DEGLACIAL ORIGIN OF BARRIER REEFS ALONG LOW LATITUDE MIXED-SILICICLASTIC AND CARBONATE CONTINENTAL SHELF EGDES

Because the initial phase of barrier reef evolution is often buried under more recent phases of coralgal growth, the origins of modern barrier reefs have remained elusive. Direct observations on the nature of the substrate on top of which barrier reefs have developed are lacking, and simple questions about whether the substrate contributes to their overall linear morphology have remained unanswered. We present here a review dedicated to late-Quaternary shelf-edge deposition in tropical mixed siliciclastic-carbonate systems which include the central Belize barrier reef, the northern extremities of the Australian Great Barrier Reef, Papua New Guinea barrier reef in the Gulf of Papua, and the New Caledonia barrier reef, all of which thrive on the edge of mixed siliciclastic-carbonate continental margins.

Based on the striking similarities between the shape of the modern barrier reefs and the morphologies observed along adjacent modern and past undelying coastal systems, we used modern analogs to develop a quantitative understanding of shelf edge barrier reef formation during different segments of relatively well established sea-level cycles. The onset of rapid sea-level rise during early deglaciations, when siliciclastics were deposited along newly formed coasts at up-dip positions, provided opportune time windows for coralgal communities to establish themselves on top of maximum lowstand siliciclastic coastal deposits, such as beach ridges, shoulders of river incisions, and lowstand shelf-edge deltas.