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Origin of molar-tooth structure Based on Sequence-Stratigraphic Position and Macroscopic Features: Example from Mesoproterozoic Gaoyuzhuang Formation at Jixian Section, Tianjin, North China

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Journal of China University of Geosciences 2006年第3期17卷 201-208,271页

作者：梅冥相 Key Laboratory of Lithospheric Tectonics and Lithoprobing Technology Ministry of Education China University of Geosciences School of Earth Sciences and Resources China University of Geosciences Beijing 100083 China

Both the macroscopic feature and the sequence-stratigraphic position of the molar-tooth structure developed in the third member of the Gaoyuzhuang （高于庄） Formation at the Jixian （蓟县） Section in Tianjin （天津） can provide some useful information about its origin and can reveal some problems to be further researched in the future. The Mesoproterozoic Gaoyuzhuang Formation is a set of 1 600 m thick carbonate strata. This formation can be divided into four members. The first member is mainly made up of stromatolitic dolomites; the second is marked by a set of manganese dolomites; the third is mainly composed of lamina limestones with the development of molar-tooth strcutures; the fourth is a set of stromatolitic-lithoherm dolomites. According to lithofacies and its succession, several types of meter-scale cycles can be discerned in the Gaoyuzhuang Formation： the L-M type, the subtidal type and the peritidal type. There is a regularly vertical stacking pattern for meter-scale cycles in the third-order sequence. Therefore, the Mesoproterozoic Gaoyuzhuang Formation can be divided into 13 third-order sequences （SQ1 to SQ13 ） and can further be grouped into 4 second-order sequences. The third member is marked by lamina limestones and can be grouped into three third-order sequences （SQ9 to SQ11 ）. The molar-tooth structure is developed in the middle part of the third sequence, i.e. SQH , in the third member. Several features of this kind of molar-tooth structure reflect some features of carbonate sedimentation in the Precambrian, such as the particular configuration, abundant organic matter, and easy silication. Stromatolites are chiefly formed in a shallow tidal-flat environment; lamina are mainly formed in the shallow ramp and molar-tooth structures are mainly generated in a relatively more deep-water environment from the middle to the deep ramp. Therefore, similar to stromatolite and lamina, the molartooth structure might also be a kind of bio-sedimentation structure. This suggestion is based on macroscopic observation an

关键词： molar-tooth structure sequence stratigraphy Gaoyuzhuang Formation Mesoproterozoic Jixian Section in Tianjin.

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molar-tooth structure from the Mesoproterozoic Wumishan Formation in Lingyuan,Yanshan Region,North China,and Geological Implications

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Acta Geologica Sinica(English Edition) 2012年第1期86卷 85-95页

作者： KUANG Hongwei LIU Yongqing PENG Nan LUO Shunshe LI Jiahua CEN Chao CHEN Mingpei Institute of Geology Chinese Academy of Geological SciencesBeijing 100037China Key Laboratory of Exploration Technologies for Oil and Gas Resources Ministry of Education of China School of Geophysics and Oil Resources of Yangtze University JingzhouHubei 434023China China University ofGeosciences Beijing 100083China School of Geosciences of Yangtze University Jingzhou Hubei 434023China

Although its origin has not yet reached a consensus so far, MTS （molar-tooth structure） has been documented for more than 100 years. Current study reports a discovery of MTS from the Mesoproterozoic Wumishan Formation, Lingyuan, Yanshan Region, North China, and the features and geological implications of MTS are further discussed. Here, straitigraphic horizons of MTS＇s occurrences show that it was mainly located within the top part of the Wumishan Formation, i.e., limestone unit. Four kinds of morphology of MTS, i.e., fine fusiform, debris, ribbon, ptigmatic and nodular （irregular）, were recognized and thought to be highly related to the sedimentary environments and facies. Geochemistry of MTS including oxides, trace elements and C, O and Sr isotopes indicates that the horizons of MTS-bearing is of higher Sr/Ba and Ca/Mg ratios, lower positive ~13C and highly negative 3180 values than the adjacent stratigraphic levels of rare MTS. Lithology, morphology and geochemistry of MTS in the Wumishan Formation suggest that MTS occurs mainly in shallow subtidal near the storm wave base, which is typically characterized by warm temperature, oversaturated calcium carbonate seawater and high organic productivity. Furthermore, occasional enrichment of algae bacteria here is more favorable for the calcification of calcium oozes and catalytic for MTS. C isotope composition of the Wumishan Formation and MTS of this study is well correlated with that of the Mesoproterozoic Belt Supergroup, North America and Riphean, Siberia, suggesting that MTS acts as a sedimentary record responding to global changes and is a perfect indicator in Precambrian stratigraphic correlation worldwide.

关键词： molar-tooth structure Wumishan Formation Mesoproterozoic Implications Lingyuan Yanshan Region

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molar tooth structure:a Contribution from the Mesoproterozoic Gaoyuzhuang Formation,Tianjin City,North China

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Acta Geologica Sinica(English Edition) 2011年第5期85卷 1084-1099页

作者： Maurice E.TUCKER Department of Earth Sciences Durham University

molar-tooth(MT) structure is an enigmatic sedimentary structure consisting of variously-shaped cracks and voids filled with a characteristically uniform,equant calcite microspar.It is globally distributed but temporally restricted to rocks from Neoarchean to Neoproterozoic age.The origin of MT structures has been debated for more than a century and the topic continues to be highly contentious.Some features of MT structure occurring in micritic limestones of the Mesoproterozoic Gaoyuzhuang Formation(ca.1500 Ma to ca.1400 Ma),Jixian section,Tianjin City,North China show that:1) there is a definite interface or lining,rich in organic material and pyrite,between the MT crack-filling calcite microspar and the micritic host rock,which is also rich in organic matter;2) the micritic host rocks are notable for the absence of stromatolites and microbial laminites;3) distinctive conglomeratic lag deposits made up of intraclasts of MT microspar result from storm reworking of the MT structures;4) the MT structure is associated with possible algal megafossils such as Chuaria;5) the MT microspar is made up of the larger calcite crystal and the MT crack is marked by the diversity of configurations;6) both the TOC content and the carbon-isotopic value(δ^(13)C_(PDB)) among the host rock, the MT microspar and the possible algae fossil are obviously different.For the forming mechanism of the Gaoyuzhuang MT structure,these features can still indicate that:A) the MT microspar was formed by rapid precipitation and lithification;B) the MT microspar precipitated directly within the cracks; C) the decomposition of organic matter within the host micrite might be the chief mechanism producing gas bubbles;D) microscale gas-sediment interaction led to the generation of the MT cracks and the precipitation of microspar therein;E) the MT cracks might represent the track of migration and expansion of gas bubbles,and that the recrystallization of host micrites cannot be eliminated during forming process of the MT microspar;F) the MT structure is o

关键词： molar-tooth structure Mesoproterozoic limestone Gaoyuzhuang Formation Tianjin North China

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Neoproterozoic molar-tooth structure and Constraint of Depositional Facies and Environment in the North China Platform in Jiangsu, Anhui and Liaoning, Eastern China

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Acta Geologica Sinica(English Edition) 2005年第4期79卷 533-539页

作者： LIU Yongqing GAO Linzhi LIU Yanxue Institute of Geology Chinese Academy of Geological Sciences Beijing 100037

molar tooth structure （MTS） represented by complex ptygmatical shapes is widely distributed in the Proterozoic of the world. MTS filled by fine, equant sparry calcite （or dolomite） displays an abrupt contact with hosting rocks, which are mainly composed of carbonaceous micrites and fine-grained carbonates with local silts and stormdominated deposits with graded, cross or wave beddings, numerous erosional surfaces and truncated and fills or guttered bases. Occurrence of MTS suggests a result of the constraint of sedimentary facies, and the storm-base in ramp settings is the maximum depth for the formation of MTS. Vertical succession of MTS-bearing carbonates shows a deposition stacked by high-frequency shallow subtidal and peritidal cycles. An individual cyclic MTS-bearing sequence is characterized by thinning, shallowing and dynamic decreasing-upward, and peritidal caps of purple red iron and organic carbonaceous sediments with more complicated shapes of MTS are common on the top of individual MTS-bearing sequences.

关键词： North China Platform Neoproterozoic molar-tooth structure carbonate facies and environment

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Morphological Characteristics and Genesis of molar-tooth structures Of Gaoyuzhuang Formation,Jixian Area

Morphological Characteristics and Genesis of Molar-Tooth Str...

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2015年全国沉积学大会

作者： Ziliang Liu Xianghua Meng College of Energy Resources Chengdu University of Technology China University of Geosciences

molar-tooth(MT) is an enigmatic carbonate fabric composed of variously shaped cracks and voids filled with a characteristically uniform,equant microspar. MT widely distribute in Mesoproterozoic and early Neoproterozoic strata, where void-filling microspar and preserved carbonate. Detailed petrographic examination of MT structures from the esoproterozoic Gaoyuzhuang formation, Jixian,permits interpretation of the microscale relationship between crack morphology and lithologic,and potentially rheologic, variability of the surrounding substrate by tracing the distribution of petrographically distinctive MT microspar. That examination suggests that grain size, substrate lithology,and substrate cohesion all play critical roles in the development of MT. By contrast,the presence of a wide range of MT morphologies within petrographically homogeneous substrates,and an apparent relationship between crack diameter and sinuosity,suggest that the void-forming process itself also effected the final morphology of MT. On this basis,we discuss the significance of MT in the analysis of ancient marine environment.

关键词： molar-tooth structure morphologies Origin Gaoyuzhuang Formation Jixian

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