WEATHERING CHARACTERISTICS AND PROVENANCE OF THE SURFACE SEDIMENTS IN THE OFFSHORE OF NORTHERN FUJIAN

The analysis of grain size and major elements was carried out for 229 surface sediment samples collected from the coastal area of northern Fujian and 54 surface samples from the surrounding rivers. The factors controlling the distribution patterns of the major elements and grain size are studied. Two weathering indicators, the component variation index (ICV) and the chemical alteration index (CIA), are used together with the (A-CN-K)-(A-CNK-FM) triangle chart to reveal the weathering characteristics and provenance indicators. Results show that the surface sediments along the coast are distributed in a quite regular pattern. From the coast to the sea, the deposits are getting thicker, and spatially in a banded manner. Sands occur near the land followed by mud-silt-sand silt-sand towards the sea. It is believed that the banded distribution pattern depends on sediment source and water dynamics. The near shore sediments are mainly coming from the Yangtze River and surrounding rivers, and deposited in the area less than 50 m in water depth. The coarse sands found in the area under 70 m of water depth are mainly residual sediments. In the area between 50～70 m in water depth, there occur the mixed sediments of the above two. Research of weathering degree suggests that chemical weathering becomes stronger off shore. The sediments below 70 m are mainly the residual sands dominated by high quartz and low clay mineral content, indicating a weak chemical weathering. The weathering degree of fluvial sediments in the Yangtze River, Oujiang River and Minjiang River shows an increase trend with the decrease in geographical latitude, and the effect of climate is obvious. The weathering status of the study area is rather similar to the Yangtze River sediments, and thus the environments are also similar and both affected by sediment sources.