Timing and intensity of groundwater movement during Egyptian Sahara pluvial periods by U-series analysis of secondary U in ores and carbonates     

J.K Osmond  Adel A Dabous 《Quaternary Research》2004,61(1):85-94

Wet climatic episodes are known to have prevailed in the Egyptian Sahara several times during the late Quaternary, most recently during the Holocene 8000 yr ago. Earlier wet episodes have been recognized as having occurred during the past 300,000 yr and have been dated by U-series methods in speleothems and in lake travertines. We show here that the times of enhanced groundwater movement can also be determined by ²³⁰Th/²³⁴U dating of secondary U in ores of uranium, iron, and phosphate. We also present evidence that such acceleration of groundwater movements is indicated by relatively low ²³⁴U/²³⁸U activity ratios in the secondary uranium. Our new data show that pluvial periods in Egypt occurred during marine oxygen isotope stages 4, 5, 6, and 7 and therefore are consistent with the view that the wet episodes are the results of migration of the tropical monsoonal belt driven primarily by the 23,000-yr precession cycle of the Milankovich curve, modulated by the 100,000-yr eccentricity cycle.  相似文献   

鲕粒,豆粒磷块岩的显微结构和生成特点   总被引：4，自引：0，他引：4  

赵东旭 《岩石学报》1989,5(4):66-75

晚震旦世陡山沱组和早寒武世渔户村组、辛集组磷矿中有各种鮞粒、豆粒磷块岩。豆粒、鮞粒内核的成分和结构复杂,有来自陆地的各种岩石砂屑、细砾,也有盆内沉积物破碎成的各种内碎屑。鮞粒、豆粒的壳层是同心纹层状磷灰石,它是内核在富磷海水扰动中逐层淀积而成。大部分豆粒、鮞粒在滨海高能浅水中与陆源砂、砾和岔内碎屑沉积在一起,少量鮞粒则沉积在滨外深水低能环境巾。豆粒、鮞粒和碎屑等沉积后又被不同物质胶结。  相似文献   

Selenium and other trace element in phosphorites: A comparison between those of the Bayovar-Sechura and other provenances     

J. Bech  M. Suarez  F. Reverter  P. Tume  P. Sánchez  N. Roca  A. Lansac 《Journal of Geochemical Exploration》2010

Data of trace element composition of phosphorites are scarce and incomplete. Phosphorites of different origins can vary substantially in trace element contents. In this paper 20 trace element concentrations of 35 sample phosphorites are reported. The geographical provenance is: Bayovar-Sechura (Peru), Khouribga, Youssoufia and Boucraa (Morocco), Gafsa (Tunisia), Florida (USA), Idaho and Phosphoria Formation (USA), North Carolina (USA), Algeria, Israel, Senegal, Syria and Togo. Aqua regia extracts were used to estimate the “pseudototal” values, following standard procedures (ISO 11466, 2002) and measured by ICP-AES and ICP-MS.  相似文献   

Ca isotopic compositions of dolomite, phosphorite and the oldest animal embryo fossils from the Neoproterozoic in Weng'an, South China   总被引：2，自引：2，他引：0  

Tsuyoshi Komiya  Akinobu Suga  Tsuyoshi Ohno  Jian Han  Junfeng Guo  Shinji Yamamoto  Takafumi Hirata  Yong Li 《Gondwana Research》2008,14(1-2):209

Deciphering the drastic changes of surface environment and the emergence of animals after the Neoproterozoic Snowball Earth event are important for understanding the changes of surface environment and its influence on the evolution of life through geologic time. Especially, the emergence of two types of Metazoan animals such as animal embryo fossils, cnidarians or sponges, and Ediacaran fauna in the late Neoproterozoic was one of the critical turning points in the biological evolution.Calcium is one of the essential elements for the growth of most animals. In this study, in order to evaluate the Ca cycles in the Neoproterozoic, we have measured Ca isotopic ratios (⁴⁴Ca/⁴²Ca and ⁴³Ca/⁴²Ca) for phosphorite, dolostone and phosphatic animal embryo fossils with a multiple collector, inductively coupled plasma-mass spectrometer (MC-ICP-MS). The resulting ⁴⁴Ca/⁴²Ca ratio defined by the relative deviation from the ratio of NIST SRM915a (δ^44/42Ca_NIST915) for phosphorite and dolostone ranges from 0.83 to 0.95‰, demonstrating that the fractionation between phosphorite/dolostone and seawater was very small. This evidence indicates that at the emergence of the Weng'an biota seawater was deficient in Ca probably due to mass deposition of phosphorite/dolostone and to the beginning of Ca-biomineralization.Three phosphatic animal embryo fossils have lower δ^44/42Ca values than the phosphorite and dolomite, implying that the precursor of the phosphatic embryo fossils was able to fractionate Ca isotopes through Ca-biomineralization, consistent with marine gastropods.  相似文献   

贵州开阳磷矿矿区地质灾害分析     

孙晓松 《矿产与地质》2011,25(3):261-264

开阳磷矿为我国大型磷矿山,经过几十年的开采留下了很多地质灾害及隐患.文章针对矿山具体情况,采用高新技术手段对矿山深部开采和工程地质灾害事故隐患实施监控预警,提高矿山的本质安全程度和保障能力,达到控制和消除安全隐患,减轻灾害损失,提高企业市场竞争力.  相似文献   

沱江流域磷矿开采和加工过程中放射性环境问题探讨   总被引：1，自引：0，他引：1  

施泽明  倪师军  张成江  葛良全  郑林  裴云倩 《地球科学进展》2012,27(10):1134-1139

大多数磷矿伴随着高含量的放射性元素U,通过对龙门山地区磷矿开采和加工过程中U,Th迁移的研究,初步查明了沱江流域放射性环境问题。研究结果显示,除含U磷块岩外,四川省磷肥及磷矿石中U含量水平相对偏高,磷矿开采加工是造成区域放射性元素含量偏高的主要原因;磷矿加工过程中放射性元素U,Th主要迁移到中间产物及最终产品中;磷石膏的堆放对周边土壤环境的放射性影响,水平方向上已超过2 km,垂向上近50 cm;磷矿的开采与加工已对流域产生了一定程度的放射性环境影响。  相似文献   

开阳县永温片区磷矿扩采对温泉影响与否考析     

张磊  李强 《贵州地质》2013,(4):297-301

本文以开阳县永温片区拟设磷矿探矿权区为研究区,以实际的勘查和实验资料为依据,以对比分析为方法,对拟设磷矿探矿权区及相邻地带地下水系统的流场、温度场、化学场、同位素年龄开展了研究.研究结果表明,拟设探矿权区与相邻的温泉分属两个独立的地下水系统,研究成果对该区内磷矿资源的开发利用以及温泉的保护有重要的指导意义.  相似文献   

翁昭断裂对清水江磷矿影响及其控制浅析     

张晗彬  邓旭升 《贵州地质》2013,(4):262-265,301

通过对开阳县花梨乡清水江磷矿调查,磷矿主要赋存在下震旦统洋水组合磷岩系内.本文通过矿区断裂特征及构造解析认为磷矿层主要受三条北北西向断层的影响及控制,构造样式反映为北东向南西逆冲的断裂组合.磷矿主要赋矿层位为同一层位,反映为逆冲断层形成的叠瓦状构造造成的“三层式”矿层.  相似文献   

云南镇雄县银厂湾磷矿地质特征及成因分析     

沈燕飞  贺班艳  谢江 《云南地质》2020,(1):92-97

云南省镇雄县银厂湾磷矿为隐伏矿,矿体呈层状赋存于下寒武统梅树村组( 1ms),现已控制三个矿体,矿体产状与岩层产状一致,均较为平缓。矿体矿石矿物为胶磷矿、微晶碳磷灰石和氟磷灰石。通过研究,该矿床形成于海湾潮下低能带的古地理环境,主要由富磷生物碎屑沉积聚集而成,属沉积的碳酸盐-硅质层状磷块岩矿床。  相似文献   

晋宁磷矿表生改造型矿床及其判别标志   总被引：2，自引：0，他引：2  

罗朋志 《云南地质》2003,22(4):409-417

根据晋宁磷矿次生风化作用过程中磷块岩组成和结构的变化，归纳晋宁磷矿矿床特征及其影响因素，正确确定该矿风化矿石的判别指标。  相似文献