In 2004 the International Commission on Stratigraphy (ICS) completed a new geologic time scale. An important innovation in this time scale is the use of Earth's orbitally forced stratigraphy, or cyclostratigraphy, to define time over the entire Neogene Period (0 to 23.03 million years ago) at an unprecedented resolution of 0.02 million years. In addition, 'floating' astronomical time scales were proposed for entire stages or epochs in the Paleogene and all three Mesozoic periods. Also in 2004, a new astro-geodynamical model was presented that provides an accurate ephemeris for Earth's orbital parameters for the past 0.25 billion years. These results led the ICS to establish a task group to develop an astronomically calibrated time scale for the past 250 million years. I was appointed as co-chair for the Mesozoic Era (65 to 251 million years ago).

The ICS task group aims to develop stratigraphic continuity and redundancy in the datasets that are used for the astronomical time calibrations. The co-chairs must independently identify and evaluate potential data from throughout the international research community and compile the data into the ICS global stratigraphic framework. The output time scale will be tested against other, independent dating techniques, e.g., radioisotope dating, and other, relative correlation techniques (e.g., biostratigraphy and chemostratigraphy) in collaboration with NSF's CHRONOS and EARTHTIME community projects.

Significance

An astronomically calibrated geologic time scale defined at a 0.02 to 0.40 million year resolution represents a major breakthrough in the geosciences. Estimates of rates and magnitudes of Earth system processes that can be examined only in the context of Earth history will be improved by at least an order of magnitude over what is available today (0.5 to 5.0 million year resolution). This moves cyclostratigraphic science into an applied field that can address problems in disciplines as far-ranging as astrodynamics, geodynamics, geochronology, paleoclimatology, paleoceanography, paleomagnetism, plate tectonics, geochemical cycling and biotic evolution. By example, recently it was demonstrated that orbital stratigraphy can be used to validate astrodynamical models. This opens up new possibilities for exploring the model limits of solar system behavior at time scales on the order of 100 to 1000 million years.

Main Collaborators

Felix Gradstein (ICS), Frits Hilgen (Utrecht), Jim Ogg (Purdue), Heiko Pälike (Southampton)

Links

•International Union of Geological Sciences - http://www.iugs.org/

•International Commission on Stratigraphy - http://www.stratigraphy.org/

•NSF-CHRONOS Network - http://www.chronos.org/

•NSF-EARTHTIME Project - http://www.earth-time.org/