Stromatactis cavities and stromatactis-like cavities in the Upper Jurassic carbonate buildups at Mlynka and Zabierzów (Oxfordian, Southern Poland)

Jacek Matyszkiewicz


Kawerny stromatactis i stromatactis sensu lato w górnojurajskich budowlach węglanowych w Młynce i Zabierzowie (oksford, południowa Polska)

Stromatactis cavities (SCs) and stromatactis-like cavities (SICs) occur in Upper Jurassic carbonate buildups of southern Poland. The carbonate buildups vary in the development of their rigid framework. Internal erosion, resulting from various agents, is the process leading to the formation of the SCs and SICs.

In carbonate buildups of the cyanobacterial-sponge mud-mound type with weakly developed rigid framework, formation of the SCs occurred in the subtidal zone, on the slope of a buildup, and was caused by partial winnowing of unlithified sediment. This winnowing took place during early diagenesis and rapid tectonic uplifting movements, when water within large pore spaces and growth cavities was strongly turbulent due to submarine mass flows which resulted in the formation of a network of cavities.

In reef-like carbonate buildups of the Tubiphytes-reef type with well developed rigid framework the internal erosion was caused by cavitation linked to intensive wave action in the intertidal zone. The rigid framework, where it was well developed, prevented the formation of networked cavities permitting the development of a single SICs only. Such process of stromatactis formation occurred with a break after the growth of the Tubiphytes-Reef.

Precipitation of sparry calcite cement took place at various stages of the diagenesis. In the SCs formed in the subtidal zone, on the slope of a cyanobacterial-sponge mud mound, the formation of the cements began under marine phreatic conditions and continued during late diagenesis in various environments. In the SICs originated in the intertidal zone in Tubiphytes-reef the early diagenetic cementation usually did not take place because the stromatactis were subaerially exposed soon after their formation. Some of them were slightly restructured and got filled with cement as a result of hydrothermal processes in Tertiary time.

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