Hydrodynamic behaviour of Nummulites: implications for depositional models

Type Article
Date 2006-05
Language English
Author(s) Jorry StephanORCID1, 3, Hasler Ca2, Davaud E3
Affiliation(s) 1 : Rice Univ, Dept Earth Sci, Houston, TX 77005 USA.
2 : Univ Cambridge, Dept Earth Sci, Cambridge CB2 3EQ, England.
3 : Univ Geneva, Dept Geol, CH-1205 Geneva, Switzerland.
Source Facies (0172-9179) (Springer), 2006-05 , Vol. 52 , N. 2 , P. 221-235
DOI 10.1007/s10347-005-0035-z
WOS© Times Cited 83
Keyword(s) carbonates, eocene, large benthic foraminifera, test density, taphocoenosis
Abstract 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.
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