Mudstone Samples Research Articles

Elemental geochemical characteristics of Lower—Middle Permian mudstones in Taikang Uplift, southern North China Basin: implications for the FOUR-PALEO conditions

The paleo-sedimentary environment can be restored qualitatively or semiqualitatively using elements or combinations of elements that are sensitive to the depositional environment. Through the analysis and testing of the main elements, trace elements and rare earth elements of twenty-one Lower—Middle Permian coal-bearing strata mudstone samples in Taikang Uplift, southern North China Basin, this study explored the FOUR-PALEO conditions (paleo-water depth, paleo-redox conditions, paleoclimate and paleo-provenance). The La and Co contents indicate that the water depth of the northern margin of the southern North China Basin became gradually shallower during the Lower—Middle Permian period. According to the U/Th, Uau, V/Cr, Ni/Co and V/Sc ratios, it is known that this section of the basin is in an oxidizing environment, and the oxidation is gradually enhanced from the Taiyuan Formation to the Lower Shihezi Formation. Paleoclimate from bivariate plot diagrams of C-value and Sr/Cu versus Ga/Rb shows that the Taikang Uplift was characterized by a warm and arid climate during the depositional period of Permian Taiyuan Formation and a warm and humid climate during the Lower Shihezi Formation and shows that the depositional period of Permian Shanxi Formation was in a transitional period of humid and arid. CIA, PIA, ICV, Th/U and K/Rb reflect the tectonic settings of the source area. From the Taiyuan Formation to the Lower Shihezi Formation, the CIA and PIA gradually increase, and the ICV gradually decreases, indicating enhanced chemical weathering and the transition from arid to humid in the source area, the arid and humid frequent change in the Taiyuan Formation, and a sudden climate change in the Shanxi Formation. Additionally, the provenance discriminant function, Zr/Sc-Th/Sr, REEs ratios, Th versus Hf-Co, Hf versus La/Th and ZREE vs. La/Yb indicate that the type of provenance is associated with magmatic differentiation. Moreover, discriminant diagrams, consisting of K2O/Na2O versus SiO2, La-Th-Sc, Th-Sc-Zr/10 and Th-Co-Zr/10, suggest that the mudstones of Lower-Middle Permian were deposited in active continental margin tectonic settings.

Detrital zircon U-Pb and Hf constraints on provenance and timing of deposition of the Mesoproterozoic to Cambrian sedimentary cover of the East European Craton, Belarus

The sedimentary cover of the East European Craton (EEC) is unique because of its low degree of diagenetic alteration that allows preservation of the original “source to sink” relationships. The present study provides U-Pb and Hf zircon data for the entire Proterozoic sedimentary section of the EEC based on samples from five boreholes in Belarus within the Volyn-Orsha Basin, one of the most important sedimentary basins of the craton. Twenty-one samples of mudstones and sandstones were selected for detrital zircon U-Pb geochronology, supplemented by the Hf isotope analyses of zircons from 6 samples representing different U-Pb age spectra and bulk rock XRD mineralogy of all mudstone samples collected from the studied boreholes. Five clastic successions in the Volyn-Orsha Basin are characterized by different sources of detrital material: (1) The Mesoproterozoic Pinsk Suite with a narrow population of c. 2.0 Ga zircons, (2) The Orsha Suite with a broad 1.3–3.2 Ga zircon age distribution, (3) Glacial sediments of the Vilchitsy Series with an age spectra similar to the Orsha Suite, except for a c. 1.0 and 1.2 Ga cluster, (4) The Volyn and Valdai Series, including lowermost Cambrian, with a narrow trimodal population of 0.5, 1.5, and 1.8 Ga zircons, and (5) lower Cambrian (?) sediments with a diffused zircon age spectrum, including a 500–700 Ma cluster. Maximum depositional ages were constrained for the Vilchitsy Series at 977 ± 6 Ma and for the Volyn Series at 579–545 ± 4 Ma. Combined Hf zircon data indicate four episodes of new continental crust generation at 3.3, 2.8, 2.1–2.3 and 1.8 Ga, suggestive of source terrains within the crust of the present-day EEC. These sources experienced subsequent reworking of crust at c. 1.8 Ga and 550–600 Ma. Only a lower Cambrian sample lacks any trend or clustering within the Hf data probably due to mixing of zircons from exotic and local sources. Paleogeographic models explaining these provenance signals in terms of intracratonic erosion and sediment transport are presented.

Early Cretaceous redbeds from the Minle Basin, Hexi Corridor, northwest China: Mineralogy and geochemistry implications for paleoweathering, provenance, and tectonic settings

Redbeds with a large thickness in the lower Cretaceous record abundant geologic information in the Minle Basin. We have conducted the paleoweathering conditions, provenance, and tectonic settings based on mineralogy and geochemistry. Our results indicate that mudstone samples are characterized by abundant illite with negligible amounts of K-feldspars and analcime. The lower part of the lower Cretaceous is rich in quartz, whereas the upper part is dominated by dolomite and analcime. We suggest that this is caused by the decreasing input of the clastic influx during the middle-late early Cretaceous. High index of compositional variation values (average 1.33) indicate first-cycle sediment supply, suggesting an overall compositional immaturity and short-distance transportation. These characteristics are consistent with an active regional extension tectonic setting. The [Formula: see text] system ([Formula: see text];[Formula: see text];[Formula: see text]) and Th/U versus Th consistently reveal that the lower Cretaceous experienced a positive gradient in chemical weathering from young to old formations. Although the patterns of trace elements in three formations of the lower Cretaceous are different, those of the rare earth elements (REEs) tend to be consistent. The significant enrichment of light REEs, heavy REEs fractionation, and distinctive negative Eu anomalies suggest derivation from an old, upper continental crust composed of predominantly felsic sediments. This interpretation is supported by several discrimination diagrams such as titanium dioxide-nickel ([Formula: see text]), which shows the characteristics of immature recycled sediments. A few sensitive elements, ratios, and normalized REE patterns indicate a provenance of an active continental margin and a continental island arc (CIA). The La-Th-Sc, Th-Co-Zr/10, and Th-Sc-Zr/10 discrimination plots further confirm the CIA signature. Thus, we conclude that the early Cretaceous redbeds in the Minle Basin, Hexi Corridor, were deposited in a dustpan-shaped half-graben basin in a CIA setting when northwest China was influenced by intense regional extension.

Study on Expansion Mechanism of Mudstone Under Structural Strength

As the structural swelling soft rock, mudstone’s expansion mechanism is similar to expansive soil, but it has its own particularity. In this paper, based on the analysis of the difference between the undisturbed and remolded samples of mudstone in terms of expansion and deformation, the expansion mechanism considering the strength of mudstone structure was proposed, and the verification test was designed. The following research results were obtained: In judging the potential of mudstone expansion, it is defective to rely solely on the free expansion rate, and its structural strength should be fully considered; The expansive force of mudstone is divided into the external expansive force resisting the external action and the internal expansive force resisting the interaction between internal particles. The external expansive force is the main reason of the increase of the volume of mudstone, and the internal expansive force is related to the cementation strength inside mudstone; The expansion theory based on free expansion rate, expansion force and uniaxial compressive strength is proposed.

The complex spatial distribution of trichloroethene and the probability of NAPL occurrence in the rock matrix of a mudstone aquifer

Methanol extractions for chloroethene analyses are conducted on rock samples from seven closely spaced coreholes in a mudstone aquifer that was subject to releases of the nonaqueous phase liquid (NAPL) form of trichloroethene (TCE) between the 1950's and 1990's. Although TCE concentration in the rock matrix over the length of coreholes is dictated by proximity to subhorizontal bedding plane fractures, elevated TCE concentrations in the rock matrix are not continuous along the most permeable bedding plane fractures. A complex configuration of subvertical and subhorizontal fractures appears to be responsible for the TCE distribution from prior TCE releases at land surface. Phase partitioning calculations of TCE in the rock matrix show that most TCE is adsorbed to solid surfaces because of the large fraction of organic carbon (foc) in the mudstone. Large TCE content in some cores indicate the likely presence of the NAPL form of TCE in the rock matrix. Using average values of porosity (n) and foc in phase partitioning calculations identifies a number of locations of possible NAPL occurrence in the rock matrix. Samples of mudstone analyzed for n and foc show variability in these properties over several orders of magnitude. Accounting for this variability in phase partitioning calculations identifies a probability of NAPL occurrence, PNAPL. The spatial variability of PNAPL along coreholes identifies a configuration that may be attributed to a TCE source zone that has evolved after emplacement due to NAPL dissolution, adsorption, and matrix diffusion.

Organic geochemical characteristics and depositional setting of Paleogene oil shale, mudstone and sandstone from onshore Penyu Basin, Chenor, Pahang, Malaysia

The eastern Chenor Pahang area of the Penyu Basin contains an untapped potential, in part due to poor knowledge of its organic facies characteristics The sedimentary succession of eastern Chenor Pahang area is dominated by fine to coarse grained sandstone occurring in association with oil shale and mudstone in a predominantly fining upward sequence. Detailed geochemical and petrographic characterization was carried out on oil shale and mudstone samples to evaluate the origin and type of organic matter (OM), as well as the paleoenvironmental conditions and organic richness of the Paleogene sedimentary succession. The facies are only enriched in total organic carbon (TOC), potential hydrocarbon yield (S2) and extractible organic matter (EOM) the types of organic matter are important index reflecting the potential of the source rock(s). Based on elemental ratios, the analyzed samples are shown to contain Types I and II kerogens. This finding is supported by the high hydrogen index (HI) of >300 mg HC/g TOC and the presence of abundant liptinitic materials. Biomarker signatures [n-alkanes >n-C25, high C29/C30 17α (H) hopane ratios (0.8–3.3) and high C29 steranes (49–78%)]. Low total sulfur and V/(V + Ni) ratio] suggest a predominantly terrestrial source input with some contribution from aquatic microorganisms as indicated by the common occurrence of amorphous organic matter. Combining this results with n-alkane patterns, kerogen types and organic petrography, predominance of C29 sterane probably indicates a contribution of aquatic organisms such as green and brown algae (consistent with Botrycoccus braunii race A and Pediastrum contribution) and some influence of higher plants OM. Integration of biomarker studies with bulk geochemical and petrographic analysis suggests that the analyzed samples were deposited under suboxic conditions in a fresh water lacustrine environment. This finding is corroborated by the ratios of pristane/phytane, V/Ni and Sr/Br. High bioproductivity and a stratified fresh water column with suboxic bottom water condition enhanced OM preservation in the analyzed mudstone and shale facies. The high OM content in these samples maybe related to the fine-grained matrix of the mud rocks and the paleoclimate in the area.

Northern Cedar Mountains Red Beds, Tooele County

Recent mapping for the Tooele 30' x 60' quadrangle geologic map revealed more information about interesting exposures of red beds cropping out in an 11-mile (18-km) swath along the northwestern flank of the Cedar Mountains (Clark and others, 2017, 2019 in review). They are unusual because such rocks are seldom preserved in northwestern Utah, an area known for thick thrust sheets of Paleozoic marine carbonate and sandstone. These rocks were first mapped by Robert Maurer for his Ph.D. dissertation on the geology of the Cedar Mountains (Maurer, 1970). He called them North Horn (?) Formation and noted the presence of fresh-water snails (Gyraulus sp.) that a paleontologist said were probably of late Paleocene or Eocene age. The North Horn Formation is considered Late Cretaceous (Maastrichtian age) to Paleocene or Eocene (~70 to 60 Ma) in age. However, recent detrital zircon analysis from sandstone in the unit suggest a much older age, with the youngest grains (maximum depositional age) of 117 Ma, or Early Cretaceous, Aptian (UGS and O’Sullivan, 2017). Two samples of gray mudstone taken for fossil pollen in the unit did not produce any usable material. Inspection of these rocks by Don DeBlieux (Utah Geological Survey paleontologist) revealed no bone or other biological material at this location.

Oil-oil and oil-source rock correlations in the Muglad Basin, Sudan and South Sudan: New insights from molecular markers analyses

Abstract Oil-oil and oil-source rock correlations for nineteen crude oils and eight mudstone extracts from four sub-basins in the Muglad Basin were achieved by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Based on the characteristics of biomarker compositions and hierarchical cluster analysis, an outlier crude oil has been discovered in the Muglad Basin. The majority of discovered oils have similar geochemical characteristics and belong to an established oil family. This oil family has relatively higher (C19+C20)/C23TT and C24TeT/C26TT ratios, small amounts of long-chain tricyclic terpanes with a dominance of C21TT among C19 C23TT homologues, a lower abundance of C28 regular steranes with abundant C30 4α-methylsteranes, an unusually higher content of diasteranes and diahopanes. These biomarker ratios indicate the mixed inputs of aquatic plankton and terrigenous organic matter deposited under oxic to sub-oxic, and fresh to brackish water sedimentary environments. This oil family belongs to source rocks of the Abu Gabra Formation as proven by oil-source rock correlation. In contrast, the distribution characteristics of tricyclic and tetracyclic terpanes, C28 regular steranes, C30 4α-methylsteranes, diasteranes and diahopanes are all significantly different than those of the established oil family in the well Kela-1 oil (2563 m) within the Darfur Group reservoir. The geochemical signatures indicate that their related source rock is an algal dominated organic matter input, deposited in sub-oxic condition, and brackish to saline sedimentary environment. Moreover, the composition and characteristics of molecular markers of the well Kela-1 oil are highly consistent with those of the two mudstone samples from the Darfur Group. This clearly demonstrates that the Darfur Group mudstones are the potential source rocks for the outlier crude oil. Identification of the outlier crude oil shows that the Darfur Group mudstones have a certain potential regarding hydrocarbons resources that could provide petroleum companies an impetus to enhance their exploration efforts.

Evaluation of Cretaceous Hinterland Weathering and Climate in the Sichuan Basin, SW China

Cretaceous is characterized by high atmospheric CO2 concentration and a resultantly high temperature. Thus, the Earth system, which operated during the greenhouse condition, can be deduced by the investigation of the paleoclimate during the Cretaceous. However, information of paleoclimate from continental inland-basins is scarce compared to that from continental margin marine-basins. In this research, the changes of weathering condition through the whole Cretaceous Period were reconstructed by analyzing the whole-rock chemical composition and clay mineral composition of mudstone samples collected in the Sichuan Basin, SW China. The reconstructed paleoweathering intensity positively correlates with paleotemperature estimate, indicating that Cenomanian-Turonian stages were climatic optimum in the Sichuan Basin as well. Furthermore, the result suggests a Cenomanian-Turonian extremely high amplitude humidity fluctuation.

Evolution Characteristics of the Cracks in the Completely Disintegrated Carbonaceous Mudstone Subjected to Cyclic Wetting and Drying

Completely disintegrated carbonaceous mudstone, a common embankment material, has significant swelling‐shrinkage behavior under cyclic wetting and drying, which often causes the instability of embankments. In this paper, the evolution of the cracks in the completely disintegrated carbonaceous mudstone subjected to cyclic wetting and drying was studied by laboratory tests. The vacuum saturation method and the drying method based on heat lamps and a fan were employed to simulate the wetting and drying processes, respectively. The image processing technique was used to treat the images of the sample surface. Afterward, various geometric parameters of the cracks appeared on the sample surface were measured, and the evolution characteristics of the cracks were analyzed. The results show that with the increase in the number of wetting and drying cycles, the number of cracks on the sample surface gradually increases. After four wetting and drying cycles, the existing cracks produce a large number of small branches, which are connected to form irregular polygonal grids. The development of the cracks in the completely disintegrated carbonaceous mudstone sample can be divided into three stages, i.e., slow development, rapid development, and stable development. Both the surface density of crack and the crack rate first increase and then tend to be stable with the increasing number of wetting and drying cycles. New cracks are mainly generated on the basis of the existing cracks, and some cracks appear to heal under cyclic wetting and drying. The early cracks are mainly developed in the directions of 0°–90° and 300°–360°, and the development rate of the cracks in the directions of 30°, 90°, 140°–150°, and 180°–270° is significantly higher than that of the cracks in other directions.

Areoligeracean dinoflagellate cysts from the upper Campanian (Upper Cretaceous) of Hornby Island, British Columbia, Canada

Twenty-nine mudstone samples from coastal exposures of the upper Campanian Northumberland Formation on Hornby Island, British Columbia, Canada, have yielded diverse assemblages of exceptionally well-preserved dinoflagellate cysts belonging to the family Areoligeraceae. In total, at least 11 species belonging to eight genera occur throughout the studied section. Emendations are proposed for the genera Canningia, Canninginopsis, Circulodinium, Cyclonephelium and Senoniasphaera. The new species Canningia diastatikos sp. nov. is proposed. The assemblages include one species complex, which we refer to as the ‘Areoligera volata complex’, that exhibits morphological intergradation between forms typical of Areoligera coronata and Areoligera volata. It is postulated that morphological intergradation may reflect ecophenotypic variability which may present utility for palaeoenvironmental reconstructions.

Empirical plot of gas generation from oil-prone marine shales at different maturity stages and its application to assess gas preservation in organic-rich shale system

Abstract Determining the degree of gas preservation and loss in shale gas system is critical to evaluate unconventional shale gas potential, particularly in the tectonically faults developed areas. In this study, an empirical plot of gas yields from marine shales at different stages of maturity and residual TOC content is derived from pyrolysis results and applied to evaluate the extent of shale gas loss. Miniature core plugs drilled from immature Barnett mudstone, Eagle Ford limestone, Woodford chert and mudstone samples were isothermally heated at 130 °C, 300 °C, 310 °C, 333 °C, 367 °C, 400 °C, and 425 °C for 72 h under a confining pressure of 68.0 MPa, corresponding to immature, early stage of oil window, main stage of oil window, late stage of oil window, main stage of oil cracking to wet gas, and late stage of oil cracking, respectively. The generated gas yields from marine shales with increasing thermal maturity are evaluated quantitatively by anhydrous closed-system pyrolysis. Experimental results show that gaseous hydrocarbon yields (C1 C5) from type II kerogen-dominated marine shales are linearly proportional to their residual TOC content at each stage of petroleum formation. The regression lines in the plot of generated gas yield and residual TOC content thus represent different gas-generation stages of type II kerogen-dominated marine shales. In the application to three geologic cases, the measured total gas content and present-day TOC content from a variety of shale gas wells with varying thermal maturity levels were incorporated into the empirical plot. And the comparative results show that, the gas contents of these core samples investigated for the low thermal maturity New Albany Shale in the Illinois Basin are somewhat higher than the estimated yield of generated gas from type II kerogen-dominated marine shales at the early stage of oil window, suggesting that microbial gas made contribution to the excess gas content in the New Albany shale gas system and it represents a typical gas mixture containing both early thermogenic gas and biogenic gas. In contrast, significant gas loss was observed in both the high thermal maturity Barnett Shale in the Fort Worth Basin and the overmature Silurian Longmaxi Shale in the Sichuan Basin as compared to each the estimated yield of generated gas. This phenomenon is probably caused by either petroleum expulsion or tectonic dissipation, or coupling of two processes. As for the Silurian Longmaxi Shale, it is estimated that approximately 60%–90% of total generated gas in quantities has been lost in the overmature Silurian Longmaxi shale gas system where industrial gas flow had been achieved. This provides an upper-limit measure to shale gas loss caused by petroleum expulsion and tectonic dissipation throughout geological time.

Failure Characterization of Three Typical Coal-Bearing Formation Rocks Using Acoustic Emission Monitoring and X-ray Computed Tomography Techniques

In coal mining engineering, the mechanical properties of rocks in coal-bearing formations are important for mining safety. In addition, lithological properties are among the most crucial factors affecting the mechanical properties of a given rock. To preliminarily address this important issue, several uniaxial compression tests were conducted on three types of rocks in coal-bearing formations: argillaceous siltstone, mudstone and silty mudstone. In all of the experiments, the acoustic emission (AE) technique was employed to detect the initiation and evolution of microcracks during the testing process, and the computed tomography method was then employed to further investigate the failure patterns of the different types of rock mass. The AE results showed that failure initiated at stress levels of approximately 0.18, 0.48 and 0.05 times the peak stresses for argillaceous siltstone, mudstone and silty mudstone, respectively. Furthermore, in the argillaceous siltstone, the accumulated AE events increased gradually during loading until macrofailure occurred; in contrast, obvious plateaus in the AE parameter curves existed in the stress regions at 60–70% and 35.5–50% peak stress for mudstone and silty mudstone, respectively. In the crack coalescence stage, a large number of low-energy microfractures occurred in the argillaceous siltstone, whereas a small number of high-energy microfractures occurred in the mudstone and silty mudstone. The results revealed that (1) the argillaceous siltstone was essentially destroyed by splitting, while the mudstone and silty mudstone samples were broken by shear fracture propagation; (2) for all of the coal-bearing formation rocks investigated in this work, when the fracture surface area was larger, the strain energy to be translated into surface energy was greater, and thus, more input energy was required when the peak strength was greater. Clearly, lithological properties, especially microstructural features, play a critical role in the mechanical properties of coal-bearing formation rocks. Therefore, a comprehensive evaluation should be considered in any analysis of mining safety.

Thermodynamic stability of methyldibenzothiophenes in sedimentary rock extracts: Based on molecular simulation and geochemical data

The thermodynamic stabilities of methyldibenzothiophene (MDBT) isomers and the mechanisms of 1,2-methyl shift, methylation and demethylation have been systematically investigated by molecular modelling. Combining with the geochemical data from a set of lacustrine mudstone samples in the Liaohe Basin (East China), this study reveals the possible reaction mechanisms governing the formation and occurrence of MDBT isomers in source rocks. The Boltzmann distribution of MDBTs in gas, water and cyclohexane was calculated to show the relative thermal stability with the increasing of temperature (burial depth). A total of eight reaction pathways involving in 1,2-methyl shift, methylation and demethylation chemical processes via ionic and free radical reactions, and the transition states and energy barriers are calculated. The results show that three main reaction pathways (P1, P3 and P6) are three possible pathways for the transformation reactions between DBT and MDBTs during the onset of the oil generation window to high maturity stages of sedimentary organic matter. The 1,2-methyl shift isomerization (P1) and low concentration of the possible precursor (2-methylbiphenyl) for 1-MDBT, cause the relative low abundance of 1-MDBT isomer during the oil generative window. Methylation of DBT with methyl radical attack (P3), the formation of MDBTs with TMAB as methyl donor (P6), the prevailing degradation reactions and much higher thermodynamic stability of 4-MDBT relative to 1-MDBT, makes the MDR maturity indicator regularly increase during the oil generative window to high maturity stages. Therefore, a previously proposed MDR maturity indicator was further confirmed by the theoretical calculations, molecular simulations and the geochemical data of the lacustrine mudstone samples in this study.

Preliminary characteristics of rare earth elements and other trace elements in fine-grained deposits from the Triassic-Jurassic transition in the former Mid-Polish Trough

Fine-grained siliciclastic rocks from the Triassic-Jurassic transition (Rhaetian–Hettangian) in the former Mid-Polish Trough were the subject of the geochemical study at the Polish Geological Institute – National Research Institute in Warsaw. Ninety-four samples of claystones and mudstones from six archived drill cores were analysed by ICP-MS and XRF for rare earth elements (REE) and other trace elements. The results indicate that the sources of most of the claystones and mudstones were sedimentary rocks of the upper continental crust of old cratonic areas, where the protolith had a moderately felsic character. Weathering and recycling processes modified the original chemical composition to some extent. However, during Rhaetian and early Hettangian, some geochemical data in the south-eastern segment of the MPT suggest significant input from a mafic volcanic protolith. Moreover, a clear enrichment in rare-earth elements was observed in few samples, caused by admixtures of accessory minerals (being a main carrier of REE). Nevertheless, based on currently obtained data, the Rhaetian–Hettangian concentrations of REE (and other trace elements) in the MPT are low and they are of scientific indicative significance, not of raw material importance.

Organic matter accumulation on the Dalong Formation (Upper Permian) in western Hubei, South China: Constraints from multiple geochemical proxies and pyrite morphology

Organic-rich black shales in the Upper Permian Dalong Formation are considered excellent source rocks in the western Hubei Basin, South China. However, the mechanisms of organic matter (OM) accumulation remain controversial. Furthermore, the evolution of primary productivity and ocean hypoxia during the Late Permian in the western Hubei Basin is unclear. In this study, we discuss the paleoclimate, paleoceanography, paleoenvironment and the mechanisms of OM accumulation based on geochemical characteristics and pyrite framboid data from drillcore H 1 in Ensi, western Hubei Province. Black shales from the Dalong Formation have high total organic carbon (TOC) contents (2.8–9.3%), while the mudstone samples contain low TOC contents (0.48–1.96%). The weak chemical weathering indicates paleoclimate conditions were relatively cold during black shale deposition, whereas rapid warming occurred during gray mudstone deposition, which may be connected with the Late Permian Changhsingian global climate event. Redox indices, namely, V, U, and Mo concentrations, and the relationship of UEF and MoEF combined with pyrite framboid data suggest that an anoxic to euxinic environment predominated during black shale accumulation. In contrast, oxic to hypoxic marine conditions pervaded the western Hubei Basin during the deposition of mudstone. The primary productivity indices (Cu/Al and Nixs) suggest that high paleoproductivity occurred in the Late Permian, especially during periods of transgression. However, declining primary productivity with enhanced intensity of chemical weathering may indicate that biological extinction was associated with a rapid increase in temperature during the Late Permian. Negative/positive relationships between the TOC contents and Baxs and Nixs values demonstrate that sulfate was consumed by a higher OM input and OM accumulation was mainly controlled by high primary productivity. The study implies that ocean hypoxia and high primary productivity played important roles in OM accumulation. The depositional model shows that high primary productivity possibly resulted from weathering of volcanic ash from land during transgressions and that intense degradation of OM resulted in an euxinic environment.

Dinoflagellate cysts from the upper Campanian (Upper Cretaceous) of Hornby Island, British Columbia, Canada, with implications for Nanaimo Group biostratigraphy and paleoenvironmental reconstructions

Abstract Thirty mudstone samples from coastal exposures of the Northumberland Formation on Hornby Island, British Columbia, Canada, yielded diverse dinoflagellate cyst and terrestrial sporomorph assemblages. A late Campanian age for the formation has been well defined through magnetostratigraphy, macrofossil biostratigraphy, and geochemical studies of the Hornby Island section. Dinoflagellate cyst taxa corresponding to 61 genera are exceptionally well preserved and include specimens referable to at least 68 formally established species. The earliest occurrences of Canninginopsis maastrichtiensis, Druggidium cf. discretum, Phanerodinium belgicum, Renidinium cf. vitilaire, Senegalinium simplex, Spiniferella cornuta, and Xenicodinium delicatum sensu Slimani et al. are reported along with the most recent occurrence of Senoniasphaera protrusa, extending their stratigraphic ranges into the upper Campanian. The palynomorph assemblages support a late Campanian age. Two dinoflagellate cyst ecozones are recognized (ecozone 1 and ecozone 2). Assemblages suggest sediment deposition in an inner shelf environment with moderate to high nutrient input and primary productivity.

Influence of wetting-drying cycles on the pore structure and mechanical properties of mudstone from Simian Mountain

The deterioration of mudstone induced by cyclic fluctuations in the groundwater level in subtropical regions affects the stability of underground construction. To investigate the evolution of the micropores and mechanical properties of mudstone under cyclic wetting-drying conditions, mudstone samples from Simian Mountain in southwest China are subjected to different numbers of wetting-drying cycles in the laboratory. The pore structure change induced by periodic wetting and drying process is evaluated through low-field nuclear magnetic resonance (NMR), a nondestructive detection method. The results from the experiments show that the porosities of the mudstone samples dramatically increase during cyclic wetting-drying. A significant linear relationship between the incremental in porosity and the number of wetting-drying cycles was established. The influence of wetting-drying cycles on the mechanical properties of mudstone is analyzed in terms of the pore structure. The increase in porosity leads to the decline of the uniaxial compressive strength (UCS) and elastic modulus of the mudstone samples. A quantitative equation is tentatively established to describe the relationship between the porosity and UCS of mudstone damages by wetting-drying cycles.

Gas and liquid permeability measurements in Wolfcamp samples

Argon gas and liquid (dodecane) permeability measurements in two mixed quality siliceous mudstone samples within the Wolfcamp formation demonstrate that it is possible to close multiple bedding parallel open artificial micro-fractures and obtain representative matrix permeability by applying two confining stress cycles at a constant pore pressure under effective stresses ranging from 6.9 MPa to 59.7 MPa. The clearly micro-fractured sample exhibited a three-order decrease in permeability from 4.4 × 10−17 m2 to 2.1 × 10−20 m2. In contrast, the relatively intact sample exhibited initial liquid permeability of 1.6 × 10−19 m2 that declined gradually with stress to 3.0 × 10−20 m2. In this study, we developed a new permeability testing protocol and analytical approaches to interpret the evolution of micro-fractures and estimate the matrix permeability based on initial pulse-decay gas permeability measurements. The insights gained are useful to identify pore-scale controls on fluid flow behavior using SEM petrography and pore-space characterization and validate fundamental fluid flow mechanisms examined using pore-scale numerical models.

Organic matter, mineral composition, pore size, and gas sorption capacity of lacustrine mudstones: Implications for the shale oil and gas exploration in the Dongying depression, eastern China

Because clay minerals and pore-size distribution are important for oil and gas accumulation in lacustrine mudstone reservoirs, this study aimed to characterize the pore-size distribution in lacustrine mudstone, reveal the importance of clay minerals in gas sorption capacity (GSC), provide insights into the primary GSC controls for lacustrine mudstones, and discuss the shale oil and gas resource potential and possible risks in their future production. A total of 256 core samples from the lower Paleogene sequence of the Dongying depression in the Bohai Bay Basin in China were analyzed to determine organic richness and hydrocarbon generation potential. A series of analyses was conducted on a suite of 28 mudstone samples from the S121 well to investigate the mineral composition, pore-size distribution, and primary controls on GSC. Scanning electron microscopy and x-ray diffraction were used to observe the microscopic characteristics and identify various minerals. Nitrogen adsorption experiments at low temperatures and a methane isothermal adsorption test were conducted to study the pore sizes and gas adsorption capacities. Experimental results show that the majority of the samples were rich in type II and I kerogen with moderate to high hydrocarbon generation potential and are thermally mature in the main oil window. The contents of illite and mixed layer illite–smectite (I–S) are high (>40%) in these lacustrine mudstones. The pores were mainly thin, long, and bottleneck shaped and dominated by type IV and H2 hysteresis loop characteristics. The abundance of quartz, feldspar, illite, and mixed layer I–S all presented a positive correlation with their Brunauer–Emmett–Teller surface area and total pore volume, whereas the abundance of carbonate minerals (dominated by calcite) showed a negative correlation. The volume of micropores and clay minerals were the main factors controlling GSCs. The results highlight the importance of clay minerals, including the illite and mixed layer I–S, in the lacustrine mudstones because of their considerable GSC. High content of illite and mixed layer I–S in lacustrine mudstone is in favor of gas storage, whereas at the same time, it is not conducive to shale gas development because of its reducing the brittleness of shale. The Paleogene of Dongying depression has shale oil and gas resources; however, several key geological factors, including pore-size distributions, pore diameters, oil density, and low brittleness, may pose risks in shale oil and gas development.