Doctoral thesis (Dissertations and theses)
Lower Carboniferous shallow marine sequences from the Central Alborz Basin, Iran (north-eastern margin of Gondwana): sedimentology, biostratigraphy and rock– magnetic studies
Sardar Abadi, Mehrdad
2016
 

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Keywords :
Lower Carboniferous; Iran; sedimentology; biostratigraphy; rock-magnetic studies
Abstract :
[en] The Lower Carboniferous Mobarak Formation records the development of a carbonate platform on the southern Paleo-Tethyan passive margin. This pervasive carbonate factory was deposited following the opening of the Paleo-Tethys Ocean into the Alborz Basin along the northern margin of Gondwana. The depositional facies range from the most proximal to the most distal and include coastal environments, inner ramp peritidal facies, peloidal to crinoidal shoals, storm to fair-weather influenced mid-ramps, proximal to distal shell beds and low energy outer ramps. Storms clearly played a dominant role in the distribution of skeletal and non-skeletal shoals on the carbonate ramp. Sedimentological analyses complemented with foraminiferal biostratigraphy reveal four events which are interpreted to represent the principal factors controlling carbonate platform evolution in the Alborz Basin during 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. 2) the Hastarian–Ivorian boundary glaciation phase, 3) Upper Ivorian–Lower Viséan? tectonic block faulting. 4) the Viséan- Serpukhovian glaciation phase. The three foraminiferal assemblages encountered in the Tournaisian interval of the Mobarak Formation are restricted to specific periods within the Ivorian. The occurrence of specific foraminiferal taxa in Alborz is tightly governed by transgressions and migration of North Paleo–Tethyan biotic elements as response to the thermal period. We also combined proxies for ambient paleothermometry in addition to the indications for arid conditions and arid conditions and the presence of foraminiferal taxa with a North Paleo-Tethyan affinity in the Lower Carboniferous Mobarak Formation to suggest a paleo-position for the Alborz Basin at lower latitudes than approximately 45  –50  southern paleolatitude reported thus far. Magnetic susceptibility ( in ) was measured and compared with facies from the same sample. There is a clear link between  in and facies, and the average  in values are higher for distal facies than for proximal ones. The  in profile of Lower Carboniferous carbonate sequence reflects stratigraphic variations in response to relative sea level changes and detrital input. In the context of the sequence stratigraphic framework, the average  in values for lowstand and transgressive system tracts deposits are higher than for the highstand system tracts deposits. The clear link between  in and facies points to at least partly preserved primary  in signal, related to detrital inputs. In respect to the hysteresis measurements the in signal is mainly carried by low coercivity ferromagnetic minerals such as magnetite, with a mixture of relatively coarse grains (detrital fraction) and ultra-fine grains (probably formed during diagenesis).
Disciplines :
Earth sciences & physical geography
Author, co-author :
Sardar Abadi, Mehrdad ;  Université de Liège - ULiège > Form. doct. sc. (géologie - Bologne)
Language :
English
Title :
Lower Carboniferous shallow marine sequences from the Central Alborz Basin, Iran (north-eastern margin of Gondwana): sedimentology, biostratigraphy and rock– magnetic studies
Defense date :
26 February 2016
Number of pages :
174
Institution :
ULiège - Université de Liège
Degree :
Docteur en Sciences
Promotor :
Da Silva, Anne-Christine  ;  Université de Liège - ULiège > Geology
President :
Fischer, Valentin  ;  Université de Liège - ULiège > Geology
Secretary :
Boulvain, Frédéric  ;  Université de Liège - ULiège > Geology
Jury member :
Poty, Edouard ;  Université de Liège - ULiège > Département de géologie
Vennin, Emmanuelle
Spassov, Simo
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since 01 March 2016

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