Biostratigraphy of the Pabdeh Formation in the Parsi Oil Field (Dezful Embayment, South-West Iran)

Abstract

AbstractIn order to study biostratigraphy and the determination of biozonation in the Pabdeh Formation based on the new planktonic foraminifera biozonation in the Tethys region, one subsurface section in well 1 of the Parsi Oil Field was selected in the southern Dezful Embayment. Based on this study, a biostratigraphic study of 320 thin sections from well 1 of Parsi Oil Field has been carried out. The Pabdeh Formation with a thickness of 404 m consists mainly of shales, marls, argillaceous limestones, and cherty limestone. The lower boundary of the Pabdeh Formation with the Gurpi Formation is unconformable and the upper boundary with the Asmari Formation is conformable. Biostratigraphic studies led to the recognition of 25 genera and 75 species of planktonic foraminifera and then 19 biozones equivalent to the new biozone of Wade et al. (2011) in the Tethys region. These identified biozones include three biozones in the Paleocene, 11 biozones in the Eocene and five biozones in the Oligocene in the studied section in well 1 of Parsi Oil Field and are well correlated with some biozones in the Tethys region. Based on the identified biozones and fossil contents, the age of the Pabdeh Formation is Middle Paleocene (Selandian)–Late Oligocene (Chattian). Keywords: Pabdeh Formation; Paleocene; Oligocene; Dezful Embayment; Parsi Oil Field IntroductionThe Pabdeh Formation as a hydrocarbon source rock is widespread in the Zagros Basin. The type section of the Pabdeh Formation is located in Tange Pabdeh (North of Lali Oil Field) with a thickness of about 800 meters of shales and purple marls, grey shales, layers of argillaceous limestone and sometimes cherty limestones. It contains well-preserved foraminifera that gradually reaches the limestone of the Asmari Formation and spreads in the southwest of Lorestan, Khuzestan, and Fars provinces (Motiei 1995).Most of the biostratigraphic studies of the Pabdeh Formation in the Dezful Embayment are based on biozones (James and Wynd 1965) which are local and have not the capability to correlate with the global biozones. The purpose of this paper is to study the biostratigraphy of the Pabdeh Formation based on foraminifera and biozones based on standard biozones in the Tethys region (Wade et al. 2011) in the Parsi Oil Field (well No. 1). Material & MethodsIn order to identify the biozones of the Pabdeh Formation based on planktonic foraminifera and the new biozonation in the Tethys region, 320 thin sections microscopy of the subsurface section in well No. 1 of the Parsi Oil Field has been studied. Identification of genus and species, the age range of planktonic foraminifera and biozone of the Pabdeh Formation has been studied based on the following literatures (Postuma 1971; Olsson et al. 1999; Premoli Silva et al. 2003; Iaccarino et al. 2005; Berggren and Pearson 2005; Berggren and Pearson 2006; Pearson et al. 2006; Wade et al. 2011; 2018; BouDagher 2015; Berggren et al. 2018). Discussion of Results & ConclusionsPlanktonic foraminifera is widely utilized for the biostratigraphy of Cretaceous and Cenozoic marine sediments and is a fundamental component of Cenozoic chronostratigraphic biozonation (Wade et al. 2011). In this study, biostratigraphy of the Pabdeh Formation in the studied section led to the recognition of 75 species belonging to 25 genus of planktonic foraminifera and 19 biozones based and/or equivalent new biozonation (Wade et al. 2011) were identified and determined. These identified biozones, (P4) belonging to Paleocene and (E2-E5-E7-E8-E9-E10-E11) to Eocene in the studied section, are well correlated with biozones of Tethys region and other identified biozones:The equivalent of Zone P3. Globanomalina pseudomenardii Lowest-occurrence Zone Zone P4. Globanomalina pseudomenardii Taxon- range ZoneEquivalent of Zones (P5&E1). Globanomalina pseudomenardii/Pseudohastigerina wilcoxensis Interval ZoneZone E2. Pseudohastigerina wilcoxensis/Morozovella velascoensis Concurrent-range ZoneEquivalent of Zones (E3 & E4). Acarinina pseudotopilensis Partial-range ZoneZone E5. Morozovella aragonensis/Morozovella subbotinae Concurrent- range ZoneThe equivalent of Zone E6. Morozovella subbotinae /Acarinina cuneicamerata Interval ZoneZone E7. Acarinina cuneicamerata Lowest- occurrence ZoneZone E8. Guembelitrioides nuttalli Lowest-occurrence ZoneZone E9. Globigerinatheka kugleri/ Morozovella aragonensis Concurrent- range ZoneZone E10. Acarinina topilensis Partial-range ZoneZone E11. Morozovelloides lehneri Partial-range ZoneThe equivalent of Zones (E12 & E13). Orbulinoides beckmanni /Morozovelloides crassatus Interval ZoneThe equivalent of Zones (E14 - E15- E16). Hantkenina Highest-occurrence ZoneThe equivalent of Zone O1. Pseudohastigerina Highest-occurrence Zone The equivalent of Zone O2. Turborotalia ampliapertura Highest-occurrence ZoneThe equivalent of Zone O3. Turborotalia ampliapertura /Ciperoella angulisuturalis Interval ZoneThe equivalent of Zone O4. Ciperoella angulisuturalis /Chiloguembelina Interval ZoneThe equivalent of Zones (O5-O6-O7). Trilobatus primordius / Pragloborotalia / Ciperoella assemblage ZoneBased on this study, the lower boundary of the Pabdeh Formation with the Gurpi Formation is unconformable. Studies by Jalali (1971) indicated that there was no sedimentation at the base of the Paleocene and at the end of the Cretaceous. A lack of stratigraphy is evident during the Late Maastrichtian, Early Paleocene (Danin), and earlyMiddle Paleocene. Defined biozones are compared with the other sections presented in the Izeh Zone (Tange Hatti, north flank of Tange Pabdeh and Chahardeh) in the Zagros Basin (SW Iran).Based on biostratigraphic studies of the Pabdeh Formation by Hadavandkhani (2015), in Tange Hatti, north flank of Tange Pabdeh and Chahardeh in the Izeh Zone and studies on Parsi Oil Field (well No. 1) in the Dezful Embayment show that standard biozonation of Tethys region, specially biozonation (Wade et al. 2011) can be considered as a model zonation in the Zagros Basin for the Pabdeh Formation

Keywords

• pabdeh formation
• paleocene
• oligocene
• dezful embayment
• parsi oil field