滇东、滇西地区主要河流低阶地地貌面的年代学研究

在流水沉积物热释光测年适用性和测年数据可靠性研究的基础上 ,对滇东、滇西地区几条主要河流的低阶地进行了系统采样和多方法的综合测年 ,获得了该区主要河流低阶地沉积物的堆积年代及其阶地面的形成时代 ,该区I级支流T1阶地堆积于 4 50 0～ 110 0 0aB .P .,其阶地地貌面形成于 4 50 0～ 50 0 0aB .P .;T2 阶地堆积于 90 0 0～ 2 2 0 0 0aB .P .,该级地貌面形成于 90 0 0～ 10 0 0 0aB .P .;主流T1阶地的堆积年龄为 90 0 0～ 170 0 0aB .P .,阶地面形成于 90 0 0～ 10 0 0 0aB .P .;T2 阶地的沉积年龄为 150 0 0～ 4 50 0 0aB .P .,阶地地貌面形成于 150 0 0aB .P .左右。同时 ,通过阶地堆积时期古气候、古环境的分析 ,探讨了该区低阶地地貌面的成因     

新疆叶尔羌河上游全新世阶地的释光年代与河流下切速率

采用细颗粒石英简单多片再生法对新疆叶尔羌河上游阶地进行了光释光测年,并在不同实验室进行了等效剂量对比测试,结果基本一致.测年结果显示,该阶地沉积形成于距今4.3～7.3ka,自阶地形成以来,河流下切(27±5)m,下切速率(6.3±1.2)mm/a.塔什库尔干河中上游河流的快速下切可能与慕士塔格山穹窿的快速隆升或第四纪...     

三阳川盆地渭河阶地发育与河谷地貌演化

阶地是研究现代河谷形成发育的重要地貌标志,结合年代学研究可以为区域古环境提供丰富的构造、气候和古水文变化信息.通过古地磁、电子自旋共振、光释光及黄土-古土壤地层序列的对比,初步确定渭河上游三阳川盆地1.2Ma以来共发育和保存着13级河流阶地.阶地特征与成因分析表明,阶地是在构造抬升背景下,河流系统对轨道尺度气候变化的响应,侧蚀堆积和深切下蚀作用交替进行.阶地序列的河漫滩顶部大多对应于古土壤层发育,表明河流下切阶地形成主要发生在古土壤开始发育的冰期向间冰期过渡阶段.河流两侧阶地时空展布的差异表明,0.62Ma三阳川盆地发生了构造反转,由过去盆地的整体抬升为主逐渐转变为断陷沉降.综合流域内阶地序列的研究,表明渭河上游现代河谷的形成发育起始于早更新世晚期1.4~1.2Ma.     

乌鲁木齐河河谷地貌与天山第四纪抬升研究

乌鲁木齐河谷出山口分布400多米厚的沙尔巧克砾石层, 是本段天山隆升形成的磨拉石建造. 一次扩大边界的构造抬升事件使沙尔巧克砾石层堆积终止, 于其前缘发生褶皱断裂, 并开始下切. 砾石层顶部测年表明, 这一时间发生于1148 kaBP, 应该是天山对青藏高原昆-黄运动的响应. 此后是河流反复切割和堆积的阶地形成时期, 共形成9级阶地. 运用ESR和TL测年技术, 第3级阶地与后峡至二营第2级阶地堆积于氧同位素6阶段, 5, 6级阶地分别堆积于338 ka和562～591 kaBP. 同位素12阶段发生最早的高望峰冰期.     

黄河中游河流阶地的对比及阶地系列形成中构造作用的多层次性分析

黄河在流经青藏市原东北缘海原－同以弧形构造区的过程中,发育了多达10－21组的斯座和侵蚀型阶地,其最大拔河高度为40lm,最高阶地的发育年代为1．57MaBP。通过对该区米家山、车木峡和黑山峡河口3处黄河阶地以及我国北方大范围内河流阶地的对比分析发现,河流阶地系列形成中在构造作用上具有多层次性特征,即它包含了不同范围或规模和不同级次构造隆升作用所导致的阶地。研究区的黄河阶地系列可以划分为3个层次。其中,第一层次的阶地共有6级,为我国北方大范围内同期形成的阶地,它们代表1．6Ma以来青藏高原阶段性隆升的次数,其隆升幅度由西向东逐渐减小;第二层次的阶地共有5级,为海原－天景山构造区内同期发育的阶地,它们代表1．6Ma以来该构造区本身自隆升的次数和幅度;第三层次阶地为发育在米家山东坡的10级不同期阶地,它们代表1．6Ma以来海原构造山地独自的抬升的次数和幅度。阶地发育时间与黄土－古土壤序列的对比还表明,反映青藏高原大范围构造隆升的第一层次阶地与气候变化之间有很好的可对比性,其形成年代均与相应古土壤发育时间的间冰期对应,暗示导致河流下切的在范围构造抬升与强干冷期后同样可导致河流下切的气候暖湿期紧密相关,它们共同组成了构造－气候旋回。第二层次和第三层次阶地的形成时间与气候变化之间无统一特定的关系,显示它们的形成更主要的受控于天景山块体和海原构造带的隆升作用。因此,研究区的河流阶地主要可分为2种成因类型。一种是在大范围构造抬升和气候变化联合作用下形成的构造－气候旋回阶地,此类阶地分布范围广,具有区域间的可对比性;另一种是以局部构造抬升为主导因素形成的脉动式构造旋回阶地,此类阶地的分布受 控于活动构造带,在构造区带内自成体系,不具有区域间的可对比性。     

宁夏沙坡头黄河大弯的成因分析

黄河在宁夏沙坡头形成了"几"字形河曲地貌,并在河曲凸岸发育了3级河流阶地。本文针对沙坡头大弯河流阶地特征、阶地年龄,以及大拐弯的成因进行了分析,探讨本区地貌发育的机制。结果表明:(1)沙坡头大弯3级河流阶地形成的主要原因是构造抬升作用,气候变化对此处阶地形成的作用不明显。在区域新构造活动强烈的背景下,约中更新世末期中卫盆地开始抬升,黄河河道被固定,河流下切形成本区的最高阶地T3;约在70kaB.P.、8kaB.P.形成T2、T1阶地。(2)沙坡头黄河大拐弯是由香山—天景山断裂左旋走滑位错,以及水流受地球自转偏向力的河流内生动力共同作用的结果,并且河流的内生动力作用远大于前者的贡献。     

兰州马衔山北缘断裂带古地震初步研究

兰州马衔山北缘断裂带为一条全新世活动断裂 ,大致由 4条次级断裂段组成 .沿断裂带发现了多期古地震事件 ,其活动具有时空不均匀性 .其中东段的马衔山段可以确定 2次古地震事件 ,距今 5850± 50 0aB .P .,2 0 60± 42 0aB .P .,复发间隔约 380 0a ;震级 7～ 7.5级左右 .中段的七道梁段发现 2次古地震事件 ,距今 1 682 0± 80aB .P .,1 0 80 0± 1 40aB .P ..西段的雾宿山咸水沟段可以确定一次古地震事件 ,其年代为 1 2 45± 560aB .P .,结合史料考证结果 ,认为就是 1 1 2 5年兰州 7级地震 .从古地震活动年代及复发间隔分析 ,马衔山北缘断裂带未来的强震危险段应为东段的马衔山段和西段的雾宿山咸水沟段 .     

华山山前断裂中段晚第四纪活动的地貌表现及响应

调查了华山山前断裂中段（石堤峪-杜峪）晚更新世以来,尤其是全新世以来的断层构造地貌,讨论了它们的成因、特点及对断裂活动的响应关系。断层构造地貌主要包括：断层三角面、断层陡坎、洪积阶地、埋藏型洪积扇以及冲沟裂点。对各大沟峪峪口的洪积阶地进行了大比例尺微地貌测量,并在部分沟峪两侧沿断层崖陡坎及冲沟沟床布置了测线。结合T1、T2级洪积阶地位错测量结果及其14C年龄计算得到,华山山前断裂中段6000a-2000aB.P.的垂直滑动速率为1.485mm/a;2000aB.P.以来的垂直滑动速率为3.73mm/a。最后结合野外调查与理论认识,建立了正断层作用下洪积阶地与埋藏型洪积扇的演化模式。本研究结果支持华山山前断裂是1556年华县814级地震发震构造的观点。     

福建深沪湾地区晚更新世中晚期以来的地壳运动

研究表明 ,深沪湾地区晚更新世早中期地壳运动以下沉为主 ,沉积了冲洪积含砾砂粘土层。晚更新世中晚期以来地壳先升后降 ,近 15 0 0aB .P .以来地壳较为稳定。在 (2 5 5 80± 2 4 90 )～15 4 6 0aB .P .期间 ,该区地壳与水动型海平面大致同步升高 ,上升幅度为 8m左右 ,速率达 0 .78mm/a ,深沪湾内生长了古牡蛎。 15 4 6 0～ 110 0 0aB .P .期间 ,该区地壳快速上升 ,上升幅度超过 10m ,速率超过 2mm/a ,形成多个由晚更新世含砾砂粘土构成的低凹洼地 ,古牡蛎滩成为台地。其后地壳稳定 ,在低凹洼地内生长了古森林。 70 0 0aB .P .深沪湾发生了由强古地震导致的地壳快速下沉 ,古森林生长的凹陷洼地变成泻湖环境 ,古牡蛎滩台地与海面很接近。 2 0 0 0aB .P .左右 ,深沪湾又一次发生由强古地震导致的地壳快速下沉 ,古森林下沉到更深的海底 ,古牡蛎滩回到潮间带海域     

黄河上游盆地重组所导致的快速侵蚀下切

高起伏的造山高原边缘的快速剥蚀常被用来指代区域地表隆升~(1～3)。然而,诸如岩体隆升的空间差异~4,降雨的地形效应以及冰川~5、滑坡导致的河道堵塞~(6,7)等阻碍河流下切的因素,可能会使剥蚀作用严重滞后于地表抬升~8。本文中,我们通过研究青藏高原东北缘黄河沿岸沉积盆地的地层学、年代学和地貌学特征,重建黄河上游侵蚀下切的时间、速率以及模式。我们发现河流下切的起始时间明显晚于山体开始隆升的时间(14～8Ma)~9。高原边缘的河流下切始于1.8Ma~(10),然后以大约350km/Ma的速度向上游传递~(11)。我们认为该地区在气候驱动下的湖泊扩张并溢出作用是黄河上游快速下切的主要原因,并最终导致了现代黄河地貌的形成。     

天山北麓活动背斜区河流阶地与古地震事件

利用航空遥感照片和Google earth卫星影像,对天山北麓独山子活动背斜区奎屯河两侧的河流地貌进行解释,结合野外调查发现,奎屯河流经独山子背斜段发育7级基座阶地,阶地基座为上新统独山子组泥岩,其上部为2.5 ～ 15m厚的砂砾石层和砂质黏土.在开挖或剥离的各级阶地堆积物剖面中采集细粒堆积物样品,实验室中采用细粒石英...     

Slip Rate on the Altyn Tagh Fault on the West of the Cherchen River (Between 85°～85°45′E) Since Late Quaternary

Because of the significance to the formation and evolution of the Tibetan plateau, the displacement and slip rate of the Altyn Tagh fault have been topics full of disputation. Scientists who hold different opinions on the evolution of Tibet insist on different slip rates and displacements of the fault zone. In the article, study is focused on the late Quaternary slip rate of the Altyn Tagh fault west of the Cherchen River (between 85°E and 85°45'E). On the basis of high resolution SPOT images of the region, three sites, namely Koramlik, Aqqan pasture and Dalakuansay, were chosen for field investigation. To calculate the slip rate of the fault, displacement of terraces was measured on SPOT satellite images or in situ during fieldwork and thermo-luminescence (TL) dating method was used. To get the ages of terraces, samples of sand were collected from the uppermost sand beds that lie just under loess. The method for calculating slip rate of fault is to divide the displacement of terrace risers by the age of its neighboring lower terrace. The displacement of rivers is not considered in this article because of its uncertainties. At Koramlik, the slip rate of the Altyn Tagh fault is 11.6±2.6mm/a since 6.02±0.47ka B.P and 9.6±2.6mm/a since 15.76±1.19ka B.P. At Aqqan pasture, about 30km west of Koramlik, the slip rate is 12.1±1.9mm/a since 2.06±0.16 ka B.P. At Dalakuansayi, the slip rate of the fault is 12.2±3.0mm/a since 4.91±0.39ka B.P. Hence, we get the average slip rate of 11.4±2.5mm/a for the western part of the Altyn Tagh Fault since Holocene. This result is close to the latest results from GPS research.     

Luminescence chronology of the Sankosh river terraces in the Assam- Bhutan foothills of the Himalayas: Implications to climate and tectonics

Himalaya is an active fold and thrust belt formed due to continent-continent collision between the Eurasian and Indian plates. It comprises a 3000 km long chain of mountains that span ∼1000 km across, with major boundary thrusts viz., Main Central Thrust (MCT), Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT). MFT is marked as mountain front and is the most active thrust; however, evidence of tectonic activity along MCT and MBT also exists.Tectonic activity along MFT created uplifted terraces which now serve as geomorphic archives of past tectonic events. The present study focussed on a glacial-fed river Sankosh that originates in northern Bhutan, and crosses MCT, MBT and MFT before joining the Brahmaputra River in Assam. Due to tectonic uplift, the river shows a deflection at MFT, incising and thus forming four levels of strath terraces. Luminescence chronology, geomorphic studies and analysis of satellite images suggest four levels of terraces T4 (highest level, 195 m asl), T3, T2 and T1 (lowest level, 120 m asl).The quartz was found insensitive for luminescence dating, and thus fading corrected Infra-Red Stimulated Luminescence (IRSL) ages on feldspar minerals were measured that provided ages of 143-77 ka (T4), 65-36 ka (T2) and 35-14 ka (T1), respectively. The T3 terrace was present only on the right bank of the river and could not be accessed. These ages accord with other studies at the Chalsa and Malbazar, North Bengal (west of the study area) and this regional disposition of similar ages suggest that these formed during glacial-interglacial periods. The strath terraces indicate a time-averaged tectonic uplift with a 0.5 mm/year rate over the past 150 ka.     

祁连山西段酒西盆地区阶地构造变形的研究

对祁连山西段酒西盆地晚第四纪阶地的研究表明,该区早第四纪以挤压褶皱、逆冲为特征的构造变形在晚更新世期间乃至全新世仍继承性地进行着,表现为横穿褶皱和逆断裂带的河流及冲沟阶地面的形成、阶地类型的转变、阶地级数的增多和阶地面被断错或发生拱曲变形．其中祁连山北缘大断裂晚更新世晚期以来的垂直运动速率约为１．９２～２．００ｍｍ／ａ．老君庙背斜逆断裂带在晚更新世初以来的垂直运动速率约为１．１５～２．５６ｍｍ／ａ．白杨河背斜逆断裂带晚更新世初以来的垂直运动速率约为０．３２～０．５８ｍｍ／ａ．     

Optically stimulated luminescence dating of sediments from the Yellow River terraces in Lanzhou: Tectonic and climatic implications

The stratigraphic chronology of Yellow River terraces was investigated and studied in Lanzhou Basin, western Chinese Loess Plateau. The optically stimulated luminescence (OSL) dating results show that terraces T₁, T₂ and T₃ formed at 8 ka, 20 ka and 70 ka, respectively. Lateral accretion of the riverbed facies gravel sediments occurred during interglacial periods while vertical aggradations of the terrace sediments deposited predominantly under cold and dry glacial period. A thick layer of aeolian loess with a basal age about 35 ka indicates a remarkable drop of air temperature and a dry, cold climate. The temporal correlation between terrace formation and tectonic movement has not yet been established in this research, but the stratigraphic chronology of the terrace sections provides the timing of the terrace formation, the incision rate of the Yellow River, and the slip rate of the fault horizon.     

武威盆地晚更新世河流阶地变形与新构造活动

根据武威盆地 7条河流的阶地测量资料和测年数据探讨了河流阶地变形与新构造活动的关系。河流阶地的变形特征反映出新构造活动的方式 ,断层活动以逆冲为主 ,河流阶地的错断状况表明活动断层活动的次数 ,盆地西部活动至少有 7次 ,东部活动至少有 5次 ;同时可表明断层活动的幅度与强度 ,以及不同时期活动强烈区具有迁移变化的特点。武威盆地晚更新世以来发育的第四纪断层主要有 3条 ,各条断裂活动次数、强度不尽相同 ,以山前断裂活动最为强烈 ,至今活动仍未停息。 6 0ka前后西部活动强烈 ,2 0ka以来东强西弱     

K-feldspar IRSL dating of a Pleistocene river terrace staircase sequence of the Lower Tejo River (Portugal,western Iberia)

We present the results of K-feldspar IRSL dating of the four lower terraces (T3–T6) of the Portuguese Tejo River, in the Arripiado-Chamusca area. Terrace correlation was based upon: a) analysis of aerial photographs, geomorphological mapping and field topographic survey; b) sedimentology of the deposits; and c) luminescence dating. Sediment sampled for luminescence dating gave unusually high dose rates, of between 3.4 and 6.2 Gy/ka and, as a result, quartz OSL was often found to be in saturation. We therefore used the IRSL signal from K-feldspar as the principal luminescence technique. The K-feldspar age results support sometimes complex geomorphic correlations, as fluvial terraces have been vertically displaced by faults (known from previous studies). Integration of these new ages with those obtained previously in the more upstream reaches of the Tejo River in Portugal indicates that the corrected K-feldspar IRSL ages are stratigraphically and geomorphologically consistent over a distance of 120 km along the Tejo valley. However, we are sceptical of the accuracy of the K-feldspar ages of samples from the T3 and T4 terraces (with uncorrected D_e values >500 Gy). In these cases the Dose Rate Correction (DRC) model puts the natural signals close to luminescence saturation, giving a minimum corrected D_e of about 1000 Gy, and thus minimum terrace ages; this may even be true for those doses >200 Gy. Luminescence dating results suggest that: T3 is older than 300 ka, probably ca. 420–360 ka (～Marine Isotope Stage [MIS]11); T4 is ca. 340–150 ka (～MIS9-6); T5 is 136–75 ka (～MIS5); T6 is 60–30 ka (MIS3); an aeolian sand unit that blankets T6 and some of the older terraces is 30–≥12 ka. Collectively, the luminescence ages seem to indicate that regional river downcutting events may be coincident with periods of low sea level (associated, respectively, with the MIS10, MIS6, MIS4 and MIS2).     

海南岛北西部新构造特征及其演化研究

利用DGPS系统测量海南岛西部阶地, 绘制地质地貌综合剖面, 将西部阶地分为海成阶地和河流阶地两种。 其中海成地貌包括一条砂堤和四级阶地: 砂堤宽2～10 m, 高程约10 m, 形成于5 ka以来; 海成一级阶地发育较好, 阶地面高程21～22 m, 形成于晚更新世至全新世之间; 海成二级阶地顶面高程约32 m左右, 形成于晚更新世晚期; 海成三级阶地较为发育, 阶地面高程40～42 m, 形成于121.8 ka; 海成四级阶地零星分布, 阶地面高程约57 m, 形成于中更新世晚期。 河流阶地也可分出四级: 一级阶地高程约20 m, 局部发育, 形成于11.4 ka; 二级阶地高程约34 m, 形成于47.2 ka; 三级阶地高约50 m, 其基座顶面标高约41 m, 形成于晚更新世早期; 四级阶地高程约71 m, 基座面标高约60 m, 形成于中更新世晚期。 这些阶地中均以二级最为发育。 晚更新世以来全区处于整体加速抬升的状态。 依据阶地面的综合剖面特征, 认为王五-文教断裂晚更新世以来的活动性较弱。     

A quantitative soil-stratigraphic approach to the correlation and dating of post-glacial river terraces in Glen Feshie,western Cairngorms

Little is known about Holocene river terrace development in upland Scottish valleys. Interpretation of many of the terrace sequences, previously suggested to have been formed by meltwaters either from the last Scottish ice sheet or the Loch Lomond Advance, has generally been based on morphological data. In this paper an alternative approach to the traditional height-based method of terrace correlation and dating is presented using data from Glen Feshie, western Cairngorms. Terrace fragments are numerically classified and objectively grouped using quantitative soil-stratigraphic data. Principal Components Analysis is used to both quantify pedological data and separate temporal trends in the data from variance due to local site factors. The scores on the temporal component are used to derive soil-stratigraphic units developed on the surficial sediments of the Glen Feshie terraces by grouping soil sites using a hierarchical clustering technique. This provides evidence for at least five soil-stratigraphic units developed on the fluvial surfaces. Various methods of absolute dating control permits association of these surfaces with five phases of terrace development. These are placed tentatively at 13 000, 10 000, 3600, 1000, and 80 radiocarbon years B.P., suggesting at least three phases of valley floor incision in Glen Feshie during the late Holocene.     

Luminescence dating of cobbles from Pleistocene fluvial terrace deposits of the Ara River,Japan

Constraining the ages of fluvial terraces is essential to understanding fluvial responses to climate and sea-level changes and estimating uplift/incision. Luminescence dating of sand or silt grains from fluvial terrace deposits in Japan is difficult because sand layers are often absent from gravelly deposits, quartz grains are typically dominated by medium/slow components and/or contaminated by feldspars, and short transport distances and short residence times in riverbeds result in poor bleaching of luminescence signals. Luminescence dating of cobbles may overcome these difficulties, but few studies have applied this technique to fluvial terrace deposits. Here, we examine the utility of luminescence dating applied to three granodiorite cobbles from a late Pleistocene fluvial terrace deposit of the Ara River, Japan. We investigated variations of the infrared stimulated luminescence (IRSL) and post-IR IRSL signals with depth in each cobble. The IRSL and post-IR IRSL signals generally increase with depth, indicating that the cobbles were not completely bleached before deposition. Nonetheless, the IRSL ages of the cobble surfaces (19–17 ka) are consistent with the age of a tephra layer (16–15 ka) at the base of loess deposits overlying the terrace. In contrast, IRSL ages of sand-sized feldspar grains overestimate the depositional age because of incomplete bleaching, whereas silt-sized quartz grains greatly underestimate the depositional age, likely because of the thermal instability of the medium component. Our results demonstrate that luminescence dating of cobbles could provide a better understanding of fluvial systems in which luminescence dating of sand grains is difficult.