Phytoliths reveal cycling Pleistocene climate changes at a Paleolithic site in the lower reaches of the Yangtze River, East China

Abstract

Phytoliths in the laterite profile of a Paleolithic site reveal Pleistocene climate variations in the lower reaches of the Yangtze River. Two group of phytoliths including chloridoid, panicoid, bulliform flabellate and saddle (long) phytoliths in the warm group, and festucoid, elongate entire and acute bulbosus phytoliths in the cool group are recognized. A warm index is calculated on the ratio of warm group to total warm and cool groups, and an aridity index on the ratio of chloridoid to total chloridoid and panicoid phytoliths. Climate indices of the phytoliths show at least 16 climatic stages indicating 8 warm-cool cycles, which are largely comparable with the variations between MIS-5 to MIS-23. It also reveals that the warm periods mostly correspond to the paleosols, while the cool ones to the clay and sandy layers. However, the relationship between the warm index and the aridity index is not clearly correlated, and chance for the occurrence of dry and less dry conditions is nearly the same under the warm or cool climate. Changes in aridity are more distinct and frequent at the lower part than at the upper part of the profile, and a changing tendency of less dry is recognized at the upper part of the profile. The overall warm indices of the profile are relatively higher in values. It suggests that frequent activities of early Pleistocene human beings took place under mild climate, especially during the dry and cool periods in the lower reaches of the Yangtze River area.