Precambrian—Cambrian boundary and correlation from southwestern and central part of Spain

Abstract This paper comprises the first palaeontological correlation between the Upper Proterozoic–Lower Cambrian Series of Ossa-Morena, Luso-Oriental-Alcúdica and Galaico-Castellana Zones of the Iberian Peninsula. The authors show the palaeontological events on acritarchs, stromatolites, cyanophyta, soft-bodied metazoa, trilobites, archaeocyathans and skeletal microfossils from three representative sequences of the above mentioned zones and discuss the position of the Precambrian–Cambrian boundary in the sequences. The Sierra de Córdoba general Series (Ossa-Morena Zone) has an erosive discontinuity between the rocks with the first record of Cambrian metazoan activity (Skolithossp.,Monomorphichnussp.,Phycodes pedumandRusophycussp.) and the rocks with a palynological association (Bavlinella faveolata, Protosphaeridium flexosum, Trachisphaeridiumsp., aff.Octoedryxium truncatum, Phycomicetes? sp. and cf.Ooidiumsp.) which suggests a Lower–Middle Vendian age. For this reason we suggest that the Precambrian–Cambrian boundary be placed at this unconformity. The upper part of the Sierra de Guadalupe Series (Luso-Oriental-Alcúdica Zone) includes detrital beds withPhycodes pedum, Planolitessp. andTreptichnussp. which are also the first record of Cambrian metazoan activity. In the middle part of the sequences, acritarchs attributed to the genusMicrhystridiumare found at the top of the Calcareous Beds. This is taken to indicate an early Cambrian age. Vendotaenids andBavlinella faveolataare found in abundance, thus indicating a Late Vendian age for the middle part of this unit. Thus, we propose the Precambrian–Cambrian boundary be located in the upper part of the Calcareous Beds. In the Rio Uso Series (Galaico-Castellana Zone), the Azorejo Sandstones containRusophycusgr.radwanskii, Planolitessp. andGordiasp. Trace fossils produced by trilobite-like arthropoda (Monomorphichnus) have been cited in the upper part of the underlying Pusa Shales. Moreover,Octoedryxium truncatumandBavlinella faveolataare found in the lower part of this unit which suggest that the Precambrian–Cambrian boundary could be situated in the Pusa Shales. Calcareous microfossils related to annelid polychaetes are found associated with Upper Vendian acritarchs in the Calcareous Beds of Sierra de Guadalupe. They are the oldest record of skeletal metazoa in the Spanish Series. The medusoids found are associated with a Vendian flora and they are also the oldest non-skeletal metazoa record known in the Iberian Peninsula.