engleski

The composition of acervulinid−red algal macroids from the Paleogene of Croatia and their distribution in the wider Mediterranean region 

Numerous samples of macroids were randomly collected from the area between Omiš and Mimice in Dalmatia (southern Croatia) in order to determine the principal bioconstructors and reveal their distribution patterns. Macroids occur within the Nummulitic rudstones, dominated by the large benthic foraminifera, a common facies of ramp crests, deposited along the coasts of the Tethys Ocean in the Eocene Epoch. Algal bioconstructors occur in form of crusts, branched forms and nodules. We determined the following taxa: Sporolithon lugeonii (Pfender) Ghosh & Maithy, 1996, Sporolithon sp., Lithoporella melobesioides (Foslie) Foslie, 1909, L. minus Johnson, 1964, Mesophyllum mengaudii (Lemoine, 1934), Polystrata alba (Pfender) Denizot, 1968, Acervulina linearis Hanzawa, 1947 and Solenomeris ogormani Douvillé, 1924. Serpulids (Rotularia spirulea (Lamarck, 1818), Rotularia (Praerotularia) marcinowskii Radwanska, 1996), corals, bryozoans, echinoids, crinoids (Isselicrinites sp.) and other biota also occur as bioclasts, but they are less abundant. Macroids are compared with similar bioconstructions from Northern Croatia. Regularly shaped macroids can be classified as rhodoliths, as they are dominated by the genus Sporolithon. Irregularly shaped macroids were formed by intercalation of red algal and encrusting foraminiferal layers. In modern oceans and seas, Acervulina flourishes in the lower parts of the fore-reef zone. The demise of the (first green and then red) algae, and their replacement with encrusting foraminifera during the Paleogene can be correlated with the deepening of the basin and/or increased turbidity, a scenario related with the Alpine tectonics in this area.

Acervulinidae, Florideophyceae, macroids, Paleogene, Croatia

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