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

Abstract

The structural and subsidence history of the Neo- gene Transylvanian basin is reviewed in order to analyse its relation to the tectonic and erosional history of the sur- rounding Carpathian mountains that has been defined by ap- atite fission track data from previous studies. The main pro- cesses studied are redistribution of mass by erosion, and tec- tonic loading. A mass balance is calculated between ma- terial 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 co- evally 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 tec- tonic and erosional processes. From Badenian to Pannon- ian the combined load of the surrounding mountains and the basin fill lead to a minimum of 2 km of basin subsi- dence. During this period the Transylvanian basin can be regarded as a retro foreland basin of the Carpathian moun- tain 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 sub- sidence history of the basin and field observations on struc- tures and paleostress. The quantitative approach constrains the processes that dominated the formation of the Transyl- vanian basin since the Late Badenian and explain its present day enigmatic relative high altitude of 400 m above sealevel.