The Pilis Mountains is located in the NE part of the Transdanubian Range. It is a narrow fault-bounded range of NW–SE strike, 30 km NW of Budapest that consists of Triassic platform carbonates and coeval slope and basin facies. Due to the NW general dip of the succession the oldest formations crop out at the southwestern end of the range. Here the Norian Main Dolomite is overlain by bedded Dachstein Limestone of Middle to Late Norian age. Further NW, along the steep northeastern slope of the range Norian slope and basin facies are exposed (Feketehegy Formation). The slope facies are characterised by redeposited platform-derived carbonates and mollusc coquinas. Above the coquina beds of the Feketehegy Formation near-reef facies was encountered in the north-westernmost Triassic blocks of the Pilis Mountains. Based on investigation of the bio- and lithofacies, palaeographic setting and evolution of a Late Triassic intraplatform basin (Feketehegy Basin) could be outlined.
The NE part of the Transdanubian Range was relatively close to the edge of the passive margin of the Neotethys Ocean. The extensional regime due to the continuing ocean opening led to development of smaller or larger intraplatform basins in the outer platform belt during the Late Triassic. The Feketehegy Basin was one of them, which formed in the Middle to Late Norian. Low-angle slopes developed between the platform and the basin, site of deposition of large amount of platform-derived sediments. Patch reefs and ooid shoals came into being along the margin of the newly formed basin. Bivalves Pseudomyoconcha and Pteria inhabited the platform margin and the upper slope from where large amount of shells redeposited by storm currents and accumulated on the low-angle slope in the form of storm coquinas. Reworked ooids, strongly abraded bioclasts and locally reef-derived bioclasts and lithoclasts of various origins were deposited in the deeper part of the slope, above the storm wave base. Further basinward fine-grained tempestites were deposited below the storm wave base in a restricted, oxygen-depleted basin. The basin evolution came to an end probably in the latest Norian to Rhaetian when the prograding platform reoccupied the former basin.