Charakterystyka jurajskich mszywiołów południowej Polski w aspekcie warunków paleośrodowiska i biogeografii

Abstract

Characteristics of Jurassic bryozoans from southern Poland in palaeoecological and biogeographical aspects.S u m m a r y. A few distinctive bryozoan assemblages have been recognized in the Middle and Upper Jurassic sediments of southern Poland. The biota moderately rich in bryozoan taxa are generally restricted to a few cyclostome genera and dominated respectively by tubuloporines among which the majority form a fan-shaped or discoidal (bereniciform), encrusting colonies previously called “Berenieca”, a bryozoan ubiquitous in the Jurassic. The Lower and Upper Callovian epifaunal bryozoan community of the vicinity of Cracow at Zalas in the Cracow Upland is represented by well-known Jurassic Stomatopora Bronn, Hyporosopora Canu & Bassler and Microeciella Taylor & Sequeiros, genera, as well as the other undeterminated, numerous bereniciform colonies. In terms of the species richness the most diversified is the Early Oxfordian bryozoan assemblage of the Ćmielów area (NW margin of the Holy Cross Mts), associated with an open shelf biohermal sedimentation, which was replaced later (during the transversarium and bifurcatues zones) by the shallow water, soft-bottom coral buildups, among which the bryozoans are well-represented and described from Bałtów. The presence of the ?Late Tithonian–Berriasian bryozoan fauna has been documented in the thin-sections of the Stramberk limestones of the Polish Flysch Carpathians. Palaeoecological aspects of the studied bryozoan biotas are related to the nature and relative abundance of the colonial growth forms, the substrate type and other ecological factors. The moderately rich occurrence of the bryozoans in the Late Middle and Upper Jurassic sequences of Poland shows a different pattern of distribution than the biotas of the northwestern Europe which display the greatest species diversity in the Middle Jurassic (Bathonian). The taxonomical and biogeographical studies of the Jurassic bryozoan biotas of Poland, in spite of the great patchiness in the global distribution of the Jurassic cyclostomes, has a key significance for the evolutionary radiation pattern and may add new data, whether this fauna originated and started to radiate in the Late Middle or the Upper Jurassic, or this event was mostly connected with the facies migration from west to east.