VOLUME 52 (3)/December 2023

Groundwater vulnerability to contaminant infiltration from the surface, and to state deterioration, is related to the spatial distribution of rocks with diverse porosities, flow characteristics and unsaturated zone thickness. For the present regional assessment of groundwater vulnerability, it is considered most appropriate to adopt a method based on spatial differences in the geological and tectonic, and related hydrogeological, conditions in Bulgaria. The objective of the present study is to compile a vulnerability map of the unconfined groundwater in the country. This groundwater type is very important for drinking water supply, and it is at the highest risk of contamination. The groundwater on the territory of the Republic of Bulgaria has been divided into seven vulnerability classes, based on the corresponding hydrogeological units. The map is based on the geological map of Bulgaria in scale 1:100 000. It shows that groundwater is of low vulnerability over a large part of the country’s area (57%). Medium to medium-high groundwater vulnerability is defined for approximately 31% of the total area, while high and very high vulnerability are defined for 7% and 5%, correspondingly.

Early Jurassic U-Pb age is obtained for both foliated and undeformed granites on Horseshoe Island, Antarctic Peninsula. Some microstructures in the foliated granites/orthogneisses indicate high-temperature greenschist or low- to medium-temperature amphibolite facies deformation conditions. Additionally, a Late Cretaceous age is yielded for a gabbro intruding the deformed granitoids.

The possibility of occlusion in melts of useful components of some of the most economically advantageous materials, obtained during zeolitization of fly ash – Na-X, sodalite and cancrinite, was investigated. A very high degree of occlusion of ZnCl₂ in zeolite Na-X was achieved along with complete exchange of Na extra framework cations with Zn²⁺. By elution, it was proved that, in the interaction of zeolite Na-X with ZnCl₂ melt, occlusion takes place without destroying the zeolite aluminum-silicate framework. In a KNO₃ melt, in the narrowest pore structure – the sodalite structure, occlusion does not proceed, only ion exchange occurs. Through computer modeling, the ion exchange of both the charge-balancing cations and the synthetically incorporated cation-anion pairs has been proven. The interaction of cancrinite-SO₄ with a KNO₃ melt results in the formation of a material with an altered cationic composition and occluded KNO₃, which gradually comes out of the structure upon elution. The results obtained in the work can be a basis for the development of future applications of the modified minerals as materials with antibacterial properties (occluded ZnCl₂ in the structure of zeolite Na-X) and as slow-acting fertilizers or micro-fertilizers (occluded with KNО₃ cancrinite and sodalite forms).

The Lower Cretaceous to Miocene South Shetlands Islands’ volcanic arc is a result of the subduction of the Phoenix Oceanic Microplate (part of the Pacific Plate) beneath the Antarctic Peninsula. The magmatic activity on Livingston Island has been going on for a long time: since the Early Cretaceous to the present. The evolution of the volcanic arc resulted in the formation of various sedimentary basins and paleoenvironments (turbiditic to shallow marine and continental) that formed varied sedimentary successions and tholeiitic to potassium calc-alkaline subduction-related magmatic rocks. Considering the magmatic activity on Livingston Island, a general trend of rejuvenation can be observed from the WNW (Byers Peninsula) to the ESE (to Hannah Point, Point Williams and further to the Hurd Peninsula and the Tangra Mountain). The rejuvenation of the magmatic rocks in the direction of the thrust plate can be explained as an effect of a flattening subduction that was active from the Early Cretaceous (135 Ma) up to around 90–70 Ma. The mixed ages of the dikes and small intrusions in the Hurd Peninsula are most probably due to periods of rotation and probably beginning of а slab-roll back. A regional Paleocene–Eocene (65–47 Ma) compressional episode that caused a low temperature to high-pressure metamorphism is registered on Smith and Elephant islands. The regional metamorphism was followed by a vast extension between 50–30 Ma that culminated with the opening of the Drake Passage around 34–30 Ma. The magmatic response of that regional scale extension was the intrusion of the Eocene Barnard Point Pluton (46–40 Ma) and dikes with youngest ages of around 30 Ma. The major uplift phase and the exhumation of the Tangra Mountain happened between 22–16 Ma as indicated by the Ap FT thermochronology. The last magmatic event on the island produced the contrastingly different in composition Quaternary alkaline mafic rocks that occupy the area between Innot Point and Burdick Peak. This episode is interpreted as related to a process of crustal extension that culminated in asthenospheric upwelling and rifting along the Bransfield Strait. The latter is due to a slab roll-back that led to the break-up of the South Shetlands from the Antarctic Peninsula and consequent subduction termination.

Inoceramid data were used to characterize the lower Maastrichtian strata in the Western Fore-Balkan (Bulgaria), based on the newly discovered Oslen Krivodol section. The upper part of the Kunino Formation yielded a well-defined inoceramid-bearing level. A number of characteristic taxa make up the inoceramid assemblage, including Cataceramus palliseri (Douglas, 1942), C. subcircularis (Meek, 1876), C. barabini (Morton, 1834), C. glendivensis Walaszczyk, Cobban and Harries, 2001 and Endocostea typica Whitfield, 1880. Additionally, Trochoceramus spp. and “Inoceramus” sp. were also found. It is, therefore, assumed that both the Endocostea typica Zone and an undetermined (probably lower) part of the Trochoceramus radiosus inoceramid Zone are present in the section. It is also assumed that there is a mixing of faunas due to low sedimentation rates and local submarine washout.