Calpionellid, Nanno.Ossil and Calcareous Dinocyst

GEOLOGICA CARPATHICA, 50, 2, BRATISLAVA, APRIL 1999 151–168 CALPIONELLID, NANNO OSSIL AND CALCAREOUS DINOCYST BIOEVENTS AND INTEGRATED BIOCHRONOLOGY O THE TITHONIAN TO VALANGINIAN IN THE WESTERN BALKANIDES, BULGARIA

ISKRA LAKOVA, KRISTALINA STOYKOVA and DARIA IVANOVA

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. Bl. 24, 1113 Sofia, Bulgaria

(Manuscript received January 26, 1998; accepted in revised form December 9, 1998)

Abstract: This joint study on calpionellids, calcareous nannofossils and calcareous dinocysts of the Tithonian, Berriasian and Valanginian sediments in the Western Balkanides allowed detailed documentation of the stratigraphic ranges and selection of reliable diagnostic bioevents, within the parallel microfossil successions. The individual zonations based on calpionellids, nannofossils and dinocysts are made more precise, refined and directly correlated to each other. The calpionellid zones and subzones recorded in Bulgaria are widely accepted for the Mediterranean. The proposed nannofossil zonation is considered as a regional one for the Western Balkanides. Ten dinocyst zones are recognized three of them being introduced here: Stomiosphaera wanneri, Colomisphaera conferta and Carpistomiosphaera valanginiana. A number of intrinsic coin- ciding bioevents between two or all the three planktonic microfossil groups are documented and interpreted related to certain stage and substage boundaries. This approach of direct correlation of three fossil groups enhances the argumenta- tion and resolution of the zonation. It may represent a basis for a reference biochronology of the Tithonian to Valanginian, applicable to various lithologies in the Tethyan Realm.

Key words: Bulgaria, Western Balkanides, Tithonian, Berriasian, Valanginian, integrated biochronology, calpionellids, calcareous nannofossils, calcareous dinocysts.

Introduction and sections studied vides an uninterrupted stratigraphic Kimmeridgian to Hau- terivian succession. We sampled the uppermost 20 m of the The thick and continuous Upper Jurassic and Lower Creta- Gintsi 5ormation, the whole Glozhene 5ormation (37 m) and ceous pelagic carbonate sequence outcropping extensively in the lower part of the Salash 5ormation (108 m) (5igs. 2, 4, 6). the area of the West Balkan Mountains and West 5ore-Bal- kan, Bulgaria, provides excellent material for detailed, com- prehensive biostratigraphic studies on several planktonic mi- crofossil groups and working out of a joint scale of successive bioevents and integrated zonations. This study encompasses the individual biostratigraphic re- sults on the following microfossil groups: calpionellids, cal- careous nannofossils and calcareous dinocysts (cadosinids and stomiosphaerids) from successions of pelagic nodular, pure micritic and clayey limestones of Tithonian, Berriasian and Valanginian age in the Western Balkanides (West Balkan Mountains and West 5ore-Balkan) (5ig. 1). Three formations have been studied: the Gintsi 5ormation (pink and grey nod- ular limestones), Glozhene 5ormation (grey hard micritic limestones) and Salash 5ormation (alternation of micritic limestones, clayey limestones and marls). A detailed combined sampling has been carried out of three reference sections — Barlya, Gorno Belotintsi 1 and Gorno Belotintsi 2 (5igs. 2–8). Calpionellids and calcare- ous dinocysts are determined in thin-sections, and calcare- ous nannofossils in smear slides. The section of Barlya is lo- cated at the northern end of the village of Barlya, Sofia ig. 1. Outcrops of the Gintsi, Glozhene and Salash 5ormation in District, very close to the Bulgarian-Yugoslavian border, in the West Balkan Mountains and West 5ore-Balkan and location of the area of the West Balkan Mountains. This section pro- the sections studied. 152 LAKOVA, STOYKOVA and IVANOVA

The sections of Gorno Belotintsi 1 and Gorno Belotintsi 2 Praetintinnopsella Zone are situated 3 km to the north of the village of Gorno Be- lotintsi, Montana District, in the area of the West 5ore-Bal- The Praetintinnopsella Zone is defined between the 5O of kan. In Gorno Belotintsi 1 section we sampled the upper part Praetintinnopsella andrusovi and the 5O of representatives of Gintsi 5ormation (20 m) and the Glozhene 5ormation, its of the family Calpionellidae with hyaline calcite wall thickness there being 240 m, and in Gorno Belotintsi 2 sec- (Grandesso 1977). This zone corresponds to the Middle/Up- tion — the lowest 40 m of the Salash 5ormation. These two per Tithonian boundary interval. sections are positioned stratigraphically one over another but the lithological transitions between the Glozhene and Salash Crassicollaria Zone 5ormations and the Berriasian-Valanginian boundary are ob- scured by some absences of exposures. The standard Crassicollaria Zone is restricted between the The calpionellids were studied by I. Lakova, calcareous 5Os of calpionellids with hyaline wall and the explosion of nannofossils by K. Stoykova and calcareous dinocysts by D. Calpionella alpina. In most of the sections studied else- Ivanova. where in the West Balkan Mountains three species appear si- multaneously at the lower boundary of the zone — Tintin- nopsella carpathica, Tintinnopsella remanei and Calpionellids Crassicollaria intermedia. The Crassicollaria Zone cor- responds to the Late Tithonian. In the last four decades, the taxonomic and bio- There is no agreement on the subzonal division of this stratigraphic studies on calpionellids proved that these zone. We follow the bipartite division proposed at the planktonic microfossils are essential for the fine division, Sümeg Meeting (Remane et al. 1986), the name of the upper precise dating and reliable long-distance correlation of Mid- “Intermedia” Subzone being replaced by “Crassicollaria dle Tithonian to Valanginian pelagic carbonates throughout massutiniana” because of the controversial and confusing the Mediterranean Realm. The advantages of the calpionel- use of the “Intermedia” Subzone. The base of the Crassicol- lids in biostratigraphy are their relatively rapid evolution laria massutiniana Subzone is marked by the 5O of Calpi- consisting of distinguished steps, the unequivocal succes- onella grandalpina, i.e. the large-sized elongated Tithonian sion of numerous bioevents (first and last occurrences, phyl- form of Calpionella alpina s.l. etic transitions and dramatic increases in abundance) which There is, indeed, a potential to define a third, uppermost are used to define the boundaries of 7 interval-zones and to- subzone within the Crassicollaria Zone on the basis of the tal-range zones and at least 12 interval subzones, as well as 5O of Crassicollaria brevis, which is usually later than the the common geographical distribution, the lack of provin- 5O of Calpionella grandalpina. We do not accept, however, cialism and quantitative abundance. the “Colomi” Subzone erected by Pop (1994) and Reháková The originally proposed calpionellid zonal schemes by Re- & Michalík (1997) since our studies have proved that Cras- mane (1971) and Alleman et al. (1971) were progressively sicollaria colomi occurs only in the lower part of the over- refined, divided into subzones, completed and the criteria of laying Calpionella Zone and has nothing to do with the Cras- placing the boundaries were specified (Pop 1974, 1976; sicolaria Zone. An additional criterion to determine the Borza 1984; Remane et al. 1986; Trejo 1980; Altiner & Öz- upper boundary of the Crassicollaria Zone is the last occur- kan 1991; Lakova 1993). Previously, Tithonian and Berria- rence (LO) of Calpionella elliptalpina, the so-called “ho- sian calpionellids of the Western Balkanides were studied by meomorph of Calpionella elliptica”. This event coincides Bakalova-Ivanova (1986). We apply here a slightly modified with the explosion of C. alpina (5igs. 2, 3). version (Lakova & Stoyanova 1997) of the zonal and sub- zonal subdivisions by Pop (1994, 1997) and Reháková & Michalík (1997) which differs significantly in terms of sub- Berriasian zones from Blau & Grün’s (1997) zonation. Calpionella Zone

Middle and Late Tithonian The Standard Calpionella Zone is defined between two easily determinable biostratigraphic events — the explosion Chitinoidella Zone of Calpionella alpina s.s., i.e. the medium-sized spherical form of C. alpina s.l., and the 5O of Calpionellopsis sim- The first occurrence (5O) of Chitinoidella dobeni and re- plex. The boundary between the Crassicollaria and Calpi- lated species (Chitinoidella colomi, Chitinoidella tithonica, onella zones was recommended as boundary between the Ti- Chitinoidella slovenica) which are the first representatives thonian and Berriasian stages at the Lyon–Neu Châttel of the family Codonellidae with microgranular wall indicate Colloquium in 1973. In terms of ammonite zones and sub- the base of the Chitinoidella Zone. This level coincides with stages, the Calpionella Zone corresponds to the Berriasella the Lower/Middle Tithonian boundary. The zone is divided jacobi Zone (Early Berriasian) + Tirnovella occitanica Zone into two subzones — Chitinoidella dobeni and Chitinoidella (Middle Berriasian). boneti, the base of the latter being marked by the 5O of The zone has been divided into three subzones. Within the Chitinoidella boneti (Grandesso 1977; Borza 1984). Calpionella Zone, two successive bioevents are used for def- CALPIONELLID, NANNOOSSIL AND CALCAREOUS DINOCYST BIOEVENTS 153

ig. 2. Range chart of calpionellids and zonation of Barlya section, West Balkan Mountains. inition of subzones. The 5Os of Remaniella ferasini and/or to Blau & Grün (1997) and Bulot (1996). The cited authors Remaniella duranddelgai indicate the lower boundary of changed the definition of the lower boundary of the Valang- Remaniella ferasini Subzone, and the 5O of Calpionella el- inian at the base of the ammonite “Pertransiens” Zone. How- liptica — the base of Calpionella elliptica Subzone. In addi- ever, Pop (1994, 1997) followed the classical definition of tion, we documented in many sections another two bioevents the base of the Valanginian at the lower boundary of the am- within the Calpionella alpina Subzone which offer a tool for monite “Otopeta” Zone; in this case the uppermost Prae- further refining the division of the Early Berriasian. These calpionellites murgeanui Subzone of the Calpionellopsis are the 5O of Crassicollaria colomi in the lower portion and Zone belongs to the basal part of the Valanginian. the 5O of Calpionella minuta, the so-called “small degener- Within the Calpionellopsis oblonga Subzone the diversity ative Berriasian form of Calpionella alpina s.l.”, in the up- of calpionellid species reached its culmination thus enabling per half of the Calpionella alpina Subzone (5ig. 3). In the a recognition of additional bioevents. In the section of Bar- uppermost part of the Calpionella Zone, within the Calpi- lya, the successive 5Os of Calpionellopsis oblonga, Loren- onella elliptica Subzone, the 5O of Tintinnopsella longa en- ziella hungarica and/or Lorenziella plicata and Remaniella ables the definition of a forth subzone, the Tintinnopsella filipescui are documented. This series of successive bioev- longa Subzone, as proposed by Pop (1994) but this subzone ents may represent an additional tool for finer subdivision is still not widely accepted. and correlations.

Calpionellopsis Zone Valanginian The Standard Calpionellopsis Zone is defined between the 5Os of Calpionellopsis simplex and Calpionellites darderi. Calpionellites Zone It is divided into three subzones: Calpionellopsis simplex, Calpionellopsis oblonga and Praecalpionellites murgeanui. The Standard Calpionellites Zone is a total-range zone of The lower boundary of the Calpionellopsis oblonga Subzone the genus Calpionellites. The 5O of Calpionellites darderi is is placed at the 5O of Calpionellopsis oblonga, and the base the criterion for its lower boundary, whereas the LO of spe- of the Praecalpionellites murgeanui Subzone — at the 5O of cies of genus Calpionellites (Calpionellites coronata, Calpi- Praecalpionellites murgeanui. onellites major, Calpionellites caravacaensis) indicates the The Calpionellopsis Zone coincides totally with the am- upper boundary. The zone is divided into two subzones — monite 5auriella boissieri Zone (Late Berriasian) according the Calpionellites darderi Subzone and Calpionellites major 154 LAKOVA, STOYKOVA and IVANOVA

ig. 3. Range chart of calpionellids and zonation of Gorno Belotintsi 1 section, West 5ore-Balkan: 1 — nodular limestones (Gintsi 5orma- tion); 2 — micritic and/or intraclastic limestones (Glozhene 5ormation); 3 — marly limestones and marls (Salash 5ormation); 4 — no ex- posures. CALPIONELLID, NANNOOSSIL AND CALCAREOUS DINOCYST BIOEVENTS 155

ig. 4. Range chart of calcareous nannofossils and zonation of Barlya section, West Balkan Mountains.

Subzone, as proposed by Pop (1994) and widely accepted Late Valanginian part of the Tintinnopsella Zone has been and confirmed in many areas of the Mediterranean Bioprov- studied so far. In this lower part, the successive LOs of ince. The lower boundary of the Calpionellites major Sub- Lorenziella hungarica, Lorenziella plicata and Tintinnopsel- zone is placed at the 5O of Calpionellites major. la longa represent a potential for definition of subzones. The Calpionellites Zone corresponds to the ammonite “Pertransiens” and “Campylotoxum” zones (Early Valangin- ian except its base). Calcareous nannofossils We have also documented the 5O of Calpionellites coro- nata within the Calpionellites darderi Subzone, as well as Calcareous nannofossil studies of the Tithonian–Valangin- the 5O of Calpionellites caravacaensis within the Calpion- ian interval in Bulgaria have been done since 1995. The first ellites major Subzone (5ig. 8). These two bioevents may be work does not appear to have reached a satisfying degree of used for further subdivision of the Calpionellites Zone. biostratigraphic resolution (Stoykova 1995). Detailed nan- nofossil studies both in the Tethyan and Boreal Bioprovinces Tintinnopsella Zone were done by Thierstein (1971, 1973, 1976) and Roth (1983). Recently, Bralower et al. (1989) and Gardin & The disappearance of genus Calpionellites at the Early/Late Manivit (1993) published refined nannofossil biostratigra- Valanginian boundary marks a significant decline of calpi- phy for this interval (Jurassic–Cretaceous). In conclusion, onellids in both diversity and abundance. After this event, the there is no one widely accepted nannofossil scheme yet. In calpionellid associations consist only of a small number of this work we propose five calcareous nannofossil biozones species of the genera Tintinnopsella and Lorenziella. The up- for the Kimmeridgian–Valanginian interval considered as a permost Tintinnopsella Zone is defined between the LO of regional zonation for the area of the Western Balkanides. Calpionellites and the total extinction of calpionellids. This zonation is comparable to some extent to the zonal This zone corresponds to the Late Valanginian and to a schemes mentioned above. great part of the Hauterivian, too, according to Pop (1994) The main advantage of the present joint study is the direct and Reháková (1995). In the Western Balkanides, only the correlation of the recorded nannofossil events with calpi- 156 LAKOVA, STOYKOVA and IVANOVA

ig. 5. Range chart of calcareous nannofossils and zonation of Gorno Belotintsi 1 section, West 5ore-Balkan (for legend see 5ig. 3). onellid and calcareous dinocyst ones. The samples originating ered of less biostratigraphic importance because they are not from the section of Barlya yielded relatively diverse and mod- recognizable in each section. erately well preserved nannofloras (5ig. 4), whereas in the The zonation proposed here consists of five interval-zones Gorno Belotintsi sections the assemblages are less diverse and based on successive 5Os of the index-species, spanning the preservation is poorer (5igs. 5, 8). Taking into account these Late Kimmeridgian to Valanginian interval: Parhabdolithus preservation problems affecting nannofossil occurrence we embergeri Zone (Late Kimmeridgian), Conusphaera mexica- have compiled a series of nannofossil bioevents (5ig. 9). na Zone (Early to Late Tithonian), Microstaurus chiastius When selecting events for zonation, we attempted to Zone (Latest Tithonian–Early and Middle Berriasian), Nan- choose the most reliable, clearly distinctive and repeatable noconus steinmannii Zone (Late Berriasian–Early Valangi- ones in all sections. Bioevents within the zones are consid- nian) and Tubodiscus verenae Zone (Late Valanginian). CALPIONELLID, NANNOOSSIL AND CALCAREOUS DINOCYST BIOEVENTS 157

ig. 6. Range chart of calcareous dinocysts and zonation of Barlya section, West Balkan Mountains.

Late Kimmeridgian nofossil assemblages change significantly starting from the base of this zone. They are dominated by Conusphaera mex- Only the uppermost part of the Kimmeridgian is studied in icana mexicana, Conusphaera mexicana minor and ellip- this work. sagelosphaerids. In the lower part of the zone, the stepwise 5Os of Polycostella beckmannii and Polycostella senaria Parhabdolithus embergeri Zone are recorded (5ig. 4). The 5O of Umbria granulosa in the upper part of this zone requires further specification. The zone is defined as an interval between the 5O of Par- habdolithus embergeri and the 5O of Conusphaera mexica- na mexicana. The nannofossil assemblages of this zone are Berriasian of low diversity and are dominated by Ellipsagelosphaera and Cyclagelosphaera representatives. The 5O of Conus- Microstaurus chiastius Zone phaera mexicana minor, the immediate precursor of Conus- phaera mexicana mexicana, is documented within this zone The interval from the 5O of Microstaurus chiastius to the in the section of Barlya (5ig. 4). 5O of Nannoconus steinmannii. The zone equates to the topmost Tithonian and Early and Middle Berriasian. The 5O of Microstaurus chiastius at the base of the zone is a suitable Tithonian diagnostic event, occurring in all the sections studied (5igs. 4, 5). Conusphaera mexicana mexicana Zone Within this zone, a succession of first occurrences is ob- served, some of them representing the early evolution of the The zone is regarded as an interval between two clearly nannoconids group: Nannoconus sp.n., N. compressus, N. determinable bioevents: the 5O of Conusphaera mexicana globulus minor. The last occurrence of Polycostella beck- mexicana at the beginning of Tithonian and the 5O of Mi- mannii is a less reliable event, but it could also be helpful crostaurus chiastius in the Late Tithonian. In addition, the and needs further elucidation. Cretarhabdus angustiforatus, 5O of ;aviconus multicolumnatus is another reliable event, another commonly used marker-species has its 5O restricted approximating to the base of this zone (5igs. 4, 5). The nan- at the middle of the Calpionella elliptica calpionellid zone. 158 LAKOVA, STOYKOVA and IVANOVA

ig. 7. Range chart of calcareous dinocysts and zonation of Gorno Belotintsi 1 section, West 5ore-Balkan (for legend see 5ig. 3).

Nannoconus steinmannii Zone Late Valanginian

This zone is considered to be an interval between the 5Os Tubodiscus verenae Zone of Nannoconus steinmannii minor and Tubodiscus verenae. Nannoconids are the major dominant component of the as- The base of this zone is marked by the 5O of Tubodiscus semblages. The base of this zone corresponds to the explo- verenae — an event which approximates to the Lower/Upper sion in nannoconid abundance, a prominent broadly recog- Valanginian boundary in terms of calpionellids. A couple of nizable event (5igs. 4, 5). additional first co-occurrences makes the base of the zone It should be noted that the 5O of Micrantholithus speeton- easily determinable: the 5Os of Nannoconus cornuta, N. ensis is recorded in the lower part of the zone. Micran- quadratus, etc. Other stratigraphically important species ap- tholithus speetonensis is usually regarded as an Late Valang- pearing within this zones are Calcicalathina oblongata, inian Boreal marker-species. Recently, Gardin (in Bulot Nannoconus bermudezii and Diadorhombus rectus (5ig. 4). 1996) has shown its 5O during the Late Berriasian and earli- est Valanginian in the NW Tethyan basin. These data are consistent to our finds (5igs. 4, 5). Calcareous dinocysts The nannofossil data in the present study enable a good biostratigraphic resolution in the middle and upper part of The interest in the study of calcisphaerids concentrated in this zone. Therefore, it should be further examined in other, the past mainly on its biostratigraphic implication, was direct- more suitable localities. ed in the last 15–20 years to another aspect — elucidation of CALPIONELLID, NANNOOSSIL AND CALCAREOUS DINOCYST BIOEVENTS 159

ig. 8. Range chart and zonations of calpionellids, calcareous nannofossils and calcareous dinocysts of Gorno Belotintsi 2 section, West 5ore-Balkan. their biological affinities and taxonomical identification of misphaera tenuis, Colomisphaera fortis, Stomiosphaerina species belonging to the calcareous dinocysts. In spite of the proxima and Stomiosphaera echinata. In this study, the defini- new approaches and tendencies in the study of calcisphaerids, tion of their bases and the chronostratigraphic assignment of their stratigraphic importance for the Late Kimmeridgian–Ear- these zone are specified. Three new dinocyst interval-zones ly Valanginian time interval remains significant. are introduced within the Uppermost Berriasian–Valanginian On the basis of the succession of vertical ranges of ca- interval: Stomiosphaera wanneri, Colomisphaera conferta and dosinid and stomiosphaerid species proved in several sec- Carpistomiosphaera valanginiana zones (5igs. 6, 7, 8). tions, Nowak (1968) proposed 6 zones from the Late Kim- meridgian to the Hauterivian: Moluccana, Pulla, Malmica, Cieszynica-carpathica, Minutissima-carpathica and Echina- Late Kimmeridgian ta. Later on, Nowak (1976) revised his first zonation. 5urther contributions to the biostratigraphy of calcisphaerids were Carpistomiosphaera borzai Zone made by Borza (1969, 1984), Borza & Michalík (1986), Øe- hánek (1992), Øehánek & Heliasz (1993), Øehánek & Cecca The lower boundary is defined at the 5O of Carpistomi- (1993), Vašíèek et al. (1994). osphaera borzai. The index-species is associated with Cado- The detailed and parallel microfossil studies carried out on sina parvula, Colomisphaera pieniniensis, C. lapidosa and C. the Tithonian to Valanginian of the Western Balkanides allow carpathica. The zone corresponds partly to Parhabdolithus a series of successive 5Os of calcareous dinocyst species to be embergeri nannofossil zone and to the Late Kimmeridgian recorded (5igs. 6, 7). These 5Os are directly correlated to the (5igs. 6, 7). calpionellid events and to the stratigraphic time scale. The cal- careous dinocyst zonation here recorded consists of 10 inter- Tithonian val-zones, the bases of all being defined by the 5O of index- species (5ig. 9). The following dinocyst zones previously Carpistomiosphaera tithonica Zone proposed by different authors are confirmed in the West Bal- kan and West 5ore-Balkan: Carpistomiosphaera borzai, Carp- The 5O of Carpistomiosphaera tithonica at the base of the istomiosphaera tithonica, Parastomiosphaera malmica, Colo- Tithonian marks the lower boundary of this zone. The suc- 160 LAKOVA, STOYKOVA and IVANOVA

ig. 9. Bioevents and integrated zonations of the Tithonian, Berriasian and Valanginian of the Western Balkanides. CALPIONELLID, NANNOOSSIL AND CALCAREOUS DINOCYST BIOEVENTS 161 cessive first occurrences of Cadosina semiradiata semiradi- Stomiosphaera wanneri Zone, Colomisphaera heliosphaera ata, C. fusca fusca and Committosphaera pulla are docu- makes its 5O. This zone corresponds approximately to the up- mented within the zone. The Carpistomiosphaera tithonica per third of the calpionellid Calpionellopsis oblonga Subzone Zone spans the Kimmeridgian-Tithonian boundary interval and the Praecalpionellites murgeanui Subzone (latest Berria- (5ig. 7). sian and Early Valanginian) (5igs. 6, 7).

Parastomiosphaera malmica Zone Valanginian The base of this zone is defined at the 5O of Parastomi- osphaera malmica. The zone corresponds to the Early Titho- Colomisphaera conferta Zone nian. Its upper boundary is placed in the basal part of the calpionellid Chitinoidella Zone thus the top of Parastomi- This zone is the interval between the 5O of Colomisphaera ophaera malmica Zone slightly overlaps the very base of conferta and the 5Os of Carpistomiosphaera valanginiana Chitinoidella Zone (5igs. 6, 7). and/or Colomisphaera vogleri. The zone is introduced in this paper. In terms of calpionellid zonation, the Colomisphaera Colomisphaera tenuis Zone conferta Zone corresponds to the calpionellid Calpionellites darderi and Calpionellites major subzones (Early Valanginian) The 5O of the index-species Colomisphaera tenuis marks (5igs. 6, 7, 8). the base of this zone. Colomisphaera tenuis Zone corre- sponds exactly to the calpionellid Chitinoidella Zone (Mid- Carpistomiosphaera valanginiana Zone dle Tithonian). Our combined calpionellid and dinocyst studies proved the coeval 5Os of Chitinoidella dobeni and The 5O of the index-species Carpistomiosphaera valangini- Colomisphaera tenuis (5igs. 6, 7). ana defines the lower boundary of the zone. The zone is first defined in this study. It is comparable to the calpionellid Tintin- Colomisphaera fortis Zone nopsella Zone in its Late Valanginian part (5igs. 6, 8)

The lower boundary of this zone is defined by the 5O of Stomiosphaera echinata Zone Colomisphaera fortis in the middle of the Praetintinnopsella Zone. Within the Colomisphaera fortis Zone, the abundance The 5O of the index-species marks the lower boundary of and diversity of calcareous dinocysts significantly de- this zone, whereas the upper boundary is still not deter- creased. This zone coincides with the upper part of the calpi- mined. The studied part of Stomiosphaera echinata Zone is onellid Praetintinnopsella Zone and the Tintinnopsella rema- tentatively assigned to the Late Valanginian and Early Hau- nei Subzone of Crassicollaria Zone (earliest Late Tithonian) terivian on the basis of diagnostic ammonite finds in the top- (5igs. 6, 7). most part of the section of Barlya (5ig. 6).

Berriasian Microfossil bioevents, zonations and chronostratigraphic subdivision Stomiosphaerina proxima Zone The chronostratigraphic assignment of the calpionellid The lower boundary of this zone is defined by the 5O of Sto- zones from Chitinoidella to Tintinnopsella (Middle Titho- miosphaerina proxima an event coinciding with the 5Os of nian–Hauterivian) is given according to Pop (1994) and the Calpionella grandalpina and Microstaurus chiastius in the bioevents and zonations on nannofossils and calcareous di- middle of the Upper Tithonian (5ig. 9). It suggests that Øe- nocysts are correlated to those on calpionellids (5ig. 9). The hánek’s (1992) proposal to place the Tithonian-Berriasian Kimmeridgian-Tithonian boundary is fixed on the basis of boundary at the 5O of Stomiosphaerina proxima is not applica- diagnostic 5O of nannofossil and calcareous dinocyst spe- ble. This is a relatively longer-ranging zone which is compara- cies. ble to the sum of the calpionellid Crassicollaria massutiniana, The 5Os of nannofossils ;aviconus multicolumnatus and Calpionella alpina, Remaniella ferasini, Calpionella elliptica, Conusphaera mexicana mexicana (the lower boundary of Co- Calpionellopsis simplex subzones and the lower part of the nusphaera mexicana nannofossil zone) and the simultaneous Calpionellopsis oblonga Subzone (latest Late Tithonian and the 5O of dinocyst species Committosphaera pulla in the middle whole Berriasian except its very top) (5igs. 6, 7). portion of Carpistomiosphaera tithonica dinocyst zone mark the Kimmeridgian-Tithonian boundary (5igs. 4, 6). Stomiosphaera wanneri Zone At the Lower/Middle Tithonian boundary, the almost co- eval first occurrences of the calpionellid Chitinoidella dobe- The 5O of the index-species Stomiosphaera wanneri marks ni and dinocyst Colomisphaera tenuis are documented, thus the base of this zone and the 5O of Colomisphaera conferta determining the bases of Chitinoidella dobeni calpionellid — its top. The zone is here proposed as a new one. Within the subzone and Colomisphaera tenuis dinocyst zone, respec- 162 LAKOVA, STOYKOVA and IVANOVA tively. Later in the Tithonian, the 5O of Praetintinnopsella Apart from the coinciding events in the evolution of calpi- andrusovi (i.e. the base of Praetintinnopsella calpionellid onellids, nannofossils and calcareous dinocysts reviewed zone) coincides with the 5O of the nannofossil Umbria above, there is a number of non-coinciding events which granulosa granulosa close to the Middle/Upper Tithonian can be helpful for finer and more precise subdivision and boundary. Within the Late Tithonian (Crassicollaria Zone) correlation of the Tithonian, Berriasian and Valanginian there are a clearly documented simultaneous 5Os of repre- stages (5ig. 9). Moreover, this triple common study of strati- sentatives of calpionellides, nannofossils and dinocysts: graphic ranges, bioevents and zonations may serve as a ref- Calpionella grandalpina, Microstaurus chiastius, Nannoco- erence biochronology of the Tithonian to Valanginian age nus sp.n., Stomiosphaerina proxima. This gives ground to and provides a background for further application of inde- define the coinciding lower boundaries of three biostrati- pendent studies on nannofossils and/or dinocysts in different graphic units: Crassicollaria massutiniana calpionellid sub- lithologies lacking calpionellids. zone, Microstaurus chiastius nannofossil zone and Stomio- sphaerina proxima dinocyst zone (5ig. 9). Acknowledgements: We would like to thank Prof. I. The Tithonian/Berriasian boundary is easily determinated Sapunov and Prof. P. Tchoumatchenco, Geological Institute, in terms of calpionellids at the base of the Calpionella Zone Sofia, for their kind advices on the regional geology of the on the explosion of Calpionella alpina and the LO of C. el- Western Balkanides and their critical notes on the text. This liptalpina, events occurring together with the 5Os of nanno- work was undertaken in the framework of Project 72/95-96 fossil species Cruciellipsis cuvillieri and Nannoconus com- “Mesozoic correlations of the Moesian Platform” funded by pressus (5igs. 2, 4). the Peri-Tethyan Program and Project 515/95 of the Bulgari- Another coinciding microfossil events to be mentioned are an Scientific 5und. the 5Os of calpionellid Calpionellopsis simplex (base of the Calpionellopsis Zone) and the nannofossils Nannoconus steinmannii minor and N. dolomiticus (base of the N. stein-

mannii nannofossil zone). The base of Calpionellopsis Zone ▲ corresponds to the boundary between the T. occitanica and 5. boissieri ammonite zones commonly regarded as Middle/Up- Plate I: Calpionellids of the Western Balkanides, Bulgaria. (All figures 500×). ig. 1. Chitinoidella dobeni Borza, Middle Titho- per Berriasian boundary (Blau & Grün 1997), even though nian, Chitinoidella Zone, Ch. dobeni Subzone, Gorno Belotintsi 1 there is no final agreement on the substage division of the section, sample 15. ig. 2. Chitinoidella boneti Doben, Middle Ti- Berriasian. Later on, Calpionellopsis oblonga and Nannoco- thonian, Chitinoidella Zone, Ch. boneti Subzone, Barlya section, nus steinmannii steinmannii make their first co-occurrences sample 0302. ig. 3. Tintinnopsella remanei Borza, Upper Titho- (at the base of the Calpionellopsis oblonga Subzone). In the nian, Crassicollaria Zone, T. remanei Subzone, Barlya section, upper portion of this subzone there is a coincidence of the sample 301. ig. 4. Calpionella minuta Houša, Middle Berriasian, 5Os of calpionellid Remaniella filipescui and the dinocyst Calpionella Zone, C. elliptica Subzone, Gorno Belotintsi 1 section, Stomiosphaera wanneri, the latter event defining the base of sample 48. ig. 5. Lorenziella hungarica Knauer & Nagy, Lower Valanginian, Calpionellites Zone, Ctes major Subzone, Gorno Be- the St. wanneri dinocyst zone (5ig. 9). lotintsi 2 section, sample 70. ig. 6. Crassicollaria brevis Remane, The Berriasian/Valanginian boundary remains hardly de- Upper Tithonian, Crassicollaria Zone, Cr. massutiniana Subzone, terminable in terms of microfossil bioevents and zonations Gorno Belotintsi 1 section, sample 27. ig. 7. Calpionella gran- because the only criterion to place this boundary is the 5O of dalpina Nagy, Upper Tithonian, Crassicollaria Zone, Cr. massutini- Praecalpionellites murgeanui (the lower boundary of Pr. ana Subzone, sample 28. ig. 8. Calpionella elliptalpina Nagy, murgeanui calpionellid subzone), a species which is very Upper Tithonian, Crassicollaria Zone, Cr. massutiniana Subzone, rare indeed. On the other hand, within the basal Valanginian Gorno Belotintsi 1 section, sample 26. ig. 9. Calpionella alpina it is much easier to recognize the lower boundary of the Lorenz, Middle Berriasian, Calpionella Zone, C. elliptica Subzone, Calpionellites Zone (5O of Calpionellites darderi), coincid- Gorno Belotintsi 1 section, sample 48. ig. 10. Remaniella ferasini (Catalano), Middle Berriasian, Calpionella Zone, C. elliptica Sub- ing with the lower boundary of the Colomisphaera conferta zone, Gorno Belotintsi 1 section, sample 51. ig. 11. Calpionella dinocyst zone defined by the 5O of C. conferta (5ig. 9). elliptica Cadisch, Middle Berriasian, Calpionella Zone, C. elliptica At the Lower/Upper Valanginian boundary or a little low- Subzone, Gorno Belotintsi 1 section, sample 51. ig. 12. Calpi- er, the 5Os of two dinocyst species, Carpistomiosphaera va- onellopsis simplex (Colom), Upper Berriasian, Calpionellopsis langiniana and Colomisphaera vogleri, are used to define Zone, Csis simplex Subzone, Barlya section, sample 332. ig. 13. the base of the C. valanginiana Zone. The LO of representa- Calpionellites darderi (Colom), Lower Valanginian, Calpionellites tives of the genus Calpionellites which approximates this Zone, Ctes major Subzone, Gorno Belotintsi 2 section, sample 75. event is much more difficult to recognize because the extinc- ig. 14. Tintinnopsella longa (Colom), Upper Berriasian, Calpi- onellopsis Zone, Csis oblonga Subzone, Barlya section, sample tion is rather gradual and slow. In the Late Valanginian (low- 334. ig. 15. Calpionellopsis oblonga (Cadisch), Upper Berria- er part of Tintinnopsella Zone) the first co-occurrences of sian, Calpionellopsis Zone, Csis oblonga Subzone, Barlya section, the nannofossil species Diadorhombus rectus and the calcar- sample 335. ig. 16. Praecalpionellites murgeanui (Pop), Lower eous dinocyst Stomiosphaera echinata are recorded (the Valanginian, Calpionellites Zone, Ctes darderi Subzone, Barlya base of the St. echinata Zone) (5igs. 4, 6). A Late Valangin- section, sample 340. ig. 17. Calpionellites major (Colom), Lower ian–Early Hauterivian age is suggested for this zone on the Valanginian, Calpionellites Zone, Ctes major Subzone, Gorno Be- basis of diagnostic ammonite finds. lotintsi 2 section, sample 67. PLATE I 163 164 LAKOVA, STOYKOVA and IVANOVA

Plate II: Calcareous nannofossils from the Western Balkanides, Bulgaria. (All figures 2000×, except otherwise stated). ig. 1. Parhabdo- lithus embergeri (Noël) Stradner, Upper Kimmeridgian, P. embergeri Zone, Barlya section, sample 59. igs. 2, 3. ;aviconus multicolum- natus Bralower, Lower Berriasian, M. chiastius Zone, Barlya section, sample 319. ig. 4. Conusphaera mexicana mexicana Trejo, Lower Berriasian, M. chiastius Zone, Barlya section, sample 320. ig. 5. Cyclagelosphaera deflandrei Manivit, Lower Valanginian, N. steinman- nii Zone, sample 339. ig. 6. Cyclagelosphaera deflandrei Manivit, Upper Valanginian, Gorno Belotintsi 2 section, sample 80. ig. 7. Cruciellipsis cuvillieri (Manivit) Thierstein, Lower Valanginian, N. steinmannii Zone, Gorno Belotintsi 2 section, sample 67. ig. 8. Nan- noconus globulus globulus Brönnimann, Lower Valanginian, N. steinmannii Zone, Barlya section, sample 339. ig. 9. Nannoconus com- pressus Bralower & Thierstein, Lower Berriasian, M. chiastius Zone, Barlya section, sample 310. ig. 10. Nannoconus steinmannii minor Deres & Achéritéguy, Upper Berriasian, N. steinmannii Zone, Barlya section, sample 332. ig. 11. Nannoconus steinmannii steinmannii CALPIONELLID, NANNOOSSIL AND CALCAREOUS DINOCYST BIOEVENTS 165 List of taxa recorded Cyclagelosphaera deflandrei Manivit Diadorhombus rectus Worsley ;aviconus multicolumnatus Bralower Calpionellids Micrantholithus hoschultzii (Reinhardt) Thierstein Micrantholithus speetonensis Perch-Nielsen Chitinoidella dobeni Borza Microstaurus chiastius (Worsley) Grün in Grün & Allemann Chitinoidella slovenica Borza Nannoconus bermudezii Brönnimann Chitinoidella colomi Borza Nannoconus compressus Bralower & Thierstein Chitinoidella tithonica Borza Nannoconus cornuta Deres & Achéritéguy Chitinoidella boneti Doben Nannoconus dolomiticus Cita & Pasquaré Praetintinnopsella andrusovi Borza Nannoconus globulus globulus Brönnimann Tintinnopsella carpathica (Murgeanu & 5ilipescu) Nannoconus globulus minor Bralower Tintinnopsella remanei Borza Nannoconus quadratus (Noël) Deres & Achéritéguy Tintinnopsella longa (Colom) Nannoconus steinmannii steinmannii Kamptner Tintinnopsella subacuta (Colom) Nannoconus steinmannii minor Deres & Achéritéguy Tintinnopsella dacica 5ilipescu & Dragastan Parhabdolithus embergeri (Noël) Strander Crassicollaria intermedia (Durand Delga) Polycostella beckmannii Thierstein Crassicollaria massutiniana (Colom) Polycostella senaria Thierstein Crassicollaria brevis Remane Tubodiscus verenae Thierstein Crassicollaria parvula Remane Umbria granulosa granulosa Bralower & Thierstein Crassicollaria colomi Doben Calpionella alpina Lorenz Calcareous dinocysts Calpionella grandalpina Nagy Calpionella elliptalpina Nagy Cadosina fusca fusca Wanner Calpionella minuta Houša Cadosina fusca cieszynica Nowak Calpionella elliptica Cadisch Cadosina minuta Borza Remaniella ferasini (Catalano) Cadosina parvula Nagy Remaniella duranddelgai Pop Cadosina semiradiata olzae Nowak Remaniella cadischiana (Colom) Cadosina semiradiata semiradiata Wanner Remaniella filipescui Pop Carpistomiosphaera borzai (Nagy) Calpionellopsis simplex (Colom) Carpistomiosphaera tithonica Nowak Calpionellopsis oblonga (Colom) Carpistomiosphaera valanginiana Borza Lorenziella hungarica Knauer & Nagy Colomisphaera carpathica (Borza) Lorenziella plicata Remane Colomisphaera cieszynica Nowak Sturiella oblonga Borza Colomisphaera conferta Øehánek Sturiella dolomitica Grün & Blau Colomisphaera fortis Øehánek Praecalpionellites murgeanui (Pop) Colomisphaera heliosphaera (Vogler) Praecalpionellites siriniaensis Pop Colomisphaera lapidosa (Vogler) Calpionellites darderi (Colom) Colomisphaera lucida Borza Calpionellites coronata Trejo Colomisphaera minutissima (Colom) Calpionellites uncinata Cita & Pasquaré Colomisphaera nagyi (Borza) Calpionellites major (Colom) Colomisphaera pieniniensis (Borza) Calpionellites caravacaensis Allemann Colomisphaera tenuis (Nagy) Colomisphaera vogleri (Borza) Calcareous nannofossils Committosphaera pulla (Borza) Committosphaera sublapidosa (Vogler) Assipetra infracretacea (Thierstein) Roth Parastomiosphaera malmica (Borza) Calcicalathina oblongata (Worsley) Thierstein Stomiosphaera alpina (Leischner) Conusphaera mexicana mexicana Trejo Stomiosphaera echinata Nowak Conusphaera mexicana minor Bralower Stomiosphaera moluccana Wanner Cretarhabdus angustiforatus (Black) Bukry Stomiosphaera wanneri Borza Cruciellipsis cuvillieri (Manivit) Thierstein Stomiosphaerina proxima Øehánek ▲ Continuation of the text to Plate II

Kamptner, Upper Berriasian, N. steinmannii Zone. ig. 12. Nannoconus steinmannii steinmannii Kamptner, Upper Berriasian, N. stein- mannii Zone, Gorno Belotintsi 1 section, sample 52. ig. 13. Microstaurus chiastius (Worsley) Grün in Grün & Allemann, Upper Titho- nian, M. chiastius Zone, Barlya section, sample 307, 1000×. ig. 14. Micrantholithus speetonensis Perch-Nielsen, Upper Berriasian, N. steinmannii Zone, Barlya section, sample 335, 1000×. ig. 15. Micrantholithus speetonensis Perch-Nielsen, Upper Valanginian, T. verenae Zone, Barlya section, sample 107, 1000×. ig. 16. Micrantholithus speetonensis Perch-Nielsen, Upper Berriasian, N. steinmannii Zone, Gorno Belotintsi 1 section, sample 53, 1000×. 166 PLATE III CALPIONELLID, NANNOOSSIL AND CALCAREOUS DINOCYST BIOEVENTS 167 References in Bulgaria. Acta Geol. Hung., 29, 1–2, 89–92. 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