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Jipa D.C.,Romanian National Institute of Marine Geology and Geoecology GeoEcoMar
Quaternary International | Year: 2014

New information on the entire Lower Danube Basin was obtained through the selection, reworking and integration of previously published data concerning the loess accumulations from the Romanian Danube Plain, Bulgarian Danube Plain, and Dobrogea Highland. A conceptual sedimentary model was outlined, based on the integrated textural and isopach maps of the Lower Danube loess and loess-like deposits. The loess in the Lower Danube Basin appears as an accumulation with the coarsest-grained and thickest loess deposits situated along the Lower Danube River channel. Both grain-size and thickness gradually decrease to the basin margin. During the initial genetic stage, the Lower Danube loess basin functioned as a large flood plain. The alluvial and eolian loess generation stages repeatedly alternated. Several sources supplied the Lower Danube loess clastics, determining the Danubian, Carpathian/Balkan and Black Sea littoral provenance of the detrital material. © 2013 Elsevier Ltd and INQUA. Source


Melinte-Dobrinescu M.C.,Romanian National Institute of Marine Geology and Geoecology GeoEcoMar | Roban R.-D.,University of Bucharest
Sedimentary Geology | Year: 2011

This study focused on the Cretaceous black shale successions, followed by red shales that crop out at the outer regions of the Romanian Carpathians, in the Moldavids. The oldest parts of the black shale units deposited in an abyssal plain during Late Valanginian-Late Barremian time; they are mainly characterized by hemipelagic and pelagic muddy siliciclastic rocks and carbonates, commonly intercalated with fine-grained turbidites. During the sedimentation of the middle part of the black shale units in the Late Barremian-Early Albian interval, the depth of the basin increased, as the carbonate hemipelagic sedimentation was replaced by a mainly siliceous one. Only a few thin turbidite intercalations are present. The youngest part (Albian pro parte) of the black shale units is characterized by a turbiditic sedimentation, with mainly sandy sequences of middle and lower deep-water fans. We may assume that the depth of the basin continuously decreased. The presence of authigenic glauconite in the Albian sandstones suggests a palaeoenvironmental change, linked to the occurrence of oxygenated turbidity current circulation. A significant shift in the sedimentation regime in the Eastern Carpathian Moldavids took place in the Late Albian, when Cretaceous Oceanic Red Beds (CORB) occurred. This type of sedimentation lasted up to the Coniacian. The lower part of the CORBs that contains radiolarites intercalated with variegated shales, pyroclastic tuffs and thin sandstones is interpreted as a hemipelagic and pelagic sedimentation in the abyssal plain environment, where rarely turbidites occurred. Upwards, there are mainly burrowed variegated red and green shales. The youngest parts of CORBs are characterized by increased thickness and frequency of the turbidites. While the main part of the CORB is carbonate free or has very low carbonate content, the upper part of these strata becomes rich in marl and mudstone strata, indicating a decrease of the basin-depth. The accumulation of black shales in the Eastern Carpathians during the Late Valanginian-Late Albian interval is linked to the existence of a small, silled basin of the Moldavian Trough, in which restricted circulation led to the density stratification of the water column, resulting in the deposition of anoxic Lower Cretaceous sediments (i.e., the black shales). Because of the tectonic deformation that took place within the Lower-Upper Cretaceous boundary interval, the restricted circulation had changed to an open circulation regime in the Moldavian Trough. Hence, the anoxic regime was progressively replaced by an oxic one, across the Albian-Cenomanian boundary interval. The beginning and the end of the CORBs in the Moldavid units depend thus on various palaeogeographic and palaeoenvironmental settings, and it was controlled by the regional tectonic activity. © 2010 Elsevier B.V. Source


Seghedi A.,Romanian National Institute of Marine Geology and Geoecology GeoEcoMar
Turkish Journal of Earth Sciences | Year: 2012

An overview of lithological, palaeontological and geochronological evidence existing for the Palaeozoic formations from Dobrogea and Pre-Dobrogea has enabled a better understanding of the Palaeozoic history of these areas. The Lower Palaeozoic of Pre-Dobrogea, in places in continuity with the pelitic-silty facies of the underlying Vendian (Ediacaran) deposits, was one of the peri-Tornquist basins of Baltica, suggesting that the Scythian Platform in the Pre-Dobrogea basement represents the rift ed margin of the East European Craton. In North Dobrogea two types of Palaeozoic succession have formed in different tectonic settings. Deep marine Ordovician-Devonian deposits, including pelagic cherts and shales, associated with turbidites, and facing Devonian carbonate platform deposits of the East European Craton, form northward-younging tectonic units of an accretionary wedge, tectonically accreted above a south-dipping subduction zone. South of the accretionary prism, the basinal to shallow marine Silurian-Devonian deposits of North Dobrogea, showing a similar lithology to the East Moesian successions, accumulated on top of lowgrade Cambrian clastics with Avalonian affinity indicated by detrital zircons. Late Palaeozoic erosion was accompanied by deposition of continental alluvial, fluvial and volcano-sedimentary successions, overlying their basement above an imprecise Carboniferous gap. The low-grade metamorphic Boclugea terrane, showing Avalonian affinity, and the associated Lower Palaeozoic deposits represent East Moesian successions, docked to Baltica by the Lower Devonian and subsequently involved in the Hercynian orogeny, being affected by Late Carboniferous-Early Permian regional metamorphism and granite intrusion. The Late Carboniferous-Early Permian syn-tectonic sedimentation, regional metamorphism of Palaeozoic formations and development of a calc-alkaline volcano-plutonic arc indicate an active plate margin setting and an upper plate position of the Mǎcin-type successions during the Variscan collision, when the Orliga terrane, with Cadomian affinity, was accreted to Laurussia along a north-dipping subduction zone of the Rheic Ocean. The East Moesian Lower Palaeozoic succession, overstepping its Ediacaran basement, represents an Avalonian terrane, docked to the Baltica margin in the Early Palaeozoic. A narrow terrane detached from the Trans-European Suture Zone (TESZ) margin of the Baltica palaeocontinent forms a tectonic wedge within the East Moesian basement. The Palaeozoic sedimentary record of East Moesia shows a quartzitic facies in the Ordovician, graptolite shales in Upper Ordovician-Wenlock, black argillites in the Ludlow-Pridoli and fine-grained clastics in the Lower Devonian. Eifelian continental sandstones are followed by a carbonate platform from Givetian to Tournaisian times and coalbearing clastics in the Carboniferous, indicating a foredeep basin evolution. By the Eifelian both East Moesia and Pre-Dobrogea were part of Laurussia, sharing the same old red sandstone facies. The Permian is a time of rifting in Dobrogea and Pre-Dobrogea, although evidence for rifting in the East Moesian sedimentary record is very limited. In the eastern basins of Pre-Dobrogea, Permian rifting was accompanied by alkaline bimodal volcanism of the basalttrachyte association, that affected also the northern margin of North Dobrogea. Late Permian within-plate alkaline magmatic activity emplaced plutonic and hypabyssal complexes along the south-western margin of North Dobrogea. The model proposed for the Palaeozoic history based on existing data for the north-western margin of the Black Sea records early Palaeozoic docking to Baltica of the Avalonian terrane of East Moesia, including the Boclugea terrane of North Dobrogea. Late Carboniferous-Early Permian accretion of the Cadomian Orliga terrane from North Dobrogea, accompanied by Hercynian metamorphism and granite intrusion, correlates with the closure of the Rheic Ocean. Subsequently, Avalonian and Cadomian terranes, together with a narrow terrane detached from the TESZ margin of Baltica palaeocontinent, were displaced southward along the strike-slip fault system of the TESZ. © TÜBİTAK. Source


Dimitriu R.G.,Romanian National Institute of Marine Geology and Geoecology GeoEcoMar
Quaternary International | Year: 2012

An obvious discrepancy is noticed between the very few archaeological sites discovered until now on the Danube Delta plain area and the large number of such sites, whose ages range from the Middle Paleolithic to the Middle Ages and more recently, identified on its higher topography surroundings.The combined effects of the regional subsidence of the coast and delta area, with amplitudes of -2 to -4 mm/y and of the secular mean sea level rise (+0.5/1.0 mm/y) continuously change the " land-mean sea level" relative relationship, placing the prospective archaeo-cultural layer corresponding to the Late Prehistory - Antiquity period at a burial depth which now exceeds 4-5 m. This situation partly explains the limited success of the archaeological research carried out until now within the Danube Delta plain area and recommends a systematic use of the geophysical investigation methods in future. The integrated interpretation of the coastal zone bathymetry and sedimentology mappings and of the shoreline geomorphological evolution in time highlights the sedimentary processes that presently shape the littoral study zone allowing to divide it in sectors where either sediments accumulation or erosion processes prevail. The study draws attention to the împuţita - Câşla Vâdanei and Coşna - Vadu littoral sectors where the intense marine erosion of the shoreline and the adjacent seabed also imminently endangers their prospective archaeo-cultural load. © 2010 Elsevier Ltd and INQUA. Source


Balintoni I.,Babes - Bolyai University | Balica C.,Babes - Bolyai University | Seghedi A.,Romanian National Institute of Marine Geology and Geoecology GeoEcoMar | Ducea M.N.,University of Arizona
Precambrian Research | Year: 2010

The North Dobrogea orogen is a collage of dismembered terrane fragments between the Moesian platform and East European craton (Baltica). It records Alpine and Variscan deformation, magmatism and metamorphism. Its basement comprises three metamorphic complexes (Boclugea, Megina and Orliga) that are separated by tectonic boundaries. Detrital zircon U/Pb ages suggest the Boclugea and Orliga complexes represent two peri-Gondwanan terranes of Avalonian and Cadomian affinities, respectively. The new data clarify the original relationships between the North Dobrogea terranes, and Baltica and Moesia platform. © 2010 Elsevier B.V. Source

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