Palaeoenvironmental signature of the Late Campanian-Early Maastrichtian benthonic foraminiferal assemblages of Kurdistan, Northeast Iraq

摘要

The Late Campanian to Early Maastrichtian benthic foraminiferal assemblages in the Shiranish Formation of Kurdistan region (NE- Iraq) are placed into three temporally distinct assemblages that are interpreted to reflect environmental changes, principally involving factors associated with paleodepth. In stratigraphic succession the assemblages are: the Lenticulina macrodiscus-Lenticulina pseudosecans Assemblage (Late Campanian), occupying a succession of strata that are equivalent to the lower and upper parts of the Bolivinoides decoratus subzone within the Bolivinoides decoratus benthic foraminiferal biozone; the Gavelinella monterelensis-Gavelinella stephensoni Assemblage (Late to Latest Campanian), occupying a succession of strata that are equivalent to the uppermost part of the Bolivinoides decoratus and B. laevigatus subzones within the Bolivinoides decoratus benthic foraminiferal biozone; and the Coryphostoma incrassata gigantea-Praebulimina carseyae-Loxostomum eleyi Assemblage (Early Maastrichtian), occupying a succession of strata that are equivalent to the Bolivinoides miliaris and B. draco benthic foraminiferal biozones. The foraminiferal assemblages are interpreted as representing outer shelf to middle slope environments, between ca 200 m to at least 600 m water depth, with maximum water depths in the Late Campanian, followed by shallowing into the Early Maastrichtian. The most likely control mechanism for shallowing sea level was the beginning of southern Neo-Tethys Ocean closure at this time. Almost manifesting the turnover from pre-flysch facies to the overlying flysch facies within Kurdistan foreland basin. Such variation in the benthic foraminiferal assemblages controlled essentially by the interactions between the palaeobasin configuration and sea level changes from the Late Campanian to Early Maastrichtian.