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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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    An uneven rhodolith distribution controlled by sea-bottom conditions near Jeju Island, Korea

    Jeong, Joo BongLim, Moon SooSeo, Young KyoWoo, Kyung Sik...
    16页
    查看更多>>摘要：Actively growing, dense rhodolith beds are found in the wide channel between the volcanic Jeju and Udo islands in Korea. This shallow area (water depths of up to 25 m) has unique geological features affected by the marine hydraulic regime. Spheroidal and sub-spheroidal, living or dead rhodoliths with the size range from sand to pebble are common (mostly 2-4 cm in diameter), but some of them are actively growing up to over 10 cm. Most sand-to granule-sized sediments are characterized by nonliving fragments, and the pebble-sized sediment beds are a mixture. In order to understand the factors affecting the characteristics (morphology, distribution, the living portion of rhodoliths, etc.) Seabed topography and sedimentary texture associated with hydraulic energy were investigated. We divided the study area into four types based on topographical properties. Among these classifications, the "Flat plain" and "Gentle slope" geomorphic categories have dense rhodolith beds, whereas a low distribution of rhodoliths was identified in areas with uneven topography or extreme high hydraulic energy flux. In addition, rhodolith growth was affected by the size of carbonate grains on the seafloor, and rhodoliths with more spheroidal shapes tend to occur on flatter floors. This study delineates that the substrate with coarse sized substrate at relatively deeper water depth as well as flatter bottom topography provides favorable conditions for continuous growth of rhodoliths. Our findings will help the understanding of the growth conditions of rhodoliths in other parts of the world.
      原文链接:
    • NSTL
    • Elsevier

    Potential and limitation of Th-230-excess as a chronostratigraphic tool for late Quaternary Arctic Ocean sediment studies: An example from the Southern Lomonosov Ridge

    Purcell, KarlHillaire-Marcel, Claudede Vernal, AnneGhaleb, Bassam...
    11页
    查看更多>>摘要：Recently, the use of "extinction ages " of excesses in U-series isotopes (Th-230(xs), Pa-231(xs)) has been proposed for the setting of benchmark ages of up to ~350 and ~150 ka, respectively, in late Quaternary marine records from the Arctic Ocean. However, the use of such U-series-based chronostratigraphic approaches has some limitations. These limitations are illustrated by U-series measurements in a cored sequence from the southern Lomonosov Ridge (PS2757). In this core, the final measurable excess in Th-230 (Th-230(xs)), strictly linked to the sedimentary flux of this isotope from the overlying water column (Th-230(xs)-marine), is observed at a depth of ~590 cm downcore. An "extinction age " of ~230 ka can be estimated for the residual (230)Th(xs )at this depth. It approximately matches the Marine Isotope Stage 7/8 transition. Below this transition, strong redox gradients constrained by a layer enriched in organic carbon resulted in a late-diagenetic relocation of uranium leached from detrital minerals in the over-and underlying oxidized layers. This uranium relocation resulted in large amplitude radioactive disequilibria within a core section otherwise characterized by near secular equilibria between inventories of U-238-series isotopes, implying an age greater than the "Th-230(xs)-marine extinction age " for the whole section. In the overlying part of the core, the (230)Th(xs )distribution correlates with other Th-230(xs)-documented sequences from the Central Arctic Ocean. (230)Th(xs )can be thus used for stratigraphic correlations between the relatively low-sedimentation rate marine sequences of this basin, over the last two or three glacial cycles, but special attention to potential diagenetic effects is recommended. Moreover, as for a given Th-230(xs)-marine flux at the seafloor, initial Th-230(xs)-values are broadly inversely-proportional to the sedimentation rate, the resulting estimates of Th-230(xs ) "extinction age " vary accordingly. This variability restricts the chronostratigraphic use of (230)Th(xs )to sequences with relatively low sedimentation rates, such as those where the initial Th-230(xs)-marine significantly exceeds the Th-230-fraction carried by detrital minerals.
      原文链接:
    • NSTL
    • Elsevier

    Terrigenous and volcanogenic contribution to the deep basin of the South China Sea: Evidence from trace elements and Sr-Nd isotopes

    Cai, GuanqiangXu, YonghangZhong, HexianCheng, Yulong...
    13页
    查看更多>>摘要：The deep basin of the South China Sea (SCS) receives terrigenous materials from the surrounding continents and islands, making it an ideal region for studies on source-to-sink transport. The analysis of grain size, major and trace elements, and Sr-Nd isotopes of 130 surface sediment samples throughout the SCS deep basin has been performed for identifying the contribution of terrigenous and volcanic materials. Based on the analysis results, the SCS deep basin can be divided into three geographic areas with different provenances: the northern area of the East Subbasin (NES), the southern region of the East Subbasin (SES), and the Southwest Subbasin (SWS). The predominant provenances of sediments in the NES and SWS are Taiwan rivers and Mekong River, respectively. Sediments from the SES exhibit higher mean grain size, less radiogenic Sr-87/Sr-86, and more radiogenic Nd-143/Nd-144 than those from the NES and SWS. Pinatubo ash input from the Luzon Island may be a predominant source in the SES. The contribution of Pinatubo ash decreased westward from 80% to 20% in the SES. The supply of Pinatubo ash could be considered insignificant to the NES and SWS. Sediments from Taiwan rivers or Mekong River were the subordinate source in the SES. The deep-water current and mesoscale eddies may play a role in transporting terrigenous materials into the SCS deep basin as well as the turbidity current.
      原文链接:
    • NSTL
    • Elsevier

    Mid-Miocene to recent tectonic evolution of the Punta Stilo Swell (Calabrian Arc, southern Italy): An effect of Calabrian Arc migration

    Mangano, GiacomoZecchin, MassimoCivile, DarioCeramicola, Silvia...
    11页
    查看更多>>摘要：The development of Punta Stilo Swell (PSS), a submerged lobate-shaped promontory located in the Crotone-Spartivento Basin, is inferred to be closely linked to the Calabrian Arc kinematics since mid-Miocene onward. The latter consists of an alternation between long-term phases of subsidence related to forward migration of the Calabrian accretionary complex, and short-term compressional-transpressional phases, characterized by episodes of uplift and formation of regional unconformities, in a context of stopping or slowdown of Calabrian accretionary complex migration. In particular, the study area is supposed to have respectively experienced phases of compressional and extensional tectonics during late Messinian and early Pliocene, which likely produced a reactivation of inherited compressional and extensional structures. Late Pliocene/Pleistocene transtensional tectonics is documented along the offshore extension of the Soverato-Lamezia Fault Zone (SLFZ), in the N sector of the PSS. The resulting physiographic modifications associated with such compressional, extensional and transtensional tectonics is believed to have controlled the accumulation of the thick Plio-Pleistocene succession of the PSS. The northern continental slope is inferred to be the result of late Pliocene/Pleistocene transtensional tectonics occurred along the SLFZ, whereas the shelf break is considered the result of an early Pliocene extensional tectonics. The considerable steepness (>10 degrees) of the southern and eastern continental slope of the PSS is associated with the late Messinian compressional tectonic activity and is marked by the occurrence of slope failure-associated events.
      原文链接:
    • NSTL
    • Elsevier

    Coastal vs volcanic processes: Procida Island as a case of complex morpho-evolutive response

    Aucelli, Pietro P. C.Mattei, GaiaCaporizzo, ClaudiaDi Luccio, Diana...
    19页
    查看更多>>摘要：The island of Procida (Gulf of Naples, Italy) is a site of considerable importance from a historical, cultural, and landscape point of view. The island is located along a volcanic active area in the mid-Tyrrhenian and owes its formation to several explosive eruptions started more than 70 ka BP. Presently, the entire perimeter of the island is bordered by cliffs, often articulated in an alternation of headlands and coves, sometimes with shallow sandy beaches at the base (pocket beaches). However, the presence of different orders of submarine terraced surfaces represents a significant clue to coastal response to former sea-level stands.This paper aims at reconstructing the main coastal changes that occurred in the area during the Holocene mainly driven by the interaction between the post-glacial sea-level rise, vertical ground movements (VGMs) of volcano-tectonic origin, and wave action. The coastal sector was investigated using a multi-techniques approach including direct and indirect methods, in order to obtain a detailed geomorphological characterization of the whole study area. In particular, data from direct coastal surveys were integrated with photo-interpretation of areal and satellite photos, morphometric analysis of high-resolution DTMs from Lidar and bathymetric data, interpretation of morpho-acoustic data, archaeological, geomorphological and geological sea-level markers. The geomorphological analysis of this multidisciplinary dataset resulted in the detection of the main morphological elements interpreted as evidence of ancient seascapes. In particular, three orders of paleo-shore platforms were mapped in the underwater sector, allowing the evaluation of as many phases of relative sea-level stand, at-23.2 m,-11.2 m, and -4.2 m MSL dated at approximately 4.0, 2.0, and 1.0 ka BP. These coastal landforms were interpreted as the main consequence of a seacliff retreat, exacerbated by volcano-tectonic intermittent subsidence that favoured their poly-cyclic formation. However, the integration between the geomorphological and meteo-marine analysis allowed discriminating differentiated cliff backwearing responses between the western and eastern coastal sectors of the island, due to a prevailing occurrence of storms from the south-western sector. The proposed methodological approach focused on a multi-temporal geomorphological analysis applied to a multi-modal dataset, aims to comprehensive reconstruct the coastal response of a volcanic high rocky coast to the complex interaction between endogenous and exogenous forcing factors during the Holocene.
      原文链接:
    • NSTL
    • Elsevier

    A mechanism for high-frequency variability in sapropels

    Dirksen, J. P.Meijer, P.
    9页
    查看更多>>摘要：Sapropels deposited in the Mediterranean Sea provide high resolution records of past oceanographic changes. Previous studies have found abrupt transitions in chemical composition of these sediments. We present a transient box model that provides a potential mechanism for these transitions. The high-frequency variability is a result of fluxes stopping or changing direction, causing a relaxation towards a new equilibrium. The time scales depend on the volume of the reservoirs and the magnitude of the fluxes. We find typical periods in the order of 100-1000 years, similar to what has been found in sediment cores.
      原文链接:
    • NSTL
    • Elsevier

    Tracing glacial-interglacial water mass changes in the Gulf of Corinth (IODP Expedition 381) using iron-sulphur geochemistry and magnetic susceptibility

    Marz, ChristianMahoney, Carol
    11页
    查看更多>>摘要：The Gulf of Corinth is a rapidly rifting basin that has been alternately connected to/isolated from the Mediterranean due to Quaternary global sea levels fluctuations. A recently retrieved sediment record from the Gulf of Corinth (IODP Expedition 381) shows variations in magnetic susceptibility, with relatively higher and more variable values in isolated/glacial sediments and lower, more stable values in connected/interglacial sediments. Using geochemical methods, we find that not the primary input of magnetic minerals, but diagenetic processes generated the magnetic susceptibility pattern. Easily reducible sulphides (most likely greigite) increase in high magnetic susceptibility (isolated/glacial) sediments, whilst magnetite shows no systematic relationship to magnetic susceptibility. After discounting several possible causes for the formation and preservation of greigite (bottom water redox conditions, high sedimentation rates, reactive Fe and organic matter availability), a decrease in sulphate concentrations in the Gulf of Corinth during isolated/glacial periods is the most likely explanation, supporting parallel microfossil evidence for a freshening of the water column. This sulphate limitation appears to stall sedimentary pyrite formation at the stage of ferrimagnetic monosulphides like greigite. Greigite formation as an indicator of paleosalinity variations has been observed in other depositional settings (e. g., Chesapeake Bay, the Baltic Sea, the Miocene Paratethys and the Black Sea), supporting our interpretation. Specific to the Gulf of Corinth, linking a proxy for basin connectivity to a high resolution (at least 40, and up to 7 year temporal resolution) magnetic susceptibility record over 750,000 years offers an opportunity to investigate, in detail, the tectonic evolution of this rift basin and its link to global sea level fluctuations.
      原文链接:
    • NSTL
    • Elsevier

    Boosting riverine sediment by artificial flood in the Yellow River and the implication for delta restoration

    Wu, XiaoWang, HoujieSaito, YoshikiSyvitski, Jaia...
    9页
    查看更多>>摘要：Due to accelerated river-derived sediment deficits, global deltas are presently under an increasing risk of being submerged. To address the fundamental need to save Earth's deltas, boosting riverine sediment supply can be considered a reasonable option, but only if the new supply of sediment is prolonged and greater than the opposing forces: sea level rise, delta subsidence and compaction, and ocean energy. In July 2018, an artificial flood with a peak discharge of 3780 m3/s was released from the Xiaolangdi Reservoir, the last reservoir located on the mainstream of Yellow River, China. From July 03 to July 29, 412 million tons (Mt) of sediment was discharged out of the dam, including 240 Mt. that was previously sequestered within the reservoir. During this event, 140 Mt. of the escaped sediment directly reached the estuary. A total of 245 Mt. of sediment was deposited along the lower river channel bed, of which 83.6 Mt. was eroded once again and transported to the sea in the subsequent five months. This dam-released pulse, coupled with channel diversion and tidal shear fronts, nourished the deltaic area. New land was built, with the submarine offshore gaining up to 2.6 m in seafloor shoaling. Sediment impounded behind the dam, if properly released, could thus become a potential savior for sedimentstarved deltas.
      原文链接:
    • NSTL
    • Elsevier

    Microbially induced sedimentary structures (MISS) generated by episodic storm surges in a temperate coast

    Gomez, Eduardo A.Maisano, LuciaStempels Bautista, CamilaCuadrado, Diana G....
    12页
    查看更多>>摘要：This study recognizes the creation of primary sedimentary structures in a modern environment that reports valuable insights into the role of microbiota in sculpting sedimentary structures, and it may explain many previously confusing sedimentary structures in the rock record. The research considered the frequent flooding events on a coastal sedimentary flat colonized by microbial mats and the effect produced by severe storm surge events. Large-scale microbially induced sedimentary structures (MISS) were created; thus, the interaction between meteorologic, oceanographic, and geomorphologic conditions necessary to form them was analysed. The study was developed in Paso Seco, Argentina (40 degrees 38 ' 31" S - 62 degrees 12 ' 54" W), a sedimentary flat behind a sand spit, coated by thick microbial mats recurrently affected by storm events. Water level measurements were recorded continuously for five years (measurement interval 10 min). The seawater inundations were related to synoptic weather maps and oceanographic parameters (wave height, period, and tides) to analyse the cause of storm surges. Two situations of severe storms were studied in 2018 and 2019. The inundation of the study area occurs when a cold front in association with a low-pressure centre in the Atlantic Ocean, moving in an SW-NE direction, produces strong SW winds higher than 45 km h-1 and wave height higher than 2 m. Strong winds and storm duration (two or three days) in co-occurrence with spring tides create an extreme erosional event that affects the sedimentary microbial flat. In sum, the interaction between storm surge, high tide, wave setups and wave heights in Paso Seco produces coastal hinterland flooding that creates meter-sized MISS such as roll-ups, erosional pockets, and remnants mats structures. The impact of storm surges on the coast is common and catastrophic in modern times but is challenging to identify in the sedimentary record. Therefore, the microbial structures presented here could help interpret high-energy events occurrence, favourable to assessing past environmental conditions.
      原文链接:
    • NSTL
    • Elsevier