Characteristics of storm deposits in Wangcun Lagoon on the southern China coast during Typhoon Rammasun.

Through study of the 210Pb, sedimentology, geochemistry, and microfossil characteristics of six core samples taken in Wangcun Lagoon on the Guangdong Province coast (China) before and after the passage of Typhoon Rammasun (2014), we determined the modern storm depositional dynamic process and its deposition characteristics. During Typhoon Rammasun, a storm deposit with thickness of 40–70 cm was formed in Wangcun Lagoon. The storm deposit gradually thickened from the entrance to the interior of the lagoon, and from the edge of the tidal channel to the tidal flat, and it showed an obvious three-layered structure. The lowest layer had finer grain size, higher total organic carbon (TOC) and C/N contents, and higher abundance of diatoms. The middle layer had coarser grain size, lower TOC and C/N contents, and lower abundance of diatoms, especially near the entrance and the tidal channel. The upper layer mainly existed in the interior of the lagoon, with finer grain size, higher TOC content, higher (lower) C/N contents in the tidal channel (tidal flat), and the second-highest diatom abundance. The fragmentation rate of diatoms was very high in all storm deposit layers. We believe the most likely explanation for the formation of such storm deposit layers is attributable to special storm dynamic processes that are influenced by tides and storm waves. The erosion maximum was reached when the hydrodynamic force was strongest, and then a fine-grained layer was formed during the sedimentary window that occurred as the hydrodynamic force of the ebb tide weakened. Later, part of the fine-grained matter was resuspended under the sub-strong dynamic environment of the subsequent flood tide. Finally, as the hydrodynamic force of the storm weakened further, two layers that were coarser at the bottom and finer at the top were formed. The numbers of storm sediment sequences depend on whether there are multiple sedimentary windows in which sediments can be retained. Storm deposits can be recorded continuously and completely in a lagoon, different from event sedimentary records, and they have specific sedimentological, geochemical, and microfossil characteristics. • Storm deposits from Wangcun Lagoon on the southern China coast before and after Typhoon Rommasun in 2014 were researched. • Typhoon Rammasun formed a storm sediment layer with thickness of approximately 40–70 cm in Wangcun Lagoon. • The interior of the storm deposits showed an obvious three-layered structure. • A fine-grained layer at the bottom of storm deposits formed during the deposition window period. [ABSTRACT FROM AUTHOR]