palaeoenvironmental reconstruction of a middle miocene alluvial fan to cyclic shallow lacustrine depositional system in the calatayud basin ne spain the middle miocene sedimentary fill of the calatayud basin in north eastern spain consists of proximal to distal alluvial fan floodplain and shallow lacustrine deposits four main facies groups characteristic of differentsedimentary environments are recognized 1 proximal and medial alluvial fan facies that comprise clast supported gravel and subordinate sandstone and mudstone the latter exhibiting incipient pedogenic features 2 distal alluvial fan facies formed mainly of massive mudstone carbonate rich palaeosols and local carbonate pond deposits 3 lake margin facies which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system i e front lithofacies a comprising massive siliciclastic mudstone and tabular carbonates or lateral lithofacies b showing laminated and or massive siliciclastic mudstone alternating with tabular and or laminated carbonate beds and 4 mudflat shallow lake facies showing a remarkable cyclical alternation of green grey and or red siliciclastic mudstone units and white dolomitic carbonate beds the cyclic mudflat shallow lake succession as exposed in the orera composite section ocs is dominantly composed of small scale mudstone carbonate dolomite cycles the mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods the deposits evolving either under subaerial exposure or water saturated conditions depending on their location on the lacustrine mudflat and on climate the dolomite intervals accumulated during lake level highstands with mg rich waters becoming increasingly concentrated lowstand to highstand lake level changes indicated by the mudstone dolomite units of the small scale cycles reflect a climate control from dry to wet conditions on the sedimentation in the area the spatial distribution of the different lithofacies implies that deposition of the small scale cycles took place in a low gradient shallow lake basin located in an interfan zone the development of the basin was constrained by gradual alluvial fan aggradation additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of 1 8 o and 1 3 c values varying from 7 9 to 3 0 pdb and from 9 2 to 1 7 pdb respectively more negative 1 8 d and 1 3 c values are from carbonate rich palaeosols and lake margin carbonates which extended in front of the alluvial fan systems whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment the results show a clear trend of 1 8 o enrichment in the carbonates from lake margin to the centre of the shallow lake basin thereby also demonstrating that the lake evolved under hydrologically closed conditions

pattern of sedimentary infilling of fossil mammal traps formed in pseudokarst at cerro de los batallones madrid basin central spain fossil mammal sites of late miocene age ca 9 ma occur in hourglass shaped non interconnected cavities up to 15 m deep hosted in mudstone mostly sepiolite chert and carbonate bedrock in cerro de los batallones this paper provides a model for the sedimentary infilling of the cavities which functioned as traps for vertebrate faunas and contain one of the richest and best preserved neogene mammal assemblages of the iberian peninsula generation of the mammal bearing cavities started with the solution of underlying evaporites which resulted in fissures that were subsequently enlarged by subsurface piping a process rarely preserved in the ancient sedimentary record the system of subterranean cavities evolved into a pseudokarst landscape resulting in doline like shafts reaching the ancient land surface the sedimentary infilling of the cavities comprises both clastic and carbonate lithofacies that were investigated by outcrop observation standard and scanning electron microscope petrography mineralogical analysis and stable isotope geochemistry gravel and breccia talus deposits clast and mud supported gravel pebbly sandstone and mudstone are common detrital infill deposits mostly derived by overflow erosion of bedrock the deposits containing the mammal bones are marls and occur both in subsurface cavities and doline like depressions in the underground cavities marlstone was mainly of clastic origin and accumulated in ponds scattered over the floor of the cavity in contrast marlstone deposits in the surface dolines formed mostly as a result of biochemical carbonate deposition in small shallow lakes subjected to fluctuation of the water level the 18o and 13c carbonate values indicate different origins for the two kinds of marls during the final phases of pipe infill the doline marlstone sealed the mammal sites usually off lapping the adjacent bedrock

the indosinian orogeny a perspective from sedimentary archives of north vietnam the triassic stratigraphic framework for the song da and the sam nua basins north vietnam suffers important discrepancies regarding both the depositional environments and ages of the main formations they contain using sedimentological analyses and dating foraminifer biostratigraphy and u pb dating on detrital zircon we provide an improved stratigraphic framework for both basins a striking feature in the song da basin located on the southern margin of the south china block is the diachronous deposition over a basal unconformity of terrestrial and marine deposits the sedimentary succession of the song da basin points to a foreland setting during the late early to the middle triassic which contrasts with the commonly interpreted rift setting on the northern margin of the indochina block the sam nua basin recorded the activity of a proximal magmatic arc during the late permian up to the anisian this arc resulted from the subduction of a southward dipping oceanic slab that separated the south china block from the indochina block during the middle to the late triassic the song da and sam nua basins underwent erosion that led to the formation of a major unconformity resulting from the erosion of the middle triassic indosinian mountain belt built after an ongoing continental collision between the south china and the indochina blocks later during the late triassic as syn to post orogenic foreland basins in a terrestrial setting the song da and sam nua basins experienced the deposition of very coarse detrital material representing products of the mountain belt erosion

transient landscapes at fault tips 1 fault growth produces patterns of displacement and slip rate that are highly variable in both space and time this transience is most pronounced near fault tips where along strike displacement gradients vary in time as the fault array lengthens we use a set of statistical and field observations to quantify the response of catchments and their associated fans in three large normal fault arrays to transient patterns of displacement and slip rate catchments near the fault tips show distinct scaling of channel slope with drainage area compared with catchments near the strike center this scaling becomes uniform beyond about 10 km from the fault tips and is therefore like footwall relief largely decoupled from the fault displacement profile the estimated catchment response times to a change in slip rate also vary between fault tips and strike center the response times for tip catchments are much longer than the inferred time since fault activity began indicating that they are unlikely to be in equilibrium with the current fault displacement field this disequilibrium combined with the decoupling of slope area scaling from displacement indicates that landscapes are most sensitive to fault activity near fault tips active faults characterized by along strike variation in slip rate thus provide excellent opportunities to explore the transient response of landscapes to tectonic forcing

the genesis and recognition of anastomosed fluvial deposits data from the st mary river formation southwestern alberta canada abstract data from modern fluvial systems show that the term anastomosed is best reserved for suspended load systems with multiple channels and very low slope that flow in regions where the hydrograph has a seasonal peak the interchannel areas are topographic lows relative to the channel hanks and are places where crevasse splay marsh and lacustrine sedimentation occurs channel geometry is intrinsically a function of the rate of sediment partitioning the coarsest sediment is deposited in the channels on the levees and in proximal splay complexes whereas the silts and clays are deposited on the rest of the floodplain extrinsic controls on the formation of these systems are geological and climatic they include a source of suspended sediment and a highly seasonal water budget preservat on of anastomosed fluvial deposits requires a mechanism for maintaining very low depositional slopes over geologic time scales data from the st mary river formation in southwestern alberta show that the stratigraphic equivalents of these rivers are ribbon sandstone bodies encased in thin sandstones shales and siltstones the total distribution of facies rather than proof of simultaneous flow in multiple channels can be used to interpret correctly a deposit as anastomosed fluvial although anastomosed fluvial deposits form in a variety of tectonic settings they are apparently most common in foreland basins because these basins provide suitable source rocks and thrusting as a mechanism that can maintain the low depositional slopes over millions of years the mutual interaction among source rock climate and subsidence all of which play critical roles in forming and preserving these distinctive fluvial deposits allows inferences to be drawn regarding paleoclimate and paleoslope that may help constrain models of basin evolution

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

the trollheim alluvial fan and facies model revisited widely held fundamental alluvial fan facies concepts generated in past literature based on the trollheim fan deep springs valley california are inconsistent with the actual characteristics of this fan previous publications have established mostly without field study that the trollheim fan consists of debris flow sieve lobe sheetflood and channel facies debris flow and sieve deposits comprise the proximal area giving way to channel or sheetflood deposits distally contrary to these views clayey and gravelly matrix supported debris flow deposits dominate all parts of the trollheim exposures suggesting that this fan has been built almost exclusively by mass wasting events channel fill deposits constitute only a small component of the fan and most are restricted to the proximal area where they have an inset relationship with debris flow sequences the channel facies consists of laterally restricted clast supported gravel lenses formed primarily through the winnowing of debris flow fines by streamflow the most widespread facies on the surface of the fan is a mantle of varnished matrix free pebbles cobbles and boulders that commonly are distributed in radially oriented lobes or levees characteristic of debris flow deposits this mantle was produced by the surficial winnowing of the fine fraction from debris flow deposits primarily by overland water flow in contrast to previous conclusions sheetflood and sieve deposits were not identified anywhere on the fan additionally many of the facies depicted in the widely cited trollheim vertical profile including ripple bedded sand cross bedded sand and overbank mud are not present on or in stratigraphic cuts of the fan after which the profile was named

tectono sedimentary evolution of lower to middle miocene half graben basins related to an extensional detachment fault western crete greece crustal extension in the overriding plate at the aegean subduction zone related to the rollback of the subducting african slab in the miocene resulted in a detachment fault separating high pressure low temperature hp lt metamorphic lower from non metamorphic upper tectonic units on crete in western crete detachment faulting at deeper crustal levels was accompanied by structural disintegration of the hangingwall leading to the formation of half graben type sedimentary basins filled by alluvial fan and fan delta deposits the coarse grained clastic sediments in these half grabens are exclusively derived from the non metamorphic units atop the detachment fault being in direct tectonic contact with hp lt metamorphic rocks of the lower tectonic units today the basins must have formed in the period between c 20 and 15 ma prior to the exposure of the hp lt metamorphic rocks at the surface and juxtaposed with the latter during ongoing deformation

the butte valley and layton well thrusts of eastern california distribution and regional significance the butte valley and layton well thrusts are major structural features in two adjacent mountain ranges west of southern death valley the butte valley thrust in the southern panamint range underlies most of the range and emplaces proterozoic rocks over strata as young as jurassic in age the layton well thrust to the southwest in the slate range has been interpreted to have proterozoic rocks juxtaposed on rocks as young as jurassic suggesting that the butte valley thrust and the layton well thrust might be correlative new information indicates that the allochthonous rocks of the layton well thrust are mesozoic in age and are not likely part of the same allochthon as that above the butte valley thrust in addition the butte valley thrust cuts sharply downward to the north and west across lower plate paleozoic strata suggesting that the fault roots beneath the layton well thrust the layton well thrust probably belongs to the east sierran thrust system and thus would be in the upper plate of the butte valley thrust

bedrock lithology control on contemporaneous alluvial fan facies oligo miocene southern pyrenees spain climate and tectonics play important roles in controlling processes of transport and deposition on alluvial fans but the bedrock lithology in the fan catchment area is also a significant independent factor adjacent oligo miocene alluvial fan deposits on the northern margin of the ebro basin display contrasting depositional characteristics with one dominated by the deposits of debris flows and the other by deposition from flows of water a difference in clast compositions indicates that the two studied fans the nueno and san julian fans had contrasting bedrock lithology in their drainage basins the proximal facies of the nueno fan body contains matrix supported conglomerate beds with up to 80 pebble clasts of gypsum in a matrix of gypsiferous sand interbedded with gypsarenite beds the drainage basin of this fan was dominated by triassic bedrock consisting of beds of gypsum marl and micritic limestone the san julian fan body comprises clast supported polymict conglomerate beds containing pebbles from triassic cretaceous and palaeogene limestone units that are exposed in the adjacent part of the basin margin the interfingering of the deposits of these two fans demonstrates that they were contemporaneous given the consistent climate the differences in fan depositional processes must therefore be attributed to the contrasting bedrock lithology in their drainage basins a drainage basin consisting mainly of marl and gypsum bedrock provided sufficient fine grained material to generate debris flows whereas more dilute water lain processes dominated where the drainage basin was largely limestone strata

source to sink dynamics in the kyrgyz tien shan from the jurassic to the paleogene insights from sedimentological and detrital zircon u pb analyses new insights in the mesozoic geodynamic evolution and related basin range interactions in the kyrgyz tien shan were obtained based on new sedimentological and detrital zircon u pb la icp ms results from jurassic to paleogene sedimentary sequences studied sedimentary sections are located in the fergana and yarkand fergana basins to the west of the talas fergana fault tff and in the issyk kul and ming kush kokomeren basins to the east the ages of the phanerozoic zircon grains found in 18 jurassic to paleogene sandstones can be divided into four groups caledonian 470 390 ma hercynian 315 260 ma triassic 250 210 ma and jurassic 190 160 ma ages the differences in sedimentation pattern and zircon u pb results suggest that the tff played an important role in the distribution of the sedimentary deposits in the mesozoic during the early middle jurassic the tff was active and the strongest subsidence occurred in the yarkand fergana basin the provenance of its sediments can be explained both by local sources close to the tff and by more distal sources to the south west probably stretching into the present day pamir during the late jurassic early cretaceous renewed compression led to the inversion of the yarkand fergana basin around the jurassic cretaceous transition large alluvial fans developing in a semi arid to arid climate traceable around the whole tien shan were also deposited in the fergana basin a mafic sill intruded within these alluvial fans provides an emplacement age of 144 8 ma apatite u pb indicating sub volcanic activity during the early cretaceous during the late cretaceous to early paleogene the area to the west of the tff experienced marine incursions related to the proto paratethys sea the dominance of caledonian ages in the upper cretaceous lower paleogene detrital samples indicates a change in provenance whereby the drainage areas became larger towards low relief land area east of the tff

paleowind velocity and paleocurrents of pluvial lake manly death valley usa pluvial lake deposits are found throughout western north america and are frequently used to reconstruct regional paleoclimate in death valley california usa we apply the beach particle technique bpt of adams 2003 sedimentology 50 565 577 and adams 2004 sedimentology 51 671 673 to lake manly deposits at the beatty junction bar complex bjbc desolation canyon and manly terraces and calculate paleowind velocities of 14 27 m s these wind velocities are within the range of present day wind velocities recorded in the surrounding area sedimentary structures and clast provenance at desolation canyon and the manly terraces indicate sediment transport from north to south lake level based on the elevation of constructional features indicates that the hill west of the bjbc was an island and that the bjbc spits formed during simple lake regression the data are consistent with the hypothesis that the present wind regime velocity and direction formed the pluvial lake manly features

depositional evolution of miocene coal successions in the soma coalfield western turkey abstract miocene alluvial and fluvial lacustrine deposits comprising three lignite successions lower middle and upper are exposed in the soma coalfield in western anatolia the total thickness of the coal successions is about 900 m and they rest unconformably on mesozoic carbonate and siliciclastic basement rocks several lithofacies are recognised and are arranged into 15 facies assemblages fa1 to fa15 within coal successions the lower coal succession fa1 to fa3 has been interpreted as the deposits of alluvial fan to ephemeral lacustrine and forest lower mire system resulting in a subbituminous coal which averages thickness of 20 m the freshwater carbonate dominated middle coal succession fa4 to fa7 has been interpreted as the deposits of an anastomosed river system including shallow carbonate mudflats to lake and ponds and frequently drying poor forest mires depositing lignitic coal the volcanic influenced upper coal uc succession fa8 to fa15 has been interpreted as the fluvial channel floodplain and allochthonous peat mire deposits fa8 to fa10 associated with a braided river system that was rapidly buried and eroded by volcaniclastic apron deposits fa11 to fa14 and culminated in large carbonate dominated shallow lake deposits fa15 the miocene coal successions were probably deposited in a slowly subsiding and fault controlled karst based paleovalley and lowlands of the intramontane paleomorphology that resulted from the early tertiary collision of the eurasian and anatolian plates

sedimentation model of gravel dominated alluvial piedmont fan ganga plain india the piedmont zone of the indo gangetic plain contains numerous laterally coalescing small alluvial fans the latest pleistocene holocene 30 km long gaula fan can be divided into gravelly proximal fan 0 14 km down stream gravel sand rich mid fan 14 22 km and sand mud dominated distal fan 22 30 km the fan succession is composed of two fan expansion cycles a and b separated by an undulatory erosional contact of regional extent cycle a is characterized by river borne clast supported gravelly deposits and the overlying fan expansion cycle b by matrix supported gravely debris flows the main process behind fan development has been lateral migration of channels over the fan surface probably due to rapid sedimentation caused by increased sediment supply and the fluctuating water budget in response to changing climate the water laid expansion cycle a represents a humid phase the debris flow deposits of expansion cycle b suggest a dry phase approximately between 8 and 3 ka cycle b also indicates a phase of tectonic instability in the siwalik hills forming the mountain front the tectonic activity caused incision of rivers into the fan surface and in turn resulted in reduced fan building activity at present the fan surface is accreting by sheet flow processes

role of in situ cosmogenic nuclides 10be and 26al in the study of diverse geomorphic processes the central premises of applications of the in situ cosmogenic dating method for studying specific problems in geomorphology are outlined for simple and complex exposure settings in the light of these general models we discuss the information that can be derived about geomorphic processes utilizing concentrations of in situ produced cosmogenic radionuclides 10be half life 1 5 ma and 26a1 half life 0 7 ma in a variety of geomorphic contexts glacial polish and tills meteorite impact craters alluvial fans paleo beach ridges marine terraces sand dunes and bedrock slopes we also compare 10be 26al data with results obtained by other dating methods we conclude that the technique of measuring in situ cosmic ray produced nuclides holds promise for quantitative studies of processes and time scales in a wide range of geomorphological problems

short term evolution of an active basin fan system aspromonte south italy abstract alluvial fans are widespread throughout calabria southern italy but only a minority of them show evidence of current activity by means of interpretation of aerial photographs orthophotos and satellite images comparison of topographic maps reconstruction of major rainfall events and geomorphologic and sedimentologic field observations we reconstructed the recent history of the geomorphic and sedimentation events and the consequent morphological changes of an active basin fan system merging with the bed of an ephemeral stream locally named fiumara the case study is located along the ionian side of the aspromonte massif a sector of calabria where mass movement intensive erosion and channel mass transport are the predominant morphodynamic processes evidence is available of large volumes of debris produced by mass movements and erosion processes affecting the upper sector of the feeder basin the aggressive climate with intense winter storms is the principal cause of erosion and mass movements largest rainfall events occurred in clusters of 4 6 events between the 1930s and the early 1970s at roughly 20 year time intervals the development of the fan appeared as incipient in 1955 air photos activity continues today with events of sediment output from the feeder basin large rainfall events are reflected with a delay of ca eight years by aggradation dissection and progradation retrogradation cycles in the feeder channel and the fan respectively mutual interference between fan development and human activity exists as well as does the interaction between the fan progradation and the floods of the receiving fiumara stream based on the aforementioned survey tools two almost 10 year cycles were recognised feeder channel aggradation owing to the debris input of the feeder subbasin and to the presence of check dams built along the feeder channel continues until the channel slope reaches a threshold value this can also be caused by the trimming of the fan toe by the fiumara the stored alluvium is therefore released resulting in progradation at the fan site until the feeder channel slope decreases subsequently a renewed cycle starts again in response to sediment input from the source area the morphological and sedimentological evolution of the active basin fan system indicates how short term trends and cyclic modifications of such systems can be important especially where tributary basins join larger stream beds of a fiumara type torrent

arabia eurasia continental collision insights from late tertiary foreland basin evolution in the alborz mountains northern iran a poorly understood lag time of 15 20 m y exists between the initial arabia eurasia continental collision in late eocene to early oligocene time and the acceleration of tectonic and sedimentary processes across the collision zone in the early to late miocene the late eocene to miocene pliocene clastic and shallow marine sedimentary rocks of the kond eyvanekey and semnan basins in the alborz mountains northern iran offer the possibility to track the evolution of this orogen in the framework of collision processes a transition from volcaniclastic submarine deposits to shallow marine evaporites and terrestrial sediments occurred shortly after 36 ma in association with reversals in sediment provenance strata tilting and erosional unroofing these events followed the termination of subduction arc magmatism and marked a changeover from an extensional to a contractional regime in response to initiation of continental collision with the subduction of stretched arabian lithosphere this early stage of collision produced topographic relief associated with shallow foreland basins suggesting that shortening and tectonic loading occurred at low rates starting from the early miocene 17 5 ma flexural subsidence in response to foreland basin initiation occurred fast sediment accumulation rates and erosional unroofing trends point to acceleration of shortening by the early miocene we suggest that the lag time between the initiation of continental collision 36 ma and the acceleration of regional deformation 20 17 5 ma reflects a two stage collision process involving the soft collision of stretched lithosphere at first and hard collision following the arrival of unstretched arabian continental lithosphere in the subduction zone

overwash processes along a gravel beach in south east ireland recent overwashing and to a more limited extent overtopping has occurred on a gravel dominated beach just west of carnsore point in south east ireland at relatively low points swash excursions have breached the duneline and extensive gravel fans have formed on landward facing slopes also at interbreach positions swash ramps have been built up in front of previously eroding dune cliffs allowing overtopping at heights of up to 5 m above mhwost spreading a veneer of sediment over the adjacent dune ridge in both cases events appear to be preceded by erosion and backbeach sand and gravel deposition stratigraphic textural and fabric analyses assist in identifying environmental conditions that prevailed during overwash throat and fan and overtopping ramp sedimentation

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

the mesozoic successions of western sierra de zacatecas central mexico provenance and tectonic implications central mexico was subject to active tectonics related to subduction processes while it occupied a position in western equatorial pangea during early mesozoic time the subduction of the palaeo pacific plate along the western north american and south american active continental margins produced volcanic arc successions which were subsequently rifted and re incorporated to the continental margin in this context the fringing arcs are important in unravelling the continental accretionary record using petrographic analysis detrital zircon geochronology and structural geology this paper demonstrates that the guerrero arc guerrero terrane formed on top of a felsic volcaniclastic unit middle jurassic la pimienta formation and siliciclastic strata upper triassic zacatecas formation and arteaga complex of continental mexican provenance deposited across the continental margin and oceanic substrate this assemblage was rifted away from continental mexico to form an intervening oceanic assemblage upper jurassic lower cretaceous las pilas volcanosedimentary complex of the arperos basin then accreted back more or less at the same place all above the same east dipping subduction zone the accretion of the guerrero arc to the mexican continental mainland sierra madre terrane caused the deposition of a siliciclastic unit la escondida phyllite which recycled detritus from the volcaniclastic and siliciclastic underlying strata

photogeologic mapping and the geologic history of the hellas basin floor mars abstract the hellas basin on mars is the second largest topographically well defined impact structure in the solar system and has repeatedly been interpreted as a major sink of volcanic glacio fluvial and eolian materials based on established guidelines for planetary mapping we compiled a comprehensive photogeological map of hellas planitia i e the hellas basin floor 1 2 000 000 1 8 106 km2 see supplementary online material using the thermal emission imaging system themis ir day time mosaic as basemap supplemented by several other datasets we identified 33 units which were categorized into a rim assemblage containing dissected units a layered rim sequence and other basin rim units as well as a floor assemblage containing the honeycomb formation an interior formation and a plains sequence relative dating of units was performed wherever contacts revealed stratigraphic relationships and was complemented by absolute model ages amas of all units that lend themselves to reliable crater size frequency distribution csfds measurements on the basis of our results as well as amas of circum hellas volcanic provinces by previous authors we compiled a chronostratigraphic model of the hellas basin floor the northern basin rim shows evidence vast layered hydrous mineral bearing deposits containing meandering channel like valleys that the early history of the basin until 3 8 ga ago experienced extended periods of low energy fluvial and possibly lacustrine activity superposing the layered rim sequence the majority of the hellas basin infill 1 5 1 7 106 km3 consists of volcanic material a lower and an upper wrinkle ridged plains unit which was shortened by a compressive stress field relatively soon after its emplacement based on their ages and stratigraphic considerations we identified malea patera and possibly also tyrrhena patera as a suitable source for the older lower plains 3 8 ga and hadriaca and or amphitrites paterae for the younger upper plains 3 7 ga shortly after these volcanic episodes the entire basin floor was covered by large amounts of deposits 106 km3 containing aqueously altered mafic materials we interpret the deposits to have originated from hesperia planum and the hesperia hellas trough where they might have been removed by glacio fluvial processes which also sculpted the hellas rim sections along northern promethei terra and malea planum around the same time such an apparent correlation between nearby volcanic activity and increased erosion deposition is in agreement with previous models which suggest outgassing by a maximum in global volcanism at that time caused warmer episodes enabling repeated subaerial water run off after the emplacement of these deposits intense erosion likely deflation along a rim parallel annulus began to exhume the outer parts of the wrinkle ridged plains again forming an interior formation of more elevated erosional remnants including the alpheus colles since 3 7 ga ago fluvial activity of dao niger and harmakhis valles dissected the eastern plains and emplaced pancake shaped deposits in the basin center later deflation and abrasion by katabatic winds moving through the hellas basin in a clock wise direction parallel to the basin floor outline carved out the northwestern hellas planitia trough called peneus palus possibly within a time span of few hundreds of ma or less within the amazonian being consistent with erosional patterns we observed within the basin circulation models predict such winds to be ongoing today and might thus have recently exhumed the so called honeycomb formation on parts of peneus palus this enigmatic unique terrain was possibly formed by ductile deformation of pre 3 8 ga material and appears to be partially covered by another unique landform the banded terrain although we cannot rule out that it is the surface expression of a thicker unit the banded terrain might represent flows of volatile rich airfall deposits emplaced along the edges of the hellas wind alley by turbulent marginal wind currents which currently recently prevail on both sides of the hellas planitia trough in summary our investigations enabled us to draw an updated comprehensive and self consistent picture of the geologic evolution of the hellas basin floor including volcanic peri glacial fluvial and eolian processes their possible interactions and the implications on the climatic and geologic development of the circum hellas region and the entire planet

quaternary sedimentology of the rose creek fan delta walker lake nevada usa and implications to fan delta facies models the 3 2 km long rose creek fan delta of west central nevada is prograding from an active rift margin into the 32 m deep walker lake a case study of the forms processes and facies of this fan delta reveals that the proximal and medial zones mainly are of sub aerial origin and the distal zone is of lacustrine origin pebbly to bouldery rock avalanche mounds 100 m thick facies a and muddy to bouldery debris flow levees 0 5 to 2 0 m thick facies b dominate the proximal zone whereas mostly matrix supported cobbly pebbly debris flow lobes 0 1 to 1 0 m thick facies c typify the medial zone surficial pebble lags and gully fills facies d are widespread in both zones but in exposures comprise only partings or lenticles between debris flow units the distal fan delta mainly consists of lakeshore to lake bottom tracts formed by extensive wave reworking of debris flow facies nearshore deposits include erosional cobbly boulder lag beaches facies e pebbly constructional beaches attached at headcuts or on barrier spits facies f pebbly upper shoreface facies g and sandy lower shoreface facies h tracts positioned lakeward of the beach and pebbly landward dipping foresets facies i and backshore pond sand and mud facies j present landward of the spits erosional lag beaches fringe the windward north side of the fan delta front attached constructional beaches characterize the central zone and southward elongating barrier spits typify the leeward south side extending from the zone of greatest projection of the fan delta into the lake shoreline facies asymmetry results from largely unidirectional longshore drift caused by high fetch to the north and minimal fetch to the south combined with the arcuate shape of the fan delta front the spits overlie a platform deposited below common wave base consisting of south east trending cones of pebbly gilbert foresets facies k and sandy toesets facies l typically slumped silt and mud facies m fringe both this platform and lower shoreface sand in deeper water this case demonstrates facies types and patterns that are inconsistent with the widely promoted fan delta facies model having a front consisting of an apron of radially directed gilbert foresets deposited where sub aerial flows enter the lake the rose creek fan delta front instead features a sharp contact between sub aerial and lakeshore facies formed where waves erode sort and redistribute heterogeneous debris flow sediment into the various shallow to deep lake facies gilbert foresets are present only in the lee of the fan delta where sediment moving by longshore drift reaches the brink of the spit front this facies scenario results from the infrequency of fan building events versus nearly constant wind induced waves a scenario that in contrast to the popular gilbert model probably is the norm for fan deltas the level of walker lake and thus the position of wave reworking on the rose creek fan delta fluctuated over a range of 157 m during the last 18 kyr producing complex interfingering between sub aerial and lakeshore facies across a 1700 m wide radial belt typifying a wave modified freestand lacustrine fan delta

development and response of a coupled catchment fan system under changing tectonic and climatic forcing sediment fans are a potentially useful and underexploited recorder of earth s climatic and tectonic history but historical observations have led to conflicting views on the importance of tectonic climatic and lithologic variables in controlling fan morphology and deposition a one dimensional model of a sediment fan and its associated catchment is used to explore the sensitivity of such simple sediment routing systems to perturbations in fault slip and precipitation rates a transport limited catchment is coupled to a fan whose surface slope is set by the balance between catchment sediment efflux and the available tectonically generated basin accommodation rock uplift rate is spatially variable across the model space increasing the fault slip rate or decreasing the precipitation rate leads to an increase in fan slope temporary back stepping of the fan toe and a pronounced angular unconformity conversely a decrease in slip rate or an increase in precipitation rate results in a decrease in fan slope and progradation and eventual stabilization of the fan toe once perturbed the system evolves toward a new equilibrium state with time constants of 0 5 to 2 myr these response times are insensitive to slip rate but are strongly dependent on precipitation rate variations in fan slope are well described by a dimensionless parameter that expresses equilibrium slope as a function of slip rate precipitation rate system size and catchment lithology this parameter holds promise as a predictive tool in inverting the morphology of natural fans for environmental variables

facies and depositional model of alluvial fan dominated by episodic flood events in arid conditions an example from the quaternary poplar fan north western china

estimation of debris flood magnitudes based on dendrogeomorphic data and semi empirical relationships abstract magnitude estimations of hydrogeomorphic processes contain crucial information for hazard assessments and for the understanding of longer term landscape evolution in this study we reconstruct magnitudes of debris floods for a torrential catchment in tyrol by combining dendrogeomorphic time series of events with semi empirical equations used to predict event volumes reconstructed debris flood magnitudes cover eight decades a d 1930 2008 and vary from 2900 to 45 900 m 3 we illustrate that magnitude estimates derived from tree ring data and semi empirical equations represent a valuable contribution to the documentation and understanding of hydrogeomorphic processes and that they can complement fragmentary time series in small watersheds for periods covering decades up to centuries limitations of the approach are mainly inherent to the age and spatial distribution of sampled trees and may thus influence reconstructed event magnitudes as one goes back in time

fluvial morphology and sediment flux steering of axial transverse boundaries in an experimental basin abstract the distinction between depositional belts associated with the basin axis and flanking piedmont streams is a fundamental attribute of the stratigraphic architecture of intracontinental rift basins spatiotemporal distributions of these lithofacies associations are sensitive to a combination of factors including basin geometry subsidence rate and sediment discharge however most studies have focused on one or two controls and one depositional component axial or tributary of the basin fill succession a new perspective on how these depositional belts develop under simple but precisely controlled boundary conditions of steady subsidence sediment flux and water discharge is achieved through the creation of an experimental stratigraphic succession the experimental earthscape run in 2006 xes06 focused on the geomorphic evolution of sedimentary successions within an asymmetrically subsiding basin analogous to a simple half graben containing four interacting supply points of sediment and water under the imposed conditions the experimental system self organized into an axial stream flanked by transverse fans imposition of various combinations of longitudinal and lateral sediment flux showed that the locations and widths of the axial and transverse systems were strongly controlled by relative sediment fluxes flux steering and less influenced by the location of the subsidence maximum and subsidence rate the axial drainage was dominated by transversely sourced sediment through toe cutting of the transverse fans except during the highest axial sediment discharges footwall fans persisted even under conditions of very large axial sediment discharge aided by topographic inheritance of the steeper transverse depositional slopes

sedimentology of the debris flow dominated warm spring canyon alluvial fan death valley california facies analysis of widely distributed exposures of the 32 6 km2 and 8 1 km long warm spring canyon fan central death valley shows that it has been built principally by debris flow deposits these deposits were derived from a mature panamint range catchment mostly underlain by precambrian mudrock quartzite and dolomite stacked clast rich and matrix supported debris flow lobes of slightly bouldery muddy pebble cobble gravel in beds 20 150 cm thick dominate the fan from apex to toe accounting for 75 98 of most exposures interstratified with the debris flows are less abundant 2 25 of cuts thinner 5 30 cm and more discontinuous beds of clast supported and imbricated pebble cobble gravel deposited by overland flows and gully flows this facies formed by the surficial fine fraction water winnowing of the debris flows primarily during recessional flood stage of the debris flow events two other facies associations make up a small part of the fan the incised channel tract consists of a 250 m wide clast supported ribbon of irregularly to thickly bedded boulder pebble cobble gravel nested within debris flow deposits this channel fill is oriented generally perpendicular to the panamint range front it formed by extensive erosion and winnowing of debris flows deposited within the incised channel into which all water discharge from the catchment is funnelled the limited presence of this facies only straddling the present incised channel indicates that this channel overall has maintained a consistent position on the fan except for slight lateral shifts some caused by strike slip offset fault offset temporarily closed the upper incised channel causing recessional debris flow mud to be ponded behind the dam the other local facies assemblage consists of subrounded to rounded moderately sorted pebble gravel in low angle cross beds that slope both basinwards and fanwards this gravel was deposited in beachface backshore and shoreface barrier spit environments that developed where lake manly impinged on the warm spring fan during late pleistocene time these deposits straddle headcuts into and were derived from erosion of the debris flow deposits wave energy sorted finer sediment from the shore zone concentrated coarser sediment and rounded the coarse to very coarse pebble fraction by selective reworking

tectonic controls on the morphometry of alluvial fans around danehkhoshk anticline zagros iran article i nfo alluvial fans are important landforms where their morphology and morphometry reflect changes in tectonic climate base level and drainage basin characteristics along the margins of tectonically active mountain ranges like the zagros mountains alluvial fans are generally assumed to act as useful landforms for identify ing the level of tectonic activity the purpose of this paper is to evaluate the relationship between active tec tonics and morphometric characteristics of alluvial fans around danehkhoshk anticline in the simply folded belt of zagros morphometric characteristics of alluvial fans such as area fa slope sf length of base bf width length ratio w l radius r sweep angle sa and entrenchment e as well as valley floor width to height ratio vf and strata dips of anticline limbs dal were measured the study area was sub divided into eight tectonic zones and then the mean values of the above mentioned parameters were calculated in each zone result reveals that values of sa bf and e are directly proportional to dal the poor relationships between catchment characteristics slope and area and fan parameters are probably due to extensive karstic landforms of catchments having complex hydrologic systems and hence result in complex catchment fan relations the highly entrenched fans with high sweep angles and long bases are characteristic of tectonically active fronts of danehkhoshk anticline having v shaped valleys higher vf values steep triangular facets and more rotated limbs higher dal values apart from the tectonic control on fan development the fan head entrenchment and negative accumulation spaces on most alluvial fans can be attributed to decreased sediment load and discharge the drier the present day climate regime

autogenic dynamics of alluvial fans in endorheic basins outcrop examples and stratigraphic significance alluvial fans are relatively simple depositional systems due to the direct coupling of sediment sources and adjacent accumulation areas nonetheless general models of alluvial fan evolution and stratigraphy remain elusive due to the great sensitivity of such systems to allogenic controls and their strongly case specific responses autogenic processes intrinsic to alluvial fan dynamics can complicate stratigraphic architectures with effects not easily distinguishable from those of allogenic forcing a distinction is made here between lateral autogenic dynamics tied to spatial sediment distribution over fan surfaces and vertical autogenic dynamics related to independent incision aggradation cycles autogenic mechanisms have been highlighted recently by modelling studies but remain poorly constrained in field based studies examples are presented here from the margins of the cenozoic teruel and ebro basins spain where alluvial fans accumulated thick successions during phases of basin topographic closure and endorheic drainage which promoted forced aggradation fan successions consist of conformable architectures of stacked clastic sheets laterally continuous and with no evidence of internal unconformities inset architectures fan segmentation or preserved incised channels continuous aggradation in these closed basins strongly inhibited vertical autogenic dynamics in the form of fan head and through fan incision due to the forced rise in geomorphic base level and the creation of positive accommodation furthermore the lack of incised channels favoured widespread sediment transport and aggradation over broad fan sectors in relatively short time spans in contrast to the typical occurrence of active lobes and abandoned fan surfaces caused by lateral autogenic dynamics stratigraphic records of alluvial fans developed in endorheic basins are essentially complete and largely unaffected by autogenic processes the latter characteristic implies that they can be more unambiguously interpreted in terms of allogenic forcing because stratigraphic signatures are not complicated by the effects of complex fan autodynamics

late cenozoic history and styles of deformation along the southern death valley fault zone california late cenozoic deposits in the southern death valley region have been offset 35 km by right lateral strike slip faulting on the southern death valley fault zone since miocene time virtually all slip took place prior to 1 m y ago along western traces of the fault zone during the past 1 m y the eastern traces of the fault zone have been active and characterized by oblique slip with a lateral component of only a few hundred metres movement along these eastern traces has formed normal faults and gentle to isoclinal folds that have uplifted fan gravel and lacustrine sediments as much as 200 m above the modern alluvial fan surface surveying of the longitudinal profile of the amargosa river which flows within the eastern traces of the fault zone suggests that vertical deformation continues today the 35 km of right lateral offset which is based on matching offset alluvial fan gravel with its source area refines earlier estimates of 8 to 80 km of movement for the southern death valley fault zone and it is consistent with the geometry of a pull apart basin model for central death valley causes for the observed differences in the style and timing of movement of the eastern and western subzones are not well understood the study area however is located a few kilometres north of the intersection of the southern death valley and garlock fault zones the garlock fault zone changes its sense of movement from left lateral strike slip to east vergent thrusting against the southern death valley fault zone the resulting compression may have caused the shift in activity and the change in style of deformation along branches of the southern death valley fault zone

structure of the central death valley pull apart basin and vicinity from cocorp profiles in the southern great basin cocorp deep seismic reflection profiles in the vicinity of the central death valley pull apart basin in southeastern california provide three dimensional information on the subsurface of an active extensional terrane variations in the orientation and density of reflectors indicate that the crust and upper mantle of the region is divisible into three seismic zones which may represent regions of differing lithology rheology or both the reflections in the upper 5 s 15 km of the data have gentle to moderate dips between 5 and 10 s reflections are predominantly subhorizontal and below 10 s 30 km there are no notable reflections the boundaries between the above reflecting zones are marked by prominent reflecting horizons which are continuous throughout the survey region the observed reflection geometries resemble those predicted by the crustal model of the region proposed by wright and troxel 1973 on the basis of geological studies in addition many of the upper crustal reflectors can be traced directly to mapped features based on those correlations the upper reflecting zone 0 5 s is interpreted to be a region of brittle deformation with the various upper crustal reflectors interpreted as faults and basin sediments the reflecting horizon at the base of the upper zone appears to be the lower boundary of the faulted upper crustal blocks and it has been suggested that it locally includes partially molten rock the observed geometries and amplitudes of reflections from the lower crust 15 30 km depth or 5 10 s two way traveltime are consistent with the model of wright and troxel for a ductilely deformed and intruded lower crust the prominent reflecting horizon at the base of that zone is designated the reflection moho and the seismically transparent lowest zone appears to correspond to the upper mantle the seismic data define a zone of faults referred to here as the wingate wash fault zone which appears to form the southern boundary of the central death valley basin and also may have provided a conduit for the migration of magma from a mid crustal magma body to the surface the wingate wash fault zone appears to intersect the southern death valley fault zone and the frontal faults of the black mountains in the subsurface beneath the youngest volcanic edifice in the region those three fault zones appear to separate the panamint owlshead and black mountain upper crustal fault blocks from the available data a reconstruction of the possible fault block movements during the time of basin subsidence is presented that reconstruction suggests that the central death valley basin formed as a result of the combined down to the east rotation and northwest translation of the fault blocks in manner similar to that proposed by reches for other parts of the basin and range

outburst flood sedimentation on the proglacial tuttle canyon alluvial fan owens valley california u s a abstract surface deposits of the tuttle canyon alluvial fan eastern sierra nevada piedmont california mainly accumulated during a catastrophic outburst flood probably triggered by the failure of a moraine dammed lake in the steep 16 4 high relief 2361 m and high elevation to 4275 m catchment moraines of the catchment and upper fan facies a comprise unsorted sand to blocks derived from the granitic bedrock the main flood facies b is texturally like the moraine consisting of unsorted matrix supported sandy pebbly cobbly blocky boulder gravel in a single unit 3 to 8 m thick distributed across most of the 10 5 km long and 28 1 km2 fan facies b was deposited during the initial outburst flood phase as a high volume noncohesive sediment gravity flow ncsgf instigated by water rapidly descending over moraine it differs from the moraine by a planar unit geometry and a slope transverse long axis alignment of boulders ncsgf deposition was followed by a water flood phase caused by continued lake drainage subsequent to removal of loose sediment in the flood path this discharge carved channels 2 22 m deep and 5 60 m wide around and across fan ncsgf deposits with channels departing from various points along tuttle creek horseshoe separation scours also formed around bedrock spurs and laminated pebbly sand accumulated on the channel beds facies d flood discharge expanded on the distal fan into a sheetflood that first deposited a boulder unit facies e and then 4 m of cobbly sandy pebble gravel in planar beds 5 20 cm thick facies f the final flood phase entailed incision of tuttle creek wherein bouldery cobble gravel facies c was concentrated post flood modification of these deposits has been limited to secondary processes such as eolian deposition facies g and bioturbation outburst floods on fans of the sierra nevada piedmont ultimately are caused by the glacial transfer of colluvium from the upper catchment slopes into moraines on the valley floors that dam drainage to form lakes outburst floods differ from meteorological floods in the valley by the high water and sediment discharge achieved during a single event by deposition of massive ncsgf beds and by causing major changes to the landscape such as the carving of channels these differences produce fans with distinctive facies and hazards the former allowing their recognition in either modern or ancient settings

effects of debris flow composition on runout depositional mechanisms and deposit morphology in laboratory experiments predicting debris flow runout is of major importance for hazard mitigation apart from topography and volume runout distance and area depends on debris flow composition and rheology but how is poorly understood we experimentally investigated effects of composition on debris flow runout depositional mechanisms and deposit geometry the small scale experimental debris flows were largely similar to natural debris flows in terms of flow behavior deposit morphology grain size sorting channel width depth ratio and runout deposit geometry lobe thickness and width in our experimental debris flows is largely determined by composition while the effects of initial conditions of topography i e outflow plain slope and channel slope and width and volume are negligible we find a clear optimum in the relations of runout with coarse material fraction and clay fraction increasing coarse material concentration leads to larger runout however excess coarse material results in a large accumulation of coarse debris at the flow front and enhances diffusivity increasing frontal friction and decreasing runout increasing clay content initially enhances runout but too much clay leads to very viscous flows reducing runout runout increases with channel slope and width outflow plain slope debris flow volume and water fraction these results imply that debris flow runout depends at least as much on composition as on topography this study improves understanding of the effects of debris flow composition on runout and may aid future debris flow hazard assessments

topographic predictors of susceptibility to alluvial fan flooding southern apennines the flooding susceptibility of alluvial fans in the southern apennines has long been neglected to partly address this oversight we focus on the region of campania which contains highly urbanized piedmont areas particularly vulnerable to flooding our findings are based on stratigraphic analysis of the fans and morphometric analysis of the basin fan systems using geomorphological analysis we recognized active alluvial fans while stratigraphic analysis together with statistical analysis of the morphometric variables was used to classify the fans in terms of the transport process involved the results indicate that in the geological context examined the best discrimination between debris flow df and water flood wf processes is achieved by means of two related variables one for the basin feeder channel inclination cg and one for the fan fan length fl the probability that an unclassified fan belongs to group wf is computed by applying a logistic function in which a p value exceeding 0 5 indicates that a basin fan system belongs to group wf this important result led to the classification of the entire basin fan system data as regards process intensity debris flow dominated fans are susceptible to the occurrence of flows with high viscosity and hence subject to more severe events than water flood dominated fans bearing this in mind the data gathered in this study allow us to detect where alluvial fan flooding might occur and give information on the different degrees of susceptibility at a regional scale regrettably urban development in recent decades has failed to take the presence of such alluvial fans into account due to the long recurrence time 50 100 years between floods this paper outlines the distribution of such susceptibility scenarios throughout the region thereby constituting an initial step to implementing alluvial fan flooding control and mitigation copyright 2012 john wiley sons ltd

sedimentation model for the quaternary intramontane bhimtal naukuchiatal lake deposits nainital india abstract the bhimtal naukuchiatal lake was created due to blocking of the valley by a huge debris flow along a narrow outlet at about 40 ka bp the lake basin was filled intermittently due to fluvio lacustrine and colluvial processes that deposited a thick sequence of interbedded mud and gravel in the basin fill sequence five major lithofacies most of them divisible into subfacies have been identified and assigned to specific depositional environments the coarsening upward cu mud silt cycles represent sedimentation in a lake setting the clasts and mud supported gravels consists of fining upward fu and cu sequences respectively indicating deposition by channel processes and debris flows having basin wide extent the pedogenic mottled clayey silt unit represents an important tectonic event when the lake was temporarily drained and sediments were sub aerially exposed fluctuating arid semiarid to humid climatic conditions and repeated tectonic activity may have governed the mode of sedimentation and ultimately the basin fill history

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

sedimentation history of the palaeoproterozoic dhanjori formation singhbhum eastern india abstract the palaeoproterozoic dhanjori formation eastern india is a terrestrial dominantly fluvial volcano sedimentary succession basal conglomerate coarse grained sandstone and shale rests directly on the granite basement and represents the distal fringe of an alluvial fan complex sieve sheet flood mass flow and alluvial channel and overbank deposits comprise the fan segment the rest of the formation is entirely constituted by fining upward fluvial cycles an event of basin tilting and volcanic eruption intervened and resulted a second phase of dhanjori sedimentation although the general fluvial depositional framework remained unaltered the two members of the dhanjori formation display different paleocurrent trends related to fluvial response to basin tilting in the lower member spatial variability in paleocurrent directions occurs as a consequence of fan development unlike the first phase the second phase of fluvial deposition incorporates profuse volcanics and accompanying volcaniclastic deposits these volcanic and volcaniclastic rocks might have locally blocked the river courses resulting in short lived lacustrine deposition composition of the volcanics varies upward from ultramafic to mafic the dhanjori volcanism took place in an intracontinental rift setting as is evident from the interbedded terrestrial deposits interbedded volcanic and volcaniclastic rocks in different stratigraphic levels suggest episodic volcanic eruption a semiarid paleoclimate is proposed and is consistent with development of an alluvial fan comprised of coarse clastic deposits

sediment transfer processes in two alpine catchments of contrasting morphological settings summary coarse sediment transport processes in steep headwater streams may vary between bedload and debris flows events depending on basin geomorphology and sediment supply this paper compares two small catchments drainage area 4 5 km 2 located in the eastern italian alps where the dominant sediment transport processes differ substantially i e debris flows in the moscardo torrent and bedload events in the rio cordon the two basins were selected because they provided the unique opportunity to analyze long term data of debris flow and bedload volumes respectively the two basins are compared in terms of peak discharge event duration and magnitude frequency characteristics of transported sediment volumes additional bedload data from two more alpine experimental basins are also considered the results show that for comparable recurrence intervals debris flow volumes are 2 3 orders of magnitude larger than bedload volumes this contrasting sediment transfer activity can be attributed to different basin and channel morphologies which are analyzed in terms of sediment supply conditions longitudinal profiles and slope area curves

debris flow dominance of alluvial fans masked by runoff reworking and weathering arid alluvial fan aggradation is highly episodic and fans often comprise active and inactive sectors hence the morphology and texture of fan surfaces are partly determined by secondary processes of weathering and erosion in addition to primary processes of aggradation this introduces considerable uncertainty in the identification of formative processes of terrestrial and martian fans from aerial and satellite imagery the objectives of this study are i to develop a model to describe the sedimentological and morphological evolution of inactive fan surfaces in arid settings and ii to assess the relative importance of primary processes of aggradation and secondary processes of weathering and reworking for surface morphology and sedimentology and for the stratigraphic record we studied an alluvial fan characterized by a recently active sector and a long abandoned inactive sector along the coast of the hyperarid atacama desert here rates of primary geomorphic activity are exceptionally low because of extreme aridity while weathering rates are relatively high because of the effects of coastal fogs long term processes of fan aggradation and reworking were determined through sedimentological facies analysis of stratigraphic sections ground surveys for textural and morphological patterns at the fan surface were integrated with remote sensing by an unmanned airborne vehicle uav discharges and sediment transport capacities were calculated to estimate the efficiency of secondary runoff in reshaping the inactive fan sector stratigraphic sections reveal that the fan was dominantly aggraded by debris flows whereas surface morphology is dominated by debris flow signatures in the active sector and by weathering and runoff on the inactive sector on the latter rapid particle breakdown prevents the formation of a coarse desert pavement furthermore relatively frequent local runoff events erode proximal debris flow channels on the inactive sector to form local lag deposits and accumulate fine sediment in low gradient distal channels forming a well developed drainage pattern that would suggest a runoff origin from aerial images nevertheless reworking is very superficial and barely preserved in the stratigraphic record this implies that fans on earth and mars that formed dominantly by sporadic mass flows may be masked by a surface morphology related to other processes

gpr derived architecture of a lahar generated fan at cotopaxi volcano ecuador the internal geometry of volcaniclastic fans produced by aggradation during lahar events is difficult to examine in modern settings because of the frequent lack of three dimensional exposures this makes it challenging to i reconstruct the spatial and temporal evolution of such fans and ii interpret observed facies stratigraphy in the context of lahar flow dynamics from proximal to distal fan reaches this research therefore presents the results of a ground penetrating radar gpr survey of the rumipamba fan at the mouth of the burrohuaycu quebrada on the southwestern flank of cotopaxi volcano a survey grid consisting of 50 individual gpr profiles representing a total length of 19 4 km was constructed covering most of the 4 km2 large fan surface all gpr profiles were collected using a pulseekko 100 with a 400 v transmitter fan sediments consist of sandy and gravelly lahar deposits alternating with volcanic fallout including ash and pumice lapilli at times reworked by fluvial processes deposits could be ground truthed to a depth of 3 m whereas gpr penetration depth reaches 15 m data interpretation was based on classification into 15 distinct radar facies characterized by the nature of their bounding surfaces and or internal features cross referenced where possible with shallow exposures three main facies were identified parallel irregular and clinoform erosional contacts were distinguished from aggradational ones vertical channel fill and lateral accretion flow parallel versus flow transverse and proximal distal variations in deposit architecture were featured the results of this study confirm the existence of two major channel systems in the northern and southern extremities of the fan and the more recent formation of a smaller central fan channel system deposit architecture is complex and facies chronologies illustrate that lahars have affected the entire survey area

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

geometry and subsurface lithology of southern death valley basin california based on refraction analysis of multichannel seismic data the shallow structure and subsurface lithology of southern death valley basin in eastern california were studied using refraction analysis of multichannel seismic reflection data acquired by cocorp two dimensional velocity models of the upper 3 km of southern death valley were derived from iterative fitting of first arrival travel times on common shot and common receiver gathers the structural basement beneath southern death valley defined by rocks having velocities greater than 4 0 km s is asymmetric and dips gently to the east where it is terminated by a steeply dipping fault which parallels the black mountain range front and has normal down to the west displacement numerous other faults that have normal components of displacement obliquely cross the seismic lines and indicate that the southern death valley basin formed from the divergent wrench system of the southern death valley fault zone

sedimentology based reconstructions of paleoclimate changes in the central andes in response to the uplift of the andes arica region between 19 and 21 s latitude northern chile we focus on the sedimentological record of the middle miocene to modern deposits in the andes of northern chile between 19 and 21 s these sediments deposited at the western escarpment of the central depression indicate successively more moisture on the western margin of the altiplano and the western cordillera where the sources are at the pacific coast 20 ma old exposure ages and salic gypsisols reflect an existing and ongoing hyperarid climate we interpret the increased divergence of climates between the coast and the altiplano as consequence of the andean rise to elevations higher than approximately 2 500 m a s l when the topography of the altiplano was sufficiently high and areally extensive to attract atlantic moisture accordingly the inferred general increase in run off was closely coupled with the uplift of the andes if the steady rise model applies in case that the rapid rise model for andean uplift is correct the inferred changes in sediment transport would have occurred independently of uplift requiring an alternative yet unknown driver

timing and patterns of debris flow deposition on shepherd and symmes creek fans owens valley california deduced from cosmogenic 10be debris flow fans on the western side of owens valley california show differences in their depths of fan head incision and thus preserve significantly different surface records of sedimentation over glacial interglacial cycles we mapped fan lobes on two fans symmes and shepherd creek based on the geometry of the deposits using field observations and high resolution airborne laser swath mapping alsm data and established an absolute fan lobe chronology by using cosmogenic radionuclide exposure dating of large debris flow boulders while both fans and their associated catchments were subject to similar tectonic and base level conditions the shepherd creek catchment was significantly glaciated while that of symmes creek experienced only minor glaciation differences in the depth of fan head incision have led to cosmogenic surface age chronologies that differ in the length of the preserved depositional records symmes creek fan preserves evidence of exclusively holocene deposition with cosmogenic 10be ages ranging from 8 to 3 ka in contrast the shepherd creek fan surface was formed by late pleistocene and holocene debris flow activity with major deposition between 86 74 33 15 and 11 3 ka these age constraints on the depositional timing in owens valley show that debris flow deposition in owens valley occurred during both glacial and interglacial periods but may have been enhanced during marine isotope stages 4 and 2 the striking differences in the surface record of debris flow deposition on adjacent fans have implications for the use of fan surfaces as paleoenvironmental recorders and for the preservation of debris flow deposits in the stratigraphic record

alluvial fans and fluvial fans at the margins of continental sedimentary basins geomorphic and sedimentological distinction for geo energy exploration and development alluvial fans and fluvial fans are the most common depositional landforms along the margins of continental sedimentary basins their occurrence is determined by the area relief and hydrology of the catchment which ultimately control the relative ratios of sediment v flow discharge and runoff regimes fundamental morphological and process distinctions exist between these two kinds of deposystem which are seen as essentially different facies associations and internal architectures for the corresponding deposits alluvial fans commonly develop over short radial distances hundreds of metres to a few kilometres and are constructed by ephemeral flash flow events that lead to poor organization of the sedimentary facies and overall architecture of the corresponding deposits by contrast fluvial mega fans are fed by proper river systems which aggrade much larger volumes of clastic sediment over distances of up to a few hundred kilometres distinct channel belt and overbank domains are developed with a marked heterogeneity in the distribution of sedimentary facies represented by hierarchically well organized fluvial deposits the general properties of alluvial and fluvial fans reflect the different potentials for the corresponding successions to host economically attractive oil and gas resources and the different approaches required in exploration and prediction

quantifying sediment transport dynamics on alluvial fans from spatial and temporal changes in grain size death valley california how information about sediment transport processes is transmitted to the sedimentary record remains a complex problem for the interpretation of fluvial stratigraphy alluvial fan deposits represent the condensed archive of sediment transport which is at least partly controlled by tectonics and climate for three coupled catchment fan systems in northern death valley california we measure grain size across 12 well preserved holocene and late pleistocene surfaces mapped in detail from field observations and remote sensing our results show that fan surfaces correlated to the late pleistocene are on average 30 50 coarser than active or holocene fan surfaces we adopt a self similar form of grain size distribution based on the observed stability of the ratio between mean grain size and standard deviation downstream using statistical analysis we show that fan surface grain size distributions are self similar we derive a relative mobility function using our self similar grain size distributions which describes the relative probability of a given grain size being transported we show that the largest mobile grain sizes are between 20 and 35mm a value that varies over time and is clearly lower in the holocene than in the pleistocene a change we suggest is due to a drier climate in the holocene these results support recent findings that alluvial fan sedimentology can record past environmental change and that these landscapes are potentially sensitive to climatic change over a glacial interglacial cycle we demonstrate that the self similarity methodology offers a means to explore changes in relative mobility of grain sizes from preserved fluvial deposits

erosion dynamics modelling in a coupled catchment fan system with constant external forcing article i nfo recent alluvial fan models have suggested that deep alluvial fan entrenchment could occur without any change in sediment and water influx moreover other studies have shown that the evolution of a fan could strongly depend on feedback between the fan and the mountain catchment we evaluate if natural entrenchment still occurs in a coupled catchment fan system and we evaluate its possible impact on the evolution of mountain erosion we use a landscape evolution model where the mountain corresponds to an uplifting block and where fans form over an initial horizontal surface our experiments confirm that deep entrenchment at the fan apex can occur without a change in climate or in uplift rate under two conditions 1 the transport threshold critical shear stress is significant and 2 the downstream boundary condition corresponds to an open boundary with fixed elevation which stops the progradation of alluvial fans a stable entrenchment occurs when sediments reach this limit the entrenchment can be explained by a strong nonlinear dependence of the transport law on the slope when the shear stress is close to critical a fan slope increase occurs when sediments reach the model limit and this drives entrenchment fan entrenchment drives strong erosion in the mountain with intensity and a response time similar to those observed for the initial mountain uplift these results indicate that determining how much of natural erosion is from autogenic mechanisms is essential in order to link landscape entrenchment with past external changes 2010 elsevier b v all rights reserved

200 k y paleoclimate record from death valley salt core a 186 m long core dv93 1 from death valley california composed of interbedded salts and muds contains a 200 k y record of closed basin environments and paleoclimates interpreted on the basis of sedimentology ostracodes homogenization temperatures of fluid inclusions in halite and correlation with shoreline tufa the 200 k y paleoclimate record is dominated by two dry and or warm and wet and cold cycles that occurred on a 100 k y time scale these cycles begin with mud flat deposits 192 ka to bottom of core and 60 ka to 120 ka wetter and or colder conditions produced greater effective moisture saline pan and shallow saline lake evaporites overlie mud flat sediments 186 ka to 192 ka and 35 ka to 60 ka eventually enough water entered death valley to sustain perennial lakes that had fluctuating water levels and salinities 120 ka to 186 ka and 10 ka to 35 ka when more arid conditions returned mud flat deposits accumulated on top of the perennial lake sediments completing the cycle 120 ka and 10 ka of particular significance are the major lacustrine phases 10 ka to 35 ka and 120 ka to 186 ka oxygen isotope stages 2 and 5e 6 which represent markedly colder and wetter conditions than those of modern death valley of the two major lake periods the penultimate glacial lakes were deeper and far longer lasting than those of the last glacial

sedimentology of gravelly lake lahontan highstand shoreline deposits churchill butte nevada usa abstract gravelly shoreline deposits of the latest pleistocene highstand of lake lahontan occur in pristine depositional morphology and are exposed in gravel pits along churchill butte in west central nevada four environments differentiated at this site are alluvial fan colluvium lakeshore barrier spit lake lower shoreface spit platform and lake bottom lakeshore deposits abut along erosional wave headcuts either unsorted muddy to bouldery colluvium fringing churchill butte bedrock or matrix supported cobbly and pebbly debris flow deposits of the silver springs fan the lakeshore barrier spit is dominated by granule pebble gravel concentrated by wave erosion of the colluvial and alluvial fan facies the lakeward side of the barrier consists of beachface deposits of well sorted granules or pebbles in broad planar beds 1 10 cm thick and sloping 10 15 they interfinger downslope with thicker 10 25 cm and less steep 5 10 lakeward dipping beds of fine to medium pebble gravel of the lake upper shoreface interstratified with the latter are 10 40 cm thick sets of high angle cross beds that dip southward alongshore higher angle 15 20 landward dipping foresets of similar texture but poorer sorting comprise the proximal backshore on the landward side of the barrier they were deposited during storm surges that overtopped the barrier berm gastropod rich sand and mud also deposited by storm induced washover are found landward of the gravel foresets in a 15 m wide backshore pond algal stromatolites ostracodes and diatoms accumulated in this pond between storm events the lake lower shoreface extending from water depths of 2 to 8 m consists of a southward prograding spit platform built by longshore drift the key component of this platform is large scale sandy pebble gravel in 16 southward dipping gilbert foresets that grade at a water depth of about 6 7 m to 4 dipping sandy toesets a shift from bioturbated lower shoreface sand and silt to flat and laminated lake bottom silt and mud occurs between water depths of 10 40 m and over a shore normal distance of 250 m this lake bottom mud facies unlike the others is areally expansive

gis analysis of depositional slope change at alluvial fan toes in japan and the american southwest abstract slope change at alluvial fan toes provides a clue to understanding differences between alluvial fans and other depositional landforms this paper analyses topographic data for 430 alluvial fans and their adjacent lowlands in japan and the american southwest asw typical humid and arid regions with abundant alluvial fans arcs showing fan toes were identified and representative areas above and below each arc were then delineated based on a gis buffer analysis the mean slope of the area above sa and below the fan toe sb and the ratio of sa to sb rs were computed overall fan slope so total fan length l and angle of the fan apex af were also measured relationships among these morphometric parameters reflect differences in climate and sedimentary processes fans in the asw tend to have straight profiles with similar values for sa and so indicating that fan gradients from deposition resulted from low frequency high magnitude storms have been preserved well under an arid climate higher rs values result from good preservation of both steep fan surfaces and gentle adjacent lowlands which is also ascribable to infrequent sediment redistribution in japan sa tends to be smaller than so and rs is often close to unity reflecting frequent sediment redistribution on fans and across fan toes under a humid climate rs in both the regions tends to converge into unity with increasing l longer alluvial fans are more strongly dominated by fluvial processes than by mass flows especially at their toes longer fans also tend to have small af leading to fluvial processes similar to those on floodplains sediment re mobilisation at the toes of such fans is more frequent resulting in smaller differences between sa and sb

non marine sedimentation associated with oligocene recent exhumation and uplift of the central taurus mountains s turkey abstract three related basins in southern turkey the ecemis basin the karsanti basin and the aktoprak basin document the neogene recent regional exhumation and surface uplift history of the central taurus mountains the regional tectonic framework was established by a late eocene phase of compressional deformation that ended tethys related marine deposition during the oligocene early miocene non marine sedimentation was dominantly from braided rivers flowing from the nascent taurus mountains and from the nigde metamorphic massif further north during this period erosion more or less kept pace with exhumation and the topography remained subdued allowing a marine incursion probably eustatically controlled into the karsanti basin in the east during early oligocene time regional exhumation was possibly controlled by thermal uplift of an actively extending area located behind the subducting s neotethys in the eastern mediterranean sea during exhumation largely ophiolitic rocks were eroded revealing the deformed mesozoic tauride carbonate platform beneath the area was affected by a short lived pulse of compressional deformation transpression probably in mid miocene time but extensional exhumation then resumed as indicated by the presence of metamorphic derived clasts from the adjacent nigde massif late miocene deposition was dominated by large inward draining lakes consistent with regional evidence of a humid climate during this time strong surface uplift took place during plio quaternary time drainage to the mediterranean became established allowing river valleys to incise deeply into the flanks of the taurus mountains palaeo valleys were successively infilled with coarse alluvial sediments this deposition was influenced by ne sw trending extensional faults in addition the sedimentary evolution of the area was strongly influenced by the nne ssw trending ecemis fault zone which has experienced ca 60 km of left lateral strike slip since the late eocene an important pulse of normal faulting transtension in latest miocene early pliocene time generated large fault scarps these acted as sources for large plio quaternary alluvial fans which prograded across active strike slip faults the morphology of these fans was influenced by a combination of quaternary climatic change axial fluvial downcutting and active strike slip tectonics in general the plio quaternary regional uplift of the taurus mountains may relate to underplating of material derived from the african plate during progressive collision with the anatolian eurasian plate in the vicinity of the easternmost mediterranean sea

source controlled carbonates in a small eocene half graben lake basin shulu sag in central hebei province north china carbonate deposits which unconformably overlie the palaeozoic bedrocks extensively occur in the base of the tertiary lake succession in the half graben shulu sag central hebei province north china this study focuses on the basal carbonate successions on the hinged western slope based on seismic borehole and core data nine facies are identified in the carbonate successions and are further grouped into five facies associations mid proximal alluvial fan distal alluvial fan fan fringe moderately deep lake and deep lake the first two facies associations constitute alluvial fans formed by debrisflows at the edge of lake and are dominated by mounded to lobate shaped matrix to clastsupported carbonate rudstones with minor calcretes in the lowermost rudstone units and basinward increase in interfingering with lacustrine carbonate facies the fan fringe moderately deep lake and deep lake associations are dominated by pebbly carbonate arenites or rare carbonate arenites calcisiltitecalcilutites and varve like calcilutites calcareous shales and oil shales respectively widespread occurrences of fine grained limestone packages containing varve like organic rich laminations minor authigenic glauconite and pyrite and planktonic and plant fossils suggest a meromictic anoxic deep lake under a semi humid to humid climate probably with a connection to marine basins similarities in lithology and fossil assemblages e g trilobites of lithoclasts with those of the mid upper cambro ordovician bedrock carbonates suggest that the clastic and dissolved carbonate loads were sourced from this lower palaeozoic catchment and shed off the surrounding highlands into the basin these carbonate facies associations represent the lake lowstand and transgressive deposits of the basal third order sequence ia in which the highstand deposits are composed of lacustrine siliciclastics during the lake lowstand stage or initiation of basin filling under an intermediate climate carbonate alluvial fans occurred mostly subaerially at the bottom of the hinged slope with a narrow shallow lake zone basinwards and locally were perched within the palaeovalley on the mid upper slope during the transgressive deepening stage under a semi humid to humid climate carbonate alluvial fans became smaller in size and episodically stepped backwards upon the slope with greatly expanded and deepened lake nevertheless the carbonate system was switched to an exclusively siliciclastic system during the highstand stage the exhumation and erosion of the mid lower cambrian bedrock dominated by siliciclastics was probably the cause due to further uplift of the drainage basin all these facts indicate

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

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

fossil and recent debris flows in medium high mountains moravskoslezske beskydy mts czech republic abstract the significance of debris flows for the morphogenesis of the medium high mountains of central europe has long been neglected herein we provide evidence from the moravskoslezske beskydy mountains flysch western carpathians czech republic where fossil pleistocene debris flow events in spite of their low recent activity were important erosion and accumulation agents in shaping the mountainous terrain geomorphological and sedimentological analyses helped to differentiate between two classes of debris flow deposits deposits of the 1st class are relatively voluminous contemporary terraced landforms which originated in the pleistocene transport limited conditions recent activity of debris flows presented by the 2nd class accumulations is characterized by the presence of low magnitude events mostly originated during the reworking of older diamictons the inheritance of large volumes of old debris flow diamictons in steep mountainous terrain is the evidence of slow erosional transformation of the last glacial landforms pointing to the fact that recent topography of the mountains is not in full equilibrium with contemporary climatic and environmental conditions

early diagenesis of the upper devonian escuminac formation in the gaspe peninsula quebec sedimentological and geochemical evidence abstract clay mineral investigations pyrolysis of organic matter and microscopic observation of palynomorphs are used to interpret the diagenetic conditions of the upper devonian escuminac formation quebec canada pyrolysis of kerogen vitrinite reflectance and the presence of smectite show that the sediments of this formation have been subjected only to a shallow burial diagenesis hence the geochemical signatures are informative on the palaeoenvironment concretions are observed in the escuminac formation sedimentological and geochemical evidence suggest that these concretions were formed during early diagenesis from biodegradation of organic matter the well known fish fauna of the escuminac formation show good preservation due in part to extensive early diagenetic carbonate cementation the occurrence of calcite cements and fibrous calcite is attributed to the early diagenetic transformation of pre existing organic matter

pre vegetation alluvial fan facies and processes an example from the cambro ordovician rozel conglomerate formation jersey channel islands prior to the silurian a lack of land vegetation is expected to have influenced the processes of sedimentation on alluvial fans principally by causing increased rates of run off and erosion in the fan catchments in the cambro ordovician rozel conglomerate formation this effect was central to the generation of alluvial fan deposits that are unusually deficient in sand and clay despite being sourced from a catchment dominated by sandstone and mudstone seven facies are identified interpreted as representing the deposits of i shallow stream and sheetfloods ii channelized non cohesive debrisflows iii sub aerial mud rich debrisflows iv sub aqueous mud rich debrisflows v low energy streams that reworked abandoned fan sectors vi a sandflat playa lake system and vii talus slopes the first two facies are both clast supported conglomerate comprise 98 of the deposit and represent deposition on active depositional lobes and in the fan head trench the remaining facies are the products of infrequent sedimentary processes fan abandonment processes and marginal sub environments the facies assemblage in many ways mimics that of a modern day water lain arid region fan however the palaeolatitude of these fans was high and the climate is inferred to have been cool and wet the near absence of sandstone and mudstone beds with few mudflows is ascribed to rapid hinterland uplift and high rates of erosion resulting in minimal chemical breakdown of source rocks in the catchments such high rates of erosion are in turn ascribed to a combination of frequent rainstorms and an absence of vegetation cover