A classification scheme for shale clasts in deep water sandstones

Abstract

Abstract Shale clasts are widespread in turbidites and associated facies of all ages. They may yield important information regarding the depositional process of the host sandstone and its specific environmental setting. Previous work has tended to generalize the variety of shale clasts that exist and no comprehensive classification has yet been developed. The scheme proposed here is a descriptive classification based on the nature and arrangement of shale clasts within mainly structureless sandstones. Twelve types of clasts are recognized on the basis of the clast’s position in the bed and/or characteristic features, and these have been grouped according to whether they have been derived from either basal erosion or disturbance (Group A), flow modification (Group B) or post-depositional disturbance (Group C). These clasts have also been organized into characteristic assemblages which are thought to be indicative of particular depositional environment. The classification scheme when used in association with facies analysis can provide an additional tool for core investigations, contributing to the understanding of permeability barriers and relevant architecture.