Bullion Creek and Sentinel Butte formations: a study of relative dating and specimen descriptions from near Cartwright, North Dakota

Abstract

Makenzie County in North Dakota, especially near Cartwright has not been explored by paleontologists for some time and never in great detail, yet the area is full evidence of the past. This paper focuses on the period of time between 50 and 65 million years ago when the area was believed to be a swampy sub-tropical forest skirting an inner continental seaway. It is the purpose of this paper to determine, through rock description and fossil leaf identification, the formation or formations present in this area of focus. These formations will in-turn pinpoint the time period in which the exposures were deposited. Identification of leaf impressions and molds are based on 9 key identifiers; lamina width and length, type of margin, lobation, apex and base type, apex and base angle, and vein pattern. Fossil leaf specimens can be identified to the class Magnoliopsida and other family levels, such as Taxodiaceae, Ulmaceae, Alismaceae, Betulaceae, and Sabiaceae. Additionally, some leaf specimens can be identified to the genus and species levels, including Metasequoia occidentalis, Ulmites microphylla, Alismaphyllites grandifolius, Meliosma vandaelium, and Corylus insignis. Fossils were collected on private land just outside Cartwright North Dakota where they were prepped for transport. In the lab setting they were cleaned, cataloged, and identified for the purpose of relative dating. These results demonstrate that both Sentinel Butte and Bullion Creek formations are present in the study area.