D. Tugolesov, A. Gorshkov. L. Meisner. The Black Sea Basin ancient slopes and associated breakes and unconformities. The structure of the basin's slopes is interpreted as a huge flexure which has been developing throughout alI Cenozoic. The basin is filled with a thick series of Paleocene to Quaternary deposits without apparent signs of breaks. A thin but stratigraphically relatively complete column of Cenozoic marine deposits is determined above the slope brow on paleoshelves. So, in the mode of occurrence of any Cenozoic series taken separately, a flexure is distinctly outlined, its common limb coinciding with the slope of the basin. Within the dropped side of the flexure (in the basin), each series is several times thicker than the synchronogenic series within the upper side (on the shelf). At the slope of the basin, each series thins out reaching zero thicknesses at the limit. Narrow tortuous zones of no deposits shift upslope with rejuvenation of deposits and merge into a single variable-age unconformity surface appearing as a common surface at the seismic section. Such structure of the slopes points to their underwater consedimentational washout and to the existence of a deep-water basin throughout all Cenozoic era. There are observed numerous particular differences in the character of the slope, steps at various levels, numerous local breaks in thin strata above the slope brow, gradual transitions along the strike from steep areas of the slope to gentle sloping ones, thick clinoforms of paleodeltas and submarine fans.
The present paper reports for the first time the presence of representatives of the ammonite subfamily Venezuellinae Kvantaliani in the Mediterranean area (in particular Bulgaria). Until now they were considered as endemic and were known only from Aptian sediments in South America (Venezuela). Species of g. g. Venezuella and Renziella were found in three sections on the territory of North Bulgaria. The lithology and the ammonite sequences of the sections are described. The representatives of g. Venezuella and Renziella associate with characteristic, including also zonal Aptian ammonites from A. nolani and H. jacobi zones. The concept of the Aptian Age of the ammonites of this group is advocated. The phyllogenetic concept for the origin and evolution of the subfamily is rejected. Five species of g. Venezuella and 1 species of g. Renziella are described and figured. Three of them – V. bulgarensis sp. n., V. sumerensis sp. n., V. gracilis sp. n., are new for the science.
The qualitative-interpretational analysis of the maps of the total amplitude Z of the neotectonic vertical deformation of the initial flattening surface (the so-called peneplain), according to geologo-geomorphological data, and the vertical velocity X of the recent Earth's crustal movements according to geodetic data, gives grounds to advance a working hypothesis concerning the manifestation of a regular interrelation between X and Z within the Šumen Transitional Zone. The unique periplatform-orogenetic character of this intensively developed, and rich in mineral deposits region of the northern Black Sea coast, located between the Proper Fore-Balkan and the Moesian plate, assigns both considerable fundamental and scientific-applicable actuality of new quantitative studies on therelation between X and Z. The joint and the marginal sampling distributions of X and Z are determined and normality is tested. Ani ntensive and statistically significant correlation between them, at a coefficient of 0.8±0.1 is established, and the possibility is demonstrated for a reliable determination of average values z(hm) for Z, by means of given values x(mm.a-1) for X, resulting from the linear regression equation z = 3.266+1.359.x. A respective equation is deduced for the accuracy of this retrospective forecast enabling to complement and to improve the geologo-geomorphological data of the peneplain deformation mapping, by means of the detailed recent instrumental geodetic data. The results of this study are interpreted as an evidence for the carrying on, in the recent epoch, too, of all the same general tendencies expressed in the neotectonic geodynamics of the region under examination.
D. Yosifov, B. Maneva, A. Tsvetkov, D. Tsvetkova, V. Pchelarov. Geotectonic position and structure of Spahievo ore field. Based on analysis of the physical parameters of rocks and the distribution of geophysical fields, many new data on the structure and geotectonic position of Spahievo ore field were obtained. A complex of geological and geophysical information was interpreted using physicogeological modelling. The results show that the tectonic position of the ore field is controlled mainly by the deep-seated Ardino-Spahievo and Novakovo-Pilaševo fault zones and the Momcilgrad-Spahievoregional fault. The tectonic knot, formed at their intersection, is a source structure marked by concentration of intensive magnetic anomalies of different sign. A large part of these anomalies are related to abundant comagmatic bodies both exposed on the surface (Sârnica, Mezarlâksârt, Pilaševo, Karaman) and cryptointrusive (Garno Bryastovo, Susam, Ramadan). Their magnetic properties enable to evaluate the depth, form and sometimes the approximate composition of the bodies.
The area studied shows a block-disintegrated and faulted pre-Paleogene basement, dipping westsouthwest towards Borovica Depression. Depending on the distribution of the geophysical fields, the structural, magmatic and metallogenic features, three large mesoblocks may be divided: Borovica (I), Pilaševo (II) and Sârnica (Ill). Each mesoblock contains characteristic mineralization – rare-metal, gold-polymetallic and polymetallic, respectively. The 1ead-zinc ore mineralizations are related to an uplifted block of the basement, located in the central part of the eastern segment and formed by the intersection of Ardino-Spahievo and Novakovo-Pilaševo deep-seated fault zones. The knot areas of the regional deep zones control the origin of polyformational mineralization.
No abstract is available for this article.
Potassic feldspars from the Central Rhodope amphibolite-facies metamorphic rocks between the Rivers of Vâča and Čepelarska have been studied. They comprise orthoclases, intermediate microclines and maximum microclines distributed regularly across the stratigraphic section, as follows: I) orthoclases dominate the metamorphic rocks in the lower part of the section (the Široka Lâka, Varbovo, Ljaskovo and Posestrimo Formations) affected by migmatization processes; 2) orthoclases grading into intermediate microclines prevail in the incumbent Dobralâk Formation, and 3) intermediate and maximum microclines characterize the Bačkovo Formation higher up the section. The potassic feldspar structural changes from the lower to the upper stratigraphic levels with ordering increasing even among the monoclinic feldspars reflect primarily the temperature variations across the section at the time of formation or during later periods of thermal action. The temperature variations derived from the study of potassic feldspar structural states are compatible with estimates based on the garnet-biotite geothermometer: 800-600°C for the metamorphic formations affected by migmatization; 550-500°C for the Dobralâk Formation; and 450-400°C for the Bačkovo Formation.
The evidence gained in this study on the distribution of Ba, Sr and Rb both in the potassic feldspars and in the host metamorphic rocks reveals it as reflecting largely the primary premetamorphic relations between these elements. The Bačkovo Formation leptitoid gneisses and the constituent potassic feldspars show a well defined fractionation of Rb against Ba and Sr similar to that in acid magmatic differentiates, thus suggesting a magmatic origin.
Groundwater flow in the Al Sinn basin has a major effect on the geothermal regime in the area. It also greatly influences the groundwarter chemical composition. It follows hereof that vertical, as well as horizontal distribution of groundwater temperature and composition can be used to derive the specific flow and drainage pattern in the aquifer of Cenomanian-Turonian limestones. Both the temperature and the water mineralization are lower in the places of higher flow rates. This is valid not only for the Cenomani an-Turonian limestone aquifer itself but also for the surface layers. Mapping the surface geothermal and hydrogeochemical patterns has outlined the areas where groundwater drains off into the Mediterranean. Wells drilled accordingly have confirmed the inferred drainage system. The full agreement of conclusions drawn from the analyses of hydrodynamic, geothermal and hydrogeochemical characteristics of the basin demonstrates that a complete hydrogeological study produces very good results in a short time at highly reduced exploration costs. The same methodological approach can be used in other hydrogeological exploration projects.
I. Zagorčev. Deep structure of the Earth's crust in South Bulgaria: geological aspects. The layered structure of the Earth's crust in South Bulgaria is a result of the complicated geologic development, and of changes in the physical properties of the rocks under high pressures and temperatures. The following layers are distinguished (from bottom to top): Layer "A" (dehydrated lower crust) with layer velocities from 6.4 to 6.7 km/s, and characterized by low-velocity ductile deformations: Layer "B" (hydrated upper crust) with layer velocities 5.9–6.0 km/s, and characterized by homogeneous strains, as well as by deformations by cataclastic flow; low-velocity layer which developed only partially in the west part of Rhodope Massif, and is deformed by superplastic flow; presumably, it compensated differently directed movements in adjacent layers during some deformational stages; granitoid-metamorphic crust characterized mainly by brittle deformations. This structure probably resulted from multiphase deformations during several tectonic cycles. The dynamic environment changed considerably, compression stages being replaced by extension stages; in some stages different crust layers behaved differently, e. g. with an extension environment in the granitoid-metamorphic crust, and compression – within the deeper levels. Crustal thickening is due to different mechanisms but has been bound mainly to continental collision. With reaching a crytical thickness, isostasy-bound uplift led to thinning by erosion. Other mechanisms of crustal thinning are bound to environments of generalized extension and rifting, homogeneous deformation, or non-homogeneous ductile deformation with necking. As a result of multiphase crustal thickening, Rhodope Massif formed as a peculiar crustal lensoid body. The collisional orogen on the Balkan Peninsula, at least during the Alpine cycle, had a transitional character – from Alpine towards the Himalayan-Tibethan type, the Rhodope Massif playing the part of plateau.
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