Bentonite geochronology, marine geochemistry, and the Great Ordovician Biodiversification Event (GOBE)

• Published in: Palaeogeography, Palaeoclimatology, Palaeoecology
• Main Authors: Thompson, Cara K., Kah, Linda C., Astini, Ricardo Alfredo, Bowring, Samuel A., Buchwaldt, Robert
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Science
• Subjects: Argentina; Environmental Change; Geochronology; K-Bentonite; Middle Ordovician; https://purl.org/becyt/ford/1.5; https://purl.org/becyt/ford/1; San Juan; Argentine; Table Head; Newfoundland
• Online Access: http://hdl.handle.net/11336/52203

Attribution of Ordovician climate forcing to explosive volcanism and the potential global importance of volcanism in Ordovician biodiversification suggest the necessity of evaluating the relationships between K-bentonite deposition and increasingly high-resolution records of marine biogeochemical change. Globally, Ordovician strata preserve an extensive record of explosive volcanism - including the widely recognized Lower to Middle Ordovician Famatina K-bentonite suite in Argentina and the Upper Ordovician Millbrig-Deicke-Kinnekulle suite of North America and Europe. Here, we present high-resolution ID-TIMS U-Pb zircon ages of K-bentonites from measured sections of the San Juan Formation (Talacasto and Cerro La Chilca section) of the Argentine Precordillera. K-bentonites from the Argentine Precordillera provide stratigraphically consistent (i.e., younging upward) ages that range from 473.45 ± 0.70. Ma to 469.53 ± 0.62. Ma, and constrain the age of a low-magnitude (2%), globally recorded, negative carbon-isotope excursion. Evaluation of the timing of K-bentonite deposition in the Argentina Precordillera relative to marine biostratigraphic and biogeochemical records provides insight into relationships between explosive volcanism and regional to global environmental change. From a regional standpoint, these ages provide critical direct evidence for a Dapingian to earliest Darriwilian age of the upper San Juan Formation at sampled localities. These ages are consistent with carbon-isotope data suggesting that the San Juan Formation in the region of its type section is coeval with only the base of the often-correlated Table Head Group of western Newfoundland. This data thus highlights the difficulties in using regional biostratigraphic data - particularly within erosionally truncated or otherwise diachronous units - to define the timeframe of carbon-isotope chemostratigraphy. New geochronological data also indicate that a discrete negative carbon-isotope excursion within the San Juan and Table Head formations is ...