Petrographic and Geochemical Characterisation of Organic Matter of Precambrian Black Shales from Ossa-Morena Zone, South of Portugal

Abstract

Black shale (BS) lithologies are represented in Precambrian (Ediacaran) of Ossa-Morena Zone, SW of Iberian Massif, through the Série Negra lithological succession. The organic matter (OM) investigation in BS is relevant to understanding the mechanisms and depositional paleoenvironments related to that genesis. This study aims to characterise the OM in BS from the Série Negra succession through petrographic and geochemical methodologies. The petrographic study allowed the identification of organic particles with variable abundance, size and shape in all samples. The maximum reflectance indicates that the OM corresponds to anthracite to semi-graphite. OM maturation variation in the Série Negra succession is related to variable burial evolution and metamorphic/metasomatic processes in the Ossa-Morena Zone sectors.