Ozark Dome
Location
See text below and figures 1, 2
References
Swallow 1855, Keyes 1894, Koenig 1961, Stearns and Marcher 1962, McCracken 1971, Tikrity 1968, Atherton 1971, Kisvarsanyi 1981, Houseknecht 1983
Description
The Ozark structural region has been called a dome, an uplift, and occasionally an arch. The term Ozark Dome is preferable to Ozark Uplift because the whole area has not been raised tectonically. Furthermore, during most of the Paleozoic Era the Ozark region was a shoal or low upland that remained stable while adjacent basins subsided. The region is nearly equidimensional and lacks a definite axis, so the term dome is more appropriate than arch.
The Ozark Dome covers southern Missouri, part of northern Arkansas, northeastern Oklahoma, and southwestern Illinois. Narrow strips of southwestern Illinois lie on the flanks of the structural dome and are included in the Ozark Plateaus physiographic province. The rugged terrain of north-dipping cuestas in southernmost Illinois sometimes is loosely called the "Illinois Ozarks," but that name is not correct from a geologic or physiographic standpoint.
Precambrian rocks of the Ozark Dome consist mainly of granite and rhyolite approximately 1.4 billion years old. By the Cambrian Period, a rugged topography of rounded hills had developed. The Late Cambrian sea lapped around these hills and deposited the Lamotte Sandstone (Mt. Simon equivalent). Later, the entire region was inundated except perhaps the highest peaks of what are now the St. Francois Mountains of southeastern Missouri. The Upper Cambrian through Ordovician succession of the Ozark Dome is similar to, although thinner than, that of the Illinois Basin. The Silurian and Devonian Systems are thin and the Mississippian rocks are largely stripped by erosion from the eastern Ozarks. From the Cambrian through Mississippian Period, the Ozark Dome was, at most, a minor source of elastic sediment for the Illinois Basin. The Thebes Sandstone (Maquoketa Group, Upper Ordovician) is present only on the east flank of the dome and presumably had a local provenance. Some of the sand in the Dutch Creek Sandstone Member (base of Middle Devonian) may also have come from the Ozark Dome (Smunt 1964, Summerson and Swann 1970).
The northeastern part of the Ozark Dome was uplifted along the Ste. Genevieve Fault Zone in latest Mississippian to early Pennsylvanian time (Nelson and Lumm 1985). A short-lived fault scarp apparently existed, as evidenced by Ozark-derived chert clasts in basal Pennsylvanian conglomerates (Poor 1925) and diversion of Pennsylvanian paleochannels (Desborough 1961b) along the fault zone in southwestern Illinois. Numerous Pennsylvanian outliers on the northwestern Ozark Dome indicate that the area was not greatly elevated. The dome probably was a low positive area during most of the Pennsylvanian Period (Houseknecht 1983) and since then has remained an upland.
