河控浅水三角洲沉积构型

自浅水三角洲的概念提出以来,已经历了60多年的研究历史。虽然在诸多方面取得了较大的研究进展,但在浅水三角洲的概念内涵、砂体成因类型及沉积构型样式等方面仍存在一定的分歧。本文探讨了浅水三角洲概念的内涵,并总结和分析了其沉积构型特征和样式。根据浪基面和河-盆水深比(初始河道深度与河口盆地水体深度比值),可将三角洲分为极浅水三角洲、较浅水三角洲和较深水三角洲。典型的浅水三角洲为极浅水三角洲,发育于河-盆水深比值大于或等于1的浅水水体,分流河道可下切至下伏的前三角洲沉积。根据三角洲前缘分流河道与河口坝的组合样式,将河控浅水三角洲的端元类型分为分流砂坝型和指状砂坝型。分流砂坝型三角洲为河道入海(湖)后形成的多级分叉的河口坝与分流河道系统,平面上呈扇状,河—坝组合呈现“河在坝间”的样式,而指状砂坝型三角洲为指状砂坝与分流间湾相间分布的系统,平面上呈枝状,河—坝组合呈现“河在坝内”的样式。

Depositional architecture of fluvial-dominated shoal water delta

Shoal water delta has been researched over 60 years since its concept was proposed. Although great progress in the research on shoal water delta has been made in many aspects,there are still debates on the concept,genetic types of sand bodies and depositional architectural patterns of shoal water delta. In this paper,we discuss the conceptual connotation of shoal water delta,and summarize its characteristics and patterns of depositional architecture. According to wave base and water depth ratio(ratio of initial channel depth to basin depth at river mouth),the delta could be divided into shoal water delta,relatively shallow water delta and relatively deep water delta. The shoal water delta,as the typical shallow water delta,is developed where the water depth ratio is greater or equal to 1. Within shoal water delta the distributary channel could incise through underlying prodelta deposits. According to the combination pattern of channels and mouth bars in delta front,fluvial-dominated shoal water delta can be classified into two end-member types,including distributary-mouth bar type and fingered bar type. Distributary-mouth bar type delta is the system of multi-order bifurcated mouth bars and distributary channels,which is a fan shape in the plane,and presents the combination pattern of “channels extending between mouth bars”. In contrast,fingered bar type is the system of fingered bar and inter-distributary-mouth bay,which is a branched shape in the plane,and presents the combination pattern of “channels extending within mouth bars”.