جستجوی مقالات مرتبط با کلیدواژه « Zagros Basin » در نشریات گروه « زمین شناسی »

Mishan Formation with a thickness of 395 meter which is composed of limestone, marly limestone and marl and early to middle Miocene age (Burdigalian-Langhian), has been measured and sampled in order to study the sedimentary environment and sequense stratigraphy in Bavarian stratigraphic section in the south of Kavar, Fars province. The Mishan Formation is located on the red evaporative and clastic sequence succession of the Razak Formation and under the clastic and carbonate succession of Agha Jari Formation (Miocene-Pliocene age). Based on the characteristics of petrographic features, field evidence, as well as examining the abundance and distribution of foraminifera and other other allochems and orthochems, eighteen microfacies packages were identified in six sub-environments or sedimentary zones (Facies zones) including tidal flat, lagoon, shoal, pach reef, shallow and deep open marine can be placed. The absence of barrier reefs (which are typical of rimmed platforms) and re-deposited carbonates and also gradual conversion of microfacies into each other and the existence of wide areas of tidal, indicate that the sedimentary sequence in this section was deposited on a homoclinal ramp carbonate platform. The sedimentation of limestone-marl deposits of Mishan Formation on the evaporite-clastic sedimentary rocks of Razak Formation, indicate the last transsgresion of the sea water during the Miocene age of the Zagros Basin. The investigation of the sequence stratigraphy of this Formation in the research section has led to the identification of four third-order sedimentary sequences with sequence boundaries of the second type.

This study was aimed at the biostratigraphy and sedimentary environments reconstruction in one of the wells in Maroun oilfield at Dezful embayment zone. We also compared the studied sub-surface section with the equal intervals in Mala-Kuh, Ghale-Nar oilfield, Moshkan section, and Firouzabad section. The thickness of Asmari Formation in the studied well is 370.5 m and consists mainly of limestone, dolomite, dolomitic limestone, sandstone and argillaceous limestone. In this well, the lower boundary of the Asmari Formation with Pabdeh Formation and its upper boundary with Gachsaran Formation is continuous.

For this study, 150 thin sections (mainly drilled cores) were studied in detail for paleontology, biostratigraphy, allochems identification, and microfacies determination. References such as Loeblich and Tappan (1980), Boudagher-Fadel, (2008), Adams & Bourgeois (1967), and other related articles were used to identify the available microfossils. We used the biozonation scheme of Laursen et al. (2009) and Van Buchem et al. (2010) to define and correlate the biozones. Classification of rock types was done according to Dunham (1962) and Embry & Klovan (1971), and microfacies identification and interpretation were carried out based on Wilson (1975), Buxton & Pedley (1989), Geel (2000), and Flugel (2010),

Based on paleontological studies, 43 genera and 61 species of benthic and planktonic foraminifera were identified. They have been classified into six zones (five assemblage zones and one indeterminate zone) as follows:1- Globigerina spp.-Turborotalia cerroazulensis-Hantkenina Assemblage ZoneThis biozone is 76 meters thick and lies between the depths of 3706.5 to 3630.5 m. It corresponds to the upper part of the Pabdeh Formation. In this biozone with Oligocene (Rupelian) age, Globigerina spp. are abundant, and the extinction of Turborotalia cerroazulensis occurs in this biozone.2- Lepidocyclina-Operculina-Ditrupa Assemblage ZoneThis biozone is 129.5 meters thick and lies between 3630.5 to 3501 m. The beginning of this biozone is based on the first occurrence of the Lepidocyclina sp. and Operculina complanata. Its end is marked by the first appearance of the Miogypsinoides compalanatus and Spiroclypeous blankenhorni. This biozone belongs to the Chattian-Rupellian age.3- Archaias asmaricus-Archaias hensoni-Miogypsinoides compalanatus Assemblage ZoneThe thickness of this biozone is 80 meters and lies between 3501 to 3421 meters deep. The onset of this biozone is marked by the first occurrence of Miogypsinoides compalanatus and Spiroclypeous blankenhorni. The first occurrence of Elphidium sp.14, Peneroplis farsensis and disappearance of Archaias distinguish the end of the biozone. The age of this biozone is Chattian.4- Elphidium sp.14 – Peneroplis farsensis Assemblage ZoneThis Assemblage zone is 83 meters thick and lies between 3421 to 3338 meters deep. The age of this biozone is Aquitanian. The onset of this biozone is determined by the occurrence of the Elphidium sp.14, Peneroplis farsensis, and the end of this biozone is characterized by a decrease in the fossil fauna assemblage known as the Ambiguous Zone.5-Indeterminate ZoneWith 70.44 meters thickness, this zone lies between the depths of 3338 to 3267.57 meters. A decrease in fossil assemblages characterizes this interval. According to its stratigraphic locality, this indeterminate zone is related to Aquitanian (Laursen et al., 2009). The fossils present in this biozone are very sparse and consist mainly of porcelaneous and indeterminate milliolids.6- Borelis melo curdica-Borelis melo melo Assemblage Zone?This biozone is related to the uppermost part of the Asmari Formation. The beginning of this biozone is defined based on the occurrence of the Borelis spp., continues to the end of the Asmari Formation. This biozone is 7.56 meters thick and lies between 3267.56 to 3260 meters deep. The age of this biozone is cautiously Burdigalian.Based on the mentioned biozones, the age of Asmari Formation in the studied well is Rupelian – Chattian –?Burdigalian.According to sedimentary texture, sedimentary structures, skeletal and non-skeletal elements in the microscopic studies if the provided thin section, 12 microfacies related to the outer ramp, middle ramp (distal and proximal parts), shoal and inner ramp environments (patch reef, lagoon (semi-restricted and restricted( and tidal flat were identified in the studied well. Gradual changes of facies to each other, the lack of coated structures, and the absence of coated grains are the main evidence suggesting deposition in a homoclinic carbonate ramp. Microfacies analysis shows that planktonic foraminifera in the upper part of the Pabdeh Formation belongs to the outer ramp. Due to the presence of large hyaline foraminifera, the lower part of the Asmari Formation is deposited in the distal part of the middle ramp, while the presence of lenticular foraminifera demonstrates the proximal ramp environment. A high-energy, shallow-shoal environment with the presence of thick-walled lenticular foraminifera, cementation, and grainstone textures characterize the boundary between the middle and the inner ramp. Inner ramp environment is considered by the presence of patchy corals (patch reef) and imperforate foraminifera (Archaias, Peneroplis, milliolids) of the lagoon (semi-restricted and restricted lagoon) and tidal flat zones.

In this study, the upper part of the Garau Formation with a thickness of 24 m in the section of Sheikh Saleh anticline located in the northwest of Kermanshah was investigated from the calcareous nannofossils. In this section, the Garau Formation is mainly composed of medium bedded argillaceous limestone. In order to introduce the index species and biozones, 17 slides from the Garau Formation were studied, which resulted in the identification of three biozones. As a result of this study, 20 species and 15 genera of calcareous nannofossils were identified. Based on the obtained biozones, the age of the upper part of the Garau Formation in the studied section is suggested the late early Cenomanian to the late late Cenomanian. This age is corresponding to the upper part of Eiffellithus turriseiffelii Zone (CC9), Microrhabdulus decorates Zone (CC10), lower part of Quadrum gartneri Zone (CC11) from the Sissingh (1977) zonation and UC1, UC2, UC3, and lower part of UC7 from the Burnett (1998) zonation.

The study of facies stacking and depositional environment of the Jurassic successions in the Fars region indicates important changes in the evolution history of the Zagros Basin, including subaerial exposure and drowning of the platform during that period. To investigate the different aspects of these geological events, two sections of the Jurassic sedimentary rocks in Gadvan anticline and Kuh-e Siah oilfield have been studied by sedimentology, stratigraphy and well logging. The results indicate that the Lower Jurassic sedimentary sequence is composed mainly of carbonate rocks and shales deposited in the inner part of a homoclinal ramp. This sequence terminated by a calcareous soil horizon (calcrete) which formed simultaneously with the Aalenian unconformity and related platform emergence. Subsequent marine transgression and re-establishment of the platform during early Middle Jurassic resulted in the discontinuity surface covered by peritidal carbonates, deep-marine shales and pelagic limestones. Immediate overlap of the platform deposits with the Bajocian deep-marine facies indicates a sudden increase in accommodation space and drowning of the Fars carbonate platform. The drowning was the result of rapid deepening of the basin caused by tectonic subsidence and a coeval global sea-level rise. This time slice represents a significant environmental change across the Zagros Basin during which the Early Jurassic undifferentiated platform (epeiric shelf) evolved into a new sedimentary system. This system containing deep-marine basins separated by platform areas reflects a change to more open marine conditions. Similar sedimentary environment of the Bajocian deposits in Fars and Gotnia Basin (Lurestan and northern Iraq) indicates the extension of deep-marine environment in most areas of the Zagros. Therefore, drowning of the Jurassic carbonate platform is a pervasive event and turning point in sedimentation history and structural evolution of the Zagros Basin that the sedimentary regime has since been quite different.

The Oligo/Miocene carbonate succession of the Asmari Formation from Zagros foreland Basin is cropped out in Dehdasht area (southeast of the Izeh zone). In compare to depositional area of the Asmari intra-shelf basin (more than 1500 kilometre2) and available data, the study area is nearly untouched and need more investigation. This study mostly focused on biostratigraphy of the Asmari Formation though four naturally well-exposed outcrops (Ganaveh, Siang, Arand and Dehdasht). A precise biostratigraphic interpretation of the Asmari Formation was compiled on the basis of the larger benthic foraminifera biozones allowing subdivision of the successions into four well-dated assemblages. Assemblage 1 only is present in the Ganaveh and Siang sections, indicating the Rupelian-Chattian? age. This assemblage toward the NW of the study area (Arand and Dehdasht) replaced by pelagic marl of the Pabdeh Formation. Assemblage 2 is restricted to the Chattian due to the first occurrence of Spiroclypeus blanckenhorni and also flourishing of the Archaias species. The low diversity of biotic contents and existence of Miogypsina and Favreina asmarica mark Assemblage 3 referring to the Aquitanian. Appearance of the Borelis melo group as a main characteristic of Assemblage 4 indicates Burdigalian. This investigation proves that the carbonates of the Asmari Formation in the studied area started to deposit in a proximal domain of a carbonate platform from Rupelian, whereas it was started in distal position from Chattian.

In order to study the early Aptian Oceanic Anoxic Event 1a (OAE 1a), calcareous nannofossils are investigated at the late Barremian ‒ early Aptian sediments of the Garau Formation at south west of the Kabir-Kuh anticline, Qaleh-Darreh section. Ninety species of calcareous nannofossils from 43 genus and 15 families are identified along with marker species like Hayesites irregularis and Eprolithus floralis. Based on index calcareous nannofossil taxa, the studied interval is located between the uppermost part of the CC6/NC5 and the early part of CC7/NC7A. The first occurrence of H. irregularis, the marker of the Barremian ‒ Aptian boundary, used as an index species between CC6/NC5E and CC7/NC6. Statistical analysis of the calcareous nannofossil assemblages at the studied interval indicate the presence of nannoconid decline at the Barremian ‒ Aptian boundary and early Aptian and nannoconid crisis at CC7a/NC6B biozone. Nannoconid crisis is one of the main markers of the early Aptian OAE 1a that is recorded from different parts of the world at the Tethys and Boreal realms, Atlantic and Pacific oceans at the early Aptian (NC6 biozone). At the current study the early Aptian OAE 1a is recorded from the Garau Formation based on calcareous nannofossil assemblages.

The Asmari Formation is the main reservoir rock for the Aghajari oilfieild. It is composed of about 400-meter limestone, dolostone and interlayers of sandstones. Study of 1200 meters drilling cores, 2800 microscopic thin sections, 12 SEM analyses along with 125 routine core tests in 5 cored wells indicate that the Asmari Formation was effected by various diagenetic processes such as micritization, compaction, cementation, fracturing, dissolution and dolomitization. Some of these processes (e.g. dissolution, dolomitization and fracturing) have constructive effects on the reservoir quality and created wide variety of porosity types including vuggy, intercrystaline and channel in upper parts of the Asmari Formation. Destructive diagenetic processes (micritization, compaction and cementation) have destroyed pore spaces and make the lower parts of the Asmari (specially zone 5) to a non-reservoir unit. Porosity-permeability plots on the Lucia's diagram show sandstones and carbonates rocks with interparticle porosities have good reservoir qualities and always plot on upper parts of classes 1-3. Samples with fracture porosity mainly plot on upper part of class 1. This shows fractures has no considerable role in promoting the porosity, but they strongly increase permeability. Dolostones and the rocks with vuggy porosity have plotted on classes 2 and 3 (high porosity, relatively high permeability). Paragenetic secession of the Asmari Formation shows the diagenetic processes occurred syn-sedimentary on sea floor, after sedimentation during the low-deep burry and uplift. The results of this study can be useful in detection of reservoir zones, increasing of hydrocarbon production and enhanced recovery of this oilfield.

The Pabdeh Formation (Paleocene–Oligocene) is located in the Zagros foreland basin. This formation was well appreciated as a source rock and somehow a potential reservoir particularly in the Dezful Embayment. Although it has been less appreciated due to overwhelming fine grained lithology in the majority of the Zagros basin. Microfacies analysis and depositional environment of the Pabdeh Formation was studied by examining 500 samples collected from three surface sections namely Malekshahi, Gandab and Pirmohammad, which are located around the Malekshahi city. Based on petrography, proportional abundance of foraminifera and other constituents, texture and microfacies characterizes, eight facies associations were recognized which were deposited in three facies belts on a ramp. As a whole, the Pabdeh Formation comprises marl and limestone beds. Based on geochemical analysis (calcimetry and XRF analysis), the marl lithofacies was established, although it was literally described as shale. Wet chemical oxidation method was employed to determine the organic matter content of some selected samples, which revealed relatively higher organic matter content in marlstones. A mixed carbonate-clastic system may develop, once clastic input exerted into a ramp environment. Such intervals are defined with shale, sandstone and carbonate beds (Tucker 2003). Marl could deposited instead of shale, if the clastic input are limited (Holland 1993). Periods of clastic input in such environments are probably linked to sea-level changes. In present research, the Pabdeh Formation is proposed as a typical carbonate-clastic sedimentation, which was deposited during Paleocene–Oligocene in the Zagros foreland basin. The Zagros basin comprises a thick sedimentary succession over the Precambrian basement (Alavi 2004). The basin was a part of Gondwana supercontinent during Paleozoic which was bordered by Paleotethys in the north, a passive margin during Mesozoic and a convergent orogenic belt in Cenozoic (Bahroudi and Koyi 2004; Sepehr and Cosgrove 2004). The Neotethys was initiated since Late Triassic between Iran and the Arabian plate (Berberian and King 1981; Sepehr and Cosgrove 2004), and ceased during late Cretaceous due converging movement of subducting Arabian Plate beneath the Iran sub-plate (Berberian and King 1981; Stoneley 1981; Berberian 1995). Continental collision in Cenozoic led to the formation a Zagros fold-thrust belt and foreland basin where since Late Cretaceous onward, sedimentation continued without any major break. The succession includes the Gurpi (shale and marl), Amiran (siltstone, sandstone, limestone and conglomerate), Pabdeh (argillaceous limestone, shale and marl), Taleh Zang (limestone), Kashkan (siltstone, sandstone and conglomerate), Shahbazan (dolomitic limestone and dolostone), Asmari (limestone), Gachsaran (anhydrite, marl and limestone) and Aghajari formations (calcareous sandstone, siltstone and sandstone) (James and Wynd 1965). During Paleocene–Eocene the argillaceous limestone and pelagic marls of the Pabdeh Formation were deposited in the middle part of the Zagros basin in a ramp setting (intrashelf basin) (Motiei 1993; Mohseni et al. 2011). The Pabdeh Formation was subject of numerous researches since it is considered as a potential source interval. For example Mohseni et al. (2011) untilized trace fossils for interpreting the depositional environment and recognizing turbidity currents (Mohseni and Al-Asam 2004; Khodabakhsh et al. 2009; Mohseni et al. 2011). Khavari et al. (2014) and Senemari (2018) examined the nanostratigraphy and paleoechology of the Pabdeh Formation. This formation is well defined by the purple shale member at the base with Gurpi Formation and conformably underlies by the Asmari Formation (Motiei 1993) and laterally passes into the Kashkan and Shahbazan formations (Alavi 2004). Although James and Wynd (1965) described the Pabdeh Formation as shale interval with subordinate limestone beds, recent studies revealed a major part of this formation includes limestones which were deposited in ramp setting (Mohseni 2003; Behbahani 2006). Since a major part of the so called shales beds are recognized here as marls, the main goal of this research is examining microfacies, depositional environment and petrographic reappraisal of the formation in three selected surface sections around the Malekshahi County using geochemical approaches.    Microfacies analysis and depositional environment of the Pabdeh Formation was studied by examining 500 samples collected from three surface sections namely Malekshahi, Gandab and Pirmohammad, which are located around the Malekshahi city (southeast Ilam Province, the Zagros basin; Iran). Petrographic investigations of the rhythmites was performed by using polarizing microscope (Zeiss, Axioscope, 40) on three intervals comprising pronounced rhythms. The nomenclatures of lithofacies are based on Dunham (1962) and Pettijohn (1987). Element composition was measured by S4 Explorer/ x-ray Spectrometry-Bruker (WD XRF) in XRF analysis laboratory at Yazd University. The carbonate content (= CaCO3%) were determined by titration method (Carver, 1971). The organic matter content was determined via wet chemical oxidation (by hydrogen peroxide) (Lewis and McConchie 1994).    As a whole, the Pabdeh Formation comprises marl and limestone beds. Distinction between marl/limy marl and limestone beds was done based on geochemical analysis (calcimetry and XRF analysis). Although marl lithofacies was literally described as shale. Wet chemical oxidation method was employed to determine the organic matter content of some selected samples, which revealed relatively higher organic matter content in marlstones. Based on petrography, proportional abundance of foraminifera and other constituents, texture and microfacies characterizes, three micro/lithofacies associations were recognized within the selected rhythms which were deposited in three facies belts on a carbonate ramp environment: A)            Inner Ramp, include the following microfacies (MF): MF A1- Bioclastic mudstone with extraclast and quartz MF A2- Oncoid bioclastic wackestone-packstone MF A3- Ooid packstone B)            Middle Ramp, include the following microfacies and lithofacies (LF): MF B1- Algal bioclastic packstone MF B2- Bioclastic mudstone-packstone with benthic foraminifera and echinoderm LF B3- Marl/calcareous marl lithofacies C)            Outer Ramp, include the following microfacies and lithofacies (LF): MF C1- Bioclastic mudstone-packstone with planktonic foraminifera and glauconite LF C2- Marl/calcareous marl lithofacies Two lithofacies (LF C2 and B3) alternate with the recognized limestone microfacies (as described above) resulting two cycle types: 1-             Alternation of LFC2 with microfacies type C (LF C-MF C cycle) 2-             Alternation of LFB3 with microfacies type B (LF B-MF B cycle)  Sedimentation in the ramp environment may be affected by clastic input (mainly as event deposits). In some cases, more than 90% of basins was filled by these evenest (i.e. tempestite/turbidites; Colombie et al., 2012). The cyclic (=rhythmite) deposition of micro/lithofacies in the study area indicate two depositional mechanisms: 1) background in-situ sedimentation (carbonate facies), 2) fine clastics transported by traction currents from shallow-marine that dumped siliciclastics into the deep-marine. The latter mechanism show characters of event deposits as it was reported by Khodabakhsh et al. (2009) and Mohseni et al. (2011). Limestone-marl alternations in the Pabdeh Formation was possibly controlled by periodic fluctuations in siliciclastic input by shallow-water derived currents (probably turbidity currents). The trace fossils of Zoophycos group are normally associated with turbidites and debris flows in ramp environments. Frequent occurrences of such trace fossils in the study area could be assigned to event deposits. This study revealed the Pabdeh Formation comprise 8 microfacies deposited in a carbonate ramp. The Zoophycos trace fossil displaying an evolutionary change in acceding order which suggest shift from more calm water setting toward relatively agitated condition upward throughout the formation. Marlstone lithofacies is consistently distributed throughout the whole section, which was described literally as shale beds. Relatively more Al2O3 content of marlstones in compare to limestone beds could imply more clastic input during deposition of these beds.

The Zagros mountain belt extends over 1800 km from Kurdistan in N Iraq to the Strait of Hormuz in Iran (Lacombe and Mouthereau 2006). Zagros Mountain belt is one of the richest oil provinces in the world (Emmami 2008) and is important to paleontological, sedimentological, structural and geological studies. The Cretaceous sediments in the Zagros Mountain Belt (SW Iran), is characterized by a large diversity of rocks and facies. The Gurpi Formation is one of the source rock for petroleum in Zagros basin and outcrops extensively to southwest Iran (James and Wynd 1965). The type section of this Formation (49° 13´ 47″ E, 32° 26´ 50″ N) is measured at Tang-e Pabdeh, north of the Lali oilfield in Khuzestan (James and Wynd 1965). This section is composed of 320 meters of dark bluish gray, thin-bedded marl and shale beds and occasionally thin beds of marly limestone (Motiei, 1995). The following publications have appeared for this formation (e. g. Kalantari, 1976; Vaziri Moghaddam, 2002; Ghasemi-Nejad et al. 2006; Darvishzad et al. 2007; Bahrami 2009; Rabbani et al. 2009; Bahrami and Parvaneh-Nejad Shirazi 2010; Bieranvand and Ghasemi-Nejad 2013; Parvaneh-Nejad Shirazi et al. 2013; Beiranvand et al. 2013, 2014 and Fereydoonpour et al. 2014). Late Cretaceous calcareous nannofossils study is still scarce in Zagros basin and is a strong motivation for investigating calcareous nannofossils in southwest Iran. Late Cretaceous calcareous nannofossils in Gurpi Formation were studied by (Senemari and Azizi 2012; Badri and Kani 2014; Razmjooei et al. 2014; Najafpour et al. 2015; Senemari 2015 and Hadavi et al. 2016).
The aim of the present study was to establish the biostratigraphic zonation for the Gurpi Formation and determine age range of this formation in Izeh sub- zone by means of calcareous nannofossils. A 215-m-thick, well-exposed section was chosen for this purpose. The Kuh-e Siah section is located about 15 Km to the north of Deh-Dasht area. This section was measured in detail at 30°54'31. 86 N and 50°36 38. 80 E. Lithologically, it consists of shale, shaly limestone, and shales with thin bedded limestone. It conformably overlies the Ilam Formation and is overlain unconformably by the pabdeh Formation. Material and Methods: In this study a 215-m thick of Cretaceous sediments including the upper part of Illam Formation, Gurpi Formation and the lower part of Pbdeh Formation were recognized. A total of 122 samples with ~ 1 ‒ 2 m sampling interval were collected. Calcareous nannofossils were processed by smear slides technique described by Bown and Young (1998). The slides were studied with a polarized microscope Olympous (BH2) with 1000×magnification. The zonal scheme proposed in this study is based on the ranges of the most important stratigraphically nannofossil taxa. Calcareous nannofossil taxonomy follows Perch-Neilsen (1985) and Bown, (1998). In this study the stratigraphic zonation developed by Sissingh, (1977) modified by Perch-Nielsen (1985) was applied and is compared with, Burnett, (1998) biozones. Discussion of Result and Conclusion: According to the first and last occurrences of the index species of calcareous nannofossils, Late Coniacian to Early Maastrichtian age were recognized for the sediments of Gurpi formation in this area. The standard zones identified are listed below from the oldest to the youngest:Reinhardtites anthophorus biozone (CC15) (Equivalent of Subzone UC11a and UC11b), late Coniacian.
Lucianorhabdus cayeuxii biozone (CC16) (Equivalent of Subzone UC11c and UC12), late Coniacian- middle Santonian.
Calculites obscurus biozone (CC17) (Equivalent of Subzone UC12 and UC13), middle Santonian- Santonian Campanian boundary.
Aspidolithus parcus biozone (CC18) (Equivalent of Subzone UC14 a, b, cTP), early Campanian.
Calculites ovalis biozone (CC19) (Equivalent of Subzone UC14dTP and UC15aTP), late early Campanian.
Ceratolithoides aculeus biozone (CC20) (Equivalent of Subzone UC15bTP), late early Campanian.
Quadrum sissinghii biozone (CC21) (Equivalent of Subzone UC15cTP), early late Campanian.
Quadrum trifidum biozone (CC22) (Equivalent of Subzone UC15dTP andUC15eTP), middle late Campanian.
Tranolithus phacelosus biozone (CC23) (Equivalent of Subzone UC16 and UC17), middle late Campanian- early Maastrichtian.
Reinhardtites levis biozone (CC24) (Equivalent of Subzone UC18), middle early Maastrichtian.
Arkhangelskiella cymbiformis biozone (CC25) (Equivalent of Subzone UC19), late early Maastrichtian.
Using of these results and their comparison to other global nanno events, which were reported on upper Cretaceous stage boundaries, can be used to better identify of these boundaries in this section. In this study the Coniacin- Santonian, Sntonian- Campanian and Campanian- Maastrichtian boundaries were identified as follows:Coniacin/ Santonian boundary: This boundary has been reported as the interval from the FO of M. staurophora to the FO of R. anthophorus by Perch-Nielsen (1985). Bralower et al. (1995) have been shown this boundary between the FO of the M. staurophora to the FO of L. cayeuxii. Burentt (1998), Melinte and Lamolda (2002) and Melinte and Lamolda (2007) have been considered the FOs of R. anthophorus, L. grillii, Micula concav, Lucianorhabdus inflatus and L. cayeuxii in the late Coniacin and the LO of L. septenarius in the Early Santonian. The Coniacin- Santonian boundary (CSB) has been placed between the FO of L. cayeuxii and the LO of L. septenarius, within the CC16 Zone of Sissingh (1977), and in the UC11c sub-zone of Burnett (1998). Also the presence of C. obscures after the FO of L. cayeuxii and higher abundance of M. concava, has been reported the CSB (Lamolda et al. 2014). The first sample of the Kuh-e Siah section contains R. anthophorus, L. grillii, Q. gartneri and M. staurophora. The FO of L. cayeuxii and the LO of L. septenarius has been recorded at 5m and 15 m, respectively. Based on these data, the lowermost part of the Kuh-e Siah section is late Coniacian and the CSB was considered in the Kuh-e Siah section in the UC11c/ CC16/ NC17 zones, between the FO of L. cayeuxii and the LO of L. septenarius.
Santonian/ Campanian boundary:At informal sections of GSSP (Hancock and Gale, 1996; Hampton et al. 2007). , this boundary is marked by the FO of A. parcus parcus. Two main suggested markers, i. e. the FO of A. parcus parcus and the LO of Dicarinella asymetrica occur closely to the base of Chron 33r which may be suggested as the main events for the base of the Campanian (Wagreich et al. 2015). The Santonian- Campanian boundary is described within the intetrval from the FO of A. cymbiformis (UC13a) to the FO of A. parcus parcus (UC14) (Gale et al. , 2008), while Melinte and Bojar, (2010) placed this boundary within the CC17/ UC13 and the LO of A. cymbiformis is located before the boundary. The Santonian- Campanian boundary is located at the base of CC18/UC14 zone, marked by the FO of Broinsonia parca parca, (Wagreich et al. , 2010; Cetean et al. , 2011; Russo, 2013; Dubicka et al. , 2017). In the Kuh-e Siah section, the Santonian- campanin boundary was marked by the FO of A. parcus parcus at the base of the CC18/ UC14/ NC18 at 45 m.
Campanian‒ Maastrichtian bondary: The Campanian ‒ Maastrichtian boundary (CMB) at GSSP is defined below the LO of Q. trifidum and Q. gothicus. The LO of B. parcus constricta is also recorded about 1. 8 Ma above the CMB (Gardin et al. 2001) and considered as an indicator of the CMB which is observed above the LO of Q. trifidum and Q. gothicus (Odin and Lamaurelle, 2001). At Gubbio area (Gardin et al. 2012), similar to Tercis-Les-Bains (Gardin et al. 2001), the LOs of Q. gothicus and Q. trifidum are followed by the LOs of A. parcus constrictus and Q. trifidum and differs with the proposed CC and UC zonations. It must be mentioned that the LOs of T. orionatus (Gardin et al. 2012) and A. parcus constrictus (Gardin et al. 2012; do Monte Guerra et al. 2016) are diachronous between different latitudes. Thibault also used the LO of Quadrum trifidum as marker for the CMB at low latitude site. In the Kuh-e Siah section, the Campanian- Maastrichtian boundary is identified by the LO of the Quadrum trifidum.
1- The presented data suggest that the age of sediments of Gurpi Formation in Kuh-e Siah section are late Coniacian to late early Maastrichtian. In kuhe Siah section
2- According to the continuous presence of L. grillii، M. concava و M. staurophora in samples of Illam and Gurpi Formations and the presence of Q. gartneri and R. anthophorus in the first sample of the Gurpi Formation, the Illam and Gurpi formations boundary is conformably.
3- The LO of B. hayi bio- evente has a reverse order in this study relative to biozones was described by Sissingh (1977). Although the LO of B. hayi was recorded in zone CC19 (Sissingh 1977), the LO of this species has been recorded up to the middle part of the CC20. In this section, the LO of Bukryaster hayi was recorded in the CC20. Razmjooei et al. , (2014) in the northeast of Kazeroon in Iran (Fars area) and Melinte and Bojar (2010) in southern Romania have also recorded the LO of B. hayi in zone CC20. Based on Melinte and Bojar, (2010), the LO of B. hayi in CC20 is attributed to diachronism or reworking.
4- Due to the presence of Biantholithus sparseus, Fasciculithus tympaniformis and Markalius inversus in the first sample of the Pabdeh Formation and the non-identification of the end zone of the CC25/ UC19 zones in this section, the Gurpi and Pabdeh Formations boundary is unconformably.

The Kazhdumi Formation is well exposed and accessible in Tang-e Maghar, northwest of Behbahan city, Zagros basin. In this area, this formation has a thicknees of 344 m and it mainly consists of alternation of black - gray shale with medium – thin-bedded cream – gray argillaceous limestone. The lower contact of the Kazhdumi Formation is disconformable with Daryan Formation and conformable with the Sarvack Formation at the top. A total of 220 ammonite bearing surface samples were collected including the uppermost part of the Daryan Formation (5m) and the whole thickness of the Kazhdumi Formation (344m). This investigation resulted in 21 species (15 genera) which belong to six families. The encountered ammonite species of the upper part of the Daryan Formation and the whole Kazhdumi Formation consist of Douvilleiceras sp., Douvilleiceras cf. mammillatum, Epicheloniceras subnodosocostum– buxtorfi, Hypacanithoplites cf. elegnas, Acanthohoplites cf. aschiltaensis, Nolaniceras nolani, Parahoplites cf. melchioris, Venezoliceras sp., Venezoliceras cf. venezolanum, Mirapelia cf. buarquianum, Mirapelia sp., Oxytropidoceras carbonarium, Oxytropidoceras cf. roissyanum, Hysteroceras cf. orbignyi, Hysteroceras sp., Tonohamites cf. aequicingulatus, Mortoniceras sp., Mortoniceras aff. inflatum, Dufrenoyia sp., Hemiptychoceras cf. gaultinum and Scaphites sp.Amongst these ammonite species, Scaphites sp. and Hemiptychoceras gaultinum are recorded for the first time and the remainder has previously been recorded from this rock unit in the Zagros basin. Likewise, based on stratigraphic potential of the encountered ammonite species the lower Aptian is suggested for the upper part of the Daryan Formation and upper Aptian –upper Albian for the Kazhdumi Formation.Therefore, a hiatus is present between the Daryan and Kazhdumi formations, encompassing the middle Aptian.

In order to study biostratigraphy of the Pabdeh Formation in southwest of Ilam, Marbera section was selected. In this section, Pabdeh Formation is mainly consists of marls, shale and marly limestones. The study of calcareous nannofossils led to the recognition of 72 species and 26 genera. According to the first and last occurrence of index species and based on Martini (1971) zonation, the following biozones are identified:, Tribrachiatus contortus Zone (NP10), Discoaster binodosus Zone (NP11), Tribrachiatus orthostylus Zone (NP12), Discoaster lodoensis Zone (NP13), Discoaster sunlodoensis Zone (NP14), Nannotetrina fulgens zone (NP15), Discoaster tanii nodifer Zone (NP16), Discoaster saipanensis Zone (NP17), Chiasmolithus oamaruensis Zone (NP18), Isthmolithus recurvus Zone (NP19), Sphenolithus pseudoradians Zone (NP20), Ericsonia Subdisticha zone (NP21), Helicosphaera reticulate Zone (NP22), Sphenolithus predistintus Zone (NP23), Sphenolithus distentus Zone (NP24), Sphenolithus ciperoensis Zone (NP25). As a result of this study and based on the obtained biozones, the age of Pabdeh Formation in southwest of Ilam, is Early Eocene (Ypresian) to Late Oligocene (Chattian).

The Gurpi Formation was studied from different aspects at two sections, Farhadabad and Kavar, in southwest and southeast of Ilam where it is composed of 205 m and 158 m of grey to blue marl and shale beds and occasionally thin beds of argillaceous limestones with two formal members of Seymareh (Lopha) and Emam-Hassan. In order to reconstruct paleoclimate during depositional course of the formation, paleontological and palynological data (ratio of specialist to generalist foraminifera (e.s/e.g) and warm-temperate waters dinocysts and spore and pollen grains) were used statistically. The results show that the Gurpi Formation is mainly deposited in a warm-humid climate with two sharp decreases happening in temperature in early Maastrichtian and Danian.

Introduction The Asmari Formation at Deris section has been studied in order to biostratigraphy and paleoecology observations. This section with the thickness of 460 m is located at northwest of Deris village, in interior Fars zone of the Zagros Basin with coordinates of E: 51° 32' 26'', N: 29° 41' 59''. The Asmari Formation deposits in this section consists of interbedded gray and cream to gray thin, medium, thick and massive limestone, with slightly dolomitic nodular and marl. Based on field studies and according to the thickness of the layers, color and lithology, 5 lithostratigraphic units have been nominated for the mentioned section. Method and Materials Using regional geological maps, the study section was identified and measured. Field observation focused on detailed description of bed-by-bed thickness, color, lithology and biotic components systematically. 450 samples from the Asmari Formation were collected. Field works were completed with the study of more than 270 thin-sections for identification of skeletal debris, fabric characteristics and microfacies interpretation. Biostratigraphy results have been determined and concluded based on Ehrenberg et al., (2007) and recent biozones introduced by Laursen et al., (2009) and van Buchem et al., (2010). Result and Discussion Biostratigraphy study based on the distribution of benthic foraminifera, led to identification of 19 genera and 19 species, accordingly two assemblage zones have been recognized and Oligocene (Rupelian-Chattian) age was introduced for the Asmari Formation in the Deris section. The suggested assemblage zones are: 1- Nummulites vascus - Nummulites fichteli Assemblage Zone (Rupelian) This collection has been deployed from the base of the section to the thickness of 66 m and consists of Nummulites vascus, Nummulites fichteli, Nummulites sp., Operculina sp., Amphistegina sp., Heterostegina sp., Elphidium sp.1, Elphidium sp.14, Dendritina rangi, Planorbulina sp., Neorotalia viennoti, Haplophragmium slingeri, Nephrolepidina tournoueri, Nephrolepidina sp., Sphaerogypsina sp., Eulepidina sp., Subterranophyllum thomasi, corralinacean algae, miliolids and textularids. Based on strontium isotope study by Ehrenberg et al. (2007), because of the presence of Nummulites spp. this assemblage indicates the Rupelian stage. On the other part, it is equivalent to the assemblage zone number two of Laursen et al., (2009) (Nummulites vascus - Nummulites fichteli Assemblage Zone) and van Buchem et al., (2010). The age is Rupelian stage. 2- Archaias asmaricus - Archaias hensoni - Miogypsinoides complanatus Assemblage Zone (Chattian) This association is introduced for the thickness of 66-460 m and consists of Operculina sp., Amphistegina sp., Heterostegina sp., Elphidium sp.1, Elphidium sp.14, Dendritina rangi, Planorbulina sp., Neorotalia viennoti, Haplophragmium slingeri, Sphaerogypsina sp., Eulepidina sp., Nephrolepidina tournoueri, Nephrolepidina sp., Reussella sp., Valvulinid sp., Borelis cf. pygmaea, Triloculina trigonula, Triloculina cf. tricarinata, Pyrgo sp., Archaias asmaricus, Archaias operculiniformis, Archaias sp., Peneroplis thomasi, Peneroplis evolutus, Peneroplis sp., Austrotrillina howchini, Austrotrillina sp., Meandropsina iranica, Discorbis sp., Ditrupa sp., Spirolina sp., Spiroloculina sp., Bigenerina sp., Miogypsinoides cf. complanatus, Subterranophyllum thomasi, corralinacean algae, miliolids and textularids. It is equivalent to the assemblage number four of Laursen et al., (2009) (Archaias asmaricus - Archaias hensoni - Miogypsinoides complanatus Assemblage Zone) and van Buchem et al., (2010). So, it is considered as Chattian in age. In this study, the Asmari Formation biozones of Deris section also have been correlated with two other sections in the Internal Fars zone and Dezful Embayment zone of Zagros Basin. This comparison confirms that the foreland basin of Zagros becomes deeper in SE to NW protraction. Some ecological factors such as sedimentary basin substrate, depth and hydrostatic pressure, water energy, temperature, turbidity and light influence the distribution and frequency of organisms specially benthic foraminifera (Hottinger, 1983; Romero et al., 2002; Bassi et al., 2007; Flugel, 2010). By study of skeletal elements and accumulation of carbonate grains, it was found that the Oligocene Asmari Formation carbonates have been deposited in the waters of the tropics. Moreover, detailed analysis of microfacies and paleoecology shows that the association of skeletal debris is heterozoan (foralgal, rodalgal and foramol) in this section.

Sedimentary setting and paleoecology of the rudist-bearing Upper Cretaceous strata were studied in three sections in Khorram abad. The sections include: Tang Shabi Khone, Cham Sangar (Tarbur Formation) and Pir Shams Eldin (upper part of Amiran Formation). The Tang- E Shabi Khone and Chamsangar sections are located in Zagros Trust zone while, the Pir Shams Eldin in Lorestan zone. On the basis of the recognized fossils, the three sections are assigned to the Late Cretaceous (Middle to Late Masstrichtian) and are comparable to Omphalocyclus- Loftusia Assemblage Zone. The petrography study showed that the three sections contain nine microfacies that deposited in an open marine, shoal and restricted marine that based on rudist sedimentary models, are comparable to the Inner- shelf basin prograding margin complexes (Tarbur Formation) and the low- angel open shelf margin complexes (Amiran Formation). Probably, Sepid Kuh Fault was detaching the these settings. Augmentation of entering the detrital and silica due to river injection and runoff and consequently to the eurotrophic conditions in the Tnage Shabi Khone and Pir Shams Eldin, frequency of agglutinate foraminifera were increased but in the chamsangar section due to oligotraphy condition , frequency of hyaline foraminifera is increased. Distribution of the foraminifera and algae indicated that the Tarbur Formation is deposited in a photic zone though, some parts of the carbonates of the Amiran Formation were deposited in a aphotic zone.

Calcareous Nannofossils of the Gurpi Formation have been investigated at Kalchenar section (Northwest of Izeh). In this section, the Gurpi Formation is mainly consists of marls, shaly marls and marly limestones. For introducing index species, calcareous nannofossil assemblages and biozones, 150 slides have been studied which led to the recognition of twelve biozones. As a result, 61 species, 35 genera of calcareous nannofossils were detected. According to the identified biozones, the age of the Gurpi Formation is Late Campanian to Late Paleocene (Late Selandian) and K/Pg boundary is continuous at the studied interval, that is corresponding to CC21- CC26of zonation scheme of Sissingh (1977) and NP1- NP6 of zonation of Martini (1971).