Plio-Quaternary coastal sequences, sea-level changes and coastal geodynamics

International audienceSequences of Plio-Quaternary shorelines generated by sea-level cyclicity and tectonics massively shape the coasts worldwide. Here, we compile a worldwide synthesis of sea-level changes for the following highstands : MIS 1, MIS 3, MIS5e, and MIS 11 and explore the relationships to regional geodynamics. We identified 896 sequences including the MIS 5e benchmark, out of which 177 also feature the highest Holocene shorelines, 6 where the elevation of the MIS 3 shorelines are known, and 40 including that of MIS 11 shorelines. We considered 8 main geodynamical contexts for a statistical analysis: passive margin (337 sites, 14 domains, U=0.06 0.01 mm/a), hot spot chains (45 sites, 14 domains, U=0.02 0.02 mm/a), rifts (45 sites, 2 domains, U=0.12 0.02 mm/a), ridges (3 sites, 1 domain, U=0.14 0.02 mm/a), transform plate boundaries (119 sites, 7 domains, U=0.25 0.03 mm/a), intra-oceanic subductions (131 sites, 4 domains, U=0.43 0.04 mm/a), continental subductions underneath oceanic plates (12 sites, 1 domain, U=0.54+/- 0.04 mm/a), oceanic subductions underneath continental plates (166 sites, 7 domains, U=0.06 0.01 mm/a), intra-continental convergence (10 sites, 2 domains, U=1.47 0.08 mm/a). Counter-intuitive is the fact that passive margin are ubiquitously uplifting, while tectonic segmentation is more important on active margins. Additionally, 511 sites document the elevation of the highest shoreline of the sequence, from which we extrapolate a minimum age of onset for the sequence (based on MIS 5e uplift rates). 99% (511 sites) were formed at least during Pliocene and/or Quaternary, showing that potentially more ancient records are either eroded or non-existent

Les réseaux de drainage développés sur les séquences de terrasses coralliennes quaternaires de l'île de Sumba (Indonésie), marqueurs de la déformation verticale

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Plio-Quaternary coastal sequences, sea-level changes and coastal geodynamics

International audienceSequences of Plio-Quaternary shorelines generated by sea-level cyclicity and tectonics massively shape the coasts worldwide. Here, we compile a worldwide synthesis of sea-level changes for the following highstands : MIS 1, MIS 3, MIS5e, and MIS 11 and explore the relationships to regional geodynamics. We identified 896 sequences including the MIS 5e benchmark, out of which 177 also feature the highest Holocene shorelines, 6 where the elevation of the MIS 3 shorelines are known, and 40 including that of MIS 11 shorelines. We considered 8 main geodynamical contexts for a statistical analysis: passive margin (337 sites, 14 domains, U=0.06 0.01 mm/a), hot spot chains (45 sites, 14 domains, U=0.02 0.02 mm/a), rifts (45 sites, 2 domains, U=0.12 0.02 mm/a), ridges (3 sites, 1 domain, U=0.14 0.02 mm/a), transform plate boundaries (119 sites, 7 domains, U=0.25 0.03 mm/a), intra-oceanic subductions (131 sites, 4 domains, U=0.43 0.04 mm/a), continental subductions underneath oceanic plates (12 sites, 1 domain, U=0.54+/- 0.04 mm/a), oceanic subductions underneath continental plates (166 sites, 7 domains, U=0.06 0.01 mm/a), intra-continental convergence (10 sites, 2 domains, U=1.47 0.08 mm/a). Counter-intuitive is the fact that passive margin are ubiquitously uplifting, while tectonic segmentation is more important on active margins. Additionally, 511 sites document the elevation of the highest shoreline of the sequence, from which we extrapolate a minimum age of onset for the sequence (based on MIS 5e uplift rates). 99% (511 sites) were formed at least during Pliocene and/or Quaternary, showing that potentially more ancient records are either eroded or non-existent

Analyse géomorphologique de la déformation d’avant-arc au niveau d’une transition subduction océanique/subduction continentale;

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Geomorphologic Indices for Transition from Subduction to Arc-Continent Collision in Sumba Island, Indonesia

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"Arc-continent collision" of the Aleutian-Komandorsky arc into Kamchatka: Insight into Quaternary tectonic segmentation through Pleistocene marine terraces and morphometric analysis of fluvial drainage

At the NW corner of the Pacific region, just south of the Kamchatsky Peninsula, the northern tip of the Pacific plate subduction and associated volcanic arc interacts with the western end of the Aleutian-Komandorsky dextral transform plate boundary and associated arc. Study of both Holocene and Pleistocene sequences of uplifted marine terraces and also of fluvial drainage patterns on the Kamchatsky Peninsula allows us to highlight active tectonics produced by complex plate interaction. Our results show that the central eastern coast of the peninsula is currently divided into four different zones consisting in uplifted blocks associated with various uplift rates in front of a fold-and-thrust zone to the west. Our main tectonic benchmark—the altitude of the shoreline correlated to the Last Interglacial Maximum (Marine Isotopic Stage 5e)—yields late Pleistocene uplift rates ranging from 0.2 to 2.74 mm/yr. One of the main active faults bounding the coastal blocks is dextral and is interpreted as a prolongation of an offshore fault of the Aleutian-Komandorsky dextral transform plate boundary. We suggest that structures on the Kamchatsky Peninsula accommodate a part of the transform motion, but that mainly, the arc-continent collision of the Aleutian arc against Kamchatka produces a “bulldozer” effect on the Kamchatsky Peninsula

Comment on "Active coastal thrusting and folding, and uplift rate of the Sahel Anticline and Zemmouri earthquake area (Tell Atlas, Algeria)", by S. Maouche, M. Meghraoui, C. Morhange, S. Belabbes, Y. Bouhadad, H. Haddoum. [Tectonophysics, 2011, 509, 69-80]

International audienceBased on geomorphologic analyses and leveling survey of Quaternary coastal indicators (i.e. marine terraces and notches) along of a 50-km-long coastal stretch of the Algerian coast west of Algiers, Maouche et al. (2011) interpret the coastal segment to have undergone high uplift rates, i.e. 0.84-1.19 mm/yr since last interglacial maximum (MIS 5e, 122±6 ka in Table 1, ~140 ka in Maouche et al., 2011) and ~2.5 mm/yr for the last 31 ka. This uplift was said to be due to repeated seismic events that would have occurred during the last ~140 ka, and more particularly during the late Pleistocene. We raise major issues about the interpretation proposed by Maouche et al. (2011). These issues deal with 1) the use of previous chronological data and the chronostratigraphy proposed, 2) processes involved in the creation of coastal staircase morphology on the coast west of Algiers, 3) anomalously high uplift rates compared to other available data on the same geomorphic features (marine terraces) in the same setting of reactivated passive margins, and 4) the fold geometry used for modeling of fold growth and its implications for coseismic surface deformation and uplift estimates. In other words, we contest the statements that coseismic deformation is the cause of staircase morphology on the Mediterranean coast west of Algiers and that very large (M>7) earthquakes have occurred there in the past

Morphometric assessment of uplifting coral reef sequences, Sumba Island, Indonesia.

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Seasonal dynamic of the benthic food web in subtidal sandbanks

International audienceSubmarine sandbanks are prevalent worldwide but, paradoxically, these ecosystems and their dynamics remain largely unknown. As submarine sandbanks are targeted by a large variety of human activities, there is an urgent need for sound scientific knowledge for environmental impact assessments (EIAs) and the appropriate management of biodiversity in these areas. To our knowledge, the present study is the first to investigate the seasonal dynamics of the benthic food web in sandbank areas. We performed a stable isotope analysis in the French part of the southern North Sea. This area is typified by numerous sandbanks and by massive phytoplankton blooms in spring. We found a very simple food web structure that is heavily dependent on organic matter particles in seawater. Primary consumers, i.e. deposit feeders and, to a lesser extent, suspension feeders, dominate the benthic biomass. Small predator-scavengers such as annelids, shrimps and crabs prey upon them. Fish predators such as Echiichthys vipera represent a very restricted proportion of the biomass. We observed that the general structure of the food web is relatively well preserved over seasons. We thus propose that the functioning of the ecosystem is resilient to natural disruptions-such as dune migrations-and, probably, to anthropogenic disturbances

Morphometric assessment of uplifting coral reef sequences, Sumba Island, Indonesia.

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