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<tJKUHIUlbHble JlKTO· rnational Stratigraphic Guide. ~a4JH'feCKHe ellHHHUbl BBOllliTCll BDepsble B HaUHO· The Upper Triassic Kobile Formation is situated at the top of ZLiloB)'10 CTJ'8THrpa4JK'feCK)'IO HOMCHKJiaT:ypy, B COOTBCT· the Triassic section (over the red beds of the Norian Komshtitsa c HauHOHBJibHblM CTJ'BTHrpa<tJH<tCCKHM JCOllCJCCOM H c Formation). It consists of phosphate- and sulphate-bearing l*:&.:t)'llapOllHbiM CTJ)aTHrpa<tJH<tCCJCHM pyJCOBOllCTBOM. yellowish sandstone and siltstone interbedded with grey Bepue-rpHacosall Ko6HJJCKall CBHTa pacnonaraeTCll B ca­ limestone and dolomitic limestone. Occasionally, they contain .:p~ TJ)HaCOBOfO pa3pC3a, Hall HOpCICOH KOMWTHUJ:OK echinids, gastropods, crinoid ossicles, algae and foraminifers . a.TOi. 01:1a COCTOHT HJ 4Joc4JaT· H C)'Jib4JaT-COllCpliCalllHX The Metohiya Formation (basal conglomerate built up of -=.c:t OIIilThlX DCC'iaHHICOB HanespOJIKTOB nepecnaHBaiOlllHXCll quartz and lydite pebbles; quartz sandstone; loose yellowish api10i11 113BeCTHJIJCaMH HllOJIOMHTOBhiMH H3BCCTHJIIC&MH. sandstones and occasional limestone interbeds) covers the Upper li=cTa.wH OHH COllepJKaT 3XHHHllbl, raCTJ)ODOllbl, 'lJICH'fHXH Triassic with unconformable depositional contact. The age is JI¥IE3111llll.ll08, BOllOpOCJIH H 4JopaMHHHif!Cpb1. considered as Middle Jurassic (eventually beginning in upper­ e-TOll HHCKall cs•na (6aJBJibHblK XOHfJIOMepaT, most Lower Jurassic) on the basis of regional correlations. cwc:=wwsswii HJ JCBapueBOK H JIHllHTHOH ranbXH; ICBBpUCBblC The other two newly introduced Jurassic formations belong ...,... .,.._..IIUl; DJIOXO CUCMCHTHpOBBHHblC DCC'faHHICH H to the Treklyano Group and are of Middle- Late? Jurassic age . ~II:.I~Bhi C DJiaCTbl H3BCCTHliKOB) DCpeiCphiBaCT BCpXHHH The Momchil Formation is built up of shales and siltstones C liCCOrJiaCHblM CCllHMCHTBUHOHHblM ICOHT&KTOM . interbedded with limestones. The Sredorek Formation consists _,_,N"T pacMaTJ)HB&CTCll K&IC HHJICHC? - cpCllHCIOpCI:HJi Ha of limestones and marls with shaly interbeds and olistostrome ......BIIH perHOHaJibHblll XOppCJIJIUHJi. built up ofTriassic limestones and siltstones. Lateral correlations e llBC HOBOBBCllCHHhiC CBHThl · cpC)lHC- BCpXHe? with the deep marine sequence (shales and radiolarites) of the .m~a~ilrO BOOpaCTa npKHBllJICJKaT TpelCJUiacJ:oA rpynne. MoM­ Dobridol and Rayantsi Formation make possible the recon­ ._......,ULII CBHTa CJIOJKCH& H3 apri!JIJIHTOB ll aneBpOJIHTOB struction of a Jurassic narrow and deep submarine canyon within * w<' MIIUIOlllHXCll C H3BCCTHJIJCaMH. CpellOpeXCUJI CBHTa the Peri-Tethyan shallow sea. KJ ll3BCCTHJIICOB H McprCJICH C aprHJIJIHTOBblMH DpO· ::::111:'11!1~0., II OJIHCTOCTJ'OMOM H3 TJ'HBCOBblll H3BCCTHliKOBhiX ~ BhiX OJIHCTOJIHTOB. Ha ocHose naTepam.Hwx ~:op ­ p:.-.:n- C rny60J:OM0pCICOH DOCJIC)lOBaTCJibHOCTH (aprHJI· • panaonllpHTbl) )lo6pHJlOJICJ:Oii H PaaHcJ:oii CBHT IIIK!~!Z!rapaoHCTJ'YICUHll rny6oxoMopc~:oro yJ~:oro J:llllholfa attE..-In' ITepi!TeTHCCJ:oro wen~><tJoro Mopa. ~ , 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