JOURNAL OF SEDIMENT AND SEDIMENTARY ROCK
Year:2009 | Volume:2 | Issue:6|Papers Count:8

The goal of this study was to use petrographic and other sedimentary features to experimentally interpret depositional environment of Faraghan Formation (Lower Permian). Golshan Gas Field is located at about 180 km southeast of Bushehr between South Pars and North Pars and Ferdowsi Field. In this study, 130 thin sections of cutting belonging to petrofacies and facies analyses have been studied, and 8 petrofacies and 5 carbonate facies were identified in the well. Textural maturity of sediments, such as well sorted and rounded quartz grains, show that the Faraghan Formation was deposited in coastal and shallow marine environments. The identified facieses has been deposited in Sabkha, estuarine, foreshore, shoreface and offshore subenvironments.

This study is on Lower Cretaceous deposits in Northwest of Tabriz. Lower Cretaceous carbonates in the studied area with a thickness of 76.5 meters consist mainly of limestone and sandy limestone. The lower as well as the upper boundary is disconformable. Petrographic studies led to recognition of 12 microfacies that were deposited in four facies belts including tidal flat, lagoon, bar and open marine. The observed facies patterns of these deposits indicated a rimmed carbonate platform depositional environment.

Neogene deposits are considered the most extensive sedimentary outcrops in northwestern Iran whose base of units and beds are different from region to region. The dominant lithology of these deposits is mostly coglumerate, sandstone, mudstone, marl and represents fluvial sedimentary conditions and playa environments. The sedimentary succession of Neogene consists of three major sequences equal to Lower Red, Qom and Upper Red Formations. In some areas in northwestern Iran, the first and second sequences exist and in some parts, there is no sedimentation. Angular unconformity is recognized in the beginning of the first sequence and erosional and parallel disconformity at the base of the second and third sequence. The results of this research can be useful for historical geology and paleogeography in northwestern Iran.

In this research, two stratigraphic sections of Asmari Formation were selected. These sections include Runiz and Shamsabad totally 280 meters with 251 thin-sections of Chatian to Burdigalian sediments.Studying microfacies led to the recognition of six environment groups: open marine (Fore bar shelf), bar, lagoon, open marine, shoal and lagoon facies. In general, considering sequence stratigraphy studies, two sediment sequences (3rd class cycle) were identified for Asmari Formation in the studied area. Sequence 1 (Chatian-Aquitanian) which is related to lower and middle part of Asmari Formation and include open marine (Fore bar shelf), bar and lagoon, and sequence 2 (Burdigalian) which is related to the upper part of Asmari Formation and includes open marine, shoal, and lagoon facies.

In order to study sequence stratigraphy, facies and depositional environment of Bahram (Devonian) Formation, a stratigraphic section with a thickness of 368 m in Mountain.Shurab, located in southern Damghan, was selected. This Formation Consist Mainly Of Carbonate And Dolomite Facies. Microscopic studies of Bahram Formation led to the recognition of four Facies Groups, coastal subenvironment, tidal flat, lagoonal and shoal. Coastal facies consist of three microfacies: sublitarnite, quartzarnite and calclitite. Tidal flat facies consist of stromatolite boundstone and lime mudstone. Lagoonal facies consist of bioclast wackestone, peloidal bioclast grainstone, peloidal bioclast packstone and umbella/osteracoda packstone. Finally, shoal facies include bioclast packstone/grainstone microfacies. This Formation was depositional in a ramp sequence. Microfacies vertical changes and their comparison with sea level fluctuations led to the distinction of three large-scale sedimentary sequences.The first sequence is contain TST and HST para sequences upper part of this sequence is of type SB2. secondary sequence begin with alternative of thin limestone belong tidal flat (TST) environment that upward change to dolomite and thick beded limestone. Maximum flooding surface is located in Bioclactic grainstone facies. Hrid sequence is contain TST and HST. The upper boundary of Third sequence is of type SB2.

Delichai Formation (Bajocian-Callovian) in Anbaran region (North of Ardebil) comprises about 49 meters of Sandy–marl limestone with interbeded marly shale layers. Accurate field and laboratory studies upon limestone layer of Delichai Formation lead to the discovery of seven microfacies indicating sedimentary environments related to barrier, dam or open marine under open-sea environments. Facies in deeper areas sometimes reveal turbidite facies which are attributed to slope currents. Sedimentary model offered for these facies suggests that a regression sequence comprising at least three smaller sequences has been deposited in the continental slope to barrier in the Jurassic Sea.

The 3rd, 4th and 5th stratigraphic members of the Mila Formation (Middle Cambrian - Lower Ordovician) are about 120 m thick in the Hasanakdar section and mainly are composed of carbonate and clastic successions. Field and microscopic investigations of this formation have shown that member 3 is mainly comprised of shallow marine mixed carbonate and clastic facies; member 4 is attributed by continental facies and member 5 is mainly marked by a set of deep sea clastic facies. Sequence stratigraphic analysis of the 3rd, 4th and 5th stratigraphic members led to recognition of 3 depositional sequences (third-order cycles).

Carboniferous deposits in Darchaleh area, 70 km southeast of Esfahan, are 323 meters thick and mainly composed of carbonate and clastic rocks. The lower part of the Carboniferous strata in this area is covered by alluvial deposits and their upper port is marked by a disconformity with Permian deposits. Based on petrographic and field studies the sediments in this area are belong to 4 sedimentary environments including coastal, tidal flat, lagoon and barrier environments. These environments have been part of a carbonate homoclinal ramp. Sequence stratigraphy analysis based on Martin- Chivelet method led to the identification of 3, third order depositional sequence that consist of LST, TST and HST. These sequences are bounded by type 1 and 2 sequence boundaries.