牛庄洼陷南坡坡移扇沉积特征

SEDIMENTARY CHARACTERISTICS OF THE SLOPE-SHIFTING FANS IN SOUTH SLOPE OF NIUZHUANG LOW

牛庄洼陷南坡沙三段三角洲—浊积岩体系中广泛发育一种沉积特征更加接近三角洲前缘的坡移扇,运用传统的沉积物重力流理论难以准确描述。通过厘米级岩心观察、粒度分析、测井响应及地震反射特征等研究,建立了坡移扇识别标志,探讨其沉积主控因素及分布范围。研究表明:坡移扇是由于断裂、坡度角等原因造成的三角洲前缘砂体与主体断开脱离,并整体滑移至前缘斜坡或坡角处堆积而形成的岩性体;坡移扇砂体近源滑动,尚未完全液化即沉积,其沉积构造兼具重力流和牵引流特征;斜坡坡度6°~8°且横切三角洲前缘砂体的盆倾断层发育区,有利于坡移扇发育。

The wide-developed sedimentary features in the delta-turbidite system of Member Es3 of South Slope of Niuzhuang Low are pretty closer to the slope-shifting fans of the delta front,and moreover they are rather difficult to describe by the traditional gravity-flow theory of the sediments. By means of the following researches on the centimeter-level core observations,particle size analysis,well logging response,seismic reflected characteristics and so on,the recognizing markers of the slope-shifting fan are established,the main controlling factors and distribution range of the deposition are explored. The achievements show that for the slope-shifting fans,because of the faults,slope angle and so forth,the sandbodies of the delta front are separated and fractured from the main bodies,and moreover the whole sandbodies are drifted to the front slopes or slope angles and piled into the lithological bodies;the sandbodies of the slope-shifting fan slide nearby the sources,and are not yet completely liquefied i. e. deposited,the sedimentary structures are characterized by the gravity flow and traction flow; The well-developed dippingbasin faults with 6°- 8° slope angle and crosscutting the delta-front sandbodies are conducive to the development of the slope-shifting fan.