Evolutionary aspects of Lepidocyclina ( Nephrolepidina ) from Baba Formation (late Oligocene) in Bai-Hassan well-25, Kir
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ORIGINAL PAPER
Evolutionary aspects of Lepidocyclina (Nephrolepidina) from Baba Formation (late Oligocene) in Bai-Hassan well-25, Kirkuk area, Northeast Iraq Imad Mahmood Ghafor
Received: 9 December 2014 / Accepted: 24 February 2015 # Saudi Society for Geosciences 2015
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 praemarginatamorgani, 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. Keywords Lepidocyclina (Nephrolepidind) . Larger foraminifera . Bai-Hassan well-25 . Kurdistan Region . North Iraq
differentiated megalospheric test and special attention, is directed toward the embryonic apparatus and periembryonic chambers. He added that parts are likely to have been affected by abnormal environmental conditions during life; he further added that this genus is usually divided into a number of subgenera, and in the Indo-Pacific province, there are three common subgenera Lepidocyclina (Lepidocyclina), Lepidocyclina (Eulepidina), and Lepidocyclina (Nephrolepidina). As early as 1936–1937, Tan Sin Hok was the first to emphasize the importance of periembryonic chambers for the classification and evolutionary trends in Lepidocyclina, but it was Van Der Vlerk (Van Der Vlerk 1929; Van Der Vlerk 1957; Van Der Vlerk 1959a, b; Van Der Vlerk 1963a, b, and Van Der Vlerk 1974) who introduced numerical methods by defining a number of parameters in the classification of Lepidocyclina. The principle of nepionic acceleration was tested in successive European Lepidocyclinidae by Drooger and Freudenthal 1964, Freudenthal (1966), Mulenkamp and Amato (1972), Geerates (1983), Drooger and Laagland (1986), and Drooger (1993) that mentioned using numerical methods. Ghafor 2004 mentioned that these studies supported the idea of more than one pattern of evolution in the group. In the present now, the subgenus Lepidocyclina (Nephrolepidina) is found in the bioclastic limestone of late Oligocene age, in the Bai-Hassan well-25 (Fig. 1).
Introduction
Previous research on Lepidocyclinidae
The genus Lepidocyclina Douvillé, classified by Cole (1938) and reviewed by Adams (1987), who emphasizes on well-
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