柴达木盆地北缘西段古近纪以来沉积模式研究

Sedimentary model since Paleogene in northern margin of Qaidam Basin

通过对柴达木盆地北缘(简称"柴北缘")西段古近系和新近系的沉积序列、岩心特征、薄片特征、测井资料及录井资料的分析,结合野外露头考察,对该区的沉积模式进行了系统研究。结果表明:古近系和新近系发育以砾岩、砂岩和泥岩为主的碎屑岩沉积,且沉积体系以辫状河—辫状河三角洲平原—辫状河三角洲前缘—滨浅湖沉积为主;古近系的岩性变化较大,主要为砾岩,具有正旋回特征,说明古近纪时期为一水进过程;新近系地层发育以粗碎屑岩和细碎屑岩不等厚为主的交互沉积,水动力条件变化频繁。通过进一步的研究认为,古近纪以后的柴北缘由于降水量(或气候)的周期性变化,形成了湖盆周缘粗碎屑岩和细碎屑岩不等厚交互沉积,即在盆地边缘有泥岩发育,并且在靠近盆地的沉积中心也有中—细砂岩的发育,这种粗碎屑岩和细碎屑岩的交互沉积层容易形成较好的储盖组合,有利于构造-岩性油气藏的形成。沉积模式研究清楚地展示了柴北缘地区古近纪以来的沉积演化规律,为该区下一步的油气勘探提供了可靠的地质依据。

Based on core observation,cast thin section,well logging data and analysis of sedimentary sequence of the Paleogene and Neogene in the northern margin of Qaidam Basin,Combined with field observations,we studied the sedimentary model in this area.The result shows that clastic rocks are developed in Paleogene and Neogene in the northern margin of Qaidam Basin,such as conglomerate,sandstone and mudstone,and the sedimentary facies are mainly of braided river,braided river delta plain,braided river delta front and shore shallow lacustrine depositional systems.Conglomerate of Paleogene has the characteristic of upright cycle,so it is a water immersion process,and in Neogene it mainly develops alternating deposits of megaclast and fine grained detrital rocks which show frequent hydrodynamic conditions change.Due to the cyclical changes in precipitation,mudstone developed in megaclast deposit area at the basin margin,and middle-fine sandstone also exsited in the mudstone deposit area at the basin sedimentary centre.This alternating deposits of megaclast and fine grained detrital rocks can form perfect reservoir-cap combination,and it is favorable for the formation of structural-lithologic reservoir.The sedimentary model shows the process of sedimentary evolution since the Paleogene clearly,which can provide reliable geological evidence for the further oil exploration.