Sedimentary evolution of the Holocene subaqueous clinoform off the Shandong Peninsula in the Yellow Sea
Sedimentary evolution of the Holocene subaqueous clinoform off the Shandong Peninsula in the Yellow Sea
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DOI：
10.1016/j.margeo.2006.10.031
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发表时间：
2007-02
期刊：
影响因子：
2.9
通讯作者：
Jian Liu;Y. Saito;Hong Wang;Zigeng Yang;R. Nakashima
中科院分区：
文献类型：
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作者：
Jian Liu;Y. Saito;Hong Wang;Zigeng Yang;R. Nakashima
黄海山东半岛的末端是一个水下斜坡。斜坡，以前称为山东泥楔，是高达40米厚的近岸和薄向海。自1980年代首次被注意到以来，它的起源一直存在争议。最近在山东半岛东北部近海进行的调查中，获得了覆盖约1700 km的高分辨率浅层地震剖面，并回收了两个穿透斜坡的钻井岩心。通过对28个样品的岩相特征、底栖有孔虫和介形虫的鉴定、粒度测定、矿物成分分析和AMS 14 C测年，揭示了冰后期海平面变化对坡形沉积演化的影响。浅层地震剖面显示，斜坡由三个单元组成：最低地震单元（SU 3，厚度小于2-3 m），显示退积/加积叠加样式，具有近水平的内部反射层，为中间地震单元（SU 2，厚达35 m），显示出一个主要由几个侵蚀面隔开的向海步进反射体的反射图形，以及最高的地震单元（SU 1，最大厚度18 m），具有近平行反射体的加积反射图案。这三个地震单元的底部由不同的侵蚀面界定。对两个岩心的分析表明，斜坡由DU 1、DU 2和DU 3三个沉积单元组成，依次对应SU 1、SU 2和SU 3。根据岩相特征和底栖有孔虫和介形虫组合的分布特征划分了沉积单元。岩芯的矿物成分表明，斜坡的物源主要是黄河源沉积物。AMS 14 C测年表明，DU 3形成于约11.6 - 9.6 cal kyr BP，DU 2形成于约9.6 - 6.5 cal kyr BP，DU 1形成于约11.6 - 9.6 cal kyr BP。6.5卡尔基尔BP。冰消期海侵期间的一些主要的融水脉冲（MWP）事件记录在斜坡地层中，DU 3和DU 2的基底表面/沉积物分别对应于MWP-1B（约）。11.6-11.3 cal kyr BP）和MWP-1C（ca. 9.6-9.2 cal kyr BP）事件，而DU 2主要形成于8.4-8.2 cal kyr融水事件之后。快速百年到几十年规模的洪水事件可能是负责分离的侵蚀表面在SU 2下重叠的内部反射。这种沉积格局由SU 1的加积型向SU 2的外积型的转变，是由于渤海由强的、以往复运动为主的潮流向现代环流的转变，以及6500 calyr BP后高水位期潮流场的减弱。作为沉积物供给、海平面变化和水动力系统之间复杂相互作用的产物，斜坡可以被认为是渤海东部潮汐沉积体系的远端部分，该体系主要来自黄河。
A subaqueous clinoform wraps around the end of the Shandong Peninsula in the Yellow Sea. The clinoform, previously called the Shandong mud wedge, is up to 40 m thick nearshore and thins seaward. Its origin has been controversial since it was first noted in the 1980s. For our recent investigation offshore of the northeastern Shandong Peninsula, high-resolution shallow seismic profiles covering about 1700 km were obtained, and two drilling cores penetrating the clinoform were recovered. We described the lithofacies characteristics, identified benthic foraminifera and ostracoda, measured grain size, analyzed the mineral components of the cores, and obtained AMS14C dates on 28 samples, to decipher the sedimentary evolution of the clinoform in response to postglacial sea-level changes. The shallow seismic profiles show that the clinoform comprises three units: a lowermost seismic unit (SU 3, less than 2–3 m thick) showing a retrogradational/aggradational stacking pattern with subhorizontal internal reflectors, a middle seismic unit (SU 2, up to 35 m thick) showing a prograding reflection pattern with mostly seaward-stepping reflectors separated by several erosive surfaces, and an uppermost seismic unit (SU 1, maximum thickness 18 m) exhibiting an aggradational reflection pattern with subparallel reflectors. The three seismic units are bounded on the bottom by distinct erosion surfaces. Analyses of the two cores indicate that the clinoform comprises three depositional units, DU 1, DU 2, and DU 3 in descending order, corresponding respectively to SU 1, SU 2, and SU 3. The depositional units are distinguished by lithofacies characteristics and the downcore distributions of benthic foraminiferal and ostracod assemblages. Mineral components of the cores suggest that the clinoform's provenance is predominantly Yellow River-derived sediments. AMS14C dates suggest that DU 3 was formed from about 11.6 to 9.6 cal kyr BP, DU 2 from 9.6 to 6.5 cal kyr BP, and DU 1 after ca. 6.5 cal kyr BP. Some major meltwater pulse (MWP) events during the deglacial transgression were registered in the clinoform stratigraphy, with the basal surfaces/sediments of DU 3 and DU 2 corresponding respectively to MWP-1B (ca. 11.6–11.3 cal kyr BP) and MWP-1C (ca. 9.6–9.2 cal kyr BP) events, and with DU 2 being largely formed after the 8.4–8.2 cal kyr meltwater event. Rapid centennial- to multidecadal-scale flooding events were presumably responsible for the erosive surfaces separating the downlapping internal reflectors in SU 2. The change of depositional pattern from progradational in SU 2 to aggradational in SU 1 is attributed to a change from strong, dominantly to-and-fro tidal currents to the modern circulation in the Bohai Sea as well as to the weakening of the tidal-current field during the highstand after about 6500 cal yr BP. As a product of complex interactions among sediment supply, sea-level changes, and hydrodynamic regimes, the clinoform can be regarded as the distal part of the tidal depositional system in the eastern Bohai Sea, which was largely derived from the Yellow River.