Passive Continental Margin Basin Research Articles

Prototypical basin reconstruction and evolutionary models for the Precambrian of the Qinshui Basin, North China craton

The thick Precambrian strata in the Qinshui Basin (QB) have high potential for hydrocarbon exploration. Tectonic evolution restoration and prototype basin reconstruction are key to hydrocarbon exploration and evaluation for Precambrian strata. We studied the 2D/3D seismic data and Precambrian field outcrops of the QB to elucidate its geological attributes, major regional unconformities, tectonostratigraphic framework, tectonic evolution and prototype basin. The Precambrian strata of the QB are the sedimentary products of the continuous transgression from south to north and are more appropriately attributed to the Xiong'er Aulacogen in the Changchengian and Jixian periods. We identified six regional unconformities: the Archean or Palaeoproterozoic/Xiong'er Group, the Xiong'er Group/Chy, Chc/Chl, Chl/Jxl, the Jxl/Cambrian System, and the Ordovician/Carboniferous. Seven tectonostratigraphic units can be delineated: the Archean–Palaeoproterozoic, Xiong'er Group, Yunmengshan–Cuizhuang, Luoyukou, Jixian, Cambrian–Ordovician, and Carboniferous–Triassic tectonostratigraphic units. The tectonic evolution was divided into seven stages: the formation and evolution of the basement (∼1800 Ma), the synrift stage in the Xiong'er period (1800–1720 Ma), the postrift stage in the Yunmengshan–Luoyukou period (1720–1600 Ma), the passive continental margin basin stage in the Jixian period (1600–1400 Ma), the marine craton stage during the Cambrian–Ordovician (542–440 Ma), the marine–continental transitional–continental craton stage during the Carboniferous–Triassic (316–200 Ma), and the intense deformation stage (200–0 Ma). Three stages of prototype basin models of the Precambrian in the QB have been reconstructed: (1) In the synrift basin model, numerous normal faults have developed, and the section shows a symmetrical composite graben. The topography in the south is low, that in the north is high, and the northeast and northwest areas are palaeo-uplifted. A set of volcanic rocks with coarse-grained clasts was deposited. (2) In the postrift basin model, the fault activity weakened, and the depositional range became larger than that of the synrift stage, and a set of marine clastic–carbonate rocks was deposited showing a gradual coarsening–upwards trend. (3) In the passive continental margin basin model, the fault became almost inactive, the topography was low in the southeast and high in the northwest, and the depositional area was more widespread, resulting in a set of marine carbonates. These results contribute to a better understanding of the break-up process of the Columbia supercontinent and the Precambrian evolution of the North China Craton (NCC) and can be used to predict the distributions of source rocks and hydrocarbons.

Prediction of Structural Fracture Distribution and Analysis of Controlling Factors in a Passive Continental Margin Basin—An Example of a Clastic Reservoir in Basin A, South America

Structural fracture distribution is essential in oil and gas transportation and development in passive continental margin basins. In this paper, taking as an example the clastic reservoirs in the A-Basin, a passive continental margin in northeastern South America, the paleotectonic stress field of the Late Cretaceous Maastrichtian formation in Basin A was numerically simulated by finite element technique through the integrated interpretation of seismic total data, logging data and core data, and the distribution of tectonic fractures was later predicted based on rock fracture criterion. The results of the study show that: (1) The distribution of tectonic stress and fractures during the Late Cretaceous Maastrichtian formation of Basin A is affected by the fracture zone, mechanical properties of rocks and tectonic stress, regions with extensive fracture development are susceptible to stress concentrations, resulting in significant stress gradients. (2) The development of structural fractures in the study area was predicted using the Griffiths criterion, and the tensile rupture coefficient T was introduced to quantitatively characterise the intensity of fracture development, with larger values reflecting a higher degree of fracture development. The well-developed and relatively well-developed fractures are mainly located in the fracture zones and the interior of submarine fans. (3) Fracture zones and sedimentary phases mainly control structural fractures in Basin A; within 5 km outside the fracture zones, the development of fractures is controlled by the fracture zones, beyond which the regional tectonic stress field controls them; inside the sedimentary fan, the development of fractures is controlled by the sedimentary subphase, which decreases in the order of the upper fan, the middle fan, and the lower fan; inside the subphase, they are controlled by the regional tectonic stress field, and the fractures show the increasing trend in the direction of NW-NE.

Sedimentary build-ups of pre-salt isolated carbonate platforms and formation of deep-water giant oil fields in Santos Basin, Brazil

In response to the problems of unclear distribution of deep-water pre-salt carbonate reservoirs and formation conditions of large oil fields in the Santos passive continental margin basin, based on comprehensive utilization of geological, seismic, and core data, and reconstruction of Early Cretaceous prototype basin and lithofacies paleogeography, it is proposed for the first time that the construction of pre-salt carbonate build-ups was controlled by two types of isolated platforms: inter-depression fault-uplift and intra-depression fault-high. The inter-depression fault-uplift isolated platforms are distributed on the present-day pre-salt uplifted zones between depressions, and are built on half- and fault-horst blocks that were inherited and developed in the early intra-continental and inter-continental rift stages. The late intra-continental rift coquinas of the ITP Formation and the early inter-continental rift microbial limestones of the BVE Formation are continuously constructed; intra-depression fault-high isolated platforms are distributed in the current pre-salt depression zones, built on the uplifted zones formed by volcanic rock build-ups in the early prototype stage of intra-continental rifts, and only the BVE microbial limestones are developed. Both types of limestones formed into mound-shoal bodies, that have the characteristics of large reservoir thickness and good physical properties. Based on the dissection of large pre-salt oil fields discovered in the Santos Basin, it has been found that both types of platforms could form large-scale combined structural-stratigraphic traps, surrounded by high-quality lacustrine and lagoon source rocks at the periphery, and efficiently sealed by thick high-quality evaporite rocks above, forming the optimal combination of source, reservoir and cap in the form of “lower generation, middle storage, and upper cap”, with a high degree of oil and gas enrichment. It has been found that the large oil fields are all bottom water massive oil fields with a unified pressure system, and they are all filled to the spill-point. The future exploration is recommended to focus on the inter-depression fault-uplift isolated platforms in the western uplift zone and the southern section of eastern uplift zones, as well as intra-depression fault-high isolated platforms in the central depression zone. The result not only provides an important basis for the advanced selection of potential play fairways, bidding of new blocks, and deployment of awarded exploration blocks in the Santos Basin, but also provides a reference for the global selection of deep-water exploration blocks in passive continental margin basins.

Lithofacies and Depositional Models of the Fine-Grained Sedimentary Rocks of the Albian–Turonian Stage in the Rio Muni Basin, West Africa

The Rio Muni Basin is a hotspot for deep-water oil exploration in West Africa. The discovery of thirteen oil and gas fields, including Ceiba, Akom 1, and Oveng, proves the basin’s excellent exploration prospects, but only limited research has thus far been carried out there. The recent new drilling indicates that there are organic matter-rich fine-grained sedimentary rocks in the Albian and Cenomanian–Turonian stages of the Cretaceous strata. However, the depositional models of organic-rich, fine-grained sedimentary rocks are not clear. The main objectives of this study are as follows: (1) to identify the lithofacies characteristics of fine-grained sedimentary rocks in the Albian–Turonian stages of the Rio Muni Basin; and (2) to establish a depositional model for organic-rich fine-grained sediments. In this study, the mineralogical characteristics of Albian–Turonian fine-grained were determined by means of X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and thin section analysis. In addition, the integration of mineralogical features with the total organic carbon (TOC) content allows for the recognition of three distinct lithofacies: (1) siliceous-clayey rock, (2) terrigenous clastic mixed fine-grained rock, and (3) lime-mixed fine-grained rock. Based on the evolutionary history of the passive continental margin basins in West Africa and the lithofacies characteristics, the deposition mode of organic-rich fine-grained sedimentary rocks in the Albian–Turonian stages was reconstructed by combining geochemical features with the characteristics of framboidal pyrite. The depositional models for the Albian stage are “continental margin–restricted sea–marine algae–source rocks” with the development of organic-rich fine-grained sedimentary rocks. The depositional models for the Cenomanian–Turonian stage are “continental margin–semiopen sea–mixed-source rocks”. The Albian and Cenomanian–Turonian organic-rich fine-grained sedimentary rocks represent two different deposition modes with restricted sea and semiopen sea conditions. The sedimentary characteristics in the study area during the two periods were both inherited and notably different.

Architecture Differences and Hydrocarbon Accumulation in Passive Continental Margin Basins in East Africa

In this paper, we study the structural characteristics and sedimentary filling differences of the passive continental margin basins of East Africa and establish hydrocarbon accumulation models in different basins. In the research process, the research methods of prototype basin and lithofacies paleogeography restoration, oil and gas reservoir anatomy, two-dimensional seismic data interpretation, etc. The passive continental margin basins in East Africa are divided into four types of passive continental margin basins, namely “rifted type,” “depressed type,” “faulted depression type,” and “reformed delta type,” based on the three prototype stages of intracontinental aborted rift, intracontinental-intercontinental rift, and passive continental margin basin, and the difference in sedimentary filling thickness between rift and depression periods. Finally, the accumulation models of different types of basins are established, and the favorable accumulation combinations and future exploration directions are discussed.

Analysis of the world deepwater oil and gas exploration situation

The global trends in deepwater oil and gas exploration, characteristics of deepwater oil and gas discovery, and layout of deepwater oil and gas exploration business by seven major international oil companies are systematically analyzed using commercial databases (e.g. S&P Global and Rystad) and public information of oil companies. The deepwater area is currently the most important domain for global oil and gas exploration and discovery, with the most discoveries and reserves in passive continental margin basins. The deepwater discoveries have the greatest contribution to the total newly discovered oil and gas reserves in the sea areas, with an increasing number of lithological reservoirs discovered, and oil and gas discoveries mainly distributed in the Mesozoic–Cenozoic. The seven major international oil companies are widely active in various aspects of deepwater oil and gas exploration and development, and play a leading role. Based on years of theoretical understanding of global oil and gas geology and resource evaluation, it is proposed that favorable deepwater exploration areas in the future will mainly focus on three major areas: the Atlantic coast, the Indian Ocean periphery, and the Arctic Ocean periphery. Six suggestions are put forward for expanding overseas deepwater oil and gas exploration business: first, expand the sources for obtaining multi-user seismic data and improve the scientific selection of deepwater exploration areas; second, increase efforts to obtain deepwater exploration projects in key areas; third, adopt various methods to access into/exit from resource licenses flexibly; fourth, acquire licenses with large equity and operate in “dual-exploration” model; fifth, strengthen cooperation with leading international oil companies in deepwater technology; and sixth, improve business operation capabilities and gradually transform from “non-operators” to “operators”.

Petrology and geochemistry of sandstone from Lower Cretaceous Kikhla Formation, NW Libya: Implications for provenance and depositional setting.

This study aims to determine and investigate the provenance of the source rocks and the depositional setting of the Kikhla Formation, northwestern Libya. It is mainly composed of mature quartzitic sandstone alternating with conglomerate and clay. The study proved that the sandstone is yellow-white in color and commonly carries quartz granular and small fragments of silicified wood. The environmental deposition is under differing fluvial conditions and by a large braided river. Texturally, the Kikhla sandstone is poorly cemented, coarse to very coarse grained and strongly unimodal and is classified as litharenite and subarkose by the modal composition, which is supported by geochemical studies. According to petrography and geochemistry, the Kikhla sandstone was deposited in a passive continental margin basin, mainly from granitic sources. On the basis of major elements ratios, and petrographic interpretation, the source rocks are most likely recognized as Proterozoic granites that were exposed via rifting. The CIA values (73.28-93.97) indicate a high degree of chemical weathering, which could be attributed to the arid climate conditions in the source area and mainly controlled by the source-rock provenance, hydraulic sorting during transport and deposition, diagenesis and depositional environment. According to chemical investigations, sandstone exhibits significant concentrations of SiO2, Na2O> K2O, and Fe2O3, which is compatible with the modal data.

Provenance and paleogeography of the Early Paleozoic basin in the northern Yangtze Block: Constraints from detrital zircon U-Pb-Hf data

The Proto-Tethys was a significant post-Rodinia breakup ocean that eventually vanished during the Paleozoic. The closure timing and amalgamation history of numerous microblocks within this ocean remain uncertain, while the Early Paleozoic strata on the northern margin of the Yangtze Block archive valuable information about the evolution of the Shangdan Ocean, the branch of the Proto-Tethys. By comparing the detrital zircon U-Pb-Hf isotopic data from Cambrian, Ordovician, and Silurian sedimentary rocks in the northern Yangtze Block with adjacent blocks, it was found that detrital zircons in Cambrian strata exhibit a prominent age peak at ∼ 900–700 Ma, which indicates that the primary source of clastic material in the basin was the uplifted inner and margin regions of the Yangtze Block. In the Silurian, abundant detrital material from the North Qinling Block was transported to the basin due to the continuous subduction and eventual closure of the Shangdan Ocean. This process led to two distinct age peaks at ∼500–400 Ma and ∼900–700 Ma, indicating a bidirectional provenance contribution from both the North Qinling Block and the Yangtze Block. This shift demonstrates that the initial collision between these two blocks occurred no later than the Silurian. The northern Yangtze Basin transitioned from a passive continental margin basin in the Cambrian to a peripheral foreland basin in the Silurian. Major blocks in East Asia, including South Tarim, North Qilian, North Qinling, and North Yangtze, underwent peripheral subduction and magmatic activity to varying degrees during the late Early Paleozoic, signifying the convergence and rapid contraction of microplates within northern Gondwana and the Proto-Tethys Ocean. These findings provide new insights on the tectonic evolution of the Proto-Tethys Ocean.

Present geothermal field of the Santos Basin, Brazil

The Santos Basin, located in the southeastern waters of Brazil, is a passive continental margin basin with the most abundant deepwater petroleum resources in the world discovered to date. However, few studies have been conducted on the present geothermal fields of the Santos Basin, which severely restricts the oil and gas resource evaluation of the basin. This study first utilizes 35 temperature data from 16 post-salt drilling wells and 370 temperature data from 31 pre-salt drilling wells to calculate the post-salt and pre-salt geothermal gradients and terrestrial heat flows in the Santos Basin. Then, the basin simulation software BasinMod 1D is used to quantitatively evaluate the impacts of salt rock sedimentation on the present geothermal fields and the maturity of pre-salt hydrocarbon source rocks. The results demonstrate that the present post-salt geothermal gradient in the Santos Basin is 2.20–3.97 °C/100 m, with an average value of 2.99 °C /100 m, and the post-salt terrestrial heat flow is 54.00–97.32 mW/m2, with an average value of 73.36 mW/m2, while the present pre-salt geothermal gradient is 2.21–2.95 °C/100 m, with an average value of 2.53 °C/100 m, and the pre-salt terrestrial heat flow is 61.85–82.59 mW/m2, with an average value of 70.69 mW/m2. These values are characteristic of a low-temperature geothermal field in a zone with a stable structure. The sedimentation of the salt rock causes a decrease in the temperature of the pre-salt strata, which inhibits pre-salt hydrocarbon source rock maturity, with an inhibition rate of up to 1.32%. The inhibition degree decreases with increasing salt rock thickness. At the same time, the salt rock thickness is positively correlated with the present surface heat flow. The unique distribution of the salt rock and related salt structures lead to present terrestrial heat flow differences among different structural units in the basin. This study is of great significance for evaluating and exploring the pre-salt oil and gas resources in the Santos Basin.

The Origin of the Black Shale Series and Bentonites from the Wufeng Formation in the Southwestern Upper Yangtze: Implications for the Convergence of the Yangtze and Cathaysia Blocks in the Late Ordovician

AbstractEarly Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boundary. However, the intimate relationship between their origins and the dynamic mechanisms are unclear, as exemplified by the genesis of the black shale series and bentonites from the Wufeng Formation during the Ordovician–Silurian transition (OST). In order to reveal the relationship between the Wufeng Formation and the convergence of the Yangtze and Cathaysia blocks (i.e., the intracontinental Kwangsian Orogeny), two stratigraphic sections respectively in Zhaotong area (Northeast Yunnan) and Puyi area (Northwestern Guizhou) that were located in the semi‐restricted inner Yangtze Sea during the OST were systematically studied, on the basis of whole‐rock geochemical composition, pyrite δ34S (δ34Spy), total organic carbon (TOC), stable Sr isotope, pyrite framboid size distribution and zircon U‐Pb age, trace elements. The evidence shows that the paleo‐oceanic environment changed significantly at the turn of the early–late Katian and formed the black shale series in the Wufeng Formation. These acritarch assemblages were formed in the transition process of the Upper Yangtze Basin from passive continental margin basin to foreland basin during this interval. Based on previous research on the genetic relationship between black shale series and plate tectonic movement, a basin‐mountain evolution model suitable for South China in the Late Ordovician is presented. The two bentonites in the Wufeng Formation with U‐Pb ages of 445.5 ± 0.8 Ma and 441.9 ± 2.4 Ma primarily originated from the intermediate–acid volcanic eruption during the collision and convergence between the Yangtze and Cathaysia blocks in the Late Ordovician, the provenance region probably being located in the Jiangnan orogenic belt. Thus, we believe that the appearance of the black shale series and bentonite in the Wufeng Formation at the turn of the early–late Katian may represent the initiation of basin‐mountain transformation and the Kwangsian Orogeny in South China, which provides important evidence for the collision and convergence of the Yangtze and Cathaysia blocks in the Late Ordovician.

Newly discovered ca. 1.6 Ga K-bentonite layers from the Lakharpata Group in Nepal Lesser Himalaya: Implications for basin evolution during the Columbia breakup

• Zircon U-Pb age for newly discovered K-bentonite (ca. 1.6 Ga) constrained the deposition time of the Lakharpata Group. • The Lakharpata Group in Nepal Lesser Himalaya is coeval sediment with the Lower Vindhyan in India. • The Lakharpata Group was deposited in a passive continental margin basin during the Columbia breakup. The Lakharpata Group, a set of marine sediments with a thickness of over 5000 m, occupies the middle part of the Lesser Himalayan sequence and records important tectono-sedimentary evolution in the northern margin of the Indian continent. However, the duration of deposition and tectonic background of the Lakharpata Group are poorly defined. This study presents zircon U-Pb ages and Hf isotopes, as well as petrochemical data for the newly discovered K-bentonite layers in the Aru Formation, the upper part of the Lakharpata Group. Integrating the detrital zircon ages of the underlying metasedimentary rocks and the sedimentation rate of dolomite in the South China Block, we suggest that the Lakharpata Group was deposited during the late Paleoproterozoic to early Mesoproterozoic (ca. 1680–1580 Ma) rather than from Mesoproterozoic to Early Paleozoic as previously presumed. Stratigraphic correlations show the Lakharpata Group in Nepal Lesser Himalaya correlates to the Lower Vindhyan Supergroup, as well as to the Deoban and Rautgara formations in Kumaun Lesser Himalaya and the Baxa Group in Sikkim Lesser Himalaya, India. The Lakharpata Group comprises two depositional sub-sequences that record two transgression-regression sedimentary processes, which are comparable to the Lower Vindhyan. Geochemical and sedimentological studies suggest that the Lakharpata Group may represent the deposition of a passive continental margin basin during the breakup of the Columbia supercontinent.

Analysis of the world oil and gas exploration situation in 2021

The global exploration investment, new oil and gas discoveries, exploration business adjustment strategies of oil companies in 2021, and future favorable exploration domains are systematically analyzed using commercial databases such as IHS and public information of oil companies. It has been found that the world oil and gas exploration situation in 2021 has continued the downturn since the outbreak of COVID-19. The investment and drilling workload decreased slightly, but the success rate of exploration wells, especially deepwater exploration wells, increased significantly, and the newly discovered reserves increased slightly compared with last year. Deep waters of the passive continental margin basins are still the leading sites for discovering conventional large and medium-sized oil and gas fields. The conventional oil and gas exploration in deep formations of onshore petroliferous basins has been keeping a good state, with tight/shale oil and gas discoveries made in Saudi Arabia, Russia, and other countries. While strengthening the exploration and development of local resources, national, international, and independent oil companies have been focusing on major overseas frontiers using their advantages, including risk exploration in deep waters and natural gas. Future favorable exploration directions in the three major frontiers, the global deep waters, deep onshore formations, and unconventional resources, have been clarified. Four suggestions are put forward for the global exploration business of Chinese oil companies: first, a farm in global deepwater frontier basins in advance through bidding at a low cost and adopt the “dual exploration model” after making large-scale discoveries; second, enter new blocks of emerging hot basins in the world through farm-in and other ways, to find large oil and gas fields quickly; third, cooperate with national oil companies of the resource host countries in the form of joint research and actively participate exploration of deep onshore formations of petroliferous basins; fourth, track tight/shale oil and gas cooperation opportunities in a few countries such as Saudi Arabia and Russia, and take advantage of mature domestic theories and technologies to farm in at an appropriate time.

The Late Cretaceous—Miocene supra‐salt structures in Block M, Lower Congo Basin (Congo, West Africa) and the controls on channel development

The Lower Congo Basin is a typical passive continental margin basin of West Africa and is currently the focus and hot spot of deep‐sea oil and gas exploration. Previous studies have focused on the deformation process and mechanism of the salt rock itself, but have ignored the interaction process between the faults and salt diapirs. The direct influence of the interaction process between the faults and salt diapirs on oil and gas exploration is reflected in the control of the reservoir distribution. In recent years, most of the oil and gas discovered in the Lower Congo Basin have been concentrated in the Oligocene–Miocene turbidite reservoirs, and the distribution of channel sand bodies is largely affected by supra‐salt tectonic activity. In this study, Block M in the Lower Congo Basin was selected for study. Based on the 3D seismic, drilling, and logging data, the typical structural styles and stress mechanisms were analysed. The 2D Move software was used to restore the tectonic evolution history and, based on this, established the interaction model of salt diapirs and faults, and summarized the action modes of diverse types of sedimentary channels. The research results are expected to lay the foundation for follow‐up studies on the laws of hydrocarbon accumulation.

Neoproterozoic extensional basins and its control on the distribution of hydrocarbon source rocks in the Yangtze Craton, South China

• Neoproterozoic source rocks in the Yangtze Craton. • Structural and sedimentary patterns of the extensional basins evaluated. • The source rocks are related to the extensional basins, climate and life evolution. • Favorable areas for the source rock distribution are predicted. Hydrocarbon exploration in the Neoproterozoic extensional basins in the Yangtze Craton of South China has made prominent progresses in the past decades. However, the spatial distribution of source rocks across the craton still remains unclear. Here, we use outcrop observations, borehole data, and reflective seismic profiles to investigate the prototype, distribution and sediment infilling of these basins in the Yangtze Craton during the periods of source rock deposition. The basin prototype is categorized based on its tectonic origin and structural-sedimentary feature as follows. (1) During the deposition of the Datangpo Formation, rift basins extensively developed, band are characterized by a series of graben or half graben structures that consist of basin-controlling normal faults. The source rocks in the Datangpo Formation were deposited as the inner shelf basin or deep shelf facies, obtaining high thickness (i.e., 200 m) in the Wuling rift basin. (2) During the deposition of the Doushantuo Formation, the intracratonic rift basin and passive continental margin basin formed. These basins were controlled by syn-depositional faults that inherited the existing rift fault structures. The source rocks of the Doushantuo Formation were deposited as shelf lagoon, slope to deep-water basin facies. (3) During the deposition of the Dengying Formation, the intraplatform rift basin and passive continental margin basin developed with influence of regional tectonic extension. Not only are these basins affected by the preexisting faults, but also by the newly developed syn-depositional faults. The argillaceous source rocks of the Dengying Formation deposited as slope and deep-water basin facies. Further in-depth analyses revealed that a range of mechanisms may have contributed to the formation and distribution of source rocks in the Yangtze Craton, such as the break-up of the Rodinia Supercontinent, paleaolatitudes, glacial-interglacial geological events, basin extension and sedimentary environments. By integrating the distribution of the source rocks and the late tectonic reworking, this study predicts several targets for the source rock distribution in the Yangtze Craton, including in the central Sichuan, northeastern Sichuan, southern Shanxi, western Hubei, northeastern Guizhou-western Hunan, and the northeastern Guangxi-central Hunan areas.

Ordovician Proto–basin in South China and its Tectonic Implications: Evidence from the Detrital Zircon U–Pb Ages of the Ordovician in Central Hunan, China

AbstractCaledonian orogeny is another important tectonic event in South China Block after the breakup of the Rodinia supercontinent. With a view to constrain the tectonic evolution and proto–basin in South China, this paper reports the geochemical and zircon U‐Pb dating data of the Ordovician strata in central Hunan, South China. Geochemical features and paleocurrent directions suggest that the lower Ordovician deposited in a passive continental margin basin with a provenance of quartzose components and showing an affinity with the Yangtze Block. U‐Pb age data for 260 detrital zircons from upper Ordovician identify three major age populations as: 900–1200 Ma, 1400–1800 Ma and 2400–2700 Ma. The detrital zircon age spectrum as well as the paleocurrent directions suggest that upper Ordovician deposited in a foreland basin and showing a close affinity with the Cathaysia Block. It is also suggest that the lower Ordovician continuously accepted the mineral from the Yangtze Block, whereas the provenance of the upper Ordovician sedimentary basin changed from the Yangtze Block to the Cathaysia Block. This change implies a tectonic movement, which caused the transformation of the proto–basin in the Hunan area in SCB from passive continental margin basin to foreland basin probably took place during late Ordovician. This fact also demonstrate that the Caledonian orogeny in South China Block began no later than 453 Ma, and a new crustal evolution model is proposed.

Petrography, geochemistry, and provenance of Jurassic sandstones from the Sakarya Zone, NW Turkey

The Jurassic sandstones exposed in the western part of the Sakarya Zone are yellowish to brown, moderate to well sorted, medium to coarse-grained, grain-supported, and cemented by calcareous and minor silica. Sandstones are mainly classified as litharenite, subarkose, and arkose according to the relative proportions of quartz, feldspar and rock fragments, and major element ratios. On the SiO2 variation diagram, Na2O and K2O show slight positive correlations, which could reflect abundance of sodic plagioclase and K-feldspar with quartz within high Si-content sandstones. Sandstones generally exhibit slight LREE enrichment with respect to HREEs. The REE plots are characteristic for sedimentary rocks derived from the upper continental crust. Combining the results of several provenance discrimination diagrams, elemental ratios (Th/Sc, Zr/Sc, La/Th), and REE contents in sandstones, they reveal that the sandstones originated from intermediate to felsic source rocks. Accordingly, the probable source of the Jurassic sandstones is the crystalline basement of the Sakarya Zone consisting of Devonian, Carboniferous, and Permian granitoids, and high-grade metamorphic basement rocks. The Jurassic sandstones mostly have characteristic features of passive continental margin basins. It can be noted that the sandstones may have been deposited in a marginal basin that began to open in Early Jurassic time. CIA and CIW values for the Jurassic sandstones suggest that the source area was subject to low to moderate chemical weathering under semihumid to semiarid climatic conditions.

Sedimentologic and stratigraphic constraints on the orientation of the Late Triassic northern Indian passive continental margin

The orientation and distribution of the northern Indian passive continental margin basin during different epochs constrained the geometric characteristics of the hyperextended northern Indian edge (“Greater India”). Traditional paleogeographic reconstructions envisage the Late Triassic northern Indian passive continental margin as E/W-trending, whereas paleomagnetic data support an ~55° counterclockwise rotation during northward drifting. This case study of Upper Triassic units from the northern Indian margin, based on facies analysis, sandstone petrography, heavy mineral assemblages, U-Pb detrital zircon geochronology, and stratigraphic correlation from the Zanskar Range to southern Tibet, provides new constraints and suggests that the northern Indian passive continental margin might have been N/S-trending in the Late Triassic. Given the dominance of quartz sandstones with zircon, tourmaline and rutile—indicating a provenance from continental blocks and the recycling of older quartz-rich sandstones—and detrital zircon age spectra characterized by a Neoproterozoic detrital zircon U-Pb age peak (921 ± 13 Ma), the Upper Triassic sandstones widespread along the Tethyan Himalayas may have been partly derived from the Eastern Ghats Mobile Belt in eastern India and the Rayner Orogen in eastern Antarctica. The Upper Triassic Quartzite Series comprises feldspatho-quartzose to pure quartzose sandstones with intercalated bioclastic oosparites deposited in backshore, foreshore and shoreface coastal environments. Without considering the subsequent counterclockwise rotation of India, the consistent pattern of the Upper Triassic bidirectional E-W paleocurrent observed throughout the Himalaya suggests that the paleoshoreline was striking near N-S, approximately perpendicular to the regional orientation of the northern Indian margin. Progressive eastward thickening of the sandstone layers and eastward younging of the Quartzite Series suggest diachronous sedimentation. Such stratal patterns and the strike of the Late Triassic paleoshoreline were attributed to the Neo-Tethys transgression from the Zanskar Range to southern Tibet.

Cenozoic thermal history reconstruction of the Dongpu Sag, Bohai Bay Basin: Insights from apatite fission‐track thermochronology

AbstractKnowledge of the thermal history of the onshore Dongpu Sag (DPS), Bohai Bay Basin is important for understanding its tectonic development within a broader regional context and for elucidating its poorly studied source‐rock maturation history. To unravel DPS time‐temperature development, apatite fission‐track data were acquired from eight sandstone samples in three deep wells. Thermal history modelling indicates continuous heating during the rifting stage (early Eocene to late Oligocene), followed by cooling attributed to tectonic uplift between ~27 and ~16 Ma, which resulted in the removal of ~1,400 to 1,800 m of section. Reheating occurred during the subsidence stage from middle Miocene until present. Unlike typical passive continental margin basins, the DPS experienced accelerated post‐rifting subsidence from ~5.8 Ma, which was especially marked since ~2.6 Ma. This phase was probably triggered by normal fault reactivation, in combination with a variation in the deep heat flow pattern.

Cambrian tectonic evolution of the northwestern Ordos Terrane, North China: constraints of stratigraphy, sedimentology and zircon U–Pb geochronology

The Helanshan Tectonic Belt and its environs within the northwestern Ordos Terrane, western North China Craton, have been envisaged as aulacogen or plate boundary separating the Alxa Massif from the Ordos Block during Cambrian. However, it conflicts with geological and geophysical facts. This study presents integrated stratigraphic, sedimentary and geochronological data from the Cambrian strata in the northwestern Ordos Terrane to constrain the Cambrian tectonic evolutionary process of the western North China Craton. The Cambrian successions comprise, in ascending order, evaporite platform facies, restricted-open platform facies and evaporite platform facies, featuring a vertical transgression–regression sequence. An eastward-shoaling paleogeography was documented, evidenced by shallow-water dolomite layers enriched in the east and the detritus derived from northeast. Ages of detrital zircons span from 2566 to 1649 Ma with predominant two peaks around 2500 and 1850 Ma, suggesting these Cambrian detritus were sourced from the Archean–Paleoproterozoic rocks in the Yimeng highland. Comparable fossil associations and unified paleogeography system supported that there was no Cambrian plate boundary in the northwestern Ordos Terrane, implying the Alxa Massif was part of the North China Craton during the Cambrian. The westward-deepening facies differentiation with low-angle topography contradicts with the tectonic model of “Helan aulacogen”. In combination with the relatively low subsidence rate and rare magmatic–metamorphic activities, we argue that the Cambrian shallow marine system in the western North China Craton was the continent-ward extension of passive continental margin basin system related to the spreading of the Paleo-Asian Ocean.

The Neoproterozoic southern passive margin of the São Francisco craton: Insights on the pre-amalgamation of West Gondwana from U-Pb and Hf-Nd isotopes

Sedimentary basins are, in many cases, the only preserved record of the geological processes active through geological time. These deposits preserve age, isotopic and geochemical signatures of the source rocks, providing insights into tectonic setting. In this context, we investigate the lithostratigraphy, provenance and tectonic environment of the Carrancas Group, a meta-sedimentary sequence characterised by a basal psammitic unit (Lower Unit) passing up into interbedded psammo-pelites (Intermediate Unit), which are overlain by a further psammitic unit (Upper Unit). This succession, along with the Canastra, Paranoá and Vazante groups (Brasília orogen), comprises a mature passive margin developed at the western-southern margin of the São Francisco craton during the Neoproterozoic. Detrital zircon U-Pb ages and Nd-Hf isotope data enable revised stratigraphic correlations across the basin, highlighting variations in the source of detritus. Deposition began after 0.92 Ga, with the sedimentation of the Lower Unit, with input of juvenile ∼2.1 Ga detritus (εNdt = −0.1 to +3.2) derived from the São Francisco craton. A marine transgression characterises the transition to the Intermediate Unit, which gradually covered over juvenile ∼2.1 Ga terrains and rendered them unavailable as possible source rocks for detrital zircons. Evolved Archaean-Palaeoproterozoic basement rocks, the Espinhaço Supergroup and evolved Neoproterozoic granitoids, all belonging to the São Francisco craton, acted as sources for the Intermediate and Upper units (U-Pb = 2.7 Ga to 0.9 Ga; εNdt = −10.4 to +7.1). The Goiás massif might also have acted as a source, providing juvenile Mesoproterozoic detritus. The sediments of the Upper Unit register a significant shift in source, with incoming of juvenile Mesoproterozoic and crustal 1.9 – 1.7 Ga detritus. This change in the ages of the detrital material may be related to exhumation of the Espinhaço Supergroup during the evolution of the passive continental margin basin. The whole-rock Nd TDM model ages become progressively younger from the base to the top of the sequence (Nd TDM = 2.6–1.8 Ga). The collisional events between Amazonian and São Francisco cratons and the Paranapanema block set the minimum age of deposition along this passive continental margin at around 0.67 Ga.