Contributions à la paleontology du Miocène moyen continental du basin du tage

This study on middle Miocene Charophytes from the Tagus'basin indicates the presence of two species. hitherto undescribed from these strata in Portugal, Correlation diagrams of height and width of gyrogonite demonstrate that the populations of Nitellopsis (Tectochara) etrusca from the localities Póvoa de Santarém and Pêro Filho are identical to that from La Grenatière (Hérault, France), The population of Lychnothamnus duplicicarinatus from Tremês is identical to that already known from Anwill (Switzerland). The age of this flora is therefore suggested as being the upper part of the middle Miocene. The results of Charophyte studies are in accordance with stratigraphical conclusions from previously conducted mammalian studies (Antunes and Mein), A table showing the distribution of species in the three portuguese localities is given

Contributions à la paleontology du Miocène moyen continental du basin du Tage; (IV) Charophytes - Póvoa de Santarém, Pero Filho et Tremês

This study on middle Miocene Charophytes from the Tagus' basin indicates the presence of two species, hitherto undescribed from these strata in Portugal. Correlation diagrams of height and width of gyrogonite demonstrate that the populations of Nitellopsis (Tectochara) etrusca from the localities Póvoa de Santarém and Pêro Filho are identical to that from La Grenatière (Hérault, France), The population of Lychnothamnus duplicicarinatus from Tremês is identical to that already known from Anwill (Switzerland). The age of this flora is therefore suggested as being the upper part of the middle Miocene. The results of Charophyte studies are in accordance with stratigraphical conclusions from previously conducted mammalian studies (Antunes and Mein). A table showing the distribution of species in the three portuguese localities is given

Le gisement de Asseiceira, Portugal (Miocène supérieur) Données complémentaires sur Freiria de Rio Maior

A new upper Miocene locality at Asseiceira (Rio Maior), near the top of the "Calcários de Almoster e Santarém" unit (Almoster and Santarém limestones) is studied. Animal and plant fossils are described. Comparisons are drawn to other localities related to the same unit: Freiria and Azambujeira (middle and upper levels, both with large mammals). Small mammals from Asseiceira and Freiria point out to a rather old age amidst the upper Vallesian, MN 10 mammal-unit. This gives a fairly accurate datation for the "Calcários de Almoster e Santarém" and for the short time span of the corresponding sedimentation. Climate was warm and quite dry, with contrasting seasons and arid events. During upper Vallesian times, climate in Iberian Peninsula was varied but drier than in France, and specially so in the inner basins. However in Portugal and in Catalonia climate would he less different in comparison with that of the Rhône basin. Environmental evolution has been important: at Freiria and Azambujeira (middle level) there were mainly shallow lacustrine environments that received ressurgence waters from the nearby "Maciço calcário". Humid areas were closely surrounded by dense forests and these by broader and drier savanna or steppe areas. Still later, carbonate sedimentation ended. For some time there was still a river system with oxbows; humid areas probably were decreasing in favour of surrounding, rather dry environments. This study stressed the nced for revision of the geology of the region of Rio Maior and for a new geological mapping of that area. Environmental evolution has been important: at Freiria and Azambujeira (middle level) there were mainly shallow lacustrine environments that received ressurgence waters from the nearby "Maciço calcário"

Charophytes, indicators for low salinity phases in North African sebkhet

International audienceAmong water plants of lakes and ponds, the charophytes are useful for palaeolimnology because they provide autochthonous fossils in the form of their calcified fructifications, termed gyrogonites. Particular species of the Characeae are adapted to brackish water and serve as a modern analogue to infer the salinity of salt lake sediments. Here we focus on Lamprothamnium papulosum whose significance in terms of palaeo-salinity is reviewed with particular attention to the ecological requirements for calcification. New data describe the finding of L. papulosum from Holocene sediments at Sebkha Mellala, Algeria. Previous Quaternary records of this species from North Africa (Mauritania, Libya (Fezzan), Sudan, Mali and Morocco) are discussed in terms of their significance for palaeolimnology. The present paper highlights the potential of fossil charophyte gyrogonites as indicators of former low salinity phases in present-day hyper-saline environments. (C) 2007 Elsevier Ltd. All rights reserved

Palaeoenvironment of a Late Quaternary lacustrine-palustrine carbonate complex: Zarand Basin, Saveh, central Iran

International audienceThe continental carbonate deposits of the Zarand Basin were deposited within an intra-continental strike-slip basin situated in the northwestern corner of central Iran. They consist of distal alluvial mudstones to marlstones, carbonate pond deposits, carbonate and siliciclastic-infilled channels, and lacustrine carbonates deposited within a distal alluvial-lacustrine-palustrine complex. Both sedimentological and palaeontological evidence suggest that these sediments mostly formed within an open hydrological system. The common presence of root traces, greyish green mudstones, calcareous nodulisation, mottling, and desiccation breccias indicate a palustrine setting. The carbonate deposits of the Zarand Basin were formed under an overall semi-arid climate but periods of more aridity characterised by extensive calcretization can be distinguished in the stratigraphical sections. Both tectonics and climate have contributed in controlling the sedimentation of the Zarand Basin. Archaeological and geomorphological evidence provides a unique sub-recent analogue for ancient palustrine limestones developed within an intra-continental basin under a semi-arid climatic regime. The combination of geological and archaeological data and their comparison with historical documents show that the so-called historical lake of Saveh was the remnant of the more ancient wetland system which dominated the Zarand region during the late Quaternary. (c) 2005 Elsevier B.V All rights reserved

Charophytes, indicateurs de paléobathymétrie du lac Tigalmamine (Moyen Atlas, Maroc)

International audienceLes études paléolimnologiques s'avèrent particulièrement pertinentes lorsque les espèces trouvées dans les sédiments sont toujours présentes à l'état vivant dans le milieu et que la végétation submergée peut fournir un analogue direct pour l'interprétation. Ainsi, le lac de Tigalmamine représente un cas exceptionnellement favorable, par rapport à la plupart des paléolacs en Afrique du Nord, puisque les restes fossiles des Characées peuvent ici être comparés à ceux produits par les plantes actuelles dans un contexte écologique connu. Tigalmamine est un hydrosystème composé de trois lacs d'origine karstique, situés à 1626 m d'altitude dans le Moyen Atlas marocain. Le site avait fait l'objet d'une carotte de 16 m de longueur prélevée dans le centre du lac central sous 16 m d'eau (core C 86 in Lamb and Kaars, 1995 [The Holocene 5 (1995) 400–408]). Les sédiments représentent la totalité de l'Holocène depuis 10 200 BP jusqu'à l'Actuel (El Hamouti et al., 1991 [Comptes Rendus de l'Académie des Sciences de Paris 2 (1991) 259–265] ; Lamb et al., 1995 [Nature 373 (1995) 134–137]). De nombreuses gyrogonites de Charophytes, isolées de ce sondage, avaient été déterminées comme Chara hispida (Soulié-Märsche dans Benkaddour, 1993 [Changements hydrologiques et climatiques dans le Moyen-Atlas marocain : chronologie, minéralogie, géochimie isotopique et élémentaire des sédiments lacustres de Tigalmamine. PhD thesis, Université Paris-Sud, Orsay (inédit)]). Une prospection ultérieure à Tigalmamine par les auteurs du présent article en 2000, a montré que cette espèce est toujours présente dans le lac où elle forme une couronne de végétation submergée strictement limitée entre 2 et 9 m de profondeur. Le présent travail décrit les caractéristiques morphologiques et écologiques de Chara hispida comme référence pour l'interprétation des fossiles. Sur la base de ces données, les variations de fréquence des gyrogonites dans les sédiments de la carotte reçoivent une signification en termes de bathymétrie. L'étude détaillée des charophytes et de leur répartition dans le sondage, en complément aux travaux antérieurs, confirme l'existence de quatre phases de bas niveau lacustre au cours de l'Holocène. Le but du présent travail est de montrer que les charophytes peuvent fournir des informations complémentaires et utiles pour la reconstitution paléolimnologique

Contribución a la Paleolimnología del Pleistoceno inferior de la Cuenca de Baza (sector Orce -Venta Micena).

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The early messinian Velona basin (Siena, Central Italy): palaeoenvironmental and palaeobiogeographical implications

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The Early Messinian Velona basin (Siena, central Italy): Paleoenvironmental and paleobiogeographical reconstructions

A multi-disciplinary study of the basal lacustrine succession of the Velona basin (Tuscany, central Italy) provides informations about the paleoenvironmental and paleogeographical evolution of a post-collisional basin located in the Mediterranean area. Detailed sedimentological, paleontological (molluscs, ostracods, mammals, charophytes and pollen) and geochemical analyses on biogenic carbonates were carried out on a 66-m-thick muddy-sandy succession. Integrating the vertical distribution of selected species of ostracods and molluscs with the range of the mammal assemblage it has been possible to correlate the basal succession of the Velona basin to the Early Messinian (pre-evaporitic) corresponding to the lower part of the MN 13 zone. The basal portion of the Velona filling deposits corresponds to an unstable shallow lacustrine/marshy environment, rich in aquatic vegetation, surrounded by swamps dominated by Taxodiaceae and uplands dominated by warm temperate deciduous forests. Waters were generally brackish (oligo/mesohaline), alternating with hypohaline episodes. Salinity changes recorded by the faunal assemblages do not parallel with changes in the geochemical signatures in ostracod shells and charophyte gyrogonites. Geochemistry of biogenic carbonates points to an athalassic origin of the water salinity probably linked to the dissolution of the Triassic evaporites of the basement. Thus, the absence of connections between the Velona basin and the Mediterranean Sea during Early Messinian is confirmed. Ostracods, molluscs and mammals show a central European paleobiogeographical affinity, showing that, at the time of deposition of the Velona filling deposit, the endemic Tusco-Sardinian paleobioprovince was already disrupted and the northwards connections were noticeable. On the other hand, ostracods do not show any paleobiogeographic affinity with the ostracod assemblages of the Paratethyan realm, suggesting that no links between Mediterranean and Paratethys were present at that time. © 2002 Elsevier Science B.V. All rights reserved.Peer Reviewe

The Velona basin (Tuscany, Italia)

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