Age determination and sedimentation rates of ODP Hole 119-740A (Table 1)

Unconsolidated sediments recovered at Site 740 include approximately 23 m of interbedded siliceous ooze and silty clay (pebbly mud), which was tentatively assigned a late Pliocene to Quaternary age by shipboard scientists. In order to clarify the chronology of this sequence, six samples of siliceous ooze were analyzed for their 14C content using the University of Arizona Tandem Accelerator Mass-Spectrometer (TAMS) facility. Uncorrected ages ranged from 1915 ± 50 yr B.P. (0.21 mbsf) to 11,140 ± 75 yr B.P. (15.80 mbsf). These ages provide estimates for interval sedimentation rates of the siliceous ooze, which varied from 0.150 to 0.067 cm/yr. A reservoir correction of 1750 yr is used to determine absolute ages for the sample intervals. These dates ranged from 165 to 9390 14C yr B.P. Overall sediment-accumulation rates vary from 0.144 to 0.187 cm/yr, with maximum rates associated with the pebbly muds rather than the siliceous oozes. Extrapolated sedimentation rates and reservoir corrections allow for an age estimate of about 10,700 yr B.P. for the initiation of open-marine conditions at Site 740. Resumption of terrigenous sedimentation, with increased ice rafting, took place from approximately 7300 to 3800 yr B.P. This may have been related to the readvance of floating ice tongues along the eastern side of Prydz Bay. Open-marine conditions with seasonal sea ice have apparently been in existence near Site 740 for approximately the last 3800 yr