Foraminiferal biozonation and morphogroups from shale memberof the Aitamir Formation in Maraveh Tappeh section, northwest Koppeh-Dagh Basin

AbstractThe Aitamir Formation is divided into two members the lower sandstone and the upper shale. 32 genera and 57 species of foraminifera have been recognized. According to identified foraminifera Rotalipora appenninica Interval Zone, Rotalipora globotruncanoides (Rotalipora brotzeni) interval zone and Whiteinella aumalensis-Dicarinella canaliculata assemblage zone are proposed and a l Albian-l Cenomanian age is attributed for upper shale member of the Aitamir Formation. Palaeoecological studies led to recognition of three calcareous, two agglutinated benthic and three planktonic foraminifera morphogroups. In the lower one third of shale member, the planktonic foraminifera are more abundant than agglutinated benthic foraminifera, while in the upper one third, the frecuency of all morphogroups increase. Calcareous benthic morphogroups could be attributed to aerobic, shallow to slightly deep water, oligotrophic environment; while the agglutinated benthic morphogroups show aerobic, mesotrophic to eutrophic condition that are characterized by a dominance of arenaceous shallow infaunal specimens which are active deposit feeders. Planktonic foraminifera morphogroups with trochospiral and smooth test show that may have lived near the surface water in the aerobic to semi aerobic environmental conditions. The increasing number of planktonic foraminifera and specially keeled species could suggest recovery in paleoenvironmental conditions.