Davor Vrsaljko

The coralline flora of a Miocene maërl: the Croatian “ Litavac”

The fossil coralline flora of the Badenian bioclastic limestone outcropping in Northern Croatia is known by the name “Litavac”, shortened from “Lithothamnium Limestone”. The name was given to indicate that unidentified coralline algae are the major component. In this first contribution to the knowledge of the coralline flora of the Litavac, Lithothamnion valens seems to be the most common species, with an unattached, branched growth-form. Small rhodoliths composed of Phymatolithon calcareum and Mesophyllum roveretoi also occur. The Badenian benthic association is dominated by melobesioid corallines, thus it can be compared with the modern maerl facies of the Atlantic Ocean and Mediterranean Sea. Since L. valens still survives in the present-day Mediterranean, an analogy between the Badenian Litavac and the living L. valens facies of the Mediterranean is suggested.

Early Miocene ostracods from the Sadovi section (Mt Požeška gora, Croatia)

Early Miocene ostracods from the Sadovi section (Mt Požeška gora, Croatia) The study of the Early Miocene (Late Ottnangian/Early Karpatian) ostracod fauna from the Sadovi section (Mt Požeška gora, Croatia) led to several results concerning Neogene paleobiogeography and paleoecology. Brackish deposits of Late Ottnangian and Early Karpatian age have been recognized for the first time in the North Croatian Basin. These deposits indicate the first marine ingression into the Early Miocene lake in this area. Twenty-nine ostracod species were determined, including the new taxa Fabaeformiscandona slavonica nov. sp. and Herpetocypris sadovii nov. sp.

The Pannonian Palaeoecology and Biostratigraphy of Molluscs from Kostanjek - Medvednica Mt., Croatia

On the south-western slope of Medvednica Mt., an 83 m thick geological column Kostanjek-1, composed of strata representing the Sarmatian and Pannonian stages, was investigated in detail. Facies analysis allowed separation of five lithofacies units (A, AB, B, C and D) and the sedimentary mechanisms for particular successions were defined. A rich community of fossil molluscs (50 species) and ostracods (42 species) was sampled and determined. From these fossil determinations, the sediment age was defined, and biofacies analysis allowed the determination of three basic palaeobiocenosis types: 1) a community from Sarmatian brackish lagoons, 2) a community from an Early Pannonian littoral lake, and 3) a lake basin community in the Late Pannonian. The main “record” of the salinity crisis (drop) at the Sarmatian-Pannonian boundary influences in a selective way the majority of organisms, and is shown best in the evolutionary form changes of cardid bivalves, for which phylogenetic series were made. On the basis of dominant and characteristic forms in the entire association of Pannonian molluscs five biozones were separated: I) Lymno cardium praeponticum acrozone, II) Radix croatica - L y m n o c a r d i u m plicataeformis - Gyraulus praeponticus cenozone, III) Neodelminiella venusta - Lymnocardium cekusi cenozone, IV) Congeria banatica Lymnocardium gorjanovici - Gyraulus tenuistriatus cenozone and V) Congeria czjzeki - Lymnocardium winkleri - Gyraulus tenuistriatus cenozone. Many ostracod forms supply and test the stratigraphic value of molluscs and support zonality of Pannonian layers.

Stratigraphy and Palaeogeography of Miocene Deposits from the Marginal Area of Žumberak Mt. and the Samoborsko Gorje Mts. (Northwestern Croatia)

Miocene sediments rimming the Palaeozoic–Mesozoic–Palaeogene rocks, form Žumberak Mt. and the Samoborsko Gorje Mts. Spatial analysis of the setting and development of the surface Miocene stratigraphy, at the marginal areas of the Žumberak and Samoborsko Gorje Mts., allows four palaeogeographic areas to be distinguished: Žumberak, Plesivica–Sveta Jana, Samobor–Sveta Nedelja and Grdanjci. In the Miocene deposits (totaling 350 m), within the area of Žumberak, coarse-grained clastics from deltaic deposits of Pannonian age prevail. Here only, 50 m of sediments of Pliocene–Pleistocene age overlie the Miocene deposits whereas Mesozoic carbonates represent the basement. The Plesivica–Sveta Jana area is characterized by a 600 m sequence of Miocene deposits, mainly overlying Triassic dolomites, where finely-grained layers of marls and silts prevail. In this area, Miocene successions from the Badenian to the Pontian are characterized by a continuity of sedimentation with an inherited depositional environment. In the area of Samobor–Sveta Nedelja, the basement is diverse: Triassic dolomites, volcanogenic–sedimentary complex of Cretaceous age and a clastic–carbonate complex of Palaeogene age. The Miocene succession shows a regressive trend from the Badenian to the Pontian and the total thickness is estimated at 400 m. The area of Grdanjci differs considerably from the other Miocene palaeorelief. An approximately 50 m-thick series of coarsegrained clastics with coal is distinguished, of unclear stratigraphic age (Ottnangian?). Miocene sediments of the Grdanjci area are represented by both a transgressive type of conglomerates and shallow water limestones of Badenian age, with a total thickness of about 100 m. The development of the Miocene stratigraphy of the Žumberak and Samoborsko Gorje Mts. is generally correlative with that in the other parts of the Pannonian area, though it does exhibit local variations. Comparison of the Miocene palaeorelief of Žumberak Mt. with the Samoborsko Gorje Mts., together with neighbouring areas, enabled wider correlation with other parts of northern Croatia, and the more distant Western and Central Paratethys.

New Congerian Species and Their Similarity with Congeria banatica from the Pannonian Sediments in Northern Croatia

Congeria baschi n.sp. and Congeria susedana n.sp. are two new species from the Pannonian sediments of the Medvednica Mts. (NW Croatia). C. baschi n. s p . was found in the Lower Pannonian limestones, and C. susedana n.s p . was collected from the Upper Pannonian marls. Relationships with the affiliated taxa enable reconstruction of a phyletic lineage beginning with Congeria soceni JEKELIUS, through C. baschi n.sp. to Congeria banatica HORNES. C. banatica is the ancestor of two branches, leading to C. susedana n. sp. and C. vugro veci SREMAC, respectively. Dreissenomya digitifera (ANDRUSOV) is the probable descendant of C. vugroveci. The accompanying assemblages of fossil molluscs and ostracods from the same horizons facilitate the precise stratigraphic and palaeoenvironmental positioning of the new taxa.

Mid-Miocene (Badenian) transgression on Mesozoic basement rocks in the Mt. Medvednica area of northern Croatia

Rocky shorelines in the geological record, which represent major transgressive surfaces and provide us with crucial information about paleoshorelines and ancient sea levels, often involve a basal conglomerate associated with an unconformity. The unconformity between the Mesozoic basement and the overlying Middle Miocene (Badenian) deposits (which belong paleo-geographically to the southwestern margins of the Central Paratethys, and geotectonically to the Pannonian Basin System) in the Gornje Orešje section (northeast Mt. Medvednica, northern Croatia) is marked by basal Badenian conglomerates. The Upper Cretaceous limestone lithoclasts occurring in basal conglomerates show abundant truncated Gastrochaenolites and Entobia borings (represented by an in situ rocky substrate community of bivalves and sponges, respectively), with Gastrochaenolites being the dominant ichnogenus. Gastrochaenolites-Entobia ichnofossil assemblage related to the Entobia subichnofacies and in turn assignable to the Trypanites Ichnofacies, is very typical of Neogene rocky shores. This association characterizes littoral rockground environments, indicating wave-cut platforms and marine flooding surfaces (transgressive surfaces) with a low or null rate of sedimentation. Erosion of a pre-existing Mesozoic basement rocky shore during a marine transgressive phase in these high-energy littoral conditions, which formed basal conglomerates analyzed here, is also evidenced by truncation and the occurrence of Gastrochaenolites borings on all sides of limestone clasts. Calcareous red algae encrusting bored lithoclasts and often-forming rhodoliths also imply that the basal conglomerates occur at the start of a deepening-upwards succession of a transgressive systems tract deposits. The biostratigraphic correlation of the transgressive deepening-upward sequence from the Gornje Orešje section (ascribed to a single Badenian transgressive event that affected the Mesozoic basement) is based on the presence of the orbulinas in the uppermost outer shelf marl interval. The co-occurrence of Praeorbulina glomerosa circularis and Orbulina suturalis points to the short interval between FO (first occurrence) of Orbulina suturalis and LO (last occurrence) of Praeorbulina glomerosa circularis. These samples belong to the plankton zone M6 (Orbulina suturalis Zone) or the base of NN5 zone, marking the third-order sequence TB 2.4, which represents the second, main Badenian transgression in the Central Paratethys.

The Miocene “Pteropod event” in the SW part of the Central Paratethys (Medvednica Mt., northern Croatia)

Abstract Deep marine Miocene deposits exposed sporadically in the Medvednica Mt. (northern Croatia) comprise pelagic organisms such as coccolithophores, planktic foraminifera and pteropods. The pteropod fauna from yellow marls at the Vejalnica locality (central part of Medvednica Mt.) encompasses abundant specimens of Vaginella austriaca Kittl, 1886, accompanied with scarce Clio fallauxi (Kittl, 1886). Calcareous nannoplankton points to the presence of NN5 nannozone at this locality. Highly fossiliferous grey marls at the Marija Bistrica locality (north-eastern area of Medvednica Mt.) comprise limacinid pteropods: Limacina valvatina (Reuss, 1867), L. gramensis (Rasmussen, 1968) and Limacina sp. Late Badenian (NN5 to NN6 nannozone) age of these marls is presumed on the basis of coccolithophores. Most of the determined pteropods on species level, except V. austriaca have been found and described from this region for the first time. New pteropod records from Croatia point to two pteropod horizons coinciding with the Badenian marine transgressions in Central Paratethys. These pteropod assemblages confirm the existence of W–E marine connection (“Transtethyan Trench Corridor”) during the Badenian NN5 nannozone. Limacinids point to the possible immigration of the “North Sea fauna” through a northern European marine passage during the Late Badenian (end of NN5-beginning of NN6 zone), as previously presumed by some other authors.

REEFS AND BIOACCUMULATIONS IN THE MIOCENE DEPOSITS OF THE NORTH CROATIAN BASIN – AMAZING DIVERSITY YET TO BE DESCRIBED

During the early stages of the Middle Miocene transgression marine biota invaded the newly formed Paratethys Sea. Reefs and reef-like structures particularly flourished with life, supported by the favourable climate conditions. Miocene biogene buildups show a variety of fossil assemblages and lithologic features. The main reef-builders were bryozoans, coralline algae, corals, oysters, vermetids, sponges and serpulids. Water turbidity and depth were major ecological factors controlling the reef biota. Lithofacies types at the studied localities in Northern Croatia show significant similarity with the Upper Langhian (Middle Badenian) of the Leitha Mountains in Austria, but can also be well compared with Miocene to recent reef structures in the Mediterranean. The Miocene reef-like buildups exhibit different porosity rates and other lithological characteristics.