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Fine-grained marine sandstones within the Kemp Clay of the Navarro Group (Maestrichtian) of east-central Texas were deposited on a muddy, shallow shelf by migrating sandbars. These sands were transported in traction from deltaic headlands by seaward-deflected coastal/shelf currents. The sand formed thin (3-20 ft; 1-6 m) arcuate belts (shelf sand plumes) which were 17-20 mi (27-32 km) wide and extended 27-30 mi (43-48 km) downdrift and 21-40 mi (34-64 km) onto the shelf. Orientation of the long axes of ridges, formed by the stacking of individual bars within the shelf sand plume, changes (from dip to strike-oriented downdrift) corresponding to the flow directions of the shelf currents.
Southwestward, fair-weather reworking of these delta-supplied sands by shelf currents resulted in the down-current stratigraphic climbing of the migrating shelf-bar complexes. Onshore stratigraphic climbing in the landward parts of the plume complexes was related to storm activity. Current patterns and the resulting distribution of sand were influenced by the configuration of the shelf and the topographic relief inherited from previously deposited deltaic/shelf depositional platforms.
Three variations of the basic shelf sandstone-plume model were recognized in the study area: (1) a rapidly deposited, immature plume, (2) an abandoned, current-reworked plume, and (3) a storm-modified, onshore-reworked plume. Each of these variants displays unique characteristics which influence their potential as hydrocarbon reservoirs.
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