The Application of Macro- and Microfossils to Identify Paleoearthquakes in Sumatra, Indonesia and to Characterize Geomorphic and Ecological Succession on a Marsh Platform After Hurricane Isabel in North Carolina, USA

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Doctor of Philosophy (PhD)
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Earth & Environmental Science
paleoenvironmental change
subsidence stratigraphy
Earth Sciences
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@font-face { font-family: "Verdana"; }@font-face { font-family: "Cambria"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0in 0in 0.0001pt; text-align: justify; line-height: 200%; font-size: 10pt; font-family: "Times New Roman"; }div.Section1 { page: Section1; } In this research I revealed evidence for two buried soils in the Aceh Province, Sumatra. I focused on the litho- and biostratigraphy of the lower buried soil, which is indicative of coseismic subsidence from a paleoearthquake estimated to have occurred ca. 6500-7000 years BP. Approximately 1-3 m above the lower buried soil sequence is an upper buried soil with an age of ca. 5500-6000 years BP. I used a multi-proxy method that included pollen, foraminifera, and the gastropod Cerithidea cingulata (Gmelin, 1791) to identify the lower buried soil, establish the preseismic and postseismic paleoenvironments, and estimate the amount of coseismic subsidence to be 0.4 ± 0.3 m. Using our own distribution study and previous work, I determined the indicative meaning of C. cingulata in the modern environment. I then used this species as a sea-level indicator in the lower buried soil sequence to determine the elevation of the postseismic land surface and constrain the age of the paleoearthquake. I calibrated the 14C age of a C. cingulata shell in the postseismic unit of the lower soil by incorporating a species-specific regional correction (ΔR) to the marine reservoir effect. I developed the correction from 11 shells of known age collected prior to 1950 from sites across southeast Asia. Hurricane Isabel deposited overwash sand on a back-barrier salt marsh of Ocracoke Island, North Carolina on September 18th 2003. Data collected annually between May 2004 and October 2010 showed changes in the elevation, geomorphology, and the ecological evolution of the overwash deposit. The results indicated that marsh foraminifera and plants did not recolonize until the surface of the overwash deposit was eroded to an elevation within the intertidal zone. Once this elevation was crossed, recolonization occurred in less than one year. The erosion of the overwash deposit suggests that the stratigraphic record of storm-driven overwash is likely not representative of the actual number of landfalling hurricanes in environments such as the Outer Banks of North Carolina.

Dr. Benjamin Horton
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