Caracterización geoquímica de las pizarras negras de las formaciones del Ordovícico Medio-Silúrico dei sinclinal de Truchas

Abstract

The contents of TÍO,, Al2Oy P20., Rb, rare earth elements and Zr and some element ratios such as Al2OJ TiOy Rb/Zr and Ti/Nb in black shales can be combined to discriminate among different Middle and Upper Ordovician formations in the La Cabrera region. Thus, the Casaio Fm. (lowermost Upper Ordovician) shows sharp chemical differences with the over -and -underlying formations. The Silurian black shales have negative cerium anomalies (Ce/Ce* = 0,82-0,92) probably related to the Silurian transgression. The lower Silurian beds also show variable and high contents (ppm) of Ba (636-3413), U (15-16), Mo (25-110), V (319-3147), Co (34-294) and Ni (54-197) with respect to all other black shales