Miocene Sediments and Micropaleontology in Gravity Cores from RISP/J9 Comparisons with DVDP and DSDP Drillcore Successions

• Main Author: Peter-Noel Webb
• Format: Report
• Language: English
• Published: Department of Geology, Northern Illinois University 1979
• Subjects: Browning; Ross Ice Shelf; Ross Sea; Webb; Antarc*; Ice Shelf; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=992; http://id.nii.ac.jp/1291/00000992/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=992&item_no=1&attribute_id=18&file_no=1

Eleven short gravity cores (up to 102cm in length at time of collection) were obtained through the Browning access hole at Ross Ice Shelf Project Site J9 during December 1977 (P. N. WEBB : Ross Ice Shelf Rep., 78/1,46p., 1978; P. N. WEBB and H. T. BRADY : EOS, 59,309,1978; P. N. WEBB et al. : Science, 203,435,1979). Site J9 is located at 82°22'S; 186°38'W (Fig. 1). The mudline at this site is 597m below present sea level. The seafloor in this area exhibits a very subdued relief. At J9 the Ross Ice Shelf is 420m thick and overlies a marine water column of about 237m. The site is some 400km from the open water of the Ross Sea. The collection of gravity cores took place over a two week period. The daily movement of the ice shelf in this area amounts to about 1m/day in a northerly direction. The short sedimentary succession obtained during repeated coring may be separated into two distinct lithological units, an upper light olive gray diatomaceous (±15% diatoms) sandy mud (<20cm thick) and lower olive gray diatomaceous (±15% diatoms) sandy mud. A thin (<1cm) microlaminated iron-rich unit marks the boundary between the two units. Igneous, metamorphic and diatomaceous ooze pebble and granule-sized clasts are distributed through the fine-grained sediments. Smear slide analysis shows clay, quartz and feldspar to be the dominant minerals in the fine fraction. Volcanic glass, zeolites and micromanganese nodules and carbonate make up a minor part of the smear slide preparations. X-ray analyses of the <2μ fraction indicates the presence of quartz, feldspar, illite (mica), chlorite, and smectite (montmorillonite is present in minor amounts) in the lower unit and quartz, feldspar, illite (mica), chlorite (minor amounts), smectite (montmorillonite is again present in minor amounts) and vermiculite in the upper unit. The biogenic component includes diatoms (abundant) (H. T. BRADY and H. MARTIN : Science, 203,437,1979; H. T. BRADY : Antarct. J. U. S., 13,123,1978), silicoflagellates (rare), sponge spicules (common) ...