Geochemistry of Late Cambrian-Early Ordovician fluvial to shallow marine sandstones, western Tasmania, Australia: Implications for provenance, weathering, tectonic settings, and chemostratigraphy

抄録

A geochemical study of the Late Cambrian-Early Ordovician sandstones exposed in the West Coast Range, Tasmania, Australia, was carried out to develop an understanding of the provenance and tectonic settings. The average composition of these sandstones displayed high SiO₂ (92.72%), moderate Al₂O₃ (3.34%) and Fe₂O₃ (1.71%), low K₂O (0.90%) and MgO (0.15%), and very low CaO and Na₂O (<0.01%) concentrations. The sandstones were mainly classified as quartzarenite, and some samples were classified as sublitharenite. Tectonic discrimination diagrams based on major and trace elements suggest passive margin settings. Provenance diagram (Al₂O₃ vs. TiO₂) revealed that the Owen Group was derived from a silica-rich source. The average chemical index of alteration (CIA) was 78.45, indicating that the source area suffered severe weathering due to persistent warm and humid climate. High amounts of rare earth elements (REE) and strong negative anomalies on the chondrite-normalized REE pattern indicate an oxidizing deposition environment. The trace element chemostratigraphy reflects sharp contrasts in concentrations, distinguishing the unconformity between the lower and upper sequences and also shows the effect of alteration assemblages.