Reconsideration of the Richardson Clay with subglacial defoming bed at an outcrop at the northern foot of Mt. Riiser-Larsen, West Enderby Land, East Antarctica

Abstract

Outcrops bearing clayish stratified sediments at the northern foot of Mt. Riiser-Larsen, West Enderby Land, East Antarctica (named "Richardson Clay" by M. Hayashi, Proc. NIPR Symp. Antarct. Geosci., 4,119,1990) have been observed by several authors of the Japanese Antarctic Research Expeditions (JAREs). The Richardson Clay occurs as an interbed within a thick layer of angular gravels interpreted as glacial deposits. In a 1-day short visit of JARE-35 to this outcrop, several additional features of the sediments were identified, contributing to reconstruction of the former sub-ice sheet environment and historical change in this region. The most notable points are 1) the Richardson Clay layer has boundary layers between the Richardson Clay and gravel layers above and below it, and 2) these three layers have significant deformed structures. Recent development of the knowledge on subglacial geological processes suggests that these features were affected by glacial motion and glacial erosional, depositional and sedimentary processes. The Richardson Clay appears to consist of glacilacustrine sediments deposited on the bottom of a proglacial lake which appeared between two glacial advances. However, whether these advances were part of a small terminus fluctuation of a major glaciation or two distinct different glaciations has not been evaluated yet. Nevertheless, we provisionally define these layers as the Richardson Till. Consequently, it is strongly recommended that further investigation of these sediments should be conducted to reconstruct the ice sheet fluctuation in this region and to obtain general information for studies on subglacial geological processes.