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Objective Mixed sediments were widely developed in the lower First member of the Shahejie Formation in the Lixian slope and their influence on the development of hydrocarbon reservoirs is of great significance. The aim of this study was to clarify their properties to determine the target area for exploration and development in the next step. Methods The types， distribution regularity， control factors， sedimentary model and mechanism of high-quality reservoir formation in mixed sediments were analyzed from cores， thin sections， seismic well logging and laboratory analysis data. Results Two types of mixed sedimentation occur in the study area： mixed sedimentary rock and mixed sedimentary strata. Three major categories of mixed sedimentary rock （mixed sandstones， mixed mudstones and mixed carbonate rocks） are further divided into six types. The mixed sedimentary strata are divided into 16 types in four lithofacies assemblages： terrigenous rock-carbonate rock， terrigenous rock-mixosedimentite， carbonate rock-mixosedimentite， and mixosedimentite. The lower First member of Shahejie Formation in the Lixian slope has typical mixed features， which occur in eight microfacies types： underwater distributary channel microfacies， mouth bar sheet microfacies， underwater diversion bay microfacies， mud flat microfacies， sandy beach bar microfacies， carbonate beach bar microfacies， inner beach microfacies and semi-deep lake mud microfacies. The mixed sediments display rapid phase transformation laterally， and multiple rock types are frequently superimposed vertically. The mixed sediments are distributed differently at different intervals， two mixed depositional models are evident， one developed during lowstand periods， and one during highstand periods influenced by climatic and water environments， tectonic background， paleogeomorphology， sediment supply and lake level changes. The mixed sediments play a significant role in reservoir control； the sandy beach bars and carbonate beach bars that were developed in high-energy facies zones contain the most favorable mixed sedimentary microfacies. A closed saline water environment is the foundation of reservoir formation， controlling the formation and distribution of high-quality reservoirs； sedimentary cycles control the degree of development and distribution. Conclusions The paleogeomorphology highland in the southwestern region contains favorable areas for mixed beach bar development and exploration.
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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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