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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 39 (1989), Pages 563-569

Glacial Eustatic Controls on Seismic Sequences and Parasequences of the Trinity/Sabine Incised Valley, Texas Continental Shelf

Mark A. Thomas, John B. Anderson (1)

ABSTRACT

Since the summer of 1987 Rice University has collected nearly 700 miles of high resolution geophysical surveys of Texas bays and the inner continental shelf, from Sabine Pass to Freeport, Texas. These studies focus on 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 Trinity/Sabine incised valley system has been mapped to forty miles from the present shoreline. Valley incision results from long-term cycles of sea level change (100,000 to 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 B.P. to present) suggests that short-term cycles (500, to several thousand, years) are superimposed on the sea level curve. Short-term cycles are manifested as back-stepping parasequences within valley-fill and deltaic deposits. One such parasequence has been seismically defined within the Trinity/Sabine valley and is interpreted as a prograding bayhead delta deposit.

Short-term cycles may also be attributed to changes in sediment supply. To better constrain this variable we are investigating separate drainage systems (the Trinity/Sabine valley versus the Brazos valley) to see if these cycles are synchronous. Presently we are sampling these high frequency cycles, and plan to test for synchroneity with radiocarbon dating.


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