channel arrangements and depositional styles in the sao lourenco fluvial megafan brazilian pantanal wetland abstract the brazilian pantanal is an extensive lowland tropical basin characterized by the presence of fluvial megafans and seasonally inundated savanna floodplain wetlands with an area of about 16 000 km 2 the sao lourenco is the second largest megafan in the pantanal three distinct fluvial channel styles that formed at different times during the late quaternary are found here a geomorphological and sedimentary assessment of these depositional patterns provides valuable insight on the environmental context of their evolution new optically stimulated luminescence data indicate that the upper five meters of sediment in the sao lourenco megafan has been accumulating since the late pleistocene ancient fan lobes located in upper and intermediate fan settings consist of medium and coarse grained fluvial sands and exhibit well preserved distributary braided paleochannels on their surfaces as the megafan evolved through time pleistocene lobes were incised by a prominent valley filled with holocene aged meander belt deposits which consist of silts interbedded with very fine sands and clays currently the incised valley is a zone of sediment bypass modern deposition occurs along the distal toe of the megafan system where lobes characterized by distributary channel levee ridges are widespread these features formed by progradation of avulsion belts into a broad swampy floodbasin which caused the lower portion of the meander belt to be abandoned the significant differences observed in intra fan morphology appear to be linked to the variability in effective precipitation fan lobes deposited with braided distributary channels occurred under relatively dry conditions in the late pleistocene by contrast aggradational meander belt deposits and lobes with distributary channel levee ridges formed during fluctuating precipitation conditions of the holocene when the pantanal emerged from deglacial aridity modern lobes form under heavy seasonal flooding and deposition occurs in response to very rapid and common avulsion events these results have implications for interpreting the complexity of megafan facies in similar continental basins

low sinuosity and meandering bedload rivers of the okavango fan channel confinement by vegetated levees without fine sediment abstract the river systems of the okavango fan negate present fluviological perceptions that fluvial geometry is primarily dependent upon the type of sediment load being carried by the river in northwest botswana meandering and low sinuosity rivers both of which may show anastomosis are distinctly bedload in character this is mainly because of a restricted source of clastic sediment consisting of aeolian sand from the tertiary to recent kalahari basin all that seems to be required therefore to control low sinuosity and meandering geometries is adequate confinement of channels in the study examples this is provided by heavily vegetated levees comprising peat formed from and colonised by a cyperus papyrus dominated flora fine sediment plays almost no role in the confinement process active and abandoned examples of low sinuosity river channels were studied an inversion of topography develops in the latter caused by the low survival probability of metres thick peat levees desiccation and burning of peat ultimately form a degraded ash layer only tens of centimetres thick the channel sand then stands as a ridge rising above the surrounding fan surface in both examples studied no crevasse splays occur but hippopotami trails breach the levees to form minor distributary channels which become filled with sand the sand ultimately grades backwards to plug the breach meander belts are also developed particularly in the upper fan and entry corridor cut banks incise into the sand substrate and scroll bar topographies can be discerned beneath their peat cover fine sediment plays no role in the confinement of these channels which are maintained by peat levees similar to those encountered in the low sinuosity river channels the recognition of these bedload low sinuosity and meandering river channels now completes the matrix whereby any geometry of river channel can be developed in bedload mixed load and suspended load rivers important aspects of the modern channels for the study of ancient river systems are 1 the confining effect of peat levees which have low preservation potential geologically and 2 in helping to explain river systems which show contradictory evidence of semi arid and more humid climatic conditions the latter may be explained as perennial rivers entering an otherwise semi arid climatic regime from a distant source which provide a shifting more humid overprint to the inherent environmental characteristics

late quaternary hydrological dynamics in the middle kalahari forcing and feedbacks the kalahari region has become a major source of quaternary palaeoenvironmental data derived primarily from the analysis of geomorphological proxies of environmental change one suite of data from palaeolacustrine landforms has recently provided a new record of major hydrological changes in the last 150 ka burrough s l thomas d s g bailey r m 2009 mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system quaternary science reviews in press here we present an improved analysis of the drivers and feedbacks of lake level change utilising information from three main sources data from the lake system itself from analyses of other late quaternary records within the region and from climate modelling simulations using the hadley centre coupled climate model hadcm3 suggest that once triggered the lake body was large enough to potentially affect both local and regional climates surface waters and their interactions with the climate are therefore an important component of environmental dynamics during the late quaternary through its capacity to couple middle kalahari environments to distant forcing mechanisms and to itself force environmental change we demonstrate that the existence or absence of megalake makgadikgadi adds a new level of complexity to the interpretations of environmental proxy records in southern africa s summer rainfall zone

mapping of a major paleodrainage system in eastern libya using orbital imaging radar the kufrah river paillou p schuster m tooth s farr t rosenqvist a lopez s malezieux j m 2009 mapping of a major paleodrainage system in eastern libya using orbital imaging radar the kufrah river earth and planetary science letters 277 3 4 327 333 sponsorship french space agency cnes centre national d etudes spatiales

eocene sedimentation and tectonics in the hampshire basin sedimentary evidence in the eocene cuisian lutetian of the hampshire basin indicates important intra eocene movement on the isle of wight and purbeck monoclines and on the ridgeway fault evidence for syn depositional movement includes jurassic and cretaceous chert and flint pebbles in the eocene the distribution of which suggests derivation from both e and w at whitecliff bay two units of cross bedded sand have northward directed palaeocurrents and may have been deposited as localized fans of debris reworked from earlier tertiary sediments on the upwarped side of the monocline three units of laminated muds are intercalated with marine sediments in the eastern part of the basin and suggest periods of low salinity tideless conditions these episodes are attributed to the periodic isolation of the hampshire basin from the fully marine dieppe basin to the se this may have been the result of intermittent movement on a tectonic barrier to the se of selsey the onset of uplift and subsequent exposure of the chalk along the southern margin of the basin proceeded unevenly from early cuisian to late lutetian times movement on the portsdown anticline probably occurred over a similar period the isle of wight and purbeck monoclines are the superficial expressions of faults in the palaeozoic basement and not the result of lateral alpine pressures a minor series of syn depositional folds trend nw se across the basin and may reflect a component of sinistral strike slip on basement faults

paleogene island arc collision related conglomerates yarlung tsangpo suture zone tibet abstract coarse clastic rocks in the liuqu conglomerate formed in both terrestrial and subaqueous settings record a paleogene phase in the tectonic evolution of tibet facies changes are commonly abrupt with rapid changes in clast types grain size and stratal patterns sediments were derived from the leading northern edge of the indian margin and a late jurassic cretaceous intraoceanic island arc that lay within tethys the coarse clastic sedimentary rocks of the liuqu conglomerates are extremely proximal but are locally offset relative to their original source terranes they record aspects of the history of collision between these terranes and are interpreted to have been deposited in oblique slip basins that developed along the zone of collision the absence of clasts derived from terranes to the north of the yarlung tsangpo suture suggests that basins associated with deposition of the liuqu conglomerate developed prior to the final collision between india and asia

the structural development of the wessex basin the mesozoic and cenozoic structures of southern england form part of a system of disturbances which extends across the channel into northern france they are reviewed in the light of published data from south dorset basin development started with permo triassic rifting and is believed to have continued through the jurassic and early cretaceous with intermittent growth on deep seated listric normal faults probably associated with roll over anticlines this regime had ceased by the aptian and the basin passed through a period of relative stability in the late cretaceous followed by tectonic inversion and in the miocene by northwards compressive movement along the former normal faults this partially restored the earlier separative displacement at depth and probably accentuated pre existing roll over anticlines it was expressed in the surficial upper cretaceous palaeogene sequence as monoclinal flexuring the early rifting and the change from overall n s crustal stretching to compression may reflect plate tectonic events in the north atlantic region

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

hoanib river flood deposits of namib desert interdunes asanalogues for thin permeability barrier mudstone layers inaeolianite reservoirs abstract the ephemeral braided hoanib river of nw namibia ows for a few days ayear and only high discharges enable the river to pass through interdunaldepressions within the northern namib desert dune eld to the atlantic thedune eld comprises mainly large transverse dunes resulting frompredominant ssw winds river ood deposits between aeolian dunes areanalogous to mudstone layers conformably interbedded with ancientaeolianite dune foresets deep oods pond laterally to considerable depths metres to 10 m in adjacent interdunes depositing mud layers 1 50 cm toconsiderable heights on avalanche and stoss faces of bounding dunes fairlypassive ooding only disturbs aeolian strati cation minimally floodwaterclay in ltrates and settles as an impermeable seal with a ood pond on top perched above regional groundwater flood ponds evaporate slowly for longperiods 3 years early emergence desiccates higher parts of a mud layer subsequent oods can re ll a predecessor pond bene ting from the existingimpervious seal potential preservation of such mud layers is lower on thestoss face but high on the avalanche face after burial by subsequent dunereactivation and migration the leeward right hoanib bank a dune stoss face is river and wind eroded to exhume fossil interdune pond mud layers of anearlier hoanib channel the highly inclined layers are interbedded with duneavalanche foresets and represent the edges of two successive fossil pondsexposed in plan ancient ood pond mudstones occur in the permian triassichydrocarbon reservoir the sherwood sandstone group of the cheshire basin kinnerton formation and irish sea basin and were previously usederroneously to argue against the aeolian origin of cross bed sets hoanibstudies show that primary river interaction with a dune eld might preserveonly localized erosional omission surfaces in ancient aeolianites with littlesandy barform preservation prone to aeolian reworking around the main uvial channel locus however ood pond mudstone layers should form apredictable halo within which uid permeability will decrease keywords aeolian dunes aeolianite reservoir ash ood interdune namibdesert namibia permeability introductionhigh discharge oods of the hoanib river occa sionally break through the skeleton coast dune eld which forms part of the extensive namibdesert that parallels the western margin of thesouthern african subcontinent this arid regionis 140 km wide and over 2000 km long fromsouth western angola to the northern capeprovince south africa the northern namib dune eld termed the skeleton coast dune eld bywilson 1973 lancaster 1982 and ward sedimentology 2002 49 719 736

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

pliocene pleistocene climate change sea level and uplift history recorded by the horingbaai fan delta nw namibia its location on a tectonically relatively stable passive margin and its degree of interaction with the sea make the horingbaai fan delta nw namibia an exceptional record of coastal activity providing insights into the response of ephemeral fluvial systems to changes in climate sea level and continent scale uplift the fan comprises upper middle and lower segments the upper fan and middle fan are dominated by a braided river system only in the upper fan are fluvial sediments interleaved with hyperconcentrated flow deposits plio pleistocene sea level highstands have left marine terraces on the fan surface which enable correlation with the offshore marine record and provide timelines to constrain fan growth the bulk of fan delta progradation took place at 2 7 2 4 ma between the formation of a widespread erosional surface incising the middle pliocene karpfenkliff and kamberg formations but prior to the emplacement of the warm water fauna bearing late pliocene oyster terrace 2 4 2 2 ma an equivalent of the 30 mp marine terrace package in coastal southwestern africa major fan progradation is contemporaneous with widespread regional uplift 12 5 m ma and climate change in southwestern africa the latter associated with intensification of northern hemisphere glaciations younger fan growth phases are weaker and constrained by 10 m asl marine terrace bodies that yield mostly cold water fauna corresponding to the onset of strong glacial interglacial climatic fluctuations superimposed on a general aridification trend and the introduction of colder sea surface temperatures after 2 2 ma

a combined study of radar facies lithofacies and three dimensional architecture of an alpine alluvial fan illgraben fan switzerland alluvial fans serve as useful archives that record the history of depositional and erosional processes in mountainous regions and thus can reveal the environmental controls that influenced their development economically they play an important role as groundwater reservoirs as well as host rocks for hydrocarbons in deeply buried systems the interpretation of these archives and the evaluation of their reservoir architecture however are problematic because marked heterogeneity in the distribution of sedimentary facies makes correlation difficult this problem is compounded because the accumulated sedimentary deposits of modern unconsolidated fan systems tend to be poorly exposed and few such systems have been the focus of investigation using high resolution subsurface analytical techniques to overcome this limitation of standard outcrop analogue studies a geophysical survey of an alpine alluvial fan was performed using ground penetrating radar to devise a scaled three dimensional subsurface model radar facies were classified and calibrated to lithofacies within a fan system that provided outcropping walls and these were used to derive a three dimensional model of the sedimentary architecture and identify evolutionary fan stages the illgraben fan in the swiss alps was selected as a case study and a network of ca 60 km sections of ground penetrating radar was surveyed seven radar facies types could be distinguished which were grouped into debris flow deposits and stream flow deposits assemblages of these radar facies types show three depositional units which are separated by continuous fan wide reflectors they were interpreted as palaeo surfaces corresponding to episodes of sediment starvation that affected the entire fan an overall upward decline in the proportion of debris flow deposits from ca 50 to 15 and a corresponding increase in stream flow deposits were identified the uppermost depositional unit is bounded at its base by a significant incision surface up to 700 m wide which was subsequently filled up mostly by stream flow deposits the pronounced palaeo surfaces and depositional trends suggest that allocyclic controls governed the evolution of the illgraben fan making this fan a valuable archive from which to reconstruct past sediment fluxes and environmental change in the alps the results of the integrated outcrop geophysical approach encourage similar future studies on fans to retrieve their depositional history as well as their potential reservoir properties

after the flood the fluvio lacustrine landforms of northern botswana abstract the middle kalahari of northern botswana contains three palaeolake basins with shorelands enclosing an area of 60 000 km2 linked to the okavango delta and the adjacent chobe and zambezi rivers two major stages of the palaeolake system at 940 945 m lake palaeo makgadikgadi and 936 m lake thamalakane are identified prior to the final desiccation of the lakes over the last 2 000 years the former is tectonic in origin and last existed c 35 000 b p whilst the lake thamalakane stage has existed on a number of occasions particularly at 17 000 12 000 b p and can be explained by increased precipitation and inflow feeding a complex system of fault controlled lakes ultimately controlled by the mambova falls at the chobe zambezi confluence a number of factors influencing the behaviour of the okavango delta and its adjoining basins can be identified on different time scales and are discussed in relation to planning for future water development

facies analysis of a probable large fluvial fan depositional system the upper triassic chinle formation at petrified forest national park arizona u s a abstract the upper triassic blue mesa member and the overlying sonsela member of the chinle formation consist of paleosol bearing alluvial strata whose characteristics vary markedly strata exposed within a 4 km2 study area at petrified forest national park were evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria to formulate potential depositional models that may account for varying alluvial deposition the study succession records a progressive up section increase in grain size increase in channel depth and width increase in lateral and vertical connectivity of channel deposits decrease in overbank preservation and crevasse splay and or sheetflood deposition and increase in overbank drainage mean annual precipitation from the calmag paleosol weathering proxy suggests precipitation averages approximately 1300 mm yr 1 3 m yr throughout the succession despite changing paleosol drainage these features are consistent with deposition in a progradational fluvial system such as a large fan or splay complex sediment accumulation rates in the study interval suggest decreased subsidence in the upper blue mesa member reduced rates of accommodation gain may have promoted progradation of the fluvial system an up section decrease in sandstone mineralogical maturity may be related to increasing sediment bypass in proximal fan positions or increased rates of erosion and sedimentation increasingly better drained paleosols are attributed to deposition in more upland positions during fan or avulsion complex progradation rather than changing climate

late quaternary sedimentary dynamics in western amazonia implications for the origin of open vegetation forest contrasts abstract this work investigated the evolution of sedimentary environments during the latest quaternary and their influence on the paradoxical occurrence of open vegetation patches in sharp contact with the amazonian forest the approach integrated pre existing geological and floristic data from lowlands in the brazilian amazonia with remote sensing imagery including multispectral optical images tm etm and aster phased array l band synthetic aperture radar palsar insar c band srtm dems and high resolution images obtained from google earth the detection of an abundance of paleomorphologies provided evidence of a scenario in which constant environmental shifts were linked to the evolution of fluvial and megafan depositional systems in all studied areas the open vegetation patches are not random but associated with sedimentary deposits representative of environments either deactivated during the holocene or presently in the process of deactivation sedimentary evolution would have determined the distribution of wetlands and terra firme in many areas of the amazonian lowlands and would have a major impact on the development of open vegetated patches within the modern rainforest subsiding areas were filled up with megafan deposits and many fluvial tributaries were rearranged on the landscape the close relationship between vegetation and the physical environment suggests that sedimentary history related to the evolution of depositional settings during the latest quaternary played a major role in the distribution of flooded and non flooded areas of the amazonian lowlands with a direct impact on the distribution of modern floristic patterns as the depositional sites were abandoned and their sedimentary deposits were exposed to the surface they became sites suitable for vegetation growth first of herbaceous species and then of forest although climate fluctuations might have been involved fault reactivation appears to have been the main cause of changes in depositional dynamics through time a process that had an immediate effect on the development of large open vegetation patches intermingled with the amazonian rainforest

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

chemical sedimentation in the semi arid environment of the okavango delta botswana abstract the okavango basin of northern botswana is an area of active diagenetic carbonate and silica accumulation the basin is formed by grabens which represent an extension of the east african rift system the okavango delta a large marshy alluvial fan 22 000 km2 occupies most of the surface area of the basin evapotranspiration exceeds precipitation by a factor of 3 and 96 of incoming water is lost to the atmosphere evaporative concentration of dissolved solids occurs and they precipitate in the capillary fringes of islands the less soluble components caco3 and sio2 precipitate in the soils which results in a significant volume increase which has important implications for the topography of the area and the character of the sediment fill the more soluble salts mainly alkali carbonates accumulate at the surface as efflorescent crusts but are leached into the soil during the rainy season this salt accumulation destroys vegetation swamp abandonment leads to leaching to greater depth and with reflooding to the removal of these salts possibly to form a deep saline groundwater mass balance calculations indicate that this form of chemical accumulation is the dominant aggradational process occurring in the delta at present

the okavango fan and the classification of subaerial fan systems abstract controversy exists over the classification of fluvially formed subaerial fans authors either restrict alluvial fans to debris flow dominated types or extend the spectrum to fans dominated by braided rivers the okavango fan provides an end member which extends this spectrum to fans dominated by meandering and low sinuosity rivers the fan is a large 150 km radial axis shallowly sloping 0 00036 highly vegetated subaerial fan which can be subdivided into four subenvironments these are 1 the entry corridor or panhandle characterized by single and anastomosing meander belts 2 the upper fan characterized by meander belts diverging from the fan apex comprising peat confined meandering channels with interchannel swamps forming thick peats 3 the middle fan with highly confined single and anastomosing low sinuosity rivers and less common prograding meander belts whose channels are confined by thick peats with however little chance of peat preservation and 4 the lower fan in which annual floods from relatively unconfined channels spread over the fan surface and interact with pre existing aeolian and lacustrine deposits with the recognition of this new fan type the spectrum of subaerial fan types can be expressed in terms of 1 debris flow dominated fans of which the death valley fans are a member 2 braided river dominated fans of which the kosi fan is a member and 3 low sinuosity meandering losimean river dominated fans of which the okavango fan is a member this spectrum can be expressed in terms of variation in slope maximum size and percentage of surface vegetation but crucial to the evolution of the various fan types is variation in the flashy to continuous nature of the discharge and the degree of channel confinement evident on the fan surface comparable ancient examples of the three fan types are recognizable many of which provide intermediates between the ideal end members debris flow dominated and braid dominated fan types are known from throughout earth history however the losimean fan type because of its reliance on confining vegetation may only have developed after the devonian period the spectrum of subaerial fan types can be expressed on a triangular field of variation with the vertices defined by the relative importance of the processes which shaped a particular fan system be they debris flows processes associated with braided rivers or processes associated with meandering and low sinuosity rivers

crustal structure beneath southern england from deep seismic reflection profiles seismic reflection events from recently acquired profiles in southern england are interpreted in terms of stratigraphic and structural interfaces between rock units in particular evidence is brought forward that a series of reflection events dipping between 22 and 27 with azimuth averaging 160 represents 2 major thrust zones occurring in the variscan floor beneath mesozoic cover a geological model based upon borehole information and regional geological considerations is presented the tentative recognition of crystalline basement overlain and overstepped by late proterozoic rocks of variable thickness suggests that basement in this area was unstable from late precambrian times the mesozoic structural evolution can be related to tectonic re activation of major concealed thrust zones in the palaeozoic 9basement9

groundwater in the wetlands of the okavango delta botswana and its contribution to the structure and function of the ecosystem abstract the okavango delta of northern botswana is a large 40 000 km2 alluvial fan located at the terminus of the okavango river the river discharges about 10 km3 of water onto the fan each year augmented by about 6 km3 of rainfall which sustains about 2500 km2 of permanent wetland and up to 8000 km2 of seasonal wetland interaction between this surface water and the groundwater strongly influences the structure and function of the wetland ecosystem the climate is semi arid and only 2 of the water leaves as surface flow and probably very little as groundwater flow the bulk of the water is lost to the atmosphere the okavango river also delivers about 170 000 tonnes of bedload sediment and about 360 000 tonnes of solutes to the delta each year most of which are deposited on the fan bedload is deposited in the proximal permanent wetland whilst much of the solute load is deposited in the seasonal wetland notwithstanding the high evapotranspirational loss saline surface water is rare between 80 and 90 of the seasonal flood water infiltrates the ground recharging the groundwater beneath the flood plains and the many islands on the flood plains the remainder is lost by evaporation this groundwater reservoir is transpired into the atmosphere by both aquatic vegetation on the flood plains and terrestrial vegetation on the islands and the water table is steadily lowered following passage of the seasonal flood trees which are almost exclusively confined to islands are particularly important as they lower the water table beneath islands relative to the surrounding wetlands there is therefore a net flow of groundwater towards islands accumulation of dissolved salts in this groundwater leads to precipitation of solutes mainly of silica and calcite in the soils beneath island fringes and the islands grow by vertical expansion islands are thus an expression of the chemical sedimentation taking place on the fan sodium bicarbonate accumulates in the groundwater beneath island centres and this impacts on the vegetation leading ultimately to barren island interiors dense saline brine thus produced subsides under density driven flow this cycling of seasonal flood water through the groundwater reservoir thus plays a key role in creating and maintaining the biological and habitat diversity of the wetland and inhibits the formation of saline surface water

quantification of a distributive fluvial system the salt wash dfs of the morrison formation sw u s a abstract recent analysis of modern aggradational continental sedimentary basins reveals that sedimentation patterns are dominated by distributive fluvial systems dfss the salt wash member of the late jurassic morrison formation has previously been described as a fan shaped fluvial system this study characterizes facies variations across the salt wash dfs to quantitatively test predicted trends in conceptual dfs models notable proximal to distal trends include a change in total thickness of the fluvial succession from 174 m to 40 m and an average grain size from coarse sand to silt while the percentage of sand decreased from 70 in the proximal region to 8 in the distal region the proportion of amalgamated channel belt deposits decreased from 67 to 0 while floodplain facies and lacustrine deposits increase 38 to 94 and 0 1 to 7 respectively a downstream decrease in average channel belt thickness 15 m to 3 8 m from thickest to thinnest and average story thickness 7 7 m to 2 3 m from thickest to thinnest is also recorded significant downstream changes in deposit architecture were also noted with proximal regions dominated by stacked channel belt deposits with a high degree of amalgamation distal deposits are dominated by floodplain muds and sheet sandstones and sparse ribbon channels with little to no amalgamation of channel deposits this study provides quantified information for an ancient dfss with the aim of providing a dataset that can be used for objective comparison between different dfss as well as providing numerical data to aid resource exploration and modelling efforts

dinosaur egg bearing deposits upper cretaceous of boseong korea occurrence palaeoenvironments taphonomy and preservation abstract dinosaur sauropod and ornithopod egg bearing deposits of the upper cretaceous seonso conglomerate boseong korea were examined sedimentologically for palaeoenvironmental and preservational interpretation dinosaur eggs are commonly preserved as clutches although isolated eggs also occur the clutches are found in at least six horizons consisting of sandy mudstones to mudstones these strata are interpreted as terminal fan deposits calcite rims and calcite aureols around detrital grains pedotubular to nodular calcretes and circumgranular to circumnodular cracks are present in the dinosaur egg deposits these features indicate calcareous pedogenesis which appears to have assisted in the preservation of the eggs in one egg deposit in which clutches are mostly found vertic features including pedogenic slickensides pseudoanticlines and calcite filled deep desiccation cracks occur the preservation of these dinosaur eggs in calcic and vertic palaeosols suggests that the palaeoclimate of the nested area was semiarid the lack of displacement of eggs and egg shells the presence of some egg clutches 5 10 cm below flood deposits and the porous nature of the eggshells suggest that the eggs were laid in excavated nests that were buried during incubation the preservation of numerous dinosaur clutches in several horizons at boseong is consistent with site fidelity

airborne dust deposition in the okavango delta botswana and its impact on landforms this study investigated the local scale generation and movement of dust in the seasonal swamps of the okavango delta botswana with a view to examining possible transfer of material between ood plains and islands it was found that most of the dust load was carried in the lowest 3 m of the air column and consisted mainly of amorphous silica indicating that dust was generated largely on the ood plains dust loads were found to be highest above the ood plains and lowest over the interiors of islands probably due to the baf ing effect of the island trees on wind velocity the contrast in dust loads between islands and ood plains suggests that there is a net transfer of dust from ood plains to islands but it was not possible to quantify this transfer it is evident however that ood plains experience net erosion and islands net aggradation a strong seasonality in dust loads was observed with the maximum dust loads coinciding with maximum wind velocity in october this also coincides with peak seasonal ooding in the delta and only non inundated ood plains are capable of generating dust years of low ood therefore appear to be more dusty there may also be transfer of material from higher lying to lower lying ood plains which may reduce the topographic contrast on the ood plains copyright 2004 john wiley sons ltd

river avulsions on the taquari megafan pantanal wetland brazil abstract the pantanal wetland is located in a tectonically active interior sedimentary basin in west central brazil the south flowing paraguay river is the trunk river of an alluvial constructional landform comprising several large alluvial fans the largest one of which is the taquari megafan the taquari river flows in two distinct geomorphologic zones within the megafan entrenched on sediments of pleistocene fan lobes the taquari river flows in a 3 to 5 km wide meander belt in the upper fan where avulsion is hindered by entrenchment downstream of the intersection point stream discharge progressively decreases and the taquari river becomes narrow and shallow toward the paraguay river plain within the distributary fan lobe the channel levee sandy complex is topographically higher than the adjacent floodplains and avulsion is a natural consequence of crevasses in the natural levees many channel avulsions have occurred during the last decades and documented cases show that significant channel changes may take place in a few years beginning with crevassing in 1988 and ending with the abandonment of the former channel in 1998 the river completely changed course in the lower fan presently a major avulsion is occurring in the upper portion of the growing fan lobe where many crevasses have appeared in the natural levees with associated splays onto the floodbasin new anastomosed channels have formed north of the taquari river but downstream of them the flow is unconfined and the water spreads into natural floodbasins this avulsion is still in process and allows observation of channel evolution the geomorphic features produced the sedimentary processes involved and resulting effects if the new channels do not rejoin the main channel the river mouth may abandon its present master channel and shift to a position a hundred kilometers north from its present position a large volume of sediment has been transferred to the floodbasin with progradation of crevasse splay deposits over fine overbank sediments many geomorphic features recognizable in satellite and radar images clearly show that avulsion has occurred many times before in the taquari river avulsion belt deposits and former diverted channels testify to ancient avulsion events within the fan lobe and show that progradation of splays onto the floodbasin is the most important infilling process within the taquari distributary fan lobe the avulsion process in the lower taquari river has accelerated in the last 30 years along with the magnitude of flooding pasture and intensive agriculture in the catchment area has increased the sediment supply to the wetland but larger floods are also a consequence of higher rainfall since 1973 avulsion and floods have been a cause of great concern among the local population and landowners before human intervention in attempting to control floods however a better understanding of the avulsive river system is needed especially because a major navigation project including the channelization of the paraguay river was recently proposed

paleocurrent and fabric analyses of fluvial conglomerates of the paleogene noda group northeast japan abstract clast supported fluvial conglomerates of the paleogene noda group northeast japan consist of two contrasting formations the lower minato formation comprising dominantly acidic volcanic gravels and the conformably overlying kuki formation of mesozoic basement gravels crudely horizontally stratified or massive sheets of conglomerates facies gm comprise most of the sediments of both the formations and show no abrupt lateral changes of facies debris flow deposits are absent from the sediments of the group paleocurrent analysis from gravel imbrication of facies gm suggests that sediments of the minato formation were deposited by eastward paleoflow and had multiple sources in the western volcanic range such characteristics of the formation seem to show contrasting sedimentological aspects when compared with a typical alluvial fan or a fan delta sediments of the lower part of the group were formed as a coalescing braid delta elsewhere denudation of lower mesozoic basement rocks in the northern source area provided sources for the uppermost part of the group kuki formation fabric and structure of the deposits give some clues to understand the complexities of small scale fluvial topographies symmetrical or asymmetrical concave up gravel alignments of the conglomerate facies gt suggest a small scale channel dissecting obliquely into a broad longitudinal bar of facies gm elsewhere dip orientations of imbricated gravels of facies gm coincide well with the maximum dip direction of cross bedding within the overlying sand bar facies sp however the facies change from gm to sp is remarkable features of gravel imbrication provide useful information to understand bounding surface problems

lithofacies and depositional environments of miocene deposits from tectonically controlled basins red river fault zone northern vietnam abstract the lao cai yen bai and bao yen basins connected with the red river fault zone rrfz are filled with over 1000 m thick neogene miocene clastic deposits of different type and origin coarse grained alluvial deposits predominate along the south western margin of the lao cai and yen bai basins while different types of conglomerates and sandstones even siltstones occur in their central and along their north eastern parts such asymmetry in the cross section basin fill points to the south western active margin of these basins three main facies associations composed of 12 lithofacies have been recognized in the miocene succession filling the studied basins 1 debris flow dominated alluvial fan association 2 sheetflood dominated alluvial fan association and 3 lacustrine association both alluvial fan facies associations are broadly spread in the studied basins especially along their south western margins the debris flow dominated deposits are represented by decimetre to several meters thick sand and mud supported disorganized pebble to cobble size occasionally boulder breccia and conglomerate beds the sheetflood dominated deposits are represented by alternating planar bedded pebble and cobble gravel couplets the occurrence of conglomerate bodies within and overlapping fine deposits of the lacustrine facies association may suggest deposition in a debris flow and sheetflood dominated alluvial fan setting associated with narrow elongated basins that could be occupied by lakes and bordered by active fault scarps the facies pattern of the particular basins is connected with the evolution of the rrfz the origin of these basins may be correlated with a sinistral transtensional regime which occurred in the early to middle miocene moreover the high grade metamorphic core of the day nui con voi massif presently the main structural element of the rrfz was probably not exposed during sedimentation of most of the strata in the studied basins

comment on origin of the highly elevated pyrenean peneplain by julien babault jean van den driessche and stephane bonnet sebastien castelltort and alain crave

subaerial debris flow deposition in the upper paleozoic cutler formation western colorado abstract outcrops of the lower part of the cutler formation near gateway colorado contain proximal alluvial fan deposits of two principal lithofacies the diamictite lithofacies d consists of a variety of sharply bounded massive muddy beds which are interpreted as deposits of subaerial debris flows the gravelly sandstone lithofacies s consists of amalgamated beds of laminated and cross bedded conglomeratic sandstones which are interpreted as water deposited sediments clasts in s are rarely larger than 0 5 m in maximum diameter but clasts in d are commonly much larger up to 8 m both normal and inverse grading are visible in d but grading is generally not well developed in either lithofacies imbrication of clasts although more pronounced and more consistent in s is fairly commo in both lithofacies four subfacies of diamictite are distinguishable on the basis of clast packing and grading massive matrix supported dram graded matrix supported dmg inversely graded clast supported dci and massive clast supported dcm given the hydrodynamic and rheologic properties of debris flows as reported by previous workers four debris flow regimes are postulated on the basis of varying water content and clast interaction subfacies dram and drag typify deposits of flows having viscous clast interactions subfacies dci represents deposits of flows having inertial or colliding clast interactions subfacies dram comprises deposits of flows with demonstrably high yield strengths subfacies dcm represents deposits of flows in which yield strength was insufficient to support most clasts this classification specifically recognizes turbulence selective deposition and bedload transport of clasts as essential characteristics of certain dilute debris flows it also accommodates as debris flow deposits some beds which have features usually associated with aqueous deposition including clast frameworks channelization imbrication and normal grading

architectural styles and sedimentology of the fluvial lower beaufort group karoo basin south africa abstract the permo triassic beaufort group comprises in excess of 3000 m of sandstone and mudstone rich fluvial deposits that vary both laterally and vertically in abundance architecture and clustering styles the lower 1370 m has been studied in detail detailed stratigraphic logging and photographic interpretation have been carried out on river cliffs and hillside sections and sedimentary structures have been mapped by close inspection of clean outcrops seven fluvial architectural styles have been identified encompassing sand body and sand body cluster scales 1 flat topped sheets dominated by lateral accretion 2 concave up topped sheets dominated by lateral accretion 3 heterolithic ribbons dominated by lateral accretion 4 flat topped ribbons with attached splays dominated by downstream accretion 5 unconfined moderately amalgamated concave up topped complexes 6 unconfined strongly amalgamated sheet complexes and 7 valley confined strongly amalgamated ribbon complexes the internal architecture of each indicates mixed lateral and downstream accretion modes on several scales with local variability lateral accretion deposits differ from typically published facies models in that trough cross bedding is rare possibly the result of an inability to generate dunes due to the dominant very fine sandstone grain size the observed architecture and sedimentary structures are the product of 1 a semiarid climate producing fluvial and debris flows and cementation of sediment packages at the surface which exerts a strong control on the magnitude of channel scour the nature of channel fill and compaction history 2 local variability in subsidence rate causing variation in the vertical spacing of channel belts channel slope and plan form and variation in preservation of topographically higher features e g levees 3 relative position in a fluvial megafan influencing suspended load to bedload partitioning from proximal to distal locations and formation of channel belt complexes and 4 relative sea level changes causing incised valley formation and fill only in the most distal parts of the system

crevasse splay processes and deposits in an ancient distributive fluvial system the lower beaufort group south africa abstract up to 12 of the mud prone ephemeral distributive fluvial system stratigraphy in the permo triassic lower beaufort group south africa comprises tabular fine grained sandstone to coarse grained siltstone bodies which are interpreted as proximal to distal crevasse splay deposits crevasse splay sandstones predominantly exhibit ripple to climbing ripple cross lamination with some structureless and planar laminated beds a hierarchical architectural scheme is adopted in which 1 m thick crevasse splay elements extend for tens to several hundreds of meters laterally and stack with other splay elements to form crevasse splay sets up to 4 m thick and several kilometers in width and length paleosols and nodular horizons developed during periods or in areas of reduced overbank flooding are used to subdivide the stratigraphy separating crevasse splay sets deposits from crevasse splays differ from frontal splays as their proximal deposits are much thinner and narrower with paleocurrents oblique to the main paleochannel in order for crevasse splay sets to develop the parent channel belt and the location where crevasse splays form must stay relatively fixed during a period of multiple flood events beaufort group splays have similar geometries to those of contemporary perennial rivers but exhibit more lateral variability in facies which is interpreted to be the result of more extreme fluctuations in discharge regime sharp based crevasse splay packages are associated with channel avulsion but most are characterized by a gradual coarsening upward interpreted to represent progradation the dominance of progradational splays beneath channel belt deposits may be more characteristic of progradational stratigraphy in a distributive fluvial system rather than dominated by avulsion processes in a trunk river system this stratigraphic motif may therefore be an additional criterion for recognition of distributive fluvial systems in the ancient record

a reinterpretation of the concealed variscan structure beneath southern england by section balancing recently chadwick et al 1983 presented an interpretation of the concealed variscan structure beneath southern england based on deep seismic reflection profiles we re evaluate the status of reflection events identified along some of the profiles and draw attention to major uncertainties in the interpretation presented the geological section of chadwick et al is admissible in that it portrays similar structures to those seen to the west in the mendips however the section is not a valid balanced section as it cannot be restored to a pre thrusting stratigraphy using the published seismic reflection data and borehole information we present a new balanced cross section of the variscan structures for which a total tectonic shortening of about 20 is calculated

incremental aggradation on the okavango delta fan botswana abstract distributary channel switching is a relatively frequent event in the upper reaches of the okavango delta fan botswana this phenomenon was investigated by means of detailed topographic surveys and excavations along an abandoned channel and depth probing along an active channel system this work has confirmed that channel switching is the result of aggradation within the channel systems initially new channel systems are erosive but later in their evolution both channel bed and adjacent swamp peat areas begin to aggrade this phase leads to a change in channel gradient and causes the channel to become moribund abandonment follows with consequent desiccation of the peat burning of the peat completes the cycle of the channel evolution the entire process taking about one hundred years under present flow conditions the intial aggradation phase results in the accumulation of about 4 m of peat but net aggradation after collapse of the peat following a peat fire is 30 40 cm channel beds probably also experience about 4 m of aggradation as measured from the eroded channel floor after a peat fire the channel bed sands remain elevated by about 1 m relative to the surrounding burnt out peat as a result of the collapse of the peat the abandoned area becomes available for reflooding

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

high resolution sequence stratigraphy of an alluvial fan fan delta environment stratigraphic and geodynamic implications an example from the keuper chaunoy sandstones paris basin abstract facies analysis of the chaunoy formation conducted as the first stage of this study reveals that the corresponding fluvial system essentially involved bedload deposition 2 d and 3 d megaripple migration and debris flow deposition such processes are characteristic of alluvial fan depositional environments these alluvial fan deposits pass laterally eastward into a shallow lacustrine environment in stage 2 of the study electrofacies are defined by well log analysis and then matched with sedimentary facies defined by core analysis electrofacies associations and depositional environments are then inferred directly from well logs on this basis six electrofacies characterizing the main sedimentary facies associations and depositional environments within the chaunoy formation are defined channel lag deposits channel infilling lake or flood plain overflow deposits and paleosols stage 3 involves establishing correlations based on high resolution sequence stratigraphy within these continental deposits the procedure consists in analysing high frequency fluctuations in baselevel defined from sedimentological studies and calibrated on well log signatures the correlations show that the top of the chaunoy formation is diachronous the formation is subdivided here into three stratigraphic units from base to top chaunoy i ii and iii this study shows that the degree of preservation of continental deposits varies with stratigraphic cycle genetic sequences and genetic sequence sets are asymmetrical with the baselevel rise being better preserved than the baselevel fall while for minor cycle deposits may be similarly preserved during baselevel rise and fall the sequence stratigraphy pattern of the genetic sequences and the genetic sequence sets can result from climatic and or tectonic factors but their effects are difficult to distinguish at the scale of the minor chaunoy i cycle or the chaunoy ii cycle preservation is similar during the baselevel rise and fall that implies that the chaunoy minor cycles were influenced by load discharge resulting in greater accommodation space which could result from climatic or tectonic fluctuations the chaunoy formation was deposited as part of a major baselevel rise during the carnian liassic cycle during this cycle the paris basin was generally tilted to the northwest producing the intra marnes irisees superieures truncation which seems to have been induced by large scale wavelength tectonic deformation detailed isopach maps of minor baselevel cycles in chaunoy i with inferred depositional environments are used to define the extent of depositional environments and fault activity during baselevel rise and fall during emplacement of the braided alluvial fan and lacustrine deposits of the chaunoy formation fault activity which was confined to the western part of the basin controlled the preservation potential i e the thickness of the deposits and depositional environment profiles within the chaunoy i and ii cycles the increased thickness of the sandstone deposits to the northeast and the onlap at the top of chaunoy i can be explained by local fault activity and by the general tilting of the basin the chaunoy iii sandstones are confined to the western part of the basin and seem to have been controlled by local factors only

shifting of the kosi river northern india the kosi river shifts laterally over the himalaya foreland plain by continual minor cutoffs and bank cutting and by episodic major shifts across watersheds by moving into and then out of preexisting adjacent less actively aggrading streams migration is unidirectional because after a channel is filled to instability floodwater will drain preferentially into a new adjacent low rather than across it to the next watershed or back to the last abandoned channel major shifts seem stochastic and autocyclic they do not correlate with the many severe quakes and floods that undoubtedly helped prime the system for shifts

three dimensional accommodation analysis of the keuper of the paris basin discrimination between tectonics eustasy and sediment supply in the stratigraphic record abstract during the keuper the paris basin was an intracratonic sedimentary basin filled by continental deposits using paleo environmental isopach and paleo altitude maps we estimate the variations of accommodation rate at the scale of stratigraphic minor hemi cycle 1 3 ma an analysis of the short and long wavelength accommodation variations allows us to assess the relative influence of tectonics eustasy and sediment supply on the stratigraphic record our data suggest a pattern of subsidence along three trends e w in the carnian e w to nne ssw in the norian and ne sw in the norian rhaetian during the keuper the paris basin accurately records the different phases of the opening of the tethys ocean associated with a rotation of the extension direction the norian cycle could thus reflect the intraplate stresses in a transitional period between the triassic and the liassic

volcaniclastic debris flows in the clanio valley campania italy insights for the assessment of hazard potential abstract the rugged and steep slopes of the clanio valley campania southern italy mantled by volcaniclastic deposits from explosive eruptions of somma vesuvius and phlegraean fields volcanoes have a great potential for generating volcaniclastic debris flows during the well known meteorological event of may 5 6 1998 which triggered tens of debris flows causing enormous damage and casualties in the area of sarno quindici siano bracigliano sqsb the clanio valley was also affected by these hazardous phenomena debris flows were triggered by the failure of the volcaniclastic cover of the carbonate relief in the form of soil slips mainly on the sides of steep valleys slope between 26 and 45 a map of the hazard potential was created on the basis of both field and computer assisted morphometric data three classes characterised by a high medium and low hazard potential were distinguished within the higher class a better and more detailed zonation was obtained by studying the shape of the disrupted and undisrupted basins during the may 5 6 1998 event in the nearby sarno quindici siano bracigliano area this type of morphometric analysis can be applied rapidly by using a digital elevation model dem which allows a rapid investigation of large scale areas such an approach can be useful in areas characterised by similar geological and geomorphological settings

the deposits internal structure and geometry in six alluvial fan fan delta bodies devonian norway a study in the significance of bedding sequence in conglomerates discussion and reply

fan deltas and braid deltas varieties of coarse grained deltas two types of coarse grained deltas are recognized fan deltas and braid deltas fan deltas are gravel rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland they occupy a space between the highland usually a fault bounded margin and the standing body of water in contrast braid deltas here introduced are gravel rich deltas that form where a braided fluvial system progrades into a standing body of water braid deltas have no necessary relationship with alluvial fans as exemplified by fluvioglacial braid deltas braid deltas have previously been classified as fan deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different braid deltas are a common present day geomorphic feature and are abundant in the geological record fan deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems the shoreline and subaqueous components of both are similar fan delta sequences have a subaerial component that is an alluvial fan facies comprising interbedded sheetflood debris flow and braided channel deposits fan deltas produce small a few tens of square kilometres wedge shaped bodies of sediment commonly displaying high variability in paleocurrent patterns and abrupt changes in facies the deposits are generally very coarse grained with large out sized clasts very poorly sorted matrix rich polymictic heterolithic partially cemented by penecontemporaneous carbonate and have low porosity and permeability braid deltas in contrast have a subaerial component consisting entirely of braided river or braidplain facies their deposits display better sorting roundness and clast orientation than do fan delta sediments they lack a muddy matrix they display size grading and bar migration they commonly have a sheet geometry with high lateral continuity tens to hundreds of square kilometres and they exhibit moderate to high porosity and permeability valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse grained deltaic systems are not differentiated

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

the sedimentary dynamics of active fluvial channels on the okavango fan botswana the 1800 km2 okavango alluvial fan of northern botswana represents an unusual depositional setting in which peat forming perennial swamps 6000 km2 occur in a region of aeolian and semi arid sedimentation within an incipient graben of the east african rift a channel system distributes water and sediment on the fan surface but cannot contain seasonal flood water which spreads laterally from the channels through permeable channel margins sustaining the flanking swamps all sediment introduced is deposited on the fan a detailed study of sediment movement and associated hydrological conditions in the channels was undertaken to examine sediment dispersal bedload greatly exceeds suspended load at least by a factor of four vegetation and peat form permeable levees which confine the channels in the upper reaches two way exchange of water occurs between channel and swamp depending on the season but on the fan itself channels lose water to the swamp bedload measurements reveal that the channel system is in a state of grade disequilibrium with interspersed depositional and erosional reaches deposition of most of the incoming bedload occurs on the upper portion of the fan in a meandering and anastomosed channel system but on the midfan deposition of bedload occurs by channel bed aggradation at a rate of up to 5 cm yr 1 further down slope the channel enters a large lake where all remaining bedload is deposited the presently observed sedimentation patterns may be due to a recent disturbance of the fluvial system either by avulsion or neotectonics

influence of landscape evolution on the distribution of floristic patterns in northern amazonia revealed by δ13c data the amazonian lowlands include large patches of open vegetation which contrast sharply with the rainforest and the origin of these patches has been debated this study focuses on a large area of open vegetation in northern brazil where d 13 c and in some instances c n analyses of the organic matter preserved in late quaternary sediments were used to achieve floristic reconstructions over time the main goal was to determine when the modern open vegetation started to develop in this area the variability in d 13 c data derived from nine cores ranges from 32 2 to 19 6 but with nearly 60 of data above 26 5 the most enriched values were detected only in ecotone and open vegetated areas the development of open vegetation communities was asynchronous varying between estimated ages of 6400 and 3000 cal a bp this suggests that the origin of the studied patches of open vegetation might be linked to sedimentary dynamics of a late quaternary megafan system as sedimentation ended this vegetation type became established over the megafan surface in addition the data presented here show that the presence of c4 plants must be used carefully as a proxy to interpret dry paleoclimatic episodes in amazonian areas copyright 2012 john wiley sons ltd

tectonic evolution of the intra uplift vigodi gugriana khirasra netra fault system in the seismically active kachchh rift basin india implications for the western continental margin of the indian plate abstract the e w striking kachchh rift basin krb at the western continental margin of indian plate is located in the northern part of gujarat state india krb has undergone polyphase deformation owing to changing stress field since late triassic we establish the kinematic framework along the nw striking intra uplift vigodi gugriana khirasra netra fault system vgknfs located at the western part of the krb the vgknfs consists of 0 25 50 km long sub parallel striated reactivated dip slip faults a total of 1150 fault slip data consisting of fault planes and striations attitude were recorded from 66 sites including a single site with systematic joints slip sense of faults was determined by documenting kinematic indicators paleostress analysis was carried out using win tensor t tecto faultkin and sg2ps to compare and validate the results the chi square statistical analysis was undertaken to evaluate how relevant are paleostress analysis results to the present day compressional stress field geophysical investigations were conducted at selected sites using ground penetrating radar gpr to understand the shallow subsurface geometry and trace the continuity of faults buried below patchy alluvial cover 15 17 m long 2d gpr cross sections were recorded across faults using monostatic antenna of 200 mhz frequency two major deformation events d1 and d2 are determined in the present study the extension event d1 shows w and nw nnw extension during late triassic to late cretaceous it occurred during the rift phase of krb in response of the break up of gondwanaland the latest event d2 shows nne ne compression from late cretaceous up to the present it is interpreted to have developed during post rift inversion phase induced by collision of the indian plate with the eurasian plate at 55 ma

mid carboniferous diversification of continental ecosystems inferred from trace fossil suites in the tynemouth creek formation of new brunswick canada we report skolithos scoyenia and mermia ichnofacies from sub humid tropical fluvial megafan deposits in the lower pennsylvanian tynemouth creek formation of new brunswick canada and discuss their evolutionary and palaeoecological implications especially regarding the colonization of continental freshwater terrestrial environments the skolithos ichnofacies comprises annelid arthropod spreite in the upper storey of a fluvial channel the scoyenia ichnofacies comprises tetrapod tracks arthropleurid trackways and shallow annelid arthropod burrows in active abandoned fluvial channels and rapidly aggrading levees splays in proximal interfluve areas the mermia ichnofacies comprises abundant xiphosuran trackways along with diverse traces of other arthropods annelids mollusks and fish in shallow freshwater lakes ponds and coastal bays in slowly aggrading distal interfluve areas transitional mermia scoyenia ichnofacies comprise tetrapod mollusk and annelid arthropod traces in coastal bay deposits on the distal edge of the megafan these trace fossil suites 1 provide the clearest documentation yet of the mid carboniferous diversification event when tropical continental environments became more densely populated 2 suggest that euryhaline visitors xiphosurans microconchids and other taxa from open marine settings played a key role in this episode of freshwater colonization and 3 provide empirical support for the deja vu effect the evolutionary concept that new or empty ecospace recurrent in spatially and temporally variable environments is colonized by simple ichnocoenoses

sediment routing system and sink preservation during the post orogenic evolution of a retro foreland basin the case example of the north pyrenean aquitaine bay of biscay basins abstract we investigated here the evolution of the sediment routing system i e the sediment transport and deposition evolution along successive depositional topographies and environments and the sink i e deposited sediments preservation in a foreland basin from the period of mountain belt shortening to its post orogenic stage the studied system is the north pyrenean retro foreland basin from 50 ma to today which is composed of a subsiding platform the aquitaine basin fed by the erosion of the pyrenees passing laterally to a slope and a deep sea plain the bay of biscay deep basin the ultimate area of deposition this study is based on a double seismic stratigraphic and structural analysis of an extensive seismic dataset and on an age model of the sediments combining biostratigraphy orbitostratigraphy and sequence stratigraphy with a time resolution of 0 1 ma four major periods of deformation corresponding to a single or a set of stratigraphic sequence boundaries were characterized the pyrenean shortening decrease may be recorded by a basin scale uplift at 49 8 ma late ypresian the paroxysm of the piggy back shortening and related uplift is dated at 35 8 ma priabonian the end of the pyrenees shortening transition to post orogenic conditions is well dated between 27 1 and 25 2 ma chattian a major west european scale deformation of possible mantle origin uplifted the basin from 16 4 to 10 6 ma late burdigalian to early tortonian these major periods of deformations controlled the sink preservation at the first order through the ratio between the accommodation space created by subsidence on the aquitaine platform asub and the siliciclastic sediment supply coming from the erosion of the pyrenees ssc a general model is proposed at the time of the foreland basin when asub ssc most of the sediments are preserved on the platform as a progradational aggradational wedge up to 25 2 ma here at the time of the post foreland evolution when asub the continental sediment routing system is mainly provided along nearly flat alluvial plains with extensive lakes and or humid zones i e the local base levels of the alluvial fans the aquitaine retro foreland was never overfilled

influence of syntectonic sedimentation on thrust geometry field examples from the iberian chain spain and analogue modelling abstract steep thrusts are usually interpreted as oblique slip thrusts or inverted normal faults however recent analogical and numerical models have emphasised the influence of surface mass transfer phenomena on the structural evolution of compressive systems this research points to sedimentation and erosion during deformation as an additional explanation for the origin of steeply dipping thrusts the present study uses both field observations and analogue modelling to attempt to isolate critical parameters of syntectonic sedimentation that might control the geometry of the upper part of thrust systems a field study of thrust systems bounding two compressive intermountain tertiary basins of the iberian chain is first briefly presented we describe the surface geometry of thrusts surrounding the montalban basin and the alto tajo syncline at the vicinity of deposits of oligocene early miocene alluvial fans at the footwall of faults field observations suggest that synthrusting sedimentation should influence the structure of thrusts indeed the faults are steeper and splitted at the edge of the syntectonic deposits effects of sedimentation rate on footwall of thrusts and of its change along fault strike are further investigated on two layer brittle ductile analogue models submitted to compression and syntectonic sediment supply two series of experiments were made corresponding to two end members of depositional geometries in the first series the sedimentation was homogeneously distributed on both sides of the relief developed above the thrust front in the second series deposits were localised on a particular area of the footwall of thrust front in all experiments the sedimentation rate controls the number and the dip of faults for low sedimentation rates a single low angle thrust develops whereas for high sedimentation rates a series of steeper dipping thrust is observed in experiments with changing sedimentation rate along fault strike the thrust geometry varies behind the areas with the thickest sediment pile

time place and mode of propagation of foreland basin systems as recorded by the sedimentary fill examples of the late cretaceous and eocene retro foreland basins of the north eastern pyrenees the relationship between tectonics and sedimentary fill has been studied in two syncontractional basins of the western corbieres eastern north pyrenean retro foreland basin the late cretaceous basin formed during c 10 12 ma as a result of left lateral transpressional deformation and is composed of forward younging sub basins characterized by reworking of the forelimbs of growing fold propagation folds thrust wedge advance and cratonward migration of the platform are recorded by a deepening upward stacking pattern indicating increased regional subsidence with a limited contribution of the submarine orogen tectonic quiescence and erosional unloading lasting 29 30 ma are recorded by a shallowingupward stacking pattern and fluvial sedimentation issued from widespread sources in the emerging inner orogen the early to middle eocene basin formed as a result of pure shortening normal to the range the marine early eocene basin developed during c 2 ma by widening of a single basin provoked by the two step propagation of a basement duplex this is recorded by growth stratal patterns and coarsening upward depositional sequences indicating the increasing contribution of the emerged orogen the middle eocene continental deposits infilled two sub basins working synchronously and were transported by alluvial fans with a provenance in the inner orogen during decreasing thrust wedge advance and increasing erosional unloading

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

the influence of lateral topographic confinement on fluvial channel belt clustering compensation and connectivity lower wasatch formation and dakota sandstone utah usa fluvial channel belt clustering has recently been documented using quantitative metrics for systems dominated by autogenic controls it has long been recognized that allogenic forcing tectonic and eustatic controls can lead to confinement of fluvial systems resulting in clustering of channel belts to date no study has quantitatively documented the differences in channel belt clustering compensational stacking of channel belts and inter channel belt connectivity in unconfined and confined systems this study quantitatively compares world class outcrops of an unconfined fluvial system palaeocene lower wasatch formation with outcrops of a confined fluvial system cretaceous dakota sandstone two new methods have been developed to quantitatively document channel belt clustering and intra channel belt connectivity these new methods and other previously developed methods are used to document an increase in channel belt clustering and intra channel belt connectivity downdip in both systems additionally it was found that channel belts within the unconfined system stack more compensationally than those in the confined system these new methods and empirical relationships can be used for predicting intra channel belt connectivity and accurately modelling unconfined and confined fluvial systems in the subsurface this article is protected by copyright all rights reserved

the coupling status of alluvial fans and debris cones a review and synthesis alluvial fans and debris cones link two zones of the fluvial system e g hillslope gully systems to stream channels mountain catchment sediment source areas to main river systems or to sedimentary basins and therefore have important coupling or buffering roles these roles may be both functional and preservational the functional role includes debris cone coupling which controls sediment supply from hillslope gully systems to stream channels influencing channel morphology coupling through larger alluvial fans expressed by fanhead trenching causes a distal shift in sedimentation zones or when expressed by through fan trenching causes complete sediment by pass the preservational role stems from the fact that fans and cones are temporary sediment storage zones and may preserve a record of source area environmental change more sensitively than would sediments preserved further downsystem fan coupling mechanisms include distally induced coupling basal scour toe cutting marginal incision and proximally induced coupling fanhead and midfan trenching these mechanisms lead initially to partial coupling either extending the immediate sediment source area to the stream system or shifting the focus of sedimentation distally complete coupling involves transmission of sediment from the feeder catchment through the fan environment into the downstream drainage or a sedimentary basin the implications of coupling relate to downstream channel response fan morphology sedimentation patterns and vertical sedimentary sequences temporal and spatial scales of coupling are related and with increasing scales the dominant controls shift from storm events to land cover to climatic and base level change and ultimately to the relationships between tectonics and accommodation space finally future research challenges are identified modern dating techniques and sophisticated analysis of remotely sensed data can greatly improve our understanding of fan dynamics and should lead to better cross scale integration between short term process based approaches and long term sedimentological applications while maintaining high quality field based observations copyright 2011 john wiley sons ltd

contrasting fluvial styles of the paraguay river in the northwestern border of the pantanal wetland brazil abstract the upper paraguay drainage basin is situated mainly in west central brazil near the bolivian border flowing from north to south the paraguay is the trunk river of an alluvial depositional tract characterized by complex geomorphologic zonation that resulted from an intricate geologic evolution since the late pleistocene this paper focuses on the geomorphology of the paraguay river at the northwestern border of the pantanal wetland where two broad geomorphologic zones were distinguished north from the pantanal wetland the paraguay river flows in an aggradational fluvial plain 5 km wide and incised into older alluvial deposits the river exhibits a meandering style over most of its course but sinuosity drops from 2 2 to 1 1 near the northwest border of the pantanal wetland where the river has been forming the paraguay fluvial megafan since the late pleistocene the river deflects 90 eastward at the entrance into the pantanal changing its fluvial style because of a progressive loss of confinement downstream of the point where the river reaches lowland plains the river becomes more sinuous adopts a distributary pattern within the wetland and brings about the creation of the modern depositional lobe characterized by higher topographic gradient and active sedimentation likely linked to increased accommodation space allowing progradation fluvial discharge diminishes in the pantanal wetland because of channel overbank flow during the rainy season and frequent levee crevassing avulsion belts and channel levee complex are preserved on the floodplain as relict forms south of the convergence of the two main channels that define the taiama island a loss of gradient marks the base of the depositional lobe further downstream the paraguay river returns to a meandering fluvial style but crossing a large fluvial plain populated by hundreds of small lakes and seasonally flooded that characterizes the pantanal wetland

avulsion mechanisms on the okavango fan botswana the control of a fluvial system by vegetation a study of the avulsion of a major distributory channel on the alluvial fan 22 000 km2 in area of the okavango river in northern botswana has revealed that channels serve as arterial systems distributing water which sustains large areas of permanent swamp the channels are vegetatively confined a primary channel defined here as a channel which receives water and sediment directly from the fan apex aggrades vertically as a result of bedload deposition the rate of aggradation increases downchannel and may exceed 5 cm yr 1 in the distal reaches rapid aggradation is associated with a decline in flow velocity this initiates a series of feedback mechanisms involving invasion of the channel by aquatic plants which trap floating plant debris further reducing flow rate and causing the channel water surface to become elevated thereby increasing rate of water loss from the channel accelerating blockage and aggradation the channel ultimately fails enhanced water loss from the channel promotes the growth of flanking swamp vegetation which confines the failing channel increased flow through the swamp erodes pre existing hippopotamus trails producing a secondary channel system which overlaps but does not connect directly to the failing reach of the primary channel the region of failure of the primary channel migrates upstream accompanied by headward propagation of the secondary channel system the swamp distal to the failed primary channel dessicates and is destroyed by peat fires secondary channels are stable and not prone to blockage comparison with avulsions described in other river systems indicates that the influence of plants in the okavango river system is exceptionally strong

late pliocene grassland from olduvai gorge tanzania abstract the olduvai fossil plants documented by us in this paper are the first direct evidence for open grassland in the late neogene of africa based on macroplant remains silicified remains of herbaceous ground cover are exceptionally well preserved in situ within late pliocene sediments below the initial pyroclastic ash surge unit of tuff if in the uppermost part of bed i olduvai gorge northern tanzania published radiometric and palaeomagnetic dates place this grass layer between 1 839 0 005 ma and 1 785 0 01 ma exposed at localities on the south side of the gorge this herbaceous ground cover grew on a floodplain developed on a dried out lake bed following pronounced lake retreat of saline alkaline palaeo lake olduvai during a developing dry climatic phase sheathed basal culms rhizomes and roots are interpreted as those of one or more small mat forming grasses or less likely sedges small dicotyledonous herbs were probably also present the proximity of adjacent plants indicates a relatively dense ground cover roots extended at least 8 cm below the ground surface aerial parts of the plants were absent or were not preserved when the weathered basal culms were covered by a thin layer of brown waxy clay followed by fallout of pyroclastic ash both units were mostly eroded away prior to emplacement of a wet cool pyroclastic surge which then buried and preserved in situ remnants of the herbaceous ground cover preservation of the semi woody rhizomes implies well drained soils otherwise the plant material would have quickly rotted collections from discontinuous exposures indicate the grassland covered an area of at least a few hectares this open grassland would have provided grazing for the late pliocene fauna

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

grain size characteristics of linear dunes in the southwestern kalahari abstract linear dunes in the southwestern kalahari sand sea exhibit characteristic grain size and sorting patterns in which sands become coarser better sorted and more finely skewed from interdune to crest in addition at a regional scale sands tend to become finer and better sorted in the direction of transport these patterns can best be explained in terms of the differential movement of sand in creep and saltation populations whereby the saltating population moves more rapidly and is concentrated downwind and in dunes slower moving creep populations remain close to source areas and in interdunes the fines will tend to be concentrated in interdunes because they can penetrate between coarse grains where they are protected from further movement this type of model probably explains most grain size and sorting relationships in desert sand seas

sequence stratigraphy and marine to nonmarine facies architecture of foreland basin strata book cliffs utah u s a the desert member of the blackhawk formation and the castlegate sandstone in the book cliffs of utah and colorado were analyzed to develop a model of sequence stratigraphy and facies architecture in foreland basins stratal architecture of these rocks is controlled by two regionally extensive surfaces of incision and subaerial exposure interpreted as major sequence boundaries and at least six surfaces of incision and subaerial exposure with more limited lateral extent interpreted as minor sequence boundaries each sequence boundary is a regionally correlatable single surface major sequence boundaries can be traced from marine into proximal alluvial plain environments sequence boundaries have different physical expressions depending upon where in the basin they are observed strata beneath sequence boundaries are unrelated to strata above and time lines cannot be carried across these boundaries flooding surfaces called parasequence or parasequence set boundaries also exert an important control on facies architecture based on parasequence stacking patterns position of sequence boundaries and facies associations the desert member and castlegate sandstone have been divided into sequences with durations of 200 000 to 300 000 yr there are an order of magnitude more sequences in this interval than are predicted by the global sea level chart of haq et al 1988 the major sequences have been divided into the following systems tracts or sequence sets 1 grassy highstand sequence set below the desert sequence boundary named for the grassy member of the blackhawk formation 2 desert lowstand transgressive and highstand systems tracts between the desert and castlegate sequence boundaries 3 castlegate lowstand sequence set resting on the castlegate sequence boundary and 4 castlegate transgressive systems tract parasequence stacking patterns suggest that the grassy highstand sequence set and the desert highstand systems tract were deposited during a relative rise in baselevel the grassy highstand sequence set is punctuated by minor relative falls in baselevel both of these stratal units contain thick

ground truthing chemostratigraphic correlations in fluvial systems changes in elemental chemistry have been used to define stratigraphic correlations between wellbores in petroleum basins few publications however relate defined chemical stratigraphy to physical correlations and none have been found that do so in fluvial systems here chemostratigraphy is applied to permian fluvial sediments within the beaufort group of the karoo basin in south africa and a correlation between three logged sections is defined this correlation is tested against physically determined chronostratigraphic correlations achieved using heli lidar data to provide a high resolution correlation between two sections 7 km 4 4 mi apart and mapping of strata using google earth to produce a correlation between sections 25 5 km 15 8 mi apart the chemostratigraphic characterization that is defined using data from fine grained lithologies resulted in the recognition of eight chemostratigraphic packages with thicknesses between 50 and 250 m 164 and 820 ft over a stratigraphic interval of approximately 900 m 2953 ft two distinctive changes in geochemical composition of the coarser lithologies fluvial channel belts were seen over this interval in the two sections that are 7 km 4 4 mi apart higher resolution subdivision of chemostratigraphic packages was achieved to produce four correlative geochemical units 30 60 m 98 197 ft in thickness that provide a high resolution correlation the chemostratigraphic and chronostratigraphic correlations are in close agreement in both the 7 km 4 4 mi and the 25 5 km 15 8 mi spaced sections the thickness of the study interval and spacing of sections is analogous to published chemostratigraphy studies on subsurface sequences thereby ground truthing the use of chemostratigraphy for correlation in subsurface fluvial systems that are to some degree analogous to the beaufort group sediments of this paper

ages and stratigraphical architecture of late miocene deposits in the lorca basin betics se spain new insights for the salinity crisis in marginal basins unlike most neogene basins of the betic cordillera where the salinity crisis is dated to the messinian a contradictory tortonian dating was proposed for evaporites of the lorca basin as a consequence complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites in order to integrate the lorca basin into the geological context of the western mediterranean domain during the late miocene new sedimentological and stratigraphical studies coupled with new dating were performed which allow us to propose a messinian age for both diatomite bearing deposits and evaporites of the lorca basin these new ages challenge the idea of a tortonian salinity crisis in the lorca basin three main events of base level drop were evidenced during the messinian each event is correlated with successive steps of basin restriction shallow salina evaporites were deposited after a base level fall during the messinian before a final base level drop which led to the entire exposure of the basin this last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep mediterranean basins the reflooding which allowed the deposition of brackish deposits and a short lived marine incursion occurred at the end of the messinian base level drops occurred during eustatic falls amplified by the gradual uplift of the betic cordillera the exhumation of the tercia ridge along the strike slip alhama de murcia fault system during the messinian probably favoured the gradual restriction of the basin a discussion on correlations of main unconformities between several neogene basins of the betics is proposed suggesting a similar structural evolution at the regional scale

coupled mineral fluid evolution of a basin and high kaolinization in the sw england granites in relation to the development of the plymouth basin

the pleistocene end moraine fans controls on their sedimentation and location abstract this paper presents a model of end moraine sedimentation based on data from pleistocene ice sheet margins according to this model end moraines quite often constitute alluvial fans or coalesced fans formed at the ice margin by redeposition of supraglacial material three types of end moraine fan have been recognized those composed mainly of mass flow deposits type a equivalent to dry alluvial fan in nonglacial settings those containing both mass flow and waterlain sediments type b and those that contain mainly sorted waterlain material type c equivalent to wet alluvial fan in nonglacial settings for each type of fan several sedimentary subenvironments differentiated by distance from the ice front are identified the diagnostic processes on the end moraine fans are cohesive and cohesionless debris flows or grain flows types a and b or hyperconcentrated flows and sheetflows types b and c the type b fan seems to represent the most typical sequence in the end moraine zones but the type c fan is also quite common at the pleistocene ice sheet margins our studies also suggest that the terminal supraglacial drainage controls the type of end moraine fan sedimentary subenvironment moraine types a b c whereas subglacial hydrology and ice stream regime which determine the mobility of the ice front and larger scale conditions of sediment supply to the ice margin control the location and size of the end moraine fan

late cenozoic deformation and uplift of the western flank of the altiplano evidence from the depositional tectonic and geomorphologic evolution and shallow seismic activity northern chile at 19 30 s 1 we analyze the west vergent thrust system wts along the western flank of the altiplano in northern chile 18 s 21 s in our study area 19 20 s 19 50 s the wts consists of three thrust propagation monocline folds flexures developing growth strata the relative uplift accommodated by the flexures is rapid between 26 and 8 ma 0 1 mm yr diminishing to 0 02 mm yr after 8 ma approximately 2000 m of relative surface uplift was accommodated by the flexures since the late oligocene sedimentological and geomorphological analysis shows that westward tilting of the forearc occurred after 10 ma coeval with the shifting of deformation from the altiplano to the sub andean zone where the underthrusting of the brazilian craton would have resulted in crustal thickening surface uplift in the orogen and westward ductile subcrustal flow forearc tilting is accommodated by east vergent thrusts ets issued from the benioff zone beneath the central depression emerging into the western cordillera contributing 500 1400 m of surface uplift the wts connects the ets in the brittle ductile crustal transition 25 km depth continuing farther east as the altiplano low velocity zone configuring the western altiplano as a crustal scale fault bend fold forearc tilting would be caused by westward ductile flow in the lower crust pushing the rigid forearc in the ets meanwhile between 19 s and 21 s the wts accommodates dextral strike slip and 3 km of n s shortening occurred in the coastal cordillera transcurrence and strain partitioning are probably the result of slight plate convergence obliquity strong coupling within the interplate zone westward continental concavity and high elevation opposing horizontal contraction

late quaternary tectonics of the vallo di diano basin southern apennines italy italian ministry of university and research project firb research and development of new technologies for protection and defence of territory from natural risks w p c3 crustal imaging in italy