Ordovician chitinozoan diversification events in China

Chitinozoans, as a group of organic shelly fossils,are widely found in the Ordovician (Late Tremadocian)to the latest Devonian marine deposits since Eisenack(1931) first introduced the term of chitinozoa and de-scribed first species. Based on the detailed observa-tions and reviews of representative species of 143genera or subgenera described in the literature fromthe scanning electron microscopy, only 56 genera areultimately retained[1]. Paris and N?lvak[2] postulatedthat chitinozoans are th…     

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.     

Late Paleozoic brachiopod faunas of the South Kitakami Belt, northeast Japan, and their paleobiogeographic and tectonic implications

Abstract    Late Paleozoic (Middle Devonian, Early Carboniferous and Middle Permian) brachiopod faunas of the South Kitakami Belt, northeast Japan, are closely related paleobiogeographically to those of the Xinjiang–Inner Mongolia–Jilin region, northwest–northeast China. This relationship suggests that the South Kitakami Belt was part of the trench or continental shelf bordering the northern and eastern margins of North China (Sino-Korea) during the Middle Devonian to Middle Permian times. Among the three models on the origin and tectonic development of the South Kitakami Belt, the strike–slip model is most consistent, but both the microcontinent model and the nappe model have considerable inconsistencies with the above paleobiogeographic and paleogeographic evidence.     

Upper Ordovician continuous lithological succession in outer‐shelf facies,Yangtze Platform,South China: Facies changes and oceanographic reconstruction up to the Late Ordovician Hirnantian glaciation

Ordovician sequences at Huanghuachang, northern Yichang City of Hubei Province, Central China, are representative of an outer‐shelf setting of the Yangtze epicontinental sea, South China Block. Continuous drill cores of the Well Yihuang 1 penetrated the Upper Ordovician units of the Miaopo, Pagoda, Linhsiang, Wufeng, and Kuanyinchiao Formations in ascending order. Such a continuous succession gives valuable insights into environmental changes and an extinction event through Late Ordovician time. Results suggest that sluggish circulation and oligotrophic conditions were characteristic of the region from Sandbian to early Hirnantian Epochs of the Late Ordovician. Thin‐bedded limestones within the Miaopo Formation shales and nodular limestones of the Pagoda and Linhsiang Formations are mainly wackestones and mudstones with sparse and fine‐grained trilobite, cephalopod, gastropod, ostracod, and crinoid bioclasts with rare brachiopod and bivalve bioclasts, further showing gradual decreasing in abundance and grain size upwards through the succession. Such biological and lithological changes are interpreted as a trend towards a deeper and calmer seafloor below storm wave‐base. The Kwangsian Orogeny of the late Katian Epoch altered the geography of the region, creating a large embayment in the area of the Well Yihuang 1 core. Thus the sequence developed upwards to the Wufeng Formation graptolitic black shales consistent with formation in a dysoxic and stagnant embayment that excluded carbonate production and benthic biota, but ideal for preservation of planktic graptolite fossils. Bioclastic packstone and quartz grain lenses interlayered with the black shales are occasionally sourced from southeastward shallow submarine highs closed to the Cathaysian Land. Change from this interpreted sluggish ocean circulation affecting the ocean floor was delayed to the early Hirnantian Epoch, when active circulation is related to the onset of the latest Ordovician glaciation which resulted in an oxygenated ocean floor during regression, favorable for the thriving shelly Hirnantia Fauna.     

Coupling relationships between brachiopods and Girvanella during the Late Devonian F-F transition in Guilin, South China

The abundance curves derived from area proportions of brachiopods and Girvanella in the thin sections from the Yangdi section, South China, exhibits complex relationships during the Late Devonian Frasnian-Famennian transition. The living activity of brachiopods such as grazing and borrowing did great damage to the growth of Girvanella. However, there was more to just a mere a survival competing relationship between them, Girvanella actually improved marine environments by oxygenating the dysoxic ambient sea-water through photosynthesis in the lower Kellwasser Horizon. Profited from this improvement brachiopods' abundance increased subsequently and suppressed Girvanella again. Nonetheless, without Girvanella's photosynthesis, brachiopods were wiped out by the farther anoxic environments in the upper Kellwasser Horizon. The complex relationships between Girvanella and brachiopods may be a key to unlocking the relationships between geomicrobes and metazoans in the geological overturn periods.     

Sedimentary and biotic evidence of a warm-water enclave in the cooler oceans of the latest Ordovician glacial phase, Yangtze Platform, South China block

Abstract   During the Hirnantian period, the Yangtze Platform was situated in the western part of the South China block (SCB) before its later rotation, in the middle–low paleolatitudes of the southern hemisphere in the northeast side of peri-Gondwana. It is part of the Kosov faunal province as indicated by the Hirnantia fauna. Sedimentary evidence shows the domination of cool ventilated marine water from its offshore ramp and shelf. Hirnantian shallow-water carbonate facies (Kuanyinchiao Bed) overlie earlier Ashgill graptolitic black shales (Wufeng Formation) as a result of marine regression. In the Yangtze Platform, however, we have found local areas of intertidal to nearshore facies that lack the typical highly diverse Hirnantia fauna. Some warm-water features (radial oolites, peloids, diverse solitary rugose corals and other benthic shelly fauna) occur commonly in some limited shallow areas, forming grainstones and packstones. Although interglacial episodes within the Hirnantian glaciation could be responsible for these features, their limited occurrence within the interior of the platform leads us to interpret the deposits as indicating that cold-water currents from the southeastern high latitudes were partly excluded from the nearshore area of the Yangtze Platform. The landmass of the eastern SCB in the Hirnantian epoch prevented access to some areas of the cold marine water masses that flowed from higher latitudes of Gondwana; the result was a persistence of warm-water shallow marine facies in some areas.     

Chief sources of brachiopod recovery from the end Ordovician mass extinction with special references to progenitors

Survivor, Lazarus and progenitor taxa are sources of biotic recovery following mass extinction. Investigations of the benthic brachiopods through the latest Ordovician mass extinction shows that progenitors developed many evolutionary novelties and successful surviving mechanisms. They are superior to survivors and Lazarus taxa in their ability to adapt to environmental changes. They are the primary source of macroevolution and the ancestors of a number of new taxa. Three kinds of progenitors are recognized based on the Ordovician-Silurian brachiopods from South China: survivor-progenitors, crisis-progenitors and Lazarus-progenitors; the last has the strongest ability to resist adverse environments, and is the most diverse and abundant. Project supported by the National Natural Science Foundation of China (Grant No. 49672083) and Major Project of the Chinese Academy of Sciences (CAS) (Grant KZ952-51-023).     

Diversity history of Ordovician graptolites and its relationship with environmental change

Statistical analysis based on global data indicated that the planktonic graptolites presented a distinguished pattern from that of benthic communities during the great Ordovician biodiversification. The graptolites started to diversify from the beginning of Ordovician and reached an acme in the early Middle Ordovician, but subsequently underwent a steady decline to the end of Ordovician. During the Ordovician, many clades of the graptolites made their originations, flourishing and replacements. However, in different regions and distinct environments across the world, graptolites may presumably display distinct patterns of radiation and evolution, a hypothesis to be tested. Herein a study of the graptolite diversity in the Early to Middle Ordovician in the Upper Yangtze Region (Platform) and Jiangnan Region (Slope), South China, is conducted. The results indicate that graptolites underwent a remarkable increase in both regions, but with distinct magnitude, scope, process and patterns. The diversification of graptolites in the Upper Yangtze Region, though less prominent, is divided into four stages and includes two peaks. In the Jiangnan Region, the graptolite diversification is far more prominent and includes three stages and one peak. Based on the distinct diversity histories and composition of graptolites in the two representative regions, a 'deep-water origin and shallow-water dispersal' model is proposed for the Ordovician graptolite faunas. According to the model, the major graptolite faunas of Ordovician originated in the deep-water region on the continental slope, the source of the graptolite novelties, and subsequently spread into shallow-water region on the shelf. Besides, we also conduct a comparison study of the Ordovician graptolite diversity in South China and other major regions. The results display that the graptolites diversified globally in the Early and Middle Ordovician. At the beginning of Ordovician, graptolites underwent a significant ecological innovation of graptolites: planktonic forms were derived from their benthic ancestors. This derivation resulted in the great guild expansion of graptolites. In late Early Ordovician (Floian), the global expansion of graptolites commenced. From the Floian to the end of Middle Ordovician, the graptolites diversity increased remarkably and displayed three peaks for all the regions. However, the peaks are somewhat distinct in magnitude and timing among regions. The Darriwilian peak is prominent in both South China and Baltic region, but inconspicuous in Australasia. No close relationship between the graptolite diversification and the palaeolatitudes are supported herein. Instead, the graptolite diversification seems to coincide with the global sea-level rises, suggesting a possible intrinsic relationship between them.     

Succession of Cambrian conodonts from South China

More than 4200 kg, the total weight, of 980 productive conodont samples mainly from four key sections in western Hunan and northwestern Hunan, South China have been processed. It is found that the paraconodonts occurring below Fengshanian (upper Upper Cambrian) may be used for stratigraphic subdivision and correlation. Accordingly, eight conodont zones ranging from upper Middle Cambrian to upper Upper Cambrian in South China are erected for the first time. The correlation between these zones and those of North China, North America and Iran is discussed. These eight zones are in ascending order as follows:Gapparodus bisulcatus-Westergaardodina brevidens zone, Shandongodus priscus-Hunano- gnathus tricuspidatus zone, Westergaardodina quadrata zone, Westergaardodina matsushitai-W. grandidens zone, Westergaardodina proligula zone, Westergaardodina cf. behrae-Prooneotodus rotundatus zone, Proconodontus zone, Cordylodus proavus zone.     

Tectonic and stratigraphic significance of the Middle Ordovician carbonate breccias in the Ogcheon Belt, South Korea

Abstract Carbonate breccias occur sporadically in the Lower–Middle Ordovician Maggol Limestone exposed in the Taebacksan Basin in the northeastern part of the northeast–southwest‐trending Ogcheon Belt, South Korea. These carbonate breccias have been previously interpreted as intraformational or fault‐related breccias. Thus, little attention has been focused on tectonic and stratigraphic significance of these carbonate breccias. The present study, however, indicates that the majority of these carbonate breccias are solution–collapse breccias, which are causally linked to paleokarstification. Carbonate facies analysis in conjunction with conodont biostratigraphy suggests that an overall regression toward the top of the Maggol Limestone probably culminated in subaerial exposure of platform carbonates during the early Middle Ordovician (earliest Darriwilian). Extensive subaerial exposure of platform carbonates resulted in paleokarst‐related solution–collapse breccias in the upper Maggol Limestone. This subaerial exposure event is manifested as a major paleokarst unconformity at the Sauk–Tippecanoe sequence boundary elsewhere beneath the Middle Ordovician succession and its equivalents, most notably North America and North China. Due to its global extent, this paleokarst unconformity has been viewed as a product of second‐ or third‐order eustatic sealevel drop during the early Middle Ordovician. Although a paleokarst breccia zone is recognized beneath the Middle Ordovician succession in South Korea, the Sauk–Tippecanoe sequence boundary appears to be a conformable transgressive surface on the top of the paleokarst breccia zone in the upper Maggol Limestone. The paleokarst breccia zone beneath the conformable transgressive surface is represented by a thinning‐upward stack of exposure‐capped tidal flat‐dominated cycles that are closely associated with multiple occurrences of paleokarst‐related solution–collapse breccias. This paleokarst breccia zone was a likely consequence of repeated fourth‐ and fifth‐order sealevel fluctuations. It suggests that second‐ and third‐order eustatic sealevel drop may have been significantly tempered by substantial tectonic subsidence near the end of the Maggol deposition. The tectonic subsidence in the basin is also evidenced by the occurrence of coeval off‐platform lowstand siliciclastic quartzite lenses as well as debris flow carbonate breccias (i.e. the Yemi Breccia). With the continued tectonic subsidence, subsequent rise in the eustatic cycle caused drowning and deep flooding of carbonate platform, forming a transgressive surface on the top of the paleokarst breccia zone. This tectonic implication contrasts notably with the slowly subsiding carbonate platform model for the basin as has been previously interpreted. Thus, it is proposed that the Taebacksan Basin in the northeastern part of the Ogcheon Belt evolved from a slowly subsiding carbonate platform to a rapidly subsiding intracontinental rift basin during the early Middle Ordovician. The proposed tectonic model in the basin gives much better insight to unravel the stratigraphic response to tectonic evolution of the Ogcheon Belt, which remains an enigmatic feature in formulating a tectonic framework of the Korean peninsula. The present study also provides a good example that the falling part of the eustatic sealevel cycle may not produce a significant event in a rapidly subsiding basin where the rate of eustatic fall always remained lower than the rate of subsidence.     

Coupling relationships between brachiopods and Girvanella during the Late Devonian F-F transition in Guilin, South China

The abundance curves derived from area proportions of brachiopods and Girvanella in the thin sections from the Yangdi section, South China, exhibits complex relationships during the Late Devonian Frasnian-Famennian transition. The living activity of brachiopods such as grazing and borrowing did great damage to the growth of Girvanella. However, there was more to just a mere a survival competing relationship between them, Girvanella actually improved marine environments by oxygenating the dysoxic ambient sea-water through photosynthesis in the lower Kellwasser Horizon. Profited from this improvement brachiopods’ abundance increased subsequently and suppressed Girvanella again. Nonetheless, without Girvanella’s photosynthesis, brachiopods were wiped out by the farther anoxic environments in the upper Kellwasser Horizon. The complex relationships between Girvanella and brachiopods may be a key to unlocking the relationships between geomicrobes and metazoans in the geological overturn periods. Supported by NSFC Innovation Research Group Program (Grant No. 40621002), MOE Innovative Research Team Program (Grant No. IRT0546), the National Natural Science Foundation of China (Grant Nos. 40472020, 40730209, 40802005 and 40872001) and SINOPEC Project (Grant No. G0800-06-ZS-319)     

华南及南海北部地区瑞利面波层析成像

基于华南及周边地区106个宽频带地震台站多年记录的MS≥5.0中浅源地震事件, 开展瑞利面波层析成像和速度结构特征研究, 获得了华南大陆及南海北部地区10~100 s瑞利波群速度分布图像和典型剖面下方地壳上地幔速度结构, 为理解该地区构造演化和深部过程提供约束.考虑到实际地震射线的覆盖情况以及华南地区主要构造的主体展布特征, 本文同时采用传统的规则网格剖分和平行主要构造走向的非规则网格剖分方法, 分别进行分格频散反演, 开展了不同参数化方案对反演结果影响的对比分析研究.基于瑞利面波层析成像结果, 进行了典型剖面横波速度结构反演, 重建了华南地区由内陆至南海海域主要构造单元的壳幔横波速度结构.研究结果表明, 扬子和华夏块体地壳上地幔结构特征差异显著, 扬子块体地壳和岩石圈厚度均大于华夏地块, 且扬子块体上地幔顶部速度较华夏块体低, 岩石圈厚度在雪峰山造山带下方发生过渡和转换;南海北部陆缘和南海海盆上地幔速度较高且形态相对完整, 表现为非火山型大陆边缘和已停止扩张海盆的壳幔结构特征.     

Proposed new Lower Triassic stages in South China

As the global Lower Triassic stages are not properly defined, a Chinese scheme of the Lower Triassic subdivision was recently proposed to meet the insistent need of the general investigation in China. The Lower Triassic sequences of South China are briefly summarized and the twofold Lower Triassic subdivision is discussed. The type sections of the two Chinese Lower Triassic stages, Yinkengian and Chaohuan, and their definitions are stated.     

华南强震动力分析

根据华南陆缘扩张的动力来源和现代构造运动特征及强震震源断层最新活动性质,通过对华南地震活动与地球自转速率变化、GPS观测基线变化、理论面应变的关系分析,认为地幔流向洋侧的蠕散是造成华南现今地壳变形和张剪性构造运动为主的原因,而区域地球的波动膨胀拉张是引发强震的动力。     

中国南方现今地热特征

根据中国南方地温梯度和大地热流的数据各418个,编制了中国南方地温梯度图和中国南方大地热流图,研究了中国南方现今地温梯度分布特征和大地热流分布特征.结果显示,中国南方地温梯度介于7.82～162.5℃/km,平均24.1℃/km;大地热流变化于22～220 mW/m2之间,平均值为64.2 mW/m2.东南沿海和滇西南地区为高地温梯度分布区,扬子地块为中－低温地温梯度区.地温梯度不仅与区域热构造背景有关,还显著地受地下水热活动、断裂以及地层热导率影响.中国南方大地热流东部、西南部高,中部低,且异常高值点主要沿板块边界缝合带、深大断裂活动带分布.大地热流与区域构造运动、最后一次热事件发生的时间、岩石圈拉张程度、地壳厚度、壳内高导层埋深等因素具有明显的相关性.     

Paleoceanographic evolution recorded in the northern South China Sea since 4 Ma

The late Pliocene-Pleistocene is of great interest for understanding the Earth’s climate system, because not only the late Pliocene is the latest period with tem-perature significantly higher than the Holocene, but also during the Pliocene/Pleistocene transition the Earth’s environment changed from a warm and uni-form climate state into an extreme one with typical glacial-interglacial cycles. During this period the Earth’s climate experienced through the grandly phased rising of the Qing…     

南海北部地震危险性分析

在建立了比较可靠的南海北部地震目录以后,采用编制中国地震动参数区划图（2001）的方法,重新划分了南海北部海域的潜在震源区和调整了相关的地球物理参数,最终计算了南海北部海域50年超越概率10％的地震动峰值加速度。南海北部的地震动峰值加速度可分成东部高值区和西部低值区。东区的地震动峰值加速度在0．160g以上,西区大部分海域的地震动峰值加速度小于0．114g,并且与它们北侧的陆区大致相似。     

南海含天然气水合物地层地震反射特征及可能分布研究

天然气水合物是当前能源与环境领域的研究热点之一,南中国海是天然气水合物赋存的有利区域。天然气水合物的存在改变了沉积地层的声学特征,这一性质使多道地震勘探成为发现海洋天然气水合物的主要手段。本文首先根据地震成像结果定性分析南海可能含天然气水合物沉积地层的地震反射特征,初步确定天然气水合物存在的可能性并指出地震成像关键技术。在无井条件下,构建虚拟井进行波阻抗反演得到定量的地层速度参数进一步证实这一可能性,最后将反演获得的速度场与ODP184 航次在此区域获得的地球物理、地球化学信息综合分析,可以确定此区域天然气水合物的存在及其空间展布。     

华南地区地磁场长期变化特征

使用华南地区5个国家基准地磁台2008—2018年地磁观测数据,通过对磁偏角D、磁倾角I、总强度F、北向分量X、东向分量Y、水平分量H、垂直分量Z月均值及年变率的分析,研究该区地磁场长期变化特征。结果表明,华南地区5个地磁台近10年来七要素月均值及年变率均呈缓慢变化趋势,且变化量相当,反映了该区域地磁场长期变化的特征。     

Pleistocene radiolarian biostratigraphy in the South China Sea*

Based on a quantitative radiolarian analysis, 5 radiolarian zones (NR1-NR5) have been defined at Core. 17957-2 from the South China Sea, considering radiolarian zonations from low latitudes. The absolute age assignment of the radiolarian zones and the ranges of the six marker species is based on the direct correlation with the paleomagnetic and isotopic record, respectively. A comparison of the radiolarian stratigraphic data obtained from Core 17957-2 from the South China Sea with those from the equatorial Pacific and the tropical Indian Ocean shows a close similarity to the ages defined in the equatorial Pacific. The obtained biostratigraphic data provide an excellent tool for further dating of Pleistocene sediments in the China Sea. Project supported by the National Natural Science Foundation of China (Grant No. 49291100) and by the German Federal Ministry for Education, Science, Research and Technology (BMBF) as part of a GermadChinese scientific cooperation program. This is Alfred Wegener Contribution No. 1473.