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Numerical calibration of the Devonian-Carboniferous boundary: Two new U-Pb isotope dilution–thermal ionization mass spectrometry single-zircon ages from Hasselbachtal (Sauerland, Germany)

¹ Zentrallabor für Geochronologie, Institut für Mineralogie, Universität Münster, Corrensstrasse 24, 48149 Münster, Germany
² Institut für Geowissenschaften, Universität Tübingen, Sigwartstrasse 10, 72076 Tübingen, Germany
³ Zentrallabor für Geochronologie, Institut für Mineralogie, Universität Münster, Corrensstrasse 24, 48149 Münster, Germany
⁴ Museum für Naturkunde, Humboldt-Universität, Invalidenstrasse 43, 10115 Berlin, Germany
⁵ Löwestrasse 15, 10249 Berlin, Germany

The Hasselbachtal section (Sauerland, Germany) is an auxiliary global stratotype of the Devonian-Carboniferous boundary and one of the most important reference sections for the evolution of the latest Famennian to earliest Tournaisian pelagic fauna. Biostratigraphically well controlled altered volcanic ash layers (metabentonites) intercalated in the section afford a perfect opportunity for a numerical fixing of this important Paleozoic period boundary. We have performed U-Pb isotope dilution–thermal ionization mass spectrometry (ID-TIMS) analyses on (sub)microgram-sized single zircons and zircon fragments extracted from two metabentonites (beds 79 and 70) in the lowermost Tournaisian part of the section. Bed 79 metabentonite is positioned directly above the Devonian-Carboniferous boundary within the Siphonodella sulcata conodont zone. Five concordant analyses form a cluster with a ²⁰⁶Pb/²³⁸U concordia age of 360.5 ± 0.8 Ma. Zircons of the next younger metabentonite (bed 70), in the lower Siphonodella duplicata conodont zone, yielded a tightly grouped cluster of 10 concordant analyses with a ²⁰⁶Pb/²³⁸U concordia age of 360.2 ± 0.7 Ma. On the basis of these two new single-zircon ages and previously published late Famennian U-Pb ID-TIMS ages, the Devonian-Carboniferous boundary is reinterpolated herein to 360.7 ± 0.7 Ma.

Key Words: Devonian-Carboniferous boundary • metabentonites • U-Pb • zircon • absolute age

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