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Upper Jurassic Smackover carbonate deposition in south Alabama was significantly influenced by a number of paleotopographic highs which divided the region into several subbasins or embayments. The Manila embayment in Monroe, Conecuh, and Clarke Counties was bounded to the south by the Conecuh ridge and the Wiggins arch and to the west by diapiric salt ridges. These paleotopographic highs protected the interior of the embayment from wave and current energy and significantly influenced Smackover deposition.
Initial carbonate deposition, represented by intertidal oncolitic and peloidal packstones and algally laminated mudstones, occurred in the deeper portions of the embayment, and was accompanied by the continuation of subaerial clastic deposition on the still-emergent highs. With sea level rise, these intertidal deposits graded upward into subtidal peloidal packstones containing sparse faunal assemblages indicative of the restricted circulation within the embayment. By middle Oxfordian time, sea level rise had inundated the paleohighs, eliminating restrictive conditions in the embayment. Deposition in the embayment is represented by peloidal, oolitic, and oncolitic packstones and grainstones containing open marine faunal assemblages, while the paleohighs became the site of oolitic shoal with local patch-reef development.
A decrease in the rate of sea level rise during late Oxfordian time allowed the carbonate deposits to build toward sea level. The oolitic shoal deposits on the paleohighs pass upward into evaporitic sabkha deposits, whereas the deposits of the embayment grade into oolitic shoal and intertidal flat deposits and finally into sabkha and evaporitic lagoon deposits.
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