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Objective The southern Persian Gulf Fars region is strategically significant for Chinese overseas exploration due to its abundant Middle Permian to Lower Triassic oil and gas resources. However， currently available research lacks a comprehensive description of sequence stratigraphy and sedimentary evolution in this geological succession. The objective is to bridge these gaps. Methods This study focused on the middle to Late Permian Dalan Formation and the Lower Triassic Kangan Formation. Utilizing data from individual wells， cross-sections， core samples， thin sections， well logging， along with consideration of the regional geological context and taking existing knowledge into account， the study conducted sequence stratigraphic division of the target succession in the research area and conducted a detailed analysis of the characteristics and evolution of the depositional systems of each sequence. Results It was found that， in the study area， the Dalan Formation and Kangan Formation exhibit six sequence boundaries and five maximum flooding surfaces. On this basis， the stratum were divided into five third-order sequences， each comprising a transgressive systems tract and a highstand systems tract. Fischer plots based on gamma ray log curves for the Dalan Formation show significant transgressive and regressive processes during the SQ1 and SQ4 depositional periods. During the SQ3⁃SQ4 sequence development， limited accommodation space and a relatively low sea level were evident in the study area. The target succession represents a carbonate ramp depositional environment， further divided into inner-， middle- and outer ramp sub-environments. The inner ramp predominates， and was subdivided into six depositional microfacies： sabkha in the tidal zone， intertidal flat， lagoon， leeward shoal， mid-shoal， and seaward shoal. Each microfacies exhibits distinct lithologies such as anhydrite and anhydritic limestone in the sabkha and intertidal flat environments， limestone and anhydritic limestone in the lagoon environment， and grainstone and packstone in the shoal environments. The middle and outer ramp depositional environments were characterized by muddy limestone and marlstone with bioclasts. The sedimentation period in the study area was an arid and hot shallow-water carbonate depositional environment. During SQ1⁃SQ2 deposition， the rate of accommodation space growth was less than the sedimentation rate， leading to the development of a progradational depositional pattern. In the SQ3 deposition period， the rate of accommodation space growth exceeded the sedimentation rate， resulting in a retrogradational and aggradational depositional pattern. The SQ4 deposition period experienced a sea-level decrease， leading to a progradational depositional pattern. In the SQ5 deposition period， influenced by the expansion of the NeoTethys Ocean， tectonic activity along the basement fault caused subsidence in the eastern region， increasing accommodation space. The main depositional pattern was retrogradational. Conclusions Through the analysis of sequence stratigraphic characteristics and depositional systems， combined with the evolution of global sea level and the Neo-Tethys Ocean， it is concluded that the relative change between tectonically controlled accommodation space and sedimentation rate is the primary controlling factor for the regional sedimentary evolution.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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