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1.
珍珠层中文石晶体择优取向的XRD极图分析 总被引：4，自引：0，他引：4
本文采用XRD极图方法对海水大珠母贝、企鹅珍珠贝及淡水三角帆蚌贝壳珍珠层中文石晶体的结晶学定向进行了研究。根据文石的 ( 0 0 2 )和 ( 0 12 )极图可以推断 ,三种贝壳珍珠层文石的a轴平行珍珠层面 ,c轴垂直珍珠层面。在珍珠层面上 ,二种海水壳珍珠层中文石的a轴亦存在强烈的择优取向现象 ,大珠母珍珠层中文石a轴沿与壳生长纹方向呈 2 0 0°左右的夹角分布 ,企鹅珍珠贝沿近平行壳生长纹的方向分布 ;淡水三角帆蚌珍珠层文石a轴亦平行珍珠层面分布 ,但其择优取向不如海水壳明显 ,在珍珠层面上沿各个角度上均有分布。 相似文献
2.
Genevive Findlater Adam SheltonTimothy Rolin Julian Andrews 《Proceedings of the Geologists' Association. Geologists' Association》2014
This paper revisits the utility of sodium (Na) content in aragonite and calcite mollusc shells as an indicator of palaeosalinity. The data come mainly from a related suite of Middle Pleistocene marine and freshwater fossils that have been subject to broadly similar diagenetic histories. Environmental salinity is re-affirmed as the primary factor in determining the sodium content of modern and ancient mollusc shells: values <2000 ppm Na are generally indicative of non-marine environments while values >2000 Na ppm are typically from marine shells. There is a positive relationship between Na (salinity) and Sr which is a helpful discriminator of palaeosalinity in the fossil data set. The Na and Sr data give confidence that the fossil shells have not suffered pervasive diagenetic alteration and that the marine fossils lived in fully marine conditions. Oxygen isotope values in the best-preserved, fully marine fossil shells, suggest Middle Pleistocene ‘eastern England’ seawater temperatures were broadly similar to those of the modern North Sea. 相似文献
3.
Fossil cytoplasm is a new research topic of interest in paleobotany. Atomic force microscope （AFM） is a new technology applied widely in physics and biology; however, it is rarely used in paleontology. Here we applied AFM for the first time to study fossil cytoplasm. The results indicate that the fossil cytoplasm is heterogeneous and full of ultrastructures, just like extant cytoplasm, and that the application of AFM, especially in combination with other techniques, can reveal the subcellular details of fossil plants with more confidence. 相似文献
4.
前人在黄土—古土壤地层的14C年代学研究中,探讨了不同测年物质的可靠性,但不同物质组分获得的年代差异较大,这是由于选用的样品不符合定年条件,所以选择可靠的样品组分和有效的前处理方法显得尤为重要。对关中地区2万年以来黄土序列中有机质、花粉浓缩物和蜗牛化石进行了AMS14C年代学研究。运用现生蜗牛壳体的AMS14C测定来校正化石蜗牛的年龄,结合剖面中孢粉浓缩物、土壤有机质的AMS14C年代学对比研究,发现蜗牛化石壳体的文石可以提供较可靠的年代数据,为14C测年的可靠性研究提供了一种可能的途径。 相似文献
5.
Hucai Zhang Guoliang Lei Fengqin Chang Yang Pu Hongfang Fan Yanbin Lei Mingsheng Yang Wenxiang Zhang Lunqing Yang 《Frontiers of Earth Science》2008,2(2):225-235
Shell bar, composed of abundant fossil shells of Corbicula fluminea müller and Corbicula largillierti philippi and located at the southeastern end (36°30′N, 96°12′E) of the paleolake Quarhan, is one of the most prominent features
in the Qaidam basin. It is the highest site where such species of fossil shells have been found in the Late Pleistocene age.
A 2.6-m-thick fresh profile was manually excavated to determine the formation ages and the scope of the high paleolake levels.
Accelerator mass spectrometry (AMS), conventional radiocarbon dating, and sector inductively coupled plasma-mass spectroscopy
230Th methods were used to investigate the reliability and accuracy of dating results in different laboratories. Ages of various
components (e.g. acid residual and acid soluble fraction of the organic matter) from the same sample were determined. Age
differences of a variety of materials (e.g. organic matter, fossil shells, and salt crystals), and age differences at the
same sampling position were evaluated. Dating shows that the AMS ages given by alkali residue and acid soluble fractions vary
greatly, e.g., from 124.5 cm upwards. The dates given by the acid soluble fraction were normal. Down the column, the dates
show a reverse pattern and those of alkali residues, especially the lower part of the section, show an unstable pattern. These
imply that organic matter had been influenced by two separate processes. One possible explanation is that the alkali residual
fraction most likely had been contaminated by dead carbon-bearing reworked material because the study section is located near
the edge of the paleolake and could have been easily influenced by old eroded deposits. Another is that the acid soluble fraction
could have been contaminated by upward-flowing groundwater containing soluble organic matter. The amount of this soluble organic
material should be very small because the strongest age reversal is in the lower part, where the TOC content remains low,
meaning that the change of soluble organic fraction alters neither TOC content nor the δ
13C dramatically. It is concluded that a uniform mega-paleolake developed in the Qaidam basin in the northeastern Tibetan plateau
between 39.7 and 17.5 14C kaB.P. During the period when the high paleolake level of Qarhan was formed, the huge paleolake covered a vast area with
dramatic lake level fluctuations. It is found that the ages determined may be influenced by either radioactive 14C variations of repeated deposition or content variations in the atmosphere. The ages given by fossil shells are 15–18 ka
older than those given by organic matter. The large differences between the ages of fossil shells and organic matter might
have resulted from the large water areas and huge water volume and the special location of the high-elevation Qaidam basin.
This study also shows the reliability and accuracy of the 230Th dating method on the salt crystals but further study is needed to determine whether this method could be applied to the
study area.
__________
Translated from Quaternary Sciences, 2007, 27(4): 511–521 [译自: 第四纪研究] 相似文献
6.
Charlotte Prud'homme Olivier Moine Jerome Mathieu Segolene Saulnier‐Copard Pierre Antoine 《Boreas: An International Journal of Quaternary Research》2019,48(1):257-268
High concentrations of calcite fossil granules produced by earthworms (ECG) have been identified in most of the stratigraphical units along the loess‐palaeosol reference sequence of Nussloch (Germany). They are particularly abundant in interstadial brown soils and in tundra gley horizons, the latter reflecting short‐term phases of aggradation then degradation of permafrost. These granules are characterized by a radial crystalline structure produced in the earthworms by specific bio‐mineralization processes. In our study, we used this biological indicator combined with 14C and OSL dating, and sedimentological parameters to characterize millennial‐time scale climatic variations recorded in loess sequences. The approach is based on high‐resolution counts of ECG throughout a 17‐m‐thick loess sequence (332 samples). Strong increases in granule and mollusc concentrations suggest warmer climate conditions during palaeosol formation phases, associated with increasing biodiversity, biological activity and vegetation cover. Decreased granule concentrations occur within primary loess deposits, indicating a strong correlation with palaeoenvironmental conditions and demonstrating the reliability of ECG concentration variations as a new palaeoenvironmental proxy. Finally, this pattern is also recorded in loess sequences located about 600 km westward in northern France demonstrating the large‐scale validity of this new palaeoclimatic proxy. 相似文献
7.
8.
An enhanced start-up of an upflow anaerobic sludge blanket (UASB) reactor for diosgenin wastewater treatment was designed
and experimentally tested. Gran-ular sludge was formed on day 35 in the reactor with high concentrations of chloride (4000–7000
mg/L) and COD (5000–13000 mg/L) as substrate. A new model for the granulation was proposed which divides the formation of
anaerobic granules into six consecutive stages; they include semi-embryonic granule formation, embryonic granule formation,
single-nucleus granule formation, multi-nuclei granule formation, granule growth and granule maturation. A model of the granule
structure was also proposed based on scanning electron microscope observation. The microspores occurring on the surface and
further leading into the interior of the granules were considered as the channels and the passage of the materials and the
products of the microorganisms’ metabolism inside the granules. 相似文献
9.
10.
11.
Modern and Holocene carbonate sedimentology of two saline volcanic maar lakes, southern Australia 总被引：4，自引：0，他引：4
The Basin Lakes are two adjacent maar lakes located in the centre of the Western Volcanic Plains District of Victoria, Australia. Both lakes are saline and alkaline; West Basin Lake is meromictic whereas East Basin is a warm monomictic lake. The carbonate mineral suite of the modern offshore bottom sediments of these Basins consists mainly of dolomite and calcite, with smaller amounts of hydromagnesite and magnesite in West Basin and monohydrocalcite in East Basin. The dolomite, hydromagnesite, magnesite, and monohydrocalcite are endogenic in origin, being derived by primary inorganic precipitation within the water columns of the lakes or at the sediment-water interface. The calcite is biologically precipitated as ostracod valves. In addition to the carbonates in the modern offshore (deep-water) sediments, the lakes also contain a girdle of nearshore carbonate hardgrounds. Both beachrock and microbialites (algal boundstones) are present. These modern lithified carbonate units exhibit a wide range of depositional and diagenetic fabrics, morphologies and compositions. In West Basin, the hardgrounds are composed mainly of dolomite, hydromagnesite, and magnesite, whereas dolomite and monohydrocalcite dominate the East Basin sediments. Aragonite, high-Mg calcite, kutnahorite, siderite, and protohydromagnesite also occur in these lithified carbonate units. Stratigraphic variations in the carbonate mineralogy of the Holocene sediment record in the lakes were used to help decipher the palaeochemistry and palaeohydrology of the Basins. These changes, in conjunction with fluctuations in organic remains and fossil content, indicate a pattern of lake level histories similar to that deciphered from other maar lakes in western Victoria. 相似文献
12.
Stable carbon isotopes in freshwater mussel shells: Environmental record or marker for metabolic activity? 总被引：1，自引：0，他引：1
Mussel shells have been used in a number of paleoecological and environmental studies. The interpretation of stable carbon isotopic composition of shell material is still controversial. The carbon for shell carbonate precipitation can either be derived from ambient dissolved inorganic carbon (DIC), with shells recording environmental signals, or from metabolic CO2, with the potential to disguise environmental signals. To gain insight into this question, we investigated four nearly 100-yr long-term records of aragonite shells from an extant freshwater bivalve species, the endangered freshwater pearl mussel (Margaritifera margaritifera L.). Single growth increments of the outer prismatic and the inner nacreous zones were successfully and easily separated with a simple heat treatment for chronological analyses of δ13C in single layers of each zone. Autocorrelation and semivariance statistical methods reveal that mussels show distinct individual signal patterns, which extend up to 25 yr. Signal patterns are reliably reproduced with replicate samples from defined layers within one shell and show similar patterns with a slight offset for inner nacreous and outer prismatic layers for individual animals. Mussels exposed to the same environmental conditions exhibit distinct and contradictory signature patterns, which do not match between individuals. This observation can only be explained by strong metabolic influences on shell precipitation. Environmental changes in pH, temperature, electric conductivity and atmospheric carbon signature had no or little (<5%) influence, whereas body tissue protein and body tissue δ13C signatures negatively correlated with the youngest produced shell δ13C signatures, indicating that respiration causes a preferential loss of light isotopes from body mass and an inverse enrichment in shell aragonite. Hence, the shells of the freshwater pearl mussel yield a long-term record of metabolic activity, whereas the use of δ13C in these shells as recorder for environmental signals is questionable. This may also be true for shells from other species, for which metabolic carbon incorporation has been acknowledged. 相似文献
13.
A suite of elements (B, Na, Mg, S, K, Ca, V, Mn, Cr, Sr, and Ba) was measured in aragonitic shells of the estuarine bivalve Corbula amurensis, the Asian clam, using the Sensitive High-Resolution Ion MicroProbe with Reverse Geometry (SHRIMP RG). Our initial intent was to explore potential geochemical proxy relationships between shell chemistry and salinity (freshwater inflow) in northern San Francisco Bay (SFB). In the course of this study we observed variations in shell trace element to calcium ([M]/Ca) ratios that could only be attributed to internal biological processes. This paper discusses the nature and sources of internal trace element variability in C. amurensis shells related to the shell organic fraction and shell calcification rates. The average organic content of whole C. amurensis shells is 19%. After treating whole powdered shells with an oxidative cleaning procedure to remove organic matter, shells contained on average 33% less total Mg and 78% less total Mn. Within our analytical uncertainty, Sr and Ba contents were unchanged by the removal of organic matter. These results show that aragonitic C. amurensis shells have a large component of non-lattice-bound Mg and Mn that probably contribute to the dissimilarity of [M]/Ca profiles among five same-sized shells. Non-lattice-bound trace elements could complicate the development and application of geochemical proxy relationships in bivalve shells. Because B, Ba and Sr occur exclusively in shell aragonite, they are good candidates for external proxy relationships. [M]/Ca ratios were significantly different in prismatic and nacreous aragonite and in two valves of the same shell that had different crystal growth rates. Some part of these differences can be attributed to non-lattice-bound trace elements associated with the organic fraction. The differences in [M]/Ca ratios were also consistent with the calcification rate-dependent ion transport model developed by Carré et al. [Carré M., Bentaleb I., Bruguier O., Ordinola E., Barrett N. T. and Fontugne M. (2006) Calcification rate influence on trace element concentrations in aragonitic bivalve shells: evidences and mechanisms. Geochim. Cosmochim. Acta70, 4906-4920] which predicts that [M]/Ca ratios increase as calcification rates increase and Ca2+ channel specificity decreases. This result, in combination with the possibility that there were ontogenetic variations in growth rates among individuals younger than 2 years, underscores the need to develop an independent age model for C. amurensis shells. If growth-rate effects on lattice-bound [M]/Ca ratios can be constrained, it may yet be possible to develop high-resolution geochemical proxies for external solution chemistry in low-salinity regions of SFB. 相似文献
14.
对黄土高原西部秦安地区晚新近纪甘肃群中的一套黄土-古土壤序列以20cm间距采集的310个蜗牛化石样品进行了系统的研究。结果表明,黄土层与古土壤层中的蜗牛化石全部为陆生种类,以Gastrocopta,Pupilla,Vallonia,Metodontia,Cathaica和Punctum等占优势,与黄土高原第四纪黄土-古土壤序列中蜗牛化石的种属组成基本一致,这表明研究剖面是一套陆生成因的地层,与黄土高原第四纪黄土-古土壤序列有着相似的沉积环境。上述结果为提取古环境信息从生物学角度提供了证据。 相似文献
15.
J.K.W Toporski A Steele F WestallR Avci D.M MartillD.S McKay 《Geochimica et cosmochimica acta》2002,66(10):1773-1791
The fossilised soft tissues of a tadpole and an associated coprolitic structure from the organic-rich volcanoclastic lacustrine Upper Oligocene Enspel sediments (Germany) were investigated using high-resolution imaging techniques and nondestructive in situ surface analysis. Total organic carbon analysis of the coprolite and the sediment revealed values of 28.9 and 8.9% respectively. The soft tissues from the tadpole and the coprolite were found to be composed of 0.5 to 1 μm-sized spheres and rod shapes. These features are interpreted as the fossil remains of bacterial biofilms consisting probably of heterotrophic bacteria and fossilised extracellular polymeric substances. They became fossilised while in the process of degrading the organic matter of the organism and the coprolite. Comparison with a modern marine biofilm revealed morphologic details identical to those observed in the fossil bacterial biofilms. Although the fossil biofilms on both macrofossils exhibited identical microtextures, their mode of preservation was inhomogeneous and varied between calcium phosphate and an as yet unidentified mineral phase consisting mainly of Si, Ca, Ti, P, and S, but also showing the presence of Mg, Al, and Fe. The coprolite consists purely of fossilised bacterial cells in a densely packed arrangement and associated fossilised extracellular polymeric substances.In addition to preliminary imaging and energy-dispersive X-ray analysis, both the fossil biofilms and the sediment were investigated by nondestructive in situ analysis using time of flight-secondary ion mass spectroscopy (ToF-SIMS). The mass spectra obtained on the coprolite in mass-resolved chemical mapping mode allowed the tentative identification of a number of organic secondary ion species. Some spectra appear to indicate the presence of bacterial hopanoids, but further work using standard techniques such as gas chromatography mass spectroscopy is needed to conclusively verify the presence of these substances. Nevertheless, ToF-SIMS chemical maps were successfully correlated with electron microscopy images, allowing the correlation of molecular spectra, the spatial distribution of individual organic species, and specific morphologic features to demonstrate the potential of this approach in the analysis of microfossils. 相似文献
16.
为了研究染色对海水珍珠结构和表面光泽的影响以及染料的主要渗透途径与结合部位,通过对比染色实验、扫描电子显微镜和宝石显微镜,对染色前、后的海水珍珠样品表面和内部特征进行了观察与分析,采用显微分光光度-偏光显微镜测量染色前、后海水珍珠样品的表面反射率变化以及运用红外光谱测定染色前、后海水珍珠样品的成分。结果表明,在染色过程中,染料是通过海水珍珠珠孔处珠核和珍珠层间的有机质空隙以及漂白造成海水珍珠表面有机质疏松结构而渗透到珍珠的内部,主要与海水珍珠内的有机成分作用而使其着色。染色后海水珍珠样品的砖墙型层状结构未改变;染料对海水珍珠表面的有机质疏松结构具有填充作用,增强了其表面的镜面效应,使光泽度增强。 相似文献
17.
柴达木盆地察尔汗贝壳堤剖面年代学研究* 总被引：9，自引：6，他引：9
利用常规14 C、加速器(AMS)和230 Th等测年方法,对位于青藏高原东北部柴达木盆地察尔汗古湖贝壳堤剖面化石贝壳、湖泊沉积(包括现代沉积)样品有机质(包括碱性残留和胡敏酸组分)、碳酸盐(CaCO3)和剖面顶部石盐(NaCl)晶体在不同实验室进行了系统的实验研究,探讨了不同样品测年结果的可靠性和精确性,并通过与已有研究结果的对比,对柴达木盆地贝壳堤剖面记录的察尔汗古湖高湖面演化历史进行了探讨,得出察尔汗古湖高湖面形成于约39.7~17.5 14 C kaB.P. ; 研究证明柴达木盆地沉积物中有机质含量很低,且主要来源于菌藻类等低等藻类和微生物,受老碳和溶解物质影响强烈,因此必须经过多种方法综合测年才能比较可靠地确定所测样品的形成年代; 测年结果的不确定性不仅来源于样品自身元素(同位素)的特性和沉积过程中再沉积作用的影响,也可能源自于放射性14 C产生过程的不稳定性; 对比发现贝壳化石老于同层位有机质14 C年龄15~18ka,这可能与柴达木盆地所处的特殊地理位置和巨大的古湖泊面积及水体有关; 同时,不平衡铀系测年在确定开放体系矿物晶体年代应用中的可靠性尚须进一步深入分析,其机理也还需要探讨和实验研究。 相似文献
18.
对5种禾本科植物种子中的淀粉粒（包括粟、黍、青狗尾草、高粱及薏苡等）进行了形态学观察和描述,结合颗粒长度的测量和统计学分析,建立了区分这些作物淀粉粒的一般方法。结果显示,粟和黍的淀粉粒以多边形居多,比例分别为75％和96％;青狗尾草中的淀粉粒以圆形为主;高粱和薏苡的淀粉粒形态具有较高的多样性。表现在消光臂上,高粱淀粉粒的消光臂呈现弯曲特征,而其他4种作物淀粉粒的消光臂则较为平直。在颗粒的长度分布上,粟淀粉粒为2.77～18.40μm,黍淀粉粒为3.93～12.85μm,青狗尾草淀粉粒为 2.19～11.90μm,高粱淀粉粒为4.11～30.30μm,薏苡淀粉粒为 5.48～25.44μm。研究表明,粟、黍、青狗尾草、高粱及薏苡等5种禾本科植物的淀粉粒形态特征存在相似性,但是也有差异。综合运用二维形状、脐点位置、表面特征、消光臂特征及长度等多种指标,可以对这几种作物的淀粉粒进行一定程度的区分。这一研究结果可用于辅助对古代淀粉粒的种属鉴定。 相似文献
19.
北票-义县地区义县组珍稀化石层位对比及时代 总被引：3，自引：0，他引：3
北票-义县地区义县组以火山-沉积地层为主体,具有4个火山活动亚旋回,生物化石主要形成于第一、第二、第四亚旋回期间,构成了3个产出层位.以中华龙鸟、孔子鸟、辽宁古果为代表的珍稀化石组合产在义县组二段中,形成于125~127Ma期间.枕状熔岩、淬火岩等特殊岩石的出现和高频层序地层研究表明,北票、义县地区的含珍稀化石沉积层(义县组二段)都处于相对较深的湖盆沉积环境,表现为湖扩展体系域沉积,两地含珍稀化石沉积地层层位基本相当.义县组形成于135~120Ma期间,属于早白垩世.多方面证据表明侏罗系-白垩系界限应当置于义县组底界. 相似文献
20.
The degrees and rates of isoleucine epimerization in heating experiments with pure di- and tripeptides are dependent on: (1) the position of isoleucine in the peptide chain; (2) the formation from dipeptides of diketopiperazines, cyclic intermediates that are in equilbrium with, and hydrolyze to, both the parent and inverted dipeptides as follows: NH2-terminal?diketopiperazine?COOH-terminal. The results of heating experiments show that isoleucine residues in diketopiperazine are the most highly epimerized form in both di- and tripeptide solutions. NH2-terminal isoleucine also undergoes relatively rapid epimerization, while the rates of epimerization of COOH-terminal and free isoleucine are much slower. Through hydrolysis reactions, high degrees of isoleucine epimerization are transferred to slower epimerizing species. Consequently, the relative rate of isoleucine epimerization in the various positions differs from the relative degree of epimerization.The relative rates of isoleucine epimerization are: NH2 ? diketopiperazine ? COOH ≈ interior ≈ free, while the relative degrees of isoleucine epimerization are: diketopiperazine > NH2 > COOH ? interior. The high degree of epimerization exhibited by COOH-terminal isoleucine in fossil dipeptides is due to prior preferential epimerization in diketopiperazine. The high degree of epimerization of free isoleucine in carbonate fossils is due to the hydrolysis of highly epimerized terminal isoleucine. These results are applicable to peptides both in fossil shells and in aqueous solutions and form the basis for a revised model of isoleucine epimerization in fossil shells. 相似文献