ABSTRACT

In subsurface studies, clues from various disciplines can be integrated to identify regional and local environments of deposition. Paleoenvironments that can be identified include deltaic plain, open shelf, littoral zone, distal bar, long shore bar, swamp, lagoon, and fluvial channel system. The accuracy of interpretations is governed by the types of samples available, types of disciplines applied, spacing of control wells and the experience and imagination of the interpreters. The confidence level ordinarily ranges from 80 to 95% for Tertiary and younger strata and from 70 to 95% for pre-Tertiary environments of deposition.

Since paleoenvironments resulted from the interaction of climatic, physical, chemical and biotic factors, each must be evaluated separately and in combination. The physical-chemical system is determined from the mineralogy, textures, sedimentary structures, and trace chemical gradients ascertained with petrologic, X-ray mineralogy and geochemical methods. These methods are applicable to the study of all environments. Palynology utilizes pollen and spores and other plant and animal microentities. Their abundance in sediments permits statistical applications to paleoecological as well as stratigraphic problems. Evaluations are principally botanical with an environmental range of terrestrial to open marine shelf. Fossil fauna assemblages utilized are chiefly marine and contribute information concerning water depths, salinities, and turbidity. For each specific environment, one discipline dominates the interpretation and others increase the confidence level.

Interpretive procedures are illustrated by studies of the following: (1) a regressive marine wedge in the Miocene sediments of Terrbonne Parish, Louisiana, (2) supralittoral, littoral, sub-littoral sequences in the Oligocene sediments of Starr County, Texas, and (3) a channel system in the Lower Tuscaloosa (Cretaceous) sediments of Amite County, Mississippi.