Sediment Physical Properties Research Articles

Full particle size distribution characteristics of land surface sediment and their effect on wind erosion resistance in arid and semiarid regions of Northwest China

Particle size distribution (PSD) is one of the fundamental physical properties of clastic sediment. Although many mathematical models have been proposed to describe the PSD of sediment, the physical meaning behind model parameter characterization remains poorly understood, which means it is seldom used in studies of the environment, geomorphologic evolution, and related surface wind–sand processes in arid areas. In this study, based on the Li model of the PSD of sediment, the parameters of sediment obtained from different landscapes in Northwest China were investigated and their relationship with the resistance of sediment to wind erosion was analyzed. Results showed that the full PSD parameters (μ and Dc) of the Li model not only revealed the full PSD of the surface sediment of the various landscapes, but also reflected the differences in sediment structure. The full PSD parameters of fine silty, sandy, and sandy gravel surface sediment were −0.2 < μ < 0 and Dc < 0.08, −0.2 < μ < 0 and 0.08 ≤ Dc ≤ 0.2, and μ < 0 and Dc > 0.2, respectively. Parameter Dc not only represents the mean particle size of sediment, but it also indicates the degree of sorting, that is, it has a positive linear correlation with the component content of coarser particles in the sediment structure. Results also showed that vegetation cover markedly enhances surface resistance to wind erosion. Under different vegetation cover scenarios, the resistance of sandy and sandy gravel surfaces to wind erosion increased as the Dc value increased.

Compaction Simulator: A Novel Device for Pressure Experiments of Subsurface Sediments

Increasing overburden pressure is a key factor that alters the chemical and physical properties of soils and sediments. However, limited information is presently available on how aquifer compression impacts water quality. We introduced a novel compaction device, which is composited of four parts, including pressure simulator reactor system (PSRS), gas-liquid separator (GLS), automatic collector (AC) and composite control system (CCS). We conducted experiments at various pressures to test the functionality and outcomes of the device. In general, this device can be used to examine changes in water chemistry associated with aquifer compression resulting from compaction (overburden pressure) or groundwater overdraft.

Biodiversity and Habitat Assessment of Coastal Benthic Communities in a Sub-Arctic Industrial Harbor Area

Coastal ecosystems face increasing anthropogenic pressures worldwide and their management requires a solid assessment and understanding of the cumulative impacts from human activities. This study evaluates the spatial variation of benthic macrofaunal communities, sediments, and heavy metals in the sub-Arctic coastal ecosystems around Sept-Îles (Québec, Canada)—a major port area in the Gulf of St. Lawrence. Physical sediment properties varied in the studied area, with a general sandy-silty profile except for specific locations in Baie des Sept Îles where higher organic matter and heavy metal concentrations were detected. Macrofaunal assemblages were evaluated for two taxa size classes (organisms &gt; 0.5 mm and &gt; 1 mm) and linked to habitat parameters using regression models. Communities of smaller organisms showed signs of perturbation for one assemblage close to industrial activities at Baie des Sept Îles, with an increased number of tolerant and opportunistic species, contrasting to neighboring regions whose compositions were similar to other ecosystems in the Gulf of St. Lawrence. This study enhances the understanding of sub-Arctic benthic communities and will contribute to monitoring programs for industrial harbor ecosystems.

Holocene glacier and ice cap fluctuations in southwest Greenland inferred from two lake records

Glaciers and ice caps (GICs) respond rapidly to changes in temperature and precipitation. Thus, records of their past fluctuations yield valuable information on past climate. However, relatively little is known about the long-term, Holocene history of Greenland’s local GICs, peripheral to the Greenland Ice Sheet. Here we report sediment records of Holocene glacier activity from two distally fed glacial lakes near Buksefjord, southwest Greenland. The two lakes’ watersheds host modern GICs of contrasting size. The Pers Lake (informal name) watershed drains part (3 km2) of a single small ice cap. In contrast, nearby Lake T3’s (informal name) watershed drains numerous GICs totaling 100 km2. At the time it emerged from the sea ∼8.6 ka BP, Pers Lake was receiving no glacial meltwater input. Sediment physical and geochemical properties indicate persistent meltwater input and regrowth of the ice cap within the Pers Lake catchment beginning at ∼1.4 ka BP, after almost 3000 years of sporadic meltwater input beginning ∼4.3 ka BP. The ice cap above Pers Lake reached a maximum late Holocene extent during the final phase of the Little Ice Age (LIA), ∼0.1 ka BP. The complementary Lake T3 sediment record suggests continued meltwater input from the larger suite of upstream GICs from the time of the lake’s isolation from the sea ∼8.4–7.5 ka BP through to the present. This indicates that some GICs here probably survived the Holocene Thermal Maximum (HTM), although were significantly reduced in size for an extended period (of unknown age and duration). Combined with evidence from Pers Lake and prior studies that show GICs at low and intermediate elevations in this region melted away completely during the HTM, and evidence for GIC presence at Lake T3, we provide lower and upper bounds on regional HTM equilibrium-line altitudes (ELAs). We estimate that regional ELAs were between ∼1370 and 1470 m above sea level in the early-to-middle Holocene. From the middle to late Holocene, our results, along with other regional GIC studies, indicate progressive lowering of regional glacier ELAs in response to Neoglacial summer cooling of ∼2.7 °C, assuming no change in precipitation.

Chemical and physical drivers of beryllium retention in two soil endmembers

Meteoric 10Be and 7Be produced in the atmosphere from high-energy spallation reactions are deposited onto the Earth's surface through wet and dry deposition and are sorbed onto the surfaces of particles. On land, the sorbed concentrations scale with the residence time of sediments in a landscape–offset by slow (10Be) and fast (7Be) radioactive decay. Additionally, the amount of native 9Be, leached from minerals, correlates with the chemical weathering of soils. However, previous work has shown that chemical and physical properties of soils and river sediments affects sorption of beryllium. Therefore, the magnitude of sorbed beryllium concentrations may be more representative of the sorption capacity of the system rather than its erosional or weathering history.Although previous work has examined the physical and chemical properties of soil that influence beryllium sorption, these studies either lack consensus or exclude potentially important variables. In this work, we provide a thorough examination of variables previously reported to have influence on beryllium chemistry as well as new variables such as nitrogen, phosphorus and sulfur concentrations in order to determine which factors best predict beryllium sorption. We selected two soil endmembers with differing compositions, separated them into different size fractions, and characterized the surface area, cation exchange capacity (CEC), mineralogy, sulfur, carbon, nitrogen and phosphorus concentrations. We determined that the inverse percent abundance of quartz and the CEC best predict beryllium sorption potential in these soils. By deriving a model that relates these two variables to the percent sorbed beryllium, we were able to predict the sorption capacity of our system and reduced the error in sorbed beryllium amounts due to differences in soil properties by about 42%. From these results, we provide insight as to why there is inconsistency in the literature with regards to the physio-chemical controls on the environmental behavior of beryllium.

Assessment of the impacts of shallow gas on taxonomic structure of benthic communities in Bahía Blanca estuary (Argentina)

Shallow biogenic gas deposits located in the surface of the seabed may affect abundance, diversity, biomass and structure of benthic communities. Nevertheless, the magnitude and responsible variables of this effect still not clear. For this, the current study applies sedimentological metrics to the different community patterns associated with gas presence detected by acoustic methods across two seasons (spring and winter). Gas-bearing sediments showed higher organic matter content, lower shear strength and greater textural homogeneity across the column. Gas trapped in sediments was found associated with changes in the structure of benthic community, in species composition as well as in relative abundance and biomass of each taxa. Also, lower total abundance, species richness and diversity and higher total biomass was found in gas site. Higher organic matter content of sediments in gas site explained benthic community patterns across seasons. Gas bubbles trapped in surface of seabed sediments changed physical and chemical properties of sediments affecting benthic communities in ways that seems comparable with shallow water gas seeps and reducing environment. Unlike the latter, gas bubbles trapped have the advantage of having been widely mapped in coastal systems by geophysicists and marine geologists, with high resolution seismic (3.5 kHz) which according to our results seems to affect benthic communities.

Evaluation of high‐flow rate continuous‐flow centrifugation and filtration devices for sampling and concentrating fine‐grained suspended sediment

AbstractFine‐grained (&lt;63 μm) suspended sediment is an important vector for transporting contaminants in aquatic systems. Characterization of physical and biogeochemical properties of suspended sediment usually requires bulk samples to assess its quality and to determine its source. Low‐flow rate (~2 to 4 L min−1) continuous‐flow centrifugation (CFC) systems may need a time period from several hours to one day to collect such samples, and thus, due to their low inflow rate, limits application of these devices. A field study was conducted in three different freshwater systems in Manitoba, Canada to examine and compare the performance of two high‐flow rate systems as alternative approaches: the M512 continuous‐flow centrifuge (M512); and continuous filtration using PENTEK 1 μm filtration bags (filtration system). It was determined that the mass collection efficiency (MCE) for the M512 (in absolute terms) was similar to low‐flow rate CFC systems. As with low‐flow rate CFC systems, the M512 preferentially collected particles of a certain size range (i.e., in the case of M512, particles ≥ 0.83 μm) and accordingly this may affect the collection of a truly geochemically and physically representative sample in waters containing a high proportion of finer particles (≤1 μm). Several filtration systems in series improved its MCE performance and, in terms of total collected mass, this configuration appears to be as efficient as the low‐flow rate CFC systems in an equivalent sampling time. The results of this study confirmed that, in nearly all cases, the filtration system collected a representative sample of ambient suspended sediment, in terms of particle size composition, and geochemical and colour properties. In practice, it is suggested that the filtration systems in series have advantages over M512 as the filtration system is more portable and cost‐effective with a lower power demand.

The distribution of sediment residence times at the foot of mountains and its implications for proxies recorded in sedimentary basins

The geochemical and physical properties of terrigenous sediment stacked in sedimentary basins are used as proxies for the paleo-environmental conditions that prevailed during their period of deposition. Nevertheless, sediment grains have a stochastic transit from mountain sources to sedimentary basins: a fraction of grains are stored for a long time while others are recycled from old deposits. Consequently, the temporal representativity of a population of grains in a sedimentary stratum is uncertain. The potential recycling of old material is a major concern in the reconstruction of paleo-environments and this recycling is usually difficult to evaluate. In particular, the distribution of grain residence times in basins, between sources and sinks, is out of reach. Here we use a landscape evolution model that traces grains to analyse the distribution of residence times in an alluvial apron at the foot of a mountain relief. We study an end-member scenario that is the least favourable for the storage of grains: when the mountain is eroding at the same rate as rock is uplifting. In this case, the alluvial apron behaves as a by-pass zone, when averaging sediment flux over Ma, and the storage of grains of any size should be minimal. Yet, the model predicts that some grains are stored for hundreds of thousands of years before exiting the alluvial apron. Consequently, the mean residence time of sediment grains is much higher than the observed residence time of 95% of the grains exported by the alluvial apron rivers. This process may explain very long residence times found in fluvial systems by geochemical methods based on bulk measurements of sediment. Furthermore, it suggests that grains stored for a very long time, although a minority, can bias time-dependent proxies.

Long-term quality record (1996-2018) of coastal sediments at the complex industrial site along the Jordanian coast of the Gulf of Aqaba.

To evaluate the effect of the industrial activities on the sediment quality, we investigated long-term records of physical and chemical properties of bottom-surface sediments from a complex industrial site along the Jordanian coast of the Gulf of Aqaba. Sediment samples were collected from 10 m depth once a year from six different stations (S1-S6) and analyzed for grain size, loss on ignition (LOI), organic carbon (OC), hydrogen sulfide (H2S), total nitrogen (TN), total phosphorus (TP), and heavy metal contents. Temporal variations show a constant/decreasing trend for H2S, OC, and LOI, whereas an increasing trend for TN and TP was observed. Heavy metal concentrations reveal almost constant trends over time for Cd, Cu, and Zn and a decreasing trend for Cr and Pb. Statistical analysis indicates that the differences between the different sampling stations were insignificant for almost all variables. However, some differences were observed, as the highest values were recorded in S3 and the lowest values in S1. The textural proprieties show no significant variation among sites. As a result, the sediment quality at the industrial site is comparable with that in other sites along the northern Gulf of Aqaba. Sediments at the industrial site appear to have attained steady-state equilibrium where basic environmental parameters are insignificantly modified from the baseline values of the area. The decreasing trend observed over time indicates a significant improvement in the environmental quality attributed to the stringent implementation of environmental regulation in Aqaba (e.g., zero discharge policy).

Dependence of acoustic properties on hydrate-bearing sediments with heterogeneous distribution

The relationship between the hydrate-bearing sediments with physical properties such as wave velocity is of importance for the exploration and exploitation of natural gas hydrate. The distribution modes of naturally occurring gas hydrates in sediments are diverse and have significant influence on physical properties of rocks. However, hydrates in homogeneous distribution are in general investigated in laboratory currently. In this work, to simulate the diverse distribution modes of naturally occurring gas hydrates, a novel method to prepare the hydrate-bearing sediments with heterogeneous distribution including layered distribution was proposed by controlling the temperature, water migration, and water saturation distribution. Velocity and amplitude of P-wave are investigated to evaluate the physical properties of hydrate-bearing sediments with homogeneous or heterogeneous distribution. The results showed that the hydrate formation process apparently consists of unconsolidated and consolidated steps according to the amplitude curve. The amplitude of P-wave in the unconsolidated stage increases slowly, while it increases suddenly and rapidly in the consolidated stage. The P-wave velocity of the hydrate deposits with homogeneous distribution is faster than that with heterogeneous distribution when under a same hydrate saturation. This is also verified from the experiments performed on hydrate-bearing sediments with layered distribution, which provided direct evidence and quantification about heterogeneous degree of hydrate distribution in sediment. This difference of the P-wave velocity between heterogeneous and homogeneous hydrate-bearing sediments would provide a guidance in the future development of natural gas hydrate.

Does parasitism influence sediment stability? Evaluation of trait-mediated effects of the trematode Bucephalus minimus on the key role of cockles Cerastoderma edule in sediment erosion dynamics

In coastal environments, bioturbators greatly influence the physical and biogeochemical properties of sediments with consequences for central ecological processes such as erosion dynamics. In addition to their direct impact on sediment stability, bioturbators can have an impact on sediment erosion processes by modulating the growth of microphytobenthic organisms that stabilise the surface layer of sediments. The direct and indirect influences of bioturbators on sediment dynamics depend on the magnitude of their activity and inherently on their physiological state. Bioturbators are infected by various parasites, which have a substantial impact on their physiology and behaviour. However, the knock-on effects of parasites on key ecosystem functions like sediment dynamics remain poorly studied. We conducted flume experiments to investigate the indirect influence of the trematode Bucephalus minimus parasitising the common cockle Cerastoderma edule on the dynamics of sandy sediments enriched or not with microphytobenthos (MPB). Cockles modified bed roughness, sediment surface erodibility and hence destabilised sandy sediments. In sediments not enriched with MPB, both unparasitised and parasitised organisms had a similar impact on the stability of sandy sediments. In contrast, parasitism slightly reduced the destabilisation effect of cockles in MPB-enriched sediments. In the latter, parasitised cockles did not interfere with MPB growth whereas unparasitised organisms constrained the microalgae development. However, the enrichment of the surface layers of sandy sediments with MPB did not modulate the erosion dynamics of these environments. Thus, the lower destabilisation effect of parasitised cockles was not here linked to a stabilisation effect of MPB. When standardised for length, parasitised cockles were lighter than unparasitised organisms. Weakened cockles may have had a lower bioturbation potential than unparasitised conspecifics. If so, the influence parasitised cockles had on sediment erodibility and sediment roughness may have been reduced. The absence of a parasitism effect on the dynamics of MPB-unenriched sediments remains nonetheless unclear.

Sedimentation rate and physical properties of bottom sediments in the Angara reservoirs under the cyclical conditions of the level regime

Research subject. The article presents the results of a study of sedimentation rate and physical properties of bottom sediments in the Angara reservoirs under controlled level regimes. Materials and methods. The work was based on the materials of fieldwork carried out by the author on the Angara reservoirs in 1972–2017 and open-access literature sources. The physical properties and particle size distribution of bottom sediments were determined by the standard methods of engineering geology. Results. It was found that the controlled level regime determines the time cycles of sedimentation in reservoirs, sources of sediment-forming material, sedimentation rate and ambiguity of the physical properties of bottom sediments. Conclusions. During transgressions, sands, coarse aleurites and fine-aleurite silts accumulate in reservoirs most intensively; however, during regressions, coarse aleurites and aleurite-clayey silts are accumulated. During transgressions, all types of sediments are characterised by the highest sediment density, sediment skeleton density and absorption capacity, while coarse aleurites and fine-aleurite silts exhibit high natural humidity levels. In addition, coarse aleurites are characterised by a high porosity, while fine-aleurite and aleurite-clayey silts are characterised by a high content of organic matter. During regressions, the porosity of sands, fine-aleurite and aleurite-clayey silts increases, the content of organic matter in sands and coarse aleurites increases, and all types of sediments become more saturated with carbonates.

Pore-scale evidence of ion exclusion during methane hydrate growth and evolution of hydrate pore-habit in sandy sediments

Hydrate-bearing sediments constitute complex hydrological systems, within which the pore habit of hydrate significantly affects all physical properties. However, there is scarce pore-scale evidence of the evolution of hydrate growth in porous media and the influence of water salinity in the micro-morphology of hydrate. In this paper, we used X-ray computed micro-tomography (CT) to monitor three experiments of methane hydrate growth in sand partially saturated with either NaBr or KI brine under excess-gas conditions. Gas, brine and hydrate are observed to co-exist at the pore-scale during the evolution of hydrate pore-habit towards three-phase equilibrium. The experiments and data analysis reveal that (1) hydrate forms as a porous medium mixed with inclusions of brine and gas, where hydrate and brine evolve gradually into separate phases as hydrate cages exclude salt ions, (2) hydrate growth mobilizes water over fairly long distances resulting in heterogeneous hydrate distribution, and (3) hydrate can exhibit interconnecting pore-habit at local hydrate saturations higher than ~50%, even if grown under excess-gas conditions. The results imply that hydrate micro-morphology and pore habit evolve during hydrate formation and, we suggest, so do the physical properties of hydrate-bearing sediments. Our findings provide new insights into the micro-morphology of hydrate and evolution of the properties of hydrate-bearing sediments synthesized in the laboratory and in natural systems.

Numerical analysis of microwave stimulation for enhancing energy recovery from depressurized methane hydrate sediments

In addressing the global demand for clean and renewable energy, natural gas hydrate stands out as one of the most suitable alternative energy resources with great potential and has aroused intense research interest. In this study, a two-dimensional axisymmetric model was developed and validated to investigate the effect of microwave stimulation on energy recovery from depressurized methane hydrate sediments. Simulation results indicate that the microwave stimulation can provide timely and sufficient energy to promote the rapid and continuous hydrate dissociation. Discrepant energy absorption and conversion leads to a rapid hydrate dissociation rate in the upper region of the sediments. The increasing microwave radiation density accelerates the average gas production rate but weakens the energy efficiency ratio. For evaluating the effects of selected factors including initial conditions and sediment's physical properties on hydrate dissociation, an optimal value of microwave radiation density was determined by using the Pareto optimality criterion. Compared results of the energy efficiency reveal that the effect of microwave heating on the hydrate dissociation is advantageous in the sediments with the condition of high initial water and hydrate saturation, low specific heat capacity, high thermal conductivity, and low absolute permeability. Moreover, the intensity of thermal stimulation and the range of depressurization should be adjusted to be suitable for the reservoir conditions through considering the balance between the gas generation rate and the gas production rate. Although there are still many uncertainties in the hydrate dissociation behaviors, the findings of this study can provide some insights for evaluating and optimizing the methodology for gas recovery from gas hydrate reservoirs.

Impacts of simulated infaunal activities on acoustic wave propagation in marine sediments.

The activities of infaunal organisms, including feeding, locomotion, and home building, alter sediment physical properties including grain size and sorting, porosity, bulk density, permeability, packing, tortuosity, and consolidation behavior. These activities are also known to affect the acoustic properties of marine sediments, although previous studies have demonstrated complicated relationships between infaunal activities and geoacoustic properties. To avoid difficulties associated with real animals, whose exact locations and activities are unknown, this work uses artificial burrows and simulates infaunal activities such as irrigation, compaction, and tube building in controlled laboratory experiments. The results show statistically significant changes in sound speed and attenuation over a frequency range of 100-400 kHz, corresponding to wavelengths on the order of the burrow diameter. The greatest effects were observed for tubes constructed of hard shells which increased the attenuation by ∼30 dB m-1 across the measurement band. These results highlight the importance of biogenic hard structures such as tubes on sound attenuation and suggest that organisms that create hard structures may be good targets for acoustic mapping of infaunal abundance and distribution.

Riverine biota as environmental indicators of artisanal small-scale and large-scale gold mining impacts on riverine ecosystems in Brong Ahafo Region, Ghana

A study on two adjacent small ephemeral river systems in the upper Tano River Basin in Brong Ahafo, Ghana; one impacted by ASGM and the other by a modern large gold mining (LSM), showed that impacts of mining on river sediment and water quality and quantity were reflected in the macroinvertebrate and microbial communities. This study investigated the impacts of ASGM on the ecology of the Surow River and that of a large-scale mining (LSM, the Ahafo mine) on the Subri River between February 2013 and April 2014 Macroinvertebrate communities responded to the shift in river water and sediment qualities, whilst microbial communities tended to respond to water quality only. Bioaccumulation and biomagnification of mercury were evident in fishes in the river system impacted by ASGM, although mercury was barely detected in river water and sediment. The study confirmed that impact assessment of ASGM or the modern LSM on rivers should not be limited to the physical and chemical properties of water and sediment, but also include its riverine biota.

Regional variations of carbonates in postglacial sediments and response of physical sediment properties to climatic events and vegetation

Despite an increasing number of geochemical and palynological data representing the Lateglacial and Holocene sediment sequences that are used to evaluate long-term and short-term interactions between soil and vegetation, the main environmental drivers of these processes are not fully understood so far. Soil composition, vegetation and lake evolution are diverse in all sites analysed in this study. The work was aimed to provide a comparison of the evolution of conifer and broad-leafed plant taxa spread with sediment geochemical data, including organic carbon and CaCO3 changes during the same sedimentation period. Problems addressed here analyze the increased carbonate mobility initiated by the invasion of conifers and a subsequent drop in soil pH. Together with this, the influence of organic material on accumulation of carbonates and sensitivity of Mn and Fe to redox conditions was evaluated. In general, chronologically defined changes in sediment composition revealed the intervals of more stable environmental conditions during which biotic factors were of greater importance in altering vegetation structure and the periods during which scarce vegetation had a negative impact on soil development leading to its progressive deterioration. Related changes occurred in sediments from different lakes; however, due to geographical position, responses to warming or cold events were a bit asynchronous.

From gravity cores to overpressure history: the importance of measured sediment physical properties in hydrogeological models

Abstract The development of overpressure in continental margins is typically evaluated with hydrogeological models. Such approaches are used to both identify fluid flow patterns and to evaluate the development of high pore pressures within layers with particular physical properties that may promote slope instability. In some instances, these models are defined with sediment properties based on facies characterization and proxy values of porosity; permeability or compressibility are derived from the existing literature as direct measurements are rarely available. This study uses finite-element models to quantify the differences in computed overpressure generated by fine-grained hemipelagic sediments from the Gulf of Cadiz, offshore Martinique and the Gulf of Mexico, and their consequences in terms of submarine slope stability. By comparing our simulation results with in situ pore pressure data measured in the Gulf of Mexico, we demonstrate that physical properties measured on volcanic-influenced hemipelagic sediments underestimate the computed stability of a submarine slope. Physical properties measured on sediments from the study area are key to improving the reliability and accuracy of overpressure models, and when that information is unavailable, literature data from samples with similar lithologies, composition and depositional settings enable better assessment of the overpressure role as a pre-conditioning factor in submarine landslide initiation.

Large-scale and high-similarity experimental study of the effect of drilling fluid penetration on physical properties of gas hydrate-bearing sediments in the Gulf of Mexico

In this study, the process of drilling fluid penetrating into gas hydrate-bearing sediments in the Gulf of Mexico Hydrate Joint Industry Project was simulated with conditions similar to in situ drilling process parameters and reservoir temperatures and pressures. Natural sediments were replaced by artificial sediments columns with approximately similar physical properties. The temperature, pressure, and resistivity were measured in real time, and the effects of drilling fluid penetration on the physical properties were analyzed. The hydrate saturation, penetration depth, and influence mechanism of temperature and pressure difference were obtained. By orthogonal analysis, the porosity and resistivity of the artificial sediments columns were found to be optimized closely to natural conditions, with a difference of 1.29% and 4.0%, respectively. During penetration, a positive pressure difference was useful for maintaining hydrate stability, while the temperature difference had an opposite influence. High density, low temperature, and low filtration loss drilling fluid were found to be beneficial for field drilling. Hydrate decomposition gradually occurred with increasing depth, accompanied by reformation. The front edge of resistivity lagged behind the pressure and temperature, with a depth of ~0.65 m. Therefore, for resistivity logging after drilling, logging methods with a coordinated detection depth should be considered; thus, a dual laterolog with deep focused resistivity measurements would be a better choice.

Provenance discrimination of fine sediments by mid‐infrared spectroscopy: Calibration and application to fluvial palaeo‐environmental reconstruction

AbstractDetermining sediment provenance allows a better understanding of fluvial palaeo‐dynamics, and identifying involved watersheds, at broad spatio‐temporal scales. Conventional approaches for source identification are usually based on the physical, mineralogical, geochemical, magnetic or isotopic properties of sediments. Rapid, non‐destructive and, in well‐established contexts, highly accurate, mid‐infrared spectroscopy is an alternative method for investigating sediment sources. The present research objectives are: (i) to use the mid‐infrared spectroscopy method to discriminate the provenance of fine sediments, by applying discriminant analysis on a large set of reference samples from three different watersheds in the Upper Rhine area (associated with the Rhine, Ill and Vosges tributaries); (ii) to clarify whether the provenance spectra signatures are influenced by riverine depositional contexts (bars versus banks) and, to some extent, by grain size and/or high organic matter content; and (iii) to apply the mid‐infrared spectroscopy – discriminant analysis method to a study of fluvial palaeo‐dynamics and determine the provenance of palaeo‐channel infillings. Three main sedimentary sources, divided into eight sub‐categories, have been characterized by 196 modern reference samples from 78 collecting sites. Discriminant analysis displayed a strong separating power by classifying correctly the origin of samples without any inter‐group overlap, independently from the geomorphological context (bar or bank) and associated slight changes in organic matter contents or grain size. Mid‐infrared spectroscopy – discriminant analysis investigations of the palaeo‐channel infill, complemented by radiocarbon dates and mineralogical data, allowed reconstructing general trends for the local morpho‐sedimentary dynamics over the last ca 12 millennia.