--> --> Development of the Cretaceous Stratigraphic Framework of Western Interior North America by William Aubrey Cobban (1916-2015) and colleagues

AAPG Rocky Mountain Section Meeting

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Development of the Cretaceous Stratigraphic Framework of Western Interior North America by William Aubrey Cobban (1916-2015) and colleagues

Abstract

From the beginning of Bill Cobban's fascination with fossils around 1930 in Montana, until his last USGS work in field and office in Colorado in 2012, his 95th year, he developed a high-resolution biostratigraphic ammonite zonation that was applied to field and subsurface studies of the diverse sedimentary environments and deposits of the Cretaceous Western Interior Seaway. He documented the evolution of Western Interior ammonite biostratigraphic zonations from 10 to 66 index species, with coeval inoceramids by Walaszczyk, in USGS Open-file Report 2006-1250. His collaborative disposition led to co-authored publications and an extensive correspondence with many, a selection of whom form a 20th century "pantheon" of Upper Cretaceous paleontologists and stratigraphers around the world, including Reeside, Gill, G.R. Scott, Hancock, Matsumoto, Kennedy, Landman, Walaszczyk, among others. Cobban transferred to the rapidly growing USGS center in Denver, Colorado in 1954 from the Paleontology and Stratigraphy Branch at the Smithsonian Institution in Washington, D.C. He brought a modest reference collection of about 500 Cretaceous invertebrates (primarily ammonites, inoceramids, and oysters), and added, over nearly 60 years, to build a vast Denver Mesozoic fossil collection of over 15,000 localities. Cobban did not collect all of these samples, he received collections from dozens of USGS mapping and stratigraphic investigations, from academia, and local fossil collectors; many are documented in internal E&R reports and his published bibliography. In collaboration with USGS colleague John Obradovich, isotope geochronology was applied to this ammonite zonation, bridging the eras of relative biostratigraphic dating and high-resolution 40Ar/39Ar and U/Pb isotope geochronology. What's left to the next generation to accomplish? A great deal remains to secure the legacy of Bill Cobban's work and extend it into the 21st century. The most important part, the physical legacy of fossil collections tied to actual geographic and stratigraphic locations has been kept intact since 1995 and documented at the USGS in Denver by K.C. McKinney. His prodigious efforts with the entire USGS Denver Paleontology collections have transformed analog working papers into the digital information age. The physical fossil collection and supporting documentation are currently being transferred to their permanent home at the Smithsonian National Museum of Natural History on the Mall in Washington, D.C.