地球深部过程与极热和极冷事件

地球气候以频繁冷暖波动为特征,在百万年时间尺度上可划分为温室期和冰室期,期间发生持续时间相对短的极热和极冷事件.大多数学者将这些温室期、冰室期以及极热和极冷事件归因于大气CO_(2)浓度变化,即地球深部碳释放和表层碳消耗之间的动态平衡.地球深部碳是CO_(2)的主要来源,通过大火成岩省、俯冲带、裂谷岩浆活动等过程释放到大气中,从而引发全球增温.但是,深部过程又可通过4种途径引发降温:(1)火山活动释放SO_(2)形成硫酸盐气溶胶,导致“火山冬天”;(2)岩浆活动峰期之后的化学风化消耗大气CO_(2),其中,镁铁质岩化学风化速率高于长英质岩,降温作用更显著;(3)火山喷发及岩浆岩化学风化释放营养元素,促进大洋初级生产力,加快碳埋藏;(4)板块运动增大陆地面积以及使大陆聚集于高温、湿润的低纬地区,增强化学风化对CO_(2)的消耗.大体上,温室和冰室气候与俯冲带大陆弧岩浆活动强度(通常用大陆弧长度和年轻碎屑锆石相对丰度指代)及低纬地区弧-陆碰撞带长度有关,如果大陆弧活跃且低纬地区弧-陆碰撞带规模小,易形成温室气候,反之则形成冰室气候.极热事件普遍由镁铁质大火成岩省的快速巨量碳释放引发;极冷事件成因较为复杂,例如低纬地区大火成岩省强烈化学风化(如前寒武纪斯图特雪球地球)和硅质大火成岩省或大规模长英质火山活动的“火山冬天”效应(如晚古生代冰期极盛期).目前,从发生时间一致和关联机制合理性这两个角度考虑,大部分极热和极冷事件的发生都可归因于大规模岩浆活动,但是岩浆活动引发的系列反馈过程以及对极热和极冷事件的触发与维持机制仍缺乏深入理解.就此而论,高精度定年、岩浆活动过程及其气候反馈的数值模拟应该是今后研究的重点.

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

The complex evolutionary history of the Qinghai-Tibetan Plateau and its surrounding areas,including the continental blocks(Indian,Lhasa,South Qiangtang,Tarim,Olongbuluk,Central Qilian,Alxa,North China,Yangtze,Central Iran and Oman)and the orogenic belts between them,has long been the frontier in Earth science research.The Cryogenian and Ediacaran strata are extensively distributed in these blocks.Specifically,relatively complete Cryogenian and Ediacaran successions have been discovered in Oman,Indian,Yangtze,and Tarim blocks,while only the Ediacaran successions have been reported in Iran,the South Qiangtang,Central Qilian,Alxa,and North China blocks.Based on previous studies together with the integration of new materials and advancement obtained through the Second Tibetan Plateau Scientific Expedition and Research,this review aims to synthesize a correlative stratigraphic framework of the representative Cryogenian and Ediacaran sequences from the Qinghai-Tibetan Plateau and its surrounding areas.Furthermore,the Cryogenian and Ediacaran biotas and major geological events in these areas are comprehensively discussed in aspects of current research status.The results indicate that,in general,Ediacaran fossils of each area exhibit distinct features in preservation and assemblage composition,but the typical late Ediacaran fossils Cloudina and Shaanxilithes have been reported from most of these areas.In addition to the two global Cryogenian glaciations,late Ediacaran glaciogenic deposits are extensively recorded in the areas within and around the northern QinghaiTibetan Plateau(including the North China,Alxa,Central Qilian,Olongbuluk,and Tarim blocks,and the North Qilian Accretionary Belt),as well as central and southern Iran.However,further research is required to determine the age,distribution,and origin of these late Ediacaran glaciogenic deposits.Meanwhile,the middle Ediacaran DOUNCE/Shuram Excursion is widely documented in the Qinghai-Tibetan Plateau and its surrounding areas.The available data show that,after the break-up of the Rodinia supercontinent,most of the continental blocks in the areas were located along the northern margin of East Gondwana and a few(such as North China)were located between the Gondwana and Laurentia.In general,the paleogeographic evolution of most of these blocks during the Cryogenian and Ediacaran remains disputatious,necessitating further research to resolve the controversies surrounding their paleogeographic reconstruction models during this critical time interval.

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

The Qinghai-Tibetan Plateau and its surrounding areas have a long and complex tectonic evolutionary history.Cratons and blocks,such as northern India,Lhasa,Qiangtang,Qaidam and Central Qilian,and their in-between orogenic belts constitute the main part of the Qinghai-Tibetan Plateau.During the Cambrian Period,most of these cratons and blocks were on the northwestern periphery of Gondwana,and were associated with the surrounding blocks,e.g.Arabian,Central Iran,Afghanistan,Tarim,Alxa,North China,South China and Sibumasu through the Proto-Tethys Ocean.The Cambrian stratigraphic sequences on these stable blocks are composed of mixed siliciclastic and carbonate rocks deposited in the shallow-water marine environments,and contain the trilobite assemblages of shelf facies.The Cambrian stratigraphic sequences in the Qilian tectonic belts,however,are characterized by the intermediate-basic igneous rocks and silicates formed in the Proto-Tethys Ocean,and contain the trilobite assemblages of deep-water slope facies.Combining with previous data,field observations and newly discovered fossils through funding by the Second Tibetan Plateau Scientific Expedition and Research,the general characteristics of the Cambrian strata in different tectonic units of the Qinghai-Tibetan Plateau and its surrounding areas have been summarized in this paper.Furthermore,efforts have been made to subdivide and correlate the Cambrian strata across these areas by utilizing available biostratigraphic and geochronological data.As a result,a comprehensive litho-and biostratigraphy chart has been compiled.Finally,from the biogeographic perspective,this paper also provides a brief overview of the Cambrian paleogeographical reconstruction of the major tectonic blocks,and discusses the problems associated with the evolution of the ProtoTethys tectonic belt.

A holistic perspective on Earth system science

Earth system can be categorized into three parts, solid Earth system, surface Earth system, and Sun-Earth space system. These three subsystems not only have mutual transmission and coupling relationships in both energy and matter but also involve multiple scales from microscopic to macroscopic. Earth system science is characterized by its globality and unity with a holistic view and a systematic view at multiple scales in both space and time. It focuses not only on the physical, chemical and biological interactions between various geospheres but also on the properties, behaviors, processes, and mechanisms of the entire Earth and its spheres. Although significant progress has been made in the study of internal disciplines of these three subsystems,there is still insufficient understanding of their overall behavior and interactions between individuals, thus facing challenges of different types and levels. The solid Earth system is composed of the crust, mantle, and core. Existing observational techniques struggle to penetrate deep into the mantle, making direct observation and data acquisition difficult;the extreme environments within Earth, such as high temperature, high pressure, and strong magnetic fields, also pose great challenges to observational equipment and scientific experiments. The surface Earth system is an open complex mega-system, in which there are complex interactions and feedback mechanisms among its geospheres(such as atmosphere, hydrosphere, biosphere, pedosphere and lithosphere), leading to difficulties in understanding of its overall behavior and long-term evolution. Biological activities have become increasingly significant in affecting the surface Earth system. The coupling between the internal and external Earth systems becomes more complex. Distinguishing and quantifying the impacts of Earth spherical interactions and biological activities on the surface Earth system is a major challenge. The Sun-Earth space system involves multiple physical processes such as solar activity, Earth's magnetic field, atmosphere, and space weather. Solar activity significantly affects the Earth's space environment, but existing observational and reconstruction methods and prediction models still lack precision and timeliness.Thus it is important to improve the prediction capability of solar activity and reduce the impact of space weather disasters. How to cross different scales and establish coupled models of multiple physical processes is a significant challenge in the study of the Sun-Earth space system. Because the various processes and phenomena within and between these three Earth subsystems often span multiple scales in both space and time and exhibit strong nonlinear characteristics, understanding their behaviors and processes becomes complex and variable, posing great challenges for theoretical modelling and numerical simulation. Therefore,the study of Earth system science requires in-depth interdisciplinary integration to jointly reveal the basic laws and operating mechanisms of Earth system.

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

The Qinghai-Tibetan Plateau(QTP)is well known as the Roof of the World,the Third Pole and the Asian Water Tower.It spans a vast area from the Pamir Plateau in the west to the Longmenshan-Hengduan Mountains in the east,from the Himalaya Mountains in the south to the Kunlun-Qilian Mountains in the north.It stretches approximately 1,200 km from north to south and 2,500 km from east to west.When did the QTP start to uplift?This is still controversial between early and late Cenozoic scenarios.While some scholars advocated its uplift since the India-Asia continental collision at about 65 million years ago in the Paleogene(e.g.,Ding et al.,2017,2022),and the others suggested its uplift since the Miocene(Zheng and Wu,2018).

水循环的地质演变:研究现状与关键问题

由大陆-海洋-大气之间水的3种相态(固态-液态-气态)相互转换和位移构成的水循环,是地球气候系统的主要过程之一.太阳辐射量在地球表面分布不均匀,是地表水循环的基本驱动力.水循环与碳循环密切关联,是气候系统演变中的两条主线.不同时空尺度的水循环和碳循环受天文、地质和生物因素以及它们之间相互作用的控制,揭示水循环地质演变过程及其与气候变化之间的关系,可为了解当今水文气候变化提供宝贵启示.通过水循环地质演变研究现状回顾,提出如下5个科学问题应在未来予以重点关注:(1)雪球地球时期的水循环;(2)植被起源和演化对水循环的影响;(3)深时热带辐合带(inter-tropical convergence zone, ITCZ)的演变与水循环;(4)暖室期地下水与海平面变化;(5)深时水循环中的氧同位素示踪.同时建议我国未来亟须加强的4个研究方向:(1)深时冰室期向暖室期转变中的水循环;(2)深时水循环与生态系统演变;(3)深时水循环研究方法的发展;(4)深时水循环与长周期地球系统演变的数值模型.

水循环地质演变研究的重要性

水是维持地球生物多样性和生态系统健康的根本保障,更是地球表层系统机体运作的“血液”.当今全球变暖背景下,与水循环变化密切相关的干旱、森林大火和洪涝等极端灾害天气频发,以及海平面上升、海洋热浪与酸化等全球性生态危机问题日益突出,深刻影响了全球生态系统健康和人类社会的可持续发展.政府间气候变化专门委员会(Intergovernmental Panel on Climate Change,IPCC)第6次评估报告中,特别突出了系统性评估气候变化对全球水循环影响的重要性[1].毋容置疑,水循环是地球系统中的基本过程之一.

Cambrian integrative stratigraphy and timescale of China

The Cambrian Period is the first period of the Phanerozoic Eon and witnessed the explosive appearance of the metazoans, representing the beginning of the modern earth-life system characterized by animals in contrary to the Precambrian earth-life system dominated by microbial life. However, understanding Cambrian earth-life system evolution is hampered by regional and global stratigraphic correlations due to an incomplete chronostratigraphy and consequent absence of a highresolution timescale. Here we briefly review the historical narrative of the present international chronostratigraphic framework of the Cambrian System and summarize recent advances and problems of the undefined Cambrian stage GSSPs, in particular we challenge the global correlation of the GSSP for the Cambrian base, in addition to Cambrian chemostratigraphy and geochronology. Based on the recent advances of the international Cambrian chronostratigraphy, revisions to the Cambrian chronostratigraphy of China, which are largely based on the stratigraphic record of South China, are suggested, and the Xiaotanian Stage is newly proposed for the Cambrian Stage 2 of China. We further summarize the integrative stratigraphy of South China, North China and Tarim platforms respectively with an emphasis on the facies variations of the Precambrian-Cambrian boundary successions and problems for identification of the Cambrian base in the different facies and areas of China. Moreover, we discuss stratigraphic complications that are introduced by poorly fossiliferous dolomite successions in the upper Cambrian System which are widespread in South China, North China and Tarim platforms.

A Chengjiang-type fossil assemblage from the Hongjingshao Formation(Cambrian Stage 3) at Chenggong, Kunming, Yunnan

A new Chengjiang-type fossil assemblage is reported herein from the lower part of the Hongjingshao Formation at Xiazhuang village of Chenggong,Kunming,Yunnan.The fossil assemblage,named as Xiazhuang fossil assemblage,yields predominantly soft-bodied fossils,including arthropods,brachiopods,priapulids,lobopods and some problematic taxa,with arthropods being the most dominant group.Preservation and composition of the fossil assemblage are very similar to the typical Chengjiang biota,which is preserved in the middle Yu’anshan Formation in the large area of eastern Yunnan.The associated trilobites demonstrate that the soft-bodied fossil assemblage belongs to the late Qiongzhusian in age(Stage 3,Cambrian),suggesting that the Hongjingshao Formation is probably a diachronous lithostratigraphic unit ranging from the upper Qiongzhusian to the lower Canglangpuan stages in eastern Yunnan.The fossil assemblage from the Xiazhuang area fills up the missing link between the typical older Chengjiang biota and the younger Malong and Guanshan biotas,making eastern Yunnan a unique area in the world to reveal the early evolutionary history of animals and palaeocommunity dynamics during the‘‘Cambrian explosion’’.

A comparison of the biological,geological events and environmental backgrounds between the Neoproterozoic-Cambrian and Permian-Triassic transitions

The Neoproterozoic-Cambrian(N-C) and Permian-Triassic(P-T) transitions have been regarded the two most critical transitions in earth history because of the explosive biological radiation in the early Cambrian(the Cambrian Explosion) and the largest mass extinction at the end-Permian.Previous studies suggest that these two critical transitions showed certain comparability in major evolutionary events.In other words,a series of biological,geological,and geochemical events that had happened in the N-C transition occurred repeatedly during the P-T transition.Those events included continental re-configuration related to the deep mantle dynamics,global-scale glaciations,large C-,Sr-,and S-isotope perturbations indicating atmospheric and oceanic changes,abnormal precipitation of carbonates,and associated multiple biological radiations and mass extinctions.The coupling of those events in both N-C and P-T transitions suggests that deep mantle dynamics could be a primary mechanism driving dramatic changes of environment on the earth's surface,which in turn caused major biological re-organizations.A detailed comparison of those events during the two critical transitions indicates that despite their general comparability,significant differences do exist in magnitude,duration,and frequency.The supercontinent Rodinia began to rift before the Snowball Earth time.By contrast,the supercontinent Pangea entered the dispersal stage after the greatest glaciation from the Late Carboniferous to Cisuralian.Quantitative data and qualitative analyses of different fossil groups show a more profound mass extinction during the N-C transition than at the end-Permian in terms of ecosystem disruption.This is indicated by the disappearance of the whole Ediacaran biota at the N-C boundary.The subsequent appearances of many new complex animals at phylum level in the early Cambrian mark the establishment of a brand new ecosystem.However,the end-Permian mass extinction is manifested mainly by the extinction of many different taxa at class and order levels.Although it caused the extinction of 95% of marine species and 75% of terrestrial species as well as complete cessation of coal and reef deposits after the mass extinction,this high-level biological re-organization still occurred within an established ecosystem,however drastic it may seem.Survived or Lazarus taxa re-occupied the existing ecospace in a relatively short duration after the end-Permian mass extinction.C-isotope excursions display large perturbations during both transitions,yet also in different magnitudes and frequencies,which suggest different atmospheric and oceanic conditions.The recurrent geological and geochemical events as well as the coupled major biological turnovers during the two transitions provide new clues to understanding the interplays among the earth-life system.Thus,it is essential to carry out multidisciplinary studies from the deep internal system to the surface of the Earth as a whole in order to unravel the interactions of different spheres of the earth.

Atmospheric and Oceanic Oxygenation and Evolution of Early Life on Earth: New Contributions from China

The buildup of oxygen in the Earth＇s atmosphere and oceans has fundamentally reshaped the dynamics of nearly all major biogeochemical cycles and ultimately paved the way for the diversification of complex life on Earth. Over the past decades there have been sustained efforts to develop a more comprehensive understanding of ocean-atmosphere redox evolution and its relationship to the evolution of early life （Fig. 1）. It is generally accepted that the development of oxygenic photosynthesis at ~2.7 Ga may have been responsible for the Great Oxidation Event （GOE） at the beginning of the Proterozoic Eon, whereas a second big O2 rise at the end of the Proterozoic Eon （the so-called Neoproterozoic Oxidation Event or NOE） was responsible for the diversification of metazoans （Lyons et al., 2014）.

Biodiversity and taphonomy of the early Cambrian Guanshan biota,eastern Yunnan

趋势生物多样性和早寒武纪的 Guanshan 生物区系的 taphonomy。

A~60-Ma-long,high-resolution record of Ediacaran paleotemperature

The Ediacaran Period(~635–539 Ma)was a critical time in Earth history due to large increases in atmospheric and oceanic oxygen levels and rapid evolution of early animals[1].It was also an interval of major climatic and geochemical perturbations,such as the~580-Ma Gaskiers Glaciation[2](Fig.S1 online)and the late Ediacaran Shuram Excursion(SE;also known as DOUNCE or EN3 in South China,see Fig.S2 online),which was the largest negative carbonate carbon isotope(δ13Ccarb)excursion in Earth history[3,4].In contrast to established redox,biological,and C-cycling records for the Ediacaran,however,no secular,high-resolution paleotemperature record with climatic significance has been reported to date,impeding our understanding of the relationships among major environmental,biological,geochemical,and climatic processes and milestones.