海南岛北部新近纪—第四纪地层结构与沉积演化模式

NEOGENE-QUATERNARY STRATA STRUCTURE AND SEDIMENTARY EVOLUTION MODEL OF NORTHERN HAINAN ISLAND

以海口江东新区为中心的琼北"海澄文"经济区缺乏新近纪以来的精细地层结构和系统沉积模式研究。为了支撑该区域城市地质工作和水工环地质调查研究,本文以海口江东新区内264个地质钻孔和大量地质实物资料为研究对象,综合微体古生物、孢粉、光释光和14C测年等成果,系统分析了新近纪—第四纪地层的空间分布、岩性组合、沉积环境、年代及古生物特征,对研究区的地层结构进行了梳理,总结了新近纪以来的沉积演化模式。研究表明:(1)海南岛北部新近系—第四系共划分出冲积扇、三角洲平原、湖泊、滨海、浅海陆棚和无障壁海岸6种沉积体系。(2)中中新世沉积期,因盆地沉降、海侵作用加剧等,形成统一的琼北断陷盆地;进入上新世,盆地在整体沉降的基础上,有过两次明显的构造抬升;早更新世继承了上新世的断块升降运动,但幅度明显减小;中更新世时期,研究区气候湿热且伴随着强烈的地壳升降运动,造成风化剥蚀作用加剧;晚更新世—全新世,海侵达到最鼎盛后持续海退,海浪与河水交替成为主控因素。沉积演化模式的建立为琼北及北部湾盆地新近纪以来沉积-构造演化史提供新的认识。

There are a lack of fine stratigraphic structure and systematic sedimentary model research since the Neogene of Qiongbei “Haichengwen” economic zone, centred on Jiangdong New District in Haikou. To support the urban geological work and hydrogeological survey in this area, 264 geological boreholes and a large amount of geological data, combine the results of micro-paleontology, spore-pollen and optical luminescence and;C dating, were used to analyze spatial distribution, lithology combination, sedimentary environment, age and paleontological characteristics of the Neogene-Quaternary strata. This study sorted out the stratigraphic structure, and reconstructed the sedimentary evolution model since the Neogene in Jiangdong New District in Haikou. The results show that:(1) The Neogene-Quaternary strata in the northern part of Hainan Island were divided into six sedimentary systems: alluvial fan, delta plain, lake, coastal, shallow sea shelf, and barrier-free coast.(2) During the Middle Miocene depositional period, basin subsidence and transgression were intensified, forming a unified Qiongbei faulted basin;then in the Pliocene, the basin experienced two obvious structural uplifts based on overall subsidence. The early Pleistocene inherited the movement of the fault block in the Pliocene, but the amplitude was greatly reduced. During the Middle Pleistocene, the climate in the study area was hot and humid and accompanied by strong crustal movement, resulting in increased weathering and denudation. In the Late Pleistocene to Holocene, the transgression reached the peak, then the sea continued to retreat, and sea waves and river water alternately became the dominant factors. The establishment of the sedimentary evolution model provides a better understanding of the sedimentary-tectonic evolution history of Qiongbei and Beibu Gulf Basin since the Neogene.