Stable isotope (C, S, N) and molecular studies on the Precambrian Nonesuch Shale (Wisconsin-Michigan, U.S.A.); evidence for differential preservation rates, depositional environment and hydrothermal influence

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Authors:Imbus, Scott W.; Macko, Stephen A.; Elmore, R. Douglas; Engel, Michael H.
Author Affiliations:Primary:
Texaco E&P Technology Department, Houston, TX, United States
University of Oklahoma, United States
University of Virginia, United States
Volume Title:Isotope fractionations in organic matter; biosynthetic and diagenetic processes
Volume Authors:Macko, Stephen A., editor
Source:Chemical Geology, 101(3-4), p.255-281; Geological Society of America, annual meeting, symposium on Isotope fractionations in organic matter; biosynthetic and diagenetic processes, Dallas, TX, Nov. 1, 1990, edited by Stephen A. Macko and Michael H. Engel. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541
Publication Date:1992
Note:In English. 57 refs.; illus. incl. 5 tables, geol. sketch map
Summary:This organic-rich, middle Proterozoic formation is part of a thick volcaniclastic rift-fill sequence (Mid-Continent Rift system, N Wisconsin and Upper Peninsula Michigan) with a mild thermal history. Despite stratigraphic/sedimentological similarities between the east (Michigan) and west (Wisconsin) study areas, distinctions in organic petrological, elemental and stable isotopic parameters are noted. Geological arguments and predictable relationships among organic C content, bulk and molecular pyrolysate composition and petrological parameters are sufficient to invoke differential preservation of the same (or similar) primary producers as the principal cause of variability. Isotopic signals indicating precipitation of calcite via intense organic production (planktonic blooms) is evident among carbonate laminites. Incorporation or concentration of organic degradation by-products is evident, particularly in the W, from C and N stable isotope data. It is proposed that whereas preservation of organic productivity of a particular organism may be nearly complete in one organic facies in the E and W, organic remains in other intervals in the W were subject to extensive degradation and reconstitution to form protokerogens. Implications of the study include establishing parameters for recognising pre-Devonian lacustine vs marine euxinic system, clues to the complexity of middle Proterozoic aquatic systems and in recognizing the input of hydrothermal fluids to water bodies and early sediments. [Authors' abstract] [P.Br.]
Subjects:Anaerobic environment; C-13/C-12; Carbon; Chromatograms; Clastic rocks; Diagenesis; Experimental studies; Geochemistry; Hydrothermal conditions; Isotopes; Kerogen; Lacustrine environment; N-15/N-14; Nitrogen; Nonesuch Shale; O-18/O-16; Organic compounds; Oxygen; Precambrian; Proterozoic; Pyrolysis; S-34/S-32; Sedimentary rocks; Shale; Stable isotopes; Statistical analysis; Sulfur; Upper Precambrian; Ashland County Wisconsin; Bayfield County Wisconsin; Houghton County Michigan; Keweenawan Rift; Michigan; Michigan Upper Peninsula; North America; Ontonagon County Michigan; United States; Wisconsin; Northern Wisconsin; Organic materials
Abstract Numbers:93M/2046
Record ID:1992065641
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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