the messinian salinity crisis in the dacic basin sw romania and early zanclean mediterranean eastern paratethys high sea level connection new field observations and fossil analyses complete and clarify the strong impact of the mediterranean sea level changes linked to the peak of the messinian salinity crisis on the dacic basin in southwestern romania in addition to the gilbert type fan delta already evidenced along the danube river in the area of turnu severin a new gilbert type fan delta is described northward early zanclean bottomset beds are evidenced and dated based on nannofossils at the junction of the two coalescing gilbert type fan deltas a clear sedimentological morphological and chronologic differentiation is established in the area between the carpathians late miocene piedmont alluvial fans and the early zanclean gilbert type fan deltas the early zanclean age of the hinova clays where the bottomset beds of the gilbert type fan deltas are mostly developed is confirmed by the occurrence of nannofossil markers of subzone nn12b and a bosphorian mollusk macrofauna early zanclean inflow of mediterranean marine waters into the dacic basin is also supported by the record of planktonic foraminifers in the dacic basin the messinian salinity crisis resulted in the cutting of the iron gates by a carpathians river fluvial erosion also affected the residual pannonian basin and probably catched the paleo tisza river which contributed to the erosion of the iron gates and to the fluvial drainage of the partly desiccated dacic basin arguments are reinforced in favor of a marine gateway between the mediterranean and dacic basin through the balkans before and after the messinian salinity crisis

neogene palaeoenvironmental evolution in the atlantic side of the rifian corridor morocco abstract outcrops of upper miocene to upper pliocene deposits in the atlantic side of the rifian corridor northwest morocco provide data that allow an assessment of the palaeoenvironmental evolution of the main seaway that connected the mediterranean to the atlantic ocean until its final closure at the end of the miocene a reconstruction of the sedimentary regimes and palaeobathymetries in the gharb and saiss basins has been carried out from the physical and microfaunal benthic foraminifera characteristics of sediments and three sedimentary sequences are distinguished from the oldest rocks deposited at the opening of the corridor more than 8 ma to the upper pliocene sediments younger than 4 ma that ended the marine sedimentation the maximum palaeodepth recognised about 500 m occurs in marly sediments of the coastal area bou regreg composite section between 8 and 5 9 ma this is followed by a tectonically controlled shallowing phase leading to the establishment of neritic conditions and corresponding to a relative sea level lowering of about 300 m that we suggest relates to closure of the passageway and consequent onset of the mediterranean evaporite deposition the persistence in the saiss basin of middle neritic palaeodepths since the upper tortonian about 7 8 ma suggests for this internal basin a sill physiography evidence from the present and previously documented palaeobathymetric reconstructions indicates that the tectonic activity in the atlantic corridor started from the eastern side and moved to the west

the declining but non rejuvenating base level the lisan lake the dead sea area israel laboratory experiments investigating the effects of a lowering base level do not simulate natural eustatic lowering along concave river profiles the field data on this issue are also quite limited in evaluating the control exercised by lowering base level on a drainage network distinction must be made between its influence and those of other hydromorphological processes operating within the basin field data on morphological relations based on photogrammetric mapping and longitudinal profiling have been gathered in the dead sea area israel where a rapid fall in base level has occurred during the holocene the study area is an entrenched fan delta with a sequence of 14 unpaired fan terraces which die out at intersection points within an alluvial fan system the results suggest that the intersection points did not function as base levels the receding base level played only a passive role allowing entrenchment without transmitting a head cutting feedback basinwards the arid environment caused a delay in transmission of information through the system the results support the model of short episodic and discontinuous erosional events inherent in the evolution of drainage basins it is suggested that base level effects in temperate and humid regions are not transferrable to arid zones

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

calcrete profile development in quaternary alluvial sequences southeast spain implications for using calcretes as a basis for landform chronologies a detailed study of the morphology and micro morphology of quaternary alluvial calcrete profiles from the sorbas basin shows that calcretes may be morphologically simple or complex the simple profiles reflect pedogenesis occurring after alluvial terrace formation and consist of a single pedogenic horizon near the land surface the complex profiles reflect the occurrence of multiple calcrete events during terrace sediment aggradation and further periods of pedogenesis after terrace formation these complex calcrete profiles are consequently described as composite profiles the exact morphology of the composite profiles depends upon 1 the number of calcrete forming events occurring during terrace sediment aggradation 2 the amount of sediment accretion that occurs between each period of calcrete formation and 3 the degree of pedogenesis after terrace formation simple calcrete profiles are most useful in establishing landform chronologies because they represent a single phase of pedogenesis after terrace formation composite profiles are more problematic pedogenic calcretes that form within them may inherit carbonate from calcrete horizons occurring lower down in the terrace sediments in addition erosion may lead to the exhumation of older calcretes within the terrace sediment calcrete inheritance may make pedogenic horizons appear more mature than they actually are and produce horizons containing carbonate embracing a range of ages calcrete exhumation exposes calcrete horizons whose morphology and radiometric ages are wholly unrelated to terrace surface age composite profiles are therefore only suitable for chronological studies if the pedogenic horizon capping the terrace sequence can be clearly distinguished from earlier calcrete forming events thus a detailed morphological micro morphological study is required before any chronological study is undertaken this is the only way to establish whether particular calcrete profiles are suitable for dating purposes copyright 2003 john wiley sons ltd

controls on fan development evidence from fan morphometry and sedimentology sierra nevada se spain abstract we have studied the morphology and the morphometric relations between alluvial fans and drainage basins in a bajada system including more than 20 coalescent fans developed since the late pleistocene as a result of the recent uplift of the sierra nevada betic cordillera spain three allocycles of tectonic origin were recognised across which there is a clear evolution from debris flow to sheet flow dominated fans in connection with a decrease in the volume of fines available in the source areas the larger volume of accommodation space created by higher tectonic subsidence in the northern sector favoured vertical accumulation of sediment with the appearance of less elongated fans in the rest of the system where subsidence is less more elongated fans appear with the development of incised channels and irregular distribution of sediment in depositional lobes this involves the appearance of markedly asymmetric transverse profiles as well as lengthy recurrence between the sedimentation events on particular sectors of the fans where headward eroding gullies develop the lithology of the source area where intensely fractured rocks are found is responsible for an important sediment supply and a significant degree of clast sorting from the source area consequently a weak longitudinal trend in particle size can be recognised which influences the predominance of longitudinal constant slope profiles and anomalous relations between both fan area and fan slope and their drainage areas recent intense tectonic activity has caused the appearance of abnormally low slopes in upper sectors of some catchments where mass flows are trapped and the fans present a subsequently higher proportion of sheet flows recent piracy phenomena can be recognised in some of the drainage basins which indicate rejuvenation of the source area in which case the fan presents a rapid increase in the proportion of mass flows with the development of a segmented longitudinal profile due to the recent nature of the processes the morphometric relations in the fan fed by the basin affected by capture do not coincide with the other fans in the area

fluvio lacustrine sedimentary processes and landforms on the distal paraguay fluvial megafan brazil abstract tropical fluvio lacustrine depositional processes along the toe of the paraguay fluvial megafan were investigated with a focus on lake uberaba lu the largest lake in the pantanal wetlands a limnogeological analysis of lu was conducted using remote sensing imagery lake water chemistry sedimentological and radiochemical data from lake floor samples and short cores echo sounding revealed that lu is deepest z max 3 5 m near its southern shoreline and outlet the lake is hydrologically open throughout the year and is characterized by a dilute ca 2 na hco 3 chemistry key environmental controls on sedimentation in lu include inflowing transverse and axial rivers and water level changes which influence the composition mixing accumulation and the organization of facies structureless brown sandy silts with relatively low organic carbon toc mean 1 7 wt and low to moderate biogenic silica bisi mean 1 9 wt comprise most offshore lake floor sediments whereas northern lake margin sediments consist of peaty silts and sandy silts whose origins are linked to inflowing paraguay megafan distributary channels sediment core stratigraphy revealed that extant lacustrine deposits are underlain by oxidized clayey silts and sands suggesting recent subaerial exposure of the basin floor sedimentary datasets conclusively suggest that lu is a shallow overfilled lake basin that is strongly influenced as a depositional system by its persistently open hydrology shoreline channel density and absence of margin coincident topography this study provides new insights on lacustrine landform development in distal megafan settings which is important for improving our understanding of fluvial landscapes

foraminiferes benthiques et bathymetrie le cenozoique du golfe de gascogne abstract benthonic foraminifera are studied in the limited area of the bay of biscay and the present aquitanian coasts recent populations have been dredged between 0 and 4450 m their associations show a bathymetric zonation faunas from an estuary gironde in shore and off shore shelf upper middle and lower continental slope abyssal fauna the distribution of agglutinated foraminifera and size architectural variations of shells are also useful for bathymetrical zonation cenozoic foraminifera are studied in two continental and four off shore drillings in the bay of biscay and aquitaine basin results of recent faunal studies are used to select some species among the whole tertiary population main bathymetric associations are found that can illustrate the history of the aquitanian area from eocene to recent two different areas can be described a southern one with the gouf de cap breton and its anyon facies a northern one with a continental margin which progrades to the west and is disturbed by the pyrenean tectonic movements it is only possible to make such a study in a restricted area where water masses have almost constant bathymetric limits

the role of alluvial fans in the mountain fluvial systems of southeast spain implications of climatic change the mountain fluvial systems of southeast spain involve sediment supply from steep mountain slopes into headwater channels alluvial fans often occur where these headwater channels emerge from the mountain areas and may influence the connectivity of the sediment transport system from the mountain source areas to the main lowland drainages critical in this role is whether the alluvial fans are aggrading or dissecting and whether there is a break or continuity in the channel through the fan environment previous work has identified some of the factors influencing the behaviour of the alluvial fans in southeast spain this paper deals with the mountain front alluvial fans in the semi arid areas of murcia and almeria provinces it attempts by mapping the location of alluvial fans then their classification into aggrading or dissecting fans to identify the extent to which the mountain fluvial systems are buffered by aggrading alluvial fans or exhibit channel continuity through the mountain front environment it further considers the implications of climatically induced changes between aggradational and dissectional behaviour on alluvial fans

integration of seismic and sedimentological methods for analysis of quaternary alluvial depositional systems due to the high potential of unconsolidated sedimentary bodies to form aquifers and reservoirs an identification of their exact geometry and location is of great importance current conceptual models of these bodies are often developed using scattered data from hydrogeological wells more reliable results can be achieved by application of methods that can provide continuous subsurface record of the actual geological situation in the investigated area in this article a combination of two different approaches is used on a case study of alluvial quaternary sediments from the east slovakian basin including the discussion how these methods contribute to the final geological interpretation first a sedimentological analysis was performed with the use of data acquired from auger drilled hydrogeological wells which enabled identification of depositional processes depositional systems and the possible source areas due to the shallow depth of the studied area a second approach based on the geophysical measurement using seismic refraction and tomography was applied this method provided information mainly about the geometry of these systems the position of the sediments within them and highlighted where the main changes in the sediment texture and composition occurred integration of both methods allows us to obtain a more precise image of the subsurface which contributes to a better understanding and prediction of the occurring sediments in the studied area

geomorphologic relationships and ages of soils on alluvial fans in the rio general valley costa rica abstract soil geomorphic relationships on alluvial fans in the rio general valley costa rica show that the sequence of alluvial fan surfaces and soil development on them is related chiefly to uplift of the bordering mountain ranges and not significantly to climatic change the oldest and most strongly developed soils are found only on the highest surfaces successively younger and less developed soils have lower positions oxisols characterize the oldest surfaces alfisols the intermediate ones and entisols the youngest surfaces minimum ages of these surfaces are estimated from the extrapolation of sedimentation rates solum development rates and the rate of channel incision based on two radiocarbon dates to range from about 45 000 to 65 000 years for the oldest to approximately 100 years for the most recent surface pedons representative of the soils on the principal alluvial surfaces are described in terms of the physical chemical and mineralogic characteristic we propose that the soils studied are a chrono catena that represents soils development through time for this region and can be used to establish a minimum time scale by which to guage stage and rate of soil development in a humid tropical environment

alluvial fans on volcanic islands a morphometric perspective sao vicente cape verde abstract the distribution morphology and development of volcanic island alluvial fans are investigated using sao vicente from the cape verde volcanic chain east central atlantic ocean this is a tectonically and volcanically inactive dryland setting comprising an eroded plio pleistocene composite volcano overlying a submarine shield volcano we mapped 228 alluvial fans quantifying fan f and catchment c morphological properties area a gradient g relief r length l fans and catchments of varying size and gradient are distributed around the island coastal margins 6 and along interior valley sides 94 regression results i e ve ve slopes of best fit lines conformed to broader fan research but with weak correlations and coefficient exponent values outside or at the lower end of values reported from non volcanic settings analysis of fan area and gradient vs catchment area regression residuals revealed fans were dominated by small steep gradient 28 and large low gradient forms 39 fan building space is a fundamental control specifically linked to volcano structure but with interplay between rock strength base level and climate fans around the volcanic edifice flanks are uncommon due to steep flank slopes where flank margin fans occur they are typically small and steep forms due to marine erosion fans along flank incised valleys are common large low gradient fans are associated with a major volcanic rift aligned valley structure with extensive erosion into altered and weathered edifice core lithologies small steep gradient fans are associated with edifice flank valleys steeper and narrower valley forms reflect incision into stronger lithologies of the composite volcano flanks restricting fan building space fans located within the volcano central depression are amongst the largest and lowest gradient types building into the eroded and unconfined edifice core space coalescence apex toe incision toe erosion and catchment stream channel backfilling displayed by most fans suggest landscape erosion dominates during more arid periods e g interglacials with the dryland setting generating limited sediment and insufficient flood runoff for transport and fan deposition fan building likely occurs during wetter periods linked to quaternary climate variability quaternary eustatic variations are relevant for the volcano edifice margins where sea level changes control fan building space and erosion

climatic versus tectonic controls of fan sequences lessons from the dead sea israel tectonic activity is commonly held responsible for abrupt coarsening of alluvial fan sequences and the role of climate is often relegated the pleistocene fans of the dead sea rift indicate clearly the problems of differentiating the sedimentary signatures of climatic and tectonic adjustments in a closed lake basin exposures are excellent the rivers are currently incising in response to the low lake levels of the holocene producing cliffs 50m high these reveal an interdigitation of lake deposits dominantly fine grained carbonates and the coarse river gravels which characterize the fan deposits the bounds of each facies are sharp river sediments are superimposed on lake sediments with little evidence of either reworking or loading in turn aragonite crusts are draped over alluvial gravels indicating the sudden return of still water conditions neither can be explained by gradual adjustment of the hinterland river system after tectonic shock instead it is clear that the coarse alluvium was deposited by discrete high magnitude floods that occurred only sporadically because of the infrequent nature of rainfall in this arid environment in interpreting basin development in ancient settings it is always tempting to assume that coarse deposits are indicative of tectonism however the dead sea fans demonstrate that climate is just as likely to be responsible for the conglomerates in a sedimentary sequence

the impact of quaternary sea level and climatic change on coastal alluvial fans in the cabo de gata ranges southeast spain conventionally a fall in base level is seen as stimulating incision into the distal zones of alluvial fans in the cabo de gata ranges of southeast spain evidence exists to the contrary two sets of quaternary coastal alluvial fans demonstrate the interaction between climatically driven variations in the supply of sediment and eustatically driven changes in base level the fans are supplied from miocene volcanic terrain within which no evidence can be found for major tectonic deformation during the period of fan development the evolution of the east coast fans has been affected by variations in sediment supply and changes in sea level the west coast fans were buffered from the effects of changes in sea level by coastal barriers three phases of past sedimentation can be identified on the fans these can be differentiated on the basis of field observations of soil profiles particularly colour of the b horizons and accumulation of caco3 and laboratory analyses of sequential iron oxide extractions and magnetic mineral properties the two earlier major sedimentation phases were coincident with global glacials ca 135 ka and ca 85 10 ka based on the stratigraphy and uranium thorium dating of the coastal sediments high sea levels during the intervening interglacial and during the holocene caused erosion of the distal zones of the east coast fans which led to channel incision into the fan surfaces on the west coast fans no such incision occurred simply proximal incision by small fanhead trenches the youngest relatively minor phase of fan sedimentation has occurred during the holocene these contrasting contexts have produced differing styles of fans with telescopic fan morphology on the east coast and stacked morphology on the west coast fans the differences are reflected in the fan profiles with steeper gradients dominating the east coast fans and extensive lower gradient distal surfaces on the west coast fans fan morphometry based on analysis of the residuals from drainage area to fan area and gradient regressions also differentiates between the fan contexts the fan building phases appear to be controlled proximally by climatically driven pulses of sediment supplied to the fans these occurred during global glacials coincident with low sea levels and caused fan progradation onto the exposed foreshore the intervening global interglacials were times of little fan sedimentation and on the east coast where high sea levels were able to erode the fan toes deep through fan dissection ensued

a calcrete based u th chronology for landform evolution in the sorbas basin southeast spain nodular and massive calcretes from alluvial terraces in the sorbas area of southeast spain have been dated by the u th isochron method to between 8 350 ka alternative approaches have been used to generate the multiple samples for the isochron method for several of the calcretes dates agreed closely when obtained by total dissolution of a number of nodules or by the sequential dissolution in different acids of a single nodule however fractional dissolution of a single nodule in the same acid revealed two stages of precipitation of different age it is considered that the calcretes may not be strictly pedogenic in origin and that groundwater processes linked to the alluvial environment may have been involved also nevertheless their dates provide minimum ages for a chronostratigraphic framework for terrace evolution

contrasts between debris flows hyperconcentrated flows and stream flows at a channel of mount semeru east java indonesia abstract in order to differentiate between different types of sediment laden flows in volcanic channels we carried out observation of debris flows hyperconcentrated flows and stream flows in the curah lengkong river on the southeast slope of mount semeru in east java indonesia the aims of this study are 1 to provide quantitative data for these flows in motion 2 to compare the data for different types of flow that occur in the same river 3 to assess the influence of rainfall on debris flows hyperconcentrated flows and streamflow generation the curah lengkong river transports large volumes of sediment in the range of 1 10 5 to 5 10 5 m 3 per debris flow and 10 3 to 10 5 m 3 per hyperconcentrated flow and stream flow large sediment discharges result from the following factors continuous and voluminous sediment supply of fine juvenile material by daily explosions of the semeru volcano pyroclastic source material emplaced on steep slopes strong erosion of weathered river banks and strong rainfall intensities the occurrence of the flows focuses in the period from november through april and the daily timing of it is the mid to late afternoon nearly all debris flows are triggered by stationary rainfall confined to the upper slopes of mount semeru whereas hyperconcentrated flows and stream flows are mainly generated by migratory or regional rains driven upwards on the eastern slope this slope receives its maximum of annual rainfall 3800 mm at 800 m asl the peak surface velocity of debris flows is always greater than the peak frontal velocity the peak discharge of debris flows occurs several minutes after the passage of the flow front volumetric concentrations of sediment are high 48 to 69 between the debris flow front and the point of peak discharge after the peak discharge it usually decreases gradually contrary to the case of debris flows high concentration of sediment appears in various portion of hyperconcentrated flows and stream flows near the front in the mid point or at the back of flows although the concentration of sediments in them is much less than in of debris flows relationships between sediment discharge total volume and peak discharge show a very strong positive correlation for debris flows and hyperconcentrated flows therefore sediment discharge can be roughly estimated from direct visual observation

quantifying time scales of pedogenic calcrete formation using u series disequilibria abstract time scales of pedogenic calcrete development are quantified by subsampling carbonate from within a mature stage v pedogenic calcrete profile from southeast spain and dating the material by u series disequilibria the location of the earliest and latest cements can be estimated by comparing previous studies of calcrete morphological development with micromorphological analysis of the study profile carbonate was sampled and dated from three locations within the profile 1 below the lower surface of clasts within the hardpan representing the earliest cement present 207 11 ka 2 from the centre of cement filled pores within the hardpan reflecting the final plugging of the calcrete hardpan 155 9 ka and 3 from the laminar calcrete overlying the hardpan representing the latest cement 112 15 ka these results show that the hardpan took between 73 and 31 ka to form whilst the mature stage v profile took between 121 and 69 ka to form this is the first time that rates of mature calcrete development have been established by direct radiometric dating of the authigenic carbonate the technique is appropriate for dating mature calcretes in dryland regions worldwide and offers the opportunity of increasing our understanding of the spatial and temporal variability in rates of pedogenic calcrete development

physical characterization of explosive volcanic eruptions based on tephra deposits propagation of uncertainties and sensitivity analysis abstract regardless of the recent advances in geophysical monitoring and real time quantitative observations of explosive volcanic eruptions the characterization of tephra deposits remains one of the largest sources of information on eruption source parameters esps i e plume height erupted volume mass mass eruption rate mer eruption duration total grain size distribution tgsd esps are crucial for the characterization of volcanic systems and for the compilation of comprehensive hazard scenarios but are naturally associated with various degrees of uncertainties that are traditionally not well quantified recent studies have highlighted the uncertainties associated with the estimation of esps mostly related to i the intrinsic variability of the natural system ii the observational error and iii the strategies used to determine physical parameters here we review recent studies focused on the characterization of these uncertainties and we present a sensitivity analysis for the determination of esps and a systematic investigation to quantify the propagation of uncertainty applied to two case studies in particular we highlight the dependence of esps on specific observations used as input parameters i e diameter of the largest clasts thickness measurements area of isopach contours deposit density downwind and crosswind range of isopleth maps and empirical constants and wind speed for the determination of mer the highest uncertainty is associated to the estimation of mer and eruption duration and is related to the determination of crosswind range of isopleth maps and the empirical constants used in the empirical parameterization relating mer and plume height given the exponential nature of the relation between mer and plume height the propagation of uncertainty is not symmetrical and both an underestimation of the empirical constant and an overestimation of plume height have the highest impact on the final outcome a 20 uncertainty on thickness measurements area of isopach contours integration limit for the power law fit and deposit density result in esp uncertainties 20 for plume height and erupted volume mass finally a third case study has also been used to explore the sensitivity of the voronoi tessellation strategy for the determination of tgsd and the inversion on both mass area and grain size data for the determination of erupted mass and plume height results confirm the validity of the methods but also the strong dependence on the distribution and number of observations

reconciling the roles of tectonism and climate in quaternary alluvial fan evolution tectonism and climate are the primary variables considered in conceptual models of alluvial fan evolution and basin fill architecture yet their roles and relative importance are far from resolved the madison range and madison river valley southwestern montana were affected during late quaternary time by varying degrees of tectonic activity as well as by climate change through multiple glaciations we are thus able to evaluate the impact of tectonism and climate on fan evolution two primary fan deposits were correlated along the range front they were deposited as proglacial outwash fans during glacial periods of increased sediment and water discharge during the present interglacial period these deposits were entrenched and secondary fans formed on lower fan areas temporal and stratigraphic relations indicate that climate was largely responsible for driving both fan aggradation and entrenchment in contrast stratigraphic relations between fan deposits and surface faults do not support a direct relation either spatial or temporal between local faulting and fan deposition because tectonism produces and maintains the relief necessary for fans to form its primary role is long term controlling the duration over which fan deposition may occur along a mountain front if quaternary alluvial fan evolution is representative of ancient alluvial fan evolution this study has important implications for interpreting primary controls on deposition of the ancient alluvial fan sequences

depositional process and alluvial fan drainage basin morphometric relationships near banff alberta canada two distinct types of alluvial fans occur in the bow river valley alberta canada fluvially dominated and debris flow dominated large gently sloping fans dominated by fluvial processes are associated with large and less rugged drainage basins and small rugged basins have produced small steep fans dominated by debris flow processes quantitative analysis demonstrates that strong fan basin morphometric relationships occur despite a short fan history statistical analysis of fan area basin area relationships indicate that debris flow fan areas do not increase in size as quickly as contributing basins the relationship of fluvial fan area to basin area is not statistically significant however this relationship is probably affected by fan erosion examination of fan slope to basin ruggedness relationships indicates that fan slope increases more rapidly than basin ruggedness for both fan types this is likely related to non linear discharge and sediment size effects on fluvial fans and reworking of larger fan surfaces by fluvial processes on debris flow fans

control of alongshore oriented sand spits on the dynamics of a wave dominated coastal system holocene deposits northern gulf of lions france article the maguelone shore extends along the northern coast of the gulf of lions west of the rhone delta and east of high gradient coastal streams that have provided most of the clastic sediments to the gulf of lions margin since the early miocene this 10 km wide area is constituted by a small coastal watershed 15 km long in low lying carbonate hills a kilometre wide marsh a sandy beach barrier and a shoreface experiencing local low sedimentation rates this onshore offshore transition zone is a key area to understand the relationships between erosion by pass deposition and preservation processes unlike the neighbouring rhone deposits that display numerous thick deltaic sequences related to a continuous sediment flux the maguelone shore exhibits peculiar sedimentary bodies the analysis of about 250 km of new vhr seismic profiles acquired over the study area 9 short cores and outcrops data allowed us to determine the three dimensional high resolution geometry of the coastal system tracts from quaternary to present day this revealed dominant denudation processes in the upstream catchments associated with the formation of incised valleys during quaternary lowstands in addition this study investigates the erosion and deposition mechanisms controlled by littoral hydrodynamics that have been taken place on this shore since the last transgression in particular metre high and hundreds of metre long sandy bodies constructed by alongshore hydrodynamics were identified and their effect on the morphodynamics of the whole littoral system is discussed the maguelone shore can be used as an experimental study for onshore offshore dynamics under the influence of microtidal wave current hydrodynamics and very low river derived sediment flux during a eustatic cycle geometry of system tracts across flood plain to shoreface is usually considered to be controlled by relative sea level changes and is successfully analysed with 2d sequence stratigraphy cross shore models it is observed that in areas like the maguelone shore traditional sequence stratigraphy methods might not be fully relevant and need to integrate alongshore hydrodynamical processes

palaeobathymetry and palaeogeography of the bakony eocene basin in western hungary abstract the authors studied two new outcrops and the cores of 10 new bore holes drilled through the marine eocene of the bakony hills the main purpose was to recognize palaeoenvironments and their changes in the bakony eocene basin earlier research rather neglected this aspect palaeoecologic analyses of different groups of fossils nannoplankton foraminifera molluscs ostracods and to a lesser extent sedimentologic observations and field studies served as tools for the reconstruction of bathymetric conditions and subsidence history by studying the trends in lateral facies changes the reconstruction of paleaogeographic patterns was made possible vertical facies successions are clear due to the excellent core material and the rather simple tectonic structure accurate datings have been possible using the sophisticated stratigraphy worked out for the bakony eocene by a combination of magnetostratigraphic and planktonic zonations published elsewhere in part 1 the authors present the description and palaeoecologic analyses of the studied sections the vertical succession of the main facies units in the sw bakony basin is as follows bottom to top coastal sandy pelites pebbly sands biogenic shelf limestone glauconitic calcareous marl hemipelagic globigerina marl with turbiditic sandstone intercalations the same sequence in the ne bakony basin is as follows alluvial coastal sediments with coal seams nummulitic shelly sands glauconitic sands and marls laminated clay globigerina marl and bathyal clays the authors discuss palaeonvironments and their evolution in part ii the coastal facies in the sw bakony basin is a few million years older than in the ne nevertheless this facies indicates in both areas flat coastal plains and seashores probably covered by mangrove a carbonate shelf developed in the sw bakony basin with very low sedimentation and subsidence rates the shelf period was much shorter in the ne the shelves were influenced by intense currents that were active in the whole basin since mid bartonian times retrogradation of the shelves is demonstrated by the sequence first sediments of shelf break and upper basin slope environment overlie the shallow marine deposits strong glauconitization indicates current activity the glauconitic facies is overlain by a globigerina marl and silts described earlier as shelf sediments the authors set out to prove that the maximum depth of its deposition has been at least 800 m turbidites are intercalating with the globigerina marl in the sw in part iii mainly palaeogeographic conclusions are discussed the authors recognized on the basis of lateral facies changes that shallow marine conditions prevailed to the east and south of the bakony basin during the entire bartonian priabonian the position of erosional source areas and the direction of dense turbidity currents suggest the same conditions the correlation with the late eocene early oligocene zala velence andesitic arc is also discussed in some detail and is based on tephra layers found in the globigerina marl the authors recognized a remarkable middle bartonian coincidence of several different events such as increasing andesitic volcanism sudden acceleration of basin subsidence increase of sea depth beginning of turbidity current activity this may indicate a coeval increase in tectonism the transgressions are younging towards the ne the basin generation shows a similar shift a complete palaeogeographic and probably a tectonic inversion took place in the priabonian the southern alpine dinaric character of the eocene fauna and lithofacies changed gradually to an eastern alpine carpathian one during the priabonian from the beginning of the oligocene only the latter influence did exist also during the priabonian a new marine basin was formed in hungary to the ne of the balkony hills

holocene debris cone evolution in glen etive western grampian highlands scotland stratigraphic investigations radiocarbon dating of buried soils and pollen analyses were employed to reconstruct the history of development of a fluvially reworked debris cone in glen etive paraglacial aggradation of debris flow deposits resulted in cone formation between c 10000 yr b p and c 4000 yr b p until supplies of sediment from upslope were effectively exhausted and debris flow activity ceased there ensued a prolonged period of stability and soil development on the cone surface this ended sometime after c 550 yr b p when human interference including burning resulted in destruction of the natural vegetation cover and triggered fluvial incision and the development of an alluvial fan of reworked sediment that buried the lower part of the debris cone the wider implications of these findings are discussed

early syn rift evolution in the west cameros basin upper jurassic nw iberian range spain abstract alluvial systems are sensitive sedimentary systems that can preserve useful information about tectonics drainage area lithology and size and climate however research on this subject over the last three decades has made it evident that the interaction of these three factors and their control over the alluvial architecture and facies are complex the stratigraphic and sedimentological analysis of the earliest syn rift sedimentary record tithonian in the west cameros basin has confirmed that sedimentation during the beginning of extension in this area took place in a series of halfgraben basins in which three different types of fan shaped alluvial systems were deposited two relatively large systems specifically a highly channelized alluvial fan system and a distributive fluvial fan system changing downstream to an axial tributary fluvial system were the exception and small poorly channelized alluvial fan systems were the norm a semiarid climate is inferred during this earliest syn rift sedimentary record from the steady and extensive calcrete development this semiarid climate should play an important role both in how coarser sediment discharges to the rift halfgraben basins occurred and in the dominant transverse organization of the alluvial depositional systems however the climate and source area lithology can be considered steady factors so the main factors considered as the cause of these sedimentary and architectural heterogeneities are the tectonics and drainage area sizes and specifically the different behavior of each extensional structure in terms of the rate of tectonic uplift and subsidence this indicates how fault activity and drainage area sizes during the earliest stages of a rift system can generate high degrees of heterogeneity in the architecture of alluvial basins and how this heterogeneity is recorded by the alluvial systems in the form of differences in their facies association and architecture therefore this work concludes that both tectonics and catchment sizes exerted primary control on the sedimentary characteristics of associated alluvial systems in basins generated from this type of extensional setting and care must be taken when making climatic and tectonic interpretations using the sedimentary record of these alluvial systems because many changes that traditionally have been attributed to climate variability can be explained solely by the differential behavior of each extensional structure and or changes in its associated drainage area

stages and rate of the gravel shattering process by salts in desert reg soils abstract gravel shattering by salts is a common process in gravelly young to mature desert reg soils the shattered gravel is found on the surface and in the b and c horizons down to a maximum depth of 50 cm field studies on the process of salt weathering in deserts are scarce therefore the objectives of this study are to present the stages of development of the gravel shattering process by salts in desert reg soils and to discuss factors influencing the rate of development under natural conditions prevailing in the negev desert the studied reg soils were developed on two alluvial fan chronosequences in the negev desert the fan of nahal ze elim and the fan of nahal shehoret the development of the shattering process can be divided into five stages a e based on chemical physical and micromorphological features of the reg soils stages a d very young yo young reg soils represent the early holocene to the present some 14 000 years salinity values are between 0 27 16 mmho cm and the percentage of the shattered gravel is between 20 and 70 the shattered gravel however still maintains its original shape stage e mature reg soil represents the middle pleistocene to early holocene or 500 000 years salinity values at this stage reach 62 mmho cm although part of the gravel does not keep its original shape and starts to disperse in the profile the percentage of shattered gravel is only 75 80 it was found that the process of salt shattering in reg soils does not depend on concentrations or mineralogy of the salts but on the micro environmental conditions of the soil profile the process requires extreme and rapid variations of temperatures and moisture conditions such as found close to the soil surface to cause salt crystallization in a confined system with time the sealing of the soil surface through the development of desert pavement and a gravel free b horizon results in a change in the soil micro environment this change impedes the process irrespective of the amounts concentrations and types of salt minerals which exist in the profile the fact that in extreme arid regions the gravel shattering process develops primarily close to the reg soil surface suggests that it can be used to identify buried reg soils and to reconstruct climatic and micro environmental conditions of paleosols

fan surface dynamics and biogenic calcrete development interactions during ultimate phases of fan evolution in the semiarid se spain murcia abstract pleistocene alluvial fan surfaces of the campo de cartagena mar menor basin murcia se spain are capped by thick mature calcretes calcrete profiles consist mainly of six different horizons prismatic chalky nodular massive laminar and coated gravels petrographic study of the calcretes has shown the occurrence of features such as alveolar septal structures calcified filaments coated grains spherulites calcified root cells and calcispheres that indicate the biogenic origin of the calcretes mainly induced by plant root related microbial activity the calcretes studied were formed initially in the soil and represented the k horizon development of the calcrete profiles took place in six main stages and was driven by multiple phases of soil formation erosion and reworking the relationships between these processes caused the formation of different calcrete profiles in proximal and distal fan areas in the distal areas which are controlled by limited distal fan aggradation episodic sediment input buried previously developed calcretes and generated new space for calcrete growth by plants growing in the overlying unconsolidated materials this allowed the renewal of calcrete formation and it led to the development of complex composite profiles which are thicker than in proximal areas where surface stabilisation and or dissection enabled calcrete reworking and brecciation these processes of erosion sedimentation reworking and renewed calcrete formation initiated by vegetation were repeated through time they explain the complex macro and microstructures of these calcretes and indicate that calcrete development even reaching mature stages can start before the fan surface is completely abandoned but it requires episodic sedimentation eventually distal fan aggradation and continuous calcrete development throughout the entire fan surface led to the ultimate fan surface induration controlling subsequent landscape evolution so fan surface calcretes cannot be envisaged as simple top surface carbonate accumulations but as complex feedback systems in which pedogenic biogenic and sedimentary processes interact in response to the evolving fan surface dynamics during the terminal phases of fan development in semiarid environments

hyperconcentrated flow and sediment transport at steep slopes in order to simulate a fine material slurry of a debris flow a clay suspension of various concentrations was recirculated in a steep flume the effect of an increasing fluid density and viscosity on the flow behavior and the bed load transport capacity of the flow was examined viscous effects were found to become important below a limiting particle reynolds number of about 10 above this limiting value density effects cause an increase in the bed load transport rates as compared to similar conditions with clear water as transporting fluid the experimental data in this range can be described with conventional newtonian formulas and is analyzed together with other bed load transport data two different calculation schemes are proposed for the steep slope range is n n 10 where the bed load concentration is significant with respect to the total flow depth below the critical particle reynolds number of 10 the bed load transport rates decreased strongly

instability of hyperconcentrated flow the instability of hyperconcentrated flow observed in nature is reproducible in laboratory flumes using suspensions of bentonite similar instabilities are observed in a much simpler hydraulic system consisting of a container feeding a closed conduit the behavior of two different clay suspensions kaoline and bentonite was investigated and the rheological properties were measured in a rotating viscosimeter the result of the analysis is that the instability is associated with some specific rheological properties by a simple mathematical model it has been explained why the bentonite suspension was unstable at small discharges and stable at sufficiently large discharges the kaoline suspensions were always stable the agreement between calculations and observations is encouraging

aggradation and dissection sequences on spanish alluvial fans influence on morphological development abstract similarities in quaternary alluvial fan development are identified throughout southeast spain pre wurm aggradation phases culminate in calcrete crusted upper fan surfaces which are followed by wurm dissection phases producing deep fanhead or through trenches deposits of the aggradation phases reflect source area size relief and geology and in addition to proximal distal facies variations show vertical decreases in debris flow and increases in gravel deposition the dissection phases were complicated by cut and fill sequences forming within trench terraces which show a southward decrease in complexity the sequences are expressed in progressive changes in fan terrace and channel slopes and intersection point location fan morphological development during the quaternary reflects long term progressive change complicated by short term responses to climatic fluctuations and further comolicated by the locally variable effectiveness of trenching thresholds

response of alluvial fan systems to the late pleistocene to holocene climatic transition contrasts between the margins of pluvial lakes lahontan and mojave nevada and california usa abstract dated shorelines of late pleistocene pluvial lakes lahontan great basin desert northwest nevada and mojave mojave desert eastern california provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late pleistocene to early holocene two sets of alluvial fan systems have been mapped the stillwater fans feeding lake lahontan and the zzyzx fans feeding lake mojave their contrasting morphologies suggest different responses of the two fan systems to late pleistocene to early holocene climatic change at the time the stillwater fan systems underwent minimal sedimentation with the catchment hillslopes apparently stable the zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes there was a major phase of hillslope debris flow activity followed by fanhead trenching and distal fan progradation both areas were wetter and colder in the late pleistocene than they are today but during the transition to the holocene the zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the southwest vegetation reconstructions for the late pleistocene to the early holocene suggest that catchment hillslopes in the mojave supported a desert shrub vegetation but those in the stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the pleistocene to holocene climatic transition after the falls in lake levels of lakes lahontan and mojave in the early holocene both areas underwent aridification resulting in reductions in hillslope vegetation cover increased storm runoff led to fanhead trenching and distal progradation of the alluvial fans variations in fan style at that time may relate primarily to base level conditions resulting from different gradients on the exposed lake shores

the role of base level change in the dissection of alluvial fans case studies from southeast spain and nevada abstract tectonics climate and base level are the underlying controls of alluvial fan development on many fans base level is stable but where base level change occurs it may itself be a response to tectonics or climatic change tectonically induced base level change will be temporally independent of climatic change and will show spatial variability depending on the rate of propagation of tectonically induced regional dissection this is illustrated by the tabernas fans southeast spain the timing of climatically induced base level change follows the timing of climatic change itself and will show more consistency of spatial relationships within groups of fans affected alluvial fans which toe out in coastal zones or at lake shorelines may be influenced by climatically controlled base level changes conventionally a fall in base level would be expected to cause dissection of the distal fan zone however the reverse may occur with fan progradation taking place in response to a base level fall and dissection occurring in response to a base level rise two contrasted case studies are considered based in part on previously published work from dry region alluvial fan zones the coastal cabo de gata fans in southeast spain and the stillwater and cold springs fans in nevada usa in these areas base level changes occurred in response to late quaternary eustatic changes of sea level and changes in the levels of pluvial lakes respectively within both areas there are fans not affected by base level change cabo de gata west coast and inland fans cold springs fans and others where base level change has been important in fan evolution cabo de gata east coast fans stillwater fans the differences in geomorphic regime between those fans influenced by base level changes and those not are expressed in morphometric contrasts and different fan profile and plan characteristics within those fans influenced by base level changes the different mechanisms have influenced the location and elevation of the zone of incision the differences can be attributed in part to the temporal interactions of base level change with climatically induced changes in sediment supply and in part to differences in gradients of the foreshore exposed by the falling sea or lake base levels

tectonic controls of the north anatolian fault system nafs on the geomorphic evolution of the alluvial fans and fan catchments in erzincan pull apart basin turkey abstract the erzincan pull apart basin is located in the eastern section of the north anatolian fault system nafs the tectonic evolution of this basin is mostly controlled by strike slip master faults of the nafs this study examines the topography structure relationships in an effort to evaluate the tectonic signatures in the landscape paying special attention to recent tectonic activity in the study the main focus is on the tectonic controls of the nafs on the geomorphic evolution of alluvial fans and fan catchments in the erzincan pull apart basin the observations of the amount of tilting of the alluvial fans and its relation with morphometric asymmetry factor af hypsometric integral hi fractal analysis of drainage networks d properties of the fan catchments provide valuable information about the tectonic evolution of the basin area the results of the analyses showed that the alluvial fan and fan catchment morphology in the pull apart basin are mainly controlled by the ongoing tectonic activity of the nafs the fault system in the basin has controlled the accommodation space by causing differential subsidence of the basin and aggradation processes by causing channel migration channel incision and tilting the alluvial fans

pliocene pleistocene sedimentary and geomorphologic development of the vasilikos river catchment s cyprus in relation to uplift of the troodos ophiolite and climate related changes the pleistocene development of the vasilikos river exemplifies the interaction of focused tectonically induced surface uplift and climate influenced changes the resulting sediments are well exposed in vasilikos quarry and in the main river catchment further east an important erosional surface incises the highest level oldest fluvial conglomerates down into late pliocene early pleistocene open marine mudrocks nicosia formation allowing integration with the circum cyprus sedimentary geomorphic development f1 f4 stages to determine where the quarry deposits lie in relation to the vasilikos river catchment the fluvial deposits were mapped and valley profiles were constructed revealing four main episodes each associated with incision and distinctive fluvial deposition source lithology strongly influenced channel morphology infill and adjacent slope sediment colluvium composition palaeosols particularly red brown terra rossa developed on abandoned fluvial terraces and adjacent hillslopes especially overlying f3 surfaces the combined evidence allows close correlation of the vasilikos river and quarry deposits relatively coarse chalky conglomerate breccia and fine grained colluvium calcareous silt cyprus harvara developed especially on lower hillslopes following incision mainly above f2 and f3 surfaces based on regional comparisons overall sediment aggregation ended during the early pleistocene the f1 f2 surfaces and deposits are inferred to be middle pleistocene the f3 ones later middle pleistocene and the f4 ones near the middle late pleistocene boundary geomorphology and deposition were tectonically forced during strong focused early middle pleistocene surface uplift coarse clastic ruff off and palaeosol development terra rossa and related sediment aggradation are inferred to have increased during warm humid periods late pleistocene geomorphology and deposition were more influenced by climatic change with semi perennial streamflow rapid sediment aggradation and palaeosol terra rossa development during warm humid periods interglacials cooler glacial periods enhanced fluvial incision sediment bypassing and hillslope colluvial processes e g frost shattering downslope creep and mass flow when sediment transport bypassing exceeded sediment supply neotectonic faulting affected the catchment but did not greatly affect geomorphology or sediment supply although climate climate change and eustatic sea level change had an important influence tectonics is interpreted as the fundamental driver of geomorphological development and fluvial sedimentation with implications for other areas regionally to globally

erosion storage and transport of sediment in two subbasins of the rio puerco new mexico arroyos in the american southwest proceed through cut and fill cycles that operate at centennial to millennial time scales the geomorphic community has put much effort into understanding the causes of arroyo cutting in the late quaternary and in the modern record late 1800s while little effort has gone into understanding how arroyos fill and the sources of this fill here we successfully develop a geographic information system gis modeled sediment budget that is based on detailed field measurements of hillslope and channel erosion and deposition field measurements were made in two arroyo basins draining different lithologies and undergoing different land disturbance volcano hill wash 9 30 km 2 arroyo chavez 2 11 km 2 over a 3 yr period both basins have incised channels that formed in response to the late nineteenth century incision of the rio puerco large volumes of sediment were generated during arroyo incision equal to more than 100 yr of the current annual total sediment load bed load suspended load in each basin downstream reaches in both arroyos are presently aggrading and the main source of the sediment is from channel erosion in upstream reaches and first and second order tributaries the sediment budget shows that channel erosion is the largest source of sediment in the current stage of the arroyo cycle 98 and 80 of the sediment exported out of volcano hill wash and arroyo chavez respectively the geomorphic surface most affected by arroyo incision and one of the most important sediment sources is the valley alluvium where channel erosion gullying soil piping and grazing all occur erosion rates calculated for the entire volcano hill wash 0 26 mm yr and arroyo chavez 0 53 mm yr basins are higher than the modeled upland erosion rates in each basin reflecting the large contributions from channel erosion erosion rates in each basin are affected by a combination of land disturbance grazing and lithology erodible sandstones and shales in arroyo chavez compared with basalt for volcano hill wash despite these differences hillslope sediment yields are similar to long term denudation rates as the arroyo fills over time from mouth to headwaters hillslope sediment becomes a more significant sediment source

lateral erosion toe cutting of alluvial fans by axial rivers implications for basin analysis and architecture abstract we document the neglected phenomenon of lateral erosion toe cutting of alluvial fans by non incising axial river channels field examples from the holocene of the big lost river basin idaho and the plio pleistocene of the rio grande rift new mexico help to establish architectural models with more general application to basin analysis the process of toe cutting can lead to complete fan destruction and may be a response to climate change tectonic tilting fault propagation or a combination of these variables it gives rise to near horizontal erosion surfaces cut in fan sediment steep fan margin scarps progressive up fan incision from the scarp by a network of channels soil formation up fan away from the incised channel network a deposit of axial alluvium that overlies the erosion surface and onlaps the scarp once avulsion occurs to take the axial channel away from the bajada margin distinctive healing wedges of fan alluvium prograde across abandoned axial river channel and floodplain deposits gradually onlapping the eroded scarp and its upstream network of incised channels toe cutting has important stratigraphic basin analysis and economic consequences bajada deposits subject to the process exhibit appreciable extra groundwater and petroleum reservoir potential in the intercalations of more porous and permeable axial fluvial sediments

late quaternary alluvial fan terraces langshan inner mongolia china abstract alluvial fan terraces of the langshan range in the northwestern hetao basin of northern china records uplift on range bounding faults and late quaternary climate change alluvial fan profiles are segmented in the central part of the range front which lack strath terraces that developed in the southwest sw and northeast ne parts the stream channels in the central part have higher channel gradients and lower ratios of the valley floor width to valley height v four episodes of alluvial fan terraces were upstream from the range bounding fault which formation ages were estimated as 116 64 35 and 10 ka bp according to optically stimulated luminescence osl dating combined with previous 14 c and osl ages the correlation between time of the terraces formation and climatic fluctuations recorded in a guliya ice core reveals that alluvial fan aggradation was concentrated during the cold stages and that incision occurred during the succeeding cold to warm transitions a majority of alluvial fan terraces developed in accelerated uplift since 64 ka which indicates that tectonic uplift provided the driving force for continuous downcutting after climatic change triggered it geomorphic indices channel gradient and v distribution reconstructs the model of discrepant uplift in the langshan range with the fastest uplift rate in the central part which is controlled by range bounding faults

a combined morphometric sedimentary gis and modelling analysis of flooding and debris flow hazard on a composite alluvial fan caveside tasmania abstract two episodes of intense flooding and sediment movement occurred in the westmorland stream alluvial system near caveside australia in january 2011 and june 2016 the events were investigated in order to better understand the drivers and functioning of this composite alluvial system on a larger scale so as to provide awareness of the potential hazard from future flood and debris flow events a novel combination of methods was employed including field surveys catchment morphometry gis mapping from lidar and aerial imagery and hydraulic modelling using riverflow 2d software both events were initiated by extreme rainfall events

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

quantifying long term catchment changes of alluvial fan systems in mountain areas affected by uplift significant reorganization of drainage networks can occur through river capture this modification can dramatically affect sediment flux and routing into adjacent sedimentary basins it is thus important to obtain information on rates and direction of changes in catchment areas in such environments this can be achieved where the original precapture catchments can be compared with the postcapture scenario this paper examines three modern mountain catchments from southeast spain that were affected by river capture and that fed relict pliocene pleistocene alluvial fan systems morphometric data have been collated for complete quaternary mountain catchment piedmont fan systems these data are used to establish regressions to determine catchment area and basin relief from a combination of fan characteristics area and gradient these relationships are then used to predict the original catchment characteristics for the three pliocene pleistocene relict fans and compared with the modern catchments to quantify the magnitude and direction of changes which have affected the drainage basins since fan abandonment in the early pleistocene the figures suggest that the catchment areas are responding to regional uplift most significantly by drainage net expansion facilitated by river capture rather than lowering of surface relief as a result sediment routing into the sedimentary basins has been radically altered

late pleistocene highstand and recession of a small high altitude pluvial lake jakes valley central great basin usa abstract models of factors controlling late pleistocene pluvial lake level fluctuations in the great basin are evaluated by dating lake levels in jakes valley jakes lake rose to a highstand at 13 870 50 14c yr b p receded to a stillstand at 12 440 50 14c yr b p and receded steadily to desiccation thereafter the jakes lake highstand is roughly coincident with highstands of lakes bonneville lahontan and russell the rise to highstand and recession of jakes lake were most likely controlled by a storm track steered by the polar jet stream the final stillstand of jakes lake helps constrain timing of northward retreat of the polar jet stream during the pleistocene holocene transition

the tabernas alluvial fan and lake system southeast spain applications of mineral magnetic and pedogenic iron oxide analyses towards clarifying the quaternary sediment sequences abstract mineral magnetic and soil iron oxide data are applied to questions of relative age correlation of alluvial fans and lake sediments in the tabernas basin southeast spain within a context of interaction between tectonics and climatic change within the tabernas basin the sediment sequences and morphological evolution of late quaternary alluvial fans suggest climatic change as the primary control the fans toe out at the upper margins of a former lake created in response to tectonic uplift magnetic and iron oxide data from soils particularly dithionite extractable iron fe d and frequency dependent magnetic susceptibility fd accord with the relative age relationships suggested by more conventional field based geomorphic observations magnetic data from the lake sediments suggest the main provenance characteristics of the sediments but also reveal a shift in sediment sources towards the end of the lake period probably during the late pleistocene to sediment supplied from a more active fluvial system from soil erosion within the sierra de los filabres part of the catchment hence although the locations of the fans and the existence of the lake relate primarily to tectonics the fan sequences themselves appear to be primarily climatically controlled and there is evidence of a climatic influence over the source of sediment input into the lake during the late pleistocene

alluvial fan shifts and stream captures driven by extensional tectonics in central italy subsidence over the last 0 78 myr of a basin in central italy bounded by a normal fault caused the deactivation and uplift of an early middle pleistocene alluvial fan at the fault footwall uplift of the fan occurred with a basin bounding fault slip rate of the order of 0 2 mm a 1 subsidence resulted in the reorganization of the river network due to a fall in base level which triggered headward erosion stream piracy effects and drainage inversion the mapped river inversions and catchment piracy were related to the distribution of a quantile regression of 134 alluvial fans v basin areas despite the fact that the two parameters were well fitted by a power law relationship all the fans corresponding to the captured rivers lay above the regression line in the fan area field whereas those corresponding to the capturing rivers were below the regression line in the basin area field we propose a general model of alluvial fan growth in active extensional settings that helps to interpret this scatter of fan v basin area distribution and to identify the most active fault segments such an approach can better constrain fault activity in a time window that bridges long term deformation and the present day deformation inferred from geodesy and or seismology increasing our understanding of the steadiness unsteadiness behaviour of faults

impacts of small scale faults on continental to coastal plain deposition evidence from the realgrunnen subgroup in the goliat field southwest barents sea norway abstract in this study we synthesise sedimentological fault and amplitude versus angle ava analysis and propose that the fruholmen and tubaen formations realgrunnen subgroup are syn kinematic deposits that record a previously undocumented early phase of mesozoic rifting on the troms finnmark fault complex and within the hammerfest basin the realgrunnen subgroup hosts one of two triassic reservoirs currently being produced in the goliat field here the subgroup sits unconformably on top of the storfjorden subgroup carnian snadd formation away from the goliat field which is characterised by a periclinal anticline the realgrunnen subgroup also comprises the lower middle jurassic nordmela and sto formations sedimentological analysis of six exploration wells reveals that the fruholmen formation was deposited in a prodelta to delta plain environment where tide influenced and fluvial dominated distributary channels are represented by clay siltstones and very fine grained sandstones the overlying tubaen formation is characterised by medium to very coarse grained deposits locally conglomeratic and represents a widespread braid plain with localised alluvial fans displacement profiles of faults and along fault thickness variations demonstrate that an immature fault system was active during deposition of the realgrunnen subgroup a series of unconnected fault segments hosted isolated sub basins and erosional catchment areas in their hanging and footwalls respectively an ava attribute map generated from a 10 ms interval of the uppermost part of the subgroup reveals gross sand prone depositional bodies i e individual and amalgamated channels some of which show meandering geometries ox bow lakes and alluvial fans sand bodies frequently show elongate geometries parallel to faults indicative of syn depositional fault related subsidence driving mechanisms responsible for the norian to rhaetian event may relate to contemporaneous rejuvenation of the fennoscandian hinterland development of the novaya zemlya fold and thrust belt and or the early cimmerian tectonic phase in northern europe

delineation of alluvial fans from digital elevation models with a gis algorithm for the geomorphological mapping of the earth and mars alluvial fans are prominent depositional geomorphic features present in nearly all global climates on earth and also found on mars in this study we present a geographic information system gis algorithm designed for the semi automated detection of alluvial fans that are connected to their contributing upstream drainage network from the analysis of digital elevation models dems through a combination of spatial analysis procedures the gis algorithm generates maps of alluvial fans and their upstream source drainage and watersheds tests of the algorithm in areas with well known alluvial fans indicate that this new gis procedure is capable of high accuracy mapping of the fan apexes and correct delineation of fan deposits in both arid and humid climates possible future applications of the gis algorithm presented in this study include the systematic survey of alluvial fans at the local regional and planetary scales important for geologic hazard assessment studies on the evolution of climate analysis of continental sedimentary environments understanding of the interplay between the endogenous dynamics and exogenous processes and the evaluation of natural resources

megafans and outsize fans from catastrophic slope failures in alpine glacial troughs the malser haide and the val venosta cluster italy

slope of alluvial fans in humid regions of japan taiwan and the philippines abstract this study constructed a database for 690 alluvial fans in humid regions of japan taiwan and the philippines and analyzed their slopes and other morphometric parameters such as the area and relief ratio of the source area this type of comprehensive geomorphological research on alluvial fans in humid regions has been limited although numerous studies have dealt with fans in arid and semi arid regions semi conical depositional landforms larger than 2 km2 and steeper than 0 11 0 002 m m were selected as alluvial fans about 60 of the fans formed during the holocene and the rest 40 formed during the pleistocene mean fan slopes for both all the quaternary fans and holocene fans follow a lognormal frequency distribution the distribution also fits slopes of fans belonging to a certain areal range the area and relief ratio of the source area which correlate well with the fan slope also follow a lognormal distribution indicating the dimensions of fan basin systems vary gradually rather than abruptly these findings contrast with a previous notion that depositional landforms rarely have slopes of 0 5 0 009 to 1 5 0 026 and hence only semi conical landforms steeper than 1 5 should be called alluvial fans

recent debris flow processes and resultant form and facies of the dolomite alluvial fan owens valley california abstract a multiphase debris flow triggered by an afternoon thunderstorm was deposited 22 august 1984 on the dolomite alluvial fan of owens valley california two tracts 10 300 cm thick accumulated during this event together covering 68 000 m2 26 of the fan with 50 000 m3 of sediment both tracts consist of numerous paired boulder rich levees 100 300 cm high on the proximal fan and multiple attached lobes 20 100 cm thick on the distal fan each levee lobe pathway was built by an individual surge with flow path switching caused by clogging of the frontal bouldery snout of the ensuing surge the levees consist of clast supported to matrix supported muddy pebbly cobbly boulder gravel displaying a well developed radially aligned a axis clast fabric the lobes mostly consist of matrix supported muddy pebbly cobble gravel the clast supported lobe margins are enriched in cobbles displaying a strongly preferred slope parallel a axis fabric along the sides that changes to a slope perpendicular fabric at the snout the distal ends of most of the clast rich lobes are overlain and offlapped by clast poor debris flow lobes of granular mud 10 30 cm thick the central zones of the levees and most lobes were surficially washed by recessional stage water flows that moved winnowed granules sand and mud off the fan the radial change from levees in the proximal fan to lobes distally is morphologically expressed as two intersecting slope segments the upper one sloping 9 12 and the lower one 3 5 this direct relationship between the constituent forms and slope values also is characteristic of pre 1984 deposits suggesting that the 1984 event is typical of the primary processes constructing the dolomite fan the pronounced radial change from levees to lobes and its manifestation as a slope inflection was caused by the selective loss on the upper fan of most of the boulders from the passing debris flow surges boulders were sorted from the surges because of their greater buoyancy which caused them to be preferentially concentrated in the part of the flow that subsequently was sheared off as levees this selective boulder removal depleted the flow of the clasts that provided lateral support facilitating flow expansion and the onset of lobe development thus the resultant facies assemblage is a function of the specific sediment grain size suite available in the catchment colluvium and the transport characteristics of this mix when transformed into a debris flow by the rapid addition of heavy rainfall during infrequent thunderstorms

comparison of logistic regression and neural network models in assessing geomorphic control on alluvial fan depositional processes calabria southern italy at the outlet of steep catchments depositional processes ranging from stream flow to debris flow usually lead to alluvial fan development apart from geological and tectonic factors controlling basin sediment availability several authors highlighted the control role of basin fan morphometry on fan sedimentary processes in this framework the paper was aimed to identify the feeder basin variables that can best differentiate fan processes in southern italy to evaluate the effect of the statistical method on variable selection we compared logistic regression lr and artificial neural network ann the latter not commonly used in fan studies alluvial fans were mapped at the mouth of steep v shaped valleys dissecting the tyrrhenian coast of northern calabria where crystalline metamorphic and subordinate carbonate rocks crop out fans were classified through field survey into two groups those with f1 and those without f0 any debris flow evidence morphometric variables were derived for each basin fan system percentage of lithological units cropping out in the catchments was also considered non parametric statistics revealed that f0 and f1 significantly differ in fan size area perimeter and length main channel slope lowermost valley width melton s number and geologic index the relationships between morphometric variables were stronger for f0 than f1 the lr and ann highlighted the primary control of basin lithology on fan dynamics followed by basin mean slope although ann outperformed lr in model calibration both the approaches correctly classified most of the validation samples 87 alluvial fans with unknown depositional process were classified as belonging to the same group

testing the potential of k feldspar pir irsl and quartz esr for dating coastal alluvial fan complexes in arid environments abstract coastal alluvial fans caf are important geo archives due to their sensitivity to both tectonic activity and climatic changes thus they can give key insights for geomorphic and sedimentary processes in this study we test the potential of k feldspar post infrared infrared stimulated luminescence pir irsl and quartz electron spin resonance esr methods for dating alluvial fan complexes in arid environments the existing chronological data from marine terraces that interact with caf make the atacama desert in northern chile an excellent setting for this research samples have been collected from alluvial marine and aeolian sediments embedded in the caf complexes allowing evaluation of the different signal properties and bleaching characteristics of the pir irsl and esr signals over late pleistocene time scales pir irsl dose distributions of clast rich alluvial fan samples are characterised by higher scatter and demonstrate heterogeneous bleaching while matrix rich alluvial fan deposits show rather homogeneous poor bleaching in the dose dispersion as indicated by a modern analogue sample in contrast marine and aeolian deposits are homogeneously well bleached supported by a modern littoral sample following the quartz multiple centre mc esr dating approach al and ti centres bleaching of the different centres prior to deposition has been achieved while the ti h centre provides mostly lower doses than the ti li centre in most cases the al centre provides the highest dose values this pattern is consistent with their respective bleaching kinetics and suggests that the ti centre signals most likely provide the closest estimate to the true burial dose for samples with doses 200 gy esr and pir irsl ages are consistent at 2 for the marine aeolian and clast rich debris flow deposits which is in agreement with existing chronological data in this area it appears that the mode of sediment transport on alluvial fans either as matrix or clast rich flows plays an important role in sediment bleaching while clast rich alluvial fan deposits are likely better bleached we cannot exclude insufficient bleaching during matrix rich alluvial fan flows our dating results suggest that both pir irsl and esr dating overestimate the true burial age the combination of pir irsl and mc esr dating can be considered as a promising tool for deciphering alluvial fan formation over late pleistocene time scales

oligocene through palaeogene neogene boundary foraminifera of the northern mesohellenic basin macedonia greece biostratigraphy and palaeoecologic implications abstract foraminifera of the oligocene and early miocene siliciclastic units from the northern part of the mesohellenic basin macedonia northern greece provide good biostratigraphic potential taxa identified from a number of sections cropping out in the study area indicate that these deposits fan in zones p20 upper part p21 p22 and most of zone n4 of blow s zonal scheme the occurrence within the lowest part of the pendalofos formation of abundant globigerinoides primordius together with other earliest miocene planktonics defines the base of the miocene although a remarkable planktonic foraminiferal turnover occurred close to the palaeogene neogene boundary the benthic populations do not show any clear change except in relation to palaeoecologic conditioning analysis of benthic foraminifera led to the definition of a palaeodepth curve indicating that the deposition during the late oligocene and early miocene occurred in a middle to upper mostly bathyal and outer neritic conditions the distribution of selected benthic foraminifera is compared with sedimentologically derived depositional environments the correlation between the major global unconformities predicted by the exxon coastal onlap chart and the mesohellenic succession is based on the joint use of biochronologic and biostratigraphic palaeoecologic tools

development of a holocene glacier fed composite alluvial fan based on surface exposure age dating techniques the illae fan jotunheimen norway abstract holocene development of a composite alpine alluvial fan is reconstructed and dated based on its geomorphology and schmidt hammer exposure age dating shd supplemented by terrestrial cosmogenic nuclide dating tcnd lichenometry radiocarbon dating soil development and palaeohydrological analysis shd ages of 7080 450 to 8220 440 years and a tcnd age of 6075 1220 years from the fan surface indicate that fan aggradation occurred in the early holocene through episodic debris floods phase 1 in response to paraglacial processes following deglaciation of the catchment 9 7 ka stabilisation during the holocene thermal maximum phase 2 was followed by re activation of the fan involving entrenchment and terrace formation phase 3 which occurred in response to neoglaciation after 5 5 ka and culminated in the little ice age the main control on fan development was the effect of the changing extent of glaciers in the catchment on sediment supply initially evinced in high magnitude debris floods hyperconcentrated flows and later in water floods typical fluvial processes aggradation switched to stabilisation as paraglacial activity waned while later entrenchment was associated with relatively low bedload results provide the basis of a conceptual model of alluvial fan evolution for glacierized catchments related to holocene environmental change

changes in whangaehu river lahar characteristics during the 1995 eruption sequence ruapehu volcano new zealand abstract during the 1995 ruapehu eruptive sequence multiple lahars occurred in the whangaehu river which drains ruapehu s crater lake during the earlier phreatic and phreatomagmatic eruptions lahars were generated by expulsion of waters from the lake but once the lake had emptied lahars were formed by remobilisation of seasonal snowpack laden with saturated freshly erupted tephra four types of lahars occurred during the eruptive sequence 1 initial snow slurry lahars composed of granular snow and ice incorporated by eruptively expelled crater lake waters which left behind frozen deposits with 2 5 20 clastic sediment 2 large dilute lahars generated as the volumes of ejected lake water increased and removed much of the readily available snow at least one third of the pre eruption crater lake volume was expelled during one day producing the largest lahars of the series these lahars were hyperconcentrated flows for up to 84 km from source leaving extensive deposits along the channel margins 3 concentrated lahars smaller volume lahars generated as the frequency of eruptions and volumes of expelled water declined these lahars were able to maintain high sediment concentrations measured at 46 52 by volume suspended sediment at 42 km from source their high sediment concentrations were maintained by erosion and incorporation of sand from the deposits of earlier flows which were lining the channel margins 4 remobilised tephra lahars generated following the two largest tephra eruptions of the sequence seasonal snowpack was covered by water saturated tephra warmer spring temperatures and heavy rainfall events caused collapse and remobilisation of snow and tephra producing several lahars in catchments draining eastern ruapehu

controls on modern fan morphology in calabria southern italy abstract alluvial fans are widespread throughout calabria but only a minority display evidence of current activity in order to understand if and to what extent fan types and their morphology are dependent on the physical environment including characteristics and processes of the depositional site and drainage basin we performed a series of discriminant analyses these analyses used as classification factors the presence or absence of fill in the feeder channel conditions of confinement by host terrain the dominant depositional process debris flow or sheetflood and morphometric attributes of fans and drainage basins as the discriminant function variables in general fan slope area and width length ratio and for basins melton s ruggedness number and source ratio were the most useful variables for classification best results were obtained by discriminating the types of fan deposits and the presence versus absence of fill in the feeder channel if the feeder source is singular fan morphology is controlled by constructional processes and is tightly linked to basin morphology on the other hand fan and basin morphology are also strongly dependent on the rock mechanical characteristics with hard rocks imparting to the basin a high ruggedness and to fans a high gradient larger fans however are those where sheetflooding predominates results of discriminant analysis based on fan and basin variables are much more significant than those based on fan variables only this means that the differences between characteristics of fan and basin systems are better defined than those between characteristics of fans only

channel slope reversal near the martian dichotomy boundary testing tectonic hypotheses abstract faults along the martian dichotomy boundary are evidence of tectonic activity which by analogy with terrestrial tectonism may cause changes in or even reversal of fluvial longitudinal profiles in the eastern hemisphere between 30 e and 150 e this tectonic activity has been hypothesized to result from lower crustal flow or from lithospheric flexure for which loading e g by material deposition of the northern lowlands is a possible cause watters 2003a nimmo 2005 the topographic slope changes resulting from these two different mechanisms are distinct and can provide a means for distinguishing between them although other processes may complicate interpretations of reversed longitudinal profiles two fan shaped networks of inverted channels are located near 150 e in the aeolis dorsa region just north of the dichotomy boundary their original flow directions inferred from planform morphology suggest flow to the northeast in contrast to their current longitudinal profiles sloping down to the southwest this contrast indicates slope reversal we investigate the lower crustal flow and flexure mechanisms for slope reversal by testing three different hypotheses 1 lower crustal flow 2 flexure caused by material erosion from the highlands and deposition in the lowlands and 3 flexure caused by highland erosion and deposition in the lowlands plus deposition of the medusae fossae formation in the lowlands we test these three hypotheses by comparing the inferred magnitudes of the slope reversals with predicted slope changes from geophysical models for these processes taking the possibility of non tectonic i e collapse processes into account our results suggest that among these three models the slope reversal is most consistent with the predicted tectonic response to erosion and deposition of highland material in conjunction with deposition of the medusae fossae formation contrary to previous findings our results do not support the mechanism of lateral crustal flow although they do not rule it out because lower crustal flow and erosion may both have been operating but on different time scales the result of this hypothesis testing provides insight into the evolution of the dichotomy boundary and martian crust in this location

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

quantifying sediment transport on desert piedmonts using 10be and 26al in situ produced 10 be and 26 al measured in 40 sediment samples collected from the iron and granite mountain piedmonts eastern mojave desert provide a unique view of piedmont modification processes and process rates over the 10 3 to 10 5 year time scale cosmogenic nuclide based models suggest that the iron and granite mountains generate 0 11 0 13 and 0 082 0 097 m 3 of sediment per year per meter of rangefront respectively the sediment moves down the piedmont in an active transport layer atl which is 20 to 30 cm thick based on visual observations measurements of depth to a buried b horizon cosmogenic nuclide data and maximum ephemeral channel depths sediment in this layer is well mixed vertically and horizontally on the 10 2 year time scale indicating that the small ephemeral channels which dominate the piedmont surface migrate quickly interpretive models of increasing nuclide activities at depth in two pits suggest steady sediment deposition on the piedmont at rates between 17 21 and 38 45 m ma 1 until the late pleistocene epoch when a discontinuity to markedly lower nuclide activities in the isotopically well mixed active transport layer suggests that deposition stopped a significant change in piedmont behavior nuclide activities in 10 amalgamated surface samples each collected along a different 4 km long transect increase steadily away from the mountain front thus we infer that sediment is uniformly dosed by cosmic rays as it is transported down the iron and granite mountain piedmonts interpretive models suggest that long term average sediment speeds down the iron and granite mountain piedmonts are a few decimeters to a meter per year d 2002 published by elsevier science b v

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

climatic and tectonic controls on the sedimentary processes of an alluvial fan of the western ganga plain india detailed facies analysis and morphotectonic investigations of the malin river9s alluvial fan in the western ganga plain india reveal that the morphology of the fan is largely tectonically controlled whereas the sedimentary processes are mainly climatically controlled the sedimentation occurred in two distinct evolutionary cycles which are separated by a time gap the older cycle deposited thick gravelly units up to the distal fan area whereas the sediment fill of the younger cycle is gavel dominated in the proximal fan area gravel sand dominated in the middle fan area and sand mud dominated in the distal fan area the gravels of the older cycle were emplaced by intense sediment gravity flows during periods of strengthened monsoon and steeper regional gradient during the younger cycle the proximal to distal parts of the fan were dominated by different sedimentary processes this was a time of relatively weaker monsoon and gentler regional slopes when gravels could travel only up to the middle fan area the gravels in the proximal fan area have mainly been deposited by sediment gravity flows and channel processes in the middle fan area channel processes sheetfloods and sediment gravity flows have been the main sedimentary processes and in the distal fan area fluvial processes of channel migration and overbank deposition have been the main sedimentary processes

the role of long term human impact on avulsion and fan development this study aims to understand mainly qualitatively the long term role of human impact on avulsion processes and the development of fluvial mega fans in semi arid environments in this paper we refer to human impact as the direct influences of actions on the river s hydraulics i e flow regulation flow diversion and channel engineering in five case studies drawn from the khuzestan plains in southwest iran we have analysed the setup and triggering conditions of specific avulsions that occurred in the past timescale of millennia and identified the role of human interference in their causation our analysis is based on the integration of historical archaeological geomorphological and geological data through this study we demonstrate that avulsions in the khuzestan plains are the result of long term and complex interplay between multiple human induced and natural causes in similar ways human induced actions may play important roles during different phases of avulsion development the success of an avulsion in the post triggering phase may be defined by human induced setup causes as well as morphodynamic processes we suggest that present day flood events may be partly inherited from long term human alterations of the natural processes these finding could have implications for any fluvial system e g distributive fluvial systems deltas where avulsion plays a major role in their development and research tends to emphasize on natural mechanisms copyright 2016 john wiley sons ltd

use of multiparameter relative age methods for age estimation and correlation of alluvial fan surfaces on a desert piedmont eastern mojave desert california numerical and calibrated age determinations of the late quaternary alluvial fan deposits of the soda mountains piedmont in the mojave desert provide an opportunity to study the utility of the multiparameter relative age ra method for distinguishing and mapping geomorphic surfaces on a desert piedmont most ra parameters could not discriminate between deposits of holocene age although pavements have formed over locally significant parts of surfaces as young as middle holocene several parameters including lithologic composition particle size soil development and varnish cover permit distinguishing between holocene surfaces and late pleistocene surfaces statistically significant differences in initial particle size and lithology of the deposits inferred to be the result of complex interaction among hillslope alluvial fan and eolian processes and climatic change create conditions unfavorable for use of most ra techniques in contrast soil profile development and varnish cover data are successful in discrimination among deposits of holocene and pleistocene age this is attributed to the development of pedogenic features and varnish that are strongly dependent on dust influx and to the relatively minor dependence of these features on differences in the depositional character of the fan

sedimentologic and geomorphic variations in storm generated alluvial fans howgill fells northwest england in june 1982 a storm with a return period greater than 100 yr but lasting less than 2 5 hr destabilized hillslopes and produced a suite of geomorphologically and sedimentologically diverse alluvial fans thirteen major fans were deposited at the tributary junctions between small 2 catchments and two north flowing headwater streams of the river lune northwest england storm generated fans spread over or became inset into older stable fans and produced localized vertical accretion of as much as 3 m and lateral accretion of as much as 100 m sedimentary processes operating during deposition involved debris flow transitional flow and streamflow six facies types are recognized on the basis of depositional topography sedimentary texture and fabric and matrix content viscous debris flow d1 dilute debris flow d2 transitional flow t1 fluvial bars and lobes s1 s2 and fluvial sheet gravels s3 regionally streamflow deposition prevails over debris flow deposition and type s3 facies has the greatest areal extent temporal and spatial variations in facies deposition during the storm however resulted from water sediment ratio variations fan deposition involved an early phase of debris flow to transitional flow due to large inputs of sediment from hillslope failures this was followed by a systematic change to more dilute conditions resulting in streamflow deposition and eventually in channel incision a significant amount of geomorphic work and complex variations in sedimentary processes during the storm resulted in part from extensive overland flow and hillslope destabilization discriminant analyses indicate that catchment size channel gradient and percentage of area eroded during the storm controlled whether debris flow or streamflow facies dominated a fan sequence smaller steeper catchments had a greater percentage of the area yielding sediment and are dominanted by debris flows whereas larger catchments produced more runoff resulting in dilution and streamflow the results indicate that the facies sequences and fan entrenchment in the howgill fells which are typically considered products of longer term climatic change or tectonics in other localities are here primarily affected by thresholds related to catchment geomorphology by the type of sediment available and by the position within the storm cell

the late early miocene acipayam piggy back basin refining the last stages of lycian nappe emplacement in sw turkey abstract alluvial fan to shallow marine sedimentation in the acipayam piggy back basin took place in the hinterland zone of the se facing lycian nappe stack and constrains the age and style of late stage advance of these nappes syn orogenic sedimentation commenced in burdigalian time and is marked by coarse grained alluvial fan deposits that directly overlie mesozoic ophiolitic rocks palaeocurrent data obtained from these coarse clastic units suggest a south southeastward drainage the succession fines upwards and passes into fluvial deposits that become increasingly enriched in carbonate clasts derived from tectonically deeper seated nappes suggesting progressive unroofening of the nappe pile upwards the succession is transitional to a late burdigalian early langhian marginal marine succession consisting of off shore fines with coal seams that overly both the coarse clastic sediments and basement rocks clastic sedimentation ceased at the end of early langhian based on reef carbonates that cap the succession shallow marine deposits and overlying reef carbonates confirm a marine transgression that has been reported from elsewhere in the tauride belt detailed sedimentology of the acipayam basin fill succession its age and overall tectonic setting imply that during burdigalian time the succession was deposited in a piggy back basin located in the hinterland zone of actively moving thrust sheets we propose a model in which thick skinned thrusting invoked inversion of early extensional faults in the autochthon and may explain the generation of large open folds with thick sedimentary sequences in their core the formation of these large folds may have importantly influenced the frontal accretion such that active shortening moved into the hanging wall resulting in episodic nappe advanced of structurally higher nappes in a mode similar to thin skin thrusting the tectonosedimentary evolution of the acipayam piggy back is strongly dependent on its position relative to the hinge of the large open fold the absence of any compressional signatures in the basin fill succession indicates that these thrust translations ceased shortly after aquitanian time by serravallian the succession was interrupted and the region was uplifted to its present elevation probably by gravitationally isostatic orogenic rebound of the nappe stack after these episodes tectonic extension predominated and the succession became dissected by nappe front parallel normal faults that bound the present cameli basin

desert pavement characteristics on wadi terrace and alluvial fan surfaces wadi al bih u a e and oman abstract in arid mountain areas the dating and correlation of alluvial depositional surfaces is often uncertain especially in regions where the geomorphology is not well known surface modification by the development of soil and desert pavement may allow the correlation of geomorphic surfaces and estimation of at least their relative ages pleistocene wadi terraces and associated alluvial fans occur in wadi al bih u a e and oman for which correlations and age relationships are not known three age related groups of fans and terraces have been identified and mapped on the basis of their morphostratigraphic relationships deposition of the oldest terrace sediments and associated fans followed a long period of sustained incision after miocene uplift of the region the younger two groups of terraces and fans are inset within the older group to identify the gross effects of pavement development comparisons have been made between terrace surface and subsurface particle size distributions the older terraces have finer surface sediments and a greater contrast between finer surface and subsurface sediments than the younger terraces this reflects the degree of pavement development particle size on the fan surfaces is comparable with that on the equivalent terrace surfaces criteria for the classification of pavements were developed based on clast fracturing and angularity size sorting packing and surface texture from which a simple index of pavement development has been derived other properties rock varnish and weathering characteristics were also recorded but these proved to be less discriminatory than pavement characteristics the pavement data have been augmented by observations on soils detailed studies of pavements on terraces 8 sites 12 samples covering the three age groups and fans 5 sites 10 samples covering the three age groups allow differentiation between age groups the three terraces show three different age related pavement types expressed by differences in the pavement development index weakly developed pavements little fracturing sub rounded clasts some modification of the depositional fabric incipient soil development stage i caco3 accumulation occur on the youngest terrace and fan surfaces moderately developed pavements clast fracturing sub angular clasts moderate sorting and packing deeper soil development stage ii caco3 accumulation occur on the middle terrace and fan surfaces well developed pavements complete clast fracturing into small angular fragments mature sorting and packing of the pavement surface deep soil development with strong horizonation stage iii caco3 accumulation occur on the highest terrace and oldest fan surfaces there are minor differences between the youngest pavements on terraces and fans which reflect initial sedimentological differences these differences become less as the pavements develop on the basis of comparative studies the oldest terrace is estimated to date from sometime prior to ca 100 ka bp the second terrace and the most extensive fan surface from the late pleistocene and the youngest terrace and fan phase from the latest pleistocene or early holocene

differential features of alluvial fans controlled by tectonic or eustatic accommodation space examples from the betic cordillera spain abstract the creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area along basin margin faults or to a rise in base level depending amongst others on the relative importance of these two factors the margins of terrestrial sedimentary basins where alluvial fans develop produce aggradational progradational or retrogradational stratigraphic architecture we studied a total of 43 quaternary alluvial fans in the granada and bajo segura basins betic cordillera spain the analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns which is the result of differences in eustasy and tectonics the qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related in each case to the main mechanism operative in the creation of accommodation space these patterns are described as follows 1 alluvial aggradation is the main result of high tectonic subsidence with the development of quite open but small fans with a constant steep slope lacking incised channels and headward eroding gullies 2 in contrast when the principal mechanism in creating accommodation space is low tectonic subsidence progradation occurs and the fans are narrower and larger moreover the slopes of such fans are less steep in relation to the drainage area than in the above case being constant or even concave in longitudinal profile they also have short deep incised channels culminating downfan in a depositional lobe in inactive zones long deep headward eroding gullies develop 3 areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin although with a pronounced mountain embayment which gives them a characteristic mushroom shape in plan view in the latter case retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas usually showing a segmented longitudinal profile with a low gradient the feeder channels do not surpass stream order 3 and various extremely long and shallow incised channels can appear 4 contrary to the case of fans developing under a regime of subsidence when the accommodation is due to base level rise the fan slopes bear no relation to the extent of the catchment basins in such a case the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet flows over the alluvial surface

alluvial fan facies of the yongchong basin implications for tectonic and paleoclimatic changes during late cretaceous in se china abstract late cretaceous continental redbeds the guifeng group of the yongchong basin in se china have been investigated to conduct detailed fan facies description and interpretation tectonic activities determined the alluvial fan development along the basin margin but the alluvial facies was linked with paleoclimate changes the guifeng group is divided into the hekou tangbian and lianhe formations in ascending order the hekou conglomerates are typically polymict moderately sorted with erosional bases cut and fill features normal grading and sieve deposits representing dominant stream flows on alluvial fans during the initial opening stage of the basin infill the tangbian formation however is characterized by structureless fine grained sediments with dispersed coarse clasts and couplets of conglomerate and sandstone or siltstone and mudstone recording a change to a playa and ephemeral lake environments with occasional stream flooding thus indicating a basin expanding stage the hallmark of the lianhe formation is disorganized poorly sorted conglomerates lack of erosional bases and a wide particle size range from clay to boulders together reflect mud rich debris flows accumulating on fans likely related to reactivation of faulting along the northwestern mountain fronts during a post rift stage the depositional system changes from stream flows up through playa with ephemeral streams to debris flows during the accumulation of the three formations are thus attributed to different source rocks and climatic conditions therefore the fluvial dominated fans of the hekou formation recorded a subhumid paleoclimate coniacian santonian age the dominant semiarid climate during the campanian age produced abundant fine grained sediments in the playa and ephemeral lake environments of the tangbian formation a climatic change towards more humidity during the late stage of the guifeng group maastrichtian age probably yielded high deposition rate of coarse clasts in debris flow dominated fans of the lianhe formation thus the late cretaceous climate changes are inferred to have influenced and preserved signals in the alluvial stratigraphy of the yongchong basin