Late Eocene–Pliocene basin evolution in the Eastern Cordillera of northwestern Argentina (25°–26°S): regional implications for Andean orogenic wedge development

Important aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from Eocene–Pliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (Pucará–Angastaco and La Viña areas) provide an Eocene (ca. 38 Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca. 14 Ma and the coarse‐grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial‐lacustrine intramontane setting. By ca. 4 Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐Eocene strata (Santa Barbara Subgroup) within the region.     

Climatic and halokinetic controls on alluvial–lacustrine sedimentation during compressional deformation,Andean forearc,northern Chile

The Salar de Atacama forms one of a series of forearc basins developed along the western flank of the Central Andes. Exposed along the northwest margin of the basin, a salt‐cored range, the Cordillera de la Sal, records the Mid‐Miocene to recent sedimentological and structural development of this basin. Sediments of the Mid‐Miocene Vilama Formation record the complex interaction between regional/local climate change, halokinesis and compressional deformation. This study reveals how these factors have controlled the facies development and distribution within the Salar de Atacama. Detailed sedimentary logging, cross‐sections and present day geomorphology through the northern Cordillera de la Sal have been used to establish a lithostratigraphy, chronostratigraphy and the regional distribution of the Vilama Formation. The Vilama Formation documents an increase in aridity with a hiatus in sedimentation from Mid‐Miocene to 9 Ma with initial uplift of the Cordillera de la Sal. From 9 Ma to 8.5 Ma deposition of a meandering fluvial system is recorded followed by a rapid decrease in sedimentation till 6 Ma. From 6 to 2 Ma, the deposition of extensive palustrine carbonates and distal alluvial–mudflat–lacustrine demonstrates the existence of an extensive lake within the Salar de Atacama. Post 2 Ma, the lake decreased in size and braided alluvial gravels associated with alluvial fans were widespread through the region suggesting a final shift to hyperarid conditions. By comparing the Vilama Formation with similar age facies throughout northern Chile and southern Peru, several shifts in climate are recognized. Climate signatures within northern Chile appear to be largely diachronous with the last regional event in the Mid‐Miocene. Since that time, humid events have been restricted to either Precordillerian basins or the Central Atacama. Within the Central Atacama, the final switch to hyperarid conditions was not till the earliest Pleistocene, much later than previously estimated within the region.     

Miocene sedimentation,volcanism and deformation in the Eastern Cordillera (24°30′ S,NW Argentina): tracking the evolution of the foreland basin of the Central Andes

Understanding the relationships between sedimentation, tectonics and magmatism is crucial to defining the evolution of orogens and convergent plate boundaries. Here, we consider the lithostratigraphy, clastic provenance, syndepositional deformation and volcanism of the Almagro‐El Toro basin of NW Argentina (24°30′ S, 65°50′ W), which experienced eruptive and depositional episodes between 14.3 and 6.4 Ma. Our aims were to elucidate the spatial and temporal record of the onset and style of the shortening and exhumation of the Eastern Cordillera in the frame of the Miocene evolution of the Central Andes foreland basin. The volcano‐sedimentary sequence of the Almagro‐El Toro basin consists of lower red floodplain sandstones and siltstones, medial non‐volcanogenic conglomerates with localised volcanic centres and upper volcanogenic coarse conglomerates and breccia. Coarse, gravity flow‐dominated (debris‐flow and sheet‐flow) alluvial fan systems developed proximal to the source area in the upper and medial sequence. Growing frontal and intrabasinal structures suggest that the Almagro‐El Toro portion of the foreland basin accumulated on top of the eastward‐propagating active thrust front of the Eastern Cordillera. Synorogenic deposits indicate that the shortening of the foreland deposits was occurring by 11.1 Ma, but conglomerates derived from the erosion of western sources suggest that the uplift and erosion of this portion of the Eastern Cordillera has occurred since ca.12.5 Ma. An unroofing reconstruction suggests that 6.5 km of rocks were exhumed. A tectono‐sedimentary model of an episodically evolving thick‐skinned foreland basin is proposed. In this frame, the NW‐trending, transtensive Calama–Olacapato–El Toro (COT) structures interacted with the orogen, influencing the deposition and deformation of synorogenic conglomerates, the location of volcanic centres and the differential tilt and exhumation of the foreland.     

Neotectonic basin and landscape evolution in the Eastern Cordillera of NW Argentina,Humahuaca Basin (~24°S)

The intermontane Quebrada de Humahuaca Basin (Humahuaca Basin) in the Eastern Cordillera of the southern Central Andes of NW Argentina (23°–24°S) records the evolution of a formerly contiguous foreland‐basin setting to an intermontane depositional environment during the late stages of Cenozoic Andean mountain building. This basin has been and continues to be subject to shortening and surface uplift, which has resulted in the establishment of an orographic barrier for easterly sourced moisture‐bearing winds along its eastern margin, followed by leeward aridification. We present new U–Pb zircon ages and palaeocurrent reconstructions suggesting that from at least 6 Ma until 4.2 Ma, the Humahuaca Basin was an integral part of a largely contiguous depositional system that became progressively decoupled from the foreland as deformation migrated eastward. The Humahuaca Basin experienced multiple cycles of severed hydrological conditions and subsequent re‐captured drainage, fluvial connectivity with the foreland and sediment evacuation. Depositional and structural relationships among faults, regional unconformities and deformed landforms reveal a general pattern of intrabasin deformation that appears to be associated with different cycles of alluviation and basin excavation in which deformation is focused on basin‐internal structures during or subsequent to phases of large‐scale sediment removal.     

Miocene to Quaternary basin evolution at the southeastern Andean Plateau (Puna) margin (ca. 24°S lat,Northwestern Argentina)

The Andean Plateau of NW Argentina is a prominent example of a high‐elevation orogenic plateau characterized by internal drainage, arid to hyper‐arid climatic conditions and a compressional basin‐and‐range morphology comprising thick sedimentary basins. However, the development of the plateau as a geomorphic entity is not well understood. Enhanced orographic rainout along the eastern, windward plateau flank causes reduced fluvial run‐off and thus subdued surface‐process rates in the arid hinterland. Despite this, many Puna basins document a complex history of fluvial processes that have transformed the landscape from aggrading basins with coalescing alluvial fans to the formation of multiple fluvial terraces that are now abandoned. Here, we present data from the San Antonio de los Cobres (SAC) area, a sub‐catchment of the Salinas Grandes Basin located on the eastern Puna Plateau bordering the externally drained Eastern Cordillera. Our data include: (a) new radiometric U‐Pb zircon data from intercalated volcanic ash layers and detrital zircons from sedimentary key horizons; (b) sedimentary and geochemical provenance indicators; (c) river profile analysis; and (d) palaeo‐landscape reconstruction to assess aggradation, incision and basin connectivity. Our results suggest that the eastern Puna margin evolved from a structurally controlled intermontane basin during the Middle Miocene, similar to intermontane basins in the Mio‐Pliocene Eastern Cordillera and the broken Andean foreland. Our refined basin stratigraphy implies that sedimentation continued during the Late Mio‐Pliocene and the Quaternary, after which the SAC area was subjected to basin incision and excavation of the sedimentary fill. Because this incision is unrelated to baselevel changes and tectonic processes, and is similar in timing to the onset of basin fill and excavation cycles of intermontane basins in the adjacent Eastern Cordillera, we suspect a regional climatic driver, triggered by the Mid‐Pleistocene Climate Transition, caused the present‐day morphology. Our observations suggest that lateral orogenic growth, aridification of orogenic interiors, and protracted plateau sedimentation are all part of a complex process chain necessary to establish and maintain geomorphic characteristics of orogenic plateaus in tectonically active mountain belts.     

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.     

Gravitational deformation and inherited structural control on slope morphology in the subduction zone of north‐central Chile (ca. 29–33°S)

Subduction zones provide direct insight into plate boundary deformation and by studying these areas we better understand tectonic processes and variability over time. We studied the structure of the offshore subduction zone system of the Pampean flat‐slab segment (ca. 29–33°S) of the Chilean margin using seismic and bathymetric constraints. Here, we related and analysed the structural styles of the offshore and onshore western fore‐arc. Overlying the acoustic top of the continental basement, two syn‐extensional seismic sequences were recognised and correlated with onshore geological units and the Valparaíso Forearc Basin seismic sequences: (SII) Pliocene‐Pleistocene and (SI) Miocene‐Pliocene (Late Cretaceous (?) to Miocene‐Pliocene) syn‐extensional sequences. These sequences are separated by an unconformity (i.e. Valparaíso Unconformity). Seismic reflection data reveal that the eastward dipping extensional system (EI) recognised at the upper slope can be extended to the middle slope and controlled the accumulation of the older seismic package (SI). The westward dipping extensional system (EII) is essentially restricted to the middle slope. Here, EII cuts the eastward dipping extensional system (EI), preferentially parallel to the inclination of the older sequences (SI), and controlled a series of middle slope basins which are filled by the Pliocene‐Pleistocene seismic sequence (SII). At the upper slope and in the western Coastal Cordillera, the SII sequence is controlled by eastward dipping faults (EII) which are the local reactivation of older extensional faults (EI). The tectonic boundary between the middle (eastern outermost forearc block) and upper continental slope (western coastal block) is a prominent system of trenchward dipping normal fault scarps (ca. 1 km offset) that resemble a major trenchward dipping extensional fault system. This prominent structural feature can be readily detected along the Chilean erosive margin as well as the two extensional sets (EI and EII). Evidence of slumping, thrusting, reactivated faults and mass transport deposits, were recognised in the slope domain and locally restricted to some eastern dipping faults. These features could be related to gravitational effects or slope deformation due to coseismic deformation. The regional inclination of the pre‐Pliocene sequences favoured the gravitational collapse of the outermost forearc block. We propose that the structural configuration of the study area is dominantly controlled by tectonic erosion as well as the uplift of the Coastal Cordillera, which is partially controlled by pre‐Pliocene architecture.     

The synrift phase of the early Domeyko Basin (Triassic,northern Chile): Sedimentary,volcanic, and tectonic interplay in the evolution of an ancient subduction‐related rift basin

The geodynamic setting along the SW Gondwana margin during its early breakup (Triassic) remains poorly understood. Recent models calling for an uninterrupted subduction since Late Palaeozoic only slightly consider the geotectonic significance of coeval basins. The Domeyko Basin initiated as a rift basin during the Triassic being filled by sedimentary and volcanic deposits. Stratigraphic, sedimentological, and geochronological analyses are presented in order to determine the tectonostratigraphic evolution of this basin and to propose a tectonic model suitable for other SW Gondwana‐margin rift basins. The Domeyko Basin recorded two synrift stages. The Synrift I (~240–225 Ma) initiated the Sierra Exploradora sub‐basin, whereas the Synrift II (~217–200 Ma) reactivated this sub‐basin and originated small depocentres grouped in the Sierra de Varas sub‐basin. During the rift evolution, the sedimentary systems developed were largely controlled by the interplay between tectonics and volcanism through the accommodation/sediment supply ratio (A/S). High‐volcaniclastic depocentres record a net dominance of the syn‐eruptive period lacking rift‐climax sequences, whereas low‐volcaniclastic depocentres of the Sierra de Varas sub‐basin developed a complete rift cycle during the Synrift II stage. The architecture of the Domeyko Basin suggests a transtensional kinematic where N‐S master faults interacted with ~NW‐SE basement structures producing highly asymmetric releasing bends. We suggest that the early Domeyko Basin was a continental subduction‐related rift basin likely developed under an oblique convergence in a back‐arc setting. Subduction would have acted as a primary driving mechanism for the extension along the Gondwanan margin, unlike inland rift basins. Slab‐induced dynamic can strongly influence the tectonostratigraphic evolution of subduction‐related rift basins through controls in the localization and style of magmatism and faulting, settling the interplay between tectonics, volcanism, and sedimentation during the rifting.     

Why is there no Coastal Cordillera at the Arica Bend (Western Central Andes)?

The architecture of the Western Andes is remarkably constant between southern Peru and northern Chile. An exception, however, is present near Arica at 18°S, where the Andes change their strike direction by ca. 50° and the Coastal Cordillera is absent over an along‐strike width of 50 km. Although this feature has been mentioned in several previous studies, no effort has been made yet to describe and explain this peculiar morphology of the Western Central Andean forearc. Here, we propose a large‐scale model to explain the Myr‐long low uplift rate of the Arica Bend concerning seismic coupling and continental wedge‐top basin evolution. New geomorphic and sedimentologic data are integrated with seismicity and structural data from the literature to interpret the post‐Oligocene pattern of uplift, erosion and sediment transport to the trench. Results show that the Arica Bend has been marked by exceptionally low coastal uplift rates over post‐Oligocene timescales. In addition, this uplift anomaly at the Arica Bend correlates with relatively high sediment discharge to the corresponding trench segment since late Oligocene time. We interpret that before 25 Ma, the forming seaward concavity of the subduction zone induced trench‐parallel extension at the curvature apex of the overriding forearc. The subsequent low uplift rate would have then triggered a feedback mechanism, where the interplay between relatively low interplate friction, low coastal uplift and relatively high sediment discharge favoured Myr‐long relative subsidence at the Arica Bend, in contrast to Myr‐long uplift of the Coastal Cordillera north and south of it.     

Mid Campanian‐Lower Maastrichtian magnetostratigraphy of the James Ross Basin,Antarctica: Chronostratigraphical implications

The James Ross Basin, in the northern Antarctic Peninsula, exposes which is probably the world thickest and most complete Late Cretaceous sedimentary succession of southern high latitudes. Despite its very good exposures and varied and abundant fossil fauna, precise chronological determination of its infill is still lacking. We report results from a magnetostratigraphic study on shelfal sedimentary rocks of the Marambio Group, southeastern James Ross Basin, Antarctica. The succession studied covers a ~1,200 m‐thick stratigraphic interval within the Hamilton Point, Sanctuary Cliffs and Karlsen Cliffs Members of the Snow Hill Island Formation, the Haslum Crag Formation, and the lower López de Bertodano Formation. The basic chronological reference framework is given by ammonite assemblages, which indicate a Late Campanian – Early Maastrichtian age for the studied units. Magnetostratigraphic samples were obtained from five partial sections located on James Ross and Snow Hill islands, the results from which agree partially with this previous biostratigraphical framework. Seven geomagnetic polarity reversals are identified in this work, allowing to identify the Chron C32/C33 boundary in Ammonite Assemblage 8‐1, confirming the Late Campanian age of the Hamilton Point Member. However, the identification of the Chron C32/C31 boundary in Ammonite Assemblage 8‐2 assigns the base of the Sanctuary Cliffs Member to the early Maastrichtian, which differs from the Late Campanian age previously assigned by ammonite biostratigraphy. This magnetostratigraphy spans ~14 Ma of sedimentary succession and together with previous partial magnetostratigraphies on Early‐Mid Campanian and Middle Maastrichtian to Danian columns permits a complete and continuous record of the Late Cretaceous distal deposits of the James Ross Basin. This provides the required chronological resolution to solve the intra‐basin and global correlation problems of the Late Cretaceous in the Southern Hemisphere in general and in the Weddellian province in particular, given by endemism and diachronic extinctions on invertebrate fossils, including ammonites. The new chronostratigraphic scheme allowed us to calculate sediment accumulation rates for almost the entire Late Cretaceous infill of the distal James Ross Basin (the Marambio Group), showing a monotonous accumulation for more than 8 Myr during the upper Campanian and a dramatic increase during the early Maastrichtian, controlled by tectonic and/or eustatic causes.     

Controls on intermontane basin filling,isolation and incision on the margin of the Puna Plateau,NW Argentina (~23°S)

Intermontane basins are illuminating stratigraphic archives of uplift, denudation and environmental conditions within the heart of actively growing mountain ranges. Commonly, however, it is difficult to determine from the sedimentary record of an individual basin whether basin formation, aggradation and dissection were controlled primarily by climatic, tectonic or lithological changes and whether these drivers were local or regional in nature. By comparing the onset of deposition, sediment‐accumulation rates, incision, deformation, changes in fluvial connectivity and sediment provenance in two interrelated intermontane basins, we can identify diverse controls on basin evolution. Here, we focus on the Casa Grande basin and the adjacent Humahuaca basin along the eastern margin of the Puna Plateau in northwest Argentina. Underpinning this analysis is the robust temporal framework provided by U‐Pb geochronology of multiple volcanic ashes and our new magnetostratigraphical record in the Humahuaca basin. Between 3.8 and 0.8 Ma, ~120 m of fluvial and lacustrine sediments accumulated in the Casa Grande basin as the rate of uplift of the Sierra Alta, the bounding range to its east, outpaced fluvial incision by the Río Yacoraite, which presently flows eastward across the range into the Humahuaca basin. Detrital zircon provenance analysis indicates a progressive loss of fluvial connectivity from the Casa Grande basin to the downstream Humahuaca basin between 3 and 2.1 Ma, resulting in the isolation of the Casa Grande basin from 2.1 Ma to <1.7 Ma. This episode of basin isolation is attributed to aridification due to the uplift of the ranges to the east. Enhanced aridity decreased sediment supply to the Casa Grande basin to the point that aggradation could no longer keep pace with the rate of the surface uplift at the outlet of the basin. Synchronous events in the Casa Grande and Humahuaca basins suggest that both the initial onset of deposition above unconformities at ~3.8 Ma and the re‐establishment of fluvial connectivity at ~0.8 Ma were controlled by climatic and/or tectonic changes affecting both basins. Reintegration of the fluvial network allowed subsequent incision in the Humahuaca basin to propagate upstream into the Casa Grande basin.     

Provenance of the Lower Triassic Bunter Sandstone Formation: implications for distribution and architecture of aeolian vs. fluvial reservoirs in the North German Basin

Zircon U–Pb geochronometry, heavy mineral analyses and conventional seismic reflection data were used to interpret the provenance of the Lower Triassic Bunter Sandstone Formation. The succession was sampled in five Danish wells in the northern part of the North German Basin. The results show that sediment supply was mainly derived from the Ringkøbing‐Fyn High situated north of the basin and from the Variscan belt located south of the basin. Seismic reflection data document that the Ringkøbing‐Fyn High was a local barrier for sediment transport during the Early Triassic. Hence, the Fennoscandian Shield did not supply much sediment to the basin as opposed to what was previously believed. Sediment from the Variscan belt was transported by wind activity across the North German Basin when it was dried out during deposition of the aeolian part of the Volpriehausen Member (lower Bunter Sandstone). Fluvial sand was supplied from the Ringkøbing‐Fyn High to the basin during precipitation events which occurred most frequently when the Solling Member was deposited (upper Bunter Sandstone). Late Neoproterozoic to Carboniferous zircon ages predominate in the Volpriehausen Member where the dominant age population with a peak age of 337 Ma corresponds to the culmination of Variscan high‐grade metamorphism, whereas a secondary age population with a peak at 300 Ma matches the timing of volcanism and magmatism at the Carboniferous/Permian boundary in the northern Variscan belt. Parts of the basement in the Ringkøbing‐Fyn High were outcropping during the Early Triassic and zircon ages similar to this Mesoproterozoic basement are present in the Bunter Sandstone. The heavy mineral assemblage of the Solling Member is uniform and has a high garnet content compared to the contemporaneous sediments in the Norwegian‐Danish Basin and in the southern part of the North German Basin. This finding confirms that a local source in the Ringkøbing‐Fyn High supplied most of the fluvial sediment in the northern part of the North German Basin. The northernmost part of the Bunter Sandstone is situated on a platform area that is separated from the basin area by a broad WNW–ESE‐oriented fault zone. The most promising reservoir in the basin area is the aeolian Volpriehausen Member since the sandstone has a wide lateral distribution and a constant thickness. The alluvial to ephemeral fluvial Solling Member may be a good reservoir in the platform area and marginal basin area, but the complex sand‐body architecture makes it difficult to predict the reservoir quality.     

Using basin thermal history to evaluate the role of Miocene–Pliocene flat‐slab subduction in the southern Central Andes (27° S–30° S)

Studies in both modern and ancient Cordilleran‐type orogenic systems suggest that processes associated with flat‐slab subduction control the geological and thermal history of the upper plate; however, these effects prove difficult to deconvolve from processes associated with normal subduction in an active orogenic system. We present new geochronological and thermochronological data from four depositional areas in the western Sierras Pampeanas above the Central Andean flat‐slab subduction zone between 27° S and 30° S evaluating the spatial and temporal thermal conditions of the Miocene–Pliocene foreland basin. Our results show that a relatively high late Miocene–early Pliocene geothermal gradient of 25–35 °C km⁻¹ was typical of this region. The absence of along‐strike geothermal heterogeneities, as would be expected in the case of migrating flat‐slab subduction, suggests that either the response of the upper plate to refrigeration may be delayed by several millions of years or that subduction occurred normally throughout this region through the late Miocene. Exhumation of the foreland basin occurred nearly synchronously along strike from 27 to 30° S between ca. 7 Ma and 4 Ma. We propose that coincident flat‐slab subduction facilitated this wide‐spread exhumation event. Flexural modelling coupled with geohistory analysis show that dynamic subsidence and/or uplift associated with flat‐slab subduction is not required to explain the unique deep and narrow geometry of the foreland basin in the region implying that dynamic processes were a minor component in the creation of accommodation space during Miocene–Pliocene deposition.     

Relationships between tectonic activity and sedimentary source-to-sink system parameters in a lacustrine rift basin: A quantitative case study of the Huanghekou Depression (Bohai Bay Basin,E China)

Lacustrine rift basins commonly preserve a fairly complete record of the sediment source-to-sink (S2S) system, and consequently may form an ideal natural laboratory for establishing quantitative relationships between the various elements within the S2S system. The tectonic-activity rate in the source (e.g., fault-growth rate and fault-activity rate), accommodation space and depositional system in the sink (e.g., areal extent and volume, as well as the depositional dip of the fan- and braid-deltas) are genetically related and their quantitative correlations are explored. The Palaeogene succession on the southwestern margin of the Huanghekou Depressionin the Bohai Bay Basin, one of the largest lacustrine rift basins in eastern China, was chosen to study these relationships, using 3-D seismic, core and well-log data. The tectonic activity was strongly related to the sediment supply, accommodation space and morphology of the sink area. Three different rates of tectonic activity are identified; these led to changes in the basic features of the S2S system that influenced each other. In Members 4 and 3 (lower unit) of the Shahejie Fm. (40.44–44.7 Ma), strong tectonic activity led to significant uplift, resulting in the widest exposure of the provenance area to erosion, to a high sediment-supply rate, to a steep slope and to a large accommodation space which controlled the development of several fan-deltas with steep progradational angles. In Member 3 (upper unit) of Shahejie Fm. (37.89–40.44 Ma) and Member 3 of Dongying Fm. (30.2–33.28 Ma), decreased tectonic activity led to slower uplifting, resulting in a wider alluvial plain, longer transport distances, a lower sediment-supply rate and less accommodation space, so that braid-deltas with larger volumes and a gentler slope developed; In Members 1 and 2 of Shahejie Fm. (33.28–37.89 Ma) and Member 2 of Dongying Fm. (26.71–30.2 Ma), still further decreasing tectonic activity led to a still lower sediment-supply rate, a more gentle depositional slope, less accommodation space, and the development of several braid-deltas with a gentle angle. The quantitative relationships established here advance our understanding of the relationships within lacustrine source-to-sink systems, especially for tectonically controlled rift basins.     

Structural and depositional controls on Plio‐Pleistocene submarine channel geometry (Taranaki Basin,New Zealand)

High‐quality 3D seismic data are used to investigate the effect of the Parihaka Fault on the geometry of submarine channels in Northern Graben of the Taranaki Basin, New Zealand. The Parihaka Fault comprises of four segments (S1–S4) with variable displacements. As part of the Plio‐Pleistocene Giant Foresets Formation, the older Channel Complex Systems 1 and 2 reveal a two‐stage evolution: (a) a syn‐tectonic depositional stage with channels incising the slope during early fault growth (ca. 4.5 Ma) and (b) a stage of sediment bypass (ca. 3 Ma) leading to the infill of hanging‐wall depocentres. The Channel Complex System 3 is syn‐tectonic relative to segment S3 and was formed at ca. 2.5 Ma. We show that the successive generation of new fault segments towards the north controlled the formation of depocentres in the study area. This occurred in association to rotation and uplift of the footwall block of the Parihaka Fault and subsidence of its hanging‐wall block, with fault activity controlling the orientation of channel systems. As a result, we observe three drainage types in the study area: oblique, transverse and parallel to the Parihaka Fault. This work is important as it shows that relay zones separating the Parihaka Fault segments had limited influence on the geometry and location of channel systems. Submarine channels were diverted from their original courses close to the Parihaka Fault and flowed transversally to fault segments instead of running through relay ramps, contrasting to what is often recorded in the literature. A plausible explanation for such a discrepancy relates to rapid progradation of the Giant Foresets Formation during the Plio‐Pleistocene, with channel complexes becoming less confined, favouring footwall incision and basinward deposition of submarine fans.     

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.     

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.     

Rapid exhumation of basement rocks along the northern margin of the North China craton in the early Jurassic: evidence from the Xiabancheng Basin,Yanshan Tectonic Belt

Early Mesozoic Basins in the Yanshan Fold–Thrust Belt (YFTB), located along the northern margin of the North China Craton (NCC), record significant intraplate deformation of unknown age. In this article, we present evidence for the rapid exhumation of high‐grade basement rocks along the northern margin of the NCC in the Early Mesozoic. U–Pb geochronology of detrital zircons constrains the maximum depositional ages of syntectonic sedimentary units that formed during the unroofing of basement rocks and plutons in the Xiabancheng Basin. In the Early Mesozoic, the Xiabancheng Basin recorded a dramatic transformation in depositional environments, related to a significant change in the regional tectonic setting. In this study, the tectonic evolution of the YFTB is established from paleocurrent data and U–Pb zircon ages of sandstone and granitic gravels of the Xingshikou Formation, Xiabancheng Basin. The paleocurrent direction of meandering fluvial facies in the Triassic Liujiagou and Ermaying Formations are from east to west. In contrast, the overlying Xingshikou Formation consists of alluvial fan facies with paleocurrent directions from north‐northwest to south‐southeast. The lower and middle segments of the Xingshikou Formation record rapid exhumation of basement rocks along the northern margin of the NCC. U‐Pb ages of detrital zircons within the Xingshikou Formation are characterized by three major U–Pb age groups: 2.2–2.5 Ga, 1.7–1.8 Ga and 193–356 Ma. From 193 Ma to 356 Ma, a subsidiary peak occurs at 198 ± 5 Ma, constraining the sedimentation age of the Xingshikou Formation to the Early Jurassic. Zircon from the Wangtufang pluton in the northern portion of the Xiabancheng Basin yields U–Pb ages of 191 ± 1 Ma and 207 ± 1 Ma. Within error, these crystallization ages are identical to detrital zircon ages of 206 ± 1 Ma and 206 ± 2 Ma obtained for granitic gravel clasts in the Xingshikou Formation. Thus, the Wangtufang pluton and surrounding basement rocks must have experienced rapid uplift and exhumation during the Early Jurassic. The onset of exhumation along the northern margin of the NCC occurred at ca. 198–180 Ma.     

Unroofing the core of the central Andean fold‐thrust belt during focused late Miocene exhumation: evidence from the Tipuani‐Mapiri wedge‐top basin,Bolivia

As the highest part of the central Andean fold‐thrust belt, the Eastern Cordillera defines an orographic barrier dividing the Altiplano hinterland from the South American foreland. Although the Eastern Cordillera influences the climatic and geomorphic evolution of the central Andes, the interplay among tectonics, climate and erosion remains unclear. We investigate these relationships through analyses of the depositional systems, sediment provenance and ⁴⁰Ar/³⁹Ar geochronology of the upper Miocene Cangalli Formation exposed in the Tipuani‐Mapiri basin (15–16°S) along the boundary of the Eastern Cordillera and Interandean Zone in Bolivia. Results indicate that coarse‐grained nonmarine sediments accumulated in a wedge‐top basin upon a palaeotopographic surface deeply incised into deformed Palaeozoic rocks. Seven lithofacies and three lithofacies associations reflect deposition by high‐energy braided river systems, with stratigraphic relationships revealing significant (～500 m) palaeorelief. Palaeocurrents and compositional provenance data link sediment accumulation to pronounced late Miocene erosion of the deepest levels of the Eastern Cordillera. ⁴⁰Ar/³⁹Ar ages of interbedded tuffs suggest that sedimentation along the Eastern Cordillera–Interandean Zone boundary was ongoing by 9.2 Ma and continued until at least ～7.4 Ma. Limited deformation of subhorizontal basin fill, in comparison with folded and faulted rocks of the unconformably underlying Palaeozoic section, implies that the thrust front had advanced into the Subandean Zone by the 11–9 Ma onset of basin filling. Documented rapid exhumation of the Eastern Cordillera from ～11 Ma onward was decoupled from upper‐crustal shortening and coeval with sedimentation in the Tipuani‐Mapiri basin, suggesting climate change (enhanced precipitation) or lower crustal and mantle processes (stacking of basement thrust sheets or removal of mantle lithosphere) as possible controls on late Cenozoic erosion and wedge‐top accumulation. Regardless of the precise trigger, we propose that an abruptly increased supply of wedge‐top sediment produced an additional sedimentary load that helped promote late Miocene advance of the central Andean thrust front in the Subandean Zone.     

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.