Initial concentration and diagenetic transformation of organic carbon and sulfur in black shales

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5878690

Pratt, L M ^[1]

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1. Indiana Univ., Bloomington, IN (United States). Dept. of Geological Sciences

Classification of kerogen types based on concentration of hydrogen and oxygen relative to concentration of carbon is widely used in studies of fossil fuels and mineralization. Such elemental ratios or indices incorporate information on biomass source (algal/bacterial versus terrestrial) and on biomass transformation during transportation and burial. Hydrogen-rich types of kerogen are relatively unusual in the rock record and are of particular interest as potential sources of petroleum and as potential sites of strong reducing power. Strata containing these reactive kerogens are typically associated with productive-lacustrine and upwelling-marine depositional systems. Anoxic conditions often occur near the sediment-water interface in these depositional systems, and high concentrations of organic sulfur compounds (OSC) can develop if sulfate-reducing bacteria are active and reduced forms of sulfur react with functional groups or carbon-carbon double bonds in the organic matter. Differences in composition of OSC between immature and more mature organic matter suggest that molecular changes continue during thermal maturation. High atomic ratios of Sorg/C in some black shales like the Miocene Monterey Formation indicate that organic matter can be both a reductant and a source of sulfur during mineralization. Recent studies of sulfur isotopic ratios in co-existing pyrite and OSC support the hypothesis that rates of sulfate reduction equaled or exceeded rates of sulfate transport into Monterey sediment, resulting in anomalously heavy sulfur isotopic compositions. Interpretation of isotopic data from mineralized black shales requires careful evaluation of all reduced sulfur species in the precursor sediment.

• OSTI ID: 5878690
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000* -- Geosciences
BITUMINOUS MATERIALS
BLACK SHALES
CARBONACEOUS MATERIALS
CHEMISTRY
CLASSIFICATION
DIAGENESIS
GEOCHEMISTRY
GEOLOGIC FORMATIONS
ISOTOPE RATIO
KEROGEN
MATERIALS
MATTER
MINERALIZATION
ORGANIC MATTER
ROCKS
SEDIMENTARY ROCKS
SHALES
SULFUR COMPOUNDS