In-situ U-Pb dating of Ries Crater lacustrine carbonates (Miocene, South-West Germany): Implications for continental carbonate chronostratigraphy

1,2,3,4Damaris Montano,1,5Marta Gasparrini,2,3Axel Gerdes,5Giovanna Della Porta,2,3Richard Albert
Earth and Planetary Science Letters 568, 117011 Link to Article []
1IFP Energies nouvelles, 1-4 avenue de Bois-Préau, 92852, Rueil-Malmaison, France
2Institut für Geowissenschaften, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt am Main, Germany
3Frankfurt Isotope and Element Research Center (FIERCE), Goethe University Frankfurt, Frankfurt am Main, Germany
4Sorbonne Université; ED 398 – GRNE, 4, place Jussieu, 75252 Paris, France
5Università degli Studi di Milano; Dipartimento di Scienze della Terra “Ardito Desio”, via Mangiagalli 34, 20133 Milan, Italy
Copyright Elsevier

The Nördlinger Ries Crater lacustrine basin (South-West Germany), formed by a meteorite impact in the Miocene (Langhian; ∼14.9 Ma), offers a well-established geological framework to understand the strengths and limitations of U-Pb LA-ICPMS (in situ Laser Ablation-Inductively Coupled Plasma Mass Spectrometry) geochronology as chronostratigraphic tool for lacustrine (and more broadly continental) carbonates. The post-impact deposits include siliciclastic basinal facies at the lake centre and carbonate facies at the lake margins, coevally deposited in a time window of >1.2 and <2 Ma. Depositional and diagenetic carbonate phases (micrites and calcite cements) were investigated from three marginal carbonate facies (Hainsfarth bioherm, Adlersberg bioherm and Wallerstein mound). Petrography combined with C and O stable isotope analyses indicate that most depositional and early diagenetic carbonates preserved pristine geochemical compositions and thus the U-Pb system should reflect the timing of original precipitation. In total, 22 U-Pb ages were obtained on 10 different carbonate phases from five samples. The reproducibility and accuracy of the U-Pb (LA-ICPMS) method were estimated to be down to 1.5% based on repeated analyses of a secondary standard (speleothem calcite ASH-15d) and propagated to the obtained ages. Micrites from the Hainsfarth, Adlersberg and Wallerstein facies yielded ages of 13.90 ± 0.25, 14.14 ± 0.20 and 14.33 ± 0.27 Ma, respectively, which overlap within uncertainties, and are consistent with the weighted average age of 14.30 ± 0.20 Ma obtained from all the preserved depositional and early diagenetic phases. Data indicate that sedimentation started shortly after the impact and persisted for >1.2 and <2 Ma, in agreement with previous constraints from literature, therefore validating the accuracy of the applied method. Later calcite cements were dated at 13.2 ± 1.1 (), 10.2 ± 2.7 and 9.51 ± 0.77 Ma, implying multiple post-depositional fluid events. This study demonstrates the great potential of the U-Pb method for chronostratigraphy in continental systems, where correlations between time-equivalent lateral facies are often out of reach. In Miocene deposits the method yields a time resolution within the 3rd order depositional sequences (0.5–5 Ma).


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