Cambrian-Ordovician Subsurface Stratigraphy of the Black Warrior Basin in Mississippi
HENDERSON, KEVIN S., and S. CRAGIN KNOX, Mississippi Office of Geology, Jackson, MS
The stratigraphy of the Cambrian-Ordovician sequence in the Black Warrior basin of northern Mississippi is known only from subsurface data. Little has been published on this thick sequence of carbonates, and a great deal of confusion exists with regard to formational boundaries and ages. A recent study using conodonts from the Magnolia Petroleum 1 Pierce well (Monroe County, Mississippi) affords a much better understanding of the age relationships of the sequence than was previously available. The present study is an effort to differentiate the Cambrian-Ordovician strata based on the available conodont data and the lithologic character of the strata.
Of the 152 wells that have reached at least the Ordovician, only two have penetrated the entire Cambrian-Ordovician sequence. These two wells are the 1 Pruet & Hughes 1 Dunlap Brothers (Lafayette County, Mississippi) and the 1 Exxon Fulgham (Oktibbeha County, Mississippi). The sequence as revealed in the Dunlap well consists of an apparently "complete" section of 7950 ft of carbonates with minor amounts of quartzitic sand in the base of the section. The 6744-ft section of Cambrian-Ordovician strata in the Fulgham well is incomplete; much of the Cambrian section is absent apparently due to nondeposition.
Because only eight wells have reached the Cambrian, it is difficult to ascertain what a "normal" section is, but the subsurface in Mississippi as it is presently known is similar to the Cambrian section exposed in the southern Appalachians of Alabama. The Cambrian System attains a maximum composite thickness of 6343 ft and is differentiated into five formations. In ascending order, these are Weisner Quartzite, Shady Dolostone, Rome Formation, Conasauga Limestone, and Copper Ridge Dolostone.
The Ordovician System is represented by a maximum composite thickness of 6778 ft of nearly pure carbonate strata. Only Lower Ordovician and earliest Middle Ordovician (White Rockian) strata are present, and these sediments are differentiated into four formations based on lithology. In ascending order, these are the Knox Dolostone, Longview Limestone, lower Stones River Dolostone, and upper Stones River Limestone.
Despite the fact that only a small amount of oil (7811 bbl) and gas (800,000 mcf) has been produced from the Cambrian-Ordovician section to date in Mississippi, large reservoirs may be present in these strata analogous to the prolific Ellenburger-Arbuckle trend of Texas and Oklahoma. All production to date has occurred in what is informally referred to as the "Snow Zone" of the lower Stones River Dolostone. Numerous hydrocarbon shows, excellent reservoir rocks, and the existence of large undrilled structures suggest that commercial oil and gas fields in this vast relatively unexplored trend await the drill bit in Mississippi.
AAPG Search and Discovery Article #91006 © 1991 GCAGS and GC-SEPM Meeting, Houston, Texas, October 16-18, 1991 (2009)