东海丽水凹陷西次凹明月峰组海底扇沉积特征及沉积模式

东海陆架盆地丽水凹陷古新统明月峰组发育典型的海底扇沉积，且已获得工业油气发现。该文利用现有地震地质资料，运用层序地层学理论方法，总结出丽水凹陷的海底扇沉积模式。海底扇沉积相标志包括：岩心主要表现为滑塌揉皱、包卷层理、泄水构造、块状砂岩、黑色泥岩撕裂屑、漂砾、砂注等构造；C-M图主要表现为重力流沉积特征；结构成熟度和成分成熟度中等—差。扇体地震反射结构主要为顺物源方向双向下超，垂直物源方向丘状反射特征，平面地震属性显示为典型扇形。丽水凹陷明月峰组由低位体系域、水进体系域和高位体系域组成，其中海底扇发育在低位体系域，在扇体近端发育多个下切谷，下切谷下切规模较大；坡折主要划分为断裂坡折和沉积坡折，其中断坡坡度较大，坡度7.2°左右，沉积坡折坡度较小，一般在5°左右，与下切谷相对应在谷口形成一系列的扇体，沟–坡–扇耦合关系良好。扇体规模较大，单个扇体面积最大124 km2，整个低位域由6个扇体组成，展示了丽水凹陷良好的岩性圈闭勘探前景。本次研究根据扇体的成因特点建立明月峰组低位域时期沟–坡–扇沉积模式，对指导勘探寻找出岩性圈闭和开创丽水凹陷油气勘探新局面具有一定意义。

Sedimentary features and depositional model of the submarine fan of Mingyuefeng Formation in the Western Lishui Sag,East China Sea

The Mingyuefeng Formation of Paleocene in the Lishui Sag of East China Sea Shelf Basin is characterized by typical submarine fan deposits,in which industrial hydrocarbon has been discovered. In this paper, a depositional model for the Sag is summarized based upon the existing seismic-geological data under the guidance of sequence stratigraphy. Sedimentary facies features of the submarine fan observed from cores include collapse and crumpling structures, entrapment beddings, drainage structures, massive sandstone, tear debris of black mudstone, drifting gravel structures, sand injection and other structures. The C-M diagrams show a typical pattern of gravity flow deposits with moderate to poor component and textural maturities. The seismic reflection of the fan body is characterized by two-way dipping along source direction, hill-like reflection in cross sections, and typical fan-shaped seismic attributes in plane views. The Mingyuefeng Formation in the Lishui Sag is composed of lowstand system tract, transgressive system tract and highstandl system tract of a sequence, in which submarine fans occur in the lowstand system tract. Multiple incised large valleys develop in the proximal end of the fan body. Both the fault breaks and sedimentary breaks are observed and the fault breaks are always in large scale with a slope of about 7.2 degrees, while the sedimentary slope breaks are relatively smaller with a slope around 5 degrees. Most of the depositional fans occur at the mouth of the incised valleys in a pattern including valley, slope and submarine fans. The largest fan covers an area of 124 km2, and the lowstand system tact is composed of six fans, showing good prospects for lithologic traps in the Lishui Sag. According to the genesis of the fan bodies, we established in this paper a ditch-slope-fan depositional model for the lowstand system tract of the Mingyuefeng Formation as a guide for exploration of lithologic traps in the sag.