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The river drainage basin is the basic unit for conducting quantitative research for river basins. Measuring the morphometric and hydrological characteristics of river valleys is one of the recent developments in the field of quantitative geomorphology that relies on statistical and mathematical analysis to describe land forms. The river basin and its relationship to the factors controlling its composition on the one hand, and to the amount of water and its geomorphological effect on the other hand, and to determine the measurement of morphometric features, which include characteristics (areal, morphological and topographical) and hydrological characteristics in the Wadi Abu Karisha basin, northeast of Ali al-Gharbi district in Maysan governorate, which is located astronomically Between two latitudes (0 42 32 - 30 49 32 degrees) north, and arcs of length (0 33 46 - 30 40 46 degrees east), topographic maps were used at a scale (1: 100,000) and the satellite visualization of the sensor (Landsat 8), on (4/6) / 2019) and the digital elevation model for the year (2019) with a discriminatory accuracy (12.5 m) using the (ARC GIS 9.5) program and the (Global Mapper) program. The important conclusions about the morphometrics and hydrology of the basin, in particular, the effect of the natural characteristics on the variation of the morphometric and hydrological characteristics of the basin represented by the geological formations in it and the structural characteristics that characterize the area as well as the surface characteristics, the degree of slope and its directions, the quality and characteristics of the soil and the quality and density of the natural vegetation. The morphometrics, especially the spatial ones, contributed to influencing the morphometric and hydrological characteristics of the basin, as the basin area reached (79.2 km2), a length of (18.2 km) and an average width of (5.9 km), while the basin circumference amounted to (48.6) km, While the morphological characteristics of the basin, especially the ratio of elongation and roundness, were recorded respectively (0.99, 0.96), while the shape factor of the basin was recorded (0.21) and the ratio of ocean cohesion (1.06), and it was found that there is a close relationship between the morphometric characteristics The hydrology of the basin. [ABSTRACT FROM AUTHOR]

• The inclusion of hydrogen in the existing energy mix for global Net-Zero target is discussed. • Prospects and feasibility of underground hydrogen storage (UHS) in India are presented. • The connection between the human development index, hydrogen energy, and carbon footprint is emphasized. • Indian geological basins and formations suitable for UHS are highlighted. • Technical data, regulations, and policies to explore the opportunity of UHS are described. The world is combating climate change by adopting a low-carbon energy mix and pursuing a net-zero target. Being the third-largest CO 2 emitter, net-zero target for India is crucial for global decarbonization. Hydrogen is a promising fuel for the future to aid in this transition, but its storage is a significant challenge. Surface-based storage options are inadequate and expensive, making underground hydrogen storage (UHS) in geological formations a more practical solution for its ample storage capacity and economic feasibility. Herein, this review critically investigates (i) the possibility of surplus renewable energy storage in India, (ii) UHS's applicability to store this surplus energy, and (iii) scientific aspects, feasibility, and challenges with suitable geological storage locations for storage of hydrogen in India. This review starts with briefing 'net-zero' at both the global and national (India) levels. The urgency for green energy is highlighted by the disparity between the Human Development Index and ecological footprint. The Indian hydrogen market and the production of green hydrogen from renewable resources are also discussed. The review discusses UHS storage types, reservoir and fluid parameters, and flow behavior, including physiochemical, geochemical, and microbial interactions. Based on the geological basins and formation, availability and capacity of renewable energy sources, the potential of UHS in India is analysed. This review also provides vital information including technical data, regulations, initiatives, and policies needed to explore the opportunity of UHS and its development. Finally, the article presents challenges and opportunities for UHS development and emphasizes the need for continued research and development. [ABSTRACT FROM AUTHOR]

Abstract The tetrapod footprint record of Permian eolian environments has long been underestimated because of overall poor preservation and its apparent monospecifity. The best known and most abundant Cisuralian record of tetrapod footprints is from the Coconino and De Chelly formations of Arizona, which, however, thus far encompassed only the ichnogenera Chelichnus and Dromopus. We revised the locomotion and taphonomy of these footprints and propose a new model, basing it on: 1) trackways changing direction, 2) trackways heading in different directions on the same surface, 3) trackways in situ, and 4) laboratory experiments with common wall lizards, Podarcis muralis. In all cases, the Chelichnus -like appearance of footprints is due to digit tip sliding on inclined depositional surfaces, masking the original footprint shape and orientation. Also, the trackway pattern and body position are largely influenced by the angle of inclination (dip) of the substrate being walked on. Based on an anatomy-consistent ichnotaxonomy, Chelichnus and Laoporus are here considered nomina dubia, and the footprints from the Coconino and De Chelly formations are revised and assigned to: parareptiles/captorhinomorph eureptiles (Erpetopus, Varanopus curvidactylus), bolosaurid parareptiles/ diapsid eureptiles (cf. Dromopus), varanopid synapsid (cf. Tambachichnium) and reptiliomorph amphibians (Amphisauropus, Ichniotherium sphaerodactylum). The ichnoassociation is dominated by parareptile/captorhinomorph tracks, similarly to all the late Cisuralian marginal marine, floodplain, alluvial fan and ephemeral lacustrine tetrapod ichnoassociations of North America, Europe and North Africa. A review of all the available data including the new results suggests a facies-crossing transition between an early-Cisuralian amphibian- and synapsid-dominated ichnofauna (Dromopus track biochron) and a late Cisuralian parareptile/captorhinomorph-dominated ichnofauna (Erpetopus track biochron) at low latitudes of Pangea. [ABSTRACT FROM AUTHOR]

Abstract For tight sandstone reservoirs, the pore structure is sensitive to the stress variations during the production process. The alternation of pore structure influences the petrophysical properties and therefore the dynamic flow of tight sandstone reservoirs. In this research, Nuclear Magnetic Resonance (NMR) technique is employed to quantitatively study the pore volume variation under different confining pressures. Not only during the compression process, this research also investigated the sandstone pore sensitivity to stress during the recovery process of rock samples, which is equally important and happens during the production process when the formation pressure is building up due to the temporary well shut-in or water injection. The core samples selected from Ordos basin are first tested routinely for basic parameters like porosity, permeability and detrital components, and then through both compression and recovery processes where the pressure decreases and increases, respectively. It is found that the core samples with high permeability show stronger stress sensitivity of pores than those with low permeability due to the higher content of large pores. Besides permeability, detrital components and interstitial material can also affect the stress sensitivity of pores. During the recovery process, the low recovery degree of pore volume is related to the recoverable pore size (mainly smaller size pores) and the narrow distribution range of recovered pores. Furthermore, the power function relationship and the exponential relationship are suggested to evaluate the variation of pore volume in compression and recovery process, respectively. The results demonstrated that the compressibility of larger pores is bigger than that of smaller pores. During the compression process, the higher permeability rocks, containing a higher content of larger pores, are easier to be compressed, and has a greater decrease in permeability. Besides, the recoverability of the total pore volume after compression is mainly controlled by smaller pores, which results in the lower recoverability of the total pore volume and the permeability for the higher permeability core samples. Highlights • Using Nuclear Magnetic Resonance (NMR) technique to quantitatively study stress sensitivity. • High permeability cores show stronger stress sensitivity than that in low permeability. • Detrital component and interstitial material can affect stress sensitivity of pores. • Power function relationship can be used to evaluate the variation of pore volume. • Exponential relationship can be used to estimate the recovery degree of pore volume. [ABSTRACT FROM AUTHOR]

Abstract This study investigated the geochemical characteristics of source rocks in each sequence and studied on the oil-source correlation under a sequence stratigraphic framework of the Upper Cretaceous Yogou Formation. The Yogou Formation as the most primary and productive source bed in the Termit Basin (Niger), was further divided into three third-order sequences (i.e. YSQ1, YSQ2 and YSQ3, from bottom to top) in the study. On the basis of the geochemical analysis of a total of 35 rock samples from YSQ3, YSQ2 and YSQ1, the variation of the organic matter abundances, types and maturity of source rocks within different sequences were compared. The TOC content of YSQ2 and YSQ1 source rocks ranges from 0.76% to 1.69% with mature to high mature thermal evaluation stage (R o : 0.63%–1.29%), while the TOC content of YSQ3 source rocks is much higher (1.11%–6.63%) with a relatively lower maturation levels (R o : 0.59%–0.91%). All source rocks are dominated by Type II 2 –III kerogen. Moreover, in order to determine the oil-source correlation under a sequence stratigraphic framework, the composition of biomarkers in 35 source rocks and 25 crude oils were analyzed systematically. Various non-biomarker and biomarker parameters were applied involving source-related, maturity-related and environment-related parameters. The YSQ3 source rocks are typically characterized by relatively higher Pr/Ph ratio, higher concentration of dibenzofurans (DBFs) and lower gammacerane index indicating a suboxic transitional environment, and the relatively higher values of oleanane index and C 24 TeT/(C 24 TeT + C 26 TT) ratio reflecting a significant terrigenous organic matter input. Conversely, the YSQ2, YSQ1 source rocks and studied oils have relatively lower Pr/Ph ratios, higher content of gammacerane and dibenzothiophenes (DBTs) suggesting suboxic to anoxic conditions under shallow marine depositional environment, and low values of oleanane index and C 24 TeT/(C 24 TeT + C 26 TT) ratios indicating predominant algal aquatic organisms input. In addition, other molecular parameters in crude oils, including OEP, CPI, TAR, n C 21 -/ n C 22 +, (n C 21 + n C 22)/(n C 28 + n C 29), Pr/ n C 17 , Ph/ n C 18 ratios and the distribution patterns and relevant parameters of tricyclic terpane series, also have the obviously similar characteristics to YSQ2 and YSQ1 source rocks, rather than YSQ3 source rocks. The result of oil-source correlation shows that the discovered oils are dominantly derived from YSQ2 and YSQ1 source rocks, with minor contribution of YSQ3 source rocks. Therefore, the oil-source correlation within a sequence stratigraphic framework can provide a practical model for source rock assessment and petroleum system study. Highlights • The source rock was evaluated under a sequence stratigraphic framework. • The compositions of molecular markers for 3 sequences were discussed. • Oil-source correlation shows that the YSQ1 and YSQ2 are the main source beds. • Geochemical sequence stratigraphy has practical implication in petroleum system. [ABSTRACT FROM AUTHOR]

Abstract The bioturbated horizons identified from Member Two of the Paleocene Funing Formation (E 1 f 2) in the Jinhu sag, have not been previously assessed to ascertain their influence on reservoir quality. Owing to that, conventional thin section, pulse decay permeametry, pressure decay porosimetry, Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-ray Spectroscopy (EDS) methods were used to analyze the significance of bioturbation in controlling porosity and permeability on selected cored intervals from one well. Intensely bioturbated core slab samples A and B selected from Bian-5 Well are dominantly controlled by Ophiomorpha and Macaronichnus , and Macaronichnus , respectively. Results showed that Ophiomorpha and Macaronichnus in sample A exhibited sediment cleaning activity with better sorted grains in burrow fillings. Mud and clay were removed from the burrow filling and directed towards burrow lining and/or host sediment by burrowing organism resulting in well sorted burrow fill matter; the net effect, enhanced isotropy and increased porosity in burrows fills. Macaronichnus ichnofabrics in sample B also exhibited sediment cleaning activity causing reduction of local porosity in host sediment and an outcome of permeability improvement in burrows. Reservoir quality of bioturbated sandstone of Bian-5 well in the Jinhu sag is, therefore, dependent on activity of burrowing organism, burrow structure, bioturbation extent as well as the existence or nonexistence of burrow fill or lining. Highlights • Intensely bioturbated samples embody Ophiomorpha – Macaronichnus and Macaronichnus ichnofabrics. • Sediment cleaning activity resulted in better isotropy and increased porosity in burrow fills. • Permeability enhancement resultant from well sorted and clean burrow fill by burrowing organism. [ABSTRACT FROM AUTHOR]

Highlights • Laterally Confined Volcanic Successions record rift-jumps during SDR emplacement. • 2 km of subsidence can be generated during SDR emplacement without faulting. • Rift-jumps may occur to establish a laterally continuous magmatic spreading centre. Abstract Seaward Dipping Reflectors (SDRs) are a characteristic feature of magma-rich margins, and represent the generation of large volumes of flood basalts at the point of continental breakup. A number of recent studies provide new insights into the emplacement and tilting of SDRs and conclude that the majority of SDRs are contained within new magmatic crust that has a close affinity to oceanic crust. However, the process by which these initial magmatic systems evolve into a fully established spreading centre remains poorly understood. Several characteristic features of magma-rich margins may be explained by the occurrence of rift-jumps during SDR emplacement, yet the cause and prevalence of such rift-jumps remain unknown. Here we constrain the 3D geometry of the continent–ocean transition in the Orange Basin, offshore South Africa. This allows us to test if, where and why such rift jumps occur. Our results demonstrate an order of along-strike segmentation previously unobserved in these settings. We demonstrate that the SDR belt is disrupted by the occurrence of a volcanic-stratigraphic package, defined as the Laterally Confined Volcanic Succession (LCVS), not previously identified on a rifted margin. We interpret this as a magmatic spreading centre that was abandoned by a subsequent rift-jump. Identification of LCVSs is important for two reasons. First, we argue that the LCVS formed via the same process as SDRs, and hence provides a unique example of SDR geometry prior to their separation onto conjugate plates. Second, as we can map out the 3D geometry of the LCVS and SDRs, we propose that rift-jumps during magma-rich margin formation may be fundamental to the establishment of a laterally continuous incipient spreading centre. [ABSTRACT FROM AUTHOR]

Highlights • Redox-stratified water column in a Mesoarchean epicontinental sea, Pongola basin. • Mesoarchean aerobic iron and manganese cycling in the Pongola epicontinental sea. • Aerobic biological catalysis enhanced manganese oxidation in a Mesoarchean sea. • Evidence for oxygenated surface seawater ca. 3 billion years ago. Abstract Redox conditions in the marine realm prior to the Great Oxidation Event (GOE; ∼2.46–2.32 Ga ago), during which the atmospheric oxygen level rose dramatically for the first time, are still debated. Here, we present C, O, Fe, and Mo stable isotope systematics of Fe-, Mn-, and carbonate-rich shales, deposited at different water depths in association with iron formations (IFs) of the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa. δ 13 C values between −22.3 and −13.5‰ VPDB, and δ 18 O values between −21.1 and −8.6‰ VPDB for Fe–Mn-rich carbonate minerals indicate their precipitation out of equilibrium with seawater. Instead, early diagenetic reduction of Fe–Mn-oxyhydroxide precursor minerals, along with microbially induced oxidation of organic matter (OM), formed these carbonates. δ 56 Fe IRMM - 014 values between −1.27 and 0.14‰ and δ 98 Mo NIST 3134 + 0.25 values between −0.46 and 0.56‰ co-vary with Mn concentrations and inferred water depth of deposition. This suggests that, despite the diagenetic origin of the Fe–Mn carbonates, the primary light Fe and Mo isotopic signature of Fe–Mn-oxyhydroxides that originally precipitated from seawater is still preserved. While isotopically light Mo implies that Mn(II) was oxidized to Mn(IV) due to the availability of free, photosynthetically produced O 2 , Mn enrichment suggests that the water column was redox stratified with a Mn-redoxcline situated at a depth below the storm wave base. A trend to highly negative δ 56 Fe values with increasing Mn/Fe ratios and decreasing depositional depth suggests progressive oxidation of Fe(II) as deep-waters upwelled across a redoxcline towards shallow, locally oxygenated waters where Mn(IV) oxyhydroxides precipitated. Combined δ 56 Fe and δ 98 Mo data indicate pervasive oxygenation of seawater with the O 2 content in the photic zone likely reaching levels higher than the maximum value of 10 μM proposed for Archean oxygen oases. Since abiotic Mn(II) oxidation is kinetically very slow in marine environments, it is likely that Mn-oxidizing microorganisms catalyzed Mn-oxidation in the oxygenated Pongola surface waters during deposition of IFs. This implies that aerobic metabolism had evolved before the GOE in shallow, aquatic habitats, where it exerted a first-order control on the deposition of shallow-marine, Mn-rich iron formations. [ABSTRACT FROM AUTHOR]

Due to deeper buried, multi-stage tectonic influences, rapid changing, and unclear originate of oil and gas in Jinlong 2 wellblock, we analyzed the volcanic reservoir characteristics and the genesis of hydrocarbon by cores, thin slices, loggings, physical properties, oil testing data, and carbon isotopes. Results demonstrated that the major lithology were pyroclastic rocks and lavas, the reservoir was generally poor and strongly homogeneous, the main reservoir space were primary pores, and the favorable reservoir mainly developed in the pyroclastic rocks of the third phase. Furthermore, the results of carbon isotopes indicated that the crude oil and dissolved gas originated from Fengcheng formation, while the condensate gas derived from Jiamuhe formation. [ABSTRACT FROM AUTHOR]

Reconstructing the evolution of paleofluid pressure in carbonate reservoirs is a challenging problem, particularly when no oil-bearing fluid inclusions are available to provide barometric constraints on the fluid system. To recover the paleofluid pressure in the Sinian Dengying Formation (Z 2 dn) and the Cambrian Longwangmiao Formation (Є 1 l) of the central paleo-uplift of the Sichuan Basin, we conducted a comprehensive analysis combining the inclusion pressure-volume-temperature simulation, inclusions in situ Raman shifts, and basin modeling. The results showed that the evolution of the pore pressure could be divided into four stages. Prior to the end of the late Triassic, the whole central paleo-uplift was in a normal pressure state. During the Jurassic, a moderate overpressure prevailed in the dolomitic reservoirs of the Gaoshiti-Moxi area and decreased in the adjacent units. At the end of the early Cretaceous, the overpressure reached a maximum in the whole region and was strongest in the Longnüsi area, decreasing to the west. From the late Cretaceous to the present day, the central area of the basin has uplifted rapidly with the overpressure significantly decreasing. Z 2 dn has been restored to normal pressure during the Neogene, while Є 1 l remains moderately overpressurized. Based on an analysis of the structural background and preservation conditions, the types of sedimentary facies, the preservation condition of the traps, and the differential weathering process are the primary reasons for the different pressure states in Z 2 dn and Є 1 l during the last stages. [ABSTRACT FROM AUTHOR]

The Lower Permian Collyhurst Sandstone Formation is an important gas reservoir both offshore and onshore in the East Irish Sea Basin of north-western UK, and is considered to be a tight gas reservoir. Diagenetic processes have significantly influenced the reservoir quality of the sandstone. This study employs petrographic, mineralogical, and stable isotopic analyses on two different onshore core successions to investigate the composition and texture, the diagenetic history, and the impact of lithology and diagenesis on reservoir quality. The Collyhurst Sandstone Formation consists of fine- to very coarse-grained, poorly to well-sorted, sub-arkosic to lithic arenite sands. The reservoir properties of the sandstone are relatively poor, with average porosity and permeability of 6.6% and 0.387 mD respectively. On the basis of petrographic analyses, five sandstone lithofacies were identified: fine-grained, conglomeratic, carbonate-cemented, quartz-cemented and matrix-free. Contrasting characteristics between the reservoir units suggest the development of divergent diagenetic pathways. Features observed during early diagenesis include compaction, growth of pore-filling early carbonate cements (calcite I, dolomite and siderite I) and vermicular kaolinite. Late diagenetic features include: further carbonate cementations (ferroan dolomite/ankerite, calcite II and siderite II-III), clay mineral cementation (illite and chlorite) with both grain-coating and pore-filling textures. Also common in late diagenesis are syntaxial quartz overgrowths. Albite, barite and anhydrite are minor late diagenetic cement phases. Compaction processes rather than cementation accounts for the major destruction of the initial sandstone porosity. But cementation still accounts for up to 32% of porosity loss. Carbonate cements mostly fill intergranular pores, thus block pore throat and prevent migration of fluid. Clay minerals bridge and occlude pores, resulting in further destruction of the reservoir quality. The study provides insights into how lithofacies (primary composition, texture and sorting) and diagenesis can influence reservoir qualities of tight gas sandstones. [ABSTRACT FROM AUTHOR]

We present a case-study in Palaeolithic archaeology focusing on formation processes at cave- and rock-shelter-sites in a Mediterranean context and on the correlation between site deposits, Quaternary surface sediments and the morphology of the surrounding land. We study three sites located in the basin of River Mula (Murcia, Spain): the cave-site of Cueva Antón and the rock-shelters of Finca Doña Martina and Abrigo de la Boja, in the Rambla Perea valley. They are examined through an integrated geoarchaeological approach that takes into account geomorphological, stratigraphic and soil micromorphological data. The three sites are found within a short distance and cover similar time spans within the Upper Pleistocene but have different formations and show distinct degrees of preservation of the archaeological record. Cueva Antón features a densely-stratified, mostly alluvial succession, with excellent preservation of stratigraphic layout and sedimentary facies. The succession represents a well-preserved record of past activity of the River Mula and can be correlated to its open-air alluvial system. The Rambla Perea sites, despite their immediate vicinity, underwent distinct formation dynamics, with a complex interaction among the site deposits and the hillslope along which they are found, and exhibit different degrees of preservation of archaeological layers and features. We summarise the evidence from these sites and then discuss its implications for site formation, for the preservation of the archaeological record and for the correlation between the ‘inside’ (the archaeological successions preserved within caves and in rock-shelters) and the ‘outside’ (the geomorphological setting of the land and the evolution of Quaternary surface dynamics through time). [ABSTRACT FROM AUTHOR]

During the Early Carboniferous, the northeastern Qaidam Basin probably formed in an active continental margin setting. Due to marine regression after the late Early Carboniferous, the marginal shelf began to receive more terrestrial clastic sediments, and alternating occurrence of carbonates and siliciclastics characterized this region. Consequently, shales or mudstones with considerable thickness were deposited in the Upper Carboniferous, especially in the Keluke Formation. In order to illuminate a more accurate sedimentary environment of shales and further evaluate the shale gas potential, multidisciplinary traditional methods were conducted including rock core examinations and laboratory analysis. Results reveal that the sedimentary microfacies of shales in the Keluke Formation can be divided into the upper shoreface, the lower shoreface, and the upper to transition offshore. These microfacies developed on a homoclinal carbonate ramp with a gentle slope. The thickest succession of mudstone develops in the lower shoreface, which is a counterpart with the lagoonal setting of a stationary hydraulic system. The quartz content of shale samples ranges from 30% to 66% and clay minerals from 24% to 43% by bulk compositional analysis, which indicates the content of brittle minerals and shales fissility to some extent. The total organic carbon content ranges from 0.5% to 7.6% by weight, with an average value of 2.69% in ZK1‐1 and 1.11% in ZK3‐2, indicating abundant organic matter richness. The kerogen is mainly of type II, which indicates that source for the organic matter is a mixture of higher terrestrial plants and acquatic organisms. The vitrinite reflectance ranges from 1.22% to 1.55%, indicating a moderate to high thermal maturity. Three types of pores are recognized in the shales, including organic pores, intrapartical pores, and interparticle pores. The significance of this work emphasizes two aspects. First, it gives a more detailed classification of sedimentary environment of the mudstone succession; second, it acquires the preliminary subsurface data regarding to the shale gas potential evaluation. [ABSTRACT FROM AUTHOR]

Permo–Triassic (P–T) successions in Iran are known as one of the most extensive carbonate–evaporite sequences in the world, holding prolific hydrocarbon accumulations, such as the gas fields in the Zagros Basin. This study addresses the impact of paleoenvironmental changes across the P–T extinction boundary, variations in eustatic level and diagenesis on the carbonate reservoir quality of the Permo–Triassic Upper Dalan and Kangan formations in the Lavan Gas Field (offshore Zagros). A total of eight lithofacies have been defined and interpreted, representing the shallower parts (inner ramp to shoal) of a carbonate homoclinal ramp. The diagenetic features show the mixing influence of marine, meteoric and burial processes, with prevalence of multistage dolomitization and late meteoric‐related imprints. The main dolomitization processes are interpreted to be penecontemporaneous and associated with continuous seawater reflux and high evaporation within the intertidal environment. Combined analysis of facies and petrophysical properties has been utilized to define six rock types, including RT4 (grainstones from oolitic shoals) as the best reservoir, whereas RT1 (supratidal anhydrite) is acting as the main cap rock within the studied carbonate–evaporite sequence. Multiscale characterization of lithological and petrophysical properties suggest that the Upper Dalan Formation has a single reservoir unit (D1), whereas the Kangan Formation may be divided into two reservoir units (K1 and K2). The best reservoir quality is promoted by dissolution and dolomitization associated with late Transgressive Sequence Tracts (TST) to early Highstand Sequence Tracts (HST) sequences, while low reservoir quality corresponds to late HST sequences accompanied by pore‐occluded cements. Petrophysical analysis suggest better porosity‐permability for the Upper Dalan than for the Kangan Formation. This observation is closely associated with the different nature of lithofacies, where the Kangan Formation contains more fine‐grained carbonate rocks, and the higher intensity of porosity‐grain dolomitization in the Upper Dalan Formation. This study provides a better understanding on reservoir quality prediction across the P–T boundary and the effect of eustatic fluctuations and diagenesis in controlling porosity‐permeability evolution with similar settings elsewhere. [ABSTRACT FROM AUTHOR]

The thermal and diagenetic evolution of shale units has received renewed focus because of their emergence as unconventional hydrocarbon reservoirs. The Serra Alta Formation (SAF) is a Permian shale unit of the Paraná Basin, which is the largest South American cratonic basin. The SAF stands out as a pathway for aqueous fluids and hydrocarbon migration from the Irati organic-rich shales to the Pirambóia fluvial-eolian sandstone reservoirs. Vertical NNW and NNE opening fractures would be the main pathways for the migration of buried pore waters and aqueous fluids, besides the input of meteoric water. These fractures would be associated to the reactivation of basement discontinuities such as the Jacutinga (NE) and Guapiara (NW) faults. Thus, vertical NNE and NNW associated fractures would represent the main pathways for fluid migration in the studied area. The vertical calcite filled opening fractures from SAF record moderately low salinity (0–4.5 wt % of NaCl eq.) aqueous fluids, suggesting the input of meteoric water in the buried fracture system. Eutectic melting temperatures at −52±5 °C indicate an H 2 O + NaCl + CaCl 2 system with CaCl 2 or MgCl 2 in solution. Homogenization temperatures recorded in fluid inclusion assemblages (FIAs) of calcite filled opening fractures indicate that the SAF in the studied area reached temperatures above 200 °C, suitable for generation of gaseous hydrocarbons. The recorded paleotemperatures point to a thermal peak associated with Serra Geral volcanic event during the Early Cretaceous, with the thermal effect of volcanic rock cap possibly overcoming the effect of intrusive igneous bodies. The detection of methane in SAF shale pores indicates conditions for hydrocarbon generation. However, additionally studies are necessary to confirm the thermogenic and/or biogenic origin of the methane within the SAF. [ABSTRACT FROM AUTHOR]

The Pico do Itapeva Formation is a key metasedimentary unit to the understanding of the extensional events that occurred between the late stage of the southern Brasília Orogen collision and the main collision in the central Ribeira Orogen. The formation crops out in a 20 km long NE-trending narrow belt in the Mantiqueira mountain range in eastern São Paulo State, Brazil. It is located in the interference zone of the southern Brasília and the central Ribeira orogens and records deformation and greenschist facies metamorphism (biotite zone) related to the Brasiliano orogeny. The Pico do Itapeva Formation rests unconformably on a metaigneous substratum of the Socorro-Guaxupé Nappe/Embu Terrane and, on the southern side, is truncated by a steep SE-dipping dextral reverse shear zone. It consists of a coarsening- and thickening-upward succession, with minimum thickness of 800 m, composed of lutite, arkose and conglomerate. These rocks constitute three distinct lithofacies associations: LAI- arkose, arkose-lutite composite beds, lutite and fine conglomerate beds; LAII- arkose, pebbly arkose and scarce lutite and; LAIII- conglomerate and pebbly arkose. Most of the beds are massive; graded beds, dish and convolute structures occur locally. Bed thickness varies from thin to very thick and amalgamated bodies constitute up to 30m thick strata. Three mappable units at scale 1:20,000 were recognized based on different proportions of the three lithofacies associations. The deposits are interpreted as the record of mass flows and associated processes in a fan delta setting developed in an intermontane rift basin. U-Pb LA-ICP-MS detrital zircon ages suggest the maximum depositional age at ca. 611 Ma and the basin evolution is interpreted in the range between 611 and 580 Ma during an inter-orogenic stage between the Brasília and Ribeira orogenies. [ABSTRACT FROM AUTHOR]

Based on seven measured sections from Svalbard, the marine strata of the Permian Kapp Starostin Formation are arranged into seven transgressive–regressive sequences (TR1–TR7) of c. 4–5 Ma average duration, each bound by a maximum regressive surface. Facies, including heterozoan-dominated limestones, spiculitic cherts, sandstones, siltstones and shales, record deposition within inner, middle and outer shelf areas. The lowermost sequence, TR1, comprises most of the basal Vøringen Member, which records a transgression across the Gipshuken Formation following a hiatus of unknown duration. Temperate to cold, storm-dominated facies established in inner to middle shelf areas between the latest Artinskian and Kungurian. Prolonged deepening during sequences TR2 and TR3 was succeeded by a long-term shallowing-upward trend that lasted until the latest Permian (TR4–TR7). A major depocentre existed in central and western Spitsbergen while to the north, Dickson Land remained a shallow platform, leading to a shallow homoclinal ramp in NE Spitsbergen and Nordaustlandet. The Middle Permian extinction (late Capitanian) is recorded near the base of TR6 in deeper parts of the basin only; elsewhere this sequence is not recorded. Likewise the youngest sequence, TR7, extending to the upper formational contact of latest Permian age, is found only in the basin depocentre. Comparison with age-equivalent strata in the Sverdrup Basin of Canada reveals a remarkably similar depositional history, with, for example, two (third-order) sea-level cycles recorded in the Late Permian of both regions, in keeping with the global record. Sequence stratigraphy may therefore be a powerful correlative tool for onshore and offshore Permian deposits across NW Pangaea. [ABSTRACT FROM AUTHOR]

Shales in the middle Permian Lucaogou Formation in the intracontinental Santanghu rift basin have been considered as “typical” organic-rich profundal shales for decades. Our study of well cores using petrographic microscope and scanning electron microscopy suggests an otherwise complex hydrovolcanic and hydrothermal origin. This paper describes characteristics of a particular type of the shales, composed of fine-grained detrital minerals and lithic grains. Some of them are orthopyroxene, calcite, peralkaline feldspars, and analcime that are interpreted as derived from peralkaline-alkaline carbonatite, pyroxenite, analcime phonolite, and andesite, whereas others are quartz, dolomite, ankerite, serpentine, and calcite that were precipitated from syndepositional or penecontemporary hydrothermal fluids. Grain size ranges from 0.001 to 2 mm, mostly 0.01–0.1 mm. Well-developed laminae are mostly 0.5–3 mm thick and alternate with tuffaceous dolomicrite. The rocks are interpreted as sublacustrine hydrovolcanic deposits, which had been altered by syndepositional hydrothermal fluids. The interpretation is substantiated by abundant cone-shaped stratigraphic buildups on seismic sections in the basin. This study shows an ancient example of volcanic-hydrothermal deposits in a rift basin. [ABSTRACT FROM AUTHOR]

In the present study, we carried out trace element analyses of black shales of the Ediacaran Doushantou Formation from two sections (Jiulongwan, Baiguoyuan) in Hubei Province, South China. Mo-U characteristics of black shales from the two sections and compiled Mo-U data of Doushantuo black shales from sections of a variety of sedimentary facies described the temporal/spatial variability in the redox conditions of paleo-seawater during deposition of the Doushantuo Formation. Changes in Mo-U patterns of the Doushantuo Member II (DST2) shales of open marine environments are consistent with a shift from a predominately oxic to a predominately anoxic ocean during their deposition. Mo-U patterns of the DST2 black shales from intra-shelf sections reflect basin restriction may have happened in the intra-shelf basin and are compatible with the redox-stratified model of the intra-shelf basin. Mo-U patterns of black shales of the Doushantuo Member IV (DST4) reveal that the shales from intra-shelf sections have more pronounced Mo enrichment and more significant enrichment of Mo over U than the slope shales, indicating the operation of a Mn particulate shuttle in the intra-shelf basin. High Mo/TOC ratios of the DST4 at the intra-shelf sections, in combination with similar Mo-TOC patterns of the DST4 from both intra-shelf and slope sections, indicate the intrashelf basin was well connected to the open ocean during deposition of the DST4. [ABSTRACT FROM AUTHOR]

The Xujiaweizi (XJWZ) fault depression is a primary area for deep-seated gas exploration in Daqing. Through seismic profile interpretation, the main sag-controlling fault and structural characteristics in the XJWZ fault depression were analyzed based on folds and faults analysis. A three-dimensional geological model of the XJWZ fault depression was also set up to enable further discussion by means of structural physical modeling. According to our research, the basic structural framework of the XJWZ fault depression was the result of regional extension. Its formation and evolution were mainly controlled by the Xuxi fault. The structural framework of S-N blocking was due to changes in the fracture attitude. The Xuzhong uplift and the depressions on both sides belong to a normal-fault-related fold and were formed by controlling of the ramp/flat normal fault in the same tectonic movement period. [ABSTRACT FROM AUTHOR]

In this paper, in a case study of Santanghu Basin in China, the morphological characteristics and size distribution of nanoscale pores in the volcanic rocks of the Haerjiawu Formation were investigated using the results of low temperature nitrogen adsorption experiments. This research showed that within the target layer, a large number of nanoscale, eroded pores showed an 'ink bottle' morphology with narrow pore mouths and wide bodies. The fractal dimension of pores increases gradually with increasing depth. Moreover, as fractal dimension increases, BET-specific surface area gradually increases, average pore diameter decreases and total pore volume gradually increases. The deeper burial of the Haerjiawu volcanic rocks in the Santanghu Basin leads to more intense erosion by organic acids derived from the basin's source rocks. Furthermore, the internal surface roughness of these corrosion pores results in poor connectivity. As stated above, the corrosion process is directly related to the organic acids generated by the source rock of the interbedded volcanic rocks. The deeper the reservoir, the more the organic acids being released from the source rock. However, due to the fact that the Haerjiawu volcanic rocks are tight reservoirs and have complicated pore-throat systems, while organic acids dissolve unstable minerals such as feldspars which improve the effective reservoir space; the dissolution of feldspars results in the formation of new minerals, which cannot be expelled from the tight reservoirs. They are instead precipitated in the fine pore throats, thereby reducing pore connectivity, while enhancing reservoir micro-preservation conditions. [ABSTRACT FROM AUTHOR]

In this study, the geochemistry (major, trace and rare earth elements) of fluvial deposits of the Çaybağı and Palu Formations, Eastern Elazığ, have been investigated. The basement of the studied basin is composed of the Guleman Group, Elazığ Magmatics, Hazar-Maden Group, and Kırkgeçit Formation which consist of volcanic materials derived from the Elazığ Magmatics. The Çaybağı Formation is composed of thick fluvio-lacustrine sedimentary sequence. Palu Formation consists of alluvial fan deposits and braided river, lacustrine sedimentary deposits. Samples were collected from braided river deposits of Çaybağı and Palu Formation along Hacısamdere-Çaybağı section (Ç-samples) and Hacısamdere-Palu section (PL samples). Significant positive correlation between Zr/Sc and Th/Sc ratios of two sample groups show that the siliciclastic sample groups do not represent considerable sediment recycling. Çaybağı and Palu samples have similar geochemical indices (Al2O3/TiO2, Ti/Zr, La/Th, La/Sc, Cr/Th, Co/Th, (La/Yb)N, (Gd/Yb)N, LREE/HREE ratios) and indicate derivation from intermediate-basic source rocks. In Si vs. Na/K diagram samples plot in arc field and La/Sc and Ti/Zr ratios show that samples were plotted in an oceanic island arc environment. [ABSTRACT FROM AUTHOR]

Metagabbros and amphibolites exposed in the Bou-Maïza area of the Edough massif (northeast Algeria) are described in detail. Field and petro-structural observations point to the syn-sedimentary emplacement of gabbros as clasts, blocks and lenses of polymictic gabbroic breccias. Associated amphibolites display fine-scale parallel sedimentary bedding and represent mafic epiclastites, litharenites and mafic greywackes. The mafic beds and lenses are intercalated with aluminous pelitic schists of continental origin, quartzite and marble. It is concluded that all mafic rocks from this locality derive from the erosion of an oceanic plutono-volcanic complex of MORB affinity that was reworked in a block matrix mélange and emplaced as turbidites and debris flows during the Mesozoic. We propose a convergent plate margin setting for these formations connected with the subducted Calabrian branch of the Tethyan slab. [ABSTRACT FROM AUTHOR]

The SW Barents Sea margin experienced a pulse of extensional deformation in the Middle-Late Devonian through the Carboniferous, after the Caledonian Orogeny terminated. These events marked the initial stages of formation of major offshore basins such as the Hammerfest and Nordkapp basins. We mapped and analyzed three major fault complexes, (i) the Måsøy Fault Complex, (ii) the Rolvsøya fault, and (iii) the Troms-Finnmark Fault Complex. We discuss the formation of the Måsøy Fault Complex as a possible extensional splay of an overall NE-SW-trending, NW-dipping, basement-seated Caledonian shear zone, the Sørøya-Ingøya shear zone, which was partly inverted during the collapse of the Caledonides and accommodated top-NW normal displacement in Middle to Late Devonian-Carboniferous times. The Troms-Finnmark Fault Complex displays a zigzag-shaped pattern of NNE-SSW- and ENE-WSW-trending extensional faults before it terminates to the north as a WNW-ESE-trending, NE-dipping normal fault that separates the southwesternmost Nordkapp basin in the northeast from the western Finnmark Platform and the Gjesvær Low in the southwest. The WNW-ESE-trending, margin-oblique segment of the Troms-Finnmark Fault Complex is considered to represent the offshore prolongation of a major Neoproterozoic fault complex, the Trollfjorden-Komagelva Fault Zone, which is made of WNW-ESE-trending, subvertical faults that crop out on the island of Magerøya in NW Finnmark. Our results suggest that the Trollfjorden-Komagelva Fault Zone dies out to the northwest before reaching the western Finnmark Platform. We propose an alternative model for the origin of the WNW-ESE-trending segment of the Troms-Finnmark Fault Complex as a possible hard-linked, accommodation cross fault that developed along the Sørøy-Ingøya shear zone. This brittle fault decoupled the western Finnmark Platform from the southwesternmost Nordkapp basin and merged with the Måsøy Fault Complex in Carboniferous times. Seismic data over the Gjesvær Low and southwesternmost Nordkapp basin show that the low-gravity anomaly observed in these areas may result from the presence of Middle to Upper Devonian sedimentary units resembling those in Middle Devonian, spoon-shaped, late- to post-orogenic collapse basins in western and mid-Norway. We propose a model for the formation of the southwesternmost Nordkapp basin and its counterpart Devonian basin in the Gjesvær Low by exhumation of narrow, ENE-WSW- to NE-SW-trending basement ridges along a bowed portion of the Sørøya-Ingøya shear zone in the Middle to Late Devonian-early Carboniferous. Exhumation may have involved part of a large-scale metamorphic core complex that potentially included the Lofoten Ridge, the West Troms Basement Complex and the Norsel High. Finally, we argue that the Sørøya-Ingøya shear zone truncated and decapitated the Trollfjorden-Komagelva Fault Zone during the Caledonian Orogeny and that the western continuation of the Trollfjorden-Komagelva Fault Zone was mostly eroded and potentially partly preserved in basement highs in the SW Barents Sea. [ABSTRACT FROM AUTHOR]

Measurements of TOC, Rock-Eval pyrolysis, carbon isotope composition, solvent extract, extract fractionation, and the gas chromatography-mass spectrum (GC-MS) of the saturated fraction were conducted on the Lower Permian Fengcheng Formation carbonate-bearing shales and argillaceous dolomites of Well FN7 in the northwestern Junggar Basin to understand the geochemistry and depositional environmental evolution of the carbonate-bearing lacustrine source rocks. The results indicate that the Fengcheng Formation carbonate-bearing shales are fair to good source rocks with Type II kerogen for generating oil and minor gas, and the argillaceous dolomites are poor source rocks. The thermal mature shales contain more residually generated hydrocarbon, whereas the argillaceous dolomites contain more migrated hydrocarbon. This property is favorable for shale oil or tight oil accumulation in the Fengcheng Formation. Biomarker analyses indicate that the Fengcheng Formation source rocks were formed in the anoxic reducing lacustrine depositional environment with a stratified water column and high salinity. The source rock organic matter has major aquatic phytoplankton and algae input and less terrestrial organic matter input. During the Fengcheng Formation period, oxidation had a weak increasing tendency and salinity had a weak decreasing tendency from the early to late periods under the background of a reducing environment. Except for poor source rocks in upper and lower parts, the good source rocks are primarily in the middle part of the Fengcheng Formation. [ABSTRACT FROM AUTHOR]

A geometrically quantitative plate-kinematic model, based on paleomagnetism, for the initial assembly of Laurentia has taken form in the past few decades. Within this framework, there remains but one problematic interval of data predominantly from the Slave craton, which is the 1.96–1.87 Ga Coronation apparent polar wander path (APWP). The Coronation APWP shows large (∼110°) back-and-forth oscillations that are difficult to explain in terms of plate motion. Nonetheless, poles from the Coronation APWP have been incorporated in various paleogeographic reconstructions of Laurentia and the supercontinent Nuna, pointing to the importance of testing its veracity. In this study, we conducted a detailed paleomagnetic and rock magnetic study of the ca. 1.87 Ga Pearson Formation, East Arm of Great Slave Lake, Northwest Territories, Canada. Our results show that Pearson Formation yields a characteristic remanent magnetization carried by single-domain or small pseudo-single-domain magnetite. The age of the magnetization is constrained to be older than Paleoproterozoic deformation and is interpreted as primary. Paleomagnetic declinations reveal a one-to-one correlation with local structural attitudes, indicating that some small blocks in the fold belt likely experienced significant (∼60°) vertical-axis rotations, presumably related to large dextral displacements along the McDonald Fault system. Alternative explanations, such as true polar wander or a non-dipole magnetic field, are considered less parsimonious for the data presented here. It is suspected that some existing Christie Bay Group poles (the Stark and Tochatwi Formations), which were sampled in areas with anomalous structural attitudes and differ from time-equivalent poles obtained from areas of the Slave craton far from major transcurrent faults, may similarly suffer from vertical-axis rotation. We suggest further study before using possibly rotated Christie Bay Group poles for paleogeographic reconstructions. [ABSTRACT FROM AUTHOR]

Abstract: Floodplains, paleosols, and antecedent landforms near the apex of the Brahmaputra fan delta in north‐central Bangladesh preserve cycles of fluvial sediment deposition, erosion and weathering. Together these landforms and their associated deposits comprise morphostratigraphic units that define the river's history and have influenced its channel position and avulsion behaviour through the Late Quaternary. Previously, temporal differentiation within these units has not been sufficient to decipher their sequence of deposition, an important step in understanding the spatial pattern of migration of the Brahmaputra River. Holocene units in this region are fairly well established by radiocarbon dating of in situ organic material, but pre‐Holocene units are considered Pleistocene‐aged if organic material is dated >48 000 year BP (the limit of radiocarbon dating) or the sediments are positioned beneath a prominent paleosol, interpreted as a buried soil horizon that developed during a previous sea level lowstand. In such cases, these morphostratigraphic units have been broadly interpreted as Pleistocene without knowing their absolute depositional ages or relative evolutionary chronology. Here we use detailed sediment analysis to better differentiate morphostratigraphic units at the Brahmaputra's avulsion node, establishing the sequence of deposition and subsequent weathering of these bodies. We then test this relative chronology by luminescence dating of the sands beneath these landform surfaces. This work provides the first absolute depositional age constraints of terrace sediments for the Middle to Late Pleistocene Brahmaputra River and upper Bengal basin. The luminescence ages are complemented by detailed compositional trends in the terrace deposits, including clay mineralogy and the degree of weathering. Together, these newly dated and carefully described morphostratigraphic units reflect eustasy‐driven cycles of terrace development by way of highstand floodplain deposition and subsequent lowstand exposure and weathering, along with active tectonic deformation. Defining this Late Quaternary history of terrace development and position of the Brahmaputra River is a first step toward an integrated understanding of basin and delta evolution over multiple glacioeustatic cycles and tectonically relevant timescales. [ABSTRACT FROM AUTHOR]

The paleolake that once existed in the Hetao Basin, China, represents an important stage of the Yellow River drainage system evolution in the region, but it has not been studied in detail to date. In particular, the formation and driving forces of the paleolake evolution since the late Pleistocene is still poorly understood. In this study, optically stimulated luminescence and radiocarbon dating were combined with multiproxy analysis of lacustrine sediments in the central Hetao Basin to reconstruct the paleolake evolution. Proxies included carbonate 18 O and 13 C isotopes, grain size, magnetic susceptibility, and color. In combination with stratigraphic records, the proxies indicated the existence of a lake environment in the Hetao Basin between ∼150 and ∼18 ka BP. The paleolake between 150 and 130 ka BP was an open system. Between 130 and 54 ka BP, the paleolake basin closed, with high lake levels at the beginning of the period and then a gradual decrease. After 54 ka BP, the paleolake began to outflow and gradually shrank in size, and after 18 ka BP an alluvial fan covered the region, and the paleolake disappeared. We propose a combination of tectonic uplift and climate changes as the main drivers of paleolake formation and evolution since the late Pleistocene. [ABSTRACT FROM AUTHOR]

Large quantities of natural gases have recently been discovered in the marine carbonate formations in the Sichuan Basin, southern China. The origins and isotopic compositions of the gases are poorly understood and highly controversial. We examined the chemical and isotopic compositions of the carbonate reservoir gases in marine formations from the Sinian to Lower Triassic as well as shale gas from the Silurian and Cambrian Formation in the Sichuan Basin. It is found that the carbon isotopes of the carbonate reservoir gases had been evolved through three stages corresponding to pre-rollover, rollover and post-rollover in the plot of δ 13 C 2 versus wetness, which is consistent with that found in shale gas by Tilley and Muehlenbachs (2013). The unique carbon isotopic compositions indicate that both kerogen and oil-cracking gas have contributed to the accumulation of the carbonate reservoir gases in the Sichuan Basin. A mixing of two thermogenic gases with different maturities can cause the δ 13 C reversal between methane and ethane, which is commonly observed in the carbonate reservoir gases in the Carboniferous, Permian and Triassic formations, and the shale gas in the Silurian and Cambrian formations in the Sichuan Basin. We established two mixing models for quantitatively determining the contribution of each type gas for the natural gases in different formations. Kinetic extrapolation based on thermal history of the Anyue gas field demonstrates that ethane cracking indeed occurred in the deep reservoir formations, which may explain the disappearance of the 13 C reversal for methane and ethane in the carbonate reservoir gases in the post-rollover zone. It is proposed that organic-inorganic interactions may be responsible for the presence of D isotope rollover for methane in carbonate reservoir gases with ultra-high maturity. The organic-inorganic interactions include thermal reactions between water and residual organic matters or carbons and hydrogen isotope exchange between water and methane, and their mechanism needs further investigations in future. [ABSTRACT FROM AUTHOR]

A time series of produced shale gas samples from Lower Silurian Longmaxi Formation (Fm.) were collected from six production wells during 3.5 years production period from the Weiyuan and Changning shale gas pilots in Sichuan basin, China. The molecular compositions and carbon isotopes of CH 4 , C 2 H 6 , C 3 H 8 and CO 2 , and the hydrogen isotope of methane were analyzed for these samples by an integrated method of gas chromatography combined with mass spectrometry. The results showed that the produced shale gases are dominated by CH 4 (90.1–99.3%) with minor C 2 H 6 (0.3–0.8%) and non-hydrocarbon gases, and have low wetness (0.3–0.8%). The non-hydrocarbon gases are mainly CO 2 and N 2 , and trace amount of He. The Longmaxi shale gases display completed reversal pattern of carbon isotopic compositions with carbon number (i.e., δ 13 C 1 > δ 13 C 2 > δ 13 C 3 ) except for Wells W201 and W201-H1 with normal patterns between C 2 H 6 and C 3 H 8 (i.e., δ 13 C 2 < δ 13 C 3 ), and it is a mixture of oil cracking gas and kerogen cracking gas at high-over level of thermal maturity. Some CO 2 (δ 13 C CO2 ranging from −2.5 to −6.0‰) is mainly derived from the decomposition of carbonate minerals. CH 4 concentration and the carbon isotopes of methane and ethane during 3.5 years shale gas production from year 2012 to 2016 displayed small fluctuations, which possibly suggested that gas supply from shale matrix to fracture network after hydraulic fracturing is abundant. The Weiyuan shale gases show larger decrease of CH 4 content than the Changning shale gases, indicated more adequate supply in the Changning area. The difference in δ 13 C 1 values between horizontal and vertical wells on the same drilling site in the Weiyuan pilot indicated that the vertical heterogeneity of Lower Silurian Longmaxi shale plays an important role to shale gas production. Interestingly, the shale gases in the Weiyuan pilot display much lighter δ 13 C 1 (−34.46 to −36.82‰) and δ 13 C 2 (−37.59 to −41.89‰) values than those (δ 13 C 1 = −27.18–−27.27‰, δ 13 C 2 = −33.70–−34.14‰) in the Changning pilot. The difference in carbon isotopic compositions in Weiyuan and Changning pilots mainly attributes to mixing between varied proportion of oil cracking gas and kerogen cracking gas because of the regional heterogeneity of the Longmaxi marine shale, in particular amount of residual oil retained in organic matter rich shale. The isotopic difference between Weiyuan and Changning shale gases doesn't disappear in the period about 3.5 years of shale gas development, which further suggests the regional heterogeneity of retained residual oil exists in the Longmaxi Fm. marine shale. [ABSTRACT FROM AUTHOR]

Source rock screening analysis was performed on four stratigraphic units from the Muglad basin namely; Abu Gabra, Zarqa, Ghazal, and Baraka formations using pyrolysis and Vitrinite Reflectance (Ro). Results, integrated with the chromatographic and isotopic data from these rocks extracts and a Tertiary oil from El Mahafir-1 wild cat, were used to determine the origin of the oil. A good organic source within the Middle Abu Gabra Formation is observed in wells El Toor-6 and Neem Deep-1 (TOC, 1.0–2.0% & S2 5.0–10.0 mg C/g rock), with mixed kerogens I, II, & III, and thermally mature (% Ro = 0.74–0.94). The Campanian-Early Maastrichtian sequence, i.e. Zarqa and Ghazal formations are generally poor (TOC, <0.5% & S2 <2.5 mg C/g rock), dominated by type III kerogens, and immature at the studied locations. The Baraka shale nevertheless, is good at El Mahafir-1 well (avg. TOC 1.8% & S2 5.0–10.0 mg C/g rock) and fair at Timsah-1 well (Avg. TOC 0.69% & S2 2.5–5.0 mg C/g rock) with a Kerogen that is predominantly Sapropellic at the former, and an exclusively Humic at the later. The formation is mature at Timsah (% Ro = 0.77–1.16) and early mature at El Mahafir-1 (% Ro = 0.64–0.81). Consistent with the pyrolysis, chromatographic data of the rock extracts confirms the mixed source nature of the Abu Gabra Formation which consists of both algal [prominent LMW n-alkanes & elevated C 27 steranes (36–47%)], as well as terrigenous material [higher diasterane/regular sterane ratios (0.50–0.56), abundant rearranged hopanes, & relatively high CPIs (1.22–1.9)], accumulated in an oxic to sub-oxic environment (Pr/Ph, 1.3–3.0). Abu Gabra further shows low C 29 /C 30 hopanes (0.45–0.54), low C 28 steranes (21–26%) with high Gammacerane index (20.3). In contrast, the environment during the Late Cretaceous was strongly reducing (Pr/Ph, 0.37–1.0), associated with a wide organic diversity, both in space and time and is characterized by dominant algal input at some areas and or stratigraphic intervals [Elevated tricyclics, higher C 29 /C 30 hopanes (0.5–1.14), and relatively low Gammacerane indices (4.6–14.4)], while mixed with abundant terrigenous material at others. A direct correlation between El Mahafir oil and the Abu Gabra extracts is thus inferred based on: its mixed organic source nature, oxic to sub-oxic depositional environment (Pr/Ph 1.22), relatively low C 29 /C 30 hopanes (0.54), low C 28 steranes (29%), and a high gammacerane index (20.5). This is largely supported by the maturity modeling results which suggest generation is only from the Abu Gabra at this location. [ABSTRACT FROM AUTHOR]

Facies analysis of the Cretaceous Bima Formation in the Gongola Sub –basin of the Northern Benue Trough northeastern Nigeria indicated that the Lower Bima Member is composed of alluvial fan and braided river facies associations. The alluvial fan depositional environment dominantly consists of debris flow facies that commonly occur as matrix supported conglomerate. This facies is locally associated with grain supported conglomerate and mudstone facies, representing sieve channel and mud flow deposits respectively, and these deposits may account for the proximal alluvial fan region of the Lower Bima Member. The distal fan facies were represented by gravel-bed braided river system of probably Scot – type model. This grade into sandy braided river systems with well developed floodplains facies, forming probably at the lowermost portion of the alluvial fan depositional gradient, where it inter-fingers with basinal facies. In the Middle Bima Member, the facies architecture is dominantly suggestive of deep perennial sand-bed braided river system with thickly developed amalgamated trough crossbedded sandstone facies fining to mudstone. Couplets of shallow channels are also locally common, attesting to the varying topography of the basin. The Upper Bima Member is characterized by shallow perennial sand-bed braided river system composed of successive succession of planar and trough crossbedded sandstone facies associations, and shallower channels of the flashy ephemeral sheetflood sand – bed river systems defined by interbedded succession of small scale trough crossbedded sandstone facies and parallel laminated sandstone facies. The overall stacking pattern of the facies succession of the Bima Formation in the Gongola Sub – basin is generally thinning and fining upwards cycles, indicating scarp retreat and deposition in a relatively passive margin setting. Dominance of kaolinite in the clay mineral fraction of the Bima Formation points to predominance of humid sub – tropical to tropical climatic conditions. This favors pedogenic activities which are manifested in the several occurrences of paleosols. Pronounced periods of arid climatic conditions are also notable from the subordinate smectite mineralization. Chlorite mineralization at some localities is indicative of elevation of the provenance area, and this is synonymous with deposition of the Bima Formation, because of its syn – depositional tectonics. The absences of lacustrine shales in the syn – rift stratigraphic architecture of the Bima Formation indicates that the lower Cretaceous petroleum system that are common in the West and Central African Rift basins are generally barren in the Gongola Sub – basin of the Northern Benue Trough. [ABSTRACT FROM AUTHOR]

This paper investigated the porosity controlling factors for tight sandstone reservoir in the Daniudi gas field, Ordos Basin based on an integrated petrographic, petrophysical and geostatistical analyses, and proposed a comprehensive prediction model for reservoir porosity. Compaction was found to be a key factor for causing reservoir densification. The degree of sandstone compaction appears to be affected by grain sizes and sorting. Under normal compaction conditions (e.g., cement content less than 6%, and with no dissolution), the variation in reservoir porosity with burial depth can be well correlated with grain compositions, grain sizes, and sorting. Based on qualitative examination of the controlling factors for reservoir porosities, geostatistics were used to quantify the effects of various geological parameters on reservoir porosities. A statistical model for comprehensive prediction of porosity was then established, on the assumption that the present reservoir porosity directly relates to both normal compaction and diagenesis. This model is easy to use, and has been validated with measured porosity data. The porosity controlling factors and the comprehensive porosity prediction can be used to quantify effects of the main controlling factors and their interaction on reservoir property evolution, and may provide a reference model for log interpretation. [ABSTRACT FROM AUTHOR]

The Lower Permian Lucaogou Formation in the Jimsar sag, Junggar Basin is a typical tight-oil reservoir in China. For effective exploration and production, the formation of a high-quality reservoir must be thoroughly studied. In this work, the tight-oil reservoir was examined using a variety of methods, including core and thin-section observations, XRD, SEM, CL and fluid inclusion and isotope testing. The tight-oil reservoirs were primarily deposited in saline lake environments, which are dominated by variable admixture of dolomite, quartz, feldspar, tuff, calcite and pyrite. Nine main lithofacies were identified: (1) siliceous mudstone, (2) dolomitic siliceous mudstone, (3) dolomitic mudstone, (4) intraclast packstone/grainstone, (5) ooid grainstone, (6) bioclast grainstone, (7) dolomitic siltstone, (8) mixed siliclastic and intraclast grainstone and (9) brecciated dolomitic mudstone. The pore types are classified into four categories: primary intergranular, moldic, intercrystalline and fracture pores. The properties of tight-oil reservoirs are quite poor, with low porosity (ave. 7.85%) and permeability (ave. 0.110 mD) and a small pore-throat radius (ave. 0.086 μm). The tight-oil reservoirs are dominated by the aggradation of a repetitive meter-scale sedimentary facies succession that records distinct lacustrine expansions and contractions. These tight carbonates have also undergone significant diagenetic alterations, such as dolomitization, dissolution, neomorphism and fracture created intercrystalline and moldic pores, vug and fractures; chemical and mechanical compaction and carbonate cementation have decreased the reservoir quality. Variations in reservoir quality in the Jimusar sag are due to a combination of lithofacies type, high-frequency cyclic depositional architecture, dissolution intensity, dolomitization and tectonic related deformation. This integrated study has helped in understanding the reservoir heterogeneity and hydrocarbon potential of the Jimusar fine-grained rocks. [ABSTRACT FROM AUTHOR]

Based on the sedimentary and tectonic background of the Termit Basin, this paper focuses on the Upper Cretaceous Yogou Formation and uses organic geochemistry, logging, oil testing and seismic data to analyze the primary control factors of the hydrocarbon accumulation and establish corresponding model in order to predict favorable exploration target zones of hydrocarbon reservoirs. This study demonstrates that the Upper Cretaceous Yogou Formation is a self-generation and self-accumulation type reservoir. The Yogou Formation hydrocarbon reservoirs in the Koulele area are controlled by four factors: (1) the source rock is controlled by a wide range of YS1-YS2 marine shale, (2) the sandstone reservoir is controlled by the YS3 underwater distributary channel and storm dunes, (3) migration of hydrocarbons is controlled by faults and the regional monocline structure, and (4) the accumulation of hydrocarbons is controlled by lateral seal. The structures in the western Koulele area are primarily reverse fault-blocks with large throws, and the structures in the east are dominantly fault-blocks with small throws (co-rotating and reverse) and a fault-nose. In the western Koulele area, where the facies are dominated by storm dunes on a larger scale, it is easier to form lithologic reservoirs of sandstone lens. In the eastern Koulele area, high-quality channel sandstone reservoirs, fault-blocks with small throws, and the monocline structure benefit for the formation of updip pinch out lithologic traps, fault lithologic reservoirs and fault-nose structural reservoirs. Future exploration targets should be focused in the western storm dunes zone and eastern distributary channel sand zone with small fault-blocks. [ABSTRACT FROM AUTHOR]

Based on observations made on cores and cuttings from several wells in the lowermost part of the third member of the Shahejie Formation, several rock types, specifically clast-supported rudstone, matrix-supported rudstone, mixed-source rudstone, calcisiltite/calcarenite, massive calcilutite and laminated calcilutite, have been identified in the Shulu sag. According to the sedimentary structures and distribution characteristics of these rocks, the carbonate breccias fall into two categories, based on their origins: one formed by fan-delta channel sedimentation, whereas the other formed by earthquake-induced slump fan deposition. Clast-supported rudstone and matrixsupported rudstone are the main lithologies deposited by braided rivers in the fan delta plain and front, of which the pore space is mainly dissolution pores within gravels and tectonic fissures. Clastsupported rudstone, matrix-supported rudstone and mixed-source rudstone are the main lithologies of the earthquake-induced slump fans. These carbonate breccias developed along with soft-sediment deformation structures, which are interpreted as seismites and are widely distributed in the sag, in which intercrystalline pores, intergranular pores and fissures created from diagenetic shrinkage are developed. The two kinds of rudstones have different reservoir characteristics and oil/gas testing results. The rudstones generated in the fan delta have higher porosity and permeability, as well as better oil/gas testing results. Thus, they are key targets for petroleum exploration. [ABSTRACT FROM AUTHOR]

The concentration and distribution of organic matter, phosphate nodules, and framboidal pyrite preserved in shales are controlled by organic matter decomposition and the cycles of phosphorus, sulfur, and iron, which, in turn, are controlled by bottom-water redox conditions. The organic-rich shale in the 7th member of the Upper Triassic Yanchang Formation (Ch7) contains high organic carbon concentrations and abundant phosphate nodules and pyrite framboids, providing an opportunity to better understand the redox conditions at the time of deposition. Framboidal pyrite in the Ch7 organic-rich shales are composed of octahedral, pyritohedral, and spherulitic microcrystals with uniform crystal size. SEM photographs and statistical data suggest that pyrite framboids have large mean diameters (10.0 to 18.1 μm) and standard deviations (2.8 to 5.9 μm). This may indicate that the organic-rich shale was deposited under oxic-suboxic bottom-water conditions. The C org :P ratios of the organic-rich shale exhibit considerable variation, ranging from 7.2 to 216, but the majority of them (83.2%) belong to the lower-intermediate range (< 130), suggesting that the redox conditions were predominantly oxic-suboxic and intermittently anoxic. The C org :P ratios also show periodic vertical variation, which suggests that redox conditions fluctuated between oxic-suboxic and anoxic. Additional support for the trends based on C org :P ratios is provided by DOP T values, which show similar vertical variation and redox patterns. All evidence shows that the redox conditions during deposition of the Ch7 organic-rich shale was predominantly oxic-suboxic accompanied by intermittent anoxic environments. The result of this study will be helpful in better understanding the formation mechanism of the Ch7 organic-rich shale. [ABSTRACT FROM AUTHOR]

To gain a better understanding of the oceanic environment of the transitional Lower-Middle Cambrian boundary and provide additional data for the global ROECE correlation, we studied the carbon isotope records of shallow-water platform carbonates of the Cambrian Stage 4 Longwangmiao Formation in the Bandenggou section in Chongqing, South China, and correlated with previously reported contemporaneous δ 13 C carb records across a range of depositional environments on the Yangtze Platform and other basins. The δ 13 C carb curve of the Longwangmiao Formation fluctuates frequently approximately 0‰ with multiple excursions at its lower sequence, exhibits a conspicuous negative δ 13 C excursion with a minimum peak value of − 4.76‰ at the middle sequence, and then possesses a stable positive distribution upward. The correlation across the platform-to-basin transect on the Yangtze Platform shows that the Toyonian sections, from slope to basin, have similar shapes of δ 13 C curves, with a depleted trend upward and consistent timings of the largest-amplitude negative δ 13 C excursion, termed ROECE, while contemporaneous shallow-water platform sections have different δ 13 C profile shapes and timings of their largest-amplitude negative δ 13 C excursions, as do sections at a range of depositional environments from a multitude of continents. We infer that the carbon isotopic compositions from the Bandenggou section in the shallow-water environment layer may retain a regional signal. The negative δ 13 C distribution of the lower sequence is primarily due to a local, long-term riverine influx and low relative sea level at the early stage, which amplified organic matter decay and diminished primary productivity. Eventually, this elevated the oxidation and eutrophication of the shallow water, while the stable positive δ 13 C distribution upward is attributed to the integrated influence of a long-term scant riverine flux and high relative sea level. Additionally, the location of ROECE in the shallow-water sections still needs substantiation at the global scale. [ABSTRACT FROM AUTHOR]

A combined investigation of bulk geochemistry and molecular geochemistry was carried out on 31 source rock samples from the Lower Permian Lucaogou Formation, in the Jimsar Sag of the Junggar Basin, northwestern China. Geochemical characterization reveals the depositional environments and other factors favorable for the generation and accumulation of β-carotane, an important hydrocarbon precursor. Many core samples have a total organic carbon content > 1%, and Rock-Eval S 2 values > 2 mg HC/g rock, suggesting relatively high hydrocarbon generation potential. Biomarkers in the Lucaogou source rock extracts are characterized by short- to long-chain n-alkanes, a wide range of Pr/Ph ratios (0.74–1.42) and β-carotane index values (β-carotane/C max , 0.16–1.92), high concentrations of C 29 sterane, relatively low tricyclic terpane content, and moderate gammacerane index values (0.14–0.29). This is consistent with a weakly oxidizing to weakly reducing depositional environment, with fresh to brackish water conditions, rapid input of terrigenous organic matter, and a relatively small contribution of aquatic algal-bacterial organic matter. Cross-plots of biomarker parameters and the β-carotane index show that β-carotane in the Lucaogou source rocks is mainly derived from terrigenous organic matter, and is found predominantly in sediments deposited in weakly reducing, brackish environments. It does not appear to have been affected by thermal maturation. [ABSTRACT FROM AUTHOR]

The Permian-Triassic sedimentary succession of the southern Sydney Basin in southeastern Australia contains a wealth of well-preserved trace fossils that are important for systematic ichnological, palaeoecological, and palaeoenvironmental interpretations. In this study, a new ichnofossil assemblage comprising Macaronichnus , Palaeophycus , Psammichnites , Protovirgularia , Rosselia , and Teichichnus is documented from the tide-influenced shoreface deposit of the Middle Permian Jamberoo Sandstone Member of the Broughton Formation. Two distinct ichnofabrics are recognized: i) the Psammichnites ichnofabric characteristic of the upper–middle shoreface deposit; and ii) the crowded Rosselia ichnofabric (CRI) representing the lower shoreface. The Psammichnites -dominated ichnofabric is interpreted to have resulted from opportunistic behaviours of unknown trace makers, whereas the CRI is interpreted to represent possible strategic behaviours of stress-tolerant polychaetes (e.g., terebellid, spionid, and cirratulid polychaetes) in a distal shoreface with high sedimentation rate. Thus, the Psammichnites –crowded Rosselia ichnofabric succession can be considered to represent a response to an environmental shift from proximal to distal shoreface. As such, this study highlights the utility of these two ichnofabrics as stressed environmental indicators. [ABSTRACT FROM AUTHOR]

During the Early Cretaceous, a large area in Brazil and other South American countries was covered by an extensive paleoerg field, the Botucatu Desert. The Araraquara County (São Paulo State, Brazil) contains some of the most diverse ichnological assemblages in the Botucatu Formation. Mammaliform trace fossils from the Botucatu Formation are of great interest, as they may represent the only record of Lower Cretaceous Mammaliamorpha from Brazil. These trace fossils can be grouped into two distinct classes, based on the dimensions of the footprints. The larger morphotype is described and classified as a new ichnotaxon, Aracoaraichnium leonardii igen. nov. isp. nov., with a discussion of preservational features and paleoecological aspects. This morphotype can be differentiated from Brasilichnium Leonardi, 1981 by digit morphology, with digits III and IV being larger and sub-equal in size. The tracks are mesaxonic, unlike Brasilichnium , which is ectaxonic, and the stride is proportionally smaller, suggesting a trackmaker with shorter limbs in relation to body length. Another characteristic that reinforces the new ichnotaxon is the larger size of the footprints of Aracoaraichnium igen. nov. Footprints representing intermediate ontogenetic stages between Brasilichnium and the larger morphotype are not observed, suggesting that the two track types were made by different taxa. Compared with others tetrapod ichnotaxa, the new ichnotaxon is characterized by differences in the number and morphology of the digits, track morphology, the degree of heteropody, and locomotor parameters. Tracks with good preservation quality were likely originally produced in the humid subsurface, below the surficial dry sand layer. Tracks with smaller dimensions, and trackways with the presence or absence of the manus, may be due to variable degrees of impression into subsurface layers, and substrate heterogeneity. The Aracoaraichnium igen. nov. trackmakers probably inhabited areas near the desert, making occasional incursions into desert areas, while Brasilichnium trackmakers may have been mostly nocturnal residents of the desert environment. [ABSTRACT FROM AUTHOR]

The giant sediment-hosted Jinding zinc-lead deposit is located in the Lanping Basin, northwestern Yunnan Province, China. The genesis of the deposit has long been debated and the sources of the ore-forming fluids and metals are controversial. This study presents rare earth element (REE) and noble gas isotope data that constrain the origins of the ore fluids and the heat source driving the hydrothermal circulation. The early-stage sulfides are enriched in light REEs and have high ∑REE values (30.8–94.8 ppm) and weakly negative Eu (δEu 0.85–0.89) and Ce anomalies (δCe 0.84–0.95), suggesting that the fluids were likely derived from dissolution of Upper Triassic marine carbonates with input of REEs from aluminosilicate rocks in the basin. In contrast, the late-stage sulfides have irregular REE patterns, generally low ∑REE values (0.24–10.8 ppm) and positive Eu (δEu 1.22–10.9) and weakly negative Ce anomalies (δCe 0.53–0.90), which suggest that the ore-forming fluids interacted with evaporite minerals. The 3 He/ 4 He (0.01–0.04 R a ) and 40 Ar/ 36 Ar values (301–340) of the ore-forming fluids indicate crustal and atmospheric origins for these noble gases. These findings are in agreement with the published fluid inclusion microthermometry data and the results of H, O, C, S, Pb and Sr isotope studies. Our data, in combination with published results, support a two-stage hydrothermal mineralization model, involving early-stage basinal brines and late-stage meteoric water that acquired metals and heat from crustal sources. [ABSTRACT FROM AUTHOR]

Sediment gravity flow deposits are common, particularly in sandy formations, but their origin has been a matter of debate and there is no consensus about the classification of such deposits. However, sediment gravity flow sandstones are economically important and have the potential to meet a growing demand in oil and gas exploration, so there is a drive to better understand them. This study focuses on sediment gravity flow deposits identified from well cores in Palaeogene deposits from the Liaodong Bay Depression in Bohai Bay Basin, China. We classify the sediment gravity flow deposits into eight lithofacies using lithological characteristics, grain size, and sedimentary structures, and interpret the associated depositional processes. Based on the scale, spatial distribution, and contact relationships of sediment gravity flow deposits, we defined six types of lithofacies associations (LAs) that reflect transformation processes and depositional morphology: LA1 (unconfined proximal breccia deposits), LA2 (confined channel deposits), LA3 (braided-channel lobe deposits), LA4 (unconfined lobe deposits), LA5 (distal sheet deposits), and LA6 (non-channelized sheet deposits). Finally, we established three depositional models that reflect the sedimentological characteristics and depositional processes of sediment gravity flow deposits: (1) slope-apron gravel-rich depositional model, which involves cohesive debris flows deposited as LA1 and dilute turbidity currents deposited as LA5; (2) non-channelized surge-like turbidity current depositional model, which mainly comprises sandy slumping, suspended load dominated turbidity currents, and dilute turbidity currents deposited as LA5 and LA6; and (3) channelized subaqueous-fan depositional model, which consists of non-cohesive bedload dominated turbidity currents, suspended load dominated turbidity currents, and dilute turbidity currents deposited as LA2–LA5, originating from sustained extrabasinal turbidity currents (hyperpycnal flow). The depositional models may be applicable to oil and gas exploration and production from sediment gravity flow systems in similar lacustrine depositional environments elsewhere. [ABSTRACT FROM AUTHOR]

The ∼1500 km diameter Caloris basin is the largest, most well-preserved impact structure on Mercury. The interior of Caloris contains an enigmatic geological unit at depth subsequently excavated by smaller impacts – low-reflectance material (LRM). LRM is interpreted to be the original basin floor material and be composed of melted and re-crystallized mantle material. In this work, a comprehensive numerical modeling study of Caloris basin formation is undertaken to provide insight into basin formation on Mercury (which may differ to that on the Moon), and to address the origin of the LRM. Analysis of the modeled basin attributes demonstrates that the Caloris impact would have penetrated to depths approaching the core/mantle boundary, excavating mantle material to the surface and producing melt volumes on the order of 10 7 km 3 . Such a melt volume could differentiate, forming a layer (buried beneath later volcanism) that could be the LRM, in agreement with previous spectroscopic analyses. Furthermore, LRM deposits at other smaller basins on Mercury may also represent impact melted mantle material. A comparison to lunar basin counterparts demonstrates that basin formation on Mercury is similar to that on the Moon. This observation suggests that the observed difference in the number of large basins between the two bodies (fewer on Mercury) is due to processes that modify basins (i.e., greater impact melt volume and more extensive volcanism on Mercury), rather than first-order impact process differences. The greater average impact velocity and gravity exert a slight effect on some basin properties, including an increased excavation depth-to-transient crater diameter ratio on Mercury. [ABSTRACT FROM AUTHOR]

With the recent discovery of new oil fields around the Dongying Depression, Bohai Bay Basin, a better understanding of the origin of its high-quality lacustrine carbonate reservoirs has become important. The lacustrine carbonates of the upper fourth member of the Eocene Shahejie Formation (ES4s) have been examined using a variety of methods, including core and thin section observations, XRD, SEM, CL and fluid inclusion and isotope testing. The δ13C and δ18O values of the Dongying carbonates differ significantly from Eocene marine values, and the 87Sr/86Sr ratios of carbonate minerals are higher than Eocene marine water and the same as the surrounding Palaeozoic carbonate bedrock. Additionally, the distribution of the carbonates is controlled by the surrounding Palaeozoic carbonate bedrock, all of which indicate their lacustrine origin. Six major carbonate lithofacies are distinguished in the southern gentle slope zone. Bioclastic, oolitic and intraclastic grainstones dominate the littoral to sublittoral zones, while mudstones are mainly distributed in the profundal zone. The ES4s interval is composed of a third-order depositional sequence that contains several small-scale, higher frequency depositional cycles. Overall, stacking patterns of high-frequency depositional cycles are consistent with the general facies variation from basin to shore. Shallow-water grainstones contain both primary intergranular and secondary dissolution pores, whereas the dolomitized mudstones in the profundal zone contain intercrystalline pores and fractures. Diagenetic processes that improve reservoir quality include dissolution and dolomitization. Reservoir quality was diminished by burial calcite cementation and compaction. High-quality reservoirs are mostly distributed in dolomitized grainstones and wackestones, which are deposited in the shoal facies of shallow lakes. Variations in reservoir quality in the Dongying Depression are due to a combination of lithofacies type, dissolution intensity, early dolomitization and tectonic-related deformation. Due to the influx of meteoric waters and shallow burial depth, the grainstones in the littoral zone have the best reservoir quality. Integrated studies have helped to understand the reservoir heterogeneity and hydrocarbon potential of the Dongying lacustrine carbonates. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A trilobite faunule from the Lower Ktaoua Formation at Jbel Tijarfaouine in the eastern part of the Anti-Atlas, Morocco, includes well-preserved articulated specimens of the trinucleid Declivolithus titan sp. nov., the cyclopygids Cyclopyge sibilla Šnajdr, 1982, and Heterocyclopyge sp., and the dalmanitid Eudolatites cf. E. galafrea Šnajdr, 1987. All species are either most closely related to or are conspecific with taxa from the middle Katian Bohdalec Formation in the Prague Basin, consistent with a supposed Katian age for the middle part of the Lower Ktaoua Formation and amplifying the close palaeogeographic affinities of Perunica and west Gondwana in the Late Ordovician. However, the Cyclopyge species is much more widespread, consistent with its supposed pelagic life habit, being found as far eastwards as Xinjiang Province, China. [ABSTRACT FROM AUTHOR]

Mantle convection could have a significant effect on basin evolution; however, research quantifying this relationship is controversial. To understand the formation mechanism and evolution of the Cenozoic rift basins in eastern China, we applied the back-stripping technique and strain rate inversion modeling to 119 wells from Sangjiang Basin, Bohai Bay Basin, North Yellow Sea Basin, South Yellow Sea Basin, East China Sea Shelf Basin, and four basins within the northern South China Sea margin. The modeled results can be used to reconstruct the tectonic subsidence history and further assess the potential subsidence mechanisms of eastern China. Residual subsidence is defined as the difference between the theoretical and observed tectonic subsidences. Our results show that the residual subsidence since 20 Ma in eastern China generally increases from ∼100 to 300 m in terrestrial areas to ∼1.2–1.8 km on the continental shelf. Our observed residual subsidence is generally consistent with the present-day dynamic topography that is predicted from mantle flow models, and it is associated with a stagnant slab within the mantle that has been observed by seismic tomography. The migration pathway of the residual subsidence since 20 Ma is consistent with the movement direction of the Pacific and Philippine plates. Therefore, we suggest that the residual subsidence might be a dynamic subsidence induced by a negative buoyancy of the sinking slab in the deep mantle beneath eastern China. [ABSTRACT FROM AUTHOR]

The origin of anhydrite caprocks found in many evaporite basins is currently under debate. Existing models in the literature for anhydrite formation include rotated stratigraphic layering, rotated crestal caprock and diagenetic anhydrite. In this work, we interpret high-quality 2D seismic reflection data to understand the processes associated with anhydrite caprock formation. Our study focuses on anhydrite caprock formation in the Tromsø Basin, which represents one of several underexplored salt basins in the Arctic. We use well log data and seismic stratigraphic as well as seismic attribute analyses to characterize the ‘anhydrite’ layers associated with salt diapirs. Our results reveal that the anhydrite layers are high-amplitude reflections at the crests, which are often found close to the seabed and lateral caprocks on the flanks of salt diapirs. A third class of anhydrite layers is folded, faulted and boudinaged intrasalt stringers encased by the salt diapirs. Lateral caprocks in the Tromsø Basin are formed in response to rotated crestal caprock failure. The crestal caprocks are secondary in origin, occur at shallow depths, and are formed as insoluble residues from the dissolution of halite by the ingress of basinal fluids into the tops of diapirs. Anhydrite stringers, or floaters, originate from tectonic-related multi-dimensional salt flow. Salt diapirs in the Tromsø Basin are associated with varied anhydrite caprocks; their formation cannot be fully explained using a single model. Our work demonstrates from seismic reflection data the occurrence of caprock events that formed progressively on the flanks of salt diapirs due to local folding. [ABSTRACT FROM AUTHOR]

The image logs played a key role in interpreting the lithology and sedimentary structures of uncored units. An integrated analysis of the borehole images and open-hole logs, which are calibrated with core observations, is conducted to reveal the detailed sedimentary characteristics of the Upper Triassic Xujiahe Formation in the Central Sichuan Basin. To establish borehole image interpretation guidelines, the interpretations of sedimentary textures and lithology from cores and outcrops are calibrated with borehole images and conventional logs. Lithologies in the Xujiahe Formation include conglomerates, fine to medium-grained sandstones, siltstones, mudstones and coals. Sedimentary structures in terms of bedding, scour surface and stacking style of beds are interpreted from the image and open-hole logs. Depositional microfacies are defined on the basis of grain size and sediment texture, sedimentary structures, thickness, basal and upper contacts derived from core observations, openhole logs and image logs. The Xujiahe Formation sandstones in Central Sichuan Basin are deposited in a braided delta front, of which the depositional microfacies consist of underwater distributary channel, river mouth bar, distal bar or sand sheet and underwater interdistributary bay. The depositional microfacies is predicted in a single well using a combination of openhole conventional logs, borehole images, and cores. The distributary channels, which show box-shaped or bell-shaped GR log character, are generally infilled with fine to medium-grained sandstone with massive, tabular, wedge-shaped or trough-cross-laminated bedding. Repeated fining-upwards cycles, as well as the stacked nature of individual bedsets and the presence of scour surfaces represent multistory, amalgamated, channel-fill deposits. The underwater distributary channel deposits can also be overlain by interdistributary bay mudstones, known as channel abandonment. Mouth-bar deposits, which are characterized by coarsening- up successions, infill the channels as they migrate laterally, and sometimes could be overlain by a channel deposit. The methodology has potential application to other braided delta front reservoirs with appropriate calibration and scaling. [ABSTRACT FROM AUTHOR]