Abstract

This chapter introduces the key aspects of mudstone and the naming scheme we recommend and use when characterizing mudstone in outcrops, cores, and thin sections. This naming scheme is based on three key rock attributes: texture, bedding, and composition. This scheme has been designed to enable textural (grain size), bedding, compositional, and grain origin attributes to be captured and compared consistently for the entire spectrum of fine-grained sedimentary rocks and across a range of scales—from hand specimen to scanning electron microscopy image. Texture, composition, bedding, and grain origin are important for the following reasons:

• They reveal depositional conditions and environments (e.g., provenance, transport, reworking, and burial).

• They provide a tie to well-log and seismic data.

• They can be used in stratigraphic context to recognize long-term and large-scale depositional trends (i.e., vertical stratal stacking patterns and map views). These trends are then used to recognize large-scale stratigraphic packages and surfaces (e.g., parasequences, sequences, flooding surfaces, and sequence boundaries), whose stacking in a sequence-stratigraphic framework reveals the basin-fill history.

• They link rock properties of economic interest to key economic variables: total organic carbon, hydrogen index, porosity, permeability, seal capacity, and geomechanical attributes (e.g., Poisson’s ratio, Young’s modulus).

This chapter presents the key aspects of texture, bedding, and composition; guidelines for describing these aspects; and applications and complications of this approach. Lazar et al. (2022a, Chapter 3 this Memoir) provides an overview of the tools and practical workflows we use to facilitate consistent, repeatable, and efficient capture of mudstone texture, bedding, and composition in outcrops, cores, and thin sections.