Salinity episodes and their reversal in the late Pliocene of south-western Australia

Fossil pollen and grain size analysis of sediments from Yallalie in south-western Australia is used to reconstruct the history of salinization and aridity of the region between 2.63 and 2.56 Ma. Three well-defined episodes of aridity are defined by a reduction in humid woodland and expansion of chenopod shrubland around 2.59, 2.56 and 2.558 Ma. Each episode lasted an estimated 2-3000 years. The grain size data supports the general aridity conclusion but also demonstrates there was a large amount of environmental variability, especially between about 2.59 and 2.56 Ma, which included short term wetting and drying cycles. These cycles are at sub-Milankovitch time scales and suggest that the vegetation patterns show much more inertia to change than do the sediment dynamics. The general pattern of change at Yallalie is similar to that revealed in the Chinese Loess and Red Clay sequence but the detail of change is much greater in the lake sediment than revealed for the aeolian sediment of central Asia.