پديد آورندگان :
سالاري سرگرو ، شكوفه نويسنده كارشناس ارشد زمين‌شناسي، دانشگاه هرمزگان , , رضايي ، پيمان نويسنده استاديار، گروه زمين‌شناسي، دانشگاه هرمزگان ,
كليدواژه :
سنگ‌رخساره , محيط‌رسوبي , باختر بندرعباس , سازند گچساران
چكيده فارسي :
سازند گچساران (ميوسن پيشين) به‌عنوان مهم‌ترين پوش‌سنگ مخازن هيدروكربوري زاگرس از يك سو و برخورداري از نمك، گوگرد و گچ از سوي ديگر، اهميت فراواني در زمين‌شناسي ايران دارد. به منظور شناسايي و تفكيك رخساره‌ها و شناخت محيط‌رسوبي اين سازند، برشي در باختر بندرعباس انتخاب و مطالعه گرديد. سازند گچساران در ناحيه مورد مطالعه (واقع در جنوب كوه نمكي خمير) با ستبراي 310 متر، از سه بخش چهل، چمپه و مول تشكيل شده و تركيب سنگ‌شناسي آن، ژيپس ـ انيدريت (265 متر، 5/85 درصد)، آهك (25 متر، 8 درصد) و مارن (20 متر، 5/6 درصد) مي‌باشد. مطالعه مقاطع نازك ميكروسكپي به شناسايي هفت ريز رخساره تبخيري- آهكي شامل: ريز رخساره‌هاي ژيپس- انيدريت، مادستون آهكي، مادستون آهكي دولوميتي شده با فابريك روزنه‌اي، مادستون آهكي ژيپسي ـ انيدريتي شده، مادستون آهكي سيلتي لامينه‌بندي شده، پكستون ـ گرينستون بيوكلاستي دولوميتي شده و وكستون اينتراكلاستي دولوميتي شده با فابريك روزنه‌اي منجر شد. يافته‌هاي اين تحقيق نشان مي‌دهد كه رخساره‌هاي مارني، آهكي و ژيپس ـ انيدريتي به ترتيب در محيط لاگوني، بين جزر و مدي و بالاي مدي بجاي گذاشته شده‌اند. توالي اين سه رخساره، معرف ناحيه پشت يك رمپ كربناته (رمپ داخلي) است. نهشته‌هاي سازند گچساران در برش مورد مطالعه، در يك گستره لاگوني تا سبخايي با اقليم گرم و خشك، با پيشروي و پسروي‌هاي محدود آب دريا و شرايط زمين ساختي آرام پديد آمده است.
چكيده لاتين :
Introduction:
The resulting stratigraphic column of Phanerozoic sediment in the Zagros basin contains evaporites at different levels in different parts. Of these, the Neo-Proterozoic Hormuz salt located at the base sedimentary column and the Gachsaran Formation higher in the Zagros stratigraphic column are thickest and most wide-spread evaporitic units (Bahroudi and koyi, 2004). Gahsaran Formation (Early Miocene) (Aghanabati and Rezaee, 2008) is the most important caprock of hydrocarbon reserviors area and is important in geology of Iran, because is rich from salt, sulfur and gypsum deposits. This Formation is the first member of Fars Group in Zagros and consist of seven members (James and Wynd, 1965). The thickness of the Gachsaran Formation usually varies over short distances typically from several hundred up to 2000 in metres (James and Wynd, 1965). Gachsaran Formation in studied section, overlies the Asmari Formation with a comformable and Transitional boundary and under Mishan Formation by a disconformity. Despite many geological studies in around Gahsaran Formation in hydrocarbon fields, there are few detailed reports of the sedimentology of the Gachsaran Formation in southwest of Zagros.
Aims: In southwest of Zagros belt, Gahsaran Formation has good outcrops, especially in Hormozgan province. Unfortunately, in the pointed area, this Formation is not studied from the view of sedimentary geology. So a section of this formation was studied in South of Khamir salt dome. This section was studied for recognize of lithofacies and sedimentary environment of Gahsaran Formation in the west of Bandar- e- abbas.
Material & Methods: The studied section of Gahsaran Formation has 310 m thickness. This section was studied by field common methods in sedimentary geology and took 65 sampels from Gypsum/ Anhydrite and limestone for make thin section and 3 samples from marls for XRD.
Discussion of Results & Conclusions: Gahsaran Formation in this section consist of Chehel, Champe and Mol members and Gypsum/ Anhydrite (265 m, 85.5 %), limestone (25 m, 8%) and marl (20 m, 605 %) lithofacies. There is a horizon of palaesol in top of this formation in the studied section. Microscopic study of thin section based on Dunhum (1962) classification, caused on identify of seven evaporate – carbonate microfacies consist of: Gypsum/ Anhydrite, lime mudstone, fenestral dolomitzed lime mudstone, gypsum- anhydrited lime mudstone, laminated silty lime mudstone, dolomitzed bioclast packstone – grainstone and fenestral dolomitzed intraclast wackestone. The marls of this formation is made by paligorskite, dolomite, calcite and halite (major minerals), quarts and anhydrite (minor minerals).
This research shows that marls, limestone and gypsum anhydrite facies, respectively has deposited in the lagoon, intertidal and supratidal environment. The sedimemtary cycles in this formation indicate a big shallowing-upward sequence. Sedimentary characters show that clastic load input to deposational basin of this formation, was been low. Correlation the resulted data with Wilson (1975) and Flugel (2010) models, indicated that the sequence of three Facies were deposited in the back of a carbonate ramp (inner ramp) environment with warm and dry climate, limited regresses and progresses of sea water level and stable tectonic conditions.
Keywords: Lithofasies, Sedimentary environment, Gachsaran Formation, West of Bandar- e- Abbas
