STRATIGRAPHIC CONTROLS ON DIAGENESIS AND RESERVOIR QUALITY IN THE LATE JURASSIC (OXFORDIAN) SMACKOVER FORMATION, SOUTHERN ARKANSAS, USA

The Upper Jurassic (Oxfordian) Smackover Formation of the U.S. Gulf Coast Region is a mature hydrocarbon play that, in recent decades, has become a target for producing bromine and lithium-rich brines. This study aims to establish the sequence stratigraphic framework to understand the spatiotemporal relationship between depositional and diagenetic processes and its impact on reservoir quality in the Smackover Formation. Based on log-correlations, we interpret the Smackover “B”/UJ III Sequence to consist of progradational sequences to have top-set beds with a dip of 0.25° along the inner ramp, foreset beds with a dip of 0.5° – 1.0° along the mid ramp, and bottomset beds with a dip of 0.25° along the outer ramp in this area. The Smackover “B” and overlying Buckner Formation are characterized by seven depositional facies, reflecting a profile from coastal interdune salinas or sabkhas to a shallow marine mid-outer ramp, with the Smackover “B” exhibiting a shallowing upward trend from peloidal wacke-to-packstone to ooid-oncoid grainstone, capped by silty dolomitic mudstone and shaley nodular anhydrite. The underlying Smackover “C”/UJ II Sequence consists predominantly of peloidal wacke-to-packstone. The Smackover “B” and “C” exhibit varying degrees of diagenesis, including cementation, dissolution, and dolomitization, resulting in the identification of sixteen diagenetic facies. Vertical patterns in cementation, dissolution, and micritization within the Smackover "B" reflect oscillations between meteoric vadose, meteoric phreatic, and marine phreatic zones driven by low-amplitude relative sea-level fluctuations during the UJ III sequence. The uppermost Smackover “C” exhibits a decreasing degree of dolomitization with depth, interpreted to have formed during the UJ III lowstand. Spatiotemporal variability in the degree and style of diagenesis in the Smackover Formation is interpreted to be driven by changes in relative sea level along a low-angle ramp depositional system. This study demonstrates how the interplay between relative sea level drives the evolution of diagenetic fluids, significantly impacting reservoir quality in the Smackover Formation “B” and “C” in southern Arkansas.