8th International Nannoplankton Association Conference


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Daria Ivanova:
Oxfordian to Hauterivian calcareous dinoflagellate cyst sequences from NW Bulgaria: vertical distribution and long-distance correlations

Investigations of calcareous dinoflagellate cysts (previously known as cadosinids and stomiosphaerids) started in 1940, with the studies of Wanner on small, spherical forms found in thin-sections from Upper Jurassic and Lower Cretaceous limestones of the East Indian Archipelago. Due to the favourable environmental and facies conditions during Late Jurassic and Early Cretaceous times, the sedimentary rocks in the Carpathian-Balkan area contain diverse microplanktonic organisms, namely calcareous nannofossils, calcareous dinocysts and calpionellids. The mass occurrence of calcareous dinocysts enforces studies on changes, and clarification of their taxonomy and vertical distributions. However, because of strong secondary recrystallisation of the limestones in this area, it was impossible to apply the usual method of studying isolated calcareous dinocysts (Rehakova & Michalik, 1996; Ivanova & Keupp, 1999), but an attempt at correlation with species found in thin-sections has been made.

The present study embraces the biostratigraphic investigations on dinoflagellate cysts from successions of pelagic, nodular, pure micritic and clayey limestones of Oxfordian, Kimmeridgian, Tithonian, Berriasian, Valanginian and Hauterivian (lowermost part) ages in the W Forebalkan and W Balkan, Bulgaria. Five formations have been studied, namely the Javorets, Gintsi, Glozhene, Salash and Simeonovo Formations.

The Yavorets Formation is represented by medium- to thickly-bedded, grey micritic limestones. The thickness of the formation in the studied area is about 15m. The Gintsi Formation is built up of grey to pink, variously clayey limestones with nodular structure, irregularly intercalated with micritic and intraclastic limestones (ammonitico rosso facies). The thickness of the formation in the investigated area is from 3m to 17m. The Glozhene Formation is represented by dark grey to grey, hard micritic limestones with intraclasts. The thickness of the formation in the studied sections varies from 30m to 107m. The Salash Formation is built up of alternating micritic limestones, clayey limestones and marls. The studied part of the formation is from 5m to 108m thick. The Simeonovo Formation is built up of thickly-bedded to massive, pale grey to whitish, organogenic and, less commonly, micritic limestones. The thickness of the formation in the investigated section is about 25m.

A detailed sampling has been carried out on five reference sections: Barlya (B), Ruzhintsi (R), Nikolovo (N), Gorno Belotintsi-1 (GB-1) and Gorno Belotintsi-2 (GB-2), and the calcareous dinoflagellate cyst sequences have been studied. Their vertical distribution, diversity and abundance, as well as the parallel correlation with calpionellids and calcareous nannofossils in the same sections, enables revision of the previously-established biozonations.

As a result, the following 13 biointerval zones, based on the first occurrences of the index-species, have been proposed: C. fibrata Biozone (Oxfordian); C. parvula Biozone (Early Kimmeridgian); S. moluccana Biozone (Middle Kimmeridgian); C. borzai Biozone (Late Kimmeridgian); C. tithonica Biozone (Kimmeridgian/Tithonian boundary interval); P. malmica (Early Tithonian); C. tenuis (Middle Tithonian); C. fortis (earliest Late Tithonian); S. proxima (Late Tithonian-Late Berriasian; S. wanneri (latest Berriasian); C. conferta (Early Valanginian); C. valanginiana (earliest Late Valanginian); S. echinata (Late Valanginian). Besides these biozones, a new one, named C. nowaki (Early Hauterivian), has been introduced. The results obtained permit long-distance correlations across the whole Carpathian-Balkan realm.


Ivanova, D. & Keupp, H. 1999. Calcareous dinoflagellate cysts from the Late Jurassic and Early Cretaceous of the Western Forebalkan, Bulgaria. Berliner Geowiss. Abh., E0; 3-31.

Lakova, I., Stoykova, K. & Ivanova, D. 1999. Calpionellid, nannofossil and calcareous dinocyst bioevents and integrated biochronology of the Tithonian to Valanginian in the Western Balkanides, Bulgaria. Geol. Carpathica, 50(2): 1-18.

Rehakova, D. & Michalik, J. 1996. Stomiosphaera or Orthopithonella? Cadosina or Obliquipithonella? Notes on ultrastructure and systematic position of some Jurassic-Cretaceous calcareous dinoflagellates from Western Carpathians. Miner. Slovaca, 28: 92-98.

Wanner, J. 1940. Gesteinbildende Foraminiferen aus Malm und Unterkreide des Ostindischen Archipels. Paläont. Z., 22(2): 75-99.


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