The diatom mat deposits are giant shade flora diatoms bloom and quickly deposit to the ocean bottom.At the same time,some other species of diatoms also bloom.A total of 101 diatom taxa(including variation) belonging to 40 genera has been identified from the 155 samples based on the two cores of WPD03 and WPD12.It was found that the relative percentage of Thalassionema frauenfeldii is the highest,and that of Thalassionema nitzschioides,Azpeitia nodulifera,Nitzschia marina,and Hemidiscus cuneiformis takes the second place.The five species take about 85% of all diatom species’ relative percentage.The result indicated the five species are the easiest to coexist and bloom with the diatoms forming mats in the diatom mats’ deposit process of the surface water in this area.We estimated that the period for forming mats was a tropical environment of open-ocean circulation.

In this study,rare earth elements(REEs) of 70 surface samples have been analyzed to investigate the provenance in the eastern Beibu Gulf.The samples show relative enrichments in light REEs,with flat HREE patterns and moderate Eu anomalies.REEs compositions of sediments were constrained by grain size and carbonate content.The REEs characteristics of sediments are the same as weathered upper continental crust and the sources of sediments are mainly from continental crust with felsic rocks.The studied area can be separated into four zones based on REEs characteristics and the UCC-normalized patterns of each zone are different.Provenance discrimination indicates the west of the eastern Beibu Gulf(Zone 1) is mixing zone.The sediments mainly originate from rivers of Hainan Island and coastal bed rock erosion around,the sediments offshore transported from south to north(in winter),and the sediments from the northwestern and western Beibu Gulf in summer or winter.The provenance of coarse sands in the middle of the Beibu Gulf(Zone 2) is the same as that of the western sediments,mainly originated from the Red River.Sands in the northeast(Zone 3) maybe come from coastal bed rock erosion of the northwestern Leizhou Peninsula.The sediments in the northeast(Zone 4) are mainly derived from coastal erosion of northern Beibu Gulf,Qiongzhou Strait and western Leizhou Peninsula.Furthermore,several sediments may be derived from the Pearl River basin,the shelf of southern South China Sea and northwestern Beibu Gulf.

The methods on determining the carbonate grain-size distribution have not been well developed up to date, although it is a useful parameter for paleographyic study. In the light of the principle of laser grain-size analyzing ( LGA ) method, we used the Malvern 2000 type LGA to measure and calculate the carbonate content and grain-size distribution in A37 core sediments taken from the Ryukyu Trench. The results showed that the carbonate content and grain-size distribution data could be achieved successfully through analyzing the original and decarbonated deep sea sediment samples. The carbonate content of the sediments is suggested to be more than 15 % because of the limitation of the LGA itself. Compared to the ordinary optical method, the present method supplies us a rapid, effective way to measure the carbonate contents and grain-size distribution for deep-sea sediments.