Biohermy gąbkowe warstw jasnogórskich (oksford Jury Polskiej)

Abstract

SPONGE BIOHERMS IN THE JASNA GÓRA BEDS (OXFORDIAN OF THE POLISH JURA CHAIN) Summary In the area of the Polish Jura Chain (Fig. 1 ), the Jasna Góra Beds and their time equivalents known as Grójec Marls represent the oldest members of the Oxfordian (Fig. 2). The former unit is represented by alternating limestones and marls, originating on platforms, and the latter - by marls originating in a basin. Sediments of the two units were formed below the photic sone and waving base. The Jasna Góra Beds display a few sponge bioherms, situated (Fig. 3) at either rised parts of the platform (Jasna Góra and Wrzosowa localities) or margin of the platform, close to its basin facing slope (Wysoka and Zalas localities). Benthic fauna of the bioherm from Zalas (Figs. 4 and 5), here discussed as an example, is almost completely dominated by sponges of the order Lithistida (Fig. 6). Sponges occurring in that bioherm are surrounded by marły mass (Fig. 4). In the bioherm from Zalas, a rigid framework (resulting from overgrowing of one sponge by another) did not originate as the majority of sponges presumably lived with lower part of body buried in sediment.