The Study On Community Structure And Typical Elements Of Foraminifera In Sediment Core From The Beibu Gulf

In this study,foraminifera in a total of 233 samples of the sediment cores B1 and B2 in the Beibu Gulf are identified and quantitatively analyzed.Then pick the benthic foraminifera Psedodrotalia indopacific in 19 layers of B1 cores and 48 layers of B2 cores,and determine the contents of magnesium,aluminum,manganese,cadmium,barium,thorium and uranium by inductively coupled plasma mass spectrometry.The paleoenvironmental changes of the Beibu Gulf reflected by the community structure of the foraminifera and the geochemistry of metal elements are studied.The results indicate that:(1)In the two cores of the Beibu Gulf,the abundance of planktonic foraminifera was low and the species were rare.The abundance of benthic foraminifera was high and the species were abundant.Most samples were dominated by the vitreous shell of benthic foraminifera,and a few samples were dominated by the cement shell or porcelain shell of benthic foraminifera.The dominant species combinations of the two cores were basically the same.(2)In terms of the palaeobathymetry,the Beibu Gulf experienced several small sea level rises and falls during the Late Pleistocene(70-12.52 kaBP),In the Holocene,the sea level of the Beibu Gulf is at the lowest level,which means that it was in the sea-land transition phase.The sea level rose rapidly at 8.38 kaBP,reached the highest sea level at 5.13 kaBP,began to fluctuate slowly to the current level at 3.9 kaBP.(3)With respect to the paleo temperature,the Beibu Gulf experienced several small-scale water temperature rise and fall during the last glacial period(7012.52 kaBP).In the Holocene,the temperature increased sharply.The Beibu Gulf experienced three relatively cold periods and two relatively warm periods.(4)For the paleoproductivity,from a relatively large time scale such as the last glacial period to the Holocene,Palaeo-productivity showed a pattern of increasing glaciation and decreasing interglacial period.In the last glacial period(70-12.52 kaBP),the Beibu Gulf experienced several small-scale paleo-productivity changes,entered the Holocene,the temperature increased significantly,and the productivity decreased overall.Most of the indicators show the rule that increasing in the relatively warm period and decreasing in the relatively cold period.To some extent,foraminifera-related parameters can be used to indicate the changes of paleoproductivity in beibu gulf,but it is not accurate to indicate the paleoproductivity with high precision.(5)As far as the paleosalinity is concerned,the paleosalinity has underwent a small three-liter and two-drop process since 70 kaBP in the Beibu gulf.However,the salinity is all at a low level,which is related to the dilution effect of several rivers around the Beibu gulf.(6)To the paleooceanographical nutrient levels,the evolution of paleooceanographical nutrient levels in the Beibu Gulf at 70-12.52 kaBP has gone through five stages:? 68.4358.18kaBP,higher nutrient level;?58.18-44.54 kaBP,the nutrient level decreased;?44.54-32.21 kaBP,the nutrient level increased;? 32.21-23.04 kaBP,the nutrient level decreased;? 32.21-12.52 kaBP,the nutrient level increased slightly.(7)For the paleooceanographical redox environment,the redox environment since 70 kaBP in the Beibu Gulf can be divided into four stages:?68.43-37.19 kaBP,in the reducing environment;?37.19-28.01 kaBP,in the oxidizing environment;?28.01-23.04 kaBP,in the reducing environment;?23.04-12.52 kaBP,in the oxidizing environment.(8)In terms of the input of terrestrial materials,the input of terrestrial materials in the Beibu Gulf 70-12.52 kaBP is divided into four stages:?68.43-52.93 kaBP,low terrestrial input level;?52.93-36.66 kaBP,terrestrial input level increased;?36.66-25.85 kaBP,terrestrial input level decreased;?25.85-12.52 kaBP,terrestrial input level increased.In addition,during the Holocene in the Beibu Gulf,there may be climate change cycles of 6.4 ka,4.3 ka,3.2 ka,2.6 ka,2.1 ka,1.8 ka,1.6 ka and 1.1 ka,and unapparent cycles of 0.9 ka,0.8 ka,0.6 ka and 0.5 ka.From the Late Pleistocene to the beginning of the Holocene(70-12.52 kaBP),there may be Climate change cycle of 64 ka,32 ka,21.3 ka,16 ka,12.8 ka,10.7 ka,8.5 ka,7.1 ka,6.4 ka,5.8 ka,4.9 ka,3.8 ka,3.4 ka.