Abstract. In recent years, the origin of the BeticRif orocline has been the subject of considerable debate. Mudi of this debate has, focused on mechanisms required to generate rapid late-orogenic extension with coeval shortening. Here we summarize the principal geological and geophysical observations and propose a model for the Miocene evolution of the Betic-lq. if mountain belts, which is compatible with the evolution of the rest of the western Mediterranean. We regard palaeomagnetic data, which indicate that there have been large rotations about vertical axes, and earthquake data, which show that deep seismicity occurs beneath the Alboran Sea, to be the most significant data sets. Neither data set is satisfactorily accounted for by models which invoke convective removal or delamination of lithospheric mantle. Existing geological and geophysical observations are, however, entirely consistent with the existence of a subduction zone which rolled or peeled back until it collided with North Africa. We suggest that this ancient subducting slab consequently split into two fragments, one of which has continued to roll back, generating the Tyrrhenian Sea and forming the presentday Calabnan Arc The other slab fragment rolled back to the west, generating the Alboran Sea and the BeticRif oroctine during the early to middle Miocene.

Sandstone intrusions are found in all sedimentary environments but have been reported most commonly from deep-water settings. They also appear to be more frequently developed in tectonically active settings where applied tectonic stresses facilitate development of high fluid pressures within the sediments. A variety of mechanisms have been cited as triggers for clastic intrusions. These include seismicity induced liquefaction, application of tectonic stresses, excess pore fluid pressures generated by deposition-related processes and the influx of an overpressured fluid from deeper within the basin into a shallow sand body. The formation of sandstone dykes and sills is investigated here by considering them as natural hydraulic fractures. When the seal on an unconsolidated, overpressured sand body fails the resulting steep hydraulic gradient may cause the sand to fluidize. The fluidized slurry can then inject along pre-existing or new fractures to form clastic intrusions. The scale and the geometry of an intrusive complex is governed by the stress state, depth and pre-existing joints or faults within the sedimentary succession, as well as the nature of the host sediments. For the simplest tectonic setting, where the maximum stress in a basin is vertical (gravitational loading), small irregular intrusions commonly result in the formation of sills at shallow depths within a few metres of the surface, whereas at greater depth dykes and sills forming clastic intrusion networks are more typical. A simple relationship is derived to calculate the maximum burial depth at which a dyke–sill complex forms as a function of the source-bed to sill height, the bulk density of the surrounding sediments, and the ratio of the vertical to horizontal effective stresses, K 0 . When applied to three examples of large-scale dyke–sill complexes developed within Paleocene and Eocene deep-water reservoir sand bodies of the North Sea, maximum burial depths in a range of 375 to c . 500 m, 450–700 m and 550–850 m are estimated for intrusion of each of the three complexes.

This paper describes the geometry and strain characteristics of a complex system of small extensional faults affecting Lower Tertiary mudrock‐dominated successions throughout the central North Sea Basin. Structural mapping using three‐dimensional seismic data shows that the fault trace geometry is polygonal. The shallow origin of the faults is confirmed by the recognition of growth sequences developed in their hangingwalls. Line balancing techniques were used to measure the extensional strain in two survey areas. This was found to be radially isotropic in the map plane. Extension in any line of section was found to vary from 6 to 19%. Since the deformation is clearly layer‐bound and there is no evidence for displacement transfer to basement structures, it is argued that the only explanation for this apparent extension is by layer‐parallel volumetric contraction. This is believed to occur in response to fluid expulsion from the mudrocks during early compaction. The conditions for failure may be achieved through increased pore fluid pressure or through tensile stresses generated as a result of pore fluid loss, or a combination of these two processes. Far‐field tectonic stresses are not considered to be responsible for the formation of this fault system.

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A comprehensive interpretation of single and multichannel seismic reflection profiles integrated with biostratigraphical data and log information from nearby DSDP and ODP wells has been used to constrain the late Messinian to Quaternary basin evolution of the central part of the Alboran Sea Basin. We found that deformation is heterogeneously distributed in space and time and that three major shortening phases have affected the basin as a result of convergence between the Eurasian and African plates. During the Messinian salinity crisis, significant erosion and local subsidence resulted in the formation of small, isolated, basins with shallow marine and lacustrine sedimentation. The first shortening event occurred during the Early Pliocene (ca. 5.33–4.57 Ma) along the Alboran Ridge. This was followed by a major transgression that widened the basin and was accompanied by increased sediment accumulation rates. The second, and main, phase of shortening on the Alboran Ridge took place during the Late Pliocene (ca. 3.28–2.59 Ma) as a result of thrusting and folding which was accompanied by a change in the Eurasian/African plate convergence vector from NW‐SE to WNW‐ESE. This phase also caused uplift of the southern basins and right‐lateral transtension along the WNW‐ENE Yusuf fault zone. Deformation along the Yusuf and Alboran ridges continued during the early Pleistocene (ca. 1.81–1.19 Ma) and appears to continue at the present day together with the active NNE‐SSW trending Al‐Idrisi strike‐slip fault. The Alboran Sea Basin is a region of complex interplay between sediment supply from the surrounding Betic and Rif mountains and tectonics in a zone of transpression between the converging African and European plates. The partitioning of the deformation since the Pliocene, and the resulting subsidence and uplift in the basin was partially controlled by the inherited pre‐Messinian basin geometry.