High-Precision Geochronology and Earth History in Deep Time

Bowring, Samuel ¹; Ramezani, Jahandar ¹; Johnson, Kirk R.²; Clyde, W. C.³; Machlus, Malka ^4
1 EAPS, MIT, Cambridge, MA.
² Denver Museum of Nature & Science, Denver, CO.
³ Department of Earth Sciences, University of New Hampshire, Durham, NH.
⁴ Schlumberger-Doll Research, Denver, CO.

High-precision geochronology plays a crucial role in understanding the causes of climatic, biotic, and geologic changes in deep time. It is now possible to use U-Pb and Ar-Ar geochronology to determine the age of volcanic ash-beds intercalated with sedimentary rocks at the 0.1% level or better. When integrated with astronomically tuned cyclostratigraphy, magnetostratigraphy, biostratigraphy, and chemostratigraphy there is great potential for examining rates of change in deep time. However, this approach will require much effort to resolve systematic differences between the U-Pb and Ar-Ar geochronometers and high-precision calibration/testing of astronomical timescales.

The uppermost Cretaceous through Eocene is characterized by major biotic events including the K-T extinction, the radiation of mammals and the emergence of modern floras. This period also saw dramatic climatic variations like the PETM, which provide invaluable context for understanding the relationships between marine and terrestrial records and the dynamics and evolution of greenhouse climate systems. High-precision sequencing and calibration of geologic history is critical for determining the order and pacing of these events. The existing timescale relies on interpolation between relatively few 40Ar/39Ar age constraints on the Geomagnetic Polarity Time Scale (GPTS). Large uncertainties exist due to a lack of dates at key magnetic/fossil intervals that limit the precision of interpolation between tie-points; major improvements are possible. We are engaged in an attempt to calibrate Maastrichtian-Eocene time at a much higher resolution than currently exists by integrating U-Pb geochronology, magnetostratigraphy, and astrochronology.

Our ultimate goal is to link volcanic ash bearing terrestrial sections with the high fidelity isotopic/climatic records from ocean basins in order to test cyclostratigraphic models and better understand greenhouse climate dynamics and associated biotic events.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009