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1. The Neoproterozoic molar-tooth carbonatite types in Northern Anhui and Jiangsu Provinces and the forming mechanism | |||
Jia Zhihai,Zhang Liwei,Hong Tianqiu,Zheng Wenwu | |||
Earth Science 08 January 2010 | |||
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Abstract:Molar-tooth carbonatites can be found in almost all the Neoproterozoic carbonatite strata in Northern Anhui and Jiangsu Provinces. According to their features in different strata, two molar-tooth carbonatite types can be differentiated in this area. Type 1 molar-tooth carbonatites coexisted with stromatolite bioherms, gravels, debris, slump structures, swash channels and hummocky crossbeddings, were formed in the upper Liulaobei Formation and Jiuliqiao Formaiton which belong to the lower Neoproterozoic in this area. Type 2 molar-tooth carbonatites consisted in widely spread rhythmic units with graded beds and typical erosion surfaces, were formed in other Formations which belong to the upper Neoproterozoic in this area. The initial forming power of the molar-tooth carbonatites in this area might be the crustal movements which were caused by the break-up of the Rodinia. Type 1 molar-tooth carbonatites formed in tempestuously changing environments might be a signal of the break-up prelude of the Rodinia, while Type 2 molar-tooth carbonatites formed in steadily, periodically changing environments might indicate the intermittent release of the earth stress during the break-up period of the Rodinia. | |||
TO cite this article:Jia Zhihai,Zhang Liwei,Hong Tianqiu, et al. The Neoproterozoic molar-tooth carbonatite types in Northern Anhui and Jiangsu Provinces and the forming mechanism[OL].[ 8 January 2010] http://en.paper.edu.cn/en_releasepaper/content/38685 |
2. A Model for the Wumishan Cycle and Their Vertical Stacking Patterns: Cyclic Sedimentation Genetically Related to Milankovitch Cycles in the Precambrian | |||
Mei Mingxiang,Zhou Hongrui,Du Benming,Luo Zhiqing | |||
Earth Science 19 December 2005 | |||
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Abstract: Carbonate strata of the Meso-Proterozoic Wumishan Formation in the Jixian area near Tianjin are ~3300 m thick and were deposited over some 100 million years (from ~1310±20 Ma to ~1207±10 Ma). Metre-scale cycles (parasequences) dominate the succession. They are generally of the peritidal carbonate type, and mostly show an approximately symmetrical lithofacies succession with thin stromatolite biostromes and small thrombolite bioherms constituting the central part and tidal-flat dolomites forming the upper and lower parts. Lagoonal dolomitic shales with palaeosoil caps make up the topmost layers. The boundaries of the Wumishan cycles are typically exposure surfaces, and there is abundant evidence for fresh-water diagenesis. Widespread 1:4 stacking patterns indicate that the individual Wumishan cycles are sixth-order parasequences, with 4 parasequences constituting one fifth-order parasequence set. Locally, 5-8 seventh-order beds or couplets, can be discerned in some of the cycles. The regular vertical stacking pattern of seventh-order beds within the sixth-order parasequences, forming the fifth-order parasequence sets, are interpreted as the result of environmental fluctuations controlled by Milankovitch rhythms, namely the superimposition of precession, and short and long-eccentricity. The widespread 1:4 stacking pattern in the cyclic succession, as well as the local 1:5-8 stacking patterns of the beds within the cycles, suggest that the Milankovitch rhythms had similar ratios in the Meso-Proterozoic as in the Phanerozoic. Based on the cycle stacking patterns, 26 third-order sequences can be distinguished and these group into 6 second-order, transgressive-regressive megasequences, all reflecting a composite, hierarchical succession of sea-level changes. | |||
TO cite this article:Mei Mingxiang,Zhou Hongrui,Du Benming, et al. A Model for the Wumishan Cycle and Their Vertical Stacking Patterns: Cyclic Sedimentation Genetically Related to Milankovitch Cycles in the Precambrian[OL].[19 December 2005] http://en.paper.edu.cn/en_releasepaper/content/4458 |
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