Nature and provenance of the sandstone used for Bayon style sculptures produced during the reign of Jayavarman VII

Under Jayavarman VII (1182/83-ca.1218 CE) the Khmer empire reached its apex, leaving a heritage of major construction works and unique artistic production. The stone materials of several sculptures produced under his reign were characterized and compared to possible geological sources in northern and eastern Cambodia. The data suggest that a specific type of sandstone, rich in volcanic detritus, was deliberately selected and quarried from a Triassic sedimentary sequence exposed far from Angkor, the main political and economic center at that time.     

Salt weathering of sandstone at the Angkor monuments,Cambodia: identification of the origins of salts using sulfur and strontium isotopes

The Angkor monuments in northwestern Cambodia, which are primarily made of sandstone, are suffering from deterioration due to salt weathering. In order to elucidate the sources of the salts and salt weathering process, this paper analyzed bulk chemical compositions and S (sulfur) and Sr (strontium) isotopic ratios for the salts and surrounding environmental materials. At places where bats inhabit the structures, various kinds of sulfate and phosphate salts are formed on the surface of the sandstone. The results of the analysis demonstrate that the S and P (phosphorus) components in the salts are primarily derived from bat guano. Moreover, Ca (calcium), which is the major element in the salts, is suggested to be derived from both bat guano and the sandstone. The isotopic data strongly suggests that bat guano is related to salt weathering. Removal of these animal excrements is essential for future conservation of these monuments. On the other hand, exfoliation of sandstone commonly occurs due to crystallization of calcite (CaCO₃) on platform surfaces of pyramid-type monuments. A large amount of Ca in calcite is suggested to be derived from calcite cement of the building sandstone.     

一种新的壁画修复材料黏结性评价装置及应用研究

为了可直接考察修复材料对壁画颜料层-地仗层(地仗层-地仗层)的黏结性,借鉴敦煌石窟泥塑制作"木骨泥胎"原理和涂层、黏接剂附着力和黏结强度测试方法,设计了一套拉拔模具。该装置解决了壁画修复材料评价中黏结界面错位,客观数据获取难,适用性差,耗时长等问题。试验测定了6种常用修复材料在质量浓度5%条件下的黏结强度,确定其黏结性强弱顺序为:纯丙乳液聚乙烯醇PVA-1788白乳胶硅丙乳液明胶(Paraloid b-72)。基于试验数据,提出选择修复材料及工作浓度时,应以接近原有胶结材料(明胶)黏结强度为宜。     

微波技术在砖石质文物含水率检测中的应用

水是造成砖石质文物劣化的主要因素之一,因此探明其在文物内部的分布、运移规律是开展保护研究的重要基础。微波技术在检测材料内部的水分含量方面表现出较好前景,但在文物保护领域还未普遍应用。基于此,本研究首先介绍了微波技术的理论基础和相关仪器,并选取山西省的长春玉皇庙为对象,针对砖石材料的内部含水率开展了室内样块检测和现场墙体检测。结果表明,微波技术能够较为准确地揭示出文物内部的空间含水率分布规律,这对于研究其病害成因等具有重要作用。此外,与其他多种无损检测技术相比,微波技术检测材料含水率的优点更多,值得文物工作者进一步研究与应用。     

Discussion on the variation characteristics of water content of Quaternary soil cover on the top of Yungang Grottoes and the problem of water seepage in caves北大核心

为研究云冈石窟顶部土壤覆盖层的含水率变化情况,建设了土壤环境监测网收集云冈石窟土壤含水率实时监测数据,并分析其时空变化特征及影响因素。结果表明,平坦地形条件下云冈石窟顶部第四纪土壤覆盖层含水率时空变化特征明显:年变化具有周期性,垂向上随深度逐层降低(冬季除外)。春、夏季土壤含水率抬升、储水,秋、冬季下降、失水;在春、夏日土壤含水率呈白天上升、夜晚下降趋势,秋、冬日则呈白天下降、夜晚也下降趋势。土壤含水率时刻处于不停的运动变化之中,受温度、大气降水、微地形等众多因素影响,山体边坡浅层土壤可能为侧向饱和流的入渗通道。降雨对土壤含水率的影响深度与实际入渗深度不一致。云冈窟内顶板及岩壁上部、中部含水率主要受降雨渗透窟顶土壤层、沿岩体裂隙通道进入洞窟的渗漏水控制,而岩壁底部含水率更多受窟前不饱带和与地下毛细水的影响。多年的防水实践也证明云冈洞窟渗漏水主要来自于石窟顶部及附近区域。防渗排水始终是云冈洞窟渗漏水治理的主导思路,建议应根据窟顶土壤厚度、地形地貌和遗址分布等分区治理,充分发挥土壤的防渗作用,减少对土壤覆盖层的过度干预。防渗层材料在具有防渗作用的前提下,应具备一定的透气性,满足“洞窟—覆盖层—大气环境”之间的水汽循环。     

Evaluating effects of chemical weathering and surface contamination on the in situ provenance analysis of building stones in the Cuzco region of Peru with portable XRF

As the only type of instrument capable of determining artifact geochemistry in a wide variety of settings, portable X-Ray Fluorescence (PXRF) may be frequently utilized as probably the best option for collecting data when removal of objects in part or in whole is unfeasible. However, using PXRF in circumstances where sample selection and preparation diverge from standards developed for lab-based instrumentation requires assessing the impact of new and potentially limiting factors to establish the validity of the method in these new contexts. Here we examine the effects of surface contamination and chemical weathering on the ability to assess provenance of igneous building stones used in the Cuzco region of Peru. Surface contamination was assessed through comparing low-impact cleaning methods on diorite and andesite blocks, and weathering was examined by comparing weathered vs. fresh surfaces of samples from two andesite quarries. In general, the lightest elements were most impacted by contamination and weathering while measurements of many of the heavier elements commonly used in provenance studies were relatively unaffected. Concentrations of Pb and Zn were problematic in the urban context of Cuzco because of pollution. Ability to determine provenance of building stones within those limitations (i.e., the validity of this application of PXRF) was demonstrated in a preliminary study by comparing measurements from uncleaned, exposed building stones in the region to fresh quarry samples.     

Computing geochemical mass transfer and water/rock ratios in submarine hydrothermal systems: implications for estimating the vigour of convection

A method of calculating chemical water/rock ratios is presented that enables the estimation of fluid velocities in open, flow‐through hydrologic systems. The approach is based on relating the gain/loss of a chemical species per kilogram of solid phase to the loss/gain of that species in the fluid phase, integrated across a specified length of the flowpath. After examining the underlying approximations of the approach using a one‐dimensional model of seawater moving through a basalt under nonisothermal conditions, the method is applied to representative zones within a two‐dimensional hydrothermal convective system. The method requires that regions within the flow system can be identified in which the direction of flow is steady for an extended period of time. Estimates of fluid velocity are spatial and temporal averages for the length of the flowpath used in the calculation. The location within the flow system and the nature of the alteration reactions determine which species can provide reliable values of the chemical water/rock ratio and useful estimates of fluid velocities. Over the length of the flowpath considered, the calculation of water/rock ratios works best when a species is controlled by a single reaction. Accurate estimates are favoured if the concentration profile of a species along the flowpath increases or decreases monotonically. If the length of the flowpath extends over more than one reaction zone, then erroneous estimates of the water/rock ratio and fluid velocity are more likely. Model calculations suggest that the quartz/silica system should provide reliable estimates for fluid velocity under a wide range of temperature and flow conditions, in particular in those regions of a system at or near quartz equilibrium, so that the aqueous silica concentration is buffered by quartz and correlated with the temperature distribution.