Post‐depositional alteration of shallow‐marine tsunami‐induced sand layers: A comparison of recent and ancient tsunami deposits, Onagawa Bay, northeastern Japan

Seike, Koji; Kobayashi, Gorô; Kogure, Kazuhiro

doi:10.1111/iar.12174

Cited by 18 publications

(13 citation statements)

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“…The complexity of drawing the topmost limit of L1 and L2 events might be explained by the fact that tsunami deposits can be modified or removed by subsequent physical (Shinozaki et al, 2015;Tamura et al, 2015) and/or biological processes (Seike et al, 2016). Indeed, after the 2011 tsunami some offshore stations were monitored, revealing that the recolonization by benthic organisms began within several months after the event (Seike et al, 2013), and post-depositional biogenic alteration continued over much longer timescales (Seike et al, 2016) concealing the topmost limit of the Tohoku-oki deposit (Seike et al, 2017). Furthermore, even if the Bh horizon represents an important stratigraphic signature recognizable all along the shelf (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…After the 2004 Indian Ocean and 2011 Tohoku-oki tsunamis, offshore surveys were conducted to collect material, mainly from the inner continental shelf [0 to 30 m below sea level (bsl)] and over the shelfbreak (>100 m bsl). These studies highlighted that in the marine realm the tsunami-related units are subjected to the action of currents, waves and bioturbation that occur immediately after their deposition Sakuna et al, 2012;Ikehara et al, 2014;Tamura et al, 2015;Yoshikawa et al, 2015;Seike et al, 2017). Thus, it is often not easy to recognize offshore tsunami deposits even when they are related to recent events or with a precise age control (Toyofuku et al, 2014) because of their potentially low preservation in shallow water due to reworking and transport by currents, waves (Weiss & Bahlburg, 2006) and gravity flows which disperse sediment on the continental shelves.…”

Section: Introductionmentioning

confidence: 99%

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New coring study in Augusta Bay expands understanding of offshore tsunami deposits (Eastern Sicily, Italy)

et al. 2019

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Tsunami deposits present an important archive for understanding tsunami histories and dynamics. Most research in this field has focused on onshore preserved remains, while the offshore deposits have received less attention. In 2009, during a coring campaign with the Italian Navy Magnaghi, four 1 m long gravity cores (MG cores) were sampled from the northern part of Augusta Bay, along a transect in 60 to 110 m water depth. These cores were taken in the same area where a core (MS06) was collected in 2007 about 2·3 km offshore Augusta at a water depth of 72 m below sea level. Core MS06 consisted of a 6·7 m long sequence that included 12 anomalous intervals interpreted as the primary effect of tsunami backwash waves in the last 4500 years. In this study, tsunami deposits were identified, based on sedimentology and displaced benthic foraminifera (as for core MS06) reinforced by X‐ray fluorescence data. Two erosional surfaces (L1 and L2) were recognized coupled with grain‐size increase, abundant Posidonia oceanica seagrass remains and a significant amount of Nubecularia lucifuga, an epiphytic sessile benthic foraminifera considered to be transported from the inner shelf. The occurrence of Ti/Ca and Ti/Sr increments, coinciding with peaks in organic matter (Mo incoherent/coherent) suggests terrestrial run‐off coupled with an input of organic matter. The L1 and L2 horizons were attributed to two distinct historical tsunamis (ad 1542 and ad 1693) by indirect age‐estimation methods using 210Pb profiles and the comparison of Volume Magnetic Susceptibility data between MG cores and MS06 cores. One most recent bioturbated horizon (Bh), despite not matching the above listed interpretative features, recorded an important palaeoenvironmental change that may correspond to the ad 1908 tsunami. These findings reinforce the value of offshore sediment records as an underutilized resource for the identification of past tsunamis.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

New coring study in Augusta Bay expands understanding of offshore tsunami deposits (Eastern Sicily, Italy)

et al. 2019

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“…海啸和风暴潮是将近海沉积大规模搬运至海岸带的主要事件 [24,25] . 对现代海啸和风暴潮的研究已经证明这类灾害能够在海岸带形成延伸至内陆几百米至几千米、厚度达几十厘米的岸上沉积 [24,26] , 其物质来源包括近岸海底沉积和海滩沉积 [7,27] . 在排除河流作用之后, 可以确认宋井和九溪澳的A, D两个沉积层是约一千年前由海啸或风暴潮形成的产物.…”

Section: 材料与方法unclassified

Nan'ao, an archaeological site of Song dynasty destroyed by tsunami

Yang¹,

Sun²,

Yang³

et al. 2018

Chin. Sci. Bull.

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“…They are well preserved as anomalous coarse layers in peat or mud deposits typical of low-energy terrestrial or shallow-seabed environments (Atwater, 1992;Bourgeois et al, 1988;Dawson & Stewart, 2007;Monecke et al, 2008;Sawai et al, 2015;Seike et al, 2016Seike et al, , 2017a. Although tsunami deposits might be modified or obliterated by subsequent physical (Shinozaki et al, 2015;Szczuci nski, 2012;Tamura et al, 2015) and/or biological processes (Seike et al, 2016), they can remain for long periods in calm coastal embayments (Seike et al, 2017a). This indicates that tsunamis have semipermanent effects on the seafloor topography and the grain-size composition of seafloor sediments; in other words, tsunami sedimentation is a short-term phenomenon that has a major effect on the benthic environment over the longer term.…”

Section: Introductionmentioning

confidence: 99%

Lasting Impact of a Tsunami Event on Sediment‐Organism Interactions in the Ocean

et al. 2018

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Although tsunami sedimentation is a short‐term phenomenon, it may control the long‐term benthic environment by altering seafloor surface characteristics such as topography and grain‐size composition. By analyzing sediment cores, we investigated the long‐term effect of the 2011 tsunami generated by the Tohoku Earthquake off the Pacific coast of Japan on sediment mixing (bioturbation) by an important ecosystem engineer, the heart urchin Echinocardium cordatum. Recent tsunami deposits allow accurate estimation of the depth of current bioturbation by E. cordatum, because there are no preexisting burrows in the sediments. The in situ hardness of the substrate decreased significantly with increasing abundance of E. cordatum, suggesting that echinoid bioturbation softens the seafloor sediment. Sediment‐core analysis revealed that this echinoid rarely burrows into the coarser‐grained (medium‐grained to coarse‐grained) sandy layer deposited by the 2011 tsunami; thus, the vertical grain‐size distribution resulting from tsunami sedimentation controls the depth of E. cordatum bioturbation. As sandy tsunami layers are preserved in the seafloor substrate, their restriction on bioturbation continues for an extended period. The results demonstrate that understanding the effects on seafloor processes of extreme natural events that occur on geological timescales, including tsunami events, is important in revealing continuing interactions between seafloor sediments and marine benthic invertebrates.

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Post‐depositional alteration of shallow‐marine tsunami‐induced sand layers: A comparison of recent and ancient tsunami deposits, Onagawa Bay, northeastern Japan

Cited by 18 publications

References 7 publications

New coring study in Augusta Bay expands understanding of offshore tsunami deposits (Eastern Sicily, Italy)

New coring study in Augusta Bay expands understanding of offshore tsunami deposits (Eastern Sicily, Italy)

Nan'ao, an archaeological site of Song dynasty destroyed by tsunami

Lasting Impact of a Tsunami Event on Sediment‐Organism Interactions in the Ocean

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