Changes In Fluvial Systems Research Articles

The impact of natural and anthropogenic factors on the landforms and landscapes of mountains and their forelands

This paper is an introduction to a collection of nine studies that are intended to fill the gap in the literature associated with landform development and landscape changes related to natural forces and human activities in the Central European Mountains and their close forelands. The papers are grouped into four general categories that describe the influence of climate on glacial landforms and snow avalanches, the evolution of slopes in high mountains, the development of mid-mountain relief, and changes in fluvial systems in mountains and their forelands. This paper summarises the contributions of these studies to this special issue and attempts to outline possible avenues of future research on landforms and landscapes in mountainous areas.

Chronology and Dynamics of Fluvial System Changes in the Younger Dryas and Early Holocene in Central Europe (with the Lower San River as an Example, Se Poland)

Chronology and Dynamics of Fluvial System Changes in the Younger Dryas and Early Holocene in Central Europe (with the Lower San River as an Example, Se Poland)

Does fluvial channel-belt clustering predict net sand to gross rock volume? Architectural metrics and point-pattern analysis of a digital outcrop model

ABSTRACTSpatial point-pattern analyses (PPAs) are used to quantify clustering, randomness, and uniformity of the distribution of channel belts in fluvial strata. Point patterns may reflect end-member fluvial architecture, e.g., uniform compensational stacking and avulsion-generated clustering, which may change laterally, especially at greater scales. To investigate spatial and temporal changes in fluvial systems, we performed PPA and architectural analyses on extensive outcrops of the Cretaceous John Henry Member of the Straight Cliffs Formation in southern Utah, USA. Digital outcrop models (DOMs) produced using unmanned aircraft system-based stereophotogrammetry form the basis of detailed interpretations of a 250-m-thick fluvial succession over a total outcrop length of 4.5 km. The outcrops are oriented roughly perpendicular to fluvial transport direction. This transverse cross-sectional exposure of the fluvial system allows a study of the system's variation along depositional strike. We developed a workflow that examines spatial point patterns using the quadrat method, and architectural metrics such as net sand to gross rock volume (NTG), amalgamation index, and channel-belt width and thickness within moving windows. Quadrat cell sizes that are ∼ 50% of the average channel-belt width-to-thickness ratio (16:1 aspect ratio) provide an optimized scale to investigate laterally elongate distributions of fluvial-channel-belt centroids. Large-scale quadrat point patterns were recognized using an array of four quadrat cells, each with 237× greater area than the median channel belt. Large-scale point patterns and NTG correlate negatively, which is a result of using centroid-based PPA on a dataset with disparately sized channel belts. Small-scale quadrat point patterns were recognized using an array of 16 quadrat cells, each with 21× greater area than the median channel belt. Small-scale point patterns and NTG correlate positively, and match previously observed stratigraphic trends in the fluvial John Henry Member, suggesting that these are regional trends. There are deviations from these trends in architectural statistics over small distances (hundreds of meters) which are interpreted to reflect autogenic avulsion processes. Small-scale autogenic processes result in architecture that is difficult to correlate between 1D datasets, for example when characterizing a reservoir using well logs. We show that 1D NTG provides the most accurate prediction for surrounding 2D architecture.

Impacts of Channel Morphodynamics on Fish Habitat Utilization.

It is reasonable to expect that hydro-morphodynamic processes in fluvial systems can affect fish habitat availability, but the impacts of morphological changes in fluvial systems on fish habitat are not well studied. Herein we investigate the impact of morphological development of a cohesive meandering stream on the quality of fish habitat available for juvenile yellow perch (Perca flavescens) and white sucker (Catostomus commersonii). A three-dimensional (3D) morphodynamic model was first developed to simulate the hydro-morphodynamics of the study creek. The results of the morphodynamic model were then incorporated into a fish habitat availability assessment. The 3D hydro-morphodynamic model was successfully calibrated using an intensive acoustic Doppler current profiler (ADCP) spatial survey of the entire 3D velocity field and total station surveys of topographic changes in a meander bend in the study creek. Two fish sampling surveys were carried out at the beginning and the end of the study period to determine presence-absence of fish as an indicator of the habitat utilization of each fish species in the study reach. It was shown that morphological development of the stream was a significant factor for the observed changes in the habitat utilization of juvenile yellow perch. It is shown that juvenile yellow perch mostly utilized habitat where deposition occurred whereas they avoided areas of erosion. The results of this study and the proposed methodology could provide some insights into the potential impact of sediment transport processes on the fish occurrence, and distribution and has implications for management of small fluvial systems.

A Workflow to Estimate Topographic and Volumetric Changes and Errors in Channel Sedimentation after Disturbance

Light Detection and Ranging (LiDAR) methods, such as ground-based Terrestrial Laser Scanning (TLS), have enabled collection of high-resolution point clouds of elevation data to calculate changes in fluvial systems after disturbance, but are often accompanied by uncertainty and errors. This paper reviews and compares TLS analysis methods and develops a workflow to estimate topographic and volumetric changes in channel sedimentation after disturbance. Four analytic methods to estimate topographic and volumetric changes were compared by quantifying the uncertainty in TLS-derived products: Digital Elevation Model (DEM) of difference (DOD), Cloud to Cloud (C2C), Cloud to Mesh (C2M), and Multiple Model to Model Cloud Comparison (M3C2). Mean errors across surfaces within each dataset contributed to a propagation error of 0.015–0.016 m and 0.017–0.018 m for the point clouds and derived DEMs, respectively. The estimated error of the total volumetric change implied increased errors in the conversion of point clouds into a surface by C2M and DOD; whereas C2C and M3C2 were generally simpler, efficient, and accurate techniques for evaluating topographic changes. The comparison of methods to analyze TLS data will contribute to applications of remote sensing of hydro-geomorphic processes in stream channels after disturbance. The workflow presented also aids in estimating uncertainties inherent in data collection and analytic methods for topographic and volumetric change analysis.

Evolution of Early Pleistocene fluvial systems in central Poland prior to the first ice sheet advance – a case study from the Bełchatów lignite mine

Abstract Deposits formed between the Neogene/Pleistocene transition and into the Early Pleistocene have been studied, mainly on the basis of drillings and at rare, small outcrops in the lowland part of Polish territory. At the Bełchatów lignite mine (Kleszczów Graben, central Poland), one of the largest opencast pits in Europe, strata of this age have long been exposed in extensive outcrops. The present paper is based on our field studies and laboratory analyses, as well as on research data presented by other authors. For that reason, it can be seen as an overview of current knowledge of lowermost Pleistocene deposits at Bełchatów, where exploitation of the Quaternary overburden has just been completed. The results of cartographic work, sedimentological, mineralogical and palynological analyses as well as assessment of sand grain morphology have been considered. All of these studies have allowed the distinction of three Lower Pleistocene series, i.e., the Łękińsko, Faustynów and Krzaki series. These were laid down in fluvial environments between the end of the Pliocene up to the advance of the first Scandinavian ice sheet on central Poland. The following environmental features have been interpreted: phases of river incision and aggradation, changes of river channel patterns, source sediments for alluvia, rates of aeolian supply to rivers and roles of fluvial systems in morphological and geological development of the area. The two older series studied, i.e., Łękińsko and Faustynów, share common characteristics. They were formed by sinuous rivers in boreal forest and open forest environments. The Neogene substratum was the source of the alluvium. The younger series (Krzaki) formed mainly in a braided river setting, under conditions of progressive climatic cooling. Over time, a gradual increase of aeolian supply to the fluvial system can be noted; initially, silt and sand were laid down, followed by sand only during cold desert conditions. These fluvio-periglacial conditions are identified in the foreground of the advance of the oldest ice sheet into this part of central Poland. The series studied have been compared with other fluvial successions which accumulated in the Kleszczów Graben during subsequent glaciations so as to document general changes in fluvial systems as reactions to climatic evolution. Thus, a palaeoenvironmental scenario has emerged which could be considered to be characteristic of central Poland during the Early Pleistocene.

Lateglacial and early Holocene vegetation development and fluvial system changes in the northern Meuse valley, the Netherlands: a review of palynological data

AbstractThis study provides an overview of existing palynological and chronological data of the northern Meuse valley which have been collected over recent decades. The palynological data were used to make a vegetation reconstruction in time and space for the Lateglacial and early Holocene. The vegetation development is strongly influenced by the rapid climate changes that occurred during this time period. It is shown that the biostratigraphy can be used to provide better age estimates for the abandoned channel fills, which have been dated in most cases using conventional bulk14C dates. Furthermore, the combination with a geomorphological reconstruction based on AHN (actual height model of the Netherlands) lidar data has been used to evaluate the interactions between fluvial terrace formation and vegetation development. It appears that, although the vegetation development is comparable to the general vegetation development in the Netherlands, slight differences occur, in particular of the vegetation composition, presumably linked to the dynamic geomorphological activity in the Meuse valley. Finally, the spatial distribution of sites may give indications for the migration routes of pine (Pinus) and poplar (Populus) during this period of rapid vegetation development over the Last Glacial–Interglacial Transition.

Fluvial archives, a valuable record of vertical crustal deformation

The study of drainage network response to uplift is important not only for understanding river system dynamics and associated channel properties and fluvial landforms, but also for identifying the nature of crustal deformation and its history. In recent decades, geomorphic analysis of rivers has proved powerful in elucidating the tectonic evolution of actively uplifting and eroding orogens. Here, we review the main recent developments that have improved and expanded qualitative and quantitative information about vertical tectonic motions (the effects of horizontal deformation are not addressed). Channel long profiles have received considerable attention in the literature, and we briefly introduce basic aspects of the behaviour of bedrock rivers from field and numerical modelling perspectives, before describing the various metrics that have been proposed to identify the information on crustal deformation contained within their steady-state characteristics. Then, we review the literature dealing with the transient response of rivers to tectonic perturbation, through the production of knickpoints propagating through the drainage network. Inverse modelling of river profiles for uplift in time and space is also shown to be very effective in reconstructing regional tectonic histories. Finally, we present a synthetic morphometric approach for deducing the tectonic record of fluvial landscapes.As well as the erosional imprint of tectonic forcing, sedimentary deposits, such as fluvial terrace staircases, are also considered as a classical component of tectonic geomorphology. We show that these studies have recently benefited from rapid advances in dating techniques, allowing more reliable reconstruction of incision histories and estimation of incision rates. The combination of progress in the understanding of transient river profiles and larger, more rigorous data sets of terrace ages has led to improved understanding of river erosion and the implications for terrace profile correlation, i.e., extrapolation of local data to entire profiles. Finally, planform changes in fluvial systems are considered at the channel scale in alluvial rivers and regional level in terms of drainage reorganisation. Examples are given of how numerical modelling can efficiently combine with topographic data to shed new light on the (dis)equilibrium state of drainage systems across regional drainage divides.

Natural and anthropogenic indicators of fluvial system changes, the Bobrza Valley (Holy Cross Mts) as an example.

Abstract Transformations of a fluvial system are caused both by natural factors and human pressure. These factors model the system independently at different times and with different intensities or they affect it simultaneously. The aim of this study is to identify the transformation of the Bobrza river valley system occurring under natural conditions and that occurring under the influence of human activity. The identification was based on specific indicators The study was conducted in the valley mouth of the Bobrza River (Holy Cross Mountains), where three research sites were located. The investigation concerned the relief of the valley and the mineral and organic deposits. A wide range of research methods were used during the study e.g. analysis of LiDAR data, macronutrient analysis, and radioactive dating. The analyses enabled the natural and anthropogenic transformations of the Bobrza river system to be distinguished using the following indicators: morphometric and sedimentological characteristics of the palaeomeander (natural transformation), the sequence of mineral and organic deposits in exposures on the contemporary floodplain (natural and anthropogenic transformation) and transformation associated with the operation of a water mill (anthropogenic transformation). In addition, it is worth mentioning that the Bobrza channel is the location which has provided the only fossils of Juncus subnodulosus in south-east Poland.

Historical changes in channel network extent and channel planform in an intensively managed landscape: Natural versus human-induced effects

Humans have become major geomorphological agents, effecting substantial change in the characteristics of Earth's physical landscapes. The agricultural Midwest of the United States is a region marked by pronounced human influence at the landscape scale. Humans undoubtedly have strongly influenced critical zone processes, including fluvial processes, in intensively managed agricultural landscapes, yet the exact nature of human alteration of these processes is unknown. This study documents historical changes in the extent of the stream channel network and in channel planform within the upper Sangamon River basin — an intensively managed agricultural watershed in Illinois. Results indicate that the modern channel network is nearly three times more extensive than the channel network in the 1820s. Most change in drainage density has occurred in headwater portions of the basin where numerous drainage ditches have been added to the network to drain flat uplands. No detectable change in channel position is evident between 1940 and 2012 along about 60% of the total length of the Sangamon River and its major tributaries. Nearly 30% of the total length exhibits change related to meander dynamics (cutoffs and lateral migration), whereas about 8% has changed as a result of channelization. Channelized sections typically remain straight for decades following human modification, supporting the notion that humans produce long-lasting catastrophic change in channel planform in this region. The findings confirm that humans are effective agents of morphological change in fluvial systems in this intensively managed watershed. Documenting human-induced versus natural changes in fluvial systems is important for evaluating how other critical zone processes in intensively managed landscapes have been affected by these changes. Human-induced changes in channel extent and planform most likely have altered this landscape from one dominated by biogeochemical transformations and storage of water and sediment prior to agricultural development into one now characterized by enhanced fluxes of water, sediment, and nutrients.

Zmiany układu koryt Wisły spowodowane funkcjonowaniem stopnia wodnego „Włocławek” na podstawie analizy zdjęć lotniczych

In line with the classification after Brice (1975), the system of the contemporary Vistula channel may be identified as a complex anabranched (anastomosing) river system, consisting of the main channel of the braided river type with bars and islands, as well as meandering side channels separated by holms. In turn, following the views of Smith and Smith (1980), this system is in a transition phase from a braided to an anastomosing river system. The phase of transformation to an anastomosing one in the central and lower Vistula braided system could have started at the beginning of the Holocene and continued uninterrupted through to the present day (Starkel, 2001). Currently, the Vistula fluvial system changes in the vicinity of the dam on the Wloclawek reservoir and is under the strong influence of the anthropogenic impact the functioning of the dam is able to exert. To analyze the effects of this transformation, we have studied changes in channel structure using a method proposed by Brice and Blodgett (1978), as modified by Szmanda and Luc (2010). Analyzing aerial photographs, we have measured the widths of channels (w), as well as the lengths (L) and widths of bars (w’) and inter-channel forms in the bottom of the valley (islands fixed by vegetation and inter-channel areas called holms). Dimensionless parameters of forms were also calculated: L/w – for length, w’/w – for width, and L/w’ for shape. Aerial photographs from the area of the two holms located in the Vistula valley – i.e. the Bogpomoz Holm (below the Reservoir) and the Wykowska Holm (above it) were our research material. These photos come in both cases from two periods, before and after the construction of the dam in Wloclawek. The survey allowed the following conclusions to be drawn: (1) In the research period, the average width of the river channels below the dam has increased slightly, while above the barrier there has been a slight decrease. (2) By numbers of given forms, islands fixed by vegetation are found to be in the majority, whereas holms were more frequent in the floodplain inter-channel area. Irrespective of the type of form, most were elongated. (3) Both above and below the Reservoir, there has been a decrease in the number of (channel and valley) forms. The number of bars in the Vistula channel has decreased. The area of the inter-channel islands colonised by vegetation has increased through evolution in the direction of inter-channel and floodplain areas. As a result of the disappearance of the side arms, inter-channel areas have been absorbed by floodplains. (4) These processes have resulted in the slow preservation of the fixed multiple-channel fluvial system. We suggest calling this system an “anabranching river” as opposed to the classical anastomosing river (Smith and Smith, 1980).

Fluvial style changes during the last glacial–interglacial transition in the middle Tisza valley (Hungary)

The Weichselian Late Pleniglacial, Lateglacial and Holocene fluvial history of the middle Tisza valley in Hungary has been compared with other river systems in West and Central Europe, enabling us to define local and regional forcing factors in fluvial system change. Four Weichselian to Holocene floodplain generations, differing in palaeochannel characteristics and elevation, were defined by geomorphological analysis. Coring transects enabled the construction of the channel geometry and fluvial architecture. Pollen analysis of the fine-grained deposits has determined the vegetation development over time and, for the first time, a bio(chrono)stratigraphic framework for the changes in the fluvial system. Radiocarbon dating has provided an absolute chronology; however, the results are problematic due to the partly reworked character of the organic material in the loamy sediments. During the Late Pleniglacial, aggradation by a braided precursor system of the Tisza and local deflation and dune formation took place in a steppe or open coniferous forest landscape. A channel pattern change from braided to large-scale meandering and gradual incision occurred during the Late Pleniglacial or start of the Lateglacial, due to climate warming and climate-related boreal forest development, leading to lower stream power and lower sediment supply, although bank-full discharges were still high. Alternatively, this fluvial change might reflect the tectonically induced avulsion of the River Tisza into the area. The climatic deterioration of the Younger Dryas Stadial, frequently registered by fluvial system changes along the North Atlantic margin, is not reflected in the middle Tisza valley and meandering persisted. The Lateglacial to Holocene climatic warming resulted in the growth of deciduous forest and channel incision and a prominent terrace scarp developed. The Holocene floodplain was formed by laterally migrating smaller meandering channels reflecting lower bank-full discharges. Intra-Holocene river changes have not been observed.

Geomorphic changes in Ras Al-Subiyah area, Kuwait

The Ras Al-Subiyah area is considered one of the most promising areas in Kuwait for future development. This development will include a new town called Subiyah and its associated infrastructure. This area is also being considered as the location for connection between Boubyan Island, which is now undergoing major development and the Kuwait mainland. The present study investigates the geomorphology of the Ras Al-Sabiyah area in the northern sector of Kuwait. The study area is generally flat, and it is located west of the Jal Az-Zor escarpment. It is bordered on the east by the Khor Al-Sabiyah tidal channel and on the south by Kuwait Bay. The area receives sediments from several sources; currently the most important are aeolian sediments and the deposition of mud delivered through the Khor Al-Sabiyah from the Iraqi marshes. The study area has been subjected to severe environmental changes due to the Gulf wars and the drainage of Iraqi marshes and the associated artificial changes in fluvial system. Twenty-two surface sediments were collected from the Ras Al-Subiyah area. Samples were collected to include the main geomorphologic characteristic features of the study area. Field observations and remote sensing images from 1990 and 2001 were used to produce an updated geomorphologic map for the Ras Al-Subiyah and a map showing geomorphic changes between 1990 and 2001. Grain size of the surface sediment ranges from gravel to medium sand. In general, grain size statistical analysis indicates that most of the areas are composed of two or more classes of sands transported and deposited from different sources including aeolian, sabkhas, river and the bays. The variability in the grain size statistical parameters may be attributed to the complexity of surface morphology as well as the diversity in the type of depositional environment in the Ras Al-Subiyah area. The total area subjected to change during the 12-year period (1990–2001) is about 32 km2 as calculated using GIS techniques.

Fluvial system evolution and environmental changes during the Holocene in the Mue valley (Western France)

Geomorphological and palaeoenvironmental research on Holocene sedimentation in the Mue valley provides evidence for fluvial system changes related to climate and human activities in Normandy, a poorly studied area of the Paris basin. The 24-km long valley bottom has been investigated through a systematic survey. It shows an original longitudinal sedimentary pattern in relation with valley morphology and local geological controls. Minerogenic, tufaceous and peaty deposits provide opportunities for multi-proxy analyses and radiocarbon dating control. Sedimentation began around 9500 14C BP with silt deposition in a meandering system. The Boreal and the Lower Atlantic periods (8500–6000 14C BP) were mainly characterized by unlithified calcareous tufa. Locally, these deposits are very thick (7 to 13 m). The tufa formed barrages across the valley bottom, providing an autogenic control on upstream sedimentation. During the Upper Atlantic period (6000–4700 14C BP), the valley experienced a decrease in calcareous sedimentation and the development of organic deposits. At the beginning of the Subboreal (4700–3500 14C BP), peat deposits expanded, especially behind the tufa barrages. The valley bottom was characterized by large marshy areas whereas the regional vegetation was progressively modified by human activities. At the end of the Subboreal (3300–3000 14C BP) the infilling of the valley by calcareous silt was caused by an increase of river activity related to climatic and land use changes. From the Iron Age and Gallo-Roman periods (2800–1700 14C BP), the valley bottom was filled by silty overbank deposits related to an increase of soil erosion. The slopes and river system were once again coupled and the fluvial system functioned as a continuum from upstream to downstream. The alluvial record of the Mue valley reflects a broad regional pattern of environmental changes but presents particular features, which highlight the need of longitudinal studies to take into account spatial and temporal discontinuities of Holocene hydro-sedimentary systems, even in small order valleys.

Dynamiques holocènes de systèmes fluviaux en Grèce du Nord : une approche comparative et multi-scalaire des interactions entre Nature et Société

Les recherches sur les dynamiques morphosédimentaires et paléoenvironnementales au cours de l’Holocène sont maintenant nombreuses dans l’espace égéen, mais, portant sur des espaces de dimensions différentes (environnement immédiat de sites archéologiques, petits bassins versants, plaines alluviales, plaines littorales, grands deltas), leurs résultats sont difficilement comparables. Afin de comprendre le fonctionnement global du système fluvial sur le long terme holocène, de nouvelles recherches géomorphologiques ont été entreprises en Grèce du Nord (des bassins versants élémentaires à la large plaine alluviale du Strymon). Chaque petit bassin versant possède une histoire propre en relation avec la succession des activités humaines et des événements hydroclimatiques exceptionnels (crues). Celle-ci ne se traduit pas de manière identique et parallèle dans les bassins d’ordre supérieur. Les forçages climatiques et anthropiques s’y combinent avec des degrés d’importance variable d’où la nécessité de définir avec précision le degré d’anthropisation des bassins versants et l’évolution des interactions à différentes échelles au sein des systèmes fluviaux.

Morphologic expression of Quaternary deformation in the northwestern foothills of the Ysyk-Köl basin, Tien Shan

The Tien Shan is one of the most active intracontinental mountain belts exhibiting numerous examples of Quaternary fault-related folding. To provide insight into the deformation of the Quaternary intermontane basins, the territory of the northwestern Ysyk-Kol region, where the growing Ak-Teke Anticline divided the piedmont apron of alluvial fans, is studied. It is shown that the Ak-Teke Hills are a sharply asymmetric anticline, which formed as a result of tectonic uplift and erosion related to motions along the South Ak-Teke Thrust Fault. The tectonic uplift gave rise to the local deviation of the drainage network in front of the northern limb of the fold. Optical (luminescent) dating suggests that the tectonic uplifting of the young anticline and the antecedent downcutting started 157 ka ago. The last upthrow of the high floodplain of the Toru-Aygyr River took place 1300 years ago. The structure of the South Ak-Teke Fault is examined by means of seismologic trenching and shallow seismic profiling across the fault. A laser tachymeter is applied to determine the vertical deformation of alluvial terraces in the Toru-Aygyr River valley at its intersection with the South Ak-Teke Fault. The rates of vertical deformation and an inferred number of strong earthquakes, which resulted in the upthrow of Quaternary river terraces of different ages, are calculated. The study territory is an example of changes in fluvial systems on growing folds in piedmont regions. As a result of shortening of the Earth’s crust in the mountainous belt owing to thrusting, new territories of previous sedimentation are involved in emergence. The tectonic activity migrates with time from the framing ridges toward the axial parts of intramontane basins.

Depositional environments and fluvial system changes in the dinosaur-bearing Sânpetru Formation (Late Cretaceous, Romania): Post-orogenic sedimentation in an active extensional basin

The Sânpetru Formation (Haţeg Basin, Romania) was deposited in an active extensional basin in response to the post-orogenic collapse of the Southern Carpathians. Despite being one of the best exposed latest Cretaceous continental successions of Eastern Europe and having great potential to improve knowledge about the Mesozoic evolution of the Carpathian orogen and the latest Cretaceous terrestrial paleoenvironments of Europe, this formation has been the subject of limited sedimentologic research. Fourteen stratigraphic sections were measured in the Sânpetru Formation throughout an 860-m-thick interval exposed along the Sibişel Valley in order to conduct the most detailed stratigraphic and sedimentologic study of this formation to date. The Sânpetru Formation is a repetitive succession of fining-upward units composed of stratified and structureless sandstones, conglomerates, and mudstones. Facies analysis reveals that the Sânpetru Formation was deposited by braided streams that flowed through a symmetrical, extensional basin. The low variability of paleocurrent direction, the sheet-like architecture of the deposits, and the paucity of channel-shaped scours indicate poorly channelized flow across a shallow, broad braidplain. Small-scale fluctuations in sandstone/mudstone ratio and maximum grain size of channel deposits in the lower Sânpetru Formation reflect autocyclic shifts in paleochannel position. In the upper Sânpetru Formation, sandstone/mudstone ratios and maximum grain size of channel deposits increase, paleocurrent direction changes significantly, and hydromorphic paleosols become the sole type of paleosols present. These changes reflect an episode of rapid uplift of the source area and the basinward creation of accommodation space below the local water table, which resulted in the creation of extensive wetlands. The wetlands of the upper Sânpetru Formation were not an environment favorable for the formation of dinosaur bonebeds, which are found in the lower part of the formation. The apparent absence of fossils in the upper part of the formation led previous researchers to incorrectly interpret the Cretaceous–Tertiary boundary at the transition between the lower and upper Sânpetru Formation.

Detection of rapid climate change in Last Glacial fluvial successions in The Netherlands

Climate change during the Last Glacial is considered as a major forcing factor of fluvial system changes. A continuous succession of fluvial sediments, reflecting adaptations to climate change from the Weichselian Middle Pleniglacial (oxygen isotope stage 3) onwards, occurs in lowland river basins in the Netherlands. A comparison of the Pleniglacial and Late Glacial fluvial record in the Netherlands shows that climatic oscillations of similar magnitude did not produce changes in the fluvial sedimentary system of equal magnitude. The Late Glacial fluvial system proves to be highly sensitive to climate change. By contrast, many of the rapid climate changes that have occurred during oxygen isotope stage 3, according to the Greenland ice core record, are not detectable in the fluvial sediments. This can be explained by differences in the impact of the climate variations on drainage basin vegetation. During the Late Glacial, the tree line repeatedly shifted through the Netherlands, whereas the area remained within the tundra zone during the Middle Pleniglacial. Precipitation variations and permafrost aggradation and degradation have played a secondary role. The Weichselian fluvial succession in the Netherlands demonstrates that detection of a change in the fluvial sedimentary system and relating this change to climate change is subject to methodological limitations. The climatic significance of changes in the fluvial record should be carefully evaluated, as well as their chronology. The possibility that climate did not influence the fluvial system should always be considered as a null hypothesis in studies on fluvial successions.

Adjustment of a drainage network to capture induced base-level change: an example from the Sorbas Basin, SE Spain

Quaternary catchments in the south of the Sorbas Basin, SE Spain have been affected by two regionally significant river captures. The river captures were triggered by changes in regional gradients associated with sustained Quaternary uplift in the region of 160 m Ma −1. The first capture occurred in the early Pleistocene and re-routed 15% of the original Sorbas Basin drainage into the Carboneras Basin to the south. The second occurred in the late Pleistocene and re-routed 73% of the original Sorbas Basin drainage to the east. This latter capture had dramatic consequences for base-level in the Sorbas Basin master drainage. Local base-level was lowered by 90 m at the capture site, 50 m at 7 km upstream and 25 m at 13 km upstream of the site. The base-level change instigated a complex re-organisation of the drainage networks in systems tributary to the master drainage over the ensuing period (some 100 ka). After the capture, drainage systems closer to the capture site experienced a tenfold increase in incision rates over most of their network. Those located some 13 km upstream of the capture site experienced a fivefold increase in incision, although in this instance, the changes do not appear to have propagated to the headwater regions of the drainage nets. The sensitivity of individual catchments was largely governed by geological controls (structure and lithology). The detailed network evolution in the most sensitive areas can be traced by reconstructing former drainage pathways using abandoned drainage cols and the alignment and degree of incision of the drainage networks. Three main stages of evolution can be identified which record the progressive spread of base-level changes from the master drainage. These are Stage 1 (pre-capture): original south-to-north consequent drainage; Stage 2 (early stage, post capture): aggressive subsequent southwest-to-northeast and east–west drainage developed along structural lineaments first in the east of the area (Stage 2a), and later in the west of the area (Stage 2b); and Stage 3 (late stage, post capture): obsequent drainage developing on the topography of the Stage 2 drainage. All stages of the network evolution are associated with drainage re-routing as a function of river capture at a variety of scales. The results highlight the complex response of the fluvial system, and the very different geomorphological histories of adjacent catchments, emphasising the need for regional approaches for examining long-term changes in fluvial systems.

Geomorphic responses to climatic change

Conceptual models for changing landscapes Impacts of pleistocene-holocene climatic changes on desert streams Lithologic controls of geomorphic responses to climatic changes on desert hillslopes Climatic geomorphology of a lofty, semiarid to subhumid mountain range Changing climate, geomorphic processes, and landscapes in a humid fluvial system Comparisons of geomorphic responses to climatic changes in fluvial systems of extremely arid to humid regions References Glossary Index.