Stomatolity a organizmy penetrujące w osadzie na przykładzie utworów jurajskich Wyżyny Krakowsko-Wieluńskiej

Abstract

W artykule przedstawiono analizę relacji zachodzących między stromatolitami a organizmami penetrującymi w osadzie, zarówno współcześnie, jak i w środowiskach kopalnych. Szczegółowiej rozpatrzono to zagadnienie na przykładzie utworów jurajskich Wyżyny Krakowsko-Wieluńskiej. Uzasadniono znaczenie działalności organizmów penetrujących w osadzie dla ograniczenia występowania fanerozoicznych stromatolitów do środowisk pływowych oraz niektórych struktur rafowych i powierzchni twardych den.

STROMATOLITES VERSUS BURROWING ORGANISMS AT THE EXAMPLE OF JURASSIC DEPOSITS OF CRACOW–WIELUŃ UPLAND

The studies on modern sediments and analysis of data concerning the ancient ones suggest that not trying to belittle the role of activity of algophages, competition of green- and red-algae and changes in chemistry of hydrosphere the burrowing organisms may be treated as important agents delimiting distribution of stromatolites to tidal zones, some reef structures and hardground surfaces in the past as well as in the present.

Jurassic deposits or the Cracow-Wieluń Upland supply valuable information on the relations between stromatolites and burrowing organisms. Stromatolites are here present in stratigraphically condensed Callovian–Oxfordian passage beds (areas of Krzeszowice and Zalas and between Zawiercie and Wieluń), usually above sandy crinoidal limestones with numerous systems of Thalassinoides channels. Interstices and “pockets” in stromatolite layers are infilled with red limestones (biomicrites) which also laterally replace the stromatolites or overlay them (Krzeszowice and Zalas area). The limestones also display very numerous bioturbations and Chondrites traces.

In the area between Olkusz and Zawiercie, Upper Callovian deposits with stromatolites are replaced by marly deposits a few meters thick and without any traces of stratigraphic condensation.

Traces of Zoophycos and Chondrites are fairly common there also.

In the Cracow-Wieluń Upland, stromatolites were originating in subaqueous shoals, under sublittoral conditions (evidenced by the presence of nektonic and planktonic fossils and the lack of any traces typical of both tidal environment and emergence in under- and overlying deposits) and their development was facilitated by low rate of sedimentation, the presence of hardground and the lack

of burrowing effectively burrowing organisms.

Stromatolites are sporadically present in sublittoral marly deposits of the Lower Oxfordian, where they form domes on sponges and ammonite shells. They also represent an important rock-forming component of bioherm massive (Felsenkalk) limestones of the Middle and Upper Oxfordian, which may be termed as stromatolitic-spongy ones. The limestones laterally pass into the platy ones, which do not yield stromatolites but display numerous structures formed by burrowing organisms.