Previous   |    Next

doi:10.2204/iodp.proc.308.202.2007

Materials and methods

During IODP Expedition 308, a total of eight holes at three sites (Sites U1322, U1323, and U1324) were drilled in the Ursa Basin, northern Gulf of Mexico. Hole U1322B (28°5.9642′N, 89°1.4995′W; water depth = 1319.5 m) was the only hole drilled at Site U1322 for retrieving sediment cores without logging. The 234.5 m sediment sequence recovered in Hole U1322B is dominated by dark, organic-rich mud truncated by frequent mass flow layers and fine-grained turbidites (Expedition 308 Scientists, 2005). Preliminary shipboard paleontological investigation indicates that the sediment was deposited in a rapid depositional environment over the last 65 k.y., in marine isotopic Stages (MIS) 1–4 (Expedition 308 Scientists, 2005).

For this study, we collected 141 samples (20 cm³) with a resolution of 1.5 m from Hole U1322B. Samples were oven-dried at 60°C, weighed, and washed through a 63 µm sieve. Dry residues were weighed again for the purpose of calculating the >63 µm coarse fraction. All planktonic and benthic foraminifers in the dry residues were counted and identified under a binocular microscope. Globigerina ruber specimens were picked for measuring stable isotopes as reported elsewhere (Li et al., this volume), and their numbers were included in the calculation of relative abundance of planktonic species. Apart from calculating the percent abundances of most foraminifer species, planktonic and benthic group abundances were also estimated by converting their counted number to a total sum in a dry sediment volume of 50 g. For early biostratigraphic work in the region, we mainly refer to Kennett and Huddle-stun (1972) and Healy-Williams (1984). The modern benthic foraminifer work of Poag (1981) also provides a valuable reference for comparison and paleo-environmental interpretation of various benthic foraminifer assemblages.

Top of page   |    Previous   |    Next