Cambrian Stem-group Cnidarians with a New Species from the Cambrian Series 3 of the Taebaeksan Basin, Korea

Five species, Lipopora lissa Jell and Jell, 1976, Lipopora daseia Jell and Jell, 1976, Tretocylichne perplexa Engeibretsen, 1993 from Australia, Cambroctoconus orientalis Park, Woo, Lee, Lee, Lee, Han and Chough, 2011 from China, and Cambroctoconus kyrgyzstanicus Peel, 2014 from Kyrgyzstan, belonging to the Cambrian stem-group cnidarians have been documented in the fossil record. Cambroctoconus coreaensis sp. nov., interpreted here as a stem-group cnidarian, from the Seokgaejae section in the Daegi Formation, Taebaek Group （Cambrian Series 3）, Taebaeksan Basin, central-eastern Korean Peninsula, has a slender cup-shaped skeleton. A cladistic analysis produced 21 most parsimonious trees, which invariably placed the six stem-group cnidarians below the crown-group, but their relationships within the stem-group are unresolved. Nine out of the 21 trees suggest a monophyletic relationship for the Cambrian stem-group cnidarians, whereas in six other trees a monophyly of Cambroctoconus and Tretocylichne appeared as the sister-group to the crown-group cnidarians with Lipopora at the most basal branch. This result may reflect the fact that crown-group cnidarians evolved in the Precambrian, and suggests that the diversity of stem-group cnidarians was a result of an independent radiation in the Cambrian.

Conodont Biostratigraphy of Ordovician Deep-Water Turbiditic Sequences in Eastern Australia——A New Biozonal Scheme for the Open-Sea Realm

Ordovician conodonts representing 28 genera and 28 named and three unnamed species were identified from 740 chert and siliceous siltstone spot samples(>3000 thin sections)from deep-water turbiditic sequences of the Lachlan Orogen in central and southern New South Wales,Australia.Based on these faunas,a new conodont biozonal scheme has been established to divide the Ordovician turbiditic successions of the Lachlan Orogen into 12 superbiozones and biozones.They are(in ascending order)the Paracordylodus gracilis Superbiozone(including the Prioniodus oepiki Biozone),Periodon flabellum Superbiozone(including the Oepikodus evae Biozone in the lower part),Periodon hankensis Biozone,Periodon aculeatus Superbiozone(including the Histiodella labiosa,Histiodella holodentata,Histiodella kristinae,Pygodus serra and Pygodus anserinus biozones)and the Periodon grandis Biozone.The Pygodus anserinus Biozone is divided further into the lower and upper subbiozones.This new conodont biozonation scheme spanning the upper Tremadocian to middle Katian interval permits precise age-dating and correlation of deep-water siliciclastic rocks that characterize the Ordovician Deep-Sea Realm regionally and internationally.

Ordovician integrative stratigraphy,biotas,and paleogeographical evolution of the Qinghai-Tibetan Plateau and its surrounding areas

The Ordovician rocks on the Qinghai-Tibetan Plateau represent the oldest non-metamorphic strata,and are critical to understanding the history of regional geology and biotic evolution of the entire plateau.Strata of Floian,Darriwilian,Sandbian,Katian and Hirnantian are represented in the plateau with a hiatus of variable duration occurring underneath the basal Ordovician across the area.Five stratigraphical regions,including the Himalaya,Gangdise-Zayu,Qiangtang-Qamdo,Songpan-Garze,and Karakoram-Kunlun-Altun,are differentiated for the Ordovician strata,which are correlated with their equivalents in the Sibumasu,Indochina,Qaidam-Qilian,Tarim-Tianshan,and the Yangtze(western margin)stratigraphical regions.On the QinghaiTibetan Plateau,graptolites,conodonts,and cephalopods are the most common and useful fossils for the Ordovician biostratigraphy.The Ordovician biotas of the Qinghai-Tibetan Plateau bear some distinguishable palaeobiogeographical signatures,among which the cephalopods are characterized by the flourishing actinocerids of North China affinity in the Early-Middle Ordovician,and by the thriving lituitids and orthocerids of South China affinity in the Middle-Late Ordovician.Fossil occurrences and their palaeobiogeographical evolution provide critical evidence bearing on the reconstruction of the geological history of the Qinghai-Tibetan Plateau and surrounding terranes in northeastern peri-Gondwana.The stratigraphical successions of the Cambrian-Ordovician transition in the Himalaya and Lhasa and nearby Sibumasu terranes were significantly affected by the Kurgiakh Orogeny,which resulted in the extensive unconformity between the Ordovician and the underlying rocks in most areas of the Qinghai-Tibetan Plateau.In southern Xizang,a warm-water biota of Middle Ordovician age was recovered from oolitic limestones,suggesting a likely palaeogeographical location in low-latitudes near the equator.In the Himalaya and Sibumasu regions,the Upper Ordovician was typified by the occurrence of red carbonates with distinctive reticulate structures,which are correlative to their equivalents in the Yangtze region of South China,and might be deposited under similar geological conditions.The global end-Ordovician glaciation and sea-level drop likely caused the wide absence of late Katian strata in western Yunnan of China and the Shan State of Myanma,and may have also affected deposition in the Xainza and Nyalam areas of the QinghaiTibetan Plateau during this time interval.

Circumjacent distribution pattern of the Lungmachian graptolitic black shale(early Silurian) on the Yichang Uplift and its peripheral region

Stratigraphic hiatuses of variable time intervals within the Rhuddanian to early Aeronian （Llandovery, Silurian） are identified in the area bordering East Chongqing, West Hubei and Northwest Hunan in central China. Their distribution suggested the existence of a local uplift, traditionally named the Yichang Uplift. The diachronous nature of the basal black shale of the Lungmachi Formation crossing different belts of this Uplift signifies the various developing stages during the uplifting process. The present paper defines the temporal and spatial distribution pattern of the Yichang Uplift, which might be one of the important controlling factors for the preservation and distribution of the shale gas in this region, as it has been demonstrated that the shale gas exploration is generally less promising in the areas where more of the basal part of the Lungmachi Formation is missing. Therefore, better understanding of the circumjacent distribution pattern developed throughout the uplifting process may provide the important guidance for the shale gas exploration. The present work is a sister study to the published paper, ＂Stage-progressive distribution pattern of the Lungrnachian black graplolitic shales from Guizhou to Chongqing, Central China＂. These two studies thus provide a complete Ordovician-Silurian black shale distribution pattern in the Middle and Upper Yangtze, a region with the major shale gas fields in China.

Middle Ordovician Conodont Biostratigraphy of Australasia

Seven conodont biozones are recognized in the carbonate-dominated shelf-marine Middle Ordovician developed in the intracratonic sedimentary basins(Canning,Amadeus and Georgina)of central and north-western Australia,in the Lachlan and New England orogens of New South Wales,and in the Takaka Terrane of New Zealand.A separate scheme identifying seven conodont biozones spanning the Middle Ordovician has also been developed for siliciclastic sequences deposited in slopebasinal environments in the Lachlan Orogen in New South Wales and Victoria.This biozonal classification consisting of two parallel biostratigraphic schemes for the shelf-marine and deep-marine successions respectively has significantly increased precision in regional and global biostratigraphic correlation and laid a solid foundation for the Middle Ordovician chronostratigraphy of Australia and New Zealand.Recognition of short-ranging pandemic species as the eponymous species of the biozones also supports direct correlation with the classical conodont successions established in Baltoscandia and the North American Midcontinent,and with those of the major Chinese terranes(South and North China and Tarim).The Lachlan Orogen appears to be globally unique in enabling correlation of contemporaneous conodont faunas over a considerable spectrum of water depths and biofacies ranging from carbonate shelves,slopes to deep-water basins.

Conodont diversification during the Ordovician:A perspective from North China and Tarim(Northwestern China)

Review of the literature on Ordovician conodont diversification in palaeoplates of North and Western China reveals that four diversity peaks are present in North China,occurring in the middle Tremadocian,early Floian,late Floian,and late Darriwilian,with three of these peaks(excepting that in the late Floian)also being recorded in Tarim.Three diversification intervals are present in North China,during the Tremadocian,late Floian,early and middle Darriwilian;comparable intervals are observed in the early and late Tremadocian,early Floian,and the Middle Ordovician in Tarim.The main conodont diversification episode in both palaeoplates took place in the Darriwilian,at the time of the Great Ordovician Biodiversification Event.A comparison of conodont diversity patterns in different palaeoplates(North China,Tarim,and South China)demonstrates that conodont radiation events mainly occurred within the Tremadocian,Floian,and Darriwilian.Conodont diversifications in these paleoplates also display some differences.In contrasting with Tarim and South China,North China witnessed a rapid conodont diversification during late Floian time.Conodont diversity in North China and Tarim increased continually and reached a peak in the late Darriwilian,concurrent with a prominent decreasing trend in South China.Differences of conodont diversification in these three palaeoplates may be related to their palaeogeography and tectonic history.When conodont diversifications in North China and Tarim are analysed on the background of palaeoenvironments,the main episodes are seen to be partly coincident with second order sea-level changes,particularly in North China.In general,conodont radiation correlates with large scale transgressions.

青藏高原及其周边奥陶纪综合地层、生物群与古地理演化

青藏高原奥陶系代表该地区未变质沉积地层的最古老记录,是解读该地区早期地质历史和生物演化的关键层段.青藏高原地区奥陶系底部地层存在不同程度的缺失,但具有下奥陶统弗洛阶、中奥陶统达瑞威尔阶,以及上奥陶统桑比阶、凯迪阶和赫南特阶,可划分为喜马拉雅、冈底斯-察隅、羌塘-昌都、松潘-甘孜、喀喇昆仑-昆仑-阿尔金等地层区,并可与周边的滇缅马、印支、柴达木-祁连、塔里木-天山和扬子区(西缘)等地层区进行综合地层对比.笔石、牙形刺和头足类是青藏高原地区奥陶系最常见的、据以构建该地区生物地层框架的化石门类.青藏高原奥陶纪生物群具有鲜明的生物古地理区系特色,其中头足类在早-中奥陶世以珠角石类繁盛为特征,显示与华北板块具有密切亲缘关系,但到晚奥陶世则以喇叭角石和直角石类繁盛为特征,表现出与华南的密切关系.青藏高原的奥陶纪多门类动物群及其生物古地理演化,为冈瓦纳东北缘地区的奥陶纪古板块重建提供了重要依据.西藏南部喜马拉雅地体、拉萨地体及周边的滇缅马地体在寒武纪晚期-奥陶纪早期经历了库尔加克运动,这次影响深远的构造热事件造成了奥陶纪地层与下伏基底地层之间的角度不整合接触关系,这一间断面在青藏高原大部分地区存在.西藏南部中奥陶统发育鲕粒灰岩和暖水生物群,指示当时位于赤道附近的低纬度地带.喜马拉雅地体及滇缅马地体的上奥陶统普遍发育大套具有网纹结构的海相碳酸盐岩红层,可与华南扬子区的同期地层进行对比,二者可能具有相同或相似的成因背景.奥陶纪末全球性冰期与海平面下降事件也造成了滇西和缅甸掸邦等地区普遍缺失凯迪晚期地层,对青藏高原的申扎和聂拉木等地区也有较大影响.

中国奥陶纪综合地层和时间框架

简要回顾中国奥陶纪年代地层研究的历史和现状,从岩石地层、生物地层、地质年龄、化学地层和磁性地层等学科的角度,详细阐述和讨论了国际和中国奥陶系划分方案、各条界线的定义标准、识别特征和存在问题,初步建立了多学科的地层对比关系.目前,国际奥陶系采用"三统七阶"的标准划分方案,即自下而上:下奥陶统(特马豆克阶、弗洛阶)、中奥陶统(大坪阶、达瑞威尔阶)和上奥陶统(桑比阶、凯迪阶、赫南特阶).这7个阶的底界金钉子已于1997~2007年全部确立,其中有三个阶的"金钉子"确立在中国.中国的年代地层方案与国际标准方案基本一致(惟部分阶名有别),包括下奥陶统(新厂阶、益阳阶)、中奥陶统(大坪阶、达瑞威尔阶)、上奥陶统(艾家山阶、钱塘江阶、赫南特阶).在多数情况下中国可以直接采用国际标准划分,在特殊情况下,也可以结合使用中国地区性的上奥陶统艾家山阶和钱塘江阶.在详细总结中国各个块体奥陶系发育特征及其差异的基础上,根据近年来的最新研究成果,建立华南、华北(含塔里木、柴达木)和西藏-滇西等主要块体之间的最新奥陶系对比格架,提出特马豆克阶、大坪阶和凯迪阶底界存在的定义、识别和跨相区对比问题,认为特马豆克阶底界主要是牙形刺的分类学问题,而大坪阶和凯迪阶的底界则主要是跨相区对比问题.中国奥陶纪化学地层学研究显示,中奥陶统达瑞威尔阶和上奥陶统凯迪阶的无机碳同位素曲线与国际综合曲线存在较明显的不一致现象,值得高度重视.中国奥陶系的同位素年龄值匮乏,且仅有的3个可靠锆石年龄均集中在晚奥陶世凯迪晚期-赫南特期,华南上奥陶统含有丰富斑脱岩层,亟待开展同位素测年进一步研究.中国奥陶纪磁性地层研究非常薄弱,迄今为止的研究主要局限于华北下奥陶统,结果可与国外其他地区进行对比.对奥陶系内"阶"的悬殊的时限差异进行了分析,建议对长时限的特马豆克阶、达瑞威尔阶和凯迪阶分别进一步细分为二个亚阶.

志留纪初宜昌上升及其周缘龙马溪组黑色笔石页岩的圈层展布模式

渝东、鄂西和湘西北志留系兰多维列统鲁丹阶至埃隆阶下部的地层存在不同程度的缺失,因此这一地区性的抬升被称为宜昌上升.本文通过丰富的剖面地层资料,阐明了宜昌上升的时空分布模式.由于与之相关的龙马溪组底部黑色页岩的不同程度的缺失,关系到对其中赋存的页岩气的勘探,因此,宜昌上升的分布模型对该地区及其周缘页岩气的勘探开发布局有指导作用.本文与"黔渝地区志留系龙马溪组黑色页岩的阶段性渐进展布模式"一文,共同提供了中国中上扬子区奥陶-志留系之交黑色页岩地层的一个完整的分布模式.

中国奥陶系研究的若干问题

以统一的时间轴为标尺,本文对我国奥陶纪年代地层、生物地层、化学地层进行精确对比,同时对全球海平面、磁极性反转、古气候和生物多样性等长周期全球变化,以及奥陶纪重大生物和地质事件进行简要总结、讨论和梳理。在此基础上,指出我国应重点关注和聚焦以下若干科学问题:1)奥陶系底界问题;2)奥陶系"阶"的时限长短不均衡,有必要进行再划分;3)我国奥陶纪地层并不连续和完整,需要重新认识;4)追求更高精度的地层划分对比;5)奥陶纪长周期变化及快速生物和地质事件的过程和发生机制。

西藏南部和中部地区的奥陶系

本文系统梳理了前人对西藏南部和中部地区奥陶纪地层的建组和划分对比工作,提出这些地区最新的地层划分和对比方案。对西藏南部聂拉木地区的甲村群、中部申扎地区的柯耳多群和察隅地区的桑曲组的定义进行厘定;介绍3个新建的岩石地层单元,分别是甲村群中的阿当组、柯耳多群中的知洼作古组及桑曲组中的白云质灰岩段。结合近年来发表的研究成果,将这些地区的岩石地层和生物地层与华南、华北及澳大利亚等地进行精确对比,为进一步开展西藏地区奥陶纪岩相和古地理研究提供依据。