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Abstract: Controls on the Deposition of the Upper Jurassic Haynesville Formation, Clarke County, Southwestern Alabama

Rachel A. Eustice, Lynton S. Land

The Upper Jurassic Haynesville Formation in the Champion-Klepac l core, Clarke County, southwestern Alabama, is a cyclic, bedded halite deposit, which was deposited in three distinct depositional environments. In stratigraphic succession, these environments include (1) 38 m of stacked shallow water, chevron-dominated salt pan cycles, (2) two cumulate halite units, 44.5 m and 16 m thick, deposited in deeper coastal salinas, and (3) 134 m of intercalated evaporites and siliciclastics deposited in a series of muddy salt pans and siliciclastic sabkhas.

Within the basal 82.5 m of halite (chevron and cumulate facies), bromide concentrations rise systematically from 36 to 440 ppm, reflecting an increase in evaporative concentration and the incorporation of solutes from dense, preconcentrated brines into the brine pans. Sr isotope ratios through these two zones increase from the Sr isotope ratio of coeval seawater (0.7068) near the base of the salt to 0.7084 in the first cumulate zone. The radiogenic Sr isotope ratios cannot be explained unless a source of radiogenic Sr is involved other than the input of radiogenic meteoric water into the system. Above this zone, bromide concentrations fall from 359 to 53 ppm, and then stabilize at approximately 85 ppm, indicating increased recycling of solutes (dissolution of preexisting salts) and pr cipitation from less-evaporated brines. Sr isotope ratios of these deposits range from 0.7070 to 0.7074, consistent with the addition of radiogenic Sr from meteoric water and siliciclastics to evaporated Kimmeridgian seawater.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994