No abstract is available for this article.
Several transcontinental structures controlled the Cambrian-Ordovician development of pericontinental platform and intracontinental molassic Gondwanaland basins. Two main structural lineaments that connect Northern Africa with the Andean area are described. These continental lineaments display a bipolar geodynamic behaviour with "pull-apart" basins on both continental extremes. The pericontinental characteristics are similar, showing the presence of marginal, rift-type basins.
The basin trends, geometry, and internal active structure are interpreted to result from the reactivation of ancient shear systems.
Both the structural transgondwanic continuity and the platform development indicate the necessity of further studies on the general Gondwanaland behaviour, and supply data for a possible comparison with the fragments of the present-day Paleotethys region including the Balkan domains.
Foraminiferal populations consisting of Albian sediments in the western and central parts of North Bulgaria are analysed. On the base of the regularities in the vertical distribution of the species, from the bottom upwards, two zones and four subzones are subdivided and defined: (I) Lingulogavelinelia albiensis albiensis Zone with subzones – (a) Lenticulina turgidula – Lingulogavelinella albiensis albiensis Subzone (Lower Albian); (b) Lenticulina pulchella – Arenobulimina macfadyeni Subzone (Middle Albian); (2) Arenobulimina chapmani Zone with subzones – (a) Lingulogavelinella cibicidoides – Tristix excavata Subzone (Upper Albian); (b) Eggerellina mariae – Valvulineria praestans Subzone (Upper Albian).
No abstract is available for this article.
R. Combémorel, M. Stoyanova-Vergilova. Biostratigraphy of the Lower Cretaceous belemnites in France and Bulgaria. Comparative analysis. In Bulgaria the Lower Cretaceous belemnites become abundant as late as the beginning of the Hauterivian Stage. At the same time, the French belemnite faunas, still rare in the Berriasian, where a few species are to be found coming from the Tithonian, gradually become richer as the Valanginian develops. In the latter they are of a considerable stratigraphic significance. From the Hauterivian through the Aptian Stage the belemnites faunas in both countries grow quite varied, being much richer in Bulgaria. Through the Aptian Stage the belemnites decrease in variety, especially in France. The belemnites fauna diminishes much more gradually in Bulgaria, where a number of species from the European and Tethys provinces persist till the Cenomanian.
No abstract is available for this article.
During the Upper Cretaceous, the land concerned in this study was part of an extensive area of monotonous tectofacies evolution involving a spatially uniform, rhythmic (mostly flysch), carbonate-terrigenous and volcanic-terrigenous (there was active volcanism in adjacent areas) sedimentation, the general monotony being broken by events of olistostrome deposition and consedimentation block movements restricted both in space and in time. From the north to the south, the post-Illirian structural pattern has been found to involve parts of the Illirian Luda-Kamčija synclinorium and the contemporaneous Kačulka anticline and Vrailec anticlinorium surrounding it from the south. By either thrust faulting or recumbent folding, the latter's western periclinorium was overlaid by the northeastern margin of the eastern end of the Laramide Srednogorie anticlinorium, the margin manifesting intense polyphase deformation and block fragmenting. The existence of the so-called Kozuina syncline, named after a mountain peak west of the town of Sliven, has not been confirmed in this study. Essential structural differences have been found between the Srednogorie anticlinorium and the adjacent major Illirian folds. In the area studied, there is the largest areal concentration of faults of Tvârdica orientation and Upper Cretaceous tectonic activity indicating that the Tvârdica strike-slip fault set axis active during the Upper Cretaceous geochron to the south of the Balkan Range should be sought there.
An Upper Cretaceous carbonaceous-phosphatic-chert horizon is traced throughout the Ionian Zone on the territories of Albania and Greece. It crops out predominantly within anticlinal belts. Two phosphorogenic belts can be distinguished. The formation of the horizon has apparently taken place in an opensea basin. Separation of phosphorus is supposed to have occurred as a result of precipitation during the sedimentation and in a diagenetic way, by phosphoritization of microfauna and carbonates.
The Čiprovci ore zone is known for its polygenic and polychronous mineralizations formed in a siderite-calcite marble bed of Early Paleozoic age. Its general leatures as well as structures, textures and mineral composition record the following events.
1. Deposition of chemogene calcite limestone with hydrothermal-sedimentary siderite interlayers associated with a basic volcanism. Presumable age: Cambrian.
2. Greenschist regional dynamothermal metamorphism that transformed the carbonate rocks into finegrained marbles. Siderite contains 27 ± 5 mol% MnCO3, 6 ± 3 mol% MgCO3 and 1-2 mol% CaCO3. The two kinds of ma1ble are compositionally mosaic due to each grain growing with the composition of its seed carbonate during the metamorphic recrystallization.
3. Formation of a hydrothermal low-temperature silver-lead sulphide mineralization (Pb-Pb model age of 320-340 Ma). It developed metasomatically in the siderite bodies mainly. The hydrothermal fluids were magnesium-rich and their first product was dolomite MgO0.8FeO0.1Mn0.1. They gradually became richer in Fe and Mn supplied during the metasomatic replacement of earlier material, and the dolomite crystals were overgrown by ankerite (up to Fe0.7Mg0.3) and manganian ankerite (up to Fe0.5Mn0.4Mg0.1). Siderite and calcite were redeposited during the later stages of the process. The main characteristics of these metasomatic·carbonate crystals is that they are idiomorphic and compositionally zoned.
4. Formation of syn- and postmagmatic mineralizations associated with a granite intrusion (Pb-Pb model age of 255 ± 17 Ma). Carbonate minerals formed and were transformed during asuccession of processes involving: 1. Thermal metamorphism that converted the siderite marble partly or completely into magnetite ore; 2. Skarn formation in the calcite marbles; and 3. Deposition of a post-skarn oxide-sulphide-arsenide high to medium-temperature mineralization. During the magnetite fo rmation, the fluids were enriched in manganese and magnesium solutes: (Fe, Mn. Mg)CO3+H2O → Fe3O4+Mn2++Mg2++CO-. They deposited high-temperature zoned Ca-Mg-Fe-rhodochrosite, Fe-Mn-magnesite and Mg-Mn-sideritc with end members Mn0.6Fe0.2Ca0.1 Mg0.1 and Mg0.5,Fe0.3,Mn0.2. The rhodochrosite-magnesite solid-solution interval shows a solubility gap observable even on areas smaller than 1 mm2. The end of the process produced also ankerites part of which show high manganese contents (reaching kutnahorite compositions Mn0.5Fe0.3Mg0.2).
Formation of a quartz-barite mineralisat ion (Late Cretaceous?). The earlier carbonates were partly redeposited or recrystallized.
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