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Record: oai:ARNO:505667

AuthorP.H.W. Mey
TitleGeology of the Upper Ribagorzana and Tor valleys, Central Pyrenees, Spain Sheet 8, 1 : 50,000
JournalLeidse Geologische Mededelingen
AbstractThe geology of the region of map sheet 8, Ribagorzana-Tor, of the 1 : 50,000 geological maps of the Central Pyrenees, is described. The map covers part of the southern axial zone, the Nogueras zone, and the northern part of the Southern Cretaceous zone. The stratigraphie sequence consists of marine Palaeozoic rocks from the Cambro-Ordovician to the Carboniferous, unconformably overlain by mainly fluvial deposits ranging in age from the Upper Westphalian to the Lower Triassic. The Middle and Upper Triassic is represented by a lagunal evaporite sequence. The fully marine Mesozoic rocks, mainly limestones and marls, range in age from Liassic to Upper Cretaceous. The entire sequence is again unconformably overlain by fluvial piedmont deposits of the Upper Eocene-Oligocene.
Hercynian and Alpine orogenies acted on this intercontinental mountain chain. In the axial zone at least five individual deformation phases with different trending axes can be attributed to the Hercynian stress field. The second, or major, folding phase produced a generally northward-dipping axial-plane slaty cleavage. Granodiorite batholiths and numerous dykes intruded almost at the end of this compressional phase.
The major Alpine deformation shortened the axial zone by means of north to south up- and overthrusts along the Hercynian cleavage or fault planes, which at the same time caused asymmetric folding of the post-Hercynian strata above the unconformity. The Nogueras zone is interpreted as a steep flexure zone that collapsed due to the vulnerability of the easily deformed Keuper series filling the space between this flexure and the rigid mass of the overlying Mesozoic calcareous rocks; the latter is thought to have moved towards the south mainly under the influence of the gravitational pull.
The post-Miocene erosion following the Alpine uplift led to various aplanation levels, some remnants of which are preserved in our area. Glacial forms developed during the Pleistocene, and subsequent river erosion modified the glacial morphology.
Document typearticle
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