Distinguishing fault reactivation from flexural deformation in the distal stratigraphy of the Peripheral Blountian Foreland Basin, southern Appalachians, USA

Reactivation of intraplate structures and weak zones within the foreland lithosphere disrupt the modelled geometry and pattern of migration of the flexural wave in foreland basins. In the southern Appalachians (USA), the Middle Ordovician unconformity, irregular Middle Ordovician distal foreland deposition and backstepping of Middle–lower Upper Ordovician carbonate strata have been related to migration of the flexural wave. However, integration of stratigraphy, tectonic subsidence history and composition of palinspastically restored distal foreland strata, using a map of subsurface basement structures as reference, allows us to distinguish an early event of inversion from two events of flexural migration. Sections restoring at very short distances outside the boundaries of a former basement graben have the youngest passive‐margin strata preserved beneath Middle Ordovician (～466 Ma) peritidal to deep lagoonal carbonates with gravel‐size chert clasts. In contrast, sections restoring inside the graben record >470 m of truncation of pre‐Middle Ordovician passive‐margin strata, late onset of deposition (～456 Ma), and subaerial features in carbonate and siliciclastic strata. The lacuna geometry and early patterns of distal foreland uplift and carbonate deposition indicate that inversion of a basement graben in response to Middle Ordovician convergence, rather than a migrating or semi‐fixed forebulge, was the primary control on the early evolution of the distal foreland. Drowning of the carbonate platform in more proximal settings, northeastward onset of deposition on upthrown blocks, and thick accumulation of carbonates in downthrown blocks record northwestward and northeastward flexural wave migration at the Middle–Late Ordovician boundary. In early Late Ordovician, the overall shoaling of carbonate and siliciclastic depocentres and the rise of tectonic subsidence curves indicate hinterlandward migration of flexural uplift. Both events of flexural migration were accompanied by influx of volcanic ash and synorogenic sediments.     

Sequence architecture and depositional evolution of the Ordovician carbonate platform margins in the Tarim Basin and its response to tectonism and sea‐level change

The sequence architecture and depositional evolution of the Ordovician carbonate platform margins in the Tarim Basin, China, were formed in response to the interplay of tectonism and sea‐level change, their history being documented by the integrated analysis of many seismic lines, drilling and outcrop data. The Ordovician carbonate system in the basin is divided into four composite sequences defined by major unconformities. Each sequence consists of a regional depositional cycle from transgression with an onlapping transgressive systems tract (TST) to regression with a prograding highstand systems tract (HST), and can be further subdivided into 10 third‐order sequences based on subordinate discontinuous boundaries at the carbonate platform marginal zones. Constrained by the marginal slope of the early‐rifted Manjiaer aulacogen, the carbonate platform margins of the Lower and Middle Ordovician that prograded eastward in an arcuate belt extending generally north‐south across the northern part of the basin. The development of the Tazhong uplift due to compression resulted in an extensive paleokarst hiatus between the Middle and the Upper Ordovician in the south‐central basin, and subsequently constrained the formation of a peninsula‐shaped carbonate platform whose margins were controlled by marginal thrust‐fault belts of the paleo‐uplift during the Late Ordovician. In the northern basin, the Late Ordovician carbonate platform margin developed around the marginal slope of the Tabei paleouplift. The transgressive–regressive cycles of the carbonate system are comparable and seem to have occurred simultaneously across the entire basin, suggesting that the cyclic sequence architecture was fundamentally controlled by eustatic fluctuations. Stacking patterns of the composite sequences varied due to the interplay between the accommodation produced by tectonism and sea‐level change, and the carbonate production rate. The reef–shoal facies complexes that developed along the platform margins, with paleokarst development at unconformities, constitute the major reservoir of large petroleum reserves in the basin.     

Ordovician tectonic transition from passive margin into peripheral foreland in the southern Ordos: A diagnostic insight into the closure of Erlangping Ocean between the North Qinling Arc and North China Block

Achieving a reliable closure time of a back-arc ocean is an essential aspect in studies on detailed tectonic processes of an active continental margin and arc–continent collision. This is particularly the case for the northern Qinling Orogen, which records the accretion of the North Qinling Arc (NQA) onto the North China Block (NCB) after the Erlangping back-arc ocean closure. Sedimentological, petrological and geochronological signatures from the Ordovician successions in the southern Ordos reveal a tectonic transition from passive continental margin to peripheral foreland in the southern NCB at the beginning of Katian. Sedimentological and geochronological investigations reveal an abrupt shift of accelerating basin subsidence and deepening at the earliest Katian, separating ca. 300-m-thick shallow-marine carbonate shelf assemblages from overlying ca. 2000-m-thick deep-water carbonate slope and turbidite associations. Zircon age spectra of the Katian turbidites are characterized by early-Palaeozoic and Neoproterozoic age clusters, which are different from those of the Middle Ordovician quartz arenites sourced merely from the NCB basement. Instead, these age patterns match well with those of the coeval successions in the northern NQA, indicating a spatially linked abyssal deposystem. Stratigraphic architecture deciphers a typical foreland basin geometry, involving, from south to north, northward-propagating turbiditic wedge, northward-backstepping carbonate slope and progressively shoaling carbonate platform, embodying foredeep, forebulge and backbulge, respectively. These characteristics of basin-fill evolution reflect the northward migration of the flexural wave as a dynamic response to the northward expansion of the thickened NQA thrust wedge. Together with the other geological and geochronological data, our new insights indicate a southward subduction polarity of the Erlangping back-arc oceanic crust followed by its termination at ca. 450 Ma, which was earlier than that of the main Proto-Tethyan Shangdan Ocean between the NCB and South China Block. Our new data provide an updated view of the complex history of the Proto-Tethys closure during the Gondwana assembly.     

Appalachian basin stratigraphic response to convergent-margin structural evolution

ABSTRACT From study of Palaeozoic formations in the Appalachian foreland basin, a predictive stratigraphic model is proposed based on facies tract development during convergent-margin structural evolution. Five major facies tracts are recognized: shallow-water carbonates that formed during interorogenic quiescence and initial foreland subsidence; deep-water siliciclastics that accumulated in the proximal foreland basin during early collision; syn-collisional shallow-water siliciclastics; syn-collisional, channellized fluvial sandstones that aggraded in the proximal foreland; and progradational shoreline sandstones that were deposited in response to filling of the proximal foreland. Two other facies tracts that occur are organic-rich siliciclastics ('black shales'), which accumulated in oxygen-deficient areas of low clastic-sediment influx, and incised valley-fill deposits, which formed where subsidence rate was low.
Because the origin of each facies tract is dependent upon a unique combination of rate of accommodation change and rate of sediment supply, facies tract distribution is predictable from spatial and temporal patterns of subsidence and uplift associated with plate convergence. Alternating phases of thrust loading and quiescence caused fluctuations between underfilled and overfilled conditions during Palaeozoic evolution of the Appalachian basin. Along-strike variations in stratigraphic thickness, facies tract distribution, and development of unconformities in the Appalachian basin reflect the influence of structural irregularities along the collisional margin. In distal parts of the Appalachian foreland and in areas of structural recesses, eustatic influence on stratigraphic patterns is expressed more clearly than in areas of higher subsidence rate.     

Along-strike variations in foreland basin evolution: possible evidence for continental collision along an irregular margin

Abstract The evolution of a passive margin to a foreland basin is generally assumed to entail early load-induced up warping of the stable continental platform followed by foreland subsidence. This relatively straightforward elastic response of the continental platform, however, may be complicated if the colliding passive margin is irregular in outline. In a tectonic scenario in which an irregular margin is migrating toward a trench (A-subduction), those areas of the margin which project seaward, the continental promontories, would be the first to 'feel' the approaching thrust terrane by flexing upward and eroding to form shelf unconformities. Those parts of the continental margin that are convex to the craton, the continental re-entrants, however, would remain subsiding depocentres unaffected by load-induced uplift at the promontories. Careful analysis of the geographic distribution of shelf unconformities in orogenic belts, then, may help to reveal the pre-deformation morphology of the passive continental margin. An example of this may be found in the early phases of Ordovician foreland basin development in the central Appalachian orogen. Here, the shelf unconformities are most pronounced (greatest erosional relief) at the inferred Virginia and New York continental promontories. An adjacent inferred continental re-entrant, the Pennsylvania re-entrant, is characterized by an uninterrupted Ordovician sequence suggesting that the area of the proto-North American platform, represented by this segment of the orogen, remained a depocentre during uplift in adjacent areas of the continental margin.     

Anticosti foreland basin offshore of western Newfoundland: Concealed record of northern Appalachian orogen development

The Anticosti Basin, largely hidden beneath the Gulf of St. Lawrence, includes foreland basin successions that record multiple tectonic events associated with the Ordovician to Devonian evolution of the northern Appalachian orogen. Due to the lack of well ties and minimal onshore exposure, geophysical data must be used in mapping the offshore stratigraphy. Outcropping geologic boundaries are tied to magnetic lineaments that parallel stratigraphy. These lineaments are correlated with reflections on seismic profiles in order to interpret the subsurface. Seismic isochron maps for successive basin development episodes display differences in geometry, implying that orogenic loading varied through time. The geometry and subsidence rates recorded by the Middle Ordovician Goose Tickle Group imply that it formed in a pro-arc setting associated with loading during arc-continent collision that was most intense in the northern Newfoundland Appalachians. The geometry and subsidence recorded by the overlying Long Point Group imply pro-arc loading by Taconian allochthons in the Québec segment of the orogen. Diachronous subduction polarity reversal along the margin placed the Long Point Group in a combined retro-arc and pro-arc setting, comparable to that experienced by parts of the north Australian margin at the present day. The uppermost Silurian to Lower Devonian Clam Bank Formation and Lower Devonian Red Island Road Formation represent foreland basin successions associated with the later Salinian and Acadian orogenies. Their consistent thickness implies a broad, shallow basin, suggesting that the lithosphere was cooler and stronger than during earlier subsidence, and are consistent with a retro-arc setting.     

The Miocene Saint-Florent Basin in northern Corsica: stratigraphy, sedimentology, and tectonic implications

Late early–early middle Miocene (Burdigalian–Langhian) time on the island of Corsica (western Mediterranean) was characterized by a combination of (i) postcollisional structural inversion of the main boundary thrust system between the Alpine orogenic wedge and the foreland, (ii) eustatic sealevel rise and (iii) subsidence related to the development of the Ligurian‐Provençal basin. These processes created the accommodation for a distinctive continental to shallow‐marine sedimentary succession along narrow and elongated basins. Much of these deposits have been eroded and presently only a few scattered outcrop areas remain, most notably at Saint‐Florent and Francardo. The Burdigalian–Langhian sedimentary succession at Saint‐Florent is composed of three distinguishing detrital components: (i) siliciclastic detritus derived from erosion of the nearby Alpine orogenic wedge, (ii) carbonate intrabasinal detritus (bioclasts of shallow‐marine and pelagic organisms), and (iii) siliciclastic detritus derived from Hercynian‐age foreland terraines. The basal deposits (Fium Albino Formation) are fluvial and composed of Alpine‐derived detritus, with subordinate foreland‐derived volcanic detritus. All three detrital components are present in the middle portion of the succession (Torra and Monte Sant'Angelo Formations), which is characterized by thin transitional deposits evolving vertically into fully marine deposits, although the carbonate intrabasinal component is predominant. The Monte Sant'Angelo Formation is characteristically dominated by the deposits of large gravel and sandwaves, possibly the result of current amplification in narrow seaways that developed between the foreland and the tectonically collapsing Alpine orogenic wedge. The laterally equivalent Saint‐Florent conglomerate is composed of clasts derived from the late Permian Cinto volcanic district within the foreland. The uppermost unit (Farinole Formation) is dominated by bioclasts of pelagic organisms. The Saint‐Florent succession was deposited during the last phase of the counterclockwise rotation of the Corsica–Sardinia–Calabria continental block and the resulting development of the Provençal oceanic basin. The succession sits at the paleogeographic boundary between the Alpine orogenic wedge (to the east), its foreland (to the west), and the Ligurian‐Provençal basin (to the northwest). Abrupt compositional changes in the succession resulted from the complex, varying interplay of post‐collisional extensional tectonism, eustacy and competing drainage systems.     

Late Ordovician,deep‐water gravity‐flow deposits,palaeogeography and tectonic setting,Tarim Basin,Northwest China

The Upper Ordovician in the Tarim Basin contains 5000–7000 m of siliciclastic and calciclastic deep‐water, gravity‐flow deposits. Their depositional architecture and palaeogeographical setting are documented in this investigation based on an integrated analysis of seismic, borehole and outcrop data. Six gravity‐flow depositional–palaeogeomorphological elements have been identified as follows: submarine canyon or deeply incised channels, broad and shallow erosional channels, erosional–depositional channel and levee–overbank complexes, frontal splays‐lobes and nonchannelized sheets, calciclastic lower slope fans and channel lobes or sheets, and debris‐flow complexes. Gravity‐flow deposits of the Sangtamu and Tierekeawati formations comprise a regional transgressive‐regressive megacycle, which can be further classified into six sequences bounded by unconformities and their correlative conformities. A series of incised valleys or canyons and erosional–depositional channels are identifiable along the major sequence boundaries which might have been formed as the result of global sea‐level falls. The depositional architecture of sequences varies from the upper slope to abyssal basin plain. Palaeogeographical patterns and distribution of the gravity‐flow deposits in the basin can be related to the change in tectonic setting from a passive continental margin in the Cambrian and Early to Middle Ordovician to a retroarc foreland setting in the Late Ordovician. More than 3000 m of siliciclastic submarine‐fan deposits accumulated in south‐eastern Tangguzibasi and north‐eastern Manjiaer depressions. Sedimentary units thin onto intrabasinal palaeotopographical highs of forebulge origin and thicken into backbulge depocentres. Sediments were sourced predominantly from arc terranes in the south‐east and the north‐east. Slide and mass‐transport complexes and a series of debris‐flow and turbidite deposits developed along the toes of unstable slopes on the margins of the deep‐water basins. Turbidite sandstones of channel‐fill and frontal‐splay origin and turbidite lobes comprise potential stratigraphic hydrocarbon reservoirs in the basin.     

Importance of predecessor basin history on sedimentary fill of a retroarc foreland basin: provenance analysis of the Cretaceous Magallanes basin,Chile (50–52°S)

An integrated provenance analysis of the Upper Cretaceous Magallanes retroarc foreland basin of southern Chile (50°30′–52°S) provides new constraints on source area evolution, regional patterns of sediment dispersal and depositional age. Over 450 new single‐grain detrital‐zircon U‐Pb ages, which are integrated with sandstone petrographic and mudstone geochemical data, provide a comprehensive detrital record of the northern Magallanes foreland basin‐filling succession (>4000‐m‐thick). Prominent peaks in detrital‐zircon age distribution among the Punta Barrosa, Cerro Toro, Tres Pasos and Dorotea Formations indicate that the incorporation and exhumation of Upper Jurassic igneous rocks (ca. 147–155 Ma) into the Andean fold‐thrust belt was established in the Santonian (ca. 85 Ma) and was a significant source of detritus to the basin by the Maastrichtian (ca. 70 Ma). Sandstone compositional trends indicate an increase in volcanic and volcaniclastic grains upward through the basin fill corroborating the interpretation of an unroofing sequence. Detrital‐zircon ages indicate that the Magallanes foredeep received young arc‐derived detritus throughout its ca. 20 m.y. filling history, constraining the timing of basin‐filling phases previously based only on biostratigraphy. Additionally, spatial patterns of detrital‐zircon ages in the Tres Pasos and Dorotea Formations support interpretations that they are genetically linked depositional systems, thus demonstrating the utility of provenance indicators for evaluating stratigraphic relationships of diachronous lithostratigraphic units. This integrated provenance dataset highlights how the sedimentary fill of the Magallanes basin is unique among other retroarc foreland basins and from the well‐studied Andean foreland basins farther north, which is attributed to nature of the predecessor rift and backarc basin.     

Ordovician tectonic shift in the western North China Craton constrained by stratigraphic and geochronological analyses

The western North China Craton (W-NCC) comprises the Alxa Terrane in the west and the Ordos Block in the east; they are separated by the Helanshan Tectonic Belt (HTB). There is an extensive debate regarding the significant Ordovician tectonic setting of the W-NCC. Most paleogeographic reconstructions emphasized the formation and rapid subsidence of an aulacogen along the HTB during the Middle–Late Ordovician, whereas paleomagnetic and geochronologic results suggested that the Alxa Terrane and the Ordos Block were independent blocks separated by the HTB. In this study, stratigraphic and geochronologic methods were used to constrain the Ordovician tectonic processes of the W-NCC. Stratigraphic correlations show that the Early Ordovician strata comprise ~500-m-thick tidal flat and lagoon carbonate successions with a progressive eastward onlap, featuring a west-deepening shallow-water carbonate shelf. In contrast, the Late Ordovician strata are composed of ~3,000-m-thick abyssal turbidites in the west and ~400-m-thick shallow-water carbonates in the east, defining an eastward-tapering basin architecture. Early Ordovician detrital zircons with ages of ~2,800–1,700 Ma were derived from the Ordos Block; the Late Ordovician turbidites were sourced from the western Alxa Terrane, based on zircon ages clustered at ~1,000–900 Ma. The petrographic modal composition and zircon age distribution imply a provenance shift from a stable craton to a recycled orogen in the Middle Ordovician. These shifts define a tectonic conversion from a passive continental margin to a foreland basin at ~467 Ma, resulting in the eastward progradation of the turbidite wedge around the HTB, the eastward backstepping of the carbonate platform in the east and the eastward expansion of orogenic thrusting in the western Alxa Terrane. This tectono-sedimentary shift coincided with the advancing subduction of the southern Paleo-Asian Ocean beneath the Alxa Terrane, generating the western Alxa continental arc and the paired retro-arc foredeep in the east under a compressional tectonic regime.     

Detrital zircon geochronology of pre‐ and syncollisional strata,Acadian orogen,Maine Appalachians

The Central Maine Basin is the largest expanse of deep‐marine, Upper Ordovician to Devonian metasedimentary rocks in the New England Appalachians, and is a key to the tectonics of the Acadian Orogeny. Detrital zircon ages are reported from two groups of strata: (1) the Quimby, Rangeley, Perry Mountain and Smalls Falls Formations, which were derived from inboard, northwesterly sources and are supposedly older; and (2) the Madrid, Carrabassett and Littleton Formations, which were derived from outboard, easterly sources and are supposedly younger. Deep‐water deposition prevailed throughout, with the provenance shift inferred to mark the onset of foredeep deposition and orogeny. The detrital zircon age distribution of a composite of the inboard‐derived units shows maxima at 988 and 429 Ma; a composite from the outboard‐derived units shows maxima at 1324, 1141, 957, 628, and 437 Ma. The inboard‐derived units have a greater proportion of zircons between 450 and 400 Ma. Three samples from the inboard‐derived group have youngest age maxima that are significantly younger than the nominal depositional ages. The outboard‐derived group does not share this problem. These results are consistent with the hypothesised provenance shift, but they signal potential problems with the established stratigraphy, structure, and (or) regional mapping. Shallow‐marine deposits of the Silurian to Devonian Ripogenus Formation, from northwest of the Central Maine Basin, yielded detrital zircons featuring a single age maximum at 441 Ma. These zircons were likely derived from a nearby magmatic arc now concealed by younger strata. Detrital zircons from the Tarratine Formation, part of the Acadian foreland‐basin succession in this strike belt, shows age maxima at 1615, 980 and 429 Ma. These results are consistent with three episodes of zircon recycling beginning with the deposition of inboard‐derived strata of the Central Maine Basin, which were shed from post‐Taconic highlands located to the northwest. Next, southeasterly parts of this succession were deformed in the Acadian orogeny, shedding detritus towards the northwest into what remained of the basin. Finally, by Pragian time, all strata in the Central Maine Basin had been deformed and detritus from this new source accumulated as the Tarratine Formation in a new incarnation of the foreland basin. Silurian‐Devonian strata from the Central Maine Basin have similar detrital zircon age distributions to coeval rocks from the Arctic Alaska and Farewell terranes of Alaska and the Northwestern terrane of Svalbard. We suggest that these strata were derived from different segments of the 6500‐km‐long Appalachian‐Caledonide orogen.     

Evolution of the Longmen Shan Foreland Basin (Western Sichuan, China) during the Late Triassic Indosinian Orogeny

The Longmen Shan Foreland Basin developed as a flexural foredeep during the Late Triassic Indosinian orogeny, spanning the time period c. 227–206 Ma. The basin fill can be divided into three tectonostratigraphic units overlying a basal megasequence boundary, and is superimposed on the Palaeozoic–Middle Triassic (Anisian) carbonate‐dominated margin of the South China Block. The remains of the load system responsible for flexure of the South China foreland can be seen in the Songpan‐Ganzi Fold Belt and Longmen Shan Thrust Belt. Early in its history the Longmen Shan Foreland Basin extended well beyond its present northwestern boundary along the trace of the Pengguan Fault, to at least the palinspastically restored position of the Beichuan Fault. The basal boundary of the foreland basin megasequence is a good candidate for a flexural forebulge unconformity, passing from conformity close to the present trace of the Beichuan Fault to a karstified surface towards the southeast. The overlying tectonostratigraphic unit shows establishment and drowning of a distal margin carbonate ramp and sponge build‐up, deepening into offshore marine muds, followed by progradation of marginal marine siliciclastics, collectively reminiscent of the Alpine underfilled trinity of Sinclair (1997) . Tectonostratigraphic unit 2 is marked by the severing of the basin's oceanic connection, a major lake flooding and the gradual establishment of major deltaic‐paralic systems that prograded from the eroding Longmen Shan orogen. The third tectonostratigraphic unit is typified by coarse, proximal conglomerates, commonly truncating underlying rocks, which fine upwards into lacustrine shales. The foreland basin stratigraphy has been further investigated using a simple analytical model based on the deflection by supracrustal loads of a continuous elastic plate overlying a fluid substratum. Load configurations have been partly informed by field geology and constrained by maximum elevations and topographic profiles of present‐day mountain belts. The closest match between model predictions and stratigraphic observations is for a relatively rigid plate with flexural rigidity on the order of 5 × 10²³ to 5 × 10²⁴ N m (equivalent elastic thickness of c. 43–54 km). The orogenic load system initially (c. 227–220 Ma) advanced rapidly (>15 mm yr^?1) towards the South China Block in the Carnian, associated with the rapid closure of the Songpan‐Ganzi ocean, before slowing to < 5 mm yr^?1 during the sedimentation of the upper two tectonostratigraphic units (c. 220–206 Ma).     

Late Triassic tectonic inversion in the upper Yangtze Block: Insights from detrital zircon U–Pb geochronology from south‐western Sichuan Basin

The Sichuan Basin and the Songpan‐Ganze terrane, separated by the Longmen Shan fold‐and‐thrust belt (the eastern margin of the Tibetan Plateau), are two main Triassic depositional centres, south of the Qinling‐Dabie orogen. During the Middle–Late Triassic closure of the Paleo‐Tethys Ocean, the Sichuan Basin region, located at the western margin of the Yangtze Block, transitioned from a passive continental margin into a foreland basin. In the meantime, the Songpan‐Granze terrane evolved from a marine turbidite basin into a fold‐and‐thrust belt. To understand if and how the regional sediment routing system adjusted to these tectonic changes, we monitored sediment provenance primarily by using detrital zircon U‐Pb analyses of representative stratigraphic samples from the south‐western edge of the Sichuan Basin. Integration of the results with paleocurrent, sandstone petrology and published detrital zircon data from other parts of the basin identified a marked change in provenance. Early–Middle Triassic samples were dominated by Neoproterozoic (~700–900 Ma) zircons sourced mainly from the northern Kangdian basement, whereas Late Triassic sandstones that contain a more diverse range of zircon ages sourced from the Qinling, Longmen Shan and Songpan‐Ganze terrane. This change reflects a major drainage adjustment in response to the Late Triassic closure of the Paleo‐Tethys Ocean and significant shortening in the Longmen Shan thrust belt and the eastern Songpan‐Ganze terrane. Furthermore, by Late Triassic time, the uplifted northern Kangdian basement had subsided. Considering the eastward paleocurrent and depocenter geometry of the Upper Triassic deposits, subsidence of the northern Kangdian basement probably resulted from eastward shortening and loading of the Songpan‐Ganze terrane over the western margin of the Yangtze Block in response to the Late Triassic collision among Yangtze Block, Yidun arc and Qiangtang terrane along the Ganze‐Litang and Jinshajiang sutures.     

The Svalbard Eocene‐Oligocene (?) Central Basin succession: Sedimentation patterns and controls

A synthesis has been undertaken based on regionally compiled data from the post early Eocene foreland basin succession of Svalbard. The aim has been to generate an updated depositional model and link this to controlling factors. The more than kilometer thick progradational succession includes the offshore shales of the Gilsonryggen Member of the Frysjaodden Formation, the shallow marine sandstones of the Battfjellet Formation and the predominantly heterolithic Aspelintoppen Formation, together recording the progressive eastwards infill of the foredeep flanking the West Spitsbergen fold‐and‐thrust belt. Here we present a summary of the paleo‐environmental depositional systems across the basin, their facies and regional distribution and link these together in an updated depositional model. The basin‐margin system prograded with an ascending shelf‐edge trajectory in the order of 1°. The basin fill was bipartite, with offset stacked shelf and shelf‐edge deltas, slope clinothems and basin floor fans in the western and deepest part and a simpler architecture of stacked shelf‐deltas in the shallower eastern part. We suggest a foredeep setting governed by flexural loading, likely influenced by buckling, and potentially developing into a wedge top basin in the mature stage of basin filling. High‐subsidence rates probably counteracted eustatic falls with the result that relative sea‐level falls were uncommon. Distance to the source terrain was small and sedimentation rates was temporarily high. Time‐equivalent deposits can be found outbound of Stappen High in the Vestbakken Volcanic Province and the Sørvestsnaget Basin 300 km further south on the Barents Shelf margin. We cannot see any direct evidence of coupling between these more southerly systems and the studied one; southerly diversion of the sediment‐routing, if any, may have taken place beyond the limit of the preserved deposits.     

Influence of the mechanical behaviour of brittle–ductile fold–thrust belts on the development of foreland basins

A two‐dimensional mathematical model considering coupling between a deforming elasto‐visco‐plastic fold–thrust belt, flexural subsidence and diffusional surface processes is solved using the Finite Element Method to investigate how the mechanical behaviour of brittle–ductile wedges influences the development of foreland basins. Results show that, depending mainly on the strength of the basal décollement, two end‐member types of foreland basin are possible. When the basal detachment is relatively strong, the foreland basin system is characterised by: (1) Highly asymmetrical orogen formed by thrusts concentrated in the incoming pro‐wedge. (2) Sedimentation on retro‐side takes place in one major foredeep basin which grows throughout orogen evolution. (3) Deposition on the pro‐side occurs initially in the foredeep, and continues in the wedge‐top before isolated basins are advected towards the orogen core where they become uplifted and exhumed. (4) Most pro‐wedge basins show an upward progression from low altitude, foredeep deposits at the base to high altitude, wedge‐top deposits near the surface. In contrast, when the basal detachment behaves weakly due to the presence of low viscosity material such as salt, the foreland basin system is characterised by (1) Broad, low relief orogen showing little preferential vergence and predominance of folding relative to faulting. (2) Deposition mainly in wedge‐top basins showing growth strata. (3) Many basins are initiated contemporaneously but form discontinuously due to the locus of active deformation jumping back and forth between different structures. Model results successfully reproduce first order observations of deforming brittle–ductile wedges and foreland basins. Moreover, the results support and provide a framework for understanding the existence of two main end‐member foreland basin types, simple and complex, associated with fold–thrust belts whose detachments are relatively strong and weak, respectively.     

Long-term Callovian–Oxfordian sea-level changes and sedimentation in the Iberian carbonate platform (Jurassic, Spain): possible eustatic implications

Facies analysis across the carbonate platform developed during the Callovian–Oxfordian in the northern Iberian basin (Jurassic, Northeast Spain) is used to characterize successive stages of sedimentary evolution, including palaeoenvironmental reconstructions showing the distribution of a wide spectrum of facies, from ferruginous oolitic, peloidal, spongiolithic to intraclastic. The studied successions consist of two long‐term transgressive–regressive cycles bounded by a major unconformity with a major gap, comprising at least the upper Lamberti (Callovian) and Mariae (Oxfordian) Zones. Major transgressive peaks of these two cycles occurred at the end of the Early Callovian (late Gracilis Zone) and at the end of the Middle Oxfordian. The Callovian and Oxfordian successions were further divided into three and seven higher frequency cycles, respectively. The modelling of two sections (i.e. Ricla and Tosos) located 40 km apart in the more subsident open platform areas, allows the reconstruction of two curves showing a similar evolution of long‐term sea‐level changes that are in theory eustatic, though subject to uncertainties derived form the assumptions required for their construction. The changes affecting the northern Iberian basin seem to reflect nearly homogeneous subsidence (rates around 2 cm kyr^?1) combined with possible eustatic changes including an Early Callovian rise, a fall at the middle Callovian–earliest Oxfordian (i.e. the Anceps–Mariae Zones), with average long‐term rates around 2 cm kyr^?1 (total fall of 40–60 m), a period of lowstand at the Early–Middle Oxfordian transition and a long‐term rise at the Middle–Late Oxfordian transition (Transversarium and Bifurcatus Zones). Facies distribution across the Iberian platform indicates a progressive Middle–Late Callovian relative sea‐level fall rather than a rapid relative sea‐level fall at the end of the Callovian. After this falling episode, the progressive onlap over the swell areas during the Early Oxfordian and at the beginning of the Middle Oxfordian indicates a period of accommodation gain, which is explained by the combined effects of continuous subsidence across the platform and reduced sedimentation rates in spite of the possible eustatic lowstand. Eustatic lowstand, combined with other factors (ocean water circulation, volcanism) could help to explain the loss of carbonate production during the latest Callovian–Early Oxfordian, previous to the widespread eustatic rise and warning recorded at the onset of the Transversarium Zone (Middle Oxfordian).     

Early Palaeozoic evolution of Libya: perspectives from Jabal Eghei with implications for hydrocarbon exploration in Al Kufrah Basin

This paper presents new stratigraphic and sedimentological data of the Ordovician, Silurian, and Mesozoic succession exposed on the western flank of Al Kufrah Basin. Field data (logged sections, photographs, palaeocurrent analyses) are presented from the Jabal Eghei region. This region lies ca. 200 km E of the closest stratigraphic tie point at Mourizidie on the eastern flank of the Murzuq Basin. The succession starts with the Hawaz Formation (Middle Ordovician) comprising >100 m of cross‐bedded and bioturbated sandstones that are interpreted as deposits of tidal currents in an open shelf setting. The contact between the Hawaz and Mamuniyat formations is an erosional unconformity, incised during advance of Late Ordovician ice sheets towards the NE. The Mamuniyat Formation comprises >150 m of massive and graded sandstones tentatively assigned to the Hirnantian, and contains an intraformational, soft‐sediment striated surface that is interpreted to record re‐advance of ice sheets over Jabal Eghei. The outcrop section suggests the sandstone would form an excellent reservoir in the subsurface. The Mamuniyat Formation is overlain by the Tanezzuft Formation (uppermost Ordovician–lowermost Silurian). This includes sandy limestone/calcareous sandstone, a Planolites horizon, and then 50 m of interbedded shale, silt and fine‐grained, graded and hummocky cross‐stratified sandstone recording deposition from both shallow marine turbidity currents and storm flows. A striated pavement in the lower part of this sequence is overlain by calcareous lonestone‐bearing intervals (interpreted as ice‐rafted debris). These features testify to late phases of glacial advance probably post‐dating the regional Hirnantian glacial maximum. The basal Silurian ‘hot shale’ facies is not developed in this area, probably because late glacial advance suppressed the preservation of organic matter. The upper part of the Tanezzuft Formation is truncated by an unconformity above which palaeosol‐bearing fluvial deposits (undifferentiated Mesozoic) occur.     

Hinterland basin development and infilling through tectonic and eustatic processes: latest Messinian‐Gelasian Valdelsa Basin,Northern Apennines,Italy

This article reports a stratigraphic and structural analysis of the Neogene‐Quaternary Valdelsa Basin (Central Italy), filled with up to 1000 m of uppermost Miocene to lower Pleistocene strata. The succession is subdivided into seven unconformity‐bounded stratigraphic units (synthems, or large‐scale depositional sequences) that include fluvio‐deltaic and shallow‐marine deposits. Structures related to basin shoulders and internal boundaries controlled the Neogene location and geometry of different depocentres. During the Tortonian‐Messinian, a buried NE‐trending high related to regional, basin‐transverse lineaments separated two adjacent sub‐basins. During the lower Pliocene, compressional displacement along NW‐trending, thrust‐related highs controlled the distribution of depocentres and dispersal of sediment. Extensional tectonics, although previously considered the dominant deformation style affecting the rear of the Northern Apennines since the late Miocene, is no longer considered a dominant control on tectono‐sedimentary development of the Valdelsa basin. Instead, the Valdelsa Basin shares features with continental hinterland basins of orogenic belts where compression, extension, and transcurrent stress fields determine a complex spatial and temporal record of accommodation and sediment supply. In the Valdelsa Basin tectonics and eustatic sea‐level fluctuations were dominant in forcing the deposition of sedimentary cycles at several scales. Zanclean and Gelasian large‐scale depositional sequences were mainly controlled by crustal shortening, whereas a eustatic signal was preferentially recorded during the Piacenzian. Smaller scale depositional sequences, common to most synthems, were controlled by orbitally forced glacio‐eustatic cycles.     

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.     

The dynamics of foreland basin carbonate platforms: tectonic and eustatic controls

A numerical model linking a coral growth algorithm and an algorithm for flexural subsidence reproduces many of the characteristics of drowned foreland basin carbonate platforms. This model successfully matches the observed distribution and drowning age of drowned carbonate platforms in the Huon Gulf, Papua New Guinea, a modern submarine foreland basin. Analysis of equations describing flexural subsidence and eustatic sea-level variations suggest that there are minimum convergence rates and periodicities of sea-level variation required to drown foreland basin carbonate platforms. For convergence rates on the order of a few millimetres per year, sea-level must vary on time-scales of about 10⁵ years in order to induce a rate of relative sea-level rise great enough to drown an otherwise healthy foreland basin carbonate platform.