古新世—始新世最热事件对地球表层循环的影响及其触发机制

古新世—始新世最热事件（PETM, Paleocene Eocene Thermal Maximum）是发生在古新世—始新世交界时的一次全球性的气候突变事件。它造成了大洋环流模式的突然倒转和海水盐度、大气湿度的迅速上升。海洋表层生态系统和陆地生态系统生产力迅速上升,许多属种的植物、动物、微生物生活范围向高纬区扩大;大洋底栖微生物发生集群灭绝。现代哺乳动物的主要属种（灵长类、奇蹄类及偶蹄类）产生,哺乳动物演化进程发生重大改变。地球表层碳循环系统发生不同程度的碳同位素负偏移,全球碳循环系统发生大规模搅动。对于PETM的触发机制,主流的观点认为是海底天然气水合物突然释放造成巨量甲烷迅速进入表层系统引发的碳循环系统内部反馈。而对于甲烷释放的原因,又存在着减压释放和热释放两种解释;此外还有科学家用岩浆作用和地外星体撞击来解释PETM的发生。     

云南兰坪盆地古近系云龙组上段沉积环境研究——来自碳、氧同位素的证据

云南兰坪盆地古近系云龙组地层记录了盆地由淡水湖泊→盐湖、干盐湖→淡水湖泊沉积的一个完整的Ⅰ级韵律。在云龙组上段沉积了一套灰岩地层,上覆于云龙组上段含盐层之上,对此套灰岩共取样25个,测试结果显示,δ~(13)C和δ18O均为负值,δ~(13)C介于–13.13‰~–6.67‰之间,均值为–11.57‰,δ18O介于–15.55‰~–13.90‰之间,均值为–15.02‰,δ~(13)C和δ~(18)O具有较小相关性(0.57),表明当时湖泊封闭性较差。根据Z值和δ~(13)C表明,当时为陆相淡水或微咸水湖泊沉积,含盐度较低。根据经验公式计算所得温度为35.5~44.3℃,平均为41.4℃。相对于现代湖水温度,当时水体温度较高,可能与PETM事件有关。因此,整个云龙组沉积时期气候炎热干旱,造成蒸发岩沉积中断的主要原因为湖泊的封闭性降低。     

陆相坳陷湖盆沉积对深时古气候的响应信号:以准噶尔盆地西北缘安集海河组为例

"深时"古气候研究范围为前第四纪地质记录,目的在于为未来气候预测提供依据.准噶尔盆地西北缘安集海河组沉积期,研究区处于早古近纪极热气候(PETM)时期,由于其温室气体排放与当前工业废气排放水平相当,对于全球变化以及地球系统科学研究具有重要意义,一直以来都是古近纪气候研究的热点.准噶尔盆地西北缘在早古近纪沉积期发育大范围...     

Carbon isotope and REE characteristics of the Paleocene–Eocene shallow marine Subathu formation from the NW Himalaya (India) and their paleo-environmental implications

Carbon isotope (δ¹³C) and rare earth element (REE) concentrations in representative samples of the shallow marine Subathu Formation, explored from the Neelkanth and Dogadda sections of Northwestern Himalaya (India) were determined to infer the palaeo-environmental condition during the late Paleocene and middle Eocene. δ¹³C values show variation of ～5.0‰ with maximum excursion (?27.34‰) in calcareous sandstone at the basal part and minimum (?22‰) in red shale towards the terminal end. Total REE concentration varies (due to lithology) from 27.23?ppm to 564.35?ppm with an average of 187.60?ppm. The chondrite and PAAS normalized patterns exhibit positive Ce anomaly (0.95–4.45), enriched LREE, and depleted HREE, medium Y/Ho ratio (～30–45) along with positive correlation between Y/Dy and Y/Ho ratio. In addition, calcite veins present in some shale samples indicate redox sensitive trace elements. The overall REE abundance and distribution suggests highly oxygenated environment under the shallow marine regressive phase of deposition. The depositional setting, biostratigraphical constrained age along with δ¹³C values and lower TOC suggested an intense warm period, that might be coeval with the Paleocene-Eocene Thermal Maxima event (PETM).     

Calcareous nannofossil changes linked to climate deterioration during the Paleocene-Eocene thermal maximum in Tarim Basin,NW China

The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwestern Tarim Basin of China exposes successive Paleogene strata as a result of Tethys evolution and is considered an ideal region for PETM research.Based on calcareous nannoplankton biostratigraphy, we also used stable isotopes and XRD to analyse the Paleocene-Eocene transition in the Tarim Basin. At the Bashibulake Section, the PETM interval is characterized by(1) an abrupt negative shifts in σ13 C_(org), σ13 C_(carb) and σ18 O(-3%, -4.5% and -3%respectively);(2) an obvious negative correlation between the K-mode(Discoaster, Fasciculithus, Ericsonia, Sphenolithus and Rhomboaster) and r-mode(Biscutum, Chiasmolithus, Toweius) nannofossil taxa coincident with a robust Rhomboaster-Discoaster assemblage; and(3) a significant increase in the percentage of detrital input along with an increase in gypsum content. In the upper part of the Qimugen Formation Micrantholithus and Braarudosphaera are commonly found right up to the top where most of the nannofloras suffer a sharp decrease. In the overlying Gaijitage Formation, calcareous nannofossils disappear completely. These events indicate that the southwestern Tarim Basin was a warm shallow continental shelf during the deposition of the Qimugen Formation. From the early Eocene, the environment changed conspicuously. Evaporation increased and sea level fell, which led to an acid climate.This climate mode continued within the youngest unit studied, the Gaijitage Formation, characterized by the deposition of thick evaporates. Consequently, most of the marine plankton, i.e. calcareous nannoplankton, became disappear, because of the significant climate shift.     

古近纪重大气候事件及其生物响应

古近纪气候演化是由“温室气候”向“冰室气候”转变的过程,大致可划分为3个阶段:古新世-始新世早期的升温期,始新世中期-始新世末期的稳定降温期及渐新世-中新世早期的冰室气候期.在此期间发生了3次显著的气候事件,分别为PETM极热事件、Oi-1骤冷事件和Mi-1降温事件.这3次大的气候事件引起了生物圈的巨大波动:PETM期间发生了全球底栖大有孔虫灭绝事件及浮游有孔虫的辐射演化,并且是哺乳动物演化的关键时期;Oi-1期间全球植物群落由热带型密集雨林向寒冷干燥的森林草原过渡,在欧亚大陆出现了哺乳动物种群大规模改变的Grande Coupure和Mongolian Remodelling事件,也发生热水型浮游及底栖有孔虫的灭绝事件;Mi-1前后,浮游有孔虫部分属种绝灭,钙质超微化石也出现暖水种数量的急剧减少,现代植物群落在这一时期开始形成.古近纪气候的大幅波动和转折由诸多因素控制,主流观点认为PETM事件与天然气水合物的大量释放有关,但其喷发机制尚不明确;降温事件则与区域性构造隆升、洋流榕局变化等因素有关.     

Calcareous Nannofossils and Molecular Fossils in Cobalt-rich Crusts and their Response to the P/E Global Event

A biostratigraphic study on calcareous nannofossils from the CM3D06 Co-rich ferromanganese crust from the Magellan seamounts in the northwestern Pacific enabled estimation of depositional age.The bio-imprinting of calcareous nannofossils and other fossil species suggests six age ranges for the nannofossils: late Cretaceous,late Paleocene,(early,middle,late) Eocene,middle Miocene,late Pliocene,and Pleistocene.Gas chromatography(GC) and gas chromatography-mass spectrometry(GC-MS) were used to test the Co-rich crusts,and a variety of molecular fossils were detected,such as chloroform bituminous "A",n-alkane,isoprenoid and sterol.Peak carbon and molecular indices(such as ΣC23 /ΣC24 +,CPI,Pr/Ph,Pr/nC17,Ph/nC18 and δ13C) indicate that the parent organic matter is dominated by marine phytoplankton and thallogen whereas there is little input of terrestrial organic matter.Researches on calcareous nannofossils,molecular fossils and molecular organic geochemistry data reveal that the Paleocene/Eocene(P/E) global event is recorded in the cobaltrich crusts from the northwestern Pacific Ocean.A succession of biomes can be observed near the 85 mm boundary(about 55 Ma),i.e.,the disappearance of the late Cretaceous Watznaueria barnesae and Zigodicus spiralis,and Broisonia parka microbiotas above the P/E boundary,and the bloom of Coccolithus formosus,Discoaster multiradiatus,Discoaster mohleri and Discoaster sp.below the boundary.Typical parameters of molecular fossils,such as saturated hydrocarbon components and carbon-number maxima,Pr/Ph,Pr/C17,Ph/C18,distribution types of sterols,Ts/Tm ratios and bacterial hopane,also exhibit dramatic changes near the P/E boundary.These integrated results illustrate that the biome succession of calcareous nannofossils,relative content of molecular fossils and molecular indices in the cobalt-rich crusts near the 85 mm boundary faithfully record the P/E global event.     

白垩纪至早第三纪的极端气候事件

地球科学界正在将预测未来气候变化的研究重点放到地球过去突然发生的气候变暖事件。白垩纪至早第三纪发生的极端气候事件被认为是最接近于现今的地球系统,对其研究有利于理解现今地球系统过程在碳循环快速搅动时的响应。这些气候事件主要包括：古新世-始新世最热事件（PETM,～5 5 MaBP）、早阿普第晚期和森诺曼-土仑界线的大洋缺氧事件（OAE1a,～120 Ma;OAE2,～93．5 MaBP）。PETM事件是中白垩世以来一次突然变暖事件,在10 ka年以内深海温度增加～5 ℃,表层海水温度增加 4～8 ℃,而δ¹³C至少发生 3．0‰的负偏移。目前普遍认为PETM事件是由于海洋气水化合物（CH₄）的巨量释放造成的。大洋缺氧事件（OAEs）记录了海洋环境下有机质的大量埋藏,代表了碳循环和海洋生物系统的重大搅动事件。综合大洋钻探计划（IODP）将极端气候确定为优先研究领域,将采取特定的钻探策略,在世界大洋范围内获取最低限度蚀变的新生代至白垩纪沉积物,研究精度要求达到米兰柯维奇的天文调谐时间尺度,其最终目标是定量描述过去全球气候变化,并为未来气候变化预测提供依据。     

江陵凹陷早始新世石盐流体包裹体均一温度研究及其古气候意义

近年来江陵凹陷因深层富钾卤水及钾盐矿物的发现受到各界的关注。而钾盐的形成与古环境有着密切的联系。本文通过石盐包裹体均一温度的研究,对江陵凹陷早始新世古气候进行了初步探讨,力求为确定江陵凹陷成钾有利期提供一定依据。通过对石盐样品中的单一液相流体包裹体采用冷冻法进行均一温度测定,测温结果显示其均一温度范围是14.9~32.3℃,均值23.7℃,且各样品间温度数据波动不大。由此说明,江陵凹陷早始新世新沟嘴组中段的古气温较高,且比较稳定,属于温暖干旱的气候。此外,还通过分析比对前人研究成果,发现该区域古气温自沙市组至新沟嘴组下段有明显降低的趋势,这可能与古新世—始新世极热事件(PETM)之后的降温期有关。     

Warming and environmental changes in the eastern North Sea Basin during the Palaeocene–Eocene Thermal Maximum as revealed by biomarker lipids

Analysis of sediments deposited at different latitudes around the world during the Palaeocene–Eocene Thermal Maximum (PETM; ∼56 Ma) have revealed a globally profound warming phase, regionally varying from 5–8 °C. Such records from Europe have not yet been obtained. We studied the variations in sea surface and continental mean annual air temperatures (SST and MAT, respectively) and the distribution patterns and stable carbon isotopes of higher plant derived n-alkanes in two proximal PETM sections (Fur and Store Bælt, Denmark) from the epicontinental North Sea Basin. A negative carbon isotope excursion (CIE) of 4–7‰ was recorded in land plant derived n-alkanes, similar to what has been observed for other PETM sections. However, differences observed between the two proximal sites suggest that local factors, such as regional vegetation and precipitation patterns, also influenced the CIE. The presence of S-bound isorenieratene derivatives at the onset of the PETM and increased organic carbon contents points to a rapid shift in depositional environment; from well oxygenated to anoxic and sulfidic. These euxinic conditions are comparable with those during the PETM in the Arctic Ocean. SSTs inferred from TEX₈₆ show relatively low temperatures followed by an increase of ∼7 °C across the PETM. At the Fur section, a remarkably similar temperature record was obtained for MAT using the MBT′/CBT proxy. However, the MAT record of the Store Bælt section did not reveal this warming.