Arkadiusz Derkowski - Academia.edu (original) (raw)

Papers by Arkadiusz Derkowski

Cation exchange capacity (CEC) is among most important properties of sedimentary rocks, broadly a... more Cation exchange capacity (CEC) is among most important properties of sedimentary rocks, broadly applied in various means of geosciences research and industry. The organic matter (OM) in ancient black shales is thought to be a negligible source of cation exchange capacity (CEC), due to the loss of polar functional groups from extensive diagenetic transformations that occur during burial. OM in modern soils and sediments contains weakly bound hydrogen on carboxyl and phenolic hydroxyl groups, providing negatively charged functional groups that facilitate CEC on the order of hundreds of cmol (+) /kg. Kerogen in ancient sediments may either retain a portion of polar oxygen groups or these functional groups can be (re)gained upon drying, revealing an overlooked source of charge in black shales. Analyzing an extensive series of shales from the Baltic Basin (Poland) and Marcellus Shale (USA) with varying OM content and diagenesis we found that CEC, measured using Hexamminecobalt(III), of heated samples (≥200 °C) is up to ten times greater than CEC measured on air-dry samples. Moreover, CEC measured on the heated samples is greater than theoretical CEC estimated from clay minerals composition. The excess CEC correlates with the content of oxygen-rich groups determined with OM pyrolysis and infrared spectroscopy. Carboxyl groups formed in OM due to thermal oxidation at temperatures ranging from 200 °C to 310 °C, in the presence of oxygen and under vacuum, are responsible for excess CEC. Our results reveal that kerogen in black shales is not chemically inert in the case of cation exchange and the OM can provide a considerable portion of the apparent CEC measured in bulk rock samples.

—Layer charge (LC) is a fundamental property of smectite but its measurement remains challenging ... more —Layer charge (LC) is a fundamental property of smectite but its measurement remains challenging and tedious to apply on a high-throughput basis. The present study demonstrates that the position of a sharp, high-energy OÀD stretching band of adsorbed D 2 O (nOÀD, at ~2686À2700 cm À1), determined by infrared spectroscopy, correlates with LC and provides a simple method for its measurement. Twenty nine natural dioctahedral smectites and 14 reduced-charge montmorillonites with LC determined previously by different methodologies were saturated with D 2 O and examined by attenuated total reflectance infrared spectroscopy (ATR-IR). The samples included smectites in Mg, Ca, Na, Li, K, and Cs forms and covered the full range of the smectite LC (0.2 to 0.6 e per formula unit). Statistically significant correlations were found between nOÀD and LC values determined with each of the two main methods of LC determination: the structural formula method (R 2 = 0.96, s = 0.02, ~0.2 < LC < 0.6) and the alkylammonium method (R 2 = 0.92, s = 0.01, 0.27 < LC < 0.37). These correlations were based on Li-and Na-saturated smectites, respectively, but other cationic forms can be employed provided that the exchangeable cations are of sufficiently high hydration enthalpy (e.g. Mg 2+ or Ca 2+ , but not K + or Cs +). The new method is fast, low-cost, implemented easily in laboratories equipped with ATR-FTIR, and applicable to samples as small as ~5 mg.

Measuring and differentiating effective and ineffective porosity in oil-and gas-shale remains a c... more Measuring and differentiating effective and ineffective porosity in oil-and gas-shale remains a challenging step in the calculation of hydrocarbon reserves. Shale composition, typically dominated by clay minerals and organic matter (OM), forms a complex pore system, making the proportion between effective and ineffective porosity variable and difficult to determine in the course of porosity measurement. In this study, total porosity was measured from a set of rock chips using both light kerosene (kerosene immersion porosimetry-KIP) and deionized (DI) water (water immersion porosimetry-WIP) as saturation-immersion fluids. Both KIP and WIP measurements were performed on samples equilibrated at 40% and 80% relative humidity (RH) and combined with water adsorption isotherms to estimate the range of clay-bound water (CBW). A combination of these procedures, and the use of kerosene and water as the saturation-immersion fluids, is hereafter called dual-liquid porosimetry (DLP). To test the method, two different burial diagenetic sequences of mudstone with different mineralogy and OM content were used. The results demonstrate that all the porosity values show a consistent declining trend with depth regardless of sample origin and type of saturation-immersion fluid used in the measurement process. Samples saturated with DI water were susceptible to swelling and the swelling decreased with sample depth, maturation and cementation, and increased with illite-smectite mineral content and degree of expandability. A consistently lower calculated grain density for KIP samples compared with WIP samples reflected incomplete pore saturation by kerosene. Kerosene saturation can be restricted by the presence of residual water that blocks kerosene pathways to small pores. This limitation, however, reflects geologic formation conditions making KIP measurement a good approximation for maximum liquid hydrocarbon-available porosity. Equilibrating the rock chips at 40% and 80% RH provides a rapid evaluation of the range of CBW that may represent ineffective porosity under various formation conditions. CBW min (40% RH) constitutes roughly 1W–2W smectite equivalent layers and gives an estimation of bound water close to high hydrocarbon saturation. CBW max (80% RH) represents the maximum possible bound water content in formations with higher water saturation. For samples, with low porosity and a significant

The mineralogical and chemical compositions of Lower Carboniferous (Tournaisian) marine black sha... more The mineralogical and chemical compositions of Lower Carboniferous (Tournaisian) marine black shale from the Kowala quarry, the Holy Cross Mountains, Poland, were investigated. This study focuses on disturbances in palaeoenvironmental proxies caused by palaeoweathering, which progressively changed the major and trace element abundances. Palaeomagnetic investigations reveal that the Devonian – Carboniferous succession was weathered during the Permian-Triassic by the infiltration of oxidizing fluids related to karstification following post-Variscan exhumation. The weathering process led to vermiculitization of chlorite, partial dissolution of cal-cite and replacement of pyrite by hematite and goethite. Moreover, the concentrations of some trace metals, including Co, Cu, Pb, Mo, Ni, As and U, significantly decreased. Consequently, some elemental abundance ratios that are used as environmental proxies, including U/Th, Ni/Co and V/Cr, were altered. Elements that are bound to iron sulphides (e.g., Mo) appear to be especially prone to mobilization by even a lightly weathered black shale. The documented weathering, including changes in elemental concentrations, can potentially create misinterpretations of the original palaeoenvironmental conditions. In addition, the palaeoweathering of the studied samples appears to have substantially changed the carbon, oxygen, nitrogen and molybdenum stable isotope values. The nitrogen and molybdenum stable isotope ratios, in particular, appear to be most sensitive to the effects of weathering and therefore are good indicators of (palaeo)weathering processes. The major cause of these changes is the decay of organic matter and pyrite. For the organic carbon stable isotopes ratios, the main factor that controlls this process appears to be the preferential degradation of labile organic matter. A combination of the total organic carbon (TOC), total sulphur (TS) content, Mo concentration and stable isotope compositions seems to be the most useful for identify (palaeo)weathering. Our results suggest that reductions in TS and Mo in tandem with diminished Mo stable isotope values in the absence of obvious changes to the TOC content provide the most compelling evidence of (palaeo)weathering.

Supercritical CH4 and subcritical CO2 and N2 gas adsorption measurements, combined with scanning ... more Supercritical CH4 and subcritical CO2 and N2 gas adsorption measurements, combined with scanning electron
microscopy (SEM) have been used to determine CH4 sorption capacity and pore characteristics for immature,
mature and overmature shales from the Baltic Basin (Poland).
Organic matter (OM) maturity exerts a dominant control on porosity evolution in micro- and mesoscale. In
the Baltic Basin shales, the initial formation of micro- (< 2 nm) and mesopores (2–50 nm) occurs in the oil
window (beginning of catagenesis, vitrinite reflectance Ro ~ 0.5-0.9%) due to primary cracking of kerogen that
left OM highly porous. The expelled liquid hydrocarbons turned into solid bitumen that is responsible for pore
blocking and significant decrease in micro- and mesopore volume in late mature shales (middle catagenesis
Ro ~ 0.9–1.2%). Micro- and mesopores were regenerated in advanced catagenesis (Ro ~ 1.4–1.9%) due to secondary
cracking of OM. The micropore volume in the Baltic Basin shales is mostly controlled by the OM content
while the influence of clay content is minor and masked by OM.
The CH4 adsorption in the Baltic Basin shales is predominantly controlled by OM micropore structure. The
mesopore surface area and volume do not play an important role in CH4 sorption. The proposed adsorbed CH4
density equivalent (maximal absolute CH4 adsorption divided by micropore volume), revealed that the CH4
loading potential decreases in micropores with increasing maturity. The highest CH4 loading potential is linked
to OM before metagenesis (Ro < 2%) where the adsorbed CH4 density equivalent was found greater than the
density of liquid CH4. This suggests that in addition to physical adsorption, absorption (dissolution) of CH4 in
OM occurs. When OM content was reduced by the treatment with NaOCl solution, CH4 adsorption decreased
significantly, suggesting that OM microstructure has much higher adsorption potential than that of clay microstructure.

Total porosity measurement for gas shales without using crushed rock is presented. The method use... more Total porosity measurement for gas shales without using crushed rock is presented. The method uses a modified saturation – immersion technique with deionized water. Porosity values are reproducible within a low average absolute uncertainty. Swelling in gas shales during saturation with deionized water is not significant. Solvent extraction pretreatment can remove solid organic matter. a b s t r a c t Over the past decade interest in shale properties has increased due to the commercial success of gas shale plays. Despite their commercial importance, porosity measurement from gas shale samples is still challenging due to their extremely low permeability and complex pore structure. This leads to a significant uncertainty in the economic assessment of these plays. The current energy industry standard technique for measuring porosity in gas shales is based on methodology developed by the Gas Research Institute (GRI) that involves crushing a rock and aggressive pretreatment. The objective of this study is to develop an alternative method of measuring total porosity in gas shales. A porosity measurement using a liquid saturation and immersion technique with deionized water was adopted and modified for such applications. The water immersion porosimetry (WIP) technique was used to measure total porosity of shale samples from an Eastern Europe Silurian gas shale play and the Haynesville Shale from East Texas, USA. The samples were characterized for whole rock quantitative mineral and elemental composition, along with cation exchange capacity (CEC) and organic matter. The results from the WIP measurements are compared with other standard techniques including the GRI method and mercury intrusion porosi-metry (MIP). An assessment of the advantages, potential errors, pitfalls and reproducibility of this method are also presented. The experimental results indicate that WIP provides (i) highly reproducible porosity, grain density, and bulk density measurements for gas shales, (ii) the average absolute experimental uncertainty is AE0:22 porosity unit (p.u.), compared to the reported uncertainty level of 0.5 p.u. for GRI measurements, (iii) standard MIP techniques systematically underestimate the porosity and grain density compared to WIP, because mercury cannot access the entire pore structure in shales, and (iv) grain density values obtained by the GRI method in samples with high organic matter content are higher compared to WIP measurements, probably because of dissolution of solid organic matter during solvent extraction pretreatment.

Despite similarities in geochemical behavior, Cs and Rb concentrate in the upper continental crus... more Despite similarities in geochemical behavior, Cs and Rb concentrate in the upper continental crust (UCC) preferentially to K. Illite, a K-depleted dioctahedral mica occurring in large proportions in all types of sedimentary rocks, has high selectivity to Cs and Rb with irreversible adsorption in crystallite wedges and frayed edge sites. Analyzing 4000+ samples from 22 basins and sub-basins throughout the world using statistical computation, we found that Cs concentrates almost exclusively in illitic minerals (illite, illite-smectite) while Rb is equally distributed between K-feldspar and illite. Illite has Cs/K ratios up to 3× (median 1.97×) higher than average UCC, whereas its Rb/K variability corresponds to 1.0× to 1.08× the UCC's. Cs/Rb ratios in illite fall within the range covering average ratios for UCC, loess, and river suspension. Cs/K and Cs/Rb ratios in illite are formation specific and are higher with thinner illite crystallites, where the proportion of frayed edges to basal plane is high. With average Cs content of 17.7 ppm, illite is suggested to be a global sink for Cs on Earth's surface. Using mass balance, we present that parts-per-million concentrations of Cs adsorbed by illite crystallite edges constitute up to 20% of Cs present in UCC. Based on cation hydra-tion enthalpy, we introduce the " water-incompatibility " concept to explain the Cs > Rb > K order of cation selectivity in illite, which is also the order of the cations' relative depletion in global seawater with respect to the UCC.

Dehydroxylation-rehydroxylation experiments were performed on various dioctahedral aluminous 2:1 ... more Dehydroxylation-rehydroxylation experiments were performed on various dioctahedral aluminous 2:1 layer clay minerals using the precise thermogravimetry (TG) system equipped with a continuous N 2 gas flow enriched with H 2 O vapor of controlled concentration. The setup and rehydroxylation conditions applied are specifically sensitive to study in-situ rehydroxylation of smectites with various octahedral compositions and vacancy, saturated with counterions in various sizes and valences. Under the conditions applied, the pyrophyllite structure does not rehydroxylate, illite shows a minor ability to rehydroxylate, and smectites present an entire range of potential rehydroxylation, from remaining in the completely dehydroxylated state to an almost complete rebuild of the octahedral sheet. The mass gained during single-or multi-isotherm rehydroxylation matches the mass lost during the subsequent (secondary) dehydroxylation. In smectites, the Al-pyrophyllite-like arrangement is preferentially rehydroxylated, but at higher degrees of rehydroxylation, OH groups in other octahedral arrangements are also rebuilt. Among the temperatures tested, smectites and illite rehydroxylate most intensively during isother-mal heating at 400 °C (H 2 O content = 0.28 mol H 2 O/m 3), which is the onset temperature of dehydroxylation of their rehydroxylated forms. The smectites capability to rehydroxylate comes from an interplay of the counter-ions' size, the tetrahedral substitution in the 2:1 layers, and the negative charge generated in the former-octahe-dral sheet that controls the ability of cations to move from the surface of the tetrahedral sheet or from the octahedral sheet back to the interlayer. The conventional (time) 1/4 power law and the logarithmic kinetic models of rehydroxylation produced good fits of the experimental data. Calculation of activation energies (E a) for the rehydroxylation reaction produced values from 30 kJ/mol to 173 kJ/mol, highly dependent on the interlayer cation, 2:1 layer structure, and the experimental protocol. The kinetic models developed for rehydroxylation at temperature near ambient remain valid for the experiments up to 400 °C. At 500 °C the mechanism of rehydroxylation is influenced by other factors.

—The increasing exploration and exploitation of hydrocarbon resources hosted by oil and gas shale... more —The increasing exploration and exploitation of hydrocarbon resources hosted by oil and gas shales demands the correct measurement of certain properties of sedimentary rocks rich in organic matter (OM). Two essential properties of OM-rich shales, the total specific surface area (TSSA) and cation exchange capacity (CEC), are primarily controlled by the rock's clay mineral content (i.e. the type and quantity). This paper presents the limitations of two commonly used methods of measuring bulk-rock TSSA and CEC, ethylene glycol monoethyl ether (EGME) retention and visible light spectrometry of Co(III)-hexamine, in OM-rich rocks. The limitations were investigated using a suite of OM-rich shales and mudstones that vary in origin, age, clay mineral content, and thermal maturity. Ethylene glycol monoethyl ether reacted strongly with and was retained by natural OM, producing excess TSSA if calculated using commonly applied adsorption coefficients. Although the intensity of the reaction seems to depend on thermal maturity, OM in all the samples analyzed reacted with EGME to an extent that made TSSA values unreliable; therefore, EGME is not recommended for TSSA measurements on samples containing >3% OM. Some evidence indicated that drying at 5200ºC may influence bulk-rock CEC values by altering OM in early mature rocks. In light of this evidence, drying at 110ºC is recommended as a more suitable pre-treatment for CEC measurements in OM-rich shales. When using visible light spectrometry for CEC determination, leachable sample components contributed to the absorbance of the measured wavelength (470 nm), decreasing the calculated bulk rock CEC value. A test of sample-derived excess absorbance with zero-absorbance solutions (i.e. NaCl) and the introduction of corrections to the CEC calculation are recommended.

The radioactive decay of 40 K to 40 Ar is the basis of isotope age determination of micaceous cla... more The radioactive decay of 40 K to 40 Ar is the basis of isotope age determination of micaceous clay minerals formed during diagenesis. The difference in K–Ar ages between fine and coarse grained illite particles has been interpreted using detrital-au-thigenic components system, its crystallization history or post-crystallization diffusion. Yet another mechanism should also be considered: natural 40 Ar recoil. Whether this recoil mechanism can result in a significant enough loss of 40 Ar to provide observable decrease of K–Ar age of the finest illite crystallites at diagenetic temperatures – is the primary objective of this study which is based on molecular dynamics (MD) computer simulations. All the simulations were performed for the same kinetic energy (initial velocity) of the 40 Ar atom, but for varying recoil angles that cover the entire range of their possible values. The results show that 40 Ar recoil can lead to various deformations of the illite structure, often accompanied by the displacement of OH groups or breaking of the Si–O bonds. Depending on the recoil angle, there are four possible final positions of the 40 Ar atom with respect to the 2:1 layer at the end of the simulation: it can remain in the interlayer space or end up in the closest tetrahedral, octahedral or the opposite tetrahedral sheet. No simulation angles were found for which the 40 Ar atom after recoil passes completely through the 2:1 layer. The energy barrier for 40 Ar passing through the hexagonal cavity from the tetrahedral sheet into the interlayer was calculated to be 17 kcal/mol. This reaction is strongly exothermic, therefore there is almost no possibility for 40 Ar to remain in the tetrahedral sheet of the 2:1 layer over geological time periods. It will either leave the crystal, if close enough to the edge, or return to the interlayer space. On the other hand, if 40 Ar ends up in the octahedral sheet after recoil, a substantially higher energy barrier of 55 kcal/mol prevents it from leaving the TOT layer over geological time. Based on the results of MD simulations, the estimates of the potential effect of 40 Ar recoil on the K–Ar dating of illite show that some of 40 Ar is lost and the loss is substantially dependent on the crystallite dimensions. The 40 Ar loss can vary from 10% for the finest crystallites (two 2:1 layers thickness and <0.02 lm in diameter) to close to zero for the thickest and largest (in the ab plane) ones. Because the decrease of the K–Ar estimated age is approximately proportional to the 40 Ar loss, the finer crystallites show lower apparent age than the coarser ones, although the age of crystallization is assumed equal for all the crystallites. From the model it is also clear that the lack of K removal from illite fringes (potentially Ar-free) strongly increases the apparent age differences among crystallites of different size.

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights Abstract In sedimentary basins, immediate equilibration with surface and pore waters of Ar, released from K-bearing minerals during their diagenesis or weathering, has been a paradigm for geochemistry and geochronology. Consequently, K–Ar and Ar–Ar isotope geochronology techniques applied to sedimentary rocks are based on an assumption that no measurable external radiogenic 40 Ar (" excess argon ") has been locked in the rock components during their formation and alteration. Our results indicate that the reaction of micaceous sedimentary and diagenetic clay minerals (illite, glauconite) with acid produces microporous silica that retains a great fraction of the initial argon, releasing potassium to the solution. In all tested cases the evolution of K–Ar isotope ages followed the very same pattern: the apparent K–Ar isotope age increased enormously after acid treatment and dropped significantly after silica removal (with hot Na 2 CO 3), but never decreased lower than the initial K–Ar isotope age of the untreated sample. The amorphous silica content and the apparent K–Ar age increased with the acid reaction time. Using the molecular dynamics simulations, the clay-acid reaction by-product was shown to bend and wrap, producing three-dimensional, protonated and hydrated silica. As a consequence of dramatically different hydration energies of Ar and K, potassium is instantaneously released and hydrated outside the residual structure while Ar atoms remain inside the silica network, adsorbed on the surface. This is, to our knowledge, the first experimental evidence that the excess argon can be retained in solid mineral reaction products formed under pressure and temperature close to those of the Earth surface (1 atm, <80 °C).

AbstrAct Thermal analysis experiments in the environment of an extremely low water vapor concentr... more AbstrAct Thermal analysis experiments in the environment of an extremely low water vapor concentration provide insight into the first steps of the rehydration mechanism in smectite when completely dehydrated and the interlayer region is collapsed. The relative structural and compositional controls on dehydration and rehydration reactions are compared from a well-characterized suite of samples that vary with respect to chemical composition, octahedral and tetrahedral substitution, octahedral cation site vacancy, and degree of dehydroxylation. Techniques including multi-cycle heating-cooling thermogravimetric analysis and nitrogen gas adsorption on various smectite samples preheated at different temperatures followed by rehydration at ambient conditions were used to characterize the interaction of water molecules with completely dehydrated montmorillonite, beidellite, and nontronite smectite types. Beidellite with high-Al 3+ tetrahedral substitution results in electrostatically undersaturated basal oxygen atoms that exert strong repulsion between the tetrahedral sheets of adjacent 2:1 layers. The in-terlayer region of dehydrated or dehydroxylated beidellite is capable of being spontaneously rehydrated even in low water vapor environments. In completely dehydrated montmorillonite and nontronite, the external surface area of the crystallites is a primary control on water adsorption at low humidity when the molecules form a shell around the exchangeable cations present on external surfaces. The potential of montmorillonite and nontronite to reopen a collapsed interlayer is significantly lower than beidellite because of their crystal-chemical features that result in 2:1 layer and interlayer cation attraction. With increasing water vapor partial pressure, the hydration potential of interlayer cations provokes a reopening of the interlayer. In a dehydroxylated nontronite, the undersaturated residual oxygen atom strongly bonds the interlayer cation within the ditrigonal ring of the tetrahedral sheet, resulting in a permanent interlayer collapse. The specific surface area calculated from a conventional N 2 gas adsorption measurement using the BET model represents the external surface area of a dehydrated smectite crystallite and can be converted into the mean crystallite thickness. The mean crystallite thickness of a completely dehydrated smectite increases with an increase in preheating temperature.

AbstrAct Rehydroxylation of the previously dehydroxylated dioctahedral 2:1 layer clay mineral occ... more AbstrAct Rehydroxylation of the previously dehydroxylated dioctahedral 2:1 layer clay mineral occurs preferentially in specific sites within the former octahedral sheet. The rehydroxylation of dehydroxylated Al-rich and Al,Mg-rich 2:1 layers occurs as trans-vacant (tv) structural arrangements, regardless of whether the initial structure was tv or cis-vacant (cv). In nontronite (Fe-rich 2:1 layer clay), the dehy-droxylate pseudo-cv structure is probably directly reconstructed into the rehydroxylated cv structure without migration of octahedral cations. Rehydroxylation occurs preferentially in the R 3+-O r-R 3+ former octahedral structural arrangements (O r = residual oxygen) over R 2+-O r-R (R = R 3+ or R 2+ = Al 3+ , Fe 3+ or Mg 2+ , Fe 2+). In the case of the R 2+ octahedral substitution, the interlayer cation is attracted to the electrostatically undersaturated residual oxygen of the R 2+-O r-R arrangement, which blocks the ability of water molecules to pass through the ditrigonal cavity and rehydroxylate the previously dehydroxyl-ated local arrangement. The pyrophyllite-like type of octahedral R 3+-O r-R 3+ arrangements, formed due to the lack of tetrahedral substitution and resulting in the absence of interlayer cations, is thus favored for rehydroxylation over the mica-like R 3+-O r-R 3+ arrangements where Al occurs in the tetrahedral sheet. The valence of the interlayer cation and the charge density of the 2:1 layer clay mineral, which controls the interlayer cation content, also affect the degree of rehydroxylation. Dehydroxylated 2:1 layer minerals with a high-rehydroxylation potential, including beidellite and illite, use all the adsorbed water molecules that persist above 200 °C for rehydroxylation; the water vapor from the ambient environment also becomes a source of H 2 O molecules for rehydroxylation. The high demand for water molecules to use for rehydroxyltion results in a noticeable gain of mass in the temperature interval between 200 and 350 °C even during heating.

The geochemical and fossil record preserved in the Ediacaran age (635–551 Ma) Doushantuo Formatio... more The geochemical and fossil record preserved in the Ediacaran age (635–551 Ma) Doushantuo Formation of South China has been extensively examined to explore the impact of changing climate and the oxidation state of the oceans on the development and distribution of early multicellular life. In the Yangtze Gorges area, this formation shows many of the geochemical trends and features thought to typify global ocean chemistry in the Ediacaran Period, but there are indications that post-sed-imentary processes modified these signals. This study of clay minerals and organic matter builds a more detailed picture of the type and degree of post-sedimentary alteration at different stratigraphic levels of the formation and focuses on how this alteration influenced stable carbon and oxygen isotope records. In the cratonward Jiulongwan and Huajipo sections of the Doushantuo Formation, its lower part (Members 1 and 2) consists largely of dolomitic shale, rich in authigenic saponite that crystallized in an alkaline sedimentary basin. Saponite has been altered to chlorite via corrensite across tens of meters of strata in lower Member 2, with increased alteration downward toward the cap dolostone. The greater chloritization is accompanied by lower d 18 O and higher dD values of trioctahedral clays. This pattern of alteration of trioctahedral clays is likely due to hydrothermal fluid activity in the underlying, relatively permeable Nantuo Formation and cap dolostone. A concomitant increase of solid bitumen reflectance toward the base of the formation supports this idea. In the uppermost part of the formation in the Yangtze Gorges area (Member 4), a typical open water marine dolomitic shale rich in illite and organic matter, increases in the methylphenanthrenes ratio index and solid bitu-men reflectance correlate with decrease of the bulk rock K/Al ratio upward, providing evidence for hot fluid migration above the nearly impermeable shale. Clay from the upper part of the formation is enriched in 18 O, but not in D, relative to clay from the lower parts, indicating progressive 18 O-enrichment of hydrothermal fluids that percolated upward and laterally through permeable 18 O-rich carbon-ates. A maximum hydrothermal-alteration temperature of 200°Cisestimatedfromacalibrationcurveforillitizationduringburialdiagenesis,butgiventhatthehydrothermalactivityprobablyoccurredinshortpulses,thetemperaturecouldhavebeenmuchhigher.K–AragesareconsistentacrossdifferentsizefractionsoffineillitefromMember4shale(200 °C is estimated from a calibration curve for illitization during burial diagenesis, but given that the hydrothermal activity probably occurred in short pulses, the temperature could have been much higher. K–Ar ages are consistent across different size fractions of fine illite from Member 4 shale (200°Cisestimatedfromacalibrationcurveforillitizationduringburialdiagenesis,butgiventhatthehydrothermalactivityprobablyoccurredinshortpulses,thetemperaturecouldhavebeenmuchhigher.K–AragesareconsistentacrossdifferentsizefractionsoffineillitefromMember4shale(430 Ma) and from a K-bentonite bed near the base of Member 2 in the Jiuqunao section ($325 Ma), $25 km from Jiulongwan and Huajipo. These age values show that the diagenetic illite of the Doushantuo Formation is a product of either deep burial diagenesis over-printed by spatially limited hydrothermal activity or of two localized hydrothermal events. Patterns of carbonate 13 C and 18 O depletion in the basal Doushantuo Formation are similar to chloritization trends and 18 O variation in diagenetic clay minerals. Given independent evidence for 13 C depletion of hydrothermal fluids, these trends Geochimica et Cosmochimica Acta 107 (2013) 279–298 indicate carbonate–fluid isotope exchange commensurate with the degree of post-sedimentary alteration, supporting a model of lithologically controlled differential diagenesis induced by hydrothermal fluids as the main control on C and O isotope variability in this stratigraphic interval. This model could potentially explain other notable d 13 C excursions higher up in Member 3.

AbstrAct The <1 µm fraction of a trans-vacant 1M illite (RM30) was studied by conventional and sy... more AbstrAct The <1 µm fraction of a trans-vacant 1M illite (RM30) was studied by conventional and synchrotron X-ray diffraction (XRD) techniques, combined with thermogravimetric (TG, DTG) methods to investigate the structural transformation of illite at different temperatures and degrees of dehydroxylation (D T). The oriented specimens preheated at 300 and 680 °C correspond to the non-dehydroxylated (D T = 0) and completely dehydroxylated (D T = 100%) 1 M illite structures. Deviation of the basal reflection positions from rationality, expressed by the coefficient of variation of d(00l) values, progressively increase from 0.05 at D T = 4%, to 0.14 at D T = 51%, and then decrease to 0.06 at D T = 95%. Similarly, for each 00l reflection the full width at half-maximum (FWHM) shows a bell-like evolution with increasing preheating temperature. Both of these features are characteristic for mixed-layered structures. The experimental profiles of 00l reflections from the oriented partially dehydroxylated specimens perfectly matched the profiles from XRD pattern simulations calculated in terms of a mixed-layered structure in which the non-dehydroxylated (ND) and completely dehydroxylated (CD) illite layers are interstratified with a strong tendency to segregation. The content of the CD layers in the modeled mixed-layered structures of the preheated specimens show a significant linear correlation with the corresponding D T values (R 2 = 0.99). In random powder XRD patterns collected with synchrotron radiation, the preheated specimens show a distinctive trend in the unit-cell parameters. However, the accuracy in determination of the unit-cell parameters at first decreases up to D T = 61% and then increases with a further increase in D T. The evolution of FWHM values of individual hkl reflections is also similar to that observed for each 00l peak from oriented sample preparations. The unexpected evolution of the unit-cell parameters during progressive dehydroxylation is explained by the interstratification of ND and CD layers in illite. The formation of the mixed-layered structures during Al-rich 1M illite dehydroxylation is in agreement with the prediction from the kinetic model of partially dehydroxylated dioctahedral 2:1 clay structures where dehydroxylation of each portion of the initial OH groups corresponds to a zero-order reaction that is independent of the structural and chemical composition. The reaction is homogeneous and during partial dehydroxylation of the illite structure, ND layers transform into the CD layers without formation of an intermediate phase. A layer-by-layer dehydroxylation mechanism is suggested for thermally induced illite structural transformation.

AbstrAct The multi-cycle heating and cooling thermogravimetric (TG) method was used to study the ... more AbstrAct The multi-cycle heating and cooling thermogravimetric (TG) method was used to study the kinetic behavior of three kaolinite samples: defect-free Keokuk kaolinite, KGa-2 with a very low degree of structural order, and KGa-1 having intermediate structural order. In each cycle, the maximum cycle temperature (MCT) was set to 25 °C higher than the preceding cycle. The TG patterns consist of a set of subsequent DTG maxima representing the portions of OH groups that did not dehydroxylate in previous cycles. Each stage of partial dehydroxylation consists of two kinetic mechanisms and for each of them the experimental dα/dt values that characterize the reaction rate of the dehydroxylated fraction, α, within a period of the reaction time, t, were computed. One mechanism corresponds to a zero-order reaction that occurs in each cycle and indicates that the reaction is homogeneous and each non-dehydoxylated layer is transformed into metakaolinite layer without formation of intermediate derivatives. For this step of the cycles activation energy, E a , was calculated from the linear relationship between ln(dα/ dt) and reciprocal temperature, T; for KGa-2 kaolinite, the E a varies from 32.0 to 38.1 kcal/mol; in KGa-1, E a varies from 37.1 to 40.4 kcal/mol, whereas in Keokuk, E a varies from 42.7 to 47.5 kcal/ mol. The particular variation of the E a is discussed in terms of structural and morphological features of the samples. The kinetic mechanism of the second step of reaction corresponds to the temperature range higher than the first step of the same heating cycle. The second step starts from the point where α = α P that was found to vary between 0.25 and 0.45. The acceleration of the reaction rate of dehydroxylation within this interval decreases with increasing α and T, and the mechanism observed for each of the studied samples is independent of its stacking order, average particle size, and particle size distribution. The f(α) is a function of the reaction mechanism in the second step and has the form f(α) = (1 – α) n /(1 – n) where n is an empirical parameter and its value was found from <0.01 to 0.06–0.08 among cycles and samples. The value of n controls the reaction rate slowing or the deviation from the zero-order reaction and increases with increasing metakaolinite content. Using parameters n, α, and T determined for the second step, E a values were calculated for the second step of reaction in each heating cycle. For the Keokuk kaolinite, E a value varies from 31.6 to 37.5 kcal/mol, in KGa-1 E a is 27.0–35.6 kcal/ mol, and in KGa-2 the E a value varies from 26.3 to 34.9 kcal/mol. A structural model explaining the acceleration rate slowing is discussed.

h i g h l i g h t s DLP determines porosity and Clay-Bound Water range using the same rock portio... more h i g h l i g h t s DLP determines porosity and Clay-Bound Water range using the same rock portion. Water immersion may cause bulk rock swelling thus return overestimated porosity. KIP measures maximum theoretical porosity available for hydrocarbon saturation. CBW min constitutes 1W–2W and gives bound water under high hydrocarbon saturation. CBW max gives values close to maximum possible bound water content. a b s t r a c t Measuring and differentiating effective and ineffective porosity in oil-and gas-shale remains a challenging step in the calculation of hydrocarbon reserves. Shale composition, typically dominated by clay minerals and organic matter (OM), forms a complex pore system, making the proportion between effective and ineffective porosity variable and difficult to determine in the course of porosity measurement. In this study, total porosity was measured from a set of rock chips using both light kerosene (kerosene immersion porosimetry-KIP) and deionized (DI) water (water immersion porosimetry-WIP) as saturation-immersion fluids. Both KIP and WIP measurements were performed on samples equilibrated at 40% and 80% relative humidity (RH) and combined with water adsorption isotherms to estimate the range of clay-bound water (CBW). A combination of these procedures, and the use of kerosene and water as the saturation-immersion fluids, is hereafter called dual-liquid porosimetry (DLP). To test the method, two different burial diagenetic sequences of mudstone with different mineralogy and OM content were used. The results demonstrate that all the porosity values show a consistent declining trend with depth regardless of sample origin and type of saturation-immersion fluid used in the measurement process. Samples saturated with DI water were susceptible to swelling and the swelling decreased with sample depth, maturation and cementation, and increased with illite-smectite mineral content and degree of expandability. A consistently lower calculated grain density for KIP samples compared with WIP samples reflected incomplete pore saturation by kerosene. Kerosene saturation can be restricted by the presence of residual water that blocks kerosene pathways to small pores. This limitation, however, reflects geologic formation conditions making KIP measurement a good approximation for maximum liquid hydrocarbon-available porosity. Equilibrating the rock chips at 40% and 80% RH provides a rapid evaluation of the range of CBW that may represent ineffective porosity under various formation conditions. CBW min (40% RH) constitutes roughly 1W–2W smectite equivalent layers and gives an estimation of bound water close to high hydrocarbon saturation. CBW max (80% RH) represents the maximum possible bound water content in formations with higher water saturation. For samples, with low porosity and a significant