Deciphering of the complex depositional and diagenetic history of a scarp limestone breccia (Middle Jurassic Krasin Breccia, Pieniny Klippen Belt, Western Carpathians)

The Pieniny Klippen Belt (boundary between the Central and Outer Western Carpathians) is a tectonic melange of various Mesozoic sedimentary units. In the shallowest unit, a Czorsztyn Succession, syntectonic Middle Jurassic (Bajocian) sedimentary breccia to megabreccia was discovered. It resulted from extensional tectonic movements tied to Jurassic Neotethys rifting. The breccia was investigated by standard petrographic methods, cathodoluminescence, microfacies analysis and isotope analysis (C, O). It represents the whole spectrum from crackled breccia, through mosaic breccia to mixed rubble breccia. All of them consist mostly of crinoidal limestone clasts. The crackled breccias are penetrated by a network of radiaxial fibrous calcite; the mosaic breccias have interstitial pores mostly filled with a younger generation of crinoidal limestone. The rubble breccia usually possesses the most complex filling. As a rule, the clasts are coated by at least one generation of stromatolite and then cemented by radiaxial fibrous calcite. The stromatolites may appear at various levels of the breccia diagenesis (most of them are cryptic stromatolites). The remaining void filling starts with the crinoidal detritus which indicates that the breccia was formed due to synsedimentary tectonics occurring during the deposition of crinoidal limestones (Bajocian). The rest was filled by micritic limestone with “filamentous” microfacies (Bathonian–Callovian), which also contained local planktonic foraminifers, Globuligerina sp. The latest sedimentary filling is represented by sterile micrite containing a few allochems and fauna of cavity-dwelling ostracods Pokornyopsis sp. The latest cement is represented by clear blocky calcite filling veinlets cutting the whole rock. Numerous instances of disturbance, resedimentation and recementation are evident in the breccia. The isotope composition of some early generations of stromatolites, local etching of the clasts and early cements, together with some earlier generations of blocky-calcite veinlets, possibly indicate a presence of fresh-water diagenesis.