Jurassic-Cretaceous Boundary Strata of the Somanakamura Group in NE Japan and their Correlation with Coeval Terrestrial Deposits in China

Defining the Jurassic-Cretaceous boundary is a controversy in stratigraphic study of the world. It has been widely accepted that this boundary can be defined at the bottom of Berriasian in Tetbys, with the appearance of the ammonite Berriasellajacobi dating to ca. 145 Ma. However, it is difficult for the widespread terrestrial deposits in China to correlate with the international standard of marine facies. The Somanakamura Group in Japan is represented by a succession of marinecontinental transitional strata. It provides a bridge of marine and nonmarine stratigraphic correlation. The ammonite and radiolarian fossils preserved in this group suggest an age from Bajocian to early Valanginian. The J-K boundary was defined in or atop the Tomizawa Formation of the group according to the ammonite data. The present authors study the fossil spores and pollen newly found from the Tomizawa and Koyamada formations. Three assemblages have been recognized. They are Assemblage 1 （Cyathidites-Classopollis） from the upper part of the Tomizawa Formation, Assemblage 2 （Cyathidites-Jiaohepollis） from the lower part of the Koyamada Formation, and Assemblage 3 （Cyathidites-Spheripollenites-Ephedripites） from the middle to upper part of the Koyamada Formation. With the reference of ammonite evidence, the J-K boundary can be defined between Assemblage 1 and Assemblage 2. This palynological J-K boundary can be correlated with that of terrestrial sequence in China. However, local biostratigraphy imply that the continental J-K boundary in China is of 135 or 137 Ma age. It has a considerable discrepancy from the marine standard. Biogeographically, the distribution pattern of spores and pollen in southern China is in accordance with that in the Somanakamura Group, which parallels the Tuchengzi Formation in northeastern China. By the palynological correlation between the Somanakamura Group and the strata in southern China, and then with the sequence in northeastern China, it is suggested that the continental J-K boundary is located in the Tuchengzi Formation.

Study on a Terrestrial Permian-Triassic Boundary Section-Zhejue Section, Weining County, Guizhou Province, China

The Zhejue Section is an excellent terrestrial Permian Triassic boundary (TPTB) section not only for its convenient accessibility and good outcrop, but also for its abundant fossils. In addition, there are two claystone beds that were formed by events across the Permian Triassic boundary (PTB) at this section. The claystones provide a bridge for high resolution correlation between marine and terrestrial PTBs. Another advantage is that the PTB at the Zhejue Section can be correlated with that of littoral and neritic facies by tracing westwards. Synthesized stratigraphic studies, including biostratigraphy, eventostratigraphy (susceptibilities and carbon isotopes across the TPTB, and microspherules found in the boundary claystones) and sequence stratigraphy, are carried out at this section.

A Proposed Area for Study of Accessory Section and Point of Terrestrial Permian-Triassic Boundary

After the establishment of the global stratotype section and point (GSSP) of the Permian Triassic boundary (PTB), the definition of the accessory section and point (ASP) of the terrestrial Permian Triassic boundary (TPTB) is now on the agenda. However, all good TPTB sections so far known have the following shortcomings: (1) the exact TPTB horizon is difficult to define paleontologically with high resolution, and (2) accurate correlation between marine and terrestrial PTBs is hard to attain. In order to enhance the understanding of the nature of the global life crisis in both the marine and terrestrial environments across the Paleozoic Mesozoic transition, these shortcomings need to be addressed. In western Guizhou and eastern Yunnan, Southwest China, some fossiliferous PTB sections which include marine, paralic and terrestrial are well developed, allowing bed to bed correlation of the PTB sequences. Fortunately, the marine PTB sequence in this area is almost the same as found at the Meishan Section, where the GSSP of the PTB is located, which may provide a reliable auxiliary marker for high resolution demarcation of the TPTB. These features found in western Guizhou and eastern Yunnan make this area a good place to study the ASP of the TPTB, so we propose to study the ASP of the TPTB in this area.

KT Boundary Chromites Determined to be Terrestrial:Cr Isotopic Evidence for Excavation and Ejection of Mafic/Ultramafic Rocks by the KT Boundary Impact

Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on;5km thick continental crust（De Paolo et al.,1983;Montanari et al.,1983;Hildebrand and Boynton,1988,1990）.Evidence for mafic/ultramafic target rocks was reinforced by discovery of chromites,some with shock planar deformation features（PDF）,in impact layer samples from sites in southern Colorado and eastern Wyoming（Bohor et al.,1990）.However,until now it was unclear whether the chromites originated with an impactor or with terrestrial target rocks.To this end,high-precision 54Cr/52Cr isotope ratios were measured on KT boundary chromites along with known terrestrial chromites.We find a terrestrial 54Cr/52Cr ratio in KT boundary chromites from impact layer samples collected at the above sites over the last several years（Fig.1）.Ejected terrestrial chromites suggest the impact sampled terrestrial mafic and/or ultramafic target rocks not known to exist in the Chicxulub target area.

Comparison of the Palaeomagnetic Parameters of Non-Marine Jurassic-Cretaceous Boundary Sediments in Dorset(SW England),Hebei and Liaoning(NE China)—A Preliminary Study

The Purbeck beds in Dorset, the Tuchengzi Formation in western Liaoning Liaoning Province or the Houcheng Formation in northern Hebei Province are non-marine Jurassic/Cretaceous (J/K) boundary sequences. A Czech-China Inter-Governmental S&T Cooperation Project has been carried out to search for the non-marine J/K boundary in northern China and making international correlation with the Purbeck beds in southern England. The combination of palaeomagnetism and biostratigraphy in northern China and southern England localities proves that these distant places had similar climatic conditions and the same fauna during the Late Jurassic and Early Cretaceous. A preliminary joint research has shown a fruitful result in searching for the non-marine J/K boundary in northern China.

Timing of the terrestrial Permian-Triassic boundary biotic crisis:Implications from U-Pb dating of authigenic zircons

The Late Permian to Early Triassic transition represents one of the most important Phanerozoic mass extinction episodes. The cause of this event is still in debate between catastrophic and gradual mechanisms. This study uses the U-Pb method on zircons from the uppermost Permian/lowermost Triassic clay deposits at Chahe (Guizhou Province, SW China) to examine time constraints for this event. The results of both this and previous studies show that the ages of Bed 68a and 68c (the upper clay bed of the terrestrial Permian-Triassic boundary (PTB)) respectively are 252.6±2.8 and 247.5±2.8 Ma. This age (within the margin of error) almost accords with the upper clay bed (Bed 28) age of Meishan and the eruption age of Tunguss Basalt, and is so far the most accurate age obtained from terrestrial PTB. The claystone of Bed 68 was formed in the earliest Triassic. The biotic crisis occurred at nearly the same time in terrestrial and marine environments during Permian-Triassic interval; however the extinction patterns and processes are different. The extinction pattern of the terrestrial plants shows a major decline at the PTB after long-term evolution, followed by a retarded extinction of the relicts in the earliest Triassic.

Sequence stratigraphy of Jurassic-Cretaceous boundary strata in Luanping, Northern Hebei, China

A sediment-continuous section of Jurassic-Cretaceous (J-K) boundary strata was found in Zhangjiagou of Luanping, northern Hebei Province, China. The boundary strata were systematically divided into 5 sequences, 13 subsequences and 139 parasequences by sedimentary cyclicities and facies analysis. According to stable time-ranges of subsequences and parasequences, some boundary ages can be marked as 142.90 Ma of the SQ I (Dabeigou Fm) basal bound, 141.16 Ma of the SQ II basal bound, 140.00 Ma of the SQ III (Dadianzi Fm) basal bound, 138.24 Ma of the SQ VI (Zhangjiagou Fm) basal bound and 135.34 Ma of the SQ V (Zhangjiagou Fm) top-bound. A sequence-stratigraphic framework of the Dabeigou-Zhangjiagou Fms has been constructed by tracing sequence-bounds, marker-beds and fossil zones. The basin-development and tectonic activities are studied based on sequence-stratigraphic evidence. 5 sequences represent 5 tectonic cycles and all the 6 sequence-bounds reflect tectonic activities. Tectonic activities clearly influence the basin-development that can be divided into 3 stages in the J-K transitional period. Each stage consists of a down-faulting-rising process, i.e. from strongly rising of basin-bottom, then violently faulting down (with volcanic eruptions) and to gently rising. The development shows a pattern of bottom down-faulting with basin narrowing and rising with spreading. Keywords sequence - stratigraphy - terrestrial stratotype - Jurassic-Cretaceous bound DOI: 10.1360/03yd0451

冀北滦平盆地陆相侏罗系—白垩系界线候选层型剖面初步研究

在发现陆相侏罗系—白垩系界线地层连续剖面的基础上,补充大北沟组和大店子组的含义,将2组系统分为7个岩段,命名4个标志层;确定年代地层层序,完善大北沟阶和义县阶定义内容;研究重点门类化石分布和演化,建立系统生物地层分带序列,包括7个介形虫带和6个叶肢介带;划分陆相生物群发展阶段,将侏罗系—白垩系界线置于“早期热河生物群”阶段的底部;开展旋回地层和层序地层学研究,建立地层等时格架,识别盆地演化的3个阶段和5个构造期;测得界线层型剖面点存在O同位素高值异常;锆石206Pb/238U测得张家口组顶部年龄为135.4Ma±1.6Ma,大北沟组中部为133.9Ma±2.5Ma和130.1Ma±2.5Ma。综合多学科研究成果,将界线层型剖面点定在张家沟剖面第9层底,以介形虫化石Cyprideastenolonga的首现为标志。

侏罗系、白垩系界线问题及对中国北方陆相界线的思考

侏罗系、白垩系间是显生宙唯一还没有定义系级GSSP的界线。生物演替在Thithonian期与Berriasian期之间不存在明显变化,很难找到可以进行全球对比的标志。作为中生代生物年代地层学主要划分依据的菊石类生物,亦受生物区系影响而难作为侏罗系、白垩系界线的标志。微体化石具有优势。近期,国际上趋于将瓮虫类Calpionella alpina带之底、钙质超微化石Nannoconus steinmannii minor和N.kamptneri minor二者的始现面作为侏罗系、白垩系界线,对应于极性带M19n.2n内部,年龄为145 Ma。国际地层划分与对比以海相为标准。中国侏罗系、白垩系以陆相地层发育为特征,与海相对比颇具难度。以陆相生物为标志的界线划分产生了地区性的生物年代地层格架,也形成了地方生物地层与国际年代地层对比的错位,导致中国陆相侏罗系、白垩系界线成为地学界争议的问题。本文认为,在综合考虑不同学科研究结果的同时,问题解决的实质是客观认识陆相生物对比的缺陷,结合考虑非生物的标准,如磁性地层、旋回地层和同位素测年的精度,获得超越相区的对比结果。基于陆相生物特点,着眼于宏观演化阶段来识别界线位置是问题解决的初期阶段。燕辽生物群与热河生物群是代表侏罗纪和白垩纪的两大生物演化类群,其间年龄可为土城子组顶部的139 Ma。这是为全方位研究而铺设的临时工作界线。今后将土城子组作为侏罗纪、白垩纪过渡地层而加大研究力度,有可能在该组顶部或其内部发现界线生物标志和同层位绝对年龄值,或许会使其向目前国际推荐年龄(145Ma)更靠近一步;也不排除GSSP未定的国际侏罗系、白垩系界线年龄会向年轻方向变化,趋于139Ma的Valanginian阶底界位置。

论中国陆相侏罗系—白垩系界线

介绍了中国学者近几年在陆相侏罗系—白垩系界线研究领域的最新成果,讨论了陆相侏罗系—白垩系界线研究的原则和方法,指出了目前工作中存在的问题,初步认为在建立中国陆相中生界区域年代系统时要特别注意系、统的界线必须与国际接轨,时间上应与国际系、统界线相一致。如果国际地质科学联合会和国际地层委员会最终采用135Ma作为国际侏罗系—白垩系界线的年龄值,那么冀北—辽西地区陆相侏罗系—白垩系界线推测应在张家口组底部,与区域不整合面相一致,表明热河生物群的时代肯定为早白垩世。如果国际侏罗系—白垩系界线的年龄值将来确定为145Ma,那么冀北—辽西地区陆相侏罗系—白垩系界线推测位于土城子组的上部,意味着冀北地区缺失凡兰吟阶的地层,辽西地区可能缺失凡兰吟阶和欧特里沃阶的地层。

黔西滇东地区浅海、滨海及海陆交互相二叠系—三叠系界线附近粘土岩研究

对黔西滇东地区的贵州普定高窝、贵州六枝中寨和云南宣威密德3条剖面二叠系—三叠系界线附近粘土岩的大山物源成因和界线地质意义进行研究发现:在界线粘土岩中,其主要粘土矿物均为伊/蒙混层矿物,见少量高岭石、伊利石或绿泥石;碎屑物质中有六方双锥石英、锆石、长石等与火山活动有关的物质。推断该地区在晚二叠世晚期—早三叠世早期至少经历一至两次强烈的火山作用,并且有多个火山喷发源。界线粘土岩中火山物质的富集与贫乏可能与剖面离火山喷发源的远近有关。粘土岩物源物质的成因均为火山喷发,火山灰伴随正常沉积物沉积而形成即凝灰沉积而形成,与华南大部分地区二叠系—三叠系界线粘土岩的物源成因是一致的。

新疆准噶尔盆地中、晚侏罗世多重地层研究

对新疆维吾尔自治区沙湾县玛纳斯河红沟侏罗系剖面开展了生物地层学、同位素年代地层学、旋回地层学和磁性地层学等的综合研究。研究结果表明,头屯河组的时代为中侏罗世中晚期到晚侏罗世早期,包括巴通阶的最顶部、卡洛维阶和牛津阶的中下部;其底界年龄约为166.2 Ma,顶界线年龄约为160.8 Ma,沉积时间约5.4 Ma。齐古组顶部年龄值为155.3 Ma,沉积时间约5.5 Ma,包括了牛津阶的上部和基默里奇阶的中下部,其顶部与东部冀北、辽西地区髫髻山组顶部大体相当,比土城子组层位低。喀拉扎组的时代为晚侏罗世基默里奇期晚期,而其上覆地层吐谷鲁群的时代为早白垩世早期,两者之间存在一个相当大的不整合,缺失了晚侏罗世提塘期以及可能包括早白垩世最早期的地层,有超过了7 Ma的地层缺失量。侏罗系与白垩系的界线为此不整合面,侏罗纪/白垩纪之交的地层未保存。

黔西威宁岔河陆相二叠系—三叠系界线粘土岩研究——基于X射线衍射、扫描电镜分析

利用X射线衍射、扫描电镜等分析方法,对黔西威宁岔河陆相剖面二叠系—三叠系界线附近的粘土岩进行了研究。在界线粘土岩中,粘土矿物组合为伊—蒙混层矿物+蒙脱石+绿泥石;碎屑物质中有六方双锥石英和锆石,无球粒;多种化学成分在界线粘土岩中出现了异常。据此得出岔河剖面的二叠系—三叠系事件地层界线确定在第66f层比较合适;第66f和68a这两层粘土岩为此剖面的界线粘土岩;自第66f层底部至第68a层顶部这一段地层为二叠系—三叠系的界线层(组);界线粘土岩的成因可能是由于火山喷发、火山灰降落伴随正常沉积物沉积形成的。

陆相二叠系—三叠系界线研究进展

着重介绍了几个目前陆相二叠系—三叠系界线 (TPTB)研究的重点剖面及其生物地层学研究进展 ;分析了陆相二叠系—三叠系界线综合地层学研究现状 ,包括生物地层学、事件地层学、同位素年代学、磁性地层学和层序地层学等 ;剖析了陆相二叠系—三叠系界线地层学研究中存在的问题及进一步的研究方向。生物地层方面 ,陆相二叠系—三叠系界线附近存在晚二叠世与早三叠世生物混生的层位 ,其中不同类别生物的时间界线常不一致 ,又由于陆相界线地层中含脊椎动物化石的层位一般较少 ,以脊椎动物化石 (Lystrosaurus)为标准的精确界线常不确定 ,因而需重新寻找并确定陆相三叠系底界的标准化石。事件地层标志可能会成为连结海、陆相二叠系—三叠系界线地层高精度对比的纽带。

陆相湖盆碎屑岩层序地层对储层成岩作用的控制

现今岩性地层等隐蔽油气藏的勘探需要高精度和可预测性的成岩作用研究,通过深入探讨层序地层格架内层序边界和不同体系域对成岩作用类型及成岩演化的控制及其对储层物性的影响,可为油气储层的区域评价和预测提供新的思路。目前关于陆相湖盆碎屑岩层序地层对成岩作用控制的研究还较少。本文结合国内外文献,分别就层序界面和不同体系域对成岩作用类型和强度、成岩矿物、成岩演化序列等的控制进行了归纳总结。并探讨了成岩层序地层学学科的概念起源及其发展历程、主要研究内容、流程、应用前景和尚存在的问题,最后从自身方法理论完善、实验分析测试技术、学科交叉渗透3方面展望了未来研究发展方向。

一种建筑物点云轮廓线的自动提取方法

针对地面激光点云包含大量冗余数据、特征信息不明显等缺点,提出了一种自动提取建筑物点云轮廓线的方法。首先基于主成分分析和熵函数计算每个点的最佳邻域,再根据几何位置关系,滤除散乱点和平面中的点,保留轮廓线点云。针对不同地面激光点云数据,无需反复调整阈值。实验证明,该方法提取的建筑物点云轮廓线清晰完整,与现有方法提取的结果相比正确率有一定的提高,且冗余点云几乎全部被滤除,自动化程度高,具有良好的适用性。

基于地面激光扫描数据的建筑物边界规则化方法研究（英文）

基于地面激光扫描数据,提出了一种新的建筑物边界规则化方法,不仅可以对建筑物整体而且可以对不同侧面进行规则化,包括立面墙面、门和窗户等.首先对海量原始激光点云利用高效的随机采样一致性算法分割为不同的平面面片,然后利用2Dα-shapes算法提取建筑物点云数据.在此基础上,利用本文提出的边界规则化算法产生一个规则多边形进而实现建筑物边界规则化.利用实际地面扫描数据对该算法进行验证,表明本文方法可以针对不同密度的点云进行自适应调整,不仅效率高,而且可以达到非常满意的建筑边界规则化效果.该研究成果对于利用地面激光扫描数据进行建筑物三维建模具有一定的参考意义.

河南宜阳地区陆相二叠系—三叠系界线附近微生物成因沉积构造特征及意义

有关微生物成因沉积构造及其生物地质过程的研究近年来发展迅速,成为深刻认识地球早期生命演化以及生物与环境相互作用过程的重要桥梁。目前报道的微生物成因沉积构造主要集中在海相沉积中,而陆相碎屑岩沉积中的微生物成因沉积构造研究较少。本文介绍了河南省宜阳地区二叠系—三叠系界线附近陆相碎屑岩中发育的以微生物席生长特征、微生物席破坏特征为主的微生物成因沉积构造,认为这些沉积构造的发育与二叠纪末地质灾变事件造成的特殊水体化学环境和严重退化的生态系统相关,属陆相环境中的"错时相"沉积。研究区微生物成因沉积构造的发现对于二叠纪末地质灾变期生物绝灭与复苏奥秘的探索、陆相地层的划分、海相—陆相地层的对比均具有重要意义。

南非陆相二叠系—三叠系界线研究进展

从岩石地层研究着手,介绍了南非卡鲁盆地内综合地层研究的相关成果。在生物地层方面,脊椎动物和植物化石的研究在该区具有传统优势,孢粉化石的研究则是在最近几年才取得较大进展,在陆相界线地层研究中菌孢化石在二叠系—三叠系界线处约1 m厚的地层内的富集事件属首次报道。在地球化学地层方面,南非有机碳同位素在二叠系—三叠系界线附近的变化趋势与海相二叠系—三叠系界线地层存在相似的对应关系,可以作为海、陆相界线地层对比的辅助标志。在磁性地层方面,南非卡鲁盆地内的磁极性存在从反向到正向然后再反转(R-N-R)的变化,二叠系—三叠系界线则位于第一反向极性带的顶部。同时,结合目前全球陆相二叠系—三叠系界线的研究现状及特点,分析了陆相界线地层研究中存在的基本问题,指出华南地区可能为突破传统观念的研究地区,陆地事件地层研究意义重大。

豫西荥阳P⁃Tr之交孙家沟组沉积环境及古气候变化

荥阳万山地区出露的孙家沟组陆源碎屑岩沉积,保存了丰富的二叠纪—三叠纪之交陆相沉积记录,有助于探究二叠纪末生物大灭绝事件前后陆相沉积环境和古气候的变化规律。在实测野外地质剖面的基础上,结合传统岩性分析、粒度分析、沉积相分析和微量元素地球化学分析,综合分析了研究区孙家沟组的沉积环境及其古气候变化特征。结果表明:孙家沟组主要为早中期的河流沉积过渡为三角洲平原亚相和三角洲前缘亚相的陆相浅水富氧沉积环境;孙家沟组沉积期的古气候主要为温暖湿润,前期出现了几次干热变化,且整个沉积期风化剧烈。