Romanian Black Sea Shelf Research Articles

Three new species of Gromia (Protista, Rhizaria) identified from the Romanian Black Sea shelf

The protist genus Gromia was first described in 1835 by Dujardin and while gromiids are prominent in the marine environment, Gromia oviformis was, for a long time, the only valid species regularly recorded. To date, 16 species that are morphologically and/or genetically distinct have been described. While recent studies are documenting their diversity and their ecological importance, G. oviformis has been the sole gromiid species identified in the Black Sea, although unnamed Gromia species have also been recorded. We collected sediment samples from the Romanian continental shelf at varying depths (48 – 58 m) to study the morphological and genetic diversity of gromiids in this part of the Black Sea. Three new species, Gromia bugnae sp. nov., Gromia dianae sp. nov. and Gromia fabi sp. nov., were identified based on an integrative taxonomic approach, thus bringing the total described gromiid species to 19. Analysis of partial SSU rRNA gene sequences confirms that these are distinct species. Additionally, an undescribed species is represented by a sequence from the northern part of the Black Sea (Sevastopol, Kazachya Bay). The study provides further evidence of the diversity of gromiids in the Black Sea and underlines the importance of this little-known group in marginal seas.

ROLE OF ENVIRONMENTAL PARAMETERS IN THE DISTRIBUTION OF MEIOBENTHIC FAUNA (OSTRACODA AND FORAMINIFERA) IN THE ROMANIAN BLACK SEA SHELF

With limited research undertaken on the distribution and biodiversity of meiobenthic fauna (living Ostracoda and Foraminifera) in the Black Sea, the present study has focused to create the baseline data for the Romanian Black Sea continental shelf. For this purpose, 9 short core samples were collected using a multi-corer in water depth ranging from 27.8 m to 41.8 m in May 2018 around the Sf. Gheorghe area (map sheet L35-120B). A total of 14 species were found belonging to Ostracoda (7 families), Cercozoa (one family), Foraminifera (5 families). The highest density of meiobenthic species was correlated with the highest concentration of CaCO3 where the substrate is dominated by a clayey silt or sandy silt while TOC concentrations were negatively correlated with the low densities occurring in the western part of the perimeter silt clay substrate is found. The density of soft-shelled foraminifera has a positive correlation with the concentration of salinity in the bottom water samples, and depth and a negative correlation with the bottom water temperature. The density of Ostracoda has a positive correlation with temperature and depth but a negative correlation with salinity in the bottom water samples. The relationships between high concentrations of CaCO3and increased abundances of meiobenthic fauna and high concentrations of TOC and low meiofauna abundances, respectively, reinforce the hypothesis according to which the dispersal of meiofaunal species is strongly influenced by environmental gradients. The data collected from Romanian Black Sea Shelf (Sf. Gheorghe Area) in the perimeter of the map sheet L35-120B, suggest another record of soft shelled monothalamous Foraminifera and Gromiidae group.

New records of soft‐shelled monothalamous Foraminifera and gromiids on the Romanian Black Sea shelf

The current study reveals the presence of both “soft-shelled monothalamous” Foraminifera (Saccamminidae and Allogromiidae families) and Cercozoa (Gromiidae family) for the first time in the studied areas of Sulina, Sf. Gheorghe, Portița, Constanța, Tuzla and Mangalia. The investigated areas are located from North to South, belonging to the Romanian continental shelf of the Black Sea. The samples transect ranged from shallow to deep water between 19.5 and 149 m depth. The measurement campaign was conducted in three consecutive years, 2017, 2018 and 2019 with the GeoEcoMar’s research vessel Mare Nigrum. The main objective of this contribution is to present the taxonomic composition of soft-shelled monothalamous foraminiferans and gromiids and their spatial distribution in the Romanian Black Sea shelf. In the Black Sea, soft-shelled monothalamous foraminiferans and gromiids are poorly documented and few species have been described. Some of these species may be new to science. Therefore, further analysis is required, encompassing both morphological and molecular criteria, for an accurate identification of these taxa.

GAS ESCAPE FEATURES ON THE ROMANIAN BLACK SEA SHELF – EXAMPLES FROM 2D SEISMIC INTERPRETATION

Gas escape features are a common presence on any young sedimentary basins where large amounts of organic-rich sediments are deposited within a short time. The fast burial process conducts to maturation and carbonization of the sedimentary organic matter by bacterial and, later, by temperature transformations. The Black Sea is one such basin, where numerous shallow gas accumulation and gas escape features were observed and analyzed, ranging from gas hydrates, gas chimneys, flares, and mud volcanos. The study of such geological phenomena is important for identifying present seabed geohazards, and nonetheless for hydrocarbon exploration. Our study integrates newly acquired 2D high-resolution seismic lines, further used to correlate the gas escape features and their relationship with deep-seated faults, such as Peceneaga-Camena, and petroleum system of the Romanian Black Sea Shelf area. Our results show that in the studied area the gas escape features are confined into the Pliocene-Quaternary sequence, hence not related to Peceneaga-Camena Fault or to a deeper thermogenic petroleum system, and most probably, the gas is sourced from the shallower biogenic system.

Rhaetian (Late Triassic) ostracods (Crustacea, Ostracoda) from the offshore prolongation of the North Dobrogean Orogen into the Romanian Black Sea shelf

The present study evaluates the significance of Triassic ostracods from the Romanian Black Sea shelf as part of a project for the understanding of the palaeoceanographical evolution of the offshore extension of the North Dobrogean Orogen. The drill core CM31, sampled from the borehole 817 Lebăda Vest drilled on the western Romanian portion of the Black Sea shelf, contains sediments of Rhaetian, Late Triassic age. The taxonomy of ostracods obtained is discussed and adds to the scientific understanding of marine ostracods during the Rhaetian stage. We document 72 species, of which seven are new: Histriabairdia pontuseuxinusensis Forel gen. et sp. nov., Bairdiacypris argonautaii Forel sp. nov., Ceratobairdia? akhilleusi Forel sp. nov., Isobythocypris atalantella Forel sp. nov., Petasobairdia amazonella Forel sp. nov., Paracypris ovidi Forel sp. nov. and Pseudomacrocypris? kerabani Forel sp. nov. Histriabairdia Forel gen. nov. is introduced to accommodate species of the Triassic–Jurassic interval previously attributed to the modern genus Anchistrocheles. These assemblages point to an outer shelf environmental with relatively normal marine oxygenation. The oldest occurrence of Pokornyopsis, found in this material, indicates that this forerunner of modern troglobitic ostracods may not have been troglobitic in the Triassic.

MORPHOLOGICAL DEFORMITIES IN BENTHIC FORAMINIFERA TESTS AS INDICATORS OF MERINE ENVIRONMENTAL STRESS UNDER THE FRESHWATER RUNOFF

Problem Statement and Purpose. This article represents the results of studying the lateral distribution of morphological deformations in foraminifera shells on the Roma­nian shelf of the Black Sea in connection with the influence of the freshwater inflow of the Danube River. In comparison with other organisms, features of the morphology and life cycle of benthic foraminifera offer a number of advantages for this kind of study, allowing using them to be readily used as indicators of various conditions in marine ecosystems. The purpose of this project is to study morphological features of foraminifera in connection with the influence on them of river inflow.Materials S Methods. The study area includes the northwestern part of the Black Sea shelf adjacent to the Romanian part of the Danube delta. Seventeen stations were sampled on-board the Romanian research vessel «Mare Nigrum» on 3-7 May 2012 (Cruise MN-103) within the framework of the WAPCOAST project. Sediments were recovered by 0.1 m2 Van Veen Grab. For foraminiferal analysis, the sediment samples were recovered by grab from undisturbed surface (0-2 cm) sediment. All specimens were morphologically examined and taxonomically identified. Examples of all spe­cies were imaged using Scanning Election Microscopy (SEM) at the University of Manitoba. Winnipeg. Canada.Results. 15 species of benthic foraminifera were recovered. Deformations were found in 6 species: Ammonia tepida, Ammonia compacta, Ammonia ammoniformis, Porosononion subgranosus mediteiraniens, Nonion matagordanus, and Canalifera parkerae. After statistical analysis, only 3 species gave significant correlation coef­ficients with parameters of the bottom environment: Ammonia tepida, Porosononion subgranosus mediterranicus, and Nonion matagordanus. There are two main types of abnormalities: simple and combined. The basic simple deformations are "tumors" on test chambers, breaking the spiral of the test. "Siamese twins." (accreted tests), underdevelopment and swelling of the test. In the article, only simple deformations are considered. The most common simple deformations for all the species encountered were tumors. Most often, these appear in the species Ammonia tepida. The taxonomic diversity and quantitative characteristics of foraminifera on the Romanian Black Sea shelf suggest three main factors at work. Factor 1 (the main one) is the distance from the coast. The second most significant is Factor 2, which is the eutrophication of the water column. Factor 3 is anthropogenic pollution of the bottom layer of water that enters the study area from the Danube.The Danube River creates stressfiil conditions for the individual development of A. tepida and P. subgranosus mediterranicus, and. accordingly, it may cause the morphological deformations. Deformations of the "Siamese twins" type can be used as indicators of deterioration hi the oxygen regime of the basin, and the swelling of the tests - an excess of nutrients. The findings are consistent with the results of previous studies that have shown that freshwater drainage causes stress in marine ecosystems.

The geological history of the Istria ‘Depression’, Romanian Black Sea shelf: tectonic controls on second-/third-order sequence architecture

Abstract The Istria ‘Depression’ or sub-basin of offshore Romania lies at the intersection of the trans-European Tornquist–Teisseyre ‘Zone’ and the Black Sea back-arc basin, just outboard of the East Carpathian orogenic welt. Its Late Mesozoic–Cenozoic succession records an extraordinary polyphase history of subsidence and sedimentation, interrupted by several quite spectacular second-/third-order erosional unconformities, reflecting the interplay between these tectonic domains. The unconformities divide the succession into a number of stratigraphic sequences. The sub-basin first developed as a transtensional rift in the Triassic–Early Jurassic, evolving into a narrow oceanized trough in the later Jurassic. This was tilted west during the Early Cretaceous, and the residual Late Jurassic topography was filled and buried by a west-facing clastic–evaporite wedge. Following Late Aptian–Albian(?) rifting, post-rift subsidence and spreading in the Western Black Sea imposed a strong easterly tilt, encouraging the partial evacuation of its Early Cretaceous sedimentary fill by gravity-driven mass wastage. The incised valley topography was subsequently infilled and buried during the later Cretaceous and Early Cenozoic. During the mid-Late Cenozoic, the Black Sea Basin experienced intermittent periods of partial to complete isolation from the world ocean and significant base-level drawdown. The first major sea-level fall occurred in the Eocene when the Istria ‘Depression’ was deeply incised, to be healed by Oligocene shales during the subsequent rise. Yet another period of drawdown and exposure occurred in the mid-Miocene, with extensive shelf-margin mass wastage and erosion, followed by re-flooding and deposition of a transgressive backstepping sequence in the middle-late Miocene. Messinian drawdown in the Mediterranean caused a further period of isolation and falling base level. The shelf margin was again exposed, and experienced widespread mass wastage and slumping. Rising sea level eroded the earlier slumped sequence and the margin was healed by a lowstand prograding wedge in the late Miocene–early Pliocene. This was followed by shelf sedimentation in the Plio-Pleistocene periodically interrupted by canyon-incision events, testifying to continued climatically or tectonically imposed base-level fluctuations. Several direct and indirect tectonic factors were responsible for valley/canyon incision within the Istria Depression and erosion of the Romanian Black Sea shelf margin. These include: (1) the local structural framework; (2) direct tectonic uplift and tilting; and (3) more indirect tectonically imposed isolation encouraging significant base-level falls.

Emiliania huxleyi fluctuation and associated microalgae in superficial sediments of the Romanian Black Sea shelf

Emiliania huxleyi fluctuation and associated microalgae in superficial sediments of the Romanian Black Sea shelf

Holocene ostracod and foraminiferal assemblages of the Romanian Black Sea shelf

Qualitative and quantitative study of the ostracod and foraminiferal assemblages were performed on two cores, around 0.30 m depth bsf in thickness, collected from the Romanian Black Sea shelf. The lithology of the studied cores is characterised by grey and black muds, topped by a centimetre thick fluffy mud layer. One of the cores, MN 103_09, is placed on the Romanian inner shelf, at water depth of 17.80 m. The sediments of this core contain very few and small bivalve fragments and no gastropods. In this core, the ostracod and foraminiferal assemblages are influenced by a quite high-energy environment, due to the Sulina arm of the Danube Delta. This feature is mirrored in the poor preservation and low abundance of the species, as well as the mixed Caspian and Mediterranean character of the ostracod assemblages. The other studied core, MN 103_04, is situated on the Romanian outer shelf, at a water depth of 78 m. Its deposits commonly contain gastropods and bivalves, as well as microfauna displaying a low diversity and a very high abundance; the character of the ostracod assemblages is a Mediterranean one. Overall, the identified microfaunas of the two investigated cores reflect the environmental conditions of modern and/or latest Holocene sea-floor assemblages and their relationships to salinity, sediment input and water depth. Even the depositional time of the 30 cm cored interval in the two studied cores is quite different, i.e., possibly several hundreds of years, up to 1000 years, on the inner shelf and several thousands (from 3000 BP to the Present), in the outer shelf, the results are indicative for modern Black Sea conditions. A stable marine environment with a salinity around 17–18‰, comparable with the present one, could be assumed for the whole cored interval of the Romanian shelf. Besides, the age structure, i.e., the ratio between adults and juvenile taxa of ostracod population in the outer shelf indicates a moderate to high energy autochthonous thanatocoenosis, with some post-mortem disturbance by currents. By contrast, the ratio between adults and juvenile ostracod taxa in the inner shelf mirrored a taphocoenosis with post-mortem disturbance, sorting and transport. This assemblage, dominated mainly by disarticulated valves of juveniles, does not represent the environment in which the ostracods lived.

Maleimides in recent sediments – Using chlorophyll degradation products for palaeoenvironmental reconstructions

Maleimides (transformation products of chlorophylls and bacteriochlorophylls) were studied in recent sediments from the Swiss lake Rotsee and the Romanian Black Sea Shelf to investigate chlorophyll degradation, the role of oxygen in maleimide formation, and to identify their sources. Naturally occurring maleimides (i.e. “free” maleimides) and maleimides obtained after chromic acid oxidation of sediment extracts (i.e. “bound” maleimides) were analysed. 2-Methyl-maleimide (Me,H maleimide), 2,3-dimethyl-maleimide (Me,Me maleimide), 2-methyl-3-vinyl-maleimide (Me,vinyl maleimide), 2-methyl-3-ethyl-maleimide (Me,Et maleimide) and traces of 2-methyl-3-iso-butyl-maleimide (Me,i-Bu maleimide) occurred naturally in the sediment with a large predominance of the Me,Et homologue. Tetrapyrrolic pigments related to chlorophylls were the main source of maleimides, although variable contributions of other sources such as cytochromes and/or phycobilins cannot be completely ruled out. The predominant Me,Et maleimide and Me,vinyl maleimide most likely originate mainly from chlorophyll a related pigments. The same holds for Me,H maleimide, which might be formed following degradation of ring E from the tetrapyrrolic nucleus. Alternatively, Me,H maleimide and Me,Me maleimides might be formed by a recently discovered transformation pathway involving the oxidation of vinylic chlorophyll substituents and the formation of an aldehyde intermediate. 2-Methyl-3-n-propyl-maleimide (Me,n-Pr maleimide) and Me,i-Bu maleimide arising from bacteriochlorophyll related pigments traced the presence of phototrophic sulfur bacteria (Chlorobi), indicating photic zone euxinic and anoxic conditions in Rotsee during the last 150years and throughout the Black Sea history, including the limnic phase of the Black Sea (Unit 3). Some other minor maleimides with specific alkylation pattern also originate from bacteriochlorophylls, while the source of others could not be identified. Free maleimides were mainly formed in the sediment in the absence of oxygen. Novel maleimide degradation indices are proposed to estimate the degree of OM degradation (OM freshness/degradability). These proxies are applicable on longer timescales than e.g. the chlorin index.

Holocene litho- and biostratigraphy of the NW Black Sea (Romanian shelf)

Detailed lithological and micropaleontological studies were performed on several cores from the Romanian Black Sea shelf, located in front of the Danube Delta, in front of the Razelm–Sinoe lagoonal complex, close to the Eforie beach, as well as on the Romanian inner shelf. All the studied cores are situated at a water depth varying between 12m and 67m. The purpose of the investigations was to reveal Upper Holocene lithological changes and the associated calcareous nannoplankton fluctuations in a very shallow marine setting such as the Romanian Black Sea inner shelf. The youngest Holocene unit or “Shallow Unit” is composed of alternating sequences of mud, silt, clay and coquina layers, containing marine mollusc faunas. The upper part of the Shallow Unit contains blooms of the nannoplankton species Emiliania huxleyi, while its lower part yields, besides common E. huxleyi, rare specimens of Braarudosphaera bigelowii. The Shallow Unit overlies a “shell hash layer”, mainly made by coquinas, containing mixing marine and brackish mollusc faunas. Towards the upper part of this level, monospecific assemblages with B. bigelowii were observed in a layer rich in carbonate acicular crystals. The Shallow Unit partly corresponds to the Unit 1 (finely laminated coccolith ooze) and Unit 2 (sapropelic sediments) of slope and basinal settings of the Black Sea. The layer rich in carbonate acicular crystals could be a shallower equivalent of the oldest layer of aragonite bands placed at the lower part of the Unit 2 in deep parts of the Black Sea. In the analyzed cores, the oldest lithological unit (Unit 3, the muddy clay sediments deposited in a brackish to freshwater environment) is characterized by the deposition of green-yellowish clay devoid of any Holocene calcareous nannoplankton species and containing brackish mollusc faunas. Based on nannofloral fluctuations, an increasing salinity from the base towards the upper part of the Shallow Unit may be supposed, together with the progressive establishment of a stable marine setting, similar to today.

Seismic sequence stratigraphy, structure and subsidence history of the Romanian Black Sea shelf

Abstract The Black Sea is an extensional back-arc basin developed along the northern active margin of the Tethys Ocean which was subducted northward from the Triassic to Miocene times. The Romanian Black Sea shelf is dominated by mid-Cretaceous extensional structures and their sedimentary cover, subsequently affected by Cenozoic compression. Here we analyse the post-Oligocene structural and sedimentological evolution of the shelf, based on Romanian oil industry data consisting of (1) 5300 line-km reflection seismic profiles situated on the shelf and continental slope; and (2) depth and lithostratigraphic information from 60 boreholes on the shelf. Our study provides evidence for a changing evolution of the shelf during a relatively short period of time directly related to the pre-Miocene period and the evolution of the Romanian onshore. Mio-Pleistocene subsidence of the Romanian Black Sea shelf is highly variable and is directly dependent on sediment input, tectonic activity as well as water-level fluctuations. Subsidence during the Badenian–Sarmatian and the Dacian–Quaternary was limited. In contrast, during the Pontian, shelf subsidence was progressively faster in the basinward direction. Subsidence on the outer shelf was much more significant than elsewhere on the shelf. Tectonically, the most active period during the Mio-Pleistocene was the Pontian. The Badenian–Sarmatian was largely quiescent and the Dacian–Quaternary saw a decrease in the Pontian tectonic activity, coming possibly even to a halt. From a sequence-stratigraphical point of view, eight systems tracts were identified for the Mio-Pleistocene sedimentary section. The Badenian-Sarmatian unit was attributed to a HST (highstand systems tract). The Pontian unit was subdivided into P1, P2, P3 and P4. Subunit P1, which was laid down on the slope at the time of deposition, is progradational and attributable to the lowstand wedge of a LST (lowstand systems tract). Subunit P2 is likewise also attributed to a LST, having the continental slope and the deep basin as palaeo-depositional environments. The reflection terminations and the wedge-shape of P3 suggest that it was deposited in the deep basin during a sea level lowstand. The next transgressive systems tract (TST) and HST developed during the deposition of P4. The boundary between P4 and the Dacian is represented by an erosional hiatus, which comprises the LST that follows the formation of the sequence boundary at the end of the Pontian. During the Dacian–Quaternary, the subsequent TST and HST were deposited on the inner and middle shelves. Sedimentation on the Romanian shelf during the Mio-Pleistocene period was thus strongly influenced by sediment input and subsidence, while sea level fluctuations played a lesser role. As sediment input is related to the evolution of the adjacent land and subsidence is dependent on sediment supply, tectonic activity and sea level fluctuations, these two factors are not totally independent.

Stratigraphic and structural characteristics of the Romanian Black Sea shelf

The Western Black Sea basin opened during Cretaceous times by back-arc rifting in association with a north dipping subduction at the rear of the Cretaceous–Early Tertiary Pontide volcanic arc. The sedimentary wedge developed on the shelf of the Romanian Black Sea sector reflects a complex interplay between large scale rifting, uplift of the orogenic flanks, large-scale post-rift subsidence and sea level changes. We examine the detailed structural configuration of this sector for a regional correlation with the adjacent offshore in Ukraine and Bulgaria. The evolution of the western Black Sea basin started in the Albian–Cenomanian times, when two extensional phases with significantly different directions (N–S and subsequently E–W) lead to the formation of a complex interplay between isolated blocks organised in horsts and grabens generally deepening eastwards. Superposition of normal faults footwall blocks from the two extensional episodes generated a deeply subsided area with enhanced accommodation space, i.e., the Histria Depression, and, consequently, recorded a larger thickness of Paleogene sediments in the post-rift stage. (Re)activation of faults and associated folding reflects repeated inversion during the Late Cretaceous–Oligocene times, associated with subsequent periods of non-deposition and/or erosion during moments of basin fill exposure. These periods of inversion recorded in the Black Sea are controlled by coeval orogenic deformations taking place in the Balkans, Pontides and the Crimean thrust belt. Sea level fluctuations during the Neogene and late Alpine tectonics in the neighbouring orogens caused massive sedimentation followed by sediment starvation and/or significant erosion. Large thicknesses of sediments accumulated during the Pontian, presumably associated with an extensional episode deepening the distal parts of the basin and with differential compaction structures. The interpretation of a high-quality seismic dataset combined with published data allowed the correlation of major structural units and lineaments defined onshore towards the Carpathians with the ones deeply buried below the western Black Sea basin sediments. Unit correlations are furthermore used to derive an integrated tectonic image of the western Black Sea area.

The Geotectonical Framework of the Romanian Black Sea Shelf and Its Position in the South - East Europe  :ABSTRACT

The Geotectonical Framework of the Romanian Black Sea Shelf and Its Position in the South - East Europe  :ABSTRACT