Dr. Brenda Hall, Institute for Quaternary and Climate Studies and Department of Geological Sciences, Bryand Global Science Center, University of Maine, Orono, ME 04469 USA (brendah@maine.edu)

Neoglacial moraines are preserved at several locations in the South Shetland Islands (i.e., Clapperton and Sugden, 1988 and references therein; Lopez-Martinez et al., 1992; Birkenmajer, 1994; Martinez de Pison et al., 1996). These moraines represent relatively minor expansion of small alpine glaciers, as well as of ice caps on King George and Livingston Islands. Chronology for the moraines generally comes from bracketing ages derived from raised beaches. At many sites in the South Shetland Islands, raised beaches occur to higher elevations outside of the moraines than within them. For example, at some locations, the marine limit within the moraines is at 6 m elevation, whereas higher beaches occur immediately outside. Coupled with the fact that tills in the area commonly contain reworked beach material, this geometric relationship suggests readvance before or coincident with the age of the highest beach within the moraines, but after the age of the next highest beach, located outside. Based on these relationships, several researchers (see above refs.) have suggested two or more glacial readvances during the period known elsewhere as the Little Ice Age.

Ice-rafting records yield information regarding glacial extent and paleoclimate. Large amounts of ice-rafted detritus (IRD) suggest glacial expansion and/or colder water temperatures. Our preliminary data from the South Shetland Islands indicate strong variations in the amount and origin of IRD through the mid and late Holocene. On Byers Peninsula, the number and composition of boulders on the beach surfaces vary markedly. Such boulders occur only rarely within the beaches themselves, which are composed of stratified sand and gravel. Moreover, they are clustered on the front or foreslope of the beaches. Therefore, we believe that the boulders were ice-rafted and not reworked from locally derived sediments. To assess the variations in IRD, we counted and determined the lithology of boulders on five different beaches, ranging from 2.0 m to 10.5 m above mean sea level. The modern beach displays few ice-rafted boulders and, of those present, all are of local origin. The 5-m beach, however, has abundant boulders, with up to 15% being either from farther east on Livingston I. or from the Antarctic Peninsula. IRD is very common on the 9-m beach, but is nearly absent on the 10-m beach. Dating is underway; some previous dates suggest that all of these beaches are younger than about 3000 14C yr B.P. The increase in IRD recorded by the 5-m beach may correspond to Little Ice Age glacial advances.

References
Birkenmajer, K., 1994. Quaternary geology at Lions Rump (SSSI # 34), King George Island, South Shetland Islands (West Antarctica): Bulletin of the Polish Academy of Sciences, v. 42, p. 207-220.
Clapperton, C.M., and Sugden, D.E.,1988. Holocene glacier fluctuations in South America and Antarctica: Quaternary Science Reviews, v. 7, p. 185-198.
John,B.S., and Sugden, D.E., 1971. Raised marine features and phases of glaciation in the South Shetland Islands: British Antarctic Survey Bulletin, v. 24, p. 45-111.
Lopez-Martinez, J., Martinez de Pison, E., and Arche, A., 1992. Geomorphology of Hurd Peninsula, Livingston Island, South Shetland Islands, in, Recent Progress in Antarctic Earth Science, Y.Yoshida, ed., p. 751-756.
Martinez de Pison, E., Serrano, E., Arche, A., and Lopez-Martinez, J., 1996. Glacial Geomorphology, in, Geomorphological Map of Byers Peninsula, Livingston Island, BAS GEOMAP 5A, p. 23-27.