Cyclostratigraphic calibration of the Middle Devonian time scale (Eifelian Stage, Appalachian Basin, western NY, USA)

Over the last decade, a growing amount of research has been directed towards building an astronomical time scale for the Devonian. This has led to major improvements in estimates of the duration for most of the Devonian stages, and as a corollary in constraining timing and causes of Devonian environmental changes. Currently, duration estimates for the Emsian and the Eifelian stages of respectively the Lower and Middle Devonian are the only missing pieces to reach the first fully calibrated Devonian time scale, which is expected to be published in the coming Geological Time Scale 2020.

In this research we focus on the Eifelian Stage (GTS2012; base at 393.3 ± 1.2 Myr and duration estimate of 5.6 ± 1.9 Myr), Middle Devonian, which is bracketed by two major bioevents, respectively the Choteč event at its base and the Kačák event just prior to the Eifelian - Givetian boundary. Both events are characterized by significant physical and biotic turn-overs in the marine realm including sea-level rise, faunal extinctions, appearance of new life forms, and maximum radiation. During the Eifelian a complete succession of outer-ramp and deep-shelf deposits accumulated within the Appalachian Basin in the eastern mid-continent of North America. In the Seneca Stone quarry (western NY), a 18 m-thick complete succession, with good biostratigraphy includes the early to the late Eifelian (Po. costatus costatus - T. kockelianus kockelianus) and exposing carbonate, marl, organic-rich shale and two bentonites (Tioga F and Onandanga Indian Nation).

To capture the astronomically-forced sedimentary cycles and to develop a model of the climatic and oceanographic variations that affected the Appalachian Basin, 800 samples were collected typically at 2.5 cm-intervals throughout the entire succession, and trace and major elements were measured on each sample with ICP-MS and ICP-OES. The cyclicity recorded in this high-resolution geochemical dataset will be used to construct a robust cyclostratigraphyic framework for the Eifelian Stage, which will be anchored to the radiometrically dated bentonites. To estimate the duration of the Eifelian Stage, multiple spectral techniques will be applied to different climatically-driven elemental signals (e.g., Ti, Al, K, Zr), using the stable 405-kyr eccentricity cycle as a starting point for the calibration.