离石北部北川河阶地特征及其新构造指示

详细研究了离石北部一带阶地的地层地貌特征,并尝试对吕梁山山体的隆升进行分析探讨。结果表明,晚更新世以来该区有过三次间歇性隆升,并且三级阶地形成以来即晚更新世早期山体隆升相对快速强烈,二级阶地形成以来即晚更新世晚期至全新世时期山体隆升处于相对缓慢的过程。     

Holocene valley aggradation and gully erosion in headwater catchments,south-eastern highlands of Australia

Late Quaternary stratigraphy of a 50 km² catchment on the south-eastern highlands of Australia reveals processes and history of denudation, and helps resolve a long-standing debate about factors controlling episodic valley aggradation and degradation during Holocene times. Valley sedimentation occurred when swampy vegetation fully colonized valley floors and obliterated all channels, promoting aggradation for periods of several thousand years, with most incoming sediment being trapped in swampy meadows. Much of the sediment was reworked from late Pleistocene alluvial fan and valley fill deposits, and primary hillslope erosion was minor during the Holocene. Differing sedimentation patterns between the Late Pleistocene, Holocene and Post-European settlement periods reflect regional changes in sediment supply and transport capacity as a result of major environmental change. Within the Holocene, however, valley fill stratigraphy is controlled by massive, episodic gully erosion terminating aggradation. Gully initiation appears to be controlled more by thresholds of incision into vegetated valley floors than by changes to sediment supply. Whether the thresholds are exceeded because of climatic change, autonomous change or extreme events cannot yet be determined. Overall, the Holocene history represents continuing complex response to events of the Late Pleistocene, and does not support the K-cycle concept, which has strongly influenced late Quaternary geomorphology in Australia.     

Topographically associated but chronologically disjunct late Quaternary floodplains and terraces in a partly confined valley,south‐eastern Australia

The Bellinger River catchment in the New England Fold Belt on the mid‐north coast of New South Wales is characterized by an assemblage of stepped late Quaternary alluvial units. Late Pleistocene terraces were formed by large, more competent rivers that eroded almost entire valley floors; however, a decline in discharge prior to the Holocene has resulted in the abandonment of these deposits as elevated terraces or residual alluvium, onlapped by contemporary floodplains. Intrinsic controls on floodplain formation appear to be superimposed over an early–mid‐Holocene climatic signature. A fluvially active period, known as the Nambucca Phase, from 10 to 4·5 ka, eroded Late Pleistocene terraces. Two floodplain surfaces, one higher than the other, both started to accrete vertically from 4 ka but with some valley locations remaining vulnerable to episodes of erosion, resulting in substantial units of even younger basal alluvium. The high floodplain is dominated by horizontally laminated, vertically accreted sequences, while the low floodplain, which overlaps in age, is characterized by pronounced cut‐and‐fill stratigraphy. Terraces and floodplains in partly confined settings can have similar elevations but be polycyclic, with very different basal ages. In such landscapes the classical assumption that individual terrace or floodplain profiles along a valley represent periods of coeval formation is shown to be frequently invalid. Copyright © 2007 John Wiley & Sons, Ltd.     

26Al and 10Be dating of late pleistocene and holocene fill terraces: a record of fluvial deposition and incision,Colorado front range

Cosmogenic ²⁶Al, ¹⁰Be, and ¹⁴C dating of fluvial fill terraces in steep canyons of the Colorado Front Range provides a temporal framework for analysing episodic aggradation and incision. Results from Boulder Canyon show that terrace heights above the modern channel (grade) can be divided into: (1) Bull Lake (≳100 ka; 20–15 m above grade); (2) Pinedale (32–10 ka; 15–4 m above grade); and (3) Holocene age (<4 m above grade). No pre‐Bull Lake deposits are preserved along Boulder Canyon, and only three small remnants >15 m above grade record Bull Lake deposition. Well‐preserved terraces of Pinedale age suggest that the range of terrace height above grade reflects short‐term fluctuations in the river profile during periods of rapidly changing stream load and power. Net river incision apparently occurred during transitions to interglacial periods. Soil development and stratigraphic position, along with limited cosmogenic and ¹⁴C dating, suggest that ∼130 ka terraces in Boulder Canyon correlate with the Louviers Alluvium, and that 32 to 10 ka fills in the canyon correlate with the Broadway Alluvium on the adjacent High Plains. Late Pleistocene incision rates (∼0·15 m ka⁻¹) along Boulder Canyon exceed pre‐late Pleistocene incision rates, and are higher than middle to late Pleistocene incision rates (∼0·04 m ka⁻¹) on the High Plains. This study provides an example of how modern geochronologic techniques allow us to understand better rivers that drain glaciated catchments. Copyright © 2002 John Wiley & Sons, Ltd.     

Morphological,sedimentological and tectonic features of diamante-m. Carpinoso Marine terrace flight (tyrrhenian coast of northern Calabria,Italy)

Marine terrace flights resulting from the interaction of Quaternary glacio-eustatic fluctuations and tectonic uplift are a typical feature of the Tyrrhenian coast of Calabria in Southern Italy; in particular a térrace flight with four orders of terraces is evident in the Diamante area. The lowest terrace levels (fourth order: Diamante-Cirella terrace) are typified by a calcarenitic deposit with Cladocora caespitosa which give a Th/U age > 300,000 years. The third order terrace has a sedimentary cover formed of a basal discontinuous level of well rounded pebbles which underlies a deeply weathered coarse-grained sand horizon. The deposit ends with a paleosol locally cut by erosional scours filled by yellowish tuff deposits. The formation of this terrace dates from the Middle Pleistocene. The second order terrace presents a sedimentary cover composed of two generations of soils and is attributed to Middle Pleistocene age. The first order terrace (M. Carpinoso terrace) presents a wave-cut platform covered by a clastic deposit of marine and continental origin; this deposit consists of superimposed depositional events separated by unconformities, bounded by two diachronous surfaces. The formation of the wave-cut platform could be related to several sea-level stands during a long-lasting slow subsidence phase of the coastal area during the Lower Pleistocene. The uplift following terrace formation displaced the first order terrace most markedly; tectonic lineations controlled the hydrographic pattern and erosion of the surfaces.     

Upper Pleistocene‐Holocene geomorphic changes dictating sedimentation rates and historical land use in the valley system of the Chifeng region,Inner Mongolia,northern China

This study focuses on the late Quaternary landscape evolution in the Chifeng region of Inner Mongolia, China, its relations to the history of the Pleistocene‐Holocene loess accumulation, erosion and redeposition, and their impact on human occupation. Based on 57 optically stimulated luminescence (OSL) ages of loess sediments, fluvial sand and floodplain deposits accumulated on the hill slopes and floodplains, we conclude that during most of the Pleistocene period the region was blanketed by a thick layer of aeolian loess, as well as by alluvial and fluvial deposits. The loess section is divided into two main units that are separated by unconformity. The OSL ages at the top of the lower reddish loess unit yielded an approximate age of 193 ka, roughly corresponding to the transition from MIS 7 to 6, though they could be older. The upper gray loess unit accumulated during the upper Pleistocene glacial phase (MIS 4–3) at a mean accumulation rate of 0·22 m/ka. Parallel to the loess accumulation on top of the hilly topography, active fans were operating during MIS 4–2 at the outlet of large gullies surrounding the major valley at a mean accumulation rate of 0·24 m/ka. This co‐accumulation indicates that gullies have been a long‐term geomorphic feature at the margins of the Gobi Desert since at least the middle Pleistocene. During the Holocene, the erosion of the Pleistocene loess on the hills led to the burial of the valley floors by the redeposited sediments at a rate that decreases from 3·2 m/ka near the hills to 1–0·4 m/ka¹ in the central part of the Chifeng Valley. This rapid accumulation and the frequent shifts of the courses of the river prevented the construction of permanent settlements in the valley floors, a situation which changed only with improved man‐made control of the local rivers from the tenth century AD. Copyright © 2010 John Wiley & Sons, Ltd.     

Late Quaternary biotic and abiotic controls on long-term sediment flux in a northern Australian tropical river system

The modern distribution of monsoonal rainforest in the Australian tropics is patchy and is mainly associated with river corridors and groundwater springs, which indicates a strong dependence on hydrologic and geomorphic conditions. While their present distribution is well known, very little data exists on past spatial and temporal dynamics of these ecosystems, or their medium- to longer-term controls. Factors such as (i) fire frequency and type, and/or (ii) hydroclimatic conditions (e.g. droughts) have been proposed to control riverine corridor rainforest extent. Recent observations, however, also suggest an additional (iii) geomorphic control induced by alluvial knickpoint migration. Sediment sequences provide valuable archives for the reconstruction of longer-term (a) floodplain sedimentary dynamics, (b) local vegetation history, and (c) catchment-wide fire histories. This study investigates such a sediment sequence at Wangi Creek, and shows that a phase of aggradation, lasting ~4000 years, was recently disrupted by channel incision and floodplain erosion. The aggradational phase is characterized by sand deposition with average vertical floodplain accretion rates of 0.8 cm/yr and includes phases of soil development. The recent incisional phase has changed hydro-geomorphic conditions and caused widespread degradation of vegetation, erosion and lowering of the macro-channel surface. While there is no evidence in our data for an erosional event of similar magnitude since the onset of late Holocene floodplain aggradation, Wangi Creek experienced significant erosion and incision immediately before ~4000 years, providing the first evidence for a tropical cut-and-fill river system. We hence argue that phases of aggradation mainly controlled by biotic processes alternate and depend on feedbacks with incision phases controlled mainly by abiotic processes. The results show that eco-hydro-geomorphic feedbacks may play a crucial role in the medium- to longer-term history of tropical fluvial systems and need to be considered when interpreting fluvial archives with regards to climate, fire or human induced change. © 2019 John Wiley & Sons, Ltd.     

涉县盆地控盆构造晚第四纪活动特征

涉县断裂为太行山隆起区内涉县盆地的控盆构造,走向由NE转为近EW向,倾向NW/N,中部在井店东被EW向断裂错断,是控制涉县盆地的一组断裂。本文采用地质地貌调查、河流阶地分析和地质测年等方法,研究了涉县断裂晚第四纪活动特征。研究发现,涉县断裂带由多组断裂构成,带宽约200m,在清漳河两侧表现为山前的陡崖地貌、基岩破碎变形带,具有正断兼走滑特征,在基岩变形带上部发育走向NNE向和NWW向次级滑动面,次级滑动面错断第四系黄土,最新活动到晚更新世;断裂在盆地区通过,地表形成低缓陡坎,断裂错断Q2-3地层,表现为上陡下缓的正断层。通过对涉县断裂两侧清漳河河流阶地、夷平面和地层年龄综合分析,估算涉县断裂晚更新世以来平均垂直滑动速率为0.06～0.08mm/a,中更新世以来平均垂直滑动速率为0.22～0.34mm/a,垂直差异活动主要发生于中更新世期间。     

Identifying slope processes over time and their imprint in soils of medium‐high mountains of Central Europe (the Karkonosze Mountains,Poland)

Soils in mountainous areas are often polygenetic, developed in slope covers that relate to glacial and periglacial activities of the Pleistocene and Holocene and reflect climatic variations. Landscape development during the Holocene may have been influenced by erosion/solifluction that often started after the Holocene climatic optimum. To trace back soil evolution and its timing, we applied a multi‐methodological approach. This approach helped us to outline scenario of soil transformation. According to our results, some aeolian input must have occurred in the late Pleistocene. During that time and the early Holocene, the soils most likely had features of Cryosols or Leptosols. Physico‐chemical and mineralogical analyses have indicated that the material was denudated (between late Boreal to the Atlantic) from the ridge and upper‐slope positions forming a colluvium at mid‐slope positions. Later, during the Sub‐Boreal, mass wasting of the remains of silt material deposited at the end of the Pleistocene age on the ridge top seems to have occurred. In addition, the cool and moist conditions caused the deposition of a colluvium at the lower‐slope positions. The next phase was characterized by the transformation of Leptosols/Cambisols into Podzols at upper‐slope or shoulder positions and to Albic Cambisols at mid‐slope positions. During the Sub‐Boreal period, Stagnosols started to form at the lower part of the slope catena. Overall, the highest erosion rates were calculated at the upper‐slope position and the lowest rates at mid‐slope sites. Berylium‐10 (¹⁰Be) data showed that the Bs, BC/C were covered during the Holocene by a colluvium with a different geological composition which complicated the calculation of erosion or accumulation rates. The interpretation of erosion and accumulation rates in such multi‐layered materials may, therefore, be hampered. However, the multi‐methodological reconstruction we applied shed light on the soil and landscape evolution of the eastern Karkonosze Mountains. Copyright © 2017 John Wiley & Sons, Ltd.     

鄂尔多斯高原河曲段黄河阶地构造变形研究

通过对河曲县城一带出露较好的黄河阶地剖面进行研究,认为河曲一带黄河三、四级阶地形成于中更新世时期,晚更新世早期形成二级阶地,全新世形成一级阶地。本区中更新世抬升速率为0．14mm／a,晚更新世抬升速率为0．18mm／a,全新世抬升速率为0．70mm／a,晚更新世和全新世抬升速率的突然加大,可能与黄河下游三门湖的贯通、区域侵蚀基准面突然降低、河流侵蚀加大有关。     

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。     

Sediment sequences and paleosols in the Kyichu Valley, southern Tibet (China), indicating Late Quaternary environmental changes

Abstract The Tibetan Plateau is highly sensitive to environmental changes and affects the settings of a far larger territory in Central Asia and beyond. Thus, knowledge on past environmental changes in that area is essential. Even though the Kyichu (Lhasa River) Valley and its tributaries is an easily accessible area, the Late Quaternary landscape evolution of southern Tibet is in general scarcely known. Therefore, 12 sedimentary sections in the middle and lower catchment were subjected to multidisciplinary analyses (sedimentology, paleopedology, AMS ¹⁴C and luminescence dating, and charcoal determination) aiming at results on regional paleoenvironmental changes. At the altitude studied (3600–4000 m above sealevel), no glacial relics could be detected, indicating that the valley positions have been unglaciated since the Last Interglacial. The lack of fluvial–lacustrine structures above the floodplain is due to the aggradational character of this tectonically (sub‐)active valley, which caused an alluvial burying of older valley bottoms. During the Late Pleistocene the mouth area of the Kyichu was occupied by a lake which was part of a larger dam‐lake in the superordinate Yarlung Zhangbo Valley. On the valley flanks, loesses were predominantly deposited before the Last Glacial Maximum (LGM), whereas eolian sands were predominantly deposited around and after the LGM. Paleosols of Last Interglacial, Last Glacial and Holocene ages regularly occur at terrestrial sites representing temperate to cool and humid to semiarid conditions during soil formation. Ages of colluvial sediments indicate that the widespread barren valley slopes were primarily formed by Late Pleistocene erosion followed by a secondary Holocene erosion phase. Charcoal spectra indicate a Late Holocene change from a forest environment to a pastoral environment with sparse grasses, herbs and dwarf shrubs. It is assumed that the Late Holocene environmental changes, such as loss of forests/woodlands and erosion, have at least been reinforced by humans, enhancing a regional climatic aridification and cooling trend.     

Holocene valley aggradation driven by river mouth progradation: examples from Australia

Since the end of the post‐glacial sea level rise 6800 years ago, progradation of river mouths into estuaries has been a global phenomenon. The responses of upstream alluvial river reaches to this progradation have received little attention. Here, the links between river mouth progradation and Holocene valley aggradation are examined for the Macdonald and Tuross Rivers in south‐eastern Australia. Optical and radiocarbon dating of floodplain sediments indicates that since the mid‐Holocene sea level highstand 6800 years ago vertical floodplain aggradation along the two valleys has generally been consistent with the rate at which each river prograded into its estuary. This link between river mouth progradation and alluvial aggradation drove floodplain aggradation for many tens of kilometres upstream of the estuarine limits. Both rivers have abandoned their main Holocene floodplains over the last 2000 years and their channels have contracted. A regional shift to smaller floods is inferred to be responsible for this change, though a greater relative sea level fall experienced by the Macdonald River since the mid‐Holocene sea level highstand appears to have been an additional influence upon floodplain evolution in this valley. Copyright © 2006 John Wiley & Sons, Ltd.     

Late Holocene channel and floodplain development in a wandering gravel‐bed river: the River South Tyne at Lambley,northern England

Geomorphological analyses of the morphology, lithostratigraphy and chronology of Holocene alluvial fills in a 2·75 km long piedmont reach of the wandering gravel‐bed River South Tyne at Lambley in Northumberland, northern England, have identified spatial and temporal patterns of late Holocene channel and floodplain development and elucidated the relationship between reach‐ and subreach‐scale channel transformation and terrace formation. Five terraced alluvial fills have been dated to periods sometime between c. 1400 BC –AD 1100, AD 1100–1300, AD 1300–1700, AD 1700–1850 and from AD 1850 to the present. Palaeochannel morphology and lithofacies architecture of alluvial deposits indicate that the past 3000 years has been characterized by episodic channel and floodplain change associated with development and subsequent recovery of subreach‐scale zones of instability which have been fixed in neither time nor space. Cartographic and photographic evidence spanning the past 130 years suggests channel transformation can be accomplished in as little as 50 years. The localized and episodic nature of fluvial adjustment at Lambley points to the operation of subreach‐scale controls of coarse sediment transfers. These include downstream propagation of sediment waves, as well as internal controls imposed by differing valley floor morphology, gradient and boundary materials. However, the preservation of correlated terrace levels indicates that major phases of floodplain construction and entrenchment have been superimposed over locally complex patterns of sediment transfer. Reach‐scale lateral and vertical channel adjustments at Lambley appear to be closely related to climatically driven changes in flood frequency and magnitude, with clusters of extreme floods being particularly important for accomplishing entrenchment and reconfiguring the pattern of localized instability zones. Confinement of flood flows by valley entrenchment, and contamination of catchment river courses by metal‐rich fine sediments following recent historic mining operations, have combined to render the South Tyne at Lambley increasingly sensitive to changes in flood regimes over the past 1000 years. Copyright © 2000 John Wiley & Sons, Ltd.     

Holocene alluvial fan and terrace formation in the Bowland Fells,Northwest England

In the Bowland Fells, Lancashire, northwest England, in the headwater valleys of the Hodder river system, is a suite of Holocene fluvial landforms. Debris cones and alluvial fans at tributary junctions, and river terraces along the main valleys post-date late Pleistocene forms and pre-date the modern valley floor alluvial forms. Eight ¹⁴C dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of Holocene erosion to be identified with debris cone/fan deposition taking place after c. 5400 BP but before c. 1900 BP and again at c. 900 BP. Some of the fans and cones are complex with deposits attributable to both phases; others are simple and attributable only to the later phase. In the headwaters an upper terrace at c. 5400 BP pre-dates the cones and a lower terrace is contemporaneous with the first debris cone phase. Lower downvalley the youngest of three terraces date from c. 5000 BP or earlier indicating that the sequence is less complex downstream.     

Sediment storage and transport in Pancho Rico Valley during and after the Pleistocene‐Holocene transition,Coast Ranges of central California (Monterey County)

Factors influencing sediment transport and storage within the 156·6 km² drainage basin of Pancho Rico Creek (PRC), and sediment transport from the PRC drainage basin to its c. 11 000 km² mainstem drainage (Salinas River) are investigated. Numeric age estimates are determined by optically stimulated luminescence (OSL) dating on quartz grains from three sediment samples collected from a ‘quaternary terrace a (Qta)’ PRC terrace/PRC‐tributary fan sequence, which consists dominantly of debris flow deposits overlying fluvial sediments. OSL dating results, morphometric analyses of topography, and field results indicate that the stormy climate of the Pleistocene‐Holocene transition caused intense debris‐flow erosion of PRC‐tributary valleys. However, during that time, the PRC channel was backfilled by Qta sediment, which indicates that there was insufficient discharge in PRC to transport the sediment load produced by tributary‐valley denudation. Locally, Salinas Valley alluvial stratigraphy lacks any record of hillslope erosion occurring during the Pleistocene‐Holocene transition, in that the alluvial fan formed where PRC enters the Salinas Valley lacks lobes correlative to Qta. This indicates that sediment stripped from PRC tributaries was mostly trapped in Pancho Rico Valley despite the relatively moist climate of the Pleistocene‐Holocene transition. Incision into Qta did not occur until PRC enlarged its drainage basin by c. 50% through capture of the upper part of San Lorenzo Creek, which occurred some time after the Pleistocene‐Holocene transition. During the relatively dry Holocene, PRC incision through Qta and into bedrock, as well as delivery of sediment to the San Ardo Fan, were facilitated by the discharge increase associated with stream‐capture. The influence of multiple mechanisms on sediment storage and transport in the Pancho Rico Valley‐Salinas Valley system exemplifies the complexity that (in some instances) must be recognized in order to correctly interpret terrestrial sedimentary sequences in tectonically active areas. Copyright © 2009 John Wiley & Sons, Ltd.     

Drainage migration and out of sequence thrusting in Bhalukpong,Western Arunachal Himalaya,India

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 (T_2b) 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.     

新西兰韦恩加瓦河砾石的沉积环境、阶地断错和8级地震重复率

新西兰北岛南部韦恩加瓦河地区在晚更新世冰缘气候控制下,由沉积和侵蚀的交替作用形成较高较老的阶地。较低较新的阶地是在全新世中期以来的现代正常气候条件下形成的。这些阶地分别被怀拉拉帕断层水平错动297米、100米,57米和28米。距今10000年以来,怀拉拉帕断层的平均水平滑动速度为10毫米/年。1855年8级地震的重复率为1500年     

中全新世以来的川江大洪水初步分析

在忠县中坝文化遗址剖面中发现了10个古洪水沉积层,时代为中全新世以来,之后又被1981年大洪水淹没.11次大洪水洪水位的变化显示洪水位总体呈上升趋势,其间有数个周期性起伏.前者反映中全新世以来河床堆积的影响,后者反映西南季风强度的周期变化.     

Deciphering the Holocene evolution of the St. Lawrence River drainage system using luminescence and radiocarbon dating

The St. Lawrence River is an important drainage route for eastern North American fresh waters. Following Late Pleistocene deglaciation, several fluctuations in base level have fine-tuned the evolution of the ancestral St. Lawrence. These fluctuations are hereby dated using K-feldspar infrared stimulated luminescence (IRSL) and radiocarbon. The accuracy of the individual IRSL dates was achieved by properly correcting for thermal transfer and anomalous fading. For each site investigated, widely used statistical approaches in equivalent dose data have been used to establish which age model, the central or the minimum model, would be appropriate to define the “true” depositional age. The chronology of the succession of regional lake levels is based on careful mapping and dating of the regional dunes, beaches and deltaic sediments. A relative time-space evolution history could be drawn, from ca. 8000 years BP to the present time period. Three major fluctuations are documented for the middle to late Holocene. An unexpected finding, from the ages cluster diagram, is that there have been times in the recent past (ca. 1000–4000 years BP) when the river level was lower or at the same elevation as today. The potential for K-feldspar IRSL to accurately date the Holocene lacustrine evolution is critical in the St. Lawrence River modern drainage basin, an environment that might be negatively impacted over the next century.