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The Cambrian Tonto Group of the Grand Canyon was used by Edwin McKee in 1945 to make an insightful visual representation of how sedimentary facies record transgression across a craton--a common conceptual framework still used in geologic education. Although the tenets of McKee's facies diagram persist, the integration of new stratigraphy, depositional models, paleontology, biostratigraphy, and other data is refining the underlying dynamics of this cratonic transgression. Instead of McKee's interpretation of one major transgression with only minor regressions, there are at least five stratigraphic sequences, of which the lower three are separated by disconformities. These hiatal surfaces likely represent erosion of previously deposited Cambrian sediments that were laid down on the tropical, pre-vegetated landscape. Rather than being fully marine in origin, these sequences were formed by a mosaic of depositional environments including braided coastal plain, eolian, marginal marine, and various shallow marine environments. McKee, not having the insights of sequence stratigraphy and plate tectonics, concluded that the preservation of these sediments were due to predepositional topography and subsidence of the "geosyncline." Our modern interpretation is that accommodation space was a result of eustasy and differential subsidence on the continental margin. Our modified depositional model provides a more effective teaching tool for fundamentals and nuances of modern stratigraphic thinking, using the Tonto Group as a stillinfluential type location for understanding transgressive successions. [ABSTRACT FROM AUTHOR]

The Cryogenian 'Sturtian' snowball Earth glaciation (c. 717–658 Ma) likely had a major role in shaping continental landscapes and biotic radiations of the late Neoproterozoic Era. However, an incomplete sedimentary record and inadequate syn-glacial age constraints make Cryogenian studies challenging. We present detrital zircon U–Pb ages for >2000 zircons from 11 sandstone samples taken at <200 m stratigraphic resolution throughout the Port Askaig Formation, a c. 1.1 km thick glaciogenic succession within the Dalradian Supergroup of Scotland and Ireland. Eight new maximum depositional age constraints, including a key constraint on deglaciation (<662.7 ± 7.8 Ma), support lithostratigraphic and stable isotope evidence that suggests the Port Askaig Formation preserves a relatively complete record of the global 'Sturtian' glaciation. An increasing contribution from Archean and Paleoproterozoic detritus to the sandstones through the lower c. 500 m of the Port Askaig Formation likely reflects the progressive glacial unroofing of the previously buried Lewisian Gneiss terrane. Archean and Paleoproterozoic grains then become scarce in the uppermost c. 300 m of the formation, which we attribute to glacial modification of the Laurentian continental margin landscape during the waning stage of 'Sturtian' glaciation. The disruption to sediment transport pathways caused by this modification, and evidenced by the detrital zircon data, points to partially warm-based 'Sturtian' ice sheets that were, to some degree, dynamic. [ABSTRACT FROM AUTHOR]

The article provides information on the Drakensberg Mountains in Southern Africa, which are culturally significant and may have inspired J.R.R. Tolkien's Misty Mountains. It explores the geological evolution of the Drakensberg Escarpment and its role in understanding the formation of elevated passive continental margins. The rocks in the Drakensberg belong to the Karoo Supergroup and contain records of mass extinction events. The article also discusses the environmental impact of flood basalts and their potential connection to mass extinctions. Additionally, it emphasizes the importance of establishing more UNESCO Global Geoparks in Africa to protect and promote the continent's valuable geoheritage. [Extracted from the article]

The External Ligurian Units are regarded as representative of the ocean continent transition between the Ligure‒Piemontese oceanic basin and the hyperextended Adria continental margin. The remnants of this transition are preserved as slide blocks embedded in a sedimentary mélange. This mélange sedimented during the Santonian to Campanian in the rear of the accretionary wedge that developed during the east-dipping subduction of the oceanic lithosphere below Adria. The main characteristic of this mélange is the occurrence of slide blocks of subcontinental mantle, lower continental crust, granitoids, gabbro, basalt and sedimentary rocks in a sedimentary matrix. In this paper, we provide petrographic observations coupled with U‒Pb zircon ages and δ 18O zircon isotopes of the slide blocks of felsic granulites and granitoids. U‒Pb data indicate ages ranging from Neoproterozoic to Late Triassic. δ 18O isotopes help to define the source of the magma of granitoids and felsic granulites, which was the continental crust. Overall, the collected data indicate that the slide blocks from sedimentary mélanges can be regarded as true archives that are able to provide useful constraints about the geodynamic history of the source area of these deposits. Supplementary material: The dataset related to the U–Pb and ∂18O analysisis available at https://doi.org/10.6084/m9.figshare.c.6922535 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists [ABSTRACT FROM AUTHOR]

Ophiolite obduction, the process during which part of the oceanic crust overlaps the continental margin, presents a challenge in geodynamic reconstructions of lithospheric processes. The difference in buoyancy between the dense oceanic crust and the relatively buoyant continental crust makes obduction of the oceanic crust difficult, if not impossible, if we only consider the buoyancy forces. The initial configuration of the oceanic basins must have specific thermal and geometric constraints to overcome the difficulties posed by the negative buoyancy. Here, we present a systematic investigation of the geometric and geodynamic parameters controlling the process of ophiolite emplacement. We show which parameters are the most important during ophiolite emplacement and the optimum geometries favouring this emplacement. We focus on 'Tethyan' ophiolites, which are characterized by a relatively small inferred basin size and are commonly found in the Mediterranean region. Based on a combination of parameters, we identify the configurations most susceptible to ophiolite obduction. Our models, in agreement with the geological data, show that to achieve ophiolite obduction, the obducted lithosphere must be young and the length of the ocean–continent transition zone must be relatively sharp. Supplementary material: Supplementary figures S1–S5, that are mentioned in the main text, are available at https://doi.org/10.6084/m9.figshare.c.6922526 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists [ABSTRACT FROM AUTHOR]

The fault locations and orientation of the Zabargad Transform Fault Zone, also called the Zabargad Fracture Zone (ZFZ), have previously only been delineated by satellite-based geophysical data, causing intense debate over the last few decades. Newly recognized geomorphological features identified in bathymetric and LiDAR data from the NE Red Sea margin present the first ground evidence for the northern extent of the ZFZ. The features are aligned over 84 km, starting from the Mabahiss Deep, near the spreading axis, and continuing to the shallow Saudi Arabian shelf along the northern termination of the Al Wajh carbonate platform. Analysis of the seafloor morphology reveals three geomorphic terrains: (1) a deeply incised canyon feeding into the Mabahiss Deep, which is characterized by dozens of amphitheatre-shaped scarps; (2) a 22 km wide head-scarp that follows the edge of the Al Wajh platform; and (3) multiple fault scars and graben-like structures on the shallow shelf. We interpret these morphological features as deformation indicators associated with the deformation processes in the ZFZ and postulate that they represent the northern end of the ZFZ. In addition, the fault zone delineates the NW margin of the Al Wajh carbonate platform and most likely continues to shape it. This paper gives new insights into the interaction between fracture zones and continental margins and their role in the morphogenesis of the seafloor. [ABSTRACT FROM AUTHOR]

The Indo-Myanmar Ranges make up an enigmatic mountain belt occupying a complex tectonic zone in western Myanmar, extending from the northern continuation of the active Sunda–Andaman arc into the eastern Himalayan Syntaxis. The Indo-Myanmar Ranges are part of an accretionary forearc basin–arc complex that includes the Central Myanmar Basin and the Wuntho–Popa Arc to the east. New biostratigraphic, petrological and detrital zircon U–Pb age data are presented and used to test and refine the divergent tectonic models that have been proposed for western Myanmar. These data suggest that: (1) the Upper Triassic Pane Chaung Formation was originally deposited adjacent to the NE Indian continental margin within northern Gondwana during the Late Triassic; and (2) the Upper Cretaceous–Paleogene rocks of the Indo-Myanmar Ranges were mainly derived from the Wuntho–Popa Arc and Inner Belt, with a subordinate input from a crustal source, potentially from the Naga metamorphic-type Paleozoic basement. The Kalemyo Ophiolite has an Early Cretaceous age similar to the ages of ophiolites in the Indus–Yarlung Tsangpo Suture Zone, south Tibet and Nagaland, reinforcing the hypothesis that they were once part of the same Neotethyan ocean floor. Supplementary material: Sample locality details, detailed methodologies and geochemical data are available at https://doi.org/10.6084/m9.figshare.c.6487105 [ABSTRACT FROM AUTHOR]

A recent study by Curtin University has revealed the complex geological history of Rottnest Island and the Swan River in Western Australia. Researchers collected sediment samples to track changes as ocean levels rose over thousands of years, finding ancient mineral grains offshore dating back up to 3.6 billion years. The study highlights the region's past as a drowned continental margin and emphasizes the importance of understanding past coastline adaptations to prepare for rising sea levels in the future. The findings were published in Basin Research and provide valuable insights into the region's evolution. [Extracted from the article]

The Sindong Group (Aptian–Albian), distributed in southeastern Korea, is a fluvio-lacustrine sequence deposited in the NE–SW-trending Nakdong Trough formed in an active continental margin. Sediments were derived from the Yeongnam Massif located west and NW of the Nakdong Trough, where Early Jurassic arc magmatism began in the southern part of the Korean Peninsula. We report mineral chemistry of detrital chromian spinels of first-cycle origin occurring as an accessory mineral in arkose to feldspathic litharenites of the Sindong Group. Chromian spinel grains have Cr/(Cr + Al) atomic ratio between 0.36 and 0.94, Mg/(Mg + Fe2+) atomic ratio between 0.12 and 0.74, Fe3+/(Fe3+ + Al + Cr) value mostly <0.1, and <0.2 wt% TiO2; these values are consistent with spinel composition of forearc mantle peridotites, but are different from spinel composition of ultramafic rocks exposed in the southern Korean Peninsula. The results of this study indicate that forearc mantle peridotite or serpentinite was present in the Yeongnam Massif, and its tectonic emplacement is interpreted to have occurred by protrusion through the NE–SW-trending strike-slip fault zone developed in Middle Jurassic–Early Cretaceous time in the Yeongnam Massif and along the border with the adjacent tectonic province to the NW as a result of oblique convergence. Supplementary material: Locations of sandstone samples and compositions of spinels are available at https://doi.org/10.6084/m9.figshare.c.6004354 [ABSTRACT FROM AUTHOR]

The Nambour Basin provides the easternmost record of Jurassic sedimentation for Australia. U–Pb detrital zircon age spectra constrain basin infill as Early–Middle Jurassic (c. 195–163 Ma). Early Jurassic samples are dominated by 650–500 Ma detrital zircon sourced from the Lachlan Orogen of southeastern Australia. Distal Jurassic upland associated with this orogen was generated by epeiric uplift. Sediment sourced from it was transported northwards and eastwards into the Nambour Basin as corroborated by basinal paleocurrent data. In contrast, Devonian to Triassic detrital zircon from the New England Orogen, which abuts the Nambour Basin margin, are scarce. Topographic relief across this orogen generated by the Permo-Triassic (c. 260–230 Ma) Hunter Bowen Orogeny, had been largely eliminated by the Early Jurassic. Dominant Jurassic detrital zircon for one sample of this age, combined with related paleocurrent data and the absence of a Jurassic zircon source in eastern Australia, reflects an easterly Jurassic igneous assemblage now located on submerged northern Zealandia. The detrital zircon data presented herein constrains tectonic interpretations proposed for Jurassic east Gondwana, continental margin sedimentary assemblages in New Caledonia and New Zealand. Documentation of continental epeiric uplift from detrital zircon age data obtained from basin fill has potential yet to be explored. Supplementary material: Tables S1 and S2 are available at https://doi.org/10.6084/m9.figshare.c.5988017 [ABSTRACT FROM AUTHOR]

The architecture of canyon-fills can provide a valuable record of the link between tectonics, sedimentation and depositional processes in submarine settings. We investigated the role of plate tectonics in the initiation and evolution of submarine canyons. We demonstrate that events at the plate tectonic scale (i.e. continental break-up and shortening) have a first-order influence on the initiation and development of submarine canyons. The Late Cretaceous (c. 65 Ma) separation of Australia and Antarctica initially resulted in extensional fault systems, which then formed a steep stair-shaped palaeoseabed. Subsequently, the Late Miocene (c. 5 Ma) collision of Australia and Eurasia resulted in substantial uplift and exhumation on the SE Australian continental margin. These tectonic events led to elevated seismicity, which ultimately gave rise to gravity-driven processes (i.e. turbidity currents and mass wasting processes) and formed the base of the canyon. The inherited stair-shaped topography then facilitated further gravity-driven processes that established a mature sediment conduit extending from the shallow marine shelf to the abyssal plain. We suggest that the stratigraphic architecture of canyons can be used as an archive to record tectonic movements. Moreover, the factors that precondition and trigger gravity-driven processes can induce canyon initiation and facilitate canyon development. Supplementary material: A PDF file containing all the clean, uninterpreted seismic sections is available at https://doi.org/10.6084/m9.figshare.c.5937760 [ABSTRACT FROM AUTHOR]

The article focuses on the emerging exploration activity in the South Brazil-Uruguay-North Argentina conjugate margin, a historically underexplored region with significant potential for oil and gas discoveries, attracting substantial investment from international companies. It mentions this interest is fueled by the success in the Namibian Orange Basin, leading to seismic correlations across continents.

In a significant breakthrough, we report the first discovery of twenty-six genera and thirty-five species of Early Permian (Asselian-Sakmarian and Artinskian; 299 Ma to 276 Ma) Gondwanic palynomorphs from a tectonically emplaced metasedimentary sliver of Shyok Ophiolitic Mélange of the India-Asia Collision zone of Northern Ladakh, India. These palynofloral assemblages are of peri-Gondwanian (Cimmerian) origin and have a strong affinity with the Gondwana assemblage of peninsular India. Similar palynofloral assemblages are also known from Extra-Peninsular India, Salt Range, Karakoram, Antarctica, Australia, South Africa, and South America. The occurrence of Gondwanic sliver within the Shyok Suture is interpreted as a thin flake of active continental margin of peri-Gondwanic microcontinent/Kshiroda plate, which was sliced off during the subduction/collision process, between Ladakh block and Karakoram-Qiangtang-Lhasa terrane and amalgamated with obducted remnants of the accretionary prism of the nascent Shyok Suture. The Shyok Suture closed during the mid- to Late Cretaceous period. Subsequent syn- and post-collision synkinematic episodes tectonically juxtaposed the peri-Gondwanic sliver in the tectonized zone of Shyok Ophiolitic Mélange. The India-Asia collision, which took place ca. 60-50 Ma with the demise of Neo-Tethys Ocean, along the Indus Tsangpo Suture Zone, modified the geometry of accreted ophiolitic stack of the Shyok Suture. [ABSTRACT FROM AUTHOR]

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New structural data from a mid-crustal segment in the Eastern Sierras Pampeanas, coupled with geochronological methods and P–T estimates, reveal polyphase contractional deformation and metamorphism during the Famatinian Orogeny over a long period of time. Peaks of metamorphic monazite and zircon ages are recorded at c. 500 Ma, between 484 and 465 Ma and at c. 440 Ma. Between 484 and 465 Ma the region attained high-temperature (HT) low-pressure (LP) conditions that resulted in widespread partial melting (peak at c. 470 Ma). A contractional phase occurred during this event, as suggested by syn-anatectic structures, as well as folding at subsolidus conditions. Renewed contraction under subsolidus conditions is evidenced by reverse ductile shearing and folding at c. 440 Ma. Thrusting along the La Chilca Shear Zone caused metamorphic inversion. The consistent orientation of folds in the Quebrada del Molle Metamorphic Complex, El Portezuelo Metamorphic–Igneous Complex and the La Chilca Shear Zone as well as WSW-directed thrusting at the later shear zone indicate uniform WSW–ENE-directed shortening. This late deformation records the Ocloyic tectonic phase and brought the Famatinian Orogeny to an end in the Late Ordovician to Early Silurian. Supplementary material: Analytical methods, methods and description of the calculated P–T pseudosection diagrams, bulk compositions, and electron microprobe, U–Pb and 40Ar–39Ar data are available at https://doi.org/10.6084/m9.figshare.c.4697189 [ABSTRACT FROM AUTHOR]

Elevated topography is evident across the continental margins of the Atlantic. The Cumberland Peninsula, Baffin Island, formed as the result of rifting along the Labrador–Baffin margins in the late Mesozoic and is dominated by low-relief high-elevation topography. Apatite fission-track (AFT) analysis of the landscape previously concluded that the area has experienced a differential protracted cooling regime since the Devonian; however, defined periods of cooling and the direct causes of exhumation were unresolved. This work combines the original AFT data with 98 apatite new (U–Th)/He (AHe) ages from 16 samples and applies the newly developed 'broken crystals' technique to provide a greater number of thermal constraints for thermal history modelling to better constrain the topographic evolution. The spatial distribution of AFT and AHe ages implies that exhumation has been significant toward the SE (Labrador) coastline, and results of thermal modelling outline three notable periods of cooling: in the pre-rift stage (460–200 Ma), from synrift stage to present (120–0 Ma) and within the post-rift stage (30–0 Ma). Pre-rift cooling is interpreted as the result of exhumation of Laurentia and synrift cooling as the result of rift-flank uplift to the SE and differential erosion of landscape, whereas the final post-rift period is probably an artefact of the modelling process. These results suggest that the source of the Cumberland Peninsula's modern-day elevated topography is uplift during rifting in the Cretaceous and the isostatic compensation following continuous Mesozoic and Cenozoic differential erosion. This work highlights how interaction of rift tectonics and isostasy can be the principal source for modern elevated continental margins, and also provides insight into the pre-rift exhumational history of central Laurentia. Supplementary material: Thermal histories are available at: https://doi.org/10.6084/m9.figshare.c.4528409 [ABSTRACT FROM AUTHOR]

Progradation of deltaic systems that reach the shelf edge is considered a primary mechanism to deliver sand to continental margins. Sediment bypass processes can dominate the outer shelf to upper slope transition, causing poor preservation of reservoir quality sandstones. Turbidites can carry the bulk of the coarse fraction downdip where a thicker sand pile can be deposited once the channel-to-lobe transition is reached. Predicting this lateral and vertical variability along the slope is challenging. This configuration can be further complicated when mixed siliciclastic-carbonate systems are present. The Roseway-Missisauga case study from Nova Scotia is used here to explore potential implications associated with the development of deep-water turbidites that are time equivalent to outer-shelf mixed siliciclastic-carbonate units. Two scenarios are possible: (1) The carbonate factory is dominant, and the development of carbonate reefs and pinnacles on the outer shelf prevents the passage of siliciclastic systems beyond the shelf break; in this case, the siliciclastic component is sequestered within the inner-outer shelf. (2) Favorable conditions for carbonate production gradually deteriorate by the activation of fluviodeltaic systems that prograde outboard reaching the slope region. In this last scenario, low relief and lateral discontinuous carbonate shoals are ubiquitous in the outer shelf representing the last outboard remnants of the carbonate factory. Shelf-edge deltas circumvent or breach these carbonate shoals, establishing sedimentary pathways on the shelf-break region that connect with deep-water turbidites. Observations suggest that this last scenario is the most likely in this part of the Scotian margin during the Late Jurassic to Early Cretaceous. [ABSTRACT FROM AUTHOR]

Zircons from Late Triassic deep-water sandstone turbidites of the Mamonia Complex (west Cyprus) have prominent Ediacaran–Cryogenian and Tonian–Stenian age populations, with smaller populations at c. 2.0 and 2.7–2.5 Ga, but only minor concordant Paleozoic zircons. Late Jurassic–Early Cretaceous deep-water gravity-deposited sandstone, also from the Mamonia Complex, has a greater proportion of Ediacaran–Cryogenian and Tonian–Stenian zircons, but less abundant Paleoproterozoic, Archean and Paleozoic zircons. Similar zircon populations characterize an Early Cretaceous shallow-marine sandstone block in the Moni Melange (southern Cyprus). The dominant Ediacaran–Cryogenian and Tonian–Stenian zircon populations originated in the NE Africa/Arabian–Nubian Shield (north Gondwana). However, they were probably recycled from Paleozoic sandstones within Anatolia following South Neotethyan rifting, which also gave rise to sparse Permian–Triassic zircons. Paleozoic zircons reflect Variscan magmatism within Anatolia. Both Late Cretaceous and overlying Eocene sandstone turbidites in the Kyrenia Range (north Cyprus) contain prominent Ediacaran–Cryogenian populations, together with small Archean, Tonian, Carboniferous and Late Cretaceous populations, with additional Triassic zircons in the Eocene sample. Late Cretaceous zircons dominate an overlying Late Miocene sandstone turbidite, together with minor Ediacaran–Cryogenian, Eocene and Miocene populations. The Late Cretaceous zircons record continental margin arc and/or ophiolite-related magmatism, whereas the Eocene and Miocene zircons represent collision-related magmatism, both located in southern Turkey. Supplementary materials: Detailed zircon U–Pb geochronological data and supplementary figures are available at https://doi.org/10.6084/m9.figshare.c.4483736 [ABSTRACT FROM AUTHOR]

We present field, chemical and U–Pb age data for metamafic–ultramafic bodies of the Triassic rift-related Therma–Volvi–Gomati (TVG) complex of the Serbo-Macedonian Massif (SMM) in the northern Aegean region. The TVG rocks record igneous textures overprinted by Alpine metamorphism and deformation. The high-Ti Volvi body was transformed into amphibolites, which also rim the low-Ti Gomati and Nea Roda bodies. The compositions are compatible with normal (N-) and enriched (E-) mid-ocean ridge basalt (MORB) and weak ocean island basalt (OIB) signatures of the high-Ti rocks, whereas the low-Ti rocks are depleted with respect to MORB, suggesting melt extraction from a mantle source. U–Pb geochronology reveals Triassic crystallization of the Volvi body at 240 Ma. Ordovician to Carboniferous xenocrystic zircons were found in the Stratoni body of the TVG complex, which were sampled from the SMM basement. The Triassic Arnea rift-related metagranite intrudes the Volvi body. Comparison of the compositions of the Volvi body and the Arnea metagranite of the SMM with Triassic metagranite of the Rhodope Massif (RM) supports the presence of a regional bimodal rift suite. The location of the TVG complex at the SMM–RM margin of Eurasia confirms its origin as a Middle Triassic rift suite, and its nature as a continental margin ophiolite representing an ocean–continent transition of the propagating Neotethys. Supplementary material: Whole-rock chemical analyses and U–Pb geochronology analytical results data tables are available at https://doi.org/10.6084/m9.figshare.c.4087022 Thematic collection: This article is part of the 'Tethyan ophiolites and Tethyan seaways collection' available at: https://www.lyellcollection.org/cc/tethyan-ophiolites-and-tethyan-seaways [ABSTRACT FROM AUTHOR]

Two Cenozoic magmatic cycles occurred in Sardinia separated by a 5 myr gap: Oligo-Miocene subduction-related calc-alkaline magmatism associated with Sardinia migrating from the European continental margin to its current location, and Plio-Pleistocene intraplate alkaline magmatism associated with the opening of the southern Tyrrhenian basin. Based on an integration of new and published geochemical data on the Cenozoic volcanic rocks of Sardinia, and regional tectonics, we propose that a northward propagating slab tear formed south of Sardinia at the end of the Oligo-Miocene cycle. This was responsible for the transition from subduction-controlled calc-alkaline to extension-controlled mildly alkaline to peralkaline magmatism in the Sulcis area (SW Sardinia), and for the end of the Oligo-Miocene magmatism. The inflow of hotter material from the European Asthenospheric Reservoir (EAR) through the slab window could have produced the minor EAR-type alkaline lavas that erupted at the end of the Oligo-Miocene cycle and at the beginning of the Plio-Pleistocene cycle. The dominant younger Plio-Pleistocene lavas with EMI-type compositions probably formed from decompression melting of a shallower lithospheric mantle with little influence from the EAR-forming event. [ABSTRACT FROM AUTHOR]

Paleozoic continental margin strata in the western Foreland Belt of the Canadian Cordillera are characterized in part by alkaline volcanic sequences, carbonatite intrusions, coarse clastic sedimentary units, and erosional unconformities. These strata also contain a record of mid-Paleozoic contractional deformation unseen in coeval passive margin strata in the eastern Foreland Belt. In order to test potential genetic links between Paleozoic alkaline igneous activity, active margin sedimentation, and deformation in thewestern Foreland Belt, and better understand their implications for the evolution of the Foreland Belt as a whole, we have undertaken a detailed mapping and structural study of the Aley carbonatite intrusion and its host strata in the western Foreland Belt of NE British Columbia. Our work demonstrates that carbonatite emplacement was coeval with a Late Devonian contractional nappe-forming tectonic event. Interpreting tectonism as associated with continental collision along a long-lived active margin provides the best explanation for our structural and stratigraphic observations, and suggests that the western Foreland Belt is far-travelled and exotic relative to coeval passive margin strata in the eastern Foreland Belt. Deformed alkaline-carbonatite intrusions that characterize continental suture zones in Africa may provide an analogue for the Aley carbonatite and correlative alkaline-carbonatite complexes in the western Foreland Belt. [ABSTRACT FROM AUTHOR]

The southern U.S. continental margin records a history spanning ca. 1.2 Ga, including two Wilson cycles. However, due to a thick sediment cover, the paucity of significant local seismicity, and, until recently, sparse instrumentation, details of this passive margin's tectonomagmatic evolution remain disputed. This paper compares recent S-wave tomography and crustal thickness models based on USArray data to help establish a framework for geodynamic interpretation. Large-scale patterns of crustal velocity anomalies, corresponding to major regional features such as the Ouachita orogenic front and the Precambrian margin, are generally consistent between the models. The spatial extent of smaller-scale tectonic features, such as the Sabine Uplift and Wiggins block, remains poorly resolved. An inverse relationship between crustal thickness and Bouguer gravity across the continental margin is observed. This model comparison highlights the need for additional P-wave tomography studies and targeted, higher density station deployments to better constrain tectonic features. [ABSTRACT FROM AUTHOR]

The thick sedimentary cover (=18 km) along the Eastern Continental Margin of India (ECMI) and over the Bay of Bengal has hindered understanding of the mechanisms of rifting that operated on the eastern Indian and Bangladesh margins. Analysis of multichannel seismic reflection data, together with 3D gravity inversion and 2D gravity forward modelling, illuminates basement configuration, crustal thickness and Moho topography, thereby revealing the modes of rift evolution and the location of the continent-ocean boundary (COB) along these margins. The basement, particularly in the shelf and slope regions of eastern peninsular India, is traversed by nearly coast-perpendicular graben, and their seaward continuity is delineated up to 125 km from the coastline. Three different types of continental margin are present along the ECMI: (1) sheared rift on the southern segment of the ECMI, up to 14° N latitude (offshore the Southern Granulite Terrain); (2) hyper-extended rift in the central segment between 14° N and 17° N (offshore the Dharwar Craton); and (3) hypo-extended rift on the northern segment between 17° N and 20° N (offshore the Eastern Ghats Mobile Belt). The graben terminations, crustal thickness and Moho topography of both the ECMI and offshore Bengal Basin clearly suggest that the COB runs nearly parallel to the coastline of peninsular India, but takes an orthogonal turn offshore in the Bengal Basin and connects the palaeo-continental shelf and the Rajmahal-Sylhet Line onshore in the Bengal Basin. Crustal thickness (8-10 km) and depth to the Moho discontinuity (=28 km) beneath the Bangladesh margin are unusual because the crustal thickness increased through interaction of the Kerguelen plume with the existing oceanic lithosphere. The Moho deepened largely due to the load of the Bengal Fan sediments. The absence of rifted crustal blocks on the Bangladesh margin and the continuity of the COB into the onshore Bengal Basin together imply that the present Bangladesh region was under marine conditions at least until the beginning of Bengal Fan sedimentation (i.e. no less than 23 Ma). [ABSTRACT FROM AUTHOR]

Fault systems in extensional basins commonly display geometries that vary with depth, reflecting depth- and lithology-dependent mechanical strength. Using an experimental approach, we investigate this relationship by deploying physical analog models with stratified sequences consisting of brittle-ductile (sand-silicone polymer) sequences subject to single and polyphase deformation. The experiments were used as analogs for a sandstone sequence interlayered by beds of evaporates or overpressured or unconsolidated mudstone in nature [the latter being representative of decollement horizons). Experiments [series 1 [SI]) using homogeneous and stratified quartz and feldspar sand produced asymmetric, composite single grabens with diverse fault frequencies and fault styles for the graben margin faults. For the mechanically stratified experiments with one decollement level (series 2), contrasting graben configurations were produced, in that the lowermost sequence was characterized by graben geometries of similar type to that of the SI experiments, whereas the sequence above the decollement was characterized by large fault blocks, delineated by steepened or oversteepened faults. The experiments with two decollements [series 3) were displayed similarly but included graben geometries that widened upward, with each level being characterized by independent fault systems. The results can be used to explain strata-bound fault patterns and depth-dependent extension as seen in several places along the Norwegian continental margin and elsewhere. [ABSTRACT FROM AUTHOR]

The article offers a look at marine life from the surface layers of the open sea down through the intermediate layers to the deep-sea floor and from there to the living communities on continental shelves and coral reefs. A sampling of the inhabitants of each region and the dominant factors that typify each domain is presented. The article also discusses the conditions, principles and interactions that have influenced the forms of life in the sea.

The article discusses the geological and geophysical aspects of the continental shelves that comprise 18 percent of the total land area of the Earth. The early recorded observations on the continental shelves are presented. The political interest in the sovereignty of the ocean is discussed. The article also discusses the types of continental shelves by composition.

The article focuses on continental terrace, the underwater borderland between continent and ocean. It is a shelf of varying width from tens of miles to as much as 300-400 miles off some coasts. Terrace is one of the major subjects that submarine geologists are investigating, wherein processes of transportation and deposition are examined. In addition, the author discussed the terrace in the Atlantic Ocean off the eastern coast of the U.S. and that in the Gulf of Mexico off the southern coast.

The article focuses on revealing sedimentological insights from a core obtained in the Suriname-Guyana basin, highlighting the discovery of double mud drapes in the sandy and oil-stained reservoir, influence of tidal forces in shaping the marine turbiditic deposit in addition to turbiditic dynamics.

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The article focuses on the subsurface geology of the Barents Sea.

The article offers information about the ION's new mega-regional re-imaged three-dimensional (3D )seismic dataset across the Mauritanian continental margin which provides new insights into numerous plays from the Mauritanian margin.

Byline: Tahseenullah Khan, Waqas Javaid, Hafiz Muhammad Danial Amin and Muneeb Arshad Abstract The Chilas Complex is a ~40 wide and 300 long composite plutonic body exposed in the central [...]

Byline: Tahseenullah Khan, Waqas Javaid, Hafiz Muhammad Danial Amin, Muneeb Arshad and M.Q. Jan Abstract The Chilas Complex is a ~40 wide and 300 long composite plutonic body exposed in [...]

Byline: Syed Irfanullah Hashmi, Irfan U. Jan, Suleman Khan and Nowrad Ali Keywords: Diagenetic and sequence stratigraphic controls, Chichali formation, Lumshiwal formation, Nizampur Basin. 1. Introduction Sea level fluctuations control [...]

The article offers information on a study which provides understanding for South American Central Equatorial Atlantic margin. Topics discussed include hydrocarbon potential for the margin, reservoir of petroleum system in West Africa and Venezuela, and the importance of lineaments in Atlantic margin.

Because of its geographic extent of over 2500 km (1553 mi), the West Greenland margin provides a much understudied example of a divergent continental margin, both with respect to hydrocarbon exploration and academic studies. A seismic interpretation study of representative two-dimensional reflection profiles from the Labrador Sea, Davis Strait, and Baffin Bay was undertaken to identify sedimentary and structural components to elucidate the tectonic development of the margin. Nine horizons were interpreted from six representative seismic lines in the area. Margin-scale tectono-stratigraphy was derived from isochron maps, the geometry of mappable faults and their associated stratal architecture. Rifting began in Early to Late Cretaceous at ca. 145-130 Ma, which was followed by two pulses of volcanism in Eocene and Paleocene ages. The transition to the drift stage includes a typical subsidence phase but also erosion, uplift, and deposition of Neogene postrift packages. The shift in the position of depocenters in the Davis Strait and the Labrador Sea during Paleocene and Miocene times is evidence for structural modification of the basin bounding faults. Drift stage deformation suggests a possible anticlockwise rotation in the orientation of the spreading axis in Baffin Bay culminating in an ultraslow sea-floor spreading. Sea-floor spreading on the West Greenland margin started in the south at 70 Ma in the Labrador Sea and propagated northward into the Baffin Bay by 60 Ma. Prospective petroleum systems include thick Cretaceous age strata, with structural traps provided by grabens and inversion structures. Our structural model provides insight into a margin that is highly variable in its structural configuration, further modified by other processes such as magma-assisted rifting that may result in elevated regional heat flow, which has considerable impact on hydrocarbon maturation. Further constraining the implications of heat flow associated with volcanic activities in comparison to that associated with lithospheric stretching will be critical in future exploration. [ABSTRACT FROM AUTHOR]

The Plio-Quaternary magmatism in the Tyrrhenian Sea area exhibits wide compositional variations, which cover almost entirely those observed for volcanic rocks worldwide. Some volcanoes (Etna, Iblei, Sardinia, etc.) range from tholeiitic to Na-alkaline, and display elemental and isotope signatures typical of FOZO and EM-1 ocean-island basalts (OIB). Other volcanoes (Aeolian Arc, Italian peninsula) range from calc-alkaline-shoshonitic to K-alkaline, exhibit typical 'subduction- related' trace element signatures (low Ta-Nb, high Rb-Cs-LREE), and show a large range of radiogenic isotope ratios, from mantle-like in the Aeolian Arc to crustal-like in central Italy. Geochemical data suggest that OIB-type magmatism originated in lithosphere-asthenosphere sources that were unaffected by recent subduction. In contrast, subduction-related magmas come from mantle sources that underwent Eocene to present mixing with various amounts and types of subducted crustal components. Fluxing of the mantle wedge by water-rich fluids from a mid-ocean ridge basalt-type slab occurred in the southern Tyrrhenian Sea, whereas interaction between peridotite and various types of sediments occurred in central Italy. These contrasting styles of mantle contaminations relate to the nature (oceanic or continental) of the foreland, slab geometry and pre-metasomatic mantle compositions, which vary greatly along the Apennine arc and are the reason for the formation of the wide variety of orogenic magmas in Italy. [ABSTRACT FROM AUTHOR]

Many CO2-rich (up to 97% by volume) natural gas pools have been found in the continental margin basins of the northern South China Sea. By combining the geochemical data from 53 samples with their geologic backgrounds, this study investigated the origins and accumulation mechanism of CO2, and discussed the role of CO2 in driving oil as it charged the reservoirs. The results reveal that the CO2 gases in the Yinggehai basin originate mainly from the thermal decomposition of both Miocene calcareous shales and Paleozoic carbonates, and that CO2 from mantle degassing is only a minor contributor. The CO2 accumulations in the Yinggehai basin are mainly controlled by diapiric faults and episodic thermal fluid movements. The CO2 gases in the eastern Qiongdongnan and western Pearl River Mouth basins are mainly related to magmatic or mantle degassing, and the volatiles from magmatic degassing during the igneous intrusion stage are the most likely major source of CO2 in these reservoirs, with basement faults providing pathways for upward migration of CO2-rich mantle fluids. Natural displacements of oil by CO2 appear to be common in the eastern Qiongdongnan and western Pearl River Mouth basins. The CO2-flooded oil or gas reservoirs have two common features that the present CO2 gas pools or oil-bearing structures have residual oils representing prior charge, and are close to the basement faults that provide pathways along which the mantle-derived CO2-rich gas was migrated. The oils from prior hydrocarbon reservoirs have been naturally driven out by CO2 to form secondary oil reservoirs in the eastern Qiongdongnan and western Pearl River Mouth basins. Therefore, a full understanding of the origin and distribution of CO2 cannot just be used to trace hydrocarbon migration pathways, but also provide useful information for risk assessment prior to drilling. [ABSTRACT FROM AUTHOR]

Since the 1970s, the largest oil and gas reservoirs have been discovered in the Permian-Early Triassic formations in Saudi Arabia. Thus, this time period is important for the discovery of new oil reserves in Iran. The Arabian passive continental margin has undergone lithospheric extension during the Permian-Triassic, which led to the formation of the Neo-Tethys. The aim of this paper is to describe the development of the continental rift basin in the Zagros region based on the tectono-sedimentological evolution. We have studied well-log data to specify the distribution of synrift deposits in the Zagros and have related this information to the modelling. Environmental changes indicated by various sedimentary sequences, from a siliciclastic basin to a carbonate platform setting, are described. The Cambrian Hormuz salt, which overlies the metamorphosed Precambrian basement, becomes effective as a basal detachment layer influencing the style of overburden deformation during the Permian-Triassic extension event. We have investigated the formation of various structures linked to the presence or absence of the Hormuz layer by analogue modelling and relating these structures to the Late Palaeozoic sedimentation. Based on results of the analogue modelling, we argue that the basal detachment layer (Hormuz series) has contributed to the various structural styles of the extensional basin development in the Fars domain and the Lorestan domain. [ABSTRACT FROM AUTHOR]

Submarine slope failures are a widespread, hazardous phenomenon on continental margins. The prevailing opinion links large submarine landslides along the glaciated NW European continental margins to overpressure generated by the alternation of rapidly deposited glacigenic and hemipelagic material. Here, we report a newly discovered large landslide complex off NW Svalbard. It differs from all known large slides off NW Europe, as the available data rule out that this slope failure resulted from rapid glacigenic deposition. This suggests that processes such as contour currents, tectonic faulting, and overpressure build-up related to the gas hydrate system must be considered for hazard assessment. [ABSTRACT FROM AUTHOR]

Palaeozoic-Mesozoic brittle normal faults onshore along the SW Barents Sea passive margin off northern Norway give valuable insight into fault and fluid flow processes from the lower brittle crust. Microstructural evidence suggests that Late Permian-Early Triassic faulting took place during multiple phases, with initial fault movement at minimum P-T conditions of c. 300 °C and c. 240 MPa (c. 10 km depth), followed by later fault movement at minimum P-T conditions of c. 275 °C and c. 220 MPa (c. 8.5 km depth). The study shows that pore pressures locally reached lithostatic levels (240 MPa) during faulting and that faulting came to a halt during early (deep) stages of rifting along the margin. Fault permeability has been controlled by healing and precipitation processes through time, which have sealed off the core zone and eventually the damage zones after faulting. A minimum average exhumation rate of c. 40 m Ma-1 since the Late Permian is estimated. It implies that the debated Late Cenozoic uplift of the margin may be explained by increased erosion rates in the coastal regions owing to climate detoriation, which caused subsequent isostatic recalibration and uplift of the marginal crust. The studied faults may be used as analogues of basement-involved fault complexes offshore, revealing details about the offshore nature of faulting, including past and present basement and fault zone permeability. [ABSTRACT FROM AUTHOR]

The only place where Neogene-Quaternary rocks crop out for the entire Tuscan Archipelago in the Northern Tyrrhenian Sea is the island of Pianosa. In particular, the Miocene deposits record the depositional and tectonic evolution of the Northern Tyrrhenian region during this time period. These deposits are subdivided into two successions separated by a low-angle unconformity. The older, middle Burdigalian succession represents a calciturbidite shallow marine system, whereas the younger late Tortonian-early Messinian succession comprises a continental alluvial system that evolves upwards into a lagoonal-marginal marine environment. Here we present sedimentological, palaeontological and petrographical data that support a new stratigraphic and palaeogeographical framework for reconstructing the opening of the Northern Tyrrhenian back-arc basin. The early Miocene succession records a pre-rift marine depositional phase followed by a late Burdigalian-Langhian erosional phase. This was followed by a period of synrift continental-marginal deposition, as recorded by the late Miocene succession, terminated by an important phase of uplift, probably induced by the start of magmatic activity in the Tuscan Archipelago area. [ABSTRACT FROM AUTHOR]

Radiometric dating by the 40Ar-39Ar incremental heating method was carried out on lavas, sills, dykes, and a central intrusion from NE Greenland. Eighteen samples gave acceptable crystallization ages. Lavas of both Lower and Upper Plateau Lava Series gave ages in the range 55.5-53.5 Ma and cannot be constrained to better than 56-53 Ma. Sills and dykes from Traill Ø to Shannon, with compositions fairly similar to those of the lavas, gave ages of 55.1-51.3 Ma, contemporaneous with and slightly younger than the lavas. Alkaline lavas on inland nunataks have ages of 53-50 Ma, and the Kap Broer Ruys intrusive centre has an age of 48.7 ± 0.5 Ma. An alkaline sill on Hvalrosø is much younger at 20.3 ± 0.1 Ma. There are no pre-breakup lavas onshore NE Greenland. We surmise that the hot mantle of the Iceland plume arrived and melted extensively beneath the northern basins only at the time of breakup around 55 Ma. Post-breakup intrusive events in NE Greenland coincided with plate-tectonic events such as reorganization, uplift and opening in the north. The Hvalrosø sill represents a local small melting event that may be related to coeval opening of the Lena Trough. [ABSTRACT FROM AUTHOR]

We use three-dimensional seismic reflection data and new map-based structural restoration methods to define the displacement history and characteristics of a series of tear faults in the deep-water Niger Delta. Deformation in the deep-water Niger Delta is focused mostiy within two fold-and-thrust belts that accom-modate downdip shortening produced by updip extension on the continental shelf. This shortening is accommodated by a series of thrust sheets that are locally cut by strike-slip faults. Through seismic mapping and interpretation, we resolve these strike-slip faults to be tear faults that share a common detach-ment level with the thrust faults. Acting in conjunction, these structures have accommodated a north-south gradient in westward-directed shortening. We apply a map-based resto-ration technique implemented in Gocad to restore an upper stratigraphie horizon of the late Oligocene and use this analysis to calculate slip profiles along the strike-slip faults. The slip magnitudes and directions change abruptly along the lengths of the tear faults as they interact with numerous thrust sheets. The discontinuous nature of these slip profiles reflects the man-ner in which they have accommodated differential movement between the footwall and hanging-wall blocks of the thrust sheets. In cases for which the relationship between a strike-slip fault and multiple thrust faults is unclear, the recognition of this type of slip profile may distinguish thin-skinned tear faults from more conventional deep-seated, throughgoing strike-slip faults. [ABSTRACT FROM AUTHOR]

Evolution of slab geometry beneath the North Island, New Zealand, has been investigated using a combination of published arc-type volcanic ages and earthquake locations in the subducting Pacific plate. Arc-front volcanoes migrated SE by 150 km in the last 8 myr subparallel to the present active arc. Migration of the arc is interpreted to mainly reflect slab rollback along the Tonga-Kermadec subduction system changing to fixed hinge slab steepening beneath the central North Island. The strike of the Pacific plate beneath the North Island, imaged by Benioff zone seismicity (50-200 km) and positive mantle velocity anomalies (200-600 km), is parallel to the NE-SW trend of arc-front volcanism. Arc parallelism since 16 Ma indicates that the strike of the subducting plate beneath the North Island was constant over this time interval, in contrast to clockwise vertical-axis rotations of =50° of the overriding plate over the same period along the eastern and southern Hikurangi margin. Acceleration of arc-front migration rates (from c. 4 to c. 18 mm a-1), eruption of high-Mg# andesites, increasing eruption frequency and size, and uplift of the overriding plate indicate an increase in the hydration, temperature and size of the mantle wedge beneath the central North Island from c. 7 Ma. [ABSTRACT FROM AUTHOR]

Examples of epigenetic hematite mineralization located at the margins of the East Irish Sea Basin have been sampled for palaeomagnetic investigation to establish the timing of ore formation. Samples collected from 10 sites in Cumbria are dominated by hematite of near-pure composition and characterized by dual polarity and, in part, dual component magnetizations that yield palaeopoles (nine sites) between 50°N, 130°E and 50°N, 150°E. In contrast, samples recovered from seven sites on the Isle of Man have more varied mineralogical compositions that include ferromagnets with lower unblocking temperatures. Manx hematite mineralization also exhibits dual polarity, but magnetizations yield steeper inclinations with palaeopoles lying between 55°N, 130°E and 70°N, 150°E. Steeper directions probably reflect minor tilting of the Manx block following hematite emplacement. Correlation of poles with the European apparent polar wander path indicates that these ore deposits formed during the Middle Triassic. Results show that hematite mineralization sited at the margins of the East Irish Sea Basin is essentially contemporaneous and establishes, for the first time, an underlying temporal relationship between these geographically dispersed ore bodies. Dating places the mineralization within a broader extensional geotectonic regime associated with the early rifting of Pangaea in the North Atlantic. The context implies a causal link between crustal extension, development of ore-forming fluids within the evolving East Irish Sea Basin, and subsequent migration of fluids to basin margins where iron was precipitated as hematite. [ABSTRACT FROM AUTHOR]

Early Ordovician collision of the Lough Nafooey Arc (part of the Baie Verte Oceanic Tract) with the passive continental margin of Laurentia peaked at c. 475 Ma in Scotland and Ireland and was followed by subduction polarity reversal. We examined Upper Ordovician–Silurian sedimentary rocks from western Ireland to see whether collision was followed by renewed arc magmatism. Despite the scarcity of dated igneous intrusions between the Grampian (c. 470 Ma) and Acadian (c. 420 Ma) orogenies in Ireland, detrital zircons show a continuity of activity peaking at 480–440 Ma, implying no hiatus in regional magmatism. Differences in zircon U–Pb age spectra highlight the isolation of basins in the southern Killary Harbour area from those north of the South Mayo Trough. These latter rocks were largely derived by erosion from Moine and Upper Dalradian sources. By contrast, the Killary Harbour Basin shows a decreasing influence from the Dalradian after c. 436 Ma and an increasing influence of contemporaneous magmatic zircons. These were transported from sources along-strike from the present NE, probably at the southern end of the Scandian Mountains in SE Greenland. The western Irish basins formed as pull-apart basins in a forearc setting and are analogous to Cenozoic pull-apart basins in Sumatra. Supplementary material: U-Pb zircon analytical data is available at a decreasing influence from the Dalradian after c. 436 Ma and an increasing influence of contemporaneous https://doi.org/10.6084/m9.figshare.c.5209849 [ABSTRACT FROM AUTHOR]

Recent ultradeep exploration in the northern Gulf of Mexico has revealed a broad diffuse zone of salt-cored folding beneath the present continental shelf. This zone is a pillow fold belt, where salt pillows grew halokinetically and were then mildly shortened. Below the Louisiana shelf, a contractional early-to-late Miocene pillow fold belt is separated by a partly welded canopy from an overlying early Miocene-to-Pliocene extensional system. This anomalous juxtaposition raises two paradoxes: (1) Why was mid-Miocene shortening close to the Miocene shelf break, where extension is expected? and (2) Why did shortening below the canopy overlap in time with extension above the canopy? Coastal uplift can explain both paradoxes. Cenozoic uplift and exhumation of the north rim of the Gulf of Mexico created the observed coastal offlap and truncation around the rim. Uplift tilted the continental margin and overpowered the influence of the paleoshelf break, causing shortening much farther updip than before uplift. Physical models confirm that this hypothesis is mechanically sound. Our other models had two stacked detachments, each pinned in different locations. Because of this, deep shortening below the canopy was coeval with shallow extension above the canopy. The deep detachment was pinned far inland, equivalent to the uplifted continental interior. Extension above this deep detachment was partly balanced by shortening far downdip to form a pillow fold belt where a network of thrusts linked the squeezed pillows. In contrast, the shallow extensional system above the canopy was pinned farther seaward, equivalent to the upper continental slope. [ABSTRACT FROM AUTHOR]