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The Global boundary Stratotype Section and Point (GSSP) of the Ladinian Stage (Middle Triassic) at Bagolino (Southern Alps, Northern Italy) and its implications for the Triassic time scale 被引量:15
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作者 Peter Brack Hans Riebe +1 位作者 Alda Nicora Roland Mundil 《Episodes》 SCIE 2005年第4期233-244,共12页
The Global boundary Stratotype Section and Point (GSSP) for the base of the Ladinian Stage (Middle Triassic) is defined in the Caffaro river bed (45°49'09.5"N, 10°28'15.5"E), south of the village o... The Global boundary Stratotype Section and Point (GSSP) for the base of the Ladinian Stage (Middle Triassic) is defined in the Caffaro river bed (45°49'09.5"N, 10°28'15.5"E), south of the village of Bagolino (Province of Brescia, northern Italy), at the base of a 15-20-cm-thick limestone bed overlying a distinct groove ("Chiesense groove ") of limestone nodules in a shaly matrix, located about 5 m above the base of the Buchenstein Formation. The lower surface of the thick limestone bed has the lowest occurrence of the ammonoid Eoprotrachyceras curionii (base of the E. curionii Zone; onset of the Trachyceratidae ammonoid family). Secondary global markers in the uppermost Anisian include the lowest occurrence of conodont Neogondolella praehungafica and a brief normal-polarity magnetic zone recognized in closely correlated sections including the principal auxiliary section at Seceda in the Dolomites. The GSSP-level is bracketed by U-Pb single zircon age data from volcaniclastic horizons, indicating a boundary age of ca 241 Ma. 展开更多
关键词 三叠纪 阿尔卑斯山 意大利 GSSP
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Implications of a new, biostratigraphically well-controlled, radio-isotopic age for the lower Telychian Stage of the Llandovery Series (Lower Silurian, Sweden) 被引量:2
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作者 Stig M. Bergstrom Funda Ozlem Toprak +1 位作者 Warren D. Huff Roland Mundil 《Episodes》 SCIE 2008年第3期309-314,共6页
Radio-isotopic analysis of single zircons from two early Telychian K-bentonites, one of which is among the most widespread Lower Paleozoic volcanic ash falls in north- ern Europe, yields overlapping weighted mean 206p... Radio-isotopic analysis of single zircons from two early Telychian K-bentonites, one of which is among the most widespread Lower Paleozoic volcanic ash falls in north- ern Europe, yields overlapping weighted mean 206pb/238U ages of 438. 7± 1.0 Ma and 437.8 ± 0.5 Ma, respectively. The former age is from zircons of the Osmundsberg K-bentonite from the type locality at Osmundsberget in the Siljan area of central Sweden where it occurs in the lower part of the Spirograptus tur- riculatus Graptolite Zone and in the lower part of the Angochitina longicollis Chitinozoan Zone. Zircons giv- ing the latter age are from a bed previously identified as the Osmundsberg K-bentonite at the Kallholn Quarry in the same area. Based on new biostratigraphic data, the latter bed is now considered to be slightly younger than the Osmundsberg K-bentonite. The dated stratigraphic level of the ash layers is slightly younger than the base of the Telychian Stage and thus represents a minimum age for the Aeronian/Telychian Stage boundary. A U-Pb age of 〉 438 Ma for the base of this stage, however, is older and in conflict with estimates in the most recent compilation of the Silurian time scale. In view of the fact that only three radio-isotopic dates from the entire Llan- dovery have been previously accepted, this new and biostratigraphically exceptionally well-controlled radio-isotopic date fills an important gap in the Lower Silurian geochronology. 展开更多
关键词 无线电 同位素 蓝达夫里阶 志留纪
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Evidence of An Early Cretaceous Giant Dyke Swarm in Northeast Brazil(South America):A Geodynamic Overview
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作者 Maria Helena B.M.HOLLANDA Carlos J.ARCHANJO +4 位作者 Paul R.RENNE Donald E.NGONGE David L.CASTRO Diógenes C.OLIVEIRA Antomat A.MACEDO FILHO 《Acta Geologica Sinica(English Edition)》 SCIE CAS CSCD 2016年第S1期109-110,共2页
The Mesozoic break-up and drifting of the Equatorial Atlantic margin in the northeast Brazil(South America)is characterized by a modest magmatic activity compared with the Southern Atlantic margin,where the Paraná-
关键词 Evidence of An Early Cretaceous Giant Dyke Swarm in Northeast Brazil South America A Geodynamic Overview
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激光40Ar/39Ar定年数据高斯数学模型分析与 腾冲火山喷发的分期 被引量:2
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作者 赵昕炜 周晶 +2 位作者 马芳 季建清 Alan DEINO 《中国科学:地球科学》 CSCD 北大核心 2020年第6期807-818,共12页
确定火山岩的喷发期次是重建火山喷发相关的第四纪环境、研究晚新生代地球动力学和预测火山喷发危险性的前提.激光40Ar/39Ar年代学方法对年轻火山岩样品的定年有明显的优势,具有自动化测试稳定、本底低、高灵敏度等特点,适用于年轻火山... 确定火山岩的喷发期次是重建火山喷发相关的第四纪环境、研究晚新生代地球动力学和预测火山喷发危险性的前提.激光40Ar/39Ar年代学方法对年轻火山岩样品的定年有明显的优势,具有自动化测试稳定、本底低、高灵敏度等特点,适用于年轻火山岩样品的定年工作.文章采用激光40Ar/39Ar年代学方法对腾冲火山岩区主要岩石单元进行了精细的年代学研究,通过常规的数据处理得到了腾冲火山喷发的时限为0.025~5.1Ma.但年轻火山岩定年因放射成因的40Ar含量极少,偶然因素较多,数据的稳定性较差,甚至得出偏差很大的年龄结果,其分期结果值得商榷.另外,传统分期方法缺乏统一的时间尺度标准,无法对腾冲火山喷发进行严格的时间限定,导致对期次划分认识的分歧.文章尝试引入新的数学模型,对13件样品一共378个年龄测试值进行了重新分期,得到了包含3个波形曲线、彼此独立的表观年龄概率分布图,利用高斯数学模型对波形进行分析,分别对确认的3个正态波形涵盖的年龄数据进行等时线年代学计算,很好地限定了腾冲火山的3期喷发,分别为上新世((3.78±0.04)Ma)、中更新世早期((0.63±0.03)Ma)和中更新末期到晚更新世早期((0.139±0.005)Ma).这3期喷发时限具有相同的实验精度和时间尺度,降低了年龄数据的误差和偶然性,能准确地限定和代表腾冲火山的整体喷发分期. 展开更多
关键词 激光40Ar/39Ar定年 高斯数学模型 喷发分期 表观年龄概率统计图 年龄偏差 等时线年龄
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Using a Gaussian mathematical model to define eruptive stages of young volcanic rocks in Tengchong based on laser 40Ar/39Ar dating 被引量:2
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作者 Xinwei ZHAO Jing ZHOU +2 位作者 Fang MA Jianqing JI Alan DEINO 《Science China Earth Sciences》 SCIE EI CAS CSCD 2020年第5期662-673,共12页
Reconstruction of Quaternary environments,late Cenozoic geodynamics and evaluation of volcanic hazards,all depend on the precise delineation of eruptive stages.In recent years,laser 40Ar/39Ar dating methods have been ... Reconstruction of Quaternary environments,late Cenozoic geodynamics and evaluation of volcanic hazards,all depend on the precise delineation of eruptive stages.In recent years,laser 40Ar/39Ar dating methods have been widely used for dating young volcanic rocks,given their stable automated testing process,very low background level and high sensitivity,which meet the requirements for precise dating of young samples.This paper applied high-precision laser 40Ar/39Ar dating to the main volcanic units in the Tengchong area and obtained ages in the range of 0.025–5.1 Ma using conventional data processing methods.However,conventional dating highlighted issues related to very low radiogenic 40Ar content,accidental errors and poor data stability,which led to huge age deviations.Moreover,lacking a unified timescale,conventional methods were unable to strictly define the stages of the Tengchong volcanic eruptions,leading to ongoing controversy.In this study,we applied a Gaussian mathematical model to deal with all 378 original ages from 13 samples.An apparent age-probability diagram,consisting of three independent waveforms,have been obtained.The corresponding isochron ages of these three waveforms suggest there were three volcanic eruptive stages,namely during the Pliocene(3.78±0.04 Ma),early Middle Pleistocene(0.63±0.03 Ma)and late Middle Pleistocene to early Late Pleistocene(0.139±0.005 Ma).These results accurately define eruptive stages in the Tengchong area. 展开更多
关键词 LASER 40AR/39AR DATING GAUSSIAN mathematical model ERUPTIVE STAGES Apparent age-probability diagram Age deviations Isochron age
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