GEOLOGIC MAP OF THE JANE 7.5-MINUTE QUADRANGLE, SOUTHWESTERN MISSOURI: EVIDENCE FOR PRE-PENNSYLVANIAN TECTONIC DEVELOPMENT OF THE OZARKS UPLIFT

Geologic mapping is essential for understanding regional patterns of tectonism and sedimentation. Mapping of Jane quadrangle provides support for the idea that tectonism occurred during the mid- to late Devonian and early to mid-Mississippian in southwestern Missouri, predating a widely known episode of uplift during the Pennsylvanian. During early episodes of uplift, the crest of the Ozarks in southern Missouri was exhumed to the lower Ordovician and to the Cambrian and Precambrian in the St. Francois Mountains. A few isolated locations of late Devonian and mid-Mississippian paleokarst sinkhole-fills indicate the widespread nature of overlap successions on the deeply eroded crest.

In contrast, in northern Arkansas and part of northeastern Oklahoma, nearly 500 m of post-lower Ordovician strata are preserved below the sub-Mississippian unconformity, however, some of the units preserved in Arkansas have been reported in impact breccias from Decaturville impact structure in Missouri. Exotic clasts there indicate overlap sedimentation during the late Ordovician and middle Silurian, pre-dating epeirogenesis and erosion of the units regionally. At Weaubleau impact structure, breccias include late Devonian clasts and conodonts but no middle Paleozoic faunas, indicating post-uplift impact. Thus, the most significant phase of uplift likely pre-dated the late Devonian.

Gravity data collection and analysis are consistent with the existence of a structural high in northeastern Oklahoma and northwestern Arkansas that has been referred to as the Spavinaw Arch. In southwesternmost Missouri, northwestern Arkansas, and northeastern Oklahoma a wedge of Chattanooga Shale truncates units below and records sedimentation during the late Devonian tectonic sequence. By Mississippian time, mud mounds preserved in lower to middle Mississippian carbonate successions near Jane, which have been interpreted as Waulsortian-like mounds, occur only in close proximity to Brush Creek Fault. Some show folding and lateral syn-sedimentary truncations. We interpret these as slumps and unindurated slide blocks.

In summary, the southern margin of Laurentia experienced contraction, flexure, epeirogenic uplift, minor structural deformation, and syn-tectonic sedimentation long before docking of the Ouachita allochthon.