USING X-RAY DIFFRACTION TO IDENTIFY MINERALOGIC DISTRIBUTION PATTERNS IN OTTER CREEK, ST. JOHN, USVI

Sediment cores and surface samples were collected in Otter Creek, St. John, US Virgin Islands (USVI) in 2013 and 2014 to determine spatial and temporal distribution patterns of sediment mineralogy, and what they may tell us about natural and anthropogenic process that impact the coastal environments. Otter Creek, a unique embayment where both mangroves and corals exist in close proximity, is located in the protected Coral Reef National Monument along the SE coast of St. John. XRD results of over 100 sample analyses, using powder diffraction methods on a Bruker D4 Endeavor processed with the TOPAS software, show a spatial relationship between marine carbonate and terrigenous minerals. As expected, terrigenous minerals such as quartz, albite, and labradorite decrease seaward, and carbonate minerals aragonite, magnesium calcite, and calcite increase. Aragonite tends to decrease with water depth, while magnesium calcite increases. Terrigenous input increases through time, represented by up-core increases in all terrigenous indicator elements (quartz, albite, and labradorite), potentially in response to enhanced island runoff associated with the recent anthropogenic development in the up-slope watershed. With increased human activity in St. John, it is important to identify current mineralogical patterns, as well as to determine if human activities are impacting carbonate producing communities.