Braided rivers within an arid alluvial plain (example from the Lower Triassic,western German Basin): recognition criteria and expression of stratigraphic cycles

Based on a detailed sedimentological analysis of Lower Triassic continental deposits in the western Germanic sag Basin (i.e. the eastern part of the present‐day Paris Basin: the ‘Conglomérat basal’, ‘Grès vosgien’ and ‘Conglomérat principal’ Formations), three main depositional environments were identified: (i) braided rivers in an arid alluvial plain with some preserved aeolian dunes and very few floodplain deposits; (ii) marginal erg (i.e. braided rivers, aeolian dunes and aeolian sand‐sheets); and (iii) playa lake (an ephemeral lake environment with fluvial and aeolian sediments). Most of the time, aeolian deposits in arid environments that are dominated by fluvial systems are poorly preserved and particular attention should be paid to any sedimentological marker of aridity, such as wind‐worn pebbles (ventifacts), sand‐drift surfaces and aeolian sand‐sheets. In such arid continental environments, stratigraphic surfaces of allocyclic origin correspond to bounding surfaces of regional extension. Elementary stratigraphic cycles, i.e. the genetic units, have been identified for the three main continental environments: the fluvial type, fluvial–aeolian type and fluvial/playa lake type. At the time scale of tens to hundreds of thousands of years, these high‐frequency cycles of climatic origin are controlled either by the groundwater level in the basin or by the fluvial siliciclastic sediment input supplied from the highland. Lower Triassic deposits from the Germanic Basin are preserved mostly in endoreic basins. The central part of the basin is arid but the rivers are supplied with water by precipitation falling on the remnants of the Hercynian (Variscan)–Appalachian Mountains. Consequently, a detailed study of alluvial plain facies provides indications of local climatic conditions in the place of deposition, whereas fluvial systems only reflect climatic conditions of the upstream erosional catchments.     

The Pleistocene climate-controlled fluvial sedimentary record in the Bełchatów mine (central Poland)

Sedimentological analyses of fluvial formations in the Bełchatów mine have yielded results that have more than regional significance. They concern the reaction of rivers to climatic changes in the Pleistocene. Changes in river geometry and their depositional records are examined from two fluvial formations. These formations represent different times, but show similar palaeoenvironmental changes. Cool temperate climate conditions resulted in meandering (or anastomosing) river sedimentation, which was controlled by equalized precipitation and by a well-developed vegetation cover. Cold periglacial climate conditions resulted in braided river sedimentation immediately before the Glacial Maximum, with high discharges and a high sediment load. The palaeoclimatic and palaeohydrologic analyses of the Weichselian fluvial deposits in Bełchatów provide additional information to that from similar studies in Germany and the Netherlands, thus jointly resulting in a consistent palaeogeographic model of western-middle Europe.     

Climatic versus halokinetic control on sedimentation in a dryland fluvial succession

Fluvial systems and their preserved stratigraphic expression as the fill of evolving basins are controlled by multiple factors, which can vary both spatially and temporally, including prevailing climate, sediment provenance, localized changes in the rates of creation and infill of accommodation in response to subsidence, and diversion by surface topographic features. In basins that develop in response to halokinesis, mobilized salt tends to be displaced by sediment loading to create a series of rapidly subsiding mini‐basins, each separated by growing salt walls. The style and pattern of fluvial sedimentation governs the rate at which accommodation becomes filled, whereas the rate of growth of basin‐bounding salt walls governs whether an emergent surface topography will develop that has the potential to divert and modify fluvial drainage pathways and thereby dictate the resultant fluvial stratigraphic architecture. Discerning the relative roles played by halokinesis and other factors, such as climate‐driven variations in the rate and style of sediment supply, is far from straightforward. Diverse stratigraphic architectures present in temporally equivalent, neighbouring salt‐walled mini‐basins demonstrate the effectiveness of topographically elevated salt walls as agents that partition and guide fluvial pathways, and thereby control the loci of accumulation of fluvial successions in evolving mini‐basins: drainage pathways can be focused into a single mini‐basin to preserve a sand‐prone fill style, whilst leaving adjoining basins relatively sand‐starved. By contrast, over the evolutionary history of a suite of salt‐walled mini‐basins, region‐wide changes in fluvial style can be shown to have been driven by changes in palaeoclimate and sediment‐delivery style. The Triassic Moenkopi Formation of the south‐western USA represents the preserved expression of a dryland fluvial system that accumulated across a broad, low‐relief alluvial plain, in a regressive continental to paralic setting. Within south‐eastern Utah, the Moenkopi Formation accumulated in a series of actively subsiding salt‐walled mini‐basins, ongoing evolution of which exerted a significant control on the style of drainage and resultant pattern of stratigraphic accumulation. Drainage pathways developed axial (parallel) to salt walls, resulting in compartmentalized accumulation of strata whereby neighbouring mini‐basins record significant variations in sedimentary style at the same stratigraphic level. Despite the complexities created by halokinetic controls, the signature of climate‐driven sediment delivery can be deciphered from the preserved succession by comparison with the stratigraphic expression of part of the system that accumulated beyond the influence of halokinesis, and this approach can be used to demonstrate regional variations in climate‐controlled styles of sediment delivery.     

Climate Changes and Cyclic Sedimentation in the Mid-Late Permian: Kennedy Group, Carnarvon Basin, Western Australia

Climate has an important direct and indirect influence of sedimentation, and especially on the development of cyclic sedimentation. Climate influences both accommodation and supply, the major controls on the architecture of sedimentary sequences. The Permian paleoclimate is the subject of increasing controversy, giving rise to numerous differing models developed and an expanding database of fossil evidence for climatic conditions.Western Australian basins, in particular the Carnarvon Basin, are unique among nearby Gondwanan basins in that they do not have extensive coal measures within their Permian successions. The Kennedy Group, the uppermost unit in the onshore Carnarvon Basin Permian succession, has a detrital composition indicative of arid weathering conditions. Within the Kennedy Group, even lagoonal and very nearshore sediments are devoid of plant debris or indications of the nearby presence of extensive flora. Presumed surfaces of subaerial exposure do not show paleosol development or root-traces. There has been little development of clay and chemical grain degradation is almost entirely related to diagenetic cementation and dissolution phases, rather than transport and source weathering. Nearby basins, at similar latitudes, in India and East Australia contain coal measures, consistent with the humid climates that are predicted for this latitude. It is suggested therefore that the inferred aridity in the climate of the Carnarvon Basin and other Western Australian Basins is due to local climatic effects, probably related to an interruption in atmospheric circulation caused by tectonic rifting and uplift to the west.Cyclicity in the Kennedy Group indicates regular Late Permian, Milankovitch scale eustatic sea-level change, and may signify the presence of some ice at the poles. The development of cycles may have been enhanced by shifting climate belts controlled by Milankovitch cyclicity.     

Late Cenozoic fluvial successions in northern and western India: an overview and synthesis

Late Cenozoic fluvial successions are widespread in India. They include the deposits of the Siwalik basin which represent the accumulations of the ancient river systems of the Himalayan foreland basin. Palaeomagnetic studies reveal that fluvial architecture and styles of deposition were controlled by Himalayan tectonics as well as by major climatic fluctuations during the long (∼13 Ma) span of formation. The Indo-Gangetic plains form the world's most extensive Quaternary alluvial plains, and display spatially variable controls on sedimentation: Himalayan tectonics in the frontal parts, climate in the middle reaches, and eustasy in the lower reaches close to the Ganga–Brahmaputra delta. Climatic effects were mediated by strong fluctuations in the SW Indian Monsoon, and Himalayan rivers occupy deep valleys in the western Ganga plains where stream power is high, cut in part during early Holocene monsoon intensification; the broad interfluves record the simultaneous aggradation of plains-fed rivers since ∼100 ka. The eastward increase in precipitation across the Ganga Plains results in rivers with low stream power and a very high sediment flux, resulting in an aggradational mode and little incision. The river deposits of semi-arid to arid western India form important archives of Quaternary climate change through their intercalation with the eolian deposits of the Thar Desert. Although the synthesis documents strong variability—both spatial and temporal—in fluvial stratigraphy, climatic events such as the decline in precipitation during the Last Glacial Maximum and monsoon intensification in the early Holocene have influenced fluvial dynamics throughout the region.     

我国沿海不同气候带山溪性河流沉积物输运特征

近年来许多研究发现山溪性小河流具有瞬时大通量、受极端气候事件控制、沉积物快速输运等特性,但是由于缺乏充足的监测数据和系统总结,其对全球沉积物输运的影响被低估,导致对于这个不同于大河流域的河海交互和风化传输系统的研究是不充分的.揭示不同气候带山溪性河流在自然变化与人类活动共同影响下的沉积物输运特征有助于深入理解地球表生过...     

Quaternary stratigraphy of the Koratallaiyar-Cooum basin,Chennai

In this paper we present Quaternary stratigraphy of the area around Chennai based on archaeological findings on the ferricrete surface, geomorphological observations supplemented by radiocarbon dating. The coastal landscape around Chennai, Tamil Nadu, has preserved ferruginised boulder gravel deposits, ferricretes and fluvial deposits of varying thickness. The area studied is approximately 150 km east to west and 180 km north to south with a broad continental shelf towards the seaward. Several rivers enter the Bay of Bengal along its shores like the Koratallaiyar, Cooum and the Adyar. Precambrian charnockite and Upper Gondwana sandstone and shale bedrock rim the shelf margin. For the most part, the Upper Pleistocene-Holocene fluvial sediments overlie an erosion surface that has cut into older Pleistocene sediments and ferricrete surface. Incised valleys that cut into this erosion surface are up to 5–6 km wide and have a relief of at least 30 m. The largest valley is that cut by the Koratallaiyar River. Holocene sediments deposited in the incised valleys include fluvial gravels, early transgressive channel sands and floodplain silts. Older Pleistocene sediments are deposited before and during the 120-ka high stand (Marine isotope stage 5). They consist of ferricretes and ferricrete gravel formed in nearshore humid environments. Muddy and sandy clastic sediments dated to the ca. 5 ka highstand suggest that the climate was semi arid at this time with less fluvial transport. The coarsening up sequence indicates deposition by high intensity channel processes. Pedogenic mottled, clayey silt unit represents an important tectonic event when the channel was temporarily drained and sediment were sub aerially exposed. Uplift of the region has caused the local rivers to incise into the landscape, forming degradation terraces.     

Sediment records as archives of the Late Pleistocene-Holocene hydrological change in the alluvial Narmada River basin, western India

The rivers of western India are monsoon dominated and have been so throughout the late Quaternary. Sediment accumulation in these river basins has been controlled by climatic and tectonic changes over a time span from the Late Pleistocene to the recent. The lithofacies assemblages associated with the various sediment archives in the Narmada basin range from the boulders of the alluvial fans to overbank fines on the alluvial plains. Estimates, based on clast size, of stream power and competence, bed shear stress and discharge reveal that hydrological conditions during the Late Pleistocene (∼90 ka) were comparable to the present day. The size of the transported clasts and the thickness of the accumulated sediment indicate the influence of basin subsidence rather than an increase in discharge. Discharge estimates based on sedimentary structures preserved in the alluvial-plain facies suggest that the channel had a persistent flow, with a low width-depth ratio and large meander wavelength. The hydrological changes during the Holocene are more pronounced where the early Holocene is marked by a high-intensity hydrological regime that induced erosion and incision of the earlier sediments. The mid-Holocene stream channel was less sinuous and had a higher width-depth ratio and a higher meander amplitude in comparison with the present-day channel. Palaeo-fluvial reconstructions based on the sediment archives in the alluvial reach of the river basin are important tools in understanding the long-term hydrological changes and the intricate fluvial architecture preserved in the Narmada River basin ensures scope for detailed studies to identify phases of weak and enhanced hydrological regimes.     

Mineral magnetic properties of Holocene lake sediments and soils from the Kårsa valley,Lappland, Sweden,and their relevance to palaeoenvironmental reconstruction

A mineral magnetic study of lacustrine sediments and soils from the Kårsa valley in Lappland, Sweden was undertaken to estimate the potential of mineral magnetic techniques in elucidating the variability of climate, recorded by glacier fluctuations and soil development. Sediment cores from two lake basins receiving sediment input from a glacial outflow stream, and their respective catchments, show a mineral magnetic record that can be interpreted in terms of glacial activity and soil development. Dissolution of magnetite is indicated during periods of climatic amelioration and causes a high S-ratio. During periods of glacial advance (and colder, wetter climate) the minerogenic sediment supply is increased and magnetite is preserved in the sediment, resulting in a low S-ratio. Variations in the S-ratio can then be used as a proxy-climate indicator.     

Middle and Late Weichselian stratigraphy and palaeoenvironments in central Poland

The moraine plateau near BetchatÓw (central Poland) was incised at the beginning of the Middle Weichselian. Valleys 20–35 m deep were formed and then infilled with silts, sands, gravels, organic sediments and slope diamictons of the Piaski Formation, which is characterized by highly varying sedimentary environments. Initially - 40,000–30,000 BP - lacustrine sediments with an obvious colian supply (re-worked loess) and locally fluvial suites were deposited in depressions. Slope sediments were simultaneously deposited at the valley margins. The Middle Weichselian was relatively mild and dry, but the milder interstadial periods have not been precisely established. Semi-anastomosing, stable-channel, highly aggrading and ephemeral streams of a semi-arid climate (subpolar desert) formed c. 30,000–22,000 BP. Continuous permafrost is implied from cyclic sedimentary processes reflecting summer melting and from periglacial structures. This was succeeded by a highly aggrading, high-energy and ephemeral braided fluvial system in an arid climate (polar desert), reflecting a complete lack of vegetation and increased eolian activity. These braided rivers formed during a period which may be directly correlated with the time of the maximum extent of the last ice sheet (22,000–14,350 BP), characterized by the most severe climatic conditions with strong periglacial activity. Finally - (14,350-12,700 BP)- eolian sediments were deposited, reflecting milder climatic conditions at the time of the abrupt ice sheet decay.     

Evidence for Regional Stream Aggradation in the Central Oregon Coast Range during the Pleistocene-Holocene Transition

Low, nearly continuous terraces of similar age are present along streams in drainage basins that range in size from Drift Creek (190 km²) to the Umpqua River (11,800 km²) in the Oregon Coast Range. Radiocarbon ages from near the bose of fluvial sediments underlying these terraces are clustered at about 9000-11,000 ¹⁴C yr B.P. Beveled bedrock surfaces (straths) that underlie the fluvial sediments are 1-8 m above summer stream levels and are present along most of the nontidal reaches of the rivers that we studied. Where exposed, the bedrock straths are overlain by 2-11 m of fluvial sediment that consists of a bottom-stratum (channel) facies of sandy pebble-cobble gravel and a top-stratum (overbank) facies of sandy silt or silt. Eight radiocarbon ages from the fluvial sediments allow correlation of the lowest continuous terrace over a wide area and thus indicate that a regional aggradation episode occurred in Coast Range drainage basins during the Pleistocene-Holocene transition. The cause of such widespread aggradation is unknown but may be related to climate-induced changes in the frequency of evacuation of colluvium from hollows, which are common in all drainage basins in the region.     

Cyclicity of shallow-water carbonate sediments in different climatic zones

Based on the study of several different-age shallow-water carbonate sediments from different regions, it is established that cyclothems formed in basins of arid and humid climatic zones differ in their composition and structure. It is shown that the influence of climate was indirect. The climate governed salinity (particularly, in extremely shallow-water settings of initial and terminal stages of the formation of cyclothems) and, thus, stimulated changes in the biota. The biota, in turn, controlled the composition of carbonate material and mechanisms of its sedimentation.     

Pliocene sedimentation in a shallow, cool-water, estuarine gulf, Murray Basin, South Australia

The Pliocene Norwest Bend Formation is a well‐preserved succession of terrestrial and shallow‐marine deposits in the Murray Basin, South Australia. Sediments in this unit consist of two discrete terrigenous clastic‐rich, decametre‐scale sequences, or informal members, which record episodes of marine incursion during the Early and Late Pliocene respectively. The base of each sequence is a transgressive lag and/or strandline deposit that is transitional upwards into a highstand, subtidal, terrigenous clastic and cool‐water carbonate sediment accumulation. The top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea‐level fell and terrestrial environments prograded basinward. Sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy. Differences in sedimentary style between these two sequences, however, reflect a major climatic change that took place in southern Australia during the mid‐Pliocene. The lower quartzose sand member is formed of siliciclastic sediment derived from prolonged, deep, subaerial weathering and contains a bivalve‐dominated, cool‐temperate, open‐marine mollusc assemblage. These sediments accumulated under an equitable, relatively warm, humid climate. The Murray Basin during this time, because of high fluvial discharge, was a salt‐wedge estuary with typical estuarine circulation. In contrast, the upper, oyster‐rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments. Strandline deposits contain a warm‐temperate skeletal assemblage. Contemporaneous aeolian sediments accumulated under warm, semi‐arid climatic conditions. Well‐developed ferricrete, silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern Australia today. Highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed. These Pliocene sediments support the notion that mollusc‐rich facies are the signature of cool‐water carbonate accumulations in inboard neritic environments. Unlike bryozoans that dominate the outer parts of Cenozoic cool‐water carbonate shelves, molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates.     

Climate-induced sediment-palaeosol cycles in a Late Cretaceous dry aeolian sand sheet: Marília Formation (North-West Bauru Basin, Brazil)

Aeolian sand sheets, which are characterized by low relief surfaces that lack dunes, are common in arid and semi‐arid climatic settings. The surface of an aeolian sand sheet can either be stable and subject to pedogenetic effects, or unstable such that it is affected by deflation or sedimentation. The Marília Formation (Late Cretaceous) may be interpreted as an ancient aeolian sand sheet area, where alternating phases of stability and instability of the accumulation surface have been recorded. Detailed field studies were carried out in several sections of the Marília Formation, where cyclic alternations of palaeosols and aeolian deposits were evident, using palaeopedological and facies analysis methods, supported in the laboratory by the analysis of rock samples, cut and polished in slabs, thin sections, scanning electron microscope images and X‐ray diffraction data from the clay minerals. The deposits comprise three lithofacies that, in order of abundance, are characterized by: (i) translatent wind‐ripple strata; (ii) flood deposits; and (iii) ephemeral river channel deposits. Palaeosols constitute, on average, 65% of the vertical succession. Three types of palaeosols (pedotypes) are recognized: (i) Aridisols; (ii) Entisols; and (iii) Vertisols. Erosional surfaces due to aeolian deflation divide the top of the palaeosol profiles from the overlying aeolian deposits. The palaeoenvironmental interpretation of the deposits and the palaeosols allows the depositional system of the Marília Formation to be defined as a flat area, dominated by aeolian sedimentation, with subordinate ephemeral river sedimentation, and characterized by a dry climatic setting with occasional rainfall. The climate is the main forcing factor controlling the alternation between episodes of active sedimentation and periods of palaeosol development. A climate‐controlled model is proposed in which: (i) the palaeosols are indicative of a stable surface that is developed during the more humid climatic phases; and (ii) the erosional surfaces and the overlying aeolian sediments attest to periods of deflation and subsequent sedimentation, thereby increasing the availability of sediment during the drier climatic phases. The ephemeral fluvial deposits mark the more humid climatic conditions and contribute to the lagged sediment influx caused during the drier periods by the erosion of previously stored sediment.     

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.     

Geological,geophysical, and inherited tectonic imprints on the climate and contrasting coastal geomorphology of the Indian peninsula

The Indian subcontinent comprises accreted cratonic fragments that underwent subsequent rifting–subduction–collision processes along major mobile belts. It is also a storehouse of a prolonged history of crustal evolution involving repeated episodes of magmatism, volcanism, sedimentation, and metamorphism, and the formation of intracratonic and foreland basins. The geologic–geomorphic evolution of the Peninsula is recorded in relic faults/suture zones that confine Paleozoic, Mesozoic, and Cenozoic sedimentary basins and landforms. In addition, escarpments, plateaus, waterfalls, deltas, planation surfaces, and strandlines are either aligned parallel and/or formed over them. Asymmetric relief across the western–eastern parts of the Peninsula, orographic effect on the precipitation pattern and climatic zones provide important constrains on the geologic and geomorphic evolution of the region. Though extensive continental and coastal deposition occurred during Permo-Triassic and Early Cretaceous, only the downwarped grabens of Gondwana basins preserved the sedimentary records. Occurrences of extensive Cenozoic deposits offshore and Neogene–Holocene deltaic deposits along the entire east coast as opposed to the absence of comparable deltaic sequences in the west coast are linked to intense and recurrent episodes of denudation indicating first-order control of basement structures over landscape evolution.Inheritance and continuum of basement structures over climate, and landscape evolution of Peninsular India can also be witnessed by the unique and diverse drainage patterns of major rivers. While most of the major rivers follow a general easterly direction, the landscape morphology of their catchments indicates youthful character and tectonically active nature. The east flowing rivers show an asymmetry between the areal extents of drainage basin size and delta, whereas the west-flowing rivers are short and straight and their catchments are miniscule in comparison with the rivers flowing toward east. The Western Ghats Escarpment forms an orographic barrier and acts as the main divide between these two drainage systems. There is a disparity between the quanta of sediment discharge as well. In addition, the eastern and western parts of India, across the Western Ghats Escarpment, show significant differences in terms of climatic zones (humid to per-humid on the west while it is arid to subhumid on the east). The west coast is characterized by > 3000 mm/year annual rainfall, that often reaches > 5000 mm/year, dominance of SW monsoon winds, occurrence of narrow (< 60 km), rocky, crenulated and coastal cliffs and pocket beaches, and net southerly long shore sediment transport. In contrast, the east coast is characterized by several hundred kilometers wide deltaic low lands built by major rivers. These rivers show trellis to dendritic stream patterns and follow major basement faults that are associated with geologic–historic–recent seismic activity. The sedimentary basins and delta heads, strandlines, and active delta lobes whose western boundary is always limited by basement faults have shown activity since the formation of the Gondwanan supercontinent. The eastern coastal region is also different from the west in terms of active NE monsoon, long shore sediment transport (toward north), and the formation of extensive lagoon-beach barrier systems since Neogene that in turn continue to occur until recent.Here we propose a conceptual tectono-geomorphic model demonstrating the inheritance and continuum of Gondwanan structural trends on the transient landscape of Peninsular India.     

Spatiotemporal and lithological-facies distribution of natural radioactive elements in Jurassic and Early Cretaceous deposits of the Western Siberian Plate

The paper presents original data on the K, U, and Th distribution over the areas of Jurassic and Early Cretaceous sedimentation basins on the Western Siberian Plate and on the distribution of natural radioactive elements in all major lithological–stratigraphic complexes and through the facies profile of the humid and arid sedimentation basins. These data can be utilized in lithological-facies analysis, reconstructions of sedimentation conditions, lithological and stratigraphic subdivision of stratigraphic sections, and in mapping boundaries between oil and gas complexes and assaying the hydrocarbon potential of the region.     

Flood‐plain responses to contemporary climate change in small High‐Arctic basins (Svalbard,Norway)

Changes in the supply of water and sediment to high‐latitude rivers related to contemporary climate change and glacier fluctuations largely determine the activity of fluvial processes. This study reconstructs fluvial dynamics since the end of the Little Ice Age (LIA) in two small, partially glaciated basins in the southern part of Spitsbergen, Svalbard Archipelago. We use a combination of aerial photograph interpretation, field mapping and dendrochronological analysis. Sequences of abandoned channels and glacifluvial terraces are distinctly visible in middle and lower parts of the Brattegg and Arie basins in this area. The advance of glaciers during the LIA in the upper part of the basins led to the development of a braiding pattern and to channel aggradation corresponding to the highest glacifluvial levels. The decreasing activity of these braidplains occurred at the turn of the 19th and 20th centuries, immediately prior to a significant incision period. A second generation of braided channels developed during the first half of the 20th century. Ice‐marginal lake development, less input of fine‐grained sediment to the river channel, and fast incision began from the second half of the 20th century onward. During the last two decades, the main fluvial response to the climatic warming has been contraction of flow within a narrower channel and the abandonment of braidplains. The increased lateral erosion and rate of downcutting and the formation of the most downstream reaches of the modern valley bottom occurred in the 1980s and 1990s. This process was intensified under flood conditions generated by extreme rainfall events. These micro‐scale (small partially glaciated basins) observations concerning the changes of the activity of fluvial processes since the end of LIA may be helpful for the reconstruction of past fluvial changes over longer time scales.