JACKFORK SANDSTONE/FORMATION (GROUP)

Age: Pennsylvanian Period, Morrowan Series
Distribution: West-central Arkansas, Ouachita Mountains; southeastern and central southern Oklahoma
Geology: The Jackfork Sandstone is thin- to massive-bedded, fine- to coarse-grained, brown, tan, or bluish-gray quartzitic sandstones with subordinate brown, silty sandstones and gray-black shales. Toward the north of its outcrop area the shale units of the lower and middle Jackfork Sandstone take up more of the section and the sandstones are more lenticular, often occurring as chaotic masses in the shale. Minor conglomerates composed of quartz, chert, and metaquartzite occur notably in the southern exposures of the formation. A few poorly preserved invertebrate and plant fossils have been recovered from the Jackfork Formation. The Jackfork Sandstone rests conformably on the Stanley Shale and varies between 3,500 to 6,000 feet in thickness.
Original reference: J. A. Taff, 1902, U. S. Geological Survey Geological Atlas, Folio 79.
Type locality: Named for Jackfork Mountain, Pittsburg and Pushmataha Counties, Oklahoma