Bleached Sediments Research Articles

Flood events in the lower reaches of the Yellow River: OSL and radiocarbon dating on the Anshang site

The lower reaches of the Yellow River have witnessed numerous episodes of flooding and considerable shifts in its course. Examining flood records within the Yellow River basin offers invaluable insights into ancient human settlements, agricultural practices, trade routes, and technological advancements of ancient Chinese civilizations. However, dating these fluvial sediments poses a considerable challenge due to either the scarcity of organic material for radiocarbon (14C) dating or the potential incomplete bleaching of sediments for optically stimulated luminescence (OSL) techniques. This study focused on the Anshang site located in Henan Province, we obtained OSL ages from distinct grain size fractions of quartz and cross-verified them with independent acceleration mass spectrometry (AMS) 14C ages. The findings revealed that both coarse quartz grains (CG) and medium quartz grains (MG) underwent complete bleaching in silt-dominated flood deposits and shallow lacustrine deposits. Conversely, the OSL ages of CG and MG quartz were notably overestimated by approximately 3–6 ka in silty clay-dominated flood deposits. Upon comparing the OSL ages with AMS 14C ages, it was evident that bulk organic matter AMS 14C ages aligned with CG OSL ages in shallow lacustrine deposits, but they appeared older than CG OSL ages in flood deposits. However, the AMS 14C ages from plant demonstrated good consistency. Consequently, we successfully identified flood-lacustrine sediments dating back to approximately ∼13 ka, ∼8–3 ka, ∼2.6 ka, ∼1 ka, and the last few hundred years, aligning well with historical documentation and earlier research. The regional evidence presented herein enhances our understanding of the applicability of OSL dating and AMS 14C dating in fluvial-lacustrine sediments. Armed with these new ages, we constructed a reference chronology for archaeological localities situated in the fluvial sediments of the lower reaches of the Yellow River.

Red-green-bleached redox interfaces in the proximal Permian Cutler red beds: implications for regional fluid alteration

Siliciclastic strata of the Colorado Plateau attract attention for their striking red, green, bleached, and variegated colors that potentially record both early depositional and later diagenetic events. We investigated the proximal-most strata of the Paradox Basin, from their onlap contact with the Precambrian basement of the Uncompahgre Plateau to the younger Cutler strata exposed within 10 km of the Uncompahgre Plateau to attempt to understand the significance of the striking colors that occur here. These strata preserve a complex geology associated with buried paleorelief and sediment-related permeability variations at a major basin-uplift interface. Strata exposed within ∼1.5 km of the onlap contact exhibit a pervasive drab color in contrast to the generally red colors that predominate farther from this front. In-between, strata commonly host variegated red/green/bleached intercalations. Thin-section petrography, SEM, XRD, Raman spectroscopy, Mössbauer spectroscopy, and whole-rock geochemistry of samples representing different color variations from demonstrate that water–rock interactions charged the rocks with Fe(II) that persists primarily in the phyllosilicate fraction. Color variations reflect grain-size differences that allowed the reduction of fluids from regional fault and basement/fill contacts to permeate coarser-grained Cutler sediments. Hematite and chlorite occur in both red and green sediments but are absent in the bleached sediments. Pervasive hematite in both red and green layers suggests that sediments were hematite-rich before later alteration. Chlorite and smectite are elevated in green samples and inversely correlated with biotite content. Green coloration is generally associated with 1) coarser grain sizes, 2) spatial association with basement contacts, 3) elevated smectite and/or chlorite, 4) less total Fe but greater Fe(II)/Fe(III) primarily in the phyllosilicate fraction, and 5) uranium enrichment. The bleached coloration reflects the removal of pigmentary Fe(III) oxide, while the green coloration is due to the removal of pigmentary hematite and the abundance of Fe(II)-bearing phyllosilicates. Abundant mixed-layer and swelling clays such as smectite, illite/smectite, and chlorite/smectite (including tosudite) dominate the mineralogy of the clay fraction. These results are consistent with other studies demonstrating fault-associated fluid alteration in the Paradox Basin region. However, the pervasive greening was not observed in many of these studies and appears to reflect the unique aspects of the paleovalley system and the importance of biotite alteration to Fe(II)-bearing phyllosilicates.

Luminescence dating of Holocene sediment cores from a wave-dominated and mountainous river delta in central Vietnam

Sediments of river deltas provide valuable records of past coastal environments. Optically-stimulated luminescence (OSL) dating has become an alternative to radiocarbon dating for constraining the sediment chronology in large deltas that allow for sufficient sunlight bleaching of sediments during the fluvial transport. However, its applicability to smaller deltas with mountainous riverine systems has not been confirmed yet. To check this, we examine multiple signals from two Holocene sediment cores in the wave-dominated Thu Bon River delta in central Vietnam. Two cores were collected, respectively, 3.9 km and 1.2 km inland from the present shoreline and both show a >-25-m thick succession of coarsening-upward mud to sand deposits. Coarse grains (180–250 μm in diameter) of quartz and K-feldspar, and fine grains (4–11 μm in diameter) of quartz and polymineral were extracted from the upper and lower parts of the cores for multi-grain measurements of quartz OSL, and of feldspar infrared-stimulated luminescence (IRSL) at 50 °C (IR50) and post-IR IRSL at 175 °C (pIRIR175) to determine burial ages. In addition, facies analysis and radiocarbon dating were conducted. The landward core consists of transgressive to early regressive estuarine and prodelta facies, which is overlain by a sandy beach-shoreface facies. The seaward core consists of a relatively simple shallowing-upward succession from muddy prodelta facies to sandy beach-shoreface facies. All luminescence ages except for pIRIR175 of fine grains are mostly consistent with the radiocarbon ages. Instead, pIRIR175 ages of fine grains are significantly overestimated with variable offsets. OSL and IR50 of fine grains provide reasonable age estimates, as these grains were likely well bleached during the transport even along a short and steep mountainous river. Consistent age estimates of all signals from sand indicate that sand was well-bleached in the beach and shoreface owing to the frequent sediment reworking by waves and currents. These results support the hypothesis that luminescence dating is applicable to Holocene wave-dominated deltas and reiterate that comparing different luminescence signals is an effective way to check reliability of the age estimates in environments where the sunlight bleaching is not ensured.

Testing the potential of K-feldspar pIR-IRSL and quartz ESR for dating coastal alluvial fan complexes in arid environments

Coastal alluvial fans (CAF) are important geo-archives due to their sensitivity to both tectonic activity and climatic changes. Thus, they can give key insights for geomorphic and sedimentary processes. In this study we test the potential of K-feldspar post infrared-infrared stimulated luminescence (pIR-IRSL) and quartz electron spin resonance (ESR) methods for dating alluvial fan complexes in arid environments. The existing chronological data from marine terraces that interact with CAF make the Atacama Desert in northern Chile an excellent setting for this research. Samples have been collected from alluvial, marine and aeolian sediments embedded in the CAF complexes, allowing evaluation of the different signal properties and bleaching characteristics of the pIR-IRSL and ESR signals over Late Pleistocene time scales.pIR-IRSL dose distributions of clast-rich alluvial fan samples are characterised by higher scatter and demonstrate heterogeneous bleaching, while matrix-rich alluvial fan deposits show rather homogeneous poor bleaching in the dose dispersion as indicated by a modern analogue sample. In contrast, marine and aeolian deposits are homogeneously well bleached, supported by a modern littoral sample. Following the quartz multiple centre (MC) ESR dating approach (Al and Ti centres), bleaching of the different centres prior to deposition has been achieved. While the Ti–H centre provides mostly lower doses than the Ti–Li centre, in most cases the Al centre provides the highest dose values. This pattern is consistent with their respective bleaching kinetics and suggests that the Ti centre signals most likely provide the closest estimate to the true burial dose for samples with doses >200 Gy.ESR and pIR-IRSL ages are consistent at 2σ for the marine, aeolian and clast-rich debris-flow deposits, which is in agreement with existing chronological data in this area. It appears that the mode of sediment transport on alluvial fans, either as matrix- or clast-rich flows, plays an important role in sediment bleaching. While clast-rich alluvial fan deposits are likely better bleached, we cannot exclude insufficient bleaching during matrix-rich alluvial fan flows; our dating results suggest that both pIR-IRSL and ESR dating overestimate the true burial age. The combination of pIR-IRSL and MC ESR dating can be considered as a promising tool for deciphering alluvial fan formation over (Late) Pleistocene time scales.

Luminescence chronology of late-Holocene palaeofloods in the upper Kaveri basin, India: An insight into the climate–flood relationship

Instrumental/historic records have helped to understand the extreme flood–climate relationship in the modern environment; however, few studies are available to understand their long-term relation (102–103 years) due to the poor preservation and lack of dating techniques. It remains uncertain whether extreme flooding is linked with long-term wet phases of climate or a random event caused by an unusual downpour irrespective of climate. Luminescence analysis of quartz grains from river/floodplain sediments in the Kaveri basin, southern India, showed heterogeneous bleaching. We demonstrated the successful application of various statistical age models in estimating ages of heterogeneously bleached young sediments. This study shows distinct flood clusters occurred during the times of major shifts in the monsoon climate, from fluvial dormancy to sudden outburst of monsoons (~2 ka), from warmer to colder (onset of ‘Little Ice Age’ (LIA) ~ 14th century), from colder to warmer (end of LIA ~ 19th century) and ~20th century, indicating that climatic pattern can be associated with more frequent occurrences of extreme flood events. The study also shows that the two major flood events of the 20th century reported from the upper Kaveri were produced by high intensity short duration storms, suggesting that not all wet phases are associated with major floods and all dry phases with low floods/droughts. The excellent match of the chronology with the historical data, instrumental data and published literature based on proxy data on the Indian summer monsoon validates the chronology and the potential of sedimentary archives for future palaeoenvironmental reconstruction of the study area.

Application of luminescence age models to heterogeneously bleached quartz grains from flood deposits in Tamilnadu, southern India: Reconstruction of past flooding

High magnitude floods are generally associated with wet periods or shift in climate. Recent events of increased flooding in southern India raises the question of these to be either associated with human impact or a general climate shift. Due to lack of instrumental/historical records beyond a certain period, one need to look for fluvial records e.g. slack water deposit, levees deposit and signature of high discharge events. Luminescence dating dates the last daylight exposure of sediments. Therefore, dating of young extreme fluvial events may be challenging due to presence of significant remnant geological luminescence resulting in overestimation of ages. The present work examines this in a variety of fluvial deposits e.g. channel sediment, overbank deposit and flood plain deposits of ephemeral system of rivers in southern India to reconstruct past flooding events. The study demonstrated successful application of various age models often used in optical dating i.e. Common Age model (CAM), Minimum Age Model (MAM) and least 5% on the calculated equivalent doses obtained in heterogeneously bleached sediment and suggests that optical dating of fluvial sediments with heterogeneous bleaching can give dependable outcomes when proper age models are utilized. Results suggests duration of the extreme floods occurred during 50–60, 100–120, 180–200, 280–300 and 750–800 years ago. The gap indicates effect of Little Ice Ages (LIA) and several flooding events at 750–800 years ago indicate the end of Medieval Warm Period (MWP). The results indicate that the flooding events increase at the boundary of major climatic changes probably because these changes are associated with an increase in the depressions and cyclonic activity. The recent increase in flooding events which are associated with depressions and cyclonic activity could be an early warning of either a major climate shift or human impact.

A pre‐LGM sandur at Fiskarheden in NW Dalarna, central Sweden – sedimentology and glaciotectonic deformation

The Fiskarheden quarry, situated in NW Dalarna, central Sweden, reveals thick coarse‐grained sediments of Scott type facies association representing a sandur deposited in an ice‐proximal proglacial environment. Optically Stimulated Luminescence (OSL) dating of the sandur sediments suggests a pre‐Last Glacial Maximum (LGM) age. Most acquired ages are pre‐Saalian (>200 ka) and we regard each of these ages to represent non/poorly bleached sediment except for one small‐aliquot OSL age of 98±6 ka. This age comes from the top surface of an arguably well‐bleached sand bed deposited on the lee‐side of a braid‐bar, putting the sandur build‐up into the Early Weichselian. Large‐scale glaciotectonic structures show an imbricate thrust fan involving both ductile and brittle deformation. The deformation was from the WNW, which largely coincides with the formative trend of the predominating streamlined terrain and Rogen moraine tracts surrounding Fiskarheden. It is suggested that the deformation of the sandur sediments took place when the advancing glacier approached and pushed its own proglacial outwash sediment, during an ice‐marginal oscillation either at the inception of one of the Early Weichselian glaciations in the area, or during a general ice retreat amid a deglacial phase. The Fiskarheden sandur deposits are covered by a subglacial traction till deposited from the NE/NNE. This direction corresponds with younger streamlined terrain flowsets cross‐cutting the older NNW–SSE system and probably represents deglaciation in the area following the LGM. This study will add to the understanding of the formation and deformation of Pleistocene sandur successions and their relationship to past ice‐sheet behaviour.

Optical dating of Holocene sediments from the Yangtze River (Changjiang) Delta, China

Establishing a reliable chronology is essential for understanding delta evolution, which is normally performed using radiocarbon (14C) dating and the recently emerging technique of optically stimulated luminescence (OSL). The application of the latter one to the Holocene Yangtze River (Changjiang) Delta deposit is still quite limited. In this study, two 60.9-m-long cores were collected from Taizhou (TZ) and Nantong (NT) within the paleo-incised valley of the Yangtze River, and a total of seven and nine OSL samples were collected from the TZ and NT cores, respectively. In addition, ten accelerator mass spectrometry (AMS) 14C ages of the TZ core were presented with eight AMS 14C ages that were previously obtained from the NT core. The single-aliquot regenerative-dose (SAR) protocol was applied to coarse silt-sized (45–63 μm) and fine sand-sized (90–125 μm) quartz. The results showed that the grains in the 45–63 μm size fractions appeared to be better bleached than those in the 90–125 μm size fractions, and the detection of insufficiently bleached sediments is required in order to obtain accurate age estimates. The ages adopted for the samples range from 3 ka to 9 ka for the TZ core, and from 1 ka to 14 ka for the NT core, which were in general internally coherent within the limits of experimental errors and with respect to their stratigraphic order. The AMS 14C age of the TZ core were significantly older than their OSL ages, while those from the NT core generally showed good agreement with their OSL ages. One should be cautious when using AMS 14C to date deltatic deposits. Based on the OSL ages, two periods of rapid accumulation rates can be found in both cores, which are linked to the rapid sea level rise in early Holocene and migration of delta front facies in late Holocene. These investigations indicate that OSL technique is an effective method with which to date Holocene deltaic deposits, especially in coarse sedimentary layers where organic carbon material is sparse.

Chronostratigraphic interpretation of intermediate layer formation cycles based on OSL-dates from intercalated slope wash sediments

Stratified periglacial sediments extensively cover the slopes of central European low mountain areas. Periglacial cover beds and loess-like sediments as most abundant strata influence many near-surface processes, forming an important component of the Earth's critical zone.The present study focusses on the analysis of a complex sequence of periglacial slope deposits with multiple intermediate layers and intercalated slope wash sediments in order to determine and date periods of intermediate layer formation.Since luminescence dating often provides inconsistent data for cover beds, there is need to reconsider the numerical dating strategy. This study hence places stronger emphasis on numerical dating of interbedded, sufficiently bleached slope wash sediments. The gained OSL-ages are more reliable and consistent and thus, provide a temporal framework for relative dating of intermediate layer formation cycles. In combination with paleosol relics the numerical ages allowed a chronostratigraphic interpretation of Late Pleistocene paleoenvironmental dynamics and slope evolution.Our findings not only prove multiple phases of intermediate layer formation in the study area during the last glacial period but also enabled the correlation of single intermediate layers with specific time spans, including Early and Middle Weichselian as well as the Late Glacial. Remnants of the Eemian soil in the studied sequence even indicate a Saalian age for the lowermost intermediate layer.The present study shows that luminescence dating of intercalated slope wash deposits instead of cover beds is a promising numerical dating strategy for the chronostratigraphic interpretation of cover bed sequences. The findings further illustrate that complex, fanned out periglacial sediment sequences form despite their scarcity important paleoenvironmental archives for Late Pleistocene periglacial landscape dynamics in central European low mountain areas.

Role of Bleach Sedimentation Technique for the Diagnosis of Tuberculosis.

Tuberculosis remains a major threat to world health. The main aim of this study was to improve the microscopic detection of AFB from sputum by Bleach sedimentation technique using household bleach. This was a cross sectional type of study conducted for a period of one year from July 2010 to June 2011 in the Department of Laboratory Services, Khwaja Yunus Ali Medical College Hospital (KYAMCH), Sirajgonj. A total of 115 clinically suspected tuberculosis patients aged between 7-85 years were included in the study. Among them 35 (30.4%) patients had TB positive by routine (Direct microscopy) method; whereas, by bleach concentration method 42 (36.5%) were found positive; diagnosing 07 additional patients. The rise of 16.7% in sputum positivity by bleach sedimentation microscopy over the direct smear microscopy was found to be statistically significant (p= <0.005). Paired samples t test analysis of sputum showed a significant correlation between this two methods (r=0.896, p <0.001). This study suggests that Bleach sedimentation method is better than direct conventional method. So it should be applied to all laboratories across the country because it is cheap early available and also safety to the laboratory staffs.KYAMC Journal Vol. 5, No.-2, Jan 2015, Page 497-502

Evaluating isothermal thermoluminescence and thermally transferred optically stimulated luminescence for dating of Pleistocene sediments in Amazonia

Abstract The paleogeography of Amazonia lowlands during the Pleistocene remains hampered by the lack of reliable absolute ages to constrain sediment deposition in the hundred thousand to few million years timescales. Optically stimulated luminescence (OSL) dating applied to quartz has provided important chronological control for late Quaternary sediments, but the method is limited to the last ∼150 ka. In order to extend the age range of luminescence dating, new signals from quartz have been investigated. This study tested the application of isothermal thermoluminescence (ITL) and thermally transferred optically stimulated luminescence (TT-OSL) signals of quartz for dating of fluvial terraces from eastern Amazonia. ITL and TT-OSL signals measured in a modern fluvial sediment sample have shown small residual doses (4 and 16 Gy), suggesting adequate bleached sediments for the target dose range (>150 Gy). This sample responded well to dose recovery test, which showed that the ITL and TT-OSL signals grow to higher doses compared to the doses estimated by the conventional OSL signal. The ITL signal saturated for doses significantly lower than doses reported in the literature. Most dating samples were beyond the ITL saturation doses and only TT-OSL signals were suitable to estimate equivalent doses. Burial ages ranging from 107 to 340 ka were estimated for the fluvial terraces in the lower Xingu River. The main ages uncertainties are related to dose rate changes through time. Despite the uncertainties, these ages should indicate a higher channel base level during the Middle Pleistocene followed by channel incision, possibly due to episodes of increased precipitation in the Xingu watershed.

Optically stimulated luminescence and isothermal thermoluminescence dating of high sensitivity and well bleached quartz from Brazilian sediments: from Late Holocene to beyond the Quaternary?

ABSTRACT: The development of optically stimulated luminescence (OSL) dating of sediments has led to considerable advance in the geochronology of the Quaternary. OSL dating is a well established technique to determine sediment burial ages from tens of years to few hundred thousand years. Recent studies have shown that Quaternary sediments of Brazil are dominated by quartz grains with high luminescence sensitivity, allowing the determination of precise and reliable OSL burial ages. In this paper, we show examples of OSL dating of quartz aliquots and single grains from different regions in Brazil, including young coastal-eolian Late Holocene (< 100 years) to Late Pleistocene (~ 150 ka) fluvial sediments. We discuss the OSL data and ages of sediments from carbonate and terrigenous (distributary and tributary systems) fluvial depositional contexts in Brazil. Most of the studied fluvial sediments show equivalent dose distributions with low to moderate dispersion, suggesting well bleached sediments. The comparison between aliquot and single grain data suggests that high overdispersion in equivalent dose distributions of some samples is more related with sediment mixture due to bioturbation than with incomplete bleaching during transport. Well bleached fluvial sediments contrast with the poor bleached pattern usually described for fluvial sediments in the literature. A large part of the fluvial sedimentary record in Brazil is older than the age limit for quartz OSL dating using blue light stimulation. Thus, isothermal thermoluminescence (ITL) dating protocols were tested for dating of fluvial sands from the Xingu River (eastern Amazonia). The studied sample can recover reliable equivalent doses up to 1600 Gy using the ITL 310oC signal. Therefore, this signal would be suitable to extend the age limit of quartz luminescence to the whole Quaternary or beyond (> 2 Ma) in the low dose rate (0.5 - 1.0 Gy/ka) environments typical for Brazilian sediments.

Asteroid impact vs. Deccan eruptions: The origin of low magnetic susceptibility beds below the Cretaceous–Paleogene boundary revisited

The respective roles of an asteroid impact and Deccan Traps eruptions in biotic changes at the Cretaceous–Paleogene (K–Pg) boundary are still debated. In many shallow marine sediments from around the world, the K–Pg boundary is marked by a distinct clay layer that is often underlain by a several decimeter-thick low susceptibility zone. A previous study of the Gubbio section, Italy (Lowrie et al., 1990), attributed low magnetization intensity in this interval to post-depositional dissolution of ferrimagnetic minerals. Dissolution was thought to be a consequence of downward infiltration of reducing waters that resulted from rapid accumulation of organic matter produced by mass extinctions after the K–Pg event. We compare the magnetic properties of sediments from the Gubbio section with those of the Bidart section in southern France. The two sections are similar in their carbonate lithology and the presence of a boundary clay and low susceptibility zone. When compared to background Cretaceous sediments, the low susceptibility zone in both sections is marked by an absence of biogenic magnetite, a decrease in total ferrimagnetic mineral content, and a preferential loss of magnetite with respect to hematite – features that are consistent with reductive dissolution. However, unlike the Gubbio section, where the low susceptibility zone starts immediately below the boundary clay, the low susceptibility zone and the clay layer at Bidart are separated by a ∼4-cm carbonate interval that contains abundant biogenic magnetite. Such separation casts doubt on a causal link between the impact and sediment bleaching. More likely, the low susceptibility layer marks a different environmental event that preceded the impact. An episode of increased atmospheric and oceanic acidity associated with Deccan Traps volcanism that occurred well before the K–Pg impact is argued here to account for the distinct magnetic properties of the low susceptibility intervals.

Evidence of shallow TL peak contributions in infrared radiofluorescence

The notion of what is a ‘zero age’ is skewed in IR-RF. For bleached sediment, the IR-RF intensities are found to be at their highest values while it falls at its lowest when it reaches dose saturation. During bleaching, it was shown that a sample emits phosphorescence immediately after bleaching, yet very little is known about it. Here, we will try to identify the source for these trapped electrons.Recent communications in radiofluorescence, have observed an unexpected increase in the beginning of an irradiation, mostly seen in regenerated luminescence. At first glance, this would imply that the increase is tied to an increasingly higher electron capture by the dating trap, during the onset of irradiation. We show that this initial increase is simply due to minute variation in temperature, occurring during the measurements.

Reconstructing the tsunami record in Tirúa, Central Chile beyond the historical record with quartz-based SAR-OSL

The most recent high magnitude seismic events, e.g. the Mw 8.2 Iquique earthquake (April 1st, 2014) and the Mw 8.8 Maule earthquake (February 27th, 2010) are reminders of the pronounced vulnerability of the Chilean coast to the impact of natural hazards like earthquakes and tsunamis. Therefore it is crucial to understand the complex tsunami history of Chile which can be deciphered by studying the geological record of former tsunamis in the form of tsunami deposits.At the coastal locality of Tirúa (Central Chile) six distinct, successive tsunamigenic sand layers are intercalated in fine grained floodplain sediments. We present the optically stimulated luminescence (OSL) analysis of quartz from samples of this sedimentological river marsh profile of 1.5 m depth.After the assessment of the applicability of OSL to these samples, it could be noted that despite of an expected low OSL sensitivity of the quartz from the South American Cordillera, most of the sampled quartz yielded a detectable natural signal. After performance tests according to the SAR-protocol, the measurements of the different tsunami sand layers were conducted with small (2.5 mm) aliquots of quartz with the preheat temperature 180 °C. The calculation of De was provided by applying both the central age and minimum age models. All samples are heterogeneous in their De distributions due to incomplete or absent significant bleaching during transport by tsunami. The resulting ages of the tsunami sediments yield an offset of nearly 200 years for CAM ages and less than 50 years for MAM ages, consequently favouring MAM ages for true burial age determination. In some tsunami sand layers and their surrounding river marsh sediments age inversions occur. They were caused by the initial deposition of well bleached sediments derived from beach and dunes followed by older sediments redeposited from beach and intertidal environments during tsunami flow. Despite the offset and age inversion six different tsunami events were dated in the Tirúa profile. Three of these events extend the historical record to pre-Columbian time with the oldest tsunami dated to over 1500 years before present.

Improved sensitivity, safety and laboratory turnaround time in the diagnosis of pulmonary tuberculosis by use of bleach sedimentation

Background: Inadequate diagnostic processes and human resources in laboratories contribute to a high burden of tuberculosis (TB) in low- and middle-income countries. Direct smear microscopy is relied on for TB diagnosis; however, sensitivity rates vary. To improve sensitivity of direct microscopy, the researchers employed several approaches, including sputum digestion and concentration of acid-fast bacilli (AFB), a technique which uses commercial bleach.Objectives: This study compared methods used to diagnose active Mycobacterium tuberculosis infections.Methods: Three sputum specimens were collected from each of 340 participants in Abuja, Nigeria, over two consecutive days. Direct microscopy was performed on all specimens; following microscopy, one specimen from each patient was selected randomly for bleach sedimentation and one for Lowenstein-Jensen culture.Results: Direct microscopy produced 28.8% AFB-positive results, whilst bleach sedimentation resulted in 30.3%. When compared with the cultures, 26.5% were AFB true positive using direct microscopy and 27.1% using bleach sedimentation. Whilst the specificity rate between these two methods was not statistically significant (P = 0.548), the sensitivity rate was significant (P = 0.004).Conclusion: Based on these results, bleach increases the sensitivity of microscopy compared with direct smear and has similar specificity. When diagnosing new cases of pulmonary TB, one bleach-digested smear is as sensitive as three direct smears, reducing waiting times for patients and ensuring the safety of laboratory technicians.

Digging your own grave: OSL signatures in experimental graves

Excavation of mock graves in sediments of aeolian and fluvial origin were conducted to test the bleaching efficiency of grave digging in materials that commonly host ancient burials in Australia. Grave-size pits were dug into Pleistocene aeolian sediments at Willandra Lakes and younger fluvial sediments on the Lachlan River, backfilled, and re-excavated. Samples for optical dating were taken from sediment infilling the mock graves and from the adjacent, undisturbed substrate, and analysed using the single aliquot-regenerative dose (SAR) protocol applied to single quartz grains. The resulting equivalent dose (De) distributions revealed that ≤1% of grains had been fully zeroed in both settings, and an additional 1–6% of poorly bleached grains were apparent in the fluvial sediments. Insufficient and heterogeneous bleaching of sediments during excavation and backfilling produced a decrease in the central dose of between 3 and 6 Gy, and an increase in over-dispersion values of between 5 and 10%. These differences were insufficient to clearly distinguish the disturbance event from the effects of bioturbation, biological mixing, or other sources of De variation. The use of the Minimum Age Model substantially over-estimated the burial age (zero years) in both depositional environments, with the degree of over-estimation increasing with the age of the host sediments. These results suggest that optically stimulated luminescence (OSL) techniques will not produce accurate ages for grave infill in a number of forensic and archaeological settings. Further study of the bleaching susceptibility of grains within grave infills, as well as the effectiveness of grave-digging as a bleaching mechanism is required. In other archaeological and geomorphological applications of OSL dating we recommend routine checks on the effective zeroing of sediments in modern equivalent situations.

Understanding processes of sediment bleaching in glacial settings using a portable OSL reader

Analysis of a high‐resolution suite of modern glacial sediments from Jostedalen, southern Norway, using a portable optically stimulated luminescence (OSL) reader, provides insights into the processes of sediment bleaching in glacial environments at the catchment scale. High‐magnitude, low‐frequency processes result in the least effective sediment bleaching, whereas low‐magnitude, high‐frequency events provide greater bleaching opportunities. Changes in sediment bleaching can also be identified at the scale of individual bar features: tails of braid‐bars and side‐attached bar deposits have the lowest portable reader signal intensities, as well as the smallest conventional OSL residual doses. In addition to improving our understanding of the processes of sediment bleaching, portable reader investigations can also facilitate more rapid and comprehensive modern analogue investigations, which are commonly used to confirm that the OSL signals of modern glacial sediments are well bleached.

Towards successful OSL sampling strategies in glacial environments: deciphering the influence of depositional processes on bleaching of modern glacial sediments from Jostedalen, Southern Norway

The optically stimulated luminescence (OSL) signals of quartz and K-feldspar are known to bleach poorly within some glacial settings, and can present a major challenge to dating applications. However, because the OSL signal is extremely sensitive to sunlight exposure history, the residual luminescence signals of modern glacial sediments also encode information about transport and depositional processes. Through examination of the residual luminescence properties (equivalent dose (De) and overdispersion values) of a suite of modern glacial sediments from different depositional settings (sandar, proglacial delta and main meltwater channel), this study provides insights not only into which sediments are likely to be fully bleached within glacial settings, but also into how OSL can be used to trace different depositional processes across sedimentary landforms. Improved understanding of the processes of sediment bleaching will enable better sample selection and may improve the accuracy and precision of OSL dating of glacial sediments.The luminescence signals of both coarse-grained quartz and K-feldspar with similar sediment sources are found to be sensitive to both depositional process and specific depositional setting. Whereas modern braid-bar-head deposits from the Nigardsdalen ice-proximal proglacial delta typically have ages of ≤3 ka, similar depositional features from the Fåbergstølsgrandane sandur have residual ages of ≥26 ka. Exploration of changing residual luminescence signals across individual sandur and proglacial delta braid-bar features shows that braid-bar-head deposits can retain large residual De values, while the partner braid-bar-tail deposits are almost completely bleached. The quartz OSL signal and K-feldspar IRSL50 and post-IR IRSL250 signals are shown to bleach at the same rate across the same bar feature and the IRSL50 K-feldspar signal is also shown to be completely bleached for bar-tail deposits in Nigardsdalen. Therefore the IRSL50 K-feldspar signal is suitable for dating some glacial deposits, circumventing the challenges associated with dim quartz signals.

Apparent OSL ages of modern deposits from Fåbergstølsdalen, Norway: implications for sampling glacial sediments

ABSTRACTThe application of optically stimulated luminescence (OSL) dating within glacial settings can be limited where sediments have not had their OSL signal fully reset by sunlight exposure. Heterogeneous bleaching can result in age overestimations, and although it is recognized that certain depositional settings are more likely to have experienced sufficient sunlight exposure to bleach the OSL signal, no comprehensive study has empirically investigated the processes of sediment bleaching, or the variability in bleaching between deposits of the same type and within the same glacial catchment. A suite of modern glacial and glaciofluvial sediments from Fåbergstølsdalen, southern Norway, have been analysed to explore the controls that sedimentary processes and depositional setting have on bleaching of the OSL signal of quartz. There is considerable variability in the residual OSL ages of similar modern deposits, which reflects high sensitivity of the OSL signal to sediment source, sedimentary process, transport distance and depositional setting. Overdispersion values are greatest for the sediments which have been most heterogeneously bleached and these sediments have the lowest residual ages. Sampling strategies that incorporate sufficient consideration of the depositional framework of sample settings can minimize the effects of unbleached residuals on OSL age determinations.