Effects of sources and diagenesis on the isotopic and chemical composition of carbon and sulfur in cretaceous shales

Journal Article · Mon Oct 01 04:00:00 EDT 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90014-C· OSTI ID:6106370

Whittaker, S G; Kyser, T K ^[1]

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1. Univ. of Saskatchewan, Saskatoon (Canada)

The Cretaceous Lea Park Formation of south-central Saskatchewan contains organic matter from marine and terrestrial sources in proportions that vary as a result of deposition during the Campanian Claggett transgressive-regressive cycle in the Western Interior seaway of North America. The relative proportions of organic matter from these sources were determined using a terrestrial index (TI) that compares n-alkanes considered to be of terrestrial origin, n-C{sub 25} to n-C{sub 29}, to those considered to be of marine origin, n-C{sub 15} to n-C{sub 22}. The C isotopic composition of Cretaceous marine organic matter is found to be near {minus}32{per thousand} while terrestrial organic matter is near {minus}24{per thousand}. The lower {delta}{sup 13}C values of marine organic matter from the Lea Park Formation, as compared with those of Recent marine organic matter, are similar to the relation observed in other Cretaceous rocks; {delta}{sup 13}C values of terrestrial organic matter, however, are similar to those of the present. Pyrite formation in the Lea Park mudstones was limited by the availability of metabolizable organic matter, with the great amount of pyrite typically associated with organic matter having the lowest TI values. {delta}{sup 34}Spy values range nearly 30{per thousand} and vary directly with the composition of associated organic matter. Variations in the supply of metabolizable organic matter were more important than differences in sedimentation rate in producing the range of {delta}{sup 34}Spy values. {Delta}{sup 34}S values vary with the composition of organic matter and become larger when associated with more metabolizable organic matter.

• OSTI ID: 6106370
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:10; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CANADA
CARBON COMPOUNDS
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMISTRY
COMPARATIVE EVALUATIONS
CRETACEOUS PERIOD
DIAGENESIS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
IRON COMPOUNDS
IRON SULFIDES
ISOTOPE RATIO
MESOZOIC ERA
MINERALS
NORTH AMERICA
ORGANIC MATTER
PALEOCLIMATOLOGY
PALEONTOLOGY
PYRITE
ROCKS
SASKATCHEWAN
SEDIMENTARY ROCKS
SHALES
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS