The Smrekovec Tertiary (Slovenia) represented an important marine connection between the Tethys Ocean and the developing Paratethys. The Paleogene sequence rests unconformably on Permotriassic rocks of the Southalpine Kamnik Alps. It starts with Eocene terrigenous sediments and marine carbonates grading into Oligocene shallow marine sediments. After an increasing deepening of the environment, explosive eruptions of the Smrekovec volcano to the N led to the deposition of thick volcaniclastics. The calc-alkaline volcanic rocks and their associated volcaniclastics are of andesitic to (rhyo)dacitic composition. Volcanic activity lasted from Rupelian until Chattian (if not earliest Miocene) times. The present appearance of the Smrekovec Tertiary is interpreted to result from late-Alpine tectonics along the Periadriatic Fault possibly representing a pull-apart or extensional duplex structure within the Permotriassic succession of the Kamnik Alps. It is thus an erosional remnant of a former larger depositional area and did not have the form of the present basin around Smrekovec in Paleogene times.