Conference Presentations by Pedro Proença Cunha
Tectonic displacements affecting the culminant sedimentary unit (probable Late Pliocene to lowerm... more Tectonic displacements affecting the culminant sedimentary unit (probable Late Pliocene to lowermost Pleistocene) of the Lower Tejo Basin are common. Using geomorphologic and stratigraphic references, these vertical displacements can reach up to 70 m. There are geomorphologic evidences that the faults have been active during the Pleistocene, displacing the terraces, whose ages are known in the lower ones (Martins, et al., 2010). However, faulted surfaces affecting terrace deposits have been very difficult to found and are often considered unreliable. This seems strange because a staircase of six terrace levels (T1 to T6, from the upper to the lower), indicating a long-term uplift during the Pleistocene, is present.
6th International Conference on Geomorphology (Abstracts Volume), 2005
The Dezful Embayment (DE) is part of the Zagros Fold Belt (ZFB) in SW Iran. The DE hosts most of ... more The Dezful Embayment (DE) is part of the Zagros Fold Belt (ZFB) in SW Iran. The DE hosts most of the oil reservoir of the country. The northern portion of the DE is mostly covered by the Gachsaran Formation (Gs) of Miocene age which constitutes anhydrite, gypsum, red and grayish marls and thick salt layers. The presence of this suite of rock types facilitates ductile deformational behavior and hence plays an important role in controlling structural style in the study area. It has acted as a decollement layer between relatively competent older and younger rocks which resulted in disharmony between surface and subsurface structures. The study of satellite data in conjunction with subsurface information reveals the presence of folds and thrust movement with NW-SE directions which has caused giant over thrusting of Gs on younger formations. The morpho-tectonic indices such as Smf, Vf, and Sl demonstrate the relatively high neo-tectonic activity in the area. It is concluded that the Gs Formation created an environment of fault related fold mechanisms and therefore the type of folding is identified as fault propagation folds.
Apresenta-se uma síntese da caracterização sedimentológica e hidrodinâmica actual dos sub-sistema... more Apresenta-se uma síntese da caracterização sedimentológica e hidrodinâmica actual dos sub-sistemas do Estuário do Mondego. Os dados foram obtidos pelo registo de parâmetros hidrodinâmicos e físico-químicos (salinidade, temperatura, velocidade e orientação das correntes, turbidez, concentração de silte/argila, pH e Eh), ao longo de perfis longitudinais, de 1994 a 1996; para além da obtenção de uma pormenorizada carta de sedimentos, o estudo sedimentológico incluiu uma abundante amostragem de sedimentos superficiais para a determinação laboratorial da granulometria, mineralogia e morfoscopia. Discute-se a circulação sedimentar na área estuarina e a influência relativa dos controles sedimentares.
The stratigraphic units that record the evolution of the Tagus River in Portugal (study area betw... more The stratigraphic units that record the evolution of the Tagus River in Portugal (study area between Vila Velha de Ródão and Porto Alto villages; Fig. 1) have different sedimentary characteristics and lithic industries (Cunha et al., 2012):
- a culminant sedimentary unit (the ancestral Tagus, before the drainage network entrenchment) – SLD13 (+142 to 262 m above river bed – a.r.b.; with probable age ca. 3,6 to 1,8 Ma), without artefacts;
- T1 terrace (+84 to 180 m; ca. 1000? to 900 ka), without artefacts;
- T2 terrace (+57 to 150 m; top deposits with a probable age ca. 600 ka), without artefacts;
- T3 terrace (+43 to 113 m; ca. 460 to 360? ka), without artefacts;
- T4 terrace (+26 to 55 m; ca. 335 a 155 ka), Lower Paleolithic (Acheulian) at basal and middle levels but early Middle Paleolithic at top levels;
- T5 terrace (+5 to 34 m; 135 to 73 ka), Middle Paleolithic (Mousterian; Levallois technique);
- T6 terrace (+3 to 14 m; 62 to 32 ka), late Middle Paleolithic (late Mousterian);
- Carregueira Sands (aeolian sands) and colluvium (+3 a ca. 100 m; 32 to 12 ka), Upper Paleolithic to Epipaleolithic;
- alluvial plain (+0 to 8 m; ca. 12 ka to present), Mesolithic and more recent industries.
The differences in elevation (a.r.b.) of the several terrace staircases results from differential uplift due to active faults.
Longitudinal correlation with the terrace levels indicates that a graded profile ca. 200 km long was achieved during terrace formation periods and a strong control by sea base level was determinant for terrace formation. The Neogene sedimentary units constituted the main source of sediments for the fluvial terraces (Fig. 2).
Geomorphological mapping, coupled with lithostratigraphy, sedimentology and luminescence dating (quartz-OSL and K-feldspar post-IRIR290) were used in this study focused on the T4 terrace, which comprises a Lower Gravels (LG) unit and an Upper Sand (US) unit.
The thick, coarse and dominantly massive gravels of the LG unit indicate deposition by a coarse bed-load braided river, with strong sediment supply, high gradient and fluvial competence, during conditions of rapidly rising sea level. Luminescence dating only provided minimum ages but it is probable that the LG unit corresponds to the earlier part of the MIS9 (ca. 335 to 325 ka), immediately postdating the incision promoted by the very low sea level (reaching ca. -140 m) during MIS10 (362 to 337 ka), a period of relatively cold climate conditions with weak vegetation cover on slopes and low sea level.
The lower and middle parts of the US unit, comprising an alternation of clayish silts with paleosols and minor sands to the east (flood-plain deposits) and sand deposits to the west (channel belt), have a probable age of ca. 325 to 200 ka. This points to formation during MIS9 to MIS7, under conditions of high to medium sea levels and warm to mild conditions.
The upper part of the US unit, dominated by sand facies and with OSL ages of ca. 200 to 154 ka, correlates with the early part of the MIS6. During this period, progradation resulted from climate deterioration and relative depletion of vegetation that promoted enhanced sediment production in the catchment, coupled with initiation of sea-level lowering that increased the longitudinal slope.
The Vale do Forno and Vale da Atela archaeological sites (Alpiarça, central Portugal) document the earliest human occupation in the Lower Tagus River, well established in geomorphological and environmental terms, within the Middle Pleistocene. The Lower Palaeolithic sites were found on the T4 terrace (+26 m, a.r.b.).
The oldest artefacts previously found in the LG unit, display crude bifacial forms that can be attributed to the Acheulian, with a probable age of ca. 335 to 325 ka.
The T4 US unit has archaeological sites stratigraphically documenting successive phases of an evolved Acheulian, that probably date ca. 325 to 300 ka. Notably, these Lower Palaeolithic artisans were able to produce tools with different sophistication levels, simply by applying different strategies: more elaborated reduction sequences in case of bifaces and simple reduction sequences to obtain cleavers.
The VF3 site (Milharós), containing a Final Acheulian industry, with fine and elaborated bifaces) found in a stratigraphic level located between the T4 terrace deposits and a colluvium associated with Late Pleistocene aeolian sands (32 to 12 ka), has an age younger than ca. 154 ka but much older than 32 ka.
In the study area, the sedimentary units of the T4 terrace seem to record the river response to sea-level changes and climatically-driven fluctuations in sediment supply.
REFERENCES
Cunha P. P., Almeida N. A. C., Aubry T., Martins A. A., Murray A. S., Buylaert J.-P., Sohbati R., Raposo L., Rocha L., 2012, Records of human occupation from Pleistocene river terrace and aeolian sediments in the Arneiro depression (Lower Tejo River, central eastern Portugal). Geomorphology, vol. 165-166, pp. 78-90.
This study examines the long profiles of tributaries of the Tejo (Tagus) rivers in central easter... more This study examines the long profiles of tributaries of the Tejo (Tagus) rivers in central eastern Portugal (West Iberia) in order to provide new insights into the patterns, timing and controls on drainage development during the Pleistocene to Holocene incision stage. The long profiles were extracted from lower order tributary streams associated with the trunk drainage of the Tejo Ri (Fig. 1).These streams flow through a landscape strongly influenced by variations in bedrock lithology (mainly granites and metasediments), fault structures delimiting crustal blocks with distinct uplift rates, and a base-level lowering history (tectonic uplift / eustatic). The long profiles of thetributaries of the T ejo transient and permanent knickpoints. The permanent knickpoints have direct correlation with the bedrock strength, corresponding to the outcropping of very hard quartzites or to the transition from softer (slates/metagreywaques) to harder (granite) basement. The analyzed streams/rivers record also an older transient knickpoint/knickzone separating: a) an upstream relict graded profile, with lower steepness and higher concavity, that reflects a long period of quasi-equilibrium conditions reached after the beginning of the incision stage; and b) a downstream reach displaying a rejuvenated long profile, with steeper gradient and lower concavity, particularly for the final segment, which is often convex (Fig. 2). The rejuvenated reaches testify the upstream propagation of several incision waves that are the response of each stream to continuous or increasing crustal uplift and dominant periods of base-level lowering by the trunk drainages, coeval of low sea level conditions. The long profiles and their morphological configurations enabled spatial and relative temporal patterns of incision to be quantified for each individual tributary stream. The incision values of streams flowing in uplifted blocks of the Portuguese Central Range (PCR) (ca.380-280 m) indicate differential uplift and are higher than the incision values of streams flowing on the adjacent South Portugal planation surface the Meseta(ca. 200 m). The normalized steepnessindex,calculated using the method of Wobus et al. (2006), proved to be sensitive to active tectonics, as lower k sn values were found in relict graded profiles of streams located in less uplifted blocks, (e.g. in the PCR), or in those flowing through tectonic depressions.
The differential uplift indicated by the distribution of the ksn values and by the fluvial incision was likely accumulated on a few major faults, as the Sobreira Formosa fault (SFf), thus corroborating the tectonic activity of these faults.
Due to the fact that the relict graded profiles can be correlated with other geomorphic references documented in the study area, namely the T1 terrace of the Tagus River (with an age of ca. 1 Myr), the following incision rates can be estimated: a) for the studied streams located in uplifted blocks of the PCR, 0.38 m/kyr to 0.28 m/kyr; b) for the streams flowing on the South Portugal planation surface, 0.20 m/kyr.
The differential uplift inferred between crustal blocks in the study area corroborates the neotectonic activity of the bordering faults, which has been proposed in previous studies based upon less robust data.
REFERENCES
Antón L., De Vicente G., Muñoz-Martín A., Stokes M., 2014. Using river long profiles and geomorphic indices to evaluate the geomorphological signature of continental scale drainage capture, Duero basin (NW Iberia). Geomorphology 206, 240-251.
Goldrick G., Bishop P., 2007. Regional analysis of bedrock stream long profiles: Evaluation of Hack’s SL form, and formulation and assessment of an alternative (the DS form). Earth Surface Processes and Landforms, 32, 649-671.
Kirby E., Whipple K., 2012. Expression of active tectonics in erosional landscapes, Journal of Structural Geology 44, 54-74.
Wobus C.W., Whipple K.X., Kirby E., Snyder N.P., Johnson J., Spyropolou K., Crosby B.T., Sheehan D., 2006. Tectonics from topography: Procedures, promise and pitfalls. In: Willett, S.D., Hovius, N., Brandon, M.T., Fisher, D.M. (Eds.), Tectonics, Climate and Landscape Evolution: Geological Society of America Special Paper 398, Penrose Conference Series, 55-74.
This study addresses coastal terrace staircases of western central Portugal (Cape Mondego to Cape... more This study addresses coastal terrace staircases of western central Portugal (Cape Mondego to Cape Espichel). Below the culminant marine unit, that records the last episode of aggradation before the ongoing stage of incision, several terrace levels are identified. The following methodology was used: a) production of geomorphological maps, combining analysis of detailed MDT’s and aerial photos, with field surveys calibrated with GPS data; b) stratigraphic and sedimentological study of the sedimentary deposits associated with the marine platforms; c) luminescence dating. On each terrace staircase, the number of platforms and their elevations are different, indicating differential uplift. Quartz OSL provided age estimates up ca. 150 kyr and post-IR IRSL on K-feldspar up to ca. 700 kyr for the marine terraces under study. Using the culminant platform as reference and assuming that it is 3.6 Ma old, uplift rates were estimated as ranging from 0.071 m/ky to 0.019 m/ky. The ongoing luminescence dating will provide the uplift rates estimated for the lower and middle marine terraces.
Several Mesozoic limestone elevations of E-W elongated shape rise up in the central region of the... more Several Mesozoic limestone elevations of E-W elongated shape rise up in the central region of the Algarve Barrocal (Portuguese southwestern margin). Tectonic geomorphology suggests that these reliefs correspond to right lateral strike-slip contractional duplexes of a large, NW-SE trending, shear zone, with a pronounced topographic expression, whose southern boundary, located southeast of the Serra de Monchique hill, is defined by the São Marcos–Quarteira Fault Zone.
This study addresses the Holocene sedimentary succession at Martinhal coastal lowland (Algarve), ... more This study addresses the Holocene sedimentary succession at Martinhal coastal lowland (Algarve), a site recording the AD1755 Lisbon tsunami. Data on twenty-four short cores and sixteen trenches, retrieved from both the literature and new field work were combined to improve the stratigraphic resolution and lateral correlation of sedimentary units accumulated in this lowland. Four fining-upward depositional sequences (S1 to S4) were identified, showing spatial variation with maximum thickness - S1: 0-3 m; S2: 1.0-2.4 m; S3: 0.2-1.0 m; S4: 0.3-2.3 m. Sequences S1, S2 and S3 consist of medium to coarse yellow sands with levels rich in bioclasts that give place upsequence to brown organic silt and clay. Sequences S1 to S3 testify to the progressive infilling of a small estuary, coeval with the progressive development and changes in efficiency of a sandy barrier. The uppermost sequence (S4) is clearly different and also shows contrast in facies at seaward and landward locations. S4 comprises: 1) seaward (ESE), a basal subunit with boulders to pebbly gravels and coarse to medium well sorted sands, interpreted as deposited by the AD1755 tsunami, covered by an upper subunit comprising an alternation of well sorted white sands and brown silts, interpreted as aeolian/washover and flood deposits; 2) upstream (WNW), alternating layers of poorly sorted very coarse to medium sands and brown silts represent flood plain accretion and channel infill within the lowland. Quartz OSL dating was done by measuring small aliquots in samples from the AD1755 event-layer and large aliquots in samples from other deposits. The coarser and more basal sediment of the AD1755 sediment yielded overestimated OSL ages due to partial bleaching; at the top, and in finer sediment, and also in the more landward locations, OSL ages are closer to the true age of this event. At this location, routine Quartz OSL dating using large aliquots can give useful data on the burial ages for a variety of sediments, provided that the burial time exceeds ca. 1 ky. In contrast, recent abrupt-event sediments should be dated by measuring small aliquots or single grains to get a better control on partial bleaching effects on OSL results.
Neste artigo analisam-se alguns perfis longitudinais de afluentes do rio Douro. Estes afluentes c... more Neste artigo analisam-se alguns perfis longitudinais de afluentes do rio Douro. Estes afluentes correm numa paisagem marcada por variações constantes de litologia, sistema de falhas (ex: falha da Vilariça) e descida do nível de base. Os tributários do rio Douro exibem um troço com forma côncava a montante e um troço rejuvenescido a jusante, separados por uma rotura de declive (knickpoint/knickzone). O troço côncavo a montante corresponde a um perfil relíquia regularizado, de idade provável Placenciano – Gelasiano, enquanto o troço rejuvenescido resulta do prosseguimento de vagas de incisão, relacionadas com o escavamento fluvial durante o Plistocénico. Usou-se a projecção do perfil relíquia para estimar a máxima incisão na desembocadura e o equivalente uplift crustal. Os diferentes valores da incisão fluvial que variam de cerca de 400 m no rio Coa a mais de 600 m no rio Paiva refletem o uplift diferencial da superfície da Meseta e dos Planaltos Centrais. As taxas de incisão, calculadas pressupondo o início do encaixe da drenagem entre 2,5 e 1,8 e Ma são consistentes com o uplift regional calculado em trabalhos anteriores nesta região.
Este estudo aborda as escadarias de terraço em Portugal centro-ocidental (Cabo Mondego ao Cabo Es... more Este estudo aborda as escadarias de terraço em Portugal centro-ocidental (Cabo Mondego ao Cabo Espichel). Em posição topográfica inferior à da unidade marinha culminante, que regista o episódio de agradação sedimentar que antecedeu a etapa de incisão fluvial quaternária, identificam-se vários níveis de terraços marinhos. Foi usada a seguinte metodologia: a) elaboração de mapas geomorfológicos, combinando a análise de pormenorizados Modelos Digitais de Terreno e fotografias aéreas, com reconhecimentos de campo calibrados com GPS; b) estudo estratigráfico e sedimentológico dos depósitos sedimentares associados com as plataformas marinhas; c) datação por luminescência. Nas diversas escadarias de terraços costeiros já reconhecidas o número de plataformas marinhas e as respectivas altitudes são diferentes, indicando soerguimento tectónico diferencial. O método de datação por luminescência opticamente estimulada em grãos sedimentares de quartzo sedimentar já forneceu estimativas de idade até ca. 150 ka (limite de saturação) e o método post-IR IRSL em grãos de feldspato-K até ca. 700 ka, para os terraços marinhos em estudo. Usando a plataforma marinha culminante como referência geomorfológica e uma idade de ca. 3,6 Ma, estimaram-se taxas de soerguimento crustal na zona litoral em estudo variando espacialmente de 0,071 m/ka a 0,019 m/ka para este intervalo. O processo de datação por luminescência em curso conduzirá à obtenção de estimativas das taxas de soerguimento crustal com base nos terraços marinhos, o que permitirá determinar se está a correr um aceleramento do soerguimento crustal.
Papers by Pedro Proença Cunha
Chemie der Erde, Dec 1, 2016
Journal of Geochemical Exploration, 2014
portuguesNum contexto de mudanca climatica e de subida global do nivel do mar, o estudo de potenc... more portuguesNum contexto de mudanca climatica e de subida global do nivel do mar, o estudo de potenciais analogos do passado pode desempenhar um papel chave na melhoria do conhecimento sobre a variabilidade climatica em funcao de controlos naturais versus antropogenicos. Tem sido dada especial atencao ao maximo eustatico do ultimo interglacial (MIS5e), de ha ca. 125 ka e ca. +6 m (acima do nivel do mar actual). Analisamos a sequencia sedimentar de um terraco costeiro localizado em Oyambre (Costa Cantabrica, norte de Espanha), com base erosiva aos +6,9 m (acima do ordnance datum de Bilbao). A analise sedimentologica identificou dois antigos ambientes deposicionais: um de praia, com cascalheiras e areias cascalhentas castanhas; e um eolico costeiro, constituido por areias amarelas (parte superior da sucessao). A datacao por OLS, com protocolos SAR OSLquartzo e pIRIR (feld.-K), determinou que os depositos de praia correspondem com o alto nivel do mar do ultimo interglaciario (ca. 125–108 ka). EnglishIn a context of climate change and global sea-level rise, the study of potential past analogues can play a key role in improving knowledge of natural- versus anthropogenic-induced climate variability. Special attention has been paid so far to the last interglacial stage maximum (MIS5e), that occurred at ca. 125 ka (ca. +6 m above present sea level). In this study, we have analysed a coastal sedimentary sequence located in Oyambre (Cantabria, north of Spain) above an erosive surface at about +6.9 m (above Bilbao ordnance datum). Based on sedimentological analysis, two depositional environments have been identified: an ancient beach environment, formed by gravels and brown pebbly sands, and an aeolian environment represented by yellow sands, that comprises the upper part of this coastal succession. OSL dating, using SAR quartz-OSL and pIRIR (K-feldspar) protocols, determined that the basal beach deposits correspond to a sea-level highstand during the last interglacial stage (ca. 125–108 ka).
Scientific Reports
In the Iberian Peninsula the fossil record of artiodactyls spans over 53 million years. During th... more In the Iberian Peninsula the fossil record of artiodactyls spans over 53 million years. During the Pleistocene, wild cattle species such as Bison and especially Bos became common. In Late Pleistocene, the aurochs (Bos primigenius) was widespread and the only bovine living along the large river valleys of southern Iberia. Although commonly found in fossil sites and especially in cave bone assemblages, the trace fossil record of aurochs was known worldwide only from the Holocene. Large bovine and roe deer/caprine tracks were found in at least five horizons of the early Late Pleistocene (MIS 5) beach and eolian deposits of Cape Trafalgar (Cadiz Province, South of Spain). The large bovine tracks are formally described as Bovinichnus uripeda igen. et isp. nov. and compared with the record of aurochs tracks, large red deer tracks and steppe bison biogeographical distribution in Iberia. Aurochs were the most likely producers of the newly described Trafalgar Trampled Surface (TTS) and some ...
Journal of iberian geology: an international publication of earth sciences, 1994
The ogres belasianos» unit represents alluvial silicielastie sediments deposited during late Apti... more The ogres belasianos» unit represents alluvial silicielastie sediments deposited during late Aptian to Cenomanian times in the Lusitanian Basin, on the western margin of the Iberian plate. Two fining-upward successions have been identitied in the unit by studies of vertical changes of lithofacies associations in tbe northern part of the basin. The Iower fining-upward succession corresponds to deposits of coalescent wet alluvial fans, changing to a braidplain witli local sinuosity. The upper succcssion records the transition from high slope braidplains with increasing sinuosity to fluvial-dominated deltaic deposits. Considering the available biostratigraphic data, the allocyclic controls on vertical changes of lithofacies assoeiations is discussed. It was inferred that the climate or a basin margin uplift were not the main control on system charaeter clianges. Furthermore, evidence in the offshore suggests that sea-level changes probably had a major influence. We believe that the ons...
Journal of Geoscience and Environment Protection, 2021
We present a new tracksite with multiple dinosaur tracks from the lowermost Barremian (Lower Cret... more We present a new tracksite with multiple dinosaur tracks from the lowermost Barremian (Lower Cretaceous) of the Cape Espichel (Sesimbra, Portugal). The tracks are localized on three beds on the top carbonate beds of the Areia do Mastro Formation. Those bioclastic, nodular limestones were deposited in a very shallow subtidal-intertidal, restricted lagoon environment. The track surfaces are very dinoturbated, with a substantial number of tracks. Several tracks assign to sauropods, ornithopods and theropods dinosaurs were recorded. Due to heavy bioturbation and the preservation conditions, it is not possible to define trackways; some preliminary work done on the tracks could disclose some behaviours of their producers. Several species of carnivore and herbivore dinosaurs crossed that large area at different times. Herbivores may have used the lagoon margin as passage between feeding spots, while carnivores frequented the area to hunt in groups or individually.
Journal of Iberian Geology, 2021
There is no consensus about the geological nature of the westernmost portion 15 of the Iberian Ma... more There is no consensus about the geological nature of the westernmost portion 15 of the Iberian Massif. In the present research, the detrital zircon U-Pb signatures of 16 Jurassic strata of the Lusitanian Basin, known to be west-sourced, are combined with 17 published U-Pb data for the Precambrian-Palaeozoic basement and the Lusitanian Basin 18 units to better understand this poorly exposed portion of the Iberian Massif. Cryogenian to 19 Ediacaran ages prevail in a northern Upper Jurassic unit, while Lower and Upper Jurassic 20 rocks in southern locations yield mostly Carboniferous to upper Permian zircons. These 21 age results, coupled with their respective U/Th ratios, suggest that the basin covers two 22 distinct terranes of the Iberian Massif. Another noteworthy feature of west-derived 23 deposits is the abundance of <310 Ma ages. It is proposed that a combination of crustal 24 thinning in the West Iberian Margin with regional eastward basement tilt, favoured the 25 enrichment of relatively young zircon in the western shoulder of the basin relative to its 26 eastern margin. The detrital zircon age signatures also reveal a middle to late Permian 27 thermal event in restricted areas, which is probably associated with the oldest stages of 28 Alpine extension in West Iberia.
Scientific Reports, 2021
Tracks and trackways of newborns, calves and juveniles attributed to straight-tusked elephants we... more Tracks and trackways of newborns, calves and juveniles attributed to straight-tusked elephants were found in the MIS 5 site (Upper Pleistocene) known as the Matalascañas Trampled Surface (MTS) at Huelva, SW Spain. Evidence of a snapshot of social behaviour, especially parental care, can be determined from the concentration of elephant tracks and trackways, and especially from apparently contemporaneous converging trackways, of small juvenile and larger, presumably young adult female tracks. The size frequency of the tracks enabled us to infer body mass and age distribution of the animals that crossed the MTS. Comparisons of the MTS demographic frequency with the morphology of the fore- and hind limbs of extant and fossil proboscideans shed light into the reproductive ecology of the straight-tusked elephant, Palaeloxodon antiquus. The interdune pond habitat appeared to have been an important water and food resource for matriarchal herds of straight-tusked elephants and likely functio...
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Conference Presentations by Pedro Proença Cunha
- a culminant sedimentary unit (the ancestral Tagus, before the drainage network entrenchment) – SLD13 (+142 to 262 m above river bed – a.r.b.; with probable age ca. 3,6 to 1,8 Ma), without artefacts;
- T1 terrace (+84 to 180 m; ca. 1000? to 900 ka), without artefacts;
- T2 terrace (+57 to 150 m; top deposits with a probable age ca. 600 ka), without artefacts;
- T3 terrace (+43 to 113 m; ca. 460 to 360? ka), without artefacts;
- T4 terrace (+26 to 55 m; ca. 335 a 155 ka), Lower Paleolithic (Acheulian) at basal and middle levels but early Middle Paleolithic at top levels;
- T5 terrace (+5 to 34 m; 135 to 73 ka), Middle Paleolithic (Mousterian; Levallois technique);
- T6 terrace (+3 to 14 m; 62 to 32 ka), late Middle Paleolithic (late Mousterian);
- Carregueira Sands (aeolian sands) and colluvium (+3 a ca. 100 m; 32 to 12 ka), Upper Paleolithic to Epipaleolithic;
- alluvial plain (+0 to 8 m; ca. 12 ka to present), Mesolithic and more recent industries.
The differences in elevation (a.r.b.) of the several terrace staircases results from differential uplift due to active faults.
Longitudinal correlation with the terrace levels indicates that a graded profile ca. 200 km long was achieved during terrace formation periods and a strong control by sea base level was determinant for terrace formation. The Neogene sedimentary units constituted the main source of sediments for the fluvial terraces (Fig. 2).
Geomorphological mapping, coupled with lithostratigraphy, sedimentology and luminescence dating (quartz-OSL and K-feldspar post-IRIR290) were used in this study focused on the T4 terrace, which comprises a Lower Gravels (LG) unit and an Upper Sand (US) unit.
The thick, coarse and dominantly massive gravels of the LG unit indicate deposition by a coarse bed-load braided river, with strong sediment supply, high gradient and fluvial competence, during conditions of rapidly rising sea level. Luminescence dating only provided minimum ages but it is probable that the LG unit corresponds to the earlier part of the MIS9 (ca. 335 to 325 ka), immediately postdating the incision promoted by the very low sea level (reaching ca. -140 m) during MIS10 (362 to 337 ka), a period of relatively cold climate conditions with weak vegetation cover on slopes and low sea level.
The lower and middle parts of the US unit, comprising an alternation of clayish silts with paleosols and minor sands to the east (flood-plain deposits) and sand deposits to the west (channel belt), have a probable age of ca. 325 to 200 ka. This points to formation during MIS9 to MIS7, under conditions of high to medium sea levels and warm to mild conditions.
The upper part of the US unit, dominated by sand facies and with OSL ages of ca. 200 to 154 ka, correlates with the early part of the MIS6. During this period, progradation resulted from climate deterioration and relative depletion of vegetation that promoted enhanced sediment production in the catchment, coupled with initiation of sea-level lowering that increased the longitudinal slope.
The Vale do Forno and Vale da Atela archaeological sites (Alpiarça, central Portugal) document the earliest human occupation in the Lower Tagus River, well established in geomorphological and environmental terms, within the Middle Pleistocene. The Lower Palaeolithic sites were found on the T4 terrace (+26 m, a.r.b.).
The oldest artefacts previously found in the LG unit, display crude bifacial forms that can be attributed to the Acheulian, with a probable age of ca. 335 to 325 ka.
The T4 US unit has archaeological sites stratigraphically documenting successive phases of an evolved Acheulian, that probably date ca. 325 to 300 ka. Notably, these Lower Palaeolithic artisans were able to produce tools with different sophistication levels, simply by applying different strategies: more elaborated reduction sequences in case of bifaces and simple reduction sequences to obtain cleavers.
The VF3 site (Milharós), containing a Final Acheulian industry, with fine and elaborated bifaces) found in a stratigraphic level located between the T4 terrace deposits and a colluvium associated with Late Pleistocene aeolian sands (32 to 12 ka), has an age younger than ca. 154 ka but much older than 32 ka.
In the study area, the sedimentary units of the T4 terrace seem to record the river response to sea-level changes and climatically-driven fluctuations in sediment supply.
REFERENCES
Cunha P. P., Almeida N. A. C., Aubry T., Martins A. A., Murray A. S., Buylaert J.-P., Sohbati R., Raposo L., Rocha L., 2012, Records of human occupation from Pleistocene river terrace and aeolian sediments in the Arneiro depression (Lower Tejo River, central eastern Portugal). Geomorphology, vol. 165-166, pp. 78-90.
The differential uplift indicated by the distribution of the ksn values and by the fluvial incision was likely accumulated on a few major faults, as the Sobreira Formosa fault (SFf), thus corroborating the tectonic activity of these faults.
Due to the fact that the relict graded profiles can be correlated with other geomorphic references documented in the study area, namely the T1 terrace of the Tagus River (with an age of ca. 1 Myr), the following incision rates can be estimated: a) for the studied streams located in uplifted blocks of the PCR, 0.38 m/kyr to 0.28 m/kyr; b) for the streams flowing on the South Portugal planation surface, 0.20 m/kyr.
The differential uplift inferred between crustal blocks in the study area corroborates the neotectonic activity of the bordering faults, which has been proposed in previous studies based upon less robust data.
REFERENCES
Antón L., De Vicente G., Muñoz-Martín A., Stokes M., 2014. Using river long profiles and geomorphic indices to evaluate the geomorphological signature of continental scale drainage capture, Duero basin (NW Iberia). Geomorphology 206, 240-251.
Goldrick G., Bishop P., 2007. Regional analysis of bedrock stream long profiles: Evaluation of Hack’s SL form, and formulation and assessment of an alternative (the DS form). Earth Surface Processes and Landforms, 32, 649-671.
Kirby E., Whipple K., 2012. Expression of active tectonics in erosional landscapes, Journal of Structural Geology 44, 54-74.
Wobus C.W., Whipple K.X., Kirby E., Snyder N.P., Johnson J., Spyropolou K., Crosby B.T., Sheehan D., 2006. Tectonics from topography: Procedures, promise and pitfalls. In: Willett, S.D., Hovius, N., Brandon, M.T., Fisher, D.M. (Eds.), Tectonics, Climate and Landscape Evolution: Geological Society of America Special Paper 398, Penrose Conference Series, 55-74.
Papers by Pedro Proença Cunha
- a culminant sedimentary unit (the ancestral Tagus, before the drainage network entrenchment) – SLD13 (+142 to 262 m above river bed – a.r.b.; with probable age ca. 3,6 to 1,8 Ma), without artefacts;
- T1 terrace (+84 to 180 m; ca. 1000? to 900 ka), without artefacts;
- T2 terrace (+57 to 150 m; top deposits with a probable age ca. 600 ka), without artefacts;
- T3 terrace (+43 to 113 m; ca. 460 to 360? ka), without artefacts;
- T4 terrace (+26 to 55 m; ca. 335 a 155 ka), Lower Paleolithic (Acheulian) at basal and middle levels but early Middle Paleolithic at top levels;
- T5 terrace (+5 to 34 m; 135 to 73 ka), Middle Paleolithic (Mousterian; Levallois technique);
- T6 terrace (+3 to 14 m; 62 to 32 ka), late Middle Paleolithic (late Mousterian);
- Carregueira Sands (aeolian sands) and colluvium (+3 a ca. 100 m; 32 to 12 ka), Upper Paleolithic to Epipaleolithic;
- alluvial plain (+0 to 8 m; ca. 12 ka to present), Mesolithic and more recent industries.
The differences in elevation (a.r.b.) of the several terrace staircases results from differential uplift due to active faults.
Longitudinal correlation with the terrace levels indicates that a graded profile ca. 200 km long was achieved during terrace formation periods and a strong control by sea base level was determinant for terrace formation. The Neogene sedimentary units constituted the main source of sediments for the fluvial terraces (Fig. 2).
Geomorphological mapping, coupled with lithostratigraphy, sedimentology and luminescence dating (quartz-OSL and K-feldspar post-IRIR290) were used in this study focused on the T4 terrace, which comprises a Lower Gravels (LG) unit and an Upper Sand (US) unit.
The thick, coarse and dominantly massive gravels of the LG unit indicate deposition by a coarse bed-load braided river, with strong sediment supply, high gradient and fluvial competence, during conditions of rapidly rising sea level. Luminescence dating only provided minimum ages but it is probable that the LG unit corresponds to the earlier part of the MIS9 (ca. 335 to 325 ka), immediately postdating the incision promoted by the very low sea level (reaching ca. -140 m) during MIS10 (362 to 337 ka), a period of relatively cold climate conditions with weak vegetation cover on slopes and low sea level.
The lower and middle parts of the US unit, comprising an alternation of clayish silts with paleosols and minor sands to the east (flood-plain deposits) and sand deposits to the west (channel belt), have a probable age of ca. 325 to 200 ka. This points to formation during MIS9 to MIS7, under conditions of high to medium sea levels and warm to mild conditions.
The upper part of the US unit, dominated by sand facies and with OSL ages of ca. 200 to 154 ka, correlates with the early part of the MIS6. During this period, progradation resulted from climate deterioration and relative depletion of vegetation that promoted enhanced sediment production in the catchment, coupled with initiation of sea-level lowering that increased the longitudinal slope.
The Vale do Forno and Vale da Atela archaeological sites (Alpiarça, central Portugal) document the earliest human occupation in the Lower Tagus River, well established in geomorphological and environmental terms, within the Middle Pleistocene. The Lower Palaeolithic sites were found on the T4 terrace (+26 m, a.r.b.).
The oldest artefacts previously found in the LG unit, display crude bifacial forms that can be attributed to the Acheulian, with a probable age of ca. 335 to 325 ka.
The T4 US unit has archaeological sites stratigraphically documenting successive phases of an evolved Acheulian, that probably date ca. 325 to 300 ka. Notably, these Lower Palaeolithic artisans were able to produce tools with different sophistication levels, simply by applying different strategies: more elaborated reduction sequences in case of bifaces and simple reduction sequences to obtain cleavers.
The VF3 site (Milharós), containing a Final Acheulian industry, with fine and elaborated bifaces) found in a stratigraphic level located between the T4 terrace deposits and a colluvium associated with Late Pleistocene aeolian sands (32 to 12 ka), has an age younger than ca. 154 ka but much older than 32 ka.
In the study area, the sedimentary units of the T4 terrace seem to record the river response to sea-level changes and climatically-driven fluctuations in sediment supply.
REFERENCES
Cunha P. P., Almeida N. A. C., Aubry T., Martins A. A., Murray A. S., Buylaert J.-P., Sohbati R., Raposo L., Rocha L., 2012, Records of human occupation from Pleistocene river terrace and aeolian sediments in the Arneiro depression (Lower Tejo River, central eastern Portugal). Geomorphology, vol. 165-166, pp. 78-90.
The differential uplift indicated by the distribution of the ksn values and by the fluvial incision was likely accumulated on a few major faults, as the Sobreira Formosa fault (SFf), thus corroborating the tectonic activity of these faults.
Due to the fact that the relict graded profiles can be correlated with other geomorphic references documented in the study area, namely the T1 terrace of the Tagus River (with an age of ca. 1 Myr), the following incision rates can be estimated: a) for the studied streams located in uplifted blocks of the PCR, 0.38 m/kyr to 0.28 m/kyr; b) for the streams flowing on the South Portugal planation surface, 0.20 m/kyr.
The differential uplift inferred between crustal blocks in the study area corroborates the neotectonic activity of the bordering faults, which has been proposed in previous studies based upon less robust data.
REFERENCES
Antón L., De Vicente G., Muñoz-Martín A., Stokes M., 2014. Using river long profiles and geomorphic indices to evaluate the geomorphological signature of continental scale drainage capture, Duero basin (NW Iberia). Geomorphology 206, 240-251.
Goldrick G., Bishop P., 2007. Regional analysis of bedrock stream long profiles: Evaluation of Hack’s SL form, and formulation and assessment of an alternative (the DS form). Earth Surface Processes and Landforms, 32, 649-671.
Kirby E., Whipple K., 2012. Expression of active tectonics in erosional landscapes, Journal of Structural Geology 44, 54-74.
Wobus C.W., Whipple K.X., Kirby E., Snyder N.P., Johnson J., Spyropolou K., Crosby B.T., Sheehan D., 2006. Tectonics from topography: Procedures, promise and pitfalls. In: Willett, S.D., Hovius, N., Brandon, M.T., Fisher, D.M. (Eds.), Tectonics, Climate and Landscape Evolution: Geological Society of America Special Paper 398, Penrose Conference Series, 55-74.
Na área vestibular do rio Mondego, Ramos (2008); Ramos et al. (2009) distinguiram seis episódios de escavação-agradação, cujos níveis foram designados por M1 a M6 (do mais alto para o mais baixo), situados abaixo da superfície culminante do enchimento sedimentar e acima da planície aluvial actual (3m de altitude).
A maioria dos níveis inferiores correspondem a terraços sedimentares, com associações de fácies deposicionais distintas nos vários níveis.
As associações de fácies que caracterizam M1, M2 e M3 (depósitos dos níveis mais antigos) são de natureza areno-cascalhenta e lutítica associadas a processos fluviais, bem como arenosas finas de génese eólica. Contudo, as fácies são difíceis de analisar espacialmente, nomeadamente as cascalhentas, por os depósitos estarem dispersos em retalhos e porque a unidade subjacente (do Cretácico) também é conglomerática. São exemplos destes depósitos os que se observam na Serra de S. Bento (126m de altitude; 123m acima da planície aluvial); Serra de Castros (118m) e Serra de Moinhos (100m).
O registo sedimentar de M4, M5 e M6 (terraços mais recentes) é o que está melhor preservado e as associações de fácies distinguem-se claramente das dos terraços mais antigos. A sua observação pode fazer-se entre Lares e Vila Verde, a altitudes que rondam os 10-20m. Interpretam-se associações de fácies fluviais, estuarinas e de praia.
Palabras clave: paleossismologia, falhas activas, geomorfologia tectónica, falha da Vilariça
Abstract: Two new trenches were recently opened in the central segment (Vilariça) of the Manteigas-Vilariça-Bragança fault to undertake a detailed paleoseismological study at Quinta do Vale Meão (Vilariça Basin) and an exploratory study at Quinta da Canameira (Longroiva Basin), respectively. Preliminary results show that recent sediments are deformed and faulted in Vale Meão, while at Canameira they showed apparent deformation requiring further exploration to confirm the observations. The new data obtained in Vale Meão confirmed the paleoseismic activity previously inferred from a nearby trench, though the deformation observed in this study was much lower than expected. The smaller amount of deformation that was detected at the Vale Meão trench may be due to the predominant strike-slip (left-lateral) kinematics and to strain distribution in the affected fine grained sediments, which are locally more than 8 m thick.