Late Miocene Extensional Tectonics in the Evolution of the Eastern Betics, an Example from the Neogene- Quaternary Sorbas Basin (SE Spain)

Flavio Giaconia, Guillermo Booth-Rea, José Miguel Martínez-Martínez, and José Miguel Azañón

In the eastern Betics, Neogene to Quaternary basins occur in synclines among near E/W-elongated antiformal ridges that are related to or cut by large-scale strike-slip faults. Both folds and strike-slip faults developed because the NW-SE Africa-Iberia convergence. Most literature related this strike-slip regime with the origin and evolution of the Neogene-Quaternary eastern Betics basins. However, recent work showed the great importance of extensional tectonics in the development and evolution of these basins during the middle to late Miocene.

In order to define the role of Miocene extensional tectonics in the origin and evolution of Neogene – Quaternary basins, we have carefully mapped the western termination of Sierra Cabrera in the southeastern Betics, analyzing the age and linking relationships between brittle fault segments, and finally we constructed a balanced cross section. We identified a NW-SE listric normal fault system that was active during the Tortonian producing southwestward hangingwall displacement. Normal faults show hard linkage relationships with E-W to N70E vertical strike-slip and oblique-slip extensional transfer faults that show both dextral and sinistral kinematics. The balanced cross section shows that the fault system controlled the thickness of the Tortonian sediments deposited between 11 and 8 Ma, which change thickness across the main faults from approximately 50 m thick in the footwall of the system to up to 1 km in the main depocentre. Furthermore, the fault system controlled the sedimentary facies shifting from continental and deltaic conglomerates in the footwall to silts and basin marls in the main depocentre. Two main extensional episodes can be distinguished that result in two main angular unconformities between early Tortonian continental conglomerates and the Tortonian marine Chozas formation (approx. 10 Ma) and between the Chozas and Turre formations at approx. 8 Ma.

Many strike-slip faults interpreted as transcurrent in origin in the eastern Betics represent extensional transfer faults or folded extensional detachments produced during the middle to late Miocene extensional regime. Extension represented the main control process in the origin and evolution of eastern Betics Neogene Quaternary basins that were later inverted by the current NW-SE convergence between Africa and Europe.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013