Gurpi Formation Research Articles

Depositional environment, sequence stratigraphy and biostratigraphy of the Gurpi formation in Fars zone, Zagros Basin (SW Iran)

To study the Gurpi Formation deposits in Fars area, 230 thin-sections which belong to Well No. 43 have been studied. The Gurpi Formation is 155 m in thickness. Lithology of the Gurpi Formation is mainly composed of thin to medium limestone, argillaceous limestone and shale. Lower boundary of the Gurpi Formation with the Ilam Formation is continuous and its upper boundary with the Pabdeh Formation is disconformity. In biostratigraphy analysis, 14 species belonging to 31 genera of planktonic and benthic foraminifers were identified, and 6 biozones were recognized based on planktonic foraminifera as follow: (1) Globotruncanita elevata Partial range Zone, (2) Globotruncana ventricosa Interval Zone, (3) Radotruncana calcarata Total range Zone, (4) Globotruncanella havanensis Partial range Zone, (5) Globotruncana aegyptiaca Interval range Zone, (6) Gansserina gansseri Interval range Zone. Based on the fossil contents and the identified biozones, the relative age of the Gurpi Formation is Early Campanian–Maastrichtian. Petrographic studies of the Gurpi Formation led to recognition of six facies including five carbonate facies and one shale facies. All facies of the Gurpi Formation belong to the open marine environment, which are deposited in a shelf model. Based on facies analysis and sea level curves, three depositional sequences along with four sequence boundaries due to discontinuities and relative levels of sea level falling were identified. The sequence boundaries at the lower boundary and in the middle part of the Gurpi Formation are type II sequence boundary (SB2). Only the upper boundary of depositional sequence 3 (the boundary between the Gurpi and Pabdeh formations) due to exposure and presence of erosion effects is revealed as a type I sequence boundary (SB1).

Biostratigraphy of Campanian—Maastrichtian sequences and facies analysis in Anaran and Samand Anticlines, Zagros, Iran

Gurpi Formation is an important sedimentary sequence in the Zagros area of southwest Iran. It provides effective cap rock at the top of the Bangestan reservoirs and acts as a possible source for younger hydrocarbon reservoirs. Integrated facies analysis and paleontological study of this formation are presented in two surface sections located on the Samand and Anaran anticlines of Lorestan Province. The formation has mainly composed of 203–298 m of argillaceous limestones with two clean limestone members of “Seymareh” and “Imam Hassan.” In the biostratigraphic part of this study, 51 species related to 16 genera of planktonic foraminifers in the Dareh Vorazan section and 44 species belong to 16 genera of planktonic foraminifera in Pahleh section were distinguished. Accordingly, four biozones have been determined in the Dareh Vorazan and the Pahleh sections which are Globotruncana aegyptiaca, Gansserina gansseri, Contusotruncana contusa, and Abathomphalus mayaroensis. Consequently, the Gurpi Formation has an age of Late Campanian–Late Maastrichtian. The location of the Cretaceous–Paleogene (K-Pg) boundary is detected at the top of this formation. Macroscopic field observations integrated with microscopic studies have resulted in the recognition of four microfacies types that belong to open lagoon, shoal, proximal, and distal open marine environments of shallow inner to deep basinal settings. Depositional facies and environments of studied sections are interpreted in a regional depositional model.

Facies development, palaeoecology, and palaeoenvironment of the Seymareh (Lopha Limestone) Member of the Gurpi Formation (Upper Campanian), Lurestan Province, SW Iran

The Seymareh (Lopha Limestone) Member of the Gurpi Formation (Upper Campanian) has been investigated to evaluate facies development and macrofaunal content and to interpret their palaeoecology and palaeoenvironment of the area. In this area, a total of seven exposed stratigraphic sections at Lurestan Province of south‐west Iran were measured and described. Depending upon the lithology, microfacies characteristics, and palaeontological criteria, the Seymareh Member could be subdivided into four stratigraphic units from base to top: Unit 1, fossiliferous grey shale interbedded with fine‐grained nodular limestone; Unit 2, thick massive fossiliferous limestone; Unit 3, grey and olive‐green argillaceous moderately fossiliferous limestone; and Unit 4, light grey to creamy, medium‐ to thick‐bedded fossiliferous limestone. Petrographically, the Seymareh facies are composed mainly of bioclastic grainstone, floatstone‐rudstone, and packstone/wackestone that contain a mixed benthic/pelagic microfossil associated with macrofossils (mainly oysters and echinoids). The obtained information confirmed that the Upper Campanian Seymareh Member was deposited in a shallow submarine palaeo‐canyon environment.

Investigations of Natural Bitumen mineralization in Gilan-e- Gharb exploration block, Iran

The Gilan-e-Gharb exploration block is structurally located in the Zagros fold-thrust belt, the eastern parts of which are part of the Lurestan sedimentary basin and the western part of the northern Dezful sedimentary basin. This area has been considered as a high prospective area for hydrocarbon resources, due to its deep potential in form of oil and gas, and natural bitumen on surface. Many of the known hydrocarbon sources of Gilan-e-Gharb block are related to anticline structures. The most important factor of controlling natural bitumen placement is the dominant geological structures of Gilan-e-Gharb block. Regarding the frequency of faults and fractures in this area, mineral deposits are controlled by structures of fold. Folding as a container of hydrocarbon material, fracture and fault are responsible for its distribution of the area. Based on this, primarily, after identifying stratigraphy units of mineralization hosts including Gachsaran, Asmari, Pabdeh and Gurpi formations, the main and minor anticlines of Gilan-e-Gharb block were investigated and analyzed. At this stage, monitoring of fractures and faults based on trending were done, then, positioning of these structures relative to folding axis and their stratigraphic sett was prepared as well as placement and distribution of natural bitumen in form of a three-dimensional Structural-Mineralization Modeling. The model is presented in this paper for the first time that could be a new approach to exploration of natural bitumen or gilsonite according to the exact study of the Gilan-e-Gharb exploration block.

Biostratigraphy of the Gurpi Formation (Zagros Basin, western Iran) based on planktonic foraminifera

Micropalaeontological and biostratigraphic studies of the Gurpi Formation were carried out at the Kuhe-Surgah section (Zagros Basin, Iran). In this research, 62 species of planktonic foraminifera, belonging to 23 genera, were recognized and used to describe the following zones: 1) Contusotruncana plummerae Interval Zone; 2) Radotruncana calcarata Total Range Zone; 3) Globotruncanella havanensis Partial Range Zone; 4) Globotruncana aegyptiaca Interval Zone; 5) Gansserina gansseri Interval Zone; 6) Contusotruncana contusa Interval Zone; 7) Abathomphalus mayaroensis Interval Zone; 8) Pseudoguembelina hariaensis Interval Zone; 9) Pseudotextularia elegans Interval Zone; 10) Parvularugoglobigerina eugubina Total Range Zone; 11) Parasubbotina pseudobulloides Interval Zone; and 12) Praemurica unicinata Interval Zone. Based on the ranges of planktonic foraminifera, the age of the Kuhe-Surgah section was estimated to be middle Campanian–late Danian.

Biostratigraphic correlation of Santonian-Maastrichtian calcareous nanofossil biozones with planktonic foraminifera zonation, Interior Fars region of the Zagros, southwest Iran

Received data considered the stratigraphic distribution of nanofossils and compared with planktonic foraminifera in the Sepidan section. The Gurpi Formation is well exposed in the Sepidan section, Interior Fars, southwest Iran. It consists of 358 m of shale and argillaceous limestone with lime shale. Thirty-nine calcareous nannofossils species from 19 genera were identified in the Sepidan section. According to the distribution of calcareous nannofossil assemblages, the Upper Cretaceous succession was subdivided into 12 biostratigraphic zones, suggesting the late early Santonian to latest Maastrichtian age. Also, the examination of the studied samples resulted in the identification of 20 planktonic foraminifer taxa, assigned to seven genera. Based on the stratigraphic distribution of the planktonic foraminifera, nine foraminiferal biozones were determined. Foraminiferal investigations show that the age of the Gurpi Formation is assigned to the Santonian to late Maastrichtian. Both established nanofossil and planktonic foraminifera biozones were correlated.

Biostratigraphy of the Gurpi Formation based on Calcareous Nannofossil in the Kouh-e Sefid Anticline Section, Izeh Structural Zone

Biostratigraphy of the Gurpi Formation based on Calcareous Nannofossil in the Kouh-e Sefid Anticline Section, Izeh Structural Zone

New Approach in Application of the AHP–Fuzzy TOPSIS Method in Mineral Potential Mapping of the Natural Bitumen (Gilsonite): A Case Study from the Gilan-e-Gharb Block, the Kermanshah, West of Iran

The Gilan-e-Gharb block is known as a prospective area for hydrocarbon resources in the form of oil, gas in deep potential and natural bitumen (Gilsonite) on the surface. Natural bitumen is not clearly detectable by geochemical or geophysical methods. Hereupon, identifying high potential areas for further exploration, attempted with the help of AHP-Fuzzy and TOPSIS methods. The comprehensive database of geological and geostructural records, satellite imagery analysis by remote sensing and mine indexes counted as the inputs for this method. First, the lithological unit as the main mineralization hosts determined with respect to the dominant geological structures as a factor of controlling natural bitumen placement (fold, fracture and faults) in the Gilan-e-Gharb block. The Gachsaran, Asmari, Pabdeh and Gurpi Formations identified as the most important lithological units for mineralization. Placement and distribution of natural bitumen mineralization in the form of mine indexes are added to the geology database. Finally, we assigned appropriate weights to applied information layers using Analytical Hierarchy Processing (AHP) based on knowledgeable information and field studies to synthesize exploratory data. Then, we used the FTOPSIS method to define the Positive Ideal Solution (FPIS, A+) that allows maximizing the beneficial characteristics and minimizing the impediment characteristics and the Negative Ideal Solution (FNIS, A-) that minimizes the beneficial characteristics and maximizes the impediment characteristics. This method, as a new approach in the exploration of minerals with a shortage of data, is applicable to other mineral deposits.

Biozonation, Paleobathymetry and paleoenvironmental study of the Gurpi Formation in southwestern Iran

Planktonic foraminifera and major palynomorph groups (i.e. terrestrial, marine, and amorphous organic matter) of the Campanian-Selandian strata of the Gurpi Formation were studied to evaluate the changes in the Zagros paleobasin in southwestern Iran. Planktonic foraminifera were categorized into four morphotypes according to their paleodepth, extending from Morphotype 1, comprising surface generalists, to Morphotype 4, comprising deep-water aphotic heterotrophic species. The relative amount of species belonging to Morphotype 4 is noticeable in the Campanian-Maastrichtian. It shows that the depth of the basin was generally greater than 200 m in the Late Cretaceous. Two major sea-level regressional phases could be recognized during the formation deposition. The first one occurred near the middle of the Maastrichtian in the Contusotruncana contusa Biozone, during which the relative abundance of terrestrial palynomorphs increased prominently, and the species belonging to Morphotype 4 became notably rare. This regression correlates well with the eustatic curves, suggesting that it was controlled by global factors. Also, the species belonging to Morphotype 4 disappeared in the Danian, the relative abundance of terrestrial palynomorphs increased, and the relative abundance of planktonic foraminifera (P%) decreased prominently. However, this regression does not correlate with the eustatic curves and indicates that local tectonic events should be considered. The palynofacies study of the strata shows that during the Campanian-Maastrichtian, the strata were deposited in a deep suboxic-anoxic setting (Palynofacies IX), whereas the Danian strata were deposited in a shallow-shelf setting (Palynofacies VI). The studies show that during the Selandian, the depth of the basin increased again.

Santonian-Maastrichtian carbon-isotope stratigraphy and calcareous nannofossil biostratigraphy of the Zagros Basin: Long-range correlation, similarities and differences of carbon-isotope trends at global scale

Abstract A high-resolution study of carbon isotope stratigraphy and calcareous nannofossil biostratigraphy has been undertaken on the Upper Cretaceous sediments of the Gurpi Formation (Fm.) in the Bowan section (Zagros Basin, Iran). The integrated stratigraphy of the section allows for large-scale correlation with Upper Cretaceous reference sections (Gubbio, Italy; German Chalk; Shahneshin, Iran) and suggests the age of the Gurpi Fm. at Bowan to be latest Santonian to early Selandian. Correlation of the isotopic data from Bowan to the Shahneshin section in the central Zagros mountains shows remarkable similarity that may be related to effects specific to the peculiar stratigraphy of the area and, possibly, to the long-term evolution of seawater δ13C in the Zagros Basin. A sequence stratigraphic framework is proposed for both sections. Correlation of the two sections to data from the Boreal realm, Indian Ocean, equatorial Pacific Ocean, and other Tethyan sections suggests that it is possible to identify some of the previously defined major carbon isotope events in the Iranian sections. Significant differences, however, are observed in absolute values and overall amplitude of carbon isotope trends. In particular, our results show that the Santonian/Campanian boundary event (SCBE) which is a well-defined, double-peaked, positive excursion at Gubbio and in the Boreal realm is absent in the Zagros Basin, eroded by a major sequence boundary. Moreover, the most pronounced feature in Upper Cretaceous carbon isotope ratios of the Zagros Basin carbonates is an overarching maximum culminating in the early Campanian which correlates with a discrete, low-amplitude (0.25‰) positive excursion defined as the papillosa Zone event at Gubbio and in the Boreal realm. Our results thus reveal a contrasting evolution of carbonate δ13C during the early Campanian between different oceanic basins but also within the Tethys.

Study of hydrocarbon generation and 1D-2D modeling of hydrocarbon migration at the Karanj and Parsi oilfields, Southern Dezful Embayment, SW Iran

Abstract This study is a 2D basin modeling to determine the petroleum system (i.e. Cretaceous-Neogene play) of the Karanj and Parsi oilfields in the Southern Dezful Embayment, SW Iran. This system is characterized by occurrence of source rocks of Middle Cretaceous, Late Cretaceous and Paleocene to Eocene (Kazhdumi, Pabdeh and Gurpi Formation), reservoirs of Upper Cretaceous and Late Oligocene–Early Miocene (Ilam-Sarvak and Asmari formations), and seals of Paleocene and Miocene (Pabdeh and Gachsaran Formation). Considering temperature, transformation ratio and vitrinite reflectance, the maturity of source rocks (Kazhdumi, Pabdeh and Gurpi Formation) was investigated. A maturity history analysis showed that the maturity of Kazhdumi, Pabdeh and Gurpi Formation started during 70–60 and 4 Ma, respectively. Generation and expulsion of hydrocarbons started ~16 Ma in the Kazhdumi Formation and ~3 Ma in the Pabdeh Formation that continued up to the present. The analysis of the transformation ratio indicates transformation of significant amounts of Kazhdumi source rocks for generating hydrocarbons. Migration of hydrocarbons from the Kazhdumi Formation is mainly vertically upward. From Pabdeh Formation migration is both vertically upward (to the Asmari reservoir) and downwards (to the Ilam-Sarvak reservoir). However, some local traps have formed due to the hydrocarbon accumulation above the faults. Our results reveal that petroleum generation, migration and entrapment occurred at proper timing which facilitated the migration of hydrocarbons and their accumulation in the reservoirs.

Biostratigraphy and lithostratigraphy of Late Cretaceous–Early Palaeogene deposits in Tang-e-Abolhayat, Zagros basin (SW Iran)

In this study, to consider microbiostratigraphy of Cretaceous and Palaeocene planktic foraminifera, a stratigraphic section of the Gurpi and Pabdeh formations named Tang-e-Abolhayat was selected. On the basis of the identified planktic foraminiferal assemblages, seven biozones and two sub-biozones have been recorded (four biozones from the uppermost part of the Cretaceous, (Gurpi Formation), and three biozones from the lower part of the Lower Palaeocene (Pabdeh Formation). The biostratigraphic correlations based on planktic foraminiferal zonations showed a comparison between the biostratigraphic zones in this study and other equivalents of the commonly used planktic zonal scheme around the Cretaceous–Palaeogene in and outside Iran. Biostratigraphic analysis confirms that the studied section is incomplete across the Cretaceous–Tertiary boundary and a hiatus is suggested by the absence of the Plummerita hantkeninoides, Guembelitria cretacea, Parvularugoglobigerina eugubina Zones and Parasubbotina pseudobulloides Subzone (CFl to Pla zones). These absences could reflect the restriction of the above-mentioned zones to shallower settings, slow sedimentation rates or an interval of erosion or no deposition. There is no obvious evidence of erosion. On the other hand, the Pabdeh Formation overlies Gurpi Formation paraconformably.

Erodibility and sedimentation potential of marly formations at the watershed scale

Grupi and Kashkan marl formations comprise a considerable part of Zagros region. These formations have a considerable erodibility and sedimentation potential because of their special geological and mineralogical characteristics. The objective of this study was to compare the erosion and sediment yield of Kashkan and Grupi formations in Merk watershed located in southeast Kermanshah, using the Modified Pacific Southwest Inter-Agency Committee model. This model is suitable for estimating erosion and sediment intensity within each geomorphologic unit comprising nine effective environmental factors as geological, pedological, climate, runoff, topography, land cover, land use, surface, and river erosion factors. The results indicated that Kashkan formation comprises siltstone, sandstone, shale, and conglomerate, and Grupi formation contains shale, clay, and limestone with a high erodibility potential. Field measurements and soil samples analyzed for effective factors releaved that sediment yield for Merek watershed was 18080.6 m3/ha/y. Furthermore, field measurement and soil samples analyzed for effective factors releaved that sediment yields for Kashkan and Gurpi were 7243.3 and 10837.5 m3/ha/y, respectively. The reasons for erosion intensity and sedimentation in the two mentioned formations are slopes, vegetation and land use in addition to the type of rocks in Kashkan and Gurpi formations which are predominantly marl and shale.

Serrakielina chahtorshiana n. gen. et n. sp., and other (larger) benthic Foraminifera from Danian-Selandian carbonates of Mount Chah Torsh (Yazd Block, Central Iran)

Mount Chah Torsh in the Yazd area of Central Iran exposes the Cretaceous-Paleogene boundary within a carbonatic siliciclastic shallow-water succession. From the territory of Iran the K/Pg boundary was so far only recorded from deeper-water successions of the Kopet Dagh Basin in the northeast and the Zagros Zone (Gurpi Formation) in the southwest. From the Paleocene (Danian–Selandian, Shallow Benthic Zones 1–2) carbonates of Mount Chah Torsh the new porcelaneous Larger Benthic Foraminifera Serrakielina chahtorshiana n. gen. et n. sp. is described. In the uniserial adult part the chambers are subdivided by radial partitions. Together with the single, stellate foramina Serrakielina n. gen. compares closely to the soritacean Praerhapydionina Henson. It differs in its juvenile stage (trochospiral in the former vs. planispiral in the latter). From the same section, Haymanella ex. gr. paleocenica Sirel, Kolchidina paleocenica (Cushman), Sistanites iranicus Rahaghi, Orduella sphaerica Sirel, and other taxa (rotaliids, miliolids) are reported. Anew larger agglutinated taxon is described as Socotraella? yazdiana n. sp. Socotraella ashawqi the type-species of the genus was described from the Lower Oligocene of Yemen (Socotra Island) and Oman. The samples from the Mount Chah Torsh section also display a comparably rich association of Dasycladales and other algae. The locality can be considered a standard section for Danian–Selandian shallow-water carbonates in Iran. Exposing also the K/Pg boundary in a conformable transition, this locality offers several topics for future research.

Integrated bio- and carbon-isotope stratigraphy of the Upper Cretaceous Gurpi Formation (Iran): A new reference for the eastern Tethys and its implications for large-scale correlation of stage boundaries

A high-resolution stratigraphic analysis of the Upper Cretaceous Gurpi Formation has been undertaken in the Shahneshin section (Zagros Basin, Iran). New results on calcareous nannofossils, planktic foraminifers, dinoflagellate cysts and high-resolution carbon and oxygen stable isotopes form the basis of a reference section for the eastern Tethys that spans the upper Coniacian to the late Danian. Carbon-isotope correlation to Gubbio, Italy and the NW German chalk allows for the identification of many isotopic events as well as for the definition of new events in the Campanian and Maastrichtian. Our results allow for a review of the accurate position of the Coniacian/Santonian, Santonian/Campanian, and Campanian/Maastrichtian stage boundaries relative to carbon isotopes and plankton bioevents. The reliability of Coniacian to Maastrichtian planktic foraminifer, dinoflagellate cysts and calcareous nannofossil biohorizons is assessed.

Thin Section Studies on Foraminifera from Limestone of Gurpi Formation (Cretaceous) Sarableh, North of Ilam Area, Iran

Thin Section Studies on Foraminifera from Limestone of Gurpi Formation (Cretaceous) Sarableh, North of Ilam Area, Iran

Biostratigraphy and Sequence Stratigraphy of Campanian and Maastrichtian Succession, Qutbabad Well, Zagros (Iran)

The Qutbabad section of the Gurpi, Tarbur and Sachun Formations in the Fars Province (Zagros Basin) has been studied, in order to determinate its microfacies and sequence stratigraphy. On the basis of thin section studies of cores from Qutbabad Well in the Gurpi, Tarbur and Sachun Formations of the Zagros Basin, four main microfacies have been recognized within four stratigraphic sequences deposited during the Campanian to Maastrichtian. Depth and sea level changes were the main controls on the distribution of these microfacies. The microfacies are: Pelagic; Hemi-Pelagic; Outer ramp; and Middle ramp. The lowermost sequence was deposited in the Early Campanian-early Late Campanian and includes wackestone to packestone textures with biozones Globotruncanita elevate and Globotruncana ventricosa representative of the Pelagic, Hemipelagic and Outer (ramp/shelf). The intermediate and uppermost sequences (sequence two, three and four) display well developed deposits formed at the end of the Campanian (Radotruncana calcarata zone and Globotruncanella havanensis zone), beginning of the Maastrichtian (Globotruncana aegyptiaca zone and Gansserina gansseri zone) and the end of the Maastrichtian (Omphalocyclus macroporus - loftusia sp assemblage zone) on the Pelagic, Hemipelagic, Outer and Middle ramp. On the basis of the sequence stratigraphic chart, the transgression of the Upper Cretaceous Sea started from the Early Campanian and continued gradually towards the Early Maastrichtian. Then, until the end of Maastrichtian, has had regression. This resulted that the sequence stratigraphic model of the Campanian- Maastrichtian Gurpi, Tarbur and Sachun Formations has architecture similar to those that have developed from global sea level changes.

Structural framework and tectono-stratigraphic evolution of the eastern Persian Gulf, offshore Iran

Seismic and well data are utilised to describe the tectono-stratigraphic evolution of the eastern Persian Gulf during the Late Mesozoic and Cenozoic. The structural framework of the study area is the result of the Late Cretaceous to Early Miocene Oman Orogeny overprinted by the southwestward advance of the Zagros Orogeny through the Late Miocene and Pliocene. Two structural domains can be identified; The NE-SW trending Musandam Fold-Thrust Belt (MFTB) and the NW-SE trending Persian Gulf foredeep basin. The MFTB formed as a result of multiple compressional events (Late Cretaceous, Late Paleocene to Early Eocene and Late Oligocene to Early Miocene). The first compressional event (Cenomanian- Turonian to the Maastrichtian) is characterized by emplacement-obduction of the allochthonous rocks onto the passive continental margin of the Arabian plate in the Oman Mountains. This event led to regional deformation and uplift which caused deep erosion of the Albian to Santonian units. During the Santonian to Maastrichtian, in addition to regional deformation, a NE-SW trending foredeep basin developed in front of the Late Cretaceous thrust sheets creating accommodation space for turbiditic deposits of the Gurpi Formation. During the Late Paleocene- Early Eocene, initiation of a new compressional deformation led to establishment of the Pabdeh foredeep basin. In this stage, the basin depocenter migrated ∼30 km to the west. The third compressional event began in the Late Oligocene reaching a climax in the Early Miocene. This event resulted in regional deformation and uplift which caused deep erosion of the pre-Middle Miocene strata. The Persian Gulf foredeep basin has developed in front of the rising Zagros Mountains since Late Miocene- Pliocene. Folding related to advancement of the Zagros Orogeny into the Persian Gulf is mainly restricted to northeastern flank (near the coast of Iran). The effect of folding decreases to the south of the Zagros Deformational Front.

Planktonic foraminifera and sea-level changes in the upper Cretaceous of the Gurpi Formation, Lorestan basin, SW Iran

The Gurpi Formation, one of the geological units of the Zagros Basin, stretches with in the Folded Zagros in the provinces of Khuzestan, Lorestan, and Fars, in southwest Iran. In total 490 samples were collected from the three sections to document the planktonic foraminifera. Overall, 58 species from 23 Planktonic foraminifera genera were recognized in this study. From a biochronostratigraphic point of view, 7 biozones were identified. Also, the age of Gurpi Formation in three sections were determined based on the identified biozones of early Campanian to late Maastrichtian. A depth of over 450–600 m has been designated for of the formation based on determine percentage planktonic in the total foraminiferal association (%P*) and the regression equation Depth = e (3.58718+(0.03534 × %P∗)).

Paleogeographic evolution of the Maastrichtian deposits in the eastern Fars area (Zagros, Iran) using high-resolution sequence stratigraphic analysis

Upper Cretaceous depositional systems of the Zagros area were influenced by a series of local and regional tectono-sedimentary events such as progressively southwestward foreland basin migration, which locally was overprinted by salt movements. The Maastrichtian interval is characterized by filling out of the NE foredeep by obducted units and development of SW facing ophiolitic and radiolite nappe in the most interior parts of the Fars area. This tectono-sedimentary loading led to the migration of the mid-foreland basin bulge to the southwest. To reconstruct the depositional settings during this time, three outcrop sections (Kuh-e Chadur, Gach, and Parak) and two wells (Pishvar-1 and Bavush-1) are organized in an SW–NE trending cross section. Maastrichtian sedimentary succession is introduced by pelagic marls of the Gurpi Formation, carbonates of the Tarbur, and evaporates of the Sachun formations along with obducted radiolaritic and ophiolitic complexes. Field and microscopic investigations led to the recognition of several facies’ belts in carbonate domain including intertidal, restricted and open lagoonal, reefal, open marine, and basinal settings, which organized in one regional third- and five local fourth-order sequences that generally show a sharp decreasing trend in sequence thickness of Maastrichtian deposits from NE toward SW. Facies’ variations along this transect show that sequences 1 and 2 are present only in the northern part of the basin. Sequence 3 dominated by rudistid facies, showing progradational pattern toward the southern basinal setting over the time-equivalent pelagic marls of the Gurpi Formation. Sequence 4 has mainly composed of inner shelf deposits in the north and progrades into the outer shelf deposits, toward the south. Sequence 5 consists mainly of dolomites and evaporites of restricted lagoon (Sachun Formation). Accordingly, salt tectonics has resulted in thickness and facies’ variations as well as sequence patterns. In addition, uplifting and migration of the bulge, controlled the exposure area and subsequent diagenetic events such as meteoric dissolution, dolomitization, neomorphism, brecciation, and Fe-staining. Halokinetic events show a strong influence on the intensity and development of diagenetic processes, particularly dolomitization and dissolution.