Chemostratigraphic analyses of legacy and late Holocene, presettlement deposits, Upper Stick Elliott Creek, North Carolina

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
Samantha Nicole Sullivan (Creator)
Western Carolina University (WCU )
Web Site:
Carmen Huffman

Abstract: Chemostratigraphy is a technique that defines and spatially correlates stratigraphic units usingsubtle variations in the elemental composition of the sediments. A collaborative study of UpperStick Elliott Creek within the Big Harris River basin near Polkville, NC was conducted todetermine the occurrence of chemostratigraphic units in floodplain sediments. Field studiesshowed that the alluvial floodplain deposits primarily consisted of organic rich, pre-settlement deposits dating between approximately 3460 YBP and 210 YBP. The legacy sediments wereproduced in response to basin wide changes in land use from predominantly forest cover tocotton farming. The changes in land use resulted in extensive upland erosion and gully formationas well as channel and valley floor aggradation. Depositional rates during aggradation of thelegacy deposits were an order of magnitude higher than those associated with pre-settlementdeposits. Beginning in the late 1940s and early 1950s, erosion control methods wereimplemented, and cotton farming was replaced by pasture and turkey farming, which incombination led to channel incision and the exposure of legacy and pre-settlement deposits in the channel banks. These deposits were described in detail at four sites located along Upper Stick Elliott Creek. At each site, between 26 and 39 samples were collected at approximately 5 cmincrements from the ground surface to the base of the channel banks. The samples were subsequently analyzed for 45 elements by XRF as well as their grain size distribution. More than 120 samples were collected and analyzed in total. The geochemical data showed that legacy andpre-settlement deposits exhibited significant differences in elemental concentrations. In addition, concentrations varied systematically as a function of depth with these two deposit types. Thus, multivariate statistical techniques including hierarchical cluster analysis and principle component analysis (PCA) were used to define chemostratigraphic units at each of the sampling sites. Hierarchical cluster analysis was able to identify chemostratigraphic units within the lithostratigraphic sites. However, it was not able to separate different stratigraphic sectionsclearly. PCA of normalized metal concentrations to a conservative element (Al, Fe, or Ti) provedto be most effective at defining chemostratigraphic units within legacy deposits at a site. These units could be correlated along the stream, thereby providing information needed to more fully understand sediment transport and depositional processes within the drainage basin. While presettlement deposits exhibited distinct chemostratigraphic units at a site, these units were more difficult to correlate between sites. Differences in the ability to correlate units along the channel may reflect differences in the rates and processes of sediment transport and deposition before and after significant changes in land use.

Additional Information

Language: English
Date: 2020
Chemostratigraphy, Hierarchical clustering, Principle component analysis, Sediment, X-Ray Fluorescence

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