Middle Pleistocene to Holocene fluvial terrace development and uplift-driven valley incision in the SE Carpathians, Romania

Abstract

Abstract This study reveals that in the SE Carpathians terrace development and fluvial incision during the Middle Pleistocene–Holocene are predominantly controlled by tectonic uplift as shown by terrace distributions and uplift amounts and rates. The work focuses on a transect from the internal nappes and Brasov intramontane basin (western domain) to the external nappes and Focsani foredeep basin (eastern domain). New infrared stimulated luminescence ages were obtained and minimum terrace formation ages were determined to derive fluvial incision rates, and thereby, to constrain tectonic uplift. In the eastern domain, non-uniform terrace distributions in adjacent sub-parallel more active Punta and less active Susiţa rivers and an eastward migrated fluvial incision from the orogen to the foredeep basin indicate tectonic uplift as dominant control on terrace development. Strath-terraces in the western and eastern domains indicate repeated events of vertical fluvial incision and lateral erosion during the early Middle Pleistocene and late Middle Pleistocene–Holocene, respectively. These events imply successive recurrent disturbances of equilibrium conditions due to pulses of increased tectonic uplift. Fill-terraces in the western domain show that initial aggradation periods were followed by uplift-driven vertical incision during the late Middle–Late Pleistocene. As fill-terraces show a wide-spread development, climatic change and complex response cannot be excluded as contributing factors. Synchronous to terrace development, loess deposition periods during the late Middle–Late Pleistocene and Latest Pleistocene and intercalated episodes of palaeosol formation during the Late Pleistocene imply comparable climatic conditions across the SE Carpathians. Dominant strath-terraces of the eastern domain indicate stronger fluvial incision (~ 240 m) since the late Middle Pleistocene, whereas older strath- and younger dominant fill-terraces of the western domain designate a lower amount (~ 90 m) since the early Middle Pleistocene. Middle Pleistocene–Holocene fluvial incision rates document higher tectonic uplift in the external nappes and lower towards the western intramontane and eastern foredeep basins.