Paper No. 378-6
Presentation Time: 9:00 AM-6:30 PM
TIMESCALE AND PROVENANCE OF PLEISTOCENE SEDIMENT FROM ODP LEG 113 SITE 693
Creating an accurate age model for Antarctic sediment is difficult due to a general lack of preserved carbonate. Core 693A-2R, from the Ocean Discovery Program (ODP) Leg 113, is an exception. Cored in 2560 m of water, this 9.5 m long core contains abundant foraminifera. Site 693 is located adjacent to Dronning Maud Land in the Northeast Weddell Sea on an upper slope bench near Wegener Canyon. Based on the shipboard timescale, it appears that Core 2R ranges from 0.25 to 0.95 Ma, placing it across the Brunhes-Matuyama reversal. We hope to better constrain the age of the core using the abundant foraminifera. We will present a down-core stable oxygen isotope record for Core 2R using planktonic foraminifera species N. pachyderma (sinistral). This record will be compared to the LR04 benthic stack to refine the age-model of the core. Comparison with other measurements on the same samples shows that the d18O signature of the foraminifera is heavier, indicating greater ice volume and/or colder conditions, when the carbonate concentration and weight percent ice rafted detritus (IRD) are higher. Higher concentrations of carbonate and IRD are generally thought to occur during warmer periods, making these data intriguing. In addition to stable isotope measurements, hornblendes and biotite were dated with 40Ar/39Ar in order to document the provenance of IRD at Site 693. The grains from the top of Core 2R show a dominant 500 Ma signature, likely indicating a local source of icebergs. In contrast, Pierce et al. (2014, Earth Science Reviews) looked at provenance of present day IRD from nearby core tops and found a mix of local and distant icebergs. Further 40Ar/39Ar analyses of detrital hornblende and biotite are underway.