晚全新世以来澎湖峡谷群东部浊流沉积特征及其成因机制

Turbidite deposition and the controlling mechanism in the eastern Penghu Canyon System since the Late Holocene

  • 摘要: 浊流是南海东北部陆源沉积物通过海底峡谷向深海输送的重要方式。本研究选取澎湖峡谷群东部,位于高屏峡谷与澎湖峡谷下游之间的DZ35-GC21岩芯,综合加速器质谱(AMS)14C测年、沉积物粒度和黏土矿物数据,探讨了1633 cal. aBP以来澎湖峡谷群东部的浊流沉积特征、物质来源、输送过程及其成因机制。结果表明,DZ35-GC21岩芯以黏土质粉砂为主,其次为粉砂,为半深海沉积与浊流沉积交替沉积。岩芯中共识别出63个具有底部侵蚀面与粒度突变的浊流沉积单元,其累计厚度约占岩芯总长40%,表明浊流是该区域沉积演化的重要控制因素。黏土矿物以伊利石和绿泥石为主(平均为89%),且垂向相对含量变化不大,表明晚全新世以来沉积物主要源自台湾西南部河流且供给较为稳定。浊流是驱动澎湖峡谷群东部沉积物源-汇过程的主要机制,同时表层流、南海暖流、中层环流及等深流等多种区域海洋动力也对研究区产生一定的影响。本文进一步将DZ35-GC21岩芯的浊积层频率与相应时期的厄尔尼诺-南方涛动(ENSO)事件频率变化进行对比,结果表明ENSO驱动下的强台风事件频发可能是导致研究区浊流活动增强的关键因素。此外,密集的中-细粒砂质浊积层可能与高屏峡谷下游的横向溢出沉积物持续补给有关。

     

    Abstract: Turbidity currents are a critical mechanism for transporting terrigenous sediments from the northeastern South China Sea to the deep sea via submarine canyons. I This study examines the characteristics, material sources, transport processes, and genetic mechanisms of turbidity current deposits in the eastern Penghu Canyon Group since 1633 cal.aBP, using the DZ35-GC21 core sample located between the Kaoping-Penghu Canyon and the downstream section of the Penghu Canyon Group. The analysis integrates accelerator mass spectrometry (AMS) 14C dating, sediment grain size, and clay mineral data. Core DZ35-GC21 sediments are mainly clayey silts and some silts, representing an intercalation of hemipelagic deposits and turbidites. Sixty-three turbidite units that are divided by basal erosional surfaces and abrupt grain-size shifts, comprised approximately 40% of the total core length, indicating that turbidity currents exerted a major control on sedimentary evolution in this region. Clay mineral assemblages are dominated by illite and chlorite (average 89%), exhibiting minimal downcore variation in relative abundances, suggesting a persistent sediment source of rivers from the southwestern Taiwan throughout the Late Holocene. Turbidity currents were the main driver of the source-to-sink transport processes in the eastern Penghu Canyon System, while various regional oceanic dynamics—including surface currents, the South China Sea Warm Current, mid-depth circulation, internal waves, internal tides, and contour currents—also exerted supplementary influences on the study area. Comparison in turbidite frequency of core DZ35-GC21 with contemporaneous El Niño-Southern Oscillation (ENSO) variability reveals that turbidity current activity was enhanced in the study area, which was likely triggered by increased frequency of intense typhoon events driven by ENSO. Additionally, the dense medium-fine sandy turbidite layers may be related to the continuous supply of transverse overbank deposits downstream of the Gaoping Canyon.

     

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