UPDATED CHRONOSTRATIGRAPHY OF THE BASAL TURONIAN GSSP IN ROCK CANYON, LAKE PUEBLO STATE PARK, CO (Invited Presentation)

A GSSP for the base of the Turonian Stage was proposed for the Rock Canyon locality near Pueblo CO by Kennedy, Walaszczyk and Cobban and ratified by the ISC in 2003. This site had long been a major focus for Cretaceous chronostratigraphers because of its excellent exposures of fossiliferous, rhythmically bedded strata bearing intercalated bentonitic horizons with datable sanidine phenocrysts. The combination of macro- and microfossil biostratigraphy, radioisotopic age determinations, an astrochronologic framework, and detailed chemostratigraphic profiles spanning the boundary interval make the basal Turonian GSSP one of the best constrained stage boundary sections in the world. It is one of relatively few GSSP’s located in North America, and thanks to NSF funding, the site is marked by a public outreach display in an easily accessible part of the Lake Pueblo State Park. This talk will review the historical development of the basal Turonian GSSP, summarize recent local and regional chronostratigraphic studies that address questions raised about the relative conformity of the succession (including new geochronologic data), and conclude with information about the public outreach display at the site. The development and construction of this site constituted the Broader Impacts effort of an NSF-funded project to update the Late Cretaceous time scale, building on the seminal work of the late John Obradovich, U.S. Geological Survey.