This study documents the formation of optically anomalous biaxial apatite resulting from partial fluid-mediated metasomatic alteration of pegmatitic apatite containing a britholite component. The optical anomaly was identified using a refractometer. SEM and EDX data constrain alteration conditions to interaction with acidic, oxidizing, highly saline, Si-bearing fluids at temperatures below 400–500 °C, accompanied by elevated fluorine activity. Pervasive partial metasomatic modification produced patchy compositional zoning and increased porosity within the apatite crystals. Microscale variations in F, OH, and Cl define compositional domains with differing proportions of fluorapatite, hydroxylapatite, and chlorapatite end members. These chemical differences result in variable light propagation velocities and refractive indices, giving rise to anomalous biaxial optical behavior. Single-crystal X-ray diffraction shows that all crystals retain the hexagonal apatite structure (P6₃/m). At the same time, fluid-induced apatite alteration generated non-uniform channel-site occupancies, accompanied by substitution of apatite by britholite along with the formation of vacancies in the calcium positions, and local structural distortions without symmetry lowering. The integration of optical, structural, and chemical data demonstrates that microscale compositional heterogeneity, produced by fluid–apatite interaction, is responsible for the observed optical anomaly.
This study presents new geochemical data on heavy metals and As in sediments from the Topolnitsa River catchment - a region of both historical and present-day industrial, mining, and agricultural activities. Systematic sampling, analysis, and sediment quality assessment were carried out following the EU Water Framework Directive and SIMONA project methodologies suitable for the predictive survey methods of metal contamination processes in fluvial sediment systems. The sampling of bottom and floodplain sediments, as well as a single suspended sediment sample was performed in three strategic locations along the Topolnitsa River. We explored spatial and temporal patterns in heavy metal (Cu, Pb, Zn, Cd, Hg, Ni, Cr) and As distribution in those sediments. The results showed consistently higher heavy metal loads in river bottom sediments compared with flood sediments for most elements at a given location. The top flood sediments, on the other hand, had systematically lower heavy metal contents compared with bottom flood sediments. The first monitoring point at Staria Kemer had significantly lower heavy metal concentrations for most elements compared with the other two locations (Chavdar and Petrich). On the other hand, As, Hg, Ni, and Pb contents in top flood sediments decreased from Chavdar to Petrich monitorimg points, the latter being the last location studied down the river course. Consistently high Cu concentrations in all analyzed samples indicate an ongoing and/or cycling pollution, suggesting the need for mitigation measures, as well as continued sediment monitoring.
Seventeen Neogene avian localities are documented in Bulgaria, including 12 Miocene and 5 Pliocene sites, distributed across lowland and semi-mountainous regions of both Northern and Southern Bulgaria. The known avifauna comprises 24 taxa, including three new genera — Euroceros (ground hornbill), Balcanas (dabbling duck), and Eremarida (lark) — and 11 new species, highlighting the previously underestimated diversity of Neogene birds in Southeastern Europe. In addition to its taxonomic significance, the Bulgarian Neogene avifauna provides important insights into paleornithogeographic patterns in the Eastern Paratethys region. The composition of these assemblages indicates faunal affinities with both Western Eurasian and, to a lesser extent, Asian provinces, supporting the role of the Balkan region as a biogeographic corridor during the Neogene. In a broader context, Bulgarian fossil birds represent a small but non-negligible fraction of the global Neogene avifauna, accounting for approximately 1.0 % of known taxa. Their stratigraphic distribution and taxonomic composition, however, suggest that the region preserves key evidence for avian dispersal and diversification in Southeastern Europe. These findings emphasize the importance of the Balkan Peninsula as an underexplored area with significant potential for refining Neogene avian paleobiogeography.
The Palaeozoic metamorphic basement hosting the Upper Cretaceous Elatsite porphyry-copper deposit in the Etropole Mountain consists of a greenschist facies fine-grained silicate to carbonate-silicate sedimentary sequence further affected by contact metamorphic transformations in a tide aureole next to the Upper Carboniferous Vezhen pluton. Field and petrographic observations distinguish alternating phyllite, chlorite-sericite-biotite, chlorite-sericite, and chlorite-sericite-calcite schists with chlorite and biotite porphyroblasts, and local carbonate and sulfide saturation. Their trace-element patterns, including LREE enrichment (LaN/SmN = 2.6–4.4), negative Eu anomalies (Eu/Eu* = 0.6–1.0), and low Zr/Sc–Th/Sc ratios indicate a felsic continental provenance with limited sediment recycling and deposition in a continental island-arc setting. Elevated Sr (up to 794 ppm) reflects primary carbonate input, while localized Cr-Ni enrichment (up to ~900 ppm and 440 ppm, respectively) is linked to Fe-oxides and sulfides rather than to a mafic protolith. U-Pb detrital zircon geochronology reveals two major age clusters, Neoproterozoic zircon cores (600–580 Ma) and Carboniferous zircon metamorphic rims (340–330 Ma), together with minor presence of younger Late Ordovician–Early Devonian ages (414–411 Ma). The obtained age of a hydrothermal rutile of ~100 ± 36 Ma records the influence of the Cretaceous hydrothermal activity on these rocks. All these data point to a complex evolution of the studied metamorphic basement including: (1) post-late Neoproterozoic sedimentation which continued up to Early Devonian, (2) mid Carboniferous greenschists facies metamorphism and late Variscan contact metamorphic transformations, and (3) Cretaceous hydrothermal overprint related to the porphyry-copper hydrothermal alteration and mineralization. These features suggest that the metamorphic basement of the Elatsite porphyry-copper deposit acted as a structurally and chemically active constituent, providing pathways for movement and sources of components for the hydrothermal fluids during the Late Cretaceous magmatic-hydrothermal activity.
The Circum-Rhodope Belt is a major tectonic unit that surrounds both the Rhodope and the Serbo-Macedonian zones of the Alpine orogen in the northern Aegean region. The arc-related, supra-subduction zone Evros ophiolite represents the most important crustal element in the eastern part of the Circum-Rhodope Belt. A new U-Pb LA-ICP-MS zircon magmatic crystallization age of 174.6 ± 1.8 Ma obtained for the Agriani gabbro, together with the reviewed crystallization ages of other magmatic bodies reveal that the magmatic history of the Evros ophiolite spans 176 Ma to 169 Ma time interval. Reviewed ages of the medium to lowtemperature cooling history from 550 °C (40Ar/39Ar amphibole) down to 120 °C (fission-track apatite) show that it immediately followed the magmatic crystallization starting around 174 Ma and continued up to 140 Ma for the Evros ophiolite.
This publication considers the geological settings, distribution, mineral paragenesis, chemistry and physical properties of alabandite from Bulgarian ore deposits. At present, it has been established in 8 deposits. Seven of them are vein-type lead-zinc deposits located in SW Bulgaria, related to Paleogene magmatic activity. These are: Rouen, Shapka, and Tsarni Kamak, belonging to the Rouen Ore Field and Belevitsa, Metlivko, Erma River and Yurukovi Kolibi, belonging to the Madan Ore Field. One occurrence of alabandite belongs to the manganese deposit Obrochishte located in NE Bulgaria, northeast of the city of Varna, hosted in Oligocene sediments. Alabandite from the SW Bulgaria lead-zinc deposits is associated with quartz-rhodonite-galena-sphalerite veins and metasomatic bodies controlled by fault structures with a northwest and west-northwest trend or by zones of cataclasis with a west-northwest trend. The ore veins are hosted in high grade metamorphites and Tertiary rhyolite (Madan ore field) and metamorphites and Tertiary granite-porphyry stocks and dikes (Rouen ore field). In these deposits, alabandite is deposited in two mineral paragenesis: early – quartz-sphalerite-galena with alabandine I, imposed on massive quartz-johansenite-rhodonite skarns and late – quartz-carbonatesilver with alabandite II. In the Obrochishte deposit, alabandite participates in a paragenesis, described as alabandite-rhodochrosite-barite with manganocalcite, hauerite and chalcedony. Based on the macroscopic color, chemistry and color in reflected light, the alabandite from SW Bulgaria (Madan Ore Field) is identified as ferroalabandite with iron 2.60 to 5.60%, and that from the Obrochishte deposit – represents pure MnS with a grassy green color and pronounced internal greenish and brownish reflexes. The two types of alabandites are characterized by different microhardness, reflectance and character of the reflection spectra. Their origin is explained, respectively by hydrothermal alteration of quartz-rhodonite-johansenite skarns and by diagenetic – volcanogenic – hydrothermal deposits during the Oligocene in the Black Sea manganese province.
Floods and landslides are among the most significant natural hazards in Bulgaria, posing substantial risks to human life, infrastructure, and the environment. This study aims to assess the risks associated with these hazards, focusing on their frequency, intensity, and impact on human settlements, infrastructure, and the environment. The main goal of the research is a comparative analysis between two of the most recognized methodologies for risk assessment. We implemented the framework in two adjacent coastal municipalities in southeastern Bulgaria. This study is focused on summer storms and landslides. The framework acknowledges that summer storms comprise several natural hazards, including high winds, storm surges, and significant precipitation levels. The impact of natural phenomena, such as landslides induced by substantial rainfall or severe storm surges, is also taken into account. The current approaches rely on established methodologies from international organizations and institutions, such as the Inter-American Development Bank (IDB), United Nations International Strategy for Disaster Reduction (UNISDR), and Joint Research Center – European Commission (EC-JRC). These approaches stress the significance of risk assessment and locally specific management plans. The findings point out that it requires integrated, multidisciplinary approaches to address the growing challenges posed by natural hazards in an increasingly uncertain environment. These methods not only improve our comprehension of risk factors but also make it easier for different stakeholders to work together.
A developed model translates lithology into expected concentrations of 40K, 238U-series, and 232Th-series progeny using literature-based transfer functions, and subsequently converts these concentrations into ambient dose equivalent rates. The outdoor radiation background across the territory of Bulgaria was assessed theoretically and mapped in terms of expected gamma dose rates and previously evaluated geogenic radon potential. The results highlight regional-scale variations associated with granite and metamorphic units (elevated values), consolidated and semi-consolidated sedimentary rock (suggested low values), and localized anomalies related to uranium-bearing formations. The model outputs will be validated against data from a planned national survey conducted in the framework of a fundamental scientific project. This integrated, geology- driven approach provides an effective baseline for future evaluation of outdoor radiation background, using integrated systems radiation surveys in Bulgaria.
In latest Tithonian times, in the Crassicollaria colomi Subzone, dominant Crassicollaria species suffered a decline. Next, the ultimate calpionellid crisis occurred in the Calpionella alpina Subzone, where practically nothing, but the taxon C. alpina, survived. The same succession of calpionellid associations and the same crisis has been demonstrated in all continents in a large body of literature, as we illustrate it herein. The event, and the base of the Alpina Subzone that it marks, is the outstanding level for definition of the Tithonian/Berriasian (J/K) boundary. This level is also close to the original top of the “Portlandian”, d’Orbigny’s topmost Jurassic stage. And, in Tethys, close above the ammonite level (Jacobi Subzone) that was previously used to define the boundary. In the Jacobi Subzone, the appearance of the ammonite genus Delphinella acts as a proxy for the base of the calpionellid Alpina Subzone. In the Caribbean and Mexico, the Alpina Subzone is also proved. In the Andes, the Alpina subzone’s base lies close to the base of the ammonite Substeueroceras koeneni Zone, and it is marked by the last appearance of Calpionella elliptalpina, as it is at sites in Tethys. No other boundary level that has been suggested in the J/K interval has such a strong primary marker, and no other has so many proxies to support it.
The interaction of Ge-containing solutions with solid fossil fuel samples confirm its organic mode of occurrence. Based on the maximum sorption capacities, the samples follow the order: vitrain and xylain > peat (Romania) > bituminous coal > peat (Belarus) > lignite > semifusain. The results show the dependence between the sorption capacity of the studied samples and the pH medium, as well as the time of soaking. It was found that Ge is strongly associated with organic matter.
