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

Chapter Four
Depositional Environmenment and Paleoecology
foraminiferal diversity (species richness) increases from shallower to deeper
waters across shelf areas. (Van Der Zwaan et al., 1990)
Sediment deposition at these localities occurred at outer neritic upper
bathyal and middle-outer neritic depth, respectively. Comparable depth
localities in Tunisia, Spain, and Mexico average 45-55 species (Lopez and
Keller, 1996 in Keller, 2004; Pardo et al., 1996; Abramovich and Keller, 2002).
Fossil preservation is excellent at Smaquli sections and relatively good in other
studied localities and does not account for the low species richness, which
appears to be regional throughout the studied area. To recognize these
abnormally poor species assemblages exactly at the uppermost Maastrichtian
Plummerita hantkeninoides zone (CF1), it is available to study species richness
patterns across the Cretaceous/Tertiary boundary within high resolution
biostratigraphic researches of all studied localities previously in Iraq and
neighboring countries.
Species richness and diversity tend to be highest in outer shelf-upper slope
environments (250-500m) and gradually decrease in shallower waters across
the continental shelf. (Keller, 2004), this can be confirmed in the present studied
area.
In the upper Maastrichtian zones (CF1 to CF3), species richness varies
between 42-54 species at the outer shelf-upper slope section at El Kef (Keller,
1988; Li and Keller, 1998c: Keller et al., 2002b in Keller, 2004). At the shallower
middle neritic trends (Abramovich. and Keller, 2002), the lowest species
richness is found at the innermiddle neritic locality of Seldja in southern Tunisia
where on average only (10-15) species are present. Species richness is directly
related to niche availability, which is related to water depth and watermass
stratification. In shallow inner neritic environment, species richness is lowest
because ecological niches are largely restricted to the surface mixed layer (50m)
of the upper photic zone (Keller,2004) (Fig 4,1)
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