Abstract: Lithofacies and Depositional Environments of Hosston Formation (Lower Cretaceous), South-Central Texas

Ralph L. Nelson, Donald F. Reaser

The subsurface Hosston Formation was studied in a 5,500-sq km (2,150 sq mi) area centered approximately 70 km (45 mi) south of Austin, Texas. The formation thickens gulfward from about 60 m (200 ft) to more than 390 m (1,300 ft) within the area of investigation. The rock body was subdivided into the following six lithofacies: (1) quartz conglomerate and litharenite, (2) dolomite and nodular anhydrite, (3) laminated biogenic dolomite, (4) quartz sublitharenite and dolomitic shale, (5) intraclastic biogenic dolomite, and (6) quartz arenite. These strata were deposited in three depositional environments: alluvial plain, supratidal, and intertidal. The oldest sediments were coarse clastic materials shed from an ancestral Llano uplift and deposited on eroded Ouachita rock.

The first Cretaceous marine transgression developed broad tidal flats adjacent to the land area. Both quartzose clastic and carbonate sediments were deposited on the tidal flats. Coral and rudistid reefs, present in the downdip, laterally equivalent Sligo, partly restricted water circulation in the nearshore Hosston environment. The distance from shore to shelf edge, approximately 100 km, also reduced normal circulation.

Carbonate accumulation in the area was probably similar to the modern depositional patterns along the arid Trucial Coast of the Persian Gulf. Supratidal dolomite and nodular anhydrite as well as biogenic, finely laminated intertidal dolomite reflect episodes of clear-water sedimentation. Periodically, carbonate deposition was interrupted by an influx of terrigenous material. The clastic phase of Hosston tidal-flat deposition was characterized by rippled, cross-bedded, and well-sorted quartz arenite interbedded with burrowed, silty quartz sublitharenite and dolomitic shale.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma