STRATIGRAPHIC ANALYSIS OF THE CRETACEOUS EAGLE COAL IN ELK BASIN WYOMING WITH XRD AND XRF

X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) are used to analyze chemical composition of the peats and lignite within the Eagle Formation at Elk Basin Oil Field, Wyoming and Montana. Due to their poor economic viability, the depositional environments and lithologies of the coals are poorly studied and understood. However, these lithofacies are important to understanding the environmental processes influencing coal formation in the Eagle Formation. This study contributes to ongoing research that investigates paleoenvironments of the Wyoming Cretaceous through chemostratigraphic techniques.

The sandstone units located in the Elk Basin oil field of northern Wyoming and southern Montana document transgressive-regressive cycles of the Western Interior Seaway during the Upper Cretaceous. The Eagle Formation, composed primarily of sandstones with iron concretions, was deposited during a regressive series. The Eagle contains sporadic coal seams of peat and lignite that are well-exposed.

This study applies X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) techniques to analyze chemical composition of the peats and lignite present within this site. The use of XRF in this study focuses on recognizing associations between the Eagle coal seams and the occurrence of trace elements. It is anticipated that elemental occurrences will vary by coal type in a predictable manner and potentially display patterns that can be associated with depositional conditions. XRD is used for identifying the crystalline constituents within the samples to narrow down the composition of the coal samples.

The stratigraphic layering within the Eagle suggests changing environmental conditions likely influenced by the Western Interior Seaway. Deposition of beds occurred in a deltaic environment with deposition of restricted embayments during the regression contributing to the observed variety of low-grade coal types. Well-exposed outcrops on the Wyoming side of the basin contains alternating layers of peat and lignite capped by a shale.

The results collected from this study assist with the interpretation of environmental and geological processes influencing coal formation in the Eagle Formation and contributes to ongoing research that investigates paleoenvironments of the Wyoming Cretaceous through chemostratigraphic techniques.