Kiril Budurov’s research while affiliated with Institute of Mechanics and other places

The Moesian Group consists of terrigenous and carbonate red beds of different lithology. Conglomerate and sandstone of various pebble and grain size are interbedded with siltstone, shale and marl. Limestone or dolomite interbeds are also observed as well as lenses and concretions of anhydrite, and halite bodies. The formations of the group are referred to parts of the Upper Triassic on the basis of marine fossil faunas found. The introduction of lithostratigraphic units (formations and members) is based upon the predominance of one, two or more lithologic components. The end members of the lithologic range (the carbonates and the psephytic sediments) form in some cases almost uniform lithologic (lithostratigraphic) bodies. The Chelyustnitsa Formation is introduced herewith as a specific and independent lithostratigraphic unit. It consists of dominant red conglomerates built up almost exclusively of rounded or angular to semi-rounded fragments of Middle Triassic carbonate rocks and Lower Triassic and Permian red sandstones and siltstones. The thickness of the formation is between 300 and 500 m. Most probably the formation was interfingering with and wedging out fast within the Komshtitsa Formation. The present outcrops of the formation are situated north of the villages of Chelyustnitsa and Belimel as well as south-east of the village of Gavril Genovo and south and west of the village of Gaganitsa. They are in the shape of thick lenses covered by Jurassic and/or by younger formations. The defining features are the coarse lithology and the pebble composition. The formation originated from the fast deposition of fans of coarse terrigenous material supplied from adjacent uplifting island horsts within the regressing Late Triassic sea.

The Sinivir Formation (Fm.) was introduced as official lithostratigraphic unit by Tchoumatchenco & Chernyavska (1989) for an alternation of sandstones and mudstones, lying below the Balaban and Kotel Fm. These rocks were individualized for the first time by Berndt (1934) as "Schieflysch", later described by Ganev (1961) as Senonian flysch, and by Kanchev & Encheva (1967) and Kanchev (1995) as "Flysch formation" (5Tn 3) with Norian age. Tchoumatchenco & Chernyavska (1989) and Tchoumatchenco et al. (1992) described them as siliciclastic turbidites, structured predominantly by the Ta and Tb Bouma intervals - all previous authors stressed on the attribute "flysch" as a synonym of "turbidite". The term "turbidite" was subjected to revisions by Shanmugam and Moiola (1995) for the last time. For these authors turbidite sediments are only these with complete Bouma intervals - Ta-Tb-Tc-Td-Te. Deposits interpreted by different authors as proximal or distal turbidites are not a re- sult of turbidite currents but are predominantly interpreted as debrites - the result of mass debris flows (sandy or muddy), and sediments of bottom currents, which reworked the sus- pension settling mudstones representing the background sedi- ments.

Two types (basin and shelf) of Triassic and Jurassic Tethyan sediments participate in the structure of eastern Stara Planina Mts. (eastern Bulgaria). A parautochthonous position is assumed for the basin type rocks. The shelf sediments are allochthonous and can be observed as olistolites included in the Lower Jurassic Sini Vir Formation and in the Middle Jurassic Kotel Formation. The parautochthonous sediments take part in the composition of the probable overthrust structures refolded in antiformal and synformal structures, and intensely eroded before Late Cretaceous times. From the geological heritage point of view, the Triassic and Jurassic sediments of the region are included in a large unit--geosites framework--composed of 19 geosites: 10 in the parautochtonous and 9 in the allochthonous sediments. They exhibit different geological (tectonical, stratigraphical, palaeontological, etc.) features.

The Sinivir Formation (Fm.) was introduced as official lithostratigraphic unit by ×óìà÷åíêî & ×åðíÿâñêà (1989) for an alternation of sandstones and mudstones, lying below the Balaban and Kotel Fm. These rocks were individualized for the first time by Berndt (1934) as "Schieflysch", later described by Ãàíåâ (1961) as Senonian flysch, and by Êúí÷åâ & Åí÷åâà (1967) and Êúí÷åâ (1995) as "Ôëèøêà çàäðóãà" (5Tn 3) with Norian age. ×óìà÷åíêî & ×åðíÿâñêà (1989) and Tchoumatchenco et al. (1992) described them as siliciclastic turbidites, structured predominantly by the Ta and Tb Bouma intervals – all previous authors stressed on the attribute "flysch" as a synonym of "turbidite". The term "turbidite" was subjected to revisions by Shanmugam and Moiola (1995) for the last time. For these authors turbidite sediments are only these with complete Bouma intervals – Ta-Tb-Tc-Td-Te. Deposits interpreted by different authors as proximal or distal turbidites are not a re-sult of turbidite currents but are predominantly interpreted as debrites -the result of mass debris flows (sandy or muddy), and sediments of bottom currents, which reworked the sus-pension settling mudstones representing the background sedi-ments. In this paper we studied the best exposed section across the Sinivir Fm., situated along the forest road in the Cheshme Bair Hill in the valley of Balaban Dere, south of Dobromir Village, district of Varna. Here the sediments (Fig. 1, 2) con-sist of mudstones -marls to calcareous argillites and argillites (interpreted as the result of suspension settling processes), interbedded by two types of sediments: (1) calcareous biodetritic sandstones to gravellitic biodetritical limestones, with sharp lower and upper boundaries, thick from 10-50 cm up to 100 cm. In many cases they are massive in the basal part and thinner bedded in the upper part (for example unit 44). These sediments are interpreted by us as debrites, resulted from sandy debris flow; (2) Generally the biodetritic sedi-ments are capped by 10 to 70 cm fine grained, horizontally laminated sandstones (in single cases –unit 37, followed by 5-10 cm rippled laminated interval). The mudstones are interbedded by 5-20cm (rarely thicker) fine grained sandstones with horizontal lamination. The fine grained and laminated sandstones (in both cases) when they cap the bioclastic debrites and interbed the mudstones are interpreted as a result of bot-tom currents depositional processes. We interpret the Sinivir Fm. as a result of the sus-pension settling mudstones, reworked by bottom currents and by sandy debris flows. In the region of railway station Dropla black shales with cobbles predominantly of different Triassic limestones crop out. These rocks are not presented in the Balaban Dere Valley, and are interpreted now as deposited by muddy debris flow. These muddy debrites represent the sedi-ments of a fan, coming from the shelf of the paleo basin. Age. The Sinivir Fm. is attributed by ×óìà÷åíêî & ×åðíÿâñêà (1989, 1990) to Lower Jurassic – to the Pliensbachian and to the Toarcian (p.p), and by Êúí÷åâ & Åí÷åâà (1967) and by Êúí÷åâ (1995) to the Upper Triassic – Norian. Budurov et al. (2004), based on the fact that ×óìà÷åíêî & ×åðíÿâñêà (1989,1990) collected their mate-rial from the uppermost parts of the Sinivir Fm. and Êúí÷åâ (1995) – from the lower part – concluded that the Sinivir Fm. is dated as Norian up to the lower Toarcian age, and the Trias-sic/Jurassic boundary crosses its sediments. Acknowledgements The present study was made under the project NZ-1310/ 03 of the Bulgarian NCSR.

Introduction The study of the Triassic and Jurassic rocks in Eastern Stara Planina Mts. started in the beginning of the 20th century. Kockel (1929) and Bernd (1934) already demonstrated that a large number of Triassic and Jurassic outcrops represented huge exotic blocks (later named olistolites), and this view has been entirely or partially shared by later authors (Ганев, 1961; Кънчев, Енчева, 1967; Кънчев, 1993, 1995, etc.). Начев et al. (1967) introduced the hypothesis that all Triassic and Jurassic rocks in eastern Stara Planina Mts. represented olistolites into the Upper Cretaceous black shales of the Kotel Fm. Чумаченко & Чернявска (1989) established a lithostratigraphy for the Jurassic, and Будуров et al. (1997), for the Triassic sediments. Budurov et al. (2004) suggested that in many localities in the Louda Kamchia Valley the Tri-assic and the Jurassic rocks are in superposition, and the boundary Triassic/Jurassic is situated within the Sini Vir Formation. Stratigraphy The Triassic and Jurassic deposits in eastern Stara Planina Mts. are of two types (Fig. 1): (a) parautochtonous (basinal Tethyan) type, and (b) allochtonous -olistolites, formed by shelf (Peri-Thethyan) Triassic and Jurassic sediments, and by exotic blocks, coming from the partly destroyed Mator rift basin (Fig. 2). The Tethyan (parautochtonous) Triassic rocks are subdivided into: Mayadere Fm. (Spathian), Gyurgenliya Fm. (Lower Anisian-Lower Carnian), and Glogova Fm. (Upper Carnian-Norian to Rhaetian) (Будуров et al., 1997), and the Jurassic sediments in Sini Vir Fm. (now referred to Norian-Toarcian, p.p.), Balaban Fm. (Toarcian p.p.) (Чумаченко, Чернявска, 1989), and Kotel Fm (Начев et al., 1967) (Aalenian-Middle Bathonian?). The stratotype of Mayadere Fm. (93.5m) is located in the Maya Dere Valley South of the village Veselinovo. It is represented by irregular alternation of marls, shales, silstones, sandstones and limestones. The relative amount of shales and silstones is greater in the basal parts of the section, and is gradually replaced upwards by marls with limestones interbeds. The age corresponds to the upper parts of the Olenekian Stage (Spathian).The stratotype of Gyurgenliya Fm. (29.7 m) is located also in the Maya Dere Valley and follows upwards above the Mayadere Fm. and is built up of gray, gray-greenish, reddish or yellowish limestones, in the lower part interbedded with marls, and locally, with silicites. The age is determined as Lower Anisian-Lower Carnian. The stratotype of Glogova Fm. (cc. 30m) is situated along the road Kotel-Omourtag. There the formation is represented by an irregular alternation of marls (dominating in the lower parts) with thin-bedded limestones, silty limestones, calcareous siltstones and peloidal limestones (mainly in the upper parts). The age is Late Carnian-Norian-Rhaetian (?). The stratotype of Sini Vir Fm. (c. 500-800 m.) is situated in the valley of Eleshnitsa River. The unit is characterized by a siliciclastic alternation – sandstones to calcareous sandstones, aleurolites and argillites to marls, containing many sideritic concretions. In the vicinities of Dropla Village it contains abundant conglomerates, regarded as the result of a paleo-delta. In some sediments, described by Kockel (1929) as "Schwarzflysch serie" (regarded here as lower parts of the Sini Vir Fm), Кънчев & Енчева (1967) and Кънчев (1993, 1995) indicated the presence of Upper Triassic Halobia. Budurov et al. (2004) unified the "black flysch" and the Sini Vir Fm. in a single lithostratigraphic unit, referred to Norian –Toarcian (p.p.). The holostratotype of Balaban Fm. is located in the Balaban Dere Valley, South of the Dobromir Village; and it is built by thick beded sandstones (cc. 60 m); in the vicinities of Dropla Village it contains abundant conglomerates formed in a paleo-delta. The age is attributed to the Toarcian, due to its stratigraphic position. The Kotel Fm. (cc. 1000 m) has an Aalenian-Middle Bathonian age. It is introduced by Начев et al. (1967) as an Upper Cretaceous lithostratigraphic unit. Later Чумаченко & Чернявска (1989) returned its Middle Jurassic age, assumed by Чернявска (1965). The Kotel Fm. is built up by black shales containing many Triassic and Jurassic olistolites.

Magnetostratigraphic and biostratigraphic data are presented from the Anisian (Middle Triassic) Peri-Tethyan Edivetur section of northwestern Bulgaria. A dual-polarity component of magnetization carried by magnetite delineates a magnetic stratigraphy of mainly reversed polarity. Magnetozones are dated by means of foraminifer and conodont biostratigraphy. Data from Edivetur are compared with data from Middle Triassic Tethyan limestone sections with the aim of contributing to the completion of the Middle Triassic magnetic polarity time scale. We also propose that paleomagnetic data from Edivetur can be used as proxy data for the paleogeographic position of the Moesian platform. The Moesian platform was located at 21–24°N along the southern margin of Europe. It was probably marginally separated, but not detached or rotated away from Europe by the North Dobrugea transtensional trough, which is interpreted as a back-arc basin resulting from the northward subduction of the Neo-Tethys (Vardar) or Paleo-Tethys ocean. Paleomagnetic data from this study and other minor tectonic elements are used to generate a paleogeographic sketch map of the Pangea-bounded western Tethys and Peri-Tethys at Middle/early Late Triassic time.