On the structure and evolution of the Sorbas basin, S.E. Spain

Geological mapping and gravity surveying were used to constrain the shape of the Serravallian and Tortonian (U. Miocene) rocks of the Sorbas basin, SE Spain, and hence its tectonic evolution and place in the overall regional tectonic scheme. The present-day basin floor forms a westerly-deepening trough ~2.0 km deep, infilled with mainly clastic turbidites and mass-flow deposits. Basin-fill rocks underwent broadly ENE-WSW extension during accumulation, with extensional faulting on the flank of the Sierra Cabrera to the east. Acoustic velocity measurements demonstrate a petrophysical impact of the syndepositional deformation. Post-deposition but prior to uplift and erosion, the sediments were folded into a large-scale monoclinal structure, inferred to have formed in response to gravitational sliding of sediments off the rising western flank of the Sierra Cabrera. This fold structure was deformed and rotated by 3 km of extension-related uplift of the basement block to the south during late Tortonian time, then erosion and flooding to produce a shallow-marine Messinian sequence, partially burying the older rocks. The geodynamic setting was the back-arc sector (the Betic zone) produced by Serravallian-Tortonian rollback of the Gibraltar arc subduction zone. It is bounded to the south by the Carboneras stretching transform fault, that accumulated about 40 km of left-lateral offset coevally with sediment deposition and deformation within the Sorbas basin. These events are inferred to be geodynamically linked.