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Lower Albian microfossil assemblages with Charophyta and Dasycladales as indicator of brackish environment on the of Adriatic-Dinaridic carbonate platform (Mt. Velika Kapela, Karst Dinarides)

Mt. Velika Kapela represents a part of the ancient Adriatic-Dinaric carbonate platform (ADCP), one of the largest Mesozoic carbonate platforms of the Perimediterranean region (ancient Tethys area). The ADCP deposits comprise 3500 to 5000 m thick carbonate succession of the Karst (External) Dinarides with a stratigraphic range from the Late Triassic to the Eocene. This study focuses on the Lower Cretaceous deposits that in the investigated area, as well as in the great majority of other regions in Karst Dinarides, are characterized by a relatively uniform succession of shallow water limestones with dominance of two groups of microorganisms: benthic foraminifera and calcareous algae. At the selected localities of Mt. Velika Kapela five microfossil assemblages (I-V), ranging from the Early Barremian to the Albian, have been distinguished. However, the Early Albian microfossil assemblage V is unusual. It differs from the earlier ones, concerning fossil content and environmental origin. Lower levels of the microfossil assemblage V are represented by common occurrence of Orbitolina (Mesorbitolina) texana. In the upper levels, the microfossil assemblage V is characterized by high diversity, but lacking O. (M) texana. Instead, numerous other foraminifea: Cuneolina pavonia, C. parva, C. sliteri, Sabaudia minuta, S. auruncensis, Vercorsella laurentii, V. scarsellai, V. cf. immaturata, Pseudonummoloculina aurigerica, Rumanoloculina cf. minima, Istriloculina cf. granumtrici and other forms occur there. These microfossil assemblages are present in shallow subtidal, and, to lesser extent, intertidal environments of the inner ADCP area. Increasing fresh water influence is indicated in the upper levels of microfossil assemblage V by abundant occurrence of charophytes, identified as Munieria cf. grambasti sarda. The strata with charophytes also contain dasyclad alga Salpingoporella cf. dinarica, which differs from "true" S. dinarica by a modified structure of the calcareous envelope also reflecting a change in environmental conditions. The new morphological study of the Cretaceous type species of Munieria (M. baconica) combined with a critical analysis of charophyte thalli, with the aim of clearing up the systematic attribution of the genus Munieria, either to the Dasycladales or to the Charophyta, shows that thalli of Munieria are organized as in the Dasycladales. The presence of S. cf. dinarica and Munieria cf. grambasti sarda in microfossil assemblage of the investigated Lower Albian strata confirms that fossil dasyclads can inhabit brackish environments.

Lower Cretaceous; microfossil assemblages; Charophyta; Dasycladales; Adriatic-Dinaridic carbonate platform

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