Molecular and carbon isotopic analysis of specific biological markers: Evidence for distinguishing between marine and lacustrine depositional environments in sedimentary basins of Brazil
- Petrobras Research and Development Center, Rio de Janeiro (Brazil)
A suite of organic-rich, immature shales (TOC`s ranging between 0.7 to 28.4 %) from various basins throughout Brazil were selected for carbon isotopic ({delta}{sup 13}C) analysis of individual biological compounds in order to characterize marine and lacustrine depositional environments. Carbon isotopic compositions of pristane, phytane, n-heptadecane; 28, 30-bisnorhopane; 17{alpha}(H), 21{beta}(H)-hopane, and gammacerane, together with other commonly used biomarker parameters show variations that are related to sources of organic matter and to depositional processes in the paleoenvironment. Plots relating hopane/sterane ratios to the {delta}{sup 13}C compositions pristane, phytane, n-heptadecane; 28, 30-bisnorhopane, and 17{alpha}(H), 21{beta}(H)-hopane show that these compounds in lacustrine shales are consistently more depleted in {sup 13}C than in marine shales. For example, the {delta}{sup 13}C values of pristane and phytane in lacustrine shales vary from -28 to -32 %. and in marine shales from -22 to -24 {per_thousand}. The correlation between high abundance of hopanes relative to steranes with depleted {sup 13}C compositions in these compounds is supporting evidence for a more abundant input of methanogenic bacteria in these lacustrine shales.
- OSTI ID:
- 425589
- Report Number(s):
- CONF-960527--
- Country of Publication:
- United States
- Language:
- English
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