The Neogene history of the Transylvanian basin in relation to its surrounding mountains

The structural and subsidence history of the Neogene Transylvanian basin is reviewed in order to analyse its relation to the tectonic and erosional history of the surrounding Carpathian mountains that has been defined by apatite fission track data from previous studies. The main processes studied are redistribution of mass by erosion, and tectonic loading. A mass balance is calculated between material eroded from the mountains and material deposited in the sedimentary basin. The mass balance fits to within 20% and confirms the restricted nature of the Transylvanian basin from Late Badenian to Pannonian, and directly links the mass transfer from the tectonically active mountains to the coevally subsiding basin. From Pliocene to recent both the basin and the now tectonically inactive mountains have been eroding leading to a change in the mass redistribution and isostatic uplift of the basin. Numerical flexural-isostatic 3-D modelling is used to study the effect of loading and subsequent unloading of the lithosphere as a consequence of the mass transfers by tectonic and erosional processes. From Badenian to Pannonian the combined load of the surrounding mountains and the basin fill lead to a minimum of 2 km of basin subsidence. During this period the Transylvanian basin can be regarded as a retro foreland basin of the Carpathian mountain belt. From Pliocene to recent the erosianal abrasion of both the mountains and the basin lead to a isostatic uplift of the basin surface between 300 and 500 m. The modelling results fit well with apatite fission track constraints, the subsidence history of the basin and field observations on structures and paleostress. The quantitative approach constrains the processes that dominated the formation of the Transylvanian basin since the Late Badenian and explain its present day enigmatic relative high altitude of 400 m above sealevel. Correspondence to: C. Sanders ([email protected])