Graptólitos do Silúrico do Sinclinal de Buçaco : paleontologia e biostratigrafia = Graptolite faunas from Silurian of the Buçaco Syncline : paleontology and biostratigraphy

Estudaram-se exemplares de Graptólitos do Silúrico do sinclinal de Buçaco proveninentes de colecções de Nery Delgado e de amostragem recente. Foi realizada a actualização taxonómica das colecções antigas. Determinaram-se novas espécies e biozonas. Os novos resultados permitem precisar o Silúrico do Buçaco que tem muitas características estratigráficas e sedimentológicas em comum com o de outras áreas da parte sul da Zona Centro Ibérica

Main steps of the Ossa Morena tectono-stratigraphic evolution, in Portugal

[Resumo] Na parte portuguesa da Zona de Ossa Morena sao identificados vários sectores com estratigrafia e estrutura diferenciadas, os quais constituem, na sua maioria, prolongamentos dos correspondentes domínios tectono-estratigráficos reconhecidos em Espanha. De norte para sul identificam-se os seguintes sectores: Faixa Blastomilonítica, Alter do Chao-Elvas, Estremoz-Barrancos (onde se diferencia o Anticlinal de Estremoz), Montemor-Ficalho (com individualizaftlo do Sinclinal de Cabrela) e o Maci~o de Beja (com o sub-sector Santa Suzana-Odivelas). Das sequencias estratigráficas e dos episódios vulcanicos intercalados é possível reconstruir os trag->s gerais da evolu~ao da 20M, em Portugal. O soco proterozóico, constituído por séries metamórficas de grau elevado a baixo, reflecte a constru~ao de urna margem passiva durante o Rifeano , que passou a urna margem activa, com subduc~ao, responsável pela Orogenia Cadomiana, durante o Vendiano. Após o arrasamento desta Cadeia Orogénica instalou-se extensa plataforma carbonatada, no Cambrico inferior, que durante o Marianiano entrou em distensao, de que resultaram várias bacias, onde localmente se gerou vulcanismo básico toleítico, que rapidamente se colmataram devido a regressao marinha generalizada. A partir do Cambrico médio reiniciou-se a distensao, que provocou o aparecimento de novas bacias sedimentares, onde se desenvolveu imponante vulcannismo básico alcalino, localmente peralcalino. Desta distensao terá resultado a rota~ao e subida de alguns blocos, o que provocou a carsifica~ao das séries carbonatadas. Sobre os sedimentos e vulcanitos do Cambrico médio depositaram-se conglomerados e arenitos de base do Ordovícico, o que indica importante lacuna no Cambrico superior. A sedimenta~ao ordovícica é predominantemente constituída por sedimentos finos, associados localmente a vulcanismo básico alcalino. Nas zonas elevadas poder-se-a ter desenvolvido vulcanismo bimodal, parcialmente peralcalino, o que mais urna vez indica a continua~ao'da distensao crustal. No topo da sequencia ordovícica ocorre extensa barra arenítica (Form'a~a:o de Colorada) sobre a qual, em transi~ao para os sedimentos silúricos, se disp5e un conglomerado poligénico, que materializa período erosivo (de origem glaciar?). Durante o Silúrico as bacias sedimentares tornaram-se euxínicas (e mais profundas a sul?) e na passagem para o Devónico predominou a sedimenta~ao terrígena e carbonatada, com características litorais. No Devónico médio deu-se o levantamento, mais ou menos generalizado, da ZOM, provocado pela actua~ao da zona de subduc~ao que se desenvolvia a sudoeste. No Devónico superior e Carbónico inferior deu-se a colisao entre as ZDnas de Ossa Morena e Sul Portuguesa, tendo ocorrido, provavelmente, obduc~ao a sudeste e subduc~o a noroeste (com gera~ao de vulcanismo orogénico). Desta colisao resultou a migra~ao de onda orogenica para nordeste a qual é responsavel pela forma~ao de bacias «pull-apart», sucessivamente mais jovens para nordeste. Da reactiva~aoda antiga zona de subdu~ao, no Namuriano-Vestfaliano inferior, agora em regime intra-continental, resultou a deforma~ao transpressiva generalizada da ZOM e da ZDna Sul Portuguesa.[Abstract] In the portuguese pan of the Ossa Morena ZDne several sectors with distinct stratigraphy and structure are identified. They represent the continuation to Portugal of well established tectono-stratigraphic domains in Spain. From north to south the following sectors are recognized: Blastomilonitic Belt, Alter do Chao-Elvas, Estremoz-Barrancos (in which the Estremoz Anticline is differentiated), Montemor-Ficalho (with the Cabrela Syncline) and Beja Massif (where the Santa Suzana-Odivelas sub-sector is outlined). The stratigraphic sequences and interbedded volcanics of the distinct sectors allow the visualization of the main steps of the OMZ tectono-stratigraphic evolution. The high to low grade metamorphic sequences of the Proterozoic basement reflect the construction of a passive margin during the Riphean, and the inversion to an active margin during the Vendian, which led to the development of the Cadomian Orogeny. After the erosion of this chain, in late Proterozoic time, a large lower Cambrian carbonate platform was build up all over the entire area. Distensive tectonism during the Marianian generated tholeitic basic volcanics and several sedimentary depocenters, which were rapidly filled up with sediments, due to a low middle Cambrian marine regression. During the middle Cambrian the distensive tectonism was renewed and, again, this led to the development of sedimentary basins (two in the portuguese part) filled up with terrigenous sediments, alcaline basalts and minor peralcaline volcanics. Tectonic blocks generated during this distension were rotated and uplifted leading to the karstification of the lower Cambrian carbonates. Lower Ordovician conglomerates and associated Fe /Mn rich sandstones Iy unconformable on the middle Cambrian sediments, indicating so an upper Cambrian gap, probably related to sardic distensive tectonism. The ordovician sediments are usually fine grained and, in places, have interbed alcaline basalts towards its base. On the uplifed blocks bimodal volcanism (partially peralcaline) took probably place, once again indicating the continuation of the crustal distension. At the top of the ordovician sediments occurs an extensive shallow water sandstone unit (Colorada Formation) which is overlain, in many places, by a metric thick poligenic conglomerate. This may represent an erosive period (related to the upper Ordovician-lower Silurian glaciation known in other parts of Iberia?). During the Silurian sedimentation was mostly euxinic and condensed in the nonhern areas, and possibly more deep in the southern ones. Shallow water terrigenous and carbonate sediments dominate in early Devonian times. During the middle Devonian generalized uplifting of the OMZ took place as a consequence of subduction movements in the south. Upper Devonian and lower Carboniferous were times of oblique collision between the OMZ and the South Ponuguese Zone, characterized by obduction in the SE and subduction (with associated orogenic volcanics) in the NW. These collisional events are responsible for the northeastward mi~ratio1). of the oro~enicwave, to which pull apan tensionallacustrine, fluvio-marine and marine basins may be related. The reactivatian of the former Benioff Zone, in an intracontinental regime, during the Namurian-lower Westfalian time, caused the widespread transpresive tectonism which affected the OMZ (and alsa the South Portuguese Zone)

Three-dimensionally preserved graptolites from the Silurian of the Central Iberian Zone (Spain and Portugal)

[ES] Los graptolitos silúricos de la Zona Centroibérica suelen conservarse aplastados en pizarras negras, pero en algunos yacimientos los rabdosomas pueden retener parte de su relieve original o conservarse incluso en tres dimensiones. La mayoría de las veces existe una piritización temprana de los rabdosomas por la acción de bacterias sulforreductoras en ambiente anóxico, a la que se suma la génesis de nódulos. La alteración posterior de la pirita deja los graptolitos en forma de moldes, que pueden ser estudiados mediante vaciados en látex. Otros fenómenos de piritización multifásica en sedimentos gruesos conducen a la formación de nódulos de pirita que incluyen en su interior graptolitos huecos y en tres dimensiones, con el peridermo replicado delicadamente en óxidos de hierro. En otras ocasiones, los graptolitos preservados en nódulos generados en sedimentos pelágicos incluyen el recrecimiento de fosfatos sobre el peridermo de los graptolitos, que llegan a conservarse huecos y con estructuras de rellenos geopetales. Finalmente, se presenta el único caso de calizas con graptolitos conocido en el Silúrico centroibérico.[EN] Silurian graptolites form the Central-Iberian Zone are often preserved as flattened moulds in black shales, but in some cases rhabdosomes can maintain a part of its original relief, and even can appear three-dimensionally preserved. The majority of these cases can be related to an early pyritisation of the periderm favoured by bacterial activity under anoxic conditions, which also led to the genesis of nodules on the same beds. Further oxidation and dissapearance of iron minerals limited the preservation of graptolites to external moulds, that can be studied through latex casts. A different way of preservation of 3-D graptolites occurs in coarse sandstone that enhanced multiphase pyritisation fenomena, where ferruginous nodules enclosing rhabdosomes reveal that the framboidal pyrite that mineralized the periderm during very early diagenesis was remarkably resilient not only to subsequent deformation, but also to the differential weathering of the massive overpyrite that constitute the nodules. The pyritised graptolite periderm was finally replicated by iron-oxides with a minor proportion of phyllosilicates. The occurrence of “hollow” graptolites is also known from silico-phosphatic nodules, where the organic periderm was finely replicated by phosphatic overgrowths that coated the inner and outer surfaces of the rhabdosome. Occasional pseudostalactites of phosphatic minerals and colloidal silica partially occupied the empty spaces. Graptolite internal moulds occurring in limestone are very rare and are restricted to a single locality within the studied region.Peer reviewe

Preliminary account of the Silurian carbon isotope record (d13Corg) from the Barrancos region, Ossa Morena Zone, Portugal

The Barrancos region provides one of the reference sections for the Silurian of the Ossa Morena Zone in Portugal. In this area the Silurian succession is condensed, with a maximum thickness of 50 m and the ages provided by graptolite faunas indicates that all the Silurian system is represented here. The lithologies are fairly homogenous throughout the succession consisting of black carbonaceous shales interbedded with black cherts, that were deposited in marine basins that developed at the northen margins of the Gondwana continent. This study is the first attempt to characterize the variation of 13Corg in this region, in order to assess well-documented Silurian climatic events. The studied section is located at Monte do Carreba, near Barrancos village, and consists of a 45 m thick succession of black shales and cherts with graptolite faunas that indicates a Llandovery to lower Ludlow age. The base of the section is faulted against Upper Ordovician greywackes and quartzites. In this section 13Corg shows a baseline of consistent low values ranging from -25.88 to -25.10%. This is interrupted by three positive excursions with maximum values of: -22.73% at the transition between the Llandovery (Telychian) and Wenlock (Sheinwoodian), -23.33% at the Homerian and -23.09% at the transition between the Wenlock and Ludlow (Gorstian). The excursions have positive shifts between +2.55 and +3.15% and are tentatively related to the three first global climatic events recognized for the Silurian (Ireviken, Mulde and Linde). Although this study is a preliminary account of 13Corg in this region, it could provide usefull data for the recognition and discussion of climatic global events in high latitude regions as was the OMZ located during Silurian times and for sections with high level of thermal maturation.Fundação para a Ciência e Tecnologia (FCT) (PhD grant SFRH/BD/48534/2008)

Silurian stratigraphy and paleontology of the Valongo anticline and Arouca-Tamames syncline, Central-Iberian Zone (Portugal and Spain)

2 páginas.-- Comunicación presentada en Time and Life in the Silurian: a multidisciplinary approach, Italy , June 4-11, 2009; (Subcommission on Silurian Stratigraphy Field Meeting 2009).-- Abstract.This work is a contribution to the projects CGL2006-07628/BTE (Spain) and PTDC/ CTE-GEX/64966/2006 (Portugal).Peer reviewe

Silurian to Lower Devonian Palynomorphs from the Barrancos region, Ossa Morena Zone, Portugal

New miospore results were obtained from the Palaeozoic stratigraphic succession present in the Barrancos region, Portugal. The studied formations comprise the Silurian carbonaceous shales intercalated with cherts and rare lenticular carbonates of the Xistos com Nódulos Formation, as well as, the dark shales that alternates with thin psammit beds of Late Silurian to Early Devonian age from the Xistos Raiados Formation. Two miospore biozones were identified: the cf. protophanus verrucatus Miospore Biozone, of the Lower Wenlock (Homerian) (Richardson &McGregor, 1986) and the Verrucosisporites polygonalis (Po)Miospore Biozone of the Lower Pragian (Streel et al., 1987). For the first time cryptospores are reported. Rare acritarchs and chitinozoans are also present. This new preliminary data allow correlation with the graptolite biozonation already established in this region (Piçarra, et al., 1995, 1998; Piçarra, 2000) and completes previous palynological studies (Pereira et al., 1999). Even so, detailed palynostratigraphic research is needed and is currently being undertaken to better understand the complex geology of the region

Palynomorphs from the Gorstian (Silurian) of the Sazes Formation (Buçaco Syncline), Central Iberian Zone, Portugal - preliminary results

Occuring in a complex syncline that extends from Buçaco to Penedo de Góis, the studied area is located in the Central Iberian Zone of the Iberian Massif. In this region outcrops a well-preserved and complete stratigraphic succession of Lower Paleozoic age. At the top of the Buçaco Syncline stratigraphic succession, the Silurian Sazes Formation (Paris, 1981), is currently being studied at a palynological (miospores and chitinozoans) and macrofossil (graptolites) level, allowing a preliminary revision and completion of the initial biostratigraphy of this area. This studies will also provide information to support the undergoing surveying mapping project (1:50 000) that is being undertaken by the “Laboratório Nacional de Energia e Geologia” (Portuguese Geological Survey) (Sequeira, in prep)

Dados palinoestratigráficos preliminares do Gorstiano (Silúrico) da Formação de Sazes (Sinclinal do Buçaco)

Novos dados bioestratigráficos foram obtidos na sucessão estratigráfica do Paleozóico Inferior da região do Buçaco. A Formação de Sazes (Silúrico) está a ser estudada ao nível palinológico (miosporos e quitinozoários) e de macrofósseis (graptólitos), com o intuito de rever e complementar dados bioestratigráficos anteriormente descritos. Com base nos dados palinológicos, parte da Fm. de Sazes foi datada com mais precisão como pertencendo ao Gorstiano e, pela primeira vez nesta região, também foram identificados criptosporos. Novos dados são esperados com a continuação deste estudo

New insights on the Hirnantian palynostratigraphy of the rio Ceira section, Buçaco, Portugal

The Lower Palaeozoic successions of Portugal are well represented in the Central Iberian Zone (Cll), one of the main tectonostratigraphic domains of the Iberian Massif. Located in the CIZ, the Bu<;aco Syncline presents one of its most complete Palaeozoic sequences. With a NW-SE orientation, the Lower Palaeozoic lithostratigraphic succession, includes several Ordovician units that ranges from the Lower Ordovician (Tremadocian stage) to the Upper Ordovician (Hirnantian stage) and are unconformably overlain by the Silurian Sazes Formation, at least of Wenlock and Ludlow epochs, in the Rio Ceira Section (Fig.1). This sequence is also well known by its rich palaeontological content in macrofauna (e.g. trilobites, briozoans, echinoderms, ostracods, brachiopods, graptolites) and microfauna (conodonts, chitinozoans, acritarchs) (Delgado, 1908; Henry and Thadeu, 1971; Mitchell, 1974; Henry et al., 1974, 1976; ElaouadDebbaj, 1978; Henry, 1980; Paris, 1979, 1981; Romano, 1982; Romano et aI., 1986; Young, 1985, 1987, 1988,1989)

Right Atrial Thrombus: a Rare Presentation of Plasminogen Activator Inhibitor Deficiency

A presença de trombos móveis na aurícula direita são fenómenos raros, mas associados a uma elevada mortalidade. Apesar de a ecocardiografia ter permitido avanços no seu diagnóstico, a sua abordagem continua a ser motivo de debate. Neste artigo apresentamos o caso de uma doente do sexo feminino, de 24 anos, com antecedentes de tabagismo, obesidade e sob terapêutica anovulatória que recorre ao serviço de urgência por cansaço fácil e tosse com expetoração hemoptoica. O ecocardiograma transtorácico revelou massa, móvel, multilobulada de grandes dimensões na aurícula direita, condicionando abertura da válvula tricúspide. Perante episódios recorrentes de embolia pulmonar, foi submetida a cirurgia cardíaca com exérese da massa, sendo o resultado anatomopatológico compatível com trombo organizado com calcificação. O estudo genético revelou homozigotia para a variante alélica PAI-1:-675G >A(4G/4G) do inibidor do ativador do plasminogénio e heterozigotia para a variante alélica MTHFR 1298 A/C da 5,10-metilenotetrahidrofolato redutase