基于光释光测年的中国黄土中氧同位素阶段2/1和3/2界限位置及年代的确定

文章简要总结了近几年来在确定黄土中氧同位素阶段2/1和3/2界线位置、年代以及与此相关的光释光测年方面的最新进展。在黄土与全球变化的研究中,更新世与全新世界线的位置及其年代的确定始终难于解决。常用的方法是用磁化率曲线来定性确定这一界线,而其年代则从别处引用。近几年来光释光测年的一些最新进展为黄土高分辨率的光释光年代序列提供了条件,基于高分辨率光释光测年的沉积速率模型较好地解决了这一难题。由于冰期时黄土沉积速率较高,而间冰期(或间冰阶)时沉积速率相对较低,沉积速率模型认为,沉积速率变化的拐点即是冰期和间冰期的界线。运用这一模型,测算得出甘肃省临夏盆地塬堡剖面氧同位素阶段2/1和3/2界线的年代分别为13148±1115ka和2518±211ka.

LOCATING AND DATING THE BOUNDARIES OF MIS 2/1 AND 3/2 IN CHINESE LOESS USING LUMINESCENCE TECHNIQUES

This paper briefly reviews the recent progress in efforts of locating and dating the boundaries of MIS2/1 and 3/2 in Chinese loess using optically stimulated luminescence(OSL)of quartz.In loess and Quaternary geology research,the boundary between the Marine Isotope Stages(MIS)2/1 is routinely located using magnetic susceptibility(MS)curve,its age is imported from other records;and the MIS3/2 boundary has never been located and dated yet.Due to the penetration of pedogenetic process and the relevance of MS to this process,it is difficult to locate accurately the MIS2/1 boundary using MS.Recently,a sedimentation rate model was proposed to locate and date accurately the MIS2/1 boundary in loess-paleo～sol sequences.The assumption for this model is that:loess in the Chinese Loess Plateau is an eolian deposit,transported from deserts(which are to the north or the northwest)by the winter monsoon;as a result,the sedimentation rate is higher during the glacial(a cold and dry period),and lower during the interglacial(a warm and humid period).The model then proposed that the sedimentation rate change point during the transition zone from L1 to S0 is the right position for the MIS2/1 boundary.The sedimentation rate can be determined using high resolution OSL dating.The recent progresses in OSL dating,especially the development of a single-aliquot regenerative-dose protocol and the existence of a common growth curve for OSL of quartz,enable the establishment of a high resolution OSL chronology for Chinese loess.Combined with high resolution OSL dating,it has been demonstrated that the sedimentation rate model can not only accurately locate boundaries of MIS2/1 and 3/2,but also obtain the ages of these boundaries.For the Yuanbao section which is located in the Linxia Basin in Gansu Province,the so-determined ages for boundaries of MIS2/1 and 3/2 are 13.48±1.15 and 25.8±2.1ka,respectively.