Calibrating ¹³C and ¹⁸O chemostratigraphic correlations across Cambrian strata of SW Europe and Morocco, West Gondwana

The Cambrian remains one of the least constrained Phanerozoic periods from the International Geological Timescale. Several global boundaries of series and stages are still awaiting formal definition and ratification. Particularly in West Gondwana, a major obstacle to the development of a common regional Cambrian timescale and its global correlation is the endemic character of its shelly fauna (mainly trilobites, archaeocyaths, echinoderms and brachiopods) due to the rare exposure of fossiliferous slope-to-basinal strata bearing cosmopolitan taxa. Over the past two decades, there has been a growing interest in the application of isotopic chemostratigraphic methods to regional studies, in an effort to solve and calibrate the timescale resolution in the Cambrian Atlas-Ossa-Morena rift axes and their lateral flanks preserved in Morocco, the Iberian Peninsula and South France. A critical re-appraisal of the resulting chemostratigraphic methods and results applied to the recognition and regional correlation of the Ediacaran-Cambrian (BACE event), Cambrian Series 2-Miaolingian (ROECE) and Miaolingian-Furongian (SPICE) boundaries is presented here. The reliability of isotopic data is mainly controlled by (i) the preferential analysis of bulk rock in carbonates and shales with total organic contents (TOC) lesser than 1wt%; (ii) the unequal record of diagenetic (e.g., early vs. late diagenetic dolomitization) and metamorphic processes related to Variscan tectono-thermal events; and (iii) dating uncertainty of chemostratigraphic fluctuations by chronostratigraphic and radiometric constraints.