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The studied Cretaceous-Tertiary succession from northern Iraq is characterized by a thick deposition of carbonate and clastics represented by Shiranish Formation (Late Campanian-Maastrichtian) and Kolosh Formation (Late Paleocene-Early Eocene). The Shiranish Formation is composed of thin bedded argillaceous limestone overlain by blue pelagic marl and represents deposition in outer shelf basinal setting. The Kolosh Formation comprises shale, sandstone, marl and limestone and is deposited in marginal marine depositional environment in a narrow rapidly subsiding trough. Clay mineral investigation proved the presence of smectite, illite, smectite-chlorite mixed layers, chlorite and kaolinite. The first three types are predominantly higher in the Shiarnish Formation, while kaoloinite and chlorite more available in Kolosh Formation. The overall variation, as might be expected, reflects differences in behaviour as a function of grain size, cation exchange capacity and thus differential flocculation. The interaction of those parameters is inferred to be responsible for distribution of smectite and kaolinite and invariably related to depth and distance of the ultimate site of deposition. The kaolinite of larger size and less ionic absorption is probably indicative of near-shore conditions, while smectite and mixed layers which is of small size fraction and higher absorption of ions is deposited in more deeper conditions. Foraminiferal assemblages in these successions supports the clay mineral environmental indications and give an idea about the climatic evolution during this period.
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