Abstract

Radiolaria recovered from the uppermost member of the Caballos Novaculite through the base of the overlying Tesnus Formation show a time gap roughly equivalent to the Early Mississippian. In two sections, Late Mississippian (Meramecian) radiolarians overlie earliest Mississippian (early Kinderhookian) radiolarians in an apparently conformable sequence of siliceous shale. In a third section, Meramecian radiolarians overlie Late Devonian (Famennian) radiolarians and conodonts, separated by a thin conglomerate layer. These data suggest that a hiatus equivalent to the late Kinderhookian - Osagean time period is present and that local erosion into the Fammenian occurred.

Lithostratigraphically, this hiatus is coincident with the Caballos-Tesnus boundary in the central portion of the basin, while at the western margin, it occurs 8 m above the base of the Tesnus immediately above a clastic zone containing olistoliths. Results from this preliminary investigation show that localized deposition of olistoliths occurred in the western basin margin during the Famennian (Late Devonian), followed by an interval of nondeposition in the Early Mississippian, and finally the onset of basin-wide flysch deposition began in the Meramecian. These findings will be further tested by the examination of boundary sections in other localities throughout the basin.