ABSTRACT Astronomically forced climate cycles and hyperpycnal flow deposits are the forefront of contemporary geological research. Climate significantly influences the formation of hyperpycnal flows, with these changes being driven by astronomical cycles. However, the relationship between astronomical cycles and hyperpycnal flows has not been sufficiently explored. Additionally, although hyperpycnal flows can transport terrigenous clastic particles to the deep-water areas of basins, their impact on organic matter enrichment remains inadequately studied. Therefore, this study analyzed the characteristics of hyperpycnal flow deposits within the Chang 7 Oil Member (Chang 7 Member) in the southern Ordos Basin, assessed their frequency of occurrence, and investigated their correlation with long-eccentricity cycles. By examining the geochemical signatures and sedimentary accumulation rates (SARs) of different genetic types of deposits, this study also explored the controlling factors of hyperpycnal flows on organic matter enrichment. The analysis indicates that hyperpycnal flows within the Chang 7 Member exhibit periodic development, significantly influenced by long-eccentricity cycles. Hyperpycnal flows not only transport nutrients into the lake basin but also increase SARs, thereby facilitating the rapid burial of organic matter and promoting its enrichment. These findings underscore the significant role of astronomical cycles in governing the development of hyperpycnal flows and highlight their positive influence on organic matter enrichment.

ABSTRACT Astronomical forcing is widely recognized as a key driver of sedimentary cyclicity; however, its control on lacustrine hydrological changes—and the relationship of these changes to global sea‐level fluctuations under greenhouse conditions—remains insufficiently understood. To better investigate these controls and their interrelationships, a high‐resolution floating astronomical timescale spanning 7.676 million years was established for the Chang 7 member of the Triassic Yanchang Formation in the Ordos Basin, which was deposited under greenhouse conditions. This timescale was constructed using the multi‐taper method (MTM), correlation coefficient (COCO), evolutive correlation coefficient (eCOCO), and sedimentary noise modelling methods implemented in Acycle, as well as the average spectral misfit (ASM) method in the Astrochron toolkit. The timescale was obtained by tuning gamma‐ray log data to the 405‐ka eccentricity cycle. The astronomical forcing mechanisms of lake‐level fluctuations and their relationship with global sea‐level changes could thus be established. The lacustrine system showed a stable response to long‐term modulations of Earth's orbital eccentricity and obliquity. The ~2.4‐Myr eccentricity and ~1.2‐Myr obliquity modulation cycles correspond closely with the lake‐level fluctuations, demonstrating that the lacustrine system responded sensitively to Myr‐scale orbital forcing. In the absence of polar ice sheets, the lacustrine hydrological system was highly sensitive to orbital obliquity, showing a stronger response than global sea‐level variations. When orbital obliquity was high, increased precipitation at high latitudes boosted aquifer recharge, raising lake levels, while marine water sequestration into continental aquifers reduced ocean volume. The consequence was a rise in lake level but a drop in the sea level. It implies that orbital modulations, by altering mid‐ to high‐latitude precipitation and groundwater recharge, can induce an inverse relationship between lake‐ and sea‐level fluctuations. This supports the applicability of the aquifer–eustasy mechanism: lacustrine systems, as sensitive recorders of hydroclimatic changes, demonstrate long‐term “hydrological memory”, capable of capturing regionally expressed water redistribution at orbital timescales. These findings provide new geological evidence for reconstructing the Middle to Late Triassic climate and hydrological evolution, and offer theoretical support for understanding the sea/lake system's coupling mechanisms under greenhouse conditions.

ABSTRACT Lacustrine sedimentary environments and sand‐body architectures are influenced by lake‐level fluctuations and climate, but understanding their relative contributions in deeply buried successions remains challenging due to the overprinting of diagenetic and tectonic processes. The Permian Shihezi Formation in the southwestern Ordos Basin provides an ideal setting for investigating how lake‐level variability influenced shallow‐water braided delta migration and reorganisation. Recent hydrocarbon exploration has yielded high‐quality cores and well logs, enabling detailed reconstructions of depositional processes. Using these datasets, we reconstruct the sedimentary characteristics, facies architecture and controlling processes of the Permian Shihezi Formation, developing an updated depositional model for its braided‐delta system. A revised sequence‐stratigraphic framework was established from integrated core‐log interpretation, aiding facies and systems‐tract identification. Facies analysis reveals that the braided‐delta system developed on a gently inclined basin margin with strong but variable hydrodynamics, frequent lake‐level shifts and significant long‐distance sediment transport. These characteristics make the Shihezi Formation a valuable analogue for shallow‐water continental systems preserved in other deeply buried basins worldwide. Stratigraphic patterns indicate a transition from early deposition characterised by climate‐related lake‐level variability broadly coincident with global eustatic cycles to later deposition increasingly controlled by regional tectonics, aridification and variations in sediment supply. Early‐stage sedimentation shows a broad temporal correspondence with higher‐order global highstand–lowstand cycles, while later stages record autogenic feedbacks through delta progradation, channel mobility and shoreline stabilisation. These trends suggest that the broad temporal correspondence between global eustatic cycles and regional lake‐level variability may reflect a common climatic background, whereas regional tectono‐climatic controls increasingly shaped later lake‐level and lacustrine‐system evolution.

This study presents a detailed palynofacies analysis integrated with lacustrine sequence stratigraphy to evaluate the role of climate-driven hydrological balance on basin infill and its impact on the organic matter accumulation in the Jurassic Ca & ntilde;ad & oacute;n Asfalto Formation, Cerro C & oacute;ndor depocentre, Extra-Andean Patagonia, Argentina. It provides valuable insights into the changes in the nature and taphonomic history of the organic matter throughout the different stages of a lacustrine system's evolution based on the analysis of 51 outcrop samples from the Ca & ntilde;ad & oacute;n Lahuinc & oacute; "A" section. Two depositional sequences are recognised. Sequence I documents the evolution from underfilled to balanced-fill/overfilled lake stages. Underfilled conditions are characterised by extreme lake-level variability, while the transition to balanced-fill/overfilled conditions is marked by stacked coarsening-upward successions. Sequence II is bounded by an abrupt accommodation increase and initially records renewed underfilled conditions, followed by the establishment of a fully overfilled lake stage characterised by persistent progradational stacking patterns. The most conspicuous feature of the Ca & ntilde;ad & oacute;n Asfalto Formation's organic matter is the overall dominance of land-derived fraction. The variations between the allochthonous and autochthonous (algae and algal-derived amorphous organic matter) material suggests variable climatic conditions, with the alternation of wetter and drier periods at least during the Sequence I and part of the Sequence II. Four palynofacies types (PT-A to PT-D) were defined recording variations in depositional energy, redox conditions, and sediment-water balance. PT-A and PT-D indicate wetter periods, while PT-B indicates relatively drier intervals. PT-C shows the changes between these two opposite situations. The underfilled stage is characterised by the dominance of reworked terrestrial phytoclasts (indicating high-energy inflow events) and poor sporomorph preservation. Conversely, the balanced-fill stage shows sporomorph-rich palynofacies. In both lake stages, blooms of well-preserved strong fluorescence Botryococcus colonies (chlorophytic algae) are registered during drier periods. The overfilled conditions are characterised by the lack of palynomorphs. Kerogen varies from Type III (PT-A) to mixed Type I/III in algae-rich intervals (PT-B, PTC), confirming hydrological balance as the control on organic matter preservation.

The magmatic-mineralization response during the early stage of the North China Craton (NCC) destruction is key to understanding its evolutionary history. The Tongshi complex, located within the Guilaizhuang gold field in the southwestern NCC, is closely related to regional gold mineralization. However, its emplacement age, magma sources, and genetic link with gold mineralization remain controversial. This study focuses on the two dominant rock types of the complex, the monzodioritic and syenitic porphyries, and presents a systematic investigation including zircon U-Pb geochronology, zircon trace element and Hf-O isotopic analyses, as well as whole-rock geochemistry and Sr-Nd-Pb isotopic compositions on them. Zircon U-Pb dating yields ages of 175.9 +/- 4.3Ma and 176.3 +/- 1.8Ma for the monzodioritic porphyry, and 174.7 +/- 0.6Ma and 175.0 +/- 1.6Ma for the syenitic porphyry. Geochemical and isotopic data reveal that the monzodioritic porphyry within the complex was derived from partial melting of an enriched sub-continental lithospheric mantle beneath the NCC, with its source region having been modified by materials from the delaminated lower crust of the NCC, subducted continental crust from the Yangtze Plate, and fluids associated with the Paleo-Pacific Plate. In contrast, the syenitic porphyry originated from partial melting of the asthenospheric mantle, with its parental magma mixing with delaminated lower crustal components of the NCC at depth. The complex is characterized by high oxygen fugacity and high-water content (monzodioritic porphyry: Delta FMQ =1.89, Eu-N/Eu-N(*) = 0.64 similar to 0.98; syenitic porphyry: Delta FMQ = 2.23, Eu-N/Eu-N(*) = 0.34 similar to 0.67), indicating that the magmatic system was favorable for gold mobilization and transport, thus possessing significant mineralization potential. Notably, the syenitic porphyry exhibits higher gold mineralization potential than the monzodioritic porphyry, as reflected in its superior magmatic oxygen fugacity and water content. Pyrite from the Guilaizhuang deposit exhibits similar Pb isotopic compositions to the whole-rock samples of the syenitic porphyry, suggesting that the Tongshi complex may have provided the primary metal sources for the mineralization. Combined with the observation that various types of gold mineralization in the deposit are strictly controlled by this complex, we propose that the Tongshi complex and the Guilaizhuang gold deposit are spatially and temporally associated, constituting a typical subvolcanic magmatic-hydrothermal mineralization system. Our integrated study suggests that the formation of both the Tongshi complex and the Guilaizhuang gold deposit was closely related to the successive subduction of the Yangtze Plate and the Paleo-Pacific Plate, collectively representing the magmatic evolution and gold mineralization event during the early NCC destruction. Specifically, the subduction of the Yangtze Plate metasomatically modified and weakened the sub-continental lithospheric mantle of the NCC, while the subsequent subduction of the Paleo-Pacific Plate triggered the detachment of the lithospheric root formed by continental collision and the upwelling of the asthenosphere, thereby laying the material and structural foundation for the large-scale decratonization of the NCC in the Cretaceous.

Volcanic materials are highly susceptible to diagenetic alteration due to their geochemical instability, and their presence can exert a strong control on the evolution of sandstone reservoirs. In the southwestern Ordos Basin, the Lower Shihezi Formation contains abundant volcanic material, providing an ideal natural laboratory for investigating the diagenetic behavior of mixed volcanic-terrigenous sandstones. This study considers the diagenetic history of the Lower Shihezi Formation sandstones through a multifaceted approach, including thin-section observation, electron probe analyses, carbon and oxygen isotope analyses, fluid inclusion microthermometry, X-ray diffraction (XRD) analyses, and physical property measurements. Petrographic observations show that volcanic material occurs predominantly as tuffaceous matrix, accompanied by subordinate volcanic quartz. Combined petrographic and geochemical evidence indicates that volcanic materials underwent hydration- and acid-driven alteration during burial, but the dominant diagenetic pathways varied systematically with volcanic material abundance, leading to distinct assemblages of diagenetic minerals, including chlorite, kaolinite, Fe-calcite and siliceous cements. Sandstones rich in tuffaceous matrix experienced restricted fluid circulation and were dominated by hydration-related alteration and pore-filling cementation within the tuffaceous matrix, resulting in poor pore connectivity and overall degradation of reservoir quality. In contrast, sandstones with minor volcanic input developed more effective acidic alteration, leading to enhanced dissolution, macropore development, and limited cementation, thereby preserving relatively better porosity and permeability. These contrasting diagenetic pathways produced strong reservoir heterogeneity. When combined with regional geological constraints, the data suggest that volcanic material was supplied to the depositional system through a combination of atmospheric fallout and traction-transported sediment input. Overall, the results highlight how variations in volcanic material abundance fundamentally govern diagenetic pathways and exert a predominantly negative net impact on reservoir quality in volcanic materials-influenced sandstone reservoirs.

The oldest undisputed metazoan body fossils are often represented by tubular remains, which led to the characterization of early ecosystems as the Ediacaran 'worm-world' fauna. Tubular body fossils continued to dominate during the Cambrian Bioradiation Event, primarily as three-dimensionally preserved small skeletal fossils, although their preservation varied widely. Most tubular fossils, however, lack soft tissue preservation, making it challenging to determine their biological affinities based solely on tube morphology. Here we describe well-preserved tubular fossils, Longgangia bilamellata gen. et sp. nov. and Selkirkia cf. columbia, from the Cambrian Mantou Formation (Miaolingian Series, Wuliuan Stage) in Burgess Shale-type preservation. Longgangia bilamellata gen. et sp. nov. features a double-layered tube wall, transversal annulations, and Y-shaped branching of half-ring annulations. The new species shows importance because of its resemblance in construction and preservation with Ediacaran tubular fossils, such as Sinospongia, Sinotubulites, and Sabellidites, therefore providing evidence for the persistence of the tube-dwelling lifestyle from the Ediacaran to the Cambrian (Miaolingian). This also highlights the evolutionary and ecological significance of tube-forming organisms during the Cambrian Bioradiation Event, an interval characterized by explosive metazoan diversification, biomineralization, genetic innovation, and niche specialization. The potential affinity with cnidarians, annelids, and hemichordates is discussed and an assignment of Longgangia gen. nov. to Annelida is considered most plausible. The new material also reveals that annelids are capable to create tubes by half-ring construction with Y-branchings of growth lines, thus emphasizing this tube construction is not exclusive to hemichordate pterobranchs.

Integrating geochronological and sequence stratigraphic analyses in a basin can significantly enhance the understanding of its evolution. The Paleogene Middle Sha 3 Member (Es3m) in the Dongying Sag is characterized by a lake-delta sedimentary system and is of particular interest due to its abundant hydrocarbon resources. However, the Es 3 m currently lacks a robust chronostratigraphic framework, and the existing sequence stratigraphic framework, primarily based on seismic data from the delta zone, exhibits relatively low resolution. In this study, a cyclostratigraphic analysis was conducted on fine-grained lacustrine sediments of the Es 3 m in the Dongying Sag, utilizing natural gamma (GR) data from three wells. The objective was to establish a high-resolution astronomical time scale (ATS) and a high-frequency sequence framework. Lake-level changes were reconstructed using lag-1 autocorrelation coefficient (rho 1) analysis and dynamic noise after orbital tuning (DYNOT) analysis. The findings suggest that the Es 3 m spans a duration of approximately 34.7-39.2 Ma. Sedimentary accumulation rates (SARs) of lake sediments within the study area range from approximately 11 to 25 cm/kyr. Furthermore, the lake-level exhibits significant periodic variations, and 11 fourth-order sequences and 3 systems tracts (transgressive systems tract, early highstand systems tract, and late highstand systems tract) were successfully identified in the Es3m. This research serves as a typical case study for delineating high-frequency sequences in lacustrine fine-grained sediments and refining the geochronological framework.

The behavior of the global climate system on scales from years to centuries is related to several mechanisms, including solar forcing and the El Niño-Southern Oscillation (ENSO). However, due to limited stratigraphic resolution and the accuracy of dating methods, pre-Quaternary archives are rare. A middle Eocene lacustrine shale in the Bohai Bay Basin of East China contains annual laminae which provides a site to study the astronomical and varve chronology of the basin. Principal component analysis of the sediments in the cored material, their magnetic susceptibility and grayscale scans as well as analysis of the varve thickness in thin sections, jointly reveal variations between a warm/dry and cold/wet climate on the scale of centuries (~200–240 years and ~350 years, respectively), probably corresponding with cycles in solar activity. In situ δ13C and δ18O values of the light carbonate laminae indicate, in combination with varve-thickness data, that algal blooming and carbonate production occurred at ~2.1–8.7-year cycles, which could be ascribed to ENSO activity. Our finding of the ENSO variability during this notably warm interval indicates that evident interannual variability will likely continue to exist in our future greenhouse planet.

Sediment gravity flows are critical sediment transport mechanisms in deepwater environments and play a key role in hydrocarbon accumulation. The well-developed sediment gravity flow deposits of the Shahejie Formation are major oil-bearing units in the Dongying Depression (Bohai Bay Basin, eastern China), yet the types of sediment gravity flow deposits and their controlling factors remain debated. This study introduces a novel step-fault-controlled framework in the lower section of the third member of the Eocene Shahejie Formation (ES3L sub-member) that goes beyond traditional models by highlighting the finer-scale structural influences on sediment distribution. The research discusses sedimentary characteristics, lithofacies types, facies distribution, and depositional models based on core samples, well logs, and seismic data from the relay ramp of the Dongying Depression, offering important insights for hydrocarbon exploration strategies. The results indicate that the sediment gravity flows responsible for the deposition in the study area were mainly sandy debris flows, turbidity currents, and hyperpycnal flows. Debrite sandstone deposits are characterised by numerous floating mud clasts, often associated with soft-sediment deformation structures. Turbidite sandstones are characterised by load casts and normal grading. Hyperpycnites are characterised by couplets of inverse grading and normal grading, periodic changes in grain size, and abundant plant debris. The development of sediment gravity flows within the study area was controlled by step faults. As a result, a step-fault-controlled sedimentary model of sediment gravity flow deposition was developed with the following characteristics: 1) Delta front deposition prevailed on the upper step fault, with minor deposition from gravity flows; 2) hybrid deposition of sandy debris flows and turbidity currents took precedence on the middle step fault; and 3) hyperpycnites dominated on the lower step fault. This study investigates the impact of stair-step faults on the sedimentary facies of gravity flows, providing guidance for oil and gas exploration and development in rifted lacustrine basins worldwide.

Well-exposed soft-sediment deformation structures (SSDS) outcrops are rare and often mistaken for tectonic folds, leading to limited research and underutilisation in sedimentary geology. The Taitongshan section of the Middle-Permian Shihezi Formation in the Ordos Basin, China, provides insights into SSDS, whose spatial distribution and sedimentation reveal information about paleoenvironments, tectonic movements, and seismic events crucial for understanding basin development. This study uses fieldwork and sedimentology to investigate SSDS formation and triggers. Fieldwork identified six siliciclastic facies with SSDS and associated syndepositional structures. Sedimentological interpretations highlighted the connection between seismic activity and the genesis of SSDS, reinforcing their value as proxies for tectonic events in basin evolution studies. SSDS formation is triggered by seismic shaking, initiating liquefaction, erosion, slurry-clump formation, hydroplastic deformation, mass consolidation, and lithification. Rayleigh waves-induced liquefaction in partially-lithified subsurface sediments forms water escape structures. Provenance analysis reveals seismically active, orogenic source areas southwest and southeast of the NCC, with significant uplift and erosion during the Middle-Permian. Key findings indicate that the Middle-Permian braided river facies of the Taitongshan section originated from the Qilian Orogenic Belt, followed by a subsequent provenance shift towards the eastern-North Qinling Orogeny (NQLO), highlighting the dynamic tectonic forces driving rapid provenance shifts, further shaping sediment deposition and advancing basin evolution. Furthermore, the southeastern NCC experienced a more rapid uplift than the southwestern part during that time. These facies were deposited on the distal fan region of a prograding alluvial fan, where seismites likely formed due to active seismicity in the NQLO. The study identifies inter-facies shifts during seismite formation, introducing an innovative concept beyond traditional in-situ genesis models and broadening the understanding of sedimentary dynamics. This critical role of SSDS in sedimentation architecture enhances the understanding of basin evolution in sedimentary geology and provides a framework for interpreting similar structures globally.

The Anambra Basin of Nigeria, part of the larger West and Central African Rift System (WCARS) across Africa, contains primarily Cretaceous to Palaeocene shallow to marginal marine and freshwater sedimentary deposits. The organic-rich deposits of the Cretaceous Nkporo and Mamu formations within the Anambra Basin and the Palaeocene Imo Formation of the Niger Delta Basin constitute important conventional source rocks. Despite its economic significance, research on organic matter characterisation, palynofacies, sea-level fluctuations, palaeoclimate, hydrogeography, basin restriction, palaeobathymetry and the factors controlling organic matter preservation remains largely undocumented. The here presented new inorganic and organic geochemical and organic petrography data of the Cretaceous to Palaeocene deposits serve to refine the regional interpretation at a basinal scale and within the supra-regional context of the WCARS. Geochemical palaeotemperature proxies suggest a warm and humid tropical palaeoclimate during the Late Cretaceous within the study area. Furthermore, the measured TOC values indicate poor to very good organic content. Palynofacies analysis revealed high abundances of opaque and translucent phytoclasts and low amounts of palynomorphs with negligible amorphous organic matter (AOM) in the studied mudrocks. Two palynofacies groups suggest shallow-marine conditions in a proximal shelf setting and a heterolithic oxic basin. The palynofacies of the upper Imo Formation reveal higher percentages of dinoflagellate cysts during the early highstand phase, with equidimensional, opaque phytoclasts representing the maximum flooding phase, accompanied by warmer conditions. Additionally, abundant terrestrial phytoclasts, Deltoidospora spp., Classopollis spp. and geochemical indicators collectively indicate warm tropical climatic conditions consistent with geochemical interpretations. The palaeobathymetry reconstructions suggest a shallow seaway during the Upper Cretaceous in the Anambra Basin.

The Guilaizhuang Au-Te deposit is the most representative alkaline igneous-rock-related epithermal Au deposit on the southeastern margin of the North China Craton (NCC). Key aspects regarding the occurrence states and enrichment mechanisms of Au remain unclear. Pyrite, as a principal gold-hosting mineral, plays a crucial role in deciphering the ore-forming process; however, detailed data on its textural characterization and in-situ geochemistry are scarce. In this study, the ore-forming process is divided into three stages, (1) quartz-pyrite (stage I), (2) Au-polymetallic sulfide-telluride (stage II), and (3) carbonate (stage III). Two types of pyrite are identified, including euhedral disseminated pyrite (Py1) from the early stage (stage I) and coarse-grained anhedral pyrite (Py2) from the main mineralization stage (stage II). In addition, LA(-MC)-ICP-MS is employed for the first time to conduct in-situ trace element spot/mapping and S isotope analyses on these two types of pyrite. Through comprehensive petrography, EPMA, and LA-ICP-MS analyses, four main occurrence states of Au are determined, including auriferous telluride, native Au, "invisible gold" and electrum. "Invisible gold" occurs as both solid solution (Au+) within the crystal lattice of pyrite and micro-scale mineral inclusions enclosed within pyrite. Py2 shows higher concentrations of As, Au, Ag, and Te compared to Py1. In As-pyrite, As substitutes for Sas As-rather than for Fe2+ as As2+/3+ and is incorporated into the pyrite. The coupled distribution and positive correlation between Au and As indicate that As facilitates the incorporation of Au into the pyrite lattice. Tellurium mainly occurs as solid solution within pyrite, whereas Pb exists as galena and minor altaite inclusions within pyrite. Py1 exhibits delta 34S values ranging from-2.60 to +3.1 %o (mean =-1.1 %o), whereas Py2 yields values from-10.6 to +2.0 %o (mean =-4.5 %o), indicating that the S in pyrite is of magmatic origin. The lower delta 34S values in Py2 result from isotopic fractionation during fluid boiling, where 34S is preferentially partitioned into sulfate while 32S enriches in sulfide phases. Furthermore, the concentric zoning of Co-Ni and As-Au-Te within the pyrite provides additional evidence for fluid boiling. Based on the comprehensive analyses above, this study proposes that the gold enrichment at Guilaizhuang is not only influenced by the changes of physicochemical conditions (e.g., temperature and pH) but also facilitated by Te-rich metallic melts that enhance Au scavenging and deposition during the ore-forming process. These findings are of considerable significance for understanding trace element incorporation into pyrite, and for revealing the mechanism of Au enrichment and hydrothermal evolution processes in alkaline igneous-rock-related epithermal Au deposit.

The organic‐rich shale of the seventh Oil Member (Chang 7 Member for short) of the Middle‐Late Triassic Yanchang Formation is extensively distributed in the southern margin of the Ordos Basin. Understanding the palaeoenvironmental conditions during the sedimentary period of the Chang 7 Member is crucial to exploring the main factors that control the enrichment of organic matter in high‐quality source rocks. In this study, lithofacies analysis was conducted, and samples were collected from the N36 well located in the southern part of the Ordos Basin. Subsequently, element geochemical analysis was performed to reconstruct the palaeoenvironment, and total organic carbon (TOC) tests were conducted to analyse the characteristics of organic matter enrichment. The findings indicate that the sedimentary period of the Chang 7 Member was characterized by a relatively warm and humid palaeo‐climate and a brackish water environment with oxygen‐poor or sub‐oxygen‐rich conditions, and a gradual decrease in palaeo‐water depth. The parent rock types were mainly felsic igneous rock and intermediate igneous rock, which provide limited nutritional elements for primary producers. The enrichment of organic matter in the Chang 7 Member is influenced by several factors, mainly including palaeo‐salinity, palaeo‐water depth, palaeo‐redox conditions, terrestrial inputs, and palaeo‐climate. The warm and humid palaeo‐climate, higher palaeo‐productivity, relatively higher palaeo‐salinity, lower terrigenous input, deeper palaeo‐water depth, and better preservation conditions are conducive to the development of high‐quality source rock in the Chang 7 Member.

The Anambra Basin in southwestern Nigeria is part of the West and Central Africa Rift System (WCARS), with sedimentary successions comprising freshwater, deltaic, and marginal marine deposits. In the present study, we provide new mineralogical and geochemical data from mudrocks of the Campano-Maastrichtian Nkporo and Mamu formations and the Paleocene Imo Formation, intersected by the Owan-1 and Ubiaja wells. The analyses aim to identify source composition, sedimentary grain sorting, hydrothermal influence, and depositional environment, focusing on the understudied southwestern margin of the basin. Additionally, the data provide insights into the tectonic evolution of the Anambra Basin and its genetic link to the Benue Trough and other WCARS basins. The studied mudrocks contain detrital grains predominantly composed of quartz and clay minerals, with little feldspar. Major and trace element proxies used to evaluate sediment grain sorting reveal primarily fine-grained clastics, indicating long transport distances that correlate with the high clay mineral contents. The few coarse-grained deposits suggest periods of direct sediment input into the basin and less recycling. There is no evidence of hydrothermal influence in the basin. Therefore, a significant pelagic influence is proposed for the analysed sequence. This hypothesis is corroborated by the presence of gypsum, which is typically precipitated from seawater. Based on provenance-sensitive inorganic geochemical proxies (i.e., Cr/Th vs. Sc/Th, La/Th vs. Hf, Th/Co vs. La/Sc, Th/Sc vs. La/Sc, Th/U vs. Th/Sc, TiO2 vs. Zr) and the identified detrital contributions to the Paleocene Imo Formation and Cretaceous Mamu and Nkporo formations, the studied siliciclastic rocks are interpreted to be derived primarily from proximal felsic plutonic rocks that were uplifted to the surface by tectonic processes. Distinction diagrams from discriminant functions show that the sediments of the Anambra Basin were deposited in a rift setting, which is consistent with the other WCARS basins.