Laterite is an iron-rich, subaerial, weathering product, commonly believed to develop as a result of intense, in situ substrate alteration. It comprises an important subset of a wider range of ferruginous and related aluminous (i.e., bauxitic) weathering products. Laterites owe their chief compositional characteristics to the relative enrichment of iron (and often aluminium), and the other less mobile parent rock constituents. This enrichment occurs under aggressive weathering conditions as a consequence of the greater mobility, and hence loss, of constituent silica, alkalis, and alkaline earths (Widdowson 2009). Diagenetic physicochemical conditions reflect the climate regime. In arid to semi-arid areas, low annual precipitation creates an overall oxidizing environment, under which detrital magnetite is replaced by red-coloured hematite and hematite remains unaltered. Redbeds are notable in Gondwanan Triassic strata (Fig. 8). 2. Paleogeography The worldwide synchronous switch from meandering to high-energy braided rivers, along with the expansion of alluvial fans at the Permian-Triassic transition has been documented (for example, in Russia, the Karoo Basin, and Australia). This change in fluvial style is consistent with the transition to Triassic aridity and mass wasting, and is against a background of global marine regression (Valentine and Moores 1970). In addition, soil carbonate oxygen isotope (δ18O), carbon isotope (δ13C), and geochemical signatures of weathering intensity provide evidence for a consistent pattern of deteriorating environments (Zhu et al. 2019). Lacustrine basins can be recognised by their morphology, commonly fine-grained sediments, together with the absence of marine faunas (Picard and High 1972; Selley 1978). Lacustrine basin fossils may instead include freshwater bivalves and freshwater algae (Hallam 1981). Organic facies and geochemistry also provide evidence for lacustrine sediments (Michaelsen and McKirdy 1989). The successive widening of Triassic arid and semi-arid belts of a suFigure 9. Map and cross-section through the Collie Basin, which is an outlier of the Perth Basin (after Le Blanc Smith 1993). DICKENS Flood Waters Lead to Seafloor Spreading 2023 ICC 456
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