峨眉山大火成岩省的风化碳汇效应:玄武岩粉末水-岩反应实验研究

在实现“双碳”目标背景下,有效的碳封存技术成为近年来学界关注的焦点。在众多碳封存技术中,基于玄武岩粉末的增强风化碳汇技术具有较强的成本优势,同时也对促进作物生长、改善粮食产量具有积极作用。流域研究揭示玄武岩风化具有非常高的速率,但与玄武岩粉末增强风化碳汇技术在时间尺度和反应条件上存在较大差异。中国西南地区广泛分布有峨眉山玄武岩,其在喷发之后的快速化学风化被认为是晚二叠世冰川活动的驱动机制,有可能成为增强风化碳汇技术的基础原料。为深入理解峨眉山玄武岩的风化碳汇效应,增进对玄武岩增强风化碳汇技术的认识,本文利用不同粒径玄武岩粉末和天然雨水及河水开展了水岩反应实验研究。结果显示,雨水与玄武岩粉末经历720 h常温条件的封闭反应后,其pH值接近河水的pH值,且Na+、K^(+)、Ca^(2+)、Mg^(2+)等离子浓度显著升高,其活动性和溶出速率受所在岩石结构、矿物组成、元素赋存状态、溶液饱和状态等因素共同影响与控制。玄武岩粉末与雨水的反应实验中Si元素的溶出速率最快,为4.36×10^(-12)mol/m^(2)/s,Ca^(2+)和Mg^(2+)的最大浸出速率分别为1.36×10^(-12)mol/m^(2)/s和0.91×10^(-12)mol/m^(2)/s;同时,反应溶液HCO_(3)^(-)浓度快速升高,在720 h左右达到最大浓度,表明了溶液中溶解的CO_(2)快速转变为HCO3-,而随后HCO_(3)^(-)浓度趋于降低,PHREEQC模拟结果显示Ca-Mg碳酸盐矿物达到饱和状态。初步的反应实验研究表明,峨眉山玄武岩风化具有重要的碳汇效应,可应用于增强风化碳汇技术进行地表碳封存。

中扬子区中生代含变质岩屑砂岩的显微图像数据集

本文收集和归纳了中扬子北缘三叠系至侏罗系砂岩的显微图像数据。样品主要为中粗粒砂岩。我们系统鉴定和部分统计了86件岩石样品的碎屑组分,识别出岩屑石英砂岩、石英岩屑砂岩和长石石英砂岩等8种不同类型的砂岩,拍摄了287张岩石显微图像照片。我们重点描述了含变质岩屑的砂岩显微图像特征,并对变质岩屑的变质等级和原岩类型进行了分类。本图集的建立丰富了中扬子区中生代沉积地质演化的基础研究,并可作为变质岩屑的识别与分类的案例,为追溯变质岩屑源区,重塑造山带剥露历史等研究提供一定的参考。

中扬子区巴东组凝灰岩层的锆石U-Pb年龄约束

印支运动深刻地改变了华南大陆和东亚的古地理格局,导致了大规模的海陆变迁。在扬子北缘发育有以紫红色碎屑岩为主的巴东组及相关地层,代表了从碳酸盐岩为主的海相沉积到碎屑岩为主的陆相沉积的转变。巴东组可划分为三段,即一、三段的紫红色粉砂岩、泥岩夹二段灰岩泥灰岩。由于巴东组三段的化石稀少,其年代归属一直存有争议。本文运用LA-ICP-MS定年方法,对新发现于鄂西秭归地区巴东组二段的凝灰岩夹层进行了锆石U-Pb定年。结果表明,来自于巴东组二段中部和顶部的两件凝灰岩样品分别形成于241.7±1.7Ma和237.5±2Ma。结合凝灰岩层的就位年龄和生物化石记录,巴东组地层时代被限定为中三叠世安尼期至晚三叠世卡尼期。凝灰岩中锆石颗粒多呈长柱状,无磨圆,发育明显的振荡环带,且具有与造山型岩浆锆石一致的微量元素化学特征。以巴东组灰岩为代表的"最高海相层"穿时地分布于鄂东南至川西一线,反映了上、中扬子区由中三叠世安尼期晚期至晚三叠世卡尼期海水大规模向西退去的海陆变迁特征。

南华北早二叠世泥岩沉积与深时陆地古温度重建

地球在地质历史时期经历过多次冰室与温室气候状态间的相互转换,也发生了以雪球地球为特征的极冷和以快速升温为特征的极热气候事件。二叠纪是晚古生代冰期到中生代温室气候转换的关键时期。为深入认识二叠纪的重大气候演变,急需解决的一个科学问题是如何获取高精年代地层约束的陆地古气候信息。通过总结近年来报道的华北南部石炭—二叠纪含煤岩系的同位素年代学和泥岩风化地球化学数据,建立了基于高精年代地层格架的化学风化趋势,定量重建了华南南部在约300~286 Ma的陆地古温度变化曲线,揭示了低纬陆地古气候对高纬冰川活动和全球气候变化的响应。新建的南华北陆地古温度曲线指示了与早二叠世Asselian初期和Sakmarian晚期两次冰川消融相对应的气候变暖事件,也指示了与Asselian早期和Artinskian早期两次冰川扩张相对应的气候变冷事件。

黔西南下三叠统飞仙关组沉积物源分析对峨眉山大火成岩省火山剥蚀序列的重建约束

峨眉山大火成岩省在形成后遭受了强烈的风化剥蚀,与右江盆地构成了独特的源-汇沉积体系,相关的碎屑沉积记录是重建峨眉山大火成岩省晚期火山序列、揭示大火成岩省岩浆演化的关键。本文对黔西南地区右江盆地北缘下三叠统下部飞仙关组开展了详细的沉积物源研究。飞仙关组泥岩由长石、石英和黏矿物等组成,具有低SiO_(2)、高TiO_(2)含量和低Al_(2)O_(3)/TiO_(2)值的特征,具Eu的弱负异常,微弱的Nb、Ta负异常。基于Al_(2)O_(3)/TiO_(2)和La/Sm物源图解分析,研究样品的主要物源由峨眉山大火成岩省的高-Ti玄武岩和少量酸性火山岩构成,这与右江盆地晚二叠世的碎屑沉积物源组成一致。碎屑锆石具有~260 Ma的年龄峰值,对应锆石具有较低的Th/Nb和较高的Nb/Hf值,均支持峨眉山大火成岩省作为主要的沉积物源区,而同时存在的>400 Ma的碎屑锆石则对应于峨眉山玄武质岩浆上升时所捕获的华南地壳物质。与上二叠统的碎屑锆石U-Pb年龄组成和锆石化学组成对比分析表明,峨眉山大火成岩省在晚二叠世到早三叠世早期剥蚀的火山岩构成了一定的火山序列,反映了该大火成岩省晚期从强烈地壳混染到分异结晶为主的岩浆演化过程。

南华北石炭-二叠纪太原组灰岩显微图像数据集

本文收集和整理了华北板块南缘石炭-二叠纪含生物碎屑灰岩的显微图像。选择豫西地区跨潟湖-局限台地-开阔台地-斜坡多相带的3条太原组野外剖面为研究对象,对代表性的图像及其岩石特征进行分类描述。样品以灰泥含量较高的含生物碎屑粒泥灰岩为主要特征。利用装有显微照相系统的蔡司偏光显微镜对灰岩薄片进行观察和照相。灰岩显微图像集共包含95件灰岩样品,380张显微照片,可分为泥晶灰岩、泥粒灰岩和粒泥灰岩3类。本图像集的建立可为研究晚古生代大冰期时北半球中纬度地区的古气候、古环境、古生物面貌及相带沉积分异提供基本素材和参考。

Soft-sediment Deformation Structures Related to Earthquake from the Devonian of the Eastern North Qilian Mts.and Its Tectonic Significance

Devonian in the North Qilian orogenic belt and Hexi Corridor developed terrestrial molasse of later stage of foreland basin caused by collision between the North China plate and Qaidam microplate. The foreland basin triggered a intense earthquake, and formed seismites and earthquake-related soft-sediment deformation. The soft-sediment deformation structures of Devonian in the eastern North Qilian Mts. consist of seismo-cracks, sandstone dykes, syn-depositional faults, microfoids （micro-corrugated lamination）, fluidized veins, load casts, flame structures, pillow structures and brecciation. The seismo-cracks, syn-depositional faults and microfolds are cracks, faults and folds formed directly by oscillation of earthquake. The seismic dykes formed by sediment instilling into seismic cracks. Fluidized veins were made by instilling into the seismo-fissures of the fluidized sands. The load casts, flame structures and pillow structures were formed by sinking and instilling caused from oscillation of earthquake along the face between sandy and muddy beds. The brecciation resulted from the oscillation of earthquake and cracking of sedimentary layers. The seismites and soft-sediment deformations in Devonian triggered the earthquake related to tectonic activities during the orogeny and uplift of North Qilian Mts.

New Zircon U-Pb Age of the Babu Ophiolites in Southeast Yunnan,China and Constrains of Plate Subduction Time

Objective The Babu ophiolite in Malipo County of southeastern Yunnan is interpreted as remanant ocean crust and represents a possible branch of Paleo-Tethyan Ocean in South China. It consists mainly of mafic and ultramafic rocks. These rocks are very important to understand the evolution of the Paleo-Tethyan Ocean. However, the Babu ophiolite is still disputed and the mafic and ultramafic rocks have been inferred to be part of the Emeishan large igneous province （LIP） by some researchers. In this paper, we present zircon U-Pb data on the metabasalts in Malipo to reveal the formation time of mafic and ultramafic rocks and their tectonic nature.

The Sedimentological Knowledge Tree:Significance,Method and Progress

On the platform of the Deep-time Digital Earth Program(DDE),sedimentary data are essential for achieving its scientific objectives.These data will take stratigraphic units as their core data carrier,for quantitative or qualitative data analysis.The DDE Sedimentary Data Group is responsible for the management of the sedimentary data on the DDE platform and has now developed into a group of nearly 40 disciplinary experts.

An Exploration of Building a Thematic Sub-database within the Framework of DDE:A New Detrital Zircon U-Pb Dating Database

Within the framework of the Deep-time Digital Earth(DDE)project,thematic databases driven by scientific issues will have strong scientific vitality.In the field of sedimentology,thematic databases based on the current unified sedimentary knowledge tree established by the Sedimentary Data Group(Fig.1),can solve specific scientific problems effectively and improve the scope and utility of the DDE platform significantly.

掺硼直拉单晶硅棒不同位置硅片制备的PERC电池光衰及复原

为了探究产业化发射极和背面钝化电池(Passivated Emitter and Rear Cells,简称PERC电池)光衰以及复原随硅片在硅棒位置的变化规律,将一根产业化掺硼直拉单晶硅棒从头至尾每隔一定距离进行切割得到6组硅片。在测量了硼、氧、碳、过渡金属杂质含量以及少子寿命之后,采用标准化工业过程将它们制成PERC电池。然后,使用太阳电池I-V特性测试仪测量在45℃、1 sun、12 h光衰→100℃、1 sun、24 h复原→45℃、1 sun、12 h再光衰实验中各参数随时间的变化。结果表明,尾部硅片制备的PERC电池的效率、开路电压和短路电流具有最高的复原上升幅度,在第二次光衰时其不仅效率最高而且最初光衰的幅度也较小,这说明100℃、1 sun光强、24 h的复原条件足以让PERC电池内部的硼氧缺陷近乎完全失活。第二次光衰时效率在初始阶段的小幅光衰可归因于未达到复原状态的硼氧缺陷所致,也证明了达到复原状态的硼氧缺陷具有很好的抗光衰性能。

川东地区天然气场站固化池渗滤液污染特征及其对地下水影响研究

为了解天然气开采过程中钻井废弃物用固化池处置前后污染物随时间的消减变化及固化池渗滤液对地下水的影响,本研究分别采集川东气田固化池的渗滤液和气田作业区域地下水样品,分析渗滤液和地下水中污染物浓度水平.结果显示,与2013年原完井废弃物浸出液污染物浓度相比,川东地区2022年各场站大部分固化池渗滤液中污染物仍以常规污染物COD为主(92.6%),而氯化物、石油类和硫化物等特征污染物浓度经固化池处理后均未达到GB/T 16848-2017《地下水质量标准》Ⅲ类标准所规定的标准限值.沿江地区和非沿江地区固化池渗滤液中氯化物浓度具有显著性差异(p<0.05),而硫化物差异不显著(p>0.05).2022年部分地下水监测井检测结果显示川东气田固化池渗滤液并未对周边地下水质产生明显影响,但渗滤液指数计算结果显示,240个场站中有3处场站固化池渗滤液呈较高环境风险,可能对当地地下水资源造成潜在污染风险.

Geochemical significance of the Paleogene soda-deposits bearing strata in Biyang Depression,Henan Province

The Biyang Depression,lying in the eastern Nanxiang Basin,has a dustpan-shape with faults developed to the southwest and southeast.The Paleogene Hetaoyuan Formation in this depression hosts one of the oldest soda-deposits,the Anpeng deposit.These sodium carbonate-bearing strata consist of lutites,muddy dolomites,and bedded soda-deposits,which are dominated by nahcolite with little trona,mirabilite,and halite.In the top Unit 3 and lower Unit 2 of Hetaoyuan Formation where the sodium carbonates are concentrated,dolomitic shale,muddy carbonate,and sodium carbonate can be separated based on their distinct Al2O3,Ti O2,Na2O,Mg O+Ca O,and LOI(loss on ignition)contents.By using Na2O/(Mg O+Ca O)ratio as an indicator for the relative concentration of Na carbonates to Mg-Ca carbonates,the muddy dolomites can be classified into two groups.One group with Na2O/(Mg O+Ca O)<0.6 exhibits a positive correlation between this ratio and Al2O3+Ti O2 content,an proxy for terrigenous clastic input and the other group with Na2O/(Mg O+Ca O)>0.6 presents a negative correlation.As the clastic proportion decreases,the former indicates that it tends to form pure Mg-Ca carbonates reflecting evaporation less than or equal to replenishment for the lake water in a relative humid climate,and the latter reveals a trend to form sodium carbonates with lake water’s evaporation more than replenishment in a relatively dry climate.From muddy dolomite to sodium carbonate samples,with Na2O/(Mg O+Ca O)ratio increasing,the Al normalized Zr,Ti,La,K,Rb,and Ba tend to be enriched and the post-Archean Average Shale(PAAS)normalized positive Eu anomaly becomes more obvious.Integrated with the high B contents and the report of searlesite in the bedded sodium carbonates and the regional extensional tectonic regime,the above geochemical characteristics were interpreted to signify hydrothermal contribution to forming these soda-deposits through the deep fault systems of basin margins.

Depositional chemistry of chert during late Paleozoic from western Guangxi and its implication for the tectonic evolution of the Youjiang Basin

Continual deep-water sediments from the late Early Devonian to the Late Permian extended in wide areas of western Guangxi.We analyzed the major,trace,and rare earth elements of the Upper Paleozoic cherts in Badu,western Guangxi.High non-terrigenous SiO2 contents(Sinon-ter/Sibulk(%)> 80%) and pure chert components(> 70%) indicate a large extent of silicification in the Upper Paleozoic cherts,except for the Upper Devonian-Lower Carboniferous Luzhai Formation cherts,which have lower non-terrigenous SiO2 contents(avg.71.8%) and pure chert components(40%-70%).The Al/(Al+Fe+Mn) ratios and Feter/Febulk(%) values of samples from the lowest horizon of the Pingen Formation are 0.05-0.26,13.1%-14.5%,respectively,indicating hydrothermal origins.All other samples show high Al/(Al+Fe+Mn) ratios(0.39-0.81) and high Feter/Febulk(%) values(23.1%-186.8%),indicating non-hydrothermal origins.The Pingen Formation and Liujiang Formation cherts show slightly-moderately negative Ce anomalies(0.71±0.07,0.81±0.08,respectively) and higher Y/Ho ratios(33.49±1.27,36.10±2.05,respectively) than PAAS.This suggests that these cherts were deposited in the open marine basin,rather than in the intracontinental rift basin as previously assumed.The Luzhai Formation cherts may be deposited near the seamount or seafloor plateaus with no negative Ce anomalies(1.09±0.07) and no significant Y-Ho fractionation(Y/Ho=28.60±1.25).The Nandan Formation and Sidazhai Formation cherts were deposited in the open-ocean basin with moderately negative Ce anomalies(0.67±0.08,0.73±0.11,respectively) and high Y/Ho ratios(36.01±1.00,32.00±2.25,respectively).On the basis of our studies about cherts,we conclude that the Youjiang Basin originated as part of the Paleo-Tethys that controlled the depositional environments of cherts during late Paleozoic.The rift of the Youjiang Basin had occurred at least since the Early-Middle Devonian.The basin had a trend of evolving into an open-ocean basin during the Early-Middle Permian.

Sedimentary geochemistry and provenance of the Lower and Middle Devonian Laojunshan Formation,the North Qilian Orogenic Belt

The Laojunshan Formation is a suite of molasse formed during the rapid uplift of the North Qilian Orogenic Belt (NQOB). Forty-one samples of sandstone have been collected from the Sunan and Minle sections in the western sector and the Gulang and Jingyuan sections in the eastern sector of the NQOB belt. Geochemical analyses of those samples indicated: 1) The MgO+Fe2O3T and Al2O3/SiO2 values are higher, and K2O/Na2O ratios are lower in the western sector than those in the eastern sector. 2) All of them are depleted in Nb and Ta elements. The samples from the western sector are depleted in Rb element and enriched with Sc, Co, Ni, V, and Cr elements in the Upper Crust-normalized patterns. However, those from the eastern sector are depleted in Sr without enrichments of Sc, Co, Ni, V, and Cr. 3) All of the samples display a right-inclined REE pattern af- ter Chondrite-normalized REE pattern. But LaN/YbN and Eu/Eu* ratios of the samples from the western sector are lower than those of the samples from the eastern sector. These geochemical characteristics suggest the prominent input of mafic clast with minor granitic rocks into the Sunan area, felsic clast into the Gulang and Jingyuan area, and both mafic and felsic clast into the Minle area. The angular shapes of gravels imply that these ill-sorted sediments were deposited near their sources without recy- cling. Geochemical features above also demonstrated that no major chemical weathering occurred for the western provenance, but deposits in the eastern sector resulted from low or middle degree chemical weathering. Evidences combining tectonic discriminations and comparisons with potential provenances revealed that sediments in the Sunan area were derived mainly from the North Qilian Continental arc, whereas sediments in the Minle, Gulang, and Jingyuan areas were derived not only from the North Qilian Continental arc but also from the basement of the Middle Qilian block. Integrated with the characteristics of development of Silurian and Devonian, these imply that the orogeny of NQOB is diachronous in the trending direction due to the oblique collision.

Devonian Frasnian-Famennian transitional event deposits of Guangxi, South China and their possible tsunami origin

A suite of event deposits, isochronous and interrelated in origin, occurs widely near the Frasnian- Famennian boundary in Guangxi, South China. It is mainly distributed in the facies areas of the platform-margin slope and inter-platform rift-trough. The rudstone or calcirudite occur in the Liujing section of Hengxian and Luoxiu and Baqi sections of Xiangzhou in the facies area of platform-margin slope. The turbidites are observed in the sections of Yangdi and Baisha of Guilin, Du'an of Debao, Nandong and Sanli of Wuxuan, Xiangtian, Ma'anshan of Xiangzhou, Nayi of Chongzuo, Yunpan of Shanglin in the facies area of inter-platform rift-trough. The massive homogenites occur in sections of Mangchang, Luofu and Road from Nandan to Tian'e and Ma'anshan etc in the facies area of inter-platform rift-trough. Herein event deposits can be correlated in stratohorizon to the turbidite in the bottom of the Lower triangularis Zone in Hony railroad cut of Belgium, Devils Gate of Nevada, USA, Atrous of Morocco, South Urals and Fore-Kolyma of northeastern Siberia of Russia, and erosional discontinuities and brecciation in the Frasnian-Famennian boundary in South Polish-Moravian shelf. The event deposits could be caused by a violent tsunami related to bolide impacts into ocean.

Geochemistry of the Late Paleozoic cherts in the Youjiang Basin:Implications for the basin evolution

We analyzed the major and rare earth element compositions of siliceous deposits from the Upper Devonian Liujiang Formation,Lower Carboniferous Luzhai Formation,Lower-Middle Permian Sidazhai Formation and Tapi Formation,which are widely distributed as bedded cherts in the interplatform basinal successions of the Youjiang Basin.The Liujiang Formation and Luzhai Formation cherts generally have high Al/(Al+Fe+Mn) values(0.38-0.94) and are non-hydrothermal cherts.These cherts are generally characterized by moderately negative Ce anomalies and high Y/Ho values relatived to PAAS,indicating that the Youjiang Basin might have evolved into an open rift basin during the Late Devonian-Early Carboniferous.The Sidazhai Formation cherts from Ziyun generally have high Al/(Al+Fe+Mn) values(0.60-0.78),suggesting negligible contribution from a hydrothermal component.The Sidazhai Formation cherts from Hechi and the Tapi Formation cherts from Malipo generally have low Al/(Al+Fe+Mn) values(0.09-0.41),indicating an intense hydrothermal input.Relatived to the Sidazhai Formation cherts,the Tapi Formation cherts have higher Ce/Ce*values(0.68±0.19) and lower Y/Ho values(41.83±13.27),which may be affected by the terrigenous input from the Vietnam Block.The Sidazhai Formation cherts from Ziyun and Hechi exhibit negative Ce anomalies(0.43±0.12,0.33±0.17,respectively) with high Y/Ho values(57.44±16.20,46.02±4.27,respectively),resembling the geochemical characteristics of open-ocean basin cherts.These cherts were deposited on a passive continental margin adjacent to the Babu branch ocean,which may have contributed to upwelling.Detailed spatial studies on geochemical characteristics of the Late Paleozoic cherts can unravel the evolution of the Youjiang Basin.

U-Pb geochronology of hydrothermal zircon from the Mesoproterozoic Gaoyuzhuang Formation on the northern margin of the North China Block and its geological implications

This paper reports LA-ICP-MS zircon U-Pb ages and REE compositions on detrital zircons (Type 1) and hydrothermal zircons (Type 2) from low-metasedimentary rocks in the Mesoproterozoic Gaoyuzhuang Formation,Pingquan area,Hebei Province that provide important constraints on the tectonic evolution along the northern margin of the North China Block.The detrital zircons are characterized by an oscillatory magmatic core,surrounded by a narrow structureless rim in CL images.They yield 207Pb/206 Pb ages ranging from 1703 to 2543 Ma with two age peaks at 2473 and 1794 Ma,which is consistent with the Neoarchean and Paleoproterozoic tectono-thermal events recorded in the NCB basement,indicating that the source of the detritus was locally derived.By contrast,the hydrothermal ones are euhedral,sector zoning or internally structureless.They have relatively higher U and Th contents and Th/U ratios (U=139 2918 ppm,Th=35 1327 ppm,Th/U (average) =0.78 vs.U=15 1044 ppm,Th=8 341 ppm,Th/U (average) =0.57 for detrital zircons).Moreover,they are also enriched in REEs relative to detrital zircons and show a lower positive Ce anomaly (REE=659 2418 ppm vs.231 611 ppm for detrital zircon;Ce/Ce =2 13 vs.33 174 for detrital zircons),similar to known hydrothermal zircons derived from many locations.These characteristics,combined with our field petrographic observations,indicate that the hydrothermal zircons possibly formed from a low temperature aqueous fluid.Twelve concordant or near-concordant analyses on hydrothermal zircons yield weighted mean 206 Pb/238 U ages of 325 327 Ma,which provide unambiguous evidence that the northern NCB underwent late Paleozoic low temperature hydrothermal modification.This timing of this hydrothermal event is compatible with that of the late Paleozoic magmatic and metamorphic-deformational events occurred on the northern margin of the NCB,it appears likely that the hydrothermal activity resulted from southward subduction of the Paleo-Asian Oceanic plate underneath the NCB during late Paleozoic.

Trace and rare earth elemental geochemistry of carbonate succession in the Middle Gaoyuzhuang Formation,Pingquan Section:Implications for Early Mesoproterozoic ocean redox conditions

The concentrations of redox-sensitive trace elements,such as uranium(U),vanadium(V),molybdenum(Mo),cobalt(Co),chromium(Cr) and rare earth elements(REE+Y) were determined in a given carbonate succession in the Gaoyuzhuang Formation(～1.56 Ga),which spans depths from outer shelf to intertidal,to explore the Early Mesoproterozoic ocean redox conditions.The values of the Zr-normalized redox-sensitive trace element concentrations and some relevant ratios show obvious changes from bottom to top in the succession.Samples from the outer shelf setting(M1 interval) demonstrate significantly enhanced values in Zr-normalized redox-sensitive trace element concentrations and relevant ratios(the peaks of Mo/U,V/Cr and Ni/Co ratios larger than 8,4.25,and 7,respectively).Authigenic framboidal pyrites were also found within oncolite-like carbonate concretions and surrounding host rocks in this interval.These all indicate a euxinic state in the outer shelf environment.Less enrichment of Zr-normalized redox-sensitive elemental abundances and a mild decrease in the values of geochemical ratios were present in the inner shelf environment(M2 interval)(the V/Cr and Ni/Co ratios fall into a range of 2.5 4.25 and 4 5,respectively),suggesting dysoxic conditions dominant in the inner shelf setting.Samples from the shallower subtidal and intertidal settings(M3 and M4 intervals) are mostly invariable with much lower values of Zr-normalized redox-sensitive elements and relevant ratios,with the V/Cr and Ni/Co ratios typically near or less than 2 and 5 respectively,indicative of oxic conditions in the high energy subtidal/intertidal zones.A remarkable negative Ce anomaly exhibited in the shale-normalized REE+Y diagram in the M4 interval may provide evidence in support of the hypothesis.Taken together,our results suggest a relatively shallow chemocline in the Early Mesoproterozoic ocean:the transitions between euxinic,dysoxic and oxic may occur in quiet-water outer shelf and highenergy subtidal zone,respectively.The presence of euxinic ocean bottom waters is compatible with low concentrations of seawater sulfate and reduced levels of atmospheric oxygen during this period.The extreme environmental conditions induced by these anoxic oceans could have been responsible for the delayed oxygenation of the biosphere and hindered the evolution of multicellular life.