Planktonic foraminiferal and isotope stratigraphy of the upper Cenomanian-Turonian interval in the Zagros Basin, SW Iran

Platform carbonate sediments of Oligocene–Miocene age (Asmari Formation) in the Zagros Basin (SW Iran) have been investigated in order to determine their paleoecology and depositional environment. The Zagros Basin is the result of the opening and closure of the Neo-Tethys Ocean along the northeastern border of the Arabian Plate. The thick sedimentary sequences of the Zagros Basin contain rocks ranging in age from Cambrian to recent. The geological evidence suggests that the region was part of a passive continental margin, which subsequently underwent rifting in the Permo-Trias and collision in the Late Tertiary. The Asmari carbonate system was dominated by foraminifera and corallinacean assemblage. Based on the distribution of the larger foraminifera, four assemblage zones have been recognised. Facies analysis allowed the recognition of nine microfacies types that are grouped into three depositional environments that correspond to the inner, middle and outer shelf. The biota assemblage of the Asmari Formation suggests that carbonate sedimentation took place in tropical waters and oligotrophic to slightly mesotrophic conditions. Our detailed analysis of microfacies and paleoecology shows that the Asmari Formation deposited on a carbonate open shelf dominated by heterozoan and, subordinately, photozoan skeletal assemblage.

New planktonic foraminiferal record across the Aptian–Albian transition in Interior Fars, Zagros Basin, SW Iran: Implication for latest Aptian paleogeography along the southern shallower Neo-Tethys

The article Biostratigraphy of the Kazhdumi Formation (Albian), northeast of Shiraz, Zagros Basin (SW of Iran)”.

A very detailed biostratigraphical analysis, sequential interpretation and paleoecological investigations have been carried out based on the Dasycladacean algae and accompanied benthic foraminifera on the Fahliyan Formation in Kuh-e-Khartang and Kuh-e-Gavbast and correlated with Kuh-e-Surmeh, SW of Iran. Vertical variations of lithofacies and cyclic deposits in the shallow water carbonates can be interpreted in terms of sequence stratigraphy. Sequential interpretations reveal at least three 2nd-order and 3rd-order sequences with several parasequence sets throughout the studied successions. The sequences are given in Berrisian – Early Valanginian, Early Valanginian and Hauterivian age. Family Dasycladacea and subfamily Clypeineae are the most frequent and occasionally reported for the first time from the Zagros Basin and/or from the Southern Tethys. The paleoecological and paleobathymetrical investigations indicate that these strata have been deposited in a shallow internal subtidal (protected lagoon) to external subtidal and platform margins with the interval depths of 5 m to 40 m and their salinity ranges from normal marine to super saturated (hypersaline) conditions.

Chapter 5 - Sedimentology and Geochemistry of the Late Miocene–Pliocene Succession in the Fars Interior (SW Iran): Implications on Depositional and Tectonic Setting, Provenance and Paleoweathering in the Zagros Basin

Paleo-facies distribution and sequence stratigraphic architecture of the Oligo-Miocene Asmari carbonate platform (southeast Dezful Embayment, Zagros Basin, SW Iran)

Assessment of reservoir and fracture parameters is necessary to optimize oil production, especially in heterogeneous reservoirs. Core and image logs are regarded as two of the best methods for this aim. However, due to core limitations, using image log is considered as the best method. This study aims to use electrical image logs in the carbonate Asmari Formation reservoir in Zagros Basin, SW Iran, in order to evaluate natural fractures, porosity system, permeability profile and heterogeneity index and accordingly compare the results with core and well data. The results indicated that the electrical image logs are reliable for evaluating fracture and reservoir parameters, when there is no core available for a well. Based on the results from formation micro-imager (FMI) and electrical micro-imager (EMI), Asmari was recognized as a completely fractured reservoir in studied field and the reservoir parameters are mainly controlled by fractures. Furthermore, core and image logs indicated that the secondary porosity varies from 0% to 10%. The permeability indicator indicates that zones 3 and 5 have higher permeability index. Image log permeability index shows a very reasonable permeability profile after scaling against core and modular dynamics tester mobility, mud loss and production index which vary between 1 and 1000 md. In addition, no relationship was observed between core porosity and permeability, while the permeability relied heavily on fracture aperture. Therefore, fracture aperture was considered as the most important parameter for the determination of permeability. Sudden changes were also observed at zones 1-1 and 5 in the permeability trend, due to the high fracture aperture. It can be concluded that the electrical image logs (FMI and EMI) are usable for evaluating both reservoir and fracture parameters in wells with no core data in the Zagros Basin, SW Iran.

The early Palaeozoic represents an important geological period characterized by a series of major climatic, biological and geodynamic events. The Zagros Basin (SW Iran) is a key area for the study of this time interval, due to the widespread and well-exposed Cambrian-Ordovician successions. The Tang-e- Ilbeyk section (293 m thick), characterized by the superimposition of carbonate- siliciclastic lithological units, provided useful data for palaeoenvironmental and palaeoclimatic reconstructions and new constraints for the lower Palaeozoic palaeogeography of Middle East.

New biostratigraphic observations of planktonic foraminifera and ammonites on the Aptian–Albian intrashelf succession, Zagros Basin, SW Iran

In the Izeh section (Zagros Basin, SW Iran), about two third of the planktonic foraminiferal species, representing less than 20% of the individuals, present in the Maastrichtian polytaxic assemblages, became suddenly extinct at the K/Pg boundary. This mass species extinction testifies end-Cretaceous catastrophic bioevent. The Cretaceous species remain became apparently extinct gradually during the earliest Danian. In fact the unkeeled globotruncanids (Globotruncanella and Rugoglobigerina) as well as the small heterohelicids (Heterohelix and Pseudoguembelina) were also affected by extinction and they were reworked in the basal Danian. Except guembelitriids which persisted longer time. The sudden species extinctions were selective, eliminating geographically restricted large, complex, and deeper dwelling forms (i.e., globotruncanids and large heterohelicids). Contrary, few cosmopolitan small, simple surface-subsurface dwellers (i.e., guembelitriids among small heterohelicids and hedbergellids) crossed the K/Pg boundary and survived the catastrophic event. This selective bioevent is related to the end-Cretaceous bolide and produced ejecta impact inducing major environmental changes as decrease in temperature, collapse of nutriment, and flow breakdown in the water mass stratification. Our geochemical results (δ13C negative shift, δ 18O positive shift, and trace elements anomalies) are consistent with the cooling due to the collision winter triggering collapse of nutriment. Especially the δ 18O values across the upper Maastrichtian and the K-Pg transition in Izeh section although they are lower; they report similar fluctuations to those in El Kef section. Thus these lower values may be indicative of somewhat warmer water at the sea floor. Besides, like as elsewhere, in Izeh, this Cretaceous end catastrophic bioevent is followed by a delayed gradual recovery. Thus, immediately after the K/Pg boundary was created a nearly empty niche in which persisted few Cretaceous survivors with dwarf individuals. These survivors despite they suffered very stressful environmental conditions, they constituted the root stock of globigerinids from which the Cenozoic planktonic foraminiferal species evolved and developed carnivorous food diet.

This study deals with foraminiferal biostratigraphy and paleoecological interpretations for the Late Paleocene to the Early Oligocene carbonate sequence in the Zagros Basin, the Hajiabad Area, SW Iran. This sequence could be divided into three parts, basal fossil-less strata have related to Sachun Formation base on their stratigraphical position, the middle part involves dolomitic to dolomitic limestone of Jahrum Formation, and the upper part consists of the Lower Asmari Formation. In general, the bulk of the section consists of marine deposits, and it is possible to divide them in to several parts base on benthic foraminiferal biozones. The Late Paleocene to the Early Eocene (the Lower Jahrum Formation) has been distinguished by the Miscellanea, Kathina, Alveolina, Fallotella, Lokhartia, Orbitolites, and small rotalids Assemblage Zone. The Middle Eocene (the Middle Jahrum Formation) has been characterized by the Somalina Total Range Zone and the Nummulites-Alveolina Assemblage Zone. The Late Eocene (the Upper Jahrum Formation) has been distinguished by the Chapmanina, Pllatispira, Baccullogypsinoides Assemblage zone, and the outcrop of the Asmari Formation belongs to the Early Oligocene Base on the Nummulites vascus, Nummulites fichteli Assemblage Zone. Clustering content benthic foraminifera in the studied section base on their morphology, coiling, feeding habits, and habitats lead to identification of 15 distinct assemblages with similar ecological niches. Paleoecological reconstructions base on benthic foraminiferal communities indicate that five major ecological habitats include tidal flat and shore, restricted shelf, nonrestricted shelf, oligotrophic shelf, and open marine.

The Tarbur Formation is a Reef carbonate lithostratigraphic unit that outcrops in the Zagros basin. To study biostratigraphy and lithostratigraphy of Tarbur Formation in Zagros basin, Hossein Abad Section was selected. In this section, the Tarbur Formation lies unconformably on the Pre-Campanian radiolarite beds and the Sachun Formation overlies the Tarbur Formation uncorformably. 39 foraminifera species belonging to 27 genera were identified from the Hossein Abad section in the Tarbur Formation. Orbitoides media, Orbitoides cf. concavatus, Orbitoides apiculata, Orbitoides sp., Omphalocyclus macroporus, Omphalocyclus sp., Pseudomphalocyclus blumenthalis, Lepidorbitoides sp., Antalyna korayi, Dicyclina shlumbergeri, Archaecyclus midorietalis and Goupillaudina shirazensis are the most significant foraminifers. Based on faunal assemblages, three biozones were proposed: Archaecyclus midorietalis range zone (late Campanian), Orbitoides—Goupillaudina assemblage Zone (early Maastrichtian and Antalyna korayi range subzone (late Maastrichtian). Foraminiferal assemblage of the Tarbur Formation supports late Campanian to late Maastrichtian age in section of Hossien Abad.

Lower Miocene in SW Iran consists of Gachsaran formation. This formation forms one of the main caprocks of reservoirs of oil fields in the SW of Iran that comprises a thick succession of evaporitic rocks in the Zagros basin. This study presents a facies analysis, sedimentary environments and correlative sequence stratigraphy in the SW of Iran. To study petrography, facies, sedimentary environments and sequence stratigraphy of Gachsaran formation, 10 subsurface sections from Aghajari and Rag-e-Sefid oil fields in the SW of Iran and one surface stratigraphic section in the Shiraz area have been chosen and studied (Hossini-Al-Hashemi section). Facies analysis led to the recognition of 13 facies which are deposited in 2 major sub sedimentary environments, tidal flat (sabkha) and lagoon in homoclinal ramp sedimentary environment. Petrography, microfacies analysis and sedimentary environment of Gachsaran formation show this formation in the study area consists of 4 depositional sequences. These depositional sequences have been separated by both type-1 and type-2 sequence boundaries. Based on gamma-ray, sonic log and thin section from cutting sample permit the identification of six 5th, two 4th and a small part of 3rd order depositional sequences in caprock member 1 and lower part of member 2 Gachsaran formation. Lower sequence boundary with Asmari formation is erosional SB1. Fifth order sequences are observed in a different thickness between 4 and 10 m. In caprock two 4th order sequence with the thickness of about 20 m was recognized, which is only a part of the depositional sequence (3rd order). Lower boundary with Asmari formation is SB1. TST systems tract consists of sabkha and lagoon facies parasequences. MFS in this sequence are designated by bitominous shale and early HST systems tract consists of interbedded sabkha and lagoon facies. Gachsaran Formation in the surface section consists of nine 4th order depositional sequences, which are located in four 3rd order depositional sequences. These parasequences are composed of evaparite carbonate succession of green marl, limestone, sandstone, gypsum and red marl, respectively. In Oligocene–Miocene sea-level transgressive and carbonate Asmari formation has deposited in the south-west of Iran and in the Miocene sea-level regressive, and Gachsaran formation has deposited in the study area under a succession of sabkha/tidal flat conditions.

A regional transect is selected to study the paleoenvironment of the Oligocene and Lower Miocene deposits in the Zagros Basin (Persian Gulf Foreland Basin to the High Zagros). This study rebuilds the sedimentary environments and paleogeography of the Zagros basin deposits in the Oligocene and the Lower Miocene. A transect consists of two stratigraphic subsurface sections at the Persian Gulf Foreland Basin, five stratigraphic subsurface sections at the Dezful Embayment, two stratigraphic outcrop sections at the Zagros Simply Folded and one exposure section at the High Zagros. The sediments are included Asmari Formation and the Pabdeh Formation. Lithostratigraphy studies show that the Pabdeh Formation has been composed of an alternation of marls and medium-bedded argillaceous limestone. The Asmari Formation is generally composed of medium- to thick-bedded limestone. Micropaleontology studies offer Early Oligocene for Pabdeh Formation and Early–Late Oligocene to Early Miocene age for Asmari Formation. Variety in fabrics, textures and fauna features has produced 13 microfacies and based on geometry, lateral and vertical facies relationships, the homoclinal ramp is proposed for the Oligocene and Lower Miocene deposits. Hence, corresponding to this research, the Rupelian sedimentation has occurred in the Dezful Embayment and Zagros Simply Folded, so that a systematic progradation suggests from Zagros Simply Folded (N/NE) (Asmari/Pabdeh Formation) to the Dezful Embayment (S/SW) (Asmari carbonate system). Following a regression system during the Late Oligocene to the Early Miocene, continuing sedimentation uniformly has been felt out in the shallow water system throughout the study area.

The Kazhdumi Formation is one of the most significant rock units in the Bangestan Group in Zagros Basin. In this study, one section of the Kazhdumi Formation (Kuh-e-Rahmat) was selected for research. The section is extended approximately 89 m thick. The lower lithostratigraphic limit of the Kazhdumi Formation is marked by an oxidized zone, while the upper boundary is described as gradational type. The stratigraphic distribution of foraminifer taxa confirms two biozones in the studied section: Hemicyclammina sigali and Mesorbitolina subconcava in the Assemblage Zone and Mesorbitolina aperta in the range zone. Based on the investigated calcareous algae, Trinocladus tripolitanus, Range Zone is described. The identified calcareous algae are well distributed along Kazhdumi Formation. According to the received data of the established biozones, the age of the Kazhdumi Formation is Albian.