High-Resolution Seismic Stratigraphy of Inner Continental Shelf, Texas Gulf Coast: Long Term and Short Term Cyclicity

John B. Anderson, Mark A. Thomas

Since the summer of 1987, scientists at Rice University have conducted high-resolution geophysical surveys of Texas bays and the inner continental shelf from Sabine Pass to Freeport, Texas. To date, nearly 1,500 km of seismic profiles have been collected and we are now integrating these data with industry platform borings and our own cores. These studies address a variety of problems, which include the late Wisconsinan-Holocene sea level history of the northern Gulf of Mexico, the facies architecture of wave-dominated deltas and incised valley-fill sequences, the origin of modern shelf sand deposits, and the stratigraphy of recent storm deposits.

The sequence stratigraphy suggests that two time scales of sea level change are observed in the seismic profiles. First are the long-term cycles (100,000-20,000 years in duration), which are related to major glacial episodes and correlate to stages of the ¹⁸O curve. Sea level changes occurring at this rate are manifested by sequence boundaries, condensed sections, and river terrace development. The sedimentary record for the latest transgression (20,000 years ago to present) suggests that short-term cycles (500 to several thousand years) are superimposed on the sea level curve. Short-term cycles are manifested by discontinuities within valley-fill and deltaic sequences, and observed in the architecture of the sedimentary (seismic) facies.

Short-term cycles may also be attributed to changes in sediment supply. To better constrain this variable, we are investigating separate drainage systems to see if these cycles are synchronous. So far, the Trinity/Sabine and the Brazos/Colorado rivers systems have been mapped to 40 mi from the present shoreline. Presently, we are sampling these high-frequency cycles, and plan to test for synchroneity with radiocarbon dating.

AAPG Search and Discovery Article #91029©1989 AAPG GCAGS and GC Section of SEPM Meeting, October 25-27, 1989, Corpus Christi, Texas.