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The Middle Jurassic–Early Cretaceous evolution of the Neuquén Basin is traditionally attributed to a long phase of thermal subsidence. However, recent works have challenged this model. In view of this, we study the Late Jurassic Tordillo Formation, a non‐marine depositional unit that marks a shift to regional regression across the basin. Previous studies propose different causes for this regression, including the growth of the magmatic arc in the west, uplift in the south or extension in the north. We studied the Tordillo Formation in sections located at an intermediate position in the Neuquén Basin, in order to understand the tectonic processes active during sedimentation. We present evidence of normal faulting within the Tordillo Formation and the base of the overlying Vaca Muerta Formation. Some of these faults can be attributed as syndepositional. We characterize the Tordillo Formation as part of a distal fan‐playa lake depositional system with a contemporaneous western magmatic arc as the main source of sediment. When compared to the Late Triassic–Early Jurassic NE to NNE‐oriented rifting, which marks the opening of the Neuquén Basin, the Late Jurassic extension shows a switch in stress orientation; the latter is orthogonal to the north‐trending subduction zone. We interpret this change as a renewed phase of back‐arc extension induced by slab rollback along with minor distributed intraplate extension prior to opening of the South Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Recognizing detrital contributions from sediment source regions is fundamental to provenance studies of active and ancient orogenic settings. Detrital zircon U-Pb geochronology of unconsolidated sands from modern rivers that have source catchments with contrasting bedrock signatures provides insight into the fidelity of U-Pb age signatures in discriminating tectonic provenance and downstream propagation of environmental signals. We present 1705 new detrital zircon U-Pb ages for 15 samples of unconsolidated river sands from 12 modern rivers over a large spatial extent of Ecuador (~1°N-5°S and ~79°-77°W). Results show distinctive U-Pb age distributions with characteristic zircon age populations for various tectonic provinces along the Andean convergent margin, including the forearc, magmatic arc, and internal (hinterland) and external (foreland) segments of the fold-thrust belt. (1) Forearc and magmatic arc (Western Cordillera) river sands are characterized by Neogene-Quaternary age populations from magmatic sources. (2) Rivers in the hinterland (Eastern Cordillera) segment of the Andean fold-thrust belt have substantial populations of Proterozoic and Paleozoic ages, representing upper Paleozoic-Mesozoic sedimentary and metasedimentary rocks of ultimate cratonic origin. (3) River sands in the frontal fold-thrust belt (Subandean Zone to Oriente Basin) show distinctive bimodal Jurassic age populations, a secondary Triassic population, and subordinate Early Cretaceous ages representative of Mesozoic plutonic and metamorphic bedrock. Detrital zircon U-Pb results from a single regional watershed (Rio Pastaza) spanning the magmatic arc to foreland basin show drastic downstream variations, including the downstream loss of magmatic arc and hinterland signatures and abrupt introduction and dominance of selected sources within the fold-thrust belt. Disproportionate contributions from Mesozoic crystalline metamorphic rocks, which form high-elevation, high-relief areas subject to focused precipitation and active tectonic deformation, are likely the product of focused erosion and high volumes of local sediment input from the frontal fold-thrust belt, leading to dilution of upstream signatures from the hinterland and magmatic arc. [ABSTRACT FROM AUTHOR]

Carbon dioxide drawdown resulting from enhanced chemical weathering during orogenesis has been invoked to explain late Cenozoic global cooling. Establishing chemical weathering records from the India–Asia collision zone is important to test this hypothesis because uplift of the Tibetan Plateau is thought to be responsible for Cenozoic cooling. However, proxies for the intensity of chemical weathering can be affected by additional factors, such as sediment grain size and provenance. Here we report major element compositions and calculated chemical weathering intensity records of three size fractions (0–5, 5–20, 20–63 μm) from the Dahonggou section of the Qaidam Basin in the northeastern Tibetan Plateau, and compare those records with published provenance data from the same section. Results show that the indices of the fine (0–5 μm) fraction vary in coordination with provenance shifts, but variations of the 5–20 and 20–63 μm fractions are less affected by provenance variations. Comparison with Upper Continental Crust reveals that some labile elements are not leached but instead are enriched in the fine fraction, indicating that it does not faithfully record chemical weathering intensity. In addition, weathering can result in clay mineral transformation instead of elemental variations, complicating the relationship between element‐based parameters and weathering intensity. This work suggests that changes in sediment provenance must be accounted for when inferring variations in chemical weathering intensity on the basis of element‐based weathering intensity indices of the clay fraction. Plain Language Summary: Understanding the relationships among climate change, chemical weathering, and uplift of the Tibetan Plateau is significant for predicting future climate change. However, this relationship is unclear due to the lack of accurate nonmarine chemical weathering records. In this contribution, we compare geochemical records of multiple grain‐size fractions from Cenozoic strata in the Qaidam Basin with changes in sediment provenance. The weathering indices of the 5–20 and 20–63 μm fractions show less influence of provenance changes than the finest (0–5 μm) fraction. We conclude that the silt‐sized fraction provides a better proxy to reconstruct weathering history than a finer fraction. We also recommend that weathering studies be accompanied by sediment provenance data to screen for provenance‐driven changes. Key Points: We report major element compositions of different sediment size fractions from the Qaidam BasinChanges in major element compositions of the 0–5 μm fraction correlate with provenance changesMajor element compositions of coarser fractions are less affected by provenance shifts and are inferred to reflect chemical weathering [ABSTRACT FROM AUTHOR]

Integration of regional stratigraphic relationships with data on sediment accumulation, provenance, paleodrainage, and deformation timing enables a reconstruction of Mesozoic-Cenozoic subduction-related mountain building along the western margin of South America. Sedimentary basins evolved in a wide range of structural settings on both flanks of the Andean magmatic arc, with strong signatures of retroarc crustal shortening, flexure, and rapid accumulation in long-lived foreland and hinterland basins. Extensional basins also formed during pre-Andean backarc extension and locally in selected forearc, arc, and retroarc zones during Late Cretaceous-Cenozoic Andean orogenesis. Major transitions in topography and sediment routing are recovered through provenance studies, particularly detrital zircon U-Pb geochronological applications, which distinguish three principal sediment source regions—the South American craton, Andean magmatic arc, and retroarc fold-thrust belt. Following the cessation of Late Triassic–Early Cretaceous extensional and/or postextensional neutral-stress conditions, a Late Cretaceous-early Paleocene inception of Andean shortening was chronicled in retroarc regions along the western margin by rapid flexural subsidence, a wholesale reversal in drainage patterns, and provenance switch from eastern cratonic sources to Andean sources. An enigmatic Paleogene hiatus in the Andean foreland succession recorded diminished accumulation and/or regional unconformity development, contemporaneous with a phase of limited shortening or neutral to locally extensional conditions. Seemingly contradictory temporal fluctuations in tectonic regimes, defined by contrasting (possibly cyclical) phases of shortening, neutral, and extensional conditions, can be linked to the degree of mechanical coupling along the subduction plate boundary. Along-strike variations in Late Cretaceous-Cenozoic deformation and crustal thickening demonstrate contrasting high-shortening versus low-shortening modes of Andean orogenesis, in which the central Andes are distinguished by large-magnitude east-west shortening (> 150–300 km) and corresponding cratonward advance of the fold-thrust belt and foreland basin system, several times that of the northern and southern Andes. These temporal and spatial changes in shortening and overall tectonic regime can be related to variable plate coupling during first-order shifts in plate convergence, second-order cycles of slab shallowing and steepening, and second-order cycles of shortening, lithospheric removal and local partial extensional collapse in highly shortened and thickened segments of the orogen. [ABSTRACT FROM AUTHOR]

A >15-20 km-thick succession in southern Bolivia forms the most-complete stratigraphic record in western Gondwana. Upper Neoproterozoic–Carboniferous clastic rocks record ∼300 Myr of marine, nonmarine, and glacially influenced sedimentation in diverse basin systems generated by variable tectonic regimes along the western edge of Gondwana during active and passive-margin conditions. New provenance results help resolve key uncertainties regarding source regions and sediment dispersal patterns. The findings are integrated with spatial variations in stratigraphic thicknesses to evaluate regional patterns of basin subsidence, magmatism, and deformation during long-term evolution of the western Gondwanan margin in the central Andes. Detrital zircon U–Pb geochronological data for 17 sandstone samples reveal sedimentary input from Precambrian cratonic basement provinces and pre-Andean basement, magmatic arc, and fold-thrust belt source regions. The basement age signatures indicate derivation from the flanking Brasiliano (900-560 Ma) and Pampean (650-500 Ma) provinces to the south and east, and the distal Rio de la Plata craton (2400-2000 Ma) along the eastern South American margin ∼1000–1500 km to the southeast. Although the greater Amazonian craton was not a major contributor, subordinate Amazonian signatures from the Sunsás (1300-950 Ma) province to the east and northeast selectively fed the northern basin regions of the central Andes. Despite the lack of Paleozoic igneous rocks in Bolivia, detrital zircons of Ordovician age attest to the pre-Andean influence of the subduction-related Famatinian magmatic arc. Limited Devonian-Carboniferous igneous material was contributed locally from western pre-Andean highlands or regionally by axial northward transport from selected igneous sources in Argentina and Chile. Episodic recycling of Neoproterozoic–Paleozoic basin fill, including a sharp reappearance of Famatinian-age detritus, can be linked to periods of Paleozoic crustal shortening and foreland sedimentation ascribed to Famatinian, Ocloyic, Chañic, or Gondwanide phases of deformation. The spatial distribution of sediment sources along with temporal shifts in sediment routing highlight several stages in the paleogeographic evolution of the western Gondwanan margin preserved in the central Andes. Initial regional subsidence spanned a multiphase Neoproterozoic to early Paleozoic history of Rodinia breakup, Brasiliano-Pampean orogenesis, and post-orogenic back-arc extension prior to final late Paleozoic amalgamation of Gondwana. The early Paleozoic onset of subduction and Famatinian arc magmatism led to high-magnitude subsidence (>10–15 km) likely driven by Ordovician slab rollback in an extensional back-arc basin. Thereafter, intermittent Paleozoic contraction in a poorly understood pre-Andean system (best expressed in the Eastern Cordillera of Bolivia and neighboring segments of northern Argentina and southern Peru) generated transient topographic loads that produced superimposed flexural foreland and successor basin systems. • Southern Bolivia contains the most-complete stratigraphic record of western Gondwana. • Detrital zircon U-Pb ages reveal Neoproterozoic-Paleozoic shifts in sediment sources. • Proximal and distal (>1000 km) cratonic sources fed pre-Andean sedimentary basins. • Slab rollback in a back-arc basin likely caused >10 km of Ordovician subsidence. • Cratonic and Famatinian arc/orogenic sources fed Paleozoic foreland/successor basins. [ABSTRACT FROM AUTHOR]

Detrital zircon U-Pb geochronology has been used extensively to develop provenance histories for surface outcrops of key stratigraphic localities within sedimentary basins. However, many basins lack sufficiently continuous and widespread exposures of complete successions to evaluate proposed longterm tectonic histories, stratigraphic correlations, and paleodrainage patterns within individual basins. Here, we demonstrate the utility of subsurface detrital zircon U-Pb analysis by integrating ages from three key wells (21 subsurface samples) with previously reported data from six exposed intervals (90 surface samples) within a single basin. Samples from the 5-10-km-thick clastic successions span several structural blocks over an ~300 × 50 km swath of the Middle Magdalena Valley Basin, a north-trending intermontane basin in the northern Andes of Colombia. Available U-Pb age distributions for modern rivers highlight the distinctive signatures of several competing sediment sources, including two major contiguous ranges (Central Cordillera and Eastern Cordillera) and two localized block uplifts (Santander Massif and San Lucas range). U-Pb results from Jurassic through Neogene stratigraphic units spanning the nine surface and subsurface sites, including several type localities, enable comparisons of provenance shifts at specific sites and spatial variations among key stratigraphic intervals across multiple sites. Distinctive age populations for the Andean magmatic arc, retroarc foldthrust belt, and South American craton facilitate correlation of stratigraphic units and reconstruction of the long-term provenance and tectonic evolution of the Middle Magdalena Valley Basin. Nearly all surface and subsurface localities show up-section changes in age spectra consistent with (1) Jurassic growth of extensional subbasins fed by local igneous sources, (2) Cretaceous deposition in an extensive postrift setting, and (3) protracted Cenozoic growth of basin-bounding ranges during Andean crustal shortening. Subsurface samples augment surface samples, highlighting their utility in developing regional source-to-sink relationships, the timing of paleodrainage integration, and tectonic reconstructions. Provenance shifts of mid-Paleocene and latest Eocene-earliest Oligocene age are consistent with incipient uplift of the flanking Central Cordillera and Eastern Cordillera, respectively. However, a well-documented phase of latest Paleocene-middle Eocene beveling of basement uplifts in the Middle Magdalena Valley Basin appears to be largely aliased in the detrital record. Moreover, despite the proximity of the magmatic arc, there is insufficient syndepositional evidence for a proposed Paleogene pulse of magmatism and, in this case, limited utility of U-Pb ages in pinpointing precise depositional (stratigraphic) ages. U-Pb age spectra for Oligocene through Pliocene basin fill underscore complex along-strike (north-south) and cross-strike (east-west) variations reflective of compartmentalized transverse deposystems demarcated by pointsource contributions from the Central Cordillera and Eastern Cordillera. The late Miocene appearance of 100-0 Ma grains and a regional switch to broad, multimodal age distributions suggest the initial integration of the longitudinal proto-Magdalena River, linking the Middle Magdalena Valley Basin with southern headwaters in the Upper Magdalena Valley and likely driving increased sedimentation rates farther north in the offshore Magdalena submarine fan of the southern Caribbean margin. [ABSTRACT FROM AUTHOR]

Laramide basement blocks of the U.S. Rocky Mountain Province have long been considered the sediment source of the Paleocene-Eocene Wilcox Group, implying that large-scale progradation driven by Laramide uplift induced a transition from carbonate to clastic deposition in the Gulf of Mexico. Detrital zircon U-Pb age spectra from 10 samples collected from the Wilcox Group in south Texas reveal a complex grain assemblage with major age populations at ca. 1800-1300 Ma and 350-50 Ma and minor populations at 1300-950 Ma, 3250-1850 Ma, and 900-400 Ma. Modal data for Wilcox Group sand grain populations from the same region suggest a diverse provenance, including sources from the Cordilleran magmatic arc and subordinate reworked sedimentary rocks. Sediment was primarily derived from a mix of crystalline basement blocks in the U.S. southern Rocky Mountains and northern Mexico, the Cordilleran arc of western Mexico and the southwestern United States, and Mesozoic-Paleogene magmatic rocks of northern Mexico. Secondary sources include recycled strata from Sevier-Laramide basins in the southwestern United States and northern Mexico. Comparisons of detrital zircon U-Pb age spectra show that the Lower Wilcox subunit contains significant magmatic arc-derived sediment, whereas the Upper Wilcox subunit is more enriched in basement and recycled sedimentary detritus. Therefore, the relatively quartzose composition of the bulk detrital assemblages throughout the Wilcox Group of south Texas is not an accurate reflection of the range of volcanic and basement sources indicated by the associated U-Pb ages, suggesting significant attrition of unstable grains during long-distance (>500-1000 km) transport. [ABSTRACT FROM AUTHOR]

The Cretaceous-Cenozoic evolution of the Patagonian broken foreland basin system at 42–43°S in the northern Chubut province of Argentina is associated with variable retroarc phases of fold-thrust belt shortening, extension, and basement uplift during changes in the dynamics of oceanic slab subduction. Basement inheritance and progressive shallowing of an east-dipping subducting slab are important mechanisms of foreland partitioning, as dictated by the preexisting (pre-Andean) structural architecture and forelandward (eastward) advance of Late Cretaceous arc magmatism. Previously recognized growth strata help define the timing of fold-thrust belt shortening and retroarc basement-involved uplift, but the precise consequences for sediment routing remain poorly understood, with uncertainties in patterns of basin evolution before, during, and after shallowing and resteepening of the subducting slab. In this study, distinctive sediment source regions and magmatic histories enable evaluation of the stratigraphic and tectonic evolution of the retroarc foreland basin using new provenance results, maximum depositional ages, and isotopic signatures from detrital zircon U-Pb geochronology and Lu-Hf geochemical analyses. A compilation of published bedrock crystallization ages and distributions of metamorphic and igneous basement rocks identify: a western source region defined by the Andean magmatic arc and associated pre-Andean basement; and an eastern source region consisting of intraplate magmatic units and the North Patagonian Massif. We demonstrate that Aptian-Cenomanian retroarc basin fill was derived principally from the basement massif and intraplate volcanic units to the east, followed by a Late Cretaceous (Campanian-Maastrichtian) reversal in sedimentary polarity and subsequent exclusive derivation from the Andean arc and orogenic belt to the west. Late Cretaceous-Paleocene slab shallowing and arc cessation was succeeded by late Eocene–earliest Miocene extension during slab rollback and renewal of arc magmatism. Thereafter, Miocene sedimentation was closely linked to shortening in the Andean fold-thrust belt. Within the retroarc succession, new U-Pb ages provide estimates of depositional ages for Lower Cretaceous through Miocene stratigraphic units. Finally, in addition to U-Pb provenance and chronostratigraphic constraints, zircon Hf isotopic signatures from the detrital record provide confirmation of a Cretaceous-Cenozoic history involving: (1) initial establishment of a continental magmatic arc; (2) transition from a neutral to compressive tectonic regime; (3) shallowing of the subducting slab and arc cessation during retroarc basement partitioning; (4) arc retreat and foreland basin abandonment during slab rollback (with modest extension and crustal thinning); and (5) final renewed shortening during arc rejuvenation. • Detrital zircon U-Pb ages demonstrate Late Cretaceous reversal in sediment polarity. • Depositional ages for growth strata constrain thrust-belt and intraforeland uplift. • Hf isotopes record tectonic reorganization and overriding plate deformational mode. [ABSTRACT FROM AUTHOR]

The Cretaceous Alamor-Lancones Basin is located in the forearc region of southern Ecuador and northern Peru. The eastern (Río Playas) domain includes the upper stratigraphic levels of the 1800 m thick basin-fill succession. Sedimentological, provenance and chronostratigraphic analyses of the Río Playas region help to elucidate the Late Cretaceous to Eocene evolution of the forearc region in southern Ecuador and neighboring regions. The oldest strata of the Río Playas region include Lower Cretaceous volcanic and volcaniclastic deposits of the Celica and Alamor formations, which were deposited in an arc-related extensional basin. These units are unconformably overlain by the Coniacian to Maastrichtian El Naranjo and Casanga formations. Lithofacies described for the El Naranjo and Casanga formations include sandy debrites, sandy turbidites, silty-muddy turbidites, sandy slumps, clast-supported debrites and rafted blocks. These lithofacies association suggests a deepwater submarine fan depositional environment. Provenance analyses for the Casanga and El Naranjo formations, including heavy mineral and petrographic data, show that these formations were derived from erosion of a volcanic arc and a minor granitic and metamorphic source terrane. Detrital zircon U-Pb ages for the Casanga Formation indicate contributions from Santonian age sources, which partially overlap stratigraphic ages, suggesting volcanism contemporaneous with deposition. In addition, paleocurrent analyses indicate sediment transport to the southeast, pointing to a sediment source along the South American margin. Volcanic and volcaniclastic rocks of the Paleocene Sacapalca Formation overlie the Casanga and Naranjo formations in angular unconformity. The Sacapalca Formation passes transitionally into fluvial sandstone, conglomerate and red beds of the Río Playas Formation. Overall, the succession recorded a transition from volcanic to alluvial fan deposition. Heavy mineral and sandstone QFL analyses show a significant input of metamorphic detritus in the Río Playas Formation, which indicates derivation from the Cordillera Real. This interpretation is also supported by detrital zircons of Proterozoic age. The change from submarine fan deposits of the El Naranjo and Casanga formations to the nonmarine Río Playas Formation suggests exhumation in response to an important tectonic event, likely deformation related to collision of the Caribbean Plateau to South America at 73–70 Ma. • Provenance analyses of the Río Playas region elucidate the Cretaceous to Eocene evolution of the Alamor-Lancones Basin. • El Naranjo and Casanga formations were deposited by sediment gravity-flows in a deep-marine environment. • The volcanic record of Sacapalca Formation shows volcanic arc migration from Early Cretaceous to Paleocene time. • Río Playas Formation was deposited in an alluvial fan environment. • Exhumation of Alamor-Lancones Basin was driven by collision of the Caribbean Plateau. [ABSTRACT FROM AUTHOR]

A clear understanding of the provenance of late Cenozoic Chinese loess and the underlying Red Clay deposits will shed light on the history and mechanisms of Asian aridification. Although much progress has been made in understanding the source of Quaternary loess on the Chinese Loess Plateau (CLP), the provenance of the underlying upper Miocene–Pliocene Red Clay sequence is largely unknown. Here we present the first provenance history of the Red Clay sequence based on zircon U–Pb ages from the central CLP. Visual and statistical analyses of the U–Pb age populations and comparison with results from potential source regions reveals that (1) the lowermost Red Clay of the late Miocene (depositional age of ∼8 Ma) is likely sourced from the nearby Liupan Mountains and the Qaidam Basin; (2) the middle Red Clay (5.5–4 Ma) of the early-mid Pliocene is sourced mainly from the Taklamakan desert, transported via lower-level westerly winds; (3) the upper Red Clay of the late Pliocene (∼3 Ma) is sourced from mixed areas, although western source materials from middle-northern Tibetan plateau (including Qaidam Desert sediments and materials eroded from the Qilian Mountains) sediments appear to dominate; and (4) the Quaternary loess is also sourced from mixed source regions, albeit with dominant northern CLP proximal desert sediments transported via winter monsoon winds, which in turn may be transported from mountain source regions of the northeastern Tibet and Gobi Altai via major river systems. This long term shift in sources suggests a progressive eastward aridification during the Pliocene in Asia with the specific timing of provenance shifts synchronous with large-scale climatic transitions and Tibetan uplift, demonstrating that Asian desertification is controlled by both factors. [ABSTRACT FROM AUTHOR]

The Magallanes-Austral foreland basin preserves an important record of orogenesis and landscape evolution in the Patagonian Andes of Chile and Argentina. Throughout the retroarc foreland basin, a regional disconformity with little to no angular discordance separates Upper Cretaceous–lower Paleocene strata from overlying deposits of diachronous Eocene to Miocene age. Here we report detrital zircon U-Pb geochronological results for 11 sandstone samples, and vitrinite reflectance data for 6 samples of organic matter from a fossiliferous dinosaur-bearing mixed nonmarine and marine clastic succession in the Río de las Chinas valley (50–51°S) of central-southern Patagonia to: (1) determine the timing and duration of the unconformity using U-Pb maximum depositional age constraints, (2) reconstruct sediment provenance and dispersal patterns, (3) assess possible temporal variations in arc magmatism, (4) evaluate the amount of sedimentary overburden removed during unconformity development, and (5) confirm the presence of a fossiliferous southern hemisphere Cretaceous–Paleogene (K/Pg) boundary site. Samples from the Dorotea Formation yield maximum depositional ages spanning Maastrichtian to Danian time (with ages as young as ∼65–63 Ma), confirming preservation of the K/Pg boundary in a section with recently discovered fossils of dinosaurs, other terrestrial vertebrates, and plants. Samples from directly above the unconformity in the Man Aike Formation, yield middle Eocene maximum depositional ages (with a prominent 45–40 Ma age cluster), indicating a long-lived ∼20 Myr hiatus representative of nondeposition or erosion. Analyses of organic matter preserved in multiple coal horizons of the uppermost Dorotea Formation show consistently low vitrinite reflectance values, requiring limited sedimentary burial, consistent with nondeposition or sediment bypass rather than deposition and later erosional removal of a previously proposed thick package of Paleocene to middle Eocene clastic material. On the basis of regional trends in the age and geometry of the unconformity, timing of arc magmatism, and temporal variations in sediment provenance, we consider a range of potential mechanisms for unconformity genesis, including (1) shortening-related uplift of the frontal fold-thrust belt, (2) cratonward advance of a flexural forebulge, (3) accommodation changes driven by regional or eustatic variations in sea level, (4) ridge collision and slab-window genesis, (5) isostatic rebound during tectonic quiescence (or minor extension), or (6) regional foreland uplift during flat-slab subduction. • Detrital zircon U-Pb ages in the Río de las Chinas valley support the presence of the K/Pg boundary. • U-Pb age spectra indicate two lulls in magmatic productivity from ca. 140–115 Ma and ca. 60–45 Ma. • A major unconformity is constrained to ∼20 Myr between the early Paleocene and middle Eocene. • Results from vitrinite reflectance data suggest limited removal of sedimentary overburden during unconformity genesis. [ABSTRACT FROM AUTHOR]