Subsidence analyses from the Betic Cordillera, southeast Spain
Fifty-four Mesozoic-Cenozoic stratigraphic sections from the Betic Cordillera of southeast Spain have been analysed in order to estimate the timing and amount of lithospheric stretching that occurred at the western end of the Tethyan Ocean since the Hercynian Orogeny. The standard backstripping technique has been used in order to calculate the water-loaded subsidence of basement for each section. Water-loaded subsidence curves were then inverted in order to determine the variation of lithospheric strain rate as a function of time, which yields estimates of timing, magnitude and intensity of stretching. Rifting commenced during the Late Permian/Early Triassic times and continued intermittently throughout the Mesozoic in response to the opening of the Tethyan Ocean to the east and the opening of the Atlantic Ocean to the west. Two major events in the Permo-Triassic/Early Jurassic and the Late Jurassic/Early Cretaceous can be clearly identified. Stretching factors are generally small (1.1-1.25) probably because the Betic Cordillera was located at the westernmost end of the Tethys. Peak strain rates of ~ 10-15 S-1 were obtained for Mesozoic rift events and these values are in broad agreement with those obtained throughout the Tethyan Realm. We have also analysed the Neogene extensional event, which played an important role in forming the existing Mediterranean Sea. A combination of well-log information and calibrated seismic reflection data was modelled. Peak strain rates in these younger basins are almost one order of magnitude faster than those estimated for the Mesozoic basins. These higher values appear to be typical of back-arc extensional basins elsewhere. To the west and north of the Betic Cordillera, the Guadalquivir foreland basin developed as extension took place further east. Backstripped sections from this basin clearly record the northward migration of foreland basin subsidence through time.