محیط تکتونورسوبی نهشته‌های تبخیری کربناته ژوراسیک پسین پهنه راور، جنوب بلوک طبس

پهنه راور واقع در جنوب بلوک طبس، سرزمینی گوه‌ای شکل است که بین دو گسل مرزی نایبند در شرق و کوهبنان در غرب محصور گشته است. نهشته‌های دوران دوم خصوصاً رخساره‌های ژوراسیک از گسترش، تنوع و رخنمون‌های مناسبی در این پهنه برخوردار هستند. نهشته‌های تبخیری کربناته ژوراسیک پسین موسوم به آهک‌های پکتن‌دار، سری راور، گچ مگو و تبخیری‌های قرمز بیدو مهم‌ترین بخش‌های سازنده این نهشته‌ها هستند. نهشته‌های مذکور در پنج برش زمین‌شناسی در مناطق حورجند، لکرکوه1 و 2، خورند و شرق بهاباد به ترتیب از جنوب به شمال بررسی شده‌اند. 11 رخساره‌ شاخص در این نهشته‌ها شناسایی شد که به محیط‌های کمربند پهنه‌های جزر و مدی، لاگون، پشته‌های کربناته و دریای آزاد ختم می‌شوند. بررسی تغییرات رخساره‌ای حکایت از تشکیل تبخیری‌ها در یک محیط پلاتفرمی احتمالاً شبیه به رمپ کربناتی کم عمق هموکلینال دارد. این حوضههای سبخایی به شکل نوارهای باریک و طویلی در راستای شمال غربی گسترش داشته‌اند. در مقابل در راستای عمود بر روند حوضه به سمت شرق یا غرب این نهشته‌ها جای خود را به رسوبات تخریبی با رخساره‌های عمیق‌تر و لغزش‌های زیر دریایی در سازندهای هجدک و بغمشاه داده‌اند. از آنجایی که کربنات‌های کرتاسه با ناپیوستگی زاویه‌دار در پهنه راور اغلب سازندهای مذکور را می‌پوشاند بنابراین حوضه رسوبی می‌بایست در ژوراسیک پسین تکاپوی تکتونیکی بارزی را پشت سر گذاشته باشد. این جنبش تکتونیکی ممکن است مربوط به مرحله ریفت قاره‌ای بوده و تغییرات رخساره‌ای جانبی مربوط به رسوبگذاری بر روی بلوک گسله‌ها و یا دره‌های حاشیه آنها باشد.

Tectono sedimentary environment of Upper Jurassic evaporite carbonate deposits in the Ravar Zone, south of Tabas Block

Extended abstractThe Ravar terrane, is situated at the south of the Tabas block. At the Ravar series Mesozoic strata, especially the Jurassic carbonate evaporite deposits known as Pectinid limestone, Magu gypsum and Bido red evaporates are the most important parts of this deposits and have a variety of facies, distribution, and suitable exposure. Upper Jurassic Sequence stratigraphy of the mentioned deposits were messed up and even their position on the geological maps are not coherently elaborated. So investigation on the sedimentary environment and tectonic controller factors will be a great help in understanding the sequence stratigraphy position of these deposits. Thickness of mostly shale, interbedded Pectinid limestone, gypsiferous marl, red gypsum to white and finally red evaporates sequences were measured 470, 725, 50, more than 1450 (possibly contains Hojedk and Baghamshah Formations), and 1300 m, respectively. Eleven indicator facies were identified in the studied deposits which ended in tidal flat, lagoon, shoal and open marine belts. These facies illustrate environmental characteristics of carbonateevaporite sequences. The facies changes, display the shallow carbonate homocline ramp setting.  Material and methodsAfter studying satellite images and field surveys in the Ravar region of Kerman, 5 sections of Lakarkuh1 and 2, Horjond, Khorand and East of Bahabad were selected as the most suitable geological sections. Total of 68 thin sections from four sections of LakarKuh1 and 2, Horjand and Khorand were examined by petrography. Of course, it is worth mentioning that no samples were taken from the Bahabad section and these were examined only to compare the thickness and lithological facies and especially evaporite deposits.ConclusionAfter extensive field surveys, five geological sections with the most complete outcrops were finally selected. The reason for the decrease in the thickness of evaporative deposits from 1450 m in the Khordand, 1300 m in the Bahabad, 725 m in the Horjond, 450 m in Lakarkuh1 and 50 m in LakarKuh2 can probably be due to the local changes in sea water levels and availability of more evaporative conditions. In order to identify and interpret gypsum and anhydrite facies and related fabrics, several sections have been selected in the Lakarkuh and Horjond areas. First, after introducing field photos, some of the important identified fabrics were examined. The microfacies investigation of 4 sections has led to the identification of 11 microfacies with the acronyms A, B, C and D, which belong to the 4 facies belts of intertidal, lagoon, shoal and open sea environments. Finally, according to the identified facies, a sedimentary environment model was presented.ResultsThe unusual and high thicknesses of gypsum in the Ravar region often have a tectonic origin and are mainly related to the formation of disharmonic folds. Evidence such as single nodules, enterolytic, and fenestral textures in evaporites show that these factories formed simultaneously with deposition or in the early stages of diagenesis. Three facies’ belts including intertidal zone facies (A1, A2 and A3 facies), high tidal zone facies (A4 and A5), and lagoon (B1) have been identified. The sedimentary model presented for the studied deposits in the shallow parts of a carbonateevaporative system, which was probably a hemoclinical ramp. Examination of evaporitic facies in Lakarkuh and Horjond regions indicates that these facies are often deposited in sabkha and intertidal and lagoon environments.