Converging Clastic Wedges in the Mississippian of Alabama

A Mississippian carbonate facies in north-central Alabama is bordered on the southwest and on the northeast by separate prograding clastic wedges. The southwestern clastic wedge comprises a major delta complex which prograded northeastward onto the carbonate shelf and associated barrier sediments. The clastic sequence grades upward from shale (Floyd) through sandstone and shale (Parkwood) to a quartz-pebble conglomerate and coal-bearing interval (Pottsville), and the Floyd-Parkwood grades laterally northeastward into the carbonate facies across a transition zone marked by shelf-edge barrier sands and oölites. Stratigraphic strike of the Floyd-Parkwood trends southeastward across northwestern Alabama, but in the Appalachian structural system it is deflected northeastward along structural strike of contemporaneous synclines. The Floyd-Parkwood-Pottsville thickens southwestward and is probably continuous with the Ouachita clastic wedge. The northeastern clastic wedge includes a shale and sandstone unit (Pennington) overlain by quartz-pebble conglomerate and associated coalbearing strata. The Pennington grades southwestward to the upper part of the carbonate facies in northeastern Alabama and apparently is only the fringe of a clastic wedge centered farther northeast. The prograding clastic wedges, which converge in Alabama from the southwest and northeast, suggest major clastic provenances in the Ouachita and Tennessee Appalachian structural salients. The carbonate shelf in the Alabama Appalachian structural recess was progressively overlapped from the southwest and northeast by laterally derived clastic sediments which were partly channeled along contemporaneous synclines in the recess.