Neogene Clays Research Articles

Reclaimed mine soil substrates and tree stands vs. successional forest floor vegetation: A case study of developing ecosystems on afforested mine sites

This study presents an analysis of the relationships among tree species, the type of mine soil substrate vs. vegetation development and features of plant communities. The study was conducted on two types of afforested mine sites (open strip sulphur and sand pit mine) built from various parential rocks: mixed quaternary sands and Neogene clays (QsNc) and quaternary loams (Ql). The study plots were arranged in stands of Scots pine (Pinus sylvestris L.), European larch (Larix decidua Mill.), silver birch (Betula pendula Roth) and black alder (Alnus glutinosa Gaertn.) from 25 to 35 years old. Tree stand parameter measurements and analyses of soil substrate properties and vegetation characteristics based on phytosociological surveys were done. The diversity expressed as the number of species (S) and Shannon-Wiener index (H), the Simpson dominance index (C) and ecological indicator values of vascular plants (EIVP) were assayed. We hypothesised that in similar substrates (parent rock conditions) the influence of tree stand species in the early phase of reclaimed ecosystem development is significant. Based on the results, we concluded that forest floor vegetation under deciduous species had clearly more herb layer cover and less moss in comparison to vegetation under coniferous species, which confirmed a significant influence only on the level of the ecological group of trees and not at the level of individual tree species. In contrast, the diversity of plant communities was influenced mainly by tree stand species. The highest diversity indexes (H) of communities were under birch and larch, and the lowest H was noted under alder. This phenomenon may be explained by the impact of the alder on soil nitrogen content, which led to the domination of communities by highly competitive species such as Aegopodium podagraria L. and Geranium robertianum L. on QsNc and Calamagrostis epigejos (L.) Roth on Ql. Only EIVP values depended more strongly on soil substrate than tree stand species, and these were only slightly affected by tree stand species composition. Among the tree species, alder significantly increased the value of trophy indicators.

Neogene clay and its relation to landslides in the southwestern Loess Plateau, China

Loess occurs widely in Northwestern China, covering Neogene clay and other sedimentary units that overlie the bedrock. The Neogene clays of the Baoji Region of Shaanxi Province, north China, including the eolian Hipparion and paleo-Sanmen Lake fluvial deposits, are typical clays of the southern Chinese Loess Plateau. These clays are also sensitive key strata controlling the development of large-scale landslides along the slope of the loess tableland surrounding the Guanzhong Basin. To investigate the Neogene clay types and landslides in the region, soil samples were tested and the macro- and micro-structures of the clay strata were analyzed. Comprehensive analysis methods, including the pipette method and fine X-ray diffraction, were applied to quantitatively analyze the sample composition and determine the clay mineral types. The Neogene clays are mainly composed of illite and montmorillonite mixed-layer minerals. On the Williams’ discrimination diagram of swelling potential, both types of clay are medium to strongly expansive soil. Two case studies illustrate that rainfall reduces the shear strength of the Neogene clay and raises the groundwater level. Rainfall has gradually destroyed the structure of the Neogene clay, transforming it to sliding belt soil. The sliding belt lies mainly within the Neogene clay layers, significantly affecting the occurrence and characteristics of landslides in Baoji. The rise in groundwater level and weakening of the shear strength of the Neogene clay are important factors in the occurrence of landslides. The long-term strength is a key factor affecting the development of loess landslides along the loess tableland in Baoji.

Prediction of swell pressure in Neogene clays from Warsaw, based on the swell index

The paper presents the results of swell measurements of Neogene clays (Posnanian clay) from the Mazovia region with different grain size distribution and mineral composition. The study was conducted with model soil with initial moisture contents of 15%, 20%, 25% and 30%. The basic physical properties of clays, their mineral composition and swelling parameters such as free swelling index and swelling pressure were determined. Free swell index was correlated to liquid limit, plasticity index, clay content and water content. A very high fit was found for a proposed relationship between the free swell index and swell pressure which offers an inexpensive method of predicting swell pressure in the preliminary stages of site investigation.

НОВІТНЯ ЗАБУДОВА ХМЕЛЬНИЦЬКОГО: ЗМІНИ МОРФОЛОГІЇ ПОВЕРХНІ ТА СУПУТНІ ПРОЦЕСИ

The article presents results of research in 2010–2017 on site in the Pivnichnyi (ukr.North) district of the Khmelnytskyi City. The terrain topography evolved here from mostly natural into almost completely anthropogenic. This change was caused by the latest construction development. As a result, gentle and moderate slopes of balka turned into cascades of artificial terraces with ledges up to 6 m high, the valley bottom is now bulked. In general, the maximal capacity of bulk deposits in the studied area reaches 7,5 m. Natural features contributed to linear erosion, landslides, subsidence, waterlogging, human activities stopped the action of some (erosion, waterlogging, subsidence), but activated other (landslides). After human impact landsliding occurs in the bulk deposits and engineered sediments, as well as in the recently opened naturalsediments. For example, Neogene clays get dry, crack and spread. Other types of landslides are the rotational, shallow translational and slowearthflow. Earlier only the small rotational landslides and, most likely, earthflows have happened on the left balka's flank. Activation of landslides began in 2013. The conclusions are based on the field observations in 2010, 2014–2017, interviews, as well as on interpretation of geotechnical engineering data by "Khmelnytskyi Budrozviduvannya" and "Zhytomyr Budrozviduvannya" (ukr.Khmelnytskyi / ZhytomyrConstr[uctional] Investigation). Key words: urban geomorpology, artificial terrain, artificial terraces, engineered sediments and bulk deposits, landslides, Khmelnytskyi City.

Preliminary Investigations of Creep Strain of Neogene Clay from Warsaw in Drained Triaxial Tests Assisted by Computed Microtomography

Abstract The study concerns soil creep deformation in multistage triaxial stress tests under drained conditions. High resolution X-ray computed microtomography (XμCT) was involved in structure recognition before and after triaxial tests. Undisturbed Neogene clay samples, which are widespread in central Poland, were used in this study. XμCT was used to identify representative sample series and informed the detection and rejection of unreliable ones. Maximum deviatoric stress for in situ stress confining condition was equal 95.1 kPa. This result helped in the design of further multistage investigations. The study identified the rheological strain course, which can be broken down into three characterizations: decreasing creep strain rate, transitional constant creep velocity, and accelerating creep deformation. The study found that due to multistage creep loading, the samples were strengthened. Furthermore, there is a visibly “brittle” character of failure, which may be the consequence of the microstructure transformation as a function of time as well as collapse of voids. Due to the glacial tectonic history of the analyzed samples, the reactivation of microcracks might also serve as an explanation. The number of the various sizes of shear planes after failure is confirmed by XμCT overexposure.

Determination of swell index and swelling pressure from suction tests – a case study of Neogene clays from Warsaw (Poland)

The paper presents the results of swell index, swelling pressure and soil suction tests carried out on Neogene clays from Warsaw, depending on the water content, clay fraction, liquid limit, plasticity index, cation exchange capacity, and content of clay minerals and beidellite. These clays are considered expansive soils in Poland, as they are vulnerable to water content variations in the active zone, which result in their volume change and, in consequence, cause damage of foundations and other construction elements. A number of physical, chemical and mineral properties were determined for these clays. The swelling tests were carried out on samples precompacted in Proctor apparatus, at various initial values of water content. The analyses have shown exponential relation of swell index, swelling pressure and suction versus water content. In addition, the investigated relationship between the suction and swell characteristics of tested clays shows good correlation as a power function between these parameters. In addition, validity of correlations between fitting parameters of obtained relationships and soil index properties, such as clay fraction, liquid limit, plasticity index, cation exchange capacity, and content of clay minerals and beidellite, have been demonstrated. The empirical relations are characterized by high values of the correlation coefficient. A very high fit has also been found for a proposed relationship between the swell index and swelling pressure for tested clays

Elsterian ice sheet dynamics in a topographically varied area (southern part of the Racibórz–Oświęcim Basin and its vicinity, southern Poland)

During the Elsterian Glaciation, the Scandinavian Ice Sheet, before reaching its maximum extent, advanced over the mountainous foreland of Southern Poland, which was characterized by a substrate of increasingly varied relief. One such area was the hilly Rybnik Plateau of the southern part of the Raciborz–Oświecim Basin, located directly north of the Ostrava Basin and Moravian Gate, where the ice sheet advanced far south and formed a large lobe. In this study, till from the Łaziska site, located in southern part of the Rybnik Plateau, was analysed and interpreted. The till was deposited at the top of an W–E oriented ridge composed of Neogene clays. The study indicates that a high basal water pressure occurred at the base of the ice sheet, favouring a basal mechanism of ice sheet movement. Till fabric and kinematic structures indicate that ice flowed easily from the west over the ridge, parallel to its axis. Reconstructed patterns of ice flow direction reflect an ice sheet that was characterized by a strong spatially varied dynamics. The Odra Valley was the main corridor of fast flowing ice to the Ostrava Basin, from where ice was distributed radially in different directions. The second corridor of actively flowing ice was probably located in the Ruda palaeovalley to the north of the Rybnik Plateau. In the central part of the Rybnik Plateau, ice flow was restricted. This less dynamic ice sheet behaviour resulted mostly from the much higher location of the area. This study indicates that the large morphological and lithological variations of the ice sheet substrate induced varied frictional resistance, producing a spatially varied stress field within the ice sheet. This generated active zones of streaming ice adjacent to more passive zones. Potential switching between neighbouring active zones transporting ice towards the ice sheet margin is postulated.

Full-scale Testing of Ground Anchors in Neogene Clay

The research campaign aimed on the better understanding of behavior of prestressed soil anchors in neogene clay, including conduction of variety of in-situ (CPT, PMT) and laboratory (Triaxial test, Simple shear test an Oedometric test) ground investigation methods, has been done during 2012 – 2015 in Czech Republic. The stress – strain diagrams and distribution of axial force along the anchor free length and anchor bond length was determined, based on the data obtained from variety types of sensors placed onto the tendon and into the gravity and post-grouted part of the grout body. On the basis of this information the software application for prediction of the anchor pull-out force and stress-strain diagram was developed, calibrated and verified. The application for purposes of conduction of prestressing tests and test reports elaboration was programmed also. Research activities leading to development of the pair of forenamed software are described in paper.

IDENTIFICATION OF CLAY SOIL MINERALOGY AND SWELLING BY THE FREE SWELL RATIO METHOD

The paper presents the results of free swell measurements of Neogene clays and model clay mixtures composed of Wyoming bentonite and Sedlec kaolinite. Modified free swell index (MFSI) as well as free swell ratio (FSR) were determined and analyzed with respect to pore fluid chemistry, mineral composition and clay content. The FSR, defined as the ratio of the equilibrium sediment volume of 10-g oven dried soil in 0.0025% NaCl solution to that in kerosene, has proved to provide only a rough prediction of clay mineralogy in natural soils.

Mineralogical characterization of Neogene clay areas from the Jijel basin for ceramic purposes (NE Algeria -Africa)

Clayey marl from four localities in the Neogene basin of Jijel (NE Algeria) were studied by mineralogical and physico-chemical characterization in order to evaluate their potential suitability as raw materials in ceramic applications. X-ray diffraction (XRD) and Fourier Transform-Infrared (FT-IR) spectrometry are used to establish the mineralogical composition. Chemical and physical properties were carried out by XRF and particle size distribution, consistency limits, calcimetry of Bernard and density of solid particles, respectively. Quartz, clay and calcite were present as dominant mineral phases associated with feldspars, plagioclase and dolomite. The clay minerals prevail in all samples, with kaolinite and illite being the dominant phase and interstratified 10–14Å and chlorite, comprising the rest of the clay components. The chemical compositions indicated that SiO2 (42–54%), Al2O3 (12–19%) and CaO (2–17%) are major elements while Fe2O3 is less abundant (4–8%). The classification of the clays using appropriate ternary diagrams suggests their possible use in the production of red products like tiles and masonry bricks.

Factors and mechanisms of soil salinization under vineyards of southern Taman

The spatial distribution of saline soils under vineyards in the south of Taman Peninsular is discussed. The Paleogene–Neogene clays of the Komendantskaya Mount serve as the source of salts. Vineyards were planted on an inclined plain at the foot of this mount. At present, their state on salt-affected soils worsens. In the upper part of the plain, solonchakous or deep-solonchakous slightly saline and nonsaline (within the upper 2 m) dark quasigley vertic soils (Vertisols) are formed. The salts are of the sulfate–sodium composition. Their vertical distribution has an eluvial pattern with a quick rise in the salt content from the surface layer to the depth of 50–100 cm and with a gradual increase in the salt content in the deeper layers. The absence of chlorides in the soils of flat areas within the slope attests to the predominance of lateral leaching of salts down the slope over their vertical leaching in the soil profiles. In the lower part of the slope, soil salinization mainly takes place in the hollow crossing the plain and the vineyard from the north to the south. In the middle part of the slope, nonsaline (to a depth of 2 m) agrohumus quasigley soils (Haplic Chernozems (Clayic, Aric, Stagnic)) are formed. Slight chloride–sulfate sodium salinization is only seen in the soils of the hollow, which contain fine-crystalline gypsum in the solid phase and display the accumulation of sodium chlorides in the middle part of the soil profile (in the 60–150-cm-thick layer). Heavy loamy agrochernozems with migrational and segregational forms of carbonates (Haplic Chernozems (Loamic, Aric, Pachic) are developed in the lower part of the slope; they are nonsaline to the depth of 2.5 m. In the area of transition from the humusquasigley soils to chernozems, specific horizons are formed in the hollow at the depth of more than 250 cm. Their soil solutions contain sodium, calcium, and magnesium chlorides against the background of the presence of fine-crystalline gypsum in the solid phase, which is typical of secondary salinization.

An assessment of Palaeogene and Neogene clay deposits in Denmark as possible host rocks for final disposal of low- and intermediate-level radioactive waste

Abstract In Denmark, mapping and preliminary investigations of Palaeogene and Early Neogene clay deposits have been performed over the past 5 years. The goal was to locate potential host rocks for the final disposal of low- and intermediate-level radioactive waste from the Danish Research Centre Risø, which has to be decommissioned within the next 5–8 years. Five areas with low-permeability Paleocene and Oligocene clay formations, situated in northern Jylland, NE Fyn and southern Lolland, not far from the Baltic coast at Femern Belt, have been suggested. The clay formations are between 75 and 150 m thick, and have large lateral distribution. They are covered by thin layers of glacial clayey tills and the shallow depth to the clay formations is attractive, partly because they are easy to access and partly because there are no groundwater aquifers situated above or below the clay deposits. The paper gives an overall review of the characteristics of the six different clay formations within four of the areas.

Tree species and soil substrate effects on soil biota during early soil forming stages at afforested mine sites

Development of soil microbial and soil fauna communities is a key factor in the soil forming process at reclaimed post-mine sites. The objective of this study was to determine the influence of reclaimed mine soil (RMS) properties (texture, pH, total organic carbon (TOC) and total nitrogen (TN)) and planted tree species on soil biological activity (dehydrogenase activity (DHA), microbial biomass carbon (MBC), enchytraeids (Enchytraeidae) and earthworm (Lumbricidae) communities). Research sites were located in southern Poland on an afforested sand mine pit (Szczakowa) and a sulphur mine spoil heap (Piaseczno). Study plots were arranged in pure tree stands of pine, larch, oak, birch and alder with 25- to 35-year-old trees growing on different RMS substrates: quaternary sands; quaternary loamy sands and loams; neogene clays; and mixed quaternary sands and neogene clay. Microbial biomass carbon depended mainly on the texture, TOC and TN content in the uppermost soil layer, whereas DHA was associated with the fine root annual increment. Earthworm biomass was significantly correlated with clay content, pH and TOC in the uppermost organic soil layers. Among planted tree species, black alder clearly altered soil microbial parameters, biomass and density of earthworms. The strongest effect on DHA was noted under birch trees. Among the studied tree species, deciduous trees (birch, alder and oak) had a greater impact on soil biological properties compared to coniferous trees (pine and larch).

Stability of earth slopes under the effect of main environmental properties of weathered clay–marl deposits in Belgrade (Serbia)

In the present paper, the impact of the main environmental factors on slope stability is analyzed by deriving a model for slope safety factor as a nonlinear function of geomechanical soil properties (bulk density γ, cohesion c, angle of internal friction φ and pore water pressure coefficient r u ) and terrain geometry (slope height H, bedrock depth d and slope angle β). The suggested model is derived using the response surface method, based on Spencer’s stability analyses of homogeneous slopes with circular slip surface. The analyzed parameter ranges were chosen according to the commonly determined values for unstable slopes in Neogene clay–marl deposits in Belgrade. The statistical reliability of the suggested model was confirmed by analyzing the stability of slopes with random geomechanical soil properties and terrain geometry. The obtained results indicate that all the examined environmental factors have statistically significant impact on the slope stability with prevailing linear effect, while geometrical factors and cohesion also show substantial quadratic effect. The existence of two-factor interactions imply that the impact of slope height on its stability is strongly dependent on slope angle, cohesion and bedrock depth, while the latter two also significantly affect the impact of slope angle on F s .

Simulation of Birch and Pine Litter Influence on Early Stage of Reclaimed Soil Formation Process under Controlled Conditions.

The impact of litter decomposition on chemical substrate properties and element leaching during early soil formation in afforested post-mine sites and the influence of different tree species are key issues in new ecosystem development. Scots pine ( L.) and common birch ( Roth) are important pioneering species used in afforestation of post-mine sites in central and eastern Europe. The aim of this study was to assess the impact of litter decomposition of these species on the chemical properties of mine soil substrates. The impact of litter decomposition on soil properties was tested on quaternary and neogene substrates with different textures (sands, loams, and mixtures of clays and sands) in a controlled incubation experiment using PVC columns. Simulation of precipitation and leaching was undertaken for 10 wk at a temperature of 16°C with distilled water (200 mL wk) through cylinders with litter, substrate + litter, and control substrate (no litter). Filtrated water solution was collected once a week for laboratory analysis, and the concentrations of dissolved organic C, total N, K, Ca, Mg, and P were determined. The study results indicate a stronger impact of the common birch on the chemical properties of reclaimed mine soils compared with pine. After the experiment, birch litter caused significant changes in pH in quaternary sands, concentration of P in quaternary loams (Ql) and mixtures of neogene clays and quaternary sands (QsNc), exchangeable Ca in QsNc, and Mg in Ql and QsNc compared with pine litter. Birch, in comparison to pine, may affect the intensity of early-stage soil-forming processes by increasing nutrient availability and transport into the soil profile, which may affect the development of soil microbial communities. This process results in different soil properties under the two tree species.

Development of the topography-controlled Upper Odra ice lobe (Scandinavian Ice Sheet) in the fore-mountain area of southern Poland during the Saalian glaciation

During the Saalian (Drenthe) glaciation, the Upper Odra ice lobe constituted the most southern part of the Scandinavian Ice Sheet in central Europe. The lobe was situated in an area with varied topography in the foreland of a mountain range. The ice lobe had a complex form because it was subdivided into several smaller sublobes. The primary factors that controlled the lobe were investigated. It was found that the ice-lobe development depended largely on the topography, but the lithology of the ice sheet substratum was also highly important. The topography controlled the main movement direction of the ice and caused a concentration of the ice flow in the axial part of the Silesian Lowland between subglacial morphological barriers, which thereby formed a corridor of relatively fast flowing ice, which was probably streaming and which supplied the lobe. The topography also determined the ice flow within the lobe, which strongly matched the valley system. The presence of sediments with relatively low permeability at the base of the lobe (the Quaternary deposits are underlain by Neogene clays) caused high pore-water pressure in the subglacial zone and triggered the basal movement of the ice sheet, which promoted a rapid flow of the ice and favoured the development of the lobe. The basal tills deposited from the active and passive ice and extant till patches without a fluvioglacial cover atop some parts of the studied area indicate spatially varying ice flow dynamics, especially in the later stage of glaciation. Certain parts of the lobe underwent stagnation, while in other parts, the ice was probably still active. The varied behaviour of the ice within the lobe was determined primarily by the topography and lithology of the substratum, which produced spatially varied marginal compression and basal friction. A model of the development of the lobe is proposed.

Evaluation of expansivity of Neogene clays and glacial tills from central Poland (Warsaw area) on the basis of suction tests

This paper presents the characteristics of the expansivity and quantitative prediction of heave of clay soils from Poland based on suction testing. 11 Neogene clays and 6 glacial tills, differing in genesis and plasticity, were analyzed to identify the expansive potential using eight empirical methods. The laboratory studies included measurements of soil-water characteristic curves and soil index properties . Data from water content, volume and suction measurements served to determine the suction compression index C h and the suction-water content index Dh/Dw of the soils examined. The values of these indices are clearly dependent of the clay fraction content in tested soils. Compared with glacial tills, Neogene clays are expected to exhibit larger changes in volume due to changes in soil suction. Comparative results of the evaluation of expansivity suggest that the chosen classification methodologies provided consistent expansion ratings for glacial tills, while values for Neogene clays vary from low to very high. The lowest expansivity classes have been obtained from evaluation based on soil suction. The McKeen (1992) method has been adopted for calculations of the potential field heave of Neogene clays and glacial tills. In order to provide a rational estimation of expansive soil behavior, specialists should take into consideration the specific site and design features.

Hydrogeothermal characteristics of groundwater from Ribarska Banja spa, central Serbia

Ribarska Banja spa is one of the most popular balneotherapy and recreation centers in Serbia. It features several thermal groundwater sources whose temperatures range from 26 to 54?C. The mineral content of these waters is low and their composition is of the SO4-Na or HCO3-Na type. Thermal water exploration has been conducted in the general area for many years, to assess the hydrogeothermal potential in order to extract larger amounts of thermal water for multiple uses. The hydrogeothermal system of Ribarska Banja spa was defined based on a synthesis of the results of comprehensive structural geology, geophysical, hydrogeological, hydrochemical and geothermal research. The primary groundwater reservoir of the hydrogeothermal system is comprised of tectonic zones (systems of faults and fractures) within Cretaceous-Paleogene metamorphosed and non-metamorphosed rocks. The overlying hydrogeological and temperature barrier is made up of a series of low metamorphosed rocks (chlorite, chlorite-sericite schists, gabbros, etc.), highly metamorphosed rocks (gneisses) and Neogene clay and sand sediments. The system is recharged by infiltration of atmospheric precipitation and surface water at the highest elevations of Mt. Jastrebac. Investigations have also shown that the system?s heat source is younger granitoide intrusion spreading northwest of Ribarska Banja spa. Based on the quartz geothermometers, expected reservoir temperatures are in the range of 85-97?C that can be expected at a depth of 1.87 km. Total energy usage at Ribarska Banja spa is 31 TJ/y with thermal capacity of 1.65 MWt and utilization factor of 0.58. Geothermal gradient is 0,051?C/m, while heat flow density is 163.5 mW/m2.

GEOMECHANICKÉ VLASTNOSTI NEOGENNÍCH JÍLŮ NA ÚZEMÍ MĚSTA BRNA

Neogene clays in Brno area are formations belonging to the Carpathian Foredeep Basin. They form common foundation soil in this strongly urbanized area. Due to their specific mechanical characteristics and a large spreaded area in Brno a detailed study of the geomechanical properties of Neogene clays has practical importance for engineering geology and geotechnics. There are compared analyzed data of physical and mechanical properties from 81 engineering-geological reports at the Brno agglomeration (452 samples of Neogene clays from 180 bores). There are presented the anomalous, distant values, arithmetic average and mode of the Neogene clays. On the basis of assumed data from various geological-engineering reports are defined typical characteristics of these soils. Neogene clays are fine-grained cohesive soils. In terms of ČSN EN ISO 14688-1, 14688-2 and UCSC classification these are classified mainly as clay or silt with high, very high or extremely high plasticity. It is usually with high plasticity index, stiff and very stiff consistence and with medium and high undrained shear strength. Low values of cohesion could be related to soil damaged by landslide movements. Due to its unfavourable properties, Neogene clays refer to partly suitable environment for shallow strip-foundations mainly due to the possibilities of volume changes in the subground. For all projection of foundations, there should be paid special attention to good engineering-geological investigation at real site.

The effect of sedimentary redbeds on coalbed methane occurrence in the Xutuan and Zhaoji Coal Mines, Huaibei Coalfield, China

The lithologies and permeabilities of caprocks have significant effects on coalbed methane (CBM) preservation. To study the controlling effects of redbeds deposits on CBM occurrence in the Xutuan and Zhaoji Coal Mines of the Huaibei Coalfield in China, the variations in mineralogical composition, microstructure, pore structure, permeability and diffusion among the redbeds caprock samples, Neogene clay rock and ordinary coal measure strata (sandstone, mudstone and siltstone) have been investigated. The results indicate that redbeds are porous rocks with weaker sealing capabilities than coal strata caprocks, allowing CBM to escape from the coal seam. The formation of the lithological properties of the redbeds is closely related to their mineralogical composition and diagenesis. Redbeds are mainly composed of illite (57–64%), calcite (25–33%), quartz (6–12%), muscovite (3–8%) and pyrite (<1%). The high content of fragile minerals and the later formation age of this rock lead to unapparent compaction and cementation, resulting in a loose structure, low degrees of consolidation and pore structure development. Mercury intrusion experiments show that the porosity of redbeds is 3.8–5.2 times higher than that of sandstone and 8–13 times higher than those of mudstone and siltstone; the pore size distribution of this rock is primarily centralized in transition pores (57.82%–74.72%) and mesopores (9.08%–22.51%), which favors gas diffusion. The permeability and diffusion coefficient tests demonstrate that the sealing capability of redbeds is much weaker than that of coal strata caprocks. Although the origins of the CBM gas pool in the Huaibei Coalfield remain controversial, the findings of this study along with the mining practices indicate that the deposition of thick redbeds can be treated as indicative of low gas contents in the coal mines, which has a significant meaning for the engineering of coal mine gas control.