Mineralogy and geochemistry of. delta. sup 13 C-depleted carbonates in offshore Trinidad

Conference · Tue May 01 04:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6692477

Falls, W F; Williams, D F ^[1]

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1. Univ. of South Carolina, Columbia (USA)

{delta}{sup 13}C records from the fine fraction (< 63 {mu}m) of well cuttings provide an important tool for detecting stratigraphic intervals that derive a stable isotopic signal from authigenic carbonates. The purpose of this study is to evaluate the mineralogy and geochemistry of the authigenic carbonates responsible for a significantly depleted interval in a {delta}{sup 13}C fine-fraction record for the Pliocene-Pleistocene deposits of offshore Trinidad. To achieve this goal, the coarse fraction (> 63 {mu}m) of the well cuttings are examined and analyzed. The {delta}{sup 13}C-depletion event in the fine-fraction record corresponds to a carbonate-cemented sand with extremely depleted {delta}{sup 13}C values of {minus}25 to {minus}58 {per thousand} (PDB). Calcite with 11 to 14 mole % MgCO{sub 3} forms equant spherulitic crystals, which, when polished and viewed with reflected light, display several growth stages. Dolomite cement found in one sample does not have growth stages that are recognizable by similar means. Both types of cement have extremely depleted carbon isotope values and {delta}{sup 13}C values between 0.3 and 1.9 {per thousand} (PDB). The stable isotope data suggest that the Trinidad shelf during the Pliocene-Pleistocene was a site of carbonate cementation either at the sediment/water interface or under shallow burial where pore-water conditions were strongly influenced by the oxidation of methane.

• OSTI ID: 6692477
• Report Number(s): CONF-900605--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON 13
CARBON COMPOUNDS
CARBON ISOTOPES
CARBONATE MINERALS
CARBONATE ROCKS
CARBONATES
CENOZOIC ERA
CHEMISTRY
DOLOMITE
EVEN-ODD NUCLEI
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGY
ISLANDS
ISOTOPE RATIO
ISOTOPES
LESSER ANTILLES
LIGHT NUCLEI
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERALOGY
MINERALS
NUCLEI
OXYGEN COMPOUNDS
QUATERNARY PERIOD
ROCKS
SEDIMENTARY ROCKS
STABLE ISOTOPES
STRATIGRAPHY
TRINIDAD AND TOBAGO
WEST INDIES