| Sediment samples were collected from Beibu Gulf in July and Augest, 2006, and then analyzed in the laboratory to obtain grain size distributions and mineral components. Multi-variable analysis on grain size shows that Q-clustering results can distinguish the diversity of grain size characteristics and can be used to show the distribution pattern of sediment types. Four main control factors are obtained clearly by using factor analysis, which represent 4 grain-size fractions(2.5~3.75&5.75~7.75,8.5~11.5, 4.25~5.25). Score distribution of each factor is related with sedimentary environment (provenance character and dynamic condition). Sediment source character and dynamic condition of sedimentary system should be both included when using grain-size data to indicate sedimentary environment. Mixing of materials from different sources makes responsible for the formation of grain-size trends. Thus, grain size trend vector should be used carefully to define sediment transport pathways when multi-sources are present. Especially in a large dimension area, grain size trends reveal a cumulate impression that responses to long time period of sediment transport and deposit processes, which contains complex superposition information of sediment provenance and sedimentary dynamic condition. Then, the whole area are seprated into 4 sub-area due to the sediment sources on the basis of heavy mineral analysis. The grain size trend analysis model are used for the 4 sub-areas to obtain the whole sediment transport pattern in the bay. It shows that in the northern gulf there is a converge center of sediment transport, which is well agreement with the geomorphological structure, large scale of ocean circulation current and sediment provenance. Accumulation of muddy sediment here is the result of sedimentary dynamic condition and sediment source. The formation of grain-size trend vectors in the area west to Hainan Island may result from sedimentary dynamic selective transport combined with mixing of material derived from different sources. It is uncertainty on the sediment transport pattern in this area; further study are required in the futrue. Hence, sketch map based on general consideration of dynamic condition, sediment provenance and grain size trends may produce a reasonable sediment transport patterns. |
