Assinatura tectono-sedimentar do auge da compressão bética em Portugal: a descontinuidade sedimentar Valesiano terminal-Turoliano

An Upper Miocene important sedimentary break can be accurately recognised in the Portuguese basins and is reflected by a drastic palaeogeographic change in relation to a large-scale tectonic event of probable uppermost Vallesian-Turolian (9,5 Ma; middle Tortonian) age. The characterisation of the sedimentary record of this tectonic event, as well as its relations with interpreted active faults is made for different situations: Douro (NW border), Mondego, Lower-Tagus and Sado Tertiary basins. The sedimentary record, considered upper Tortonian-Messinian ? (uppermost Vallesian-Turolian ?) is interpreted mainly as endorheic alluvial fans (internal drainage), developed along active NNE-SSW indent-linked strike-slip faults and NE-SW reverse faults. At NE Portugal, proximal fluvial systems of an endorheic hydrographic network drained eastwards to the Spanish Duero interior Basin. The main evidences of the betic compression clímax in Portugal mainland are presented; the interpreted active tectonic structures are in accordance with an intense NNW-SSE crustal shortening, but some regional differences are also documented.

Estratigrafia e interpretação paleogeográfica do Cenozóico continental do norte de Portugal

Palaeogeographic and tectono-sedimentary interpretation of northern Portugal, in which previous studies (geomorphology, lithostratigraphy, mineralogy, sedimentology, palaeontology, etc.) were considered, is here proposed. Cenozoic shows different features according to its morphotectonic setting in the eestern region (Trás-os-Montes) or near to the Atlantic coast (western region, Minho and Douro Litoral areas). Although in the eastern region the sedimentary record is considered late Neogene, in some places Paleogene (?) was identified. This oldest record, represented by alluvial deposits, was preserved from complete erosion because of its position inside Bragança-Vilariça-Manteigas fault zone grabens. Later sedimentary episodes (upper Tortonian-Zanclean ?), represented by two allostratigraphical units, were interpreted as proximal fluvial braided systems of an endorheic hydrographic network, draining to the Spanish Duero Basin (eastwards); nowadays, they still remained in tectonic depressions and incised-valleys. Later on, eastern sedimentation becomes scarcer because Atlantic fluvial systems (e.g. the pre-Douro), successively, captured previous endorheic drainages. The proximal reaches of the allostratigraphic unit considered Placencian is recorded in Mirandela (western Trás-os-Montes) but the following fluvial episode (Gelasian-early Pleistocene ?) was already documented in east Trás-os-Montes, preserved in high platforms and in tectonic depressions. Placencian and Quaternary sedimentary records in the western coastal zone, mainly represented by terraces, are located in the Minho, Lima, Alverães, Cávado and Ave large fluvial valleys and in the Oporto littoral platform. In conclusion, northern Portugal Tertiary sedimentary episodes were mainly controlled by tectonics, but later on (Placencian-Quaternary) also by eustasy.

Mineralogia da fracção argilosa da Formação de Vale Álvaro (Bragança, NE Portugal)

The studied materials were sampled from several conglomerate and carbonate sandstone units, overlapped for 23 meters. This formation represents a debris flow dominated alluvial fan alternating with quiet sedimentary conditions. These deposits of probably Paleogene age were placed upon mafic and ultramafic rocks that are the exclusive source of sediments. Optical and SEM identification, microanalysis and XRD studies (with decomposition procedures) of clay fractions obtained after high-speed centrifugation were performed in order to characterise the clay minerals content. The results of the analytical program allowed the establishment of the following remarks: a) Fe-rich montmorillonite dominance over paligorskite, chlorite, chlorite-smectite mixed-layers, serpentine and talc; b) smectites in the 12.4 - 15 A range, expanding to about 17 A after EG treatment; c) serpentine and talc as secondary minerals in the interior of altered clasts; d) chlorite and clorite smectite mixed-layer compositions in the borders of the clasts and in the cement. The composition of sediments results from coarse clasts eroded from mafic and ultramafic rocks and clayey material. Clasts show evidences of post-depositional weathering (coatings of chlorite and smectite). Clayey material has the contributions of i) inherired chlorite, smectite and chlorite-smectite mixed-layers; ii ) authigenic crystallisation of Fe-montmorillonite (due to availability of Fe in the crystallising solutions following previous weathering events); iii) authigenic paligorskite associated to a carbonate cement.

Evolução cenozóica da área de Longroiva-Vilariça (NE Portugal)

In the Longroiva-Vilariça area, the identification of Cenozoic lithostratigraphic units, the sedimentology and the characterization of its geometric relations with tectonic structures allowed the interpretation of the palaeogeographic main stages: 1) the greenwhitish Vilariça Arkoses (Middle Eocene to Oligocene ?) represent proximal sediments of a very low gradient drainage towards the eastern Spanish Tertiary Duero Basin; 2)Quintãs Formation (late Miocene ?) are brown-reddish coloured piedmont alluvial deposits, correlative of important vertical displacement (western tectonic block relative uplift) along the NNE-SSW indent-linked strike-slip Bragança-Vilariça-Longroiva fault zone, interpreted as a reactivated deep hercynian fracture, with left-lateral movement; 3) the red Sampaio Formation (Gelasian-early Pleistocene ?)was interpreted as downhill conglomeratic deposits related with important overtrusting along this fault zone (the definition of the present-day narrow graben configuration) and correlative of the atlantic hydrographic incision stage beginning; 4) conglomeratic terraces (middle and late Pleistocene ?); 5) alluvial plains and colluvial deposits (Holocene).

Depósitos continentais e marinhos na plataforma litoral da região do Porto. Importância da tectónica na sua organização espacial

One of the most common characteristics of Portuguese littoral is the existence of a planed surface (the so-called "littoral platform"), situated at different altitudes and bordered from the inland by a straight relief, strongly contrasting with that planed surface. This one is generally covered with several outcrops of the so-called Plio-Pleistocene deposits. Till the eighties this platform has been interpreted as stable staircase of old marine levels, registering in a passive way the eustatic variations. The rigid step bordering it easterly should be a fossil cliff. However, our study has proved that many of these deposits have a continental origin. These continental deposits have fluvial or alluvial fan facies and they are lying above 40 meters. Marine deposits seem to be quite rare and they only occupy a small western area, beneath the altitude of 40 meters and developing into three different marine levels. There is a rigid step between the two kinds of deposits. We think that the clear geometric separation between these deposits together with this rigid step, indicates a tectonic origin. It seems that the sea must have touched only the western part of this surface, when neotectonic movements lowered it down. There are more evidences for neotectonic movements: a) there are faults (mainly inverse faults) affecting the higher deposits of this littoral platform; b) the same marine level seems to appear at different altitudes, developing an irregular pattern with a general trend dipping from the North to the South.

Litostratigrafia do Terciario da região Miranda do Corvo-Viseu (Bacia do Mondego, Portugal)

The lithostratigraphic units (2 groups, 5 formations and 4 members) of the Tertiary of the Miranda do Corvo-Viseu region (Central Portugal) are here described. For each unit the characterization and description (boundaries, diagnostic properties and atributes) were included. The stratigraphic, lithological, sequential and tectonic data allow correlations with other units of the same Tertiary basin located more to west and support the chronostratigraphic attribution. Sedimentologic characteristics of the deposits lead to the interpretation of the influence of tectonism, climate and eustasy during the sedimentary evolution of this Basin.

Significado regional dos depósitos neogénicos continentais da área de Vila de Rei (Portugal Central)

In the Vila de Rei area (Central Portugal) the continental deposits of the Lower Tagus Tertiary Basin lay upon the pediment of the Portuguese Central Chain. Three conglomerate units are recorded from the base upwards, separated by regional or basinal unconformities; Conglomerados de Rio de Moinhos (RM); Conglomerados de Serra de Almeirim (SA) and Conglomerados de Vila de Rei (VR). The first two units (RM and SA) have been sites of gold exploitation in huge open pit mines probably during Roman colonisation times. The contact of this units, on the Paleozoic basement or on the Paleogene unit Grés de Monsanto, is unconform, defining in both limits a large nondepositional and/or erosional hiatus. Those conglomerates seal the sedimentation of the Lower Tagus Tertiary Basin along its northern border. Taking into account the significance assigned to their basinal unconformity limits, the uplift of the Portuguese Central Chain, and the fact of this continental units yielded no fossils with chronostratigraphic significance, they have been considered ranging from Upper Miocene to the beginning of the Quaternary. Finally, a lithostraligraphic equivalence with the Neogenic units of the Bierzo and Duerna basins (NW of the Iberian Peninsula), where exploitations from Roman times are also evident, is presented.

Tertiary evolution of the São Vicente and Setúbal submarine canyons, Southwest Portugal: insights from seismic stratigraphy

The Setúbal and São Vicente canyons are two major modern submarine canyons located in the southwest Iberian margin of Portugal. Although recognised as Pliocene to Quaternary features, their development during the Tertiary has not been fully understood up to date. A grid of 2D seismic data has been used to characterise the sedimentary deposits of the adjacent flanks to the submarine canyons. The relationship between the geological structure of the margin and the canyon's present location has been investigated. The interpretation of the main seismic units allowed the recognition of three generations of ravinements probably originated after middle Oligocene. Six units grouped in two distinctive seismic sequences have been identified and correlated with offshore stratigraphic data. Seismic Sequence 2 (SS2), the oldest, overlies Mesozoic and upper Eocene deformed units. Seismic Sequence I (SS1) is composed of four different seismic packages separated from SS2 by an erosional surface. The base of the studied sediment ridges is marked by an extensive erosional surface derived from a early/middle Oligocene relative sea-level fall. Deposition in the adjacent area to the actual canyons was reinitiated in late Oligocene in the form of transgressive and channel-fill deposits. A new depositional hiatus is recorded onshore during the Burdigalian, coincident with the unconformity separating SS1 and SS2. This can be correlated with the Arrábida unconformity and with the paroxysmal Burdigalian phase of the Betic domain. Presently, the Setúbal and São Vicente submarine canyons locally cut SS1 and SS2, forming distinctive channels from those recognised on the seismic data. On the upper shelf both dissect highly deformed areas subject to important erosion.

The Neogene of Algarve (Portugal)

A synthesis about the Neogene and Quaternary of Algarve (Southern Portugal) is presented. New isotopic 87Sr/86Sr ages as well as biostratigraphic data about the Miocene deposits allow to present a new stratigraphic frame for the previously characterized units. The Lagos-Portimão Formation corresponds to deposits of temperate carbonate platform sedimentological type, developed during a long time span (Lower Burdigalian to Upper Serravallian). A major change in sedimentation conditions (carbonate to siliciclastic environments) occurred in the Lower Tortonian with the deposition of yellowish sands. Spongoliths rich in microfossils are represented in Algarve inland. Their age is not well established; calcareous nannofossils indicate the CN5a zone (Upper Serravallian) while foraminifera point out at least Nl6 zone (Lower Tortonian). In the Upper Tortonian, the sedimentation is widespread in Eastern Algarve, related with the Guadalquivir Basin infill. The deposits begin with detrital limestones, locally very rich in Heterostegina, passing to fossiliferous conglomerates and siltstones (Cacela Formation). Coarse-grained conglomerates at Galvana (Faro) pose some age problems. K/Ar age on glauconite indicates 6.72±0.17 Ma. However, glauconites may be reworked from older deposits (Cacela Formation). The Galvana Conglomerate could be related to Pliocene deposits are not well characterized. Olhos de Água sands, with a thin marine intercalation rich in marine vertebrates (fishes, a crocodile, cetaceans, sirenians), may be Upper Pliocene; however, the vertebrates point out to a Serravallian to Tortonian age. 87Sr/86Sr ages on oysters from above the level with vertebrates point out to 3.0(+2.5-1.0) Ma. Similar sand deposits occur at Morgadinho (Luz de Tavira). These sands are overlain by marls, lignite clays, lacustrine limestones and a silty calcareous crust. A small mammals association indicate an age span between Upper Pliocene and Lower Middle Pleistocene (MN17-MN20). A Biharian mammal fauna (Lower Pleistocene) was collected at Algoz in similar deposits. In the present state of knowledge, Morgadinho and Algoz deposits may be correlative.

The three main marine depositional cycles of the Neogene of Portugal

The present work follows a stratigraphic model for the marine Neogene of Portugal based on the definition of three main marine sedimentary cycles. Conceptually the I, II and III Neogene Cycles can be defined as 2nd order sedimentary sequences with duration ranging from 5 to 8 Ma. The I Neogene Cycle is fully represented only in the Lower Tagus Basin. Ranging from the Early Aquitanian to the Late Burdigalian the I Neogene Cycle testify a transgressive episode in the region of Lisbon and Setúbal Peninsula. Rapid lateral facies variations suggest a shallowmarine basin. This cycle ends with an important Late Burdigalian tectonic compressive event expressed by uplift of the surrounding areas and deformation affecting the Early Miocene deposits of the Arrábida Chain. The II Neogene Cycle includes thick sedimentary sequences covering Paleozoic and Mesozoic formations in the Algarve and Alvalade-Melides regions and it extends as far north as Santarém in the Lower Tagus Basin. Mainly controlled by global eustasy, it was generated by the important positive eustatic trend that characterized the Middle Miocene worldwide to which the Portuguese continental margin acted more or less passively. This cycle ended with a second and the most important compression event starting after the end of the Serravallian affecting the entire Portuguese onshore and shelf areas. This led to an important depositional hiatus of marine sediments for more than 2.5 Ma. During the Early and the Middle Tortonian occurred the clockwise rotation of the Guadalquivir Basin. The thickmarine units deposited afterwards in this basin produced a litostatic load, which seems to have induced subsidence farther west resuming the Neogene marine sedimentation in the Cacela region (Eastern Algarve), during the Late Tortonian. This marks the beginning of the III Neogene Cycle. To the north, in the Sado Basin (Alvalade-Melides region), a similar depositional sequence starts its sedimentation during the Messinian. Further north, in the Pombal-Caldas da Rainha region, marine sedimentation started during the Late Pliocene (Piacenzian). The migration in time, from south to north for the beginning of the marine sedimentation of this cycle is interpreted as reflecting a visco-elastic propagation of the deformation from the Betic chain northwards.

Late Quaternary warm marine mollusks from Santa Maria (Azores); paleoecologic and paleobiogeographic considerations

The sub-fossil fauna from the Late Quaternary marine deposits of Santa Maria is made of more than 50 species of gastropods and bivalves, 19 of them collected recently and for the first time in the northern coast of the island (Lagoinhas Bay). The sub-fossil shells are found in deposits of beach sands, situated 2-3 meters above the present low tide. The carbonated sands from the basal part of the succession yield an autochthonous association of borers dominated by the bivalve Myoforceps aristata (Dillwin, 1817). Upwards, the marine sands contain concentrations of beach drift shells, including well-preserved supratidal and intertidal gastropods, among them a large number of Rissoidae. The bivalve fauna is dominated by disarticulated valves of Ervilia castanea (Montagu, 1803), a small infaunal coloniser of mobile sandy substrates. The composition of the fauna is made essentially of West European species, many of them common to the West Coast of Portugal. However, a few "warm guests" with West African or Caribbean affinities were also found, suggesting a close relation with some of the "Tyrrhenian" warm associations found in the Western Mediterranean.

Miocene marine mammals from Portugal. Paleogeographical and paleoecological significance

Neogene marine mammals are still incompletely known in Portugal. However, a general overview of the geographic and stratigraphic distribution of marine mammal localities in the Miocene of Portugal is already possible. An attempt of correlation between the trends shown by these distributions and the horizontal and vertical environmental shifts is presented. In general, sirenians occur in deposits representing shallow, warm, low energy aquatic environments; while cetaceans are more frequent in more open, deep and temperate marine environments.

Uppermost Miocene Lamniform Selachians (Pisces) from the Alvalade basin (Portugal)

This paper deals with Lamniform teeth collected in deposits from the Esbarrondadoiro Formation, Alvalade Basin in Southern Portugal. The following genera were recognized: Carcharias, Pseudocarcharias, Alopias, Isurus and Carcharocles. The species Carcharias acutissima is by far the most predominant, all other taxa being rare or very rare. This situation points to neritic, tropical to subtropical, rather shallow waters not far away from the coast. This is corroborated by the rarity of the associated, mainly pelagic, taxa. The ratio between C. acutissima and the remaining Lamniforms as a whole is markedly uneven between Esbarrondadoiro and the localities of Santa Margarida and Vale de Zebro. This suggests quite different environmental conditions, a matter that will require a more thorough examination taking into account all palaeontologic and geologic data.

Rediscovery of Leptaxis vetusta (Morelet & Drouet, 1857), a subfossil land snail from the Quaternary of Santa Maria (Azores)

During a recent field work on the southern coast of the island of Santa Maria (Azores) a bulk sample of 37 shells and 25 fragments of Leptaxis vetusta was assembled from Late Pleistocene and Holocene slope deposits outcropping in the area. These specimens are the first of this rare subfossil species to be mentioned since the original descriptions of Arthur Morelet and Henri Drouet (1857). The purposes of our paper are a systematic and biometric description of L. vestuta. For the first time, the original type: locality was localized with accuracy over the southern downslopes of Pico do Facho, between Figueiral and Prainha. The subfossil specimens were collected in slope deposits and detritic fans, overlying a fossiliferous marine deposit situated over the 2-3 m abrasion platform of Praia and Prainha bay. The age and factors associated to the extinction of this species are discussed, including the destruction of the original laurel cover and the colonization by Otala lactea (Muller, 1774), a continental helicid introduced and widespread in Santa Maria.

On the hydrogeology of the Lower Tagus Basin and its Cenozoic geologic evolution

The chemical features of the ground water in the Lower Tagus Cenozoic deposits are strongly influenced by lithology, by the velocity and direction of the water movement as well as by the localization of the recharge and discharge zones. The mineralization varies between 80 and 900 mg/l. It is minimal in the recharge zones and in the Pliocene sand and maximum in the Miocene carbonated and along the alluvial valley. Mineralization always reflects the time of permanence, the temperature and the pressure. The natural process of water mineralization is disturbed in agricultural areas because the saline concentration of the infiltration water exceeds that of the infiltrated rainwater. In the discharge zones, the rise of the more mineralized, some times thermal deep waters related to tectonic accidents give rise to anomalies in the distribution of the aquiferous system mineralization model. The diversity of the hydrochemical facies of the ground water may be related to several factors whose identification is some times difficult.