187Re–187Os geochronology of Precambrian organic-rich sedimentary rocks
Published:January 01, 2009
Brian Kendall, Robert A. Creaser, David Selby, 2009. "187Re–187Os geochronology of Precambrian organic-rich sedimentary rocks", Global Neoproterozoic Petroleum Systems: The Emerging Potential in North Africa, J. Craig, J. Thurow, B. Thusu, A. Whitham, Y. Abutarruma
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Global correlations of Precambrian stratigraphic successions can be hampered by the coarse resolution of biostratigraphic and chemostratigraphic records, and by the scarcity of reliable U–Pb zircon age constraints. The development of the 187Re (rhenium)–187Os (osmium) radioisotope system as an accurate deposition-age geochronometer for organic-rich sedimentary rocks (e.g. black shales) holds great potential for an improved radiometric calibration of the Precambrian rock record. Here, we review Re–Os isotope data obtained for Precambrian black shales and revisit the discrepancy in Re–Os ages for the Neoproterozoic Aralka Formation (central Australia). In addition, we introduce new Re–Os isotope data for the Late Neoproterozoic Doushantuo Formation (South China) that highlights the necessity of a rigorous sampling protocol for depositional age determinations. Improvements in sampling and analytical methodologies have permitted the determination of precise ages (<1%, 2σ) from Late Neoproterozoic to Late Archaean shales. Whole-rock digestion using a CrVI–H2SO4 solution minimizes the release of detrital Re and Os from shale matrices, and selectively attacks organic matter that hosts hydrogenous Re and Os. The Re–Os system in organic-rich sedimentary rocks appears to be robust during hydrocarbon maturation and up to the onset of lowermost greenschist facies metamorphism, but post-depositional hydrothermal fluid flow can result in scattered Re–Os isotope data. The Re–Os black shale geochronometer should find utility for constraining the age of a diverse range of Precambrian geological phenomena. In addition, the initial 187Os/188Os composition determined from Re–Os isochron regressions serves as a tracer for the Os isotope composition of Precambrian sea water.
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Global Neoproterozoic Petroleum Systems: The Emerging Potential in North Africa
Neoproterozoic successions are major hydrocarbon producers around the world. In North Africa, large basins with significant surface outcrops and thick sedimentary fills are widespread. These basins are now emerging as potential sources of hydrocarbons and are attracting interest from geological researchers in academia and the oil and gas industry.
This volume focuses on recent developments in the understanding and correlation of North African basin fills and explores novel approaches to prospecting for source and reservoir rocks. The papers cover aspects of petroleum prospectivity and age-equivalent global petroleum systems, Neoproterozoic tectonics and palaeogeography, sequence stratigraphy, glacial events and global climatic models, faunal and floral evolution and the deposition of source rocks.
The broader aim of this volume is to compare major environmental change, the emergence of life, the global carbon cycle and the implications for hydrocarbon exploration of well-studied Neoproterozoic successions worldwide.