Microfacies and diagenesis of an upper oxfordian carbonate buildup in Mydlniki (Cracow Area,Southern Poland) |
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Authors: | Dr Jacek Matyszkiewicz Dr Ireneusz Felisiak |
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Institution: | (1) Institute of Metallurgy, Al. Mickiewicza 30, Pl-30-059 Cracow, Poland |
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Abstract: | Summary A carbonate buildup near the top of the Upper Jurassic limestone sequence in the Cracow area with a rigid framework built
ofTubiphytes and thrombolites, and some fragments of encrusted siliceous sponges and serpules is described. The limestones form a dome-like
elevation at the eastern wall of a 15 m high quarry flanked on both sides by stratified limestones with cherts. Six microfacies
have been distinguished within the buildup: (1)Tubiphytes/thrombolite boundstone and (2) bioclasticTubiphytes/thrombolite wackestone dominate in the central and bottom part of the buildup. They gradually replace the cyanobacterial
crusts and siliceous sponges (3. sponge-algal boundstone), which are sporadically the rock-forming elements in the basal part
of the buildup as well as the top. Serpules randomly distributed within the buildup also form small cm-sized structures with
a rigid framework (4. serpula-peloid boundstone). (5) tuberoid-peloid wackestone/floatstone and (6) ooid intraclastic grainstone
exhibit no significant distributional pattern. Bioclastic-peloidal packstone comprising material derived from the destruction
of the buildup occurs in the highest part of the outcrop, overlying the buildup.
The sediments of the buildup were subject to rapid lithification, evidence by borings and neptunian microdykes filled with
internal sediments, as well as by fracturedTubiphytes. Numerous petrographic features indicate probable episodic emergence of the buildup during its growth; these include asymmetric
dissolution textures, asymmetric cements, vadose crystal silt and calcite pseudomorphs after gypsum.
Upper Oxfordian carbonate buildups in the Cracow area display various stages of evolution. The carbonate buildup in Mydlniki
most closely resembles classical Upper Jurassic reefs. |
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Keywords: | Microfacies Carbonate buildup Tubiphytes reef Diagenesis Southern Poland Upper Jurassic |
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