大洋沉积物中^(10)Be和^(26)Al的浓度变化与定年

DISTRIBUTIONS OF 10Be AND 26Al IN OCEANIC SYSTEM AND THEIR POTENTIAL FOR THE DATING OF MARINE SEDIMENTS

１０Ｂｅ和２６Ａｌ都是长寿命宇宙成因放射性核素（半衰期分别为１．５１和０．７Ｍａ）。在深海沉积物剖面上１０Ｂｅ浓度随深度的增加并不是成简单的指数衰减，而往往表现出较大幅度的起伏和跳跃，沉积物中１０Ｂｅ的初始浓度不仅仅取决于１０Ｂｅ的海底通量，而且还与沉积物的成分以及沉积速率密切相关，１０Ｂｅ在广海海水中的滞留时间可以达到５００～３０００年，这意味着在沉积到海底之前１０Ｂｅ与９Ｂｅ可能已混合均匀，虽然不同海域海底沉积物表面可交换离子相和自生相１０Ｂｅ／９Ｂｅ比值变化很大，但在一个洋盆之内却相对一致并且与洋底海水接近。

オオ┆?0Be and 26Al are longlived radionuclides primarily produced by interaction between cosmic ray and nitrogen and oxygen in the atmosphere.For their long life(their halflives are 15 and 07 Ma respectively)and particle reactive nature,both of them are not only the effective tracers for many geological processes,but also the ideal dating tools for the Late Neogene and Quaternary marine sediments.The concentrations of 10Be do not simply decrease with increasing of depth in deepsea sediment sections,but show a fluctuation.The primary contents of 10Be in sediments not only depend on the deposit flux of 10Be on sea floor,but also on the sedimentation rate and composition of sediments.From available data,it can be seen that the retention time of 10Be in open ocean is in a range of 500～3000 years.This means that 10Be and 9Be might be mixed thoroughly before reaching to the floor.Although 10Be/9Be ratios of exchangeable or authigenic phases in the surface sediments from different oceans vary notably,they are relative consistent within an ocean and close to in the bottom water(075125×10-7).This constancy shows a light on dating marine sediments using the 10Be/9Be ratios of authigenic minerals.This paper reveals the distribution regularity of 10Be and 26Al in oceanic system by summing up the available data of 10Be and 26Al in sea water and sediments,and introduces the basic principles,methods and recent progresses of dating marine sediments using 10Be and 26Al.It is pointed out that 10Be and 26Al,though unlike 14C as a global dating tool,can provide very useful information for determining the ages of marine sediments.