Sedimentary Environment

Geologists associate subenvironments with specific sediment features by observing modern sedimentary environments and the resulting sediments. These features include sediment composition, sediment texture (size, shape and sorting), vertical changes in grain size, and various sedimentary structures such as wave and current ripples, desiccation cracks in mud, plant and animal remains, and bedding thickness. The assortment of sediment features that is typical of a particular subenvironment is called a sedimentary facies.

Geologists compile characteristic facies from each sedimentary environment and produce what is called a facies model. A facies model may be a complex diagram, a table of information, or simply a detailed verbal description. It indicates which sedimentary features characterize a particular environment, and the lateral and vertical distribution of facies within sedimentary deposits.

Geologists use facies models for paleoenvironmental reconstruction—deducing the environment where sediments or sedimentary rocks originate. This is useful for predicting the distribution of economically important earth materials, such as gold, tin, coal, oil, or gas, in a sedimentary deposit. When doing paleoenvironmental reconstructions, geologists look for sources of variation in environmental conditions. For example, rising sea level or a decreasing sediment supply influence the sediment deposit formed, so facies models are altered accordingly. Geologists constantly work on refining facies models to improve the accuracy of paleoenvironmental reconstructions.