Facies Transition Research Articles

Sedimentary facies controlled biogeochemical process of biotic extinction and turnover across the Cambrian SPICE event

The Steptoean positive carbon isotope excursion (SPICE) event, one of the largest carbon cycle perturbations in the Cambrian, coincides with shallow-shelf-fauna extinction and plankton revolution (critical transition of plankton). The event is globally documented, but biogeochemical responses of these biotic evolutions in varying facies environments are not well understood. Here high-resolution paired δ18Ocarb, δ13Ccarb and δ13Corg datasets from varied paleodepth environments in the Tarim Basin, NW China reveal facies-dependent signatures of the event, with globally synchronous patterns but notable intra-basinal variability. Shallow marine facies record the end-Marjuman extinction with a distinct negative δ13Corg excursion prior to the event, while the transitional facies region marks twice positive δ13C excursions corresponding to an asynchronous plankton revolution from shallow and deep areas during the event. The varying isotope responses are interpreted in the context of primary productivity and redox conditions, with deeper basins recording more 13C enriched signals (i.e., higher δ13C) due to greater organic matter preservation under anoxic conditions, compared to the platform area. The biotic extinction, the planktonic revolution and the interaction of organisms along the shallow to deep marine depth gradient were reflected by the significant isotopic shifts recorded during the event, suggesting depth-dependent biogeochemical processes that shaped marine ecosystems.

The foresight methodology for transitional shale gas reservoirs prediction based on a knowledge graph

The sedimentary environment in the eastern Ordos area of China is complex and contains a large number of transitional facies environments. Yet, there are many characteristics such as large vertical lithology changes, complex lateral sedimentary environment changes, small monolith thickness and large organic matter content changes, which lead to large uncertainty in the prediction of favorable areas for transitional shale gas. As the intricate reservoirs continue to unfold, the conventional linear prediction methods find themselves facing an arduous path to meet the demands of development. The ever-evolving complexity of these reservoirs has outpaced the capabilities of these traditional approaches. It becomes apparent that a more comprehensive and adaptable approach is necessary to navigate the intricacies of these reservoirs and unlock their hidden potential. Therefore, we put forward a method of introducing knowledge graph into transitional shale gas reservoir prediction in the eastern Ordos region by using big data technology. Because artificial intelligence big data relies heavily on data tags, it is particularly important for the construction of tags. Firstly, a top-down knowledge graph in the field of reservoir prediction is constructed to determine the key parameters used in prediction, namely porosity, total organic carbon and brittleness index. Secondly, the decision tree knowledge graph optimization label is constructed in a bottom-up way. The key parameter of this prediction is the knowledge graph obtained according to the professional knowledge of reservoir prediction, so as to optimize the school label of U-net and reduce the workload of artificial judgment. The results of the combination of the two methods are applied to 11 wells in Daji area of Ordos, and the experimental results are consistent with the actual situation of the reservoir. Based on the foundation of theoretical knowledge, this method enhances the efficiency and accuracy of interpretation and evaluation. It provides fundamental and technical support for the selection of favorable areas in shale gas exploration and the evaluation of exploration and development prospects, particularly in transitional shale gas areas, which is innovative and advanced in the field.

Application of Seismic Sedimentology in Identifying Submarine Fan Bodies

Abstract The research area is located in the Yenisai Hatanga Basin of Russia, which is a transitional facies sedimentary rock between sea and land. Oil and gas are mostly concentrated in turbidite sand bodies of the low level domain submarine fans of Lower hutt formation in the Lower Cretaceous, and locally developed in the slope fan sand bodies of the high postion domain. which is good oil and gas reservoir, however, due to limitations of geological research conditions and data, the sedimentary characteristics and planar distribution of the submarine fan sand bodies are not clear in research area. This article conducts research on the identification and plane distribution prediction of submarine fan bodies using seismic sedimentology methods, By combining sequence stratigraphy, seismic profile, and RGB fusion technology, the sand bodies of submarine fans are analyzed. Through the correlation analysis of seismic profiles and seismic facies, corresponding relationship between sedimentary microfacies and typical seismic wave patterns is established. The study shows that the study area mainly develops continental shelf slope facies, submarine fans, and shallow to semi deep marine facies. Sediments formed a turbidite submarine fan composed of sandstone siltstone mudstone in the ancient trough. There are 5 sand groups developed in the Hutt Formation under the main target layer in the study area. Among them, the IV oil group is the main oil-bearing layer. The 0, Ⅰ, and Ⅱ sand groups have limited distribution and poor sand body connectivity. The Ⅲ sand group is mainly developed in the study area. In the north, it is distributed in the middle of the study area on the plane. The IV sand group is widely developed and distributed in the middle of the study area on the plane. Seismic sedimentology can provide technical support for prediction research of reservoirs.

Evolution of a confined gravelly river to a braided-meandering river in the Late Cretaceous Khasi group, southern Shillong plateau, NE India

This paper intends to unravel the depositional condition of the Basal Conglomerate/Jadukata Formation and the Lower Mahadek Formation in southern Shillong Plateau, NE India deposited during the Late Cretaceous period. The studied succession is entirely siliciclastics in composition and was built up on the Precambrian basement rocks. State-of-art facies analysis and palaeocurrent evidence helped us to reconstruct the palaeogeography and palaeoenvironment. The facies tracts reveal that frequent hyperconcentrated mass flow deposits dominated the proximal part of the river channels. Gradually, the river evolved to a sandy braided and finally mud-dominated, meandering system. The river channel changed its pattern through onlapping and progressive elimination of the accommodation space created by the tectonic subsidence/upliftment. Major shifts in palaeocurrent direction at different stages of the river evolution confirm the role of tectonics on the river channel evolution. QFL detrital modes of the sandstones reflecting lithic wacke composition and the recycled orogeny corroborate the interpretation. Rapid lateral and vertical facies transition suggests a pull-apart type basin due to ongoing rifting. Geochemical analyses also show signatures of the overlapping tectonic conditions supporting the pull-apart basin model.

Latest Pleistocene-Holocene sedimentary evolution from sediment records of the Tam Giang-Cau Hai coastal lagoon system, central Vietnam

The latest Pleistocene-Holocene sedimentary evolution was reconstructed from two boreholes collected in the Tam Giang-Cau Hai coastal lagoon region of central Vietnam. This research was based on analyzing radiocarbon dating, grain size, sedimentary structure, petrological components, and diatom assemblages. Besides, some high-resolution seismic data from the lagoon water body were interpreted to estimate Holocene sediment thickness. Sedimentary records of two boreholes revealed various sedimentary facies under the sea-level change since the Last Glacial Maximum (LGM): Fluvial channel facies, fluvial-lagoonal transition facies, lagoon facies, lagoonal-to-fluvial facies, and flood plain facies. Radiocarbon dating indicated that the coastal lagoon system possibly initiated around 8.8–8.5 cal kyr BP, corresponding to the meltwater pulse 1 C when saltwater intruded into the lagoon system. The borehole-sediment data combined with the high-resolution seismic data shows the thickness of Holocene sediments is approximately 20–35 m in the lagoon region. The study also suggested that the sandy barrier complex along the coast between the lagoon system and the open sea has been likely built during the transgression since 10–8.8 cal kyr BP. Additionally, five ecological zones were identified based on diatom assemblages in borehole HK02 indicating variations in marine and fluvial influence in the coastal lagoon system during the past 8.8 kyr: Dia-HK02–1 indicates a low presence of diatoms, suggesting a weak marine influence in the coastal lagoon system; Dia-HK02–02 shows the strongest marine influence and stable ecological conditions in the coastal lagoon system; Dia-HK02–03 demonstrates a partial decrease in marine influence; Dia-HK02–4 shows an increasing fluvial influence; and Dia-HK02–5 developed under completely dominated fluvial conditions on land.

Weathering-induced organic matter enrichment in marine-continental transitional shale: A case study on the early Permian Taiyuan Formation in the Ordos Basin, China

A comparative analysis of the factors controlling organic matter (OM) enrichment between marine-continental transitional (transitional hereafter) and marine or lacustrine shales is lacking. The early Permian Taiyuan Formation in the Ordos Basin, deposited during a shift from marine to continental settings in northern China, provides a unique opportunity to unravel the differences in OM enrichment mechanisms among these shales. The Taiyuan Formation is characterized by high TOC content (average 4.50%) and kerogen type II2-III. Most samples are thermally mature with a few high to post-mature samples relating to the Late Jurassic–Early Cretaceous Yanshanian magmatism. Rare earth elements and yttrium (REY) are dominated by light- and medium-types enrichments, with distinctly positive Gd anomaly, likely due to seawater incursion. A warm and humid climate prevailed during deposition of the Taiyuan Formation, consistent with the tropical-subtropical location of the North China Plate in the early Permian. The climatic conditions promoted intense continental weathering as reflected by high Th/Sc ratios, chemical index of alteration values, and feldspar alteration to scaly kaolinite. The V/(V + Ni) ratio is inconsistent with the other redox proxies, presumably due to variations in the redox buffer supply in the transitional facies (e.g., OM and pyrite), varying burial rates and dissimilar redox potential of different elements. Hence, this proxy should be interpreted with caution in such settings. Most redox proxies indicate oxic bottom water during deposition of the Taiyuan Formation transitional shale, in contrast to typical OM enriched marine and lacustrine shales where redox stratification or euxinic conditions are common. Instead, the dominant factor for OM enrichment in transitional shales appears to have been a high influx of terrestrial weathering products, including abundant higher-plants OM, associated with preservation of OM due to rapid burial. This process minimizes the detrimental effects of oxic conditions on OM accumulation in the transitional shale facies. This mechanism may hold relevance for analogous basins elsewhere.

Fluid–Melt–Rock Interaction during the Transition from Magmatism to HT-UHT-Granulite- and Amphibolite-Facies Metamorphism in the Ediacaran Adrar–Suttuf Metamafic Complex, NW Margin of the West African Craton (Southern Morocco)

Abstract Underplated mafic intrusions ponded at the base of the lower continental crust in extensional settings can experience ultra-high-temperature (UHT) granulite-facies metamorphism during tens of My due to slow cooling rates. These intrusions are also the source of heat and carbonic fluids for regional high-temperature (HT) granulite-facies metamorphism in the continental crust. This work analyses the fluid–melt–rock interaction processes that occurred during the magmatic to HT-UHT-granulite- and amphibolite-facies metamorphic evolution of high-grade mafic rocks from the Eastern Ediacaran Adrar–Suttuf Metamafic Complex (EASMC) of the Oulad Dlim Massif (West African Craton Margin, Southern Morocco). P–T conditions were determined using Ti-in-amphibole thermometry, two-pyroxene and amphibole–plagioclase thermobarometry, and phase diagram calculations. The thermobarometric study reveals the presence of tectonically juxtaposed lower- and mid-crustal blocks in EASMC that experienced decompression-cooling paths from, respectively, UHT and HT granulite-facies conditions at ca. 1.2 ± 0.28 GPa and 975 ± 50°C, and ca. 0.82 ± 0.15 GPa and 894 ± 50°C, to amphibole-facies conditions at ca. 0.28 ± 0.28 GPa and 787 ± 45°C (precision reported for the calibrations at 1 s level). An age for the magmatic to UHT granulite-facies metamorphic transition of 604 Ma was constrained from published SHRIMP Th–U–Pb zircon ages of the igneous protoliths. An amphibole 40Ar–39Ar cooling age of 499 ± 8 Ma (precision at 2 s level) was obtained for the lower-crustal blocks. Amphibole 40Ar–39Ar closure temperatures of 520–555°C were obtained for an age range of 604–499 Ma and an average constant cooling rate of 4.2°C/My, suggesting that the lower-crustal blocks cooled down to the greenschist–amphibolite facies transition in ca. 100 My. During the high-temperature stage, interstitial hydrous melts assisted textural maturation of the rock matrix and caused incongruent dissolution melting of olivine and pyroxenes, and, probably, development of An-rich spikes at the grain rims of plagioclase, and local segregation of pargasite into veins. Subsequent infiltration of reactive hydrous metamorphic fluids along mineral grain boundaries during cooling down to amphibolite-facies conditions promoted mineral replacements by coupled dissolution-precipitation mechanisms and metasomatism. Ubiquitous dolomite grains, with, in some cases, evidence for significant textural maturation, appear in the granoblastic aggregates of the high-grade mafic rocks. However, calculated phase relationships reveal that dolomite could not coexist with H2O–CO2 fluids at HT-UHT granulite- and low-medium P amphibolite-facies conditions. Therefore, it is proposed that it may have been generated from another CO2-bearing phase, such as an immiscible carbonatitic melt exsolved from the parental mafic magma, and preserved during cooling due to the prevalence of fluid-absent conditions in the granoblastic matrix containing dolomite. The lower-crustal mafic intrusions from EASMC can represent an example of a source of heat for granulitisation of the mid crust, but a sink for carbon due to the apparent stability of dolomite under fluid-absent conditions.

Granulites of the Larba Block of the Dzhugdzhur–Stanovoi Superterrane: Reconstruction of the Formation Conditions

Abstract —We discuss the rocks of the Larba granulite block in the Ilikan zone of the Dzhugdzhur–Stanovoi superterrane. The Larba block is dominated by basic schists and garnet–biotite–orthopyroxene and garnet–biotite–cordierite–sillimanite gneisses (metabasites and metapelites). Calculation of temperatures and pressures of mineral formation was carried out by multi-equilibrium geothermobarometry, which makes it possible to evaluate the degree of equilibrium of mineral compositions along with P–T parameters. The P–T estimates have shown metamorphism of aluminous gneisses under moderate-pressure granulite facies conditions (7–8 kbar, 800–850 °C). Orthopyroxene granulites formed under granulite-amphibolite transition facies conditions. The mineral compositions and parageneses in highly ferrous metabasites permitted estimation of the conditions of metamorphism, P = 4–5 kbar and T = 630–700 °C, and show no influence of earlier granulite facies metamorphism. The bimodal P–T distribution for most samples of aluminous gneisses most probably reflects progressive and near-peak conditions of granulite metamorphism. The time of enderbite magmatism is determined from the upper intercept of discordia with concordia at 2546 ± 52 Ma and should be verified. The age of metamorphic rims over enderbite zircon is 1882 ± 11 Ma. The model Nd age of enderbites, TNd(DM) = 2.57–2.58 Ga, is close to the age of the core of enderbite zircon and differs significantly from the model Nd age of the host metamorphic rocks (2.8–3.0 Ga). The Paleoproterozoic metamorphism of the Larba block rocks regionally coincides with the third stage of collisional granitoid magmatism of the southeastern Siberian craton and records the formation of this structure.

Dehydration‐driven deformation of eclogite: Interplay between fluid discharge and rheology

AbstractAqueous fluids released during dehydration of a subducting slab have a large effect on the rheology of the subduction interface. While high‐pressure experiments and natural‐case studies link deformation with critical dehydration reactions during eclogitization, the exact interplay between these processes remains ambiguous. To investigate fluid–rock interaction and associated deformation at high‐pressure, we studied a suite of eclogites from the Tsäkkok Lens of the Scandinavian Caledonides that record prograde metamorphism within an Early Palaeozoic cold subduction zone. Our results show that in‐situ dehydration during the blueschist to eclogite facies transition produces fluid fluxes leading to rheological weakening and densification, consequently promoting ductile‐brittle deformation. Petrographic evidence, supported by thermodynamic modelling and thermobarometry, attest to a prograde passage from lawsonite‐blueschist to peak eclogite facies of ~2.5 GPa and ~620°C. Phengite‐bearing eclogites imply interaction with an externally‐derived fluid, whereas rare phengite‐free, kyanite‐eclogites only record internally‐derived fluid production. Models predict that prograde breakdown of chlorite, lawsonite and amphibole between 500 and 610°C lead to progressive dehydration and release of up to 4.6 wt.% of aqueous fluid. Microstructural data reveal elongated shapes of highly strained omphacite porphyroblasts, displaying minor yet gradual changes in misorientation towards the grain boundaries. Occasionally, these intragranular structures form subgrain cells that have similar sizes to those of neoblasts in the rock matrix. These observations point to the potential onset of dynamic recrystallization processes via dislocation creep. Moreover, the omphacite neoblasts and rutile show non‐random crystallographic preferred orientations (CPOs), which are characterized by the subparallel alignment of point‐like maxima in rutile [001] and [100] axes to those of [001] and (010) of omphacite neoblasts, respectively. Additionally, the [001] axes of these minerals are also subparallel to the weak stretching mineral lineation, and the (100) of rutile and the (010) of omphacite neoblasts are distributed in the plane of the foliation. This suggests that the development of their CPOs was coeval and structurally controlled. Garnet microfractures normal to the foliation are dilated and sealed predominantly by omphacite. The lack of obliquity between CPO and foliation plane, as well as the systematic orientation of garnet microfracture orientations, are consistent with coaxial deformation at peak‐pressure conditions. Unlike other studies, we show that neither an external fluid source nor channelized fluid flow is needed to facilitate a ductile‐brittle deformation of eclogite in a subduction setting.

Differential sedimentary evolution of typical aulacogens of Meso-Neoproterozoic in North China craton

Many countries and regions in the world have obtained industrial oil flow in the Meso-Neoproterozoic sedimentary strata and formed commercial exploitation in recent years. The development horizon of high-quality source rocks in the Proterozoic in North China can be compared with the international, indicating that the Meso-Neoproterozoic in North China has great exploration potential. The sedimentary characteristics of typical aulacogen in multiple cratons in the Meso-Neoproterozoic North China Craton are compared and studied by using field outcrop data, drilling data and analysis and test data, aiming to provide sedimentary support for the prediction of oil and gas distribution and evaluation of exploration field in the Meso-Neoproterozoic in this area. The results show that there are four sedimentary systems in the study area, including Marine clastic rock sedimentary system, Marine carbonate sedimentary system, Marine-continental transitional facies sedimentary system and glacial sedimentary system. They are divided into seven sedimentary facies types: barrier coastal facies, non-barrier coast facies, shallow shelf facies, carbonate platform facies, reef facies, fan delta facies and glacial facies, and further divided into 15 subfacies and 21 microfacies. On this basis, the Meso-Neoproterozoic sedimentary filling sequences of two typical aulacogens, Yanliao and Xiong 'er, in the study area are clarified, showing that the formation time of each sedimentary filling sequence stage of different aulacogens is different, and the rock characteristics, lithology combination, lithologic structure, contact relationship, vertical sequence and sedimentary facies assemblage of the same sedimentary filling sequence stage are obviously different. The filling characteristics of the two aulacogens completely record the geological events related to the breakup of the Colombian supercontinent.

Devonian–Carboniferous transition in various facies of Northeast Laurussia (North Urals)

This study analyzed 14 stratigraphic sections exposing the Devonian–Carboniferous boundary interval in the North Urals, representing different facies from shallow-water carbonate platform to bathyal, in order to assess the possibility of recognizing regional levels corresponding to the base of the conodont zones S. sulcata and Protognathodus kockeli. The base of the S. sulcata Zone is regionally recognized by the first appearances of the conodonts Siphonodella sulcata (Huddle), S. semichatovae Kononova and Lipnjagov and Patrognathus crassus Kononova and Migdisova, roughly correlated with the first appearance of the foraminifer Tournayellina pseudobeata Reitlinger and Kulagina, and with the first appearances of the ostracods Cribroconcha primaris Kochetkova, Chamishaella grekoffi Tchizhova, Glyptolichvinella spiralis (Jones and Kirkby), Armilla uralica Sobolev, Calcarofera ex gr. media Schornikov, Compositocostata cumina Sobolev, Spinoalacia tschigovae Sobolev, Richterina latior Rabien. The base of the S. sulcata Zone occurs in the interval between two positive inorganic carbon isotope excursions. The base of the Protognathodus kockeli Zone is marked by the first appearance of Protognathodus kockeli (Bischoff) in a very narrow facies belt on the slope of the carbonate platform, recognized regionally by the onset of the last phase of the positive inorganic carbon isotope excursion, the beginning of the transgression after the terminal Famennian regression, the beginning of the unilocular foraminifera Bisphaera bloom and probably the appearance of the ostracods Monoceratina sp. 1. The level corresponding to the base of Pr. kockeli Zone is poorly supported biostratigraphically, but is characterized by clear isotope-stratigraphic and cyclostratigraphic data, although the eustatic signal may be obscured in places by local tectonics.

Cross-border correlations showing diachronous lithostratigraphic units in the southeastern North Sea Basin during the Early Oligocene (middle-late Rupelian)

Abstract Wireline log correlation panels of palynologically analysed boreholes illustrate lateral facies transitions within Rupelian age strata of the Dutch Rupel Formation across the southeastern North Sea Basin. The middle to upper part of the Rupel Formation consists of clays and silts of the Boom Member and the overlying sandier Steensel Member. In the Mill and Goirle boreholes in the Dutch Province of North Brabant, the Boom Member is thickly developed and represents the middle to upper Rupelian (biozones NSO3 to NSO5a), while the Steensel Member is rather thinly developed and only comprises the uppermost Rupelian (biozone NSO5a). Borehole log correlations show that towards the south (or more proximal to the palaeo-continent) the Rupel Formation becomes sandier and the clayey Boom Member thins in favour of the sandy superjacent Steensel Member. Palynological analyses confirm that the Boom Member is restricted to the middle Rupelian (biozone NSO3) age here, and that the superjacent Steensel Member is of middle to upper Rupelian age (biozones NSO3 to NSO5a). Geological models constructed for northern Belgium propose that this facies transition occurs rather sharply, along a WSW-ENE oriented zone parallel to the presumed shoreline at that time. The results of this study support this interpretation and extend the trend towards the Netherlands.

Environmental evolution of the south shore of Kandalaksha Bay, as indicated by the study of bottom sediments from small lakes

Environmental changes on the south shore of Kandalaksha Bay in Holocene time were reconstructed by analyzing the data obtained by palynological and 14C methods. Diatom complexes of marine, freshwater and transition facies are described. The possible application of pollen indicators for a better understanding of the genesis of sediments is discussed.

The transition from normal marine to evaporitic conditions recorded in a cold seep environment: The Messinian succession of Northern Italy

Messinian pre-evaporitic seep carbonates outcropping in the Tuscan-Romagna area share a common upward stratigraphic trend: massive seep carbonates rich in large lucinids, modiolids and planktonic foraminifera pass upward to horizontally laminated carbonates free of macrofauna and foraminifera. A transitional macrofauna-free facies marks the passage in some sections, sometimes with faint lamination. Thin section petrography, SEM-EDS analyses, and X-ray diffraction revealed a high textural and mineralogical variability between the studied sections and facies. In general, the upward facies transition is associated with a switch from massive packstone/grainstone with complex carbonate mineralogy to laminated mudstone microfacies with monomineralic, mostly dolomitic, carbonate composition. The δ13C values of all facies indicate domination of methane-derived carbon, thus demonstrating a methane-charged sedimentary setting with precipitation of authigenic carbonates induced by anaerobic oxidation of methane. The transitional and laminated facies contain several structures typical of microbial sediments, such as peloids, filamentous features, clotted micrite, fibrous cement, and frequent fenestrae; web-like structures are remnants of cyanobacterial mats and resemble Entophysalidaceae thriving at the bottom of the Messinian sea. The distinctive depositional and biotic switch (abrupt disappearance of macrofauna and planktonic foraminifera, predominance of dolomite over calcite, absence of aragonite, presence of horizontal lamination) reflects important environmental changes taking place in the basin. The rise of δ18O from the massive, through transitional, to the laminated facies suggests either a drop of bottom-water temperature or an increase of salinity. Nevertheless, other paleoenvironmental changes must have co-occurred in order to account for the dramatic facies shift observed. We hypothesize that this change could reflect the development of water-column stratification with respect to both salinity and oxygen concentration shortly before the Messinian Salinity Crisis.

Diagenetic Evolution Sequence and Pore Evolution Characteristics: Study on Marine-Continental Transitional Facies Shale in Southeastern Sichuan Basin

Diagenesis and pore structure are essential factors for reservoir evaluation. marine-continental transitional facies shale is a new shale gas reservoir of concern in the Sichuan Basin. The research on its diagenesis pore evolution model has important guiding significance in its later exploration and development. However, the current research on pore structure changes, diagenesis, and the evolution of marine-continental transitional facies shale is not sufficient and systematic. In order to reveal the internal relationship between pore structure changes and diagenesis, the evolution of marine-continental transitional facies shale was tested by X-ray diffraction, field emission scanning electron microscopy, low-pressure gas adsorption, nuclear magnetic resonance, and the diagenetic evolution sequence and nanopore system evolution of Longtan Formation shale was systematically studied. The results show that the Longtan Formation shale underwent short-term shallow after sedimentation, followed by long-term deep burial. The main diagenetic mechanisms of the Longtan Formation shale include compaction, dissolution, cementation, thermal maturation of organic matter, and transformation of clay minerals, which are generally in the middle-late diagenetic stage. The pore structure undergoes significant changes with increasing maturity, with the pore volumes of both micropores and mesopores reaching their minimum values at Ro = 1.43% and subsequently increasing. The change process of a specific surface area is similar to that of pore volumes. Finally, the diagenetic pore evolution model of Longtan Formation MCFS in Southeastern Sichuan was established.

High-resolution lithostratigraphy and reconnaissance sedimentology of Changotaung structure, Chittagong Tripura fold belt, Bengal Basin, Bangladesh

Unlike other structures in the vicinity of the Chittagong Tripura Fold Belt, the Changotaung anticline is one of Bangladesh's least explored structures. An attempt has been made for the first time to understand and document sedimentary deposits, environments, structure, and tectonic activity based on the high-resolution outcrop and reconnaissance study with the knowledge of broad-brush geology. We found that Changotaung is a symmetrical box-folded structure with an extensive western flank where the amount of dip varies between 11° and 45°. The exposed Cenozoic succession was categorized into three separate sedimentary sequences and correlated with the conventional stratigraphic unit. A first-order simple Markovian approach was presented for the exposed litho-section in an effort to illustrate vertical facies variations in the Upper Surma group. We quantified that heterolithic bed mostly overlies both trough cross-bedding ({P}_{ij}U = 0.706) and parallel laminated bed ({P}_{ij}U=0.955) according to the facies transition probability matrix. According to the results of the stationary distribution, there is a 40% chance of coming across heterolithic beds within the Upper Surma group during any given event that is completely random whereas trough cross-bedding, parallel laminated bed, cumulative sandstone facies, and cumulative shale facies shows around 10.8%, 15.2%, 20.6%, 13.4% probability. We hypothesized, based on the interpretive facies analysis, that the Chittagong Tripura fold belt region's Upper Surma Group underwent three interrelated depositional settings (wave-dominated shallow marine, tide-dominated shallow marine, and fluvio-deltaic distributary).

Textural characteristics and sediment transport dynamics of the sandstones of the Nkporo group, Southern Anambra Basin (Nigeria): evidence for the upper cretaceous sea-level lowstand

The Anambra sedimentary basin is one of the major inland basins in Nigeria. It covers an area of approximately 30,000 square kilometres and is named after the Anambra River, which traverses the basin. The geology of the basin is characterized by a complex sequence of sedimentary rocks that record a long history of deposition and tectonic activity. Detailed and systematic field investigation of its rock sequences exposed at Leru junction and adjoining localities revealed five dominant lithologic units consisting of massive sandstone facies, argillaceous sandstone facies, fissile black shale and mudstone facies, planar and ripple laminated sandstone facies, and massive and pebbly sandstone facies. The area is dominated by transgressive facies characterized by alternating sequences of thinly and parallel laminated fissile black shales, mudstones, and argillaceous sandstones overlain by regressive deposits dominated by massive and partly pebbly sandstones. The transgressive sequences perhaps represented shelf mud sedimentation that was probably interrupted by episodic influxes of sands rich in argillaceous materials transported down the shelf probably by shoreface waves or gravity-driven flows, while the regressive facies may have probably been emplaced by liquefied sand flows of the frontal slope of an advancing mouth bar. The erosion of the shelf deposits by the pebbly sandstones possibly reflected seaward migration of shallow distributary channels during sea-level low stand. Thus, facies transition from argillaceous sandstones to massive and pebbly sandstones within the continental shelf perhaps signified a fall in the relative sea level possibly triggered by the erosion of the shelf or perhaps a high rate of sediment supply.

Co-simulation of hydrofacies and piezometric data in the West Thessaly basin, Greece: A geostatistical application using the GeoSim R package

In the present study, we co-simulate hydrofacies and piezometric data in order to construct geostatistical realizations of underground geology in an area of the West Thessaly basin. This basin is of great importance in terms of sustainable water management and environmental perspective in Greece. Through Plurigaussian modeling, the hydrofacies are first transformed into Gaussian Random Fields. Then, a Linear Coregionalization Model is established to account for the dependencies between hydrofacies and the Normal scores of piezometric data. The effect of co-simulation shows an improvement of the facies transition probabilities in comparison with those of Plurigaussian simulation. For the purpose of this study, we use the GeoSim package in R developed by our team for the implementation of Plurigaussian simulation and co-simulation.

A new isochron for stratigraphic correlation in the Permian Delaware Basin and beyond

Altered volcanic ash, preserved as bentonite clay within sedimentary depositional units, can facilitate regional stratigraphic correlation. While many bentonite ash beds have been documented in core extracted over decades of hydrocarbon exploration in the Delaware Basin, a particular ∼1 cm-thick bentonite has been identified at a distinct stratigraphic position, at a sedimentary facies transition from thin-bedded calciclastic turbidites to thick-bedded siliciclastic turbidites, in the compositionally-mixed upper Wolfcamp formation. A comparison of geochemical analyses of the ash from two cores and petrophysical correlations across eight wells was conducted to test the regional correlation of the ash. Despite diagenetic alteration since seafloor deposition ∼280 Ma, nearly identical geochemical trends between incompatible elemental subsets, including light and heavy rare earth elements, large ion lithophiles, and high field strength elements, suggest that these two ash deposits originated from the same volcanic center. Detailed sedimentologic analyses and lithostratigraphic correlations across three cores spaced tens of km apart confirm that the ash bed is bound by correlative quiescent deepwater strata. Based on the chemical composition, probable timing of deposition, and proximity, we speculate that the Las Delicias Arc produced this ash, and it was transported by wind and deposited as a hemipelagite into the Delaware Basin deep marine environment. This discovery implies the existence of the ash marker in other cores within Late Paleozoic western equatorial Pangea, e.g. in compositionally-mixed deep marine deposits of the Midland Basin and outcropping deposits around the Greater Permian Basin and beyond, which would facilitate regional chronostratigraphic correlation for a critical time in Earth's history.

Tectonic and sedimentary evolution of a potential supra-detachment fault basin, Archaean Moodies Group (~3.22 Ga), central Barberton Greenstone Belt

Abstract Greenstone belt dynamics are a key to understanding the formation and evolution of continental crust but the scarcity, commonly poor exposure, strong deformation, and high metamorphic grades of many Archaean supracrustal rocks preserved in greenstone belts often hinder geological insights. Exceptionally, the largely siliciclastic Palaeoarchaean (ca. 3.22 Ga) Moodies Group, uppermost unit of the Barberton Greenstone Belt (BGB) in South Africa and Eswatini, allows a detailed understanding of regional depositional processes and stratigraphic architecture due to its low degree of deformation, considerable thickness, generally good exposure, and diverse sedimentary facies. We here investigate the Powerline Road Syncline (PRS) and the adjacent Maid-of-the-Mists Syncline (MMS), two east-west-trending, tightly to isoclinally folded, locally northwardly overturned synclines in Moodies Group strata in the central BGB. The northern and southeastern margins of the PRS and the southern to southwestern margin of MMS are bounded by the bedding-parallel 24-Hour-Camp Fault. Along this fault, Moodies Group strata and stratigraphically underlying units of the Auber Villiers Formation of the upper Fig Tree Group structurally overlie lower Fig Tree strata above Onverwacht Group strata. Stratigraphic architecture and palaeocurrent analysis of Moodies Group strata in both synclines document a northeastward (depositionally downdip) facies transition from proximal fan delta conglomerates to fluvial- to coastal-plain and estuarine sandstones in which thick foresets likely represent subtidal channel fills. The overall deepening- and fining-upward trend in this sequence, corresponding to an increasing mineralogical maturity of sandstones, is partially obscured by local hydrothermal alteration which was contemporaneous with sedimentation, minor volcanism, and sill intrusion. Moodies Group conglomerates and sandstones were largely shed from the rising Onverwacht Anticline to the southwest. Lithologies and stratigraphy in the PRS-MMS region closely resemble strata of the lower Moodies Group in the Sadddleback Syncline, located nearby to the north but across the Inyoka Fault. If the 24-Hour-Camp Fault was part of a group of extensional faults accompanying the rise of the Onverwacht Anticline and of tonalitic-trondhjemitic-granodioritic plutons around the BGB margins at ca. 3 224 Ma, it would have acted as one of numerous basin-bounding normal faults during early Moodies time. This would place the deposition of Moodies Group strata in the PRS-MMS region in a supra-detachment fault environment which was subsequently tightly folded.