The Composition of Acervulinid – Red Algal Macroids from the Paleogene of Croatia and Their Distribution in the Wider Mediterranean Region

This research is a continuation of the previous biometrical study of the Eocene macroids in Dalmatia (southern Croatia), with the aim to determine the principal bioconstructors and reveal the composition and distribution patterns of macroids during the Paleogene Period. We randomly collected 322 samples of extracted macroids and 12 samples of host rocks, from the beaches between Omiš and Mimice in Dalmatia. Thin sections were prepared at the University of Zagreb/Faculty of Science, studied and photographed using a light microscope with camera. Macroids occur within the Eocene “Nummulitic” packstones, floatstones to rudstones, dominated by the large benthic foraminifera, a common facies of ramp crests, deposited along the coasts of the Tethys Ocean. Algal-dominant genera are Sporolithon and Lithoporella. Among the encrusting foraminifera, Acervulina and Solenomeris prevail. Serpulids, corals, bryozoans, echinoids, crinoids, and other biota also occur as bioclasts, but they are less abundant. Regularly shaped macroids can be classified as rhodoliths, as they are dominated by the genus Sporolithon. Irregularly shaped macroids were formed by the intercalation of red algal and encrusting foraminiferal layers, pointing to the slightly deeper depositional environment. The subsequent demise of green and then red algae, and their replacement with encrusting foraminifera during the Paleogene can be correlated with the basin subsidence and/or increased turbidity, a scenario related to the Alpine tectonics in this area.