【摘要】 能够利用TIMS-U系方法精确定年,是石笋应用于古环境重建的重要优势。但石笋实际测定的TIMS-U系年龄往往出现与石笋自然生长规律不符合的异常序列,从而限制了大批石笋的进一步研究。以湘西龙山莲花洞LL1石笋为例,发现并从地球化学的角度解释了文石向方解石转化,以及方解石次生结晶加大的结构构造转变过程中,石笋具有238U、230Th含量明显减小,石笋测定年龄比实际年龄偏小的趋势。并在排除污染等条件下,以230Th/238U为校正指标,假设其损失率分别为1%、10%、50%,对LL1进行TIMS-U系法测年结果校正。结果发现,230Th/238U损失的百分数与年龄偏小的百分数相差不多,且相同230Th/238U损失比例下,石笋年龄越老,实测年龄比实际年龄却偏年轻。该研究为今后校正石笋异常年龄序列,建立石笋正常、准确年龄时标提供了思路。更多还原

【Abstract】 Stalagmite has the advantage of high precision dating in paleoclimate reconstruction because of the advance in TIMS-U series dating. However, the measured ages of stalagmite usually don’t accord with the nature rule of stalagmite growth, which makes a lot of measured ages can’t be used. Taking stalagmite LL1 got in the Lianhua Cave in Longshan, west of Hunan province as an example, this study found that the quantity of 238 U、230Th reduce and measured ages of stalagmite grow young in the process of the change of stalagmite structure, especially the process of wenshi changed into calcite and calcite re-crystallization. What’s more, based on the condition that eliminates potential affecting factors such as sample pollution, this study calculated the calibration age of LL1 the on the assumption that the 230 Th/238U lost rate is 1%,10%,50% respectively. The result shows that the rate of lost 230 Th/238U is similar to the rate of reduced age caused by the change of stalagmite structure. In addition, we find that the older the stalagmite, the younger measured ages grow compared with the real ages of stalagmite. Therefore, The study on the method of the correction of TIMS-U series ages helps to establish normal and precise stalagmite chronology.更多还原