Structural evolution of the Gediz Graben,SW Turkey: temporal and spatial variation of the graben basin

The structural evolution of the Miocene to Recent Gediz Graben is intimately related to the evolution of its southern margin. This margin is shaped by a time‐transgressive, composite structure that possesses flat‐ramp geometry with three separate dip domains: a low‐angle shallow segment; a steeper middle segment; and a low‐angle deeper segment. This geometry was probably produced by one of two mechanisms, which operated perpendicular to the general trend of the graben, resulting in gradual back‐rotation followed by abandonment of the shallow segment as it was dissected by the high‐angle normal fault(s). The geometry of the southern margin structure is not simple along‐strike. It includes broad undulations and discrete fault segments, developed by large‐scale fault growth processes through segment linkage. The along‐strike growth of the southern margin‐bounding structure is responsible for the composite character of the Gediz Graben and controls the observed stratigraphic variability. Two sub‐basins aligned with the major segments of the southern graben margin structure have been investigated. The Salihli and Ala?ehir sub‐basins comprising 3000 m sedimentary thickness are separated by an intervening basement high, that is covered by a thin veneer of post‐Miocene sediments. The two sub‐basins, which evolved as isolated basins during most of the graben history, amalgamated during post‐Miocene time to form the composite configuration of the graben. There is a general east to west trend of growth for the Gediz Graben.     

Synclinal-horst basins: examples from the southern Rio Grande rift and southern transition zone of southwestern New Mexico, USA

In areas of broadly distributed extensional strain, the back‐tilted edges of a wider than normal horst block may create a synclinal‐horst basin. Three Neogene synclinal‐horst basins are described from the southern Rio Grande rift and southern Transition Zone of southwestern New Mexico, USA. The late Miocene–Quaternary Uvas Valley basin developed between two fault blocks that dip 6–8° toward one another. Containing a maximum of 200 m of sediment, the Uvas Valley basin has a nearly symmetrical distribution of sediment thickness and appears to have been hydrologically closed throughout its history. The Miocene Gila Wilderness synclinal‐horst basin is bordered on three sides by gently tilted (10°, 15°, 20°) fault blocks. Despite evidence of an axial drainage that may have exited the northern edge of the basin, 200–300 m of sediment accumulated in the basin, probably as a result of high sediment yields from the large, high‐relief catchments. The Jornada del Muerto synclinal‐horst basin is positioned between the east‐tilted Caballo and west‐tilted San Andres fault blocks. Despite uplift and probable tilting of the adjacent fault blocks in the latest Oligocene and Miocene time, sediment was transported off the horst and deposited in an adjacent basin to the south. Sediment only began to accumulate in the Jornada del Muerto basin in Pliocene and Quaternary time, when an east‐dipping normal fault along the axis of the syncline created a small half graben. Overall, synclinal‐horst basins are rare, because horsts wide enough to develop broad synclines are uncommon in extensional terrains. Synclinal‐horst basins may be most common along the margins of extensional terrains, where thicker, colder crust results in wider fault spacing.     

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.     

Quantitative analysis of Miocene to Recent forearc basin evolution along the Colombian convergent margin

The Colombian accretionary complex forms the active convergent margin of the North Andes block of South America beneath which the east Panama Basin of the Nazca plate is subducted at a rate of 50–64 km Myr^?1. Multichannel seismic reflection data, collected as part of RRS Charles Darwin cruise CD40, image a series of well-developed forearc basins along the length of the margin, bounded on their oceanward side by an active accretionary complex and on their landward side by oceanward-dipping continental basement. Sedimentary sequences within the forearc basins indicate successive landward migration of the basin depocentre as the structural high bounding its oceanward edge is forced upward and landward by continued growth of the accretionary complex. Uplift beneath the oceanward side of the basins has resulted in progressive landward rotation of the older sedimentary sequences. Prominent seismic reflectors across the basins show a complex onlap–offlap relationship between successive sequences that reflects the interplay between tectonic uplift, sediment supply, differential sediment compaction and basement subsidence due to loading. A numerical model has been devised to investigate how Miocene to Recent forearc basin stratigraphy is controlled by progressive growth of the accretionary complex resulting in elevation of the outer-arc high and landward motion of the rear of the complex up the seaward-dipping backstop formed by the leading edge of the continental lithosphere. The effects of sediment accretion are modelled by treating the accretionary complex as a doubly vergent, noncohesive Coulomb wedge, where forces exerted by the proto- and retro-wedges must be balanced for the system to be in equilibrium. The model generates synthetic basin-fill architecture over a series of steps, each of which represents the deposition of individual sedimentary sequences and their subsequent deformation due to wedge growth. The model accounts for differential sediment compaction and the flexural response of the underlying lithosphere to changes in load distribution over time. Forearc basin evolution is simulated for various rates of sediment supply to the forearc and accretionary complex growth until the synthetic basin-fill geometry matches the observed geometry. The model enables either the rate of accretionary wedge growth or the rate of sediment supply to the forearc basin to be established. The technique is generally applicable to those convergent margins with forearc basins that have developed between an actively accreting wedge and a seaward-dipping backstop. Other examples include Peru, S. Chile, Sumatra and Barbados.     

Neogene tectonostratigraphic history of the southern Neuquén basin (39°–40°30′S,Argentina): implications for foreland basin evolution

Although the Neuquén basin in Argentina forms a key transitional domain between the south‐central Andes and the Patagonian Andes, its Cenozoic history is poorly documented. We focus on the sedimentologic and tectonic evolution of the southern part of this basin, at 39–40°30′S, based on study of 14 sedimentary sections. We provide evidence that this basin underwent alternating erosion and deposition of reworked volcaniclastic material in continental and fluvial settings during the Neogene. In particular, basement uplift of the Sañico Massif, due to Late Miocene–Pliocene intensification of tectonic activity, led to sediment partitioning in the basin. During this interval, sedimentation was restricted to the internal domain and the Collon Cura basin evolved towards an endorheic intermontane basin. From stratigraphic interpretation, this basin remained isolated 7–11 Myr. Nevertheless, ephemeral gateways seem to have existed, because we observe a thin succession downstream of the Sañico Massif contemporaneous with the Collon Cura basin‐fill sequence. Comparisons of stratigraphic, paleoenvironmental and tectonic features of the southern Neuquén basin with other foreland basins of South America allow us to classify it as a broken foreland with the development of an intermontane basin from Late Miocene to Late Pliocene. This implies a thick‐skinned structural style for this basin, with reactivation of basement faults responsible for exhumation of the Sañico Massif. Comparison of several broken forelands of South America allows us to propose two categories of intermontane basins according to their structural setting: subsiding or uplifted basins, which has strong implications on their excavation histories.     

Structural evolution and the partitioning of deformation during basin growth and inversion: A case study from the Mizen Basin Celtic Sea,offshore Ireland

The Celtic Sea basins lie on the continental shelf between Ireland and northwest France and consist of a series of ENE–WSW trending elongate basins that extend from St George’s Channel Basin in the east to the Fastnet Basin in the west. The basins, which contain Triassic to Neogene stratigraphic sequences, evolved through a complex geological history that includes multiple Mesozoic rift stages and later Cenozoic inversion. The Mizen Basin represents the NW termination of the Celtic Sea basins and consists of two NE–SW-trending half-grabens developed as a result of the reactivation of Palaeozoic (Caledonian, Lower Carboniferous and Variscan) faults. The faults bounding the Mizen Basin were active as normal faults from Early Triassic to Late Cretaceous times. Most of the fault displacement took place during Berriasian to Hauterivian (Early Cretaceous) times, with a NW–SE direction of extension. A later phase of Aptian to Cenomanian (Early to Late Cretaceous) N–S-oriented extension gave rise to E–W-striking minor normal faults and reactivation of the pre-existing basin bounding faults that propagated upwards as left-stepping arrays of segmented normal faults. In common with most of the Celtic Sea basins, the Mizen Basin experienced a period of major erosion, attributed to tectonic uplift, during the Paleocene. Approximately N–S Alpine regional compression-causing basin inversion is dated as Middle Eocene to Miocene by a well-preserved syn-inversion stratigraphy. Reverse reactivation of the basin bounding faults was broadly synchronous with the formation of a set of near-orthogonal NW–SE dextral strike-slip faults so that compression was partitioned onto two fault sets, the geometrical configuration of which is partly inherited from Palaeozoic basement structure. The segmented character of the fault forming the southern boundary of the Mizen Basin was preserved during Alpine inversion so that Cenozoic reverse displacement distribution on syn-inversion horizons mirrors the earlier extensional displacements. Segmentation of normal faults therefore controls the geometry and location of inversion structures, including inversion anticlines and the back rotation of earlier relay ramps.     

Stratigraphic record and palaeogeographical context of the Neogene basins in the Betic Cordillera, Spain

The Betic Cordillera (Southern Spain) acquired its present configuration during the Neogene. The formation, evolution and total or partial destruction of Neogene sedimentary basins were highly controlled by the geodynamic situations and the positions of the basins in the Betic Cordillera. It is impossible to reconstruct the geometry of basins formed during the Early and Middle Miocene, concurrently with the westward drift of the Internal Zones, because in many cases only small outcrops remain. The basins formed on the mobile substratum (the Internal Zones) are characterized by a sedimentary infill made up of synorogenic deposits, which were intensely deformed towards the end of the Middle Miocene, and which were heavily eroded before the beginning of the Late Miocene. In the External Zones, deposition mainly took place in the North Betic Strait, an area across which there was wide communication between the Atlantic and the Mediterranean, which received huge olistostromic masses in its more mobile sector (the foredeep basin), and which evolved differently in its eastern and western sectors. The palaeogeography of the Cordillera changed radically at the beginning of the Late Miocene, when the westward drift of the Internal Zones ceased. During this time the North Betic Strait disappeared and, in what had been its northwestern half approximately, the Guadalquivir Basin became individualized. This basin, which was located between the Betic Chain and the emerged Hercynian Massif, acquired a structure similar to that of the present basin and its extension was also similar to that of the present Neogene outcrops. Intramontane basins became individualized in the recently formed and progressively emerged mountain chain, reaching a development and size in this Cordillera much greater than in other Alpine chains. These basins are characterized by their thick infills, which are unconformable on the folded and deformed substratum, and which can be subdivided according to the different movements of the fault sets that controlled their evolution.     

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.     

Late Miocene evaporite geochemistry of Lorca and Fortuna basins (Eastern Betics,SE Spain): Evidence of restriction and continentalization

The Lorca and Fortuna basins are two intramontane Neogene basins located in the eastern Betic Cordillera (SE Spain). During the Late Tortonian—Early Messinian, marine and continental evaporites precipitated in these basins as a consequence of increased marine restriction and isolation. Here we show a stratigraphic correlation between the evaporite records of these basins based on geochemical indicators. We use SO₄ isotope compositions and Sr isotopic ratios in gypsum, and halite Br contents to characterize these units and to identify the marine or continental source of the waters feeding the evaporite basins. In addition, we review the available chronological information used to date these evaporites in Lorca (La Serrata Fm), including a thick saline deposit, that we correlate with the First Evaporitic Group in Fortuna (Los Baños Fm). This correlation is also supported by micropalaeontological data, giving a Late Tortonian age for this sequence. The Second Evaporitic Group, (Chicamo Fm), and the Third Evaporitic Group (Rambla Salada Fm) developed only in Fortuna during the Messinian. According to the palaeogeographical scheme presented here, the evaporites of the Lorca and Fortuna basins were formed during the Late Tortonian—Early Messinian, close to the Betic Seaway closure. Sulphate isotope compositions and Sr isotopic ratios of the Ribera Gypsum Mb, at the base of the Rambla Salada Fm (Fortuna basin), match those of the Late Messinian selenite gypsum beds in San Miguel de Salinas, in the near Bajo Segura basin (40 km to the East), and other Messinian Salinity Crisis gypsum deposits in the Mediterranean. According to these geochemical indicators and the uncertainty of the chronology of this unit, the assignment of the Rambla Salada Fm to the MSC cannot be ruled out.     

Tectonic heritage in drainage pattern and dynamics: the case of the French South Alpine Foreland Basin (ca. 45–20 Ma)

The spatial and temporal organization of depositional environments in drainage networks of foreland basins reflect the tectonic and erosional dynamics associated with the development of mountain belts. We provide field evidences for the initiation and evolution of a complex drainage system in the French South Alpine Foreland Basin related to Western Alps exhumation. Sedimentological and structural analyses of the Eocene–Early Miocene succession were investigated in the (1) Argens/Peyresq, (2) Barrême/Blieux/Taulanne and (3) Montmaur/St‐Disdier sectors. Combined with the existing structural data set, we propose a new model that integrates the regional tectonic activity, the palaeovalley orientation and their dynamics through time. The Eocene–Miocene deposits clearly show the existence of N–S‐oriented palaeovalleys. The systematic presence of early NE–SW‐ to N–S‐oriented strike‐slip and extensional faults in the palaeovalleys suggests that these tectonic structures were responsible for the formation of the initial N–S‐oriented basin‐floor topographies. The vertical offset of the strike‐slip faults induced sufficient accommodation space for the Cenozoic sedimentation since the Middle Eocene. It implies the creation of N–S‐oriented palaeovalleys during the northward Pyrenean‐Provençal phase, pre‐dating westward Alpine compression. Later, the Oligocene Alpine tectonic phase induced drainage expansion toward the orogenic wedge and the erosion of the exhumed internal massifs by transverse streams. The establishment of new connections between the old topographic lows formed a longitudinal drainage pattern that remains the locus of deposition in a regional sedimentary routing system. In this model, former strike‐slip faults correspond to weakness zones overprinted by the westward Alpine shortening that allowed the formation of the modern piggyback basin structure of the foreland and the long‐time preservation of the palaeovalley geometry.     

Anomalous passive subsidence of deep‐water sedimentary basins: a prearc basin example,southern New Caledonia Trough and Taranaki Basin,New Zealand

Stratigraphic data from petroleum wells and seismic reflection analysis reveal two distinct episodes of subsidence in the southern New Caledonia Trough and deep‐water Taranaki Basin. Tectonic subsidence of ~2.5 km was related to Cretaceous rift faulting and post‐rift thermal subsidence, and ~1.5 km of anomalous passive tectonic subsidence occurred during Cenozoic time. Pure‐shear stretching by factors of up to 2 is estimated for the first phase of subsidence from the exponential decay of post‐rift subsidence. The second subsidence event occured ~40 Ma after rifting ceased, and was not associated with faulting in the upper crust. Eocene subsidence patterns indicate northward tilting of the basin, followed by rapid regional subsidence during the Oligocene and Early Miocene. The resulting basin is 300–500 km wide and over 2000 km long, includes part of Taranaki Basin, and is not easily explained by any classic model of lithosphere deformation or cooling. The spatial scale of the basin, paucity of Cenozoic crustal faulting, and magnitudes of subsidence suggest a regional process that acted from below, probably originating within the upper mantle. This process was likely associated with inception of nearby Australia‐Pacific plate convergence, which ultimately formed the Tonga‐Kermadec subduction zone. Our study demonstrates that shallow‐water environments persisted for longer and their associated sedimentary sequences are hence thicker than would be predicted by any rift basin model that produces such large values of subsidence and an equivalent water depth. We suggest that convective processes within the upper mantle can influence the sedimentary facies distribution and thermal architecture of deep‐water basins, and that not all deep‐water basins are simply the evolved products of the same processes that produce shallow‐water sedimentary basins. This may be particularly true during the inception of subduction zones, and we suggest the term ‘prearc’ basin to describe this tectonic setting.     

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.     

Characteristics of the wedge-top depozone of the southern Taiwan foreland basin system

The wedge‐top depozone in the southern Taiwan foreland basin system is confined by the topographic front of the Chaochou Fault to the east and by a submarine deformation front to the west. The Pingtung Plain, Kaoping Shelf and Kaoping Slope constitute the main body of the wedge‐top depozone. In a subaerial setting, the alluvial and fluvial sediments accumulate on top of the frontal parts of the Taiwan orogenic wedge to form the Pingtung Plain proximal to high topographic relief. In a submarine setting, fine‐grained sediments accumulate on the Kaoping Shelf and dominant mass‐wasting sediment forms the Kaoping Slope. Wedge‐top sediments are deformed into a series of west‐vergent imbricated thrusts and folds and associated piggyback basins. A major piggyback basin occurs in the Pingtung Plain. Four smaller piggyback basins appear in the shelf–slope region. Many small‐sized piggyback basins developed over ramp folds in the lower slope region. Pliocene–Quaternary deep marine to fluvial sediments about 5000 m thick have been deposited on top of the frontal orogenic wedge in southern Taiwan. Sedimentary facies shows lateral variations from extremely coarse fluvial conglomerates proximal to the topographic front (Chaochou Fault) to fine‐grained deep marine mud close to the deformation front near the base of the slope. The stratigraphic column indicates that offshore deep‐water mud is gradationally overlain by shallow marine sands and then fluvial deposits. The transverse cross‐section of the wedge‐top depozone in the southern Taiwan is a doubly tapered prism. The northern boundary of the wedge‐top depozone in southern Taiwan is placed along the southern limit of the Western Foothills where the frontal orogenic wedge progressively changes southward to a wedge‐top depozone (Pingtung Plain), reflecting ongoing southward oblique collision between the Luzon Arc and the Chinese margin. The wedge‐top depozone is bounded to the south by the continent–ocean crust boundary. The deep slope west of the Hengchun Ridge can be viewed as an infant wedge‐top depozone, showing initial mountain building and the beginning of wedge‐top depozone.     

Evolution of a Neoproterozoic to Palaeozoic intracratonic setting, Officer Basin, South Australia

The Neoproterozoic basins of central Australia share many features of architecture and sedimentary fill, suggesting common large-scale extrinsic causal mechanisms. In an attempt to improve understanding of these mechanisms we have gathered and analysed new deep seismic reflection data and re-evaluated existing seismic and well-log data from the eastern Officer Basin, the largest and most poorly known of Australia's intracratonic basins. The Officer Basin is asymmetric and has a steep thrust-controlled northern margin paralleled by sub-basins as much as 10 km in depth. Further south the basin shallows gradually onto a broad platform. The basin rests on a thick crust (≈42 km) that is pervaded by a complex of northward-dipping surfaces most of which terminate erosionally against the sediments of the Officer Basin and are interpreted as prebasinal features, possibly faults. Some appear to have been zones of crustal weakness which were reactivated as thrust complexes and played a major role in basin evolution. The sedimentary succession can be subdivided into six megasequences separated by major tectonically and erosionally enhanced sequence boundaries. The megasequences have distinctive sequence stacking patterns suggesting that they were deposited in response to episodic subsidence induced by a major extrinsic tectonic event. The basin initially formed as part of a giant sag basin which incorporated all the present-day intracratonic basins (Amadeus, Georgina, Ngalia, Officer and Savory Basins) in a single large ‘superbasin’ perhaps as a response to mantle processes. Subsidence then ceased for ≈100 Myr producing a regional erosion surface. Beginning in the Torrensian or Sturtian five more major events of varying regional significance influenced the basin's evolution. Four were compressional events, the first of which activated major thrust complexes along the present basin margins, forming deep foreland sub-basins with elevated intervening basement blocks. Once activated, the thrust complexes and sub-basins persisted throughout the life of the intracratonic basins. From this epoch the intracratonic basins of central Australia were decoupled from the giant sag basin and became interrelated but independent features. Available information suggests that the Officer, Amadeus, Georgina, Ngalia and Savory Basins are related and are perhaps products of major tectonic events associated with the assembly and ultimate dispersal of the Proterozoic supercontinent. The closing phases of these basins were strongly influenced by events occurring along the newly created active eastern margin of the Australian continent in the Palaeozoic.     

Early Middle Miocene broken foreland development in the southern Central Andes: evidence for extension prior to regional shortening

Most authors suggest that the main contraction phases in the southern Central Andes started in the Late Miocene. Along the flat‐slab segment, deformation has progressively involved basement and a broken foreland has developed. Recent work suggests that construction of the Andes by late Neogene shortening may have been controlled by lithospheric thinning and crustal structure generated during mid‐Tertiary times in the Southern and Central Andes. Exposures at the eastern border of the Famatina Ranges in western Argentina in the flat‐slab segment document basement involved extension of approximately this age. The Del Abra Formation, the lower unit of a major Andean synorogenic cycle (Angulos Group), reveals a distinct and previously unrecognized early Middle Miocene tectonic event. This is suggested by a 505‐m‐thick thinning‐ and fining‐upward megasequence. Dominantly conglomeratic facies record a continuous progression from fault‐scarp‐related high‐gradient colluvium to relatively distal terminal‐fan facies. The fining–thinning upward megasequence characterizes progressive scarp backstepping and decreasing relief after active extension. Interpretation of the stratigraphic fill and the associated structure (high‐angle hinterland‐dipping fault) favours tectonic inversion of an originally normal fault. This allows reappraisal and new understanding of the early‐stage architecture of the Central Andean foreland. Early Middle Miocene extension may have had an important bearing on the later evolution of the broken foreland.     

Extensional tectonic regimes in the Aegean basins during the Cenozoic

Abstract Kinematics of faults in the Northern Aegean show three extensional tectonic regimes the tensional directions of which trend (1) WNW-ESE, (2) NE-SW and (3) N-S. These were active during the Upper Miocene, Pliocene-Lower Pleistocene and Mid Pleistocene-Present day, respectively. The main characteristics of the stress patterns (1) and (2) on the overall Aegean is tentatively explained by variations of the horizontal lithospheric stress value σ_zz due to the slab push and of the vertical lithospheric stress value σ_zz due to mass heterogeneities. During the Mid Pleistocene-Present, due to the slab push, tectonics were compressional along the arc boundary: σ_zz was σ1. In the Aegean basins, tectonics were extensional, c_2Z was σ1 as a consequence of the thickness of the continental crust and, possibly of an updoming asthenosphere; thus σ_zz became σ2, allowing tension σ3 to be orthogonal to the compression along the arc, i.e. to be roughly parallel to the arc trend. During the Pliocene-Lower Pleistocene, the extensional regime was distinctly different. The tensional directions were roughly radial to the arc. It is suggested that σ_zz was weakly compressional, or eventually tensional, due a seaward migration of the slab so that σ_zz became σ3. In the Northern Aegean, the stress pattern has been also controlled by the westward push of the Anatolian landmass. During the Mid Pleistocene-Present day, this was typically extensional (al was vertical) and the right lateral strike-slip motion on the North Anatolian Fault transformed into a N-S-stretching, E-W-shortening of the Northern Aegean. Dextral strike-slip motions along the North Aegean Trough fault zone were possible on NE-SW-striking faults. During the Pliocene-Lower Pleistocene, normal fault components were higher; however, because the angle between the NE-SW trend of the tensional axis and the strike of the fault zone was acute, dextral strike-slip components were possible on all the faults striking NE-SW to E-W. A clockwise 15^o rotation of Limnos with respect to Samothraki, Thraki and Thassos, suggested by structural data, was probably associated with these dextral motions. The WNW-ESE trending tension during the Upper Miocene indicates that the dextral North Anatolian Fault had not yet merged into the North Aegean Trough fault zone at that time. We propose that the formation of Aegean basins during the Cenozoic was related to the activity of two major Hellenic arcs. The ‘Pelagonian-Pindic Arc’ resulted in the formation of the subsident Aegean basins of Middle Eocene-Lower Miocene age and of the older Northern Aegean orogenic volcanism. The ‘Aegean Arc’ resulted in the formation of the subsident Aegean basins of Middle Miocene to Present day age and of the Southern Aegean orogenic volcanism. Were these arcs associated with a unique subduction zone or with two such zones ? In the first case, the slab is no more than 16 Myr old, in the second it may be as old as 45–50 Myr. The answer depends on the accuracy of the seismic tomography profiles.     

Tectonic and oceanographic control of sedimentary patterns in a small oceanic basin: Dove Basin (Scotia Sea,Antarctica)

Dove Basin, a small oceanic domain located within the southern Scotia Sea, evidences a complex tectonic evolution linked to the development of the Scotia Arc. The basin also straddles the junction between the main Southern Ocean water masses: the Antarctic Circumpolar Current (ACC), the Southeast Pacific Deep Water (SPDW) and the Weddell Sea Deep Water (WSDW). Analysis of multichannel seismic reflection profiles, together with swath bathymetry data, reveals the main structure and sediment distribution of the basin, allowing a reconstruction of the tectonostratigraphic evolution of the basin and assessment of the main bottom water flows that influenced its depositional development. Sediment dispersed in the basin was largely influenced by gravity‐driven transport from adjacent continental margins, later modified by deep bottom currents. Sediments derived from melting icebergs and extensive ice sheets also contributed to a fraction of the basin deposits. We identify four stages in the basin evolution which – based on regional age assumptions – took place during the early Miocene, middle Miocene, late Miocene–early Pliocene and late Pliocene–Quaternary. The onsets of the ACC flow in Dove Basin during the early Miocene, the WSDW flow during the middle Miocene, and the SPDW during the late Miocene were influenced by tectonic events that facilitated the opening of new oceanic gateways in the region. The analysis of Dove Basin reveals that tectonics is a primary factor influencing its sedimentary stacking patterns, the structural development of new oceanic gateways permitting the inception of deep‐water flows that have since controlled the sedimentary processes.     

Gravity constraints on the dynamics of the crust–mantle system during Calabrian subduction

The thermomechanic evolution of the lithosphere–upper mantle system during Calabrian subduction is analysed using a 2-D finite element approach, in which the lithosphere is compositionally stratified into crust and mantle. Gravity and topography predictions are cross-checked with observed gravity and topography patterns of the Calabrian region. Modelling results indicate that the gravity pattern in the arc-trench region is shaped by the sinking of light material, belonging to both the overriding and subduction plates. The sinking of light crustal material, up to depths of the order of 100–150 km is the ultimate responsible for the peculiar gravity signature of subduction, characterized by a minimum of gravity anomaly located at the trench, bounded by two highs located on the overriding and subducting plates, with a variation in magnitude of the order of 200 mGal along a wavelength of 200 km, in agreement with the isostatically compensated component of gravity anomaly observed along a transect crossing the Calabrian Arc, from the Tyrrhenian to the Ionian Seas. The striking agreement between the geodetic retrieved profiles and the modelled ones in the trench region confirms the crucial role of compositional stratification of the lithosphere in the subduction process and the correctness of the kinematic hypotheses considered in our modelling, that the present-day configuration of crust–mantle system below the Calabrian arc results from trench's retreat at a rate of about 3 cm yr⁻¹, followed by gravitational sinking of the subducted slab in the last 5 Myr.     

Tectono-sedimentary evolution of Jurassic–Cretaceous diapiric structures: Miravete anticline,Maestrat Basin,Spain

Integration of extensive fieldwork, remote sensing mapping and 3D models from high-quality drone photographs relates tectonics and sedimentation to define the Jurassic–early Albian diapiric evolution of the N–S Miravete anticline, the NW-SE Castel de Cabra anticline and the NW-SE Cañada Vellida ridge in the Maestrat Basin (Iberian Ranges, Spain). The pre shortening diapiric structures are defined by well-exposed and unambiguous halokinetic geometries such as hooks and flaps, salt walls and collapse normal faults. These were developed on Triassic salt-bearing deposits, previously misinterpreted because they were hidden and overprinted by the Alpine shortening. The Miravete anticline grew during the Jurassic and Early Cretaceous and was rejuvenated during Cenozoic shortening. Its evolution is separated into four halokinetic stages, including the latest Alpine compression. Regionally, the well-exposed Castel de Cabra salt anticline and Cañada Vellida salt wall confirm the widespread Jurassic and Early Cretaceous diapiric evolution of the Maestrat Basin. The NE flank of the Cañada Vellida salt wall is characterized by hook patterns and by a 500-m-long thin Upper Jurassic carbonates defining an upturned flap, inferred as the roof of the salt wall before NE-directed salt extrusion. A regional E-W cross section through the Ababuj, Miravete and Cañada-Benatanduz anticlines shows typical geometries of salt-related rift basins, partly decoupled from basement faults. These structures could form a broader diapiric region still to be investigated. In this section, the Camarillas and Fortanete minibasins displayed well-developed bowl geometries at the onset of shortening. The most active period of diapiric growth in the Maestrat Basin occurred during the Early Cretaceous, which is also recorded in the Eastern Betics, Asturias and Basque-Cantabrian basins. This period coincides with the peak of eastward drift of the Iberian microplate, with speeds of 20 mm/year. The transtensional regime is interpreted to have played a role in diapiric development.     

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.