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Homogenization and final melting temperature data from primary and secondary two-phase fluid inclusions within carbonate and sulfate mineral phases reflect the physical re-equilibration of pre-burial calcites and the precipitation of late diagenetic mineral phases during the burial of the upper Smackover (Upper Jurassic, Oxfordian) lime-grainstones in southwestern Arkansas and northeastern Texas. Homogenization temperatures range from 83.0°C to 153.8°C (uncorrected for excess ambient formation pressures at time of trapping). Final melting points range from -33.4°C to -13.5°C.
Statistically distinct temperature populations reveal the re-equilibration of pre-burial bladed calcite cements and parallel the subsequent paragenesis during burial of nonfabric-selective dolomite, zoned equant mosaic calcite, anhydrite, celestite, unzoned poikilitic calcite cement, and baroque dolomite cement under conditions of increasing temperature and salinity.
Re-equilibration/precipitation began after a minimum depth of burial in the range of 0.95 to 1.75 km. Re-equilibration/precipitation resulted, in part, in response to the original connate meteoric to marine pore water system being mixed with, and subsequently replaced by, basinal brines that migrated into the upper Smackover grainstones from the Louann Salt.
Melting temperature data indicate that fluids trapped within the two-phase fluid inclusions are highly saline, varying from 17 to 27 wt. % NaCl. Melting temperature data also indicate that the fluids are CaCl2-rich brines with NaCl and probably MgCl2 and FeCl2 as additional chloride components.
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