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Objective Recent significant discoveries of marine clastic gas reservoirs in the Shiqiantan Formation （Shiqiantan Sag， Junggar Basin， NW China） necessitate the refined understanding of depositional systems to guide future hydrocarbon exploration. Methods This study reconstructs paleogeomorphology through isochronous sequence stratigraphic correlation and integrates seismic facies analysis， well-log cross-sections， and core/thin-section observations to delineate depositional facies and establish an evolutionary model. ［Results and Conclusions］ Results reveal a complete third-order sequence in the Shiqiantan Formation， subdivided by paleogeomorphic slope breaks into early transgressive systems tract （TST）， late TST， and highstand systems tract （HST）. During deposition， the sag formed a narrow NW-SE-trending marine seaway featuring rift-controlled troughs， multi-stage slope breaks， fault-bounded steep margins， and erosional valleys. Depositional systems identified include nearshore subaqueous fans， fan deltas， slope fans， and basin-floor fans. Paleogeomorphology exerted primary control on facies distribution： fan deltas and nearshore subaqueous fans developed along southern fault-controlled steep slopes； slope fans dominated the northern multi-stage gentle slopes； basin-floor fans occupied the central trough. Deposition occurred under rapid transgression， forming multi-stage imbricate retrogradational basin-floor/slope fan complexes during TST， overlain by extensive braided delta systems in HST. The TST hosts high-quality mature source rocks. Critically， basin-floor fans and slope fans on the northern gentle slope exhibit "finger-like interdigitation" with marine source rocks—creating optimal "source-on-top" and "source-adjacent" reservoir configurations. These zones represent prime targets for concealed hydrocarbon exploration due to superior charge conditions.
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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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