- 1State Key Laboratory of Earthquake Dynamics and Forecasting, Institute of Geology, China Earthquake Administration, Beijing, China (jtqin@ies.ac.cn)
- 2Xinjiang Pamir Intracontinental Subduction National Field Observation and Research Station, Beijing, China
- 3Urumqi Institute of Central Asia Earthquake, China Earthquake Administration, Urumqi, China
Understanding the temporal pace and spatial pattern of alluvial fan-river system evolution in front of active orogens would help us properly extract information of active tectonics and increase our resilience to landscape evolution of this habitable area. The northern piedmont of Chinese Tianshan, where the landscape is shaped by the interactions among fan building and abandonment, river aggradation and degradation and fault related fold growth. Comprehensive studies have been performed to delineate fan distribution, river incision and fold growth history. However, it is lack of investigation on the detailed spatial and temporal pattern of river channel evolution in a full aggradation and degradation cycle, which hinders formulating the law for alluvial system evolution. In this study, we address this question by using luminescence dating technique to constrain the chronological sequences of sandy samples collected from the terrace deposits. The architecture of the terrace deposits is characterized by upper very coarse gravels and cobbles (VCGC) unit and lower medium and coarse gravels (MCG) unit. The VCGC unit is attributed to the deposition during the incisional phase while the MCG unit is related to the aggradation phase of Jingou River. The coupled luminescence ages from VCGC and MCG units suggested a gradual and slow aggradation of 25 m sediments from 16 ka to 8 ka ago, which was followed by an almost instant incision around 5.5 ka ago by 25 m at least. These observations echo to the patterns unveiled by previous numerical studies. Further, the abandonment ages determined by employing the samples from the MCG unit of the most extensively distributed terrace surface T5 along the middle reach of Jingou river decrease in downstream direction from 16 ka to 5.5 ka, which poses an evidence of diachronous terrace formation. The implication of asymmetric degradation-aggradation phases and diachronous terrace formation will be discussed, with respect to the mass redistribution processes and active tectonics characterization of the alluvial fan and river system.
How to cite: Qin, J., Li, K., Chen, J., Liu, J., and Yao, Y.: Unconventional spatial and temporal pattern of alluvial river aggradation and degradation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16613, https://doi.org/10.5194/egusphere-egu25-16613, 2025.
