一种计算沉积速率的新方法——宇宙尘埃特征元素法

Using the Characteristic Elements from Meteoritic Must in Strata to Calculate Sedimentation Rate

地球每时每刻都在接受宇宙尘埃的沉降 ,且其年沉降量相对稳定 ,加之宇宙尘埃中的Ir、Co等特征元素的平均含量较恒定 ,因此沉积物中宇宙尘埃特征元素Ir、Co的丰度值能够体现出沉积物的沉积速率。当沉积速率较慢时 ,沉积物中宇宙尘埃特征元素的丰度值较大 ,反之 ,则较小。本文在前人工作的基础上 ,对利用宇宙尘埃特征元素计算沉积速率的方法和原理进行了探讨 ,并运用该方法对山东临朐N/E界线地层的沉积速率进行了实例研究。与传统方法相比 ,依据宇宙尘埃特征元素在地层中的分布特征计算沉积速率具有更好的实用性和准确性。

In the study of sedimentology,one of the most fundamental quantities that geoscientists seek to measure is the sedimentation rate,and it is crucial to a complete understanding of depositional process. The meteoritic dust is a kind of extraterestrial material with high abundance of iridium and cobalt.Most people think that the deposition quantity of meteoritic dust per year is almost constant on earth surface,and the average abundance of some characteristic elements such as Ir and Co in meteoritic dust are fixed,so there is a correlation between sedimentation rate and Ir (or Co) concentration.The abundance of Ir (or Co) in the sedimentary sample with low sedimentation rate is higher than in the sample with high sedimentation rate.According to this,the abundance of the element Ir or Co in sediment can be used to measure the deposition rate as a dating tool.Based on the previous work,the theory and method of using characteristic element from meteoritic dust ot calculate sediment rate have been suggested,and the formulae can be pariticularly expressed as follows: V s= V (Co)/｛ ρ ×[ A (Co)- w (Co)× A ”(Co)]｝ where V s is the sedimentation rate of the sample which we want to calculate, V (Co) is the deposition rate of Co from meteoritic dust (6.48×10 -7 g/cm 2a), ρ is the density of the sample, A (Co) is the total abundance of Co in the sample, A ”(Co) is the abundance of Co in the source rock and w (Co) is contribution coefficient of Co from the terrigenious sources. Using this method,the sedimentation rates of the Eogene-Neogene section in Linqu County of Shandong Province has been measured as a case in this paper. Comparing with common methods,the method of using characteristic element from meteoritic dust to calculate sedimentation rate is more practical and accurate.