陆相前陆盆地层序地层学研究——以塔里木盆地北部下白垩统地层为例

陆相层序地层学是层序地层学今后进一步发展的一个重要研究领域和方向。因此,探索不同构造背景下、不同类型陆相盆地层序的边界性质、内部结构特征、控制因素及其模式将极大地丰富和完善层序地层学的理论与方法。本文通过对塔里木盆地北部早白垩世陆相前陆盆地地层进行层序地层分析,确定出4个层序边界,划分出1个超层序和3个三级层序,识别出冲积体系域(AST)、湖泊扩展体系域(EST)和湖泊萎缩体系域(CST),并探讨了陆相前陆盆地层序地层的特征及其控制因素。研究表明,构造作用是控制该陆相前陆盆地层序形成与发育的首要因素;远离和邻近南天山造山带的盆地南、北两侧构造作用的不均一性,造成层序边界性质、体系域特征等在南、北两侧存在很大差异;层序内部体系域发育的不完整性(即由两个层序界面限定的一个三级层序在全盆范围内仅发育一种或两种体系域),反映了陆相层序的复杂性和特殊性。

APPROACHES TO SEQUENCE STRATIGRAPHY OF CONTINENTAL FORELAND BASINS:AN EXAMPLE FROM THE EARLY CRETACEOUS NORTHERN TARIM BASIN

The continental sequence stratigraphy of continental basins is an important branch forthe further development of sequence stratigraphy in the future. The theory and methodlogyof sequence stratigraphy will be greatly enriched and improved by the studies of the natureof sequence boundary, internal architectures, controlling factors and models for the se-quence stratigraphy of various continental basihs in distinctive tectonic settings. In the pre-sent paper, four sequence boundaries, i. e. one supersequence (second-order ) and threethird-order sequences are determined for the sequences of an Early Cretaceous continentalforeland basin in the northern Tarim Basin. Three systems tracts are recognized as well,in-cluding the alluvial systems tract(AST),lacustrine expanding systems tract(EST)and la-custrine contraeting systems tract (CST). Furthermore, the main characteristics and con-trolling factors of these sequences in the continental foreland basin are described in moredetail.The research demonstrates that the tectonic movement is the chief factor controllingthe formation and development of the sequences in the study area. The formation of the su-persequence boundary and its nature tend to be governed by higher-rank regional tectonicmorements,where the third-order sequence boundaries are the result of the interaction oftectonism, denivellation,sediment supply and climate,of which tectonism is more impor-tant and significant. When the tectonic movement and climate remain stable,denivellation,sediment supply and palaeotopography(slope)may act as the main controls on the deposi-tion of the sedimentary systems and stacking patterns of the parasequences within the sy5-tems tracts. The inhomogeneity of the tectonism in the northern and southern parts of theforeland basin is responsible for the large di8crepancies in the nature of the sequenceboundaries and the characteristics of the systems tracts. For example,the third-order se-quence boundaries appear to be discordant in the zone near the South Tianshan fold-thrustblock (i. e. on the northern side),while they are conformable in the zone of the southernforeland upIift. The incompleteness of the development of systems tracts within a sequence(a third-order sequence bounded by two sequence boundaries is only made up of one or twosystems tracts within the extent of the whole basin) reflects the complexity and particular-ity of the continental sequences.