Clay Mineral Control of Organic Carbon Deposition in Marine Source Rocks

Kennedy, Martin J.¹, Arkadiusz Derkowski¹, Thomas Bristow¹ (1) University of California, Riverside, Riverside, CA

Previous work has shown a strong positive correlation between mineral surface area and adsorption of organic carbon in modern continental margin marine sediments. Our studies focus on the role this mechanism may play in the formation of organic rich black shales and petroleum source rocks. Our studies of the Miocene Monterey and Cretaceous Sharon Springs Formation (among others) show a strong positive correlation between mineral surface area and total organic carbon across a range values from 2-20%. This relation suggests that adsorption of dissolved carbon compounds or other mechanisms of preservation by clay mineral surfaces played a fundamental role in the burial and preservation of organic carbon. Our measurements of surface area focus on the interlayer space of 2:1 smectitic clays and inicate imply that both polar and non-polar organic compounds are capable of gaining entry to the interlayer sites, though several other possible physical relations may explain this relation. As the dominant source of detrital clays deposited in marine environments form in soil horizons, clay mineral associated organic enrichments, such as those in the Pierre Shale, result from depositional processes that concentrate clay minerals such as condensation or terrestrial climate patterns or volcanic provenances favorable to the production of 2:1 clay minerals. This suggests that organic carbon sequestration in at least some prominent petroleum source rocks may be more closely related to patterns of continental weathering and secular clay mineral trends than to the traditional models that consider ocean water chemistry or marine productivity.