ريزرخساره ها، محيط رسوبي، چينه نگاري سكانسي و كيفيت مخزني برش انارك (دونين پسين-كربونيفر پيشين)، زون ايران مركزي

Microfacies, Sedimentary environment and Sequence stratigraphy of Anarak section (Late Devonian-Early Carboniferous), central Iran

در اﯾﻦ ﭘﮋوﻫﺶ ﺗﻮاﻟﯽ ﺑﺮش اﻧﺎرك در ﺷﻤﺎل ﺷﺮﻗﯽ اﺻﻔﻬﺎن، زون اﯾﺮان ﻣﺮﮐﺰي ﺷﺎﻣﻞ دو ﺳﺎزﻧﺪ ﺑﻬﺮام و ﺷﯿﺸﺘﻮ1، ﺑﻪ ﺳﻦ دوﻧﯿﻦ ﭘﺴﯿﻦ- ﮐﺮﺑﻨﯿﻔﺮ ﭘﯿﺸﯿﻦ )ﻣﯽ ﺳﯽ ﺳﯽ ﭘﯿﻦ( از دﯾﺪﮔﺎه ﻣﺤﯿﻂ رﺳﻮﺑﮕﺬاري و ﭼﯿﻨﻪ ﻧﮕﺎري ﺳﮑﺎﻧﺴﯽ ﻣﻮرد ارزﯾﺎﺑﯽ ﻗﺮار ﮔﺮﻓﺘﻪ اﺳﺖ. ﺑﺮرﺳﯽ ﻫﺎي ﺻﺤﺮاﯾﯽ و ﻣﻄﺎﻟﻌﻪ رﯾﺰرﺧﺴﺎرهﻫﺎ، ﻣﻨﺠﺮ ﺑﻪ ﺷﻨﺎﺳﺎﯾﯽ12 رﯾﺰرﺧﺴﺎره ﻣﺮﺑﻮط ﺑﻪ ﻣﺤﯿﻂ درﯾﺎي ﺑﺎز، ﺳﺪ ﺑﺎﯾﻮﮐﻼﺳﺘﯽ، ﻻﮔﻮن و ﭘﻬﻨﻪ ﺟﺰروﻣﺪي ﮔﺮدﯾﺪ. ﺗﻐﯿﯿﺮات ﺗﺪرﯾﺠﯽ رﯾﺰرﺧﺴﺎره ﻫﺎ، ﻧﺒﻮد ﮐﻠﺴﯽﺗﻮرﺑﯿﺪاﯾﺖﻫﺎ و ﻧﺒﻮد رﯾﻒ ﻫﺎي ﺳﺪي ﮔﺴﺘﺮش ﯾﺎﻓﺘﻪ ﻣﻌﺮف ﻧﻬﺸﺘﻪ ﺷﺪن ﺗﻮاﻟﯽ رﺳﻮﺑﯽ در ﯾﮏ ﻣﺤﯿﻂ رﻣﭗ ﮐﺮﺑﻨﺎﺗﻪ ﻫﻤﻮﮐﻠﯿﻨﺎل ﯾﺎ ﻫﻢ ﺷﯿﺐ اﺳﺖ. ﺑﺎ ﺑﺮرﺳﯽ ﻫﺎي ﭼﯿﻨﻪ ﻧﮕﺎري ﺳﮑﺎﻧﺴﯽ 2 ﺳﮑﺎﻧﺲ رده ﺳﻮم ﺷﻨﺎﺳﺎﯾﯽ ﺷﺪ. در ﻫﺮ دو ﺳﮑﺎﻧﺲ ﺑﺴﺘﻪﻫﺎي رﺳﻮﺑﯽ ﻓﺮازﯾﻦ و ﭘﯿﺸﺮوﻧﺪه ﻗﺎﺑﻞ ﺗﻔﮑﯿﮏ ﻣﯽ ﺑﺎﺷﻨﺪ. ﺳﮑﺎﻧﺲ اول ﺑﻪ ﺳﻦ دوﻧﯿﻦ ﭘﺴﯿﻦ )ﺳﺎزﻧﺪ ﺑﻬﺮام( ﻣﯽﺑﺎﺷﺪ و ﺿﺨﺎﻣﺖ آن 32/5 ﻣﺘﺮ ﻣﯽﺑﺎﺷﺪ. ﺳﮑﺎﻧﺲ دوم ﺑﻪ ﺿﺨﺎﻣﺖ 80/5 ﻣﺘﺮ داراي ﺳﻦ دوﻧﯿﻦ ﭘﺴﯿﻦ و ﮐﺮﺑﻨﯿﻔﺮ ﭘﯿﺸﯿﻦ )ﻗﺴﻤﺖ ﺑﺎﻻي ﺳﺎزﻧﺪ ﺑﻬﺮام و ﺳﺎزﻧﺪ ﺷﯿﺸﺘﻮ1( ﻣﯽﺑﺎﺷﺪ. ﻣﺮز ﺳﮑﺎﻧﺲ اول و ﺳﮑﺎﻧﺲ دوم ﺑﺎ ﺗﻮﺟﻪ ﺑﻪ ﻋﺪم وﺟﻮد ﺷﻮاﻫﺪ ﺧﺮوج از آب، ﻧﻮع دوم ﻣﯽ ﺑﺎﺷد.

Anarak section in northeast Isfahan, central Iran is evaluated regarding to sedimentary environment and sequence stratigraphy. Field studies and micro-facies analysis led to the identification of 12 micro-facies related to the open marine, the shoal, the lagoon and the tidal flat environments. Micro-facieses gradual change, lack of calciturbidite and lack of expanded barrier reef indicate the deposition of a sedimentary interval in a homoclinal ramp environment. Two type 3 sequences were identified by sequence stratigraphic study. Both of these sequences are separable TST and HST packages. The age of first sequence is Late Devonian (Bahram Formation) and its thickness is 42.3 meters and the second sequence with a thickness of 70.7 meters is Late Devonian-Early Carboniferous (Upper part of Bahram Formation and Shishtu2 Formation). The sequence boundary between first and second sequences is the second type boundary due to the lack of evidence for exposure.