Cainozoic stratigraphy, palaeoenvironments and geological evolution of the Lake Eyre Basin

Abstract

For a large part of inland Australia weathering and erosion prevailed from the Cenomanian to the Late Paleocene. Subsidence commencing in the Late Paleocene produced a depocentre, the Lake Eyre Basin, in which sedimentation occurred in three main phases: (1) fluviolacustrine sand, silt, clay and carbonaceous horizons from latest Paleocene to Middle Eocene; (2) dolomite and magnesium-rich clay and sand deposited in extensive shallow, alkaline lakes from ?latest Oligocene–Miocene; and (3) red clay, silt and sand were deposited in fluvial, lacustrine and aeolian settings during the Pliocene and Quaternary. Widespread weathering and silicification of sediments occurred in the Late Eocene–Oligocene and again in the Pliocene, the latter also accompanied by ferruginisation. The silcrete sheets were folded into broad domes 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 conditions. By the Middle Eocene vegetation had changed to localised riparian forest in valley bottoms and more open sclerophyllous woodland in the hinterland, indicating monsoonal conditions. For most of this early Tertiary interval 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 temperatures promoted the deposition of thick dolomites in giant alkaline lakes. The lakes and the diverse vegetation were home to a rich aquatic and terrestrial fauna. By the Pliocene, climate was semiarid and vegetation mainly open Casuarinaceae-dominated woodland with very rare stands of forest confined to 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 conditions during the glacials, particularly the last, led to the development of extensive dunefields.