Devonian and Carboniferous Palynostratigraphy of the South Portuguese Zone, Portugal - an Overview 67

Comunicacoes Geologicas, 2007, t. 94, pp. 53-79 Devonian and Carboniferous palynostratigraphy ofthe South Portuguese Zone, Portugal - An overview. Z. PEREIRA*, 1. MATOS**, P. FERNANDES*** & J. T. OLIVEIRA**** Keywords: Devonian, Carboniferous, Palynostratigraphy, South Portuguese Zone. Abstract: The South Portuguese Zone (SPZ) represents the southern branch of the Iberian Variscides and comprehends the following geologic domains: the Pulo do Lobo Antiform, the Iberian Pyrite Belt, the Baixo Alentejo Flysch Group and the Southwest Portugal (Aljezur and Bordeira Anticlines). An overview ofall the results recently achieved in palynostratigraphic research ofselected sections all over the SPZ is presented. A chronostratigraphic correlation of the stratigraphic units recognized across the ZPZ and its geodynamic and palaeogeographic implications is attempted. Palavras-chave: Devonico, Carbonifero, Palinostratigrafia, Zona Sui Portuguesa. Resumo: A Zona Sui Portuguesa (ZSP) representa 0 ramo sui do Orogeno Varisco Iberico e compreende os seguintes dominios, de norte para sui: 0 Antiforma do Pulo do Lobo, a Faixa Piritosa Iberica, 0 Grupo do Flysch do Baixo Alentejo e 0 Sector Sudoeste (Anticlinais da Bordeira e Aljezur). No presente trabalho apresenta-se uma sintese dos conhecimentos palinoestratigraficos obtidos em seccoes seleccionadas dos varios dominios da ZSP. Os dados obtidos permitem estabelecer correlacoes cronoestratigraficas em toda a Zona Sui Portuguesa, contribuindo assim para 0 melhor conhecimento da sua evolucao paleogeografica e geodinamica. 1. INTRODUCTION shallow siliciclastic sea that underwent crustal extention during the late Devonian (Strunian) and the lower The South Portuguese Zone (SPZ) represents the Carboniferous giving rise to an impressive bimodal southern branch ofthe Iberian Variscides (Figure 1). It is volcanism. Related with this volcanism near 90 massive almost entirely composed of Upper Palaeozoic sedimen sulphide deposits were formed. The Baixo Alentejo tary rocks of late Devonian to the Moscovian (Late Flysch Group (BAFG) is composed of southwestward Carboniferous) age. The following geological domains prograding sandy turbidites ofLate Visean to Moscovian are recognized in the SPZ (OLIVEIRA, 1990): the Pulo do age that filled a foreland basin. Finally, the Southwest Lobo Antiform, the Iberian Pyrite Belt, the Baixo Portugal Sector (SWPS) still part of the siliciclastic sea Alentejo Flysch Group and the Southwest Portugal during the late Devonian, evolved to a distal carbo (Bordeira and Aljezur Anticlines). nate/shale platform that only during the Moscovian The boundary between the Pulo do Lobo Antiform became part of the Variscan orogeny. and the Ossa Morena Zone, a major shear zone, is in The rock succession ofthe SPZ attracted researchers, several places underlined by the Beja-Acebuches particularly exploration companies, because of its famous Ophiolite, a remnant of an oceanic realm closure. The IPB polymetallic massive sulphides ore deposits (e.g., Pulo do Lobo Antiform is currently interpreted as a the world class Neves Corvo deposit). Geological research Variscan palaeo-accretionary prism (OLIVEIRA, 1990). was mainly concentrated on lithostratigraphy, petrology The Iberian Pyrite Belt (IPB) was part ofa late Devonian and geochemistry. More recently, biostratigraphy, sedi- * LNEG-LGM, Rua da Amieira, 4465-965 S. Mamede lnfesta, Portugal ([email protected]). ** LNEG-LGM, Rua Frei Amador Arrais 3, Ap.104, 7801-902 Beja, Portugal. *** ICIMA, Centro de Investigacao Marinha e Arnbiental, Universidade do Algarve, 8005-139, Faro, Portugal. **** LNEG-LGM, Estrada Portela, Zambujal Alfragide, Ap.7586 , 2720-866 Amadora, Portugal. © INETI 2007. Todos os direitos reservados . 54 Z. PEREIRA, J. MATOS, P. FER NAN DES & J. T. OLI VEIRA A N ATLANTI C OCEAN 38' FARO '" 9' 8' Pyrite Belt Sado Basin o pos-mesozctc cover [: '"is. :j Volca no Sed imentary Comp lex ",- Volcano Sedimentary Complex o Sines and Mon ch iqu e Mesoz oic Ma ssifs CVS in bore holes: I::PO:1 Phylli t e Quart:nte Group o Volcan ics E =~~~1I nd i f e r enc i a t ed Mesozo ic rndtteren ctated Pateeozotc sedim ents (Upper sae c Basin} Pula do Lobo AntUorm Baix o Alen tejo flysch Gro up E::::~=i Charu;a Groop FauLt, norma l fa ult • Brej eira Formation T hrust EiF7- ~ Fe rretre -Ftc etbo Group Mira Formation Village Ift'.,:1 ~ nl · Pula do Lobo Oceanic Sediments o . Borehole . studied bore hole J and MORB basalts (-, t g1~~a Mert ola fo rmati on SW Port ugal 0IIIIIl Alj ez ur and Borde ira Anticlines Fig. I- Geological sketch map of the South Portuguese Zone (adapted after OLI VEI RA , 1990; Geological Map of Portugal 1/500000, Oliveira et al. 1996). Devonian and Carboniferous palynostratigraphy ofthe South Portuguese Zone, Portugal - An overview 55 mentary geology, physical volcanism and sediment OWENS et al., 2004 ; STREEL et al., 1987; STREEL, 1996). geochemistry deserved more attention and are now The choice ofalternative schemes was stated by the presence current fields of research. of very consistent local miospore assemblages in South Palynological studies of the SPZ extend back to Portugal. The defined zonal taxa used for the latest 1980s. Palynostratigraphy was for the first time tested in Devonian and Carboniferous of the South Portuguese sev eral units of the SPZ as part of a mapping pro Zone are presented in Figure 2. Stratigraphically impor gramme carried out by the Portuguese .Geological tant and typical taxa are illustrated in Plates I and II. Survey (OLIVEIRA et al., 1986; CUNHA & OLIVEIRA, 1989). At that time palynostratigraphic work was also undertaken in the Spanish sector of the Pulo do Lobo 3. GEOLOGICAL SETTING Antiform (GIESEet al., 1988; LAKE, 1991). In the following AND PALYNOSTRATIGRAPHIC years more focussed projects on the biostratigraphy were FRAMEWORK OF SPZ developed. Palynostratigraphy represents the best tool to date the This section deals with the stratigraphic palynology SPZ lithostratigraphic units, allowing reliable stratigraphic ofall sections, boreholes and spot samples studied by the correlations across the basins and giving support to struc authors. Description of the new palynological data is tural, palaeogeographic and geodynamic interpretations. .presented here. In case ofpreviously published data only This paper presents an overview of all results recently a brief review is presented. achieved in palynostratigraphic research of selected sections all over the SPZ. The palynology data has allowed the establi shment of the general chronostratigraphic 3.1. Pulo do Lobo Antiform correlation chart for all the domain s ofthe SPZ (Figure 2). The Pulo do Lobo Domain is an antiformal structure located in the northern part ofthe SPZ, wher it is in direct 2. METHODS contact with the Ossa Morena Zone (OMZ). In the core of the structure crops out the Pulo do Lobo Fm. and is The studied samples were collected in complete compo sed of phyllites , quartzites, minor felsic volcanics outcrop sections, boreholes and occasionally spot and amphibolites (former basalts) with MORB-type samples. In the IPB, where a large number of boreholes geochemical affinity at the lower part (MUNHA, 1983; are available, drilled by mining and exploration compa EDEN, 1991; QUESADAet al., 1994). nies and by the Portuguese Geological Survey. Samples In the north limb ofthe structure, the Ferreira-Ficalho Were preferably collected from cores and in a few cases Group (Figure 3) includes from base to top the following sample s were also collected from the mine addits (e.g., units (CARVALHO et al., 1976; OLI VEIRA et al., 1986; Neves Corvo and Aljustrel). In the SW Sector samples GIE SE et al., 1988; OLIVEIRA, 1990; EDEN, 1991 ; were mainly collected along the costal sections of the QUESADA et al., 1994): the Ribeira de Limas Fm. is area. compo sed ofphyllites, quartzwakes and minor intercala Biostratigraphic research is based on palynomorphs tions of tuffites with a tectonic deformation similar to and standard palynological laboratory procedures were that of the Pulo do Lobo Fm.; the Santa Iria Fm. is made employed in the extraction and conc entration of the up of greywackes, siltstones and shales, forming a palynomorphs from the host sediments (WOOD et al., flysch-like succession; and the Horta da Torre Fm. is 1996). The slides were examined with transmitted light, compo sed of dark shales, impure sandstones, siltstones per BX40 Olympus micro scope equipped with an and quartzite beds with strong bioturbation. The Santa Olympu s C5050 digital camera facility. All sample s, Iria and Horta da Torre Fms. are affected by a main fold residues and slides are stored in the Geolo gical Survey of ing phase with associated cleavage. The group thickness Portugal (LNE G - LGM). The miospore biozonal is unknow, but estimated at 500 m. scheme used follows the standard Western Europe The south limb of the structure is represented by the Mio spore Zon ations (after : CLAYTON et al. , 1977; Chanca Group (Figure 3), which comprises the following CLAYTON 1996; CLAYTON et al., 2003; HIGGS et al., 1988; units (PFEFFERKORN, 1968; SILVA, 1989; CUNHA & HIGGS et al., 2000 ; MAZIANE et al., 2002 ; OWENS, 1996; OLI VEIRA, 1989; OLI VEIRA, 1990; SILVA et al., 1990): the Bio str at ig ra p hy Vl Cro nostr a ti gr a p hy Pa ly nologlc,,1e ve nts So ut h Port ug ue se Zo ne (SP Z) 0\ Gonlatit e s Mi o spo re s Fa u ll har b on. SWSP W.Eu rop" Portu. "l Portugal Pulo do Lobo Antiform I Regional GrobillISt",,,, Port". ..1 pyrlt"e"lt BAFG SW PS ! W.E " rop" " n St "g.. (Korn. 19911 e iozones (l ) 81010n ".(21 lnd.." sp"d"s(:i) FFGroup GCGroup Ka si m o vian ST ......................... Stepha nia n -----_._- ---~ ~ O T OT Th ymospo r a p 5e vdolhiessen;; First a p pearance o f Th ym osporo sp p. Mo scovll.., Rol strickict oculeoto C SL SL Torlsp ora ~'ecuris First appearance 01 romoora Br"J"I,.. Fm. I-- NJ NJ Florinlte 5 j u nior Westphalian B SrejelraFm I-- RA RA Ro di iz onotes a ligerens A First a p pearance of R.

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