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1.
《Quaternary Science Reviews》2003,22(10-13):1373-1382
U and Th concentration profiles in fossil hominid and faunal teeth have been measured by laser ablation ICPMS. These profiles record diverse modes of U and Th uptake, particularly within enamel, that can be broadly related to the state of sample preservation. Observed U profiles are in general inconsistent with existing diffusion–adsorption models developed for U-uptake in bone and teeth. Where the models appear applicable, calculated diffusion rates are several orders of magnitude smaller than previous estimates. Laser ablation ICPMS offers a means of rapidly characterizing U and Th distributions in the enamel and dentine components of teeth as a precursor to ESR and U-series dating. In particular, it should allow the identification of teeth (and also bone) samples that have simple U-uptake histories and are amenable to precise dating by time-consuming and expensive Th–U and Pa–U TIMS techniques. We also demonstrated the use of laser ablation ICPMS to measure U-series isotopes in dentine and enamel samples with relatively high U concentrations (>20 ppm). These results, obtained using a quadrupole ICPMS, illustrate significant promise for in situ U-series isotope analysis, particularly when combined with the greater sensitivity and multi-collection capabilities of new sector ICPMS instrumentation. The latter may permit precise isotope ratio measurements on samples containing only a few ppm of U. 相似文献
2.
Qingfeng Shao Wei Wang Chenglong Deng Pierre Voinchet Min Lin Antoine Zazzo Eric Douville Jean-Michel Dolo Christophe Falguères Jean-Jacques Bahain 《Quaternary Research》2014
Several Gigantopithecus faunas associated with taxonomically undetermined hominoid fossils and/or stone artifacts are known from southern China. These faunas are particularly important for the study of the evolution of humans and other mammals in Asia. However, the geochronology of the Gigantopithecus faunas remains uncertain. In order to solve this problem, a program of geochronological studies of Gigantopithecus faunas in Guangxi Province was recently initiated. Chuifeng Cave is the first studied site, which yielded 92 Gigantopithecus blacki teeth associated with numerous other mammalian fossils. We carried out combined ESR/U-series dating of fossil teeth and sediment paleomagnetic studies. Our ESR results suggest that the lower layers at this cave can be dated to 1.92 ± 0.14 Ma and the upper layers can be dated to older than 1.38 ± 0.17 Ma. Correlation of the recognized magnetozones to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic, biostratigraphic and ESR data. The combined chronologies establish an Olduvai subchron (1.945–1.778 Ma) for the lowermost Chuifeng Cave sediments. We also analyzed the enamel δ13C values of the Gigantopithecus faunas. Our results show that southern China was dominated by C3 plants during the early Pleistocene and that the Gigantopithecus faunas lived in a woodland-forest ecosystem. 相似文献
3.
Trace element profiles for common divalent cations (Sr, Zn, Ba), rare-earth elements (REE), Y, U, and Th were measured in fossil bones and teeth from the c. 25 ka Merrell locality, Montana, USA, by using laser-ablation ICP-MS. Multiple traverses in teeth were transformed into 2-D trace element maps for visualizing structural influences on trace element uptake. Trace element compositions of different soils from the fossil site were also analyzed by solution ICP-MS, employing progressive leaches that included distilled H2O, 0.1 M acetic acid, and microwave digestion in concentrated HCl-HNO3. In teeth, trace element uptake in enamel is 2-4 orders of magnitude slower than in dentine, forming an effective trace element barrier. Uptake in dentine parallel to the dentine-enamel interface is enhanced by at least 2 orders of magnitude compared to transverse, causing trace element “plumes” down the tooth core. In bone, U, Ba and Sr are nearly homogeneous, implying diffusivities ∼5 orders of magnitude faster than in enamel and virtually complete equilibration with host soils. In contrast all REE show strong depletions inward, with stepwise linear segments in log-normal or inverse complementary error function plots; these data require a multi-medium diffusion model, with about 2 orders of magnitude difference in slowest vs. fastest diffusivities. Differences in REE diffusivities in bone (slow) vs. dentine (fast) reflect different partition coefficients (Kd’s). Although acid leaches and bulk digestion of soils yield comparable fossil-soil Kd’s among different elements, natural solutions are expected to be neutral to slightly basic. Distilled H2O leachates instead reveal radically different Kd’s in bone for REE than for U-Sr-Ba, suggest orders of magnitude lower effective diffusivities for REE, and readily explain steep vs. flat profiles for REE vs. U-Sr-Ba, respectively. Differences among REE Kd’s and diffusivities may explain inward changes in Ce anomalies. Acid washes and bulk soil compositions yield misleading Kd’s for many trace elements, especially the REE, and H2O-leaches are preferred. Patterns of trace element distributions indicate diagenetic alteration at all scales, including enamel, and challenge the use of trace elements in paleodietary studies. 相似文献
4.
Rare earth elements (REE), while not essential for the physiologic functions of animals, are ingested and incorporated in ppb concentrations in bones and teeth. Nd isotope compositions of modern bones of animals from isotopically distinct habitats demonstrate that the 143Nd/144Nd of the apatite can be used as a fingerprint for bedrock geology or ambient water mass. This potentially allows the provenance and migration of extant vertebrates to be traced, similar to the use of Sr isotopes. Although REE may be enriched by up to 5 orders of magnitude during diagenesis and recrystallization of bone apatite, in vivo143Nd/144Nd may be preserved in the inner cortex of fossil bones or enamel. However, tracking the provenance of ancient or extinct vertebrates is possible only for well-preserved archeological and paleontological skeletal remains with in vivo-like Nd contents at the ppb-level. Intra-bone and -tooth REE analysis can be used to screen for appropriate areas. Large intra-bone Nd concentration gradients of 101-103 are often measured. Nd concentrations in the inner bone cortex increase over timescales of millions of years, while bone rims may be enriched over millenial timescales. Nevertheless, εNd values are often similar within one εNd unit within a single bone. Larger intra-bone differences in specimens may either reflect a partial preservation of in vivo values or changing εNd values of the diagenetic fluid during fossilization. However, most fossil specimens and the outer rims of bones will record taphonomic 143Nd/144Nd incorporated post mortem during diagenesis. Unlike REE patterns, 143Nd/144Nd are not biased by fractionation processes during REE-uptake into the apatite crystal lattice, hence the εNd value is an important tracer for taphonomy and reworking. Bones and teeth from autochthonous fossil assemblages have small variations of ±1 εNd unit only. In contrast, fossil bones and teeth from over 20 different marine and terrestrial fossil sites have a total range of εNd values from -13.0 to 4.9 (n = 80), often matching the composition of the embedding sediment. This implies that the surrounding sediment is the source of Nd in the fossil bones and that the specimens of this study seem not to have been reworked. Differences in εNd values between skeletal remains and embedding sediment may either indicate reworking of fossils and/or a REE-uptake from a diagenetic fluid with non-sediment derived εNd values. The latter often applies to fossil shark teeth, which may preserve paleo-seawater values. Complementary to εNd values, 87Sr/86Sr can help to further constrain the fossil provenance and reworking. 相似文献
5.
Daniel Herwartz Thomas Tütken Klaus Peter Jochum P. Martin Sander 《Geochimica et cosmochimica acta》2011,75(1):82-5970
Rare earth element (REE) patterns of fossil bones and teeth are widely used as proxies for provenance, taphonomy, and palaeoenvironment. In order to investigate if fossil bones behave as closed systems over geologic time, REE profiles were analysed by LA-ICPMS along cross sections of 54 bones from various well-characterised and well-dated settings. These include terrestrial and marine diagenetic environments, covering Early Triassic to Holocene ages. In general, all fossil bones exhibit the highest REE concentrations at the outer rim, gradually decreasing by up to four orders of magnitude toward the inner bone cortex. Intra-bone REE concentration gradients decrease significantly from Quaternary via Tertiary to Mesozoic specimens, suggesting long term REE uptake and open system behaviour of fossil bone. This view is further corroborated by 176Lu-176Hf dating of selected samples, all yielding significantly younger ages than the known chronostratigraphic ages. Hence, there is clear evidence for long term open system behaviour of fossil bones with respect to REE, which is in marked contrast to currently accepted models suggesting that REE uptake is only early diagenetic. Although unexpected, statistically significant four to seven point isochrons are observed for four fossil dinosaur bone samples and one Upper Triassic Mastodonsaurus tooth with MSWDs ranging from 0.083 to 4.5. Notably, mobility of Lu alone cannot account for the observed age patterns. Assuming constant Lu uptake rates over time, the radiometric ages should only be as low as half of the chronostratigraphic age. However, a six-point isochron defined by subsamples of a single Upper Triassic Mastodonsaurus tooth yields an age of 65.2 ± 1.1 Ma (MSWD = 0.68), much younger than half of the stratigraphic age (ca. 234 Ma). Hence, Hf must also undergo late diagenetic exchange. Likely mechanisms to account for the presence of statistically meaningful isochrons as well as for the late diagenetic exchange of both REE and Hf are diffusion, adsorption, and dissolution-reprecipitation processes. 相似文献
6.
在青海共和盆地晚更新世河湖相沉积地层中发现了象类化石,对化石的基本特征进行了描述,依据牙片的釉质层、齿脊频率等特征初步鉴定为猛犸象类化石,并在同一层位发现了钙化树木化石.结合区域地质以及产出猛犸象属化石地层的沉积学特征、孢粉组合等的简要分析认为,共和盆地晚更新世晚期为干燥寒冷的气候环境.这一发现有助于认识中国猛犸象属动物的迁徙过程,以及青藏高原晚更新世的生物演化、气候变化和构造活动.同时,也为研究青藏高原第四纪以来生物进化、湖泊与河流演化、气候变化、古地理与古环境变迁等提供了新资料. 相似文献
7.
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
8.
Alexander Heuser Thomas Tütken Stephen J.G. Galer 《Geochimica et cosmochimica acta》2011,75(12):3419-8
We present the first systematic study of Ca isotopes (δ44/40Ca) in Late Triassic to Late Cretaceous dinosaur bones and teeth (enamel and dentin) from sympatric herbivorous and carnivorous dinosaurs. The samples derive from five different localities, and data from embedding sediments are also presented. Additional δ44/40Ca in skeletal tissues from modern reptiles and birds (avian dinosaurs) were measured for comparison in order to examine whether the original Ca isotopic composition in dinosaur skeletal apatite was preserved or might have changed during the diagenesis and fossilization process.δ44/40Ca of fossil skeletal tissues range from −1.62‰ (Tyrannosaurus rex enamel) to +1.08‰ (Brachiosaurus brancai bone), while values in modern archosaur bones and teeth range from −1.63‰ (caiman enamel) to −0.37‰ (ostrich bone). The average δ44/40Ca of the three types of fossil skeletal tissue analyzed - bone, dentin and enamel - show some systematic differences: while δ44/40Ca in bone exhibits the highest values, while δ44/40Ca in enamel has the lowest values, and dentin δ44/40Ca falls in between. Values of δ44/40Ca in the remains of herbivorous dinosaurs (0.1-1.1‰) are generally higher than those of bones of modern mammalian herbivores (−2.6‰ to −0.8‰) and from modern herbivorous archosaurs, which exhibit intermediate δ44/40Ca (−0.8‰ to −0.4‰). These systematic isotopic shifts may reflect physiological differences between dinosaurs, mammals and reptiles representing different taxonomic groups of vertebrates.Systematic offsets in skeletal apatite δ44/40Ca between herbivorous and carnivorous dinosaurs are not obvious, indicating a lack of a clear-cut Trophic Level Effect (TLE) shift between herbivores and carnivores in dinosaurs. This observation can be explained if the carnivorous dinosaurs in this study fed mainly on soft tissues from their prey and did not ingest hard (calcified) tissue to much extent. The most striking indication that the primary δ44/40Ca is actually preserved in most of the fossil teeth is a difference in δ44/40Ca of about 0.35 ± 0.10‰ (1SD) between dentin and enamel, based upon 11 of 16 analyzed dentin-enamel pairs. This difference is close to that found in modern reptiles (0.28 ± 0.05‰), and strongly suggests that this tell-tale signature is a primary feature of the fossilized dinosaur material as well. Furthermore, simple mass balance calculations show that changes of the original δ44/40Ca in bones and teeth by diagenetically-formed calcium-bearing minerals are either small or would require implausible high original δ44/40Ca values in the skeletal apatite. 相似文献
9.
Wu Liu Xianzhu Wu Shuwen Pei Xiujie Wu Christopher J. Norton 《Quaternary International》2010,211(1-2):29-41
This contribution discusses recent paleoanthropological findings from Huanglong Cave, a Late Pleistocene human fossil site from Yunxi County, Hubei Province, China. Three excavations in the Huanglong Cave from 2004 to 2006 yielded seven human teeth, some stone and bone tools, possible burnt sediment and other evidence possibly related to hominin activities. Based on the presence of extinct faunas (20% of total taxa identified), the deposits dated to the Late Pleistocene. Electron spin resonance (ESR) and uranium-series (U-series) dating analyses on associated teeth and speleothems have resulted in divergent chronometric ages (ESR: 44–34 ka; U-series: 103–79 ka). Analysis indicates: (1) most of the morphological and metric features of the human teeth from Huanglong Cave fall within the range of variation of modern Chinese, but a few characters may still link them to more archaic hominins; (2) some activity-induced abrasion and other tooth use-marks were identified, including pronounced tooth chipping and interproximal grooves on the anterior teeth; (3) the sample of blackened deposit has a high carbon content (over 70%), experienced high temperatures, and likely was of cultural origin and not natural; (4) the mammal fossils represent the “Ailuropoda-Stegodon” faunal unit which lived in southern China throughout the Pleistocene. Synthesizing all of these findings, especially the human teeth that display modern human characteristics, Huanglong Cave will offer some new insights into various issues currently being debated in Late Pleistocene human evolutionary research. 相似文献
10.
Elemental ratio data from archaeological and paleontological bone have often been used for paleoecological reconstruction, but recent studies have shown that, even when solubility profiling techniques are employed in an attempt to recover biogenic signals, bone is an unreliable material. As a result, there has been renewed interest in using enamel for such studies, as it is known to be less susceptible to diagenesis. Nevertheless, enamel is not immune from diagenetic processes, and several studies have suggested that paleoecologically relevant elements may be altered in fossil enamel. Here, we investigate Sr, Ba, Zn, and Pb compositions of enamel from South African karstic cave sites in an effort to ascertain whether or not this material provides reliable paleoecological information. We compared enamel data for mammals from three fossil sites aged 1.8-3.0 Ma, all of which are on dolomites, with data from modern mammals living on dolomitic and granitic substrates. Sr/Ca and Ba/Ca are about three times higher in enamel from modern mammals on granites than those living on dolomites, stressing the need for geologically appropriate modern/fossil comparisons. After pretreatment with dilute acid, we found no evidence of increased Sr/Ca, Ba/Ca, or Pb/Ca in fossil enamel. In contrast, Zn/Ca increased by over five times at one site (Makapansgat), but much more subtly elsewhere. Ecological patterning in Sr/Ca, Ba/Ca, and Sr/Ba ratios was also retained in fossil enamel. This study suggests that Sr/Ca, Ba/Ca, and Pb/Ca data likely preserve paleoecological information from these sites, but also demonstrates that geologically similar sites can differ in the degree to which they impart certain elements (Zn in this case) to fossils. Thus, screening is probably necessary on a site-by-site basis. Lastly, further investigation of elemental distributions in modern foodwebs is necessary before elemental ratio analysis can become a common tool for paleoecological reconstruction. 相似文献
11.
Matthew J. Kohn 《Geochimica et cosmochimica acta》2006,70(4):931-946
During fossilization, bone is thought to recrystallize and alter chemically on timescales of kyr to a few tens of kyr, i.e., similar to the timescale for formation of soils. Therefore, C- and O-isotope compositions of bone apatite should correlate with trends in soil water composition and aridity, and serve as paleoclimate indicators. This hypothesis was tested by analyzing C- and O-isotope compositions of the CO3 component of fossil bone apatite from mid-Oligocene through late Pleistocene units in Oregon and western Idaho, including the John Day (19.4-30.0 Ma), Mascall (15.2-15.8 Ma), and Rattlesnake (7.2-7.8 Ma) Formations, whose paleosol sequences have been studied in detail, and the Juntura (10-11 Ma), Hagerman (3.2 Ma), and Fossil Lake (<23-650 ka) fossil localities. Tooth enamel δ18O values provide a baseline of meteoric water compositions. Stable isotope compositions of bone CO3 do change in response to broad climatic trends, but show poor correlation with compositions of corresponding paleosol CO3 at specific horizons. Instead, compositional deviations between bone and paleosol CO3 correlate with compositional deviations with the next higher paleosol; this suggests that the timescale for fossilization exceeds one paleosol cycle. Based on stratigraphic evidence and simple alteration models, fossilization timescales are estimated at 20-50 kyr, indicating that bone CO3 will prove most useful for sequences spanning >100 kyr. C-isotopes show negative and strong positive deviations during wet and dry climates respectively, and short-term trends correspond well with changes in aridity within the Mascall and Rattlesnake Formations, as inferred from paleosols. A proposed correction to δ18O values based on δ13C anomalies implies a small, ∼1.5‰ increase in meteoric water δ18O during the late Oligocene global warming event, consistent with a minimum temperature increase of ∼4 °C. A strong inferred decrease in δ18O of 4-5‰ after 7 Ma closely parallels compositional changes in tooth enamel, and reflects a doubling in the height of the Cascade Range. 相似文献
12.
Bone apatite acts as a natural, timed sampling device, scavenging trace elements from local pore waters over timescales of ca. 1-50 ka. The rare earth element (REE) and U/Th composition of fossil bones reflects associated pore water compositions during the period of recrystallisation. The REE composition of fossil bones is controlled by partitioning of REE between pore waters and particle surfaces, and the REE composition of fossil bones reflects the REE composition of pore waters which vary spatially and temporally. Light REE are preferentially sorped onto particle surfaces, thus the high La/Yb values seen in many bones from coastal marine and aeolian environments are best explained by release of REE from light REE-enriched particles to local pore waters and subsequent immobilisation in recrystallising bones. The REE compositions of bones recovered from pedogenically altered diatomite sediments of the Olorgesailie Formation of southern Kenya vary over spatial scales of less than 10 m. Location accounts for 48% of the observed variation in bone chemistry and bones recovered from eight discrete excavations within the same time-equivalent stratigraphic layer can be assigned to their excavation location with >70% accuracy based on a discriminant analysis of REE, U, and Th composition. Despite this within-layer variation, bones recovered from different stratigraphic horizons within the Olorgesailie Formation can also be distinguished on the basis of their trace element composition. Bones recovered from four stratigraphic horizons spanning ca. 0.5 million years were assigned to their correct stratigraphic layer with >90% accuracy. Where sedimentological conditions are favourable, the trace element composition of fossil bone may be used to test stratigraphic provenance and burial location in excavated bone with a temporal resolution of <10 ka and a spatial resolution of <10 m. The trace element composition of fossil bone may also be used to investigate the accumulation history of vertebrate assemblages and to reconstruct pore water variability across land surfaces. 相似文献
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自20世纪50年代发现长阳人化石以来,迄今在鄂西-三峡地区已经发现了至少10处古人类化石地点,时代跨越了整个更新世时期,尤其以更新世中、晚期人类化石最为丰富。除人类化石外,在这一地区还发现了大量的古人类制作的石器、骨器、艺术品、装饰品等人类活动遗存,以及与古人类伴生的动物化石。近年的野外发掘及实验室研究证明鄂西-三峡地区更新世中期以来一直是古人类生存与繁衍昌盛的区域,该地区丰富的古人类资源对研究与中国古人类演化有关的一系列关键学术问题具有非常重要的价值。 相似文献
15.
The first appearance of mammoth (Mammuthus) is currently used to define the beginning of the Irvingtonian North American Land Mammal Age at about 1.4 Ma. Thereafter, mammoth fossils are common and widespread in North America until the end of the Pleistocene. In contrast to this generally accepted biochronology, recent reports have asserted that mammoth occurs in late Pliocene (ca. 2.5 Ma) alluvium from the Santa Fe River of northern Florida. The supposedly contemporaneous late Pliocene fossil assemblage from the Santa Fe River that produced the mammoth specimens actually consists of a mixture of diagnostic Blancan (late Pliocene) and late Rancholabrean (latest Pleistocene) species. Fossil bones and teeth of the two mammalian faunas mixed together along the Santa Fe River have significantly different rare earth element (REE) signatures. The REE signatures of mammoth are indistinguishable from those of Rancholabrean mammals, yet they are different from those of diagnostic Blancan vertebrates from these same temporally mixed faunas of the Santa Fe River. Thus, no evidence for late Pliocene mammoth exists in Florida, and mammoth fossils remain reliable biochronological indicators for Irvingtonian and Rancholabrean terrestrial sequences throughout mid- and lower-latitude North America. 相似文献
16.
人类为获取食物和满足其他需求而使用牙齿从事的各类非咀嚼性活动在牙齿表面形成使用痕迹。牙齿使用痕迹与古人类的行为特征关系密切,记录了丰富的古人类生存环境、食物构成、获取食物的方式、行为模式及生活习俗等方面的信息。对黄龙洞更新世晚期人类牙齿的观察发现:黄龙洞人类前部牙齿表面具有釉质破损与崩裂、齿冠唇面破损、齿间邻接面沟3种类型的使用痕迹。根据这些牙齿使用痕迹的分布和表现特点,推测生活在黄龙洞的更新世晚期人类经常使用前部牙齿从事啃咬、叼衔、或剥离坚韧的食物或非食物物品等活动,并可能将前部牙齿作为工具使用;齿间邻接面沟提示当时人类经常从事剔牙活动。结合已经在黄龙洞发现的其他人类活动证据,我们认为当时人类可能从事狩猎活动,食物构成中包含有较多的肉类及粗纤维植物。 相似文献
17.
《Quaternary Science Reviews》2003,22(10-13):1345-1351
In the last 20 years, the electron spin resonance (ESR) dating method has allowed the establishment of a chronological time frame over most of the history of human evolution. Despite many difficulties found for ESR dating of bones and carbonates, tooth enamel dated by ESR has been proven as a reliable method in its application to fossil teeth and quartz. Both of the latter materials have allowed dating of Early and Middle Pleistocene sites which are not datable using other methods such as the Argon–Argon method. In particular, recent discoveries of human remains in western Europe have been proposed to be sites of the earliest arrival of humans there, and have been dated to the Early Pleistocene by ESR using quartz and tooth enamel.Combined ESR and U-series dating of fossil herbivore teeth are the only means of dating layers from which such ancient remains have been recovered in western Europe. Good examples are the sites of Atapuerca Gran Dolina, Spain and Visogliano, Italy which have been dated using tooth enamel.When no bones and teeth can be found in prehistoric sites, ESR dating on quartz extracted from sediments has been used to date sites whose ages range over the entire Quaternary period. We present here two examples that occur in fluvial terraces of the river Creuse, France and at Monte Poggiolo site, Italy, where several artefacts of an archaic pebble industry have been recovered. 相似文献
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Rainer Grün Maxime Aubert Marie-Hélène Moncel 《Geochimica et cosmochimica acta》2008,72(21):5278-5290
We have mapped U (238U) and Th (232Th) elemental concentrations as well as U-series isotope distributions in a Neanderthal tooth from the Middle Palaeolithic site of Payre using laser ablation ICP-MS. The U-concentrations in an enamel section varied between 1 and 1500 ppb. The U-concentration maps show that U-migration through the external enamel surface is minute, the bulk of the uranium having migrated internally via the dentine into the enamel. The uranium migration and uptake is critically dependent on the mineralogical structure of the enamel. Increased U-concentrations are observed along lineaments, some of which are associated with cracks, and others may be related to intra-prismatic zones or structural weaknesses reaching from the dentine into the enamel. The uranium concentrations in the dentine vary between about 25,000 and 45,000 ppb. Our systematic mapping of U-concentration and U-series isotopes provides insight into the time domain of U-accumulation. Most of the uranium was accumulated in an early stage of burial, with some much later overprints. None of the uranium concentration and U-series profiles across the root of the tooth complied with a single stage diffusion-adsorption (D-A) model that is used for quality control in U-series dating of bones and teeth. Nevertheless, in the domains that yielded the oldest apparent U-series age estimates, U-leaching could be excluded. This means that the oldest apparent U-series ages of around 200 ka represent a minimum age for this Neanderthal specimen. This is in good agreement with independent age assessments (200-230 ka) for the archaeological layer, in which it was found.The Th elemental concentrations in the dental tissues were generally low (between about 1 and 20 ppb), and show little relationship with the nature of the tissue. 相似文献
20.
马牙氧同位素组成与气候指标的定量关系 总被引：5，自引：0，他引：5
提出以马牙的氧同位素组成作为一种新的代用性气候指标，根据全球不同地点现代野生马类（Ｅｑｕｕｓ属）的牙齿釉质层氧同位素组成建立了与年平均温度的线性关系：δ（１８）Ｏ＝０．５０８０Ｔ＋１０．４９（ｒ＝０．８２），证明马牙氧同位素组成响应于大气降水的氧同位素组成，并且能够代表某一生态区域内的多年平均值。由于哺乳动物牙齿的釉质层具有良好的抗成岩作用能力，因此可以利用马牙化石的氧同位素组成来推算地质历史时期的年平均温度值，对第四纪以来的气候环境演变提供定量化的分析资料。 相似文献