Temporal and spatial variations in tectonic subsidence in the Iberian Basin (eastern Spain): inferences from automated forward modelling of high-resolution stratigraphy (Permian–Mesozoic)

By subsidence analysis on eighteen surface sections and 6 wells, which cover large part of the Iberian Basin (E Spain) and which are marked by high-resolution stratigraphy of the Permian, Triassic, Jurassic and Cretaceous, we quantify the complex Permian and Mesozoic tectonic subsidence history of the basin. Backstripping analysis of the available high resolution and high surface density of the database allows to quantify spatial and temporal patterns of tectonically driven subsidence to a much higher degree than previous studies. The sections and wells have also been forward modelled with a new ‘automated' modelling technique, with unlimited number of stretching phases, in order to quantify variations in timing and magnitude of rifting. It is demonstrated that the tectonic subsidence history in the Iberian Basin is characterized by pulsating periods of stretching intermitted by periods of relative tectonic quiescence and thermal subsidence. The number of stretching phases appears to be much larger than found by earlier studies, showing a close match with stretching phases found in other parts of the Iberian Peninsula and allowing a clear correlation with discrete phases in the opening of the Tethys and Atlantic.     

Evidence for an active sinistral shear zone in the western Alboran region

A compilation of gravity, seismicity, neotectonics, geology, tomography and topography data from the Alboran region reveals distinctive differences between the eastern and western part of the Alboran region and Betic Cordillera. Calculated profiles of integrated crustal strength reveal that lateral differences in mechanical behaviour are caused by marked inherited differences in crustal make-up. The two domains with different tectonic behaviour are separated by a N025°-trending lineament in the western Alboran and central Betic Cordillera. This lineament can be interpreted as an upper mantle – lower crustal sinistral shear zone accommodating a large part of the convergence between Africa and Iberia.     

Crustal structure of the Alpine–Pannonian transition zone: a combined seismic and gravity study

 The crustal structure of the transition zone between the Eastern Alps and the western part of the Pannonian depression (Danube basin) is traditionally interpreted in terms of subvertical Tertiary strike-slip and normal faults separating different Alpine tectonic units. Reevaluation of approximately 4000-km-long hydrocarbon exploration reflection seismic sections and a few deep seismic profiles, together with data from approximately 300 wells, suggests a different structural model. It implies that extensional collapse of the Alpine orogene in the Middle Miocene was controlled by listric normal faults, which usually crosscut Alpine nappes at shallow levels, but at depth merge with overthrust planes separating the different Alpine units. The alternative structural model was tested along a transect across the Danube basin by gravity model calculations, and the results show that the model of low-angle extensional faulting is indeed viable. Regarding the whole lithosphere of the western Pannonian basin, gravity modelling indicates a remarkable asymmetry in the thickness minima of the attenuated crust and upper mantle. The approximately 160 km lateral offset between the two minima suggests that during the Miocene extension of the Pannonian basin detachment of the upper crust from the mantle lithosphere took place along a rheologically weak lower crust. Received: 13 July 1998 / Accepted: 18 March 1999     

Relating petroleum system and play development to basin evolution: West African South Atlantic basins

Sedimentary basins can be classified according to their structural genesis and evolutionary history and the latter can be linked to petroleum system and play development. We propose an approach in which we use the established concepts in a new way: breaking basins down into their natural basin cycle division, then defining the characteristics of each basin cycle (including the type of petroleum systems and plays they may contain) and comparing them with similar basin cycles in other basins, thereby providing a means to learn through a greater population of (perhaps not immediately obvious) analogues. Furthermore, we introduce the use of the trajectory plot as a new tool in such an analysis. This methodology has been applied to the West African South Atlantic marginal basins between Cameroon and Angola, and we demonstrate that the similar tectonostratigraphic evolution of the individual basins along this margin has led to the development of similar types of petroleum systems and play (level)s. Consequently, we can make analogue comparisons among these basins in order to evaluate and predict the presence of potential, yet undiscovered, hydrocarbon accumulations in less well explored parts of the margin.     

Tectonics and global change - inferences from Late Cenozoic subsidence and uplift patterns in the Atlantic/ Mediterranean region

Quantitative subsidence analysis for a number of rifted basins in the northern Atlantic/Mediterranean region provides evidence for rapid phases of PlioQuaternary subsidence. The observed acceleration in tectonic subsidence occurs after a phase of general quiescence in subsidence in these basins and deviates from predictions of stretching models. The latter indicate a decay of subsidence with time after Mesozoic-Tertiary basin formatioh and a slow tectonic subsidence in Plio-Quaternary times. A possible explanation for the observed patterns of anomalous subsidence could be an increase in the level of intraplate compression in the northern Atlantic region. Intraplate stress changes in the Plio-Quaternary are related to the dynamics of African/ Eurasian collision processes and a reorganization of spreading directions in the AtlAntic, possibly reflecting a plate reorganization of global nature.
It seems that the Plio-Quaternary record reflects a period of increased levels of neotectonic activity, interplaying with periods of (de)glaciation. Stress-induced topography in the onshore parts of continental margins, coupled with the stress-induced subsidence in the offshore deeper parts of the basins, could have contributed to recent phases of uplift in Fennoscandia, augmenting the uplift induced by glacial unloading. Estimates of ice thicknesses are directly inferred from the observed uplift ignoring other driving mechanisms whereas topography plays a crucial role in the dynamics of glaciation. It is, therefore, important to quantdy the interplay of rapid tectonic uplift and subsidence phases with climatic effects during the Plio-Quaternary.     

Salt tectonics in pull-apart basins with application to the Dead Sea Basin

The Dead Sea Basin displays a broad range of salt-related structures that developed in a sinistral strike-slip tectonic environment: en échelon salt ridges, large salt diapirs, transverse oblique normal faults, salt walls and rollovers. Laboratory experiments are used to investigate the mechanics of salt tectonics in pull-apart systems. The results show that in an elongated pull-apart basin the basin fill, although decoupled from the underlying basement by a salt layer, remains frictionally coupled to the boundary. The basin fill, therefore, undergoes a strike-slip shear couple that simultaneously generates en échelon fold trains and oblique normal faults, trending mutually perpendicular. According to the orientation of basin boundaries, sedimentary cover deformation can be dominantly contractional or extensional, at the extremities of pull-apart basins forming either folds and thrusts or normal faults, respectively. These guidelines, applied to the analysis of the Dead Sea Basin, show that the various salt-related structures form a coherent set in the frame of a sinistral strike-slip shearing deformation of the sedimentary basin fill.     

Flexural interaction and the dynamics of neogene extensional Basin formation in the Alboran-Betic region

Quantitative tectonic modelling demonstrates an interaction of flexure of the lithosphere underlying the western Betics with crustal thinning in the Alboran Basin and flank uplift in the Internal Zone. In the eastern Betics the flexural response is overprinted by post-thrusting extensional events. Lateral variations in thermal structure and rheology of the lithosphere along strike of the Betics shed light on changes in tectonic configuration and are consistent with evidence for lateral variations in the mode of extension in the Alboran Basin. Flexural modelling and subsidence analysis of Neogene basins in the Internal Zone of the Betics, with spatial development controlled by contrasts in lithosphere rheology, demonstrate that at least two extensional events have affected the orogenic evolution of the Betics. The first event appears to reflect Oligocene-Early Miocene rifting observed throughout the Western Mediterranean. The second phase, which caused the present configuration of the Betics, corresponds to Tortonian-Recent extension centered in the Alboran Basin.     

A structural model from local earthquake tomography: Application to present-day tectonics of the Upper Rhine Graben

We present a novel numerical approach to construct quantitative tectonic models from crustal velocity distributions derived from local earthquake tomography. Independent constraints on the location and orientation of structures are obtained from earthquake hypocenters and seismic reflection profiles. An application of this method is given for the southern end of the Upper Rhine Graben (northwestern Europe). Kinematic boundary conditions are imposed on the structural model to investigate the large scale intraplate deformation in the region. A 3-D finite element code is used to calculate the displacements, the distribution of stresses, and the potential for brittle failure in the Graben. The modeling takes into account the intersection and curvature of crustal faults. The results demonstrate the dependence of fault interaction in the system on kinematic conditions, as well as the influence of minor faults on the kinematics of major basin bounding master faults. We show that although most of the deformation in the region is taken up by the eastern boundary faults of the Rhine Graben, all faults in the system have the potential to be (re)activated. In particular, a fault system underlying the front of the Jura fold and thrust belt appears to accommodate a large part of the intraplate deformation.     

Finite-element modelling of pull-apart basin formation

We present the results of a finite-element modelling study of pull-apart basin formation related to left-stepping left lateral strike-slip faults. The modelling quantifies the relationship between fault geometry (i.e., fault overlap and separation) and pull-apart basin formation. Two depocentres (subbasins) separated by a broad zone of relative uplift in between may develop if the strike-slip domain is characterized by fault underlap. For overlapping faults migration of the subbasins is predicted by the models. Deep subbasins in a large area of subsidence which spans the entire inner fault zone may form if fault overlap is about three times the fault separation.

The models suggest that a topographic asymmetry within the fault zone may arise due to a different displacement ratio of the strike-slip faults. The modelling results show that this asymmetry in topography becomes more pronounced towards the more active fault. Thus, basin deepening occurs progressively towards the fault characterized by the largest amount of lateral displacement. Moreover, the results indicate that the smaller the fault separation (less than basin length) the less pronounced the topographic asymmetry.

The models provide quantitative estimates for the effects of changes in elastic material properties, the magnitude of the compressive far-field stress and the coefficient of friction of the faults on the resulting topography.

Comparison of the modelling results with field observations from the Cerro Blanco-El Barranquete (CBB) subbasin located in the Internal Zone of the Betic Cordillera, southeastern Spain support an interpretation in which the interplay of major faults has formed the CBB subbasin.