High-resolution stratigraphy and zircon U–Pb geochronology of the Middle Triassic Buchenstein Formation (Dolomites, northern Italy): precession-forcing of hemipelagic carbonate sedimentation and calibration of the Anisian–Ladinian boundary interval

Abstract

Orbitally forced cyclic variations in sedimentary sequences provide evidence for short-term fluctuations of Earth climate and a tool for high-resolution timescale calibration. We here present stratigraphic and geochronological evidence for precession-forcing in Middle Triassic hemipelagic limestones of the Buchenstein Formation (Dolomites, northern Italy). High-resolution stratigraphy of several correlative sections of the Buchenstein Formation documents a coherent cycle pattern. Isotope dilution thermal ionization mass spectrometry zircon U–Pb geochronology of tuffs bracketing the cyclic interval reveals an average cycle duration of 18.5 ± 2.1 kyr, consistent with a shorter climatic precession cycle in the Middle Triassic compared with today. This suggests a predominantly precession-controlled climate in this low-latitude setting of the western Tethys and allows high-precision calibration of the Anisian–Ladinian boundary interval. From integrating cyclostratigraphic and U–Pb geochronological constraints, our best estimate for the age of the Anisian–Ladinian boundary is 241.464 ± 0.064/0.097/0.28 Ma. We also provide precise estimates for lithostratigraphic boundaries, biostratigraphic markers and magnetic reversals within the boundary interval. Stratigraphic intervals with elevated sedimentation rate record a sub-Milankovitch signal that may be equivalent to patterns in adjacent carbonate platforms such as the Latemar platform. The origin of this sub-Milankovitch signal remains unknown but highlights the potential to investigate shorter-term climatic variations in Mesozoic sedimentary sequences. Supplementary material: Isotope dilution thermal ionization mass spectrometry U–Pb and laser ablation inductively coupled plasma mass spectrometry trace element data tables as well as the results of the Bayesian age modelling are available at https://doi.org/10.6084/m9.figshare.c.3861817 .

High-precision U–Pb ages in the early Tithonian to early Berriasian and implications for the numerical age of the Jurassic–Cretaceous boundary

“…New geochronological data from stage boundaries from the Late Jurassic to Early Cretaceous suggest that the age of the stage boundaries in this interval could be younger than used in the M-sequence model of Ogg (2012). For instance, Zhang et al (2018) provided magnetostratigraphic data for the U-Pb ages of Midtkandal et al (2016) in the Svalbard cores, which suggest that the age of the M0 (base of the Aptian) is 121-122 Ma rather than ∼ 126 Ma. presented a high-precision U-Pb age of 127.24 ± 0.03 Ma in the late Hauterivian (close to the base of the Barremian) in the Agrio Fm., Neuquén Basin, which Martinez et al (2015) used to anchor cyclostratigraphic studies in the in Río Argos, Spain, and calculated an age for the base of the Hauterivian at 131.96 ± 1 Ma and the base of the Barremian at 126.02±1 Ma.…”

“…We present highprecision U-Pb age determinations using chemical abrasionisotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) techniques to date zircon from interbedded volcanic ash layers in the Las Loicas section, Neuquén Basin, Argentina, and the Mazatepec section, Mexico. Such dates have proved to yield robust estimates for the timing of the stratigraphic record, especially in combination with Bayesian age-depth modeling (e.g., Ovtcharova et al, 2015;Baresel et al, 2017;Wotzlaw et al, 2017). The coupling of highprecision U-Pb geochronology and age-depth modeling allowed us to ascribe specific numerical ages to key taxa in the early Berriasian and late Tithonian in the studied sections.…”

Timing and evolution of Middle Triassic magmatism in the Southern Alps (northern Italy)

“…Such ash layers can be traced over hundreds of kilometres and have previously been used to calibrate the stratigraphic record (Brack & Rieber 1993;Mundil et al 1996), including the Global Boundary Stratotype Section and Point (GSSP) of the base of the Ladinian Stage (Brack et al 2005). New high-precision zircon U-Pb geochronology of several volcanic ash beds by Wotzlaw et al (2018) provide a significant refinement for a restricted interval of this chronostratigraphic framework, with a temporal resolution of individual age data below the per mil level. These precise new age data have allowed a re-evaluation of the interpretation of stratigraphic patterns.…”

“…We present here a comprehensive high-precision zircon U-Pb geochronology dataset for 12 silicic volcanic ash beds and two intrusive complexes in the Southern Alps. The ash data provide a significant extension of the recalibrated stratigraphic record of Wotzlaw et al (2018) and allow the episode of Triassic magmatism in the Southern Alps to be much better constrained (Fig. 2).…”

Metre‐scale cycles in shallow water carbonate successions: Milankovitch and stochastic origins

“…Importantly, Wotzlaw et al . () also linked an interval of apparent sub‐Milankovitch HFS development in the nearby and broadly coeval Buchenstein Formation to an interval of high subsidence/accumulation rate.…”