塔中地区奥陶系米级旋回层序分析

Aanlyses of Ordovician Meter-Scale Cyclic-Sequence in Tazhong Area

塔中地区奥陶系米级旋回层序非常发育且典型多样,孕含着丰富的构造、海平面变化及沉积物堆积作用等方面的信息。在认真总结前人研究成果的基础上,结合区域地质资料及详细的岩芯观察和描述,将本区奥陶系米级旋回层序分为四大类:远洋—半远洋L-M型米级旋回层序、下斜坡—深水盆地非对称型米级旋回层序、潮下型米级旋回层序及环潮坪型米级旋回层序。在相序组构特征上,都表现为发育在瞬时淹没间断面之上以反粒序序列为特征的米级旋回层序和发育在瞬时暴露间断面之上以反粒序或正粒序序列为特征的米级旋回层序,并且在长周期三级层序中表现为有序的垂直叠加形式。这些米级旋回层序的沉积速率及形成周期与米兰柯维奇(Milankovitch)天文旋回轨道及周期变化具有明显的相关性。因此,塔中地区奥陶系米级旋回层序的发育主要受高频率海平面变化的控制,而这种高频率海平面升降则是由米兰柯维奇天文旋回轨道及周期变化所造成全球气候变化及大陆冰川的消长所控制。

There are many types of meter-scale cyclic-sequence developed in Ordovician of Tazhong area. They contain abundant information on structure, sea-level change and the accumulated action of sediment. On the basis of the previous work, and combining region geological data and detailed observation as well as description of the rock column, the meter-scale cyclic-sequence in Ordovician of Tazhong area are subdivided into four types： ocean-semiocean L-M type,lower slope-deep water asymmetrical type, subtidal type and peritidal type. On the characters of facies serial and structure, the meter-scale cyclic-sequences have the character of reverse grain serial developed on the instantaneous submerge discontinuous surface, or have the character of reverse or correctitude grain serial developed on the instantaneous emerge discontinuous surface. They all behave serial and vertical congruence format in long cycle thirdorder sequence. The sedimentary velocity and forming cycle of the meter-scale cyclic-sequence developed in Ordovician of Tazhong area and the periodic changes of Milankovitch cycles have evidence relativity, it is concluded that the development of the Ordovician meter-scale cyclic-sequence in Tazhong area is controlled by the high-frequency changes of sea-level, and the high-frequency changes of sea-level is controlled by the change of global climate and the melt and flow of the continental glacier, which controlled by the periodic changes of Milankovitch cycles.