Age constraints from small shelly fossils on the early Cambrian terminal Cadomian Phase in Iberia

Abstract

The records of biotic and biogeochemical events around the Proterozoic-Cambrian transition are well preserved in sedimentary rock successions in Iberia. Until recently, sparsely fossiliferous siliciclastic and carbonate successions in central Spain were believed to be largely Proterozoic in age and to have suffered late Cadomian deformation. Small shelly fossils identified as Anabarella sp. cf. A. plana are here reported from south-central Spain and are consistent with broadly Ne-makit-Daldynian to Tommotian, early Cambrian age. At a location in southwestern Spain, siliciclastics that yield Platysolenites antiquissimus in association with an unidentified trilobite are interpreted to be coeval with the upper stratigraphic record of P. antiquissimus in Baltica. Both fossil occurrences are nearly time-equivalent to Tommotian-age rocks in North Iberia that yield ichnofossils and acritarchs. These beds unconformably overlie Neoproterozoic turbidites deformed by late Cadomian folding. Small shelly fossil (SSF) faunas in central Iberia (Spain) have “Acado-Baltic” and “Gondwanan” affinities, and their presently known distribution supplements previous palaeogeographic reconstructions that imply near contemporaneity with broadly Tommotian-age faunas from medium to low latitude shelf settings in Iberia, Siberia, Avalonia, Armorica, southern China, Iran, India and Australia. The new biostratigraphic data allow clarification of the magnitude of the sub-Tommotian unconformity in parts of Iberia and set firm minimum age constraints for the terminal Cadomian Phase of the Pan-African orogeny in Iberia.

Keywords:

• Small shelly faunas
• acritarchs
• Nemakit-Daldynian
• Tommotian
• Lower Cambrian
• Neoproterozoic
• Iberia
• Baltica
• Gondwana