T92 Sigma Gamma Epsilon Undergraduate Research (Posters)

Monday, 5 November 2012
9:00 AM - 6:00 PM
Hall B

MIDDLE THROUGH UPPER MIOCENE DEPOSITIONAL HISTORY IN THE WEDDELL SEA

Paper number: T92-67
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Understanding the stability of Antarctic Ice Sheets is the key to understanding past climates and the response of ice-sheets to warming. Here we examine the middle through early Miocene marine depositional record in the Weddell Sea. Sediments were recovered at Ocean Drilling Program (ODP) Site 694 located in 4653 m of water in the Weddell Sea Abyssal Plain. Environmental interpretation of the sediment was hampered by poor recovery, poor magnetostratigraphy and siliceous biostratigraphy. Recovery averaged 57%, but ranged from 0 to 100% throughout the cores. Turbidite sediments at this site could have been sourced from East or West Antarctica. Ice-rafted sediments are most likely from the East Antarctic Ice Sheet (EAIS) since the ice sheet formed about 34 mya, while the West Antarctic Ice Sheet (WAIS), which includes the Antarctic Peninsula, probably didn’t form until about 5 mya.

Using visual descriptions, smear slides, grain size and XRF analyses, and the shipboard report, we determined that the > 350 m Miocene sequence consists of six sedimentary facies: silt, laminated silt, diatom clayey mud/mudstone, diatom clay/claystone, diamictite, sandy mud and sand. Facies associations suggest deposition via turbidity currents, ice-rafted detritus and hemipelagic settling. Turbidites dominate the stratigraphy between about 17-16.3, 13.9-9.8 and after 9.0 m.y. Ice-rafted sediments, defined here are large (>1 cm in diameter) dropstones and isolated sand grains. Ice –rafted sediments dominate between about 14.2 and 13.7 m.y., but they are also present in hemipelagic sediments and in turbidites, where they are observed in the fine-grained intervals. Clay mineralogy, U-Pb ages of zircons and Ar/Ar ages of hornblendes support an East Antarctic source.

Hemipelagic sedimentation, which consists of clay, silt and diatoms, shows varying abundance of diatoms indicating changes in surface water (climate) conditions. These changes correlate with diatom abundance at ODP Sites 689 and 690. Continued investigation will correlate the Miocene diatom abundances at other Weddell Sea locations.