Chronostratigraphic framework and evolution of the Fortuna basin (Eastern Betics) since the Late Miocene

ABSTRACT A Tortonian to Pliocene magnetostratigraphy of the Fortuna basin supports a new chronostratigraphic framework, which is significant for the palaeogeographical and geodynamic evolution of the Eastern Betics in SE Spain.
The Neogene Fortuna basin is an elongated trough which formed over a left-lateral strike-slip zone in the Eastern Betics in the context of the convergence between the African and Iberian plates. Coeval with other basins in the Alicante–Cartagena area (Eastern Betics), rapid initial subsidence in the Fortuna basin started in the Tortonian as a result of WNW–ESE stretching. This led to transgression and deposition of marine sediments over extensive areas in open connection with the neighbouring basins. Since the late Tortonian, N–S to NW–SE compression led to inversion of older extensional structures. The transpressional tectonics along the NE–SW-trending Alhama de Murcia Fault is related to the rising of a structural high which isolated the Fortuna basin from the open Mediterranean basin. The progression of basin confinement is indicated by the development of restricted marine environments and deposition of evaporites (7.8–7.6 Ma). The new basin configuration favoured rapid sediment accumulation and marine regression. The basin subsided rapidly during the Messinian, leading to the accumulation of thick continental sequences. During the Pliocene, left-lateral shear along the Alhama de Murcia Fault caused synsedimentary folding, vertical axis block rotations and uplift of both the basin and its margins. The overall sedimentary evolution of the Fortuna basin can be regarded as a developing pull-apart basin controlled by NE–SW strike-slip faults. This resembles the evolution that has taken place in some areas of the Eastern Alboran basin since the late Tortonian.     

Oligocene to middle Miocene basin development in the Eastern Betic Cordilleras, SE Spain (Vélez Rubio Corridor – Espuña): reflections of West Mediterranean plate-tectonic reorganizations

The suture between two West Mediterranean crustal blocks once situated several hundreds of kilometres apart can be studied in the Vélez Rubio Corridor – Espuña area of the Eastern Betic Cordilleras. This suture, or Internal–External Zone Boundary, separates the former passive southern margin of Iberia (the External Zone) from a stack of allochthonous nappe complexes (the Internal Zone), of which the highest unit is formed by the weakly or nonmetamorphosed Malaguide Complex. Analysis of the Oligocene to middle Miocene sediments of the Vélez Rubio Corridor and the Espuña, and comparison with coeval deposits elsewhere in the Western Mediterranean shows that (a) up to the middle Miocene, the southern part of the External Zone (Southern Subbetic) was positioned some 100 km more eastward; (b) up to the early Aquitanian, the Malaguide Complex, forming part of the South Sardinian block (the southern section of a West Mediterranean continental segment) was juxtaposed to the North Sardinian block (the northern part of that continental fragment), some 400 km more eastward; (c) West European extensional rifting during the late Oligocene to earliest Aquitanian resulted in deposition of rift valley sediments (Ciudad Granada and Pliego Formations) in the Malaguide realm; (d) during the Aquitanian, the West Mediterranean segment disintegrated and the West Mediterranean oceanic basins opened, resulting in, for example, the south-westward drift of the Internal Zone, with concomitant thrusting and thinning and deposition of submarine fans (Solana-Algeciras Formation) along the margin; (e) in the early Burdigalian, the allochthonous Internal Zone collided with the Iberian margin, causing the disruption of the platform-slope configuration of the External Zone; (f) after the collision a deep basin was formed upon the suture filled in with erosional products from both Internal and External Zones (Espejos–Viñuelas–Millanas Formations); (g) a strong compressive event in the late Burdigalian caused the southward thrusting of the Subbetic over the Espejos Formation, thus double-sealing the collisional contact; (h) in the latest Burdigalian to Langhian, new strongly subsiding basins were formed in the Western Mediterranean, e.g. along the Internal–External Zone Boundary; (i) dextral strike-slip faulting in the Serravallian resulted in a westward displacement of over 100 km of the southern Subbetic plus Internal Zone; (j) onset of a new pattern of strike-slip faulting induced the formation of a new suite of basins in the Tortonian.     

Sedimentology,provenance and geochronology of the upper Cretaceous–lower Eocene western Xigaze forearc basin,southern Tibet

Located on the southern margin of the Lhasa terrane in southern Tibet, the Xigaze forearc basin records Cretaceous to lower Eocene sedimentation along the southern margin of Asia, prior to and during the initial stages of continental collision with the Tethyan Himalaya in the Early Eocene. We present new measured stratigraphic sections, totalling 4.5 km stratigraphic thickness, from a 60 km E–W segment of the western portion of the Xigaze forearc basin, northeast of the Lopu Kangri Range (29.8007° N, 84.91827° E). In addition, we apply U–Pb detrital zircon geochronology to constrain the provenance and maximum depositional ages of investigated strata. Stratigraphic ages range between ca. 88 and ca. 54 Ma and sedimentary facies indicate a shoaling‐upward trend from deep‐marine turbidites to fluvial deposits. Depositional environments of coeval Cretaceous strata along strike include deep‐marine distal turbidites, slope‐apron debris‐flow deposits and marginal marine carbonates. This along‐strike variability in facies suggests an irregular paleogeography of the Asian margin prior to collision. Paleocene–Eocene strata are composed of shallow marine carbonates with abundant foraminifera such as Nummulites‐Discocyclina and Miscellanea‐Daviesina and transition into fluvial deposits dated at ca. 54 Ma. Sandstone modal analyses, conglomerate clast compositions and detrital zircon U–Pb geochronology indicate that forearc detritus in this region was derived solely from the Gangdese magmatic arc to the north. In addition, U–Pb detrital zircon age spectra within the upper Xigaze forearc stratigraphy are similar to those from Eocene foreland basin strata south of the Indus‐Yarlung suture near Sangdanlin, suggesting that the Xigaze forearc was a possible source of Sangdanlin detritus by ca. 55 Ma. We propose a model in which the Xigaze forearc prograded south over the accretionary prism and onto the advancing Tethyan Himalayan passive margin between 58 and 54 Ma, during late stage evolution of the forearc basin and the beginning of collision with the Tethyan Himalaya. The lack of documented forearc strata younger than ca. 51 Ma suggests that sedimentation in the forearc basin ceased at this time owing to uplift resulting from continued continental collision.     

Cenozoic tectonic activity in a Variscan basement: Evidence from geomorphological markers and structural mapping (NW Iberian Massif)

The NW Iberian Massif is part of an ancient basement that has been considered a seismically stable area with no outstanding Cenozoic tectonics. However, recent seismic activity revealed the need for better knowledge of the Cenozoic structures in the area. Because of the lack of Mesozoic deposits and the scarcity of Cenozoic sediments, as well as the intense deformation of the Pre-Mesozoic Variscan basement, it is difficult to study the Cenozoic tectonic structures. In this work, the combination of detailed structural mapping and study of geomorphological markers in the Variscan basement has allowed recognition of Cenozoic tectonic structures, kinematics and processes that otherwise would not have been identified. The identified structures have been gathered into three groups: a) NE–SW-trending strike-slip faults, mainly sinistral, b) NNW-vergent thrusts that uplift the Caurel Mountains and Galaico-Leoneses Mountains, and c) E–W and ENE–WSW thrusts that uplift the Ancares Mountains in a pop-up structure. The structures cut the Pre-Cenozoic erosion surface and affect the drainage network that shows patterns characteristic of tectonic activity. The three groups of structures define sectors with different relief showing a strong link between geomorphological elements and tectonic structures. The intense drainage reorganisations observed in the area and the deformation of Miocene–Pliocene deposits, point out to a significant Late Miocene tectonic activity in the region. Thus, the Cenozoic tectonic activity in the northwest of the Iberian Peninsula takes place during an extensive period of time which started with the episodes of compression in the Cantabrian Margin and it is identified nowadays by the recent seismic activity recorded in the north-western Iberian Peninsula (1995 and 1997 Lugo events). The seismicity is related to the Cenozoic structures identified in the area, which move under the present SE–NW horizontal maximum compression and coincide with the proposed seismogenic faults.     

Active tectonics of an apparently aseismic region: distributed active strike-slip faulting in the Hangay Mountains of central Mongolia

We identify and describe a series of east–west left-lateral strike-slip faults (named the Songino-Margats, the Hag Nuur, the Uliastay and the South Hangay fault systems) in the Hangay mountains of central Mongolia: an area that has little in the way of recorded seismicity and which is often considered as a rigid block within the India–Eurasia collision zone. The strike-slip faults of central Mongolia constitute a previously unrecognized hazard in this part of Mongolia. Each of the strike-slip faults show indications of late Quaternary activity in the form of aligned sequences of sag-ponds and pressure-ridges developed in alluvial deposits. Total bed-rock displacements of ∼3 km are measured on both the Songino-Margats and South Hangay fault systems. Bed-rock displacements of 11 km are observed across the Hag Nuur fault. Cumulative offset across the Uliastay fault systems are unknown but are unlikely to be large. We have no quantitative constraint on the age of faulting in the Hangay. The ≤20 km of cumulative slip on the Hangay faults might, at least in part, be inherited from earlier tectonic movements. Our observations show that, despite the almost complete absence of instrumentally recorded seismicity in the Hangay, this part of Mongolia is cut through by numerous distributed strike-slip faults that accommodate regional left-lateral shear between Siberia and China. Central Mongolia is thus an important component of the India–Eurasia collision that would be overlooked in models of the active tectonics based on the distribution of seismicity. We suggest that active faults such as those identified in the Hangay of Mongolia might exist in other, apparently aseismic, regions within continental collision zones.     

Tectono-sedimentary evolution of transverse extensional faults in a foreland basin: Response to changes in tectonic plate processes

Late Paleocene to Middle Eocene strata in the easternmost part of the Southern Pyrenees, up to 4 km thick, provide information on tectono-sedimentary evolution of faults transversal to the Pyrenean chain. To know how changes in tectonic plate processes control the structural evolution of transverse faults and the synchronous thickness and lithological distribution of sedimentary strata in a foreland basin, field observations, interpretation of 2D seismic lines tied to lithostratigraphic data of exploration wells and gravity modelling constrains were carried out. This resulted in the following two tectono-sedimentary phases in a foreland basin: first phase, dominated by transverse extensional faulting, synchronous with deposition of marine carbonates (ca. 57 to 51 Ma); and second phase, characterized by transverse contractional faulting, coeval to accumulation of marine and transitional siliciclastics (51 to 44 Ma). During the first phase, Iberia and Adria were moving to the east and west respectively. Therefore, lithospheric flexure in the easternmost part of the Iberian plate was developed due to that Sardinia was over-thrusting Iberia. Consequently, activation of E-dipping normal faults was generated giving rise to thick-deep and thin-shallow carbonate platform deposits across the hanging walls and footwalls of the transverse structures. During the second phase, a shearing interaction between Iberia and Sardinia prevailed re-activating the transverse faults as contractional structures generating thin-shelf and thick-submarine fan deposits across the hanging walls and footwalls of the transverse structures. In the transition between the first and second phases, evaporitic conditions dominated in the basin suggesting a tectonic control on basin marine restriction. The results of our study demonstrate how thickness and lithology distribution, controlled by transverse faulting in a compressional regimen, are influenced by phases related to processes affecting motions and interactions between tectonic plates and continental blocks.     

Seismic stratigraphy of the Miocene–Pleistocene sedimentary basins of the Northern Tyrrhenian Sea and western Tuscany (Italy)

Seismic and stratigraphic data of the inland Volterra Basin and of the Tuscan Shelf (Northern Tyrrhenian Sea) have been analysed to determine the tectono-sedimentary evolution of this part of the Northern Apennines from the early Miocene (about 20 Ma) to the present. The area is a good example for better understanding the evolution of postcollisional related basins. The study area is characterized by a series of sedimentary basins separated by tectonic ridges. Similar environmental conditions existed both onshore and offshore as indicated by the occurrence of similar seismic units. The units are separated by major unconformities. The cross-sectional geometries of the deposits of these basins, as defined through seismic reflection profiles, change in a quasi-regular manner through time and space. Early stages (late Burdigalian to early Tortonian) of evolution of the basins are marked by either flat-lying deposits, quasi-uniform in thickness, probably remnants of originally wider and shallow settings, or, in places, by relatively small bowl-shaped basins. The latter may have been strongly affected by the pre-existing topography and tectonics, as they developed at or near the leading edges of pre-Neogene substrate thrusts. These early deposits represent sedimentation during a transitional period from the end of compressional tectonics to the start of an extensional phase and represent a pre-narrow rift stage of evolution of the region. The subsequent stage of tectonic evolution (late Tortonian to early Messinian), where preserved, is recorded by fault-bounded triangular-shaped basins interpreted as half-grabens. This is one of the periods of major development of narrow rifts in the area. The following stage (late Messinian to Early Pliocene) is marked by variable types of basins, showing wide and deep bowl-shaped geometries persistent in the offshore, whereas inshore (Volterra Basin) they alternate with half-graben, synrift deposits. This period thus represents a transitional stage where part of the system is still affected by synrift sedimentation and part is developing into incipient post-rift conditions. This stage was followed in early to middle Pliocene times by wide bowl-shaped to blanket-type deposits both in offshore and in inshore areas, indicating regional post-rifting conditions. The pre-, syn- and post-rift stages have followed each other through time and space, starting first in the westernmost offshore area and shifting later toward the east, inshore.     

Neogene tectonics and basin fill patterns in the Hellenic outer-arc (Crete, Greece)

Six time-slice reconstructions in the form of palaeogeographical maps show the large-scale tectonic and sedimentary evolution of the Hellenic outer-arc basins in central and eastern Crete for the middle and late Miocene. The reconstructions are based on extensive field mapping and a detailed chronostratigraphy. Latest compressional features related to subduction and associated crustal thickening are poorly dated and assigned a middle Miocene age. These are possibly contemporaneous with widespread occurrence of breccia deposits all over Crete. The precise date for the onset of extension, possibly controlled by the roll-back of the subsiding African lithosphere, remains at this point a discussion. We present circumstantial evidence to place the beginning of the roll back in the middle Miocene, during the accumulation of an arc-parallel, westward-draining fluvial complex. The continental succession is transgressed steadily until it is interrupted by an important tectonic event at the boundary of the middle and late Miocene (normally seen as the onset of slab roll-back). In the earliest late Miocene a few large-sized fault blocks along arc-parallel normal faults subsided rapidly causing a deepening of the half-graben basins up to approximately 900 m. About 1 Myr later, a new N020E and N100E fault system developed fragmenting the existing half-grabens into orthogonal horst and graben structure. The development of the new fault system caused original continental regions to subside and original deep basins to emerge, which is not easy to reconcile with roll back controlled extensional processes alone. Underplating and inherited basement structure may have played here an additional role, although evidence for firm conclusions is lacking. In late Miocene times (late Tortonian, ≈7.2 Ma), the extensional outer arc basins become deformed by N075E-orientated strike-slip. The new tectonic regime begins with strong uplift along existing N100E fault zones, which developed about E–W-striking topographical highs (e.g. Central Iraklion Ridge and Anatoli anticline) in about 0.4 Myr. The strong uplift is contemporaneous with abundant landsliding observed along an important N075E fault zone crossing eastern Crete and with renewed volcanic activity of the arc. The origin of the ridges may be due to active folding related to the sinistral slip.     

Tectono‐sedimentary development of early syn‐rift deposits: the Abura Graben,Suez Rift,Egypt

The thickness and distribution of early syn‐rift deposits record the evolution of structures accommodating the earliest phases of continental extension. However, our understanding of the detailed tectono‐sedimentary evolution of these deposits is poor, because in the subsurface, they are often deeply buried and below seismic resolution and sparsely sampled by borehole data. Furthermore, early syn‐rift deposits are typically poorly exposed in the field, being buried beneath thick, late syn‐rift and post‐rift deposits. To improve our understanding of the tectono‐sedimentary development of early syn‐rift strata during the initial stages of rifting, we examined quasi‐3D exposures in the Abura Graben, Suez Rift, Egypt. During the earliest stage of extension, forced folding above blind normal fault segments, rather than half‐graben formation adjacent to surface‐breaking faults, controlled rift physiography, accommodation development and the stratigraphic architecture of non‐marine, early syn‐rift deposits. Fluvial systems incised into underlying pre‐rift deposits and were structurally focused in the axis of the embryonic depocentre, which, at this time, was characterized by a fold‐bound syncline rather than a fault‐bound half graben. During this earliest phase of extension, sediment was sourced from the rift shoulder some 3 km to the NE of the depocentre, rather than from the crests of the flanking, intra‐basin extensional forced folds. Fault‐driven subsidence, perhaps augmented by a eustatic sea‐level rise, resulted in basin deepening and the deposition of a series of fluvial‐dominated mouth bars, which, like the preceding fluvial systems, were structurally pinned within the axis of the growing depocentre, which was still bound by extensional forced folds rather than faults. The extensional forced folds were eventually locally breached by surface‐breaking faults, resulting in the establishment of a half graben, basin deepening and the deposition of shallow marine sandstone and fan‐delta conglomerates. Because growth folding and faulting were coeval along‐strike, syn‐rift stratal units deposited at this time show a highly variable along‐strike stratigraphic architecture, locally thinning towards the growth fold but, only a few kilometres along‐strike, thickening towards the surface‐breaking fault. Despite displaying the classic early syn‐rift stratigraphic motif recording net upward‐deepening, extensional forced folding rather than surface faulting played a key role in controlling basin physiography, accommodation development, and syn‐rift stratal architecture and facies development during the early stages of extension. This structural and stratigraphic observations required to make this interpretation are relatively subtle and may go unrecognized in low‐resolution subsurface data sets.     

Strike‐slip tectonics and basin inversion in the Western Mediterranean: the Post‐Messinian evolution of the Alboran Sea

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.     

Tectonic evolution of the Alboran Sea basin

The Alboran Sea is an extensional basin of Neogene age that is surrounded by highly arcuate thrust belts. Multichannel seismic (MCS) reflection profile data suggest the basin has a complex tectonic fabric that includes extensional, compressional and strike-slip structures. The early Miocene history appears to be dominated by graben formation with border faults that are in large part contemporaneous with thrust movements in the external zones of the Betic and Rif mountains. Extension appears to have continued into the late Miocene although the main movements were probably completed by the time of the Messinian ‘salinity crisis’. The Pliocene and younger history of the basin is dominated by infilling of the Messinian topography, gentle subsidence, and extensional, compressional and strike-slip movements. There is evidence from the sea-floor morphology and seismicity patterns that the basin is actively deforming in response to present-day plate motions. Backstripping of well data in the basin margin suggests that the initial extensional event was accompanied by crustal and lithospheric thinning. The depth to Moho inferred from backstripping is greater than the depth expected based on seismic and gravity modelling, suggesting that backstripping underestimates the true amount of thinning. One explanation is that some of the thinning occurred while the crust was above sea level, perhaps as a result of either crustal thickening, or a period of lithospheric heating and thinning, prior to rifting. We found that a model with a ‘normal’ crustal thickness of 31.2 km, a lithospheric thickness of 50 km, and β= 1.4 predicts 0.8 km of initial uplift. These parameters fit the well subsidence data and bring the backstripped Moho into better agreement with the seismic and gravity Moho. The origin of such a thin lithosphere is not constrained by the data, but we believe that it may be a result of the detachment of a cold lithospheric ‘root’ that formed during pre-Neogene collisional orogeny in the region.     

Interaction of tectonics, eustasy, climate and carbonate production on the sedimentary evolution of an early/middle Jurassic extensional basin (Southern Provence Sub-basin, SE France)

This paper describes the evolution of an extensional basin in regard to the nature and sequence stratigraphic arrangement of its carbonate deposits. The purpose of this study is to evaluate the respective effects of tectonism, eustasy, climate and oceanography on a carbonate sedimentary record. The case study is the early to mid‐Jurassic age carbonate succession of the Southern Provence Sub‐basin (SE France), located within the southern part of the extensional Western European Tethyan Margin. This work is based on sedimentologic, biostratigraphic (using ammonites and brachiopods) and sequence stratigraphic analysis of the carbonate facies of the Cherty Reddish Limestone Formation (late Sinemurian to earliest Bajocian). These strata were deposited in shoreface to lower offshore depositional environments. The succession of the various environments together with the recognition of key stratigraphic surfaces allow us to define four second‐order depositional sequences; of late Sinemurian to earliest Pliensbachian, early Pliensbachian to late Pliensbachian, earliest Toarcian to middle Aalenian and late Aalenian to early Bathonian ages. The architecture of the depositional sequences (thickness and facies variations within the systems tracts, wedge‐shaped geometries) reflects a strong tectonic control. The sub‐basin was structured by extensional faults (oriented approximately 070–090/250–270). Sea‐level variations, fluctuations in carbonate production and preservation, and environmental changes were also significant controlling factors of the carbonate deposition. The interplay of the tectonic control with the other factors resulted in five main phases in the sedimentary evolution of the sub‐basin: (1) dominant tectonic control during the initial rifting stage (late Sinemurian to early Pliensbachian); (2) increasing extensional tectonics (mid‐Pliensbachian); (3) global climato‐eustatic sea‐level fall (latest Pliensbachian) and global climato‐eustatic sea‐level rise plus hypoxia/anoxia (early Toarcian); (4) relative sea‐level fall linked to tectonic uplift related to the ‘Mid‐Cimmerian phase’ (mid‐Aalenian) and (5) oceanographic events (upwelling) and reduction in carbonate production (hypoxia/anoxia) plus tectonic downwarping (late Aalenian/earliest Bajocian).     

The Miocene tectono-sedimentary evolution of the southern Tyrrhenian Sea: stratigraphy, structural and palaeomagnetic data from the on-shore Amantea basin (Calabrian Arc, Italy)

We report on new stratigraphic, palaeomagnetic and anisotropy of magnetic susceptibility (AMS) results from the Amantea basin, located on‐shore along the Tyrrhenian coast of the Calabrian Arc (Italy). The Miocene Amantea Basin formed on the top of a brittlely extended upper plate, separated from a blueschist lower plate by a low‐angle top‐to‐the‐west extensional detachment fault. The stratigraphic architecture of the basin is mainly controlled by the geometry of the detachment fault and is organized in several depositional sequences, separated by major unconformities. The first sequence (DS1) directly overlaps the basement units, and is constituted by Serravallian coarse‐grained conglomerates and sandstones. The upper boundary of this sequence is a major angular unconformity locally marked by a thick palaeosol (type 1 sequence boundary). The second depositional sequence DS2 (middle Tortonian‐early Messinian) is mainly formed by conglomerates, passing upwards to calcarenites, sandstones, claystones and diatomites. Finally, Messinian limestones and evaporites form the third depositional sequence (DS3). Our new biostratigraphic data on the Neogene deposits of the Amantea basin indicate a hiatus of 3 Ma separating sequences DS1 and DS2. The structural architecture of the basin is characterized by faulted homoclines, generally westward dipping, dissected by eastward dipping normal faults. Strike‐slip faults are also present along the margins of the intrabasinal structural highs. Several episodes of syn‐depositional tectonic activity are marked by well‐exposed progressive unconformities, folds and capped normal faults. Three main stages of extensional tectonics affected the area during Neogene‐Quaternary times: (1) Serravallian low‐angle normal faulting; (2) middle Tortonian high‐angle syn‐sedimentary normal faulting; (3) Messinian‐Quaternary high‐angle normal faulting. Extensional tectonics controlled the exhumation of high‐P/low‐T metamorphic rocks and later the foundering of the Amantea basin, with a constant WNW‐ESE stretching direction (present‐day coordinates), defined by means of structural analyses and by AMS data. Palaeomagnetic analyses performed mainly on the claystone deposits of DS1 show a post‐Serravallian clockwise rotation of the Amantea basin. The data presented in this paper constrain better the overall timing, structure and kinematics of the early stages of extensional tectonics of the southern Tyrrhenian Sea. In particular, extensional basins in the southern Tyrrhenian Sea opened during Serravallian and evolved during late Miocene. These data confirm that, at that time, the Amantea basin represented the conjugate extensional margin of the Sardinian border, and that it later drifted south‐eastward and rotated clockwise as a part of the Calabria‐Peloritani terrane.     

Tectonic control of facies architecture, sequence stratigraphy and drowning of a Liassic carbonate platform (Betic Cordillera, Southern Spain)

This paper develops a tectono‐stratigraphic model for the evolution and drowning of Early Jurassic carbonate platforms. The model arises from outcrop analysis and Sr isotope dating of successions exposed in the Betic Cordillera in southeastern Spain. Here, an extensive Early Jurassic (Sinemurian) carbonate platform developed on the rifted Tethyan margin of the Iberian Plate. The platform was dissected by extensional faults in early jamesoni times (ca. 191 Ma) and again in late ibex times (ca.188 Ma) during the Pliensbachian stage. Extensional faults and fault block rotation are shown to control the formation of three sequence boundaries that divide the platform stratigraphy (the Gavilan Formation) into three depositional sequences. The last sequence boundary marks localised drowning of the platform and deposition of the deeper water Zegri Formation, whereas adjacent platforms remain exposed or continue as the site of shallow‐marine sediment accumulation. This study is based on mapping, facies analysis and dating of platform carbonates exposed in three tectonic units within the zone: Gabar, Ponce and Canteras. Facies analysis leads to the recognition of facies associations deposited in carbonate ramp environments and adjacent to synsedimentary, marine, fault scarps. Sr isotope dating enables us to correlate platform‐top carbonates from the different tectonic units at a precision equivalent to ammonite zones. A sequence stratigraphic analysis of sections from the three tectonic units is carried out using the facies models together with the Sr isotope dates. This analysis indicates a clear tectonic control on the development of the stratigraphy: depositional sequences vary in thickness, have wedge‐shaped geometries and vary in facies, internal geometries and systems tracts from one tectonic unit to another. Criteria characterising depositional sequences and sequence boundaries from the Gabar and Ponce units are used to establish a tectono‐stratigraphic model for carbonate platform depositional sequences and sequence boundaries in maritime rifts, which can be applied to other less well‐exposed or subsurface successions from other sedimentary basins. Onlapping transgressive and progradational highstand systems tracts are recognised on dip slope ramps. Falling stage and lowstand systems tracts are developed as thick breccia units in hangingwall areas adjacent to extensional faults. Sequence boundaries vary in character, amplitude and/or duration of sea‐level fall and persistence across the area. Some boundaries coalesce onto the Canteras unit, which remained as a relatively positive area throughout the early Pliensbachian (Carixian). The carbonate platform on the Ponce tectonic unit drowned in the latest Carixian (davoei biozone). However, the adjacent tectonic units remained emergent and developed a long‐lived sequence boundary, indicating tectonic subsidence as the major cause for platform drowning. The stratigraphic evolution of this area on the rifted southern Iberian margin indicates that a widespread restricted shallow‐water carbonate platform environment accumulating peritidal carbonates evolved with faulting to a more open‐marine setting. Sr dating indicates that this transition took place around the Sinemurian–Pliesbachian boundary and it was driven by local fault‐related subsidence together with likely post‐faulting regional subsidence.     

Magnetostratigraphy of the Northern Tian Shan foreland,Taxi He section,China

The Tian Shan range formed in the late Cenozoic in response to the northward propagation of deformation related to the India–Eurasia continental collision. Precise timing of the Tian Shan uplift is required to understand possible mechanisms of continental lithosphere deformation and interactions between climate, tectonism and erosion. Here, we provide magnetostratigraphic age control on the northern Chinese Tian Shan foreland successions. A thorough rock magnetic analysis identifies haematite‐ and magnetite‐bearing alluvial fan deposits in the upper portion of the sampled strata as more reliable palaeomagnetic recorders than magnetite‐bearing fluvial and lacustrine deposits that are often maghaemitized in the lower part of the record. As a result, a robust correlation to the geomagnetic polarity time scale is obtained from 6 to 2 Ma while a tentative correlation is proposed from 6 to 16 Ma. Sediment accumulation rates increase from 155 to 260 m Myr^?1 at 3.9±0.3 Ma. This change coincides with a gradual lithologic transition from fluvial (sandstone‐dominated) to alluvial fan (conglomerate‐dominated) deposits that likely records an approaching erosional source related to tectonically increased subsidence rather than differential compaction. Clear evidence for growth strata starting at an estimated age of ～2 Ma provides a minimum age for folding. These results are compared with previous magneotstratigraphic studies from the same and other sections of the northern Tian Shan foreland basin fill, thus enabling a critical assessment of the reliability of magnetostratigraphic dating and the significance of sediment accumulation rate variations with respect to facies variations and growth strata. Our results in the Taxi He section provide a sequence of events that is consistent with enhanced tectonic forcing starting at ～4 Ma, although a climatic contribution must be considered given the close relationship of these ages with the Pliocene climate deterioration.     

Quantifying the contribution of tectonics vs. differential compaction in the development of domes along the Mid-Norwegian Atlantic margin

A sequential restoration based on combined backstripping and unfolding methods affords the opportunity to study the Cenozoic evolution of two low amplitude domes in the Mid‐Norwegian extensional margin, the Helland Hansen Arch and the Vema Dome. The integration of growth strata geometries observed in both flanks of the domes demonstrate that the structures grew by a variable combination of tectonics and differential compaction mechanisms. Sequential restoration shows that the Helland Hansen Arch grew between Early Oligocene and earliest Late Pliocene times (33–1.9 Ma). During the first phase of growth (33–9 Ma), the tectonic compression accounted for a minimum of 27% of the total dome amplitude. During Late Miocene to Pliocene times (9–1.9 Ma), differential compaction was the mechanism for dome growth. During Late Pliocene times, the Helland Hansen Arch grew with the highest rates coinciding with initial deposition of prograding wedges (3.6–1.9 Ma). In contrast, the Vema Dome started to develop in Early Eocene times and grew at a fairly constant rate up to Early Pliocene times at 3.6 Ma. The amplification of the Vema Dome took place through both differential compaction and tectonics between Early Eocene and Late Miocene times (54.8–7 Ma). The tectonic contribution accounted for a minimum of a 37% of the total dome amplitude. During Pleistocene times, the progradation of clastic wedges led to a decrease of the amplitudes of both the Helland Hansen Arch and the Vema Dome. The different timing of tectonic growth for analysed domes and arches suggest that a small and protracted phase of compression affected the Mid‐Norwegian Margin. This agrees with well‐known widespread contractional deformation affecting the Atlantic Margin of the European Plate during the Tertiary.     

Detrital fission track thermochronology of Upper Cretaceous syn-orogenic sediments in the South Carpathians (Romania): inferences on the tectonic evolution of a collisional hinterland

ABSTRACT The tectonic evolution of a collisional hinterland sourcing the Ha?eg Basin, a Late Cretaceous syn‐orogenic sedimentary basin in the South Carpathians (Romania), is revealed through fission track thermochronology of detrital apatite and zircon grains. This basin formed on the upper plate (Getic unit) in response to Late Cretaceous collision with the lower plate (Danubian unit), an allochtonous continental block of the Moesian Platform, upon closure of a narrow oceanic basin (Severin Basin). The fission track results suggest that Turonian to lower Maastrichtian sediments of the Ha?eg Basin have been dominantly derived from pre‐Late Cretaceous sources. The age components they contain relate to pre‐Cretaceous tectonothermal events such as the Variscan orogenic cycle, Jurassic rifting and Severin Basin formation, and to Early Cretaceous compressional tectonics. These results are compatible with the tectonic evolution of the upper plate that is identified as the primary source. From the onset of sedimentation (late Albian) until the early Campanian the Ha?eg Basin resembles a piggy‐back basin formed on the upper plate concomitant with underthrusting and internal stacking of the lower plate. In contrast, important tectonic subsidence during the late Campanian and early Maastrichtian reflects a shift to extensional tectonics causing the unroofing of the collision zone and the exhumation of lower plate rocks back to the surface. Our fission track data place important constraints on the timing of lower plate erosion that must have commenced during the late Maastrichtian, as documented by the completely reset Late Cretaceous age component within upper Maastrichtian sediments (Sînpetru Formation). Late Maastrichtian uplift of the basin and the formation of positive relief at the site of the collision zone is an expression of continuous convergence. The mismatch between the amount of denudation and the amount of sediments trapped in the Ha?eg Basin underlines the importance of concomitant extensional unroofing.     

Strike-slip tectonics and development of the Tertiary Queen Charlotte Basin, offshore western Canada: evidence from seismic reflection data

Interpretation of seismic reflection data have led to a new model of the development of the Queen Charlotte Basin. New multi-channel data collected in 1988 and an extensive network of unpublished older single- and multi-channel profiles from industry image a complex network of sub-basins. Structural styles vary along the axis of the basin from broadly spaced mainly N-trending sub-basins in Queen Charlotte Sound, to closely spaced NW-trending sub-basins in Hecate Strait, to an E-W en echelon belt of sub-basins in Dixon Entrance. Transtensional tectonics dominated in the Miocene and transpression dominated in the Pliocene except in Queen Charlotte Sound. The data we present prove that the origin of the basin is extensional and its most recent deformation is compressive. Evidence for the strike-slip origin of tectonism includes along-axis variations in structures, simultaneous extension and compression in adjacent sub-basins, lack of correlations across faults, and mixed normal and reverse faults within structures. We infer that the Pacific-North America plate boundary has been west of the Queen Charlotte Islands since the Miocene when relative plate motions have been dominantly strike-slip. The formation and development of the Queen Charlotte Basin is the result of distributed shear; by which a small percentage of the plate motion has been taken up in a network of faults across the continental margin. As this region of crust deforms it interacts with neighbouring rigid crust resulting in extension dominating in the south of the basin and compression in the north. Continental crust adjacent to some transform plate boundaries can be sheared over a wide region; the network of basins in southwestern California is a good analogue for the Queen Charlotte Basin.     

Salt tectonics vs. inversion tectonics: The anticlines of the western Maestrazgo revisited (eastern Iberian Chain,Spain)

Many works in the last decades underline the role of evaporites, not just as a conditioning factor but as the engine for subsidence and eventually basin inversion. The western Mediterranean alpine ranges are being investigated in this regard because of the presence of discontinuous units of Permian to Triassic evaporites, deposited in the western Tethys basins. This work presents a thorough analysis of two particular structures (Cañada Vellida and Miravete anticlines) in the intraplate Maestrazgo basin (eastern Iberian Chain, Spain) in which evidence to support their reinterpretation as salt-driven structures have been recently reported. Our analysis includes (i) a comprehensive stratigraphic and structural study of the folds along their entire trace, (ii) the compilation of thickness and distribution of evaporite–bearing and supraevaporite units, paying special attention to changes in the thickness of units in relation to anticlines, and (iii) the study of fault patterns, sometimes in relation to the mechanical stratigraphy. All three aspects are also documented and discussed on a regional scale. The new data and interpretations reported here reinforce the extensional origin of the Late Jurassic–Early Cretaceous basins, and the role of regional extensional tectonics as the responsible for the development of first-order syn-sedimentary normal fault zones driving the formation and evolution of sub-basins. These basins were subsequently inverted and deformed, including the formation of complex, box-geometry anticlines that, in their turn, controlled deposition in Cenozoic basins. The review of the arguments that support the alternative of salt tectonics for the origin of such anticlines has allowed us to delve into the sedimentary and tectonic evolution of the inverted extensional basins and to propose a specific model for the development of these faulted anticlines. The role of salt levels and other interlayered detachments in the structuring of sedimentary basins and their inversion is also pondered. The observations in the eastern Iberian Chain reported here have implications to assess ongoing reinterpretations in terms of salt tectonics in other alpine basins and ranges of the western Mediterranean.     

Tectono‐climatic evolution of a Neogene intramontane basin (Late Miocene Carboneras subbasin,southeast Spain): revelations from basin mapping and biofacies analysis

Exceptional 3‐D exposures of fault blocks forming a 5 km × 10 km clastic sediment‐starved, marine basin (Carboneras subbasin, southeast Spain) allow a test of the response of carbonate sequence stratigraphic architectures to climatic and tectonic forcing. Temperate and tropical climatic periods recorded in biofacies serve as a chronostratigraphic framework to reconstruct the status of the basin within three time‐slices (late Tortonian–early Messinian, late Messinian, Pliocene). Structural maps and isopach maps trace out the distribution of fault blocks, faults, and over time, their relative motions, propagational patterns and life times, which demonstrate a changing layout of the basin because of a rotation of the regional transtensional stress field. Progradation of early Messinian reefal systems was perpendicular to the master faults of the blocks, which were draped by condensed fore‐slope sediments. The hangingwall basins coincided with the toe‐of‐slope of the reef systems. The main phase of block faulting during the late Tortonian and earliest Messinian influenced the palaeogeography until the late Pliocene (cumulative throw < 150–240 m), whereas displacements along block bounding faults, which moved into the hangingwall, died out over time. An associated shift of the depocentres of calciturbidites, slump masses and fault scarp degradation breccias reflects 500–700 m of fault propagation into the hangingwall. The shallow‐water systems of the footwall areas were repeatedly subject to emergence and deep peripheral erosion, which imply slow net relative uplift of the footwall. In the dip‐slope settings, erosional truncations of tilted proximal deposits prevail, which indicate rotational relative uplift. Block movements were on the order of magnitude of third order sea‐level fluctuations during the late Tortonian and earliest Messinian. We suggest that this might be the reason for the common presence of offlapping geometries in early Messinian reef systems of the Betic Cordilleras. During the late Pliocene, uplift rates fell below third order rates of sea‐level variations. However, at this stage, the basin was uplifted too far to be inundated by the sea again. The evolution of the basin may serve as a model for many other extensional basins around the world.