Joan Guimerà

The Neogene structure of the eastern Iberian margin: Structural constraints on the crustal evolution of the Valencia trough (western Mediterranean)

Abstract The presence of a thinned crust beneath the Valencia trough has been recognized for a long time. However, to date no attempt to link this thinning, inferred from geophysical data, with the superficial structures has been made. A quantification of the Neogene extensional processes in the crustal evolution of the Valencia trough is presented. As a consequence of the complexity of the Betic-Balearic domain, the analysis has been done for the Catalan-Valencian domain (northwestern areas of the trough). Crustal and superficial data in this area show that Neogene extension was accommodated by a listric normal fault system detached in a deep upper crustal level (13–15 km) in the marginal zone of the domain. Quantitative analysis of the Neogene structure shows the incoherence between the upper crustal thinning inferred from the geometric analysis of the superficial structures (β factor 1.4–1.5) and from geophysical data (1.8). Although the latter value agrees with that deduced from the analysis of Neogene subsidence, this incoherence suggests that the present thinned crust would be partially inherited from the Mesozoic extension. In this way, Mesozoic subsidence analysts and the recognized Mesozoic structure show that the Mesozoic extension was almost as important as the Neogene one.

Evolution of the central Catalan margin of the Valencia trough (western Mediterranean)

Abstract The evolution of the central Catalan margin was conditioned by major fault activity and thermal processes generated by crustal thinning. The continental margin structure is characterised by major NE-SW-striking, southeast-dipping basement faults which have given rise to a graben, half-graben and horst system. These faults acted essentially as normal faults. No major Neogene strike-slip activity has affected the continental margin, although minor episodic variations from the dominant extensional regime to strike-slip tectonics cannot be discounted. Two major structural evolutionary stages took place at the margin, the transition from one stage to the other being gradual: (1) rifting stage (Late Oligocene? to early Burdigalian) related to the opening of the Valencia trough and from which originated both the Barcelona and Valles-Penedes half-grabens; (2) thermal subsidence stage (late Burdigalian to present) generated by the subsequent crustal cooling and thinning. Fault activity during this stage was essentially concentrated in the major half-graben bounding faults. The sedimentary evolution of the central sector of the Catalan margin was controlled by the tectonic and crustal evolution as well as by the successive sea-level and paleoclimatic changes which affected the region. Drastic changes in the depositional systems took place during the transition from the rifting stage into the thermal subsidence stage. During Aquitanian-Langhian time—characterized by an overall trend of pulsating encroachment of marine conditions over the continental margin—a noticeable diversity of depositional systems (alluvial, lacustrine, coastal evaporitic, fan delta-bay-shelf, carbonate platform systems) developed. From the latest Serravallian up to the present, the depositional framework was less varied due to a general lowering of sea-level and to the final onlapping of most of older structural highs, which are now buried below the Miocene sediments. Two progradational terrigenous shelf-talus systems separated by the Messinian erosive surface developed during the latest Serravallian-Tortonian and Pliocene-Quaternary.

Palaegene evolution of deformation in the northeastern Iberian Peninsula

During the Palaeogene Alpine compression three units were differentiated in the studied area (south of the Ebro Basin): the Catalan Coastal Range, dominated by NE–SW major basement faults with a sinistral movement; The Iberian Range, where the important basement faults have a NW–SE direction and a reverse movement (often with a dextral component); the Linking Zone, between these two ranges, where an E–W dominant structural direction is marked by an array of folds and thrusts (with a northward vergence) in the Mesozoic cover.From the analysis of both these major structures and the small-scale structures, it can be deduced that the compression in the studied area has evolved from a NW–SE direction (lower-middle Eocene) to a N–S direction and to a NE–SW one (uppermost Oligocene). The major structures are due to the N–S compression. Later, the stress-field progressively changed to a distensive regime.We suggest a relation between the compressive phases and the displacement direction of the Iberian Plate with reference to the European Plate.

Inversion of an extensional-ramp basin by a newly formed thrust: the Cameros basin (N. Spain)

Abstract The Cameros basin (Iberian Chain) was developed under a very subsident extensional regime during the latest Jurassic-Early Cretaceous. Its sedimentary fill constitutes a megasequence of more than 5000 m of vertical thickness which contains six depositional sequences. Most of the sediments are continental (alluvial and lacustrine) with only minor marine intercalations. A lateral accretionary geometry at the basin scale shows a SSW-NNE migration of the depocentre and an onlap to the north of the sedimentary sequences on the Mesozoic substratum of the northern boundary of the basin. The overall Mesozoic structure of the basin, as seen from field studies and seismic profile interpretation, is a gentle WNW-ESE synclinorium 30–70 km wide and 150 km long. Extension in the pre-basin Mesozoic rocks is very small. The basin boundaries are defined by an unconformity of the basin filling rocks on the former Mesozoic substratum; it is bounded only locally by major faults at surface. The basin is interpreted as an extensional-ramp basin produced over an S-dipping ramp in a blind, flat-lying extensional fault some kilometres deep in the basement. The extensional displacement on the fault produced a synclinal basin which progressively widened with time. The depocentres of the successive depositional sequences were always located above the ramp and migrated to the north, inside the basin, as a result of the hangingwall displacement to the south. From a computer-modelled cross-section, we estimate the total displacement on the extensional fault to be about 33 km. This extension, in the hangingwall, would have taken place in the Pyrenean basin, north of the Cameros basin. Tertiary compression (Palaeogene to Lower-Middle Miocene) inverted the basin by means of a newly formed E-W north-directed thrust. Overthrusting in the Tertiary Ebro basin fill, this new fault formed in the Keuper beds, in a weakness zone with uniform dip within the extensional hangingwall (about 30 km in cross-section). During the deformation it expanded to the north and south until it branched to the Iberian sole thrust, which might coincide with the Mesozoic extensional sole fault. Although this thrust produced a slight (2–3 km) inversion of the basement-Mesozoic cover unconformity, its maximum displacement was of about 28 km. Pre-basin Mesozoic rocks overlie the thrust surface and are overlain by the basin-filling rocks. A south-directed imbricate-fan thrust system developed in the southern margin. The total shortening was about 38 km, leading to the complete inversion of the basin.

Intraplate deformation in the NW Iberian Chain: Mesozoic extension and Tertiary contractional inversion

The Iberian Chain developed within the Iberian plate during the Palaeogene and Early Miocene as a result of convergence between the African and Eurasian plates. It is a fold-and-thrust belt, which involves the Hercynian basement and the Mesozoic and Cenozoic cover. A generalized cross-section of the NW part of the Chain, of 195 km length, is presented. Mesozoic basins, developed on the Hercynian basement, display thickness variations across normal faults that bounded them and that can be recognized in the field. The Tertiary contraction deformed and inverted the Mesozoic basins, and it is inferred to have produced a thrust sheet about 5 km thick in its frontal (northeastern) part, which thickens to the SW. The total Tertiary shortening in the section is 66.6 km (26%). The structure and the crustal shortening and thickening of the Iberian Chain are explained by a major upper-crustal thrust system with simple flat-and-ramp geometry, which may branch to the Pyrenees or the Betics. This is combined with internal deformation of the thrust sheet. The contribution of the Iberian Chain shortening to the convergence of the African and Eurasian plates during the Tertiary is about one-half of that of the Pyrenees, and should be taken into account in any reconstruction of the kinematics of these plates.

Mesozoic extensional tectonics in the southeast Iberian Chain

The Desert de les Palmes area, in the southeast Iberian Chain, belongs to a Mesozoic NE–SW high which separated the early Cretaceous basins of the Maestrat and Aliaga-Penyagolosa from the little Orpesa basin. Its structure is characterized by the development of a system of NE–SW to ENE–WSW extensional listric faults detached in a shallow upper crustal level (1.7–2.2 km), mostly affecting the pre-Upper Cretaceous rocks. These faults record two well-differentiated rifting periods: (1) a first late Triassic–early Jurassic rifting period that divided the Desert de les Palmes high in several blocks; (2) a second early Cretaceous rifting period, only developed in the eastern margin of the Desert de les Palmes high, which was related to the opening of the Maestrat, Aliaga-Penyagolosa and Orpesa basins. Based on the comparison of the main features of this Mesozoic structure with an analysis of the structural and subsidence data already known in the neighbouring Mesozoic basins (Maestrat, Aliaga-Penyagolosa and Columbrets), a geodynamic scenario for the crustal evolution of the eastern Iberian Chain is also suggested. This involves four evolutionary stages: (1) Triassic rift (late Permian–Hettangian); (2) early and middle Jurassic postrift (Sinemurian–Oxfordian); (3) late Jurassic and early Cretaceous rift (Kimmeridgian–middle Albian), which includes a short Hauterivian postrift period; and (4) late Cretaceous postrift (late Albian–Maastrichtian).

Kinematic-stratigraphic evolution of a growth syncline and its implications for tectonic development of the proximal foreland basin, southeastern Ebro basin, Catalunya, Spain

In the southeastern Ebro basin of Spain, analysis of sequential fold history in combination with stacking patterns of conglomerate deposited in a growing syncline demonstrates the impact of local uplift attendant upon fold growth on nonmarine depositional systems in a foreland basin. The Penyagalera syncline is part of a belt of asymmetric folds developed in proximal Paleogene foreland-basin deposits by foreland-directed propagation of a detachment beneath the basin. Foreland-basin strata form a progradational succession of interbedded siltstone, sandstone, and evaporite overlain by conglomerate. Stratal stacking patterns and fold history indicate that conglomerate of the syncline marks the transition within the foreland-basin succession from foredeep to wedge-top depositional zones. The conglomerate is divided into three informal members separated by unconformities. The members are divided in turn into lithosomes separated by prominent bounding surfaces. Lithosomes represent depositional elements deposited by episodic progradation of alluvial-fan lobes. Older conglomerate members are more tightly folded than younger members, demonstrating that folding accompanied conglomerate deposition. The uplift of opposing limbs of the Penyagalera syncline was diachronous. The asymmetric syncline comprises an overturned interior (southeastern) limb and a gently dipping exterior (northwestern) limb. The interior limb rotated to a steep to slightly overturned attitude before significant rotation and uplift of the exterior limb took place. Rotation of the interior fold limb was episodic and punctuated by periods of erosion of older conglomerate. Uplift rates during rotation events along the interior limb generally were more rapid than sediment-accumulation rates and caused sediment bypass to the foreland basin; however, sediment-accumulation rates overtook uplift rates during late limb rotation, causing alluvial-fan lithosomes to onlap previously formed unconformities. Offlap, signifying a slight excess of uplift over sediment-accumulation rates, is not observed in the syncline. On the exterior limb, sedimentation rates exceeded early limb-uplift rates, but the relationship of later folding and deposition is not preserved. Most synclinal closure postdated the youngest preserved lithosomes in the fold. Young lithosomes occupy a paleocanyon incised deeply into the interior limb of the syncline and Mesozoic strata of the thrust belt. The paleocanyon was backfilled during late aggradation of the Ebro basin, an event independent of local folding.

Tectono-stratigraphic evolution of an inverted extensional basin: the Cameros Basin (north of Spain)

Abstract The Cameros Basin is a part of the Mesozoic Iberian Rift. It is an extensional basin formed during the late Jurassic and early Cretaceous, in the Mesozoic Iberian Rift context, and it was inverted in the Cenozoic as a result of the Alpine contraction. This work aims to reconstruct the tectono-stratigraphic evolution of the basin during the Mesozoic, using new and revised field, geophysical and subsurface data. The construction of a basin-wide balanced section with partial restorations herein offers new insights into the geometry of the syn-rift deposits. Field data, seismic lines and oil well data were used to identify the main structures of the basin and the basin-forming mechanisms. Mapping and cross-sectional data indicate the marked thickness variation of the depositional sequences across the basin, suggesting that the extension of the depositional area varied during the syn-rift stage and that the depocentres migrated towards the north. From field observation and seismic line interpretation, an onlap of the depositional sequences to the north, over the marine Jurassic substratum, can be deduced. In the last few decades, the structure and geometry of the basin have been strongly debated. The structure and geometry of the basin infill reconstructed herein strongly support the interpretation of the Cameros Basin as an extensional-ramp synclinal basin formed on a blind south-dipping extensional ramp. The gradual hanging-wall displacement to the south shifted the depocentres to the north over time, thus increasing the basin in size northwards, with onlap geometry on the pre-rift substratum. The basin was inverted by means of a main thrust located in a detachment located in the Upper Triassic beds (Keuper), which branched in depth with the Mesozoic extensional fault flat. The reconstruction of the tectono-stratigraphic evolution of the Cameros Basin proposed herein represents a synthesis and an integration of previous studies of the structure and geometry of the basin. This study can be used as the basis for future basin-scale research and for modelling the ancient petroleum system of the basin.