International Journal of Coal Geology最新文献

{"title":"Spatial distribution of remaining movable and non-movable oil fractions in a depleted Maastrichtian chalk reservoir, Danish North Sea: Implications for CO2 storage","authors":"Henrik I. Petersen ,&nbsp;Kasper H. Blinkenberg ,&nbsp;Kresten Anderskouv ,&nbsp;Arka Rudra ,&nbsp;Xiaowei Zheng ,&nbsp;Hamed Sanei","doi":"10.1016/j.coal.2024.104624","DOIUrl":"10.1016/j.coal.2024.104624","url":null,"abstract":"<div><div>Depleted oil and gas fields constitute potentially important storage sites for CO₂ in the subsurface, but large-scale injection of supercritical (sc) CO₂ in chalk has not yet been attempted. One of the risks is the adverse effect of the substantial amount of remaining oil in the chalk reservoirs on scCO₂ injection. In order to counter an undesired effect on injectivity, a fundamental understanding of the spatial distribution and quantity of the movable, semi-movable, and non-movable oil, and solid bitumen/asphaltenes fractions of the remaining oil is critical. In this study a combination of organic geochemistry (gas chromatography of the saturated fraction and programmed pyrolysis), and reflected light microscopy was applied to evaluate and measure the spatial distribution, volume, and saturation of different oil fractions in a well-defined reservoir interval of a waterflooded Maastrichtian chalk reservoir in the Danish Central Graben, North Sea. A total of 127 samples from a slightly deviated vertical well and two ∼5 km-long horizontal wells from the Halfdan and Dan fields were analyzed. An original uneven distribution of oil saturation and composition or different production efficiency of different levels in the reservoir may account for variations in the total oil and oil fraction saturations. Gas chromatography shows that the solvent extractable oil is quite similar in composition, characterized by a dominance of polar compounds and a high content of asphaltenes. Extended slow heating (ESH) pyrolysis reveals that most of the remaining oil saturation consists of semi-movable oil and total non-movable oil (non-movable oil plus solid bitumen/asphaltenes). Reduced oil gravity values (API) are related to evaporation loss of the lightest hydrocarbon fraction during core storage and increase of the relative proportion of the heavier oil fractions by waterflooding during production. Microscopy disclosed three forms of oil: i) Patchy distributed lighter, movable oil showing a bluish fluorescence, ii) Brownish staining with a dark orange to brownish fluorescence, and iii) Dark brown non-fluorescing oil and black solid bitumen/asphaltenes occurring in microfossils and along deformation bands and stylolites, constituting the heavy non-movable oil fractions. There is a general correlation between bulk rock porosity and the total non-movable oil saturation. It thus appears that the heavy non-movable oil fractions preferentially occur in association with low-permeability heterogeneities within high-permeability stratigraphic intervals. These intervals appear to favor accumulation of non-movable oil and solid bitumen/asphaltenes and may carry a higher risk for impeding scCO₂ flow.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"295 ","pages":"Article 104624"},"PeriodicalIF":5.6,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142538558","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An improved convolutional architecture for quantitative characterization of pore networks in fine-grained rocks using FIB-SEM","authors":"Bo Liu ,&nbsp;Qamar Yasin ,&nbsp;Mengdi Sun ,&nbsp;Atif Ismail ,&nbsp;David A. Wood ,&nbsp;Xin Tian ,&nbsp;Baiquan Yan ,&nbsp;Li Fu","doi":"10.1016/j.coal.2024.104625","DOIUrl":"10.1016/j.coal.2024.104625","url":null,"abstract":"<div><div>Focused ion beam scanning electron microscope (FIB-SEM) is one of the most advanced imaging techniques for analyzing and understanding complex pore networks in shale and other fine-grained formations. However, FIB-SEM imaging tends to be time-consuming and labor-intensive and can result in biased interpretations associated with pore analysis. Recently, U-Net or its variants for image segmentation have been applied to capture microscopic pores at higher resolutions. The ‘traditional’ encoder-decoder-based approaches tend to detect very fine-scale microscopic pores poorly. This study presents an improved convolutional architecture for automatically analyzing pore structures in shale reservoirs using FIB-SEM. It does so by applying an overcomplete convolutional architecture, KiU-Net, to capture very fine-scale microscopic pores by accurately defining their edges in the input FIB-SEM images. The KiU-Net learns low and high-level features by making the model more sensitive to fine-scale microscopic pores in the input images. The purpose of this study is to demonstrate KiU-Net's capabilities by analyzing different shale formations with varying characteristics. The results indicate that KiU-Net is more accurate and efficient than other methods in predicting nanopores in the Longmaxi, Niutitang, Qingshankou, Qianjiang, and Yanchang Formations (China), Bakken shale (Canada), and coal reservoirs (China). Furthermore, KiU-Net demonstrated the advantage of requiring fewer parameters and achieving super convergence compared to the Attention U-Net technique. KiU-Net addresses the challenges of the Edge-Threshold Automatic Processing (ETAP) methods by capturing very fine-scale microscopic pores with accurate edges. This study further enhances the accuracy and efficiency of pore analysis in shales, thereby offering an improved method for understanding shale reservoir quality with the potential to improve petroleum recovery from such formations.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"295 ","pages":"Article 104625"},"PeriodicalIF":5.6,"publicationDate":"2024-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142538557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Organic petrographic and geochemical insights into organic matter derived from land plants and marine algae in the Lark Formation, Danish North Sea","authors":"Zhiheng Zhou ,&nbsp;Qingyong Luo ,&nbsp;Arka Rudra ,&nbsp;Henrik Ingermann Petersen ,&nbsp;Niels Hemmingsen Schovsbo ,&nbsp;Hamed Sanei","doi":"10.1016/j.coal.2024.104627","DOIUrl":"10.1016/j.coal.2024.104627","url":null,"abstract":"<div><div>Climatic fluctuations from the Eocene to the Miocene highlight the importance of investigating the paleoenvironment of the latest Eocene to the Middle Miocene Lark Formation in the Danish North Sea. This study investigates immature sedimentary organic matter in the Lark Formation using 54 cuttings samples and one core sample collected from seven wells in the eastern North Sea Basin. Organic petrography and molecular geochemistry analyses were performed to determine the variations in the quantity and origin of allochthonous and autochthonous organic matter. Additionally, the study assesses the impact of climate fluctuations on marine productivity in the eastern North Sea Basin and land plant vegetation at the basin margins during the latest Eocene to the Middle Miocene.</div><div>The organic matter in the Lark Formation originated from mixed sources, primarily land plants, with a secondary contribution from marine algae. This is indicated by the maceral composition and the types and abundance of aliphatic and aromatic hydrocarbon biomarker compounds. Moreover, the presence of diterpenoids (gymnosperm biomarkers) and non-hopanoid triterpenoids (angiosperm biomarkers) reveals that the allochthonous organic matter originated from conifers and angiosperms.</div><div>Climatic impacts on land plants and marine algae during the latest Eocene to the Middle Miocene are revealed by several parameters: the Averaged Chain Length (ACL) of land plant waxes, the proportion of coniferous contribution (C/(C + A)), and the whole rock volume percentages of huminite, inertinite (H + I, vol%) and liptinite (L, vol%). The shifts to cooler and drier climates highlighted the cold adaptation of onshore conifers and resulted in the input of higher molecular weight waxy components into the sediments. However, under these conditions, reduced precipitation and runoff resulted in lower amounts of terrigenous organic matter supplied to the basin. Additionally, the drop in water temperature and the warm-affinity of local algae assemblage led to reduced marine productivity. Together, these factors contributed to an overall decrease in organic richness. In contrast, during shifts to warmer and more humid climates, the trend reversed. The contribution of conifers to the floral assemblage diminished, but higher amounts of terrigenous organic matter were transported to the basin due to increased precipitation and runoff. This was accompanied by warmer water temperatures, boosting the productivity of organic-walled microplankton in the marine environment and contributing to greater organic richness.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"295 ","pages":"Article 104627"},"PeriodicalIF":5.6,"publicationDate":"2024-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142538559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geological and hydrological controls on the pressure regime of coalbed methane reservoir in the Yanchuannan field: Implications for deep coalbed methane exploitation in the eastern Ordos Basin, China","authors":"Xiaoming Wang ,&nbsp;Shihui Hou ,&nbsp;Xingjin Wang ,&nbsp;Yudong Yuan ,&nbsp;Zheng Dang ,&nbsp;Mingkai Tu","doi":"10.1016/j.coal.2024.104619","DOIUrl":"10.1016/j.coal.2024.104619","url":null,"abstract":"<div><div>The pressure regimes of the No. 2 coalbed methane (CBM) reservoir in the Yanchuannan field located in the southeastern Ordos Basin are highly variable and divided into overpressured (pressure gradient &gt;9.80 kPa/m), slightly underpressured (pressure gradient of 8–9.80 kPa/m), and moderately underpressured (pressure gradient of 5–8 kPa/m). The controlling factors for the variable pressure regimes were investigated through the analysis of geological and hydrological characteristics. The pressure regimes are controlled by different mechanisms in different hydrodynamic environments. In the closed hydrodynamic environment characterized by TDS &gt; 10,000 mg/L and NaCl type of groundwater, the pressure regime is dominated by overpressured to slightly underpressured and is controlled by CBM migration. Overpressure was developed by thermogenic CBM generation during the coalification process and is maintained by thermogenic CBM migration from the extended northwestward and deeply buried CBM reservoir during tectonic uplift. The transition from overpressure to slight underpressure and then to moderate underpressure towards the southeast is the result of the progressively weakened migrated thermogenic CBM with increasing migration distance. In the open hydrodynamic environment characterized by TDS &lt; 10,000 mg/L and NaHCO₃ type of groundwater, the pressure regime is dominated by slightly to moderately underpressured and is governed by hydrodynamics. Groundwater is fed by meteoric recharge along the structurally upturned basin margin and creates the hydrodynamic framework during tectonic uplift. The transition from moderate to slight underpressure towards the southwest is associated with the minor decrease range in ground elevation from basin margin to basin interior and the gradually weakened runoff intensity of groundwater with increasing distance to meteoric recharge. The idealized models for the pressure regimes are established, which can provide guidance to deep CBM sweet spot identification in CBM fields in the eastern Ordos Basin and elsewhere.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"294 ","pages":"Article 104619"},"PeriodicalIF":5.6,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142531320","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Calcite UPb dating and geochemical constraints on fracture opening in organic-rich shales","authors":"Dadong Liu ,&nbsp;Hui Tian ,&nbsp;Chengzao Jia ,&nbsp;Qingqing Fan ,&nbsp;Xuesong Lu ,&nbsp;Mingyang Xu ,&nbsp;Yan Song ,&nbsp;Chen Zhang","doi":"10.1016/j.coal.2024.104621","DOIUrl":"10.1016/j.coal.2024.104621","url":null,"abstract":"<div><div>Gas-bearing, organic-rich shales commonly host numerous opening-mode fractures; however, their formation mechanism remains controversial, with competing arguments of tectonic-origin and/or hydrocarbon generation pressurization-origin. Here, we studied fracture fillings in shale reservoirs of the lower Silurian Longmaxi Formation in the Luzhou area, southern Sichuan Basin, SW China. Using in-situ U<img>Pb geochronology, rare earth elements (REEs) and C-O-Sr isotope geochemistry, and fluid inclusion analyses, we investigated the timing and geochemical attributions of fracture fills and identify the mechanism of fracture formation. The results show that, the cements that occupy fractures in the Longmaxi Formation shales contain mainly calcite and quartz. The calcite cements show crack-seal and fibrous textures, indicating that they are <em>syn</em>-kinematic mineral deposits. The ⁸⁷Sr/⁸⁶Sr values of the calcite cements essentially overlap with those of their proximal host shales. This result, combined with slight depletions in δ¹³C_PDB and relatively uniform fluid δ¹⁸O_SMOW isotopic features, indicate that the fluids from which the calcite precipitated were largely derived from their surrounding host shales. Abundant methane inclusions are present in fracture cements, with trapping pressures of 104.5–157.5 MPa and pressure coefficients of 1.92–2.43, suggesting they were trapped in an overpressurized fluid system. In-situ U<img>Pb dating of calcite cements yielded ages of ca. 160 Ma and ca. 110 Ma, which coincide with the timing of thermal cracking of oil to gas during burial. In combination with the overpressurized, geochemically closed fluid system, the fractures were most likely triggered by gas generation. Our study emphasizes that natural fracturing induced by hydrocarbon generation overpressurization is an essential mode of brittle failure in tectonically quiescent basins worldwide.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"294 ","pages":"Article 104621"},"PeriodicalIF":5.6,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142531317","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petroleum evolution and its genetic relationship with the associated Jinding PbZn deposit in Lanping Basin, Southwest China","authors":"Xiang Ge ,&nbsp;Jiajia Xiang ,&nbsp;Yulin Jin ,&nbsp;Wenpan Cen ,&nbsp;Guangyou Zhu ,&nbsp;Chuanbo Shen","doi":"10.1016/j.coal.2024.104620","DOIUrl":"10.1016/j.coal.2024.104620","url":null,"abstract":"<div><div>The spatial association of hydrocarbons with metalliferous ore deposits is found worldwide and is particularly common to MVT Pb<img>Zn deposits. Heavy oil and bitumen are found in the Jinding Pb<img>Zn deposit within the Lanping Basin, South China. However, the temporal and genetic associations between hydrocarbons and the deposit are still controversial. To this end, integrating Raman analysis, Re<img>Os geochronology and transmission electron microscopy analysis of the bitumen and in situ S isotope analyses of the sulfide, the petroleum evolution of the Jinding reservoir and its genetic relationship with the Pb<img>Zn deposits were discussed. Bitumen Re<img>Os data from this study and published works indicate that the late Triassic shales underwent two distinct oil-generation events before mineralisation (∼25 Ma), with initial oil generation occurring during the early Cretaceous (∼116 Ma) and the second during the early Paleogene (ca. 68–59 Ma). These two ages agree with the modelled thermal history of the Jinding reservoir. Combining the oil-before-ore timing sequence, high metal abundance of the bitumen, two negative sulfur isotope peaks of the sulfide and high S/C atomic ratio of the bitumen from the Jinding deposit, the oil-containing aqueous solutions were considered as one metal carrier during the hydrocarbon migration and accumulation; further, bacterial sulfate reduction and thermo-chemically induced sulfate reduction processes could have participated in the supply of reduced sulfur for the Pb<img>Zn deposit precipitation.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"294 ","pages":"Article 104620"},"PeriodicalIF":5.6,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142531318","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pyrite trace metal and sulfur isotopic compositions track metalliferous fluid circulation within the Ordovician/Silurian organic-rich black shales in the eastern Sichuan Basin, southwestern China","authors":"Shaojie Li ,&nbsp;Qilin Xiao ,&nbsp;Suyang Cai","doi":"10.1016/j.coal.2024.104617","DOIUrl":"10.1016/j.coal.2024.104617","url":null,"abstract":"<div><div>Depicting metalliferous fluid flows in sedimentary basins has a remarkable implication for understanding the formation and evolution of organic-rich sediments. The Middle-Upper Yangtze region in South China hosts voluminous gaseous hydrocarbons and MVT-type Zn<img>Pb deposits. Natural gases are mainly distributed in the Sichuan Basin, yet Zn<img>Pb deposits are found in surrounding regions of the basin. Such a unique distribution pattern implies that the interplay between metalliferous fluids and organic-rich sediments may be extensive in the boundary of these two types of deposits. A typical Ordovician/Silurian (Wufeng/Longmaxi formations) organic-rich black shale outcrop occurs in the eastern boundary of the Sichuan Basin. Pyrites are frequently distributed across this section, providing an ideal opportunity to investigate features of metalliferous fluids and their potential impacts on organic-rich sediments. Pyrites associated with high-angle carbonate veinlets are recognized in the studied area, and this group of pyrites (“Group 2”) commonly display planar-laminated morphologies, moderate δ³⁴S values (0.78 ‰–8.86 ‰), and elevated trace metal contents (Ni, Pb, Mn, Mo, Tl, and REE) than those not associated with carbonate veinlets. These features suggest that this group of pyrites may be precipitated via local metalliferous fluid flows. Besides, pyrites with relatively lower trace metal contents can be further divided into two groups, including a group of euhedral/subhedral pyrites with more depleted δ³⁴S values (−18.06 ‰ – -1.15 ‰; “Group 1”) and a group of planar-laminated/cubic pyrites with enriched δ³⁴S values (10.55 ‰–37.62 ‰; “Group 3”). Pyrites of Group 1 and Group 3 may be formed via bacterial sulfate reduction (BSR) and thermochemical sulfate reduction (TSR), respectively. The discovery of fluid-related, trace-metal-enriched pyrites implies that fluid circulation within organic-rich black shales has the potential to remobilize, transport, and re-deposit trace metals. Besides, metalliferous fluid may also promote organic matter maturation within the Sichuan Basin. The outcomes of this study, combined with previous findings of metalliferous fluid flows in the center of the basin and Zn<img>Pb mineralization belts surrounding the basin, imply that a widespread Ediacaran-Palaeozoic fluid circulation system may exist in the Middle-Upper Yangtze region.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"294 ","pages":"Article 104617"},"PeriodicalIF":5.6,"publicationDate":"2024-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142446305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental investigation on the oil occurrence and mobility of lacustrine shales in offshore area of China using 1D/2D nuclear magnetic resonance and centrifugal techniques","authors":"Sijia Nie ,&nbsp;Feng Yang ,&nbsp;Long Luo ,&nbsp;Kong Deng ,&nbsp;Luyu Du","doi":"10.1016/j.coal.2024.104618","DOIUrl":"10.1016/j.coal.2024.104618","url":null,"abstract":"<div><div>Shale oil occurrence mechanism and mobility have significant influences on hydrocarbons extraction from shale systems. However, the effects of petrophysical and petroleum geochemical properties on oil mobility are not understood. In this study, shales with different lithofacies were investigated using thin sections, scanning electron microscopy, nuclear magnetic resonance (NMR), and organic geochemical analysis. Shales at original, extracted, oil-saturated, and centrifugal states were systematically scanned using 1D and 2D NMR technologies. The multi-scaled pores were obtained by comparing the T₂ spectra of samples at different states. The 2D NMR identification spectra for hydrocarbon-bearing components were established. The free oil, adsorbed oil, mobile oil contents were quantitatively evaluated and the geological controls on oil mobility were discussed.</div><div>Results show that the siliceous shales have the highest total oil and movable oil contents, while the argillaceous shales have the lowest values due to the limited pore space and poor connectivity. Mobile oil mainly stores in interparticle pores, dissolution-related pores and bedding fractures. Its content increases with the increasing felsic minerals. Oil in siliceous shales are rich in low carbon-chain hydrocarbons and has high mobility. Based on oil distribution in multi-scaled pores, a strategy about the mobile oil distribution were proposed: Ultramicropores region is the immobile oil zone; Micropores region is the oil difficult-to-flow zone; Transition pores region is the oil easy-to-flow zone; Macropores region is the completely mobile oil zone. The mobile oil mainly accommodates in transition pores and macropores (pore size &gt;20 nm and mobile oil saturation exceeds 60 %).</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"294 ","pages":"Article 104618"},"PeriodicalIF":5.6,"publicationDate":"2024-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142531316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Occurrences of paleo-wildfires in the early Albian, Erlian Basin, NE China: Evidence from coal petrography and geochemistry","authors":"Shuang Gao ,&nbsp;Yong Li ,&nbsp;Longyi Shao ,&nbsp;Cai Tie ,&nbsp;Junhui Li ,&nbsp;Yuping Zhou","doi":"10.1016/j.coal.2024.104616","DOIUrl":"10.1016/j.coal.2024.104616","url":null,"abstract":"<div><div>The Albian in the early Cretaceous was a period with extensive and frequent wildfires, yet the wildfire types, intensity, and implications are not well understood due to the lack of continuous wildfire records. In this study, a total of 79 coal samples were collected from a 13 m thick coal seam in the early Cretaceous in the Erlian Basin, Inner Mongolia, China, which were analyzed using Zircon U<img>Pb dating, coal petrography analysis, scanning electron microscopy, and gas chromatography–mass spectrometry techniques. Zircon dating of an interbedded volcanic ash layer shows the coal was deposited in the early Albian, at 111.14 ± 1.14 Ma. Petrographic and proximate analysis show that the coals are characterized by mainly huminite (18.7–84.2 vol%, average 52.7 vol%, mmf—mineral matter free) and inertinite (15.1–80.7 vol%, average 46.2 vol%, mmf), with high volatile matter yields (average 39.7 %, dry and ash-free basis) and low ash yields (average 7.45 %, air dry basis). The frequent wildfire events are recognized by: (1) the inertinite content, mostly composed of fusinite, semifusinite, and inertodetrinite, and higher than most of the reported inertinite contents in the other Cretaceous coals around the world; (2) inertinite, representative of fossil charcoal is typified by homogenized cell walls and vesicles generated under high temperature; and (3) the polycyclic aromatic hydrocarbons (PAHs) are composed of 16 types of 2–6 ring aromatic hydrocarbon compounds, with the average pyrogenic PAHs accounting for 73.9 % of the total PAHs and the medium and high-molecular-weight PAHs accounting for 70.6 % of total molecular-weight PAHs. The average inertinite reflectance values range between 0.86 % and 1.60 %, with an average of 1.21 %, reflecting the fire temperature values ranging from 230 to 436 °C, with an average of 327 °C. The main wildfire types were ground and surface fires under low to moderate temperatures, and wildfire intensity variation was shown by the total content of fusinite and semifusinite, pyrogenic PAHs concentrations, and inertinite reflectance of the coals. Maceral and mineral matter composition indicated that the coals were formed under wet moor with intermittent moderate to high flooding. The peat in topogenous and ombrotrophic raised mires is evidenced by the presence of tonstein and a low ash yield. Changes in fire types and intensity in the Erlian Basin provide new evidence that the Albian is a unique “high fire” period within the Cretaceous.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"294 ","pages":"Article 104616"},"PeriodicalIF":5.6,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142446304","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleoredox and lithofacies assessments in Deepwater intervals of the Monterey Formation, Santa Maria Basin, California: Insights from organic sulfur geochemistry","authors":"Ana Vielma ,&nbsp;Joseph A. Curiale ,&nbsp;Humberto Carvajal-Ortiz ,&nbsp;Jagoš R. Radović ,&nbsp;Qi Fu ,&nbsp;Thomas B. Malloy ,&nbsp;K.K. (Adry) Bissada","doi":"10.1016/j.coal.2024.104606","DOIUrl":"10.1016/j.coal.2024.104606","url":null,"abstract":"<div><p>Although the Monterey Formation has been studied extensively for its petroleum system and Miocene climate insights, debates persist regarding its paleo-redox conditions. Furthermore, its characteristic lithofacies offer a natural laboratory for developing tools to differentiate siliceous and calcareous rocks in deepwater environments. This study evaluated the potential of the Sulfur Index (SI = mg S_org/g TOC), measured by Rock-Eval 7S, as a proxy for assessing paleoredox conditions by comparing the SI with iron speciation data. Additionally, high-resolution molecular analyses were performed to investigate possible relationships between sulfur compounds and rocks with different carbonate content. The findings indicate higher SI values and higher concentrations of benzothiophenes over dibenzothiophenes in the siliceous lithofacies compared to the calcareous lithofacies. This suggests that the mineral matrix plays a crucial role in influencing the process by which sulfur-rich kerogen undergoes cracking when placed under thermal stress. The SI may support a paleoredox interpretation for the Monterey Formation, differing from previous interpretations based only on iron speciation. This alternative interpretation involves a more extensive water-column euxinia, distinct from the seasonal euxinia suggested in previous work. This study represents a practical and pioneering workflow based on sulfur data derived from Rock-Eval 7S for paleoredox and lithofacies assessments, opening avenues for further research.</p></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"294 ","pages":"Article 104606"},"PeriodicalIF":5.6,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142168503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}