Depositional Setting Research Articles

Revealing Yukon’s hidden treasure: an atomic-scale investigation of Carlin-type gold mineralization in the Nadaleen Trend, Canada

AbstractThe invisible-gold deposits known as Carlin-type are becoming more important as easier to find deposits are progressively depleted. The combination of the invisible nature of the Au in these deposits, as well as the limited surface indicators of these deposits, makes exploration to find new Carlin-type deposits extremely difficult. Comprehensive mineralization models are essential to find new Carlin-type deposits in similar geologic settings. The Nadaleen Trend of Yukon, Canada, is one such district where an improved understanding of this deposit type has led to new discoveries. Previous studies compared and contrasted the tectonic setting, host rock depositional setting, structural preparation, and mineralization style of the Nadaleen Trend with those in Carlin-type localities, Nevada. However, the comparisons at an atomic scale, between Carlin-type Au deposits in the Nadaleen Trend and those in Nevada, has yet to be investigated. This study fills this knowledge gap by combining high resolution microanalytical techniques with atom probe tomography to examine the distribution of Au and other trace elements in the Nadaleen Trend, compare them to a representative Carlin-type deposit in Nevada (Turquoise Ridge), and determine how widespread the mineralization model is. Our findings show that in the Nadaleen Trend, as in Nevada, Au is generally directly linked with As at the macro to atomic scale, and is incorporated into As/Au rich overgrowths on sedimentary/diagenetic pyrite. Gold-rich pyrite rims in the Nadaleen Trend are generally smaller than those found in Nevada (0.5–2 µm vs > 10 µm), although the ore grades appear comparable. We find that the Au in the pyrite of the Nadaleen Trend is homogenously distributed (i.e. lattice bound) at the atomic scale, but that there is a notable enrichment of As surrounding individual Au atoms. These findings are in agreement with those from previous work on a representative deposit in Nevada, and support the assertation that As is the key ingredient in facilitating the incorporation of Au into the pyrite lattice. Arsenic as an essential component in the trapping mechanisms of Au in CTG deposits, is something that has been as to yet underappreciated in the current models of CTG deposit formation.

Mineralogical and Maturation Considerations of the Coqueiros Formation (Campos Basin, Brazil): Insights from Multi-Technique Analyses of Source Rocks

The Coqueiros Formation, a strategic stratigraphic unit within the Lagoa Feia Group (LFG) in the Campos Basin offshore Brazil, is known for its lacustrine carbonate deposits, which include both organic-rich shales and economically important “coquina” reservoirs. While coquina facies are widely recognized as reservoirs, the source-rock potential of the intercalated shales remains relatively underexplored. This study aims to characterize the mineralogy and thermal maturity of the Coqueiros Formation to assess its potential as a source rock, using a multi-technique approach integrating X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Raman spectroscopy analyses of shale samples from two wells: 3-BP-11-RJS and 6-DEV-18P-RJS. XRD analyses revealed a heterogeneous mineralogy dominated by carbonates (calcite and dolomite) and quartz, with significant contributions from clay minerals and trace minerals such as pyrite and barite. SEM imaging revealed a heterogeneous fabric with grain size, morphology, and porosity variations, reflecting a dynamic lacustrine depositional setting influenced by storm events and fluctuations in terrigenous input. The presence of authigenic minerals, as reported in other studies, such as saddle dolomite, mega-quartz, and various sulfides, provides evidence for hydrothermal alteration, likely related to Late Cretaceous magmatic activity in the Campos Basin. Raman spectroscopy yielded equivalent vitrinite reflectance (Ro%) values consistently exceeding 1.00, ranging from 1.03 to 1.40, indicating that the organic matter in the Coqueiros Formation shales has attained a high thermal maturity level, surpassing the oil window and reaching the condensate wet gas zone. The mineralogical and equivalent maturation data presented herein provide a valuable foundation for future studies, highlighting the complexity and heterogeneity of the Coqueiros Formation and its potential significance as a source rock within the Campos Basin petroleum system.

Lithology, source areas and formation settings of upper triassic deposits of South-Western Primorye

The article considers the material composition of sandy rocks from the Upper Triassic deposits of the Mongugai formation of South-Western Primorye and presents the results of its paleogeodynamic interpretation. It has been established that, according to their mineralogical and geochemical parameters, sandstones are petrogenic, correspond to graywackes and, only partially, to lithite arenites, are characterized by a significant degree of geochemical maturity of the clastic material, and their formation occurred due to the erosion of significantly weathered parent rocks of the source areas. Generalization and paleogeodynamic interpretation of the data obtained indicate that in the Late Triassic in the southwestern part of Primorye, sedimentation occurred in basins associated with the environment of the active continental margin and, probably, complicated by strike-slip dislocations along transform faults. The dominant source of clastic matter was continental land: cratons and projections of crystalline basement framed by rift zones or along transform faults. Acidic granite-metamorphic complexes were eroded with the participation of sedimentary rocks enriched with ancient components. A secondary source was a deeply dissected continental margin magmatic arc, which supplied the basin with an additional amount of sialic material, as well as a small amount of the basic-medium volcanoclastic. U-Pb geochronological studies of detrital zircons from sandy rocks of the formation made it possible to establish the age and possible location of magmatic complexes, due to the destruction of which the deposits were formed.

Development and distribution of submarine channels associated with sediment gravity flows in the modern Huanghe (Yellow River) subaqueous delta

BackgroundGravity-driven depositional processes play a pivotal role in shaping the geomorphology of subaqueous deltas worldwide, particularly by eroding the seafloor, leading to the formation of rugged submarine channels (SCs) and triggering various subaqueous geohazards. A comprehensive understanding of SCs is crucial for elucidating these depositional mechanisms and mitigating the risks associated with submarine geohazards. Although SCs in the Huanghe delta front have been previously identified, often described as seafloor gullies or subsurface “disturbed strata,” most studies have primarily concentrated on their engineering geological properties. However, there has been limited research on the scale, morphology, and development of these SCs, especially those that are buried within the stratigraphy.MethodsThis study integrates high-resolution sub-bottom data, sediment core analyses, and historical bathymetric data to investigate the morphology, distribution, and formation mechanisms of SCs in the Huanghe subaqueous delta.ResultsThe SCs, both buried and exposed, are widespread along the middle and upper delta front, predominantly located at or near the landward flank of sediment gravity flow (SGF) -related accumulations. The buried SCs are characterized by cut-and-fill structures with transparent to semi-transparent fills, indicating rapid infilling processes as SGF energy dissipates. These buried channels were preserved within different sets of delta front deposits formed during 1855–1964 CE, 1964–1976 CE, and 1976–2007 CE, with the latter two periods separated by a significant lobe-switching event in 1976 CE. This event, combined with prevailing southeastward sediment transport and erosional regimes, appears to have controlled the preservation of SCs along the delta front: SCs in the Diaokou Lobe's delta front (pre-1976) suffered significant erosion, leaving only one set of channel (erosional remnants) preserved, while the SCs in the Qingshuigou Lobe's delta front (post-1976) are characterized by well-preserved, multi-phase channels at different horizons. The cross-section morphology of the SCs reveal three primary types: symmetrical, asymmetrical, and composite, corresponding respectively to (1) idealized SGF incision, (2) uneven incision intensity on either side of the SCs, and (3) the merging of two or more symmetrical/asymmetrical SCs.ConclusionsWe describe in detail the morphology, distribution and development of SCs in the modern Huanghe subaqueous delta. These findings provide insights into the formation and distribution of SCs in other shallow marine settings, particularly in delta front areas, and potentially offer information for disaster prevention and engineering development in such regions.

A Regional Paleoclimate Record of the Tropical Aeolian Sands during the Last Deglaciation in Hainan, China

The KLD segment of the Kenweiyuan section in Wenchang, Hainan, China is a set of aeolian sand deposits of the Last Deglaciation. The chemical element and heavy mineral analysis performed in this study reveals the chemical index of alteration (CIA) in the segment to be as high as 93–95, with all the heavy minerals identified as stable and extremely stable making up 38–45% of the total. Furthermore, the zircon, tourmaline, and rutile content (ZTR index) of the segment is determined to range between 48–71. The (Al2O3 + TOFE)/SiO2 ratios display obvious fluctuations from old to new strata in the segment, with the low values corresponding to Heinrich event (H1), Dansgaard-Oeschager (D-O), and Younger Dryas (YD) and the high values corresponding to Bølling and Allerød. Our study suggests that these fluctuations are attributed to the alternation of the East Asian winter and summer monsoons. Hainan Island is also impacted by the surface ocean climate of the South China Sea, and characteristics of the KLD segment may be connected to the climate changes in the North Atlantic related to the winter monsoon season or westerlies. Furthermore, the segment presents a clear response to millennium-scale climate changes during the Last Deglaciation on Hainan Island. Based on the high CIA values in the KLD segment, and particularly due to the observed stable detrital minerals, the ratios can be linked to the overall tropical climate, indicating a relatively warm tropical climate environment in the Last Deglaciation in Hainan. The high CIA values also reveal the cause of aeolian sand formation under the tropical environmental conditions in the low latitude region of China in the Late Quaternary.

The success rate of processed predicted models in molecular replacement: implications for experimental phasing in the AlphaFold era.

The availability of highly accurate protein structure predictions from AlphaFold2 (AF2) and similar tools has hugely expanded the applicability of molecular replacement (MR) for crystal structure solution. Many structures can be solved routinely using raw models, structures processed to remove unreliable parts or models split into distinct structural units. There is therefore an open question around how many and which cases still require experimental phasing methods such as single-wavelength anomalous diffraction (SAD). Here, this question is addressed using a large set of PDB depositions that were solved by SAD. A large majority (87%) could be solved using unedited or minimally edited AF2 predictions. A further 18 (4%) yield straightforwardly to MR after splitting of the AF2 prediction using Slice'N'Dice, although different splitting methods succeeded on slightly different sets of cases. It is also found that further unique targets can be solved by alternative modelling approaches such as ESMFold (four cases), alternative MR approaches such as ARCIMBOLDO and AMPLE (two cases each), and multimeric model building with AlphaFold-Multimer or UniFold (three cases). Ultimately, only 12 cases, or 3% of the SAD-phased set, did not yield to any form of MR tested here, offering valuable hints as to the number and the characteristics of cases where experimental phasing remains essential for macromolecular structure solution.

Sedimentary organic matter and paleoenvironmental reconstruction of the Santana Group (Lower Cretaceous), Araripe Basin, Northeast Brazil

Depositional controls of the Santana Group in the Araripe Basin are still being debated. The main controversial subject is their marine influence and paleoenvironmental evolution. In this study, palynofacies analysis was performed on 59 samples from one core drilled at Sítio Romualdo in the Araripe Basin to investigate sedimentary organic matter. Three palynofacies associations (structureless, continental particles, and aquatic + opaque) were identified. The Santana Group consist of Barbalha, Crato, Ipubi and Romualdo formations. Based on palynofacies associations we conclude that the depositional setting of the Barbalha Formation reflects a fluvially-fed lacustrine system under oxic conditions. The Crato Formation, associated with tidal flats, coastal lakes, and lagoons within an open bay environment, represents a bayhead delta system. The Ipubi Formation corresponds to a coastal plain typical of sabkha paleoenvironments, characterized by low energy under reducing conditions, during drier climate conditions. The Romualdo Formation records mainly an estuarine paleoenvironment characterized by dysoxic to anoxic conditions. The presence of palynomorph groups typifies a late Aptian age for the Santana Group, which is based on the range of guide species marked mainly by the presence of Sergipea variverrucata biozone (P-270), as well as the occurrence of Complicatisaccus cearensis and Equisetosporites maculosus. The identification of marine palynomorphs (dinoflagellate cysts Subtilisphaera and foraminiferal test linings) are indicative of several, local marine incursions.

The role of the production geologist in carbonate reservoir development

Carbonate production geologists are deployed to tackle field management and (re)development issues on increasingly brownfields. This paper shares examples of how geologists raise awareness of current and potential production opportunities with insights into permeability architecture and its uncertainty. The examples represent diverse fluid types and a range of depositional, diagenetic and structural settings. “Plumbing diagram” examples communicate what matters to flow from the reservoir to the well perforations. In the Luconia gas fields, thin low porosity horizons either accentuate or baffle vertical permeability to rising aquifers. In a Middle Eastern GOGD development constrained by gas re-injection, well placement into unfractured intervals led to an oil redevelopment at a lower gas cut. In a Middle Eastern waterflood, dynamic characterisation of permeability contrasts facilitates improved oil recovery through sweep management. The examples stress the importance of continued geological data analyses in brownfield settings, as well as active engagement during engineering-dominated discussions on fluid flow that inevitably follow field development plan execution and monitoring. A discussion examines why brownfield development opportunities delay to later field life, and into the energy transition, how production geologists might improve geothermal and sequestration reservoir developments.

Microplastic and Associated Black Particles From Road‐Tire Wear: Implications for Radiative Effects Across the Cryosphere and in the Atmosphere

AbstractThe environmental effects of airborne micro‐ and nano‐size plastic particles are poorly understood. Microscopy and chemical analyses of atmospherically deposited particles on snow surfaces at high elevation (2,865–3,690 m) in the Upper Colorado River basin (UCRB; Colorado Rocky Mountains) revealed the presence of black substances intimately associated with microplastic fibers, particles interpreted to have originated as tire matter. Identical and similar particles occur in shredded tires and road‐surface samples. The substance responsible for the black color of all tires is carbon black, a graphitic light‐absorbing tire additive produced by hydrocarbon combustion that homogeneously permeates the mixture of tire polymers and other additives. Such black tire matter may thus exert radiative effects closely similar to those of black carbon. The presence in snow of many organic compound types common to tires, measured by two‐dimensional gas chromatography, suggests that atmospherically deposited black road‐tire‐wear matter is among the light‐absorbing particulates that advance the onset and rate of snow melt in the UCRB. The mass of road‐tire‐wear particles shed from vehicles may be estimated by multiplying measured amounts of eroded tire‐per‐distance traveled by vehicular distances. Under a combination of measurements and assumptions about the amounts and radiative properties of atmospheric tire‐wear particles, the radiative effects of these particles might add about 10%–30% to those effects from black carbon, an estimate ripe for revision. On regional and global scales, the amounts and effects of emitted and deposited tire‐wear matter likely vary by factors of geographic source, transport pathway, and depositional setting.

Paleogeographic reconstruction and sedimentary evolution of tidal-dominated estuarine depositional systems: Insights from the campanian M1 sandstone formation, Oriente Basin, Ecuador

The Oriente Basin is a back-arc basin located east of the Ecuadorian Andes in South America. Evidence suggests that during the Cretaceous period, the basin's margins received a terrigenous shallow marine sedimentation. Due to regional variations in accommodation and depositional controlling factors near a shoreline, the sedimentary environments in the fluvial-marine transitional zones exhibit considerable variability. In this study, we analyzed the sedimentological characteristics of the M1 Sandstone Formation unit (∼83 Ma-72 Ma), which comprises a set of ancient estuarine deposits preserved in the northern part of the basin. We quantified the impact of mixed hydrodynamic processes on the distribution of tidal-dominated estuarine facies and discussed the development conditions and evolutionary processes of an estuarine formation under the background of persistent transgression. Core, well log, and seismic data provide evidence for reconstructing the tidal-dominated estuarine environment. In the core section, we identified 14 lithofacies and 7 major facies association types. The frequent occurrence of sedimentary structures associated with tidal currents indicates that tidal processes extensively reworked the deposits. The spatial distribution trends of facies associations reveal the evolution of mixed hydrodynamic conditions dominated by tidal processes in the estuary and allow us to divide the M1 Sandstone Formation into four depositional periods: the initial development, rapid development, decline, and the post-infilling open coast tidal flat development periods. Furthermore, through a systematic analysis of hydrodynamic conditions and sediment distributions, we identified multiple depositional centers in the tidal-dominated estuary influenced by different hydrodynamic processes. These correspond to the upstream fluvial-dominated tidal point bar depositional region, the middle mixed-energy depositional interaction zone, and the downstream tidal-dominated tidal sand bar depositional region. In these regions, the substantial accumulation of sandy deposits, represented by tidal sand bars, reflects the high accommodation space characteristic of tidal-dominated estuaries. Our findings indicate that the slow subsidence of a broad and gently sloping coastal topography, stable material transport, and sea level change dominated by marine transgression ensured the necessary accommodation for the development of the estuary in the M1 Sandstone Formation. The sedimentological study of the M1 Sandstone Formation provides a case for understanding the sedimentary evolution in fluvial-marine transitional zones.

Sequence stratigraphic architecture and depositional evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate successions, N Cyrenaica Promontory, NE Libya – Interplay of tectonics and eustasy

The interactions of tectonics and eustasy on the stratigraphic architectural evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate sedimentary successions were evaluated. This evaluation was achieved through detailed analyses of microfacies, depositional interpretation, and sequence stratigraphic framework of five measured sections located within the Al Jabal Al Akhdar Uplift, northeast Libya. The study interval was subdivided into distinct microfacies based on lithological changes, grain size and components, sedimentary texture and structures, fossil contents, color, and vertical stacking pattern. Six major depositional settings were delineated: restricted lagoon, open marine lagoon, platform margin and shoals, platform-margin reefs, foreslope, and middle to lower slope. Four third-order unconformity-bounded depositional sequences were identified based on vertical and lateral facies distribution, variations in fossil contents, and diagenetic features. Each sequence is composed of a transgressive-regressive interval, except for the younger sequence, which only contains a transgressive unit. Four evolutionary stages are recognized: initiation, growth, high-relief platform, and subaerial exposure. Subsidence resulting from tectonism and sediment loading, coupled with rising sea-level, created the accommodation space for the sedimentation of the studied carbonates. Repeated eustatic sea-level fluctuations controlled the internal stratigraphic heterogeneity and sequence development. Tectonic uplift caused a major sea-level retreat, resulting in the emersion of the carbonate sequences. The pre-existing Mesozoic and Paleocene sequences that underwent major uplift during the Late Cretaceous-early Eocene formed a shallow-water positive-antecedent topography for the formation of the carbonate sediments. This study establishes a carbonate sequence stratigraphic hierarchy of different cyclic sedimentation orders and improves our knowledge of sedimentary and stratigraphic architectural evolution and depositional mechanisms of carbonate platforms in an inverted basin setting. This knowledge can aid in predicting the distribution of lithofacies and depositional systems of economic importance.

Morphological characteristics and controlling factors of the piedmont fan systems in the Zanskar region, Northwest Himalaya, India

Piedmont fans are prominent geomorphic features formed at the transition between mountain slopes and valley floors. This study investigates the morphology of alluvial fans in the Zanskar Basin (ZB) to uncover the key variables influencing their development and morphodynamics. Utilizing advanced GIS and remote sensing techniques, along with field investigations, we conducted a detailed spatial analysis of 103 alluvial fans along the Doda, Tsarap, and Zanskar rivers. This approach allowed for precise mapping and characterization of these fans within complex depositional settings of ZB, particularly where fans merge into bajadas. Our analysis revealed distinct characteristics for the fans, including Fan Area (FA), Fan Slope (SF), Radius (R), Base Length of Fan (BF), Fan Maximum Entrenchment (FME), and Flow Expansion Angle (FEA). A morphometric analysis was then conducted to evaluate the correlation between the fans and their upstream basins. The linear regression analysis demonstrated both positive and negative correlations between these parameters, highlighting the important role of the upstream basins in controlling sediment delivery to fans. The findings suggest that larger basins contribute to the morphological development of fan systems, with larger, less steep fans forming as a result of greater flows and increased sediment supply from basins with denser drainage networks. Lower values of Mountain Front Sinuosity, Valley Floor Width to Valley Height ratio and Basin Elongation suggest that upstream basins in the ZB are significantly influenced by tectonic forces, resulting in linear mountain fronts, V-shaped valleys and elongated upstream basins. The F-99 fan, in particular, has developed a prominent stepped-fan morphology, attributed to differential uplift, vertical incision, and lateral migration of channels across the fan surface. Along the various fronts of the Zanskar, fan morphology is controlled by a complex interplay of long-term tectonic processes, climate, upstream lithology, and basin characteristics. Tectonic forces, particularly the NW-SE-trending ZSZ/STD and ZCT, exert first-order control on fan morphology by influencing sediment-flux and accommodation space. This influence is evident in tectonically modified landforms such as active mountain fronts, fan terraces, elongated basin shapes, wine-glass valleys and triangular facets, all indicating recent uplift and active tectonics in the region. Our results indicate that ZSZ and ZCT exert significant tectonic control over the geometry and evolution of fans, alongside substantial climatic influences.

Reservoir characterization of GABO field in the niger delta basin using facies and petrophysical analyses

This study investigates the GABO field in the onshore Niger Delta Basin using well logs and core samples, with a focus on rock type distribution, reservoir continuity, and petrophysical properties to enhance hydrocarbon exploration accuracy. The research involved detailed analysis of core descriptions and images from GABO-20, along with petrophysical data from wells GABO-4, GABO-12, GABO-13, GABO-20, and GABO-51, aiming to identify rock types, evaluate reservoir quality, and determine the spatial distribution of petrophysical properties. The methodology included rigorous well log quality checks, data correlation between wells, petrophysical property evaluation, and lithofacies description. The analysis revealed thirty-five hydrocarbon-bearing zones, with GABO-20 showing average shale fraction values between 0.111 and 0.335, total porosity ranging from 0.242 to 0.329, and hydrocarbon saturation from 0.667 to 0.923, indicating substantial porosity and hydrocarbon saturation conducive to extraction. Well correlations demonstrated excellent sand-shale continuity within the reservoir intervals. Lithofacies analysis of the GABO-20 core identified eight distinct facies, including shale poles, liquid-rich shales, and sandstone poles, revealing a complex distribution of reservoir qualities with significant variations in potential. Cores 1 and 2 exhibited favourable conditions for hydrocarbon production, while Core 3 showed lower reservoir quality due to increased clay content. The depositional settings of the GABO field, particularly in the lower delta plain and delta front zones, showed well-developed reservoir bodies with moderate potential in the tidal zone and little potential in the shaly prodelta environment. This distribution highlights the complexity of the deltaic system and its implications for reservoir modeling and utilization. Reservoir zones associated with High-Quality Reservoir Facies exhibited strong petrophysical properties, suggesting excellent hydrocarbon production potential. The study underscores the importance of detailed reservoir characterization to optimize recovery strategies, offering valuable insights into the distribution and quality of reservoir sands, reducing subsurface uncertainty, and emphasizing the integration of facies and petrophysical approaches for a better understanding of reservoir characteristics in the GABO field.

Mass production and cutting performance of diamond coated cutting tools for machining titanium alloys

Diamond coated cutting tools are applied for machining difficult-to-machine materials of titanium alloys. However, the temperature field uniformity needs to be further improved for the mass production of diamond coated tools using the hot filament chemical vapor deposition (HFCVD) method. In this paper, the tools temperature distribution is simulated by the finite volume method (FVM) during the deposition of diamond coatings. An optimization method of deposition setting with fine filaments in dense arrangement (FFDA) is proposed, and the temperature distributions of the tools under the coarse filament in sparse arrangement (CFSA) and FFDA are simulated to systematically elucidate the effects of fine filament densification. Subsequently, the different hot filament arrangements are adopted to mass production experiment for deposition of micro/nano composite diamond (MCD/NCD) coatings on WC-6%Co cutting tools. In addition, the cutting experiments on titanium alloys are conducted using diamond coated tools, and the cutting performance of tools at different locations is evaluated. The results indicate that the FFDA method can improve the temperature field uniformity of mass-produced diamond coated cutting tools, and the cutting tools have better consistency in surface morphology, thickness, chemical composition, surface roughness and cutting performance.

Morphology and ethology of Rosselia erecta in Eocene lignitic mudstone

The Middle Eocene lignite-mudstone deposits of the Kutch (Kachchh) Basin, western India, manifest a highly restricted marginal-marine depositional setting, in which an unusual preservation of Rosselia erecta can be observed within organic-carbonaceous-rich mudstone beds. It is the earliest Cenozoic record of the ichnospecies hitherto reported. Rosselia erecta occurs in a paucispecific R. erecta–Trichichnus isp. ichnofabric within thinly laminated mudstones that are intercalated with lignite seams and laminae. The burrows are primarily vertical, characterized by cone-in-cone structures that are penetrated by a centrally positioned cylindrical shaft with concentric or intermittently eccentric lining. The lining intermittently contains sulfide-mineralization, often with the framboidal pustules that probably formed as a result of anaerobiosis by chemautotrophic symbiotic bacteria. The cone opening at the bedding surface displays radial striae, indicating surface-detrital foraging behaviour. We propose that the burrow serves as a facultative multifunctional structure, with the tracemaker employing two distinct feeding mechanisms: (1) surface-detritus-feeding (fodinichnia) and (2) cultivating microbial colonies (agrichnia) of sulfate-reducing bacteria in a mutualistic symbiotic relationship. The well-preserved morphological features in the newly examined specimens facilitate a reassessment of the constructional mechanisms and functional implications of the ichnospecies R. erecta reminiscent of the recently established ethological category sequestrichnia.

Absolute 230Th/U chronologies and Δ47 thermometry paleoclimate reconstruction from soil carbonates in Central Asian loess over the past 1 million years

Pleistocene loess records of the Khovaling Loess Plateau (KLP) in Tajikistan provide rich collections of lithic artifacts demonstrating past human presence in the region. To understand the timing of human activity and environmental conditions prevailing at that time U–Th dating and clumped/stable C/O isotope measurements have been applied to modern and Pleistocene soil carbonates (SCs) collected at several sites on the KLP and surroundings. U–Th ages were corrected by two methods: 1) assuming an initial [230Th/232Th] activity ratio of 0.85 ± 0.25 based on gamma spectrometry of loess/paleosol samples, and 2) the isochron technique using leachates and fully dissolved subsamples. Diagenetic alteration and potential U/Th mobilization and related isotope fractionation due to alpha-recoil was also modelled and found to be minor in the studied soil carbonates. Compared to model ages as references, uncorrected 230Th ages are only acceptable if measured [230Th/232Th] activity ratios of leachates are high (>30), while 230Th ages derived using method 1 are mostly overcorrected. It appears that SCs can be reliably dated by the U-series disequilibrium method in this sedimentary setting, but isochron dating cannot be spared. Application of the isochron method is required to derive 230Thmodel ages, which ensures that the non-zero initial 230Th and possible U–Th gain/loss due to alpha-recoil can be simultaneously corrected and reliable U–Th ages obtained. U–Th ages of Pleistocene SCs clearly demonstrate post-pedogenic ingrowth of multiple, non-contemporaneous populations of SCs within loess/paleosol units, and that SC formation happened in many cases under cold, presumably dry glacial climate conditions. Considering that U–Th ages of SCs provide minimum ages of the sediment in which they form, these ages can be useful in developing loess stratigraphic models and for correlation of paleosols with marine isotope stages. This implies that the age of a given paleosol and any lithic artifacts it may contain, indicating human activity, cannot be younger than the age of SCs formed in that paleosol. This is due to the nature of soil carbonates, which can be the product of both syn- and post-depositional processes.Clumped isotope thermometry of SCs collected from modern soils at three sites in Tajikistan provide evidence for SCs dominantly recording summer season soil temperatures, while the calculated soil water oxygen isotope signatures reflect annual signals and carbonate precipitation from source waters incorporating rainfall from prior to and during SC formation. In contrast, some Pleistocene SCs record soil temperatures and stable isotope compositions more appropriate to glacial conditions, confirming the findings of U–Th ages, and highlighting the primary role of aridity-driven soil moisture changes in SC precipitation in this setting. Considering the interpretative complexities of SC stable isotope compositions, involving issues such as SC formation depth within a soil/paleosol profile, seasonality of SC growth and violation of the law of superposition, SC stable isotope proxy records of past climates cannot be considered as a set of clearly sequential data through time. This implies that such SC-based stable isotope records must be accompanied by U–Th dating of carbonates to be meaningful.

Heterolytic tide-dominated sedimentary facies and depositional environment: An Example from the Boka Bil formation, Sitapahar anticline, Bangladesh

The Baraichari Shale Formation, which is equivalent to the Boka Bil Formation, is well exposed within the Neogene sequence of the Sitapahar Anticline in the Chittagong-Tripura Fold Belt, Bengal Basin, Bangladesh. Regardless of its importance in hydrocarbon accumulation, a comprehensive facies analysis is essential to understand and explain the heterogeneity within different depositional architectural elements. The purpose of this work is to delineate the lithofacies characteristics, depositional environment heterogeneities and propose a generic depositional model for the Middle to Late Miocene shallow marine sediments of the formation. The sedimentary facies were investigated at three outcrops along the Kaptai–Chandraghona road cut sections of the Sitapahar anticline. The formation is composed of dark to bluish-gray shale, silty shale, yellowish brown siltstone, and gray to yellowish brown fine-to medium-grained sandstone. Eight distinct sedimentary facies have been identified and were categorized into three facies associations: subtidal or estuarine, mixed flats with tidal creeks, and tidal mud flats. The subtidal facies, predominant in the middle member, consists of fine to medium-grained ripple cross-stratified sandstone-siltstone, herringbone cross-stratified sandstone, and trough cross-stratified sandstone, indicating sub-tidal channel deposition. Mixed flats with tidal creeks exhibit heterolithic facies, suggesting energy level changes in intertidal to sub-tidal zones influenced by tidal currents. Tidal mud flats are predominantly laminated shale/mudstone and lenticular laminated sandstone-siltstone, reflecting deposition during tide transitions in the intertidal zone. Fining upward cycles within the formation indicate progressive progradation or changes in inner tidal flats conditions during regressive periods. These depositional settings serve as analogs for equivalent subsurface reservoirs and contribute to the construction of reservoir models with greater accuracy.

Phosphorus flux during the Ediacaran: Rooted in continental weathering or pelagic upwelling?

The Ediacaran Period was punctuated by major environmental and evolutionary milestones, including large-scale phosphogenesis during intervals of elevated phosphorous (P) flux. Although increased P flux could be an important driver of animal evolution and associated ocean oxygenation, the processes responsible for triggering the remarkable Ediacaran phosphogenesis episodes remain unclear. In this study, we present new δ138Ba, 87Sr/86Sr, and major and trace element data from Ediacaran phosphorites of the Doushantou Formation (Nanhua Basin, China). Low-to-negative δ138Ba (−0.31 to 0.06 ‰, analogous to δ138Ba of modern and ancient restricted depositional settings) and elevated 87Sr/86Sr values (0.7100 ± 0.0002, greater than the global average) from lower Doushantuo phosphorites indicate intense local continental weathering enhanced P delivery to the restricted Nanhua Basin at ∼630–600 Ma. During this early phosphogenesis stage, macroeukaryote blooms stimulated atmospheric oxygenation and eutrophication of deep seawater in the Nanhua Basin. In contrast to the lower phosphorites, the elevated and open-marine-like δ138Ba of 0.17 to 0.35 ‰, as well as lower 87Sr/86Sr values (mostly lower than 0.7096, comparable to the global average), from overlying ∼587–574 Ma phosphorites indicate that this later phosphogenesis interval was characterized by upwelling of pelagic deep ocean waters rich in re-mineralized P. Global-scale P burial (as phosphorite) could not lead to decreased eutrophic conditions in the global ocean, but, together with increasing oxygen levels in deep seawater and/or the atmosphere, this process may have finally facilitated the evolution of Ediacaran fauna.

Micritisation products in the inner ramp settings of the Abu Dhabi Lagoon

AbstractIn numerous carbonate reservoirs in the Middle East, peloidal packstone‐grainstones are rock types with excellent pore storage potential in micritised microporous grains. However, the origin of the micro‐porosity and associated micro‐spar remains unclear, and one hypothesis is that both micro‐spar and porosity originate from early marine micritisation and were later altered during subsequent diagenesis (i.e. cementation recrystallisation). The south‐eastern coast of the Arabian Gulf is recognised as a modern, albeit miniature, depositional setting analogue to Mesozoic carbonate sequences that form the supergiant reservoirs of the Middle East. Using optical microscopy, backscattered scanning electron microscopy and carbon and oxygen stable isotope analysis the present study aims to document the nature of internal microstructures of micritic envelopes and peloids from the surface sediments of various sub‐environments of the Abu Dhabi Lagoon. Results highlight a high degree of diversity and heterogeneities of most micritic envelopes and peloids observed across the sub‐environments. First, carbonate grains from ooid and bioclastic shoals show the simpler micritic envelopes. Here, micritic envelopes and peloids show sparse microborings filled with banded radial aragonite cement, a pattern of production of cryptocrystalline texture (e.g. micritisation) that is similar to the sequence of micritisation observed in the modern sediment of the Great Bahama Bank. Conversely, in the subtidal and intertidal zones with mangroves or seagrass, the micritic envelopes and peloids are much more complex and show multiple generations of microborings that are either empty or filled with carbonate materials of varying types (i.e. various cements, fragments, etc.).

Diagenesis and reservoir quality evolution of estuarine sandstones: Insights from the Cenomanian-Turonian Yolde Formation, northern Benue Trough, NE Nigeria

Estuarine sandstones often exhibit complex diagenetic pathways due to the interaction of fluvial and shallow marine processes, resulting in significant reservoir heterogeneities. The Yolde Formation is an important petroleum reservoir in the Northern Benue Trough, NE Nigeria. However, diagenetic and reservoir quality evolution of the formation are still poorly understood. This study utilizes thin-section petrography, XRD, SEM, and fluid inclusion microthermometry to analyse the composition, diagenesis, and reservoir quality of the sandstones. Results show that the sandstones are mainly arkose and subarkose in composition; they are generally well-sorted and vary in grain size from very fine-to coarse-grained. Three diagenetic stages are identified: early, middle, and late. The early stage includes feldspar dissolution, formation of kaolinite, development of clay coating, and mechanical compaction. The middle stage comprises the formation of authigenic chlorite and Fe-oxide cements. The late-stage diagenesis involves illitization of kaolinite, formation of dickite, albitization of K-feldspar, and precipitation of quartz overgrowths. The diagenetic evolution of the sandstones was strongly controlled by their compositional makeup. The feldspathic nature of the sandstones resulted in the formation of kaolinite, illite, and quartz overgrowths, through feldspar dissolution and silica supply. The inner and middle estuarine facies have inhibited the development of quartz overgrowths due to well-developed clay coatings, whereas the outer estuarine facies were well-cemented by quartz overgrowths due to lack of clay coatings. Illitic clay coatings were found to be effective in preventing quartz cementation. Fluid inclusion analysis reveals that the formation temperatures of the quartz overgrowths range from 98 °C to 135.5 °C, corresponding to burial depths ranging between 2.3 and 3.5 km. These findings would provide useful insights that would reduce the risks of exploration of the sandstones and also supplies potential input data for forward diagenetic modelling of their subsurface equivalents in similar depositional settings elsewhere.