South Basin Research Articles

Ritual Deposit of the Sarmatian Age from the Barrow on the Lower Don Basin

Introduction. In 2007 the archaeological expedition of the State Autonomic Cultural Facility of Rostov Region “The Don Heritage” excavated burial ground Krasny IV in Aksay district of Rostov Region. In the mound of barrow No. 13 a bronze rod-shaped frontlet plate with a hook, a bronze lunula-shaped harness pendant, six bronze bridle roundels, a bone cheek-piece, and iron fragments of the, most likely, bits have been discovered. Methods and materials. In the study the standard methods of archaeological analysis are used: comparative-typological, the method of analogies, chronological, and cartographic ones. The materials are the discovered artifacts. Analysis. According to the conditions of location and composition, the assemblage from barrow No. 13 can be identified as a ritual deposit. Such assemblages are known in special literature as “hoards”, “strange assemblages” or “votive hoards”. They have been found in mounds of barrows or in natural hills without traces of human burials. Usually they consist of cauldrons or situlae (often the rest items are put into them), bridle sets with peculiar frontlet plate with a hook, silver and bronze phalerae, helmets of Western types, weapons (most often spear- and arrowheads), expensive and socially prestigious items (silver and glassware, jewelry). The presence of all these items in the ritual deposit is not necessary. These sites are concentrated in geographically opposite regions: the basins of the Southern Bug, Dniester and Prut and in the east of European Sarmatia – in the AzovDonbass, Don and Kuban basins, the Lower Volga basin and North Caucasus. Results. Close parallels to the frontlet plate, bronze lunula-shaped pendant, and bridle roundels were found in the South Bug basin (Marievka), the Dniester and Prut interfluve (Brãviceni), Romania (Zimnicea), the North Caucasus (Prochnookopskaya, Geymanovsky, Giaginskaya), the Don and Volga interfluve (Kachalinskaya). All of these sites are identified as ritual deposits of the late 2nd – 1st centuries BC. The assemblage from barrow No. 13 should be dated to the same time. The ritual deposits of Eastern Europe could be divided into two chronologically different groups. The sites of the early group (3rd – early 2nd century BC) have appeared in the North Caucasus and concentrated in the North-Western Pontic region. It is assumed that they belong to the Хsaiai, Saudaratai and Thissamatai mentioned in the Olbian decree in honor of Protogenes. The sites of the late group (the late 2nd – 1st centuries BC) in the Northern Pontic Region, the Don basin, the North Caucasus and adjacent territories belong, most likely, to the Sarmatians.

Evolution of a Normal Fault System Along Eastern Gondwana, New Zealand

AbstractThe Great South Basin (GSB) developed in the Cretaceous from continental rifting at the southeastern margin of Gondwana. The basin contains a thick Cretaceous succession that is largely unaffected by Neogene compressional tectonics, with rift faults and associated growth strata imaged by good‐quality 2‐D and 3‐D seismic data tied to wells. These data show three distinct stages of normal faulting here referred to as fault system initiation (Stage 1), fault system growth (Stage 2), and fault system death (Stage 3). The different stages of fault system evolution comprise dominant NE trending faults (NW‐SE extension), and minor NW trending faults (NE‐SW extension). Fault initiation at ~105–101 Ma mainly occurred in the central GSB with rift depocenters mostly on, or close to, NW trending basement terrane boundaries. These preexisting basement boundaries represent zones of weakness that locally promoted early localization of NW faults and retarded the propagation of NE faults. With increasing regional extension and fault system growth from ~101 to 90 Ma the influence of the basement fabric gradually decreased, while NE trending faults increased in length, number, displacements, and spatial distribution. Finally, during the fault system death stage from ~90 to 83 Ma the length, number and displacements of faults decreased. Fault death coincided in time with Gondwana breakup and reflects the localization of extension along spreading centers distal to the GSB.

Association of aerobic anoxygenic phototrophs and zebra mussels, Dreissena polymorpha, within the littoral zone of Lake Winnipeg

While nutrient loading has affected all levels of Lake Winnipeg’s ecology, its greatest influence has likely been on the microbial community. In addition to eutrophication, zebra mussels (Dreissena polymorpha) have recently invaded the ecosystem and threaten food web dynamics. Their filter-feeding predation and association with bacteria, specifically phototrophs, was investigated. A sampling trip to Lake Winnipeg in October 2017, focused on the isolation, enumeration, and identification of aerobic anoxygenic phototrophs in littoral water, sediment, and tissues of mussels. Gimli, Patricia, and Grand beaches, separated by >15 km across the South Basin, had similar bacterial counts when cultivated on rich organic, BG-11, purple non-sulphur, and K2TeO3-supplemented media. Culture-based enumeration on rich organic medium revealed 1.74% of heterotrophs from littoral waters were aerobic anoxygenic phototrophs, and represented 13.98% within sediments. In contrast, 0.48, 1.15, and 0.16% of cultured heterotrophs were aerobic anoxygenic phototrophs within zebra mussel gill, gut, and gonadal tissues, respectively. High-throughput sequencing of bacterial 16S V4 rDNA maintained similar trends in respective bivalve organs, where 0.22, 1.13, and 0.20% of total 16S genes belonged to these phototrophs. Several Sphingomonadaceae isolates were recovered from gut tissues, all with filamentous morphology large enough for predation. Bioaccumulation of metals was also studied in D. polymorpha. All tested associated aerobic anoxygenic phototrophs were capable of resisting the metalloid oxide tellurite. The consistent distribution of aerobic anoxygenic phototrophs within microbial communities across Lake Winnipeg, and their predominance in the gut tissues of zebra mussels suggested bacterial consumption by this invasive species.

Multi-compartment chemical characterization and risk assessment of chemicals of emerging concern in freshwater systems of western Kenya

BackgroundWithin the last decades, there has been increasing research on the occurrence of chemicals of emerging concern (CECs) in aquatic ecosystems due to their potential adverse effects on freshwater organisms and risk to human health. However, information on CECs in freshwater environments in sub-Saharan countries is very limited. Here, we investigated the occurrence of CECs in snails and sediments collected from 48 sites within the Lake Victoria South Basin, Kenya, which have been previously investigated for water contamination. Samples were analyzed by liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) with a target list of 429 compounds.ResultsIn total, 30 compounds have been detected in snails and 78 in sediment samples, compared to 79 previously identified compounds in water. By extending the monitoring of CECs to snails and sediments, we found 68 compounds that were not previously detected in water. These compounds include the anti-cancer drug anastrozole, detected for the first time in the Kenyan environment. Individual compound concentrations were detected up to 480 ng/g wet weight (N-ethyl-o-toluenesulfonamide) in snails and 110 ng/g organic carbon (pirimiphos-methyl) in sediments. Higher contaminant concentrations were found in agricultural sites than in areas not impacted by anthropogenic activities. Crustaceans were the organisms at greatest toxic risk from sediment contamination [toxic unit (TU) up to 0.99] with diazinon and pirimiphos-methyl driving this risk. Acute and chronic risks to algae were driven by diuron (TU up to 0.24), whereas fish were found to be at low-to-no acute risk (TU up to 0.007).ConclusionsThe compound classes present at the highest frequencies in all matrices were pesticides and biocides. This study shows substantial contamination of surface water in rural western Kenya. By filling data gaps on contamination of sediments and aquatic biota, our study reveals that CECs pose a substantial risk to environmental health in Kenya demanding for monitoring and mitigation.

Lower Cretaceous non-marine ostracods of the Orós Formation, Iguatu basin: Taxonomy and biostratigraphic considerations

Non-marine ostracods have been used for a long time to aid in the understanding of the Lower Cretaceous sedimentary deposits of Brazil, with various studies showing their value for biostratigraphic zonation in different basins. The northeastern region of Brazil contains several basins south of the Potiguar Basin which originated from the rifting that resulted from the opening of the Atlantic Ocean, and thus contain an important record of the Cretaceous Period. This paper has the objective of studying the ostracods recovered from two adjacent sections (Transnordestina A and Transnordestina B) belonging to the Orós Formation, Iguatu Basin, Ceará, Brazil, detailing their taxonomy and developing biostratigraphic inferences based on the observed fauna. A total of 19 species were found in the analyzed samples, distributed among 11 genera and five families: Cypridea hystricoides, Cypridea paraibensis, Cypridea cf. C. clavata, Cypridea punctacentralis sp. nov., Brasacypris ovum, Pattersoncypris sinuata, Pattersoncypris cf. P. sinuata, Pattersoncypris? sp., Ilyocypris? arca sp. nov., Ilyocypris? latanodi sp. nov., Rhinocypris? ericius sp. nov., Pythagoracypris latavectis gen. et sp. nov., Hastacypris adamantem gen. et sp. nov., Looneyellopsis mvili, Musacchiocythere plastica, Musacchiocythere? sp., Alicenula leguminella, Alicenula cf. D. oblonga, and an incertae sedis species. From the recovered species, a Hauterivian–Aptian interval can be inferred for the studied sections.

Tropical cyclone formation regions in CMIP5 models: a global performance assessment and projected changes

Tropical Cyclone (TC) formation regions are analysed in twelve CMIP5 models using a recently developed diagnostic that provides a model-performance summary in a single image for the mid-summer TC season. A subjective assessment provides an indication of how well the models perform in each TC basin throughout the globe, and which basins can be used to determine possible changes in TC formation regions in a warmer climate. The analysis is necessarily succinct so that seven basins in twelve models can be examined. Consequently, basin performance was reduced to an assessment of two common problems specific to each basin. Basins that were not too adversely affected were included in the projection exercise. The North Indian basin was excluded because the mid-summer analysis period covers a lull in TC activity. Surprisingly, the North Atlantic basin also had to be excluded, because all twelve models failed the performance assessment. A slight poleward expansion in the western North Pacific and an expansion towards the Hawaiian Islands in the eastern North Pacific is plausible in the future, while a contraction in the TC formation regions in the eastern South Indian and western South Pacific basins would reduce the Australian region TC formation area. More than half the models were too active in the eastern South Pacific and South Atlantic basins. However, projections based on the remaining models suggest these basins will remain hostile for TC formation in the future. These southern hemisphere changes are consistent with existing projections of fewer southern hemisphere TCs in a future warming world

Spatio-Temporal Dynamics of Sediment yield across the Imo River Basin South- East Nigeria

Soil and water are the two main natural resources that sustain human existence on earth. Proper monitoring and maintenance of these resources are done on basin level. The IRB drains an area of 7,951.03 km2. The basin has a mean annual discharge of 120m3/sec and generates significant surface runoff and sediment. The study aim was to evaluate the sediment yield across IRB using the Soil and Water Assessment Tool (SWAT) model. SWAT is a watershed-based, semi-distributed hydrologic model for simulating hydrological processes at different spatial scales. The model utilized digital elevation model DEM to extract the river network, basin delineation, and sub-basin division. The sub-basins were further divided into hydrological response unit HRU at a threshold of 5% slope, 5% the land use and 5% soil. Harmonized soil data and two land-use data of 1995 and 2010 were used to simulate the sediment yield across IRB. The study result shows an increase in sediment yield of 0.73 t/ha from1995 to 2010. Sub-basin 10 has the highest sediment yield during the two periods; September and October are the months with the highest sediment yield.

Volcanic reconstruction and geochemistry of the Powderhouse formation in the Paleoproterozoic VMS-hosting Chisel sequence, Snow Lake, Manitoba, Canada

The Powderhouse formation of the Paleoproterozoic Snow Lake arc assemblage comprises the stratigraphic footwall to six volcanogenic massive sulfide (VMS) deposits at Snow Lake, Manitoba, Canada. It is interpreted to be a product of voluminous pyroclastic eruptions and concomitant subsidence followed by a period of relative volcanic quiescence that was dominated by suspension sedimentation, the reworking of previously deposited pyroclastic units by debris flows and bottom currents, and localized emplacement of rhyolite domes. The rhyolite domes are spatially associated with the Chisel, Chisel North, Lost, Ghost, Photo, and Lalor deposits. The Chisel, Lalor, and Lost members compose the Powderhouse formation and are subdivided into 13 lithologically distinct lithofacies, which allows, for the first time, correlation of stratigraphy between the South Chisel basin and Lalor areas, critical in predicting the location of largely stratiform VMS deposits. The Chisel and Lalor members contain lithofacies and bedforms that are characteristic of emplacement by subaqueous pyroclastic mass flows and concomitant subsidence. The Chisel member also contains coarse volcaniclastic breccias emplaced by mass debris flows derived from movement along fault scarps following early pyroclastic eruptions, and during continued subsidence. The Lost member consists of lithofacies deposited by mass flows generated from faults scraps during continued subsidence, but also contains lithofacies reworked by bottom currents, those deposited by suspension sedimentation, and, locally, coherent rhyolite. The Lost member represents a time stratigraphic interval, the “ore interval”, that marks contemporaneous rhyolite dome emplacement, VMS formation, and a hiatus in explosive volcanism.

Stressed from above and stressed from below: dissolved oxygen fluctuations in Lough Hyne, a semi-enclosed marine lake

AbstractDissolved oxygen (DO) concentrations of the fully marine Lough Hyne, SW Ireland, were sampled in biologically different habitats between 2014 and 2019 to investigate the declining water quality in the marine reserve and the severity of oxidative stress on benthic communities. DO was measured above and below shallow subtidal rocks, in the Rapids connection to the Celtic Sea, in seagrass meadows (Zostera marina), and at various water depths (1–15 m) in the South Basin. DO values above rocks were normoxic to hyperoxic in daytime (7.8–17.3 mg l−1); below rocks were often hypoxic (0.24–2 mg l−1). South Basin sites experienced hypoxia less often than the North Basin, except for the Goleen, presumably due to differential current flow. DO fluctuations occurred in spring (before ephemeral macroalgae proliferate), summer (when algal mats smother the benthos), and autumn (when macroalgae decay). While the Rapids were normoxic, the seagrass meadows below them exhibited periodic DO stress. Labhra Cliff (9–14.5 m) was normoxic to hyperoxic in autumn but experienced suboxic and hypoxic events in summer. Many organisms in Lough Hyne are experiencing periods of hypoxia below their published sublethal limits, the effects of which could be exacerbated by periodic hyperoxia.

The Ust’-Barguzin Transfer Zone (Central Baikal): Seismological Evidence on the Transtensive Stress Field of the Crust

According to seismological and geodetic data, the central part of the South Baikal basin is under an extension regime of the Earth’s crust. This study presents for the first time seismological evidence of a transtensive stress field in a local area adjacent to the eastern side of the Central Baikal subbasin. Two independent approaches to determining the orientation of the principal stress axes show a subhorizontal orientation of the axes of stresses of minimum and maximum compression, which results in a strike–slip component in the focal mechanisms of the earthquakes. The area under consideration is a part of the Ust’-Barguzin transfer zone, in which the transfer of deformations between South Baikal and the Barguzin basin takes place. The results obtained are in agreement with the geological and structural data and may indicate the contribution of horizontal displacements in the transfer of deformations between the segments of the rift zone.

Structural controls on the location, geometry and longevity of an intraplate volcanic system: the Tuatara Volcanic Field, Great South Basin, New Zealand

Intraplate volcanism is widely distributed across the continents, but the controls on the 3D geometry and longevity of individual volcanic systems remain poorly understood. Geophysical data provide insights into magma plumbing systems, but, as a result of the relatively low resolution of these techniques, it is difficult to evaluate how magma transits highly heterogeneous continental interiors. We use borehole-constrained 2D seismic reflection data to characterize the 3D geometry of the Tuatara Volcanic Field located offshore New Zealand's South Island and investigate its relationship with the pre-existing structure. This c . 270 km 2 field is dominated by a dome-shaped lava edifice, surrounded and overlain by c . 69 volcanoes and >70 sills emplaced over 40 myr from the Late Cretaceous to Early Eocene ( c . 85–45 Ma). The Tuatara Volcanic Field is located above a basement terrane boundary represented by the Livingstone Fault; the recently active Auckland Volcanic Field is similarly located along-strike on North Island. We suggest that the Livingstone Fault controlled the location of the Tuatara Volcanic Field by producing relief at the base of the lithosphere, thereby focussing lithospheric detachment over c . 40 myr, and provided a pathway that facilitated the ascent of magma. We highlight how observations from ancient intraplate volcanic systems may inform our understanding of active intraplate volcanic systems, including the Auckland Volcanic Field. Supplementary material: Interpreted seismic section showing well control on stratigraphic interpretation is available at https://doi.org/10.6084/m9.figshare.c.5004464

Diverse provenance of the Lower Cretaceous sediments of the Eromanga Basin, South Australia: constraints on basin evolution

This study presents new geochemical and mineralogical data collected on 13 drill holes across the South Australian part of the Eromanga Basin, with a focus on the Lower Cretaceous Cadna-owie Formation, Bulldog Shale, Coorikiana Sandstone and Oodnadatta Formation. Mineralogical and geochemical data are used to determine the provenance of the sediments along with the paleoenvironments at the time of deposition. The dominant clay species across the formations are kaolinite and montmorillonite, although each drill hole shows individual mineralogical assemblages. The Cadna-owie Formation is mainly composed of quartz and kaolinite; montmorillonite is the dominant clay species in the other formations. Differences in major-element chemistry are best shown on the K–Na–Ca ternary diagram and display a strong relationship with mineralogy. Trace and rare earth elements are preserved at similar average concentrations between formations and are depleted relative to the upper continental crust. The signature of the sediments is interpreted to be derived from a mix of felsic and mafic igneous rocks with almost no sedimentary recycling. Sources of the sediments are likely to be from exposed basement packages surrounding the study area such as the Gawler Range Volcanics, the Musgrave Province, the Benagerie Volcanic Suite, the Mount Painter Inlier and the Arunta Block. The variations in dominant clay species between the formations could have been driven by an increase in temperature and a decrease in rainfall during the Early Cretaceous along with seasonal variations, and/or by the input in volcanogenic sediments from the active volcanoes located along the eastern margin of Australia. KEY POINTS Lower Cretaceous formations in the South Australian Eromanga Basin show limited regional lateral and vertical geochemical and mineralogical variations. Sediments are a mix of mafic through felsic igneous rocks derived from basement terranes exposed in the Early Cretaceous. The paleoclimate during deposition evolved from cold and humid to warm and arid.

Anomalous geochemical fields of ore elements of the South Tatarian sedimentary basin (Tatar Strait, Sea of Japan)

Introduction. Currently, sea territories for production and exploration of hydrocarbon raw materials and ore deposits have been increased. Geochemical survey of seafloor sediments is of great interest among direct methods for finding deposits. One of the most important objects for such work is the Tatar Strait, in the territory of which high concentrations of useful elements can be found. Purpose of the work: to study the geochemical characteristics of seafloor sediments of the South Tatarian sedimentary basin in order to identify possible ore fields within its territory. Methods and materials. The chemical composition of seafloor sediments was analyzed, according to which maps of geochemical fields were constructed using the ArcGis program. The results of the chemical assays are obtained from the Delta Olympus X-ray fluorescent spectrometer. The number of samples obtained is 62. Results. The contents and redistribution of 21 chemical elements on the studied area were studied. Only five elements have geochemical anomalies or elevated contents that may indicate possible ore deposits: Ti, Zr, Mn, V, S. The main zones of concentration of these elements are in the shelf and bathyal areas. The characteristics of distribution of these elements over the area of the South Tatarian sedimentary basin are given and anomalous geochemical fields are identified. Conclusions. The presence of geochemical indicators of placers of titanium raw materials confined to the river fans of the Tokhtinka, Zhulman, Nemi, Ptichya and to the mechanical barrier in the region of Sovgavan uplift has been established. Promising zones of hydrocarbon concentration due to the high sulfur contents in the zone of the dynamic influence of faults (mainly fissure displacement) along the boundaries of the Terneysky trough in its western and eastern regions have been identified.

Geological structure of South Caspian depression and onshore of Azerbaijan based on temperature data and gravimetric modelling

The paper aims to justify the thickness of sedimentary cover along the aquatory of South Caspian basin and Azerbaijan onshore (including South and Middle Kur basin and Yevlakh-Aghjabedy downfall), the cover thickness of crystalline basement, specifying its structural position and key tectonic borders, as well as the confirmation of some issues on geodynamic evolution. Such comparison was carried out via published seismic temperature, gravimetric and magnitometric data. Definite dependences of geothermal gradients, the thickness of sedimentary cover and crystalline basement depth have been specified.

The Neoproterozoic Andrelândia group: Evolution from an intraplate continental margin to an early collisional basin south of the São francisco craton, Brazil

New U–Pb and Lu–Hf zircon data for the Andrelândia Group are presented and discussed with the previously published data to propose an evolutionary model. The Andrelândia Group consists of two depositional sequences that record the geotectonic evolution from Tonian to Ediacaran times. Both sequences are part of the Andrelândia Nappe System, a fold-and-thrust system, generated in the 630-600 Ma interval, during the evolution of the Neoproterozoic convergence in the interference zone between the Southern Brasília and the Ribeira orogens, SE Brazil. The Andrelândia Group rocks record greenschist to granulite facies metamorphism related to this convergence. The lower sequence consists of paragneiss, metapelite, quartzite, metachert, calc-silicate and mafic rocks distributed in five lithofacies associations. They record shallow to deep water sedimentation coeval with mafic magmatism at the southern border of the São Francisco Craton. U–Pb data obtained from detrital zircon grains of deep water quartzites indicate a maximum depositional age of ca. 970 Ma. The U–Pb age peaks can be correlated to major events in the adjacent São Francisco paleocontinent. εHft isotopic signature obtained in this study shows a predominance of juvenile sources for the Mesoproterozoic and crustal reworking and juvenile additions for the Paleoproterozoic. This can be related to source rocks from the Espinhaço Supergroup and from the Mineiro Belt, respectively. We interpret our data together with previous published detrital zircon data and whole-rock εNdt signatures to suggest that the lower sequence of the Andrelândia Group is related to a passive margin of the São Francisco paleocontinent with a platformal and a deep water succession with roughly similar sources, indicating likely a resedimentation process. The upper sequence of the Andrelândia Group consists of a monotonous package of biotite schist interpreted as metamorphosed plagioclase sandstones and siltstones. The upper sequence covers the lower sequence units unconformably. Deposition occurred in a relatively deep and fast subsiding basin during the early collisional stage of the southern Brasília Orogen. Previously published U–Pb, Sm–Nd and Lu–Hf data for the upper sequence constrain likely sources in the southern São Francisco Craton and possibly in the early stages of the Neoproterozoic Socorro-Guaxupé arc, established at the eastern margin of the Paranapanema paleocontinent, which collided with the São Francisco paleocontinent during West Gondwana assembly.

Marginal basins of the NW Pacific and Eastern Eurasia

ABSTRACT The broad zone between old oceanic lithosphere of the NW Pacific and Eastern Eurasian continental lithosphere is home to a chain of marginal basins. Different from oceans, marginal basins are more influenced by the underlying subduction zone both geophysically and geochemically and are more likely to be blanketed by sediments from the nearby continent. This special issue collects 19 papers that explore the tectonic, magmatic, sedimentary and fluid activity features of marginal basins during rifting, spreading and post-spreading stages. Most papers in this special issue focus on South China Sea marginal basins, where abundant research provides interesting insights into how marginal sea basins evolve. Because South China Sea basins are fully evolved and their key features have not been overprinted by younger deformation, the results of this special issue are very useful for understanding the evolution of other marginal basins.

A Paleoproterozoic nappe on Meso-Archean gneisses exhumed by a Cretaceous metamorphic core complex in northeastern North China Craton

The Paleoproterozoic Jiao-Liao-Ji Orogenic Belt provides key evidence of evolution from an early rift-basin (or back-arc basin) to final collision of the Longgang block (Eo-Meso Archean granitic gneiss) and the Nangrim block in the Liaodong peninsula, northeastern North China Craton. A structural investigation of schists and phyllites in the Langzishan Formation of the North Liaohe Group reveals two new major structures: (1) a sub-horizontal nappe on Meso-Archean granitic gneiss belonging to a ~ 1.95–1.9 Ga Paleoproterozoic D1-2 fold-thrust system produced by terminal collision; From the south basin to the north basement, the metamorphic gradient transferred from greenschist facies metamorphism into amphibolite facies produced by crustal thickening in the Paleoproterozoic orogenesis; the intensity of deformation was also increasing from south to north, the pure shearing style changed into simple shearing. (2) A metamorphic core complex (The Gongchangling metamorphic core complex) formed during Cretaceous extension and doming enabled delamination and diapiric rise and exhumation in the core complex. This extensional-delamination event affected a wide area of the orogenic belt, as part of the delamination of the northeastern half of the North China Craton. This is the first example of the Paleoproterozoic thrust-nappe tectonics exhumed and preserved by Cretaceous diapirism in northeast China.

Late Mio-Pliocene landscape evolution around the Chaka Basin in the NE Tibetan Plateau: Insights from geochemical perspectives

The present NE Tibetan Plateau is characterized by a rugged mountain range and basin landforms. Knowledge of the landscape evolution, as recorded by basin sediments, will help to understand the growth history of the NE Tibetan Plateau. Our present contribution targeted the Neogene Chaka Basin south of the Qinghai Nan Shan and reports 40 geochemical Sr, Nd, trace element, and rare earth element (REE) results of the sediments. Values of εNd vary from −15.6 to −11.6 for all samples, but εNd is higher for samples younger than 5.5 Ma. 87Sr/86Sr ratios are all between 0.71441 and 0.71844, with the variation becoming less after 4.5 Ma. Little variation in the SrNd isotopes and in the REE trend indicates that the source regions have very similar geochemical features. The contribution of aeolian loess into the basin sediments after ~3.5 Ma is also speculated from the trace element and REE results. These geochemical results reveal a change in the source region to the Qinghai Nan Shan around 4.5–5.5 Ma, which is consistent with previous lithoface evidence. Since ~3.5 Ma, landscape and topographic relief were further developed; thus, aeolian loess was deposited onto the fluvial fans south of the Qinghai Nan Shan, while global cooling and aridification began to dominate. Collectively, our present geochemical study of the Chaka Basin sediments reveals stages of landscape evolution in NE Tibet since the late Miocene.

Effect of precipitation-influenced river influx on Lake Biwa water levels: time scale analysis based on an impulse response function

ABSTRACT Lake water levels fluctuate at time scales ranging from minutes to many years. While extensive research has been devoted to seasonal and multiannual time scales, we examined water level changes at time scales of minutes to hours. By applying impulse response functions to Lake Biwa and its catchment, we demonstrated that it is possible to (1) identify the effects of natural oscillations governed by the shape of the lake, (2) determine the precipitation retention time at the surface (above the impermeable layer) of the catchment, and (3) estimate how long it takes precipitation falling in catchment areas to reach the lake. Between 2010 and 2012 we recorded water levels at high frequency in the South Basin of Lake Biwa and calculated response functions between precipitation and water levels. We categorized the delay time determined from the calculated response functions as direct precipitation on the lake, seiches, and river inflow (surface flow, return inflow). We then identified the runoff patterns of surface and return flows by considering the time scale of the delay. The method used in this study enables flood predictions in cases involving heavy rain and appropriate planning of preventive measures against flood damage. These results will be valuable for the development of management strategies to respond to climate change in lake catchment systems.

Tracing lake pollution, eutrophication and partial recovery from the sediments of Windermere, UK, using geochemistry and sediment microfabrics

Many lakes undergo anthropogenically driven eutrophication and pollution leading to decreased water and sediment quality. These effects can enhance seasonally changing lake redox conditions that may concentrate potentially toxic elements. Here we report the results of a multi-method geochemical and sediment microfabric analysis applied to reconstruct the history of cultural eutrophication and pollution of the North and South Basins of Windermere, UK. Eutrophication developed from the mid-19th to the earliest 20th centuries. Enhanced lake productivity is indicated by increased sedimentary δ13C, and increased pollution by a higher concentration of metals (Pb, Hg, and As) in the sediment, likely enhanced by incorporation and adsorption to settling diatom aggregates, preserved as sedimentary laminae. In the South Basin, increasing sediment δ15N values occur in step with Zn, Hg, and Cu, linking metal enrichment to isotopically heavy nitrate (N) from anthropogenic sources. From around 1930, decreases in Mn and Fe-rich laminae indicate reduced deep-water ventilation, whereas periods of sediment anoxia increased, being most severe in the deeper North Basin. Strongly reducing sediment conditions promoted Fe and Mn reduction and Pb-bearing barite formation, hitherto only described from toxic mine wastes and contaminated soils. From 1980 there was an increase in indicators of bottom water oxygenation, although not to before 1930. But in the South Basin, the continued impacts of sewage are indicated by elevated sediment δ15N. Imaging and X-ray microanalysis using scanning electron microscopy has shown seasonal-scale redox mineralisation of Mn, Fe, and Ba related to intermittent sediment anoxia. Elevated concentrations of these metals and As also occur in the surficial sediment and provide evidence for dynamic redox mobilisation of potentially toxic elements to the lake water. Concentrations of As (up to 80 ppm), exceed international Sediment Quality Standards. This process may become more prevalent in the future with climate change driving lengthened summer stratification.