中全新世福建沿海地区海平面波动:基于NDQK5岩芯介形类化石记录

Mid-Holocene sea-level fluctuation in the Fujian coastal area:Evidence from the ostracod records of the core NDQK5

福建沿海地区第四系较为发育,是研究晚更新世以来相对海平面变化的理想区域。本文以福建宁德NDQK5岩芯中产出的高分辨率介形类化石为研究对象,结合加速器质谱法(accelerator mass spectrometry,AMS)14C和光释光测年技术建立岩芯年代框架,重建了中全新世期间福建沿海地区的相对海平面变化。结果显示,NDQK5岩芯中的介形类化石记录主要分布于4~17.1 m段,对应年代约为8.2~6.9 ka BP。岩芯内共计识别出海相介形类23属26种,根据优势种以及特征种的相对丰度变化特征可将岩芯内的介形类动物群划分为3个组合:①介形类组合A以Bicornucythere bisanensis和Sinocytheridea impressa为主,代表潮下带环境;②介形类组合B以Sinocytheridea impressa和Neomonoceratina delicata为优势种,指示近岸内陆架的沉积环境;③介形类组合C以Sinocytheridea impressa和Loxoconcha ocellifera为主,代表潮间带的沉积环境。基于介形类组合的分布特征,本文推断福建沿海地区海平面约在8.2~7.4 ka BP期间持续上升,并在约7.9~7.4 ka BP区间达到最高;7.4~7.0 ka BP期间海平面下降,随后再次上升。因此,介形类化石记录指示福建沿海地区在全新世高海平面背景下依然存在相对海平面的次一级波动。同时,结合已有福建沿海地区海平面变化驱动机制的研究结果,本研究推断8.2~7 ka BP期间福建沿海地区的海平面变化可能主要受控于冰盖融水;7 ka BP后该地区的海平面波动可能受控于“冰川-水均衡调整”作用。

The Fujian coastal area,with its extensive distribution of Quaternary deposits,offers an ideal location for studying relative sea level changes since the late Pleistocene.In this study,we utilized AMS 14C and optical stimulated luminescence(OSL)dating techniques to analyze the high-resolution ostracod records from core NDQK5,which was obtained from Ningde in Fujian Province.Our objective was to reconstruct the relative sea level changes during the Mid-Holocene in this area.The ostracods found incore NDQK5 were located at a depth interval of 4~17.1 m,corresponding to approximately 8.2~6.9 ka BP We identified twenty-six marine ostracod species belonging to twenty-three genera from the core samples.By analyzing the relative abundance of the main ostracod elements,we identified three distinct ostracod assemblages.Ostracod assemblage A,characterized by the dominance of Bicornucytherebisanensis and Sinocytheridea impressa,indicatesa subtidal zone environment.Assemblage B,with Sinocytheridea impressa and Neomonoceratina delicata asthe dominant species,represents the nearshore inner shelf.Assemblage C,marked by the dominance of Sinocytheridea impressa and Loxoconcha ocellifera,indicates an intertidal zone environment.Our ostracod data reveals a continuous rise in sea level in the Fujian coastal area since approximately 8.2 ka BP,with the sea level reaching its highstand between 7.9 and 7.4 ka BP.Subsequently,a decline in sea level existed during the period of 7.4 to 7.0 ka BP,followed by a minor rise.These findings indicate the presence of several minor fluctuations in sea level during the Holocene sea-level highstand period in the Fujian coastal area.Combining our result with the previous studies,we conclude that the sea level change in the Fujian coastal area was probably influenced by meltwater from the ice sheet during the period of 8.2 to 7 ka BP.However,it is probable that the glacio-hydro isostatic adjustment(GIA)effect played a role in controlling sea level after 7 ka BP.