Determination Of Sedimentation Rate Research Articles

Determination of geochronology and sedimentation rates of shallow lakes in the middle Yangtze reaches using 210Pb, 137Cs and spheroidal carbonaceous particles

Accurate chronologies for recent sediments of shallow lakes in the Yangtze floodplain are critical to calibrate proxy records for reconstructing environmental changes during the past century. This study presents the results of detailed 210Pb analysis from eight lake sediment cores collected from the middle Yangtze reaches, southeast China. Unsupported 210Pb activities generally declined exponentially with mass depth in the eight cores. The chronologies and sedimentation rates for the sediment cores were calculated using different 210Pb-based mathematical models. The 137Cs chronomarker (i.e. the 1963 fallout peak) and the spheroidal carbonaceous particle (SCP) chronomarker (i.e. the start of the rapid increase in 1970 CE) were selected to validate the 210Pb dating. Sedimentation rates derived from different models were validated using historical data including lake area, arable land area, sediment discharge and reservoir volume in the Yangtze basin. The SCP-corrected CRS (constant rate of supply) model performs better than other models, based on validation using historical documents in the Yangtze basin. The 137Cs chronomarker might be erroneous due to catchment-driven 137Cs inputs from soil erosion and post-depositional diffusion. Both SCPs and 137Cs are susceptible to inputs from catchment soil erosion, but SCPs show no apparent degradation and post-depositional changes in lake sediments. The SCP profile provides a relatively reliable chronomarker, which can be used for validating 210Pb chronologies in these floodplain lakes. Generally, sedimentation rates in the eight lakes were <0.2 g cm−2 yr−1 before the 1930s, and then increased to a peak in the 1960s. Afterwards, sedimentation rates decreased and remained low after the 1980s.

A 210Pb chronological study in sediments from poços de caldas alkaline massif (PCAM), Brazil

The Constant Flux and Constant Sedimentation (CF:CS) of supported/excess 210Pb model was successfully used to study sediment profiles from Antas stream, located in the region of Poços de Caldas city, Minas Gerais State, Brazil. Historical changes in the region were tracked from evaluating the sedimentation rate by the 210Pb method. In that site, Osamu Utsumi mine was the first mining-industrial complex for the production of concentrated uranium in Brazil. Four sediment testimonies were sampled along Antas stream in order to determine sedimentation rates using 210Pb as geochronometer. 210Pb and 238U activity concentrations were determined in sediment samples by alpha spectrometry, allowing to find the excess 210Pb present in the sediments. Additionally, the main oxides, organic matter, particles size and water composition were determined in order to assist the results interpretation from radionuclides data. The results allowed find one (profile PKS-4) or two (profiles PKS-1, PKS-2 and PKS-3) sedimentation rates, probably due to changes in the sediments input regime in the region. The sedimentation rates were in the range between 0.26 and 0.94 g/cm2.year, corresponding to the interval of linear sedimentation rate of 0.21 – 0.92 cm/year. The deposition year in the bottom of PKS-4 profile as estimated from the sedimentation rate coincided with the construction year of Bortolan dam (1956). Large touristic interventions carried out at Poços de Caldas city from 1920s coupled to unbridled urbanization, industrialization and demographic growth there in the second half of the twentieth century possibly caused the changes found in the sedimentation rates.

Examining Storage Capacity Loss and Sedimentation Rate of Large Reservoirs in the Central U.S. Great Plains

Reservoirs created by impounding sediment-laden streams infill over time, reducing storage capacity and altering water quality. Increasing freshwater demand on a limited supply is adding pressure on reservoir water storage and management across much of the western and central U.S. Determining sedimentation rates is helpful to ensure a reliable and sustainable clean water supply for drinking, irrigation and recreation purposes. In the state of Kansas, located in the central Great Plains, bathymetric surveys have been completed recently for many major state and federally constructed reservoirs. In this paper, we examine sediment infill rate and storage capacity loss for all 24 federally operated reservoirs in Kansas. As of 2016, these reservoirs have an average age of 52 years and collectively have lost approximately 17% of their original capacity, with the highest single-reservoir loss of 45%, the highest annual loss rate of 0.84%, and the highest annual sediment yield of 1688 m3/km2/year. Results from this paper provide baseline information pertinent to the development, prioritization and assessment of remediation and mitigation strategies for addressing the sediment infill problem in Kansas, with general implications for other large reservoirs across the Great Plains as well as other climatologically and ecologically similar regions around the world.

Determination of sedimentation, diffusion, and mixing rates in coastal sediments of the eastern Red Sea via natural and anthropogenic fallout radionuclides

The Red Sea is a unique ecosystem with high biodiversity in one of the warmest regions of the world. In the last five decades, Red Sea coastal development has rapidly increased. Sediments from continental margins are delivered to depths by advection and diffusion-like processes which are difficult to quantify yet provide invaluable data to researchers. Beryllium-7, lead-210 and ceseium-137 were analyzed from sediment cores from the near-coast Red Sea near Jeddah, Saudi Arabia. The results of this work are the first estimates of diffusion, mixing, and sedimentation rates of the Red Sea coastal sediments. Maximum chemical diffusion and particle mixing rates range from 69.1 to 380cm−2y−1 and 2.54 to 6.80cm−2y−1, respectively. Sedimentation rate is constrained to approximately 0.6cm/yr via multiple methods. These data provide baselines for tracking changes in various environmental problems including erosion, marine benthic ecosystem silting, and particle-bound contaminant delivery to the seafloor.

Determination of the sedimentation rate of the pollen particles of anemophilous plants growing in Western Siberia

Determination of the sedimentation rate of the pollen particles of anemophilous plants growing in Western Siberia

Anthropic influences on the sedimentation rates of lakes situated in different geographic areas

The aim of this study is to determine the effects of natural and anthropic events occurring in the last 30 years in the catchment areas of four Romanian lakes (St. Anna Lake, Red Lake, Vârşolţ Lake and Matiţa Lake) originating from four different geomorphologic areas. A total of eleven sediment cores have been processed for age and sedimentation rate determination using the 210Pb dating method. Total 210Pb was measured via alpha spectrometry by 210Po using PIPS detectors, while supported 210Pb was measured by 226Ra using HPGe detectors. Ages and sedimentation rates were calculated using the CRS model. The values of the sedimentation rates have grown multiply in the last three decades: 2.66 times in case of the St. Anna Lake (from 0.06 ± 0.01 g/cm2y to 0.16 ± 0.02 g/cm2y), up to 6.72 times in case of Red Lake (0.36 ± 0.04 g/cm2y to 2.42 ± 0.36 g/cm2y), 4.02 times in case of Vârşolţ Lake (04 g/cm2y to 1.53 ± 0.18 g/cm2y) and up to 16.18 times in case of Matiţa Lake (0.27 ± 0.03 g/cm2y to 4.37 ± 0.32).

Evaluation of Sediment Deposition in a Mediterranean Reservoir: Comparison of Long Term Bathymetric Measurements and SWAT Estimations

AbstractThis study aims to demonstrate that the SWAT model can be used to predict discharge and sediment yield values in reservoir contributing catchments helping also to define the main factors that determine sedimentation rates in semi‐arid Mediterranean environments. This aim was achieved by comparing SWAT simulation results with water flows (over 29 years) and sediment deposition (over 47 years) volumes collected (by a campaign of bathymetric surveys) in a Sicilian reservoir. The mean monthly runoff coefficient calculated for the period 1980–2008 was 0·17. The mean sedimentation volume in the reservoir during the period 1963–2009 was 51,000 m3 year−1. Field surveys and collection of spatially distributed databases of soil, topography and climate were carried out in order to characterize the contributing catchment. The SWAT model was applied to simulate sediment volumes cumulated over group of years as well as water flow volumes reaching annual and monthly the reservoir. The performance of the hydrological and erosion components of the model was evaluated by a combination of both summary and difference statistical measures after a sensitivity analysis and a calibration/validation process. The model was able to simulate observed runoff volumes at both annual and monthly scale. The mean sedimentation volume simulated by SWAT during the whole period was 8·1% lower than the value obtained by the bathymetric measurements (equal to 72·103 Mg) with very good values of the efficiency coefficient (equal to 0·91). Copyright © 2016 John Wiley &amp; Sons, Ltd.

Estimation of sedimentation rates based on the excess of radium 228 in granitic reservoir sediments

Knowledge of sedimentation rates in lakes is required to understand and quantify the geochemical processes involved in scavenging and remobilization of contaminants at the Sediment-Water Interface (SWI). The well-known 210Pb excess (210Pbex) method cannot be used for quantifying sedimentation rates in uranium-enriched catchments, as large amounts of 210Pb produced by weathering and human activities may dilute the atmospheric 210Pb. As an alternative dating method in these cases, we propose an original method based on 232Th decay series nuclides.This study focuses on an artificial lake located in a granitic catchment downstream from a former uranium mine site. The exponential decay of 228Ra excess (228Raex) with depth in two long cores yields sedimentation rates of 2.4 and 5.2 cm yr−1 respectively. These sedimentation rates lead to the attribution of the 137Cs activity peak observed at depth to the Chernobyl fallout event of 1986. The 228Raex method was also applied to two short cores which did not display the 137Cs peak, and mean sedimentation rates of 2.1 and 4.0 cm y−1 were deduced. The proposed method may replace the classical radiochronological methods (210Pbex, 137Cs) to determine sedimentation rates in granitic catchments.

Using detrital zircon U‐Pb ages to calculate Late Cretaceous sedimentation rates in the Magallanes‐Austral basin, Patagonia

AbstractDetermining both short‐ and long‐term sedimentation rates is becoming increasingly important in geomorphic (exhumation and sediment flux), structural (subsidence/flexure) and natural resource (predictive modelling) studies. Determining sedimentation rates for ancient sedimentary sequences is often hampered by poor understanding of stratigraphic architecture, long‐term variability in large‐scale sediment dispersal patterns and inconsistent availability of absolute age data. Uranium–Lead (U‐Pb) detrital zircon (DZ) geochronology is not only a popular method to determine the provenance of siliciclastic sedimentary rocks but also helps delimit the age of sedimentary sequences, especially in basins associated with protracted volcanism. This study assesses the reliability of U‐Pb DZ ages as proxies for depositional ages of Upper Cretaceous strata in the Magallanes‐Austral retroarc foreland basin of Patagonia. Progressive younging of maximum depositional ages (MDAs) calculated from young zircon populations in the Upper Cretaceous Dorotea Formation suggests that the MDAs are potential proxies for absolute age, and constrain the age of the Dorotea Formation to be ca. 82–69 Ma. Even if the MDAs do not truly represent ages of contemporaneous volcanic eruptions in the arc, they may still indicate progressive‐but‐lagged delivery of increasingly younger volcanogenic zircon to the basin. In this case, MDAs may still be a means to determine long‐term (≥1–2 Myr) average sedimentation rates. Burial history models built using the MDAs reveal high aggradation rates during an initial, deep‐marine phase of the basin. As the basin shoaled to shelfal depths, aggradation rates decreased significantly and were outpaced by progradation of the deposystem. This transition is likely linked to eastward propagation of the Magallanes fold‐thrust belt during Campanian‐Maastrichtian time, and demonstrates the influence of predecessor basin history on foreland basin dynamics.

Influence of lake basin morphology on recent sedimentation rates based on the example of Lake Raduńskie Górne, N Poland

Abstract The study relates to the use of the 210Pb method for determining sedimentation rates, sedimentation accumulation rates and identifying post-depositional processes. The analysis was based on seven cores of recent sediments collected from different parts of Lake Raduńskie Górne, which is a typical channel lake with diverse bottom morphology. We used alpha spectrometry to determine 210Pb activities in sediment samples and a CF:CS dating model to obtain mean sediment accumulation rates. The results show significant differences between coring sites with highest values in the deepest part of the lake and lowest within the shallow and flat bottom areas. The reason for such a large diversity is the lake basin morphology, e.g. steep slopes and complex configuration of the lake bottom, most probably responsible for the post-depositional sediment replacements.

Recent Sedimentation Dynamics Indicated by 210Pbexc and 137Cs Records from the Subtidal Area of Bohai Bay, China

ABSTRACT Wang, F.; Zong, Y.Q.; Li, J.F.; Tian, L.Z.; Shang, Z.W.; Chen, Y.S.; Jiang, X.Y.; Yang, J.L.; Yang, B., and Wang, H., 2016. Recent sedimentation dynamics indicated by 210Pbexc and 137Cs records from the subtidal area of Bohai Bay, China. To determine sedimentation rate changes across an open marine area along the west coast of Bohai Bay, more than 50 short sediment cores were collected and analyzed with their sedimentation rates estimated by excess 210Pb (210Pbexc) and 137Cs in the sediment. The surveys enabled us to explore the relationship between sediment supply changes from the rivers and the spatial/temporal deposition patterns in the shallow marine areas. Several core records show that sedimentation rates can be overestimated by the conventional constant initial concentration model based on the 210Pbexc curves alone. The overestimation was caused by a change of 210Pbexc in the top layers of these cores and this is confirmed by comparing 210Pbexc curves with the respective 137Cs curves. This...

SEDIMENTATION RATE AND DISPERSION OF ORGANIC WASTE FROM LOBSTER CULTURE ON CAGE IN EKAS BAY, WEST NUSA TENGGARA PROVINCE

The objective of this study was to determine sedimentation rate and dispersion of organic waste from lobster culture on cage in Ekas Bay, West Nusa Tenggara Province. Measurement of sedimentation rate was conducted every month during the process of cultivation lobster. This measurement was done by setting up a sediment trap under and around the cage. The result of this study showed that sedimentation rate under the lobster cage within 270 days ranged from 14.92 to 27.33 (20.66±4.60) g/m2/day. The organic waste did not disperse far away from the cage because of the small current rate around the cage location of 0.068 to 0.2 m/s. Feces and residual feed settling velocities followed the current direction within the range of 0.0373 to 0.072 m/s with 8.50 m of water depth. According to this result, dispersion of feces particle and residual food was between 8.24 and 45.58 m from the cage. In order to prevent an accumulation of waste particle on the water bottom, the distance between cages needs to be set to at least twice of the farthest distance of particle dispersion which is 2 x 45.58 = 91.16 m or about 100 m. Keywords: sedimentation rate, waste dispersion, lobster culture, Ekas Bay

Undifferentiated spondyloarthritis is more frequently seen in women than in men

Spondyloarthritis (SpA) are a group of inflammatory rheumatic diseases that share some common clinical and genetic features such as inflammatory back pain, peripheral arthritis, enthesitis, anterior uveitis, sacroiliitis, and HLA-B27 positivity. The aim of the present study was to describe the clinical, radiologic, and genetic features of patients with undifferentiated spondyloarthritis (uSpA) and ankylosing spondylitis (AS). This study included 225 SpA patients (134 uSpA and 91 AS) attending our Rheumatology Outpatient Clinic consecutively. Patients underwent peripheral and axial joint and enthesitis assessment, erythrocyte sedimentation rate or C-reactive protein determination, HLA-B27 tissue typing, radiographic evaluation, and sacroiliac MRI. In total, 26 of 91 AS patients and 115 of 134 uSpA patients were women (28.6 vs. 85.8%) and 65 of AS and 19 of uSpA were men (71.4 vs. 14.2%). The time for diagnosis was 15.82 ± 20.7 months for AS patients and 5.91 ± 3.63 months for uSpA patients. Diagnostic delay was 102.46 ± 88.99 (median 83, range 8–377) months for AS and 74.23 ± 60.7 (median 55.5, range 0–238) months for uSpA patients. HLA-B27 positivity was present in 51.6% of AS and 14.9% of uSpA patients. The mean BASDAI level of patients with AS was 6.4 ± 1.1 and that of uSpA patients was 4.8 ± 2.1. SpA are frequent diseases and physicians other than rheumatologists should also be aware of them. uSpA is more frequent in women than men. Early diagnosis of SpA is important because early treatment with new biological therapies may lead to much better results than applying them in the advanced stages.

From global 137Cs to determinations of the sedimentation rate in deep lakes and sea estuaries

Sedimentation rate in deep lakes and estiaries of the Baltic, Pechora, and Laptev Seas was determined using global 137Cs as a sedimentogenesis marker. The sedimentation rate in Lake Ladoga and Levinson- Lessing Lake was 0.3–3 mm year−1, and that in estuaries of the Baltic, Pechora, and Laptev Seas was 0.74–1.76, 1.0, and 3.3–5.0 mm year−1, respectively. At a sedimentation rate of >1–2 mm year–1, the concentration peaks of global and “Chernobyl” 137Cs in the bulk of the bottom sediments do not overlap, and the sedimentation rate is estimated for each kind of nuclides separately. At a sedimentation rate of <1 mm year−1, “Chernobyl” 137Cs + 137Cs from dumping into sea mask in the bottom sediments the subsurface maximum of the global 137Cs concentration and prevent the sedimentation rate determination. The use of 137Cs for sedimentation rate determinations is appropriate for the poorly studied shelf zone of Russian Arctic seas.

Trace metal and rare earth elements in a sediment profile from the Rio Grande Reservoir, São Paulo, Brazil: determination of anthropogenic contamination, dating, and sedimentation rates

The Rio Grande Reservoir supplies water to four counties. Two sediment cores were collected, one was sliced every 2 cm for INAA and dating determinations; the other was cut every 5 cm, for grain size and Hg, Cd, Pb, Ni, Mn and Cu determinations. Sedimentation rates and sediment ages of every layer were determined by 210Pb method. Enrichment Factor (EF) and Geoaccumulation Index (I geo) were calculated. Significant enrichment was found for Na, Mn, Ni, Pb, Sb and Zn and extremely high enrichment for Hg, Cu and Cd, in upper layers. A 90 year pollution history of this reservoir was traced.

Sedimentation rates and age modeling of Late Quaternary marine sediments with unsupported 230Th

230Th is a radionuclide of the 238U decay series, characterized by natural abundance in sediments and a half-life of 75,380 years, suitable for direct evaluation of sedimentation rates and sediment ages in a time scale of 700,000 years before the present. 230Th cycle creates a contrast between supported and unsupported 230Th in the sedimentary matrix due to the different geochemical behaviors of 230Th and its parent, 234U. This study aimed at establishing and validating a mathematical model that evaluates sedimentation rates and age modeling based on 230Th data retrieved from a sediment core sampled in the southeastern Brazilian continental margin. The validation of the age modeling of this method was made through a statistical comparison between its results and those of benthic foraminifera δ 18O record technique, widely used for sediment dating and determination of sedimentation rates. It was observed that the model of unsupported 230Th was successful in determining Late Quaternary sedimentation rates and ages in a confidence level of 95 %. It was possible to determine several breaking points in unsupported 230Th vertical profile, and it was shown that those divides correspond to some major intervals between glacial and interglacial periods when compared with the benthic foraminifera record.

Определение скорости седиментации пыльцы сорных трав, как индивидуальных зерен, так и их агломератов

Определение скорости седиментации пыльцы сорных трав, как индивидуальных зерен, так и их агломератов

Xinfeng capsule improves pulmonary function in ankylosing spondylitis patients via NF-κB-iNOS-NO signaling pathway

ObjectiveTo study changes in the nuclear factor-κB p65 (NF-κB p65)-inducible nitric oxide synthase (iNOS)-nitric oxide (NO) signaling pathway and the effects of Xinfeng capsules (XFC) in patients with ankylosing spondylitis (AS) MethodsOne hundred twenty patients with AS were randomly divided into an XFC group and a Salazopyrin group. Sixty health subjects were included as a normal control group. In the two treatment groups, pulmonary functional parameters, forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), maximal voluntary ventilation (MVV), peak expiratory flow (PEF), forced expiratory flow at 25% of forced vital capacity (FEF25), forced expiratory flow at 50% of forced vital capacity (FEF50), and forced expiratory flow at 75% of forced vital capacity (FEF75) were determined. Enzyme linked immunosorbent assays were used for detection of the serum oxidative stress indexes, NF-κB p65, iNOS, NO, reactive oxygen species (ROS), reactive nitrogen species (RNS), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), total antioxidative capacity (TAOC) and interleukin-4 (IL-4), IL-10, IL-1β, and tumor necrosis factor-α (TNF-α) contents. Westergren's method was used for determination of erythrocyte sedimentation rate (ESR). High-sensitivity C-reactive protein (Hs-CRP) was detected with a 7060 full-automatic biochemical analyzer (Hitachi, Japan). ResultsThe clinical therapeutic effect in the XFC group was significantly superior to that in the Salazopyrin group (P<0.01). Compared with the normal control group, FEV1, MVV, PEF, FEF50, FEF75, SOD, CAT, TAOC, IL-4, IL-10 were significantly lower, and NF-κB p65, iNOS, NO, ROS, RNS, MDA, IL-1β, TNF-α, ESR, and Hs-CRP significantly higher in patients with AS (P<0.01 or P<0.05). Compared with before treatment, FEV1, MVV, PEF, FEF50, FEF75, SOD, CAT, TAOC, IL-4, and IL-10 were significantly increased, and NF-κB p65, iNOS, NO, ROS, RNS, MDA, IL-1β, TNF-α, ESR, CRP, visual analog scales (VAS), Bath ankylosing spondylitis disease active index, Bath ankylosing spondylitis functional index, and Bath ankylosing spondylitis global index significantly decreased in the two treatment groups after treatment (P< 0.01 or P<0.05), with significant differences between the XFC and Salazopyrin groups (P<0.01 or P<0.05). Spearman correlation analysis indicated that FEV1, MVV, PEF, FEF50, and FEF75 were positively correlated with SOD, CAT, TAOC, IL-4, and IL-10, and were negatively correlated with NF-κB p65, iNOS, NO, ROS, RNS, MDA, IL-1β, TNF-α, ESR, and CRP. ConclusionPatients with AS have local pathologic changes in the spinal cord and other joints. They also have decreased pulmonary function, which is negatively correlated with the NF-κB-iNOS-NO signaling pathway, oxidative indexes, and inflammatory factors. XFC improves rigidity and pain in spinal joints and other symptoms, laboratory indexes, and pulmonary function. The mechanism is possibly related to inhibition of the NF-κB-iNOS-NO signaling pathway.

Estimation of Small Reservoir Sedimentation in Semi-Arid Southern Zimbabwe

Small surface reservoirs play an important role of providing ready and convenient source of water for various uses in semi-arid areas which are characterized by erratic and low rainfall. Lack of current data on reservoir capacity loss due to sedimentation is one of the challenges to the sustainable management of surface reservoirs. The study investigated the capacity loss due to sedimentation from 2000-2012, and estimated the trap efficiency of the Mutangi reservoir which is located in semi-arid Chivi, Southern of Zimbabwe. Hydrographic surveys, grab sampling and water depth-capacity methods were used to determine the capacity of the dam as of 2012. To compute capacity loss from 2000 to 2012, the 2000 and 2012 dam capacities were compared whilst the trap efficiency of the reservoir was determined using a set of empirical models that relates trap efficiency to the capacity-watershed area ratio and capacity-inflow ratio. The results show that Mutangi reservoir has a trap efficiency of 95% - 98% (av = 96.4%) and has lost 37% of its capacity due to sedimentation in 12 years (2000 and 2012). Rates of sedimentation were 8539 t·yr-1, 9110 t·yr-1 and 8265 t·yr-1 for the hydrographic survey, grab sampling and water depth-capacity method respectively, and the little difference in these figures demonstrates that any method can be used to determine sedimentation rates. The area specific sediment yield (ASY) ranged from 14 - 15.5 t·ha-1·yr-1 (av = 14.956 t·ha-1·yr-1). At the current rate of sedimentation the projected dead level of the reservoir will be lost to sedimentation in 8 years while the useful life of the reservoir is estimated to be 30 years. Capacity loss due to sedimentation is further complicating the already strained water scarcity situation in semi-arid areas and management decisions should be made based on the current sedimentation rates estimated by different methods. These results imply that management practices that reduce erosion, hence sedimentation in these small reservoirs should be practiced in order to prolong their lifespan.

Cosmic-ray exposure ages of fossil micrometeorites from mid-Ordovician sediments at Lynna River, Russia

We measured the He and Ne concentrations of 50 individual extraterrestrial chromite grains recovered from mid-Ordovician (lower Darriwilian) sediments from the Lynna River section near St. Petersburg, Russia. High concentrations of solar wind-like He and Ne found in most grains indicate that they were delivered to Earth as micrometeoritic dust, while their abundance, stratigraphic position and major element composition indicate an origin related to the L chondrite parent body (LCPB) break-up event, 470Ma ago. Compared to sediment-dispersed extraterrestrial chromite (SEC) grains extracted from coeval sediments at other localities, the grains from Lynna River are both highly concentrated and well preserved. As in previous work, in most grains from Lynna River, high concentrations of solar wind-derived He and Ne impede a clear quantification of cosmic-ray produced He and Ne. However, we have found several SEC grains poor in solar wind Ne, showing a resolvable contribution of cosmogenic 21Ne. This makes it possible, for the first time, to determine robust cosmic-ray exposure (CRE) ages in these fossil micrometeorites, on the order of a few hundred-thousand years. These ages are similar to the CRE ages measured in chromite grains from cm-sized fossil meteorites recovered from coeval sediments in Sweden. As the CRE ages are shorter than the orbital decay time of grains of this size by Poynting–Robertson drag, this suggests that the grains were delivered to Earth through direct injection into an orbital resonance. We demonstrate how CRE ages of fossil micrometeorites can be used, in principle, to determine sedimentation rates, and to correlate the sediments at Lynna River with the fossil meteorite-bearing sediment layers in Sweden. In some grains with high concentrations of solar wind Ne, we nevertheless find a well-resolved cosmogenic 21Ne signal. These grains must have been exposed for up to several 10Ma in the regolith layer of the pre-break-up L chondrite parent body. This confirms an earlier suggestion that such regolith grains should be abundant in sediments deposited shortly after the break-up of the LCPB asteroid.