engleski

How tectonic, sea level changes and (dis)connections with others marine areas influenced on calcareous nannoplankton asemblage during the Sarmatian/Pannonian transition.

The Croatian Basin belongs to south western part of the Central Paratethys. This intercontinental region is developed in the early Miocene as a result of the African and European plate collision. It’s surrounded by the Alps, Dinaride and Carpathian Mts. The evolution of the Central Paratethys was controlled by regional tectonic events, sea-level changes and connections with Mediterranean, Boreal and Indopacific oceans. These connections have been several times repeatedly disrupted and re-established, which had a direct influence on the evolution of the organisms and their endemism. In the upper Sarmatian the marine littoral development prevails. Lack of the coccospheres in the assemblage with Braarudosphaera bigelowii (GRAN & BRAARUD) DEFLANDRE, Lithostromatium perdurum DEFLANDRE, Perforocalcinella fusiformis BÓNA, and reworked species of the NN6 zone imply on regresive trend and their development in typically shallow, oligotrophic, and warm marine environments (BÓNA & GÁL, 1985 ; BUCCHERI et al., 2002) at žumberak Mts. (Draganić}; section) and Dilj Mt. (Bečic section). Percentage of calcareous nannoplankton (Reticulofenestra minuta ROTH, Sphenolithus abies DEFLANDRE and Syracosphaera pulchra LOHMANN) in the assemblages is drastically increased (up to 99.5 %) at the end of the Sarmatian. Mentioned species are characteristic for warmer marine areas (RAHMAN et al., 1990 ; AUBRY et al., 1992 ; PROBERT&HOUDAN, 2004). The communications with the other marine areas are broken in the upper part of the Sarmatian on the Medvednica Mt. In the area of Samobor hills and Krndija Mt. the connections oscillate but are still present. The regional tectonic movements caused shallowing and much more influence of the river input. The lowstand at the end of the Sarmatian (Sarmatian/Pannonian boundary) discovered in the NN8 zone of calcareous nannoplankton can be correlated with the Ser4 sequence boundary (GALOVIĆ & BAJRAKTAREVIĆ], 2006). This event is detected at 11.1 Ma (VASILIEV, 2006) and noticed in drastic decrease in the number of species and genus with monofloral development of the calcareous nannoplankton characterising more changes in the environment (shallowing, river input…). The most representative calcareous nannoplankton in laminated sediments belongs to ascidian spicules known in Paratethys as an endemic Perforocalcinella fusiformis BÓNA and also to Isolithus semenenko LULJEVAin association with Reticulofenestra spp., Sphenolithus spp. and Syracosphaera pulchra LOHMANN. The typical endemical form Noelaerhabdus bozinovicae JERKOVIĆ is also a conseguence of those changes in the environment and it’s adjustment to them. On the other hand, the first detected appearance of the Amaurolithus group (Nicklithus amplificus (BUKRY & PERCIVAL) RAFFI et al., Amaurolithus tricorniculatus (GARTNER) GARTNER & BUKRY) on the Samobor hills (Jurjevčan section) and Krndija Mt. is typical for the tropical marine regions (RAFFI et al., 1998). The reason for their appearance might be in periodic influx of warm marine waters within the coastal lake or influence of warm marine current into restricted environment during the warmer season. It’s evident that in the North Croatian Basin (Samobor hills and Krndija Mt.) the marine (weak) connections oscillate but are still present with the beginning of the Pannonian.

calcareous nannoplankton; Sarmatian/Pannonian transition; environmental changes; Croatian Basin; Central Paratethys

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