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

Grain sizes and minerals of sediments from the Gulf of Tonkin were evaluated from 30 surface samples and 50 samples from two cores. The distribution of grain sizes and minerals from these samples were determined to help understand sediment characteristics, origins, and environmental dynamics. There were five sediment types: fine and very fine sands, very coarse, coarse, and medium silts. Minerals in the sediment were identified as decreasing in terms of the content of quartz, illite, kaolinite, chlorite, feldspar, goethite, halite, calcite, gibbsite, aragonite, and montmorillonite. Contents 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 from nearshore were lower than offshore; calcite and aragonite were low nearshore and higher in the offshore; goethite was lower offshore and higher nearshore; and, finally, 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 was 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 found present in the sediment. Geochemical processes produced goethite, gibbsite, halite, and pyrite in the sediments while biological substances produced calcite and aragonite.