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

Chapter Four
Depositional Environmenment and Paleoecology
The number of benthonic species at Sirwan valley decreased from 12
species at Plummerita hantkeninoides Zone (CF1) to 7 species in (P0 & Pá),
then increased again upward to 20 species in both Parvularugoglobigerina
eugubina- Subbotina triloculinoides Zone (P1a) and Subbotina triloculinoides-
Praemurica inconstans Zone(P1b) (Fig. 3.2)
The benthonic foraminiferal assemblage represented by calcareous tests
about %80 in all studied sections, except for the lower and middle part of the
Qishlagh section decreased to %60 while at the Cretaceous/Tertiary boundary,
from the upper part of Pseudoguembelina palpebra zone (CF2) to (P0 & Pá)
lowest Danian, there was slightly increasing in agglutinated percent to about
30-40 in all studied section (Gali, Qulka and Sirwan valley). (Figs. 4.3 - 4.5),
4.6- Method of graphical correlation
The American stratigrapher AB. Shaw devised a new technique of semiquantitative
correlation of biostratigraphical sequences. Shaw's method utilizes
a single stratigraphical section which is taken as the standard likely present. In
the study area, the Gali section is selected as standard because it represented
the most simple continuous section and unaffected tectonically by structural
complications. From this section, the limit boundary of (First appearance datum
event FAD and last appearance datum event LAD) for standard zonal scheme
of biostratigraphic zonation utilized and recorded and constructed in state of
total ranges of species, with particular importance being assigned to the first
and last appearance of fossil species. A graph can be constructed using the
data collected from all stratigraphical section. The first and last datum events of
the Biozones provide points on the graph, then the best-fit line is constructed.
Any Changes in the gradient or the graph (dog-legs) indicate changes in the
rate of sedimentation which is observed in graphical correlation between Gali
section (Smaquli area) and both Dokan and Sirwan sections (Figs 4. 8, 4. 9)
which refer to low sedimentation rate in initial part on (R. fructicosa Zone) at
Smaquli area, compared with highest sedimentation rate at both Qulka and
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