Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
AAPG Annual Convention, Calgary, Alberta, Canada, June 19–22, 2005
Upper Pennsylvanian and Lower Permian Sequence Stratigraphy and Depositional Systems Tracts, Intracratonic Eastern Shelf and Adjacent West Texas Basin, North- and West-Central Texas
Sixteen depositional sequences (principally limestone transgressive and siliciclastic highstand and lowstand systems tracts) record paleogeography during Late Pennsylvanian Virgilian and Early Permian Wolfcampian Epochs (~275-296 Ma) on the Eastern Shelf and adjacent Midland Basin, Northwest-Central Texas. Strata ranging from 1,200 ft (365 m) on-shelf to more than 2,800 ft (853 m) within the eastern part of the Midland Basin were deposited under the influence of regional foreland tectonic elements, diverse source areas, variable subsidence, and glacio-eustatic sea-level variations.
To understand local sedimentary dynamics, regional tectonic events, and global sea-level cycles on the depositional history of these strata, we analyzed lithogenetic depositional systems and chronostratigraphic sequence stratigraphy. Cross sections covering ~2,000 mi (3,200 km), extensive outcrop data, and >5,000 wireline logs permitted delineation and mapping of highstand and lowstand siliciclastic genetic units within ~22,000 mi2 (~57,000 km2). Specific goals were (1) provide regional net-sandstone distribution within each regressive (HST/LST) package, (2) document sequential depositional history, (3) delineate and map depositional systems and paleogeography for each depositional sequence, (4) analyze depositional response to paleobathymetry and tectonics, and (5) construct a regional sequence (chronostratigraphic) framework relative to sediment-supply rates needed to understand relative cyclic changes of sea level.
Sedimentary cycles reflect interplay of differential subsidence and marginal uplifts, eustatic (glacially driven) sea-level cycles, and localized autocyclic sediment supply, deltaic shifting, differential compaction, and growth faulting.