Variations In Sedimentation Rate Research Articles

Sedimentation Pattern and its Controlling Factors in Indian Lakes

Sedimentation in lakes occurs from the time of its formation and continues till the final deposition. The rate of sedimentation varies depending upon climate, geology, soil cover and relief. In the present study, an attempt has been made to investigate the distribution and variation of sedimentation rate in Indian lakes. For this purpose, Indian lakes are classified into three zones viz., North Indian lakes (NIL), Central Indian lakes (CIL), South Indian lakes (SIL) and 27 sampling points distributed throughout India has been considered among all three zones. Correlation of rate of sedimentation data with catchment area, surface area and lithology is done in order to understand the controlling factors, rainfall and temperature data are also taken into consideration to know the effect on the sedimentation rate. In all three zones, the highest precipitation observed 2488, 1800 and 4000 mm/yr in the Nainital lake, Chilika lake and Pookot lake, respectively and temperature fluctuations in the northern region of India is higher than the central and southern region. The results showed that the NIL have relatively higher sedimentation rate compared to the CIL and SIL due to slopy terrain, higher precipitation, temperature and lithological inconsistency in northern Indian region whereas all these factors are less effective in other two zones with a minor contribution from other independent factors. NIL have ~0.634-0.804 cm/yr and ~0.636-1.117 cm/yr more sedimentation rate than CIL and SIL, respectively.

Sedimentation rate variations of the proglacial lake (Qiangyong Co) and its implications for glacial fluctuations over the past century, southern Tibet, China<sup>*</sup>

青藏高原上分布着大量的大陆性冰川，其对区域及全球气候变化响应极其敏感.工业革命以来，随着全球升温速率加快（特别是北半球），青藏高原部分地区的冰川在近百年显著退缩.冰前湖沉积物是最直接的冰川变化记录载体之一，但其沉积速率如何响应冰川及气候变化，能否反演冰川进退过程却知之甚少.本文依据²¹⁰Pb和¹³⁷Cs限定藏南冰前湖枪勇错QY5沉积岩芯的年龄，计算出不同深度沉积物的沉积速率，且与前人（QY-3）的沉积速率进行对比，揭示了近百年来枪勇错流域冰川变化历史及其与气温之间的关系.结果表明，枪勇错QY5近百年来的平均沉积速率为0.21 cm/a，比湖心（QY-3）快2倍左右，但两者的变化基本同步，高沉积速率对应温度上升期，是冰川退缩的直接响应：（1）1900-1960年，枪勇错沉积速率整体增加且变幅较大，与1890-1950年之间西藏温度波动式升高相对应，反映枪勇冰川总体处于退缩状态；（2）1960-1985年，沉积速率低且变幅较小，同期气温下降，枪勇冰川退缩程度相对较低且保持平稳；（3）1985年以来，枪勇错沉积速率呈上升趋势，是全球增暖下冰川显著退缩的直接响应.在短时间尺度内冰前湖沉积速率所揭示的枪勇冰川变化主要受控于温度，降水量对冰川变化的影响较小，但冰川对温度变化的响应滞后5~10 a.由于全球变暖和冰川对温度响应的滞后，在未来几十年高原冰川的融化速率可能会加快，亚洲水塔将面临着新的挑战.;Continental glaciers on the Tibetan Plateau are sensitive to regional and global climate change. Since the industrial revolution, with the acceleration of global warming (especially in the Northern Hemisphere), glaciers in most parts of the Tibetan Plateau have shrunk significantly over the past century. The sediments in proglacial lakes are one of the direct record carriers of glacial fluctuations, but little is known about how their sedimentation rate (SR) responds to glacier and climate changes, particularly under the background of global warming. In this study, the ²¹⁰Pb and ¹³⁷Cs activities were used to constrain the age of a core (QY5) from Qiangyong Co in southern Tibet and to calculate the SRs of the core sediments at different depths. By comparing the SRs of the core (QY5) with those of the QY-3 core from central Qiangyong Co, the history of glacial fluctuations and its relationship with air temperature during the last century were revealed. The results show that the average SR of upstream of Qiangyong Co (QY5) is 0.21 cm/a, about double of the centre of the lake (QY-3), but with the same patterns. High SRs are corresponded to warm temperatures, as a direct response to the glacial retreat within the Qiangyong catchment: (1) from 1900s to 1960s, the SR of Qiangyong Co increased and fluctuated greatly as a result of the glacial retreat, corresponding to increased temperature in Tibet between 1890s and 1950s; (2) during 1960s-1985 when temperature decreased, the SR was low and stable, indicating stable Qiangyong glacier; (3) since 1985, the SR in Qiangyong Co increased gradually, as a direct response to glacier retreat under the acceleration of the global warming. Over a short time scale, the change of the Qiangyong glacier revealed by the SR in the proglacial lake is mainly controlled by air temperature, rather than by precipitation. However, there is a 5 to 10 years delay of glacier retreat to increased temperature. Due to global warming and the delayed response of glacier retreat to temperature, the melting rate of the Qiangyong glacier may accelerate in the next decades, and the Asian water tower will face a new challenge.

Numerical Characterization of Cohesive and Non-Cohesive ‘Sediments’ under Different Consolidation States Using 3D DEM Triaxial Experiments

The Discrete Element Method has been widely used to simulate geo-materials due to time and scale limitations met in the field and laboratories. While cohesionless geo-materials were the focus of many previous studies, the deformation of cohesive geo-materials in 3D remained poorly characterized. Here, we aimed to generate a range of numerical ‘sediments’, assess their mechanical response to stress and compare their response with laboratory tests, focusing on differences between the micro- and macro-material properties. We simulated two endmembers—clay (cohesive) and sand (cohesionless). The materials were tested in a 3D triaxial numerical setup, under different simulated burial stresses and consolidation states. Variations in particle contact or individual bond strengths generate first order influence on the stress–strain response, i.e., a different deformation style of the numerical sand or clay. Increased burial depth generates a second order influence, elevating peak shear strength. Loose and dense consolidation states generate a third order influence of the endmember level. The results replicate a range of sediment compositions, empirical behaviors and conditions. We propose a procedure to characterize sediments numerically. The numerical ‘sediments’ can be applied to simulate processes in sediments exhibiting variations in strength due to post-seismic consolidation, bioturbation or variations in sedimentation rates.

Effects of changing phytoplankton species composition on carbon and nitrogen uptake in benthic invertebrates

AbstractPelagic primary production is the main input of organic energy for benthic production below the photic zone. In the Baltic Sea, spring phytoplankton blooms are dominated by diatoms that sink out rapidly and export nutritionally favorable matter to benthic secondary production, while the summer blooms have more variable sedimentation rates and nutritional profile. Changes in phytoplankton species composition and bloom dynamics, as a consequence of climate change and eutrophication are reducing high quality diatoms reaching the benthic fauna, while promoting cyanobacteria. Here, we test uptake and assimilation of changing phytoplankton composition for three common benthic invertebrates, a clam, an amphipod and a polychaete under varying degrees of spring‐bloom associated diatoms (Skeletonema costatum) and summer‐bloom associated cyanobacteria (Nodularia spumigena). The phytoplankton were labeled with stable isotopes (15N and 13C, respectively) in order to trace assimilation in consumers' tissues. We found that all three macrofauna species fed on both diatoms and cyanobacteria. A linear pattern was found for all three species in assimilation of carbon and nitrogen from diatoms, with increasing assimilation associated with higher proportion of diatoms. There was no clear pattern found between proportion of cyanobacteria and assimilation of carbon and nitrogen for any of the species. This study shows that the investigated macrofaunal species display a selective feeding behavior with preference for spring‐bloom associated diatoms. Thus, changes in phytoplankton bloom composition are likely affecting benthic species composition and production.

Revealing soil erosion characteristics using deposited sediment sources in a complex small catchment in the wind-water erosion crisscross region of the Chinese Loess Plateau

Sediment sources in catchments under the control of check dams in the wind-water erosion crisscross region are more complicated compared to other regions on the Chinese Loess Plateau. This is due to their general complexity, which mainly results from variation in soil, landform, vegetation, and erosion agents. Accordingly, we used the composite fingerprinting approach to trace sediment sources in a typical small catchment in this region. The aim was to reveal the erosion characteristics of the catchment throughout the trapping history of the check dam. Sediment sources were classified into three-source (paleosol, loess and sand) and four-source (paleosol-gully, loess-gully, slope bare of sand and slope covered by sand) groups on the basis of soil and landform types, respectively. Sediment sources throughout the whole trapping history of the check dam (1978–2010) could be classified into three stages according to variation in sedimentation rate. Results showed that depositional sediment in the check dam was primarily from gullies (averaging 80.1%), especially the paleosol-gully (>54.1%). The large contribution of gullies indicated that the main erosion agents were streamflow from rainstorm events and gravity. Coal mining also had a significant impact on contribution of sediment sources, especially for slopes. Since 1987, mining began to change the structure of hills in this region, leading to slope fissures, collapse, and landslides at junctions where gullies meet slopes, which increased the risk of slope erosion. This has caused an increase in sediment from slopes bare of sand distributed under condition of continues implementation of soil conservation measures, which converted sloping cropland into grassland or forest. Further studies are necessary to gain better insight into sediment transport and deposition within such complex environments, as well as to distinguish between the effects of multiple erosion agents.

10 Myr evolution of sedimentation rates in a deep marine to non‐marine foreland basin system: Tectonic and sedimentary controls (Eocene, Tremp–Jaca Basin, Southern Pyrenees, NE Spain)

AbstractThe propagation of the deformation front in foreland systems is typically accompanied by the incorporation of parts of the basin into wedge‐top piggy‐back basins, this process is likely producing considerable changes to sedimentation rates (SR). Here we investigate the spatial‐temporal evolution of SR for the Tremp–Jaca Basin in the Southern Pyrenees during its evolution from a wedge‐top, foreredeep, forebulge configuration to a wedge‐top stage. SR were controlled by a series of tectonic structures that influenced subsidence distribution and modified the sediment dispersal patterns. We compare the decompacted SR calculated from 12 magnetostratigraphic sections located throughout the Tremp–Jaca Basin represent the full range of depositional environment and times. While the derived long‐term SR range between 9.0 and 84.5 cm/kyr, compiled data at the scale of magnetozones (0.1–2.5 Myr) yield SR that range from 3.0 to 170 cm/kyr. From this analysis, three main types of depocenter are recognized: a regional depocenter in the foredeep depozone; depocenters related to both regional subsidence and salt tectonics in the wedge‐top depozone; and a depocenter related to clastic shelf building showing transgressive and regressive trends with graded and non‐graded episodes. From the evolution of SR we distinguish two stages. The Lutetian Stage (from 49.1–41.2 Ma) portrays a compartmentalized basin characterized by variable SR in dominantly underfilled accommodation areas. The markedly different advance of the deformation front between the Central and Western Pyrenees resulted in a complex distribution of the foreland depozones during this stage. The Bartonian–Priabonian Stage (41.2–36.9 Ma) represents the integration of the whole basin into the wedge‐top, showing a generalized reduction of SR in a mostly overfilled relatively uniform basin. The stacking of basement units in the hinterland during the whole period produced unusually high SR in the wedge‐top depozone.

210Pb dating of recent sediments from the continental shelf of western India: factors influencing sedimentation rates.

Several cores from the continental shelf of the Arabian Sea along theIndian Coast were investigated for change in sedimentation rates duly constrained for chronology based on 210Pb and 137Cs dating techniques. The emphasis was to look for spatial and temporal variation in the sedimentation rate along the continental shelf of eastern Arabian Sea between Goa to Kochi for water depth ≤ 150m. This study showed varying sedimentation rates in coastal and distant sediment cores. Both 210Pb and 137Cs dating techniques showed comparable sedimentation rate in most sediment cores. The sedimentation in the continental shelf region of the coastal Arabian Seais primarily controlled by discharge of sediments from rivers during Indian summer monsoon. Increased sedimentation rate from the north (off Goa) to the south (off Kochi) wastriggered by high riverine flux and longshore sediment transport.

Interplay of eustatic, tectonic and autogenic controls on a Late Devonian carbonate platform, northern Canning Basin, Australia

AbstractFrasnian reef complexes along the northern margin of the Canning Basin in northwestern Australia evolved during rifting of the Fitzroy Trough. Geological investigations of the Frasnian Hull platform, which developed on an active tilted fault‐block, reveal significant lateral and vertical facies variations superimposed on prominent metre‐scale cyclicity. This study uses numerical analyses of facies and magnetic susceptibility data from three measured sections along the Hull platform to test whether a tectonic signal can be distinguished from eustatic and other signals.Geostatistical analysis of facies variations reveals an exponential distribution of thin (<3 m) facies, characteristic of stochastic depositional processes. Thick subtidal facies predominate in the Guppy Hills (GH) and southeastern Hull Range (SHR) sections near the hangingwall margin, and thick shallow‐subtidal to intertidal facies dominate the Horse Springs drillcore (HD 14) section near the footwall margin. Power and wavelet spectral analyses indicate a strong periodic component; Average Spectral Misfit and spectral optimisation methods confirm the presence of Milankovitch eccentricity signals and suggest the presence of obliquity and precession signals. However, the results also expose strong temporal and spatial variation providing evidence for tectonic control. Spectral analyses show strongest periodicity is recorded in short intervals that are not correlated across the platform and provide evidence of variations in sedimentation rate and hiatuses. Time series for the neighbouring GH and SHR sections show no overall statistical correlation, and Markov analysis indicates weakly ordered vertical facies transitions that do not correlate across the platform. Subtidal to intertidal facies data from HD 14 core suggest that at least 35% of the section is absent, almost obscuring the Milankovitch signal. The results indicate a complex set of controls on deposition on the Hull platform with local tectonic effects having produced spatio‐temporal moderation of the underlying eustatic signals and autogenic processes adding a localised stochastic response.

Sr-isotope stratigraphy (87Sr/86Sr) of the lowermost Toarcian of Peniche, Portugal, and its relation to ammonite zonations

At Peniche, Portugal, the GSSP for the base of the Toarcian and in a Submediterranean province, a value of 0.707 073 ± 0.000 002 (2s.e., n = 13) is determined for 87Sr/86Sr at the base of the Toarcian. In Yorkshire, UK, a Subboreal province, the base of the Toarcian has an 87Sr/86Sr value of0.707 072 ± 0.000 002 (2s.e., n = 23). The similarity of the values shows that, within analytical uncertainty, these levels are exactly equivalent in time. At Peniche, the base of the Serpentinum (Falciferum/Levisoni) Chronozone has an 87Sr/86Sr value of 0.707 096 ± 0.000 003 (2.s.e). The value for this boundary in Yorkshire is 0.707 094 ± 0.000 002 (2s.e., n = 27). The similarity of the values shows that, within analytical uncertainty, these levels are exactly equivalent in time. The same ammonite successions occur through the lowermost Toarcian successions at Peniche and in Yorkshire. Between Peniche and Yorkshire, there is therefore an exact coincidence, within measurement uncertainty, between the Lower Toarcian, Tethyan Realm, Tenuicostatum (Polymorphum) [ammonite] Chronozone of Peniche and the Lower Toarcian, Boreal Realm, Tenuicostatum [ammonite] Chronozone of Yorkshire. The 87Sr/86Sr profile through the Tenuicostatum Subchronozone at Peniche reveals large variations in sedimentation rate, with lowest rates in a condensed basal 3 m of the zone, highest rates in mid-zone, with rates decreasing upward through the upper half of the zone. Apportioning time in proportion to 87Sr/86Sr shows that around half of Tenuicostatum time is condensed into the basal 3 m of the section.

Paleomagnetic Constraint of the Brunhes Age Sedimentary Record From Lake Junín, Peru

Normalized remanence, a proxy for relative geomagnetic paleointensity, along with radiocarbon and U-Th dates, facilitates the generation of a well-constrained chronology for sediments recovered during International Continental Scientific Drilling Program (ICDP) coring of Lake Junín, Peru. The paleomagnetic record of the ~88 meter stratigraphic section from Lake Junín was studied, and rock magnetic variability constrained, through analysis of 109 u-channel samples and 56 discrete samples. Downcore variations in sediment lithology reflect climate and hydrological processes over glacial-interglacial time frames and these changes are strongly reflected in the bulk magnetic properties. Glacial sediments are characterized by higher detrital silt content, higher magnetic susceptibility and magnetic remanence values, and a magnetic coercivity that is characteristic of ferrimagnetic (titano)magnetite and/or maghemite. Interglacial sediments and low lake-level facies are dominated by carbonate lithologies and/or peat horizons that result in lower magnetic concentration values. Sediments with moderately high NRM intensity (>1 x 10-3 A/m) have well-resolved component directions and inclination values that vary around geocentric axial dipole expectations. This remanence value can be used as a threshold to filter the lowest quality paleomagnetic data from the record. Normalized NRM intensity values are also sensitive to lithologic variability, but following NRM remanence filtering, only the highest quality ferrimagnetic dominated data are retained which then show no coherence with bulk magnetic properties. Constrained by the existing radiocarbon based chronology over the last 50 kyrs and 18 U-Th ages that are restricted to five interglacial sediment packages, filtered normalized remanence parameters compare well with global relative paleointensity stacks, suggesting relative variations in geomagnetic intensity are preserved. By adjusting the existing age-depth model we improve the correlation between the Junín normalized intensity record and a well-dated RPI stack and RPI model. We then incorporate these paleomagnetic tie points with the existing radiometric dates using a modeling approach to assess uncertainty and refine the age-depth model for Lake Junín. In combining relative and radiometric dating, the new age-depth model captures glacial-interglacial variations in sedimentation rate and improves the orbital-scale age model for the sediments accumulated in Lake Junín basin over most of the Brunhes.

A Numerical Model to Estimate the Effects of Variable Sedimentation Rates on Methane Hydrate Formation—Application to the ODP Site 997 on Blake Ridge, Southeastern North American Continental Margin

AbstractSedimentation and burial rate can vary considerably at continental slopes, due to constantly changing tectonic processes on the geological timescale. This variation may affect the transport of methane in sediment, as manifested in the change of pore water flux, methanogenesis, methane diffusion and hydrate removal from hydrate stability zone (HSZ) and further affect the accumulation of hydrate in submarine sediments. Most of previous models assumed a constant sedimentation rate and thus may result in inaccurate estimates of total amount of hydrate within the HSZ. In this study, we developed a hydrate accumulation model that is capable of handling multiple sedimentation stages. Site 997 of ODP Leg 164, with data indicating its recent history of four sedimentation stages of different rates, is chosen to investigate the significance of sedimentation rate variation experienced at this location. We examined the effect of varying sedimentation rates on hydrate accumulation by taking in consideration sediment compaction, in situ methanogenesis, and composition and component transport processes. Simulation results suggest that the history of hydrate accumulation at Site 997 is characterized by a sequence of increase, decrease, and then increase till the present day. At present, the hydrate deposit has accumulated to 8.30 × 104 mol/m2, and the average hydrate saturation near the base of the HSZ is 6.3%, which is in general agreement with published estimates in the literature. The accumulation of hydrate at Site 997 was significantly affected by variable sedimentation rates, and nearly one half of the hydrate deposit was accumulated during the last 2.5 Myr.

Trace metal elements as paleoenvironmental proxies: Why should we account for sedimentation rate variations?

Abstract Trace metal elements (TMEs) are commonly used to reconstruct the environmental conditions present during the deposition of organic-rich sediments. For example, TME concentrations controlled by changes in primary productivity and redox conditions are widely used in paleoenvironmental studies. Recently, these proxies have undergone a resurgence of interest and are commonly used in large-scale (10–1000 km) studies. However, applying these geochemical proxies at basin scale while ignoring variations in sedimentation rates (SR) may lead to misinterpretation of paleoenvironmental conditions. Here, we show how SR can affect the geochemical records and may lead to incorrect interpretations of TME evolution. Accounting for SR, we computed the authigenic fraction accumulation rates of key TMEs in the Upper Montney Formation and Doig Phosphate (Triassic, western Canada), and we correct the concentration of these elements in the Vaca-Muerta Formation (Jurassic–Cretaceous, Argentina). Our SR-corrected TME proxies require a different interpretation of paleoenvironmental conditions (e.g., primary productivity, basin restriction) compared to conventional TME results and highlight that elementary enrichments commonly interpreted as indicative of anoxic depositional environments may reflect low SR and the formation of condensed intervals. This work also introduces a new workflow to account for SR in paleoenvironmental studies at basin scale and over long time periods.

Beyond redox: Control of trace-metal enrichment in anoxic marine facies by watermass chemistry and sedimentation rate

Although redox conditions are the dominant control on authigenic enrichment of trace metals in marine sediments, other factors may be important within environments having relatively uniform redox characteristics, such as some anoxic silled basins. Notably, watermass chemistry (specifically, aqueous trace-metal concentrations) and sedimentation rate can also influence the authigenic accumulation of redox-sensitive trace metals such as molybdenum (Mo) and uranium (U) in the sediment, although these effects have received less attention than redox controls to date. Here, we (1) utilize a diffusion-reaction model to evaluate the effects of variations in watermass chemistry and sedimentation rate on authigenic trace-metal enrichment, and (2) present case studies of Mo and U enrichment in modern Black Sea sediments and North American Devonian-Carboniferous boundary (DCB) black shales that illustrate these influences. In both case studies, redox conditions were assessed using non-trace-metal-based proxies (i.e., C-S-Fe, FeT/Al, and Corg:P). Stations 6 and 7 of the modern Black Sea, at water depths of 380 and 1176 m, respectively, exhibit marked differences in authigenic Mo and U enrichment: median Mo/TOC is 13.2 at Station 6 (range 11.5–14.8) versus 5.7 at Station 7 (range 3.7–7.6), and median U/TOC is 2.6 at Station 6 (range 1.5–3.0) versus 1.3 at Station 7 (range 0.7–1.9) (note: units are ppm/% or 10−4, and ranges are 16th-84th percentiles). Given the nearly identical redox conditions and sedimentation rates at these two sites, the most likely cause of the >2× enrichment of Mo and U at Station 6 relative to Station 7 is differences in aqueous Mo and U concentrations, which decline steeply through the upper part of the Black Sea water column, demonstrating the influence of watermass chemistry on patterns of authigenic trace-metal enrichment in the sediment. For the DCB black shales, the median Mo/TOC is 22.2 in the Lower and Upper Bakken (range 15.8–27.0), 28.8 in the Sunbury (range 19.2–37.2), and 14.3 in the Cleveland (range 9.3–22.5), and the median U/TOC is 6.2 in the Lower and Upper Bakken (range 3.5–9.6), 2.6 in the Sunbury (range 1.7–3.4), and 1.2 in the Cleveland (range 0.7–1.7). Differences in Mo and U concentrations between these formations show no relationship to inferred aqueous trace-metal concentrations, Mn–Fe particulate shuttles, or paleoenvironmental redox conditions, but they broadly correlate with variation in sedimentation rates, providing evidence that sedimentation rates can measurably influence the degree of authigenic trace-metal enrichment of marine sediments.

Depositional and organic carbon-controlled regimes during the Coniacian-Santonian event: First results from the southern Tethys (Egypt)

Abstract Geochemical and palynological proxies were determined for 31 samples representing the upper Coniacian-lowermost Campanian Abu Roash A Member, collected from the BED2-3 well. This was done to assess the prevailing paleoredox conditions, productivity levels, and water-column settings to: (1) understand controls and mechanisms related to accumulation of organic carbon within the sedimentary record; (2) assess principal environmental processes that triggered the preservation of organic matter-poor, calcareous shale and limestone facies of the Abo Roash A Member; and (3) to interpret the paleoceanographic settings and confirm the occurrence of either Oceanic Anoxic Event 3 (OAE3) or Cretaceous Oceanic Red Beds (CORBs) within the Abu Gharadig Basin in the southern part of the Tethyan Ocean, Egypt. Sedimentation rates were reconstructed based on the biostratigraphic-age constraints of marine dinoflagellate cysts (dinocysts). Trace elements-based ratios and relationships were used in order to study the role of clastic terrestrial input. Three groups of dinocysts and freshwater Pediastrum algae were used to study the water-column conditions. Results showed that the Abu Roash A Member was deposited under oxic to intermittently dysoxic conditions in a distal inner to middle neritic environment, with varying sedimentation rates from 32 to 119 mm kyr−1. Productivity appeared to be a significant factor for determining magnitudes of the organic carbon accumulation; however, low productivity was prevalent during deposition. Carbonate content was high, which resulted in dilution of organic matter during varied rates of sediment input. Such results indicate that the paleoceanographic conditions in the southern Tethys witnessed the absence of prevalent oceanic anoxia (i.e., the Coniacian-Santonian OAE 3) and deposition of the CORBs as in several parts of the Tethys, the Pacific, and the Indian oceans.

Globally enhanced Hg deposition and Hg isotopes in sections straddling the Permian–Triassic boundary: Link to volcanism

Mercury (Hg/TOC) spikes from eight Permian–Triassic boundary (PTB) sections in this study display patterns similar to each other across the so-called extinction interval as well as strong variation in sedimentation rates from section to section. Mercury may have been originated from the synchronous magmatism of the Siberian Traps Large Igneous Province (STLIP).At the GSSP in Meishan, China, Hg/TOC peaks were observed in the latest Permian mass extinction interval (LPME) and Early Triassic mass extinctions (ETME). The successions at Hovea-3 (Australia), Ursula Creek (Canada), Idrijca (Slovenia), Rizvanuša (Croatia) exhibit Hg/TOC peaks at the LPME and PTB. The Rizvanuša section displays one peak at the ETME horizon, Zal and Abadeh (Iran) successions at the LPME and ETME horizons, while Misci/Seres (Tyrol/Italy) section shows an enrichment at the LPME. The largest Hg/TOC peaks at the LPME, PTB and ETME are, perhaps, linked to the beginning of stage 2 (extrusive hiatus) of the Siberian Traps LIP. The meaning of the Hg/TOC spike between the LPME event and the PTB in seven of these sections is fuzzy.In the δ202Hg (MDF) vs Δ201Hg (MIF) cross plot, the majority of samples from the extinction interval appear within the volcanic-emission box and a few samples plot in the sediment/soil/peat box. Hg-isotope signatures resulted from mixing processes of volcanic and normal marine sediment Hg, generating four horizontal trends whose Δ201Hg shows negligible to no variation. Less terrigenous-Hg influx was noticed in the sections closer to the STLIP (Rizvanuša, Idrijca and Seres/Misci, all in Europe) in which Δ201Hg (MIF) is close to zero. Marked influence occurs in sections far distant from the STLIP (Meishan, Ursula Creek and Hovea-3) that exhibit negative Δ201Hg (MIF). The two sections from Iran, at intermediate distance from the STLIP, exhibit the highest, positive Δ201Hg values (Abadeh section) and the lowest, negative Δ201Hg values (Zal section). A Δ199Hg (MIF) vs Hg (n·ng−1) cross plot suggests that volcanic Hg has been contaminated by normal marine source-Hg influx in these sections helping to shape two major curved trends.The negative C-isotope excursions and Hg/TOC enrichments in the studied sections are nearly coeval and this supports the hypothesis of synchronism between the Permian–Triassic transition biotic crises (LPME and ETME) and the start of the stage 2 of the Siberian Traps (sill-intrusion style of magmatism).

Reef-carbonate diagenesis in the Pleistocene–Holocene of the well Xike#1, Xisha Islands, South China Sea: implications on sea-level changes

The Pleistocene was characterized by an unstable meteoric–marine diagenetic environment, influenced by high-amplitude global and regional eustatic variations. This paper focuses on the diagenetic characteristics of the Pleistocene–Holocene reef-carbonate rocks in the well Xike#1, drilled on the Stone Island (part of the Xisha Islands) in the South China Sea. A petrographic, cathodoluminescence and stable isotope study allowed the evaluation of the diagenetic evolution of the reef-carbonate rocks. The rock types present include framestones, packstones, wackestones and grainstones. Rock fabric analysis reveals the existence of skeletal grains, biodetritus, intraclasts, matrix and calcite cements. The upper part of the cored interval (0–180 m) has been heavily altered by meteoric fluids. Unequivocal evidence of meteoric diagenesis includes consistently negative δ18O values, well-developed subaerial exposure horizons and typical vadose cements. The deepest exposure surface is ~ 80 m above the base of meteoric diagenesis, which means that the paleowater table could be extended to as deep as 80 m. The grainstone present at 7.74 m represents the boundary between the vadose and phreatic zones, which is marked by the first appearance of isopachous dogtooth cements and well-developed moldic pores. The reef-carbonate rocks between depths of 21.66 m and 180 m have undergone diagenesis in both meteoric and marine environments, in which the early-stage fibrous marine cements are surrounded by later meteoric drusy calcite cements. The end products of phreatic meteoric diagenesis are the limestones composed of low-Mg calcite with micrite envelopes, moldic pores, blocky spar calcite cementation, and aragonite neomorphism. The interval from 180 to 216 m has undergone a marine diagenesis, which is marked by cements with non-luminescent CL characteristic and a limited, relatively enriched C and O isotope composition. The study reveals that the diagenetic evolution of reef carbonate is mainly controlled by high-frequency eustatic sea-level changes, while the sedimentation rate variations, which were induced by regional subsidence and nutrient variations could also have had an impact on the diagenetic evolution.

Statistic and Isotopic Characterization of Deep‐Sea Sediments in the Western North Pacific Ocean: Implications for Genesis of the Sediment Extremely Enriched in Rare Earth Elements

AbstractA certain type of deep‐sea sediment exhibits very high content of rare earth elements and yttrium (REY) and is therefore expected to serve as a novel resource for these industrially essential metals. In this paper, we statistically analyzed the bulk chemical composition of deep‐sea sediments collected from the western North Pacific Ocean. By applying independent component analysis to the multielemental data set, we extracted three independent components (ICs) that can be interpreted as the influence of Mn‐oxides (IC1), REY‐enriched biogenic calcium phosphate (IC2), and possibly a diagenetic effect involving Cu enrichment (IC3) on bulk sediment geochemistry. Subsequently, we selected representative samples based on the independent component analysis result, and implemented Sr–Nd–Pb isotopic analyses of bulk sediments. The results indicate that the extremely REY‐rich mud characterized by IC2 inherits the geochemical signature of deep Pacific seawater, whereas the non‐REY‐rich mud with less diagenetic alterations, characterized by IC3, implies an influence of terrigenous dust probably from the Taklimakan desert–Chinese loess plateau. IC1 may reflect the variation in sedimentation rates. Characteristic downhole variations of IC1 and IC3 scores imply the presence of hiatus and/or erosion of the sediment column across the REY content peak. The putative cause is an enhanced bottom current, which can physically separate coarse biogenic calcium phosphate grains with very high REY content and thus produce an extremely REY‐enriched sediment layer.

Estimation of sedimentation rate of Tikvesh Reservoir in Republic of Macedonia using SWAT

The objective of this study was to perform a long-term modeling of the sedimentation rate of one of the largest reservoirs in the Republic of Macedonia, i.e., the “Tikvesh” reservoir. The developed mathematical model should serve for detailed analysis of the sedimentation rate in the reservoir over time, and if the obtained results are acceptable, it should be further developed and used in defining practices of sustainable management of the reservoir in future. For this purpose, a widely applied, semi-distributed, and process-based watershed-scale model SWAT was used. Using SWAT, the production of sediments in the watershed as well as their transport through the river network was modeled. Based on the empirically estimated reservoir trap efficiency as well as bulk density of the settled material, volumetric sediment budgeting was done, whereby the temporal distribution of the reservoir sedimentation rate was defined. The obtained results were compared with the information from several bathymetric surveys of the reservoir whereat a satisfactory match was found. The model was generated for the period extending from 1969, when the reservoir was put into operation, to 2016, when the last bathymetric survey was conducted. The period between 1969 and 1985 was used for calibration of the model, while the period from 1986 to 1991 was used for its validation. Forecast referring to the change of the deposited quantities of sediments in the reservoir was made for the period from 1992 to 2016. In the absence of reliable data from measurements done in this period, climate data generation and consequently watershed sedimentation yield estimation by using the WXGEN—weather generator—were conducted. The obtained results point to variable sedimentation rate of the reservoir in different periods, depending on the variability of the weather conditions within the watershed. The average sedimentation rate of the reservoir in the analyzed period 1969–2016 at an annual level is 0.02–1.28% of the initial volume, which is around the estimated world average amounting to 0.5–1%.

Chronostratigraphic model of a high-resolution drill core record of the past million years from the Koora Basin, south Kenya Rift: Overcoming the difficulties of variable sedimentation rate and hiatuses

The Olorgesailie Drilling Project and the related Hominin Sites and Paleolakes Drilling Project in East Africa were initiated to test hypotheses and models linking environmental change to hominin evolution by drilling lake basin sediments adjacent to important archeological and paleoanthropological sites. Drill core OLO12-1A recovered 139 m of sedimentary and volcaniclastic strata from the Koora paleolake basin, southern Kenya Rift, providing the opportunity to compare paleoenvironmental influences over the past million years with the parallel record exposed at the nearby Olorgesailie archeological site. To refine our ability to link core-to-outcrop paleoenvironmental records, we institute here a methodological framework for deriving a robust age model for the complex lithostratigraphy of OLO12-1A. Firstly, chronostratigraphic control points for the core were established based on 40Ar/39Ar ages from intercalated tephra deposits and a basal trachyte flow, as well as the stratigraphic position of the Brunhes-Matuyama geomagnetic reversal. This dataset was combined with the position and duration of paleosols, and analyzed using a new Bayesian algorithm for high-resolution age-depth modeling of hiatus-bearing stratigraphic sections. This model addresses three important aspects relevant to highly dynamic, non-linear depositional environments: 1) correcting for variable rates of deposition, 2) accommodating hiatuses, and 3) quantifying realistic age uncertainty with centimetric resolution. Our method is applicable to typical depositional systems in extensional rifts as well as to drill cores from other dynamic terrestrial or aquatic environments. We use the core age model and lithostratigraphy to examine the interconnectivity of the Koora Basin to adjacent areas and sources of volcanism.

An improved approach to age-modeling in deep time: Implications for the Santa Cruz Formation, Argentina

AbstractAccurate age-depth models for proxy records are crucial for inferring changes to the environment through space and time, yet traditional methods of constructing these models assume unrealistically small age uncertainties and do not account for many geologic complexities. Here we modify an existing Bayesian age-depth model to foster its application for deep time U-Pb and 40Ar/39Ar geochronology. More flexible input likelihood functions and use of an adaptive proposal algorithm in the Markov Chain Monte Carlo engine better account for the age variability often observed in magmatic crystal populations, whose dispersion can reflect inheritance, crystal residence times and daughter isotope loss. We illustrate this approach by calculating an age-depth model with a contiguous and realistic uncertainty envelope for the Miocene Santa Cruz Formation (early Miocene; Burdigalian), Argentina. The model is calibrated using new, high-precision isotope dilution U-Pb zircon ages for stratigraphically located interbedded tuffs, whose weighted mean ages range from ca. 16.78 ± 0.03 Ma to 17.62 ± 0.03 Ma. We document how the Bayesian age-depth model objectively reallocates probability across the posterior ages of dated horizons, and thus produces better estimates of relative ages among strata and variations in sedimentation rate. We also present a simple method to propagate age-depth model uncertainties onto stratigraphic proxy data using a Monte Carlo technique. This approach allows us to estimate robust uncertainties on isotope composition through time, important for comparisons of terrestrial systems to other proxy records.