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Volume 36, Issue 1, 2024
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Controls on sedimentation in a deep‐water foredeep: Central Pindos foreland basin, western Greece
More Less[3D model reconstruction illustrating the depositional setting of the Pindos Foreland Basin during the Late Eocene–Early Oligocene.
This study provides a sedimentological, stratigraphic and palaeocurrent investigation of Upper Eocene to Lower Oligocene deep‐sea fan deposits found in the central part of the Pindos foreland basin in western Greece. According to facies analysis, the examined succession at Amfilochia area has 13 sedimentary facies and 10 facies and sub‐facies associations. Depositional elements include abyssal plain pelagics, outer fan, inner fan, and slope deposits. Outer fan sediments are classified as lobe‐axis, lobe‐off‐axis, lobe‐fringe, and distant lobe‐fringe deposits, while inner fan sediments are classified as channel‐fill, crevasse‐splay, internal and external levee deposits. The stratigraphic study shows an upward shift from abyssal plain pelagics to outer, inner fan, and finally slope deposits, implying submarine fan system progradation and progressive infilling of a deep‐water sediment depocentre. The sediments were deposited in the foredeep of the Pindos foreland system and correspond to the system's underfilled stage, when sedimentation was unable to exceed the accommodation provided by lithospheric flexure. They point to deposition near the onset of the Pindos orogen, after the closure of the Pindos basin because of the collision of the Apulian with the Pelagonian microplate during the Cretaceous‐Palaeogene period. Palaeocurrent data from sole marks show bipolar directions associated with two distinct spreading sub‐marine fan deposits. As a result, the study region was split into Upper (major SE‐direction flow) and Lower (major NW‐direction flow) parts, indicating that axial flows were predominant during sediment deposition. However, as the deposition of the elements continued, the progradation of both systems constrained the space accommodation because of the increased basin sediment supply and forced an increase in the degree of basin confinement that changed the compensational to aggradational stacking pattern. The goals of this research are to develop an updated facies model for these deep‐sea fans as well as a robust correlation framework for the various stratigraphic units in the central Pindos foreland basin. This research also connects the stratigraphic development of deep‐sea fan deposits to the evolutionary phases of the Pindos foreland system, providing fresh insights into the palaeogeographic circumstances in the Pindos foreland basin.
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Seismic stratigraphy and structural evolution of the South Korea Plateau, East Sea (Sea of Japan)
Authors Kyoung‐Jin Kim, Dong‐Geun Yoo, Bo‐Yeon Yi and Nyeon‐Keon Kang[This study presents an intergrated tectonostratigraphic framework of the South Korea Plateau (SKP), East Sea using 2D seismic profiles and borehole data. Based on seismic stratigraphy analysis, we proposed a four‐stage structural and sedimentary evolution model of the SKP which provides a window into understanding potential targets for sandstone reservoirs.
The South Korea Plateau (SKP), a typical submarine plateau, preserves an important tectono‐sedimentary evolutionary record and represents a major frontier area for petroleum exploration in the East Sea (Sea of Japan). However, its tectonic mechanisms and their controls on sedimentary fill are underexplored. Here, we present the first integrated tectonostratigraphic framework of the SKP using reprocessed, two‐dimensional, seismic‐reflection profiles and borehole data. Four regional megasequence boundaries are interpreted, delineating four tectonostratigraphic packages: the syn‐rift (MS1), post‐rift phase 1 (MS2), post‐rift phase 2 (MS3) and syn‐compression (MS4) megasequences. We propose a four‐stage structural and sedimentary evolution model for the SKP based on the megasequences and structural development. Stage‐1 (latest Late Oligocene−Early Miocene): the SKP was rifted and extended through block faulting, resulting in the formation of rift basins dominated by fan‐delta and shallow‐lacustrine depositional systems. Stage‐2 (late Early Miocene−Middle Miocene): hemipelagic sedimentation prevailed with gravity‐controlled slope failures under a tectonically stable environment associated with slow thermal subsidence. Stage‐3 (late Middle Miocene−Late Miocene): continued thermal subsidence allowed the predominance of hemipelagic biogenic deposits accompanied by intermittent mass‐wasting‐induced turbidites and resulted in the development of a polygonal fault system. Stage‐4 (Early Pliocene−present): the SKP was influenced by E−W compression caused by an eastward movement of the Eurasian plate. Turbiditic and hemipelagic sedimentation was predominant with turbidity‐flow‐leveed channels derived from direct riverine input or through slope failures. Based on this tectonostratigraphic analysis, we reveal the variation in depositional systems and sand‐dispersal patterns for the SKP, highlighting potential targets for sandstone reservoirs: MS1, fan‐deltas and lacustrine‐fan turbidites; MS3, deepwater fan turbidites; and MS4, deepwater fan turbidites, channel‐levee complexes and turbidite frontal‐splay deposits. This study proposes a structural and sedimentary evolution model for the SKP that could enhance our understanding of reservoir potential for petroleum‐exploration in the future.
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How displacement analysis may aid fault risking strategies for CO2 storage
Authors Emma Alexandra Harrower Michie and Alvar Braathen[AbstractDeveloping an accurate understanding of the ways in which faults have grown within a particular region and stratigraphy can aid risk management for CO2 storage sites. Areas of fault interaction lead to differences in the stress field, resulting in an increased strain, which is often accommodated by a high intensity of deformation bands and/or fracturing, dependent on host rock properties. These structures alter the permeability surrounding faults. Hence, detecting areas of interaction of structures throughout the fault growth history allows the identification of locations where high risk may occur in terms of the hydraulic properties of a fault zone. The Vette Fault Zone (VFZ), bounding the Alpha prospect within the potential CO2 Smeaheia storage site, Northern Horda Platform, is shown to have grown from a minimum of seven fault segments. By utilising a comparison with the adjacent Tusse Fault Zone (TFZ), we can identify potential areas of high risk, where fluids may have the ability to flow across or along the VFZ. The high seal strength of the TFZ holding back a large gas column is likely to be created by shale juxtaposition and smearing with cataclastic processes. The same could be assumed for the VFZ, associated with similar tectonics and displaced stratigraphy. However, rather than membrane breaching causing fluids to flow across the fault, potential areas of high risk have been identified at locations of relict breached relay zones, where the initial displacement of the intersecting faults and area of overlap was high. These areas appear to correspond with the location of hydrocarbon contact depth (spill point) along the TFZ. Using the same assumptions for the VFZ, we can observe one potential area of high risk, which lies within the area of suggested CO2 accumulation.
,The size of relict breached relay zones has shown to have a potential influence on fault seal integrity, where breached relay zones that had large overlap areas and high throw amplitudes have a greater potential to fracture and allow fluids to flow along/across the fault zone.
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New detrital petrographic and thermochronologic constraints on the Late Cretaceous–Neogene erosional history of the equatorial margin of Brazil: Implications for the surface evolution of a complex rift margin
[Since the Late Cretaceous, the equatorial margin of Brazil has undergone a rift phase, with the erosion of a moderate rift escarpment, a Late Cretaceous–Paleogene post‐rift phase, with major drainage reorganization and significant vertical erosion, and a Late Oligocene‐to‐Recent post‐rift phase, with moderate vertical erosion and river headwater migration.
The equatorial margin of Brazil is an example of a rift margin with a complex landscape, dominated by an escarpment perpendicular to the continental margin, which testifies to an equally complex rift and post‐rift surface and tectonic evolution. This has been the focus of a long debate on the driving mechanism for post‐rift tectonics and on the amount of exhumation. This study contributes to this debate with new petrographic and thermochronologic data on 152 samples from three basins, Pará‐Maranhão, Barreirinhas and Ceará, on the offshore continental platform. Our detrital record goes back to the rift time at ca. 100 Ma ago and outlines three major evolutionary phases of a changing landscape: a rift phase, with the erosion of a moderate rift escarpment, a Late Cretaceous‐Palaeogene post‐rift phase of major drainage reorganization and significant vertical erosion and a Late Oligocene‐to‐Recent post‐rift phase of moderate vertical erosion and river headwater migration. We estimate that along the equatorial margin of Brazil, over a large onshore area, exhumation since the Late Cretaceous has totalled locally up to 2–2.5 km and since the late Oligocene did not exceed 1 km.
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Syn‐ and post‐rift lower crustal flow under the Sunda Shelf, southern Vietnam: A role for climatically modulated erosion
Authors Peter D. Clift and Leora J. Wilson[AbstractTectonic subsidence on rifted, passive continental margins are largely controlled by patterns of extension and the nature of strain partitioning in the lithosphere. The Sunda Shelf, adjacent to the SW South China Sea, is characterized by deep basins linked to regional Cenozoic extension associated with propagating seafloor spreading caused by slab pull from the south. Analysis of seismic reflection profiles and drilled sections crossing the Nam Con Son and Cuu Long basins highlight Oligocene extension, with most of the thinning concentrated in the ductile mid‐lower crust. Upper crustal extension was modest and ductile flow is inferred to be directed northwestwards, towards the oceanic crust. Basin inversion occurred in the Mid Miocene, associated with the collision of the Dangerous Grounds Block and Borneo. Subsequent accelerated tectonic subsidence exceeded predictions from uniform extension models assumed to relate to extensional collapse after inversion. We correlate this to a period of faster erosion onshore driven by strong monsoon rains in Indochina and Peninsular Thailand at that time. Erosion of the onshore basement, inducing rock uplift and coupled with loading of the basins offshore, drives ductile mid‐lower crustal flow, likely to the northeast under Indochina, and/or to the west where Plio‐Pleistocene subsidence of the shelf is very slow. Significant sediment delivery from the Mekong River into the Cuu Long Basin began in the Late Miocene and migrated seawards as the basin filled. Mass balancing suggests that the basins of this part of the Sunda Shelf are filled through erosion of bedrock sources around the Gulf of Thailand. There is no need for sediment delivery from a major river draining the Tibetan Plateau to account for the deposited volumes.
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Cretaceous to Recent tectono‐sedimentary history and subsidence of the Barreirinhas, Ceará and Potiguar Basins, Brazilian Equatorial Margin
[AbstractStratigraphy along the Brazilian Equatorial Margin is a crucial guide to the geodynamic history of rifting of Pangea and formation of the South Atlantic Ocean. Understanding the evolution of the Brazilian Equatorial Margin, which intersects the Saint Paul and Romanche Fracture Zones on the western margin of South Atlantic Ocean, is also key for reconstructing eustatic histories and natural resource exploration. In this study, we quantify the stratigraphic and subsidence histories of three sedimentary basins—Barreirinhas, Ceará, Potiguar—that sit within the margin. Stratigraphy was mapped using ca. 900‐line‐km of two‐dimensional seismic data. Biostratigraphic and check‐shot data from 23 wells drilled on the continental shelf, slope and in the distal parts of these basins were used to date and depth‐convert stratigraphy. Check‐shot data were also used to parameterise compaction. The mapped stratigraphy was backstripped to calculate subsidence histories for the basins. Subsidence curves were decompacted, water‐loaded and corrected for palaeo‐water depths using biostratigraphic data from well reports. The mapped stratigraphy of the Barreirinhas and Ceará Basins and theoretical subsidence curves indicate that stretching factors did not exceed 1.6. These values suggest that these basins can be regarded as failed rifts. In contrast, more distal stratigraphy mapped in the Potiguar Basin to the south indicates that it stretched by a factor of 5–6. Calculated subsidence histories indicate that this basin formed primarily because of Cretaceous rifting and Cretaceous to Recent post‐rift thermal sag, with amplitudes governed by the amount of initial stretching.
,Sketch showing stratigraphy, shape and structure of Barreirinhas, Ceará and Potiguar Basins, highlighting their different tectono‐sedimentary evolution. Barreirinhas and Ceará Basins are considered to be failed rifts, Potiguar Basin formed as a result of Cretaceous rifting and subsequent post‐rift thermal sag.
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Introducing conceptual geological information into Bayesian tomographic imaging
Authors Hugo Bloem, Andrew Curtis and Daniel Tetzlaff[AbstractGeological process models typically simulate a range of dynamic processes to evolve a base topography into a final two‐dimensional cross section or three‐dimensional geological scenario. In principle, process parameters may be updated to better align with observed geophysical or geological data. However, it is hard to find any process model realisations that fit all observations if data sets are complex and sparse in space or time because the simulations typically depend highly non‐linearly on base topography and dynamic parameters. As an alternative, geophysical probabilistic tomographic methods may be used to estimate the family of models of a target subsurface structure that are consistent both with information obtained from previous experiments and with new data (the Bayesian posterior probability distribution). However, this family seldom embodies geologically reasonable images. Here we show that the posterior distribution of tomographic images obtained from travel time data can be fully geological by injecting geological prior information into Bayesian inference and that we can do this near‐instantaneously by using trained mixture density networks (MDNs). We invoke two geological concepts as prior information about the possible depositional environment of an imaged target structure: a braided river system and a set of marine parasequences. Each concept is parameterised by the latent parameters of a generative adversarial network. Data from a target structure can then be used to infer the family of compatible latent parameter values using either geological concept using MDNs. Our near‐instantaneous MDN solutions closely resemble those found using relatively expensive Monte Carlo methods. We show that while the use of incorrect geological conceptual models provides significantly less accurate results, a classifier neural network can infer which geological conceptual model is most consistent with the data. It is thus demonstrated that even apparently barely related geophysical data may contain information about abstract geological concepts, and that geological conceptual models are key to creating reasonable images from geophysical data.
,The true marine parasequences parameter matrix (left) and the summary statistics for the posterior estimates from the MDN (top) and McMC (bottom). The statistics are the posterior mean, posterior standard deviation, and the travel time misfits.
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New insights into the crustal architecture and tectonic evolution of the Eastern Gulf of Mexico
[The Gulf of Mexico is an intraplate oceanic basin where rifting commenced in the Late Triassic, leading to drifting and ensuing oceanic accretion by Middle‐Late Jurassic, which ceased by the Early Cretaceous. Its tectonic evolution encompasses multiple rifting phases dominated by orthogonal extension, variable magmatism and salt deposition. This complex tectonic history is recorded within the rifted margins of the Gulf of Mexico, including along the eastern part of the basin, where considerable uncertainty remains regarding the tectonic evolution and resulting crustal configuration. This study presents new insights into the crustal types and an updated tectonic framework for the Florida margin. An integrated analysis of seismic and potential field data allows us to characterize the nature of the crust, which shows wide zones of hyperextended continental crust, seaward dipping reflection (SDR) packages, exhumed mantle and magmatic crust. Our results propose elements that could improve the plate model of the Gulf of Mexico, by accounting for the polyphase nature of rifting, the counter‐clockwise rotation of the Yucatan block and the observed increase in magmatic supply.
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Joint application of fluid inclusion and clumped isotope (∆47) thermometry unravels the complexity of thermal and fluid‐flow history reconstruction in sedimentary basins—Upper Triassic Chaunoy Formation reservoirs (Paris Basin)
More Less[AbstractWe investigated calcites and dolomites precipitated during burial diagenesis of the Upper Triassic (Norian) continental siliciclastics from sub‐surface reservoirs of the northern Paris Basin (Chaunoy Formation) that experienced a thermal maximum >100°C during Late Cretaceous times. Relative carbonate precipitation timing was established via petrographic analyses. The diagenetic carbonates were further investigated by fluid inclusion and clumped isotope (Δ47) thermometry. The two thermometric datasets were interpreted by evaluating the possible occurrence of inclusion thermal reequilibration and Δ47 solid‐state reordering, based on the known basin thermal history and the three existing Δ47 reordering models. By considering the fluid inclusion and Δ47 datasets obtained and the various Δ47 reordering models, different carbonate precipitation scenarios, in terms of timing and parent fluid composition (δ18Ofluid), were inferred. These results underline that in samples having experienced thermal maximum >100°C, accuracy and interpretation of fluid inclusion and Δ47 thermometry data (especially on calcite) may be biased by thermal reequilibration and solid‐state reordering. The results converge towards the need of jointly applying fluid inclusion and Δ47 thermometry on the same carbonate phases to evaluate all the possible precipitation scenarios. The most likely carbonate precipitation scenarios, based on Δ47 thermometry data, point at the precipitation of two calcite phases during Early to Late Jurassic times and of one dolomite phase during the Late Cretaceous. The parent fluids possibly were original formation waters of the Chaunoy Fm. that mixed with brines migrating from the East, where time equivalent evaporitic deposits occur. The proposed precipitation model for calcites and dolomites, involving different pulses of brine migration, and the dominance of calcite phases were not recorded by previous studies on the Upper Triassic units. These latter results may be of interest to evaluate the reservoir potential of the Chaunoy Fm. in this underexplored portion of the Paris Basin.
,Precipitation timing and δ18Ofluid for the studied diagenetic carbonates obtained from different temperature datasets (fluid inclusions, ∆47).
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Simulations of the effect of smectite‐to‐illite transition in shales on permeability and overpressures using a stochastic approach, a Norwegian margin case study
[(a) Simulated log permeability versus depth (m TVD) for Skarv Field pressure cell with 1000 realizations, compared to published shale permeability data. For own shale samples are smectite and mixed layer conted plotted in percent. (b) Corresponding simulated overpressures versus depth for the same 1000 realizations. Magnitude of measured overpressures observed for the pressure cell is shown in blue. No data for the Lysing Fm was available.
The smectite‐illite transition in shales due to subsidence, temperature changes and diagenesis influences many processes in a sedimentary basin that can contribute to overpressure build up like reducing the shale permeability. The smectite‐rich layers can form sealing barriers to fluid flows that will influence pore pressure prognosis for drilling campaigns, contribute to sealing caprocks for possible CO2 storage and to sealing of plugging and abandonment wells. In this work, we have included the diagenetic smectite‐illite transition into a three‐dimensional pressure simulation model to simulate its effect on pressure build‐up due to reduced shale permeabilities over geological time scale. We have also tested effect of thermal history and potassium concentration on the process of smectite‐illite transition and the associated smectite‐illite correction on permeability. A new smectite‐illite correction has been introduced, to mimic how shale permeability will vary dependent on the smectite‐illite transition. Stochastic Monte Carlo simulations have been carried out to test the sensitivity of the new correction parameters. Finally, a 3D Monte Carlo pore pressure simulation with 1000 drawings has been carried out on a case study covering Skarv Field, and Dønna Terrace offshore Mid‐Norway. The simulated mean overpressures are in range with observed overpressures from exploration wells in the area for the Cretaceous sandy Lysing Formation and for the two Cretaceous Intra Lange Formation sandstones. The simulated smectite content versus depth is in line with published XRD dataset from wells. The corresponding modelled present‐day permeabilities for the shales including the smectite‐illite transition are two magnitudes higher than measured permeabilities on small samples in the laboratory using transient decay method. The measured permeabilities are in the range of 2.66·10−18 to 3.94·10−22 m2 (2695 to 0.39 nD) for the North Sea database and represent the end members for shales‐permeabilities with the lowest values, since the small samples are selected with no or minor natural fractures. This work shows that by upscaling shale permeabilities from mm‐scale to km scale, natural fractures and sedimentary heterogeneities will increase the shale permeabilities with a factor of two and that by including permeability correction controlled by the smectite fraction, pressure ramp can be simulated due to diagenesis effect in shales.
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Structure and morphology of an active conjugate relay zone, Messina Strait, southern Italy
Authors Rebecca J. Dorsey, Sergio G. Longhitano and Domenico Chiarella[Normal faults in Messina Strait define an active conjugate relay zone where strain is transferred along strike between facing normal faults in southern Calabria and northeast Sicily. Stratigraphic and geomorphic data record tectonic narrowing of the strait in the past ca. 2.5 Myr by inward migration of facing normal faults and rapid mantle‐driven uplift.
Messina Strait is a narrow fault‐bounded marine basin that separates the Calabrian peninsula from Sicily in southern Italy. It sits in a seismically active region where normal fault scarps and raised Quaternary marine terraces record ongoing extension driven by southeastward rollback of the Calabrian subduction zone. A review of published studies and new data shows that normal faults in the Messina Strait region define a conjugate relay zone where displacement is transferred along strike from NW‐dipping normal faults in the northeast (southern Calabria) to the SE‐dipping Messina‐Taormina normal fault in the southwest (offshore eastern Sicily). The narrow marine strait is a graben undergoing active subsidence within the relay zone, where pronounced curvature of normal faults results from large strain gradients and clockwise rotations related to fault interactions. Based on regional fault geometries and published age constraints, we infer that normal faults in southern Calabria migrated northwest while normal faults in NE Sicily migrated southeast during the past ca. 2–2.5 Myr. This pattern has resulted in tectonic narrowing of the strait through time by inward migration of facing normal faults and rapid mantle‐driven uplift.
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Identification and differentiation of vertical movement through morphological changes and stratigraphic imprint: Two distinct uplifting mechanisms in the upper Calabrian accretionary wedge, western Ionian Sea
Authors Bruna T. Pandolpho, Morelia Urlaub, Christian Berndt and Jörg Bialas[AbstractThe seafloor morphology reflects both past and on‐going sedimentary, oceanographic and tectonic processes. Vertical movement is one of the drivers responsible for reshaping the seafloor through forming steep flanks that decrease slope stability, favour landslides, change current paths, form minibasins and control the sediment deposition, distribution and geometry. Here, we make use of these interactions to derive vertical movements and constrain the active tectonic processes at the western termination of the upper Calabrian accretionary wedge from the integrated analysis of bathymetric, backscatter, surface attributes and high‐resolution reflection seismic data. Within this area, we identify two types of deformational features and mechanisms that affect the depositional, erosional and tectonic processes at different scales. These include the deviation of channels, landslide scars, mass transport deposits (MTDs), separated drifts, sediment waves, lineaments and offset seafloor structures. The first type (long‐wavelength uplift) is an uplifted 22‐km‐wide region, in which seismic onlap relationships and the dip of deep reflectors suggest long‐lasting but slow tectonic uplift affecting sedimentation, and the second type (short‐wavelength uplift) includes three narrow elongated structures and one circular dome encircling the first region of uplift. We interpret that the first type of uplift feature was caused by tectonic deformation, while the second type is interpreted as formed by the fast uplift, tilting and faulting of modern sediments caused by diapirism due to rapid sedimentation in response to the first tectonically driven uplift. The study provides insight into the complex interaction of tectonic and sedimentary processes in the upper Calabrian accretionary wedge.
,Reconstruction of thesedimentary processes active on the basin before, during, and after thevertical movement of the long‐wavelength uplift (Central Area) and the short‐wavelengthuplift (diapirs D1 to D4). This model is based on the interpretation ofgeomorphological proxies.
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The cryptic stratigraphic record of the syn‐ to post‐rift transition in the offshore Campos Basin, SE Brazil
[Uninterpreted and seismic lines, with the mapped stratigraphic surfaces and tectono‐stratigraphic intervals. Some reflectors are traced in black to evidence syn‐, post‐ and syn‐ to post‐tectonic configurations (sensu Péron‐Pinvidic et al., 2007).
Rift basins typically comprise three main tectono‐stratigraphic stages; pre‐, syn‐ and post‐rift. The syn‐rift stage is often characterised by the deposition of asymmetric wedges of growth strata that record differential subsidence caused by active normal faulting. The subsequent post‐rift stage is defined by long‐wavelength subsidence driven by lithospheric cooling and is typified by the deposition of broadly tabular stratal packages that drape any rift‐related relief. The stratigraphic contact between syn‐ and post‐rift rocks is often thought to be represented by an erosional unconformity. However, the late syn‐rift to early post‐rift stratigraphic record is commonly far more complex since (i) the associated tectonic transition is not instantaneous; (ii) net subsidence may be punctuated by transient periods of uplift; and (iii) strain often migrates oceanward during rifting until continental breakup is achieved with crustal rupture. Previous publications on the Eastern Brazilian marginal basins have not historically used the tripartite scheme outlined above, with the post–pre‐rift interval instead being subdivided into rift, sag and passive margin tectono‐stratigraphic stages. In addition, the sag stage has been previously described as late syn‐rift, early post‐rift or as a transition between the two, with the passive margin stage being equivalent to the classically defined post‐rift, drift stage. Two (rather than one) erosional unconformities are also identified within the rift‐to‐sag succession. In this work, we use 2D and 3D seismic reflection and borehole data to discuss the expression of and controls on the syn‐ to post‐rift transition in the shallow and deep water domains of the south‐central Campos Basin, south‐east Brazil. We identified three seismic–stratigraphic sequences bounded by unconformities, named lower and upper pre‐salt and salt. The lower pre‐salt interval is characterised by wedge‐shaped packages of reflections that thicken towards graben and half‐graben‐bounding normal faults. This stage ends with the development of an angular unconformity, inferred to form as a result of the onset of the oceanward migration of deformation. The upper pre‐salt is typically defined by packages of subparallel and relatively continuous reflections that are broadly lenticular and thin towards fault‐bound basement highs, but that locally contain packages that thicken against faults. The pre‐salt to salt contact is defined by an erosional unconformity that is largely restricted to basement highs, and which is inferred to have formed due to base‐level fall and uplift associated with local fault reactivation, resulting in the formation of channels of possible fluvial origin. Based on its geometries and seismic facies, we conclude that the lower pre‐salt interval is syn‐rifting and syn‐tectonic, deposited during active continental extension and upper crustal faulting affecting the entire evolving margin, whereas the overlying upper pre‐salt is syn‐rifting and post‐tectonic in the Campos Basin, deposited when extension and faulting had migrated seaward to the future location of the spreading centre. The results of our study support the arising notion that the syn‐rift sequence does not only display syn‐tectonic sedimentary packages, and thus the tripartite tectono‐stratigraphic model for rift development is too simplistic and cannot be applied when assessing rifts in the context of the regional development of continental margins.
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Decoupling external forcings during the development of Miocene fluvial stratigraphy of the North Patagonian Foreland
AbstractThe Patagonian Andean foreland system includes several intermountain basins filled with a Miocene non‐marine record deposited under syn‐tectonic conditions related to the Andean uplift and a regional climate change triggered by a rain shadow effect. Many of those basins, such as the Collón Cura basin in Neuquén Province, Argentina, present a well‐preserved fluvial record (i.e. the Limay Chico Member of the Caleufú Formation). Sedimentological and palaeomagnetic studies have allowed the interpretation of coeval transverse distributary fan and axial mixed‐load fluvial systems deposited between 10.6 ± 0.2 and 12.8 Ma. The basin infill arrangement shows that, while the axial mixed‐load fluvial system exhibits an aggradational stacking pattern, the transverse distributary fluvial fan system denotes three different orders of stratigraphic patterns: (i) large‐scale progradation of the transverse fluvial fan system over a time scale of 106 year; (ii) intermediate‐scale progradational–retrogradational transverse intra‐basinal fluvial fan episodes over a time scale of 105 year; and (iii) small‐scale transverse lobe progradation over a time scale of 105–104 year. These patterns were interpreted as transverse sediment flux variations triggered by variable external forcings. To decouple those forcings, we estimated the Collón Cura basin equilibrium time at 3–5 × 105 year and compared it with the time scale over which different external forcings varied in the Patagonian Andean and foreland regions during Miocene times. Large‐scale progradation is linked to an increase in sediment flux triggered by a long‐term tectonically driven exhumation forcing associated with the Miocene Patagonian Andean contractional phase. Intermediate‐scale progradational–retrogradational episodes are linked to variations in sediment flux due to a mid‐term tectonic forcing associated with the western fault system activity. The small‐scale fan lobe progradation is related to increases in sediment flux triggered by indistinguishable short‐term autogenic processes and/or high‐frequency tectonic and climatic forcings. This contribution shows the applicability and limitations of the basin equilibrium time concept to decouple external forcings from the geological record, considering their magnitude, nature and time scale, as well as the basin characteristics.
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Interactions between pre‐existing structures and rift faults: Implications for basin geometry in the northern South China Sea
Authors Wei Guan, Lei Huang, Chiyang Liu, Guangrong Peng, Han Li, Chao Liang, Lili Zhang, Hongbo Li, Zhe Wu, Xin Li and Ruining Hu[AbstractThe northern South China Sea (SCS) margin evolved from the Mesozoic convergent to Cenozoic divergent continental margin, and thus, it developed on a heterogeneous crystalline basement with inherited Mesozoic structures. Pre‐existing structures and their interactions with rift faults have historically not been described or interpreted in the intensely stretched Baiyun sub‐basin. Large‐scale 3D seismic reflection data allow us to identify four types of Mesozoic tectonic fabrics within the basement and explain their genesis: (1) Thin, isolated and north‐dipping seismic reflections 1, interpreted as thrust faults representing orogenic processes. Tilted thick seismic reflections 2 are formed by reactivation of seismic reflections 1 during post‐orogenic extension, which are all related to the NW‐ward subduction of the palaeo‐Pacific plate. (2) Thin, isolated and shallowly dipping seismic reflections 3 and low‐amplitude, semi‐transparent and chaotic seismic reflections 4 represent the low‐angle thrust system and the associated nappe units, which are related to the shift from NW‐ to NNW‐ward subduction of the paleo‐Pacific plate. Subsequently, we investigate the structural interaction between Mesozoic intra‐basement and Cenozoic rift structures. Syn‐rift, post‐rift and long‐term faults are developed in Cenozoic strata, and quantitative statistical and qualitative analyses revealed two main types of structural interactions between them and underlying intra‐basement structures: (1) Rift faults develop with inheritance of intra‐basement structures, including fully and partially inherited faults. (2) Rift faults modify intra‐basement structures, although they are controlled by intra‐basement structures at an earlier stage. Finally, our results reveal the control of pre‐existing structures on the geometry of the Baiyun sub‐basin, especially the selective reactivation of NE‐trending shear zones (SR2), which are influenced by the regional stress field and the width and dip of the shear zones.
,Pre‐existing structures and their types of interaction with rift faults during the evolution of the northern South China Sea from a convergent to a divergent continental margin.
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Progradational‐to‐retrogradational styles of Palaeogene fluvial fan successions in the San Juan Basin, New Mexico
Authors Kristine L. Zellman, Piret Plink‐Björklund and Leland Spangler[AbstractBasin‐scale outcrop analyses of fluvial architecture in the Palaeogene San Juan Basin, New Mexico, document lateral and vertical trends in channel, floodplain and palaeosol characteristics. Herein, the uppermost part of the Palaeocene Nacimiento Formation and lower Eocene Cuba Mesa and Regina Members of the San Jose Formation are identified as deposits of large fluvial fans based on trends observed across the basin. Stratigraphic trends suggest two packages originated by fluvial fan progradation. Progradation of the lower fan system provides a new explanation for the transitional nature of a disconformity at the Nacimiento–San Jose Formation contact, previously thought to be a low‐angle unconformity. The two fan systems are separated by a retrogradational interval that culminates in a depositional hiatus at the contact between the Cuba Mesa and Regina Members. This, combined with poor age constraints, indicates that the duration of the disconformity at the base of the Cuba Mesa Member may have been overestimated. Furthermore, the succession is interpreted as deposits of variable‐discharge rivers, based on the combined abundance of upper flow regime and high deposition rate sedimentary structures indicative of intense flooding events, preservation of in‐channel bioturbation and paedogenic modification indicating periods of prolonged dryness, lack of identifiable bar strata and alternations of poorly drained and well‐drained floodplain deposits with pedofacies indicating alternating wet–dry cycles. This dataset adds to a growing body of evidence linking the formation of large fluvial fans to discharge variability and thus to hydroclimates with significant inter‐ and intra‐annual precipitation variability and intense rainfall. A long‐term stratigraphic shift from poorly drained to well‐drained floodplain deposits across two progradational fan successions indicates that a predictive model suggesting downstream decreases in soil drainage conditions is not encompassing of all large fan systems, and instead suggests a transition to a more arid climate across the Palaeocene–Eocene boundary.
,Examples of architectural styles observed in the study area and a comparison with proximal, medial, and distal areas of a modern fluvial fan. (a) Amalgamated channel fills and minor floodplain, interpreted as proximal fan deposits. The degree of channel amalgamation is highest in the most proximal sector where the fan area is smallest, and the aggradation rates and channel‐return frequency are highest. (b) Heterolithic channel fills and floodplain, interpreted as medial fan deposits. Increased spacing between channel deposits and decreased channel belt size are attributed to losses from infiltration and to the medial fan's larger area, allowing for greater preservation potential for mudrock‐prone floodplain deposits. (c) Isolated channel fills and dominant floodplain, interpreted as distal fan deposits. The more isolated channels are thought to result from a continued widening of the area covered by the fan and additional decreases in discharge due to losses from infiltration (d) Satellite image obtained from Google Earth of a 60‐km long fluvial fan in the Taklamakan Desert, Xinjiang, China with approximate locations of modern proximal, medial and distal fan annotated.
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Late Permian‐Early Triassic intracontinental tectonic inversion in the Junggar Basin, NW China: New insights from detrital zircon geochronology and seismic reflection data
[AbstractThe Junggar Basin is located on the southwestern margin of the Central Asian Orogenic Belt (CAOB). Whether the Late Permian‐Early Triassic tectonic inversion there recorded the final closure of the North Tianshan Ocean or post‐accretionary intracontinental deformation remains controversial. Linking the structural style and provenance analysis of the western and northern margins of the Junggar Basin can provide a better understanding of this tectonic event and its geodynamic mechanisms. Seismic reflection profiles show that Early Permian syn‐rift half‐grabens were followed by the Middle Permian thermal sag, which is characterized by regional onlap and the migration of the depocentre to the centre of the basin. Together with the published isopach and palaeogeography maps in the western margin of the Junggar Basin, the seismic profiles demonstrate that the reactivation of the Ke‐Bai and Wu‐Xia dextral transpressive fault zones between the West Junggar terrane and the Mahu sag controlled the tilting and deformation of pre‐Permian strata and the distribution of Late Permian‐Early Triassic fan deltas. The reported igneous and sedimentological evidence indicates that the southern margin of the Junggar Basin was a rift basin controlled by transtensional strike‐slip faults in the Early Permian, and also was followed by a Middle Permian thermal sag. Quantitative provenance analysis using detrital zircon geochronology and the DZmix program shows that the West Junggar terrane and Tianshan orogenic belts experienced varied uplift, indicative of a transition from the Middle Permian thermal sag peneplanation to the Late Permian‐Early Triassic tectonic inversion involving reactivation of Early Permian normal faults. This intracontinental deformation event in the Junggar Basin was taken up by block counterclockwise rotation during the final amalgamation of the Pangea, which may be the long‐range effect of the final closure of Paleo‐Asia Ocean in the eastern part of the CAOB.
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Episodic evolution of a protracted convergent margin revealed by detrital zircon geochronology in the Greater Caucasus
Authors Dylan A. Vasey, Leslie Garcia, Eric Cowgill, Charles C. Trexler and Tea Godoladze[Detrital zircon geochronology delineates four phases of deposition in the Greater Caucasus: (1) Devonian to Early Carboniferous deposition prior to Late Carboniferous accretion, (2) Permian to Triassic deposition in the forearc of a volcanic arc, (3) Jurassic deposition during back‐arc extension and magmatism, and (4) Cretaceous deposition during tectonic quiescence.
Convergent margins play a fundamental role in the construction and modification of Earth's lithosphere and are characterized by poorly understood episodic processes that occur during the progression from subduction to terminal collision. On the northern margin of the active Arabia‐Eurasia collision zone, the Greater Caucasus Mountains provide an opportunity to study a protracted convergent margin that spanned most of the Phanerozoic and culminated in Cenozoic continental collision. However, the main episodes of lithosphere formation and deformation along this margin remain enigmatic. Here, we use detrital zircon U–Pb geochronology from Paleozoic and Mesozoic (meta)sedimentary rocks in the Greater Caucasus, along with select zircon U–Pb and Hf isotopic data from coeval igneous rocks, to link key magmatic and depositional episodes along the Caucasus convergent margin. Devonian to Early Carboniferous rocks were deposited prior to Late Carboniferous accretion of the Greater Caucasus crystalline core onto the Laurussian margin. Permian to Triassic rocks document a period of northward subduction and forearc deposition south of a continental margin volcanic arc in the Northern Caucasus and Scythian Platform. Jurassic rocks record the opening of the Caucasus Basin as a back‐arc rift during southward migration of the arc front into the Lesser Caucasus. Cretaceous rocks have few Jurassic‐Cretaceous zircons, indicating a period of relative magmatic quiescence and minimal exhumation within this basin. Late Cenozoic closure of the Caucasus Basin juxtaposed the Lesser Caucasus arc to the south against the crystalline core of the Greater Caucasus to the north and led to the formation of a hypothesized terminal suture. We expect this suture to be within ~20 km of the southern range front of the Greater Caucasus because all analysed rocks to the north exhibit a provenance affinity with the crystalline core of the Greater Caucasus.
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Triassic temporal and spatial migration of the provenance along the South Ordos Basin: Insights into the tectonic evolution of Eastern Palaeo‐Tethys Ocean
Authors Yanhua Xu, Dengfa He, Di Li, Hanyu Huang and Xiang Cheng[Tectonic dynamics model of time‐transgressive tectono‐sedimentary responses in the SOB and adjacent areas during the (a) Early Triassic, (b) early Middle Triassic, (c) late Middle Triassic and (d) Late Triassic. Solid coloured arrows represent different provenance regions: green (QB and SOB); blue (NQLB); red (Alxa Block); and purple (northern NCB).
Clarifying the role of mountain‐building processes in the filling history of large hinterland basins is an essential aspect of basin–mountain system research. We consider the case of the Triassic South Ordos Basin (SOB) to clarify these points. Located in the south‐western North China Block (NCB), the SOB which preserves the most complete Triassic deposition on the north of the Qinling Orogenic Belt (QB) is crucial for understanding the detailed tectonic processes of the QB. Sedimentological, petrological and zircon U–Pb geochronological signatures from the three parts (eastern, central and western) in the SOB indicate that the sediment source migrated both temporally and spatially. Stratigraphic correlation identified two fluvial progradational episodes from south to north in the fluvial–deltaic–lacustrine sedimentary system, one in the eastern SOB and the other in the central SOB. The Late Triassic detrital zircons in the central SOB with distinguishing Neoproterozoic ages were derived from the southern margin of the NCB and the QB. The western SOB exhibited the sediment source shifted from pre‐Triassic North Qilian Belt sedimentary cover to basement from the Middle‐to‐Late Triassic based on a zircon age transition from ca. 2000 to ca. 430 Ma. Late Triassic sediment sources also included the southern margin of the NCB and the QB. Differing provenances from east to west were also confirmed using thin section and heavy mineral analyses. Regional comparisons of zircon age distributions in the eastern SOB with published data indicate that detritus from the QB was first transported to the eastern SOB and then to the central and western SOB. Spatiotemporal changes in the sediment source and sedimentary filling transitions in the three parts of the SOB suggest that the QB underwent asynchronous uplift that began in the east during the Early Triassic and propagated westward, reaching its maximum extent in the early Late Triassic.
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The interplay between siliciclastic and carbonate depositional systems: Maastrichtian to Danian basin‐floor sediments of the mid‐Norwegian Møre Basin
[Interplay between siliciclastic and carbonate depositional systems.
Source‐to‐sink sedimentary systems associated with volcanic rifted margins serve as important archives for basin development by recording lithospheric changes affecting the depositional systems. Distinguishing between sediment transport processes and their sediment source(s) can guide the interpretation of a basin's history, and thereby inform regional paleogeographic reconstructions. In this contribution, we integrate and utilize wireline geophysical logs, detailed petrographic observations from side‐wall cores, and seismic analysis to describe and decipher a Maastrichtian to Danian‐aged basin‐floor depositional system in the deep outer Møre Basin, mid‐Norwegian margin. Well 6302/6‐1 (Tulipan) is a spatially isolated borehole drilled in 2001 that penetrates Maastrichtian and younger strata. A succession of hitherto undescribed carbonates and sandstones in the outer Møre Basin was discovered. It is investigated for sediment transport, provenance, and depositional processes on the basin floor surrounded by structural highs and ridges. The strata from the lower parts form a basin‐floor apron consisting of redeposited carbonate sourced from a westerly sub‐aerial high. The apron transitions vertically from mixed siliciclastic and carbonate into a purely siliciclastic fan with intercalated sandstone and mudstone, providing a rare high‐resolution record of how depositional environments experience a complete shift in dominant processes. The development coincides with similar latest Cretaceous‐earliest Palaeocene sequences recorded south of this region (e.g., well 219/20‐1) and may have been influenced by regional uplift associated with the onset of magmatism in the Northeast Atlantic. This study improves our understanding of a late, pre‐breakup source‐to‐sink sedimentary system developed near the breakup axis of an infant ocean, and documents what is possibly the northernmost chalk deposit in the Chalk Group.
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Neogene drainage reorganization of Longzhong Basin driven by growth of the northeastern Tibetan Plateau: A Sr isotope hydrological perspective
Authors Yudong Liu, Yibo Yang, Zhantao Feng, Zhongyi Yan, Yahui Yue, Fuli Wu, Bowen Song and Xiaomin Fang[AbstractThe Tibetan Plateau uplift has significantly influenced Asian geomorphic and climate patterns. Drainage evolution across the plateau and its surroundings as the consequence of such changes in landscape and climate provides an opportunity to understand the growth of the Tibetan Plateau. However, the evolution history of major drainage areas around the Tibetan Plateau is largely unknown. Here, we reconstructed the evolution of drainage patterns of the Cenozoic Longzhong Basin in the northeastern Tibetan Plateau since the India–Asia collision using palaeo‐water solute 87Sr/86Sr ratio records from its subbasins. Higher solute 87Sr/86Sr ratios of the Lanzhou and Xining Basins and their consistent temporal variations before ca. 22 Ma as well as lower solute 87Sr/86Sr ratios in the Linxia Basin collectively indicate a relatively steady drainage pattern of the integrated Longzhong Basin. A diverse evolution of the solute 87Sr/86Sr ratio in the Lanzhou and Xining Basins after ca. 22 Ma suggests that there was a drainage reorganization, characterized by the division of one into multiple catchment centres, in response to the growth of the northeastern Tibetan Plateau. Subsequently, the identical solute 87Sr/86Sr ratios in the Lanzhou and Xining Basins were further approached at ca. 16 Ma, and the rise in the solute 87Sr/86Sr ratios of the Linxia and Tianshui Basins occurred at ca. 9–8 Ma, indicating two subsequent changes in solute composition induced by the middle Miocene uplift and late Miocene dust expansion, respectively. Our reconstructions of Cenozoic hydrological evolution in the Longzhong Basin indicate accelerated basin segmentation and drainage adjustment with solute change in response to the growth of the northeastern Tibetan Plateau during the Neogene.
,Cenozoic drainage reorganization of the Longzhong Basin, as revealed by the evolution of palaeo‐water 87Sr/86Sr ratios.
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Sedimentary architecture of submarine lobes affected by bottom currents: Insights from the Rovuma Basin offshore East Africa
Authors Mei Chen, Shenghe Wu, Ruifeng Wang, Jiajia Zhang, Pengfei Xie, Min Wang, Xiaofeng Wang, Qicong Xiong, Jitao Yu and Elda Miramontes[Bottom currents play a key role in controlling the evolution of submarine lobes by creating asymmetrical channel‐levee systems that direct the migration of lobes in the upstream direction of the current.
The influence of bottom currents on submarine channels has been widely recognized, for instance, by the formation of asymmetric channel‐levee systems and drifts. In contrast, it is often considered that submarine lobes can be only reworked by strong bottom currents and are not affected by bottom currents during their deposition. In this study, we analyse the potential effect of bottom currents on different hierarchical lobe architectures that formed during the lower Oligocene in the Rovuma Basin offshore East Africa. We characterize the stacking patterns, morphology and connectivity of different hierarchy lobes using well data and three‐dimensional seismic data. We found no direct influence of bottom currents on the lobe complexes and single lobes that show a unidirectional stacking pattern that is opposite to the direction of bottom currents. Lobe elements in single lobes display vertical accretion with no obvious relationship with bottom currents. Additionally, the first deposited single lobe morphology presents an asymmetric shape, with a thicker lobe margin on the downstream side of the bottom currents, but this is due to an initial low topography on the downstream side rather than bottom currents. The architectural distribution reflects that the topography present before the depositions of the submarine lobes was controlled by previous asymmetrical channel‐levee systems formed by the synchronous interaction of bottom currents and gravity flows. This asymmetric topography controls the subsequent deposition of lobes and results in the migration of single lobes in the upstream direction of bottom currents. Although weak to moderate bottom currents may not be able to substantially rework submarine lobes, our results demonstrate that they may control the geometry and evolution of submarine channels and thus indirectly affect the thickness and migration of lobes in more environments than previously thought.
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Stratigraphy, palaeogeography and evolution of the lower Nanaimo Group (Cretaceous), Georgia Basin, Canada
[AbstractThe Cretaceous lower Nanaimo Group in the Georgia Basin, Canada comprises multiple depositional phases with distinct depocentres that accumulated in a tectonically active forearc basin setting. Basal coarse‐clastic strata are preserved in paleotopographic depressions and grade upwards into coal‐bearing coastal plains and shallow‐marine deposits. Coal‐bearing and shallow‐marine strata grade laterally into and are overlain by, regionally extensive mudstones and turbidites deposited in deep water. A glauconitic sandstone bed within the deep‐water strata is interpreted as a condensed section and underlies a major disconformity that developed during a pause in the deposition of the lower Nanaimo Group. A second major coarse‐clastic succession occurs hundreds of metres above the glauconite bed in the central Georgia Basin and comprises conglomerate, sandstone, mudstone and coal deposited in continental depositional environments. The shift in sedimentation from the northern Georgia Basin to the central Georgia Basin is interpreted to record the emergence of an island (Nanoose Uplift) in the central Georgia Basin that acted as a major sediment source to the adjacent depocentres. The stratigraphic break between the coal‐bearing coarse‐clastic strata in the northern Georgia Basin and the significantly younger coal‐bearing coarse‐clastic strata in the central Georgia Basin indicates that the lower Nanaimo Group was deposited in distinct depocentres. Between the older, coarse‐clastic strata in the north and younger, coarse‐clastic strata in the central Georgia Basin, we hypothesize that a major deepwater canyon system (Qualicum Canyon) existed and transferred sediment from the semi‐restricted Georgia Basin to the Pacific Ocean to the west. Development of the Qualicum Canyon and exposure of the Nanoose Uplift during deposition of the younger, central coarse‐clastic strata suggests that syntectonic activity drove basin uplift and erosion and this occurred throughout the deposition of the lower Nanaimo Group.
,The siliciclastic lower Nanaimo Group records the initiation and depositional evolution of a forearc basin (Georgia Basin, Canada). Our research revises the traditional lithostratigraphic framework and proposes a new stratigraphic framework for the lower Nanaimo Group. We identify two major coalfields and two deep‐water sediment routing systems, and showcase the link between sedimentation and syntectonism.
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Cenozoic subsidence‐driving mechanisms in the southernmost Patagonian basins of Tierra del Fuego and SW Atlantic
Authors Federico M. Dávila and Xuesong Ding[AbstractForeland basins are ideal laboratories to examine and quantify forces that contribute to Earth's topography. The interaction of these driving mechanisms (atmospheric, lithospheric and asthenospheric) affects the accumulation and preservation of strata in marine or terrestrial depocentres. For foreland basins that cover thousands of kilometres along orogens, geodynamic processes or lithospheric structure might differ and/or overlap differently along or across strike. The Magallanes‐Austral basin in the southernmost Patagonia serves as a good analogue to analyse the interactions between subcrustal forces and foreland sedimentation. While to the northern part of southern Patagonia, Cenozoic basins were predominantly terrigenous and above sea level; at the southernmost end of Patagonia, sedimentation in the island of Tierra del Fuego was mostly submarine. We analysed in this contribution the southernmost foreland of Patagonia by combining backstripping with reconstruction of flexural and dynamic subsidence. These results were compared with terrestrial records exposed further north of southern Patagonia. We found that, in addition to crustal contributions (as deformation and sedimentation), subcrustal forces are required to accommodate the proximal and distal foreland strata and explain the palaeoenvironmental and subsidence discrepancies that resulted after our analysis. When our models are compared with dynamic topographic curves, strong correlations are observed during the Palaeogene, whereas strong topographic differences occurred in the Neogene. Dynamic topography models in the Neogene have reproduced clear uplift, whereas our residual topography results show equilibrium (close to the orogen) to subsidence values (to the distal foreland). We propose that changes in the lithospheric mantle had to work together with the rest of the tectonics and dynamic forces to match 1‐D backstripping and flexural curves. This suggests that foreland basins in southern Patagonia were controlled differently along strike the southern Andes and that crustal deformation, asthenospheric flows and a heterogeneous lithospheric mantle structure affected the Cenozoic basin evolution.
,Geodynamic evolution of southernmost Patagonia. Note the changes in marine and terrestrial sedimentation was strongly controlled by changes in the lithospheric and asthenospheric mantle evolution.
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Placing constraints on the nature of short‐term eustatic curves
Authors Andrew Davies and Michael D. Simmons[AbstractThe isolation of the eustatic signal from the sedimentary record is a challenging task, and accordingly, there is no consensus on the magnitude and pace (rate) of eustatic events in the geological record. Here we critically assess various published short‐term Cretaceous eustatic curves using insights from forward stratigraphic modelling. We generate a range of simulations with varying eustatic rates and sediment supply against a background of constant subsidence. From these, we generate statistics on the accommodation change associated with the various systems tracts for different sediment supply. We quantify the minimum rate needed to generate transgressive systems tracts (TST). Using this threshold and average subsidence rates for passive margins and intracratonic basins, we document some key challenges with a range of Cretaceous eustatic curves. While it is possible to complexify, this approach through the inclusion of other parameters, our results provide a framework for evaluating eustatic (or relative sea level) curves in terms of the implied rate of change of accommodation. Given these caveats, we also show that many estimates of the magnitude of short‐term transgressions are of insufficient rate to generate observable TST. Further, our work places an upper limit on the time frame over which aquifer and thermo‐eustasy can have observable impacts on the rock record, providing support for the action of glacio‐eustasy during the Cretaceous.
,Eustatic curve coloured by the systems tracts predicted from an analysis of a suite of forward stratigraphic models. The two curves use different assumptions on the subsidence rate and rate of change of accommodation needed to generate a TST.
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Facies analysis and sequence stratigraphy of shallow marine, coarse‐grained siliciclastic deposits in the southern Utsira High: The Late Jurassic intra‐Draupne Formation sandstones in the Johan Sverdrup Field (Norwegian North Sea)
Authors Josep M. Puig López, Miquel Poyatos‐Moré and John Howell[Evolution of the different Late Jurassic‐Early Cretaceous depositional environments identified in the Johan Sverdrup Field.
Thin, condensed coarse‐grained shallow marine successions can be difficult to describe and interpret, especially in the subsurface since the recognition of finer‐grained intervals, typically associated with sequence stratigraphic surfaces, is challenging. This lack of mudstones and siltstones means that they also typically make excellent reservoir intervals. The Oxfordian to Volgian intra‐Draupne Formation sandstones in the Johan Sverdrup Field, southern Utsira High, represent such a system. This study presents a new sequence stratigraphic model for the Johan Sverdrup Field that unravels the detailed depositional history of the succession and places its formation within a regional Late Jurassic tectonostratigraphic framework. The intra‐Draupne Formation sandstones comprise four parasequences deposited following a regional Kimmeridgian marine flooding event. Sediments were mainly supplied through West‐derived fan deltas from the Haugaland High and NW‐SE‐directed tidal currents reworking the Augvald Graben and the Avaldsnes High at the East. The oldest parasequence shows a distinctive suite of facies consisting of fine‐grained and mud‐rich bioturbated sandstones deposited in a semi‐restricted lagoon. Subsequent parasequences lack fine‐grained sediments and are dominated by bidirectional cross‐stratified, very coarse‐to coarse‐grained sandstones and gravels deposited in a tidal strait. A progressive reduction of fault‐related subsidence in the Middle Volgian along with Late Volgian‐Ryazanian sea‐level rise and inversion of pre‐existing structures promoted backstepping of the feeder systems, sediment starvation and the progressive deposition of the black and green‐red shales of the Draupne and Asgard formations. The results of this study account for features previously unidentified in the Johan Sverdrup Field and which have implications for understanding the deposition of coarse‐grained shallow marine successions around the Utsira High and other transgressed basement highs.
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Early Jurassic initiation of the modern drainage pattern of the Dabie orogen (East China) revealed by a multi‐proxy provenance approach
Authors Tao Deng, Xiumian Hu, David Chew, Jan Schönig, Anlin Ma, Wendong Liang and Foteini Drakou[AbstractThe timing of the initiation of the present‐day tectonic architecture and drainage systems in eastern China remains debated. This study presents a comprehensive provenance study of the Early Jurassic peripheral basins surrounding the Dabie orogen including framework petrography, heavy‐mineral analysis, single‐grain chronology and chemistry. Clasts of high‐grade schist, muscovite grains, rare gneissic fragments, abundant metamorphic garnet and phengite (Si > 3.3 pfu), combined with a main 216–256 Ma rutile U–Pb population found in these Early Jurassic sandstones, indicate a source from the Triassic (U)HP belt in the Dabie orogen. Sedimentary lithics and ultra‐stable heavy‐mineral assemblages indicate an additional source of recycled sedimentary rocks. Combined with the continuous shift of the youngest detrital rutile age population toward younger ages toward the north that mimics the pattern of metamorphic bedrock ages in the Dabie orogen, we infer that the present surface tectonic architecture and paleodrainage patterns of the Dabie orogen were established in the Early Jurassic. Thus, the Early Jurassic exhumation of the Dabie orogen marked the development of the watershed between Northern and Southern China, namely the Huai River and several principal tributary systems of the middle‐lower Yangtze River.
,Schematic model of the Early Jurassic Dabie orogen. (a) 3D tectonic reconstruction of exhumed tectonometamorphic units and the location of peripheral sedimentary basins. (b) Reconstruction of the palaeo‐drainage pattern. (c) Present‐day drainage pattern for comparison.
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High‐frequency temporal variability of provenance signal in the submarine fan with the narrow shelf: Insights from sediment delivery and formation of late Triassic Zhuoni fan in the northeastern Paleo‐Tethys Ocean
Authors Mingxuan Tan, Haonan Sun, Yilin Fu, Haonan Cui and Chengcheng Zhang[Schematic models illustrating different source‐to‐sink signal propagation patterns, provenance mixing, and formation mechanisms of the late Triassic Zhuoni fan in response to high‐frequency sea‐level fluctuations and monsoon‐induced climate variability.
The submarine fan with a narrow shelf is usually reactive to environmental signal propagation; however, source‐to‐sink functioning can be further complicated by several allogenic forcings. Here, we document the high‐frequency provenance variations and different sediment delivery models recorded in the late Triassic Zhuoni fan developed in the northeastern Paleo‐Tethys Ocean, mainly based on process‐based sedimentological and provenance study of the Panyuan section in the West Qinling area in the northeastern margin of Tibetan Plateau. High‐, low‐density turbidites, hybrid event beds and hyperpycnites are distributed in the lobe‐dominated submarine fan succession. Field sedimentological evidence from surrounding outcrops suggests that shelf‐edge failure was the main cause of most high‐ and low‐density turbidites with the overall absence of submarine slides or slumps, whereas the narrow shelf configuration together with late Triassic humid pulses is favourable for the occurrence of flood‐related hyperpycnites in the Zhuoni fan. Detrital zircon grains (N = 6; n = 123–272) generally have Palaeozoic‐Mesozoic ages (ca. 350–250 Ma and 500–400 Ma) and Neoarchean‐Paleoproterozoic ages (ca. 2100–1750 Ma and 2600–2400 Ma), but they can be further categized into three age groups due to different proportions of Precambrian age populations. The results demonstrate that the potential source areas may include the South and North Qinling Orogenic Belt, Qilian Orogenic Belt, different segments of North China Craton and the tectonic junction area between the Qinling and Qilian Orogenic Belts. The temporal changes in provenance signals, which are reflected by both the detrital zircon age spectra and heavy mineral assemblages, indicate different contributions of those sources in response to sea‐level fluctuation. It could thus give rise to temporal variations between reactive and buffered source‐to‐sink sediment delivery models of the Zhuoni fan, despite the overall narrow shelf configuration. The development of the lowstand Zhuoni fan was directly related to extrabasinal hyperpycnal delivery from the river mouth and its high‐frequency provenance variability recorded different efficiencies of signal transfer through the onshore catchment with significantly influence of temporal storage, fluvial rejuvenation or even regional climate variability. The highstand submarine fan was thought to be formed by shelf‐edge failure with sediment buffering in the shelf region, which was associated with a strong magnitude of provenance mixing. Our work provides a new perspective for deciphering the different origins of deep‐water sediment delivery in response to high‐frequency sea‐level and climate changes.
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Sedimentology and sequence stratigraphy of shallow and deeper marine Miocene deposits: A case study from the St. Paul and Gebel El‐Zeit blocks, Gulf of Suez, Egypt
More Less[AbstractMarginal and deeper marine facies typify the Miocene exposures along the western margin of the Gulf of Suez rift basin. The stratigraphic setting of these facies is a subject of debate and confusing at best. Integrative sedimentological and sequence stratigraphic study of successions exposed in the St. Paul and El‐Zeit blocks provides insight into the lateral relationships between the two facies and their evolution, a topic that is not fully understood. The St. Paul block, located at the basin margin, has thin shallow marine facies, while the succession of El‐Zeit block, situated near the basin axis, consists of basal conglomerates, thin shallow marine carbonates, thick deeper marine shale and marginal evaporites. The facies architecture of these successions is interpreted as belonging to two different depositional models: a fan‐delta/lagoon system followed upwards by an alluvial fans/sabkha‐tidal flat system in the St. Paul hangingwall basin, and carbonate–siliciclastic–evaporite systems on the hangingwall dip‐slope ramp of El‐Zeit block. These models may help understanding the sedimentary history of other similar blocks in the rift basin. The studied facies show many striking features such as deposition during tilting of fault block, abrupt facies and thickness variations, coarse clastic shedding, erosion channel filling, onlapping of high standing blocks and evaporite accumulation. These features are the result of major tectonic events that triggered the formation of unconformities at different hierarchical levels during the late early to middle Miocene. These unconformities subdivide the Miocene facies into five depositional sequences separated by basin‐wide erosional boundaries. This division greatly improves the age control of marginal marine facies. It affords new insight into the evolution of marginal marine facies along the western margin of the basin in relation to deeper facies in the basin centre. Facies and thickness changes in these tectonically induced sequences indicate that basin floor irregularities, subsidence rates, climatic changes, variable sediment influx, sea‐level/brine‐level changes and basin isolation/connection to the Mediterranean Sea are also important factors responsible for their evolution.
,The Miocene facies in the St. Paul and Gebel El‐Zeit display distinct features indicative of rift events, which greatly influenced facies characteristics and stratal architectures. The inferred sequences significantly improve the correlation of the Miocene facies, and enable a better understanding of the complex facies’ variations and their evolution.
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Submarine fluid flow system feeding methane emission in the northern South China Sea
Authors Jiliang Wang, Ang Li, Lawrence Hongliang Wang, Shiguo Wu and Qingping Li[Schematic model showing the submarine fluid flow system feeding methane emassion in the northern South China Sea.
Submarine fluid flow system can transport methane into ocean. However, its evolution is not fully understood, particularly methane migration through the gas hydrate stability zone (GHSZ) in deep‐water settings. Here, we used 3D seismic and well‐logging data to show the currently active fluid flow system in the northern South China Sea. It was interpreted to have two parts and they together feed intermittent methane emission. Three gas clouds have been seismically imaged beneath the base of gas hydrate stability zone (BGHSZ) and a set of new faults can be identified within them. Twenty‐eight seismic pipes were found to penetrate three vertically stacked mass transport deposits (MTDs) above the gas clouds. Log‐seismic correlation shows that the seismic reflections in the pipe represent MTD sediment, bulk carbonate and gas hydrate‐ or free gas‐bearing sediments. We interpreted faults and pipes as the main migration conduits below and above the BGHSZ respectively. The MTD within the GHSZ could seal the underlying free gas transported by faults and thus overpressure built up at the base prior to the occurrences of the pipes and the fracturing through the overlying sedimentary succession. Subsequently, focused fluid flow entered the GHSZ, with the methane probably bypassing the GHSZ before pore clogging of gas hydrates occurred. Additionally, mapping of high‐amplitude reflections surrounding the upper portion of gas clouds reveals the relict free gas associated with three paleo‐GHSZ bases. Episodic emplacements of new MTDs repeatedly caused the upward shifts of the BGHSZ and the resultant gas hydrate dissociation, contributing to methane emission. We proposed that the occurrences of MTDs may facilitate methane emission by intermittently trapping methane and inducing gas hydrate dissociation in deep‐water settings.
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An exploratory study of “large‐n” detrital zircon geochronology of the Book Cliffs, UT via rapid (3 s/analysis) U–Pb dating
[U–Pb geochronology methods using multicollector laser ablation ICP‐MS: (a) “Standard” (30 s/analysis) acquisition rate compared to (b) rapid (3 s/analysis) acquisition rate (3 s instead of 30 s). Maximum depositional age (MDA) plots generated using DZmda (github.com/kurtsundell/DZmda) for Castlegate Formation with (c) standard acquisition and (d) rapid acquisition; and Blackhawk Formation with (e) standard acquisition and (f) rapid acquisition. Common MDA calculation methods include Youngest Single Grain (YSG), Youngest Graphical Peak (YPP), Youngest Gaussian Fit (YGF), Youngest Grain Cluster at 1 s (YGC1s), Youngest Grain Cluster at 2 s (YGC2s), Youngest Three Zircons (Y3Zo, a), the Tau Method (TAU); Youngest Statistical Population (YSP), and Maximum Likelihood Age (MLA). PDP, probability density plot.
Detrital zircon (DZ) U–Pb geochronology has improved the way geologists approach questions of sediment provenance and stratigraphic age. However, there is debate about what constitutes an appropriate sample size (i.e., the number of dates in a DZ sample, n), which depends on project objectives, sample complexity, and, critically, analytical budget. Additionally, there is ongoing concern about bias introduced by zircon grain size. We tested a recently developed rapid (3 s/analysis) data acquisition method by multicollector laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) that incorporates an automated selection routine and calculates two‐dimensional grain geometry from polished sample surfaces. Eleven samples were analysed from below and above the Late Cretaceous (Campanian) basal Castlegate unconformity of the Book Cliffs, Utah, in a down‐depositional‐dip transect including Price, Horse, Tusher, and Thompson canyons. 12,448 new concordant dates were generated during two measurement sessions. Results are consistent with recent studies suggesting there is no major provenance change and little time (1–2 Myr) represented across the unconformity. Grain size and sample size both exert a strong control on sample dissimilarity. Age distributions constructed from subsamples of large grains are systematically less similar to whole samples; age distributions composed of small grains are overall more similar to whole samples. As such, North American sediment sources that produce large grains such as the Grenville and Yavapi‐Mazatzal belts can bias age distributions if only large grains are analysed. A sample size of n = 100 is inadequate for characterizing age distributions as complex as those of the Book Cliffs, whereas a sample size of n = 300 provides good characterization. Sample size of n ≈ 1000 or more is unnecessary unless project objectives include scanning for subordinate age groups, such as when identifying the youngest grains for calculating a maximum depositional age (MDA). Dates used in MDA calculations acquired with rapid acquisition are best re‐analysed with longer LA‐ICP‐MS acquisition methods or isotope dilution thermal ionization mass spectrometry for increased accuracy and precision. We include new MATLAB code and open‐source software programs, DZpick and DZmda, for automated spot picking and calculating MDAs.
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Rift segmentation caused by reactivation of multiple basement structure systems: Evidence from the Hailar‐Tamtsag Rift, northeast Asia
Authors Lulu Wu, Chuanbo Shen, Douglas A. Paton, Yanping Hou, Estelle J. Mortimer, Xiaowei Zeng, Wei Wu and Junfeng Lin[The pre‐rift 3D geometries of multiple basement structure systems (a) and their influence on rift segmentation (b).
Since the influence of structural inheritance on rift geometry has been widely documented, it is easy to assume that rift segmentation, a prominent feature of rift geometry, may have been also influenced by structural heterogeneity. However, limited studies using high‐quality seismic data have considered how basement reactivation is accommodated at individual fault scale and then how this results in rift segmentation at sub‐basin scale. Using extensive high‐quality 3D seismic data and 76 borehole data, we investigate the characteristics of rift architecture, rift‐related fault systems, basement structures and rift evolution in the Hailar‐Tamtsag Rift, northeast Asia. We identify three distinct rift segments which are defined by three rift‐related fault systems and accompanied by three underlying basement structure systems. We recognize three phases of basement reactivation and three types (including five styles) of interactions between basement structures and rift‐related faults. Our study shows that rift segmentation has been caused by reactivation of multiple basement structure systems which not only influence the orientation of rift segments and type of rift architecture, but also control the location, strike, dip and style of the major rift‐related faults. Rift segmentation was completely achieved through multiple phases of basement reactivation, while the main structural framework of segmentation was established through ‘extensive reactivation’ during the second phase extension. Our study examines how multiple basement structure systems control rift segmentation at both individual fault and sub‐basin scales, which can significantly improve our understanding of relationship between structural inheritance and rift segmentation.
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Syn‐rift tectono‐stratigraphic development of the Thebe‐0 fault system, Exmouth Plateau, offshore NW Australia: The role of fault‐scarp degradation
[3D view of the Thebe‐0 fault system. The top pre‐rift surface (TR30.1TS) is displayed to reveal the fault system geometry. Two seismic profiles are displayed oriented perpendicular to the fault and showing the hanging wall syn‐rift interval of interest (latest Triassic to Early Cretaceous). The studied fault‐scarp degradation complex extension is shaded in brown.
The syn‐rift architecture of extensional basins records deposition from and interactions between footwall‐, hangingwall‐, and axially‐derived systems. However, the exact controls on their relative contributions and the overall variable depositional architecture, and how their sediment volume varies through time, remains understudied. We undertook a quantitative approach to determine temporal and spatial changes in the contribution of fault‐scarp degradation to the syn‐rift tectono‐stratigraphic development of the Thebe‐0 fault system on the Exmouth Plateau (NW Shelf, offshore Australia), using high‐quality 3D seismic reflection and boreholes data. The magnitude of footwall erosion was measured in terms of vertical (VE) and headward (HE) erosion by calculating the volume of eroded material along the footwall scarp. A detailed seismic‐stratigraphic and facies analysis allowed us to constrain the architectural variability of the hangingwall depositional systems and the types of resulting deposits (i.e., fault‐controlled base‐of‐scarp, settling from suspension, and hangingwall‐derived). After addressing the syn‐rift tectono‐stratigraphic framework, we suggest that periods of significant erosion along the Thebe‐0 fault scarp are related to the accumulation of fault‐controlled base‐of‐scarp deposits characterised by comprising a lower wedge with chaotic to low‐continuity reflections. Footwall‐derived deposits characterised by an upward decrease in stratigraphic dip are interpreted as related to periods of reduced fault activity and sustained sediment delivery sourced from the footwall scarp and systems beyond it (e.g., antecedent systems). We then analysed the tectono‐stratigraphic framework and the volumetric comparison between material eroded from the fault‐scarp and accumulated in the basin, aiming to estimate the contribution of fault‐scarp degradation to the hangingwall syn‐rift fill. Our results suggest periods of enhanced fault activity control fault‐scarp degradation variability through time, and we agree with that described by previous researchers—fault throw variability along‐strike regulates the variability in the magnitude of erosion. However, we propose that fault‐scarp degradation timing and its spatial variability are also influenced by the interaction and linkage with adjacent normal faults and by sea level variations. Lastly, we determine broader similarities and differences with a system located in the same fault array (i.e., Thebe‐2 fault system), aiming to give insights into the tectono‐stratigraphic evolution of a broader area and the spatial variability in fault‐scarp degradation.
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Thermal evolution and sediment provenance of the Cooper–Eromanga Basin: Insights from detrital apatite
Authors Angus L. Nixon, Nicholas Fernie, Stijn Glorie, Martin Hand and Betina Bendell[AbstractThe prolific hydrocarbon and geothermal potential of the Cooper–Eromanga Basin has long been recognised and studied, however, the thermal history which underpins these resources has largely remained elusive. This study presents new apatite fission track and U–Pb data for eight wells within the southwestern domain of the Cooper–Eromanga Basin, from which thermal history and detrital provenance reconstructions were conducted. Samples taken from sedimentary rocks of the upper Eromanga Basin (Winton, Mackunda and Cadna‐owie Formations) yield dominant Early‐Cretaceous and minor Late‐Permian–Triassic apatite U–Pb ages that are (within uncertainty) equivalent to corresponding fission track age populations. Furthermore, the obtained Cretaceous apatite ages correlate well with the stratigraphic ages for each analysed formation, suggesting (1) little time lag between apatite exposure in the source region and sediment deposition, and (2) that no significant (>ca. 100°C) reheating affected these formations in this region following deposition. Cretaceous apatites were likely distally sourced from an eastern Australian volcanic arc, (e.g. the Whitsunday Igneous Association), and mixed with Permian–Triassic sediment sources from the New England and/or Mossman Orogens. Deeper samples (>2000 m) from within the southwestern Cooper Basin yielded partially reset fission track ages, indicative of heating to temperatures exceeding ca. 100–80°C after deposition. The associated thermal history models are broadly consistent with previous studies and suggest that maximum temperatures were reached at ca. 100–70 Ma as a result of hydrothermal circulation correlating with high rates of sedimentation. Subsequent Late‐Cretaceous–Palaeogene cooling is interpreted to reflect post magmatic thermal subsidence and cessation of hydrothermal activity, as well as potential modified rock thermal conductivity as a response to fluid flow. Five of the seven modelled wells record a Neogene heating event, the geological significance of which remains tentative but may suggest possible reactivation of the Cooper Hot Spot and associated hydrothermal circulation.
,Time–temperature models for the Sturt 8, Pogona 1, Dunoon 1, Pinna 1, Narcoonowie 1 and combined Moomba 1 and Moomba 72 wells, shown by location within the Cooper–Eromanga Basin. The apatite partial annealing zone (APAZ) is the thermal range at which fission tracks in apatite sensitive over geological time scales (ca. 120–60°C; Gleadow et al., 1986; Wagner & Van den haute, 1992), and has been indicated for each reconstruction. Present day stratigraphic levels of the Eromanga Basin, Cooper Basin and pre‐Permian basement are shown to the right of each thermal history profile. Wells previously studied for thermal history and referenced from Duddy and Moore (1999) and Duddy et al. (2002) are additionally shown, with well names as follows: Bu2 = Burley 2; Da1 = Daralingie 1; Gi1 = Gidgelpa 1; Gi5 = Gidgelpa 5; Gi7 = Gidgelpa 7; Me2 = Merrimelia 2; Me4 = Merrimelia 4; Pa1 = Pando 1; St7 = Sturt 7; TT1 = Tinga Tingana 1.
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Middle Miocene volcanic flare up preceding and synchronous with the Langhian/Serravallian sea‐level decline in the North Pannonian Basin: Insights from 40Ar/39Ar dating, geo‐seismic analysis and 3D visualization of the subterranean Kráľová stratovolcano
Authors Samuel Rybár, Katarína Šarinová, Fred Jourdan, Celia Mayers and Ľubomír Sliva[AbstractThe Pannonian Basin System originated from the collision of the African and European tectonic plates, followed by the Miocene extensional collapse that led to the development of a back‐arc basins. Accurate dating is essential to comprehend the tectono‐volcanic evolution of the region, particularly in the under‐studied Danube Basin. Single‐grain 40Ar/39Ar dating has revealed that volcanic activity in the Danube Basin commenced around 14.1 million years ago, aligning with previous biostratigraphic and radioisotope data from nearby volcanic fields. The initial Middle Miocene pyroclastic deposits were generated by intermediate high K calc‐alkaline magmas, contributing significantly to the deposition of thick layers of fine vitric tuffs. The timing and chemistry of the volcanism are consistent with the Badenian rift phase in the Middle Miocene within the Carpathian–Pannonian region, suggesting an intraplate back‐arc volcanic environment. Three‐dimensional imaging has exposed the buried Kráľová stratovolcano, revealing its impressive scale with a thickness between 2620 and 5000 m and a base diameter of 18–30 km. Such dimensions place it among the ranks of the world's largest stratovolcanoes, indicating its substantial impact on the evolution of the Carpathian–Pannonian area. The complex formation history of the stratovolcano points to multiple phases of growth. Furthermore, the basin controlling Mojmírovce‐Rába fault's intersection with the stratovolcano implies that fault activity was subsequent to the volcanic activity, being younger than 14.1 million years. Regional age data consistently indicates that volcanic activity in the Danube Basin reached its zenith just prior to and during the lower/upper Badenian sea‐level fall (Langhian/Serravallian). K‐metasomatism is unique to the stratovolcanic structures and is not observed in the wider regional setting. This study supports the notion of an intricate, interconnected subterranean intrusive system within the stratovolcano, underscoring the complex interplay between geological structures and volcanic processes.
,Middle Miocene Volcanic Flare‐up Preceding and Synchronous with the Langhian/Serravallian Sea Level Decline in the North Pannonian Basin. The top part of the graphical abstract depicts a geological overview of the Pannonian Basin System, featuring the Danube Basin within it. This period is marked by significant volcanic activity and tectonic shifts as evidenced by the displayed Middle Miocene volcanic fields, and faults. Key geographical markers are labeled: TR – Transdanubian Range; EA – Eastern Alps; WC – Western Carpathians; HDL – Hurbanovo–Diósjenő Fault; DB – Danube Basin; PBS – Pannonian Basin System. The middle part of the figure shows detailed geo‐seismic profile of the line MXS3‐93, through the Gabčíkovo‐Győr sub‐basin with projected Kráľová‐1 well which documents the presence of the Kráľová stratovolcano. The lower part of the figure describes a comprehensive map highlighting the top of pre‐Cenozoic basement and the topography of the Kráľová stratovolcano, all displayed in the True Vertical Depth (TVD) domain.
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Integrated uplift, subsidence, erosion and deposition in a tightly coupled source‐to‐sink system, Pagliara basin, northeastern Sicily, Italy
Authors F. Pavano, F. J. Pazzaglia, T. M. Rittenour, S. Catalano, L. B. Corbett and P. Bierman[AbstractHow tectonic forcing, expressed as base level change, is encoded in the stratigraphic and geomorphic records of coupled source‐to‐sink systems remains uncertain. Using sedimentological, geochronological and geomorphic approaches, we describe the relationship between transient topographic change and sediment deposition for a low‐storage system forced by rapid rock uplift. We present five new luminescence ages and two terrestrial cosmogenic nuclide paleo‐erosion rates for the late Pleistocene Pagliara fan‐delta complex and we model corresponding base level fall history and erosion of the source catchment located on the Ionian flank of the Peloritani Mountains (NE‐Sicily, Italy). The Pagliara delta complex is part of the broader Messina Gravel‐and‐Sands lithostratigraphic unit that outcrops along the Peloritani coastal belt as extensional basins have been recently inverted by both normal faults and regional uplift at the Messina Straits. The deltas exposed at the mouth of the Pagliara River have constructional tops at ca. 300 m a.s.l. and onlap steeply east‐dipping bedrock at the coast to thickness between ca. 100 and 200 m. Five infrared‐stimulated luminescence (IRSL) ages collected from the delta range in age from ca. 327 to 208 ka and indicate a vertical long‐term sediment accumulation rate as rapid as ca. 2.2 cm/yr during MIS 7. Two cosmogenic 10Be concentrations measured in samples of delta sediment indicate paleo‐erosion rates during MIS 8–7 near or slightly higher than the modern rates of ca. 1 mm/yr. Linear inversion of Pagliara fluvial topography indicates an unsteady base level fall history in phase with eustasy that is superimposed on a longer, tectonically driven trend that doubled in rate from ca. 0.95 to 1.8 mm/yr in the past 150 ky. The combination of footwall uplift rate and eustasy determines the accommodation space history to trap the fan‐deltas at the Peloritani coast in hanging wall basins, which are now inverted, uplifted and exposed hundreds of metres above the sea level.
,(a) Photo showing a panoramic view of the sedimentary architecture of the Rocchenere delta system fan delta deposits of the Messina Gravel and Sands Formation located at the outlet of the tight source‐to‐sink system of the Pagliara basin (b). Sequence and facies boundaries, as well as foresets layering, measured sections and IRSL samples location are also reported. The sampled stratigraphy shows alternation of massive and stratified sedimentary facies, stacked in coarsening‐up meter‐scale bed sets with opposing dips. Numbers refers to the sampled sections of the sequence; (c) the reconstructed and simplified stratigraphic section is also shown by a color's palette according with the deposits’ grain size. The numbers in red refer to the corresponding portion of the measured section, whereas the red asterisks with letters refers to the location along the section of the corresponding facies shown in the pictures of Figure 3b–d above. The dark blue dots represent the gauging stations for sedimentological measurements, whereas the differently open grey triangle, side of the stratigraphic column, indicate the measured paleo‐flow direction. Note that the tringles are open towards the paleo‐flow direction and their openness is related to the total angle range provided by multiple measures at the same gauging location. (d) Rose diagram showing the paleo‐flow direction (shaded area) measurements (n = 29) carried out at different location along the stratigraphic sequence (c). More intense color corresponds to more represented azimuths. Overlapped is the Pagliara fan cone angle (dotted dark red lines).
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Translation, collision and vertical‐axis rotation in the Organyà and Montsec minibasins (South‐Central Pyrenees, Spain)
[AbstractThis paper presents a sequentially restored cross‐section of the Organyà and Montsec minibasins based on geological mapping, new field observations and available borehole data. The main objective was to describe the geometry and evolution of both basins in terms of salt tectonics and minibasin mobility. To this end, a comprehensive palaeomagnetic database has been used to constrain vertical‐axis rotations potentially related to minibasin translation and pivoting. The Organyà minibasin constitutes an asymmetric depocentre formed during the Upper Jurassic‐Lower Cretaceous by translation above a southerly inclined salt layer. Salt evacuation and minibasin touchdown induced salt accumulation on the northern side of the basin that culminated in the development of the major Santa Fe unconformity during the late Albian—early Cenomanian. Indicative of salt quiescence is the following isopachous Cenomanian to lower Santonian sequence Salt tectonics resumed during the late Santonian—Palaeocene, with the Montsec minibasin downbuilding coinciding with the onset of Pyrenean convergence. Changes of the base‐salt topography reflects regional‐scale geodynamic processes. The acceleration of crustal thinning in the North Pyrenean zone during the late Albian‐early Cenomanian favoured uplift in the Axial Zone, increasing slope and triggering salt mobilization in the Southern Pyrenees. Likewise, the onset of contraction renewed the downslope gliding of the Organyà and Montsec minbasins, and supports the idea that the early stages of basin inversion were governed by gravity tectonics. The kinematic reconstruction suggests that the more that 30° counterclockwise vertical axis rotation records pivoting during the suprasalt translation of the Organyà minibasin rather than solely the Iberian microplate rotation.
,Key steps in the development of the Organyà and Montsec minibasins.
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Tectonic control on the palaeogeographic evolution of thrust‐top basins at the active margin of the Guadalquivir Basin (central Betic Cordillera, S Spain)
Authors Julio Aguirre, Juan C. Braga, José M. Martín and Ángel Puga‐Bernabéu[AbstractThe Guadalquivir Basin is the foreland basin of the Betic Cordillera (S Spain). Closest to the orogen, several thrust‐top basins evolved during the Late Miocene in the central part of the cordillera. Here, we study the Upper Miocene deposits in five of these satellite basins: Montefrío, Iznájar‐Cuevas de San Marcos, Antequera, Bobadilla Estación and Teba, in order to (1) update the stratigraphic framework, (2) infer a depositional model, (3) establish the relationship between sedimentary record and tectonic context and (4) reconstruct the palaeogeography of the area during the Late Miocene. Upper Miocene sediments mostly consist of mixed carbonate‐terrigenous deposits. Facies characterization allows inferring a sedimentary model corresponding to a ramp with foreshore deposits changing to a shoal belt offshore in the inner ramp. Swaley and hummocky cross‐stratified deposits formed in the transition to the middle ramp, and plane parallel carbonate beds in the distal middle‐outer ramp. Factory facies, dominated by rhodoliths and bryozoans, also occur in the middle‐outer ramp environments. Silts and marls formed in the deepest outer ramp and basin settings respectively. Breccias accumulated at the toe of palaeocliffs and conglomerates and massive coarse sands were deposited in fluvio‐deltaic systems. Conglomerates and sands were also reworked as gravity flows and redeposited offshore. Local facies include rudstones‐grainstones displaying large‐scale trough‐cross bedding formed in a strait in Montefrío, and marls with chalky carbonates deposited in a shallow marine, sheltered lagoon with hydromorphic soils in Bobadilla Estación. The study basins evolved in an N‐S compressive tectonic context responsible of the emersion of the main Betic reliefs. Concomitantly, E‐W and ESE‐WNW extension originated the main depocentres. The influence of the tectonic activity on the sedimentary infills is indicated by the presence of synsedimentary deformations and several diachronic unconformities, which are younger westward. Tectonism, in turn, also controlled the palaeogeographic evolution during the late Tortonian‐early Messinian interval.
,Summary chart of the stratigraphic framework of the study sub‐basins in the wedge‐top depozone of the Guadalquivir Basin compare with olistostromic deposits emplaced in the foredeep depozone. The stratigraphic division of the Upper Miocene deposits in the foredeep (at the right part of the figure) is based on different authors: MO.19: Martínez del Olmo (2019); Sie.96: Sierro et al. (1996); Led.00: Ledesma (2000). Unc‐1 to Unc‐4: Unconformities. Ol‐1 to Ol‐3: Olstostrome emplacements. Thick black lines indicate the final emersion of the different areas.
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Neogene evolution of the margin adjacent to the La Plata River Delta (Pelotas Basin): Sedimentary pathways and the origins of the Rio Grande Cone
[AbstractContinental margins that exhibit high terrigenous input are generally located near deltas that are capable of transporting large quantities of sediments into the basin. However, in rare cases, high terrigenous sedimentation occurs in regions deprived of major riverine systems where the sedimentary pathway is enigmatic. One such case is the Neogene of the Pelotas Basin of Brazil and Uruguay, adjacent to the La Plata River mouth. Since the Miocene, anomalous sedimentation formed a giant progradational wedge, the Rio Grande Cone, one of the largest submarine fan‐like features on Earth. To understand the Neogene evolution of the margin and the origins of the Rio Grande Cone, here we present a seismic‐stratigraphic framework based on well‐logs and 2D seismic data. Three depositional environments are identified: (1) on the shelf, upper Miocene to Pliocene fluvial channels delivered sand deposits on the mud‐dominated shelf; (2) on the slope, sediment instability resulted in structural deformation and multiple phases of mass transport deposition and (3) on the lower slope and basin floor, large contourite drifts formed by sediment reworking. We classify the Rio Grande Cone as a megaslide complex, due to its depositional and structural setting. Local deltaic systems were active on the shelf in the Neogene, but the limited size of their paleo‐drainage systems in comparison to the volume of sedimentation in the margin suggests that an additional sedimentary pathway existed. In this sense, the demise of an epicontinental sea over the La Plata Basin during the Neogene likely enabled the input of large volumes of fine sediments into the margin, via the La Plata plume water. We suggest that the desiccation of this epicontinental sea and the intensification of ocean currents since the middle Miocene explains the anomalous Neogene terrigenous influx into the SW Atlantic margin.
,The Neogene Evolution of the Pelotas Basin (South Atlantic) was marked by the interplay of anomalous sediment input, sea‐level changes, slope instability and the intensification of bottom currents which led to the establishment of submarine megaslides (e.g., Rio Grande Cone) and widespread contourite drifts.
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Reconstructing the Zama (Mexico) discovery source to sink palaeogeography, Part II: Sediment routing from the Late Miocene shelf‐margin to deepwater basin
Authors J. W. Snedden, M. G. Rowan, D. F. Stockli, M. Albertson and J. Pasley[Three plausible pathways (white lines) to Zama Upper Miocene minibasin depocenter from interpreted shelf‐margin entry point. Upper Miocene well‐based net sandstone contours are superimposed on an Upper Miocene interval thickness map derived from seismic analysis. Reconstructed coeval shelf‐margin is shown by the red line. The blue line is the location inferred for Palaeo‐Rio Grijalva. Grey‐lined polygons denote present‐day locations of allochthonous salt bodies. Plausible pathways follow trends in interval and sandstone thicknesses.
The Late Miocene source terrane tectonic history in the southern Gulf of Mexico Basin, as informed by detrital zircon geothermochronology data, supports a detailed regional palaeogeographic reconstruction from palaeoshoreline to the deepwater Zama minibasin of the Sureste salt basin. Seismic mapping points to a trio of pathways that converge upon two entry points into the Zama minibasin, illuminating how sediment gravity flows transit a complex seascape defined by shallow salt bodies. Consideration of empirical scaling relationships within and between segments of this sediment dispersal system allows for testable predictions of Upper Miocene submarine fan‐runout lengths over basin exploration areas. Distances from the reconstructed shelf‐margin to the Zama wells vary around 100 km, an increase of 20% over a straight‐line distance as flows likely navigated around extant salt stocks, walls and sheets. This 100‐km fan length is about 40% of the reconstructed minimum palaeo‐river length, within predicted ranges for smaller source‐to‐sink systems in tectonically active areas (25 to 50%). The estimated fan‐runout distance can be extended even further basinwards, considering the contemporaneous passage of the mobile Chortis block along the Tonala shear zone, expanding the Palaeo‐Rio Grijalva drainage network during the Tortonian. These Late Miocene deepwater systems linked to the Palaeo‐Rio Grijalva differ substantially from onshore Mexico‐sourced turbidity flows feeding into the axis of the north‐trending Veracruz Trough. Textural data from wells here suggests these systems were less effective at larger grain transport and sorting. Local (intrabasinal) variations are also evident within the Zama minibasin, as well data (image logs and cores) indicate that axially oriented sediment gravity flows involved fewer high‐density turbidities, depositing lower net‐to‐gross sandstones and thicker shales than those flowing transverse to the basin axis from a southeastern basin entry point. These interpretations will guide both local exploitation of these economic resources and could also support future exploration for analogous salt‐influenced deepwater reservoir systems in the Sureste basin and globally.
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Influence of preexisting structures on salt structures in the Kuqa Depression, Tarim Basin, Western China: Insights from seismic data and numerical simulations
Authors Keji Yang, Jiafu Qi, Liangwei Xu, Yanqiu Yu, Tong Sun, Fangle Shen, Li Peng, Ji Lv and Hanting Zhao[AbstractThe preexisting structures that developed in the basement and subsalt strata play a key role in the salt structural deformation in the Kuqa Depression, Tarim Basin. The characteristics of preexisting structures and their controls on the salt structure are investigated via the latest three‐dimensional seismic data and numerical modelling. The results show that the preexisting structures that developed in the Kuqa Depression mainly consist of basement faults, palaeouplifts, subsalt slopes and early passive salt diapirs. Basement faults are mainly distributed in the Kelasu and Qiulitag structural belts and control the position of development and deformation style of the Miocene compressive salt structure. The differences in styles and reactivation degrees of basement faults lead to great diversity in the salt structure. The palaeouplifts mainly include the Wensu, western Qiulitag, Xinhe and Yaha‐Luntai palaeouplifts. The original sedimentary range and later deformation space of the salt layer are limited by the palaeouplift, resulting in strong salt thrusting in the Awate sag in the western part of the Kuqa Depression. The heterogeneous spatial distribution of the palaeouplift promoted the development of regional strike‐slip transform belts. Subsalt slopes are located mainly on the northern edge of the western Qiulitag low uplift and block the southward flow of the salt, causing the salt to form salt domes; the size of these domes is closely related to the subsalt slope. Early passive salt diapirs mainly developed in the Quele and Bozidun areas of the western Kuqa Depression, and they were preferentially active during the compression period, inducing the formation of a piercement salt nappe. Numerical modelling revealed that the preexisting structure strongly controlled the stress–strain distribution during the deformation of the salt structure. The spatial distribution heterogeneity of the basement structure is an important factor in the structural zonation along the north–south strike and segmentation along the west–east strike in the Kuqa Depression, as well as an important inducer of the piercement salt structure.
,Different salt structural deformation models controlled by preexisting structures in the Kuqa Depression. (a) In the Wensu segment, the sedimentary range and deformation space of the salt layer are restricted, resulting in the strong thrust of the subsalt faults and piercement of the salt. (b) In the Quele segment, progradational sedimentary load induces a passive salt diapir. Influenced by the blocking of the steep subsalt slope and the reactivation of the preexisting salt diapir, a piercement salt wall was formed on the right edge of subsalt slope. (c) In the Dabei segment, a salt dome was formed at the northern edge of the western Qiulitag palaeouplift due to the blocking of the steep subsalt slope. (d) In the Keshen segment, the subsalt slope and preexisting salt diapir are not developed, and finally, two salt domes are formed at the top of the basement faults in the Kelasu and Qiulitag structural belts.
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Penecontemporaneous polygonal faulting triggered by sand overloading onto unconsolidated clays: Evidence from the northern South China Sea
Authors Qingfeng Meng and Fang Hao[Enriched sands close to the point with the maximum fault throw as domonstrated by RMS amplitude
Layer‐bound polygonal fault systems (PFS) are a prevalent feature in fine‐grained sediments across many continental margin basins worldwide, yet their origin remains enigmatic. In this study, we report on the structural characteristics of polygonal faults recently discovered in Middle Miocene mudrocks of the Yinggehai Basin, northern South China Sea. Our data reveal that the polygonal arrays of normal faults, which comprise master faults and minor synthetic/antithetic faults with complex tiers, exhibit either straight or curvilinear traces with frequent orthogonal intersections, forming a highly interconnected fault network. We observe several sub‐circular to elliptical‐shaped depressions that lie above the faulted interval and are filled with syn‐deformation deposits, with the long axis of these depressions aligned sub‐parallel to the structure contour lines. Our findings suggest that the polygonal faults emerged during the sediment deposition and compaction preceding the deposition of overlying sediments. The faults were created through the nucleation of penecontemporaneous faults due to the overloading of sandy sediments onto unconsolidated clays, followed by the propagation of the faults along with continuous sediment deposition. The cessation of fault propagation coincided with the termination of sedimentation in the faulted interval. Additionally, the local horizontal stress anisotropy resulting from topographic‐gravitational effects may have played a crucial role in the development of polygonal faults. Our study provides novel insights into early sediment deformations in the northern South China Sea region and sheds light on the timing and genesis of PFS.
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Sensitivity of modelled passive margin stratigraphy to variations in sea level, sediment supply and subsidence
[Modelledstratigraphy reconstructed using Bayesian inversion. The top panels show the reconstructedstratigraphy (panel a) and a wheeler diagram of this model output (panel b). Thethree other panels show the original and reconstructed values of: 1) flexure,thermal subsidence, and total subsidence (panel c); 2) sea‐level change (paneld); and 3) sediment supply variations (panel e). The greater variability in theposterior distribution of sediment supply values relative to those for sealevel suggests that the development of passive continental margin stratigraphic architecture is particularlysensitive to sea‐level variation.
We produced a 10 Myr synthetic stratigraphic section using a forward stratigraphic model that generates marine deltaic stratigraphy over geological timescales. We recursively fit the model using a Bayesian inversion algorithm to test: (1) if it could be accurately reconstructed; (2) if the parameters used to create it could be recovered; and (3) the sensitivity of the model output to given model parameters and the attendant physical processes. The original synthetic stratigraphic section was produced with cyclical sea‐level variations of 40 and 30 m with 2.4 and 10 Myr periods respectively. Sediment was also supplied cyclically, in 2.4 and 10 Myr cycles with amplitudes of 30 and 80 tons/100 kyr, respectively, varying from a mean of 232 tons/100 kyr. Parameter values were sampled to fit the model using a Markov chain Monte Carlo algorithm, resulting in a ±5 m (1σ) variation between the experimental output and the original. Sea level varied by ±7 m (1σ) within the posterior distribution of parameters. As a result, both the 10 Myr and 2.4 Myr sea‐level cycles could be extracted from the original output. The variation in sediment supply was approximately ±38 tons/100 kyr (1σ) and, as a result, only the larger long‐term supply variations could be accurately recovered in refitting the model. The variation in thermal, flexural and total subsidence across those parameter sets is less than ±10 m (1σ). The original section experienced 150 m of total subsidence at the depocentre. Our results demonstrate the distinct and interpretable imprint of sea level and subsidence on continental margin stratigraphy can be quantified. Moreover, we conclude that sea‐level change produces a defined effect on the geometries of stratigraphic architecture, and that techniques applied for the purpose of delineating sea‐level variation from continental margin strata have a well‐founded conceptual basis.
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Geometry and evolution of polygonal fault systems under a regionally anisotropic stress field: Insights from 3D seismic analysis of the Qiongdongnan Basin, NW South China Sea
Authors Shouxiang Hu, Alte Rotevatn, Christopher Jackson, Wei Li and Xiaochuan Wu[AbstractPolygonal fault systems (PFS) are developed in many sedimentary basins, and their formation, growth, and ultimate geometry have been widely studied. The geometry and growth of PFS forming under the influence of regionally anisotropic stresses, however, are poorly understood, despite the fact these structures may serve as key paleo‐stress indicators that can help reconstruct the tectonic and stress history of their host basins. We here use high‐quality 3D seismic reflection data and quantitative fault analysis to determine the geometry and evolution of a PFS in the Qiongdongnan Basin (NW South China Sea), and its possible relationship with the geological and stress history of the basin. The PFS is dominated by two intersecting NNW‐to‐N‐ and E‐striking fault sets, which initiated in the Early Miocene. The dominant fault strike at the structural level at which the faults nucleated and where strain is greatest (i.e., Lower Miocene) is close to NW–SE. However, at the top and bottom of the PFS tier faults strike NNW–SSE, thereby defining a very slight vertical, clockwise rotation of strike. Based on the observation that the host rock is flat‐lying, it is unlikely that basin‐tilting perturbed (i.e., δ2 ≠ δ3) the otherwise radially isotropic stress field that typically characterize PFS. Likewise, diapirs that punctuate the host rock and that are spatially related to the PFS appear not to control fault geometry. We instead infer that the PFS geometry reflects a combination of local isotropic and regional, extension‐related tectonics stress affecting the Qiongdongnan Basin during the Early Oligocene to Middle Miocene. Regional studies suggest that during this time, extensional stresses in eastern Qiongdongnan Basin rotated clockwise from roughly NNW to N; we noticed the rotation of strike of the PFS, within which the vertical change in fault strike being relatively minor. Our study determines the timing of polygonal fault growth within the Qiongdongnan Basin and the associated geometry, highlighting the key role played by regional and local stresses.
,The polygonal faults are dominated by two intersecting NNW‐to‐N‐ and E‐trending fault sets of the Qiongdongnan Basin, NW South China Sea, which initiated in the Early Miocene. The geometry of the polygonal faults was mainly influenced by isotropic stresses in the Qiongdongnan Basin during the Early Oligocene to Middle Miocene.
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Northward expansion of the Jiaolai Basin during the Early Cretaceous: Insights from source‐to‐sink reconstruction
Authors Bo Zhang, Shaofeng Liu, Chengfa Lin and Pengfei Ma[Model depicting the northward expansion evolution of the Jiaolai Basin in East Asia during the Early Cretaceous period. The left column illustrates the new stratigraphic framework as presented in this study. The grey arrows in the diagram indicate the primary provenance directions, with the size of the arrows representing the relative contribution of each source.
The Jiaolai Basin, situated in the northern Sulu orogenic belt along East Aisa continental margin, preserves evidence of the extensional events in East Asia and the post‐orogenic evolution of the Sulu orogenic belt during the Cretaceous period. In this study, multiple provenance analyses were employed to reconstruct the source‐to‐sink system of the Laiyang Group within the Jiaolai Basin. These studies reveal a history of northward expansion dictated by two significant rift events. During the early Early Cretaceous period (ca. 135–121 Ma), the Zhucheng and Gaomi sags in southern region developed initially. Subsequently, in the late Early Cretaceous period (ca. 120–113 Ma), the Laiyang sag in northern region emerged. Furthermore, these sags were fed by independent source‐to‐sink systems in their early stages but eventually shared a similar source‐to‐sink system towards the end of the Laiyang Group deposition (ca. 113 Ma). The provenance analysis results indicate that ca. 121 Ma, ultrahigh‐pressure rocks in the northern segment of the Sulu orogenic belt experienced rapid exhumation, while those in the southern segment might have remained concealed until ca. 113 Ma. The two rift events in East Asia, coupled with the alteration in the direction and magnitude of extension documented in the Jiaolai Basin, suggests that trench retreat and the change in subduction direction from E–W to NW–SE of the Izanagi plate played a principal role in driving the extensional events in East Asia during the Early Cretaceous. Our findings imply that the change in Izanagi subduction direction may have occurred ca. 121 Ma.
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Multi‐source detrital contributions in the Po alluvial basin (northern Italy) since the Middle Pleistocene. Insights into sediment accumulation in intermediate sinks
Authors Luca Demurtas, Daniela Fontana, Stefano Lugli and Luigi Bruno[AbstractIntegrated stratigraphic‐compositional studies on alluvial successions provide a valuable tool to investigate the provenance of detritus in multi‐source systems. The Po Plain is an intermediate sink of the Po‐Adriatic source‐to‐sink system, fed by rivers draining two orogens. The Alps are characterized by extensive outcrops of plutonic‐metamorphic and ultramafic rocks to the north‐west and of Mesozoic carbonates to the east (Southern Alps). The Northern Apennines, to the south, are dominated by sedimentary successions. The Po River flows from the Western Alps to the Adriatic Sea, interacting with a dense network of transverse tributaries that drain the two orogens. Stratigraphic, sedimentological and compositional analyses of two 101 and 77.5 m‐long cores, recovered from the Central Po Plain, reveal the stacking of three petrofacies, which reflects distinct provenance and configurations of the fluvial network. A South‐Alpine sedimentary input between MIS 12 and MIS 10 is testified by petrofacies 1, characterized by carbonate‐ and volcanic‐rich detritus from rocks exposed in the Southern Alps. A northward shift of the Po River of more than 30 km is marked by a quartz‐feldspar and metamorphic‐rich detritus (petrofacies 2), similar to modern Po River sands. This dramatic reorganization of the fluvial network likely occurred around MIS 9–MIS 8 and is possibly structurally controlled. A further northward shift of the Po River and the onset of Apennine sedimentation in the Late Holocene is revealed by petrofacies 3, rich in sedimentary lithics from the Apennine successions. The results of this study document how compositional analysis, if framed in a robust stratigraphic picture, may provide clues on the evolution of multi‐source alluvial systems.
,Inferred palaeogeography of the central Po Plain, deduced from compositional variations of core sands, during: (a) MIS 12 and MIS 10 (petrofacies 1). (b) MIS 5–4 (petrofacies 2). (c) MIS 2 (petrofacies 2). (d) The early Holocene (petrofacies 2). (e) The late Holocene (petrofacies 3).
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