The origin and development of neogene basins in the SE Betic Cordillera (SE Spain): A case study of the Tabernas-Sorbas and Huercal Overa basins

Neogene- Quaternary sedimentary basins in SE Spain contain a record of the geodynamic evolution of the Internal zone of the Betic Cordillera. The base ment of the Internal Zone is composed of Palaeozoic and Mesozoic metasedime nts which have undergone variable degrees of metamorphism. The External zon es consist of largely unmetamorphosed sedimentary rocks which were deposite d on the SE margin of the Iberian Plate during the Mesozoic and Early Cenoz oic. Westward tectonic emplacement of these terranes onto the Iberian Plate took place between the end of the Palaeogene and the middle Miocene. In th is paper, we investigate the late Miocene (Tortonian-Messinian) stratigraph y of two basins in the Internal Zone - the Tabernas-Sorbas and Huercal Over a Basins. We also consider some recently-acquired structural data. The Tabernas-Sorbas and Huercal Overa Basins are east-west trending depress ions bounded to north and south by sierras in which basement rocks are expo sed. The basins contain very similar sedimentary successions in which plank tonic foraminifera have been preserved. However, the faunal composition is very variable, and the observed sporadic and abrupt changes in foraminifera l populations imply palaeo-ecologic and palaeo-oceanographic instabilities which may be associated with local tectonism. Stratigraphic markers were af fected by these changes, making precise dating difficult near the Tortonian -Messinian boundary. Our data indicate that Messinian rocks are more widely distributed than has hitherto been suspected. A Messinian age for the prominent coral limestone s in the Tabernas-Sorbas Basin has long been accepted; similar coral limest ones in the Huercal Overa Basin have previously been dated at Tortonian. Ho wever, our data show that these carbonates are of Messinian age in both bas ins. The origin and development of the Tabernas-Sorbas and Huercal Overa Basins have previously been interpreted in a number of ways. Many (but not all) mo dels favour strike-slip movement on NE-SW or east-west trending basin-bound ing faults. The formation and deformation of the basins occurred during the Tortonian and Messinian, at the same time as the uplift of the sierras. Th e sierras are here interpreted to represent structural culminations above w estward-verging, deep-seated thrust faults, and the basins to be lateral fo lds (or lateral ramps, i.e. oriented parallel to the thrust transport direc tion). The east-west trending strike-slip faults at the margin of the Sorba s-Tabernas Basin may be compatible with such a model. Major NE-SW trending, left-lateral wrench faults have been described in thi s area. These faults cut through late Miocene and Pliocene deposits, and ar e still active at the present day. Although these faults were initiated dur ing the late Miocene, they do not appear to have influenced the development of the Tabernas-Sorbas and Huercal Overa Basins during the early Tortonian .