3-D density structure and geological evolution of Stromboli volcano (Aeolian Islands, Italy) inferred from land-based and sea-surface gravity data

We present the first density model of Stromboli volcano (Aeolian Islands, Italy) obtained by simultaneously inverting land-based (543) and sea-surface (327) relative gravity data. Modern positioning technology, a 1 x 1 m digital elevation model, and a 15 x 15 m bathymetric model made it possible to obtain a detailed 3-D density model through an iteratively reweighted smoothness-constrained least-squares inversion that explained the land-based gravity data to 0.09 mGal and the sea-surface data to 5 mGal. Our inverse formulation avoids introducing any assumptions about density magnitudes. At 125 m depth from the land surface, the inferred mean density of the island is 2380 kg m(-3), with corresponding 2.5 and 97.5 percentiles of 2200 and 2530 kg m-3. This density range covers the rock densities of new and previously published samples of Paleostromboli I, Vancori, Neostromboli and San Bartolo lava flows. High-density anomalies in the central and southern part of the island can be related to two main degassing faults crossing the island (N41 and NM) that are interpreted as preferential regions of dyke intrusions. In addition, two low-density anomalies are found in the northeastern part and in the summit area of the island. These anomalies seem to be geographically related with past paroxysmal explosive phreato-magmatic events that have played important roles in the evolution of Stromboli Island by forming the Scari caldera and the Neostromboli crater, respectively. (C) 2014 Elsevier B.V. All rights reserved.

ESR dating of pleistocene mammal teeth and its implications for the biostratigraphy and geological evolution of the coastal plain, Rio Grande do Sul, southern Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Geological evolution of the basement rocks in the east-central part of the Rondonia Tin Province, SW Amazonian craton, Brazil: U-Pb and Sm-Nd isotopic constraints

On the basis of geologic, petrologic, and U-Pb geochronologic data the basement rocks in the east-central part of the Rondonia Tin Province (RTP, southwestern Amazonian craton) are grouped into five lithologic associations: (1) tonalitic gneiss (1.75 Ga); (2) enderbitic granulite (1.73 Ga); (3) paragneiss; (4) granitic and charnockitic augen gneisses (1.57-1.53 Ga); and (5) fine-grained granitic gneiss and charnockitic granulite (1.43-1.42 Ga). The first three are related to development of the Paleoproterozoic Rio Negro-Juruena Province and represent the oldest crust in the region. The tonalitic gneisses and enderbitic granulites show calc-alkaline affinities and Nd isotopic compositions (initial epsilon(Nd) = +0-1 to -1.5; T-DM of 2.2-2.1 Ga) that suggest a continental arc margin setting for the original magmas. The paragneisses yield T-DM values of 2.2-2.1 Ga suggesting that source material was primarily derived from the Ventuari-Tapajos and Rio Negro-Juruena crusts, but detrital zircon ages and an intrusive granitoid bracket deposition between 1.67 and 1.57 Ga. The granitic and charnockitic augen gneisses show predominantly A-type and within-plate granite affinities, but also some volcanic arc granite characteristics. The initial epsilon(Nd) values (+0.6 to +2.0) indicate mixing of magmas derived from depleted mantle and older crustal sources. These rocks are correlated to the 1.60-1.53 Ga Serra da Providencia intrusive suite that reflects inboard magmatism coeval with the Cachoeirinha orogen located to the southeast. The fine-grained granitic gneiss and charnockitic granulites represent the first record of widespread magmatism at 1.43-1.42 Ga in northern Rondonia. Their geochemical signatures and the slightly positive initial epsilon(Nd) values (+0.7 to +1.2) are very similar to those of the most evolved granites of the calc-alkaline Santa Helena batholith farther southeast. U-Pb monazite and Sm-Nd whole-rock-garnet ages demonstrate that a high-grade tectonometa-morphic episode occurred in this region at 1.33-1.30 Ga. This episode attained upper-amphibolite conditions and is interpreted as the peak of the Rondonian-San Ignacio orogeny. The U-Pb and Sm-Nd data presented here and data published on rapakivi granites elsewhere indicate that the east-central part of the RTP is a poly-orogenic region characterized by successive episodes of magmatism, metamorphism, and deformation between 1.75 and 0.97 Ga. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Geological evolution of the Monte Rosa

Eine detaillierte geochemische und geochronologische Studie an Gesteinen der Monte Rosa Decke (MR; Westalpen) wurde durchgeführt. Die MR wurde während der alpinen Orogenese zunächst eklogitfaziell und nachfolgend grünschieferfaziell überprägt.Eine detaillierte U-Pb geochronologische Studie an Zirkonen und Monaziten des MR Granits ergab ein Permisches Intrusionsalter (270 ± 4 Ma). Der MR Granit gehört zu den post-variszischen magmatischen Einheiten, welche die Instabilität der variszischen kontinentalen Kruste andeuten. Für die MR kann eine paläogeographische Position als Teil der 'Briançonnais-Schwelle' angenommen werden.Innerhalb des MR Granits treten Talk-Kyanit-Chloritoid-Gesteine ('Weißschiefer') auf. Diese stellen wesentliche Indikatoren für eine alpine Hochdruckmetamorphose in der MR dar. Massenbilanzberechnungen wurden durchgeführt, um den Massentransfer zu quantifizieren, welcher für die Bildung eines Weißschiefers aus einem granitischen Protolith notwendig ist. Ein Modell für die Entwicklung der Weißschiefer wurde entwickelt.Es wurde eine in-situ 40Ar/39Ar UV-Laser-Ablationsstudie an Hellglimmern der alpinen Mineralparagenese durchgeführt. Sie ergab eine heterogene Altersverteilung. Diese Alter können durch Glimmerrekristallisation unter relativ 'trockenen' hochdruckmetamorphen Bedingungen begleitet von partiellem Verlust von radiogenem Argon während der alpinen Metamorphose erklärt werden. Eine ähnlich komplexe Entwicklung mit partieller Homogenisierung des Isotopensystems kann in der Strontium-Isotopie beobachtet werden. Diese Isotopenstudien liefern Hinweise auf das Schließverhalten von Isotopensystemen unter hochdruckmetamorphen Bedingungen.

Late Quaternary geological evolution of the Montenegro and Northern Albania continental margins

The object of this work has been the analysis of natural processes controlling the geological evolution of the Montenegro and Northern Albania Continental Margin (MACM) during the Late Quaternary. These include the modern sediment dispersal system and oceanographic regime, the building and shaping of the shelf margin at the scale of 100 kyr and relative to the most recent transition between glacial and interglacial periods. The analysis of the new data shows that the MACM is a shelf-slope system formed by a suite of physiographic elements, including: an inner and an outer continental shelf, separated by two tectonically-controlled morphological highs; a lobated drowned mid-shelf paleodelta, formed during the last sea level fall and low stand; an upper continental slope, affected by gravity-driven instability and a system of extensional faults with surficial displacement, featuring an orientation coherent with the regional tectonics. The stratigraphic study of the MACM shows a clear correspondence between the Late Pleistocene/Holocene mud-wedge and the low reflectivity sectors of the inner shelf. Conversely, most of the outer shelf and part of the continental slope expose deposits from the last sea level low stand, featuring a general sediment starving condition or the presence of a thin postglacial sediments cover. The MACM shows uplift in correspondence of the Kotor and Bar ridges, and subsidence in the outer shelf and upper slope sectors. In fact, seaward of these tectonic ridges, the sparker seismic profile show the presence of four well-defined seismo-stratigraphic sequences, interpreted as forced regression deposits, formed during the last four main glacial phases. In this way, the MACM records the 100 kyr scale sea level fluctuations on its seismo-stratigraphic architecture over the last 350 kyr. Over such time range, through the identification of the paleoshoreline deposits, we estimated an average subsidence rate of about 1.2 mm/yr.

Geological Evolution of Coastal and Marine Environments off the Campania Continental Shelf Through Marine Geological Mapping - The Example of the Cilento Promontory

The geological evolution of coastal and marine environments offshore the Cilento Promontory through marine geological mapping is discussed here. The marine geological map n. 502 “Agropoli,” located offshore the Cilento Promontory (southern Italy), is described and put in regional geologic setting. The study area covers water depths ranging between 30 and 200 m isobaths. The geologic map has been constructed in the frame of a research program financed by the National Geological Survey of Italy (CARG Project), finalized to the construction of an up-to-date cartography of the Campania region. Geological and geophysical data on the continental shelf and slope offshore the southern Campania region have been acquired in an area bounded northward by the Gulf of Salerno and southward by the Gulf of Policastro. A high-resolution multibeam bathymetry has permitted the construction of a digital elevation model (DEM). Sidescan sonar profiles have also been collected and interpreted, and their merging with bathymetric data has allowed for the realization of the base for the marine geologic cartography. The calibration of geophysical data has been attempted through sea-bottom samples. The morpho-structures and the seismic sequences overlying the outcrops of acoustic basement reported in the cartographic representation have been studied in detail using single-channel seismics. The interpretation of seismic profiles has been a support for the reconstruction of the stratigraphic and structural setting of the Quaternary continental shelf successions and the outcrops of rocky acoustic basement in correspondence to the Licosa Cape morphostructural high. These areas result from the seaward prolongation of the stratigraphic and structural units, widely cropping out in the surrounding emerged sector of the Cilento Promontory. The cartographic approach is based on the recognition of laterally coeval depositional systems, interpreted in the frame of system tracts of the Late Quaternary depositional sequence.

ESR dating of pleistocene mammal teeth and its implications for the biostratigraphy and geological evolution of the coastal plain, Rio Grande do Sul, southern Brazil

The fossiliferous deposits in the coastal plain of the Rio Grande do Sul State, Southern Brazil, have been known since the late XIX century; however, the biostratigraphic and chronostratigraphic context is still poorly understood. The present work describes the results of electron spin resonance (ESR) dating in eleven fossil teeth of three extinct taxa (Toxodon platensis, Stegomastodon waringi and Hippidion principale) collected along Chui Creek and nearshore continental shelf, in an attempt to assess more accurately the ages of the fossils and its deposits. This method is based upon the analysis of paramagnetic defects found in biominerals, produced by ionizing radiation emitted by radioactive elements present in the surrounding sediment and by cosmic rays. Three fossils from Chui Creek, collected from the same stratigraphic horizon, exhibit ages between (42 +/- 3) Ka and (34 +/- 7) Ka, using the Combination Uptake model for radioisotopes uptake, while a incisor of Toxodon platensis collected from a stratigraphic level below is much older. Fossils from the shelf have ages ranging from (7 +/- 1) 10(5) Ka to (18 +/- 3) Ka, indicating the mixing of fossils of different epochs. The origin of the submarine fossiliferous deposits seems to be the result of multiple reworking and redeposition cycles by sea-level changes caused by the glacial-interglacial cycles during the Quaternary. The ages indicate that the fossiliferous outcrops at Chui Creek are much younger than previously thought, and that the fossiliferous deposits from the continental shelf encompass Ensenadan to late Lujanian ages (middle to late Pleistocene). (C) 2009 Elsevier Ltd and INQUA. All rights reserved.

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.

The insular shelves of the Faial-Pico Ridge (Azores archipelago): a morphological record of its evolution

Shelves surrounding reefless volcanic ocean islands are formed by surf erosion of their slopes during changing sea levels. Posterosional lava flows, if abundant, can cross the coastal cliffs and fill partially or completely the accommodation space left by erosion. In this study, multibeam bathymetry, high-resolution seismic reflection profiles, and sediment samples are used to characterize the morphology of the insular shelves adjacent to Pico Island. The data show offshore fresh lava flow morphologies, as well as an irregular basement beneath shelf sedimentary bodies and reduced shelf width adjacent to older volcanic edifices in Pico. These observations suggest that these shelves have been significantly filled by volcanic progradation and can thus be classified as rejuvenated. Despite the general volcanic infilling of the shelves around Pico, most of their edges are below the depth of the Last Glacial Maximum, revealing that at least parts of the island have subsided after the shelves formed by surf erosion. Prograding lava deltas reached the shelf edge in some areas triggering small slope failures, locally decreasing the shelf width and depth of their edges. These areas can represent a significant risk for the local population; hence, their identification can be useful for hazard assessment and contribute to wiser land use planning. Shelf and subaerial geomorphology, magnetic anomalies and crustal structure data of the two islands were also interpreted to reconstruct the long-term combined onshore and offshore evolution of the Faial-Pico ridge. The subaerial emergence of this ridge is apparently older than previously thought, i.e., before approximate to 850 ka.

Stratigraphic significance of siliceous microfossils collected during Nautiperc dives (Off Peru, 5°-6° S)

The geological evolution of the northern Peru convergent margin can be traced using samples collected during deep-sea dives of the submersible Nautile. In the Paita area (5 degrees-6 degrees S), the sedimentary sequence was intensively sampled along the main scarp of the middle slope area. It consists of Upper Miocene (7-9 Ma) to Pleistocene siltstone, sandstone and rare dolostone. The age distribution of these samples is the basis for a new geologic interpretation of the multichannel seismic line CDP3. Siliceous microfossils (both diatoms and radiolarians) show influence of both cold and temperate waters (local species mixed with upwelling ones). Diatom assemblages studied from the NP1-13 and NP1-15 dives bear a strong resemblance to assemblages from the Pisco Formation of southern Peru. Micropaleontological data from siliceous microfossils, provide evidence for two main unconformities, one is at the base of the Quaternary sequence and the other corresponds to a hiatus of 1 Myr, separating the Upper Miocene (7-8 Ma) sediments from uppermost Miocene (5-6 Ma) sediments. During the past 400 kyr, a wide rollover fold developed in the middle slope area associated with a major seaward dipping detachment fault. A catastrophic debris avalanche occurred as the result of an oversteepening of the landward flank of the rollover fold. The gravity failure of the slope, recognized by SeaBEAM and hydrosweep mapping, displaced enough material to produce a destructive tsunami which occurred 13.8 +/- 2.7 kyr ago.

Geologia de la Plana del Baix Empordà

The geological features of the Baix Empordà Plain are mainly related to the sedimentary processes that took place during the Holocen, when a stable sea level was reached at the end of the Versilian transgression. In this paper, all the sedimentary environments which have given rise to the present morphology are described: alluvial, coastal and palustrine environments as well as colluvial and aeolian deposits. We conclude with a scheme in which the geological evolution of the Plain is shown

Contribution to the geology of Southern Turkey: new insights from the Mersin mélanges and from the Lycian and Antalya nappes

Abstract The study of fossil Tethyan continental margins implies the consideration of the oceanic domains to which they were connected. The advent of plate tectonics confirmed the importance of the detection of accretion-related mélanges. Ophiolitic mélanges are derived from both an upper ophiolitic obducting plate and a lower oceanic plate. Besides ophiolitic elements, the mélanges may incorporate parts of a magmatic arc and dismembered fragments of a passive continental margin. As the lower plate usually totally disappears during the obduction process, it can only be reconstructed from its elements found in the mélanges. Because of their key location at active margin boundaries, preserved accretion-related mélanges provide strong constraints on the geological evolution of former oceanic domains and their adjacent margins. The identification of Palaeotethyan remnants as accretionary series or reworked during the Late Triassic Eo-Cimmerian event, as well as the recognition of HugluPindos marginal sequences in southern Turkey and in the external Hellenides represent the main achievements of this work, making possible to establish new palaeogeographical correlations. The Mersin mélanges (Turkey), together with the Antalya and Mamonia (Cyprus) domains, are characterized by a series of exotic units found now south of the main Taurus range and compose the South-Taurides Exotic Units. The Mersin mélanges are subdivided in a Triassic and a Late Cretaceous unit. These units consist of the remnants of three major Tethyan oceans, the Palaeotethys, the Neotethys and the Huglu-Pindos. The definition and inventory of the Upper Antalya Nappes (Turkey) are still a matter of controversies and often conflicting interpretations. The recognition of Campanian radiolarians on top of the Kerner Gorge unit directly overlain by the Ordovician Seydi§ehir Fm. of the Tahtah Dag Nappe outlines a tectonic contact and demonstrates that the Upper Antalya Nappes system is composed of three different nappes, the Kerner Gorge, Bakirli and the Tahtah Dag nappes. Additionally, a limestone block in a doubtful tectonic position at the base of the Upper Antalya Nappes yielded for the first time two middle Viséan associations of foraminifers and problematic algae. The Tavas Nappe in the Lycian Nappes (Turkey) is classically divided into the Karadag, Teke Dere, Köycegiz and Haticeana units. As for the Mersin mélanges, the Tavas Nappe is highly composite and includes dismembered units belonging to the Palaeotethyan, Neotethyan and HugluPindos realms. The Karadag unit consists of a Gondwana-type platform succession ranging from the Late Devonian to the Late Triassic. It belongs to the Cimmerian Taurus terrane and was part of the northern passive margin of the Neotethys. The Teke Dere unit is composed of different parts of the Palaeotethyan succession including Late Carboniferous OIB-type basalts, Carboniferous MORB-type basalts, an Early Carboniferous siliciclastic series and a Middle Permian arc sequence. The microfauna and microflora identified in different horizons within the Teke Dere unit share strong biogeographical affinities with the northern Palaeotethyan borders. Kubergandian limestones in primary contact above the Early Carboniferous siliciclastics yielded a rich and diverse microfauna and microflora also identified in reworked cobbles within the Late Triassic Gevne Fm. of the Aladag unit (Turkey). The sedimentological evolution of the Köycegiz and Haticeana series is in many points similar to classical Pindos sequences. These series originated in the Huglu-Pindos Ocean along the northern passive margin of the Anatolian (Turkish transect) and Sitia-Pindos (Greek transect) terranes. Conglomerates at the base of the Lentas Unit in southern Crete (Greece) yielded a microfauna and microflora presenting also strong affinities with the northern borders of the Palaeotethys. This type of reworked sediments at the base of Pindos-like series would suggest a derivation from the Palaeotethyan active margin. -Résumé (French abstract) L'étude des marges continentales fossiles de l'espace téthysien implique d'étudier les domaines océaniques qui y étaient rattachés. Les progrès de la tectonique des plaques ont confirmé l'importance de la reconnaissance des mélanges d'accrétion. Les mélanges ophiolitiques dérivent d'une plaque supérieure ophiolitique qui obducte, et d'une plaque inférieure océanique. En plus d'éléments ophiolitiques, les mélanges peuvent aussi incorporer des parties d'un arc magmatique, ou des fragments d'une marge continentale passive. Comme la plaque inférieure disparaît généralement complètement durant le processus d'obduction, elle ne peut être reconstruite qu'au travers de ses éléments trouvés dans les mélanges. A cause de leur situation aux limites de marges actives, les mélanges d'accrétion bien préservés permettent de contraindre l'évolution géologique d'anciens océans et de leurs marges. L'identification de vestiges de la Paléotéthys en série d'accrétion ou remaniés lors de l'orogenèse éo-cimmérienne au Trias supérieur, ainsi que l'observation de séquences marginales de Huglu-Pinde en Turquie du sud et dans les Hellénides externes représentent les principaux résultats de ce travail, permettant d'établir de nouvelles corrélations paléogéographiques. Les mélanges de Mersin (Turquie), avec les domaines d'Antalya et de Mamonia (Chypre), sont caractérisés par des unités exotiques se trouvant au sud de la chaîne taurique, et forment les Unités Exotiques Sud-Tauriques. Les mélanges de Mersin sont subdivisés en une unité triasique, et une autre du Crétacé supérieur. Ces unités comprennent les reliques de trois principaux océans téthysiens, la Paléotéthys, la Néotéthys et Huglu-Pinde. L'inventaire et la définition des nappes supérieures d'Antalya (Turquie) sont encore matière à controverse et donne lieu à des interprétations conflictuelles. La découverte de radiolaires campaniens au sommet de l'unité de la Gorge de Kemer, directement recouverts par la formation ordovicienne de Seydisehir de la nappe du Tahtali Dag met en évidence un contact tectonique et démontre que les nappes supérieures sont composées de trois différentes nappes, celle de la Gorge de Kemer, celle du Bakirli et celle Tahtali Dag. De plus, un bloc de calcaire dont la position tectonique demeure incertaine à la base des nappes supérieures a fourni pour la première fois deux associations viséennes de foraminifères et d'algues problématiques. La nappe de Tavas dans les nappes lyciennes (Turquie) est séparée en unités du Karadag, du Teke Dere, de Köycegiz et d'Haticeana. Comme pour les mélanges de Mersin, la nappe de Tavas est composite et inclut des unités appartenant à la Paléotéthys, à la Néotéthys et à Huglu-Pinde. L'unité du Karadag est une plateforme carbonatée de type Gondwana se développant du Dévonien supérieur au Trias supérieur. Elle appartient au domaine cimmérien du Taurus et formait la marge nord de la Néotéthys. L'unité du Teke Dere est composée de différentes écailles paléotéthysiennes et inclut des basaltes d'île océanique du Carbonifère supérieur, des basaltes de ride océanique du Carbonifère, une série siliciclastique du Carbonifère supérieur et un arc du Permien moyen. Les microfaunes et -flores trouvées à différents niveaux de la série du Teke Dere partagent de fortes affinités paléogéographiques avec les marges nord de la Paléotéthys. Des calcaires du Kubergandien en contact primaire au-dessus de la série siliciclastique a donné de riches microfaunes et -flores, également identifiées dans des galets remaniés dans la formation de Gevne du Trias supérieur de l'Aladag. L'évolution sédimentologique des séries de Köycegiz et d'Haticeana sont très similaires aux séries classiques du Pinde. Ces séquences prennent leur racine dans l'océan de Huglu-Pinde, le long de la marge passive nord anatolienne (profil turc) et de la marge de Sitia-Pinde (profil grec). Des conglomérats à la base de l'unité de Lentas au sud de la Crète (Grèce) ont donné des microfaunes et flores partageant également de fortes similitudes avec les bordures nord de la Paléotéthys. Le type de sédiments remaniés à la base d'unités de type Pinde suggère une dérivation depuis la marge active de la Paléotéthys. -Résumé grand public (non-specialized abstract) Au début du 20ème siècle, Alfred Wegener bouleverse les croyances géologiques de l'époque et publie plusieurs articles sur la dérive ou la translation des continents. En utilisant des arguments géographiques (similarités des lignes de côte), paléontologiques (faunes et flores similaires) et climatiques (dépôts tropicaux et glaciaires), Wegener explique qu'il y a plusieurs millions d'années, les terres émergées actuelles ne devaient former qu'un seul et grand continent. La fin du 20ème siècle verra l'avènement de la théorie de la tectonique des plaques suite à la reconnaissance du cycle de Wilson, des rides médio-océaniques, des anomalies magnétiques dans les océans et des sutures océaniques qui représentent les reliques d'océans disparus. Le Cycle de Wilson se caractérise par une suite d'évènements géologiques majeurs pouvant se résumer de la manière suivante : (1) séparation d'un craton continental en deux parties, créant une limite de plaque divergente. C'est ce que l'on appelle un rift; (2) développement et croissance d'un océan entre ces deux blocs. Des roches magmatiques remontent à la surface de la terre et forment une chaîne de montagne sous-marine que l'on appelle ride médio-océanique ou dorsale. L'océan continue de se développer, et des sédiments se déposent à sa surface formant la suite ophiolitique ou trinité de Steinmann; (3) après une phase d'expansion plus ou moins longue, les conditions imposées aux limites des plaques à la surface de la terre changent, et l'océan se met à se refermer par disparition progressive (subduction) de sa croûte océanique sous une croûte continentale par exemple. Ceci crée une nouvelle limite de plaque, convergente cette fois; (4) la subduction de la plaque océanique sous la plaque continentale provoque une remontée de magma formant des chaînes volcaniques à la surface de la Terre ; (5) une fois que la plaque océanique a complètement disparu, les deux blocs préalablement séparés par l'océan font collision, formant ainsi une chaîne de montagne. Les chaînes de montagnes sont de manière générale formées par un empilement plus ou moins complexe de nappes. C'est au coeur de certaines de ces nappes que se trouvent les vestiges de l'océan disparu. Un des objectifs de ce travail était la recherche de ces vestiges dans le domaine téthysien de la Méditerranée orientale. Pour ce faire, nous avons parcourus une grande partie du sud de la Turquie, nous sommes allés à Chypre, dans le Sultanat d'Oman, en Iran, en Crète, et nous avons visités quelques îles grecques du Dodécanèse. La région de la Méditerranée orientale est une zone qui a été tectoniquement très active, et qui continue de l'être de nos jours par des phénomènes de subduction (ex. les volcans de Santorin), et par des mouvements coulissants entre des plaques continentales (ex. la faille nord-anatolienne) qui donnent régulièrement lieu à des tremblements de terre. Pour le géologue, la complexité de ces zones d'étude réside dans le fait que les chaînes de montagne actuelles ne contiennent en général pas seulement les restes d'un océan, mais bien de plusieurs bassins océaniques qui se sont succédés dans l'espace et dans le temps. Les nappes qui se trouvent au sud de la Turquie et dans le Dodécanèse forment un important jalon dans la chaîne alpine qui s'étend depuis les Alpes jusque dans l'Himalaya. L'idée d'un continuum au coeur de ce système se basait principalement sur l'âge des océans et sur la reconnaissance de similarités dans l'évolution des séries sédimentaires. La localisation des vestiges de la Paléotéthys ainsi que l'identification des séries sédimentaires ayant appartenu à l'océan de HugluPinde repris sous forme de nappes en Turquie et en Grèce sont cruciales pour permettre de bonnes corrélations locales et régionales. La reconnaissance, la compréhension et l'interprétation de ces séries sédimentaires permettront d'élaborer un modèle d'évolution géodynamique régional, s'appuyant sur des faits de terrains indiscutables, et prenant en compte les contraintes globales que ce genre d'exercice implique.

Phylogenetic relationships, diversification and biogeography in Neotropical Brotogeris parakeets

Aim We present a molecular phylogenetic analysis of Brotogeris (Psittacidae) using several distinct and complementary approaches: we test the monophyly of the genus, delineate the basal taxa within it, uncover their phylogenetic relationships, and finally, based on these results, we perform temporal and spatial comparative analyses to help elucidate the historical biogeography of the Neotropical region. Location Neotropical lowlands, including dry and humid forests. Methods Phylogenetic relationships within Brotogeris were investigated using the complete sequences of the mitochondrial genes cyt b and ND2, and partial sequences of the nuclear intron 7 of the gene for Beta Fibrinogen for all eight species and 12 of the 17 taxa recognized within the genus (total of 63 individuals). In order to delinetae the basal taxa within the genus we used both molecular and plumage variation, the latter being based on the examination of 597 skin specimens. Dates of divergence and confidence intervals were estimated using penalized likelihood. Spatial and temporal comparative analyses were performed including several closely related parrot genera. Results Brotogeris was found to be a monophyletic genus, sister to Myiopsitta. The phylogenetic analyses recovered eight well-supported clades representing the recognized biological species. Although some described subspecies are diagnosably distinct based on morphology, there was generally little intraspecific mtDNA variation. The Amazonian species had different phylogenetic affinities and did not group in a monophyletic clade. Brotogeris diversification took place during the last 6 Myr, the same time-frame as previously found for Pionus and Pyrilia. Main conclusions The biogeographical history of Brotogeris implies a dynamic history for South American biomes since the Pliocene. It corroborates the idea that the geological evolution of Amazonia has been important in shaping its biodiversity, argues against the idea that the region has been environmentally stable during the Quaternary, and suggests dynamic interactions between wet and dry forest habitats in South America, with representatives of the Amazonian biota having several independent close relationships with taxa endemic to other biomes.