90 kaBP以来阿拉伯海中部海域沉积物来源及沉积过程

Sediment sources and sedimentary processes in the middle Arabian Sea since 90 kaBP

通过对阿拉伯海中部AS06-13岩芯的地球化学特征、黏土矿物组成特征分析,结合有孔虫壳体AMS14C年龄和氧同位素数据建立的年代框架,探讨了阿拉伯海中部海域沉积物的来源及沉积过程。结果显示:AS06-13岩芯涵盖了阿拉伯海90 kaBP以来的沉积序列,平均沉积速率为2.34 cm/ka;稀土元素含量为64~194μg/g,平均值为114μg/g,δEu(平均值为0.71)负异常显著;黏土矿物主要由伊利石(平均含量为56%)、坡缕石(平均含量为18%)、绿泥石(平均含量为15%)、高岭石(平均含量为8%)和蒙脱石(平均含量为2%)组成。球粒陨石标准化的稀土元素配分曲线表现为轻稀土元素富集,重稀土元素亏损的右倾模式,表明研究区沉积物以陆源碎屑为主,通过δEuUCC-(La/Yb)UCC判别图进一步将90 kaBP以来阿拉伯海中部海域沉积物来源变化划分为3个阶段:S1阶段(90~73 kaBP)研究区主要接受印度河入海物质和阿拉伯半岛风尘物质的输入;S2阶段(73~11 kaBP)仍然以印度河和阿拉伯半岛风尘的物质输入为主,但逐渐受到印度半岛的片麻岩区物质的影响;S3阶段(11~0 kaBP)主要接受来自印度河的河流沉积物、阿拉伯半岛风尘、印度半岛的片麻岩区和德干高原物质的共同沉积。坡缕石含量和高岭石/伊利石比值指示90 kaBP以来阿拉伯海中部海域沉积物的陆源物质输入和沉积演化主要受季风和海平面的共同控制,西南季风的减弱和海平面下降导致印度河、德干高原物质对研究区的输入量增多,东北季风的增强和西北风相对增强使阿拉伯半岛的风尘输入增加;全新世海平面快速上升使输入阿拉伯海的河流沉积物急剧减少。

Based on the geochemical characteristics and clay mineral composition of Core AS06-13 in the middle Arabian Sea,we combined the age of foraminifera shell AMS14C and the dating framework of oxygen isotope data,the provenance and sedimentary evolution of the middle Arabian Sea were studied.Results show that Core AS06-13 was deposited since 90 kaBP,with average depositional rate of 2.34 cm/ka.The Rare Earth Element(REE)content ranged from 64.38 to 194.33μg/g,with average of 113.66μg/g.TheδEu,on average of 0.71,dispalyed significant negative anomaly.The clay minerals were mainly composed of illite(56%in average),palychite(18%in average),chlorite(15%in average),kaolinite(8%in average),and montmorillonite(2%in average).The chondrites normalized patterns of REEs had shown a rightleaning pattern of the enrichment in light REEs and deficit in heavy REEs,suggesting that sediments in the study area were mainly terrigenous detritals.According to theδEuUCC-(La/Yb)UCC discriminant diagram,the provenance changes in the middle Arabian Sea can be divide into three stages since 90 kaBP.The stage S1(90~73 kaBP)were mainly sourced from the Indus River and the Arabian Peninsula dust.The stage S2(73~11 kaBP)exhibited similarities to the stage S1,albeit with a discernible tendency towards being influenced by the Peninsular Gneissic rock region.The stage S3(11~0 kaBP)had a mixed sources including the Indus River,Arabian Peninsula dust,gneiss region,and the Deccan Plateau.The content of palygorskite and the ratio of kaolinite/illite indicated that the terrigenous input and sedimentary evolution in the central Arabian Sea were mainly controlled by monsoon and sea level changes since 90 kaBP.The weakening of the southwest monsoon and decrease in sea level led to an increase in fluvial sediment inputs from Indus River and Deccan Plateau to the study area.The enhanced winter winds and the relative strengthened northwesterly winds resulted in an elevated dust input originating from the Arabian Peninsula.The Holocene sea-level rise led to a rapid decline in fluvial sediments supply to the Arabian Sea.