四川盆地宣汉渡口和重庆北碚下三叠统海相碳酸盐碳同位素组成与演化

早三叠世海水的碳同位素组成与演化是二叠纪-三叠纪生物群体灭绝事件之后全球生态萧条与重建时期地球碳循环的重要记录,为地学界长期高度关注。文中测试了四川盆地宣汉渡口和重庆北碚下三叠统及相邻地层258个海相碳酸盐样品的碳、氧同位素组成,以便探讨早三叠世海水的碳同位素组成与演化。这些样品对海水碳同位素组成具有不同的保存性,飞仙关组及嘉陵江组第一、三段保存较好,而嘉陵江组第二、四段保存较差。基于氧同位素可以更为敏感地反映海相碳酸盐成岩蚀变性的原理,在碳、氧同位素相关性分析的基础上,以δ¹⁸O<-7.5‰为剔除标准,筛选出近200个有效数据建立了碳同位素演化曲线,该曲线与前人在贵州建立的同期曲线具有很好的可对比性。曲线显示出海水碳同位素组成的巨大波动,变化幅度达8.55‰,包括2个完整的上升-下降旋回,第1个旋回由飞仙关组和嘉陵江组第一段组成,第2个旋回由嘉陵江组第二段、第三段和部分第四段组成,同时还包括若干短周期的次级旋回。利用曲线形态与前人建立的同期曲线进行了岩石地层与年代地层单位的对比,飞仙关组可大致与Induan阶对应,嘉一段可大致与Smithian亚阶对应,嘉二段、嘉三段和嘉四段下部可大致Spathian亚阶对应;绿豆岩作为下-中三叠统界线其位置可能偏高,下-中三叠统界线应该位于绿豆岩之下的嘉四段内部。早三叠世海水碳同位素组成高频率大幅度的波动指示了生物大灭绝后环境的不稳定性,其中菌藻类等微生物灾后过度繁盛,可能导致了有机碳在短时间内的快速埋藏和海水碳同位素的正漂移;而碳同位素大规模的负漂移可能与甲烷水合物释放带来的轻碳有关。研究认为,白云岩所在的地层段往往具有更高的δ¹³C值,这可能说明微生物活动、白云岩形成和海水δ¹³C值升高之间的有机联系。下三叠统的白云岩、尤其是嘉二段和嘉四段的白云岩可能是微生物成因的,嘉陵江组有机碳的生产和埋藏可能主要是与白云岩形成有关的微生物的贡献,具最高δ¹³C值的嘉二段的烃类在一定程度上可能具有自生自储的特点。     

早三叠世下扬子古海洋地球化学环境的修复过程

巢湖平顶山北坡剖面下三叠统岩石化学成分分析表明, SiO₂、Al₂O₃、Fe₂O₃、FeO、MgO、Na₂O、K₂O、TiO₂、P₂O₅及微量元素Ba、V、Be、Nb、Zn、Cu、Ni、Co、Pb主要富集在下三叠统格里斯巴赫(Griesbachian)、迪纳(Dienerian)及斯密斯(Smithian)亚阶中, 形成了8次显著的正异常, 异常的强度、规模由下向上呈下降趋势; 微量元素Sr和常量元素CaO主要富集在下三叠统上部斯帕斯(Spathian)亚阶中, 其含量由下向上呈逐渐增加趋势.前者含量与碳酸盐岩的碳同位素组成(δ13C)呈负相关关系, 后者含量与碳酸盐岩的碳同位素组成(δ13C)呈正相关关系.海相碳酸盐岩碳同位素组成(δ13C)指示初始生产力大小, 同时亦是海洋生态环境改善的指示标志; 负相关表明环境恶化、生物萧条, 正相关表明环境适宜、生物繁盛.据常量元素和微量元素分布异常特点在下三叠统地层中识别出8次地质事件, 其规模及影响强度由早到晚逐渐变小及减弱; 晚二叠世末期及早三叠世初期的火山喷发将各种有害元素大量输向海洋, 导致海水中粘土矿物、微量元素含量异常增高, 海洋生态环境恶化.随着时间推移, 火山活动逐渐平息, 海洋中各种有害组分逐渐排除, 海水得到净化, 生态环境渐渐恢复.      

南盘江盆地首次发现早三叠世海生爬行动物化石

首次在南盘江盆地望谟地区下三叠统罗楼组灰岩中发现了海生爬行动物化石,爬行动物化石层位相伴产出大量菊石、腕足、双壳、牙形石等,其时代属早三叠世奥伦尼克期的Spathian亚期。该发现对于研究早三叠世海洋生态复苏、海生爬行动物类群起源、早期演化具有十分重要的科学意义。     

Controls on carbonate platform architecture and reef recovery across the Palaeozoic to Mesozoic transition: A high-resolution analysis of the Great Bank of Guizhou

Carbonate platforms spanning intervals of global change provide an opportunity to identify causal links between the evolution of marine environment and depositional architecture. This study investigates the controls on platform geometry across the Palaeozoic to Mesozoic transition and yields new stratigraphic and palaeoenvironmental constraints on the Great Bank of Guizhou, a latest Permian to earliest Late Triassic isolated carbonate platform in the Nanpanjiang Basin of south China. Reconstruction of platform architecture was achieved by integrating field mapping, petrography, biostratigraphy, satellite imagery analysis and δ¹³C chemostratigraphy. In contrast to previous interpretations, this study indicates that: (i) the Great Bank of Guizhou transitioned during Early Triassic time from a low-relief bank to a platform with high relief above the basin floor (up to 600 m) and steep slope angles (preserved up to 50°); and (ii) the oldest-known platform-margin reef of the Mesozoic Era grew along steep, prograding clinoforms in an outer-margin to lower-slope environment. Increasing platform relief during Early Triassic time was caused by limited sediment delivery to the basin margin and a high rate of accommodation creation driven by Indosinian convergence. The steep upper Olenekian (upper Lower Triassic) slope is dominated by well-cemented grainstone, suggesting that high carbonate saturation states led to syndepositional or rapid post-depositional sediment stabilization. Latest Spathian reef initiation coincided with global cooling following Early Triassic global warmth. The first Triassic framework-building metazoans on the Great Bank of Guizhou were small calcareous sponges restricted to deeper water settings, but early Mesozoic reef builders were volumetrically dominated by Tubiphytes, a fossil genus of uncertain taxonomic affinity. In aggregate, the stratigraphic architecture of the Great Bank of Guizhou records sedimentary response to long-term environmental and biological recovery from the end-Permian mass extinction, highlighting the close connections among marine chemistry, marine ecosystems and carbonate depositional systems.     

三叠纪年代地层与生物复苏

二叠纪末大灭绝之后，三叠纪初残存期和复苏期生态系研究成为当今热点。这也是2005年5月在安徽巢湖召开的“三叠纪年代地层与生物复苏国际学术会议”上的主导论题。逐一介绍了会议学术报告的主题内容，以期提炼相关领域的学术关键和学科发展趋向。学术主题之一是早三叠世年代地层格架，尤其是印度阶―奥伦尼克阶界线层型；第二是二叠纪―三叠纪之交灭绝和环境事件的表现形式和过程；第三是二叠纪―三叠纪之交及早三叠世微生物岩及其代表的特殊生态系；第四是灭绝事件后三叠纪初一些关键生物类别的演变历程；第五是中生代初生态系复苏过程和型式；第六是早三叠世生物迟滞复苏的原因。     

Late Permian and Early Triassic evolution of the Northern Indian margin: carbon isotope and sequence stratigraphy

Abstract

The Northern part of Great-India underwent an early rifting phase in the late Paleozoic, just at the end of the large scale Gondwanian glaciation. The beginning of the rifting processes is marked by large hiatus and discontinuities (para- conformities) between the early or middle Paleozoic sedimentary succession and the discontinuous middle-late Permian Traps and transgressive sediments. The Northern Indian passive margin consists of the present High and Lower Himalaya and a small part of the Indian craton and their sedimentary cover. The Permian rift shoulder is located in the Higher Himalaya, with part being in the underthrusted Lower Himalaya. The rim basin (landward of the shoulder) is well developed in the Pottawar- Salt Range area. From the rifting to the beginning of the drifting stages (early late Permian to late early Triassic time), the sedimentary evolution is characterised by three transgressive- regressive (T-R) second order cycles, two in the late Permian and one in the early Triassic. The break-up of the rift occurred during the second cycle (late Dzhulfian).

In the Salt Range area, these three T-R cycles have been subdivided in eight third order sequences, five sequences for the upper Permian and three for the lower Triassic.

At the end of Permian, hiatuses, gaps and local erosion of part of the margin are direct consequences of a first order relative sea-level fall; this is also the time of the largest extinction event of the Phanerozoic that deeply affected the carbonate productivity and the stratal patterns. With the following worldwide sea-level rise, a rapid and large scale transgression occurred in the early Triassic, well dated and recorded on the whole margin. High rate thermal subsidence gave way to generalized pelagic deposits about 2 My after the transgression.

Profiles of whole rock inorganic carbon and oxygen isotopes from Guryul Ravine and Palgham sections in Kashmir, Nammal Gorge and Landu sections in Trans Indus Ranges (Pakistan), Thini Chu section in Kali Gandaki Valley, Central Nepal are presented in connection with the sequence stratigraphic analysis. The upper Permian record of high positive δ¹³C values are closely correlated with the second order T-R cycles and the third order sequences. The results presented in this study confirm the drastic drop of δ¹³C from the high positive values that characterised the upper Permian to lower values in the lower Triassic time. Stratigraphic correlation problems in the lower Triassic using carbon isotope geochemistry are briefly discussed. A positive δ¹³C excursion of 4–5% near the Smithian - Spathian substages boundary is observed for the first time. The δ¹⁸O values of samples from all the sections display major variations suggesting that the oxygen isotope record has been significantly affected by meteoric diagenesis, deep burial diagenesis or/and monsoon signature.     

Lower Triassic δC isotope curve from shallow-marine carbonates in Japan, Panthalassa realm: Confirmation of the Tethys δC curve

δ¹³C data from Tethyan sections provide evidence of profound changes in the carbon cycle during the Lower Triassic. Sections from the Panthalassa realm were investigated to establish whether these variations are also present there. In the Jurassic accretionary wedges in Japan, exotic blocks having a Panthalassan affinity, have been incorporated. The majority of the blocks are pelagic cherts but rare shallow-water carbonates are also present. We present a δ¹³C study on the Lower Triassic of a shallow-water carbonate succession deposited on a mid-oceanic seamount and accreted to the Chichibu Belt, Japan. Two sections have been measured at Kamura, central Kyushu Island. The carbon isotope curve shows depleted values across the Permian–Triassic boundary (PTB), subsequently followed by an increase to heavier values into the Dienerian, culminating in a maximum of almost +4‰ V-PDB, before a steep drop at a stratigraphic gap. Low values are recorded in the Smithian, but rise to enriched δ¹³C values > +3.5‰ near the Smithian–Spathian boundary. The observed trend of the stable carbon isotope curve from Japanese sediments mirrors the curves derived from sections in the Tethys (e.g. Italy, Iran, Turkey, Oman and the South China Nanpanjing Basin). Our results support the interpretation of this curve as representing a global trend across the PTB and in the Lower Triassic, although some distinct features are absent around the Dienerian/Smithian boundary. Profound variations of the carbon isotope curve in the Lower Triassic are presented for the first time from a marine section outside of the Tethys. They indicate severe, global changes in the Lower Triassic carbon cycle, and the causative processes must have significantly contributed to the delayed biotic recovery after the PTB. Large amounts of carbon were shifted between carbon reservoirs, most probably between shallow- and deep-ocean waters, and/or ocean and sediment. Anoxia followed by overturn of the ocean water masses may have been the mechanism which quickly altered ecological conditions in the ocean leading to variable availability of nutrients and oxygen, and changes in isotope composition of the available carbon in the surface waters that was incorporated in the precipitated carbonate.     

豫西宜阳地区晚二叠世晚期—早三叠世沉积记录及其对古气候变化的响应

晚二叠世—早三叠世宜阳地区位于东特提斯低纬度地区的华北板块南缘，发育一套连续且沉积特征显著的陆相碎屑 岩相沉积，是研究陆相晚二叠世—早三叠世古环境与古气候变化的理想地层。本文在前人研究与野外实测的基础上，采用 岩石学、沉积学、古生物学方法综合分析研究区的沉积记录，识别出宜阳地区在该时期由陆源近海的滨湖沉积环境向河流 沉积环境过渡的古环境，重建了晚二叠世晚期—早三叠世宜阳地区的古地理面貌。沉积特征显示，此期整体气候条件为炎 热—半干旱，并且在长兴期末期与奥伦尼克期早期出现了极端干旱气候，可能是受到当时全球性巨型季风环流的影响。这 一时期的古气候与古环境的变化可能对二叠纪末陆地大灭绝事件起到了推动作用，并抑制了早三叠世生物复苏的进展。     

豫西宜阳地区晚二叠世晚期—早三叠世沉积记录及其对古气候变化的响应

晚二叠世-早三叠世宜阳地区位于东特提斯低纬度地区的华北板块南缘,发育一套连续且沉积特征显著的陆相碎屑 岩相沉积,是研究陆相晚二叠世-早三叠世古环境与古气候变化的理想地层。本文在前人研究与野外实测的基础上,采用 岩石学、沉积学、古生物学方法综合分析研究区的沉积记录,识别出宜阳地区在该时期由陆源近海的滨湖沉积环境向河流 沉积环境过渡的古环境,重建了晚二叠世晚期-早三叠世宜阳地区的古地理面貌。沉积特征显示,此期整体气候条件为炎 热-半干旱,并且在长兴期末期与奥伦尼克期早期出现了极端干旱气候,可能是受到当时全球性巨型季风环流的影响。这 一时期的古气候与古环境的变化可能对二叠纪末陆地大灭绝事件起到了推动作用,并抑制了早三叠世生物复苏的进展。     

Oceanic events and biotic effects of the Cenomanian-Turonian anoxic event, Tarfaya Basin, Morocco

Profound biotic changes accompanied the late Cenomanian δ¹³C excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of Morocco. Planktic foraminifera experienced a severe turnover, though no mass extinction, beginning with the rapid δ¹³C excursion and accelerating with the influx of oxic bottom waters during the first peak and trough of the excursion. Species extinctions equaled the number of evolving species, though only the disaster opportunists Guembelitria and Hedbergella thrived along with a low oxygen tolerant benthic assemblage. The succeeding δ¹³C plateau and organic-rich black shale deposition marks the anoxic event and maximum biotic stress accompanied by a prolonged drop in diversity to just two species, the dominant (80–90%) low oxygen tolerant Heterohelix moremani and surface dweller Hedbergella planispira. After the anoxic event other species returned, but remained rare and sporadically present well into the lower Turonian, whereas Heterohelix moremani remained the single dominant species. The OAE2 biotic turnover suggests that the stress to calcareous plankton was related to changes in the watermass stratification, intensity of upwelling, nutrient flux and oxic levels in the water column driven by changes in climate and oceanic circulation. Results presented here demonstrate a 4-stage pattern of biotic response to the onset, duration, and recovery of OAE2 that is observed widely across the Tethys and its bordering epicontinental seas.     

The δ13C excursions spanning the Cambrian explosion to the Canglangpuian mass extinction in the Three Gorges area,South China

A remarkable increase of the animal genera and a subsequent mass extinction in the late Early Cambrian are well known as the “Cambrian explosion” and the “Botomian–Toyonian crisis.” A composite global curve of the carbon isotope ratios for inorganic carbon (δ¹³C_carb) shows multiple fluctuations during the evolution events, and it indicates significant changes of the oceanic carbon cycle at that time. This study reveals a new continuous isotopic chemostratigraphy for inorganic carbon (δ¹³C_carb) from the bottom of the Shipai to the base of the Shilongdong formations in Three Gorges area, South China. This section covers the Canglangpuian to the Longwangmiaoian stages in the Lower Cambrian. The δ¹³C_carb variation exhibits three negative excursions: a remarkably negative excursion down to ca. − 12‰ in the middle Canglangpuian stage, a negative excursion to ca. − 1.0‰ in the upper Canglangpuian stage, and a negative excursion to ca. − 1.0‰ in the Longwangmiaoian stage, respectively. The largest negative δ¹³C_carb excursion and a positive excursion before the excursion are definitely consistent with the δ¹³C_carb negative shift (AECE) during the mass extinction and the δ¹³C_carb positive values (MICE) during the increase of animal genera, respectively. However, the minimum values of the negative shifts among South China, Siberia, and Canada sections are different from each other. The positive δ¹³C_carb excursion at the bottom of the Canglangpuian stage indicates that primary productivities and organic carbon burial were enhanced. A sea level rise in the Qiongzhusian to bottom of the Canglangpuian stages in South China corresponds to the Sinsk transgression event in Siberia and Canada. A eutrophication due to higher continental weathering during the transgression after the long-term retrogression enhanced the high primary production and consequently promoted the significant increase of animal diversity.On the other hand, deposition of laminated black shales without bioturbation signatures and a decline of trilobite diversity are observed during the negative δ¹³C_carb excursion in the Canglangpuian stage, indicating that the shallow water environment became anoxic at that time. The negative δ¹³C_carb shift indicates an influx of abundant ¹²CO₂ due to oxidation of organic carbons in seawater. The difference of the minimum values among sections implies the local difference in size of the organic carbon reservoirs and extent of the degradation of the carbons. The largest δ¹³C anomaly in South China suggests the presence of the largest OCPs due to higher activity of primary production and high degree of oxidation of the OCPs because of higher activity of animals. The coincidence of the timing of the negative δ¹³C excursions in the Canglangpuian stage among the sections indicates a global event, and suggests that the onset was caused by increase of oxygen contents of seawater and atmosphere. Abundant oxygen yielded by the increased primary productivity in the Atdabanian and the Qiongzhusian stages caused onset of the oxidation of OCP, and possibly led to the shallow water anoxia and the mass extinction of benthic animals in the Botomian and the Canglangpuian stage.     

Microbial deposits in the aftermath of the end‐Permian mass extinction: A diverging case from the Mineral Mountains (Utah,USA)

The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian reefs and bioaccumulations that contain fenestral‐microbialites and various benthic and pelagic organisms. Ecological and environmental changes during the Early Triassic are commonly assumed to be associated with numerous perturbations (productivity changes, acidifica‐tion, redox changes, hypercapnia, eustatism and temperature changes) post‐dating the Permian–Triassic mass extinction. New data acquired in the Mineral Mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial structures. These data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the Smithian–early Spathian. The studied section records a large‐scale depositional sequence during the Dienerian(?)–Spathian interval. During the transgression, depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral–microbial limestones, shallow subtidal marine sponge–microbial reefs to deep subtidal mud‐dominated limestones. Storm‐induced deposits, microbialite–sponge reefs and shallow subtidal deposits indicate the regression. Three microbialite associations occur in ascending order: (i) a red beds microbialite association deposited in low‐energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure; (ii) a Smithian microbialite association formed in moderate to high‐energy, tidal conditions where microbialites include stromatolites and associated carbonate grains (oncoids, ooids and peloids); and (iii) a Spathian microbialite association developed in low‐energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes. Data indicate that the morphologies of the three microbialite associations are controlled primarily by accommodation, hydrodynamics, bathymetry and grain supply. This study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions. Due to the presence of numerous metazoans associated with microbialites throughout the Smithian increase in accommodation and Spathian decrease in accommodation, the commonly assumed anachronistic character of the Early Triassic microbialites and the traditional view of prolonged deleterious conditions during the Early Triassic time interval is questioned.     

广西柳桥深水相二叠系/三叠系界线剖面有机碳同位素地层学对比研究及事件响应

研究了广西柳桥地区东攀剖面有机碳同位素的组成,并和浙江煤山剖面进行了对比。结果表明东攀剖面在1δ3Corg变化趋势上,既具有全球PTB剖面普遍存在的共性,又具有其独特性。在东攀剖面一个显著的1δ3Corg负漂移出现在事件界线(EB)之上和二叠系/三叠系界线(PTB)之下,这与煤山剖面具有相似性。显著的1δ3Corg负漂移指示了P/T之交生物绝灭后海水表层水原始生产率的降低以及大气和海水中CO2含量的增加,并得到放射虫绝灭事件、火山事件和海退事件的响应。煤山剖面1δ3Corg负漂移从第27层就开始向13C富集的方向恢复,而东攀剖面1δ3Corg在下Induan阶仍持续亏损,表明东攀剖面早三叠世的生物复苏明显滞后于煤山剖面的。     

Global climate perturbations during the Permo-Triassic mass extinctions recorded by continental tetrapods from South Africa

Several studies of the marine sedimentary record have documented the evolution of global climate during the Permo-Triassic mass extinction. By contrast, the continental records have been less exploited due to the scarcity of continuous sections from the latest Permian into the Early Triassic. The South African Karoo Basin exposes one of the most continuous geological successions of this time interval, thus offering the possibility to reconstruct climate variations in southern Laurasia from the Middle Permian to Middle Triassic interval. Both air temperature and humidity variations were estimated using stable oxygen (δ¹⁸O_p) and carbon (δ¹³C_c) isotope compositions of vertebrate apatite. Significant fluctuations in both δ¹⁸O_p and δ¹³C_c values mimic those of marine records and suggest that stable isotope compositions recorded in vertebrate apatite reflect global climate evolution. In terms of air temperature, oxygen isotopes show an abrupt increase of about + 8 °C toward the end of the Wuchiapingian. This occurred during a slight cooling trend from the Capitanian to the Permo-Triassic boundary (PTB). At the end of the Permian, an intense and fast warming of + 16 °C occurred and kept increasing during the Olenekian. These thermal fluctuations may be related to the Emeishan (South China) and Siberian volcanic paroxysms that took place at the end of the Capitanian and at the end of the Permian, respectively. Vertebrate apatite δ¹³C_c partly reflects the important fluctuations of the atmospheric δ¹³C values, the differences with marine curves being likely due to the evolution of local humidity. Both the oxygen and carbon isotope compositions indicate that the PTB was followed by a warm and arid phase that lasted 6 Ma before temperatures decreased, during the Late Anisian, toward that of the end-Permian. Environmental fluctuations occurring around the PTB that affected both continental and marine realms with similar magnitude likely originated from volcanism and methane release.     

燕山地区1.6～1.0Ga时期碳酸盐岩碳、氧同位素组成、演化及其地质意义

依据实测的燕山地区(1.6～1.0Ga)高于庄组—景儿峪组114个碳、氧同位素数据,研究、讨论了中、新元古界碳酸盐岩碳、氧同位素组成、演化及其地质意义。研究表明,燕山中、新元古界由下至上的地层序列上,碳、氧同位素表现明显的旋回性演化特征,二者多显正相关关系;δ13C在-3‰～3‰区间低幅、高频振荡;δ18O则表现为-2‰～-8‰的高幅、高频波动;δ13C值的增大与沉积环境由潮间向潮下演变、海平面上升、海水变淡、生物量增多相关;降低的δ13C多代表潮间—潮上环境。高于庄组瘤状灰岩及洪水庄组页岩δ13C为低负值,代表最大海泛期沉积。氧同位素组成和变化指示研究区总体为咸化环境,杨庄组上部和雾迷山组下部古海水盐度最高,之后盐度逐渐降低,至雾迷山组上部又有所升高。研究区与天津蓟县和北京十三陵地区的中、新元古代碳酸盐岩碳、氧同位素组成与演化表现出明显的相似性,反映了它们共同受燕山裂陷槽发育的控制;同时,与北美Belt超群和俄罗斯乌拉尔里菲期碳酸盐岩碳、氧同位素组成、演变的高度协同性,又说明了中、新元古代碳酸盐岩中碳、氧同位素组成、演化响应于全球古海洋背景和地球化学条件。     

贵州罗甸二叠纪末生物大灭绝事件后沉积的微生物岩时代和沉积学特征

二叠纪末期发生的显生宙以来最大的生物绝灭事件,使海洋生态系统和陆地生态系统均受到重创之后,微生物岩广泛分布于全球正常浅海地区。研究认为,扬子地台在二叠纪末期存在一次海平面降低的事件,造成研究区二叠纪地层与早三叠世微生物岩之间存在沉积间断或剥蚀,并使三叠纪牙形石混入二叠纪末期的沉积物中。二叠-三叠系界线位于微生物岩层的底界;微生物岩形成于早三叠世最早期,相当于Hindeodus parvus带,是早三叠世最早期开始的海侵事件为其提供生长所需的可容纳空间。在Isarcicella staeschei带-I. isarcica带早期再次发生相对海平面降低事件,之后海平面开始快速上升。研究区早三叠世早期的微生物岩以凝块构造发育为特征,具有斑状、层状、枝状和网状凝块构造4种典型中型构造。结合前人的工作,认为微生物群落通过生物沉积和物理沉积作用形成球状体,球状体汇聚形成不同的中型凝块构造。研究扬子地台早三叠世凝块石的确切时代和结构、构造类型特征,为准确恢复生物大灭绝事件前后的环境变迁以及生物演化事件与环境变化的相互作用关系提供重要的证据。     

塔里木盆地库车河剖面有机碳同位素地层学及三叠系—侏罗系界线

三叠纪—侏罗纪之交发生了地史上五次最大规模之一的生物灭绝事件、中大西洋大火成岩省喷发、泛大陆进一步裂解导致的中大西洋开启以及大气CO₂浓度急剧升高等。然而该时期中国各板块主要发育陆相沉积,其三叠系—侏罗系界线（TJB）很难与定义于海相地层的全球层型剖面和点（GSSP）进行精细对比。应用基于C3植物的碳同位素地层学,进行了两次独立地、系统地以高等植物木质部为研究对象的采样和测试,获得了可以指示同期大气CO₂的δ13C演化和进行全球等时对比的碳同位素地层曲线。并在植物大化石和孢粉的生物地层约束基础上,首次完成了库车河剖面与海相三叠纪末期生物大灭绝事件（ETE）底界和TJB的精细对比;推测与全球其他剖面ETE等时的地层界线位于38层底部附近,与TJB的GSSP等时地层界线位于41层底部附近。海相与陆相的ETE和TJB层位附近均出现了δ13C负偏,指示全球性的碳同位素的波动,推论该时期发生了全球规模的、地表圈层的碳储库扰动。     

四川广安谢家槽剖面早三叠世地层中的时错相沉积及其古生态意义——一个传统地层剖面的重新解读

四川广安谢家槽剖面下三叠统夜郎组和嘉陵江组中含有扁平砾石灰岩、蠕虫状灰岩、叠层石、层纹状灰岩、薄层泥晶灰岩、条带状灰岩和水平分布的遗迹化石等类型丰富的时错相沉积,由下至上时错相沉积呈现出逐渐减弱的总趋势。早三叠世晚期,时错相沉积从正常海洋环境沉积中退出,只是出现在高压力环境的沉积物中。时错相沉积的这种时空分布和发育程度的变化,反映二叠纪末生物大灭绝事件后,早三叠世海洋生态系复苏的历程。     

Sedimentology,biostratigraphy and event stratigraphy of the Early Aptian Oceanic Anoxic Event (OAE1A) in the Apulia Carbonate Platform Margin – Ionian Basin System (Gargano Promontory,southern Italy)

The stratigraphic and biotic signatures of severe environmental changes across the late Early Aptian Oceanic Anoxic Event (OAE1a) in central Tethyan settings have been investigated in the almost undeformed Apulia Carbonate Platform Margin-Ionian Basin system (ACPM-IB) exposed in the Gargano Promontory (southeastern Italy). The nature of the observed Lower Aptian biofacies shifts within the investigated carbonate system are analyzed using an integrated biostratigraphic approach, based on ammonite-calibrated orbitolinids and caprinids coupled with the published δ¹³C and δ¹⁸O record of coeval pelagic sections of the Ionian basin (Coppitella, eastern Gargano, and Paliambela, northwestern Greece). Detailed field analysis of facies and tracing out of key biosedimentary and chemostratigraphic markers of the Lower Aptian have elucidated the evolution of the platform margin and allowed integrated correlations across the Gargano margin to basin transition.It is shown here that the global-scale environmental changes leading to the OAE1a event (i.e., fluctuations of surface-ocean temperature, available trophic resources and, above all, pCO₂) are matched consistently by significant shifts of the biotic associations inhabiting the ACPM. The onset of greenhouse, mesotrophic conditions in the surface ocean undergoing an increasing acidification by CO₂ excess favored the rapid spread of calcite shelled, filter feeding, eurytopic opportunist organisms (chondrodontids, ostreids, chaetetids sponges, along with minor bryozoans) as well as echinoids and orbitolinids (foramol productivity mode); this change is recorded by the deposition of a 4–6 m Crisis Interval (CI) that sharply overlies the “Urgonian”-type, rudist-rich platform margin complex (Montagna degli Angeli Limestones) formed from predominantly aragonite shelled, stenotopic organisms (mostly caprinid rudists, with minor corals and Dasycladales and Bryopsidales green algae) (chlorozoan productivity mode). The CI heralded the incipient drowning of the ACPM which occurred immediately after the deposition of a hothouse “out of balance” brachiopod (Orbirhynchia nadiae)-cyanobacteria association (microbial productivity mode). The biostratigraphically constrained CI and the related drowning of the ACPM have been physically correlated with specific chemostratigraphic segments of the δ¹³C_carb curve that is available for the facing, proximal Ionian Basin. The early (earliest ?) Late Bedoulian, greenhouse CI (early D. deshayesi – early P. cormyi zones) was deposited during the late C2 interval, whereas the early Late Bedoulian, hothouse “out-of-balance” guild and the ACPM drowning (early deshayesi zone) accompanied the subsequent negative excursion and culmination, respectively, at the very base of the Chemostratigraphic Selli Level (CSL) (latest C2 and C3 interval). These correlations permit regional to global interpretations of historical patterns and explanatory paleoeanographic and paleoecologic hypotheses; furthermore, they suggest that the Apulia shallow-water ecosystem reacted to the environmental disruptions linked with the OAE1a sooner than that of the facing open ocean. The onset of the drowning event was synchronous with the hothouse-induced bloom of the “out of balance” brachiopod-cyanobacteria association that occurred simultaneously with the pronounced negative excursion of the δ¹³C_carb curve. This suggests a cause-and-effect relationship with the sudden environmental perturbations linked with the injection into the atmosphere-hydrosphere system of ¹³C-depleted CO₂. The numerical age model of the major biotic and stratigraphic events at the Lower Aptian ACPM, along with their inferred genetic processes call for different timings and causal mechanisms associated with platform demise in northern and central Tethyan settings.     

二叠纪-三叠纪之交的古海洋水化学条件变化证据--以贵州织金剖面为例

基于贵州织金剖面的二叠系-三叠系界线附近的岩石薄片鉴定及古生物化石识别,划分出了2种碳酸盐岩沉积相、2种亚相和5种微相;有机质碳同位素组成测试结果表明晚二叠世时期有机质的δ13C_org值（-27.7‰）向早三叠世时期的δ13C_org值（-28.3‰）逐渐偏负,反映了有机质类型由高等植物向低等微生物变化的过程;全岩的δ13C_rock值由晚二叠世（-24.2‰）向早三叠世（-20.9‰）变大,反映了二叠纪末期生物大灭绝事件造成了海洋生物的消失,进而引起12C在海洋中强烈富集;Fe-_HR/Fe-_T、Fe_py/Fe-_HR以及微量元素V/（V+Ni）与V/（V+Cr）比值大小,反映了二叠纪末期该区域的海水为氧化环境或弱还原环境,而三叠纪初期海水处于还原与铁化环境,在盆地内部没有发生硫化作用;V/Ni的值从晚二叠世的0.97~1.97向早三叠世的1.67~7.33明显变大,表明水体逐渐加深的过程,该结论与沉积微相变化相符;在生物演化上,从二叠纪末期的有孔虫-藻屑-三叶虫生物组合演变到三叠纪初期小型介壳-微生物组合,反映了该时期中国南方统一的两幕式生物灭绝与演化样式。