GEOWGICA BALCANICA. 26. 3, Sofia, October, 1996, p. 39-46

Turonian biostratigraphy in a part of Southwestern Bulgaria

Velislav Minev, Polina Pavlishina, Ekaterina Dimitrova

Geological Istitute, Bulgarian Academy of Sciences, 1113 Sofia

(Received 23.10.1995; accepted 29.02.1996)

B. MuHe8, n. lla8JIUWUHa, EK. ,auMumposa- Euocm­pamuzpaljjUR mypoHcKozo Rpyca s otacmu /Oi!03ana{}­Hoii Eo;uapuu. Hccne.noBaHbl n.ATb BepXHeMenoBhle pa3-pe3a K 3ana.11y ropo.na lipe3HHK. CoBMeCTHoe BepTH­QJibHoe pacnpOCTpaHeHHC aMMOHHTOB, 4>opaMHHH4lep, .D.HHOUHCT, coop H Dhlnblla npe.nnarae-rcH BnepBble B lion­rapHH. 3TO .D,MO B03MO)I(HOCTb TO'IHO OT.D.enHT H .D.e<t>H­HHpOB8T Bcex TYJ)OHCKHX no,u.ApycoB. YcnuosneHble rpa­HJHll>l HH)I(HOfO·cpe.D.HerOBO H cpe.D,Hero-BepXHOfO DO.D,.A­pyCOB, a TaK)I(e H BepXH8JI rpaHHUa TYJ)OHCKOfO .Apyca B H3Y'feHLIX pa3pe3ax.

Abstract. A succession of outcrops in the region west of the town of Breznik has brought new biostratigraphic re­sults concerning the Turonian Stage in the area. Integrat­ed vertical distnbution of ammonites, foraminifers, di­noflagellate cysts, pollen and spores is proposed for the first time in Bulgaria. This combined study enables the recognition of the three Turonian substages for the first time in the region. The lower and upper boundaries of the Middle Turonian and the upper Turonian boundary are defined by ammonites, elaborated with the data obtained from the other microfossil groups.

Minev, V. PavJishina, P., Dimitrova, 1996. Turonian biostratigraphy in a part of southwestern Bulgaria. - Geologica Balcanica, 26. 3; 39-46.

Key words: Turouian biostratigraphy, ammonites, foraminifers, dinoflagellate cysts, pollen and spores, Southwestern Bulgaria

Introduction

The present paper is a report of the integrated biostratigraphical investigations on the Turoni­an succession in a part of Southwestern Bulgar­ia It involves the data obtained from the study of four fossil groups: ammonites, foraminifers, dinoflagellate cysts, pollen and spores. The need to reconsider the existing stratigraphical scheme for the Turonian in the region and the lack of convincing biostratigraphical evidence for its subdivision was apparent when undertaking this srudy. Thus, its main goal is to draw out the integrated vertical distribution of macro- and microfossils, correlation of the studied sections and detailed biostratigraphical subdivision of the Turonian Stage in the area. This combined study enables the founded recognition of the three Turonian substages for the first time in the re­gion and may considerably clarify the existing inexactness and discrepancy connected with this stratigraphic interval here.

This study is made under the Project NZ -204 "Geological evolution and palaeogeodynam­ics of Bulgaria in the Mesozoic and Tertiary", financed by the National Fund "Scientific re­search" and is a contribution to the IGCP Project 362 - "Tethyan and Boreal Cretaceous".

Previous investigations The main biostratigraphical investigations con­cerning the Upper Cretaceous sediments in the study area were done in the sixties. In these ear­lier important works Tzankov (QanKOB H .np., 1960; QanKoB, EaKaJIOBa, 1962; QanKoB, 1968) recognized "Upper Turonian, Lower Senonian, Upper Senonian and Maastrichtian". This "scheme" was based on several unillustrated macro- and microfaunistical finds, often with­out information about the s'i.udied sections and their stratigraphic position. Part of the consid­ered ammonite and inoceramid taxa were im­properly determined or with incorrect strati-

39

graphic evaluation. The speciesLewesiceras per­amp/urn (Mantell) was reported by Tzankov as Pachydiscus peramplus (Mant.) (QaHKOB H .np., 1960) or as Lewisoceras peramplus (Mantell) (QaHKOB, 1968); in both cases the author im­properly referred it to the Upper Turonian. The known occurrence of this species is in the Low­er and Middle Turonian (Housa, 1967; Kennedy, Wright, 1981; Wright, Kennedy, 1981; Kennedy, 1984, 1985; Minev, 1994 a, b). The zonal index of the currently adopted Lower Turonian zone Inoceramus labiatus (Schlotheim) in all cases has been referred to the Upper Turonian. Pri­onocyclus wyomigensis (Meek) was reported from the "Lower Senonian". This species is charac­teristic marker for Late Turonian age and is drawn as zonal index in the scheme proposed by Cobban (1984, 1990) for the Turonian in USA. The specification of the most Collignoceratid species has been already discussed by Minev (1994 b), while the so-called "Upper Senonian" was not argumented by fossils. w

Y olkichev and Karagyuleva (HoJIKH'IeB, Kapanonesa, 1962) recorded Lower Turonian ammonite faunas from the Melovete Hill in the surrou~dings of the village Kosharevo, an area close to the study region. The Early Turonian age was evidenced by finds of M ammites cf. no­dosoides Schlotheim and Collignoniceras (Selvi­noceras) sch/uterianum (Laube & Bruder). The former species is zonal index of the currently adopted uppermost Lower Turonian zone, whereas the latter is a junior synonym of the species Collignoniceras woollgari (Mantell) (Kennedy, Wright, Hancock, 1980; Kennedy, Wright, 1981; Wright, Kennedy, 1981; Minev,

_,-,C •

PARAMOUN

• BREZNIK

SOFIA

-1011m111 Fig. 1. Sketch-map of the study region with location of the sections: 1 - "lzvor", 2- "lzvor- B", 3- "Rebro", 4-"Lyalintsi", S- "Paramoun"; formations (after Kostadinov in 3arop~ea et al., 1995): I -coal-bearing formation, II- marl-limestone formation, III - limestone-marl formation

40

1994 b) - a zonal index of a Middle Turonian zone of the same name.

Dimitrova et al. (1981) proposed generalized stratigraphic scheme of the Upper Cretaceous in the Western Srednogorie based on foramini­fers. The authors used again in their stratigraphic conclusions Tzankov's macrofaunistic fmds with the above considered improperties, which ques­tions their correlation with the foraminiferal associations and some of the conclusions.

Recently Sinnyovsky (CHHLOBCKH, 1993) in­dicated nine nannofossil zones in the stratigra­phic interval of Turonian to Maastrichtian in the Western Srednogorie. The paper did not con­sider the detailed stratigraphic subdivision of the Turonian Stage in the area.

Sedimentological investigations were provid­ed by Ganeva et al. (1978) for the region of Slivnitsa and by Nachev et al. (Haqes H .np., 1981) for the Western Srednogorie. In both papers the biostratigraphical base for the stage definition is conditional.

Kostadinov in Zagorchev et al. (3aropqes H

.np., 1995) recognized the following four Upper Cretaceous formations in the area: coal-bear­ing, marl-limestone,limestone-marl and calcar­eous-clayey-sandstone ones.

Formal lithostratigraphical units have been not introduced for the Upper Cretaceous suc­cession in the study region.

Material and methods

The study is based on five sections in the area (Fig. 1 ). Approximately 100 samples have been analyzed for microfossils and more than 80 ammonite, inoceramid and echinid specimens and pieces have been collected from this se­quence. The whole macrofauna is kept at the Museum of Palaeontology, Sofia University "St. Kl. Ohridski". Most of the foraminiferal exami­nations have been done in thin sections. All·thin sections and isolated fossils are stored at the Geological Institute, Bulgarian Academy of Sci­ences. The samples were prepared for palyno­logical analysis according to standard prepara­tion techniques. The slides containing palyno­morphs are stored at the Geological Institute, BAS.

Unfortunately, both macro- and microfossils vary quantitatively and in their species diversity in the sections. So, ammonites were collected mainly by three of them - "lzvor", "lzvor - B" and "Lyalintsi". The Turonian sediments in the section "Paramoun" remain barren of palyno­morphs. Foraminifers were obtained from all sections, but in some intervals their associations are poor and (or) badly preserved.

Description of the sections

The Turonian succession was studied in five principal sections in the Lyubasha Unit by Zagorchev et al. (3aropqeo H ,llp., 1995), where the three Turonian substages were recognized and biostratigraphically defined. From east­southeast to west-northwest direction the sec­tions are as follows: "lzvor", "lzvor - B", "Re­bro", "Lyalintsi" and "Paramoun". Location of the sections is shown on Fig. 1. Lithology and sample positions are presented on Fig. 2.

Section southeast of the village of Izvor

This section is studied along the deepest ravine in the slope southeast of the village. The Turo­nian sequence is represented by two packets (No 2-1) (70.00 m). 2. (47.00 m) Continuos flyschoidal alternation of sandy to clayey limestones and marls. Marls predominate in the upper part of the packet. The following taxa are defined from this interval: ammonites - Scaphites geinitzii ( d'Orbigny),Subprionocyclus neptuni (Geinitz), Collignon-

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IZVOR 120m

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REBRO 120m

iceras bravaisianum (d'Orbigny), Co/lignoniceras caroli­num (d'Orbigny) and Co//ignoniceras wool/gari (Mantell); foraminifers- Marginotruncana pseudo/inneiana Pessa­gno,Marginotruncana renzi (Gongolfi), Marssonella oxy­cona Reuss, a lot of Hedbergella sp. and Whiteine//a sp.; singie specimens of Ostracoda and many Radiolaria. 1. (23.00 m) The upper 3-4 m of the packet consist of limestones with glauconite to glauconitic limestones. Downwards yellowish and sheeted sandy marls, interca­lated by thin (0.10-0.15 m) limestones occur. The lime­stone beds become thicker and rare in the lowermost parts of the packet. The following taxa are found: ammonites­Co/lignoniceras woo/lgari (Mantell), Collignoniceras car­olinum (d'Orbigny) andLewesiceras peramplum (Mantell); foraminifers - Whiteinella archaeocretacea Pessagno, M arginotruncana pseudolinneiana Pessagno, M arssonella oxycona Reuss, single Lenliculina sp., Rabdammina sp., Hedbergella sp. and a lot of Radiolaria; dinoflagellate· cysts - Subti/isphaera pontis-mariae (Deflandre) Len tin & Wil­liams, Isabelidinium cooksoniae (Alberti) Lentin & Will­iams, lsabelidinium acuminatum (Cookson & Eisenack) Stover & Evitt, Epelidosphaeridia spinosa (Cookson & Hughes) Davey, Microdinium omatum Cookson & Eisen­ack and Gonyaulacysta cassidata (Eisenack & Cookson) Sarjeant; pollen and spores - Atlantopollis microreticu/a­tus Krutzsch, Complexiopol/is complicatus Goczan, Cic­atricosisporites hughesii Dettmann and Vadaszisporites urkuticus (Deak) Deak & Combaz.

~09

~08

R-07

R-06 R-05

R-o4 fH)3

~

LYALINTSI lOOm

W-NW }J;i>

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PARAMOUN 95m

Fig. 2. Summarized lithology of the sections and sample positions; I - alternation oflimestones, clayey limestones and marls, II - limestone with glauconite, DI - conglomerate, IV - no outcrops, V - sample position

6 41

Section southwest of the village of Izvor

The section "lzvor - B" is situated along the slope southwest of the village. The sequence in­cludes several outcrops in three shallow gullies. The base of the sequence is represented in the eastern one and continues in the other two gul­lies. Two packets are recognized in the Turoni­an part of the sequence (No 2-1) (55.00 m). 2. (40.00 m) Irregular alternation of marls, clayey lime­stones intercalated by medium thick, distinct limestone beds. The clayey limestones and marls contain small Col­lignoniceratids- Collignoniceras carolinum (d'Orbigny), Collignoniceras bravaisianum (d'Orbigny) and Subprion­ocyclus neptuni (Geinitz); single and obscure ? Trocholi­na sp., ? Praeglobotruncana sp. and some other indeter­minable foraminifers. The uppermost parts of the packet yielded rich dinocyst association: Subtilisphaera pontis­mariae (Deflandre) Lentin & Williams,lsabelidinium cook­soniae (Deflandre) Lentin & Williams, lsabelidinium acuminatum (Cookson & Eisenack) Stover & Evitt, Se­noniasphaera rotundata Clarke & Verdier, Odontochitina costata Albert~ Circulodinium distinctum (Deflandre & Cookson) Jansonius and Microdinium omatum Cookson & Eisenack as well as the pollen species Atlantopollis mi­croreticulatus Krutzsch, Complexiopollis christae (Ameron) Krutzsch and Complexiopollis complicatus Goczan. 1. (15.00 m) The upper 3-4m of the packet are built up of glauconitic limestones, successively replaced by limestones with glauconite. Downwards an alternation of clayey lime­stones and marls with thin limestone intercalations oc­curs. These sediments yielded single specimens from the ammonite taxa Collignoniceras woollgari (Mantell) and Collignoniceras carolinum (d'Orbigni); bad preserved planktonic foraminifers and some Orbitolina sp.; the di­nocyst species Subtilisphaera pontis-mariae (Deflandre) Len tin & Williams, lsabelidinium cooksoniae (Deflandre) Lentin & Williams, lsabelidinium acuminatum (Cookson & Eisenack) Stover & Evitt and Senoniasphaera rotunda­to, Clarke & Verdier; the pollen taxaAtlantopo/lis microre­ticulatus Krutzsch H Complexiopollis christae (Ameron) Krutzsch.

Section south of the village of Rebro

The section is exposed in a little ravine, south of the viJlage and 0, 7 km northwest of the road to viJlage Krivonos. The outcrops are not very representative, often slumped or covered by grass. Two packets are described (No 2-1) (about 75.00 m). 2. (above 45.00 m) Marls, alternated by clayey limestones and limestones. Limestone beds are frequent and thicker in the uppermost 11-12 m. Marls and clayey limestones become more sandy in the middle 18-20 m of the packet. The fossils are rare and badly preserved. l. (about 30.00 m) Yellowish, very clayey marls to clays, overlaid by grey-yellow sandy marls and grey clayey lime­stones followed by 0.5 m thick limestone bed with glauco­nite. The lower parts yielded very poor foraminiferal asso­ciation of Hedbergella sp. and Whiteinella sp., small Het­erohelicidae and some Radiolaria.

Section southwest of the village of Lyalintsi

This section is described in the southwestern end of the village. The Turonian sequence is 42

represented by three packets (No 3-1) (above 50.00 m). 3. (above 30.00 m) Yellowish sandy limestones with rare intercalations of marls. Two ammonite taxa are determined - Subprionocyclus neptuni (Geinitz) and Collignoniceras bravaisianum (d'Orbigny). The upper boundary of the packet is not clear and continues in a pine-wood. Thick­ness determination is approximate. 2. (16.00 m) Grey sandy marls, interbeded by yellowish to ~ey limestones of various thickness. Two ammonite spec­unens are found: one Collignoniceras wool/gari (Mantell) and one Co/lignoniceras carolinum (d'Orbigny). The fora­miniferal association is similar to that, obtained from the same levels in section lzvor - a lot of Hedbergella sp. Whiteinella sp., one ? Praeg/obotruncana sp. and many Radiolaria. Dinocyst assemblages are like those, established in packet No 1 from the sections Izvor and Izvor - B: lsabelidinium cooksoniae (Deflandre) Lentin & Williams, Isabelidinium acuminatum (Cookson & Eisenack) Stover & Evitt and Senoniasphaera rotundata Clarke & Verdier. The pollen taxa Complexiopollis christae (Ameron) Krutzsch, Complexiopollis complicatus Goczan predomi­nate as well as Vadaszisporites urkuticus (Deak) Deak & Combaz. 1. (about 2.00 m) Conglomerate bed. The matrix is red and sandy, with glauconite. Barren of fossils.

Section northeast of the village of Paramoun

The sequence is represented in two outcrops. The lowermost part is situated east of the vil­lage. The upper part is exposed along the high­way Breznik- Trun, west of the road to Para­moun. Two packets can be recognized (No2-l) (above 60.00 m). 2. (above 55.00 m) Medium to thick-bedded grey-yellow­ish clayey limestones with intercalations of reddish marls. Downwards sandy and whitish marls, interbedded by grey­greenish and dense limestones occur. A fairly rich fora­miniferal association of Middle and Late Turonian age is determinated- Marginotruncana coronata (Bolli), Mar­ginotruncana pseudolinneiana Pessagno, Marginotrunca­na renzi (Gandolfi), Marginotruncana tarfayaensis (Leh­man), Sigalitruncana sigali (Reichel), Sigalitruncana schneegansi (Sigal), Concavatotruncana primitiva (Dalbi­ez), Marssonella oxycona Reuss. 1. (above 5.00 m) Fine-grained conglomerate to gravel and yellowish coarse-grained sandstone, without any fossils.

Biostratigraphic results

Ammonites

The Turonian succession of the studied sections yielded good Turonian ammonite faunas, al­though in certain intervals ammonites are rare and not very well preserved. The so defined taxa are represented by comparatively low species diversity, but the number of specimens belong­ing to one and the same species is high and their associations are quite characteristic. The strati­graphic distribution of the established taxa is summarized on Fig. 3.

Two of the defined ammonite taxa are very important for the Turonian stratigraphy- Col-

lignoniceras woollgari and Subprionocyclus nep­tuni. The former is a zonal index of the current­ly adopted standard Middle Turonian zone in Europe, America, North Africa and Japan (Kennedy, 1984, 1985; Cobban, 1984, 1990; Matsumoto, 1984, 1991; Matsumoto et al., 1991 ), whereas the latter is an index species or the stan­dard Upper Turonian zone in Europe and Ja­pan (Kennedy, 1984, 1985; Matsumoto, 1984, 1991; Matsumoto et al., 1991). Both species are documented and indicate the presence of Colli­gnoniceras woollgari Zone and Subprionocyclus neptuni Zone in three of the investigated sec­tions ("lzvor", "lzvor - B" and "Lyalintsi"). Their succession enables the definition of the Lower, Middle and Upper Turonian substages and their boundaries. The lower boundary of the Middle Turonian is worldwide currently traced by the first occurrence of the representatives of C. woollgari. Their disappearance and the first occurrence of S. neptuni is taken to coincide with the boundary between the Middle and Up­per Turonian substages. The last occurrence of S. neptuni is considered to draw out the upper boundary of the Turonian Stage in Europe (Kennedy, 1984, 1985).

The species Collignoniceras carolinum is also biostratigraphically important. It follows the stratigraphic range of the zonal index C. wooll­gari and is restricted within the Middle Turoni­an zone of the same name (Kennedy et al., 1980; Wright, Kennedy, 1981, Minev, 1994 b). Lewesiceras peramplum is characteristic mark­er for the upper parts of the Lower Turonian (Mammites nodosoides Zone) and for the Mid­dle Turonian substage (Collignoniceras wool/gari Zone) (Housa, 1967; Kennedy, Wright, 1981; Wright, Kennedy, 1981; Minev, 1994 a, b). The stratigraphic distribution ofCollignoniceras bra­vaisianum is from the middle part of the Mid­dle Turonian to the middle part of the Upper Turonian substage (Futakami, 1990; Minev, 1994 b). Only Scaphites geinitzii occurs above the Upper Turonian but its first occurrence and presence is considered to be characteristic for the Upper Turonian substage.

Foraminifers

The foraminiferal associations established in the investigated sections are comparatively poor and represented mainly by planktonic species. Most of the examinations have been done in thin sec­tions. Isolated fossils were obtained from sam­ples, originating from the upper parts of the sec­tions. The taxonomical list follows the classifi­cation, published by Loeblich & Tappan (1988). The stratigraphic distribution of the important species is shown on Fig. 3.

TURONIAN CQliLWj STAGES/

LOWER \MIDDLE I UPPER lOMEli un/fOSSILS l.e'll1llblaiP8QT¥1lm

§: ~lltdP ~adun 3:: ~toalbrun ~ ~repl\tl

~ .. Scqllllll gefizl CJ)

t=:> jC. ~ lS. repl\lll Z 0 N E S

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i ~~ WtM'etl ca:IIIIJoaltr*l -· ~~ .. ~~ z .. ~- :;; .. t;,:llrarD 'P m .. ~~ ~ .. ~CCIII'Im .. ~irl:¥**

- ~ccrm:m Q - ~11*'00 E - ---- - tbcttmcmM\ .. ~!nll'bMl "T1

~ .. lmtitrn toamJe .. ~~ m .. Seratlstara lttrdlkl ~ -- -· ~cattl .. Ocltlctlln dltrun en

Atrlq)(a ni::IOiei:lttl -~ ~dib .. ~~ SP

~ 'ttxillilpales \lll.ba Ck:alt~tujal

Fig. 3. Integrated stratigraphic range of the fossils

The Early Turonian associations are not char­acteristic, comprising rare representatives of the genera Hedbergella, Whiteinel/a and Praeglo­botruncana imbricata. Single specimens from the genera Lenticulina, Nodosaria, Marssone/la, Arenobulimina, Orb ito/ina and ? Trocholina were also encountered.

The Middle Turonian sediments yielded for­aminiferal assemblages represented by rare spec­imens of M arginotruncana pseudolinneiana, M. renzi and Siga/itruncana sigali. These species make their first appearance in the lowermost part of the Middle Turonian. They associate with Praeglobotruncana delrioensis, Whiteinella ar­chaeocretacea, Hedbergella sp. and Heterohelix sp., which range from lower stratigraphical lev­els. The abundant presence of Radiolaria in all lower and middle Turonian samples has to be noticed.

The Upper Turonian substage is character­ized by comparatively richer foraminiferal as­sociations, dominated by Sigalitruncana schnee­gansi, Marginotruncana coronata and M. tar­fayaensis. These species make their first occur­rence in the upper parts of the Middle Turoni-

43

an. The associations are completed by Margin­otruncana pseudolinneiana, M. renzi, Sigalitrun­cana sigali as well as the last representatives of Praeglobotruncana imbricata and Whiteinella archaeocretacea. The main face of the assem­blages is given by the two keeled plateform rep­resentatives of the genusMarginotruncana, char­acterizing the boundary between Turonian and Coniacian Stages.

The so established associations are very close and could be easily correlated with those from the European Tethyan basin (Robaszynski, Ca­ron, 1979). The Early and Late Turonian zonal markers Whiteinella archaeocretacea and Sigal­itruncana schneegansi were documented in the investigated sections. Only Helvetotruncana hel­vetica - the zonal index of the Middle Turoni­an zone was not observed.

Dinoflagellate cysts

The Turonian sediments in the investigated sec­tions yielded dinocyst assemblages, character­ized by comparatively not very high species di­versity and number of specimens belonging to one and same species. All important stratigraph­ic information is summarized on Fig. 3.

The stratigraphic distribution of the estab­lished taxa is calibrated against the ammonite finds in the sections, i.e. against the substage subdivision of the Turonian Stage based on ammonites. So, it could be concluded that the Lower Turonian is characterized by the pres­ence of Gonyaulacysta cassidata, Epeli­dosphaeridia spinosa, Isabelidinium acuminatum and M icrodinium ornatum. The species Gonyaul­acysta cassidata and Epelidosphaeridia spinosa make their last occurrence in the upper part of the Lower Turonian. This fact is of high strati­graphic significance outside the studied area and coincides with their range in the type Turonian area (Foucher in Robaszynski et al., 1982), in the Paris Basin and Central North Europe (Foucher, 1979, 1983).

Registered biostratigraphic event with corre­lation value is the first appearance of Senonias­phaera rotundata, Subtilisphaera pontis-mariae and Isabelidinium cooksoniae in the upper part of the Lower Turonian. These species range into the overlaying middle and upper Turonian stra­ta in association with Odontochitina costata, ls­abelidinium acuminatum, Circulodinium distinc­tum and single specimens of Microdinium orna­tum. The so obtained dinocyst associations from Southwestern Bulgaria correlate fairly well and share mutual characteristics with the palynos­tratigraphic schemes previously reported for the

44

type Turonian area (Foucher in Robaszynski et al., 1982), the Isle of Wight (Clarke & Verdier, 1967), for the Paris Basin and Central Europe (Foucher, 1979). In these schemes the species Senoniasphaera rotundata, Isabelidinium cook­soniae and Subtilisphaera pontis-mariae are drawn as characteristic markers for Turonian and Coniacian age and their first appearance is considered to be in the middle part of the Turo­nian.

Pollen and spores

Continental elements are subordinate in quan­tity in the palynological assemblages. They are represented mainly by pollen from the Nor­mapolles group. Although few, the encountered pollen species are quite characteristic and their associations give ground for reliable biostrati­graphic conclusions. The stratigraphic evalua­tion of registered spores and pollen is made by taking into account the ammonite finds in the sections. Their range is shown on Fig. 3.

The samples originating from lower part of the sections "Izvor", "Izvor - B" and "Lyalin­tsi" have yielded palynofloras comprisingAtlan­topollis microreticulatus, Complexiopollis chris­tae, Vadaszisporites urkuticus and Cicatrico­sisporites hughesii. The association of the pol­len species Atlantopollis microreticulatus and Complexiopollis christae is drawn as character­istic in the previously reported Early Turonian assemblages from Southern France and Portu­gal (Medus et al., 1980; Robaszynski et al., 1982). Krutzsch (in Goczan et al., 1967) noticed that the representatives of Atlantopollis make their final occurrences within the Middle Turonian in Central Europe. This conclusion is support­ed by the disappearance ofAtlantopollis microre­ticulatus near the base of the Middle Turonian in the investigated sections.

The succeeding Middle and Late Turonian palynofloras could be differentiated from the preceeding one through the presence of Com­plexiopollis complicatus and might be denomi­nated as association of Complexiopollis christae and C. complicatus. The former species is re­stricted only within the Turonian Stage and its last occurrence is near the upper Turonian boundary. Complexiopollis complicatus is new element for the Turonian palynoflora and ranges also in the overlaying Coniacian sediments.

These conclusions support and fill out the previously published data for the region of Northeastern Bulgaria (Pavlishina, 1994) and are comparable to the schemes known from Cen­tral and Southwestern Europe.

IZVOR 120m

- -- -- -

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IZVOR- B lOOm

·-· -

REBRO 120m

T

W-NW~

LYAUNTSI lOOm

PAAAMOUt\ 95m

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- --....- - -Mr

- - ------- - Sc. ger.IZI. :;:.;-.-r t -s. niiF&I ....-z~ <(~_ --? -- --- - L. perarTl)Un ....

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..... Fig. 4. Correlation of the studied sections and main biostratigraphic events within the Turonian Stage

Conclusions

A succession of outcrops in the region west of the town of Breznik has brought new biostrati­graphic results concerning the Turonian Stage in the area. Integrated vertical distribution of ammonites, foraminifers, dinoflagellate cysts, spores and pollen is proposed. This combined study enables the recognition of the three Turo­nian substages for the first time in the region and gives possibilities for palaeoenvironmental interpretations. The scope of the substages and their boundaries are defined by ammonites, elab­orated with the data obtained from the other microfossil groups. The correlation scheme of the sections and the most important biostrati­graphic events are presented on Fig. 4.

The Lower Turonian sediments contain com­paratively poor foraminiferal associations, rep­resented mainly by planktonic species of low stratigraphic value. Ammonite finds are also rare. In the palynomorph assemblages the ratio of marine to non-marine elements is 1, i.e. di­noflagellate cysts and sporomorphs are repre­sented in equal quantities. These fossil eviden­ces suggest shallow marine depositional envi­ronment with high input of terrestrial material.

In the Middle Turonian sediments ammonites are markedly more frequent and various. The

foraminiferal associations still retain their main face, but there is a change in the encountered palynomorph assemblages, marked by the in­creased ratio of dinoflagellate cysts to sporo­morphs. These data could be explained with gradual deepening of the basin in which the in­put of terrestrial ·material is reduced.

The dominant presence of planktonic fora­minifers, the high diversity and abundance of marine palynomorphs in addition to the gene­ral scarcity of ammonites in the Upper Turoni­an succession can be interpreted as indicating rather deep palaeoenvironments during the Late Turonian. The input of terrestrial material has, however, been fairly low during the deposition of these sediments.

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