Integrated Anisian–Ladinian boundary chronology

Abstract

We report magnetostratigraphic and biostratigraphic data from the Seceda core and the correlative outcrop section from the Dolomites of northern Italy. The Seceda rock succession consists of Tethyan marine limestones and radiometrically dated volcaniclastic layers of the Buchenstein Beds of Middle Triassic age (∼238–242 Ma). The Seceda outcrop section was correlated to coeval sections from the literature using magnetic polarity reversals and a selection of laterally traceable and isochronous lithostratigraphic marker beds. This allowed us to import the distribution of age-diagnostic conodonts, ammonoids, and daonellas from these sections into a Seceda reference stratigraphy for the construction of an integrated biochronology extending across a consistent portion of the Anisian–Ladinian boundary interval. Among the three options selected by the Subcommission for Triassic Stratigraphy to establish the Ladinian Global Stratigraphic Section and Point, we propose to adopt the level containing the base of the Curionii ammonoid Zone at Bagolino (Southern Alps, Italy) because this level is closely associated with a global means of correlation represented by the base of polarity submagnetozone SC2r.2r. The first occurrence of Neogondolella praehungarica in the Dolomites predates slightly the base of the Curionii Zone and can be used to approximate the Anisian–Ladinian boundary in the absence of ammonoids.