Abstract
Mainly acidic Stephanian to early Permian volcanic rocks and intercalated sediments accumulated in the Thuringian Forest Basin (TFB) in central Germany to a total thickness of ca. 2000 m. This basin offers a wide range of biostratigraphic information. New high-precision U–Pb CA–ID–TIMS (chemical abrasion–isotope dilution–thermal ionization mass spectrometry) zircon data are obtained from volcanic rocks for the first time in the TFB. Pre-treatment of the zircons by chemical abrasion was important to get rid of severe Pb loss. The zircon ages of the investigated formations indicate that the total duration of the volcanic activity in the TFB was considerably shorter [ca. 4 Myr: from 300 Ma for the oldest formation (Möhrenbach) until ca. 296 Ma for the youngest volcanic-rock-bearing formation (Rotterode)] than suggested in previous studies (ca. 20 Myr; 295 Ma to 275 Ma). Consequently, the well-documented gap of the sedimentary record from the early Permian volcanic rocks up to the Illawarra geomagnetic reversal has to be extended to ca. 25 Myr from the previously proposed 5 Myr. The zircon ages of the investigated volcanic rocks allow the constraining of some intercalated fossiliferous horizons crucial for biostratigraphic correlation of latest Carboniferous–early Permian (Rotliegend) sections. The high-precision age data require a new interpretation of the evolution of the TFB but also offer the chance to obtain a more reliable comparison of the timing of the main magmatic activity across intramontane basins as well as to obtain links to the Standard Global Stratigraphic Scale.
Highlights
From the late Carboniferous to the early Permian, the transition from the final stage of the Variscan orogeny to the stable continental regime of Pangea in Central Europe led to a change from compressive regimes to extensional/transtensional ones (Ziegler 1990; van Wees et al 2000; McCann et al 2006; Timmerman 2008; Kroner et al 2016, 2020)
We present new geochronological data from seven felsic volcanic rock samples of the Thuringian Forest Basin (TFB) with zircons dated by the U–Pb chemical abrasion (CA)–ID–TIMS method to: 1. Define the age range of volcanic activity in the TFB and compare it to the existing biostratigraphic data, 2
We report the first investigation by the U–Pb CA–ID–TIMS method of a Stephanian to early Permian profile in the Thuringian Forest Basin
Summary
From the late Carboniferous to the early Permian, the transition from the final stage of the Variscan orogeny to the stable continental regime of Pangea in Central Europe led to a change from compressive regimes to extensional/transtensional ones (Ziegler 1990; van Wees et al 2000; McCann et al 2006; Timmerman 2008; Kroner et al 2016, 2020). The TFB is situated in a central and important geographic position in the Variscan orogenic belt in the Mid-German Crystalline Rise and Saxothuringian Zone between the Saar–Nahe and Kraichgau Basins in the SW and the Saale Basin in the NE (Lützner and Kowalczyk 2012; Andreas 2014). These basins were thoroughly studied during the last > 70 years for their geological structure, volcanosedimentary successions (e.g., Lützner et al 2012), magnetostratigraphy (e.g., Menning and Bachtadse 2012), and biostratigraphy
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