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The Transylvania Basin (Romania) and Its Relation to the Carpathians Fold and Thrust Belt: Insights in Gravitational Salt Tectonics

Csaba Krezsek1 and Albert W. Bally2
1 Dalhousie University, Halifax, NS
2 Rice University, Houston, TX

The Transylvania Basin represents a post-Cenomanian episutural sedimentary basin developed on top of the „backstop” of the Carpathians foreland folded belt. The basin evolution was coeval with the post Mid-Cretaceous to Present deformation of the Carpathians.

Regionally important evaporite deposition occurred (~ 300 m) in the Middle Miocene. The evaporites are covered by 2-5 km thick Middle to Upper Miocene mainly deep-marine deposits.

The Mid-Miocene collision in the Eastern Carpathians is associated with the rising Carpathians. Intense Late Miocene to Pliocene magmatic activity accompanied the Carpathian deformations and led to the formation of a volcanic arc behind the Carpathian accretionary wedge.

The Carpathians uplift enhanced the differential load on salt deposits which together with the high-heat flow induced by backarc volcanism triggered large-scale Mio-Pliocene gravitational gliding of the salt overburden. The Late Neogene to Recent Carpathians uplift, backarc volcanism and gravitational gliding are largely coeval.

The gravitational gliding triggered extensive salt-weld formation in the eastern part of the basin (extensional salt domain). The reduced salt was expulsed toward the west and squeezed to the surface westwards of volcanic edifices, creating salt walls. The salt-cored fold lineaments of the central Transylvania Basin represent compressional structures related to the gravitational gliding. The thrusting and related salt extrusion in the western part of the basin represents the toe of basin-scale gravitational slide as abuts against the subsurface flank of the Apuseni Mts.

The Transylvania Basin salt-structures significantly differ from the Carpathians salt-structures and superficially resemble the gravity driven structures on passive margins.