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1.
Stereospondyls survived the Permo-Triassic extinctions in a refuge probably located in the landmass that nowadays comprises Australia. Subsequently, they radiated to other parts of Pangaea, reaching their highest distribution and diversification during the Early Triassic. An incomplete interclavicle from the Caturrita Formation represents their first record in the Upper Triassic of Brazil. Previously, Upper Triassic South American stereospondyls were restricted to Argentina. This new record reinforces a former hypothesis that suggests the presence of a more diverse stereospondyl fauna in South America during the Late Triassic than previously assumed. Additionally, the presence of a stereospondyl and a phytosaur in the Caturrita Formation reinforces the hypothesis of a change to more humid climatic conditions in the Paraná Basin during the Upper Triassic. The record of Early Triassic stereospondyls in South America suggests that they first colonized Brazil and/or Uruguay, spreading from South Africa during the Early Triassic, subsequently reaching Argentina. Up till now, there is no record of Middle Triassic stereospondyls in either Argentina and Brazil, probably due to either taphonomic bias or insufficient prospecting. Despite the lack of direct evidence, one should not dismiss an earlier stereospondyl colonization of Argentina still during the Early or Middle Triassic. 相似文献
2.
Kay-Christian Emeis David M. Anderson Heidi Doose Dick Kroon Detlef Schulz-Bull 《Quaternary Research》1995,43(3)
Arabian Sea sediments record changes in the upwelling system off Arabia, which is driven by the monsoon circulation system over the NW Indian Ocean. In accordance with climate models, and differing from other large upwelling areas of the tropical ocean, a 500,000-yr record of productivity at ODP Site 723 shows consistently stronger upwelling during interglaciations than during glaciations. Sea-surface temperatures (SSTs) reconstructed from the alkenone unsaturation index (UK′37) are high (up to 27°C) during interglaciations and low (22-24°C) during glaciations, indicating a glacial-interglacial temperature change of >3°C in spite of the dampening effect of enhanced or weakened upwelling. The increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times, whereas the difference in SSTs must be unrelated to upwelling and to the summer monsoon intensity. The winter (NE) monsoon was more effective in cooling the Arabian Sea during glaciations then it is now. 相似文献
3.
The Ediacaran Period takes its name from the fossils of the Ediacara biota, which represent the first appearance of large and diverse assemblages of organisms in the fossil record. Although the global record of these distinctive body fossils is now well known, a previously unrecognized megascopic organic record of textured organic surfaces (TOS) occurs in the Ediacara biota. However, TOS is also a feature over a wider range of paleoenvironmental settings, where body fossils are unknown, in Ediacaran siliciclastic successions that have been studied in Australia, Namibia and western North America.Paleoecological analysis of successive bedding planes of strata from the late Ediacaran Rawnsley Quartzite in the Flinders Ranges of South Australia, reveals that TOS represent the most common organic features in bedding-surface assemblages of the Ediacara biota. The TOS consist of preserved, patterned assemblages of textured organic mats, fibers and simple tubular body fossils. Complex Ediacara body fossils while striking for their distinctive body plans, and dominating some of the beds, are relatively minor components of combined overall surface area. Many elements of TOS have previously been miss-diagnosed as trace fossils, which are in practice limited to two or at most three morphotypes that indicate the presence of Bilateria. Although TOS represent a simpler grade of organismic construction than discrete and more complex Ediacara body fossils, they were preserved in a similar manner. Marked variability in all components of the biota between successive surfaces suggests that Ediacara ecologies fluctuated at short intervals despite an apparently consistent sedimentary regime. 相似文献
4.
R.J. Bailey 《地学学报》1998,10(4):222-230
An alternative approach to stratigraphic analysis is proposed. It takes as its starting point the simple general characteristics of the stratigraphic record and the complex, chaotic behaviours of the systems that combine to generate this record. In this context, Smith’s Stratigraphy Machine (SM) concept is developed. The SM is a chaotic global system, combining the operations of the atmosphere, hydrosphere, lithosphere and asthenosphere, which everywhere tends to self-organize towards a critical state in which continuous loading of the system with rock waste, over time, is balanced by the unloading that creates the record. The outputs of the SM are simple and nonscale dependent in character, with residence times in the record ranging from a second, or less, to 1 billion years. However, only those long-lived in the human time-frame are judged to be of stratigraphic significance; and the range of residence times entails that the stratigraphic record embraces a similar range of hiatuses, or gaps. The value of the SM, as developed here, is that it can be regarded as a meta-stratigraphic concept that transcends the usual frameworks of stratigraphic classification and interpretation and thus allows a reappraisal of significant features of the record such as its perceived cycles and sequences. There are three outcomes of this meta-stratigraphic analysis. First, the geometric units employed in sequence stratigraphy are components of a self-similar series of essentially lenticular bodies, with no fundamental characteristics to distinguish them from larger and smaller bodies in the generally self-similar series. Secondly, the interactions and feedbacks within the SM are so complex, and its outputs so repetitive in general character, that it is dangerous to assume that any perceived cyclicity provides an unambiguous chronicle of process cyclicity, whether eustatic, climatic or tectonic. The classic coarsening upward cyclicity of shallow marine facies can, for example, be viewed solely as the outcome of the lack of phasing between the chaotic behaviours tending to unload the SM and those creating accommodation space. Finally, the meta-stratigraphic approach reinforces the view that, in the absence of demonstrable stratal continuity, chronostratigraphic correlation must continue to rely on sample-based, mainly biostratigraphical, methods, rather than sequence stratigraphy. 相似文献
5.
David R. Bridgland Mark J. White 《Boreas: An International Journal of Quaternary Research》2014,43(2):543-555
With the adoption of an ‘expanded chronology’ for the Middle Pleistocene, based on the greater number of warm and cold episodes evident in the marine oxygen isotope record from deep ocean cores, has come the recognition of a meaningful progression of artefact types, something that could not be achieved with reference to the previous ‘compressed chronology’. In Britain, at least, it has been established that Levallois knapping techniques appeared in MIS 9–8, that bout coupé handaxes are indicative of MIS 3 and, rather more tentatively, that assemblages with twisted ovate handaxes in significant numbers represent MIS 11 occupation. Added to these key markers, it is now possible to suggest that further tool types occur preferentially in deposits of particular age: assemblages with significant proportions of cleavers and ‘ficron’ handaxes appear to be correlated with deposits formed at around the time of the MIS 9 interglacial. This newly recognized patterning within the Lower and Middle Palaeolithic record differs markedly from the previous use, in the mid‐20th century, of archaeological typology as a means of dating Pleistocene sequences, which was based on a relative refinement of tool making that is now recognized to be unrelated to age. Indeed, the authors would wish to emphasize that, even with reference to the new scheme presented here, the archaeological record should only be seen as dating evidence ‘of last resort’. 相似文献
6.
The first fossil record of the Compsocidae, Burmacompsocus perreaui gen. et sp. nov., is described from Late Albian Burmese amber. Its strong similarity to the two extant compsocid genera suggests a remarkable morphological stability within this group of 100 Ma. This family, now known only in Central America, was certainly more widespread in the past. 相似文献
7.
The stratigraphy of the Pedwardine inlier of Precambrian (Longmyndian), Tremadoc, and what are now shown to be upper Llandovery rocks is described. The inlier is surrounded by Silurian rocks, including upper Llandovery (two very small areas), Wenlock, Ludlow and Přídolí (Red Downton Formation). The Ludlow rocks provide a distal record of the mass movement recorded more fully in the Wigmore Rolls area to the east. The Pedwardine area lies along the Church Stretton Fault Zone. Though ill-exposed, it shows evidence of the history of faulting, including thrusting. © 1997 John Wiley & Sons, Ltd. 相似文献
8.
General circulation models (GCMs) use the laws of physics and an understanding of past geography to simulate climatic responses. They are objective in character. However, they tend to require powerful computers to handle vast numbers of calculations. Nevertheless, it is now possible to compare results from different GCMs for a range of times and over a wide range of parameterisations for the past, present and future (e.g. in terms of predictions of surface air temperature, surface moisture, precipitation, etc.). GCMs are currently producing simulated climate predictions for the Mesozoic, which compare favourably with the distributions of climatically sensitive facies (e.g. coals, evaporites and palaeosols). They can be used effectively in the prediction of oceanic upwelling sites and the distribution of petroleum source rocks and phosphorites. Models also produce evaluations of other parameters that do not leave a geological record (e.g. cloud cover, snow cover) and equivocal phenomena such as storminess. Parameterisation of sub-grid scale processes is the main weakness in GCMs (e.g. land surfaces, convection, cloud behaviour) and model output for continental interiors is still too cold in winter by comparison with palaeontological data. The sedimentary and palaeontological record provides an important way that GCMs may themselves be evaluated and this is important because the same GCMs are being used currently to predict possible changes in future climate.
The Mesozoic Earth was, by comparison with the present, an alien world, as we illustrate here by reference to late Triassic, late Jurassic and late Cretaceous simulations. Dense forests grew close to both poles but experienced months-long daylight in warm summers and months-long darkness in cold snowy winters. Ocean depths were warm (8 °C or more to the ocean floor) and reefs, with corals, grew 10° of latitude further north and south than at the present time. The whole Earth was warmer than now by 6 °C or more, giving more atmospheric humidity and a greatly enhanced hydrological cycle. Much of the rainfall was predominantly convective in character, often focused over the oceans and leaving major desert expanses on the continental areas. Polar ice sheets are unlikely to have been present because of the high summer temperatures achieved. The model indicates extensive sea ice in the nearly enclosed Arctic seaway through a large portion of the year during the late Cretaceous, and the possibility of sea ice in adjacent parts of the Midwest Seaway over North America. The Triassic world was a predominantly warm world, the model output for evaporation and precipitation conforming well with the known distributions of evaporites, calcretes and other climatically sensitive facies for that time.
The message from the geological record is clear. Through the Phanerozoic, Earth's climate has changed significantly, both on a variety of time scales and over a range of climatic states, usually baldly referred to as “greenhouse” and “icehouse”, although these terms disguise more subtle states between these extremes. Any notion that the climate can remain constant for the convenience of one species of anthropoid is a delusion (although the recent rate of climatic change is exceptional). 相似文献
9.
Gary Gibson Vaughan Wesson Russell Cuthbertson 《Australian Journal of Earth Sciences》2013,60(3-4):341-356
Since 1976 a number of analogue and digital seismographs, which record high frequency seismic waves in the range 4 to 20 Hz, have been installed in Victoria. These enable the detection and location of microearthquakes with Richter magnitude Ml down to less than zero. Because there are many more smaller than larger earthquakes, about 250 events are now being located in Victoria each year, compared with about 25 per year between 1960 and 1975, and an average of two per year between 1840 and 1959. Despite an uneven statewide seismograph coverage, the new instruments and new lithospheric models have led to substantial improvements in earthquake location accuracy. All Victorian earthquakes with reliable depth determinations have been found to lie within the crust, most at a depth of less than 18 km. Some very small but shallow microearthquakes have been felt or heard. The isoseismal map for such an event (of magnitude Ml 1.3) which occurred at Preston during July 1976, is given. The greater range of magnitudes now recorded permits more reliable estimates of seismicity. On average, the recurrence of earthquakes in Victoria is represented by: log10 (P) = 0.92ML —2.40, where P is the return period of an earthquake with magnitude greater than Ml in an area of 100 km square. It is suggested that attenuation of seismic wave amplitudes with distance is quite high in Victoria. 相似文献
10.
Characteristic global climatic events are employed to interpret the regional, land-based European stratigraphy. The Chinese loess record shows well expressed, continuous and reliably dated climatic signals of worldwide significance, which are well correlated with the marine oxygen isotope stratigraphy. The sequence in the surroundings of Ferdinandow in Poland plays a key role in the correlation of the European stratigraphy with the loess record and the oxygen isotope record. In particular, the complex but well-expressed Ferdinandowian Interglacial is a key marker because it shows striking similarities with the most pronounced soil complex of the last 700 ka years of the Chinese loess sequence (S5) and, by correlation, Oxygen isotope stages (OIS) 13–15. It follows that the Holsteinian Interglacial corresponds with the S4-soil and OIS 11. This appears to be confirmed by sequences deposited in the craters of the Central Massif, France. Problems of regional stratigraphical correlation in Europe persist, but is suggested that a general framework is now established. 相似文献
11.
唐古拉山冬克玛底冰川雪层中淋溶作用的初步研究 总被引：7，自引：7，他引：7
利用唐古拉山冬克玛底冰川雪坑和表层积雪样品的实测资料，初步探讨本区雪层中离子淋溶作用的特征，影响因素及其对冰芯记录的干扰。研究发现淋溶作用能够对数周至数月时间尺度的雪层记录产生“平滑”作用，但不会影响冰芯记录的长期变化趋势。 相似文献
12.
Late Quaternary climates of Australia and New Guinea 总被引：3，自引：0，他引：3
Between 60,000 and 40,000 B.P., northeastern Queensland, south New South Wales, and southeastern South Australia were drier than at present. From 40,000–30,000 B.P. a colder climate than at present is indicated from one New Guinea area. Dryness became even more accentuated in northeastern Queensland, whereas many lakes filled up in the southern mainland, probably because of increasing precipitation effectiveness there. Before the end of this period colder conditions than now were already giving rise to slope instability in the Snowy Mountains of New South Wales.The period of 25,000–15,000 B.P. saw the greatest lowering of the New Guinea treeline, reaching an extreme at 17,000 B.P. when glaciers also achieved their maximum extent. This was the time of extensive glaciation in Tasmania and small glaciers formed in the Snowy Mountains. Estimates of the lowering of mean annual temperature range from 6°–10°C. Northeastern Queensland experienced its driest Late Quaternary climate; lakes were contracting throughout the southern mainland and the final phase of substantial desert dune building took place before the period ended.In the Snowy Mountains ice retreat began before 20,000 B.P., as did the construction of clay dunes in the southern semi-arid belt, a process demanding higher temperatures. However, in New Guinea and Tasmania ice retreat and treeline rise did not begin till after 15,000 B.P. Temperatures rose rapidly and everywhere most of the ice had gone by 10,000 B.P., when some lakes filled up in southern Australia, implying an increase in absolute precipitation.In the last 10,000 years climate has been relatively stable although there are some indications that temperature and rainfall were marginally higher than now between 8000 and 5000 B.P. Since then, lake levels have oscillated; a brief, limited resumption of periglacial activity took place in the Snowy Mountains and there were small glacier advances in New Guinea. 相似文献
13.
陇西黄土高原马兰黄土划分与末次冰期气候快速变化研究 总被引：9，自引：0，他引：9
陇西黄土高原马兰黄土内存在９个弱成壤组（层），记录末次冰期内多达２２个间冰段气候的环境状况。马兰黄土中部古土壤是末次冰期大间冰段的记录，共有上、中、下３层古土壤，含１１个亚层，尤以下层古土壤发育最好，表明当时气候较温暖湿润。 相似文献
14.
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16.
We here argue the need for a multidisciplinary, integrated geophysical/geological survey across southern India and Sri Lanka, part of the largest exposed Neoproterozoic high-grade metamorphic terrain in the world. The purpose is to stimulate deep seismic profiling and other geophysical and geological investigations in order to better understand the structure, composition and evolution of a keystone of Precambrian continental crust and the role it played in the amalgamation and subsequent break-up of the Gondwana supercontinent. Of particular importance is that this lithospheric fragment records a 2 billion year long history of magmatism, sedimentation, deformation and metamorphism and now exposes at the surface rocks that once formed at depths of 30 km or more and that record unusually high metamorphic temperatures of up to 1000°C. Modern geophysical data should help to determine what lies underneath these high-T surface rocks and whether the terrain consists of structural distinct subunits separated by (now hidden) sutures. It is likely that the crustal-scale structures generated during the formation of the SGT may extend to other, now dispersed, segments of the Gondwana landmass and their identification in geophysical data will provide a fresh basis for reconstructing the process of supercontinent assemblage and break-up. 相似文献
17.
Edward B. Evenson William R. Farrand Donald F. Eschman David M. Mickelson Louis J. Maher 《Quaternary Research》1976,6(3):411-424
New evidence from recent field and seismic investigations in the Lake Michigan basin and in the type areas of the Valders, Two Creeks and Two Rivers deposits necessitates revision of late-glacial ice-front positions, rock- and time-stratigraphic nomenclature and climatic interpretations and deglaciation patterns for the period ca. 14,000–7,000 radiocarbon years B.P. The previously reported and long accepted pattern of deglaciation for the Lake Michigan basin started with a regular retreat from the Lake Border Morainic System, with a minor oscillation marked by the Port Huron moraine(s) and then an extensive Twocreekan deglaciation followed by a major (320 km) post-Twocreekan advance (Valders). However, we now record a major retreat between the times of the Lake Border and Port Huron moraines, followed by a gradual retreat from the Port Huron limit and interrupted by a minor standstill (deposition of Manitowoc Till), a retreat (Twocreekan) and a readvance (Two Rivers Till). No Woodfordian or younger readvance was as extensive as had been the preceding one. This sequence argues for a normal, climatically controlled, progressive deglaciation rather than one interrupted by a major post-Twocreekan (formerly Valderan) surge. This revision appears finally to harmonize the geologic evidence and the palynological record for the Great Lakes region. Our investigations show that Valders Till from which the Valderan Substage was named is late-Woodfordian in age. We propose the term “Greatlakean” as a replacement for the now misleading time-stratigraphic term “Valderan”. The type section and the definition of the upper and lower boundaries of the Greatlakean Substage remain the same as those originally proposed for the Valderan Substage but the name is changed. 相似文献
18.
Kenneth Cole 《Quaternary Research》1983,19(1):117-129
Seven packrat midden samples make possible a comparison between the modern and late Pleistocene vegetation in Kings Canyon on the western side of the southern Sierra Nevada. One modern sample contains macrofossils and pollen derived from the present-day oak-chaparral vegetation. Macrofossils from the six late Pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifers Juniperus occidentalis, Pinus cf. ponderosa, and P. monophylla. The pollen spectra of these Pleistocene middens are dominated by Pinus sp., Taxodiaceae-Cupressaceae-Taxaceae (TCT), and Artemisia sp. Mesophytic conifers are represented by low macrofossil concentrations. Sequoiadendron giganteum is represented by a few pollen grains in the full glacial. Edaphic control and snow dispersal are the most likely causes of these mixed assemblages.The dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the Sierra Nevada. These assemblages suggest that late Wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values. This conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late Wisconsin. The records in these middens also suggest that S. giganteum grew at lower elevations along the western side of the range and that P. monophylla was more widely distributed in cismontane California during the Pleistocene. 相似文献
19.
《Quaternary Science Reviews》1999,18(10-11):1151-1171
We constructed a radiometrically calibrated proxy record of Late Pleistocene and Holocene climate change exceeding 230,000 yr duration, using pollen profiles from two cores taken through age-equivalent dry lakes—one core having greater age control (via 230Th alpha mass-spectrometry) and the other having greater stratigraphic completeness. The better dated of these two serial pollen records (Searles Lake) served as a reference section for improving the effective radiometric age control in a nearby and more complete pollen record (Owens Lake) because they: (1) are situated ∼90 km apart in the same drainage system (on, and immediately leeward of, the eastern flank of the Sierra Nevada), and (2) preserved strikingly similar pollen profiles and concordant sequences of sedimentological changes. Pollen assemblages from both lakes are well preserved and diverse, and document serial changes in Late Pleistocene and Holocene plant zone distribution and composition in the westernmost Great Basin; they consist of taxa now inhabiting montane forest, woodland, steppe, and desert-scrub environments. The studied core intervals are interpreted here to be the terrestrial equivalent of marine δ18O stages 1 through 9; these pollen profiles now appear to be among the best radiometrically dated Late Pleistocene records of terrestrial climate change known. 相似文献
20.
对北方干旱区表生介质（土壤或水系沉积物）中的金进行了七种存在形式的研究,即自然金相、水溶相、有机相、吸附相、硫化物相、硅酸盐相和铁锰氧化物相。结果表明：金主要以自然金相为主（５０％以上）,其次为水溶相、吸附相和有机相等。水溶相金无论北方干旱气候带,还是南方潮湿气候带都普遍存在。说明不同自然景观区的金矿床,其表生介质中的金具有明显的溶解作用,呈水溶相金的形式进行迁移。当环境物化条件改变时,金沉淀形成局部富集。应用提取水溶相金的技术而制定的野外泡塑吸附金法,金异常衬度大,稳定性好,具有较好的找矿效果。 相似文献