Cambrian and Ordovician Stratigraphy and Oil and Gas Possibilities in Indiana

Abstract

Cambrian and Ordovician rocks throughout most of Indiana are subdivided in ascending order as follows: lower part of the St. Croixan series, consisting of the Mt. Simon sandstone and the Eau Claire formation, upper part of the St. Croixan series and the Canadian series consisting of the Knox dolomite; the Chazyan series consisting of the St. Peter sandstone and the Joachim dolomite; the Mohawkian series consisting of the Black River limestone and the Trenton limestone; and the Cincinnatian series consisting of the Eden group (undifferentiated) and the Maysville-Richmond group (undifferentiated).

The Mt. Simon sandstone, the Eau Claire formation and the lower part of the Knox dolomite may be facies that represent contemporaneous environments, respectively, of beach or littoral deposition, near-shore deposition, and offshore deposition. The St. Peter sandstone, was deposited unconformably on the eroded surface of the Knox and was succeeded by carbonate deposition until late Ordovician time. The Cincinnatian series represents shallow-water deposition where the physical and biological environments alternated rapidly between clear water and optimum conditions for life and muddy water and unfavorable conditions for life.

The Mt. Simon sandstone and the Eau Claire formation are virtually untested for oil and gas, although the Mt. Simon has ideal reservoir characteristics of the "blanket-sand" type, and the Eau Claire exhibits rapid local changes in porosity which might serve to localize accumulations of oil or gas. The Knox dolomite contains highly permeable zones, and many shows of gas have been reported, although commercial production is lacking. The St. Peter sandstone has been considered a good prospect for oil or gas, but remarkably few shows of either have been reported. Any oil or gas found in the Black River most likely will be in local dolomitized lenses. Additional Trenton production might be found in northern Indiana, where the formation consists of dolomite, and possibly in southern Indiana, where the formation contains interbedded shale. Only a few shows have been reported from Cincinnatian rocks, and possibilities are not attractive because of the lack of good reservoir rocks.