بررسی ریزرخساره‌ها و تفسیر محیط رسوبی نهشته‌های کوه مارکش در شمال راور (استان کرمان)

نهشته‌های کرتاسه‌ زیرین در کوه مارکش در 15کیلومتری شمال راور (شمال کرمان) با ضخامت 143 متر قرار دارد و این برش شامل توالی مارن‌های ژیپس‌دار، آهک نازک‌لایه، آهک نازک تا متوسط‌لایه و آهک متوسط تا ضخیم‌لایه است. برای رسوبات شیل و مارن‌های ژیپس‌دار در پایین ستون چینه‌شناسی با توجه به نبود فسیل و نیز براساس مطالعات زمین‌شناسی پیشین روی رسوبات راور، سن ژوراسیک بالایی در نظر گرفته شده است. در توالی مطالعه‌شده، فرامینیفرها، جلبک‌ها و استراکدها مطالعه و سن بارمین آلبین تعیین شده است. به سمت بالا نهشته‌های رسوبی کرتاسه‌ زیرین در کوه مارکش با رسوبات نئوژن پوشیده شده است. به‌طور کلی نهشته‌های مطالعه‌شده شامل یک رخساره‌ تبخیری و دو رخساره‌ مارنی و آهکی است. رخساره‌ آهکی براساس محیط تشکیل شامل سه زیررخساره‌ a مربوط به محیط ساحلی بالای پهنه‌ جزر و مدی، b مربوط به محیط لاگونی و c مربوط به محیط سدی معادل مدل رخساره‌ای ویلسون است که از سمت خشکی به طرف دریای باز تفسیر شده است. براساس مطالعات انجام‌شده رسوبات کرتاسه‌ زیرین برش کوه مارکش در یک پلاتفرم کربناته‌ کم‌عمق نهشته شده‌اند.

Study of microfacies and interpretation of sedimentary environment of the Lower Cretaceous succession at Markesh Mountain in the north of Ravar

AbstractLower Cretaceous deposits are outcropped in the Markesh Mountain, 15 km north of Ravar (Kerman Province), with a thickness of 143 m, and this section includes intercalation of gypsiferous marls, thinbedded limestones, thin to mediumbedded limestones, and medium to thickbedded limestones. For the shale and gypsiferous marls in the base of stratigraphic column due to the absence of fossils and also based on previous geological studies, the Upper Jurassic age has been considered. In the studied succession, 14 genera and 17 species of foraminifera, three genera and four species of calcareous algae, as well as 16 genera and 24 species of ostracods were identified, and the Barremian to Albian age was determined. The upward section, the Lower Cretaceous succession at the Markesh Mountain are covered by Neogene deposits. In general, the studied deposits include evaporitic facies and two marl and calcareous facies. The calcareous facies based on the microfacies characteristic consist of three subfacies, (A) corresponding to the coastal subenvironment above the tidal zone, (B) the lagoonand (C) the bar subenvironment. Based on studies, Lower Cretaceous succession at the Markesh Mountain section was deposited in a shallow carbonate platform.Keywords: Sedimentary facies, Lower Cretaceous, Markesh Mountain, Ravar, Kerman.  IntroductionThe great structuralsedimentary cycle in the Bajocin is started with the transgression of the sea and led to the Late Cimmerian event in the Late Jurassic and Early Cretaceous (SeyyedEmami 1999). The rocks related to this cycle  consist of various detrital, marl, calcareous and evaporitic rock facies. Many lateral changes in these facies are an indication for tectonic movements. These rocks have been deposited in continental, coastal, intertidal, sabkha and marine environments. Huber and Stocklin (1954) refer to the Ravar evaporitic rocks as Mesozoic &colored melange& or gypsum domes  belonging to the Cretaceous system. The sedimentary succession at the Markesh Mountain is considered one of the Lower Cretaceous sections in the Kerman Province and this section belongs to the Central Iran zone. The Lower Cretaceous succession in this area is exposed as high mountain in North of Ravar in the Kerman Province. The Lower Cretaceous deposits in the Kerman Province have a very good spread and many outcrops can be seen in this province. Neither has a comprehensive study been done nor the formal formation has been introduced in this area. The aim of this study is to investigate the sedimentary succession of the Lower Cretaceous at the Markesh Mountain section by studying  the sedimentary facies of this section. Material MethodsAfter field studies, a suitable stratigraphic section at the Markesh Mountain, 15 km north of Ravar (Kerman Province), was selected and 70 samples from 143 m thickness were systematically collected. The age of studied succession at the Markesh Mountain is Lower Cretaceous (Barremian to Albian). The lithology of the studied section is mainly composed of marls, gypsums, and limestones. In order to do microfacies studies, the thin section was prepared from limestones. To study the sedimentary facies, the prepared thin sections were studied microscopically, and its components were identified. After a careful study of thin sections, microfacies were described. For the study of rocks and identification of sedimentary facies, the skeletal and nonskeletal grains were identified, and the microfacies distribution along this succession was drawn. Discussion of Results ConclusionsThe lithology of this section consists of 15 m gypsiferous marls, 37 m thinbedded limestones, 59 m of medium to thinbedded limestones, 32 m of medium to thickbedded limestones. There are a variety of microfossils in the Markesh Mountain section, including 14 genera and 17 species of benthonic foraminifera, three genera and four species of calcareous algae, as well as 16 genera and 24 species of ostracods. The main constitute skeletal grains of the microfacies consist of gastropods, ostracods, algae, orbitolinids and miliolids and the nonskeletal grains include peloids and ooids. In general, the Markesh Mountain section deposits include evaporitic facies and two marls and calcareous facies. The calcareous facies of this section were thoroughly studied. The carbonate facies of the Markesh Mountain section deposited in coastal environments, above the tidal zone, lagoon and bar subenvironments.