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181.
Julie Brigham-Grette Martin Melles Pavel Minyuk Scientific Party 《Journal of Paleolimnology》2007,37(1):1-16
Sediment piston cores from Lake El’gygytgyn (67°N, 172°E), a 3.6 million year old meteorite impact crater in northeastern
Siberia, have been analyzed to extract a multi-proxy millennial-scale climate record extending to nearly 250 ka, with distinct
fluctuations in sedimentological, physical, biochemical, and paleoecological parameters. Five major themes emerge from this
research. First the pilot cores and seismic data show that El’gygytygn Crater Lake contains what is expected to be the longest,
most continuous terrestrial record of past climate change in the entire Arctic back to the time of impact. Second, processes
operating in the El’gygytygn basin lead to changes in the limnogeology and the biogeochemistry that reflect robust changes
in the regional climate and paleoecology over a large part of the western Arctic. Third, the magnetic susceptibility and other
proxies record numerous rapid change events. The recovered lake sediment contains both the best-resolved record of the last
interglacial and the longest terrestrial record of millennial scale climate change in the Arctic, yielding a high fidelity
multi-proxy record extending nearly 150,000 years beyond what has been obtained from the Greenland Ice Sheet. Fourth, the
potential for evaluating teleconnections under different mean climate states is high. Despite the heterogeneous nature of
recent Arctic climate change, millennial scale climate events in the North Atlantic/Greenland region are recorded in the most
distal regions of the Arctic under variable boundary conditions. Finally, deep drilling of the complete depositional record
in Lake El’gygytgyn will offer new insights and, perhaps, surprises into the late Cenozoic evolution of Arctic climate.
This is the first in a series of eleven papers published in
this special issue dedicated to initial studies of El'gygytgyn
Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest
editors of this special issue. 相似文献
182.
In the central Great Plains of North America, loess stratigraphy suggests that climate during the late Pleistocene was cold and dry. However, this record is discontinuous, and there are few other records of late-Pleistocene conditions. Cobb Basin, located on the northern edge of the Nebraska Sand Hills, contains lacustrine sediments deposited during Marine Isotope Stage 3, beginning approximately 45,000 cal yr BP and continuing for at least 10,000 yr. The lake was formed by a dune dam blockage on the ancient Niobrara River, and its deposits contain a diatom record that indicates changes through time in lake depth driven by changes in effective moisture. During the earliest stages of lake formation, the climate was arid enough to mobilize dunes and emplace dune sand into a blocking position within the Niobrara streambed. Diatom assemblages suggest that lake-level was shallow at formation, increased substantially during a wet interval, and then became shallow again, as arid conditions resumed. By about 27,000 cal yr BP the lake was filled, and a shallow ephemeral river occupied the basin. 相似文献
183.
The Kaiparowits Formation contains an exceptionally rich history of tectonic, climatic, and biologic conditions within the Western Interior of North America during the Campanian. Here we reconstruct aspects of the southern Cordilleran foreland basin's paleohydrology using δ18O and δ13C values determined from unionoid bivalve shells and pedogenic carbonate nodules derived from a suite of lithofacies associations. Unionoid shells derived from fluvial deposits display average water δ18O estimates of −13.7‰ ± 2.1 (1σ) (VSMOW) and shell δ13C values of −4.0‰ ± 1.5 (VPDB), whereas pedogenic carbonate nodules display average values of −6.0‰ ± 0.5 and −8.7‰ ± 0.8, respectively. Unionoid shells derived from pond deposits fall in between the two other environments with average values of −9.5‰ ± 1.8 and −5.7‰ ± 2.1, in δ18O and δ13C values respectively. Water δ18O estimates are interpreted to represent high altitude runoff within river systems, low elevation precipitation within the basin onto floodplain soils, and varying degrees of mixing between these two components within floodplain ponds. δ13C values track the isotopic composition of dissolved inorganic carbon within river, soil, and pond waters with high values likely reflecting greater contribution from chemically weathered marine carbonates exposed in the hinterland and lower values reflecting greater contributions from the in situ degradation of plant matter. Up-section there is a shift to lower δ18O values and higher δ13C values in fluvially-derived unionoid shells that post-dates an incursion of the Western Interior Seaway, but coincides with a shift in sediment provenance, an increase in basin sedimentation rates, and a change to a more anastomosed-style channel morphology within the basin foredeep depocentre. By combining the isotopic patterns with previously published sedimentologic, climate model, and paleofloral records we find: 1) additional evidence for humid, wet, and potentially monsoonal conditions within the region, 2) support for a tectonic uplift event, potentially related to Laramide deformation, and 3) greater aggradation and overbank flooding within the alluvial system in response to the uplift event. 相似文献
184.
Authigenic calcite silts at Wadi Midauwara in Kharga Oasis, Egypt, indicate the prolonged presence of surface water during the Marine Isotope Stage 5e pluvial phase recognized across North Africa. Exposed over an area of 4.25 km2, these silts record the ponding of water derived from springs along the Libyan Plateau escarpment and from surface drainage. The δ18O values of these lacustrine carbonates (− 11.3‰ to − 8.0‰ PDB), are too high to reflect equilibrium precipitation with Nubian aquifer water or water of an exclusively Atlantic origin. Mg/Ca and Sr/Ca of the silts have a modest negative covariance with silt δ18O values, suggesting that the water may have experienced the shortest residence time in local aquifers when the water δ18O values were highest. Furthermore, intra-shell δ18O, Sr/Ca, and Ba/Ca analyses of the freshwater gastropod Melanoides tuberculata are consistent with a perennially fresh water source, suggesting that strong evaporative effects expected in a monsoonal climate did not occur, or that dry season spring flow was of sufficient magnitude to mute the effects of evaporation. The input of a second, isotopically heavier water source to aquifers, possibly Indian Ocean monsoonal rain, could explain the observed trends in δ18O and minor element ratios. 相似文献
185.
柴北缘大煤沟地区侏罗系记录了西北地区古环境演化的重要信息。文章通过对大煤沟剖面进行有机地球化学分析,尝试恢复大煤沟地区侏罗系的环境演化。分析认为,H/C比与C/N比、δ 13C呈现良好的负相关性。早侏罗世:C/N比和δ 13C整体逐渐减小,H/C比逐渐变大;中侏罗世:C/N比和δ 13C在前期保持稳定,后期急剧负偏,而H/C比则反之;晚侏罗世:C/N比和δ 13C基本保持低值不变,H/C比稳定在高值区间。早—中侏罗世有机元素C/N比多大于15,表明有机质来源主要以
陆生高等植物为主。大煤沟剖面古气候表现为两个旋回,在早侏罗世小煤沟组时期古气候特征为温湿—干热,自中侏罗世晚期古气候开始从温湿向干热演化。 相似文献
186.
Agathe Fourmont Jean-Jacques Macaire Jean-Gabriel Bréhéret 《Journal of Paleolimnology》2009,41(3):471-490
Since the end of the Last Glacial Maximum, hydrology in Europe has been influenced by both climate changes, and since Neolithic
times, an increase in human activity. Paleohydrological reconstructions, especially from lake studies, can help identify the
respective impact of these two factors. The present work focuses on a lacustrine geosystem, the Sarliève paleolake in the
Massif Central (France), in an unusually dry, temperate area. The lake sediment geometry (core drillings, geotechnical methods),
and the geochemical and mineralogical characterization of the catchment rocks and soils, and of the lacustrine deposits, indicate
major variations in paleohydrology during the last 12,000 years as dated by 14C, palynology and tephrochronology. In addition, a model quantifying detrital versus biochemical lacustrine components was
developed to identify hydrological trends. The data show that the Sarliève area was characterized mainly by remarkably dry
conditions, hence sharpening the climatic trends at middle latitudes in Western Europe. Three main hydrological phases are
distinguished since the Late Glacial: (1) 13.7–7.5 ka cal BP, a dominant dry climate, with a peak at ca. 8 ka cal BP, leading
to a lowstand in water level and unusual mineral authigenesis, zeolite then dolomite, constituting up to 60% of the lacustrine
sediments; (2) 7.5 to ca. 5.3 ka cal BP, repeated short-duration hydrological alternations that could have been climate-driven:
lowstands in water level with up to 60% biochemical minerals versus higher water levels with <10% biochemical minerals; (3)
5.3 ka cal BP to the Middle Ages (i.e. beginning in the 5th century AD), a hydrological trend towards perennial high water
level, with mainly detrital sediments, probably linked to climate evolution, except periods of obvious human-driven drying
during the last two millennia. 相似文献
187.
Subfossil midge remains were identified in surface sediment recovered from 88 lakes in the central Canadian Arctic. These
lakes spanned five vegetation zones, with the southern-most lakes located in boreal forest and the northern-most lakes located
in mid-Arctic tundra. The lakes in the calibration are characterized by ranges in depth, summer surface-water temperature
(SSWT), average July air temperature (AJAT) and pH of 15.5 m, 10.60°C, 8.40°C and 3.69, respectively. Redundancy analysis
(RDA) indicated that maximum depth, pH, AJAT, total nitrogen-unfiltered (TN-UF), Cl and Al capture a large and statistically
significant fraction of the overall variance in the midge data. Inference models relating midge abundances and AJAT were developed
using different approaches including: weighted averaging (WA), weighted averaging-partial least squares (WA-PLS) and partial
least squares (PLS). A chironomid-based inference model, based on a two-component WA-PLS approach, provided robust performance
statistics with a high coefficient of determination (r
2 = 0.77) and low root mean square error of prediction (RMSEP = 1.03°C) and low maximum bias. The use of a high-resolution
gridded climate data set facilitated the development of the midge-based inference model for AJAT in a region with a paucity
of meteorological stations and where previously only the development of a SSWT inference model was possible.
David Porinchu and Nicolas Rolland contributed equally to the work. 相似文献
188.
Late Holocene paleoenvironmental changes in subtropical Taiwan inferred from pollen and diatoms in lake sediments 总被引:1,自引:0,他引:1
Su-Hwa Chen Jiunn-Tzong Wu Tien-Nan Yang Pei-Pei Chuang Shu-Yue Huang Yun-Sen Wang 《Journal of Paleolimnology》2009,41(2):315-327
We analyzed pollen, spores, diatoms, organic carbon, nitrogen, and δ13C of organic matter in lake sediments to infer climate changes and reconstruct the paleo-environment of subtropical Taiwan
over the past ∼1300 years. A 31.5-cm sediment core that represents deposition from 650 AD to present was taken from a mountain
lake, Duck Pond, located 760 m a.s.l. We differentiated five zones using cluster analysis on pollen and spore assemblages.
Fluctuations in the relative abundances of arboreal taxa, herbaceous plants, and ferns reflect changes in the relative amounts
of woody versus grassland vegetation. Such shifts are associated with changes in temperature and humidity and are consistent
with climatic periods reported for the temperate region of central China. Climate changes inferred from the pollen assemblages
are also correlated well with changes in the ratios of fern spores to pollen, with organic carbon to nitrogen, and with the
δ13C values in the sediments. Fluctuations in these data throughout the entire core were in good agreement with the changes in
pH inferred from diatom assemblages. This study provides evidence of climate change in northern Taiwan over the past 1.3 millennia,
assuming that climate can be inferred from the ratio of arboreal to non-arboreal pollen and from the pH of the aquatic environment. 相似文献
189.
昆特依盐湖位于柴达木盆地西北部,是一个相对独立的沉积盆地,可反映盆地西北部的演化历史,对研究盆地内盐湖演化有重要意义。基于研究区已有的研究成果,总结和评价了昆特依盐湖沉积与盐类矿产资源,并得到以下结论:1)昆特依湖自1 925~774 ka期间以暖湿型气候为主,其后呈干冷与暖湿气候交替出现,最早成盐期为1150 ka,最终于30.6 ka成为干盐湖。昆特依盆地早期沉积的细碎屑沉积物沉积速率(0.22 mm/a)慢于晚期沉积的石盐层(0.33 mm/a);2)昆特依盐湖液体KCl储量为1.32×10~8 t,MgCl储量为2.79×10~8 t,NaCl储量为24.15×10~8 t;3)估算出赋存于昆特依盐湖石盐矿中的锂资源量达39×10~4 t,同时估算出液体中的锂资源量约有74×10~4 t,二者总量达百万吨;4)昆特依矿田的成因属典型的内陆湖相沉积,成矿控制因素以构造作用为主,其次为气候及物质来源。关于昆特依盐湖沉积特征与盐类矿产资源特征的研究,有利于对本地区地质演化更全面的认识,对合理开发利用盐类资源有重要意义。 相似文献
190.
A freeze-drying technique for cutting thin-sections of soft sediments without disturbance is used to study several Lake Baikal
sedimentary microstructures. Image analysis methodology is applied to selected thin-sections. This new technique provides
quantification of the size, shape, orientation and packing of the objects forming the sedimentary structures. Sedimentary
processes, which were previously poorly documented, have been identified, and others are better understood. Spheroidal lens-like
pure aggregates of the diatom genus Synedra are found in hemipelagic sediments, providing a new insight into their traditional paleoecological interpretation. They are
possibly related to a transportation mechanism from the littoral zone or to lacustrine snow. Laminae of Aulacoseira have also been recorded. Evidence of rapid sedimentation suggests they are due to massive algal blooms. The depositional mechanism
that was suggested by other studies for explaining the laminations at the Buguldeika uplift is confirmed: the hemipelagic
sedimentation is interrupted by terrigenous pulses due to discharge events. The sedimentation rate appears to be increasing
during these pulses. Preliminary results from the Academician Ridge show stronger microbioturbation during cold periods. This
observation strengthens the hypothesis of intense water circulation during colder times. Thin-section image analysis provides
crucial information for deciphering lacustrine records and their regional and palaeoclimatic significance.
Received: 27 November 1998 / Accepted: 13 September 1999 相似文献