摘要： 针对准噶尔盆地腹部石南31井区下白垩统清水河组一段三角洲相沉积的不同认识,根据砾岩的成层性、组构、结构成熟度、孔隙发育等特征,以及砂岩的结构、构造、粒度特征、砂体的空间展布特征,笔者认为清水河组一段是较强水动力条件下牵引流沉积的产物,其沉积环境属辫状河三角洲。通过对岩心的详细观察与描述,结合测井相分析,以石南31井区211口井的单井相分析为基础,依据连井相剖面分析和平面沉积相综合研究,认为该区辫状河三角洲的各亚相发育齐全,并识别出了辫状河道、河漫、水下分流河道、支流间湾、河口砂坝、远砂坝、前三角洲泥、前三角洲沟道砂等微相。在清一段早期（K₁q²₁）,研究区以湖泊相沉积为主,仅东南部为辫状河三角洲沉积。其后,研究区南北两个方向的辫状河三角洲相向推进（K₁q^1-3-4₁ 、K₁q^1-3-3₁）；继而,东南部的辫状河三角洲平原消失,研究区内仅见三角洲前缘（K₁q^1-3-2₁）沉积；K₁q^1-3-1₁沉积时期以细粒沉积为主,而沉积相格局则大致同前。同样，K₁q^1-2₁沉积时期,北方发育辫状河三角洲平原及前缘,东南方仅发育三角洲前缘。清一段晚期（K₁q^1-1₁），由于湖平面快速上升,全区均演化为前辫状河三角洲亚相,主要由前三角洲泥构成,并且发育条带状分布的沟道砂沉积。

关键词: 辫状河三角洲, 沉积特征, 沉积演化, 下白垩统, 准噶尔盆地

Abstract: Different viewpoints have been proposed about the delta sedimentary facies developed in the Member 1 of Qingshuihe Formation of Lower Cretaceous in Shinan 31 wellblock in central Junggar Basin. The authors considered it was the product of tractive current with strong hydrodynamic conditions according to the stratification character, the composition texture, the texture maturity, the developing characteristic of the pore of the conglomerates and the texture, structure, granularity and distribution characteristics of the sandstones. Its sedimentary environment belonged to the braided fluvial delta. Through the detailed observation and description of cores, combining with the logging facies analyses, on the basis of single well facies analyses of the 211 wells in the Shinan 31 wellblock, according to the across-well analyses and the synthetic analyses of sedimentary facies, it is concluded that all kinds of subfacies of the braided fluvial delta facies were developed in the study area. The sedimentary microfacies including the braided channel, fluvial flood deposit, subaquaeous distributary channel, mouth bar, front delta mud etc.， were identified. During the earlier sedimentary period of the Member 1 of Qingshuihe Formation(K₁q²₁), the study area was dominated by lacustrine facies and braided fluvial delta was only developed in the southeast of the study area. Then the two deltas in two directions developed towards the same direction(K₁q^1-3-4₁,K₁q^1-3-3₁). Then, the delta plain disappeared in the southeast and only delta front was developed(K₁q^1-3-2₁). During the sedimentary period of K₁q^1-3-1₁, it was dominated by fine-grained sediments and the sedimentary setting was similar as the former period. During the sedimentary period of K₁q^1-2₁, the braided fluvial delta plain and delta front were developed in the north, while in the southeast, only delta front was developed. In the late period of the Member 1 of Qingshuihe Formation(K₁q^1-1₁), due to the sudden rise of the lake level, the study area was dominated by front delta facies and was composed of front delta muds with the development of strip-belt-shaped front delta ditch sandstones.

Key words: braided river delta, sedimentary characteristic, depositional evolution, Lower Cretaceous, Junggar Basin

中图分类号: 

• TE121.3+2