Preservation of orbital forcing in intraplatform carbonates and an astronomical time frame for a multiproxy record of end-Triassic global change from a western Tethyan section (Csővár, Hungary)
Zsolt Vallner, Emma Blanka Kovács, János Haas, Ferenc Móricz, Micha Ruhl, Norbert Zajzon, József Pálfy
Abstract
High temporal resolution is of paramount importance in stratigraphic studies of major events in earth history such as the end-Triassic extinction (ETE). Although it ranks among the most severe Phanerozoic mass extinctions, the precise timing and duration of the cascade of environmental and biotic changes across the Triassic-Jurassic boundary (TJB) interval remains controversial. Here we present a cyclostratigraphic study of the Csővár section (Hungary), a continuous carbonate succession from an intraplatform basin that yielded significant geochemical and paleontological data from around the TJB. We analyzed ten elemental time series and stable isotope data series and detected cyclicities with periodicities similar to the orbital cycles of the ∼405 kyr long and ∼124 kyr short eccentricity, the ∼34 kyr obliquity, and the ∼17–21 kyr precession. The astrochronologic age model suggests that the ∼52 m thick section was deposited in 2.9–3 Myr, with an average sedimentation rate of 1.73–1.79 cm/kyr. We establish that the section contains the last ∼1.3 million years of the Rhaetian and most of the Hettangian, supporting a <2 Myr duration for this stage. The duration of the initial carbon isotope anomaly (ICIE) is estimated at ∼40–80 kyr. Previously recognised meter-scale sequences are in agreement with the long eccentricity cycles up to the level of the ICIE but subsequently this relationship becomes less clear, possibly reflecting the effects of the end-Triassic climatic/environmental perturbations and associated changes in the depositional environment superimposed onto overarching astronomical forcing. We propose a cyclicity-based environmental model for sedimentation in the Csővár basin where the observed antiphase behaviour of the carbonate accumulation and the terrigenous input and dissolved silica was driven by a combination of aquifer- and limno-eustasy and the ˝megamonsoon˝ system that dominated the climate of the peri-Tethyan realm. This study highlights that intraplatform carbonate successions can be suitable archives to preserve orbital cyclicities and the new astrochronological age model helps improve our understanding of the ETE and other events in the TJB interval.