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1.
通过野外考察观测,结合土壤学与沉积学多种指标测试分析,在官亭盆地喇家遗址东侧的二方村遗址建立了完整的全新世土壤沉积物地层序列。选择关键层位系统采集年代学样品,应用单片再生剂量法(SAR),进行光释光(OSL)年代测定,结合文化层考古断代,建立了可靠的土壤与沉积物地层年代框架。发现在全新世大暖期温暖湿润气候条件之下,以风成堆积为主的基础上,发育形成了肥沃疏松的黑垆土类古土壤,成为史前人类种植农业开发利用的宝贵资源。但是全新世大暖期后期全球性气候恶化背景条件下,在二方村遗址OSL年龄3940～3780a BP之间,对应喇家遗址~(14)C年龄3850～3600a BP期间,官亭盆地发生多场大地震,加上全球气候恶化致使青藏高原边缘频繁发生强对流天气,造成大规模暴雨山洪泥流事件频繁发生,导致黑垆土发育的突然中断。黄河北岸第二级阶地的肥沃黑垆土类土壤被厚达1.0～4.0 m坚硬贫瘠的红色黏土覆盖。这不仅毁灭了以稷粟类谷物种植为主的喇家村齐家文化大型聚落(4150～3850a BP),也导致土壤与土地资源严重退化。由此可知,从4200a BP开始的全球性气候恶化,对青藏高原东北边缘环境敏感带造成了严重影响,灾害性地表过程造成了黄河第二级阶地土壤土地资源严重退化。这些都成为驱动官亭盆地在3600a BP时期辛店/卡约文化原始农牧混合型土地利用方式形成的重要因素。该研究结果对于深入理解青藏高原东北边缘资源环境演变、自然灾害以及人地关系演变规律等,都具有十分重要的科学价值。  相似文献   

2.
Small isolated dune fields in the northern Mojave Desert are important centers of biodiversity and archaeological occupation sites. Currently dunes at Ash Meadows, Nevada, are stabilized by vegetation and are experiencing erosion of their upwind margins, indicating a negative sediment budget. New OSL ages from dunes at Ash Meadows indicate continuous eolian accumulation from 1.5 to 0.8 ka, with further accumulation around 0.2 ka. Prior studies (e.g., Mehringer and Warren, 1976) indicate periods of dune accumulation prior to 3.3 ka; 1.9–1 ka; and after 0.9 ka. These periods of eolian accumulation are largely synchronous with those identified elsewhere in the Mojave Desert. The composition of the Ash Meadows dunes indicates their derivation from regional fluvial sources, most likely during periods when axial washes were active as a result of enhanced winter precipitation.  相似文献   

3.
《Quaternary Science Reviews》2003,22(10-13):1207-1211
The time-integrated slip rate in fault zones can be determined if the deformed deposits are reliably dated. Here, we report optically stimulated luminescence (OSL) ages of Late Pleistocene fluvial deposits cut by the Wangsan fault, southeastern Korea, which displaces a hanging wall block of about 28 m. Five sandy samples of the deformed Quaternary deposits were dated by quartz OSL using the single aliquot regenerative-dose (SAR) protocol. Three samples taken from the footwall block show stratigraphically consistent OSL ages of 54±7, 76±5 and 90±6 ka, from top to bottom. Two samples collected from the same layer in the hanging wall block show reproducible OSL ages of 81±5 and 82±5 ka, which are also in good agreement with the stratigraphic relationships. Our OSL ages yield an average sedimentation rate of the Quaternary deposits as around 0.04 mm a−1, and a minimum value of time-integrated slip rate as 0.52 mm a−1. This minimum slip rate is considerably higher than those reported earlier for Quaternary faults in southeastern Korea. The youngest OSL age (54±7 ka) constrains the maximum value of the recurrence interval of the fault movement.  相似文献   

4.
《Quaternary Research》2014,81(3):445-451
Some scholars have argued that the formation and outburst of an ancient dammed lake in the Jishi Gorge at ca. 3700 cal yr BP resulted in the destruction of Lajia, the site of a famous prehistoric disaster in the Guanting Basin, upper Yellow River valley, China. However, the cause of the dammed lake and the exact age of the dam breaching are still debated. We investigated ancient landslides and evidence for the dammed lake in the Jishi Gorge, including dating of soil from the shear zone of an ancient landslide, sediments of the ancient dammed lake, and loess above lacustrine sediments using radiocarbon and optically stimulated luminescence (OSL) dating methods. Six radiocarbon dates and two OSL dates suggested that the ancient landslides and dammed lake events in the Jishi Gorge probably occurred around 8100 cal yr BP, and the ancient dammed lake was breached between 6780 cal yr BP and 5750 cal yr BP. Hence, the outburst of the ancient dammed lake in the Jishi Gorge was unrelated to the ruin of the Lajia site, but likely resulted in flood disasters in the Guanting Basin around 6500 cal yr BP.  相似文献   

5.
Extensive coastal dunes occur in the Great Lakes region of North America, including northwestern Michigan where some are perched on high (~ 100 m) bluffs. This study focuses on such a system at Arcadia Dunes and is the first to systematically generate optical ages from stratigraphic sections containing buried soils. Dune growth began ca. 4.5 ka during the Nipissing high lake stand and continued episodically thereafter, with periods of increased sand supply at ca. 3.5 ka and ca. 1.7 ka. The most volumetrically dominant phase of dune growth began ca. 1.0 ka and continued intermittently for about 500 years. It may have begun due to the combined effects of a high lake phase, potential changes in lake hydrodynamics with final isostatic separation of Lake Superior from Lakes Michigan and Huron, and increased drought and hydrologic variability associated with the Medieval Warm Period. Thus, this latest eolian phase likely reflects multiple processes associated with Great Lakes water level and climate variability that may also explain older eolian depositional events. Comparison of Arcadia ages and calendar corrected 14C ages from previous studies indicate broad chronological agreement between events at all sites, although it appears that dune growth began later at Arcadia.  相似文献   

6.
Quaternary glaciation of Mount Everest   总被引：1，自引：0，他引：1  
The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and 10Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24–27 ka (Jilong moraine), 14–17 ka (Rongbuk moraine), 8–2 ka (Samdupo moraines) and ～1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8–7.7 ka) and Samdupo II (～2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation.  相似文献   

7.
This paper reports the main sedimentary characteristics, soil micromorphology and optically-stimulated luminescence (OSL) ages, and details the pedosedimentary reconstruction, of the Hudson site situated in the northern Pampas of Buenos Aires province. It also provides the OSL chronology and a reinterpretation of previously reported micromorphological features for the nearby site of Gorina. Finally, the stratigraphic records of both sites are compared and the main environmental events discussed in a regional context.At Hudson, situated at a low altitude environment close to the coastal plain, the basal fine-grained paludal deposits were unconformably covered by coastal marine sediments with an OSL age of ca. 128 ka supporting its correlation with the high stand of sea level of marine isotope stage 5e. A paleosol developed on the marine deposits and the underlying paludal sediments. OSL ages suggest that soil development and its subsequent erosion occurred over some period between ca. 128 and 54 ka. Fine sediment accumulation in a paludal environment continued until prior to ca. 23 ka when the accumulation of the uppermost loess mantle started. It continued until the early Holocene when present soil development began. At Gorina, OSL ages suggest that the upper part of the pedocomplex formed at some stage between ca. 194 and 56 ka. Loess then accumulated followed by an erosional phase; loess deposition restarted by ca. 29 ka and continued until the beginning of the Holocene (ca. 9 ka) when the present land surface was established.The stratigraphic and paleoenvironmental differences exhibited by the Hudson and Gorina records result from their contrasting geomorphological settings. The OSL geochronology suggests that the last interglacial (MIS 5) at Hudson is marked by the accumulation of marine deposits (MIS 5e) and the subsequent development of a paleosol. The equivalent soil-forming interval at Gorina is represented by the upper part of the buried pedocomplex. Both at Gorina and Hudson, loess accumulation was dominant especially during MIS 2. Loess accumulation continued during MIS 1 until the early Holocene with apparently somewhat higher sedimentation rates in Hudson. Pedogenesis has been predominant during the rest of the Holocene, resulting in the formation of the surface soil profiles.  相似文献   

8.
Dun structures are common in the Sub-Himalayan zone of the Himalaya bounded by the Main Boundary Thrust (MBT) and the Himalayan Frontal Thrust (HFT). They are broad synclinal longitudinal valleys formed as a consequence of the exhumation of the range front of the Himalaya. In the Garhwal Sub-Himalaya, these structures have grown since 0.5 Ma, with the peak activity postdating ∼100 ka. A series of out-of-sequence deformation structures have been identified within the MBT-HFT-bounded Dun structures. They are identified on the basis of geomorphic, post-100 ka stratigraphic, and structural expressions, with activity as young as the early Holocene. To the south of the range front of the Himalaya, uplift has been observed in the Piedmont Zone, with peculiar active tectonic geomorphic expressions. Piedmont sediments of 15–5 ka, determined by Optically Simulated Luminescence (OSL), have been affected by the above uplift. The complete tectonic scenario has been analyzed and an attempt has been made to delineate the sequential evolution of these structures during the post-100 ka period (Late Quaternary–Holocene) in the Himalayan range front.  相似文献   

9.
The evolution processes and forcing mechanisms of the Horqin dunefield in northern China are poorly understood. In this study, systematic OSL dating of multiple sites is used together with pollen analysis of a representative section in order to reconstruct the evolution of the dunefield since the Last Glacial Maximum (LGM). Our results show that there was extensive dune mobilization 25–10 ka, transition to stabilization 10–8 ka, considerable dune stabilization 8–3 ka, and multiple episodes of stabilization and mobilization after 3 ka. Comparison of dune evolution of the dunefields in northern China during the Holocene showed that Asian monsoon and resultant effective moisture have played an important role in the evolution of dunefields at the millennial time scale. Further analysis indicated that the dune evolution in the Horqin dunefield before 3 ka was synchronous with climatic changes. However, increasing human activity has impacted dune evolution during the last 3 ka.  相似文献   

10.
The competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain. Most of recent studies have attributed terrace formation to climatic changes and held that, even in tectonically active settings, climate variations control cycles of terrace planation and abandonment. Based on field investigations of loess-paleosol sequences, magnetostratigraphy and optically stimulated luminescence (OSL) dating, we develop a new chronology for a spectacular flight of terraces along the Yellow River near Lanzhou, China over past 1.24 Ma. All the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads, suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates. However, the ages of terraces cluster in two relatively short time periods (1.24–0.86 Ma and 0.13 Ma – present). During the intervening time between 0.86 Ma and 0.13 Ma, terraces either did not form or were not preserved. We suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation/preservation. Thus, our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision.  相似文献   

11.
Paleoenvironmental records extending well into the last glacial period are scarce in the steppe regions of southern South America. Here, we present a continuous record for the past 55 ka from the maar lake Laguna Potrok Aike (51°58′ S, 70°23′ W, southern Patagonia, Argentina). Previous studies on a sedimentary core from a lake level terrace near the northern margin of the lake covered parts of Oxygen Isotope Stage (OIS) 3 (59–29 ka) whereas a second core from the centre of the basin comprised the last 16 ka. Tephrostratigraphical constraints and OSL ages from a third core located below the lake level terrace provide the crucial piece to close the gap between the previous coring sites. High-resolution XRF and magnetic susceptibility as well as grain size data indicate a positive hydrological balance alongside with relatively high aeolian activity during the glacial which is contemporaneous with increased dust fluxes in Antarctica. This is therefore the first evidence for contemporaneity of aeolian deposition in both the target area (Antarctica) and in the major source area of Patagonia. During the Holocene climatic conditions driving sediment deposition seem to have been more variable and less dominated by wind compared to glacial times. The identification of a minor lake level lowering at approximately 4 cal ka BP allows to refine earlier paleoenvironmental reconstructions for the Holocene. Within error margins the OSL ages are consistent with published radiocarbon-dated records offering hence a valuable tool for further studies of the sediments from Laguna Potrok Aike. The new chronology confirms the age of three tephra layers up to now only found in Laguna Potrok Aike sediments and ascribed to OIS 3.  相似文献   

12.
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   

13.
《Quaternary Science Reviews》2003,22(10-13):1067-1076
This study is concerned with the Late Quaternary climatic chronology of the Strzelecki Desert dunefields in central Australia. The sand ridges comprise layers of quartz sand, some of which include palaeosol horizons with carbonated rootlets providing excellent opportunity for dating of alternations of dune building and stability by using optically stimulated luminescence (OSL). Deduced from the OSL age of the oldest aeolian layer dated, we conclude that the onset of aridity dates back to at least ∼65 ka. Older phases of aeolian activity though, following a fluvial depositional phase 160 ka ago, cannot be excluded, although no aeolian layers giving evidence for this have been found in the two dunes dated here. Unconsolidated dune sands in the upper part of one section with Late Holocene (4 ka to modern) depositional ages indicate a reactivation of the dunefield in recent times.From the crosscheck of 14C ages of the carbonated rootlets with OSL results it is concluded that under the given environmental conditions radiocarbon dating of the calcareous rootlets is not able to provide reliable ages for the phase of soil development.  相似文献   

14.
《Quaternary Research》2014,81(3):488-499
Paleoclimatic reconstruction based on aeolian sediments in the eastern Qaidam Basin (QB) has been hindered by the limited chronological data. Here we present 61 Optically Stimulated Luminescence (OSL) ages. On the basis of these OSL ages and the lithologic stratigraphy, we propose the ‘effective moisture index (EMI)’ for aeolian sediments to reconstruct the effective moisture change. Based on the EMI from twelve sections, the effective moisture change, moisture sources and relevant mechanisms for paleoclimatic change in the eastern QB are discussed. The results indicate that (1) aeolian deposition started at least before 12.4 ± 0.7 ka during the deglaciation, the paleosols developed at the early and mid-Holocene, and aeolian sand and loess accumulated at mid- and late Holocene; (2) effective moisture history was: hyper-arid at 12.8–11.6 ka, humid and variable at 11.6–8.3 ka, moderately humid and stable at 8.3–3.5 ka, and increasingly arid at 3.5–0 ka; (3) the effective moisture change was mainly controlled by the Asian summer monsoon (ASM), which mainly followed the change of Northern Hemispheric summer insolation, and the westerlies strengthened and increased the aridity in the QB when the ASM shrank.  相似文献   

15.
Stratigraphical, mineralogical, geochemical and optical dating methods were used to reconstruct paleo-hydrological changes in two playas (Phulera, 500 mm/a and Pokharan, 200 mm/a) in near extremum climatic regions of the Thar Desert. Sediment successions in shallow profiles from Phulera and Pokharan contain three and four stratigraphic units, respectively, each with characteristic geochemical properties. These units reflect changes in chemical weathering, detrital input, salinity and provide a measure of the changes in precipitation (i.e. monsoon) through time.Sediments from Pokharan suggest short rainfall events during ca. 6.6–4 ka, relatively stable fresh water (higher and persistent rainfall) regime during 4–2.3 ka, and a hyper saline (low rainfall) condition during 2.3–1.1 ka. Sediments at Phulera, record hyper saline (low rainfall) lacustrine conditions during <2.3 ka to >1.4 ka. Higher abundance of gypsum in Pokharan (2.3–1.1 ka) and proto-dolomite in Phulera (2.3–1.4 ka) are nearly synchronous and reflect enhancement of salinity. Selenite crystals in Pokharan and large desiccation cracks in buried horizons at Phulera reflect desiccation of playas at ca. 2 ka. Both playas progressively became less saline after 1.4 ka. Given the regional nature of this record, these changes are attributed to fluctuation of the monsoon over the Indian sub continent.  相似文献   

16.
The extensive shoreline deposits of Lake Chilwa, southern Malawi, a shallow water body today covering 600 km2 of a basin of 7500 km2, are investigated for their record of late Quaternary highstands. OSL dating, applied to 36 samples from five sediment cores from the northern and western marginal sand ridges, reveal a highstand record spanning 44 ka. Using two different grouping methods, highstand phases are identified at 43.7–33.3 ka, 26.2–21.0 ka and 17.9–12.0 ka (total error method) or 38.4–35.5 ka, 24.3–22.3 ka, 16.2–15.1 ka and 13.5–12.7 ka (Finite Mixture Model age components) with two further discrete events recorded at 11.01 ± 0.76 ka and 8.52 ± 0.56 ka. Highstands are comparable to the timing of wet phases from other basins in East and southern Africa, demonstrating wet conditions in the region before the LGM, which was dry, and a wet Lateglacial, which commenced earlier in the southern compared to northern hemisphere in East Africa. We find no evidence that wet phases are insolation driven, but analysis of the dataset and GCM modelling experiments suggest that Heinrich events may be associated with enhanced monsoon activity in East Africa in both timing and as a possible causal mechanism.  相似文献   

17.
青海官亭盆地喇家遗址史前巨大灾难事件,是我国史前环境变化与文明演变研究领域的热点之一。通过对官亭盆地喇家遗址北侧大红山前古洪积扇前沿地带的野外考察,进行土壤沉积物地层划分、结合理化指标测试分析,发现该地带土壤与沉积物的基本层序,自下而上依次为晚更新世马兰黄土（L1）—全新世早期过渡性风成黄土（Lt）—全新世中期古土壤（S0）—全新世晚期风成黄土（L0）—现代耕作土壤（MS）。这个层序特点与黄河北岸第二级阶地喇家遗址区域相同,也与黄土高原地区全新世土壤沉积物的层序相同。在全新世中期黑垆土古土壤（S0）中夹有三层红色泥流沉积层（RC1、RC2、RC3）,是全新世中期后段气候恶化条件之下,暴雨山洪泥流溢出沟槽在地面扩散沉积形成。该地带以RC1为代表第一期山洪泥流事件早于喇家遗址毁灭的年代。以RC2为代表的第二期山洪泥流层卷入密集的木炭屑和杂物,表明在山洪泥流发生的时候有火灾发生,这对应着3 850 a B.P.毁灭喇家遗址的大地震和山洪泥流群发生灾难事件。以RC3为代表的第三期山洪泥流事件,与喇家遗址区域相同发生在3 600 a B.P.。其后在古洪积扇前沿到黄河第二级阶地的范围,再没有发生山洪泥流溢出沟槽扩散覆盖土地并且毁灭聚落成灾的现象。在喇家遗址北侧古洪积扇区域建立了全新世土壤地层序列,分析了该地带山洪泥流与喇家遗址灾难事件的联系。这对于研究揭示史前时期以来官亭盆地人地关系演变具有科学意义。  相似文献   

18.
The Holocene and late Pleistocene environmental history of the teri (‘sandy waste’ in local parlance) red sands in the southeast coastal Tamil Nadu was examined using remote sensing, stratigraphy, and optically stimulated luminescence (OSL) dating. Geomorphological surveys enabled the classification of the teri red sands as, 1) inland fluvial teri, 2) coastal teri and, 3) near-coastal teri dunes. The inland teri sediments have higher clay and silty-sand component than the coastal and near-coastal teri, suggesting that these sediments were deposited by the fluvial process during a stronger winter monsoon around > 15 ka. The coastal teri dunes were deposited prior to 11.4 ± 0.9 ka, and the near-coastal dunes aggraded at around 5.6 ± 0.4 ka. We interpret that the coastal dunes were formed during a period of lower relative sea level and the near-coastal dunes formed during a period of higher sea level. Dune reddening is post deposition occurred after 11.4 ± 0.9 ka for the coastal teri dunes and after 5.6 ± 0.4 ka for the near-coastal teri dunes. Presence of microlithic sites associated with the coastal dunes suggest that the cultures existed in the region during 11.4 ± 0.9 ka and 5.6 ± 0.4 ka.  相似文献   

19.
Activity and stability phases as well as geomorphic processes within the Critical Zone are well known. Erosion and deposition of sediments represent activity; soils represent geomorphic stability phases. Data are presented from a 4 m deep sediment section that was dated by luminescence techniques. Upslope erosion and resulting sedimentation started in the late Pleistocene around 18 ka until 12 ka. Conditions at the study site then changed, which led to the formation of a well-developed soil. Radiocarbon dating of the organic matter yielded ages between 8552 and 8995 cal. BP. From roughly 6.2 to 5.4 ka another activity phase accompanied by according sediment deposition buried the soil and a new soil, a Cambisol, was formed at the surface. The buried soil is a strongly developed Luvisol. The black colors in the upper part of the buried soil are not the result of pedogenic accumulation of normal organic matter within an A-horizon. Nuclear magnetic resonance spectroscopy clearly documents the high amount of aromatic components (charcoal), which is responsible for the dark color. This indicates severe burning events at the site and the smaller charcoal dust (black carbon) was transported to deeper parts of the profile during the process of clay translocation.  相似文献   

20.
《Quaternary Science Reviews》2003,22(10-13):1273-1278
Here we report on investigations into optical dating of fossil mud-wasp nests as a means of constraining the ages of overlying and underlying rock paintings in northern Australia. We describe the application of a ‘dual-signal’ regenerative-dose approach, using the easy-to-bleach (‘fast’) and hard-to-bleach (‘slow’) components of optically stimulated luminescence (OSL) emitted by individual sand-sized grains of quartz extracted from two nests: a modern nest (<2 yr old) and a nest dated by 14C to about 30,000 calendar years (∼30 ka). For the modern nest, most of the palaeodoses obtained from both the fast and slow components are consistent with a zero age, while the 14C-dated nest yielded an age of 27.1±1.5 ka from those grains that yielded concordant palaeodoses from the fast and slow components (as measured by linearly modulated OSL). Our findings indicate that a dual-signal approach permits grains that were fully bleached by sunlight at the time of nest construction, and that have since remained concealed in the light-safe ‘core’ of a nest, to be distinguished from (a) grains that were incompletely bleached before nest construction, and (b) grains embedded in the continuously light-exposed, exterior portion of a nest. We conclude that reliable optical ages for small mud-wasp nests associated with ancient rock art may be obtained using the dual-signal approach and the light-safe grains.  相似文献   

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