Browsing by Subject "sea level"
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Item Landscape Scale Impacts of Sea Level Rise and Elevation Changes Along the Matagorda Fault in Matagorda, Texas(2012-10-19) Cline, MarieMovement of growth faults, a type of normal fault which is formed during sedimentation and is characterized by having greater vertical thickness on the downthrown fault side, on barrier islands contributes to wetland losses. The opening objective of this study was to quantify land cover change within a Matagorda, Texas wetland that results from sea level rise and elevation change over time due to coastal faulting. The closing objective of this study was to simulate land cover conversion as a function of relative sea level rise (RSLR) within the wetland and to compare and contrast the impact of specific rates of both fault-induced elevation change and predicted International Panel on Climate Change (IPCC) sea level rise projections. To accomplish these objectives a time series of aerial images was classified using automated unsupervised classification and hand digitization. After classification, total wetland losses on both the upthrown and downthrown sides of the fault were evaluated as a function of spatial distance from the fault plane. This classified product was draped over a digital elevation model (DEM) layer to evaluate elevations of land cover classes and model potential future outcomes based on RSLR. Classification results show that while wetland loss occurred on both sides of the fault, losses were far more extensive on the downthrown side. It was concluded that this vertical fault movement impacts wetland losses, especially on the downthrown side. Modeling results show that rapid water level rise can force wetland land cover class conversion regardless of whether this relative rise is caused by vertical fault displacement or eustatic sea level rise, resulting in the destruction of vital wetland areas. Current recorded conditions of sea level rise along the Texas Gulf Coast leave a grim outlook for regions similar to this study area.Item Late Pleistocene New Jersey Shelf sedimentation as a response to glacio-eustatic sea level rise(2009-08) Stackhouse, Stanley B.; Fisher, W. L. (William Lawrence), 1932-; Goff, John A.; Steel, Ronald J.Shallowly-buried channel systems have been imaged on the New Jersey Shelf with high-resolution seismic imaging. These channels formed as riverine systems that occupied the exposed shelf during the Last Glacial Maximum, ~18 ka. Subsequent sea level rise ~15-12 ka modified the valleys, forming estuaries and filling the channels with estuarine sediments. The infill sediments within the channel provide evidence for the response of the shelf to the Late Pleistocene glacio-eustatic sea level rise, but little work has been done on samples from these strata. This study aids in the ground-truthing of previous stratigraphic results by analyzing the cores collected within the infill sediments. The seismic stratigraphy of fill sediments from the mid-shelf and outer-shelf channels are structurally dissimilar. The mid-shelf channel fill stratigraphy is dominated by finely-laminated U-shaped reflectors throughout the section, with cut and fill geometries. In contrast, the outer shelf channel fill stratigraphy is a well-ordered sequence of 4 identifiable, primarily flat-lying seismic units. We collected five cores in mid-shelf channels (~30 m water depth), one in an outer shelf channel (~80 m of water depth) and one core in the trangressive ravinement surface. Cores were logged for density and seismic velocity. Grain size analysis was conducted by settling column and laser particle size analyzer. Radiocarbon analysis of the stratigraphy was conducted with the shell fragments and organic mud within the samples. The foraminiferal assemblages aided in determining the depositional environment. Using these data I investigated the differences in depositional environment of the mid- and outer-shelf channels systems, and consider these results in the context of sedimentary models for estuarine processes. The radiocarbon dates and foraminiferal are consistent with channel infill in an estuarine environment. Grain size and density log data indicate that the mid-shelf channel fills are sandier than the outer-shelf channel fills, which leads me to infer that the sediment from the mid-shelf channels was deposited in a higher energy environment than that of the sediment in the outer shelf channels. The stratigraphic differences and locations of the channel systems are similar to the Zaitlin (1994) model of incised valley infill, but infill of the mid-shelf channel system could possibly be the result of a catastrophic meltwater flood event occurring ~14 ka as glacial lakes to the north broke their dams and flooded the mid-shelf.Item Processes Influencing the Diversity of Middle Permian Brachiopods in the Bell Canyon Formation of the Delaware Basin (West Texas, Guadalupe Mountains National Park)(2011-10-21) Fall, Leigh MargaretA fundamental question of long standing in the study of life on Earth is, ?Why are there so many species?? This question concerns the distribution of and relationships among species in the present day, but also requires an understanding of the history of diversity. Patterns of diversity result from multiple, interconnected ecological processes operating at different spatial scales. The goal of this research is to gain knowledge about processes that control diversity by using fossil data to provide a temporal perspective that is unavailable when studying modern ecological communities. The fossil record provides the only natural historical account of changes in the diversity of ecological communities in Earth?s past. This research examines the taxonomic composition and diversity of brachiopod paleocommunities in the Delaware Basin of west Texas (Guadalupe Mountains National Park). The study interval is the Bell Canyon Formation, a 5.4-Myr interval of upper Middle Permian (Capitanian) siliciclastic and carbonate rocks deposited on the toe-ofslope of the basin. Silicified brachiopods extracted from the carbonate rocks provide the basis to test two hypotheses: (1) the taxonomic composition of local fossil brachiopod paleocommunities remains uniform, and (2) the changes in diversity of local fossil brachiopod paleocommunities reflects the relative importance of regional processes. Multivariate analyses of clustering analysis and ordination, diversity partitioning, and rank abundance plots are used to evaluate brachiopod taxonomic composition and diversity within an ecological framework. Sequence stratigraphic analysis provides the means to place the results within an environmental context related to sea-level changes. Results indicate that the reorganization of brachiopod paleocommunity structure coincides with major basinal-scale disruptions. Large disruptions allowed rare taxa and invaders from outside the basin to become dominant within paleocommunities. The dynamics within paleocommunities do not appear to prevent the replacement of the incumbent taxa with new taxa. The importance of these findings indicate that paleocommunities are not static through this interval and can be perturbed into configurations with new dominant taxa. Therefore, ecological responses of paleocommunities are resolvable at the geological time scale.