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

Chapter Four
Depositional Environmenment and Paleoecology
benthonic forams, the Planktonic/Benthonic ratios and the
Agglutinated/Calcareous ratios are the most important parameters in this chapter.
4.2- Planktonic species diversity or species richness
Species diversity is the total number of species in an assemblage, whereas
species richness reflects the actual number of species present at a given time
and is therefore a measure of environmental variability (e.g., climate, seasonality,
nutrient fluctuations), but may be influenced by fossil preservation (e.g.,
dissolution, breakage of shells). Species richness may be significantly less than
species diversity as a result of sample preservation, climate variations and/or
local environmental conditions. (Keller 2004)
Species richness at Smaquli, Dokan and Sirwan sections is unusually low
during the latest Maastrichtian which starts from the end of Pseudoguembelina
palpebra Zone (CF2) around 65.5 Ma and upward, it fluctuates about 30-20
species in Plummerita hantkeninoides Zone, except for the lower and middle
part of the studied sections where 40-50 species are present and across the
Cretaceous/Tertiary contact at Kolosh Formation where it drops down to 17-14
species (Figs. 4. 3 - 4.7). Even lower species richness was observed at Kato
and Qishlagh sections with 25-28 species in Pseudotextularia intermedia and
Racemiguembelina fructicosa Zones CF5 -CF4. While the planktonic
foraminiferal assemblages interrupted their occurrences due to environmental
changes in both Kato section from the lower part of Pseudoguembelina
hariaensis (CF3) and lower part of Racemiguembelina fructicosa Zone in
Qishlagh section, and replaced by shallow benthonic larger foraminiferal
assemblages of platform biotope communities. (Figs 4.3-4)
There is the fact that increasing distances from the shoreline, the turbidity
decreases , enabling principal production to increase. In addition, the complex
pelagic ecosystem, with many nutrient chains, is only developed at a certain
water depth around the total photic zone and has noted that planktonic
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