Storm-deposited coral blocks: A mechanism of island genesis, Tutaga island, Funafuti atoll, Tuvalu.

A new storm model of reef island formation is presented for Tutaga island, Funafuti atoll, Tuvalu, based on detailed observations and radiometric dating of large coral blocks (>2 m diameter) deposited in a dense array across the reef flat and which compose the island fabric. Dating of coral blocks indicates that island formation was nonlinear and characterized by a mixed age structure resulting from episodic deposition of spatially dispersed fields of coral heads and boulders associated with four discrete storm phases over the past 1100 yr. Island accumulation occurred 750-300 yr ago at current sea level across a sea level-constrained reef flat. Results highlight a critical relationship between coral growth and temporal lag between the storms necessary to generate blocks for island building. Results also indicate that island deposits are promising archives for unraveling paleo-storm frequencies at mid-ocean locations. [ABSTRACT FROM AUTHOR]