R/S Analyses of Some Geochemical Indexes for Tianshuihai Lake Core in West Kunlun Mountain and Their Environmental Implications

With the decrease of global temperature, glacial epoch came over the earth and global climate fluctuated over a great range since the beginning of Quaternary. Paleoclimotologists of various countries have focussed attention to the periodic characteristics and dynamics of climatic fluctuation in the past many years (Berger, 1977; Imbrie and Hays, 1984; Ding Zhongli et al., 1990; Yu Zhiwei et al., 1992; Liu Youmei et al., 1996). Although some of the workers have paid their attention to the nonlinear characteristics of the global Quaternary environmental evolution (Nicolis and Nicolis, 1984; Lu Houyuan et al., 1993), it is worth while to do this kind of work in some special areas in the world, for example the Qinghai\|Tibet Plateau.\; Using R/S analysis, the authors calculated the Hurst indexes H of some geochemical proxies, including organic carbon, FeO, Fe\-2O\-3 and FeO/ Fe\-2O\-3, from the Tianshuihai Lake core in West Kunlun Mountain of the Qinghai\|Tibet Plateau. The proxies satisfy the Hurst law with H\-\{org.carbon\}=0.735, H\-\{Fe\-2O\-3\}=0.757, H\-\{FeO\}=0.848 and H\-\{FeO/Fe\-2O\-3\}=0.646. All the indexes are greater than 0.5, meaning that from 240 to 15 ka B.P., there were some long\|run dependencies\|persistence in the climatic and environmental evolution around the Tianshuihai Lake area. This is in accordance with the climate there from 240 to 15 ka B.P. (Yu Suhua et al., 1996). The paleo\|climate and paleo\|environment evolution around the Tianshuihai Lake area is of persistence as well as of fluctuation and is a combination of these two components. There are some differences between the four Hurst indexes, which probably resulted from the different intensities of persistence of the four proxies, organic carbon, FeO, Fe\-2O\-3 and FeO/ Fe\-2O\-3, or from the change of drainage system around the Tianshuihai Lake area from openness to closeness(Li Bingyuan et al., 1991; Sun Honglie, 1996; Shi Yafeng et al., 1998).\; The Qinghai\|Tibet plateau was the starter and sensor of the climatic and environmental variation of the surrounding areas (Yao Tandong et al., 1991; Feng Song et al., 1998) and some other scientists even regarded it as the driver and amplifier of global climatic variations (Pan Baotian and Li Jijun, 1996). The persistence in which the climate and environment around the Tianshuihai Lake area evolved from 240 to 15 ka B.P. is probably a function of the continuous uplift of the plateau in the same period of time.

Application of isolation forest to extract multivariate anomalies from geochemical exploration data

Constructing a statistical model that best fits the background is a key step in geochemical anomaly identification. But the model is hard to be constructed in situations where the sample population has unknown and/or complex distribution. Isolation forest is an outlier detection approach that explicitly isolates anomaly samples rather than models the population distribution. It can extract multivariate anomalies from huge-sized high-dimensional data with unknown population distribution. For this reason,we tentatively applied the method to identify multivariate anomalies from the stream sediment survey data of the Lalingzaohuo district,an area with a complex geological setting,in Qinghai Province in China. The performance of the isolation forest algorithm in anomaly identification was compared with that of a continuous restricted Boltzmann machine. The results show that the isolation forest model performs superiorly to the continuous restricted Boltzmann machine in multivariate anomaly identification in terms of receiver operating characteristic curve,area under the curve,and data-processing efficiency. The anomalies identified by the isolation forest model occupy 19% of the study area and contain 82% of the known mineral deposits,whereas the anomalies identified by the continuous restricted Boltzmann machine occupy 35% of the study area and contain 88% of the known mineral deposits. It takes 4. 07 and 279. 36 seconds respectively handling the dataset using the two models. Therefore,isolation forest is a useful anomaly detection method that can quickly extract multivariate anomalies from geochemical exploration data.

Geochemical baseline determination and contamination of heavy metals in the urban topsoil of Fuxin City,China

Urban topsoil is the most frequent interface between human society and natural environment.The accumulation of heavy metals in the urban topsoil has a direct effect on residents'life and health.The geochemical baseline of heavy metals is an objective description of the general level of heavy metals in the urban topsoil.Meanwhile,the determination of geochemical baseline is necessary for regional environmental management,especially in coal cities prone to heavy metal pollution.Heavy metal pollution has become an environmental problem in Fuxin City,China for a long time.To establish the geochemical baseline of heavy metals in the topsoil of Fuxin City and to evaluate the ecological risk of the topsoil,we collected 75 topsoil samples(0–20 cm)and analyzed the concentrations of Cu,Ni,Zn,Pb,Cr,Cd,Hg and As through X-ray fluorescence spectrometry,atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry.We determined the geochemical baseline of heavy metals in the topsoil of Fuxin City by using iteration removal,box-whisker plot,cumulative frequency curve and reference metal normalization;evaluated the contamination risk and ecological risk of the topsoil by using the baseline factor index,Nemerow index and Hakanson potential ecological risk index;and identified the source category of heavy metals in the topsoil by using a pedigree clustering heatmap.Results showed that the geochemical baseline values were 42.86,89.34,92.23,60.55,145.21,0.09,0.08 and 4.17 mg/kg for Cu,Ni,Zn,Pb,Cr,Cd,Hg and As,respectively.The results of Nemerow index and Hakanson potential ecological risk index indicated that the urban topsoil in the study area was slightly contaminated and suffering low potential ecological risk.The main contaminated areas dominated in the middle part and northeast part of the study area,especially in the western Haizhou Strip Mine.The result of baseline factor index indicated that Hg and Cd were the major pollution elements.Using a pedigree clustering heatmap,we divided the sources of these heavy metals into three types:type I for Ni and Cr,largely represented the enrichment of heavy metals from natural sources;type II for Cu,Pb,Zn,Cd and As,mainly represented the enrichment of heavy metals from anthropogenic sources;and type III for Hg,represented the form of both natural and anthropogenic inputs.

Identification model of geochemical anomaly based on isolation forest algorithm

The methods for geochemical anomaly detection are usually based on statistical models, and it needs to assume that the sample population satisfies a specific distribution, which may reduce the performance of geochemical anomaly detection. In this paper, the isolation forest model is used to detect geochemical anomalies and it does not require geochemical data to satisfy a particular distribution. By constructing a tree to traverse the average path length of all data, anomaly scores are used to characterize the anomaly and background fields, and the optimal threshold is selected to identify geochemical anomalies. Taking 1∶200 000 geochemical exploration data of Fusong area in Jilin Province, NE China as an example, Fe2O3 and Pb were selected as the indicator elements to identify geochemical anomalies, and the results were compared with traditional statistical methods. The results show that the isolation forest model can effectively identify univariate geochemical anomalies, and the identified anomalies results have significant spatial correlation with known mine locations. Moreover, it can identify both high value anomalies and weak anomalies.

Evaluation of hydro-chemistry in a phreatic aquifer in the Vindhyan Region, India, using entropy weighted approach and geochemical modelling

Groundwater quality monitoring and geochemical characterization in the phreatic aquifer are critical for ensuring universal and equitable access to clean,reliable,and inexpensive drinking water for all.This research was intended to investigate the hydrogeochemical attributes and mechanisms regulating the chemistry of groundwater as well as to assess spatial variation in groundwater quality in Satna district,India.To accomplish this,the groundwater data comprising 13 physio-chemical parameters from thirty-eight phreatic aquifer locations were analysed for May 2020 by combining entropy-weighted water quality index(EWQI),multivariate statistics,geochemical modelling,and geographical information system.The findings revealed that the groundwater is fresh and slightly alkaline.Hardness was a significant concern as 57.89% of samples were beyond the permissible limit of the World Health Organisation.The dominance of ions were in the order of Ca^(2+)> Na^(+)> Mg^(2+)> K^(+) and HCO_(3)^(-)> SO_(4)^(2-)> Cl^-> NO_(3)^(-)> F^(-).Higher concentration of these ions is mainly concentrated in the northeast and eastern regions.Pearson correlation analysis and principal component analysis(PCA) demonstrated that both natural and human factors regulate groundwater chemistry in the region.The analysis of Q-mode agglomerative hierarchical clustering highlighted three significant water clusters.Ca-HCO_3 was the most prevalent hydro-chemical facies in all three clusters.Geochemical modelling through various conventional plots indicated that groundwater chemistry in the research region is influenced by the dissolution of calcite/dolomite,reverse ion exchange,and by silicate and halite weathering.EWQI data of the study area disclosed that 73.69% of the samples were appropriate for drinking.Due to high salinity,Magnesium(Mg^(2+)),Nitrate(NO_(3)^(-)),and Bicarbonate(HCO_(3)^(-)) concentrations,the north-central and north-eastern regions are particularly susceptible.The findings of the study may be accomplished by policymakers and groundwater managers to achieve sustainable groundwater development at the regional scale.

Organic geochemical and petrographic characteristics of the Cambrian-Ordovician organic-rich marine shales in Scandinavia

This work used organic geochemistry and organic petrology to study the depositional environment,organic matter characteristics,and thermal maturity of the Cambrian-Ordovician organic-rich marine shales in the Baltic Basin.The main macerals in Cambrian samples include alginite,bituminite and solid bitumen,while zooclastic macerals become the major proportion of organic matter in the Ordovician samples.As the maturity increase,solid bitumen becomes abundant and dispersed.Semifusinite-like maceral was observed only in Furongian of well DBH15/73,which probably indicates the local intrusion of Permo-Carboniferous dolerite dikes.The programmed pyrolysis results show that immature,early mature,and over-mature samples are developed.However,the data of high-uranium Furongian samples were greatly altered by igneous intrusives from local dikes.HIo calculation model is simulated based on pyrolysis data and fitted according to the least-square fitting method.The simulated fitting HIo:400mg HC/g TOC(369.5 mg HC/g TOC,430.5 mg HC/g TOC as 95%confidence bounds)is within the worldwide marine shale HI_(o)and indicates a marine anoxia and transgressive sea with shallow water column(organofacies B).

Petrography and Geochemical Characteristic of Koohrig Intrusive Rocks in Kerman, Iran

Koohrig intrusive mass is located in the east of Rafsanjan, Kerman Province, Iran and it is part of because it has cut the sandstone, limestone, shale units and conglomerate of Upper Cretaceous. Its intrusive rock includes quartz, plagioclase and alkali feldspar and its ferromagnesian mineral which is biotite has changed into chlorite. This Intrusive mass is characterized by the presence of metamorphic geochemical studies led to the detection of granite and granodiorite and quartz monzonite rocks.

Geochemistry, Paleoenvironment and Mechanism of Organic-Matter Enrichment in the Lower Silurian Longmaxi Formation Shale in the Sichuan Basin, China

To investigate the mechanism of the organic-matter enrichment in the Lower Longmaxi Formation shale,the geochemistry and total organic carbon(TOC)of the Longmaxi Formation black shales in the Jiaoshiba,Zhaotong,and Weiyuan areas of the Sichuan Basin were analyzed.Paleoproductivity proxy parameters(Babio,Siex,and Ni/Al),clastic influx proxies(TiO2 and Ti/Al),redox indices(V/Cr,Ni/Co,V/(V+Ni),and U/Th),and hydrothermal indicators(Fe,Mn,and Y concentrations;Fe/Ti ratio and a Ni-Zn-Co diagram)were employed to decipher the paleoenvironment of the Lower Longmaxi Formation shales.TiO2 and Ti/Al indicated low terrigenous detrital influx in all three areas.However,Babio,Siex,and Ni/Al indicated high productivity in the Jiaoshiba area.V/Cr,Ni/Co,and U/Th indicated higher oxygen content with larger fluctuations in the Zhaotong and Weiyuan areas.Fe,Mn,and Y concentrations and the Fe/Ti ratio implied greater active hydrothermal activity in the Weiyuan area.These heterogeneities were considered to be closely related to the paleoenvironment and paleogeography,and the large basement faults that developed during the Chuanzhong paleo-uplift could have provided vents for deep-hydrothermal-fluid upwelling.The redox indices(V/Cr,Ni/Co,and U/Th)and a paleoproductivity proxy(Ni/Al)displayed a significant correlation with the TOC,suggesting that both excellent preservation conditions and high paleoproductivity were the controlling factors for the enrichment of organic matter in the Longmaxi Formation shale.There was no obvious correlation between the clastic influx proxy(Ti/Al)and the TOC due to the extremely low supply of terrigenous debris.The hydrothermal indicator(Fe/Ti)was negatively correlated with the TOC in the Weiyuan area,indicating that hydrothermal activity may have played a negative role in the accumulation of organic matter.This study suggests that the enrichment of organic matter in the Longmaxi Formation marine shale varied according to the paleogeography and sedimentary environment.

基于突变理论的土地质量地球化学评价方法研究

为实现土壤肥力和土壤环境质量相结合的土地质量地球化学综合评价结果的高精度量化,依据赣南南康地区采集的6266组表层土壤样品测试结果,构建了以As、Hg、Cd、Pb、Cr含量等为基础的内梅罗指数和以有机质(SOM)、P、N、K、Mo、Mn、B、Cu、Zn含量等为基础的土壤综合肥力指数为控制因素的突变理论法土地质量地球化学综合评价方法,将内梅罗指数3.0修订为3.1,通过突变理论对数据进行标准化和归一化分析,比较原始内梅罗指数和修订内梅罗指数评价结果以及本文方法与DZ/T 0295—2016《土地质量地球化学评价规范》方法的土地质量地球化学综合等级划分结果。结果表明:研究区土壤综合肥力指数均值为0.75,总体综合肥力为Ⅲ等,土壤肥力较低;土壤综合内梅罗指数均值为0.59,总体尚清洁。采用修订后的内梅罗指数3.1计算的土壤肥力指数分界值基本呈等级等间距划分。与DZ/T 0295—2016《土地质量地球化学评价规范》评价结果比较,83.57%的结果等级未发生变化,近16%等级结果增加1个等级,主要为1级和2级升为3级和4级,未出现2个及以上等级的变化,评价结果显示3级、4级面积占比为94.11%、5.30%。本文方法可用于土地质量地球化学综合等级评价,评价结果更加数值化、精细化,评价过程更简便,是对已有土地质量地球化学综合评价方法的补充,可为土地利用、农业生产和管理提供借鉴和参考。

基于PHREEQC模拟分析铀矿退役采区地下水铀形态及其影响因素

酸法地浸退役采区地下水常遗留铀浓度超标的难题,其高效修复亟待解决,而探明地下水中铀的形态及影响因素是实现其高效修复的关键。以新疆某酸法地浸采铀矿山退役采区地下水为研究对象,采用PHREEQC模拟分析了温度、pH、电子势(pe)、Fe^(3+)浓度及Fe^(2+)浓度对地下水中铀形态及矿物饱和状态的影响。结果表明:1)地下水中铀的主要形态为UO_(2)SO_(4)和UO_(2)^(2+),分别占63.43%和32.54%;2)铀的赋存形态受地下水pH、pe、温度、Fe^(2+)和Fe^(3+)共同影响,其中pe是控制地下水铀价态的主要因素;3)地下水pH和pe对矿物的饱和状态影响较大,而温度、Fe^(2+)和Fe^(3+)浓度的影响较小,其中pH和pe对沥青铀矿、柱铀矿和Fe(OH)_(3)的饱和状态影响最明显。研究结果可为酸法地浸采铀矿山退役采区地下水修复方案的制定提供理论指导。

洛阳盆地古洪水剖面地球化学指标的古气候指示意义

地球化学指标在古气候研究中多用于黄土、湖泊等沉积物的分析,河流沉积物由于沉积水动力变化大,对其化学元素及其古气候指示意义的研究较少。文中对洛阳盆地4~3.8 ka BP龙山晚期古洪水(SQ)剖面地球化学指标的古气候指示意义进行了探讨。分析显示,古洪水剖面的化学元素含量与中值粒径相关性显著。在排除物源、沉积再旋回和成岩钾交代作用对于化学元素的影响后,根据各化学元素与中值粒径的相关系数进行分组,并在同组内按照元素迁移强弱建立化学元素参数指标,其结果与CIA粒度效应校正结果具有一致性,均在距今4000年前后的古洪水层呈低值,指示相对干凉的气候。结合该剖面孢粉的分析结果,认为洛阳盆地温凉的气候条件是距今4000年前后古洪水事件发生的重要环境背景。虽然河流沉积过程的复杂性导致本研究具有一定的局限性,但是通过相关系数分组建立比值参数的方法,为探讨河流沉积物化学元素指标的古气候指示意义提供了新的思路。

Outcrops as windows to petroleum systems:Insights from the southern Bida Basin,Nigeria

The study assessed petroleum systems in the southern Bida Basin,Nigeria,focusing on the Cretaceous sediments.Reservoirs comprise Lokoja and Patti Formation sandstones,while shales,claystone,and siltstone serve as source rocks and stratigraphic traps/seals.Detailed studies delineating the key elements of the petroleum systems in the basin have not been conducted due to a lack of subsurface data.The goal of the current study was to use field observations,Scanning Electron Microscopy(SEM),X-ray diffraction(XRD),and geochemical and geomechanical data to evaluate key components of petroleum systems in the southern Bida Basin.The results presented in this investigation are intended to attain specific objectives,especially those lacking in the basin's study sections.Petrophysical analysis revealed that the Lokoja Sandstone has porosity of 37%-39.5%and moderate permeability of 23.22-42.29 mD.The Patti Formation sandstone reservoirs exhibited high porosity(38%-42%)and moderate to good permeability(31.54-66.48 mD),suggesting good potential reservoirs.SEM results revealed intragranular pores and micro-fractures in the Patti Shale,whereas the sandstone reservoirs in the Lokoja and Patti formations displayed fractures,facilitating hydrocarbon migration.Quartz was the dominant mineral in the sandstone units of both formations.XRD analysis revealed that brittle and clay minerals influenced the microstructure of Patti Shale.Geochemical analysis indicated promising petroleum potential in the Patti Shale,with a total organic carbon(TOC)content of 1.87 wt%,free hydrocarbon from kerogen(S1)of 0.41 mg/g,hydrogen index(HI)of 0.75 mg HC/g TOC,and production index(PI)of 0.17.The Patti and Lokoja formations'shale,claystone,and siltstone exhibited sealing potential,with a plasticity index of 24-35 and coefficient permeability of 2.8×10^(-4)-3.6×10^(-4)cm/s.Field studies,XRD,geochemical data,and geomechanical index values have confirmed the key components of the petroleum system,which in turn facilitate hydrocarbon generation,migration,accumulation,and entrapment in the basin.

贵州省灰岩分布区土壤镉地球化学基线研究

为判别贵州省灰岩分布区土壤中Cd的元素来源,分析土壤中Cd的富集程度,按标准化方法获取了全省灰岩分布区不同地质年代形成的土壤Cd地球化学基线值,并进行地质累积指数评价.结果表明:二叠系和石炭系灰岩发育形成的土壤Cd基线值明显高于灰岩其他地层发育形成土壤.将土壤Cd基线值与岩石Cd平均含量对比分析显示,岩石自然风化是贵州灰岩发育土壤中Cd元素的主要来源.根据地质累积指数评价结果,贵州省灰岩分布区土壤Cd污染程度总体处于较低水平.

高原黄土Sr、CaO的古气候意义以及记录的环境变化

青藏高原东北部的西宁盆地紧邻柴达木盆地戈壁沙漠,沉积了厚层的、序列完整的黄土物质,对其进行研究可望得到高原古气候演化信息。通过对西宁盆地盘子山黄土剖面酸溶相Sr、CaO含量变化的测试分析,获得了自末次间冰期以来多次不同时间尺度变化的信息,证明Sr、CaO可以作为该地区黄土研究更为灵敏的气候代用指标。

应用地质累积指数评价沉积物中重金属污染:选择地球化学背景的影响

地质累积指数是评价沉积物中重金属污染的常用参数。选择地球化学背景对地质累积指数的影响 ,在应用地质累积指数评价沉积物中的重金属污染时 ,应选择与该沉积物有直接联系的地球化学背景 ,由此而进行的污染状况分析才更真实。

海相沉积氧化还原环境的地球化学识别指标

全球海洋在10～5．4亿年间演变成氧化环境，此后历经多次全球性的缺氧事件后演变到现在的氧化环境。海水和沉积物中多种元素的循环、分异和富集明显受氧化还原条件的影响。Mn、Mo、Cr、V和u等变价元素的溶解度随氧化还原条件的改变产生极大变化，导致沉积物中的元素含量分异；Ni、Co、Cu和Zn等在还原条件下形成硫化物沉淀，导致沉积物中对应元素的富集。这些元素的地球化学行为是古海洋氧化还原条件变化的灵敏指示剂，可以作为恢复古海洋氧化还原环境变化的地球化学指标。黄铁矿化程度（DOP）、生物标志化合物和Ce异常等也是沉积环境氧化还原条件的常用判别指标。泥岩研究中通常采用DOP、U/Th、自生U、V/Cr、Ni/Co和生物标志化合物等指标，碳酸盐岩则主要采用Ce异常指标。当前各种指标的定性分析都取得比较一致的结果，但是用一种或几种定量的地球化学指标来恢复整个古海洋的氧化还原环境目前还有很大的问题。

地球化学模拟及其在水文地质中的应用

从正向地球化学模拟、反向地球化学模拟和水文地球化学模拟三方面系统概述了地球化学模拟的研究进展；结合笔者近年来的科研实践，对其在水文地质中的应用作了介绍，并着重讨论了在地下水化学组分存在形式、矿物饱和指数的计算、水化学组分预测及地下水地球化学演化等方面的应用；最后，指出了这一领域中当前存在的问题和今后的研究方向。

冀东平原土壤中重金属元素的地球化学特征

通过分析冀东平原土壤中有害重金属元素Pb、Cr、Cd、As、Hg的含量变化特征,显示有害重金属元素Hg、Cd、Pb在冀东平原表层土壤的富集已较为明显,Cr、As也形成局部的异常,原有的地球化学特征发生较大变化。初步认为表层土壤中重金属元素的高含量与当地地质背景和人为活动有关,局部异常成因需要进一步研究。研究区地积累指数污染评价结果表明:以全国土壤背景值计算,重金属未造成污染;以研究区背景值计算,Hg表现为轻度—中度污染状况,As、Cd、Cr、Pb未造成污染。

斑岩型铜矿床地球化学勘查中岩石化学指标

依据江西城门山和内蒙古乌努格吐山2个斑岩型铜矿床试验资料,探讨了用于斑岩型铜矿床勘查的岩石化学指标。结果表明,常量化学组分MgO、CaO和Na2O等在斑岩型矿化体中的含量显著低于其在中酸性岩中的丰度值,w(Na2O)/w(K2O)、w(CaO)/w(MgO)值随Cu矿化强度增强有规律地变化,可以有效指示斑岩型矿化体的存在及其矿化强度。此项成果丰富了地球化学勘查指标。

云南省镇雄县土壤重金属污染及潜在生态风险评估

为查明镇雄县调查区土壤重金属污染环境风险等级及空间分布特征,基于现行土壤环境质量评价和食品安全评价标准,开展土地质量地球化学调查;运用单因子指数法、内梅罗综合指数法和Hakanson潜在生态危害指数法开展土壤重金属污染及潜在生态风险评估。内梅罗综合评估结果表明:调查区土壤存在重金属污染,其土壤轻度污染、中度污染、重度污染比例分别为39.03%、16.62%和28.57%。但8种重金属中Cu、Hg、As、Ni、Pb、Cr、Zn潜在生态危害程度低,仅Cd存在较高等级的潜在生态风险,其潜在生态危害等级程度低、中、较高、高、严重的样品数比例分别为17.71%、39.21%、22.77%、12.31%和8.00%,潜在生态危害指数(Er^i)均值为118.24。土壤Cd高潜在生态危害和较高潜在生态危害样点主要位于下二叠统地层单元中。同时,调查区45件农作物玉米籽实重金属评价结果显示,仅1件玉米籽实样品Cd含量超标,农作物玉米籽实与其对应的农作物根系土中的重金属Cd全量无明显的相关性。调查区土壤Cd高含量主要受地质背景影响,对调查区内玉米籽实影响较小,在强酸性土壤环境下,随土壤中可溶态Cd含量增加,导致农作物对Cd的吸收富集风险加大。