Item Number: OP31
Map Scale: 1:236,418

The post-Knox unconformity provides the principal trapping conditions for underground gas storage at Unionport in Randolph County. Erosion remnants of the porous Knox Dolomite protrude upward into the overlying impermeable Black River Limestone. Although the unconformity has long been recognized in Indiana, data for detailed mapping of its surface are lacking except at Unionport. Here about 50 wells drilled to the Knox outline a surface of steep-sided, ovate erosion remnants of limited lateral extent with vertical relief of about 150 feet. No drainage pattern is evident. The unconformity is postulated to have been developed in an arid environment with wind as the primary erosion agent. The erosion-induced irregularity of the post-Knox unconformity is only slightly reflected on the top of the Trenton Limestone. The composite thickness from the top of the Trenton to the top of the Knox ranges from 400 to 530 feet at the Unionport gas-storage project. Petroleum has been produced in Indiana, Ohio, Kentucky, and southern Ontario from erosion remnants associated with the post-Knox unconformity. We feel that petroleum deposits under similar geologic conditions exist in Indiana and that the crestal area of the Cincinnati Arch provides the most favorable general area for exploration.

Keller, S. J., and Abdulkareem, T. F., 1980, Post-Knox unconformity—significance at Unionport gas-storage project and relationship to petroleum exploration in Indiana: Indiana Geological Survey Occasional Paper 31, 19 p., 10 figs.

You may also like:

Keywords: Knox Dolomite, Black River Limestone, Trenton Limestone, gas, energy resources

Can't find what you're looking for? Feel free to contact us directly:

Indiana Geological and Water Survey
1001 E. 10th St.
Bloomington, IN 47405
812-855-7636 (phone)
812-855-2862 (fax)

IGS Return Policy

  • Original sales receipt required.
  • Returns accepted within 30 days of purchase date.
  • Refund will be issued by the same method of payment as purchased.
  • Products must be returned in the same new condition as purchased.
  • Refunds on custom orders and digital products are NOT allowed.
  • Customers are responsible for paying shipping costs to return products.

Updated 8/19/2020