Paleoenvironments of the lower strata of the Tuscaloosa Group (Upper Cretaceous) of southwestern Alabama
In the subsurface of southwestern Alabama, the lower strata of the Tuscaloosa Group (Upper Cretaceous) can be divided into a lower unit, the Massive Sand, and an upper unit, the Pilot Sand. The lower Tuscaloosa sandstones are texturally submature subarkoses and, overall, exhibit a decrease in grain size and an increase in grain sorting and roundness from the base to the top of the section. These sedimentologic trends along with paleontologic evidence suggest that the lower Tuscaloosa sediments accumulated as part of a destructive deltaic-marine shelf complex. The Massive Sand interval, which overlies undifferentiated Lower Cretaceous nonmarine to marginal marine sediments, includes very fine to medium grained, moderately to well sorted, micaceous, glauconitic, calcareous, fossiliferous, argillaceous, quartz-rich sandstones containing subangular quartz grains. Sedimentologic and paleontologic data suggest that these sandstones accumulated as part of a wave dominated, high-destructive deltaic system. Lithofacies recognized included distributary channel, strandplain-lagoonal-marsh, and stacked coastal barrier sands. The Pilot Sand interval includes very fine to fine grained, well sorted, micaceous, glauconitic, calcareous, fossiliferous, argillaceous, bioturbated, quartz-rich sandstones containing subangular quartz grains. Sedimentologic and paleontologic data indicate that these sandstones were deposited as bars as a result of tidal current action on a shallow marine shelf. The Marine Shale of the Tuscaloosa Group, which overlies the Pilot Sand, consists of silty, micaceous, fossiliferous, laminated claystone and contains a diverse assemblage of macroinvertebrates, planktonic foraminifera, and calcareous nannoplankton characteristic of open-marine shelf conditions.
- Research Organization:
- Geological Survey of Alabama, Tuscaloosa (USA)
- OSTI ID:
- 6454990
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
Similar Records
Regional geological framework and petroleum geology of Miocene sandstones in coastal and offshore Alabama
Tight Abo gas sands, east-central New Mexico