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Transitional Beds (Eocene, Croatia and Slovenia): New lights on an old Problem

Transitionl Beds marked the end of one of the largest Mesozoic carbonate platform depositional sequences of the Perimediterranean region. Several sections (Gračišče, Osp, Slavec, Buzet, Šterna, Ragancini, Sveti Tom, Florinčići and Pićan) were studied in detail to document vertical and lateral lithological and paleontological variation along the platform to basin transition. We focused our research on the so-called Orthophragmina-bearing parts of the Foraminiferal limestones and overlying Marls. We considered the beginning of the Transitional Beds to correspond with sediments deposited in a paleoenvironment where orthophragminids "lived at their limit". The microfacies types are wackestones with flattened orthophragminids and diverse associations of planktonic foraminifera (surface muricate and non-muricate to deeper dwelling genera and species). Thus, the Transitional Beds partly belong to the unit known as the Foraminiferal limestones. They were deposited under a very low energy depositional conditions, probably in outer ramp. They range in age from Late Cuisisna (SBZ 12, Slavec) to Middle (SBZ 13 - SBZ 14, Gračišče, Osp, Pićan, Sveti Tom, Buzet, Florinčići) to Late Lutetian (SBZ 15, Ragancini and Šterna). The pecularity of the deposits along with their diachronic commencement includes an increase of diversity of orthophragminids within the lowe limit of the photic zone. A variety of macrofossil remains, such as crabs, shark teeth, nautilids, ahermatypic corals, serpulids, echinoids fragments and glauconite grains.

Trasitional Beds; Eocene; Croatia; Slovenia

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