Fabric of muds and shales: an overview

Summary This contribution essentially constitutes an attempt to update a previous review of clay sediment microstructure written over a decade ago. Recent developments in this field are considered and a scheme has been developed in which the fabric of argillaceous sediments is traced from its inception during sedimentation and its subsequent modification at and below the depositional interface. It is held throughout that the primary control in the determination of clay fabric is the chemical environment that prevails during and after the deposition of the sediment. Consideration of the evidence from a variety of sources suggests that fissility in mudrocks is the result of an anisotropic microfabric in which clay aggregates are preferentially aligned. This microstructure is thought to result from the dispersing action of organic compounds common in certain sedimentary environments; a brief discussion of these compounds is included. Other factors are also taken into account which have been offered as the cause of differing mudrock fabrics.