A Triassic/jurassic Boundary Age for the Rochechouart Impact Structure (france)
نویسندگان
چکیده
Introduction: The age of the ~23 km in diameter Rochechouart impact structure, France, hosted by Precambrian to Paleozoic (Variscan) crystalline rocks of the northwestern French Massif Central, has long time been a matter of debate. Previous studies, including K-Ar, Rb-Sr, apatite and glass fission track, as well as paleomagnetic dating (see [1] for summary of ages), resulted in a broad (Middle Triassic to Late Jurassic) time window for the Rochechouart impact. More recently, 40 Ar/ 39 Ar laser dating of pseudotachylites from Champagnac yielded a 214 ± 8 Ma Late Triassic age [1] currently accepted as the most robust impact age, supporting the theory that Rochechouart is a member of a ~214 Ma terrestrial impact crater chain [2]. Precise and accurate dating is critical to this interpretation and, furthermore, essential as regards the proximity and possible influence of the nearby Triassic to Jurassic shoreline and/or sediments upon crater formation and vice versa. We here present new 40 Ar/ 39 Ar age data for the Rochechouart impact structure.
منابع مشابه
A new high-precision Ar/Ar age for the Rochechouart impact structure: At least 5 Ma older than the Triassic–Jurassic boundary
The Rochechourt impact structure in south-central France, with maximum diameter of 40–50 km, has previously been dated to within 1% uncertainty of the Triassic– Jurassic boundary, at which time ~30% of global genera became extinct. To evaluate the temporal relationship between the impact and the Triassic–Jurassic boundary at high precision, we have re-examined the structure’s age using multicol...
متن کاملEvidence for coeval Late Triassic terrestrial impacts from the Rochechouart (France) meteorite crater
High temperature impact melt breccias from the Rochechouart (France) meteorite crater record a magnetization component with antipodal, normal and reverse polarities. The corresponding paleomagnetic pole for this component lies between the 220 Ma and 210 Ma reference poles on the Eurasian apparent polar wander path, consistent with the 214±8 Ma Ar/Ar age of the crater. Late Triassic tectonic rec...
متن کاملNew early Jurassic tetrapod assemblages constrain Triassic-Jurassic tetrapod extinction event.
The discovery of the first definitively correlated earliest Jurassic (200 million years before present) tetrapod assemblage (Fundy basin, Newark Supergroup, Nova Scotia) allows reevaluation of the duration of the Triassic-Jurassic tetrapod extinction event. Present are tritheledont and mammal-like reptiles, prosauropod, theropod, and ornithischian dinosaurs, protosuchian and sphenosuchian croco...
متن کاملRe-evaluating the Rochechouart Impactites: Petrographic Classification, Hydrothermal Alteration and Evidence for Carbonate Bearing
Introduction: The Rochechouart impact structure is a deeply eroded, late Triassic impact site located in south-central France [1,2]. Rochechouart impactites comprise five main lithological units from the base of the structure upwards, originally described as follows: unit 1) shocked autochthonous basement rock; unit 2) finely crystalline melt rock; unit 3) red 'welded' breccia/suevite; unit 4) ...
متن کاملTriassic-jurassic Boundary on the Southern Margin of Tethys: Implications of Facies, Tectonics and Volcanism
The facies changes, tectonics and magmatism across the Triassic–Jurassic boundary in the southern Tethyan margin have been studied in Egypt, Sudan, Jordan and Saudi Arabia. In Saudi Arabia and Jordan an unconformable contact is recognized between the Upper Triassic and Lower Jurassic rocks. This unconformity surface is marked by the truncation of the fluvial clastics of the uppermost Triassic b...
متن کامل