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A new mollusc material from the Ilona Valley Section (Mátra Mts, Hungary) is investigated. Strata of the section represent the Ilonavölgy Member of the Pétervására Sandstone Formation. Based on geochemical data and mollusc biostratigraphy these deposits appear to be early Ottnangian in age. The mollusc fauna displays much higher diversity than was recognized in earlier studies from the locality in question and from other Ottnangian sites in the Paratethys. The rich material verifies the extended stratigraphic and palaeogeographic ranges of numerous taxa, and allows of designating 12 new gastropod species: Clanculus s. l. gulyasi n. sp., Gibbula kralli n. sp., Calliostoma nandori n. sp., Ormastralium erazmusi n. sp., Sconsia landaui n. sp., Cirsotrema kokayi n. sp., Ocinebrina deaki n. sp., Calagrassor mathiasi n. sp., Clavatula s. l. barnabasi n. sp., Clavatula s. l. istvani n. sp., Dentimargo barnai n. sp., Solatisonax pozsgayae n. sp. With 106 figures and 1 table. [ABSTRACT FROM AUTHOR]

The geochemistry of actinides under reducing conditions in a deep geological nuclear waste repository is characterized by low solubility and strong sorption to mineral surfaces. The quantification of actinide migration (i.e. diffusion) at resulting concentration levels requires an analytical method able to determine actinide concentrations down to ultra-trace levels (≈fg g−1). In the actual study, such an analytical procedure was tested by using accelerator mass spectrometry (AMS), one of the very few analytical techniques that can presently meet those requirements. Specimens simulating the sample matrix representative for a diffusion experiment in natural clay rock were produced by spiking clay rock powders (Opalinus Clay or Callovo-Oxfordian Clay) and aliquots of corresponding pore waters with the actinide nuclides 233U, 237Np, 244Pu, and 248Cm in amounts ranging from approximately 3 × 10−19 to 5 × 10−15 mol per sample (≈0.07–1000 fg per sample). The actinide nuclides were separated as group via Fe(OH)3 co-precipitation and then analyzed sequentially with AMS. During such analysis a decrease in count rates by up to a factor of 6 was observed in high-matrix clay rock samples compared to low-matrix standard solutions. Since the chemical yield of the actinides in the Fe(OH)3 co-precipitation step prior to analysis turned out to be quantitative, this observation must originate from a reduction of the sputter rate of the actinide nuclides in the AMS ion source, which can be described partly as a dilution effect. By determining chemical-ionization-yield factors, suitable non-isotopic tracers were identified for 237Np and 243Am. This allowed for the concurrent determination of all actinide nuclides at levels down to 3 × 10−19 mol per sample. Different actinides in a deep geological formation may be present in concentration ranges differing by orders of magnitude depending on their chemical form and solubility. Such concentration spreads were simulated by preparing clay rock/pore water samples where each individual sample contained 233U, 237Np, 244Pu, 243Am, and 248Cm at quantities ranging from approximately 3 × 10−19 to 4 × 10−15 mol per sample. The presented sample preparation procedure, in combination with the extraordinary detection sensitivity of AMS allows for the simultaneous determination of diffusion profiles of several actinides at ultra-trace levels within one experiment. [ABSTRACT FROM AUTHOR]

Mapping of regolith is significant to identify and discriminate geomorphic expression, regolith evolution, weathering histories and assistance in clarification of relationships between parent and surface materials. In this research work, the hydrothermally altered regolith of Western Jahajpur Belt, Bhilwara, India is studied using ASTER and AVIRIS imageries by PCA, decorrelation stretching supervised classification image processing methods. Results of decorrelation stretching of ASTER spectral bands 6, 7 and 9 showed the regolith in blue, green and red colour with the associated geological formations. Analyses of VNIR-SWIR spectral bands of ASTER by PCA showed the bed rocks associated to the regolith green, yellow, white and red colours, respectively. The minerals of the regolith and parent geological formations are identified using AVIRIS data by supervised classification and endmember spectral analyses. The study also identified six regolith-landforms which include the regolith (vegetation cover), crop land (vegetation cover), water, crop land with vegetation, alluvium and regolith (ferruginous and calcareous mineral zone). The discrimination of regoliths and geological formations are verified in the field and confirmed by XRF and ICP-MS geochemical analysis of samples. [ABSTRACT FROM AUTHOR]

During the Upper Cretaceous the northwestern margin of South America was characterized by a complex tectonic environment represented by the accretion of multiple terranes and the generation of varied magmatic events. The Sabanalarga quartz-diorite and the Santa Fe Gabbro previously described as a single body called Sabanalarga Batholith, present multiple differences among themselves and today are considered two independent plutons, representing two of the upper Cretaceous magmatics events. Both plutons intrude crusts of different affinity; The Santa Fe Gabbro intrudes a Plateau-type and island arc crust while the Sabanalarga quartz-diorite intrude into continental crust. The carried total rock chemical analysis showed anomalies of Nb-Ti, patterns of HFSE and REE in the multielemental diagrams indicatives of rocks generated in subduction environments. The Santa Fe Gabbro presents adakitic characteristics that are not present in the Sabanalarga quartz-diorite. The low Zr content and relations (La / Yb) n vs Sr / Y < 10 suggest that the Santa Fe Gabbro magma was formed in an oceanic environment, contrary to the Sabanalarga quartz-diorite with high Zr and relationships (La / Yb) n vs Sr / Y> 10 who suggest an origin in a continental environment for this magma. U-Pb LA ICPMs were analyzed for both intrusives: Santa Fe Gabbro showed ages between 78.4 and 81.8 Ma and Sabanalarga quartz-diorite ages between 71.5 and 76.7 Ma. Due to the new geochemical and geochronological data, it is suggested that Santa Fe Gabbro and Sabanalarga quartz-diorite are two different bodies with no temporal relationship and whose spatial relationship is still debatable. Is suggested for the geological setting of formation for these plutons a double subduction model type Molucca. [ABSTRACT FROM AUTHOR]

The results of gas-geochemical studies of the Chaun Depression and the Ayon sedimentary basin of the East Siberian Sea are presented. The natural gas composition in rocks, gas manifestations, and bottom sediments is determined. The indicators of the molecular mass of hydrocarbon fractions and weight concentrations of individual hydrocarbons, in which ratios are of correlation-genetic significance for hydrocarbon gases of the geological formations, are identified. The geochemical classification of hydrocarbon gases from bottom sediments and a schematic map of gas geochemical zoning of the study area are presented. The oil and gas potential of the Chaun Depression and the Ayon sedimentary basin is evaluated. [ABSTRACT FROM AUTHOR]

The geographical name of Monegros has traditionally been used to describe a high‐quality, dark‐coloured chert originating in a carbonate lacustrine environment, being one of the most important long‐distance tracers in south‐west Europe during prehistory. This chert type outcrops in the Monegros region, situated in the Ebro Basin (north‐eastern Iberia), but not only there, as cherts with the same descriptions are found in other regions, some far from the homonymous area. Nevertheless, prehistorians working on the characterization of lithic sources have frequently used the term 'Monegros' to define this chert, basing their attributions solely on macroscopic descriptions. These are not sufficient as they do not allow cherts from the Monegros region to be distinguished from cherts from other regions. In this study, the area where Monegros cherts outcrop was delimited and fieldwork was carried out to identify the origin of the geological formations and the preserved outcrops. The classic approach has proved to be insufficient for this purpose, so geochemical fingerprinting using energy‐dispersive X‐ray fluorescence (ED‐XRF) spectroscopy was performed. The results obtained after this first geochemical approach show that some differences can be found between the different formations in the Monegros region in terms of their major and minor components. [ABSTRACT FROM AUTHOR]

Volcaniclastic units are exposed at the base of the Puerto Blanco Formation in the Caborca region, northwestern Mexico. The lower unit reveals the presence of Early Cambrian mafic volcanism in this region. It consists of a volcano-sedimentary sequence represented by tuffaceous conglomerates, agglomerates, lapillistones, tuffs, and altered mafic volcanic flows. Petrographic analysis classified the volcanic clasts as albite-sphene-calcite-actinolite granofels, with a moderate to intense hydrothermal alteration, precisely characterized by EPMA analysis. Albite-actinolite geothermometry indicates temperatures from 400 to 500°C, suggesting metamorphic conditions in the upper temperature greenschist facies. Geochemistry analysis shows a high TiO2 basic–ultrabasic volcanism that originated the volcanic clasts. Rock protoliths were studied using immobile trace elements, which classified them as OIB-type alkaline basalts with the characteristic spider hump-shaped pattern, situated in an anorogenic intracontinental tectonic setting with enriched mantle signatures. 40Ar/39Ar geochronology shows metamorphic ages of 52.58 ± 2.0 and 91.67 ± 0.55 Ma, consistent with the emplacement of Laramidic granitoids identified in the region. Possible correlations of this alkaline volcanism include the Southern Oklahoma Aulacogen and the late stages of the rifting of north western Laurentia represented in western United States. [ABSTRACT FROM AUTHOR]

Detailed geochemical analyses of clastic fraction of the oldest exposed Salt Range Formation in the famous salt producing region (Salt and Trans-Indus Ranges) Pakistan was carried out in order to understand provenance, paleoclimate, depositional and tectonic settings. Sandstone and shale samples of Salt Range Formation were analysed for major, trace and Rare Earth Elements and various geochemical models and ratios were used to interpret. Geochemical analyses of both sandstone and shale fraction mostly display similar results and interpretations. The samples are classified as arkose, subarkose, litharenites and were sourced from felsic and/or intermediate igneous rocks. The sedimentation of the detritus was occurred in fluvial to restricted shelf conditions under arid to semi-arid and oxygenated climate conditions. The tectonic settings of the sediments were mainly Oceanic and Continental Island arcs as well as Active Continental margin. [ABSTRACT FROM AUTHOR]

Abstract The Second White Specks is an enigmatic unconventional shale play in the Western Canada Foreland Basin (WCFB). This play has an inconsistent production performance that has impacted exploration and production risk, preventing extensive development. In this contribution, geochemical properties are studied with the purpose to identify possible geochemical factors that could contribute to the production variability of this unconventional petroleum system. The studied succession consists of the Second White Specks (SWS) and Upper Belle Fourche (UBF) alloformations, which are part of the SWS shale play. Organic petrology and Rock-Eval pyrolysis were combined to characterize the organic matter (OM), and assess OM richness, thermal maturity and hydrocarbon generation potential in the foredeep section of the basin. The results show that the OM richness and hydrocarbon generation potential in this area is good, and comparison with other studies show that they do not exhibit major lateral variations. The kerogen is marine Type II and is dominated by liptinite, vitrinite, inertinite macerals, and solid bitumen. Alginite and bituminite are the most abundant macerals. Altered bituminite provides evidence of anaerobic bacteria degradation. There is a modest contribution of inertinite that may be responsible for a dilution effect of the pyrolyzable carbon. The thermal maturity indicators in this study such as vitrinite reflectance, Tmax, and alginite UV fluorescence color indicate that the controls on thermal maturity and hydrocarbon generation are not well understood. There are lateral short scale variations or maturity anomalies that require further investigation, to reduce the exploration risk. Highlights • Exsudatinite, bituminized alginite and oil inclusions corroborate endogenous hydrocarbon generation. • The thermal maturity in most of the study area indicates onset of petroleum generation to peak oil window. • A low maturity anomaly was identified. Further research is needed to test hypotheses for lateral maturity variability. • The organic matter experienced several degrees of anaerobic degradation. [ABSTRACT FROM AUTHOR]

The middle Eocene Fulra Limestone Formation of the Kachchh Basin, western India was investigated to interpret depositional environments and sources of limestones based on facies analysis, mineralogy, and major, trace, and rare earth elements (REEs) geochemistry. Facies stacking pattern of the Fulra Limestone Formation exhibits an overall shallowing‐upward sedimentary succession developed in the middle to inner ramp to lagoonal set‐up. Staining of the thin sections and X‐ray diffraction patterns show dominance of calcite mineral. The CaO, ranging from 40.45% to 49.69%, is the dominant oxide among the major oxides followed by SiO2 (4.04–10.3%). The dominance of CaO over MgO suggests that the major mineral phase has been calcite and no dolomitization occurred during the deposition of the Fulra limestone. The low proportion of SiO2 and Al2O3 suggests low siliciclastic input during the precipitation of the Fulra limestone that is confirmed by the positive correlation of ∑REE with Al2O3, Fe2O3, Ni, Th, Sc, and Y and the negative correlation of SiO2, Al2O3, and Sr with CaO. The average value of REE contents in the Fulra Limestone Formation are lower (*16.02 ppm) than the average value of typical marine carbonates (*28 ppm). The Post‐Archean Australian Shale‐normalized REE + Y patterns of the Fulra limestone exhibit seawater like shale‐normalized REE + Y pattern, whereas slightly lower average value of Y/Ho ratio (34.60) than the typical seawater value (~44–74) suggests modification of the seawater, to some extent, by input of freshwater in a coastal environment. The REEs of the Fulra Limestone Formation have similarity with the carbonates of the Arabian Sea and/or shallow marine carbonates with exception of a few elements. It is envisaged from this study that the Fulra limestone was deposited in a shallow marine to coastal set‐up where mixing of the continental material in seawater was feasible. [ABSTRACT FROM AUTHOR]

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

Graphical abstract Highlights • The Karing Volcanic Complex and the Dusunbaru Pluton represent a volcaniccentre. • Volcanicity took place over 630,000 years within the Asselian Stage of the Permian. • The West Sumatra Permian Block was a southern continuation of the Indochina Block. Abstract The Karing Volcanic Complex and the Dusunbaru Pluton comprise an Early Permian volcanic-plutonic centre in the Volcanic-Plutonic Arc on the western margin of the Kluet-Kuantan basin of the West Sumatra Block in Sumatra, Indonesia. The Karing Volcanic Complex is mostly composed of 'Monotonous Intermediate Type' tuffs which interfinger with the volcaniclastics and coastal and marine sediments of the Mengkarang Formation. Eight lithological Intervals each commencing with tuffs overlain by volcaniclastics and sediments, have been mapped in the Merangin river section. The climax of the volcanicity occurred in Interval IV. In the waning stages of volcanism basalt flows were extruded and the volcanic pile was eroded by lahars and debris flows. Zircon CA-IDTMS dates from tuff beds at the base and top of the section bracket the volcanic activity as having taken place over a period of 630,000 years within the Asselian Stage of the Permian. The Dusunbaru pluton is composed of Gabbroids, Granitoids with subordinate Metabasalts and Metatuffs occurring as xenoliths. These lithologies are present as lithic clasts within the Karing Volcanic Complex tuffs, and it is considered that the Dusunbaru Pluton represents a former magma chamber from which the tuffs were vented. The Mildly-alkaline to Sub-alkaline Metabasalts and Gabbroids, were derived from the N-MORB sector of the lithospheric 'Mantle Array' while the compositions of the Granitoids (including gabbroid-granitoid hybrid rocks) were influenced by the reaction of basic magmas with the lower crust. The Sub-alkaline and High–K Late Basalt Lava flows were derived from the melting of basalt below the crust-mantle interface. The rock suites were variably hydrated as a result of alterations. Magmatic alteration has affected the Metabasalts, Gabbroids, Granitoids, their xenoliths and the Late Basalts. Hydrothermal alteration has weakly affected the aubaerial tuffs and strongly changed the mineralogy of some of the Late Basalt flows, in particular the entablatures. The chemistry of the Dusunbaru Pluton is of Cordilleran-type, typical of continent margin volcanic-plutonic arcs. The Dusunbaru Pluton was likely originally emplaced at the interface between the Kuantan Formation (Visean to Permian) and a Proterozoic gneissic basement. A late hydrothermal event/tectonic event during which the Dusunbaru Pluton was faulted against the Karing Volcanic Complex, is attributed to the collision of the Woyla oceanic terrains with Sumatra in the late-mid Cretaceous. The stratigraphy of the West Sumatra Volcanic Arc and the Kluet-Kuantan Basin resembles that of the Sukhothai Volcanic Arc and associated basin sediments in the Indochina Block. A palaeogeographical reconstruction suggests that the West Sumatra Block originally was an appendage to the Indochina Block at a palaeolatitude between 5 and 15° S. [ABSTRACT FROM AUTHOR]

Highlights • The Lucaogou mudstones are still in the early oil window. • The biological sources are predominately algae and bacteria. • The Lucaogou mudstones were deposited in a hypersaline and anoxic environment. • The Lucaogou mudstones hold a significant exploration potential of tight oil. Abstract The mudstones of the Lucaogou Formation are the most important and organic-rich sediments and tight oil exploration target in the northwestern China. The organic and stable isotope geochemistry, and organic petrology were used to evaluate their sedimentary environments and hydrocarbon generative potential. The Lucaogou mudstones contain abundant organic matter, S 2 , hydrogen index (HI) and extractable organic matter (EOM), whereas S 1 values are low. The δ13C values of EOM are very light and display a negative correlation with HI. Rock pyrolysis data imply a low maturity (0.6–0.7 %R o equivalent) of the Lucaogou Formation, consistent with aliphatic and aromatic hydrocarbon ratios. The biological sources are predominately algae and bacteria, with less contribution of higher plants in the Lucaogou Formation as indicated by δ13C EOM , biomarkers and maceral composition. The Lucaogou mudstones contain low ratios of C 31 R/C 30 hopane, C 29 /C 30 hopane and C 22 /C 21 tricyclic terpane, and high C 24 /C 23 tricyclic terpane value, which are consistent with their depositional environments (i.e., lacustrine). The abundant β-carotane, gammacerane and hop-17(21)-enes indicate a hypersaline and anoxic environment. The studied samples are predominantly oil-prone with a dominant type I and II 1 kerogen. High contents of total organic carbon (TOC), S 2 , HI, EOM, saturated and aromatic hydrocarbons indicate that the Lucaogou Formation hold significant exploration potential of tight oil. [ABSTRACT FROM AUTHOR]

Abstract The Lower Permian Fengcheng Formation in the Mahu Sag of northwestern China is well-known for its alkaline lacustrine deposits. However, previous research is scarce due to this formation's notable burial depth (up to 5000 m) and limited oil and gas exploration. Using XRD, XRF, micro-XRF, and C-O isotope analyses, we determined: (1) the stratigraphic trends in mineral compositions, (2) the cyclic depositional processes, and (3) paleoclimate variations. The petrologic and geochemical data elucidate depositional and diagenetic processes in the mixed siliciclastic, volcaniclastic and chemical strata of the Fengcheng Formation. Sodium carbonate minerals in the studied core are dominated by wegscheiderite (Na 2 CO 3 ·3NaHCO 3) and trona (Na 2 CO 3 ·NaHCO 3 ·2H 2 O). Nahcolite (NaHCO 3) and a Mg-Na carbonate mineral, northupite (Na 2 CO 3 ·MgCO 3 ·NaCl), also occur, although their abundance is obviously lower than that of wegscheiderite and trona. These substances grew as bottom-growth crystals from lakes overlying tuffs. The volumetrically important Ca-Na carbonate mineral, shortite (Na 2 CO 3 ·2CaCO 3), and some northupite precipitated diagenetically from shallow groundwater brines in unlithified, dark-colored siliciclastic sediment and volcanic ash. Shortite mainly precipitated from the Ca-Na-CO 3 -rich shallow groundwater, whereas northupite precipitated from the Mg-Na-CO 3 -Cl-rich shallow groundwater. Sodium carbonates and tuffs, fine-grained tuffaceous rocks, and siliciclastic rocks formed repetitive centimeter- and meter-scale cycles that are shown as dark-colored lithological layers during lake expansion and contraction stages or during volcanic eruptions. The brine composition, which controlled the precipitation of sodium carbonates, was influenced strongly by volcanism and volcanism-related hydrothermal activity. Changes in climate and volcanic eruptions controlled the deposition of alternating beds of sodium carbonates and dark-colored lithologies. Changes in climate caused the expansion and contraction stages in the lakes. During relatively humid climate stages, diluted water entered the basin and resupplied the lake water with calcium and magnesium during flooding events. Sandy to silty beds were deposited by turbidity currents during this stage. During arid climate stages, bedded sodium carbonates grew in the lakes, and their co-occurrence suggests high atmospheric pCO 2 and high temperatures. The ashes that are provided by volcanic eruptions during arid climate stages can also stop the precipitation of sodium carbonates. Highlights • Sodium carbonates successions consist of alternating light-colored sodium carbonates layer and dark-colored tuff/tuffaceous layer. • The sodium carbonate minerals dominated by wegscheiderite and trona. Shortite and northupite occurred as transitional carbonate minerals. • Climates evolutions and periodic volcano eruptions joint to control the formation of depositional cycles in the sodium carbonates successions. [ABSTRACT FROM AUTHOR]

The metasedimentary Lujiapuzi Formation crops out along the northeastern margin of the North China Craton, close to the Yan‐Liao Rift. The age and tectonic setting of the formation, and its relationship with the Yan‐Liao Rift are currently unclear. Here we present detrital zircon U‐Pb ages, and Hf isotopic and geochemical data for the Lujiapuzi Formation to constrain the timing of deposition, the provenance of the formation, and the regional stratigraphy relationship. Zircon U‐Pb dating constrains the timing of deposition of the Lujiapuzi Formation to younger than 1780 Ma, and indicates that most grains were sourced from the Longgang Block and the Paleoproterozoic Liao‐Ji Belt. Detailed field investigations and a correlation of the regional stratigraphy reveal that much of the Lujiapuzi Formation is equivalent to the Tuanshanzi Formation in the Yan‐Liao Rift; the lower section may represent the earliest sediments deposited within the Fanhe Basin. Based on these results and the findings of previous studies, we suggest that the base of the Changcheng System has an age of 1.80 Ga. Zircon Hf isotopic data indicate that the main period of crustal growth along the northeastern margin of the North China Craton occurred at 3.2–2.5 Ga, with a peak at 2.9–2.7 Ga. [ABSTRACT FROM AUTHOR]

Abstract The exceptionally organic-rich rocks of the 1.98 Ga Zaonega Formation deposited in the Onega Basin, NW Russia, have refined our understanding of Earth System evolution during the Paleoproterozoic rise in atmospheric oxygen. These rocks were formed in vent- or seep-influenced settings contemporaneous with voluminous mafic volcanism and contain strongly 13C-depleted organic matter. Here we report new isotopic (δ34S, Δ33S, Δ36S, δ13C org) and mineralogical, major element, total sulphur and organic carbon data for the upper part of the Zaonega Formation, which was deposited shortly after the termination of the Lomagundi-Jatuli positive carbon isotope excursion. The data were collected on a recently obtained 102 m drill-core section and show a δ13C org shift from −38‰ to −25‰. Sedimentary sulphides have δ34S values typically between +15‰ and +25‰ reflecting closed-system sulphur isotope behaviour driven by high rates of microbial sulphate reduction, high sulphate demand, hydrothermal activity and hydrocarbon seepage. Four intervals record δ34S values that exceed +30‰. We interpret these unusually 34S-enriched sulphides to be a result of limited sulphate diffusion into pore waters due to changes in sedimentation and/or periods of basinal restriction. Additionally, there are four negative δ34S excursions that are interpreted to reflect changes in the open/closed-system behaviour of sulphate reduction or availability of reactive iron. Our findings highlight the influence of basinal processes in regulating sulphur isotope records and the need for care before interpreting such signals as reflecting global conditions. Highlights • Zaonega Formation Δ33S-δ34S data track basin-specific rather than global processes. • Opposing Δ33S-δ34S relationship relates to rapid microbial sulphate reduction. • Positive δ34S excursions reflect partial basinal restriction. [ABSTRACT FROM AUTHOR]

Abstract The formation of the Shiquanhe–Namco Ophiolite Mélange Zone (SNMZ) and its relationship to the Bangong–Nujiang Suture Zone (BNSZ) in central Tibet are key to understanding the Mesozoic tectonic evolution of the Meso-Tethys Ocean. This study presents zircon U Pb geochronological, whole-rock geochemical, and Lu Hf isotopic data for gabbros from the Asa Ophiolite of the central SNMZ. Four gabbros yielded zircon U Pb ages of 117.3 ± 0.6, 117.3 ± 0.5, 115.3 ± 0.5, and 114.9 ± 0.6 Ma. Whole-rock geochemical analyses indicate that these rocks are tholeiitic, enriched in light rare earth and large-ion lithophile elements, and depleted in Nb and Ta. These gabbros have geochemical affinities to island arc and mid-ocean ridge basalts, suggesting that they originated in an oceanic back-arc basin. Whole-rock geochemical data and isotopically juvenile εHf(t) values suggest that the gabbros were derived from a depleted mantle source that was enriched by slab-derived fluids and partial melts of sediment. Our data, combined with previous work, suggest that the BNSZ records the Early Cretaceous subduction of the Meso-Tethys oceanic crust and that the SNMZ represents a back-arc basin. During the Early Cretaceous, the Meso-Tethys Ocean remained open and contained an intra-oceanic subduction system and back-arc basin. Highlights • Ophiolite has Early Cretaceous ages (114-118 Ma). • Ophiolite has an oceanic back-arc spreading ridge setting. • The Bangon-Nujiang Meso-Tethys Ocean remained open during the Early Cretaceous. [ABSTRACT FROM AUTHOR]

Earth's core formation set the initial compositions of the core and mantle. Various aspects of core formation, such as the degree of metal–silicate equilibration, oxygen fugacity, and depth of equilibration, have significant consequences for the resulting compositions, yet are poorly constrained. The Hf–W isotopic system can provide unique constraints on these aspects relative to other geochemical or geophysical methods. Here we model the Hf–W isotopic evolution of the Earth, improving over previous studies by combining a large number of N -body simulations of planetary accretion with a core formation model that includes self-consistent evolution of oxygen fugacity and a partition coefficient of tungsten that evolves with changing pressure, temperature, composition, and oxygen fugacity. The effective average fraction of equilibrating metal is constrained to be k > 0.2 for a range of equilibrating silicate masses (for canonical accretion scenarios), and is likely <0.55 if the Moon formed later than 65 Ma. These values of k typically correspond to an effective equilibration depth of ∼0.5–0.7× the evolving core–mantle boundary pressure as the planet grows. The average mass of equilibrating silicate was likely at least 3× the impactor's silicate mass. Equilibration temperature, initial f O 2 , initial differentiation time, semimajor axis, and planetary mass (above ∼0.9 M ⊕ ) have no systematic effect on the 182 W anomaly, or on f Hf/W (except for f O 2 ), when applying the constraint that the model must reproduce Earth's mantle W abundance. There are strong tradeoffs between the effects of k , equilibrating silicate mass, depth of equilibration, and timing of core formation, so the terrestrial Hf–W isotopic system should be interpreted with caution when used as a chronometer of Earth's core formation. Because of these strong tradeoffs, the Earth's tungsten anomaly can be reproduced for Moon-forming impact timescales spanning at least 10–175 Ma. Early Moon formation ages require a higher degree of metal–silicate equilibration to produce Earth's 182 W anomaly. [ABSTRACT FROM AUTHOR]

Palaeo-exposure surfaces are common geologic features in the Cretaceous sedimentary record of the Middle East. Two important disconformity surfaces have influenced the Cenomanian-Turonian intervals of the Sarvak Formation in the Abadan Plain. These surfaces had substantial controls on reservoir quality of their underlying succession. In this study obtained data from macroscopic core descriptions, microscopic petrography, geochemical analysis, spectral gamma ray log signatures, and clay minerals frequency in three hydrocarbon fields are combined and used for interpretations. Dissolution, cementation and recrystallization are the main diagenetic features related to the disconformity surfaces. Intensity and development of these diagenetic alterations are highly dependent on depositional facies characteristics of the underlying sequences. In mud-dominated facies, the main diagenetic process is recrystallization, while the grain-dominated facies were highly subjected by dissolution and cementation. Based on the geochemical analysis, there is an increase in Al 2 O 3 , SiO 2 , Fe 2 O 3 , Al, Fe, Mn, and Rb content beneath the disconformities. In contrast, the Sr concentration displays a decreasing trend towards the disconformities. On spectral gamma ray logs, depletion of the uranium and high values of CGR/SGR and TH/U ratios are attributed to the meteoric diagenesis. In addition, obtained data from SEM and XRD analysis indicate that the montmorillonite is the most abundant clay mineral in uppermost part of the Sarvak Formation. It shows the highest concentration at the disconformity surfaces which can be quoted to the impact of meteoric diagenesis and development of palaeo-soil horizons. These results are used for reconstruction of diagenetic sequence of the upper Sarvak Formation in subsurface sections of the Abadan Plain. [ABSTRACT FROM AUTHOR]

In order to explore the marine redox structure on the earliest Cambrian (ca. 542–529 Ma) Yangtze Platform, South China, new Fe-Mo-C-S geochemical data from the slope Xugongping section for the Liuchapo and the base of Niutitang Formation are reported here. Integrated Fe speciation and Mo abundance data from the Xugongping section, in combination with previously published data from slope-basinal Longbizui section and others, suggest oxic surface waters and ferruginous deep waters coexisting with occasional mid-depth euxinic waters during the Fortunian Stage, and with widespread euxinic waters during the early Stage 2 marine transgression. A compilation of new and published sulfur isotope data of pyrite for the Liuchapo and the base of Niutitang Formations presents high isotopic values (mostly >+10‰) and distinctly different spatiotemporal gradient characteristics during the Fortunian Stage and the beginning of the Stage 2. We propose that redox stratification developed in the earliest Cambrian protected basin, and eustatic change and the connectivity of the protected basin with the open ocean controlled the materials supply from riverine input and open ocean reservoir and thus spatiotemporal variability of ocean chemistry. [ABSTRACT FROM AUTHOR]

This study aims to establish the diagenetic evolution of carbonate rocks of the Barremian-Aptian Tirgan Formation (Kopet-Dagh Basin, NE Iran), with special emphasis in their impact on reservoir quality to be used as analog for their equivalent carbonate reservoirs. To achieve this target, basic petrography complemented by elemental and stable isotopic (δ 18 O and δ 13 C) analyses of the studied carbonate rocks was used. In addition, the visible porosity was detected. The recognized carbonate diagenetic processes include micritization, cementation, dolomitization, compaction, dissolution, stylolitization, fracturing, silicification and neomorphism. These diagenetic processes took place in four diagenetic environments: marine-phreatic, meteoric-phreatic, meteoric-vadose and burial. Early dolomitization of lime muds, micritization of skeletal allochems and cementation by isopachous equant calcite represent marine-phreatic diagenesis. The meteoric-phreatic diagenesis was accompanied with the development of granular non-ferroan calcite cement, neomorphosed carbonate matrix and recrystallized bioclasts. The meteoric-vadose diagenesis led to prevalence of dissolution process and sparry calcite infilling the fractures. Late dolomitization, ferroan blocky and poikilotopic calcite cement, stylolitization and silicification processes were developed during burial diagenesis. An integration of the petrographic study with the geochemical analysis confirms that the studied carbonate rocks were originally composed of aragonite, which was eventually recrystallized to calcite and replaced by dolomite during diagenesis. In terms of reservoir quality, the recognized diagenetic alterations and visible porosities show that the diagenetic processes have a direct effect on modification of both inter- and intra-granular/crystalline porosity. In this manner, it is found that the calcite cementation, micritization and compaction decline the pore spaces, whereas the dolomitization, dissolution, formation of moldic pores and fracturing increase the pore volumes. Consequently, prevalence of dolomitization, dissolution, occurrence of moldic pores and fracturing in the Tirgan carbonate rocks gives the Tirgan Formation and its equivalent rocks a good opportunity to be an excellent reservoirs. [ABSTRACT FROM AUTHOR]

The timing and mechanisms of continental crust formation represent major outstanding questions in the Earth sciences. Extinct-nuclide radioactive systems offer the potential to evaluate the temporal relations of a variety of differentiation processes on the early Earth, including crust formation. Here, we investigate the whole-rock 182 W/ 184 W and 142 Nd/ 144 Nd ratios and zircon Δ 17 O values of a suite of well-studied and lithologically-homogeneous meta-igneous rocks from the Acasta Gneiss Complex, Northwest Territories, Canada, including the oldest-known zircon-bearing rocks on Earth. In the context of previously published geochemical data and petrogenetic models, the new 142 Nd/ 144 Nd data indicate that formation of the Hadean–Eoarchean Acasta crust was ultimately derived from variable sources, both in age and composition. Although 4.02 Ga crust was extracted from a nearly bulk-Earth source, heterogeneous μ 142 Nd signatures indicate that Eoarchean rocks of the Acasta Gneiss Complex were formed by partial melting of hydrated, Hadean-age mafic crust at depths shallower than the garnet stability field. By ∼3.6 Ga, granodioritic–granitic rocks were formed by partial melting of Archean hydrated mafic crust that was melted at greater depth, well into the garnet stability field. Our 182 W results indicate that the sources to the Acasta Gneiss Complex had homogeneous, high-μ 182 W on the order of +10 ppm—a signature ubiquitous in other Eoarchean terranes. No significant deviation from the terrestrial mass fractionation line was found in the triple oxygen isotope ( 16 O– 17 O– 18 O) compositions of Acasta zircons, confirming homogeneous oxygen isotope compositions in Earth's mantle by 4.02 Ga. [ABSTRACT FROM AUTHOR]

The roof, floor and gangue samples of coal seams were collected from a borehole in the Gujiao mining area. The vertical distribution of major elements, trace elements and rare earth elements (REEs) was tested through X-ray fluorescence spectrometry and inductively coupled plasma-mass spectrometry (ICP-MS). The formation environment and material source of the strata were analysed. The results showed that the major elements of the coal seam roof, floor and gangue are Si and Al, followed by Fe, K, and Ti. In the Shanxi Formation, Sn, B, Ta, Bi, Th, U, Li, Be, Nb, In, Cs and Hf are enriched. In the Taiyuan Formation, B, Bi, U, Li, Sr, Mo and Sb are enriched. Sn, B, Th, U, and Be of the Shanxi Formation and B, U, Mo, and Sb of Taiyuan Formation are enriched hazardous elements. The ratios of Sr/Ba, U/Th, Ni/Co and V/Cr could indicate the paleosalinity and redox conditions. The Shanxi Formation was mainly formed in an oxic environment. The roof and floor of the No. 7 coal and the roof of the No. 8 coal are limestone, indicating anoxic and suboxic to dysoxic environments. The lithology of the Shanxi Formation and Taiyuan Formation material source is complex, including sedimentary rocks, granite and alkaline basalt. Most samples are distributed at the intersection of the granite and alkaline basalt, indicating dual sourcing from the granite and alkaline basalt. [ABSTRACT FROM AUTHOR]

A significant proportion of shale gas resources occurs in Lower Silurian Longmaxi Formation in southeast Sichuan Basin, South China, where commercial gas production has been achieved at Fuling Shale Gas Field. This study area is located adjacent to Fuling Jiaoshiba shale play. Elemental geochemistry regarding paleoenvironment aspects of lower Silurian Longmaxi shale gas is poorly understood. However, the samples in this study are representative, revealing the complete elemental geochemical characteristics of Longmaxi Shale. This research has analysed trace and rare earth elements of lower Silurian Longmaxi Shale and investigated the depositional environment, provenance, and tectonic settings when this type of shale formed. Sedimentary structures include horizontal lamination, massive lamination, and deformation structures that are well developed in black shale and grey silty shale of lower Silurian Longmaxi Formation. Gamma ray, total organic carbon, and pyrite contents are relatively higher in the lower part of the shale. The enrichment of sulfophile heavy metal elements (Cu, Zn, Pb, Mo, Ni) indicates that a reducing environment is common during the deposition of Longmaxi Formation. The concentration of rare earth elements is generally constant with relatively high concentration of light rare earth elements, stable concentration of heavy rare earth elements, and negative Eu anomalies. The sediments of Longmaxi Formation are derived primarily from the sedimentary rocks and granites in continental crust. The combination of trace and rare earth elements indicates that the tectonic settings of the provenance are continental island arc and active continental margin. [ABSTRACT FROM AUTHOR]

The North Qilian orogenic belt is the key in the exploration of the formation and assembly of Asia. The Early–Middle Devonian Xueshan Formation, which is deposited in the north area of North Qilian Orogenic Belt, is the most important for revealing the evolution basin–mountain transition of the North Qilian Belt. In order to reveal the tectonic evolution of the central orogenic belt in China and Paleozoic global plate reconstruction, it is necessary to perform provenance analysis of the Xueshan Formation. Eighteen samples were collected from Yumen and Yongchang profiles in the west of North Qilian Belt (WN), and 16 samples were obtained from Gulang and Jingtai profiles in the east of North Qilian Belt (EN). The compositions of clastic conglomerates and the sandstones suggested that felsic volcanic was the main source of the WN Xueshan Formation deposits and that the sedimentary and metamorphic rocks were the main source of the EN sediments. According to major geochemistry indexes, such as Al2O3/SiO2 ratio ranging from 0.08 to 0.37 and the chemical index of alteration less than 80, the source rocks were moderately weathered and of moderately matured. The samples from the EN were relatively enriched in Cr, Ni, Sc, and V elements and depleted in Hf element. However, those from the WN were enriched in Hf without the enrichment of Cr, Ni, Sc, or V. The samples from WN showed a strong negative Eu anomaly, but the samples from EN showed a weak negative Eu anomaly or a positive Eu anomaly. All the above geochemical characteristics suggested the prominent input of felsic clasts with granitic rocks into the WN. Meanwhile, the discrimination diagrams of trace elements implied that WN rocks were derived from continental island arc and that the EN rocks were derived from orogenic belt and the passive continental margin. The North China Plate subducted southwards and formed subduction‐related arc magmatism along the southern margin of the North Qilian Terrane during the Early–Middle Devonian. In conclusion, the WN is a fore‐arc basin, but EN is a foreland basin. [ABSTRACT FROM AUTHOR]

The volcanism hosted by the Ediacaran-Terreneuvian Canaveilles Group of the Eastern Pyrenees displays two distinct geochemical affinities: (1) metabasites of the Nyer and Olette formations reflect the emplacement of a tholeiitic magmatism linked to extensional conditions, whereas (2) subsequent felsic and calc-alkaline magmatic rocks marking the top of the Olette Formation and forming the overlying Fabert and Finestrelles members represent Cadomian magmatic events. Based on U-Pb zircon dating constraints, palaeotopographic relationships linked to onlap geometries and distance from vent sources, three volcanosedimentary edifices can be distinguished, the so-called Tregurà (ca. 565-552 Ma), Cap de Creus (ca. 558 Ma) and Coll d’Ares (ca. 542-532 Ma) edifices. The top of their palaeoreliefs recorded locally the nucleation of centres of microbial carbonate productivity (Puig Sec Member) linked to synsedimentary tilting and karstification. Throughout West Gondwana, the presence of carbonate production across the Ediacaran-Cambrian transition is exclusively located in back-arc settings (Central-Iberian Zone) and areas far from the Cadomian subduction trench and devoid of significant terrigenous input, such as those reported in the Eastern Pyrenees and the neighbouring Montagne Noire. [ABSTRACT FROM AUTHOR]

The tectonic evolution and Paleoposition of the North China Craton (NCC) in the Columbia supercontinent during Mesoproterozoic is still not well constrained owing to scarce outcrops of the Mesoproterozoic geological records. Here we present detailed U-Pb geochronological study on detrital zircons and trace elemental geochemistry of the Mesoproterozoic meta-sedimentary rocks from the Sanxiatian Formation, the upper Huade Group, in the northern NCC. The youngest cluster of detrital zircons from the Sanxiatian Formation has U-Pb age peak at ∼1357 Ma, which constrains the deposition of the Sanxiatian Formation after ∼1400 Ma. We suggest a stratigraphic correlation among the Sanxiatian, Baiyinbaolage, Liuhongwan and Xiamaling formations, all of which were deposited simultaneously in the northern NCC. The small portion of ∼2530 Ma zircons possibly corresponds with the growth of juvenile crust in the NCC at the late Neoarchean. The distinct ∼1850 Ma population may have originated from the syn-and post- tectonic granites distributed in the Trans-North China Orogen (TNCO), which is related with the collision between the Western and Eastern blocks in the NCC. The ∼1750–∼1600 Ma zircon populations were also sourced from the NCC and are possibly characterized by the post-collisional magmatic events after the amalgamation of the NCC. The zircon clusters younger than 1600 Ma with peaks at ∼1575 Ma and ∼1357 Ma, were interpreted as exotic sources, while the latter possibly related with the final breakup of the supercontinent Columbia. With the compilation of the detrital zircon dataset from the North India, the West Australia, the North Australia, the Siberia blocks and the northwestern Laurentia, the final fragmentation of the supercontinent Columbia is suggested to be characterized by the separation between the NCC, the Australia or the India blocks during the late Mesoproterozoic. [ABSTRACT FROM AUTHOR]

The South Anhui ophiolite (SAO) and the Northeast Jiangxi ophiolite (NJO) are the only two known Precambrian ophiolite suites within the eastern segment of the Jiangnan Orogen, South China. These ophiolites may provide significant insights into the convergence history of the South China Block during the Rodinia supercontinent cycle. SHRIMP zircon U–Pb dating indicates that the SAO formed at 831 ± 5 Ma whereas the NJO formed at ca. 1000 Ma. Modal mineral assemblages and the preservation of relict primary mineral assemblages indicate that serpentinized peridotites from both ophiolites were mainly harzburgite in protolith. Relict olivine and orthopyroxene fragments within both ophiolite suites yield similarly high Mg# values. The serpentinized peridotite samples yield U-shaped rare earth element patterns and contain high-Cr# spinel, both of which are indicative of supra-subduction zone ophiolites. However, serpentinized peridotites within the SAO contain olivine and clinopyroxene with slightly higher Mg# values, and have lower platinum-group element (PGE) and trace element concentrations than peridotites from the NJO. The SAO peridotites are also depleted in Ir, Pt, and Pd, in contrast to the flat and chondrite-like PGE patterns of the NJO peridotites. These observations indicate that compared with the NJO, SAO peridotites were subjected to a greater degree of melt extraction prior to emplacement. Furthermore, gabbro and basalt from the SAO have N-MORB- or arc-like geochemical characteristics that reflect the incorporation of crustal materials into the mantle source, suggesting that this ophiolite formed in a continental marginal back-arc basin setting. In comparison, the less pronounced depletions in trace elements and PGEs, as well as the restricted 187 Os/ 188 Os isotopic compositions of NJO serpentinized peridotites, suggest that they formed in a fore-arc setting. The contrasting geochemical characteristics of the two ophiolite suites indicate that they were generated during distinct stages of convergence along the southeastern margin of the Yangtze Block. Our results show that ophiolite suites produced within a single orogenic cycle could preserve diverse geochemical characteristics, and may provide insights into the initiation and cessation of continental amalgamation. [ABSTRACT FROM AUTHOR]

An integrated study of zircon U-Pb geochronology and geochemistry, together with Nd-Hf isotopes, have been carried out on the rhyodacite and rhyolitic tuff of the Jingtan Formation in the eastern part of the Jiangnan orogen. SIMS zircon U-Pb dating of two samples yielded weighted mean 206 Pb/ 238 U ages of 784 ± 6 Ma and 788 ± 6 Ma, respectively. Geochemically, they are peraluminous (A/CNK mostly around 1.2) and are characterized by enrichments in Rb, Th, REEs and HFSEs (e.g. Zr and Y) but depletions in Ba, Sr, P, Eu and Ti. The volcanic rocks show a clear A-type granite geochemical signature with high total alkalis (K 2 O + Na 2 O = 5.3–7.64 wt%), FeO t /MgO ratios and low CaO, MgO and TiO 2 contents. They have negative whole-rock ε Nd (t) (−4.2 to −1) and positive zircon ε Hf (t) (+1.26 to +11.6) values, illustrating decoupled Nd-Hf isotopes which may be genetically related to their petrogenesis process. The positive ε Hf (t) values and juvenile T Hf DM1 (0.89–1.3 Ga) of zircons indicate that the volcanic rocks may have been derived from the partial melting of the Neoproterozoic to late Mesoproterozoic crustal materials. Combined with the occurrence of significant volumes of contemporary bimodal volcanic rocks in eastern section of the Jiangnan orogen, it is inferred that the Jingtan felsic volcanic rocks formed during post-collisional extension shortly after the final amalgamation of Yangtze and Cathaysia blocks. [ABSTRACT FROM AUTHOR]

Xenotime (YPO4) is a trace component in many metasedimentary and some igneous rocks, altered rocks and many hydrothermal ore assemblages, where it forms in response to a range of different processes from igneous crystallisation to low-temperature early diagenesis. Due to its wide range of formation temperatures, its suitability and isotopic robustness for reliable U-Pb geochronology, dissolution/precipitation characteristics during overprint events, and widespread occurrence, it is one of the most valuable minerals for U-Pb geochronology leading to four-dimensional (4D) studies of many terranes. The formation environment of xenotime can be deduced from careful petrography and reliable U-Pb in-situ geochronology within a 4D framework. Further, xenotime is a physically robust mineral during sediment transport and may carry distinctive geochemical fingerprints, including age, to secondary environments. From published works, we review the U-Th-contents of well-characterised examples of xenotime formation to provide chemical fingerprints, which assist in identifying the xenotime formation environment. Although the U-Th characteristics of xenotime from all formation environments show considerable overlap, we make the following observations which may be distinctive of some ore formation environments: (i) hydrothermal xenotime formed from low salinity ore fluids (e.g. iron ore and orogenic gold deposits) trend to have the lowest U-contents (< 100 ppm U) and U/Th (< 4), in contrast to xenotime formed from higher salinity ore fluids (Sn-W and base metal deposits); (ii) xenotime associated with unconformity-related U-ores have the highest U-contents at U/Th > 10; (iii) diagenetic xenotime has the most variable and highest U/Th, whereas (iv) xenotime from Precambrian orogenic gold deposits has the least variable and lowest U/Th. Petrogenetic inferences from these observations for ore deposit research and exploration include: (i) support for the homogenising effect of the crustal scale of the fluid system in Precambrian orogenic gold deposits, and (ii) the potential for distinctive U-Th geochemical fingerprints for U ores and some Au ores. These characteristics may be reflected in detrital xenotime grains recovered from routine exploration sampling programs. [ABSTRACT FROM AUTHOR]

This paper presents data on the geological position, geochemistry, age, and isotopic characteristics of the granitoids of the southern part of the Voznesenka terrane, Southern Primorye (Muraviev-Amursky Peninsula and its vicinities). All of the studied granitoids were formed in three stages: the Ordovician, Silurian, and Permian. The Silurian and Permian ages of the granitoid intrusions have been previously determined (Ostrovorussky Massif, 432-422 Ma, and 250 ± 4 Ma, early and late associations, respectively; Sedanka massif, 261 ± 3 Ma). The granites of the Artem and Nadezhdinsky massifs define an U-Pb zircon age of 481 ± 6 and 452 ± 4 Ma, respectively. The geochemical and isotope data show mainly the crustal nature of the granitoids. Their formation was related to melting of relatively immature rocks of the continental crust (mafic-intermediate volcanic rocks). The Nd isotope composition of the granitods (TNd(DM-2) = 1.3 Ga) indicates the absence of the mature ancient crust at the basement of the southern Voznesenka terrane. The maximum contribution of mantle sources to the granite formation is recorded in the Permian associations. A comparison of the peaks of intrusive magmatism in the southern part of the Voznesenka terrane and adjacent territories suggests that the formation of the granitoids of the Muraviev-Amursky Peninsula and its vicinities was caused by the interaction of continental blocks with two oceanic basins: the Paleoasian (and its fragments) and Paleopacific ones. [ABSTRACT FROM AUTHOR]

Complex mineralogical, geochemical, and geochronological studies of the gabbroids from the Dzhigdinskii Massif located in the western part of the Dzhugdzhur-Stanovoy Superterrane are performed. It is established that the age of the rocks from the Dzhigdinskii Massif is Middle Triassic (244 ± 5 Ma), rather than Early Archean, as was previously assumed. The age of the Dzhigdinskii Massif is close to the age of the formation of the other Triassic gabbroid massifs, such as the Amnunaktinskii (~240 Ma), Lukindinskii (~250 Ma), and Luchinskii (~248 Ma) in the southeastern environ of the North Asian Craton. One of the stages in the formation of the Selenga-Vitim volcanoplutonic belt falls in this period as well. This indicates that the Selenga-Vitim volcanoplutonic belt, along with the granitoids and volcanic rocks, is composed of ultrabasic-basic and basic massifs and that this belt is superposed on the structures of the Selenga-Stanovoy Superterrane, as well as on the western part of the Dzhugdzhur-Stanovoy Superterrane. The gabbro, gabbro-diorite, and series of gabbro and gabbro-diorite with high sodic alkalinity from the Dzhigdinskii Massif show obvious geochemical features of duality, including combination of intraplate and super-subduction origin. In this relation, we can assume that the origin of the gabbroids of the Dzhigdinskii Massif is related to the detachment of the oceanic lithosphere and its subduction into the mantle with the formation of an “asthenospheric window.” [ABSTRACT FROM AUTHOR]

Utilizing four shale samples from a mine at Ibese, Southwest, Nigeria, this study evaluated the source rock potential of the shales of the Ewekoro Formation, Benin Basin. The four shale samples, Sample-1, Sample-2, Sample-3 and Sample-4, were analysed for their total organic carbon (TOC) content, elemental concentration of major, trace and transition elements as well as the type of organic matter they contain. Using the log (Fe2O3/K2O) versus log (SiO2/Al2O3) classification technique for terrigenous sediments, the samples were classified as iron-rich shales. The paleo-redox condition of deposition for the sediments was determined using the Vanadium-Chromium ratio (V/Cr). V/Cr ratios of 0.9, 1.3, 0.7 and 1.0 were estimated for Sample-1, Sample-2, Sample-3 and Sample-4 respectively. V/Cr ratio below 2.0 is indicative of sediment deposition in an oxic environment. The weight percentage of the total organic carbon of the samples ranged from 0.076 - 0.585 wt. %; this low values are indicative of poor to fair source rock potential. The kerogen extracts from Samples 1 through to 3 were interpreted as Type IV kerogen, while the extracts from Sample-4 were classified as Type III kerogen. The results of this study show that the shales of the Ewekoro Formation of the Benin Basin have poor to fair source rock potential. The constituent Type IV kerogen of Samples 1 - 3 are incapable of generating oil or gas, while the Type III kerogen of Sample-4 can generate gas and little oil. [ABSTRACT FROM AUTHOR]

The compositions of the tonalite-trondhjemite-granodiorite (TTG) assemblage and volcanic rocks of the Archaean greenstone belts from different domains of the Karelian province of the Baltic Shield are compared. Neoarchean medium felsic volcanic rocks and TTG of the Central Karelian domain drastically differ from analogous Mesoarchean rocks of the neighboring Vodlozero and West Karelian domains in higher Rb, Sr, P, La, and Ce contents and, correspondingly, values of Sr/Y, La/Yb, and La/Sm, and also in a different REE content distribution owing to different rock sources of these domains. This fact is confirmed by differences in the composition and the nature of the REE distribution in the basic and ultrabasic volcanic rocks making up the greenstone belts of these domains. It is established that the average compositions of Mesoarchean TTG rocks and volcanic rocks of the Karelian province differ markedly from those of plagiogranitoids and volcanic rocks of the recent geotectonic environments in high Mg (mg#) and Sr contents. Neoarchean volcanic rocks of Karelia differ from recent island-arc volcanic rocks, but are similar in composition to recent volcanic rocks of the continental arcs. On the basis of the cumulative evidence, the Karelian province of the Baltic Shield was subject to dramatic changes in the crust formation conditions at the beginning of the Neoarchean at the turn of about 2.75-2.78 Ga. These changes led to formation of volcano-sedimentary and plutonic rock complexes, different in composition from Mesoarchean rocks, and specific complexes of intrusive sanukitoids and granites. Changes and variations in the rock composition were related to the mixing of plume sources with continental crust and/or lithospheric mantle material, likely as a result of the combined effect of plumes and plate tectonics. This process resulted in formation of a younger large fragment of the Archean crust such as the Central Karelian domain which factually connected more ancient fragments of the crust and likely contributed to development of the Neoarchean Kenorland Supercontinent. [ABSTRACT FROM AUTHOR]

Subduction of sediments affects the composition of the Earth's mantle and the formation of melts in subduction zones. The sediment thickness of ~8 km along the Hellenic Trench is the largest observed globally and significant volumes of these sediments are subducted. Magmas erupting in the Aegean Arc reflect sediment subduction but they also assimilated sediments during ascent, making distinction of the two processes difficult. In this study, we present geochemical data from olivines in lavas and enclaves from the peninsula of Methana in the western Aegean Arc. The olivines have high forsterite (Fo) contents of 90–92% and contain Cr-spinel with Cr# >60 originating from a primitive melt in equilibrium with a highly depleted mantle wedge. The high δ 18 O VSMOW of ~6.5‰ of the olivines imply input of up to 6.5% sediment component into the mantle wedge. Incompatible element and radiogenic isotope ratios suggest that the sediment component is added as a carbonate-rich melt. Low Ni contents and small rounded sulphide inclusions in the Fo-rich olivines indicate the formation of an immiscible sulphide liquid during olivine crystallization. The input of carbonate-rich sediment reduced the mantle and the co-existing primitive melts, and possibly added S leading to sulphide saturation. This study shows that olivine crystals and their inclusions provide important insights into the mantle wedge, sediment subduction and its effects on the primary magma composition and can indeed be used to distinguish between a mantle and crustal origin of the sediment signature. [ABSTRACT FROM AUTHOR]

Rare earth element (REE) and Y concentrations, and 87Sr/86Sr ratios were analyzed in 33 carbonate samples from the Paleogene Shahejie Formation in the Qikou depression, eastern China, with the goal of determining depositional environments and post-depositional conditions of carbonates in the region. The REE and Y concentrations were normalized to the post-Archean Australian shale (PAAS) standard. The La*PAAS/Yb*PAAS ratios of 0.35-1.52, where *PAAS indicates values for the PAAS standard, show light REE enrichment and heavy REE depletion in most samples. Values of La*PAAS (0.775-1.284) and Ce*PAAS (0.822-1.224), coupled with a relatively flat REE distribution, indicate that the Shahejie carbonates were deposited in lacustrine environments. Values of Y anomalies (1.009-1.527) and Y/Ho ratios (28.43-45.00) in the Shahejie Formation are greater than those of lacustrine carbonates and closer to those of marine carbonates, indicating that diagenetic fluids were probably influenced by seawater. In the carbonates from Well Kou-42, Eu anomalies (1.171-1.604), 87Sr/86Sr ratios (0.708 001-0.710 893), and high homogenization temperatures (104-151 ºC) suggest that the carbonates were affected by hydrothermal fluids. The REEs and Sr isotope ratios show that the carbonates from the Shahejie Formation in the Qikou depression were deposited in lacustrine environments, and were influenced by seawater and hydrothermal fluids. [ABSTRACT FROM AUTHOR]

The sediment-hosted huntite-magnesite deposits are located in the Egirdir-Hoyran lake basin in the Isparta Angle (southern Turkey). The deposits occur at two different localities in the region: (1) Kemersirti huntite deposit, (2) Köytepe huntite-magnesite deposit. The huntite-magnesite occurrences are found in shallow lacustrine rocks of the Miocene-Pliocene Kizilcik Formation and formed as a result of Neogene tectonic activity. Based on X-ray diffraction and scanning electron microscopic studies, the mineral assemblage of huntite deposits contains mostly huntite, less magnesite, dolomite, very little calcite, illite, simectite, brucite, and quartz in the Kemersirti area but contain huntite, magnesite, dolomite, and calcite in the Köytepe area.In the huntite and magnesite-bearing huntite samples, MgO varies from 32.70 to 37.95 wt. %, CaO from 7.83 to 15.10 w.t. %, and SiO2 from 0.99 to 10.60 w.t. %. Ba and Sr are dominant minor elements in the deposits. Ba and Sr for huntite and magnesite bearing huntite in the study area vary from 11 to 233 ppm and from 325 to 765 ppm, respectively. As, U, Zr, V and Ce contents ranged from 11.5-146 ppm, 0.5-3.7 ppm, 1.4-13.2 ppm, 7-34 ppm, and 0.9-2.7 ppm respectively. The huntite-magnesite is characterized by relatively lower Ni (0.5-2.4 ppm) and Co (0.5-1.1 ppm) contents. The huntite and magnesite-bearing huntite occurrences have higher Ba, Sr, As, Zr, V, and U contents than those of the other elements. The d13C isotope values vary between 7.8‰ to 8.8‰ PDB for huntite+magnesite, 8.2‰ PDB for huntite, 1.4‰ PDB for magnesite+dolomite, and 4.0‰ PDB for limestone from deposits in the study area. The δ18O isotope values of the huntite deposits ranged from 30.4 to 35.5‰ SMOW for huntite+magnesite, 32.4‰ SMOW for huntite, 29.8‰ SMOW for magnesite+ dolomite, and 26.9‰ SMOW for limestone.The presence of nodular huntite and the abundance of gastropod, ostracoda and Chura shells in the carbonate units indicate that the huntite occurrences are precipitated at shallow, alkaline (8.5-9.5 pH) and lower temperature (approximately 25°C) lake conditions. The Mg++, Ca++ and Si++ ions for the huntite formation were derived from the surrounding rocks such as ultrabasic rocks, dolomite, dolomitic limestone, and limestone in the Egirdir-Hoyran lake basin. Also, the C isotope ratios indicate that the CO2 source for the huntite formations results to sedimentary basin from metamorphic CO2, carbonate rocks, fresh water carbonates, and ground water. The source of oxygen for the huntite formation may come from marine limestone, fresh water carbonates and meteoric water. [ABSTRACT FROM AUTHOR]

Earlier studies on the ferricrete of Sriperumbudur Formation were focused on their types of occurrences and mode of formation. However, in the present study, an attempt is made to understand the physico-chemical changes across seven saprolite-ferricrete profiles developed over sedimentary protolith after upliftment to decipher the paleoenvironmental conditions to which the Sriperumbudur Formation was exposed and to understand the processes of ferricretisation. For this purpose, the ferricrete exposures around Sriperumbudur were surveyed and mapped for their occurrences and types of ferricretes, collected samples were examined for various physio-chemical aspects. Geochemical and petrographic studies exhibit a relatively high percentage of iron content. The Fe2O3 content varies from 7.71% to 14.9% followed by the higher concentration of Al2O3 and SiO2 as a result of deep weathering of the Sriperumbudur beds. Other major oxides such as CaO, MgO, Na2O, K2O, MnO and TiO2 show lower concentrations. The bulk X-ray diffraction of the ferricrete samples shows the occurrence of tourmaline, muscovite and magnetite. SEM analysis of the ferricrete samples exhibits solution channels and pits in the matrix, on the limonite, quartz and magnetite revealing intense chemical weathering. Petrographic studies show the occurrence of quartz in a variety of shapes, sizes and sediment sorting, cemented by iron oxides in varying stages. It also reveals iron oxide mobilization due to the alteration of ferruginous sandstone forming a hard ferricrete crust. Iron oxide cementation is due to leaching and re-cementing from the parent sedimentary rock with subsequent re-deposition of the earlier material taking place in a near shore environment and in wetter conditions after the Sriperumbudur beds were exposed since the lower Cretaceous period. [ABSTRACT FROM AUTHOR]

Detail results of microfaunal, sedimentological and geochemical investigations are documented from a newly discovered section of the Permian-Triassic boundary (PTB) interval in the area of the town of Valjevo (northwestern Serbia). The presence of various and abundant microfossils (conodonts, foraminifers, and ostracodes) found in the Upper Permian "Bituminous limestone" Formation enabled a determination of the Changhsingian Hindeodus praeparvus conodont Zone. This paper is the first report of latest Permian strata from the region, as well as from all of Serbia, where the PTB interval sediments have been part of a complex/integrated study by means of biostratigraphy and geochemistry. [ABSTRACT FROM AUTHOR]

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

The study of Globotruncanids of the Gurpi Formation at Sepidar anticline in Zagros Mountains led to distinguishing Santonian to Late Maastrichtian biozones. Eight biozones were determined: biozone I (Dicarinella asymmetrica Zone) belongs to Santonian. Biozone II (Globotruncanita elevata Zone), biozone III (Globotruncana ventricosa Zone), biozone IV (Radotruncana calcarata Zone), biozone V (Globotruncana stuarti Zone) and biozone VI (Globotruncanella havanensis Zone) are of the Early to Late Campanian. Biozone VII (Gansserina gansseri Zone) and VIII (Contusotruncana contusa Zone) suggest the latest Campanian to Late Maastrichtian. [ABSTRACT FROM AUTHOR]

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

We report zircon U-Pb geochronologic and geochemical data for the post-collisional volcanic rocks from the Batamayineishan (BS) Formation in the Shuangjingzi area, northwestern China. The zircon U-Pb ages of seven volcanic samples from the BS Formation show that the magmatic activity in the study area occurred during 342-304Ma in the Carboniferous. The ages also indicate that the Palaeo-KaramailiOcean had already closed by 342Ma. Moreover, the volcanic rocks also contained 10 inherited zirconswith ages ranging from 565 to 2626 Ma, indicating that Precambrian continental crust or microcontinents with accretionary arcs are two possible interpretations for the basement underlying the East Junggar terrane. The sampled mafic-intermediate rocks belong to the medium-K to high-K calc-alkaline and shoshonitic series, and the formation of these rocks involved fractional crystallization with little crustal contamination. These Carboniferous mafic-intermediate rocks show depletions in Nb and Ta and enrichments in large ion lithophile elements (e.g. Rb, Ba, U, and Th) and light rare earth elements. The low initial 87Sr/86Sr values (0.7034-0.7042) and positive εNd(t) values (+2.63 to +6.46) of these rocks suggest that they formed from depleted mantle material. The mafic-intermediate rocks were most likely generated by 5-10% partial melting of a mantle source composed primarily of spinel lherzolite withminor garnet lherzolite that had been metasomatized by slab-derived fluids and minor slab melts. In contrast, the felsic rocks in the BS Formation are A-type rhyolites with positive εNd(t) values and young model ages. These rocks are interpreted to be derived from the partial melting of juvenile basaltic lower crustal material. Taken together, the mafic-intermediate rocks formed in a post-collisional extensional setting generated by slap breakoff in the early Carboniferous (342-330 Ma) and the A-type rhyolites formed in a post-collisional extensional setting triggered by the upwelling asthenosphere in the late Carboniferous (330-304 Ma). [ABSTRACT FROM AUTHOR]

Constructing an accurate timeline is critical for reconstructing the Earth systems through critical transitions in climate, geochemistry, and life. Existing dates constrain synchronous initiation (ca. 717 Ma) and termination (ca. 660 Ma) of the Sturtian glaciation from multiple continents. The termination of the younger Marinoan glaciation is also well dated at ca. 635 Ma, but the onset of this glaciation is only roughly constrained as ≤ ca. 654 Ma (South China) and ≥ ca. 639 Ma (Namibia). To test if the Marinoan glaciation started close to ca. 654 Ma or ca. 639 Ma, we have conducted a cyclostratigraphic study on the Cryogenian non-glacial Datangpo Formation that conformably overlies and underlies Sturtian and Marinoan glacial diamictites, respectively, in a deep-water basin section in South China. A total of 28,765 magnetic susceptibility (MS) measurements from a drillcore of the 292-m-thick, muddy siltstone- and shale-dominated Datangpo Formation are used for cyclostratigraphic analysis. The results reveal significant decameter- to meter-scale sedimentary cycles of 16–12 m, 3.6–3.0 m, 1.0–0.8 m, and 0.6–0.4 m. The ratios of these cycle wavelengths match well with those of the Milankovitch cycles calibrated for the Cryogenian Period. The established astrochronologic time scale suggests that the duration of the Datangpo Formation is about 9.8 million years. Together with the radiometric age of ca. 660 Ma for the termination of the Sturtian glaciation, the cyclostratigraphic data suggest that the Nantuo (Marinoan) glaciation in South China initiated at ca. 650 Ma, which is slightly younger than but consistent with the ca. 654 Ma U–Pb age from the top of the Datangpo Formation in shelf sections. This age, however, is significantly older than the ages obtained from Marinoan-age glacial diamictites in South China (ca. 636 Ma) and Namibia (ca. 639 Ma). Given that most of the shelf sections may have suffered from glacial erosion, obtaining the onset age of the Marinoan glaciation should focus on relatively complete, deep-water successions. [ABSTRACT FROM AUTHOR]

The Paleocene volcanic rocks in the Nuussuaq Basin on Disko and Nuussuaq comprise the picritic Vaigat Formation (c. 62-61 Ma) and the overlying basaltic Maligât Formation (c. 60 Ma). The Maligât Formation is up to 2000 m thick on western Disko where the top of the formation is least eroded. The formation is divided into four members, the Rinks Dal, Nordfjord, Niaqussat and Sapernuvik members, which are formally defined here. On central and eastern Disko and Nuussuaq the Maligât Formation lavas are interbedded with fluvial and lacustrine sandstones and mudstones of the Atanikerluk Formation. The Rinks Dal Member is the lowest member and originally constituted around 61% by volume of the formation. It is divided into 12 informal units based on chemically recognisable oscillations in the fractionation state of the basalts. The oldest units are present on central and south Disko close to the Disko Gneiss Ridge. The younger lavas spread farther to the east, north and west, filled the Assoq Lake basin east of the ridge and gradually onlapped the shield of the earlier Vaigat Formation that rose to the north. Only the lavas of the upper Rinks Dal Member reached far into Nuussuaq. The lavas are generally not crustally contaminated and comprise evolved basalts with 4.4-9.2 wt% MgO and a few picrites. The most evolved basalts with 3.2-4.8 wt% TiO2 occur in the middle part of the member where they form the Akuarut unit. The Nordfjord Member originally constituted around 6% by volume of the formation. It is not subdivided because the lithological variability is local. The member is widespread but has its depocentre on north-western Disko where thicknesses reach 350 m and eruption sites, intermediate lavas and acid tuffs are present. Over most of the area the member consists of just a few lava flows with combined thicknesses of 30-100 m. The member has a very diverse lithology with rock types ranging from silicic basalt with 5.3-10.0 wt% MgO through magnesian basaltic andesite and andesite with 2.4-10.6 wt% MgO to dacite with 1.2-2.2 wt% MgO. Rhyolite with 0.2-1.2 wt% MgO and up to 77 wt% SiO2 occur in tuffs and conglomerate clasts. All rocks are crustally contaminated and some are native-iron-bearing. The Niaqussat Member originally constituted around 33% by volume of the formation. It is subdivided into three informal units. The member is widespread, but much of it has been removed by erosion. Lithologies in the lower unit range from silicic picrite with up to 15 wt% MgO to basalt with 6-12 wt% MgO and a few basaltic andesite flows. The middle and upper parts of the Niaqussat Member comprise more evolved basalts with respectively 6.1-7.2 wt% MgO and 4.9-6.4 wt% MgO. All rocks are crustally contaminated and a few lava flows are native-iron-bearing. The Sapernuvik Member comprises three uncontaminated basalt flows with 7.5-10.7 wt% MgO. It is only preserved in a small area on western Disko. Dyke systems with up to 80 km long dykes and subvolcanic intrusions associated with the Nordfjord and Niaqussat members occur on western and north-eastern Disko. The rocks are crustally contaminated and range from silicic basalt with 4-13 wt% MgO to magnesian andesite with 3-10 wt% MgO. They commonly form composite intrusions, some of which contain accumulations of native iron and sulfides. The contaminants are carbon- and sulfur-bearing sediments of the Nuussuaq Group. Major contamination mechanisms were mixing with partial melts from the sediment sidewall and xenoliths and selective exchange of some elements, including carbon and sulfur, between magma and sediment. Degrees of contamination vary from 2-5% in the basalts to 10-50% in the more silicic rocks. No rocks more evolved than basalt were produced by ordinary fractional crystallisation. [ABSTRACT FROM AUTHOR]

Loess formations in Poland display a close relationship with cooling and warming trends of the Northern Hemisphere during the Pleistocene. Loess sequences sensitively record regional palaeoclimatic and palaeoecological changes. The Złota loess profile (21°39'E, 50°39'N) provides a unique opportunity to reconstruct climate conditions in the past in this part of Poland. This continuous sequence of loess and palaeosol deposits allows to distinguish between warmer and more humid climate which is favourable for soil development and much colder and dry periods which are conducive to loess accumulation. The silty and sandy aeolian material originates mainly from weathered rock surfaces affected by frost shattering or from glaciofluvial/fluvial deposits of river flood plains. In Poland, loess and loess-like formations occur in the southern part of the country, mostly in the south polish uplands, i.e. in the Lublin, Sandomierz, and Cracow Uplands. We used different techniques to establish a chronological framework for this site. 21 samples for luminescence dating were collected from the investigated loess profile in Złota. Infrared post-IR IRSL dating method was applied to the polymineral fine grains (4-11µm). The dating results are accompanied by detailed analyses of the geochemical composition, organic carbon and carbonate. Also, analysis of magnetic susceptibility and grain-size distribution were investigated. Based on such a large stratigraphic dataset an age-depth model using OxCal has also been constructed for this site. [ABSTRACT FROM AUTHOR]

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

New detailed lithological, sedimentological, chemostratigraphic data were obtained from exploration drilling samples on the C5 carbonate-dominated formation of the Neoproterozoic Lukala Subgroup (former Schisto-Calcaire Subgroup) from the West Congo Belt (WCB) in the Democratic Republic of Congo. This formation records the last post-Marinoan sea-level events that occurred in the whole basin, followed by the development of the Araçuaï-West Congo Orogen between 630 and 560 Ma. The C5 Formation consists of back-reef lagoonal and peritidal/sabkha cycles of ∼2.0 m in thickness, that record a short-time marine regression, rapidly flooded by a marine transgression with deposition of organic-rich argillaceous carbonates or shales under dysoxia and anoxia conditions. These dysoxic/anoxic waters were rapidly followed by a regional-scale marine transgression, favouring mixing with well-oxygenated waters, and the development of benthic Tonian to Cambro-Ordovician Obruchevella parva -type ‘seagrasses’ in the nearshore zones of the lagoons. New δ 13 C and 87 Sr/ 86 Sr isotopic data in the C5 Formation of the Lukala Subgroup are used in the frame of a correlation with the Sete Lagoas Formation in Brazil. Relatively comparable negative to positive δ 13 C excursions point to marine flooding of the whole basin and allow extension of the debatable Late Ediacaran age of the uppermost Sete Lagoas and C5 formations. Sr isotope “blind dating” failed due to low Sr concentration related to a dolomitization event close 540 Ma. Several tentative datings of the C5 Formation converge to a Late Ediacaran age ranging between 575 and 540 Ma. As the overlying Mpioka folded Subgroup, the C5 series suffered the Pan African deformation, dated at 566 ± 42 Ma. Unlike the previously generally accepted interpretation, our data suggests that the Mpioka Subgroup was deposited in the Early Cambrian. [ABSTRACT FROM AUTHOR]