PLANKTIC FORAMINIFERA BIOSTRATIGRAPHY OF CORE MD02-2555, GULF OF MEXICO

Creating age models are essential to stitch together a sequence of time-specific events and compare records from different locations. In 2002 scientists on the IMAGES VIII/PAGE 127 expedition proposed a rough age-depth model for Gulf of Mexico Site MD02-2555 based of color reflectance. A dark interval at 500-650 cmbsf was interpreted as the Last Glacial Maximum (LGM; Winters et al., 2007) and was used to correlate to other regional sites. More recently, the cores were carbon dated which placed the end of the LGM at ~1040 cmbsf, and the dark interval was reinterpreted as a deglacial meltwater pulse (Melander et al., 2017). At the time, limited biostratigraphic analysis also placed a biozone boundary (9.8 ka) at 258 cmbsf. The purpose my study was to refine and extend the planktic foraminifera biostratigraphic analysis for MD02-2555. 14 samples were taken 100 cm apart, and ~300 individuals were picked and sorted per sample. The zonal scheme used by the IODP Expedition 308 science party (2006) was used to define zonal boundaries. Three planktic foraminifera biozones boundaries were identified: The Z1/Z2 boundary (6 ka) at ~200 cmbsf, based on the increased abundance of P. obliquiculata and others; the Y/Z boundary (9.8 ka) at ~265 cmbsf based on the first consistent appearance of G. menardii; and the Y1/Y2 boundary (16 ka) tentatively placed between 500 and 636 cmbsf (difficult to determine because of near absence of forams at these depths) based on the last occurrence of G. inflata. The linear sedimentation rates (LSR) for each biozone are: 33.3 cm/kyr for Z1, 17.1 cm/kyr for Z2 , and 59.8 cm/kyr for Y1. The planktic foram biozone data and the C-14 data produce similar LSRs, except between 200 and 359 cmbsf where they differ by 20 cm/kyr. This is because of differences in the age picks at approximately 265 cmbsf; the biostratigraphic data at 265 cmbsf suggests an older age (9.8 ka) than the C-14 data measured from a sample slightly deeper (269 cmbsf; 8.3 ka). Nevertheless the biostratigraphic age model confirms the recent interpretation that the dark interval between 500 and 636 cmbsf cannot be the LGM, and must be a record of a deglacial depositional event. The next step to take in this project would be to extend sampling deeper to determine the stratigraphic location of the LGM, and compare to biostratigraphic findings from other nearby sites.