5 - Sedimentary Structures

Abstract

This chapter describes the internal megascopic features of a sediment. These are termed sedimentary structures, and are distinguished from the microscopic structural features of a sediment. Sedimentary structures are divided into primary and secondary classes. Primary structures are those generated in a sediment during or shortly after deposition, whereas secondary sedimentary structures are those that form sometime after sedimentation. The chapter discusses various examples of both primary and secondary structures. Primary sedimentary structures are divisible into inorganic structures, and organic structures. The observation, interpretation, and classification of inorganic sedimentary structures are considered. The chapter describes two basic approaches to observe sedimentary structures. The first approach is to pretend the outcrop is a borehole and to measure a detailed sedimentological log. This records a vertical section of limited lateral extent. The second method is to create a two-dimensional survey of all, or a major part, of the outcrop.