| 雾迷山旋回层的费希尔图解及其在定义前寒武纪三级海平面变化中的应用 |
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| 关键词:Wumishan cyclothems Fischer plot cyclic sedimentation Precambrian Jixian of Tianjin |
| 基金项目:国家自然科学基金会资助项目(49802012)，九五攀登专项(SSER)的成果之一 |
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| The Fischer Plots of Wumishan Cyclothems as Records of Third-Order Sea Level Changes in Precambrian |
| The Middle Proterozoic Wumishan Formation(1310±20～1207±10 Ma) in Jixian County of Tianjin represents a succession of 3 300 m carbonate strata, in which stromatolite biostromes and thrombolite bioherms are best developed. These biostromes and bioherms, together with tidal-flat dolomites and sandy-muddy dolostones, form Wumishan cyclothems with an approximately symmetrical lithofacies succession, belonging to a particular type of peritidal carbonate meter-scale cyclic sequences. The lagoon muddy shales with the caps of paleosoil layer constitute the top of Wumishan cyclothems, and a lot of freshwater diagenetic marks were formed in tidal-flat dolomites, which suggests that the boundaries of Wumishan cyclothems are mostly instantaneously-exposed punctuated surfaces. In the light of the regular vertical stacking patterns in long-term third-order sequences, 26 third-order sequences that may be incorporated into 6 second-order sequences can be discerned in Wumishan Formation. In order to study the changing extent of the long-term sea-level, the authors recognized 626 cyclothems in the middle and upper part of Wumishan Formation in which the outcrops are well developed. Considering the total thickness of Wumishan Formation and the general duration of its formation, the authors hold that the subsidence rate of the crust in the sedimentary period of Wumishan Formation was probably 2～4 meters in each interval of 100 thousand years. On the basis of this assumption, the Fischer plot might be used to calculate the changing extent of the third-order sea level. According to the Fischer plot, some meaningful conclusions can be reached and many useful data can be obtained on sequence stratigraphy of Precambrian. |
| MEI Ming-xiang,MA Yong-sheng,ZHOU Hong-rui,DE Ben-ming,LUO Zhi-qing,GUO Qing-yin.2001.The Fischer Plots of Wumishan Cyclothems as Records of Third-Order Sea Level Changes in Precambrian[J].Acta Geoscientica Sinica,22(5):429-436. |
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