| Title | Depositional controls on mineral assemblage and organic matter accumulation of Upper Ordovician-Lower Silurian mudstones in northwestern Guizhou area, China |
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| Author | Wang, Y; Liang, X; Zhang, J; Chen, Z |
| Source | International Journal of Coal Geology vol. 231, 103611, 2022 p. 1-18, https://doi.org/10.1016/j.coal.2020.103611 |
| Image |  |
| Year | 2022 |
| Alt Series | Natural Resources Canada, Contribution Series 20220263 |
| Publisher | Elsevier |
| Document | serial |
| Lang. | English |
| Media | paper; digital; on-line |
| File format | pdf; html |
| Area | Guizhou; China |
| Lat/Long WENS | 102.0000 110.0000 33.0000 27.0000 |
| Subjects | Science and Technology; Nature and Environment; minerals; Yangtze Platform; Ordovician; Silurian |
| Illustrations | location maps; diagrams; cross-plots; photomicrographs |
| Program | Geoscience for New Energy Supply (GNES) Shale-hosted petroleum resource assessment |
| Released | 2020 10 08 |
| Abstract | The control of depositional conditions on sedimentary records spanning the Ordovician Wufeng-Silurian Longmaxi successions on the Yangtze Platform is not fully understood due to a lack of
high-resolution faices analysis. This study aims to build a regional depositional model of this stratigraphic interval, to reveal the fundamental controls on the mineral assemblage and organic matter (OM) accumulation. Vertical lithofacies
variability of two continuous cores in northwestern Guizhou area, south China, was analyzed at high resolution by RoqSCAN (an automated mineralogy tool) and field emission scanning electron microscope (FE-SEM) imaging. Based on multiscale sedimentary
structure, mineral composition, total organic carbon (TOC) content, and geochemical characteristics, seven lithofacies were identified and interpreted as four facies associations (FA A-D) to characterize the spatio-temporal variation in these
sedimentary environments. The deep-siliceous shelf FA-A is the richest in TOC content and biogenetic quartz, attributed to the strong anaerobic watermass, minimal terrestrial- flux, and enhanced organic-productivity during two global transgressions.
The middle mixed shelf FA-B has moderate TOC and mixed minerals resulting from reworking processes during a fall of sea level caused by regional uplifts. Although the primary organic-productivity was promoted by increased volcanic ash fall, dilution
due to increased terrestrial inputs made OM difficult to accumulate. The shallow muddy shelf FA-C and the shallow silty shelf FA-D were not favorable for OM accumulations because of the low organic productivity, strong oxygenated watermass, and high
detrital dilution, through long-term sea level drops. The facies attributes of the target mudstones were remarkably influenced by regional tectonic-eustasy, in addition to global glacioeustasy. |
| Summary | (Plain Language Summary, not published)
The factors controlling depositional conditions on sedimentary records from the Ordovician Wufeng-Silurian Longmaxi successions on the Yangtze Platform
are not fully understood due to a lack of high-resolution faices analysis. This study builds a regional depositional model to show the fundamental controls on the mineral assemblage and organic matter (OM) accumulation of the strata. Two continuous
cores from shale gas wells in northwestern Guizhou area, south China, were analyzed through high resolution RoqSCAN (an automated mineralogy tool) and field emission scanning electron microscope (FE-SEM) imaging. Based on sedimentary structure at
different scales, mineral composition, total organic carbon (TOC) content, and geochemical characteristics, seven lithofacies were identified and four facies associations (FA) were interpreted to demonstrate the spatio-temporal variation of the
sedimentary environments. The deep-siliceous shelf FA-A is the richest in TOC content and biogenetic quartz, attributed to the strong anaerobic water mass, minimal terrestrial- flux, and enhanced organic-productivity during two global see-level
highs. The middle mixed shelf FA-B has moderate TOC and mixed minerals resulting from reworking processes during a fall of sea level caused by regional uplifts. Although the primary organic-productivity was promoted by increased volcanic ash fall,
increased terrestrial inputs diluted OM accumulate. The shallow muddy shelf FA-C and the shallow silty shelf FA-D were not favorable for OM accumulations because of low organic productivity, strong oxygenated water mass, and high detrital dilution,
through long-term sea level drops. The facies attributes of the target mudstones were remarkably influenced by regional tectonic-sea level changes, in addition to global glacioeustasy. |
| GEOSCAN ID | 330644 |
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