MESOZOIC TIME SCALE: INTEGRATION AND IMPLICATIONS OF RADIO-ISOTOPIC DATING, CYCLE STRATIGRAPHY, MAGNETO-BIOSTRATIGRAPHY, ISOTOPIC EXCURSIONS AND OTHER EVENTS

The Triassic, Jurassic and Cretaceous periods have been the target of an intensive international program to apply cycle stratigraphy, obtain high-precision radio-isotopic dates and utilize magnetostratigraphy and carbon-isotope stratigraphy for inter-regional correlations. Radio-isotopic dating in Mesozoic from single crystals of zircon and sanidine has now approached the precision required to unambiguously assign sedimentary rhythms in strata to a particular “named” cycle of the fundamental 405-kyr long-eccentricity Milankovitch suite. This synthesis of many group efforts has enabled astronomical tuning via the long- and short-eccentricity Milankovitch cycles of biozones and magnetic polarity zones. In addition to aiding in the development of a more robust age model for the Mesozoic stages, these integrated studies yielded additional exciting results, such as (1) spreading rates for the Middle Jurassic through Early Cretaceous ocean ridges of the Pacific were remarkably stable or very gradually slowing, and (2) many of the named depositional sequences from the “Exxon/SEPM98 charts” correspond to the periodic 405-kyr long-eccentricity cycles. The main remaining intervals that have not yet yielded a robust age model and scaled stratigraphy are the majority of the Middle and Upper Triassic and portions of the Early Jurassic. This poster summarizes aspects of the current Mesozoic synthesis that have been achieved by numerous groups.