Palynostratigraphy of the Toca Da Moura and Cabrela Complexes, Ossa Morena Zone, Portugal

Upper Devonian palynostratigraphy and organic matter maturation of the Pulo do Lobo Domain, South Portuguese Zone, Portugal In:Comunicações Geológicas, Tomo 93, 23-38, 2006

ZÉLIA PEREIRA*, PAULO FERNANDES** & JOSÉ TOMÁS OLIVEIRA***

* INETI, Departamento de Geologia, Rua da Amieira, 4465 S. Mamede Infesta, Portugal. [email protected] ** UA, Faculdade Ciências do Mar e Ambiente, Campus Gambelas 8005-139 Faro *** INETI, Departamento de Geologia, Estrada Portela, Zambujal, 2720 Alfragide, Portugal.

Palavras-chave: miosporos, palinoestratigrafia, maturação da matéria orgânica, Devónico Superior, Domínio do Pulo do Lobo, Faixa Piritosa, Zona Sul Portuguesa

Resumo: Investigações palinoestratigráficas efectuadas na parte portuguesa do Domínio do Pulo do Lobo, Zona Sul Portuguesa, permitiram rever as datações das suas unidades constituintes e estabelecer as seguintes correlações: as Formações de Pulo do Lobo e Atalaia exibem afinidade litológica e de deformação e não permitiram obtenção de datações; as Formações de Ribeira de Limas e Gafo possuem miosporos de idade Frasniano inferior e as Formações Santa Iria, Horta da Torre e Represa foram datadas do Fameniano superior. Os índices de maturação da matéria orgânica das unidades Pulo do Lobo e Atalaia indicam condições de metamorfismo da fácies xistos verdes alta, enquanto os das restantes unidades indicam a parte alta da epizona. Os contrastes metamórficos e estruturais sugerem que o par Fm Pulo do Lobo/ Fm. Atalaia foi parte integante do paleoprisma acrecionário, de idade pré-Fameniano, associado a uma zona de subducção para Norte, enquanto que as restantes unidades depositaram-se numa bacia sedimentar discordante sobre aquele paleoprisma. É sugerido que esta bacia e a da Faixa Piritosa estiveram em continuidade e pertenceram à mesma área paleogeográfica durante o Devónico superior.

Key-words: miospores, palinostratigraphy, organic matter maturation Upper Devonian, Pulo do Lobo Domain, Pyrite Belt , South Portuguese Zone

Abstract: Palynostratigraphic research in the Pulo do Lobo Domain, South Portuguese Zone, Iberian Variscides, allow the age revision and the following correlations among the composing stratigraphic units: the Pulo do Lobo and Atalaia Formations exhibit lithological and deformational affinities, and no age determination was achieved; the Ribeira de Limas and Gafo Formations are of early Frasnian and the Santa Iria, Horta da Torre and Represa Fms. yielded palynomorphs of late Famennian age. Vitrinite Reflectance values of the organic matter indicate that the Pulo do Lobo and Atalaia Fms reach the higher greenschist facies of metamorphism while all the overlying units belong to the upper epizone. The metamorphic and structural contrasts suggest that the pair Pulo do Lobo/Atalaia Fms was once part of a pre-Famennian acretionary prism related to a northward subduction while all the other overlying units were laid down in a sedimentary basin discordant over that paleoprism. From all these data, it is inferred that this basin and the Iberian Pyrite Belt basin were part of the same paleogeographic realm during the late Devonian.

1. INTRODUCTION the structure is represented by the Ferreira- The Pulo do Lobo Domain is situated Ficalho Group which includes from base to top between the Ossa Morena Zone and the Iberian the following units (CARVALHO et al., 1977;

Pyrite Belt, Iberian Variscides (Figure 1). In the OLIVEIRA et al., 1986; GIESE et al., 1988; core of the structure, marking the base of the OLIVEIRA, 1990; EDEN, 1991; QUESADA et al., stratigraphic sequence outlines the Pulo do 1994): the Ribeira de Limas Formation Lobo Formation composed of highly sheared composed of phyllites, quartzwackes and minor phyllites and quartzites, and intercalations of intercalations of tuffites, in apparent amphibolites with MORB-type geochemical downwarding to the Pulo do Lobo Formation; affinity at the lower levels (MUNHÁ, 1983; the Santa Iria Formation made up of

EDEN, 1991; QUESADA et al., 1994). A common greywackes, siltstones and shales, forming a feature of this unit is the widespread occurrence flysch like succession; the Horta da Torre of exudation quartz veinlets which are related to Formation composed of dark shales, impure a strong tectonic deformation. The north limb of sandstones, siltstones and quartzite beds with

1 bioturbation. The latter unit grades downward MUNHÁ (1983, 1990) the regional metamorphism and laterally into the Santa Iria Fm. and both are varies from the upper epizone to the upper affected by a single main cleavage, while de greenschist facies. Ribeira de Limas and the Pulo do Lobo Fms. The overall structure has been interpreted show two main episodes of cleavage. The group as an anticline (SCHERMERHORN, 1971; thickness is estimated in 500 m. CARVALHO et al, 1976; OLIVEIRA et al., 2006;

In the south limb of the structure outcrop the PEREIRA et al., 2006) as an accretionary prism units of the Chança Group which are disposed, related to a northward dipping subduction from base to top, as follows (PFEFFERKORN,1968; (SILVA et al., 1990; QUESADA et al., 1994, SILVA,

SILVA,1988; CUNHA & OLIVEIRA, 1989; OLIVEIRA, 1998) and as a suspected terrain (RIBEIRO et al.,

1990; SILVA et al., 1990): the Atalaia Formation, 1990). composed mostly of phyllites, quartzites and This paper describes in detail the most quartzwackes; the Gafo Formation with recent advances accomplished on the greywackes, siltstones and shales forming a palynostratigraphy and organic matter turbidite succession, with intercalations of acidic maturation of the Portuguese part of the Pulo do and mafic volcanics and basic and acidic dikes; Lobo Domain and discuss their implications in the Represa Formation consists of siliceous the interpretation of the regional geodynamic silstones, shales and greywackes. The group evolution. thickness is estimated in 1100 m. According to Fig. 1 - Geological sketch map of the South Portuguese Zone (adapted after Oliveira, 1990; Geological Map of Portugal 1/500 000).

2 2. PREVIOUS PALYNOLOGICAL investigation of the Represa Formation and STUDIES ON THE PULO DO LOBO other units of the Pyrite Belt. The Represa DOMAIN Formation, north of Tapada Grande, provided The history of palynological studies of the three productive samples indicating an early Pulo do Lobo extends back to the 1980s. In upper Famennian age. The poorly preserved

1986, T. CUNHA (OLIVEIRA et al., 1986) miospore assemblage contains Aneurospora developing a palynostratigraphic project as part greggsii, Auroraspora asperella, A. solisorta, of a mapping programme carried out by the Pustulatisporites rugulatus, Retusotriletes Portuguese Geological Survey, recorded for the incohatus, R. planus and Rugospora flexuosa. first time a fairly preserved palynomorph In an unpublished PhD thesis, LAKE (1991) assemblage of mid Famennian age in the Horta studied the palynology of the Pulo do Lobo da Torre Formation. Three localities were Domain succession in Spain. The Aroche road sampled near Corte Condessa, west of Guadiana section, in the north limb of the antiform, River. Miospore species identified include yielded a palynoflora comprising Aneurospora Aneurospora greggsii, Ancyrospora langii, greggsii, Cristatisporites inusitatus, C. Diducites mucronatus, D. poljessicus, D. triangulatus, Diducites mucronatus, plicabilis, Pustulatisporites rugulatus, Geminospora lemurata and Retusotriletes Retusotriletes planus, Samarisporites sp. A and rugulatus, indicating a Givetian to early Samarisporites sp. cf. Acanthotriletes hirtus. Famennian age. The studied section was Acritarch species recovered include compared and correlated with the Ephelopalla cf. gorkae, Unellidium piriforme lithostratigraphic sequence of the Santa Iria and U. winslowae. Formation in Portugal. In the south limb of the

GIESE et al. (1988) working further east in antiform, this author studied three samples from the Almonaster la Real region, northern limb of the Chança section, located 8 km southwest of the Pulo do Lobo Domain, in Spain, have Paymogo. The miospore assemblage recovered subsequently determined a late Famennian to indicated a late Givetian to early Famennian Tournaisian age for a sequence of greywackes age, based on the presence of Aneurospora possible correlatives of Santa Iria Formation. In greggsii, Cristatisporites inusitatus, this work, the Horta da Torre Formation was Geminospora lemurata and Rugospora flexuosa. considered to stratigraphically underlay the The suited section was correlated with the Gafo Santa Iria Formation. Due to the high termal Formation in Portugal. maturity of the assemblages, reflected light Recent research on all the units of the microscopy was used, allowing the domain allowed preliminary age determinations identification of the miospore species, (PEREIRA & OLIVEIRA 2006, OLIVEIRA et al., Grandispora gracilis, Vallatisporites pusillites, 2006) which are here described in detail. Retusotriletes incohatus and Retispora lepidophyta. 3. PALYNOSTRATIGRAPHY

In 1989, CUNHA & OLIVEIRA studied the The present study is based on 93 rock palynostratigraphy of the Mina de São samples collected from all units of the Pulo do Domingos region, in a project that allowed the Lobo Domain, exposed in roads and river cuts

3 (Figure 1). Standard palynological laboratory assigned to the upper part of the BM Biozone of procedures were employed in the extraction and early Frasnian age. The assemblage includes concentration of the palynomorphs (WOOD et Aneurospora greggsii, Chelinospora concinna, al., 1996). The slides were examined with Cristatisporites triangulatus, Cristatisporites sp. transmitted light, with a BX40 Olympus cf. C. inusitatus, Cymbosporites sp., microscope equipped with an Olympus C5050 Emphanisporites rotatus, Geminospora digital camera. All samples, residues and slides lemurata, Lophozonotriletes sp., are stored in the Geological Survey of Verrucosisporites bulliferus, V. premnus and V. Portugal/INETI, S. Mamede Infesta, Portugal. scurrus. All samples contain rare acritarchs and The spore biozonal scheme used follows prasinophytes. the standard Western Europe Miospore

Zonation (after: CLAYTON et al., 1977; STREEL et Santa Iria Formation al., 1987; HIGGS et al., 1988; CLAYTON, 1996; The Santa Iria Formation was sampled in

PEREIRA, Z, 1999 and MAZIANE et al., 2002). several sections, Moinho da Vargem (Chança Ranges of selected spore taxa recovered and the River) section, road cut section near Santa Iria zonal scheme used are presented in Figure 2. village and in Moinho da Misericórdia section, Stratigraphically important and typical taxa are Guadiana River,. In this last section outcrops the illustrated in Plate I. unit most typical facies, composed of dark laminated shales and greywackes. The dark 3.1. Pulo do Lobo Formation shales revealed well preserved spore The unit is very well exposed along the assemblages assigned to the VH Biozone of late Guadiana river and in road cuts from Corte Famennian age. The assemblages include Gafo to Amendoeira and from Corte Pinto to Grandispora echinata that indicates the base of Serpa. The black phyllites sampled revealed the Biozone, together with Ancyrospora sp, absent in organic matter probably due to Apiculiretusispora sp., Auroraspora macra, metamorphism destruction. Cristicavatispora dispersa, Diducites versabilis, D. poljessicus, Emphanisporites annulatus, 3.2. Ferreira - Ficalho Group Grandispora cornuta, G. famenensis, G. Ribeira de Limas Formation gracilis, Plicatispora sp., Punctatisporites spp., This unit was sampled in a road cut section, Retusotriletes planus, R. triangulatus, R. located at 100m north of the Ribeira de Limas rugulatus, Rugospora explicata, R. radiata and bridge. This section, the type section for the Teichestospora iberica. All samples contain Ribeira de Limas Formation, is composed of very rich assemblages of acritarchs and black shales and phyllites, interbedded in prasinophytes. quartzwakes. Black shales provided 5 productive samples. The assemblages are composed of poorly preserved miospores

4 Fig. 2. - Ranges of selected miospore species recovered and spore biozonal scheme used. cornuta, G. famenensis, G. gracilis, Rugospora Horta da Torre Formation explicata, R. radiata and Teichestospora This unit was sampled in several road cuts, near Santa Iria village and in the Moinho da iberica. All samples showed very rich Ordem section, Guadiana river. Black shales assemblages of acritarchs and prasinophytes interbbeded in centimetric thick quartzite beds provided several productive samples, with well 3.3. Chança Group preserved assemblages of miospores assigned to the basal VH Biozone of late Famennian age. Atalaia Formation The assemblages contain Grandispora echinata The Atalaia Formation was sampled near toghether with Ancyrospora sp, the boundary between the Atalaia and the Pulo Apiculiretusispora verrucosa, Auroraspora do Lobo Fms., in road cut sections north of macra, Cristicavatispora dispersa, Diducites Corte Gafo de Cima and in a road section spp., Emphanisporites annulatus, Grandispora between Corte Pinto and Serpa, near Sta Luzia. This unit is characterized by alternating layers

5 of highly deformed phyllites and quartzites .The interbbedded in quarztwakes revealed the sampled black phyllites provided residual but presence of well preserved miospores assigned highly mature organic matter possibly due to the to the basal VH Biozone of late Famennian age. high grade of metamorphism. No palynomorph The assemblage showed the presence of was identified. Ancyrospora sp., Aneurospora greggsii, Apiculiretusispora cf. verrucosa, Auroraspora Gafo Formation sp., A. solisorta, Crassispora sp., This unit was sampled in several road Cristicavatispora dispersa, Cymbosporites sp., sections, from Mértola to Corte Gafo de Cima, C. triangulatus, Diducites spp., in the region north of Corte Sines (Cemetery Emphanisporites spp., Geminospora lemurata, section) and along the Chança River, in the Grandispora cornuta, G. echinata, Rugospora Volta Falsa section. The dark shales provided explicata, R. radiata and Teichestospora several productive samples which yielded iberica. All samples contain very rich poorly preserved miospores assigned to the assemblages of acritarchs and prasinophytes. upper part of the BM Biozone of early Frasnian age. The assemblage includes Aneurospora 3.4. Comments on the miospore greggsii, Auroraspora sp., Chelinospora sp., assemblages Convolutispora ampla, Cristatisporites Comparison between the triangulatus, Cristatisporites sp. cf. C. palynostratigraphic results obtained in the Pulo inusitatus, Cymbosporites sp., Emphanisporites do Lobo Domain and those from the Pyrite Belt rotatus, Grandispora sp., Retusotriletes sp., in Portugal (OLIVEIRA et al., 1997; OLIVEIRA et

Verrucosisporites bulliferus, V. premnus and V. al., 2004; 2005; 2006; PEREIRA, 1999; PEREIRA scurrus. All samples contain rich assemblages et al., 2006; 2007; PEREIRA & OLIVEIRA, 2006) of acritarchs and prasinophytes. and Spain (LAKE, 1991; GONZALEZ et al., 2004;

GONZALEZ, 2005) indicates a number of Represa Formation similarities (Figure 3). The Represa Formation was sampled along The age of the Phyllite-Quartzite Group, based the section of the Ribeira de Vale Travessos on miospores, ranges from the early Frasnian, (West of Tapada Grande, Mina de S. dated in Puebla de Guzman Anticline, SW

Domingos), where dark shales, siltstones and Spain (GONZALEZ et al., 2004), to late Strunian quartzwackes are the dominant lithologies, with in Portugal (CUNHA & OLIVEIRA, 1989; rare intercalations of green and purple shales. OLIVEIRA et al., 2004; OLIVEIRA et al, 2005;

The dark shale samples showed a rather poor MATOS et al., 2006). miospore content. Complementary sampling The Puebla de Guzman Frasnian assemblage was done in the MP 3 borehole, situated on the was recovered from the lower levels of the west margin of Tapada Grande, Mina de S. Phyllite-Quartzite Group, and contains Domingos. This borehole cuts, amongst other Aneurospora greggsii, Chelinospora concinna, units, the Represa Formation, on the first Cristatisporites triangulatus, Geminospora profound 80 meters, and the boundary with lemurata, Retusotriletes rugulatus and felsic rocks at the 88,4 m deepth. Black shales Verrucosisporites scurrus. It is worth noting

6 that this assemblage is similar to that found in common presence at the late Famennian the Ribeira de Limas and Gafo Formations. assemblages of the Iberian Pyrite Belt detritic The Volcano-Sedimentary Complex of the substrate (Phyllite-Quartzite Group) and in the Pyrite Belt yielded miospores of late Famennian Horta da Torre/Santa Iria/Represa Fms of the to mid late Visean age (OLIVEIRA et al., 1986; Pulo do Lobo Domain.

OLIVEIRA et al., 2004; 2005; 2006; PEREIRA et Another characteristic is the consistent al., 2006; 2007). The late Famennian presence, in both domains Pyrite Belt and Pulo assemblage contains Ancyrospora sp., do Lobo, of the miospore species Aneurospora greggsii, Auroraspora spp., Cristicavatispora dispersa, Rugospora Cristatisporites triangulatus, Diducites spp., explicata and Teichestospora iberica lately

Emphanisporites spp., Geminospora lemurata, described by GONZALEZ (2005). These species Grandispora cornuta, G. echinata, G. were only documented, at the present, in the famenensis, and R. radiate. These taxa are also South Portuguese Zone.

Fig. 3 - Comparison of the palynostratigraphic results obtained from Pulo do Lobo Domain and Pyrite Belt.

7 The evidence clearly shows that sedimentation using BARKER & GOLDSTEIN (1990) empirical in the Pulo do Lobo Domain and in the Pyrite equations (Table 1). With the exception of the Belt was coeval, at least during the Upper sample AT1, from the Atalaia Formation, there Devonian. is no clear correlation between VR and the stratigraphic age of the samples. Most VR 4. ORGANIC MATURATION values fall between 4 - 5%Rr coinciding with From the samples collected for the onset and the lower field of meta-anthracite palynostratigraphy, 17 from outcrops of the coal rank and the lower epizone (Figure 4). Pulo do Lobo Domain, 7 from borehole MP3 Standard deviations are relatively higher and 2 from borehole MSD1 (Figure 1), were resulting in part from significant bireflectance at studied by means of vitrinite reflectance (VR) in these higher maturity levels and possibly from order to assess the regional maturity and to some misidentification of some smaller organic elucidate the thermal history of the area. The particles in the residues. This was probably the lithologies sampled were black to grey schists case for some samples of the Santa Íria, Ribeira and dark phyllites from the lithostratigraphic de Limas and Gafo formations, which are rich in units of the north and south limbs of the Pulo do amorphous organic matter and vitrinite particles Lobo Antiform. are, in general, very small. Comparing the Organic residues were extracted from the highest VR values from the data set, the samples using standard cold hydrofluoric acid measurements from the Chança Group in the (HF) techniques. All the post-HF residues were south limb of the Pulo do Lobo Anticline seems mounted and polished using a method adapted slightly higher than those of the Ferreira - from that described by Hillier and Marshall Ficalho Group in the northern limb, although (1988). Mean random vitrinite reflectance more data are needed to ascertain this. With a (%Rr) was determined using standard value of 11.19%Rr sample AT1 is in clear techniques for samples where sufficient well contrast with VR values from the other samples, preserved vitrinite grains were present. %Rr falling within the upper greenschist facies of measurements were taken using an Olympus metamorphism. BX51 microscope equipped with a Colour View VR values measured from samples of the III photographic camera. Pyrite Belt domain in boreholes MP3 and MDS1 are consistent with VR values measured 4.1 Results from the Pulo do Lobo Domain (Figure 4), The vitrinite reflectance results obtained are especially from those measured in the Gafo and summarised in Table 1. Palaeotemperatures for Represa units of the Chança Group. all the VR data compiled were also calculated

8 9 Sample No. Palaeo- Formation Age %Rr STD Reference Grains temperature (ºC)

HT5 Horta da Torre Upper Fammenian 4.32 0.37 100 336.1 HT9 Horta da Torre Upper Fammenian 4.39 0.5 50 338 MM1 Santa Íria Upper Fammenian 3.26 0.53 60 302.6 MM5 Santa Íria Upper Fammenian 4.95 0.65 53 352.3 MM9 Santa Íria Upper Fammenian 3.52 0.59 100 311.8 MM13 Santa Íria Upper Fammenian 3.87 0.39 55 323 RL1 Ribeira de Limas Lower Frasnian 4.47 0.62 86 340,2 RL2 Ribeira de Limas Lower Frasnian 3.98 0.51 50 326.4 EM1 Represa Upper Fammenian 5.06 0.56 67 355 EM3 Represa Upper Fammenian 4.77 0.4 100 347.9 EM8 Represa Upper Fammenian 5.1 0.5 100 353.8 MP3(75.3) Represa Upper Fammenian 5.1 0.4 100 353.8 MP3(83.6) Represa Upper Fammenian 5.58 0.46 100 366.6 MP3(86.8) Represa Upper Fammenian 5.09 0.48 100 355.7 GF13 Gafo Lower Frasnian 5.12 0.59 100 356.4 GF14 Gafo Lower Frasnian 4.92 0.82 21 351.6 GF18 Gafo Lower Frasnian 3.92 0.64 51 324.6 VF6 Gafo Lower Frasnian 5.2 0.5 80 358.2 VF7 Gafo Lower Frasnian 4.59 0.6 78 343.4 AT1 Atalaia Middle Devonian(?) 11.19 0.22 70 449.4 Strunian - Latest MSD1(55.8) Phyllite-Quartzite 4.66 0.27 100 345.2 Fammenian Strunian – Latest MSD1(216) Phyllite-Quartzite 5.27 0.37 100 359.8 Fammenian MP3(140) VSC Lower Viséan 4.94 0.34 100 352.1 MP3(295.8) VSC Lower Viséan 4.67 0.31 100 345.4 MP3(313.5) VSC Lower Viséan 4.77 0.26 100 347.9 MP3(321.1) VSC Lower Viséan 4.62 0.22 100 344.1 Table 1 - Vitrinite reflectance and palaeotemperature results. Abbreviations used: %Rr = Mean random vitrinite reflectance and STD = standard deviation. Numbers in brackets next borehole references (MP3 and MSD1 correspond to depth of the samples in meters. grade of metamorphism. Due to the similarity of VR values obtained from the units of the VR values, the time hiatus between the Ribeira southern part of Pulo do Lobo Domain are de Limas/Gafo and Santa Íria-Horta da consistent with the metamorphic zones of Torre/Represa Fms suggested by PEREIRA et al.,

MUNHÁ (1983, 1990) for the same region. 2006 was not detected. The units of the Ferreira - Ficalho Group in the north, have similar VR values to the Gafo and Represa Fms of the Chança Group in the south. This fact together with the age agreement of the formations, strongly suggests that the Pulo do Lobo Domain is an anticline structure.

The high VR values observed in the Atalaia Fm., together with the of absence of preserved organic matter in the Pulo do Lobo Fm. suggest that both units were subjected to the same high

10 The similarities of the VR values measured in the stratigraphic units of the north and south limb of the Pulo do Lobo Anticline were produced by the same maturation event that occurred in post-Upper Devonian times. Since peak temperatures attained by the Atalaia Formation are ca. 100ºC higher than the highest palaeotemperatures calculated from the other units, the upper greenschist facies conditions that characterise this formation could have been reached prior to the deposition of the Ribeira de Limas/Gafo Formations of Frasnian age, therefore recording an earlier thermal event pre- Frasnian in age. However, the possibility that

maturation was caused by the same thermal event everywhere in the Pulo do Lobo domain cannot be totally ruled out. The results obtained for the Phyllite- Quartzite Fm and the Volcano Sedimentary Complex in the MP3 and MDS1 drill cores, although still very preliminary indicate that both were also affected by the same post-Upper Devonian metamorphic event.

Fig. 4 – Vitrinite reflectance results from the different units of the Pulo do Lobo Domain and Pyrite Belt studied, and its correlation with different maturation indices. Shadow areas indicate the range of values observed showing the highest and lowest values measured. CONCLUSIONS

11 The present study allows the following Phyllite-Quartzite and the lower units of the main conclusions: Volcano Sedimentary Complex of the Pyrite 1. No age determination was achieved for Belt are similar in magnitude to the VR values the Pulo do Lobo and Atalaia Fms, probably due of the upper units of the Pulo do Lobo Domain. to the high grade of metamorphism that affected This indicates that the Pulo do Lobo Domain these units. The units are surely older than early and the Pyrite Belt, in this region, have a similar Frasnian. thermal history, at least in post-late Devonian time. 7. The units of the Pulo do Lobo Domain 2. The Ribeira de Limas and Gafo Fms. have been interpreted as an accretionary prism revealed the presence of moderately preserved in close relation with a northward directed miospore assemblages assigned to the BM (present coordinates) subduction zone. The clear Biozone of early Frasnian. contrast in terms of organic matter maturation 3. The Santa Iria, Horta da Torre and and structural style between the pair Pulo do Represa Fms. yielded well-preserved Lobo/ Atalaia Fms and the overlying units led to assemblages of miospores assigned to the VH the conclusion that only that pair was

Biozone of Late Famennian age. incorporated in the acretionary prism (PEREIRA

4. The ages of the units Ribeira de et al, 2006; OLIVEIRA et al. 2006). The upper Limas/Gafo and Santa Iria-Horta da units, much less metamorphosed and Torre/Represa are separated of about 14 My. tectonically deformed were laid down in a basin This hiatus could be due to an unconformity, as superimposed over the accretionary prim and suggested by previous structural interpretations, contemporaneous of the Iberian Pyrite Belt which, however, was not detected in terms of detritic substrate (Phyllite-Quartzite Group) and organic matter maturation. the overlying first volcanic episodes. 5. VR results suggest that the Atalaia Fm. It is suggested that this superimposed (and possibly the Pulo do Lobo Fm.) records a sedimentary basin and the Pyrite Belt basin first pre-Frasnian thermal event that reached the were part of the same paleogeographic realm greenschist metamorphic facies prior to the during the late Devonian. deposition of the Gafo/Atalaia and Santa Iria- Horta da Torre /Represa Fms. These conditions 7. ACKNOWLEDGEMENTS were never reached by the other units of the This work was sponsored by the project Pulo do Lobo Domain since maturation grades POCI/CTE-GIN/56450/2004 (PYBE) of measured are lower and consistent to the meta- Fundação para a Ciência e Tecnologia, Portugal. anthracite coal rank. The timing of this later Thanks are due to Filipe Barreira (INETI) for maturation event cannot be fully constrained, figures treatment. however, it probably occurred in post Upper Devonian times (the age of the younger units of REFERENCES the Pulo do Lobo Domain). BARKER, C. E. & GOLDSTEIN, R. H. (1990) - Fluid- 6. Although restricted to the São Domingos inclusion technique for determining maximum mine area, VR values measured from the temperature in calcite and its comparison to

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15 Figure Captions Fig. 1 - Geological sketch map of the South Portuguese Zone (adapted after Oliveira, 1990; Geological Map of Portugal 1/500 000). Fig. 2 - Ranges of selected miospore species recovered and spore biozonal scheme used. Fig. 3 - Comparison of the palynostratigraphic results obtained from Pulo do Lobo Domain and Pyrite Belt. Fig. 4 - Vitrinite reflectance results from the different units of the Pulo do Lobo Domain and Pyrite Belt studied, and its correlation with different maturation indices. Shadow areas indicate the range of values observed showing the highest and lowest values measured. Table 1. Vitrinite reflectance and palaeotemperature results. Abbreviations used: %Rr = Mean random vitrinite reflectance and STD = standard deviation. Numbers in brackets next borehole references (MP3 and MSD1 correspond to depth of the samples in meters.

Plate I. Miospores Plate captions list the taxonomic name of the figured specimen, followed by the formation, sample number, slide number, microscopic coordinates and INETI/SG collection number of the specimen.

1. Verrucosisporites bulliferus Richardson & McGregor, 1986, RL3-1, 1190-218, INETI 0701. 2. Cristatisporites triangulatus (Allen) McGregor & Camfield, 1982, GF 13-2, 1315-165, INETI 0702. 3. Cristatisporites sp. cf. C. inusitatus (Allen) McGregor & Camfield, 1982, RL3-3, 1260-228, INETI 0703. 4. Aneurospora greggsii (McGregor) Streel in Becker, Bless, Streel & Thorez, 1974, GF13-3, 1290-100, INETI 0704. 5. Chelinospora concinna Allen, 1965, RL1-1, 1320-205, INETI 0705. 6. Emphanisporites rotatus McGregor emend. McGregor, 1973, RL2-3-1285-230, INETI 0706. 7. Verrucosisporites scurrus (Naumova) McGregor & Camfield, 1982, GF13-4, 1275-90, INETI 0707. 8. Auroraspora macra Sullivan, 1968, HT8-1, 1445-245, INETI 0708. 9. Ancyrospora sp., HT8-1, 1440-120, INETI 0709. 10. Teichertospora iberica Gonzalez, Playford &Moreno, 2005, HT7-2b-1450-185, INETI 0710. 11. Retusotriletes phillipsii Clendening, Eames & Wood, 1980, HT7-2a, 1395-50, INETI 0711. 12. Rugospora explicata Gonzalez, Playford &Moreno, 2005, HT7-3, 1505-200, INETI 0712. 13. Rugospora flexuosa (Jushko) Streel, 1974, HT7-1a, 1390-105, INETI 0713. 14. Grandispora echinata Hacquebard emend. Utting,1987, HT8-2, 1015-246, INETI 0714.