MARINE RED BEDS IN THE UPPER ORDOVICIAN AND LOWER SILURIAN OF EASTERN NORTH AMERICA—RECORD OF OCEANOGRAPHIC OXIDATION EVENTS

The Upper Ordovician and Lower Silurian strata of the Appalachian Basin and Cincinnati Arch contain four intervals of marine red beds whose facies cross-cutting nature and widespread distribution suggests they represent circum Iapetus to global oceanographic oxidation events (OOEs). These marine red beds are of late Richmondian, late Rhuddanian, early Telychian, and late Telychian age.

Widespread Upper Ordovician and Lower Silurian marine red beds cut across lithologic boundaries, representing deposition across a range of environments, tectonic regimes, and sedimentation rates. In particular, the late Richmondian and late Telychian red beds can be traced cratonward into greatly thinned deposits of the Midcontinent Platform in Indiana, greater than 500 kilometers from the Taconic-Salinic orogenic highlands, the most likely source of abundant iron oxides. This widespread distribution, in places under very low sedimentation rates, rejects the premise that such deposits result from rapid burial of river-transported iron oxides derived exclusively from terrestrial sources. All four intervals can be traced continuously along much of the length of the Appalachian Basin showing little to no relationship to the position of the Queenston delta. Ziegler and McKerrow (1975) reported three intervals of Silurian marine red beds, age equivalent to those described here, from across Avalonia and parts of Baltica, suggesting a circum Iapetus distribution.

Late Richmondian and late Telychian marine red beds contrast sharply with overlying organic-rich strata deposited during the Hirnantian and Ireviken carbon isotope excursions. This relationship parallels that described for oceanic red beds (ORBs) and oceanic anoxic events (OAEs) described by Hu et al. (2005) and others for the Middle and Upper Cretaceous of the Tethyan and Atlantic realms.