Neoproterozoic Deposits Research Articles

Predicting Well Productivity in Cratonic Regions Using Remote Sensing Lineaments and Weathered Cover Thickness: A Case Study from Bobo Dioulasso, Burkina Faso

In western African cratonic regions, fractured crystalline bedrock, Neoproterozoic sedimentary covers, and regolith deposits constitute the most productive aquifer systems. Structural lineaments derived from remote sensing data and weathered cover thickness from borehole interpretations provide cost-effective methods for evaluating well productivity in regions with limited economic resources and hydrogeological knowledge, such as Houet province in Western Burkina Faso. Structural lineaments were interpreted using 1:200,000 Landsat TM images and 1:50,000 aerial photographs, revealing NE and NW as the most significant directions. An analysis of 101 borehole stratigraphic profiles from rural water supply program reports revealed the weathering depth and cover thickness. Borehole productivity exhibited a strong correlation with increased weathered cover thickness. Negative well results were concentrated in areas with less than 5 meters of cover. In contrast, significant differences in specific yield rates were observed with greater thicknesses, ranging from 2.5 m³/d for 20 meters of saturated thickness to 7.6 m³/d when the regolith reached a depth of 40 meters. These preliminary groundwater exploration tools effectively target successful well sites by accounting for differing lithologies, regional tectonics, and regolith development. This approach is particularly relevant for cratonic regions with limited resources and hydrogeological knowledge, aiding in sustainable groundwater development and land-use planning.

Cu and Au Mineralization of the Tolparovo Ore Occurrence: Evidence for the Formation of Redbed Copper Occurrences in Neoproterozoic Deposits of the Southern Urals

The mineralization and geochemical features of the Tolparovo ore occurrence are studied to reveal the contribution of diagenetic and epigenetic processes in the formation of copper mineralization in redbed deposits. The methods of electron microscopy, ICP MS, X-ray fluorescence, X-ray phase, atomic absorption, thermogravimetric analyses, and C and O isotopic composition were used. The ore is confined to the fault zone and feathering dolomite–calcite veins, having formed at temperatures of ~330–200 °C and pressures of 0.8–0.2 kbar. Similar to other copper redbed occurrences of the Bashkirian uplift, the Tolparovo copper ore occurrence is confined to basal Neoproterozoic deposits. Siliciclastic and carbonate deposits of this level were accumulated at low paleoequator latitudes in arid climates of continental and coastal–marine environments close to evaporite ones. Rocks of this stratigraphic interval demonstrate increased background concentrations of copper (~2–5 times exceeding the clark), which explains the stratification of redbed copper ore occurrences, indicating a predominantly sedimentary copper source. However, most of the redbed copper ore occurrences of the Bashkirian uplift are located in tectonic zones and are associated with the dikes of the Inzer gabbrodolerite complex. This connects the generation of ore occurrences with the formation of the Southern Urals Arsha Large Igneous Province (707–732 Ma) and the activity of postmagmatic fluids. Magmatic processes were presumably activated due to the collapse of the Rodinia supercontinent. It is shown that copper mineralization in stratiform deposits may result from a joint manifestation of dia- and epigenesis processes.

Высокобарический метаморфизм в харбейском метаморфическом комплексе (Полярный Урал)

Glaucophane-bearing rocks — indicators of high-pressure metamorphism — were earlier found in the Polar Urals in the Neoproterozoic deposits of the Nyarovey series, in the northern part of the Marunkeu eclogite-amphibolite-gneiss complex, and in the foot of the ultramafic massifs of the Main Ural Fault (MUF) zone. We have discovered high-pressure rocks in the western endocontact of the Kharbey amphibolite-gneiss complex, where they are represented by garnet-glaucophane, garnet-glaucophane-barroisite rocks and garnet-barroisite amphibolites formed during progressive zonal metamorphism. From the western boundary of the complex to the east, temperature gradually increases from 400—480 °C (for garnet-glaucophane rocks) to 495—570 °C (for garnet-glaucophane-barroisite rocks and garnet-barroisite amphibolites) at a pressure of 11—16 kbar. We determined that the high-pressure metamorphism had an areal distribution within the Kharbey metamorphic complex and, apparently, marked the Paleozoic subduction-collision processes of formation of Uralides.

Geochemical features of HC- occurrence in carbonates of the Minyar formation of the Upper Riphean, Bashkir Meganticlinorium, Southern Urals

The results of a geochemical study of organic matter found in carbonate deposits of a typical section of the Minyar formation of the Upper Riphean, exposed within the Karatau structural complex in the western part of the Bashkir meganticlinorium, are presented.
 Analytical methods of gas chromatography and chromato-mass spectrometry in extracted hydrocarbons have been used to diagnose diamantanes, alkanes and specific biomarkers – tricyclic terpanes, gopanes and steranes. The thermal maturity corresponding to the upper part of the oil window is determined by the diamantanes. The quantitative ratios of other hydrocarbons strongly depend on the facies nature of carbonates – in thin-layered lagoon carbonates, where there are significantly more of them, they are recognized as autochthonous, in the stromatolite bioherm located next to them, light alkanes were lost, organic matter was probably subject to consedimentary biodegradation due to periodic subaeral exposure. Dibenzothiophene, an organosulfur biomarker, was also found in organic matter, which can be used to assess the content of sulfates in the sedimentation basin. The concentration of dibenzothiophene is significantly higher than the concentrations in the occurrence of hydrocarbons in Neoproterozoic sediments of other regions of the world, which indicates the existence of strong regional differences in the content of sulfate in Late Precambrian seawater.

The critical role of recycling of post-Grenvillian, Neoproterozoic sediments for Phanerozoic Laurentian clastic systems: evidence from detrital-zircon and -monazite geochronology and textures

ABSTRACT Lithic and quartz arenites of the Central Appalachian Basin deposited by late Paleozoic Laurentian fluvial systems are widely interpreted to be sourced by recycling of late Precambrian and early Paleozoic clastic sequences in the Appalachian Orogen. U-Pb and (U-Th)/He age distributions for detrital-zircon and Th-Pb age distributions for detrital-monazite, detrital-zircon and monazite textures (including detrital diagenetic monazite, which prove recycling), sandstone petrology, heavy-mineral abundances, and other detrital proxies are all accounted for by the following: 1) lithic arenite is directly sourced from late Neoproterozoic metasediments in the proximal Appalachian fold and thrust belt via transverse drainages, 2) the late Neoproterozoic sediments were recycled from early Neoproterozoic, post-Grenvillian clastic sequences, 3) Cambrian quartz arenites along the Laurentian margin were recycled from Neoproterozoic sequences with local cratonic input, 4) although dominated by sediment of ultimate Grenvillian age, quartz arenites require ∼ 40% of Paleoproterozoic and Archean input, interpreted to be recycled from late Neoproterozoic to Devonian clastic sequences of the northern Appalachians and/or southern (Scottish–Irish) Caledonides in the distal reaches of a longitudinal drainage system. Ordovician to Mississippian clastic sequences and their metamorphosed equivalents in the Appalachian crystalline core were also likely sediment sources. Quartz arenite does not result from mixing of lithic arenite with other sources because of differences in textural and compositional maturity, and in heavy-mineral characteristics. Input from the Laurentian craton, commonly cited as the source for Paleoproterozoic and Archean detrital zircon in the eastern Laurentian clastic systems, is untenable here because of: 1) the presence of Paleozoic monazite derived from Appalachian Neoproterozoic and early Paleozoic metasediments, 2) abundant detrital chromite, and 3) abundant Paleozoic detrital muscovite. Multiple recycling explains all observed sedimentologic and mineralogic characteristics of the two lithic types. Incorporation of published detrital-zircon data for Paleozoic to modern clastic sequences in eastern Laurentia reveals that Grenville-age zircons experienced at least five and potentially ten recycling events since entering the clastic system in the Neoproterozoic. Recycling also explains the abundance of quartz pebbles in conglomerates of the quartz-arenite lithofacies, and the range of detrital-muscovite 40Ar/39Ar ages in quartz arenites of the Appalachian Basin.

Electromagnetic Surveys for Petroleum Exploration: Challenges and Prospects

Transient electromagnetic (TEM) surveys constitute an important element in exploration projects and can be successfully used in the search for oil and gas. Different modifications of the method include shallow (sTEM), 2D, 3D, and 4D (time-lapse) soundings. TEM data allow for solving a large scope of problems for estimating resources and reserves of hydrocarbons, discriminating reservoir rocks, detecting tectonic features, and characterizing drilling conditions. TEM surveys are applicable at all stages, from initial prospecting to production, and are especially efficient when combined with seismic surveys. Each stage has its specific objectives: estimation of net pay thickness, porosity, and fluid type during prospecting, optimization of well placement and prediction of drilling conditions in exploration, and monitoring of flooding during production. Electromagnetic soundings resolve permafrost features well and thus have a high potentiality for exploration in the Arctic petroleum province. At the first reconnaissance stage of regional prospecting in East Siberia, electromagnetic and seismic data were used jointly to map the junction of the Aldan basin (part of the Aldan-Maya foredeep) with the eastern slope of the Aldan uplift and to constrain the limits of Neoproterozoic sediments. The TEM-based images revealed reservoir rocks in the Upper and Middle Neoproterozoic strata. TEM data have implications for the amount of in-place oil and gas resources in prospects, leads, and plays (Russian categories D1–3) at the prospecting and exploration stages and contingent recoverable reserves (C2) during exploration (latest stage). The contribution of the TEM survey to oil and gas evaluation is quantified via economic variables, such as the value of information (VOI) and expected monetary value (EMV).

Early neoproterozoic supracrustal successions in the central Korean Peninsula: Implications for the paleotectonic history of East Asia

The Early Neoproterozoic supracrustal metasedimentary succession from the Paju–Yangju–Dongducheon area in the central Korean Peninsula is distributed along the northwestern margin of the basement gneisses in the Middle Paleoproterozoic Gyeonggi Massif. The metasedimentary succession includes quartzite, quartz–mica schist, mica schist, calc schist, marble, and calc-silicate, showing alternating layering and large-scale isoclinal folds with Middle Paleoproterozoic gneisses. The basement gneisses yield zircon LA–MC–ICPMS U-Pb ages of 1.87–1.86 Ga. Detrital zircon U-Pb ages of eight quartzites, seven quartz–mica schists and four calc schists suggest the following features. (1) Early Neoproterozoic (ca. 0.92 Ga) sedimentation, (2) prominent age peaks in the Late Paleoproterozoic to Mesoproterozoic range, (3) sandy proximal and muddy to calcic distal provenances, and (4) age population under extensional and trailing edge settings. The detritus of the quartzites were mainly derived from the peripheral Middle Paleoproterozoic basement. In contrast, quartz–mica schists and calc schists show detritus derived from distal Late Paleoproterozoic to Mesoproterozoic clastic sources in the southeastern North China Craton and central Korean Peninsula where magmatic rocks related to the extensional tectonics associated with the disruption of the Columbia supercontinent occur. The detrital zircon records and litho-tectonic features indicate that the Early Neoproterozoic rocks in the Paju–Yangju–Dongducheon area, as well as the central Korean Peninsula, show similarities with the southeastern North China Craton. We therefore interpret that the Early Neoproterozoic supracrustal metasedimentary successions were deposited in marginal shallow marine to fluvial environments from the marginal part of the linked central Korean Peninsula and the southeastern North China Craton which were located at the southwestern margin of western part of the Columbia supercontinent during the Early Neoproterozoic (ca. 0.92 Ga). However, metamorphic overgrowths on zircons and large-scale isoclinal folding in the alternation of the Early Neoproterozoic metasedimentary and the Middle Paleoproterozoic rocks in the Paju–Yangju–Dongducheon area are related to Late Permian to Triassic compressional collision tectonics in the central Korean Peninsula after the Early Neoproterozoic sedimentation.

Triassic multistage antimony-gold mineralization in the Precambrian sedimentary rocks of South China: Insights from structural analysis, paragenesis, 40Ar/39Ar age, in-situ S-Pb isotope and trace elements of the Longwangjiang-Jiangdongwan orefield, Xuefengshan Mountain

The Xiangzhong (XZ) Basin and its neighboring Xuefengshan (XFS) Mountain in South China, as one of the world-class antimony (Sb) producers, have provided appropriately 67% of globally exploited Sb metal (0.46 million tons) in human history. The associated gold (Au) with Sb in this region is also of significant economic values. In previous studies, these Sb-Au deposits were debated as a diversity of genetic types such as epithermal, magmatic-hydrothermal, sedimentary exhalative (SEDEX) and orogenic Sb-Au deposits. To evaluate these genesis hypotheses, we select the representative Longwangjiang-Jiangdongwan (LWJ-JDW) orefield to reveal the Sb-Au accumulation process and metal-fluid sources of these deposits. Our orefield-scale structural analysis shows that the localization of principal Sb-Au orebodies is controlled by a NE-striking sinistral shearing system composed by an integrated set of NE-striking and SE-dipping fractures in the pre-ore folded Neoproterozoic Wuqiangxi slate. Two chief ore periods were identified, including the marine sedimentation (SI, pyrite nodular) and tectonic-metamorphic hydrothermal period (SⅡ−SⅣ, Sb-Au veins). The second period is further subdivided into three stages of SⅡ (pre-tectonic deformed pyrite-milky quartz veins), Siii (syn-tectonic pyrite-arsenopyrite-stibnite-quartz veins) and SⅣ (post-tectonic stibnite-calcite veinlets). It is notable that gold precipitation is significantly prior to Sb ores at LWJ-JDW. Three sericite samples throughout SⅡ−SⅣ yield a group of well-defined 40Ar/39Ar plateau ages (253 ± 4, 234 ± 3 and 206 ± 2 Ma, respectively). This indicates the multistage Sb-Au mineralization initiated from Early Triassic and terminated at Late Triassic time. Further trace elements analyses show the earliest nodular PyI is enriched in a list of As, Ni, Sb, Cu, Se, Co, Pb, Zn and Ti that can be analogy to the diagenetic pyrite in the organic-rich marine sedimentary rocks. Extremely high Sb (median, 1107 ppm) and mediate Au (0.07 ppm) are monitored in PyI, indicative of the initial Sb and Au involvement from the Neoproterozoic sedimentation. Comparably, sulfides of the later SⅡ−SⅣ possess a similar spectrum of trace elements but with highly variable concentrations. All the sulfide generations host the wide range of in-situ δ34SV-CDT values (–23.9 to −3.7‰ for SⅠ, −7.6 to −2.9‰ for SⅡ−SⅣ, respectively), indicating sulfur originally sourced from bacterial sulfate reaction (BSR) of the Neoproterozoic seawater sulfates, and then gradually reduced by thermochemical sulfate reaction (TSR) during the subsequent Au-Sb-induced tectonic-metamorphic hydrothermal activity. The lead isotope compositions in accordance with the evolution lines of upper crust and orogen, implying that the Pb were chiefly sourced from host slate of the Wuqiangxi Formation and its underlying basement. Synthesis of these data, we proposed that the Sb-Au accumulation at LWJ-JDW was caused by the multistage mineralization from Neoproterozoic marine sedimentation to Triassic episodic deformation and metamorphic processes (253–206 Ma).

Ediacaran magmatism and rifting along the northern margin of the Tarim craton: Implications for the late Neoproterozoic Rodinia configuration and breakup

Abstract The Tarim craton in modern Central Asia was an important component of the supercontinent Rodinia in the Neoproterozoic, although its paleogeography in Rodinia during that era is still controversial. Here, we present new stratigraphic, geochemical, and geochronological data from the Neoproterozoic sedimentary and volcanic rock successions along the northwestern margin of the Tarim craton and discuss the significance of these data and our interpretations for its tectonic evolution and paleogeographic position within Rodinia. The Lower Ediacaran sedimentary sequence (Sugetbrak Formation) in northwest Tarim includes terrestrial and shallow-marine clastic rocks intercalated with two discrete basaltic lava flows near the top. The Upper Ediacaran sedimentary sequence conformably overlying the volcanic and clastic rocks consists mainly of stromatolitic dolomite (Chigebrak Formation), representing a transgressive shallow-marine environment. Previous U-Pb zircon dating of the basaltic lava flows has constrained the timing of their eruption in the early Ediacaran (615 Ma). Detrital zircon U-Pb dating of a feldspar-quartz-sandstone unit situated between the two lava flows revealed an oldest age of 2517 ± 18 Ma and a youngest age of 612 ± 6 Ma, with a majority of zircon grains (n = 42) dated at 891–754 Ma (Tonian). A quartz-sandstone unit above the upper lava flow revealed an oldest age of 2724 ± 15 Ma and a youngest age of 607 ± 8 Ma, with a missing age group of 891–800 Ma. These data and observations indicate: (1) a major switch in the depositional setting from a terrestrial (synrifting) to shallow-marine environment following the eruption of the upper lava unit; and (2) an abrupt disappearance of the source rocks of the 891–800 Ma zircons and sediments from the provenance of the post-615 Ma (postrifting) sedimentary sequence. The basaltic rocks have low SiO2 and MgO but high total Fe2O3 and TiO2 contents (2.34–3.19 wt%), analogous to high-Ti basalts and continental flood basalts. Their Ti/V ratios (65–88), low Th/Nb ratios (~0.1), and high TiO2/Yb ratios (~1.1) are similar to those of ocean-island basalt (OIB). Combined with their Sm/Yb and La/Sm ratios and Sr-Nd-Pb-Hf isotope values, we infer that magmas of the Sugetbrak basalts were likely derived from partial melting of an enriched mantle source (EM I) in a transitional spinel-garnet lherzolite field. This petrogenetic evolution was a result of mantle plume–influenced rift magmatism during the Ediacaran breakup of Rodinia. The Central Tianshan terrane, which was attached to the northern Tarim craton until the Ediacaran Period, was the provenance of 891–800 Ma (Tonian) zircons in the synrift sedimentary succession. As the Central Tianshan terrane broke away from the Tarim craton after ca. 615 Ma, Tonianaged zircons were no longer available to the depocenter of the postrift sedimentary sequence. The transition from rifting to drifting between the Tarim craton and the Central Tianshan terrane marked the final breakup of Rodinia, a global event that was possibly driven by mantle plume activities coeval with the development of the Central Iapetus magmatic province in Laurentia during the Ediacaran.

Paleogeographic and sedimentary evolution of Meso–Neoproterozoic strata in the Ordos Basin, western North China Craton

Exploration for deep and ultra–deep hydrocarbon resources plays a significant role in meeting the world's increasing energy demand. Meso–Neoproterozoic strata are considered as a possible target interval for hydrocarbon exploration in deep formations. In this regard, bitumen and potential source rocks have been identified in the Meso–Neoproterozoic strata of the Ordos Basin, western North China Craton, yet the distribution and paleogeographic evolution of these strata remain unclear. In this study, recent drilling data were combined with seismic data and fieldwork to examine the paleo environment of these Meso–Neoproterozoic strata. The results indicate that the Meso–Neoproterozoic strata are mostly distributed in the southwestern part of the basin and grow thinner from the southwest to the northeast. These sediments developed in an intracontinental rift setting with four NE–trending rift troughs having formed during the Changcheng Period. Sedimentary facies during this period were mainly fluvial–deltaic, littoral–neritic marine (quartzitic), and transitional facies. In the Jixian Period, the basin was mainly a marginal depression with a narrow sedimentation range in which carbonate tidal flats and dolomites with stromatolites and siliceous interlayers developed. During the Sinian Period, the basin was a marginal depression characterized by deposition of glacial moraine conglomerate along the southwestern margin. The Changcheng System neritic facies developed in the rift margin and northern margin of the basin controlling the distribution of total organic carbon of argillaceous source rock. The determination of the distribution, characteristics, and paleogeographic evolution of Meso–Neoproterozoic sediments is conductive to the prediction of source rock distribution, and is important for hydrocarbon exploration in the Ordos Basin.

Gravity surveys and 3D integrated model with magnetic and geological data of the granite-greenstone terrane in Pitangui Synclinorium, NW of the Quadrilátero Ferrífero (MG, Brazil)

The Pitangui Greenstone Belt (PGB) is a Meso to Neoarchean metavolcano-sedimentary sequence, inserted in the Pitangui Synclinorium, located in the northwest portion of the Archean-Paleoproterozoic metallogenic province of the Quadrilátero Ferrífero, southern of the São Francisco craton (Brazil). The PGB holds important gold mines like the Turmalina Complex and recently discovered deposits, as São Sebastião. The PGB is mapped in detail scale, but there is still little information about its subsurface configuration. This paper presents gravity surveys, constrained by geological, structural, boreholes, aeromagnetic and seismic data, aiming to provide a better understanding of the 3D geometry of this granite-greenstone terrane. The treatment of the available data resulted in Bouguer anomaly maps, 2D gravity modelling and a 3D geological-geophysical integrated model. The gravity Bouguer anomalies of the region present high amplitudes associated with the PGB, alternating with low zones related to the surrounding granite-gneiss rocks. The profiles and the model suggest that the maximum depth of the greenstone belt is approximately 5 km in its central portion, being strangled by granitic intrusions in its southernmost region. The PGB is about 100 km long, but most of it is covered by Neoproterozoic sediments of the Bambuí Group and Quaternary deposits, which significantly increase its metallogenic potential, especially in regions with few mineral exploration works. The 3D model contributes to the understanding of the tectonic framework and evolution of the PGB, showing the spatial relation with the surrounding granite-gneiss basement and intrusions, and younger sedimentary covers, providing valuable insights about their depth, vertical and lateral geometry. Additionally, this new data can become a valuable tool for developing strategies to select deep mineral targets, expanding the exploratory potential for this mineral province.

Vendian of the Middle Urals: Paleoclimatic reconstructions based on chemical weathering indices

Research subject. The clayey rocks of the Vendian Serebryanka and Sylvitsa groups on the western slope of the Middle Urals.Material and methods. The research materials comprised data on the content of main rock-forming oxides in clayey rocks (mudstones, shales, fine-grained clayey siltstones, ≈180 samples in total) with the values of losses on ignition <6 wt %. This information, obtained at the beginning of 2000 by the X-ray fluorescence method at the Institute of Geology and Geochemistry, Ural Branch of RAS, was used to calculate the average, minimum and maximum values of various weathering indices. Samples were taken from natural outcrops in the basins of the Chusovaya, Serebryanka, Sylvitsa, Mezhevaya Utka, Usva and Koiva rivers.Results. It was established that the sedimentary sequences of the Serebryanka and Sylvitsa groups, in which diamictites are present at several levels, do not exhibit a noticeable contrast in the values of various chemical indices of weathering. For example, taking into account the values of standard deviations (±1σ), the values of the Ruxton coefficient for all nine Vendian formations are statistically comparable. The same is characteristic of the average values of CIA, CIW, PIA, ICV and MIA(o) for clayey rocks of different formations. Variations in the average CPA values show that, taking into account ±1σ, only the rocks of the Starye Pechi, Garevka and Perevalok formations can be considered statistically different. Taking into account ±1σ, the clayey rocks of the Buton Formation differ significantly from the fine-grained clastic rocks of the Garevka and Kernos formations in terms of the average value of the Mg-index. The clayey rocks of the Tanin and Kernos formations have a weak or moderate positive correlation between the TiO2/Al2O3 ratio and the Ruxton, PIA, ICV indices and the hydrolyzate modulus. This suggests the dependence of the listed indicators of the intensity of weathering from the composition of rocks in paleocatchments.Conclusions. The data obtained suggest that, when averaging at the level of formations (even if the formations include quite a lot of undoubtedly glaciogenic deposits), we apparently do not record the specific contribution of the latter and, as a result, we obtain a substantially different picture than that which emerges for other Neoproterozoic deposits, including diamictites, varved clays, and intervals with dropstone.

Reappraising the Provenance of Early Neoproterozoic Strata in the Southern–Southeastern North China Craton and Its Implication for Paleogeographic Reconstruction

The early Neoproterozoic sediments in the southern–southeastern (S-SE) North China Craton (NCC) are critical in paleogeographic reconstruction. We present new detrital zircon U–Pb–Hf data of five sandstone samples from the Sangwon Supergroup in SE-NCC and the Wufoshan Group in S-NCC. We integrate published zircon U–Pb data to appraise their provenance. The new dataset constrains the maximum depositional age of the Sangwon Supergroup to be ca. 1.0 Ga. The similar provenance transition and the comparable sequence stratigraphy imply that the Wufoshan Group could be an extension of the Xuhuai–Dalian–Pyongnam basins in the SE NCC with a maximum depositional age of ca. 1.0 Ga. The zircon age spectra of the successions show four major populations at ca. 2.5 Ga, ca. 2.0–1.8 Ga, ca. 1.6–1.4 Ga, ca. 1.3–1.0 Ga, with rare >2.5 Ga grains. The Archean–Paleoproterozoic grains could be derived from the NCC, which is confirmed by their εHf(t) values. After a review of the possible paleocontinental reconstructions, we suggest that the ca. 1.6–1.0 Ga grains with different εHf(t) values (mostly positive) were from the southwestern Congo craton, supporting a NCC–SW Congo/SE NCC-S São Francisco connection at ca. 0.9 Ga.

Mineralogy, Geochemistry, and Geochronology of the Yehe-Shigna Ophiolitic Massif, Tuva-Mongolian Microcontinent, Southern Siberia: Evidence for a Back-Arc Origin and Geodynamic Implications

The new results have been represented of mineralogical–geochemical and geochronological studies of rocks of the Yehe-Shigna ophiolite massif located in the Tuva-Mongolian microcontinent in the northern part of the Central Asian orogenic belt (Eastern Sayan, Southern Siberia). The Yehe-Shigna ophiolite massif is part of the Belsk-Dugda ophiolite belt. The structural position, age, and geochemical characteristics of the belt indicate its formation in the setting of the back-arc basin of the Shishkhid intraoceanic island arc, developing in the period of 810–750 million years. It is assumed that together with the same-age formations of the Oka accretion wedge and the Sarkhoi active margin, it formed on the convergent margin of the Gondwana supercontinent. Its basement is represented by the Archean-Early Precambrian crystalline rocks and carbonate cover (“Gargan Glyba”). The gold-bearing Neoproterozoic deposits with dominant gold-telluride assemblages are localization in large ophiolites thrust zones along with the frame of the “Gargan Glyba”. They are allochthonous with respect to the Late Neoproterozoic-Cambrian Tuva-Mongolian island arc of the Siberian continent. A similar type of gold deposit is probably worth looking for ophiolites thrust zones in other Precambrian Gondwana-derived microcontinents.

Aeromagnetic-Imaged Basement Fault Structure of the Eastern Tarim Basin and Its Tectonic Implication

The property of the magnetic basement and the faults in the basement is significant for structural evolution, the Phanerozoic deposition, and oil resource exploration of the Tarim Basin. Based on the newly acquired aeromagnetic and industry seismic data, we mapped the distribution of basement faults by applying magnetic gradient-processing methods such as the horizontal gradient derivative, the first vertical derivative, the tilt derivative, and the upward continuation method. The dips of basement faults were confirmed and the susceptibilities of basement blocks were obtained by forward modeling of five profiles using the constraint of sedimentary strata depth and Moho topography. On the basis of comprehensive analysis of the magnetic anomalies, the distribution and inclination of basement faults, and susceptibilities differentiation obtained by forward modeling and field measurement, the property of the basement faults and their implication were discussed and interpreted. Our results show that the origin of the Central Highly Magnetic Anomaly Belt is highly magnetic Archean metamorphic rocks. The weakly magnetic Southeastern Domain and highly magnetic Central Tadong Domain assembled along the Tadong South Fault during the Paleoproterozoic. The Paleozoic Cherchen Fault is just an interior fault in the weakly magnetic Southeastern Domain although it presents a large vertical fault displacement. Considering the prominent variation of strikes of the Tadong North Fault system, and the moderately magnetic anomalies in the Northeastern Mangal Domain corresponding to the center of Neoproterozoic deposition, it is likely that the basement of the Northeastern Mangal Domain modified by the Neoproterozoic rifting could be originally the same as the basement of Central Highly Magnetic Anomaly Belt.

Neoproterozoic Deposits of the Bashkir Mega-Anticlinorium (Southern Urals): State of the Art in Regional Stratigraphy

Abstract—This paper presents an alternative variant of stratigraphic subdivision of the upper Riphean–Vendian deposits (approximately corresponding to the Neoproterozoic Erathem of the International Chronostratigraphic Chart (ICC)) of the Bashkir Mega-Anticlinorium (BMA), based on the modern concepts of changes in the biosphere, atmosphere, and hydrosphere (and, accordingly, in the climate and the course of sedimentary processes) in the period ~1000–540 Ma, with regard to the results of recent studies and the proposals for improving the Russian General Stratigraphic Scale (GSS) of the Precambrian. The strict necessity of subdividing chronostratigraphic and lithostratigraphic units is shown. The presented data give grounds to regard the Zil’merdak Formation as a Group and assign three of its lower formations to the Middle Riphean (Yurmatinian). It is shown that the period of accumulation of the Karatau Group (comprising the Katav, Inzer, Min’yar, and Uk formations) was significantly shorter than the duration of the Late Riphean (Karatavian). Special attention is focused on the age of the Uk Formation (analysis of the existing data made it possible to refine its stratigraphic position): It formed, most likely, in the period 780–740 Ma. A high uncertainty of the stratigraphic position of the overlying geologic bodies is demonstrated. The Bakeevo, Tolparovo, Suirovo, and Kurgashla formations must be regarded as part of the Terminal Riphean (Arshinian). The Arsha Group, comprising the Bainas, Makhmutovo, Igonino, and Shum formations in the Tirlyan trough and represented by the Krivaya Luka Formation in the Krivaya Luka syncline, should not be totally assigned to the Terminal Riphean. It is proposed to exclude the Bakeevo Formation and the Tolparovo–Suirovo sequence from the Asha Group, because these deposits are, most likely, a modification of the Arsha Group located on the western flank of the BMA. The Uryuk Formation is probably of pre-Vendian age. The current contradictory data on the stratigraphy of the supra-Uryuk unit of the Asha Group are interpreted. The ages of the geologic bodies composing the Group and its stratigraphic interval still call for a thorough study.

Pre-orogenic connection of the foreland domains of the Kaoko–Dom Feliciano–Gariep orogenic system

Neoproterozoic metasedimentary rocks in the foreland domains of the Kaoko–Dom Feliciano–Gariep orogenic system record sedimentation from the breakup of Rodinia to the amalgamation of Gondwana, and thus provide ideal subjects for investigation of the mutual pre-orogenic positions of rifted margins of the African and South American cratonic blocks. U–Pb isotopic dating of zircon in the Brusque Complex of the northern Dom Feliciano Belt, Brazil, provides new constraints on the timing and sources of Neoproterozoic sedimentation along the eastern margin of the Luis Alves Craton. The minimum age of sedimentation is constrained by a U–Pb zircon age of 811 ± 6 Ma from a dyke cross-cutting the Brusque Complex. U–Pb detrital zircon analysis reveals two distinct groups: one with ages ca. 2.2–2.0 Ga consistent with erosion of the adjacent Luis Alves Craton, and another with ages ca. 2.1–1.8 and 1.6–1.0 Ga consistent with erosion of Paleoproterozoic to Mesoproterozoic igneous provinces and/or supracrustal sequences at the edge of the Congo Craton. The age distributions match with analogous rocks of the central Dom Feliciano Belt and the Kaoko Belt, and show similarities with the Gariep Belt, suggesting deposition in a system of coeval and spatially related paleobasins around the time of Rodinia breakup. The absence of Neoproterozoic detrital zircon close to the age of sedimentation suggests deposition in an intracontinental rift or passive margin. A third group contains a significant proportion of Neoproterozoic ca. 670–560 Ma zircon, suggesting similarities with the adjacent Itajaí Basin syn-orogenic foreland sedimentary rocks. This indicates that foreland basin sediments were partly tectonically interleaved with the pre-orogenic metasediments of the Brusque Complex during late-stage orogenic deformation. The findings support an intracontinental rifting model for the formation of the Kaoko–Dom Feliciano–Gariep basin system. The data further indicate that the Luis Alves Craton was in close proximity to the Congo Craton, and likely with the Nico Pérez Terrane and the Kalahari Craton, at the onset of Tonian rifting and the breakup of Rodinia.

Algal origin of sponge sterane biomarkers negates the oldest evidence for animals in the rock record.

The earliest fossils of animal-like organisms occur in Ediacaran rocks that are approximately 571 million years old. Yet 24-isopropylcholestanes and other C30 fossil sterol molecules have been suggested to reflect an important ecological role of demosponges as the first abundant animals by the end of the Cryogenian period (>635 million years ago). Here, we demonstrate that C30 24-isopropylcholestane is not diagnostic for sponges and probably formed in Neoproterozoic sediments through the geological methylation of C29 sterols of chlorophyte algae, the dominant eukaryotes at that time. These findings reconcile biomarker evidence with the geological record and revert the oldest evidence for animals back into the latest Ediacaran.

Neoproterozoic sedimentation and depositional environment: an example from Narji Formation, Cuddapah Basin, India

In the west-central part of Kurnool sub-basin of Cuddapah Basin, around Betamcherla–Bagannapali area, the Neoproterozoic Narji Formation rocks (Kurnool Group) of Cuddapah Supergroup are deposited. Sedimentary facies analysis including sedimentary structures and petrographic analysis of the studied samples have been carried out for understanding the depositional environment of the studied formation during Neoproterozoic time period. Sedimentological investigation of the studied formation rocks reveals intertidal-to-subtidal facies associations consisting of six lithofacies such as quartzite bearing massive purple limestone, laminated limestone, calcareous shale, heterolithic, massive whitish grey limestone and intra-formational conglomerate. Sedimentary deformation structures such as load structures and slump structures (micro-faults and folds) indicate perturbation and basin subsidence. Presence of pyrite (reducing condition) and glauconite also indicates shallow marine sediments (at depths of 50–300 m). Overall, the entire basin-fills are inferred to be deposited in shallow marine tidal flat area with occasional deep burial condition in an isolated basin with little clastic influx. Comparing with other coeval successions of Narji Formation lithology, it can be concluded that similar type of depositional milieu prevailed over the globe at early Neo-Proterozoic time during the formation of Rodinia.

PETROLEUM POTENTIAL OF THE EDIACARAN SUCCESSION RELATED TO GEOLOGICAL AND GEOCHEMICAL CONDITIONS IN THE VOLYN-PODILIAN

This work is concerned with the studying of Ediacaran petroleum potential within Volyn-Podyllian. For the first time ever, the lithostratigraphycal, geological, geothermal, geochemical and paleohistorical analysis was provided for the whole Ediacaran section to determine its petroleum potential.The description of Precambrian succession in the world with its hydrocarbon occurrence was included. In addition to that, this work contains methodology and methods of the basin analysis study, which was perfomed. The potential source rocks, reservoirs and seals within the study area were defined and described.Based on the computer-integrated instruments, for the Neoproterozoic deposits were created: third-dimensional model of its succession, depth map, schematic map of katagenetic zones and concentration model of organic carbon. The paleoconditions of deposition and maturation processes of organic matter were reconstructed. Key words: Ediacaran deposits, Volyn-Podillian, oil-and-gas potential, computer modelling, basin analysis, sedimentary