Petrographic differentiation of depositional environments of sandstones of the Pennsylvanian Breathitt Formation, northeastern Kentucky and southwestern West Virginia

Abstract

Petrographic properties of sandstone samples from the lower and middle Pennsylvanian Breathitt Formation in northeastern Kentucky and southwestern West Virginia were utilized to classify their environments of deposition. Simultaneous consideration of mineral composition, grain size, and sorting of the sandstones by using stepwise multiple discriminant-function analysis has permitted differentiation between alluvial-plain and delta-plain sandstones. Stepwise multiple discriminant-function analysis of the sandstone samples- was performed in two parts. The first analysis assigned the sandstones of all grain-size classes to one of three environments of deposition: (1) alluvial plain, (2) upper delta plain, and (3) lower delta plain. The second analysis classed the sandstones by grain size and subdivided each grain-size class into these environmental groups. Discriminant analyses of sandstones of all grain-size classes led to correct assignment of depositional environment to 76 percent of the samples. Analyses of the sandstones classed by grain size led to correct classification of 67 percent of the medium-grained sandstones, 83 percent of the fine-grained sandstones, and 91 percent of the very fine grained sandstones. The discriminantfunction method was adopted to classify the depositional environment and stratigraphic position of test sandstone samples. Analyses of fine-grained and very fine grained sandstones resulted in correct classification of 84 percent of the test samples to their depositional setting and stratigraphic position. The best discrimination is offered by analyses of fine-grained sandstones, which resulted in correct classification of 88 percent of the samples. Thus, this statistical method can be adopted as a powerful tool for exploration programs that concern delineation of genetically similar sandstones.