Paper No. 6
Presentation Time: 10:15 AM
THE HANGENBERG EVENT WAS ABRUPT AND SHORT AT THE GLOBAL SCALE: THE QUANTITATIVE INTERGRATION AND INTERCALIBRATION OF BIOTIC AND GEOCHRONOLOGIC DATA WITHIN THE DEVONIAN-CARBONIFEROUS TRANSITION
The late Devonian period hosts a set of profound biotic crises accompanying episodes of tropical ocean anoxia, positive carbon isotope excursions, relative sea level rise and fall, and apparent global climatic cooling. The Hangenberg event, at the close of the Devonian, is the last of these crises which ushered in a new and long-lived icehouse climate regime spanning the Carboniferous and early Permian. The mass extinction accompanying the Hangenberg event witnessed the demise of many fossil groups and initiated a dramatic change in marine benthic biota, with the rise of foraminifera and the progressively less significant role of trilobite, coral and ostracod dominated communities. New high-precision U-Pb zircon ages for bracketing volcanic tuffs constrain the timing and tempo of the Hangenberg biotic crisis and glacial event at the close of the Devonian period. When combined with quantitative biostratigraphic analysis (25 sections global wide; 161 events, including FAD’s, LAD’s of the taxa, ashes, the base of the Hangenberg black shale), these data constrain the duration of tropical ocean anoxia, mass extinction and carbon cycle perturbation to less than 100 thousand years, and are used to constrain a model of orbitally-forced enhancement of oceanic circulation promoting catastrophic overturn, upwelling of anoxic bottom waters onto the tropical continental shelves, and consequent mass extinction.