Sedimentological and chronological aspects of the Younger Dryas : Holocene transition record in southern Finland and northern Baltic
Sedimentological and chronological aspects of the Younger Dryas : Holocene transition record in southern Finland and northern Baltic
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新仙女木期的沉积学和年代学方面：芬兰南部和波罗的海北部的全新世过渡记录
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发表时间：
2012
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通讯作者：
O. Hyttinen
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作者：
O. Hyttinen
在这项研究中，对波罗的海冰湖（BIL）排水前后芬兰南部波罗的海盆地和芬兰湾沉积的不同类型的沉积物进行了检查。目的是更好地了解近海、浅水和陆上海滩环境的沉积变化，为排水事件提供独立的年龄控制，并测试树木年代互相关方法对 varve 粘土数据的适用性。该研究包括来自近海的声学探测数据、一个近海海洋沉积岩芯、与 BIL/Yoldia 海过渡沉积物相关的六个露头，以及 Sauramo 原始 varve 测量的数字化版本。在波罗的海盆地地区，BIL 的排水发生在新仙女木期寒冷事件即将结束时。水位突然下降 25-28 m 最初被选为芬兰 varve 粘土年代学的零基准，但“关键层位”概念没有得到进一步发展，其年代地层联系和重要性仍不清楚。自 20 世纪初以来，每年层压或变化的沉积物已成功用于构建晚更新世全新世冰退缩年表和冰边缘地层测年。这也适用于芬兰。由于新仙女木期期间冰退缩速度缓慢和冰锋振荡，将萨尔保塞尔卡地区的冰层年代学关联起来很困难。因此，年代学中较早的部分，即早于排水事件的部分，与全新世 varve 系列仅存在松散的联系。在近海环境（水深> 40 m）中，水位下降引发泥石流，侵蚀并重新沉积较旧的、变化的沉积物，形成明显的变形单元。在波罗的海北部和芬兰湾，沉积了厚达 4 m 的不连续沉积物，均质粘土带有旋转塌陷和变形的痕迹。在约克拉 (Jokela)，Sauramo (1923) 首次描述了原始的零瓦维，观察到含有变形的沙荚和层的均质粘土单元。该单位对应于 BIL 中水位突然下降而形成的零压力。在浅水环境（水深< 40 m），泥沙沉积物停止沉积，由于快速回归，海岸过程开始运行，在此期间形成了渐进的海洋阶地。盐水入侵芬兰南部地区的第一个迹象是在 BIL 排水后约 100 年。在新出现的土地上，裸露的沉积物很容易遭受风蚀。第二萨尔保塞尔卡地区出现的大量覆盖砂（“拉米黄土”）传统上被归因于快速沙尘暴类型的沉积。然而，也有迹象表明这些矿床的非风成起源。形态清晰的沿海阶地与最古老的约尔迪亚海平面 (YI) 有关，约尔迪亚海平面是在 BIL 排水之后形成的。第一 Salpausselka 区域内的其中一个阶地是通过光激发光 (OSL) 方法测年的。这是芬兰第一次直接进行 YI 级别的约会，年龄为
In this study, different types of sediments deposited in the Baltic Sea Basin in Southern Finland and the Gulf of Finland before and after the Baltic Ice Lake (BIL) drainage were examined. The aim was to gain a better understanding of changes in sedimentation in offshore, shallow water and onshore beach environments, to provide an independent age control for the drainage event, and to test the applicability of dendrochronological cross-correlation methods to varve clay data. The study consisted of acoustic sounding data from offshore, one offshore marine sediment core, six outcrops related to the BIL/Yoldia Sea transition sediments, and a digitized version of original varve measurements by Sauramo. In the Baltic basin area, the drainage of the BIL occurred close to end of the Younger Dryas cold event. This sudden 25–28 m fall in water level had originally been chosen as the zero datum for the Finnish varve clay chronology, but the "key horizon" concept was not developed further and its chronostratigraphical connection and importance remain unclear. Since the early 20th century annually laminated, or varved, sediments have been used succesfully in constructing Late Pleistocene Holocene ice retreat chronologies and in dating ice marginal formations. This also applies to Finland. Correlating varve chronnologies across the Salpausselka zone is difficult, due to slow ice retreat rates and ice front oscillations during the Younger Dryas period. Therefore, the older part of the chronology, which pre-dates the drainage event, is only loosely connected to Holocene varve series. In offshore environment (water depth > 40 m), the falling water level triggered debris flows, which eroded and redeposited older, varved sediments creating a distinct deformation unit. In the northern Baltic proper and Gulf of Finland, up to 4 m thick, discontinuous deposits of homogeneous clay bearing traces of rotational slump and deformation were deposited. In Jokela, where the original zero varve was first described by Sauramo (1923), a homogeneous clay unit containing deformed sandy pods and layers was observed. This unit corresponds to a zero varve which was formed as a consequence of a sudden water level drop in the BIL. In shallow water environment (water depth < 40 m), deposition of varved sediments ceased and, as a result of rapid regression, shore processes started to operate, during which progressive marine terraces were formed. The first signs of saline incursion into southern Finnish area were ca 100 varve years after the BIL drainage. On newly emerged land, exposed sediments were prone to wind erosion. The occurrence of massive cover sands, "Lammi loess", in the Second Salpausselka area has traditionally been attributed to rapid dust-storm type of deposition. However, there are also indications of non-aeolian origin of these deposits. Morphologically well-defined coastal terraces are related to the oldest Yoldia Sea level (YI), which was developed after the BIL drainage. One of these terraces within the First Salpausselka zone was dated by optically stimulated luminescence (OSL) method. This is the first direct YI-level date in Finland and it yielded ages of