Abstract
The Yamama Formation was studied in three wells (Fh-1, Fh-2, and Fh-3) within Faihaa oil field, south Iraq. Thin sections were studied by using the polarizing microscope examination in order to determine microfossils and biozone. Thirty-five species of benthic foraminifera were recognized, including four index species. In addition, twelve species of calcareous green algae were recognized, including two index species. Other fossils that were recognized in Yamama Formation include Gastropoda, Bryozoa, Coral, Rudist, and Pelecypoda.
 Six biozones were observed, which are Charentia cuvillieri sp. (Range Zone of Berriasian age), Psudochryalidina infracretacea sp. (Range Zone of Berriasian age), Pseudocyclammina Lituus sp. (Range Zone of Valanginian age), Nezzazata Perforate sp.andChoffatella sp.(Assemblage Zoneof Berriasian-Valanginian age), Desycladales Green Algae- Cylindroporella sp. (Range Zone of Early Cretaceous- Berriasian age), and Desycladales Green Algae- Salpingoporella cf. circassa sp. (Range Zone of Valanginian age). According to these biozones, the age of Yamama Formation was distinguished to be the Berriasian-Valanginian.
Highlights
Yamama Formation is one of the most important oil production reservoirs in the southernMesopotamian Zone, which belongs to the Early Cretaceous (Berriasian-Valanginian) sequence
Biostratigraphy of Yamama Formation at Well Fh-1 The following microfossils are identified in the core samples of Yamama Formation at Fh-1 (Figure.4); benthic foraminifera species: Choffatella sp. (d'orbigeny, 1904), Pl.A (Fig.1), Nezzazata perforate sp. (Omara, 1956), Pl.A (Fig.2), PL, Charentia cuvillieri sp. .(d'orbigny, 1904), Pl.A (Fig.3), Pseudocyclammina lituus sp. (Yokoyama, 1890), Pl.A (Fig.4), Suborder Miliolina: Spirologulina sp
Biostratigraphy of Yamama Formation at Well Fh-2 The following microfossils are identified in the core samples of Yamama Formation at Fh-1 (Figure. 5); Benthic foraminifera species include Korkyrella texana sp
Summary
Yamama Formation is one of the most important oil production reservoirs in the southern. The Early Cretaceous succession (late Berriasian- Aptian) extends, from the shore to deep basin, by the Zubair, Ratawi, Yamama, Shuiaba, and Sulaiy formations. It includes important carbonate reservoirs in southern Iraq, namely in the West Qurna, North Rumaila, and Majnoon fields [1]. The present study includes biostratigraphic investigation of Yamama Formation in the wells of Faihaa-1 (Fh-1), Faihaa-2 (Fh-2), and Faihaa (Fh-3) (Table 1), at Faihaa oil field (Figure.). In the southern part of Iraq, Yamama Formation was subdivided into two upper and lower members or reservoir units separated by barriers [5].
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