Evolutionary Aspects of Lepidocyclina (Nephrolepidina) from Baba Formation (Late Oligocene) in Bai-Hassan Well-25, Kirkuk area, Northeast Iraq

Abstract

The study is based on subsurface sequences of bioclastic limestone in Kirkuk area, Northeastern Iraq. These sequences were deposited in a shallow, open marine environment during late Oligocene. Tests of larger foraminifera Lepidocyclina (Nephrolepidina) are abundant in the lower and upper parts of the Baba Formation. Biometric investigations of the oriented tests megalospheric of Nephrolepidina assemblages from, Bai-Hassan well-25 section, identified three morphometrically species (Lepidocyclina praemarginata, Lepidocyclina ex.interc praemarginata-morgani, and Lepidocyclina morgani). The identification is based on the combination of three parameters, the first is factor A which consist of degree of embracement of protoconch by the deuteroconch. The second one (factor B) includes the number of accessory auxiliary chambers on the deuteroconch. The last one (factor C) is the expression of the angle (Alfa) which is formed by the two hypothetical line from the center of protoconch through the outer attachment points of the deuteroconch walls protoconch.