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Cross-shore and longshore sediment size distribution on southern Currituck Spit, North Carolina
Calliari, Lauro Julio
Calliari, Lauro Julio
Abstract
Using Q-mode factor analysis, 87 surficial sediment samples collected from Duck and Whalehead beach, North Carolina, were analyzed using the weight percent of the gravel and sand fraction subdivided at 0.5 phi class interval as variables. An additional data set composed of 178 surficial sediment samples from Duck beach (bimodal) and Coquina beach (unimodal fine) representing three years of sampling at monthly intervals were analyzed by the same technique using only the sand fraction. The spatial and temporal patterns of sediment factor groups support three main inferences. (1) Bimodal beaches display a more distinct sediment zonation than unimodal beaches. (2) On a long term basis (yearly), cross-shore grain-size distributions represent depositional processes. Particularly on bimodal beaches, the association of sediment factor groups with specific zones of the beach profile delineates a textural differentiation produced by the type and amount of energy inherent in each zone. Combinations of Q-mode factor analysis and other environmental sensitive techniques (e.g. log-probability plots of grain-size distributions) proved to be useful for interpreting sedimentary processes at the depositional site. (3) The cross-shore patterns which represent an average of the sedimentary processes occurring under fair weather and storm conditions indicate that coarse sediments are concentrated on the backshore. In contrast, fine sediments are located landward or shoreward of this zone where they are exposed to energy conditions that result in their depletion in the subaerial beach. Using the Q-mode factor model, 350 new sediment samples from beaches located between Duck and Oregon Inlet were "mapped" in the factor space defined by the Duck-Coquina data set. The along-coast results support the cross-shore trends observed in the previous studies and indicates that there are several sources of coarse sediments between Duck and Oregon Inlet. Sedimentologic, stratigraphic and seismic data offshore and landward of the barrier substantiate these findings and demonstrate that differences in subaerial beach morphology in this part of Currituck Spit, is primarily due to the availability of coarse sediments from the paleodrainage of the Albemarle river.
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1990
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9033120.pdf
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Virginia Institute of Marine Science
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https://dx.doi.org/doi:10.25773/v5-ftfs-5268