风化过程中硒背景值的定量表征

硒是人和动物必需的微量元素,基于58件标准物质的化学风化指标和硒的认定值,采用微量元素地球化学背景值的经验方程形式拟合得到表征全国范围内硒背景值的经验方程：lgc=0822×(12-WIG/100)-1061×lg(K2O/SiO2)-2704,式中c为Se的含量(单位为μg/g),风化指标WIG的变化范围为43~1116,风化指标K2O/SiO2变化范围为0020~0137。该方程所表征的是样品因风化程度不同所呈现出的硒地球化学背景值,风化程度强的样品总体上具有较高的Se地球化学背景值。将该经验方程式在广东河台和广东南昆山两个研究区进行应用,认为寻找富硒区应当优先将风化程度较强的地区视为备选区,依据全国区域化探扫面数据可以方便地确定风化程度较强的地区。在环境质量评价中可以利用Se实测值确定足硒和富硒区,利用实测值扣除背景值获得的元素含量剩余值可以有效确定残积层土壤下伏的足硒和富硒岩石,即依据全国多目标地球化学调查数据可以有效地确定足硒和富硒地质体(残积层土壤及其下伏岩石)的分布区。广东南昆山岩体中西部的岩石应属于足硒和富硒地质体。     

成兰铁路绵竹—茂县段茂县群浅变质千枚岩风化指数研究

本文以成兰铁路茂县群千枚岩为研究对象, 通过电子探针、电子显微镜和岩石地球化学分析等实验方法对其地球化学特征、微观成分结构特征以及原岩特征进行分析研究, 同时对该区风化千枚岩样及其新鲜岩的化学成分进行分析对比, 使用SPSS.22软件对各主要元素进行相关性分析, 得出其风化过程中的控制性元素后进行判别方程式拟合, 同时与前人已有的风化指标进行对比, 得出新生成的判别式更适用于本区域的风化千枚岩类判识。     

山东蓬莱史家沟西山火山碎屑岩风化壳元素地球化学特征

以山东蓬莱城西史家沟的西山火山碎屑岩风化壳为研究对象,系统采集样品,并测试了微量元素、主量元素、稀土元素以及黏土矿物等指标,揭示了西山火山碎屑岩风化壳的元素地球化学特征,讨论了风化壳的形成年代及其气候条件。史家沟火山碎屑岩风化壳源自基性-超基性玻屑凝灰岩母岩,CIA平均值为92.3,总体上处于为强度风化水平,K、Na、Ca和Mg等元素淋失殆尽,出现了脱硅富铝铁现象,为轻稀土富集型风化壳。西山火山碎屑岩风化壳可分为两个喷发旋回,大致以200 cm为界限,在此以下第一旋回,以上为第二旋回。第一旋回的CIA介于94.0~97.2之间,V、Rb、Sb、Mo、Li和Ga等微量元素出现淋失,在213 cm处并出现了?REE、?LREE和?HREE的峰值、Ce的负异常,蒙脱石化彻底,风化壳呈现灰白色。第二旋回的CIA在86.3~89.2之间,风化程度较第一旋回稍低,微量元素和稀土元素垂直变化较小,蒙脱石化并不完全彻底,仍残留长石、赤铁矿和石英等原生矿物,因而仍然呈现红色或淡红色。西山火山碎屑岩风化壳形成于中新世末到上新世,为温暖湿润的亚热带环境;中新世后的气候趋冷造成了两个旋回风化程度和元素地球化学特征的差异。     

赣南山区矿泉水出露模式探讨

赣南属于典型的山区,也是严重缺水区,一般在山区沟谷两侧有优质矿泉水涌出地表。宁都县位于赣南北部,具有赣南典型的地貌特征、构造特征。现以宁都县为例,探讨矿泉水的分布与出露模式。通过区域地质调查、水文地质条件分析及水质分析,发现:矿泉水类型主要为偏硅酸矿泉水,含量30.72~48.56 mg/L,水化学类型为HCO_3-CaNa型水,水温普遍低于25℃,溶解性总固体小于153.53 mg/L,属于低矿化冷矿泉;断裂构造为矿泉水形成提供水动力条件,也为矿泉水的运移、贮存提供良好空间;地形地貌以侵蚀构造山地丘陵为主,高差大、切割深的径流条件促进了地下水中偏硅酸的富集;花岗岩中的高含量SiO_2为矿泉水提供了物质基础,且风化程度高、裂隙发育,水岩作用进行充分。     

重庆市西部地区浅层地下水化学特征及污染现状分析

以重庆市沙坪坝区、北碚区、璧山县、铜梁县等9个区县地下水为对象,对表层土壤物理性质、地下水化学特征及地下水水质进行了测试分析,根据《地下水质量标准》(GB/T14848-93),对地下水进行了单项组分评价和质量综合评价,并对污染成因进行了分析。结果显示研究区内地下水以HCO3-、SO42--Ca2+、Mg2+型和HCO3--Ca2+、Mg2+型为主,地下水质量不容乐观,超标率达到了78%,地下水中总硬度、硫酸盐、锰等因子的背景值较高,超标显著,亚硝酸氮和氨氮的超标率达到了18.5%,最大超标倍数分别为86.5倍和44.9倍。     

环渤海湿地沉积物球囊霉素相关土壤蛋白分布特征及其对湿地土壤风化的影响

【研究目的】球囊霉素作为丛枝菌根真菌（AMF）分泌的一种难降解土壤蛋白,广泛分布于陆地生态系统中,是长期碳贮的重要组成。当前鲜有研究涉及其在滨海湿地中的分布。基于此,本文对中国环渤海主要滨海湿地表层沉积物中球囊霉素相关土壤蛋白（GRSP）的空间分布进行表征,探讨不同湿地生境下GRSP分布及其对沉积物风化的指示意义。【研究方法】本文选取辽河三角洲、北大港和黄河三角洲湿地作为研究区,对166个表层样（0~5 cm）和4个柱状样（0~35 cm）的GRSP、粒度以及常量元素进行测定,并计算化学蚀变系数（CIA）。【研究结果】研究区GRSP在空间上的动态变化受植被类型影响显著,范围在0.06~11.31 mg/g,均值为（2.35±0.16） mg/g;沉积物以粉砂质砂和砂为主,CIA值分布范围为44.79~69.59,部分区域达到中等化学风化;CIA与GRSP呈显著相关（R=~0.49,p<0.01）,总体上CIA随GRSP的增加呈现先增加后减少的趋势。【结论】GRSP在滨海湿地沉积物中的分布受到生境差异性的影响,其与CIA的相关性表征AMF及其代谢产物在地质体风化过程中发挥了潜在的生态功能。创新点：揭示了球囊霉素相关土壤蛋白与地质过程的互馈作用;阐明了丛枝菌根真菌潜在的生态功能。     

火成岩风化壳储集层特征与油气产能关系研究:以准噶尔盆地红山嘴石炭系油藏为例

红山嘴油田是准噶尔盆地典型的风化壳型油藏,具有广阔的勘探前景。利用宏微观岩矿分析、地球物理、地球化学等多种实验分析手段,对红山嘴地区火成岩岩石学特征、结构发育特征及控制因素开展综合研究,结果表明:(1)红山嘴地区发育侵入岩、次火山岩、火山熔岩、火山碎屑熔岩、火山碎屑岩和沉火山碎屑岩等6大类火成岩,其中安山岩和凝灰岩最为发育;(2)火成岩储集空间组合包括原生气孔—溶蚀孔—Ⅰ级裂缝型、溶蚀孔—Ⅰ/Ⅱ级裂缝型、Ⅲ级裂缝型和Ⅳ级裂缝型4类,Ⅰ—Ⅳ类储层物性依次变差;(3)风化壳自上而下发育水解带、淋蚀带、崩解Ⅰ带、崩解Ⅱ带、母岩带5个分带,顶部水解带风化强,多被分解成致密的泥土层,可作盖层,而淋蚀带和崩解Ⅰ带是风化淋蚀改造较好区,储层物性最好;(4)不同油气产能井与风化壳结构具有很好的对应关系,可为风化壳型火成岩油藏优势区带划分和产能预测提供指导。     

全球变暖背景下北美育空河流域化学风化增强

硅酸盐岩风化对气候变化和构造运动的反馈对长尺度气候变化可能起到重要的调节作用,对该反馈过程的定量认识有助于更确切理解地球碳循环的运行规律。通常认为风化类型可分为两种,分别是供应限制和动力学限制。全球变暖可能促进了动力学限制流域的化学风化作用,然而,关于这方面的认识仍很有限。育空河流域是典型的动力学限制风化区域,研究育空河的风化对气候变暖的响应有助于深入认识气候和大陆风化之间的相互作用。正演模型是区分河流风化端元的重要手段,文章利用正演模型对育空河流域从1975年到2019年的主要离子组成的数据集进行分析,并获得了该流域在过去几十年的化学风化速率的变化趋势。结果表明,育空河水化学性质主要受到碳酸盐岩风化和硅酸盐岩风化控制,两者多年平均碳汇通量分别为2.1×10¹¹ mol/yr和4.1×10¹⁰ mol/yr,处于世界主要大河碳汇通量的中间水平。更重要的是,在同一时期,伴随着2.2℃的温度增幅和13.7%的径流量增加,流域内的阳离子总通量增加了35.7%,其中硅酸盐岩和碳酸盐岩风化产生的阳离子通量分别增加了41%和35%,阳离子通量/风化速率对气候的敏感性与冰岛地区的研究结果符合的很好,与风化速率加快相对应的,硅酸盐岩风化碳汇通量相对增加了59.6%。尽管碳汇的增加在绝对通量上相比人类化石燃烧产生的碳排放通量微不足道,但是考虑到构造尺度内全球硅酸盐岩风化速率的增强,尤其是在较为寒冷的高纬度地区,额外的二氧化碳固定量可能对地球历史时期的全球气候产生重要影响。     

Mineralogical and geochemical implications of weathering rates in coastal dunes and beach sands close to a volcanic rock source in the western Gulf of Mexico,Mexico

Coastal dune (CD) and beach sand samples were mineralogically and chemically studied to assess the weathering rates in a coastal area surrounded by the Trans-Mexican Volcanic Belt (TMVB). The study area is a narrow coastal plain with sub-humid warm weather and vigorous coastal dynamics located in the Western Gulf of Mexico (WGM). Our results show that the grain size parameters remain homogeneous along nine CD and beach sites, probably due to the hydrodynamic mechanisms prevailing in the area, i.e. wind deflation, longshore currents, and waves. The minerals found in the CD and beach sands are enriched in recycled, highly corroded monocrystalline quartz (Qm), with loss of plagioclase (P) and olivine (ol), with ilmenite fractions (op) especially in the northern sites. The geochemical data show that the sands are controlled by the exhumation of the TMVB rocks composed of a high volcanic lithic content with lathwork, microlithic, and negligible vitric textures. These volcanic fractions are in agreement with the presence of lavas of calc alkaline, andesite, Na-alkaline lavas, and rhyolite tuffs derived from the TMVB. Significant Spearman Rank Correlations (SRCs) resulted from high silica, titanium, iron, magnesium, calcium, vanadium, chromium, cobalt, associated with the presence of Qm, ilmenite, clinopyroxene, shell fragments, and volcanic lithics. Monocrystalline quartz enrichments, compared to a quartz dilution effect (<Qm; < Qm) at the northern and southern beach sites, reflect the vigorous coastal dynamics. The presence of ilmenite lag deposits in the northern sites indicate that high energy hydrodynamic conditions prevail at the site. The rare earth element (REE) patterns support the mineralogical and compositional framework of the CD and beach sands as part of the TMVB exhumation. We used various chemical indices such as the Chemical Index of Alteration (CIA), the Chemical Index of Weathering (CIW), the Plagioclase Index of Alteration (PIA), and the Weathering Index of Plagioclase (WIP). The WIP values reflect the depletion of mobile elements such as Ca, Na, K, and enrichment of Qm at the northern beach sites, e.g. the Istirinchiá site. The CIA/WIP ratio of 2.13 indicates intermediate weathering under warm climatic conditions and recycling of CD and beach sands.     

Elemental and Sr–Nd isotopic compositional disparity of riverine sediments around the Yellow Sea: Constraints from grain-size and chemical partitioning

To obtain a better understanding of the source compositions of the river sediments around the Yellow Sea and their relationship with source rocks, elements and strontium-neodymium (Sr–Nd) isotopes of different grain-sizes (silt and clay populations) and chemical (labile and residual phases) fractionations in riverine sediments were studied extensively. These results clearly revealed a systematic compositional disparity between Korean river (KR) and Chinese river (CR) sediments, especially in the residual (detrital) fraction. The geochemical dissimilarity between these might reflect inherited signatures of their source rocks but with minor control from chemical weathering. In particular, the remarkable enrichment of some elements (iron (Fe) and magnesium (Mg)) and the behavior of large ion lithophile elements (e.g., barium (Ba), potassium (K) and Sr) during weathering as well as less-radiogenic Sr isotopic compositions implies that CR sediments might be weathering products of relatively more mafic rocks, with abundant ferromagnesian and plagioclase feldspar minerals, compared with KR sediments derived from silicic granites with relatively higher quartz and potassium feldspar contents. This different petrological rationale is clearly evident in an A–CN–K diagram, which estimated the source rock of CR sediments as granodioritic, a composition that reflects accurately the average composition of weathered continental crust in China. The recognition of such geochemical systematics in two river sediments, especially in grain-size and chemically partitioned data, may contribute to the establishment of provenance tracers for the Yellow Sea and East China Sea sediments with multi-sources as well the dust deposition in the western Pacific.