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Hydrodynamic behaviour of Nummulites : implications for depositional models

Jorry, Stéphan ; Hasler, Claude-Alain ; Davaud, Eric

In: Facies, 2006, vol. 52, no. 2, p. 221-235

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    Title
    • Hydrodynamic behaviour of Nummulites
      implications for depositional models
    Author
    • Jorry, Stéphan. Department of Geology, University of Geneva, 13 rue des Maraîchers, 1205, Geneva, Switzerland
    • Hasler, Claude-Alain. Department of Earth Sciences, University of Cambridge, Downing Street, CB2 3EQ, Cambridge, UK
    • Davaud, Eric. Department of Geology, University of Geneva, 13 rue des Maraîchers, 1205, Geneva, Switzerland
    Document Type
    • Postprint
    OAI-PMH Identifier
    • oai:doc.rero.ch:321394
    Summary
    Large benthic foraminifers are considered to be good indicators of shallow marine carbonate environments in fossil series. Over the last 50 years, the palaeoenvironment of Tertiary Nummulites accumulations has been a matter of debate, particularly because of difficulties in interpreting these deposits, and in this way, the absence of analogues in present-day seas does not help. The aim of this paper is to insight the different ways Nummulites tests and clasts may accumulate according to their hydrodynamic behaviour. Based on experimental measurements and on SEM observations, it appears that the high primary skeletal porosity of Nummulites made them easily transportable. The calculated threshold shear velocities confirm that large-sized Nummulites can be moved by weak wave-driven currents. This peculiar hydrodynamic behaviour of Nummulites could explain the diversity of depositional models. Depending on local hydrodynamic conditions, autochthonous Nummulites deposits can be preserved as in situ winnowed bioaccumulations or be accumulated offshore, onshore or alongshore, away from the original biotope