New findings about the sea-level change, coastal environment change and delta sedimentary evolution of the southeast China have been released

2021-02-04 L  M  S 】

  Recently, the research team led by Prof. Huang Guangqing from Guangzhou Institute of geography, Guangdong Academy of Sciences and Prof. Zong Yongqiang from University of Hong Kong published a series of research findings in the journals of Quaternary Science Reviews, Earth Surface Processes and Landforms and Marine Geology. These findings include the Holocene relative sea-level change in Hangzhou Bay, the sedimentary pattern of the Pearl River Delta and the coastal event deposition of the south China:

  1. The Holocene relative sea level change for the Hangzhou Bay was reconstructed. The result reveals that the relative sea level rose from -38.3 ±1.6 m in 10,000 cal a BP to the present height by 7000 cal. a BP, and the average rate of sea-level rise decreased gradually from 19.6 ±2.6 mm/a to 2.3 ±1.5 mm/a during the 3000 years. This period of sea-level history was punctuated by two episodes of accelerated rise around 8200 and 7500 cal a BP. The relative sea level rose to 0.8 ±1.4 m above msl by 6500 cal. a BP, followed by a gradual fall back to the present height at 4500 cal a BP, implying a different response to the potential additional ice melting between 7000 and 4000 cal a BP. A comparison of the sea-level histories between the inner and outer Hangzhou Bay indicates the coastal levering effect due to the marine inundation of the continental shelves.

  For more info, see Xiong et al. 2020. QSR.

  Fig.1 Holocene sea-level changes in the Hangzhou Bay

  2. The sedimentary history of the head area of the Pearl River delta was reconstructed as an attempt to complement the Holocene evolutional model of the PRD. The results show marine transgression from 9500 to 7500 cal. a BP, followed by marine regression starting from 7500 to 4000 cal. a BP, in response to sea-level change. During the latter period, sedimentation was concentrated in the head area. The amount of sediment entering the central basin was significantly reduced. However, in locations adjacent to former/present islands, locally supplied sediment helped sedimentation to continue from 7500 to 4000 cal. a BP. By about 4000 cal. a BP, the deltaic shoreline advanced into the central basin. This period saw an increase of human activity that caused soil erosion and sediment supply, leading to a marked increase in sedimentation rate.

  For more info, see Fu et al. 2020. MR.

  Fig. 2 Sedimentary evolution model of the Pearl River Delta during the Holocene

  3. The team also reported a sedimentary hiatus that is widely observed from the late Holocene sedimentary sequence at the seabed along the southeast China coast. This hiatus was discovered by close temporal sedimentary and radiocarbon dating analyses of a seabed sedimentary sequence in the mouth area of the Pearl River estuary. The results suggest that a couple of meters in the middle to late Holocene sediment at the seabed were eroded by a catastrophic event happening 1000–800 cal. a BP. In theory, a mega-tsunami generated from the Manila Trench could have caused such erosion at the seabed, but there is a lack of direct geological and historical evidence to support such a hypothesis. Much more likely, a super-typhoon struck the coast and caused the erosion. This hypothesis is strongly supported by the region’s historical and geological records, which suggest a period characteristic of intense typhoons ranging from the Medieval Warm Period to the climate transition phase (1000–600 cal. a BP). During the subsequent Little Ice Age, deposition of sandy sediment continued, suggesting frequent but weaker typhoon activity. Over the past two centuries the deposition of sandy sediment and gravels began, implying the beginning of a phase of intensifying typhoon conditions, possibly a result of the recent warming climate.

  For more info, see Xiong et al. 2020 ESPL.