Kazhdumi Formation Research Articles

First report of Albian–Cenomanian ichthyological microremains from the Kazhdumi Formation Fars Province, Zagros Basin, South Iran

ABSTRACT Vertebrate remains are scarce in the Cretaceous of Iran, with only a few records of fishes and one genus of chelonioid turtle known from the Dariyan and Sarvak formations. Here, we describe for the first time the paleoichthyological fauna of the Kazhdumi Formation, based on disarticulated microremains that represent the first record of vertebrates in the unit, highlighting this novel Albian–Cenomanian fossil assemblage. The fauna is composed of lamniform (cf. Dallasiella sp., cf. Paranomotodon sp., Anacoracidae indet., cf. Haimirichia amonensis, cf. Scapanorhynchus, Lamniformes indet.) sharks and pycnodontiforms Osteichthyes.

Biostratigraphic Correlation of the Kazhdumi Formation in the Ghavam-Abad and Banesh Sections (Fars Province) in Southwest of Iran

Biostratigraphic Correlation of the Kazhdumi Formation in the Ghavam-Abad and Banesh Sections (Fars Province) in Southwest of Iran

Microfacies and sedimentary environment of the Kazhdumi formation in the northern flank of the Khami Anticline, Zagros Basin, southwestern Iran

Microfacies and sedimentary environment of the Kazhdumi formation in the northern flank of the Khami Anticline, Zagros Basin, southwestern Iran

Albian–Cenomanian echinoids from areas north of Bandar Abbas and south of Fars in the Zagros Mountains, Iran

Fossil echinoids have rarely been described from Iran. This study focuses on the echinoid fauna found in the Cretaceous strata (Kazhdumi Formation) of the Geno and Gerash sections in the Bandar Abbas and Fars areas of the Zagros Mountains, southern Iran. The age of the Kazhdumi Formation in both sections is determined to be Albian-Cenomanian based on the associated ammonites and microfauna, its stratigraphic position, and previous studies on this formation. Twenty-one echinoid species (twelve regular and nine irregular) belonging to seventeen genera were described in this study. Fourteen of these species are reported for the first time from Iran. In addition, a new diadematoid echinoid species, Arabicodidema jafariani sp. nov. is introduced. New age ranges are proposed for Pliotoxaster comanchei and Lambertiaster douvillei. The paleogeographic position of the Zagros Basin in the Tethyan realm is confirmed based on the distribution of the index species.

Total organic carbon (TOC) estimation using ensemble and artificial neural network methods; a case study from Kazhdumi Formation, NW Persian Gulf

Total organic carbon (TOC) estimation using ensemble and artificial neural network methods; a case study from Kazhdumi Formation, NW Persian Gulf

PETROLEUM GEOLOGY OF THE CENOZOIC SUCCESSION IN THE ZAGROS OF SW IRAN: A SEQUENCE STRATIGRAPHIC APPROACH

The Cenozoic stratigraphy of the Zagros records the ongoing collision between the Arabian and Eurasian Plates and the closure of NeoTethys. A Paleogene NW‐SE trending foreland basin was inherited from a Late Cretaceous precursor. Widespread progradation into the foredeep was a feature of both margins which, allied to ongoing tectonism, had by the late Eocene led to the narrowing and subsequent division of the foredeep into the Lurestan – Khuzestan and Lengeh Troughs, separated by the northward continuation of the rejuvenated Qatar‐Fars Arch. This sub‐division strongly influenced subsequent deposition and the petroleum geology of the area. In addition, the diachronous nature of the Arabian – Eurasian collision led to strong diachroneity in lithostratigraphic units along the length of the Zagros. Hence its petroleum geology is best understood within a regional sequence stratigraphic framework. This study identifies three tectono‐megasequences (TMS 10, TMS 11a, TMS 11b) and multiple depositional sequences.The Cenozoic contains a world class hydrocarbon province with prolific oil reservoirs in the Oligo‐Miocene Asmari Formation sealed by the evaporite‐dominated Gachsaran Formation, mostly contained within giant NW‐SE trending “whaleback” anticlines concentrated in the Dezful Embayment. Reservoirs in the SW are dominantly siliciclastic or comprise mixed siliciclastics and carbonates, whereas those to the east and NE are dominated by fractured carbonates. There remains untested potential in stratigraphic traps, especially in deeperwater sandstone reservoirs deposited along the SW margin of the foredeep.Late Miocene to Pliocene charge to the Asmari reservoirs was mostly from Aptian – Albian Kazhdumi Formation source rocks. In some fields, an additional component was from organic‐rich late Eocene to earliest Oligocene Pabdeh Formation source rocks confined to the narrowing Lurestan – Khuzestan Trough. Where mature, the latter source rock is also a potential unconventional reservoir target, although the prospective area is limited due to recent uplift and erosion. Deeper Jurassic source rocks contributed to the Cheshmeh Khush field in Dezful North. Silurian source rocks charged gas‐bearing structures in the Bandar Abbas region.

Microfacies, diagenetic processes and reservoir quality of the Aptian carbonate Dariyan Formation, southeast of the Persian Gulf, South Iran

The Aptian carbonate Dariyan Formation (Shu'aiba equivalent) is one of the most important oil reservoirs in the Zagros Basin and the Persian Gulf (South and Southwest of Iran). The Dariyan Formation with mainly carbonate facies overlies the Gadvan (Hawar) Formation and is overlain by the Kazhdumi (Nahr Umr) Formation. Despite the reservoir importance of the Dariyan Formation, it seems that not much detailed work has been done about the facies characteristics, diagenetic processes and reservoir quality of this formation in the east of the Persian Gulf Basin of Iran.By using the new and valuable data obtained from the core, this study focused on the identification of microfacies, diagenetic processes, determining the sedimentary environment, biostratigraphy and reservoir characterization of this formation in one of the wells of Reshadat oilfield in the southeast of the Persian Gulf. The results obtained from microfacies study, led to the identification of seven carbonate and one mixed carbonate-clastic microfacies that were deposited in four facies belts including the inner ramp, middle ramp, outer ramp, and deep basin. Uniform facies changes and the absence of reef-forming organisms such as rudists and its replacement by Lithocodium algae with the ability to form patch reefs indicate the homoclinal carbonate ramp environment. The study of benthic and planktonic foraminifera, as well as algae, led to the identification of five biozones, which indicated the Aptian age for this formation.Based on petrographic study, the Dariyan Formation is affected by diagenetic processes such as Cementation, dissolution, mechanical and chemical compaction, dolomitization, bioturbation and pyritization. Correspondence of porosity and permeability data of the cores and petrophysical logs indicates that the reservoir quality of the Dariyan Formation in the studied field was affected by facies, and diagenesis factors. Reservoir characterization has revealed that the high quality zone is located in the intervals containing Lithocodium algae. In the Lithocodium-bearing facies (boundstone-floatstone) the presence of many interconnected pores and cavities in the skeletal network structure of Lithocodium/Bacinella algae have created a suitable reservoir quality and a permeable facies.

An innovative approach for investigation of overpressure due to hydrocarbon generation: a regional study on Kazhdumi formation, South-western Zagros Basin, Iran

Overpressure is always considered as a severe problem in the oil industry. Besides creating life risks through serious accidents while drilling, failure to correctly identify high-pressure intervals causes a significant increase in costs and prolongs the drilling process. Kazhdumi Formation in the Abadan Plain is considered as a high-pressure formation in several wells. Various reasons can cause overpressure problem. Hydrocarbon generation is one cause of abnormal pressure in source rocks. Understanding hydrocarbon generation potential can be a helpful approach since the Kazhdumi Formation is considered as a probable source rock in this area. In this paper, in order to better understand the problem of abnormal pressure in Kazhdumi Formation, geochemical concepts and tools have been applied. To that way, 1D petroleum system modeling of five wells was done, and the thermal maturity level of Kazhdumi Formation was determined and then, compared with drilling records. The results indicate that in wells where this formation has sufficient organic matter and has reached an early mature level, there is an abnormal pressure problem. Otherwise, this formation does not show abnormal pressure. Also, geochemical data are not available in all drilled wells, which makes impossible the assessing of hydrocarbon generation role. Therefore, petrophysical well logs (sonic (DT), neutron (NPHI), density (RHOB), spectral gamma ray (SGR), and resistivity (RES)) as well as 137 sets of geochemical data belonging to 13 wells from 7 oilfields in the Abadan Plain were used to predict geochemical indicators. Using artificial neural networks, geochemical data of a well in Abadan Plain were predicted. This selected well has a high-pressure problem in Kazhdumi Formation, but no geochemical data are available in this well. The results of predicted geochemical data show that the high-pressure phenomenon in this well may also be due to hydrocarbon generation. The precise understanding of the abnormal pressure, resulting from hydrocarbons generation, requires comprehensive studies and a full investigation of the studied area. However, the results of this paper help to predict approximately the behavior of the source rocks before drilling. Acquiring this overview will aid in reducing drilling hazards and costs.

Integration of well logs and seismic attributes for prediction of thermal maturity and TOC content in the Kazhdumi Formation (central Persian Gulf basin)

This study proposes an indirect method for estimating source rock properties, specifically thermal maturity and Total Organic Carbon (TOC), using well logs and seismic data within the central Persian Gulf hydrocarbon fields. The primary focus is on the Kazhdumi Formation, an important source rock in the southern Iran. The study is carried out in two distinct steps, based on the employed data. In the first step, a Maturity Index (MI) is calculated utilizing well logs (such as neutron, density and water saturation) within the Kazhdumi Formation across six oil and gas fields. Then, the TOC content is determined using ∆Log R method across four wells. Geochemical data, including vitrinite reflectance and Rock-Eval pyrolysis data, used as validators of the calculated MI and TOC. In the second step, 2-dimensional post-stack seismic data analysis is conducted where the necessary data, including a full set of well logs are accessible. Multi-attribute regression is employed to extract seismic attributes and consequently used to predict the target parameters. MI and TOC logs are then predicted through Probabilistic Neural Network analysis (PNN) which is used for the indirect prediction of the target logs. Finally, two seismic volumes are obtained to provide a mapping of the predicted MI and TOC variations in the Kazhdumi Formation.One advantage of using this method is its efficiency and cost effective compared to the geochemical testing. Additionally, it provides a continuous prediction of the target parameter in an extensive area. Lastly, this method benefits from the availability of seismic data compared to the geochemical data in hydrocarbon fields that are typically sparse. This approach is proved to be applicable to source rock analysis in different areas for indirect estimation of thermal maturity and TOC.

Geochemical pyrolysis, petrographical analysis and burial history reconstructions of the Kazhdumi Formation in the Hendijan and Soroosh oil fields, northwestern Persian Gulf

The Kazhdumi Formation is one of the most important source units throughout the Persian Gulf and surrounded areas that mainly formed from dark, organic rich shales and marls. In this study, source characteristics of the Kazhdumi successions in the Hendijan and Soroosh oilfields (northwestern Persian Gulf) are evaluated using the Rock-Eval pyrolysis, vitrinite reflectance analysis and one-dimensional thermal modeling. The Rock-Eval data suggest good to very good and poor to fair hydrocarbon potentials for the studied formation in the Hendijan and Soroosh oil fields, respectively. In addition, pyrolyzed data reveal that the successions mainly contain kerogen type II in the Hendijan and kerogen type III in the Soroosh oil fields. Also the Tmax values and vitrinite reflectance measurements show that the Kazhdumi Formation has reached to the oil generation phase in the Hendijan, whereas this formation is immature in the Soroosh Field. Moreover, reconstructions of thermal history exhibit that variations in maturity are linked to the Kazhdumi burial depth and the values of basin heat flow. Eventually, the combination of results indicate that the Kazhdumi hydrocarbon generation in northwestern Persian Gulf increase considerably towards the Dezful Embayment.

Invertebrate fauna of the Albian–Lower Cenomanian deposits in the Fars and Isfahan provinces (Firuzabad and Fasakhod sections), Zagros Basin, Central Iran

The Albian- Cenomanian deposits of the Kazhdumi Formation at Zagros Basin (Firuzabad section and Central Iran (Fasakhod section), represents a carbonate sedimentary succession and contain rich and diverse invertebrate macro fauna. Detailed studies on about 200 specimens of invertebrate macro fauna revealed from two stratigraphic intervals led to recognition of 5 species of gastropods; (Liopeplum? sp., Columbellina sp., Cryptaulax? sp., Turritella? sp., Pleurotomaria sp.), 3 species of ammonites; (Knemiceras duberterti, Sphenodiscus sp., Knemiceras persicum), 10 species of bivalves assemblages; (Ceratostreon flabellatum, Cardium? sp., Exogyra (Costagyra) olisiponensis, Neithea (Neithea) quinquecostata, Trigonia sp., Buchia? sp., Cardium? sp., Pseudogyra sp., Ontaria? sp., Nucula? sp., Pleuromia? sp., 1 species of echinoids; Dorocidaris taouzensis with a prolific horizon of Notopocorystes xizangensis of raninoid crabs. The absence of large gastropods and bivalves fauna and abundance of suspension-feeders indicated instability of the substrate, shallow marine paleoenvironment.and a medium energy condition.

Integration of geochemical data, well logs and seismic sections for source rock characterization of the Albian Kazhdumi Formation in the central Persian Gulf basin, South Iran

This study presents indirect methods of source rocks characterization by integrating geochemical data with well logs and seismic inversion results. Well logs and seismic data are commonly more available than scarce geochemical data in oil and gas fields. Combining high vertical resolution well logs with high lateral resolution seismic data generates some enhanced geochemical data on inter-well spaces where no well is drilled.Acoustic impedance was obtained and utilized for the TOC prediction and source rock detection because of its good correlation with geological parameters such as the lithology and fluid contents. A cross-plot of log-derived water saturation versus acoustic impedance successfully differentiates source from non-source rocks based on geological variations of lithology, porosity, formations density, and the TOC content. The impact of the TOC content on acoustic properties was elaborated in the next step. Acoustic impedance is obtained as the most important seismic attribute for the TOC prediction. Well logs and seismic data are integrated to predict the TOC logs from seismic data. First, seismic data were inverted to obtain the acoustic impedance. Then, the produced acoustic impedance was used as a seismic attribute for the TOC prediction. The outcome is used to illustrate and follow the TOC variation to distinguish source rocks in the oil and gas fields. The study is carried out in the Cretaceous succession in three hydrocarbon fields in the central part of the Persian Gulf to observe the TOC variations in the Albian-aged Kazhdumi Formation.

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 Aptian–Albian (A–A) transition encompassed a critical timing in the evolution of Fars Platform (Zagros Basin, SW Iran), such that a number of previous studies on its proximal part (called “Coastal Fars”) illustrated platform recovery after sustained demise due to latest Aptian maximum sea-level lowstand. So far, much less attention has been given to the distal part of the platform – “Interior Fars” – where the lack of proper geological age interpretations, in particular, has been limiting a full paleoenvironmental reconstruction of the southern shallower Neo-Tethys. In order to establish the chronostratigraphic framework of Interior Fars, this study presents a novel set of planktonic foraminiferal record for the A–A Kazhdumi Formation at the Saroie section. The identified fauna comprises nine species from four genera, all of which are reported for the first time from Fars Platform. The observed new bioevents are generally consistent with those of the proposed reference section at a deeper intrashelf setting (Tang-e-Maghar, Dezful Embayment), allowing for the establishment of a local upper Aptian–Lower Albian zonation and leading to adequate constraints on the local Aptian/Albian boundary and the timing of prominent black shale deposition (possible “Jacob” equivalent). Based on this new Saroie chronostratigraphic scheme, it is evident that sedimentation across the A–A transition was maintained fully marine at the Saroie section, Interior Fars. This finding does not support the previous inference of extensive subaerial exposure of the entire Fars Platform at that time, thereby calling for a major revision of the published prevailing model for latest Aptian paleogeography of this region. These new insights will facilitate better understanding of the Fars Platform evolution in the Zagros Basin as well as paleoenvironmental reconstructions along the southern Neo-Tethys.

Geochemical and Tectonic Characterization of Oil–Source Rocks in the Shadegan Oilfield, Dezful Embayment, SW Iran

Geochemical methods allow us to develop a systematic understanding of petroleum system elements. Geochemical analyses were done out on the shale samples of the Pabdeh and Asmari Formations and on the Asmari reservoir oil samples in the Shadegan oilfield, southwest Iran. Rock–Eval pyrolysis, gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) data were utilized. Oil–oil and oil–source correlations using GC and GC–MS analyses indicated that the Pabdeh Formation and the Asmari Formation basal shale layer are two possible sources of Asmari reservoir oil. The results of Rock–Eval pyrolysis revealed the values of the organic matter in the samples of the Asmari Formation basal shale layer are consider poor to fair in total organic carbon content. Therefore, this layer cannot be known as the source rock for the oil in the Asmari reservoir. Based on the thermal maturity parameters including the sterane isomerization ratios and homohopanes isomerization ratio together with Rock–Eval data and 1D burial history model, both Pabdeh and Kazhdumi Formations are in the maturity levels for oil generation. Different biomarker ratios in two oil samples (for well numbers 4 and 17) compared to samples from the Shadegan oilfield, revealed that the oil of these two wells originated from carbonate source rock(s) unlike oils of other wells that originated from a shaly source rock. Oil migration from adjacent oilfields with carbonate source rock (e.g., the Maroon, Ahvaz and Mansouri oilfields) into these wells through natural fractures in paleohighs is considered as one of the controlling factors of observed difference in biomarker ratios.

The Palorbitolinoides event in the Kazhdumi Formation of Southwest Iran and equivalent strata of the Arabian Plate: An expression of the K100 middle Albian transgression

Distinctive beds with abundant large, discoidal specimens of the orbitolinid foraminifera Palorbitolinoides hedini Cherchi and Schroeder are recorded from the Kazhdumi Formation from a section in south-west Iran where ammonite data and associated microfauna suggest a middle Albian age. This taxon, partly previously referred to Orbitolina or high-evolved mesorbitolinids (subconcava-aperta group), has been reported from other sections of the Kazhdumi Formation, the Nahr Umr Formation (Kazhdumi equivalent) of Oman, and the Tisje Formation of northern Somalia. Stratigraphic context and consideration of controlling factors on orbitolinid morphology places these accumulations of flat-discoidal orbitolinids within horizons forming the transgression to the regional Arabian MFS K100 maximum flooding sensu Sharland et al. (2001). These Palorbitolinoides limestones thus form useful marker beds assisting in regional correlation and age calibration. These records also confidently extend the range of P. hedini into younger Albian strata than previously recognised by most authors.

Organic facies and paleo-depositional environments of the Aptian–Albian Kazhdumi source rock in the Zagros basin of Iran

The Kazhdumi Formation of SW Iran is considered as one of the main petroleum source rocks of the Cretaceous petroleum system. Despite an overwhelming body of research on the gross organic geochemistry of this formation, little is known about its organic facies and paleo-depositional environments. In this research, organic geochemical and sequence stratigraphic principals was used to throw light on the mechanisms controlling organic enrichment in the Kazhdumi Formation. Petrographic examinations revealed that the Kazhdumi organic-rich facies was deposited during times of relative sea-level rise and the related euxinia. In addition, the organic matter preserved in the Kazhdumi Formation varied strongly in type from SW to NE of the paleo-depositional settings. In contrast, organic-lean facies were accommodated within the Kazhdumi intra-shelf basin during periods of sea-level fall. These results have practical implications for future geochemical studies including oil-source correlations and petroleum system analysis.

Geochemical Investigation of the Cretaceous Crude Oil Reservoirs and Source Rock Samples in One of the Abadan Plain Oilfields, SW Iran

AbstractCrude oil and source rock samples from one of the main oilfields of the Abadan Plain, Zagros, Iran were analyzed geochemically. Rock‐Eval pyrolysis was conducted on Kazhdumi (Upper Cretaceous) and Gadvan (Lower Cretaceous) formations, which are the probable source rocks for the oil in the region. The results indicated that the Kazhdumi Formation can be classified as a fair‐to‐excellent source rock, while the Gadvan Formation can be identified as having poor‐to‐good source rock in the basin. Based on the cross‐plots of HI versus OI and S2 versus TOC, types II and III kerogen were identified from studied source samples in the area. Determination of the main fraction percentages of the Sarvak and Fahliyan crude oils represented that the oils from the Sarvak reservoir are paraffinic‐naphthenic and aromatic‐intermediate, whilst that from the Fahliyan reservoir is paraffinic and paraffinic‐naphthenic. Biomarker ratios of the saturated fractions of oil from both reservoirs indicate that the source rocks formed in reducing marine environments with carbonate‐shale lithology. Furthermore, biomarker data helped to distinguish the degree of biodegradation in the studied oils. According to geochemical analysis, oil samples from the Fahliyan reservoir were generated at a higher thermal maturity than the Sarvak reservoir samples.

Biostratigraphy of Albian Sediments (Kazhdumi Formation) in Zagros Area (Southwest of Iran)

Biostratigraphy of Albian Sediments (Kazhdumi Formation) in Zagros Area (Southwest of Iran)

Hydrocarbon source rocks in Kazhdumi and Pabdeh formations—a quick outlook in Gachsaran oilfield, SW Iran

Geochemical study of Kazhdumi and Pabdeh Formations as potential source rocks in Gachsaran Oilfield demonstrates that the Kazhdumi Formation has a fair to good capability of hydrocarbon generation and predominately contains type II-III kerogen. On the other hand, the Pabdeh Formation has a poor to good petroleum potential and contains different kerogen types, including type II, type II-III, type III and even for one sample, type IV, indicating different depositional conditions for this formation. The geochemical log of the Kazhdumi Formation shows that there is a close correlation between different geological parameters as noticed prominently in well number 55, which suggests the more extensive the anoxic condition, the higher the petroleum potential is for Kazhdumi Formation. By contrast, a poor correlation between TOC and other Rock–Eval-derived parameters for the Pabdeh Formation at a depth of more than 2100 m may demonstrate the inert organic matter and mineral matrix effects at this depth interval. However, biomarkers show differences in lithology and depositional environment for the Kazhdumi Formation in well numbers 55 and 83. On the other hand, the Pabdeh Formation has a mixed lithology (carbonate-shale) deposited in a marine setting under suboxic–anoxic condition. Moreover, thermal maturity indicators suggest that Pabdeh and Kazhdumi Formations are immature and early mature, respectively.

Biostratigraphy, Microfacies and Depositional Environment of the Sarvak Formation at the Pyun Anticline (Zagros Basin, Southwest of Iran)

AbstractThe Sarvak Formation is a carbonate sequence of Late Albian–Early Turonian age in Zagros Basin in Iran. In this investigation, the Sarvak Formation at the Pyun Anticline section (Izeh Zone) has been studied. It consists of 797 m thick limestone which overlies the Kazhdumi Formation conformably and underlies the Gurpi Formation unconformably at the Pyun Anticline. A very rich fossil association (85 genera and 132 species) characterizes the Pyun section. Based on the stratigraphic distribution of diagnosed foraminifera, five biozones are established: 1, Muricohedbergella‐Globigerinelloides sp. assemblage zone (Late Albian); 2, Praealveolina iberica‐Chrysalidina gradata interval zone (Early Cenomanian); 3, Chrysalidina gradata‐Cisalveolina fraasi (fallax) and C. lehneri interval zone (Middle Cenomanian); 4, C. fraasi (fallax) and C. lehneri‐Praetaberina bingistani assemblage zone (Late Cenomanian); 5, Nezzazatinella picardi‐Mangashtia‐Dicyclina assemblage zone (Early Turonian). Based on the petrographic and sedimentological analyses, some 13 carbonate microfacies were identified. The investigated microfacies confirm a ramp‐type paleoenvironment. These microfacies, from distal to proximal environments, consist of: MF1: planktonic foraminifera wackestone‐packstone; MF2: Oligostegina planktonic foraminifera wackestone to packstone; MF3: planktonic‐benthic foraminifers sponge spicules wackestone‐packstone; MF4: rudist floatstone; MF5: rudist rudstone; MF6: bioclast intraclast grainstone; MF7: peloid intraclast grainstone; MF8: benthic foraminifers rudist grainstone‐packstone; MF9: peloid bioclast grainstone‐packstone; MF10: bioclast (benthic foraminifers) wackestone‐packstone; MF11: peloid bioclast packstone; MF12: dacycladacea benthic foraminifera packstone‐wackestone; MF13: miliolids wackestone‐packstone.