Textural and chemical analyses of 115 sediment samples from Nha Trang Bay on the central coast of South Viet Nam have permitted detailed mapping of the sediment characteristics within this relatively small area. The results show marked juxtapositions of sediment types and ages. Two areas of relict sand left from a time of glacially lowered sea-level are surrounded by Recent detrital and carbonate material. The exposure of these relict sands is a result of the sweeping away of sediment entering the bay by strong currents that develop during the summer and winter monsoons.

Sediments within the bay fall into four basic groups: (1) clayey silt in low-energy areas between islands and in deeper water on the fringes of the bay, (2) sandy silt to silty sand extending out from the river mouths, (3) sand with low carbonate percentages including the relict sand in areas of vigorous currents; and (4) sand with high carbonate percentages; some of this sand occurs on shallow banks and exposed peninsulas and is in equilibrium with the energy environment, whereas that in shallow protected areas does not reflect the energy system. The distribution of organic materials in the bay is closely related to these sediment types. The highest concentrations of carbon and nitrogen occur consistently in the clayey silt areas with intermediate and low concentrations in the sandy ilt-silty sand and sand areas, respectively. Exceptions to this are revealed in the plot of carbon/nitrogen ratios where high organic-carbon contents occur in coarse-grained sediments of the nearshore and shallow-bank areas.

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