TY - JOUR

T1 - Resolving the age of the Puchezh-Katunki impact structure (Russia) against alteration and inherited Ar-40* - No link with extinctions

AU - Holm-Alwmark, Sanna

AU - Jourdan, Fred

AU - Ferriere, Ludovic

AU - Alwmark, Carl

AU - Koeberl, Christian

PY - 2021/5/15

Y1 - 2021/5/15

N2 - The possibility of a "death from above" cause for biotic crises and extinction events is intriguing, to say the least, but such claims must be supported by reliable and reproducible data, not only impact diagnostic criteria, but also accurate and precise radioisotopic ages of the impact structures/events. To date, only one example of such an impact-related global extinction event is confirmed, at the end of the Cretaceous period. Here we present and discuss results of newly obtained Ar-40/Ar-39 data from step heating analysis of impact melt rock samples from the 40 km-in-diameter Puchezh-Katunki impact structure, Russia, which allow us to precisely and accurately date its formation at 195.9 +/- 1.0 Ma (2 sigma; P = 0.10). Based on these new data, we challenge the proposed temporal correlation with as many as five different extinction events (including the end-Triassic mass extinction) that were based on previous age estimations ranging from similar to 164 to 203 Ma. Our new age for the formation of the Puchezh-Katunki impact structure allows us to exclude a relationship between this impact event and a known extinction event. We also show that careful sample preparation and methodology can overcome problems with inherited and trapped Ar-40, issues that are common when dating impact melt rocks. This is supported by Ar-40* diffusion and mixing numerical models showing that the most prominent negative effects in the case of the Puchezh-Katunki impact melt rock samples are caused by hydrothermal alteration and undegassed melt rock domains present in an otherwise homogenized melt rock. Numerical modeling also shows that the Ar-40* from high-Ca inherited crystals or clasts is decoupled from the melt rock during step heating experiments allowing to safely recover a plateau age. Finally, our results highlight the importance of improving the database of ages of impact structures and show that caution should be practiced when suggesting connections between specific impact events and extinction events, especially in the case of poorly dated impact structures. (C) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

AB - The possibility of a "death from above" cause for biotic crises and extinction events is intriguing, to say the least, but such claims must be supported by reliable and reproducible data, not only impact diagnostic criteria, but also accurate and precise radioisotopic ages of the impact structures/events. To date, only one example of such an impact-related global extinction event is confirmed, at the end of the Cretaceous period. Here we present and discuss results of newly obtained Ar-40/Ar-39 data from step heating analysis of impact melt rock samples from the 40 km-in-diameter Puchezh-Katunki impact structure, Russia, which allow us to precisely and accurately date its formation at 195.9 +/- 1.0 Ma (2 sigma; P = 0.10). Based on these new data, we challenge the proposed temporal correlation with as many as five different extinction events (including the end-Triassic mass extinction) that were based on previous age estimations ranging from similar to 164 to 203 Ma. Our new age for the formation of the Puchezh-Katunki impact structure allows us to exclude a relationship between this impact event and a known extinction event. We also show that careful sample preparation and methodology can overcome problems with inherited and trapped Ar-40, issues that are common when dating impact melt rocks. This is supported by Ar-40* diffusion and mixing numerical models showing that the most prominent negative effects in the case of the Puchezh-Katunki impact melt rock samples are caused by hydrothermal alteration and undegassed melt rock domains present in an otherwise homogenized melt rock. Numerical modeling also shows that the Ar-40* from high-Ca inherited crystals or clasts is decoupled from the melt rock during step heating experiments allowing to safely recover a plateau age. Finally, our results highlight the importance of improving the database of ages of impact structures and show that caution should be practiced when suggesting connections between specific impact events and extinction events, especially in the case of poorly dated impact structures. (C) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

KW - Puchezh-Katunki

KW - Impact crater

KW - 40Ar/39Ar dating

KW - Inherited 40Ar

KW - Extinction events

KW - PRECISION AR-40/AR-39 AGE

KW - EOCENE-OLIGOCENE BOUNDARY

KW - LARGE IGNEOUS PROVINCES

KW - U-PB GEOCHRONOLOGY

KW - MASS EXTINCTIONS

KW - TRIASSIC EXTINCTION

KW - ASTEROID IMPACT

KW - EVENTS

KW - CRATER

KW - HISTORY

U2 - 10.1016/j.gca.2021.03.001

DO - 10.1016/j.gca.2021.03.001

M3 - Journal article

VL - 301

SP - 116

EP - 140

JO - Geochimica et Cosmochimica Acta. Supplement

JF - Geochimica et Cosmochimica Acta. Supplement

SN - 0046-564X

ER -