Biostratigraphy and Paleoecology of Azkand and Anah formations (Late Oligocene) in Wadi Al-Khazgha Algarbi, Anah area, West of Iraq

Biostratigraphy and paleoecology of the Azkand and Anah formations were investigated in Wadi Al-Khazgha Algarbi, Anah area, Anbar Governorate, Western Iraq. Twenty two samples were taken from one section close to the asymmetrical ENE Anah Anticline (Wadi Al-Khazgha Algarbi), containing twenty species of larger benthic foraminifera and skeletal fragments of brachiopods, corals, pelecypods, gastropods, and calcareous algae. The carbonate deposits of the Azkand Formation from the Chattian age consisted of white, fossiliferous larger benthic foraminifera (Lepidocyclina), well-bedded, chalky limestone in the lower part, and recrystallized limestone. Anah Formation was mostly composed of creamy, porous, massive-bedded, hard recrystallized, fossiliferous (coralline red algae and larger benthic foraminifera) limestone. Based on the identification of the larger benthic foraminifera and other skeletal grains, two biozones ((Lepidocyclina Partial–Range Biozone and Miogypsinoides complanatus-Rotalia viennoti Assemblage Biozone) of Azkand Formation and two assemblage biozones (Austrotrillina asmariensis- Archaias kirkukensis Assemblage Biozone and Peneroplis evolutus-Austrotrillin asmariensis-Dendritina rangi Assemblage Biozone) for Anah Formation of Late Oligocene- Early Miocene (Chattian- Lower part of Aqutanian) age have been recognized. The biotic relationships found in this study imply that the Azkand Formation carbonate sedimentation occurred in a marine environment, tropical to subtropical, under oligotrophic to mesotrophic conditions at depths water of 12–80m, and Anah Formation was thriving in normal to slightly saline, tropical to subtropical waters, at depth of 40-80m.