Abstract: Lithofacies and Depositional Environments of Rush Creek Member of Woodbine Formation, North-Central Texas

Ron Johnson

Deposition in the nearshore environment has provided stratigraphic traps that are of special interest to the geologist. The organic-rich bays and lagoons act as source beds and caprock for potential reservoirs in nearshore sandbar deposits.

The base of the marine transgression which marks the beginning of Gulfian (Upper Cretaceous) deposition in north-central Texas is a shoreline deposit. It is characterized by distinct lithosomes recognized in part by primary sedimentary structures indicative of nearshore bar, lagoonal, tidal, estuarine, and inner shelf deposition.

The basal member of the Woodbine Formation, the Rush Creek, disconformably overlies Comanchean (Lower Cretaceous) marine strata in north-central Texas. It consists of several distinct lithofacies defined by grain size, stratification, and sedimentary structure.

Lithofacies indicate a south to north transition of shoreface, lower foreshore, estuarine, and inner shelf deposition. The shoreface deposition is represented by very fine-grained, well-sorted, quartzose sands that have low-angle planar cross-stratification and gently dipping beds. The lagoonal deposits are characterized by kaolinitic clays and the paucity of microfossils. In association with the lagoonal deposits are tidal deposits represented by lenticular and wavy flaser bedding. The estuarine deposits are composed of medium- and coarse-grained sand with large and small-scale trough cross-stratification. The inner shelf deposition is characterized by a lithology and a microfossil fauna similar to the Maness Formation of the East Texas basin, and is composed of shale, glauconitic cl ystone, and fossiliferous calcareous cemented siltstone lamellae. The entire section is capped by distributary sands of the Woodbine delta, recognized as the Dexter Member. The basal sequence indicates gradual shoreline progradation and bay-filling events near the earliest Gulfian strandline.

APG Search and Discovery Article #90974©1975 AAPG Mid-Continent Section Meeting, Wichita, Kansas