ريزرخساره‌ها، مدل رسوبي، چينه‌نگاري سكانسي و دياژنز سازند هفتومان (كرتاسه بالايي)، ناحيه خور - شرق ايران مركزي

Microfacies, Depositional Model, Sequence stratigraphy and Diagenesis of The Haftuman Formation (Upper Cretaceous), Khur area- East of Central Iran

رسوبات كرتاسه كه با رخساره‌هاي متنوع شناخته مي‌شوند، در تمام ايران گسترش يافته‌اند. در ناحيه خور، بلوك يزد و در شرق ايران مركزي اين رسوبات به خوبي رخنمون يافته‌اند. سازند هفتومان با سن سنومانين در كوه دبرسو، جنوب ناحيه خور (در شرق ايران مركزي) با رويكردي يكپارچه جزيي از مطالعات نموداري، بيواسترانيگرافي و تجزيه و تحليل چينه‌نگاري سكانسي، مطالعه رخساره‌ها بر اساس مشاهدات ميداني و مطالعات ريزرخساره‌ها مورد تجزيه و تحليل قرار گرفت. ما 240 مقطع نازك ميكروسكوپي را از حدود 514 متر از چينه‌هاي با جنس سنگ آهك، ماسه سنگ تا ماسه سنگ آهكي و از سنگ آهك ضخيم تا سنگ آهك ماسه‌اي نازك لايه از سازند هفتومان جمع‌آوري نموديم. اين سازند در يك رمپ كربناته با ريزرخساره‌هاي رمپ دروني، رمپ مياني و رمپ بيروني در كنار رسوبات آواري محيط ساحلي كه 2 پتروفاسيس را تشكيل داده‌اند؛ تشكيل شده است. بر اساس موقعيت مرزهاي ناپيوسته سكانس‌ها، دو سكانس رده 3، كه به طور غالب تغييرات جهاني سطح آب دريا كنترل كننده چرخه رسوبي در آنهاست شناسايي شدند. سيماني شدن، دولوميتي شدن، انحلال و سيماني شدن، كارستي شدن و پيريتي شدن مهم‌ترين فرآيندهاي دياژنزي در اين سازند هستند.

Intruduction The Cretaceous deposits, characterized by diverse sedimentary facies, are widespread all over Iran. These strata are excellently exposed in the Khur area, Yazd Block and east Central Iran. The Senonian Haftuman Formation in Kuhe- Debarsu, south of Khur (east Central Iran), has been investigated using an integrated approach of detailed logging, biostratigraphic, sequence-stratigraphic analysis and facies study based on field observations and thin section microscopy of limestone, sandstone to calcareous sandstone and thickly limestone to thinly nodular sandy limestone strata and conglomerate interbed. This formation have 514m thickness and both lower and upper boundaries are unconformable. The location of the study area is in 50km. south west of the Khur and 4km. south of the Haftuman village in the Esfahan- Naein sedimentary basin (54° 47ʹ 09.4ʹʹ East and 33° 30ʹ 14.8ʹʹ). Material & Methods This study is based on data from one outcrop of the Haftuman formation. We collected 280 thin sections from approximately 514 meters strata of this formation. To distinguish calcite from dolomite and their ferroan equivalents, after polishing, all samples were treated with one normal HCl for 1 minute and were then stained by potassium ferricyanide and alizarin red-S. For sedimentological analysis and interpretations, the samples were examined in detail to describe the various facies and diagenetic features. The modified Dunham (1962) textural scheme of Embry and Klovan (1972) was used together with sedimentary structures and fabrics, grain size, and rock composition. Facies analysis used standard model and microfacies descriptions (e.g. Flugel 2010). From the data, a regional conceptual depositional model and sequence stratigraphic framework was constructed for the Haftuman Formation in the studied area. Results of facies analysis (e.g., vertical facies variations), biostratigraphic analysis, diagenetic studies were used for determination of the third-order sequences in the studied intervals. Finally, facies characteristics and diagenetic features were correlated within the sequence framework (systems tracts). Discussion of Results & Conclusions Integrated facies, diagenetic and sequence stratigraphic analyses of the Haftuman Formation (Senonian) in the Kuhe- Debarsu located in east central Iran were studied. Detailed petrographic analysis of thin-section resulted in the recognition of 13 microfacies and 2 petrofacies grouped into three main facies associations, indicating a homoclinal ramp-type platform for the Haftuman Formation. Based on the stratigraphic positions of the sequences-bounding unconformities, two 3rd sequences type 1, predominantly eustatic control of the sedimentary cyclicity in them are detected. According to the petrographic studies cementation, dolomitization, micritization, phosphatization, fitted fabric and stylolitization are the main diagenetic evidence in this formation. Keywords: Central Iran, Khur area, Haftuman formation, Depositional model, Sequence stratigraphy, Diagenesis