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The second member of the Middle Jurassic Shaximiao Formation in the rejuvenated Western Sichuan Foreland Basin contains tens of metres of thick incised valley successions. Incised valleys have been widely discussed in traditional models; however, quantitative and detailed analyses of geometric variations and their interpreted controls on ancient incised valleys have rarely been attempted in the past. Using an integrated dataset of seismic profiles, well logs and cores, this study quantifies the geometric parameters of incised valleys and investigates the smaller-scale depositional patterns. (1) During this period, incised valleys (IV) were 5–17 km wide, 20–60 m deep and traceable for 120 km along their axis, placing these valleys among the longest seismically imaged incised valleys in the world. (2) Three nested incised valley successions IV-1, IV-2 and IV-3 can be identified. Except for IV-2, the incised valleys decrease in width and depth downstream. (3) In the downstream segment, the role of tectonism diminishes gradually, and periodic base-level changes control the form and evolution of the incised valleys. A downstream decrease in the stream power appears to be responsible for the decreasing trend in the incised valley geometry. Copyright © 2016 John Wiley & Sons, Ltd. |
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