A CLIMATE-DRIVEN MODEL AND DEVELOPMENT OF A FLOATING POINT TIME SCALE FOR THE ENTIRE MIDDLE DEVONIAN EIFELIAN STAGE USING MAGNETOSTRATIGRAPHY SUSCEPTIBILITY AS A CLIMATE PROXY

Here we continue our work to establish a preliminary age chronology for complete stages within the Phanerozoic by applying cyclostratigraphic methods that employ high-resolution data sets. This requires use of geochemical or geophysical data known to serve as a cyclic climate proxy. To demonstrate the method, we use the magnetostratigraphic susceptibility technique as the basis for fitting a climate model to the Eifelian Stage of the Middle Devonian System. We show a Milankovitch eccentricity climate zonation for the Eifelian that is pinned to time-series analyses from outcrop samples from its lower (Emsian-Eifelian, Germany) and upper (Eifelian-Givetian, Morocco) stage boundaries. Using these data sets we construct a uniform cyclicity model designed to conform to a ~405 kyr cyclicity, with a duration corresponding to the published duration for the Eifelian of ~5.7 myr (Ogg, 2008). To this model we fit two well-established conodont zonation schemes, thus allowing time estimates for conodont ranges for the Eifelian, indicating a range from ~1.8 myr to ~100 kyr before extinction of any given individual conodont species, similar to that reported for the Givetian (Ellwood et al., in press). We then tested and adjusted the model using independent data sets from the eastern United States. This method and its results will be discussed. MS zones developed should allow high correlation among sections to better resolve timing of major bio-events, and provide a Floating Point Time Scale to which absolute ages can be applied.