Quaternary Depositional Sequences
The coastal plain and continental shelf of Texas were sites of simultaneous erosion and deposition related to late Quaternary eustatic fluctuations in sea level. Geologic maps, deep borings, and seismic profiles from the area provide evidence of how the dominant sedimentary processes responded to changes in base level during the most recent (Sangamonian-Holocene) depositional episode.
The early Wisconsinan falling sea level and subsequent lowstand caused upstream river entrenchment and downstream deltaic pro-gradation beyond the shelf edge. Later, deltaic sedimentation shifted landward in response to a middle Wisconsinan sea-level rise and then seaward in the late Wisconsinan as sea level fell to its lowest position. Carbonate reefs grew on a broad terrace between the major deltas during the initial postglacial rise in sea level. The continued sea-level rise (Holocene) and highstand resulted in erosion and retreat of deltaic headlands, progradation of interdeltaic barriers and strandplains, and aggradation of alluvial valleys, bays, and the inner shelf. Modern patterns of shoreline deposition resemble those of the preceding (Sangamonian) highstand.
Local and regional structures controlled the position and thickness of some late Wisconsinan and early Holocene deposits, such as river channels, sand ridges, and carbonate reefs. Lowstand deltas along the basin margin are several times thicker than their updip counterparts because of rapid subsidence and progradation into relatively deep water at the shelf edge. Landward of the shelf edge, however, thicknesses of depositional sequences and individual fluvial, deltaic, and barrier island sand bodies are comparable regardless of whether they were deposited under static or falling sea-level conditions. Apparently, thicknesses of these stable-platform deposits depended nearly equally on subsidence and water depth.
Figures & Tables
Sea-Level Fluctuation and Coastal Evolution - This Special Publication is the result of a symposium in honor of W. Armstrong Price held at the first SEPM Midyear Meeting at San Jose, California, on August 12, 1984. The factors controlling relative sea-level change along our shores are varied and, at best, imperfectly understood. Yet, the relative rate of change is what controls shoreline erosion, the arrangement of sedimentary facies of the coastal zone, and the character of deformities within the coastal stratigraphic record. Therefore, these papers address sea-level changes, shoreline responses, and the controls on the three-dimensional geometry of the consequent lithosomes; in short, the architecture of the coastal depositional systems.