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(A) Map of Horn River Basin and adjacent areas (Liard Basin and Cordova Embayment), showing well locations. (B) Map of western Canada showing the location of the study area (modified after Ross and Bustin, 2008). BC-British Columbia; NWT-Northwest Territories.
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The integration of geochemistry and sequence stratigraphic models in the study of shale formations is critical to the development of robust stratigraphic correlations and paleoenvironmental interpretations. The Middle and Upper Devonian Horn River Group is a prominent organic-rich shale sequence in northeastern British Columbia, Canada, and it also...
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... Horn River Basin is located in northeastern British Columbia and the southwestern corner of the Northwest Territories (NWT; Fig. 1), occupying nearly 12,000 km 2 . It is bordered by the Presqu'ile Barrier on the east and south and by the Bovie fault on the west, which separates the Horn River Basin from the Liard Basin along a large down-to-the-west displacement (Ross and Bustin, 2008;Hulsey, 2011). The Horn River Basin, Cordova Embayment, and associated carbonate ...
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... and Bustin, 2008;Hulsey, 2011). The Horn River Basin, Cordova Embayment, and associated carbonate reefs and platforms occupy the northwest part of the Western Canada Sedimentary Basin. The southern part Horn River Basin is proximal to sources of siliciclastic and carbonate sediment, whereas the northern region of the basin is relatively distal (Fig. ...
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... collected 789 hand samples from five cores drilled in Horn River Basin: EOG Maxhamish D-012-L/094-O-15 (59.93°N, Adam C-87-K/094-O-7 (59.49°N, 122.84°W), Imperial Komie D-069-K/094-O-02 (59.22°N, 122.86°W), and Arc Snake D-020-F/094-J-16 (58.85°N, 122.37°W; Fig. 1). The core was sampled at intervals of ~0.5 m for Maxhamish well; the other wells were sampled at ~1 m intervals. Each sample represents a stratigraphic thickness of ~10 ...
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... that C org -S-Fe relationships are useful proxies for depositional redox conditions. Specifically, increasing S/Fe values indicate progressively reducing conditions, culminating in euxinic conditions where S/Fe ratios exceed that of pyrite. Differences between transgressive and regressive systems tracts in the studies cores are significant (Fig. 10). Most transgressive systems tract samples plot within the anoxic region, with a few samples in the dysoxic region. Most regressive systems tract samples are distributed within dysoxic and oxic regions, with a smaller fraction within the anoxic ...
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... in C org -S-Fe relationships among wells are also observed. From south to north, progressively fewer samples are distributed within the dysoxic and oxic fields of the C org -S-Fe diagram: Most samples from the distal Maxhamish core plot within the anoxic region (Fig. 10A), whereas more than 50% of samples from the proximal Imperial Komie and Arc Snake cores plot within the oxic region (Figs. 10D and ...
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... are also observed. From south to north, progressively fewer samples are distributed within the dysoxic and oxic fields of the C org -S-Fe diagram: Most samples from the distal Maxhamish core plot within the anoxic region (Fig. 10A), whereas more than 50% of samples from the proximal Imperial Komie and Arc Snake cores plot within the oxic region (Figs. 10D and ...
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... concentrations of the studied cores correlate positively with Al (Fig. 11), suggesting that some Ba was delivered to the basin with the clastic flux. Biogenic Ba is widely used as an indicator of productivity ( Dymond et al., 1992;Weldeab et al., 2003;Algeo et al., 2011;Wei et al., 2012;Shen et al., 2015). Biogenic Ba (Ba bio ) is estimated by subtracting the detrital Ba fraction from total Ba concentration, ...
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... Evie Member (i.e., TST1) basin show lower Al and Ti concentrations compared to the distal parts, which we relate to increased carbonate fluxes. Wright et al. (2010) proposed that biogenic silica can be distinguished from detrital silica on Si-Zr scatter plots. A positive correlation between Si and Zr indicates a detrital origin for the quartz (Fig. 12), whereas a negative correlation would be expected for quartz derived from biogenic sources such as radiolaria. With the exception of the Arc Snake core, all other studied cores, including both transgressive and regressive systems tract samples, define a biogenic trend, implying that quartz is predominantly biogenic in origin (Fig. 12). ...
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... the quartz (Fig. 12), whereas a negative correlation would be expected for quartz derived from biogenic sources such as radiolaria. With the exception of the Arc Snake core, all other studied cores, including both transgressive and regressive systems tract samples, define a biogenic trend, implying that quartz is predominantly biogenic in origin (Fig. 12). This interpretation is supported by the common presence of siliceous bioclasts, including radiolaria and sponge spicules, observed in thin sections and core samples (Figs. 3B and 3D). The proportion of detrital versus biogenic silica varies across the basin. Samples from the proximal Arc Snake and Imperial Komie cores contain more ...
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... common presence of siliceous bioclasts, including radiolaria and sponge spicules, observed in thin sections and core samples (Figs. 3B and 3D). The proportion of detrital versus biogenic silica varies across the basin. Samples from the proximal Arc Snake and Imperial Komie cores contain more detrital silica than those of the distal Maxhamish core (Figs. 4, 7, 8, and 12), which is consistent with the proximity of the former to the clastic sediment ...
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... relative changes in redox conditions. Relatively high Mo/Al and Ni/Co ratios and low Th/U ratios in transgressive systems tracts (Figs. 4-8) suggest that transgressions were accompanied by the establishment of reducing bottom-water conditions. This interpretation is consistent with redox conditions inferred from C org -S-Fe ternary diagrams (Fig. 10). However, the three T-R cycles differ significantly in terms of Mo/Al and Ni/Co. Spe Redox proxies also show systematic spatial patterns. The average Th/U ratios are highest in the Arc Snake core and lowest in the Maxhamish core, indicating that distal areas of the basin were more reducing. Mo/Al and Ni/Co ratios and C org -S-Fe ...
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... anoxic conditions in distal areas. Redox proxies of samples from proximal areas of the basin (Arc Snake and Imperial Komie cores) record dysoxic to oxic bottom-water conditions. Most samples recovered from distal areas of the basin (Maxhamish core) appear to have been deposited under anoxic conditions, regardless of position within T-R cycles (Fig. 10A). We infer the described geographic variations in redox conditions to reflect variations in water depth. In proximal, relatively shallow areas of the basin, oxygenated surface water would have mixed more readily to the seabed during sealevel lowstands. In more distal and deeper areas of the basin, the oxygenated surface mixed layer ...
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... ancient marine sediments can be related to bottom-water redox conditions. In distal wells, especially the Maxhamish core, Mo and U compositions from transgressive systems tract samples generally suggest anoxic and euxinic conditions, whereas the majority of regressive systems tract samples reflect accumulation under suboxic to anoxic conditions (Fig. 13). The bulk of the samples populating the euxinic field were collected from the lower Evie Member, which is also characterized by relatively low concentrations of Al and Ti (Figs. 4-8). Since reactive iron is typically associated with clay minerals, little reactive iron would have been available during deposition of the carbonate-rich ...
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... that biogenic silica concentration is a useful proxy of paleoproductivity, especially where other proxy elements, such as P and Ba, have been solubilized. Samples collected from transgressive systems tracts of the McAdam, Nexen Gote, and Maxhamish cores contain higher proportions of biogenic silica than samples from regressive systems tracts (Fig. 12), suggesting higher productivity during accumulation of the transgressive systems tracts. It is also possible that the elevated Si bio resulted from reduced clastic flux during accumulation of transgressive systems ...
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... Si bio data suggest that productivity varied spatially across the Horn River Basin. All samples from the Arc Snake core plot along a detrital trend (Fig. 12E), indicating that quartz content in proximal areas was largely related to detrital flux. A large fraction of samples from distal parts of the basin (Maxhamish core; Fig. 12A) populates the biogenic trend, indicating relatively high productivity. Furthermore, if the Ba bio does reflect productivity, then the much higher Ba bio ...
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... Si bio data suggest that productivity varied spatially across the Horn River Basin. All samples from the Arc Snake core plot along a detrital trend (Fig. 12E), indicating that quartz content in proximal areas was largely related to detrital flux. A large fraction of samples from distal parts of the basin (Maxhamish core; Fig. 12A) populates the biogenic trend, indicating relatively high productivity. Furthermore, if the Ba bio does reflect productivity, then the much higher Ba bio concentrations in the Maxhamish core relative to the Arc Snake core indicate higher paleoproductivity in distal locations (Figs. 4 and 8). Two models may account for the apparent ...
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... generally strong covariance of TOC and Th/U (Fig. 14) suggests that dissolved oxygen levels exerted a primary control on organic matter accumulation/preservation. The rapid decrease in TOC associated with small increases in Th/U diminishes at a Th/U ratio of 0.6 (Fig. 14), which we interpret to delineate the boundary between anoxic and dysoxic conditions in the Horn River Basin at the ...
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... generally strong covariance of TOC and Th/U (Fig. 14) suggests that dissolved oxygen levels exerted a primary control on organic matter accumulation/preservation. The rapid decrease in TOC associated with small increases in Th/U diminishes at a Th/U ratio of 0.6 (Fig. 14), which we interpret to delineate the boundary between anoxic and dysoxic conditions in the Horn River Basin at the time of deposition. These relationships suggest moderate organic enrichment occurred under dysoxic conditions, and much stronger enrichment occurred under anoxic conditions, perhaps as a consequence of more effective ...
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... under dysoxic conditions, and much stronger enrichment occurred under anoxic conditions, perhaps as a consequence of more effective nutrient recycling under strongly reducing conditions. Reducing conditions were probably not the sole factor responsible for organic matter accumulation. The modest positive correlation between TOC and Si bio (Fig. 15) suggests enhancement of organic carbon content by increased productivity. Moreover, higher primary productivity increased the flux of organic matter to the sediment-water interface, which would have elevated the rate of consumption of bottomwater ...
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... is no evident positive or negative correlations between Al concentration and TOC content in the Horn River Group (Fig. 16); thus, evidence for the dilution of organic matter as a control on organic richness is unclear. We speculate that organic matter concentration may also have been diluted by the flux of carbonate and Si bio (Bohacs et al., 2005). It is noteworthy that low and high values of Al are both associated with low TOC (Fig. 16). Indeed, the ...
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... in the Horn River Group (Fig. 16); thus, evidence for the dilution of organic matter as a control on organic richness is unclear. We speculate that organic matter concentration may also have been diluted by the flux of carbonate and Si bio (Bohacs et al., 2005). It is noteworthy that low and high values of Al are both associated with low TOC (Fig. 16). Indeed, the association of high TOC and moderate values of Al may suggest that organic matter accumulation was favored by intermediate fluxes of clay minerals (Ibach, ...
Citations
... Recent studies have shown that the accumulation of organic ma er in the shale sequence is controlled by a complex non-linear interaction between three factors: productivity, preservation conditions, and sedimentation rates. Preliminary studies of the marine environment indicate that sea level change plays a fundamental controlling role in all three factors, which in turn affects the pa ern of organic ma er enrichment [8]. For example, relative sea level rise may result in fewer detrital inputs and enhanced reduction conditions. ...
... According to this trend, LORS with TOC greater than 2.0 wt.% and corresponding HI larger than 400 mg/g TOC are considered to have good hydrocarbon generation potential. Similar categorization ratings are also found in other shale oil plays, such as the Mississippian Barne [32] and the Songliao Qingshankou [8]. ...
The paleolake level, which is controlled by the moisture balance (precipitation minus evaporation) within the lake basin, is a significant factor in determining the deposition of lacustrine organic-rich shale (LORS) across geological time, and hence influences shale oil enrichment. However, the impact of lake-level-fluctuations on shale oil enrichment of LORS is not well understood. Based on an integration of bulk geochemistry, organic petrography, pyrolysis gas chromatography, and element compositions, we address this issue using the Paleogene Biyang Depression in East China as an example. High lake levels, combined with anoxic–suboxic conditions, brackish–saline water, high productivity, and low detrital influx, are favorable for LORS deposition, which is characterized by a large distribution area and thickness, a high potential for oil generation and emplacement, and a high free shale oil content. In contrast, LORS deposited during low lake levels, with suboxic–dysoxic conditions, fresh–brackish water, low productivity, and high detrital influx, has a small distribution area and thickness, a low potential for oil generation and emplacement, and a low free shale oil content (a comparable maturity was present in all the studied LORS). Our data suggests that the elevated lake level led to higher salinity, stronger reduction conditions, higher productivity, and lower clastic inflow in the paleolake, forming LORS with higher shale oil potential. It has a positive effect on shale oil enrichment of LORS. The findings are also applicable to regional shale oil exploration.
... This stratigraphic variability may be linked to the process of sedimentation and diagenesis [37], and it is further impacted by fluctuations in relative sea levels during the evolution of sequence stratigraphy [38,39]. A multitude of previous studies have illustrated the role of sequence stratigraphy in shaping the enrichment of OM in shale [40][41][42][43][44][45]. Notably, OM tends to be most abundant in the transgressive systems tract (TST) or in proximity to the maximum flooding surface (MFS), with the highest total organic carbon (TOC) value serving as a marker for the MFS [46]. ...
Various types of pores, including organic and inorganic variations, exhibit distinct impacts on the storage capacity of shale gas reservoirs and play a significant role in shale gas occurrence. However, there is a limited number of studies that have quantitatively addressed the developmental characteristics of these diverse pore types and their primary controlling factors. This paper explores the development of inorganic pores, specifically interparticle pores and intraparticle pores, as well as organic matter (OM) pores within the shales of the Wufeng–Longmaxi Formation in the Upper Yangtze region. Parameters such as areal porosity, pore diameter, and pore number based on the FE-SEM and image digitization are discussed. Additionally, the influence of the sedimentary environment on the development of various pore types through integrated wavelet transform techniques and geochemical analysis are analyzed. This analysis reveals the distinctive mechanisms governing the development of pore types under the sequence stratigraphic constraints. The findings reveal that the Wufeng–Longmaxi Formation within the study area can be classified into four systems tracts (transgressive systems tracts TST1 and TST2, and highstand systems tracts HST1 and HST2). Within TST1+HST1, OM pores emerge as the predominant pore type, contributing to over 65% of the porosity. TST2 similarly displays OM pores as the dominant type, comprising over 45% of the total porosity, with an average OM areal porosity of 7.3%, notably lower than that of TST1+HST1 (12.7%). Differences in OM pore development between TST1+HST1 and TST2 shales are attributed to variations in OM abundance and type. In HST2, inorganic pores are the dominant pore type, primarily consisting of interparticle pores associated with clay minerals, contributing to more than 50% of the porosity, while OM pores remain almost undeveloped. The frequent sea level fluctuations during the sequence stratigraphic evolution caused variations in sedimentary environments across different depositional sequences. These differing depositional environments lead to varying OM content and types, mineral genesis, and content, ultimately resulting in disparities in the development of shale pore types within different sequences.
... For example, anoxic-euxinic conditions can enhance productivity by promoting the release of P from sinking OM (Ingall and Jahnke, 1994), whereas high productivity can consume O 2 by OM degradation during its settling through the water column (Katz, 2005). In addition, OM enrichment may be the result of the interplay of primary productivity, redox conditions, terrestrial inputs, sedimentation rates, and hydrological conditions (e.g., Demaison and Moore, 1980;Pedersen and Calvert, 1990;Tyson, 2001;Katz, 2005), which may also be affected by hydrothermal and volcanic activity, coastal upwelling, sea-level fluctuations, and climatic changes (e.g., Sageman et al., 2003;Dong et al., 2018;Zhang et al., 2018Zhang et al., , 2022Wang et al., 2023). Therefore, the roles and relative contributions of these factors in enhancing OM accumulation remain unclear. ...
... Relative sea level changes in the intraplatform basin controlled the redox conditions during the deposition of Unit 2 [117]. Intermittent euxinic and continuous anoxic environments account for the relatively high TOC values. ...
Studying the accumulation rules of organic matter (OM) in paleo-ocean sediments can not only enhance our understanding of how OM becomes enriched in ancient oceans but also provide guidance for the exploration of shale gas in unconventional shale strata. A breakthrough has been made in shale gas exploration in the early Cambrian Qiongzhusi Formation in South China. However, less attention has been paid to the intraplatform basin of the Yangtze Platform, and the factors controlling organic matter enrichment in this special region remain unclear. This study focuses on a continuous drilling core across the full well section of the Qiongzhusi Formation in the intraplatform basin of the Yangtze Platform. Through the comprehensive analysis of total organic carbon (TOC), major and trace elements, and Mo isotopes, this study investigates the controlling factors for OM enrichment with δ98/95Mo ratios utilized to identify the existence of euxinic bottom water. The examined 240 m long core can be divided into four units, where the TOC values of the lower Units 1 and 2 (0.2–5.0 wt.%) average higher than the upper Units 3 and 4 (0.2–2.5 wt.%). Redox indicators (U/Th, Ni/Co, EF(Mo)—EF(U)) indicate an increasing oxidation of bottom waters from the bottom upwards. δ98/95Mo data further confirm the presence of weakly euxinic conditions in Units 1 and 2, addressing the ongoing controversy surrounding bottom water redox environments. Primary productivity indicators (Ni/Al, Cu/Al) suggest a relatively low average productivity level within the intraplatform basin. The upwelling indicators EF(Co) * EF(Mn) of different profiles in the Yangtze Platform suggest that low productivity within the intraplatform basin can be mainly attributed to the absence of upwelling. Consequently, this study proposes an organic matter enrichment mechanism for the Qiongzhusi Formation in the intraplatform basin, which emphasizes the significance of the redox environment in the formation of high-quality hydrocarbon source rocks in restricted environments that lack upwelling, setting it apart from the deep ocean. These findings have the potential to provide valuable insights for the exploration of high-quality hydrocarbon source rocks in other similar regions.
... Both organic and inorganic geochemistry can provide clues to identify surfaces or intervals associated with maximum flooding conditions, particularly within mud-dominated successions (e.g., Harris et al., 2013Harris et al., , 2018Playter et al., 2018;LaGrange et al., 2020;Catuneanu, 2022). The amount of total organic carbon (TOC) in fine-grained successions depends on several parameters, including organic productivity, preservation potential, and terrigenous sediment supply (Dong et al., 2018). Despite this complexity, the analysis of TOC distribution is somewhat simplified because all three main parameters (i.e., productivity, preservation, and sediment supply) are linked to changes in relative sea level at syn-depositional time (Fleck et al., 2002;Arthur and Sageman, 2005;Bohacs et al., 2005;Dong et al., 2018;Harris et al., 2018). ...
... The amount of total organic carbon (TOC) in fine-grained successions depends on several parameters, including organic productivity, preservation potential, and terrigenous sediment supply (Dong et al., 2018). Despite this complexity, the analysis of TOC distribution is somewhat simplified because all three main parameters (i.e., productivity, preservation, and sediment supply) are linked to changes in relative sea level at syn-depositional time (Fleck et al., 2002;Arthur and Sageman, 2005;Bohacs et al., 2005;Dong et al., 2018;Harris et al., 2018). Stages of transgression during relative sea-level rise promote influxes of nutrient-rich upwelled water, which increase surface-water productivity; enhance water-column stratification, leading to the development of bottom-water anoxia; and result in the trapping of terrigenous sediment in coastal and nearshore environments, favoring the development of organic-rich condensed sections offshore (Dong et al., 2018;Harris et al., 2018) (Fig. 12). ...
... Despite this complexity, the analysis of TOC distribution is somewhat simplified because all three main parameters (i.e., productivity, preservation, and sediment supply) are linked to changes in relative sea level at syn-depositional time (Fleck et al., 2002;Arthur and Sageman, 2005;Bohacs et al., 2005;Dong et al., 2018;Harris et al., 2018). Stages of transgression during relative sea-level rise promote influxes of nutrient-rich upwelled water, which increase surface-water productivity; enhance water-column stratification, leading to the development of bottom-water anoxia; and result in the trapping of terrigenous sediment in coastal and nearshore environments, favoring the development of organic-rich condensed sections offshore (Dong et al., 2018;Harris et al., 2018) (Fig. 12). Posamentier and Allen, 1999). ...
... The paleo-redox conditions can be considered as controlling factors in OM preservation and accumulation in both marine and lacustrine settings [65,94,98,29]. The redox-sensitive trace elements concentrations and its associated ratios, such as the U, V, Mo and the V/Cr, U/Th, Ni/Co, C org /P tot , have been commonly applied to reconstruct the paleoredox conditions [14,3,7,26,85,92,6]. ...
... Paleoproductivity Previous studies suggested that the biogenic SiO 2 , P, and Ba contents can be used to assess the paleoproductivity due to the numerous siliceous fossils found in marine shales, such as radiolarians, spongy spicules, and diatoms [81,100,29]. The Si bio contents of the Doushantuo Shale are relatively low (Table 5 and Fig. 9), indicating that the paleoproductivity is relatively low during the deposition of Doushantuo Formation. ...
... Area I refers to the biogenic and non-hydrothermal sediments, and area II refers to the hydrothermal sediments [1]. Sedimentary Basin with an average of 3015 ppm, and the modern equatorial Pacific marine sediments with an range from 1000 to 5000 ppm [105,71,29]. Simultaneously, the relatively low Ba bio content in the Doushantuo Shale in the Yichang area indicates a relatively low paleoproductivity in this period. ...
The organic-rich Ediacaran Doushantuo Shale have been identified as a high-quality source rock and a main shale gas play in the Yichang area, South China, which was characterized by high TOC content, high thermal maturity , enormous cumulative thickness, and relatively high contents of brittle minerals. As the oldest shale gas stratum, the paleo-environmental characteristics and organic matter (OM) accumulation mechanism remain unclear in this special marine setting. In this study, core descriptions, TOC content, X-ray diffraction (XRD) miner-alogical analysis, scanning electron microscopy (SEM) observation, and elemental analysis, including the major, trace, and rare earth elements, were combined to identify lithofacies, reconstruct paleo-environmental conditions , and document organic matter (OM) accumulation mechanisms for this potential Ediacaran Doushantuo Shale in the Yichang area, South China. Four major shale lithofacies were identified based on TOC content and mineral composition. The geochemical redox proxies, such as the enrichment factors of Uranium (U-EF) and ratio of organic carbon to total phosphorus (C org /P), indicate that the Doushantuo Shale was probably deposited in a dysoxic-anoxic conditions, which is consist with the interpretation from size distribution of pyrite framboids. The terrigenous influxes suggest the Doushantuo Shale was deposited in arid climate in absence of chemical weathering. Meanwhile, the productivity proxies (biogenic SiO 2 , Ba, and P/Al) indicate that the organic-rich Doushantuo Shale was deposited under a relatively low primary productivity. In addition, hydrothermal input has limited influence on organic matter (OM) accumulation of the Doushantuo Shale, which was also reported in the Qinglinkou Section of Yichang area. It can be observed that the organic matter (OM) accumulation mechanism of the Doushantuo Shale, deposited after the Marinoan "Snow Earth" glaciation, in the Yichang area, South China, was mainly controlled by the redox conditions, which is much different from typical marine shales and transitional shales.
... Studies show that relative sea-level fluctuations directly influence biological productivity, redox conditions, detrital sediment supply, and Table 2 TOC content, δ 13 C org , sedimentation rate, and OC burial flux in the deposit intervals. Detailed data on the dry density of sediment is given in Supplementary ultimately TOC concentrations (Arthur et al., 2005;Dong et al., 2017;Harris et al., 2018). Based on a widely used global sea-level curve (e.g., Rohling et al., 2014), the preserved units represent four distinct stages in terms of sea level, which are sea-level lowstands, early transgression, late transgression to highstand, and regression (Fig. 6A). ...
... All of these factors work together to promote the development of these organic-rich deposits. The TOC content is frequently boosted in transgressive system tracts and depleted in regressive system tracts (Dong et al., 2017;Harris et al., 2018). The lowest TOC is typically recorded in deposits that occurred during sea-level lowstands (Fleck et al., 2002;Dong et al., 2017;Harris et al., 2018;Dominguez et al., 2020). ...
... The TOC content is frequently boosted in transgressive system tracts and depleted in regressive system tracts (Dong et al., 2017;Harris et al., 2018). The lowest TOC is typically recorded in deposits that occurred during sea-level lowstands (Fleck et al., 2002;Dong et al., 2017;Harris et al., 2018;Dominguez et al., 2020). ...
Coastal depositional systems play a crucial role in the sequestration of terrigenous organic carbon (OC), especially deltas and coastal mud belts, which are two of the most efficient OC burial hotspots. Investigation into long-term coastal OC burial is challenging since the analysis of modern coastal environments only provides a snapshot of OC burial. Marine Isotope Stage 3 (MIS 3) refers to a unique interval in the last glacial period, characterized by a protracted falling sea level punctuated by millennial-scale climate oscillations. The study of OC burial during MIS 3 can help to estimate and predict changes in coastal OC burial driven by sea-level oscillations and extreme climate events. Here, we target late MIS 3 strata beneath the southern East China Sea. Based on the analysis of total organic carbon, total nitrogen content, stable organic carbon isotopic composition, and major and trace elements, this study demonstrates that relative sea-level changes control sediment provenance and sedimentary processes in coastal environments, which in turn regulate coastal OC burial during the late MIS 3. The burial of OC in the coastal ocean during MIS 3 deviates from the typical expectation that carbon burial is facilitated during transgression or high sea-level periods. Sediments deposited during high sea-level periods in late MIS 3 exhibit the lowest OC burial flux and contents due to long-distance transport from distant sources. The study highlights that the highest burial flux and contents of OC were found in deposits preserved during sea-level lowstands. This indicates that short-distance transport, local sources, and mountainous rivers affected by the monsoon and experience frequent floods, are associated with the highest OC burial and contents. Short and rapid climate warming events likely contribute to OC burial in late MIS 3 by intensifying precipitation and nutrient-rich supplies, thereby increasing the input of terrestrial and marine OC. This observation is noteworthy as it challenges the conventional understanding of the relationship between sea level and carbon burial. The study of OC burial in late MIS 3 is helpful in understanding how OC burial reacts to sea level oscillations and rapid climate warming events.
... Van Geldern et al., 2006;Scotese et al., 2021), the high sea-levels (Johnson et al., 1985;Haq and Schutter, 2008), the vast ocean area (Kocsis and Scotese, 2021), the special stage in the evolution of life in which organisms "invaded" the land from the sea (Brett and Baird, 1995;Stanley and Luczaj, 2015;Becker et al., 2020), and the substantial carbonate production (Becker et al., 2012(Becker et al., , 2020, along with other events, attest that the Earth system underwent highly anomalous perturbations during the Devonian. It therefore constituted an episode characterized by the global deposition of organic-rich shales (Dong et al., 2018;Zhou et al., 2022), making the Devonian system one of the key exploration targets of unconventional oil and gas globally. ...
... Thus, the relationship between sea-level fluctuations and OM enrichment is best studied by the application of sequence stratigraphy (e.g. Dong et al., 2018;Shebl et al., 2019;Zhou et al., 2022;Shehata et al., 2023). However, the existing criteria for sequence stratigraphic division seems not to be applicable to the intra-platform basin and intra-platform shelf environments. ...
... Van Geldern et al., 2006;Scotese et al., 2021), and the diversity of marine fauna was the strongest in the Paleozoic (Brett and Baird, 1995;House, 2002;Stanley and Luczaj, 2015;Becker et al., 2020). Many organic-rich shales were also formed in North America during the Devonian, such as Ohio shale and Marcellus shale in the Appalachian basin (Lash and Blood, 2014;Hupp and Donovan, 2018;Cortland et al., 2021;Dunkel et al., 2022;Liu et al., 2023), Antrim shale in the Michigan Basin (Adeyilola et al., 2022;Mansour et al., 2022), New Albany shale in the Illinois Basin (Strąpoć et al., 2010;Mastalerz et al., 2013), and Duvernay shale and Horn River shale in the Western Canada Basin (Anfort et al., 2001;Green and Mountjoy, 2005;Dong et al., 2018;Kong et al., 2022;Zhou et al., 2022) (Table 4). ...
Objectives: Authigenic laumontite cements are widely developed in continental lake basin reservoirs
dominated by lithic arkose and arkose, which have been reported in almost all petroliferous basins in China.
Therefore, to review and summarize the characteristics, origin and distribution of laumontite is not only of great
theoretical value, but also of great significance for oil and gas exploration. The rich well data and diverse
depositional environments of Yanchang Formation in Ordos Basin lay a good foundation for the study of authigenic
第 6 期 王龙等:沉积岩中自生浊沸石的形成、分布及油气意义———以鄂尔多斯盆地中—上三叠统延长组为例 2205laumontite in sedimentary sequences, so we study the formation, distribution and its exploration significance of
laumontite by taking Yanchang Formation in Ordos Basin as an example.
Methods: The thin sections, scanning electron microscope and energy spectrum were analyzed combined with
outcrops observation, as well as the theoretical model of laumontite genesis and the regional evolution history of
Ordos Basin, to illustrate the petrological characteristics, diagenetic evolution, genetic mechanism and temporal
and spatial distribution characteristics of laumontite in Yanchang formation.
Results: It is found that laumontite can be used as a tracer mineral in the process of reservoir formation under
specific conditions, because of its relative low density, easy dissolution but resist to pressure, and sensitive to
diagenetic environment. It would fill the pores as cement in the alkaline environment from early to early middle
diagenetic stage, while it would dissolve to produce a great quantity of secondary pores when diagenetic fluid
changes into acidic for the organic acid produced by hydrocarbon expulsion. The secondary dissolution facies
related to laumontite is controlled by middle diagenetic stage in time, and by provenance, sedimentary
environments and diagenetic fluid related to source rocks and transport system in space.
Conclusions: Based on the analysis of laumontite content, dissolution, relationship with reservoir physical
properties and its implication of hydrocarbon accumulation, the favorable target areas are presented for the
exploration and evaluation of Chang-10 from Yanchang Formation in Ordos Basin, providing some new clues for the
exploration of analogous sedimentary basins.
Keywords:Ordos Basin; Yanchang Formation; laumontite; diagenesis; oil—gas exploration
... Several geochemical criteria, such as Al/(Al+Fe+Mn) < 0.35, Fe/Ti > 20, and (Fe+Mn) × Ti > 25(±5), can also be used to determine the quartz origin, implying that hydrothermal fluids have no effect [42]. The average values of the above parameters are 0. 67, 9.38, and 0.61, respectively ( The element Ti usually represents the degree of terrestrial detrital influx [27 correlation diagram between TiO2 and SiO2 shows a conspicuous negative relationsh is 0.84) ( Figure 10A), indicating that terrigenous quartz is not a primary source of Since zirconium (Zr) usually occurs in zircon, it is an effective substitute for terrige input [8,43]. A significant negative trend (R 2 is 0.84) between SiO2 versus Zr of the sam suggests that clastic quartz was not the main contributor of silica ( Figure 10B). ...
... The correlation diagram between TiO 2 and SiO 2 shows a conspicuous negative relationship (R 2 is 0.84) ( Figure 10A), indicating that terrigenous quartz is not a primary source of silica. Since zirconium (Zr) usually occurs in zircon, it is an effective substitute for terrigenous input [8,43]. A significant negative trend (R 2 is 0.84) between SiO 2 versus Zr of the samples suggests that clastic quartz was not the main contributor of silica ( Figure 10B). ...
... The correlation diagram between TiO2 and SiO2 shows a conspicuous negative relationship (R 2 is 0.84) ( Figure 10A), indicating that terrigenous quartz is not a primary source of silica. Since zirconium (Zr) usually occurs in zircon, it is an effective substitute for terrigenous input [8,43]. A significant negative trend (R 2 is 0.84) between SiO2 versus Zr of the samples suggests that clastic quartz was not the main contributor of silica ( Figure 10B). ...
The Ordovician Wulalike marine siliceous shale is a notable hydrocarbon source rock in the Northwestern Ordos Basin. However, the causes of quartz and organic matter enrichment are still a mystery to experts. In this study, the organic geochemistry (maceral compositions, Rbitu, and TOC) and elemental geochemistry (major and trace elements) with mineralogy (XRD) and petrography were jointly acquired to systematically investigate the quartz origins and the paleoenvironment, and the main controlling factors for organic matter enrichment in the Wulalike shale. The results show that the organic matter is type I kerogen with low TOC concentrations (average 0.51%), and that the thermal evolution has reached mature and high mature stages (mean Requ is 1.08%). Three types of quartz are developed in Wulalike shale: biogenic quartz (average 63%) is the most dominant, followed by clastic quartz (average 31%) and microcrystalline quartz (average 6%). Babio and Ba/Al values indicate the low paleoproductivity, which is the primary cause for the low TOC found throughout the area. Redox indexes show the anoxic or dysoxic to oxic conditions from the bottom to the top of the section. Paleoclimate and paleowater depth proxies also changed from the bottom to the top. Various paleoenvironments and sedimentological evidence show that Wulalike shale went through the changing environments, and the early sedimentary environments were conducive to organic matter enrichment, leading to a relatively high TOC. The paleoproductivity and preservation conditions have an impact on organic matter enrichment. Based on the results of biogenic quartz distribution and sedimentary environments, it is considered that the bottom of the Wulalike Formation is the most favorable for shale gas exploration and development.
... Studies show that relative sea-level fluctuations directly influence biological productivity, redox conditions, detrital sediment supply, and Table 2 TOC content, δ 13 C org , sedimentation rate, and OC burial flux in the deposit intervals. Detailed data on the dry density of sediment is given in Supplementary ultimately TOC concentrations (Arthur et al., 2005;Dong et al., 2017;Harris et al., 2018). Based on a widely used global sea-level curve (e.g., Rohling et al., 2014), the preserved units represent four distinct stages in terms of sea level, which are sea-level lowstands, early transgression, late transgression to highstand, and regression (Fig. 6A). ...
... All of these factors work together to promote the development of these organic-rich deposits. The TOC content is frequently boosted in transgressive system tracts and depleted in regressive system tracts (Dong et al., 2017;Harris et al., 2018). The lowest TOC is typically recorded in deposits that occurred during sea-level lowstands (Fleck et al., 2002;Dong et al., 2017;Harris et al., 2018;Dominguez et al., 2020). ...
... The TOC content is frequently boosted in transgressive system tracts and depleted in regressive system tracts (Dong et al., 2017;Harris et al., 2018). The lowest TOC is typically recorded in deposits that occurred during sea-level lowstands (Fleck et al., 2002;Dong et al., 2017;Harris et al., 2018;Dominguez et al., 2020). ...
