GEOLOGICA BALCANICA, 33. 3-4, Sofia, Decemb. 2003, p. 15-22 Palaeogene sediments (Mechit Formation) near Panagyurishte and Strelcha (Sredna gora Mts.) Ivan Boyanov, Ivan Zagorchev, Aleksander Goranov Geological Institute, Bulgarian Academy of Sciences. 1113 Sofia; E-mail [email protected] (submitted: 1. 12. 2203; accepted for publication: 22. 12. 2003) H6. DOJ/H06, H6. 3azop'le6, AA. ropaH06. - flaAeozeHo- Abstract. The newly-introduced Mechit Formation is a 6ble ocaoo'lHbte nopoobl (Me'lumcKaJ/ cGuma) 6 pauoHe continental (fluvial) sequence of conglomerates and flaHa210puwme u CmpeA'lU (CpeoHozopue). HosoycTa­ sandstones with occasional clays and coalefied plant de­ HOBJieHHall Me\fHTCKall CBHTa CJio:>KeHa KOHTHHeHTaJib­ bris. The pebbles derived from pre-Alpine basement HOH llOCJieJ].OBaTeJibHOCTbiO - pe'IHbiMH KOHrJIOMepa­ rocks (gneisses, amphibolites, granites, pegmatites) and TaMH H neC\faHHKaMH, MeCTaMH - C rJIHHHCTbiMH npOCJIO­ Upper Cretaceous (Coniacian - Campanian) sedimen­ liMH H o6yrneHHbiMH pacTHTeJibHbiMH o6noMKaMH. B tary, volcanic and intrusive rocks and ores. The forma­ raJi bKax npe.ncTasneHbi nopOJJ.bi .noaJibnHikKoro ocHosa­ tion is more than 570 m thick. It covers with unconform­ HHll (rHeHCbl, aM<flH60JIHTbl, rpaHHTbl H nerMaTHTbl) H able depositional contact Maastrichtian flysch and older sepxHeMeJIOBbie (KOHbliK-KaMnaHCKHe) oca.no'IHbie, syn­ Cretaceous and pre-Cretaceous rocks, and forms denu­ KaHH'IeCKHe H llJIYTOHH\feCKHe nopO.Il.bl, a TaK)I(e - opy­ dation pockets and neptunian clastic dykes in the pre­ .neHeHHll. MowHOCTb Me'IHTCKOH CBHTbi 6onee 570 m. Cretaceous basement. On the basis of taxa from the 0Ha 3aJieraeT HeCOrJiaCHO Ha MaacTpHXTCKOM <flJIHWe H Normapolles group, the formation is referred to upper­ Ha 6onee .npeBHHX MeJIOBbiX H .noMeJIOBbiX nopo.nax. B most Maastrichtian - Danian. The new data point at the .llOMeJIOBOM OCHOBaHHH ee nopOJJ.bl JanOJIHJIIOT J].eHy.na­ existence of a considerably eroded relief of the Late Cre­ UHOHHbie KapMaHbl H 06Ha)l(aJOTCll B BHJ].e HenTyHH\feC­ taceous Srednogorie orogen already in late Maastrichtian KHX KJiaCTH\feCKHX .naeK. B03paCT CBHTbl onpe.neJieH KaK time, and of a fluvial system draining the region towards ll03JJ.HeMaacTpHXTCKHH·J].aTCKHH Ha OCHOBaHHH BHJ].OB, North and East - into the then existing narrow sea gulf npHHa.nJie)l(alllHX K rpynne Normapolles. YcTaHOBJieH­ from the Emine flysch trough. Hbie <flaKTbl CBHJ].eTeJibCTByiOT 0 3Ha'IHTeJibHOH paC\fJie­ HeHHOCTH H o6 3p03HH noJ.nHeMenoBoro Cpe.nHoropcKo­ ro oporeHa ewe B noJ.nHeMaacTpHXTCKOe speMll, a TaK)I(e - 0 cyweCTBOBaHHH pe'IHOH CeTH, nepeHOCliUleH CHe­ ceH HbiH MaTepHaJI K cesepy H BOCTOKY B Y3KHH MOpCKOH JaJI HB 3MHHCKoro <flnHwesoro Tpora. Boyanov, 1., Zagorchev, 1., Goranov, A. 2003. Palaeogene sediments (Mechit Formation) near Panagyurishte and Strelcha (Sredna gora Mts.). - Geologica Bale., 33, 3-4, 15-22. Key words: Palaeocene; Srednogorie zone; palaeogeography. Introduction rocks with the Middle Eocene sediments in the central parts of Stara planina (Balkan) range. The Palaeogene sediments south of the towns Dimittova et al. (,[(HMIHpoaa et al., 1984) clai­ of Panagyurishte and Strelcha have been first med for the same rocks a Late Cretaceous mentioned as polygenic conglomerate by (Maastrichtian) age. Similar sediments have Bonchev (EoHtieB, 1907). Hristov (XpHCTOB, been found in denudation pockets and nep­ 1953, 1960) made a thorough mapping (with tunian clastic dykes as a cover over the gneis­ area exaggeration at the expense of Upper Cre­ ses and granite of the Sushtinska Sredna gora taceous sandstones) and parallelized these block ("anticlinorium") (qyHeB et al., 1966), 15 and have been considered (together with all crops shown on the geological map 1: I 00 000. other post-Cretaceous sediments in the Pana­ Most of the sections are not sufficiently ex­ gyurishte and Strelcha areas) as Priabonian. posed. Therefore, we describe here (Fig. 1) only Recently (A.rra,.ll)Kosa-XpHcl.fesa et a!., 1991 ), the type section (Strelchanska Louda Yana the Palaeogene sediments south of Panagyuri­ south of Strelcha) situated in the Mechit strip, shte and Strelcha have been referred to the and the reference section situated near the marine Middle Eocene (Lutetian) Staropatitsa spring Rayna Knyaginya north of the village of Formation. Popintsi (situated in the Popintsi strip). The present authors made field revisions and Defining features. Mechit Formation consists palynological analysis aiming at a determina­ of coarse terrigenous continental sediments: tion of the age and lithology of these sediments conglomerates with smaller amounts of sand­ within the scope of the projects 503 (National stone and coal-bearing siltstone. The pebble Fund "Scientific Research") and "Geology of composition corresponds to 1) the composi­ Bulgaria" (Geological Institute of the Bulgar­ tion of the basement of the Srednogorie zone ian Academy of Sciences). The preliminary re­ exhibited mostly in the Sredna gora crystalline sults have been already published (Zagorchev block: Precambrian two-mica, biotite and et al., 2001a). The palynological analysis made hornblende gneisses, amphibolite, Palaeozoic by S. Chernyavska and P. Pavlishina hornblende-biotite, biotite and two-mica gran­ (Zagorchev et al., 2001a; Pavlishina, 2002) has ites, pegmatite and quartz as well as the Late proven a latest Maastrichtian - Danian age. Cretaceous intrusive and dyke rocks and the The present publication aims to summarize the ore related to them; 2) the composition of the whole stratigraphic evidence gathered for to Late Cretaceous Srednogorie zone: Upper enable further palaeogeographic and palaeo­ Cretaceous andesites, dacites and trachytes, geodynamic interpretations. tuff, sandstone and marl. The rocks of the for­ The death of our esteemed colleagues and mation build irregular beds. Denudation close friends S. Chernyavska and I. Boyanov pockets and neptunian clastic dykes are also came before the finalization of our studies. present. The Mechit Formation covers with This publication is also a tribute to their me­ depositional contact all pre-Palaeogene mory. rocks of the Srednogorie zone that crop out in the area. Mechit Formation Lithological composition (new formation: The Mechit Formation is built up mostly of MeqJfTCKa CBHTa) polygenic conglomerates. The dimensions of the pebbles broadly vary: from several millime­ Name. The Formation is named after the peak ters to tens of centimeters and up to 1.2-1.5 m. Mechit situated south of Strelcha, west of the The pebbles are usually well rounded, and the type section. forming rocks show different degree of weath­ Historical notes ering. A thin weathering crust is often visible. Hristov (XpHCTOB, 1953) mapped 4 strips of The lithological composition of the pebbles sediments attributed by him to the Palaeogene usually corresponds to the immediate neigh­ (Middle Eocene). The authors of the geologi­ boring environment, and namely: 1) Upper cal map on the scale I: 100 000 (MJIHes, Cretaceous volcanic rocks: almost black and KauKoB, 1990) fully accepted the northern­ massive basalts (with rare phenocrysts), red­ most (Mechit) strip, and considerably reduced dish and gray well-crystallized latites arid the area of the second (from north to south) dacites, greenish differently crystallized strip entirely rejecting the other two (near the andesites, and (rarely) light-gray rhyodacites villages of Banya and Buta, and the prolonga­ and dacites; 2) Upper Cretaceous intrusive tion to Popintsi). rocks: subvolcanic to hypabyssal monzonites, During our studies we have visited several quartzdiorites, granodiorites and syenodiori­ sections of all four strips mapped by Hristov tes; 3) Upper Cretaceous sedimentary rocks (XpHCTOB, 1953). The two southern strips as (marls, sandstones); 4) Palaeozoic granitoids well as most of the third (Popintsi) strip turned (from the Poibrene quartzdiorite pluton, or the to be built by Upper Cretaceous sediments. Smilovene granodiorites and granites) and Thus, the Palaeogene sediments are con­ pegmatites; 5) rarely and only in some expo­ firmed, with additional outcrop reduction and sures (but abundant in the denudation pockets some tectonic detailization, within the out- and neptunian clastic dykes NNW of Pana - 16 · . · .. - .... : .. t.. ;,...,....,~tpn gyurishte) biotite and two-mica gneisses and (5) 2.5 m polymictic sanastone w1w • .,v""'"'.... migmatites, and amphibolites. pebbles, and polymictic conglomerate Sandstones are present as separate beds tens (4) 5 m polygenic conglomerate built up of me­ of centimeters to several meters thick. They are dium-sized to coarse pebbles of a grayish or yellowish colour. The grain di­ (3) 8-10 m coarse-grained polymictic sand­ mensions greatly vary, and the sandstones show stone with isolated pebbles all transitions from coarse-grained through me­ (2) 30 m polygenic conglomerate dium-grained to fine-grained sandstones and (1) thin (2-1 0 em) siltstone to shaly sandstone sandy siltstone. The cement is usually clayey, rich in coal substance sample 9j99 - coal­ and less frequently a carbonate one. Millimet­ bearing siltstone ric to centimetric pebbles are often included in - lower contact: tectonized surface striking the abundant sandstone mass. The clay content 160°/40-50°ENE over tectonized andesite. is relatively small. Coalefied plant debris are sometimes abundant, and the rock becomes a Reference section at the spring coal siltstone to sandstone. Rayna Knyaginya north of Popintsi (Plate I) Description of the sections