摘要:
从近年来对甘肃敦煌党河和敦煌阿克塞河进行的详细的工作中发现了在现代边滩砂级颗粒中也会发育叠瓦构造,且远比砾石中的叠瓦构造复杂。首先,研究发现砂级叠瓦构造的倾角比砾石叠瓦构造的倾角变化要大,介于12°~88°之间,倾角均值在51°~63°,明显大于同河段砾石叠瓦构造的倾角34°,倾角如此之大可能与颗粒的紧密堆积有关;其次,倾向无砾石叠瓦构造那么稳定,有时可在小范围内呈现出双倾向。叠瓦构造倾角的统计分析数据也表明其稳定性不好;三是砂级叠瓦构造可以受薄层的控制,也可以呈层块状;四是根据砂级颗粒的接触关系又可以将其分为两种:颗粒支撑的叠瓦构造和含杂基的颗粒支撑叠瓦构造。颗粒支撑的叠瓦构造发育在"清水"环境,一般是在洪水的稳定期形成的;而含杂基的颗粒支撑砂级叠瓦构造则是发育在浊水环境,可能是在洪水的高峰时期形成的。
砂级叠瓦构造的研究对于沉积环境的研究、古流分析和储层的研究具有重要的意义。颗粒支撑的砂级叠瓦构造还可以形成特殊的屏蔽孔隙,成为很好的储集空间,是砂岩储层出现各向异性的根本。
关键词:
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砂 /
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叠瓦构造 /
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倾角 /
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倾向 /
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水流方向 /
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边滩
Abstract:
Imbricate structure is a common sedimentary structure. Yet, so far, the research on imbricate structure is mainly confined in gravel, and no systematic study of sand grains is conducted. Actually, just like conglomerate, sand grains also develop imbricate structure, and are very perfect. Meanwhile, their imbricate structure contains much more geologic information than that of gravels. Therefore, the study of sand grains' imbricate structure is much more significant.
In this study, we preceded detailed work at Dang River and Aksai River of Dunhuang, Gansu in recent years and found that there also develop imbricate structure in sand grains of modern marginal bank, which is far more complicated than that in gravel. First, according to research, the dip angle of sand grains' imbricate structure varies larger than that of gravel grains', ranging from some 10° to 50°~60°. The maximum can reach 70°~80°, and the average is 45°~50°, in total, which is obviously larger than the dip angle, 34°, of gravel' in the same channel segment. Second, compared with the gravel' trend, the sand grains' trend is not so stable, and sometimes it can appear double trend in small scope. Third, sand grains' imbricate structure can be controlled by lamina, presenting as lamellar. Fourth, according to the contact relation of sand grains, there are two types of imbricate structure, namely grain-braced imbricate structure and matrix-braced imbricate structure. Furthermore, the grain-braced imbricate structure also can be divided into two kinds:lamina-controlled imbricate structure and folium-controlled imbricate structure, both of which develop in "clean water" environment and form in pluvial stabilization period. Meanwhile, matrix-braced sand grains' imbricate structure develops in "muddy water" environment and maybe form in pluvial peak period.
The study of sand grain imbricate structure has significant meaning to sedimentary environment research, paleocurrent analysis and reservoir study. And the grain-braced sand imbricate structure can shape peculiar shield pore and become fine reservoir space, which is the root of sandstone reservoir's emerging of anisotropy.
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