Cretaceous shales from the western interior of North America: sulfur/carbon ratios and sulfur-isotope composition

Journal Article · Sat Mar 01 04:00:00 EST 1986 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1986)14<225:CSFTWI>2.0.CO;2· OSTI ID:5549310

Gautier, D L

Carbon and sulfur abundance and ..delta../sup 34/S of pyrite sulfur were studied in cores of selected Cretaceous marine shales from the western interior of North America. Carbon ratios average 0.67, a value greater than that observed in recent marine sediments and much higher than global values calculated for the Cretaceous. Increased S/C ratios probably result from generally low levels of bioturbation and enhanced efficiency of sulfate reduction due to low oxygen levels in the Cretaceous seaway. Isotopic compositions of pyrite sulfur vary systematically with the level of oxygenation of the depositional environment and therefore with organic carbon abundance and type of organic matter. Samples with organic carbon in excess of 4 wt% contain disseminated pyrite that is extremely depleted in /sup 34/S; these samples are laminated clay shales that contain hydrogen-rich (type II) organic matter. Samples containing less than 1.5% organic carbon display relatively heavy but wide ranging ..delta../sup 34/S values; these samples are highly bioturbated and contain only type III, hydrogen-poor organic matter. Samples containing intermediate amounts of organic carbon contain pyrite with ..delta../sup 34/S values averaging -25.9% and contain mixed type II and type III organic matter. The higher organic carbon content and the preservation of hydrogen-rich organic matter generally correlate with slow sedimentation. Sulfur-isotope data are apparently a sensitive indicator of diagenetic or depositional facies of fine-grained Cretaceous rocks in the western interior. 27 references, 2 figures, 1 table.

• Research Organization: Geological Survey, Denver, CO
• OSTI ID: 5549310
• Journal Information: Geology; (United States), Journal Name: Geology; (United States) Vol. 14:3; ISSN GLGYB
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580300* -- Mineralogy
Petrology
&amp; Rock Mechanics-- (-1989)
ABUNDANCE
CARBON
CHALCOGENIDES
CORRELATIONS
CRETACEOUS PERIOD
DEPOSITION
DIAGENESIS
ELEMENTS
GEOLOGIC AGES
GEOLOGIC HISTORY
GEOLOGY
IRON COMPOUNDS
IRON SULFIDES
ISOTOPE RATIO
ISOTOPES
MESOZOIC ERA
MINERALS
NONMETALS
NORTH AMERICA
ORGANIC MATTER
PETROLOGY
PYRITE
ROCKS
SEDIMENTARY ROCKS
SEDIMENTS
SHALES
SULFIDE MINERALS
SULFIDES
SULFUR
SULFUR COMPOUNDS
SULFUR ISOTOPES
TIME DEPENDENCE
TRANSITION ELEMENT COMPOUNDS