GEOLOGICA BALCANICA, 28. 1-2, Sofia, August. 1998, p. 35-43
ewly recognized Upper Triassic and Jurassic formations in Southwest Bulgaria: palaeogeographic and palaeogeodynamic implications
h an Zagorchev, Ekaterina Trifonova, Kiril Budurov, Kristalina Stoykova
Geological Institute. Bulgarian Academy ofSciences , 1113 Sofia; ; tf [email protected]; [email protected] iued 03.07.1998: accepted for publication: 03.07. /998)
3acop'4e6. E. Tpu¢oHo6a, K. Eyoypo6, K. CmouKoBa - Abstract. Four formal lithostratigraphic units are introduced for ~HapyxeHHble BepxHempuacOBble u IOpcKue cBumbl 6 the first time in the national stratigraphic nomenclature in Lko-JanaOHou Eolli!apuu: naAeoceozpa¢u'4ecKue u naAeo accordance with the National Stratigraphic Code and the Inte ~aMu'lecKue 6bl600bl. qeTblpe o ~ , 1., Trifonova, E., Budurov, K., Stoykova, K. 1998. Newly recognized Upper Triassic and Jurassic D:=li!cri.IOns in Southwest Bulgaria: palaeogeographic and palaeogoodynamic implications.- Geologica Bale., -.-: 35-43. _ words: SW Bulgaria; Upper Triassic; Jurassic; palaeogeodynamic implications. 35 Introduction siltstones and sandstones interbedded with dolomitic limestones. The red shales and siltstones typical of The Upper Triassic stratigraphy of Southwest Bulgaria the Komshtitsa Formation are lacking or rarely obser is based mostly on studies by Tronkov ( I969; TpoH ved as thin interbeds. The X-ray and thermal phase KOB, 1983) who introduced the Komshtitsa Formation analysis (determinations by R. Mihaylova) indicated (later referred to the Moesian Group) and the Trun the presence ofphosphate and sulphate minerals: sarc Formation (topmost parts of the Iskur Carbonate Gro opside, lazulite, alunite, jarosite and goethite. up). Budurov et a!. ( 1993, I 995) made a chronostra The presence of these minerals has not been yet tigraphic detailization, and introduced the Vetroushka confirmed by other methods. and Slavey formations in the Moesian Group of the Type section: along the road from Cheshlyantsi te Golo-burdo tectonic unit. wards Sredorek (Fig. 1), beneath the thrust sheet of The Jurassic stratigraphy of the same region isba the Milevets thrust. sed on papers by ,ll.o)leKOBa et al. ( 1984) and Cany cover: 3 - 4 m quartzitized conglomerate built up HOB et al. ( 1983, 1985). The formations of Peri-Tethy of quartz, quartzite and lydite pebbles (Metohiya For an type observed have been either referred to lithostra mation) tigraphic units known in the Balkanide (Stara-planina) Kobile Formation: fold belt or introduced as new units (Zhablyano and (9-14 ): about 20 m yellowish strongly weathered Lobosh Formation). 3arop1.feB, THXOMHposa ( 1986) silty and shaly rocks with reddish intervals; sample recognized a Treklyano Group composed of the Dobri Che-25 dol and Rayantsi Formations, and typical of another (14) 1.5 m weathered whitish silty rock rich in sul environment of Tethyan type (Treklyano sedimenta phate tion zone). Later on (3arop1.feB et al., 1990), transi (13) 7 m yellowish massive phosphate-bearing tional varieties have been also found and described siltstone; sample Che-35 as informal lithostratigraphic units. The geological (12) 4 m yellow phosphate siltstone; sample Che-36 map on the scale I: I 00000 (Zagorchev, Dinkova, (I 1) 1.2 m reddish massive dense sandstone with I 991) recorded with some revisions the stratigraphic reduction spots evidence already published at that time. Some new ( 10) 0.5 - 0.8 m yellowish oligomictic quartz sands information has been obtained by the authors during tone their work on the projects NZ-204 and NZ-603 of the (9) 4 m yellowish to whitish limestone; sample National Fund "Scientific Research", too. Che-37 During the new geological mapping (I 997) on the ( 1-8): about 25 m grey-whitish thin-bedded (3-30 scale 1:25000 by SOFGEOPROOUCHVANE Ltd. em) limestones interbedded with yellowish strongly (supervision and consultations by Ivan Zagorchev), weathered shale; bedding 260°/40°; samples Che-26, the present authors found new evidence about the field in the lower part- Che-27 relations of Triassic and Jurassic rock units (Fig. I). (8) 2 m yellowish weathered dolomitic limestone We made additional sampling, and the results obtai (7) 4 m grey dolomite with clayey interbeds; sam- ned made possible to introduce four new formal litho ples Che-38, Che-39 (Radiolaria) stratigraphic units (one of Late Triassic and three of (6) 1.5 m yellowish calcareous sandstone Jurassic age). The new palaeogeographic and palaeo (5) 0.8 m dolomitic limestone geodynamic conclusions introduce some important (4) 5.5 m dolomitic limestone with clayey inter changes about the Peri-Tethyan realm. beds; sample Che-40a- 1.2 m above the base; sample The Kobile, Metohiya and Sredorek formations are Che-40 - near the base described by I van Zagorchev, Ekaterina Trifonova and (3) 7 - 8 m scarce outcrops; rock boulder of Kiril Budurov, and the Momchil Formation, by Ivan brownish massive rock (sample Che-41) Zagorchev, Ekaterina Trifonova and Kristalina Stay (2) 3 m limestone; sample Che-42: Angulodiscus kava. The other chapters are written by Ivan Za friedli (Kristan-Tollmann), Austrocolomia cf. gorchev. canaliculata (Kristan), Amphore/la cf. lageniformis Borza & Samuel, Galeanella sp., Ophthalmidium sp., Kobile Formation Nodosaria sp., Variostoma? sp., Ostracoda, Radiolaria? ( 1) I 0 m interbedding of yellowish weathered li (new Fonnation: Ko6HJICKa CBHTa) mestones and dolomitic limestones with silstone and shale interbeds Name. The formation is named after the villages of basement: unknown (after an interval without out Dolno Kobile and Gomo Kobile and the river Kobil crops, follow poor outcrops of quartz conglomerate ska situated near the type section. (Metohiya Formation) and Palaeozoic granite from Former reference: upper parts of the Komshtitsa the zone of the Milevets thrust; follows the flysch Formation (Zagorchev, Dinkova, I991 ). sequence ofthe Kastel Formation (North ofSredorek Lithologic composition and defining features. The Sapunov- cf. Can)'HOB et al., 1985, determined Titho formation consists of yellowish and whitish shales, nian ammonites in the latter). 36 -' .... --·-·\ . ... "':· .. :- . >·:: : .. : :·: ·> ::: ·-: . < 0 1 2 :3 4k.m : ·:::. : ·.·. l A L/ ' J ~ allocblhoaous r--1 K F · ~ liflUI1 ::r::::r:::J Palaeo.Joic L-J ostel ormaaaon ~ Sreclorek Ji'ormatJo• ~ Mttoltlya Formation liiiiiiJ Momchil Formatlor ~ ~~~~~;~~m . 1111111 Rayantsl formatloa ~ J(oblle Fonaadon ~ Ko-hdtsa Formation ~ c.mJ:r: Group -:- :- I. Geological sketch map (modified after Zagorchev, Dinkova, 1991) for the pre-Palaeogene formations in the Treklyano -=- .\bbreviations: D- Dobridol Formation, K- Kobile Formation, M- Momchil Formation, MIR- transitional beds ofMomchil .:. Rayamsi Formation, Mt- Metohiya Formation, R- Rayantsi Formation, S- Sredorek Formation Occurrence and relations to other lithostratigraphic probably to.the Kobile Formation, and yielded abun - · - Fig. 1). The Kobile Formation covers the red dant echinids and some brachiopods and gastropods, ; of the Komshtitsa Formation, and exhibits lateral all strongly flattened. Unfortunately, only one echinid mgering with it. (Myocidaris sp.) has been determined to the generic The Komshtitsa Formation yielded in the area of level. The foraminifers found by us indicate Late peak Beli karnak (Trifonova, Zagorchev, 1984) Triassic (Norian?) age. roraminifers Trochammina alpina Kristan-Tol The age of the Kobile Formation is determined as ..::=z:m. Agathammina austroalpina Kristan-Tollmann & Late Triassic (Norian- ?Rhaetian) on the basis of the -...... ;.r..u.cu.u•, Angufodiscus friedli (Kristan-Tollmann), fossil content and the position over the Norian Kom dinella falsofriedli (Salaj, Borza & Samuel), shtitsa Formation. saria ordinata Trifonova, Semiinvoluta clari ,.,._,0114.u.. and the newly-found by us East of the peak Metohiya Formation · ki karnak Angulodiscus paralelfus Kristan (new formation: MeToxuB:cxa CBHTa) and Oberhauserella cf. rhaetica Kristan- Xmann. It is covered with unconformable depositional Name. The formation is named after the river Meto 1 by the Metohiya Formation (Middle? Jurassic) hiyska that runs parallely to the road with the type _. me Middle Jurassic Sredorek Formation (on the section. :=o:m.rain road South of Treklyano ). Lithologic composition and defining features. The - il content and age. Radiolarians, crinoid ossi- formation consists of quartzitic conglomerate (quartz, - aJgae and foraminifers have been found in the quartzite and lydite pebbles) and sandstone, loose yel ~ section. An outcrop found in 1962 by M. Matova lowish calcareous sandstones, and occasional inter · _ the geological mapping on the scale 1:25000 beds of sandy limestone. - been destroyed during construction of the new Type section: In the road cut from the village of · _ over the river Metohiyska. It belonged most Metohiya towards the bridge on the river Metohiyska 37 (the type section begins at about 500 m from the bri Fossil content and age. Only occasional single dge) ostracods have been observed in thin sections from cover: unknown (slope gravel and soil) the limestones of the formation. The formation is Metohiya Formation: considered as lower parts of the Middle Jurassic (20) 2 m yellowish or colourless to whitish sandsto (possibly beginning in the uppermost parts of the nes with abundant mica; beds thick from 5 to 50 em Lower Jurassic) on the basis of relations with other ( 19) 8 m quartzitized conglomerate built up of lithostratigraphic units. white, grey and black quartz and quartzite pebbles ( 18) about 30 m interval without outcrops, and 15 m with bad outcrops and isolated blocks from the Sredorek Formation same conglomerate (new formation: Cpe.nopexcxa CBHTa) ( 17) 1.5 m black quartzite ( 16) 0.2 m brownish thin-bedded sandstone Name: The formation is named after the village of ( 15) 0.2 m black quartzite Sredorek situated near the type section. (14) 0.4 m yellowish-brown clayey sandstone; Formerreferences: to the Kostel Formation (flysch sample 2~67 of Tithonian- Berriasian age). ( 13) 15 m black quartzitized conglomerate and qua Lithological composition and defining features: Ty rtzite pical rock varieties are clayey limestones to marly ( 12) 1 m quartz sandstone, yellow-brownish, pa limestones with shaly interbeds, and olistostrome built ssing downwards into clayey sandstone up of Triassic limestones (mostly of the Trun Forma ( 11) 1.2 m greenish to yellowish clayey sandstone tion, and less abundant, from the Radomir Formation) with irregular bedding and of red slates and quartz oligomictic sandstones ( 10) 1.2 m red siltstone and shale (Komshtitsa Formation). about 100 m without outcrops Type section: along the road from Sredorek to the (9) 4 - 5 m loosely-cemented weathered yellowish bridge over the river Metohiyska (crossing towards rusty sandstone Metohiya) (8a) 0.6 m harder yellowish-brownish calcareous cover: Kostel Formation (flysch interbedding of sandstone (first marker) shales and marls with sandstone and conglomerate); (7a) 1 m loose yellowish sandstone, rusty in the CanyaoB et al. 1985, p. 28-29, quoted former finds lower part within the Gorochevtsi Member of the Kastel Forma (4a-5a) 0.8 m hard blueish nodular limestone, rusty tion North of Sredorek of the taxa Aulacosphinctes on a weathered surface, bedding 300°/35-45°; sample linoptychus (Uhlig) and Aulacosphinctes venustus 2223 (second marker) Collignon that indicate upper parts of the Middle (3a) l m loose sandstone Tithonian Substage and lower parts of the Upper (after the road tum the road cutting passes over a Tithonian Substage parallel section) ( 6) 12 m grey-greenish siltstones and shales, folded, (8) 0.6 m hard, calcareous sandstone (first marker) with intense cleavage (7) 2 m loose sandstone, locally calcareous (5) 20m siltstones and shales interbedded with li (6) 1.8 m dark-grey to black quartzitized sandstone mestones, in the upper parts with calcareous san (5) 0.6 m hard calcareous sandstone with marly dstones and sandy limestones with ooids and intra border (sample 2268) clasts; samples Sr 16-20; Sr-38 (sandy limestone with (4) 0.5 m blueish limestone, samples 2230, 2269 crinoid ossicles), Sr-37 (limestone, lowermost part (second marker) of the packet (3) 1.5 m quartz conglomerate (4) 15 m shaly limestones and marls; in the upper parts (2) 2 m thin-bedded sandstone, yellowish to bedding 35°/35°, in the lowerparts40°/35°; sample Sr-36- whitish, rich in mica intraclastic limestone, sample Sr-35-clayey limestone; ( 1) 0.3 - 0.5 m thin-bedded quartz sandstone before the front ofthe olistostrome (3) the beds become - irregular washed-out boundary, not very clear due vertical envelopping the olistolites; samples Sr-11 and Sr- to similar lithology 12 are situated in front of the olistostrome, and -con basement: thick pink, yellowish or red oligomictic tain: sample Sr-12 -Textularia agglutinans d 'Orbigny, quartz sandstones and conglomerates (Komshtitsa Ophthalmidium carinatum Kubler & Zwingli, Len Formation) ticulina cf. subalata Reus, Textularia sp. {Middle Ju Occurrence and relations to other lithostratigraphic rassic); sample Sr-36 - crinoid ossicles, Algae, Oph units. The Metohiya Formation covers with a uncon thalmidium sp. formable boundary the Upper Triassic Komshtitsa and (3) 60 m olistostrome with calcareous shaly-marly Kobile formations. It contains re-deposited pebbles matrix, and huge olistolites built up of sandstones and from these formations, too. The Metohiya Formation shales ofthe Komshtitsa Formation (in the upper part) is covered by the rocks ofthe Middle Jurassic Sredo and whitish grey limestones of the Trun Formation rek Formation. (in the lower parts); samples Sr-7 to Sr-10 (from bo- 38 ,.,. mnchll ~ ornuotlnn - · Type section of the Rayantsi Fonnation (after 3arop'leB, THXOMJtpoBa, 1986, modified after revisions) with structural nts and sample locations to top)- matrix from the middle parts of the oli units. The Sredorek Formation covers transgressively me the Metohiya Formation or directly (South of Trek _ 1 II m grey-greenish marly and clayey limestone; lyano) the Kobile or the Komshtitsa Formation, and :iie:ple Sr-33- upper part, Sr-32- 2m above the base; is covered by the Kostel Formation. It represents a - sample Se-32: crinoid ossicles, Trocholina cf. lateral correlate of the Rayantsi Formation. rinensis Henson, Dentalina sp. c . ) 7 m grey and grey-greenish limestones with Momchil Formation :I:EO'beds (up to 40 em) ofcalcareous sandstone; bed (new Formation: MoM'IHJICKa CBHTa) - 35°/30°; samples Sr-I to Sr-6 (from bottom to . ) contain Trocholina palastinensis Henson, Opht The Momchil Formation has been described as an ;;u..;;.:n;~· ium carinatum Kubler & Zwingli, Dentalina informal unit (silty-slaty formation) in the borehole _ 4~liddle Jurassic}; sample Sr-31 at 50 em above Zemen and at the bridge near the village ofRayantsi base (3arop'les et al., 1990). The transitional character - · the basal parts: shear planes with 340°/60° to towards the Rayantsi Formation has been also ..::.x - '35°; lineation (striae) 315/32° discussed. Ce3ement: Name. The formation is named after the spring Mo - m thin- to thick-bedded calcareous sandstones mchil situated near the type section. brownish quartz sandstones (Metohiya Forma Lithologic composition and defining features. The 'iltith imbrications; bedding 10°/35° typical rock varieties are shales and siltstones with wish calcareous shale and siltstone with limo occasional interbeds of limestones and sandstones. .::a::::ll:!:d calcareous oval nodules; bedding 35°/35° (Ko- Type section: along the road from Rayantsi to Dobri formation?). dolski vodenitsi (Fig. 2), closely after the bridge (des ,... s:il content and age. The foraminifers determined cription in 3arop'les et al., 1990, p. 58): O::~ e a Middle Jurassic age (possibly in the range cover: Kostel Formation (Tithonian- Berriasian): ~Jiiic:::!im -Bathonian). The upper parts ofthe formation are polymictic conglomerates (pebbles from quartz, Tria grobably ofCallovian to Late Jurassic age. The scarce ssic and Jurassic limestones and sandstones, etc.) content cannot provide more accurate age infor interbedded with sandstones, in the lower parts, also i:l:i!::::O!l. The upper age limit is given by the Tithonian with siltstones and shales; single specimens of Wa "the covering Kostel Formation. tznaueria bamesae (Black) Perch-Nielsen (Middle ~...... , ... nee and relations to other lithostratigraphic Jurassic to Upper Cretaceous). 39 sedio• Rayutai - llubridulookl "udenlbl - --- 0 0 0 0 ...... ~, ~,~---~- 0 0_ 0 0_ 0 ___ ---~~t5~f=L------_.,I-_-_,c; o c -co - ·- . - 6 ·- ..,, . . - -- 6 -.- . - -- ------lfJz..:~·:;:::·:::::·~·:::::::::· ::::::-~ - -~ _-_-_-__ \ . . . . . \ ·~ ... ·- \ ··~ .. . -.__ \ ~---:z_ \ \ ---- \ rh.J 1 ------ shlllc wllll allollt, liltaton• I"'ICCIolarilt ••rl. ---=- marly limeU011t lllnaroae l~o•~wtlll lrT, I I I ftlncaodulcs 1 I Fig.3. Correlation of the Upper Triassic (Moesian Group) and Jurassic (Treklyano and West-Balkan Flysch Group) formations in the Treklyano area Jurassic Formations: ksJ - Kostel Formation (Upper Jurassic); srJ • - Sredorek Formation (Middle - Upper? Jurassic); mtJ - 3 2 3 _ - - Metohiya Formation (Lower?- Middle Jurassic); raJ2 3 Rayantsi Formation (Middle- Upper Jurassic); ddJ2 Dobridol Formation (Lower- Middle Jurassic); moJ .~ - Momchil Formation (Middle- Upper? Jurassic); neJ - Neshkovtsi Formation (Kimmeridgian); 2 3 - _ - - giJ3 Gintsi Formation (Oxfordian); yaJ2 3 Yavorets Formation (Callovian - Oxfordian); poJ2 Polaten Formation (Aalenian - _ - - Bathonian); grJ 1 2 Gradets Formation (Toarcian- Aalenian); zhJ1 Zhablyano Formation (Pliensbachian); Triassic Formations: - - - koT3 Kobile Formation (Norian- Rhaetian?); kmT3 Komshtitsa Formation (Norian); trT3 Trun Formation (Carnian- Norian) ( 6) about 30m interbedding of grey to grey-greenish phaera brittanica (Stradner) Perch-Nielsen (Toarcian sandstones, siltstones and shales to Valanginian) (5) 0.2 m sandy biodetritic limestones with Bolivina ( 1) 0.8 m clayey and oolithic limestones withLenti liassica (Terquem),Protopeneroplis cf.striata Wein culina cf. quenstedti (Gumbel), Discorbis cf. scuti/i schenk, Ophthalmidium sp. formis (E. & I. Seibold), Ophthalmidium sp .. (4) 4.5 m sandy and calcareous grey-greenish shales basement: red and greenish shales and sandstones and siltstones interbedded with oligomictic quartz sandstones (3) 1.2 m oolithic and biodetritic limestones with (Komshtitsa Formation;_Upper ~riassic). Discorbis cf. scutiliformis (E. & I. Seibold), Ophthal Fossil content and age. The foraminifers determined midium sp., Lenticulina sp.; occasional finds of the define the age as Middle Jurassic (Bajocian-Bathonian); calcareous nannofossils Ellipsagellosphaera britta presence of the whole interval from uppermost Lower nica (Stradner) Perch-Nielsen (Toarcian to Valan Jurassic to lower parts of Upper Jurassic is possible. ginian), and Cyc/age/osphaera margereliiNoel (Mid The same age is indicated by the calcareous dle Jurassic to Upper Cretaceous) nannofossils. The poor assemblage of calcareous na (2) about 7 m grey-greenish sandy and calcareous nnofossil taxa most resistant to dissolution in the water shales and siltstones; single specimens from Watz column and sediment is typical of environments clo naueria barnesae (Black) Perch-Nielsen (Middle sely above the Calcite Compensation Depth (CCD). Jurassic to Upper Cretaceous) and Ellipsagellos- Occurrence and relations with other lithostratig- 40 raphic units. The Momchil Formation occurs in the by L. Tikhomirova, 3aropqes, THXoMaposa ( 1986) transitional part from the Svetlya sedimentation zone defined four informal units with probable ages Lower to the Treklyano sedimentation zone (Zagorchev, Jurassic - lower Middle Jurassic (beds I with Tri 1986). It is known also from some of the thrust sheets colocapsa plicarum Yao andStichocapsa convexa Yao ), drilled by the Zemen borehole. Laterally it passes into Middle Jurassic (beds D with Cyrtocapsa kisoensis Yao, the Rayantsi Formation (Treklyano Group), to the Eucyrtidiellum unumaensis (Yao), Dicolocapsa West, and to the Polaten Formation, to the East. The conoformis Matsuoka and Stylocapsa catenarum predominance of siltstones and shales, and the tran Matsuoka), Callovian - Oxfordian (beds ill with Gon sition to the radiolarite-slaty interbedding of the Ray gylothorax sakawaensis Matsuoka and Guexella nudata antsi Formation gives grounds to refer the Momchil (Kocher)) and Oxfordian- Kimmeridgian (beds IV with Formation to the Treklyano Group. Mirifusus guadalupensis Pessagno, Triactoma b/akei In the sections Oushtrintsi and Antova mahala, the (Pessagno ), Hsuum maxwelli Pessagno and Willirie lateral transition between the Rayantsi Formation and dellum carpathicum Dumitrica). The beginning of beds the Momchil Formation is indicated by the presence I has been supposed in the Lower Jurassic on the basis of occasional sandstone and limestone interbeds ofdeterminations ofseveral Early Jurassic (Sinemurian? within the normally shaly sequence with sideritic and - Toarcian) taxa, and namely Protopsium ehrenbergi phosphoritic concretions and some radiolarite beds. Pessagno & Whalen, Bagotum modestum Pessagno & Two very deformed belemnite rostra and a Punctap Whalen, Droltus hecatensis Pessagno & Whalen, etc. tychus sp. (determined by I. Sapunov; in the same although typical Middle Jurassic taxa have been specimen - the calcareous nannofossil Stephano identified in the same samples, too. lithion octum (Rood & Barnard) Perch-Nielsen, ran I. Boncheva succeeded recently (.60H'ieBa, 1996) ging from Bathonian to Callovian, rarely to Ox in diluting in hydrofluoric acid duplicate samples of fordian) have been found, too. I. Zagorchev, and studied the isolated radiolarians. Also in one sample from the section Oushtrintsi, The results of this study indicated in the lowermost S. Chernyavska determined (oral communication: beds (beds I, samples l, 3, 5 and 6) the Radiolarian May 1995} the spore taxa Retitriletes clavatoides Zone Tricolocapsa plicarum Yao (Aalenian - Bajo (Couper, 1958} Doring et al. 1966 (from Sinemurian cian), and for the upper parts of beds I and lower parts and during the whole Jurassic) and Duplexisporites of beds II (samples 7, 8 and 9), the zone Tricolocapsa problematicus (Couper, 1958) Playford & Dettmann, conexa Matsuoka (Bathonian). No Early Jurassic taxa 1965 (most frequent from Upper Pliensbachian to have been observed. Beginning with sample 10 and Toarcian). up to 19, a Callovian age is based upon Triactoma blakei (Pessagno), Triactoma parablakei Yang & Wang, Spongocapsula palmerae Pessagno, etc., and New data about the Treklyano Group the uppermost parts ofthe section (20 -26) are referred to Upper Callovian - Oxfordian with the taxa Hsuum The Treklyano Group has been introduced (3aropqeo, maxwelli Pessagno, Sty/ocapsa catenarum Matsuoka, THXOMHpooa, 1986) on the basis of the Dobridol and Podocapsa guembeli Pessagno, Williriedellum Rayantsi Formations, with type sections respectively carpathicum Dumitrica, Zhamoidellum ovum along the small river valley above the villsge ofDob Dumi trica and Parvicingula cosmoconica (Foreman). ridol, and in the road cut after the bridge at Rayantsi The new results confirmed the range from the Aale (West of the type section of the Momchil Formation) nian to the Oxfordian Stage. The exact dating of the and the locality Dobridolski vodenitsi. The shale-sil lower boundary of the Treklyano Group (Dobridol tstone formation (now- Momchil Formation) has been Formation and lowermost part ofRayantsi Formation) later (3aropqes et al., 1990) characterized as a lateral as well as the upper boundary of the Rayantsi Forma correlate of the Rayantsi Formation thus being also tion should be subject of further studies. an element of the Treklyano Group. Now, the group The introduction of the new Metohiya, Sredorek is fully characterized with the introduction of the and Momchil formations and the correlations with the Metohiya and Sredorek formations. Dobridol and Rayantsi formations (Fig. 3) allow a The type section of the Rayantsi Formation (Fig. better understanding of the Treklyano Group and a 2) has been studied again in detail, and re-sampled revision of the sedimentation within the Treklyano for calcareous nannofossils. The detailed studies of sedimentation zone. The beginning of the sedimen more than 30 samples did not find any. Thus, the con tation (Metohiya and Dobridol formations) is referred clusion (Zagorchev, 1986) that the Rayantsi Forma to late Early Jurassic times, and can eventually be tion consists of sediments deposited beneath the ceo parallelized with the beginning of the sedimentation has been confirmed. In the section, the Dobridol For in the Svetlya sedimentation zone (Pliensbachian) mation consists of about 3 m of sandstones and although the sedimentation within the two zones might siltstones, and is covered by about 20m of slates inter be diachronous. The possible upper limit is given by bedded with radiolarites. On the basis of deter theage(CanyHosetal., 1985, pp. 29,4l)ofthecove minations of radiolarians in numerous thin sections ring Antovo Member (Lower? -Middle Tithonian) 6 41 55J \bdC:C~fr.~=--:"< a ,... ., .. r ..W.tl&n 0(~~ ntd JIU'tlS.Ok 0 (l'~~b!... ~ote) . .liUJk Jwank Zagordlev (1986, Fig. 6) submarine deep c:anyon (Zagorc:hev, 1986) Fig. 4. Interpretative schematic sections for two possible palaeogeodynamic models of the Treklyano sedimentation zone (modified after Zagorchev, 1986) and Gorochevtsi Member (upper parts of the Middle possible correlation between the Rayantsi Formation, Tithonian - lower parts of the Upper Tithonian and the Dolno Loukovo Formation in the East Substage) of the Kostel Formation. Rhodope Mountains. Zagorchev ( 1986) emphasized on the lack ofcarbonate matter in the typical rock sequence of the Rayantsi Palaeogeographic and palaeogeodynamic Formation, and that this fact indicated sedimentation implications beneath the Calcite Compensation Depth (CCD). A depth of the order of2 km has been suggested Two possibilities have The new stratigraphic data throw new light over the been put forth, and namely: (1) deposition ofthe Rayantsi palaeogeographic and palaeogeodynamic problems Formation over the continental slope towards the Jurassic already discussed in the past. VardarOcean, and consequent uplift and eastward thrusting Previous research considered several explanations to the ofparts ofthat slope (present Morava Superunit) over the presence ofradiolarites in the Rayantsi Formation. Strowna Superunit during the eastward sulxluction ofthe Ha 'ieB ( 1969) referred the rad.iolarite-shaly interbedding Vardar Ocean; and (2) existence ofa narrow and deep gulf ("terrigenous-carbonate geocomplex") to a shorter time ofthe Vardar Ocean, similar to the present-day Gulf of span (Bajocian - Bathonian), and assummed that the California. A detailed interpretation has been given for the sedimentation continued after the Adigeian tectonic phase first option (Fig. 4) . in Callovian and Late Jurassic time according to the · The new evidence confirms the position ofthe Rayantsi sedimentation model ofthe Balkanides, i.e., with a carlxmate Formation beneath the CCD. However, transitions from this geocomplex (Callovian to Kimmeridgian), and pre formation both to the East (Momchil Formation) and West flysch (Kimmeridgian) and flysch (Tithonian) geo (Metohiya and Sredorek Formation) have been observed, complexes. In consequence, the radiolarite-shaly geo and all these formations are obviously product of complex is considered as a local deeper environment sedimentation within an enviroment transitional from interlude within the "normal" sedimentation evolution the shelf towards the continental slope. Therefore, it of the Jurassic marine basin. should be concluded that the Treklyano Group is ty .[lo.nexo.oa et al. ( 1984) and CanyHoB et al. (1983, 1985) pical of a deeper trench (Treklyano sedimentation defined several graben structures within the Krayshte region, zone) within the shallow Peri-Tethyan sea, and the the bathymetry ofthe Treklyano graben being referred to Rayantsi Formation is representative for the deepest the "upper part of the continental slope and the shelf canyon-like part of this trench. Transitions towards edge" on the basis of the trace fossil Chondrites pro the shallower Svetlya sedimentation zone (the section bably belonging to the ichnocoenosis Zoophycos. Goma Glogovitsa with radiolarite interbeds in the Following publications (e.g., Sapunov, Tchouma Yavorets, Gintsi and Neshkovtsi Formation) have been tchenco, 1994) introduced a Peri-Thracian zone si previously indicated, too (Zagorchev, 1986; Tikho tuated between the Serbo-Macedonian - Morava and mirova, Zagorchev, 1989; 3aropqes et al., 1990). No Thracian dry lands. This interpretation was based also direct links to the East-Rhodope Jurassic deeper on the suggestion by Zagorchev et al. ( 1989) about a marine environment could be assummed although 42 sedimentological correlations are obvious (Zagorchev West Bulgaria in the light of new stratigraphic data. - et al., 1989). A more detailed palaeogeodynamic Geologica Bale., 16, 5; 3-20. interpretation will be subject of another publication. Zagorchev, 1., Dinkova, J. 1991. Geological map of Bulgaria on the scale 1:100000. Sheet Bosilegrad and Radomir. Sofia. Acknowledgements. The authors are indebted to SOFGEO Zagorchev, 1., Boyanov, 1., Tikhomirova, L. 1989. Correlation PROOUCHVANE Ltd. for the financial aid to a part of the field of Jurassic sections from SW Bulgaria and Eastern Rhodopes work and the micropalaeontological studies, and to the participants by radiolarian complexes. - XIV Congress Carp.-Ba/k. Geol. in the geological mapping (Dimitar Angelski, Emil Goranov, Petko Assoc. Sofia, Extended Abstracts, 3; 795· 798. Pemov, Valeri Sachanski) for their help and support. This paper 6oa11eaa, H. 1996.10pcn~ p8,1lBOJJapaa ar pa3pe:Ja opa c. Pa is a contribution to the project NZ-603 of the National Fund llHIUI -103 li'ltJUBpu. - VI KO#Upec liuz. zeQ/1. d-eo; 62-63. "Scientific Research". .Ao.llcsoaa, JI., CaoyBos, H., liYM&'ICBJ:O, n. 1984. CJpaTBfP84lu aaneacna, 6aAOCCDIX a 6aTCKHX arnoaeul s 'I&CTH IOro- 3anll.llBol Bonrapu.- Geologica Bale., 14, 2; 3-56. 3arop'les, H., TH.XOMKposa, n. 1986. CrpaTKrpacllu 10pc-.::oi Tpeu.aca:oi rpyoow (10ro-3aouau Bonrapu) -Geolo References gica Bale., 16, 3; 23-44. 3arop'les, H., Tpa4loaosa, E., Tomes, A. 1990. Coa)UlZloT Budurov, K., Zagorchev, 1., Trifonova, E. 1993. The Triassic in opa 3eMeH,101'038D8.1lB& li"Wmlpu - reonoa-.::a pC3ynTaTB South":est Bulgaria. Upper Triassic red beds (Moesian Group) K TeiTOBCKH B3SO,IlB. - FeomeKm., meKmONOtjjU3. U zeo in the Golo-bardo Unit. - Geologica Bale., 23, 5; 35-45. duHaM., 21; 43-70. Budurov, K., Trifonova, E., Zagorchev, I. 1995. The Triassic in Ha11es, H.1969. n&TOJJOru aa XCTaHZ-IKMepll.llJ[CKHTe oTno Southwest Bulgaria. Correlation of key sections.- Geologica aeau s KpaimeTo.-Hse. Feo.11. UHcm., cep. Cmpamuzp. Bale., 25, I; 27-60. u .11Umo.11., 18; 127-156. Sapunov, 1., Tchoumatchenco, P. 1994. Introduction ill'evolution Hnea, Hs. 1985.10pcun eaonJOUHJI aa 61onrapca:aTe :JCMH. tectonique et paleogeographique de Ia Bulgarie au cours du · - Cn. liuz. zeQ/1. d-eo, 46, 2; 153-162. Jurassique. - Geobios, MS 17; 723-732. Caoyaoa, H., llepHJIBCIIl, c .. llyY8'1CHIO, n .. monos, B. 1983. Tikhomirova, L., Zagorchev, I. 1989. Radiolarian assemblages CTJ)8THrpatiiHJI HBZBeiOpCIKX OTnozeHHH B o6naCTH from the section Goma Glogovica, SW Bulgaria.-Geologica KpaHwTe (IOro-3ao8,1lHU Bonrapu). - Geologica Bale., Bale., 19, 2; 108. 13, 4; 3-30. Trifonova, E., Zagorchev, I. 1984. New biostratigraphic and CaoyHOB, H., llyY8'1CHIO, n .. .Ao.lleiosa, JI., liuanoaa, ,A. lithostratigraphic data on the Upper Triassic in SW Bulgaria. 1985. CTJ)aTHrpacllu a:ennoseicnx H sepxaeJOpCIHX - C.-r. Acad. bulg. Sci., 37, 4; 501-504. OTnoaeoaiiOro-3an8,1laol BonrapHH. - Geologica Bale., Tronkov, D. 1969. Neue Angaben iiber das Alter des bunten 15, 2; 3-62. Gesteine des "Rats" (Obere Trias) in Bulgarien.- C.-r. Acad . Tpoa.:os, ):{. 1983. CTJ)aTHrpacllH'Iecue opo6neMW HciWp bulg. Sci. , 22, I 0; 1169-1172. ca:ol np6oaaTaol rpyoow (Tpaac) 10ro-3aouaol Bon Zagorchev, I. 1986. Jurassic palaeogeography of a part ofSouth- rapHH.- Geologica Bale., 13, 5; 91-100. 43