Storm, rogue wave, or tsunami origin for megaclast deposits in western Ireland and North Island, New Zealand?
Storm, rogue wave, or tsunami origin for megaclast deposits in western Ireland and North Island, New Zealand?
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爱尔兰西部和新西兰北岛巨碎屑沉积物的风暴、狂潮或海啸起源？
DOI：
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发表时间：
2017
影响因子：
11.1
通讯作者：
P. Ryan
中科院分区：
文献类型：
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作者：
J. Dewey;P. Ryan
意义地质记录中的方石英矿床的来源存在争议。许多人认为，超过30吨的巨石是海啸的特征。我们将两个这样的沉积物与超过这个重量的巨石进行了比较和对比：新西兰中新世的海啸和爱尔兰西部安纳赫德的今天的巨石。结合野外资料、历史资料和海洋资料，我们认为后者是一种悬崖顶风暴沉积。数值模拟表明，这种CTSD中巨石的重量不仅反映了风暴波的高度，也是其形状的函数。在爱尔兰西部，风暴波的高度可能超过60米。我们回顾了区分这两个矿床的特征。根据爱尔兰西北部Annagh Head现今的前滨和新西兰下中新统Matheon组，研究了方英石矿床的成因，以解决其成因的争议，并对比和比较海啸和风暴的沉积。现场数据显示，马西森组含有超过140吨的巨石，是由一场12至13米高的海啸产生的，海啸的周期约为1小时。Annagh Head的巨石超过50吨，其来源存在争议。我们结合海洋、历史和现场数据，认为这是一个悬崖顶风暴沉积(CTSD)。建立了CTSD的数值模型，指出在将流体动力学方程应用于此类沉积物时，除考虑密度和尺寸外，还应考虑巨石的形状。该模型还预测，东北大西洋风暴能够产生巨石，当仅考虑大小时，这些巨石不能与海啸区分开来。我们回顾了识别这两个矿床成因的特征。
Significance The origin of boulderite deposits in the geological record is controversial. Many argue that boulders weighing over 30 tonnes characterize tsunamites. We compare and contrast two such deposits with boulders exceeding this weight: a tsunamite from the Miocene of New Zealand and a present-day boulderite at Annagh Head, western Ireland. Combining field, historical, and oceanographic data, we argue that the latter is a cliff-top storm deposit (CTSD). Numerical modeling shows that the weight of a boulder in such CTSDs does not just reflect storm wave height, which can be over 60 m in western Ireland, but is also a function of its shape. We review the characteristics that distinguish these two deposits. The origins of boulderite deposits are investigated with reference to the present-day foreshore of Annagh Head, NW Ireland, and the Lower Miocene Matheson Formation, New Zealand, to resolve disputes on their origin and to contrast and compare the deposits of tsunamis and storms. Field data indicate that the Matheson Formation, which contains boulders in excess of 140 tonnes, was produced by a 12- to 13-m-high tsunami with a period in the order of 1 h. The origin of the boulders at Annagh Head, which exceed 50 tonnes, is disputed. We combine oceanographic, historical, and field data to argue that this is a cliff-top storm deposit (CTSD). A numerical model for CTSDs is developed which indicates that boulder shape in addition to density and dimensions should be taken into account when applying hydrodynamic equations to such deposits. The model also predicts that the NE Atlantic storms are capable of producing boulderites that, when size alone is considered, cannot be distinguished from tsunamites. We review the characteristics that identify the origins of these two deposits.