A Review on the Global Stratotype Section and Point of the Permian-Triassic Boundary

This paper provides a synthetic review of researches on Meishan Section D, the Global Stratotype Section and Point of the Permian-Triassic Boundary （PTB）. The history of research, geographic and geological setting of the section are briefly introduced. Changhsingian to ＂Griesbachian＂ conodont and ammonoid zonations, the most perfect Permo-Triassic zonations over the world, are presented, with a short discussion on the age of Otoceras, The Changhsingian to ＂Griesbachian＂ strata are subdivided into three 3rd order sequences, and the sedimentary structure of each sequence is indicated. The paper presents a correlation of the Changhsingian to ＂Griesbachian＂ magneetostratigraphy of the Meishan section with the general scale, and informed the negation of a short magnetic reversal at the PTB suggested by Zhu and Liu （1999）. Recent developments of chemostratigraphy of δ^13C and δ^34S are introduced, especially the discovery of more than one negative δ^13C excursions across the PTB. Two important molecular researches reveal the profound changes at the base of eco-system, the microbial catastrophy, and the euxinic conditions in the photic zone during the Permian-Triassic superanoxic event. The paper reports the changes in dating the age of PTB since 2001. According to recent achievements, the age of volcanogenic claybed 25, 14 cm below the PTB, is now set at 252.4±0.3 Ma. A discussion on the eventostratigraphy concludes that, although there is a major event episode at beds 25-26, the events across the PTB at Meishan are multi-episodic and commenced prior to the Event Beds 25-26, thus the possibility that the mass extinction was mainly induced by an exterrestrial impact is largely excluded.

Suggestion of Meishan Section as GlobalStratotype Section and Point （GSSP） of Permian－Triassic Boundary

The Meishan Section of Changxing County, Zhejiang Province, China and the base of its Bed 27c,in which Hindeodus parvus first occurs, are recommended as the GSSP of Permian-Triassic boundary (PTB).The present paper introduces a description of the section. Biostratigraphic correlation with other famous sections shows the completeness of this section and justifies choice of H. Parvus as the index fossil. Chemostratigraphic investigation provides the δ￣13C excursion and the moderate but inconsistent Ir spike as auxiliary symbols for the PTB. This boundary is closely related to transgression,anoxia,volcanism,mass extinction and possible impact events which can be correlated with those in South China and other parts of the world .

Transgressive Surface as Sequence Boundary

Analysis of the four cases of the sequence boundary (SB)-transgressive surface (TS) relation in nature shows that applying transgressive surfaces as sequence boundaries has the following merits: it improves the methodology of stratigraphic subdivision; the position of transgressive surface in a sea level curve is relatively fixed; the transgressive surface is a transforming surface of the stratal structure; in platforms or ramps, the transgressive surface is the only choice for determining the sequence boundary; the transgressive surface is a readily recognized physical surface reflected by seismic records in seismostratigraphy. The paper reaches a conclusion that to delineate a SB in terms of the TS is theoretically and practically better than to delineate it between highstand and lowstand sediments as has been done traditionally.

地史时期生物对冰室气候形成的作用

在地质历史时期的碳循环中,生物的作用很大.生物产氧光合作用消耗CO_2而产生有机质与O_2;有机质及生物成因碳酸盐岩埋藏又进一步固定CO_2并减少O_2消耗,所以生物产氧光合事件与冰期、成(增)氧期应存在因果关系.论述了5次事件,分别是:与产氧光合蓝细菌有关的古元古代初期大氧化事件(Early Proterozoic great oxygenation event,GOE)、与真核生物辐射事件有关的新元古代大成氧事件(Neoproterozoic oxidation event,NOE)、与早期陆生植物繁盛事件有关的晚奥陶世增氧和冰期事件、与维管植物繁盛事件有关的石炭纪-二叠纪增氧和冰期事件及与被子植物和浮游微植物繁盛有关的第四纪冰期事件.结果表明,5次成氧事件和冰期与生物事件有因果关系,主要表现为,都有冰期和成氧事件共存或相继出现的证据,反映大气CO_2降低和O_2增加同时或相继发生,而这只能由生物的光合作用及其产物的埋藏造成.这说明生物不仅仅是适应于环境,它也对环境产生重大影响,生物与环境的这种相互作用在漫长的地质历史中表现为协同演化.但是早期生物事件并不立刻产生成氧或冰期等环境效应,这种效应开始是微量的,逐渐积累,达到阈值后才发生质变,所以在时间上是滞后的.随着生物多样性和丰度的增加,这种效应越来越大,速率越来越快,滞后性逐渐减弱,耦合性日渐明显.生物与地球环境之间的相互作用构成了生物与地球系统的自我调节,使地球与其他星球不同,其表层始终保持在生命宜居的环境范围内.今天人类更要理智地、科学地善待地球,避免对地球造成重大的负面影响.

再谈古生物学向地球生物学的发展:服务领域的拓展与创新

地球科学前沿研究为社会服务是一个永恒的主题,这在当前全球化背景下尤其迫切.古生物学作为一个受人瞩目的精品学科,在向地球生物学发展过程中,其服务领域正不断地拓展和创新.系统地总结了当前地球生物学在全球变化和油气资源两大领域的应用与拓展,以及在关键带和深地两大领域的创新性发展.在全球变化领域,藻类、古菌、细菌等地质微生物的脂类不仅能够用于估算古温度,还可以记录干旱等极端古气候事件,从而实现古温度与古降水信号的分离.地球生物学已经从探索生物对环境的响应深入到生物对环境的作用.地球生物学也在评价烃源岩、储层等常规油气资源领域得到广泛的应用,但当前其更重要的应用表现在页岩气等非常规油气资源领域,包括地质微生物形成页岩中的纳米孔隙,形成易于压裂的长石、石英等矿物.在关键带研究领域,地球生物学可以解剖碳循环与水循环之间的内在联系.聚焦于地质微生物功能群的关键带地质微生物调查,不仅可以查明污染物的分布和污染程度,还可以为环境修复提供技术方法.而在深地研究领域,为拓展对地下空间的利用,需要充分利用地下工程对地下微生物开展调查和研究,以查明地下环境中有害或者有益的微生物功能群分布及其地质作用.

Mass extinction and Pangea integration during the Paleozoic-Mesozoic transition

The greatest Phanerozoic mass extinction happened at the end-Permian to earliest Triassic. About 95% species, 82% genera, and more than half families became extinct, constituting the sole macro-mass extinction in geological history. This event not only caused the great extinction but also destroyed the 200 Myr-long Paleozoic marine ecosystem, prompted its transition to Mesozoic ecosystem, and induced coal gap on land as well as reef gap and chert gap in ocean. The biotic crisis during the Paleozoic-Mesozoic transition was a long process of co-evolution between geospheres and biosphere. The event sequence at the Permian-Triassic boundary （PTB） reveals two-episodic pattern of rapidly deteriorating global changes and biotic mass ex- tinction and the intimate relationship between them. The severe global changes coupling multiple geospheres may have affect- ed the Pangea integration on the Earth＇s surface spheres, which include： the Pangea integration→enhanced mountain height and basin depth, changes of wind and ocean current systems; enhanced ocean basin depth→the greatest Phanerozoic regression at PTB, disappearance of epeiric seas and subsequent rapid transgression; the Pangea integration→thermal isolation effect of continental lithosphere and decrease of mid-ocean ridges→development of continental volcanism; two-episode volcanism causing LIPs of the Emeishan Basalt and the Siberian Trap （25%251 Ma）→global warming and mass extinction; continental aridification and replacement of monsoon system by latitudinal wind system→destruction of vegetation; enhanced weathering and CH4 emission→negative excursion of δ^13C; mantle plume→crust doming→regression; possible relation between the Illawarra magnetic reversal and the PTB extinction, and so on. Mantle plume produced the Late Permian LIPs and mantle convection may have caused the process of the Pangea integration. Subduction, delamination, and accumulation of the earth＇s cool lithospheric material at the ＂D＂ layer of CMB started mantle plume by heat compensation and disturbed the outer core ther- too-convection, and the latter in turn would generate the mid-Permian geomagnetic reversal. These core and mantle perturbations may have caused the Pangea integration and two successive LIPs in the Permian, and probably finally the mass extinction at the PTB.

The fluctuating environment associated with the episodic biotic crisis during the Permo/Triassic transition:Evidence from microbial biomarkers in Changxing,Zhejiang Province

The environmental conditions and the biotic crisis during the Permo-Triassic (Tr/P) transition received increasing attention in the past decades. Presented herein are the molecular fossil records of cyano-bacteria and green sulfur bacteria,the base of the marine ecosystem,to highlight the episodic nature of both the environment and the biotic crisis during this critical period. At least two episodes of cyano-bacterial expansion are documented by 2-methylhopanes ranging from C28 to C32 in carbon number,indicative of the instable marine ecosystem and the fluctuant aquatic nutrients. Meanwhile,the index of 2-alkyl-1,3,4-trimethylbenzenes (biomarkers of green sulfur bacteria) and the ratio of pristane to phy-tane (Pr/Ph) witness the fluctuation of sedimentary environmental redox conditions. The above mo-lecular evidence suggests the occurrence of highly fluctuating environmental conditions during the Tr/P transition,which is consistent with,and probably the cause of,the multi-phased biotic crisis and the prolonged faunal recovery.

Progress and perspective on frontiers of geobiology

Geobiology is a new discipline on the crossing interface between earth science and life science, and aims to understand the in- teraction and co-evolution between organisms and environments. On the basis of the latest international achievements, the new data presented in the Beijing geobiology forum sponsored by Chinese Academy of Sciences in 2013, and the papers in this special issue, here we present an overview of the progress and perspectives on three important frontiers, including geobiology of the critical periods in Earth history, geomicrobes and their responses and feedbacks to global environmental changes, and geobiology in extreme environments. Knowledge is greatly improved about the close relationship of some significant biotic events such as origin, radiation, extinction, and recovery of organisms with the deep Earth processes and the resultant envi- ronmental processes among oceans, land, and atmosphere in the critical periods, although the specific dynamics of the co-evolution between ancient life and paleoenvironments is still largely unknown. A variety of geomicrobial functional groups were found to respond sensitively to paleoenvironmental changes, which enable the establishment of proxies for paleoenvi- ronmental reconstruction, and to play active roles on the Earth environmental changes via elemental biogeochemical cycles and mineral bio-transforrnations, but to be deciphered are the mechanisms of these functional groups that change paleoenvi- ronmental conditions. Microbes of potential geobiology significance were found and isolated from some extreme environments with their biological properties partly understood, but little is known about their geobiological functions to change Earth envi- ronments. The biotic processes to alter or modify the environments are thus proposed to be the very issue geobiology aims to decipher in the future. Geobiology will greatly extend the temporal and spatial scope of biotic research on Earth and beyond. It has great potential of application in the domains of resource exploration and global change. To achieve these aims needs coor- dinative multidisciplinary studies concerning geomicrobiology and related themes, database and modeling of biogeochemical cycles, typical geological environments, and coupling of biological, physical, and chemical processes.

Discussion on geobiology, biogeology and geobiofacies

Here we first discuss the definition of and the difference between geobiology and biogeology following a brief introduction of recent geobiology research in China. Geobiology is defined as an interdisciplinary study of life sciences and earth sciences, and biogeology as an interdisciplinary study of biology and geology. Scope of the term geobiology covers that of the term biogeology. Branch interdisciplines of both are listed. We then propose the term geobiofacies, defined as the facies of a geologic body embodying the whole process of interaction between organisms and environments. Differences among geobiofacies, biofacies, and organic facies are discussed. Main parameters defining a geobiofacies include habitat type, biotic composition and productivity, paleo-oxygenation regimes, and early diagenesis phases. Each of them is discussed in detail, and a semi-quantitative assessment of the biogeofacies of source rocks is proposed based on these parameters. A two-fold terminology for geobiofacies is recommended, namely, the biological and environmental aspects of biota and the redox conditions during life-burial-diagenesis process

Geobiological approach to evaluating marine carbonate source rocks of hydrocarbon

Evaluating the pre-Jurassic marine source rocks in China has been difficult because these rocks are generally too highor over-maturated for most traditional methods to work.As to the remaining parameter TOC (%),its lower limit for recognizing the carbonate source rocks in China has been in dispute.Nineteen Phanerozoic sections in the Middle-Upper Yangtze Platform and the Guizhou-Hunan-Guangxi Basin have been studied in search for a different approach to complementing the traditional evaluation method for these source rocks.We have applied a geobiological approach to tracing the organic carbon (OC) output and accumulation from the living stage (primary productivity) to the post-mortem deposited remains,and finally to the preserved burial organics.Four biological and geological parameters are employed to represent the OC of the three stages.A series of proxies of these parameters are discussed and integrated to establish a geobiological evaluation system independent of TOC and other traditional methods.Here we use the Guangyuan section in Sichuan as an example for the geobiological evaluation.Our results indicate that in the argillaceous rocks,the geobiological parameters show the qualified source rocks in accordance with high TOC values;but in the carbonates,the good source rocks delineated by the geobiological parameters have a wide range of TOC,from 0.03% to 1.59%,mostly<0.3%.We suggest that it is still premature to set TOC=0.3% or 0.5% as the lower limit for the pre-Jurassic carbonate source rocks in South China.

Evolution of drainage systems and its developing trend in connection with tectonic uplift of Eastern Kunlun Mt.

The Eastern Kunlun Mt. had been subjected to uplift together with the Qinghai-Xizang (Tibet) Plateau before the Early Pleistocene, and yet the Mt. did not protrude out of the Plateau surface. During that period lakes spread all over the studied region, with the drainage systems being all short rivers flowing into the lakes. At the end of the Early Pleistocene, intensive tectonic uplift led to the rising of the Eastern Kunlun Mt. and made the Mt. protrude onto the Plateau surface. As a result, a fault depression valley formed extending nearly from west to east along the fault belt of the Southern Kunlun Mt. Lakes in this region died out, surface runoffs joined into the valley of the Southern Kunlun Mt. resulting in a large river streaming nearly from west to east. Around 150 kaBP, because of the strong differential movement, rivers, such as the Jialu River and the Golmud River, retrogressively eroded seriously, cutting through the Burhan Budai Mt. Then they pirated the large river and divided it into