The Late Middle Devonian (Givetian) Global Taghanic Biocrisis in Its Type Area (Northern Appalachian Basin): Geologically Rapid Faunal Transitions Driven by Global and Local Environmental Changes

Abstract

The late Middle Devonian ‘Taghanic (Pharciceras) Event’ was originally named by Michael House for goniatite turnovers in the New York Appalachian Basin during deposition of the Tully Limestone; subsequently, it has been associated with the extinction of most of the long-lasting ‘Hamilton Fauna’ in this region. Stratigraphic and paleoecologic research in the type area has revealed at least three main faunal transitions, recognized as discrete bioevents: (1) replacement of much of the endemic ‘Hamilton Fauna’ (a subset of the Eastern Americas Realm) with the previously equatorial ‘Tully Fauna’ (a subset of the Old World Realm); (2) subsequent extermination of most of the ‘Tully Fauna’ and recurrence of the ‘Hamilton Fauna’, coincident with the eustatic sea-level rise termed the ‘Taghanic Onlap’; and (3) extinction of much of the ‘Hamilton Fauna’ and return of some ‘Tully’ taxa along with a further incursion of Old World Realm taxa during continued rise in global sea level. The Taghanic Biocrisis is currently recognized globally as a series of pulsed biotic transitions and extinctions, ultimately resulting in an end to previous faunal provinciality and appearance of a global cosmopolitan fauna. We review the current knowledge of these faunal transitions in the type area with respect to geologically rapid global and local environmental changes observed using a high-resolution stratigraphic framework across the entire onshore-offshore environmental gradient. Globally recognized environmental changes, specifically temperature increases, changes between arid and humid intervals, rapid sea-level fluctuations, and widespread black shale deposition account for the faunal transitions discriminated in the type area, but only in the context of regional basin dynamics associated with basin morphology and the degree to which estuarine-type watermass circulation patterns were operating, resulting in salinity variation as a dominant control on faunal distribution. Herein, we outline the interplay between global and local environmental changes that served as driving forces behind the local incursions and extinctions, including the demise of the long-stable ‘Hamilton Fauna’.