Abstract:The Cretaceous/Tertiary (K/T) boundary sequence, which crops out in the studied area is located within the High Folded Zone, in the Sirwan Valley, northeastern Iraq. These units mainly consist of flysch and flysch-type successions of thick clastic beds of Tanjero/Kolosh Formations. A detailed lithostratigraphic study is achieved on the outcropping uppermost part of the Upper Cretaceous successions (upper part of Tanjero Formation) and the lowermost part of the Kolosh Formation. On the basis of the identified planktonic foraminiferal assemblages, five biozones are recorded from the uppermost part of Tanjero Formation and four biozones from the lower part of the Kolosh Formation (Lower Paleocene) in the Sirwan section. The biostratigraphic correlations based on planktonic foraminiferal zonations showed a comparison between the biostratigraphic zones established in this study and other equivalents of the commonly used planktonic zonal scheme around the Cretaceous/Tertiary boundary in and outside Iraq.

The biometric analysis on Miogypsina from bioclastic limestone (Azkand Formation) in Kirkuk area, Iraq reveals that the evolutionary trend based on a distinct overall change in morphology of the nepiont, which change is in agreement with the principle of nepionic acceleration as defined by Tan Sin Hok,1936. The oldest species of Miogypsinoides represented by Miogypsinoides complanata and Miogypsinoides formosensis accompanied by the association Miogypsina gunteri which exhibit in the lower part of Azkand Formation of Late Oligocene age (Chattian). The early Miocene association of Miogypsina s.s. represented by Miogypsina gunteri-tani are often accompanied by Miogypsinoides. Most of these are close to Miogypsinoides bantamensis.