Possible reasons for an extreme ecological disaster event in Zhoushan Archipelago during the period 5900–5600 yr BP

A 3.3-m-thick, 74.5-m-long ancient wood layer was discovered in Zhoushan Archipelago, East China Sea. The ancient woods were well preserved except for weak silicification of wood bark, and abundant amount of leaves, fruits and seeds were found therein. The distribution characteristics of the ancient woods and well-preserved ancient wood stumps indicated the native origin of these ancient woods. The ancient plants as well as their leaves, fruits and seeds were all preserved well, pointing to a possible sudden deposition event. As inferred from the radiocarbon dating results, the abrupt deposition of ancient wood layer was during the period 5900–5600 yr BP, when the palaeoclimatic records reveal intensified summer monsoon winds, strong winter monsoon winds, and very low ENSO activity. We suggest that the formation of the ancient wood layer was very likely caused by the coaction of a strong storm surge and rapid sea level rise, which became more frequent and intensive during this period. The findings of this study imply the potential risk of strong storm surges in the coastal area of the East China Sea, which should be considered in future planning and construction of buildings.