Fernandes, Paulo

Jorge, Raul CG Santos

Matos, João Xavier

Oliveira, José Tomás

Pereira, Zélia

Repositório do LNEG

CIMP Faro09 Abstracts 75NEW LOWER GIVETIAN AGE MIOSPORES OF THE PHYLLITE QUARTZITEGROUP (SÃO FRANCISCO DA SERRA ANTICLINE, IBERIAN PYRITE BELTPORTUGAL)Zélia Pereira1*, João Matos2, Paulo Fernandes3, Raul Jorge4 and José Tomás Oliveira51. LNEG LGM, Rua da Amieira, Ap. 89, 4466 901 S. Mamede Infesta, Portugal. Corresponding author: zelia.pereira@ineti.pt2. LNEG LGM, Rua Frei Amador Arrais 3, Ap.104, 7801 902 Beja, Portugal3. CIMA, Centro de Investigação Marinha e Ambiental, Universidade do Algarve, 8005 139, Faro, Portugal4. CREMINER, Departamento de Geologia da Faculdade de Ciências da Universidade de Lisboa, Ed. C6, Campo Grande, 1749 016 Lisboa,Portugal5. LNEG LGM, Estrada Portela, Zambujal Alfragide, Ap.7586, 2720 866 Amadora, PortugalSUMMARYPalynostratigraphical analysis of Phyllite  Quartzite (PQ) Group shales recovered from a drill core and outcropsat the São Francisco da Serra anticline, in the westernmost area of the Iberian Pyrite Belt, yielded a moderatelypreserved miospore assemblage assigned to the upper part of AD miospore Biozone, subzone Lem, of lowerGivetian age. This is the oldest age recognized, up to this date, for any rocks in the Iberian Pyrite Belt.Keywords: Palynostratigraphy, miospores, lower Givetian, Phyllite Quartzite Group, Iberian Pyrite Belt_________________________________________________________________________________________________________________INTRODUCTIONThe stratigraphy of the Iberian Pyrite Belt (IPB) consists of two major units; the Phyllite QuartziteGroup (PQG) and the Volcano Sedimentary Complex (VSC). PQG is the detritic basement of the beltand consists mostly of interbedded phyllites, quartzites, quartzwackes and shales, with limestonelenses and nodules in the upper part of this unit. The base of the unit is still unknown and itsthickness is in excess of 200m.In the south branch of the IPB, the PQG occurs in the core of rooted anticline structures, from SE, thePomarão Anticline (in the western termination of the Puebla de Guzmán anticline, in Spain), RosárioAnticline (where the Neves Corvo mine is located), to NW, the Lousal and São Francisco da Serraanticlines. All of these structures are being palynologically investigated. The PQG has been dated asUpper Devonian (lower Frasnian to late Strunian) by ammonoids, conodonts and palynomorphs inPortugal (BOOGAARD, 1967, FANTINET et al. 1976; CUNHA & OLIVEIRA, 1989; OLIVEIRA et al., 1997;OLIVEIRA et al., 2004, PEREIRA et al., 2004) and in Spain (González, 2005).The aim of the present paper is to present the first palynological results from the São Francisco daSerra Anticline, which indicate the oldest age determined in the IPB stratigraphic sequenceGEOLOGICAL SETTINGThe S. Francisco da Serra Anticline represents the NW termination of the IPB in Portugal (Figure 1).The axis of the anticline plunges SE, whereas its western part is fault bounded and covered byTertiary sediments.CIMP Faro09 Abstracts 76The stratigraphic succession of the anticline shows the classic units of the IPB: at the base the PQGconsisting mostly of shales interbedded with quartzites (sometimes massive) overlain by theVolcano Sedimentary Complex (VSC), here dominated by fine volcanoclastic sediments, minor felsicvolcanics, purple shales and dark carbonaceous shales in the upper part. The thickness of the PQG isunknown and that of the VSC is approximately 100 metres. Stratigraphically above the VSC are thedeep water turbiditic sediments of the Mértola Formation of Middle Late Viséan age.MATERIALS AND METHODSSamples for this study were collected from a drill core (M1) and from outcrops located along themargins of a valley north of the Senhora do Livramento Chapel (Figure 2). Biostratigraphic researchhas been based on palynomorphs. Standard palynological laboratory procedures were employed inthe extraction and concentration of the palynomorphs from the host sediments (Wood et al., 1996).The slides were examined with transmitted light, using a BX40 Olympus microscope equipped withan Olympus C5050 digital camera. All samples, residues and slides are stored in the LNEG LGM(Geological Survey of Portugal) at S. Mamede Infesta, Portugal. The miospore biozonal scheme usedfollows the standard Western Europe Miospore Zonations (after: Clayton et al., 1977; Streel et al.,1987; Higgs et al., 1988, Clayton, 1996, Pereira , 1999, Pereira et al., 2008).Figure 1. Simplified geology of the S. Francisco da Serra Anticline (adap. Alves et al., 1985). FBAMértola Formation (Flysch); VSC Volcano Sedimentary Complex; PQG Phyllite QuartziteGroup; Tertiary sediments.CIMP Faro09 Abstracts 77PALYNOSTRATIGRAPHYThe Senhora do Livramento outcrop section and the M1 borehole were studied and sampled forpalynostratigraphic investigation.Senhora do Livramento SectionThis section is located along a river valley north of the Senhora do Livramento Chapel (Figure 2) andrepresents the upper 100 metres of the PQG succession in this anticline. The succession consists ofgrey/black shales interbedded with quartzites. The quartzite beds are concentrated in two intervals.The basal interval is organised in a thinning upward succession and the beds show wave ripples andhummocky cross stratification, suggesting deposition on a shallow siliciclastic platform. The upperinterval, the Senhora do Livramento Quartzites, consists of 30 metres of massive amalgamatedquartzites, sometimes coarse grained, showing as dominant structures, low angle current andparallel laminations, which also indicates deposition in a shallow marine environment.Seven samples were collected from the Senhora do Livramento measured section forpalynostratigraphic research. However, all the samples were barren, probably due to the intenseweathering of the shaley lithologies.M1 BoreholeThe M1 borehole (a vertical borehole 367m deepdrilled by the Sociedade Mineira Riofinex, at Quintado Poço in 1993) is located in the central part of theanticline. The succession consists of highly fracturedblack shales interbedded with thin beddedquartzites. Samples from this section yielded amoderately preserved miospore assemblageassigned to the upper part of AD miospore Biozone(subzone Lem), of lower Givetian age.The most common species present are:Acinosporites lindlarensis, Aneurospora greggsii,Cymbosporites magnificus, Emphanisporitesannulatus, E. rotatus, Grandispora protea,Retusotriletes rugulatus, Verrucosisporites premnusand V. scurrus in association with the guide specieGeminospora lemurata.Figure 2. Senhora do Livramento section, correspondingto the upper 100 m of the PQG in the S. Francisco daSerra Anticlinal. Characters on the right refer to thesamples studied.CIMP Faro09 Abstracts 78Cristatisporites triangulatus is absent. The first occurrence of this species is at the base of the TABiozone, confirming the position of the assemblage, as pre TA Miospore Biozone.Also present are reworked miospores of Lower Devonian age (e.g. Archaeozonotriletes chulus,Brochotriletes sp., Camarozonotrilestes sextantii and Diatomozonotriletes franklini).CONCLUSIONSThe present research confirms the autochthonous nature of the São Francisco structure anddemonstrates that the age of PQG is not yet definitively achived. Our new results suggest that thelower part of the PQG may be as old as lower Givetian in the westernmost part of the IPB. The firstappearance of Geminospora lemura marks the base of Lem Subzone of the AD Biozone of lowerGivetian age (Streel et al., 1987). According to Loboziak & Streel (1980; 1987; 1988; 1989), G.lemurata first occurs close to the proposed base of the Givetian stage. However, the commonpresence of reworked Lower Devonian miospores in many of the samples studied in this basinsuggests that the PQG could extend down into the Lower Devonian.

New Lower Givetian age Miospores of the Phyllite-Quartzite Group, São Francisco da Serra anticline, Iberian Pyrite Belt, Portugal

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New Lower Givetian age Miospores of the Phyllite-Quartzite Group, São Francisco da Serra anticline, Iberian Pyrite Belt, Portugal

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