Palaeoenvironmental significance and pathways of calcrete development investigated with nuclear and related methods

The genesis and development of calcretes are discussed by using nuclear and related methods of analyses. In the studied calcrete, smectite is the main clay mineral associated with palygorskite. Chemical elements proportions, particularly V, U, Mn, Cu, Ba and REE, indicate a change to more oxidizing conditions and the contribution of bio-mediated processes in the oxalate-carbonate pathway, also confirmed by the presence of needle-fibre calcite. The proposed pathways leading to the studied calcrete development comprise both abiotic and biogenic genesis, emphasizing the polygenetic character due to different agents and processes and the paleoenvironmental trend towards aridification, with a transition between lacustrine and palustrine environments.