biostratigraphy and paleoecology of cretaceous/tertiary boundary in ...

Chapter Four
Depositional Environmenment and Paleoecology
Fig (4.1) Planktonic foraminiferal species richness across the Tunisian continental shelf-slope
based on data from the inner shelf Seldja section (Keller and other,1998) , middle shelf Elles
section ( Abramovich and Keller,2002), and outer shelf to upper slope El Kef section (Li and Keller
1998c,). Note: The species richness increase with increasing depth across the shelf and is a
function of available ecological niches and depth habitats (from Keller 2004)
4.3- Signor- Lipps Effect
Abundance: relative abundance refers to the proportion of species (or group
of fauna) of the entire assemblages, e.g. percentage. While an absolute
abundance refers to the number of individuals in a unit sample or assemblages.
It is important to realize that relative and absolute abundance measurements
give different information. Despite these difficulties the relative abundance is
better for dead assemblages because of several effective parameters, which are
known as Signor- Lipps Effect, Based on reasonable interactions between
method of sampling, sampling density, sample size, preparation methods,
relative abundance, precision amount and omission in statistical measurements,
occurrence pattern, fossil preservations, and observation about last appearance
datum event LAD (or first appearance datum FAD) provide an accurate estimate
of the true LAD or FAD (Signor and Lipps, 1982, in MacLeod 1996). It does
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