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

最近在英吉利海峡进行的高分辨率声学剖面调查发现了一种独特的地貌，据解释，这种地貌是由多次极端的地下放电事件形成的，其下层基岩被切割(Gibbard，2007；Gupta等人，2007)。位于北海南部的一个冰川湖至少发生了两次灾难性的泄漏，证据包括一条基岩沟渠和阶地分叉，底部有冲刷和线条，由流线型岛屿隔开。目前，这些大洪水的发生时间与冰川极大值有松散的联系，因此第一次重大挖掘估计在425ka左右，并在180ka之前的随后的显著冰期期间发生重新激活事件。据推测，这些洪水影响了英吉利海峡的形态和第四纪排水沟的路线，阻碍了动物的迁徙，影响了水温和盐度，从而影响了大西洋地区的气候。拟议的学生身份旨在解决目前我们对英吉利海峡演变的理解中的这一缺陷，提供基于截断排水系统内保存的最古老沉积记录的陷阱电荷测年技术的年表，以及事件期间沉积的岸上沉积。现有的地震和声纳数据，经过大量钻孔数据(BGS档案和Hanson数据集)的详细相分析，将为选址和战略收集新的数据集和样本建立一个地层框架。为了建立侵蚀和沉积事件的年代学，将采用多种技术方法：用于河道充填和漫滩沉积时间的剂量测年技术，以及用于获得古环境信息的颗粒测量和微观和宏观古生物学。较年轻的序列将使用光学测年，较老的序列将使用电子自旋共振(ESR)测年。此外，来自海洋入侵的沉积物将提供切割事件的最低年龄。这些年代学和古环境数据将被证明在评估相对海平面历史和已知冰川程度的重新激活和切割程度方面具有价值。对更广泛的南部引航区广泛的地球物理、地层和古环境信息进行整理和重新分析，将为评估大洪水挖掘和运输的相关物质矿藏的潜在位置提供依据。如果时间与低海平面一致，这些沉积物可能位于陆架边缘之外，但如果洪水发生在陆架海侵期间，这些沉积物可能位于陆架外部。这需要将年龄数据与更新世期间相对海平面、排水模式和河道充填的既定记录联系起来，并将揭示对西欧河流在北海南部积水及其灾难性释放的环境限制。研究目的：1.利用剂量测年技术获得英吉利海峡河道切割年龄和上覆海洋沉积物年龄；2.综合年代、地层、沉积学、地貌、古环境和相对海平面数据，建立英吉利海峡沿岸河道开挖和充填历史，验证大洪水事件假说；3.提供英吉利海峡更新世演化模型，重点研究相对海平面下降导致灾难性洪涝和切割的环境条件，从而确定陆架切割的时间和沉积物的位置。4.研究东北大西洋的融水脉冲与气候系统之间的联系。

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.