U–Pb laser ablation ICP-MS zircon dating across the Ediacaran–Cambrian transition of the Montagne Noire, southern France

摘要

U–Pb laser ablation inductively coupled plasma mass spectrometry was used for datingrnzircon grains extracted from four sedimentary and volcano sedimentary rocks of thernMontagne Noire encompassing the presumed Ediacaran–Cambrian boundary interval.rnMagmatic zircon from two samples from the basal and middle parts of the RivernousrnFormation (a rhyolitic tuff) were deposited at 542.5 u0002 1 Ma and 537.1 u0002 2.5 Ma, bracketingrnthe 541 Ma age presently admitted as being at the Ediacaran–Cambrian boundary. In addition,rna piece of sandstone from the underlying Rivernous Formation containing mostly euhedralrnzircon grains, suggesting proximal magmatic sources, yields Neoproterozoic dates rangingrnfrom 574 Ma to 1 Ga, and subsidiary older dates from 1.25 to 2.75 Ga. Another piece ofrnsandstone from the overlying Marcory Formation yielded mostly rounded zircon grainsrnprobably issued from more remote areas, with a large spectrum dominated by Neoproterozoicrndates as well as older ages up to 3.2 Ga. A comparison of both kinds of sandstone suggests arnsignificant change in provenance, changing from a restricted source area during the Ediacaranrnto a much larger source domain during the Cambrian Epoch 2 that recorded contributionsrnfrom different cratons of Gondwana.