--> --> towards the future from atop the shoulders of Bill Cobban, John Obradovich and Richard Pearl

AAPG Rocky Mountain Section Meeting

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towards the future from atop the shoulders of Bill Cobban, John Obradovich and Richard Pearl

Abstract

Our understanding of Colorado's stratigraphic evolution is built on over a hundred and fifty years of research developed by hundreds of geologists and paleontologists. Amidst this cacophony of labor the collaboration between Bill Cobban and John Obradovich stands out. These two USGS colleagues, working on the Cretaceous marine shales of the Western Interior, established one of the best calibrated biostratigraphic records in the world. Their work on ammonite biostratigraphy and chronostratigraphy provides the lynch pin for our understanding of the Cretaceous Interior Seaway. Richard Pearl's work and publications span a vast panorama of Colorado geology and resulted in a careful compilation of Colorado's stratigraphy from Precambrian to Recent. This chart was mimeographed and Xeroxed repeatedly and used in innumerable field trips and field guides. A new digital stratigraphic chart of the Cretaceous Interior Seaway in Colorado features the work of all three of these mentors. Bill Cobban built the biostratigraphic record and his phylogeny was calibrated by John Obradovich’s radiometric dating of volcanic ashes. Richard Pearl charted this history in his Colorado stratigraphic diagram. We have used new tools to present this information. A digital, web-based, phone-available stratigraphic chart replaces Pearl's paper handout. The chart is calibrated against a time line benefiting from the dated ashes reported by John Obradovich complemented by world-wide dating and magnetic stratigraphy. The chart may be viewed at coloradostratigraphy.org on any web-connected device. The chart is accompanied by three dimensional images of selected fossils created by Shellie Luallin, allowing the viewer to match up names on the chart with almost tangible images of representative fossils. This presentation will be directly tied to the internet and will review the format and content of the web tool and offer potential for expansion beyond Colorado to Wyoming and other areas affected by sedimentation.