ORIGINAL ARTICLE Middle Miocene warm-temperate carbonates of Central Paratethys (Mt. Zrinska Gora, Croatia): paleoenvironmental reconstruction based on bryozoans, coralline red algae, foraminifera, and calcareous nannoplankton Maja Martinus ˇ • Karmen Fio • Kristina Pikelj • S ˇ imun As ˇc ˇic ´ Received: 10 February 2012 / Accepted: 12 August 2012 Ó Springer-Verlag 2012 Abstract Carbonate deposits from Zrin in the Mt. Zrinska Gora were deposited in the SW part of the Central Paratethys Sea during the Middle Badenian (Middle Mio- cene). The studied section contains a rich fossil community of non-geniculate coralline red algae (Subfamily Melobe- sioideae), bryozoans, benthic and planktonic foraminifera, echinoderms, ostracods, molluscs, and calcareous nanno- plankton. Based on lithological variations and changes in the biogenic components, four facies associations (FA) are distinguished. Their distribution points to skeletal produc- tion and sedimentation on a middle to proximal outer carbonate ramp. The main lithological feature of the sec- tion is an alternation of two lithofacies: fully lithified grainstone–rudstone and packstone, and semi-lithified rudstone–floatstone with a carbonate sandy matrix. Depo- sitional environments on the ramp were periodically influenced by minor high-frequency sea-level changes and/ or changes of hydrodynamic conditions, which are sug- gested as the driving mechanisms causing the alternation of the two lithofacies. Vertically in the succession, the two lithofacies alternate to give three thinning- and fining- upward units. The lower part of each unit is formed of a rhodolith and coralline algal FA, which passes upwards into a bryozoan-coralline algal FA and/or FA of bioclastic packstone-grainstone. Based on the vertical upward change in FAs, each unit can be interpreted as a deepening-upward sequence. Patterns in the relative abundance of bryozoan colony growth form (vinculariiform, cellariiform, adeoni- form, membraniporiform, celleporiform, and reteporiform), size and abundance of rhodoliths and coralline branches, and benthic foraminifera are interpreted by comparison with data from modern and fossil environments. Based on these data, a water depth range for each FA is interpreted, providing evidence of low-frequency relative sea-level changes. It is hypothesized that relative sea-level fluctuated in the water depth range from 30 to 80 m, and in the uppermost part of the section, rich in planktonic forami- nifera and calcareous nannoplankton, possibly deeper. Causes of the low-frequency relative sea-level fluctuations and the general deepening trend observed within the succession cannot be interpreted based on one section; however, they may be related to the subsidence of the depositional basin. The benthic biotic communities are a vertical alternation of rhodalgal and bryorhodalgal associa- tions, and this is attributed to relative sea-level fluctuations. These biotic associations gave rise to warm-temperate carbonates of the Middle Badenian N9 planktonic Zone (Orbulina suturalis, O. universa) and NN4–NN5 nanno- plankton Zones (Sphenolithus heteromorphus). Keywords Warm-temperate carbonates Á Bryozoans Á Coralline red algae Á Benthic foraminifera Á Calcareous nannoplankton Á Middle Miocene Á Central Paratethys Á Croatia Introduction The Paratethys Sea represents an epicontinental sea that was separated from the Mediterranean as a result of enhanced tectonic activity during the Eocene to Oligocene transition. It can be divided to western, central, and eastern Paratethys areas (e.g., Ro ¨gl 1999; Pavelic ´ et al. 2003; Piller et al. 2007;C ´ oric ´ et al. 2009). During its existence (from Eocene to Middle Miocene), the Paratethys Sea was M. Martinus ˇ(&) Á K. Fio Á K. Pikelj Á S ˇ . As ˇc ˇic ´ Department of Geology, Faculty of Science, University of Zagreb, Zagreb, Croatia e-mail: maja.martinus@geol.pmf.hr 123 Facies DOI 10.1007/s10347-012-0327-z