Geochemistry and mineralogy of the Lower Cretaceous of the Lusitanian Basin (western Portugal): Deciphering palaeoclimates from weathering indices and integrated vegetational data

Abstract

The present study investigates the climatic influence on the geochemistry and mineralogy of the Lower Cretaceous succession of the Ericeira region (Lusitanian Basin, western Portugal). Palaeoclimatic conditions are inferred from a combination of weathering indices and independent palynological and palaeobotanical data. A composite weathering intensity index is computed from selected geochemical and mineralogical data. The concentrations of some elements (Co, Ni, Sc, Th, V, Y, Zn, Zr) indicate variable contributions of sediments from the Lusitanian Basin margin and Iberian hinterland. It is demonstrated that the weathering intensity values are largely influenced by source area geology. The increases in weathering intensity following major unconformities (Late Barremian and Late Aptian) are partially attributed to the arrival of detritus from an evolved regolith sequence in the Iberian hinterland. A combined analysis of independent proxies is found necessary to conveniently discern the roles played by distinct processes on the weathering intensity and investigate the palaeoclimatic conditions.