The transgressive systems tract offshore eastern Louisiana and Florida/Alabama contains aggrading fluvial fill within lowstand incised valleys, transgressive deltas and their fluvial feeders, marsh and shoals/sand ridge fields. during transgression late highstand deltas and fluvial sands were reworked into an extensive transgressive sheet sand, the Mafla Sheet Sand, which covers much of the shelf and is up to 5 meters thick.

Offshore East Louisiana, the Lagniappe lowstand fluvial valley is filled with approximately 10 meters of medium to coarse-grained fluvial sand at well site Main Pass 303 (Sydow and Roberts, 1994). Integration of seismic character and biostratigraphy and lithostratigraphy at the well site led Sydow and Roberts (1994) to conclude that the remainder of the transgressive systems tract above the fluvial sands contains marsh deposits and shoals.