Sedimentary and residual gas geochemical characteristics of the Lower Cambrian organic-rich shales in Southeastern Chongqing, China

Wu, Chenjun; Tuo, Jincai; Zhang, Mingfeng; Sun, Liuyang; Qian, Yu; Yan, Long

doi:10.1016/j.marpetgeo.2016.04.013

Cited by 39 publications

(21 citation statements)

References 62 publications

(73 reference statements)

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“…These two kinds of shale samples showed high total organic carbon (TOC) content, with the value of 8.42% (YY) and 6.26% (GZ). The carbon isotope ratios of organic matter (δ 13 C org ) of the two shale samples were -31.8‰ (YY) and -32.8‰ (GZ), and the low δ 13 C org value may be related to the anoxic conditions of the sedimentary environment [25]. As shown in Table 1, the main minerals of YY shale were quartz (65%), clay minerals (14%), and feldspar (11%), with a small amount of pyrite (8%) and carbonate minerals (calcite+dolomite) (2%).…”

Section: Methodsmentioning

confidence: 99%

Pore Structure Alteration Characteristics of Different Mineralogical Composition Shale during Shale-Fracturing Fluid Physical-Chemical Interactions

et al. 2019

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Hydraulic fracturing is widely applied to economic gas production from shale reservoirs, but the effect of the shale mineral composition on the physical-chemical reactions during hydraulic fracturing is still poorly understood. To develop a foundational understanding of chemical interactions occurring on shale with different mineralogical compositions, two different types of mineral composition marine shale (carbonate-poor and carbonate-rich) from the Niutitang Formation were reacted with slick water fracturing fluid in a laboratory reactor at 100°C and 50 MPa for three days. To identify the changes of the pore structure characteristics during hydraulic fracturing, the field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), low-temperature nitrogen adsorption, and porosity measurement were performed on the original and treated shale samples. After the slick water treatment, the dissolution of pyrite in carbonate-poor shale (obtained from Youyang County, labeled as YY) was observed by FE-SEM and XRD analyses, while in carbonate-rich shale (obtained from Guzhang County, labeled as GZ), the carbonate dissolution was observed. Results from the low-temperature N2 adsorption and porosity measurement demonstrated that the variation trend of pore structure characteristics for the YY and GZ shale samples was quite different after reacting with slick water fracturing fluid. For YY shale, the specific surface area, total pore volume, and porosity increased after the reaction, whereas an opposite trend was observed in the GZ shale. Moreover, the fractal dimension analysis illustrated that the pore surface became less rough and the pore structure became more complex in the YY shale, whereas the degree of pore surface roughness and pore structure complexity of the GZ shale was reduced. The results demonstrated that the initial mineralogical composition of shale played an important role in pore structure alteration during hydraulic fracturing.

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Section: Methodsmentioning

confidence: 99%

Pore Structure Alteration Characteristics of Different Mineralogical Composition Shale during Shale-Fracturing Fluid Physical-Chemical Interactions

et al. 2019

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“…As some redox-sensitive trace elements (e.g., Mo, U and V) are sensitive to redox conditions of sedimentary environments and migrate little during diagenesis, they are excellent proxies for reconstructing redox conditions (Algeo and Maynard, 2008;Algeo and Tribovillard, 2009;Algeo and Rowe, 2012;Wu et al, 2016). For instance, previous studies of modern oceans have shown that Mo levels < 25 ppm, 25-100 ppm, and > 100 ppm indicate non-euxinic, intermittently euxinic, and euxinic environments respectively (Scott and Lyons, 2012).…”

Section: Oceanic Redox Conditions From Carbonate Platform To Basin Environmentsmentioning

confidence: 99%

Evaluating episodic hydrothermal activity in South China during the early Cambrian: Implications for biotic evolution

Wang

Tan

Boyle

et al. 2020

Marine and Petroleum Geology

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The early Cambrian (541-514 Ma) was a crucial interval for the evolution of life on Earth, popularly known as the "Cambrian Explosion". Here, we report the timing of changes in hydrothermal and depositional inputs, as well as paleo-redox state, which may have influenced biogeochemical changes. According to high-resolution petrology, fossil distributions, isotopic records, and inorganic geochemistry, the lower Cambrian of the South China can be subdivided into four intervals: the lowermost Cambrian Zhujiaqing Formation (Cam-I); the Cambrian Stage 2 Shiyantou Formation (Cam-II); the lower part of the Cambrian Stage 3 Yu'anshan Formation (CAM-III); and the midupper Cambrian Stage 3 and the middle-upper part of the Yu'anshan Formation, continuing into the Canglangpu Formation (Cam-IV). Hydrothermal events are detected during the early Cam-I, Cam-II, and Cam-III intervals. During the early Cam-I and Cam-II intervals, these events coincided with extensive bottom water euxinia, which in turn may have restricted the spread or proliferation of Ediacaran fauna and small shelly fauna. Through the whole Cam-III interval, further hydrothermal events occurred concurrently with euxinic and ferruginous conditions, probably within a single spatially stratified water column, again plausibly restricting the spread of aerobic organisms. In conjunction with the cessation of hydrothermal events and the gradual lowering of sea level during the late Cam-III, oxic water environments gradually spread into relatively deep-water regions, concurrent with the emergence of the Chengjiang and Qingjiang faunas. These data suggest that periodic hydrothermal events may have had a significant impact on the spread, radiation and extinction of macroscopic fauna 3 during the early Cambrian in South China.

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“…The region of the study area has undergone rapid population growth and economic development, accompanied by urban expansion, excessive cultivation, and forest harvesting (Lan et al 2016). Rivers are being overburdened by growing urban domestic sewage, industrial waste, and agricultural pesticides and fertilizers, causing serious water pollution and degradation of the ecological environment (Wu et al 2016). Moreover, due to a combination of natural factors and recent human activities, soil erosion is becoming increasingly severe in certain sections of the study area.…”

Section: Study Areamentioning

confidence: 99%

Monitoring vegetation cover in Chongqing between 2001 and 2010 using remote sensing data

Xiao

Tao

Xiao

et al. 2017

Environ Monit Assess

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In this study, we applied asymmetric Gaussian function fitting to reconstruct a high-quality MODIS normalized difference vegetation index (NDVI) time series dataset. Following this, we retrieved vegetation cover data from the Chongqing area between 2001 and 2010 using this dataset, applying a dimidiate pixel method. We then used several analytical indices to analyze spatial and temporal changes and trends related to these changes. We determined that a reconstruction of the MODIS NDVI dataset using asymmetric Gaussian fitting in conjunction with a data quality weight coefficient improved data quality and created a foundation for accurate estimations of vegetation cover. We also determined that vegetation cover in the Chongqing area decreased gradually from east to west. During the 10-year study period, vegetation cover in the Chongqing area generally increased, changing from low to high coverage. This increase in vegetation cover was mainly the result of ecological protection policies and improving climate conditions. We also found that changes in vegetation cover were mainly the result of urban construction and afforestation initiatives, but vegetation cover improved overall.

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Sedimentary and residual gas geochemical characteristics of the Lower Cambrian organic-rich shales in Southeastern Chongqing, China

Cited by 39 publications

References 62 publications

Pore Structure Alteration Characteristics of Different Mineralogical Composition Shale during Shale-Fracturing Fluid Physical-Chemical Interactions

Pore Structure Alteration Characteristics of Different Mineralogical Composition Shale during Shale-Fracturing Fluid Physical-Chemical Interactions

Evaluating episodic hydrothermal activity in South China during the early Cambrian: Implications for biotic evolution

Monitoring vegetation cover in Chongqing between 2001 and 2010 using remote sensing data

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