EVOLUTION OF THE COASTAL DEPOSITIONAL SYSTEMS OF THE CHANGJIANG (YANGTZE) RIVER IN RESPONSE TO LATE PLEISTOCENE–HOLOCENE SEA-LEVEL CHANGES

  • Hori K
  • Saito Y
  • Zhao Q
 et al. 
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Abstract

The paleo-Changjiang (Yangtze) incised-valley fills, ap-proximately 80–90 m thick, provide an opportunity to document the evolution of coastal depositional systems with large sediment supply in response to late Pleistocene–Holocene sea-level fluctuations on time scales of 10 3 to 10 4 years. The sedimentary facies of the incised-valley fills record three main depositional systems: fluvial, tide-dominated es-tuary, and tide-dominated delta. Radiocarbon ages for the incised-val-ley fills suggest that these depositional systems developed before about 11 ka, between 11 and 8 ka, and after approximately 8 ka, respectively. By applying sequence-stratigraphic concepts, the evolution of the de-positional systems can be divided into three systems tracts—a lowstand systems tract (LST), a transgressive systems tract (TST), and a high-stand systems tract (HST). Sea-level changes on a 10 4 -year time scale controlled the basic architecture of the sequence of the incised-valley fill. On the other hand, sea-level changes on a millennial time scale af-fected the stacking pattern of the systems tracts. In particular, the continuous sea-level rise with episodic rapid rises during the last de-glaciation affected the stacking pattern of the TST, which is charac-terized by a combination of aggradation and backstepping. The aggra-dation of fluvial and estuarine systems was dominant and the shoreline migrated only gradually landward under the relatively slow rise in sea level, and a very rapid sea-level rise around 12 and 10 ka caused the system to migrate abruptly landward. Unlike the transgressive estuarine phase, the stacking pattern of the regressive tide-dominated delta (HST), which developed within the al-most filled incised valley and on the surrounding interfluve zones, was characterized by seaward progradation with clinoform architecture. It was initiated with aggradational and progradational stacking about 8 ka during the last phase of decelerated sea-level rise, and was followed by a progradational phase after the highest sea level about 6 ka.

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Authors

  • Kazuaki Hori

  • Yoshiki Saito

  • Quanhong Zhao

  • Pinxian Wang

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