Provenance of the reworked Ordovician Palynomorphs in SDJ1 Borehole - Santa Susana Basin, Ossa Morena Zone, Portugal

Abstract

The detail palynological study of the exploration borehole SDJ1 located in the Santa Susana / Moinho da Ordem disused coal mine area (1927‐1944), western border of the Ossa Morena Zone (OMZ) in Portugal, is presented here. The borehole intersects lithologies of the Toca da Moura Complex (TMC) and the Santa Susana Formation (SSF), dated as mid late Viséan and Moscovian (Carboniferous), respectively, based on palynomorphs (Cunha in Andrade et al., 1991; Pereira et al., 2006; Machado, 2010; Pereira et al., 2011) and macroflora (Wagner & Sousa, 1983). Together with the miospore associations recovered, assemblages of exceptional well‐ preserved Lower Palaeozoic acritarchs, cryptospores and spores were identified, which are interpreted asreworked. From these, the major percentage is Ordovician acritarchs. The ages of the reworked palynomorphs suggest that considerable erosion of exposed Lower Palaeozoic OMZ basement occurred during early Carboniferous times. The exposure of these rocks may have occurred by the first phases of the Variscan Orogeny in the OMZ. In this work the acritarch assemblages recovered from the SDJ1 borehole are compared with the acritarch assemblage identified from the Phyllodocites Shales Formation (Cunha & Vanguestaine, 1988; Pereira et al, 2011) in Barrancos region. Due to the resemblance in the acritarchs assemblages of both places we suggest that the Early Ordovician Phyllodocites Shales and correlatives were one of the main sources of the reworked acritarchs (Piçarra et al., 2011).