Petroleum source rocks occur in most Ordovician sedimentary strata in North America, northern Europe, South Africa, central Australia, and the Baltic area. Many of the source rocks are condensed shales within carbonate-evaporite sequences. Compared with other geologic periods, little oil originates from Ordovician source rocks, but they are important sources for some petroleum systems. Some examples include, 1) the Albion-Scipio field, the only giant field in the Michigan Basin, which contains petroleum generated from Ordovician Trenton-Black River source rocks and 2)the very productive Ordovician Simpson and Ellenburger formations of the west Texas Permian Basin, which aregenerally recognized as sourced from the Ordovician Simpson source rocks. Widespread organic-rich source rocks were deposited during the Late Ordovician Period (Caradocian Stage) as part of an extensive marine transgression before the major glaciation. Upper Ordovician (mostly Caradocian) black shales (e. g. Vinini, Utica/Antes, Trenton, Maquoketa, Sylvan and Simpson, and equivalents) are widespread in North America, as are the Dicellograptus and Clinograptus shales of Northern Europe making many of them potential for unconventional oil exploration.
In recent years, the Utica formation in Ohio has received the majority of industry focus for unconventional oil exploration while many other North American Ordovician formations have gone relatively unexplored. Possible explanations for the limited exploration of the Ordovician Shale are possibly due understanding the maturation levels within the formations. With most of the Ordovician formations appearing in the gas window, these formations are overlooked for exploration in the present hydrocarbon markets. A complete understanding of the maturity levels of the Ordovician aged source rocks needs to be accomplished in order to locate the potential for productive unconventional oil. With a review and understanding of the regional geology, log analyses, geochemical and maturity data of the various Ordovician formations, it is believed that there are many additional areas in North America that have the potential for Ordovician unconventional oil production.