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Stable Isotope Geochemistry of Carbonate Fracture Fills in the Monterey Formation, California
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1992
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EngineeringCrystallization TemperatureSedimentary GeologyMarine ChemistryEarth ScienceOrganic GeochemistryMonterey FormationStable Isotope GeochemistryGeological DataCarbonate Fracture FillsGeochronologyCrystallization TemperaturesMarine GeologyOrganic-rich Sedimentary RockGeologySedimentologyRock PropertiesIsotope GeochemistryEarly DiagenesisGeochemistryPetrology
ABSTRACT Carbonate minerals filling fractures in the Monterey Formation at four locations along the Santa Barbara Channel coast display a 18O(SMOW) range from 20.7 to 35.7 and 13C range from - 18.6 to + 16.6. Many fracture fills display a covariation of 18O and 13C, and successive generations of carbonate have lower 18O values. These isotope systematics can be interpr ted in terms of 18O values that were controlled by crystallization temperatures and the 18O of connate pore water, and 13C values that were controlled by depth-sequential organic matter degradation reactions. Each successive generation of carbonate precipitated at progressively higher burial temperatures from isotopically evolving connate pore water. These carbonate-filled fractures developed during burial and not during uplift. Using crystallization temperature estimates from fluid inclusion data, the change in 18O of conate pore water with increasing temperature in the burial environment is modeled. From this model, the fracture fill 18O values indicate precipitation over the following temperature intervals: 25-70°C (Carpinteria Beach), 7-15°C (Goleta Slough Beach), 45-100°C (Refugio Beach), and 53-103°C (Jalama Beach).