川中大安寨段风暴沉积特征及分布模式

风暴沉积在川中大安寨段比较发育,对大安寨段风暴沉积的沉积构造特征进行研究,发现大安寨段风暴沉积虽然缺乏丘状交错层理,但顶底面构造和层理构造比较发育。综合分析顶底面构造和层理构造特征,总结了大安寨段风暴沉积的理想沉积相序结构,即一个完整的风暴层序从下向上发育:渠模或侵蚀面、砾屑层、粒序层理、波状层理、漂浮介屑段、粉砂屑层和截切或波痕。由于各微相的水动力条件的差异导致风暴沉积层序在各微相中保存的程度不同,在能量较高的滩前、滩核、滩后主要以粒序层为主,滨浅湖主要以粉砂屑层理为主,半深湖发育漂浮状介屑层、波状层理、粉砂屑层理。风暴沉积的研究加深了对大安寨段半深湖灰岩成因的认识,滩前和半深湖相的风暴成因的灰岩的孔隙度相对较好,具有较好的烃源与保存条件,是致密油勘探的有利相带。

Storm Deposition of the Da'anzhai Member(Jurassic) in Central Sichuan Basin

Storm deposits are commonly found in Da'anzhai Member, Lower Jurassic. We have studied the storm deposition's sedimentary structure, and then found that, notwithstanding the absence of hummocky cross-stratification, we can found top structure, bottom structure and the bedding structure are numerous, which can be symbols of storm deposition. After comprehensively analyzed the depositional features, we built an ideal deposition facies sequence, that is, gutter cast, surface of scour, gravel shell fragment bedding, graded bedding, ripple bedding, float thin shell bedding, silt bedding and the top surface structure, cut structure and ripple ridge. The hydrodynamic force and preservation condition variation in different microfacies, so the storm facies sequence in every microfacies are different. Graded bedding are the main residual structure in high energy microfacies, namely fore shell beach and the core shell beach, and the rear shell beach. Silt bedding can be found in littoral to shallow area, but the deep shallow lake reserve more structures, containing ripple bedding, float thin shell bedding, and silt bedding. The research of storm deposition can help us get more precise understanding on the depositional model of the shell limestone, what's more, it can give us a guide for tight oil exploration. The storm deposition in deep shallow lake and the fore shell beach have relatively high porosity, and the reservoir adjacent to source rock and has good preservation condition. So the two microfacies are the tight oil advantage facies.