ANTARCTIC GLACIAL AND GEOLOGIC HISTORY DETERMINED FROM ODP WEDDELL SEA CORES

A poorly dated and discontinuous record of late Eocene through early Pliocene sediment from ODP Sites 693, 694, and 696 in the Weddell Sea contains hemiplegic, turbidite and ice rafted sediment. Likely sources of this sediment are the South Orkney Islands, Droning Maud Land through the Filchner-Ronne ice shelf, and the Antarctic Peninsula. We examined sediment size and composition to generate a record of glacial advance and retreat around the Weddell Sea.

Grain-size analysis is used to distinguished turbidite (well sorted) and ice rafted (poorly sorted) sediments. Although not a perfect match, it is interpreted that turbidites were deposited during lower stands of sea level with large and possibly expanding ice sheets. In contrast, IRD is more likely to have been deposited when ice sheets were at their maximum extent or retreating. Using this data we have developed a sequence of expanding, stable, and shrinking ice to explain sand-size sediment delivery to these sites. This data shows an increase in coarse grain sized turbidites from the Miocene into the Pliocene, as well as similar increase in the average size of IRD during the same time period indicating larger, colder, and further traveled icebergs.

In addition to the grain size analysis, geochronological dating was completed on individual zircon and hornblende grains sampled from the same cores. The provenance of the grains was determined using known ages of Antarctic bedrock and through changes in ice flow off the continent through time. Our study shows that from the Middle Pliocene (~14 Ma) to the Early Pliocene (~4 Ma) ice rafted debris was being sourced further and further from the immediate Weddell Sea area and, most likely, sourced from increasingly eastern areas of the Dronning Maud Land. This data supports studies done in the Prydz Bay area of East Antarctica that show icebergs during the Miocene and Pliocene were far travelled and shows the first evidence this type of far travelled iceberg in the Weddell Sea area of West Antarctica.