The Eocene Kreyenhagen Formation is a widespread siliceous, organic-rich mudstone of the San Joaquin Basin. In comparison to the highly studied siliceous Monterey Formation, studies of the Kreyenhagen are limited. This study completes a stratigraphic characterization of the Kreyenhagen at the Kettleman area with emphasis on chemostratigraphy to understand its compositional variability and depositional history.
The Kreyenhagen is subdivided into 8 zones (A–H) and correlated across 128 wells to define its stratigraphic framework in the Kettleman area. Cross-sections and isopach maps show an eastward thinning from 1,100 ft (335 m) to less than 600 ft (183 m), likely due erosion during a regression. Petrophysical estimates of TOC and clay volume are coupled with bulk and trace elemental geochemistry as proxies of detrital input, paleoproductivity, and benthic redox conditions. The lower Kreyenhagen (H–F) does not display significant enrichment in any major components. The middle Kreyenhagen (E–D) encompasses the zone of greatest TOC and enrichment in elemental proxies for anoxia and euxinia (D). The upper Kreyenhagen (C–A) contains the highest biogenic silica content and minimal redox proxy character. Regional gridding of log-derived compositional data reveals a trend of high TOC sub-parallel to the present-day basin axis and an eastward increase in clay volume. Lastly, there is an eastward increase in detritus proxy content and decrease in biogenic silica and redox sensitive trace elements.
These data reveal spatial and temporal changes in benthic environments within the northern San Joaquin Basin during the Eocene. The Kreyenhagen succession records at least one major transgressive-regressive cycle. The lower Kreyenhagen corresponds to a transgression and the initiation of suboxia. The middle interval likely represents the period of highest sea-level, indicated by high TOC and enrichment of trace elemental proxies for anoxia and euxinia. Deposition of the upper Kreyenhagen records a regression and organic matter preservation by burial from terrigenous clastics and biogenic silica. The vertical increase in paleoproductivity proxies may reflect an increase in coastal upwelling associated with known middle-late Eocene climatic cooling events. Lateral compositional trends indicate that 1) the majority of clastic sediment was delivered from the eastern Sierran Magmatic Arc, and 2) western areas were more distal and oxygen deficient environments. Organic matter preservation was modulated by spatial and temporal variations in relative sea level, oxygen demand, and water mass restriction associated with the uplifted Franciscan subduction complex.
|Advisor:||Behl, Richard J.|
|Commitee:||Kelty, Thomas, Larue, David|
|School:||California State University, Long Beach|
|School Location:||United States -- California|
|Source:||MAI 81/6(E), Masters Abstracts International|
|Subjects:||Sedimentary Geology, Geochemistry, Marine Geology|
|Keywords:||Chemostratigraphy, Eocene, Kreyenhagen Formation, Lithostratigraphy, Paleoceanography, San Joaquin Basin|
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