Continental-margin sedimentation: A wet-tropical perspective from New Guinea

Continental margins can accumulate large amounts of sediment, and this is critical to nutrient cycles and interpretation of Earth history. The Indo-Pacific region receives ∼25% of global sediment discharge, and sedimentation in New Guinea is examined here to help understand the fate of these materials. Specifically, the Gulf of Papua (GOP) and Sepik margins are investigated as they have different margin morphologies. Mangrove and shelf sedimentation in the GOP as well as off-shelf sedimentation on the GOP and Sepik margins are the focus of this dissertation.; Stratigraphy in mangrove areas consists of 4 facies: (1) mangrove muds; (2) midtidal sandy muds; (3) low-tidal sand and mud; and (4) sub-tidal channel sediments, and these are arranged vertically with respect to sea level. Large 210Pb accumulation rates (>1 cm/y) are observed in many mangroves cores, and greatest rates are measured in prograding mid-tidal zones. Based on remotely sensed data, areas of erosion and accretion coexist, and sediment sequestered in mangrove environments is estimated to be 2–20% of the GOP load.; On the GOP shelf, sediment accumulation occurs primarily on a subaqueous-delta clinoform, and is estimated to account for ∼40% of the sediment supplied. Seasonal transfer of sediment from the inner topset to foreset region, probably by fluid muds, appears to produce large sediment accumulation rates. Sedimentological data suggest that wave and tidal energy are a major control on clinoform sedimentation, and sediment-transport calculations support this hypothesis.; Off-shelf sedimentation on the GOP and Sepik margins differs markedly. In the GOP, <5% of the GOP load accumulation seaward of the shelf break, and modest accumulation rates (1–5 mm/y) of bioturbated sediments suggest that nepheloid-layers are the dominant transport pathway. However, in the Sepik system, gravity-driven transport appears to dominate. Radionuclide ( 210Pb and 234Th) data and sedimentary structures reveal that frequent (∼1 every 2 years), fine-grained turbidites transport up to 90% of the Sepik load to the deep sea. Integrating New Guinea observations with other studies suggests that a continuum of off-shelf transport exists, and sediment accumulation beyond the continental shelf may be greater than previously recognized.