Sulfur isotopic analyses of disseminated pyrite in cretaceous black and green mudstones

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6649811

Bonnell, L M; Anderson, T F

Initial delta/sup 34/S measurements on disseminated pyrite from Cretaceous mudstones of DSDP Hole 386 (Bermuda Rise) range from -45 to -21 per thousand (CDT). Lower Cenomanian black mudstones have fractionations relative to coeval seawater sulfate (..delta../sup 34/S) of -58 to -60 per thousand, which appear typical for mid-Cretaceous organic carbon-rich rocks. Two explanations for the /sup 34/S enrichment are considered: (1) Pyrite formation continued after the sediment-pore water system was isolated from the influx of seawater sulfate. This is supported by the comparatively high pyritic sulfur contents and high degree of pyritization of total iron (DOP = 0.5 - 0.7) in these rocks. (2) The initial H/sub 2/S was either lost from the sediment prior to pyrite formation or reacted with organic matter. The delta/sup 34/S values of two green mudstones are about the same or more negative than those of immediately adjacent black mudstones. Previous studies have suggested that disseminated pyrite formation in organic carbon-poor green mudstones was the result of diffusion of H/sub 2/S from adjacent organic carbon-rich black mudstones. If this applied to Hole 386, then the isotopic results suggest that the iron in the green units was more easily pyritizable than the iron in the adjacent black units, and hence pyrite formation occurred earlier in the green mudstones. Relationships between DOP, pyritic sulfur content, and organic carbon content suggest that pyrite formation in these sediments was controlled by the availability of reactive iron more so than by the availability of metabolizable organic matter.

• Research Organization: Univ. of Illinois, Urbana (USA)
• OSTI ID: 6649811
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
BITUMINOUS MATERIALS
BLACK SHALES
CARBONACEOUS MATERIALS
CHALCOGENIDES
CHATTANOOGA FORMATION
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
CRETACEOUS PERIOD
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
IRON COMPOUNDS
IRON SULFIDES
ISOTOPE RATIO
ISOTOPES
MATERIALS
MESOZOIC ERA
MINERALS
OIL SHALES
ORGANIC MATTER
PYRITE
QUANTITATIVE CHEMICAL ANALYSIS
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
SULFUR ISOTOPES
TRANSITION ELEMENT COMPOUNDS