Seismic Facies Analysis of Entrenched Valley Fill: A Case Study in Galveston Bay Area, Texas: ABSTRACT

Abstract

ABSTRACT The entrenched Trinity River valley beneath Galveston Bay was studied using high resolution seismic data. The shape of the incised valley was determined on mini-sparker lines, which were obtained from the U.S. Geological Survey in Corpus Christi, Texas. Uniboom lines, shot in 1987 aboard the Rice University research vessel R/V Matagorda, provided detailed records of the sediments filling the valley. The correlation between lithofacies and high resolution seismic facies was established by integrating the uniboom data with information about sedimentary environments. Environments were interpreted from lithologic descriptions of sediment cores and tied to the seismic lines. In addition, many uniboom lines were shot directly over known modern environments (i.e., the Trinity bayhead delta, the middle estuary, and the flood tidal delta at Bolivar Roads). The good correlation between lithofacies and seismic facies warrants the use of high resolution seismic data to determine depositional environments in areas where they are unknown. Information concerning incised valley geometry and the valley-fill sequence led to conclusions concerning the evolution of the Galveston Bay estuary. Possible point bar deposits, seen overlying the Pleistocene surface on one of the uniboom lines, support the idea that the Trinity River entered a meandering phase during the Holocene transgression, prior to the flooding of the present estuary. The valley-fill sequence of fluvial sediments overlain by bayhead delta and then estuarine deposits, which is present throughout most of the estuary, seems to be interrupted in the middle of the bay. The lack of bayhead delta deposits in this area may indicate a rapid rise of sea level sometime between 6000 years B.P. and the present.