The Utility of Foraminifera in Documenting Sediment Provenance for Overwash Deposits: A Case Study Using Sediments Deposited by Tropical Cyclone Pam In Vanuatu
Tropical cyclone inundation is a major threat to the highly exposed islands of the South Pacific. This vulnerability was highlighted in March 2015 when Tropical Cyclone (TC) Pam made landfall on Vanuatu as a Category 5 storm, impacting coastlines with storm surges that produced high water marks up to 7 m above MSL and deposited sediments up to 400 m inland. We examined the foraminiferal assemblages contained within TC Pam sediments at two locations in Vanuatu: a mixed-carbonate embayment (Manuro), and a volcaniclastic beach (Port Resolution Bay; PRB). At Manuro, the TC Pam sediments were up to 10 cm thick and contained abundant foraminifera (955 to 2015 individuals per 5 cm3). At PRB, TC Pam sediments were up to 44 cm thick with lower abundances of foraminifera (27 to 206 individuals per 5 cm3). The TC Pam assemblage was dominated by intertidal and subtidal foraminifera that are characteristic of beach, reef flat, and reef crest environments. The TC Pam assemblage at Manuro was dominated by unaltered foraminifera, but some individuals also showed signs of abrasion. TC Pam sediments at PRB contained fewer unaltered and more corraded foraminifera. The modern surface foraminiferal distributions were compared with those from TC Pam sediments to assess provenance. Cluster analysis discriminated six subenvironments within the modern coastal zone, and discrete intervals sampled from TC Pam sediments at Manuro were individually clustered with the surface samples to reveal a shallow nearshore to supratidal (-4.9 to +1.3 m above MSL) source for the sand
