鄂尔多斯盆地西南部延长组长7段浊积岩沉积特征

Sedimentary characteristics of turbidite of Chang 7 member in southwestern Ordos Basin

根据野外露头、岩心观察及粒度分析,对鄂尔多斯盆地西南部延长组长7段浊积岩的沉积特征进行了研究。结果表明,浊积岩主要为岩屑长石砂岩,以次棱角状为主,成分成熟度及结构成熟度较低;粒度分布上具有典型的浊流沉积的特征,发育粒序层理、包卷层理、沟模、槽模、重荷模、滑塌变形等沉积构造;常见的鲍马序列层序组合有AB型、ABC型、ADE型、AE型。研究区浊积扇可分为上扇、中扇、下扇亚相及主沟道、辫状沟道等相应的沉积微相,上扇、中扇分布范围较广,是浊积扇的主体。在古地理演化过程中,长73浊积岩体规模较小,长72—长71湖侵作用减弱,深湖线收缩,浊积岩逐渐发育,在华池—庆城一带连片展布;湖盆地形、物源供给及构造运动是影响浊积岩发育及分布的重要原因。

Based on outcrops, cores and grain size analyses, the authors studied systematically sedimentary characteristics of turbiditeof Chang 7 member in southwestern Ordos Basin. The results show that turbidites are sub-angular lithic feldspar sandstone with lowcompositional maturity and textural maturity. The turbidites exhibit typical turbidite particle size distribution. The sedimentary struc-tures include graded bedding, flute cast, delve mold, gravity cast and collapse, and the common Bouma of turbidite sequences includesAB, ABC, ADE and AE. Hackberry facies can be divided into three sedimentary subfacies, i.e., the upper fan, mid fan, outer fan aswell as relative sedimentary microfacies such as main groove and braided groove, and the upper fan and mid fan are main bodies ofthe turbidite with a wide distribution range. During the evolution of paleogeography, turbidites were small during Chang 73 stage ofChang 7 member. With the weakening of lake invasion and the retreat of the deep lake line, turbidites were developed graduallyfrom Chang72-Chang7, and were distributed along Huachi-Qingcheng-Heshui area. Topography of the lake basin, source supplyand tectogenesis seem to have been the important factors influencing formation and distribution of turbidites.