Dacian Basin Research Articles

Strontium isotope ratios of the Eastern Paratethys during the Mio-Pliocene transition; Implications for interbasinal connectivity

Paratethys represents the large basin that extended from central Europe to inner Asia, comprising the North Alpine foreland, Pannonian and Dacian basins, the Black Sea and Caspian Sea. Connectivity between these subbasins and the connectivity of Paratethys with the open ocean varied drastically because of pervasive tectono-climatic processes affecting the region. Here, we investigate the biogenically produced carbonates of the Dacian basin for strontium analyses to monitor changes in connectivity, water geochemistry and palaeoenvironment during the Mio-Pliocene transition. Diagenetic evaluation showed that not all contamination could be removed, but that the strontium content of our samples was not affected by post-depositional processes. 87Sr/ 86Sr ratios of ostracods and molluscs are in good agreement and show relatively constant values of 0.70865–0.70885. These are much lower than coeval Mio-Pliocene ocean water (0.7089–0.7090), which indicates that no long-standing connection existed to the Mediterranean. The newly obtained strontium ratios for Paratethys are best explained by a mixture of Danube, Dnieper and Don river waters, implying connectivity between Dacian basin and Black Sea during the latest Miocene–earliest Pliocene. We observed no evidence for connectivity to the Caspian Sea during this period. The 87Sr/ 86Sr ratios of the Dacian basin are similar to the ones measured in the Mediterranean “Upper Evaporites/Lago Mare” facies. The major fresh water deluge at the end of the Messinian salinity crisis could thus have been caused by drowning of Eastern Paratethys waters into the Mediterranean.

The evolution of the Danube gateway between Central and Eastern Paratethys (SE Europe): Insight from numerical modelling of the causes and effects of connectivity between basins and its expression in the sedimentary record

The Pannonian and Dacic Basins in SE Europe are presently connected by the Danube River across the South Carpathians, to which they are in a back-arc and foreland position respectively. Part of the Paratethys realm during the Neogene, open water communication between the basins was interrupted by the Late Miocene uplift of the Carpathians. Different mechanisms have been proposed for the formation of the Danube gateway: capture of the upstream lake or an upstream river or incision of an antecedent river. Estimates on its age range from Late Miocene to Quaternary. A related issue is the effect of the large Mediterranean sea level fall related to the Messinian Salinity Crisis on the Paratethys subbasins, specifically the “isolated” Pannonian Basin. In a synthetic numerical modelling study, using a pseudo-3D code integrating tectonics, surface processes and isostasy, we addressed the causes and effects of changes in connectivity between two large sedimentary basins separated by an elevated barrier. Specifically, we aimed to find the expression of connectivity events in the sedimentary record in general and the consequences for the evolution of the Pannonian–Dacic area in particular. We studied a range of parameters including the geometry and uplift rate of the barrier, downstream sea level change and lithosphere rigidity. We found that changes in connectivity are expressed in the sedimentary record through their effect on base level in the upstream basin and supply in the downstream basin. The most important factors controlling the response are the elevation difference between the basins and the upstream accommodation space at the time of reconnection. The most pronounced effect of reconnection through lake capture is predicted for a large elevation difference and limited upstream accommodation space. Downstream increase in sediment supply is dependent on the latter rather than the reconnection event itself. Of the parameters we tested, the rigidity of the lithosphere was found to be of major importance by its control on sediment loaded subsidence and generation of accommodation space. A downstream sea level change is unlikely to induce capture, but may affect the upstream lake level by enhancing incision in a pre-existing gateway. In the Pannonian–Dacic region, the mechanically weak, continuously subsiding Pannonian lithosphere allowed accommodation of significant volumes of continental sedimentation and as a consequence, transfer of excess sediment to the downstream Dacic Basin was only gradual. The Messinian sea level fall in the Dacic Basin could have been recorded in the Pannonian Basin only if a connection between the basins already existed. More detailed modelling of river incision taking into account lateral differences in erodibility in the South Carpathians will be required to give better time constraints on the formation of the Danube Gateway.

Galeacysta etrusca complex: Dinoflagellate cyst marker of paratethyan influxes to the Mediterranean sea before and after the peak of the messinian salinity crisis

More than one thousand specimens of a morphological complex including Galeacysta etrusca Corradini & Biffi 1988 from 11 Upper Miocene and Lower Pliocene localities of the Paratethyan and Mediterranean realms have been studied using a biometric approach in part relating to the degree of separation between endocyst and ectocyst. Four stable biometric groups have been distinguished statistically, the occurrence or prevalence of which appears closely linked to environmental conditions irrespective of the realm. Group ‘a’ is related to brackish conditions, group ‘b’ to marine conditions, group ‘c’ to freshwater, and group ‘d’ to high nutrient levels. Based on an accurate chronology provided by calcareous nannoplankton bioevents and recognition of the Messinian Erosional Surface, this study reveals: 1. the high sensitivity of the Galeacysta etrusca complex for reconstructing paleoenvironments and discriminating phases of connection and isolation of basins; 2. the detailed history of this species complex which originated in the Pannonian Basin at ca. 8 Ma before invading the Dacic Basin during the interval 6–5.60 Ma, then migrating into the Mediterranean during high sea‐level connections (the ‘Lago Mare’ events just before and after the peak of the Messinian Salinity Crisis, i.e. at 5.60 Ma and during the interval ca. 5.46–5.278 Ma, respectively), and finally into the Black Sea at ca. 5.13 Ma; 3. an improved paleogeography for the Mediterranean and Paratethyan realms with focus on the location of corridors and the timing of when they were active. Based on field observations and dinoflagellate cyst data, we propose that the reflooding of the Mediterranean Basin by Atlantic waters occurred at ca. 5.46 Ma, about 130 kyr before the Zanclean GSSP (5.332 Ma).

Messinian sea level fall in the Dacic Basin (Eastern Paratethys): palaeogeographical implications from seismic sequence stratigraphy

The signature of the Mediterranean Messinian Salinity Crisis (MSC) in the Paratethys has received wide attention because of the inferred changes in connectivity and base level. In this article, we present sequence stratigraphic interpretations on a seismic transect across the western part of the semi-isolated Late Miocene–Pliocene Dacic Basin (Eastern Paratethys, Romania), chronologically constrained by biostratigraphic field observations and well data. They reveal significant sea level changes during the middle Pontian that are coeval with the MSC. These changes were most likely transmitted to the western Dacic Basin from the downstream Black Sea and controlled by the sill height of the interconnecting gateway. During the middle Pontian lowstand of the western Dacian Basin, sedimentation continued in a remnant 300 m deep lake with a positive water balance. Our observations show that the evolution of semi-isolated sedimentary basins is strongly dependent on the communication with other depositional realms through its control on base level and sediment supply.

GALEACYSTA ETRUSCA COMPLEX: DINOFLAGELLATE CYST MARKER OF PARATETHYAN INFLUXES TO THE MEDITERRANEAN SEA BEFORE AND AFTER THE PEAK OF THE MESSINIAN SALINITY CRISIS

More than one thousand specimens of a morphological complex including Galeacysta etrusca Corradini & Biffi 1988 from 11 Upper Miocene and Lower Pliocene localities of the Paratethyan and Mediterranean realms have been studied using a biometric approach in part relating to the degree of separation between endocyst and ectocyst. Four stable biometric groups have been distinguished statistically, the occurrence or prevalence of which appears closely linked to environmental conditions irrespective of the realm. Group ‘a' is related to brackish conditions, group ‘b' to marine conditions, group ‘c' to freshwater, and group ‘d' to high nutrient levels. Based on an accurate chronology provided by calcareous nannoplankton bioevents and recognition of the Messinian Erosional Surface, this study reveals: 1. the high sensitivity of the Galeacysta etrusca complex for reconstructing paleoenvironments and discriminating phases of connection and isolation of basins; 2. the detailed history of this species complex which originated in the Pannonian Basin at ca. 8 Ma before invading the Dacic Basin during the interval 6–5.60 Ma, then migrating into the Mediterranean during high sea-level connections (the ‘Lago Mare' events just before and after the peak of the Messinian Salinity Crisis, i.e. at 5.60 Ma and during the interval ca. 5.46–5.278 Ma, respectively), and finally into the Black Sea at ca. 5.13 Ma; 3. an improved paleogeography for the Mediterranean and Paratethyan realms with focus on the location of corridors and the timing of when they were active. Based on field observations and dinoflagellate cyst data, we propose that the reflooding of the Mediterranean Basin by Atlantic waters occurred at ca. 5.46 Ma, about 130 kyr before the Zanclean GSSP (5.332 Ma).

Palaeoenvironment assessment of Pliocene Lom lignite (Bulgaria) from bitumen analysis and preparative off line thermochemolysis

The Dacian coal bearing province is located in NW Bulgaria. Coal formation is thought to be connected with desiccation of the Dacian Basin during a prolonged regression in the Late Pontian and Pliocene (Dacian–Romanian age). A Lom lignite sample was characterized via micropetrography, bulk chemical analysis, spectral methods and thermochemolysis. The pollen record was poor, suggesting coal formation under oxygen-rich conditions during peatification. Straight chain alkanes, alkan-2-ones, alkanols, des-A-triterpenoids, aromatized triterpenoids, aromatized hopane, hopene/hopanes and triterpenoids with a strong dominance of oleanane-derived structures were present in the extracted bitumen. The residue after extraction was subjected to preparative off line tetramethylammonium hydroxide (TMAH) thermochemolysis. The aliphatic products released were C 22–C 27 fatty acid (FA) methyl esters, i.e. α-methoxymethyl esters, C 22–C 28 even numbered α,ω-diacids dimethyl esters with a smooth distribution and traces of i- and ai-C 15 acid methyl esters. Trapped and bound FAs were distinguished using tetraethylammonium acetate (TEAAc) treatment. The main thermochemolysis products were phenols structurally related to lignin. Vanillyl and syringyl units were produced in similar amounts, indicating nonwoody angiosperm vegetation as the main plant input to the palaeo-swamp, probably originating from marsh or grassland sources. The bitumen provided unequivocal information for an angiosperm contribution to the mire, while the results of the TMAH pyrolysis revealed a concomitant angiosperm and gymnosperm input. The biomarker assemblage makes the Lom lignite unique in Bulgaria, all the other Bulgarian Neogene lignites being dominated by coniferous vegetation, with only traces of angiosperm contributions.

Evidence for the Aeolian Origin of Loess in the Danubian Plain

The present work considers the evidences for the Aeolian origin of loess in the Danubian plain, put forward by previous authors, which have been amended with results from new investigations. One of the main proofs consists in the grain-size composition changes of the loess complex from north to south, from east to west and with depth. Other evidences are the well expressed directions of loess winnowing in the Danubian plain: from west-northwest and north-northeast. The next evidence for the Aeolian origin of loess is the sequence in the loess accumulation process. It was started before 2.59 Ma BP along the coast of the Dacian basin and after its regression loess winnowing was also spread on the occupied by the basin territories (0.82 Ma BP). The loess complex becomes younger towards the Danubian terraces. The deflation of the loess fine earth material occurred from the flooded areas of the Paleodanube River and its tributaries, from the Black sea shelf and the clayey alluvium of the Dacian basin. The orientation of the deflation area with respect to the transporting Aeolian corridor was one of the reasons for the differences in the lithostratigraphy and the thickness of the loess complex. Five loess regions were differentiated in the Danubian plain: Northeast, “Yantra-Vit”, “Vit-Ogosta”, “Ogosta-Lom” and the Black Sea region.

Messinian event in the black sea: Evidence of a Messinian erosional surface

In 1975, sediment cores from leg DSDP 42b (sites 380A and 381) revealed a thin sediment layer in the Black Sea basin which points to a shallow water environment at the Miocene-Pliocene boundary. With these facts and in the wake of hypothesis of the Messinian Salinity Crisis (MSC), it was proposed that the Black Sea, like the Mediterranean Sea, suffered a desiccation period at the end of the Messinian (Hsü, K.J. and Giovanoli, F., 1979. Messinian event in the Black Sea. Palaeogeography, Palaeoclimatology, Palaeoecology, 29: 75–93). Whereas the main topics of the MSC in the Mediterranean Sea is now widely accepted, the lack of evidence for a Messinian erosional surface in the Black Sea left the debate about the Messinian desiccation of this basin open until today. The analysis of high resolution multi-channel seismic data acquired during the BlaSON surveys brings important new elements for this scientific debate: (1) Down the slope offshore the Bosporus, we show a clear erosional surface correlated to the top of the Upper Miocene shallow water environment unit of site DSDP 381. The overlying Lower Zanclean unit inevitably dates this erosional surface of the Messinian event. (2) A wide intra-Pontian erosional surface (IPU) is evidenced on the Romanian shelf. The IPU is characterized by a sharp decrease in the incision rate from outer (deep canyons) to inner shelf (superficial incisions network). According to the most recent Paratethyan and Mediterranean stratigraphic scale correlations, the IPU erosional surface is considered as the analogue to the Messinian erosional surface described down the slope offshore the Bosporus. In addition to recently discovered inland erosional signature, the wide regional erosional surface we underline on the Western Black Sea margins validates the Black Sea Messinian desiccation hypothesis. We also demonstrate that evaporative draw-down of the Black Sea implied the installation in the basin of a negative hydrologic budget during the Messinian. The lack of a major Messinian Danube canyon on the Romanian shelf supports the hypothesis of a Messinian Danube trapped in the Dacic basin. However, the presence of a Messinian superficial incision network connecting the location of the modern Danube delta to deeply incised Messinian canyons on the outer shelf (IPU) makes the hypothesis of a Danube reaching the partially desiccated Black Sea still possible.

Earliest Zanclean age for the Colombacci and uppermost Di Tetto formations of the “latest Messinian” northern Apennines: New palaeoenvironmental data from the Maccarone section (Marche Province, Italy)

The occurrence of planktonic foraminifers in the latest Messinian deposits (uppermost Di Tetto Formation and Colombacci Formation) of the Marche Province (Apennine foredeep, Italy) has stimulated a debate since the 1970s. An earlier palynological study of the entire Maccarone section revealed a pronounced, and a sudden increasing frequency of saccate pollen grains which indicates more distal conditions, and thus a transgression. At first attributed to tectonic activity, this transgression is now interpreted as representing the Zanclean marine transgression after the discovery of Ceratolithus acutus, the calcareous nannofossil marker of the earliest Zanclean in the Mediterranean Sea. Evidence from marine dinoflagellate cysts and planktonic foraminifers supports this result. The Colombacci Formation and uppermost part of the Di Tetto Formation (i.e. the entire p–ev2 stratigraphic unit) belong to the earliest Zanclean. The so-called Lago Mare no longer has a regional chronostratigraphic sense, and should be understood as the invasion of Paratethyan organisms via surface waters owing to a connection at high sea-level between the Aegean Sea and the Eastern Paratethys (Dacic Basin). A new robust environmental reconstruction of the northern Apennine foredeep is proposed, which respectively considers the effects of tectonics and Mediterranean eustasy.

Mollusc assemblages of the Pontian and Dacian deposits from the Topolog-Argeş area (southern Carpathian foredeep – Romania)

A better understanding of Mediterranean–Paratethys water-exchange during the Messinian Salinity Crisis has since long been hampered by the absence of a reliable time frame for the Paratethys. High-resolution magnetostratigraphic studies on the sedimentary sequences of the eastern and southern Carpathian foredeep recently resulted in an accurate chronology for the Mio-Pliocene deposits of the Dacic Basin of Romania. This allowed a straightforward correlation of the Pontian and Dacian stages to the geological time scale, which revived earlier discussions on Mediterranean–Paratethys connectivity. Here, we present Pontian and Dacian mollusc assemblages of the Getic Depression (Topolog-Argeş area, southern Carpathians) of Romania, which are incorporated in a magnetostratigraphic time frame. They indicate that a hiatus – comprising the Early Pontian – is present in the stratigraphic successions, which could be related to a base level drop of the Paratethys water column or to more local tectonic processes. The mollusc assemblages furthermore show a gradual transition at the Pontian/Dacian boundary, which is magnetostratigraphically dated at ∼4.9 Ma. This is significantly later (by more than 400 kyrs) than the Mio-Pliocene boundary in the Mediterranean sequences.

Latest Messinian “Lago-Mare” Lymnocardiinae from Italy: Close relations with the Pontian fauna from the Dacic Basin

Rich hypo- to mesohaline molluscan assemblages characterising the latest Messinian “Lago-Mare” biofacies, composed of prosobranch gastropods (Neritidae, Thiaridae, Melanopsidae, Hydrobiidae) and bivalves of the families Cardiidae (subfamily Lymnocardiinae) and Dreissenidae, are widespread in shallow water basins characterized by low salinities within the Mediterranean realm, during the post-evaporitic phase in the time-span 5.5–5.3 Ma. Several genera and species are recorded in the Italian uppermost Messinian sediments. While the gastropods show endemic character being linked to continental water-systems, Lymnocardiinae and Dreissenidae have strong Paratethyan affinity. New records of significant species of Lymnocardiinae from the uppermost Messinian sediments of Tuscany, Marches and Sicily and the systematic review of the old literature data point out close relations of the Italian fauna with that from the Pontian sediments of the Dacic Basin. The palaeobiogeographical data referred to Messinian and Pontian Lymnocardiinae suggest that the Aegean Basin could be an intermediate basin from whence the Pontian Paratethyan-type fauna migrated into the Mediterranean area during the latest Messinian. Since the ecology of Lymnocardiinae is mainly tied to oligo- and mesohaline water, spreading of suitable habitats in depositional systems of marginal settings characterized by increasing freshwater influx after the “salinity crisis” favoured their dispersal into the Mediterranean area from the Paratethys realm.

Calcareous nannofossil biostratigraphy and magnetostratigraphy of the Upper Miocene and Lower Pliocene of the Northern Aegean (Orphanic Gulf–Strimon Basin areas), Greece

The transitional position of the Northern Aegean makes it an important area for studying the relation between the Mediterranean and the Eastern Paratethys. A chronostratigraphic framework has been obtained for the Late Neogene deposits along the Orphanic Gulf and in the Strimon Basin of Northern Greece by analysing calcareous nannofossil data and paleomagnetic results from eight sections. The local formations and major lithological units have been correlated with the Upper Miocene and Lower Pliocene stages. Furthermore, the obtained framework has facilitated a more detailed reconstruction of the effects of the Messinian salinity crisis on the sedimentary record. Magnetostratigraphic data from the Strimon Basin result in an age estimate of 6.3 Ma for the Dafni–Choumnikon Formation transition, between normal polarity subchrons C3An.2n and C3An.1n. Since this Late Miocene age estimate corresponds closely to estimates of the Maeotian–Pontian boundary in the Eastern Paratethys (Dacic Basin), we believe this transition from marine to brackish conditions corresponds to this latter boundary. The gypsiferous unit in the basal part of the Choumnikon-equivalent beds along the Orphanic Gulf can then be correlated with the evaporites in the Northern Aegean and the Lower Evaporites of the Mediterranean Basin. Consequently, we assume that these Northern Aegean evaporites have been deposited between 5.96 and 5.59 Ma. Freshwater deposits above the evaporites are easily traceable across the Orphanic Gulf area, as a gravel or sandstone unit topped by a travertine marker bed, and have a wide lateral continuation. Since their position is intermediate between the shallow marine gypsum/anhydrite and the more open marine clastics of the Pliocene, we argue that these beds correlate with the desiccation phase of the Mediterranean and Black Sea basins. This intra-Messinian event probably occurred between 5.59 and 5.50 Ma, thus predating the Upper Evaporites or Lago Mare of the Mediterranean. A clear recognition of the Miocene–Pliocene boundary remains problematic in the Orphanic Gulf area. Nannofossil assemblages in the sections suggest a higher position of the local base of the Pliocene than indicated by the level with the first appearance of planktonic and benthic foraminifera. Discontinuous occurrences of levels containing nannofossil assemblages of Zone MNN11b–c are found between the travertine unit and the lowermost Pliocene beds, representing brief marine ingressions. The latter show that in the latest Messinian, (presumably) temporary connections of Atlantic/Mediterranean waters with the Northern Aegean Basin existed. These marine ingressions likely extended further into the Eastern Paratethys, as demonstrated by the presence of nannofossil assemblages in the Middle and Upper Pontian of the Dacic and Euxinic Basins. The events around the Miocene–Pliocene transition resulted in a fairly abrupt change from brackish to open marine conditions in a relative deep basin, which was subject to increased rates of subsidence from the onset of evaporite deposition in the Late Messinian onward.

Late Miocene to Early Pliocene chronostratigraphic framework for the Dacic Basin, Romania

New magnetostratigraphic results and calcareous nannofossil data of seven sections in the Dacic Basin of southern Romania, covering the Latest Maeotian to Early Romanian time span (6.4–4.0 Ma), allow a correlation with the current Astronomical Polarity Time Scale. This establishes a chronological framework for the Pontian and Dacian stages of the Paratethys and facilitates to correlate the Paratethys stages with those of the Mediterranean. The Maeotian–Pontian boundary is estimated at 6.15 ± 0.11 Ma, within subchron C3An.1n, while the age of the Pontian–Dacian boundary is 5.30 ± 0.1 Ma, within subchron C3r. The Odessian–Portaferrian and Portaferrian–Bosphorian substage boundaries can be placed at about 6.0 and 5.6 Ma, at the base and near the end of chron C3r, respectively. Consequently, the Pontian stage has a duration of approximately 0.85 Myr and is coeval with the upper half of the Messinian stage. The base of the Dacian stage corresponds to the onset of the Pliocene and is coeval with the Pontian–Kimmerian boundary of the Euxinic (Black Sea) Basin. The Dacian–Romanian boundary is recorded either at 4.58 ± 0.05 Ma, in subchron C3n.2n (Nunivak), or at 4.25 ± 0.05 Ma in subchron C3n.1n (Cochiti). The length of the Dacian stage is therefore about 0.7 Myr or approximately 1 Ma. The transition of the Getian into the Parscovian substage can be dated at ∼ 4.83 Ma within subchron C3n.3n (Sidufjall), or at ∼ 4.55 Ma within subchron C3n.2n (Nunivak). The occurrence of calcareous nannofossil assemblages in the lower Portaferrian and near the Portaferrian–Bosphorian transition, belonging to the upper part of the Discoaster quinqueramus–NN11 Zone, and in the middle Bosphorian, belonging to the Amaurolithus tricorniculatus–NN12 Zone, indicates the presence of ephemeral marine connections between the Paratethys Basin and the Mediterranean during the Late Messinian. Another marine influx, inferred from nannofossil species characteristic of the NN12 Zone and found in lower Dacian sediments near the top of subchron C3n.4n (Thvera), post-dates the basal-Pliocene transgression of the Mediterranean Basin.

Pollen record and integrated high-resolution chronology of the early Pliocene Dacic Basin (southwestern Romania)

An integrated stratigraphic study has been performed on four early Pliocene fssections in the western Dacic Basin, including the long reference section of Lupoaia. Based on the integration of Mediterranean nannoplankton assemblages, the regional lignite stratigraphy, records of large and small mammals, large climatic fluctuations according to pollen grains, and climatostratigraphic relationships at the European scale, it has been possible to establish a magnetostratigraphic correlation of the different sections to the Geomagnetic Polarity Time Scale (GPTS). This correlation suggests that all normal episodes of the early Pliocene (from Thvera to Cochiti chrons) are recorded. Hence, the complete pollen record covers an almost continuous time span from about 5.33 to 4.30 Ma. In addition, the regional Dacian/Romanian stage boundary in the Dacic Basin is located in the Nunivak (C3n.3n) episode with an age of 4.55 ± 0.05 Ma. Our chronologic calibration, combined with high-resolution pollen data, results in a detailed record of paleoclimate in which the ∼100 kyrs and ∼400 kyrs eccentricity cycles are clearly identified.

Influence of Mediterranean sea‐level changes on the Dacic Basin (Eastern Paratethys) during the late Neogene: the Mediterranean Lago Mare facies deciphered

AbstractA recently published scenario viewing the Messinian salinity crisis as two evaporitic steps rather than one has led to a search for new indices of the crisis in the Eastern Paratethys. Fluvial processes characterized the southwestern Dacic Basin (Southern Romania, i.e. the Carpathian foredeep) whereas brackish sediments were continuously deposited in its northern part. This is consistent with previously evidenced responses of the Black Sea to the Messinian salinity crisis. High sea‐level exchanges between the Mediterranean Sea and Eastern Paratethys are considered to have occurred just before and just after desiccation of the Mediterranean. This accounts for two successive Mediterranean nannoplankton‐dinocyst influxes into the Eastern Paratethys that, respectively, belong to zones NN 11 and NN 12. Meanwhile, two separate events that gave rise to Lago Mare facies (with Paratethyan Congeria, ostracods and/or dinoflagellate cysts) arose in the Mediterranean Basin in response to these high sea‐level exchanges and located 5.52 and 5.33 Ma (isotopic stages TG 11 and TG 5, respectively), i.e. just before and just after the almost complete desiccation of the Mediterranean). These Lago Mare facies formed independently of lakes with ostracods of the Cyprideis group that developed in the central basins during the final stages of desiccation. The gateway faciliting these water exchanges is not completely identified. A proto‐Bosphorus strait seems unlikely. A plausible alternative route extends from the northern part of the Thessaloniki region up to the Dacic Basin and through Macedonia and the Sofia Basin. The expression ‘Lago Mare’ is chronostratigraphically ambiguous and should be discontinued for this purpose, although it might remain useful as a palaeoenvironmental term.

The main coal facies and lithotypes of the Pliocene coal basin, Oltenia, Romania

Abstract This paper presents the results of palaeobotanical studies correlated with coal petrography research carried out by the authors in the western part of the Dacic Basin (Oltenia) coal deposits. Of the seven coal facies that have been distinguished so far in the lignites of Oltenia, the present paper deals with the five main facies generated by: swamp deciduous forest, Carex ssp. grassy marsh, swamp with Glyptostrobus, reed swamp and aquatic macrophyte prairie. The palaeoecological and palaeophytocoenoical studies have led to the reconstruction of the factors that characterize the major coal facies.

Abstract: Sequence Stratigraphy Analysis of Depositional Successions, Depositional Environments, and 3D Building Model of the Badenian, Sarmatian and Meotian in the south - western part of the Dacic Basin 

Abstract: Sequence Stratigraphy Analysis of Depositional Successions, Depositional Environments, and 3D Building Model of the Badenian, Sarmatian and Meotian in the south - western part of the Dacic Basin 

Birth, life and death of the Pannonian Lake

The Miocene-Pliocene Pannonian Lake formed in an extensional basin system behind the compressional arc of the Carpathians. Its size and depth were comparable to those of the Caspian Sea. Subsidence began in Middle Miocene times, forming deep, pelagic basins, separated by reef-bearing ridges. Clastic influx filled the marginal basins during Middle Miocene time. Prograding deltas dissected the lake and completed the infilling of the basin system by the end of the Pliocene. Basin plain, prodelta, delta front, delta plain, beach, fluviatile, and marsh environments can be recognized. Terminal Miocene uplift of the Carpathians isolated the Pannonian region from the rest of Paratethys. The subsequent decrease of salinity resulted in the evolution of an endemic, freshwater mollusc fauna. Rich nutrient influx from rivers supported high organic productivity (dinoflagellates, diatoms, nannoplankton, foraminifers, ostracods, etc.), yielding organic-rich sediments. Preservation of organic matter was helped by a stratified water column and oxygen deficient bottom conditions. Deep burial, continuing subsidence, and high geothermal flux due to an extremely thin crust, led to the formation of commercially exploitable oil and gas accumulations. Shallow lacustrine zones of basin margins provided suitable environments for a rich Congeria-Melanopsis mollusc fauna. Wave action on beaches produced commercially exploitable pure quartz sand deposits. Taxodium and Alnus forests flourished around the lake producing enormous lignite deposits. Besides a rich land snail and mammal fauna, prehominids lived in the forests. There was a warm, temperate climate, with probably frostfree winters. Basaltic volcanoes overlooked the landscape, and maars hosted minor lakes with rich algal flora forming oil shale. The catchment area included most of the Carpathians and parts of the Apls and Dinarides. The positive water balance resulted in a supposed overflow in the southern margin, supplying exotic fauna to the South Carpathian and Dacian basins of the Eastern Paratethys. The Pannonian Lake was completely filled by the end of Pliocene. Recent lakes in the Carpathian Basin are not descendants of it.

Quelques considérations sur les genres Tyrrhenocythere (Ruggieri, 1955)et Hemicytheria (Pokornyi, 1955) (Ostracoda, Crustacea) du Néogène supérieur de la Paratéthys

We found one Tyrrhenocythere species ( T. incerta Olteanu, 1988 ) from the Upper Dacian, which is similar to a Hemicytheria species ( H. maeotica Olteanu, 1988 ) from the Upper Meotian (Dacic Basin) as regards the external morphology. Within a Tyrrhenocythere population (very unitary with respect to the external morphology of the valves) we found several specimens with radial pore canals of Hemicytheria type. We noticed that during the ontogenetic evolution of all the Tyrrhenocythere species, only the two larval stages present radial pore canals concentrated in fascicles. The younger juveniles have radial, simple, straight and rarely bifurcated canals, like the Hemicytheria valves. The number of these canals as well as the fascicles increasestowards the maturity of the individual. At the Tyrrhenocythere fresh-water species the number of fascicles (and implicity of the radial pore canals) differs even within the same population. The stability of the number of fascicles appears directly proportional to the salinity increase. The two groups of individuals, with radial pore canals of Tyrrhenocythereand respectively Hemicytheria types are separated only by the structure and number of the radial canals, the other morphological features being identical. In fact, Tyrrhenocythere is a Hemicytheria with radial porecanals concentrated in fascicles. We consider this organisation of the radial canals as a qualitativeleap, a specific adaptation, necessary in a certain ecological context. Under certain conditions of ecological instability — the case of the Kouialnikian — the ontogenetic evolution of some individuals within this population is very likely to have stopped before maturity preserving the simple radial pore canals as an undeveloped, primitive, but necessary character.