Depositional environment and sequence stratigraphy of the Khoshyeilagh Formation in Bojnourd and Jajarm (NE Iran)

Authors : Fatemeh JAFARBEİGLOO, Mahmoud Reza MAJİDİFARD, Bahaeddin HAMDİ, Afshin ASGHARİ, Mehran ARİAN

Pages : 853-877

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Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :In this study, depositional environment and sequence stratigraphy of the Khoshycilagh Formation has been investigated in three stratigraphic sections including Pelmis, Robat-e Qarehbil, and Kuhe Own in the northeast of Iran. The thickness of the Khoshycilagh Formation in these sections are 182, 260, and 463 m, respectively. Based on the facies analysis of the Khoshyeilagh Formation, 3 clastic facics, 11 carbonate facics, and 1 hybrid facics were identified. The vertical and lateral changes of the Khoshyeilagh Formation show a shoreface marine depositional environment that begins with alluvial sediments and continues by marine sedimentation. According to these changes, a homoclinal ramp model is proposed for the Khoshyeilagh Formation. This ramp model shows a relatively gentle slope that continues to the basin and is similar to the present-day carbonate ramps, like the southern coast of the Persian Gulf and Shark Bay in the Australian carbonate ramp. This depositional model consists of five subenviromnental units including shoreface, tidal flat, lagoon, shoal, and open marine environments. The lithofacies analyses and their interpretations represent a decrease of depth at the end of Frasnian which is followed by an intensive sea level drop like the other global examples at this time. After a period of time and during Famennian the sea level rised and the open marine facies insert ignore into journalissuearticles values(bioclast spicule wackestone-packstone); were deposited. With a regard to the identified biozone, Late Devonian age insert ignore into journalissuearticles values(Late Frasnain-Early Famennian); is obvious for the Khoshyeilagh Fonnation. The sequence stratigraphic analysis and depositional model evaluations led to the identification of two third-order complete sequences, which are limited by discontinuities as a result of sea level changes at the base and top of the sequence, and an incomplete sedimentary sequence at the end of the studied section. The transgressive systems tract insert ignore into journalissuearticles values(TST); in this sequence is mainly composed of the shoal and open marine facies, the maximum flooding surface insert ignore into journalissuearticles values(MPS); is identified by the bioclast wackestone facies, and the highstand systems tract insert ignore into journalissuearticles values(HST); mainly consists of the lagoon, tidal flat, and shoreface facies.
Keywords : Sequence stratigraphy, depositional environment, Khoshyeilagh Formation, Late Devonian, NE Iran