Hassler, Lauren E. et al. (2000): Changing Antarctic Peninsula glaciation over the last 3 Ma; clues from ice-rafted sand and pebbles deposited on continental rise sediment drifts

ODP 178

Hassler, Lauren E.
Appalachian State University, Department of Geology, Boone, NC, United States

Cowan, Ellen A.
Christian-Albrechts University, Federal Republic of Germany

Wolf-Welling, Thomas

Changing Antarctic Peninsula glaciation over the last 3 Ma; clues from ice-rafted sand and pebbles deposited on continental rise sediment drifts
In: Anonymous, Geological Society of America, 2000 annual meeting
Geological Society of America (GSA), Boulder, CO, United States
Pebbles (>1 cm) sampled from 3 drill sites on the continental rise west of the Antarctic Peninsula during Ocean Drilling Program Leg 178 were classified by shape and roundness following Krumbien (1941). In addition, sand mineralogy, pebble lithology and surface texture were visually identified. In order to increase the pebble sample size to 331 three sites drilled 94 to 213 km from the continental shelf edge were combined using magnetostratigraphy for core correlation. Ice rafted pebbles were compared in 3 groups defined by sediment characteristics: from 3.1-2.2 Ma (late Pliocene), 2.2-0.76 Ma (late Pliocene-late Pleistocene) and <0. 76 Ma to recent. Pebble lithologies originate from sources on the Antarctic Peninsula margin. Most pebbles are metamorphic and sedimentary pebbles are few (<6%). Mafic volcanic and intrusive igneous lithologies increase up section. Pebbles from 3.1 to 0.76 Ma plotted on sphericity-roundness diagrams (Boulton, 1978) show basal and supraglacial/englacial transport. Pebbles are abundant and of diverse lithology. The mass accumulation rate of sand fluctuates and includes rounded quartz grains. From 0.76 Ma to recent, the number of pebbles is low and they plot within the basal transport field. The sand accumulation rate is similar in magnitude but rounded grains are not present from 0.76 to 0.2 Ma. Observed changes in ice rafted pebbles and sand can be explained by growth of an ice sheet and topographic inundation of the Antarctic Peninsula around 0.76 Ma. Prior to this, outlet and valley glaciers transported debris at high levels within and at the base of the ice. Ice sheet growth may have been accompanied by overall cooling from subpolar to polar which halted meltwater production (as indicated by rounded quartz sand) and growth of ice shelves which reduced sediment supply to icebergs.
Coverage:Geographic coordinates:
West:-78.3000East: -56.3000

Quaternary geology; Antarctic Peninsula; Antarctica; Cenozoic; clastic sediments; continental rise; cores; correlation; deposition; glacial geology; glacial transport; glaciation; ice shelves; icebergs; Leg 178; magnetostratigraphy; meltwater; mineral composition; Neogene; Ocean Drilling Program; ocean floors; pebbles; Pleistocene; Pliocene; Quaternary; roundness; sand; sediment supply; sediment transport; sedimentation; sedimentation rates; sediments; shape analysis; Tertiary; textures; topography;