Lithology Indicator Research Articles

Characterization of Tight Gas Sandstone Properties Based on Rock Physical Modeling and Seismic Inversion Methods

Tight sandstones produce an increasing amount of natural gas worldwide. Apart from identifying the gas enrichment, the predictions of lithology and permeable zones are crucial for the prediction of tight gas sandstones. In the present study, a seismic inversion method is developed based on rock physical modeling, by which it is possible to directly predict the lithology and pore structure in tight formations. The double-porosity model is used as a modeling tool in considering complex pore structures. Based on the model, the microfracture porosity is then predicted using logging data, which are used as a factor to estimate microfractures. Parameters representing the lithology and pore structure are proposed and estimated using logging data analyses and rock physical modeling based on the framework of the Poisson impedance. Thereafter, a new AVO equation is established and extended to the form of an elastic impedance for a direct prediction of the lithology and pore structure parameters. Real data applications show that the indicators of lithology and permeable zones are consistent with the production status. They agree with the petrophysical properties measured in wellbores, thereby proving the applicability of the proposed method for the effective characterization of tight gas sandstones.

VALIDATION OF EXTENDED ELASTIC IMPEDANCE BASED ON MINIMUM ENERGY ANGLE. A CASE STUDY APPLICATION FOR OPTIMIZED PETROLEUM RESERVOIR CHARACTERIZATION

This work intends to showcase a validation of the applicability of Extended Elastic Impedance (EEI) inversion method in reservoir characterization and modeling. In order to achieve that, deterministic seismic inversion and extended elastic impedance (EEI) analysis were applied to obtain quantitative estimates of reservoir properties over the Pu field of the West African Congo basin. Optimum EEI angles corresponding to the reservoir properties were then analyzed using well logs data, together with a lithology indicator. Pre-stack seismic data were simultaneously inverted into density, acoustic and gradient impedances cubes, through model based inversion algorithm. The last two broadband inverted volumes were then projected to corresponding Chi angles proportionate to petrophysical indicators, thus resulting to two broadband EEI volumes. At well locations, the EEI versus petrophysical parameters linear trends were then applied to convert EEI volumes into porosity and shale volumes based on specified lithology. In order to generate reservoir facies distribution, minimum angle was applied based on background EEI, thus allowing for mapping of reservoir facies. In order to validate the EEI approach, a Geo-statistical model was further developed for the same field. Hence, from porosity, shale content and background EEI cubes, a comparison was made between the properties generated from the EEI and that generated based on geo-statistical method, which shows that EEI is a robust way of reservoir characterization that pinpointing favorable reservoir potentials which shall guide future drilling locations.

Quantifying climate conditions for the formation of coals and evaporites.

Coals and evaporites are commonly used as qualitative indicators of wet and dry environments in deep-time climate studies, respectively. Here, we combine geological records with climate simulations to establish quantitative relationships of coals and evaporites with temperature and precipitation over the Phanerozoic. We show that coal records were associated with a median temperature of 25°C and precipitation of 1300mmyr-1 before 250 Ma. Afterwards, coal records appeared with temperatures between 0°C and 21°C and precipitation of 900mmyr-1. Evaporite records were associated with a median temperature of 27°C and precipitation of 800mmyr-1. The most remarkable result is that net precipitation associated with coal and evaporite records remained constant across time. The results here have important implications for quantifying climate conditions for other lithologic indicators of climate and for predicting exogenetic ore deposits.

Lithology discrimination based on direct inversion of Poisson impedance for deep tight-sandstone reservoirs

AbstractLithology discrimination plays an important role in characterizing deep-hydrocarbon reservoirs, particularly for tight sandstones with special petrophysical properties. Stable prediction of lithological-sensitive parameters for deep tight sandstones is a significant challenge. In this paper, a direct inversion method of elastic impedance is developed to estimate lithological-sensitive parameters from pre-stack seismic data to improve the stability of the inversion. Elastic and physical parameter models extracted from actual wells are used to analyze the influence of petrophysical parameters on amplitude variation with offset characteristics. Cross-plots and sensitivity analysis of elastic parameters illustrate that the elastic-sensitive parameter Poisson impedance (PI) can distinguish gas-bearing sandstone and abnormal limestone in deep tight-sandstone reservoirs. In addition, a pragmatic elastic impedance direct inversion under the framework of Bayesian theory is implemented for the lithology indicator PI from pre-stack seismic data. And the Cauchy regularization and low-frequency regularization constraints are used to construct the objective function for improving the robustness of inversion. Field data examples show that the inversion results are in good agreement with the well logging interpretation results, and validate the feasibility and stability of the proposed method in the estimation of inverted parameters. Finally, we can conclude that this method has great application potential in the lithology discrimination of deep tight-sandstone reservoirs.

Color changes in yardang strata sediment in the Dunhuang Yardang National Geopark, Northwest China: Controlling factors and significance for sedimentary environments

Introduction: Yardang stratum is the basic material unit of yardang landforms. Due to their protracted age and complex sedimentary structure, formative yardang stratum mechanisms remain poorly understood. Color, being one of the most intuitive, easily accessible, and important lithological indicators, can be used to identify yardang strata sedimentary environments. However, the lack of quantitative analysis and systematic research have limited how chromatic environmental proxies can be extracted and interpreted.Materials and methods: The Dunhuang Yardang National Geopark was selected for this experiment. Based on chromaticity, grain-size, chemical element, organic matter, and carbonate content measurements of yardang strata sediment samples, this study used correlation analysis and chromaticity proxy extraction to quantitatively characterize associated color changes, controlling factors, and sedimentary environments.Results and discussion: Results found significant cyclic changes in chromaticity parameter curves were observed in the profiles, which is likely indicative of a dry/wet evolutionary process that occurred during different stages of the yardang sedimentary environment. Organic matter content was the main factor affecting changes in brightness, while iron oxide content directly affected yardang sediment redness and yellowness values. Due to its low value, effects of carbonate content on brightness were obscured. The grain-size characteristics indirectly affect the brightness value through the content of quartz, feldspar and organic matter. Moreover, based on modern analogy method, the brightness and redness values are proved to be effective proxies for distinguishing the yardang sedimentary environment. Accordingly, it is concluded that the sedimentary environment of Dunhuang yardang landforms is composed of sedimentation that derived from lacustrine, aeolian, and alluvial environments, and that the chromaticity parameter range and characteristic color for sedimentary environments are extracted and quantified. Findings from this study not only rectify the lack of quantitative research on yardang sediment color theory but also provide an important theoretical basis for identifying sedimentary environments in the field.

FLUID PREDICTION THROUGH LITHOLOGICAL ANALYSIS IN ‘M’ OIL FIELD NIGER DELTA: USING ROCK PHYSICS APPROACH

3D Lithology and reservoir fluid studies based on conventional interpretation approach, such as low Vp/Vs values indicating gas presence have been used to discriminate hydrocarbon fluids. This work was provoked by the emerging trends of noticeable uncertainties leading to drilling of dry wells in the study area. Confirming the physical indicators of hydrocarbon in the reservoirs through the employed method is worthwhile. Well log data of M oil field was investigated with the aim of identifying reservoir rocks through qualitative and quantitative interpretations of subsurface well log data of M oil field through rock properties cros-splots analysis in the select reservoir in the field (M-5000) and to derive elastic rock attributes such as Lame’s parameter terms (λρ and μρ), Vp/Vs, P-Impedance and S-Impedance from available petrophysical data. Rock attributes derived from well logs were combined to produce three major forms of crossplots, which described and characterized the reservoir in terms of fluid and lithology present. The combinations were: VP/VS versus IP, μρ against λρ and IP versus IS. These rock parameters were analyzed in cross-plots space and used to determine which of them constitutes better indicators of pore fluids and lithology. The M- oil field cross-plot analysis indicate the lowest values of VP/VS (2.05-2.40); IP (5600-6300 (m/s*(g/cc)), λρ (16-20 (GPa*g/cc)), and μρ (4-9.5 (GPa*g/cc)). However, the low values of VP/VS, IP, λρ, and μρ, perhaps IS corresponds to hydrocarbon (Gas) saturation within the M- oil field.

Evolution and driving mechanisms of water circulation during the late Paleozoic to early Mesozoic

<p indent="0mm">Water circulation plays a crucial role in the Earth’s systems, linking the atmosphere, hydrosphere, lithosphere, and biosphere. During the Paleozoic-Mesozoic transition, climatic and environmental conditions turned into crises, caused by a sudden and serious global warming, accompanied by the largest known extinction event of all time. Several studies have been conducted to discover the causes of this notable climate change. Nevertheless, the evolution of water circulation processes during the Paleozoic-Mesozoic transition is still unclear. Several lithologic indicators present in paleoclimate records have been described over the last few decades. Based on these data, we defined climate zones and calculated their area values using Thiessen polygons and Geographic Information System technology to visualize climate evolution during the Paleozoic-Mesozoic transition. Results of a few of the climate simulations showed changes in precipitation and the amplitudes of the inter-tropical convergence zone (ITCZ) seasonal migration. The results showed several changes in water circulation during the late Paleozoic to early Mesozoic. (1) The climate zones reconstructed by sedimentary and paleontological records showed a remarkable arid expansion. The distribution area of evaporites began to expand in the Middle to Late Permian and reached a peak in the Early Triassic, returned to Middle-Late Permian levels in the Middle Triassic, and thereafter continued to narrow during the Late Triassic to Early Jurassic. (2) Global precipitation was higher during the Late Carboniferous and Early Jurassic and lower in the Middle to Late Permian and Early Triassic. Such a “V” shape represents considerable swing. (3) The assembly of Pangea might have led to “giant land surface winds” in Pangaea and “trans-equatorial winds” in the Tethys region, resulting in a global “megamonsoon”. (4) Seasonal movements of the ITCZ were located at lower latitudes from the Silurian to Carboniferous and from the Jurassic to the present, while reaching higher latitudes with large seasonal oscillations during the Permian-Triassic. Depending on the timing of events, these major changes in water circulation coincided with the assembly of Pangaea, the Variscan or Hercynian orogeny, the end of the late Paleozoic ice age, major carbon emissions, and global warming. These factors are closely related to the changes in atmospheric and water circulation during the Paleozoic-Mesozoic transition. The assembly of Pangea redistributed water storage and altered atmospheric circulation and the “megamonsoon”, while the elevation reduction of mountains traversing middle Pangea weakened the resistance of north and south winds. These factors promoted the evolution of a “megamonsoon” with strong seasonal swings of the ITCZ, which led to the expansion of arid zones and reduced precipitation during the Middle and Late Permian. Meanwhile, large carbon emissions and dramatic global warming altered the energy transition within global systems, which influenced atmospheric circulation. In addition, transformations of global plant clades affected the carbon budget and altered water circulation. In summary, strong fluctuations in water circulation were present during the Paleozoic-Mesozoic transition, especially as observed through climate zones, precipitation and runoff, the “monsoon”, and ITCZ. These crucial processes reflect the interaction between the lithosphere, atmosphere, hydrosphere, and biosphere. However, we have limited knowledge of the complete process of water circulation because geological records and climate simulations are extremely imprecise for the Paleozoic-Mesozoic transition. Future research could focus on other water circulation processes, such as the evolution of underground water, reserves, and fluxes of lakes, rather than only precipitation and “monsoons”. Moreover, the upgrade and extension of big data platforms and a larger number of climate simulations should be considered in future studies.

Seismic characterization analyses of the Bulgarian Black Sea shelf for assessment of reservoir properties

In the Bulgarian Black Sea shelf, several gas fields have been discovered in Maastrichtian–Paleocene sediments to date. In this study, amplitude versus offset analysis (AVO) was carried out, and the extended elastic impedance (EEI) was also used, to predict fluid and lithology properties. Thus, in these special cases, AVO (or reflection angle) can significantly de-risk the existing Paleocene prospects and allow to focus on the Miocene–Oligocene successions, where some prospects have also been identified. By examining the variations in angle amplitude (or offset), it is possible to unravel lithology and fluid effects on the top of a reservoir. Seismic modeling is used to determine what type of seismic response, in terms of AVO, to expect at the depth of interest in the study area. There are five classes or types of AVO responses, and in the study area classes 1 and 2 were defined in the Miocene–Oligocene prospects. Brine-filled reservoirs and conglomerates exhibit class 1 AVO response, whereas gas-filled reservoirs show class 2 AVO responses. EEI has the ability to give estimates for elastic parameters, such as Vp/Vs ratio, bulk modulus, shear modulus, Poisson’s ratio and other parameters. In the current study, simultaneous inversion testing was done and, analyzing all the wells together, Poisson’s ratio is the most promising fluid and lithology indicator, showing good separation between water and gas responses, although there is some overlap. Projection of EEI at an angle of 38° through brine points gives a useful separation of brine, 10% gas and 90% gas reservoirs. However, the amplitude of the resulting projection is still low, which may make it difficult to resolve fluid variation once seismic noise has been added.

Monsoonal climate of East Asia in Eocene times inferred from an analysis of plant functional types

The spatio-temporal vegetation patterns of East Asia in the Eocene remain uncertain. In this present paper, we conduct numerical analyses of plant functional types (PFTs) for 80 Eocene floras, subdivided into three-time intervals: the early, middle, and late Eocene. Based on PFT diversity spectra, five groups are identified from cluster analysis and interpreted in terms of vegetation type. These PFT-based vegetation reconstructions suggest a northwestward retreat of dry shrub or open woodland from early to late Eocene times, coupled with the expansion of humid broadleaved forest from the southeast. This hydrological distribution is consistent with mammal distribution, lithological indicators and geochemical proxies. An overall vegetation pattern of largely east-west differentiation is detected and we note that no unequivocal tropical vegetation is observed in low-latitudes during the Eocene. Our results indicate that a monsoonal climate shaped the Eocene spatio-temporal evolution of vegetation in East Asia along with the global cooling, and rain-shadow effects by the central and southwestern China highland, as well as basin extensions in the Pacific coast in the east.

Density - Velocity Relationship and Prediction of Lithology Variation Using Physical Analysis in Kf-4 Well of The Kifl Oil Field, Yamama Formation, South of Iraq

The density-velocity relation is an important tool used to predict one of these two parameters from the other. A new empirical density –velocity equation was derived in Kf-4 well at Kifl Oil Field, south of Iraq. The density was derived from Gardner equation and the results obtained were compared with the density log (ROHB) in Kl-4 well. The petrophysical analysis was used to predict the variations in lithology of Yamama Formation depending on the well logs data, such as density, gamma, and neutron logs. The physical analysis of rocks depended on the density, Vp, and Vs values to estimate the elastic parameters, i.e. acoustic impedance (AI) and Vp/Vs ratio, to predict the lithology and hydrocarbon indicators. According to the results of physical properties, Yamama Formation is divided into five units in Kf-4 well at Kifl Oil Field. The lithology of Yamama Formation was found to consist of limestone, dolomite, shale, and anhydrite rocks.

3D Seismic stratigraphy applied to lithology estimation in a deltaic system

Seismic stratigraphy becomes a useful tool when it comes to 3D lithology distribution, since it gives the interpreter insights of the facies most likely to be present in a certain sedimentary environment. On the other hand, it is also the main input information while modeling petrophysical properties like water saturation, effective porosity and permeability, which are critical in the process of evaluation of a hydrocarbon reservoir. In this context, techniques such as seismic inversion allows the geoscientists to get 3D models of P-impedance, S-impedance and density, which are used as the main input to estimate the reservoir petrophysical properties just mentioned and additionally useful parameters used as a lithology indicator. This paper proposes a workflow to achieve the goal of integrating seismic stratigraphy, seismic inversion and attributes to get a lithology 3D model. Now, to get a suitable correlation between the facies interpreted using well logs and core data with the elastic properties, rock physic templates (RPT’s) were made where proper elastic modulus was carefully chosen to define probability distribution functions (PDF’s) for each facies defined in the correlation wells. On the other hand, based on a set of stratigraphic surfaces created on a different study, 3D models of P-impedance, S-impedance and density were obtained from seismic inversion so that the RPT’s could be built. For this specific instance, only a set of the elastic properties and seismic attributes offered a suitable correlation with the facies defined in the calibration wells. Moreover, the probability distribution functions (PDF’s) already generated allowed the distribution in 3D and the definition of the ranges in which each facies previously stated varies for the elastic modulus estimated.

Hydrocarbon Prospectivity in the undrilled area of AIMA Field in the Niger Delta Basin, Nigeria.

Field development is a very costly endeavor that requires drilling several wells in an attempt to understanding potential prospects. To help reduce the associated cost, this study integrates well and seismic based rock physics analysis with artificial neural network to evaluation identified prospects in the field.&#x0D; Results of structural and amplitude maps of three major reservoir levels revealed structural highs typical of roll over anticlines with amplitude expression that conforms to structure at the exploited zone where production is currently ongoing. Across the bounding fault to the prospective zones, only the D_2 reservoir possessed the desired amplitude expression, typical of hydrocarbon presence. To validate the observed amplitude expression at the prospective zone, well and seismic based rock physics analyses were performed. Results from the analysis presented Poisson ratio, Lambda-Rho and Lambda/Mu-Rho ratio as good fluid indicator while Mu-Rho was the preferred lithology indicator.&#x0D; These rock physics attributes were employed to validate the observed prospective direct hydrocarbon indicator expressions on seismic. Reservoir properties maps generated for porosity and water saturation prediction using Probability Neural Network gave values of 20-30% and 25-35% for water saturation and porosity respectively, indicating the presence of good quality hydrocarbon bearing reservoir at the prospective zone.

Evaluating the potential of carbonate sub-facies classification using NMR longitudinal over transverse relaxation time ratio

While the well log-based lithology classification has been extensively utilized in reservoir characterization, the classification of carbonate sub-facies remains challenging due to the subtle nuances in conventional well-logs. The nuclear magnetic resonance (NMR) log provides extra information of pore size and pore geometry features, improving differentiating carbonate sub-facies. Here we explore the feasibility of using the ratio between NMR longitudinal relaxation time and transverse relaxation time as a potential lithology indicator to determine carbonate sub-facies. We analyzed a series of logging data and corresponding core samples of Arbuckle Group carbonate containing mudstone, packstone, grainstone, incipient breccia, and breccia in northern Kansas for the characteristics of longitudinal relaxation times, transverse relaxation times, and longitudinal over transverse relaxation time ratios. The results show that mudstone, packstone, and grainstone exhibit high, intermediate, and low longitudinal over transverse relaxation time ratios, respectively, while incipient breccia and breccia have a wide range of longitudinal over transverse relaxation time ratios. Furthermore, we evaluated the potential of using longitudinal over transverse relaxation time ratios to classify carbonate sub-facies using multivariate analysis. By adding longitudinal over transverse relaxation time ratios to neutron porosity, total gamma-ray, and conductivity logs as inputs of automated facies classification, the prediction error decreased, especially for incipient breccia. On the contrary, when photoelectric log and computed gamma-ray are also available, adding longitudinal over transverse relaxation time ratios does not improve the accuracy of sub-facies classification. Our results suggest that longitudinal over transverse relaxation time ratio is an independent lithology indicator. However, it cannot replace other logs like gamma-ray and photoelectric logs in classifying carbonate sub-facies. Our study provided valuable evidence and credible elucidation of the importance and physicochemical mechanism of longitudinal over transverse relaxation time ratios, which is essential for deciphering NMR logging data in carbonate reservoirs. Cited as : Zhang, F., Zhang, C. Evaluating the potential of carbonate sub-facies classification using NMR longitudinal over transverse relaxation time ratio. Advances in Geo-Energy Research, 2021, 5(1): 87-103, doi: 10.46690/ager.2021.01.09

Brittleness computation from rock moduli without density

Brittleness is a key property for horizontal well placement, fracture development, and production sustainability assessments of unconventional shale and gas plays. Conventionally, brittleness is estimated from Young’s modulus and Poisson’s ratio, and averaged. As Young’s modulus is a function of density, field wide brittleness estimation from Young’s modulus after seismic inversion may be compromised because density is the least accurate estimate compared to acoustic impedance and shear impedance. A simple quantitatively equivalent brittleness computation can be made from using Young’s modulus × density rather than directly from Young’s modulus. Further, it is preferable to use the average brittleness estimation from Young’s modulus × density and shear modulus × density rather than the conventional average, because Poisson’s ratio is an indicator of lithology rather than brittleness. Examples of brittleness and total organic carbon estimation first from well logs, then from rock parameters inverted from 3D land seismic data successfully mapped a brittle shale zone in a Silurian hot shale, a known source rock onshore Turkey and now targeted as oil shale play. The estimated brittleness and total organic carbon showed agreement with the core analysis made at another well on the same prospect.

Patterns in river channel sinuosity of the Meuse, Roer and Rhine rivers in the Lower Rhine Embayment rift-system, are they tectonically forced?

The tectonic and fluvial setting of the Rhine-Meuse river system in the Lower Rhine Embayment rift system is exceptionally well known. The 19th century, pre-regulation river courses of three rivers are used to study a postulated sinuosity response to faulting. The fault-perpendicular Meuse River shows patterns of sinuosity changes at different spatial scales. The large-scale (>5 km) sinuosity changes are related mainly to the faulting-induced changes of the subsurface lithology, determining the bed and bank characteristics. However, at a smaller scale, some fault-related channel sinuosity anomalies are observed. The fault-parallel Roer River shows sinuosity changes related to a normal, non-tectonic longitudinal gradient change. Sinuosity patterns of the Rhine River are predominantly related to lithological differences and reduced incision rates. Sinuosity can thus be an indicator of tectonic motions, but gradient, subsurface lithology and river bank composition determine sinuosity as well. Therefore, a sinuosity change is no proof for fault activity. On the other hand, the absence of a sinuosity change does not imply inactivity of a fault at geological time-scales.

Rock physics attribute analysis for hydrocarbon prospectivity in the Eva field onshore Niger Delta Basin

Direct hydrocarbon indicator (DHI) expressions observed on seismic could arise due to various geological conditions. Such expression could lead to misinterpretation as hydrocarbon presence if not properly analyzed. This study employs rock physics attributes analysis to evaluate an identified prospect in the undrilled area of the studied reservoir. Prospect identification was actualized by analyzing structural and amplitude maps of the reservoir, which revealed a possible roll over anticline at both the exploited and prospective zone, with a very good amplitude support that conforms to structure. Well-based cross-plot analysis adopted four cross-plot techniques for feasibility study to test the applicability of rock physics for prospect evaluation in the field; Lambda-Rho versus Lambda-Rho/Mu-Rho ratio; Mu-Rho versus Lambda-Rho; and Poisson Ratio versus P-impedance. The result presented Poisson ratio, Lambda-Rho and Lambda/Mu-Rho ratio as good fluid indicator and Mu-Rho as a viable lithology indicator. As such, they were selected for seismic-based attribute and cross-plot analysis to validate the identified prospect. The results from seismic-based analysis showed consistency in the expression of the analyzed attribute at both the exploited and prospective zone. The seismic-based cross-plot analysis result was similar to the well-based analysis and was able to confirm that the observed amplitude expression in the exploited zone is an indication of hydrocarbon-bearing sand.

Rare earth elements in mineral waters in Serbia

The systematically varying properties and generally coherent and predictable behavior of rare earth elements (REE) make them potential tracers for studying water/rock interaction and weathering processes. In this work, a compilation and analysis of REE data in mineral and thermal waters were performed, focusing on their content and distributions in different hydrogeological systems, to quantify the natural REE variability and to discuss the controlling factors of REE concentrations. Quantitative challenges presented by multiply censored data were addressed with nonparametric and multivariate statistical methods. Considering a regional character of the research the application of Q and R mode Hierarchical Cluster Analysis with spatial analysis was an important approach for meaningful interpretation of large data set. An efficient approach to analyze differences between obtained HCA groups (clusters) was using a plot of reference-normalized concentrations. The results showed that REE data along with anomalies of Ce and Eu and inter-element ratios were good indicators of the aquifer lithology (hydrogeological systems formed in granitoid and volcanic rocks of various age, two main types of hydrogeological basins, and carbonate aquifers). The important mechanisms controlling REE migration in water were hydrochemical conditions in aquifers. The significance of the applied statistical analyses was represented by defining specific hydrochemical fingerprints of identified hydrogeological systems with distinct geochemical characteristics where REE showed the necessity of understanding of complex geological and hydrogeological settings, geodynamic evolution, and hydrogeochemical processes in fluid flow systems.

Lithological indicators of discontinuities in mountain soils rich in calcium carbonate in the Polish Carpathians

Six soils located within the Polish Carpathians, developed on calcium carbonate–rich sedimentary parent materials and representing various reference groups, were investigated in order to detect the lithic discontinuity. We propose using a multidirectional approach to assess the lithic discontinuity in these soils, one that includes grain size distribution, geochemical composition, heavy mineral content and micromorphology, supported by a traditional soil survey. A further aim of this process was to identify the possible admixture of allochthonous material of aeolian origin. The studied soils presented lithic discontinuities mostly at the contact of underlying calcium carbonate–rich coarsegrained slope deposits with the overlaying colluvium layer having a lower content of rock fragments. The significant changes in grain size distribution, especially in the silt and sand content, as well as high Uniformity Values and partially, high Lithological Discontinuity Index values, confirmed the occurrence of a lithic discontinuity in all studied soils. High heterogeneity in the soil profiles was also confirmed by the distribution of the major oxides; however, their distribution did not clearly indicate the lithic discontinuity. The most visible distinctions were noted from CaO content, which resulted from the deposition of carbonate-free materials (aeolian silts) and their mixing with the calcium carbonate–rich parent material. Furthermore, the analysis of heavy mineral content confirmed the allochthonous origin of the upper (and in some cases also the middle) parts of all profiles, which was manifested by the presence of highly weathering-resistant minerals such as zircon, epidote and various types of garnets. The micromorphological features of some of the studied soils showed distinctiveness within the soil profile, manifested by changes in b-fabric pattern, the occurrence and distribution of secondary carbonate and the coarse and fine coarse and fine ratio. Based on the high content of silt within the upper and middle parts of the soils, the content of Hf and Zr, as well as the higher content of weathering-resistant minerals, admixture of aeolian silt could be considered in some of the studied soils, yet with weak character. However, the dominance of minerals typical for metamorphic and igneous rocks suggested that the supply of aeolian silt was associated with loess covers rather than local sedimentary material.

Automated mineralogical profiling of soils as an indicator of local bedrock lithology: a tool for predictive forensic geolocation

Abstract The use of soil evidence to identify an unknown location is a powerful tool to determine the provenance of an item in an investigation. We are particularly interested in the use of these indicators in nuclear forensic cases, whereby identification of locations associated with, for example, a smuggled nuclear material, may be used to indicate the provenance of a find. The use of soil evidence to identify an unknown location relies on understanding and predicting how soils vary in composition depending on their geological/geographical setting. In this study, compositional links between the mineralogy of 40 soils and the underlying bedrock geology, as documented in local-scale geological maps, were established. The soil samples were collected from locations with broadly similar climate and land use across a range of geological settings in a ‘test bed’ 3500 km 2 area of SW England. In this region, the soils formed through chemical weathering of the bedrock, representing a worst case scenario for this type of forensic geolocation owing to the high degree of alteration of the parent rock during soil formation. The mineralogy was quantified using automated scanning electron microscopy–energy dispersive X-ray spectrometry analysis based on QEMSCAN technology. Soil mineralogy and texture as measured using this technique are consistent with the underlying geology as indicated by regional-scale geological mapping. Furthermore, differences between individual units of the same bedrock lithology, such as different granites, were identified by examining trace mineralogical signatures. From an investigative viewpoint, this demonstrated that rapid automated mineral profiling of soil samples could be used, in conjunction with readily available geological mapping or similar datasets, to provide indication of the areas from which a soil sample of unknown origin could, or could not, have been sourced.

Geochemical Features of Annual Layers of Bottom Sediments of Freshwater Lakes, Studied via Synchrotron Radiation–Induced XRF Microanalysis

The possibility of distinguishing layer boundaries through lithological and geochemical indicators (Rb/Sr ratio) is shown by a case study of bottom sediments from Lake Kucherlinskoe (Altai). Based on the data from scanning synchrotron radiation–induced XRF microanalysis and isotope studies, a record of the Tunguska event of 1908 is found in the bottom sediments of Lake Zapovednoye, forty kilometers from the explosion’s epicenter. An anomalous layer in the sediments is associated with an increase in the terrigenous drift in the catchment area due to massive forest outfall and subsequent fires. The possibility of a targeted search for microparticles of extraterrestrial origin in lake sediments is demonstrated.