四川江油马角坝地区船山组核形石基本特征及其环境意义
摘要: 四川江油马角坝地区船山组核形石十分发育，类型多样。基于对其内部显微结构的研究发现核形石核心和纹层各有5种类型，并伴随有3种圈层“构造”。基于对其核心、纹层和形态的研究将研究区核形石分为大球状核形石、小球状核形石、长棒状核形石、帽状核形石、不规则状核形石和复合核形石等6大类，并将它们划分成3种沉积环境，即台地边缘滩、开阔台地和局限台地，并探讨了碳酸盐岩地层中核形石的分布、形成环境和沉积环境的耦合关系。高含量、大颗粒、纹层厚度大于核心厚度、纹层复杂、核心组分与基质组分存在较大差异，亮晶胶结的核形石的形成环境与沉积环境不一致，即核形石形成于水动力较弱的局限台地或开阔台地环境，强水动力使核形石发生磨圆，基质生物碎屑破碎，进而沉积于水动力较大的台地边缘滩环境。中等含量、中等粒度、纹层简单、与完整生物碎屑共存且粒径类似、亮晶胶结的核形石的形成环境与沉积环境类似，即部分生物碎屑在中等水动力条件下，处于悬浮状态，捕获和粘附碳酸盐质点，当个体增大和水体环境变化时，核形石就地沉积于中等能量的开阔台地环境。含量低、粒径变化大、纹层厚度小于核心厚度、纹层简单、形状易受核心的影响，纹层外壳凹凸不平，基质生物含量低、泥晶基质含量特别高的核形石的形成环境与沉积环境一致，即形成并沉积于水动力偏弱的局限台地环境。
Characteristics and Environmental Significance of the Chuanshan Formation Oncoids in the Majiaoba Area, Northwestern Sichuan Province
Abstract: Oncoids are well preserved in the Chuanshan Formation in Majiaoba, Jiangyou County. Five types of core and lamina and three types of structures could be divided according to their microstructures. Five types of core are composed of bioclasts, intraclast, recrystallized bioclasts, pelletoid or early period oncoids and organic shell carbonate. Five types of lamina are commomly composed of sparry laminae, micritic laminae, clotlike laminae, micritic laminae including or alternating with layers of recognizable encrusting microfossils and porostromate laminae. Three types of structures are birdseye structure, micritization, layered structure and so on. At the same time, the relationship of the cores and laminas are discussed in the paper. The types of lamina are easy dominated by the type of core, especially the original shape of the core.Six oncoid types are distinguished by their cores, laminas and shapes, such as big ball oncoids(diameter>4mm), small ball oncoids(diameter 0.5~4 mm), longshaped oncoids(long axis and minor axis ratio>2), gibbous oncoids, irregular oncoids and combined oncoids. They are deposited in winnowed platform edge sands, open platforms or restricted platforms separately. Both the distribution of the oncoids and their forming and depositional environments are discussed in this paper. (1) Forming environments and depositional environments are inconsistent. Oncoids contents have big sizes and are cemented by sparites in the strata, laminas are more complex and thicker than cores, and constituents of core and matrix are different. The cores, which are deposited nearby open platforms with weak water power, suspended nearby winnowed platform edge sands with strong water power capturing and adhering carbonate particles. Additionally, biological clastics are seriously brokem in such samples. (2) Forming environments are not similar with depositional environments, at the same time the cores and the matrix are both composed by complete biological clasts. Medium spreaded oncoids contents have medium diameters and simple laminas and were cemented by sparites. Some biological clasts in their original places capture and adhere to carbonate particles during suspended in open platforms state. （3）Forming environments are exactly same with depositional environments. The oncoids are deposited in restricted platforms, with low contents，anomalistic diameters, polytropical edges, simple laminas, low biological clastic and thin laminas.
四川江油马角坝地区船山组核形石基本特征及其环境意义[J]. 沉积学报, 2013, 31(1): 1-9.
| 引用本文: |
四川江油马角坝地区船山组核形石基本特征及其环境意义[J]. 沉积学报, 2013, 31(1): 1-9.
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Characteristics and Environmental Significance of the Chuanshan Formation Oncoids in the Majiaoba Area, Northwestern Sichuan Province[J]. Acta Sedimentologica Sinica, 2013, 31(1): 1-9.
| Citation: |
Characteristics and Environmental Significance of the Chuanshan Formation Oncoids in the Majiaoba Area, Northwestern Sichuan Province[J]. Acta Sedimentologica Sinica, 2013, 31(1): 1-9.
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