Autor(es):
Lopes, Gilda 
; Pereira, Zélia ; Fernandes, Paulo ; Matos, João Xavier ; Rosa, Diogo ; Oliveira, José Tomás
Data: 2011
Identificador Persistente: http://hdl.handle.net/10400.1/5116
Origem: Sapientia - Universidade do Algarve
Assunto(s): Ossa Morena Zone; Reworked; Palynomorphs
Descrição
The detail study of the borehole SDJ1 from the Santa Susana coal basin western border of
the OMZ, Portugal, proved that most of the volcano sedimentary lithologic sequence
yielded palynomorphs of mid late Visean age (NM Biozone) i.e., they belong to the Toea
da Moura Volcano Sedimentary Complex (TMC). The deepest few meters of the drill core
have shales of mid Moscovian (Biozona SL) (see Pereira et ai., in this volume).Together
with the miospore assemblages that provide the age of the SDJ1 strata, mid late Visean
and Moscovian age, associations of exceptional well preserved Lower Palaeozoic
acritarchs and spores were identified and interpreted as reworked into the Carboniferous
ocks. Four ages of reworked associations were identified: 1 - Late Cambrian acritarchs:
Aeanthodiaerodium ?petrovii, Cristallinium randomense, Eliasum sp., Timofeevia
phosphoritica; 2 - Ordovician acritarchs: Navifusa punctata, Stelliferidium striatulum,
Striatotheea rarirrugulata; 3 - Mid Late Silurian to Lower Devonian, spore taxa:
Ambitisporites sp., Arehaeozonotriletes ehulus, Brochotriletes sp., Dietyotriletes
subgranifer; Emphanisporites sp. and Synorisporites Jabeonis, cryptospores taxa
aevolaneis sp., Tetrahedraletes medinensis and Quadritisporites variabilis, acritarch taxa
such as Ouvernaysphaera aranaides, Micrhystridium stellatum, Multiplicisphaeridium
ramusculosum; 4 - Late Devonian miospore taxa: Retispora lepidophyta and Rugospora
f1exuosa and acritarch taxa Craterosphaeridium ?sprueegrovense, Gorgonisphaeridium
ohioense, Stellinium eomptum, S. mieropolygonale, Vil/osaeapsula eolemanii,
Pterospermella sp.. Detail examination of the reworked assemblages, still in progress,
indicates that these are clearly dominated by Late Cambrian, Early Ordovician and Late
Devonian acritarchs. In minor amount are Mid Silurian to Lower Devonian palynomorphs
and the typical Middle Devonian species are very scarce. The TMC sediments are
interpreted as had been deposited in an intra-arc basin in close association with the
igneous rocks of the Beja Massif, a magmatic arc installed at the south border of the OMZ
(Oliveira et al. 2006). The ages of the reworked palynomorphs suggest that considerable
erosion of exposed Lower Palaeozoic OMZ basement occurred during Carboniferous
times. The exposure of these rocks may have occurred during the first phases of the
Variscan Orogeny in the OMZ. Within the OMZ the rock formations that may constitute the
sources for the reworked palynomorphs are: the Early Ordovician Phyllodoeites Shales
(Pigarra et aI., 2011); the Raiados and Nodulos Shales Fm. and the Terena Fm. of Mid
ate Silurian to Early Devonian, age (Pereira et aL, 1999; Lopes et ai., 2009). The Late
Devonian association could have come from the South Portuguese Zone, where late
amennian palynomorphs are very well documented. Lastly, there are no units of proven
late Cambrian age in the OMZ. The occurrence of reworked Late Cambrian palynomorphs
in the Santa Susana region indicates that elsewhere in the OMZ, sedimentation of this age
must have existed.
