The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge ...The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge has been acquired on the types of microbial carbonates that are present,the properties of the reservoir and the pore evolution,hampering predictions of high-quality reservoirs in these carbonates.Integrated with petrography and in-situ U-Pb dating geochronology analyses,this study aims to clarify the types of microbial carbonates present and to reconstruct the pore evolution processes of the potential reservoir rocks.The Upper Ediacaran microbial carbonates of the Tarim Basin can be divided into four types,based on their features in terms of different scales(macro-to micro-):microbial laminite,stromatolite,spongiomicrobialite and microbial-peloidal wackestone/mudstone.Petrophysical properties show that all these microbial carbonates have low porosity and very low permeability with poor connectivity.These carbonates were subject to long-term and complex diagenetic processes,mainly consisting of dissolution,compaction,pervasive dolomitization,cementation and fracturing.The most important reservoir spaces are contributed by vugs and dissolution-enlarged pores,which are likely to have been associated with the widespread uplift of the Aksu area in the terminal Ediacaran.In contrast,the cementation of the fine-to-medium crystalline dolomite greatly reduced the pre-existing pores.Pore types are closely related to different microbial fabrics,which played an important role in the pore evolution of the microbial carbonates.展开更多
Organic carbon isotope （δ-13 Corg） data from two well-preserved sections across a shallow-to-deep water transect of the late Edi- acaran-Early Cambrian Yangtze Platform in South China show significant temporal and ...Organic carbon isotope （δ-13 Corg） data from two well-preserved sections across a shallow-to-deep water transect of the late Edi- acaran-Early Cambrian Yangtze Platform in South China show significant temporal and spatial variations. In the shallow-water Jiulongwan-Jijiapo section, δ-13Corg values of the late Ediacaran Dengying Formation range from -29‰ to -24%0. In the deep-water Longbizui section, δ-13Corg values from time-equivalent strata of the Dengying Formation are mostly between -35‰ and -32‰）. These new data, in combination with δ-13Corg data reported from other sections in South China, reveal a 6‰-8‰ shallow-to-deep water δ-13Corg gradient. High δ-13Corg values （〉-30‰） occur mostly in shallow-water carbonate rocks, whereas low δ-13Corg values （〈-32‰） dominate the deep-water black shale and chert. The large temporal and spatial δ-13Corg variations imply limited buffering effect from a large dissolved organic carbon （DOC） reservoir that was inferred to have existed in Edi- acaran-Early Cambrian oceans. Instead, δ-13C-org variations between platform and basin sections are more likely caused by dif- ferential microbial biomass contribution to total organic matter. High δ-13Corg values （〉-30‰） documented from shallow-water carbonates are within the range of typical Phanerozoic δ-13Corg data and may record the isotope signature of organic matter from primary （photosynthetic） production. In contrast, low δ-13Corg values （〈-32‰） from deep-water sections may have resulted from higher chemoautotrophic or methanotrophic biomass contribution to bulk organic matter in anoxic environments. The δ-13Corg data provide indirect evidence for ocean stratification and episodic chemocline fluctuations in the Ediacaran-Early Cambrian Yangtze Platform.展开更多
A new macrofossil Lagerstatte was discovered from the uppermost Ediacaran Jiucheng Member at Jinning and Jiangchuan of the eastern Yunnan, yielding numerous diverse well-preserved thallophyte macrofossils. These inclu...A new macrofossil Lagerstatte was discovered from the uppermost Ediacaran Jiucheng Member at Jinning and Jiangchuan of the eastern Yunnan, yielding numerous diverse well-preserved thallophyte macrofossils. These include the previously-known representatives of vendobionts, Vendotaenia and Tyrasotaenia, and the biggish multicellular benthos such as Chuaria-like and Tawuia- like fossiis, as well as Longfengshaniaceaens with diverse holdfast structures. There are still some other problematic macrofossils with peculiar configurations as well as uncertain relatives. The distinct dominance of the giant, unbranching thallophytes occasionally with holdfast structures distinguishes this assemblage from the other Ediacaran macrofossil Lagerstattes in the Doushantuo Formation at Miaohe, Wenghui and Lantian, and the contemporary assemblage in the Shibantan Member of Dengying Formation, Yangtze Gorges area. This paper outlines the characteristics of some of the multicellular macrofossils from the Jiucheng Member at Jiangchuan. They include some macrofossils with different types of holdfast structure, larger Chuaria-like and Tawuia-like morphology and questionable affinities as well. The discovery of greater diverse macrofossil assemblages from the Jiucheng Member of eastern Yunnan has further indicated that an important diversification and evolutionary radiation of metaphytes took place in the latest Ediacaran time. This radiation of largescale, benthic metaphyte along with phytoplankton was likely important contributors to the early Cambrian explosion of metazoans.展开更多
基金financially supported by the National Key Research and Development(R&D)Program of China(2017YFC0603103)the National Natural Science Foundation of China(U19B6003)。
文摘The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge has been acquired on the types of microbial carbonates that are present,the properties of the reservoir and the pore evolution,hampering predictions of high-quality reservoirs in these carbonates.Integrated with petrography and in-situ U-Pb dating geochronology analyses,this study aims to clarify the types of microbial carbonates present and to reconstruct the pore evolution processes of the potential reservoir rocks.The Upper Ediacaran microbial carbonates of the Tarim Basin can be divided into four types,based on their features in terms of different scales(macro-to micro-):microbial laminite,stromatolite,spongiomicrobialite and microbial-peloidal wackestone/mudstone.Petrophysical properties show that all these microbial carbonates have low porosity and very low permeability with poor connectivity.These carbonates were subject to long-term and complex diagenetic processes,mainly consisting of dissolution,compaction,pervasive dolomitization,cementation and fracturing.The most important reservoir spaces are contributed by vugs and dissolution-enlarged pores,which are likely to have been associated with the widespread uplift of the Aksu area in the terminal Ediacaran.In contrast,the cementation of the fine-to-medium crystalline dolomite greatly reduced the pre-existing pores.Pore types are closely related to different microbial fabrics,which played an important role in the pore evolution of the microbial carbonates.
基金supported by Ministry of Science and Technology of China(Grant No.2011CB808806)US National Science Foundation(Grant No.EAR-0745825)Doctoral Fund of Ministry of Education of China(Grant No.2012002212008)
文摘Organic carbon isotope （δ-13 Corg） data from two well-preserved sections across a shallow-to-deep water transect of the late Edi- acaran-Early Cambrian Yangtze Platform in South China show significant temporal and spatial variations. In the shallow-water Jiulongwan-Jijiapo section, δ-13Corg values of the late Ediacaran Dengying Formation range from -29‰ to -24%0. In the deep-water Longbizui section, δ-13Corg values from time-equivalent strata of the Dengying Formation are mostly between -35‰ and -32‰）. These new data, in combination with δ-13Corg data reported from other sections in South China, reveal a 6‰-8‰ shallow-to-deep water δ-13Corg gradient. High δ-13Corg values （〉-30‰） occur mostly in shallow-water carbonate rocks, whereas low δ-13Corg values （〈-32‰） dominate the deep-water black shale and chert. The large temporal and spatial δ-13Corg variations imply limited buffering effect from a large dissolved organic carbon （DOC） reservoir that was inferred to have existed in Edi- acaran-Early Cambrian oceans. Instead, δ-13C-org variations between platform and basin sections are more likely caused by dif- ferential microbial biomass contribution to total organic matter. High δ-13Corg values （〉-30‰） documented from shallow-water carbonates are within the range of typical Phanerozoic δ-13Corg data and may record the isotope signature of organic matter from primary （photosynthetic） production. In contrast, low δ-13Corg values （〈-32‰） from deep-water sections may have resulted from higher chemoautotrophic or methanotrophic biomass contribution to bulk organic matter in anoxic environments. The δ-13Corg data provide indirect evidence for ocean stratification and episodic chemocline fluctuations in the Ediacaran-Early Cambrian Yangtze Platform.
基金supported by the Key Laboratory of Stratigraphy and Paleontology,Chinese Academy of Geological Sciences(Grant No.JB0705)the Institute of Geology,Chinese Academy of Geological Sciences(Grant No.J0716)+1 种基金the National Natural Science Foundation of China(Grant Nos.40272015,40672022)the China Geology Survey Grant(Grant Nos.1212010511607,200213000042)
文摘A new macrofossil Lagerstatte was discovered from the uppermost Ediacaran Jiucheng Member at Jinning and Jiangchuan of the eastern Yunnan, yielding numerous diverse well-preserved thallophyte macrofossils. These include the previously-known representatives of vendobionts, Vendotaenia and Tyrasotaenia, and the biggish multicellular benthos such as Chuaria-like and Tawuia- like fossiis, as well as Longfengshaniaceaens with diverse holdfast structures. There are still some other problematic macrofossils with peculiar configurations as well as uncertain relatives. The distinct dominance of the giant, unbranching thallophytes occasionally with holdfast structures distinguishes this assemblage from the other Ediacaran macrofossil Lagerstattes in the Doushantuo Formation at Miaohe, Wenghui and Lantian, and the contemporary assemblage in the Shibantan Member of Dengying Formation, Yangtze Gorges area. This paper outlines the characteristics of some of the multicellular macrofossils from the Jiucheng Member at Jiangchuan. They include some macrofossils with different types of holdfast structure, larger Chuaria-like and Tawuia-like morphology and questionable affinities as well. The discovery of greater diverse macrofossil assemblages from the Jiucheng Member of eastern Yunnan has further indicated that an important diversification and evolutionary radiation of metaphytes took place in the latest Ediacaran time. This radiation of largescale, benthic metaphyte along with phytoplankton was likely important contributors to the early Cambrian explosion of metazoans.
