Benkovac Stone (Eocene, Croatia): a deep-sea Plattenkalk?
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In contrast to Solnhofen-type conservation Lagerstätten, the platy limestones of the Benkovac Stone of the Eocene of Croatia contains a variety of trace fossils. They belong to the Nereites ichnofacies, characterized by a suite of highly specialized ichnogenera, turbiditic preservation, and distinctive pre-event versus post-event communities. In siliciclastic rocks, this ichnofacies stands for turbiditic deep-sea sediments. Also unusual is the lack of body fossils. The only exceptions are occasional plant debris and Bencovacina concentrica. n. gen., n. sp., which is affiliated with xenophyophorian Foraminifera. These giant protozoans survive on present deep-sea bottoms, but they were also common on the shallow-marine biomats in Ediacaran times. These findings contradict the current shallow-marine interpretation, which is based on the regional geologic setting and sedimentary structures typical for tempestites. Thus, the Benkovac Stone would be an ideal place to test the reliability of ichnological versus sedimentological depth criteria in an entirely calcareous sequence.
KeywordsLithographic limestone Trace fossils Benkovacina n. gen. Xenophyophorian Foraminifera Ichnofacies Palaeobathymetry
The senior author thanks the organizers of the 5th International Symposium on Lithographic Limestone and Plattenkalk for the invitation to present a keynote lecture and for their insistence to write it down. In doing this, he profited from the results of the “Fossil-Lagerstätten” group in the former Sonderforschungsbereich 53 at Tübingen University (Germany), funded by the Deutsche Forschungsgemeinschaft. The Benkovac Stone was brought to his attention by Croatian colleagues, including the junior author, Josip Halamic and Vili Pencinger. They also hosted the traveling exhibit “Fossil Art”, for which Hans Luginsland made a large cast at Benkovac. Miranda Paton and Edith Seilacher-Drexler helped with word processing and Wolfgang Gerber with photography. G. Schweigert and an anonymous reviewer added considerably to the improvement of the original manuscript.
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