Textural and mineralogical characterization of the late Pliensbachian-early Toarcian sediments of the Cleveland Basin, Yorkshire, U.K.

Abstract

The compositional characteristics of shales are inherently variable and the governing controls and depositional processes resulting in different facies can be expressed by the texture and mineralogy of sediments. The development of quartz grain size and mineralogy over the late Pliensbachian–early Toarcian shale succession of the Cleveland Basin is investigated using Scanning Electron Microscopy combined with Energy Dispersive X-ray analysis (SEM-EDX) to determine the distribution and overall content of quartz grains, while the clay mineral composition, in both qualitative and (semi-) qualitative sense, is determined by X-ray diffraction analysis (XRD). Due to the small grain size and difficulties of processing well cemented shales, no full evaluation of quartz grain size distributions over the course of the entire succession, and their relationship to the clay mineralogy, has ever been established. The results indicate that the current lithostratigraphic subdivisions yield no resemblance to the variability of the sedimentological properties of the shales, as determined on basis of quartz grain size distributions and clay mineralogy.