海南岛全新世海岸演化过程与沉积记录

PROCESSES AND SEDIMENTARY RECORDS FOR HOLOCENE COASTAL ENVIRONMENTAL CHANGES, HAINAN ISLAND： AN OVERVIEW

本文在总结海南岛海岸全新世环境演化及其沉积记录研究进展的基础上,基于海岸沉积的过程与产物关系,提出了新的科学问题和基础研究建议.全新世时期,海南岛海岸及邻近海域形成了多样化的沉积体系,如砂质海滩沉积、海湾潟湖泥质沉积、珊瑚礁生物沉积、红树林湿地沉积、火山灰沉积、陆架与陆坡沉积等.由于陆源沉积物供给相对较少、潮汐作用较弱,海南岛海岸在全新世高海面之后的较长时期内形成了海洋动力作用信号较弱的“混杂堆积”,只是到2000a B.P.之后才形成了在海洋作用主导和频繁台风事件的共同影响下的典型海岸和陆架沉积.通过分析多种现代过程,如全新世海面变化、河流入海通量变化、波浪与台风作用、海岸带涌升、潮汐汊道均衡态过程、海岸带人类活动等,可望以正演方式重现全新世沉积的形成、时空分布、规模及未来演化趋势.为有效提取海南岛全新世沉积体系蕴含的丰富信息,以便应用于气候、环境和生态系统变化研究,除获取沉积物粒度、地球化学、微体古生物、年代等指标或参数外,还应结合海洋沉积动力过程研究,获得沉积记录形成时的物质来源及输运、组分含量或总量特征值、台风事件强度-频率关系、地貌演化等相关过程和机理信息.

Recent progress in the research in the Holocene coastal environmental change and the resultant sedimentary systems is synthesized. On such a basis, new scientific problems are identified and proposals for future studies are suggested, from the point of view of the process-product relationships. During the Holocene, a variety of sedimentary systems were formulated in the coastal waters and on the adjacent continental shelves, including sandy beaches, mud deposits in lagoons, coral reefs, mangrove wetland deposits, volcanic ash deposits, and shelf and slope basin deposits. In terms of the temporal evolution, during a long period of time after the sea level reached its high stand, a mixture of sequences with weak marine signals, in response to river input, shelf circulations, and tide-wave induced reworking, were generated; this is due to a relatively small quantity of sediment input and weak tidal currents over the region. The coastal and shelf deposits with strong marine signal were rare until 2000a B.P., when the growth of the Holocene deposits had reached a new stage such that the hydrodynamics for sediment movement started to be dominated by waves and typhoon induced storms. Analyses of the present-day processes, e.g., Holocene sea level changes, river input to the sea, wave and storm action, upwelling at the shelf breaks, tidal inlet equilibrium, and anthropogenic activities, will help establish a quantitative modeling system to simulate the formation, spatial and temporal distributions, as well as the future development of the sedimentary sequences. Furthermore, the Holocene deposits of Hainan Island contain rich information on the past climate, environmental and ecosystem changes. In order to obtain the information, the various indices, from analyses of grain size, geochemistry, micro-organisms and radioactivity for sediment samples, have been utilized. However, in addition to these indices, information on the processes and mechanisms for the formation of the records is also required; the methodology would be to consider the marine sediment dynamic processes that are responsible for material transport and cycling, the material components of the deposit, storm induced deposition features and morphological evolution of the sedimentary environment.