GEOLOGICA BALCANICA, 30. 1-2, Sofia, Jun. 2000, p. 59-67 New data on the Middle and Upper Jurassic stratigraphy in the Konyava Mountain, SW Bulgaria 1 1 1 Ivan Zagorchev , Ekaterina Trifonova , Daria lvanova , 1 2 2 Kristalina Stoykova , Emil Goranov , Petko Pemov 1Geologicallnstitute, Bulgarian Academy of Sciences, 1113 Sofia; E-mail za&or@&eoloc bas b& 1"Sojgeoproouchvane" Ltd. (Submitted: June 23, 2000; accepted for publication: June 23, 2000) 3ai!op'leB, He .. TpurftoHOBa , E .. HeaHoea, ~. CmouKOBa, Abstract. A transition from the classical Jurassic Balkanide Kp .. ropaHOB, E .. fleMOB, n. HOBble c>aHHble 0 cpec>He- u development towards the predominantly terrigenous eepxHeiOpCKOU cmpamui!parftuu i!Opbl KoHRBbl, 103 EoAi!a ­ sedimentation pattern of the Treklyano zone is observed in the pUR. B npe.11enax ropbl KOHliBbl OC)'llleCTBJJlleTCll nepexo.ll OT Konyava Mountain. Most of the sections begin with the JUlaccH'fecKoro IOpcKoro pa3peJa lianKaHH.Il K npeKM)'llleCT­ sandstones of the Gradets Formation (Toarcian - Aalenian aeKHO TepHreHHOMY pa:1pe3y TpeiUlliHCKOH JOHbl. lioJJbWHH ­ Stage) followed by the Polaten Formation (shallow marine CTBO pa3pe30B Ha'fHHaiOTCll neC'faHHKaMH fpa.lleUKOH CBHTbl limestones; Aalenian - middle parts of the Bathonian Stage), (ryapCKHH - aaneHCKHH llpycb), CJJeD,)'IOT 00JJaTeHCK3ll CBH ­ Momchil Formation (shales and marls with limestone Ta (MeJJKOBO.IlHble MOpCKHe HJBeCTHliKH; aaneHCKHH- cpe.ll­ interbeds; upper parts of the Bathonian Stage - Oxfordian HHe 'faCTH 6aTcKoro llpyca), MoM'fHJJCKall CBHTa (aprHJJJJHTbl Stage), and the flysch Kostel Formation (Upper Jurassic). H MeprenH nepecJJaHBaiOlllHeCll nec'faHHK8MH; BepXHHe 'faCTH Some parts of the Kostel Formation are characterized here by 6aTcKoro llpyca -oKc<J>op.llCKHH llpyc) H <J>nHweBaJI KoCTen ­ a shallow-water marine sedimentation. In the north-eastern CKall CBHTa (aepxHllll 10pa). HeKOTOpble 'faCTH KocTencKoii parts of the Konyava Mountain, a lateral transition towards CBHTbl xapaKTepH3)'10TCll .llOBOJlbHO MeJJbKOBO.IlHbiM xapaKTe­ the Svetlya Jurassic graben has been observed, and the pOM ce.llHMeHTOB. B ceaepo-aoCTO'fHbiX 'faCTliX KoHliBCKOH Momchil and parts of the Kostel Formation are laterally ropbl ocyllleCTBJJlleTCll TaKliCe naTepanbH8ll CTHKOBKa KCaeT­ replaced by the carbonate breccia and conglomerate of the JJliHCKOMY IOpCKOMY rpa6eHy, a MoM'fHJJCK8ll H 'faCTH Koc­ Lobosh Formation (Callovian - parts of the Kimmeridgian TeJJcKoii CBHTbl JaMelllaiOTCll KapOOHaTHbiMH 6peK'fHliMH H Stage). KOHrJJOMepaTaMH flo60WCKOH CBHTbl (KaJJOBCKHH - 'faCTH KHMepH.IlliCCKOfO llpyca). Zagorchev, 1., Trifonova, E., Ivanova, D., Stoykova, K.., Goranov, E., Pemov, P. 2000. New data on the Middle and Upper Jurassic stratigraphy in the Konyava Mountain, SW Bulgaria- Geologica Bale., 30, 1-2; 59-67. Key words: Middle and Upper Jurassic; lateral variations; SW Bulgaria Introduction ping or extensive revisions bring forth new evidence that throws new light on palaeogeodynamic issues. The Jurassic stratigraphy, palaeogeography and The new geological mapping on the scale pa1aeogeodynamics of Bulgaria has marked con­ 1:25000 by Sofgeoproouchvane Ltd. in 1997-1999 siderable achievements and progress (s. Sapunov, gave opportunities for new revisions. Partially Tchoumatchenco, 1994). In Southwest Bulgaria, im­ published (Zagorchev et al., 1998) data about new portant evidence and conclusions (Ha'leB, 1969, Jurassic formations are here enlarged with new 1973, 1985) have found partial confmnation and biostratigraphic data on the Jurassic pre-flysch considerable improvement by ,[{o,aeKOBa et al. (1984), and flysch of the Nish-Troyan trough. The authors CanyHoB et al. (1983, 1985) and 3arop'leB, are grateful to Sofgeoproouchvane Ltd. for logistic THXOMHpooa (1986). However, the geology of the and financial support, and to Prof. I. Sapunov, for Krayshte region is so complex that every new map- field and laboratory consultations. 59 The present paper is a contribution to the (see Fig. 1). and namely (from west to east, and project 603 "Stratigraphic and tectonic correlations from bottom to top): of SW Bulgaria with the adjacent countries" of the (1) Treklyano sedimentation zone, western part: National Fund "Scientific Research". Metohiya Formation (lower Middle Jurassic) - Sredorek Formation (Middle- Upper Jurassic)­ Kostel Formation (Tithonian - Berriasian) The Middle - Upper Jurassic Treklyano sedimentation zone, central part: basin in Southwest Bulgaria Dobridol Formation (Toarcian? - Aalenian) - Rayantsi Formation (Aalenian? - Oxfordian - The Jurassic evolution of SW Bulgaria has first Kimmeridgian?) - Kostel Formation (Tithonian­ been thoroughly studied by Nachev (1970, 1974; Berriasian) Ha'feB, 1969, 1973, 1985). In his interpretation, the Treklyano sedimentation zone, eastern part: Po­ sedimentation proceeded in the consequent for­ laten Formation (Aalenian?- Bathonian) - Mom­ mation of the following geocomplexes: 1) conti­ chi! Formation (Bathonian? - Callovian - Kim­ nental terrigenous (Hettangian); 2) marine trans­ meridgian?)- Kostel Formation (Tithonian - Ber­ gressive terrigenous-carbonate (Upper Hettangian riasian) to Aalenian); 3) terrigenous (Aalenian - Bajo­ (2) Svetlya sedimentation zone (Jurassic gra­ cian); 4) terrigenous-carbonate (Bajocian- Batho­ ben): continental Zhablyano Formation (Lower nian); hiatus; 5) carbonate; 6) flysch (beginning Pliensbachian) - Ozirovo Formation (Upper with a preflysch in Kimmeridgian - Lower Titho­ Pliensbachian) - Gradets Formation (Toarcian - nian, continuing with a flysch in Tithonian to Ear­ Lower Aalenian?) - Polaten Formation (Aalenian ly Berriasian, and ending with carbonate post­ - Bathonian), hardground and hiatus - Lobosh flysch in Middle - Late Berriasian). The sedimen­ Formation (Callovian - Oxfordian) - Neshkovtsi tological features of the flysch have been also thor­ Formation (Kimmeridgian) - Kostel Formation oughly studied (e.g .• Nachev, 1970, 1974; Dimitr­ (Tithonian- Berriasian) ijevic, Dimitrijevic, eds .• 1987). Locally, the Juras­ (3) "Classical" Balkanide sedimentation with sic sedimentation has begun directly with a trans­ Upper Jurassic flysch: Gradets Formation (Toar­ gression of the terrigenous-carbonate (Bajocian - cian - Lower Aalenian) - Polaten Formation Bathonian) geocomplex. Several internal Jurassic (Aalenian- Bathonian), hardground, hiatus - Ya­ discontinuities have been referred to tectonic in­ vorets Formation (Callovian) - Gintsi Formation tra-Jurassic phases. (Oxfordian- Kimmeridgian)- Neshkovtsi Forma­ Although corresponding to the real evolution tion (Kimmeridgian) - Kostel Formation (Titho­ (with some age corrections) in large parts of the nian- Berriasian) Jurassic basin, this very generalized idea had to be (4) Sedimentation with Upper Jurassic carbon­ changed by later studies (CanyHoB H .ap., 1983, ate platform (e.g., Lyubash unit): Polaten Forma­ 1985; .l{o,aeKOBa H ,ap., 1984; JarOplfeB, THXOMH ­ tion (Aalenian- Bathonian)- Yavorets Forma­ pooa, 1986; Zagorchev, 1986; 3aropqea, .l{HHKOBa, tion (Callovian) - Gintsi Formation (Oxfordian - 1991; 3arop'feo, 1993; Zagorchev et at., 1998). Sed­ Kimmeridgian) - Slivnitsa Formation (Kimmerid­ imentation areas with substantially different devel­ gian -Hauterivian) opment have been outlined on the basis of detailed Remark. In view of the diachronous boundaries lithostratigraphy completed with new biostrati­ of the lithostratigraphic units, their range quoted graphic evidence, including new fossil groups for above is only indicative one. the region: brachiopods, miospores, foraminifers, Konyava Mountain (Fig. 2) is the border area radiolarians, calcareous nannofossils. One of the between three principal sedimentation zones. crucial problems concerns the transition from the Based on several important fossil findings, it has gradually deepening Middle - Late Jurassic basin been regarded as an area of the "classical" Bal ­ to the flysch sedimentation of the Nish-Troyan kanide sequence. Field and laboratory studies trough. Several type sections have been outlined pointed at the broad occurrence of the Momchil Fig. I . Comparative columnar sections for the Jurassic in the Konyava Mountain and some adjacent areas. Abbreviations for the names of the formations: dd - Dobridol Formation; g - Gintsi Formation; gr - Gradets Formation; zh - Zhablyano Forma­ tion; j - Yavorets Formation; lcs - Kostel Formation; lo - Lobosh Formation; mm - Momchil Formation; mt - Metohiya Formation; n - Neshlcovtsi Formation; po - Polaten Formation; ra - Rayantsi Formation; sl - Slivnitsa Formation; sr - Sre­ dorek Formation cliKr. I. CpaaHKTenHK JConoHJCOBK pa3pC3K Ja 10pan a KoHna nnaHKHa K HROK CDce.llHK o6n'llcTK. CaKpatUeHKll 3a KMeHaTa Ha CBKTKTe: dd - Jlo6piUlOnCICa; 8 - rKHCJCa; gr - rpueun; zh - >Ka6niHCJCa; j - jfaopeun; ks - KocrencJCa; lo - Jlo6owu; mm - MOM'fKncJCa; mt - MeToxKiicxa; n - Hewxoacn; po - nonaTeHcxa; ra - PuHcJCa; sl - CnKBHKWJCa; sr - Cpe.llopeJCcxa 60 Strouma superunit Lyubash time, Sredorek Rayantsi Rayantsi Klapar­ Tsurv­ Lobosb - unit Ma West East ovtsi enyano Chepino lu.cretaceous Turonian I- 100 Albian I- 110 Ill Aptian =Q ~ u 1- 120 ~• Hauterivian u BUTemlan r- 130 Beniaslan :::----:::: ks :-::: ks ••-:: ~:~::::.::.-:::.::. f..::: -••--- • ••••••--- ••••- •••••••••••.•• ---------- ----------- :.:.- k; ::::.- ::.-~ ks • :~: •••••••••••••• .!::.:.:::··.: ::;· .:::.: ks .:::.: :·;:____ :·.:: ~!.!..:'..:!~~!.!: 1----------4 ? ? ::.::.:::.:.::.:.::. ::::. .••••::::·. n ·:.... :.. .. :.: n :.:·:.:·:.:·· Kbnmerldg. ?