Provenance, palaeoclimate and palaeoenvironments of a non-marine Lower Cretaceous facies: Petrographic evidence from the Wealden Succession

Abstract

Petrographic datasets from sedimentary rocks are very useful for reconstructing their palaeoenvironmental settings especially when field and fossil datasets are unobtainable or inadequate. This study presents the first detailed and comprehensive petrographic study of the four formations constituting the non–marine Lower Cretaceous of the Weald Sub-basin of south-east England and employed petrographic descriptions to reconstruct their palaeoenvironmental settings. >120 samples were subjected to petrographic (QEMSCAN®, SEM, and thin section) analyses, which revealed that the framework composition of sediments is largely quartz-dominated (quartz arenites and subarkose) and has minor amounts of feldspar and lithics. The nature of the quartz arenites suggests that the Wealden successions were likely sourced from a stable interior craton/passive platform within a continental block and possibly from recycled flat-lying platforms such as low-lying granitic and gneissic bedrocks. The nature, maturity and the compositions of the sandstones suggest palaeoclimatic conditions were probably mildly hot and moist at the massifs and these perhaps favoured intense chemical weathering. The significant quantity of micas suggests that the Wealden sediments largely experienced very insignificant degrees of turbulence and agitation en-route depositional sites, thus yielding unwinnowed sediments. The presence of micaceous minerals, poor winnowing effect, and the general absence of diagenetic glauconite validate non-marine depositional environments. The palaeoenvironmental changes that occurred in the Lower Cretaceous in the Weald Sub-basin reflect (at least in part) palaeogeographic changes in NW Europe.