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

U-Pb laser ablation inductively coupled plasma mass spectrometry was used for dating zircon grains extracted from four sedimentary and volcano sedimentary rocks of the Montagne Noire encompassing the presumed Ediacaran-Cambrian boundary interval. Magmatic zircon from two samples from the basal and middle parts of the Rivernous Formation (a rhyolitic tuff) were deposited at 542.5 +/- 1 Ma and 537.1 +/- 2.5 Ma, bracketing the 541 Ma age presently admitted as being at the Ediacaran-Cambrian boundary. In addition, a piece of sandstone from the underlying Rivernous Formation containing mostly euhedral zircon grains, suggesting proximal magmatic sources, yields Neoproterozoic dates ranging from 574 Ma to 1 Ga, and subsidiary older dates from 1.25 to 2.75 Ga. Another piece of sandstone from the overlying Marcory Formation yielded mostly rounded zircon grains probably issued from more remote areas, with a large spectrum dominated by Neoproterozoic dates as well as older ages up to 3.2 Ga. A comparison of both kinds of sandstone suggests a significant change in provenance, changing from a restricted source area during the Ediacaran to a much larger source domain during the Cambrian Epoch 2 that recorded contributions from different cratons of Gondwana. (C) 2017 Academie des sciences. Published by Elsevier Masson SAS.