Deep-sea volcaniclastic sedimentary systems: an example from La Fournaise volcano, Réunion Island, Indian Ocean

Authors

  • Ollier,

    1. IFREMER (Institut Français de Recherches pour L’Exploitation de la Mer), Laboratoire ‘Environnements Sédimentaires’, BP 70, 29280 Plouzané, France,
    2. Current address: European Commission, Directorate-General XII-Science, Research and Development-Rue de la Loi 200-1049 Brussels, Belgium,
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  • Cochonat,

    1. IFREMER (Institut Français de Recherches pour L’Exploitation de la Mer), Laboratoire ‘Environnements Sédimentaires’, BP 70, 29280 Plouzané, France,
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  • Lénat,

    1. Centre de Recherches volcanologiques – Observatoire de Physique du Globe – URA10, C.N.R.S. – Université Blaise-Pascal – 5, rue Kessler -63038 Clermont-Ferrand Cedex -France
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  • Labazuy

    1. Centre de Recherches volcanologiques – Observatoire de Physique du Globe – URA10, C.N.R.S. – Université Blaise-Pascal – 5, rue Kessler -63038 Clermont-Ferrand Cedex -France
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Abstract

A volcaniclastic sedimentary fan extending to water depths of 4000 m is characterized using gravity cores, camera surveys, high-resolution sonar images, seismic records and bathymetry from the submarine portion of La Fournaise volcano, Réunion Island, a basaltic shield volcano in the SW Indian Ocean.

Three main areas are identified from the study: (1) the proximal fan extending from 500 m water depth down to 2000 m water depth; (2) the outer fan extending from 2000 m water depth down to 3600 m water depth; (3) the basin extending beyond 3600 m water depth. Within these three main areas, seven distinct submarine environments are defined: the proximal fan is characterized by volcanic basement outcrops, sedimentary slides, deep-water deltas, debris-avalanche deposits, and eroded floor in the valley outlets; the outer fan is characterized by a discontinuous fine-grained sedimentary cover overlying coarse-grained turbidites or undifferentiated volcanic basement; the basin is characterized by hemipelagic muds and fine-grained turbidites interbedded with sandy and gravelly turbidite lobes.

The evolution of the deep-sea volcaniclastic fan is strongly influenced by sector collapses, such as the one which occurred 0·0042 Ma ago. This collapse produced a minimum of 6 km3 of debris-avalanche deposit in the proximal area. The feeding regime of the deep-sea fan is ‘alluvial dominated’ before the occurrence of any sector collapse and ‘lava-dominated’ after the occurrence of a sector collapse.

The main deep-water lava-fed delta is prograding among the blocks of the debris-avalanche deposits as a result of turbidity flows occurring on the delta slope. These turbidity flows are triggered routinely by wave-action, earthquakes and accumulation of new volcanic debris on top of the deltas.

Both turbidity currents triggered on the deep-water delta slope, and those triggered by debris avalanche reworked volcaniclastic material as far as 100 km from the shore line.

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