--> Abstract: Restoration of Circum-Arctic Upper Jurassic Source Rock Paleolatitude Based from Crude Oil Geochemistry, by Kenneth E. Peters, L. Scott Ramos, John E. Zumberge, Zenon C. Valin, and Christopher R. Scotese; #90078 (2008)

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Restoration of Circum-Arctic Upper Jurassic Source Rock Paleolatitude Based from Crude Oil Geochemistry

Kenneth E. Peters1, L. Scott Ramos2, John E. Zumberge3, Zenon C. Valin1, and Christopher R. Scotese4
1U.S. Geological Survey, Menlo Park, CA
2Infometrix, Inc., Bothell, WA
3GeoMark Research, Ltd., Houston, TX
4U. Texas at Arlington, Arlington, TX

A three-step procedure was used to create tectonic-geochemical paleolatitude (TGP) models that predict source rock paleolatitude from the geochemical composition and location of crude oil. (1) Biomarker and carbon isotope ratios were measured for 496 oil samples inferred to originate from Upper Jurassic source rock in West Siberia, the North Sea, and Labrador. A chemometric decision tree classifies the samples into seven families and infers lithology, organic matter, and depositional environment for each organofacies. (2) The present-day location of each sample was restored to source rock paleolatitude during Late Jurassic time (~150 Ma) using published plate tectonic reconstructions. (3) Partial least squares regression was used to build TGP models that relate tectonic and geochemical paleolatitude, where the latter is based on 19 source-related biomarker and isotope ratios. Models were calibrated using a random selection of 70% of the samples in each family, where the remaining 30% were for validation. Positive relationships exist between tectonic and geochemical paleolatitude for each family. Standard error of prediction for geochemical paleolatitude is 0.9-2.6o of tectonic paleolatitude, which translates to relative standard error of prediction of 1.5-4.8%. Results suggest that source rock paleolatitude affects oil composition due to: (1) isotope fractionation during photosynthetic fixation of carbon, and (2) Late Jurassic species diversity at different latitudes. This approach offers the potential to improve understanding of source rock settings, paleoclimate, and oil distributions and can be used to study other oil families of different ages. The same biomarker and isotope ratios used to determine geochemical paleolatitude indicate depositional conditions, including aridity, water salinity, oxicity, mineralogy, marine versus terrigenous organic matter, and age.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas