گروه هاي شكلي روزنبرداران سازند قم در خاور سيرجان و جنوب باختري كاشان :كاربرد آنها در تفاسير ديرينه محيطي و ديرينه بوم شناختي

Foramniferal morphogroups of the Qom Formation in E Sirjan and SW Kashan: implication for paleoenvironmental and paleoecological interpretations

ﺳﺎزﻧﺪ ﻗﻢ ﻣﻬﻢﺗﺮﯾﻦ ﺳﻨﮓ ﻣﺨﺰن و ﺳﻨﮓ ﻣﻨﺸﺎء ﻫﯿﺪروﮐﺮﺑﻮر در اﯾﺮان ﻣﺮﮐﺰي اﺳﺖ. ﻣﻄﺎﻟﻌﻪ روزﻧﺒﺮان ﺳﺎزﻧﺪ ﻗﻢ در ﺑﺮش ﺑﻮﺟﺎن ﺧﺎور ﺳﯿﺮﺟﺎن، ﺑﺎ ﺳﻦ روﭘﻠﯿﻦ- ﺷﺎﺗﯿﻦ و 156 ﻣﺘﺮ ﺿﺨﺎﻣﺖ( و ﺑﺮش ورﮐﺎن )ﺟﻨﻮب ﺑﺎﺧﺘﺮي ﮐﺎﺷﺎن؛ ﺑﺎ ﺳﻦ روﭘﻠﯿﻦ و 190 ﻣﺘﺮ ﺿﺨﺎﻣﺖ(، ﻣﻨﺠﺮ ﺑﻪ ﺗﺸﺨﯿﺺ ﻫﻔﺖ ﮔﺮوه ﺷﮑﻠﯽ ﺷﺪ. در ﻫﺮ دو ﺑﺮش ﺑﻪﻃﻮرﮐﻠﯽ ﻓﺮمﻫﺎي اﭘﯿﻔﻮﻧﺎل ﻏﺎﻟﺐ ﺑﻮدهاﻧﺪ. آﻧﺎﻟﯿﺰ ﮔﺮوهﻫﺎي ﺷﮑﻠﯽ ﺑﯿﺎﻧﮕﺮ وﺟﻮد ﻧﻮﺳﺎﻧﺎﺗﯽ در درﺻﺪ ﮔﺮوهﻫﺎي ﺷﮑﻠﯽ ﻏﺎﻟﺐ اﺳﺖ، ﮐﻪ ﺧﻮد ﺑﯿﺎﻧﮕﺮ ﻧﻮﺳﺎﻧﺎﺗﯽ در ﺷﺮاﯾﻂ ﺑﻮم ﺷﻨﺎﺧﺘﯽ ﻣﺤﯿﻂ ﻣﯽﺑﺎﺷﺪ. در ﺑﺮش ﺑﻮﺟﺎن در ﻧﻬﺸﺘﻪﻫﺎي روﭘﻠﯿﻦ ﮔﺮوهﻫﺎي ﺷﮑﻠﯽ ﺑﺎ دﯾﻮاره ﭘﻮرﺳﻼﻧﻮز و در ﺷﺎﺗﯿﻦ ﮔﺮوهﻫﺎي ﺷﮑﻠﯽ ﺑﺎ دﯾﻮاره ﻫﯿﺎﻟﯿﻦ ﻓﺮاواﻧﯽ ﺑﯿﺸﺘﺮي دارﻧﺪ ﮐﻪ ﺑﯿﺎﻧﮕﺮ ﻧﻬﺸﺘﻪ ﺷﺪن ﺑﺨﺶﻫﺎي ﭘﺎﯾﯿﻨﯽ در ﻣﺤﯿﻂﻫﺎي ﻻﮔﻮﻧﯽ و ﻧﻬﺸﺘﻪ ﺷﺪن ﺑﺨﺶﻫﺎي ﺑﺎﻻﯾﯽ ﺑﺮش )ﻋﻤﺪﺗﺎً( در رﻣﭗ ﻣﯿﺎﻧﯽ اﺳﺖ. اﯾﻦ ﺗﻐﯿﯿﺮ ﭼﺸﻤﮕﯿﺮ در ﻃﻮل زﻣﺎن ﺑﯿﺎﻧﮕﺮ اﻓﺰاﯾﺶ ﺗﺪرﯾﺠﯽ ﻋﻤﻖ ﺣﻮﺿﻪ، ﮐﺎﻫﺶ ﺷﻮري، ﮐﺎﻫﺶ روﺷﻨﺎﯾﯽ و ﮐﺎﻫﺶ ﻣﻮاد ﻣﻐﺬي اﺳﺖ. ﻏﺎﻟﺐ ﺑﻮدن ﮔﺮوهﻫﺎي ﺷﮑﻠﯽ ﺑﺎ دﯾﻮاره ﻫﯿﺎﻟﯿﻦ در ﺳﺮﺗﺎﺳﺮ ﺑﺮش ورﮐﺎن ﺑﯿﺎﻧﮕﺮ رﺳﻮبﮔﺬاري اﯾﻦ ﺑﺮش )ﻋﻤﺪﺗﺎً( در ﻣﺤﯿﻂﻫﺎي رﻣﭗ ﻣﯿﺎﻧﯽ ﺑﺎ ﻣﯿﺰان ﺷﻮري ﻧﺮﻣﺎل درﯾﺎﯾﯽ و ﺗﺤﺖ ﺷﺮاﯾﻂ ﻧﻮري ﻣﺰوﻓﻮﺗﯿﮏ ﺗﺎ اﻟﯿﮕﻮﻓﻮﺗﯿﮏ ﻣﯽﺑﺎﺷﺪ.

The Qom Formation is the main reservoir and source rock of hydrocarbons in central Iran. Foramniferal study of the Qom Formation in the Bujan (eastern Sirjan; with Rupelin-Chattian in age and 156 m thickness) and Varkan (southwestern Kashan; with Rupelin in age and 190 m thickness) sections resulted in identification of seven morphogroups. Generaly, epifaunal morphogroups were dominated in both study sections. The morphogroup analyses showed variations in the percentage of the dominant morphotypes, suggesting fluctuations in the paleoecological conditions. In the Bujan section, the Rupelin deposits are dominated by calcareous porcelaneous morphogroups; while the Chattian deposits are dominated by hyaline morphogroups, which indicates the lower and upper parts were deposited in inner ramp (lagoonal environments) and middle ramps, respectively. This significant change through time reffers to gradual increasing of the basin depth, decreasing the light intensity, reducing the salinity, and decreacing the nutrient level. The dominance of the hyaline morphogroups throughout the Varkan section is indicative of the deposition in middle ramp environments with normal salinity under meso-photic to oligo-photic conditions.