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Systems
during the Last Glacial-Eustatic Cycle
WELLNER, J.S., C.M. FRATICELLI, J.B. ANDERSON, Department of Geology and Geophysics, Rice University, Houston, TX; and L.A. BANFIELD, BP-Amoco, 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 backstepping, 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.
WELLNER, J.S., C.M. FRATICELLI, J.B. ANDERSON, and L.A. BANFIELD
AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas