A MULTI-PROXY INTERPRETATION OF MARINE SEDIMENT LITHOLOGY ON THE TEXAS-LOUISIANA SLOPE IN THE GULF OF MEXICO AS EVIDENCE FOR DEGLACIATION OF THE LAURENTIDE ICE SHEET

In July 2002, the IMAGES Vll/PAGE 127 Gas Hydrate and Paleoclimate Cruise aboard the RV Marion Dufresne collected a series of cores in the Gulf of Mexico. Site MD02-2555 and MD02-2535 were collected from the Bush Hill Basin and the Tunica Mound, respectively. These cores were used to determine the timing and source of meltwater during deglaciation of the Laurentide Ice Sheet (LIS) as part of recent paleoclimate undergraduate course-based research projects at JMU. A regionally extensive stratigraphic dark interval (low color reflectance) was initially interpreted as being deposited during the Last Glacial Maximum (LGM) by the shipboard scientists. Recent analysis conducted by Melander et al. (2017) reinterpreted this dark interval within site 2555 as a meltwater discharge event occurring after the LGM, followed by a readvancement of the Laurentide Ice sheet during the Younger Dryas cold period, and a secondary meltwater discharge event. Here, we focused on site 2535 in order to further evaluate evidence for the regionally extensive dark interval representing either a meltwater discharge event or the LGM. 14C dating of G. ruber foraminifera was used to establish an age model and determine linear sedimentation rates. Results place this interval after the LGM. Additional work was also done on Site 2555 with the goal of further characterizing the deglaciation of the LIS. Changes in Ti/Al ratios, grain-size, and smectite/(illite+chlorite) demonstrated an inter-relationship between these proxies that can be correlated to meltwater events occurring after the LGM, separated by a poorly defined Younger-Dryas cold period. While we expected grain-size to increase during meltwater discharge, the dominant grain-size remain fine. This, however, is consistent with the observation by Montero-Serrano et al. (2011) of meltwater event 1A being dominated by 3.6 um grain size mode and coming from the NW part of the drainage basin. We noted that stratigraphic boundaries between our deglaciation events showed distinct but short-lived changes in Ti/Al ratios and clay mineral composition. Lastly, correlation between Ti/Al peak abundance and grain size indicate that XRF could be used as a grain size proxy in future study, which would allow for more efficient and non-destructive analysis, while still obtaining representative results.