The purpose of this study is to examine the sediment stratigraphy and oyster reefs
of Lavaca Bay. There has been little previous research on the bay??s stratigraphy, and
information from this study is important for industry and resources management. The
Lavaca Bay estuary is a drowned river valley containing a history of estuary development
in the late Pleistocene and Holocene. We used a chirp sonar to gather acoustic reflection
profiles, which were classified to categorize and trace reflectors. The data were plotted to
make maps of the distribution of various reflection types and contour maps of reflector
surfaces. The maps were compared with previous studies of Lavaca Bay and Galveston
Bay to aid interpretation. The vertical sediment stratigraphy showed two main reflector
packages. The upper package, bay bottom to ~25 m depth, is mostly acoustically
transparent with a few, semi-continuous, prominent reflectors in the upper 5-10 m. The
lower package ranges from 15-40 m depth with several strong reflectors sometimes
underlain by unconformities. To classify reflector characteristics, the upper package was
divided into two categories, each with 4 sub-categories: 1) surface reflectors??weak,
medium, strong, and ringing, which describe the general acoustic return of the bay
bottom, and 2) strong, shallow reflectors??surface strong, mounds, buried strong, andburied multiples, which describe strong acoustic returns in the upper 5 m of stratigraphy.
Within the lower package, four categories were recognized: 1) subbottom
reflectors/horizons, occurring ~20-40 m depth, 2) deep wipeout (incoherent/wipeout
zone), ~10-30 m depth, 3) clinoforms, ~5-30 m depth, and 4) terraces, ~10-30 m depth.
The data interpretation agrees with previous studies suggesting Lavaca Bay filled
beginning with coarse sediment and grading to finer sediment. In addition, the surface
type reflectors are indicative of bottom type, the strong, shallow reflectors are largely
indicative of oyster reef/shell, and the subbottom reflectors are related to the Pleistocene
and bay fill. The location/extent of oyster reefs in the bay does not agree well with
previous studies, suggesting either oysters do not grow over older ones or differences
between the chirp sonar response and other methods significantly differentiate the
interpretation of their locations/extents.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/2369 |
| Date | 29 August 2005 |
| Creators | Patch, Mary Catherine |
| Contributors | Sager, William W. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 7637490 bytes, electronic, application/pdf, born digital |
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