Abstract
Lamination in shales is an important feature useful in providing clues to ancient sedimentary environments and processes. Variations in types of lamination in Toarcian (Lower Jurassic) shales of Yorkshire, Great Britain are related to changes in sedimentary processes. X-radiography, petrography, and scanning electron microscopy techniques reveal three lamination types in the dark grey (Grey Shales) and black (Jet Rock and Bituminous Shales) Jurassic shales. Fine lamination is produced in deeper, more offshore anaerobic conditions in which suspension settling dominates. Thick lamination indicates the influence of bottom flowing currents in shallow water. Wavy lamination is produced by benthic microbial mats. The Toarcian transgressive shale sequence shows a progressive change from thick to wavy to fine lamination relating to progressive changes in the sedimentary processes operating in the environment. The examples of various unique macro- and microfabrics associated with lamination type offer a useful frame of reference for interpretation of conditions of shale formation.
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