The Thiviers-Payzac Unit is a metasedimentary succession of late Neoproterozoic and Cambrian age outcropping in the southern Limousin in France. The unit geologically forms part of the Variscan basement of the northwestern Massif Central. Terminology The Thiviers-Payzac Unit, sometimes still called Thiviers-Payzac Nappe or Bas-Limousin Group, was named after Thiviers and Payzac, two small towns in the northeastern Dordogne situated within the unit's outcrop area. The term nappe is somewhat misleading. Geography Geographically the Thiviers-Payzac Unit belongs to the Bas-Limousin (southern Limousin), a plateau peneplained during the Eocene and whose elevation barely reaches above 400 metres. The unit starts just west of Thiviers in the northern Dordogne and then follows for 70 kilometres a semicircular arc segment, passing through Lanouaille, Payzac, Orgnac, Donzenac and finishing just east of Brive in the Corrèze. In the beginning the unit follows a WNW-ESE strike (N110), but then just north of Orgnac swings into a NW-SE course (N 135). On its north side the unit is separated by the Estivaux Fault, a left-lateral, ductile strike-slip fault, from rocks of the Upper Gneiss Unit. On its western end appear rocks of the Lower Gneiss Unit. In the southwest the unit is overlain by liassic sediments of the Aquitaine Basin. The South Limousin Fault, also a ductile strike-slip fault but with a right-lateral shear, separates the unit from the Génis Unit in the south. The unit finally disappears in the southeast below some small occurrences of Pennsylvanian sediments, yet the bulk of the unit is covered mainly by Permotriassic red beds of the Brive Basin. Following the Auvézère the maximum width of the unit across strike is only 9 kilometers. Just northwest of Terrasson in the eastern Dordogne there is an upfaulted basement high, that is also included within the main unit. This outlier is about 10 kilometers long and also follows the ESE-direction; its width across strike is only 5 kilometers. Stratigraphy The stratigraphy of the Thiviers-Payzac Unit shows the following succession (from top to bottom): Puy-des-Âges quartzite Engastine mafics Donzenac schist Thiviers sandstone The unit hosts the Mississippian Estivaux granite and two Ordovician granitoids, the Saut-du-Saumon orthogneiss and the Corgnac granite. Puy-des-Âges quartzite The Puy-des-Âges quartzite on top is a very resistant, white, sericite-bearing quartzite and consequently forms erosion-resistant reliefs within the plateau of the Bas-Limousin. The formation crops out in a merely 200 meter wide band in the western and central part of