ABSTRACT: New sedimentological observations in the Lower Cretaceous of the Silesian Unit and integrated biostratigraphy based on calcareous nannofossils, dinoflagellate cysts, calpionellids and foraminifers have brought new insight to the stratigraphy of the Cieszyn section. The oldest exposed strata of themudstone facies of the Cieszyn Limestone Formation are of early Berriasian age, based on calcareous nannofossil evidence. This work proposes that the Jurassic–Cretaceous boundary reported by previous authors was based on reworked microfossils. The detritic facies of the Cieszyn Limestone Formation, typically dominated by detritic-limestone turbidites, appears to be completely missing. Instead, a thick body with combined slump and slide features, of Berriasian–Valanginian age, forms the transition with the overlying lower Valanginian strata of the Hradiste Formation. The slump/slide body represents a local facies, deposited on a fault scarp related to fault-controlled extension of the Proto-Silesian Basin floor.