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- Volume 32, Issue 6, 2020
Basin Research - Volume 32, Issue 6, 2020
Volume 32, Issue 6, 2020
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Four‐dimensional Variability of Composite Halokinetic Sequences
Authors Leonardo M. Pichel and Christopher A.‐L. Jackson[Representative sections illustrating the CHS variability and near‐diapir stratal architecture across two distinct diapir‐flank geometries: (a) inclined diapir flank and (b) vertical diapir.
The architecture of salt diapir‐flank strata (i.e. halokinetic sequences) is controlled by the interplay between volumetric diapiric flux and sediment accumulation. Halokinetic sequences consist of unconformity‐bounded packages of thinned and folded strata formed by drape folding around passive diapirs. They are described by two end‐members: (a) hooks, which are characterized by narrow zones of folding (<200 m) and high taper angles (>70°); and (b) wedges, typified by broad zones of folding (300–1000 m) and low taper angles (<30°). Hooks and wedges stack to form tabular and tapered composite halokinetic sequences (CHS) respectively. CHSs were most thoroughly described from outcrop‐based studies that, although able to capture their high‐resolution facies variations, are limited in describing their 4D variability. This study integrates 3D seismic data from the Precaspian Basin and restorations to examine variations in CHS architecture through time and space along diapirs with variable plan‐form and cross‐sectional geometries. The diapirs consist of curvilinear walls that vary from upright to inclined and locally display well‐developed salt shoulders and/or laterally transition into rollers. CHS are highly variable in both time and space, even along a single diapir or minibasin. A single CHS can transition along a salt wall from tabular to tapered geometries. They can be downturned and exhibit rollover‐synclinal geometries with thickening towards the diapir above salt shoulders. Inclined walls present a greater proportion of tapered CHSs implying an overall greater ratio between sediment accumulation and salt‐rise relatively to vertical walls. In terms of vertical stacking, CHS can present a typical zonation with lower tapered, intermediate tabular and upper tapered CHSs, but also unique patterns where the lower sequences are tabular and transition upward to tapered CHS. The study demonstrates that CHSs are more variable than previously documented, indicating a complex interplay between volumetric salt rise, diapir‐flank geometry, sediment accumulation and roof dimensions.
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Mass‐transport complexes (MTCs) document subsidence patterns in a northern Gulf of Mexico salt minibasin
More Less[AbstractMass‐transport complexes (MTCs) dominate the stratigraphic record of many salt‐influenced sedimentary basins. Commonly in such settings, halokinesis is invoked as a primary trigger for MTC emplacement, although the link between specific phases of salt movement, and related minibasin dynamics, remains unclear. Here, we use high‐quality 3D seismic reflection and well data to constrain the composition, geometry and distribution (in time and space) of six MTCs preserved in a salt‐confined, supra‐canopy minibasin in the northern Gulf of Mexico, and to assess how their emplacement relate to regional and local controls. We define three main tectono‐sedimentary phases in the development of the minibasin: (a) initial minibasin subsidence and passive diapirism, during which time deposition was dominated by relatively large‐volume MTCs (c. 25 km3) derived from the shelf‐edge or upper slope; (b) minibasin margin uplift and steepening, during which time small‐volume MTCs (c. 20 km3) derived from the shelf‐edge or upper slope were emplaced; and (c) active diapirism, during which time very small volume MTCs (c. 1 km3) were emplaced, locally derived from the diapir flanks or roofs. We present a generic model that emphasizes the dynamic nature of minibasin evolution, and how MTC emplacement relates to halokinetic sequence development. Although based on a single data‐rich case study, our model may be applicable to other MTC‐rich, salt‐influenced sedimentary basins.
,Two types of MTCs (shelf‐edge/upper slope‐derived and diapir‐derived) are identified based on their geometry, volume and source area in a minibasin of the Northern Gulf of Mexico. Shelf‐edge/upper slope‐derived MTCs are relatively large and sourced from the collapse of coeval shelf‐edge deltas, or supplied by reworked upper slope channels and lobes. They are preferentially deposited during the earlier phase of minibasin development. Diapir‐derived MTCs tend to be smaller than shelf‐edge/upper slope‐derived MTCs, they are sourced from the collapse of the salt diapir flanks and deposited during the latest phase of minibasin development.
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Terrestrial heat flow and lithospheric thermal structure in the Chagan Depression of the Yingen‐Ejinaqi Basin, north central China
Authors Yinhui Zuo, Shu Jiang, Shihu Wu, Wei Xu, Jiong Zhang, Renpeng Feng, Meihua Yang, Yongshui Zhou and M. Santosh[System steady‐state temperature data measurements for typical wells in the Chagan Depression.
The Chagan Depression in the Yingen‐Ejinaqi Basin, located at the intersection of the Paleo‐Asian Ocean and the Tethys Ocean domains is an important region to gain insights on terrestrial heat flow, lithospheric thermal structure and deep geodynamic processes. Here, we compute terrestrial heat flow values in the Chagan Depression using a large set of system steady‐state temperature data from four representative wells and rock thermal conductivity. We also estimate the “thermal” lithospheric thickness, mantle heat flow, ratio of mantle heat flow to surface heat flow and Moho temperature to evaluate the regional tectonic framework and deep dynamics. The results show that the heat flow in the Chagan Depression ranges from 66.5 to 69.8 mW/m2, with an average value of 68.3 ± 1.2 mW/m2. The Chagan Depression is characterized by a thin “thermal” lithosphere, high mantle heat flow, and high Moho temperature, corresponding to the lithospheric thermal structure of “cold mantle and hot crust” type. We correlate the formation of the Yingen‐Ejinaqi Basin to the Early Cretaceous and Cenozoic subduction of the western Pacific Plate and the Cenozoic multiple extrusions. Our results provide new insights into the thermal structure and dynamics of the lithospheric evolution in central China.
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The role of the Polochic Fault as part of the North American and Caribbean Plate boundary: Insights from the infill of the Lake Izabal Basin
[The Lake Izabal Basin initiated at 12 Ma. The Polochic Fault was the main plate boundary in the Miocene. Fault switch activity must have occurred along the plate boundary.
The Lake Izabal Basin in Guatemala is a major pull‐apart basin along the sinistral Polochic Fault, which is part of the North American and Caribbean plate boundary. The basin infill contains information about the tectonic and sedimentological processes that have imparted a significant control on its sedimentary section. The inception of the basin has been linked to the relative importance of the Polochic Fault in the tectonic history of the plate boundary; yet, its sedimentological record and its inception age have been poorly documented. This study integrates diverse datasets, including industry reports, well logs and reports, well cuttings, vintage seismic data, outcrop observations and geochronological data to constrain the initial infill and age of inception of the basin. The integrated data show that during the Oligocene–Miocene, a marine carbonate platform was established in the region which was later uplifted and eroded in the early Miocene. The fluvial–lacustrine deposits above this carbonate platform are part of the initial infill of the basin and are constrained with zircon weighted‐mean 206Pb/238U ages of 12.060 ± 0.008 from a volcanic tuff ~30 m above the unconformity. Sandstone, mudstone and coal dominate the interval from 12 to 4 Ma, with an increase in conglomerate correlating to the uplift of the Mico Mountains and San Gil Hill at 4 Ma. Fault switch activity between the Polochic and Motagua faults has been hypothesized to explain total offset along the Polochic Fault and the geologic and geodetic slip rates along the two faults. The 12 Ma age determined for the initial infill of the basin confirms this hypothesis. Consequently, our study confirms that at ~12 Ma the Polochic Fault served as the main fault of the plate boundary with inferred slip rates ranging from 13 to 21 mm/yr with a strong possibility that the Polochic Fault was, at some point between 15 Ma and 7 Ma, the only active fault of the plate boundary. The results of this study show that tectonic records preserved in sediments of strike‐slip basins improve the understanding of the relative significance of individual faults and the implications with respect to strain partitioning throughout its tectonic history.
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Basement‐controlled deformation of sedimentary sequences, Anadarko Shelf, Oklahoma
Authors Folarin Kolawole, Molly Simpson Turko and Brett M. Carpenter[Top Left: Curvature surface map of a sedimentary unit in the Anadarko Shelf, Oklahoma, showing large basement‐rooted faults and the associated fold deformation. Top Right: NW‐SE seismic section showing how both the intra‐basement and through‐going (basement‐rooted) faults offset basement‐bounded sills. Bottom: Implications of our findings for the tectonic evolution of the Anadarko Shelf.
Structures rooted in the crystalline basement frequently control the deformation of the host bedrock and the overlying sedimentary sequences. Here, we elucidate the structure of the c. 2‐km deep Precambrian granitic basement in the Anadarko Shelf, Oklahoma, and how the propagation of basement faults deformed the sedimentary cover. Although the basin is foreland in origin, the gently dipping shelf sequences experienced transpressional deformation in the Late Palaeozoic. We analyse a 3‐D seismic reflection data set and basement penetrating well data in an area of 824 km2. We observe: (a) pervasive deformation of the basement by basement‐bounded interconnected mafic sills, and a system of subvertical discontinuity planes (interpreted as faults) of which some penetrate the overlying sedimentary cover; (b) three large (>10 km‐long) through‐going faults, with relatively small (<100 m) vertical separation (Vsep) of the deformed stratigraphic surfaces; (c) upward propagation of the large faults characterized by faulted‐blocks near the basement, and faulted‐monoclines in the deeper sedimentary units that transition into open monoclinal flexures up‐section; (d) cumulative along‐fault deformation of the stratigraphy exhibits systematic trends that varies with offset accrual; (e) two styles of Vsep—Depth distribution which include a unidirectional decrease of Vsep from the basement through the cover rocks (Style‐1) and a bidirectional decrease of Vsep from a deep sedimentary unit towards the basement and shallower sequences (Style‐2). We find that the basement‐driven propagation (Style‐1) shows greater efficiency of driving the fault deformation to shallower depths compared to the intrasedimentary‐driven fault nucleation and propagation (Style‐2). Our study demonstrates an evolution of cumulative Vsep trends with offset accrual on the faults, and the partial inheritance of the heterogeneous intra‐basement deformation by the sedimentary cover. This contribution provides important insight into the upward propagation of basement‐driven faulting associated with structural inheritance in contractional sedimentary basins.
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Tectono‐sedimentary evolution of transverse extensional faults in a foreland basin: Response to changes in tectonic plate processes
[Crustal‐scale cross‐sections across the South‐eastern Pyrenees showing the interaction evolution between Iberia and Sardinia from Late Paleocene (57 Ma) to Middle Eocene (44 Ma). This evolution exerted a control on structural evolution of transverse faults and synchronous thickness and lithology distribution.
Late Paleocene to Middle Eocene strata in the easternmost part of the Southern Pyrenees, up to 4 km thick, provide information on tectono‐sedimentary evolution of faults transversal to the Pyrenean chain. To know how changes in tectonic plate processes control the structural evolution of transverse faults and the synchronous thickness and lithological distribution of sedimentary strata in a foreland basin, field observations, interpretation of 2D seismic lines tied to lithostratigraphic data of exploration wells and gravity modelling constrains were carried out. This resulted in the following two tectono‐sedimentary phases in a foreland basin: first phase, dominated by transverse extensional faulting, synchronous with deposition of marine carbonates (ca. 57 to 51 Ma); and second phase, characterized by transverse contractional faulting, coeval to accumulation of marine and transitional siliciclastics (51 to 44 Ma). During the first phase, Iberia and Adria were moving to the east and west respectively. Therefore, lithospheric flexure in the easternmost part of the Iberian plate was developed due to that Sardinia was over‐thrusting Iberia. Consequently, activation of E‐dipping normal faults was generated giving rise to thick‐deep and thin‐shallow carbonate platform deposits across the hanging walls and footwalls of the transverse structures. During the second phase, a shearing interaction between Iberia and Sardinia prevailed re‐activating the transverse faults as contractional structures generating thin‐shelf and thick‐submarine fan deposits across the hanging walls and footwalls of the transverse structures. In the transition between the first and second phases, evaporitic conditions dominated in the basin suggesting a tectonic control on basin marine restriction. The results of our study demonstrate how thickness and lithology distribution, controlled by transverse faulting in a compressional regimen, are influenced by phases related to processes affecting motions and interactions between tectonic plates and continental blocks.
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Ordovician tectonic shift in the western North China Craton constrained by stratigraphic and geochronological analyses
Authors Jiaopeng Sun and Yunpeng Dong[Reconstruction model of the Ordovician tectono‐sedimentology evolution of the Northwestern Ordos Terrane.
The western North China Craton (W‐NCC) comprises the Alxa Terrane in the west and the Ordos Block in the east; they are separated by the Helanshan Tectonic Belt (HTB). There is an extensive debate regarding the significant Ordovician tectonic setting of the W‐NCC. Most paleogeographic reconstructions emphasized the formation and rapid subsidence of an aulacogen along the HTB during the Middle–Late Ordovician, whereas paleomagnetic and geochronologic results suggested that the Alxa Terrane and the Ordos Block were independent blocks separated by the HTB. In this study, stratigraphic and geochronologic methods were used to constrain the Ordovician tectonic processes of the W‐NCC. Stratigraphic correlations show that the Early Ordovician strata comprise ~500‐m‐thick tidal flat and lagoon carbonate successions with a progressive eastward onlap, featuring a west‐deepening shallow‐water carbonate shelf. In contrast, the Late Ordovician strata are composed of ~3,000‐m‐thick abyssal turbidites in the west and ~400‐m‐thick shallow‐water carbonates in the east, defining an eastward‐tapering basin architecture. Early Ordovician detrital zircons with ages of ~2,800–1,700 Ma were derived from the Ordos Block; the Late Ordovician turbidites were sourced from the western Alxa Terrane, based on zircon ages clustered at ~1,000–900 Ma. The petrographic modal composition and zircon age distribution imply a provenance shift from a stable craton to a recycled orogen in the Middle Ordovician. These shifts define a tectonic conversion from a passive continental margin to a foreland basin at ~467 Ma, resulting in the eastward progradation of the turbidite wedge around the HTB, the eastward backstepping of the carbonate platform in the east and the eastward expansion of orogenic thrusting in the western Alxa Terrane. This tectono‐sedimentary shift coincided with the advancing subduction of the southern Paleo‐Asian Ocean beneath the Alxa Terrane, generating the western Alxa continental arc and the paired retro‐arc foredeep in the east under a compressional tectonic regime.
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Effects of pre‐orogenic tectonic structures on the Cenozoic evolution of Andean deformed belts: Evidence from the Salar de Punta Negra Basin in the Central Andes of Northern Chile
Authors Fernando Martínez, Cristopher López and Mauricio Parra[Geological cross‐section elaborated from the integration of field data and the two‐dimensional seismic and structural interpretation the 2F002 seismic profile and pre‐shortening restoration showing the initial geometry of the west‐dipping pre‐orogenic Paleozoic and Mesozoic extensional system under the Salar de Punta Negra Basin. Pz: Paleozoic pre‐rift basement, Per: Permian syn‐rift, Tr: Triassic syn‐rift, Jr: Jurassic syn‐rift, UC: Upper‐Cretaceous syn‐ kinematic, P: Paleocene syn‐kinematic, O‐M: Oligocene‐Miocene synkinematic.
We integrated new field observations, two‐dimensional (2‐D) seismic profiles and new and previously reported chronological data to understand the effects of pre‐orogenic structures on the tectonic evolution of the Salar de Punta Negra in the Central Andes. For first time a series of restored geological cross‐sections are presented, thus showing the pre‐orogenic tectonic architecture of the region and new ideas about the tectonic evolution of the inner forearc of the Central Andes. Our results show a series of east‐dipping normal faults as the main pre‐orogenic structures in the region, which resulted from lithospheric stretching of the western continental margin during the Paleozoic to Mesozoic (Triassic–Jurassic). These were later incorporated into the Andean orogen by tectonic inversion, forming west‐verging inversion anticlines. The beginning of the tectonic inversion is constrained by the first on‐lap of the Upper Cretaceous‐Palaeocene syn‐kinematic deposits on the top of the Mesozoic syn‐rift successions, highlighting that inversion occurred during this period. These syn‐kinematic deposits display zircons with older age peaks between ca. 200 and 300 Ma, thus indicating that some Carboniferous to Triassic sources of sediments were eroded during the uplift of the orogen. Other basement reverse faults affect the footwalls of normal inverted faults and the shoulders of ancient half‐graben structures. These truncate and decapitate previous inverted faults and completely cut the infill of the basin, leading to exhumation of the pre‐rift basement rocks. We propose that the propagation of these structures was favoured by the modified thermal‐tectonic state of the lithosphere from the eastward migration of the volcanic arc, and not by the previous pre‐orogenic structures. The structural and stratigraphic relationships recognized both in the field and 2‐D seismic profiles indicate that many reverse faults originated after the initial tectonic inversion and continued to be active from the Eocene until the Pleistocene period.
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Distinct petrographic responses to basin reorganization across the Triassic–Jurassic boundary in the southwestern Barents Sea
Authors Lina H. Line, Reidar Müller, Tore G. Klausen, Jens Jahren and Helge Hellevang[Structural reorganization of the western Barents Sea basin and surrounding hinterland terrains resulted in a shift from compositionally immature to mature sandstones during the Late Triassic.
A general shift towards higher mineralogical and textural maturity changes the reservoir character across the Triassic–Jurassic transition in the southwestern Barents Sea basin (SWBSB), largely affecting the hydrocarbon prospectivity in the region. Petrographic and geochronological provenance data presented in this paper suggest that the shift from mineralogically immature to mature sandstones initiated during the deposition of the Norian–Rhaetian Fruholmen Formation, and varies with basin location. Strong contrasts between the Fruholmen Formation and underlying formations are associated with proximity to the rejuvenated Caledonian and Fennoscandian hinterlands and are mainly restricted to the southern basin margins. In the basin interior, subtle petrographic variations between the Fruholmen Formation and older Triassic sandstones reflect a distal position relative to the southern hinterland. The long‐lived misconception of a regional compositional contrast in the Arctic at the turn of the Norian can be attributed to higher sampling frequency associated with hydrocarbon exploration activity along the southern basin margins, and masking by increased annual precipitation and subsequent reworking during the Jurassic. Geothermal signatures and rearrangement of ferric clay material across the Carnian–Norian transition support a recycled origin for the Fruholmen Formation in the basin interior. As the closest tectonically active region at the time, the Novaya Zemlya fold‐and‐thrust belt represents the best provenance candidate for polycyclic components in Norian–Rhaetian strata. In addition to recycling in the hinterland during the Late Triassic, local erosion of exposed intrabasinal highs and platforms at the Triassic–Jurassic transition represents a second process where thermodynamically unstable mineral components originally sourced from the Uralides may be removed. Textural and mineralogical modification may also have occurred in marginal‐marine depositional environments during periods with elevated sea level. Mature sediment supply from the rejuvenated hinterland in the south, multiple cycles of reworking and gradual accumulation of polycyclic grains have likely led to the extreme compositional maturity registered in the Tubåen, Nordmela and Stø formations in the SWBSB. It is likely that increased annual precipitation since the latest Carnian had an amplifying effect on sandstone maturation across the Triassic–Jurassic boundary, but we consider the effect to be inferior compared to provenance shifts and reworking. Findings from this study are important for understanding compositional and textural maturity enhancement processes in siliciclastic sedimentary basins.
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Geological mapping reveals the role of Early Jurassic rift architecture in the dispersal of calciturbidites: New insights from the Central and Northern Apennines
Authors Angelo Cipriani, Martina Caratelli and Massimo Santantonio[3D (A, B) and 2D (A’, B’) block diagrams illustrating: A‐A’) a hypothetic extensional structure, with stripped‐off post‐Calcare Massiccio sediments, and B‐B’) the possible pathways (dark arrows) of allochthonous shallow‐water material in a pelagic carbonate platform/marginal step/basin depositional system. Not to scale.
The role of sea‐bottom topography in the dispersal of shallow water‐derived calciturbidites across a submarine rift, as determined by the local extensional architecture, is under‐investigated, namely with pelagic settings along ancient passive continental margins. A comparison with modern carbonate platform/basin analogues, or with siliciclastic systems, is not always feasible, as ancient carbonate systems were commonly home to anachronistic environments (e.g. the Western Tethyan Mesozoic). Our study focuses on: (a) a reconstruction of the palaeotectonic architecture of the Umbria‐Marche Basin in the Jurassic and on (b) how this architecture produced a submarine topography which governed the dispersal of sediment, shed by the neighbouring Lazio‐Abruzzo Carbonate Platform, for >40 million years. A geological mapping project was performed in the Apennines of Central Italy, a region which in the Jurassic displayed a pattern of intrabasinal highs (pelagic carbonate platforms) and intervening basins which was exceedingly complex due to the high density, and oddly variable trends, of faults rooted in a shallow detachment layer corresponding to thick Triassic salt. A map pairing the occurrences of these resedimented beds with an updated palaeogeography becomes the natural descriptor of the itineraries followed by sediment gravity flows. This qualitative method represents a companion, or even alternative, approach to the one strictly based on physical stratigraphy, and it greatly improves our knowledge of regional geology and rift‐basin analysis. Our case history potentially represents the analogue of hydrocarbon fields both inland and in the offshore. Geological mapping shows that the marginal palaeoescarpments of pelagic carbonate platforms formed obstacles to the gravity flows as sediment load was discharged at their toes. While turbidity flows were locally vigorous enough to climb the escarpments, leaving overbank deposits on the pelagic carbonate platform‐tops, a ‘shelter’ effect is evidenced by the resediment‐free nature of those basins lying downflow, which were shielded by the highs.
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The thermal maturity of sedimentary basins as revealed by magnetic mineralogy
Authors Mansour M. Abdelmalak and Stéphane Polteau[Model showing the formation of magnetic mineral as a function of organic matter maturity and temperature. The maturity of the different samples is well constrained by Rock‐Eval pyrolysis and vitrinite reflectance.
The thermal evolution of sedimentary basins is usually constrained by maturity data, which is interpreted from Rock‐Eval pyrolysis and vitrinite reflectance analytical results on field or boreholes samples. However, some thermal evolution models may be inaccurate due to the use of elevated maturities measured in samples collected within an undetected metamorphic contact aureole surrounding a magmatic intrusion. In this context, we investigate the maturity and magnetic mineralogy of 16 claystone samples from Disko‐Svartenhuk Basin, part of the SE Baffin Bay volcanic margin. Samples were collected within thermal contact metamorphic aureoles near magma intrusions, as well as equivalent reference samples not affected by intrusions. Rock‐Eval pyrolysis (Tmax), and vitrinite reflectance (Ro) analysis were performed to assess the thermal maturity, which lies in the oil window when 435°C ≤ Tmax ≤ 470°C and 0.6%–0.7% ≤ Ro ≤ 1.3%. In addition, we performed low‐ (<300K) and high‐temperature (>300K) investigations of isothermal remanent magnetization to assess the magnetic mineralogy of the selected samples. The maturity results (0.37% ≤ Ro ≤ 2%, 22°C ≤ Tmax ≤ 604°C) show a predominance of immature to early mature Type III organic matter, but do not reliably identify the contact aureole when compared to the reference samples. The magnetic assemblage of the immature samples consists of iron sulphide (greigite), goethite and oxidized or non‐stoichiometric magnetite. The magnetic assemblage of the early mature to mature samples consists of stoichiometric magnetite and fine‐grained pyrrhotite (<1 μm). These results document the disappearance of the iron sulphide (greigite) and increase in content of magnetite during normal burial. On the other hand, magnetite is interpreted to be the dominant magnetic mineral inside the contact aureole surrounding dyke/sill intrusions where palaeotemperatures indicate mature to over‐mature state. Interestingly, the iron sulphide (greigite) is still detected in the contact aureole where palaeotemperatures exceeded 130°C. Therefore, the magnetic mineralogy is a sensitive method that can characterize normal burial history, as well as identify hidden metamorphic contact aureoles where the iron sulphide greigite is present at temperatures beyond its stability field.
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On the use of geochronology of detrital grains in determining the time of deposition of clastic sedimentary strata
More Less[AbstractPlacing geologic events in a temporal framework is essential to telling the story of Earth history. However, clastic sedimentary rocks can be difficult to date in an absolute reference because they are made up of grains that are older than the rock in which they are now found, and some clastic rocks do not contain fossils that allow precise reference to the Geologic Timescale. For such rocks, the isotopic dating of detrital minerals can be used to estimate the time of deposition; the clastic rock must be younger than the youngest grain analysed. However, many researchers eschew this simple and straightforward approach in favour of schemes that estimate the maximum allowable depositional age as the weighted mean of the age of several grains, chosen by a variety of selection criteria. This is a mistake; in the absence of a geochemical resemblance apart from the similarity of their age, detrital grains should not be assumed to have originated in the same system and therefore any averaging or other manipulation of such data is statistically invalid and produces results without geologic significance. In the absence of interbedded volcanic rocks or index fossils, dating of detrital minerals can be an important aid in understanding the time of deposition of clastic rocks, but the best estimate will come from taking note of the youngest single grain and not by inappropriately averaging data.
,Clastic sedimentary rocks are best dated by isotopic analysis of closely interbedded volcanic rocks (PLAN A). Fossils can also provide age assement of sufficient precision (PLAN B) but when volcanic rocks are not present or fossils are not diagnostic, PLAN C may be ncessary. This contribution discusses some details of using geochronology of detrital grains to determine the depositional age of clastic rocks.
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Predicting sediment discharges and erosion rates in deep time—examples from the late Cretaceous North American continent
[AbstractDepositional stratigraphy represents the only physical archive of palaeo‐sediment routing and this limits analysis of ancient source‐to‐sink systems in both space and time. Here, we use palaeo‐digital elevation models (palaeoDEMs; based on high‐resolution palaeogeographic reconstructions), HadCM3L general circulation model climate data and the BQART suspended sediment discharge model to demonstrate a predictive, forward approach to palaeo‐sediment routing system analysis. To exemplify our approach, we use palaeoDEMs and HadCM3L data to predict the configurations, geometries and climates of large continental catchments in the Cenomanian and Turonian North American continent. Then, we use BQART to estimate suspended sediment discharges and catchment‐averaged erosion rates and we map their spatial distributions. We validate our estimates with published geologic constraints from the Cenomanian Dunvegan Formation, Alberta, Canada, and the Turonian Ferron Sandstone, Utah, USA, and find that estimates are consistent or within a factor of two to three. We then evaluate the univariate and multivariate sensitivity of our estimates to a range of uncertainty margins on palaeogeographic and palaeoclimatic boundary conditions; large uncertainty margins (≤50%/±5°C) still recover estimates of suspended sediment discharge within an order of magnitude of published constraints. PalaeoDEMs are therefore suitable as a first‐order investigative tool in palaeo‐sediment routing system analysis and are particularly useful where stratigraphic records are incomplete. We highlight the potential of this approach to predict the global spatio‐temporal response of suspended sediment discharges and catchment‐averaged erosion rates to long‐period tectonic and climatic forcing in the geologic past.
,Left: Onshore palaeo‐digital elevation model (palaeoDEM) for the Cenomanian North American continent. Key palaeogeographic features are labelled, including the Sevier orogenic highlands, Laramidian landmass, Western Interior Seaway, Appalachian landmass, Hudson Seaway (HS) and Labrador Seaway (LS). Modern North American coastlines and country borders (solid black lines) have been palaeo‐rotated onto palaeoDEMs. Right: Spatial distributions of suspended sediment discharges (Qs) for the Cenomanian North American continent. Qs values overlay palaeoDEM hillshades for comparison with palaeotopography.
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Influence of orographic precipitation on the topographic and erosional evolution of mountain ranges
Authors Valeria Zavala, Sébastien Carretier and Stéphane Bonnet[The development of a precipitation peak at some elevation within mountain catchments appears to be a crucial factor that controls the denudation and topographic evolutions of a mountain. If the precipitation peak is located at low or medium elevation when the mountain has reached a dynamic equilibrium, the model predicts that denudation has strongly accelerated (b) in the early times of the mountain uplift, or even passed by a maximum resulting in a pulse of sediment outflux to basins (a). If the precipitation rate does not have a maximum in the mountain, it can be deduced that the denudation has not evolved differently from cases where the precipitation rate is constant (c). These results can be used to re‐examine the interpretation of sediment flux variations in real cases based on the current distribution of precipitation rates with altitude in mountain ranges.
The influence of climate on mountain denudation has been the topic of an intense debate for two decades. This debate partly arises from the covariation of rainfall and topography during the growth of mountain ranges, both of which influence denudation. However, the denudational response of this co‐evolution is poorly understood. Here, we use a landscape evolution model where the rainfall evolves according to a prescribed rainfall–elevation relationship. This relationship is a bell curve defined by a rainfall base level, a rainfall maximum and a width around the rainfall peak elevation. This is a first‐order model that fits a large range of orographic rainfall data at the ca. 1‐km spatial scale. We carried out simulations of an uplifting block with an alluvial apron, starting from an initially horizontal surface, and testing different rainfall–elevation relationships. We find that the denudation history is different from that with constant rainfall models. The results essentially depend on the ratio between the final steady‐state summit elevation Hss and the prescribed rainfall peak elevation Hp. This ratio is hard to predict because it depends on the transient coupling of rainfall and elevation. We identified three types of results according to Hss/Hp. If Hss/Hp > 4 (Type I), the denudation rates peak when the summits reach values close to Hp. If Hss/Hp > 1.5 and < 4 (Type II), the denudation is strongly accelerated when the elevation of the summits approaches Hp, and then the denudation increases slowly towards the uplift rate. If Hss/Hp < 1.5 (Type III), the denudation evolution is similar to situations with constant and homogeneous rainfall. In the Type I and II experiments, the mountain top is subjected to aridification once the summits have passed through Hp. To adapt to this reduced rainfall, the slopes increase. This can lead to a paradoxical situation where the mountain relief increases faster, whereas the denudation increases more slowly. The development of orographic precipitation may thus favour the stability of the mean denudation rate in a rising mountain. Despite the model limitations, including a constant rainfall–elevation relationship, our study suggests that the “classical” exponential increase in the denudation rate predicted by constant rainfall models is not the common case. Instead, the common case involves pulses and acceleration of the denudation even in the absence of uplift or global climate variations.
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Straight from the source's mouth: Controls on field‐constrained sediment export across the entire active Corinth Rift, central Greece
[AbstractThe volume and grain‐size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite their importance, few studies have constrained sediment budgets and grain‐size exported into an active rift at the basin scale. Here, we used the Corinth Rift as a natural laboratory to quantify the controls on sediment export within an active rift. In the field, we measured the hydraulic geometries, surface grain‐sizes of channel bars and full‐weighted grain‐size distributions of river sediment at the mouths of 47 catchments draining the rift (constituting 83% of the areal extent). Results show that the sediment grain‐size increases westward along the southern coast of the Gulf of Corinth, with the coarse‐fraction grain‐sizes (84th percentile of weighted grain‐size distribution) ranging from approximately 19 to 91 mm. We find that the median and coarse‐fraction of the sieved grain‐size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. Our results indicate that grain‐size export is primarily controlled by the input grain‐size within the catchment and subsequent abrasion during fluvial transport, both quantities that are sensitive to catchment lithology. We also demonstrate that the median and coarse‐fraction of the grain‐size distribution are predominantly transported in bedload; however, typical sand‐grade particles are transported as suspended load at bankfull conditions, suggesting disparate source‐to‐sink transit timescales for sand and gravel. Finally, we derive both a full Holocene sediment budget and a grain‐size‐specific bedload discharged into the Gulf of Corinth using the grain‐size measurements and previously published estimates of sediment fluxes and volumes. Results show that the bedload sediment budget is primarily comprised (~79%) of pebble to cobble grade (0.475–16 cm). Our results suggest that the grain‐size of sediment export at the rift scale is particularly sensitive to catchment lithology and fluvial mophodynamics, which complicates our ability to make direct inferences of tectonic and palaeoenvironmental forcing from local stratigraphic characteristics.
,This study presents the first constrained full‐weighted grain‐size export for an entire rift, the Corinth Rift. We find a strong grain‐size trend along the South coast of the Gulf of Corinth, with grain‐size increasing to the West. We find that grain‐size is primarily controlled by lithology with tectonics acting as a secondary control.
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Mélange development in the Neyriz region of Zagros Orogen, Iran: Record of convergence and collision in the Neotethyan Realm
[AbstractMélanges are formed by sedimentary, tectonic and diapiric processes and are generally found in collisional belts. The Zagros Orogeny provides an intriguing geological laboratory for the study of mélange‐forming processes during the progressive tectonic evolution of the Neotethys Ocean. Different types of tectonic and sedimentary mélanges occur in specific structural positions within the Zagros orogenic belt in the Neyriz Region (Iran). Based on their block‐in‐matrix fabrics, and tectonostratigraphic positions, we differentiated 14 different mélange types, which mark different episodes of the tectonic evolution of the Neyriz Region from the Cretaceous subduction to the Miocene collision. The Cretaceous subduction stage is recorded by volcanic‐sedimentary mélanges (Mv). Sedimentary mélanges characterized by megabreccia from the Cretaceous limestone (Ms1) and Eocene polymictic megabreccia (Ms2) represent epi‐nappe mélanges formed during the Palaeocene–Eocene in wedge‐top basins. The ophiolite emplacement in the Oligocene resulted in local extensional tectonics in the upper part of the ophiolitic nappe, and deposition of a polymictic megabreccia (Ms3, Ms4). As the final production of the Neotethys Ocean closure and the Eurasian‐Arabian collision, the sedimentary mélanges characterized by different types of chaotic rock units (Ms5, Ms6, Ms7 and Ms8 facies) were developed in front of the Cretaceous–Eocene nappes due to growth of the orogenic wedge in the Miocene. Our findings indicate that the recognition and distinction of different types of mélange may provide additional constraints for a better understanding of the tectono‐sedimentary evolution of the Neotethyan region.
,A tectonic model for the evolution of the Zagros Orogenic Belt based on the different types of mélanges in the Neyriz region.
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Tectono‐sedimentary evolution of Jurassic–Cretaceous diapiric structures: Miravete anticline, Maestrat Basin, Spain
[We illustrate for the first time mixed halokinetic depositional sequences in minibasins limited by salt walls displaying typical flap and hook geometries (salt‐welds and thrust‐welds after Cenozoic shortening), in the Miravete anticline and Maestrat Basin (Iberian Ranges), with Jurassic and Early Cretaceous ages and partly coeval to Iberia‐Europe sinistral motion.
Integration of extensive fieldwork, remote sensing mapping and 3D models from high‐quality drone photographs relates tectonics and sedimentation to define the Jurassic–early Albian diapiric evolution of the N–S Miravete anticline, the NW‐SE Castel de Cabra anticline and the NW‐SE Cañada Vellida ridge in the Maestrat Basin (Iberian Ranges, Spain). The pre shortening diapiric structures are defined by well‐exposed and unambiguous halokinetic geometries such as hooks and flaps, salt walls and collapse normal faults. These were developed on Triassic salt‐bearing deposits, previously misinterpreted because they were hidden and overprinted by the Alpine shortening. The Miravete anticline grew during the Jurassic and Early Cretaceous and was rejuvenated during Cenozoic shortening. Its evolution is separated into four halokinetic stages, including the latest Alpine compression. Regionally, the well‐exposed Castel de Cabra salt anticline and Cañada Vellida salt wall confirm the widespread Jurassic and Early Cretaceous diapiric evolution of the Maestrat Basin. The NE flank of the Cañada Vellida salt wall is characterized by hook patterns and by a 500‐m‐long thin Upper Jurassic carbonates defining an upturned flap, inferred as the roof of the salt wall before NE‐directed salt extrusion. A regional E‐W cross section through the Ababuj, Miravete and Cañada‐Benatanduz anticlines shows typical geometries of salt‐related rift basins, partly decoupled from basement faults. These structures could form a broader diapiric region still to be investigated. In this section, the Camarillas and Fortanete minibasins displayed well‐developed bowl geometries at the onset of shortening. The most active period of diapiric growth in the Maestrat Basin occurred during the Early Cretaceous, which is also recorded in the Eastern Betics, Asturias and Basque‐Cantabrian basins. This period coincides with the peak of eastward drift of the Iberian microplate, with speeds of 20 mm/year. The transtensional regime is interpreted to have played a role in diapiric development.
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Basement highs: Definitions, characterisation and origins
Authors David C. P. Peacock and Graham J. Banks[Example of geometric features of a basement high, illustrated using the south Rona Ridge 3D Top Basement depth structure map. A = Lancaster Field oil‐water contact at 1678 m true vertical depth sub sea level (TVDSS) (Hurricane Energy, 2019c). B = Lincoln oil discovery “oil down to” at 2258 m TVDSS. C = Whirlwind Discovery “oil down to” at TVDSS. The basement high covers an area of ~ 1200 km , so it is a 4th order basement high. It has an approximately trapezoid shape in map view shape (including the Whirlwind downthrown block). The topography of the upper surface can be described as an undulating wedge (area i) and an undulating planar slope (areas labelled ii). Structures segmenting the basement high include: 1 = Westray Fault Zone; 2 = Brynhild Fault Zone. Contour increment 100 m.
A glossary of commonly used terms related to the geometric forms and geological settings of basement highs is presented to assist cross‐disciplinary understanding, qualifying prefixes for the term basement are discussed and a scheme for characterising basement highs is presented. This scheme is designed to standardise, and to add rigour to, description of basement highs. It will thereby enhance basement high comparisons and assist understanding of basement highs across technical disciplines. The scheme enables systematic characterisation of: the geometry of a basement high; the lithologic units and structures in, above and around it; timings; tectonics and origins of the basement high and play elements relating to resource prospectivity. Use of this scheme is demonstrated using the southern Rona Ridge (West of Shetland, UK Continental Shelf). The tectonic, isostatic, erosional and stratigraphic processes that form basement highs are also discussed, and examples in proven petroleum systems are presented.
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Quantifying sand delivery to deep water during changing sea‐level: Numerical models from the Quaternary Brazos Icehouse continental margin
Authors Oriol Falivene, Bradford E. Prather and John Martin[AbstractSequence stratigraphy for clastic continental margins predicts the development of sand‐rich turbidite deposits during specific times in relation to base‐level cycles. It is now widely understood that deltas can extend to the shelf‐edge forced by high sediment flux and/or base level, providing a direct connection to transfer sediment and sand to the slope and basin floor even during high base level periods. Herein, we build a stratigraphic forward model for the last 120 kyr of the fluvio‐deltaic to deep‐water Brazos system (USA) where sediment partitioning along an Icehouse continental margin can be evaluated. The reduced‐complexity stratigraphic forward model employs geologically constrained input parameters and mass balance. The modelled architecture is consistent with the location of depositional units previously mapped in the shelf. Sand bypasses the shelf and upper slope between 35 to 15 kyr before present and only about 20%–30% of all the sediment and sand supplied to the system is transferred to deep water. Several scenarios based on the initial Brazos model investigate the relationships between base level and deep‐water sand ratio (DWSR). DWSR is defined as the relative amount of sand transferred to the deep‐water portions of the system subdivided by the total sand input to the model. Linear correlations between DWSR and base level change rates or base level are very poor. Short‐term variability due to local processes (for example avulsions) is superimposed to the long‐term trends and mask the base level signal. DWSR for an entire base‐level cycle is mainly controlled by the proportion of time the delta stays docked at the shelf‐edge. Stratigraphic forward models are useful to complement field observations and quantify how different processes control stratigraphy, which is important for making predictions in areas with limited information.
,Sand and sediment transfer to deep water in Icehouse continental margins is quantified departing from an original model of the Brazos fluvio‐deltaic system (USA). Short‐term variability due to local process is superimposed to long‐term trends and masks the base level signal. However, for entire base level cycle sand transferred to deep water is mainly controlled by the proportion of time in which the delta remains docked at the shelf‐edge.
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Volumes & issues
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Volume 36 (2024)
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Volume 35 (2023)
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Volume 34 (2022)
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Volume 33 (2021)
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Volume 32 (2020)
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Volume 31 (2019)
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Volume 30 (2018)
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Volume 29 (2017)
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Volume 28 (2016)
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Volume 27 (2015)
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Volume 26 (2014)
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Volume 25 (2013)
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Volume 24 (2012)
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Volume 23 (2011)
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Volume 22 (2010)
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Volume 21 (2009)
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Volume 20 (2008)
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Volume 19 (2007)
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Volume 18 (2006)
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Volume 17 (2005)
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Volume 16 (2004)
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Volume 15 (2003)
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Volume 14 (2002)
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Volume 13 (2001)
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Volume 12 (2000)
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Volume 11 (1999)
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Volume 10 (1998)
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Volume 9 (1997)
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Volume 8 (1996)
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Volume 7 (1994)
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Volume 6 (1994)
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Volume 5 (1993)
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Volume 4 (1992)
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Volume 3 (1991)
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Volume 2 (1989)
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Volume 1 (1988)