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Objective In the middle and late stages of oil and gas field development， studying sand architecture is the key to accessing residual oil and enhancing recovery. Precise interpretation of similar outcrops provides a comparable prototype model for predicting underground reservoir architecture. Methods The shallow-water delta profiles of the Yan’an Formation in the Kaokaowusugou and Gulf Mining Industry in the Ordos Basin were the research objects. UAV oblique photography was used to obtain images of massive outcrops from which 3D digital outcrop models were established. Detailed interpretation of digital outcrop architecture was then carried out by combined field observation and indoor analysis. Results Developmental characteristics and evolutionary models of shallow-water delta front architecture during a time of rising lake levels were defined. When the lake level is low， mainly trunk-type distributary channels are developed， measuring 23.30-48.40 m wide × 0.89-1.81 m thick， with an average width-to-thickness ratio of 26.74. The sandbody superposition patterns are mainly overlay type. As the lake level rises， fork-type distributary channels， mouth bars， sand sheets and subaqueous distributary bays gradually develop. The width of the mouth bar is 53.90 m， thickness is 2.21 m， width-to-thickness ratio is 24.39， and the sandbody superposition patterns is mainly lateral splicing type. When the lake level is higher， mainly terminal-type distributary channels， mouth bars and sheet sand architectural units are developed. Terminal-type underwater distributary channels， which are isolated in muddy deposits， have widths ranging from 4.70 to 25.30 m， thickness from 0.40 to 1.03 m， and the width-to-thickness ratio from 11.75 to 24.56. Conclusions When the source supply of material is relatively stable， an increase in lake level enlarges the accommodation space. The architectural units evolve from trunk-type to terminal-type distributary channels， depositing mouth bars and sand sheets. The size of the sandbody decreases， but its width-to-thickness ratio increases. Overall， the ratio between sandstone and stratum thickness decreases， spatial connectivity decreases， and reservoir heterogeneity is enhanced.
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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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