Sediment transport trends from a tropical Pacific lagoon as indicated by Homotrema rubra taphonomy: Wallis Island, Polynesia

The assessment of sediment transport pathways in carbonate settings is complicated by ecologically sourced sediment. Tracers such as foraminifera have previously been used in these settings to describe the movement of coastal sediments on spatial and temporal scales where traditional grain size methods have limited use. The present study builds on the foraminifera-based tracer method by using Homotrema rubra, a foraminifer with an attached life habit (i.e., defined provenance in the reef) to document modern sediment transport trends at Wallis Island, a tropical Pacific lagoon. At Wallis Island, Homotrema taphonomic results discriminated amongst modern reef, lagoon, and island (beach) samples. Reef samples contained high concentrations of fragments that were large (>. 250. μm) and exceptionally- to well-preserved (e.g., intact chambers, red color, angularity). In general, concentrations and degree of taphonomic alteration decreased with distance landward from the reef; lagoon samples were characterized by lower concentrations of Homotrema that were smaller in size and less preserved (e.g., pink in color, no chamber structure, rounding of edges). At the greatest distance from the reef, island (beach) samples contained the lowest concentrations of Homotrema fragments that were small, well rounded and bleached. In this regard, Homotrema taphonomy is a useful indicator of the direction and forcing of sediment transport and will therefore be useful in detecting overwash deposits in tropical settings, where distinguishing event deposits from surrounding sediment is problematic.