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.

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The age of the thick succession of 500m conglomerate and red claystone layers in the incised valleys at the lower part of Tanjero Formation at Chwarta area is estimated to be (1.23 m.y) duration. The age determination is achieved by Planktonic Foraminiferal biostratigraphic zonation which included the following Zones: Globotruncana aegyptiaca Interval Zone (CF8), Gansserina gansseri Interval Zone (CF7) Racemiguemblina fructicosa Interval Zone (CF4), Pseudoguembelina hariaensis Interval Zone (CF3) with missing zones of Contusotruncana contusa Interval zone (CF6) and Pseudotextularia intermedia Interval zone (CF5). Twenty six planktonic foraminiferal species and thirty benthonic foraminiferal species assigned to 33 genera have been recorded. The zonal scheme developed here is correlated with other sequences of Li and Keller (1998a) and discussed.