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.

The Late Cretaceous upper Sego Member of the Mancos Shale exposed in the Book Cliffs of east-central Utah is a 30 m thick sandstone wedge that overlies the Anchor Mine Tongue of the Mancos Shale and underlies coastal plain deposits of the Neslen Formation. Although this sandstone has been interpreted to be comprised of transgressive valley fills, recent detailed facies architecture studies of the underlying lower Sego Sandstone suggest these deposits may instead be regressive deposits of tideinfluenced deltas. This study maps facies associations, the geometry of lithic bodies, and key stratigraphic surfaces in order to define the architecture of a 12 km long cross section of the upper Sego Sandstone. This broadly depositional dip-oriented cross section exposes a vertical stack of three sandy intervals, truncated by a high-relief erosion surface, and capped by a shell rich lag. Sandy intervals are interpreted be an assemblage of forward stepping successions of tide-influenced delta lobes. Interval 1, dominantly highly marine bioturbated sandstones which thin landward over kilometers, is cut locally by an erosion surface overlain by tidal bed sets. It is capped by a localized transgressive shell lag and then a thin continuous marine shale. Intervals 2 and 3 are composed of stacked tidal bar deposits that successively coarsen upward and thicken basinward. Interval 2 is overlain by thin marine shales, whereas interval 3 is capped by a pronounced oyster shell lag ravinement surface. A high-relief erosion surface that extends from the top of the upper Sego sandstone down into the Anchor Mine Tongue Shale, is overlain by coarser-grained amalgamated fluvial channel deposits and is interpreted to be a incised valley fill. Erosion surfaces at the base of sandy intervals, thicken and decrease in marine bioturbation within successive intervals, and the valley cut into this succession reflects episodic forced regression of a deltaic shoreline.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

The fossil record is the only direct source of data for studying modes (patterns) and rates of morphological change over geologic time periods. Determining modes is critical for understanding macroevolutionary processes, but just how modes can vary within a taxon, and why, have hitherto been largely understudied. To address this, I examined patterns of morphological change in the shell of the Mesozoic marine bivalve genus Buchia over its geographic and temporal range. Buchia was chosen as a test subject because it is abundant, well-preserved across a variety of facies, and is widely distributed across the Northern Hemisphere where the likelihood of multiple lineages is low. While the focus of this thesis is on evolutionary patterns, it is also necessary to address issues of taxonomy and geographical variation, making this research applicable to a wide-variety of fields. Previous to this study there was no protocol for measuring buchiid valves, nor was the genus studied in a quantitative manner. Throughout this research I used ten morphological characters to describe shell shape and size. Multivariate methods (principle component and canonical variate analyses) were employed to discriminate between species of Buchia and examine how morphological characters change through time and space within the genus. Evolutionary patterns were delineated using two well-established programs that discriminate between multiple modes of evolution. Overall, nearly 2000 specimens from eight geographical locations around the world were studied for this thesis. I found the genus Buchia was a useful tool for evolutionary studies as it can be studied quantitatively in space and time. Specically I have found that buchiid species can be delineated using morphometrics; the genus is restricted to the Northern Hemisphere; while the environment significantly affects morphology, there is no evidence of a latitudinal gradient; diversity and disparity within Buchia are not correlated; most evolutionary modes conformed to random walks or stasis; and modes and rates vary across the geographical range of the genus. Overall, I have found that the environment plays an important role in shaping both morphology and modes.

North of Grand Rapids, Manitoba, new exposures of a carbonate succession prompted study of the lithology and paleontology of the uppermost Ordovician along the northern edge of the Williston Basin in Manitoba. Modern concepts and approaches were applied in examining the sedimentary rocks and fossils, including X-ray diffraction, stable carbon and oxygen isotope analysis, and statistical algorithms. Nine lithofacies, representing a series of shallowing events, and environmentally significant subaerial exposure surfaces, were identified. The distribution and relative abundance of identified fossils were used to delineate faunal associations, which were examined in the context of the impending end-Ordovician mass extinction. Historically, the stratigraphy of the latest Ordovician has been problematic. Therefore, detailed examination of this succession aided in clarifying unit boundaries in the Stony Mountain and Stonewall formations. Study of this new succession contributed a wealth of information to the understanding of the uppermost Ordovician of Manitoba.

No description available.

No description available.

No description available.

North of Grand Rapids, Manitoba, new exposures of a carbonate succession prompted study of the lithology and paleontology of the uppermost Ordovician along the northern edge of the Williston Basin in Manitoba. Modern concepts and approaches were applied in examining the sedimentary rocks and fossils, including X-ray diffraction, stable carbon and oxygen isotope analysis, and statistical algorithms. Nine lithofacies, representing a series of shallowing events, and environmentally significant subaerial exposure surfaces, were identified. The distribution and relative abundance of identified fossils were used to delineate faunal associations, which were examined in the context of the impending end-Ordovician mass extinction. Historically, the stratigraphy of the latest Ordovician has been problematic. Therefore, detailed examination of this succession aided in clarifying unit boundaries in the Stony Mountain and Stonewall formations. Study of this new succession contributed a wealth of information to the understanding of the uppermost Ordovician of Manitoba.

Thesis (PhD)--University of South Australia, 2001.