鄂尔多斯盆地北部延安组水下分流河道河口坝层偶型三角洲体系的沉积构成

THE DEPOSITIONAL ARCHITECTURE OF THE LACUSTRINE DELTAIC SYSTEM WITH SUBAQUEOUS DISTRIBUTARY CHANNEL-MOUTH BAR COUPLETS OF THE YAN'AN FORMATION IN NORTHERN ORDOS BASIN

在内陆湖泊沉积盆地中,三角洲沉积体系的发育决定了盆地沉积中心的位置。三角洲体系是重要的油气储集体,也是煤的重要聚积场所。对于湖泊三角洲的认识已日益详尽,其类型也日益丰富。吉尔伯特型三角洲是古代沉积序列中三角洲体系研究的开端。Farqaharson(1982)把三角洲体系分为吉尔伯特型和河口坝型两种类型。在断陷湖泊盆地中,扇三角洲体系尤其发育。夏文臣等(1991)在研究断陷湖盆和大型内陆拗陷湖盆的滨岸带沉积物时,识别出水下分流河道型湖泊三角洲体系。在湖盆的充填淤浅阶段,还有一种三角洲体系值得重视,即水下分流河道-河口坝层偶型三角洲体系。下文将对该三角洲体系作一阐述。

Based on genetic stratigraphic analysis of the Yan＇an Formation of northern Ordos Basin, a new type of the deltaic system is recognized. Within this system, subaqueous distributary channel-mouth bar couplets are developed beyond the modification of wave processes, without sheet sandstones between the couplets. Morever, a deltaic system unit is divided into three process stages in detail, i.e. constructive, abandoned and destructive. stages, during the second of which the thick coal seams are formed. The recognition of the deltaic system with subaqueous distributary channel-mouth bar couplets can be used as a tool for interpreting the history of basin fill.