New Publication on Silurian Deposits in Mt. Auburn Trend

Cover of Circular 577. Click on the image to purchase this online.The Illinois State Geological Survey has released Circular 577, Sedimentology and Reservoir Characterization of the Silurian Deposits in the Mt. Auburn Trend of the Sangamon Arch, West-Central Illinois, coauthored by Yaghoob Lasemi, Beverly Seyler, Zakaria Lasemi, and Zohreh Askari Khorasgani. The report documents petroleum reservoir characterization of the Silurian Racine Formation in the Mt. Auburn trend. The Mt. Auburn trend encompasses several oil fields (Forsyth, Decatur, Harristown, Blackland North, Blackland, and Mt. Auburn Consolidated), which have produced hydrocarbon for more than 80 years. This regional subsurface study began in late 2007, in conjunction with a long-term ISGS research project on the Silurian through Devonian succession in the Sangamon Arch and the surrounding areas. Detailed subsurface studies have revealed that several dolomitized reservoirs in the upper part of the Niagaran Racine Formation (equivalent to Moccasin Springs Formation of southern Illinois) are the petroleum producers in the Mt. Auburn trend along the southeastern flank of the Sangamon Arch. A prominent unconformity subdivides the Racine Formation into two depositional sequences; the upper part comprises several producing dolomitized skeletal carbonate facies and coral patch reef/reef-related facies. Hydrocarbon production to date has been chiefly from the carbonate reservoirs in the uppermost part of the upper sequence of the Racine Formation.

Although most of the wells drilled thus far in the Mt. Auburn trend have only tested the upper sequence, this study indicates that the lower Racine sequence also has excellent potential for additional discoveries. Results also indicate that (1) a northwest-southeast gently sloping carbonate ramp existed during the deposition, and (2) sea level fluctuations and early dolomitization controlled reservoir development and petroleum entrapment in the Silurian rocks of west-central Illinois. Various maps and stratigraphic cross sections and proposed models for depositional setting, dolomitization, and cyclicity provide important predictive tools for petroleum exploration in the Mt. Auburn trend and the surrounding areas. Note: this circular can be purchased on our Shop ISGS site.