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Stable Hydrogen Isotopes of Isoprenoids and N-Alkanes as a Proxy for Estimating the Thermal History of Sediments Through Geological Time:

By
Ercin Maslen
Ercin Maslen
WA Organic and Isotope Geochemistry Centre, The Institute for Geoscience Research, Department of Applied Chemistry, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia e-mail:ercin.maslen@gmail.com
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Kliti Grice
Kliti Grice
WA Organic and Isotope Geochemistry Centre, The Institute for Geoscience Research, Department of Applied Chemistry, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia e-mail:ercin.maslen@gmail.com
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Daniel Dawson
Daniel Dawson
WA Organic and Isotope Geochemistry Centre, The Institute for Geoscience Research, Department of Applied Chemistry, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia e-mail:ercin.maslen@gmail.com
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Sue Wang
Sue Wang
WA Organic and Isotope Geochemistry Centre, The Institute for Geoscience Research, Department of Applied Chemistry, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia e-mail:ercin.maslen@gmail.com
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Brian Horsfield
Brian Horsfield
GeoForschungsZentrum Potsdam, Section 4.3, Telegrafenberg, B425, D-14473, Potsdam, Germany
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Published:
January 01, 2012

Abstract

The effect of thermal maturation on the δD values of individual petroleum hydrocarbons (n-alkanes and regular isoprenoids) from sedimentary organic matter over geological timescales has been explored in six different sedimentary sequences covering a wide range of maturities; i.e., 0.53%–1.6% vitrinite reflectance (Ro or equivalent; i.e., Re, Rc). These include new data and recently reported literature data on formations ranging in age from the Early Cretaceous to the Permian. The application of Deuterium/Hydrogen (D/H) of biomarkers as a maturity proxy for Devonian source rocks from the Western Canada Sedimentary Basin is also presented here, extending this application to much older sediments than previously studied. In each case, pristane and phytane are predominantly derived from the lipid side chain of chlorophyll a present in most photosynthetic organisms, with an additional (but minor) contribution to pristane from tocopherol of land plants in selected cases. The n-alkanes represent contributions of algae, bacteria, and in certain cases higher plants. In general, the n-alkanes, pristane, and phytane from relatively immature sediments have δD values that retain the isotopic signature of their natural product precursors; i.e., biosynthesized lipid components made up of acetyl and isoprene subunits, respectively. With increasing maturity, pristane and phytane become more enriched in deuterium (D), while the n-alkanes generally remain at a constant isotopic composition until an overmature level is reached, at which point there is a significant enrichment of D in n-alkanes. The enrichment of D in pristane and phytane with increasing maturity correlates strongly with changes in traditional maturity parameters, including vitrinite reflectance, Tmax, and molecular parameters, providing evidence that D enrichment is associated with thermal maturation.

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SEPM Special Publication

Analyzing the Thermal History of Sedimentary Basins: Methods and Case Studies

Nicholas B. Harris
Nicholas B. Harris
University of Alberta
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Kenneth E. Peters
Kenneth E. Peters
Schlumberger and Stanford University
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SEPM Society for Sedimentary Geology
Volume
103
ISBN electronic:
9781565763173
Publication date:
January 01, 2012

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