Coral lumps in Early Kimmeridgian oyster shellbeds and oolites of Małogoszcz

Andrzej RADWAŃSKI, Ewa RONIEWICZ

Abstract


Scleractinian corals occurring scarcely in the Lower Kimmeridgian Actinostreon(=Lopha, =Alectryonia) shellbeds at Malogoszcz in the Holy Cross Mountains, Central Poland, are represented by abraded colonies densely riddled by rock-boring bivalves (Lithophaga inclusa Phillips, Gastrochaena sp.) and polychaetes (Potamilla sp.). The taxonomically recognised specimens include Complexastrea burgundiae (de Blainville, 1830), Dimorphocoenia sp., Ovalastrea caryophylloides (Goldfuss, 1826), and Thamnasteria graeilis (Miinster, 1826). AlI colonies are preserved in the form of hollows, the wall s of which bear moulds of coral calyces, and of bivalve and polychaete borings. Taking into account the structural features of shellbeds and their faunistic content (uprooted crinoids Apiocrinites, dug-out deeply-infaunal bivalves), stormy agitation is postulated as a basic agent responsible for damaging Actinostreon communities, and their associates. The studied corals are thought to have lived asidethe Actinostreon gardens, up on a muddy bottom, from where they have been stirred-up during the storm cataclysm, having been then abraded and riddled by rock-borers repeatedly until laid down in a shellbed and transferred in to the fossil record. The extremely shallow-water conditions, under which the ostreid Actinostreon has lived, suggest the typically opportunistic nature or the associated corals, the same as of Ovalastrea caryophylloides (Goldfuss, 1826) from oolitic shoals, and the only colony of which completes the coral assemblage of Malogoszcz. The opportunism or ali these corals differs them from the habit of hermatypie forms from coeval and Oxfordian patch-reef communities of the Holy Cross Mountains (cf. Roniewicz & Roniewicz 1968, 1971).


Keywords


Scleractinian corals; oyster shellbeds; eco-taphonomy; Environment; Kimmeridgian; Małogoszcz; Poland

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