Clay Mineral Composition Research Articles

Release of Mg and Fe From the Octahedral Sheets During the Transformation of Montmorillonite Into Kaolinite

AbstractIsomorphous substitutions of Mg and Fe for Al generally appear in the octahedral sheets of montmorillonite, whereas they are infrequent in kaolinite. Therefore, the release of Mg and Fe from the octahedral sheets probably happens during the transformation of montmorillonite into kaolinite, which could affect the migration of Mg and Fe from clay minerals into surrounding environments. The objective of the current study was to investigate the relationship between Mg and Fe release during the transformation of montmorillonite into kaolinite. The results showed that the d060 value of clay minerals decreased slightly, and the intensities of both the AlMg–OH and AlFe–OH bending vibrations also decreased gradually. In addition, the (Mg+Fe)/Al (major octahedral ions) atomic ratio of kaolinite was lower than that of montmorillonite, especially in identical hydrothermal products. These results indicated that Mg and Fe ions were released progressively from the octahedral sheets during the transformation of montmorillonite into kaolinite. Moreover, the changed relative concentrations of Mg and Fe ions in the supernatant solutions after hydrothermal reactions suggested a random distribution of Mg and/or Fe in the octahedral sheets of the montmorillonite. These results improve understanding of the release relationship between Mg and Fe during clay mineral evolution and of the distribution of these two ions in the octahedral sheets, as well as the chemical composition of clay minerals as an indicator of geological environments.

Toward Reducing Surfactant Adsorption on Clay Minerals by Lignin for Enhanced Oil Recovery Application.

The significant loss of surfactants during reservoir flooding is a challenge in oil field operations. The presence of clay minerals affects the surfactant performance, resulting in surfactant losses. This is because the mineralogical composition of the reservoir results in unpredicted adsorption quantity. Therefore, this paper seeks to investigate Aerosol-OT’s adsorption on different quartz/clay mineral compositions during the flow. Also, it investigates adsorption mitigation by preflushing with lignin. The dynamic experiments were conducted on sand packs composed of quartz-sand and up to a 7% clay mineral content. The results obtained from the surfactant losses were compared with/without lignin preflush at different pH values. The main observation was the direct relationship between increasing the composition of clay minerals and the surfactant pore volume required to overcome the adsorption. The highest adsorption calculated was 46 g/kg for 7% kaolinite. Moreover, lignin successfully reduced the adsorption of Aerosol-OT by 60%. Therefore, the results demonstrate that the effects of the clay mineral content on adsorption could be efficiently minimized using lignin at a high pH.

Clay mineralogy of soils from lower atrai basin of Bangladesh

The lower Atrai basin, the study area, lies in the Agroecological Zone-5 (AEZ-5) of Bangladesh. This study reveals the clay mineral composition of top soils of seven different soil series viz. Binsara, Taras, Jaonia, Hasnabad, Laskara, Manda and Mainam developed in the basin. X-ray diffraction (XRD) technique was employed to identify and quantify the minerals. Results show that mica (41 to 59%) was the most dominant mineral among all soils except Laskara. In Laskara soils, the interstratified mica-vermiculite-smectite (41%) was the predominant mineral. Next to mica, kaolinite (10 to 12%) was found to be present in the Binsara, Taras 1, Jaonia, and Taras 2 soils. Chlorite (7 to 17%) was identified in all the soils and was found to be the second dominant mineral in the Manda and Mainam soils. In contrast, the interstratified mica-vermiculitesmectite (33%) was found to be the second dominant mineral in the Hasnabad soils. Small amounts of vermiculite mineral (1 to 13%) were identified in almost all the soils except Binsara. All the soils have interstratified mica-chlorite minerals (2 to 7%). A tiny amount of smectite (1%) was identified in Taras 1 soil. As far as the clay mineralogical composition is concerned, most studied soils were found at the initial stage of weathering, indicating the high potential to sustain low input subsistence agriculture.
 Dhaka Univ. J. Biol. Sci. 30(2): 293-306, 2021 (July)

An integrated analysis of sinkholes in Kadapa region, Andra Pradesh, India: Implication to pedology

Sinkholes are one of the common karst features of geographical formations, which come into existence due to the dissolution of underneath lime-rich formations and subsequent collapse of the ceiling of the holes. Since sinkholes are formed in agricultural lands, this study aimed to understand the impact of sinkhole formation on heavy metals and minerals by collecting samples from sinkholes from various localities of Kadapa District of the state of Andhra Pradesh in India. The heavy metals were determined by ICP-AES analysis and characterization of soils in sinkholes was carried out. The FTIR spectroscopic technique was utilized to identify the minerals present in sinkholes. The XRD and SEM techniques were used to assess clay mineral composition and particle size and morphology of soil samples, respectively. Following the available literature, the minerals were identified from the location or band position of peaks from the Infra Spectrum. The minerals found were Quartz, Cesium di alumino tri silicate hydrate, Natrolite (Cs), Sodium Rhodium Oxide, Cobalt Uranium, Cesium Manganese Fluoride Hydrate, Quartz alpha, alpha-Si O2, Di copper (I) oxide, Erbium Indium Silver. Subsequently, we assessed the consequence of heavy metal pollution on soil microorganisms in sinkholes. The total population of microorganisms (bacteria, fungi, actinomycetes) was found to be decreased with increasing concentration of heavy metals.Additional analysis identified the bacteria resistant to Zinc, Manganese, lead (2 mM), copper (5 mM) metals. In sum, the findings from our integrated analysis of sinkholes provide an understanding of local pedology of the Kadapa region in India with implications for safety measures, agriculture land management and productivity.

Resolving the argument about volcanic bedrock under the West Antarctic Ice Sheet and implications for ice sheet stability and sea level change

We provide a test for recent arguments that the West Antarctic Ice Sheet (WAIS) is underlain by an extensive outcrop of volcanic rock (mainly basalt) by examining the non-clay and clay mineral composition of sediments collected in front of and under the Ross Ice Shelf. If the proposed large volume were present, then we posit that glacial erosion and transport would deliver sediments to the Ross Sea enriched in minerals diagnostic of alkaline basalt, namely olivine, pyroxene, and plagioclase, and no quartz. Using quantitative X-ray diffraction analysis, we determine the weight percent of minerals in West Antarctic alkaline basalt, dolerite, gneiss, and granite bedrock, and compare these with a suite of 49 surface and near-surface sediment samples from a 1400 km west to east transect across the Ross Sea. Fifty percent of the samples had quartz percentage values >25% and had very small wt percentages of diagnostic basalt minerals. A sediment unmixing algorithm, with basalt, dolerite, gneiss and granite bedrock, end members, showed that the sediment contained virtually no basalt, was dominated by granite compositions, but did show some samples with an admixture of material derived from the Ferrar dolerite, which crops out extensively in the Transantarctic Mountains. Indicators of possible late Cenozoic volcanic bedrock – pyroxene, forsterite, and smectite weight percentages – decrease from west to east across the Ross Sea opposite to the trend of the quartz weight percent. Our study provides no support for the presence of extensive basalt outcrop under the WAIS, hence indicates that any changes in ice stream stability will not be influenced by basal heat regime.

The Evolutionary Characteristics of Reservoir Microstructure under Long-Term Waterflooding Development and Its Fractal Description

Generally, long-term waterflooding development often leads to the change of reservoir pore and clay mineral composition, which results in the change of permeability and wettability. In order to explore the relationship between core micropore structure and water cut, based on physical simulation experiments and fractal theory, we proposed a fractal evolutionary model to describe the evolution characteristics of microstructure of long-term water driving reservoirs. In this paper, core pore structure by SEM was first conducted to analyze the change of core pore structure before and after waterflooding under the conditions of magnification of 200 times, 800 times, and 2000 times, respectively. Then, conventional and constant rate mercury injection tests were combined to perform the comparative analysis of core structural parameters before and after waterflooding. Finally, a micropore-throat structure evolution model of core was established. Research shows that the connectivity of larger pores becomes better after long-term water driving, the degree of heterogeneity weakens, and the micro heterogeneity of small pores becomes stronger and stronger. The throat characteristics change in a complex manner, the radius tends to increase, and the sorting becomes better, while the connectivity of small throat changes complex. In general, the heterogeneity of throat increases with the time of water injection in reservoirs with low porosity and permeability. On the basis of fractal theory and variation characteristics of rock pore structure in water driving reservoirs, we have established a micropore-throat structure evolution model of core pore-throat characteristics. This fractal evolution model quantitatively characterized the complexity and evolution law of pore structure and clarified the relationship between fractal dimension of core pore structure and water cut under different stages of water driving.

Early Eocene palynofloras and geochemistry from the Garo Hills in Meghalaya (India)

We analyzed a rich palynological assemblage from the Tura Formation consisting of 55 genera and 89 species of dinoflagellate cysts, fungal remains; spores and pollen grains, along with a numerous marine microforaminiferal linings. The composition of palynotaxa, clay minerals and stable isotope ratios indicate a warm, humid climate with tropical–subtropical climate conditions during sediment deposition. Based on similar palynotaxa compositions and carbon isotope signatures, we conclude that the Tura Formation was deposited during early Eocene. The presence of terrestrial, coastal and marine elements in the assemblages is indicative of a shallow marine environment in proximity to the shore line. The rock eval pyrolysis results suggest that the organic matter composition is primarily type III kerogen, which is a primary source of thermally immature hydrocarbons.

The Effect of Surfactant-Modified Montmorillonite on the Cross-Linking Efficiency of Polysiloxanes.

Polymer–clay mineral composites are an important class of materials with various applications in the industry. Despite interesting properties of polysiloxanes, such matrices were rarely used in combination with clay minerals. Thus, for the first time, a systematic study was designed to investigate the cross-linking efficiency of polysiloxane networks in the presence of 2 wt % of organo-montmorillonite. Montmorillonite (Mt) was intercalated with six quaternary ammonium salts of the cation structure [(CH3)2R’NR]+, where R = C12, C14, C16, and R’ = methyl or benzyl substituent. The intercalation efficiency was examined by X-ray diffraction, CHN elemental analysis, and Fourier transform infrared (FTIR) spectroscopy. Textural studies have shown that the application of freezing in liquid nitrogen and freeze-drying after the intercalation increases the specific surface area and the total pore volume of organo-Mt. The polymer matrix was a poly(methylhydrosiloxane) cross-linked with two linear vinylsiloxanes of different siloxane chain lengths between end functional groups. X-ray diffraction and transmission electron microscopy studies have shown that the increase in d-spacing of organo-Mt and the benzyl substituent influence the degree of nanofillers’ exfoliation in the nanocomposites. The increase in the degree of organo-Mt exfoliation reduces the efficiency of hydrosilylation reaction monitored by FTIR. This was due to physical hindrance induced by exfoliated Mt particles.

Contribution of continuously stable sediment input to the formation of the Pearl River delta since the middle Holocene

Pearl River sediments have been reported to have changed greatly in composition due to the impact of human activities on erosion and landscapes in southern China since 2500 years BP. Here, sediments from four cores (PRD-1, PRD-3, PRD-6 and PRD-7) from the Pearl River Delta (PRD) were collected for high-density clay mineral analyses to determine the vertical variations in clay mineral compositions since the middle Holocene. The results showed that the clay mineral compositions of these four cores remained constant. In the PRD, the clay mineral assemblage dominantly consists of illite and kaolinite (averaging more than 85%), with smaller amounts of chlorite (averaging 10%) and scarce smectite (averaging 1%). The stable clay mineral assemblages in the PRD confirm that the clay mineral compositions of the sediments continuously supplied by the Pearl River have not changed. However, the smectite percentage in core PRD-7 increased by 7% downward from a depth of 12.4 m, which was correlated with the weathering of local volcanic materials and sediment transport in the east of the Pearl River under the influence of the Guangdong coastal current in winter. The stable clay mineral compositions in the core sediments indicate that the Pearl River sediments have accumulated naturally in the PRD instead of under the influence of human activities, which would have altered the compositions of the core sediments.

The relationship between the geochemical and mineralogical characteristics of Calcocambisol, colluvium and recent marine lake sediment of the narrow seashore intertidal zone: a case study from the Veliko Jezero (Mljet Island, Croatia)

This study investigates the mineral composition, particle size distribution and geochemical characteristics of Calcocambisol, colluvium and recent marine lake sediment in a narrow intertidal seashore zone of the Veliko Jezero on the Island of Mljet (Croatia). The obtained results show that the fractions of Calcocambisol/colluvium less than 2 mm and 2 µm display similar particle size distribution (PSD) curves compared to marine lake sediments containing larger particles in these fractions. The smallest fractions of the investigated materials that are less than 1 µm show identical PSD curves. The bulk and clay mineral composition of the marine lake sediment show that the non-carbonate fraction is derived from weathering of the surrounding soils and colluvium containing quartz, feldspars and phyllosilicates (illitic material, kaolinites, chlorite, and a mixed-layer clay mineral, MLCM), as well as the authigenic formation of early-diagenetic pyrite, while one part is related to the yield of material by aeolian deposition (amphibole). The observed difference between the phyllosilicate mineral phases in the clay fraction of the Calcocambisol/colluvium and the carbonate-free clay fraction of the marine lake sediment is related to 1) the presence of chlorite in the marine lake sediment and 2) the higher content of MLCM in the Calcocambisol/colluvium. The chlorite in the marine lake sediment was inherited from the Calcocambisol/colluvium as a result of soil erosion prior to its complete destabilization in the soil. High Chemical Index of Alteration (CIA) values in the Calcocambisol and colluvium clearly indicate their intense weathering. Based on the Sm/Nd and Ti/Al ratios, it can be concluded that the aluminosilicates in the Calcocambisol, colluvium and marine lake sediment are of the same provenance. The distribution of each analysed element among the sequential fractions is very similar in both the Calcocambisol and colluvium. The highest concentrations for most of trace elements in the Calcocambisol, colluvium and marine lake sediment was determined in their residual fraction. Mn, Co and Pb show a different partitioning between the Calcocambisol/colluvium and marine lake sediment, respectively.

Clay mineral composition of upland soils and its implication for pedogenesis and soil taxonomy in subtropical China

Clay minerals are intermediate products generated during soil development, and their neoformation and transformation are closely related to pedogenesis. Here we aimed at identifying the difference in the clay mineral composition of upland soils derived from different parent materials and different soil-forming environments and exploring the importance of clay mineral composition in pedogenesis and soil taxonomy. We sampled 60 soil B horizons in Hunan Province of subtropical China by digging soils derived from granite (GR), slate and shale (SS), Quaternary red clay (QRC), limestone (LS), and sandstone (SDS). The clay mineral composition and its correlation with parent materials, elevation, micro-topography, and pedogenic processes were investigated using X-ray diffraction and Pearson’s correlation analysis. The clay mineral was dominated by kaolinite, followed by 2:1-type minerals (illite and vermiculite), and a small fraction of mixed-layer minerals. The composition of soil clay minerals varied with parent materials. Kaolinite was predominant in soils derived from GR and LS; mixed-layer minerals prevailed in QRC, whereas illite and vermiculite were prevalent in SDS. In addition, elevation and micro-climate could also explain the variations in clay mineral composition. Increase in elevation was associated with decreased 1:1 clay mineral content and increased 2:1 clay mineral content, especially in soils developed from LS. The composition and content of clay minerals indicated that Ferrosols, Ultisols, and Acrisols had undergone intense weathering; Primosols, Entisols, and Leptosols were characterised by weak weathering, and Plinthic Ali-Udic Cambosols, Plinthudults, and Plinthosols were characterised by strong redox status. This study suggests that clay mineral composition is related to the parent material, climate, and micro-topography, and that it can serve as an indicator of pedogenesis and soil type in subtropical China.

Interpretation and Reconstruction of Depositional Environment and Petroleum Source Rock Using Outcrop Gamma-ray Log Spectrometry From the Huai Hin Lat Formation, Thailand

Gamma ray logs are most useful in identifying subsurface lithology and interpreting depositional environments. This study highlights the use of outcrop gamma-ray logs along with outcrop observations and total organic carbon (TOC) analysis to provide the stratigraphic framework of the organic-rich rocks of Huai Hin Lat Formation in central Thailand. The study reveals five sedimentary facies including (1) structureless sandstone, (2) structured sandstone, (3) interbedded sandstone and siltstone, (4) interbedded mudstone and siltstone and (5) calcareous mudstone. These facies can be grouped into two facies associations; mudstone-dominated and sandstone-dominated facies associations. The depositional environment was interpreted as lacustrine basin-fill subdivided into deep lacustrine environment and sublacustrine fan associated with the turbidity currents. The total gamma-log characteristics are closely related to the lithologies controlled primarily by clay mineral compositions. Whist, the use of spectral gamma-ray can reveal more details on depositional environments and conditions. In this study, U concentrations is proven to be useful in highlighting organic-rich rocks in low K and Th concentration successions due to its ability to be fixed in clay minerals and organic materials under an anoxic condition. Thus, the U spectral gamma ray is suggested to combine with conventional gamma ray log for depositional environment and recognition of organic-rich rocks.

Interaction of individual meta clays with polycarboxylate (PCE) superplasticizers in cement investigated via dispersion, zeta potential and sorption measurements

Polycarboxylate (PCE) comb polymers were selected as potential dispersant for suspensions prepared from individual calcined clay samples. It was anticipated that mechanistically their dispersing effect relies on adsorption onto positively charged surfaces of the meta clays which was to be proven. Furthermore, the structural differences between two specifically selected PCE kinds were assumed to result in different dispersing performance.Using spread flow tests, the dispersing effectiveness of the PCEs on four different meta clay samples (meta kaolin, meta muscovite, meta illite and meta montmorillonite) was assessed. Moreover, the surface chemistry of the meta clays dispersed in synthetic cement pore solution (SCPS) was captured via zeta potential and sorption measurements to elucidate the interaction of the superplasticizers with the calcined clay samples.In accordance to common knowledge, the results confirmed the high water demand of calcined clays which made them asking for superplasticizers when used in mortar and concrete. It was found that the zeta potential (surface charge) of the meta clays initially was negative, but converted to positive via uptake of Ca2+ ions from the pore solution, especially in Ca2+-rich cementitious systems. Sorption measurements revealed that the PCE superplasticizers adsorbed onto these positively charged surfaces and thus achieved dispersion. The methallyl ether (HPEG) based PCE vastly outperformed the methacrylate ester (MPEG) based PCE. Surprisingly, meta illite could not be dispersed satisfactorily, in spite of high PCE adsorption. The results contribute to understand at a glance the dispersing mechanisms of PCE superplasticizers in naturally occurring calcined clays with various clay mineral compositions and to select the adequate superplasticizer easily.

Changes in sediment provenance and ocean circulation on the northern slope of the Bering Sea since the last deglaciation

Changes in water circulation in the Bering Sea have profoundly impacted biological productivity, carbon cycle and global ocean circulation, especially from the last deglaciation to the Holocene. Grain size and clay mineral composition were investigated in core ARC6-B10, collected from the northern Bering slope, in order to reveal changes in circulation and sediment provenance since the late deglaciation (~13.7 ka). The results highlight changes in sea level and atmospheric circulation as the primary controls on the variations in grain size and clay mineralogy. Deglacial sea level rise deepened the water passages along the Aleutian Arc, enhanced the inflow of North Pacific water that strengthened the circulation of the Bering Sea, and receded the coastline. These changes increased the supply of smectite-enriched sediments from the Aleutian Islands to the core site. A temporary reduction in smectite and an increase in the illite and chlorite contents during the Preboreal period correspond to the opening of the Bering Strait; this is attributed to rapid sea level rise which resulted in increased sediment resuspension from the shelf. During the mid- to late Holocene, when the sea level stabilized, changes in the Aleutian Low (AL) were a major factor modulating changes in ocean circulation. A weakened AL in the mid-Holocene intensified the northward Bering Slope Current and the increased the flow through the Bering Strait, while an intensified AL, along with an expanded sea ice cover during the late Holocene may have weakened the northward flow.

Evaporation and cracked soda soil improved by fly ash from recycled materials

AbstractThe osmotic pressure of a soil solution increases due to soil salinization and the stability and sustainability of the soil becomes poor, which will affect the movement of water in soil. In this study, the evaporation capacity and desiccation cracking characteristics of soda soil samples with different content (5, 10, 15, 20, and 25% by weight) of fly ash were investigated. After drying, the unconsumed water content of soil increased from 8.55 to 16.22%. The results indicate that the water retention capability of soda soil can be improved by the addition of the fly ash. The addition of fly ash is beneficial to the formation of soil aggregates and pores in the fly ash can store water. The fractal dimension and crack growth rate can be used to quantitatively describe the crack characteristics of a sample. The maximum fractal dimension of the soil samples decreased by 2.05, 3.92, 11.89, 8.53, and 3.07%, respectively, and the crack intensity factor (CIF) decreased by 4.65, 14.13, 22.48, 10.05, and 15.87%, respectively, with an increase of fly ash. Fly ash can therefore effectively inhibit crack growth and reduce the crack length in soda soil, since the clay content of soda soil decreased owing to the addition of fly ash, and the tensile properties were improved owing to the pore structure of fly ash. The shrinkage and evaporation of soil are closely related to soil quality factors such as clay content, mineral composition, and structure.

Clay mineral formation in Permian rocks of a geothermal borehole at Northern Upper Rhine Graben, Germany

Hydrothermally altered rhyolite rocks in the Permian Donnersberg Formation of a geothermal borehole in the Northern Upper Rhine Graben (Germany) were investigated to find out answers for the low hydraulic conductivity of the rocks. The composition of clay minerals and the temperature of smectite–illite transformation were carried out using X-ray diffraction, X-ray fluorescence, transmission electron microscopy, Fourier transform infrared spectroscopy, and polarized-light microscopy analyses. Clay mineral (CM) composition includes illite/muscovite (1M and 2M1 polytypes), illite–smectite interstratifications (IS-ml), smectite, and chlorite; and non-clay minerals such as quartz, feldspars, epidote, calcite, dolomite, and hematite were detected. The 2M1-polytype mica might be the only primary sheet silicates from the parent rocks, while the others occur as authigenic neo-formed CMs under heat flow and geothermal gradient. The development of CMs indicates different mechanisms of illitization and smectitization. Based on the texture, morphology, structure/polytype, and chemistry of rocks and minerals, in particular CMs, the study grouped the CM formation into three transformation processes: smectitization during magma cooling and possible contact metamorphisms with decreasing and low temperature, smectite illitization controlled by burial diagenesis and hydrothermal alteration, and illite smectitization followed exhumation and Cenozoic subsidence with decreasing temperature. The rhyolites were altered to all of the orders IS-R0, IS-R1, and IS-R3 by the dissolution-precipitation and layer-to-layer mechanisms. The first one supported small xenomorphic plates and flakes of 1Md, elongated particles of 1M, and pseudo-hexagonal forms of 2M1. The second one could lead to the platy particles of 1Md and 2M1 polytypes. The dominant temperature range for the transformation in the area has been 140–170 °C– ~ 230 °C.

Sorption behavior of cesium on silt and clay soil fractions

The effect of clay mineral composition on Cs adsorption behavior of silt and clay fractions (SC-fractions) of soil was investigated. Surface soil samples were collected within 2 km of Kori and Wolsong nuclear power plants in South Korea, and SC-fractions (<20 μm) were separated. The physicochemical properties of SC-fractions and types of clay minerals contained in the SC-fractions were analyzed. The cesium adsorption capacity of the SC-fractions, and affinity between the SC-fractions and Cs, were investigated by isothermal adsorption analysis using the dual-site Langmuir adsorption model. To understand selective adsorption of Cs, the radiocesium interception potential and distribution coefficient of the SC-fractions were analyzed in the presence or absence of competing ions. The radiocesium distribution coefficient of the SC-fractions showed a trend similar to that of the Langmuir sorption coefficient of high-affinity binding sites for Cs in the SC-fractions. The SC-fractions of Kori soils that contain only non-expandable clay minerals including highly weathered mica had low Cs adsorption capacity. However, the SC-fractions of Kori soils showed higher Cs adsorption selectivity compared to the SC-fractions of Wolsong soils containing expandable clay minerals and micaceous mineral with a low degree of weathering. It is predicted that the highly weathered micas have high affinity to Cs, and such clay minerals contribute the most to the adsorption process in dilute solutions.

Persistent Provenance of South Asian Monsoon‐Induced Silicate Weathering Over the Past 27 Million Years

AbstractThe development of the South Asian monsoon (SAM) and Himalaya‐Tibetan Plateau uplift were closely intertwined with some studies suggesting that uplift initiated the monsoon whereas others link tectonics with monsoon‐controlled exhumation. Silicate weathering controls atmospheric CO2 on geological timescales resulting in a large potential for monsoon strength and the Himalayan orogeny to influence global climate but detailed records of SAM‐induced weathering on million year (Myr) timescales are lacking. Here, we present radiogenic Sr, Nd, and Pb isotope compositions of clay minerals produced by silicate weathering and transported to the central Bay of Bengal. The radiogenic isotope data exhibit a relatively small range and demonstrate a remarkably consistent mixture of sources dominated by Himalayan rocks and the Indo‐Burman ranges, which consist of sediments derived from the Himalayas. This suggests that the spatial pattern of regional weathering, which today is highest in the regions of strongest monsoon rains, has persisted in a similar form for the last 27 Myrs. A pronounced increase in primary clay mineral abundance (from 9% to 22%) coincident with global cooling 13.9 Myrs ago points to a shift in the weathering regime given that the clay provenance did not change dramatically. Relatively weaker chemical weathering intensity during the mid and late Miocene cooling suggests increased aridity and changes in the large scale atmospheric circulation in the SAM domain. The establishment of the dry winter monsoon season during the mid and late Miocene may have caused this shift in the weathering regime and can reconcile much of the contrasting evidence for SAM initiation.

Effect of supercritical carbon dioxide adsorption on oil displacement in tight reservoir

The effect of CO2 adsorption on oil displacement in tight reservoirs is analyzed. The composition of clay minerals in a reservoir is analyzed, and a molecular model of the formed rock structure is established to investigate the adsorption characteristics of different clay minerals on the fluid. The effect of CO2 adsorption on oil displacement is investigated through a CO2 injection experiment. The results show that the adsorption capacity of reservoir minerals is greater for light hydrocarbons than for heavy hydrocarbons as well as for water and CO2 than for hydrocarbons, indicating that the oil recovery rate of the reservoir composed primarily of silica is higher when supercritical CO2 and water are alternately injected. The oil recovery can reach 23.78% by water and CO2 alternate flooding. Intermittent stop injection enable CO2 to enter rock samples more easily, and crude oil can subsequently be discharged more easily. As the mixing of CO2 and crude oil cannot be realized under the experimental conditions, the intermittent stop injection time is short and the gravity migration in tight cores is slow. Hence, we infer that the adsorption of CO2 significantly affects the displacement of tight reservoirs.

High-Resolution Stable Isotope Paleotopography of the John Day Region, Oregon, United States

The John Day region of central Oregon, United States contains ∼50 million years of near-continuous, fossiliferous sedimentation, representing one of the world’s richest archives of Cenozoic terrestrial ecosystems and climate. Stable isotope proxy data from this region are commonly used to infer the elevation history of the Cascades, which intercept westerly moisture in transit to the John Day region. However, the Blue Mountains, which accreted in the Mesozoic, create a region of local high topography that can confound signals of Cascades uplift. John Day deposits, including the John Day Formation, are divided into an eastern facies located within the Blue Mountains and a western facies in the adjacent plains. As a result, the Blue Mountains may have supported gradients in climate and ecology between the eastern and western facies, and constraining these gradients is necessary for reconstructing past topography and ecosystem change. In order to define the Cenozoic extent and magnitude of Blue Mountains topography we use oxygen isotopes in authigenic clay minerals to construct a spatially resolved map of local elevation. We find that the oxygen isotope composition of clay minerals within the Blue Mountains is ∼3‰ lower than in the adjacent high plains, and this offset is mostly constant throughout our record (spanning ∼50 – 5 Ma). We attribute this offset to Blue Mountains topography, either directly from upslope rainout or indirectly through the effect of elevation on local variations in precipitation seasonality. Our results highlight the importance of local topographic features in regional paleotopography reconstructions and provide important biogeographical context for the rich paleo-floral and -faunal records preserved in John Day sediments.