福建晋江海岸带老红砂多期发育模式初步研究

我国东南沿海广泛分布的老红砂是海岸环境演变的产物。通过对福建晋江海岸带科任(KR)老红砂剖面加密采样进行OSL测年和粒度分析,初步确定了老红砂发育期次及其形成时代。以OSL测年值为基础,在统一的时间标尺上综合对比全球海平面和东亚季风变化序列,探讨了老红砂发育模式及其环境意义。研究表明: 科任老红砂主要是晚更新世末次间冰期以来发育的,主要发生在约125~9ka期间,可以划分为6个沉积期,分别为125~115ka,105~97ka,84~74ka,61.5~52.0ka,39~29ka和15~9ka,期间可能存在至少5次明显的沉积间断。结合台湾海峡的水深变化特点分析,当海平面低于-70m时,由于研究区远离古海岸线,因而不可能有海岸风沙沉积; 当海平面低于-15m高于-70m时,受到较强冬季风吹扬搬运海滩砂再沉积过程的影响,研究区可能有海岸风沙发育; 当海平面高于-15m时,古今海岸线位置接近,在各种强度的冬季风作用下,研究区都会有海岸风沙广泛发育,并经历强烈的红化作用。即,科任老红砂主要发育于晚更新世末次间冰期以来气候暖湿的高海面和较高海面时期,而在末次冰期的低海面时期多次缺失海岸风沙沉积,尤其是末次盛冰期(LGM)的最低海面时期,现代海岸带所在区域老红砂发生沉积间断。

A PRIMARY RESEARCH ON MULTIPHASE DEVELOPMENT PATTERN OF "OLD RED SAND" IN JINGJIANG COAST OF SOUTH EAST FUJIAN

Coastal aeolian sand is a common aeolian geomorphology in the sandy coastal,which recorded the evolution process of the aeolian landscape system,and reflect the complex interaction among land surface,atmosphere and ocean.The southeast coast of Fujian exhibits a number of Late Pleistocene coastal aeolian dunes so called "Old Red Sand" in China,This sand sediment,in the form of single or multiple sand embankments,consists of slightly cemented,medium to fine grained sands,and is characterized by its colors of red(10R4/8),brown red(2.5YR4/8),light reddish brown(5YR5/8),dark yellowish orange(5YR/5/8),has continuous distribution along the coastal plains,or on hillslopes near the coastline,where the sediment record potentially provides important evidence for the palaeoenvironmental history of eustatic change and coastal dunefield activity.The lack of direct dating of these "Old Red Sand",however,has veiled relationships between coastal aeolian sand deposition,sea level,and other controlling factors.In this paper,quartz single aliquot regenerative Optically-Stimulated Luminescence(OSL)dating with high resolution sampling was applied to the Late Pleistocene KR "Old Red Sand"(24°34'56.3″N,118°39'14.1″E) at the Jingjiang coast,south East Fujian.Based on the OSL chronology and compare to global sea-level change and East Asian monsoon change sequence,combined with grain size character,we reveal the periods of "Old Red Sand" deposition and their formation ages.The OSL age of the 26 samples range from 125ka to 12ka shows that KR "Old Red Sand" has existed since the last interglacial,six period of costal aeolian sand activity can be division,respectively in 125~115ka,105~97ka,84~74ka,61.5~52.0ka,39~29ka,and 15~9ka,and the OSL age shows that the "Old Red Sand" deposition existed five obvious hiatus.These reveal that the KR "Old Red Sand" deposition mainly occurred in relation to the sea-level highstands,but lower sea-level of Last Glacial Maximum(LGM)have nondeposition.May be affected by the strong winter monsoon,which bring beach sand to coastal area deposition,so "Old Red Sand" deposition also occurred during the secondary low sea-level in the high sea-level period.According to the depth variation of the Taiwan Strait,and global sea-level change sequence,it would appear that a sea level of ca.-70m relative to the present was the threshold for the coastal aeolian sand activation and "Old Red Sand" deposition.When the sea level lower than ca.-70m,coastal aeolian sand activation is restricted due to longer sediment transport distances and decreased sediment supply; When the sea-level higher than ca.-15m,coastal aeolian sand and the "Old Red Sand" deposition under strong or weak winter monsoon all can form,but mainly formed at times of a descent stage in the sea-level highstands.When the sea-level lower than ca.-15m and higher than ca.-70m,the coastal aeolian sand deposition of the study area must have a powerful winter monsoon.