莺歌海盆地变密度流和喷溢流沉积及其油气勘探意义

通过详细的沉积学研究,在莺歌海盆地中央泥拱带及其向盆地边缘的过渡区发现了特征的变密度流和喷溢流沉积。区内变密度流和喷溢流沉积的沉积环境为半深海,主要表现为浊流和快速沉积的滑塌变形沉积体。变密度流沉积为灰色中—细砾岩,岩石以颗粒支撑,具有特征的正、反粒序层理,厚度大致在6~10 cm,粒度变化范围0.3~0.5 cm、0.7~0.8 cm,岩层顶面呈不规则波状。喷溢流沉积主要为陆源碎屑岩,是浅水沉积物在海平面震荡中,随着海水事件性地向盆地喷溢而进入到邻近深水盆地的沉积;沉积物呈条带状、透镜状产出,主要为黄灰色中—细砂岩,发育透镜砂和深灰色纹理,水平层理特别是透镜层理中无构造和结构,常因泄水而发生变形,这些条带和透镜体的底部基本没有侵蚀面与内波沉积物区别。莺歌海盆地变密度流和喷溢流沉积发育部位适中,大都处于盆地中央泥拱带—斜坡的过渡带,导致在深水泥质岩体系中发育大套砂质沉积,形成了良好的生、储、盖组合,是莺歌海盆地今后地层-岩性圈闭非常重要的勘探目标。

Modified-density flow and shedding flow sediments and their petroleum exploration significance in Yinggehai basin

By detailed sedimentological studies,typical sediments derived from modified-density flow and shedding flow are found in the central mud diapir zone and its transitional area towards the basin margin in Yinggehai basin.Deposited in a bathyal environment,these sediments are deformed slump bodies of turbidity current and rapid sedimentations.With grain-supported structure and irregular undulating surface,the sediments from modified-density flow are gray pebble-granule conglomerate with typical normal and reverse grading. The conglomerate varies from 0.3-0.5 to 0.7-0.8 cm in grain size,and is 6 to 10 cm in bed thickness.The sediments from shedding flow are mainly terrigenous clastics,and has formed yellow-gray and middle-fine sandstones.As shallowwater sediments,they have been shed into adjacent deep basins during sea level oscillations.These sandstones occur as bands and lenses,have horizontal and lenticular beddings without structure and texture,and are usually deformed due to water leakage.There is few erosion surface at the bottoms of the bands and lenses,without differentiating from internal-wave sediments.In Yinggehai basin,the sediments from modified-density flow and shedding flow are largely located in a transition area between the central diapir zone and the basin slope,resulting in great development of sandy sediments in a deep-water muddy system.They may constitute good source-reservoir-cap assemblages,and could be the potential exploration targets in the future.