Biostratigraphy and study of the role of planktonic foraminifera morphotype groups in palaeobathymetry of the Gurpi Formation in Lar area (Kuh - e - Kurdeh section)

In order to study the fossil contents of the Gurpi Formation in Lar area (Kuh -e- Kurdeh section) for biostratigraphical purposes, a 70 m thick section was sampled at the type section. The sequence is mainly made up of marl, limy marl, marly shale and marly limestone. The lower contact of the formation with Ilam Fm. is disconform while the upper contact with Tarbur Fm. is continuous. Twenty two species (11 genera)were identified and five biozones were differentiated: Globotruncanita elevata biozone (Early Campanian), Globotruncana ventricosa biozone (Middle Campanian), Radotruncana calcarata biozone (LateCampanian), Globotruncanita stuarti biozone (Late Campanian -Early Maastrichtian) and Gansserina gansseri biozone ((Late Campanian -Middle Maastrichtian). Based on these results, an age of Early Campanian - Middle Maastrichtian is quoted to the formation. The study of the planktonic foraminifera in isolated form resulted in differentiating three morphotype groups. The first group with trochospiral testsusually represents shallow waters; the second group contains forms with strong ornamentations and the primary keels representing mid waters. The third group with compact trochospiral tests and keels are known as deep water indices. Also the planktonic to benthic ratio explains that at the Middle Campanian the waterdepth increased in the area and then it decreased in Middle Maastrichtian.