| 湖北宜昌王家坪下寒武统天河板组古杯礁丘及其成岩作用 |
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| 引用本文： | 张俊明,彭克兴.湖北宜昌王家坪下寒武统天河板组古杯礁丘及其成岩作用[J].地质科学,1994,29(3):236-245. |
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| 作者姓名： | 张俊明 彭克兴 |
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| 作者单位： | 中国科学院南京地质古生物研究所 南京 210008 |
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| 摘 要： | 王家坪古杯礁丘是由不规则古杯和蓝绿藻Renalcis、Epiphyton、Cirvanella等组成的障积礁丘。可分为:孤立小型古杯泥丘和由丘状藻-古杯粘结岩叠置而成的点礁。以Renalcis为主的藻-古杯粘结岩与孤立小型古杯泥丘一样形成于风暴浪基面之下的低能陆架。以Epiphyton为主的藻-古杯粘结岩形成于较动荡的中-高能陆架浅滩。除造礁生物的沉积作用外,早期海底胶结作用和充填固化作用对古杯礁丘的形成亦起了十分重要的作用。
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| 关 键 词： | 古杯礁丘 生物沉积作用 胶结作用 下寒武统天河板组 王家坪 |
| 收稿时间： | 1993-05-15 |
| 修稿时间： | 1993-05-15; |
ARCHAEOCYATH REEFS FROM THE LOWER CAMBRIAN TIANHEBAN FORMATION AT WANGJIAPING,YICHANG, HUBEI AND THEIR DIAGENESIS |
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| Zhang Junming,Yuan Kexing.ARCHAEOCYATH REEFS FROM THE LOWER CAMBRIAN TIANHEBAN FORMATION AT WANGJIAPING,YICHANG, HUBEI AND THEIR DIAGENESIS[J].Chinese Journal of Geology,1994,29(3):236-245. |
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| Authors: | Zhang Junming Yuan Kexing |
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| Institution: | Nazjing Institute of Ceology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008 |
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| Abstract: | The limestone of the Tianheban Formation on the Yangtze Gorges belongs to open shelf marine deposit in middle Early Cambrian age.Two distinct types of archaeocyath reefs are preserved within an interval between the dark grey burroweddolomitic mottled lime mudstone and the grey Girvanella oncoidal packstone in the middle part of the Tianheban Formation at Wang naping stratigraphic section: an isolated archaeocyath mud mound, and a patch reef. The reefs are composed of irregular archaeocyathids and calcified microbial microfossils such as Epiphyion, Renalcis, Givanella, etc., belonging to baffling reef mounds. The archaeocyatk reef mounds at Wangjiaping represent the youngest in the archaeocyath reefs sequence of China.In the isolated archaeocyath mud mound there exists a typical structure looking like a planar-convex mound, generally 0.3-1.5m in thickness and 3-5m in length,enclosed within an interval of thin-bedded burrowed-dolomitic mottled lime mudstone.This mud mound contains 20%-25% archaeocyathids with Renalcis and Proaulopora encrusted around the outer walls of the archaeocyathid. The isolated archaeocyath mud mound occurs alone in low energy environment below the storm wave base. The patch reef consists of different-sized biconvex bioherm, up to 1-3m in thickness and 21m in length. Based on calcimicrobial composition, four kinds of boundstones are recognized from the lower to upper parts of the patch reef succession: 1. Renalcis archaeocyath boundstone, containing 30% -40% Renalcis, 30% archaeocyathids, and a small amount of Epiphyton; 2. Girvanella-Epiphyton-archaeocyatha boundstone, representing a complex intergrowth of calcimicrobes and archaeocyathids, with abundant Girvanella; 3. Epiphyton boundstone, almost entirely composed of Epiphyton, and a small amount of archaeocyathids; and 4. Epiphyton-archaeocyath boundstone, containing a large amount of archaeocyathids in addition to the abundant Epiphyton. Among those boundstones, Renalcis-dominated archaeocyath boundstone occurs in low energyenvironments, with burrowed-dolomitic mottled lime mudstone as their wall-rock; but Epiphyton-dominated archaeocyath boundstone occurs in environment of moderately high energy on shelf shoal, surrounded by Girvanella oncoidal grainstone. In the Epiphyton-dominated archaeocyath reefs, the growth cavities between frame-building organisms are possessed of fibrous calcite cements and geopetal internal sediments covering their base.Therefore, this patch reef succession at Wang naping stratigraphic section shows the hydrodynamic changing from low enegy to moderately high energy, and then to a low energy environment. |
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| Keywords: | Archaeocyath reefs Organosedimentation Cementation Lower Cambrian Tianheban Formation Wangjiaping |
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