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Marine Geology
Elsevier Science B.V.
Marine Geology

Elsevier Science B.V.

0025-3227

Marine Geology/Journal Marine GeologySCIISTPAHCIEI
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    Reply to comment on, "Sediment budget and morphological change in the Red River Delta under increasing human interferences" by ND Ve, D. Fan, BV Vuong and TD Lan [Marine Geology 431 (2021), 106,379]

    Fan, DaiduDac Ve, NguyenVan Vuong, BuiLan, Tran Dinh...
    5页
    查看更多>>摘要：Anh (2021) asserts that the sediment budget model by Ve et al. (2021) of the subaqueous Red River Delta (RRD) is inaccurate because of some fundamental flaws in the DEM analysis and budget estimation. In fact, bathymetric data from the two earliest charts have been validated with data from a survey carried out over a short time span (1927-1930) and a linear semi-variogram model used to do the kriging interpolation. Different grid cell sizes have a negligible effect on the DEM analysis, and the effect of relative sea-level rise has been ruled out by normalization of bathymetrical data from sequential charts to a common tidal datum. Furthermore, the estimation of the amount of deposited sediment on tidal flats is correct, although a typo of sediment volume unfortunately yielded a wrong value. We can thus confirm that the data in the sediment budget model of Ve et al. (2021) are reliable. The sediment budget model can be improved by full consideration of sediment from source to sink processes as suggested by Anh (2021). We therefore refine the model by considering river bedload and sand mining in the RRD in the sediment input item, and separate the subtidal RRD into three subzones to calculate their average depositional/erosional sediment volume and mass. In the revisited model, a total of 54.7 Mt./yr is inferred to be deposited in the subaqueous RRD from the intertidal flats to the delta-front slope, of which 75.3% and 24.7% are conceivably sourced by the Red River and eroded from the prodelta and offshore shelf, respectively. However, the controlling mechanism of secular erosion at the prodelta and offshore shelf is so far not well known, and this will need to be investigated in the future.
      原文链接:
    • NSTL
    • Elsevier

    A multiproxy reconstruction of the Late Pleistocene-Holocene paleoenvironment: New insights from the NW Black Sea

    Vasiliu, DanLupascu, NalianaMelinte-Dobrinescu, MihaelaIon, Gabriel...
    19页
    查看更多>>摘要：We provide new data on the Black Sea evolution during the preconnection and reconnection stages with the Mediterranean, based on sedimentology, geochemistry, calcareous nannoplankton and ostracods analysis, in 13 cores placed between 141 m and 1315 m water depths. Unit 1 - The Coccolith Mud, Unit 2 - The Sapropel Mud and Unit 3 - The Lacustrine Lutite, including red-brownish depositional intervals, were identified in all studied deep-water cores. These units are not present in a shallow setting, i.e., above 166.7 m water depth, being replaced by sandy levels and shell debris. The red-brownish layers are interpreted as hyperpycnites, but some of the red successions show turbidite features, especially the ones situated on canyon sides, at a water depth below 600 m. In the oldest intercepted Unit 3 of the Neoeuxinian lake, CaCO3 values are constantly low, but towards the top of this unit they show two distinct peaks, interpreted as signals of Bulling-Allerud and Preboreal interstadials. In between, a significant decrease in CaCO3 values, linked to the setting of the Younger Dryas, is coincident in the deep cores with diatom blooms and high frequency of ostracods related to cooler waters. The scarce but continuous occurrence of Emiliania huxleyi nannoplankton species from the top of Unit 3 indicates that the salinity was at least 10-11 parts per thousand prior the Sapropel Mud deposition and increase at a least 17 parts per thousand within the lower part of Unit. 2. In the same interval, the Ponto-Caspian ostracods are still present. The Mediterranean ostracods consistently occur from the top of Unit 2, when bottom water salinity reached values for allowing their survival. The first bloom of E. huxleyi is placed at the base of Unit 2, where coccolith laminae occur, while the second bloom is placed in Unit 1 that contains exclusively Mediterranean ostracods and consistent assemblages of benthonic foraminifers, similar with the ones present today.
      原文链接:
    • NSTL
    • Elsevier

    Oceanic passage of hurricanes across Cay Sal Bank in The Bahamas over the last 530 years

    Winkler, Tyler S.van Hengstum, Peter J.Donnelly, Jeffrey P.Wallace, Elizabeth J....
    18页
    查看更多>>摘要：Islands across the Bahamian Archipelago have been devastated by five major hurricanes from 2010 to 2020 CE, including Category 5 Hurricane Dorian in 2019 that inundated parts of Abaco and Grand Bahama with up to 4 m of surge, killing 84 people and leaving >245 others missing. Up to 1 m relative sea-level rise is estimated for The Bahamas by 2100 CE, which could enhance flooding from weaker storms (<Category 3) in low-lying coastal areas. Problematically, Bahamian hurricane activity is highly spatially-heterogenous over the last 170 years, meaning that long-term regional hurricane frequency remains poorly constrained, especially for weaker Category 1-2 events that are less-likely to be detected by most sediment-based paleo-hurricane reconstructions. We present a 530-year record of hurricane passage from Hine's Blue Hole on Cay Sal Bank, The Bahamas. Hine's Hole has an accumulation rate of 2-3.2 cm/yr, making it among the highest-resolution hurricane reconstructions to date. Unlike many paleo-hurricane reconstruction sites, Hine's Hole is not surrounded by coastal landmasses that can dampen currents and waves produced by hurricanes, so it archives most >= Category 1 hurricanes passing within 115 km during the 170-year instrumental record (1850 CE-present) and may also document intense tropical or winter storms. Hine's Hole archives similar to 16 intense storms per century from 1850 to 2016 CE, but documents three periods from 1505 to 1530 CE, 1570 to 1620 CE, and similar to 1710 to 1875 CE with over twice as many intense storms per century. These active periods correspond to other high-resolution reconstructions from the Bahamian Archipelago and Florida Keys, but the magnitude of the increase is much higher given that Hine's Hole archives evidence of weaker and more distal storms. As such, this reconstruction provides unprecedented insight into changes in hurricane activity within the pre-industrial climate system and demonstrates that recurrence intervals based on the 170-year instrumental record can severely underestimate the threat hurricanes pose certain localities.
      原文链接:
    • NSTL
    • Elsevier

    Structural controls on slope evolution and sediment dispersal pathways along the northern Tanzania continental margin, western Indian Ocean

    Kroon, DickUnderhill, John R.Stagna, Marina DottoreMaselli, Vittorio...
    17页
    查看更多>>摘要：In this study, we investigate the tectonic and stratigraphic evolution of the northern Tanzania margin (western Indian Ocean) to provide new insights on the structural drivers governing the formation of Zanzibar and Pemba islands. Using 2D seismic reflection profiles and exploration wells, we have reconstructed the evolution of the submarine drainage network throughout the last 30 Myr, from the Oligocene to recent times, providing a tape-recorder with which we determine the different tectonic events that led to the eventual subaerial exposure of the islands. In detail, we observe a decrease in the number of slope canyon-channel systems during the lower-middle Miocene offshore Pemba Island that we interpret to represent the initial uplift of the island: tectonic deformation of the seafloor impeded up-dip to down-dip sediment transfer, forcing the abandonment of canyon-channel systems. At the same time, submarine canyons were still active offshore Zanzibar Island, located similar to 35 km south of Pemba, indicating that its uplift occurred later, likely during the upper Miocene to lower Pliocene. The changes in seafloor topography and slope gradient promoted the formation of two newly discovered giant canyons that represent the main feeder systems to this sector of the western Indian Ocean since the Miocene. We propose a new conceptual model for the post-Oligocene evolution of the area, highlighting the main tectonic structures and their timing of formation. In this model, the onset of the anticlines of Pemba and Zanzibar islands resulted from tectonic inversion probably originated during the Oligocene-lower Miocene due to reactivation of Mesozoic-aged rift faults. This compressional phase is followed by the establishment of an extensional tectonic regime which promoted the subaerial exposure of the islands since the middle Miocene. Extensional faults, which dissect the post-Oligocene stratigraphy, create horsts and grabens on a variety of scales, such as Zanzibar and Pemba troughs. These grabens show comparative size and orientation to onshore rift basins, which may indicate a relation with the tectonics of the East African Rift System. Our results provide new insights on the evolution of one the least explored, though fascinating, continental margin settings worldwide that can support future source-to-sink investigations in the region.
      原文链接:
    • NSTL
    • Elsevier

    Holocene coastal evolution, past tsunamis, and extreme wave event reconstructions using sediment cores obtained from the central coast of Hidaka, Hokkaido, Japan

    Miyairi, YosukeYokoyama, YusukeNakanishi, RyoAshi, Juichiro...
    17页
    查看更多>>摘要：Investigating coastal areas far from tsunami sources can improve the understanding of the magnitude and origin of giant tsunamis. However, distinguishing tsunami deposits from extreme storm deposits is more challenging since the layers are less prominent compared to the those in the locations near a tsunami source. This study reconstructed the Holocene coastal environments on the central coast of Hidaka, Hokkaido, similar to 250 km from the Kuril Trench. Sand layers induced by extreme waves were identified by examining the sea-level index points in the late to mid-Holocene by diatom-assemblage analysis through the combination of chemical analyses with the investigation of sediment cores. Detailed facies analyses on sediment cores obtained from several transects showed that sediment preservation differs according to the location of the cores relative to the ambient coastline. In the zone behind the beach ridge, the paleoenvironments changed from a saltmarsh formed by transgression to a swamp closed by a beach ridge formed by sea regression in the mid-Holocene. Conversely, the seaward zone indicated various environmental changes due to meandering rivers and the development of the beach ridge system due to sea regression. We found four volcanic ash layers and seven sand layers with clear basal contact with peat or organic mud. According to their sedimentological features, these sand layers were formed by tsunamis or storm surges; at least four of the sand layers are likely to be tsunami deposits, considering the ages of tsunami deposits in the surrounding region. Dramatic changes in the depositional environment associated with relative sea-level changes resulted in a short period of preservation of the sand layers. In addition, their distributions were limited, ranging from a few tens of meters to hundreds of meters from the beach ridge. Thus, in an area far from tsunami sources, the traces of extreme waves may be overlooked if the coastal evolutional process is not considered.
      原文链接:
    • NSTL
    • Elsevier

    Discovery of enigmatic toroidal carbonate concretions on the Rio Grande Rise (Southwestern Atlantic Ocean)

    Millo, ChristianVieira do Nascimento e Silva, Matheus H.de Mello, Renata MouraLeckie, R. Mark...
    6页
    查看更多>>摘要：We present enigmatic toroidal carbonate concretions retrieved from 700 m water depth from two sites in the upper plateau of the Rio Grande Rise. The concretions have a diameter of similar to 15 cm and a central hole of similar to 5 cm, and were observed on top of loose bioclastic sand over an area of similar to 30 m(2) at 0.5-1.5 m from one another. They consist of brown, porous, bioclastic grainstone, lacking internal structures. Grains consist of sand (< 3% coarse, 30% medium, 35% fine, 25% very fine), composed mainly by planktonic foraminiferal tests, and < 10% lime mud. The observed foraminiferal species indicate initial deposition of the sand in an open ocean setting. Biostratigraphy suggests an age no older than Pleistocene. Petrographic thin sections and SEM reveal that the fossiliferous grainstone contains intraclastic micritic cement and isopachous rim cement made of bladed magnesian calcite. delta O-18 values range from +1.5 to +3.3 parts per thousand (V-PDB) and increase with the degree of cementation, while delta C-13 ranges from +0.5 to +2.3 parts per thousand irrespective of cementation. The cementation of the grainstones is likely to have taken place in the marine phreatic environment. Carbonate precipitation induced by methane oxidation or (subaerial) meteoric diagenesis are ruled out based on both cement fabric and isotopic composition. Plausible causes for the toroidal shape of these structures could be: 1) sediment excavation by organisms, or 2) cementation within biofilms around burrows, followed by selective seafloor erosion. However, unveiling the actual formation mechanisms warrants further investigation.
      原文链接:
    • NSTL
    • Elsevier

    Evidence of an active rift zone in the northern Okinawa Trough

    Minami, HirokiOkada, ChiakiSaito, KeitaOhara, Yasuhiko...
    14页
    查看更多>>摘要：The character of continental rifting processes in the northern part of the Okinawa Trough remains largely unknown due to the absence of an obvious axial rift zone or recent rift-related volcanism in the region. This paper describes the discovery of a tectonically and magmatically active rift zone in the northern trough, and discusses the nature of the rift. Ship-based bathymetry identified a group of NE-SW-trending surface lineaments on the western margin of the northern trough that form a small rift structure. The newly discovered rift, named the Uji Rift, is similar to 30 km long, similar to 10 km wide and similar to 180 m deep. A seismic reflection profile near the rift confirmed the existence of well-developed normal faults with large displacements, suggesting that the rift was formed by backarc rifting. A previously unknown volcanic edifice, named West Uji Knoll, which consists of multiple cones with pronounced summits and high acoustic backscatter characteristics, also exists within the rift. High-resolution mapping with an autonomous underwater vehicle at one of the cones confirmed the existence of lava flow and eruptive fissure morphologies. Lava flows cover the pre-existing lineaments that form the Uji Rift. The flows are undissected by any lineaments, suggesting that West Uji Knoll is a young submarine volcano and the most recent eruptions likely occurred after rifting activity in the early or late Pleistocene. Active magmatism is also inferred from evidence of hydrothermal venting, such as the existence of an acoustic plume and sharp temperature increases of up to similar to 0.06 degrees C, even at a depth of similar to 100 m above the seafloor. In addition, three bubble plumes were detected near the cones by the shipboard multibeam sonar, suggesting emission of magmatic gases. Our volcano-tectonic observations show that the Uji Rift developed at an unusual location, similar to 170 km behind the arc volcanic front. Continental rifting in the northern Okinawa Trough is considered to extend onshore at the Beppu-Shimabara Rift Zone in SW Japan. However, due to the small number of submarine studies in this area, where and how the rifting is developing in the trough and has extended from the ocean to the continent is poorly understood. As an active rift, the Uji Rift provides an important constraint on the continuity of rifting in the Okinawa Trough, as well as new insights into the propagation and migration processes of continental rifting in subduction systems.
      原文链接:
    • NSTL
    • Elsevier

    Laboratory investigation on morphology response of submerged artificial sandbar and its impact on beach evolution under storm wave condition

    Li, YuanZhang, ChiDai, WeiqiChen, Dake...
    13页
    查看更多>>摘要：The Submerged Artificial sandBar (SAB), recognized as one of the nature-based solutions for beach protection and restoration, has become increasingly popular in coastal engineering applications. However, its morphological response to waves and the resulting impacts on beach evolution are yet not well understood. Here, laboratory experiments are conducted considering different background profiles and various SAB designs. Morphological evolution of the SAB and berm are inspected from the measured beach profile data in the wave flume. Results show that the SAB migrates onshore with its bar shape decaying, providing a paradigm shift away from the traditional understanding that the net subaqueous sediment transport is always offshore directed under storm wave conditions. SAB can alter the beach state and berm behavior by triggering onshore sediment transport locally and temporarily. The stability of the SAB is controlled by its seaward slope and the ratio of crest water depth to the bar height. A morphological coupling is found between the SAB and berm, and an empirical relationship is proposed to quantitatively capture it. Finally, the experiment results are used to validate a process-based beach profile evolution numerical model, and an explanation for the morphological coupling is provided from the perspective of wave energy dissipation.
      原文链接:
    • NSTL
    • Elsevier

    Stratigraphy of deep-sea marine sediment using paleomagnetic secular variation: Refined dating of turbidite relating to giant earthquake in Japan Trench

    Kanamatsu, ToshiyaIkehara, KenHsiung, Kan-Hsi
    15页
    查看更多>>摘要：Recent studies of the sedimentary record of the Japan Trench indicate unique earthquake-induced depositional characteristics. To correlate such deposits to historical earthquakes, we studied the stratigraphy of two sedimentary cores obtained from basins of the Japan Trench at 7400 m and 7600 m water depth using paleomagnetic secular variation (PSV). Because of their high sedimentation rates, results show that excellent geomagnetic records are preserved in the sediments in spite of the great water depth. Paleomagnetic secular variation, especially declination during the past 3000 years revealing a distinctive feature of large oscillation, offers an opportunity to make precise stratigraphic correlations. Identification of boundaries between thick fine turbidite intervals and hemipelagite intervals was made based on rock magnetic properties. Successful applications of extraction of paleomagnetic data solely from the hemipelagic interval demonstrate that stratigraphic positions of turbidite in paleomagnetic secular variation record are mutually well correlated in PSV variations. Even over long distances between sites, the turbidites induced by earthquakes can be correlated exactly. The turbidite ages were determined by referring to the PSV master curve. Especially, the ages of turbidite units regarded as induced by the Jogan earthquake can be inferred from two cores that closely approximate its documented age.
      原文链接:
    • NSTL
    • Elsevier

    Evaluation of organic indicators derived from extractable, hydrolysable and macromolecular organic matter in sedimentary tsunami deposits

    Konechnaya, OlgaBellanova, PieroFrenken, MikeReicherter, Klaus...
    11页
    查看更多>>摘要：Due to the high population density and sensitive infrastructures, coastal areas are highly vulnerable to various geohazards such as tsunamis. The impact of tsunamis is traceable in sedimentary archives providing an important tool for reconstructing these events. Here, geochemical and physical evidence of the resulting inundations have been discussed over the last years with increasing interest on identifying and using highly specific tsumanite indicators. To investigate a broader range of potential organic indicators, a multi-tiered geochemical analysis has been applied on tsunami deposit from Japan and Hawaii in this study with the aim to detect and quantify a more comprehensive set of suitable marker compounds. Both areas of investigation differed especially in terms of population and anthropogenic influence. The analyzed fractions of organic matter covered not only the low molecular weight compounds of the extractable and hydmlysable fraction (a part of the non-extractable fraction), but also the macromolecular matter. Three consecutive analytical approaches including extraction, alkaline hydrolysis and pyrolysis have been applied on the sedimentary organic matter to study their potential to contrast between tsunami and non-tsunami layers. The analyses of compound ratios as well as individual concentration profiles in tsunami and non-tsunami layers revealed two parameters, the TAR(FA) (terrigenous to aquatic ratio of fatty acids) and the C-29/C-27 sterol ratio, which exhibit a high potential to act as tsunamite indicators. Further parameters (TAR(ALK) - terrigenous to aquatic ratio of n-alkanes, concentration profiles of long-chain n-aldehydes) showed a minor potential but are worth to be considered in organic geochemical analyses of tsunami affected sediment archives in the future.
      原文链接:
    • NSTL
    • Elsevier