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11.
Limnogeology of Laguna Miscanti: evidence for mid to late Holocene moisture changes in the Atacama Altiplano (Northern Chile) 总被引：1，自引：0，他引：1
Blas L. Valero-Garcés Martin Grosjean Antje Schwalb Mebus Geyh Bruno Messerli Kerry Kelts 《Journal of Paleolimnology》1996,16(1):1-21
Sedimentological, mineralogical and geochemical analyses of sediment cores from 9 m-deep, saline Laguna Miscanti, Chile (23 ° 44S, 67 °46W, 4140 m a.s.l.) together with high-resolution seismic profiles provide a mid to late Holocene time series of regional environmental change in the Atacama Altiplano constrained by 210Pb and conventional 14C dating. The mid Holocene was the most arid interval since the last glacial maximum, as documented by subaerial exposure and formation of hardgrounds on a playa surface. Extremely low lake levels during the mid Holocene appear consistent with lower effective moisture recorded at other sites along the Altiplano and in the Amazon Basin. Termination of this arid period represented a major shift in the regional environmental dynamics and inaugurated modern atmospheric conditions. The cores show a progressive upward increase in effective moisture interrupted by numerous century-scale drier periods of various intensities and durations that characterize a fluctuating late Holocene climate. In spite of chronological uncertainties, the major environmental changes seem to correlate with the available paleorecords from the region providing a coherent account of effective moisture variability in the tropical highlands of South America.This is the 16th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest for these papers. 相似文献
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本文根据作者多年的实地考察,并参考了有关文献,研究了莆田海岸近4 000年来的变迁与气候的关系。结果表明,4 000a,B.P.莆田岸线大约沿海拔5～6m一线分布,当时气温比现今高2℃;2 570a,B.P.莆田岸线约沿海拔4m 一线分布,当时气温比现今高1℃;1 400a,B.P.以来,莆田气候冷暖交替出现,海平面基本上也随之升降而升降。 相似文献
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Melisa P. CHARó Gisela D. CHARó Guillermo ACE?OLAZA Jose L. CAVALLOTTO 《《地质学报》英文版》2022,96(4):1181-1198
The Late Pleistocene littoral ridges of southern South America, especially those of the north of Argentinean Patagonia, contain remains of mollusk shells with bioerosion traces. Eleven sites from marine isotope stages (2 from MIS 7, 4 from MIS 5e) and five sites from modern beaches from northern Río Negro Province, with 40 taxa (17 bivalves and 23 gastropods) were analyzed, in the area between west of Baliza San Matías and Las Grutas (41°S). Three ichnogenera were identified in deposits of MIS 7: Entobia, Gastrochaenolites (Domichnia) and Oichnus (Praedichnia) with one ichnospecies (G. torpedo). Six ichnogenera were identified in deposits of MIS 5e: Entobia, Meandropolydora, Pinaceocladichnus, Iramena, Caulostrepsis and Oichnus with one ichnospecies (O. simplex). Seven ichnogenera were identified from modern beaches: Entobia, Meandropolydora, Iramena, Caulostrepsis, Pinaceocladichnus, Gastrochaenolites (Domichnia) and Oichnus (Praedicnia), with two ichnospecies (O. simplex and O. paraboloides). On this basis, it is inferred that Pleistocene benthic communities were constituted from cheilostome bryzoans and polychaete annelids, together with drilling bivalves, predatory gastropods and overall warm-water species of mollusks. Of these, Chama iudicai was found on Plicatula gibbosa from MIS 7 and MIS 5e. The record of warm temperature species suggests a higher sea surface temperature (SST) than the present one and/or the influence of the warm southward Brazilian Current affecting the waters of Golfo San Matías. On the modern beaches surveyed, there is an increase in polychaete annelids, cheilostome bryzoans, temperate-cold species and drilling bivalves, as well as sandy substrate species, which together with an increase of Gastrochaenolites and Caulostrepsis, suggest a colder climate due to the greater influence of the Malvinas Current during the Holocene. 相似文献
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Analyses of pollen, plant macrofossils, sediment mineralogy, geochemistry, and lithology of cores from Chappice Lake, southeastern Alberta, provide an outline of paleohydrological changes spanning the last 7300 radiocarbon years. Situated near the northern margin of the Great Plains, Chappice Lake is currently a small (1.5 km2), shallow (<1 m), hypersaline lake. Results of this study suggest that the lake has experienced significant changes in water level and chemistry during the Holocene.From 7300 to 6000 BP the lake oscillated between relatively high stands and desiccation. From 6000 to 4400 BP it was smaller than present and ponded highly saline water. Although extreme water level variations of the preceding period had ceased, pronounced seasonal fluctuations persisted. Between 4400 and 2600 BP, lake level was more stable but gradually rising. Carbonates were a major component of the sediments deposited during this interval. A large, relatively fresh lake existed from 2600 to 1000 BP. Illite was the dominant mineral deposited during this period, but since then has been a minor constituent in a mineral suite dominated by detrital silicates. A series of low-water, high-salinity stands occurred between 1000 and 600 BP, although these low stands were not as pronounced as low-water intervals in the middle Holocene. Relatively high water levels were sustained from 600 BP until the late 1800s. The lake declined significantly in the last one hundred years, notably during the historically documented droughts of the late 1800s, 1920s, 1930s, and 1980s.The timing of paleohydrological events at Chappice Lake corresponds closely with well documented Holocene climatic intervals, such as the Hypsithermal, Neoglaciation, Medieval Warm Period, and Little Ice Age. In addition, historic lake-level fluctuations can be related directly to climate. As a result, the Chappice Lake sedimentary succession offers a rare opportunity to obtain a high-resolution, surrogate record of Holocene climate on the northern Great Plains, and to observe the response of lake chemistry and biota to significant environmental change.Geological Survey of Canada Contribution No. 45191, Palliser Triangle Global Change Contribution No. 2This publication is the first of a series of papers presented at the Conference on Sedimentary and Paleolimnological Records of Saline Lakes. This Conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr. Evans is serving as Guest Editor for this series. 相似文献
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We present a climatic reconstruction of Holocene lacustrine episodes in the Salinas del Bebedero basin (Argentina), based on geological and diatom information.Morphological, sedimentological and diatom evidence between 11600 ± 140 yr BP and 325 ± 95 yr BP, allowed us to interpret the paleoenvironments of the basin. Episodes of high energy (sandy levels) are linked to large inflow of meltwater through the Desaguadero River, related to development of glaciers on the Andes. This inflow is characterized by peaks of relative abundance of the brackish water diatom Cyclotella choctawatcheeana Prasad. The values of C. choctawatcheeana decrease in deposits of low energy (clay levels), where it co-dominates with oligohalobous Fragilaria and Epithemia spp.To the last two peaks of large inflow of meltwater, radiocarbon dates corrected to sidereal ages, are AD 1280/1420 and AD 1443/1656. These ages agree with two cold episodes clearly recorded in dendrological studies from the Patagonian Andes and were correlated to the Little Ice Age. Thus, older Holocene episodes of large inflow of water to the basin were correlated with the Neoglacial Advances defined by Mercer (1976) for the Andes. 相似文献
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Edouard Bard Gilles Delaygue Frauke Rostek Fabrizio AntonioliSergio Silenzi Daniel P. Schrag 《Earth and Planetary Science Letters》2002,202(2):481-494
A new oxygen isotope record is reported from a stalagmite collected in the Argentarola Cave located on the Tyrrhenian coast of Italy. As shown from observations and numerical modeling of δ18O in modern precipitation, the recorded δ18O variability for this zone is dominated by the amount of precipitation (so-called ‘amount effect’). The δ18O profile measured in the stalagmite is characterized by a prominent negative excursion (ca. 2-3‰) between 180 and 170 kyr BP. This paleoclimatic feature is interpreted as being due to a relatively wet period which occurred during the penultimate glacial period, more precisely, during Marine Isotope Stage 6.5. This pluvial phase is shown to correspond chronologically to the deposition of the sapropel event 6 (S6). Although this particular sapropel event occurred during a cold phase, the δ18O excursion is similar to those corresponding to other sapropels (S4, S3 and S2). The evidence for humid conditions during S6 in the western Mediterranean basin agrees with previous studies based on deep-sea sediment cores. Taken collectively, the data suggest that during sapropel events dilution of ocean surface waters was not restricted to the output of the river Nile but was rather widespread over the entire Mediterranean Sea due to increased rainfall. 相似文献
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Kai Hou Hui Qian Qiying Zhang Tao Lin Yao Chen Yuting Zhang Wengang Qu 《地球表面变化过程与地形》2020,45(4):862-876
Permeability differences in multi-cycle loess–paleosol aeolian sediments, which are still poorly understood, have the potential to significantly improve our understanding of climatic change during the glacial–interglacial periods of the Quaternary. In this study, the permeability of a well-preserved and continuous loess–paleosol sequence in the South Jingyang Plateau was investigated. Weathering intensity was inferred using a series of climate proxies including grain-size distribution, magnetic susceptibility and mineralogy. The results of laboratory tests showed that the average saturated hydraulic conductivity of loess layers is higher than that of paleosol layers. Also, clear differences between loess and paleosol were found in terms of depth variations of the vertical and horizontal saturated hydraulic conductivities. Differences in loess–paleosol were also found for other proxies for pedogenic weathering [i.e. clay content, sand content, Kd value (ratio of coarse silt to clay), magnetic susceptibility, dolomite content and the ratios of hornblende/illite and hornblende/chlorite]. Our results showed a high permeability of loess layers associated with weak pedogenic weathering during cold/dry paleoclimatic conditions in glacial stages. On the contrary, paleosol layers developed in a warm/humid climate during the interglacial stages experienced strong pedogenic weathering that resulted in lower permeability. Based on these results, we construct a connection between Quaternary climate change theory and the modern hydrological system. This provides a scientific basis for investigating the distribution and pollution of groundwater resources in the local region. © 2020 John Wiley & Sons, Ltd. 相似文献
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Permo-Triassic paleogeographic, paleoclimatic and paleoceanographic evolutions in eastern Tethys and their coupling 总被引：3，自引：0，他引：3
Based on reconstructions of paleogeography, paleoclimate and paleoceanography of the Chihsian, Wujiapingian, Anisian and Norian
intervals in the eastern Tethys, the multiple intrinsic relationship and interaction among the lithosphere, the hydrosphere
and the atmosphere as well as their evolutions are discussed. It was demonstrated that paleogeographic change of the eastern
Tethys and the northward shift of the Pangea during the Permo-Triassic periods governed the coeval paleocurrent pattern and
its evolution, which in turn seems to be a key contributor forcing the Permo-Triassic megamonsoon to the climax. 相似文献