Petrography and mineralogy of the Wessex Basin: palaeoclimate and palaeoenvironments of Lower Cretaceous in southern England

The Wessex Basin has been the focus of extensive studies on vertebrate palaeontology and is globally famous for dinosaur remains. Nevertheless, detailed mineralogical and petrographic studies have however been recently focused on the adjacent Weald Basin. An integrated approach comprising optical microscopy, scanning electron microscopy, energy dispersive spectrometry and Quantitative Evaluation of Minerals by Scanning Electron Microscopy were used to study the sandstones, mudstones and ironstones within the basin. Feldspathic and quartz wackes, subarkose and quartz arenites are the sandstone types identified. The results revealed a high quartz content with little feldspar concentration that is largely of K-feldspars and Na-rich plagioclase. Heavy minerals include rutile, tourmaline, zircon, apatite, ilmenite, olivine, amphibole, pyroxene, magnetite, monazite, epidote, and garnet. Compositionally, the sandstones are sub-mature to super-mature while they range from immature to submature texturally. The presence of apatite within the sandstones indicates that the sediments have not been affected by any significant post-depositional diagenetic modifications at the site of deposition. The significant concentrations of heavy mineral suite of garnet and rutile indicate metamorphic origin for the sediments within the Wessex Basin with a possibility of mixture of metamorphic and igneous materials at the source areas. The high monocrystalline quartz content, with subordinate K-feldspars and heavy mineral concentration indicates that they have been recycled from older sedimentary materials within the source massifs. The textural maturity of the sandstones reflects moist and warm climatic conditions that favoured a high degree of weathering and transport processes that have removed most of the unstable grains.