Search

This study presents new geochemical and mineralogical data collected on 13 drill holes across the South Australian part of the Eromanga Basin, with a focus on the Lower Cretaceous Cadna-owie Formation, Bulldog Shale, Coorikiana Sandstone and Oodnadatta Formation. Mineralogical and geochemical data are used to determine the provenance of the sediments along with the paleoenvironments at the time of deposition. The dominant clay species across the formations are kaolinite and montmorillonite, although each drill hole shows individual mineralogical assemblages. The Cadna-owie Formation is mainly composed of quartz and kaolinite; montmorillonite is the dominant clay species in the other formations. Differences in major-element chemistry are best shown on the K–Na–Ca ternary diagram and display a strong relationship with mineralogy. Trace and rare earth elements are preserved at similar average concentrations between formations and are depleted relative to the upper continental crust. The signature of the sediments is interpreted to be derived from a mix of felsic and mafic igneous rocks with almost no sedimentary recycling. Sources of the sediments are likely to be from exposed basement packages surrounding the study area such as the Gawler Range Volcanics, the Musgrave Province, the Benagerie Volcanic Suite, the Mount Painter Inlier and the Arunta Block. The variations in dominant clay species between the formations could have been driven by an increase in temperature and a decrease in rainfall during the Early Cretaceous along with seasonal variations, and/or by the input in volcanogenic sediments from the active volcanoes located along the eastern margin of Australia. Lower Cretaceous formations in the South Australian Eromanga Basin show limited regional lateral and vertical geochemical and mineralogical variations. Sediments are a mix of mafic through felsic igneous rocks derived from basement terranes exposed in the Early Cretaceous. The paleoclimate during deposition evolved from cold and humid to warm and arid. [ABSTRACT FROM AUTHOR]