Microfossils and Brachiopods from the Lower Barremian at Prekonozi, Eastern Serbia
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GEOLO[KI ANALI BALKANSKOGA POLUOSTRVA 66 (2004–2005) 55–61 BEOGRAD, decembar 2005 ANNALES GÉOLOGIQUES DE LA PÉNINSULE BALKANIQUE BELGRADE, December 2005 Microfossils and brachiopods from the Lower Barremian at Prekonozi, eastern Serbia SVETLANA POLAVDER1 & BARBARA RADULOVI]2 Abstract. This paper presents the results of an integral biostratigraphical study based on orbitolinids and other benthic foraminifers, brachiopods and algae of a part of the Prekonozi section, eastern Serbia. The species identified are: Paracoskinolina? jourdanensis FOURY & MOULLADE, P. sunnilandensis (MAYNC), Orbitolinopsis debelmasi MOULLADE & THIEULOY, Alpillina antiqua FOURY, Pfenderina globosa FOURY, Mayncina bulgarica LEUG, PEIBERNÈS & REY, Charentia cuvilleri NEUMANI and other foraminifers, and brachiopods: Cyclothyris? pancici (ANTULA), Sellithyris sella (J. DE C. SOWERBY), Dictyothyris elongata SMIRNOVA, and Psilothyris tamarindus (J. DE C. SOWERBY). The examined limestones based on orbitolinids, are assigned to the Lower Barremian, earlier dated Upper Barremian/Lower Aptian. Key words: Orbitolinids, brachiopods, biostratigraphy, Lower Barremian, Prekonozi, eastern Serbia. Apstrakt. Prikazuju se rezultati integralnih biostratigrafskih prou~avawa jednog dela profila Prekonoga (isto~na Srbija) na osnovu orbitolinida i drugih bentoskih foraminifera, brahiopoda i algi. Odre|ene su: Paracoskinolina? jourdanensis FOURY & MOULLADE, P. sunnilandensis (MAYNC), Orbito- linopsis debelmasi MOULLADE & THIEULOY, Alpillina antiqua FOURY, Pfenderina globosa FOURY, Mayncina bul- garica LEUG, PEIBERNÈS & REY, Charentia cuvilleri NEUMANN i drugi foraminiferi, a od brahiopoda: Cyclothyris? pancici (ANTULA), Sellithyris sella (J. DE C. SOWERBY), Dictyothyris elongata SMIRNOVA i Psilo- thyris tamarindus (J. DE C. SOWERBY). Na osnovu orbitolinidske faune prou~avani kre~waci se pripisu- ju dowem baremu, a do sada se smatralo da su gorwobaremske–dowoaptske starosti. Kqu~ne re~i: orbitolinidi, brahiopodi, biostratigrafija, dowi barem, Prekonozi, isto~na Srbija. Introduction This work presents information on a part of a Lower Cretaceous sequence that has been dated Upper Barre- Lower Cretaceous sedimentary rocks exposed on the mian/Lower Aptian (KRSTI] et al., 1978, 1980), which southern slopes of Ozren (Prekonozi), south of Sokobanja, is now interpreted using orbitolinids as Lower Barre- belong to the western belt of the Carpatho-Balkanides, mian (POLAVDER, 2004). eastern Serbia. Within the study of the Lower Cretaceous biostratigra- The Lower Cretaceous of Ozren, in the northern part phy based on microfossils, orbitolinids in particular, bra- of Prekonozi syncline, lies continuously over Jurassic chiopods were also collected in the area between Sokoba- limestones and consists of: Valanginian/Hauterivian shal- nja and Ni{ and interpreted in this paper by B. RADULOVI]. low-water limestones, Barremian and Aptian rocks, rep- resented by shallow-water limestones of the Urgonian facies (KRSTI], 1977; KRSTI] et al., 1978, 1980). Biostratigraphy The results of the presented examination agree with the stratigraphical data of the latest integral study by a In a partly exposed Lower Cretaceous succession group of authors from several European countries (CLA- near Prekonozi, POLAVDER (2004) designated three bio- VEL et al., 2002). sequences: 1 Geoinstitute, Rovinjska 12, 11000 Belgrade, Serbia & Montenegro. E-mail: [email protected] 2 Natural History Museum, Njego{eva 51, 11000 Belgrade, Serbia & Montenegro. E-mail: brad@net. yu 56 SVETLANA POLAVDER & BARBARA RADULOVI] – Biosequence C, Berriasian in age, represented by FOURY (Pl. 1, Fig. 8), Mayncina bulgarica LEUG, PEY- shallow-water foraminiferal and algal limestones (upper BERNÈS & REY, Charentia cuvilleri NEUMANN, Nautilo- part of the Berriasian column); culina cretacea PEYBERNÈS, Pseudocyclammina cf. lituus – Biosequence E, Upper Hauterivian in age, desig- (YOKOYAMA), Pseudolituonella gavonensis* FOURY (Pl. nated on the abundant orbitolinids, among which the 1, Fig. 7), Everticyclammina sp., Ammobaculites* sp., most important is Valserina primitiva SCHROEDER, CHA- trocholinae, miliolids and other foraminifers, then algae: ROLAIS & CONRAD – the stratigraphical marker of the Clypeina estevezii GRANIER (Pl. 1, Fig. 9), Macroporella Upper Hauterivian; platurloni DRAGASTAN, Salpingoporella sp., Neomeris – Biosequence F, Lower Barremian in age, designated sp., Terqumella sp., fragments of Pseudocymopolia ju- on the orbitolinid species that appear in the Lower Barre- rassica (DRAGASTAN) and fragments of other species. mian and those which disappear in the Lower Barremian. – Two metres of sandy, incoherent bioclastic lime- We studied the Lower Barremian sequence in a sec- stones which bears numerous brachiopods: Cyclothyris? tion, about 25 m thick, exposed along the road from pancici (ANTULA), Sellithyris sella (J. DE C. SOWERBY), Prekonozi to Rsovci (Fig. 1). These are dominantly bio- Dictyothyris elongata SMIRNOVA, and Psilothyris tama- clastic, more or less muddy limestones of the pack- rindus (J. DE C. SOWERBY). Compared with the older stone-floatstone-rudstone type. Layers of the sequence layers of the sequence, limestones with brachiopods are contain in places numerous orbitolinids, especially at much poorer in microfossils, particularly orbitolinids the base of the section, and other foraminifers, appre- (only a few indeterminate sections). In addition to fora- ciable amounts of algae, algal fragments, bryozoans, miniferal species (marked by an asterisk in the list microgastropods and other metazoans, and brachiopods above) the rocks contain: Earlandia? conradi ARNAUD- in one of the layers. VANNEAU, Neotrocholina friburgensis GUILLUME & REI- CHEL, Trocholina alpina (LEUPOLD) and other trocholi- nae, and the mentioned dasycladales species. – Other bioclastic limestones (about eighteen metres) in this part of the section mainly bear a similar microfos- sil assemblage as the older brachiopod layers. An impor- tant find is the orbitolinid species P.? jourdanensis, which appears some three metres above the brachiopod- bearing layers and can be traced to the end of the sec- tion, and most probably a new orbitonilid species – Orbitolinid gen. et sp. indet. (Pl. 1, Fig. 6). Above these limestones, sandstone and marl-sandy deposits devoid of faunal remains occur. This investigated sequence, according to the orbi- tolinid assemblage, is certainly Lower Barremian in age. The mentioned foraminiferal and algal association has a wider biostratigraphic significance. The lower bo- undary is placed where the foraminiferal assemblage characteristic of the Upper Hauterivian (beds with Val- serina primitiva) disappears and where the orbitolinid species characteristic of the Lower Barremian appear. The species only within the Lower Barremian (A. anti- qua) and those disappearing in the Lower Barremian (O. debelmasi, P.? jourdanensis) give the rocks their principal biostratigraphic character. As the newest sam- Fig. 1. Location map of the studied area (asterisk). pled rocks in the column contain P.? jourdanensis, this part of the sequence is Lower Barremian. This latter species in sedimentary rocks younger than the Lower Over the Upper Hauterivian shallow-water lime- Barremian is not mentioned anywhere in the recent volu- stones (layers with Valserina primitiva) upward follow: minous literature on the Lower Cretaceous stratigraphy – About five metres of muddy biolithoclastic lime- (ARNAUD-VANNEAU, 1980; BUCUR et al., 1995; BUCUR, stones abounding in microfossils, orbitolinids in partic- 1997; BECKER, 1999; DAOUD et al., 2004). ular, of which are identified: Alpillina antiqua FOURY (Pl. 1, Figs. 1, 2), Orbitolinopsis debelmasi MOULLADE & THIEULOY (Pl. 1, Figs. 4, 5), O. gr. buccifer ARNAUD- Brachiopods VANNEAU & THIEULOY (Pl. 1, Fig. 3), Paracoskinolina? jourdanensis FOURY & MOULLADE, Paracoskinolina sun- The Brachiopods described in this paper are from the nilandensis (MAYNC), Valserina sp., Pfenderina globosa* part of the sequence composed dominatly of bioclastic Microfossils and brachiopods from the Lower Barremian at Prekonozi, eastern Serbia 57 packstone and very fine silty and clayey limestone and simple subtriangular costae, 6–8 on fold, 5–7 in sulcus. less of grainstone. Fold and sulcus barely perceptible. Because the brachiopod association has a greater range, The shell is composed of two calcitic layers (Fig. the age of this part of the sequence is determined as Lower 3A, B). The primary layer is microgranular, 20 µm Barremian on the basis of the orbitolinid microassocation. thick in the sulci and 30 µm in the ribs. The second- The brachiopod species determined are: Cyclothyris? ary layer is built up of isometric rhombic fibres pancici (ANTULA), Sellithyris sella (J. DE C. SOWERBY), (W = 35–45 µm; T = 8–12 µm). Dictyothyris elongata (SMIRNOVA) and Psilothyris tama- The external features as well as the shell ultrastruc- rindus (J. DE C. SOWERBY). ture (shape and dimensions of the fibres) indicate that Except C.? pancici, which is known from the Upper the specimens belong to a new genus (RADULOVI], Barremian, all the other species have a vertical distri- 2005), a detailed systematic description of which will bution, from Valanginian to Lower Aptian, and are also soon be published. known from many localities (Crnoljevica, ^oka Njalta, It is very common in the Barremian throughout east- Faca Vajali, Mali Izvor) of eastern Serbia. ern Serbia (RADULOVI], 2000, 2003). Fig. 2. Lower Baremmian brachio- pods from Prekonozi, Ozren Mt., eastern