New data on the age of the sedimentary infill of the Orava-Nowy Targ Basin : a case study of the Bystry Stream succession (Middle/Upper Miocene, Western Carpathians)

The Neogene sedimentary succession of the Orava-Nowy Targ Basin directly overlies the Central Carpathian Paleogene Basin deposits, the Magura Unit, and the Pieniny Klippen Belt. It provides an excellent geological record that postdates the main Mesoalpine structural and geomorphological processes in the Western Carpathians. Sedimentological, petrographical and geochronological investigations have allowed forthe re-examination of pyroclastic material, zircon dating, and a discussion on the relation of the Orava-Nowy Targ Basin to the exhumation of the Tatra Massif. The Bystry Stream succession is composed of NNW-inclined freshwater siltstones, sandstones and conglomerates. A few small, sometimes discontinuous, light grey intercalations of pyroclastic deposits and a single 1-2 m thick tuffite layer occur in the upper part of the succession. The tuffite contains an admixture of organic matter and siliciclastic grains (e.g., mica), suggesting that the volcanic ash fall was accompanied by normal deposition from weak currents. Sedimentation of deposits of the Bystry Stream succession took place in terrestrial settings, predominantly on floodplains and in rivers, in the vicinity of a hilly area supplying the basin with eroded material. The age of the tuffite layer from the Bystry Stream succession was determined at 11.87 +0.12/-0.24 Ma. The source of volcanogenic material in the tuffite was probably volcanic activity in the Inner Carpathians-Pannonian region, where effusive and volcanoclastic sillca-rich rocks were being produced by extrusive and explosive activity ~12 Ma. Obtained result connects the development of the Orava-Nowy Targ Basin at ~12 Ma with the late stage of the main episode of the Tatra Massif exhumation between ~22-10 Ma.