Characteristics of Pennsylvanian Sandstones from Southwest Indiana—Implications for Distinguishing the Caseyville from the Tradewater Formation in Indiana Paper

Abstract

This study examines the mineralogical and stratigraphic traits of Pennsylvanian sandstones, focusing on differentiating the Caseyville Formation from the Tradewater Formation. More than 100 sandstone samples were collected from southwestern Indiana, with additional reference samples from Illinois, Kentucky, and western Indiana. Megascopic observations, X-ray diffraction, and petrography were supplemented by statistical methods, including PCA, t-SNE, and UMAP, to analyze compositional patterns.
Caseyville Formation sandstones are typically quartz-dominated, with medium- to coarse-grained sand and discontinuous conglomeratic layers. In contrast, Tradewater Formation sandstones are fine- to medium- grained sand and mineralogically heterogeneous, with significantly more feldspar and mica. UMAP clustering effectively separated the two formations, highlighting quartz content as a key discriminant. This mineralogical distinction led to refined stratigraphic assignments, reducing the mapped extent of the Tradewater interval and increasing the apparent extent of the Caseyville Formation.
The findings show that mineralogical characterization, especially the contrast between quartz dominance and heterogeneity, is a reliable method for distinguishing the sandstone components of these formations. However, some compositional overlap exists in paleovalley settings, indicating depositional complexity and local Caseyville heterogeneity.