Sedimentary System of Platformal Trough of Feixianguan Formation of Lower Triassic in Northern Sichuan Basin and Its Evolution
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摘要: 川北地区下三叠统飞仙关组沉积主要受开江梁平海槽控制,短期存在的海槽在其两侧形成了较为对称的类似于威尔逊相模式的碳酸盐岩沉积体系。通过详细的钻井、露头等岩石学资料的研究,认为飞仙关组主要发育蒸发台地、局限台地、开阔台地、台地边缘滩、斜坡和盆地相共六类沉积相。其盆地相较深海盆地相浅,主要发育深色泥灰岩和灰质泥岩;斜坡沉积特征明显,见浊流、碎屑流沉积,但陆棚相不发育,可能是海槽深度小、面积小引起的;随着海槽的关闭,海水变浅,海槽内部的沉积由盆地相向斜坡、台地边缘滩、开阔台地、局限台地、蒸发台地相演化特征明显;到飞四段顶部,整个川北地区均一化为局限台地相或蒸发台地相沉积。由于海槽存在时间短,沉积相在平面上和纵向上的演化过程十分清晰。随着海槽的关闭,海水向广海方向退却,台缘鲕滩也向海槽边界,即向广海方向发生了迁移,而且其发育层位逐渐变高。Abstract: Kaijiang-Liangping trough existed for 700 My.controlled the deposition of Feixianguan Formation of lower Triassic in the northern Sichuan Basin. In the short period of the trough existed, relativelysymmetrical carbonate rock sedimentary system that be analogous to Wilson facies pattern could be formed in its both sides. Through researching on petrology data of detailled drilling, outcrop and so on, Feixianguan Formation mainly developed six types of sedimentary facies including evaporate platform, restricted platform, open-platform, platform marginbeach, slope and basin facies. The basin facies that was shallower than deep-sea basin which mainly developed dark marl and lime mudstone; the depositonal characteristics of the slope facies are distinct, but shelf facies poor developed which may be for the sake of the depth of the trough, because it is so small; with the gradual close of the trough, seawater became shallow, the characteristics of the depositional evolution from basin facies to slope, platform margin beach, open-platform, restricted platform and evaporate platform within the trough are dinstinct; to the top of the Member 4 of Feixianguan Formation, all of the Northern Sichuan basin were deposited equally by restricted platform facies or evaporate platform facies. The period of the trough existed is so short that the course of evolution of sedimentary facies is quite clear in plane and longitude. With the gradual close of the trough, seawater receded toward to open sea, platform margin oolitic beaches moved toward to trough too, that was open sea, growing horizons of them rised gradually at the same time.
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Key words:
- platformal trough /
- sedimentary system /
- platform margin oolitic beach /
- pattern /
- evolution /
- Sichuan /
- Feixianguan Formation
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