中国西部古老海相沉积建造的典型结构样式及勘探指向

Typical Structural Styles and Exploration Directions for Ancient Marine Sedimentary Formations in Western China

中国西部大型盆地(鄂尔多斯、四川、塔里木盆地)的古老海相地层受多期构造改造而变得复杂不一,造成难以准确识别和解析沉积建造并找准油气勘探目标。综合分析了三大盆地的海相碳酸盐岩的沉积大地构造背景和充填序列,建立了典型沉积建造的地质结构模型。结果表明:三大盆地海相碳酸盐岩主要沉积于前中生代中国陆块群的构造离散阶段,准稳定的鄂尔多斯盆地在古老碳酸盐岩建造沉积之前几乎没有碎屑岩垫底,次稳定的四川盆地和活动的塔里木盆地都具有碎屑岩垫底;基底和周缘发育古老的下伏裂谷是它们共有的特色,并形成了隐伏于盆地内部的牛头型建造;前印支期,都普遍发育若干不同规模的古隆起,围绕古隆起披覆沉积的似背斜建造是这些盆地又一显著特点;在构造相对稳定的间隙期,三大克拉通内部往往为广阔的浅水陆表海沉积,席状的台地潮坪白云岩建造是以往关注度最小的一类建造。上述古老克拉通盆地的牛头型建造、似背斜建造、席状白云岩建造埋藏深、隐伏性强,是重要的油气勘探指向。如何在被多旋回构造改造的叠合盆地中准确解析地层和岩相,并识别出这些建造的精细结构,是未来古老深层海相油气勘探极具挑战性和非常必要的研究方向。

The ancient marine strata in large basins in western China(the Ordos,Sichuan and Tarim Basins)are complicated by multi-stage structural transformation,which makes it difficult to accurately identify and analyze sedimentary formations and identify oil and gas exploration targets.This paper presents a comprehensive analysis of the sedimentary tectonic background and infill sequences of the marine carbonate rocks in these basins,and establishes the geological structural model of typical sedimentary formations.It is found that the marine carbonates in these basins were deposited during the pre-Mesozoic discrete period of the China Block;the Ordos Basin is quasi-stable,and there was almost no clastic rock cushion in most areas before the deposition of the ancient carbonate rocks.The substable Sichuan Basin and active Tarim Basin each have a clastic base.Ancient underlying rifts developed in the basement and at the margins of the three basins,containing ochsenkopf(Niutou)-type formations.During the pre-Indosinian,a number of different-scale paleo-uplifts were extensively formed,around which“para-anticlinal”formations were deposited.During tectonically stable intervals,an epicontinental sea covered the marine interior craton,and dolomite sheet formations developed in the wide tidal platform.Few of these have been studied until now.The strongly concealed“Niutou”,“para-anticlinal”and“dolomite sheet”formations at great burial depths and subject to tectonic/sedimentary differentiation,are all important targets for oil and gas exploration.Therefore,how to accurately extract information about these structures that were formed and re-formed by multiple cycles of tectonic movement,and identify the fine structures of the three basins and their hydrocarbon accumulation,are challenges for the oil and gas exploration of deep marine strata,and further study is very necessary.