| Abstract: |
Sedimentary processes on the inner Mekong Shelf were investigated by examining the characteristics of sediments sampled in gravity cores at 15 locations, including grain size, clay mineralogy, sediment accumulation rates, and the elemental and stable carbon isotopic composition of organic matter (atomic C/N ratios and delta C-13). Deltaic deposits exhibit contrasting characteristics along different sides of the delta plain (South China Sea, SCS hereafter, to the east and Gulf of Thailand, GOT hereafter, to the west) as well as on and off the subaqueous deltaic system. On one hand, cores recovered from the subaqueous delta in the SCS/GOT are consisted of poorly/well sorted sediments with similar/different clay mineral assemblage with/from Mekong sediments. Excess Pb-210 profiles, supported by C-14 chronologies, indicate either "non-steady" (SCS side) or "rapid accumulation" (GOT side) processes on the subaqueous delta. The delta C-13 and C/N ratio indicate a mixture of terrestrial and marine-sourced organic matter in the deltaic sediment. On the other hand, cores recovered from areas with no deltaic deposits or seaward of the subaqueous delta show excess Pb-210 profiles indicating "steady-state" accumulation with a greater proportion of marine-sourced organic matter. Core analysis's relevance with local depositional environment and previous acoustic profiling are discussed. (C) 2012 Elsevier Ltd. All rights reserved.
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