Date Presented:

Abstract:

Sea level indicators, such as tidal notches and beachrocks, may provide valuable information for the relative sea level (RSL) changes of an area. Although beachrocks have received various arguments regarding their accuracy as sea level indicators, they have often been used to assess Holocene shoreline changes and crustally induced RSL changes.

The study area, Okinawa, belongs to the Ryukyu Islands, Japan (Pacific Ocean), forming the emerged part of an active island arc, where the Philippine Sea plate is subducting beneath the Asian continent. Various studies have noted evidence of emergence. Beachrocks have also been studied, however, detailed examinations of their spatial extend and cement characteristics has not been accomplished.

In this context, the aim of this research is to discuss the RSL evolution in Okinawa through the re-evaluation of reported sea level indicators, along with additional observations on beachrocks and notches. Fieldwork was accomplished in the coastal zone of Okinawa, through detailed spatial mapping and sampling of beachrock occurrences. Coastal transects were accomplished in order to measure the width and depth/elevation of beachrock slabs. In order to perform petrographic analysis, stained thin sections were studied using transmitted light microscope where selected samples were studied under SEM.