biostratigraphy and paleoecology of cretaceous/tertiary boundary in ...
biostratigraphy and paleoecology of cretaceous/tertiary boundary in ...
biostratigraphy and paleoecology of cretaceous/tertiary boundary in ...
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Chapter Four<br />
Depositional Environmenment <strong>and</strong> Paleoecology<br />
foram<strong>in</strong>iferal assemblages that enjoyed a widespread geographic dispersal<br />
<strong>and</strong> equitable climatic conditions dur<strong>in</strong>g Maastrichtian <strong>and</strong> Paleocene. The<br />
cont<strong>in</strong>ental shelf fauna, termed as "Midway-type fauna" (MF), <strong>and</strong> a lower<br />
cont<strong>in</strong>ental slope <strong>and</strong> abyssal pla<strong>in</strong> fauna termed as "Velasco-type fauna"<br />
(VF). (Alegret <strong>and</strong> Thomas, 2001; Samir, 2002)<br />
The paleodepth <strong>in</strong>dicated by benthonic foram<strong>in</strong>iferal assemblages are<br />
clearly <strong>of</strong> great value for the <strong>in</strong>terpretation <strong>of</strong> the environment <strong>of</strong> deposition<br />
<strong>of</strong> the Cretaceous/Tertiary clastic unit (Alegret et al. 2003)<br />
The paleobathymetric estimation <strong>in</strong> this study also depends on the<br />
occurrence <strong>and</strong> abundancy <strong>of</strong> depth-dependent benthonic foram<strong>in</strong>iferal<br />
assemblages. The paleodepth can be derived from previous studies <strong>of</strong> other<br />
authors (Fig 4.2) which show the ma<strong>in</strong> patterns <strong>of</strong> occurrence <strong>of</strong> benthonic<br />
foram<strong>in</strong>ifera at different depths, as well as the distribution <strong>of</strong> Midway <strong>and</strong><br />
Velasco-type faunas.<br />
In the present study, the qualitative <strong>and</strong> quantitative foram<strong>in</strong>iferal<br />
count<strong>in</strong>g is carried out <strong>in</strong> detail for about 50gm <strong>of</strong> the residue <strong>of</strong> some<br />
selective sample <strong>in</strong> each biozones, the Agglut<strong>in</strong>ated / Calcareous ratios <strong>and</strong><br />
the quantity <strong>of</strong> both planktonic <strong>and</strong> benthic forams are calculated for each<br />
sample to determ<strong>in</strong>e the environmental conditions that prevailed dur<strong>in</strong>g the<br />
deposition <strong>of</strong> the Maastrichtian - Early Paleocene sequence <strong>in</strong> the studied<br />
area. In addition, their lithologic characters are significant <strong>in</strong>dicators for the<br />
paleodepth. Moreover, the pattern <strong>of</strong> sea-level oscillations is also <strong>in</strong>ferred by<br />
calculat<strong>in</strong>g the P/B ratio, the Aggl. /Calc. ratio, the planktonic diversity <strong>and</strong><br />
distribution <strong>of</strong> the planktonic groups as well as the benthonic associations.<br />
The foram<strong>in</strong>iferal distribution is a function <strong>of</strong> the water depth available over<br />
the shelf dur<strong>in</strong>g any particular <strong>in</strong>terval, (Canud et al, 1991); Elnady &<br />
Shah<strong>in</strong>, 2001; Samir, 2002; Maestas et al., 2003; Chacon <strong>and</strong> Mart<strong>in</strong>-<br />
Chivelet, 2005)<br />
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