Revised Numerical-Ages of the ‘SEPM’ Mesozoic-Cenozoic Sequence Chronostratigraphic Charts, and a Display Interface
James George Ogg and Adam Lugowski
Purdue University, West Lafayette, IN
The “Mesozoic and Cenozoic Sequence Chronostratigraphic Framework of European Basins” chart series of extensive inter-calibrated bio-, magneto-, chemo- and sequence stratigraphy (Hardenbol et al, SEPM Spec. Publ. 60, 1998) had been calibrated to the geologic time scales of 1995. Both the numerical ages and the correlations of chronostratigraphic scales had gradually improved during the following decade. In coordination with the International Commission on Stratigraphy and the CHRONOS database project of NSF, we recalibrated these charts to Geologic Time Scale 2004 (GTS2004 of Gradstein et al., 2004, Cambridge Univ. Press).
This recalibration involved the compilation of relative-age relationships among approximately 6000 stratigraphic events (first/last occurrences, zonal boundaries, magnetic polarity zones, marine isotope stages, etc.) into a database. Selected post-1995 biozonal schemes and marker events were also incorporated. Numerical ages are then assigned or interpolated from the associated calibrations to astronomical cycles (Cenozoic, portions of Cretaceous and Triassic), to radiometric dates, to marine magnetic anomalies, or other controls. Revisions of control ages or correlations will cascade through all dependent inter-calibrations. A similar database was extended through the Paleozoic. The revised chart series and a preliminary Paleozoic set are posted on websites of the International Commission on Stratigraphy (ICS; www.stratigraphy.org), of CHRONOS (www.chronos.org) and of SEPM.
We also developed a JAVA package for customized chart production and on-screen visualizations. A user of specifies the time interval, selects stratigraphic columns for plotting, and assigns the vertical scale (cm per million years). In addition to generating screen views and a scalable-vector graphics (SVG) chart file for importation into popular graphics programs (e.g., Adobe Illustrator), the screen display has “hot-curser-points” opening windows with detailed information. By providing this visualization tool and Mesozoic-Cenozoic database, we hope that community involvement will produce enhanced global and regional stratigraphic scales for Earth history.