بررسي توان هيدروكربن‌زايي و ارتباط پرتو اورانيوم با محتواي كربن‌آلي در سازندگورپي، برش‌هاي سياه‌كوه دهلران و كوه‌گورپي – زاگرس

در اين تحقيق سازندگورپي با سن كامپانين تا دانين، در برش يال‌جنوبي ‌سياه‌كوه دهلران و يال‌‌شمالي كوه‌گورپي بررسي شده است. هدف از اين پژوهش بررسي توان هيدروكربن‌زايي و ميزان بلوغ حرارتي سازندگورپي براساس پارامترهاي حاصل از پيروليز راك­اول به همراه استفاده از داده‌هاي گاماي سطحي، جهت بررسي نسبت اورانيوم به كربن‌آلي (U / TOC) مي‌باشد. ضخامت سازندگورپي در برش سياه‌كوه 122 متر و در برش كوه‌گورپي 305 متر است. براساس نتايج به دست آمده از پيروليز راك­ اول (34 نمونه برداشت شده) از سازندگورپي، اين سازند از ديدگاه توان هيدروكربن‌زايي در برش سياه‌كوه، در محدوده ضعيف و در برش كوه‌گورپي در محدوده ضعيف تا متوسط قرار مي‌گيرد. مواد آلي موجود در نمونه‌هاي سازندگورپي در برش سياه‌كوه از نوع III و II/III و مواد آلي موجود در برش كوه‌گورپي غالبا از نوع II/III و III مي‌باشند. مواد آلي موجود در اين نمونه‌ها برجا بوده و براساس ميزان بلوغ حرارتي نمونه‌هاي مورد مطالعه، سازند‌گورپي در برش‌هاي سياه‌كوه و كوه‌گورپي بالغ و مربوط به پنجره نفت‌زايي و مرحله اصلي توليد هيدروكربن مي‌باشد. همچنين بر اساس داده‌هاي اورانيوم برداشت شده توسط دستگاه پرتونگار گاماي سطحي در مقايسه با نتايج كربن‌آلي، مشخص شد كه در برش سياه‌كوه، با افزايش اورانيوم ميزان كربن‌آلي كاهش مي‌يابد. اين رابطه معكوس مي‌تواند بر اثر ارتباط اورانيم با حضور تركيبات فسفاتي و گاها گلوكونيت (نه حضور آن در كربن آلي) بوده باشد. در برش‌ كوه‌گورپي رابطه مستقيم بين تمركز ماده آلي و مقدار اورانيوم مشاهده شد، فراواني اورانيوم اغلب توسط كربن آلي كنترل شده است.

Extended Abstract Introduction Unlike similar sedimentary conditions in the Lower Cretaceous, the Upper Cretaceous sediments of Iran do not have the same facies features. Therefore, in this study, we try to study the sedimentary environment and microfacies. By using data and geochemical methods of Upper Cretaceous sediments, valuable information about the environment and conditions of formation and primary mineralogy of Upper Cretaceous sediments of Dombak-kuh are achieved. Materials and Methods In Dombak-kuh section, sampling has been done based on lithological and facies changes in the perpendicular direction towards the layers and at distances of less than 0.5 m to more than 2.5 m. These sections were stained with red alizarin solution and potassium ferrocyanide to distinguish calcite mineralogy from dolomite as well as iron content and the amount of iron in it by Dickson method (Dickson, 1965). The classification and naming of rocks is based on Dunham's method (Dunham, 1962). In sample naming, an attempt has been made to include all major allocations in sample naming in order of frequency. The percentage of abundance was obtained by comparing with Baccelle and Bosellini (1965) comparison tables. The known facies have been compared with the Flugel (2010) facies belt. In presenting the sedimentary model, the terms used in Burchett and Wright (1992) have been used. Results and Discussion Petrographic studies of this sections revealed 11 microfacies, with 2 microfacies from tidal flat, 1 microfacies from lagoon, 1 microfacies from shoal and 7 microfacies from open marine. All of them belonged to carbonate ramp and are mentioned hereforth: 1. Dolomicrites – Dolomicrosparaite 2. Intraclast Grainstone3.Bioclact Wackestone4. Bioclast Pelloidal Grainston 5. Oligosteginids Packstone6.Nezzazatinella, Dictyoconella Wackestone-Packston 7. Lenticulina/Marginotruncana/ Oligosteginids Wackestone-Packstone 8. Heterohelix /Globotruncana/Macroglobigerielloides Wackestone 9. Oligosteginids/ Macroglobigerielloides / Heterohelix Packstone 10. Heterohelix /Globotruncana/Marginotruncana packstone 11. Globotruncana/ Heterohelix /Macroglobigerielloides Wackestone-packstone. The characteristics of these deposits indicate that the sedimentary environment was a ramp (hemocline). The absence of calcite turbidite deposits, fall structures, and large reef and oncoid and piezoidal dams confirm the carbonate ramp environment. The results of elemental analysis and plotting of these values against each other indicate that the Upper Cretaceous sediment limestones had primary aragonite mineralogy. The plotting of Mn values against Sr / Ca indicates a semi-closed to open diagenetic environment with a high water/rock ratio. Conclusion According to the studies carried out in the Dombak-kuh region, the Upper Cretaceous sediments (Cenomanian-Campanian) have a thickness of 327.7 m, the lower boundary of which is the Tizkuh Formation and is of a steep type, and its upper boundary is a fault which cuts through. Cenomanian sediments, which are 54.26 m thick, start with a progressive conglomerate, and then thoronine sediments, which are 22.85 m thick, first with thick-layered limestone and then with chert limestone, and then with Oligosthenic limestones change the facies and settle on it. Kenyasin sediments with a thickness of 19.85 m with a combination of oligoesterated limestones followed by Santonin sediments with a thickness of 182.80 m and then Campanian sediments with a thickness of 48.5 m form the Upper Cretaceous stratigraphic sequence. . In these sediments, 11 micro-facies were identified, which include tidal zone with 2 micro-losses, lagoon with 1 micro-loss, a dam with 1 micro-loss and open sea with 7 micro-losses. The characteristics of these deposits indicate that the sedimentary environment was a ramp (hemocline). The absence of calcite turbidite deposits, fall structures, and large reef and oncoid and piezoidal dams confirm the carbonate ramp environment. The results of elemental analysis and mapping of these values together indicate that the Upper Cretaceous sediments in this section have an aragonite primary compound, which is placed in a semi-closed to semi-open diagenetic region with a high proportion of water to rock (W/R).