Geochemical record of fluid flow and dolomitization of carbonate platforms: Ascending freshwater–mesohaline mixing, Miocene of Spain
Zhaoqi Li, Robert H. Goldstein, Evan K. Franseen, 2015. "Geochemical record of fluid flow and dolomitization of carbonate platforms: Ascending freshwater–mesohaline mixing, Miocene of Spain", Fundamental Controls on Fluid Flow in Carbonates: Current Workflows to Emerging Technologies, S. M. Agar, S. Geiger
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This paper constrains fluid flow and chemistry in Miocene dolomites of Spain, where dolomitization has been ascribed to ascending freshwater–mesohaline mixing. End-Miocene dolomite formed as replacement and cement with the same widespread cathodoluminescence. Fluid inclusion final melting temperatures of ice (Tm ice: −0.2 to −2.3 °C) indicate mixing of freshwater and evaporated seawater. δ18O and δ13C data mostly show positive covariation, and only some have variable δ13C and invariant δ18O, arguing that mixing was more important than sulphate reduction. Data range from +0.9 to +6.0‰ for δ18O and from −4.5 to +3.0‰ for δ13C (VPDB (Vienna Pee Dee Belemnite)). Lower stratigraphic units are more depleted isotopically than upper units, suggesting upwards flow of freshwater. 87Sr/86Sr values (0.70866–0.70904) range from less than to greater than late Miocene seawater. δ18O, δ13C and Sr analyses show that freshwater interacted with basement, confirming injection of freshwater from below. Upwards flow of freshwater, driven by low density and hydraulic head, created fluid mixing and CO2 degassing. Comparison of La Molata dolomite to other dolomites of the western Mediterranean suggests that ascending freshwater–mesohaline mixing may be widespread, and that local composition of basement is not the primary driver of dolomitization. The model is broadly applicable to carbonates adjacent to highs, where freshwater discharged into slightly evaporated seawater.
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Fundamental Controls on Fluid Flow in Carbonates: Current Workflows to Emerging Technologies
This volume highlights key challenges for fluid-flow prediction in carbonate reservoirs, the approaches currently employed to address these challenges and developments in fundamental science and technology. The papers span methods and case studies that highlight workflows and emerging technologies in the fields of geology, geophysics, petrophysics, reservoir modelling and computer science. Topics include: detailed pore-scale studies that explore fundamental processes and applications of imaging and flow modelling at the pore scale; case studies of diagenetic processes with complementary perspectives from reactive transport modelling; novel methods for rock typing; petrophysical studies that investigate the impact of diagenesis and fault-rock properties on acoustic signatures; mechanical modelling and seismic imaging of faults in carbonate rocks; modelling geological influences on seismic anisotropy; novel approaches to geological modelling; methods to represent key geological details in reservoir simulations and advances in computer visualization, analytics and interactions for geoscience and engineering.