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1.
Lake-level changes are important environmental events. The paleoshorelines of a lake reflect past water levels and record information on paleoclimatic changes. Dating these events places the climatic changes in a time sequence. From shorelines ∼1, ∼4, and ∼6 m above current lake level on the eastern shore of Linggo Co, central Tibet, we collected eight samples for optically stimulated Luminescence dating. Two stratigraphic units, distinguished on the basis of color and sedimentology, were recognized beneath each shoreline. The ages obtained were 0.9 ka (upper layer) and 3.1 ka (lower layer) for lowest shoreline, 1.9 ka (upper layer), and 6.1–9.0 ka (bottom layer) for middle shoreline, and 9.6 ka for high shoreline. Two dates were considered to be unreliable due to incomplete bleaching. We attribute the higher lake levels to increased precipitation brought by the Indian monsoon in the Holocene. 相似文献
2.
Detailed mapping of geomorphological and biological sea-level markers around the Capo Vaticano promontory (western Calabria, Italy), has documented the occurrence of four Holocene paleo-shorelines raised at different altitudes. The uppermost shoreline (PS1) is represented by a deeply eroded fossiliferous beach deposit, reaching an elevation of ∼2.2 m above the present sea-level, and by a notch whose roof is at ∼2.3 m. The subjacent shoreline PS2 is found at an elevation of ∼1.8 m and is represented by a Dendropoma rim, a barnacle band and by a wave-cut platform. Shoreline PS3 includes remnants of vermetid concretions, a barnacle band, a notch and a marine deposit, and reaches an elevation of ∼1.4 m. The lowermost paleo-shoreline (PS4) includes a wave-cut platform and a notch and reaches an elevation of ∼0.8 m. Radiocarbon dating of material from individual paleo-shorelines points to an average uplift rate of 1.2–1.4 mm/yr in the last ∼6 ka at Capo Vaticano. Our data suggest that Holocene uplift was asymmetric, with a greater magnitude in the south-west sector of the promontory, in a manner similar to the long-term deformation attested by Pleistocene terraces. The larger uplift in the south-western sector is possibly related to the additional contribution, onto a large-wavelength regional signal, of co-seismic deformation events, which are not registered to the north-east. We have recognized four co-seismic uplift events at 5.7–5.4 ka, 3.9–3.5 ka, ∼1.9 ka and <1.8 ka ago, superposed on a regional uplift that in the area, is occurring at a rate of ∼1 mm/yr. Our findings places new constrains on the recent activity of border faults south of the peninsula and on the location of the seismogenic source the 1905 destructive earthquake. 相似文献
3.
Qinghai Lake, on the northeastern Qinghai-Tibetan Plateau, is the largest extant closed-basin lake in China, and has been the subject of numerous palaeoclimatological and palaeoenvironmental studies. In this study, 32 samples of aeolian sand, loess and palaeosol at six sites, and 1 sample of shoreline deposits underlying aeolian deposits were dated using optically stimulated luminescence (OSL). Where available, OSL ages are in agreement with previously published 14C ages. Our dating results, in combination with previous published ages on aeolian deposits showed that: (1) The oldest aeolian deposits around Qinghai Lake are in excess of 165 ka. (2) Aeolian deposition then began at ∼14 ka in the Qinghai Lake area. Periods of palaeosol formation occurred at ∼16.9 ka, ∼12.2–11 ka, ∼10–9 ka, ∼5.2–4 ka, and ∼3.9–0.7 ka. (3) The accumulation intervals of palaeosols are generally consistent with drilling-core-based environmental change proxies, indicating that palaeosols were formed during wet periods with higher vegetation cover. (4) A depositional hiatus period of ∼40–50 ka exists between the surface mantle aeolian deposits and underlying gravel deposits. (5) Lake levels during the Holocene did not exceed 3205.2 m elevation (11.8 m above recent lake level of April, 2010). 相似文献
4.
Lake Manas, located in northwestern China, has been formed in a structure depression since early Quaternary. Optically stimulated luminescence (OSL) dating is applied to the lacustrine and aeolian deposits collected from the lake to construct a chronological frame for lake level fluctuations since the last inter-glacial period. The results yielded two stages of high lake stands (∼20 m above the present lake bed) occurred before 66 ka and 38–27 ka ago. No evidence for Holocene high lake level was found in the studying area. 相似文献
5.
Relict (perched) lacustrine deltas around the perennially ice-covered lakes in the Taylor Valley, Antarctica, imply that these lakes were up to 40 times larger in area than at present since the last glacial maximum (LGM). These deltas have been used to constrain ice-margin positions in Taylor Valley, and the boundaries of the proposed LGM ice-damned Glacial Lake Washburn. The timing of these high lake levels has depended on 14C chronologies of algal layers within relict lacustrine deltas. To provide additional geochronometric data for the post-LGM lake-level history, we applied photon-stimulated-luminescence (PSL) sediment dating to polymineral fine silt and sand-size quartz from 7 perched-delta and 3 active-delta sites of different elevations along 3 major meltwater streams entering Lake Fryxell. Our PSL dating of 4 quartz-sand samples from core tops in the seasonal ice-free moat of Lake Fryxell (elevation ∼18 m a.s.l.) and two core-top moat samples from the seasonal moat of Lake Vanda in nearby Wright Valley establish that adequate PSL clock zeroing (by daylight) occurs in regional, modern shoreline deposits. Minimum-age micro-hole PSL results from the moats are consistently near 100 a. Minimum-age micro-hole age estimates for the deltas range from ∼50 to 100 a near the present lake level up to 13.4 ± 1.3 ka at 240 m. These are systematically younger than the comparable, reservoir-uncorrected, 14C ages that range from 7 ka (cal yr BP) to 13 ka (cal yr BP) near lake level up to 20 ka (cal yr BP) at 220–240 m elevation. Our results indicate the occurrence of a dramatic discrepancy between PSL minimum-age and 14C age estimates that is presently unresolved. 相似文献
6.
Lake level fluctuations of closed lakes in monsoonal regions are direct indicators of regional moisture variability related to the intensity of monsoon activities. In the current study, quartz OSL dating was applied to construct the chronology of two sedimentary sequences from the east and west shores of Huangqihai Lake in the East Asian monsoon area, and the history of lake level fluctuations during the late Quaternary was established. In the current study, we present field investigation findings of highstands of >87 m above the modern lake in enclosed Huangqihai Lake in northern China, and also use luminescence dating to establish the timing for the highstands. We conclude that: (1) Lake highstands occurred during both MIS 5 (>87 m above the modern lake) and early Holocene (∼9–8 ka, >54 m above the modern lake), (2) No highstands were observed for MIS 3 and MIS 2 during which loess has accumulated indicative of much drier climate; (3) The evolution of lakes in East Asian monsoon marginal area (e.g. Huangqihai Lake) is linked with the monsoon variation. 相似文献
7.
QiShun Fan ZhongPing Lai Hao Long YongJuan Sun XiangJun Liu 《Quaternary Geochronology》2010,5(2-3):223-227
The Qaidam Basin in the northeastern Qinghai–Tibetan Plateau (QTP) is one of the largest hyper-arid intermontane basins in the northern hemisphere, and has abundant records for the study on palaeo-lake level fluctuations and palaeoclimatic changes. Significant efforts have been invested to define the timing of shoreline deposits using radiocarbon dating. However, due to the dating limit, the absence of organic materials and carbon reservoir effects for radiocarbon dating in arid areas, it is difficult to establish a reliable chronology for shoreline deposits. Therefore, controversy exists regarding the chronology for the high lake level in the Qaidam Basin, as well in the QTP. Some proposed that high lake levels occurred during late Marine Isotope Stage (MIS) 3, while others recently argued that the highest lake level in the QTP and adjacent regions existed in MIS 5. In Gahai Lake (now a salt lake), we investigated a section comprising lacustrine and shoreline deposits, which was about 25 m above the present lake level. Seven samples were collected for quartz optically stimulated luminescence (OSL) dating. A sample collected from a fine sand layer (the bottom of the section, and 12 m above the present lake level), which was assumed to have been deposited underwater, gave an OSL age of 82 ± 8 ka. It suggested that the lake level was at least 12 m higher than present in late MIS 5. The high lake level could maintain till about 73 ± 6 ka, and then decreased. This lake level decrease resulted in a gravel layer deposit between 73 ± 6 and 63 ± 6 ka (roughly during MIS 4). The lake level rose again (about 24 m above the present lake level) between 63 ± 6 and 55 ± 5 ka (roughly in early MIS 3). No lacustrine or shoreline deposits higher than the top of the current section were found around Gahai Lake. Thus, higher than present lake levels in Gahai Lake occurred in both late MIS 5 and early MIS 3. 相似文献
8.
The palaeo-shorelines around the lakes on the Tibetan Plateau can be used to reconstruct water level variations, which serve as sensitive indicators of hydroclimate change. Extensive studies have been carried out to constrain the Holocene lake level fluctuations by dating shorelines with a variety of methods (e.g., luminescence, 14C, 10Be and U–Th series). In comparison, the timing of the lake level variations during the last glacial and subsequent deglaciation periods has been rarely studied. The driving factors of such changes, therefore, remain elusive. In this study, we performed a detailed luminescence dating investigation on six samples taken from a nearshore sedimentary outcrop in the south of Selin Co basin. The post-IR IRSL signals measured at 225 °C (pIRIR225) on sand-sized K-feldspar grains demonstrated a generally good behavior and yielded reliable chronologies, while the optically stimulated luminescence (OSL) signals of quartz showed systematical age underestimation, which was attributed to anomalous fading. Six pIRIR225 ages ranging from 15 to 10 ka suggested that the lake level of Selin Co during the last deglaciation reached up to 40–45 m high above the modern lake level. In view of the regional precipitation and temperature proxy records, we consider that the glacier meltwater supply has likely been the primary contributor to the lake highstands during the last deglaciation. 相似文献
9.
The Late Quaternary hydroclimatic evolution of lake systems in Mongolia remains unclear. Here we present a record of lake level variations at Orog Nuur in the Valley of Gobi Lakes in southern Mongolia, since the last interglaciation, based on paleo-shoreline dating using quartz optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) signals. Due to feldspar contamination that could not be eliminated, the OSL signals of quartz single-aliquots (SA), except for two Holocene samples, were unsuitable for dating and a double SA regenerative-dose (SAR) protocol was used for the quartz fraction of these two samples. The pIR50IR170 and pIR200IR290 signals of K-feldspar SA were used to date Holocene samples and old samples (>100 ka), respectively, with the SAR protocol. To determine the bleaching condition of the pIR200IR290 signals, the first pIRIR dating of K-feldspar single-grains of lake shoreline sediments in Mongolia was performed. The equivalent doses of K-feldspar grains show normal distributions, suggesting that the pIR200IR290 signals are well-bleached. Overall, the results, combined with those of previous studies, show that a mega-lake developed at 56 m above the modern lake level (a.m.l.) during MIS 5e (124.2 ± 6.8–114.7 ± 8.0 ka). Holocene high-stands occurred in the last deglaciation–early Holocene (11.1 ± 1.0 ka) at 23 m a.m.l. and in the mid-Holocene (6.7 ± 0.8–3.3 ± 0.4 ka) at 20–14 m a.m.l. The dimensions of the paleo-lakes were recovered, and a hydrological index indicates that the effective moisture during MIS 5e and the mid-Holocene was 10.7 times and 3.6–5.0 times larger than today, respectively. Finally, the possible mechanisms behind the lake level history are discussed based on correlation with independent paleoclimatic records. 相似文献
10.
Sedimentary deposits in the foreland basin of the northeastern Qilian Mountains are crucial documents recording tectonic activity and climate changes on the Tibetan Plateau. In this study, luminescence dating was used to date alluvial conglomerates and fluvial terrace sediments collected from the Beida River in the Jiuquan Basin, a foreland basin in the Hexi Corridor, northeastern Qilian Mountains. Detailed sedimentology and luminescence ages reveal that alluvial conglomerates accumulated from before 620 ka to 12 ka and that sediment accumulation rates increased at ∼330 ka and ∼35 ka, coinciding with the dates of two tectonic events (∼350 and ∼50 ka) and followed by climate cooling (from marine isotope stage (MIS) 9 to MIS 8 and from MIS 3 to MIS 2). This reveals that variations in the sediment accumulation rates are controlled by the coupling of tectonic uplift and climate cooling. The highest terrace (T7) that developed on the alluvial conglomerate base formed at ∼ 12 ka. The incision rate in the early Holocene was ∼2.1 mm/yr and increased to ∼14.6 mm/yr during the middle and late Holocene. The variations in the river incision rate provide geomorphic evidence for Holocene climate patterns in arid and semiarid areas. Luminescence dating offers a credible temporal framework for the deposits and reveals climate and tectonic effects on the evolution of the foreland basin, northeastern Qilian Mountains. 相似文献
11.
The island of Crete in the forearc of the Hellenic subduction zone has a rugged topography with local relief exceeding 2 km. Based on the elevation of marine shorelines, rates of rock uplift during the Late Holocene were previously estimated to range between 1 and 4 mm/a in different parts of the island. These rates may, however, not be representative for longer timescales, because subduction earthquakes with up to 9 m of vertical coseismic displacement have affected Crete in the Late Holocene. Here we use a well preserved sequence of marine terraces near Kato Zakros in eastern Crete to determine the rate of rock uplift over the last ∼600 ka. Field investigations and topographic profiles document a flight of more than 13 marine bedrock terraces that were carved into limestones of the Tripolitza unit. Preliminary age constraints for the terraces were obtained by 10Be exposure dating of rare quartz-bearing sandstone clasts, which are present on some terraces. The 10Be ages of these samples, which have been corrected for an inherited nuclide component, yielded exposure ages between ∼100 ka and zero. Combined with geomorphologic evidence the two oldest 10Be ages suggest that the terraces T4 and T5, with shoreline angles at an elevation of ∼68 and ∼76 m above sea level, respectively, formed during the marine isotope stage 5e about 120 ka ago. The correlation of the higher terraces (T6 to T13) with regional sea-level highstands indicates sustained rock uplift at a rate of ∼0.5 m/ka since at least ∼600 ka. As normal faulting has dominated the tectonics of Crete during the last several million years, upper crustal shortening can be ruled out as a cause for rock uplift. We argue that the sustained uplift of the island results from the continuous underplating of sediments, which are transferred from the subducting African plate to the base of the crust beneath Crete. 相似文献
12.
Coastal plain of Hangzhou Bay, to the south of the present Yangtze Estuary, is closely linked to the evolution of the Yangtze River delta. However, absolute age of Pre-Holocene sediments is limited, which hinders the understanding of this area's environmental evolution. In this study, using optically stimulated luminescence (OSL), single aliquots and single grains of quartz and K-feldspar were used to date the late Quaternary sediments in coastal plain on the southern Hangzhou Bay. The vertical difference in particle size composition render either silt- or sand-sized quartz for dating. Cross-checking of multiple OSL dating methods indicated that the upper ∼65 m recorded the Holocene part of the succession; sediment from a depth of 136.6 m was dated to ∼180 ka. It was found that the single-grain method was more reliable in comparison to single-aliquot age, the former minimized the effect of signal components. Single-grain quartz and K-feldspar luminescence yielded consistent ages at sample depth of 136.6 m (∼160–180 ka), while the latter gave robust age at depth of 115.5 m (∼150 ka). This chronology is in general in accordance with neighbouring cores and can constrain paleomagnetic dating results in those cores. Taking together, the study site has thickest Holocene deposits in comparison to the highland centered around Taihu Lake on the southern Yangtze delta. Moreover, the luminescence characteristics of quartz from different sample depths, behaved differently with respect to luminescence sensitivity, signal components and saturation level, perhaps reflecting varied provenance and weathering characteristics caused by climate change. 相似文献
13.
Defining rates of landscape evolution in a south Tibetan graben with in situ‐produced cosmogenic 10Be 
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下载免费PDF全文 The Tangra Yum Co graben is one of the active structures that accommodate the east‐west extension of the southern Tibetan Plateau and hosts one of the largest Tibetan lakes, which experienced lake‐level changes of ~200 m during the Holocene. In this study, cosmogenic 10Be is employed to: (1) quantify catchment‐wide denudation rates in fault‐bounded mountain ranges adjacent to the Tangra Yum Co graben; (2) date palaeo‐shorelines related to the Holocene lake‐level decline; and (3) determine the age of glacial advances in this region. The fault‐bounded, non‐glaciated mountain range north of Tangra Yum Co – and presumably most other areas around the lake – erode at low rates of 10–70 mm/ka. Owing to the slow erosion of the landscape, the sediments delivered to Tangra Yum Co have high 10Be concentrations. As a consequence, accurate exposure dating of sediment‐covered terraces and beach ridges is difficult, because the pre‐depositional 10Be concentration may exceed the post‐depositional 10Be concentration from which exposure ages are calculated. This difficulty is illustrated by a rather inaccurate 10Be exposure age of 2.3 ± 1.4 ka (i.e. an error of 60%) for a terrace that is located 67 m above the lake. Nevertheless, the age is consistent with luminescence ages for a series of beach ridges and provides further evidence for the decline of the lake level in the late Holocene. At Tangra Yum Co exposure dating of beach ridges via 10Be depth profiles is not feasible, because the pre‐depositional 10Be component in these landforms varies with depth, which violates a basic assumption of this approach. 10Be ages for boulders from two moraines are much older than the early Holocene lake‐level highstand, indicating that melting of glaciers in the mountain ranges adjacent to Tangra Yum Co has not contributed significantly to the lake‐level highstand in the early Holocene. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
14.
Lakes over the inner Tibetan Plateau (TP) are very sensitive to the regional environmental transformations and climate changes. Well-preserved lake sediments around these lakes provide critical geomorphological and sedimentary evidence that can be used to infer the past hydroclimate changes. In this study, a lacustrine section from a sandy shoreline (∼74 m above the modern lake) situated to the northwest of modern Dawa Co in the inner TP was investigated using both luminescence and radiocarbon dating methods. Our results demonstrated: (1) the quartz optically simulated luminescence (OSL) dating yielded much younger ages (∼4 ka) than that of the post-infrared IRSL (pIRIR) dating of the K-feldspar fraction; (2) fading test showed g-values ranging between 1.34 and 4.46%/decade for quartz OSL signals, which is considered to be responsible for the underestimation of the corresponding ages; (3) the AMS 14C age of the charcoal sample from the section is in line with the K-feldspar pIRIR225 ages, confirming the reliability of the pIRIR225 dates and the underestimation of the quartz OSL ages. The anomalous fading of quartz OSL signals and the consequent age underestimation have been reported in several other lakes on the TP, we presented here for the first time firm evidence of the phenomenon with the help of a robust independent control of AMS 14C age of the charcoal. Based on the pIRIR225 and AMS 14C ages, we conclude that Dawa Co underwent a prominent highstand during the early Holocene (∼9–7 ka), which was probably controlled by the large amounts of glacial meltwater input and the increased monsoonal precipitation. 相似文献
15.
Optically stimulated luminescence (OSL) dating is becoming a useful technique to yield absolute age of organic-poor sandy deposits. The buried tidal sand body (BTSB) in the coastal zone of northern Jiangsu Province, China, has been suggested to have the same origin as the offshore radial sand ridge in the Yellow Sea. However, chronological constrain of the BSTB is still quite limited. In this study, OSL measurements were conducted using silt-sized multi-grain and coarse-grained single-grain quartz to constrain the depositional history of a 25.6 m core from the BTSB. A low luminescence sensitivity of quartz was observed, and only ∼1.04% of the grains passed the standard rejection criterion for single-grain measurement. Analysis of paired OSL ages from two grain-size fractions using different protocols showed that silt-sized quartz ages were underestimated of 0.14–1.35 ka in comparison to coarse-grained quartz in the depth interval of 5.8–22.4 m. We interpret such an age discrepancy as the effects of lateral infiltration of fine-grained sediment into the sand body due to dynamic feature of channel-ridge system on the shelf. As far as we know, it is the first time that such infiltration is demonstrated through OSL dating. Our OSL data indicated that there is a significant hiatus between the Late Pleistocene stiff clay layer (50–18 ka) and the Holocene sequence. Holocene deposits only occurred in the last 2 ka, with rapid accumulation of ∼17 m-thick sediments at ∼2–1 ka, a slower accumulation between ∼1 and 0.1 ka and rapid land emergence through an accretion of ∼4 m-thick sediment over the past ∼0.1 ka. This study highlights the complexity of OSL dating in highly dynamic sedimentary environments. Therefore, examining different grain size fractions and comparing different measurement protocols are highly deserved in carrying out OSL dating in such environments. 相似文献
16.
Optically stimulated luminescence (OSL) dating was performed on Late Quaternary deltaic sequences from a 55-m-long core sampled from the Nakdong River estuary, Korea. OSL ages obtained from chemically separated fine (4–11 μm) and coarse (90–212 μm) quartz grains ranged from 29.4 ± 2.6 to 0.4 ± 0.04 ka, revealing clear consistency between the grain-size fractions. The De values from the standardized growth curve (SGC) are consistent with those from the single-aliquot regenerative-dose (SAR) procedure, which suggests that the SGC is valid for the Nakdong deltaic sediments. The 14C ages of shells and wood fragments ranged from 11 to 2.9 ka, demonstrating reasonable agreement with the OSL ages, within the error range. However, the limited number and random sampling interval of the 14C age data (10 ages) result in a simple linear and exponential trend in the depth–age curve. In contrast, OSL ages obtained by high-resolution sampling show down-section variations in the depth–age curve, indicating the occurrence of rapid changes in sedimentation rate. It is suggested that the high-sampling-resolution OSL ages provide a more realistic and detailed depth–age curve and sedimentation rate. The Nakdong deltaic sediments were divided into five units based on sedimentation rate. The lowest (unit 5) shows a break in sedimentation between the last glacial maximum (LGM) and the Holocene. The sedimentation rate increased in units 4 and 3, presumably corresponding to the early to middle Holocene sea level rise and high stand. Unit 2 shows a gradually decreasing sedimentation rate following the regression of the shoreline, until about 2 ka. The progradation of the Nakdong River delta resulted in the rapid accumulation of unit 1 during the last 2000 years. 相似文献
17.
Anne Hormes Maarten Blaauw Svein Olaf Dahl Atle Nesje Goran Possnert 《Quaternary Geochronology》2009,4(4):267-277
The problem of insufficient age-control limits the utilisation of the 8.2 ka BP event for modelling freshwater forcing in climate change studies. High-resolution radiocarbon dates, magnetic susceptibility and lithostratigraphic evidence from a lake sediment core from Nedre Hervavatnet located at Sygnefjell in western Norway provide a record of the early Holocene. We use the method of radiocarbon wiggle-match dating of the lake sediments using the non-linear relationship between the 14C calibration curve and the consecutive accumulation order of the sample series in order to build a high-resolution age-model. The timing and duration of Holocene environmental changes is estimated using 38 AMS radiocarbon dates on terrestrial macrofossils, insects and chironomids covering the time period from 9750 to 1180 cal BP. Chironomids, Salix and Betula leaves produce the most consistent results. Sedimentological and physical properties of the core suggest that three meltwater events with high sedimentation rates are superimposed on a long-term trend with glacier retreat between 9750 and 8000 cal BP. The lake sediment sequence of Nedre Hervavatnet demonstrates the following: only a reliable high-resolution geochronology based on carefully selected terrestrial macrofossils allows the reconstruction of a more refined and complex environmental change history before and during the 8.2 ka event. 相似文献
18.
A detailed survey of morphological and biological markers of paleo-shorelines has been carried out along the coastal sector of Mt. Etna volcano (eastern Sicily, Italy), in order to better define causes and timing of vertical deformation. We have mapped markers of raised Holocene shorelines, which are represented by beach rocks, wave-cut platforms, balanid, vermetid and algal rims. The timing of coastal uplift has been determined by radiocarbon dating of shells collected from the raised paleo-shorelines and, to correctly assess the total amount of tectonic uplift of the coast during the Late Holocene, we have compared the elevation-age data of sampled shells to the local curve of Holocene sea-level rise. Taking into account the nominal elevation of the associated paleo-shorelines, an uplift rate of 2.5–3.0 mm/year has been estimated for the last 6–7 ka. This general process of uplifting is only locally interrupted by subsidence related to flank sliding of the volcanic edifice, measured at docks and other manmade structures, and by acceleration along the hinge of an active anticline and at the footwall of an active fault. Based on this new data we suggest more precise time–space constraints for the dynamics of the lower eastern flank of Mt. Etna volcano. 相似文献
19.
OSL dating of paleoshorelines at Lagkor Tso, western Tibet 总被引：1，自引：0，他引：1
Lagkor Tso, a saline lake located south of Gertse in western Tibet exhibits spectacular flights of paleoshorelines. Optically stimulated luminescence (OSL) dating on quartz using the single-aliquot regenerative-dose (SAR) protocol from five paleoshoreline deposits shows that the lake level was 130 m higher than the present lake surface 5.2 ka ago. The lake level dropped rapidly by 25 m between 5.2 ka and 3.7 ka ago. Lake shrinkage further accelerated between 3.7 ka and 3.2 ka ago, when the lake level was just 74 m above the present lake surface. Luminescence characteristics and problematic samples are discussed. 相似文献
20.
In the foreland regions of the Western Arunachal Himalaya (WAH), geological studies along the Kameng river (between Tipi village and the Himalayan Frontal Thrust (HFT)) reveal four levels of unpaired terraces and a paired terrace. In WAH, wrench deformation of HFT zone resulted in a SE propagation of the Balipara anticline and it is suggested that the Mikir high basement controls its orientation. Ages of terrace surfaces from Siwaliks suggest that since the Late Pleistocene, Kameng River migrated at a rate varying between ∼7.5 cm/yr in upper reaches and ∼13.5 cm/yr towards northeast due to HFT related uplift. In the Brahmaputra plains, luminescence ages of abandoned paleochannel deposits suggest eastward shifting of the Kameng river at an average rate of ∼1 m/yr. Field evidences between Bhalukpong and Tipi villages show Pliocene strath and Quaternary terrace surfaces, displaced by faults that do not correspond to the mapped faults in the foreland region. We interpret them as out-of-sequence thrusts (OOSTs). This is the first such report of OOST in the NE Himalaya. Presence of active OOST is inferred by similar age (∼1 ka) and differing incision rates of the surface of same terrace (T2b) in adjacent locations. This suggests that OOSTs in the western Arunachal Siwalik are <1 ka. Average slip rate and horizontal shortening rate on OOST during the Holocene, are calculated as ∼12 mm/yr and 7 mm/yr respectively. Thus any estimation of Holocene shortening in the Siwalik therefore, needs to incorporate slip along the OOSTs given that it accommodates a significant amount of N-S compression of the Himalayan fold-and-thrust belt. The reason for OOST in the WAH Siwalik foreland is discussed in terms of the critical wedge dynamics arising from erosion via tectonics-climate interaction. We estimate a minimum slip rate of Siwalik as ∼27 mm/yr during the Holocene and suggest acceleration in shortening rates east of Bhutan. 相似文献