In:
Bulletin de la Société Géologique de France, EDP Sciences, Vol. 175, No. 1 ( 2004-01-01), p. 3-10
Abstract:
A trachytic tephra layer deposited in the lower part of the Upper Miocene (Turolian) diatomite sequence at la Montagne d’Andance (Coiron basaltic province, France) contains glass shards (73 % SiO2), plus crystals of sanidine, ilmenite, biotite, amphibole, clinopyroxene, zircon, sphene and apatite. This composition and other volcanological data suggest a correlation to the Cantal stratovolcano, 150 km distant, better than to the nearer (50 km) Mézenc area. The 7.54 ± 0.06 Ma (± 2 σ) isochron defined by eight 40Ar/39Ar laser fusion analyses of sanidine gives a precise age for the beginning of the fossiliferous sequence, known for its rich flora and fauna. Moreover, unspiked K-Ar ages determined from three basaltic lava flows that pre- and post-date the lacustrine sedimentation are 7.37 ± 0.06, 7.17 ± 0.06 and 7.13 ± 0.06 Ma (± 2σ), thereby bracketing the sequence to a 400 kyr period between ca. 7.5 and 7.1 Ma. These are the first radioisotopic constraints for the lower part of the Turolian continental stage. They imply an age about 20 % younger for the fauna than proposed by previous biostratigraphic correlation. This new chronology is consistent with correlation of the lower limit of the Turolian to the Tortonian-Messinian boundary (7.30 ± 0.15 Ma) of the global marine stages.
Type of Medium:
Online Resource
ISSN:
1777-5817
,
0037-9409
Language:
English
Publisher:
EDP Sciences
Publication Date:
2004
detail.hit.zdb_id:
2747870-1
detail.hit.zdb_id:
2175250-3
SSG:
13
