Stratigraphic cross sections of the Niobrara Interval of the Upper Cretaceous Cody Shale in the Bighorn Basin, Wyoming and Montana

Scientific Investigations Map 3422
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Abstract

The Bighorn Basin is one of many structural and sedimentary basins that formed in the Rocky Mountain foreland during the Laramide orogeny. The basin is nearly 180 miles long, 100 miles wide, and encompasses about 10,400 square miles in northern Wyoming and southern Montana. The basin is bounded by major basement uplifts that include the Pryor uplift on the northeast, the Beartooth uplift on the northwest, the Bighorn uplift on the east, and the Owl Creek uplift on the south. The northern margin includes a zone of faulting and folding referred to as the Nye-Bowler lineament. The western margin is formed by volcanic rocks of the Absaroka Range.

Many important conventional oil and gas fields producing from reservoirs ranging in age from Cambrian through Tertiary have been discovered in this basin. In addition, an extensive unconventional overpressured basin-centered gas accumulation may be present in Cretaceous strata in the deeper parts of the basin. It has long been suggested that various Upper Cretaceous marine shales, including the Cody Shale, are the principal hydrocarbon source rocks for many of these accumulations. With recent advances and success in horizontal drilling and multistage fracture stimulation, there has been an increase in exploration and completion of wells in these marine shales in other Rocky Mountain Laramide basins that were traditionally thought of only as hydrocarbon source rocks.

The stratigraphic cross sections presented in this report were constructed as part of a project carried out by the U.S. Geological Survey to characterize and evaluate the undiscovered continuous (unconventional) oil and gas resources of the Niobrara interval in the lower part of the Upper Cretaceous Cody Shale in the Bighorn Basin. These cross sections were constructed using borehole geophysical logs from wells drilled for oil and gas exploration and production. The stratigraphic interval extends from the upper part of the Frontier Formation to the middle part of the Cody Shale. The datum is the base of the “chalk kick” marker bed, a distinctive resistivity peak or zone in the lower part of the Cody Shale. A gamma ray and (or) spontaneous potential log was used in combination with a resistivity log to identify and correlate units. Marine molluscan index fossils collected from nearby outcrop sections were projected into the subsurface to help determine the relative ages of the strata and aid in correlation.

Suggested Citation

Finn, T.M., 2019, Stratigraphic cross sections of the Niobrara Interval of the Upper Cretaceous Cody Shale in the Bighorn Basin, Wyoming and Montana: U.S. Geological Survey Scientific Investigations Map 3422, pamphlet 19 p., 1 sheet [cross section], https://doi.org/10.3133/sim3422.

ISSN: 2329-132X (online)

Study Area

Table of Contents

  • Introduction
  • Depositional Setting
  • Stratigraphy
  • Acknowledgments
  • References Cited

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Stratigraphic cross sections of the Niobrara Interval of the Upper Cretaceous Cody Shale in the Bighorn Basin, Wyoming and Montana
Series title Scientific Investigations Map
Series number 3422
DOI 10.3133/sim3422
Year Published 2019
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Central Energy Resources Science Center
Description Pamphlet: iv, 19 p.; Sheet: 52.00 x 29.51 inches
Country United States
State Montana, Wyoming
Other Geospatial Bighorn Basin
Online Only (Y/N) Y