Quantitative modeling of water-rock interactions in meteoric diagenetic systems
- Univ. of Michigan, Ann Arbor (USA)
A quantitative model has been developed that monitors the {delta}{sup 18}O, {delta}{sup 13}C, and {sup 87}Sr/{sup 86}Sr and (Sr) of a meteoric fluid as it interacts with surrounding carbonate rocks. The model first establishes the initial chemical signatures of the meteoric water through equilibration with soil-gas CO{sub 2} and concomitant dissolution of carbonate. After the fluid reaches calcite saturation, a small volume of metastable carbonate is dissolved into the fluid and an equal volume of calcite is precipitated. This latter process is repeated, simulating increased dissolution and reprecipitation, and, consequently, lower water/rock ratios. Each system evolves toward closure, i.e., the value in the precipitated calcite equals that in the dissolving rock. This coupling among {delta}{sup 13}C, {sup 87}Sr/{sup 86}Sr, and (Sr), and the decoupling of {delta}{sup 18}O is an inescapable conclusion of their modeling efforts. Covariant trends among {delta}{sup 13}C, {sup 87}Sr/{sup 86}Sr, and (Sr) exhibited by sparry calcite cements and the adjacent matrix within Pliocene limestones of Enewetak Atoll are predicted by their model. Bimodal open-system {sup 87}Sr/{sup 86}Sr data integrated with modeling reveal two discrete episodes of meteoric diagenesis. The first episode represents subaerial exposure shortly after deposition and resulted in calcite with Pliocene {sup 87}Sr/{sup 86}Sr values. The second episode of meteoric diagenesis occurred during the Pleistocene and resulted in precipitation of calcite with Pleistocene {sup 87}Sr/{sup 86}Sr values within Pliocene rocks. As the model requires, both calcites have similar {delta}{sup 13}C and (Sr), indicating that this diagenetic transfer of younger {sup 87}Sr/{sup 86}Sr can occur without a recognizable impact on other geochemical tracers.
- OSTI ID:
- 6691884
- Report Number(s):
- CONF-900605--
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (USA), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Vol. 74:5; ISSN AABUD; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
BETA DECAY RADIOISOTOPES
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON 13
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON ISOTOPES
CARBON OXIDES
CARBONATE MINERALS
CARBONATES
CHALCOGENIDES
DIAGENESIS
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HOURS LIVING RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
MATHEMATICAL MODELS
MINERALS
NUCLEI
OXIDES
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
RADIOISOTOPES
ROCKS
SEDIMENTARY ROCKS
STABLE ISOTOPES
STRONTIUM 86
STRONTIUM 87
STRONTIUM ISOTOPES