Paper No. 4
Presentation Time: 10:05 AM
CYCLOSTRATIGRAPHY AND ITS REVOLUTIONIZING APPLICATIONS IN THE GEOSCIENCES
Over the past 25 years, the field of stratigraphy has expanded to include time-correlative geologic signals from disparate components of the Earth system. Not least of these is the global signal afforded by cyclostratigraphy, linked with the record of astronomical (Milankovitch) forcing parameters. Fossil astronomical signals are collected by dense sampling of sedimentary sections, and analysis of carbonate, iron, organic carbon, clays, isotopes, rock magnetism, color imaging, etc. In step with the documentation of astronomical forcing in progressively older geologic times, celestial mechanics now provides high-accuracy astronomical models for the past 50-60 Ma that can be used for high-resolution time scale calibration. These advances, together with the recognition of multiple responses in the Earth system to astronomical forcing, have revolutionized the geosciences. Before astronomical forcing acts on the climate system, it is altered by the Earth’s rotation rate, which affects the Earth’s precession rate and obliquity variation. Thus, embedded in cyclostratigraphy is the history of Earth’s rotation, from which the Earth-Moon system evolution may be inferred. Earth’s orbit is affected by motions of other planets, notably the orbital perihelia of Venus and Jupiter, which together impose a dominant 405-kyr eccentricity cycle on Earth’s orbital evolution. The large mass of Jupiter guarantees the robustness of this cycle over hundreds of millions of years; thus, the cyclostratigraphic record of 405-kyr cycles provides an effective high-resolution geochronometer. To date, the 405-kyr “metronome” has been used to calibrate geologic time as old as Carboniferous, and is used to correct higher-frequency eccentricity, obliquity and precession index signals affected by variable sedimentation. The geochronologic power of cyclostratigraphy has been further demonstrated by inter-calibration with high-precision radioisotope dating. Evaluation of precession index phasing relative to that of the obliquity, and models of integrated seasonal insolation, have elucidated the precise nature of astronomical forcing of the climate system. Finally, cyclostratigraphy is poised to inform solutions of the planetary orbits for times prior to 50 Ma, and to guide models of chaotic diffusion in the solar system.
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