Characteristic and distribution of grain sizes and minerals in sediments in a part of the Vietnamese Gulf of Tonkin

Abstract Grain sizes and minerals from Gulf of Tonkin sediments were evaluated from 30 surface samples and 50 samples in two cores, distribution of grain sizes and minerals to help understand sediment characteristics, origins, and environmental dynamics. There were five sediment types: Fine and very fine sands were found nearshore where land-sea interactions were stronger than offshore, whereas very coarse, coarse, and medium silts were found offshore, in small bays, river mouths with weak land-sea interactions, or near source sediment supplies. Minerals in sediment were identified as decreasing in the content of quartz, illite, kaolinite, chlorite, feldspar, goethite, halite, calcite, gibbsite, aragonite, and montmorillonite. Content of major minerals such as quartz, illite, kaolinite, and chlorite varied from nearshore to offshore; quartz was higher nearshore than offshore; illite, kaolinite, and chlorite nearshore were lower than offshore; calcite and aragonite were low nearshore and high in offshore; goethite was lower offshore and higher nearshore, while halite was high offshore and low nearshore. Surface sediments were divided into three groups based on sedimentary environment characteristics: group 1 was distributed nearshore with strong dynamics, group 2 in bays and nearshore with weak dynamics, and group 3 was distributed offshore with quiet dynamics. The origin of the sediments is weathering and erosion from the mainland and islands under the river and sea processes in the Gulf of Tonkin with quartz, illite, kaolinite, feldspar, chlorite and montmorillonite presenting in the sediment. Geochemical processes produced goethite, gibbsite, halite and pyrite in the sediments. Biological substances produced calcite and aragonite.