Early diagenetic imprints and U–Th isotope systematics of fossil land snail shells from the Chinese Loess Plateau     

《Quaternary Geochronology》2023

The loess-paleosol sequence on the Chinese Loess Plateau provides a unique archive that records climate change in East Asia in the Quaternary, yet absolute dating of the loess deposits is challenging due to the lack of directly datable materials. Fossil land snail shells, which are made from aragonite, are widely preserved in the loess deposits and have long been used to reconstruct past environmental changes. U-series dating of fossil land snail shells has the potential to provide a route for absolute dating of the loess deposits but remains largely unexplored. In this study, we present the first systematic investigation on the U-series isotope geochemistry as well as the early diagenetic imprints of fossil land snail shells (Cathaica sp.) from the Mangshan loess-paleosol sequence in Henan province, central China. Several geochemical techniques, including Raman microscopy, SEM, LA-ICPMS, LA-MC-ICPMS, solution-MC-ICPMS, and AMS ¹⁴C dating, were employed to investigate the mineralogy, chemical and isotopic compositions of both modern and fossil snail shells to micrometer level. Our results show that the fossil Cathaica sp. shells are overall characterized by a higher degree of porosity and elevated contents of organic matter compared to live-collected shells of the same species. The layers with higher porosity and organic matter content in the fossil Cathaica sp. shell are also found to be enriched in Na, Mg, Mn, Ba, and U, indicating diffusion and adsorption of these elements by specific surface binding sites of either aragonitic lattice or organic compounds of the fossil shell. Combining in-situ measurements using LA-MC-ICPMS with solution U-series determination, we further demonstrate that fossil Cathaica sp. shell is relatively homogeneous regrading both [²³⁴U/²³⁸U] and [²³⁰Th/²³⁸U] values although the distribution of U in the fossil shell is sample-specific. The comparison of different dating results suggests that the calculated apparent closed system U–Th ages are all systematically younger (∼6000 to 13,000 years) than the corresponding shell ¹⁴C ages and quartz SAR (single-aliquot regenerative-dose) ages from the Mangshan section. We suggest that the underestimation of U–Th ages of fossil Cathaica sp. shells is very likely caused by diagenetic uptake of U that started immediately after the burial of the shell and effectively ceased when the fossil shell was isolated from the pore waters due to persistent deposition of eolian dust at the Mangshan section. Our work on both modern and fossil Cathaica sp. shells thus provides detailed morphological and geochemical characterization for the diagenetic alteration of fossil snail shells and suggests that U-series dating of fossil land snail shells may provide age constraints for dust deposits in the semi-arid region although the timing of early diagenetic U-uptake by the fossil shells need to be better quantified for reliable age determination.  相似文献   

某些镁硼酸盐溶解及相转化的研究   总被引：2，自引：0，他引：2       下载免费PDF全文

孙柏  宋彭生 《盐湖研究》1999,7(2):16-22

进行了章氏硼镁石和三方硼镁石在纯水以及某些盐溶液中的溶解平衡及相转化研究。首次发现三方硼镁石在水中的转化是分两个阶段进行,从而证明尼古拉耶夫等对２５℃时ＭｇＯ－Ｂ２Ｏ３－Ｈ２O体系的研究中,三方硼镁石与章氏硼镁石的共饱点实际上是三方硼镁石向多水硼镁石发生转化的一个中间点。报导了水溶液中的某些盐类对章氏硼镁石和三方硼镁石溶解平衡及相转化有一定的增溶或阻滞相变的作用。从这些溶解转化规律中可以对盐湖镁硼酸盐的形成及其转化规律提供物理化学解释。  相似文献   

自动气象站常见的异常问题及解决方法     

黄军 《气象研究与应用》2006,27(2):54

对自动气象站常见的异常问题进行分析,并对这些异常问题提出解决方法。  相似文献   

张北地震近场观测资料的初步解释   总被引：9，自引：0，他引：9  

石金虎  赖晓玲 《中国地震》1999,15(2):151-158

本文对１９９８年１月１０日张北６．２级强震的余震观测资料进行了初步处理。测定了２０５个ＭＬ≥０．５的地震的震源位置,发现其余震多集中在一个长１０余公里,宽５￣８ｋｍ的北东向条带内;计算了较大余震的震源机制解,推测引起主震的断裂带为北东向断裂;另外,对Ｐ波记录作了频谱分析,得到其拐角频率为１０Ｈｚ左右。  相似文献   

Computation of synthetic seismograms and their partial derivatives for heterogeneous media with arbitrary natural boundary conditions using the Direct Solution Method     

Robert J. Geller  Takao Ohminato 《Geophysical Journal International》1994,116(2):421-446

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Kepler方程解法的评估     

岳锦海  黄天衣 《紫金山天文台台刊》1997,16(3):164-174

本文从初值公式和修正法两方面对近二三十年来关于解椭圆Kepler方程的各种方法做了全面的总结。列举、比较了多种初值和修正法。Markley初值离真解最近。通过在Pentium 586上的大量实验,我们认为,三阶Halley方法和Odell与Gooding初值或Nijenhuis初值构成最快的算法,且能保证收敛性。  相似文献   

Inversion and III-Posed Problem Solutions in Atmospheric Remote Sensing     

Huang Sixun 《大气科学进展》1996,13(4):489-504

With the swift advances in earth observation, satellite remote sensing and application of atmospheric radiation theory have been developed in the past decades, atmospheric sensing inversion with its algorithms is getting more and more importance. It is known that since a remote sensing equation falls into an integral equation of the first kind, thus leading to the fact that it is ill-posed and particularly the solution is unsteady, tremendous difficulties arise from the retrieval. This paper will present a simple review on the inversion techniques with some necessary remarks, before in-troducing the successful efforts with respect to such equations and the encouraging solutions achieved in recent dec-ades by researchers of the world.  相似文献   

Inversion and III-Posed Problem Solutions in Atmospheric Remote Sensing     

黄思训 《大气科学进展》1996,(4)

With the swift advances in earth observation,satellite remote sensing and application of atmospheric radiation theory have been developed in the past decades,atmospheric sensing inversion with its algorithms is getting more and more importance.It is known that since a remote sensing equation falls into an integral equation of the first kind,thus leading to the fact that it is ill-posed and particularly the solution is unsteady,tremendous difficulties arise from the retrieval.This paper will present a simple review on the inversion techniques with some necessary remarks,before introducing the successful efforts with respect to such equations and the encouraging solutions achieved in recent decades by researchers of the world.  相似文献   

充分发挥资源优势,大力开发岩盐矿产   总被引：1，自引：0，他引：1  

张永康  范广勤 《江苏地质》1996,20(4):193-198

我国目前的盐业生产主要以海盐为主，由于海盐生产受气候和土地条件的严重制约，因此，多年来我国的盐业生产一直处于一种不稳定的状态中，纵观世界盐业近几十年来的发展方向，海盐在大幅度减少，而岩盐生产却和到了大幅度的发展，并逐渐取代了海盐。与海盐相比，岩盐具有很多优势，因此，在综合分析世界盐业发展的基础上提出，我国应大力发展岩盐生产，最终实现以岩盐取代海盐的战略目标。  相似文献   

Effect of alcohol and polyglycol ether frothers on foam stability,bubble size and coal flotation     

Ashiwani Kumar Gupta  P.K. Banerjee  Arun Mishra  P. Satish  Pradip 《International Journal of Mineral Processing》2007

The frothers of alcohol family (MIBC and Alpha-terpineol) were compared with polyglycol ethers (DF-1012) in terms of two phase characterization parameters like foamability, foam stability, surface activity and bubble size distribution. In this research, fundamental two phase frother characterization parameters were linked with three phase coal flotation behavior.  相似文献