Deposition Of Sedimentary Basins Research Articles

Source-to-sink analysis of Mesozoic–Cenozoic sandstone-type uranium deposits in the Qaidam Basin

Accurate evaluation of uranium sources and identification of their spatiotemporal correlations with uranium deposits (or sinks) in sedimentary basins are important for exploring sandstone-type uranium deposits. This study examines the source-to-sink system of Mesozoic–Cenozoic sandstone-type uranium deposits in the Qaidam Basin (QB) through a literature review in conjunction with logging and seismic data and yields the following findings. (1) The uranium-supplying capacity of a source rock in the uranium source area depends on primarily its type and to a lesser extent, the tectonic zone where it is located and the episode during which it formed. (2) The initial uranium content, U0, is the core parameter for classifying and evaluating the uranium-supplying capacity of a source rock. At U0 > 1.5 ppm, uranium begins to migrate from a source rock. The uranium variation coefficient, ΔU, and the amount of uranium migration, ΔUt, decrease continuously to –55 % and –5 ppm respectively as U0 increases up to 9.5 ppm, which suggests that at most 5 ppm of uranium in the source rocks can migrate away. As U0 increases beyond 9.5 ppm, ΔU and ΔUt fluctuate around –55 % and –7 ppm respectively, which suggests that approximately 7 ppm of the uranium in the source rocks can migrate away. (3) Of the different types of rocks, silicic igneous rocks (including both intrusive and volcanic igneous rocks) and granitic gneisses have the highest uranium-supplying capacity; intermediate igneous rocks and gneisses come second; mafic–ultramafic igneous rocks and the other metamorphic rocks (except granitic gneiss and gneiss) come third. Of the sub-source areas (tectonic zones), the western segment of the Eastern Kunlun and the Qiman Tagh have the highest uranium-supplying capacity; the Central and Southern Altyn Tagh come second; the others come third. (4) Uranium sources are the fundamental prerequisite for the formation of uranium sinks. Other geological factors control the specific formation process of uranium sinks as well as their spatiotemporal distribution patterns. For QB, the most economic and prospective uranium sink, Neogene formations of Gy anticline, was fed by the source areas which had the highest uranium-supplying capacity. This suggests that the Neogene of WEK anticline belt, Quaternary of Kumukol Basin and Qarqan River Basin are the most noteworthy metallogenic prospective areas. The uranium-source evaluation scheme and “source-to-sink” ore exploration approach introduced in this study have practical value for advancing the exploration of uranium deposits in sedimentary basins in northern China and other parts of the world.

Constraints of tectonic uplift and denudation on sandstone-type uranium mineralization in Meso-Cenozoic basins in northern China: A review

The controlling effect of tectonic uplift and denudation on uranium mineralization has been much studied previously, and its important contribution to uranium mineralization has been fully recognized. However, no systematic theory and methodological criteria for uranium prospecting has been summarized. Here we present the results of an in-depth study of the characteristics and formation process of typical sandstone-type uranium deposits in the northern basin of China, and conclude with a uranium metallogenic theory: tectonic uplift and denudation events are the driving force for the formation of sandstone-type uranium deposits (or even mudstone-type uranium deposits). The stage of tectonic uplift and subsequent denudation events since the formation of the target layer determines the mineralization stages: the greater the intensity and duration of uplifting and denudation events, the larger the scale of uranium mineralization. The formation of large and mega-scale sandstone-type uranium deposits requires multiple stages of tectonic uplift and denudation events superimposed in the same direction. Single or polydirectional tectonic uplift and denudation events often do not form industrial uranium deposits. In this paper, a three-step method to predict the occurrence of sandstone-type uranium deposits is established, which includes (1) determining the tectonic framework division of the sedimentary basin being investigated, (2) a burial and denudation history study, and (3) apatite fission-track simulation of the erosion source area. Focusing on the tectonic evolution and the rapid uplift and denudation events of the basin and the erosion source area is critical (the tectonic evolution of the two areas usually is closely coupled). The desired result can be achieved only by combining the aforementioned theory with basic principles of sandstone-type uranium mineralization, and treating uranium mineralization as a result of a special tectonic event. The theory deepens the understanding of sandstone-type uranium mineralization, and the method plays a role in the rapid evaluation of sandstone-type uranium deposits in sedimentary basins, and it can be extended to research and prediction in other basins.

Roles of dispersed organic matters in sandstone-type uranium mineralization: A review of geological and geochemical processes

Among uranium deposits in sedimentary basins, sandstone-type uranium deposits are epigenetic. The development scales of sandstone-type uranium deposits are controlled by tectonic events, provenance, sand bodies, uranium sources, and reducing media, including that reducing media control the scales of redox transition zone. Dispersed organic matter (DOM) within sandstones, e.g., carbonaceous debris (CD), is one of the important reducing media. The characteristics of organic petrology and element of CD are similar in those of coals, being grouped into type III kerogen. However, the origin of CD within sandstones is unclear. Uranium occurs in uranium-bearing matter and uranium mineral, and coexists with CD in space. Adsorption, complexation, and reduction of organic matter are responsible for the mobility and precipitation of uranium in sediments. The adsorption and complexation capacity of DOM is the most intensive at the stage of immaturity to low maturity, and decreases with the increasing coalification. The reduction capacity is linked to organic matter maturity. Besides, porous macerals could provide the channels for uranium-bearing fluid migration and the space for uranium preconcentration. Under certain physical and chemical conditions, uranium-bearing fluid could permeate into macerals, and react, i.e., trapping followed by reduction. Nevertheless, the coordination characteristics of uranium within uranium-bearing DOM should be further investigated. Uranium enrichment concurrently alters organic matter, causing an increase in organic matter maturity and anisotropy through the effects of radiogenic heat or α-irradiation-induced crosslinking. However, α-irradiation-induced crosslinking should be the primary way. Besides, contributions of CD to uranium mineralization should be reckoned.

Large-scale thermal convection in sedimentary basins revealed by coupled quartz cementation-dissolution distribution pattern and reactive transport modeling – a case study of the Proterozoic Athabasca Basin (Canada)

Thermal convection has been shown to be operating in many magmatic-hydrothermal systems, but whether thermal convection driven by thermal gradients occurs in sedimentary basins devoid of magmatic activity remains disputed. Here we report a case study of the Proterozoic Athabasca Basin in which the thermal convection hypothesis is strongly supported by petrographic observations and reactive transport modeling. The basin is characterized by thick (up to 1500 m) sandstone successions separated by relatively thin (<300 m), mud-rich intervals. The top of the sandstone succession is characterized by extensive quartz overgrowths and point contacts of detrital grains, whereas the basal part contains little cement and shows extensive dissolution features and sutured contacts. This spatial distribution pattern of diagenetic features cannot be explained by gradual burial of the basin, and is instead interpreted as a result of simultaneous quartz precipitation at the top and dissolution at the bottom due to fluid convection. Numerical modeling of reactive transport of SiO2 indicates that this quartz cementation-dissolution distribution pattern can be produced only if the sandstones are sufficiently permeable and thick so that the Rayleigh number exceeds the critical value for convection. Thus, the development of such a coupled quartz cementation-dissolution distribution pattern can be used as an indicator of thermal convection. This recognition is of importance for explaining the large amounts of fluids required to form mineral deposits in sedimentary basins, as exemplified by the world-class unconformity-related uranium deposits in the Athabasca Basin.

Zircon and apatite U-Pb age constraints from the Bundelkhand craton and Proterozoic strata of central India: Insights into craton stabilization and subsequent basin evolution

The geologic processes involved in attaining strengthened cratonic lithosphere remain debated despite their importance for stabilization and long-term preservation. In central India, stabilization of the Bundelkhand craton has conventionally been attributed to the youngest magmatic event impacting the craton at ~ 2.5 Ga, though the post-amalgamation evolution of the craton prior to Proterozoic basin development is poorly understood. This study presents new basement zircon and apatite U-Pb age data along with new detrital zircon U-Pb age data from Proterozoic marginal sedimentary basin deposits to explore the post-magmatic and burial evolution of the Bundelkhand craton. Apatite from ~ 3.4–2.5 Ga granitoids and gneisses collected across the ~ 250 km wide craton yielded near uniform U-Pb ages between ~ 2.4–2.3 Ga, indicating broad-scale exhumation of the Bundelkhand craton through mid-crustal depths following amalgamation and felsic magmatism. Unroofing of the Bundelkhand craton at this time is corroborated by ~ 2.7–2.5 Ga detrital zircon U-Pb age peaks from basal sandstones of the Bijawar and Gwalior groups, which lie in direct nonconformable contact with the craton along both its southeastern and northwestern margins, respectively. These age populations reveal an abundance of zircon sourced directly from the Bundelkhand craton, and a sub-population of ~ 2.2–2.3 Ga grains provide a maximum depositional age for the oldest strata deposited on the craton. We speculate that the redistribution of heat producing elements associated with shallow emplacement of Bundelkhand granitoids and subsequent erosion may have enhanced lithospheric strengthening and facilitated a long-term thermal regime that promoted craton stability by ~ 2.2 Ga. Following stabilization, far-field marginal tectonism likely influenced the vertical motions within the Bundelkhand craton, inducing stages of broad subsidence and erosion recorded within the strata of the Lower and Upper Vindhyan successions.

Constraining provenance for the uraniferous Paleoproterozoic Francevillian Group sediments (Gabon) with detrital zircon geochronology and geochemistry

The Paleoproterozoic sandstones of the ca. 2.1 Ga Francevillian Group, southeast Gabon, host the oldest known redox-controlled high-grade uranium (U) deposits. Uranium-bearing detrital minerals (e.g., monazite) in the Francevillian Group sediments were derived by erosion of Archean basement rocks from the East Gabonian block of the northwestern Congo craton surrounding the Francevillian Basin. They are viewed as primary sources for U, but the nature of these sources remains poorly constrained. Here, U-Pb ages and Hf isotope data for detrital zircon grains are combined with literature geochemical data for igneous rocks from the Archean basement, to characterize the nature, age, and origin of the provenance for the Francevillian Basin and the ultimate source of U for the high-grade uranium deposits.Detrital zircon ages range from ca. 3.1 to 2.6 Ga with a dominant population between ca. 2.90 and 2.80 Ga, suggesting a major contribution from ca. 2.88 to 2.81 Ga high-K granitoids with a limited contribution from ca. 3.1 to 2.84 Ga TTGs and 2.75 to 2.7 Ga granitoids of the East Gabonian block. Most detrital zircon grains share similar depleted-mantle Hf model ages between ca. 3.08 and 3.30 Ga, indicating significant recycling of a Paleoarchean to Mesoarchean crust. We suggest that ca. 2.9 to 2.8 Ga high K, U, and Th granitoids, which reflect hybrid melts of both mantle and crustal parentage were the major detrital sources of U to the Francevillian Basin and, ultimately, for the U deposits. We propose that ca. 2.9 to 2.8 Ga detrital zircons with Hf TDM ages between ca. 3.1 and 3.3 Ga may thus allow for vectoring U deposits in sedimentary basins across the Congo craton.

An in-depth study of the crystalline basement of sedimentary basins is a dictate of the time

The history of studying the crystalline basement in the Republic of Tatarstan, the state of implementation of the super-deep drilling program is given. The scientific substantiation of the replenishment of exploited oil and oil-gas fields is provided by feeding them with deep hydrocarbons through oil supply channels connecting the deep source of hydrocarbons with sedimentary cover deposits. The crystalline basement is of interest for the search for hydrocarbon deposits, but its role as a transit for replenishing deposits of hydrocarbon sedimentary cover in the process of constant degassing of the Earth is more attractive and justified. To use these processes, a fundamentally new approach to the construction of geological and hydrodynamic models of oil fields is proposed, taking into account the fundamental principles of geological science on the formation and reformation of oil deposits and the deep processes of Earth degassing. Prospects are substantiated for the development of “old” fields that are in long-term development, for the calculation of oil recovery factor taking into account oil entering the reservoir from the depths of the Earth, the need for adjusting methods for calculating and accounting reserves, changing levels of material balance, and scientific and practical suggestions for accounting when calculating reserves and designing the development of fundamental principles of field geology. Further prospects for the introduction of hydrodynamic development methods and their significant expansion due to the opening of the processes of replenishment of sedimentary basin deposits with deep hydrocarbons and the reformation of deposits at a late stage of development are shown.

Review of geological and seismotectonic investigations related to 1998 Mw5.6 and 2004 Mw5.2 earthquakes in Krn Mountains

A review of geological and seismotectonic investigations conducted in the two decades after the 12 April 1998 earthquake in Krn Mountains, according to its magnitude the strongest earthquake in Slovenia in the 20th century, is given. Many of these studies have wider scientific meaning than expected from the size of the earthquake. This was the first case in Slovenia that a strong earthquake was undoubtedly related to a particular fault. Seismotectonic studies of seismogenic Ravne fault revealed that it is an actively propagating strike-slip fault growing by interaction of individual right stepping fault segments and breaching of local transtensional step-over zones. Airborne laser scanning (LiDAR) of Idrija and Ravne faults, which resulted in high resolution bare earth digital elevation model, was in 2005 for the first time used to study surface expression of an active fault in Europe. Among the primary characteristics of the 1998 earthquake were extensive environmental effects expressed mainly as massive rockfalls. They were systematically documented and evaluated for intensity assessment using European Macroseismic Scale (EMS-98) and Environmental Seismic Intensity (ESI) scale introduced in 2007, because application of the data on damage to buildings was limited in sparsely populated high mountains epicentral area. These studies were pioneering due to novelty of both intensity scales, indicating their strong points and weaknesses. Large variations in damage to buildings in the upper Soča valley at similar epicentral distances pointed to strong site effects due to very heterogeneous glacial and fluvial deposits in sedimentary basins and valleys. Therefore, different seismic microzonation maps were prepared to evaluate the influence of soft sediments on seismic ground motion. Conducted studies fostered development of several earthquake geology research methods in Slovenia as tectonic geomorphology, evaluation of environmental seismic effects and seismotectonics. They had positive impact also on the university education in the fields of geophysics, seismology and structural geology.

Atmosphere oxygen cycling through the Proterozoic and Phanerozoic

Variations in atmosphere oxygen and ocean sulfate concentrations through time are regarded as important controls on the cycles of sediment-hosted and volcanic-hosted ore deposits. However, estimates of atmosphere oxygen in the Proterozoic have been frustrated by the lack of a direct measurement method and conflicting evidence from various proposed geochemical proxies. Studies in the 1970s to 1990s suggested a relatively oxygenated atmosphere (> 3 wt% O2) in the Proterozoic. However, since the late 1990s, new proxies and modelling have suggested very much lower levels of oxygen (< 0.02 wt% O2). Focusing on redox-sensitive trace elements, here we combine a dataset of over 3000 LA-ICP-MS trace-element analyses on sedimentary pyrite, standardised against Berner’s Phanerozoic O2 modelling and direct measurement of oxygen concentrations in fluid inclusions in sedimentary halite, to develop the first detailed estimate for atmosphere O2 concentration and secular variation from 2200 Ma to the present. The estimates suggest dynamic cycles of atmosphere oxygen that increased in frequency through time. There were possibly three first-order cycles in the Proterozoic varying from 400 to 600 million years in length and a further five first-order cycles in the Phanerozoic from 60 to 120 million years in length. Our estimates of oxygen concentration are at odds with most previous estimates. We suggest, rather than very low atmosphere oxygen in the Proterozoic, the mean concentration was about 7 wt%, rising to a mean of about 10 wt% in the Phanerozoic, but with significant cyclic variation of up to a maximum concentration of possibly over 30 wt%. We observe that the proposed oxygen cycles correlate with biodiversity cycles and to the timing of major stratiform base-metal deposits in sedimentary basins. For example, minima in atmosphere oxygenation correlate with mass extinction events and stratiform Zn–Pb–Ag deposits, whereas maxima in oxygenation correlate with major evolutionary events, global periods of evaporite formation and the timing of stratiform copper deposits.

Basement fabric controls rift nucleation and postrift basin inversion in the continental margin of NE Brazil

In passive continental margins, the brittle reactivation of shear zones and their role in the deformation and deposition of sedimentary basins are still a matter of debate. In this research, we investigated the role of the brittle reactivation of Precambrian shear zones in the nucleation of rift and postrift faults in the onshore portion of the Sergipe-Alagoas and Pernambuco basins in northeastern Brazil. We combine and interpret a dataset of aeromagnetic and topographic data, associated with reflection seismic and borehole data, to analyze the evolution of a portion of the Atlantic continental margin of Brazil. Our results indicate that in the crystalline basement, the magnetic lineaments are correlated with ductile structures as shear zones, and the continuity of these lineaments in the Sergipe-Alagoas and Pernambuco basins is interpreted as the shear zones below the sedimentary cover of these basins. We document the following phases of the brittle reactivation of basement shear zones: (1) the opening of the South Atlantic Ocean in the Early Cretaceous under an extensional stress regime and (2) tectonic inversion induced by the Mid-Atlantic Ridge push and the Andean Cordillera rise in the Neogene-Quaternary under a predominantly strike-slip stress regime. During the rift phase, the brittle reactivation of the shear zones controlled the locations and architectures of the rifts. These structures acted as zones of weakness and were reactivated as normal faults. The brittle reactivation of shear zones was still active during the postrift phase and was responsible for the development of compressional structures. The reverse faulting and related folding pattern indicate tectonic inversion in the Late Cretaceous-Cenozoic. The structures formed during the postrift phase under a strike-slip regime are consistent with the present-day stress field, indicating that tectonic inversion is an active phase of the Brazilian margin.

The use of hyperspectral remote sensing for mineral exploration: a review

The hyperspectral remote sensing technology has been available to the research community for more than three decades. Since in its first steps the hyperspectral technology was also promoted as a tool for mineral exploration. Numerous mineral exploration applications of hyperspectral remote sensing have been reported. This paper provides an up-to-date and focused review of the applications of the hyperspectral remote sensing to mineral exploration. The ore deposits are grouped based on major processes of formation (magmatic, hydrothermal, sedimentary, supergene). The review shows that the hyperspectral remote sensing technology has found application to the study and exploration of a number of ore deposits including kimberlites (host-rocks of diamonds), carbonatites (host-rock of rare earth elements deposits), porphyry deposits, epithermal gold and silver deposits, skarn deposits, volcanic-hosted massive sulfide (VHMS) deposits, orogenic gold deposits, Carlin-type gold deposits, SEDEX Pb-Zn-Ag deposits. On the other hand, the possibilities of the hyperspectral technology remain still underexplored for the study and exploration of chromite deposits, Ni-sulfide deposits in mafic and ultramafic rocks, rare-metal pegmatites, greisen and related deposits, Mississippi Valley-type (MVT) Pb-Zn deposits, Kupferschiefer deposits and uranium deposits in sedimentary basins, iron ores in banded-iron formations, laterites and bauxites. A special attention has been paid in this review to the applications in mineral exploration of the emerging airborne hyperspectral thermal infrared technology. In addition, the possibilities and limitations of spaceborne hyperspectral imagery of moderate spatial resolution for detailed characterization and detection of mineralized systems are discussed for each major deposit type. The spatial resolution of the hyperspectral data is noted to be a key factor on the success of a hyperspectral exploration project. By providing a full up-to-date picture of the applications and contribution of the hyperspectral imagery to the exploration and characterization of ore deposits this review paper should be useful to the interested geological remote sensing researcher and practitioner, and to the mineral exploration manager as well.

Analyzing Factors Affecting Erosion and Sedimentary Deposits Using the Empirical Method of PSIAC

PSIAC empirical method is considered as one of the methods calculating and estimating the amount of erodibility and sedimentation of sedimentary deposits in sedimentary basins and dams’ reservoirs. This method is based on analyzing nine influential factors including: surface geology, solid, weather, runoff, unpaved area, limited plant coverage, land usage, high lands erosion, river erosion and sediment transportation. These factors are rated according to their level of importance. The case study of this research is Lali Water Catchment, Khuzestan, Iran. The amount and intensity of adorability will be ranked as low, moderate and high. This research is based on field work, laboratorial studies and analyzing results obtained from statistics. Results indicated that the unpaved area and high land erosion are identified as the most effective factors, respectively. In contrast, runoff and surface geology are considered as the lowest rate. Other factors reflect moderate effects. Since any significant studies have not been done in this regard, the current research can present a new method to scrutinize the empirical effects of these factors. It is noteworthy to highlight that different methods are compared with each other in order to scrutinize the amount of erodibility in most studies, but the present study has analyzed the influential factors of the sub-methods of one major method. This essay focuses on the affectability of each one of the nine factors, independently. In conclusion, the outcomes of this research can contribute to identify and determine suitable alternatives to stabilize sedimentary basins and increase the life span of dams and watershed management projects and also reduce the destructive effects of floods. Additionally, it contributes civil projects in such lands.

Rôle des facteurs hydrodynamiques dans le contrôle de la formation et de l’emplacement des dépôts d’uranium associés à des discordances: aperçus issus de la modélisation de transport réactif

The role of hydrodynamic factors in controlling the formation and location of unconformity-related uranium (URU) deposits in sedimentary basins during tectonically quiet periods is investigated. A number of reactive-flow modeling experiments at the deposit scale were carried out by assigning different dip angles and directions to a fault and various permeabilities to hydrostratigraphic units). The results show that the fault dip angle and direction, and permeability of the hydrostratigraphic units govern the convection pattern, temperature distribution, and uranium mineralization. A vertical fault results in uranium mineralization at the bottom of the fault within the basement, while a dipping fault leads to precipitation of uraninite below the unconformity either away from or along the plane of the fault, depending on the fault permeability. A more permeable fault causes uraninite precipitates along the fault plane, whereas a less permeable one gives rise to the precipitation of uraninite away from it. No economic ore mineralization can form when either very low or very high permeabilities are assigned to the sandstone or basement suggesting that these units seem to have an optimal window of permeability for the formation of uranium deposits. Physicochemical parameters also exert an additional control in both the location and grade of URU deposits. These results indicate that the difference in size and grade of different URU deposits may result from variation in fluid flow pattern and physicochemical conditions, caused by the change in structural features and hydraulic properties of the stratigraphic units involved.

The two-stage Aegean extension, from localized to distributed, a result of slab rollback acceleration

Back-arc extension in the Aegean, which was driven by slab rollback since 45 Ma, is described here for the first time in two stages. From Middle Eocene to Middle Miocene, deformation was localized leading to (i) the exhumation of high-pressure metamorphic rocks to crustal depths, (ii) the exhumation of high-temperature metamorphic rocks in core complexes, and (iii) the deposition of sedimentary basins. Since Middle Miocene, extension distributed over the whole Aegean domain controlled the deposition of onshore and offshore Neogene sedimentary basins. We reconstructed this two-stage evolution in 3D and four steps at Aegean scale by using available ages of metamorphic and sedimentary processes, geometry, and kinematics of ductile deformation, paleomagnetic data, and available tomographic models. The restoration model shows that the rate of trench retreat was around 0.6 cm/year during the first 30 My and then accelerated up to 3.2 cm/year during the last 15 My. The sharp transition observed in the mode of extension, localized versus distributed, in Middle Miocene correlates with the acceleration of trench retreat and is likely a consequence of the Hellenic slab tearing documented by mantle tomography. The development of large dextral northeast–southwest strike-slip faults, since Middle Miocene, is illustrated by the 450 km long fault zone, offshore from Myrthes to Ikaria and onshore from Izmir to Balikeshir, in Western Anatolia. Therefore, the interaction between the Hellenic trench retreat and the westward displacement of Anatolia started in Middle Miocene, almost 10 Ma before the propagation of the North Anatolian Fault in the North Aegean.

Temporal and spatial patterns of sediment routing across the southeast margin of the Tibetan Plateau: Insights from detrital zircon

AbstractThe Cenozoic deposits of the Tibetan Plateau's southeastern margin are often cited as part of a continental‐scale river system connecting the Paleo‐Yangtze River with the Paleo‐Red River. Confirming the purported connection and any subsequent drainage reorganization has garnered significant attention and varied proposed ages for reorganization. This study presents detrital zircon U‐Pb ages and paleocurrents in Eocene to Pleistocene sedimentary basin deposits distributed over a broad area of the southeast Tibetan Plateau margin within the area of proposed paleoriver connectivity. When combined with previously published studies, our U‐Pb ages allow examination of the temporal and spatial distributions of provenance throughout the Cenozoic. We identify six key age components of the detrital U‐Pb age distributions and use these to examine the patterns of sediment provenance for different Cenozoic epochs. Detailed analysis of these components shows that provenance for both onshore and offshore deposits is best described by local bedrock sources and provides little to no evidence of regional changes in provenance. This suggests that a stable fluvial system similar to the modern drainage network has existed since the Eocene with no evidence for major provenance‐altering river capture. Paleoflow measurements taken throughout the SE margin further corroborate the results of detrital zircon provenance. The combination of U‐Pb age components and paleocurrent directions does not support a Cenozoic connection between the Paleo‐Yangtze and Paleo‐Red Rivers.

Hydrodynamic regime as a major control on localization of uranium mineralization in sedimentary basins

Uranium deposits in sedimentary basins can be formed at various depths, from near surface to the basement. While many factors may have played a role in controlling the location of mineralization, examination of various examples in the world, coupled with numerical modeling of fluid flow, indicates that the hydrodynamic regime of a basin may have exerted a major control on the localization of uranium deposits. If a basin is strongly overpressured, due to rapid sedimentation, abundance of low-permeability sediments or generation of hydrocarbons, fluid flow is dominantly upward and uranium mineralization is likely limited at shallow depths. If a basin is moderately overpressured, upward moving fluids carrying reducing agents may meet downward moving, oxidizing, uranium-bearing fluids in the middle of the basin, forming uranium deposits at moderate depths. If a basin is weakly or not overpressured, either due to slow sedimentation or dominance of high-permeability lithologies, minor topographic disturbance or density variation may drive oxidizing fluids to the bottom of the basin, leaching uranium either from the basin or the basement, forming unconformity-type uranium deposits. It is therefore important to analyze the hydrodynamic regime of a basin in order to predict the most likely type and location of uranium deposits in the basin.

Quantifying the mass transfer from mountain ranges to deposition in sedimentary basins: Source to sink studies in the Danube Basin–Black Sea system

A source to sink system describes the natural link between mountains, plains and deltas, by analysing the (re)distribution of material at shallow crustal depth and at the Earth's surface, exploring the links between coupled tectonic and surface processes. Sediment fluxes are the product of erosion and movement of material in and from sources (mountains), the transport and movement of sediments and solutes by river systems to the plains, and deposition and storage in sink zones. The ESF-EUROCORES TOPO-EUROPE SourceSink programme is a fully integrated research effort to significantly advance our predictive capabilities on the quantitative analyses of coupled active and past drainage systems by means of step-wise 4D reconstructions of sediments mass transfer, integrating geophysics, geology, geomorphology, state of the art high-resolution dating, and numerical and analogue modelling. The area selected for this programme is the Danube River Basin–Black Sea source to sink system, a world-class natural laboratory that is uniquely suited in the heart of Europe's topography, covering almost half of its surface, providing opportunities for excellent field sites to study in integration surface and subsurface data that cover the complete chain of source, carrier and sink. Quantifying and modelling the complete system in relation to the controlling parameters has resulted in significant understanding of forcing factors and linking temporal and spatial scales across multiple orogen and basin systems. This research has provided the opportunity to widen the geographical scope to other natural scenarios, where a number of mountain chains with similar geodynamic genesis separate sedimentary basins with comparable evolution.

新生代北部九州のテクトニクス史と火山活動史―背弧火山岩区研究における重要性―

Cenozoic western Pacific is characterized by numerous subduction volcanisms, opening of back arc basins, and within-plate volcanisms in backarc regions. These phenomena suggest that thermal disturbances induced by mantle flow caused mantle melting and eruption of magmas in back-arc regions, although diverse modes have been proposed for the mantle condition. To constrain the origin of the magmatism, it is important to clarify both the geodynamics and physicochemical conditions of the mantle in the arc-back arc system. Cenozoic back-arc volcanisms and tectonics in northern Kyushu are key objectives. This paper focuses on the dynamics of the upper mantle in relation to the tectonics of the area. Cenozoic volcanism of the northern Kyushu district is characterized by eruptions of a number of alkaline volcanisms. This volcanic province extends some one hundred kilometers along the Japan Sea coast and includes the Chugoku area. Although the volcanism has been regarded as a large single volcanic province, the northern Kyushu activity is distinguishable from that in Chugoku by geochemical characteristics. Cenozoic basalt volcanism in northern Kyushu occurred mainly in the Tertiary sedimentary basins, which is common to Cenozoic volcanism in the Japan Sea Basin. The sedimentary basin deposits underwent intensive folding with extensive inversion tectonics occurring mainly around the end of Miocene. Studies on dykes and thrust faults also indicate a compressional stress field dominated in northwestern Kyushu during the late Miocene. Initiation of the basaltic activity took place in Kita-Matsuura area and expanded outwards. Basaltic rocks from the Kita-Matsuura are mostly hypersthene-normative and sub-alkalic, whereas rocks from peripheries, such as North Kyushu and Goto Islands, are predominantly less normative-hypersthene and thus are alkalic. From spatial and temporal variations and genetic conditions of basalt magmas, a most plausible source was a small-scale mantle diapir with a potential temperature of more than 1400°C. Combined with an inversion tectonic background after the Japan Sea opening event, the origin of the back-arc magmatism was unrelated to large-scale mantle upwelling. Fluid-fluxed melting of the mantle is not supported by the chemistry. My proposal is active upwelling of a small-scale mantle diapir, probably from the depth of stagnant slab or mantle transition zone.

Mesozoic fluorite veins in NE Spain record regional base metal-rich brine circulation through basin and basement during extensional events

Basinal brines are commonly involved in the formation of hydrothermal base metal ore deposits in sedimentary basins, although in many instances, the source of metals is often thought to be the underlying basement rocks. The evidence of brine infiltration through the basement is sometimes directly found in vein systems in fracture zones crosscutting the basement. That is the case of the fluorite–barite-base metal veins found throughout the Hercynian basement of Europe, North Africa and the Appalachians. A geochemical study of brines trapped in these veins can reveal their origin and evolution, but also their mineralizing potential, and coupled with the timing of fluid circulation, can give clues to elucidate the role of these, or similar brines in the genesis of base metal mineralizations, together with their possible links to tectonic events. The Sm–Nd dating of fluorite samples from one of these veins in NE Spain, the Rigròs fluorite vein, has yielded an age of 137 ± 25 Ma (2 σ) (MSWD = 0.40). The vein formation took place during the Late Jurassic–Early Cretaceous rifting event in the western European basins, which is related to the opening of the Atlantic. Inclusion fluids in samples from Rigròs and another vein system from the same region, the Berta fluorite vein, have been studied with microthermometry, crush-leach and LA-ICP-MS. The brines trapped in the two studied vein systems are Na–Ca–Cl–(K–Mg) brines, with homogenization temperatures ∼ 120 °C and salinities up to 25 equiv. mass % NaCl. The source of this salinity is related to evaporated seawater, at least in the halite precipitation field, and to the leaching of Mesozoic halite and gypsum sequences by seawater and/or meteoric water. The basinal brines later evolved through water–rock interaction with the crystalline basement, resulting in some sodium loss and potassium, calcium, strontium (the latter inferred from isotope data) and barium enrichment. The analyzed brines have concentrations of Zn between 3 and 790 ppm, of Pb between 3 and 995 ppm and of Fe between 27 and 2639 ppm, which are similar to those reported in comparable hydrothermal veins and Mississippi Valley-type deposits, but higher than in most present-day sedimentary brines. Despite the fact they were able to transport large amounts of metals, no significant precipitation of sulfides occurred in the veins and, consequently, the mineralizing potential of these brines was still preserved after fluorite vein formation.

Efficient organic carbon burial in the Bengal fan sustained by the Himalayan erosional system

Continental erosion controls atmospheric carbon dioxide levels on geological timescales through silicate weathering, riverine transport and subsequent burial of organic carbon in oceanic sediments. The efficiency of organic carbon deposition in sedimentary basins is however limited by the organic carbon load capacity of the sediments and organic carbon oxidation in continental margins. At the global scale, previous studies have suggested that about 70 per cent of riverine organic carbon is returned to the atmosphere, such as in the Amazon basin. Here we present a comprehensive organic carbon budget for the Himalayan erosional system, including source rocks, river sediments and marine sediments buried in the Bengal fan. We show that organic carbon export is controlled by sediment properties, and that oxidative loss is negligible during transport and deposition to the ocean. Our results indicate that 70 to 85 per cent of the organic carbon is recent organic matter captured during transport, which serves as a net sink for atmospheric carbon dioxide. The amount of organic carbon deposited in the Bengal basin represents about 10 to 20 per cent of the total terrestrial organic carbon buried in oceanic sediments. High erosion rates in the Himalayas generate high sedimentation rates and low oxygen availability in the Bay of Bengal that sustain the observed extreme organic carbon burial efficiency. Active orogenic systems generate enhanced physical erosion and the resulting organic carbon burial buffers atmospheric carbon dioxide levels, thereby exerting a negative feedback on climate over geological timescales.