ABSTRACT

The Norphlet Formation in southwestern Alabama has become a primary target for oil and gas exploration. Isopachous data show that Norphlet deposition was affected by a subsiding Mississippi Interior Salt Basin, early movement of the Louann salt, and stable Appalachian ridges and paleohighs, such as the Conecuh Ridge and the Wiggins Arch. The formation is over one thousand feet thick in parts of Washington, Clarke, Baldwin, and Mobile counties. The Norphlet thins or is absent over the stable Wiggins Arch.

The Norphlet consists of an upper well sorted sandstone underlain by a red bed sequence. These sediments grade updip into a conglomerate. The Denkman consists of clean, fine grained, well sorted sandstone, including a lower cross-stratified unit and an upper massive unit. The red bed sequence is mostly sandstone with shale, shaley sandstone, and a siltstone at the base. These shales, seen in Escambia and Choctaw counties, were probably deposited as distal portions of alluvial fans. Wadi gravels were deposited adjacent to the Appalachian highlands and grade downdip into the red bed sequence. Both of these units were deposited by sediment-choked braided streams and were subjected to reworking and deflation producing the Denkman Member. The Denkman consists of eolian sands, reworked at the top by the Smackover transgression into a massive sand up to 70 feet thick. Thin massive and horizontally laminated units in the cross-stratified sand indicate that narrow interdunes separated the broad, dune sands of the Norphlet. A generalized sequence of diagenetic events affecting porosity may be compaction, quartz overgrowth and carbonate cementation, and possible selective dissolution of cements followed by deep cementation by illite.