南海琼东南盆地崖13-1气田古近系陵水组海陆过渡带沉积特征及演化*

南海北部琼东南盆地中的众多凹陷均有海陆过渡相沉积，沉积相类型包括海湾辫状河三角洲和河口湾-潮坪。本次研究以高分辨率层序地层学理论为指导，将崖13-1气田古近系渐新统陵水组三段及二段各划分为1个长期基准面旋回，并在其内部进一步识别出10个中期基准面旋回(S1-S10)。在等时地层格架内，对陵水组三段及陵水组二段发育的沉积相特征及演化进行深入的探讨。陵水组三段沉积时期，研究区主要发育海湾辫状河三角洲沉积，其具有独特的层理构造、富含泥质纹层以及遗迹化石丰富。该沉积体系自下而上潮汐作用越来越强，早期以河流作用为主(S1-S4)，中期为河流和潮汐混合作用(S5-S6)，晚期逐渐过渡到以潮汐作用占主导(S7-S8)。陵水组二段沉积时期，研究区发生全面海侵，沉积作用方式及沉积特征更加复杂，生物成因构造更加独特，本次研究将其解释为河口湾-潮坪沉积(S9-S10)。研究表明，区域海平面的不断上升是研究区沉积相从海湾辫状河三角洲演化到河口湾-潮坪的主要控制因素。

Sedimentary characteristics and evolution of transitional belt of the Paleogene Lingshui Formation in Ya13-1 Gasfield of Qiongdongnan Basin,South China Sea

Fluvial-marine transitional facies, including braided river delta and estuary-tide flat, were mainly developed in sags of Qiongdongnan Basin，northern South China Sea. Under the guide of high-resolution sequence stratigraphy theory，the Members 2 and 3 of Paleogene Lingshui Formation were divided into 2 long-term base-level cycles and 10 mid-term base-level cycles. Sedimentary characteristics and evolution of the Members 2 and 3 of Lingshui Formation were discussed under isochronous stratigraphic framework. Braided river delta, with unique stratification structures, rich mud lamina and abundant trace fossils, was mainly developed in the Member 3 of Lingshui Formation, and its evolutionary process could be divided into 3 stages: the early period dominated by fluvial activities(S1-S4)，the middle period affected by fluvial and tidal activities(S5-S6), and the late period dominated by tidal activities(S7-S8). During the depositional period of Member 2 of Lingshui Formation(S9-S10)，a comprehensive transgression happened in study area, resulted in more complicated sedimentary characteristics and process with more unique biogenic structures, which was interpreted as estuary-tide flat. According to this research，the relative sea level change was the controlling factor of base-level cycle and sedimentary evolution in Qiongdongnan Basin.