WELLNER, J. S., C. M. FRATICELLI, J. B. ANDERSON, Department of Geology and Geophysics, Rice University, Houston, TX; and L. A. BANFIELD, BPAmoco, Houston, TX.
The relationship between climate and sediment supply is influenced by changes in precipitation, vegetative cover, and soil profile development. The strength of the climate fluctuations within a drainage basin may influence river systems to the extent that the system appears out of phase with the sea-level curve.
High-resolution seismic data and platform borings have been used to characterize deposition during the last glacial-eustatic cycle of the Rio Grande, Brazos/Colorado, and Western Louisiana fluvial systems. Radiocarbon dates and oxygen-isotope data allow precise ties to published sea level curves. Published and ongoing studies are used to estimate climate fluctuations within the drainage basins. Combining these data sets facilitates comparisons of the efficacy of climate variations on sediment flux in each drainage basin.
Over the last 125,000 years the Gulf of Mexico systems in this study have had different responses to changing sea level and climate conditions. The Colorado and Brazos drainage basins experienced climatic conditions that range from semi-arid to humid. The Brazos River delta changed from a mud-rich to a sand-rich fluvial-dominated system during the highstand. The Colorado River also created a sand-dominated late highstand delta. During the transgression the Brazos/Colorado system constructed back-stepping, sandy, strike-aligned deltas. The Western Louisiana system, which may be part of the paleo-Mississippi drainage, formed a large fluvial-dominated delta during the last highstand. Earlier lobes of the delta are more sand-rich than later lobes. This river system shifted to the east before the maximum lowstand. The Rio Grande, which is in a semi-arid drainage basin, constructed a large, primarily muddy, delta system during the highstand. The transgressive deposits include a fluvial-dominated delta, overlain by wave-dominated deltas, overlain by marine deposits.