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- Volume 33, Issue 2, 2021
Basin Research - Volume 33, Issue 2, 2021
Volume 33, Issue 2, 2021
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Controls of pre‐existing structures on clinoform architecture and the associated progradational system elements
Authors Roberto Clairmont, Folarin Kolawole, Abah P. Omale and Heather BedleAbstractThere remains a limited understanding of the controls of pre‐existing structures on the architecture of deep‐water progradational sequences. In the Northern Taranaki Basin (NTB), New Zealand, Pliocene post‐extensional sedimentary sequences overlie Miocene back‐arc volcaniclastic units. We utilize seismic reflection datasets to investigate the relationships between the buried back‐arc mound‐shaped structures, and the spatio‐temporal changes in clinoform architecture and the associated progradational system elements within the overlying continental slope margin sequences. Our results reveal the following: (a) buried mound‐shaped structures in the northern domain of the study area, overlain by younging progression of shelf‐to‐basin prograding clinoforms; (b) folding of the deeper clinoforms that systematically decrease in magnitude with shallowing depth from the top of the seamounts; (c) overall, the N‐S‐trending continental slope margin evolves from a highly curvilinear/angular trend in the deeper clinoforms (Units 1 and 2) into a rectilinear geometry within the shallower post‐extensional intervals (Unit 3 and shallower); (d) Units 1 and 2 characterized by dominance of stacked offlap breaks and over‐steepened (7–10°) clinoform foreset slopes in the northern domain, and dominance of gently dipping foreset slopes (<6°) in the south; (e) Unit 3 shows very low (<5°) and intermediate (5–7°) foreset slopes across the entire survey; (f) in the northern domain, differential loading by prograding sequences about the buried seamounts and horst–graben structures induced a differential compaction of the deeper units, which influenced a temporal pinning of the prograding slope margin in pre‐Unit 2 times and (g) wide, closely spaced channel incision into over‐steepened slopes dominate the deeper prograding sequence in the northern domain, whereas narrower, straighter channels dominate the south. We show that the buried pre‐existing structures constitute rigid buttresses that modulated the syn‐depositional topography and post‐depositional architecture of the prograding sequences in the NTB. Our findings present a distinction in the controls on progradational sedimentation patterns between magmatic and non‐magmatic continental margins.
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Palaeogene stratigraphy and chronology of the western Sivas Basin, central Anatolia (Turkey): Tectono‐sedimentary evolution of a well‐preserved basin along the northern Neotethys suture zone
Authors Michael H. Darin and Paul J. Umhoefer[Conceptual block diagrams showing our proposed tectono‐sedimentary evolution of the western Sivas Basin (red box in inset map) during deposition of TS‐1 (a,b,c) and TS‐2 (d); see Figure 2 for location of X‐X′. (a) Maastrichtian to Paleocene Tauride‐Pontide collision in the easternmost Sivas Basin led to incomplete subduction and a remannt ocean setting in the western Sivas Basin; additional accommodation space may have been generated by an enigmatic phase of extension. (b) Middle Eocene contraction in the Tauride thrust belt to the south led to rapid subsidence in the Sivas Basin and a transition to a flexural foreland basin setting. (c) Northward propagation of shortening during the latest Eocene marked another switch to a fragmented foreland setting involving basin inversion, uplift and isolation from the marine realm, and initiation of the southern Sivas fold‐thrust belt (SSFTB), which structurally partitioned the Sivas Basin into a southern wedge‐top and northern evaporitic foreland basin during the Oligocene (d). A – Altınyayla; B – Bünyan; other abbreviations as in Figure 1.
The Sivas Basin overlaps the northern Neotethys suture zone in central Anatolia (Turkey) and contains a ca. 12‐km thick succession of Cenozoic strata that provides an exceptional record of major tectonic transitions from subduction to continental assembly and tectonic escape. Consensus regarding the tectonic and palaeogeographic evolution of this segment of the Arabia‐Eurasia collision zone has been hindered by uncertainty in the tectonic setting of the early (Palaeogene) Sivas Basin, which has been variably interpreted as a remnant ocean, forearc, foreland, wedge‐top or intracontinental extensional basin. Here we integrate new geologic mapping (>5,000 km2), stratigraphy, facies analysis and U‐Pb geochronology from the western Sivas Basin to produce a detailed time‐stratigraphic framework and a refined Palaeogene tectono‐sedimentary model for the Sivas Basin. Earliest marine sedimentation occurred during the Maastrichtian‐Palaeocene in a remnant ocean setting due to incomplete closure of the northern Neotethys Ocean. Rapid accumulation of >2 km of basin floor turbidites during the middle to late Eocene reflect a transition to a foreland setting. A major late Eocene unconformity (ca. 38–34 Ma) coincides with the initiation of the north‐vergent southern Sivas fold‐thrust belt, which inverted and structurally partitioned the basin into a southern wedge‐top and a northern evaporitic foreland basin; the entire basin was dominantly nonmarine after this unconformity. Published palaeomagnetic data integrated with a newly discovered tuff dated at 31.9 Ma reveal that the 2.8‐km thick Altinyayla Formation was deposited from ca. 34 to 26 Ma in an unconfined braided fluvial system. Close stratigraphic correlations between the western, central and northern Sivas Basin suggest that the entire basin evolved from a remnant ocean to peripheral retro‐foreland basin during the middle to late Eocene, and finally a fragmented foreland basin since the Oligocene. This general evolution may be a characteristic of such sedimentary basins formed on suture zones across Anatolia and in other collisional orogens globally.
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Sedimentary response to a collision orogeny recorded in detrital zircon provenance of Greater Caucasus foreland basin sediments
[AbstractThe Greater Caucasus orogen on the southern margin of Eurasia is hypothesized to be a young collisional system and may present an opportunity to probe the structural, sedimentary and geodynamic effects of continental collision. We present detrital zircon U‐Pb age data from the Caucasus region that constrain changes in sediment routing and source exposure during the late Cenozoic convergence and collision between the Greater Caucasus orogen and the Lesser Caucasus, an arc terrane on the lower plate of the system. During Oligocene to Middle Miocene time, following the initiation of deformation within the Greater Caucasus, marine sandstones and shales were deposited between the Greater and Lesser Caucasus, and detrital zircon age data suggest no mixing of Greater Caucasus and Lesser Caucasus detritus. During Middle to Late Miocene time, Greater Caucasus detritus was deposited onto the Lesser Caucasus basin margin, and terrestrial, largely conglomeratic, sedimentation began between the Greater and Lesser Caucasus. Around 5.3 Ma, upper plate exhumation rates increased and shortening migrated to pro‐ and retro‐wedge fold‐thrust belts, coinciding with the initiation of foreland basin erosion. Sediment composition, provenance and structural data from the orogen together suggest the existence of a wide (230–280 km) marine basin that was progressively closed during Oligocene to Late Miocene time, probably by subduction/lithospheric underthrusting beneath the Greater Caucasus, followed by initiation of collision between the Lesser Caucasus arc terrane and the Greater Caucasus in Late Miocene to Pliocene time. The pace of the transition from hypothesized subduction to collision in the Caucasus is consistent with predictions from numerical modeling for a system with moderate convergence rates (<13 mm/yr) and hot lower plate continental lithosphere. Basement crystallization histories implied by our detrital zircon age data suggest the presence of two pre‐Jurassic sutures between stable Eurasia and the Lesser Caucasus, which likely guided later deformation.
,The Greater Caucasus may constitute a natural example of early continental collision. New detrital zircon U‐Pb geochronology data, together with published Cenozoic stratigraphy and structural data from the Greater Caucasus, suggests collision began in the Late Miocene to Pliocene, leading to diachronous changes in deformation and sedimentation in the orogen and associated basins.
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Subsidence analysis of salt tectonics‐driven carbonate minibasins (Northern Calcareous Alps, Austria)
Authors Philipp Strauss, Pablo Granado and Josep Anton Muñoz[Subsidence and growth rates of the Triassic units compared to subsidence mechanisms based on Schlager (1981). The accumulation rate of stratigraphic units is displayed in comparison to the derived total subsidence curve. Two kinds of units can be individuated based on their total subsidence curves: one group for which accommodation space was driven by thermal subsidence, and a second group falling above the thermal subsidence curve, indicating subsidence rates requiring salt expulsion in addition to cooling.
Subsidence analysis study for several Triassic carbonate platforms from the eastern Northern Calcareous Alps shows that salt expulsion allowed for the growth of thick isolated depocentres (>1.5 km) at rates faster than those tectonic subsidence alone can provide. Our results, in addition to independent regional geological evidence, argue against previous models of thick‐skinned extension controlling accommodation space. Differential sedimentary loading and stretching of the salt layer can explain the development of the Triassic isolated carbonate platforms in the Northern Calcareous Alps, with salt expulsion being proportional to the growth potential of the carbonate producers. Aside of topographic loads, early diageneses of carbonates allow for the density inversion between sediment and salt, with differential loading by carbonate aggradation leading to a self‐sustained feedback cycle of density‐driven and gradient load subsidence; stretching of the salt layer and extensional deformation of its overburden, as constrained by cross‐section restoration, also contributed to diapir initiation and salt expulsion. Our model can: (a) explain the occurrence of isolated Middle Triassic carbonate platforms in the eastern Northern Calcareous Alps, and (b) differentiate between accommodation space controlled by (local) salt expulsion and by (regional) tectonic subsidence. The Triassic Neo‐Tethys shelf of the studied area constituted therefore a salt wall and minibasin province. This contribution and methods herein can also be applied to other carbonate platform systems developed on salt basins, especially where the transition from rift to drift remains unclear.
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Tectonic control on mass‐transport deposit and canyon‐fed fan system in the Ulleung Basin, East Sea (Sea of Japan)
Authors Yongjoon Park, Donggeun Yoo, Nyeonkeon Kang, Boyeon Yi and Byoungyeop Kim[This study suggests that strike variation in shelf‐margin erosional and depositional processes were caused principally by the locations and timings of tectonic deformation.
Extensive 2D multichannel seismic (~17340 km) and well data provide an opportunity to investigate the source to sink processes and triggering factors of the Late Miocene sedimentary record in the Ulleung Basin, East Sea (Sea of Japan). The sedimentary succession of the basin comprises two distinct deep‐water depositional systems, which are characterised by stacked mass‐transport deposits (MTDs) and subsequent submarine fan. Individual MTDs spread downslope over areas as large as ~9000 km2 with NW–SE or N–S flow direction. The deep‐water fan consists of distributary channel‐lobe complexes (DLCs) that are 80 km wide and 140 km long. Two major tectonic periods driven by structural deformation characterised the Late Miocene deep‐water sedimentation growth. During early to middle Late Miocene (10.3–8.2 Ma), the MTDs were sourced from degraded fold triggered by slope oversteepening and seismicity on the southeastern basin margin, where the thrust‐and‐fold belt developed. In the middle to latest Late Miocene (8.2–6.3 Ma), the DLCs were fed by canyon‐channel systems on the southwestern basin margin, where the tectonic uplift of the anticline was active. Therefore, this study suggests that strike variation in shelf‐margin erosional and depositional processes were caused principally by the locations and timings of tectonic deformation.
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The importance of trace element analyses in detrital Cr‐spinel provenance studies: An example from the Upper Triassic of the Barents Shelf
Authors Trond Svånå Harstad, Mai Britt Mørk E. and Trond Slagstad[Cr‐spinel from the Snadd and De Geerdalen formations are distinctly different from Cr‐spinel of the same depositional age to the east of the Uralian Orogen. Major element compositions of detrital Cr‐spinel in the Carnian Osipai Fm. north Siberia is consistent with Cr‐spinel from a large igneous province, while Snadd and De Geerdalen formation Cr‐spinel indicate a ophiolitic source. The addition of trace element compositional data of the Snadd and De Geerdalen formation Cr‐spinel, help identify a metamorphic alteration history of the detrital grains.
Investigations of sandstone provenance often involve U–Pb dating and chemical/mineralogical investigations of detrital minerals that are stable in sediments. As most stable detrital minerals are from felsic–intermediate rocks, investigations of the only mafic–ultramafic mineral considered stable in sediments, chromian spinel (Cr‐spinel), can reveal contributions from mafic–ultramafic sources. Cr‐spinel chemical compositions are tied to petrogenesis, making it possible to identify the nature of, and differentiate between, potential sources. Earlier detrital Cr‐spinel studies have focused on major and minor element compositions, however, the advent of laser‐ablation analytical techniques now allow routine mineral trace element analyses. Here, we integrate major, minor and trace element compositions of detrital Cr‐spinel from sandstones with a well‐characterised provenance from the Triassic (Anisian to Early Norian) Snadd and De Geerdalen formations of the Barents Shelf. The analysed Cr‐spinel compositions are depleted in the major element cations Fe3+, Al and Mg and enriched in Cr and Fe2+. Relative to MORB chromite, the minor and trace element data show high concentrations of Zn, Co and Mn, low concentrations of Ni and Ga and variable concentrations of Ti, V and Sc. The major element compositions of the detrital Cr‐spinel are similar to ophiolite‐associated Cr‐spinel, while the trace element compositions indicate a more complex petrogenesis influenced by metamorphic alteration. The compositional variations between sample locations are small, suggesting similar source rocks for the detrital Cr‐spinel throughout the study area. The most likely sources of the Cr‐spinel grains are metamorphosed ophiolite complexes in the Uralian Orogen, in accordance with earlier provenance studies. The novel addition of trace element compositions to detrital Cr‐spinel studies adds significant source‐sensitive information.
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The Middle Jurassic to lowermost Cretaceous in the SW Barents Sea: Interplay between tectonics, coarse‐grained sediment supply and organic matter preservation
[Palaeobathymetric variations and organic matter dilution controlling TOC trends. (a) Tectonically stable areas or areas affected by minor faulting. (b) Area affected by active normal faults.
Syn‐rift successions contain both prolific organic‐rich and coarse‐grained rocks, but these rocks are usually studied independently. Thus, the interplay among organic matter deposition, tectonics and sediment supply is not commonly assessed. In this study, we use well logs, Total Organic Carbon (TOC) content, biostratigraphy and seismic data from the SW Barents Sea to unravel the variability of organic‐rich successions and its interaction with potential reservoir rocks in areas affected by active normal faulting versus tectonically stable areas. Four Transgressive‐Regressive (T‐R) sequences were defined for the Middle to Upper Jurassic Fuglen Formation and for the organic‐rich Upper Jurassic to lowermost Cretaceous Hekkingen Formation. Three TOC trends, controlled by palaeobathymetric variations, and organic matter dilution, were identified within the two main organic‐rich sequences (sequences 2 and 3): (a) wells with the highest TOC values (>10 wt %) at the base of the succession; (b) wells with the highest TOC values at the top of the succession and (c) wells with high TOC values at the base and top of the succession. Our interpretation indicates that fault activity controlled the TOC trends in two different ways: Firstly, by creating a sharp topographic contrast‐triggering hyperpycnal flows, and shallowing the footwalls, where higher oxygen content and less developed stratified waters lowered organic matter preservation. Secondly, by significantly increasing the input of clastic material, which inherently led to dilution of organic matter and resulted in lower TOC values (<6 wt %). We interpret that sand deposition was controlled by the size and geomorphology of the sediment source areas. The western part of the study area (i.e. the Loppa High) was characterized by uplifted footwall islands and localized sands along their flanks, whereas the southern part (i.e. the Finnmark Platform) constituted a larger sediment source area for the Volgian age. This work has implications for a better understanding of the distribution of reservoir and source rocks in active rift basins.
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Fault‐controlled base‐of‐scarp deposits
Authors Domenico Chiarella, Walter Capella, Sergio G. Longhitano and Francesco Muto[Base‐of‐scarp deposits represent unsteady‐state systems showing primary inclined bedding and aggradational to progradational geometries along active fault scarps. The progressive angle decrease recognised in the younger strata promotes the architectural change of the system to either shola‐water or Gilbert‐type systems.
The term base‐of‐scarp is proposed for those submarine deposits controlled by a fault and physically disconnected from their more proximal counterpart located on the footwall, although genetically linked to it. These systems differ from conventional fault‐controlled deltas, such as shoal‐ and Gilbert‐type, because they are entirely subaqueous and lack equilibrium morphology—a steady state in which the system grows in size without altering its shape. We present field examples of fault‐controlled deposits from the Crati Basin and the Messina Strait (southern Italy) consisting of stratigraphic clastic wedges that thin towards and onlap onto the active margin with primary inclined bedding. Beds are composed of immature coarse‐grained gravels and sand, lack structures representative of wave‐action and reflect gravity‐driven processes such as debris flow, debris fall and high‐density turbidity currents. These deposits represent the unsteady‐state phase in which the system grows reducing its slope angle leading to conditions under which the unsteady state may eventually turn into a Gilbert‐type or shoal‐water system. A diagram for fault‐controlled base‐of‐scarp (B), Gilbert (G) and shoal‐water (S) deposits is presented, including their steady‐ and unsteady states, and the conceptual conditions under which a base‐of‐scarp system might evolve into Gilbert‐type or shoal‐water systems and vice versa.
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Turbidites, topography and tectonics: Evolution of submarine channel‐lobe systems in the salt‐influenced Kwanza Basin, offshore Angola
[AbstractUnderstanding the evolution of submarine channel‐lobe systems on salt‐influenced slopes is challenging as these systems react to subtle, syn‐depositional changes in sea‐floor topography. The impact of large blocking structures on individual deep‐water systems is well documented, but our understanding of the spatial and temporal evolution of extensive channel‐lobe systems on slopes influenced by relatively modest salt structures is relatively poor. We focus on Late Miocene deep‐water depositional systems contained within a c. 450 ms TWTT thick interval imaged in 3D seismic reflection data from the contractional salt‐tectonic domain, offshore Angola. Advanced seismic attribute mapping, tied to seismic facies analysis and time‐thickness variations, reveal a wide range of interactions between structurally induced changes in slope relief, deep‐water sediment routing, geomorphology and sedimentology. Five seismic units record a striking tectono‐stratigraphic within eight minibasins. We observe gradual channel diversion through lateral migration during times of relatively high structural growth rate, as opposed to abrupt channel movement via avulsion nodes during times of relatively high sediment accumulation rate. Our models capture the response of deep‐water depositional systems to the initiation, maturation, and decay of contractional structures on salt‐influenced slopes. The initiation stage is defined by small, segmented folds with deep‐water depositional system being largely able to transverse multiple minibasins. In contrast, the maturity stage is characterised by large, now‐linked high‐relief structures bounding prominent minibasins leading to ponding and large‐scale diversion of channel‐lobe systems and the emplacement of MTCs derived from nearby highs. The decay stage is expressed by structures that are shorter and more subdued than those characterising the maturity stage; this leads to a more complicated array of channel‐lobe system, the evolution of which is still influenced by bypass, diversion and ponding. During the decay stage, remnant structures still exert a subtle but key control on the development and positioning of avulsion nodes.
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Reutilisation of hydrothermal vent complexes for focused fluid flow on continental margins (Modgunn Arch, Norwegian Sea)
Authors Chantelle Roelofse, Tiago M. Alves and Kamal’deen O. Omosanya[AbstractConventional three‐dimensional (3D) seismic data reveal abundant igneous activity on the Modgunn Arch, mid‐Norwegian margin. Magmatic sills and associated hydrothermal vent complexes located at various depths prove the repeated utilisation of Paleocene‐Eocene magmatic conduits. In total, 125 sills and 85 hydrothermal vent complexes were identified and mapped, with vent complexes ranging in diameter from 300 to 3,100 m and sills from 0.5 to 50 km. Three examples of stacked vent complexes are presented, revealing large eruptions of hydrothermal fluids vertically through the same conduit, from sills to the palaeo‐sea floor. The vent complexes are found throughout Paleocene strata (66–56 Ma), whilst at least ten (10) vents were active during the Eocene. This study emphasises the importance of characterising ancient magmatic structures, as hydrothermal conduits and vent structures were, and may still be, reutilised as preferential fluid flow pathways to shallower strata. A minimum of four phases of hydrothermal vent complex formation are inferred. Cretaceous faults are both bypassed and used for magma and fluid flow. The reutilisation of magmatic structures here described may bring to light previously overlooked plays and renew interest in exploring magma‐rich continental margins.
,Amplitude anomalies and stacked hydrothermal vent complexes (HTVCs) indicate reutilisation of HTVCs for fluid flow. (a) High‐amplitude anomaly shown in plan view, located above a hydrothermal vent complex (HTVC), indicating possible gas and fluid flow across the HTVC. (b) Seismic section showing an HTVC with the high‐amplitude anomaly identified and mapped in (a). (c) Seismic section with two stacked HTVCs and seismic dimming in between, indicating two episodes of hydrothermal venting. Bright amplitudes above suggest subsequent fluid flow across the HTVCs.
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Quantitative analysis of a footwall‐scarp degradation complex and syn‐rift stratigraphic architecture, Exmouth Plateau, NW Shelf, offshore Australia
[AbstractInteractions between footwall‐, hangingwall‐ and axial‐derived depositional systems make syn‐rift stratigraphic architecture difficult to predict, and preservation of net‐erosional source landscapes is limited. Distinguishing between deposits derived from fault‐scarp degradation (consequent systems) and those derived from long‐lived catchments beyond the fault block crest (antecedent systems) is also challenging, but important for hydrocarbon reservoir prospecting. We undertake geometric and volumetric analysis of a fault‐scarp degradation complex and adjacent hangingwall‐fill associated with the Thebe‐2 fault block on the Exmouth Plateau, NW Shelf, offshore Australia, using high resolution 3D seismic data. Vertical and headward erosion of the complex and fault throw are measured. Seismic‐stratigraphic and seismic facies mapping allow us to constrain the spatial and architectural variability of depositional systems in the hangingwall. Footwall‐derived systems interacted with hangingwall‐ and axial‐derived systems, through diversion around topography, interfingering or successive onlap. We calculate the volume of footwall‐sourced hangingwall fans (VHW) for nine quadrants along the fault block, and compare this to the volume of material eroded from the immediately up‐dip fault‐scarp (VFW). This analysis highlights areas of sediment bypass (VFW > VHW) and areas fed by sediment sources beyond the degraded fault scarp (VHW > VFW). Exposure of the border fault footwall and adjacent fault terraces produced small catchments located beyond the fault block crest that fed the hangingwall basin. One source persisted throughout the main syn‐rift episode, and its location coincided with: (a) an intra‐basin topographic high; (b) a local fault throw minimum; (c) increased vertical and headward erosion within the fault‐scarp degradation complex; and (d) sustained clinoform development in the immediate hangingwall. Our novel quantitative volumetric approach to identify through‐going sediment input points could be applied to other rift basin‐fills. We highlight implications for hydrocarbon exploration and emphasize the need to incorporate interaction of multiple sediment sources and their resultant architecture in tectono‐stratigraphic models for rift basins.
,An integrated approach developed to assess the relationship between footwall degradation and hangingwall deposition from an individual subsurface fault block that disentangles syn‐rift basin architecture through quantification of different sediment sources, which can be applied to other rift basins
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Landscape responses to intraplate deformation in the Kalahari constrained by sediment provenance and chronology in the Okavango Basin
Authors Shlomy Vainer, Ari Matmon, Yigal Erel, Alan J. Hidy, Onn Crouvi, Mike De Wit, Yona Geller and ASTER Team[AbstractThe structural depression that occupies the Okavango Basin in southern Africa comprises a depo‐centre within the intracratonic Kalahari Basin where sediments of the Cenozoic Kalahari Group have accumulated. The Okavango Basin has been formed due to stretching and subsidence at an area of diffused deformation, southwestwards to the main East African Rift System (EARS). Sediments from two full Kalahari Group sequences, located on opposite sides of the Gumare Fault that forms a major fault within the Okavango Basin, were studied to determine their provenance and chronology. Terrestrial Cosmogenic Nuclide (TCN) 26Al/10Be burial dating was used to constrain a chronostratigraphical framework, and Pb, Sr, and Nd isotopic ratios combined with geochemical and sedimentological analyses were applied to track the source areas of the sediments.Results indicate the following sequence of basin filling: (a) Accumulation between ca. 4–3 Ma during which the currently downthrown (southern) block received a mixture of sediments mostly from the Choma‐Kalomo, Ghanzi‐Chobe, and Damara terranes, and possibly from the Lufilian Belt and/or Karoo basalts during earlier stages of deposition. Simultaneously, the upthrown (northern) block received sediments from more distant Archean sources in the Zimbabwe and/or Kasai cratons, (b) Hiatus in sedimentation occurred at both sites between ca. 3–2 Ma, (c) Sediments on both sides of the Gumare Fault share a similar source (Angolan Shield) with minor distinct contributions to the downthrown block from the Kasai Craton and local sources input to the upthrown block, and (d) Regional distribution of aeolian sand since at least 1 Ma. The change in source areas is attributed to rearrangements of the drainage systems that were probably linked to vertical crustal movements on the margins of the Okavango Basin. The tectonically induced morphodynamics controlled the landscape evolution of the endorheic basin where vast lakes, wetlands and salt pans have developed through time.
,Capture areas of the western Okavango Basin during the Pliocene (a) and the early Pleistocene (b). The change in provenance that occured around the Pliocene‐Pleistocene transition is attributed to adjustments of the drainage systems to axial crustal uplift, resulting in the formation of large waterbodies.
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Development of an incipient Paleogene topography between the present‐day Eastern Andean Plateau (Puna) and the Eastern Cordillera, southern Central Andes, NW Argentina
[Schematic overview of the distribution and extent of Paleogene proto‐ranges (dark grey) and their present‐day pendants (light grey) in the Central Andes of NW Argentina and surrounding regions. Black and white arrows indicate the vergence of faults with Eocene activity. Documented Paleogene tectono‐sedimentary features (white dots) and Paleogene thermochronological ages (black dots) are shown. Black line shows the western limit of Cretaceous rift activity. Light‐orange filling area indicates the zone in which penetrative Paleozoic deformation dies out towards the east (Mon & Hongn, 1987). The western and eastern borders of this zone contain Lower Paleozoic sequences respectively with intense (west) and little or no (east) Paleozoic deformation.
The structural and topographic evolution of orogenic plateaus is an important research topic because of its impact on atmospheric circulation patterns, the amount and distribution of rainfall, and resulting changes in surface processes. The Puna region in the north‐western Argentina (between 13°S and 27°S) is part of the Andean Plateau, which is the world's second largest orogenic plateau. In order to investigate the deformational events responsible for the initial growth of this part of the Andean plateau, we carried out structural and stratigraphic investigations within the present‐day transition zone between the northern Puna and the adjacent Eastern Cordillera to the east. This transition zone is characterized by ubiquitous exposures of continental middle Eocene redbeds of the Casa Grande Formation. Our structural mapping, together with a sedimentological analysis of these units and their relationships with the adjacent mountain ranges, has revealed growth structures and unconformities that are indicative of syntectonic deposition. These findings support the notion that tectonic shortening in this part of the Central Andes was already active during the middle Paleogene, and that early Cenozoic deformation in the region that now constitutes the Puna occurred in a spatially irregular manner. The patterns of Paleogene deformation and uplift along the eastern margin of the present‐day plateau correspond to an approximately north‐south oriented swath of reactivated basement heterogeneities (i.e. zones of mechanical weakness) stemming from regional Paleozoic mountain building that may have led to local concentration of deformation belts.
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A 6 Ma record of palaeodenudation in the central Himalayas from in situ cosmogenic 10Be in the Surai section
[AbstractTo better constrain late Neogene denudation of the Himalayas, we analysed in situ 10Be concentrations in 17 Neogene sediment samples of the Surai section (central Nepal) and two modern sediment samples of the Rapti River. We first refined the depositional ages of the Surai section from 36 new paleomagnetic analyses, five 26Al/10Be burial ages, and, based on the Dynamic Time Warping algorithm, 104 automatically calculated likely magnetostratigraphic correlations. We also traced changing sediment sources using major element and Sr‐Nd isotopic data, finding at 4–3 Ma a switch from a large, trans‐Himalayan river to a river draining only the Lesser Himalaya and Siwalik piedmont, increasing the contribution of recycled sediments at that time. 10Be concentrations in Neogene sediments range from (1.00 ± 0.36) to (5.22 ± 0.98) × 103 at g–1 and decrease with stratigraphic age. Based on a flood plain transport model, our refined age model, and assuming a drainage change at 4–3 Ma, we reconstructed 10Be concentrations at the time of deposition. Assuming cosmogenic production rates similar to those of the modern basins, we calculated palaeodenudation rates of 0.9 ± 0.5 to 3.9 ± 2.7 mm a–1 from ca. 6 to 3 Ma in the palaeo‐Karnali basin and 0.6 ± 0.2 to 1.6 ± 0.8 mm a–1 since ca. 3 Ma in the palaeo‐Rapti basin. Given the uncertainties and similar modern values of ~2 mm a–1, the palaeo‐Karnali denudation rates may have been steady at ~1.7 ± 0.3 mm a–1 for the last ca. 6 Ma. A transient acceleration of the denudation in the palaeo‐Rapti basin of ~1.5 mm a–1 since ca. 1.5 Ma was likely due to the reworking of older, 10Be‐depleted Siwalik sediments in the foreland. If true, this steadiness of the denudation rates may suggest that Quaternary glaciations did not largely affect Himalayan denudation.
,Temporal evolution of reconstructed 10Be palaeoconcentrations and derived palaeodenudation rates in the Surai Khola. Palaeoconcentrations (left) are corrected for radioactive decay and exposure in the floodplain (see text). Denudation rates were calculated assuming that the sediments of the Surai section were deposited by a Karnali‐type trans‐Himalayan river prior to ca. 3.5 Ma (middle), and by a Rapti‐type midland‐draining river since ca. 3.5 Ma (right).
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Neogene to recent evolution of the Southern Gulf of Mexico basin: Tectonic controls on deep‐water sediment dispersal systems
Authors Zachary T. Sickmann and John W. Snedden[The evolution of southern Gulf of Mexico deep‐marine depositional systems was strongly controlled by onshore dynamic and transpressional tectonics through the Neogene and into the modern. Nearshore extensional accommodation generated by margin collapse and salt inflation served to progressively starve the deep southern Gulf of sediment. This is recorded in the deep‐water basin center as a transition from large Miocene submarine channel systems to late Miocene to modern mass transport deposits and supercritical sediment waves.
Newly available two‐dimensional (2D) and limited three‐dimensional (3D) reflection seismic data coupled with publicly available well and core data were used to generate the first comprehensive regional basin evolution model for the deep‐water Neogene to recent southern Gulf of Mexico (GoM). This evolution is presented in the context of contemporaneous onshore tectonic drivers and predecessor basin tectonic history. Dynamic uplift to the west in North America, transpression to the south and tectonically influenced salt tectonics to the east served to collapse the margins of the southern Gulf of Mexico Basin throughout the late Neogene and into the modern. This collapse and salt inflation served to shut off efficient sediment transport into the axial deep basin. Newly developed nearshore extensional accommodation along both the western margin of the basin and salt‐rooted orogenic structures to the south and east appear to have baffled coarser‐caliber sediment input from southern (Mexican) sediment sources into the deep Gulf of Mexico Basin beginning in the late Miocene. This sequence is recorded in the southern GoM basin by a transition from large early–mid Miocene submarine channel belts to late Miocene–recent sediment wave fields and mass transport deposits. Improved resolution of new 2D and 3D subsurface seismic reflection data shows that sediment waves of the southern Gulf of Mexico are supercritical bedforms, long wavelength antidunes and cyclic steps, not contourites. These supercritical bedforms are among the most spatially expansive and morphologically largest documented globally. The location and evolution of these bedforms appears closely tied to the tectonically driven history of margin collapse, salt inflation and the starving of the deep basin of coarse‐grained sediment. Cumulatively, the tectonic drivers that intuitively should have increased sediment flux into the deep southern Gulf of Mexico acted to ‘pinch off’ the basin, starving it of sediment supplied from southern sediment sources.
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Reconstructing the level of the central Red Sea evaporites at the end of the Miocene
Authors Neil C. Mitchell, Wen Shi, A.Y. Izzeldin and Ian C. F. Stewart[AbstractReconstructing the original depositional level of the Mesozoic and older c‘salt giants’ can reveal if their basins became filled to global sea level, but is complicated by dissolution, diapirism and because the time elapsed is so great. This is less of a problem in the Red Sea, a young rift basin that is transitioning to an ocean basin and where the evaporites away from coastal fringes are less affected by diapirism. In this study, we explore vertical movements of the evaporite surface of the central Red Sea imaged with deep seismic profiling, for the period of time after most evaporite deposition ended at 5.3 Ma (the Miocene‐Pliocene boundary). This boundary is readily mapped across the basin as a prominent reflection in seismic data correlated with stratigraphy at three DSDP sites. We quantify changes in the average elevation of the evaporite surface due to (a) thermal lithospheric subsidence, (b) isostatic loading by Plio‐Pleistocene sediments and water, (c) deflation needed to balance the volume of evaporites overflowing oceanic crust of 5.3 Ma age, (d) loss of halite by dissolution and (e) dynamic topography. Our best estimate of the evaporite level (−132 m air‐loaded or −192 m water‐loaded) lies below the range of estimated global sea level towards the end of the Miocene, suggesting that the basin remained under‐filled. If geological interpretations of shallow water conditions existing at the end of the Miocene (Zeit Formation) are correct, this implies that the water level of the Red Sea declined and was unstable. These calculations illustrate how spreading of evaporites can enhance thermal subsidence to cause rapid development of accommodation space above major evaporite bodies, which in the Red Sea case has remained largely unfilled.
,A series of five corrections are made to the present level of the Miocene evaporites in the central Red Seat, suggesting that the basin remained under‐filled at the Miocene‐Pliocene boundary (i, ii).
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Overpressure evolution controlled by spatial and temporal changes in the sedimentation rate: Insights from a basin modelling study in offshore Suriname
Authors Ko Nifuku, Yuki Kobayashi, Yasuhiko Araki, Takafumi Ashida and Takashi Taniwaki[AbstractThis study investigates overpressure evolution and its relationship to the spatial and temporal changes in the sedimentation rate in the passive continental margin of offshore Suriname. We analysed well data to estimate pore pressure at the well locations and to interpret relevant overpressure‐generating mechanisms. Three‐dimensional basin modelling was performed to reconstruct overpressure evolution in the area. The well data indicated disequilibrium compaction as the main overpressure‐forming mechanism. The results of the modelling indicated a temporal variation in the sedimentation rate caused cycles of overpressure formation in the region. Periods of high sedimentation lead to overpressure formation, and this overpressure dissipates during periods of quiescent sedimentation. The latest overpressure development since the Middle–Late Miocene was triggered by a notable increase in the siliciclastic supply to the basin, which reflects the Andean uplift and reorganization of the drainage system. Spatial changes in the sedimentation rate resulted in a lateral variation in the amount of overpressure. Disequilibrium compaction generated large overpressure in the area with a high‐sedimentation rate because of the fast increasing rate of overburden load. In addition, the high‐temperature condition beneath the rapid sedimentation area could cause additional mechanisms for overpressure formation in the deeper part of the basin. This study reveals that the complex overpressure history and its lateral variation in offshore Suriname were mainly caused by a single controlling factor (i.e. the sedimentation rate). This article gives an insight into overpressure evolution in sedimentary basins by considering the perspective of the spatio‐temporal variation in the sedimentation rate and its connection with hinterland evolution.
,Schematic diagram showing the relationship between spatio‐temporal changes in the sedimentation rate and overpressure evolution in offshore Suriname.
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Pliocene–Pleistocene glacimarine shelf to slope processes in the south‐western Barents Sea
[AbstractThe glacimarine shelf‐edge is a complex depositional environment in which the interplay between accommodation and glaciation has played an important role in influencing sediment deposition and margin architecture. It can be challenging to unravel the history of basin infill in these areas, particularly where landforms are deeply buried. This study presents an integrated workflow for deciphering the architecture and evolution of erosional and depositional elements in a crucial location of the south‐western Barents Sea margin, with a focus on the comparatively poorly understood processes and patterns of glacimarine sedimentation that occurred during the Pliocene and Early Pleistocene. Wellbore interpretations of lithology are combined with the analysis of seismic facies, geomorphology and attributes using merged 3D seismic reflection data to investigate the morphology and development of buried landforms and depositional features on the outer‐shelf, shelf edge and upper‐slope. The Pliocene (preglacial) slope system is dominated by upper‐slope channels, upper‐slope channels with associated sediment lobes, and mass‐transport deposits. The first appearance of mega‐scale glacial lineations in the study area is close to the onset of the Pleistocene (around 2.58 Ma), suggesting that an ice stream reached the palaeo‐shelf edge during the earliest Pleistocene. The prevalence of upper‐slope channels and mass‐transport deposits throughout the Pleistocene stratigraphy shows that the basinwards transfer of sediment took place mainly by evacuation of sediment through relatively linear channels combined with mass‐movement events. The results presented in this study have implications for understanding the glacial history of the south‐western Barents Sea and sedimentary processes on glacimarine shelf edges more generally.
,3D spatial and temporal depositional model of the study area
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Low‐temperature thermochronology as a control on vertical movements for semi‐quantitative source‐to‐sink analysis: A case study for the Permian to Neogene of Morocco and surroundings
More Less[AbstractContinental passive margins and their hinterlands in the Atlantic realm have been the locus of many Low Temperature Thermochronology (LTT) and time‐Temperature (t‐T) modelling studies that evidence pre‐, syn‐ and post‐rift episodic km‐scale exhumation and burial episodes. In this study, we integrate data from over 30 published LTT and t‐T modelling studies from Morocco and its surroundings using a three‐step workflow to obtain: (a) exhumation/burial rates, (b) erosion rates and (c) palaeoreconstructions of source‐to‐sink domains, between the Permian and the Present. Our synthesis of available t‐T modelling results predicts high exhumation rates in the Anti‐Atlas (0.1 km/Myr) during the Early to Middle Jurassic, and in the High Atlas (0.1 km/Myr) and Rif (up to 0.5 km/Myr) during the Neogene. These rates are comparable to values typical of rift flank, domal or structural uplifts settings. During the other investigated periods, exhumation rates in the Meseta, High‐Atlas, Anti‐Atlas and Reguibat shield are around 0.04 ± 0.02 km/Myr. Interpolation of the exhumation rates at the regional scale allow calculation of the volume of rocks eroded. Estimates of erosion rates are between 0.2 x 103 and 7.5 x 103 km3 (in the Meseta and the Reguibat Shield respectively). Ten erosional (quantitative, from interpolation results) and depositional (qualitative, from data synthesis) “source‐and‐sink” maps have been constructed, with emphasis on the Jurassic and Cretaceous periods. The maps integrate the extent of exhumed domains, using information from geological maps, lithofacies and biostratigraphic data from new geological fieldwork and well data from onshore and offshore basins. The results illustrate changes in the source‐to‐sink systems and allow for a better understanding of the Central Atlantic margin hinterlands evolution.
,In this study we integrate data from over thirty published LTT and t‐T modelling studies from Morocco and its surroundings using a 3‐step workflow to obtain 1) exhumation/burial rates, 2) erosion rates, and 3) paleoreconstructions of source‐to‐sink domains (Source‐and‐Sink maps), between the Permian and the Present.
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Sedimentation and viscosity controls on forearc high growth
More Less[Sedimentation and viscosity controls on temperature, vertical motions and basin architecture in subduction wedges. Figure shows the crustal wedge at the end of model run for simulations with a maximum sedimentation rate increasing from upper left to lower rigth, and crustal viscosity increasing from upper right to lower left. The thick white line bounds basin isochrons (above) from basement mesh (below).
Crustal rheology and surface processes strongly influence strain distribution and shape of orogenic wedges at their front but how they influence the wedge rear is still unclear. Here, we analyse the coupled control of viscosity and sedimentation on forearc high growth during advanced stages of subduction accretion. We use 2D thermo‐mechanical finite element models constrained with data of the south Anatolian margin. Our simulations show that forearc highs grow as a thermally‐activated viscosity drop in the lower crust induces ductile deformation and viscous flow. Initial viscosity and the amount of sediments in the forearc basin control non‐linearly the occurrence and timing of the thermally‐activated viscosity drop, and thus of the growth of the forearc high. High sedimentation rates result in thicker forearc basins that stabilise the subduction wedge and delay the onset of uplift in the forearc high. Low viscosities promote earlier onset of forearc high uplift and lead to larger morphological variability along the subduction margin. Increasing either the sedimentation rate or viscosity may prevent forearc high formation entirely. The thermo‐viscous forearc highs grow at an age set by wedge thermal state as a function of accretionary flux, wedge viscosity, and synorogenic sedimentation. Our models explain vertical motions in south Anatolia and potentially in other accretionary margins, like the Lesser Antilles or Cascadia, during the formation of their broad forearc highs.
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Sediment dispersal pathways in the Po coastal plain since the Last Glacial Maximum: Provenance signals of autogenic and eustatic forcing
Authors Daniel Tentori, Alessandro Amorosi, Salvatore Milli and Kathleen M. Marsaglia[AbstractWe examined downstream trends in sediment composition within the modern Po River system and defined provenance changes within a selected sector of the Upper Pleistocene to Holocene coastal plain in response to paleogeographic reorganisation during the last glacial‐interglacial cycle. Sediment composition of the Upper Pleistocene to Holocene alluvial and coastal plain succession overlaps with the modern petrofacies, suggesting that ancient fluvial sand was sourced from a dynamic river system attributable to a distal paleo‐Po with episodic sediment input from South Alpine and Apennine rivers. In the wave‐dominated estuarine depositional system developed under transgressive conditions, Po‐derived detritus mixed in the coastal system with sediment fed by Central/Eastern Alpine rivers, which was redistributed southwards by alongshore currents. A similar, mixed composition of late Holocene highstand depositional systems reflects the progradation of Po delta lobes (similar in composition to Po River sands) and adjacent strandplains (typified by sediment mixing due to alongshore transport). Compositional variability across the main stratigraphic surfaces suggests that autogenic processes (e.g. marine reworking, sedimentary mixing, delta switching/abandonment) in turn influenced by glacioeustasy, controlled the development of the transgressive and highstand Po Plain succession. This study clarifies the effect of fluvial‐marine interaction during the Holocene evolution of the Po coastal system and can be used as a model to interpret the evolution of many mixed‐delta types and Quaternary successions that shows alternating river‐flood and wave‐dominated deposits.
,a) The Upper Pleistocene fluvial sand was sourced from a dynamic river system attributable to a distal paleo‐Po with episodic sediment input from South Alpine and Apennine rivers. b) In the Holocene wave‐dominated estuarine depositional system developed under transgressive conditions, Po‐derived detritus mixed in the coastal system with sediment fed by Central/Eastern Alpine Rivers, which was redistributed southwards by alongshore currents. c) and d) Late Holocene highstand depositional systems reflects progradation of Po delta lobes and adjacent strandplain resulting in mixed composition.
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The influence of mantle flow on intracontinental basins: Three examples from Australia
Authors Alexander Young, Nicolas Flament, Lisa Hall and Andrew Merdith[Mechanisms by which dynamic topography can influence basin subsidence.
During the Paleozoic, sedimentary basins developed within Gondwana without evolving to diverging plate boundaries. Such intracontinental basins present long subsidence histories with multiple phases of accelerated subsidence that are not always easily explained by far‐field tectonic forces, and may be driven by processes other than rifting and thermal subsidence. Here we investigate the subsidence of Paleozoic Australian intracontinental basins by comparing one‐dimensional backstripped tectonic subsidence histories from the western Australian Canning and Southern Carnarvon Basins and the central Australian Cooper Basin to forward subsidence models for pure shear lithospheric thinning. We make the hypothesis that differences between observed and model subsidence may be explained by mantle‐flow driven topography, in addition to tectonic forces. To test this hypothesis, we compute dynamic topography from the first geodynamic models of mantle flow spanning the entire Phanerozoic Eon, and we analyse the relationship between dynamic topography and anomalous basin subsidence to dynamic topography and mantle flow. Although reconstructions of mantle flow in deep geological times are uncertain, our results suggest that long‐wavelength dynamic topography could explain aspects of the complex tectonic histories intracontinental basins. In the presented reconstruction of mantle flow, topographic rebound following the sinking of a Cambrian aged slab resulted in a minor phase of dynamic uplift in the Cooper Basin in middle Permian times. Throughout Carboniferous‐Triassic times Australia was positioned above a mantle upwelling driven by a hot structure at the base of the mantle. Structural uplift in the Canning and Southern Carnarvon basins during the Triassic‐Jurassic interval was augmented by dynamic uplift produced by that large‐scale upwelling, and possibly augmented by a focused active mantle plume during the Permo‐Triassic. In Late Jurassic‐Cretaceous times, Australia drifted east away from the mantle upwelling, resulting in a period of subsidence in the Canning and Southern Carnarvon basins. During the Cretaceous the Cooper Basin moved over a downwelling produced by long‐lived subduction along the east Australian margin, resulting in a period of accelerated subsidence.
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Sedimentology and provenance of newly identified Upper Cretaceous trench basin strata, Dênggar, southern Tibet: Implications for development of the Eurasian margin prior to India–Asia collision
Authors Devon A. Orme, Andrew K. Laskowski, Misia F. Zilinsky, Wang Chao, Xudong Guo, Fulong Cai and Ding Lin[Provenance of Upper Cretaceous trench basin strata in southern Tibet are consistent with derivation from a margin‐parallel sediment dispersal system sourced near Lhasa City. Accumulation of trench strata along the southern margin of Asia during Late Cretaceous time suggests a period of accretion and increased sediment delivery directly to the trench possibly driven by a change in plate convergence and subduction of an oceanic ridge, respectively.
Trench basins preserved along the southern margin of the Lhasa Terrane, Tibet, are sedimentologic records of convergent margin processes preceding Cenozoic India–Asia collision. We present new sedimentologic, petrographic and geochronologic data from the Rongmawa Formation and surrounding strata near Dênggar, Tibet, to determine depositional environment, provenance and age. Depositional ages range from ca. 92 to 87 Ma and lithofacies are consistent with deposition by low‐ and high‐density turbidity currents and suspension settling of pelagic detritus in a deep‐marine, trench basin setting. Sandstone modal analyses and U–Pb geochronology indicate that trench basin detritus in this region was derived from the Lhasa Terrane. We interpret that the Cretaceous subduction trench received detritus from an axial sediment dispersal system that transported sediment from headwaters in the central‐southern Lhasa terrane near Lhasa City directly to the trench and then flowed westwards parallel to the trench. The preservation of trench basin strata deposited during Late Cretaceous time compared with the lack of trench deposits prior to ca. 92 Ma and after ca. 80 Ma suggests the margin experienced a period of significant accretion during this interval. In addition, deposition of trench basin strata occurred during Late Cretaceous adakitic magmatism and high‐temperature metamorphism, which are hypothesized to be explained by subduction of an oceanic ridge or subduction zone retreat and related upper plate extension along the southern margin of the Lhasa terrane. Subduction of an oceanic ridge may provide a mechanism to potentially erode forearc basin strata and promote increased sediment delivery directly to the trench.
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Strain migration during multiphase extension, Stord Basin, northern North Sea rift
[AbstractIn regions experiencing multiple phases of extension, rift‐related strain can vary along and across the basin during and between each phase, and the location of maximum extension can differ between the rift phase. Despite having a general understanding of multiphase rift kinematics, it remains unclear why the rift axis migrates between extension episodes. The role pre‐existing structures play in influencing fault and basin geometries during later rifting events is also poorly understood. We study the Stord Basin, northern North Sea, a location characterised by strain migration between two rift episodes. To reveal and quantify the rift kinematics, we interpreted a dense grid of 2D seismic reflection profiles, produced time‐structure and isochore (thickness) maps, collected quantitative fault kinematic data and calculated the amount of extension (β‐factor). Our results show that the locations of basin‐bounding fault systems were controlled by pre‐existing crustal‐scale shear zones. Within the basin, Permo‐Triassic Rift Phase 1 (RP1) faults mainly developed orthogonal to the E‐W extension direction. Rift faults control the locus of syn‐RP1 deposition, whilst during the inter‐rift stage, areas of clastic wedge progradation are more important in controlling sediment thickness trends. The calculated amount of RP1 extension (β‐factor) for the Stord Basin is up to β = 1.55 (±10%, 55% extension). During the subsequent Middle Jurassic‐Early Cretaceous Rift Phase 2 (RP2), however, strain localised to the west along the present axis of the South Viking Graben, with the Stord Basin being almost completely abandoned. Rift axis migration during RP2 is interpreted to be related to changes in lithospheric strength profile, possibly related to the ultraslow extension (<1 mm/year during RP1), the long period of tectonic quiescence (ca. 50 myr) between RP1 and RP2 and possible underplating. Our results highlight the very heterogeneous nature of temporal and lateral strain migration during and between extension phases within a single rift basin.
,Permo‐Triassic and Middle Jurassic‐Early Cretaceous crustal extension in northern North Sea rift.
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Interplay of tectonics and magmatism during post‐rift inversion on the central West Iberian Margin (Estremadura Spur)
Authors Ricardo Pereira, Filipe Rosas, João Mata, Patrícia Represas, Cláudia Escada and Beatriz Silva[The combined effects of multiphase margin inversion and Late Cretaceous magmatism on the Central West Iberian Margin reveals that deformation is decoupled between Cretaceous and Tertiary strata, with a laccolith accommodating significant shortening and acting as a rigid body.
The combined effects of post‐rift magma emplacement and tectonic inversion on the hyper‐extended West Iberian Margin are unravelled in detail using multichannel 2D/3D seismic data. The Estremadura Spur, acting as an uplifted crustal block bounded by two first‐order transfer zones, shows evidence of four post‐rift tectonic events each with a distinctive seismic‐stratigraphic response that can be used to demonstrate the tectono‐magmatic interplay, namely: (a) the Campanian onset of magmatism (including the Fontanelas Volcano, the widespread evidence of multiple sill complexes and the detailed description of a >20 km long laccolith, the Estremadura Spur Intrusion; (b) the Campanian‐Maastrichtian NE‐SW event pervasively affecting the area, resulting in regional uplift, reverse faulting and folding; (c) the Paleocene‐mid Eocene inversion that resulted in widespread erosion and; (d) the Oligocene‐mid Miocene evidence of rejuvenated NW‐SE inversion marked by crestal faulting and forced‐fault folding establishing the final geometry of the area. The distinct deformation styles within each tectonic phase document a case of decoupled deformation between Late Cretaceous and Tertiary units, in response to the predominant stress field evolution, revealing that the magnitude of Late Cretaceous inversion is far more significant than the one affecting the latter units. A detailed analysis of the laccolith and its overburden demonstrate the distinct deformation patterns associated both with magma ascent (including extensional faulting, forced‐folding and concentric reverse faulting) and its interference as a rigid intrusive body during subsequent transpressive inversion. This reinforces the role that the combined tectono‐magmatic events played on the margin. Also analysed is the wider impact of post‐rift magmatism and the associate emplacement of sub‐lithospheric magma on the rheology of a thinned continental crust. This takes into account the simultaneous tectonic inversion of the margin, the implied alternative views on characteristic heat flow, and on how these can be incorporated in source rock organic maturity modelling.
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Cambrian syn‐rift tectonic pulses at unconformity‐bounded carbonates in the Avalon Zone of Newfoundland, Canada
More Less[AbstractIn the Avalon Zone of SE Newfoundland, several Terreneuvian to Cambrian Series 2 carbonate bodies occur associated with paraconformities and onlapping geometries. Their stratigraphic discontinuities and related gaps represent syn‐rift episodes characterized by sharply tilted and downfaulted blocks and deposition of chaotic megabreccia beds and conglomerates on neighbouring footwall areas. Microbial and shelly carbonate production nucleated on tectonically unstable palaeohorsts, where stromatolitic crusts and mats commonly reflect the onset of hiatal stratigraphic diastems, and mud‐mounds the episodic establishment of calm conditions. Short‐term uplift episodes of rift shoulders led to unroofing of the Neoproterozoic basement (yielding granitoid clasts and input of reworked exotic clasts and allochthonous fossils from underlying Cambrian strata), localized subaerial exposure and karst features, and the development of synsedimentary fracture networks that provided favourable conduits and pathways for hydrothermal fluids. These carbonate beds host vein networks of carbonate‐hosted polymetallic sulphide‐sulphate‐oxide mineral associations (Pb–Cu–Fe–barite stockworks). The mixture of parautochthonous and allochthonous bioclastic assemblages points to the record of event‐concentration strata, which may clarify the long stratigraphic ranges of some involved microfossils. The Cambrian Avalonia rift and the offshore to basinal rift sector of the neighbouring Atlas‒Ossa‐Morena rift, preserved in the Moroccan northern High Atlas and Coastal Meseta, share common temperate‐water carbonate facies and build‐ups, lacking ‘subtropical’ indicators such as archaeocyathan‐microbial reefs, ooidal shoals or evaporitic pseudomorphs. These diagnostic facies and minerals occur only in relatively stable, shallow‐water rift branches, such as those preserved in the Anti‐Atlas and the Ossa‐Morena Zone (Iberian Massif).
,Unconformity‐bounded carbonates in the Cambrian of West Avalonia reflect syn‐rift tectonic pulses associated with hydrothermal activity. These carbonate beds host vein networks of carbonate‐hosted polymetallic sulfide‐sulfate‐oxide mineral associations (Pb–Cu–Fe–barite stockworks).
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Regional correlation and seismic stratigraphy of Triassic Strata in the Greater Barents Sea: Implications for sediment transport in Arctic basins
AbstractThe Greater Barents Sea Basin (GBSB) in Arctic Russia and Norway is an intracratonic basin that accommodated an enormous amount of sediment during the Triassic. These deposits are up to 4.5 km thick over an area 2,500,000 km2, and consist of marine mudstones and mudstone‐rich fluvio‐deltaic topsets with sandstone‐dominated fluvial channels. The basin is well‐studied and data‐rich, but regional correlation between different parts is lacking. Provenance data from adjacent Arctic basins have been interpreted to imply sediment transport from the Ural orogen across the GBSB, but these are disputed because of great transport distances, poorly constrained sediment‐transport directions and unknown timing of bypass. We integrated data from 3,238 seismic lines, 257 wells and palynostratigraphy, as well as published outcrop data, to create the first unified stratigraphic framework for the Triassic deposits across the entire GBSB. Results show that (1) sediment was transported northwest by one linked sedimentary system stretching across the entire basin; (2) sediment was derived from a source in the east comprising the Urals and West Siberia; (3) the main stratigraphic boundaries are major flooding surfaces which can be traced throughout the basin; and (4) significant amounts of sediment overspilled from the Barents Sea into adjacent sedimentary basins, starting with the Lomonosov Ridge from the Early Triassic, and into basins to the northwest (e.g. Sverdrup, Chukotka) during the late Carnian. These results provide a better understanding of geodynamics and provenance data in the Arctic, to improve the prediction of reservoirs in the area, and indicate a protracted uplift‐history of the northernmost Urals that started in the Carnian ~237 Ma. Furthermore, it shows how large intracratonic basins interact with uplands and subside over tens of millions of years.
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From sink to source: Using offshore thermochronometric data to extract onshore erosion signals in Namibia
Authors Mark Wildman, Kerry Gallagher, David Chew and Andrew Carter[Pre‐ and post‐depositional rock thermal histories are obtained by inverting apatite fission track data collected from a borehole offshore Namibia. The thermal histories are interpreted as reflecting multiple episodes of syn‐ and post‐rift erosion onshore and burial and exhumation offshore.
Products of onshore passive continental margin erosion are best preserved in offshore sedimentary basins. Therefore, these basins potentially hold a recoverable record of the onshore erosion history. Here, we present apatite fission track (AFT) data for 13 samples from a borehole in the southern Walvis basin, offshore Namibia. All samples show AFT central ages older or similar to their respective stratigraphic ages, while many single grain ages are older, implying none of the samples has been totally annealed post‐deposition. Furthermore, large dispersion in single grain ages in some samples suggests multiple age components related to separate source regions. Using Bayesian mixture modelling we classify single grain ages from a given sample to particular age components to create ‘subsamples’ and then jointly invert the entire dataset to obtain a thermal history. For each sample, the post‐depositional thermal history is required to be the same for all age components, but each component (‘subsample’) has an independent pre‐depositional thermal history. With this approach we can resolve pre‐ and post‐depositional thermal events and identify changes in sediment provenance in response to the syn‐ and post‐rift tectonic evolution of Namibia and southern Africa. Apatite U‐Pb and compositional data obtained during the acquisition of LA‐ICP‐MS FT data are also presented to help track changes in provenance with time. We constrain multiple thermal events linked to the exhumation and burial history of the continental and offshore sectors of the margin over a longer timescale than has been possible using only onshore AFT thermochronological data.
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The structural evolution of pull‐apart basins in response to changes in plate motion
[The evolution of a pull‐apart basin can be considerably influenced by a change of plate motion that introduces transtension in the basin. Identifying structures of this type of pull‐apart basin evolution are asymmetric triangular basins and wide principal displacement zones with oblique‐normal faults. We identify a number of these basins across the world and model their evolution through physical analogue models.
Pull‐apart basins are structural features linked to the interactions between strike‐slip and extensional tectonics. Their morphology and structural evolution are determined by factors such as extension rate, the basin length/width ratio, and changes in extension direction. In this work, we investigate the effect of a change in the plate motion direction on a pull‐apart basin's structure, using analogue modelling experiments with a two‐layer ductile‐brittle configuration to simulate continental crust rheology. We initially impose orthogonal extension on an interconnected rift and strike‐slip system to drive pull‐apart development. Subsequently, we rotate the relative motion vector, imposing transtensional deformation and continuing with this new relative motion vector to the end of the experiment. To compare with natural examples, we analyse the model using seismic interpretation software, generating 3D fault structure and sedimentary thickness interpretations. Results show that the change in the direction of plate motion produces map‐view sigmoidal oblique slip faults that become normal‐slip when deformation adjusts to the new plate motion vector. Furthermore, sediment distribution is strongly influenced by the relative plate rotation, changing the locus of deposition inside the basin at each model stage. Finally, we compare our observations to seismic reflection images, sedimentary package thicknesses and fault interpretations from the Northern Gulf of California and find good agreement between model and nature. Similar fault arrays occur in the Bohai Basin in northern China, which suggests a rotational component in its evolution. More broadly, such similar structures could indicate a role for oblique extension and fault rotation in any pull‐apart basin.
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Review of Iberia–Eurasia plate‐boundary basins: Role of sedimentary burial and salt tectonics during rifting and continental breakup
[AbstractWe document the role of sedimentary burial and salt tectonics in controlling the deformation style of continental crust during hyperextension. The Iberian‐European boundary records a complex history of Cretaceous continental extension, which has led to the development of so‐called smooth‐slope type basins. Based on the review of the available geological constraints (crustal‐balanced cross‐sections, sedimentary profile evolution, RSCM thermometer, low‐temperature thermochronology) and geophysical data (Bouguer anomaly, Moho depth, seismic reflection profiles and Vp/Vs velocity models) on the Tartas, Arzacq, Cameros, Parentis, Columbrets, Mauléon, Basque‐Cantabrian and Internal Metamorphic Zone basins, we shed light on the main characteristics of this type of basin. This synthesis indicates that crustal thinning was influenced by two decoupling horizons: the middle crust and Triassic prerift salt, initially located between the basement and prerift sedimentary cover. These two horizons remained active throughout basin formation and were responsible for depth‐dependent thinning of the crust and syn‐rift salt tectonics. We therefore identify several successive deformation phases involving (a) pure shear dominated thinning, (b) simple shear dominated thinning and (c) continental breakup. In the first phase, distributed deformation resulted in the development of a symmetric basin. Field observations indicate that the middle and lower crust were under dominantly ductile conditions at this stage. In the second phase, deformation was localised along a crustal detachment rooted between the crust and the mantle and connecting upwards with Triassic prerift salt. During continental breakup, basin shoulders recorded the occurrence of brittle deformation, whereas the hyperextended domain remained under predominantly ductile thinning. The formation of smooth‐slope‐type extensional basins was intrinsically linked to the combined deposition of thick syn‐rift and breakup sequences, and regional salt tectonics. They induced significant burial and allowed the continental crust and the prerift sequence to deform under high temperature conditions from the rifting to continental breakup stages.
,At the beginning of the syn‐rift stage, depth‐dependent crustal thinning is dominantly controlled by distributed pure shear thinning within the lower/middle crust due to the presence of two decoupling levels: (1) the middle crust, which allows the lower crust to be extracted laterally without disturbing significantly the upper crust, and (2) within pre‐rift Triassic salt beds, which act as a décollement between the upper crust and the overlying sedimentary cover. Then simple shear becomes localized along a crustal detachment connecting upward with the Late Triassic décollement layer, inducing shearing in the pre‐rift salt. When continental breakup occurs, the basin flanks are affected by brittle deformation while the hyperextended domain undergoes dominantly ductile thinning. The rise of the 300°C to 500°C isotherms in the hyperextended domain, from the syn‐rift to the continental breakup stage, implies that the originally crystalline upper continental crust and the overlying pre‐rift and syn‐rift sedimentary pile are affected by depth‐dependent ductile thinning.
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From rifting to hyperextension: Upper Jurassic–Lower Cretaceous tectono‐stratigraphy of the Porcupine Basin, Irish Atlantic Margin
Authors Lewis Whiting, Peter D. W. Haughton and Patrick M. Shannon[Conceptual model for the development of syn‐rift and transitional sequences during hyperextended rifting. During hyperextension, strain progressively localizes towards the rift axis, leading to the development of transitional depocentres above the tectonically inactive parts of the necking domain, later followed by younger transitional sequences above the hyperextended domain.
Hyperextended basins are increasingly recognized along the outboard parts of continental margins as aborted basins created during continental break‐up. Many of the concepts for understanding and modelling basin evolution and fill were developed for regions that have undergone modest crustal stretching (β < 2) and may not be valid in basins where the crust and upper mantle are heavily modified by extreme stretching. The present study uses extensive 2D and 3D seismic and well data to analyse the Late Jurassic–Cretaceous tectono‐stratigraphic evolution of the Porcupine Basin, bracketing the timing of hyperextension. It is an instructive basin, offshore west of Ireland, preserving low‐magnitude strain in the north, with increasing degrees of hyperextension in the south. Detailed mapping of strain domains (proximal, necking and hyperextended) across the Porcupine Basin reveals five main rift segments, each with a distinctive geometry and strain history. During early low‐strain rifting, inherited crustal structures strongly influenced the rift architecture by controlling the location and geometry of fault‐controlled marine depocentres. The transition from hyperextension to post‐rift subsidence was marked by locally developed, unconformity‐bounded, marine sequences that draped the underlying rift topography. Whilst these ‘transition sequences’ are dated as Tithonian above the necking domain, similar but younger Early Cretaceous transition packages developed in the hyperextended domain, suggesting extension migrated towards the rift axis during hyperextension. Early post‐rift sequences were broadly distributed across the rift centre and basin flanks before strong, thermally‐controlled subsidence of the hyperextended crust, along with hinging of the necking domain, locally to the point of slope failure, gave rise to axially‐focused marine deposition. Hyperextension may have left the basin susceptible to intra‐plate stress changes accounting for several unconformities within the post‐rift fill. This study provides an improved basin‐wide understanding of the tectono‐stratigraphic evolution of hyperextended basins.
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