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Interpretation of caesium-137 profiles in lacustrine and other sediments: the role of catchment-derived inputs 总被引:2,自引:0,他引:2
The caesium-137 profiles obtained in many investigations which have attempted to use caesium-137 measurements as a means of assessing the rate of accumulation of recent lake sediments, have not conformed to the classic shape expected from the record of fallout input. Such deviations have been accounted for in terms of post-depositional mobility of the caesium-137 input (e.g. bioturbation) and delayed inputs from the drainage basin. There have, however, been few attempts to determine the likely character of the drainage basin input and to analyse the role of such inputs in influencing the precise form of the caesium-137 profile. This paper presents the results of an attempt to employ existing knowledge concerning the behaviour of caesium-137 in soils and the processes of sediment mobilization to predict the likely form of the record of caesium-137 input to a lake or river floodplain from its drainage basin. The influence of this input on the profile shape will depend on the relative importance of the atmospheric fallout to the lake or floodplain surface and the drainage basin input to the total caesium-137 inventory in the sediment core, and on the land use and sediment sources in the drainage basin. By incorporating the drainage basin input into a simple model of caesium-137 accumulation in lake and floodplain sediments, it was possible to account for the profile shapes measured in four cores investigated by the authors and therefore to verify their utility for assessing rates of sediment accumulation. 相似文献
84.
《Comptes Rendus Palevol》2018,17(6):399-412
Camí de Can Grau is one of the most important Neolithic necropolises of the “Pit Burials” horizon (North-East of the Iberian Peninsula. Late fifth–early fourth millennia cal BC), because of its large number of graves. However, the number of buried individuals and the type of grave goods of the site have some peculiarities suggesting that could be one of the last manifestations of this horizon. For proving that, a radiocarbon dating programme and some statistical analysis were carried out so as to determine its chronology. The results are discussed regarding the duration of the necropolis, the degree of contemporaneity between graves and grave goods and the number of buried individuals. Moreover, chronological relationships with other similar contexts of the same horizon and located in other regions are presented. This study goes beyond a purely local research, as it proposes a method for addressing the chronology of funerary contexts. 相似文献
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Pattern and timing of evolutionary divergences among hominoids based on analyses of complete mtDNAs 总被引:11,自引:0,他引:11
Ulfur Arnason Anette Gullberg Axel Janke Xiufeng Xu 《Journal of molecular evolution》1996,43(6):650-661
We have examined and dated primate divergences by applying a newly established molecular/paleontological reference, the evolutionary separation between artiodactyls and cetaceans anchored at 60 million years before present (MYBP). Owing to the morphological transformations coinciding with the transition from terrestrial to aquatic (marine) life and the large body size of the animals (which makes their fossils easier to find), this reference can be defined, paleontologically, within much narrower time limits compared to any local primate calibration marker hitherto applied for dating hominoid divergences. Application of the artiodactyl/cetacean reference (A/C-60) suggests that hominoid divergences took place much earlier than has been concluded previously. According to a homogenous-rate model of sequence evolution, the primary hominoid divergence, i.e., that between the families Hylobatidae (gibbons) and Hominidae, was dated at 36 MYBP. The corresponding dating for the divergence betweenPongo (orangutan) andGorilla-Pan (chimpanzee)-Homo is 24.5 MYBP, that forGorilla vsHomo-Pan is 18 MYBP, and that forHomo vsPan 13.5 MYBP. The split between Sumatran and Bornean orangutans was dated at 10.5 MYBP and that between the common and pygmy chimpanzees at 7 MYBP. Analyses of a single gene (cytochromeb) suggest that the divergence within the Catarrhini, i.e., between Hominoidea and Old World monkeys (Cercopithecoidea), took place >40 MYBP; that within the Anthropoidea, i.e., between Catarrhini and Platyrrhini (New World monkeys), >60 MYBP; and that between Anthropoidea and Prosimii (lemur), 80 MYBP. These separation times are about two times more ancient than those applied previously as references for the dating of hominoid divergences. The present findings automatically imply a much slower evolution in hominoid DNA (both mitochondrial and nuclear) than commonly recognized. 相似文献
87.
Comparison of the complete mitochondrial DNA (mtDNA) of the high-Arctic ringed seal (Phoca hispida) and the sub-Arctic harbour (P. vitulina) and grey (Halichoerus grypus) seals shows that they are genetically equidistant from one another. We relate the evolutionary divergence of the three species
to expanding glaciation in the Arctic Basin and establish, in conjunction with mtDNA data, a standard reference for calibration
of recent divergence events among mammalian taxa. In the present study, we apply the “Phoca standard” to the dating of divergences within the hominid phylogenetic tree. After determining the relative rates of substitution
over all mitochondrial protein-coding genes in the different evolutionary lineages, we estimate that humans and chimpanzees
diverged from each other 6.1 Mya (95% confidence limits: 5.2–6.9 Mya). The corresponding lower-limit divergence between common
chimpanzee,Pan troglodytes, and pygmy chimpanzee,P. paniscus, occurred 3 (2.4–3.6) Mya, and the primary split within theP. troglodytes complex 1.6 (1.3–2.0) Mya. The analyses suggest that the split betweenGorilla andPan/Homo occurred 8.4 (7.3–9.4) Mya. They also suggest thatPongo (orangutan) and the lineage leading to gorillas, chimpanzees, and humans diverged 18.1 (16.5–19.6) Mya. The present analysis
is independent of the hominid paleontological record and inferential morphological interpretations and thus is a novel approach
to the lower-limit dating of recent divergences.
Correspondence to: U. Arnason 相似文献
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贵州盘县大洞遗址年代位置初探 总被引:6,自引:5,他引:1
本文报道了贵州盘县大洞16个新生碳酸岩样铀系年代,洞厅前区偏北侧的表面钙板在距今~13万年前形成,该地段因此不存在晚于中更新世的文化堆积,发掘区堆积之上的第二钙板层的生成年代为距为~20万年,若以此速率类推,形成厚~20米的大洞堆积所经历的时间跨度可能较大,有2棵小石笋端的年代为~33万年,可代表其延伸钙板下伏堆积所含石制品的最小年龄,上述年代界线表明,大洞中迄今已知贵州最古老,居住时间最长的人类 相似文献
90.