The origin of magnetization and geochemical alteration in a fault zone,Kilve, England

The origin of an apparently syndeformational chemical remanent magnetization (CRM) and geochemical alteration in a fault zone in the Bristol Channel Basin, southwest England, was investigated. Deformation in the fault zone occurs in Jurassic aged, organic-rich limestones and consists of numerous normal and oblique-slip faults and associated folds. Migration of basinal, radiogenic fluids is indicated by elevated ⁸⁷Sr/⁸⁶Sr values for calcite veins that occur throughout the fault zone. Some of the calcite veins contain hydrocarbons sourced from deeper strata. Elevated ⁸⁷Sr/⁸⁶Sr values in the host Jurassic limestones indicate that they were also extensively altered by radiogenic fluids that migrated through microfractures in addition to major fault and fracture planes. Folded and tilted host limestones contain a pervasive secondary CRM residing in magnetite that was acquired during deformation in the Tertiary. The association between this pervasive CRM and the pervasive geochemical alteration is consistent with a genetic connection between the orogenic fluids and the CRM although the timing of CRM acquisition (Tertiary) is not consistent with structural interpretations for the timing of most veining. An alternative remagnetization mechanism which is not triggered by externally derived fluids, such as diagenesis of hydrocarbons, might account for the CRM. Hydrocarbon-bearing veins also contain a CRM that resides in magnetite, although the time for remanence acquisition is not well constrained by field tests. © 1998 John Wiley & Sons, Ltd.     

生态最相关水文指标的优选及其在洞庭湖环境流量估算中的应用

水文改变指标(IHA)能够较为全面地描述水文状况,在评估水文情势改变及其生态系统影响方面具有广泛的应用.尽管该指标体系较为完善,但是数量众多的水文变量仍然存在信息冗余问题.根据洞庭湖城陵矶水文站1955-2014年的径流量数据,采用主成分分析(PCA)筛选了生态最相关水文指标(ERHIs),结合ERHIs改进了用于估算环境流量的变化范围法(RVA),并将其应用在洞庭湖出口的环境流量估算中.基于PCA选取了年最大90日流量、年最小3日流量、年最小流量出现时间、3月流量、6月流量、流量逆转次数和低流量年内平均历时7个变量作为洞庭湖出口的ERHIs.纵向和横向的对比分析都表明选取的ERHIs是合理的.ERHIs不仅有效缓解了IHA的冗余性问题,还有利于抓住最关键的生态水文变量.根据ERHIs改进的RVA方法在设定洞庭湖出口环境流量时,极大地简化原来的众多管理目标,对生态水文研究、水资源管理和生态保护都具有重要的参考价值和借鉴意义.     

Presumed magnetic biosignatures observed in magnetite derived from abiotic reductive alteration of nanogoethite

The oriented chains of nanoscale Fe-oxide particles produced by magnetotactic bacteria are a striking example of biomineralization. Several distinguishing features of magnetite particles that comprise bacterial magnetosomes have been proposed to collectively constitute a biosignature of magnetotactic bacteria (Thomas-Keprta et al., 2001). These features include high crystallinity, chemical purity, a single-domain magnetic structure, well-defined crystal morphology, and arrangement of particles in chain structures. Here, we show that magnetite derived from the inorganic breakdown of nanocrystalline goethite exhibits magnetic properties and morphologies remarkably similar to those of biogenic magnetite from magnetosomes. During heating in reducing conditions, oriented nanogoethite aggregates undergo dehydroxylation and transform into stoichiometric magnetite. We demonstrate that highly crystalline single-domain magnetite with euhedral grain morphologies produced abiogenically from goethite meets several of the biogenicity criteria commonly used for the identi?cation of magnetofossils. Furthermore, the suboxic conditions necessary for magnetofossil preservation in sediments are conducive to the reductive alteration of nanogoethite, as well as the preservation of detrital magnetite originally formed from goethite. The findings of this study have potential implications for the identification of biogenic magnetite, particularly in older sediments where diagenesis commonly disrupts the chain structure of magnetosomes. Our results indicate that isolated magnetofossils cannot be positively distinguished from inorganic magnetite on the basis of their magnetic properties and morphology, and that intact chain structures remain the only reliable distinguishing feature of fossil magnetosomes.     

基于资源一号02D卫星高光谱数据的甘肃头吊泉-南大滩地区蚀变矿物填图及金矿化带识别

高光谱遥感能够根据光谱指纹特征提取蚀变矿物,在地质领域应用成效十分显著.针对最新的资源一号02D卫星高光谱数据特点,首先进行了高光谱数据预处理,选取蚀变矿物光谱特征显著波段进行数据降维,并应用三次样条插值函数对短波红外数据进行光谱波段增值,将光谱采样间隔提高到了2 nm.在优选出矿物填图端元光谱后,应用改进的SAM填图...     

Riparian responses to reduced flood flows: comparing and contrasting narrowleaf and broadleaf cottonwoods

Abstract

To enable assessment of risks of water management to riparian ecosystems at a regional scale, we developed a quantile-regression model of abundance of broadleaf cottonwoods (Populus deltoides and P. fremontii) as a function of flood flow attenuation. To test whether this model was transferrable to narrowleaf cottonwood (Populus angustifolia), we measured narrowleaf abundance along 39 river reaches in northwestern Colorado, USA. The model performed well for narrowleaf in all 32 reaches where reservoir storage was <75% of mean annual flow. Field data did not fit the model at four of seven reaches where reservoir storage was >90% of mean annual flow. In these four reaches, narrowleaf was abundant despite peak flow attenuation of 45–61%. Poor model performance in these four reaches may be explained in part by a pulse of narrowleaf cottonwood expansion as a response to channel narrowing and in part by differences between narrowleaf and broadleaf cottonwood response to floods and drought.

Editor Z.W. Kundzewicz; Guest editor M. Acreman

Citation Wilding, T.K., Sanderson, J.S., Merritt, D.M., Rood, S.B., and Poff, N.L., 2014. Riparian responses to reduced flood flows: comparing and contrasting narrowleaf and broadleaf cottonwoods. Hydrological Sciences Journal, 59 (3–4), 605–617.     

歧口凹陷新生界火成岩油藏特征及分布规律

歧口凹陷新生界发育了两类与火成岩相关的油藏：基性火山岩油藏和浅成侵入相辉绿岩蚀变带油藏,两者都为构造-岩性油藏。这两类油藏区域上受岩浆活动带控制,主要集中于NE向和EW向断裂转换带,并受烃源岩分布范围的影响而紧邻烃源岩分布;垂向上受区域盖层控制,集中于沙一中亚段和东三段。在转换带沙一中亚段和东三段内,火成岩能否富集成藏主要取决于储集系统的类型。开放式储集系统一方面利于流体替换使火成岩储集空间中的矿化水被及时排出减少次生矿物的形成,从而保护储集空间;另一方面利于富含有机酸流体进入火成岩储集体,通过溶蚀先期形成的杏仁体、裂缝充填物及火成岩中不稳定的矿物组分,使其储集空间扩大、容积增加,使火成岩的储集性能得以改善;另外,火成岩中的断裂通过与烃源岩的沟通为烃类注入富集成藏提供了必要的输导通道,致使这类储集系统能够富集烃类成藏。封闭式储集系统缺少这些条件,岩浆期后热液流体与成岩流体被包裹在火成岩储集空间内不能被排出,易形成次生矿物充填并堵塞这些空间,丧失其储集性能。部分未被充填的空间往往相互之间难以连通,并与生排烃地层隔绝而成为烃类难以注入的死孔隙,从而使这类储集系统难以聚集成藏。     

黑龙江省萝北县杜家河金矿地质特征与找矿标志

杜家河金矿产于中元古界黑龙江群联营岩组中,并受背形构造控制.在详细的野外地质调查基础上,系统研究了矿床的地质特征、矿石结构构造、金矿物学特征等.研究表明,矿石具有结晶结构、自形粒状结构,致密块状构造、浸染状构造,围岩蚀变有绢云母化、硅化、黄铁矿化等,矿床成因类型属于与韧性剪切带有关的金矿,并指出矿床在地层、构造、蚀变等找矿标志,为该地区找矿提供理论基础.     

中国微细浸染型金矿床围岩蚀变地质特征

微细浸染型金矿的围岩蚀变一般较弱,主要蚀变类型以硅化、碳酸盐化、粘土化、绢云母化为主;围岩蚀变与容矿岩石类型及其岩性组合密切相关,化学组分的变化因围岩的性质而异;金矿化强度与围岩蚀变强度和蚀变组合复杂程度成正比,金矿体出现在蚀变中心部位或蚀变分带的内带.     

鄂尔多斯盆地上古生界两大气田不同石英砂岩储层 特征对比研究

通过对鄂尔多斯盆地上古生界榆林气田和苏里格气田石英砂岩储层特征的对比,指出榆林气田山2段石英砂岩储层属于相对低孔高渗型储层,苏里格气田盒8段石英砂岩储层属于相对高孔低渗型储层;通过分析两类石英砂岩的物源、沉积条件和成岩作用等因素,认为沉积期海水改造及后期成岩作用形成了榆林气田山2段储层的低孔高渗,而沉积时的高杂基含量与后期成岩共同作用形成了苏里格气田盒8段储层的高孔低渗。     

辽宁省凤城市林家金矿地质特征及成因探讨

林家金矿的赋矿地层为早元古界辽河群变质岩系,矿体形态产状严格受断裂控制,呈脉状、扁豆状产出,沿走向呈舒缓的波状,局部有膨缩变化,矿床成因类型为岩浆期后中低温热液充填交代型金矿床。