琼东南盆地崖南凹陷海湾扇三角洲体系沉积构成及演化模式

本文以琼东南盆地崖南凹陷陵水组三段扇三角洲体系为例，详细讨论了进积于海湾背景环境下扇三角洲体系的岩性相、成因相及其空间配置关系。研究区海湾扇三角洲体系自下而上潮汐作用越来越强，其垂向演化可划分为三个阶段，早期为以河流作用占优势阶段，中期为河流和潮汐混合作用阶段，晚期为以潮汐作用占优势逐渐过渡为以潮汐作用占优势。

Internal Achitectures and Evoluting Model of Bay Fan Delta System in Yanan Sag of Qiongdongnan Basin

Fan delta system was developed in the Yacheng slope in the south margin of Yanan Sag. With uplifting, sea water inundated in this area, and alluvial fan prograded into bay environment and formed fan delta deposits. There formed characteristic lithofacies and genetic facies in fan delta system because of the effect of marine action. Research results from the core showed that there was increasing effect by marine action in the evolution of fan delta, in other words, there was a great change in dominant action from the alluvial to tidal in the formation of fan delta. The evolutionary process of fan delta in the third member of Lingshui Formation can be divided into three periods: (1)Early period-dominated by fluvial action. Sea water flooded only in the centre of the sag, so fan delta system consisted of braided channel and alluvial plain deposits, and thin coalbeds occurred in the local area. Tidal flat deposits were formed in the front or margin of lobes of fan delta. (2)Middle period-affected by fluvial and tidal actions. The most area of Yacheng slope was located in lower fan delta plain (intermediate belt) and fan delta front belt. Upper fan delta plain belt occurred in the margin of Yacheng slope. Many event deposits, for example, debris flow or transient subaqueous channel doposits, were reworked by tidal action. There were formed subtidal and intertidal shoal deposits with animal burrows and strong distortion. In general, there were n-n * 10 cm intertidal shoal deposits in the abandoned stage of each fan delta. (3)Late period-dominanted by tidal action. Fan delta system was formed dominantly by tidal action, and consisted of tidal channel, intertidal shoal, subtidal shoal and tidal flat deposits. These characters indicated a typical estuary environment.