Cainozoic stratigraphy, palaeoenvironments and geological evolution of theLake Eyre Basin

For a large part of inland Australia weathering and erosion prevailed from the Cenomanian to the Late Paleocene. Subsidence commencing in the Late Pal eocene produced a depocentre, the Lake Eyre Basin, in which sedimentation o ccurred in three main phases: (I) fluviolacustrine sand, silt, clay and car bonaceous horizons from latest Paleocene to Middle Eocene; (2) dolomite and magnesium-rich clay and sand deposited in extensive shallow, alkaline lake s from ?latest Oligocene-Miocene; and (3) red clay, silt and sand were depo sited in fluvial, lacustrine and aeolian settings during the Pliocene and Q uaternary. Widespread weathering and silicification of sediments occurred i n the Late Eocene-Oligocene and again in the Pliocene, the latter also acco mpanied by ferruginisation. The silcrete sheets were folded into broad dome s during the Oligocene and again in the Pliocene, when faulting marginal to the southern ranges also occurred. From the Late Paleocene to Early Eocene the basin supported rainforest growing in megathermal to mesothermal condi tions. By the Middle Eocene vegetation had changed to localised riparian fo rest in valley bottoms and more open sclerophyllous woodland in the hinterl and, indicating monsoonal conditions. For most of this early Tertiary inter val deposition was by broad braidstreams flowing northwards. In the Miocene , scattered elements of megathermal forest still existed, but open woodland was far more extensive. Strong climatic seasonality and elevated temperatu res promoted the deposition of thick dolomites in giant alkaline lakes. The lakes and the diverse vegetation were home to a rich aquatic and terrestri al fauna. By the Pliocene, climate was semiarid and vegetation mainly open Casuarinaceae-dominated woodland with very rare stands of forest confined t o edaphically suitable sites. Increasing aridity during the Quaternary was punctuated by pluvial intervals. Vast lakes formed during the interglacials largely as a result of higher rainfall in Queensland. Drier, windier condi tions during the glacials, particularly the last, led to the development of extensive dunefields. (C) 1998 Elsevier Science B.V. All rights reserved.