The evolution of the high‐elevated depocenters of the northern Sierras Pampeanas (ca. 28˚ SL), Argentine broken foreland,South‐Central Andes: the Pipanaco Basin

The Pipanaco Basin, in the southern margin of the Andean Puna plateau at ca. 28°SL, is one of the largest and highest intermontane basins within the northernmost Argentine broken foreland. With a surface elevation >1000 m above sea level, this basin represents a strategic location to understand the subsidence and subsequent uplift history of high‐elevation depositional surfaces within the distal Andean foreland. However, the stratigraphic record of the Pipanaco Basin is almost entirely within the subsurface, and no geophysical surveys have been conducted in the region. A high‐resolution gravity study has been designed to understand the subsurface basin geometry. This study, together with stratigraphic correlations and flexural and backstripping analysis, suggests that the region was dominated by a regional subsidence episode of ca. 2 km during the Miocene‐Pliocene, followed by basement thrusting and ca. 1–1.5 km of sediment filling within restricted intermontane basin between the Pliocene‐Pleistocene. Based on the present‐day position of the basement top as well as the Neogene‐Present sediment thicknesses across the Sierras Pampeanas, which show slight variations along strike, sediment aggradation is not the most suitable process to account for the increase in the topographic level of the high‐elevation, close‐drainage basins of Argentina. The close correlation between the depth to basement and the mean surface elevations recorded in different swaths indicates that deep‐seated geodynamic process affected the northern Sierras Pampeanas. Seismic tomography, as well as a preliminary comparison between the isostatic and seismic Moho, suggests a buoyant lithosphere beneath the northern Sierras Pampeanas, which might have driven the long‐wavelength rise of this part of the broken foreland after the major phase of deposition in these Andean basins.     

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.     

Inferring denudation variations from the sediment record; an example of the last glacial cycle record of the Golo Basin and watershed,East Corsica,western Mediterranean sea

Geophysical data and sampling of the Golo Basin (East Corsica margin) provide the opportunity to study mass balance in a single drainage system over the last 130 kyr, by comparing deposited sediments in the sink and the maximum eroded volume in the source using total denudation proxies. Evaluation of the solid sediments deposited offshore and careful integration of uncertainties from the age model and physical properties allow us to constrain three periods of sedimentation during the last climatic cycle. The peak of sedimentation initiated during Marine Isotopic Stage (MIS) 3 (ca. 45 ka) and lasted until late in MIS 2 (ca. 18 ka). This correlates with Mediterranean Sea palaeoclimatic records and the glaciation in high altitude Corsica. The yield of solid sediment into the Golo Basin drops in the observed present day Mediterranean basins (gauging stations), whereas the palaeo‐denudation estimate derived from the sediments over the last glacial period is one to ten times higher than that predicted using cosmogenic or thermochronometer estimates of exhumation. The catchment‐wide denudation rate calculated from deposited solid sediment ranges from 47 to 219 mm kyr^?1, which is higher than the estimate from palaeosurface ablation in the proximal part of the source (9–140 mm kyr^?1) and lower than the distal, narrow, incised channel of the Golo River (160–475 mm kyr^?1). This mismatch raises questions about the investigation of denudation at millennial‐time scale (kyr) and at higher integrating times (Myr) as a reliable tool for determining the effect of climate change on mountain building and on sedimentary basin models.     

Denudation rates of a subequatorial orogenic belt based on estimates of sediment yields: evidence from the Paleozoic Appalachian Basin,USA

The Upper Mississippian (ca. 325 Ma) Pride Shale and Glady Fork Member in the Central Appalachian Basin comprise an upward‐coarsening, ca. 60‐m‐thick succession of prodeltaic‐delta front, interlaminated fine‐grained sandstones and mudstones gradational upwards into mouth‐bar and distributary‐channel sandstones. Analysis of laminae bundling in the Pride Shale reveals a hierarchy of tidal cycles (semi‐diurnal, fortnightly neap‐spring) and a distinct annual cyclicity resulting from seasonal fluvial discharge. These tidal rhythmites thus represent high‐resolution chronometers that can be used in basin analysis. Annual cycles average 10 cm in thickness, thus the bulk of the Pride Shale‐Glady Fork Member in any one vertical section is estimated to have accumulated in ca. 600 years. Progradational clinoforms are assumed to have had dips of 0.3–3° with a median dip of 1.7°; the latter infilled a NE‐SW oriented foreland trough up to 300 km long by 50 km wide in the relatively short time period of 90 kyr. The total volume of sediment in the Pride basin is ca. 900 km³ which, for an average sediment density of 2700 kg m^?3, equates to a total mass of ca. 2.4 × 10⁶ Mt. Thus, mass sediment load can be estimated as 27 Mt yr^?1. For a drainage basin area of 89 000 km², based on the scale of architectural channel elements and cross‐set thicknesses in the incised‐valley‐fill deposits of the underlying Princeton Formation, suspended sediment yields are estimated at ca. 310 t km^?2 yr^?1 equating to a mechanical denudation rate of ca. 0.116 mm yr^?1. Calculated sediment yields and inferred denudation rates are comparable to modern rivers such as the Po and Fly and are compatible with a provenance of significant relief and a climate characterized by seasonal, monsoonal discharge. Inferred denudation rates also are consistent with average denudation rates for the Inner Piedmont Terrane of the Appalachians based on flexural modelling. The integration of stratigraphic architectural analysis with a novel chronometric application highlights the utility of sedimentary archives as a record of Earth surface dynamics.     

Tectonics of the Xining Basin in NW China and its implications for the evolution of the NE Qinghai‐Tibetan Plateau

The continuous Cenozoic strata in the Xining Basin record the growth and evolution of the northeastern Qinghai–Tibetan Plateau. Here, the mechanisms and evolution of the Xining Basin during the Cenozoic were investigated by studying the sedimentary facies of 22 Cenozoic sections across the basin and detrital zircon U‐Pb ages of three Cenozoic sections located in the eastern, central and western basin, respectively. In the Eocene (ca. 50–44 Ma), the India‐Eurasia Collision affected the northeastern Qinghai–Tibetan Plateau. The Central Qilian Block rotated clockwise by ca. 24° to form the Xining Basin. The Triassic flysch sediments surrounding the basin were the primary sources of sediment. Between ca. 44–40 Ma, the basin enlarged and deepened, and sedimentation was dominated by saline lake sediments. Between ca. 40–25.5 Ma, the Xining Basin began to shrink and dry, resulting in the deposition of saline pan and saline mudflat sediments in the basin. After ca. 20 Ma, the Laji Shan to the south of the Xining Basin was uplifted due to the northward compression of the Guide Basin to the south. Clasts that eroded from this range dominated the sediments as the basin evolved from a lacustrine environment into a fluvial system. The Xining Basin was an extensional basin in the Early Cenozoic, but changed into a compressive one during the Late Cenozoic, it was not a foreland basin either to the Kunlun Shan or to the western Qinling Shan in the whole Cenozoic. The formation and deformation of the Xining Basin are the direct responses of the India‐Eurasia Collision and the growth of the Qinghai‐Tibetan Plateau.     

Sedimentary evidence for late Messinian uplift of the SE margin of the Central Anatolian Plateau: Adana Basin,southern Turkey

The Adana Basin of southern Turkey, located at the SE margin of the Central Anatolian Plateau in the vicinity of the Arabia‐Eurasia collision zone, is ideally suited to record Neogene and Quaternary topographic and tectonic changes in the easternmost Mediterranean realm. On the basis of our correlation of 34 seismic reflection profiles with corresponding exposed units along the margins of the Adana Basin, we identify and characterize the seismic facies that corresponds to the upper part of the Messinian Handere Formation (ca. 5.45 to 5.33 Ma), which consists mainly of fluvial conglomerates and marls. The seismic reflection profiles indicate that ca. 1100 km³ of the Handere Formation upper sub‐unit is distributed over ca. 3000 km², reflecting local sedimentation rates of up to 12.5 mm year^?1. This indicates a major increase in both sediment supply and subsidence rates at ca. 5.45 Ma. Our provenance analysis of the Handere Formation upper sub‐unit based on clast counting and palaeocurrent measurements reveals that most of the sediment is derived from the Taurus Mountains at the SE margin of the Central Anatolian Plateau and regions farther north. A comparison of these results with the composition of recent fluvial conglomerates and the present‐day drainage basins indicates major changes between late Messinian and present‐day source areas. We suggest that these changes in drainage patterns and lithological characteristics result from uplift and ensuing erosion of the SE margin of the plateau. We interpret the tectonic evolution of the southern flank of the Anatolian Plateau and the coeval subsidence and sedimentation in the Adana Basin to be related to deep lithospheric processes, particularly lithospheric delamination and slab break‐off.     

A prograding margin during global sea‐level maxima: an example from Mahajanga Basin,northwest Madagascar

The Mesozoic shelf margin in the Mahajanga Basin, northwest Madagascar, provides an example where inherited palaeobathymetry, coupled with sea‐level changes, high sediment supply and fluctuations in accommodation influenced the stacking patterns and geometry of clinoforms that accreted onto a passive rifted margin. Two‐dimensional (2D) seismic profiles are integrated with existing field data and geological maps to study the evolution of the margin. The basin contains complete records of transgression, highstand, regression and lowstand phases that took place from Jurassic to Cretaceous. Of particular interest is the Cretaceous, Albian to Turonian (ca. 113‐93 Ma), siliciclastic shelf margin that prograded above a drowned Middle Jurassic carbonate platform. The siliciclastic phase of the shelf margin advanced ca. 70 km within ca. 20 My, and contains 10 distinct clinoforms mapped along a 2D seismic reflection data set. The clinoforms show a progressive decrease in height and slope length, and a fairly constant slope gradient through time. The successive shelf edges begin with a persistent flat to slightly downward‐directed shelf‐edge trajectory that changes to an ascending trajectory at the end of clinoform progradation. The progressive decrease in clinoform height and slope length is attributed to a decrease in accommodation. The prograding margin is interpreted to have formed when siliciclastic input increased as eastern Madagascar was uplifted. This work highlights the importance of sediment supply and inherited palaeobathymetry as controls on the evolution of shelf margins and it provides a new understanding of the evolution of the Mahajanga Basin during the Mesozoic.     

Palaeogeography and diachronous infill of an ancient deep‐marine foreland basin,Upper Cretaceous Cerro Toro Formation,Magallanes Basin

The details of how narrow, orogen‐parallel ocean basins are filled with sediment by large axial submarine channels is important to understand because these depositional systems commonly form in through‐like basins in various tectonic settings. The Magallanes foreland basin is an excellent location to study an orogen‐parallel deep‐marine system. Conglomerate lenses of the Upper Cretaceous Cerro Toro Formation have been previously interpreted to represent the fill of a single submarine channel (4–8 km wide, >100 km long) that funneled coarse detritus southward along the basin axis. This interpretation was based on lithologic correlations. New U/Pb dating of zircons from volcanic ashes and sandstones, coupled with strontium isotope stratigraphy, refine the controls on depositional ages and provenance. Results demonstrate that north‐south oriented conglomerate lenses are contemporaneous within error limits (ca. 84–82 Ma) supporting that they represent parts of an axial channel belt. Channel deposits 20 km west of the axial location are 87–82 Ma in age. These channels are partly contemporaneous with the ones within the axial channel belt, making it likely that they represent feeders to the axial channel system. The northern Cerro Toro Formation spans a Turonian to Campanian interval (ca. 90–82 Ma) whereas the formation top, 70 km to the south, is as young as ca. 76 Ma. Kolmogorov–Smirnoff statistical analysis on detrital zircon age distributions shows that the northern uppermost Cerro Toro Formation yields a statistically different age distribution than other samples from the same formation but shows no difference relative to the overlying Tres Pasos Formation. These results suggest the partly coeval deposition of both formations. Integration of previously acquired geochronologic and stratigraphic data with new data show a pronounced southward younging pattern in all four marine formations in the Magallanes Basin. Highly diachronous infilling may be an important depositional pattern for narrow, orogen‐parallel ocean basins.     

Characterisation and diachronous initiation of coarse clastic deposition in the Magallanes–Austral foreland basin,Patagonian Andes

Magallanes–Austral Basin (MAB) fill is preserved along a >1000 km north–south trending outcrop belt in the southern Patagonia region of Argentina and Chile. Although the stratigraphic evolution of the MAB has been well documented in the Chilean sector (referred to as the Magallanes Basin), its northern terminus in southern Argentina (Austral Basin) is poorly constrained. We present new stratigraphic and geochronologic analyses of the early basin fill (Aptian–Turonian) from the Argentine sector (49–51°S) of the MAB to document spatial variability in stratigraphy and timing of deposition during the initial stages of basin evolution. The initiation of the retroarc foreland basin fill is marked by the transition from mudstone to coarse‐clastic deposition, which is characterised by the consistent presence of sandstone beds > ca. 20 cm thick interpreted to represent sediment gravity flows deposited in a submarine fan system. Depositional environments within the early fill of the basin range from lower to upper deep‐water fan settings as well as previously undocumented slope deposits. These facies are present as far north as El Chalten, Argentina (ca. 49°S), indicating that facies‐equivalent rocks can be traced along‐strike for at least 5 degrees of latitude, based on correlation with strata as far south as the Cordillera Darwin (ca. 54°S). Eight new U‐Pb zircon ages from ash beds reveal an overall southward younging trend in the initiation of coarse clastic deposition. Inferred depositional ages range from ca. 115 ± 1.9 Ma in the northernmost study area to not older than 92 ± 1 Ma and 89 ± 1.5 Ma in the central and southern sectors respectively. The apparent diachronous delivery of coarse detritus into the basin may reflect (1) gradual southward progradation of a deep‐water fan system from a northerly point source and/or (2) orogen‐parallel variations in the timing and magnitude of thrust‐belt deformation and erosion that provided more local sources for sediment delivery.     

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.     

Foredeep palaeobathymetry and subsidence trends during advancing then retreating subduction: the Northern Apennine case (Oligocene‐Miocene,Italy)

The Northern Apennines provide an example of long‐term deep‐water sedimentation in an underfilled pro‐foreland basin first linked to an advancing orogenic wedge and then to a retreating subduction zone during slab rollback. New palaeobathymetric and geohistory analyses of turbidite systems that accumulated in the foredeep during the Oligocene‐Miocene are used to unravel the basin subsidence history during this geodynamic change, and to investigate how it interplayed with sediment supply and basin tectonics in controlling foredeep filling. The results show an estimated ca. 2 km decrease in palaeowater depth at ca. 17 Ma. Moreover, a change in basin subsidence is documented during Langhian time, with an average decompacted subsidence rate, during individual depocentre life, that increased from <0.3 to 0.4–0.6 mm y^?1, together with the appearance of a syndepositional backstripped subsidence bracketed between 0.1 and 0.2 mm y^?1. This change prevented the basin from complete filling during late Miocene and is interpreted as the foredeep response to initial rollback of the downgoing Adriatic slab. Thus, the Northern Apennine system provides an example of a pro‐foreland basin that experienced both a slow‐ and high‐subsidence regime as a consequence of the advancing then retreating evolution of the collisional system.     

Provenance and tectonic implications of Orán Group foreland basin sediments,Río Iruya canyon,NW Argentina (23° S)

Foreland basins are important recorders of tectonic and climatic processes in evolving mountain ranges. The Río Iruya canyon of NW Argentina (23° S) exposes ca. 7500 m of Orán Group foreland basin sediments, spanning over 8 Myr of near continuous deposition in the Central Andes. This study presents a record of sedimentary provenance for the Iruya Section in the context of a revised stratigraphic chronology. We use U‐Pb zircon ages from six interbedded ash layers and new magnetostratigraphy to constrain depositional ages in the section between 1.94 and 6.49 Ma, giving an average sedimentation rate of 0.93 ± 0.02 (2σ) km Myr^?1. We then pair U‐Pb detrital zircon dating with quartz trace‐element analysis to track changes in sedimentary provenance from ca. 7.6 to 1.8 Ma. Results suggest that from ca. 7.6 to ca. 6.3 Ma, the Iruya watershed did not tap the Salta Group or Neogene volcanics that are currently exposed in the eastern Cordillera and Puna margin. One explanation is that a long‐lived topographic barrier separated the eastern Puna from the foreland for much of the mid‐late Miocene, and that the arrival of Jurassic‐Neogene zircons records regional tectonic reactivation at ca. 6.3 Ma. A second major provenance shift at ca. 4 Ma is marked by changes in the zircon and quartz populations, which appear to be derived from a restricted source region in Proterozoic‐Ordovician meta‐sediments. Considered in conjunction with the onset of coarse conglomerate deposition, we attribute this shift to accelerated uplift of the Santa Victoria range, which currently defines the catchment's western limit. A third shift at ca. 2.3 Ma records an apparent disconnection of the Iruya with the eastern Puna, perhaps due to defeat of the proto Rio‐Iruya by the rising Santa Victoria range. This study is one of the first applications of quartz trace‐element provenance analysis, which we show to be an effective complement to U‐Pb detrital zircon dating when appropriate statistical methods are applied.     

Cretaceous continental margin evolution revealed using quantitative seismic geomorphology,offshore northwest Africa

The application of high‐resolution seismic geomorphology, integrated with lithological data from the continental margin offshore The Gambia, northwest Africa, documents a complex tectono‐stratigraphic history through the Cretaceous. This reveals the spatial‐temporal evolution of submarine canyons by quantifying the related basin depositional elements and providing an estimate of intra‐ versus extra‐basinal sediment budget. The margin developed from the Jurassic to Aptian as a carbonate escarpment. Followed by, an Albian‐aged wave‐dominated delta system that prograded to the palaeo‐shelf edge. This is the first major delivery of siliciclastic sediment into the basin during the evolution of the continental margin, with increased sediment input linked to exhumation events of the hinterland. Subaqueous channel systems (up to 320 m wide) meandered through the pro‐delta region reaching the palaeo‐shelf edge, where it is postulated they initiated early submarine canyonisation of the margin. The canyonisation was long‐lived (ca. 28 Myr) dissecting the inherited seascape topography. Thirteen submarine canyons can be mapped, associated with a Late Cretaceous‐aged regional composite unconformity (RCU), classified as shelf incised or slope confined. Major knickpoints within the canyons and the sharp inflection point along the margin are controlled by the lithological contrast between carbonate and siliciclastic subcrop lithologies. Analysis of the base‐of‐slope deposits at the terminus of the canyons identifies two end‐member lobe styles, debris‐rich and debris‐poor, reflecting the amount of carbonate detritus eroded and redeposited from the escarpment margin (blocks up to ca. 1 km³). The vast majority of canyon‐derived sediment (97%) in the base‐of‐slope is interpreted as locally derived intra‐basinal material. The average volume of sediment bypassed through shelf‐incised canyons is an order of magnitude higher than the slope‐confined systems. These results document a complex mixed‐margin evolution, with seascape evolution, sedimentation style and volume controlled by shelf‐margin collapse, far‐field tectonic activity and the effects of hinterland rejuvenation of the siliciclastic source.     

Miocene shelf‐edge deltas and their impact on deepwater slope progradation and morphology,Northwest Shelf of Australia

Late‐middle Miocene to Pliocene siliciclastics in the Northern Carnarvon Basin, Northwest Shelf of Australia, are interpreted as having been deposited by deltas. Some delta lobes deposited sediments near and at the shelf break (shelf‐edge deltas), whereas other lobes did not reach the coeval shelf break before retreating landward or being abandoned. Shelf‐margin mapview morphology changes from linear to convex‐outward in the northern part of the study area where shelf‐edge deltas were focused. Location and character of shelf‐edge deltas also had significant impact on along‐strike variability of margin progradation and shelf‐edge trajectory. Total late‐middle and late Miocene margin progradation is ca. 13 km in the south, where there were no shelf‐edge deltas, vs. ca. 34 km in the north where shelf‐edge deltas were concentrated. In the central area, the deltas were arrested and accumulated a few kilometres landward of the shelf break, resulting in an aggradational shelf‐edge trajectory, in contrast to the more progradational trajectory farther north. This illustrates a potential limitation of shelf‐edge trajectory analysis: only where shelf‐edge deltas occur, there is sufficient sediment available for the shelf‐edge trajectory to record relative sea‐level fluctuations reliably. Small‐scale (ca. 400 m wide) incisions were already conspicuous on the coeval slope even before deltas reached the shelf break. However, slope gullies immediately downdip from active shelf‐edge deltas display greater erosion of underlying strata and are wider and deeper (>1 km wide, ca. 100 m deep) than coeval incisions that are laterally offset from the deltaic depocenter (ca. 0.7 km wide, ca. 25 m deep). We interpret this change in slope‐gully dimensions as the result of greater erosion by sediment gravity flows sourced from the immediately adjacent shelf‐edge deltas. Similarly, gullies also incised further (up to 6 km) into the outer shelf in the region of active shelf‐edge deltas.     

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.     

Syntectonic subaqueous mass flows of the Neoproterozoic Otavi Group,Namibia: where is the evidence of global glaciation?

The thick (>1 km) Neoproterozoic Otavi Group of Namibia accumulated after ca. 760 Ma along >700 km of the faulted margin of the Congo Craton. The margin shows a north to south, downbasin transition from a shallow‐water carbonate shelf (Otavi Platform) to offshore deepwater slope (Outjo Basin). Within the latter, the Abenab and Tsumeb Subgroups contain large volumes of poorly sorted breccias, conglomerates and diamictites composed principally of locally derived carbonate. Diamictite facies were reported in the 1930s as tillites left by an ice sheet (although the absence of striated clasts and other key glacial indicators was viewed as problematic). Later workers rejected a glacial origin concluding that Outjo basin facies were deposited as parts of prograding submarine wedges built by mass flows during active rifting. Recently, the Snowball Earth hypothesis has returned to the earlier glacial interpretation; arguing that these strata represent a record of extraordinary late Neoproterozoic glacial and interglacial climates when global temperatures fluctuated by up to 100°C. Facies analysis of breccias, diamictites, conglomerates and sandstone strata of the Otavi Group identifies them as genetically related, subaqueously deposited sediment gravity flows. They lack diagnostic indicators of any one specific climate in source areas. These facies were all deposited in deepwater at the foot of landslide‐prone scarp blocks where debris flows and turbidity currents moved large volumes of coarse, freshly broken carbonate debris produced by faulting. Breccias, diamictites, conglomerates and sandstones occur in composite fining‐ and thinning‐upward bundles that are directly analogous to those reported from many other faulted margins in the Phanerozoic stratigraphic record. These rocks provide no clear sedimentological signature of a glacial source or catastrophic Snowball Earth‐type temperature fluctuations. Instead, they point to a dominant tectonic control on sedimentation related to faulting along the margin of the Congo Craton.     

Geodynamic context for the deposition of coarse‐grained deep‐water axial channel systems in the Patagonian Andes

We present field and seismic evidence for the existence of Coniacian–Campanian syntectonic angular unconformities within basal foreland basin sequences of the Austral or Magallanes Basin, with implications for the understanding of deformation and sedimentation in the southern Patagonian Andes. The studied sequences belong to the mainly turbiditic Upper Cretaceous Cerro Toro Formation that includes a world‐class example of conglomerate‐filled deep‐water channel bodies deposited in an axial foredeep depocentre. We present multiple evidence of syntectonic deposition showing that the present internal domain of the fold‐thrust belt was an active Coniacian–Campanian wedge‐top depozone where deposition of turbidites and conglomerate channels of Cerro Toro took place. Cretaceous synsedimentary deformation was dominated by positive inversion of Jurassic extensional structures that produced elongated axial submarine trenches separated by structural highs controlling the development and distribution of axial channels. The position of Coniacian‐Campanian unconformities indicates a ca. 50–80 km advance of the orogenic front throughout the internal domain, implying that Late Cretaceous deformation was more significant in terms of widening the orogenic wedge than all subsequent Andean deformation stages. This south Patagonian orogenic event can be related to compressional stresses generated by the combination of both the collision of the western margin of Rocas Verdes Basin during its closure, and Atlantic ridge push forces due to its accelerated opening, during a global‐scale plate reorganization event.     

Timing of Xunhua and Guide basin development and growth of the northeastern Tibetan Plateau,China

The Xunhua, Guide and Tongren intermontane basin system in the NE Tibetan Plateau, situated near the Xining basin to the N and the Linxia basin to the E, is bounded by thrust fault‐controlled ranges. These include to the N, the Riyue Shan, Laji Shan and Jishi Shan ranges, and to the S the northern West Qinling Shan (NWQ). An integrated study of the structural geology, sedimentology and provenance of the Cenozoic Xunhua and Guide basins provides a detailed record of the growth of the NE Tibetan Plateau since the early Eocene. The Xining Group (ca. 52–21 Ma) is interpreted as consisting of unified foreland basin deposits which were controlled by the bounding thrust belt of the NWQ. The Xunhua, Guide and Xining subbasins were interconnected prior to later uplift and damming by the Laji Shan and Jishi Shan ranges. Their sediment source, the NWQ, is constrained by strong unidirectional paleocurrent trends towards the N, a northward fining lithology, distinct and recognizable clast types and detrital zircon ages. Collectively, formation of this mountain–basin system indicates that the Tibetan Plateau expanded into the NWQ at a time roughly coinciding with Eocene to earliest Miocene continental collision between India and Eurasia. The Guide Group (ca. 21–1.8 Ma) is inferred to have been deposited in the separate Xunhua, Guide and Tongren broken foreland basins. Each basin was filled by locally sourced alluvial fans, braided streams and deltaic‐lacustrine systems. Structural, paleogeographic, paleocurrent and provenance data indicate that thrust faulting in the NWQ stepped northward to the Laji Shan from ca. 21 to 16 Ma. This northward shift was accompanied by E–W shortening related to nearly N–S‐striking thrust faulting in Jishi Shan after 11–13 Ma. A lower Pleistocene conglomerate (1.8–1.7 Ma) was deposited by a through‐flowing river system in the overfilled and connected Guide and Xunhua basins following the termination of thrust activity. All of the basin–mountain zones developed along the Tibetan Plateau's NE margin since Indian–Tibetan continental collision may have been driven by collision‐induced basal drag of old slab remnants in the manner of N‐dipping and flat‐slab subduction, and their subsequent sinking into the deep mantle.     

Cretaceous evolution of the Andean margin between 36°S and 40°S latitude through a multi‐proxy provenance analysis of Neuquén Basin strata (Argentina)

During the Cretaceous, the Neuquén Basin transitioned from an extensional back‐arc to a retroarc foreland basin. We present a multi‐proxy provenance study of Aptian to Santonian (125–84 Ma) continental sedimentary rocks preserved in the Neuquén Basin used to resolve changes of sediment drainage pattern in response to the change in tectonic regime. Sandstone petrology and U–Pb detrital zircon geochronology constrain the source units delivering detritus to the basin; apatite U–Pb and fission track dating further resolve provenance and determine the age and patterns of exhumation of the source rocks. Sandstone provenance records a sharp change from a mixed orogenic source during Aptian time (ca. 125 Ma), to a magmatic arc provenance in the Cenomanian (ca. 100 Ma). We interpret this provenance change as the result of the drainage pattern reorganisation from divergent to convergent caused by tectonic basin inversion. During this inversion and early stages of contraction, a transient phase of uplift and basin erosion, possibly due to continental buckling, caused the pre‐Cenomanian unconformity dividing the Lower from Upper Cretaceous strata in the Neuquén Basin. This phase was followed by the development of a retroarc foreland basin characterised by a volcanic arc sediment provenance progressively shifting to a mixed continental basement provenance during Turonian‐Santonian (90–84). According to multi‐proxy provenance data and lag times derived from apatite fission track analysis, this trend is the result of a rapidly exhuming source within the Cordillera to the west, in response to active compressional tectonics along the western margin of South America, coupled with the increasing contribution of material from the stable craton to the east; this contribution is thought to be the result of the weak uplift and exhumation of the foreland due to eastward migration of the forebulge.     

Isotopic and thermochronologic evidence of extremely cold lithosphere associated with a slab flattening in the Central Andes of Argentina

We present mineralogic, isotopic and thermochronologic analyses on psammopelitic and tuffaceous levels from the Bermejo and Vinchina basins – both foreland depocentres of the Central Andes of Argentina – that define a low‐temperature regime for the crust akin to a slab shallowing and flattening process. The contents of illite in illite/smectite interstratified (I/S) show a progressive illitization into the deeper parts of both basins. The distribution of I/S is compatible with theoretical simulations and predicted heat flow values of ca. 26 mW m^?2 in the 8–3.4 Ma interval for the Vinchina Basin and ca. 42 mW m^?2 since 9 Ma for the Bermejo Basin. The latter shows heat flow values that are comparable to those reported by magnetotelluric analysis (36–40 mW m^?2) in agreement with previously published heat flow calculations along the modern Andean foreland. The Rb–Sr isochrones in psammopelites (<2 μm fractions) show ages between 125 and 165 Ma, whereas the K–Ar ages decrease as the grain size is smaller (136–224 Ma for 1–2 μm, 112–159 Ma for 0.2–1 μm, 76–116 Ma for <0.2 μ and 39.3–42 Ma for <0.1 μm). These ages are significantly older than the sedimentation in the basins (ca. 16 Ma for the Vinchina Basin; U–Pb age), and can be explained by the presence of a significant amount of detrital components, mainly illite, even in the finer fractions. The preservation of detrital ages is consistent with the shallow diagenesis related to a low‐temperature regime, proposed here for the basins. Younger K–Ar ages (21.3–12 Ma) were obtained for a basal tuffaceous level. Clay mineralogy and R0 ordering in the deepest part of the Vinchina Basin, together with the evolution model of I/S with depth, suggest that the burial temperatures would have not exceeded ca. 100°C in agreement with (U–Th)/He analyses performed on apatite extracted from two tuffaceous units. Thermal indicators from both studied basins confirm the existence of a low‐temperature regime during flat subduction.