHC/g rock. Roughly 80 pollen, 20 spores, 15 fungal spores, 40 dinoflagellate cysts, and 1 rare acritarch suggest a swampy, maritime subtropical forest, which transitions to a dense forest proximal to upland environments. Tide-dominated and wave-dominated periods in the Coaledo delta are marked by the transition of Polysphaeridium spp. to Glaphyrocysta exuberans. The abundance of tropical species, especially Bombacacidites spp., in the Upper Coaledo provides evidence for the Middle Eocene Climatic Optimum. Average global δ¹⁸O values exhibit notable correlations with shifts in Eocene vegetation in Oregon. Biostratigraphic insights based on FAD/LAD distributions, reveal critical turnovers in the Momipites species during the Eocene. For the first time, the rare marine acritarch, Tritonites spp., previously identified in Middle Eocene Australia and New Zealand stratigraphy, emerges as a uniquely high resolution biostratigraphic marker for the Middle Eocene within the Pacific Northwest. This study proposes a new species, Insulapollenites armentroutii sp. nov., as the Coaledo Delta biomarker.

Date

4-4-2024

Recommended Citation

Barbato, Allison K., "Applied Depositional Geosystems of the Coos Bay Basin, Oregon: Organic Geochemistry, Maturation, Paleoenvironmental Reconstruction and Biostratigraphy of the Coaledo Delta during the Middle Eocene Climatic Optimum (MECO)" (2024). LSU Doctoral Dissertations. 6427.
https://repository.lsu.edu/gradschool_dissertations/6427

Committee Chair

Sophie Warny