In situ cosmogenic Be in olivines and pyroxenes     

P.-H. Blard  D. Bourls  R. Pik  J. Lav 《Quaternary Geochronology》2008,3(3):196-205

This study proposes an efficient new cleaning procedure for measuring in situ cosmogenic ¹⁰Be in olivines and pyroxenes. This chemical routine is specially designed to decontaminate the abundant meteoric ¹⁰Be from these minerals. The method was tested on mafic minerals from basaltic flows of Mt. Etna volcano and from Hawaiian flows and moraines. A sequential dissolution test shows that ¹⁰Be concentrations decrease with the number of cleaning steps until reaching a constant value. This is a necessary condition to demonstrate the efficiency of the method in properly decontaminating samples of meteoric ¹⁰Be. Moreover, cross-calibration with cosmogenic ³He measured within the same samples yielded a sea level high-latitude production rate of 4.5±0.4 at g⁻¹ a⁻¹ for cosmogenic ¹⁰Be in mafic minerals. This rate is within 1σ uncertainty of empirically or model-derived rates for ¹⁰Be on the same targets. Such concordance supports the consistency of the new method.  相似文献   

A simulation approach to quantify the parameters and limitations of the radiocarbon wiggle-match dating technique     

《Quaternary Geochronology》2023

Worldwide, radiocarbon (¹⁴C) wiggle-match dating is increasingly used to produce high-resolution, ‘near-absolute’, chronologies in a range of different contexts, yet the exact properties and limitations of the technique are not well understood. Here we present the results of extensive and systematic simulations that allow the precision limits of wiggle-match dating to be quantified for different time periods. We have also been able to quantify the effect of modeling decisions on possible precision in terms of how many measurements to make, how far apart to space them, and which calibration curve to employ. While recent trends towards large numbers of annually spaced measurements can improve precision, the effect is generally small, except when the dated sequence falls on a plateau in the calibration curve. Finally, we demonstrate that wiggle-matching against an unsmoothed record of atmospheric ¹⁴C can provide better precision than wiggle-matching against the smoothed IntCal20 or SHCal20 curves. We argue, however, that until intra-hemispheric variation in ¹⁴C is better understood, the hemispheric averages provided by IntCal20 and SHCal20 will be the more appropriate datasets for most wiggle-match applications.  相似文献   

山西永济地震台BBVS-60地震计标定异常原因分析     

邰垣东  张红秀  高志伟 《山西地震》2019,(3):54-56

针对山西永济地震台BBVS-60地震计在脉冲标定及正弦标定中出现的异常进行分析,排查原因,找出地震计和数据采集器在安装、使用及运输过程中存在的问题,进行解决,并对今后的仪器运维工作提出合理的改进建议。  相似文献   

APOD卫星大气密度数据处理与标校   总被引：2，自引：0，他引：2       下载免费PDF全文

李勰  徐寄遥  唐歌实  陈光明  满海钧  刘舒莳  李永平 《地球物理学报》2018,61(9):3567-3576

APOD卫星是我国首颗以热层大气密度探测与精密定轨为科学目标的微纳卫星,搭载大气密度探测器、双频GNSS接收机等载荷,于2015年9月20日发射入轨,2015年10月27日进入轨道高度460 km、轨道倾角97.4°、降交点地方时6∶20的工作轨道,各项载荷随即展开例行观测.本文给出了APOD卫星大气密度探测器的基本原理和数据处理流程,采用基于双行根数（TLE）反演获取的密度数据,对2015年12月至2016年12月的就位探测数据进行了标校,并与经验密度模式进行了比较.结果表明,反演密度与APOD卫星就位探测数据的线性相关性达到0.943,采用线性拟合与二次函数拟合的残差水平基本相当.两种不同方法标校密度相对于NRLMSIS00模式日均值误差的均值和标准偏差为10.1%、18.2%和5.1%、17.1%,二次函数标校略优于线性标校;相对于JB2008模式日均值误差的均值和标准偏差为0.6%、14.9%和3.9%、16.9%,线性标校略优于二次函数标校.总体而言,APOD卫星大气密度就位探测数据与常用经验模式精度基本一致,可为开展大气密度变化规律及应用研究提供数据基础.  相似文献   

Chronology of Early to Mid-Pleistocene sediments in the northern North Sea: New evidence from amino acid and strontium isotope analyses     

《Quaternary Geochronology》2022

Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka.Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.  相似文献