Search

The Bohai Sea is a semi-enclosed shallow shelf sea that has undergone a unique sediment source-to-sink process in the past. Despite this, our knowledge about the sediment budget, existence of depocenters and the factors controlling depocenter formation during the Holocene remains limited. This paper aims to address these gaps by estimating the Holocene marine deposit thickness and sediment budget in the Bohai Sea using high-resolution subbottom profiles. The results reveal that the mean thickness of Holocene marine deposits is approximately 7.8 m and a maximum thickness of 28 m was found in Jinzhou Bay. The Highstand System Tracts (HST) have a mean thickness of approximately 5.4 m and a maximum thickness of 25 m observed in the Jinzhou Bay. On the other hand, the Transgressive System Tracts (TST) have a mean thickness of approximately 2.5 m and a maximum thickness of 7 m in the north of the Laizhou Bay. The total accumulation in the Bohai Sea is estimated to be ∼713.97 × 109 tons, consisting of 489.28 × 109 tons from the HST and 224.69 × 109 tons from the TST. Three deposit centers were identified and estimated to be approximately 299 × 109 tons, accounting for approximately 42 % of the total Bohai Sea sediments. The development of Holocene marine deposit centers was mainly influenced by the Tanlu Fault zone and water circulations. Based on preliminary estimates, it is suggested that roughly half of the sediments dispersed from the estuaries are preserved on the Bohai Sea shelf since the maximum flooding (∼7000 cal yr BP). This research provides valuable insights for the post-glacial sedimentary and geomorphic evolution of the Bohai Sea. • Holocene marine accumulation in the Bohai Sea is estimated to be ∼713.97 × 109 tons. • Accumulation in HST is of ∼489.28 × 109 tons and that in TST is of ∼224.69 × 109 tons. • Three depocenters were identified and account for ∼42 % of the total accumulation. • Roughly half of the sediments were preserved on the shelf over the past 7000 years. [ABSTRACT FROM AUTHOR]

This paper documents the history of vegetation assemblage in Honghe Wetland (NE China) during the last 6200 years. Vegetation changes were reconstructed based on high-resolution plant macrofossil analysis of sedimentary sequence obtained from Honghe National Nature Reserve located in Sanjiang Plain, in conjunction with Accelerator Mass Spectrometry (AMS) 14 C radiocarbon data. Results indicate that plant macrofossil composition of Honghe wetland ecosystem are dynamic and have undergone several significant changes. Around 2500 cal yr BP, plant composition transited from Equisetum fluviatile community to Carex lasiocarpa - Drepanocladus aduncus community, and then following by Drepanocladus aduncus community at 460 cal yr BP. Another major vegetation changes occurred at 220 cal yr BP, transitioning to Carex sp. community. By comparison between the plant macrofossil assemblages and the climate changes during the last 6200 cal yr BP, we suggest that ASM (Asian summer monsoon) is the main driving force for the vegetation succession before the impacts of human activities. Since some restoration programs have been undertaken at Honghe wetland, thus our results can provide valuable baseline data for assessment of the practicability and suitability of the former restoration plan and the further designing of conservation management and restoration targets. Since the vegetation composition of Honghe wetland is pronouncedly sensitive to water level, it can be inferred that wetland ecosystem can be restored to near-natural condition through the effective management and restoration by controlling the water source of the wetland. [ABSTRACT FROM AUTHOR]

It is widely accepted that climate has a strong impact and exerts important feedbacks on erosional processes and sediment transport mechanisms. However, the extent at which climate influences erosion is still a matter of debate. In this paper we test whether frost-cracking processes and related temperature variations can influence the sediment production and surface erosion in a small catchment situated in the eastern Italian Alps. To this extent, we first present a geomorphic map of the region that we complement with published 10 Be-based denudation rates. We then apply a preexisting heat-flow model in order to analyze the variations of the frost-cracking intensity (FCI) in the study area, which could have controlled the sediment production in the basin. Finally, we compare the model results with the pattern of denudation rates and Quaternary deposits in the geomorphic map. The model results, combined with field observations, mapping, and quantitative geomorphic analyses, reveal that frost-cracking processes have had a primary role in the production of sediment where the intensity of sediment supply has been dictated and limited by the combined effect of temperature variations and conditions of bedrock preservation. These results highlight the importance of a yet poorly understood process for the production of sediment in mountain areas. [ABSTRACT FROM AUTHOR]

Abstract: This paper concerns the evolution during the Holocene of the floodplain of the Rhone River in the Basses Terres basin, 70km northeast of Lyon. Geomorphological mapping of a number of paleochannels has been carried out, using topographic maps, aerial photos, and landform surveys, and mechanical cores have been taken that enable the reconstruction of several stratigraphies in cross section. The chronology of fluvial deposits relies mainly on the radiocarbon dating of organic materials collected from the abandoned fluvial fills. Paleochannel infillings were also used to record fluvial style changes and floodplain aggradation rates. The main results show that the region has a mountainous piedmont plain controlled by local factors (inherited from glacial times) that have led to the atypical predominance of a meandering river pattern controlling the evolution of the floodplain in the Basses Terres area during the Holocene. A major avulsion of the Rhone, when it switched to its present-day northern course around 2700–2600cal. BP, strongly influenced the evolution of the Holocene floodplain, causing a sharp decrease in the aggradation of the abandoned section. In addition, four major occurrences of strong and increased sediment discharge took place around 10,000–7500, 3000–2700, 2400/1500–1000, and 230–50cal. BP. Two of these (ca. 3000–2700 and 230–50cal. BP) are correlated to a braided pattern and represent temporary fluvial metamorphoses of the Rhone. The infilling rates of several paleochannels also reveal periods of strong sediment deposition around 5500–5250, 3500–3200, 1400–1200, and 600–400cal. BP, consistent with previous regional paleohydrological phases as well as new ones. These phases are synchronous with the hydrosedimentary variations identified on a regional scale in the Rhone catchment area and the northern Alps. [Copyright &y& Elsevier]

Abstract: This paper reviews the sedimentological and geomorphological imprints of prehistoric and historical tsunamis in the four main estuaries of SW Spain. These imprints include beach erosion, filling of intertidal channels, deposition of bioclastic layers, washover fans and reworked aeolian sheets and the breaching of spits and tombolos. Most of these imprints were caused by the 218–209BC and AD1755 tsunamis, although evidence of other tsunamis has been identified. In these two events, effects on human populations were severe and diverse, such as human loss of life, changes in coastal settlements and international borders, damage to port infrastructure or flooding of marsh and inhabited areas. New radiocarbon reservoir data were included in order to obtain an approach to the recurrence period of these high-energy events (700–1000years) in this area. [Copyright &y& Elsevier]

Abstract: Holocene environmental change and environmental archaeology are important components of an international project studying the human-earth interaction system. This paper reviews the progress of Holocene environmental change and environmental archaeology research in the Yangtze River Valley over the last three decades, that includes the evolution of large freshwater lakes, Holocene transgression and sea-level changes, Holocene climate change and East Asian monsoon variation, relationship between the rise and fall of primitive civilizations and environmental changes, cultural interruptions and palaeoflood events, as well as relationship between the origin of agriculture and climate change. These research components are underpinned by the dating of lacustrine sediments, stalagmites and peat to establish a chronology of regional environmental and cultural evolution. Interdisciplinary and other environment proxy indicators need to be used in comparative studies of archaeological site formation and natural sedimentary environment in the upper, middle and lower reaches of the Yangtze River Valley. Modern technology such as remote sensing, molecular bioarchaeology, and virtual reality, should be integrated with currently used dating, geochemical, sedimentological, and palaeobotanical methods of analysis in environmental archaeology macro- and micro-studies, so as to provide a greater comprehensive insight into Holocene environmental and cultural interaction and change in the Yangtze River Valley area. [Copyright &y& Elsevier]

Abstract: This paper presents new field data pertaining to the deglaciation of the Lac Guillaume-Delisle area, aiming to establish its emplacement in time and space between the breaching of the Laurentide Ice Sheet (LIS) over Hudson Bay and the final ice disintegration over Northern Québec and Labrador. The deglaciation of the east coast of Hudson Bay started at 8200cal BP in the south-western sector of the Lac Guillaume-Delisle estuary, when the marine limit was at 271m above sea level (asl). By 8000cal BP, frontal moraines and proximal glacio-marine sediments were deposited in the transverse valleys along the coastal cuesta ridges at a mean elevation of 250m asl. They are associated with a regional topographic pinning event of the western margin of the Quebec-Labrador Ice Sheet (QLIS) on the high coastal relief. At that time, the coastal relief encouraged a change in deglaciation mode from fast calving in the open and deep Tyrrell Sea to a tidewater ice-sheet controlled by the topography. The ice front thereafter retreated eastward under very large and fast crustal unloading where ice-contact deltas fed by short sandar and eskers were deposited between 7900 and 7400cal BP (between 240 and 195m asl), as the ice front was receding inland and lost contact with Tyrrell Sea. A series of deposits and landforms characterize this modification in the sedimentation regime when the ice-sheet margin changed from tidewater to terrestrial. Dating shows that the deglaciation of the western margin of QLIS on land was very fast, i.e. faster than when the front of the ice-sheet was in contact with the Tyrrell Sea. As the fall of the relative sea-level continued, a large volume of paraglacial sediments was deposited in the river valleys making up vast fluvial terraces and deltas between 6500 and 5800cal BP (between 125 and 100m asl). Since then, land emergence has continued at a rate of about 1.3m/century. Downcutting by rivers, post-glacial deltaic sedimentation and shoreline changes still continue today. [Copyright &y& Elsevier]

Abstract: Modeling of volcanic morphometry provides reliable measurements of parameters that assist in the determination of volcanic landform degradation. Variations of the original morphology enable the understanding of patterns affecting erosion and their development, facilitating the assessment of associated hazards. A total of 24 volcanic Holocene eruptions were identified in the island of Gran Canaria (Canary Islands, Spain). 87% of these eruptions occurred in a wet environment while the rest happened in a dry environment. 45% of Holocene eruptions are located along short barrancos (S-type, less than 10km in length), 20% along large barrancos (L-type, 10–17km in length) and 35% along extra-large barrancos (XL-type, more than 17km in length). The erosional history of Holocene volcanic edifices is in the first stage of degradation, with a geomorphic signature characterized by a fresh, young cone with a sharp profile and a pristine lava flow. After intensive field work, a careful palaeo-geomorphological reconstruction of the 24 Holocene eruptions of Gran Canaria was conducted in order to obtain the Digital Terrain Models (DTMs) of the pre- and post-eruption terrains. From the difference between these DTMs, the degradation volume and the incision rate were obtained. The denudation of volcanic cones and lava flows is relatively independent both their geographical location and the climatic environment. However, local factors, such as pre-eruption topography and ravine type, have the greatest influence on the erosion of Holocene volcanic materials in Gran Canaria. Although age is a key factor to help understand the morphological evolution of monogenetic volcanic fields, the Gran Canaria Holocene volcanism presented in this paper demonstrates that local and regional factors may determine the lack of correlation between morphometric parameters and age. Consequently, the degree of transformation of the volcanic edifices evolves, in many cases, independently of their age. [Copyright &y& Elsevier]

Abstract: The aim of the study was to characterize a variety of sedimentary facies from the Mekong River delta (MRD) and to determine their geotechnical properties. The paper furthermore discusses the influences of sedimentary environment and conditions on geotechnical properties of the sedimentary facies. A core at the Vinhlong province, MRD, sufficiently presented the sedimentary facies of the area. Eight successive facies were identified based upon sedimentary properties. Characteristics of the unit showed development of sedimentary facies. Each sedimentary facies was formed under a different environment and revealed typical geotechnical properties. Estuarine channel, estuarine marine, delta front-mouth bar, and sub- to inter-tidal flat facies were formed under strong hydrodynamic conditions. The sediments are from clay to coarse sand and even pebbles, and the sedimentary structures are plentiful, such as intercalated clay, silt beddings and fine to coarse sand beddings with very different thicknesses. Strengths of these sedimentary facies vary significantly, which can be observed by cone penetration test (CPTU) results, but not by standard penetration test (SPT). The normalized values from CPTU show saw–tooth graphs with large variations, especially delta front-mouth bar and sub- to inter-tidal flat facies at shallower depth. The soil-behavior-types determined from the normalized values are plentiful from cohesionless to cohesive soils. As an example, an estuarine channel facies experiencing a large consolidation pressure, in relatively long-time (over 9920yr BP) has geotechnical properties with heavily overconsolidated conditions and high strength. On the other hand, marsh, open bay, pro-delta and March/flood plain facies, which formed under relatively low hydrodynamic conditions, have simple and homogenous sedimentary properties. The sediments are commonly silt and clay, and sedimentary structures are very faint interbedded clay and silt laminae, and rarely very fine sand laminae. Strengths of these sedimentary facies increase linearly with depth, the normalized values are all rather constant with depth, and their soil behavior-type is only normally consolidated clays from CPTU results. It could be said that the particular sedimentary conditions in the late Pleistocene–Holocene deposits of MRD can be reasonably estimated by the CPTU test. [Copyright &y& Elsevier]

Abstract: Variations in the coupling of sediment transfer between different parts of a fluvial catchment, e.g., hillslope to axial stream, can hamper understanding but are an integral part of the geomorphological record. Depositional environments respond to a combination of land use, climate, storms (floods), and autogenic conditioning. The distribution of sediment in the upland landscapes of NW England is out of equilibrium with contemporary climate and geomorphological processes; more a function of peri- and paraglacial mobilisation of glacigenic deposits. Soil and vegetation development after deglaciation have interrupted any progression toward sediment exhaustion with sediment release controlled largely by extrinsic perturbation, with late Holocene anthropogenic activity, climate and extreme hydrological events the likely candidates. This paper presents a new radiocarbon-dated Holocene geomorphological succession for the River Hodder (NW England), alongside evaluating new palaeoecological and geoarchaeological data to discern the impacts of human activity. These data show a late Holocene expansion in human occupation and use of the landscape since the Iron Age (700–0 cal. B.C.), with more substantial changes in the character and intensity of upland land use in the last 1300 years. The geomorphological responses in the uplands were the onset of considerable and widespread hillslope erosion (gullying) and associated alluvial fan development. Interpretation of the regional radiocarbon chronology limits gullying to four, more extensive and aggressive phases after 500 cal. B.C. The downstream alluvial system has responded with considerable valley floor deposition and lateral channel migration that augmented sediment supply by remobilising the existing floodplain terraces and led to the aggradation of a series of inset alluvial terraces. The timing of these changes between states of aggradation and incision in alluvial reaches reflects the increased connectivity between the hillslope and alluvial systems. Aspects of both the regional climate and land use histories are conducive to increasing discharge and sediment flux, but the region wide lowering of erosion thresholds appears a key driver conditioning these sediment-rich conditions and producing a landscape that was more susceptible to erosion under lower magnitude flows. [Copyright &y& Elsevier]

Abstract: Swarms of barchan dunes are common in arid environments. Unlike immobile or slowly moving dunes whose stratigraphy can be used to reconstruct paleoenvironmental changes, the high migration rate of barchans seems to prohibit their use as geoarchives. In this paper, a possible use of barchan swarms for paleoenvironmental reconstructions is presented. The approach is based on dune migration. In a case study based on 500 dunes in the Pampa de Jaguay aeolian transport corridor in coastal southern Peru, middle to late Holocene changes in the supply of aeolian material are inferred from calculating the time of dune initiation at the coastline. Limitations posed by the assumptions underlying this approach are discussed. [Copyright &y& Elsevier]

Abstract: The issue of determining the driving factors in gullying, apart from land use, is somewhat lagging in comparison with the study of their physical modelling and control technology. Available information focuses on the basic ideas of climatic control, anthropic determinism and internal “authigenic” dynamics. High resolution chronology of cyclic systems, common in extensively gullied areas, can provide a clue to the weight of each factor. This paper reports a study of this kind, focusing on two gully catchments in the Main Ethiopian Rift (MER), but backed by an extensive regional survey. By integrating tracing and correlation of unconformity-bounded stratigraphic units and soils with radiocarbon dating, a detailed chronology was obtained for the last 5000 years. This could be compared with proxy climate reconstructions of similar detail. Clear evidence of climatic control emerged; gully filling is triggered by decreased stream transport capacity and increased sediment supply during transitions towards drier climate phases, while gully entrenchment appears to take place at the start of moist intervals, for the reverse reasons. A broader consideration of geological setting, however, puts forward a more general interpretation. These gullies actually formed, in the beginning, as part of the land surface response to sudden, very recent tectonic events, which created accommodation space for temporary sediment stores. They should then be seen in the frame of the Discontinuous Ephemeral Stream (DES) concept; as such, they are intrinsically non-linear and complex phenomena, whose response is linearized by a strong climatic–vegetational forcing, acting on both channel flow and sediment supply. [Copyright &y& Elsevier]

Abstract: Paleoclimate research is essential to determine the natural variability of climate and to place the current climate change into its natural context. The current need is to generate the highest temporal resolution paleoclimatic reconstructions possible in order to assess the natural variability of the climate system, but also to test the ability of numerical models to simulate conditions different from the ones observed with the relatively short instrumental records. In this paper, we show that CAT-scan analysis of sedimentary sequences, with its 1 mm downcore resolution, can be used to identify millennial to seasonal cycles in sedimentary sequences. In examples from the St. Lawrence Estuary, Eastern Canada, spectral analysis of the CAT-scan data from Holocene postglacial sediments revealed millennial- to centennial-scale oscillations possibly associated with either solar variability, changes in relative sea-level or tidal amplitude. Similarly, spectral analysis of Holocene and Sangamonian glaciomarine sequences revealed decadal- to annual-scale oscillations with periods close to the one previously associated with the North Atlantic Oscillation (NAO), whereas spectral analysis of the CAT-scan data from the Sangamonian rhythmites possibly revealed seasonal cycles. [Copyright &y& Elsevier]

In tropical Africa, Late Pleistocene-Holocene climatic fluctuations heavily impacted the continental hydro-systems. The timing and magnitude of 'African Humid Period' hydrological dynamics (AHP; ~14.8 to ~5.5 ka BP) are not yet fully understood due to the extreme variability in African geomorphic patterns and the complex network of past air convergence boundary shifts. The investigation of the functioning of specific hydro-sedimentary basins is needed to improve our knowledge on the AHP spatial and chronological patterns over the continent. In this paper we present a revised Holocene lake level curve of Lake Abhe: an endorheic basin situated in the Afar Depression at the northern extremity of the East African Rift System (EARS). Located at the boundary of the Red Sea and the Indian and Atlantic Oceans' air moisture mass fluxes, the Lake Abhe watershed represents a system sensitive to changes in Northeast African hydro-climate. Based on numerous littoral lacustrine geomorphic features and 53 related radiocarbon ages on stromatolites and nearshore deposits, we have defined the main Holocene lake highstands proposing a detailed paleo-shoreline record. The first rise in water level is dated to ~11.1 ka cal. BP, while the Maximal Holocene Highstand Shoreline (~420 m a.s.l.) was rapidly reached around ~10 ka cal. BP. Evidence of the impact of the 8.2 ka North Atlantic cooling event is recognized with slow lake level regression until ~8.3 ka cal. BP and with an abrupt drop at ~8 ka cal. BP. The resurgence of humid conditions was recorded from ~7.7 ka cal. BP to ~4.6 ka cal. BP. Radiocarbon ages on littoral materials allow us to propose a Holocene subsidence rate of the Abhe basin axial valley. Furthermore, multiphase sill overflow incisions towards the downstream Hanle basin and transient fluvial connectivity with the upstream Ziway-Shala basin, indicate strong geomorphic controls on lake highstand elevations. In summary, Lake Abhe Holocene fluctuations are the result of combined hydro-climatic, tectonic and local geomorphic controls. However, the confrontation with others East African basins allows us to discuss the transport of moisture masses dynamics into the northern EARS during the Holocene. [ABSTRACT FROM AUTHOR]

Abstract: During the last few decades, many case studies focused on the dynamics of fluvial systems in response to hillslope erosion, land-use impact, and climate changes. This paper will review the current state of knowledge of the dynamics of past soil erosion and gullying in small catchments (< 1 km2), the effects to adjacent fluvial systems and possible feedback mechanisms to land-use changes for the last 7000 years in central Europe. The discussed studies were made on hillslopes and gully systems in low mountain range areas. They are characterised by coupled slope–channel systems as well as uncoupled systems like closed depressions in Pleistocene lowlands, maars, lakes, and sunken areas. The studies show that sediment fluxes in small catchments are highly sensitive to local land-use changes while river sediments show regional trends in land-use and climate changes. Peaks of soil erosion and gullying took place during phases of rapid climate change. Particularly, extreme precipitation events caused intensive runoff on slopes used for agriculture. The most remarkable phases occurred in the first half of 14th and in the mid-18th to the early 19th century. Most of the gully systems in Europe today are a result of these catastrophic occurrences. These punctuated events triggered land abandonment and influenced the ecosystem and the socio-economic situation. The results imply that a future increase in land-use intensity and extreme precipitation events during climatic change might have severe consequences regarding soil erosion, flood risk, and ecological aspects. [Copyright &y& Elsevier]

Coastal morphodynamics and environmental changes have been obviously altered by global warming, sea-level fluctuations, and human activities. Palynological analysis is one of the most important tools for providing information on vegetation, climate, and environmental change, which can be relatively sensitive indicators of human activity during the Holocene. However, Holocene coastal morphodynamics and palynological evidence from the Pearl River Delta and coastal areas has not been sufficiently studied. In this paper, we carry out analyses using detailed grain-size and palynological records of pollen, spores, freshwater algae, and marine dinoflagellate cysts from Borehole QZK13 in the Pearl River Estuary (PRE), southern China. The results show information relating coastal morphodynamics, vegetation evolution, climate changes, and anthropogenic activities during the Holocene based on radiocarbon chronology. In general, the PRE experienced marine transgressive processes; sea-level and the coastline tended to migrate landward between 10,700 and 4250 cal yr BP. Meanwhile, abundant arboreal pollen (mainly Castanopsis , Quercus -evergreen, Oleaceae, and Castanea) and small amounts of non-arboreal pollen (mainly Poaceae, Cyperaceae, and Artemisia) were observed in Borehole QZK13, which suggests that subtropical evergreen broadleaved forests were distributed throughout the PRE and adjacent areas, and relatively warm and moist climatic conditions were present during the early-middle Holocene. After that, there were relatively cool and wet climatic conditions, and marine regressive processes occurred in the PRE during the Late Holocene (ca. 4250–960 cal yr BP) indicated by an abrupt increase in aquatic herbs and Dicranopteris. Moreover, we hypothesize that the Neolithic "cultural fault" in the PRE is likely related to frequent storm surges induced by extreme typhoon events that occurred ca. 3000–2700 yr BP. • Grain size, pollen, spores, freshwater algae and dinoflagellate cysts from the Pearl River Estuary were investigated. • Three major phases shown by palynological results were corresponding to the changes in vegetation and climate. • We hypothesized that the Neolithic "cultural fault" is probably related to the storm surges induced by extreme typhoon events. • Natural vegetation cover has suffered large-scale destruction by ancient humans during the Late Holocene. [ABSTRACT FROM AUTHOR]

Abstract: This paper attempts to quantify contemporary and palaeo-discharges and changes in the hydrologic regime through the mid–late Holocene in the alluvial reach of the arid Mahi River basin in western India. The occurrence of terraces and pointbars high above active river levels and change in the width/depth ratio can be regarded as geomorphic responses to changes in discharge. Discharge estimates are made based on the channel dimensions and established empirical relations for the three types of channels: mid–late Holocene, historic (the channel that deposited extensive pointbars above the present-day average flow level) and the present ones. The bankfull discharge of the mid–late Holocene channel was ∼55000 m3 s−1 and that of the historic channel was ∼9500 m3 s−1, some ∼25 times and ∼5 times greater than that of the present river (2000 m3 s−1), respectively. Since the mid–late Holocene, the channel form has changed from wide, large-amplitude meanders to smaller meanders, and decreases in the width/depth ratio, unit stream power and the bed shear stresses have occurred. It can be inferred that there has been a trend of decreasing precipitation since the mid–late Holocene. [Copyright &y& Elsevier]

Abstract: This paper describes the activity of a small meandering stream and the development of its floodplain during the last 4600 years (calendar years BP) in the northern boreal zone of Québec. Three trenches were excavated across the floodplain''s full width and permitted the interpretation of morphosedimentary units in relation to modern analogs. Chronological controls within trenches was provided by the dendrochronological and radiocarbon dating of buried tree trunks. From 4600 to 2900 cal. BP and from 1000 to 120 cal. BP, the channel migrated and constructed its floodplain at very slow rates, mostly because of low flow velocities, vegetated streambanks and the cohesive texture of marine sediments reworked by the channel. Vertical accretion rates were extremely variable on the floodplain, with high rates proximal to the modern channel and low rates over distal (also older) portions of the floodplain. Following a major channel shift (meander cut-off or avulsion) around 2900 cal. BP, channel migration appears to have been constrained to a narrow zone adjacent to the modern channel. Within this constrained zone, the migrating channel has reworked its own sediments leading to a marked unconformity between 2900–1000 cal. BP. It is thought that underlying marine sediments protrusions, and perhaps the forested banks, protected older alluvial sediments from being eroded during the last three millenniums. Our study shows that small boreal floodplains may contain, in a very small area, abundant and diversified archives of their evolution. [Copyright &y& Elsevier]

This paper presents the preliminary results from a study of Holocene-emerged shorelines, marine notches, and their tectonic implications along the Jalisco coast. The Pacific coast of Jalisco, SW Mexico, is an active tectonic margin. This coast has been the site of two of the largest earthquakes to occur in Mexico this century: the 1932 (Mw 8.2) Jalisco earthquake and the 1995 (Mw 8.0) Colima earthquake. Measurement and preliminary radiocarbon dating of emergent paleoshorelines along the Jalisco coast provide the first constraints upon the timing for tectonic uplift. Along this coastline, uplifted Holocene marine notches and wave-cut platforms occur at elevations ranging from ca. 1 to 4.5 m amsl. In situ intertidal organisms dated with radiocarbon, the first ever reported for the Jalisco area, provide preliminary results that record tectonic uplift during at least the past 1300 years BP at an average rate of about 3 mm/year. We propose a model in which coseismic subsidence produced by offshore earthquakes is rapidly recovered during the postseismic and interseismic periods. The long-term period is characterized by slow tectonic uplift of the Jalisco coast. We found no evidence of coastal interseismic and long-term subsidence along the Jalisco coast. [Copyright &y& Elsevier]

Flood-plain aggradation within the Loup River Basin of central Nebraska was episodic and alternated with incision throughout much of the Holocene. A widespread episode of flood-plain stability, however, occurred about 5700–5100 cal. year BP. The purpose of this paper is to describe the properties of this buried flood-plain at six sites in the basin, to consider why the properties of the buried flood-plain vary from site to site, and to evaluate possible reasons why the Loup River flood-plains stabilized 5500 years ago. Episodic valley-bottom aggradation was common during flood-plain formation at five of the six sites. The radiocarbon ages, particle-size data, and organic-carbon data for the buried flood-plain reveal that valley-bottom aggradation generally slowed between about 5700 and 5100 cal. year BP. Erratic down-profile changes in percentages of sand, clay, and organic matter indicate flood-plain sedimentation and soil formation were often episodic. Sand and clay rarely show a steady fining-upward trend. Organic matter fluctuates with depth; at some sites multiple, incipient A horizons were buried during waning valley-bottom aggradation. At two localities, the buried flood-plain is evident as a clay-rich stratum that must have been deposited in a paleochannel. Flood-plain stabilization between 5700 and 5100 cal. year BP probably occurred in response to the effects of external climate forcing on vegetation and hydrologic changes. Flood-plains of other rivers in the central Great Plains also stabilized at this time, further supporting a climatic explanation for slowing of valley aggradation and formation of a flood-plain at this time. Recognition of buried flood-plains is important to both soil mapping in valleys and to the discovery of cultural resources in valleys. [Copyright &y& Elsevier]

Polar and alpine periglacial areas are traditionally regarded as necessarily submitted to very efficient frost-driven processes that control the Holocene and ongoing geomorphic activity. During the last decade, the validity of this academic view has been increasingly questioned among the international scientific community. The search for the real past and present processes responsible for landform evolution in cold nonglaciated areas is based mainly on more and more refined monitoring protocols relying upon sophisticated equipment. To assess the representativeness and significance of monitoring data collected in restricted sites, it appears necessary, however, to widen the perspective by adopting a twofold multiscale approach as proposed in the present paper: (1) in space, by integrating various scales from the general slope system to the bioclimatic nanoenvironment; and (2) in time, by taking into account the landscape history, from Tertiary inherited features to recent process changes induced by the contemporary warming. Reintegrating the historical approach should help both to place the ongoing processes within a succession and/or combination of interoperating processes, and to avoid misinterpretations of features considered wrongly as emblematic of frost action. Overall, both the historical and monitoring approaches tend to reduce the geomorphic efficiency of frost-derived processes. Instead, the role of noncold-related processes, such as chemical, thermal, biogenic and rainfall-induced ones, is being emphasized. Of special interest would be an interdisciplinary discussion between geomorphologists and various disciplines of biological sciences including biochemistry and ecology studying processes of primary successions. [Copyright &y& Elsevier]

A Holocene loess profile to the west of Xi''an China was studied multi-disciplinarily to investigate the relationships between soil erosion and monsoonal climatic change. The proxy data obtained from this aeolian loess and palaeosol sequence indicate large-scale variations of climate in the southern Loess Plateau since the last glaciation. A rainwash bed, indicative of a wetter climate, excessive runoff and erosion on the loess tablelands, was identified relating to the early Holocene before the onset of the “climatic optimum”. This is synchronous with the early Holocene physiographic erosional stage identified in the valleys in North China. It means that severe erosion took place when the region was undergoing climatic amelioration during the early Holocene. The evidence presented in this paper shows that the erosion occurred as a regional response to a monsoonal climatic shift in the southern Loess Plateau. During the last glaciation, prior to the erosion phase, the land surface on the tablelands had been largely stable except for the rapid accumulation of aeolian dust and the resultant increase in its elevation. Relatively slow dust accumulation and intensive bio-pedogenesis responding to the Holocene “climatic optimum” followed the erosion phase. The loess tablelands were most vulnerable to erosion during the large-scale monsoonal climatic shift from dry-cold glacial to humid-warm post-glacial conditions in the southern Loess Plateau. [Copyright &y& Elsevier]

Palaeomeanders are characteristic features of meandering river floodplains. Some were abandoned several millennia ago and can be used as evidence for past fluvial patterns. Despite many observations of changes undergone by meandering rivers, little is known about long-term morphological adjustment of meanders. This paper reports on investigations conducted in two reaches located in the middle valley of the Cher River (northwestern Europe, France) to examine the readjustments of lowland meanders during the second half of the Holocene. The aim of our study was to provide new insights into the complex dynamics that control low-energy meandering rivers. LiDAR DEM spatial analyses coupled with geophysical surveys and observations of sediments enabled the identification and dating of thirteen palaeomeanders embedded in coarse sediments (sand and gravel) while the whole floodplain is covered by silty overbank deposits. Sedimentological, geochemical and pollen analyses combined with radiocarbon and OSL dating allowed us to reconstruct the chronology of the cutoff and the filling of palaeochannels. No palaeochannels older than ca 6000 yr cal. BP, and no palaeochannels younger than the eleventh–thirteenth centuries cal. AD were identified. This allowed us to distinguish two periods of meandering processes. (1) Our observations demonstrate the multi-millennia persistence of an active meandering pattern in a context of land use changes (ca 6000 yr cal. BP-eleventh–thirteenth centuries cal. AD). The preserved mobility of the river can be mainly interpreted as the result of the low cohesiveness of the bank material. Too few fine sediments were delivered during the proto-historical and historical periods to help stabilize the river course. (2) Following the eleventh–thirteenth centuries cal. AD, the fluvial system underwent a laterally stable phase. The many medieval and modern hydraulic engineering works reduced the specific stream power and prevented lateral erosion. The drastic decrease in the river's capacity to generate new meanders resulted in the disappearance of floodplain lakes and loss of habitat diversity. [ABSTRACT FROM AUTHOR]