A. Vaptzarova. Lithology of the Triassic rocks in North Bulgaria and related microfacies (according to borehole data). The present study is a review of the knowledge on the lithology and composition of the Triassic sediments in North Bulgaria. The rocks aro referred to three large lithostratigraphic units – Groups – Petrohan terrigenous, lskar carbonate and Moesian Group.
Petrohan terrigenous Group includes three lithostratigraphic units ranging in age from the early to the lowermost parts of the Upper Spatian Substage. The rocks of the Group, terrigenous with high mineralogical and textural maturity, and silty-clayey wen: formed in continental conditions. Andesite-basalt(?) lava flows were extruded in subaeral environment.
lskar carbonate Group comprises 8 Formations and 2 Members. The age range of the group varies from Middle-Upper Spatian to the Carnian. Initially formed are limestones and dolomites of diverse texture, related to the stable stage in the development of the basin, followed by clay-terrigenous, dolomitic and evaporitic deposits which mark the beginning of the regressive stage in the evolution of the Triassic Sea in this area. A number of microfacies have been proved in the carbonate and clay sediments but only those of them which are widely used in lithological correlations are described in the paper. The activization of the Triassic volcanic activity in the Northwest Fore-Balkan is related to the initial and middle stages of carbonate deposition (Anisian-Ladinian). Its termination coincided with the beginning of the general intensive uplift of the territory.
The Moesian Group is subdivided into 9 Formations and 2 Members. The age range of the Group is conventionally assumed as Norian (?) - Rhaetian Substage. A complex of multicoloured terrigenous, clayey, carbonate and sulphate sediments of normal, unsaturated and mixed composition were formed in the regression phase of the development of the Triassic basin. Their diverse quantitative combinations, the rapid vertical and horizontal changes and the abrupt variation of the thickness reflect the regressive tendencies in the deposition and the more intensive tectonic activity of the territory studied in the course of the final stage of the Triassic Period.
Vitoša central magmatic structure comprises many consecutively formed magmatic bodies referred to two series: Ca-alkaline and K-alkaline. Each series is further subdivided into four complexes: volcanic, subvolcanic, intrusive and postintrusive. The volcanic complexes of the two series are divided by regional unconformity which marks a considerable time break in the volcanic activity. The other complexes show cross-cutting relationships. The Vitoša paleovolcanoe is the initial element of the structure. It is of Ca-alkaline composition, shows confocal structure with polygonal (ring) and radial faults and dykes. Apart from the Ca-alkaline volcanic and subvolcanic rocks the volcanoe is marked also by Ca-alkaline intrusive and postintrusive rocks which crop out in its vent parts or form small intrusive bodies along radial faults. They are interpreted as offshoots of Plana pluton but emplaced at higher stratigraphic level. Elements of the structure are also the K-alkaline intrusive and postintrusive complexes which intrude the central parts of the volcanoe. However, they are only structurally related to the volcanoe. In the present-day structural plan, the Vitoša central magmatic structure is a circular morphostructure (dome), complicated by numerous activated fault segments of the regional and local fault network which define a complex internal block pattern. The development of the structure began in the Early Senonian. Two tectonomagmatic stages and a neotectonic stage are distinguished. During the early (Coniacian-Santonian) tectonomagmatic stage, magma complexes of Ca-alkaline composition formed in close structural and genetic relationships to the Vitoša stratovolcanoe. During the later (Campanian) tectonomagmatic stage originated K-alkaline magmatic rocks related to another volcanoe located to the northwest. The tectonomagmatic stages took place in the conditions of impermanent rifting. The first two phase of each stage (volcanic and subvolcanic) characterize the opening of the rift, marked by numerous telescoped dykes. The third (intrusive) phase was preceded by compression witnessed by several thrust and strike-slip fault. The final shaping of the structure as a positive circular morphostructure (dome) occurred during the neotectonic stage.
No abstract is available for this article.
Four main types of signals have been fixed in the EPR-spectra of the studied perlites: structural Fe3+ with g = 4.3, iron-bearing microphases with a. broad signal at 8 = 3.2–2.1, Mn2+ with a six-component signal and a sensitive to irradiation electron center of the E1’ type with g = 1.999. Combinations of two or more of the above mentioned centers have been presented. Dependences have been established between the different colour varieties of perlites and the type and concentration of electron-hole defects: for Fe3+ high values have been obtained for the pale-coloured varieties and low values for the dark varieties with an absence among the reddish brown varieties; Mn2+ has been characteristic for some of the pale-coloured varieties and the radiation sensitive center has been observed in the reddish brown varieties. The content of magnetoconcentrated iron microphases does not influence the colour of the perlites.
Metaeclogites from the Chepelare and Ardino areas (Central Rhodope Mts.) and from the Bela-Reka area (Eastern Rbodope Mts.) have been the subject of this study. The Central Rbodope metaeclogites occur as separate lenses in the migmatized gneisses of the Chernatitsa Subgroup and also show various degrees of amphibolitization and migmatization. The Eastern Rhodope metaeclogites are found in two morphological types. Some are tabular bodies (up to several km long) associated with ultrabasic plates, highly diaphthorized. Together with garnet-mica schists they form a well-defined unit belonging to the Bela-Reka Group. Others are lenses in the migmatized rocks of the Krumovitsa Group and are also affected by rnigmatization.
Regardless of the complex metamorphic transformations, the protoliths of all metaeclogites studied show basaltoid character of pronounced tholeiitic trend of differentiation. Their geochemical characteristics indicate a close relationship to the ocean type of crust (MORB), and their spatial association with ultrabasic plates and isolated ultrabasic lenses suggests that they may be interpreted as parts of metaophiolite associations.
The rocks show a moderate extent of fractionation and cumulation of the original melt. A relatively low degree of partial melting of the mantle during the generation of protolithic magma is indicated by the relative enrichment in incompatible immobile elements such as Ti and Cr, by the high Ce/Yb ratio and by the marked alkaline affinity of the metaeclogites studied.
Enrichment in light rare-earth elements (LREE) is a typical feature of the metaeclogites referring them to the E- and T-types of MORB. This is even better shown by the MORB-normalized patterns of the highly incompatible elements which indicate an apparent tendency in the protoliths of approaching WPB. The primary geochemical characteristics of the eclogite have not been changed essentially by the metamorphic transformations excepting the migmatization processes which have led to an increase in K and LREE.
Although the geochemistry of metaeclogites from the tabular bodies and from the lenses show no significant differences they cannot be regarded as contemporaneous. This conclusion is based on the different types of metamorphic rocks embedding them as well as on the differences in the metamorphic transformations which affected them. Both, however, are of allochthonous nature and represent fragments of an ancient ocean crust which a variety of tectonic events has brought up into their present-day continental position.
The paper describes the first foraminifera found in the Strandža type of Triassic in Southeast Bulgaria. The presence of the Meandrospira pusilla Interval-zone (Spathian) is indicated by its index species found in the Gramatikovo Formation consisting of calcite phyllites. The Turriglomina mesotriasica Interval-zone (Ladinian) is indicated in the Kondolovo Formarion near the village of Kondolovo where the index species is accompanied by Pachyphloides oberhouseri and Austrocolomia cf. marschalli. In the same locality several levels of recrystallized limestones belonging to the Lipačka Formation have been found to contain assemblages of Palaeomiliolina sp., Labyrinthina? sp., Oberhauserella praeladinica, Schmidita cf. inflata, of Endothyra cf. kuepperi and Agathommina austroalpina, and of Labyrinthina cf. falsomlrabilis and Aulotortus friedli, indicative of the Paraophthalmidium corpathicum Range-zone (Karnian). The Miliolipora cuvillieri Range-zone (Norian) has been proved by its index species in the topmost stratigraphic levels of the Lipačka Formation near the village of Kondolovo. In the vicinity of the village of Zabernovo the Norian foraminiferal assemblage includes Quenquiloculina cf. nucleiformis, Schmidita cf. hedbergelloides, Variostoma cf. coniforme, V. helictum and other species indicative of an open sea environment.
No abstract is available for this article.
No abstract is available for this article.
No abstract is available for this article.
No abstract is available for this publication.
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