Iraqi Geological

Abstract


Introduction
The present study is a part of in progress MSc.Study that deals with the systematic study of ostracods obtained from Dammam Formation, that in which was described by (Bramkamp, 1941) (in Jassim and Guff, 2006) from the Dammam dome in Eastern Saudi Arabia (Bellen et al., 1959 ).Lithologicaly, in the type section, the formation consists mainly of carbonate successions that represented by chalky limestones, fossiliferous limestone (Nummulitic-Alveolinids limestones ), sometimes porous dolomitized limestone (Owen andNasar,1958 in Bellen et al.,1959), while in the studied subsurface section, the formation is consist of limestone, chalky limestone, marl and fossiliferous limestone as shown in Fig. 2. The thickness of Dammam Formation in the Iraqi supplementary type section is 250 m, while in the studied section is about 85 m.
Geographically, the studied section locates at borehole N2 in Al-Najaf city within the coordinates of 31˚31ˊ53.4˝N and 44˚24ˊ21.4˝E. Fig. 1.; and tectonically, it locates at the stabile shelf within the Mesopotamian Zone.The lower contact of the Formation is conformable lying above Rus Formation (Early_ Eocene), and the upper contact is unconformable to Eupdhtaties Formation (Miocene).

Materials and Methods
Forty five subsurface rock samples were collected from Dammam Formation in borehole N2 in Al-Najaf City.The samples were prepared for paleontological purposes as the method of Moore and Pitrat (1961), which include cutting the samples by hammer to a size of about 1 cm 3 and soaked in water for 24 hrs; boiling the soaked sample by adding (if needed) H2O2 than washing in 100 mesh sized sieve, repeating the process relatively to the lithology, finally picking the ostracode remains and store in suitable slides.The specimens are studied by binocular microscope (brand: KERN OSE) and photographed by digital microscope adapter camera (brand: UCMOS05100KPA).The obtained ostracods are reposited in University of Mosul, college of Sciences, department of Geology under the abbreviations Dam.F.Na.(Dammam Formation Najaf).

Systimatic Descriptions
The systematic description of the obtained ostracods are based on the system that established by each of Morkhoven (1963) and Hartman and Puri (1974), the ranges of the described species are illustrated in Fig. 3 Affinities: The present species is very similar to Alocopocythere attitogonensis Apostolescu, 1961, (in Morsi et. al., 2011) from northwest Tunisia, but it differs in having much wider posterior.Generally the Alocopocythere iraqaensis is different from all genera that described with Alocopocythere in its featured outline in the side view; for that, the present species is established.
Affinities: The present species is very similar to Loxoconcha sp.2 Hawramy and Ali, 2018 from the Middle Miocene on Northern Iraq, but differs in having longer carapace and more intense reticulate ornamentation.Generally the present species is different from all genera that described with Loxoconcha in its featured outline in the side view; for that, the present species is established.Biggest height locates at the middle, while the biggest length passes near the ventral margin.The anterior is narrowly rounded and reclining ventrally, the posterior is rounded and very wide related to the carapace.Dorsal margin is convex and merge steeply with the anterior and the posterior.Ventral margin is straight and also merge steeply with the both ends.The carapace is thin and the posterior half is more swollen than the anterior half.The outer surface has no ornamentation except some separated normal pores.The right valve is bigger than the left valve.Affinities: The present species is very similar to Xestoleberis derorimensis Rosenfeld, 1974(in Shahin, 1991) from th Cenomanian-Turonian of Egypt, but differs in having wider posterior.Generally the present species is different from all genera that described with Xestoleberis in its featured outline in the side view; for that, the present species is established.

Conclusions
The present study generally focused on some important genera that have important paleoenvironmental implications, which used (in unfinished MSc.work) to detect that there was some kind of marine environmental conections between the Indian sub-continent, Saudia Arabia and the Caribbean basins due to the texta similarity between theis basins.Three new species with a high level of differences were described for the first time as Alocopocythere iraqaensis sp.nov., Loxochoncha dammamensis sp.nov.and Xestolebris eocaenica sp.nov. in which have in which it represents a scientific addition to the ostracods of the Eocene age of Iraq and adjacent areas.The importance of the described genera in the present study (Cytherella, Cytherelloide, Bairdia, Bairdiobbilata, Loxoconcha, Xestoleberis, Alocopocythere, Anommatocythere) is that all of them were indicates the shallow, neritic, carbonate withe normal salinity environment where they originally exist; so they are good paleoenvironmental indicators.

Fig. 1 .
Fig.1.Tectonic map of Iraq shows the location of the studied area (Fouad, 2015 in Iraqi Bulletin of Geology and Mining, 2015)

Fig. 3 .
Fig.3.Distribution of the obtained Ostracods from Dammam Formation Siddiqui and Al-Furaih, 1981. is referred to Dammam Sample Number.Cytherella tawaica Tewari and Sing, p. l27, pl.2, figs 3 a-d Figured specimen: Dam.Fm.Na.1 Materials: Two carapaces and one valve Dimensions (μm): Length: 710 , Height: 502 Type Horizon: Da.S.No.48Remarks:TheIraqi specimens were identical with Cytherella tawaicaTewari and Singh,1966; with presence of slight differences of in having nearly straight ventral margin and somehow pitted surface.The present species is totally agree with the Tunisia species that described bySiddiqui and Al-Furaih, 1981.Carapace is sub-quadrate to sub rectangular in the side view, and sub ovate in the dorsal view.Maximum height locates at the anterior cardinal angle, the longest length pass under the center.Anterior is widely rounded; the posterior is rounded and somehow narrower than the anterior.Dorsal and ventral margins are straight and merge steeply with the anterior and posterior.The anterior and posterior cardinal angles are extremely rounded and non-prominent.The carapace is well calcified and swollen in the middle.The left valve is larger than the right valve; the overlapping is clearly presence nearly all over the outline.The outer surface is covered with distinct reticulate ornamentation that has thick muri and the reticulations are bigger centrally.Sub central tubercle is presence especially in the left valve.