Testing the English Channel megaflood hypothesis by establishing the stratigraphy, sedimentology and chronology of shelf incision

通过建立陆架切口的地层学、沉积学和年代学来检验英吉利海峡特大洪水假说

• 批准号: NE/F013388/1
• 金额: $ 8.64万
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Training Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF013388%2F1
• 关键词: Testing; English; Channel; megaflood; hypothesis

Recent high-resolution acoustic profiling investigations in the English Channel have identified a distinctive geomorphology that is interpreted to have formed by multiple extreme subaerial discharge events by which the underlying bedrock was incised (Gibbard, 2007; Gupta et al., 2007). Evidence of at least two catastrophic releases from a proglacial lake located in the southern North Sea includes anabranching bedrock channels and terraces, with basal scours and lineations, separated by streamlined islands. Currently, the timing of these megafloods is tied loosely to glacial maxima, thus the first major excavation is estimated around 425 ka, and a reactivation event during a subsequent period of significant glaciation before 180 ka. It is postulated that these floods impacted on the morphology of the English Channel and routeing of Quaternary drainages, hindered faunal migration, influenced water temperature and salinity and, hence, climate in the Atlantic region. The proposed studentship aims to address this present shortcoming in our understanding of the evolution of the English Channel by providing a chronology based on trapped charge dating techniques for the oldest sedimentary record preserved within the incised drainage system and for the overbank deposits laid down during the events. Available seismic and sonar data, calibrated to detailed facies analysis of extensive borehole data (BGS archive and Hanson datasets) will establish a stratigraphic framework for site selection and the strategic collection of new datasets and samples. To establish the chronology of erosional and depositional events a multi-technique approach will be employed: dosimetric dating techniques for the timing of channel-fill and overbank sediment deposition, and granulometric and micro- and macro-palaeontology to derive palaeoenvironmental information. Optical dating will be used for the younger sequences and electron spin resonance (ESR) dating will be used for the older sequences. In addition, deposits from marine incursions will provide minimum ages for incisional events. This chronological and palaeoenvironmental data will prove valuable in assessing the degree of re-activation and incision with respect to relative sea-level history and the known extent of glaciation. Collation and re-analysis of extensive geophysical, stratigraphical and palaeoenvironmental information from the wider southern approaches region will provide the basis for assessing the potential location of the associated deposits of material excavated and transported by the megafloods. These deposits may reside beyond the shelf-edge if timing is coincident with low sea-level stand, but might be located on the outer shelf if flooding was during shelf transgression. This requires the age data to be tied to the established record of relative sea-level, drainage pattern and channel infilling during the Pleistocene and will reveal the environmental constraints on the ponding of western European river discharge in the southern North Sea and its catastrophic release. Research aims: 1. Obtain the ages of fluvial channel incision and the ages of overlying marine sediments in the English Channel using dosimetric dating techniques; 2. Construct a history of channel excavation and fill events for the English Channel coast by integrating chronological, stratigraphical, sedimentological, morphological, palaeoenvironmental and relative sea-level data, with which to test the hypothesis of megaflood events; 3. Provide a model of Pleistocene evolution for the English Channel, focussing on the environmental conditions conducive to catastrophic flooding versus incision due to relative sea-level fall, and therefore the timing of shelf incision and location of sediments resulting from catastrophic drainage. 4. Investigate the linkage between meltwater pulses into the NE Atlantic and the climate system.

最近在英吉利海峡进行的高分辨率声学剖面调查已经确定了一种独特的地貌，该地貌被解释为是由多个极端的陆上放电事件形成的，这些事件切割了底层基岩（Gibbard，2007年; Gupta等人，2007年）。至少有两个灾难性的释放位于北海南部的一个冰前湖的证据包括分支基岩渠道和阶地，与基础冲刷和线理，分开的流线型岛屿。目前，这些大洪水的时间是松散的冰川最大，因此第一次重大挖掘估计约425万年，并在随后的一段时间内显着的冰川180万年前的再激活事件。据推测，这些洪水影响了英吉利海峡的形态和第四纪水系的路线，阻碍了动物群的迁移，影响了水温和盐度，因此影响了大西洋地区的气候。拟议的奖学金的目的是解决这个目前的缺点，在我们的理解英吉利海峡的演变提供了一个年表的基础上捕获的电荷测年技术的最古老的沉积记录保存在下切排水系统和漫滩沉积在事件。现有的地震和声纳数据，校准广泛的钻孔数据（英国地质调查局档案和汉森数据集）的详细相分析，将建立一个地层框架的选址和新的数据集和样本的战略收集。为了确定侵蚀和沉积事件的年代，将采用多种技术方法：确定渠道填充和漫滩沉积物沉积时间的剂量测定法，以及获取古环境信息的粒度和微观及宏观古生物学。光学测年将用于较年轻的序列，电子自旋共振（ESR）测年将用于较老的序列。此外，来自海洋侵入的沉积物将提供切割事件的最低年龄。这些年代和古环境数据将证明对评估相对海平面历史和已知冰川作用范围的再活化和切割程度很有价值。对更广泛的南部引道区域的广泛地球物理、地层和古环境信息进行整理和重新分析，将为评估特大洪水挖掘和运输的相关物质沉积物的潜在位置提供基础。这些存款可能居住超出陆架边缘，如果时间是一致的低海平面的立场，但可能位于外陆架，如果洪水是在陆架海侵。这就需要年龄数据被绑定到更新世期间的相对海平面，排水模式和通道填充的既定记录，并将揭示在北海南部的西欧河流排放的积水及其灾难性的释放的环境约束。研究目的：1.利用剂量测年技术获得英吉利海峡河床下切年龄和上覆海洋沉积物年龄; 2.综合年代学、地层学、沉积学、形态学、古环境学和相对海平面数据，构建英吉利海峡沿岸的河道挖填事件史，并以此检验巨型事件假说; 3.提供一个更新世的英吉利海峡的演变模型，侧重于环境条件有利于灾难性的洪水与切口由于相对海平面下降，因此，时间的货架切口和位置的沉积物造成的灾难性排水。4.调查融水脉冲进入东北大西洋和气候系统之间的联系。