Geochronology and geological significance of the strata of the Neoproterozoic Nanhua System,SW North China Craton

A set of low-grade clastic metamorphic and carbonate rocks,and greenschists outcropping in the southwestern(SW)margin of the North China Craton(NCC),was originally classified as the Paleoproterozoic Xiong’er Group according to stratigraphic correlation.To verify the age,this paper carried out detrital zircon U–Pb LA-ICP-MS dating of low-grade clastic metamorphic rocks exposed in the Changqing area at the SW margin of the Ordos Block in the SW part of the NCC.Results from detrital zircon dating indicate that the metamorphic and carbonate rocks can be classified into the Neoproterozoic Nanhua System,which is the only Nanhua System stratum in this block so far,and it probably could provide new clues to Rodinia break-up and Snowball Earth of the NCC.The nine peak ages of the low-grade clastic metamorphic rocks reflected its relatively complex provenance,and almost all major geological events experienced by the NCC basement since the Neoarchean,but some age peaks were difficult to correspond to that of the NCC,indicating that the southwestern part of the Ordos Block was also affected by the Qinling and Qiliang orogenic belts during Nanhua System of Neoproterozoic.Combined with provenance analysis,it was revealed that the current southwest boundary of the Ordos Block was the previous southwest boundary of the Ordos Block during the Qingbaikou-Nanhua Period of the Neoproterozoic.

Lower boundary age of the Nanhua System and the Gucheng glacial stage: Evidence from SHRIMPⅡ dating

In the newly revised Regional Chronostrati-graphic (Geochronologic) Scale of China, the original bipar-tite division of the Neoproterozoic is changed to tripartite division. The three 搒ystem?rank chronostratigraphic units are in ascending order of the Qingbaikou, Nanhua and Sin-ian Systems. This report presents SHRIMP zircon U-Pb dat-ing on volcanic tuffs from the candidate stratotype section of the Nanhua System at the Yangjiaping section that is geo-graphically located in Hupingshan Town, Shimen County, Hunan Province. Tuff from the upper part of the Xieshuihe Formation (equivalent to the Liantuo Formation) in the Lower Nanhua Series yields a zircon U-Pb age of 758 23 Ma, which may provide a constraint on the lower limit of the Gucheng glacial stage in the Nanhua System. Tuff from the Laoshanya Formation of its underlying Qingbaikou System (equivalent to the Banxi Group) gives a zircon U-Pb age of 809 16 Ma. The sampling locality lies 12 m from the upper boundary of the Qingbaikou System. According to the sedi-mentation rate it is estimated that the upper boundary age is about 800 Ma. The present studies also provide a resolution to the long-standing problems concerning stratigraphic cor-relation of the Late Precambrian in South China whether the Liantuo Formation is equivalent to the Banxi Group or not.

扬子地块北缘镇巴穿心店地区南华系碎屑锆石U-Pb年龄及其物源示踪

扬子地块北缘镇巴穿心店地区发育有完整的南华系—震旦系沉积地层,记录了研究区及邻区南华纪沉积特征,对于研究扬子地块北缘新元古代晚期构造演化历史和Rodinia超大陆演化过程具有重要的地质意义。研究区南华系由下至上可划分为4套岩石地层单位,分别为长安组、古城组、大塘坡组和南沱组。南华系砂岩地球化学特征表明,研究区南华系化学风化作用较弱,经历了较低程度的沉积物再旋回作用。砂岩的CIA、CIW、PIA、Rb/Sr等古气候指标显示,研究区南华系具有由寒冷干燥—有波动的寒冷干燥—趋于稳定的温暖湿润—寒冷干燥的古气候演化趋势。在Dickinson三角图解中清晰地反映了南华系各组砂岩具有再旋回造山带和切割岩浆弧物源的特征,同时砂岩岩石地球化学特征也指示南华系的物源区主体应由中酸性岩浆岩组成。南华系长安组、古城组和南沱组3件碎屑锆石U-Pb年龄样品的年龄分布特征类似,主要年龄区间为新元古代晚期(约780~约641 Ma),并显示出约750~约740 Ma的显著峰值。结合区域地质资料,研究区南华系沉积时代应为约720~约635 Ma,物源应主要来自位于现今研究区西侧的扬子地块北缘汉南—米仓山微地块的新元古代岩浆岩,其沉积事件对应于新元古代中晚期扬子地块北缘伸展-裂解阶段,为Rodinia超大陆裂解过程的沉积响应。

陕南镇巴小洋坝地区南华系物源分析:来自碎屑锆石U-Pb年龄、碎屑成分分析及地球化学的证据

扬子板块北缘镇巴小洋坝地区出露了一套完整的南华纪沉积地层,分析其沉积时限、沉积环境及物源示踪对扬子板块北缘新元古代中晚期沉积-构造演化具有重要意义。本文对陕南镇巴小洋坝地区南华系砂岩样品进行碎屑锆石U-Pb测年分析,化学蚀变指数(CIA)、化学风化指数(CIW)、斜长石蚀变指数(PIA)、成分变异指数(ICV)判别及物源分析。结果显示小洋坝地区南华系的沉积时限应为720~635 Ma。长安组、古城组、南沱组沉积于寒冷干燥气候,而大塘坡组沉积于温暖湿润气候。其物源区主要为扬子板块北缘汉南—米仓山微地块。研究区南华系对应了新元古代中晚期扬子板块北缘地区的后碰撞-裂解阶段,是新元古代中晚期Rodinia超大陆裂解在该地区的沉积响应。

粤北地区“南华系”沉积时代的重新厘定:来自碎屑锆石年代学的证据

粤北地区横跨湘桂赣和武夷两个地层分区,大地构造上位于华夏地块西部,介于武夷、云开两个微陆块之间。粤北南华纪地层是研究华夏地块新元古代晚期构造演化等问题的重要载体,但该地区南华系的确定和划分较大程度上依赖与周边省份相应岩石地层的岩性组合和层序的对比,而周边省份的相应岩石地层单位的认识近年来发生较大的变化,因此,粤北地区“南华系”的重新厘定显得极为必要。本文对粤北地区原定为“南华系”大绀山组和活道组开展碎屑锆石U-Pb年代学研究,获得最年轻一组锆石加权平均年龄分别为422±4 Ma和430±4 Ma。结合岩性组合、区域地质调查研究成果及文献数据,暂将该地区原定的南华系厘定为下泥盆统。碎屑锆石年龄谱显示,其与周边地区泥盆系均具有450~420 Ma、1000~900 Ma以及~2450 Ma为主的锆石年龄显示,且在800~550 Ma之间形成复杂的次级峰值,可能指示了相似的物源。综上,建议在开展华夏地块新元古代构造演化等研究中,需首先对南武夷-云开地区南华系的沉积层位做细致的认定。

黔东北松桃高地南华系铁丝坳组和两界河组碎屑组分及源区背景

雪峰运动的构造属性一直存在较大争议。统计黔东北松桃高地南华系铁丝坳组和两界河组的陆源碎屑组分,并应用Dickinson三角图解原理进行分析。研究结果显示:铁丝坳组和两界河组沉积时期陆源碎屑的物源主要来自火山弧源区和再旋回造山带,伴随有火山活动;铁丝坳组的碎屑成分成熟度较低,主要投点在火山弧物源区,显示了近源剥蚀、搬运堆积的特征,两界河组的石英矿物屑含量比铁丝坳组高,趋向于再旋回造山带物源;碎屑组分中岩屑的岩性组合为玄武岩、安山质玄武岩、粗面岩、凝灰岩、熔结凝灰岩、流纹岩、长英质糜棱岩等,表明在铁丝坳组和两界河组沉积时期或沉积之前,研究区就已进入陆内裂陷和板内造山的大地构造背景。研究可为该地区雪峰运动的构造属性提供微观证据。

滇东北会泽地区南华系沉积相与古气候特征——来自元素地球化学的证据

通过资料收集、剖面测制、岩矿鉴定、主微量元素分析、特征指数参数对比、沉积相综合建模等一系列工作,对滇东北会泽地区南华系沉积环境和古气候进行了探讨.该区南华系自下而上出露澄江组和南沱组,二者均为陆源碎屑岩系,呈平行不整合接触.澄江组主要包括粉砂质泥岩、粉砂岩、细砂岩、细粒石英杂砂岩和岩屑砂岩等.南沱组主要为一套灰黄色中层状复成分冰碛砾岩.澄江组中沉积旋回发育,可见小型槽状交错层理、斜层理、平行层理、水平层理等沉积构造.对澄江组细碎屑岩样品的主微量元素特征指数SD、CV、CIA、CIW、PIA、ICV、Na/K、Al/Ca、Ru/Sr、V/Cr、U/Th、Ni/Co等进行分析,其结果均指示氧化、弱氧化的沉积环境.研究认为澄江组为湖泊相,包括滨湖亚相和浅湖亚相,为温暖湿润气候类型;南沱组为冰川相,包括冰碛亚相和冰湖亚相,为寒冷干燥气候类型.

Distribution Features of the Nanhua-Sinian Rifts and their Significance to Hydrocarbon Accumulation in the Tarim Basin

On the basis of reprocessing 34 new two-dimensional spliced long sections(20,191 km) in the Tarim Basin, the deep structure features of the Tarim Basin were analyzed through interpreting 30,451 km of two-dimensional seismic data and compiling basic maps. Seismic interpretation and geological analysis conclude that the Nanhua-Sinian strata are a set of rift-depression depositional systems according to their tectonic and depositional features. The rift valley formed in the Nanhua Period, and the transformation became weaker during the late Sinian Period, which eventually turned into depression. From bottom to top, the deposited strata include mafic igneous, tillite, mudstone, and dolomite. Three major depocenters developed inside this basin during the rift stage and are distributed in the eastern Tarim Basin, the Awati area, and the southwestern Tarim Basin. Among them, the rift in the eastern Tarim Basin strikes in the near east-west direction on the plane and coincides with the aeromagnetic anomaly belt. This represents a strong magnetic zone formed by upwelling basic volcanic rock along high, steep normal faults of the Nanhua Period. Controlled by the tectonic background, two types of sedimentary systems were developed in the rift stage and depression stage, showing two types of sequence features in the Sinian depositional stage. The Nanhua System appears as a wedge-shaped formation, with its bottom in unconformable contact with the base. The rifting event has a strong influence on the current tectonic units in the Tarim Basin, and affects the distribution of source rock in the Yuertus Formation and reservoir beds in the Xiaoerbulake Formation in Lower Cambrian, as well as the gypseous cap rock in Middle Cambrian. The distribution features of the rifts have important and realistic significance for determining the direction of oil and gas exploration in the deep strata of the Tarim Basin. Comprehensive analysis suggests that the Tazhong region is the most favorable zone, and the Kalpin-Bachu region is the optimal potential zone for exploring sub-salt oil and gas in deep Cambrian strata.

Geochronological and Geochemical Evidence for the Sedimentary Transformation from the Banxi Period to Nanhua Glacial Period

Objective There has been considerable debate about the definition of the lower boundary of Nanhua System by far.One definition is based on sedimentary sequence of different stages of basin evolution,focusing on whether deposits of the Banxi Period should be classified as Nanhua System.Another is the onset time of Nanhua glacial period.

Layout Optimization of Riverside Residential Area Based on Thermal Comfort: A Case Study of Nanhua Village, Shenzhen

Based on the previous researches on building layout with thermal comfort, this paper Stud Shenzhen Nanhua Village to explore the way of using building layout to change thermal environment of riverfront residential areas. The results showed that a more comfortable outdoor thermal environment could be obtained by applying proper building layouts favorable for the thermal comfort of the Nanhua Village. It proves again that efficient and feasible building layout, which is suitable for a river microclimate, is important in improving thermal comfort of a riverside residential area. The study also provides a good example for the future architectural designs of a riverside residential area for obtaining thermal comfort.

Occurrence, Damage and Control Strategies of Major Pests, Diseases and Weeds in Sugarcane Areas of Lincang Nanhua Sugar Industry Co., Ltd.

The pests, diseases and weeds in sugarcane areas of Lincang Nanhua Sugar Industry Co.,Ltd. were investigated at seedling stage, growth stage and maturity stage of sugarcane from 2012 to 2016. The occurrence and damage of diseases, pests and weeds were analyzed, and the problems in prevention and control were discussed based on the local conditions of sugarcane production. The species, occurrence and damage characteristics of diseases, pests and weeds were ascertained, and the corresponding strategies and technical measures were proposed.

华南南华系年代地层学研究进展

华南南华系对应于国际上的成冰系,关于其沉积时限长期存在争议。近十余年来,通过高精度锆石U-Pb定年,已经基本敲定南华系的重要时间节点。长安组底界年龄被限定在ca.717 Ma,莲沱组顶部沉积时间被限定在ca.714 Ma。长安冰期中期暂时冰退的时间被限定在ca.690 Ma,冰期终止时间限定在ca.659 Ma。小行星撞击地球可能导致了长安冰期中期的暂时冰退,这期间形成的风暴沉积构造和丘状交错层理可以提供最直接的沉积学证据。结合世界其它地区报道的年龄,斯图特(长安)冰期的起止时间限定在了717~659 Ma。马力诺(南沱)冰期的启动时间被大致限定为649 Ma,终止时间被限定在ca.635 Ma。结合世界其它地区年龄数据,马力诺冰期的启动时间可限定在649~639 Ma。随着后续工作的深入,马力诺冰期的启动时间范围应会被进一步缩小。华南南华系沉积时限的准确厘定对于理解全球成冰纪地质-生物-环境事件具有重要意义。马力诺冰期持续时间约14 Myr,远远小于长安冰期的持续时间(约58 Myr)。冰期末期大规模岩浆作用是导致这两次冰期持续时间不同的直接原因。通过模拟计算发现,扬子北缘裂谷岩浆作用可以促使马力诺冰期提前2~5 Myr结束。

扬子西北缘碧口微地块南华系碎屑锆石物源示踪及其地质意义

扬子板块西北缘碧口微地块华严寺地区碧口群之上发育一套含砾沉积地层,其确切沉积时限对研究该区域的沉积—构造演化具有重要意义。本文对该套地层中的2件砂岩样品进行了碎屑锆石LA-ICP-MS U-Pb测年分析,结果显示,锆石晶型较好,无色透明,磨圆度较差,具典型岩浆生长振荡环带和韵律结构,Th/U比值为0.28~3.6,锆石U-Pb年龄介于706~2489Ma之间。存在3个主要的年龄组:新元古代年龄组(706~951 Ma),占92.9%,显著峰值为850 Ma和843 Ma;中元古代年龄组(1017~1080 Ma),占2.6%;古元古代年龄组(1628~2489 Ma),占4.5%。最小年龄组为706~715 Ma(峰值为711 Ma),结合区域地质和研究资料,华严寺地区沉积地层时代应属于南华纪,沉积时限约为720~635 Ma,物源区主要包括扬子板块西北缘碧口微地块以及南东侧的后龙门山构造带和汉南—米仓山微地块。新元古代晚期碧口微地块及扬子板块西北缘后碰撞—裂解阶段,华严寺地区南华纪沉积为碧口微地块及邻区新元古代岩浆岩在边缘裂谷环境中快速堆积形成。

华南扬子地区新元古代地层划分对比研究新进展

华南扬子地区发育有新元古代完整的沉积地层记录,是研究我国新元古代时期古大陆演化与沉积盆地演替的天然平台。四堡—晋宁造山运动（约850~820Ma）以前,新元古代早期的扬子陆块总体上处于弧陆碰撞与弧后前陆盆地充填阶段。约820Ma以后,新生裂谷盆地开启了新一轮板块构造旋回,至约635Ma,华南扬子陆块走过了一段冰与火的不平坦里程。板溪群沉积期（约820~720Ma）,在Rodinia超大陆裂解的构造背景下,伴随着三幕重要的火山岩浆事件,沉积了一套裂谷盆地充填序列。板溪晚期,由于Rodinia超大陆主要陆块的裂离（Drifting）,伴随着区域性海平面下降,迎来了南华大冰期的长安冰期沉积;实际上,南华大冰期并非严格的＂雪球地球＂,而且期间还存在一个间冰期（富禄间冰期）;随后,可能与海平面持续的海侵上超有关,南沱冰期沉积区域展布广泛。由此可见,华南扬子地区晋宁—四堡造山后至南华冰期,沉积序列、事件序列特征明显,阶段性清楚,为新元古代地层划分对比提供了基础条件。

贵州松桃大塘坡地区南华纪早期冷泉碳酸盐岩地质地球化学特征

贵州松桃大塘坡地区的南华系是研究古代天然气渗漏及冷泉碳酸盐岩的理想地区之一.该区冷泉碳酸盐岩由两类岩石组成:一是两界河组含砾砂岩中(Sturtian冰期早期)的白云岩丘或透镜体;二是之上的大塘坡组第一段黑色含锰岩系中的似层状或透镜状菱锰矿矿体及少量白云岩透镜体.该地区冷泉碳酸盐岩的碳同位素具明显的负偏特征,充填在菱锰矿矿石气孔中的沥青碳同位素为-30.98‰,并具有异常高的硫同位素正值.结合冷泉碳酸盐岩的空间分布、古天然气渗漏构造、菱锰矿的沉积有机质等特征分析,认为其与现代冷泉碳酸盐岩的特征十分相近.两界河组的白云岩丘是目前所发现的最古老的冷泉碳酸盐岩,与在它之上的菱锰矿矿体是同一个古天然气渗漏系统中不同时期的冷泉碳酸盐沉积.天然气泄漏形成的冷泉与大塘坡组烃源岩的形成关系密切.

宜昌三斗坪地区南华系化学蚀变指数特征及南华系划分、对比的讨论

化学蚀变指数（chemical index of alteration）最早作为判别源岩区化学风化程度的指标而提出，随后又应用于对沉积物沉积环境的判定。化学蚀变指数的表达式为CIA=n（Al2O3）／[n（Al2O3）＋n（CaO^＊）＋n（Na2O）＋n（K2O）]×100。CaO^＊代表硅酸盐中的CaO，n（CaO^＊）=n（CaO）-n（CO2，方解石）-O．5·n（CO2，白云石）-10／3·n（P2O5）。化学蚀变指数研究样品的选取极为重要，最佳岩性为细碎屑岩，需要清除成岩过程中钾交代作用的影响。用成分变异指数（ICV）来判别沉积再循环作用和沉积物成分被改造的程度。用A—CN—K三角图解来判别物源区的源岩性质和样品钾交代的特征及其风化趋势。宜昌三斗坪地区南华系CIA研究表明：该区南华系下统莲沱组下部的CIA值在50～65之间（干燥寒冷），上部为65～75之间（温暖潮湿）和顶部为55～60之间（干燥寒冷）；南华系上统南沱组的CIA值基本在60～65之间（干燥寒冷），近顶部两个样品的CIA值达70（温暖潮湿）。上述CIA值变化表明本区南华纪经历自老到新由冰期干燥寒冷-间冰期温暖潮湿-冰期干燥寒冷沉积环境的变化过程。本文据此提出了新的扬子古陆南华系新的划分和对比方案。

用化学地层学研究新元古代地层划分和对比

随着传统地层学向多学科相互渗透的综合地层学方向的发展，笔者开展了湖北峡东地区新元古界震旦系和南华系的化学地层学研究。分别介绍了碳酸盐岩地层的稳定同位素和碎屑岩化学蚀变指数的研究方法和成果并依此提出新元古界划分和对比方案。震旦系碳酸盐岩中所获得的δ^13C变化曲线和^87Sr／^86Sr比值与世界诸多剖面的变化曲线基本一致。南华系碎屑岩的化学蚀变指数（CIA）的特征是莲沱组下部CIA值为55-65（代表寒冷环境的CIA值），莲沱组上部CIA值则增至65～75（代表温湿环境），而莲沱组顶部两个样品的CIA值再次降为寒冷指数60-65；南沱组CIA值均为60-65，除了顶部（接近震旦系）的两个样品分别为69．4和70．9。上述CIA值的变化表明南华系以寒冷气侯为主，并且经历过“寒冷-温湿-寒冷”气候的演变条件下的沉积物。沉积相的多样性说明即使在“冰期”期间古构造、古地理环境对沉积物特征的影响依然存在。

上扬子地区新元古界含油气系统与油气勘探潜力

近年来,四川盆地震旦系天然气勘探获得重大发现,揭示上扬子克拉通盆地新元古界具备寻找原生型大气田的条件。然而,受勘探程度和认识程度的制约,对该领域油气资源潜力与分布的认识尚不清楚。国外的研究成果表明,新元古界含油气系统受气候条件、构造古地理环境控制,温室气候期冰川融化可导致海平面上升,有利于富有机质沉积物堆积,是新元古界重要油气源岩沉积的主要时期;早期裂谷—晚期克拉通坳陷的构造带利于形成油气富集区。上扬子克拉通在中—新元古代经历了可全球对比的重要地质事件,南华纪以板内拉张活动为主、震旦纪为克拉通坳陷沉积,形成了两套各具特点的含油气系统:震旦系含油气系统(也可称为后冰川期含油气系统)和南华系含油气系统(也可称为间冰川期含油气系统)。前者发育多套烃源岩和大面积分布的储集层,源—储配置条件好,是一个已被证实的含油气系统,也是近期该区天然气勘探的重点领域;后者受裂陷(谷)盆地分布控制,发育优质烃源岩,是潜在的油气勘探领域。川中地区发育南华系裂谷,应加强地质评价研究,优选风险勘探目标。

四川盆地东南缘南华系大塘坡组烃源岩特征及其油气勘探意义

随着四川盆地的油气勘探不断向深层—超深层领域拓展,以及在盆地中部地区(川中)稳定继承性古隆起区域的中上元古界—下古生界储量超1×1012 m^3大气田的发现,该盆地深部古老层系烃源岩发育环境、烃源岩有机质生源构成及其成烃特征等备受关注。为此,基于前人的研究成果,开展了四川盆地东南缘南华系大塘坡组野外露头剖面观察和烃源岩样品的有机地球化学、有机岩石学分析测试。结果表明:(1)四川盆地东南缘在南华纪古城期和南沱期2个冰期之间发育拉张背景下的大塘坡组黑色页岩优质烃源岩,其厚度介于16~180 m,矿物组成以黏土矿物和碎屑石英为主;(2)大塘坡组页岩为高丰度过成熟腐泥型优质烃源岩,其低姥植比(0.32~0.83)、低伽马蜡烷丰度、高丰度三环萜烷以及相对高含量的C_(27)、C_(29)甾烷等特征,反映了低盐度强还原环境下藻类和细菌微生物为其主要生源构成。结论认为:(1)川中地区南华纪裂谷内可能发育大塘坡组烃源岩,加里东期之前的古隆起、古斜坡区域是源于大塘坡组烃源岩的古油藏或分散液态烃的有利聚集场所;(2)该盆地内部稳定区域有可能发现源于大塘坡组烃源岩的古油藏或分散有机质裂解气的规模聚集区。

黔南—桂北地区南华系化学地层特征

化学蚀变指数（chemical index of alteration）（CIA）最早作为判别源岩化学风化程度而提出，随后又应用于对沉积物沉积环境的判定。化学蚀变指数的表达式为CIA={n（Al2O3）／[n（Al2O3）＋n（CaO^＊）＋n（Na2O）＋n（K2O）]}×100。CaO^＊代表硅酸盐中的CaO，n（CaO^＊）=n（CaO）-n（CO2方解石）-n0．5×n（CO2白云石）-10／3xn（P2O5）。化学蚀变指数样品的选取极为重要，最佳岩性为细碎屑岩，并需清除成岩过程中钾交代作用的影响，以及采用成分变异指数（ICV）来判别沉积再循环作用和沉积物成分被改造的程度。使用A—CN—K三角图解判别物源区的源岩性质和样品钾交代的程度及其风化趋势。黔南-桂北地区南华系的CIA研究表明：该地区南华系下部的长安组其下部CIA值为60～65之间，中部为70～5，上部回落到65—70之间。南华系中部富禄组CIA值高，在85-95之间。南华系上部的南沱组CIA值再次回落到60—65的范围。上述CIA值的变化表明本区南华纪时期自老至新经历多次由干燥寒冷-温暖潮湿气候期的变化。本文据此提出扬子地块南华系新的划分、对比方案。