川中地区须二、四段湖相风暴岩沉积特征及其意义

Lacustrine Tempestite Sediment Feature and Significance in Second and Fourth Members of Xujiahe Formation,Upper Triassic in Middle of Sichuan Basin

在野外剖面和岩心观察的基础上,介绍了川中地区上三叠统须家河组须二、四段湖相风暴岩沉积特征,建立了湖泊风暴沉积模式,并探讨了风暴岩发育的条件及其意义。研究区风暴沉积是由风暴浪作用于浅湖泥坪和滨岸沼泽上,使沉积物重新搅起、形成泥岩砾,并通过风暴流搬运到三角洲或滨浅湖滩坝中,与未固结的砂质沉积物一起沉积形成。研究区风暴岩典型沉积构造特征丰富,单层风暴沉积发育不完整,常见多次风暴作用形成的若干不完整风暴岩的叠置层。风暴岩的发现有利于加深对该区沉积相的认识,风暴岩的频繁发育,表明研究区在上三叠统沉积时,易受到古太平洋气候的影响,湖盆水动力较强,部分原始沉积的砂体会受到湖泊水体的改造,形成新的滨浅湖滩坝砂体。同时还指出风暴岩砂体是研究区有利的储集层,可形成良好的岩性或构造-岩性油气藏。

Based on the field section and the core observation, this paper presents the characteristics of lacustrine elastic tempestites in the second and fourth members of Xujiahc formation, Upper Triassic in the middle of Sichuan basin, sets up the storm deposition model in this area, including the conditions and significance of the tempestite formation. The tempestites are composed of unconsolidated arenaceous sediment and boulder clay, which were from the sediments of mere corcagh and shoreside swamp churned up by storm wave, and transported to delta and beach bar of shore shallow lake. A plenty of the sedimentary structures of typical tempestite appears with less of mono-layer storm sediment, and the superposed half-baked tempestites formed by polygenic storm wave are often observed. The existence of tempestites is helpful to in-depth understanding of sedimentary facies in this area, indicating that the Upper Triassic was subjected to influence of the paleopacific climate in this area, and the hydrodynamic force of lacustrine basin was correspondingly intensified. Parts of original sandy sediments were vulnerable to. be reconstructed, shaping new beach bar of shore shallow lake. It is suggested that the tempesite saint body can be as a favorable reservoir rock and could form prospective lithologic or structural-lithologic hydrocarbon reservoir.