Reconstruction of redox conditions during deposition of organic-rich shales of the Upper Triassic Yanchang Formation, Ordos Basin, China

Yuan, Wang; Liu, Guangdi; Stebbins, Alan; Xu, Liming; Niu, Xiaobing; Luo, Wenbin; Li, Chaozheng

doi:10.1016/j.palaeo.2016.12.020

Cited by 59 publications

(35 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…P is an important nutrient element that is transferred to sediment mainly as organically bound P (Algeo et al, ). P is especially useful as a palaeoproductivity proxy for sediment deposited under oxic–suboxic conditions as it is solubilized under oxygen‐deprived conditions (Algeo & Ingall, ; Shi et al, ; Tribovillard, Algeo, Lyons, & Riboulleau, ; Yuan et al, ). Some redox‐sensitive trace elements, including Ni, Cu, and Zn, are delivered to the sediment mainly in association with organic matter as organometallic complexes.…”

Section: Discussionmentioning

confidence: 99%

“…The unit can be subdivided, from bottom to top, into 10 members (Chang 10–Chang 1) based on marker beds, sedimentary cycles, and/or lithological association (Qiu et al, , ; Figure ). The Chang 7 Member, 80–120 m thick, consists of siltstone, mudstone, and black shale, with interbeds of volcanic ash layers (Yuan et al, ), and it can be further subdivided into three sub‐members based on the stacking patterns of lithofacies, referred to as Chang 7 3 to Chang 7 1 up the section (Wang et al, ). Organic‐rich shale is thickest in the south‐west Yishan Slope and southern area of the Tianhuan Depression (Figure c), covering an area of more than 1 × 10 5 km 2 (Qiu et al, ).…”

Section: Geological Settingmentioning

confidence: 99%

“…The hydrogen index of the Chang 7 shale varies from 150 to 600 mg/g, indicating moderate to high hydrocarbon generation potential (Zhang et al, ). Organic matter of the Chang 7 shale was derived from aquatic phytoplankton (Wang et al, ; Yuan et al, ; Zou et al, ) instead of terrigenous organic components (Zhang et al, ).…”

Section: Geological Settingmentioning

confidence: 99%

“…Integrated stratigraphical column of the Upper Triassic Yanchang Formation in Ordos Basin (after Yuan et al, )…”

Section: Geological Settingmentioning

confidence: 99%

“…The Chang 7 lacustrine organic‐rich shale of the Upper Triassic Yanchang Formation is the main oil source of the Mesozoic petroleum system in the Ordos Basin, Central China (Qiu et al, ; Yuan et al, ; Zou et al, ). The unit is widely distributed across the basin and characterized by high total organic carbon (TOC) content (up to 30–40%; Yang & Zhang, ).…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Palaeoproductivity and organic matter accumulation during the deposition of the Chang 7 organic‐rich shale of the Upper Triassic Yanchang Formation, Ordos Basin, China

et al. 2019

Self Cite

View full text Add to dashboard Cite

The lacustrine Chang 7 organic‐rich shale of the Upper Triassic Yanchang Formation is a very important hydrocarbon source rock and contains high total organic carbon content (average = 5.54 wt.%). Previous studies suggest that deposits of the Chang 7 accumulated slowly under dominantly oxic–suboxic bottom‐water conditions occasionally interrupted by the establishment of anoxic conditions. However, questions remain regarding the role of palaeoproductivity in accumulation of the Chang 7 organic matter. Palaeoproductivity indicators, including P/Al, Ni/Al, Cu/Al, and Zn/Al, suggest that the deposition of the Chang 7 period was accompanied by high primary productivity level. Furthermore, productivity appears to have been highest in the middle and south‐east region of the lake, diminishing to the north‐east, the north‐west, and the south‐west. Elevated productivity resulted in the flux of large amounts of organic matter to the lake floor. Intermittent anoxic bottom‐water conditions caused by oxygen consumption during organic matter degradation favoured enhanced preservation of organic matter even under oxic–suboxic water column. Low sedimentation rate made the organic matter in sediments avoid dilution of terrigenous clastics, which made it play a positive role in the accumulation of organic matter.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

“…Integrated stratigraphical column of the Upper Triassic Yanchang Formation in Ordos Basin (after Yuan et al, )…”

Section: Geological Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Palaeoproductivity and organic matter accumulation during the deposition of the Chang 7 organic‐rich shale of the Upper Triassic Yanchang Formation, Ordos Basin, China

et al. 2019

Self Cite

View full text Add to dashboard Cite

show abstract

Linking the Qinling Orogeny with the Chang 7 shale (Triassic Yanchang Formation) deposition: Evidence from major, trace, and rare earth element geochemistry

et al. 2018

Self Cite

View full text Add to dashboard Cite

The lacustrine organic-rich shale of Triassic Chang 7 Member is an unconventional shale oil reservoir that is a major hydrocarbon target in the Ordos Basin, northern China. This study uses major, trace, and rare earth element (REE) abundance documented through a 115-m-thick core obtained from the western part of the Ordos Basin to assess dominant controls on temporal variations in total organic carbon in the Chang 7 shale. Our results suggest that total organic carbon trends in the Chang 7 can be directly linked with the tectonic and magmatic evolution of Qinling orogen. The Chang 7 3 and Chang 7 2 submembers of the lower part of the Chang 7 were likely deposited in association with heighted tectonic and magmatic activity of the Qinling Orogeny. Sediments derived from these submembers display light REE and trace element compositions similar to the Tianshui rhyolites suggesting deposition contemporaneous with magmatic and/or volcanic activity of the Qinling Orogeny. Higher nutrient concentrations introduced by volcanic eruptions would have stimulated primary productivity in the surface water enhancing the organic carbon flux to the lake bottom. In addition, higher rates of mountain building in the Qinling Orogeny may have been responsible for increasing subsidence rate of the southern Ordos Basin, also favourable for the establishment of anoxic bottom-water conditions. In contrast, lower light REE and trace element abundances of the Chang 7 1 submember at the top of the Chang 7 suggest deposition during a tectonically and magmatic quiescent period of the Qinling Orogeny. The diminished volcanic flux could have lowered the rate of primary productivity. Moreover, a reduced rate of mountain building would have decreased the rate of foredeep subsidence favouring shallower water and oxic/ suboxic bottom-water conditions. Thus, the hydrography of the lake during accumulation of the Chang 7 1 was not conducive for organic carbon accumulation. Together, the correlation of the Qinling mountain building and magmatism and deposition of the Chang 7 shale provide evidence for the role of tectonism in the accumulation of organic carbon enriched sediment.

show abstract

Depositional environment of Middle Triassic organic‐rich shales in the Ordos Basin, Northwest China

et al. 2021

View full text Add to dashboard Cite

The Middle Triassic Tongchuan Formation in the Ordos Basin of northwestern China is a typical lacustrine deposit. A major component of this formation is thick layers of organic‐rich shales that are probably a potential hydrocarbon source and preserve the earliest known Mesozoic‐type lacustrine ecosystem. The exact depositional environment of the shales in the Tongchuan Formation, however, remains unknown. To address this question, we carried out high‐resolution carbon (δ13Corg) and sulphur (δ34Spy) isotope analysis as well as undertook total organic carbon (TOC)/pyrite contents and pyrite morphology investigation, and framboidal pyrite size measurements in shales of the Bawangzhuang section of the southern Ordos Basin. Remarkably high TOC (23 ± 9%) and pyrite (7 ± 3%) contents were obtained from the shales, which indicate a large amount of organic carbon and pyrite burial during shale deposition. Framboids are the dominant pyrite morphology in the pyrite crystals and show large and variable mean diameters (7.0 ± 1.7 μm to 14.3 ± 6.8 μm) across the section, indicating oxic–dysoxic bottom water during shale deposition. δ13Corg and δ34Spy revealed narrow and less variable values, ranging from −31.8‰ to −28.1‰, and −4.1‰ to 4.9‰, respectively. The δ13Corg values suggest balanced and consistent carbon cycles. Integrated with pyrite content and morphological patterns, consistent δ34Spy values probably demonstrate a relatively open environment for the formation of sedimentary pyrite, and thus a shallow chemocline that was quite close to the water‐to‐sediment interface during shale deposition. Overall, the organic‐rich shales of the Tongchuan Formation were probably deposited under oxic–dysoxic bottom‐water conditions. Shallow chemocline depth combined with moderately high sedimentation rate and high primary productivity may have played crucial roles in the deposition and formation of the organic‐rich shales in the Tongchuan Formation. The shallow chemocline also facilitates the fossil preservation in a lacustrine environment.

show abstract

Reconstruction of redox conditions during deposition of organic-rich shales of the Upper Triassic Yanchang Formation, Ordos Basin, China

Cited by 59 publications

References 55 publications

Palaeoproductivity and organic matter accumulation during the deposition of the Chang 7 organic‐rich shale of the Upper Triassic Yanchang Formation, Ordos Basin, China

Palaeoproductivity and organic matter accumulation during the deposition of the Chang 7 organic‐rich shale of the Upper Triassic Yanchang Formation, Ordos Basin, China

Linking the Qinling Orogeny with the Chang 7 shale (Triassic Yanchang Formation) deposition: Evidence from major, trace, and rare earth element geochemistry

Depositional environment of Middle Triassic organic‐rich shales in the Ordos Basin, Northwest China

Contact Info

Product

Resources

About