پديد آورندگان :
ناصري كريموند، فرخ دانشگاه فردوسي مشهد - پرديس بين الملل , موسوي حرمي، رضا دانشگاه فردوسي مشهد - دانشكده علوم - گروه زمين شناسي , محبوبي، اسداله دانشگاه فردوسي مشهد - دانشكده علوم - گروه زمين شناسي , بهداد، علي شركت ملي مناطق نفت خيز جنوب - اداره زمين شناسي
كليدواژه :
سازند آسماري , حوضه زاگرس , روزنداران كف‌زي بزرگ , اليگوسن , ميوسن
چكيده فارسي :
ﺗﻮاﻟﯽ ﮐﺮﺑﻨﺎﺗﻪ اﻟﯿﮕﻮﺳﻦ ـ ﻣﯿﻮﺳﻦ ﺳﺎزﻧﺪ آﺳﻤﺎري از ﺣﻮﺿﻪ ﭘﯿﺶﺑﻮم زاﮔﺮس در ﻧﺎﺣﯿﻪ دﻫﺪﺷﺖ )ﺟﻨﻮب ﺷﺮق ﭘﻬﻨﻪ اﯾﺬه( ﺑﺮاي اﯾﻦ ﻣﻄﺎﻟﻌﻪ اﻧﺘﺨﺎب ﺷﺪه اﺳﺖ. در اﯾﻦ ﻣﻄﺎﻟﻌﻪ ﺑﺮش ﮔﻨﺎوه در ﯾﺎل ﺟﻨﻮﺑﯽ ﺗﺎﻗﺪﯾﺲ ﻣﯿﺶ ﺑﺎ 440 ﻣﺘﺮ ﺿﺨﺎﻣﺖ، ﺑﺮش ﺳﯿﻨﮓ در ﭘﻼﻧﮋ ﻏﺮﺑﯽ ﺗﺎﻗﺪﯾﺲ ﺧﺎﻣﯽ ﺑﺎ 248 ﻣﺘﺮ ﺿﺨﺎﻣﺖ، ﺑﺮش آرﻧﺪ در ﯾﺎل ﺟﻨﻮب ﻏﺮﺑﯽ ﺗﺎﻗﺪﯾﺲ ﻻر ﺑﺎ 197 ﻣﺘﺮ ﺿﺨﺎﻣﺖ و ﺑﺮش دﻫﺪﺷﺖ در ﭘﻼﻧﮋ ﻏﺮﺑﯽ ﺗﺎﻗﺪﯾﺲ ﮐﻮه ﺳﯿﺎه ﺑﺎ 222 ﻣﺘﺮ ﺿﺨﺎﻣﺖ اﻧﺪازهﮔﯿﺮي و ﻧﻤﻮﻧﻪﺑﺮداري ﺷﺪ. ﺑﻪ ﺗﻌﺪاد 491 ﻧﻤﻮﻧﻪ از ﺑﺮشﻫﺎ ﺑﺮداﺷﺖ و ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﻣﯿﮑﺮوﺳﮑﭙﯽ ﻗﺮار ﮔﺮﻓﺖ. ﻣﺮز ﭘﺎﯾﯿﻦ ﺳﺎزﻧﺪ آﺳﻤﺎري ﺑﺎ ﺳﺎزﻧﺪ ﭘﺎﺑﺪه در ﻧﺎﺣﯿـ ﻪ ﻣﻮرد ﻣﻄﺎﻟﻌﻪ از ﻧﻮع ﻫﻤﺸﯿﺐ و ﺗﺪرﯾﺠﯽ و ﻣﺮز ﺑﺎﻻﯾﯽ آن ﺑﺎ ﺳﺎزﻧﺪ ﮔﭽﺴﺎران از ﻧﻮع ﭘﯿﻮﺳﺘﻪ و ﻫﻤﺸﯿﺐ ﻣﯽﺑﺎﺷﺪ. ﺗﻔﺴـ ﯿﺮ دﻗﯿـﻖ زﯾﺴـﺖ ﭼﯿﻨـﻪ ﻧﮕـﺎر ي ﺳﺎزﻧﺪ آﺳﻤﺎري ﺑﺮ اﺳﺎس روزنداران ﺑﺰرگ ﮐﻒزي )21 ﺟﻨﺲ و 26 ﮔﻮﻧﻪ( اﻧﺠﺎم ﮔﺮﻓﺖ ﮐﻪ ﺑﻪ ﺗﻘﺴﯿﻢ ﺗﻮاﻟﯽﻫﺎ ﺑﻪ ﭼﻬـﺎر ز ﯾﺴـﺖ زون ﺗﺠﻤﻌـ ﯽ ﺑـﺎ ﺳـﻦ دﻗﯿــﻖ ﺷــﺎﻣﻞ Archaias-Spiroclypeus blanckenhorni ،Lepidocyclina-Operculina-Ditrupa Assemblage zone (Rupelian-Chattian) Miogypsina - Elphidium sp. 14 Assemblage zone (Aquitanian) ،Assemblage zone (Chattian) و Borelis melo curdica-Borelis melo )melo- Borelis sp. Assemblage zone (Burdigalian ﻣﻨﺠﺮ ﺷﺪ. زﯾﺴﺖزون ﺷﻤﺎره 1 در ﺑﺮشﻫﺎي ﮔﻨﺎوه و ﺳﯿﻨﮓ وﺟﻮد دارد و ﺑﻪ ﺳﻤﺖ ﺑﺨﺶﻫﺎي ﻋﻤﯿﻖ ﺣﻮﺿﻪ )آرﻧﺪ و دﻫﺪﺷﺖ( ﺑﺎ ﺳﺎزﻧﺪ ﭘﺎﺑﺪه ﺟﺎﯾﮕﺰﯾﻦ ﺷﺪه اﺳﺖ. ﺑﻘﯿﻪ زﯾﺴﺖزونﻫﺎ در ﺗﻤﺎم ﺑﺮشﻫﺎي ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﺣﻀـﻮر دارﻧـﺪ. ﺑـﺮ اﺳـﺎس اﯾـﻦ ﭘﮋوﻫﺶ رﺳﻮبﮔﺬاري ﮐﺮﺑﻨﺎتﻫﺎي ﺳﺎزﻧﺪ آﺳﻤﺎري در ﺣﺎﺷﯿﻪ ﺣﻮﺿـﻪ درون ﻗـﺎره اي آﺳـﻤﺎر ي از زﻣـﺎن ا ﻟﯿﮕﻮﺳـﻦ آﻏـﺎز ﺷـﺪه ﺑـﻮد، در ﺣـﺎ ﻟﯽ ﮐـﻪ در ﻋﻤﯿﻖﺗﺮﯾﻦ ﺑﺨﺶﻫﺎي ﺣﻮﺿﻪ درون ﻗﺎرهاي رﺳﻮبﮔﺬاري اﯾﻦ ﮐﺮﺑﻨﺎتﻫﺎ در زﻣﺎن آﮐﯿﺘﺎﻧﯿﻦ ﺻﻮرت ﮔﺮﻓﺖ.
چكيده لاتين :
Introduction
The Asmari Formation, with Oligocene-Miocene age, in the Zagros foreland basin in the Dehdasht area in 4 measured stratigraphic sections were studied. This formation is mainly composed of a thick carbonate sequence with intercalations of shale and two sandstone (Ahvaz) and evaporate (Kalhor) members in Khuzestan and Lurestan Provinces. Carbonates and sandstones formed producing reservoirs in the Zagros Basin since the beginning of the 20th Century (van Buchem et al., 2010). Biostratigraphic characteristics of this formation were firstly introduced by Wynd (1965) and reevaluated by Adams and Bourgeois in 1967. In general, many biostratigraphic studies have been done in recent years by different authors to determine the age of this formation (e.g. James and Wynd, 1965; Laursen et al., 2009; Allahkarampour-Dill et al., 2010; Vaziri-Moghadam et al., 2010); Rahmani et al., 2012; Shabafrooz et al., 2014). In the studied area, the lower boundary of the Asmari Formation with Pabdeh Formation is gradual and parallel and the upper boundary with the Gachsaran Formation is continuous and parallel. The purpose of this study is to evaluate the biostratigraphic characteristics of the Asmari Formation in the Dehdasht area because it has not been studied in detail and the results can be used for a better understanding of the age changes of this stratigraphic interval in the Zagros Basin.
Material and Methods
Four stratigraphic sections were measured and sampled systematically. These sections are located in Genaveh (in the southern flank of the Mish anticline) with 440 m thickness, Siang (in the western plunge of the Khami anticline) with 248 m thickness, Arand (in the southwestern flank of the Lar anticline) with 197 m thickness and Dehdasht (in the western plunge of the Kuh-e-Siah anticline) with 222 m thickness. 500 thin sections were prepared and studied by binocular and polarized microscopes.
Results and discussion
A biostratigraphic analysis is done based on the large benthic foraminifera. In this study, 21 genus and 26 species have been identified that led to the distinction of 4 assemblage zones including: 1- Lepidocyclina- Ditrupa- Operculina Assemblage zone (Rupelian-Chattian)
2-Archaias- Spiroclypeus blanckenhorni Assemblage zone (Chattian)
3-Miogypsina - Elphidium sp. 14 Assemblage zone (Aquitanian)
4-Borelis melo curdica- Borelis melo melo- Borelis sp. Assemblage zone (Burdigalian)
Assemblage 1, with the age of Rupelian-Chattian, is only present in the shallow water sediments in the Genaveh and Siang sections and toward the north in the deep parts of the basin in the studied area (Arand and Dehdasht sections), it is placed in the deepwater marls of the Pabdeh Formation.
In Genaveh section, the assemblage zone 2 starts with the appearance of Archaias; while in deeper parts of the basin in sections Siang, Arand, and Dehdasht, this zone starts with Spiroclypeus blanckenhorni. The thickness of Assemblage zone 2 reduced from the southeast toward the northwest in the study area. The Aquitanian sequence can be identified by assemblage Zone 3 in this study and has been deposited in a more restricted environment with higher salinity. As sea level rose after Aquitanian time, accommodation space increased and a deeper water environment covered all of the studied area and the sequence deposited belonged to the Burdigalian age
