ACTA PALAEONTOLOGICA ROMANIAE V. 5 (2005), P. 27-38 MICROPALEONTOLOGICAL ASSEMBLAGES FROM THE UPPER JURASSIC-LOWER CRETACEOUS DEPOSITS OF TRASCĂU MOUNTAINS AND THEIR BIOSTRATIGRAPHIC SIGNIFICANCE Ioan I. BUCUR1 and Emanoil SĂSĂRAN1 Abstract: Upper Jurassic-Lower Cretaceous deposits from the Trascău Mountains, mainly developed in a carbonate platform facies, were investigated for their micropaleontological content in several sections, starting from Petreşti-Sănduleşti area (in the northern part) to Rîmeţi area (in the southern part). Several micropaleontological assemblages were determined corresponding to the three depositional units identified in the region: Upper Oxfordian-Lower Kimmeridgian; Kimmeridgian-Lower Tithonian, and Upper Tithonian-Berriasian-Lower Valanginian. In the Upper Oxfordian-Lower Tithonian interval the carbonate deposits are developed in a slope facies, an external platform facies (including coral-microbial reefal buildups), and less frequently in an internal platform facies. The Upper Tithonian-?Berriasian deposits are well exposed in the Cheile Turzii section, and are represented mainly by coarse granular facies. The Berriasian-Lower Valanginian deposits, represented by shallow or very shallow water facies (shallow subtidal to intertidal or supratidal) were studied in several sections (Cheile Turzii, Dealul Secului, Brădeşti) as well as in the olithosliths from Poiana Aiudului. A rich algae and foraminifera assemblages were identified in the studied deposits. They are important for both biostratigraphy (age determination of the depositional units separated through sedimentological study) and paleoecology-paleogeography as comparative material for correlations with other regions of the Tethyan realm. Keywords: Microfossils, biostratigraphy, carbonate rocks, Apuseni Mountains, Romania 1. INTRODUCTION. DEPOSITIONAL the distribution of these facies associations FRAMEWORK Săsăran (2005) separated three isolated carbonate platforms: the Tureni-Buru platform; Rimetea-Aiud The shallow water limestones from the Trascău Gorges platform, and the Bedeleu-Râmeţi platform. Mountains crop out in two parallel alignments with The three platforms were separated by deeper a generally N-S orientation: Tureni-Buru-Rimetea- basinal areas in which , “Aptychus beds”-type Cheile Aiudului alignment in the east, and the deposits accumulated during the late Jurassic- Lunca Arieşului-Râmeţi (Bedeleu ridge) in the west early Cretaceous. (Fig. 1). These limestones were studied on the The development of the Upper Jurassic-Lower following sections: Tureni Gorges, Sănduleşti Cretaceous carbonate deposits from the Trascău Quarry, Turda Gorges, Borzeşti Gorges, Buru, Mountains could be most accurately studied in the Rimetea (Piatra Secuiului), Aiud Gorges and Tureni-Buru area and is best illustrated by the Poiana Aiudului (the Quarry and Dealul Mare Turda Gorges section (Fig. 2). Săsăran (2005) olistoliths) from the first alignment; Secului Hill, separated in this area three units with well defined Brădeşti, Râmeţi Gorges from the second boundaries (Fig. 2) alignment (Fig.1) The micropaleontological study was made up of Sedimentological and facies studies of the a large number of thin sections (more than 1500). carbonate deposits from the region (Săsăran, The identified assemblages of benthic foraminifera 2005) provide evidence for five facies associations: and calcareous algae are very important for age (1) the basin floor facies associations (identified in determination of the deposits within the three Tureni-Valea Mănăstirii area, the “Aptychus beds” depositional units. senso largo); (2) Shelf slope facies associations (identified in Tureni Gorges, Buru, Rimetea, Aiud 2. MICROPALEONTOLOGICAL ASSOCIATIONS Gorges, and Bedeleu ridge); (3) open shelf edge facies associations, with bioconstructions and Preliminary data on the micropaleontological bioclastic shoals (identified in the Sănduleşti content of the Upper Jurassic-Lower Cretaceous quarry, Borzeşti Gorges, Rimetea, Aiud Gorges deposits from Trascău Mountains were published and Bedeleu ridge); (4) open shelf facies by Săsăran et al. (2000), Săsăran & Bucur (2001) associations with patch reefs (identified in the and Bucur & Săsăran (2005). This study provides a Turda Gorges, Rimetea, and Bedeleu ridge), and synthetic overview of the micropaleontological (5) sea shore and beach facies associations, content of the limestones in the area, and tries to represented by peritidal deposits (identified in the follow the microfossils repartition within the three Turda Gorges, Borzeşti Gorges, Bedeleu ridge and depositional units. in the olistiliths from Poiana Aiudului). Following 1 Babeş-Bolyai University, Department of Geology, M. Kogălniceanu str. 1, 400084 Cluj-Napoca, Romania. E-mails: [email protected]; [email protected] Ioan I. BUCUR and Emanoil SĂSĂRAN The carbonate deposits from the first two units, (RADOICIC), S. pygmaea (GUEMBEL) (Pl. I, fig. 8, mostly developed in slope facies, external platrom 10), Suppiluliumaella delphica (CARAS), facies (including coral-microbial reefal buildups), “Carpathocodium anae” (DRAGASTAN) (Pl. I, fig. and less frequently in internal platform facies, 13), Nipponophycus ramosus YABE & TOYAMA, contain an assemblage of foraminifera and Thaumatoporella parvovesiculifera RAINERI. In calcareous algae consisting of: Alveosepta jaccardi reef facies, incrusting microorganisms are (SCHRODT) (Pl. I, fig. 1; Pl. II, fig. 1), abundant: Bacinella-Lithocodium, Iberopora Andersenolina alpina (LEUPOLD) (Pl. II, fig. 11), bodeuri GRANIER, Koskinobulina socialis Bramkampella arabica REDMOND (Pl. II, fig. 6, 7), CHERCHI & SCHROEDER, Radiomura cautica Everticyclammina virguliana (KOECHLIN), SENOWBARI-DARYAN & SCHAEFER, Kurnubia palastiniensis HENSON, Labyrinthina “Tubiphytes” morronensis CRESCENTI, together mirabilis WEYNSCHENK (Pl.I, fig.1, Pl. II, fig. 2-4), with Mercierella dacica DRAGASTAN. Mohlerina basiliensis (MOHLER) (Pl. II, fig. 12), The carbonate deposits situated in the lower Neokilianina rahonensis (FOURY & VINCENT) (Pl. part of the third unit (Turda Gorges section, Fig. 2) I, fig. 2), Parurgonina caelinensis CUVILLIER, are represented mainly by coarse granular facies, FOURY & PIGNATTI MORANO (Pl. II, fig. 5), and contain an assemblage with: Andersenolina Protopeneroplis striata WEYNSCHENK (Pl. II, fig. alpina (LEUPOLD), A. cherchiae (ARNAUD- 2, 10), Pseudocyclammina lituus (YOKOYAMA), VANNEAU, BOISSEAU & DARSAC), A. elongata Redmondoides lugeoni (SEPTFONTAINE), (LEUPOLD), Achispirocyclina lusitanica (EGGER) Anisoporella (?) cretacea (DRAGASTAN), (Pl. II, fig. 13-15), Bramkampella arabica Anisoporella (?) jurassica (ENDO), Campbelliella REDMOND, Mohlerina basiliensis (MOHLER), striata CAROZZI (Pl. I, fig. 6), Clypeina sulcata Neokilianina sp. (Pl. II, fig. 8), Protopeneroplis cf. (ALTH) (Pl. I, fig. 9), Macroporella(?) lazuriensis banatica BUCUR, P. ultragranulata BUCUR (Pl. I, fig. 12), Montenegrella cf. florifera (GORBACHIK), Pseudocyclammina lituus BERNIER (Pl. I, fig. 11), Neoteutloporella socialis (YOKOYAMA), Troglotella incrustans WERNLI & (PRATURLON) (Pl. I, fig. 5), Petrascula cf. piai FOOKES, Campbelliella striata CAROZZI, BACHMAYER (Pl. III, fig. 1), Salpingoporella Clypeina catinula CAROZZI (Pl. III, fig. 5), C. annulata CAROZZI (Pl. I, fig. 7), S. grudii parasolkani FARINACCI & RADOICIC (Pl. III, fig. Fig. 1. – Sketch-map of the northern part of the Trascău Mountains, with emplacement of the sections studied: 1 - Tureni Gorges; 2 - Sănduleşti quarry; 3 - Turda Gorges; 4 - Borzeşti Gorges; 5 - Buru; 6 - Rimetea (Piatra Secuiului); 7 - Aiud Gorges; 8 - Poiana Aiudului; 9 - Secului Hill; 10 - Brădeşti; 11 - Râmeţi Gorges) 28 Micropaleontological assemblages from the Upper Jurassic-Lower Cretaceous deposits of Trascău Mountains VANNEAU, BOISSEAU & DARSAC) (Pl. IV, fig. 15), A. delphinensis (ARNAUD-VANNEAU, BOISSEAU & DARSAC) (Pl. IV, fig. 14), A. elongata (LEUPOLD) (Pl. IV, fig. 16, 17), A. aff. molesta (GORBACHIK (Pl. IV, fig. 12), Anchispirocyclina lusitanica (EGGER), Charentia cuvillieri NEUMANN, Haplophragmoides joukowskyi CHAROLLAIS, BROENNIMANN & ZANINETTI (Pl. IV, fig. 1-2), Meandrospira favrei (CHAROLLAIS, BROENNIMANN & ZANINETTI), Mohlerina basiliensis (MOHLER), Montsalevia salevensis (CHAROLLAIS, BROENNIMANN & ZANINETTI) (Pl. IV, fig. 3-8), Neotrocholina valdensis REICHEL, Protopeneroplis banatica BUCUR, P. ultragranulata (GORBACHIK) (Pl. IV, fig. 10-11), Pseudocyclammina lituus (YOKOYAMA), Clypeina catinula CAROZZI, C. parasolkani FARINACCI & RADOICIC, C. solkani CONRAD & RADOICIC, C. sulcata (ALTH) (only in Berriasian), Macroporella (?) praturlonii DRAGASTAN, Macroporella (?) incerta SOKAC & NIKLER, Pseudocymopolia jurassica (DRAGASTAN) (Pl. III, fig. 7, 9), Rajkaella bartheli (BERNIER), Salpingoporella annulata CAROZZI, S. katzeri CONRAD & RADOICIC and charophytes (Pl. III, fig. 4). 3. BIOSTRATIGRAPHIC SIGNIFICANCE Some of the benthic foraminifera and calcareous algae identified in the three assemblages are very important because they indicate the age of the three depositional units. The most significant species of the first assemblage is Alveosepta jaccardi. This foraminifer was first described from the Upper Oxfordian of Switzerland (Schrodt, 1894) as Cyclammina jaccardi. Mohler (1938) illustrated this species as Pseudocyclammina sequana (Merian) var. minor, P. sequana (Merian) var. major, and Pseudocyclammina personata Tobler from the Upper Oxfordian (Sequanian) and the Kimmeridgian of the Jura Mountains (Switzerland)