沉积过程中有机碳及Globigerinoides ruber氧、碳同位素变化特征——以南海南部为例

Changes of TOC and δ^(18)O,δ^(13)C from Globigerinoides ruber during the Deposition Process in the Southern South China Sea

由水体到沉积物,不同沉积阶段的沉积过程也有所不同。通过对比南海南部(SCS-S)水体沉降颗粒物、海底表层沉积物和岩芯柱状沉积物(上部3 m)中Globigerinoides ruber氧、碳同位素(δ^(18)O、δ^(13)C)值和有机碳(TOC)含量及堆积速率的变化,系统分析了TOC、δ^(18)O、δ^(13)C等环境演变指标参数在沉积过程中的变化特征。结果显示:1)整个沉积过程中,TOC及同位素等环境演变指标参数的变化情况并不一致。不过,由下层水体沉降到海底表层的过程中,TOC及堆积速率(分别由4.20%、0.38 g/(cm^2·ka)下降到1.^(18)2%、0.039 g/(cm^2·ka)、δ^(18)O、δ^(13)C值(分别偏重0.196‰、0.855‰)均出现了明显变化。而一旦形成表层沉积物并被埋藏覆盖形成海底沉积物层(以岩芯柱状沉积物代表)以后,在不考虑冰期—间冰期气候旋回的影响下,除TOC外,δ^(18)O、δ^(13)C值等则基本保持不变;2)不同沉积阶段,TOC含量变化与δ^(18)O、δ^(13)C值的相关性分析表明,岩芯柱状沉积物中TOC含量变化与δ^(18)O、δ^(13)C变化之间的相关性最为明显,特别是TOC含量与δ^(18)O变化间呈显著正相关(r=0.74),即由下层水体到表层沉积物这一沉降过程中,TOC含量与堆积速率的突变及其对应的底层水中溶解氧(O_2)、二氧化碳(CO_2)含量变化可能是诱导δ^(18)O、δ^(13)C大幅偏重的主要因素。因此,利用TOC等指标参数进行古环境变化分析时有必要考虑不同沉积过程的影响。

The ocean sediments are formed in surface water and finally preserved in sea floor. During this process,the sedimentary environment always changed. In this paper,the change characteristics of TOC（ %）,TOC flux and δ^18O and δ^13C values from Globigerinoides ruber during the deposition process had been discussed in detail,basing on analyzing the relationships among particulate matter,surface sediment and core sediment in Southern of South China Sea（ SCS）. Here,the results shown that： 1） The different proxies,such as TOC（ %）,TOC flux and δ^18O,δ^13C,have different changes during the deposition process. Specially,all the values of TOC（ %）,TOC flux and δ^18O,δ^13C descended visibly during the deposition satge from deep water layers to sea floor. The value of TOC% and TOC flux descend from 4.20%,0.38 g/（ cm^2·ka） to 1.-（18）2%,0.039 g/（ cm^2·ka）,respectively. The value of δ^18O,δ^13C descend from 3.298‰ and 0.431‰ to 2.923‰ and 1.461‰,respectively. Reversely,when the core sediment formed in sea floor,the value of δ^18O,δ^13C would become stable except TOC（ %） and TOC flux; 2） The relationship between TOC（ %） change and value of δ^18O,δ^13C become visibly when the core sediment formed. Specially,there are clearer coherence between TOC（ %） and value of δ^18O in core sediments than other sediment types. In other hand,the change of relationship between TOC（ %） and value of δ^18O and δ^13C indicate that the dissolution of TOC might be one of important factors leads to change of δ^18O and δ^13C value. In one word,the change characteristics of TOC（ %）,TOC flux and δ^18O,δ^13C during different sedimentary stages must be considered when reconstruct the palaeoenvironment evolution history based on these proxies.