Clastic Research Articles

Circulation of hydraulically ponded turbidity currents and the filling of continental slope minibasins

Natural depressions on continental margins termed minibasins trap turbidity currents, a class of sediment-laden seafloor density driven flow. These currents are the primary downslope vectors for clastic sediment, particulate organic carbon, and microplastics. Here, we establish a method that facilitates long-distance self-suspension of dilute sediment-laden flows, enabling study of turbidity currents with appropriately scaled natural topography. We show that flow dynamics in three-dimensional minibasins are dominated by circulation cell structures. While fluid rotation is mainly along a horizontal plane, inwards spiraling flow results in strong upwelling jets that reduce the ability of minibasins to trap particulate organic carbon, microplastics, and fine-grained clastic sediment. Circulation cells are the prime mechanism for distributing particulates in minibasins and set the geometry of deposits, which are often intricate and below the resolution of geophysical surveys. Fluid and sediment are delivered to circulation cells by turbidity currents that runup the distal wall of minibasins. The magnitude of runup increases with the discharge rate of currents entering minibasins, which influences the amount of sediment that is either trapped in minibasins or spills to downslope environs and determines the height that deposits onlap against minibasin walls.

The Late Maastrichtian Rørdal Member (Denmark): a remarkable window of climatic, environmental and biotic changes at orbital timescales

Abstract The Late Maastrichtian Rørdal Member of the Møns Klint Formation is a remarkable lithological unit of the Danish Basin, characterized by chalk–marl cyclicity, standing out from pure Maastrichtian white chalk within the Chalk Group. A cyclostratigraphic analysis across this unit suggests a control by orbital precession and a strong amplitude modulation of the precession by the 405 kyr eccentricity cycle. Oxygen isotope data from bulk carbonate, benthic foraminifera and brachiopods indicate a prominent cooling commencing at the base of the unit, with maximum cooling aligned with a 405 kyr amplitude modulation maximum. This unit thus represents a rare example of a climatic cooling associated with a 405 kyr insolation maximum. However, geochemical and calcareous nannofossil data support lower productivity levels across the unit, in contradiction to an expected ocean fertilization accompanying enhanced continental weathering as the source of the clay material. An alternative model of deposition for this lithological unit is thus proposed via dense water cascading favoured by a sea-level low, subsequent restriction of the Chalk Sea and associated gravity currents responsible for the resuspension of fine clastic deposits from the margins of the Baltic Shield.

Some lithogeochemical and isotope-geochemical features of clay rocks and hiatuses in the Riphean stratotype

Research subject. Clay rocks of the Lower, Middle, and Upper Riphean (respectively, the Burzyan, Yurmatau, and Karatau groups) of the Western slope of the Southern Urals. Changes in their characteristic values of a number of ratios of oxides and some trace elements that are indicators of rock composition in provenances are considered, taking into account the breaks of different duration present in the Riphean stratotype. Methods. Calculation of t he average values of TiO2/Al2O3, Th/Sc, La/Co and (La/Yb)N, typical for shales, fine-grained clay siltstones, and mudstones of the main lithostratigraphic units of the Riphean stratotype (formation and, in some cases, subformation) and analysis of their changes taking into account the hiatuses known in the Riphean stratotype (Pre-Mashak/Pre-Zigalga, Pre- Zilmerdak, Pre-Minyar, Pred-Uk). Results. It was established that throughout the entire Riphean, regardless of breaks in sedimentation, presumably associated with certain transformations in the areas of erosion and sedimentation, a number of lithogeochemical characteristics of fine-grained clastic rocks of the Burzyan, Yurmatau, and Karatau groups (such as TiO2/Al2O3, Th/Sc, La/Co, and, to a significant extent, (La/Yb)N) practically did not experience significant changes. Conclusions. The data obtained give reason to think that there were no fundamental changes in the composition of the sources of fine-grained aluminosiliciclastics for the Riphean sedimentary sequences for more than 1 Ga, and contradict the rather active scenario of tectonic processes at the end of the Early Precambrian and the entire Late Precambrian. Conversely, the data on the values of tNd(DM) and eNd(t) in 37 samples of clay rocks of the Riphean stratotype nevertheless reflect a change in the composition of the rocks of the feeding provinces and, one way or another, fit into the outline of subglobal events established by conventional geological methods in the stratotype area of the Riphean. In accordance with them, in the Ai and Mashak times, an increase in the proportion of juvenile material took place in the areas of erosion. Apparently, the Pre-Zilmerdak hiatus also led to the appearance of a significant proportion of basic igneous rocks among the rocks of the provenances.

Overcoming inter-dataset discrepancies in the grain size distributions of fine-grained sediments by partial least squares regression: A case study of the Belgian Boom Formation

The grain size distribution is an important property of all clastic sediments: it determines their mechanical properties and is directly related to their mode of transport and origin. Therefore, the accurate measurement and comparability of grain size data are important. The former has been studied in detail in literature and has been demonstrated to be significantly instrument-dependent, while the latter has not been given the same attention. The current study examined in detail a large set of grain size data measured on a single clay formation, the Oligocene Boom Formation, from which the large influence of sample preparation on the grain size distribution can be inferred. Especially the use of sonication to disintegrate silt-sized aggregates was found to be of a particularly big influence on the measured distributions. As a way to still be able to valorize non-comparable datasets, a statistical conversion procedure was introduced based on partial least squares regression in a compositional data space. The converted distributions follow the stratigraphical trends in grain size expected in the Boom Formation, while also being well correlated to hydraulic conductivity measurements performed on Boom Clay samples of similar depths. This is a strong indication that the conversion was successful. In the future, this approach can be used as a tool to harmonize any combination of compositional datasets, not just limited to grain size data, allowing a valorization of the maximal amount of data.

San Albino, Nicaragua: A Low-Angle, Thrust-Controlled Orogenic Gold Deposit

Abstract The San Albino deposit is an orogenic gold occurrence hosted by a low-angle thrust that is the site of a new open-pit mine in northern Nicaragua. The deposit is hosted in greenschist facies rocks of the Jurassic metasedimentary Neuvo Segovia Formation. The schist was uplifted and exposed during arc accretion and Cretaceous thin-skin deformation, forming the NE-striking Colon fold-and-thrust belt. Deformation included emplacement of the 119 to 113 Ma NE-trending Dipilto batholith into the regionally metamorphosed clastic rocks about 5 km northwest of the San Albino deposit. Mineralization is dominated by three laminated quartz vein systems (i.e., San Albino, Naranjo, Arras) that broadly follow shallowly dipping (approx. 30°) carbonaceous shears roughly concordant to schistosity along the limbs of a doubly plunging antiform. The three main parallel shears are each separated by about 90 m and individually reach a maximum thickness of about 8 m. Maximum thickness of ore zones is where post-ore local folding and reverse motion along the shallow shears has duplicated the laminated low-angle gold-bearing veins (D2 and early D3). Additional gold was added to the veins, with abundant sulfides, during a subsequent brecciation event of the early formed quartz veins that accompanied progressive thrusting (late D3). This predated boudinage of the veins during continued compression and thrust loading (D4); high gold grades are particularly notable along pyrite- and arsenopyrite-bearing stylolites formed during D4 pressure solution. The D2 to D3 gold event is likely coeval with Albian uplift of the Dipilto batholith and with back thrusting in the schist aided by the stress inhomogeneities provided by the igneous complex. Low-angle thrust-controlled orogenic gold deposits may represent world-class exploration targets because of their large linear footprints, although they are traditionally looked at as less favorable exploration targets relative to gold systems developed more commonly along high-angle reverse faults. Our case study of the San Albino deposit shows that although low-angle deposits are not inherently misoriented for failure like the more common subvertical reverse fault-related deposits, they may be sites of significant pressure buildup due to hydrothermal mineral precipitation during initial water-rock interaction or slight temperature decreases along the low-angle flow path. Resulting fluid cycling may lead to thick laminated vein development, such as seen at San Albino, where especially high-grade zones may be associated with local steepening and/or dilational zones within the broader, low-angle vein-hosting shear system.

Detrital Chromian Spinel Geochemistry from Miocene Red Bed Sandstones of Northeastern Iraq: Implication for Provenance and Tectonic Setting

The provenance and tectonic setting of clastic sediments present in the Miocene Red Bed Series located in northeastern Iraq were analyzed. The analysis is based on the composition of detrital chrome spinel and represents the first examination of this topic. The detrital chrome spinel exhibits Cr # (Cr/(Cr + Al)) values ranging from 0.54 to 0.77 and Mg # (Mg/(Mg + Fe2+)) values ranging from 0.37 to 0.69. This indicates a potential incorporation of ultramafic sources, possibly including peridotites (namely Harzburgite and Lherzolite precursors), within the supra-subduction zone. The analysis of modified Cr-spinels extracted from the Red Beds indicates that the source rocks underwent a process of metamorphism and that the Cr-spinel particles were surrounded by a magnetite rim. The Cr-spinel compositions of the examined samples are situated tectonically in the fore-arc setting of peridotite protoliths, except for a small number of samples that exhibit boninite affinity. The observed resemblance in the Cr-spinel number content between the examined specimens and the Zagros Ophiolite peridotites suggests that the Red Beds may have originated from the Cretaceous Mawat Ophiolite Complex. The deposition of Paleocene Walash-Naopurdan rocks indicates that the lower allochthon served as a source during this process. The tectonic context of the Red Bed Series suggests that the allochthonous terranes in the Mawat region were transported and obducted onto the northeastern Arabian passive margin in the early Miocene period. The deposition of the Red Bed Series occurred concurrently with the closure of the Neo-Tethys Ocean in the Miocene.

Cretaceous stratigraphy of Antarctica and its global significance

Abstract The Cretaceous Period is particularly well represented by a thick sequence of clastic sedimentary rocks exposed in the Antarctic Peninsula region of western Antarctica. This was an active margin throughout the Late Mesozoic, and in total some 7 km+ of Cretaceous sedimentary rocks accumulated in a series of fore-, intra- and back-arc basins. The Fossil Bluff Group of eastern Alexander Island can be traced from the Jurassic–Cretaceous boundary into the Upper Albian and represents a broad-scale shallowing-upward sequence from deep marine to a prominent Upper Albian fluvial interval in which high-density forests developed at a palaeolatitude of 75° S. The Cretaceous sequence exposed in the James Ross Island group continues right through the Upper Cretaceous to the Cretaceous–Paleogene boundary. The Campanian–Maastrichtian succession in particular is over 2 km in total thickness and richly fossiliferous. The improved Cretaceous stratigraphy of Antarctica is an invaluable terrestrial record of climatic change at a high palaeolatitude. This includes a gradual increase in temperature to the Cretaceous Thermal Maximum, and then a decline to the Cretaceous–Paleogene boundary. There may be no simple link between these palaeotemperature changes and Cretaceous patterns of biotic radiation and extinction.

Coevolving edge rounding and shape of glacial erratics: the case of Shap granite, UK

Abstract. The size distributions and the shapes of detrital rock clasts can shed light on the environmental history of the clast assemblages and the processes responsible for clast comminution. For example, mechanical fracture due to the stresses imposed on a basal rock surface by a body of flowing glacial ice releases initial “parent” shapes of large blocks of rock from an outcrop, which then are modified by the mechanics of abrasion and fracture during subglacial transport. The latter processes produce subsequent generations of shapes, possibly distinct in form from the parent blocks. A complete understanding of both the processes responsible for block shape changes and the trends in shape adjustment with time and distance away from the source outcrop is lacking. Field data on edge rounding and shape changes of Shap granite blocks (dispersed by Devensian ice eastwards from the outcrop) are used herein to explore the systematic changes in block form with distance from the outcrop. The degree of edge rounding for individual blocks increases in a punctuated fashion with the distance from the outcrop as blocks fracture repeatedly to introduce new fresh unrounded edges. In contrast, block shape is conservative, with parent blocks fracturing to produce self-similar “child” shapes with distance. Measured block shapes evolve in accord with two well-known models for block fracture mechanics – (1) stochastic and (2) silver ratio models – towards one or the other of these two attractor states. Progressive reduction in block size, in accord with fracture mechanics, reflects the fact that most blocks were transported at the sole of the ice mass and were subject to the compressive and tensile forces of the ice acting on the stoss surfaces of blocks lying against a bedrock or till surface. The interpretations might apply to a range of homogeneous hard rock lithologies.

Multi-stages of Paleozoic deformation of the fault system in the Tazhong Uplift, Tarim Basin, NW China: Implications for hydrocarbon accumulation

The Tazhong Uplift is an important petroliferous secondary structure unit in the Tarim Basin and has undergone multiple structural deformation. In the current study, we use 3D and 2D seismic data to investigate the nature of the fault system in the Tazhong Uplift. The deformation of the Cambrian sedimentary rocks in the Tazhong Uplift is generally neglected but noted in this study. We found that the Lower–Middle Cambrian rocks are involved in thrust faults. NE-trending weak zones acted as accommodation faults formed at the connective positions and bends of the deep thrust faults. The Middle Cambrian compressional stress stemmed from the northeastern margin of the Tarim Block, pointed SW, and caused the uprising of the Tabei Uplift. The second deformation occurred in the Late Ordovician. In this instance, the compressional stress stemmed from the SW direction of the Tazhong Uplift, which originated from the amalgamation of the Western Kunlun Terrane and Tarim Block. The main strike–slip fault surfaces and subordinate faults developed along the weak zones generated in the Middle Cambrian. The collision that occurred in the southeast part of the Tarim Block in the Middle Silurian to Middle Devonian resulted in the third deformation. The representative structures that occurred during this compressive deformation were the intensive NEE-trending thrust faults in the southeast of the Tazhong Uplift. The three stages of deformation played different and important roles in hydrocarbon accumulation. These strike–slip faults holding the high-productivity hydrocarbon wells generally experienced early-stage Cambrian deformation, had wide fracture damage zones in the Ordovician carbonate rock strata, and had weak en echelon faults in the Silurian to Middle Devonian clastic rocks.

Resource utilization of stone waste and loess to prepare grouting materials

Loess, a terrestrial clastic sediment, is formed essentially by the accumulation of wind-blown dust, while stone waste (SW) is an industrial waste produced during stone machining. Utilising loess and SW to prepare environmentally-friendly supplementary cementitious materials can not only address environmental issues caused by solid waste landfills but also meet the demand of reinforcement of coal-seam floor aquifer for grouting materials. In this paper, the effects of the loess/SW mass ratio and calcination temperature on the transformation of calcined products are investigated and their pozzolanic activities are evaluated. The workability, environmental impact and cost of grouting materials based on cement and calcined products are also assessed. Experimental results reveal that higher temperatures favour the formation of free lime and periclase, which tend to be involved in solid-state reactions. Higher temperature and loess/SW mass ratio strengthens the diffraction peaks of dodecalcium hepta-aluminate (C12A7), dicalcium ferrite (C2F) and dicalcium silicate (C2S). The clay minerals in loess become completely dehydroxylated before 825 °C, generating amorphous SiO2 and Al2O3. Covalent Si–O bonds are interrupted and that disordered silicate networks are generated in the calcined products, which is confirmed by the increased strength of the Si29 resonance region at −60 ppm to −80 ppm. Although co-calcined loess and SW contain the most four-fold aluminium at 950 °C, recrystallisation depresses the pozzolanic activity. Hence, the loess/SW sample designated LS2-825 exhibits the better hydration activity. Additionally, grouting materials composed of cement and LS2-825 exhibit good setting times, fluidity, strength and a low carbon footprint in practical engineering applications, and they also provide the additional benefit of being cost effective.

Decoding the signals of sediment weathering: Toward a quantitative approach

In order to better interpret the signals of weathering intensity recorded in terrigenous sediment archives, it is essential to appropriately assess the effects of hydrodynamic sorting and sedimentary recycling. To achieve this, we utilized a compiled dataset of major element geochemistry of river sediments from East Asia to develop a quantitative index for evaluating the extent of quartz enrichment related to hydrodynamic sorting and sedimentary recycling. By leveraging the trend of present-cycle weathering products in the CIA-WIP diagram, we proposed the chemical index of quartz-enrichmen (CIQ), which can assess the hydrodynamic sorting and sedimentary recycling effects on the present-cycle weathering products. The CIQ vs. CIA/WIP diagram clearly discriminates the influences of weathering intensity, hydrodynamic sorting and sedimentary recycling on bulk sediment chemistry. In this diagram, representative sediments for the present-cycle weathering product typically cluster around CIQ = 0, and the CIA/WIP (or CIA) of which reflect the recorded weathering intensity. The application of our method to depth profiles from the world's largest rivers provides evidence supporting the utilization of sedimentary records to reconstruct paleo-weathering intensity. This study provides a practical and efficient approach to assess whether or to what extent siliciclastic sediments can accurately depict the present-cycle weathering products. This sheds new light on the quantitative deciphering of weathering intensity signals in terrestrial clastic sediments.

A new tectonic model for the Itmurundy Zone, central Kazakhstan: linking ocean plate stratigraphy, timing of accretion and subduction polarity

The Itmurundy Zone of Central Kazakhstan is a key structure in the core of the Kazakh Orocline representing a typical Pacific-type orogenic belt hosting accretionary complex, ophiolite massifs and serpentinite mélange. The main controversies in the existing tectonic models of the Itmurundy Zone are about the timing of subduction and accretion, the direction and kinematics of subduction and the number of oceanic plates. A new model for the early Paleozoic tectonic story of the Itmurundy Zone is postulated in this paper, based on new detailed geological and U–Pb detrital zircon age data, combined with previously documented geological, U–Pb age, microfossil, geochemical and isotope data from igneous rocks, deep-sea sediments and greywacke sandstones. The present study employs the Ocean Plate Stratigraphy (OPS) model to explain the tectonic processes involved in the evolution of the Itmurundy Zone and to present a holistic story of Ordovician oceanic plate(s), which accretion formed an accretionary complex. The detailed mapping allows distinguishing three types of OPS assemblages: (1) Chert-dominated, (2) OIB-hosting, and (3) MORB-hosting. The U–Pb ages of detrital zircons from sandstones of OIB and Chert types show unimodal distributions with similar main peaks of magmatism at 460–455 Ma in the provenance, and their maximum depositional ages (MDA) span 455–433 Ma. Two samples from OPS Type 3 show the peaks of magmatism both at ca. 460 Ma and the MDA of 452 Ma and 459 Ma, respectively. The MDA of sandstones and microfossils data from chert show the younging of strata to the south and SE in Types 1 and 2 and to NEE for Type 3 (in present coordinates) suggesting double-sided subduction to the NNW and SEE and, accordingly, the co-existence of pieces of two oceanic plates in Ordovician time. The U–Pb zircon data from both igneous and clastic rocks indicate a period of subduction erosion in early Ordovician time. As a whole, the accreted OPS units of the Itmurundy Zone record the timing of subduction and accretion from the early Ordovician to the early Silurian, i.e., 60 Ma at shortest.

Differential sedimentary evolution of typical aulacogens of Meso-Neoproterozoic in North China craton

Many countries and regions in the world have obtained industrial oil flow in the Meso-Neoproterozoic sedimentary strata and formed commercial exploitation in recent years. The development horizon of high-quality source rocks in the Proterozoic in North China can be compared with the international, indicating that the Meso-Neoproterozoic in North China has great exploration potential. The sedimentary characteristics of typical aulacogen in multiple cratons in the Meso-Neoproterozoic North China Craton are compared and studied by using field outcrop data, drilling data and analysis and test data, aiming to provide sedimentary support for the prediction of oil and gas distribution and evaluation of exploration field in the Meso-Neoproterozoic in this area. The results show that there are four sedimentary systems in the study area, including Marine clastic rock sedimentary system, Marine carbonate sedimentary system, Marine-continental transitional facies sedimentary system and glacial sedimentary system. They are divided into seven sedimentary facies types: barrier coastal facies, non-barrier coast facies, shallow shelf facies, carbonate platform facies, reef facies, fan delta facies and glacial facies, and further divided into 15 subfacies and 21 microfacies. On this basis, the Meso-Neoproterozoic sedimentary filling sequences of two typical aulacogens, Yanliao and Xiong 'er, in the study area are clarified, showing that the formation time of each sedimentary filling sequence stage of different aulacogens is different, and the rock characteristics, lithology combination, lithologic structure, contact relationship, vertical sequence and sedimentary facies assemblage of the same sedimentary filling sequence stage are obviously different. The filling characteristics of the two aulacogens completely record the geological events related to the breakup of the Colombian supercontinent.

Quantitative palaeogeographical reconstruction of the North China Block during the Carboniferous and Permian transition: Implications for coal accumulation and source rock development

The Carboniferous-Permian strata of the North China Block (NCB) contain significant economic reserves of coal and gas. In this paper, a comprehensive dataset comprising 401 stratigraphic sections encompassing the Carboniferous-Permian transition in the NCB is compiled from the OneStratigraphy and Geobiodiversity databases. We conducted quantitative analyses of this dataset using ArcGIS and GPlates software, and utilized an up to date plate motion model, to perform a dynamic palaeogeographical reconstruction. The spatio-temporal distribution of depositional facies were also analysed, including basement terranes, fluvio-lacustrine settings, swamps, shorelines, tidal flats, and carbonate platforms. Our reconstructions reveal that the NCB was flanked by basement areas of the Yinshan-Yanshan landmass in the north and the Qinling-Dabie landmass in the south. Peat (coal) deposition occurred across a range of terrestrial to coastal environments, including fluvio-lacustrine settings, deltas, shorelines and tidal flats. Carbonaceous and organic-rich clastic rocks also developed in these areas while organic-rich carbonate rocks were primarily deposited in carbonate platform. The conditions conducive to peat (coal) formation were intricately connected to eustatic fluctuations, which resulted in frequent transgressions and regressions. The sea-level fluctuations during the Pennsylvanian might be, in part, a response to both the waxing and waning of continental ice sheets and tectonic process in the northern margin of the NCB. In contrast, sea-level changes during the early Permian were probably controlled by the tectonic process only. This paper provides a state-of-the-art review of palaeogeographical evolution of the NCB during the Carboniferous and Permian transition, in response to eustatic and palaeoclimate change, and sheds light on resource accumulation based on quantitative analyses.

Northwestward migration of siliciclastic sedimentation during late Tonian to Cambrian: Implications for tectonic evolution of the South China Block

The late Tonian to Cambrian sedimentary sequences in the Xiang-Gui-Yue (XGY) Basin across the potential suture zone between the Yangtze and Cathaysia blocks preserves invaluable information on the geological evolution of the South China Block, while the sedimentary provenance is not well constrained and tectonic affinity of the basin is still highly controversial. This study presents systematic provenance analysis of late Tonian to Cambrian clastic rocks to reconstruct the formation and evolution of sedimentary basin. A significant change from dominant 900–700 Ma to dominant 1300–900 Ma zircons in sediments has been observed along with the basin evolution. It has been widely considered that the 900–700 Ma detritus are largely from the Yangtze Block in the northwest, while the 1300–900 Ma detritus are from the Cathaysia Block in the southeast or terranes linked to the Cathyasia Block at that time. More remarkably, the provenance transition occurred at Cryogenian, Ediacaran and Cambrian in the southeastern, central and northwestern parts of the XGY Basin, respectively. All the above observation indicates the Yangtze-derived detritus arrived at the southeast end of the basin as early as late Tonian and gradually faded away until at least Ordovician, as probably caused by the denudation of the Jiangnan Orogenic Belt after the amalgamation of the Yangtze and Cathaysia blocks. On the other hand, the Cathaysia-derived detritus became dominant due to the uplift of the Cathaysia Block. The XGY Basin was a rift basin until ca. 660 Ma, evolved into a passive margin setting during Ediacaran-early Cambrian, and became a foreland basin after the middie-late Cambrian. Collectively, the provenance variation from late Tonian to Cambrian basin suggests that the Yangtze and Cathaysia blocks may have been amalgamated before late Tonian and an intra-plate basin has been developed along the orogenic belt, allowing the formation and evolution of the XGY Basin.

Geology, fluid inclusions, mineral and (S-O) isotope chemistry of the Badran orogenic Au deposit, Yana-Kolyma belt, eastern Siberia: implications for ore genesis

The Badran orogenic gold deposit is located in the Yana-Kolyma belt, Eastern Siberia; it has proven reserves of ∼9.3 t of gold and an average grade of 7.8 ppm. The total gold production at the Badran deposit since 1984 amounts to ∼34 t. Despite many years of study, the origin of the gold deposits of the Yana-Kolyma metallogenic belt, one of the world’s largest belts, and the Badran deposit is controversial. Synthesis of regional geology and geology of the Badran deposit, fluid inclusion analysis, mineral and (S-O) isotope chemistry defines the genetic model, origin of fluids, and source of metals in the evolution of the ore-forming system, equivalent to other orogenic gold deposits on the margin of the Siberian craton. The deposit is localized in the Upper Triassic clastic rocks and is controlled by the NW-trending thrust. Polyphase mineralization occurs as disseminated arsenian pyrite and arsenopyrite ores with invisible gold, quartz veins with native gold and Fe, Pb, Zn, Cu sulfides and sulfosalts of orogenic type, and locally post-ore Ag, Sb-bearing minerals and Hg epithermal features. The quartz veins with native gold were formed from low-medium saline (1.5–10 wt% NaCl eq.) aqueous-carbonic fluids boiling at temperatures of 290°C to 210 °C and pressures of 300–250 to 125 bar. The δ34S values of pyrite and arsenopyrite vary from −1.1‰ to +2.4‰, with an average of +0.4‰; the δ18О of quartz from +15.1‰ to +17.5‰ at constant δ18ОH2O about +7.5‰ (±1.0‰). High contents of As (up to 2.4 wt%) and Co/Ni ∼ from 0.3 to 9.9 in pyrite of proximal alteration are typical for hydrothermal systems. The results obtained confirm that the ore-forming fluids did not have a single origin, but were formed from a mixture of subcontinental lithospheric mantle and metamorphic sources. The subcrustal lithospheric mantle was fertilized in the time preceding mineralization (Late Jurassic) and was derived directly from the down-going subduction slab and overlying sediment wedge at the closure of the Oymyakon Ocean.

Geochemical transition from Cretaceous island arc basalt-like to oceanic island basalt-like basaltic rocks in the Jiurui district of the Yangtze Block, South China

The Cretaceous volcanic-sedimentary succession in the Jiurui district of the Yangtze Block contains basalts that are interlayered with fine clastic rocks, conglomerate and breccia strata. Here, we present data of whole-rock40Ar–39Ar dating, major and trace elements, Sr–Nd–Pb isotopes, zircon U–Pb dating and Hf isotopes, and plagioclasetrace element analyses to constrain the petrogenesis and tectonic background of these basaltic rocks,. Two episodiceruptions (ca. 126 Ma and ca. 91 Ma) are recognized, and the early basaltsdisplay evident enriched source characteristics such as high incompatible and low compatible elements, negative Nb, Ta, and Ti, slightly positive Pb anomaly, negative εNd(t) and εHf(t) values, higher (87Sr/86Sr)i, andhigh incompatible elements in plagioclase,indicating anisland arc basalt-like nature. The younger basalts show low incompatible and high compatible elements, negative Rb, Pb, Nb, and Ta, positive Sr anomaly, positive εNd(t) values, lower (87Sr/86Sr)i, and low incompatible elements in the plagioclase, indicating an oceanic island basalt-like characteristic. The early ca. 126 Ma basalts were probably derived from a deeper and older enriched lithospheric mantleconsisting of rutile-bearing garnet pyroxenite or eclogite, whereas the younger ca. 91 Ma basalts were derived from a shallower and younger depletedasthenospheric mantle constituting peridotite, with limited amounts of enriched lithospheric mantlecomponent. The retreat and rollback of the paleo-Pacific slab and related lithospheric thinning and mantle composition transition processes probably occurred at ca. 126 Maand ca. 91 Ma in this inland region of the Yangtze Block in northwestern Jiangxi province.

Categories of rivers that formed vendian and lower cambrian sedimentary sequences, western part of east european platform (according to lithogeochemistry data)

Based on lithogeochemical data for fine-grained clastic rocks of the Volyn, Valdai and Baltic series of the west of the East European Platform (Belarus and Volyn, partly Lithuania), categories of rivers that transported fine-grained aluminosiliciclastics to the sinks were reconstructed. It is concluded that the formation of Vendian and Lower Cambrian sedimentary sequences developed in this area was controlled mainly by river systems similar to modern large rivers (rivers with a catchment area 100000 km2) and rivers draining sedimentary formations (rivers with a catchment area 100000 km2). The fine-grained aluminosiliciclastics transported by them came mainly from areas composed of rocks of the crystalline basement of the platform and, in part, sedimentary formations. The distribution of data points of Vendian and Lower Cambrian clay rocks on the diagrams (La/Yb)N–Eu/Eu* and (La/Yb)N–Th with fields of composition of pelitic and silty-pelitic sediments in the estuarine parts of modern rivers of different categories shows that mafic rocks of the Volyn-Brest large igneous province, apparently, were not suppliers of fine-grained aluminosiliciclastics in the indicated time intervals.

Provenance of Detrital Rutiles from the Triassic–Jurassic Sandstones in Franz Josef Land (Barents Sea Region, Russian High Arctic): U-Pb Ages and Trace Element Geochemistry

Provenance study plays an important role in paleogeographic and tectonic reconstructions. Detrital zircons are commonly used to identify sediment provenance; however, a wide range of detrital zircon ages in clastic rock often represent a fingerprint of reworked older terrigenous successions rather than ages of magmatism and metamorphism in the provenance area. This study focuses on the provenance of detrital rutile grains in the Triassic–Jurassic sandstones from Franz Josef Land and shows the importance of multiproxy approaches for provenance studies. Trace element data demonstrate that most rutile grains were sourced from metapelitic rocks, with a subordinate population having a metamafic origin. The Zr-in-rutile thermometer and U-Pb geochronology suggest that detrital rutile grains were predominantly derived from rocks that underwent amphibolite facies metamorphism during the Paleozoic era, with a predominance of the Carboniferous–Permian ages. Therefore, we suggest that the provenance area for the studied sandstones on Franz Josef Land has a similar geological history to the Taimyr region and Severnaya Zemlya archipelago. We propose that this crustal domain extends across the Kara Sea and forms the basement to the north and east of FJL, representing a proximal provenance for the studied Mesozoic terrigenous rocks. This domain experienced both Middle–Late Ordovician and Carboniferous–Permian metamorphism. The comparison of U-Pb dating and the geochemistry of rutile, U-Th/He, and U-Pb dating of zircons showed that detrital rutiles are the powerful toll in provenance restoration and can give additional constrains when a provenance area locates within collisional-convergent settings.

U-Pb ages of detrital zircons and composition of clastic sedimentary rocks from the southern periphery of the Siberian craton: Implications for the earliest Cambrian evolution of southern Siberia

Data on petrography, chemistry, and U-Pb ages of detrital zircons have been obtained for clastic sedimentary rocks within the Sayan regional stratigraphic stage from different parts of the southern Siberia craton, namely for the Ust’-Tagul (Biryusa zone, Sayan area), Shamanka (Irkut zone, Sayan area), Ushakovka and Kurtun (Baikal area) formations. The sedimentary strata share much similarity in lithofacial patterns, with gradual transition from continental to shallow-marine facies. The analyzed lithic sandstones have poorly to moderately sorted clastic grains, with large percentages of lithic fragments (16–37 %). The lithic sandstones from different formations were deposited in continental and deltaic settings as a result of clastic transport from different provenance lithologies. The clastic material for the Ust’-Tagul Fm. deposition came from the Precambrian rocks of the Siberian craton and the Neoproterozoic (870–940 Ma) units: either the Yenisei Ridge of the craton or the Arzybey terrane of the Central Asian Orogenic Belt (CAOB). For the Shamanka Fm., it was Ediacaran and Early Cambrian material from blocks and terranes of the northern CAOB. The clastic inputs for the Ushakovka and Kurtun Fms. deposition were from the Precambrian basement of the Siberian craton and the Neoproterozoic (550–920 Ma) North Transbaikalian group of CAOB terranes. The youngest detrital zircons have the earliest Cambrian ages (530–540 Ma). The clastic sedimentary rocks of the Sayan regional stratigraphic stage dispersed over the southern Siberian craton were deposited in the earliest Cambrian in separate disconnected sedimentary basins which resulted from Ediacaran accretionary-collisional events in southern Siberia.