晚上新世以来菲律宾海盆XT4孔黏土矿物特征及其古环境意义

菲律宾海是典型风尘汇聚区,菲律宾海远离吕宋岛的深海沉积物是重建构造尺度亚洲风尘演化历史的良好载体。选取菲律宾海盆XT4孔沉积物开展了黏土矿物研究,并结合前人研究成果,在明确该孔黏土矿物来源的基础上,探讨了晚上新世以来亚洲风尘的演化历史及其可能的影响机制。菲律宾海盆XT4孔黏土矿物以伊利石为主,平均含量为39%,蒙脱石含量次之,平均为28%,绿泥石平均含量为18%,高岭石平均含量为15%。XT4孔黏土矿物组成符合亚洲大陆风尘与周边火山岛弧的二端元混合模型特征,其中蒙脱石主要为周边火山岛弧物质贡献,而伊利石、绿泥石和高岭石主要是亚洲风尘贡献。晚上新世以来XT4孔的伊利石/蒙脱石比值表现为阶段性变化,主要反映了北半球高纬冰川的扩张导致亚洲中纬度地区干旱化加剧。此外,东亚夏季风降雨强弱和空间分布的变化也是源区风尘释放的重要环境因子之一。本文结果初步揭示了晚上新世以来中国干旱-半干旱地区的环境演化历程,有助于深入理解多圈层相互作用下的风尘循环及其生物地球化学效应。

Evolution of clay minerals assemblages since Late Pliocene and its paleoenvironmental implications:Evidence from Core XT4 of the Philippine Sea Basin

Clay mineral assemblage data of Core XT4 from the Philippine Sea Basin in the western Philippine Sea is used by this paper as proxies to trace sediment provenance and transporting mechanisms so as to constrain past changes in Asian eolian input to the basin since 3.7 Ma.The clay minerals consist of illite(39%)and smectite(28%),with minor chlorite(18%)and kaolinite(15%).Provenance analysis suggests that smectite are sourced predominantly from the alteration of local volcanic rocks,while illite,chlorite,and kaolinite primarily derived from the central Asia continent by eolian origin.Thus,the illite/smectite ratio can be used as a proxy to seek for Asian dust input to the Philippine Sea Basin since 3.7 Ma,and to reconstruct the aridification history of the source region.On the whole,the illite/smectite ratio from Core XT4 shows three stages variation pattern,reflecting the glaciers expansion in the high latitudes of the Northern Hemisphere.This led to the intensification of drought in the middle latitudes of Asia.Within the three stages,the illite/smectite ratio is inversely related to the change in East Asian Summer Monsoon(EASM).The eolian dust flux carried by EAWM on tectonic timescales may be also controlled by the underlying surface conditions,which is in turn influenced by EASM rainfall.Our results preliminarily reveal the environmental evolution of arid and semi-arid areas in China since Late Pliocene,which is helpful to understand the dust cycle under the multisphere interaction and its biogeochemical effect.