Introduction

Few subjects in the field of sedimentology have been researched more thoroughly than sedimentary textures. This strong interest in sedimentary textures has apparently arisen out of the conviction of many workers that sedimentary texture is a valuable tool for environmental analysis. The sizes, shapes, and arrangement (fabric) of siliciclastic grains have been examined and reexamined over a period of decades in an effort to establish through empirical and experimental studies the validity of this assumption. Unfortunately, this goal of environmental interpretation remains elusive, and many problems still beset investigators who attempt to use sedimentary texture as a tool for environmental analysis. Nonetheless, texture is a fundamental attribute of siliciclastic sedimentary rocks. Along with other properties of these rocks, it helps to characterize and distinguish them from other types of rocks and it aids in their correlation. Furthermore, the texture of sedimentary rocks affects such derived properties of these rocks as porosity, permeability, bulk density, electrical conductivity, and sound transmissibility. These derived properties are of particular interest to petroleum geologists, hydrologists, and geophysicists.

Sedimentary texture encompasses three fundamental properties of sedimentary rocks: grain size, grain shape (form, roundness, and surface texture [microrelief] of grains), and fabric (grain packing and orientation). Grain size and shape are properties of individual grains. Fabric is a property of grain aggregates. The characteristics of each of these properties are explored in this chapter.

Grain size

Grain-size scales

Natural siliciclastic particles range in size from clay to boulders.