T125 New Voices in Geobiology (Posters)

Monday, 10 October 2022
2:00 PM - 6:00 PM
Exhibit Hall F

THE EFFECT OF WATER COLUMN REDOX STATE ON TOTAL ORGANIC CARBON AND HYDROGEN INDEX IN THE CRETACEOUS-DANIAN MORENO FORMATION, CALIFORNIA

Paper number: T125-13
Program: Technical Sessions
Time: 2:00 PM – 6:00 PM

Authors

Abstract

The Moreno Formation is an upper Maastrichtian to lower Danian unit deposited in the San Joaquin Basin of California. The lithostratigraphic succession indicates an upward shallowing of the basin, with sediment input coming from the Sierra Nevada magmatic arc to the east and the Franciscan Complex to the west. Seven drill cores from the Moreno Formation were sampled for elemental abundances and iron speciation analysis, with the goal of understanding how inorganic geochemical proxies correlate with organic geochemical parameters. Samples were analyzed using a Spectro XEPOS Benchtop XRF for trace metal abundances; for iron speciation, the samples were analyzed with sequential extractions and chromium reducible sulfur (CRS) to quantify the highly reactive iron pools in the samples. This inorganic geochemical data was compared to the programmed pyrolysis and Total Organic Carbon data produced by McGuire (1988) for the same samples. Preliminary trace metal data supports anoxic to suboxic bottom-water conditions occurring through the laminated intervals in the Moreno Formation. Additionally, an increase in primary production and a decrease in terrestrial input are also supported by proxy data in these intervals. Random forest regressions and partial dependence plots were generated, and it was determined that copper, zirconium, and uranium abundances best predict Hydrogen Index (HI) in the Moreno Formation. Using a workflow established in the thermally immature rocks of the Moreno Formation, it may be possible to reconstruct original HI and TOC in other, more thermally overmature rock units. This is critical for interpreting ancient primary productivity from rock units that have passed through the oil and gas window and no longer have their original TOC or HI values.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-383555

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