|  |
Program |
 |
| |
 |
Special Session 2: Changing ocean environment: from the sedimentary perspective -- processes and records |
| |
|
|
The Holocene evolution of Yangtze River (Changjiang) mouth, China: Stratigraphy, morphologic evolution and sediment budget
Wednesday 11th @ 1045-1100
Room 4
Zhangua Wang* , SKLEC, East China Normal University
Presenter Email: zhwang@geo.ecnu.edu.cn
|
| Paleo-reconstruction based on chronostratigraphy is fundamental to better modelling the nature of a river mouth’s evolution and predict its future fate. This study used more than 300 sediment cores from the Yangtze River mouth, combined with 646 radiocarbon ages and 10 optically stimulated luminescence (OSL) ages to reveal the complex sequence stratigraphy and sedimentary geomorphological environmental change and to estimate the amount of sediment trapped in the river mouth in millennial scale throughout the Holocene. Results demonstrate the distinctive stratigraphic and morphologic evolution, including the tidal ridge-and-swale system developed offshore before 10 calibrated thousand years before present (cal. kyr BP), a significant scoured depression in the apex during 10−8.2 cal. kyr BP, the rapid infilling of the depression and the development of an offshore tidal sand ridge system contemporary with the delta system during the subsequent period. We suggest such unique stratigraphy and morphology was the response in a tide-dominated setting which was formed due to the rapid sea level rise and associated change in river mouth shape from elongated into short and broad during the early Holocene. Calculation of the topographic changes demonstrates that the natural sediment trapping rate was 99−190 Mt/yr on average in millennial scale in the early to middle Holocene, during which time the sea level and monsoon climate were the major factors controlling the amount of deposition in the river mouth. Human activities contributed ca. 35% of the amount of deltaic deposition during the last 2000 years. It is both far beyond the above range of Holocene for the deltaic sedimentation of 292 Mt/yr in 1958–1978 and 68 Mt/yr in 2002–2011 after the construction of Three Gorges Dam (TGD), which indicates the Yangtze delta has changed completely into an anthropogenically-controlled state over the past six decades. |
|
|
|
|