| A study on the environmental conditions of the microsparite （Molar-tooth） carbonates |
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| 引用本文： | 旷红伟,刘燕学,孟祥化,葛铭.A study on the environmental conditions of the microsparite （Molar-tooth） carbonates[J].中国地球化学学报,2007,26(1):28-34. |
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| 作者姓名： | 旷红伟 刘燕学 孟祥化 葛铭 |
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| 作者单位： | Key Laboratory of Exploration Technologies for Oil and Gas Resources Yangtze University Ministry of Education School of Geophysics and Oil Resources of Yangtze University，Chinese Academy of Geological Sciences，Institute of Sedimentary Basin of China University of Geosciences，Institute of Sedimentary Basin of China University of Geosciences，Jingzhou 434023 China，Beijing 100037，China，Beijing 100083，China，Beijing 100083，China |
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| 基金项目： | This Project was funded by the International Geological Comparative Program 447 （IGCP447） （No. SC/GE0/546/447）, the National Natural Science Foundation of China （Grant No. 40172043） and the Natural Science Developmental Fund of the Yangtze University. |
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| 摘 要： | Along with the progress in research on the Precambrian, Molar-tooth carbonates (simplified as MT, or microsparite carbonates or MT structure) which were formed in the Middle-Late Proterozoic have become a hot subject recently. The Proterozoic Molar-tooth (MT) carbonate rocks refer to those Meso- to Neoproterozoic (1600-650 Ma) carbonates with MT structure, i.e., a series of peculiar, ptygmatically folded and spar-filled cracks in fine-grained carbonates of Precambrian age, located in the environment of mid- to inner ramp and shallow platform. MTS, like a bridge connecting the inorganic world with the organic one, are closely related to the evolution of paleo-oceans, atmosphere and biosphere. Their development and/or recession are/is related to the origin of life and the abruption of sedimentary geochemistry events of marine carbonates. By using modern instruments and testing methods adequately, the contents of oxides in sandstones were measured and the REE distribution pattern curves were established; an accurate value of isotopic ratio of 87Sr/86Sr was obtained, that is, the age of MT formation is about 750-900 Ma; C and O isotopes of some fresh micrite limestone samples were analyzed; the energy spectrum analysis revealed that the MT consists mainly of microspar calcite, while as for its chemical composition, the matrix shows outstanding peaks of Ca, Mg, Al, Si, and K. The geochemical indicators proved that Neoproterozoic MT carbonates in the Jilin-Liaoning region were developed at the margin of a stable continent, in the torrid zone where the paleo-temperature was about 50℃, the seawater had normal salinity when MT was formed during the Wanlong period in southern Jilin and during the Yingchengzi and Xingmincun periods in eastern Liaoning. The sedimentary environment was located in the inner ramp. In summary, it is of great importance to understand the origin of MT, ascertain the paleo-climate and paleo-environment characteristics, constrain the age and the stratigraphic division and comparison of the Proterozoic so as to study the geochemical characteristics of MT carbonates and their formation environment.
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| 关 键 词： | 臼齿碳酸盐 微亮晶灰岩 环境条件 地球化学 吉林-辽宁地区 新元古代 |
| 收稿时间： | 2005-12-14 |
| 修稿时间： | 2006-01-16 |
A study on the environmental conditions of the microsparite (Molar-tooth) carbonates |
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| Kuang?Hongwei,Liu?Yanxue,Meng?Xianghua,Ge?Ming.A study on the environmental conditions of the microsparite (Molar-tooth) carbonates[J].Chinese Journal of Geochemistry,2007,26(1):28-34. |
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| Authors: | Kuang Hongwei Liu Yanxue Meng Xianghua Ge Ming |
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| Institution: | (1) Key Laboratory of Exploration Technologies for Oil and Gas Resources, Yangtze University, Ministry of Education, China;(2) School of Geophysics and Oil Resources of Yangtze University, Jingzhou, 434023, China;(3) Chinese Academy of Geological Sciences, Beijing, 100037, China;(4) Institute of Sedimentary Basin of China University of Geosciences, Beijing, 100083, China |
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| Abstract: | Along with the progress in research on the Precambrian, Molar-tooth carbonates (simplified as MT, or microsparite carbonates
or MT structure) which were formed in the Middle-Late Proterozoic have become a hot subject recently. The Proterozoic Molar-tooth
(MT) carbonate rocks refer to those Meso-to Neoproterozoic (1600–650 Ma) carbonates with MT structure, i.e., a series of peculiar,
ptygmatically folded and spar-filled cracks in fine-grained carbonates of Precambrian age, located in the environment of mid-to
inner ramp and shallow platform. MTS, like a bridge connecting the inorganic world with the organic one, are closely related
to the evolution of paleo-oceans, atmosphere and biosphere. Their development and/or recession are/is related to the origin
of life and the abruption of sedimentary geochemistry events of marine carbonates. By using modern instruments and testing
methods adequately, the contents of oxides in sandstones were measured and the REE distribution pattern curves were established;
an accurate value of isotopic ratio of 87Sr/86Sr was obtained, that is, the age of MT formation is about 750–900 Ma; C and O isotopes of some fresh micrite limestone samples
were analyzed; the energy spectrum analysis revealed that the MT consists mainly of microspar calcite, while as for its chemical
composition, the matrix shows outstanding peaks of Ca, Mg, Al, Si, and K. The geochemical indicators proved that Neoproterozoic
MT carbonates in the Jilin-Liaoning region were developed at the margin of a stable continent, in the torrid zone where the
paleo-temperature was about 50°C, the seawater had normal salinity when MT was formed during the Wanlong period in southern
Jilin and during the Yingchengzi and Xingmincun periods in eastern Liaoning. The sedimentary environment was located in the
inner ramp. In summary, it is of great importance to understand the origin of MT, ascertain the paleo-climate and paleo-environment
characteristics, constrain the age and the stratigraphic division and comparison of the Proterozoic so as to study the geochemical
characteristics of MT carbonates and their formation environment. |
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| Keywords: | Molar tooth microsparite carbonate geochemistry Jilin-Liaoning region Neoproterozoic |
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