Geology of the Mena - Board Camp Quadrangles, Polk County, Arkansas
AbstractThe Mena and Board Camp quadrangles are in the Ouachita folded belt in west-central Arkansas. Rocks ranging in age from Middle Ordovician to Middle Mississippian crop out in these two quadrangles and include representatives of two distinct depositional environments. The Bigfork Chert, Polk Creek Shale, Missouri Mountain Slate, and Arkansas Novaculite were deposited during a period of tectonic inactivity and are deficient in arenaceous elastic material. The bedded siliceous sediments of this sequence are primary deposits, at least partly biochemical in origin, which probably were deposited in relatively shallow water. The northward thinning of the Arkansas Novaculite is due largely to nondeposition rather than to erosion. These Middle Ordovician to Lower Mississippian sediments have a total thickness of about 3.000 feet. They crop out in the southeast and south portions of these quadrangles and are referred to as the core of the Ouachitas. The Stanley shales and Jackfork sandstones were deposited in a subsiding basin during a period of uplift of adjacent land areas. The three formations of the Stanley Group described in Oklahoma can be recognized in this portion of Arkansas. These two groups are Middle Mississippian and are approximately 12,000 feet thick.