A Mississippian clastic facies in the southern United States is within one of several regionally extensive clastic wedges that record the evolution of the Appalachian-Ouachita orogenic belt along the eastern and southern margin of the North American craton. In the eastern fringe of the wedge in Alabama, the Hartselle Sandstone is a northwest-trending linear sandstone along the regional facies boundary between clastic-wedge rocks (Floyd-Parkwood) and carbonate rocks (Monteagle-Bangor) typical of the shallow-marine shelf of the craton. Internal facies distribution in the Hartselle Sandstone defines a depositional system consisting of a northwest-trending barrier-island complex on the southwest and migrating sand bars on a shelf on the northeast. Barrier-island facies include horizontally laminated foreshore sandstone that contains limestone interbeds, as well as crossbedded longshore bar sandstone that contains fossil logs. The shallow shelf was dominated by migration of bars, wave reworking, and deposition of fine sediment from suspension in interbar areas. These processes are indicated by a complex vertical succession of crossbedded sandstones, rippled sandstones, and mudstones. Shelf processes reworked the upper part of the barrier-island sediment during regional southwestward marine transgression that is confirmed by southwestward extent of the Bangor Limestone over the Hartselle Sandstone. The northwest-trending barrier island of the Hartselle indicates sediment supply from the southwest, and that sediment dispersal system suggests uplift at a tectonically active converging continental margin along the Appalachian-Ouachita orogen during the Mississippian.
- Geological Society of America