The biological, chemical, and environmental history of the Earth is recorded in the rock record of strata exposed at and below the surface. One of the most critical components to the ability to read this history of past changes to the Earth is the ability to determine the precise order of events (chronostratigraphy) as well as the precise timing and duration of these events (geochronometry/geochronology). In order to be able to determine the exact cause-and-effect sequences of events that produced prior biological, chemical, and environmental change, one must be able to first provide very fine controls on the precise order of events as well as the precise timing and duration of events. Such precise control is commonly available when studying events in the comparatively recent history of the Earth. For example, temporal and stratigraphic control in the order of a few thousand years or less is common when working on more recent events, but such control for the much older portions of Earth history are generally unavailable. As a general rule, the ability to determine the order of events and their timing and duration gets worse the farther back in time one looks. Therefore, when studying events that are hundreds of millions of years old, resolution is typically plus/minus tens to hundreds of thousands of years, or worse. This is a critical roadblock to determining the natural limits of variability and operational feedbacks within the ocean-atmosphere-biosphere global climate system during ancient global change events. The Paleozoic Era (541 Ma to 252 Ma) contains many of the largest biogeochemical perturbations in Earth history, and one small slice of the Paleozoic Era is the objective of this CAREER award in an effort to demonstrate that Neogene-scale resolution of the rock record of biogeochemical events is possible in deep time.
This study will help to establish an unparalleled level of chronostratigraphic and geochronologic detail to provide a framework for high-resolution evaluation of global triggers, feedbacks, and ultimately, the mechanisms responsible for two major biogeochemical events that took place during the Wenlock Epoch of the Silurian Period (431 Ma to 427 Ma). The research conducted by this study will include unprecedented detail of the early Sheinwoodian (Ireviken) and Homerian (Mulde) biogeochemical events that had major impacts on the global biosphere (extinction events) as well as the global carbon cycle. This study will utilize fully integrated high-resolution event stratigraphy (HiRES) that will include biostratigraphy (conodonts, chitinozoans), stable isotope chemostratigraphy (carbon and oxygen), sequence stratigraphy, radioisotope geochronometry (U-Pb zircons), and XRF elemental data to dramatically improve the calibration of the Silurian time scale and the ability to globally correlate Wenlock strata and events, as well as to evaluate several existing models of Silurian global change and the nature of the Paleozoic Earth-Life system.
