The formation process by which sand becomes cemented with humate compounds to form humicrete is not well understood, likely due in part to limited exposures of this material around the world. Humicrete layers along the Intracoastal Waterway in northwest Florida are some of the most well exposed units in the western hemisphere. Over a length of about ten kilometers, multiple beds with varying humate cementation can be observed throughout the lower two-thirds of bluffs that are nine to fifteen meters high. Dune deposits overlay the humicrete layers. The most prominent humicrete layer is approximately one to two meters thick and can be traced nearly continuously for over a kilometer. These layers were catalogued, photographed, and sampled for this study, in an effort to learn more about their depositional conditions, chemical composition, and the age of the material hosting the humate cementation. Specifically, this project sought to understand whether the organic matter present in the humate layers was transported laterally from nearby areas with high organic accumulation, or leached from overlying peat layers. Samples of disaggregated humate were analyzed via Fourier Transform Infrared (FTIR) spectroscopy and carbon/nitrogen isotopic analysis. The FTIR data produced indicated high concentrations of lignins and hydroxyls, similar to the chemical signature of younger humicrete samples. A table of the individual FTIR data points is included as a supplementary file titled “Appendix B–FTIR.pdf.” Isotopic analysis of these samples yielded δ13C values of −23.6‰ to −26.8‰ and a C/N ratio of 62 to 85, both of which point to terrestrial plants as the originating vegetation. Results of these tests, as well as observation of the current environment along the northwest Florida coastline, suggest that the organic matter found in these humicrete layers was carried laterally by near-surface groundwater from nearby forested swamps. The age of these host layers and the humicrete cementation is believed to be around 115,000–130,000 years old, as they are thought to have formed by interaction with groundwater during the Sangamonian interglacial period. Additional testing, especially with regard to extent, age and nature of movement of organic-rich water, would be helpful in further understanding how humicrete forms.
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|Commitee:||Ray, Peter, Wang, Yang, Means, Guy|
|School:||The Florida State University|
|Department:||Earth, Ocean & Atmospheric Science|
|School Location:||United States -- Florida|
|Source:||MAI 81/1(E), Masters Abstracts International|
|Keywords:||FTIR, Humate, Humicrete|
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