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A detailed 90,000-year tephrostratigraphic framework of Aso Volcano, southwestern Japan, has been constructed to understand the post-caldera eruptive history of the volcano. Post-caldera central cones were initiated soon after the last caldera-forming pyroclastic-flow eruption (90 ka), and have produced voluminous tephra and lava flows. The tephrostratigraphic sequence preserved above the caldera-forming stage deposits reaches a total thickness of 100 m near the eastern caldera rim. The sequence is composed mainly of mafic scoria-fall and ash-fall deposits but 36 silicic pumice-fall deposits are very useful key beds for correlation of the stratigraphic sequence. Explosive, silicic pumice-fall deposits that fell far beyond the caldera have occurred at intervals of about 2500 years in the post-caldera activity. Three pumice-fall deposits could be correlated with lava flows or an edifice in the western part of the central cones, although the other silicic tephra beds were erupted at unknown vents, which are probably buried by the younger products from the present central cones. Most of silicic eruptions produced deposits smaller than 0.1 km3, but bulk volumes of two silicic eruptions producing the Nojiri pumice (84 ka) and Kusasenrigahama pumice (Kpfa; 30 ka) were on the order of 1 km3 (VEI 5). The largest pyroclastic eruption occurred at the Kusasenrigahama crater about 30 ka. This catastrophic eruption began with a dacitic lava flow and thereafter produced Kpfa (2.2 km3). Total tephra volume in the past 90,000 years is estimated at about 18.1 km3 (dense rock equivalent: DRE), whereas total volume for edifices of the post-caldera central cones is calculated at about 112 km3, which is six times greater than the former. Therefore, the average magma discharge rate during the post-caldera stage of Aso Volcano is estimated at about 1.5 km3/ky, which is similar to the rates of other Quaternary volcanoes in Japan. 相似文献
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N. Juyal R.K. Pant N. Basavaiah R. Bhushan M. Jain N.K. Saini M.G. Yadava A.K. Singhvi 《Journal of Asian Earth Sciences》2009,34(3):437-449
Proglacial lake sediments at Goting in the Higher Central Himalaya were analyzed to reconstruct the summer monsoon variability during the Last Glacial to early Holocene. Sedimentary structures, high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced fluctuating monsoonal conditions. Optically stimulated luminescence (OSL) dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka. During this period, Goting basin witnessed moderate to strengthened monsoon conditions around 25 ka, 23.5 ka–22.5 ka, 22 ka–18 ka, 17 ka–16.5 ka and after14.5–13 ka. The Last Glacial phase ended with the deposition of outwash gravel dated at ～11 ka indicating glacial retreat and the onset of Holocene condition. Additionally, centennial scale fluctuations between 16.5 ka and 12.7 ka in the magnetic and geochemical data are seen.A close correspondence at the millennial scale between our data and that of continental and marine records from the Indian sub-continent suggests that Goting basin responded to periods of strengthened monsoon during the Last Glacial to early Holocene. We attribute the millennial scale monsoon variability to climatic instability in higher northern latitudes. However, centennial scale abrupt changes are attributed to the result of albedo changes on the Himalaya and Tibetan plateau. 相似文献
4.
唐古拉山地区第四纪冰川作用与冰川特征 总被引：4，自引：2，他引：2
自中更新世以来,唐古拉山地区发生过3次更新世冰川作用(即昆仑冰期、倒数第二次冰期和末次错冰期)和2次全新世晚期冰进(即新冰期和小冰期冰进).昆仑冰期(最大冰期)发生在中更新世早期(0.80～0.60MaBP),不仅是本区最早的一次冰期,而且也是冰川规模最大的一次冰期,当时的冰川规模比现代冰川大16～18倍;倒数第二次冰期发生在中更新世晚期(0.30～0.135MaBP),比现代冰川大13～15倍;末次冰期发生在晚更新世晚期,应分为末次冰期早冰阶(75.0～58.0kaBP)和晚冰阶(32.0～15.0kaBP,23.0kaBP时达到极盛),但在唐古拉山地区截止目前还未找到早冰阶的冰川遗迹,因此,只对末次冰期的晚冰阶(LMG)进行了探讨.LMG时,冰川规模比现代冰川大10倍;新冰期发生在全新世高温期后,冰碛物的14C测年为(3540±160)aBP,冰川规模略大于现代冰川;小冰期发生在15～1世纪,冰川规模已接近于现代冰川.由于青藏高原的上升,对高原腹部地区引起的干旱化过程和水分严重不足,使唐古拉山地区的冰川自昆仑冰期以来,冰川规模一次比一次明显的减小. 相似文献
5.
Sigrid Meiners 《GeoJournal》1999,47(1-2):341-372
The extent of the Postglacial is characterized by a main end moraine, which is called Great Lateral Moraine. In general its
outer slope is very steep and the recent ice terminal retreated inwards and lost much volume. Between this stage of historical/latest
Neoglacial an ice marginal position was found, which can only be classified into the earliest Neoglacial because of its glaciogeomorphic
position. It lies ca. 5–6 km outside of the historical moraines and leads to snow line depressions of 300–600 m. This stage
can not mixed up with the latest Late Glacial stage. Relating to the Late Glacial only moraine terraces or remnants were found
in the steep valleys. In the Kangchenjunga Valley there is a large end moraine complex of Late Glacial at 2700 m, 27 km down-valley
of the recent glacier termini and in the Yalung Valley (Simbua Khola, Kangchenjunga SW) we found a lateral moraine wall 600 m
above the valley bottom of Torontan. In the Rolwaling Valley several indicators imply a former glaciation of the whole valley,
which stretches out into the Bhote Kosi. In consideration of the maximum glaciation of Last Glacial (LGM) which has extended
lower than 1000 m in the investigated areas it can be assumed that the levels of moraines valley- inwards are younger. Snow
line depressions of 300–600 m for the Neoglacial (earliest stage) and 900–1200 m for the Late Glacial can be calculated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Dust transported by sandstorms has been an important feedback in climate change in the past, and its environmental effects are predicted to have a great impact on future global climatic change. Investigating the grain-size classes and the standard deviations of the modern sandstorm samples, and the samples in the Shagou section (situated in the eastern Hexi Corridor), lead us to suggest that the sand fraction within the range of 275.4–550 μm in this section can be used as a sensitive indicator of severe sandstorms. We selected the size range in the L1 stratum of the Shagou loess section as indicative of temporal changes in sandstorm intensity in the eastern Hexi Corridor and found that during the Last Glacial period, severe sandstorms in the eastern Hexi Corridor occurred with high frequency during these periods: I (70–54 ka B.P.), II (51–48 ka B.P.), III (45–42 ka B.P.), IV (38–33 ka B.P.), V (31–28 ka B.P.) and VI (26–12 ka B.P.) In general, the frequency and intensity of dust storms in the early (MIS 4) and late (MIS 2) periods were both high but they were reduced in the middle period (MIS 3). The primary factors controlling severe sandstorms are hydrology and wind power, followed by the expansion of the source extent. Reduced precipitation caused the source region of sandstorms to expand; in addition, wind speeds also increased at this time. These factors may have directly contributed to the abundance of severe sandstorms. Based on the grain size from a loess section (the Shagou section) in the eastern Hexi Corridor, we propose an evolutionary sequence of the severe sandstorms during the Last Glacial period. This sequence is consistent with the dust records in the Arctic, the Antarctic and low-latitude (the central equatorial Pacific) areas. Thus globally synchronous periods of high dust activity occurred in the Last Glacial period. The strong winds proposed here provide a potential explanation for the global consistency of dust flux changes during the Last Glacial period. 相似文献
8.
Mark E. Stelten Kari M. Cooper Jorge A. Vazquez Mary R. Reid Gry H. Barfod Josh Wimpenny Qing-zhu Yin 《Contributions to Mineralogy and Petrology》2013,166(2):587-613
The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U–230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source. 相似文献
9.
Millennial‐scale stratigraphy of a tide‐dominated incised valley during the last 14 kyr: Spatial and quantitative reconstruction in the Tokyo Lowland,central Japan 
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下载免费PDF全文 Susumu Tanabe Toshimichi Nakanishi Yoshiro Ishihara Rei Nakashima 《Sedimentology》2015,62(7):1837-1872
Spatial and quantitative analysis of infilling processes of the tide‐dominated incised valleys beneath the Tokyo Lowland during the last 14 kyr was undertaken by using data from 18 sediment cores, 467 radiocarbon dates and 6100 borehole logs. The post‐Last Glacial Maximum valley fills consist of braided river, meandering river, estuary, spit and delta systems in ascending order. The boundary between the estuary and delta systems is regarded as the maximum flooding surface. The maximum flooding surface beneath the Tokyo Lowland is dated at 8 ka in the Arakawa Valley and 7 ka in the Nakagawa Valley. This age difference is due to the migration of the Tone River from the Arakawa Valley to the Nakagawa Valley at 5 ka, and suggests that the widely held view that the global initiation of deltas coincided with the abrupt rise of sea‐level at 9 to 8 ka is true only where there has been steady sediment supply from major rivers. The meandering river system is dominated by sheet‐like sands that were deposited during lateral migration of channels during the Younger Dryas and isolated vertical sands within muds that reflect vertical aggradation of channels before and after the Younger Dryas. The transition between these channel geometries is controlled by a threshold sea‐level rise of 4 to 7 mm yr?1. Before migration of the Tone River at 5 ka, the tide‐dominated bay in the Nakagawa Valley was filled by upward‐fining laterally accreting muds. The muds accreted from the margin to the axis of the bay. Such lateral accretion of suspended particles derived from outside the bay has been documented in other tide‐dominated coastal environments and is probably common in other similar settings. After the migration of the Tone River, the bay was filled by upward‐coarsening deltaic sediments. 相似文献
10.
The behavior of chlorine and sulfur during differentiation of the Mt. Somma-Vesuvius magmatic system 总被引：4，自引：0，他引：4
Summary Reheated silicate melt inclusions in volcanic rock samples from Mt. Somma-Vesuvius, Italy, have been analyzed for 29 constituents
including H2O, S, Cl, F, B, and P2O5. This composite volcano consists of the older Mt. Somma caldera, formed between 14 and 3.55 ka before present, and the younger
Vesuvius cone. The melt inclusion compositions provide important constraints on pre-eruptive magma geochemistry, identify
relationships that relate to eruption behavior and magma evolution, and provide extensive evidence for magmatic fluid exsolution
well before eruption.
The melt inclusion data have been categorized by groups that reflect magma compositions, age, and style of eruptions. The
data show distinct differences in composition for eruptive products older than 14.0 ka (pre-caldera rocks) versus eruptive
products younger than 3.55 ka. Moreover, pre-caldera eruptions were associated with magmas relatively enriched in SiO2, whereas eruptions younger than 3.55 ka (i.e., the syn- and post-caldera magmas which generated the Somma caldera and the
Vesuvius cone) were derived from magmas comparatively enriched in S, Cl, CaO, MgO, P2O5, F, and many lithophile trace elements.
Melt inclusion data indicate that eruptive behavior at Vesuvius correlates with pre-eruptive volatile enrichments. Most magmas
associated with explosive plinian and subplinian events younger than 3.55 ka contained more H2O, contained significantly more S, and exhibited higher (S/Cl) ratios than syn- and post-caldera magmas which erupted during
relatively passive interplinian volcanic phenomena.
Received January 10, 2000 Revised version accepted July 17, 2000 相似文献
11.
Kathryn E. Watts Ilya N. Bindeman Axel K. Schmitt 《Contributions to Mineralogy and Petrology》2012,164(1):45-67
A voluminous (>600 km3) and long-lived (~520–75 ka) phase of rhyolitic eruptions followed collapse of the Yellowstone caldera 640 ka. Whether these eruptions represent a dying cycle, or the growth of a new magma chamber, remains an important question. We use new U–Th zircon ages and δ18O values determined by ion microprobe, and sanidine Pb isotope ratios determined by laser ablation, to investigate the genesis of voluminous post-caldera rhyolites. The oldest post-caldera rhyolites, erupted between ~520 and 470 ka, exhibit extreme age and oxygen isotopic heterogeneity, requiring derivation from individual parcels of low-δ18O melts. We find a progressive increase in zircon homogeneity for rhyolite eruptions from ~260 to 75 ka, with homogeneous low-δ18O zircon values of 2.7–2.8‰ that are in equilibrium with low-δ18O host melts for the majority of the youngest eruptions. New sanidine Pb isotope data define separate arrays for post-caldera rhyolites and the caldera-forming tuffs that preceded them, indicating that they were not sourced from a mushy Lava Creek Tuff batholith that remained after caldera collapse. Rather, our new age and isotopic data indicate that the post-caldera rhyolites were generated by remelting of a variety of intracaldera source rocks, consisting of pre-Lava Creek Tuff volcanic and plutonic rocks and earlier erupted post-Lava Creek Tuff rhyolites. Batch assembly of low-δ18O melts starting at ~260 ka resulted in progressive homogenization, followed by differentiation and cooling up until the last rhyolite eruption ~75 ka, a trend that we interpret to be characteristic of a dying magma reservoir beneath the Yellowstone caldera. 相似文献
12.
扎布耶湖9级大型沙砾堤记录了约30．0ka B P以来水位退缩历史，与北部拉果错、南部塔若错的垭口沉积记录了3个湖泊最后分离的时间。本文应用数字地面高程模型(DEM)，计算了扎布耶各级沙堤对应湖面期的湖水面积、体积与含盐量；分析了扎布耶与拉果错、塔若错的分-合历程，计算了各时期汇流盆地总面积；参考湖泊、冰川、孢粉、天文学等多学科关于古温度、辐射平衡的结论，得出了较为可信的计算参数。在此基础上，应用根据西藏实际情况得出的辐射平衡和水面蒸发、陆面蒸发计算模型，代入封闭盆地水量平衡方程，得出了较Kutzbach水-能方程更可靠的降雨量-水域面积／流域面积比的非线性方程，计算出泛湖期(9级沙堤，40．0～28．0ka B P)该区降雨量567 mm／a，盛冰阶时降至350mm／a以下，冰期后增至402mm／a，随后逐步下降直至约Ⅰ-1级阶地时(海拔4421m，3．53ka B P)为280mm／a(约为现代的两倍)。通过定量恢复该区30．0ka B P以来降水量变化，为认识西藏高原湖泊演化和古环境、古季风演化提供了定量依据。 相似文献
13.
Late Quaternary multiple incised valley systems: An unusually well‐preserved stratigraphic record of two interglacial valley‐fill successions from the Arno Plain (northern Tuscany,Italy) 下载免费PDF全文
下载免费PDF全文 Un‐fragmented stratigraphic records of late Quaternary multiple incised valley systems are rarely preserved in the subsurface of alluvial‐delta plains due to older valley reoccupation. The identification of a well‐preserved incised valley fill succession beneath the southern interfluve of the Last Glacial Maximum Arno palaeovalley (northern Italy) represents an exceptional opportunity to examine in detail evolutionary trends of a Mediterranean system over multiple glacial–interglacial cycles. Through sedimentological and quantitative meiofauna (benthic foraminifera and ostracods) analyses of two reference cores (80 m and 100 m long) and stratigraphic correlations, a mid‐Pleistocene palaeovalley, 5 km wide and 50 m deep, was reconstructed. Whereas valley filling is chronologically constrained to the penultimate interglacial (Marine Isotope Stage 7) by four electron spin resonance ages on bivalve shells (Cerastoderma glaucum), its incision is tentatively correlated with the Marine Isotope Stage 8 sea‐level fall. Above basal fluvial‐channel gravels, the incised valley fill is formed by a mud‐prone succession, up to 44 m thick, formed by a lower floodplain unit and an upper unit with brackish meiofauna that reflects the development of a wave‐dominated estuary. Subtle meiofauna changes towards less confined conditions record two marine flooding episodes, chronologically linked to the internal Marine Isotope Stage 7 climate‐eustatic variability. After the maximum transgressive phase, recorded by coastal sands, the interfluves were flooded around 200 ka (latest Marine Isotope Stage 7). The subsequent shift in river incision patterns, possibly driven by neotectonic activity, prevented valley reoccupation guiding the northward formation of the Last Glacial Maximum palaeovalley. The applied multivariate approach allowed the sedimentological characterization of the Marine Isotope Stage 7 and Marine Isotope Stage 1 palaeovalley fills, including shape, size and facies architecture, which revealed a consistent river‐coastal system response over two non‐consecutive glacial–interglacial cycles (Marine Isotope Stages 8 to 7 and Marine Isotope Stages 2 to 1). The recurring stacking pattern of facies documents a predominant control exerted on stratigraphy by Milankovitch and sub‐Milankovitch glacio‐eustatic oscillations across the late Quaternary period. 相似文献
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Manfred Frechen Dietrich Ellwanger Matthias Hinderer Jörg Lämmermann-Barthel Inge Neeb Astrid Techmer 《International Journal of Earth Sciences》2010,99(8):1955-1974
During the Pleistocene, the Rhine glacier system acted as a major south–north erosion and transport medium from the Swiss
Alps into the Upper Rhine Graben, which has been the main sediment sink forming low angle debris fans. Only some aggradation
resulted in the formation of terraces. Optically stimulated luminescence (OSL) and radiocarbon dating have been applied to
set up a more reliable chronological frame of Late Pleistocene and Holocene fluvial activity in the western Hochrhein Valley
and in the southern part of the Upper Rhine Graben. The stratigraphically oldest deposits exposed, a braided-river facies,
yielded OSL age estimates ranging from 59.6 ± 6.2 to 33.1 ± 3.0 ka. The data set does not enable to distinguish between a
linear age increase triggered by a continuous autocyclical aggradation or two (or more) age clusters, for example around 35 ka
and around 55 ka, triggered by climate change, including stadial and interstadial periods (sensu Dansgaard–Oeschger cycles).
The braided river facies is discontinuously (hiatus) covered by coarse-grained gravel-rich sediments deposited most likely
during a single event or short-time period of major melt water discharge postdating the Last Glacial Maximum. OSL age estimates
of fluvial and aeolian sediments from the above coarse-grained sediment layer are between 16.4 ± 0.8 and 10.6 ± 0.5 ka, and
make a correlation with the Late Glacial period very likely. The youngest fluvial aggradation period correlates to the beginning
of the Little Ice Age, as confirmed by OSL and radiocarbon ages. 相似文献
16.
长江水下三角洲层序地层学研究有助于全面了解长江三角洲地层特征和沉积环境演化模式。通过对长江水下三角洲下切河谷区YD0901和YD0903孔岩心的详细沉积物粒度、特征元素比值(Cl/Ti和Zr/Rb)、沉积相对比分析,恢复了冰后期以来长江水下三角洲层序地层格架。研究区冰后期以来自下而上依次出现河流相、潮汐河流相、河口湾相、浅海相和三角洲相的沉积相序。末次冰期海平面下降,古长江形成下切河谷,古河间地发育硬黏土层,构成五级Ⅰ型层序界面。之后海平面回升,分别于15 cal ka BP和8.0 cal ka BP形成最大海退和最大海侵界面,水下三角洲区域最大海侵发生时间略滞后于平原区,约为7.5 cal ka BP。据此3个层序界面将冰后期地层划分为低位体系域、海侵体系域和高位体系域。钻孔岩心记录揭示了14.8 cal ka BP海侵到达研究区;14.8~13 cal ka BP期间,受MWP-1A冰融水事件影响海平面快速上升,海岸线向陆推进速率可达71.9,km/ka;海退期间各钻孔沉积速率较低,直至2 cal ka BP开始,沉积速率明显增加。 相似文献
17.
Geomorphological evidences of post-LGM glacial advancements in the Himalaya: A study from Chorabari Glacier,Garhwal Himalaya,India 总被引：2，自引：0，他引：2
MANISH MEHTA ZAHID MAJEED D P DOBHAL PRADEEP SRIVASTAVA 《Journal of Earth System Science》2012,121(1):149-163
Field geomorphology and remote sensing data, supported by Optical Stimulated Luminescence (OSL) dating from the Mandakini
river valley of the Garhwal Himalaya enabled identification of four major glacial events; Rambara Glacial Stage (RGS) (13
± 2 ka), Ghindurpani Glacial Stage (GhGS) (9 ± 1 ka), Garuriya Glacial Stage (GGS) (7 ± 1 ka) and Kedarnath Glacial Stage
(KGS) (5 ± 1 ka). RGS was the most extensive glaciation extending for ~6 km down the valley from the present day snout and
lowered to an altitude of 2800 m asl at Rambara covering around ~31 km2 area of the Mandakini river valley. Compared to this, the other three glaciations (viz., GhGS, GGS and KGS) were of lower
magnitudes terminating around ~3000, ~3300 and ~3500 m asl, respectively. It was also observed that the mean equilibrium line
altitude (ELA) during RGS was lowered to 4747 m asl compared to the present level of 5120 m asl. This implies an ELA depression
of ~373 m during the RGS which would correspond to a lowering of ~2°C summer temperature during the RGS. The results are comparable
to that of the adjacent western and central Himalaya implying a common forcing factor that we attribute to the insolation-driven
monsoon precipitation in the western and central Himalaya. 相似文献
18.
Hreggviur Nordahl
lafur Inglfsson Erla D. Vogler Benedikt
. Steingrímsson rni Hjartarson 《Boreas: An International Journal of Quaternary Research》2019,48(3):563-580
Knowledge of the glaciation of central East Iceland between 15 and 9 cal. ka BP is important for the understanding of the extent, retreat and dynamics of the Icelandic Ice Sheet. Crucially, it is not known if the key area of Fljótsdalur‐Úthérað carried a fast‐flowing ice stream during the Last Glacial Maximum; the timing and mode of deglaciation is unclear; and the history and ages of successive lake‐phases in the Lögurinn basin are uncertain. We use the distribution of glacial and fluvioglacial deposits and gradients of former lake shorelines to reconstruct the glaciation and deglaciation history, and to constrain glacio‐isostatic age modelling. We conclude that during the Last Glacial Maximum, Fljótsdalur‐Úthérað was covered by a fast‐flowing ice stream, and that the Lögurinn basin was deglaciated between 14.7 and 13.2 cal. ka BP at the earliest. The Fljótsdalur outlet glacier re‐advanced and reached a temporary maximum extent on two separate occasions, during the Younger Dryas and the Preboreal. In the Younger Dryas, about 12.1 cal. ka BP, the outlet glacier reached the Tjarnarland terminal zone, and filled the Lögurinn basin. During deglaciation, a proglacial lake formed in the Lögurinn basin. Through time, gradients of ice‐lake shorelines increased as a result of continuous but non‐uniform glacio‐isostatic uplift as the Fljótsdalur outlet glacier retreated across the Valþjófsstaður terminal zone. Changes in shoreline gradients are defined as a function of time, expressed with an exponential equation that is used to model ages of individual shorelines. A glaciolacustrine phase of Lake Lögurinn existed between 12.1 and 9.1 cal. ka BP; as the ice retreated from the basin catchment, a wholly lacustrine phase of Lake Lögurinn commenced and lasted until about 4.2 cal. ka BP when neoglacial ice expansion started the current glaciolacustrine phase of the lake. 相似文献
19.
The upper reaches of the Yellow River in northeastern Tibetan Plateau are geohazards areas. The evolution of the Yellow River, chronology of some landslides, and spatiotemporal distribution characteristics of super large scale and giant landslides within the region are summarized using paleoclimate evidence, and the relationship between the intensive landslide period and climatic changes since the Last Glacial period is analyzed. It is concluded that(1) Super large scale and giant landslides are distributed widely within the region, particularly in the Qunke-Jianzha basin.(2) The chronological sequence of landslides is established by dating the slip zones of landslides and analyzing the relations between landslides and their overlying or underlying loess formations. Five landslide development periods are determined: 53–49 ka BP, 33–24 ka BP, 10–8 ka BP, 5–3.5 ka BP, and the present.(3) These correspond closely to warm and wet periods during the last 100,000 years, i.e., two weak paleosol development stages of Malan loess deposited during the last Glacial period in the Chinese loess Plateau, L1-4 and L1-2 that belong to the marine oxygen isotope stage 3, the last deglacial period, the Holocene Optimum, and the modern global warming period.(4) Landslide triggers may be closely linked to warm and wet periods related to rapid climatic transitions. 相似文献
20.
Jason M. Dortch Lewis A. Owen Marc W. Caffee Dewen Li Thomas V. Lowell 《第四纪科学杂志》2010,25(8):1259-1269
Glacial landforms and outwash terraces in the Nenana River valley, Reindeer Hills and Monahan Flat in the central Alaska Range were dated with 60 10Be exposure ages to determine the timing of Late Pleistocene glaciation. In the Nenana River valley, glaciation occurred at 104–180 ka (Lignite Creek glaciation), ca. 55 ka (Healy glaciation), and ca. 16 ka (Carlo Creek phase); glaciers retreated in the Reindeer Hills and Monahan Flat by ca. 14 ka and ca. 13 ka, respectively. The Carlo Creek moraine is similar in age to at least six other moraines in the Alaska Range, Ahklun Mountains and Brooks Range. The new data suggest that post‐depositional geological processes limit the usefulness of 10Be methods to the latter part (≤60 ka) of the late Quaternary in central Alaska. Ages on Healy and younger landforms cluster well, with the exception of Riley Creek moraines and Monahan Flat‐west sites, where boulders were likely affected by post‐depositional processes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献