engleski

Paleontological and lithological evidence of the late Karpatian to early Badenian marine succession from Medvednica Mountain (Croatia), Central Paratethys

The lower and middle Miocene sediments of the North Croatian Basin belong to the south-western margin of the Central Paratethys. The timing of the first marine transgression is of great importance for understanding the palaeogeography of the Paratethys. Based on micropalaeontological analyses (calcareous nannoplankton, planktonic and benthic foraminifera, ostracods and palynomorphs), we determined the local-to-regional palaeoecological characteristics of Miocene deposits from south-eastern Medvednica Mt., as well as identifying global-to-regional events. Marine index fossils point to calcareous nannofossil Zones NN4 and NN5 (equivalent to the Mediterranean MNN4 and MNN5) and planktonic foraminiferal Zones M5 and M6 (Mediterranean MMi4). The lowermost part of the investigated marls was generally deposited on a mid-outer shelf––which received an input of fine-grained clastic material––in a sedimentary basin that had a restricted connection with the Mediterranean during the Mi2 climatic event. In addition, an important nannofossil bioevent––the paracme of Sphenolithus heteromorphus––in the Mediterranean was recorded in the lower part of the section, close to the Karpatian/Badenian boundary (identified based on the Coccolithus pelagicus/Reticulofenestra minuta shift), which supports other evidence for a shift in global climate change. Warm-water ostracods (Paijenborchella iocosa) and benthic foraminifera (Glabratella and Pararotalia) in the middle part of the sequence indicate a warmer climate, an open connection with the Mediterranean Sea (and, indirectly, with the Indian Ocean), associated with the third-order TB 2.3 relative sea-level cycle of the early Badenian transgression. The upper part of the sequence (in the Plaz outcrop) contains coarsening–upwards cycles, consisting of silty and sandy sediments, sandstones and calcarenites, indicating a regional regressive phase close to the M5/M6 planktonic foraminifera zonal boundary (15.1 Ma). Infaunal benthic foraminifera species were replaced by shallow, warm-water benthic foraminifera (Elphidium, Biasterigerina, Ammonia, Amphistegina) and ostracods with ornamented shells, which occurred in tandem with shallow, warm-water R. minuta, more proximal dinocysts, coralline red algae, echinoids and bryozoans, all indicating the Middle Miocene Climatic Optimum (MMCO), with sedimentation taking place in a middle- to inner-shelf environment. A tuff layer is present at the top of the sequence ; it contains planktonic foraminifera (Globigerina tarchanensis, G. subcretacea, Globigerinita uvula), suggesting a redeepening and influence of the TB 2.4 sea-level cycle.

Microfossils ; Karpatian/Badenian boundary ; Early/mid-Miocene transition ; North Croatian Basin ; Central Paratethys

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