Geochemical analysis for palaeoenvironmental interpretations - a case study of the English Wealden (Lower Cretaceous, south-east England)

The elemental composition of terrigenous sediments is extremely important for interpreting the depositional conditions of sedimentary basins especially when traditional data are not available or insufficient. For the first time in the published literature, the elemental composition of the Lower Cretaceous Weald Basin (south-east England) is presented via X-ray fluorescence (XRF) and Spectral Gamma-ray (SGR) methods. The concentrations of Zr, Cr, Ni, Rb, and Sr in varying quantities suggest that the sediments may have been sourced from a stable craton while the enriched redox-sensitive elements such as Mo and Co confirm the presence of anoxic and reducing conditions at the sites of deposition. The spectral gamma-ray data show that the sandstone facies are more radioactive than the adjacent mudstone and shale and this trend is consistent with a freshwater origin. The higher quantity of thorium in relation to uranium indicates humid and hot palaeoclimatic conditions at the source areas that favoured intense weathering. The results of these analyses reinforce the importance of the geochemistry of sedimentary rocks as useful tools for understanding the depositional conditions of sedimentary basins.