Znalezisko Zaraiskites Semenov, 1898 z tintinnidami w wapieniach górnej jury Neskovci (Bułgaria, Stara Planina)

Wiesław Nowak


Finding of Zaraiskites Semenov1898 in company of tintinnids in Upper Jurassic limestones at Neškovci (Bulgaria, Stara Planina)

Microorganisms of the Tintinnida group acquired recently a great importance for correlation of Upper Jurassic and Cretaceous rocks in the Mediterranean province. Their mass occurrence, usually as rock-forming microfossils, in various facial types of rocks at the Uppermost Jurassic (Cretaceous boundary provided first a criterion for distinguishing Tithonian rocks from Kimmeridgian and Neocomian ones, and recently is forming the basis for delimitation of the Upper Tithonian. It is accepted, that these microfossils (Crassicollaria, Calpionella, Tintinnopsella) appear in the Late Tithonian, not older than the Virgatosphinctes transitorius zone. The finding of tintinnides at Neskovci in Bulgaria together with an index ammonite of the Zaraiskites genus (determined by Dr. A. Zeiss, Erlangen) provides a basis for the revision of the above opinion, and permits to state that at Neskovci these microfossils appeared in an older zone. The tintinnids were found in a limestone block found by the author in 1965 during the excursion of the VH-th Congress of the Carpatho-Balcanian Association, between Pleven and Plovdiv,, at the locality Neskovci, south of Trojan (see Figs. 1—4, Plate I). The block has been collected in an outcrop situated between the observation point 31 on Kimmeridgian limestones and the first outcrops of Berriasian flysch rocks (see J. Nacev in: Excursionfiihrer — A, pp. 52—55). The limestone is dark-grey, marly, with irregular fracture. Organic microstructure of biopelmicrite type with dispersed tintinnids and other microorganisms (see list in Polish text, p. 293), has been observed in thin sections. However, the assemblage of tintinnids is distinctly poorer both in the number of species and number of specimens, than the assemblages known from the Virgatosphinctes transitorius zone. It comprises forms belonging to the genera Crassicollaria and Calpionella, the specific determination of which is difficult, and single specimens of Patelloides and Chitinoidella. Numerous zoospores of Globochaete alpina Lombard and articles of the planktonie crinoid Saccocoma Agassiz are characteristic for the described assemblage. The composition of the assemblage provides a good basis for establishing it as typical for the passage from the so-called Saccocoma microfacies to the tintinnid microfaci.es, the latter showing an explosive development in the Late Tithonian. The occurrence of the described assemblage accompanied by Zaraiskites, an index ammonite for the upper part of the Lower Volgian and the upper part of the Lower Portlandian in the Boreal province (= lower part of the Upper Tithonian — Ardescien sensu A. Zeiss, 1965), indicates, that the passage between the above two microfacies in the vertical profile occurs in the lower part of the Upper Tithonian in the area of Bulgaria (Neskovci). The character of the tintinnids assemblage and the stratigraphic position indicated by the presence of Zaraiskites lead to the conclusion that the assemblage determined at Neskovci is older than the oldest tintinnids assemblage (Zone A. Crassicollaria) in the scheme of J. Remane (1963, 1964). Some similarities exist between the assemblage discussed here and the tintinnids assemblages described from the Tithonian of Eastern Alps (Bernreich, Woldrich) by E. Kristan-Tollmann (1962), from the red Rogoźnik lumachella of the Pieniny Klippen Belt (Rogoźnik, locus typicus — Lower Tithonian sensu Zittel (1870) Neumayr (1871); Middle Tithonian sensu Arkell (1956), by K. Birkenmajer (1962), from the Upper part of the Lower Tithonian — Vigne Droguet horizon in the Chambery area, by P. Donze (1958), and from the Lower Neuburg limestones mentioned by J. Th. Groiss (1963). The author expresses his thanks to Dr. A. Zeiss from Erlangen who kindly provided the determination of the ammonite found at Neskovci.

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