Response to comment on “A high-precision 40Ar/39Ar age for the Nördlinger Ries impact crater, Germany, and implications for the accurate dating of terrestrial impact events” by Schmieder et al. (Geochimica et Cosmochimica Acta 220 (2018) 146–157)

doi:10.1016/j.gca.2018.07.025

Geochimica et Cosmochimica Acta

Volume 238, 1 October 2018, Pages 602-605

https://doi.org/10.1016/j.gca.2018.07.025 Get rights and content

Abstract

Rocholl et al. (2018) claim that the ⁴⁰Ar/³⁹Ar age of 14.808 ± [0.038] Ma (2σ; full external error) for the Ries impact, recently obtained from step-heating analysis of tektites (Schmieder et al., 2018, Geochim. Cosmochim Acta 220, 146–157), is “geologically impossible” and violates paleomagnetic constraints. We demonstrate that the moldavite age of Schmieder et al. (2018) is in good agreement with recalculated isotopic ages for ash layers and magnetic (sub-)chrons that define the Langhian stage in the Astronomically Tuned Neogene Time Scale, using updated K decay constants and monitor ages in ⁴⁰Ar/³⁹Ar geochronology. Moreover, we stress that the normally magnetized basal pelitic sediments of the Ries crater lake, which are separated from the reversely magnetized suevite by a thick unit of post-impact conglomerates and sandstones, may not have been deposited ‘immediately’ after the impact. The paleomagnetic constraints proposed by Pohl (1977, 1978) and Rocholl et al. (2018) are, therefore, questionable.

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Joint determination of ⁴⁰K decay constants and ⁴⁰Ar^∗/⁴⁰K for the Fish Canyon sanidine standard, and improved accuracy for ⁴⁰Ar/³⁹Ar geochronology
Geochim. Cosmochim. Acta
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(2018)
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Integrated stratigraphy and ⁴⁰Ar/³⁹Ar chronology of early middle Miocene sediments from DSDP Leg 42A, Site 372 (western Mediterranean)

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(2008)

Cited by (16)

SEM pollen analysis of Miocene deposits of Entrischenbrunn (Bavaria, Germany) reveal considerable amounts of pollen of subhumid and sclerophyllous together with azonal water plants reflecting the vegetation mosaic of a braided river system
2023, Review of Palaeobotany and Palynology
Citation Excerpt :
The sediment succession is situated within the Upper Freshwater Molasse (OSM) between two marker horizons: the so called Brock-Horizon (Ries crater material) below, at the base of the sand pit, and 14.6 Myr old bentonites above, which were dated by Rocholl et al. (2018b) and crop out in the nearby pit of Unterwohlbach. For the Brock Horizon currently differing magneto-stratigraphic results indicate ranges ages of 14,8 and14.9 million years, respectively (Rocholl et al., 2018a, 2018b; Schmieder et al., 2018a, 2018b). However, based on small mammal stratigraphy, a cyclical subdivision of the Middle Miocene Upper Freshwater Molasse prepared by Fiest (1986; 1994) and later published by Heissig (2006), allows to narrow down the age of the Entrischenbrunn deposits to an interval between 14.9 to 14.7 million years (Fiest, pers.
The 1 m thick intercalated marly sediments of Entrischenbrunn represent a floodplain pond within a braided fluvial system of late Langhian age. The organic rich upper part of the marls that are characterized by the presence of numerous plant macrofossils, are investigated for palynomorphs with SEM. The results reveal that many typical azonal broad leaved forest elements were present (e.g., Fraxinus and Liquidambar) and some of the common macrofossils, such as Hemitrapa, Podocarpium, Platanus sp., Quercus spp. etc. However, because of non-resistant pollen walls, the two dominant components of the macroflora, Daphnogene and Populus are not represented in the palynoflora. In contrast, plants not known from macrofossils or rare for this locality are present: several aquatic plants (e.g., Callitriche sp., Ludwigia sp., Decodon sp.), and a large portion of more subhumid and sclerophyllous plants such as Celtis “tournefortii-type”, two Ephedra spp., two Erica spp. affiliable with Mediterranean species, Quercus sp. section Ilex, a Sapoteae, Sideroxylon sp., Rehderodendron sp., Ulmus sp. section Foliaceae Zelkova “abelicea/serrata-type”, and Ziziphus “mucronata/mauritania/jujube-type”, whereas Diospyros sp. and cf. Royena sp. can be interpreted to present humid to subhumid conditions. The reasons for this mixture might be threefold: 1. localized well-drained substrates and water loss on particularly pebbly, gravelly and sandy deposits of the braided river system or 2. presence of a geographically controlled localized lower humidity in that area, or 3. because of a generally drier period within the Middle Miocene.
High precision multi-collector 40Ar/39Ar dating of moldavites (Central European tektites) reconciles geochrological and paleomagnetic data
2022, Chemical Geology
Citation Excerpt :
The age of moldavites relative to the FCs reference mineral obtained here of 14.735 ± 0.013 Ma, using the most recent astronomically calibrated age (Phillips et al., 2022), would be 127 ± 15 ka older than the magnetic reverse-normal switch. However, it is important to note that the Ries crater was affected by a post-impact hydrothermal activity of uncertain duration, as much as ~250 ka according to Arp et al. (2013), and which could have delayed the establishment of the necessary conditions for the sedimentation of lacustrine deposits (see also discussion in Schmieder et al., 2018b). All data generated and analysed during this study are included in this article as Supplementary data (Tables A1 and A2).
Moldavites (Central European tektites) are genetically related to the meteorite impact event that produced the 24-km diameter Ries crater (Germany) during the Langhian, and representing one of the youngest large impact structures on Earth. Despite the numerous geochronological studies over the last decades and the potential implications for stratigraphic, paleontological and paleoclimatic studies, the age of the Ries impact is still debated. In this study, I investigate in detail moldavite samples by multicollector ⁴⁰Ar/³⁹Ar laser dating in order to address the age of the Ries impact. Data were obtained relative to the key Fish Canyon sanidine (FCs) and Alder Creek sanidine (ACs) reference materials, over a period of nearly two years, in four irradiations of different duration. Results, completed through the step-heating and the total fusion techniques, demonstrate an excellent intrasample and intersample reproducibility of moldavites and prove that analytical performances of moldavites in terms of uncertainties on the ⁴⁰Ar*/³⁹Ar_K ratios are in line with those achievable by the most widely used FCs and ACs reference minerals. Results from total fusion analyses yield a mean $R_{A C s}^{M o l d a v i t e}$ = 12.4952 ± 0.0038 (±2σ) and a mean $R_{F C s}^{M o l d a v i t e}$ = 0.52106 ± 0.00014 (±2σ). Data also allow to define a direct mean $R_{F C s}^{A C s}$ = 0.041703 ± 0.000032 (±2σ) and an indirect (using moldavites as intermediary), more precise, mean $R_{F C s}^{A C s}$ = 0.041700 ± 0.000019 (±2σ). Using the internally consistent astronomically-calibrated ages for the ACs (1.1848 ± 0.0012 Ma) and the FCs (28.201 ± 0.046 Ma) reference minerals from the literature, the R-values yield indistinguishable ages for moldavites of 14.7495 ± 0.0045 (± 0.016 Ma, including all known source of errors) and 14.7486 ± 0.0039 Ma (± 0.025 Ma), respectively. The most recent astronomically calibrated age for FCs (28.176 ± 0.023 Ma) yields a slightly younger, but more precise, age of 14.7355 ± 0.0039 Ma (± 0.013 Ma). Results place definitively the age of the Ries impact in the reverse polarity chron C5ADr of the ATNTS2022, and suggest that the Ries impact preceded the switch from reversed to normal chron by at least 127 ± 15 ka.
40Ar/39Ar systematics of melt lithologies and target rocks from the Gow Lake impact structure, Canada
2020, Geochimica et Cosmochimica Acta
Citation Excerpt :
Taking the weighted mean of the step-heating and in situ isochron ages (analytical precision only, and subsequently propagating the systematic uncertainty from the decay constant) the best age for the Gow Lake impact event is 196.8 ± 9.6/9.9 Ma (2σ, 5%, analytical/external precision), which overlaps the Triassic-Jurassic boundary (201.36 ± 0.43 Ma, 2σ, zircon 206Pb/238U, external uncertainties; Schoene et al., 2010, as recalculated by Wotzlaw et al., 2014). Our in situ 40Ar/39Ar results support the conclusions of other authors (e.g., Jourdan et al., 2009; Mark et al., 2014; Schmieder et al., 2018a; Schmieder et al., 2018b) that impact-generated glass is the best material for 40Ar/39Ar geochronology of small to medium size impact structures. The 40Ar/39Ar data show that even when derived from a granitic target rock, which typically yields relatively viscous melts, impact-generated melt glass can provide geologically meaningful 40Ar/39Ar ages.
The age of the Gow Lake impact structure (Saskatchewan, Canada) is poorly constrained, with previous estimates ranging from 100 to 250 Ma. Using a combination of step-heating and UV laser in situ ⁴⁰Ar/³⁹Ar analyses we have sought to understand the ⁴⁰Ar/³⁹Ar systematics of this small impact crater and obtain a more precise and accurate age. This structure is challenging for ⁴⁰Ar/³⁹Ar geochronology due to its small size (∼5 km diameter), the silicic composition of the target rock, and the large difference in age between the impact event and the target rock (∼1.2 Ga). These factors can serve to inhibit argon mobility in impact melts, leading to retention of ‘extraneous’ ⁴⁰Ar and anomalously older measured ages. We mitigated the undesirable effects of extraneous ⁴⁰Ar retention by analysing small volume aliquots of impact glass using step-heating and even smaller volumes via the UV laser in situ ⁴⁰Ar/³⁹Ar technique. Although primary hydration of impact-generated glasses enhanced the diffusivity of ⁴⁰Ar inherited from silica-rich melts, data still had to be corrected for extraneous ⁴⁰Ar by using isotope correlation plots to define the initial trapped ⁴⁰Ar/³⁶Ar components. Our inverse isochron age of 196.8 ± 9.6/9.9 Ma (2σ, analytical/external precision) demonstrates that the Gow Lake event occurred within uncertainty of the Triassic-Jurassic boundary, but there is no evidence that it was part of an impact cluster.
Enigmatic earthquake-generated large-scale clastic dyke in the Biberach area (SW Germany)
2020, Sedimentary Geology
Citation Excerpt :
The latter is also known for the most distal occurrence of Ries impact ejecta (the so called ‘Ries-Brockhorizont’; e.g., Buchner et al., 2007; Sach, 2014). Scholz and Frieling (2006), Scholz et al. (2011), and Keller (2012) linked the formation of the clastic dykes to Alpine seismic activity, whereas Letsch (2017) suggested the 14.808 ± 0.038 Ma Nördlinger Ries impact event (Schmieder et al., 2018a, 2018b) produced those dykes. In summer 2019, a clastic dyke of at least 15.2 m in vertical extent (Figs. 2–5) was discovered by one of the authors (V.J.S.) within a sedimentary sequence of the Upper Freshwater Molasse in an area locally known as the “Hochgeländ” (see Probst, 1873, for the first detailed geological description of the area), about 6 km south of the city of Biberach an der Riß in Southern Germany (Fig. 1).
We discovered and describe a large-scale (exposed dimensions ~17 m in lateral and ~15 m in vertical extension, and up to 10 cm in width) clastic dyke in the Middle Miocene (between ~17.1 and ~14.5 Ma) sandy deposits (‘Fluviatile Untere Serie’) of the North Alpine Foreland Basin, close to Biberach an der Riß in SW Germany. The dyke appears to be of sedimentary–tectonic origin. It formed by liquefaction and injection of clastic material that occurred simultaneously with fracture opening and propagation in sandy deposits, presumably as a result of strong seismic shaking triggered by an intense earthquake. We, therefore, interpret the dyke as a seismite and a useful palaeoseismic indicator. The clastic dyke cuts through a layer of distal Ries ejecta (‘Brockhorizont’) and, thus, postdates the Ries impact. The age of the Ries event, in combination with other stratigraphic constraints, defines a relatively narrow time frame of ~14.8 to 14.5 Ma for the formation of the clastic dyke. The source of the strong earthquake responsible for dyke formation might be seismicity related to the Alpine orogeny and tectonism, seismic activity in one of the volcanic fields of the Paleogene to Quaternary European Volcanic Province, or seismicity induced by a Miocene impact event in southern Germany. We suggest the relatively strong earthquake in question may have been triggered by a large phreatomagmatic explosion in the Urach-Kirchheim volcanic field or, perhaps more likely, the Steinheim impact event on the eastern Swabian Alb plateau.
Twinned calcite as an indicator of high differential stresses and low shock pressure conditions during impact cratering
2023, Meteoritics and Planetary Science
Event- and biostratigraphic evidence for two independent Ries and Steinheim asteroid impacts in the Middle Miocene
2022, Scientific Reports

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Geochimica et Cosmochimica Acta

Abstract

References (22)

The Neogene period

Astrochronology of the Mediterranean Langhian between 15.29 and 14.17 Ma

Earth Planet. Sci. Lett.

ArAR—a software tool to promote the robust comparison of K-Ar and ⁴⁰Ar/³⁹Ar dates published using different decay, isotopic, and monitor-age parameters

Chem. Geol.

A test for systematic errors in ⁴⁰Ar/³⁹Ar geochronology through comparison with U/Pb analysis of a 1.1-Ga rhyolite

Geochim. Cosmochim. Acta

Intercalibration of standards, absolute ages and uncertainties in ⁴⁰Ar/³⁹Ar dating

Chem. Geol.

Joint determination of ⁴⁰K decay constants and ⁴⁰Ar^∗/⁴⁰K for the Fish Canyon sanidine standard, and improved accuracy for ⁴⁰Ar/³⁹Ar geochronology

Geochim. Cosmochim. Acta

Response to the comment by WH Schwarz et al. on “Joint determination of ⁴⁰K decay constants and ⁴⁰Ar^∗/⁴⁰K for the Fish Canyon sanidine standard, and improved accuracy for ⁴⁰Ar/³⁹Ar geochronology” by PR Renne et al. (2010)

Geochim. Cosmochim. Acta

The Lappajärvi impact structure (Finland): age, duration of crater cooling, and implications for early life

Geochim. Cosmochim. Acta

A high-precision ⁴⁰Ar/³⁹Ar age for the Nördlinger Ries impact crater, Germany, and implications for the accurate dating of terrestrial impact events

Geochim. Cosmochim. Acta

Appendix 2 –Radiometric ages used in GTS2012

Integrated stratigraphy and ⁴⁰Ar/³⁹Ar chronology of early middle Miocene sediments from DSDP Leg 42A, Site 372 (western Mediterranean)

Palaeogeogr. Palaeoclimatol. Palaeoecol.

Cited by (16)

SEM pollen analysis of Miocene deposits of Entrischenbrunn (Bavaria, Germany) reveal considerable amounts of pollen of subhumid and sclerophyllous together with azonal water plants reflecting the vegetation mosaic of a braided river system

High precision multi-collector <sup>40</sup>Ar/<sup>39</sup>Ar dating of moldavites (Central European tektites) reconciles geochrological and paleomagnetic data

<sup>40</sup>Ar/<sup>39</sup>Ar systematics of melt lithologies and target rocks from the Gow Lake impact structure, Canada

Enigmatic earthquake-generated large-scale clastic dyke in the Biberach area (SW Germany)

Twinned calcite as an indicator of high differential stresses and low shock pressure conditions during impact cratering

Event- and biostratigraphic evidence for two independent Ries and Steinheim asteroid impacts in the Middle Miocene

ResponseResponse to comment on “A high-precision 40Ar/39Ar age for the Nördlinger Ries impact crater, Germany, and implications for the accurate dating of terrestrial impact events” by Schmieder et al. (Geochimica et Cosmochimica Acta 220 (2018) 146–157)

Abstract

Earth Planet. Sci. Lett.

Chem. Geol.

Geochim. Cosmochim. Acta

Chem. Geol.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Integrated stratigraphy and 40Ar/39Ar chronology of early middle Miocene sediments from DSDP Leg 42A, Site 372 (western Mediterranean)

Palaeogeogr. Palaeoclimatol. Palaeoecol.

Response
Response to comment on “A high-precision ⁴⁰Ar/³⁹Ar age for the Nördlinger Ries impact crater, Germany, and implications for the accurate dating of terrestrial impact events” by Schmieder et al. (Geochimica et Cosmochimica Acta 220 (2018) 146–157)

Integrated stratigraphy and ⁴⁰Ar/³⁹Ar chronology of early middle Miocene sediments from DSDP Leg 42A, Site 372 (western Mediterranean)