北部湾—雷琼地区新生代古海岸线重建与琼州海峡演化

Reconstruction of the Cenozoic paleocoastline and evolution of the Qiongzhou strait in the Beibu Gulf-Leizhou Peninsula-Hainan Island

古海岸线重建能为理解全球气候变化和海陆格局演变提供重要的线索。笔者等基于钻孔资料重建了北部湾—雷琼地区新生代以来古海岸线变迁与琼州海峡演变过程。结果表明,北部湾—雷州半岛—海南岛(雷琼地区)新生代经历了古近纪北部湾古湖、新近纪—早更新世早期古琼州海峡、早更新世晚期—晚更新世峡湾和全新世琼州海峡四个演化阶段。古近纪北部湾形成NEE向互不连通的断陷盆地并充填河—湖相沉积,渐新世晚期海水间歇性入侵北部湾古湖并连通孤立的断陷盆地;中新世早—中期(23.3~10.4 Ma)南海西北部海岸线快速后退,北部湾古湖演变为古琼州海峡,中新世晚期—上新世(10.4~2.58 Ma)海岸线继续后退形成宽阔的古琼州海峡,早更新世早期海退及火山喷发导致古琼州海峡萎缩;早更新世晚期—晚更新世气候频繁波动控制了峡湾与陆地的不断转化,而末次盛冰期大幅度海退直接导致北部湾—雷琼地区从海转陆;15~12 ka BP以来海岸线快速后退并在12~11 ka BP期间短暂停留,北部湾再次由陆转海,之后海平面继续上升,琼州海峡于11 ka BP自西向东完全打开,至6 ka BP海平面达到现今海平面以上2 m左右,现今海陆格局形成。

Objectives:To understand the evolution of the Qiongzhou Strait and ancient coastlines in the Beibu Gulf—Leizhou Peninsula—Hainan Island(Leiqiong area)since the Cenozoic Era,and to reveal its implications for regional land-sea pattern changes and global climate change.Methods:This article reconstructs the changes of ancient coastline and the evolution process of Qiongzhou Strait in the Beibu Gulf—Leiqiong area since the Cenozoic Era based on borehole data.Results:In the Paleogene,the Beibu Gulf formed a NEE trending disconnected fault basin and filled with fluvial—lacustrine facies deposits.In the late Oligocene,seawater intermittently invaded the ancient Beibu Gulf lake and connected the isolated fault basin.In the early-middle Miocene(23.3~10.4 Ma),the coastline in the northwest of the South China Sea rapidly retreated,and the ancient lake in the Beibu Gulf evolved into the ancient Qiongzhou Strait.In the late Miocene to Pliocene(10.4~2.58 Ma),the coastline continued to retreat,forming a wide ancient Qiongzhou Strait,early Pleistocene regression and volcanic eruptions led to the shrinkage of the ancient Qiongzhou Strait.Frequent climate fluctuations during the late Early Pleistocene to late Pleistocene controlled the continuous transformation of fjords and land.The significant regression during the last glacial maximum directly led to the transformation of the Beibu Gulf-Leiqiong area from sea to land.Since 15~12 ka BP,the coastline has rapidly retreated;and briefly stopped between 12 and 11 ka BP,the Beibu gulf has once again transitioned from land to sea.Afterwards,the sea level continued to rise,and the Qiongzhou Strait fully opened from west to east at 11 ka BP.By 6 ka BP,the sea level reached about 2 meters above the current sea level,forming the current sea land pattern.Conclusions:The results indicate that the Beibu Gulf-Leizhou Peninsula—Hainan Island area underwent four evolutionary stages in the Cenozoic,including the Paleogene Beibu Gulf ancient lake,the Neogene to early Pleistocene ancient Qiongzhou Strait,the late Early Pleistocene to late Pleistocene fjords,and the Holocene Qiongzhou Strait.