年轻冰川沉积砾石的晒退特征及其对岩石释光埋藏测年的启示

不完全晒退/晒退不均现象是冰川沉积物释光测年所面临的巨大挑战，这一问题限制了传统颗粒沉积物释光方法在冰川沉积物测年方面的应用。最新发展的岩石释光埋藏测年技术，可以根据释光-深度曲线判断砾石是否经历过充分曝光，是解决冰川沉积晒退不均问题的有效途径之一。本工作选择青藏高原东部硬普沟现代冰川前沿为研究对象，采集130个年轻冰川沉积砾石样品，包括93个现代样品和37个小冰期样品，其中20个现代样品采自地表。首先，运用表_{~2 mm}/饱和信号法区分不同冰川沉积环境中砾石样品的晒退程度；再基于SAR和SGC法初步估算样品的等效剂量及其高估情况；然后，统计砾石样品的特征（磨圆度、球度、颜色、晶粒大小、晶粒相对大小、砾石大小等）与晒退程度的关系，找寻晒退良好的砾石及其特征。结果表明大部分采样点的砾石样品呈现了被晒退的特征，平均20.6%的埋藏砾石的岩芯晒退良好，剂量高估程度低；不同沉积类型样品的晒退程度不一，侧碛垄顶部砾石样品晒退程度最好，冰水阶地和现代冰河砾石样品次之，现代冰川后退碛垄间洼地的冰水沉积砾石样品晒退程度最差，剂量高估较严重；磨圆度较差、球度较低、浅色的花岗岩砾石晒退程度较好。综上，冰川沉积砾石的晒退程度与沉积环境、沉积过程、搬运距离、砾石特征等相关，在进行岩石释光埋藏测年采样时，应综合考虑上述情况。

Bleaching characteristics of young glacial cobbles and its implications for rock luminescence burial dating

Incomplete/heterogeneous bleaching is a great challenge for glacial sediment luminescence dating， which hinders the application of traditional luminescence method using sand and silt-size grains in glacial environment. The latest developed rock luminescence burial dating technique is able to judge whether the cobble has been fully exposed to daylight according to the luminescence-depth profile， which is one of the solutions to the problem of heterogeneous bleaching of glacial sediment luminescence dating. In front of the modern glacier in Yingpu Valley， eastern Qinghai-Tibetan Plateau， 130 young glacial cobbles were collected， including 93 modern samples and 37 Little Ice Age （LIA） samples， 20 of the modern samples were collected from the ground surface. Firstly， surface_{~2 mm}/saturated signal method was used to distinguish the degree of bleaching of cobble samples， and SAR and SGC methods were used to preliminarily estimate the equivalent dose （D_e） and their overestimations. Then， the relationship between the characteristics of cobble samples （roundness， sphericity， color， grain size， relative grain size， average diameter of cobbles， etc.） and the degree of bleaching was explored， to find well bleached cobbles and their characteristics. The results indicated that there are cobbles showed characteristics of being bleached at most sampling sites. On average， 20.6% of cores of the buried cobbles were well bleached， and show very low D_e overestimations. Samples from different types of sedimentary environment show different degrees of bleaching. The cobble samples from the top of lateral moraine have the best degree of bleaching， followed by glaciofluvial terrace and modern glaciofluvial cobbles. The glaciofluvial cobbles collected from small depression between modern recessional moraines in front of modern glacier show the worst degree of bleaching， and D_e is relatively seriously overestimated. Granite cobbles with poorer roundness， lower sphericity and lighter color were better bleached. To sum up， the degree of bleaching of glacial cobbles is related to sedimentary environment， deposit process， transport distance and characteristics of cobbles. The above conditions should be comprehensively considered when sampling cobbles for rock luminescence burial dating.