Graptolitos silúricos del sinclinal de Castrillo (Zona Asturoccidental-Leonesa, NO de España): revisión del yacimiento descubierto por Casiano de Prado en 1855

Abstract

The first Silurian graptolites frorn NW Spain were discovered South of Brazuelo de Pradorrey (province of León) by Casiano de Prado in 1855. The locality lies in the core of the Castrillo syncline, where the Silurian succession is composed by a lower unit of ?Rhuddanian-Aeronian sandstones, gradually passing to an upper unit of black graptolitic shales. Aeronian graptolites (?D. triangulatus and D. convolutus biozones) were reported from the top of the sandy formation and from the transitional beds in the lower half of the overlying unit. The Brazuelo locality corresponds to the younger black shales, and includes three sucessive horizons with Telychian graptolites. The first one represents the upper part of the R. linnaei Biozone, followed up in the section by a second assemblage, which probably belongs to the M. griestoniensis Biozone, and finally, by a third horizon also representative of the M. griestonensis or even the T. tullbergi Biozone. Graptolite assemblages are poor and bad preserved, but include some species of high palaeobiogeographic and palaeoenvironmental significance, as for instance Metaclimacograptus cf. asejradi Legrand or Paraclimacograptus? flamandi (Legrand), typical of shallow sapropelitic facies in peri- and intracratonic Gondwanan basins.