摘要
鄂尔多斯盆地延长组下部(长8—长10油层组)沉积特征与中、上部(长1—长7油层组)存在较大的差异。延长组下部沉积时,盆地西部和西南地区地形相对较平坦,以辫状河、辫状河三角洲及滨浅湖沉积为主,碎屑岩中化学性质不稳定的组分含量较高;长7沉积期,沉积格局发生重大变革,盆地西缘、西南缘地区发育冲积扇、扇三角洲沉积体系,拗陷幅度急剧增大,半深湖—深湖区范围可达10×104km2以上,而且湖盆中心向西南迁移了几十公里,碎屑岩成分成熟度增高,岩矿组合具有显著的东西分异性。此外,从延长组凝灰岩的分布特征分析,长7底部沉凝灰岩分布稳定,为同期火山作用的产物,厚度由盆地西南向东北方向逐渐减薄至不发育。上述分析表明,长8沉积末期为湖盆沉积演化的重要转折期,盆地西缘和西南缘存在一次强烈的构造地质事件,火山活动频繁,为印支运动第一幕重要的表现形式。
The sedimentary characteristics of the lower part of the Yanchang Formation （ Chang 10- Chang 8 oil bearing intervals） are quite different from the middle and upper parts of the Yanchang Forma- tion （Chang 7--Chang 1 oil bearing intervals）. During the deposition of the lower part of the Yanchang Formation, the western and southwestern areas of the basin were characterized by a gentle topography and the deposition was dominated by the braided fluvial, braided fluvial deltaic and coastal-shallow lacustrine facies. The content of chemically unstable components was relatively higher in clastic rocks. The depositional framework changed greatly during the deposition of Chang 7 interval of the Yanchang Formation. The sedimentary systems changed to alluvial fan and fan delta in the west and southwest. The size of the down- warping depression increased quickly and semi-deep and deep lakes covered an area of over 10 × 10^4 km^2. Simultaneously, the depocenter of the Ordos Basin was shifted tens of kilometers southwestwards. The component maturity of the clastic rocks increased and the rock combination was obviously different in the west and east dispersal tracts of sediments. Furthermore, analyses of the distribution of the tuffs in the Yanchang Formation indicate that the tuffs are steadily distributed in the basal part of Chang 7 interval of the Yanchang Formation and they were derived from the syn-depositional volcanism. Their thickness de- creased from the southwest to the northeast. These analyses indicate that the latest depositional period of Chang 8 interval of the Yanchang Formation is an important transitional stage in the basin＇s sedimentary evolution. A strong tectonic movement occurred in the western margin and southwestern margin of the basin and volcanic activities took place frequently. These events represent the first episode of the Indosinian Movement.
出处
《古地理学报》
CAS
CSCD
2008年第2期159-166,共8页
Journal of Palaeogeography：Chinese Edition
关键词
鄂尔多斯盆地
延长组
沉积演化
凝灰岩
早印支运动
Ordos Basin, Yanchang Formation, sedimentary evolution, tuff, Early Indosinian Movement
