Ciencias da Terra (tJNLl Numeroespecial IT
THE NEOGENE OF PORTUGAL
M. Telles ANTUNES & Joao PAIS
Centro de Estratigrafia e Paleobiologia (I.N.I.C.). Faculdade de Ciencias e Tecnologia. Quinta da Torre. P-2825 Monte de Caparica
FOREWORD and Gustave Dollfus gave important contribu tions. After years of research dedicated to the After a long eclipse, there was a remark Mediterranean Neogene (Project NQ 25, IUGS able resumption of Neogene studies due to UNESCO), there has been a considerable de Portuguese geologists or foreign geologists at velopment in activities concerning the Atlantic the service of Portugal. G. Zbyszewski de Neogene. serves a special reference for his work. Within this framework, the hinge-like Finally, we have tried to develop and co situation of . Portugal is quite interesting, ordinate efforts to reach the knowledge that, in considering the fact that the neogene units here spite of the amount of data already obtained, is are well represented and complete. This is far from being complete. This justifies the fol particularly true for the Tagus basin, that has a low-up of researches that are frequently done very rich record. At the beginning of the XIX with the collaboration of colleagues from other century, research has been conducted by the countries, mainly France. Part of this data is remarkable mineralogist (and future politician) presented in the following compilation of texts. Jose Bonifacio de Andrada e Silva (1763- 1838). Towards the 30's and 40's, the contributions due to Baron Von Eschwege, THE NEOGENE Alexandre Vandelli, Daniel Sharpe and a few others followed. Meanwhile, there was a The Neogene is widely represented in considerable development in investigations with Portugal. However, its geographical distribu the second Geological Commission (1857- tion is not at all homogeneous. Generally 1867), mainly due to the field works of Carlos speaking, the Miocene formations are particu Ribeiro and the important contributions of larly important to the South of the Central Francisco Pereira da Costa. Mountain Range and the Nazare fault in the After being abandoned for a while, the continent as well as in the continental shelf as studies were vigorously restarted at the far as Algarve. Special reference is made to the Geological Survey with Jorge Candido terminal part of the Tagus basin due to its re Berkeley Cotter, towards the end of the cen markable importance in the frame of Western tury. Lithostratigraphic classification, now Europe. considered classical but still used in the Lisbon The Pliocene, whose paleogeography is Miocene, is due to him. quite different, mainly corresponds to a band Some of the most remarkable paleontolo that basically stretches along the shoreline. The gists at the time, such as Oswald Heer, F. importance of the inland Pliocene deposits is Fontannes, Perceval de Loriol, Frederic Roman smaller than one had previously thought. 13 cco ID (,) o (,) +=' coC ~ ~~ Mediterranean Sea ~ Meridional border L...... :....,J Basins [CD Borderlands and moderately deformed chains ~ ~ Alpine chain 150Km CJ Hercynian basement Fig. 1 - Morphostructural units of the Iberian Peninsula (Lautensach in RIBEIRO et al., 1979, modified). The Neogene of the TagtI) Basin two for the Pliocene. Subsidence was intensive was compensated by active sedimentation. The continental debris arrived in large quantities mainly during the orogenic movements which The Neogene of the lower Tagus basin is reactivated old hercynian faults. remarkable in several ways: its geographical position, in the limits of the Mediterranean and Atlantic domains; the very complete representa OLIGOCENE-MIOCENE BOUNDARY tions of nearly all stages, from the Lower Aquitanian up to the Pliocene; the richness of The problem in the Oligocene-Miocene the data provided; the possibilities of geological boundary is in the Tagus basin as well as in correlations and their economical importance. other basins where the Aquitanian does not In Lisbon, the thickness of the Miocene grade down to a marine Chattian. Thus, the does not exceed 300 meters, and the Pliocene is lower layers which correspond to the first hardly represented; to the South, the thickness sedimentary cycle, have supplied apparently ar of the whole Neogene increases to about 1200 chaic fossils (certain ostracods, pollens, etc.), meters (results obtained from deep boreholes) suggesting an oligocene age. Another important whereas the outcropping Pliocene reaches the fact is the presence of glauconite dated by K-Ar thickness of 50 meters or more. to 24±1 Ma and 21,1±0,5 Ma. As far as accu Generally, several marine ingressions and racy is concerned, the method used is subject to the same amount of intercalated regressions errors that are not always controllable. The date were situated at the tenninal region of the basin; in question seems to overtake the 22.5 Ma limit one may enumerate several sedimentary cycles accepted by some authors. Other authors, in framed by transgression and the following re fact, place the Oligocene-Miocene limit at 24 or gression, seven for the Miocene and one or even 25 Ma. 14 2 « iLl U 0 D Quaternary ~ Tertiary U E83...... Cretaceous .... Jurassic :z ~ cC. Triassic ..J .... -~ Carboniferous d. Devonian.Silurian and Ordovician Cambrian Cl! [ill Precambrian CDc ::l ...c ~++HI++++ Igneous rocks et III E Main faults ... --- 'Illu.. ui 0 50 Km CD - C Fig. 2 - Simplified geological map of Portugal. 15 In some places, the Aquitanian overlays Miocene. One may also recognize climatic unconformally older units. Elsewhere, there is modifications, important in marine fauna: tropi a continuous passage evidencing the develop cal conditions were predominant, at least since ment of the first miocene transgression. the genesis of the coral line barrier reefs of the Aquitanian; a maximum temperature, compara ble to the present day Gulf of Guinea, was reached at the Upper Burdigalian and Langhian. Later, the prevailing conditions were closer to those existing at the present day in the moroc can coast. The fauna and vegetation of the continent indicate humid periods alternating with rela tively dry ones, leading to forestal environ ments rather than savannah or steppe. Transgressions and regressions also had palaeogeographical consequences (Fig. 5; Fig. 6): limited ingression forming a narrow gulf (TO); aquitanian gulf spread out to the Z hinterland up to the region of Almeirim (TI); ~GastroPOdslMOlIl:ISks 6.1. Bioturbation I:: :::::: :: ISiltitic clays Coal ~ ~ Pectinids I Oysters ' ... a ~Clayey silts and Diatomites f I: :..: :. ~ :I Silts and • : '. : '.. siltstones ~umestones .!Il § { • Scarce __ Marly ~Clayey sands 'ill ~ 0 Frequent ~and sandstones _ -_limestones ~ ~ § @ Abundant .. ·,;,;,:;:,:\;.\ .... \~. Feldspathic sands • • Detrital r~.~: .. -:~\ and sandstones ~••••• limestones COngIOmerates, • •• ' .' ••'0 Gravels, · .•.. ' .'.\ Coarse sands and ~-=IMarls ~., sandstones Fig. 4 - Logs legend concerning the portuguese geology. TIlE NEOGENE OF RIBATFJO there is initially a predominance of sands and (fAGUSBASIN) clays with carbonate levels as well as lignites; above this there are some important limestone On the contrary to the region of Lisbon, layers, specially at Cartaxo-Almoster-Santarem, the Neogene of Ribatejo is essentially continen with some intercalated sandy beds. We are now tal with a few interposed marine formations, in able to date these limestones as Upper Vallesian other words, with marine or brackish influence. and can consequently recognize that its The oldest formations are as follows: deposition occurred during a quite short time - the Serra de Almerim Aquitanian, the span. only outcropping marine formation. It is The lack or paucity of available informa equivalent to part of the layers with Venus tion has made the whole interpretation for the ribeiroi, occurring in Lisbon and its surround Miocene of the left bank of the Tagus difficult, ings for the upper limestone horizons are absent. - poorly known marine layers, drilled to On the other hand, the argillaceous layers a certain depth by boreholes (Tagus right bank, outcrop in large outspreading extensions Coruche map) (mainly in the valleys) and stretch to the Sado - detrital assemblage of Arneiro and basin. Their age corresponds more or less to Ota, comprising intercalations of oysters in its the second half of the Middle Miocene or to the upper part. lower part of Upper Miocene. In places, these deposits overlie oyster deposits, which seem to This heterogeneous last unit is poorly de represent the apogee of the Serravallian trans fined. It is often admitted that it may comprise gression. The argillaceous l!lyers are covered palaeogene layers, exceeding a burdigalian age by arkosic sands with beds with gravel and (up to an "helvetian" one). pebbles, probably of Pliocene age. However, one may recognize that the ma The Neogene infilling of the Tagus basin jority of the outcrops are more modern. On the corresponds, with minute variations, to the right bank of the Tagus, one may have a precise mean-water bed and the flood plain of a river view of the stratigraphy and age of most of the and its tributaries, carrying materials from both series, which corresponds mainly to the upper the "Hesperic Massif' or the limestone massif part of the Middle Miocene and to the lower to the West. Later on, in an environment char part of Upper Miocene (continental stages: acterized by advanced relief leveling, with ex Astaracian and Vallesian). This is due to the tensive zones subject to a lacustrine regime and recent discovery and reinterpretation of a certain a certain aridity, the carbonate sedimentation number of mammalian localities. Lithologically, was predominant. 17 I ~ ~ > TAGUS BASIN Environmental conditions !i: if LITHOLOGY ~ EVENTS ~ III ~ ~ t: Continental Marine a: !l! Z C!) '" t------,-----t-----+------r------,~-I C!) "" ::E - Cl) j:: ~ -!ci: < 0 MAIN Temperature MOisture Temperature III ictllllll a: c '0 >- W ~ I!= ...I ~ In ~ :; ~ MAMMAL g: ~ <~ 00 Fig. 5 - Lithological, chronostratigraphical, environmental conditions and main events table from Tagus basin...... At Ribatejo, the last Miocene layers are the Oligocene or the Miocene. In fact, to the succeeded, with a clear contrast, by generally West of Pombal they are covered by well dated coarse - grained detrital deposits which corre· marine Pliocene formations; on the other. hand, spond again to a fluvial sedimentation. These they clearly overlie late Cretaceous formations deposits cover erosion surfaces and are recog and detrital continental series, which are Eocene nizable in several places. However, the most in age. Dating was, however, uncertain, or at important layers ascribed to the Pliocene are the least not accurate, until the discovery of fossil ones that made up the infilling of the Rio Maior mammals at Amor. This partly cleared the sit graben basin (and to a lesser degree that of Vale uation. de Santarem graben) These consist of a rather However, the well dated part is limited to thick succession of industrially exploited white the region westward of the Leiria diapir; else sands, overlain by diatomites and important where, the interpretation of these deposits, layers of lignite and some boghead coal. mostly of fluvial facies (sometimes marshy or swampy), is problematic due to the absence of any direct proof of age. However, there are some indications of mE NEOGENE OF mE ALVALADE marine deposits, even if their characterization is BASIN rather uncertain indeed: - at Casal Verde, 2 Km to the North East of Paiiio, Figueira da Foz, siliceous rocks To the South of the Tagus basin, in an area surprisingly contain Foraminifera such as corresponding to the present day hydrographic Globigerina and Miliolids; there has been in Sado basin, another one (the Alvalade basin) tensive diagenetic, secondary silification, prob was formed. This basin is separated from the ably after limestones with clastic elements de Tagus basin by a horst of paleozoic rocks posited in marine environments, their age being (Senhor das Chagas-Valverde), and was only uncertain crossed by the River Sado in Quaternary times. - boreholes drilled in the region of The Miocene is mainly represented by sandy Marinha Grande, West of Leiria, cut through marine sediments of Upper Tortonian and . clays and greenish grey marls with Messinian age. The last ones are well dated by Foraminifera (Ammobac ulites, etc.), small mammals. This unit is intercalated be Ostracoda, Characeae and Pelecypoda ascribed tween continental units: (a) a sandy-argillaceous to the Miocene; no outcrops are known. and ca1crete underlying unit of rather uncertain The deposits at Amor are most interesting, age and (b) arkosic sands, possibly Pliocene in for they are the only ones to the North of the age. Nazare fault that allow accurate dating. An ini tial survey at three points yielded large and small mammals, reptiles, amphibians and fish, NEOGENE TO mE NORm OF mE as well as gastropods. It is interesting to note CENTRAL MOUNTAIN CHAIN the existence of two different biotopes, although contemporary. One of them corre sponds to fluvial sedimentation, the other to a The Neogene deposits to the North of the marsh with many anfibian and freshwater fish Central Mountain Chain and their extensions to remnants. The mamalian fauna indicates the the Nazare great fracturing are badly known or beginning of Middle Miocene, Langhian MN5 represented. The only exceptions to his are mammal unit of Mein like the V-b of Lisboa marine Pliocene sandy deposits that are well with Hispanotherium fauna. The fossiliferous represented notably at S. Pedro de Muel, Monte horizon seems to correspond to a very limited Real, Leiria and Pombal, as well as the conti time span although the area where the formation nentallayers with lignites, clays and diatomites outcrops is rather extensive, reaching Monte which overlie them. We will return to this point Real (clays with Helix, Planorbis, Unionids in the chapter about Pliocene. and some rodents as Cricetodonts) and further more northwards; at Carvide, layers which could be more or less correlative (although a mE MIOCENE AROUND ALCOBACA, Pliocene age was admitted without any proof) LEIRIA AND COIMBRA have produced, besides Helix and C hara, Cerithium and Gobius (teleost fish) which may In this rather extensive area there are indicate slightly brackish waters maybe outcrops of sandy-argillaceous sediments communicating with the sea. The supply of which, according to their strati graphic position, detrital material, namely bipyramidal quartz were ascribed (according to Choffat) to either issued from Lower Lias marls, show that the 19 r- Syndine 0- Chaltian?- - L. Aquitanian 1- Aquitanian 2 - L. Burdigalian - Fault ~Uplift.d zones *Coral reefs .. Strain -2 + + - Q - Quaternary P - Pliocene p, - Lower P2 - Upper a, b, c - Paleovalley Fig. 6 - The three main phases of the paleogeographic evolution of the Lisboa region (Tagus basin) (COPPIER et MOUGENOT, 1982, modified). Maps: inland transgressions borders after ANTUNES (1979, modified); offshore: AR - Amibida chain; BE - Ericeira basin; CC - Cascais canyon; CL - Lisboa canyon; CS - Setlibal canyon; GR - Grandola massif; Tagus lineation; MC - CamOes mountain; PA - Albuquerque platform; S - Sintra massif.. Schematic geological sections corresponding to the three paleogeographical phases; 1 - relative sea level change; 2 - transgressions or regressions; 3 - tectonic movement. 20 H \~ :'::.:~ Holocene Q D Pleistocene P-Q c:JPlio-quat. PI [::::::::,j Pliocene ~ M3[i1l1 U.Miocene c .;" 2 c M t;Hiii':q M.M,oc'''n~''-' « M1 L.Miocene (,,+\ o Pa. Paleogene .~ E2~ U. Eocene ·c... 5 DSasement ~ c.. W E V.E. I~AAAll °r/~,,~,-~~~~~';,~~~~~~~~lIiiii~III1Ij~1 1a2 EBIH3 ~4 2 I SECTION 1 I 2Km 5 10Km 1:=::15 N.NW Arrabida Chain S.SE 1 ~6 380m C.S. E~]7 0 • 0 ~-'-- ~~ ------ 2 SECTION 2 5 lOKm I 2\ Fig. 7 - Geological map and cross-sections of the continental margin between Lisboa and Sines (COPPIER & MOUGENOT, 1982, mOdified). 1 - Lower Jurassic with evaporites; 2 - Jurassic; 3 - Cretaceous; 4 - Mesozoic; 5 - ante-tectonic Lower Miocene; 6 - post-tectonic Neogene and Quaternary; 7 - alluvions; 8 - Lisboa basalts (Uppermost Cretaceous); C.L. - Lisboa canyon; C.S. Setubal canyon; V. E. Estoril valley. 21 nearby diapir was moved during the neo sion. The latter has been ascribed to the castillan phase. This miocene series seems to be Calabrian; the Calabrian stage, being included represented northwards till Pombal region. in the Pleistocene, is not dealt with in this text. However it is poorly exposed there among Also avoided, are formations as interesting as outcrops from earlier units. the highest raised terrace covers (about 120 to There are other deposits (sands and clays 190 meters). Their remnants in the costal mor with some lignite layers) in the region of Leiria phology are evident from the northern coasts Alencarce and Fonte da Moura, from where down to Algarve, or rather, virtually all of the plant macroremains, the only fossils collected southern part of Portugal so far, do not allow any accurate dating even if In the present state of our knowledge, they have been regarded as Miocene. Pliocene deposits comprise: a) - fossiliferous sands and conglomerates between the Amibida chain in the South and the region of Pombal; b) PossmLE MIOCENE IN BEIRA ALTA - arkosic sands developed mainly to the South of the Tagus river: non marine gravels, sands Among the units that overlie the Beira Alta and clays in depressions such as in Rio Maior basement, there are essentially argillaceous and Vale de Santarem, the Tagus basin at sediments derived from the Beira pre-ordovi Cartaxo, Serra de Almerim, etc. and maybe cian slates and graywackes. Fragments of even further North at Pampilhosa; c) - clay de shales of variable sizes form the majority of posits with diatomite al)d lignite, particularly these sediments which generally evolve to important near Leiria, Obidos, Rio Maior and greenish and often reddish clays. Other impor Vale de Santarem. tant components are cobbles of vein quartz, Summing up, the study of the Portugese whereas the contribution from granites is rather Pliocene is rather restricted by the lack of up limited. Several small outcrops spared by ero dated stratigraphy as well as the lack of accurate sion witness their former vast extension. Their dating. origin is certainly related to rejuvenation of the shale relief. It is known that such deposits are later than the ludian (Upper Eocene) arkoses mE PUOCENE IN mE TAGUS BASIN from Coja. On the other hand, they are covered by blocks and other coarse grained sediments, Setubal Peninsula more or less equivalent to the rafias described in Spain and elsewhere in Portugal, possibly of Villafranchian age. These occur to the South Pliocene layers are well represented to the East of the Caramulo Mountain, at Arganil, at South of the Miocene outcrops between Folques, and elsewhere. Cacilhas and Trafaria, in the left bank of the Hence, a Miocene age is possible but far River Tagus. They follow the axial part of a from being proved. In Spain, always North of syncline, limited southwards by the Arrabida the Central Chain in the Douro basin, the Chain and by the costal cliffs of Fonte da Telha Miocene is largely represented to the East of and Adi9a and further inland towards Pinhal Toro. Remarkable deposits at Palencia, Novo and Montijo. Valladolid, etc., are ascribed to the Middle Over the last miocene layers, one can see Miocene; others are reported to the Upper coarse layers of conglomerates and arkosic Miocene. sands. These correspond to a sedimentation that Older Miocene deposits are not known; the proceeded under the double influence of high Hispanotherium fauna has never been found. energy sea and rivers. Some rather poorly pre These facts could suggest the upper part of the served molluscs were collected in this series at Middle Miocene as a possible age for certain Alfeite. Other known fossils are land plants sedimentary mantles of Beira. Without decisive which provide ecological information but are evidence, the problem remains open to discus not useful for age determination. Indirect rea sion. sons lead to the assumption that they may rep resent the Tabianian (Lower Pliocene) with a modest transgression followed by a regression shown by layers with plant fossils. PLIOCENE High above them are sands and gravels with clay intercalations that have produced a According to current ideas, during the varied malacological fauna with a costal marine Pliocene there was a succession of events com character considered as Astian. As admitted by prising a marine transgression followed by a some authors, they would belong to the Upper regressive phase and finally a new transgres- Pliocene (Piazencian), according to the interpre- 22 tation of Brebion after his revision of the gas Pombal, a well characterized Pliocene trans tropods. No doubt there was a new sea ingres gression is responsible for the deposition of sion, more important than that of the Lower fossiliferous conglomerates and sands on Pliocene, even if its inland progression did not Miocene or older formations. These sediments exceed about 25Km from the present coast. are overlain by continental diatomites and lig Uppermost units regarded as Pliocene nites (Obidos, Barraclio, etc.) and these ones comprise fine sands with rounded pebble lay by marine or fluviomarine deposits without ers, clays and diatomites. fossils related to the Upper Pliocene (that may The sands no doubt show eolian transport be Calabrian). representing the progression of coastal dunes Most authors ascribed a Lower Pliocene further inland. A strati graphic revision has to be age for the earlier marine beds. This seems done, for the relationships between certain clay contradictory to the acknowledged correlation layers, gypsum, diatomites and lignites are still with the Alfeite deposits (upper layers), Fonte not clear. As for their age, different authors, da Telha, etc. considered as Astian. Brebion, lacking decisive proofs, tentatively ascribed who also accepted this correlation, points out to them to the Pliocene, but a Pleistocene age was an Upper Pliocene age. Recent data on calcare also possible. On account of the Upper ous nannoplankton indicate Martini's NN16, or Pliocene age of the underlying layers and the Okada & Burky CN12a as corresponding to the importance of this series, it can be entirely Lower Piazencian (Upper Pliocene) confirming Quaternary or nearly so. former dating. Furthernore, all other available The assemblage of !ignites, as well as the data indicates an Upper Pliocene age. Taking levels with marine fossils that follow them, are into account the small span of the Pliocene overlain in some localities by the Belverde (about 3Ma), this practically means that at least conglomerates. and yielded archaic lithic indus part of the diatom and lignite beds must be tries. Pleistocene in age, although the chronological limits are still not accurate enough. For stronger reason the transgression Inland detrital residual soil related to the which follows it, well marked in the geomor Pliocene phology of coastal regions from the extreme North down to the Algarve, has to be treated as On the right bank of the Tagus river, a few Pleistocene. remnants of sands and clays (sometimes with As elsewhere in Europe, the Pliocene lignites) are preserved at Azambuja, Cruz do palaeogeographies are rather different from the Campo, the surroundings of Santarem, etc. Miocene ones - the so-called "Pliocene revo On the other hand, to the South of the river lution". Even if the data concerning Pliocene Tagus there are far more extensive outcrops of are incomplete and not always accurate, we arkosic sands with pebble bands (mainly to may suppose that in the Setubal Peninsula there wards the top): these are fluvial deposits corre was a ~ery limited marine ingression followed sponding to a predominantly south-southwest by another regression (Fig. 6; Fig. 7). This drainage pattern. small transgression corresponds to the lower The eolian sands of Rio Maior should be layers of Alfeite. Its age has been regarded as referred for its economic importance. These Lower Pliocene (Zanclean) according to its may represent the progression of dunes further positions and without good direct dating evi inland between the Candeeiros and Montejunto dence. Hills, starting from a broad littoral abrasion Later on, a new and more important trans platform which is today at about a 200 metres gression much enlarged the small former gulf at level. They seem to be correlated to the fine the Setubal Peninsula. The region between sands of Coina in the Setubal Peninsula; if this Pombal and Caldas da Rainha has been flooded is so, those sands were formed after the marine then. A larger abrasion platform was devel levels of Alfeite and Fonte da Telha with an opped. It may be related to the Calabrian trans Upper Pliocene fauna. Hence the diatomites gression in several places. Further inland this and lignites that at Rio Maior and Obidos over platform is limited by beautiful fossil cliffs. Its lie those sands may be Quaternary, at least in surfaces are frequently covered by rather thin part. detrital, quaternary layers where no fossils have been found. Pliocene in Estremadura REFERENCES In the region of the Caldas da Rainha di apir and further to the North until Leiria and See page 67. 23 CHRONOST. ALVALADE BASIN ALGARVE ~ Faro-Quarteira sands Clays, sands, conglomerates Sands, sandstones and !ignites and diatomites conglomerates Morgadinho deposits I.~ _ 1 1 ------Piacenzian Alfeite beds Marateca Formation Zanclean Messinian IGalv~-1 Cacela Formation I co~omerat~ Tortonian ------Glauconiticsilts Mem Moniz spongolithes CamQi.pa de Faro_ ------.,--- I Olhos de Agua sands Serravallian 1______-- ~ Calcareous sandstones and BRQuinta das Conchas limestone limestones with pebbles o Langhian Vale de Chelas sands ~ Musgueira limestone Sands with Placuna miocenica ------Casal Vistoso limestone Burdigalian Quinta do Bacalhau sands Blue clays from Areeiro Lagos-Ponimao Formation "Banco Real" Estefania sands 1------1------Aquitanian Days and limestones I--+-----+_with ------Venus ribeiroi "Benfica Complex" Guia conglomerates Fig. 8 - Main Neogene lithological units from Tejo and Alvalade basins, and from Algarve (southern Ponugal). ~