Student Research
Bobby McCoy
The
Preservation and
Evolution of the Nueces
Incised-valley Estuarine System, Nueces and Corpus Christi Bays, Texas
Texas
A&M
University - Corpus Christi
Directed
Independent Study
(Supervisor:
Dr. Garrison)
Re-evaluation
of seismic, core, well-log, and outcrop data from Corpus Christi and
Nueces
Bays and surrounding area reveals sediments recording over 120,000
years of
geologic history. Based on these data, progressive filling of the
Nueces
Incised Valley can be documented. The approximately 165 ft (50 m) thick
valley-fill succession records the development of a simple tripartite
incised-valley
stratigraphy. This incised valley serves as a modern analog for
lowstand and
transgressive systems tract deposits found within ancient incised
valleys along
micro-tidal shorelines.
The
geometry and depositional fill of the incised valley records the
sequence
stratigraphic signature of the last glacial-interglacial cycle that
represents
events from the initial valley incision at about 24,000 years BP to the
deposition of earliest high-gradient, lowstand, braided stream
sediments to
lower-gradient, late-lowstand, meandering fluvial sediments, followed
by sediments
recording the earliest transgression into the valley at the position of
the
present day shoreline, at about 10,000 years BP. This transgression
eventually
resulted in the formation of Corpus Christi and Nueces Bays. The
initial
transgression was followed by deposition of retrogradational bayhead
deltas, as
the Nueces River mouth retreated. Early-transgressive systems tract
estuarine deposits
were subsequently overlain by central bay sediments, which are
interlayered
with scattered oyster reefs.
About
5600 years BP, a barrier system developed across the estuary separating
the
open Gulf of Mexico from the estuary’s interior. This barrier system,
preserved
at Indian Point and North Beach, separates Corpus Christi and Nueces
Bays.
Except for a few passes, the estuary’s mouth was closed off from the
open Gulf,
at about 2500-2000 years BP, by the formation of Mustang Island.
Publications
Garrison, James R.,
Jr. and
Bobby
McCoy
(2007) The Nueces Incised Valley revisted: a
reinterpretation of the sedimentology and depositional sequence
stratigraphy of preserved Pleistocene and Holocene valley-fill
sediments: Gulf Coast Association of Geological Societies Transactions,
57
(in press). (download
pdf)