Structural evolution of the Transylvanian basin (Romania): A sedimentary basin in the bend zone of the Carpathians

The Transylvanian Basin with its up to l0-km-thick Upper Cretaceous to Pliocene fill is one of the most important sedimentary basins of southeastern Europe. Upper Cretaceous coarse-grained clastics lie unconformably on basement strongly tectonized during Early Cretaceous and older stages. Upper Cretaceous sediments were mainly deposited along roughly N-S-trending grabens and were subsequently folded before the end of the Paleocene. Eocene to Middle Oligocene rocks record mostly quiet sedimentation. N-S tension and extension took place in the Oligocene and was followed by widespread NW-SE compression and contraction. Important thrusts are associated with this phase in the northwestern and southeastern parts of the basin. Widespread N-S contraction followed during the Early Miocene in association with S-vergent thrusting in the northern part of the basin. A southward thinning clastic wedge developed during this stage. The Badenian basal unconformity marked a major change in the sedimentary and tectonic pattern of the Transylvanian Basin with new depocenters developing in the central parts of the present-day basin. Late Miocene E-W extension affected vast areas and caused some important normal faulting in the southeast. The youngest deformation recorded is associated with E-W contraction and is of Pliocene or younger age.