سنگچينه و زيستچينه واحدهاي دا?ن با?ئي و كنگان زيرين در ناحيه خليج فارس با نگرشي ويژه بر مرز پرموترياس

Lithostratigraphy and biostratigraphy of the Upper Dalan

واﺣﺪﻫﺎي ﺳﻨﮓ ﭼﻴﻨﻪاي داﻻن ﺑﺎﻻﺋﻲ و ﻛﻨﮕﺎن زﻳﺮﻳﻦ ﺑﻪ ﺿﺨﺎﻣﺖ 225 ﻣﺘﺮ در ﻳﻜﻲ از ﺑﺮشﻫﺎي ﺗﺤﺖ اﻻرﺿﻲ ﻧﺎﺣﻴﻪ ﺧﻠﻴﺞ ﻓﺎرس ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﻗﺮار ﮔﺮﻓﺖ. ﺑﺮ اﺳﺎس ﻣﻄﺎﻟﻌﺎت زﻳﺴﺖ ﭼﻴﻨﻪ اي ﺑﺮ روي ﺗﻮاﻟﻲﻫﺎي دوﻟﻮﻣﻴﺘﻲ و آﻫﻜﻲ واﺣﺪ داﻻن ﺑﺎﻻﺋﻲ ﺑﻴﺶ از 30 ﮔﻮﻧﻪ از ﻓﺮاﻣﻴﻨﻲﻓﺮﻫﺎي ﺷﺎﺧﺺ ﺑﻪ ﻫﻤﺮاه ﭼﻨﺪﻳﻦ ﮔﻮﻧﻪ ﻏﻴﺮ ﻓﺮاﻣﻴﻨﻲ ﻓﺮي ﺷﻨﺎﺳﺎﺋﻲ ﺷﺪه اﺳﺖ. ﺑﺮ اﺳﺎس ﻣﻄﺎﻟﻌﺎت ﻣﺬﻛﻮر ﻳﻚ زون ﺗﺠﻤﻌﻲ Paradagmarita/ Paraglobivalvulina/ Baisalina Assemblage Zone ﻛﻪ ﺑﻪ 3 زﻳﺮ زون ﺗﺠﻤﻌﻲ ﻣﺠﺰا ﺗﻔﻜﻴﻚ ﻣﻲﺷﻮد: 1. Rectostipulina quadrata/ Globivalvulina vonderschimitti Assemblage subzone 2. Dagmarita chanackchiensis/ Ichtyolaria latilimbata Assemblage subzone 3. Hemigordiopsis renzi/ Paradagmarita flabeliformis Assemblage subzone ﺑﻪ ﺳﻦ ﺟﻠﻔﻴﻦ ﺗﺎ دوراﺷﺎﻣﻴﻦ آﻏﺎزي ﻛﻪ در واﺣﺪ ﺳﻨﮓ ﭼﻴﻨﻪاي داﻻن ﺑﺎﻻﺋﻲ ﺷﻨﺎﺳﺎﺋﻲ ﮔﺮدﻳﺪ . زونﻫﺎي ﺗﺠﻤﻌﻲ ﻣﺬﻛﻮر ﻫﻤﺮاه ﺎ ﺑ وﻳﮋﮔﻲﻫﺎي ﺳﻨﮓ ﭼﻴﻨﻪاي آن ﺑﺎ ﺗﻮاﻟﻲﻫﺎ و زونﻫﺎي ﺗﺠﻤﻌﻲ ﭘﺮﻣﻴﻦ ﺑﺎﻻﺋﻲ در ﺣﻮﺿﻪ ﺗﺘﻴﺲ ﻣﻄﺎﺑﻘﺖ زﻳﺎدي دارﻧﺪ. زونﻫﺎي ﺗﺠﻤﻌﻲ ﻓﻮﻗﺎﻧﻲ ﺗﺮﻳﻦ ﺑﺨﺶ واﺣﺪ داﻻن ﺑﺎﻻﺋﻲ ﻧﺸﺎن ﻣﻲ دﻫﺪ ﻛﻪ ﻣﺮز ﺳﺎزﻧﺪﻫﺎي داﻻن و ﻛﻨﮕﺎن (ﭘﺮﻣﻮ ﺗﺮﻳﺎس) در اﻳﻦ ﻧﺎﺣﻴﻪ ﺑﺎ ﻳﻚ ﻧﺎﭘﻴﻮﺳﺘﮕﻲ ﻫﻤﺴﺎز ﻫﻤﺮاه اﺳﺖ، ﺑﻄﻮرﻳﻜﻪ ﺷﻮاﻫﺪي از وﺟﻮد رﺳﻮﺑﺎت ﻣﺮﺑﻮط ﺑﻪ اﺷﻜﻮب دوراﺷﺎﻣﻴﻦ اﻧﺘﻬﺎﻳﻲ در اﻳﻦ ﻧﺎﺣﻴﻪ ﻳﺎﻓﺖ ﻧﮕﺮدﻳﺪ. ﻧﺎﭘﻴﻮﺳﺘﮕﻲ رﺳﻮﺑﺎت در ﻣﺮز ﭘﺮﻣﻮﺗﺮﻳﺎس ﺑﺎﻋﺚ اﻧﻘﻄﺎع زونﻫﺎي زﻳﺴﺘﻲ اواﺧﺮ ﭘﺮﻣﻴﻦ در اﻳﻦ ﻧﺎﺣﻴﻪ ﺑﻮده ﻛﻪ ﺗﺎﺛﻴﺮ آن ﺑﺎ ﺳﺎﻳﺮ ﻧﻘﺎط دﻧﻴﺎ ﻗﺎﺑﻞ ﻣﻘﺎﻳﺴﻪ اﺳﺖ. واﺣﺪ ﺳﻨﮓ ﭼﻴﻨﻪاي ﻛﻨﮕﺎن زﻳﺮﻳﻦ ﺗﻨﻬﺎ ﺑﺮ اﺳﺎس ﭼﻨﺪﻳﻦ ﺟﻨﺲ از دوﻛﻔﻪايﻫﺎ (ﻛﻼراﻳﺎ) و ﺳﺮﭘﻴﻮﻟﻴﺪﻫﺎ (اﺳﭙﻴﺮورﺑﻴﺲ) ﺑﻪ اﺷﻜﻮب اﺳﻜﻴﺘﻴﻦ (اواﻳﻞ ﺗﺮﻳﺎس زﻳﺮﻳﻦ) ﻧﺴﺒﺖ داده ﻣﻲﺷﻮد. اﻳﻦ ﻧﻜﺘﻪ ﻻزم ﺑﻪ ذﻛﺮ اﺳﺖ ﻛﻪ اﺟﺘﻤﺎع ﻓﺴﻴﻠﻲ ﻓﻮق اﻟﺬﻛﺮ در ﺳﺎﻳﺮ ﻧﻮاﺣﻲ اﻳﺮان ﻧﻈﻴﺮ اﻳﺮان ﻣﺮﻛﺰي و اﻟﺒﺮز ﻧﻴﺰ ﻣﺸﺎﻫﺪه ﺷﺪه اﻧﺪ ﻛﻪ از ارﺗﺒﺎط ﭘﺎﻟﺌﻮﺑﻴﻮژﺋﻮﮔﺮاﻓﻲ ﻧﻮاﺣﻲ ﻣﺬﻛﻮر ﺑﺎ اﻗﻠﻴﻢ زاﮔﺮس در زﻣﺎنﻫﺎي ﭘﺮﻣﻴﻦ و ﺗﺮﻳﺎس ﺣﻜﺎﻳﺖ دارد.

The Upper Dalan and Lower Kangan stratigraphic units with 225m thickness were studied in one of the subsurface section in Persian Gulf area. According to the biostrarigraphic investigation on the dolomitic and limestone successions of the Upper Dalan unit, there are more than 30 index foraminifera and non-foraminifera species. One Paradagmarita/ Paraglobivalvulina/ Baisalina Assemblage Zone that divided to three distinct sub- assemblage zones 1. Rectostipulinaquadrata/ Globivalvulinavonderschimitti Assemblage subzone 2. Dagmaritachanackchiensis/ Ichtyolarialatilimbata Assemblage subzone 3. Hemigordiopsisrenzi/ Paradagmaritaflabeliformis Assemblage subzone have been distinguished in the stratigraphic section representing the Julfian to Earleast Dorashamian stage. The identified microfaunaʹ assemblages can be corresponded to the Late Permian regional biozonation in the Tethys realm. The latest microfauna assemblages in the latest part of Dalan Formation exhibits a significant chronostratigraphic hiatus, just was cited in the Dalan/ Kangan (Permo/Triassic) boundary. There is no any evidence about Latest Dorashamian sediments in the study area. The Permo/Triassic boundary is a paraconformity type in the latest Permian biozones, which can be corresponded to other areas of the world. The Lower Kangan stratigraphic unit can be attributed to the Schytian age (Early Triassic age) on basis of presence of some index fossils such as Bivalves (Claraia sp.) and Serpulids (Spirorbis sp.). It should be stressed that the similar microfauna associations can be seen in other Iranian places such as Central Iran and Alborz areas, which is documented a distinct palaeobiogeographical relationship between the above-mentioned areas and Zagros realm on Permian and Triassic ages.