Basin Evolution Research Articles

Paleobiodiversity and paleoenvironments of the eastern Paratethys Pleistocene lacustrine-palustrine sequence in the Baklan Basin (SW Anatolia, Turkey)

The Lower-Upper Pleistocene sedimentary record of the Baklan Basin, a long-lived continental half-graben basin in SW Turkey, is characterized by shallow lacustrine and palustrine deposits. The paleoenvironmental changes recorded in the basin succession allow for a multiproxy approach in reconstructing the paleoclimatic, paleoecological, and paleobiogeographical evolution of southwestern Anatolia during the Early-Late Pleistocene. Based on sedimentological, paleontological, and geochemical data, three main types of depositional intervals have been identified, corresponding to different phases of a lake expansion cycle: The first interval is characterized by the perennial shallow lake environment (PSL deposits), which represents the very early stage of the Early Expansion System Tract (VEEST). This suggests a very early stage of lake transgression in arid climate conditions. The second interval is represented by the palustrine carbonate lake center environment (PLC deposits), which corresponds to the late stage of the Early Expansion System Tract (LEEST). This indicates a late early stage of lake transgression in semiarid to subhumid climates. The third interval is marked by the palustrine lake margin environment (PLM deposits), which represents the Late Expansion System Tract (LEST) under humid conditions.The Lower-Upper Pleistocene successions of the Baklan Basin provide an excellent example of lacustrine and palustrine deposition in a laterally extensive, low-gradient, shallow lake system in the semi-isolated Pontocaspian freshwater to slightly brackish water (oligohaline-low mesohaline) long-lived lake. The presence of Pontocaspian ostracod and mollusc faunas in the studied successions indicates that the largest major Caspian transgression around 2.6 millon years ago extended to SW Anatolia. The studied successions represent a rich archive of landscape, climate, and biotic development in the eastern Paratethys region during the Early-Late Pleistocene. The biogeographic signature of fossil faunas (mammals, ostracods, molluscs, and fishes) and floras (Characeae) is predominantly modern Palearctic and Holarctic, with a minor amount of endemic Pontocaspian elements. This study presents the Pleistocene Pontocaspian species of the Anatolian lakes that may have served as refugia for the Palearctic taxa during adverse time intervals. Consequently, this study shows that Lower-Upper Pleistocene lacustrine to palustrine sedimentation in the Baklan Basin has been controlled by the combination of tectonics, climate changes, and the largest major Caspian Sea transgression. The findings of this study could be used to evaluate the impact of similar allocyclic factors on the sedimentological, hydrological, and geochemical development of other intermontane lake basins.

U–Pb geochronology of detrital zircon from the Ediacaran and Cambrian sedimentary successions of NE Estonia and Volyn region of Ukraine: Implications for the provenance and comparison with other areas within Baltica

Trends in detrital zircon age distribution patterns are used to constrain the paleotectonic and paleogeographic conditions during deposition of the late Ediacaran - Early Cambrian sedimentary successions in northwestern, western, and southwestern Baltica. Detrital zircons from three sandstone samples collected from a drill-core drilled in northeastern Estonia and four sandstone samples collected from three drill-cores located in the Volyn region of Ukraine were dated using the U-Pb LA-ICP-MS isotope technique. The resulting age patterns are compared with the published data for southwestern Ukraine and Moldova, eastern Poland, Belarus, and northwestern Russia to constrain the late Ediacaran - Early Cambrian evolution of the sedimentary basins developed on Baltica. All sedimentary basins from these areas of Baltica show a transition during that interval from a passive continental margin to collisional settings, which has been triggered by the pre-Schythides and Santacrusades orogenies along the south-southwestern and, to a lesser extent, by the Timanian Orogeny along the north-northeastern and eastern (in modern coordinates) margins of Baltica.

Mechanical strength and nature of lithospheric deformation beneath the rifted sedimentary basins of the east India passive margin

The study of gravity signatures corresponding to sediment load over the passive margins is helpful to constrain the mechanical properties of continental rift systems as well as the adjacent ocean basins. Seismic reflection, free-air gravity and well information from the East India Passive Margin (EIPM) are investigated through spectral approach and 2D process-oriented gravity modelling for quantifying effective elastic plate thickness (Te) to understand the rift mechanisms and the sedimentary basins evolution. The characteristics of lithosphere within the major structural domains along the margin are quite variable. A narrow necking zone (40 km) in the southern segment, and approximately a 70 km hyper-thinned and exhumed domains are inferred in the central segment, while a narrow hyper-thinned domain (30–35 km) is observed in the northern segment of the margin. The southern segment of EIPM, adjacent to Southern Granulite Terrain has low Te values ranging from 5 to 10 km. The segment in the central margin, offshore Dharwar Craton has moderate Te values of 15–20 km. And the northern segment adjacent to onshore Eastern Ghats Mobile Belt has relatively high mechanical strength with Te values ranging from 25 to 35 km. The pattern of Te values and extent of major structural domains along the margin indicates that the southern, central and northern segments evolved as three different modes of rifting such as transform, hyperextended and hypoextended, respectively. In the oceanic domain, the lithospheric strength broadly increases with age following the thermal induced cooling plate model (600 °C isotherm). The thick sedimentary basin of the Bay of Bengal had attained the high value of elastic thickness (Te > 45 km) in the last 23 Myrs. The significant rheological strengthening of the oceanic lithosphere may be attribute to the following reasons: 1) increase in shear-wave velocity anomaly at a depth of 150 km and upper mantle density, 2) change in plate curvature caused by excessive deposition of Bengal Fan sediments in the deep ocean basins and subduction of oceanic plate under the Eurasian plate near the Bengal Fan and 3) modification of stress state of the lithosphere as a convergent interaction of the Indian plate with SE Asia.

Structural and geochronological constraints for the Mesozoic nappe structures of the Taqian–Fuchun thrust zone, eastern Jiangnan orogenic belt, South China

The NE‐trending Jiangnan orogenic belt has experienced multi‐tectonic episodes since the Mesozoic separates the Yangtze Block in the north‐west from the Cathaysia Block in the south‐east. The Taqian–Fuchun thrust zone in north‐east Jiangxi Province is located in the eastern Jiangnan orogenic belt. It is considered as an essential unit to understand the geometry, kinematics and dynamics of the Mesozoic nappe structures in the eastern Jiangnan orogenic belt and an ideal region to reveal the Mesozoic tectonic evolution in South China. Here, we present new detailed structural data coupled with zircon U–Pb and apatite fission‐track dating studies, establishing a four‐stage deformation history and describing the geometry, kinematics, ages and dynamic background. The Middle–Late Triassic NW–SE compression event (D1, 243–226 Ma) is mainly characterized by regional angular unconformity between the Lower and Upper Triassic and asymmetric folding of the underlying strata. The associated regional NW–SE shortening was related to the intercontinental collision. The Middle–Late Jurassic NW–SE compression event (D2, 175–160 Ma) is characterized by the angular unconformity between the Middle Jurassic and Cretaceous and the SE‐vergent imbricate nappe structures. The shortening has been associated with the NW‐ward subduction of the Paleo‐Pacific Plate. The Late Jurassic–Cretaceous NW–SE extension event (D3, 160–67 Ma) includes the transition stage from compression to extension (160–145 Ma) and the intensive extension stage (145–67 Ma). The former is characterized by the development of the extensional detachment structures and intermediate‐acid magmatism, while the latter is characterized by the development of Cretaceous extensional sedimentary basins and A‐type granites. This extension was correlated to the slab roll‐back of the Paleo‐Pacific Plate. The Paleocene–Eocene compression event (D4, 67–35 Ma) is manifested by the thrusting of metamorphic rocks in the Shuangqiaoshan Group to the Cretaceous red beds. This shortening possibly originated from the collision between the India and Eurasian Plates. This study provides new constraints on the Mesozoic structural style and establish a reliable geochronological framework of the Mesozoic tectonic evolutions of the eastern Jiangnan orogenic belt.

Spatially heterogeneous lithospheric architecture of the Cambay rift basin and adjoining Aravalli-Delhi Fold Belt, western India – A synthesis of magnetotelluric results

The Cambay rift basin (CRB) evolution has been associated with separation of the Indian continent from the African continent and subsequent interaction with the Réunion mantle plume, which resulted in significant alternations in the regional lithospheric structure of western India, more prominently in the CRB due to its proximity to the plume track. In our continued effort to delineate the lithospheric structure of the CRB and adjoining regions, we acquired magnetotelluric (MT) data at 31 sites along a profile across the CRB and analyzed these. The 2D geoelectric model derived from this dataset reveals a collage of conductive and resistive formations. The resistive blocks indicate the Archaean lithosphere on the west, the uplifted crust within the CRB, and various structural units of the Precambrian Era on the east providing evidence for continuation of the Aravalli-Delhi Fold Belt trend beneath the CRB into Saurashtra. The conductive anomalies beneath the CRB infer the magmatic underplating associated with thermal influx derived from the upper mantle as a result of the Réunion plume interaction. Integration of previous geophysical and present results infers a spatially heterogeneous lithosphere possibly representing an assemblage the Archaean and Proterozoic lithospheres beneath the CRB. The Proterozoic lithosphere is more vulnerable to the impact of the Réunion plume due to its weak nature in comparison to the Archaean lithosphere. The Archaean lithosphere on the western side of CRB indicates initial stage of rifting, whereas Proterozoic lithosphere infers second stage coeval with the Deccan volcanic eruption. The heterogeneity in sedimentary thickness within the CRB spatially correlates with the contact of Archaean and Proterozoic lithospheres, which might have played a role in the formation of the basin structure, and sediment deposition.

The Cambrian sequence filling process and sedimentary evolution of the Kuruktag area in the northeastern margin of the Tarim basin

The Kuruktag area in Xinjiang is located between the northeastern margin of the Tarim Basin and the South Tianshan orogenic belt, and its complex tectonic background has been extensively studied to assess the tectonic evolution of the Central Asian orogenic belt and the Tarim Craton. Although the Cambrian strata in the study area are well developed and continuous, due to the limitations of the outcrop environment and drilling and seismic data, studies of the sequence stratigraphy and sedimentary evolution have been limited and have yielded results with low accuracy, leading to limited knowledge of the local structure. In this paper, field observations and actual measurements of the stratigraphic profile, supplemented by perimeter logging and seismic data for stratigraphic sequence comparison, are collected, and sea level changes and controlling factors are discussed. Studies have shown that various types of sequence interfaces are present in the Kuruktag area, and three grade II and six grade III type-II sequences can be identified. The grade II and III sequences are composed of a transgressive systems tract (TST) and a highstand systems tract (HST), and the depositional thickness of the TST is less than that of the HST. The northern area has experienced an evolutionary process from a deep-sea basin to a deep-sea shelf, a shallow-water shelf, and a platform edge slope, while the southern area has evolved from a deep-sea basin to a deep-water shelf and shallow-water shelf before again transitioning to a deep-water shelf during the ЄSQ1-ЄSQ6 peroid. The sedimentary facies evolution and sequence structure indicate that the Kuruktag area has experienced a process of rapid large-magnitude transgression and slow regression in terms of sea level. In addition, the curve of sea level change for the Kuruktag area is quite different from the corresponding curves for the Tarim platform facies area and the North China platform. This difference is associated with the evolution of the Kuruktag rift basin.

Cenozoic tectonosedimentary evolution of the Linxia Basin, northeast Tibetan Plateau based on an analysis of detrital zircon provenance

The Linxia Basin is an important region for understanding the tectonism and uplift history in the northeast Tibetan Plateau, and also contains rich mammalian faunas of evolutionary significance. In this paper, we conduct a provenance study of Cenozoic sediments, relying primarily on U-Pb dating of detrital zircons, to investigate the exhumation history of surrounding terranes and to gain a better understanding of the relationship between tectonism, basin development and paleoenvironment.Samples were collected from the Maogou section in the central Linxia Basin, which has been recently dated by magnetostratigraphy. Detrital zircon populations show five UPb age groups of 65–350 Ma, 350–600 Ma, 600–1600 Ma, 1600–2200 Ma and 2200–2600 Ma; however, UPb age patterns varied up-section, indicating different sources at different times.Sediments from the lower part of the section (>27.8 Ma) were sourced from multiple regions, including the distal East Kunlun Shan, Qilian Shan, and Songpan–Ganzi terranes, and as well as the proximal West Qinling region. Contributions from the Songpan–Ganzi terrane increased considerably during the late Oligocene (27.8–23 Ma), as a result of strong tectonic movements of the northeastern Tibetan Plateau. During the early Miocene (23–17.2 Ma), the northern sources of the Laji Shan–Maxian Shan region supplied more sediments to the basin, indicating the uplift and exhumation of these mountain ranges. Until the middle Miocene (17.2–12.8 Ma), the Songpan-Ganzi terrane and the northern sources dominated the basin sediments, while the northern sources and the Jishi Shan region became increasingly important sources at around 11.6 Ma. This study explores the tectonosedimentary evolution of the Linxia Basin in the northeastern Tibetan Plateau, providing a reference for further research of the paleoclimate and mammalian evolution in this critical region.

Spatio-temporal evolution characteristics of eco-efficiency in the Yellow River Basin of China based on the super-efficient SBM model.

It is of great significance to study the trends and internal differences of eco-efficiency in the Yellow River Basin for ecological protection and high-quality development of the Yellow River Basin. According to the characteristics of the Yellow River Basin in China, the eco-efficiency evaluation system was constructed, and the super-efficiency slack-based measure (SBM) model and the super-efficiency SBM model of undesired output were used to calculate the eco-efficiency levels of provinces in the Yellow River Basin from 2005 to 2020, and the variation trend and internal differences were analyzed. The results show that when only the expected output was considered, the eco-efficiency of the Yellow River Basin as a whole and each province showed a fluctuating upward trend, but there were obvious differences. Qinghai Province, Sichuan Province, and Ningxia Autonomous Region had high eco-efficiency, while Shaanxi Province, Shanxi Province, and Inner Mongolia Autonomous Region had low eco-efficiency. Compared with only considering the expected outputs, eco-efficiency of Qinghai Province had improved significantly when considering non-expected outputs. The eco-efficiency of Shandong Province and Henan Province had improved significantly after 2016, while the eco-efficiency of the two provinces had decreased significantly before 2016. The eco-efficiency of Shaanxi, Shanxi, Inner Mongolia, Ningxia, and Gansu had declined to varying degrees. Finally, the reasons for the differences in eco-efficiency in various provinces in the Yellow River Basin were analyzed, and suggestions for improving the eco-efficiency of the Yellow River Basin were put forward.

Australia’s Onshore Basin Inventories – foundational knowledge synthesis for better design of precompetitive data acquisition

Geoscience Australia’s Onshore Basin Inventories project provides a whole-of-basin inventory of geology, petroleum systems, exploration status and data coverage of hydrocarbon-prone onshore Australian sedimentary basins. Two existing volumes cover many central and north Australian onshore basins, providing a single point of reference and creating a standardised national basin inventory. In addition to summarising the current state of knowledge within each basin, the onshore basin inventory reports identify critical science questions and key exploration uncertainties that may help inform future work program planning and aid in decision making for both government and industry organisations. Under Geoscience Australia’s Exploring for the Future (EFTF) program, several new onshore basin inventory reports are being delivered. The next releases include the Adavale Basin of southern Queensland and a compilation of Australia’s Mesoproterozoic basins. These reports are supported by value-add products that address identified data gaps and evolve regional understanding of basin evolution and prospectivity, including petroleum systems modelling, seismic reprocessing and regional geochemical studies. The Onshore Basin Inventories project continues to provide scientific and strategic direction for precompetitive data acquisition under the EFTF work program, guiding program planning and shaping post-acquisition analysis programs.

Hydrocarbon potential assessment of the lacustrine fan delta reservoirs in the Lower Cretaceous syn-rift Xing’anling Formation in the Beier Sag, Hailar Basin, Northeast China

Efficient exploration and development of oil and gas resources in complex geological environments continue to pose significant challenges for the energy industry. The localization and extraction of reservoirs in basins with complex structures, developed faults, and scattered sedimentary sand bodies are topics of international interest. One such basin, the Hailar Basin in northeastern China, represents a complex geological environment with heterogeneous distributions of oil and gas reserves, along with variable reservoir conditions, leading to challenges in hydrocarbon exploration and extraction. The Sudeert oil field, situated within this basin, is known for its high productivity; nevertheless, the underlying factors responsible for its success are not yet fully comprehended. Based on seismic, logging, and core data from the Sudeert oil field, as well as previous research, this study comprehensively analyzed the sedimentary environment, sedimentary facies characteristics, sand body distribution patterns, vertical stacking relationships of sand bodies, and hydrocarbon accumulation potential of the oil reservoirs in the Lower Cretaceous Xing’anling Formation in the Sudeert oil field. The Xing’anling Formation I and II oil reservoirs are deposited in a fan-delta front sedimentary environment, and the sedimentary microfacies that are conducive to the development of reservoir sand bodies include underwater distributary channels, underwater natural levees, estuary dams, front silt beds, and turbidite sands. Among them, the underwater distributary channel microfacies is the main depositional facies for the development of reservoir sand bodies. Three major depositional patterns of fan lobes can be identified within this depositional system: 1) isolated, 2) contact, and 3) superimposed lobes. Different combinations of lobes developed in different blocks and resulted in different sand body depositional patterns. The isolated lobes mainly developed in the western oil-producing (B28 block) due to the scarcity of sand and slowly increasing accommodation space. The contact lobes mainly developed in the central oil-producing block (B14 block) due to sufficient sediment supply and steadily increasing accommodation space across a wide area. The superimposed lobes mainly developed in the southeast oil-producing block (B16 block) due to sufficient sediment input and steadily increasing accommodation space within a restricted area. In the whole study area, the superimposed lobe pattern is the most favorable depositional pattern and forms the highest-quality reservoirs because of the high degree of sand body connectivity. These results also highlight the utility of sedimentary patterns and sand body assemblage studies for the oil exploration and development of similar rifted basins.

Control of inherited structural fabric on the development and exhumation of passive margins – Insights from the Araçuaí Orogen (Brazil)

The Araçuaí Orogen, in eastern Brazil, was formed during the Neoproterozoic – Cambrian amalgamation of West Gondwana. During the Mesozoic – Cenozoic opening of the South Atlantic Ocean, and the associated divergent tectonics, the orogen developed as basement to the passive margin of South America and was progressively covered by thick offshore sedimentary basins, particularly the Espírito Santo, Mucuri, and Cumuruxatiba basins, in which hydrocarbon systems have been exploited. Our understanding of the Araçuaí Orogen's passive margin evolution, erosion, and sediment transfer to these basins ultimately depends on constraining the onshore exhumation in response to Mesozoic – Cenozoic events. Here, new and previously published data from apatite fission-track (AFT) analyses and inverse thermal history modelling of (Pre)Cambrian basement rocks from the Araçuaí Orogen resolve three discrete basement cooling and associated erosional exhumation episodes. In the Pre-Rift phase, Jurassic – Hauterivian erosion of the Araçuaí Orogen is most likely related to the adjoining intra-continental West Gondwana flexural subsidence, which increased hillslope and river erosion power. In the Rift and Transitional phases, Barremian – Albian accelerated phase of erosion is associated with the uplift of the Atlantic rift shoulders and the establishment of an oceanic base-level. In the Drift phase, reactivations in response to far-field stresses likely triggered a Late Cretaceous – Paleocene rapid erosion event. The rates at which these events unfolded vary spatially and are controlled by inherited structures. The Araçuaí Orogen experienced slower denudation rates in areas closer to the São Francisco Craton, which suggests that the tectonic reactivation and related surface uplift during the Mesozoic–Cenozoic is in first-order controlled by lithospheric rigidity. Furthermore, the structural framework of the Paramirim and Pirapora aulacogens and NE-oriented shear zones in the orogen’s southeast facilitated later reactivations. From the spatial pattern of denudation/exhumation of the Araçuaí Orogen during the Mesozoic – Cenozoic, we draw inferences on the tectonic development of the offshore basins regarding their hydrocarbon potentials.

Formation and evolution of an Early Cambrian foreland basin in the NW Yangtze Block, South China

The Ediacaran to Cambrian succession in the NW Yangtze Block has long been considered to have formed in a passive margin. The Ediacaran is dominated by thick carbonate rocks, whereas the Lower Cambrian comprises a thick clastic succession. The transition from carbonate to clastic rocks and the provenance and tectonic setting of the clastic succession are poorly understood. Stratigraphic correlation shows a distinct stratigraphic absence from the Lower Cambrian to Devonian in the Bikou terrane. A regional seismic profile shows a wedge geometry of the Lower Cambrian from NW to SE. Outcrops reveal an overall coarsening-upward Lower Cambrian succession. The petrographic analysis of clastic rocks indicates immaturity, implying a proximal source. Palaeocurrent measurements of clastic rocks point to dominant SE-vergent orientations. The age spectra of detrital zircons imply that they were derived from Early Cambrian continental arcs and older continental crust. Geological, geophysical and geochemical evidence indicates that an Early Cambrian foreland basin was formed in the NW Yangtze Block. This foreland basin appears to have been strongly influenced by orogenic loading northwestward. We propose that this orogenic event should be named the Motianling orogeny, the origin of which may be related to subduction of the Proto-Tethys ocean beneath the NW Yangtze Block. Supplementary material: Supplementary tables A–D and a petrological description of detrital zircons are available at https://doi.org/10.6084/m9.figshare.c.6332980

Geophysical Modeling and Its Contribution on the Reservoir Characterization of Al Baraka in El Gallaba Plain, South Egypt

Summary The early Cretaceous formations in recent years are considered significant potential hydrocarbon-bearing rocks in many rift basins such as Komombo, south Egypt. Therefore, this study is focused on the critical analysis and interpretation of well logging together with seismic reflection data on the Al Baraka petroliferous reservoir in the Komombo subbasin. The interpretation of these data was used to construct the first 3D geophysical models in this area which were subsequently interpreted in terms of their potential to be hydrocarbon-bearing or not. The 3D petrophysical models were deduced to illustrate the spatial distribution and propagation of the petrophysical properties (laterally and vertically) within the reservoir. Additionally, 3D seismic models were prepared to get a comprehensive, in-depth picture of how the productive hydrocarbon reservoir zones are structurally controlled in different depths. So, these models are crucial for explaining reservoir characteristics and providing supported geological reservoir models for precise reservoir performance prediction. This study aims to differentiate and determine hydrocarbon potential zones in terms of the petroleum system. The results of these progressive analyses showed that only two zones (C and D) in the Six Hills Formation are considered the most productive zones because they have a large thickness of sand bodies, low-water saturation values, high porosity, and high permeability. These zones are located in the northeastern and central parts of the studied area, which represent the depocenter of the subbasin. This evidence supported and confirmed the presence of petroleum accumulations in certain zones within the Six Hills Formation. Therefore, this work can give and encourage experts with adequate knowledge to understand the development of the rift basins in Komombo and other basins in middle and south Egypt.

Comprehensive evaluation and stability analysis of ecosystem quality of Yellow River Basin during 1980–2019

AbstractQuality and stability are the basic characteristics of ecosystems, reflecting their structure, process, functional integrity, ability to resist disturbance, self‐regulation, and dynamic balance. The quantitative description of ecosystem quality and stability is an indispensable and important task to promote the ecological protection and high‐quality development of the Yellow River Basin as a major national strategy. In this study, an index evaluation system was constructed from the perspective of system governance, considering the special characteristics of the Yellow River Basin, and an entropy weight model was used to establish a multi‐indicator long time series ecosystem quality evaluation index (EQI) to quantitatively describe the ecological quality changes in the Yellow River Basin over 40 years. The dissipative structure theory and Brussels apparatus model were used to establish quantitative indicators and methods, and provide ideas for the study of ecosystem homeostasis transformation in the Yellow River basin. This study found that: (1) the average EQI value of the Yellow River Basin ecosystem for 40 years was 63.96, the maximum and minimum values were 69.65 and 59.45, respectively; the overall quality showed an oscillating trend of improvement, with an annual increase of 0.03, and the spatial distribution was better in the downstream than in the midstream, and in the midstream than in the upstream; (2) The key factors influencing the system changed gradually from the total water consumption and total annual precipitation in the basin in the early stage to the average income of residents in the last 10 years. (3) The system steady‐state transition force values from 1980 to 2019 were all <0, the steady‐state conversion force of the Yellow River Basin ecosystem was low, but the overall trend was oscillating upward, and the overall trend was getting closer to the critical condition of steady‐state conversion.

Preface

Preface

Depositional and Sratigraphic Evolution of the Early-Middle Miocene Succession in Hamrin, Ajeel and Mansuriyha Oil Fields, Central Iraq

The Early-Middle Miocene succession in Iraq is represented by the Serikagni, Euphrates and Dhiban formations, which deposited during the Early Miocene. The Jeribe and Fatha successions were deposited during Middle Miocene age. This study includes microfacies analysis, depositional environments, sequence stratigraphy and basin development of Early – middle Miocene in Hamrin and Ajeel oil fields and Mansuriyha Gas Field. The study area includes four boreholes in three oil fields located in central Iraq: Hamrin (Hr-2) and Ajeel (Aj-13, and 19) oil feilds, and Mansuriyha (Ms-2) Gas Field. Five facies associations were distinguished within the studied fields: deep marine, slop, platform-margin, open marine, restricted interior platform, and evaporitic interior platform. The facies associations interpreted were based on texture and fauna. Deep marine facies association consists of planktonic foraminifera wackestone, it was observed in well Ms–2. Slope environment association is observed in Euphrates Formation in Hamreen-10, and it represented by bioclastic – planktonic mudstone – wackestone. The open marine association is observed in all studied wells in particular in Jeribe and Euphrates formations, and it includes bioclastic mudstone-wackestone, bioclastic peloidal wackestone-packestone and bioclastic foraminiferal wackestone- packestone. While the restricted interior platform association is dominated in all studied wells, it consists of ooidal packstone, foraminiferal peloidal packstone, dolomitic lime mudstone, dolomititic and evaporitic peloidal wackestone-packstone. In Ajil Oil Field the studied succession is consisting of two sequences (C1 and C2). The fist sequence (C1) was started with transgressive system tract (TST) reflected by open marine occupies the lower part of Euphrates Formation, the TST bounded below by SB and above by MFS. The second sequence (C2) was started with TST which is observed in the lower part of Jeribe Formation, represented by evaporitic and restricted interior platform. In Hamrin Oil Field, this succession is started with thin transgressive system tract (TST) as C1 reflected by toe of slope and it occupied a bit of lower part of Euphrates Formation. The highstand system tract (HST) is divided to five cycles (CE1, CE2, CE3, CE/Dh and CDh). Sequence C2 was started with relatively thin transgressive system tract (TST) occupies the lower part of Jeribe Formation represented by open marine environment. Two sequences are observed in Mansuriya Gas Field (C1 and C2). Sequence C1 started with thin transgressive system tract (TST) bounded below by SB1 and above by MFS which is corresponding with conformable boundary that separated between Serikagni Formation and Dhiban. Contrary, the second sequence (C2) was started with relatively thin transgressive system tract (TST) occupies the lower and middle parts of Jeribe Formation represented by restricted interior platform environment.

Monitoring Surface Water Area Changes in the Aral Sea Basin Using the Google Earth Engine Cloud Platform

The surface water area and types in the Aral Sea Basin (ASB) have undergone extensive changes due to the impacts of climate change and anthropogenic activities. This study explores the changes in the surface water area in the ASB based on the Google Earth Engine cloud platform. Then, we integrate multi-source data to identify 1559 lakes and 196 reservoirs from the Joint Research Centre Global Surface Water (JRC GSW) dataset. Our results indicate that the lake area (34,999.61 km2) is about 10 times that of the reservoir area (3879.08 km2) in the ASB. The total area of surface water in the ASB decreased by 23,194.35 km2 or 34.58% from 1992 to 2020. Specifically, the areas of permanent water shrunk at a rate of 1278.6 km2/year, while the areas of seasonal water increased at a rate of 522.5 km2/year. The proportion of lakes and reservoirs in the total surface water has decreased from 79.33% (during 1992–2000) to 75.21% (during 2000–2010) to 63.94% (during 2010–2020). The water that should have flowed into the Aral Sea to maintain its permanent water may have been converted into two parts. Part of it might continue to be permanent water but show up in other regions, while part of it might convert to seasonal water (especially in the Aral Sea itself and the ASB plain area). Our study bridges the limitations of previous studies that have ignored seasonal water change and builds a water area list for 1755 lakes/reservoirs (≥0.1 km2) for the first time. The results can serve as important knowledge for water resource management and sustainable river basin development in ASB.

A discourse on factors influencing the formation of sigmoidal and linear slope-geometries in the deltaic clinoforms of the calciclastic Sobrarbe Delta, Ainsa Basin, Spain

Clinoforms develop at the hearts of prograding sedimentary systems and are an integral part in understanding basin development and sediment partioning. The Eocene Sobrarbe Formation in the Ainsa Basin in Spain, displays well-developed dipping clinoform geometries. The study observes depositional facies, mineralogy, and performs curve-fitting calculations in 2D to better understanding of factors controlling clinoform geometries.The Sobrarbe Formation is a unique prograding calciclastic delta system, in which carbonates are dominant, but depositional environments and sedimentary processes are akin to silicilclastic systems.Four clinothems (CT 1–4) were selected for detailed study. The clinothems display an overall coarsening upward trend. The lowermost clinothems comprise dominantly pro-deltaic marlstone deposited from suspension and dilute hyperpycnal flows, with occasional thin fine-grained episodic turbidite beds. The uppermost clinothems are dominated by reworked remobilized topset deposits comprising bioturbated calcarenites with a variety of trace-fossils, shells and large assemblages of nummulites, and finally proximal subaqueous stacked calcarenites.Three clinothems (1, 2, 4) are characterized by sigmoidal geometry (Gaussian distribution curve), symmetrical sediment distribution, a simple coarsening upward trend, and where calculable, ascending regressive trajectories. Clinothem 3 comprises a more complex stratigraphic development and displays an overall ascending transgressive trajectory, linear slope and asymmetric sediment distribution.The results show that sigmoidal geometries develop in both the distal pro-delta and in the coarser-grained proximal delta, suggesting the sigmoidal form develops naturally granted sufficient accommodation. While speculative it appears that linear slopes might be associated with draping during transgression, and asymmetric distribution associated with high sedimentation rates vis a vis accommodation. Accommodation exerts the dominant control on the location of the rollover and the trajectory. The topset-foreset ratio indicates the relative rate of sedimentation compared to accommodation, as high sedimentation rates increase deposition on the foreset. Results indicate that accommodation appears to be the most important factor controlling foreset slope, with steeper inclination developing in deeper water. Meanwhile sedimentation rate, grain size, and the role of turbidity currents may play a secondary role influencing slope angle.

Strike-slip influenced stratigraphic and structural development of the Foula Sandstone Group, Shetland: implications for offshore Devonian basin development on the northern UK continental shelf

The island of Foula, located 25 km SW of Shetland, preserves a gently folded, 1.6 km thick sequence of Middle Devonian sandstones spectacularly exposed in kilometre-long cliff sections >350 m high. These rocks unconformably overlie likely Precambrian-age amphibolite facies basement rocks that are intruded by sheeted granites. The onshore succession is similar in age to the nearby Lower Clair Group offshore to the west. New mapping, incorporating the use of drone imagery in the inaccessible cliff sections, uses down-plunge projections to show that growth folding and faulting on Foula were contemporaneous with sedimentation during basin filling. The large-scale structural geometry is consistent with the regional constrictional strain due to the sinistral transtension associated with movements along the Walls Boundary–Great Glen fault zone system during the Mid-Devonian. Detrital zircon provenance studies indicate that the Devonian sequences of Foula (and nearby Melby in western Shetland) show similarities with the Clair Group and Orkney successions. We suggest that NE–SW transtensional fold development contemporaneous with regional subsidence in the Devonian basins of Scotland may be more widespread than previously realized. Large, kilometre-scale folds previously interpreted to be related to Permo-Carboniferous inversion may therefore have initiated earlier in the basin evolution sequence than previously realized. Supplementary material: Appendices A, Methodologies; B, Regional stratigraphic correlation table; C, Heavy mineral data; D, Detrital zircon data; and E, 3D virtual outcrop models are available at https://doi.org/10.6084/m9.figshare.c.6442552

Magnetic fabric analyses of basin inversion: a sandbox modelling approach

Abstract. A magnetic fabric analysis is a useful tool to display deformation in nature and in models. In this study, three sandbox models represent basin inversion above a velocity discontinuity (base plate). After complete deformation of each model, samples were taken in different parts of the models (along faults and areas away from faults) for magnetic fabric analysis. Model I, which simulates basin formation during extension, shows two kinds of magnetic fabric: an “undeformed”/initial fabric in areas away from faults and a normal fault-induced fabric with a magnetic foliation that tends to align with the fault surface. Models II and III were extended to the same stage as Model I but were subsequently shortened/inverted by 1.5 cm (Model II) and 4 cm (Model III). Both inverted models developed “thrusts” during inversion. The thrusts show an alignment of magnetic foliation parallel to the fault surfaces that depends on the maturity of the thrust. Our results highlight that thrusting is more efficient in aligning the magnetic fabric along them compared to normal faults. Moreover, models II and III reveal a magnetic fabric overprint towards a penetrative strain-induced fabric (magnetic lineation perpendicular to shortening direction) with increasing strain in areas away from thrusts. Such overprint shows a gradual transition of a magnetic fabric to a penetrative strain-induced fabric and further into a thrust-induced fabric during shortening/inversion. In contrast, extension (Model I) developed distinct magnetic fabrics without gradual overprint. In addition, pre-existing normal faults are also overprinted to a penetrative strain-induced fabric during model inversion. They define weak zones within the main pop-up imbricate and steepen during model inversion. Steepening influences the magnetic fabric at the faults and, in general, the strain propagation through the model during inversion. The magnetic fabric extracted from the models presented here reflect the different stages of basin development and inversion. This study is a first attempt of applying magnetic fabric analyses on models simulating inverted basins. This study illustrates the possibility of applying a robust tool, i.e. magnetic fabric analyses, to sandbox models, whose initial, intermediate, and final stages are well documented, to understand fabric development in inverted tectonic regimes.