Southeastern Section - 68th Annual Meeting - 2019

Paper No. 29-14
Presentation Time: 8:00 AM-12:00 PM


NEBEL, Angela, WRIGHT, Patricia, MONITO, Lindsey R., MELLERSON, Brianna, GRECO, Nicole, EVERETT, Andrew, CHIOCCA, Cara and ST. JOHN, Kristen, Department of Geology and Environmental Science, James Madison University, Dept of Geology & Env Sci, MSC 6903, Harrisonburg, VA 22807

Several cores were recovered from the Gulf of Mexico by the USGS in 2002. During the initial expedition, those aboard hypothesized that a dark-colored (low L*) stratigraphic interval common across all the recovered cores represented the Last Glacial Maximum (LGM). However, recent research (Melander et al., 2017; Richardson et al., 2018) on Sites 2535 and 2555 re-interpreted this dark interval as deglacial meltwater pulses, interrupted by the Younger Dyras event. This study aims to determine the age of the dark interval observed at Site 2560 to evaluate these competing hypotheses at a third location. Site 2560 is located on the upper continental slope (1029-m water depth) of the Kane Spur region on the eastern flank of the Mississippi Canyon. To determine the ages we chose planktic forams G. ruber and O. universa for radiocarbon dating. Additionally, biogenic (coarse fraction) analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD), and grain size analyses were conducted to evaluate this complex scenario; in particular, to examine possible changes in provenance and transport energy.

Results indicate that the dark interval (~1000-350 cmbsf) in question at Site 2560 is too young to originate during the LGM. The interval occurs between ~18-10 ka which is consistent with the hypothesis that this is a deglaciation record and includes meltwater discharges and the Younger Dryas event. Sedimentation rates are also highest during this time period suggesting high transport energy. Grain size remained in the silt-clay size range throughout the full record, but changes in grain size standard deviation (a measure of sorting) may mark times of increased transport energy and/or changes in provenance. Shifts in clay mineral relative abundances point to changes in provenance at the end of the LGM, during the deglaciation (smectite-rich from the NW upper Mississippi River drainage basin), and moving into the Holocene (at ~350 cmbsf). Lastly, forams are rare during the deglaciation, but increase dramatically in abundance above 350 cmbsf. This is consistent with an increase in L* and the Ca/Al ratio. These changes likely result from increased paleo-productivity during the warmer Holocene, as well as reduced dilution by terrigenous input.