Formation Of Sedimentary Basins Research Articles

Gravity field and crustal structure of the Eastern Arm of Sulawesi and the Banggai Archipelago, Eastern Indonesia

The occurrence of extensive ophiolite masses and the development of the Batui-Balantak foreland thrust-fold belt on the Eastern Arm of Sulawesi can be attributed to the geologic process in the Neogene period when the Sulawesi Island Arc and the Banggai-Sula collided. Following the convergence, crustal fragments were further adjusted on a regional scale. This adjustment involved the rotation of crustal fragments into strike-slip faults on Sulawesi Island and the formation of extensional faults in the Banggai Archipelago. The analyses of the gravity field in the region of the eastern Sulawesi and Banggai Archipelago have yielded models that can potentially be interpreted as a representation of the underlying crustal structure in the region. The models can also be understood in a way that has consequences for tectonics. The tectonic episodes have played a significant role in the formation and development of sedimentary basins within the region. The primary objective of this study was to investigate the crustal structures of the Eastern Arm of Sulawesi and the Banggai Archipelago by means of analyzing gravity profiles. The findings of the analysis suggest that there is a slight thickening observed in the crustal block beneath the central portion of the eastern arm region. In addition, this area exhibits significant fracturing and severe attenuation. Furthermore, the crustal block has a dipped north-eastward trend in response to the ascent of the Molucca Sea oceanic crust.

Geochemistry of BIF in the Quadrilátero ferrífero, Brazil, as a proxy to neoarchean paleoenvironmental and depositional conditions

Precambrian Algoma-type banded iron formations (BIFs) are biochemical metasedimentary rocks formed in the deep water environment relatively close to centers of volcanic expansion and can be characterized on the basis of their paleodepositional environment and the associated rock types. These rocks may contain geochemical signatures indicative of changes in the redox conditions of the Archean ocean. Such variations in the Meso- and Neoarchean are crucial in understanding the processes that led to the gradual increase of oxygen in the early atmosphere, culminating in the Great Oxidation Event (2.4–2.3 Ga). Oxide- and carbonate-facies BIFs were intercepted by drill cores in the Pilar gold deposit in the NE sector of the Quadrilátero Ferrífero (QF), Brazil, located in the Neoarchean Rio das Velhas greenstone belt. These rocks are interbedded with mafic and ultramafic metavolcanic rocks and carbonaceous phyllites. In light of the potential to reconstruct paleodepositional evidence indicative of the Earth's atmospheric redox history based on this stratigraphy, we have considered specific proxies from geological and geochemical observations. Pilar BIFs geochemistry exhibits positive anomalies of La, Eu, and Y, indicating characteristics inherited from seawater and high-temperature hydrothermal fluids. In addition, a superchondritic Y/Ho ratio further supports the influence of seawater. The signatures of the major elements Al2O3 and other immobile elements typical of detrital sediments corroborate the interpretation that these rocks were deposited in a deep marine environment with low clastic influence. Furthermore, negative Ce/Ce*SN anomalies in some sections of the Pilar BIF indicate limited oxygen availability which, together with Mo, U, V, and Zn trace-element enrichment factors, indicate deposition under suboxic/euxinic conditions. This research, together with other similar BIF data from the NW QF provide new insights into the paleoenvironmental conditions prevailing during the formation of the Archean volcano sedimentary basins that compose the southern São Francisco craton (SFC).

Review of sedimentary basin evolution in Cambodia based on tectonic setting and logical information

The paper aims to synthesize the evolution of sedimentary basins in Cambodia based on a comprehensive information on tectonic setting and existing database of their formation and sedimentation. The study includes a review on tectonic setting of Indochina, the formation of sedimentary basins around Cambodia, and the accessible data on sedimentary basins in Cambodia. Indochina, as well as Cambodia, had been influenced by the collision of three different plates or terranes such as the South China, Sibumasu-Sukhothai, and Paleo-Pacific that are associated with the evolution of Paleozoic-Mesozoic Basins namely Khorat and Kampong Som Basins. These two oldest basins, are interpreted as a Paleozoic – Mesozoic foreland basin that initially formed due to rifting during the Late Carboniferous to Late Permian, and later basin inversion and erosion took place due to the Mesozoic to earliest Cenozoic uplift. Then, Cambodia was affected by Tertiary strike-slip fault movements that also influenced the formation of Tonle Sap, Svayrieng and Khmer Tertiary rift basins. Tonle Sap and Svayrieng Basins are interpreted to be formed by extension during the Middle Eocene – Early Oligocene and inversion, uplift and denudation during the Miocene. The Khmer Basin was formed by rifting during the Eocene to the Late Oligocene, followed by rapid thermal subsidence from the Early to Middle Miocene. Finally, Khmer basin was affected by the Middle – Late Miocene to Pleistocene inversion.

Crustal structure and seismic anisotropy of rift basins in Somaliland

Rift margins provide insights into the processes governing the rupture of the continental lithosphere and the subsequence formation of sedimentary basins. The Proterozoic basement underlying Somaliland has been affected by multiple rifting; however, the crustal structure of these rifted basins remains unknown. This study utilized teleseismic receiver function analysis, Bayesian inversion, common conversion point imaging and 2D forward gravity modelling to examine the crust and upper mantle of Somaliland. The results indicate 36.8–38.2 km of crust in southern Somaliland, while the central and northern regions feature thinned crust (~ 21 km) with 5–6 km thick sediments. The joint analysis of radial and transverse components of receiver functions and shear wave splitting revealed fast axis directions trending to 50–56° in the upper mantle, indicating that azimuthal anisotropy is oriented in the regional Africa-Arabia plate motion. Such orientation may have resulted from lattice preferred orientation of olivine from the asthenospheric flow. Additionally, the fast polarization of the crust in central Somaliland is oriented at − 15°, indicating fossil deformation in the thinned crust related to the NW–SE trending Late Jurassic rift event. Further, the fast polarization for stations near the Gulf of Aden is oriented at 75–80°, suggesting crustal deformation associated with the Oligocene rift event. The crustal anisotropy at southern Somaliland revealed fast polarization oriented at − 85°, indicating a preserved far-field response of the WNW-ESE trending Late Cretaceous rift event. Overall, the study provides for the first-time insight into the rift-related extensional strain fabric in the crust and upper mantle anisotropy induced by asthenospheric flow in Somaliland.

THE WEST SIBERIAN SEDIMENTARY BASIN. AN ORIGIN WITHOUT STRONG CRUSTAL STRETCHING – THE SUPERDEEP DRILLING DATA ANALYSIS

Mechanism of formation of large sedimentary basins on the continents is among the main problems in geodynamics. The formation of such structures far from convergent plate boundaries is most often explained by intense stretching of the lithospheric layer - rifting. This should be followed by a large and prolonged crustal subsidence due to cooling of the stretched lithosphere. A characteristic feature of the post-rift subsidence is a decrease in its rate in time - several times over a hundred million years. Rifting in the West Siberian Basin was associated with the formation of Permian-Triassic graben-rifts. The subsequent (post-rift) subsidence is considered by many researchers as a cause of formation of a thick layer of Mesozoic and Cenozoic sediments in the basin. Over the 86 Ma that passed from the beginning of the Middle Triassic to the end of the Middle Jurassic, the rate of post-rift subsidence should have decreased by about a factor of three. In fact, the opposite trend took place. Judging by the data of the Tyumen (SG-6) and En-Yakhin (SG-7) superdeep wells drilled in the north of the basin, the rate of crustal subsidence increased several times during this period of time. Such a sharp difference between the expected post-rift subsidence and the actual subsidence of the crust indicates that lithospheric stretching was not the main subsidence mechanism, and it could provide only a small part of the subsidence. Under such circumstances, the main cause of the subsidence should be contraction of rocks in the Earth’s crust due to prograde metamorphism.

Time constraints on the geological evolution of the main sedimentary basins and tectono-magmatic events on Livingston Island, South Shetland Archipelago, Antarctica: a review

The Lower Cretaceous to Miocene South Shetlands Islands’ volcanic arc is a result of the subduction of the Phoenix Oceanic Microplate (part of the Pacific Plate) beneath the Antarctic Peninsula. The magmatic activity on Livingston Island has been going on for a long time: since the Early Cretaceous to the present. The evolution of the volcanic arc resulted in the formation of various sedimentary basins and paleoenvironments (turbiditic to shallow marine and continental) that formed varied sedimentary successions and tholeiitic to potassium calc-alkaline subduction-related magmatic rocks. Considering the magmatic activity on Livingston Island, a general trend of rejuvenation can be observed from the WNW (Byers Peninsula) to the ESE (to Hannah Point, Point Williams and further to the Hurd Peninsula and the Tangra Mountain). The rejuvenation of the magmatic rocks in the direction of the thrust plate can be explained as an effect of a flattening subduction that was active from the Early Cretaceous (135 Ma) up to around 90–70 Ma. The mixed ages of the dikes and small intrusions in the Hurd Peninsula are most probably due to periods of rotation and probably beginning of а slab-roll back. A regional Paleocene–Eocene (65–47 Ma) compressional episode that caused a low temperature to high-pressure metamorphism is registered on Smith and Elephant islands. The regional metamorphism was followed by a vast extension between 50–30 Ma that culminated with the opening of the Drake Passage around 34–30 Ma. The magmatic response of that regional scale extension was the intrusion of the Eocene Barnard Point Pluton (46–40 Ma) and dikes with youngest ages of around 30 Ma. The major uplift phase and the exhumation of the Tangra Mountain happened between 22–16 Ma as indicated by the Ap FT thermochronology. The last magmatic event on the island produced the contrastingly different in composition Quaternary alkaline mafic rocks that occupy the area between Innot Point and Burdick Peak. This episode is interpreted as related to a process of crustal extension that culminated in asthenospheric upwelling and rifting along the Bransfield Strait. The latter is due to a slab roll-back that led to the break-up of the South Shetlands from the Antarctic Peninsula and consequent subduction termination.

The Origin of the West Siberian Sedimentary Basin without Strong Crustal Stretching: An Analysis of Superdeep Drilling Data

The mechanism of the formation of large sedimentary basins on the continents is among the main problems in geodynamics. The formation of such structures far from convergent plate boundaries is most often explained by intense stretching of the lithospheric layer (rifting). This should be followed by a large and prolonged crustal subsidence due to cooling of the stretched lithosphere. A characteristic feature of the post-rift subsidence is a decrease in its rate in time by several times over a hundred million years. Rifting in the West Siberian Basin was associated with the formation of Permian–Triassic graben-rifts. The subsequent (post-rift) subsidence is considered by many researchers as a cause of the formation of a thick layer of Mesozoic and Cenozoic sediments in the basin. Over the 86 Ma that passed from the beginning of the Middle Triassic to the end of the Middle Jurassic, the rate of post-rift subsidence should have decreased by about a factor of three. In fact, the opposite trend developed. Judging by the data of the Tyumen (SG-6) and En-Yakhin (SG-7) superdeep wells drilled in the northern part of the basin, the rate of crustal subsidence increased several times during this period of time. Such a sharp difference between the expected post-rift subsidence and the actual subsidence of the crust indicates that lithospheric stretching was not the main subsidence mechanism, and it could support only a small part of the subsidence. Under such circumstances, the main cause of the subsidence would have to be contraction of rocks in the Earth’s crust due to prograde metamorphism.

Editorial preface to special issue: Continental evolution and sedimentary basins of the Tibetan Plateau and its environs

Continental evolution is responsible for the evolution of orogenic belts and sedimentary basins. The India–Asia convergence during the late Mesozoic to Cenozoic and the resulting tectono-sedimentary processes in the Tibetan Plateau and and its environs are among the most spectacular manifestations of continental evolution and sedimentary basin formation in recent Earth history. The aim of this special issue is to explore continental evolution and sedimentary basins in central-southern Asia since the late Mesozoic, with a main focus on the India–Asia convergence and the resulting tectono-sedimentary, tectono-geomorphologic, and paleoclimatic/paleoenvironmental processes in the Tibetan Plateau and its environs during the late Cretaceous to Neogene. The issue comprises ten papers that address the significance of Continental Evolution and Sedimentary Basins of the Tibetan Plateau and its Environs since the middle Cretaceous, and that fall into three categories. (i) The first category addresses the paleogeography of the southern-central Tibetan Plateau during the Cretaceous to Paleogene. These studies decipher the multistage collision of Inida with Asia, the opening and closing of ocean basins, and the tectonic evolution of the major blocks (such as Tibetan Himalaya, Lhasa, and southern/western Qiangtang) and especially of the major Himalayan tectonostratigraphic units during the convergence history between India and Asia. (ii) The second category addresses the tectono-sedimentary and tectono-geomorphologic evolution of the eastern and northeastern margins of the Tibetan Plateau during the late Cretaceous to Neogene. (iii) The third and the final category addresses the tectono-sedimentary basin filling and/or paleoenvironmental processes during the late Eocene to Pliocene, which are recorded in the intermontane Kuche and Tajik basins in central Asia and thus may reflect the far-field influence of the post-collisional India–Asia convergence on these sedimentary basins.

An automatic workflow for risk analysis on spatial output properties using kriging‐based surrogate models—Application to stratigraphic forward modelling

AbstractStratigraphic numerical forward process‐based models represent the formation and evolution of sedimentary basins through time. Their main deliverable is a 3D digital grid which can help to better understand the sedimentary basin infill. These models depend on several input parameters that need to be characterized for the studied basin. However, available data such as well logs and seismic data may not provide enough information to identify a unique possible value for these parameters. It is then crucial to take the uncertainty induced by this non‐uniqueness into account in the decision‐making process. As a single numerical stratigraphic forward simulation can be very time consuming, solutions are needed to limit the computational cost required to estimate such uncertainties. In particular, machine learning techniques can be used to build meta‐models that mimic the simulator and provide fast estimations of its outputs for any values of the input parameters. The key step for the efficiency of such an approach stands in the choice of the set of simulations (or training set) used to build the meta‐models: it should be informative enough to obtain accurate predictions for the output properties of interest, but also of reasonable size to limit simulation time. Then, meta‐models can be used to investigate a large number of models and make uncertainty quantification easier. Here, we focus on the prediction of spatial outputs of interest approximated from the joint use of several kriging‐based meta‐models combined to reduced basis decomposition. Sequential approaches have been proposed in the literature to identify training sets iteratively for a kriging‐based meta‐model, building upon the specific structure of such surrogates. We propose here to extend these approaches to the context of spatial output predictors. The results obtained on two synthetic test cases, representing a carbonate platform and a clastic environment, highlight the potential of the proposed approach for risk analysis to iteratively build training sets with a satisfactory efficiency in terms of simulation time and prediction accuracy.

Sustainability in agribusiness: Analysis of environmental changes in agricultural production using spatial geotechnologies

As global populations grow the growing demand for food and food security also rises. As global climate change proceeds, a growing demand for sustainability in said food production concurrently grows. Initiatives that address sustainability in agribusiness can now utilize geotechnology to identify losses in environmental quality resulting from methods of food production. The objective of this study is to evaluate the risks of environmental transformations categorized as: savannah, urban, water, forests, exposed soil, cultivation and regrowth in the municipalities of Carazinho, Marau and Passo Fundo, located in southern Brazil, demonstrating the potential of the approach in the Process Analytical Hierarchy (AHP), integrated with Geographic Information Systems (GIS) to determine areas at risk of environmental degradation. This study considered parameters of density of rural buildings, soil type, use and slope. The AHP method was used to determine the weights of the parameters, through the following categories: savanna = 0.1; urban = 0.25; water = 0.9; kill = 0.1; exposed soil = 0.4; cultivation = 0.45; and regrowth = 0.5. The results showed that the integrated approach of AHP and GIS in a computerized environment proved to be effective for the mapping and quantification of environmentally degraded areas, attributed to the percentage of exposed soil, with the formation of sedimentary basins in river beds, with a high risk of 2.49%, with 2680 patches of exposed soil fragments identified. Exposed soil detracts from the sustainability of agricultural production in the region. This research is fundamentally important as it can be replicated in other regions, making it possible to assess environmental problems in relation to food production areas, aiming to raise the levels of agribusiness on a global scale.

Late Paleoarchean to Neoarchean sedimentation on the Singhbhum Craton, eastern India: a synthesis

Subaerial rise of Earth's first continents took place 3.3–3.2 Ga years ago. This had significant influence on the ocean, atmosphere, and biosphere. Two important sedimentological consequences of continental emersion were (1) development of terrestrial (alluvial fan–fluvial–aeolian) depositional systems and (2) formation of shallow-marine sedimentary basins near the continental margin. Late Paleoarchean–Neoarchean terrestrial deposits, including development of an extensive paleosol around 3.2 Ga, and Meso–Neoarchean shallow-marine deposits have been reported from the Singhbhum Craton, eastern India from several localities. However, lateral and vertical changes in sedimentary facies associations and stratigraphic correlation between these terrestrial to shallow-marine sedimentary deposits have not yet been investigated. In this paper, we have reviewed the sedimentological characteristics of Late Paleoarchean to Neoarchean (3.2–2.8 Ga) stratigraphic successions of the Singhbhum Craton and have discussed sea level change and mode of stratigraphic sequence building. Our analysis shows that Singhbhum granitoid complex was emplaced around 3.3 Ga in an intracontinental setting, resulting in high continental freeboard conditions that triggered terrestrial (alluvial fan–braided fluvial) sedimentation (Dhosrapahar Formation). Continental sedimentation continued until ca. 3.0 Ga. In the eastern (Simlipal Group), western (Birtola Formation), and southwestern (the Mankarchua, Mahagiri, and Keonjhar formations) parts, shallow-marine sedimentation occurred after 3.0 Ga as a result of transgression. However, in the northern part (Dhanjori Formation), continental sedimentation prevailed throughout the Archean. These Late Paleoarchean to Neoarchean terrestrial and near-coastal successions of Singhbhum Craton should be the prime targets for intense geobiological research.

Structural and tectonic conditions for the development of the Bering Sea sedimentary basin

Introduction. In order to characterize the oil and gas potential of any area under exploration, its structural and tectonic evolution should be studied. In this paper, a structural and tectonic modelling of the Bering Sea is carried out.Aim. To identify the structural and tectonic characteristics of the Bering Sea by interpreting the results obtained during a geodynamic analysis of sedimentary basin formation, based on the tectonic and geodynamic paleoreconstructions and sedimentary basin modelling of the Bering Sea.Materials and methods. A structural and tectonic modelling of the Bering Sea sedimentary basins was carried out using contemporary methods of basin analysis and numerical geological modelling (PetroMod software, Schlumberger). Three-dimensional time-spatial structural-tectonic models of the Bering Sea were formed using the bottom structural maps of Pliocene-Quaternary deposits, near the Lower Miocene and Oligocene tops and along the acoustic basement bottom. Maps were digitalized and converted to grids (with a 500-m step), in which the discrepancies (intersections) were removed taking into account the available geological and geophysical data (seismogeological sections). The contemporary surface of sedimentary basins was constructed by the connection of bathymetric and topographic maps. The beginning and end time of sedimentary accumulation periods was determined in accordance with the international stratigraphic scale.Results. The performed study identified the sufficiently continuous development areas of the oceanic or suboceanic crust of deep-water (back-arc) basins, aged from the Upper Jurassic-Cretaceous to the Cenozoic and repeatedly affected by the subsequent phases of the tectonic and magmatic activation; development belts of the Cretaceous-Cenozoic block-magmatic basement of island arcs, locally including reformed basement blocks of an older, Paleozoic or Cimmerian, consolidation; extensive depth-differentiated alpine/newest (syn-oceanic) shelf platforms, occassionally partially destroyed due to the latest destruction, including blocks or large blocks of Pre-Cambrian or Paleozoic relatively rigid massifs in the structure of their base.Conclusion. The modelling results indicate the deeply submerged West Anadyr, East Anadyr and Central Anadyr basins to be possible depocentres with their own hydrocarbon generation centres.

Post‐collisional sedimentation of the Early Mesozoic Munamdong Formation in South Korea

Post‐collisional processes cause uplift and exhumation of the overthickened crust together with the formation of sedimentary basins. To determine the influence of post‐collisional processes on sedimentation, we investigated the Early Mesozoic Munamdong Formation of the Yuljeon Basin in the Korean Peninsula, deposited immediately after the orogenic events caused by the collision of the North China Block and South China Block. Facies analysis shows that the Munamdong Formation was deposited in a streamflow‐dominated alluvial fan under tropical/subtropical climatic conditions. Vertically, the Munamdong Formation exhibits a fining‐upward trend with changes in stacking patterns, from highly amalgamated channel conglomerates to floodplain fines, indicating a progressive increase in the creation of accommodation space exceeding sediment supply. Moreover, the types of gravels in the conglomerate beds and the petrographic characteristics of the sandstones suggest that the sediments were supplied rapidly from nearby Precambrian high‐grade metamorphic rocks and Triassic post‐collisional plutons. These results indicate the supply of sediment from restricted sources, implying that the drainage basins did not widen even during intermittent quiescence of basin subsidence. We interpret the fining‐upward trend and uniform composition of sediments to have resulted from rapid uplift and exhumation of the orogenic crust, together with rapid tectonic subsidence, possibly aided by post‐collisional magmatism. This study shows that the Munamdong Formation reflects a close connection between surficial sedimentation and post‐collisional tectonic processes. This study will help to fill the gap of understanding between deep crustal processes and post‐collision sedimentation with insight into the Early Mesozoic tectonic environment of the East Asian continental margins.

The dimensions of geotourism with a spotlight on geodiversity in a subdued landscape

Landscapes of high relief are often favoured tourist destinations and at the same time display complex geomorphology that may be the result of diverse geology summarised into the concept of geodiversity. In contrast areas of subdued landscape, while topographically unappealing, may also be geodiverse but need careful explanation and promotion to attract the geotourist. The mid-west of Western Australia is an area of low relief with a long history of weathering, ostensibly of little interest to visitors, is underlain by a diverse geology that is displayed in an incised landscape where erosion by rivers and the ocean displays geodiversity in attractive detail. The mid-west of Western Australia is the result of sedimentary basin formation during the separation of the Gondwanan Indian plate from the western edge of the Archean Yilgarn granitic craton. A plutonic Precambrian basement is overlain by Ordovician sediments comprising the Tumblagooda sandstone and then Permian and younger Mesozoic rocks, often capped with a complex weathered regolith. Geology is exposed in the Murchison and Irwin River valleys where interpretive signs explain the origin of the landscape and sequences of rock. Extensive weathering products from the Tertiary period, such as laterite and sandplains, provide opportunities to explain processes such as deep weathering, mobilisation and re-deposition of sediments that are integral to the development of landscapes in general. We thus provide a conceptual understanding of the nexus between tourism and geodiversity via the applied science of geotourism in a predominantly subdued landscape. We make the point that there is a general lack of attention paid to regolith in the geotourism literature, hence we have provided a relatively detailed account of a large expanse of sandplain that occurs in the study area. Furthermore, regolith geodiversity has not been investigated in the context of its wider geotourism potential and while this case study is preliminary in its wider scope, we provide a platform for further research.

Stress-strain state of the earth’s crust of the Central Asian mountain belt: distant effect of the tectonic impact of the Indo-Eurasian collision

In recent decades, extensive geological, geophysical and geochronological data have been obtained that characterize in detail the results of the distant tectonic impact of the Indo-Eurasian collision on the lithosphere of Central Asia, which led to the formation of the mountain systems of the Pamirs, Tien Shan, Altai-Sayan region and Transbaikalia from the Late Paleogene (about 25 million years ago). It has been established that the formation of the structure of Central Asia occurred as a result of the transmission of deformations from the Indo-Eurasian collision over long distances according to the “domino principle” through the rigid structures of Precambrian microcontinents located among the Paleozoic-Mesozoic folded belts. The study of peneplain surfaces deformed into simple folds on high-mountain plateaus surrounded by rugged mountain ranges made it possible to reveal the parameters of the deformations of the earth’s crust, the interrelationship of the formation of relief and sedimentary basins. Apatite track dating data, structural and stratigraphic analyses of Late Cenozoic sediments in the basins prove a period of intense tectonic activation the entire lithosphere of Central Asia from the Indian continent to the Siberian platform starting from the Pliocene (about 3.5 million years). As a result of reactivation of the heterogeneous basement of Central Asia, high seismicity was manifested, which is concentrated mainly along the border of the microcontinents (Central Tianshan, Junggar and Tuva-Mongolian) and the Siberian craton, as well as in the zones of articulation of regional faults.

Design and Practice of Virtual Simulation Teaching Experimental Platform for Marine Oil and Gas Exploration

This paper introduces a virtual simulation teaching experimental platform based on Unity 3D engine development. The platform is designed for the purpose of aiming at the frontiers of oceanography, improving teaching efficiency, stimulating interest in learning, and training practice ability. It provides a first-person roaming perspective combined with an operation mode of the human-machine dialogue UI. It is equipped with the function modules of submarine topographic and geomorphological survey, marine seismic exploration, marine geochemical exploration and hydrocarbon accumulation elements. The design of such modules enable students can learn to understand the operation of various instruments and equipment related to marine geological survey and hydrocarbon exploration, and obtain a more realistic human-machine interaction experience in the virtual scene. This platform is dedicated to guiding students to master the geological data collection and analysis methods in the field of offshore oil and gas exploration, to clarify the internal relationship between the formation and evolution of marine sedimentary basins and the enrichment of offshore oil and gas, and to reveal the offshore hydrocarbon exploration process. Therefore, we can make full use of the advantages of virtual simulation, which will help to improve the teaching effect and have a distinct practical role in the teaching of oceanography experiments.

Late Cretaceous to Early Cenozoic extension in the Lower Yangtze region (East China) driven by Izanagi-Pacific plate subduction

The intracontinental response to plate-boundary and mantle processes, such as subduction or continental collisions, is an important topic in the Earth Sciences. Cretaceous to Cenozoic extension across East China is related to the interaction between the Asian continental lithosphere and western Pacific oceanic subduction system, and the associated intra-plate structures and basins provide robust temporal and spatial records of regional continental deformation. Although extension may primarily be driven by slab rollback and/or back-arc opening, mid-ocean-ridge subduction may have played a significant role in this process. To explore how the western Pacific subduction system impacts intracontinental deformation across East China, we use onshore-offshore geological records, geophysical survey observations, and time-dependent Pacific plate models to document the temporal and spatial variation of continental deformation in the Lower Yangtze region adjacent to the Yellow Sea. Based on our compilation, we argue that mantle-wedge convection, with coupled subduction of the trench-parallel Izanagi (Paleo-Pacific)-Pacific mid-ocean ridge, exerts a first-order control on extensional deformation in East China. Beneath eastern China, the mantle wedge history consists of two phases: (1) initial development of the mantle wedge as the Cretaceous Izanagi slab transitioned from flat-slab to steep subduction; and (2) mature mantle wedge convection during Cenozoic subduction of the Pacific plate. Relatively steep subduction of the progressively younging Izanagi plate during the Late Cretaceous-Paleocene resulted in strong mantle convection and coupled upper plate extension in eastern China. The collision of the Izanagi-Pacific plate ridge system with the trench resulted in a magmatic gap and short-lived uplift of eastern China. Following this, subduction of the rapidly aging Pacific plate resulted in a larger, but relatively weaker, mantle convection cell that drove weaker upper plate extension. The vigor of wedge mantle convection was modulated by the age of the Pacific subducting slab, which directly influenced the formation and evolution of intracontinental extension and sedimentary basins across eastern China. The pre-existing Triassic Tan-Lu fault zone has reactivated since the Late Eocene (ca. 40 Ma) due to westward subduction of the Pacific slab to partition strain between extensional dextral faulting in the Bohai Bay and Lower Yangtze basins, thereby diversifying Cenozoic lithospheric extensional deformation in eastern China. Several major Cenozoic extensional basins spatially correlate with the Triassic Sulu orogenic belt, which we interpret to suggest that these basins are underlain by the older and fragmented orogenic basement that acted as mechanically weak zones for localized high-magnitude extension. We present a comprehensive tectonic model that relates intracontinental deformation to subduction zone dynamics, particularly emphasizing the importance of the age of the subducting slab, thus providing a coherent geologic process to explain the deformation kinematics in eastern China and the diversity of observed Mesozoic-Cenozoic basin formation.

MODEL OF DECOMPRESSION MELTING MECHANISM IN CONVECTIVE-UNSTABLE THERMAL LITHOSPHERE (FIRST APPROXIMATION)

We propose a model of decompression melting, separation, migration and freezing of the melt in the upper mantle during the convective instability process. The model takes into account differences between phase diagrams of the melt and the matrix and the resultant features of the melt’s behavior, without calculating reaction rates in a multicomponent medium. It is constructed under an explicit concept of the local thermodynamic equilibrium of the existing phases. Therefore, we further develop the first approximation of the descriptions of convection in the upper mantle and the formation of large epicontinental sedimentary basins, which have been presented in earlier publications. Our computational experiments show that primary melting of the upper mantle’s fertile material occurs intensively in a narrow frontal part of the ascending hot material flow. Then, the depleted and partially melted material rises farther upward from the front of primary melting. Melting of the depleted material continues at lower pressures in a rather wide range of depths (120–77 km). Further, the migrating melt is supplied by two sources, i.e. a deep-seated one, wherein the fertile material melts, and the medium-depth one, wherein melting of the depleted material takes place. Once the temperature and pressure rates of the melt reach the values corresponding to those of its solidus, a narrow freezing front is formed. Its width is almost similar to the primary melting front. As the ascending convective flow develops, the freezing front shifts upward. As a result, a quite thick (around 40–50 km) basalt-saturated layer occurs above the freezing front. An important observation in our modeling experiments is that, despite a considerably large total volume of the melted material, a one-time melt content in the mantle does not exceed tenths of one percent, when we consider averaging to volumes with a linear size of about 1.0 km. The basalt melt extraction depletes iron in the mantle and significantly reduces the mantle density. Considering the calculated basalt-depletion values for the matrix at 0.1–0.2, the density deficit doubles in comparison to the thermal expansion of the material. Logically, both the Rayleigh number and the intensity of convection also double (and this is confirmed by the calculations), which means that convection is enhanced after the melting start.Testing of the model shows that it gives a reasonable picture that is consistent with the available geological and geophysical data on the structure of the lithosphere underneath the currently developing epicontinental sedimentary basins. Furthermore, within the limits of its detail, this model is consistent with the results of modeling experiments focused on melting and melting dynamics, which are based on calculations of reactions between components of the mantle material.

Lithological and paleogeographic conditions for the formation and location of sedimentary basins of the Caspian region

Lithological and paleogeographic conditions for the formation and location of sedimentary basins of the Caspian region

RELATIONSHIP OF THE FORMATION OF OROGENS AND SEDIMENTARY BASINS OF ASIA IN THE MESOZOIC-CENOZOIC

The stages of the formation of mountain systems (orogens) and sedimentary basins of Asia are highlighted and an analogy is given. The stages are manifested in the Jurassic, Cretaceous, and Cenozoic as a result of collisions to the southern active margin of the Asian continent, respectively, of the Quingtang, North China, and Indian continental blocks, which led to the formation of large intracontinental orogenic belts that are the source of sedimentary basin demolition.