Stratigraphy and Palaeontology
Azam Mahanipour; Maryam Eftekhari; Soheila Soheili
Abstract
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 ...
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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.
Stratigraphy and Palaeontology
Katayoon Barmakizadeh; A. Mahanipour
Abstract
Abstract The lower part of the Garau Formation with a thickness of 212 m at the southwest of the Kabirkuh anticline is investigated with regard to the calcareous nannofossils. Lithology of the studied interval is mainly consists of marl, marly limestone, black shale and limestone. 67 species from 33 ...
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Abstract The lower part of the Garau Formation with a thickness of 212 m at the southwest of the Kabirkuh anticline is investigated with regard to the calcareous nannofossils. Lithology of the studied interval is mainly consists of marl, marly limestone, black shale and limestone. 67 species from 33 genus and 13 families are recognized. Nannofossil events that are recorded from base to top of the section are as follow: the first occurrence (FO) of Calcicalathina oblongata, the last occurrence (LO) of Rucinolithus wisei, the FO of Lithraphidites bollii, the LO of Cruciellipsis cuvillieri, the first occurrence of Assipetra terebrodentarius and the last occurrence of Lithraphidites bollii. According to these index calcareous nannofossils, the studied interval is ranging from the uppermost part of CC2/NK2 biozone to the middle part of CC5b/NC5C subzone Considering these zonations, the age of the studied interval is Valanginian ‒ Hauterivian. According to the calcareous nannofossil data, the Valanginian ‒ Hauterivian boundary can’t be determined. This boundary is located at the base of the Tethyan ammonite Acanthodiscus radiatus at the leading GSSP candidate in the La Charce section of southeastern France.
Stratigraphy and Palaeontology
Maryam Eftekhari; Azam Mahanipour; Mohammad Dastanpour
Abstract
Abstract Barremian sediments of the Garau Formation have been investigated at the southwest of the Kabir-kuh anticline (Qaleh-Darreh section) with regard to calcareous nannofossils. According to the presence of index calcareous nannofossils, NC5 biozone and NC5c, NC5d and NC5e subzones of Roth (1978) ...
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Abstract Barremian sediments of the Garau Formation have been investigated at the southwest of the Kabir-kuh anticline (Qaleh-Darreh section) with regard to calcareous nannofossils. According to the presence of index calcareous nannofossils, NC5 biozone and NC5c, NC5d and NC5e subzones of Roth (1978) and CC5-CC6 biozones of Sissingh (1977) have been identified. At the studied interval, warm water taxa like Cyclagelosphaera margerelii, Diazomatolithus lehmanii, Lithraphidites carniolensis, Micrantholithus spp., Nannoconus spp., Rhagodiscus asper and Watznaueria spp. have been recorded along with cool water taxa such as Biscutum constans, Helenea chiastia and Zeugrhabdotus embergeri. The abundance of warm water taxa is higher than cool water taxa and a reverse trend can be observed between them. Regarding cool and warm water taxa three warming phases and two cooling phases are identified which includes the warming event of early Early Barremian, cooling event of Early Barremian, warming event of Mid-Barremian, cooling event of late Barremian and warming event of Barremian-Aptian boundary. It must be mentioned that these data are in accord with other parts of the world in the Tethyan (e.g., Italy) and the Boreal realms (e.g., NW Germany and NE England). Keywords: Barremian, Biostratigraphy, Paleoecology, Garau Formation, Calcareous nannofossils.
A Pireh; S.A Alavi; M.R Ghassemi; A Shaban
Abstract
A major part of source rocks in the Zagros Fold Belt were deposited during Neocomian time; the lowermost part of the Garau Formation has charged the Early Cretaceous Petroleum System of the Lurestan province. These source rocks are widely distributed in the Lurestan Depression and in the NW part of the ...
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A major part of source rocks in the Zagros Fold Belt were deposited during Neocomian time; the lowermost part of the Garau Formation has charged the Early Cretaceous Petroleum System of the Lurestan province. These source rocks are widely distributed in the Lurestan Depression and in the NW part of the Dezful Embayment. The Kabir-Kuh anticline, which is a prominent structure of the Lurestan province, is more than 200 km long, and contains outcrop of the Garau Formation. Natural fracture systems have an important role in increasing of permeability and sometimes porosity of many reservoirs, and are necessary for the primary migration of hydrocarbons from the source rock to the reservoir. We have collected and analyzed field data on fracture set densities andtypes in Garau Formation and in parts of Sarvak Formation which outcrop in the Kabir kuh anticline of Zagros Belt. According to our analyses we have identified 8 fracture sets in 4 fracture systems: 1) a NNE-SSW transverse fracture system (sets A and B), 2) an ESE-WNW longitudinal fracture system (sets C and D), 3) a NE-SW and NNW-SSE oblique fracture system (sets E and F), 4) a SE-NW and ENE-WSW oblique fracture system (sets G and H). The transverse fractures and their orthogonal stylolites are Early Cretaceous to pre-late Miocene in age, while longitudinal and oblique fracture systems have formed since Late Miocene. Some transverse fractures show calcite infillings. We suggest that there have been two phases of counterclockwise rotation in orientation of the stress fields that produced these fractures, 1) a counterclockwise rotation of the stress field between development of non-mineralized fractures and open fractures and 2) a counterclockwise rotation of the stress field between development of the oblique fracture system (sets E and F) and the extension fractures (sets A and B). These rotations in the stress field have probably occurred due to rotation of the Arabian plate during its convergence to the Eurasian plate.