Paleoclimatic Controls on Clay Mineral Distribution in the Early Cretaceous (Barremian): The Wessex Basin, Southeast England

This study describes the clay mineralogy of the Lower Cretaceous (Barremian) rocks of the Wessex Basin for paleoenvironmental interpretations. Seventy-four samples were subjected to optical microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN®) techniques. The results revealed an illite-dominated sedimentation in most sections of the basin, with kaolinite, chlorite, smectite and glauconite occurring in subordinate quantities. Inferred paleoclimatic conditions from the clay mineral trends indicates a warm and dry climate, with seasonal precipitation. Kaolinite to illite ratios indicate that more arid climate conditions were prevalent but brief periods of warm and humid conditions were also present. A strong positive correlation between chlorite and tourmaline indicates that excess chlorite may have been contributed from tourmaline-chlorite-schists in a tourmaline-dominated provenance. SEM confirms that most of the clay minerals are detrital in origin but authigenic kaolinite is also present as vermiform and mica-replacive kaolinite which formed during early diagenetic modification from flushing meteoric waters in warm humid climates. This study is significant because it demonstrates the importance of multi-proxy methods for understanding clay minerals within sedimentary basins for interpreting the paleoclimatic conditions of depositional systems.