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1.
三江并流是反映地球演化主要阶段的杰出代表,区内保存着反映特提斯演化不同阶段和喜马拉雅期陆内造山阶段留下的丰富的地质遗迹,这些地质遗迹为解读三江并流地壳演化的历史提供了重要的依据。有关资料表明,三江并流是与青藏高原和横断山脉一起发育成长起来的,它们均经历了特提斯的演化,并且都是印度板块与欧亚板块强烈碰撞造山作用的产物。本文比较详细地介绍了横断山脉的形成演化过程及其与青藏高原形成演化之间的关系。 相似文献
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Eugne Morin 《Geoarchaeology》2006,21(6):541-565
This study explores the stratigraphic evolution of archaeological assemblages in faunalturbated sites. These sites are sometimes described as having limited archaeological value because of varying degrees of occupation mixing. It is argued here that the vertical distribution of assemblages is predictable in faunalturbated contexts. Understanding this vertical evolution may lead to a better assessment of the archaeological potential of a cultural sequence. In faunalturbated soils, the stratigraphic evolution of the assemblages is largely dictated by faunal activity. Tunneling by small animals tend to “sink” cultural remains through the deposits. Although objects sink at a relatively fast pace near the surface, the process slows down as the objects reach the bottom of the biomantle where the sediments are more compact. This process affects the shape of the artifact vertical distribution. The analysis of a multicomponent site from southern Québec is used to model how assemblages may evolve temporally in faunalturbated settings. At Station 3‐avant, the stratigraphic distribution of the cultural remains appears to evolve from an upward‐skewed distribution to a bottom‐skewed distribution through time. This evolution is interpreted to result from the fact that objects are often too large and/or heavy to be moved upward by the pedofauna. In situations in which this stage of stratigraphic evolution is not yet reached, enough information about temporal successions may be retained for the site to be useful for investigating diachronic change. This may prove invaluable in regions in which faunalturbated sequences are common. © 2006 Wiley Periodicals, Inc. 相似文献
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Morphology and internal structure of sand shoals and sandbanks off the Dorset coast, English Channel 总被引：1，自引：0，他引：1
The morphology and internal structure of sand shoals and sandbanks around a coastal headland (Portland Bill, southern UK) are described on the basis of sidescan sonar and high-resolution seismic data sets. Morphological and architectural evidence, combined with the spatial distribution and nature of the bedrock surface, indicates that the evolution of these deposits, especially the sandbanks, may not only be hydrodynamically controlled but also morphologically controlled. The internal structure of the sand shoals reveals a simple pattern of clinoforms dipping in the same direction as their steeper profile. In contrast, the internal structure of the sandbanks reveals that their lower seismic units consist of a sedimentary core interpreted as the remains of a lowstand deposit or an early stage of the bank development under different prevailing hydrodynamic conditions. The present morphology of the sandbanks is represented by upper seismic units characterized by large-scale sandwave foresets dipping at 6–8°. The nature and morphology of the bedrock surface may also influence the development of sandbanks in some cases. For example, to the west of Portland Bill, the morphology of the bedrock surface (basal reflector) restricts the development of the Portland Bank. This information may explain the asymmetric evolution of sandbanks around Portland Bill. 相似文献
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Cai J.T. Ladd 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(3):269-283
Centuries of coastal development has led to the loss of saltmarsh extent worldwide. As marshes are shrinking, scientific understanding of marsh expansion and erosion processes is growing. Coastal managers are also recognising the importance of marshes for flood protection, carbon sequestration, and pollutant filtering. Considerable effort is now being made to conserve saltmarshes. However, the rapid integration of science in policy remains an obstacle for ensuring successful conservation outcomes. This review explores how advances in the understanding of coastal dynamics, and the evolution of coastal management thinking, are shaping saltmarsh conservation policy in Great Britain. Saltmarsh management has shifted from reclamation, to protection, to restoration throughout the 20th and 21st centuries as calls for nature conservation grew and the importance of ecosystems in coastal erosion risk management became apparent. Studies have revealed that marshes cycle between expansion and erosion phases as part of their natural evolution, governed by processes acting across a range of spatial and temporal scales. Understanding which processes drive long-term marsh change provides an opportunity for coastal managers to undertake targeted intervention for positive conservation outcomes. The inherently dynamic nature of marshes also raises significant challenges in forecasting the long-term value provided by a given marsh. Challenges remain in the monitoring and management of sediment supply and transport, and the effective engagement with stakeholders during habitat protection and creation schemes, which are key to achieving marsh conservation goals. 相似文献
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近20年来, 古DNA研究技术和方法已迅猛发展.目前从古人类残骸中获取DNA序列, 进而讨论人类的演化、亲缘关系和迁移成为分子人类学的一个重要方向.本研究对采自陕西临潼仰韶文化6 000多年前的姜寨遗址第一期和第二期文化层中的古人类残骸进行古DNA提取、扩增和测序, 获得了169 bp的线粒体高变控制区Ⅰ的古DNA片段, 与现代西安人同源性序列有2个位点的突变.另外, 通过在不同实验室进行重复性实验和系统发育分析等方法详细地论证了所获得的DNA序列的可靠性.在所研究的6个姜寨遗址样品中有3个样品获得古DNA序列, 古DNA的提取成功率为50%, 高于一般的古DNA研究材料的提取率, 说明姜寨遗址的人类残骸是研究古DNA的理想材料, 为今后从分子水平上研究姜寨遗址及其他同地区仰韶文化遗址的古人类墓葬及中国古人类分子演化关系奠定了基础. 相似文献
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The structural evolution of the Late Precambrian and Early to Middle Paleozoic complexes is considered for the southern part of the Uraltau Zone and its extension in the Ebeta Antiform, as well as for the northeastern and northwestern frameworks of the ophiolitic Khabarny Allochthon, where the Late Precambrian and Paleozoic complexes of the continental margin in combination with ophiolites are drawn together in packets of tectonic nappes. The formation of the regional structure took place during several stages in various geodynamic settings. Five deformation stages have been recognized in the regional structural evolution from new data on mesostructural parageneses, which consist of folds that developed within outcrops and their relationships in rocks differing in age. The first stage is related to the Late Precambrian Timanian, or Cadomian Orogeny, and four subsequent deformation stages characterize Paleozoic tectonic evolution of the region. The geodynamic nature of the second stage remains unknown; the third stage is related to overthrusting of ophiolites in the Early Devonian; the fourth stage of deformations marks Late Paleozoic continental collision. The fifth stage of postcollisional strike-slip deformations completes the regional structural evolution. 相似文献
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怒江、澜沧江、金沙江地区构造与成矿作用 总被引：6，自引：0，他引：6
据野外调查资料,将怒江、澜沧江、金沙江地区划为三个大的构造单元,即扬子板块西缘、印度板块北东缘和处于上两者之间的交接带或转换构造带。本文以大地构造格架为背景,结合成矿建造与构造变动的内在联系,在本区划出11个主要金属成矿带。追溯构造演化与成矿作用关系划出6大成矿阶段,即前特提斯阶段、古特提斯阶段、古特提斯碰撞阶段、碰撞后继阶段、中特提斯阶段及陆内强挤压阶段。其中以第四、第六两个成矿阶段最重要。本文还着重描述了构造运动形式及构造变形与成矿作用的关系,解剖了川西呷村含金富银多金属矿、藏东玉龙斑岩铜矿、滇西金顶铅锌矿、哀牢山带金矿等大型典型矿产形成的构造地质背景。 相似文献
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《International Geology Review》2012,54(10):1183-1190
We consider the evolution of Albian-Cenomanian floras of the Northeast USSR for both coal-bearing and "non-coal" deposits, taking the evolution of paleofloras in single-facies (coal-bearing) deposits as a base. In general, the taphofloras have been assigned to the sequence from which the plant remains were collected. During Albian-Cenomanian time the angiosperms migrated from higher to lower levels. The observed decrease in the role of angiosperms during Cenomanian (Arkagala) time after their "expansion" during Albian time (in the Toptan and Arman suites) is explained by their establishment at different topographic levels. We show parallel increase in the role of conifers and angiosperms in the floras from the coal-bearing deposits from the Albian to the Cenomanian. A temperature minimum occurred during Arkagala time. It is likely that old, pre-Albian angiosperms may be found in sediments of the intermontane basins. In analyzing the level of evolution of the floras on the Early - Late Cretaceous boundary, especially the angiosperms, one must take into account the facies in which they are present. —Authors. 相似文献
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Louis Arbez Aurelien Royer Danielle Schreve Remi Laffont Serge David Sophie Montuire 《第四纪科学杂志》2021,36(2):224-238
Lemmus and Myopus are two lemming species with distinct habitat requirements but which show very similar dental morphologies. They are thus extremely difficult to distinguish from one another in the fossil record on the basis of their dental remains, leading to poor understanding of the palaeobiogeographical evolution of Myopus as well as inaccurate palaeoenvrionmental reconstructions. Currently, the presence of Myopus in the fossil register from the Pleistocene is still debated and no firm occurrence of this lemming in western Europe has yet been confirmed for the Late Pleistocene. In this paper, we used geometric morphometrics on modern material to establish morphological differences between Lemmus and Myopus teeth (first lower and third upper molars). Morphological data were then used to build a robust linear discriminant model able to confidently classify isolated teeth of these two genera, and finally, linear discriminant models were used on fossil remains of Lemmus/Myopus from two Late Pleistocene archaeological/palaeontological sites (Grotte des Gorges and Gully Cave). This study demonstrates, for the first time, the presence of Myopus schisticolor in west European Late Pleistocene sites between the end of Marine Isotope Stage 3 and the beginning of the Holocene, during climatic events that favoured the development of taiga forest of birch and pine in these regions. 相似文献
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Nicolas Rolland Isabelle Larocque Pierre Francus Reinhard Pienitz 《Quaternary Research》2009,72(1):27-37
This study presents the Late-Holocene evolution of a northern Southampton Island (Nunavut, Canada) lake, using fossil chironomids supported by sedimentological evidences (XRF, grain size and CNS). All proxies revealed a relatively stable environment during the last millennium with short-lived events driving changes in the entire lake ecosystem. The chironomid-based paleotemperatures revealed variations of significant amplitude coincident with changes in the sediment density and chemical composition of the core. Higher temperature intervals were generally correlated to lower sediment density with higher chironomid concentration and diversity. Higher temperatures were recorded from cal yr AD 1160 to AD 1360, which may correspond to the Medieval Warm Period. Between cal yr AD 1360 and AD 1700, lower temperatures were probably related to a Little Ice Age event. This study presents new information on the timing of known climatic events which will refine our knowledge of the paleoclimate and climatic models of the Foxe Basin region. It also provides a new framework for the evolution of such freshwater ecosystems under the “Anthropocene” and underlines the importance of including sedimentological proxies when interpreting chironomid remains as this combined approach provides an extended overview of the past hydrological and geochemical changes and their impacts on lake biota. 相似文献
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V. N. Sergeev M. A. Semikhatov M. A. Fedonkin A. F. Veis N. G. Vorob’eva 《Stratigraphy and Geological Correlation》2007,15(2):141-160
Expounded in this work are the results of critical consideration of published and original data on biologic nature and appearance chronology of different groups of Archean and Lower Proterozoic (3.5–1.65 Ga) paleontological remains known from geological record. Conclusions are substantiated by morphological analysis of structurally preserved microfossils, their facies distribution, and by inferable genesis and principal evolutionary trends of Archean stromatolites. A special attention is paid to variations of organic and carbonate carbon isotope composition in sedimentary successions with paleontological remains and to recent information about discovered, most ancient biomarkers of large groups of organic world. As a result of this approach, a detailed model of Precambrian organic world evolution is suggested. 相似文献
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INTRODUCTIONPethenreefsarewidelydistributedinSouthetna,espeCiallyinsouthernGulzhouandnorth~ternGUanghProvince,wherenamusreefsoccurandareWellexposed.TheUpperPenmanreefinZiyUnChamy,southernG~uisoneofthehotdevelopedandexposedhairierreefsinthearea(WangandFan,1994).DuetoitSspedaltectonic--geographicpositionandcompletefactesbeltd~iation,thebatherreefshavearousedagreatinterestamonggeologistS.SpstelnaticinvestigationandstudyonthebarrierreefshaveaammadebymanygeologistSsince197ds(LiuandGao,… 相似文献
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A recent test has shown that planktonic foraminifera, living for at least part of their life in the surface waters of the oceans, are limited to certain temperature zones. Since their evolution has been relatively slow, their calcareous remains, which accumulate on the deep-sea floor, can be analysed in samples taken from cores and temperature oscillations can be traced into the past by the percentage of warm, temperate and cold forms. It has been demonstrated that a count of a thousand specimens in each sample is all that is necessary to obtain these results. 相似文献
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高喜马拉雅结晶岩系中广泛发育规模不等、形态各异的混合岩,是研究地壳部分熔融作用的天然实验室。尽管观察表明,藏南许多混合岩与淡色花岗岩具有一定的时空联系,但混合岩与淡色花岗岩是否具有成因联系还存在较大的争议。本文对藏南亚东地区的混合岩中进行了野外地质、岩相学、岩石地球化学和年代学等研究。研究结果表明,亚东混合岩主要是部分熔融作用的产物,具有(近)原地熔融的特征,熔融方式以白云母和黑云母脱水熔融为主,并叠加了分离结晶作用。亚东混合岩与淡色花岗岩在成因上具有紧密联系。相关认识为建立造山带构造演化模型提供新的信息。 相似文献
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MORTEN MELDGAARD OLE BENNIKE 《Boreas: An International Journal of Quaternary Research》1989,18(4):359-366
A caribou antler from Kap København in Peary Land has been radiocarbon dated at > 40,000 B.P. A corresponding infinite date was obtained on allochthonous plant and animal remains, including five lemming droppings from Skalhøjene in Warming Land. These remains are indicative of high arctic conditions much like the present environment of the region. Because the caribou antler and the remains from Skalhojene point to biotic and climatic conditions no more severe than modern conditions, an interglacial age is suggested, and we propose that they belong to the Sangamonian Stage. The finds indicate that evolution of high arctic subspecies such as Rangifer tarandus pearyi and Dicrostonyx torquatus groenlandicus probably took place in pre-Wisconsinan times. It is unlikely that caribou and lemming survived in North Greenland during the last full glacial period. They probably re-immigrated in the early Holocene. 相似文献
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《Proceedings of the Geologists' Association. Geologists' Association》2019,130(3-4):463-472
This paper reviews recent studies of the seabed offshore from the Jurassic Coast and discusses their significance for understanding landforms of the World Heritage Site’s Setting as well as adding to understanding of the structures exposed in the cliffs. The processes of coastal formation as sea-levels rose and fell during the Pleistocene and in the recent post-glacial period are critical for this as they reveal the landforms which preserve former shorelines. Detailed surveys of the seabed provide evidence of the low slope of much of this seabed and so enhance the potential to interpret older terrestrial landforms which have been attributed to uplift of former sea beds. Considering both the seabed and the coast from the Pleistocene to the Anthropocene means that it is possible to assess the human impact on these landforms and processes, as well as the natural timescale within which changes occur. The paper describes the seabed geomorphology, relating this, where appropriate, to both the coastal landforms and the exposed structures. Current interpretations of the seabed features and their implications for our understanding of the recent evolution of the Site and Setting are explored. The features of the coast and adjacent sea bed at different phases of the changing coastal environment are discussed to the extent that the available evidence makes this possible, but for much of the area this remains speculative. 相似文献
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Luis Gómez‐Orellana Pablo Ramil‐Rego Ernestina Badal Yolanda Carrión Marco Castor Muñoz Sobrino 《Boreas: An International Journal of Quaternary Research》2014,43(4):792-806
This paper presents the results of pollen and charcoal analyses carried out in the sedimentary formation of Ponta da Passadeira, south of the Tejo River estuary, Portugal. The data provide information regarding the evolution of the coastline and ecosystem of the estuary during the mid and late Holocene. The study focuses on a group of upright woody fossilized tree remains that, together with those identified earlier by García‐Amorena et al. (2007), form part of the fossil forest of Ponta da Passadeira. Eight remains were identified as Pinus pinaster, four as Pinus pinea and one as Pinus sp. Two specimens of these species were dated to 6523 and 5805 cal. a BP. Pollen analysis was undertaken in a clay layer located at the same point as the fossil forest, which is currently below sea level; the base of the clay layer was dated to 4906 cal. a BP. The pollen spectra reflect the dynamics of the vegetation that grew on this deposit, whereas the sporopollinic input masks the contribution of the regional vegetation. Wood charcoal remains recovered at an adjacent Final Neolithic settlement were also analysed, and a Pinus sp. specimen was radiocarbon dated to 5050 cal. a BP. The correlation amongst the three records provides key ecological markers for the understanding of the evolution of coastline ecosystems, and helps to clarify and understand the Holocene sea rise on the Atlantic seaboard of Iberia. The geographical location of Ponta da Passadeira is strategic because it enables a more clear definition of the configuration of landscapes that show an inflection point in this area of central Portugal. 相似文献
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寒区环境中的古DNA分子 总被引：1，自引：0，他引：1
寒区埋藏环境常年处于负温条件下,土壤冻结或冰的形成过程产生封闭作用,可以隔离造成埋藏生物遗体同DNA氧化分解的氧气之间的接触.由于液态水含量极大地减少和冰胶结作用,使得主要依赖于液态水而发生的生物大分子的化学分解以及生物降解反应作用减慢,有机体没有成岩过程中降解以及水解作用,从而使古DNA分子可以得到较好的保存.目前绝大多数关于古DNA研究的重要成果所使用生物材料均来自寒区环境,最为引人注目的有关猛犸象、棕熊和企鹅化石古DNA的研究.这些研究分别从个体、种群和同一种群在不同时间尺度上描绘了它们与现代生物种之间的亲缘关系、过去发生的生物迁移和空间隔离以及特定生物分子水平上的时间演化.从目前来看,大量的生物标本很好地保存在那里,以至于单一考贝基因都可以获得,因此是获取古DNA并获得相应遗传信息的理想地区. 相似文献