Inter-Discipline Approach to Paleoenvironmental Interpretations: ABSTRACT

Abstract

In subsurface studies, unlike surface studies, specific environments of deposition can not be established reliably on the basis of sediment geometry because a sediment pattern can represent several environments. Clues from various disciplines can be integrated to identify regional and local environments--deltaic plain, open shelf, distal bar, longshore bar, lagoon, swamp, littoral zones, etc. 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% in Tertiary and younger strata but is in few cases more than 85% in older sediments. Because paleoenvironments resulted from the interaction of climatic, physical, chemical, and biotic factors, each factor must be evaluated in part 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 all environments. Palynology utilizes pollen and spores and other plant and animal micro-entities; their acid-resistant nature and abundance permit statistical applications to paleoecologic and stratigraphic problems. Evaluations principally are botanical with an environmental range of terrestrial to open-marine shelf. Fossil faunal assemblages chiefly are marine and contribute information abou water depths, salinity values, and turbidity. For each specific environment, one discipline End_Page 2320------------------------------ dominates the interpretation and other disciplines increase the confidence level. Interpretive procedures illustrated are: a regressive marine wedge in the Miocene sedimentary rocks of Terrebonne Parish, Louisiana; supralittoral, littoral, and sublittoral sequences in the Oligocene sedimentary rocks of Starr County, Texas; and a channel system in the Cretaceous lower Tuscaloosa sedimentary rocks of Amite County, Mississippi. End_of_Article - Last_Page 2321------------