The East Beni Suef (EBS) concession in the north Western Desert, Egypt, hosts significant reserves. This study integrates core analysis, petrophysical evaluation from well logs, and statistical assessment to characterize reservoir properties and determine hydraulic flow units (HFUs). The Upper Cretaceous Abu Roash-A (A/R-A) sandstone is a considerable reservoir, with hydrocarbons sourced mainly from the Lower Kharita shale. Facies analysis identifies two types of sandstone within a transgressive sequence: Type-1, medium to coarse-grained oil-saturated facies, and Type-2, finegrained, bioturbated facies. Hydraulic flow unit (HFU) assessment divides the reservoir into high- and low-quality zones based on flow zone indicators (FZI), highlighting porosity and permeability variations. Statistical analyses reveal porosity values ranging between 20% and 24%, with Permeability predominantly below 20 mD, exhibiting anisotropic fluid flow due to vertical and horizontal Permeability differences. The Pickett Plot analysis and Archie’s equation confirm the presence of producible hydrocarbons, with an Oil-Water Contact (OWC) identified at -3450 ft. The reservoir demonstrates heterogeneity, with Permeability strongly correlated with porosity and influenced by facies distribution. The findings provide insights into the reservoir's quality and production potential, supporting enhanced hydrocarbon recovery strategies that identified Abu Roash-A (A/R-A) sandstone as a promising hydrocarbon reservoir and more suitable site for fluids sequestration.

The Early Cambrian witnessed an increase in metazoan ecosystem complexity, likely linked to enhanced oxygen and nutrient availability. Ocean redox chemistry exerts a strong control on the biogeochemical cycling of the limiting nutrient phosphorus, but the response of phosphorus cycling to redox dynamics in the Early Cambrian ocean remains poorly resolved. Here, we report phosphorus phase association data for three sections documenting a bathymetric marine transect through terminal Ediacaran to Early Cambrian Stage 2 (post−538−521 Ma) on the Tarim Block, Northwest China. During the terminal Ediacaran to middle Fortunian, a fluctuating ferruginous-dysoxic oxygen minimum zone (OMZ) developed, with ferruginous conditions promoting phosphorus recycling in deeper water parts of the OMZ. Combined with enhanced upwelling, this stimulated high primary production and organic matter burial, resulting in the development of better oxygenated conditions during the late Fortunian to early Stage 2. The development of oxic-dysoxic conditions at this time promoted phosphorus burial in association with iron minerals, and combined with waning upwelling, the reduced supply of nutrients helped maintain these conditions. This likely promoted diversification of small shelly fauna in the late Fortunian. However, efficient phosphorus burial also suppressed oxygenic photosynthesis. Thus, the overall expanded oxygenation was punctuated by episodes of subsequent deoxygenation during Cambrian Stage 2, which were driven by relatively enhanced upwelling and an increased supply of bioavailable phosphorus from continental weathering during pulsed eustatic transgression. Enhanced phosphorus burial from early Stage 2 onward contributed to more stable and longer-lived oxic episodes, helping to facilitate the development of more complex ecosystem structures.

Carbonate-associated sulfate (CAS)-trace SO42- incorporated into carbonate mineral lattices by substituting for CO(3)(2-)serves as a valuable geochemical proxy for reconstructing seawater chemistry, redox conditions, microbial sulfate reduction activity, and diagenetic sequences in ancient marine environments, cold seeps, and gas hydrate reservoirs. However, conventional CAS extraction methods, which typically use HCl to digest bulk carbonate samples, yield mixed isotopic and concentration signals from coexisting calcite and dolomite. Therefore, it is difficult to precisely distinguish the sulfur isotopes of CAS in the original sedimentary environment from that resulting from secondary alteration. In order to isolate calcite-hosted CAS (calcite-CAS) from dolomite-hosted CAS (dolomite-CAS), we evaluated six acetic acid leaching conditions in sequence (0.1-0.5 mol/L, 1-2hours). The results indicate that treatment with 0.1 mol/L acetic acid for 1 hour effectively releases calcite-CAS while suppressing dolomite dissolution. When applied to natural carbonate outcrop samples, this approach reveals that the delta S-34 values of calcite-CAS are consistently similar to 8.22 parts per thousand higher than those of coexisting dolomite-CAS. Notably, the lowest measured delta S-34(Calcite)-(CAS) values are 2-5 parts per thousand higher than previously reported bulk CAS data, suggesting that earlier records were biased by the inclusion of dolomite-CAS. We therefore recommend the 0.1 mol/L acetic acid leaching protocol (1 hour) for extracting calcite-CAS from dolomite-bearing carbonate rocks, as this enables more accurate reconstruction of depositional and diagenetic conditions.

Volcanism at ~1.4 Ga profoundly impacted Earth’s environment, yet its role in biogeochemical cycles remains debated. Here we integrate carbon and mercury isotopes, chemical index of alteration, machine learning-driven mercury flux reconstructions, and a multi-box biogeochemical model to reveal multiple volcanic imprints across Mesoproterozoic strata in North China Craton. Distinct mercury anomalies align with subaerial volcanism in Unit 3 and large igneous provinces in Unit 2 of the Xiamaling Formation, coinciding with photic zone euxinia. Machine learning models detect synchronous mercury perturbations in North China and North Australia, confirming the global influence of large igneous provinces. Sustained volcanic activity drives a carbon cycle transition from silicate weathering to biogenic carbon sequestration, marked by enhanced physical erosion, decoupling of inorganic and organic carbon isotopes, increased surface oxygenation, and intensified deep-ocean anoxia. The biogeochemical model captures the intrinsic links between multiple volcanic events, pulsed oxygenation, and carbon-sulfur-oxygen-mercury perturbations, confirming volcanism as a trigger for Mesoproterozoic oxygenation and early eukaryotic evolution. Large igneous provinces likely restructured carbon sequestration pathways in the Mesoproterozoic, shifting the balance between organic and inorganic carbon burial and contributing to changes in redox conditions and possibly supporting early eukaryotic development, according to mercury isotope records from the North China Craton, machine learning-driven mercury flux reconstructions, and biogeochemical models.

Manganese carbonates can be formed via either diagenetic reduction of Mn oxides from hydrothermal and marine environments by organic matter, or direct growth on calcite or dolomite in anoxic environments. The Triassic Heqing manganese carbonate ores in the Heqing basin, Yunnan Province, South China provides an excellent case to show they form by redox between Mn oxides and methane during diagenesis in a low sulfate freshwater environment. The manganese ores are hosted by limestones and predominantly composed of micro-to fine-crystalline rhodochrosite and massive hausmannite. An oxic depositional environment is indicated by the bulk rocks showing negative Ce anomalies (Ce/Ce* = 0.36–1.59, average = 0.89) from which the hausmannite was deposited, and subsequently replaced or encrusted by rhodochrosite. The manganese ores exhibit no significant Eu anomaly (Eu/Eu* = 0.72–1.18, average = 1.01), and are plot on hydrogenous area of SiO2 versus Al2O3 diagram, reflecting that the manganese was supplied dominantly from chemical weathering. A low sulfate freshwater sedimentary and early diagenetic environment is indicated by low Y/Ho and La/La* ratios for the bulk rocks or Mn carbonates, the absence of pyrite and sulfate minerals. Under such an environment, hausmannite was reduced by biogenic methane and organic matter to generate rhodochrosite as shown by two mixing trends with endmember δ13C values lighter than −70‰ and − 25‰, respectively. We report a rare case showing that strongly 13C-depleted Mn carbonate ore was formed in a freshwater lacustrine environment and can serve as a methane sink.

The Yakela Faulted-Uplift in the northern Tarim Basin, China, represents a complex petroleum system where hydrocarbon origins are controversial due to its high maturity and multi-source mixing. This study integrates mercury (Hg) isotopes, sulfur isotopes, and conventional geochemical analyses to elucidate the sources and accumulation processes of hydrocarbons in this region. Results show that gases from the Yakela field exhibit moderate Δ199Hg values (−0.09‰ to 0.01‰), indicating mixing of marine sapropelic and terrestrial humic organic matter. In contrast, the associated oils exhibit δ34S (20.5‰–26.8‰) and biomarker signatures consistent with the Cambrian source rocks, clearly distinguishing them from the terrestrial source rocks in the Kuqa Depression. Oils from another region (Dalaoba) within the uplift, however, show clear terrestrial affinities with higher Pr/Ph ratios and lower δ34S values. By integrating sulfur isotopes with biomarker parameters and carbon isotopes, a clear discrimination has been achieved between the Cambrian, Ordovician, and Triassic–Jurassic source rocks in the Tarim Basin. The spatial decoupling of oil (pure marine) and gas (mixed) accumulations is explained by a two-stage, tectonically controlled charging model, i.e., the Early Himalayan northward charging of marine oils followed by the Late Himalayan southward influx of terrestrial gas. This study demonstrates that combining Hg and S isotopes provides a powerful tool for resolving complex, multi-source petroleum systems, with important implications for future exploration in the Tarim Basin and analogous geological settings worldwide.

The sulfurization mechanism within contemporary marine oxygen-deficient zones promotes the preservation of organic matter. However, it remains to be investigated whether low sulfate concentrations in Mesoproterozoic and Early Cambrian oceans restricted organic matter sulfurization. This study examines the petrological characteristics, pyrite morphology, total organic carbon (TOC) and sulfur (TS), and organic sulfur components of source rocks of the Mesoproterozoic Xiamaling Formation and the Lower Cambrian Yuertusi Formation, employing thin section observation, chromium reduction method, scanning electron microscopy, elements analyzer, and X-ray photoelectron spectroscopy (XPS). The organic S: C atomic ratios in kerogen range from 0.7–5.8

The origin of Paleozoic oils in the cratonic Tarim Basin, China, has long been debated, with previous studies attributing most oils to the Cambrian sources. However, the geochemical characteristics and distribution of the Ordovician-sourced oils remain poorly constrained. This study integrates biomarkers, carbon isotopes, and sulfur isotopes to identify the Ordovician-derived oils in the western part of the Shuntuoguole Low Uplift. Two oils (SHB7 and SHB71X) produced from the Ordovician exhibit distinct geochemical signatures, including the absence of aryl isoprenoids, high concentrations of C30 diahopane, elevated Pr/Ph ratios, and low DBT/P ratios, indicative of a clay-rich, suboxic depositional environment. Critically, these oils display significantly lighter bulk delta 34S values (4.0%o and -1.6%o), which closely match those of the Middle-Upper Ordovician kerogen (-6.7%o to 5.6%o) and are distinctly lower than the Cambrian-sourced oils (15.8%o to 23.2%o). Individual n-alkanes delta 13C compositions further support a different genetic origin compared to the typical Cambrian-derived oils. These findings confirm the existence of a previously unrecognized Ordovician-sourced petroleum system in the basin. The distribution of such oils is likely controlled by migration from the Ordovician source kitchens in the Awati Depression or intra-platform depressions. This study underscores the superiority of sulfur isotopes over conventional biomarkers in resolving complex oil-source correlations in multi-source basins like Tarim.

The emergence of land plants was a pivotal development in Earth history. It has been postulated that the evolutionary transition from freshwater streptophyte algae to land plants, or the canalization of plant meiosis, was completed during the Middle Ordovician ( 460 Ma). However, the absence of undisputed streptophyte algal fossils (for example, Charophyceae) earlier than the late Silurian ( 425 Ma) has obscured this link between streptophyte algae and land plants. Here we describe a marine Charophyceae fossil, Tarimochara miraclensis gen. et sp. nov., from early and middle Katian (Late Ordovician, 453–449 Ma) marine limestones in northwestern China. This discovery demonstrates that at least some species of Charophyceae inhabited shallow normal marine environments at that time. Moreover, these early Charophyceae show that some key morphological innovations associated with an evolutionary transition between streptophyte algae and land plants had occurred before the early Katian. This provides crucial evidence relevant to the origins of land plants. Land plants diverged from streptophyte algae around 460 million years ago. Marine Charophyceae fossils from the Upper Ordovician confirm that morphological innovations key to the evolution of terrestrial flora predate the emergence of land plants.

The South China Block hosts extensive sedimentary phosphorites that offer valuable insights into both paleoenvironmental reconstruction and rare earth element (REE) resource potential. However, the mechanisms governing REE enrichment in these deposits remain poorly understood. This study investigates two distinct phosphorite layers from the Lower Cambrian Zhujiaqing (ZJQ) Formation in the Bailongtan (BLT) area of the Yangtze Platform using integrated analyses including petrology, XRD, major and trace elements, δ¹³C and δ¹⁸O isotopes, and LA-ICP-MS. The lower thin-bedded phosphorite, composed of finer phosphatic grains (<300 μm), exhibits significantly higher REE concentrations (883.6 ± 160.9 ppm; n = 48) compared to the upper thick-bedded phosphorite (303.2 ± 82.7 ppm; n = 64), which is dominated by larger, reworked grains (300–600 μm). Intervening strata consist of laminated phosphate-bearing carbonates interbedded with quartz, dolomite, and pyrite. PAAS-normalized REE patterns display MREE–HREE enrichment, negative Ce anomalies (avg. 0.60 ± 0.18; n = 18), and positive Y anomalies—indicative of oxic depositional conditions. The elevated REE content in the lower layer, coupled with the lowest δ¹³C values (−4.59‰), suggests enrichment linked to organic matter degradation. A proposed two-stage depositional model links REE enrichment to proximity with REE-rich deep-shelf waters, underscoring the critical role of redox and depositional dynamics in phosphorite-hosted REE accumulation

The shallow-burial Neo-Tethys Cenozoic reservoirs host significant hydrocarbon resources. However, a limited understanding of the Paleogene Apollonia Formation, north Western Desert, Egypt, hinders further exploration and development. Here, RZK, WD33 and JD blocks were analyzed using a combination of petrological observations, petrophysical analysis, well logging analysis, machine learning, and deep learning. Five types of limestone and two types of dolostone were identified. Planktonic and benthic foraminifera (e.g., Nummulite) are well-developed. The sedimentary facies consists of grain shoals, shallow to deep ramp and deep-water slope facies. Grainstone and packstone from high-energy sedimentary environments yield high primary porosity and permeability. Dolomitization and bacterial sulfate reduction further enhance reservoir properties. Framboidal and granular pyrites are well-developed here. The reservoir spaces consist of framework pores, inter-granular pores, intra-granular pores, moldic pores, inter-crystalline pores, and fractures. The sedimentary facies and diagenetic history indicate that WD33 and RZK (esp. ERZK & MRZK) blocks exhibit promising reservoir performance. Drilled cores of three wells from different sedimentary facies served as the training dataset for machine learning and deep learning, while two core wells were utilized as the test group. Using XGBOOST, Random Forest, and Long Short-Term Memory algorithm, the predicted porosity values closely match core-measured values, with R2 (coefficient of determination) values of 0.72, 0.58, and 0.61, respectively. The permeability prediction results also yield similarity to the measured values. The Jurassic and Cretaceous source rocks generated hydrocarbon for the overlying Paleogene Nummulite carbonate reservoirs in the Neo-Tethys domain. This study provides valuable insights into carbonate reservoirs in the north Western Desert and holds significance for global Cenozoic carbonate exploration and development.

Solid bitumen in Southwest China often coexists with metal deposits, indicating a genetic link between organic matter and ore formation. However, this linkage remains underexplored. This study investigated the relationship between sulfur origin and organic matter maturity through sulfur isotopes of metal sulfides. Organic petrology revealed that solid bitumen associated with minerals exhibited stronger optical anisotropy (Delta BRo >3.32 %) and higher S/C atomic ratios (0.029-0.033) than non-associated bitumen (0.005-0.021). Fluid inclusion analysis showed that ore-stage calcite inclusions have higher homogenization temperatures than those in paleo-oil reservoirs, indicating that ore-forming processes accelerated hydrocarbon thermal evolution. Solid bitumen-mineral associations were classified into Mississippi Valley-type (MVT), stratiform mercury, and disseminated gold deposits. Sulfur isotope compositions identified three sulfur sources: bacterial sulfate reduction (BSR), thermochemical sulfate reduction (TSR), and thermal decomposition of sulfur-containing organic matter (TDS). In the Lanping-Simao Basin, delta S-34(CDT) values below 0 parts per thousand suggest sulfur derived from BSR, with hydrocarbons contributing reduced sulfur. In the Xuefeng Mountains Uplift, delta S-34(CDT) values exceeding 20 parts per thousand indicate TSR-driven sulfur, with metallogeny enhancing hydrocarbon accumulation and mineralization. In the Kangdian Axis, delta S-34(CDT) values under 20 parts per thousand suggest sulfur from TSR and TDS, with mineralization causing oil cracking and reservoir destruction. The findings demonstrate that metallogeny accelerates organic matter maturation, reshapes reservoirs, and drives oil cracking. Simultaneously, organic-inorganic interactions govern metal sulfide formation and precipitation, underscoring their critical role in ore genesis.

The terminal Ediacaran to Lower Cambrian (538-521 Ma) documents the disappearance of Ediacaran soft-bodied biota and the diversification of early animals, including the emergence of small shelly fauna, archaeocyath sponges, and trilobites. Despite extensive study, the role of oceanic oxygenation in macroevolutionary events across this interval remains unclear, with understanding hindered by limited constraints on temporal and spatial variability in geochemical conditions, both regionally and globally. Here, we report multi-proxy geochemical data (including organic carbon concentrations, carbonate and organic carbon isotopes, Fe speciation, and redox sensitive trace elements) from three sections documenting different water-depths through the Early Cambrian (Terreneuvian) Yurtus Formation of the Tarim Basin, Northwest China. Our data reveal a highly dynamic oxygen minimum zone (OMZ), distinguished by a core of unstable ferruginous to dysoxic conditions, with peripheral dysoxic to oxic conditions that developed on the inner-outer shelf at different stages. The temporal and spatial extent of the OMZ appears to have been controlled by changes in productivity, driven by sea-level and climatic influences on upwelling. We expand on regional observations by considering published geochemical data from globally distributed successions across this interval, in addition to the lowest global occurrence of key fossil taxa. Our integration of regional and global geochemical data sets, alongside mechanistic insight from regional and global stratal stacking patterns, suggest that marine redox fluctuations responded dynamically to changes in upwelling driven by major sea level transgression and climate. These connected processes and palaeoenvironmental conditions formed the backdrop for the main phase of the Cambrian explosion.

Tables S1 and S2 and Figures S1–S6.

Uncertainty about the source of the oils from the Halahatang region of the Tabei Uplift, Tarim Basin (NW China) presents an ongoing challenge to exploration. Previous analyses of several Halahatang oils showed isotopic (S13C < -32 %o) and aliphatic hydrocarbon distributions (e.g., V-shaped C27-C29 steranes) more typical of regional Ordovician source rocks than the Cambrian rocks that are the predominant source of petroleum of the Tarim Basin, supporting prospects for a second major regional oil source. In pursuit of a more definitive source assignment of Halahatang oils and further insight into their depositional environment and charge history, a detailed molecular appraisal of the aromatic hydrocarbon composition of 27 marine oils and complementary stable sulfur and carbon isotopic analyses were conducted. The oils were from different Halahatang wells resolved into three separate block groups, with variations to the extent molecular and isotopic data was influenced by secondary alteration (i.e., thermal maturity, biodegradation and, possibly, minor thermochemical sulfate reduction) evident among the groups. The major aromatic products of all oils were alkylated naphthalenes, phenanthrenes, dibenzothiophenes and trace levels of thiadiamondoids were detected in a few Group II and III oils. Aryl isoprenoids, typical biomarkers of an euxinic depositional environment, were also conspicuous in lower maturity Group I and II oils (Rc < 0.9 %), but absent in higher maturity oils (Rc up to 1.02 %). Molecular evidence of severe biodegradation (e.g., unresolved complex matter, 25-norterpenoids) was evident in some Group I oils, although some of these also showed coincident non-biodegradation molecular features (e.g., low MW n-alkanes) implying a mixing of biodegraded and non-biodegraded charges. The S34S values of the bulk oil and their dibenzothiophene and alkyldibenzothiophene products were generally in the range +17 to +23 %o, although some oils impacted by biodegradation showed slightly heavier S34S values (>+26 %o). The Group II oils were not significantly impacted by secondary processes and their aromatic signature (e.g., aryl isoprenoids), S34S data and whole oil S13C values were closely correlated with regional Lower Cambrian source rocks and are atypical of Upper Ordovician source rocks. These results identify the Halahatang oils as a further representation of Lower Cambrian-derived oils of the Tabei Uplift.

Enhanced hydrogeologic circulations promoted by tectonics are commonly linked to karstic cavity formation in carbonate rocks, providing superb reservoirs for hosting energy resources (i.e., hydrocarbon and geothermal) in sedimentary basins. Predicting such cavern reservoirs in the deep subsurface is difficult mainly due to uncertainties in timing the tectonics and characterizing their associated fluids, which hamper the related hydrocarbon exploration. By combining carbonate U -Pb chronology, geochemistry, and seismic data analyses of fracture and cave-filling carbonates in cavern reservoirs from the Ordovician units of the Tarim Basin, northwestern China, the current study sought new evidence for fluid activities related to tectonics. Crucially, carbonate U -Pb ages confirm that these karstification events were closely related to syn- and/or postmineralization faulting by local tectonics. Geochemistry signatures in the authigenic minerals of fractures further suggest that the episodically developed meteoric water mixed with deep basinal brine. The carbonate dissolution rate might have been markedly enhanced by active hydrologic circulation and fluids mixing or even the formation of sulfuric acid, thus promoting the formation of karstic cavities that was closely related to the deep-rooted fractures and faults. This study highlights the indispensable role of hypogenic karstifi- cation in the formation of cavern carbonate reservoirs in the Ordovician units of the Tarim Basin and the outcome from this new contribution may provide useful guidelines for hydrocarbon exploration in the basin and other global analogues.

The evolution of oxygen cycles on Earth's surface has been regulated by the balance between molecular oxygen production and consumption. The Neoproterozoic-Paleozoic transition likely marks the second rise in atmospheric and oceanic oxygen levels, widely attributed to enhanced burial of organic carbon. However, it remains disputed how marine organic carbon production and burial respond to global environmental changes and whether these feedbacks trigger global oxygenation during this interval. Here, we report a large lithium isotopic and elemental dataset from marine mudstones spanning the upper Neoproterozoic to middle Cambrian [~660 million years ago (Ma) to 500 Ma]. These data indicate a dramatic increase in continental clay formation after ~525 Ma, likely linked to secular changes in global climate and compositions of the continental crust. Using a global biogeochemical model, we suggest that intensified continental weathering and clay delivery to the oceans could have notably increased the burial efficiency of organic carbon and facilitated greater oxygen accumulation in the earliest Paleozoic oceans.

The deep-burial Cambrian Xiaoerbulake Formation microbialites reservoir hosts significant hydrocarbon in the Tarim Basin. However, limited understandings of fluid-rock interactions from deposition to deep-burial regimes hamper petroleum exploration. Here, petrological observations, in-situ elemental contents and porosity-permeability analyses were performed to understand the complex interactions and the microbialites performance. Dolo-mudstone, crystalline dolostone, and four kinds of microbialites are distinguished as dolostones types. In the depositional stage, microbialites are characterized by (evaporated) seawater dolomitization with the mediation of microbial activity. The dolostone matrix shows seawater-like δ13C, δ18O and REY patterns. Thrombolitic and foam spongy dolostones from high-energy subtidal to intertidal zones show large framework pores compared to stratiform stromatolitic dolostones from low-energy intertidal zones. In near-surface settings, meteoric diagenesis generates secondary pores, while fine-crystalline dolomite cements partially fill pores. During the shallow to intermediate burial regimes, medium-to coarse-crystalline dolomite cements yield negative δ18O values and slightly flat REY patterns. The precipitation of this dolomite phase further decreases reservoir porosity. In deep burial settings, one type of saddle dolomite is likely to be formed by replacement from carbonate precursors, while the second type might be directly precipitated from hydrothermal fluids. These two types of saddle dolomites show different cathodoluminescent characteristics and geochemical data. Subsequently, two types of calcite cements are formed by the calcification of dolomite and yield significant negative δ13C values due to thermochemical sulfate reduction. Finally, the third calcite phase is likely to be a direct precipitate from burial brines. Hydrothermal activity and thermochemical sulfate reduction generate and/or re-distribute secondary pores. Based on the plethora of depositional environments and fluid-rock interactions, thrombolitic dolostone generally yields higher porosity-permeability than other types of microbialites. Thrombolite reservoir has high potential for petroleum exploration and is significant for those concerned with microbialite hydrocarbon fields.