Quantifying paleo-environments in the Eagle Formation using trace element concentrations

Abstract

In the past decade, our understanding of paleoenvironmental and climate record in sedimentary strata has been enhanced with the portable X-ray Fluorescence (XRF). Identification and correlation of trace elements concentrations (i.e. trace element chemostratigraphy) provides a valuable indicator of changing environments and climate over time and the response of sedimentary systems. The XRF is a non-destructive tool that is used to determine the elemental compositions of rock, sediment, and fluid materials. The use of a gamma ray scintillometer (GR) helps with detection of trace elements that may have attached themselves to the surface of fine-grained sediments. To date, most chemostratigraphic trace element studies have focused on fine-grained shale and carbonate units in shallow-marine environments. This study expands upon our knowledge of elemental abundances in course-grained clastic units found in terrestrial and deltaic settings. Doing so increases the application of trace element correlations to broader sedimentary environments. The unit selected for this study is the Cretaceous Eagle Formation exposed in a Cretaceous age anticline in the Elk Basin Oil Field. The oilfield is situated in northwestern Wyoming and southern Montana. The Eagle Formation is a light gray to tan coarse-grained sandstone with iron concretions, Diplocraterion, and Ophiomorpha structures. The chemostratigraphic profile created from collected XRF and GR data will be compared to previous published paleontologic and lithologic analyses of the Eagle Formation. Samples for this study were collected in November 2022 and analyzed during the 2022-23 year. Further field work in summer of 2023 will add to initial findings. Results from this study will be compared to the limited number of published chemostratigraphic studies from deltaic and terrestrial environments.