基于浅地层记录的海南岛东南部潟湖全新世地貌演化

SHALLOW SEISMIC STRATIGRAPHIC RECORDS OF HOLOCENE GEOMORPHOLOGICAL DYNAMICS FROM BARRIER-LAGOONS OF SOUTHEAST HAINAN ISLAND

海南岛东南部新村和黎安潟湖的4条地震剖面揭示了平均厚度达30m的全新世沉积层,从中可识别出两个地层层序,厚度分别为8 ～ 20m和5～45m.新村潟湖剖面中发现了2处老珊瑚礁和3处埋藏谷;根据海湾发育历史和珊瑚礁分布特征分析,老珊瑚礁和埋藏谷在约6ka B.P.的高海面时期被埋藏.将地震地层分析与海南岛全新世地层分布以及区域钻孔对比信息相结合,本文提出全新世以来新村和黎安潟湖经历了古河道、浅海或滨海和沙坝-潟湖等环境演变过程.全新世海进淹没本区之后,海湾南部山丘之间形成与外海相通的水道.此后,波浪和潮流携带的沉积物在潟湖内堆积,海湾南部水道被封闭,并逐渐形成海湾中部的连岛沙坝,把水域分为两个部分,其西部为新村潟湖,东部为黎安潟湖.

In order to understand the Holocene coastal environmental evolution in southeast Hainan Island, we carried out shallow seismic survey over the Xincun and Li-An lagoons. The four seismic profiles obtained revealed an average thickness of 30m for the Holocene sequences. Based on these seismic profiles, we identified two seismic units with thicknesses of 8～ 20m and 5 ～ 45m, respectively. Further, two relict coral reefs and three buried valleys were present in the profiles of the Xincun lagoon, with the buried channels being around 2km away from the southern shoreline of the embayment, representing old tidal channels linking the lagoon with the open sea. In combination with the information on the distribution and evolution of the coral reefs along the southern coastlines of Hainan Island, the relict coral reefs and the buried valleys are interpreted as a result of the high sea level period of 6ka B.P. The stratigraphic correlation between the Holocene seismic sequences and the sedimentary record revealed by the cores at the locations adjacent to the study area suggests that the two lagoons had experienced rapid environmental changes since the Mid-Holocene. Between the Late Pleistocene and Early Holocene, there was a paleo-river valley, which was surrounded by a series of low lying hills in the southern part of the study area, such as Nanwanling, Pingtoushan, Jianfengling, Liuliangshan, Lingshuijiao and Gangmenling. At the early stage of the Middle Holocene, the valley was inundated to form a coastal embayment which was open to sea waves in the east; in the south there were channels linking the embayment and the open sea, including the channels to the west of Nanwanling and between the Pingtoushan and Jianfengling hills. Subsequently, wave and tidally induced sediment transport and accumulation occurred, forming a tombolo within the embayment and, at a later stage, a sand barrier beach in the east. Meanwhile, coral reefs developed previously were buried in sediment. Further sediment accumulation sealed the channel between the low hills. Eventually, the Xincun and Li-An lagoons were formed. In the future, this hypothesis may be verified by detailed core analysis and sequence stratigraphic modeling