Stromatolity w wapieniu cechsztyńskim monokliny przedsudeckiej

Abstract

Porównano typy struktur stromatolitoych i środowisk ich powstania w wapieniu cechsztyńskim obszaru przedsudeckiego z formami i środowiskami współczesnymi, stwierdzając ścisłe podobieństwo sekwencji typów. Opisano laminowane pokrywy węglanowe typu Archeolithoporella będące walnym składnikiem osadów strefy barierowej. W strelie płycizny wolsztyńskiej oraz w peryferycznej części zbiornika stwierdzono stromatolity abiogeniczne (koniatolity i kalkrety). Wyniki badań wskazują. że mimo różnego pochodzenia każdy wyróżniony typ stromatolitu jest ważnym wskaźnikiem środowiskowym ze względu na określoną strefę powstania.

STROMATOLITES IN THE ZECHSTEIN LIMESTONE OF THE FORE-SUDETIC MONOCLINE (WESTERN POLAND)

Stromatolites occurring in the upper part of the Zechstein Limestone (Upper Permian) of the Fore-Sudetic monocline (western Poland) have different origin, each distinguished stromatolite type being an important environmental indicator because of the specific zone of its formation. The unstable primary mineralogy of the biogenic (cyanobacterial) stromatolites which have been composed of high-Mg calcite (subtidal stromatolites) and of aragonite (peritidal stromatolites), combined with the quite intensive (often synsedimentary) diagenesis have resulted in obliteration and destruction of primary microstructures, yet it is possible to distinguish several types of cynobacterial stromatolites that may be com-pared to those characteristic of recent tidal environments of the Persian Gulf and the Shark Bay. It may indicate that blue-green communities have been changing parallel to the changes in sedimentary environments. Many biogenic stromatolites derive from the intertidal and supratidal zones (Tabl. II, Fig. 4; Tabl. III, Figs 5 - 7) but the existence of subtidal stromatolites is unquestionable too (Tabl. I, Figs 1 - 3). The depth of water in which subtidal stromatolites formed cannot be precisely determined, but taking into account the general paleogeographical premisses it seems that the depth did not exceed 30 m and most probably was about 10 m.

Within barrier zone of the Zechstein Limestone in the Fore-Sudetic monocline Archaeolithoporella stromatolites (Tabl. IV, Fig. 8; Tabl. V, Figs 9, 10; Tabl. VI, Fig. 11) occur. The occurring deposits testify to the origin of Archaeolithoporella in a subtidal environment. Because of the unstable - aragonitic - composition and intensive diagenesis, characteristic of the upper Zechstein Limestone, the details of Archaeolithoporella structure have been obliterated.

In the upper Zechstein Limestone in the Wolsztyn shoal of the central part of the basin and in the entire peripheral part (mainly in the barrier zone) abiogenic stromatolites - coniatolites (Tabl. VI, Fig. 12) and calcrete - occur.

Biogenic and abiogenic strornatolites occur in the top parts of the regressive cycles of the Zechstein Limestone deposition and their formation could be simultaneous and therefore the correlation of sequences that originated in different paleogeographical zones of the Zechstein Limestone basin is possible if also other additional data are taken into consideration.