Oligocene-early Miocene transgressive cover of the Betic-Rif Internal Zone. Revision of its geologic significance

Abstract

The Oligocene–early Miocene sedimentation in the Betic-Rif Internal Zone (BRIZ) occurred during the same time interval as the main tectonic events that are classically considered responsible for the structuring of this zone. Therefore, its paleogeographic and tectonic significance has been the subject of much controversy. The sedimentation developed in two successive groups of formations: the Ciudad Granada group of late Oligocene–Aquitanian in age and the Vinuela group of Burdigalian p.p. in age. The former consists of reddish marls containing clastic intercalations of Malaguide origin, while the Vinuela group is made up of siliceous-intercalated marlstones and lime-poor pelites, with a basal coarse-grained clastic material inherited from both the Malaguide and Alpujarride complexes. An overview of all the outcrops of the BRIZ leads to the conclusion that the two groups are closely related both geographically and tectonically. The paleogeographic, tectonic, stratigraphic and sedimentary relationships suggest that there was no nappe stacking stage between the two groups in the BRIZ. The transition from Ciudad Granada to Vinuela seems to have been the result of a transtensive tectonic event probably related to the westward migration of the BRIZ and to the opening of the Algero-Provencal and Alboran basins. This tectonic disturbance would have caused a severe subsidence in the downfaulted blocks, thus deepening the deposition zones; at the same time, the rapid uplifting of upfaulted blocks would have uncovered Alpujarride units, thus comprising the basement and the source of detritics for the Vinuela group.