La distribución de Paradoxides (Acadoparadoxides) mureroensis SDZUY, 1958 (Cámbrico Medio basal) y sus implicaciones paleobiogeográficas

Abstract

The northern Spain contains the best known outcrops to study the Lower-Middle Cambrian transition in the Mediterranean region. It is due to the excellent palaeontological record found in the Cantabrian Mountains and the Iberian Chains. Since the works of LOTZE (1961) and SDZUY (1971b) it has been proposed the horizon with the first record of Paradoxides (Acadoparadoxides) mureroensis as the Lower-Middle Cambrian boundary but this species was only recorded at Murero (Zaragoza), its type locality, and Tuva (Siberia) by REPINA (1969). In other localities of the Iberian Chains by VALENWELA et al. (1990), GOZALO et al. (1993), ALVARO et al. (1993), its finging has made possible the definition of the Paradoxicles (Acadoparadoxides) mureroensis biozone as the first biozone of the Middle Cambrian in this region. Now, this species is also found at Borobia (Iberia Chains), Porma and Valdoré (Cantabrian Mountains), and Ounein (Morocco) which permet us an accurate correlation between all these regions. In its locality, the mencioned biozone is placed above the Valdemiedes Geoevent which characterize an extinction phenomenon concerning to the faunas of Neoredlichiids, Hamatolenids and probable Archaeocyaths. To a certain extend this event also favoured the subsequent record of Paradoxidids and Agnostoids during the lowermost Middle Cambrian. To understand the characteristics of the Lower-Middle Cambrian transition, we studyed six sections from the Iberian Chains and other two from the Cantabrian region. This distribution of Paradoxides (Acadoparadoxides) mureroensis is analized in a palaeobiogeographical context. The new specimens of Paradoxides (Acadoparadoxides) mureroensis studied now, suggest the convenience to revise the original diagnosis of this species, to include a morphotype characterized by three glabelar furrows, which is interpreted as an evolutive phase, previous to the probable appearence of Eccaparadoxides subgenus in the Iberian Chains.