Multidisciplinary re-assessment of the Ediacaran-Cambrian boundary interval in south-western Europe

A combination of chronostratigraphic, radiometric and carbon isotopic data across the Ediacaran-Cambrian transition in south-western Europe (Portugal, Spain and southern France) provides a reliable multidisciplinary approach to recognize the Ediacaran-Cambrian boundary interval on a margin of West Gondwana unevenly affected by the Cadomian Orogeny. The geochronological boundary broadly coincides with a terminal Cadomian metamorphic event recorded throughout the island arc to proximal retro-arc basin preserved in the Ossa-Morena Zone. In the Central Iberian Zone, representing an intermediate position of the retro-arc basin, the boundary lies at the top of a carbonate succession (with its base constrained by SHRIMP, CA-ID-TIMS and CA-SHRIMP methods at 560 +/- 2 Ma, and its uppermost part comprising the chemostratigraphic Basal Cambrian Isotope Excursion or BACE) preceding the lowest occurrence of Treptichnus pedum . In the Cantabrian Zone, a tectonostratigraphic unit fringing the Gondwana margin, it is included in a major gap of about 20 m. y. far from Cadomian tectonic perturbations. Conformable strata are recognized in the Montagne Noire and the Eastern Pyrenees, where a distinct episode of felsic explosive magmatism took place across the Ediacaran-Cambrian boundary interval. In the Iberian massif, the end of the Cadomian orogeny is marked by a diachronous (intra-Terreneuvian) pre-rift unconformity, characterized by the onset of collapse structures and megabreccias. One of the phosphogenetic episodes that punctuated the Ediacaran-Cambrian transition interval recorded shelly accumulations rich in helcionellids, including Anabarella plana and Watsonella crosbyi , which represent good candidates for recognizing the base of Cambrian Stage 2 in south-western Europe. Two new regional chronostratigraphic units are defined, named Monfraguan and Calatravan stages: the base of the former is marked by the lowest occurrence of the ichnospecies Treptichnus pedum , and that of the latter by the lowest occurrence of the helcionellid Anabarella plana .