Bayesian analysis of De distributions in optical dating: Towards a robust method for dealing with outliers     

《Quaternary Geochronology》2022

In optical dating, especially single-grain dating, various patterns of distributions in equivalent dose (D_e) are usually observed and analysed using different statistical models. None of these methods, however, is designed to deal with outliers that do not form part of the population of grains associated with the event of interest (the ‘target population’), despite outliers being commonly present in single-grain D_e distributions. In this paper, we present a Bayesian method for detecting D_e outliers and making allowance for them when estimating the D_e value of the target population. We test this so-called Bayesian outlier model (BOM) using data sets obtained for individual grains of quartz from sediments deposited in a variety of settings, and in simulations. We find that the BOM is suitable for single-grain D_e distributions containing outliers that, for a variety of reasons, do not form part of the target population. For example, D_e outliers may be associated with grains that have undesirable luminescence properties (e.g., thermal instability, high rates of anomalous fading) or with contaminant grains incorporated into a sample when collected in the field or prepared in the laboratory. Grains that have much larger or smaller D_e values than the target population, due to factors such as insufficient bleaching, beta-dose heterogeneity or post-depositional disturbance, may also be identified as outliers using the BOM, enabling these values to be weighted appropriately for final D_e and age determination.  相似文献   

小冰期时中国南方地区降水模式的差异研究   总被引：1，自引：0，他引：1  

肖思雅  李廷勇  陈朝军  黄冉  王涛  吴尧  徐玉珍  邱海英  黄洋阳  李俊云 《地质论评》2021,67(1):56-67

小冰期是过去一千年中全球气候变化的重要事件之一。关于小冰期时中国季风区和西风影响区气候变化的对比研究众多,但是缺乏中国南方地区降水模式时空差异的研究,难以了解中国南方地区降水变化规律。为了系统地了解小冰期时中国南方地区降水的复杂性,本文将中国南方地区划分为东南—华南沿海地区、中部地区以及西南地区三个区域,总共选取了19条高分辨率的古气候记录进行对比研究,主要有以下几点认识:(1)相对于中世纪暖期而言,小冰期期间中国南方东南—华南沿海地区的气候偏湿,这可能与雨带在中国南方的滞留时间延长和沿海地区受台风的影响增强有关。(2)中国中部地区秦岭南麓和神农架高山林区在小冰期时期主要呈"冷湿"的模式,差异在于秦岭南麓区域主要在小冰期中后期偏湿,这与中部其他区域偏"冷干"的模式不同。这种区域差异可能是由于地形地势和大气环流的复杂性导致。(3)中国西南地区受印度夏季风和东亚夏季风的共同影响,且该区域地形复杂,其气候变化在小冰期时期存在更加明显的空间差异,没有呈现出比较一致的降水模式。与小冰期期间的降水变化不同的是,近30年东南—华南沿海地区除了台湾和雷州半岛,其他区域降水明显减少,可能受气温和人类活动等因素的影响。通过结合高分辨率的古气候记录,我们系统分析了中国南方小冰期的干湿模式在时空上的差异及其可能的影响因子,这对于认识小冰期时中国南方不同区域降水的复杂性及未来旱涝灾害的防控具有一定意义。  相似文献   

Unveiling buried aeolian landscapes: reconstructing a late Holocene dune environment using 3D ground-penetrating radar     

Luis Rees-Hughes  Natasha L. M. Barlow  Adam D. Booth  Landis J. West  George Tuckwell  Tim Grossey 《第四纪科学杂志》2021,36(3):377-390

Across the UK, sandy beaches and dunes protect coastal infrastructure from waves and extreme water levels during large-scale storms, while providing important habitats and recreational opportunities. Understanding their long-term evolution is vital in managing their condition in a changing climate. Recently, ground-penetrating radar (GPR) methods have grown in popularity in geomorphological applications, yielding centimetre-scale resolution images of near-surface stratigraphy and structure, thus allowing landscape evolution to be reconstructed. Additionally, abrupt changes in palaeo-environments can be visualized in three dimensions. Although often complemented by core data, GPR allows interpretations to be extended into areas with minimal ground-truth control. Nonetheless, GPR data interpretation can be non-intuitive and ambiguous, and radargrams may not initially resemble the expected subsurface geometry. Interpretation can be made yet more onerous when handling the large 3D data volumes that are facilitated with modern GPR technology. Here we describe the development of novel semi-automated GPR feature-extraction tools, based on ‘edge detection’ and ‘thresholding’ methods, which detect regions of increased GPR reflectivity which can be applied to aid in the reconstruction of a range Quaternary landscapes. Since reflectivity can be related to lithological and/or pore fluid changes, the 3D architecture of the palaeo-landscape can be reconstructed from the features extracted from a geophysical dataset. We present 500 MHz GPR data collected over a buried Holocene coastal dune system in North Wales, UK, now reclaimed for use as an airfield. Core data from the site, reaching a maximum depth 2 m, suggest rapid vertical changes from sand to silty-organic units, and GPR profiles suggest similar lateral complexity. By applying thresholding methods to GPR depth slices, these lateral complexities are effectively and automatically mapped. Furthermore, automatic extraction of the local reflection power yields a strong correlation with the depth variation of organic content, suggesting it is a cause of reflectivity contrast. GPR-interpolated analyses away from core control thus offer a powerful proxy for parameters derived from invasive core logging. The GPR data collected at Llanbedr airfield highlight a complex dune system to a depth of 2.8 m, probably deposited in several phases over ~700 years, similar to elsewhere in North Wales.  相似文献   

Geoarchaeological evidence on a Late Bronze Age earthquake,Ohrid Basin (North Macedonia)     

J. Hošek  M. Verčík  P. Pokorný  J. Beneš  V. Komárková  T. Radoměřský  N. Atanasoska  V. Todoroska  P. Ardjanliev 《第四纪科学杂志》2021,36(6):1003-1012

Geoarchaeological investigations on the northeastern shore of Lake Ohrid revealed 3.5 m thick deepwater lacustrine sediments overlying terrestrial vegetation macrofossils, worked wood and abundant potsherds dated to the Late Bronze Age (LBA). Distinct contact of deepwater sediment with the sub-aerial weathered limestone bedrock point to a sudden increase in lake level. According to radiocarbon data, catastrophic flooding occurred shortly after 1214 yr bc. Because the area is located in a highly active seismic zone, we propose that this event was caused by tectonically induced, metre-scale coseismic subsidence related to faults bordering the Ohrid alluvial plain. Moreover, this event coincides well with a dramatic switch in the habitation and settlement strategy in the region. More important, however, is the finding that the age of the proposed massive tectonic event and change in habitation lies within the interval of the proposed ‘earthquake storm’ in the eastern Mediterranean dated to 1225–1175 bc. As the Ohrid-Korça zone belongs to the same tectonic province, a relationship between the abovementioned earthquakes and the proposed event can be expected. This research therefore might provide the first direct evidence of a large-scale earthquake event linkable to the LBA collapse of Europe's first urban civilisation in the Aegean.  相似文献   

A chironomid-based reconstruction of summer temperatures in NW Iceland since AD 1650     

P.G. Langdon  C.J. Caseldine  I.W. Croudace  S. Jarvis  S. Wastegrd  T.C. Crowford 《Quaternary Research》2011,75(3):451-460

Few studies currently exist that aim to validate a proxy chironomid-temperature reconstruction with instrumental temperature measurements. We used a reconstruction from a chironomid percentage abundance data set to produce quantitative summer temperature estimates since AD 1650 for NW Iceland through a transfer function approach, and validated the record against instrumental temperature measurements from Stykkishólmur in western Iceland. The core was dated through Pb-210, Cs-137 and tephra analyses (Hekla 1693) which produced a well-constrained dating model across the whole study period. Little catchment disturbance, as shown through geochemical (Itrax) and loss-on-ignition data, throughout the period further reinforce the premise that the chironomids were responding to temperature and not other catchment or within-lake variables. Particularly cold phases were identified between AD 1683–1710, AD 1765–1780 and AD 1890–1917, with relative drops in summer temperatures in the order of 1.5–2°C. The timing of these cold phases agree well with other evidence of cooler temperatures, notably increased extent of Little Ice Age (LIA) glaciers. Our evidence suggests that the magnitude of summer temperature cooling (1.5–2°C) was enough to force LIA Icelandic glaciers into their maximum Holocene extent, which is in accordance with previous modelling experiments for an Icelandic ice cap (Langjökull).  相似文献   

山东长岛地区蓬莱群辅子夼组碎屑锆石年龄谱研究   总被引：19，自引：13，他引：6  

初航  陆松年  王惠初  相振群  刘欢 《岩石学报》2011,27(4):1017-1028

山东烟台长岛地区出露的蓬莱群辅子夼组浅变质沉积岩主要为变质石英砂岩夹变质粉砂岩和变质粘土岩。前人对蓬莱群的沉积时代存在较大争议, 本文根据长岛地区蓬莱群辅子夼组碎屑锆石年龄谱资料, 将辅子夼组的地层时代置于新元古代。碎屑锆石中出现1600Ma和1200~1100Ma左右两个年龄峰值, 后者表明辅子夼组曾接受来自具有格林威尔期构造热事件物源区的碎屑物质。这一物源区所反映的地质演化特点既不同于华北陆块, 也不同于扬子陆块, 应引起高度重视和进行深入的探索。  相似文献   

西天山古元古代木札尔特岩群地质特征及时代厘定   总被引：2，自引：1，他引：1  

于海峰  王福君  潘明臣  梁有为  郭洪方  王志军 《新疆地质》2011,29(1):20-25

西天山木札尔特岩群发育于塔里木原始古陆台内毗邻陆缘活动带,为一套角闪岩相中深变质岩系,主要岩石组合为变粒岩-浅粒岩-片麻岩-斜长角闪岩-大理岩等,局部受韧性变形改造形成各类糜棱岩系,原岩为中基性火山熔岩-火山碎屑岩-火山碎屑沉积岩夹碳酸盐岩建造.由于缺少古生物化石,其地层时代主要依据区域地层对比和同位素年代学数据进行确定.笔者应用钐钕全岩等时线定年法,在该岩群斜长角闪岩中获得(1966±93)Ma的同位素年龄,这是迄今为止,西天山范围内该岩群内获得的最古老同位素年龄,代表了其成岩年龄.据国际地层表(2000)关于古元古界造山系2 050~1 800 Ma的划分方案,笔者最终将西天山木札尔特岩群成岩时代厘定为古元古代造山纪.  相似文献   

The status of artisanal fishing in El Salvador     

《Marine Policy》2015

El Salvador is one of the most environmentally degraded nations in Latin America, but the declining fishing industry is under-studied compared with deforestation and landuse. This paper examines the reactions to fish stock decline of two generations of fishers in La Union, El Salvador on the Golfo de Fonseca, one of the most important fishing areas in Latin America, using face to face interviews and questionaires. Both older (>35 years) and younger (<36 years) fishers supplemented their income with trading, farming and loans from their relatives in the United States. All older fishers reported larger fish catches five and ten years previously than at present. Previously, fishers caught more fish, but significantly more younger fishers than older fishers reported their fathers caught more fish than they did, indicating an increasing gap in fish catches in recent decades. More younger fishers than older fishers had fathers or male kin who were also fishers, indicating young men were less likely to join fishing without a parent or kin already involved. Minorities of both older and younger fishers engaged in supplementary activities. Environmental degradation disuaded fishers from switching to farming or hunting. The findings are similar to findings elsewhere on the decline of fish resources and generational gaps in environmental knowledge, but differ in that some other studies report fewer opportunities for fishers to access alternative or complementary activities. These findings are relevant to Latin American studies, considering the great value of the Golfo de Fonseca to the livelihoods of Central America.  相似文献   

Stained Glass and Climate Change: How are they Connected?     

C. T. Simmons  L. A. Mysak 《大气与海洋》2013,51(2):219-240

As expressions of regional architecture, sacred (Christian) Gothic structures often possess several adaptations to their prevailing climate regime. The late medieval (Gothic) period in northern Europe is also, according to the evidence presented here, marked by a transition from warm and sunny to cooler and cloudier conditions. It is within the context of this climate change that we consider one of the most important features in Gothic churches—interior daylighting—during the transitional period (the thirteenth to the end of the fifteenth centuries) between the Medieval Warm Period (MWP) and the Little Ice Age (LIA). This paper seeks to determine whether increasingly cloudy conditions over northern continental Europe, in part due to a shift in North Atlantic Oscillation (NAO) phase, may have influenced the use of more white glass in the fourteenth century. To the best of our knowledge, this is the first time an extensive daylighting dataset has been collected in medieval sacred interiors. From an analysis of these illuminance and luminance data collected in European churches and cathedrals, we find that high-translucency glazing is associated with limited lighting gains compared to full-colour programs under sunny conditions but substantial lighting improvements (up to an order of magnitude) for cloudy conditions. Additionally, we find that backlighting from direct sunlight produces significant obscuration of some of the iconographical glass when interiors are dominated by high-translucency glazing, further suggesting that these interiors are not ideal for sunny conditions.

[Traduit par la rédaction] Étant donné que les cathédrales gothiques (chrétiennes) sont des expressions de l'architecture régionale, plusieurs adaptations au climat de l’époque y ont souvent été apportées. À la fin du Moyen Âge (période du gothique), le climat chaud et ensoleillé en Europe du nord continentale a fait place à un climat plus froid et plus nuageux, d'après les preuves que nous présentons ici. C'est donc dans la perspective de ce changement climatique que nous nous penchons sur l'un des éléments les plus importants de l'architecture des églises gothique, l’éclairage naturel intérieur, durant la transition (du XIII^e siècle à la fin du XV^e siècle) entre la période chaude médiévale (MWP) et le petit âge glaciaire (LIA). Dans le présent article, nous voulons notamment évaluer si l'utilisation de plus en plus fréquente du vitrail blanc au XIV^e siècle s'expliquerait par les conditions plus nuageuses en Europe du nord continentale, attribuables en partie à un changement dans l'indice d‘oscillation nord-atlantique (NAO). À notre connaissance, c'est la première fois qu'une série élaborée de données a été recueillie sur l’éclairage à l'intérieur des cathédrales gothiques. L'analyse des données sur l’éclairement lumineux et la luminance lumineuse dans les églises et les cathédrales d'Europe nous permet de constater que le verre très translucide présente peu d'avantages comparativement au verre plein coloré dans des conditions ensoleillées, mais qu'il améliore considérablement l’éclairage dans des conditions nuageuses (jusqu’à 10 fois). De plus, nous constatons que l’éclairage en contre-jour produit par l'ensoleillement direct obscurcit une partie des pièces de verre ornées d'icônes lorsque le verre très translucide domine à l'intérieur, ce qui confirme une fois de plus qu'il ne s'agit pas d'un aménagement idéal pour les conditions ensoleillées.  相似文献   

Issues in the absolute chronology of the Early–Middle Bronze Age transition in Sicily and southern Italy: a Bayesian radiocarbon view     

GIANMARCO ALBERTI 《第四纪科学杂志》2013,28(6):630-640

  相似文献