HOLOCENE PALEOENVIRONMENTS NEAR LAKE TYRRELL, SEMIARID NORTHWESTERN VICTORIA, AUSTRALIA

Pollen analyses from the playa Lake Tyrrell in semi-arid northwestern Victoria, Australia record major environmental changes during the Holocene. Amerioration of arid Pleistocene climates after 10,000 BP converted Lake Tyrrell from a dry deflationary basin to an ephemeral lake surrounded by Allocasuarina dominated woodlands with a grass understorey. A marked increase in rainfall at about 6600 BP transformed the lake from an ephemeral to a permanent water body. This increase in rainfall coincided with the migration of mallee vegetation to the region, a rapid expansion in Callitris populations and development of a more active fire regime. Drier conditions prevailed between 2200 BP and 800 BP but mallee remained the dominant vegetation. Fully modem conditions date from 800 BP. The magnitude of Holocene environmental change reported from Lake Tyrrell is greater than that usually recognized from sites in humid southeastern Australia. A comparison of conclusions drawn from Lake Tyrrell with previously published accounts from Lake Frome suggests that significant Holocene environmental change was widespread in the semi-arid lands of southeastern Australia.