PLANKTIC FORAMINIFERA BIOSTRATIGRAPHY OF CORE MD02-2560, KANE SPUR, GULF OF MEXICO

The IMAGES MD02 expedition recovered a 28 m sedimentary sequence at Site 2560 in 1029 m water depth, in the Mississippi Canyon, Gulf of Mexico. However, no age model was developed. Determining age is vital for paleoceanographic reconstructions and to compare and correlate to other sites. Based on color reflectance, this core extends from the Holocene through the Pleistocene. Thus, it is suited to investigate changes in biogenic input as a result of changing climate and glacial and interglacial states. The purpose of our project was to (1) develop an age model for the upper 10 m of core based on planktic foraminifera biostratigraphy, and (2) infer paleoceanographic changes. Twenty-one samples were taken every 50 cm, and sieved at 150 µm. Approximately 300 planktic foraminifera/sample were identified. Established zonal schemes were applied to develop our age model, and linear sedimentation rates (LSRs) were calculated. The Z1 subzone is dominated by warm water species of G. mendarii, G. tumida, and P. obliquiloculata. The 6ka boundary of Z1/Z2 is at 2.8 mbsf. The Z2 subzone shows increased G. crassaformis, a cool water species, and includes the Younger Dryas. The Z/Y boundary is placed at 4.8 mbsf, and marks the Holocene-Pleistocene transition at 10 ka. However, this is deeper than a bulk lithologic change at 4.5 mbsf. The 16 ka Y1/Y2 boundary is located at 5.4 mbsf. Y1 represents the late Pleistocene as cool water species of G. bulloides and G. falconensis peak. The Y2 subzone has high levels of G. crassaformis and represents the Last Glacial Maximum; its 24 ka base is placed at 7.5 mbsf. The total percent of planktic forams range from 15 to 20% between 10 and ~4 mbsf, where the percent abundance drops to ~5%. It increases to 40-50% between 3.5 and 1 mbsf, and correlates with an increase in color reflectance. In the upper 1 m, planktic forams drop to ~21%. LSRs are highest in the Holocene, 0.47 m/kyr in Z1 and 0.50 m/kyr in Z2, and may be due to increased productivity and terrigenous input from the Mississippi River. Holocene LSRs at MD02-2560 are similar to those at nearby IODP Hole U1324B, however U1324B’s Pleistocene LSRs are much higher, probably due its slope location that was prone to slumping. Further sampling and analysis will extend the biostratigraphy to 28 mbsf.