Tithonian-Hauterivian chronostratigraphy (latest Jurassic-Early Cretaceous), Mediterranean-Caucasian Subrealm and southern Andes: A stratigraphic experiment and Time Scale

Abstract

New radioisotopic dates of Tithonian-Hauterivian strata in the Neuquén Basin significantly recalibrate Early Cretaceous numerical ages. In order to evaluate the implications of these revised ages, a graphic correlation experiment of twenty-three Andean Tithonian to Hauterivian sections integrated the ranges of 254 species, sequence boundaries, polarity chrons, and radioisotopic ages that compose the ANDESCS DB. This database accurately reproduces the order of Andean ammonite zones and places them in a relative metric scale of a composite reference section. The ranges in the ANDESCS DB were correlated with the LOK2016 DB that comprises Tithonian-Albian ammonites, calpionellids, nannofossils, and polarity chrons in Mediterranean-Caucasian Subrealm stage reference sections. In 2017 these ranges were calibrated to GTS2016 mega-annums (MA). Although most Andean ammonoids were endemic to the Indo-Pacific Subrealm, nannofossils, calpionellids and polarity chrons were present in both areas. This stratigraphic experiment correlates base Berriasian as defined in France within the Substeueroceras koeneni Zone. In Andean sections this boundary is correlated with the Crassicolaria/Calpionella zone boundary dated at about 141 Ma. The base of the Valanginian defined by Calpionellites darderi correlates with the Neocomites wichmanni Zone of the Neuquén Basin (NB) recalibrated at 139.50 Ma, which is confirmed by multiple dates in Argentina, Mexico, Tibet, and elsewhere. The base Hauterivian correlates with base of Holcoptychites neuquensis Zone in the NB recalibrated at 131 Ma. Top of Hauterivian is in the Sabaudiella riverorum Zone in the NB and is dated at 127 Ma below an unconformity. Previous cyclostratigraphic astrochronologic cycles are averaged and calibrate the duration of the Tithonian at 5.67 myr, the Berriasian at 5.27 myr, the Valanginian at 5.30 myr, and the Hauterivian at 5.60 myr. The age of each stage is recalibrated by adding revised durations to the most common age of base Valanginian of 139.5 Ma. These ages revise the Berriasian to Hauterivian stages time scale, and the ages of stage boundaries are on average 2.8 myr longer than proposed by the new Neuquén Basin radioisotopic dates.