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131.
Palaeoenvironmental DNA (PalEnDNA) is defined as ancient DNA (aDNA) originating from disseminated genetic material within palaeoenvironmental samples. Sources of PalEnDNA include marine and lake sediments, peat, loess, till, ice, permafrost, palaeosols, coprolites, preserved gut contents, dental calculus, tephras, and soils as well as deposits in caves/rockshelters and at archaeological sites. PalEnDNA analysis provides a relatively new tool for Quaternary and archaeological sciences and its applications have included palaeoenvironmental and palaeodietary reconstructions, testing hypotheses regarding megafaunal extinctions, human–environment interactions, taxonomic studies, and studies of DNA damage. Because PalEnDNA samples comprise markedly different materials, and represent wide‐ranging depositional and taphonomic contexts, various issues must be addressed to achieve robust, reproducible findings. Such issues include climatic and temporal limitations, the biological origin and state (free versus bound) of PalEnDNA, stratigraphic reliability, sterile sampling, ability to distinguish modern from aDNA signals, DNA damage and PCR amplification, DNA extraction methods, and taxonomic resolution. In this review, we provide a non‐specialist introduction to the use of PalEnDNA for Quaternary and archaeological researchers, assess attributes and limitations of this palaeoenvironmental tool, and discuss future prospects of using PalEnDNA to reconstruct past environments.  相似文献   
132.
广西田林浪平地区晚石炭世生物礁古生态特征   总被引:1,自引:0,他引:1  
广西田林县浪平地区发育了几处黄龙期生物格架礁。这些发育在海百合碎屑滩上的礁体规模普遍不大,造礁和附礁生物种类多样,礁生物群落成熟度低,造礁方式单一,具有斑块式分布特点。浪平地区黄龙期点礁是在缺乏全球性主要后生骨架造礁动物的背景下发育的,没有明显优势造礁生物出现;点礁受研究区内大规模发育的碎屑滩影响显著,成礁环境多变、高能水体与碎屑选择作用明显、固结和硬质基底分布不广泛、水体能量频繁变化与适应环境的海百合繁盛、藻类在研究区内不发育,这些使得浪平地区点礁具有典型的"碎屑滩点礁模式"特征;造礁生物的生态特点对点礁的具体面貌具有重要影响。晚石炭世碎屑滩后生动物骨架点礁的发现,有助于进一步加强生物礁古生态系统研究。  相似文献   
133.
An incomplete sternum and imprints of a right part pelvis and an associated left femur from the uppermost Palaeocene/lowermost Eocene (Fur Formation) of Denmark are assigned to the extinct palaeognath bird order Lithornithiformes Houde 1988, and to the single described family thereof, the Lithornithidae. Morphological features indicate that both individuals were adult birds, smaller than Lithornis cf. nasi, which is represented by an incomplete humerus from the largely contemporaneous, marine Olst Formation in Denmark, and corresponding in size to the smallest known lithornithid, Lithornis hookeri. Lithornithiformes, common in the Palaeocene and Eocene of North America and Europe, were terrestrial birds capable of flight whose remains are often found in aquatic sediments. Both the depositional environment in which the Danish lithornithids were found, and the associated faunal components suggest that the birds were not transported by rivers. Some of the lithornithid species inhabiting NW Europe may have lived and foraged along the shores of the North Sea Basin.  相似文献   
134.
Braarudosphaera -rich sediments occur in the Turonian (nannofossil zones CC13 and UC9a) epicontinental marine sediments of the Bohemian Cretaceous Basin. This phenomenon is linked to the input of terrigenous material during deceleration of sea-level rise, or stillstand in sea level, which possibly both triggered the Braarudosphaera bigelowii bloom and reduced the diversity of the nannoplankton assemblages. The occurrence of Marthasterites furcatus and Lithastrinus septenarius probably reflects depositional conditions that were suitable for their preservation. Hence, the resultant limitations to their use as local zonal markers in the Bohemian Cretaceous Basin are discussed. The influence of the Tethyan Bioprovince is documented by the coincident first occurrences of L. septenarius and M. furcatus. The presence of the high-latitude species Thiersteinia ecclesiastica indicates penetration of Boreal biota into this depositional area within the Turonian.  相似文献   
135.
Four cores (ranging between ca. 9 and ca. 14 m in length) from Lago di Albano in Central Italy were studied for their ostracod content, as well as algal and bacterial pigments, CaCO3 and concentration of organic matter. Cores PALB 94 1E and PALB 94 1C from Site 1, located at the bottom of a steep slope at 70 m water depth, where oxygen concentration is below 6 mg l-1, spans the Holocene and the late Pleistocene until 28 kyr B.P. (calibrated age). The other cores, PALB 94 6A and PALB 94 6B taken at a depth of 30 m, where oxygen is 7--11 mg l-1, represent mainly Pleistocene deposits.Ostracod valves were found in the lowermost ca. 3 m of the sequence at Site 1, dated to ca. 28--24 kyr B.P., and throughout the sequence from Site 6 which represents the interval 23--17 kyr B.P.Candona neglecta is the dominant species in most of the levels at Site 1, whereas both C. neglecta and Cyclocypris sp. dominate during different biostratigraphic zones at Site 6. The influx of springs entering the lake at Site 1 was inferred on the basis of species of the genus Potamocypris and Ilyocypris bradyi present in the record. Wide fluctuations in species abundance and assemblages in both coring sites indicate lake-water level oscillations between 28 to 17 kyr B.P. In particular, a strong rise in water level of the order of 40 m occurred between 24 and 23 kyr B.P. Fluctuations in productivity, oxygen availability and water temperature at both sites were also reconstructed on the basis of the ostracod assemblages and the algal and bacterial pigment concentrations. The environmental reconstruction reached using ostracod remains and pigments was verified with other proxy records published elsewhere such as invertebrate remains, diatoms, magnetic properties, etc. A synthesis of climatic reconstructions for Central and Southern Italy for the late Full Glacial is attempted on the basis of previous studies on hydrology, lithostratigraphy and palynology. Sharp fluctuations in lake palaeoproductivity/palaeoclimate recorded by invertebrate and pigment remains at both sites from Lago di Albano might be related to similar events reported in North Atlantic Full-Glacial records from marine and ice cores.  相似文献   
136.
This paper presents the study and palaeoecological analysis of fossil fish vertebrae of the Arbreda Cave (Serinyà, Girona), probably the most significant Catalan palaeolithic site. Morphological and radiographical studies were used to identify vertebrae to genus and, whenever possible, to species level. The taxa identified are: Anguilla anguilla, Barbussp., Leuciscussp., Rutilus sp., Salmo salar, Salmo trutta and Salmo sp. Species distribution at various archaeological levels provided palaeoecological data. There is a high proportion of Salmo trutta remains in the Upper Gravettian level and a sudden decrease of fossil fish bones in the Solutrean level with shouldered points. This decrease coincides with the period of lower temperatures of the Late Pleniglacial. Finally, the post-glacial terra rossa level is characterised by the absence of Salmo trutta remains. The presence of Salmo salar in Mediterranean sites has often been discussed. However, the dating of remains of this Atlantic species found in the Arbreda Cave makes it likely that these specimens were caught in Atlantic rivers on the northern Pyrennean slope and then transported to the area studied. © 1997 John Wiley and Sons, Ltd.  相似文献   
137.
Sedimentary successions provide direct evidence of climate and tectonics, and these give clues about the causes of the mass extinction around the Permian–Triassic boundary. Terrestrial Permian–Triassic boundary strata in the eastern Ordos Basin, North China, include the Late Permian Sunjiagou, Early Triassic Liujiagou and late Early Triassic Heshanggou formations in ascending order. The Sunjiagou Formation comprises cross-bedded sandstones overlaid by mudstones, indicating meandering rivers with channel, point bar and floodplain deposits. The Liujiagou Formation was formed in braided rivers of arid sand bars interacting with some aeolian dune deposits, distinguished by abundant sandstones where diverse trough and planar cross-bedding and aeolian structures (for example, inverse climbing-ripple, translatent-ripple lamination, grainfall and grainflow laminations) interchange vertically and laterally. The Heshanggou Formation is a rhythmic succession of mudstones interbedded with thin medium-grained sandstones mainly deposited in a shallow lacustrine environment. Overall, the sharp meandering to braided to shallow lake sedimentary transition documents palaeoenvironmental changes from semi-arid to arid and then to semi-humid conditions across the Permian–Triassic boundary. The die-off of tetrapods and plants, decreased bioturbation levels in the uppermost Sunjiagou Formation, and the bloom of microbially-induced sedimentary structures in the Liujiagou Formation marks the mass extinction around the Permian–Triassic boundary. The disappearance of microbially-induced sedimentary structures, increasingly intense bioturbation from bottom to top and the reoccurrence of reptile footprints in the Heshanggou Formation reveal gradual recovery of the ecosystem after the Permian–Triassic boundary extinction. This study is the first to identify the intensification of aeolian activity following the end-Permian mass extinction in North China. Moreover, while northern North China continued to be uplifted tectonically from the Late Palaeozoic to Late Mesozoic, the switch of sedimentary patterns across the Permian–Triassic boundary in Shanxi is largely linked to the development of an arid and subsequently semi-humid climate condition, which probably directly affected the collapse and delayed recovery in palaeoecosystems.  相似文献   
138.
Surface sediment, speleothems, and bat guano from two adjacent, topographically different cave sites in eastern Spain have been studied palynologically to elucidate the potential of cave sediments for palaeoenvironmental reconstruction. A cave opening with a large entrance and constant width presented far fewer problems of alteration in the pollen assemblages than a sac‐like cave opening with a constricted entrance. Pollen concentration is linked primarily to the amount of pollen input rather than to the result of post‐depositional alteration. Sampling should be undertaken away from parietal and rear areas and avoiding moisture zones. Lateral differences in the pollen spectra indicate that sampling should be on the basis of a multiple‐profile approach and selection of dry rather than wet sediments. If these procedures are followed, within‐cave sediments can realistically reflect not only local but also regional vegetation of the site. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   
139.
A sudden and sharp rise in the 14C content of the atmosphere, which occurred between ca. 850 and 760 calendar yr BC (ca. 2750–2450 BP on the radiocarbon time-scale), was contemporaneous with an abrupt climate change. In northwest Europe (as indicated by palaeoecological and geological evidence) climate changed from relatively warm and continental to oceanic. As a consequence, the ground-water table rose considerably in certain low-lying areas in The Netherlands. Archaeological and palaeoecological evidence for the abandonment of such areas in the northern Netherlands is interpreted as the effect of a rise of the water table and the extension of fens and bogs. Contraction of population and finally migration from these low-lying areas, which had become marginal for occupation, and the earliest colonisation by farming communities of the newly emerged salt marshes in the northern Netherlands around 2550 BP, is interpreted as the consequence of loss of cultivated land. Thermic contraction of ocean water and/or decreased velocity and pressure on the coast by the Gulf Stream may have caused a fall in relative sea-level rise and the emergence of these salt marshes. Evidence for a synchronous climatic change elsewhere in Europe and on other continents around 2650 BP is presented. Temporary aridity in tropical regions and a reduced transport of warmth to the temperate climate regions by atmospheric and/or oceanic circulation systems could explain the observed changes. As yet there is no clear explanation for this climate change and the contemporaneous increase of 14C in the atmosphere. The strategy of 14C wiggle-match dating can play an important role in the precise dating of organic deposits, and can be used to establish possible relationships between changing 14C production in the atmosphere, climate change, and the impact of such changes on hydrology, vegetation, and human communities.  相似文献   
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