Nummulitids hydrodynamics: An example using nummulites globulus leymerie, 1846

The main physical variables influencing the hydrodynamic behaviour of nummulitid tests are size, density and shape. After measuring these variables, further parameters must be calculated to obtain an approximation to the hydrodynamic behaviour of the test. These parameters are volume, nominal diameter, critical shear velocity, critical shear stress, shape entropy, shape-independent settling velocity, settling velocity of a non spherical form, Reynolds number, and drag coefficient. Some of these data were calculated by combining shell measurements with physical properties of the seawater. The aim of this paper is to explain numerical calculations for qualifying and quantifying the hydrodynamic parameters of nummulitids. Every single step or formula is important to evaluate the hydrodynamics of a particle or test respectively, especially in shallow water environments where energy strongly varies depending on different physical factors induced by the climate and the topography of the platform. Several methods to calculate the same parameters are also presented and compared to show the best-suited one for nummulitids. In the fossil record, the faunal composition and the distribution of tests mainly depend on the two groups of cause-event effects: in vita and post mortem. Inferences about a fossil shallow benthic fauna must consider beside biological and ecological features further physical parameters like transport and deposition leading to distinct distribution patterns.