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

Chapter Four
Depositional Environmenment and Paleoecology
neritic deposits as in upper part of Tanjero Formation in Qala Cholan and
Barzinja area.
The planktonic assemblages of the lower part in Smaquli area from Zone
(CF8) to (CF1) and (CF5) to (CF2) Zones at Dokan and Sirwan valley are
characterized by high values in the percentages of planktonic foraminifera, P/B
ratios, species richness, low Agglutinated percentages and general benthonic
morphotypes of Upper Cretaceous/Early Paleocene Paleodepth indicators
reveal deeper water bathymetry of upper bathyal around 300-600m depth. In
Smaquli area and the outer neritic-upper bathyal around 200-400m depth in
Dokan and Sirwan area, (Depending on all the above mentioned references
evaluation). The paleobathymetric curve shows regular trend in their values
where they exhibit high to moderate percentages values, since the
preservation of foraminiferal species is generally good.
The terminal decreases in species richness 34 starts from the base to the
end of Zone CF1 (Gali section) and continued upwards till the upper most part
of Cretaceous biozone Zone CF1, where the species richness becomes
27. This decline coincides with the LA of Plummerita hantkeninoides and
reaches to 20 in Qulka section and 22 in Sirwan section. The decline is also
coupled with the trend of decrease in species richness, in the percentages
of planktonic foraminifera and p/b ratios. On the other hand, a slight
increase is recorded in the percentages of arenaceous morphotypes.
These criteria indicate shallowing regressive phase in the end of
Maastrichtian basin where the estimated water depth according to Van Der
Zwaan et al.,(1990) ranges from middle to outer shelf, around 50 to 150m
depth.
The present paleobathymetric interpretation is further confirmed and
sustained by the components of the cosmopolitans associated benthonic
assemblage, which resembles that recorded by Van Morkhoven et al.(1986);
Speijer (1994; Tjalsma and Lohmann (1983); Widmark (2000; Berggren and
Aubert (1975); R. Speijer, press. Comm., 2001; Widmark and Speijer 1997a;
95