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See detailEarly Carboniferous events along the north-eastern Gondwanan margin: an example from the Mobarak Formation of the Central Alborz Mountains, Northern Iran.
Sardar Abadi, Mehrdad ULg; Da Silva, Anne-Christine ULg; Poty, Edouard ULg et al

Poster (2015, July 14)

The transition from the Late Devonian to the Early Carboniferous was marked by tectonic events, environmental change and global oceanic biological turnover that influenced sedimentary regimes. The end ... [more ▼]

The transition from the Late Devonian to the Early Carboniferous was marked by tectonic events, environmental change and global oceanic biological turnover that influenced sedimentary regimes. The end-Devonian faunal extinction event, for example, eliminated most of the reef building taxa, which, coupled with an increasing rate of subsidence in response to the opening of the Paleo–Tethys and a sea-ward shift of carbonate factories during the Lower Carboniferous, led to the formation of extensive carbonate ramp platforms along the Laurasian and Gondwanan margins. This development has already been reported from the western Gondwanan and southern Laurasian margins but not from northern to north-eastern Gondwanan margin yet. We aim to improve the knowledge on the main factors controlling the development and growth of carbonate ramps during the Lower Carboniferous by examining the Alborz basin along the northern margin of Gondwana. The Lower Carboniferous Mobarak Formation records the development of a storm-sensitive pervasive carbonate factory on the southern Paleo-Tethys passive margin following the opening of the Paleo-Tethys Ocean into the Alborz basin along the northern margin of Gondwana. Four outcrops in the central Alborz Mountains were studied: the Jaban, Aroo, Shahmirzad and Labnesar sections. Four events have been described as the principal factors controlling carbonate platform evolution in the Lower Carboniferous: (1) A transgression linked to global temperature rise in the Early Tournaisian (Middle Hastarain) resulted in the formation of thick-bedded argillaceous limestones. This interval is represented by massive beds of dark mudstones–wackestones to packstones that laterally interfinger with finely laminated limestones, and with bed thickness ranging on the centimeter to meter scale. This interval correlates with Lower Tournaisian nodular to argillaceous limestones of the Moravia Basin (Czech Republic), the Rhenish Slate Mountains (Poland) and the Dinant Basin (Belgium). (2) Late Hastarian–Early Ivorian glaciations were identified in Southern Gondwana but had not been evidenced in Northern Gondwana yet. This glaciation regime is recorded through the appearance of inner-ramp channel-form facies in mid– and outer-ramp settings. (3) During Late Ivorian–Early Visean?, a differentiation block faulting regime along the basin’s margin caused uplift of the westernmost parts of the Alborz basin and resulted in a sub-marine collapse in the eastern part of the central basin. This caused vast sub-aerial exposure and brecciation the top of the Mobarak Formation at the Jaban and Aroo sections. The sub-marine collapse was recorded through the occurrence of Zoophycos bearing fine-grained limestones in the top of the Labnesar and Shahmirzad sections. (4) Tectonic activity that coincided with considerable and abrupt sea level falls as an indirect consequence of the Viséan and Serpukhovian glaciations phases. This progressive sea level drop led to the stagnation of the carbonate factory, which is expressed as an erosional surface at the top of the Mobarak Formation. [less ▲]

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See detailLower Carboniferous ramp sedimentation of the Central Alborz Basin, North Iran: integrated sedimentological and rock–magnetic studies.
Sardar Abadi, Mehrdad ULg; Da Silva, Anne-Christine ULg; Mosaddegh, hossein et al

in Special Publication - Geological Society of London (2015), 414

The Lower Carboniferous Mobarak Formation in the Alborz Basin (northern Iran) was deposited along the northeastern margin of Gondwana in a carbonate ramp setting. This paper focuses on the Tournaisian ... [more ▼]

The Lower Carboniferous Mobarak Formation in the Alborz Basin (northern Iran) was deposited along the northeastern margin of Gondwana in a carbonate ramp setting. This paper focuses on the Tournaisian stratigraphic interval of this formation that crops out at the Jaban section in the southwestern Central Alborz Basin. The following facies associations, representing different ramp palaeoenvironments, have been identified: (1) mudstone–wackestone outer-ramp facies; (2) crinoidal to skeletal grainstone–packstone mid-ramp facies; (3) peloidal to crinoidal grainstone–packstone inner-ramp facies; and (4) coastal facies, which include a variety of microbial laminated to oncoidal grainstones and mudstones with evaporitic pseudomorphs. This ramp profile was affected by frequent storms that were responsible for the formation of several skeletal to non-skeletal shoals in the distal mid-ramp to the most proximal inner-ramp areas. The development of the skeletal to non-skeletal shoals along the sea side of the ramp formed a semi-enclosed lagoon sensitive to the influence of both high tides and storm surges.The magnetic susceptibility (xin) of all the samples was measured and compared with that of the facies from which the sample was taken. There is a clear link between xin and the facies; the average xin values were higher for the distal facies than for the proximal facies. The xin profile of this Lower Carboniferous carbonate sequence reflects stratigraphic variations in response to relative changes in sea level and the input of detrital materials. In the context of the sequence stratigraphic framework, the average xin values for lowstand and transgressive systems tract deposits are higher than for the highstand systems tract deposits. The clear link between xin and facies indicates at least a partly preserved primary xin signal related to the detrital inputs. However, to obtain a better understanding of the nature and origin of the minerals carrying the xin, we performed hysteresis measurements on selected samples. It appears that the xin signal is mainly carried by lowcoercivity ferromagnetic minerals such as magnetite, with a mixture of relatively coarse grains (detrital fraction) and ultra-fine grains (probably formed during diagenesis). [less ▲]

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See detailDepositional facies and magnetic susceptibility of Mobarak formation (Lower Carboniferous in central and eastern Alborz Mountains, North of Iran).
Sardar Abadi, Mehrdad ULg; Da Silva, Anne-Christine ULg; Boulvain, Frédéric ULg et al

in Geologica Belgica Meeting 2012; Moving plates and melting icecaps. Processes and forcing factors; Abstract book (2012)

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See detailMagnetic Susceptibility and sedimentology techniques applied to unravel the interaction between eustasy and tectonic activity from the Jurassic Kashafrud Fromation (Koppeh Dagh Basin, NE Iran).
Sardar Abadi, Mehrdad ULg; Da Silva, Anne-Christine ULg; Amini et al

in Kido, E; Suttner, T; Piller, W (Eds.) et al IGCP-580, 4th annual meeting, 24-30th June 2012, Graz, Austria, Abstract book (2012)

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See detailSedimetology and magnetic susceptibility of Mobarak formation (Lower Carboniferous in central and eastern Alborz Mountains, North of Iran).
Sardar Abadi, Mehrdad ULg; Da Silva, Anne-Christine ULg; Boulvain, Frédéric ULg et al

in koptikova, Elena (Ed.) Miroslav Krs Conference: Time, Magnetism, Records, Systems and Solutions, Prague 12-18 October 2011 (2011, October 12)

The Mobarak formation (lower Carboniferous) corresponds to a carbonate platform which was located in the northern margin of Gondwana. This work is focused on the two stratigraphic sections located in ... [more ▼]

The Mobarak formation (lower Carboniferous) corresponds to a carbonate platform which was located in the northern margin of Gondwana. This work is focused on the two stratigraphic sections located in central and eastern Alborz Mountains: the Aruo and Shahmirzad sections. Palaeoenvironments are corresponding to a carbonate ramp platform with frequent storm deposits. Different facies have been observed and are from proximal to distal: (1) crinoid banks and lagoonal facies with abundant peloids and oncoid; (2) in-situ bioherms, mainly constituted by accumulations of tabulate corals, shell fragments and crinoids steams; (3) distal to proximal tempestites and (4) bioturbated dark argillaceous mudstone. The main sedimentological evolution is a shallowing-upward trend corresponding to the transition from distal to proximal tempestites, bioherms, crinoids banks and lagoonal facies. Magnetic susceptibility data are also provided in order to get a better understanding of sedimentary dynamics and correlation between the two sections. It appears that MS values are the lowest for the more energetic environments which corresponds to the trends observed in the Devonian carbonate ramp in Belgium. [less ▲]

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See detailDiagenetic factors controlling reservoir quality in the Faraghan Formation (Lower Permian), Darang Field, Southern Iran
Zamanzadeh, Seyed Mohammad; Mirzaei, Saeid; Sardar Abadi, Mehrdad ULg et al

in Energy Exploration & Exploitation (2011), 29(2), 109-128

The role of diagenesis in affecting (reduction or enhancement) reservoir quality in the Faraghan Formation in Darang #1 well was investigated. The Faraghan Formation is mainly composed of sandstone facies ... [more ▼]

The role of diagenesis in affecting (reduction or enhancement) reservoir quality in the Faraghan Formation in Darang #1 well was investigated. The Faraghan Formation is mainly composed of sandstone facies along with minor mudstone and siltstone and grades upward into mixed carbonate –siliciclastic facies and then to Dalan Formation carbonates. Depositional environment of this formation comprises various sub-environments of a delta setting in the lower part of the formation which grades upward into a shallow marine clastic environment in the upper part. The processes enhancing reservoir quality include dissolution of carbonate grains and cements and alteration of feldspar grains. Burial history diagram shows that after deposition during Lower Permain, the formation underwent a rapid burial up to 1000 meters below sea level in Upper Permian. Then a slight uplift (about 100 meters) and gradual burial followed up to Mid- Jurassic. Afterwards the formation experienced a series of rapid and moderate uplift from Mid-Jurassic to Tertiary when the formation uplifted to around 2500 meters above sea level. The suitable conditions resulting in dissolution took place in shallow buried sandstones. These conditions occurred two times during burial history: at the early stages of eodiagenesis and during telodiagenesis. The major processes deteriorating reservoir quality include compaction and cementation. Major cement types include carbonate cements (dolomite, siderite), clay cements (kaolinite, sericite, chlorite), silica cement and pyrite cement. The most abundant cement is the carbonate cement especially dolomite. The dolomite cement occurs as intergranular and poikilotopic forms. The most frequent clay cement is sericite which dominates in sitstones and lithicarenites. Silica cement, where present, fills all the pore spaces. The least frequent cement type is pyrite which is found in two forms of poikilotopic and framboidal. Where it is found in the form of poikilotopic cement, it massively fills the pore spaces and deteriorates the porosity and permeability of the sandstones. [less ▲]

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See detailDelta and deep basin Jurassic deposits from Iran: relationship between magnetic susceptibility and facies
Sardar Abadi, Mehrdad ULg; Da Silva, Anne-Christine ULg; Zamanzadeh

in Abstract 4eme Congrès Français de Stratigraphie, Strati2010, Paris, France, 30 Augustus – 2 September (2010)

This study concerns, the Kashafrud Formation from Kopet Dagh Basin in its type section, which corresponds to the first Jurassic sedimentary cycle in Iran,. Sedimentary studies were carried out to propose ... [more ▼]

This study concerns, the Kashafrud Formation from Kopet Dagh Basin in its type section, which corresponds to the first Jurassic sedimentary cycle in Iran,. Sedimentary studies were carried out to propose a paleoenvironmental model of the sedimentary succession. Furthermore, magnetic susceptibility (MS) measurements were performed and compared with sedimentological evolution. The MS curve evolution is related to the abundance of magnetic minerals, which itself is related to lithogenic supplies which could be related mostly to sea level and climatic changes. Theoretically, a regression will lead to a more important proportion of landmass exposed and so to an increase of detritic minerals in the sedimentary system and so to an increasing MS. A transgression will decrease MS (Ellwood et al., 2000). Palaeoenvironments of this Jurassic succession from base to top are: flood dominated delta, deep basin deposits, silisiclastic and mixed silisiclastic and carbonate shoreface deposits. Comparison between facies evolution and MS curve shows that the facies which are deposited in delta and shoreface zones have low MS values; on the contrary basinal deposits are presenting high MS values. The facies deposited in mixed silisiclastic and carbonate shoreface have lowest MS values. So it appears that the deeper basinal deposits have the highest MS values and the shallower deltaic and shorelines facies have the lowest MS values, in opposition with theoretical background. This could be related to water agitation and sedimentation rate during deposition. In the deltaic and shoreface environments, a high water agitation could prevent the detritic particles to settle and a high sedimentary rate could dilute the magnetic minerals (see Da Silva et al., 2009). It actually seams that the carbonate production in the upper parts of the studied interval has led to a dramatic decrease in MS values. This study clearly shows the significant role of MS in environmental analysis, and the importance of a strong sedimentological background. Ellwood, B.B., Crick, R.E., El Hassani, A., Benoist, S.L. & Young, R.H., 2000. Magnetosusceptibility event and cyclostratigraphy method applied to marine rocks: detrital input versus carbonate productivity. Geology, 28: 1135-1138. Da Silva, A.-C., Mabille, C. & Boulvain, F., 2009. Influence of sedimentary setting on the use of magnetic susceptibility: examples from the Devonian of Belgium. Sedimentology, 56: 1292-1306. [less ▲]

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