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 Three Biostratigraphy<br />
It is important to mention that the conventional <strong>in</strong>dex species Abathomphalus<br />
mayaroensis <strong>of</strong> Late Maastrichtian recorded very rare presentation <strong>and</strong> it is<br />
frequently absent <strong>in</strong> shallow cont<strong>in</strong>ental shelf sections <strong>in</strong> all studied regions<br />
which may be due to paleoenvironment condition <strong>of</strong> the deeper <strong>and</strong> more<br />
bas<strong>in</strong>al oceanic environment around low latitudes restrictions <strong>of</strong> the species<br />
Canudo et al., (1991), <strong>and</strong> <strong>in</strong> high latitudes disappear prior to K/T <strong>boundary</strong><br />
(Blow, 1979). Therefore the A. mayaroensis Biozone is geographically <strong>and</strong><br />
ecologically restricted. In such cases it is better to replace the A. mayaroensis<br />
Biozone by other biozones to avoid any ambiguous <strong>and</strong> vague situation about<br />
first appearance <strong>and</strong> last ext<strong>in</strong>ction datum event. (Figs 3.12 <strong>and</strong> 3.13)<br />
For the Paleogene subdivisions zonal scheme previously have been<br />
developed <strong>in</strong> two widely separated geographic areas: the eastern hemisphere<br />
(Caucasus mounta<strong>in</strong>s, e.g. Subbot<strong>in</strong>a, 1953; Krashen<strong>in</strong>ikov, 1969), <strong>and</strong> <strong>in</strong> the<br />
western hemisphere (Tr<strong>in</strong>idad, e.g. Bolli, 1957 a, b <strong>in</strong> Samir, 2002).<br />
A discussion <strong>of</strong> all subsequent modifications <strong>of</strong> the orig<strong>in</strong>al zonal scheme<br />
proposed by Bolli (1966), Blow (1979), Berggren & Miller (1988), Berggren et al.,<br />
(1995), Berggren & Norris (1997), Olsson et al., (2000), represent the base <strong>of</strong><br />
Paleocene zonal scheme for this study with other mentioned authors <strong>in</strong> Fig<br />
(3.13) which shows a comparison between this zonal scheme <strong>and</strong> earlier<br />
developed schemes. It is worthy to remember that the orig<strong>in</strong>al, genetic radiation,<br />
phylogenetic reconstruction relationship <strong>and</strong> geologic ranges <strong>of</strong> Paleocene<br />
planktonic foram<strong>in</strong>ifera were established by Liu & Olsson (1992), <strong>and</strong> Olsson et<br />
al., (2000), which form the base pr<strong>in</strong>ciples datum event <strong>of</strong> work<strong>in</strong>g group up on<br />
the( Atlas <strong>of</strong> Paleocene Planktonic Foram<strong>in</strong>ifera) by Olsson et al.,(2000), figs<br />
(4.9 -4.11)<br />
3.2.1- Biostratigraphy <strong>of</strong> the Upper Cretaceous Formations:<br />
Accord<strong>in</strong>g to identified planktonic foram<strong>in</strong>iferal assemblages with<strong>in</strong> upper<br />
most part <strong>of</strong> Shiranish Formation, Reddish to pale brown succession, Tanjero<br />
Formation <strong>in</strong> Smaquli area <strong>in</strong> addition <strong>in</strong> upper part <strong>of</strong> Tanjero Formation <strong>in</strong> all<br />
other sections, eight biozones are recorded from the studied sections. The<br />
biostratigraphic zones <strong>of</strong> the studied area are described from the bottom to the<br />
top as below:<br />
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