2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 2
Presentation Time: 1:30 PM-5:30 PM


RODRIGUEZ, Antonio B.1, ANDERSON, John B.2 and SIMMS, Alexander R.2, (1)Geological Sciences, Univ of Alabama, Box 870338, Tuscaloosa, AL 35487, (2)Earth Science, Rice Univ, 6100 Main Street, Houston, TX 77005, arodrigu@bama.ua.edu

Late Quaternary incised-valley fill architecture is commonly attributed to the interplay between sea-level rise, sediment supply, and hydrodynamic processes. The control variable antecedent topography has on incised-valley fill architecture is examined in the Trinity incised valley, Texas. The Trinity valley is characterized by a series of downward-stepping terraces and the Galveston Estuary formed above this irregular antecedent topography. Flooding surfaces, recognized in core by a decrease in sedimentation rates and a change from delta plain to central basin facies, formed at ~ –14 m, 8,200 cal. yr. BP and ~ –10 m, 7,700 cal. yr. BP, matching depths of the relatively flat fluvial terraces. Flooding surfaces formed rapidly and represent entire reorganization of the estuarine complex. Across the –10 m flooding surface, the river mouth and bayhead delta shifted landward at a rate of ~ 6.5 km per century and the associated barrier shoreline was stranded on the inner continental shelf forming Heald Bank. Flooding surfaces formed as the rate of sea-level rise was decreasing, and are not associated with a decrease in sediment delivery to the estuary. As sea level inundates relatively flat fluvial terraces, rates of shoreline transgression increase dramatically resulting in a sudden increase in accommodation space, and an associated landward shift in coastal facies. Terraced incised valley-fill architecture is inherent to backstepping parasequences, in spite of external forcing mechanisms.