slip along the sultanhani fault in central anatolia from deformed pleistocene shorelines of palaeo lake konya and implications for seismic hazards in low strain regions

fluvial response to climate change during and after the last glacial maximum in central anatolia turkey abstract fluvial response to climate change during and after the last glacial maximum lgm included incision aggradation phases recorded in sediment cores from the valley floor of the kizilirmak in central anatolia a numerical chronology was established by ams dating of fluvial sediments and ar ar dating of a basalt sample capping the youngest terrace late pleistocene terrace indicating that the main incision phase was completed at the end of the lgm the succeeding aggradation phase in the valley took place from the end of the lgm onwards it appears that the major climatic transition from the lgm to the late glacial gave rise to aggradation in the fluvial system and this event seems to be consistent with the timing of the regression phase of pluvial lakes and the termination of paleoglacier advances in the high mountains of anatolia this study of fluvial systems in anatolia indicates that the coldest periods are not always characterized by fluvial aggradation

event frequency and landscape stability on the floodplain systems of arid central australia abstract central australian floodplains contain landforms suggesting activity at three scales a set of large sand sheets sand threads and megaripple covered channels related to a few enormous floods the contemporary floodplain which consists of channels and levees floodouts unchannelled floodplains and floodbasins and erosion cell mosaics which result from local redistribution of sediment classical floodplain models do not fit these systems which behave more like low angle alluvial fans because they continue to accumulate sediment the sedimentary history of the central australian floodplains suggests that deposition in the last 10 000 years has been dominated by a few gigantic floods these events are not represented in the published slackwater deposit record but morphological evidence for them can be found in bedrock gorges as well as on floodplains since the last major flood channel levee systems have been growing slowly upwards and outwards and outwards from the mountain ranges away from these systems sediment supply is limited and the dominant process is local reworking this has intensified since the arrival of europeans 100 years ago and also as a result of increased flooding due to variations in rainfall

evaluating controls on crevasse splay size implications for floodplain basin filling abstract although crevasse splays are often considered important contributors to floodplain basin filling evidence from modern and ancient fluvial deposits indicates that they may not play a significant role in all river systems in order to better understand controls on the abundance and scale of crevasse splays produced in fluvial systems we used aerial photography to observe crevasse splay deposits along three rivers and conducted a targeted numerical modeling study to explore factors which promote widespread crevasse splay deposition on fluvial floodplains results demonstrate that splay size does not always scale directly with channel size or discharge and that hydrodynamic factors primarily sediment size and floodplain drainage conditions play a significant role in determining whether a fluvial system is likely to produce large floodplain filling splays this work suggests that widespread crevasse splays demand both a large supply of relatively coarse suspended sediment and a steep water surface slope away from the channel across the floodplain without both these conditions the role of crevasse splays in flood basin filling is limited

river network evolution and fluvial process responses to human activity in a hyper arid environment case of the tarim river in northwest china abstract the tarim river the longest dryland river in an extremely arid region of china has undergone ever increasing human impacts over recent centuries particularly since the late 1950s during which time large scale land reclamation in the basin has taken place historical literature maps gauged hydrological data and satellite images were analyzed to examine how the river network evolution in the basin and the fluvial morphology of the main stem of the tarim river have responded to human influences the results demonstrate that human activity inhabitation land reclamation and water resources development in the basin have had significant impacts on the tarim river causing major changes in runoff and sediment transport river network composition and river morphology especially planform patterns gauged hydrological data from the past five decades presented an obvious reduction in runoff and sediment load in the tarim river even though the runoff from source tributaries exhibited a gentle increase the annual occurrence of low flow events showed a significant increase and the occurrence of moderate high flow events followed a gentle decrease the river network system has disintegrated from a historically quasi centripetal system with nine tributaries into several isolated river systems which have mainly developed since the 20th century currently only four tributaries flow into the main stem river which is dominated by braided channel patterns in the upper reaches and meandering typically with distorted bends patterns in the middle reaches the braided reach was in aggradation and in high lateral mobility the mean width and braiding intensity of the braided reach followed a gentle decrease mainly due to the reclamation of river flood plains to farmlands and embankments the sinuosity index of the current tarim river channel is distinctively lower than the indexes of the old channels that were abandoned decades or centuries ago even though the sinuosity index of the meandering channel followed a gentle increase in recent decades due to the increased occurrence of low flow events human activity has changed the natural fluvial processes and morphology of the tarim river and has reduced the diversity of the river network system

forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction tooth s nanson g c 2004 forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction geological society of america bulletin 116 7 8 802 816 rae2008

anabranching rivers their cause character and classification anabranching rivers consist of multiple channels separated by vegetated semi permanent alluvial islands excised from existing floodplain or formed by within channel or deltaic accretion these rivers occupy a wide range of environments from low to high energy however their existence has never been adequately explained they occur concurrently with other types of channel pattern although specific requirements include a flood dominated flow regime and banks that are resistant to erosion with some systems characterized by mechanisms to block or constrict channels thereby triggering avulsion the fundamental advantage of an anabranching river is that by constructing a semi permanent system of multiple channels it can concentrate stream flow and maximize bed sediment transport work per unit area of the bed under conditions where there is little or no opportunity to increase gradient on the basis of stream energy sediment size and morphological characteristics six types of anabranching river are recognized types 1 3 are lower energy and types 4 6 are higher energy systems type 1 are cohesive sediment rivers commonly termed anastomosing with low w d ratio channels that exhibit little or no lateral migration they are divisible into three subtypes based on vegetative and sedimentary environment type 2 are sand dominated island forming rivers and type 3 are mixed load laterally active meandering rivers type 4 are sand dominated ridge forming rivers characterized by long parallel channel dividing ridges type 5 are gravel dominated laterally active systems that interface between meandering and braiding in mountainous regions type 6 are gravel dominated stable systems that occur as non migrating channels in small relatively steep basins anabranching rivers represent a relatively uncommon but widespread and distinctive group that because of particular sedimentary energy gradient and other hydraulic conditions operate most effectively as a system of multiple channels separated by vegetated floodplain islands or alluvial ridges

channel geometry bed material and inferred flow conditions in ephemeral stream systems barrier range western n s w australia streams draining the barrier range uplands in arid western n s w are ephemeral and undergo rapid channel contraction away from the uplands as a consequence of transmission loss these processes are documented on the basis of surveys of channel form and bed material at sequential sites located along the contracting lowland reaches of two representative streams channel width and depth display considerable fluctuation downstream but cross sectional area and maximum bed surface grain size decline in a very regular manner flood discharge estimated from the channel capacity and predicted critical and mean flow velocities also declines regularly the trends are well fitted by log linear models and are reported in terms of a half distance the channel length in km over which the value of a morphometric parameter declines by 50 per cent rates of channel contraction and transmission loss are inferred to be inversely proportional to the volume of flow delivered from the upland section of the drainage basin unusual channel characteristics including extensive tree growth in the bed make application of ordinary flow equations difficult because friction factors cannot be estimated with confidence systematic changes in the nature of the bed surface in contracting streams such as those studied here also have implications for the application of critical velocity equations and highlight a need for further study of desert channels

environmental and climatic changes during the pleistocene holocene in the bor plain central anatolia turkey abstract the bor plain lies in a round shaped flat basin in the southern part of the central anatolia it is located at the southeastern end of the tuzgolu fault zone which is the nw trending active normal fault zone and extends between the north of the tuzgolu lake tuz at nw and at kemerhisar nigde se according to geomorphologic and geologic studies this plain was occupied by lake during the pleistocene the first high lake level terrace and the latest high lake level terrace were determined at 1170 1150 m and 1110 1100 m respectively pleistocene and holocene alluvial and lacustrine deposits are composed of claystone sandstone mudstone limestone and paleosol units these units contain mostly calcite and clay minerals palygorskite smectites illite and chlorite and lesser amounts of quartz phillipsite cristobalite feldspar plagioclase goethite and muscovite the results of this study are compared with the results of sedimentologic and dating obtained from konya eregli plain according to this comparison 1 the latest high lake terraces were dated 23 000 to 17 000 yr bp the high lake level was changed 2 sandy level with carbonate determined in stratigraphy indicates that a dry phase dominated after 17 000 yr bp and 3 black and brown muds indicate that the shallow freshwater lacustrine phases and sandy levels were formed between 12 500 and 1100 yr bp during late glacial stage paleosols muddy levels and shallow lake deposits were formed in the environment of the holocene during 6000 5000 yr bp carbonate rich sandstone and mudstone deposits show that this period was interrupted by the second drought in the latest stage temperatures have increased due to hot climate conditions and salinization has begun and been still ongoing

vegetation and climate of anatolia and adjacent regions during the last glacial period abstract reinterpretation of vegetation and climatic conditions of anatolia and neighboring regions during last glacial 30 15 cal ka bp have been done using a non quantitative biomization approach based on previously published plant functional types the results suggest that the climate was cold and humid before 25 cal ka bp and also during the period 23 19 cal ka bp except east anatolia forest vegetation was 80 90 of the land cover in the northwestern anatolia and black sea coast and 50 60 along the mediterranean coast at the same period during heinrich event 2 from 25 to 23 cal ka bp steppe vegetation dominated the anatolian region due to the sudden change to very cold and arid conditions approximately between 18 and 16 cal ka bp in the late glacial during heinrich event 1 a brief interval of cold and arid conditions resulted in weaker steppe vegetation over some part of anatolia around at 15 cal ka bp suitable climatic conditions for forest vegetation prevailed across a great part of anatolia except for eastern anatolia and western iran which are highlands

composition and architecture of braided and sheetflood dominated ephemeral fluvial strata in the cambrian ordovician potsdam group a case example of the morphodynamics of early phanerozoic fluvial systems and climate change abstract two fluvial facies associations braided and ephemeral fluvial are recognized in strata of the cambrian ordovician potsdam group in the ottawa embayment and quebec basin in northeastern north america braided fluvial sedimentation was dominated by the migration of coarse grained sandy dunes and rare unit bars and local gravels that built up low relief 0 4 5 m thick downstream accreting compound bars in very wide and shallow braided channels rare meter scale confluence scours incision and filling of decimeter thick bypass channels and thin 7 cm overbank deposition also occurred ephemeral fluvial sedimentation was dominated by the progradation of lobate terminal splays most of which were deflated and or reworked into thin 10 95 cm sheets by eolian processes during the long recurrence intervals between floods these strata were locally incised by rare 0 3 1 9 m thick scour filling high energy supercritical bedform strata and decimeter thick bypass channels both braided and ephemeral fluvial deposits consist of meter scale stacked high order stratal units separated by horizontal laterally extensive surfaces recording the recurring buildup avulsion and finally abandonment of channel belts in braided fluvial strata of the potsdam the dominance of thin 2 m elongated compound bars with low relief 5 bar margins and internal accretion surfaces 15 suggest that braided channels and in channel compound bars expanded laterally with negligible increase in flow depth during periods of increased discharge in the absence of bank stabilizing vegetation similar to other examples of the pre vegetated sheet braided style however in areas where bedrock topography inhibited the lateral expansion of channels thicker compound braid bars 1 2 3 5 m with higher relief accretion surfaces up to 35 like those observed in post silurian and modern systems preferentially formed in relatively deep channels ephemeral fluvial deposits here are similar to ephemeral examples throughout geologic history in that they mostly comprise poorly confined sheet like terminal splays that accumulated in topographic lows however compared to several post silurian examples strata in the potsdam exhibit considerably more eolian reworking of splays and preservation of supercritical bedform strata a manifestation of greater rates of surface water infiltration due to a lack of sheltering by rooted plants and propensity for unconfined flooding finally in the upper part of the potsdam two regional ephemeral fluvial units are interstratified with two braided fluvial units providing evidence for shifts in regional climate the sharp areally extensive surfaces that separate these fluvial systems are interpreted to approximate time lines and therein provide a means for relative and absolute chronostratigraphic correlation these changes are correlated with documented late cambrian to earliest ordovician global climate fluctuations with semiarid conditions and related ephemeral fluvial systems corresponding to global cooling events at ca 491 and 487 ma

age palaeoenvironments and climatic significance of late pleistocene konya lake turkey abstract the konya basin a closed depression at the southern margin of the anatolian plateau contained a shallow but extensive lake during the late quaternary nearshore sands and gravels containing dreissena shells form prominent depositional terraces around the basin edges at elevations between 1005 and 1020 m and the highest has been dated at more than 30 000 yr b p the last major phase of limnic sedimentation occurred between 23 000 and 17 000 yr b p after which the lake fragmented into a number of subbasins or secondary depressions which evolved to become either marshes or playas a final expansion of these residual lakes has been dated to ca 11 000 yr b p in one secondary depression archaeological and other evidence indicate that only minor lake level fluctuations occurred during the holocene the dominant sedimentary process over the last 10 000 years has been alluviation at the basin margin the konya sequence confirms that the most recent period of high lake levels in the northern near east was of the last glacial age the palaeolakes of anatolia and iran were however more a product of reduced evaporation brought about by temperature depression than of changes in precipitation and thus belie their often used description as an indicator of pluvial climatic conditions

the sinuosity of alluvial river channels in the seasonally wet tropical environment case study of river elemi southwestern nigeria abstract investigations carried out in the elemi river basin southwestern nigeria suggest that small intermittent streams in the seasonally wet humid tropics have a tendency to develop very sinuous channels characterised by compound and highly convoluted loops analysis of arc symmetry and the repetition of symmetry indicate that the 153 bends along the 39 3 km long river are not true meanders as objectively defined by brice in 1964 the dominant factor controlling the degree of sinuosity is channel bank resistance to lateral erosion as influenced primarily by the nature of riparian vegetation and secondarily by the percentage silt clay in channel bank sediment the influence of bank vegetation is particularly pronounced in view of the preponderance of low flow discharges high proportion of suspended sediment and gentle bed slope the high density of riparian trees account for the relatively short length of the straight reaches and the high frequency of bends compound and convoluted loops the implications for river management of the inherent instability of small channels in seasonally wet humid tropical environments and of the considerable channel bank erosion which occurs at the numerous bends are briefly highlighted

terminal fans and the ganga plain tectonism a study of neotectonism and segmentation episodes of the indo gangetic foreland basin india abstract the study of spatial and temporal distribution of holocene terminal inland fans in the indo gangetic foreland basin suggests that the segmentation of the basin was initiated at 9 3 ka and continued up to 0 75 ka in three distinct episodes the earliest episode 9 3 7 3 ka was exclusively confined in the upper gangetic plain this episode covers 29 of total time span and contributes 13 of total faults including their reactivations development of six faults associated with terminal fans having large age gaps indicate relatively slow rate of faulting activities in the early holocene the second faulting episode was started at 6 4 ka and continued up to 2 3 ka covering 60 time of the total time span and contributed 69 of total faults including their reactivations though in most of the time the faulting events were confined in the upper gangetic plain but development of few faults in the middle gangetic plain in the middle of this episode shows a transitional shift of tectonic front from the upper to the middle gangetic plain the third faulting episode 1 5 0 75 ka is mainly confined in the middle gangetic plain this episode covers 11 time of the total time span and contributes 18 of faults out of the eight faults seven of them are in the middle gangetic plains though these three episodes have contributed in segmentation of the gangetic plains but the second episode was responsible for major segmentation of the region two major tectonically stable periods 7 3 6 4 ka and 2 3 1 5 ka and three minor periods in duration of 0 5 ka have been observed in the region episodic development of faults in individual tectonic blocks indicates that the stress distribution along the plains is non uniform which can also be correlated to the adjacent corresponding segments of the himalayan tectonics it has been observed that in each fault bounded block the faulting events start slowly and later becomes more frequent previous work pointed out four tectonically active episodes between the ghaghara and kosi rivers with the oldest faulting event at 7 89 ka however the region west of it i e between the ghaghara and ghaggar rivers which includes rest of the upper gangetic plain shows that neotectonic activities are earlier than 7 89 ka the oldest faulting event observed by previous study the youngest faulting episode of the present study coincides with that of previous study and suggests that the region between the gandak and kosi rivers is tectonically most active at present the tectonically stable periods pointed out in the previous study between the ghaghara kosi region is occupied by the faulting events in the upper gangetic plains hence instead of four tectonically active episodes the whole ganga plain witnesses three segmentation episodes with two major intervening stable periods the change of orientation of the faults in the plain may be correlated to directional change of indian plate motion differential convergence and upliftment rates along the himalayan front and the spatial extension of subsurface precambrian basement ridges into the plains

the holocene evolution and geomorphology of a chain of ponds southeast australia establishing a physical template for river management abstract chains of ponds are a discontinuous river type found in australia their unusual morphology important ecological functions and increasing rarity make them a priority for conservation and yet very little research has investigated their physical structure behaviour and evolution this paper reconstructs the holocene evolution and environmental history of crisp s creek a headwater chain of ponds in the southern tablelands of nsw australia this history establishes baseline information on the physical template that can be used to assess a range of other biophysical processes and design appropriate river rehabilitation and management strategies for these rivers sedimentary aggradation began in the late holocene at least 3 7 1 3 ka broadly synchronous with aggradation phases at other sites in southeast australia since european arrival in the nineteenth century parts of the river incised destroying intact ponds and smothering formerly swampy floodplains with post incision alluvium however sections unaffected by incision provide a rare opportunity to examine the evolutionary trajectory of an intact variant of these rivers this research deepens our understanding of the evolutionary context for contemporary river behaviour as relevant for designing appropriate and effective conservation and rehabilitation strategies for chains of ponds

desert stream sequences in the sinai peninsula abstract desert sedimentary sequences of late quaternary age mainly subrecent were studied in several stream segments of wadi el arish northern sinai egypt morphologically these stream systems can be divided into three types confined open and terminal floodplains the confined and open floodplain sequences consist of repeated flood originated sedimentation units each around 50 cm thick an idealized sequence begins with mud clasts or either sand or pebble bearing plane beds reflecting the upper flow regime during peak flow stage of the flood these are overlain by cross bedded sands and climbing ripples lower intensities of the flow result in sequences beginning with cross stratified sands cracked mud layers represent the final desiccation stage of the flood in comparison with th confined floodplain units the open up to thousands of meters wide floodplain units are thinner 20 50 cm the horizontal strata are less developed and the mud layers are thicker the terminal floodplain which in the modern examples is a flat a few kilometers wide is the area where the remaining flood energy dissipates and therefore the resultant sedimentation units axe very thin usually less than 20 cm and consist of either finely laminated massive mud or cross laminated fine sand the wadi systems studied are in close geographic relationship with eolian dune fields nevertheless the wadi sequences consist of waterlaid units only

a multiproxy lake record from inner mongolia displays a late holocene teleconnection between central asian and north atlantic climates in order to study how the holocene central asian climate is coupled to the global climate system a 4 24 m long lake core from western inner mongolia in china was studied using a multiproxy approach sedimentology and geochemical parameters such as gypsum and dolomite content presence of lakeshore sand changing to aeolian sand and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late holocene aridification is linked to the southward retreat of the northern boundary of the asian summer monsoon leaving central asia under the influence of the westerly belt the weakening of the asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation the weakening summer insolation also likely increased the intensity of the siberian high pressure system further promoting aridification of central asia on a shorter time scale the multiproxy record shows the climate to have been relatively dry during the medieval warm period ad 800 1100 with the ensuing humid environment at the end of this period gradually turning to become extremely dry ad 1100 1550 at the little ice age maximum switches in the north atlantic oscillation caused these changes through a teleconnection in the form of westerlies these westerlies provided most of central asia s moisture after the retreat of the asian summer monsoon the central asian climate therefore corresponds closely with late holocene european climate changes

palaeoenvironmental reconstruction of the eastern part of the karapinar ayranci coal deposit central turkey abstract regional tectonic movements during the neogene period resulted in the development of several fault controlled basins in central anatolia many of these basins host economic coal deposits the recently discovered karapinar ayranci coal deposit is the most important one due to its large reserves c 1 8 gt and location in the vicinity of important urban areas the paper aims to reconstruct the palaeoenvironmental conditions before during and after coal formation in the eastern part of karapinar ayranci deposit by means of coal petrography and mineralogical data combined with sedimentological and palaeontological data the basinal infilling consists of mainly lacustrine fluvial and alluvial sediments the coal seams comprise several beds intercalating with claystone mudstone and marl the coal being lignite in rank displays high ash yield 36 4 wt on dry basis and high total sulphur content avg 7 7 wt on dry ash free basis facies diagrams and lithological features of the coal seams suggest that peat was accumulating under pure telmatic to limnotelmatic conditions however peat accumulation ceased several times due to a rise in water level therefore clastic e g quartz clay minerals and authigenic e g pyrite mineral contents are variable along the seam profile gastropod and ostracod fauna points to freshwater conditions in the palaeomire high total sulphur and evaporite mineral e g halite contents usually point to brackish saline conditions during peat accumulation however in case of the karapinar ayranci deposit high sulphur contents can be related to sulphate rich karstic aquifer which contributed to the palaeomire water supply

physicochemical mineralogical and geochemical characteristics of lacustrine sediments of the konya basin turkey and their significance in relation to climatic change abstract physicochemical mineralogical and geochemical characteristics of 279 highly calcareous lacustrine sediment samples obtained from a 30 m drilling core in the western part of the great konya basin turkey were studied the sediments have a predominance of silt and clay fractions with a median diameter of 3 5 m vertical changes of the amounts of water soluble components gypsum carbonates and non salt minerals such as quartz feldspars and layer silicates in the sediments suggest that there were climatic changes in the konya basin the dominant clay mineral is smectite followed by kaolinite illite and palygorskite the oxygen isotopic 18 o ratios of six quartz samples from the konya sediments a terra rossa soil beside lake beysehir golu and paleosols at the foot of mt erciyes da ranged from 18 1 to 20 6 the dominant clay minerals and 18 o ratios suggest that part of quartz and coexisting layer silicates is of long range transported and or local aeolian dust origin from arid and semi arid regions such as north africa israel and the surroundings the relatively high deposition rate might be due to aeolian dust input and or the sediment input introduced by the rivers such as the carsamba river from the toros taurus mountains the vertical distributions of electro conductivity amounts of water soluble and non salt components and the gypsum content of the sediments suggest that gypsum rich layers were formed under shallow saline waters possibly associated with warm to hot and dry environments such as the last interglacial epoch and the early holocene the sediments characterized by relatively high amounts of non salt sediments in which gypsum did not accumulate could be deeper water phases formed under the cold and or wet environments such as the glacial epochs

fluvial connectivity and climate a comparison of channel pattern and process in two climatically contrasting fluvial sedimentary systems in south africa abstract the aim of this research was to investigate the dynamics of valley formation sediment delivery and channel pattern in two climatically contrasting fluvial sedimentary systems in south africa each system comprised a network of headwater valley fills and floodplains underlain by sedimentary karoo supergroup rocks that are intersected by resistant dolerite dykes and sills the seekoei river floodplain and gordonville valley fill site in the great karoo however experience less than half the annual precipitation of the nsonge river floodplain and hlatikhulu valley fill in the kwazulu natal drakensberg foothills furthermore rainfall is more variable in the karoo despite climatic differences headwater valley fills were geomorphically similar in contrast floodplains in the two regions were vastly different even when the same downstream control a resistant dolerite intrusion crossing the drainage line was considered upstream of a dolerite dyke the nsonge river is highly sinuous and located in a wide floodplain that has been carved by lateral planation of the underlying bedrock in comparison the seekoei river located upstream of a dolerite sill is discontinuous and characterized by floodouts and avulsing distributaries that undergo periods of bedrock incision followed by infilling it is likely that this disparity is caused by the inability of infrequent unsustained flows to develop meanders and thus adjust the channel planform to changes in discharge sediment load and valley slope flow variability thus exercises a strong control on channel pattern and causes floodouts in headwater settings and the semi arid karoo floodplain as a result sediment transport in the seekoei river is likely to be episodic and net retention of sediment in the semi arid floodplain is greater than in the sub humid nsonge river floodplain where sediment depth is limited

late holocene erosion in nw anatolia from sediments of lake manyas lake ulubat and the southern shelf of the marmara sea turkey abstract this paper deals with modern and ancient sedimentation in fresh water lakes and the marine shelf of the southern marmara region nw anatolia turkey most of the information has been obtained from monitoring of suspended load discharged into two lakes manyas and ulubat in the last 45 years and from 8 to 11 m thick lacustrine sediments in addition to radiocarbon dated shelf sediments this allows a holistic approach to the drainage basin denudation over time the results show that the sedimentation rates in the lakes were low 0 22 cm year 1 from 4000 to 2000 years bp and then they increased 0 29 cm year 1 up to sub recent times and reached 0 44 cm year 1 in the last century it is suggested that deforestation created high rates of sedimentation in the basins and or strong denudation of the region during the late holocene this study also shows that for shallow freshwater lakes the calculation of sedimentation rates must include fine particles lost by the outlets and coarse grained bed load deposited on their shores in addition a high rate of sedimentation has been created by short but repetitive intense depositions during the last century particularly during the last 45 years the rate of sedimentation or denudation has increased dramatically in nw turkey the two world wars and mismanagement of the land had important local effects by increasing deforestation and resulting in the present erosive conditions

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

early holocene basinal sediments of the dakhleh oasis region south central egypt abstract twenty samples of artifactual ostrich eggshell and hearth charcoal firmly to loosely associated with basinal lacustrine playa and sand sheet sediments in the dakhleh oasis region of south central egypt yield radiocarbon ages between ca 8800 and ca 4700 yr b p the sediments record variable sedimentary responses to an early holocene pluvial interval in this virtually rainless region differences of hydrogeology and morphometry among and within basin types complicate paleoclimatic interpretation

anabranching rivers on the northern plains of arid central australia anabranching rivers are a widespread feature of the northern plains in the alice springs region of central australia but their unusual characteristics previously have not been described on the northern plains anabranching occurs on rivers transporting bedloads of coarse sand and gravel and is characterised by channels of variable size and shape which occur within a broader typically well defined channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands ridges and islands are either depositional features formed in situ by accretionary processes or erosional features formed by excision from once continuous areas of floodplain vegetation plays a key role in the initiation survival and growth of depositional forms through its influence on flow sediment transport and ridge and island stability anabranching is also related to the influence of tributaries for some large rivers alternate from single thread to anabranching along their length in response to tributary inputs of water and sediment tributary inputs occur during flow events that are either independent from or in concert with floods in the trunk channel ridges and islands form in association with tributaries as a result of various hydrological depositional and erosional processes including irrigation of enhanced numbers of in channel trees and resulting lee side sediment accretion floodplain scour and the formation and maintenance of deferred junction tributaries the change from single thread to anabranching downstream of tributary junctions occurs in the absence of any significant change in channel gradient or degree of channel confinement on the northern plains anabranching appears to be a stable river pattern that helps to maintain the throughput of relatively coarse sediment in low gradient typically 0 0005 0 002 channels characterised by an abundance of within channel vegetation and subject to declining downstream discharges

bedforms and sediment transport processes in the ephemeral streams of kobo basin northern ethiopia abstract bedforms and channel deposits architecture were studied in the ephemeral streams of the structural basin of kobo in northern ethiopia the froude numbers calculated at bankfull flow for a few of the study reaches are in agreement with the extensive occurrence of horizontal planar lamination small bedforms not previously reported in the literature are found and described as produced mainly by scouring rather than accretion processes equations to predict particle entrainment proved that large individual boulders standing scattered on the stream bed can be transported at bankfull flow for long distances direct inspection of the old alluvium and the modern channel deposits allow to identify a typical arrangement within a single bed consisting of divisions with specific characteristics this model of division association is explained in terms of vertical distribution of shear stress and compared with hyperconcentrated flow and traction carpet models in contrast with recent theories of flat asymmetrical bed waves progradation at froude numbers close to unity

brasiliano crustal extension and emplacement fabrics of the mangerite charnockite pluton of umarizal north east brazil abstract shear zone kinematics and anisotropy of magnetic susceptibility ams data have been used in a brasiliano pan african fayalite clinopyroxene orthopyroxene syenite of umarizal ne brazil in order to reveal its emplacement mechanisms the pluton is located at the intersection of two major shear zones a ne trending transcurrent portalegre shear zone psz and a nw to e trending frutuoso gomes shear zone fgsz the fgsz dips gently ne in its nw trending branch and n in the e trending branch asymmetric porphyroclasts and s c shear planes observed in mylonitic gneisses along the fgsz point to a top to the east extensional movement hysteresis and low field susceptibility measurements on mangerites and charnockites indicate that magnetic susceptibility is principally carried by multidomain magnetite in the core of the pluton the magnetic anisotropy is weaker p f ams ellipsoids the magnetic anisotropy increases south westward p 1 10 approaching the fgsz and the ams ellipsoid becomes dominantly disc shaped f l magnetic lineations plunge gently to nw in the western part of the pluton and to ene on the east the absence of steep lineations except around a large xenolith in the center of the pluton exclude the presence of magmatic feeding zones at the actual level of exposure foliations are roughly parallel to the pluton contact but most of them dip moderately towards north east in the sw border the magnetic foliation is parallel to the mylonitic foliation displayed in the fgsz although emplaced within migmatized host rocks the kinematics of the shear zones and the magmatic fabric pattern rule out a buoyancy driven diapiric emplacement of the pluton syn magmatic shear deformation associated with e w crustal stretching accounts for the fabrics of emplacement recorded in the umarizal pluton

flood channel morphology of a quiet river the lachlan downstream from cowra southeastern australia abstract detailed geomorphic mapping and sediment analyses of floodplain features were undertaken on a 30 km reach of the lachlan river in southeastern australia the reach is located in the transitional zone between the southern great dividing range and extensive alluvial plains to the west the channel resembles other fine grained low energy alluvial channels it is muddy narrow and deep and meanders irregularly it contains fine grained accreting bench deposits and in places is influenced by inherited fluvial forms both of which indicate long term channel stability by contrast the floodplain exhibits features that have been attributed elsewhere to catastrophic flood flows including elliptical scour scars swirl pits cobble and gravel deposits large chutes and chute bars zones of floodplain stripping flood levees and multiple flood channels sorting and texture of floodplain sediments generally increases with height above the bed although deposits are variable and poorly sorted indications of recent fluvial activity at several levels above the bed are confirmed by aerial photographs dating from 1954 although changes to the channel position have been small the alluvial facies model displays a compound floodplain in which a stable low energy channel is inset within a high energy flood dominated floodplain this interpretation is consistent with streamflow and documentary evidence of recurrent large floods since 1839 which have a return period of

digital elevation models for topographic characterisation and flood flow modelling along low gradient terminal dryland rivers a comparison of spaceborne datasets for the rio colorado bolivia abstract many dryland rivers are terminal systems with small channels undergoing prominent downstream size reductions before ending on channelless floodplains in wetlands or at playa margins spaceborne digital elevation models dems provide potential for assessing subtle topographic and hydrodynamic changes in these low gradient low relief settings but challenges are posed by limitations in vertical and horizontal accuracy this study evaluates the use of different spaceborne dems for topographic characterisation and flood flow modelling of the low gradient

spatial and temporal distribution of inland fans terminal fans between the ghaghara and kosi rivers indicate eastward shift of neotectonic activities along the himalayan front a study from parts of the upper and middle gangetic plains india abstract neotectonic deformation in the indo gangetic plains is primarily manifested by surface ruptures caused by both normal faults and thrust splays the topographic breaks along these faults provide suitable sites for the formation of inland fans terminal fans on the down thrown blocks as these depositional features invariably form along the faults contemporaneously or soon after faulting they have widely been used as potential geomorphic markers in mapping faults in the flat gangetic plains based on this association infrared stimulated luminescence irsl dating of the fans has successfully been used for dating the faulting episodes in the gangetic plains thus the spatial and temporal distribution of inland fans terminal fans suggests migration of faulting activities from west to east with time and successive faulting events occur over periods of several hundreds of years to 10 3 years in the present study the correlation of eighteen dated inland fans terminal fans aligned along the faults and using the surficial and buried soil profiles suggests four deformation episodes 7 89 7 30 ka 5 84 3 99 ka 3 18 2 73 ka and 1 41 0 75 ka in the region between the ghaghara and kosi rivers in the gangetic plains these deformation episodes were witnessed by the development and reactivation of the extensional normal faults transverse to the himalayan frontal thrust hft in the ghaghara rapti interfluve and the thrust splays parallel sub parallel to the hft in the gandak kosi interfan regions the rapti gandak region in the middle serves as a transition zone in between the interfluve and the interfan region and shows both types of fault development at different times six inland fans terminal fans in the ghaghara rapti interfluve were formed between 7 89 and 2 73 ka in three deformation faulting episodes two in each phase the broad age difference between those and strongly developed soils suggests the faulting activities to be less frequent in this region the fan building episodes in the gandak kosi interfan region started at 4 92 ka by the initiation of thrusting activities out of eight inland fans terminal fans five of them were formed during 1 41 0 75 ka in association with various thrust splays these depositional features are characterised by a narrow age gap and weak to no surface soils which indicate early burial by high sediment supply from frequent thrusting activities segments of the plains having a high low population of inland fans terminal fans of narrow broad age gaps and with relatively weakly strongly developed soils lie close to or opposite to the segments having the highest lowest rate of convergence and upliftment of the himalayas along the hft

downstream changes in dryland river channels the northern plains of arid central australia abstract many dryland rivers undergo marked downstream changes owing to factors such as infrequent floods flow transmission losses and typically few tributary inflows beyond the headwaters along the sandover bundey sandover bundey and woodforde rivers on the northern plains of arid central australia downstream channel changes are broadly similar in upland zones small rocky channels transporting sand and gravel gradually increase in size before entering piedmont zones where channels and narrow floodplains are confined by bedrock alluvial terraces or aeolian dunes in lower gradient lowland zones channels and floodplains remain confined and in the absence of tributary inflows channel cross sectional areas and discharges decrease downstream confining landforms are not present in floodout zones which results in splay formation increased floodplain widths and marked overall downstream decreases in cross sectional areas eventually channelised flow and bedload transport terminate although occasional large floods continue across extensive unchanneled alluvial surfaces termed floodouts these broad similarities apart downstream changes along the three rivers differ in detail the sandover is largely a single thread channel whereas many reaches of the sandover bundey and woodforde are anabranched on the small woodforde river downstream decreases in parameters such as cross sectional area and width are roughly linear on the larger sandover and sandover bundey downstream changes are more irregular particularly through the floodout zones where there are marked fluctuations in widths depths and bed slopes the irregular downstream changes typical of the lower reaches of these large rivers may be due to the reduced influence of vegetation on bankline stability and width adjustment relative to that of smaller rivers on the northern plains as in other drylands complex interactions between discharge sediment transport slope patterns of tributary drainage bank sediment type and vegetation result in variable patterns of downstream channel change