| The late Eifelian-earliest Givetian interval (Middle Devonian) represents a time of significant faunal turnover both in the eastern North America and globally, herein termed the Late Eifelian Biocrisis. A synthesis of biostratigraphic, K-bentonite, and sequence stratigraphic data, indicates that physical and biotic events in the Appalachian foreland basin sections in New York are coeval with the predominantly carbonate platform sections of the adjacent midcontinent. The succession includes portions of three distinctive benthic faunas or ecological-evolutionary subunits (EESUs): 'Onondaga', 'lower Marcellus', and 'Hamilton'. In the northern Appalachian Basin in New York the boundaries of these bioevents show evidence of abrupt, widespread extinctions/extirpations, immigration and ecological restructuring. Regional analysis of faunas shows that EESUs comparable to the northern Appalachian Basin succession are recognizable within the coeval carbonate ramp and platform strata of central Ohio and southeastern Indiana, as well as in the Michigan Basin. However, faunas of the Wabash Platform area of central Ohio and southeastern Indiana show slightly higher persistence compared to those of the Appalachian Basin, indicating that the Wabash Platform served as a refuge for species extirpated from the Appalachian Basin by environmental changes brought on by tectonic and eustatic deepening.;This interval can be subdivided into three discrete bioevents, with the last being the widely recognized Kacak Event in the ensensis conodont Zone near the Eifelian-Givetian stage boundary. The earlier bioevents, within the australis to eiflius Zones, are defined by striking faunal changes in the Appalachian Basin and coeval formations in adjacent areas of eastern North America. The Bakoven Event (australis conodont Zone), is marked by a significant reduction in faunal diversity in the uppermost Onondaga Limestone and overlying Bakoven Black Shale that is associated with eustatic/tectonic deepening and widespread hypoxia. The Stony Hollow Event (kockelianus-eiflius Zone) is marked by an incursion of tropical Old World Realm Cordilleran Province taxa, including distinctive atrypid brachiopods, corals, and bivalves, into the subtropical to temperate shelf region of eastern North America. The Stony Hollow bioevent appears to be associated with altered current patterns and/or climatic regime during the kockelianus-eiflius Zone interval.;Approximately coeval formations in Europe and Morocco show the probable signatures of these events, indicating that the Bakoven and/or Stony Hollow may be global-scale events. In particular, the late Eifelian successions in the Eifel and Rhenish Schiefergebirge areas of Germany, and in the Cantabrian Mountains of Spain show evidence for faunal turnover during the interval of the australis-kockelianus Zones. Both the Bakoven and Stony Hollow and the terminal Kacak events appear to be associated with changes in climatic gradients and major disturbances in the global carbon cycle. |
