Volcanogenic Material Research Articles

Retrieving meaningful information from detrital zircon in Palaeoproterozoic sedimentary rocks: Provenance, timing of deposition, metamorphism and alteration of zircon in sandstones of the Pretoria Group in the Transvaal Basin, South Africa

Abstract The Palaeoproterozoic sandstones and quartzites of the Pretoria Group (Transvaal Supergroup) in the Transvaal Basin of South Africa are important markers for regional correlations and dating of events of global importance (e.g., the Great Oxidation Event). The succession has few independent age markers, and much of the discussion about the time of deposition and the source of material of these rocks has been based on data from detrital zircon suites. The clastic sedimentary rocks of the Pretoria Group contain detrital zircon grains ranging from the Mesoarchaean to ages that are near-contemporaneous to, and even younger than the overlying and crosscutting igneous rocks of the Bushveld Complex. We show that the U-Pb age and Lu-Hf isotope distributions of the detrital zircon population in the Pretoria Group are the result of three different types of processes, acting successively: (1) Crystallisation in the igneous or metamorphic protosource rock (i.e., the rock where the zircon originally crystallised), (2) Metamorphic and hydrothermal resetting of the U-Pb chronometer induced by emplacement and crystallisation of the 2 055 Ma Bushveld Complex, and (3) Late, low-temperature processes (e.g., weathering). Critical age markers of maximum ages of deposition obtained after excluding effects of (2) and (3) are the 2 200 Ma Magaliesberg Formation (outside of the Bushveld aureole) and the 2 080 to 2 100 Ma Lakenvalei Formation. The Leeuwpoort Formation is a worst-case example, containing both young (<2 200 Ma) unmodified detrital zircon and hydrothermally altered zircon in the same age range. The two can only be distinguished from trace element analyses. Age distributions of Archaean and early Palaeoproterozoic zircon age fractions overlap with detrital zircon age suites in lower (i.e., pre-Timeball Hill Formation) parts of the Transvaal Supergroup, suggesting recycling within the basin or from the basin margin. Overlaps in 2 200 to 2 350 Ma zircon ages with those of volcanogenic zircon in the Timeball Hill Formation again suggest recycling. The origin of 2 080 to 2 150 Ma zircon is uncertain, but neither poorly constrained sources in the Kaapvaal Craton (e.g., Okwa Basement Complex) nor recycling of volcanogenic material from post-Magaliesberg formations can be ruled out.

A new ‘Southern Giant Crab’ from a miocene continental slope palaeoenvironment at Taranaki, North Island, New Zealand

ABSTRACT Large-sized extinct crab specimens recovered from Waitoetoe beach, North Island, New Zealand form the basis for a new species of ‘Southern Giant Crab’, Pseudocarcinus karlraubenheimeri n. sp. The specimens originate from the upper Miocene Urenui Formation (approximately 8.8 myr) of the Taranaki Basin, in which a series of volcanoes of the Mohakatino Volcanic Centre erupted offshore, leading to the formation of a specific palaeoenvironment. The well-preserved, articulated specimens were found buried in sediments which include reworked volcanogenic material. The crabs inhabited a deep-marine setting. This is the first evidence that Pseudocarcinus inhabited the region that is now New Zealand. New Zealand Miocene environments apparently offered favourable conditions in terms of food sources, metabolic requirements, and calcium-carbonate supply for Pseudocarcinus karlraubenheimeri n. sp. Pseudocarcinus thrived on both sides of the Tasman Sea until it disappeared in New Zealand waters. Pseudocarcinus crabs are characterised by gigantism, which provided them with significant advantages in competition and defence. Their carnivorous nature is reflected in their exceptionally large major cheliped. The broader use of benthic dwelling gastropods and bivalves as prey seems to have led to subsequent advances in brachyuran claw engineering, and an increase of molluscivorous crabs in the Late Cretaceous and Palaeogene. Zoobank: urn:lsid:zoobank.org:pub:B53DB047-B18C-4CA4-946F-5E9209A581F2

Geologic predictors of drinking water well contamination in North Carolina

More than 200 million people worldwide, including 11 million in the US, are estimated to consume water containing arsenic (As) concentrations that exceed World Health Organization and US EPA standards. In most cases, the As found in drinking water wells results from interactions between groundwater and geologic materials (geogenic contamination). To that end, we used the NCWELL database, which contains chemical information for 117,960 private drinking wells across North Carolina, to determine the spatial distribution of wells containing As contaminated water within geologic units. Specific geologic units had large percentages (up to 1 in 3) of wells with water exceeding the EPA As maximum contaminant level (MCL, 10 μg/L), both revealing significant variation within areas that have been previously associated with As contamination and identifying as yet unidentified problematic geologic units. For the 19 geologic units that have >5% of wells that contain water with As concentrations in exceedance of 10 μg/L, 12 (63%) are lithogenically related to the Albemarle arc, remnants of an ancient volcanic island, indicating the importance of volcanogenic materials, as well as recycled (eroded and deposited) and metamorphosed volcanogenic material. Within geologic units, wells that have As concentrations exceeding 10 μg/L tended to have pH values greater than wells with As concentrations less than 10 μg/L, emphasizing the importance of the extent of interaction between groundwater and geologic materials. Using census information with the geologic-based exceedance percentages revealed the importance of regional geology on estimates of population at risk compared to estimates based on county boundaries. Results illustrate that relating As contamination to geologic units not only helps explain sources of geogenic contamination but sharpens the identification of communities at risk for exposure and further illuminates problematic areas through geologic interpretation.

Controls of Tellurium enrichment in the rare earth elements and yttrium (REY) rich deep-sea sediments from the Central Indian Ocean Basin (CIOB)

As a potential Te reservoir for the global budget, the occurrence, material sources, migration and enrichment mechanism of Te in deep-sea sediments remain unclear. Based on the major and trace elements measurements of bulk sediments, this study proposed a procedure to quantify the contribution of Te by main host minerals, combining with TIMA and LA-ICP-MS in two cores (GC04 and GC11) from the Central Indian Ocean Basin (CIOB) and a core from east of the 90°E Ridge (GC03). Te shows the highest enrichment coefficient of 650 referred to UCC (Upper Continental Crust) in the REY (Rare Earth Elements and Yittrium) rich sediments in GC04, GC11 and GC02 (a core at the south of GC04 and GC11). Clinoptilolite-K and osumilite are indicated as the main host minerals, which correlates Te sources with volcanogenic materials and weathering products of terrigenous rocks. The inter elements correlation, cluster analysis and factors analysis further indicate distinct hydrothermal genetic Te. So, we put forward a hypothesis that Te is mainly sourced from the submarine volcanogenic hydrothermal activities, which are closely associated with local intraplate volcanism episodes from late Miocene with spatial and temporal differences. This study is the first attempt to quantify Te from different minerals and to reveal its geochemical behavior in the deep sea sediments, which will be benefit to the understanding of Te reservoir and cycle in deep sea and the comprehensive utilization of REY-rich deep-sea sediments. However, for the abundant presence of undetectable nanoscale minerals in these sediments, the contribution of Fe-Mn (oxyhydr) oxides and clay minerals of Te need more investigation.

Volcanogenic aluminosilicate alteration drives formation of authigenic phases at the northern Hikurangi margin: Implications for subseafloor geochemical cycles

Alteration of volcanogenic aluminosilicates (VAs) in marine sediments is recognized as critical in regulating geochemical cycles and sustaining the oceanic deep biosphere, but rates of VA alteration and its associated authigenic mineral formation are not commonly reported. Here we present results on analyses of sediments and pore water recovered from the upper 150 mbsf of four sites drilled on the northern Hikurangi margin during IODP Expeditions 372 and 375. Petrographic analyses show that volcanogenic materials (glass shards, feldspar, volcanic lithoclasts) constitute important components (15–45 wt%) of the hemipelagic mud, and reveal ongoing glass alteration with accompanying authigenic phase formation. A reaction-transport model constrained by pore water Sr, 87Sr/86Sr, Ca, Mg, and Si was applied to simulate VA diagenetic reactions. Our model results yield VA alteration rates of 0.047–0.64 mmol Sr m−2 yr−1, with substantially higher values at Sites U1517 and U1520 that experienced rapid sediment emplacement. In addition, our simulations show that >99% of the dissolved Si generated by VA alteration is fixed in silica cement and authigenic clay, and that ∼50% of Ca incorporated in the authigenic carbonate is supplied by VA alteration. First-order estimates suggest that, in addition to authigenic carbonate precipitation, authigenic clay formation may represent an important sink for dissolved Mg. This study quantitatively examines the linkage between VA alteration and formation of authigenic phases, highlights its role in subsurface geochemical cycles, and indicates that slope instability may play an important role in promoting VA diagenesis.

Radiogenic Nd in bioapatite from rare earth elements rich deep sea sediments from Central Indian Oceanic Basin and its implication in material sources

Rare Earth Element and Yttrium (REY)-rich deep sea sediments have been estimated to be a highly important potential resource. However, the main material sources that supply the huge amount of REY resources, as well as geochemical procedure determines the distinct REY patterns of these sediments, remain unclear. To fill this research gap, in this study, three sediment cores (GC02, GC04, and GC11) collected from the Central Indian Ocean Basin (CIOB) and a core (GC03) from eastern of the 90° E Ridge (NER) were sampled for mineral identification and elemental (major, trace, and rare earth elements) analyses. Fish teeth and detrital minerals were isolated from the sediments, and their 87Sr/86Sr and 143Nd/144Nd ratios were measured. Accumulation of REY is revealed in three cores of GC02, GC04, and GC11 from CIOB with mean value of 511.93 μg/g, 614.79 μg/g, and 1036.14 μg/g, respectively. Most REY rich sediment exhibit obvious to slight negative Ce abnormal, slight positive Eu and Y abnormal. The detrital fraction of the REY rich sediments exhibit less radioactive εNd values of − 8.36295 and more radioactive 87Sr/86Sr of of 0.71651. On the contrary, the fish teeth exhibit less radiogenic 87Sr/86Sr ratio of 0.70915 but more radiogenic εNd values of − 5.13511 than those of the sea water of the Indian Ocean. The results reveal that the REY-rich sediments in the CIOB are characterized by multiple material sources including weathering continental products, alteration of volcanogenic glasses, hydrothermal and marine authigenic materials. Distinct volcanogenic materials input are obvious in the CIOB evidenced with radiogenic 143Nd/144Nd ratios of the fish teeth, the wide occurrence of clinoptilolite and high Te contents contained. The volcanogenic related hydrothermal materials are then indicated to provide most part of REY for the fish teeth, which contribute the most amount of REY of the sediments. However, the terrestrial input of REY cannot be neglected, which indicates the REY-rich deep sediments were formed under multi-source supply system. The study indicated that continuous exchange of Sr between fish teeth and ambient pore water after deposition, and ambient pore water was concluded to contain an abundance of released radiogenic terrestrial Sr. However, the exchange of Nd between fish teeth and bottom sea water ceased after buried in depth. Nd ratios on the fish teeth recorded the more radioactive hydrothermal material carried by bottom seawater at the early stage of precipitation.

Satellite Detection of a Massive Phytoplankton Bloom Following the 2022 Submarine Eruption of the Hunga Tonga‐Hunga Haʻapai Volcano

AbstractThe largest submarine volcanic eruption of this century led to a dramatic phytoplankton bloom north of the island of Tongatapu, in the Kingdom of Tonga. In the absence of shipboard observations, we reconstructed the dynamics of this event by using a suite of satellite observations. Two independent bio‐optical approaches confirmed that the phytoplankton bloom was a robust observation and not an optical artifact due to volcanogenic material. Furthermore, the timing, size, and position of the phytoplankton bloom suggest that plankton growth was primarily stimulated by nutrients released from volcanic ash rather than by nutrients upwelled through submarine volcanic activity. The appearance of a large region with high chlorophyll a concentrations <48 hr after the largest eruptive phase indicates a fast ecosystem response to nutrient fertilization. However, net phytoplankton growth probably initiated before the main eruption, when weaker volcanism had already fertilized the ocean.

Depositional and diagenetic processes in volcanic matrix‐rich sandstones from the Shanxi and Shihezi formations, Ordos Basin, China: Implication for volcano‐sedimentary systems

AbstractVolcanic eruptions can provide large amounts of sedimentary materials and expose fluvial valleys or lakes to catastrophic hyperpycnal flood events, but this process has not been documented in detail. The Ordos Basin Permian fluvio‐deltaic system reveals evidence for abundant volcanism linked to the tectonic evolution of orogenic belt around the basin and provides a ‘natural laboratory’ for investigating hyperpycnal flows associated with volcanic activity. This study analysed volcanic matrix‐rich sandstone (VMS) samples for petrology, mineralogy and geochemistry in order to address current and uncertain volcanogenic material provenance explanations and the lack of systematic investigations into the depositional and diagenetic processes of volcanic related sediments in the southwestern basin. By combining tectonic background surveys, detrital zircon geochronology and spatial distribution of volcanogenic materials, it was found that volcanogenic materials were not derived from the Yinshan‐Yanshan Orogenic Belt (YYOB) as previously thought, but instead evidence a southwestern origin from the North Qinling Orogenic Belt (NQOB). Volcanogenic materials retained in the provenance area during frequent volcanic eruptions were transported to the basin via fluvial systems shortly after the eruption. The associated sediments meet the criterion for hyperpycnites based on lithofacies associations, suggesting the occurrence of hyperpycnal flows during the deposition of VMS. During the subsequent burial stage, the VMS became three distinct types defined by their volcanic matrix content and have similar paragenetic sequences but different diagenetic intensities. The differing content of authigenic minerals in the three types was closely related to the sandstone pore structure characteristics and the evolution of volcanic‐matrix alteration materials. This article proposes a possible explanation for the previously unidentified tectonothermal events in the NQOB during the Permian, validating and reinforcing the theoretical work of hyperpycnal flow. This contribution provides new insights and understanding of the depositional and diagenetic processes of lacustrine basins with similar tectonic settings.

Mineralogical and geochemical characteristics of tonsteins from the Middle Jurassic Yan'an Formation, Ordos Basin, North China

Although the Jurassic features a considerable accumulation of coal worldwide, only a few tonsteins within coal seams in this coal-forming period have been investigated. This paper presents the detailed mineralogical and geochemical compositions of six tonstein layers from the Middle Jurassic Yan'an Formation, Ordos Basin, North China. Based on the typical evidence of the distinct field characteristics occurring as paler thin beds with lateral continuity; conchoidal and flint-like fracture planes; sharp contacts with adjacent coals; and the mineralogical compositions, such as vermicular kaolinite, angular quartz, and euhedral zircon crystals with a single UPb age peak, the intra-seam clay beds of the Yan'an Formation were determined to have been mainly derived from a significant pyroclastic source. However, rounded quartz, muscovite, and detrital zircon grains in the tonsteins reflect minor contribution of terrigenous debris from sediment source regions. Moreover, a line of geochemical features including low TiO2/Al2O3 values, Al2O3/TiO2-Nb/Yb, and Al2O3/TiO2-Zr/TiO2 diagrams; low REY concentrations with high fractionation between light REE and heavy REY (REY, rare earth elements and Y; REE, rare earth elements); and pronounced negative Eu anomalies, suggest that the tonsteins have a felsic (rhyolitic) magma origin. A systematic geochemical analysis of enclosing coals of the tonsteins was also conducted to determine the leaching behavior of the trace elements from the tonsteins into the enclosing coals. The results show that Th, U, Nb, Ta, Zr, and Hf tend to be enriched in the overlying and underlying coals and have an enrichment width of up to 30 cm. Similarly, the elevated concentrations of Zn, Rb, Cs, Pb, La, Ce, Pr, and Nd only occur in a relatively narrow zone above and below the tonsteins. The width of the enrichment in the enclosing coals may be mainly related to the properties of the tonsteins, e.g., thickness and original volcanogenic material, the characters of elements including mobility and concentration, and the nature of coals, such as coal rank.

Why do calcareous microfossils preferentially occur in tuffaceous sandstones of the Santa Marta formation (James Ross Island, Antarctica)?

The Santa Marta Formation (James Ross Island, Antarctica) presents one of the most complete Santonian-Campanian high-latitude marine records in the Southern Hemisphere. Recent micropaleontological studies pointed to an unusual preferential preservation of calcareous microfossils, such as foraminifera and nannofossils, in tuffaceous sandstone levels of the Santa Marta Formation. Here we aim to characterize depositional and early diagenetic conditions that influenced preservation of calcareous microfossils within the succession of the Santa Marta Formation (Alpha Member). We used X-ray fluorescence (FRX)-derived elemental ratios, as well as carbonate (CaCO3), total organic carbon (TOC), and total sulfur (TS) contents to characterize sediment properties, as well as X-ray diffraction (XRD)-derived mineralogical analysis. Elemental ratios suggest hydrothermal influence during diagenesis throughout the stratigraphic succession, as indicated by (Fe + Mn)/Ti values > 20. This interpretation is supported by the occurrence of typical low-temperature hydrothermal minerals, such as garronite and heulandite. Contribution of volcanic ashes in the tuffaceous sandstone levels is evidenced by high values of the log (Zr/Ti) ratio, and the presence of volcanogenic minerals. Since stratigraphic levels characterized by the highest abundances and richnesses of calcareous microfossils also present high log (Zr/Ti) values and CaCO3 contents, we hypothesize that the input and subsequent alteration of volcanogenic material (e.g., ashes) acted as a buffer, increasing porewater alkalinity during early diagenesis. Such a chemical mechanism was already described for modern marine sediments deposited under the influence of significant input of volcanogenic materials, and can explain the preferential preservation of calcareous microfossils in tuffaceous sandstones of the Upper Cretaceous Santa Marta Formation.

Podrobnosti o počátcích sedimantace a vulkanické činnosti na začátku permu (asselu); rudnický obzor v sz. části podkrkonošské pánve

A succession of the early Permian (Asselian) Rudník member exposed at the locality Škodějov – Hrádecký potok in the northwestern part of the Krkonoše Piedmont Basin (eastern Bohemia) contains light-colored clastic rocks with macroscopically conspicuous lamination, overlying lacustrine bituminous claystones and siltstones (ʻblack shalesʻ). This work aims to constrain the origin of those laminated strata. They can be macroscopically described as heterolithic sequence formed by fine- to medium-, exceptionally coarse-grained sandstone with intraclasts of mudstone, calcified fine-grained sandstone, mudstone and claystone with interlayers of organic-rich laminae. Volcaniclastic rocks are also present. The heterolithic volcanosedimentary sequence comprises cyclic (up to 4 dm), mostly horizontally laminated rocks, in places with soft- sediment deformation structures. Diagenetic phenomena, related to calcification of volcaniclastic layers and growth of pyrite crystals and framboids, are common. Volcaniclastic rocks with a predominance of albitized volcanic glass fragments are interpreted as vitritic tuffs. Fragments of volcanic glass floating in silty to fine-grained sandy matrix contain vesicules and are locally brown- colored. They are reinterpreted as being derived from contemporary intermediate (andesitic) volcanism, most likely extrabasinal. Extensive alteration of volcanic material makes characterization of the original composition of volcaniclastic deposits difficult. Trace element analysis using a portable XRF spectrometer revelaed negligible concentrations of V, Ni and Ti, which are indicative of rather basic volcanism. Results of outcrop-scale gammaspectrometry are presented here as trends of Th/U ratio of relevant lithotypes from several localities of the Rudník member. Organic-rich laminae present within the heterolithic succession at Hrádecký potok section are commonly rich in pyrite clusters. Those are the most probably related to formation of algal mats stimulated by input of fine-grained volcaniclastic material into the Rudník Lake. However, elevated siliciclastic and volcaniclastic input, particularly during periods of intensified volcanic activity, with related seismic events (that may have triggered gravity flows), may have disturbed or punctuated growth of algae on the lake floor. Our work has shown that the volcanic activity at the onset of deposition of the Rudník member in the northwestern part of Krkonoše Piedmont Basin (Škodějov – Hrádecký potok) was probably of intermediate nature and that it influenced depositional environment. Particularly, the fluctuating input of clastic and volcanogenic material could have caused an alternation of oxic and dysoxic conditions in the lake lacustrine environment over time. The intermediate character of volcanism in this locality contrasts with confirmed acidic volcanism documented in volcaniclastic layers in another lacustrine succession at Vrchlabí – roadcut (Martínek et al. 2006) that probably represent a different eruptive phase recorded within the Rudník member.

Geochemistry and mineralogy of the sediments in the New Britain shelf-trench continuum, offshore Papua New Guinea: Insights into sediment provenance and burial in hadal trenches

Seven short cores collected along two transects from the shelf to trench bottom in the New Britain Trench (NBT) area, Papua New Guinea (PNG), were studied to illuminate the provenance and burial of sediments across the shelf-trench continuum. Here, we present geochemical data, including major, minor and rare earth elements, bulk and clay mineralogy, grain size, and Sr–Nd isotopes. The results indicate that sediments in the NBT area were mainly derived from intermediate volcanogenic materials of the surrounding islands with the contribution of volcanogenic materials up to 90%. Volcanogenic materials from Rabaul Volcano had a significant influence on the western NBT (Transect 1), whereas the eastern NBT (Transect 2) was more strongly affected by the Tabar-Lihir-Tanga-Feni (TLTF) volcanic chain. In addition, pollen and spores analyses showed a decreasing trend in their concentrations in the order of the landward site, the trench axis site, and the abyssal site on the Transect 1 and the dominance of Cyperaceae in the herb fraction at the trench axis site NBT01. This observation, accompanied by the significant differences in the major and minor elements as well as Sr–Nd isotopes between upper 4 cm sediments and those below at NBT01, suggests that the upper 4 cm sediments were probably sourced from river sediments. Together with low chemical index of alteration (CIA) values, we suggest that terrigenous riverine materials are rapidly transported and buried at the trench axis. Our findings highlight the important role of hadal trenches in trapping terrigenous materials and have implication for understanding the fate of terrigenous materials in the deep ocean.

Late Toarcian continental palaeoenvironmental conditions: An example from the Cañadón Asfalto Formation in southern Argentina

The Cañadón Asfalto continental Basin preserves terrestrial deposits interbedded with volcanic rocks, providing a unique opportunity for palaeoenvironmental reconstructions of the Jurassic continental realm. This study presents a sedimentological, mineralogical, and geochemical analysis of three lacustrine successions in the Cerro Cóndor area of the Cañadón Asfalto Basin, Argentina. New CA ID-TIMS U–Pb data from tuffaceous deposits indicate a late Toarcian age (179.481 ± 0.059, 179.41 ± 0.13, and 177.27 ± 0.40 Ma), suggesting that the palaeolakes developed contemporaneously to the Chon Aike volcanic activity. The sedimentary successions are composed of carbonate, organic matter-rich mudstone — with up to 8 wt% total organic carbon (TOC) content — sandstone and conglomerate, all with an important contribution of volcanic and volcanogenic material. The clay mineral assemblage dominated by corrensite (chlorite-vermiculite mixed layers), smectite and vermiculite is likely related to hydrothermal activity and alteration of volcanic material, rather than to change in weathering processes and climate. Organic matter preserved in the sedimentary successions has a lacustrine and terrestrial/reworked origin. Changes in the source of carbon dioxide (CO2) and in the type and/or degree of preservation of the organic matter had a major impact on the δ13Corg values. This further exemplifies the necessity to evaluate the influence of the depositional environment before interpretation of the organic carbon isotope records. The combined high phosphorus and TOC contents suggest that episodes of increased nutrient availability into the basin enhanced lacustrine primary productivity, which favoured the development of oxygen-depleted conditions bottom waters and ultimately organic matter preservation and burial. High Corg/Ptot ratios indicate that phosphorus was likely released back into the water column in a positive feedback loop, further sustaining primary productivity. This study provides an important clue to understand the palaeoenvironmental conditions prevailing on land during the late Toarcian and on how volcanism exerted a control on the depositional conditions.

Ferruginous microbialite blooms of the Miaolingian (Cambrian) in the southern North China Craton: a response to the volcanic event?

Ferruginous microbialites of the Mantou Formation (Miaolingian, Cambrian) in the southern North China Craton are available for investigation of their formation mechanisms. The ferruginous microbial structures are existing in a deepening upwards sequence with occurrences of the oolitic limestone, oncolite, stromatolite, and thrombolite in ascending order. The ooids larger than 2 mm in diameter are made up of repeated alternations of bright coarse-grained calcites and homogeneously ferruginous fine-grained calcites. Oncoids and stromatolites comprise alternations of coarse-grained calcite and Girvanella-laminae. Thrombolites consist of massive Girvanella-clots and micritic interstitial sediments. Several filaments with ferruginous sheathes in the laminae/clots are interpreted as the remains of iron-oxidizing bacteria. Mineral components of ferruginous microbialites are mainly calcite, quartz, plagioclase, microcline, clay minerals, and some iron minerals. The sharp increases of ferruginous volcanogenic materials in the strata are ascribed to the contemporaneous ash fall. The elevated nutrient concentration dramatically spurred the cyanobacterial bloom and then caused an extensive eutrophication. Microaerophilic iron-oxidizing bacteria then thrived therein promoting oxidize ferrous solution into iron oxide/oxyhydroxide. The widespread Miaolingian ferruginous microbialites indicated the proliferation of microbial communities in the aftermath of contemporaneous volcanism in the southern North China Craton.

Preferential Riverine Export of Fine Volcanogenic Particles to the Southeast Australian Margin

We report on rare earth element and neodymium isotopic compositions in a series of grain-size fractions separated from river suspended matter in the Murray-Darling Basin (MDB) and a nearby marine sediment core (MD03-2607) offshore south-eastern Australia. This source-to-sink approach was used to further investigate the extent to which sediment sorting may control the geochemistry of suspended loads in rivers, and to provide constraints on the source of the detrital sediment material exported to the ocean. Our results provide further compelling evidence that significant size-dependent geochemical decoupling can occur in river systems, accounting here for Nd isotopic (Nd) differences of up to 8 epsilon-units between silt (>25µm) and colloidal (0.2-0.006 µm; 0.006-0.003 µm) fractions. All suspended particulate samples from the River Murray watershed display a trend towards more radiogenic (higher Nd) Nd signatures with decreasing grain-size, in addition to differing REE signatures, which collectively point towards a preferential volcanogenic origin for the fine-grained inorganic particles transported by MDB rivers. Furthermore, we show that the same river-borne volcanogenic material dominates in the fine-grained detrital fractions extracted from core MD03-2607 at the south-eastern Australian margin; a finding corroborated by REE signatures in a series of copepod faecal pellet separates from the same core. Collectively, our results suggest that river sediment discharge is accompanied by preferential export of fine-grained volcanogenic particles to the ocean. This potential source of bioavailable trace metals and nutrients in ocean surface waters could impact marine productivity.

Change of lithofacies in marine sediment core from Quaternary to Pre-Quaternary: A case study from the Central Indian Ocean Basin

A distinct change in lithofacies was observed from red clay to siliceous ooze in a core from Indian Ocean. Radiolarian index species were used to ascertain the Quaternary datum levels and an age of 2.0 Ma is determined up to 125 cm depth from surface. Below 185 cm depth, the sediment core lacked radiolarian test completely. At about 50 cm from core top, the sedimentation rate decreased drastically from 0.18 to 0.05 cm/kyr with a corresponding age of 500 kyr, marking Marine Isotope Stage 13. The changes in lithofacies and sedimentation rate are further accompanied by the change in clay mineralogy from smectite rich older sediments to smectite depleted younger sediments and presence of higher amount of volcanogenic materials in the older sediments. Higher values of chemical index of alteration (CIA) and lower K2O/Al2O3 in older sediments indicate dominance of chemical weathering in the older sediments which decreased gradually towards core top. Ti normalized concentrations of elements like Co, V, Cu, Ni, Ce, Y and ∑REEs exhibit lowest values at the transition zone above which the ratios increased steadily towards the core top. All these observations indicate a marked change in the climatic regime from late Quaternary onwards, prior to which the environment was less bio-productive.

Lithogeochemistry of clastic rocks of the Mashak Formation (western slope of the South Urals): in search of “camouflaged” pyroclastics

The article attempts to solve the problem of the presence of “camouflaged” pyroclastics in sandstones and fine-grained clastic rocks of the Middle Riphean Mashak Formation of the Southern Urals based on litho- and geochemical methods and approaches. As a result of the studies, it was established that in the NKM–GM diagram, the compositional field of silt-clayey rocks of the Mashak Formation is comparable with several clusters of Jurassic slates of the Greater Caucasus, containing volcanogenic material, while the clusters of Paleogene tuffs of the Ukrainian Carpathians and the Gromashor Formation (Pai-Khoi) have a different location. On the (Na2O + K2O) – GM diagram, in the indicated field, are situated two of four clusters ofmetatuffoids and mixed volcanic-sedimentary rocks of the Strelna Group (Kola Peninsula), and one of two clusters of tuffs of the Redkino horizon (Vendian of the East European Platform). The same is true for a number of other examples. In the diagram (Na2O + K2O) – FM, none of the four clusters of tuffs and tuffopelites of the Ordovician of the Arga-Tas zone of the Momsky horst-anticlinorium and none of the six clusters of acidic tuffs and tuffites of Ukrainian Carpathians fit in, etc. Consequently, the localization of the compositional field of silt-clayey rocks of the Mashak Formation in the above and a number of other diagrams shows that clusters of various volcanic-terrigenous rocks, metatuffosiltstones, metatuffoids, slates, etc., containing a certain admixture of volcanic products, coincide with the diagrams in half or fewer of the cases. Thus, the analysis of the absolute contents and indicator ratios of trace elements inherent in sandstones and clayey rocks, values of petrochemical modules and the systematics of rare-earth elements (REE) does not allow us to state with certainty that magmatic processes, including subsynchronous sedimentation, were the main source of their constituent material.

On the Problem of Nonmarine Cretaceous Strata Correlation in the Northeast Russia: The Conditions of Florogenesis in Volcanic Areas

The majority of fossil floras from Cretaceous volcanogenic rocks of Northeast Russia considerably differ in taxonomy from the coeval paleofloras of coastal lowlands. In order to explain the peculiarities of their formation, we used the data on the modern vegetation dynamics for volcanic plateaus of Central Kamchatka. It is shown that there was virtually no erosion where paleofloras of the Okhotsk-Chukotka volcanogenic belt, represented in the burials, existed; however, volcanogenic material, suitable for burials to form, was supplied in abundance. After massive eruptions, inner parts of the vast volcanic zone appeared to be isolated from sources of diaspores. Vegetation cover in these areas was restored mainly owing to the pool of local taxa; i.e., it was supported as a diasporic subclimax. The absence of concurrent angiosperms favored the long-term preservation of ancient taxa in these paleofloras and the appearance of new taxa on their basis.

Color and chemical composition of bottom sediments from the Kuril Basin (Sea of Okhotsk) and the Kuril–Kamchatka Trench area (Northwest Pacific)

The colorimetric method of analysis was first used to study the distribution of the color characteristics (spaces RGB and HSL) in sediment cores from the Kuril Basin of the Sea of Okhotsk and the nearby Kuril-Kamchatka Trench area of the Northwest Pacific. The statistic processing of these and in addition obtained geochemical and grain-size data made it possible to establish the controlling factors and significant relations. The most stable direct correlation is demonstrated by the characteristics of R–Mn–Mo (fine-grained oxidized sediments enriched in hydroxides of iron and manganese and related with them microelements) and H–L–SiO2 (coarse-fragmental part of sediments involving the grains of rock-forming minerals and sometimes a significant admixture of the diatom frustules). Usually, saturation S and phosphorus content gravitate to the first group of parameters, and the additive primary blue color B tends to the second group. Informative are some relations of the color characteristics, for example, the additive primary red color R and green color G (the boundary of the oxidized and reduced sediments). The admixture of the volcanogenic (pyroclastic) material can be reflected in the shift and disruption of the described relations.The results obtained show the regional conditions of sedimentation with the participation of the terrigenous, biogenic, and volcanogenic material and subsequent diagenetic redistribution of the matter. The revealed regularities together with other characteristics of the matter composition can be used for the detailed description of the sediment cores of the regions with the similar settings of sedimentation.

Local neotectonic restructuring in the North Caucasus orogene

Cases of regional neotectonic restructuring are well known in the Caucasus. Detailed geotectonic zoning and identification of local structural changes are required for the engineering geological and paleoecological studies. The Baksan River valley was studied in the North Caucasus as an example of such a restructuring. The problem about the number of Quaternary volcanogenic strata and their role in structural rearrangement is considered. The Pliocene – Plio-Pleistocene volcanogenic strata cloak-like covered the Nizhnechegemsky district before the first reconstruction. Zayuksky graben (with an amplitude of 200 m) was formed in the end of Plio-Pleistocene; and a part of Pliocene- Plio-Pleistocene volcanogenic strata sank into it. Two layers with a total thickness of more than 100 m were deposited in the resulting trough. The upper strata (baxangess) contain redeposited boulder-pebbly volcanogenic material. Colluvial, subaquatic-deltoid and lacustrian facies are registered. The orographic depression in Zayuksky graben was completely filled before Eopleistocene as a result of next restructuring. The Baksan River began to form a wide well-terraced valley without any significant left tributaries there. The baxangess strata contain pebble of liparite lavas and obsidians. This pebble was used by the Paleolithic man for making stone tools. Poor roundness of pebble indicates its short transportation distance. Contradictory ideas about the initial distribution of parental volcanic rocks are considered. It is concluded on the acuteness of identifying such neotectonic rearrangements for the analysis of various paleogeographic and paleoecological changes.