FILLING THE GAP: NEW TITHONIAN-EARLY CRETACEOUS DATA FROM THE NEUQUEN BASIN, ARGENTINE ANDES (Invited Presentation)

AGUIRRE-URRETA, BEATRIZ; MARTINEZ, MATHIEU; LESCANO, MARINA; SCMITZ, M.; TUNIK, MAISA; VENNARI, V.; LOPEZ MARTINEZ, R. ; CONCHEYRO., A. ; RAMOS, V.

Indianapolis

Congreso; GSA Annual Meeting in Indianapolis, Indiana USA; 2018

Geological Society of America

The Geological Time Scale for the Phanerozoic has one of its last geochronological gaps in the Early Cretaceous interval, includingthe base of the Berriasian (aka the J/K boundary) where no precise radio-isotopic ages are available. Up to now, the global ?standard?Early Cretaceous stages are mainly based on stratigraphic sections in the Mediterranean Province of the Tethys, and are mostlydefined by ammonite biostratigraphy and calcareous nannofossil bioevents that have been calibrated with the M sequence of magneticpolarity chrons. Presently, the base of the Cretaceous is defined by the explosion of globular forms of the microfossil Calpionellaalpina, and the calcareous nannofossils and ammonites are now considered secondary markers.The Neuquén Basin is a retro-arc basin developed in a normal subduction segment at the foothills of the southern Central Andes.Laterally continuous outcrops of marine sedimentary rocks with an abundant fossil record, combined with interbedded tuffaceouslayers make the basin an excellent site for stratigraphical, paleontological, and radio-isotopic studies. The Late Jurassic?EarlyCretaceous magmatic activity along the arc was clearly episodic with pulses that peaked in early Tithonian, middle?late Berriasian andHauterivian times.The duration of the Tithonian up to the Hauterivian stages are presently under much debate, with large discrepancies between thenumerical ages of the International Chronostratigraphic Chart 2018/v8 and the data provided by studies performed recently in theAndes and also in the Tethys. We present here high precision CA-ID TIMS Tithonian-Early Cretaceous dates combined withbiostratigraphic data provided by ammonites, calcareous nannofossils and calpionellids. We also present an astronomical calibrationto better constraint the durations of the Valanginian and the Hauterivian stages, constrained biostratigraphically by ammonites andcalcareous nannofossils which correlate with the ?standard? sequence of the Tethyan Realm. These new data show significantdifferences not only in the absolute ages of the stage boundaries, 5 millon years younger for the base of the Cretaceous (140 Ma) and3 millon years younger for the base of the Barremian (126 Ma), but also in the duration of each stage.Session No. 241T175. Late Jurassic through Early Cretaceous Geologic Time ScaleWednesday, 7 November 2018: 8:00 AM-12:00 PMSagamore Ballroom 7 (Indiana Convention Center)Geological Society