STRATIGRAPHIC ANALYSIS OF THE MOOREFIELD SHALE (MIDDLE-LATE MISSISSIPPIAN) IN ITS TYPE AREA, NORTHEASTERN ARKANSAS

Studies of the Moorefield Shale represent research that has been conducted in northern Arkansas for more than a century. Lithostratigraphically, the name was proposed initially for a sequence of black, sandy shale with interbedded limestone succeeded by dark brown, calcareous and phosphatic shale (Adams and Ulrich, 1904). Mackenzie Gordon Jr. (1944) restricted the name Moorefield to the lower limestone-bearing interval, and proposed the name Ruddell Shale to encompass the succeeding, thicker, brown shale. Currently, the name Ruddell has been abandoned, and the entire succession between the top of the Boone Limestone (Osagean) and the base of the Batesville Sandstone (Chesterian) is designated the Moorefield Formation/Shale (McFarland, 2004). Age assignments within the Moorefield, based primarily on ammonoid cephalopods, have ranged from assigning the entire interval to the Meramecian Series (Middle Mississippian) to the current recognition that the Moorefield likely spans both the Osagean-Meramecian and Meramecian-Chesterian boundaries (Middle-Late Mississippian). Sequence stratigraphic interpretations of the Moorefield regard the interval as a low-stand wedge representing a third-order, maximum regression during the Osagean and earliest Meramecian series, followed by a transgressive history extending well into the Chesterian Series. Research of the Moorefield has been significantly less than that of other southern Ozark shale formations, such as the succeeding Fayetteville Shale, but recent successful exploration has increased interest in the Moorefield as a potential natural gas reservoir.