第四纪湖相介形类壳体化石在古环境中的应用——种属组合研究进展与问题

综述了第四纪湖相介形虫化石种属组合在环境重建研究中取得的进展和存在问题,讨论了今后发展的趋势.湖泊沉积物介形类种属组合正逐渐成为古环境重建研究的常规微体生物学指标,过去几十年来国际国内研究取得重要进展,种属组合与环境参数的定量化研究成为主要趋势.化石壳体样品处理、埋藏条件评价等是提取种属组合指标的重要影响因素,需要规范化.现生种的个体与群落生态信息定量观测、调查研究是利用现代类比法(MAT)定量重建古环境的基础,也是我国介形类化石组合与环境重建中应该加强的方面.     

Quaternary fossil coral communities in uplifted strata along the Balochistan coast of Pakistan: understanding modern coral decline in the Arabian Sea

Uplifted reefs due to being important palaeoclimate archives and a rich source of information on past physical and geochemical changes globally have become the centre of marine research. The uplifted fossil Quaternary coral communities of Jiwani and Gwadar are perfect places to study the palaeoclimatic and geological changes that have shaped the Balochistan coast. Studies on the palaeodiversity of corals along the Makran coast of Pakistan are lacking. In the present study, the samples collected using line intercept method from four uplifted sites (Balochistan coast: one at Gwadar and three at Jiwani) were analysed. The relative distribution and diversity of scleractinian fossil corals was determined, and the factors responsible for coral decline along Pakistan coast were compared with modern coral distribution and diversity. A total of 48 fossil coral species were recorded in nine families and 22 genera. High coral diversity was recorded in the uplifted landward sites of Jiwani and Gwadar headland. Terraces close to the shore at Jiwani had lower diversity. The corals seem to be Quaternary: most likely Pleistocene to Holocene. The modern fauna lacks many species recorded in the fossil community, thus suggesting a faunal turnover in diversity and redistribution of coral fauna which may be linked with past geological events and increasing anthropogenic pressure.     

Climate change in Lake Baikal: diatom evidence in an area of continuous sedimentation

The presence of inhomogeneous sedimentation is acknowledged as being an important problem in palaeolimnological studies. Sediment records can be disturbed by erosional and redepositional events, which redeposit microfossils within a basin and may then lead to misinterpretations of fossil diatom assemblages. This study uses a combination of sedimentological tools, magnetic susceptibility measurements and high-resolution diatom analysis to show that a sediment core, BAIK80, taken in 345 m water depth from a shoulder region in the North Basin of Lake Baikal, is free of disturbances. Our results confirm that the sediment record is consistent and continuous for the uppermost sediment. Consequently, the fossil diatom data can be used to establish a continuous record of past climate variability over approximately the past 1300 years. Distinct changes occur in downcore abundances of endemic taxa Aulacoseira baicalensis and Cyclotella minuta, and principal components analysis (PCA) indicates a gradual transformation of taxa over the past 1300 years. These changes are likely to be related to climate, although definite links still have to be established. Received: 15 December 1998 / Accepted: 13 September 1999     

山东中新世山旺组生物群的古生态

山东临朐产出的中新世山旺组化石群,保存精美、属种分异度高。50多年来,经发掘和研究,目前已从约30余米的硅藻页岩沉积中报导了真菌、硅藻、介形虫、孢粉、昆虫、鱼类、两栖动物、爬行类、鸟类、哺乳动物及遗迹化石等十几个门类的化石,共计400余属700多种。本文总结了化石与周围无机界的关系、化石的埋藏特征、形成原因以及相关古生态学问题――古气候、古温度、古纬度、古地形、山旺湖的水文性质、湖水的季节性变化与硅藻页岩的纹层、动植物群的营养结构以及山旺盆地的沉积历史。     

Abrupt climate change and early lake development – the Lateglacial diatom flora at Hässeldala Port,southeastern Sweden

The fossil diatom record from the Hässeldala Port palaeolake, southeastern Sweden, offers an excellent opportunity to investigate how past climatic shifts influenced catchment conditions and early lake development. The record, dating to between 13 900 and 11 200 cal. a BP, covers a climatically dynamic period, starting with deglaciation followed by oscillations between warmer and colder climate states. The stratigraphical changes in the fossil diatom assemblages show a trend of less open‐water taxa and a successively more complex periphytic community as the lake shallows and the aquatic habitat structure develops. A diatom‐based reconstruction of lake water pH indicates a natural acidification trend early in the record from 13 900 to 12 500 cal. a BP. From 12 500 cal. a BP, coincident with the start of climate cooling, to 11 300 cal. a BP this trend is disrupted and lake waters become more alkaline. A cooler and drier climate most likely resulted in reduced soil organic matter build‐up as well as more frozen ground that impeded hydrological flow and decreased the input of dissolved organic matter and organic acids into the lake system. This study demonstrates the importance of the hydrological system as a link between terrestrial and aquatic ecosystems during early lake ontogeny.     

For the deep biosphere,the present is not always the key to the past: what we can learn from the geological record

Microbial life below the Earth's surface (the deep biosphere) has probably varied significantly since the Archaean. Reconstructing changes in deep biosphere activity over geological timescales is necessary to understand its role in biogeochemical cycling. Even for the last few million years, such changes are often not captured by studying the distribution of present activity. However, several studies using samples from scientific drilling have revealed mineralogical, geochemical, isotopic and fossil organic molecule imprints in the sedimentary record that document rather different past deep biosphere conditions. Changing deep biosphere conditions can also be simulated using geochemical models. While some processes occurring in the past can be understood by comparing them with the present deep biosphere, others lack any modern analogue – they are defined as non‐actualistic. A non‐actualistic consideration of the deep biosphere is therefore essential for a better understanding of how Earth and life co‐evolved through time.     

硅藻分析与第四纪定量古地理和古气候研究

本文以硅藻分析为例,叙述了综合运用古生物数据和数理统计的手段进行定量恢复古地理环境和古气候的研究方法。内容包括建立现代生物-环境变量数据库和生物化石数据库的目的、要求、方法以及具体步骤,并通过一个海洋钻孔的实例对其成果解释作了详细介绍     

辽西义县下白垩统九佛堂组木化石的发现

首次发现产自辽西义县皮家沟下白垩统九佛堂组保存有解剖构造的木化石,利用木化石切片法对木化石解剖特征进行研究。当前木化石均为硅化保存,其中一块标本保存有髓、初生木质部、次生木质部等解剖构造。其髓部主要由薄壁细胞构成,初生木质部为内始式,次生木质部为Protophyllocladoxylon型。部分木化石标本表面密布大小不一的孔洞,推测为昆虫幼虫的觅食痕迹。此外,木化石产出层位还发现有大量丝碳化石,表明义县地区早白垩世九佛堂组沉积时期存在野火事件,而频发的火山喷发活动可能是野火事件的诱因。     

Life's a beach: lessons from the Earth's rarest sedimentary rocks

Ancient rockshore deposits are the rarest sedimentary rocks on Earth. Less than 200 examples span the planet's entire history, but they preserve important records of past environments, including sea-level changes and unusual fossil communities. The most celebrated example, dating from the earliest Jurassic, is found at Ogmore-by-Sea in South Wales. This article describes the history of environmental change at Ogmore, and why these rocks can help us to interpret the deposits of ancient rocky shores world-wide.     

Carbonate formation by anaerobic oxidation of methane: Evidence from lipid biomarker and fossil 16S rDNA

Carbonate chimneys and other carbonate structures occur widespread in the Gulf of Cadiz and probably reflect the presence of cold seeps and associated release of methane in the geological past, possibly in the Early Pleistocene, but it is unclear under what conditions and by which processes these carbonates were formed. We studied a fossil methane-related carbonate crust collected from the Kidd mud volcano in the gulf. Concentrations of microbial lipids, their stable carbon isotope composition, sequences of fossil 16S rRNA genes of anaerobic methanotrophic archaea in combination with mineralogical and carbon and oxygen isotopic composition of carbonate were obtained for seven different horizons of the crust. This combination of organic and inorganic geochemical techniques with molecular ecological methods gave a consistent view on processes resulting in the formation of the crust and indicated that it took place in two phases and in a downward direction. Archaeal lipid biomarkers and fossil 16S rRNA gene sequence data revealed the dominance of archaeal ANME-2 group and elevated methane partial pressures during the formation of the top part of the crust. The lower part of the carbonate was likely formed in an environment with reduced methane fluxes as revealed by the dominance of fossil remains of ANME-1 archaea. The combination of these methods can be used as an effective tool to reconstruct in unprecedented detail the palaeo-biogeochemical processes resulting in the formation of carbonate fabrics. This interdisciplinary strategy may also be applied for other fossil methane-derived carbonates, generating new concepts and knowledge about past methane-related carbonate systems.     

Taphonomy in palaeoecological interpretations

The taphonomic history of single fossils or of fossil assemblages provides evidence additional to that given by taxonomic identification. Too often taphonomy is viewed as destructive processes biasing evidence of past life or restricting taxonomic diversity in the reconstruction of palaeoecology, but in reality it sheds light on circumstances of life and preservation of fossil organisms. Because recorded modifications of fossils are due to biotic or abiotic agents that may not be evident in a studied sequence, taphonomic modifications should be seen as providing a more dynamic view of the past rather than as destructive processes.     

青藏高原全新世1月和7月气温序列重建

青藏高原自然环境受人类干扰相对较小,为利用古孢粉记录重建气候因子提供了可能,高原过去气候因子的重建对于预测未来气候变化趋势有重要意义.通过选取的29条高原化石孢粉记录,利用现代类比法和化石孢粉点与高原气温的函数关系,把化石孢粉点古气温转化为青藏高原古气温,重建了高原全新世1月和7月古气温序列.结果表明：对于1月和7月气温而言,全新世早期（11.5～8.5 ka BP）为气温波动上升期;全新世中期（8.5～4.6 ka BP）为全新世大暖期,气温整体高于现代;全新世晚期（4.6 ka BP～至今）又可分为两个阶段,一个是4.6～2.4 ka BP,在此阶段1月和7月气温都有减小的趋势,另一个阶段则是2.4 ka BP至今,气温出现反常的趋势.     

天然气水合物研究现状与未来挑战

人类在21世纪后期面临着油气资源枯渴,寻求洁净高效的新能源成为科学界追求的目标。为此,近三十年来,世界各国相继投入了大量的资金和人力开展新能源研究。目前,人们在一种重要的新能源---气水合物的基础研究、地质调查、勘探开发等领域取得了较大的进展;但尚存在许多急待解决的重大理论问题,如天然气水合物形成与分解的动力学过程和地质条件,气水合物资源量计算办法,经济型天然气水合物开采、开发模式,气水合物对全球气候的影响等。天然气水合物作为化石燃料,具有巨大潜力;作为甲烷碳库,是海底地质灾害的诱因;作为温室气体,对全球气候变化有着重要的影响作用。天然气水合物研究未来面临挑战。     

Source-specific variability in post-depositional DNA preservation with potential implications for DNA based paleoecological records

Recent studies have shown that genotyping preserved plankton DNA in marine and lacustrine sediment records using ancient DNA methods is a promising approach for refining paleoenvironmental information. However, the extent to which the preservation of fossil plankton DNA differs between species is poorly understood. Using a continuous 2700 year sediment record from Watts Basin in Ellis Fjord (Antarctica), we compared the level of preservation of fossil DNA derived from important plankton members with varying cellular architecture. The amount of preserved small subunit ribosomal DNA (SSU rDNA; ca. 500 base pair fragments) of dinoflagellates (as extracellular DNA rather than as preserved cysts) that could be amplified by way of PCR declined up to five orders of magnitude with increasing sediment depth and age. In contrast, the amount of similar-sized, PCR-amplifiable, diatom SSU rDNA (predominantly from a cyst-forming Chaetoceros sp.) declined only up to tenfold over 2700 years of deposition. No obvious decline in copy numbers with increasing sediment age was observed for similar-sized SSU rDNA of past chemocline-associated photosynthetic green sulfur bacteria (GSB), which do not have a protective resting stage. In good agreement with the quantitative data, the extent of post-depositional natural degradation to fragments too small to serve as a template for the quantitative PCR assays was greatest for dinoflagellates and lowest for GSB. An increase in the ratio between GSB-derived DNA and intact carotenoids with sediment depth implies that short GSB DNA fragments were better preserved than intact carotenoids and provide a more accurate view into paleoproductivity and the sediment flux of GSB in Watts Basin. We discuss the possible causes behind the variation in the level of DNA preservation among the plankton groups investigated, as well as consequences for the use of using fossil DNA records in paleoecology studies.     

Holocene and Lateglacial summer temperature reconstruction in the Swiss Alps based on fossil assemblages of aquatic organisms: a review

The taxonomic composition of chironomid, cladoceran and diatom assemblages in small lakes in the Alpine region shows a strong relationship with summer temperature. Since fossils of all three organism groups preserve well and remain identifiable in lake sediments, summer temperature transfer-functions can be developed based on the modern distribution of these organisms and applied to fossil records to reconstruct past summer temperature variability. We provide a summary of the chironomid-, cladoceran- and diatom-based transfer functions available from the Swiss Alps and discuss the potential problem of co-variation between summer temperature and lake nutrient conditions for transfer-function development. Whereas the diatom-based summer temperature transfer function remains to be evaluated in down-core reconstructions, the cladoceran- and chironomid-based transfer functions have been used successfully to produce summer temperature records on Lateglacial and Holocene time scales that are in good agreement with other temperature reconstructions in the Alps. Major problems that can be encountered when using fossil assemblages of aquatic organisms for temperature reconstruction in the Alpine region are biases in the inferred temperatures associated with human impact on lakes and parameters other than temperature affecting the fossil assemblages. A multi-proxy approach to palaeoenvironmental reconstruction is recommended to keep a close control on past catchment and within-lake processes during the time interval of interest.     

寻求高分辨率的古环境记录

古气候变化突然事件的发现和对未来环境变化的预测,提出了取得高分辨率古环境记录的要求。本文试图对国际以及国内文献作一综述,以介绍晚第四纪环境变迁高分辨率研究的最新进展,并以海洋部分作为重点。综述涉及千年、百年、十年和年际的不同时间尺度,但着重阐述“亚米兰科维奇”气候变化,包括Heinrich和Dansgaard／Oeschger事件。对于放射性碳测年数据换算为日历年进行专门讨论,因为这是为环境事件建立精确年代顺序的先决条件。最后,向我国同行提出三点建议：1)在对地层记录运用高分辨率研究方法时要经过精心选择,避免盲目性,并充分意识到此类研究的特殊要求;2)依靠我国所在区域的特殊自然条件,在高分辨率古环境研究中发展独立的学术思想;3)将高分辨率研究方法推广到前第四纪的沉积序列中去。     

Spring-season changes during the Late Pleniglacial and Bølling/Allerød interstadial

Earlier spring onset and the associated extension of the growing season in high latitudes belong to the most obvious consequences of global warming. The natural dynamics of growing-season properties during past climate shifts however, are extremely difficult to reconstruct since temperature reconstructions are hardly ever seasonally resolved and the applied proxies such as chirinomid or pollen analysis are mainly sensitive to summer temperatures. Here we apply a newly developed leaf cuticle-based proxy to reconstruct growing degree-days (GDD) in a quantitative way and to estimate changes in the timing of spring onset over the last deglaciation. Cuticle analyses of fossil birch leaves preserved in lake sediments from southern Germany reveal extremely low GDD values during the Late Pleniglacial, which are rapidly increasing at the onset of the Bølling/Allerød interstadial. While temperature and GDDs show a simultaneous warming during deglaciation, a GDD decline precedes lowering of summer temperatures during the Older Dryas cooling. Later bud-burst dates support the hypothesis of a shortening the growing season during this cool pulse.     

Geochemistry of the formation waters in the Po plain (Northern Italy): an overview.

The Po Valley brines represent the base level of the Quaternary aquifer located in a thick clay-sands sedimentary sequence. Geochemistry indicates that these are marine waters, evaporated to the stage of gypsum precipitation and trapped at the bottom of the basin in the late Messinian. Most of the groundwater samples collected from different springs and wells in the plain result from a mixture of these Na–Cl brines and shallow groundwaters laterally recharged by the Alpine and Apennine chains.Natural outflows of brackish waters are associated with major tectonic features. Mud volcanoes, located in the eastern sector of the Po plain, are constantly monitored as sudden chemical changes are significant precursors of seismic activity. In the western sector, calcite-filled veins isotopically record different degrees of water-rock interaction. These are outcropping fossil conduits, where mixing between shallow groundwaters and deep seated brines has occurred. The temporal continuity of the hydrological circuits allows the reconstruction of past and present groundwater circulation patterns.This paper summarises and integrates the geochemical data produced over many years in order to obtain a regional picture of brine origins and the natural mechanisms of groundwater flow.     

雨花台砾石层内含辉木砾石的发现及其意义

通过雨花台砾石层内含辉木雨花石的发现,分析了其重要的科研意义和实用价值。指出对雨花石、辉木化石和树蕨三者的深入研究,将有助于全面探讨古长江流域的发育史,进一步弄清地层进代、研究古生侯和古环境     

甘肃省重要古植物化石产地区划及保护利用

古植物化石是地质历史时期各类植物实体或遗迹的残留。对古植物化石产地进行系统的调查和区划研究是开展古生物化石保护和利用工作的基础。在资料研究和实地调查的基础上,对甘肃省24处重要古植物化石产地进行了评价和区划研究。甘肃省古植物化石产地可划分为北山地区、祁连山——河西走廊地区、鄂尔多斯和秦岭地区4个古生物化石大区以及6个古植物化石产地集中区。根据古植物化石产地的科学价值和美学价值,具体从科学性、稀有性、完整性、保存程度、可保护性5个单因素分别对24处重要古植物化石产地进行了评价。在单因素评价基础上进行了综合鉴评,共鉴评出世界级化石产地1处,国家级化石产地7处,省级化石产地16处。根据产地自然区划、行政区划等要素划分了古植物化石产地集中保护区6个。根据保护区内古植物化石产地级别及重要程度,划分出特级保护区2个,重点保护区2个和一般保护区2个。提出对重要古植物化石产地实行化石标本保护加原产地保护的建议。