Palynostratigraphy of the Toca da Moura and Cabrela

Review of Palaeobotany and Palynology 139 (2006) 227 – 240
www.elsevier.com/locate/revpalbo
Palynostratigraphy of the Toca da Moura and Cabrela Complexes,
Ossa Morena Zone, Portugal. Geodynamic implications
Zélia Pereira a,⁎, Vítor Oliveira b , José Tomás Oliveira c
a
c
INETI, Geological Survey, Rua da Amieira, 4465 S. Mamede Infesta, Portugal
b
INETI, Geological Survey, Rua Frei Amador Arrais, 7800 Beja, Portugal
NETI, Geological Survey Estrada Portela, Zambujal, 2720 Alfragide, Portugal
Received 27 October 2004; received in revised form 7 April 2005; accepted 25 July 2005
Available online 20 March 2006
Abstract
Two volcano-sedimentary complexes, the Toca da Moura Complex (TMC) and the Cabrela Complex (CAC), situated in the
southwestern border of the Portuguese part of the OMZ, were investigated for palynostratigraphy. The TMC studied sections
provided miospores assigned to the middle late Viséan NM spore Biozone, early Viséan Pu Biozone and late Tournaisian CM
Biozone. Several stratigraphic sections of the CAC provided miospores of the same age. Reworked Devonian and Tournaisian
palynomorph assemblages are quite common in the studied samples. The TMC and the CAC thus appear to be coeval. The TMC
crops out in close association with the plutono-volcanic suite of the Beja Massif while the CAC is discordant on a Variscan
(Silurian?) well-structured substrate. The geochemical signature of the TMC volcanic rocks indicates their relationship with an
orogenic volcanic arc generated in close association with a north deeping subduction zone. The CAC has probably the same origin.
Both complexes were laid down in intra-arc small basin(s) whose margins were the locus of intense erosion.
Palynological assemblages obtained from the Ossa Morena Zone are comparable to those recognized from the Late Devonian
and Mississippian of the South Portuguese Zone. Similarities between the assemblages from the two crustal blocks show that they
were close to each other during this interval. Thus, the oceanic basin that existed between the two blocks and to which the BejaAcebuches Ophiolite is related was closed prior Late Devonian.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Carboniferous; miospores; Toca da Moura Complex; Cabrela Complex; Ossa Morena Zone; Variscan Belt; Portugal
1. Introduction
The Ossa Morena Zone (OMZ) has been subdivided
into different tectonostratigraphic units, also called
“sectors” or “domains” (Carvalho et al., 1971; Delgado
et al., 1977; Apalategui et al., 1990; Oliveira et al.,
1991) where the Paleozoic stratigraphic sequences are
⁎ Corresponding author. Tel.: +351 229511915; fax: +351
229514040.
E-mail address: [email protected] (Z. Pereira).
0034-6667/$ - see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.revpalbo.2005.07.008
different in thickness and lithology. Stratigraphic studies
and correlations between these sequences are particularly difficult, due to the scarcity of fossiliferous levels
and biostratigraphic data. The age of Paleozoic
stratigraphic formations has frequently been deduced
from lithological similarities or from their stratigraphic
position in structural units. Recent progress that came
from palynological studies in the Portuguese part of the
OMZ (Cunha in Andrade et al., 1991; Pereira, 1999;
Pereira and Oliveira, 2001a,b; Pereira et al., in press)
shows that palynostratigraphy represents an important
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Z. Pereira et al. / Review of Palaeobotany and Palynology 139 (2006) 227–240
tool to date the OMZ formations and can open new
perspectives for biostratigraphy and for correlations.
The Toca da Moura (TMC) and Cabrela Complexes (CAC) are the aim of the present study. The
former occurs in the Santa Susana–Odivelas region
of the Beja Massif, the southwestern sector of the
Portuguese part of the OMZ; the latter occurs in the
Cabrela syncline of the Montemor–Ficalho “sector”
(Oliveira et al., 1991). Their paleogeographic and
geodynamic significance within the context of the
evolution of the OMZ has been a matter of debate,
particularly due to uncertainties concerning their
ages. Data from new studied sections confirm
previous preliminary age determinations and allow
a better understanding of the significance of these
complexes in the regional geology of this part of
the OMZ.
2. Geological setting
2.1. Toca da Moura Complex
The Toca da Moura Complex (TMC) is a
volcano-sedimentary sequence that belongs to the
Beja Massif, a calc–alcaline plutono-volcanic suite
located at the southwestern border of the Portuguese
part of the OMZ. The TMC is exposed in scattered
outcrops between the villages of Santa Suzana and
Alfundão (Fig. 1) were it is composed of basalts,
diabases, microdiorites, andesites, rhyolites and
reworked tuffs, with metre-thick intercalations of
shales (Gonçalves, 1985; Santos et al., 1987; Fig. 1).
The complex is generally bounded by faults and the
outcrops are restricted to road cuts and quarries. One
only exception is the section along the São
Cristovão River where alternations of basic, intermediate and acidic volcanic rocks and interbedded
metre to decametre intercalations of shales are well
exposed. Locally the basic volcanic rocks show
pillow and hyaloclastite structures indicating a
deposition in a sub-aqueous environment. The total
thickness of the complex here is in excess of 500m.
Known ages of the TMC are based on miospores
from shales from the Corte Pereiro quarry. They
indicate a late Tournaisian age (Cunha in Andrade et
al., 1991). More recently, it has been proved that the
age of these shales reach the mid late Viséan (Pereira
and Oliveira, 2001b; Pereira et al., 2004a).
The TMC is unconformably overlain by the
continental coal-bearing detritic sediments of the
late Moscovian Santa Susana Formation (Wagner
and Sousa, 1983; Gonçalves and Carvalhosa, 1984).
2.2. Cabrela Complex
The Cabrela Complex (CAC) is exposed in the
Cabrela Syncline, near the Ossa Morena Zone border
(Fig. 1). According to Ribeiro (1983) and Carvalhosa
and Zbyzewski (1994), the stratigraphic succession
consists of (Fig. 1a) a polygenic conglomerate (0–2m)
at the base, followed by the Pedreira da Engenharia
calciturbidites (0–10m) which are in turn unconformably overlain by the Cabrela Formation. The latter is
composed of a basal conglomerate (10 m), shales,
greywackes and limestone lenses, and interbedded acidic
volcaniclastic rocks, with a total thickness of about
200 m. The Pedreira da Engenharia calciturbidites
provided conodonts of late Eifelian age (Boogard,
1972) and the limestone lenses of the Cabrela Formation,
yielded conodonts of late Frasnian age (Boogard, 1983).
Pruvost (1914) had already identified, poorly geographic
and stratigraphical located and badly preserved macrofaunas, of possible Late Devonian age in the limestones.
The unconformity between the Pedreira da Engenharia
calciturbidites and the Cabrela Formation has been
interpreted as a marker of the first Variscan orogenic
episode (Ribeiro, 1983; Quesada et al., 1990; Ribeiro et
al., 1990). More recently it has been shown (Pereira and
Oliveira, 2001a; Pereira et al., in press) that the shales of
the Cabrela Formation are of late Tournaisian to late
Viséan age and that the intercalated Frasnian limestone
lenses are true olistholiths. The stratigraphic situation for
the Eifelian Pedreira da Engenharia limestones cannot be
determined as their base is not exposed. The possibility
that they are also olistoliths cannot be ruled out.
These data demonstrate that the Frasnian limestone
lenses should not be used as markers of an unconformity
related to an orogenic episode. The Estação de Cabrela
Formation, where the limestones are intercalated, was
only tectonically deformed in post middle Visean times.
3. Materials and methods
Stratigraphic sections were logged and samples
collected in road cuts and quarries (Figs. 2 and 3).
Standard palynological laboratory procedures were
employed in the extraction and concentration of the
palynomorphs (Wood et al., 1996). The slides were
examined with transmitted light, with a BX40 Olympus
microscope equipped with an Olympus C5050 digital
camera. All samples, residues and slides are stored in the
Geological Survey of Portugal (INETI), S. Mamede
Infesta, Portugal.
The spore biozonal scheme used follows the standard
Western Europe Miospore Zonation (after: Clayton et al.,
Z. Pereira et al. / Review of Palaeobotany and Palynology 139 (2006) 227–240
229
Fig. 1. Simplified geological sketch map of the southwestern border of the Ossa Morena Zone (OMZ) and South Portuguese Zone (SPZ), with
location of the studied sections of the Toca da Moura and Cabrela Complexes (a).
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Fig. 2. Simplified stratigraphic logs of the Toca da Moura Complex, with location of studied samples and spore content.
1977; Streel et al., 1987; Higgs et al., 1988; Clayton,
1996).
4. Palynostratigraphy
Ranges of selected spore taxa recovered and the
zonal scheme used are presented in Fig. 4.
Qualitative composition of selected miospores
described is presented in Fig. 5. The miospore
and acritarch species identified are listed in
Appendix 1. Stratigraphically important and typical
taxa are illustrated in Plate I.
4.1. Toca da Moura Complex
In the TMC, four sections were studied and
sampled, Corte Pereiro, Cai Água, Ribeira dos
Marmelos Dam and Ribeira dos Marmelos Quarry
(Fig. 2).
4.1.1. Corte Pereiro section
The Corte Pereiro section is exposed in an old
quarry 5km NE of Santa Susana village. The TMC
is here represented by thin-bedded greywackes and
dark shales, slumped levels of black pelites and
mudstones, diabases and microdiorites, and minor
acidic volcaniclastic rocks (Fig. 2). It is worth
noting that peperites frequently occur at the basic
rocks/shales boundary indicating magmatic intrusions
in to still-wet sediments.
The Corte Pereiro section provided 7 productive
samples containing the richest assemblages observed from the region (Fig. 2). Assemblages are
composed of moderately well-preserved miospores
and acritarchs and may be dived into four subassemblages:
(1) Sub-assemblage 1 includes miospore taxa such
as, Acanthotriletes sp., Auroraspora solisortus, Colatisporites decorus, Dictyotriletes castaneaeformis,
Z. Pereira et al. / Review of Palaeobotany and Palynology 139 (2006) 227–240
231
Fig. 3. Simplified stratigraphic logs of the Cabrela Complex, with location of studied samples and spore content.
Granulatisporites micrograniferKnoxisporites stephanephorus, Knoxisporites triradiatus, Leiotriletes sp.,
Leiotriletes tumidus, Microreticulatisporites concavus,
Neoraistrickia sp., Rugospora sp., Triquitrites spp.,
Vallatisporites sp., Vallatisporites ciliaris? and Waltzispora sp. The occurrence of typical specimens of
Lycospora pusilla, Proprisporites laevigatus and
Raistrickia nigra indicates the NM Biozone of mid
late Viséan age. On average, this assemblage forms
18% of the total recorded palynomorphs.
(2) Sub-assemblage 2 is a distinctive association of
miospores including Auroraspora corporiga, Auroraspora macra, Crassispora trychera, Cyrtospora
cristifer, Densosporites spitsbergensis, Discernisporites micromanifestus, Emphanisporites hibernicus,
Geminospora spongiata, Grandispora echinata,
Microreticulatisporites araneum, Punctatisporites irra-
sus, Retusotriletes triangulatus, Rugospora minuta,
Rugospora polyptycha, Schopfites claviger, Spelaeotriletes sp., Spelaeotriletes pretiosus, Tumulispora
malevkensis, Vallatisporites microspinosus, Verrucosisporites gibberosus and Verrucosisporites nitidus.
On average, this sub-assemblage represents 39% of
total palynomorphs and is interpreted as a reworked
association of Tournaisian age.
(3) Sub-assemblage 3 is composed of moderately
well preserved Devonian palynomorphs. It includes
Late Devonian miospore taxa such as Ancyrospora
langii, Diducites plicabilis, Emphanisporites rotatus,
Grandispora cornuta, Knoxisporites concentricus,
Retispora lepidophyta and Rugospora radiata, and
acritarch taxa Chomotriletes vedugensis, Gorgonisphaeridium ohioense, Daillydium pentaster, Duvernaysphaera
stellata, Duvernaysphaera tessella, Multiplicisphaeridium
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Fig. 4. Ranges of selected spore species recovered and spore biozonal scheme used (after: Clayton et al., 1977; Streel et al., 1987; Higgs et al., 1988;
Clayton, 1996).
ramispinosum, Navifusa bacilla, Pterospermella sp.,
Stellinium micropolygonale and Winwaloeusia ranulaeforma and the prasinophytes Maranhites mosesii, Maranhites perplexus; Early Devonian spore taxa such as
Ambitisporites sp., Brochotriletes sp., Dictyotriletes
emsiensis, Emphanisporites micrornatus and Synorisporites sp.; the Silurian cryptospore Laevolancis sp., miospores
sp. and Synorisporites verrucatus and acritarch taxa
Duvernaysphaera aranaides, Evittia sp., Leiofusa sp. and
Neoveryhachium carminae. This Devonian sub-assemblage comprises 33% of the total studied palynomorphs and
the Silurian sub-assemblage represent less than 1%. Typical
Mid Devonian taxa are absent.
(4) Sub-assemblage 4 consists of Ordovician acritarchs such as Arbusculidium filamentosum, Cymatiogalea sp., Stelliferidium sp., Striatotheca sp. and
Rhophaliophora sp., and Cambrian acritarchs such as
Acanthodiacrodium sp., Annulum sp., Cristallinium sp.,
and Eliasum sp. This sub-assemblage comprises 9% of
the total studied palynomorphs.
Sub-assemblages 3 and 4 are interpreted, as reworked
pre-Carboniferous palynomorphs.
Z. Pereira et al. / Review of Palaeobotany and Palynology 139 (2006) 227–240
233
Fig. 5. Presence–absence of selected spores in the studied sections. R indicates occurrences interpreted as reworked.
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Z. Pereira et al. / Review of Palaeobotany and Palynology 139 (2006) 227–240
4.1.2. Cai Água section
The Cai Água section is situated at the northern
margin of the Pêgo do Altar dam (Fig. 1). In this
region the TMC is made up of acidic and basic
volcanic rocks, thin bedded reworked acidic volcaniclastics and intercalated dark shales. The thickness of
the complex here is unknown, but must be in excess
of 200 m. The measured section (Fig. 2) yielded
poorly to moderately preserved miospore assemblages
assigned to the late Tournaisian CM Biozone and the
early Viséan Pu Biozone. The CM Biozone assemblages include abundant specimens of Acanthotriletes
sp., Auroraspora corporiga, Auroraspora macra,
Crassispora trychera, Discernisporites micromanifestus, Granulatisporites microgranifer, Punctatisporites
irrasus, Retusotriletes sp., Rugospora sp., Rugospora
minuta and Schopfites claviger. The Pu Biozone is
marked by the first occurrence of Lycospora pusilla
and includes the taxa Auroraspora macra, Crassispora trychera, Granulatisporites microgranifer and
Punctatisporites irrasus. Reworked acritarchs, mainly
of Devonian age but also of Cambrian–Ordovician
age, are present in the assemblages.
4.1.3. Ribeira dos Marmelos Quarry and Dam sections
Two well-exposed sections in the Ribeira dos
Marmelos quarry (RMQ) and dam (RMD), about
8 km. west of Vila Nova da Baronia village (Fig. 1),
show an intermediate/acid volcanic sequence intercalated with dark shales (Fig. 2). These shales yielded
poorly to moderately preserved miospores assigned to
the early Viséan Pu Biozone. The assemblages contain
abundant specimens of Lycospora pusilla and Crassispora trychera and taxa such as Acanthotriletes sp.,
Auroraspora macra, Anaplanisporites baccatus, Convolutispora sp., Discernisporites micromanifestus,
Granulatisporites microgranifer, Punctatisporites irra-
235
sus, Retusotriletes sp., Rugospora minuta, Rugospora
polyptycha, Schopfites claviger and Triquitrites spp.
Reworked acritarchs of Devonian age are present in
the assemblages.
4.1.4. Alfundão village section
Dark and black shales, lithologically similar to those
described in the previous sections, crop out in the
surroundings of Alfundão (Fig. 1). The shales appear
associated to basic rocks of the Odivelas magmatic suite
and were considered in a discordant position over this
suite (Santos et al., 1990). Palynostratigraphic analysis
in several samples of Alfundão village section did not
give any results, probably because the shales are
affected by contact metamorphism as shown by the
occurrence of patches of metamorphic andalusite and
chlorite. In the present work, the Alfundão shales are
considered as the southernmost exposure of the Toca da
Moura Complex.
4.2. Cabrela Complex
A preliminary palynostratigraphic research in this
complex provided moderately preserved miospores
whose ages range from the late Tournaisian CM
Biozone to the Viséan, Pu, TS and NM Biozones
(Pereira and Oliveira, 2001a, 2003a). Revision of that
material complemented the study of new samples as
described below.
The Cabrela Railway Station Section (Fig. 3) and the
Silveiras Road Section (Fig. 3) provided miospores assigned
to the CM Biozone. Assemblages include Acanthotriletes
sp., Anaplanisporites baccatus, Auroraspora solisortus,
Colatisporites decorus, Crassispora trychera, Densosporites spitsbergensis, Discernisporites micromanifestus, Geminospora spongiata, Granulatisporites microgranifer,
Knoxisporites literatus, Rugospora minuta, Rugospora
Plate I. 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. All magnifications are 1000×.
1.
2.
3.
4.
5.
6.
7.
8.
9, 12.
10.
11.
Schopfites claviger (Sullivan 1968) Higgs, Clayton and Keegan 1988; Cabrela Formation, MN1-2, 1230-215, INETI/SG 0401.
Crassispora trychera Neves and Ioannides 1974; Toca da Moura shales, CP2-2, 1228-100, INETI/SG 0402.
Lycospora pusilla (Ibrahim 1932) Schopf, Wilson and Bentall 1944; Toca da Moura shales, CP23-1, 1205-140, INETI/SG 0403.
Rugospora polyptycha Neves and Ioannides 1974; Cabrela Formation, MN5-2, 1215-55, INETI/SG 0404.
Knoxisporites triradiatus Hoffmeiser, Staplin and Malloy 1955; Cabrela Formation, MN1-2, 1215-170, INETI/SG 0405.
Knoxisporites stephanephorus Love 1960; Cabrela Formation, PQ7-1, 1255-85, INETI/SG 0406.
Raistrickia nigra Love 1960; Toca da Moura shales CP14-1, 1075-90, INETI/SG 0407.
Proprisporites laevigatus Neves 1961; Toca da Moura shales CP14-1, 1095-100, INETI/SG 0408.
Triquitrites sp.; Toca da Moura shales, CP14-1, 1365-135, INETI/SG 0409; Toca da Moura shales, CP14-1, 1265-90, INETI/SG 0410.
Microreticulatisporites concavus Butterworth and Williams 1958; Cabrela Formation, MN1-2, 1055-75, INETI/SG 0411.
Anaplanisporites baccatus (Hoffmeister, Staplin and Malloy 1955) Smith and Butterworth 1967; Cabrela Formation, MN1-2(5), 1415145, INETI/SG 0412.
236
Z. Pereira et al. / Review of Palaeobotany and Palynology 139 (2006) 227–240
Fig. 6. Stratigraphical distribution of the units studied in the southern border of the Ossa Morena Zone compared with lithostratigraphical units from
the South Portuguese Zone.
polyptycha, Tumulispora malevkensis, Vallatisporites
vallatus and Verrucosisporites nitidus in association with
the zonal species Auroraspora macra and Schopfites
claviger.
Shales interbedded in the acidic volcaniclastic rocks
in the core of the syncline, in two quarries (Monte
Chaminé and Buraco quarry, Fig. 3) yielded miospores
of the CM Biozone and of the Pu and TS Biozones. The
CM Biozone is represented by the typical species
Auroraspora macra, Crassispora trychera, Discernisporites micromanifestus, Grandispora echinata, Granulatisporites microgranifer, Knoxisporites literatus,
Punctatisporites irrasus, Retusotriletes triangulatus,
Rugospora minuta, Schopfites claviger, Vallatisporites
microspinosus, Vallatisporites vallatus, Verrucosisporites gibberosus and Verrucosisporites nitidus. The base
of the Pu Biozone is identified by the first occurrence of
Lycospora pusilla, and the basal part of the TS Biozone
is recognized by the first combined occurrence of
Knoxisporites stephanephorus and Knoxisporites
triradiatus.
The Monte Novo Road Section (Fig. 3, Section 3)
gave the youngest recovered in the region. The
following miospore taxa were identified: Acanthotriletes sp., Anaplanisporites baccatus, Auroraspora
solisortus, Colatisporites decorus, Dictyotriletes castaneaeformis, Discernisporites micromanifestus, Granulatisporites microgranifer, Knoxisporites triradiatus,
Knoxisporites stephanephorus, Leiotriletes sp., Leiotriletes tumidus, Lycospora pusilla, Microreticulatispor-
ites concavus, Proprisporites laevigatus, Raistrickia
nigra, Rugospora sp., Tripartites sp., Vallatisporites
ciliaris? and Waltzispora sp. This assemblage identifies
the NM Biozone.
All the samples studied in this section contain two
associations of reworked miospores. One, with species
such as Auroraspora corporiga, Auroraspora macra,
Crassispora trychera, Cyrtospora cristifer, Emphanisporites hibernicus, Geminospora spongiata, Microreticulatisporites araneum, Punctatisporites irrasus,
Retusotriletes triangulatus, Rugospora minuta, Rugospora polyptycha, Schopfites claviger, Spelaeotriletes
pretiosus, Tumulispora malevkensis, Verrucosisporites
gibberosus and Verrucosisporites nitidus; belongs to
the Tournaisian. The other, assigned to the Devonian,
is marked by the taxa Brochotriletes sp., Dictyotriletes emsiensis (Early Devonian), Verrucosisporites
scurrus, Verrucosisporites premnus and Geminospora
lemurata (Mid Devonian) and Samarisporites triangulatus and Grandispora cornuta (Late Devonian).
Some Devonian acritarchs are also present.
5. Geodynamic implications
The result of the present research indicates that
the Toca da Moura and the Cabrela Complexes
have strong lithological similarities and comparable
ages.
The occurrence of abundant (80%) reworked palynomorphs is a common feature of many of the studied
Z. Pereira et al. / Review of Palaeobotany and Palynology 139 (2006) 227–240
samples. Analysis of the reworked assemblages shows:
predominance of Late Devonian and Tournaisian
miospores, with acritarchs representing much lesser
amounts; scarcity of typical Mid Devonian species; rare
Silurian palynomorphs; and the existence of Ordovician
and Cambrian acritarchs in significant proportions (9%
in several samples).
Spore and acritarch colour indices (Thermal Alteration Indices) (Staplin, 1969; Legall et al., 1981) show
that the thermal maturity of the reworked specimens is
identical to the associated mid late Viséan age material,
suggesting that the host sediments were never deeply
buried. The reworked specimens are, generally,
moderately preserved, indicating small pre-depositional
corrosion or abrasion. Such preservation could reflect a
combination of multiple factors that affect the
processes of erosion, re-transportation and re-deposition. Nevertheless, due to their durability reworked
palynomorphs are commonly preserved in pristine
conditions (Ravn and Benson, 1988; Van de Laar and
Fermont, 1989).
As the biostratigraphy of the Portuguese part of the
Ossa Morena Zone, is still poorly known, discussion on
palynomorph provenance is precluded. However, the
present data allow some consideration of the regional
geodynamic evolution.
The Cabrela Complex is discordant upon a wellstructured basement of phyllites and amphibolites of
uncertain age (Silurian?) showing three episodes of
orogenic deformation. Tectonically stretched clasts of
these lithologies appear in the basal conglomerate of the
Complex that crops out in the northern limb of the
syncline, indicating deep crustal erosion. In the
southwestern limb of the syncline, Mid and Late
Devonian limestones appear to be dispersed in the
terrigenous sediments of the Complex which is here
dated as late Tournaisian to mid late Viséan. Most of the
volcanic rocks of the Complex are reworked acidic
volcaniclastics. The Cabrela Complex sediments are
only affected by a week fracture cleavage. It is therefore
suggested that the stratigraphic sequence of the Cabrela
Complex was laid down in a basin whose margins were
subjected to extensive erosion induced by crustal uplift.
Post-Silurian (?) to pre-late Tournaisian sedimentary
units were completely removed, with only the Mid and
Late Devonian limestone lenses interbedded in the
complex remaining. These are interpreted as olistoliths
that were moved in to the basin, as gravity slides
dislocated from a Devonian carbonate platform, situated
to the present day south of the region. The Cabrela
Complex was only tectonically deformed post-late
Viséan.
237
Geochemistry of the volcanics of the Toca da Moura
Complex indicates that they were linked to the genesis
of an orogenic arc installed on the continental crust of
the OMZ in close relationship to a northward dipping
subduction zone (Santos et al., 1987). As with the
Cabrela Complex, the presence of reworked palynomorphs in the Toca da Moura sediments indicates that
they were deposited in basins surrounded by uplifted
crustal blocks subjected to intense erosion. It is
interesting to note that on the southern margin of the
Odivelas dam, near to Monte das Cortes, crop out
limestones that yield Mid Devonian macrofaunas
(Conde and Andrade, 1974). The limestones are
badly exposed but the fact that they do not show
traces of strong deformation or metamorphism is
indicative that they were probably preserved as
olistholiths. Furthermore, in the region, several outcrops of calc–silicate rocks in close association with
basic intrusives were recently identified between
Alfundão and Beja. This suggests that the limestones
are remnants of a Devonian carbonate platform that has
been intruded by basic rocks and may have extended
into the Cabrela region. The intrusives are probably
related to the Toca da Moura magmatism. However,
the contact metamorphism affected by the Alfundão
shales, indicates that the magmatic activity went on in
post Viséan time.
Comparison of the results from the southern border of
the Ossa Morena Zone with palynostratigraphic records
from the South Portuguese Zone (Oliveira et al., 1997,
2004; Pereira, 1999; Pereira and Oliveira, 2003a,b;
Pereira et al., in press) indicates a number of similarities
(Fig. 6):
(1) Late Devonian assemblages recovered from the
Phyllite–Quartzite Group of the Pyrite Belt and from the
Tercenas Formation in Southwest Portugal (Bordeira and
Aljezur Anticlines) are very similar to the reworked
assemblages of the Toca da Moura and Cabrela
Complexes.
(2) Records of palynomorphs from the Bordalete
Formation in Southwest Portugal, reworked Tournaisian associations in the Volcano-Sedimentary Complex
of the Pyrite Belt, and the reworked Tournaisian
assemblages in the OMZ all show the presence of the
same species.
(3) NM miospore biozone assemblages identified
in different units and lithologies, throughout the
Pyrite Belt and Southwest Portugal always contain
Proprisporites laevigatus associated with the first
occurrence of Raistrickia nigra, and other typical
genera of this level (e.g. Dictyotriletes, Leiotriletes,
Lycospora, Microreticulatisporites, Vallatisporites and
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Z. Pereira et al. / Review of Palaeobotany and Palynology 139 (2006) 227–240
Waltzispora). The co-occurrence of P. laevigatus and
R. nigra and the absence of other stratigraphically
useful taxa such as Rotaspora spp., Tripartites spp.
and Triquitrites spp., allow the identification of a
local spore biozone, the NL R. nigra – P. laevigatus
Biozone in Southwest Portugal (Pereira, 1999).
However, the NL Biozone is correlated with the
NM Biozone of Western Europe based in the first
appearance of R. nigra. The same biostratigraphic
situation is identified in the Toca da Moura and
Cabrela Complexes. While P. laevigatus appears
together with the first R. nigra in south Portugal, in
Western Europe the first appearance of this species is
higher, at the top of the early Serpukovian NC
Biozone (Clayton et al., 1977; Clayton, 1996).
The palynostratigraphic evidence clearly shows
that the southern margin of OMZ and the South
Portuguese Zone were close to each other during the
Late Devonian and the Mississippian. This suggests
that the oceanic basin that once existed between the
two zones, now marked by the Beja-Acebuches
Ophiolite, was closed in prior to the latest
Devonian time. The orogenic geochemical signatures
of the Toca da Moura and Cabrela Complexes and
of the magmatic suite of the Beja Massif in general
should be related to intra-continental subduction
following the pre-Late Devonian collision of the
OMZ–SPZ.
6. Conclusions
The following conclusions are reached from this
study:
(1) The age of the Toca da Moura and Cabrela
Complexes, given by miospores, ranges from the late
Tournaisian to the mid late Viséan. The Toca da Moura
and Cabrela Complex thus appear to be coeval.
(2) The Cabrela Complex rests unconformably on a
well-structured Variscan (Silurian?) substrate while the
Toca da Moura Complex is in close association with
the Beja Massif plutono-volcanic suite. Both complexes were laid down in small intra-arc basins at the
southern margin of the OMZ. The surrounding regions
of these basins were probably subject to intense
erosion induced by uplifting caused by the installation
of the volcanic arcs.
(3) Similar Late Devonian and Mississippian palynological assemblages identified in the Toca da Moura
and Cabrela Complexes and several units of the SPZ
suggest that both crustal blocks were close to each other
at this time.
(4) The oceanic basin that existed between the
OMZ and the SPZ, now underlined by the BejaAcebuches Ophiolite was closed in pre-Late Devonian
time.
Acknowledgements
This work was sponsored by the program POCTI,
CTA/14089 of Fundação para a Ciência e Tecnologia,
Portugal. The first author gratefully thanks the Fundação
Calouste Gulbenkian, for funding her participation in
the XI International Palynological Meeting in Granada,
Spain. Thanks also to the Mariana Martins for sample
processing and Eliane Marques and Filipe Barreira for
figures treatment. The authors acknowledge Duncan
McLean and Michel Robardet for their helpful reviews
of the manuscript.
Appendix A. Annotated list of palynomorph species
All the miospore, acritarch and prasinophytes taxa
recorded in the samples from the Early Carboniferous
of the Toca da Moura and Cabrela Complexes,
including the reworked taxa identity are listed
alphabetically. Stratigraphically important taxa are
illustrated on Plate I.
Miospore taxa
Anaplanisporites baccatus (Hoffmeister, Staplin and Malloy 1955)
Smith and Butterworth 1967
Ancyrospora langii Allen 1965
Auroraspora corporiga Higgs, Clayton and Keegan 1988
Auroraspora macra Sullivan, 1968
Auroraspora solisortus Hoffmeister, Staplin and Malloy 1955
Colatisporites decorus (Bharadwaj and Venkatchala 1961) Williams in
Neves et al. 1973
Crassispora trycher Neves and Ioannides 1974
Cyrtospora cristifera (Luber 1941) Van der Zwan 1979
Densosporites spitsbergensis Playford 1963
Dictyotriletes castaneaeformis (Horst 1943) Sullivan 1964
Dictyotriletes emsiensis (Allen 1965) McGregor 1973
Diducites plicabilis Van Veen 1981
Discernisporites micromanifestus (Hacquebard 1957) Sabry and
Neves 1971
Emphanisporites hibernicus Clayton, Higgs and Keegan 1977
Emphanisporites micrornatus Richardson and Lister 1969
Emphanisporites rotatus (McGregor 1961) McGregor 1973
Geminospora lemurata Balme 1962
Geminospora spongiata Higgs, Clayton and Keegan 1988
Grandispora cornuta Higgs 1975
Grandispora echinata Hacquebard 1957
Granulatisporites microgranifer Ibrahim 1933
Knoxisporites concentricus (Byvsheva 1976) Playford and McGregor
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Z. Pereira et al. / Review of Palaeobotany and Palynology 139 (2006) 227–240
Knoxisporites literatus (Waltz 1938) Playford 1963
Knoxisporites ruhlandii Doubinger and Rauscher 1966
Knoxisporites stephanephorus Love 1960
Knoxisporites triradiatus Hoffmeiser, Staplin and Malloy 1955
Leiotriletes tumidus Butterworth and Williams 1958
Lycospora pusilla (Ibrahim 1932) Schopf, Wilson and Bentall 1944
Microreticulatisporites araneum Higgs, Clayton and Keegan 1988
Microreticulatisporites concavus Butterworth and Williams 1958
Proprisporites laevigatus Neves 1961
Punctatisporites irrasus Hacquebard 1957
Raistrickia nigra Love 1960
Retispora lepidophyta (Kedo 1957) Playford 1976
Retusotriletes triangulatus (Streel 1964) Streel 1967
Rugospora minuta Neves and Ioannides 1974
Rugospora polyptycha Neves and Ioannides 1974
Rugospora radiata (Yushko 1969) Byvsheva 1985
Samarisporites triangulatus Allen 1965
Schopfites claviger (Sullivan 1968) Higgs, Clayton and Keegan 1988
Spelaeotriletes pretiosus (Playford 1963) Neves and Belt 1970
Synorisporites verrucatus Richardson and Lister 1969
Tumulispora malevkensis (Kedo 1963) Turnau 1978
Vallatisporites ciliaris (Luber 1938) Sullivan 1964
Vallatisporites microspinosus Higgs, Clayton and Keegan 1988
Vallatisporites vallatus Hacquebard 1957
Verrucosisporites gibberosus (Hacquebard 1957) Higgs, Clayton and
Keegan 1988
Verrucosisporites nitidus (Naumova 1953) Playford 1964
Verrucosisporites premnus Richardson 1965
Verrucosisporites scurrus (Naumova 1953) McGregor and Camfield
1982
Acritarch and prasinophyte species
Arbusculidium filamentosum (Vavrdová 1965) Vavrdová 1972
Chomotriletes vedugensis Naumova 1953
Daillydium pentaster (Staplin 1961) Playford 1981
Duvernaysphaera araides Deunff 1964
Duvernaysphaera stellata Deunff 1964
Duvernaysphaera tessella Deunff 1964
Gorgonisphaeridium ohioense (Winslow 1962) Wicander 1974
Maranhites mosesii (Sommer 1956) Brito 1967
Maranhites perplexus Wicander and Playford 1985
Multiplicisphaeridium ramispinosum Staplin 1961
Navifusa bacilla (Deunff 1955) Playford 1977
Neoveryhachium carminae Cramer 1964
Stellinium micropolygonale (Stockmans and Willière 1960) Playford
1977
Winwaloeusia ranulaeforma Martin 1984
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