Oligosteginid Assemblages of Basinal limestone Succession in Ismael awa Section , kurdistan region , North Iraq

Oligosteginid (calcispheres ) assemblages which found in Dokan Formation, Erbil Governorate, Kurdistan Region, have a stratigraphic distribution similar to that found in Bangestan Group (Albian-Campanian) of Lurestan Province, Iran. Ten rock samples were collected from Ismael Awa section, Dokan formation and 20 thin sections were made and studied under microscope. There are five oligosteginid species found in Dokan Formation and all these species are of Late Albian, the depositional environment of the formation is tropical to subtropical, warm water 30-32 ◦ C on the continental slope to abyssal zone and paleosalinity between 34-37 ‰. key words: oligosteginid, calcisphere, Albian, Dokan. لامش ,ناتسدرك ميلقا ,هوآ ليعامسا عطقم يف يضوحلا يريجلا رجحلا عباتتل دنجتسوجيلولاا تاعمجت قارعلا

Awa section, Dokan formation and 20 thin sections were made and studied under microscope.
There are five oligosteginid species found in Dokan Formation and all these species are of Late Albian, the depositional environment of the formation is tropical to subtropical, warm water 30-32 • C on the continental slope to abyssal zone and paleosalinity between 34-37 ‰.

Introduction
In the third edition of dictionary of earth sciences edited by [1], calcispheres are defined as small calcite spheres, up to 500 μm in diameter, commonly found in Palaeozoic limestones and believed to be of algal origin.They consist of a micrite wall enclosing an interior which is hollow or filled with sparry-calcite (sparite).The Dokan Formation crops out along the High Folded Zone, NE Iraq, it's lithology consist of grayish brown, thick bedded, recrystallized limestone, the upper contact is conformable with Gulneri Formation and the Lower contact is unconformable with Upper Qamchuqa Formation [2].The formation was deposited in tropical to subtropical, warm water 30-32 •C on the continental slope to abyssal zone and paleosalinity between 34-37 ‰ [2].The oligosteginid assemblages is well distributed along Dokan Formation, and these assemblages was already dated as Late Albian because of their association with other foraminiferal genera, [2].These mini calcareous spheres (clacispheres) regarded as algae by [3] who indicating that they are commonly found in lagoonal limestone successions from the Devonian onwards.He indicates that calcispheres are best to study in thin sections or peels.The section under study is located in the valley near the water well in Ismail Awa village near Degala Town, Erbil Governorate, NE Iraq.The coordinates of the section are (44 • 26′ 23 ″ Longitude), (36 • 12′ 43 ″ Latitude), figure 1.

Materials and methods
Ten rock samples are collected from an outcrop of Dokan Formation which were 20 thin sections prepared in order to examine their contents under microscope, the calcispheres are

Description:
Simple test, spherical, unilocular; the wall is thin, imperforate, laminated, composed of radially arranged calcite; this subspecies can be recognized in thin sections by watching that the wall looks like separated from the central body by a dark zone.Aperture not present.

Discussion:
This subspecies is composed of, imperforate, radially laminated hyaline calcite wall, it is first described by [6] from the Coniacian to Turonian rocks in Iran and thought to be an evolutionary trend of Calcisphaerula innominata, there is no difference between the Iraqi and Iranian subspecies except the stratigraphic age (Late Albian) which found by the author, figure 2.

Description:
Simple test, spherical, unilocular; the wall is thick, imperforate, laminated, composed of radially arranged calcite; no aperture present.

Discussion:
In the lowest strata, the thickness of the wall of this species is still in the same range mentioned above but it is become narrower in the middle and upper part of the Dokan Formation and the wall is more thick than the oldest species.This species is similar to that found by [6] in Bangestan Group of western Iran form the age Albian-Early Cenomanian.and similar to that which found by [9] in Sarvak Formation (Late Albian-Late Cenomanian) from Tang-e-Chenarbashi, Southwest Ilam, Eastern Iran.Calcisphaerula innominata was discriminated by [10] in Cupido Formation (Albian-Cenomanian) from Northeast Mexico, and have a similar outline morphology.According to [11]

Description:
Test simple, unilocular, elongate oval, circular in transverse section; extremities rounded; wall laminated, imperforate, composed of radially arranged calcite; aperture simple, small, located at one extremity of the test.

Discussion:
The Iraqi species is slightly different from the Iranian one due to have less wall thickness and being more ovate, this species is occur just in the lower part of Dokan Formation and disappear in middle and upper parts of the formation which indicate a short stratigraphic range, while [6] described P. ovalis from the Albian to Late Turonian.

Discussion:
The thickness of the wall is highly variable in the same sample and through the entire formation.
The Iraqi species have a wall is similar to that found in Iranian specimen composed of imperforate, laminated, radially arranged hyaline calcite which described by [6] from the Upper Albian-Coniacian, while [4]   5; [12], pl.a-d.

Description:
Simple test, subconical, unilocular, the outline is helmet-shaped, Aperture is present and simple found in the central lower part of the test, the aperture side of the wall is either concave or even.

Discussion:
The Iraqi specimen is differing from that described by [6] in Bangestan Group of western Iran due to the shape side of the aperture which is concave or even in the Iraqi one and slightly convex in the Iranian specimen, also there is a wide difference in the stratigraphic range of the Iraqi specimen which have Late Albian while the Iranian is Albian-Cenomanian.B. conoidea is similar to Mixican one described by [12] that have a heart shape and a wall formed by calcite crystals oriented in linear rows.

Figure 1 .
Figure 1.Satellite image showing location of the study area

Figure 2 .
Figure 2. Stratigraphic range chart of clacispheres in Ismael Awa section
6a. Pithonella sphaerica (Kaufmann, 1865) [13], p. 193, pl. 1, figs.7a, b; [14], p. 340, pl. 18, figs.a described P. sphaerica from Mexico as having a granular and only partially lamellar calcite wall.On the other hand, [15] discriminated a radial hyaline wall structure in similar forms from the Paris Basin.[12] discriminated the Maxican species from Cenomanian-Early Turonian that has a wall measured 25 µm and formed by two concentric layers divided by dark lines.The diameter ranged from 70 to 100 µm for the analyzed specimens.This species is occur only at the lower to the middle part and disappear from the other part of Dokan Formation.