PALEOZOIC QUARTZ SANDSTONE COMPOSITONAL CHANGES IN THE RECORD OF THE SOUTHERN OZARK DOME, NORTHERN ARKANSAS

The Paleozoic sedimentary record of the Ozark Dome records: 1) periods of erosion, and reworking, 2) intervals of first-cycle sediments, and 3) separation by intervals that lack extensive terrigneous clastics. Source and delivery directions for some of these quartz sandstones remain unclear. The Paleozoic sedimentary record of the Ozark begins in the subsurface with the Lamotte Sandstone (Upper Cambrian), which rests on Precambrian granites. The basal Lamotte is an arkose-litharenite, becoming more quartz-dominated in its upper portion. The Lower and Middle Ordovician, the section comprises orthoquartzites, such as the St. Peter, with well rounded, highly spherical grains, associated with shallow-water dolomites and dolomitic limestones. These mature to supermature sandstones were presumably derived by reworking Cambrian sandstones. Middle-Upper Ordovician deposition of dolomites and limestones blanketed the midcontinent region, and prevented reworking of the earlier section until the Middle Devonian Clifty Sandstone, another orthoquartzite, virtually indistinguishable from those of the Ordovician. The last orthoquartzite in the southern Ozark succession occurs as the Bachelor Member, St. Joe Limestone, Lower Mississippian. The succeeding chert-bearing carbonate blanket of the Lower Mississippian prevented extensive reworking of earlier sandstones. The next sandstones in the record are the Batesville and later Wedington Member, Fayetteville, both Chesterian, and both first cycle terrigenous clastics. These Upper Mississippian, first-cycle sandstones anticipate the Pennsylvanian succession in the southern Ozarks, with thick, pervasive, first cycle sandstones classified as subarkoses and sublitharenites. Close examination reveals a contribution by orthoquartzitic grains, but never in significant abundance. Although frequently cited as coming from the Canadian Shield, these Late Pennsylvanian, first-cycle sandstones likely reflect an Appalachian source.