Pleistocene climatic change in Southern Australia and its effect on speleothem deposition in some Nullarbor caves

Abstract

Abstract Activity ratios of 234 U/ 238 U, 230 Th/ 234 U, and 230 Th/ 232 Th have been determined for calcite, gypsum and halite speleothems from caves of the Nullarbor Plain, mostly in the area N and NW of Mundrabilla Station, for the purpose of U‐series dating. All calcite speleothems contain adequate amounts of uranium for dating, but some show an excess of 230 Th. Stratigraphic relationships indicate that there were at least three phases of calcium carbonate deposition in the Nullarbor caves. The calcite samples, with one possible exception, have ages in excess of ca. 400000 yrs BP. This suggests that no significant amounts of calcium carbonate deposition have taken place during the last 400ka. At present, active deposition of speleothems is restricted almost entirely to gypsum and halite. The only gypsum speleothem dated was found to have a finite age of ca. 185 ka. Six dates on a small halite speleothem containing insect and arachnid remains indicate that it formed rapidly during Holocene time.