In search of a Silurian total petroleum system in the Appalachian basin of New York, Ohio, Pennsylvania, and West Virginia
Oil and gas fields in Silurian carbonate and sandstone reservoirs in the Appalachian basin probably originated from one or more of the following source rocks: (1) Upper Ordovician Utica Shale, (2) Middle to Upper Devonian black shale, and (3) Lower to Upper Silurian shale and carbonate units. In this reconnaissance study, selected Silurian shale and carbonate rocks in the subsurface of New York, Ohio, Pennsylvania, and West Virginia were analyzed for total organic carbon (TOC) content and Rock-Eval parameters to evaluate whether or not a Silurian total petroleum system exists in the Appalachian basin. A total of 308 samples were collected and analyzed for this investigation. Dark-gray to black shale and argillaceous carbonate intervals in the Salina Group (and equivalent units), Cabot Head Shale, Rochester Shale, Rose Hill Formation, Lockport Dolomite (or Group), and McKenzie Limestone (or Member) were prioritized for sampling and analysis. Twenty nine of the 308 samples analyzed had TOC values of 0.50 or greater that qualify them as a petroleum source rock. Also, 24 of the 29 samples (with TOC values of 0.50 or greater) had TOC values between 0.50 and less than 1.00 weight percent. Only 5 samples in the dataset are classified as good to very good source rocks (TOC values of 1.00 to 3.35 weight percent). The majority (n=18) of the 29 samples of potential source rocks with a TOC value of 0.5 or greater are located in the Upper Silurian Salina Group and equivalent Wills Creek Formation. Moreover, all of the good to very good source rocks are located in the Salina Group and Wills Creek Formation in southwestern Pennsylvania and northern West Virginia. The remainder (n=11) of the 29 potential source rocks (TOC values of 0.50 to less than 1.00 weight percent) are located in the Lower Silurian Cabot Head Shale (n=2), Rochester Shale (n=6), Rose Hill Formation (n=1), and Lower to Upper Silurian Lockport Dolomite (n=2). These source rocks of secondary importance are widely distributed across eastern Ohio, western Pennsylvania, and West Virginia. Although the TOC analyses in this study indicate that good to very good source rocks are present in the Salina Group and Wills Creek Formation of southwestern Pennsylvania and northern West Virginia, data are insufficient to propose a new Silurian total petroleum system in the Appalachian basin. However, the analytical results of this investigation are encouraging enough to undertake more systematic studies of the source rock potential of the Salina Group, Wills Creek Formation, and perhaps the Tonoloway Formation (Limestone) and McKenzie Limestone (or Member).