Composition of Lower Cretaceous mudstones of the Algarve Basin and implications for Iberian palaeoclimates

Abstract

Several compositional features of mudstones are controlled by climate-driven weathering and have been used to approximate palaeoclimatic conditions. Mudstone composition, however, is also influenced by the geology of the source areas and diverse depositional and post-depositional processes. The present geochemical and mineralogical study of the Lower Cretaceous (upper Hauterivian to Aptian) of the Algarve Basin (Southern Portugal) was performed to investigate the main factors that control mudstone composition and extract possible climatic signals. Clay mineralogy partially reflects diverse contributions of felsic vs. mafic and recycled materials, and the geochemical weathering proxies applied to the detrital component of mudstones are differently affected by provenance and hydraulic fractionation. Despite these facts, a wide set of compositional data allows some robust climatic interpretations. Apart from the early Aptian (Burgau Formation), when climate was probably wetter, hot and dry conditions prevailed in south Iberia during the investigated interval, with minimum humidity during the late Hauterivian–early Barremian (Salema Formation). Independent sedimentological and palaeontogical data support these interpretations. A comparison with compositional results for the Lusitanian Basin reveals substantially drier climates in southern than central and northern Iberia. Interpreted patterns of climatic evolution can be linked to shifts in air circulation from the sub-tropical high-pressure belt.