Holocene Diatom Assemblages in Takagami Lowland, Central Part of Choshi Peninsula, and its Relation to Changes of Sea-level
Holocene Diatom Assemblages in Takagami Lowland, Central Part of Choshi Peninsula, and its Relation to Changes of Sea-level
复制标题
铫子半岛中部高神低地全新世硅藻组合及其与海平面变化的关系
DOI：
10.4116/jaqua.24.125
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发表时间：
1985
期刊：
影响因子：
--
通讯作者：
K. Kashima
中科院分区：
文献类型：
--
作者：
K. Kashima
作者对朝鲜半岛中部高上低地全新世沉积物中的138个硅藻化石组合进行了观察。高上低地全新世沉积物可分为5个硅藻组合带（图8）。每个区域的特征可以描述如下。I区（-15米--10米）淡水物种占优势，占60%以上。但鲜咸物种和海洋物种可以一起观察到。海洋物种的比例向上层增加。优势种为披针沙沟藻、胎座卵形藻、舟形藻，均生活在淡水池塘、湖泊和河流中。Ⅱ区（-10米--2.5米）海洋物种占优势，占90%以上。优势种为偏心海链藻（Thalassiosira excentrica）、条纹小环藻（Cyclotella striata）和波状辐鳍藻（Actinoptychus undulatus），均为浮游生物，生活于内湾和大洋。Ⅲ区（-2.5米-3.5米）以海洋生物为主，占90%以上。但以生活在多盐泻湖中的盾卵形藻为优势种。TR区（3.5米-4.7米）TR区可以在Loc. 1、Loc。6.该区是III区到IV区的过渡区。寡盐泻湖中的赤杆藻是优势种。Ⅳ区（3.5m-10m）淡水种类占优势，占90%以上。海洋生物无法观察到。优势种为微小曲壳藻、脆杆藻、短纹脆杆藻和颗粒直链藻，均生活在淡水池塘和湖泊中。高上低地的古环境演替如图9所示。大约8000 - 10000年. B.P.海侵开始，开始形成淹没谷（I）。由于海侵的迅速，淹没谷一直扩展到6,000y.B.P.（II）。大约5500 - 6000年. B.P.，在淹没谷东部形成了海滩脊，使该区的沉积环境由内湾转变为多盐泻湖（Ⅲ）。大约5,000年BP高上低地中、东部形成淡水沼泽，未发生第二次海侵（IV-1）。在西北部，直到约3,000y.B.P.（IV-2），风暴潮频繁地将含有贝壳碎片和海洋物种硅藻瓣的海砂沉积在淡水沼泽上。
The author observed fossil diatom assemblages of 138 samples of Holocene deposits in Takagami Lowland, central part of the Choshi Peninsula. The Holocene deposits in Takagami Lowland can be divided into 5 zones of diatom assmeblages (Fig. 8). The character of each zone can be described as follows. Zone I (-15m--10m) Fresh-water species are dominant and comprise more than 60%. But fresh-brackish species and marine species can be observed together. A ratio of marine species increases toward upper horizon. Dominant species are Achannthes lanceolata, Cocconeis placentula, Navicularadiosa, all of which live in fresh-water pond, lake and river. Zone II (-10m--2.5m) Marine species are dominant and comprise more than 90%. Dominant species are Thalassiosira excentrica, Cyclotella striata, Actinoptychus undulatus, all of which are planktonic and live in inner bay and ocean. Zone III (-2.5m-3.5m) Marine species are dominant and comprise more than 90%, too. But Cocconeis scutellum, which lives in polyhaline lagoon, is dominant. TR Zone (3.5m-4.7m) TR Zone can be observed in Loc. 1 and Loc. 6. This zone is a transitive zone from Zone III to Zone IV. Rhopalodia gibberula, which lives in oligohaline lagoon, is dominant. Zone IV (3.5m-10m) Fresh-water species are dominant and comprise more than 90%. Marine species cannot be observed. Dominant speceis are Achnanthes minutissima, Fragilaria construens, Fragilaria brevistriata, Melosira granulata, all of which live in fresh-water pond and lake. The paleo-environmental succession in Takagami lowland is shown in Fig. 9. About 8,000-10,000y.B.P., marine transgression started and a drowned valley began to be formed (I). Due to rapid transgression, the drowned valley was spread widely till 6,000y.B.P. (II). About 5,500-6,000y.B.P., the beach ridge was formed in the eastern part of this drowned valley, so that the depositional environment of this area was changed from inner bay to polyhaline lagoon (III). About 5,000y.B.P., in the middle and eastern part of Takagami lowland fresh-water marsh was formed, and a second transgression did not happen (IV-1). In the northwestern part, marine sand with shell fragments and diatom valves of marine species were deposited frequently on the freshwater marsh by storm surges till about 3,000y.B.P. (IV-2).