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

fluvial gravel facies architecture of late pleistocene age at po chue tam lantau island hong kong tectonic versus climatic control abstract a cross section of fluvial gravel deposits of late pleistocene age exposed at po chue tam lantau island hong kong contains two facies a lower facies of planar cross bedded gravel gp and an overlying facies of clast supported massive gravels gcm the gp gravels include five gravel couplets each couplet consists of a clast supported coarse gravel dominated bed and an overlying clast supported fine gravel dominated bed with a discrete bounding surface tectonic uplift predating the last interglacial transgression produced a large amount of detritus in the source area excessive peak rainfall intensity resulting from enhanced seasonality of monsoonal precipitation in the following glacial period triggered catastrophic floods which transported mature detritus in large quantities into a fault controlled piedmont basin the gp gravels were deposited by pulsating flood flows in relation to kinematic waves of particles bedload sediment was longitudinally sorted and segregated into a train of gravel sheets they draped over each other and accreted laterally due to expansion of flow producing planar cross stratifications that are characteristic of recurrent couplet style coarse fine cross beds in contrast gcm gravels were laid down as a single nearly horizontal bed by a catastrophic flood that was not subject to flow pulsation

rapid incision of a small coarse and steep fan delta in response to base level fall the case of nahal qedem the dead sea israel the dead sea has been continuously dropping 0 4 1 0 m yr 1 since the middle of the 20th century and thus provides a unique field laboratory for studying in real time the response of drainage systems to a non tectonic base level fall the aim of this work is to study the short term ongoing erosive response to a rapid base level drop in a small steep fronted erodible fan delta setting the work explores the controls of the steep qedem fan delta guided by its clinoform structure on its incision longitudinal profiles of the fan delta and of its entrenched channel were measured in the field sedimentary facies changes fluviatile shallow lacustrine and beach were followed along exposures the existence of large boulders provided an opportunity to examine the uncertain role of armouring and boulder flux on incision the field study was combined with digital elevation models dems that were extracted from pairs of overlapping aerial photos maps of erosion and deposition were prepared using a change detection algorithm the longitudinal profile of the entrenched channel was found to be steep and linear the outlet temporarily hangs elevated and ungraded above the retreating lake level indicating years without incision flow events which cause lags in response to the rapid lake level drop in spite of the large boulders the small drainage basin and precipitation volume over the basin of the qedem the recorded vertical incision rates in the unconsolidated sediments are as high as 0 8 m yr 1 i e similar to those of the largest wadis draining to the dead sea the steep front of the fan delta is suggested to be a main factor controlling the efficient incision a unique transport mechanism of rolling boulders following undercutting contributed to the entrenchment efficiency copyright 2010 john wiley sons ltd

alluvial fan and playa sedimentation in an andean arid closed basin the pacencia group antofagasta province chile the mid tertiary pacencia group comprises over 2 km of continental sediments it was deposited in a half graben basin thought to have been active since early tertiary times conglomerates along the western basin margin were deposited as longitudinal bars rare transverse bars and channel fills with subsidiary debris flows all in a distal fan pebbly braided stream environment no proximal fan sediments are exposed petrographic and palaeocurrent analysis indicates these sediments were derived from cretaceous and possibly jurassic source areas to the northwest to the east within the basin a succession of sands silts muds thick evaporites and rare carbonates were deposited in playa sub environments saliferous muds central salt pan are overlain by interbedded red mudstones and thin high energy ribbon and sheet sands marginal dry mudflat and sandflat certain sand bodies carry stratiform cui agi au mineralization lakes existed at various stages and were fed by permanent fluvial systems the playa sediments were derived from crystalline source areas to the east proximal fan facies and sediment sources are now buried under the volcanic andes

climatic and tectonic controls on fluvial incision and aggradation in the spanish pyrenees the influences of tectonic and climatic changes on upland river systems are investigated using data from plio pleistocene terraces of the rio cinca river in the southern pyrenees this river runs transverse to the main thrust fault structures and is a major conduit for sediment delivery to the ebro basin detailed field mapping combined with long profile and palaeohydraulic reconstructions yields a comprehensive picture of changes in palaeoriver character during the plio pleistocene as the area is over 150 km from the basin outlet in the mediterranean sea changes in base level are unlikely to have influenced terrace development although tectonic activity has exerted a strong control on the position of the river the main period of thrust propagation pre dates the terraces and activity has waned from the pliocene through to the present it is concluded that the main control on incision in this area is climate through its influence on sediment supply rivers which are starved of sediment by climate change will have the power to incise whereas aggradational phases are linked to periods of increased sediment flux

eocene fan delta submarine fan deposition in the wagwater trough east central jamaica the wagwater trough is a fault bounded basin which cuts across east central jamaica the basin formed during the late palaeocene or early eocene and the earliest sediments deposited in the trough were the wagwater and richmond formations of the wagwater group these formations are composed of up to 7000 m of conglomerates sandstones and shales six facies have been recognized in the wagwater group facies i unfossiliferous massive conglomerates facies ii channelized non marine conglomerates sandstones and shales facies iii interbedded fossiliferous conglomerates and sandstones facies iv fossiliferous muddy conglomerates facies v channelized marine conglomerates sandstones and shales and facies vi thin bedded sheet sandstones and shales the wagwater and richmond formations are interpreted as fan delta submarine fan deposits facies associations suggest that humid region fan deltas prograded into the basin from the adjacent highlands and discharged very coarse sediments on to a steep submarine slope at the coast waves reworked the braided fluvial deposits of the subaerial fan delta into coarse sand and gravel beaches sediments deposited on the delta front slope were frequently remobilized and moved downslope as slumps debris flows and turbidity currents at the slope basin break submarine fans were deposited the submarine fans are characterized by coarse inner and mid fan deposits which grade laterally into thin bedded turbidites of the outer fan and basin floor

response of plio pleistocene alluvial systems to tectonically induced base level changes vera basin se spain tectonics are perceived to be a major control on the positioning and long term evolution of alluvial systems by increasing slope gradients through uplift and tilting or by changing local base level incision can be stimulated leading to a switch in the active area of sedimentation an example of such a sedimentary response to tectonic activity is provided by well exposed late pliocene early pleistocene alluvial sediments of the salmeron formation from the western margins of the vera basin se spain early stage palaeogeographic reconstructions demonstrate the occurrence of two alluvial fan bodies with distinct palaeocurrent and provenance signatures that suggest sediment source areas from the north sierra lisbona and south sierra de bedar of the study area late stage reconstructions suggest fan abandonment and indicate the occurrence of a braided river system sourced from the sierra de bedar in the south proximal parts of this braided river are incised by up to 100 m into underlying fan sediments sourced from the sierra de bedar in distal areas incision is negligible and the braided system forms a conformable sedimentary succession with underlying fan sediments sourced from the sierra lisbona the switch from alluvial fan to braided river sedimentation and the spatially variable patterns of incision into the alluvial fan bodies can be accounted for by a phase of deformation which affected the vera basin during the early pleistocene extensional faulting resulted in uplift and subsidence leading to localized tilting of depositional surfaces in distal areas of the southern fan increased stream power resulted in headward incision through mid and proximal fan areas once the system became fully trenched distal base level controls became effective in generating an enlarged catchment area and continuing incision the resultant changes dramatically increased both sediment and water discharge to the alluvial system and a switch to braided river sedimentation

tectonic and climatic control of triassic sedimentation in the beryl basin northern north sea the beryl basin embayment occupies a central position along the viking graben of the northern north sea and has been a hydrocarbon play since the early 1970s detailed analysis reveals a complex half graben that was established during a rift phase of development that occurred in the early triassic teist formation after which a long period of thermal subsidence lomvi and lunde formations provided accommodation for in excess of 1000 m of sediment the teist formation sediments are complex they include shales sands and conglomerates and their superimposition on zechstein salts is indicative of both uplift and the development of a moderate relief they give way to the comparatively clean and occasionally pebbly sands of the lomvi formation for which an analysis of both bedding and texture suggests deposition by a westerly directed river system draining the hanging wall ramp the lunde formation records the spreading influence of a bajada playa complex and its eventual conversion to a more persistent lake the growing importance and eventual dominance of the succession by lacustrine sediments gives clear indication of a change in climate and this has been attributed to the rapid northward drift of pangea during the triassic period

seismic measurements in the southern dead sea abstract a seismic refraction profile and several seismic cdp reflection lines were recently occupied in the southwestern part of the dead sea the seismic data which are of good quality give a clear picture of the structure of the area the western flank of the rift comprises a series of step faults downthrown to the east with a total throw of some 7 km at which depth the cretaceous base of the post cretaceous fill is located on the east west lines the base of the fill dips to the east while on the north south lines this complex dips to the south with a change in direction of dip being evident in the southern portion of this profile the post cretaceous sediments reach a maximum thickness of 7 km but may be even thicker eastward near the main eastern rift fault these sediments are gently folded possibly due to differential compaction and are dislocated by small magnitude adjustment faults lateral transition from bedded layers of salt in the graben fill to a diapir is clearly seen

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

quaternary palaeogeomorphologic evolution of the wadi faynan area southern jordan abstract the faynan area comprises a complex assemblage of deposits and landforms of varying nature age and position in the landscape the dominant facies are fluvial slope and aeolian at least eight palaeochannels are present at different heights within the wadis dana and ghuwayr fewer terraces are preserved in the wadi faynan planated surfaces leaving low gradient straths rock cut channels and fluvial deposits are all evident the continuing drop in regional base level as a result of subsidence of the dead sea trough has driven incision and aided in the retention of many of the terrace deposits as they have been abandoned as the wadi systems have eroded downwards calcretisation has enhanced the preservation potential of many of the fluvial deposits a large proportion of these deposits are comparable to those found in the modern wadi systems and it is thought that they formed under arid conditions similar to those that exist today two of the terrace deposits appear to reflect slightly wetter conditions as they consist of finer grained better sorted materials and display evidence of biological activity there are at least four distinct alluvial fan and slope deposits that have formed at the edge of various mountain fronts the fans have been entrenched to varying degrees and are likely to have formed at different times in the quaternary possibly when conditions were more humid or during periods of increased tectonic activity aeolian deposits indicate a marginally drier phase in the late glacial maximum and similar sediments of mid holocene age could either reflect increasing aridity at this time as has been suggested by frumkin et al 1991 and or be a result of the increasing impact of humans on the landscape many of the deposits are beyond the age range of optically stimulated luminescence osl and radiocarbon dating techniques but a proposed stratigraphy is supported by some numerical dates on the younger deposits and associated archaeological artefacts

the development of organized convection in a simplified squall line model squall lines stand out from ordinary cumulonimbus convection because of a special structure that dramatically extends their duration precipitation output and area of influence time dependent models have identified surface outflow boundaries and low level environmental wind shear as the crucial elements in squall line formation and or maintenance steady state models have shown how properties of the downdraught reservoir or cold pool must be matched to the far field wind and thermodynamic profiles to sustain the convection however the dynamical role of the environmental shear and the nature of the interaction between the positively and negatively buoyant air have remained uncertain for help with these issues a time dependent numerical model is developed with all moist processes either parametrized or based on ad hoc assumptions the simplifications make it possible to distinguish more clearly than in the past between the formation and maintenance of squall lines and between the initial and disturbed far field environments the convective updraught forms within an expanding region of disturbed flow separated from the undisturbed environment by storm fronts forced or neutral ascent occurs at a surface gust front on the upwind side of the cold pool we distinguish squall lines from ordinary convection by looking at the coherence between the forced and convective updraughts it is found that subsidence over the cold pool disorganizes the updraughts whereas a deep overturning circulation downshear from the gust front has an organizing effect hence factors which allow the initial subsidence to occur ahead of the gust front namely contrasting lower and upper level winds and large potential buoyancy favour squall line development it is argued that in cases with large convective potential energy the deep mesoscale circulation is more important in the formation and maintenance of the line than either the vertical shear of the air reaching the cold pool or the strength of the forced updraught

timing and nature of alluvial fan and strath terrace formation in the eastern precordillera of argentina abstract sixty eight 10 be terrestrial cosmogenic nuclide tcn surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper arid san juan region of the argentine precordillera this region is tectonically active and numerous fault scarps traverse quaternary landforms the three study sites marquesado strath complex loma negra alluvial fan and carpinteria strath complex reveal a history of alluvial fan and strath terrace development over the past 225 ka the marquesado complex q3 m surface dates to 17 3 ka whereas the loma negra q1 ln q2 ln q3 ln q4 ln and q5 ln surfaces date to 24 3 ka 48 2 ka 65 13 ka 105 21 ka and 181 29 ka respectively the carpinteria complex comprises eight surfaces that have been dated and include the q1 c 23 3 ka q2 c 5 5 ka q3a c 25 12 ka q3b c 29 15 ka q4 c 61 12 ka q5 c 98 18 ka q6 c 93 18 ka and q7 c 212 37 ka 10 be tcn depth profile data for the loma negra alluvial fan complex and carpinteria strath terrace complex as well as osl ages on some carpinteria deposits aid in refining surface ages for comparison with local and global climate proxies and additionally offer insights into inheritance and erosion rate values for tcns 10 10 4 10 be atoms g of sio 2 and 5 m ma 1 respectively comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the carpinteria and loma negra areas with only younger alluvial fan surfaces preserved both to the north and south these data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region

special climatological conditions in the deserts of sinai and the negev during the latest pleistocene abstract results of hydrological and geological investigations carried out during the last ten years in the deserts of the sinai and the negev indicate that unique climatological and hydrological conditions prevailed between ca 100 000 and ca 10 000 yr b p the uniqueness was expressed by the following characteristics 1 1 higher precipitation and recharge rates caused the nubian sandstone aquifers to be filled up through the outcrops in central sinai and to overflow through big springs emerging along the faults of the syrian african rift system this water is of special isotopic composition namely depleted in 18o and deuterium and with a lower excess of the latter 2 2 dust laden rainstorms prevailed probably mainly during the autumn season causing the deposition of thick layers of loess the quantity of rain during the humid periods was double that of the present 3 3 the drainage system of many western and northern wadis of sinai as well as the negev could not drain out all the silt loaded water during the rainy season and shallow lakes and marshes extended in many wadis during this season 4 4 the floods and the springs flowing into the dead sea rift valley contributed to the lisan lake which was 200 m above the level of the contemporary dead sea

acquisition and processing of high resolution reflection seismic data from a survey within the complex terrain of the bavarian folded molasse a high resolution reflection seismic survey was carried out in the southern part of the bavarian molasse basin in 1998 and 1999 the survey aimed to investigate the near surface structure of the complicated transition from the unfolded foreland molasse to the folded molasse and the folded molasse to the internally complicated thrust systems of the helveticum the ultrahelveticum and the rhenodanubian flysch the study is linked to the transalp seismic project and the results help to fill the gap between the surface and the upper 300 500 ms two way traveltime twt typical of deep reflection seismic experiments the environmental conditions encountered in the study area required that particular attention be paid to the acquisition parameters for the three seismic lines each about 4 km long the energy source was a small vibrator the geophone spread spacing and frequency range were adjusted to image reflectors which were expected to dip steeply southwards in general the unprocessed field records did not show signals that could be attributed to specific reflectors individual trace processing considerably improved the data quality taking into account the influence of the quaternary cover and also the strong lateral velocity variations of the shallow subsurface the effects of the various processing steps such as muting refraction statics residual statics and velocity analysis are discussed to assess the nmo velocities the qualitative analysis of the seismic energy in a common shotpoint gather offered advantages over an analysis in a common midpoint gather or in a stacked section and proved to be very effective as demonstrated along the miesbach 9801 line low velocity zones extend locally down to about 400 ms adjacent to zones of extremely high velocities close to the surface reflecting steeply dipping strata besides the quaternary cover on top the miesbach 9801 and miesbach 9802 lines exhibit many horizontal reflections in places down as far as 1400 ms twt indicating the sedimentary sequences of the unfolded foreland molasse the southern part of both lines is dominated by southward dipping reflection bands indicating units of the folded molasse the reflection pattern shown by the miesbach 9901 line suggests that there is almost no quaternary cover southward dipping elements reflect the internal structure of the folded molasse whereas a rather diffuse reflection signature may be attributed to rhenodanubian flysch units

triassic sediments of the inner moray firth scotland early rift deposits patterns of triassic sedimentation in the inner moray firth are examined in the light of a new model of continental rift sedimentation that has been developed in the tertiary to recent rifts of east africa the major tectonic control during the trias was the great glen fault to the northwest which can be shown to have been moving in dip slip fashion at this time the structure of the firth appears to have resembled the simple half graben that makes up the great east african rift system deposits both thicken and get finer towards the fault sediments found in off shore wells are dominated by laminated fine sand and silty clay with sporadic evaporites similar sequences are characteristic of or associated with ephemeral lakes in modern semi arid continental rift settings no alluvial fans have been detected close to the faulted margin again this is consistent with general patterns of sedimentation against boundary faults in the kenyan rift the coarsest sedimentary sequences in the moray firth are on the unfaulted margin to the south around burghead they consist of fluviatile lake shore and aeolian deposits the fluvial sediments show evidence of tectonically induced cycles of sedimentation which are interpreted in terms of waves of detritus working down the drainage system beds dominated by pebbly horizontal laminae and reminiscent of steep straight and shallow ephemeral streams alternate with troughed sands of deeper more sinuous but equally ephemeral rivers these are the coarsest sediments of the unfaulted margin of the basin however the lack of thick conglomerate sheets which are a feature of east african sequences at equivalent positions within the rift basin suggests only small scale fault activity and a relatively subdued topography during triassic times this is supported by evidence of extensive calichification during the rhaetic which produced a top trias marker horizon found throughout the inner moray firth

structures and textures in triassic braided stream conglomerates bunter pebble beds in the sherwood sandstone group north staffordshire england in the northern parts of the needwood and stafford eccleshall basins england the pebble beds of the sherwood sandstone group contain thick successions of texturally mature fluvial pebble cobble conglomerates which are organized into either horizontal or cross stratified sets the horizontally lying sets generally coarser grained and more poorly sorted than the cross bedded sets are usually disorganized and either matrix or clast supported although thin lenses of well sorted occasionally openwork units interpreted as falling stage phenomena are often present the cross stratified conglomerates have foresets exhibiting remarkable textural organization with a coarse bimodal sometimes matrix supported part grading upwards or being abruptly overlain by a finer well sorted occasionally openwork part and finally capped by sandstone these rhythmic textural changes are attributed partly to an avalanche process at high stage and partly to falling stage conditions the most common types of vertical association are thick successions of horizontally bedded conglomerates up to 20 m and sequences of an upwards coarsening nature 2 12 m in which cross stratified sets are overlain by flat lying sets the environment of deposition of the gravels is interpreted as one in which water depths at high stage were greater than depths in most modern braided stream plains proglacial or alluvial fan but shallower than depths associated with the pleistocene catastrophic floods from which texturally mature giant gravel bars have been recorded recent braided streams with relatively confined channels and considerable bar channel relief are better analogues in particular medial or mid channel bars with a two tier structure subaqueous and partly emergent portions may explain the upward coarsening sequences in which horizontally lying conglomerates overlie cross stratified conglomerates the thicker sequences of horizontally stratified conglomerates represent proximal longitudinal bar deposits sheets of pebbly sandstone and argillaceous sandstone lying between the conglomerates and commonly occurring towards the top of the succession largely represent deposition from sandwaves and dunes finer interbedded argillaceous sandstones siltstones and mudstones are interpreted as overbank and waning flood deposits basin forming tectonism of increasing intensity probably caused the initial coarsening upwards of the lower part of the succession whilst more stable tectonic conditions and decreasing relief on the margins of the basins and in the areas of provenance in the midlands and the hercynides account for the upwards fining of the upper part of the succession

the evolution of holocene reg gravelly soils in deserts abstract reg soil is an aridisol developed upon a stable alluvial surface composed of sand to coarse gravel the objectives of the present study were 1 to examine the initial evolution of reg soil properties with time 2 to assess and explain the rates of development of different properties 3 to establish the suitability of different soil properties for relative age dating the time dependent soil properties examined were 1 mechanical weathering of surficial rocks and desert pavement evolution 2 chemical and biological weathering of surficial rocks 3 the thickness of soil profiles and soil horizons 4 soil texture in the different horizons 5 salts and gypsum distribution and concentration in different soil horizons 6 degree of mechanical weathering of gravel in c horizons fifteen successive surfaces of the nahal wadi ze elim sequence of alluvial fans were selected for study dead sea region israel under an extremely arid climate the sequence is of holocene age 14 000 years b p to recent the main conclusions are 1 reg soils develop rather fast in several 10 3 years since their initiation however the various soil properties developed at different rates 2 the rates of change of three soil properties decrease with time these are the texture in different horizons change in added airborne and rain washed dust salinity within the soil profile change in added salts and gypsum and the amount of mechanically shattered rocks 3 soil thickness is established rather rapidly young and older holocene soil have practically the same depth surficial weathering rates appear to remain fairly constant with time 4 in coarse gravel the evolution of reg soils is dependent on added fines and salts of airborne origin and the resultant changing hydrologic regime in the soil profile the run off infiltration ratio changes as more fines and salts are added to the soil profile and as desert pavement develops 5 surficial features and fine clay in the soil profile may be used for approximate dating of otherwise undatable holocene alluvial surfaces salts and gypsum content should be cautiously used in a rather general way

fluviatile deposits and morphology of alluvial surfaces as indicators of quaternary environmental changes in the southern negev israel summary quaternary environmental changes in the southern negev are recorded in the alluvial deposits and the geometry of depositional surfaces in the timna valley there are some distinct differences between the alluvial deposits of the holocene to modern flood plains and earlier pleistocene ones the holocene to modern alluvium is characterized by sand fine to medium sized gravel and very coarse gravel in large gravel bars the sediments indicate environments ranging between extremely arid and semi arid dominated by floods of low to moderate magnitude but with occasional short large floods the pleistocene sediments include 1 debris flow deposits indicating talus activity under a moderately arid to semi arid climate 2 alternating fine grained and gravelly layers reflecting floods of low to moderate magnitudes the nature of the soils supports these conclusions thick and argillic reg soils are typical of the pleistocene surfaces whereas shallow loamy ones are characteristic of the holocene terraces the alluvial surfaces usually converge downstream the intersection points migrate upstream following stages in the recession of a major escarpment broad pedimented surfaces and bajadas are characteristic of the pleistocene period whereas long narrow terraces of gentle declivity were formed during the holocene the latter suggest depletion of the available debris and in the effectiveness of large floods

iron coating in recent terrace sequences under extremely arid conditions summary precise documentation of ferric oxide coating on calcareous sands of 13 15 recent alluvial fan terraces in the dead sea area israel indicates a gradual ferric enrichment over the last 12 00 years airborne dust is suggested as the main source the staining on the low terraces indicates that coating during short increments of time than hitherto generally accepted up to periods of a few tenths of years is distinguishable in an extremely arid environment the results suggest an initial stage of alluvial red bed formation

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

differential effects of base level tectonic setting and climatic change on quaternary alluvial fans in the northern great basin nevada usa

depositional subenvironments in an arid closed basin the wilkins peak member of the green river formation eocene wyoming u s a the wilkins peak member of the green river formation is a non marine dolomitic deposit that formed in an arid hydrologically closed basin a transect from the margin to the centre of the wilkins peak basin was examined in outcrop exposures in the south eastern corner of the basin and was supplemented with published core descriptions the rocks were divided into seven facies based upon lithology layering style and sedimentary fabrics 1 af facies quartzose conglomerates and sandstones representing sandy alluvial fans coming from the uinta mountains 2 sf facies quartzose peloidal dolomitic sandstones which represent sheet flood deposits extending basinward from the alluvial fans 3 dm facies irregularly laminated dolomitic mudstones with abundant mudcracks which represent sheet flood deposits on a subaerially exposed mudflat 4 el facies dolomitic mudstones with regular lamination and fewer but larger mudcracks representing sporadically exposed lake margins or shallow ponds 5 pl facies finely laminated oil shales and dolomitic mudstones with rare mudcracks which represent shallow perennial lakes 6 sm facies trona or halite deposits with dolomitic mudstone partings or dolomitic mudstones and sandstones disrupted by evaporites of varied morphology these represent a central salt pan and the surrounding saline mudflat 7 as facies arkosic sandstones siltstones and mudstones which represent braided river and more basinal deltaic plain deposits the five dolomitic facies form poorly defined cycles representing the intersection of sheet floods with a lake which transgressed and regressed in response to climatic variations there are at least forty 3 4 m thick cycles in the wilkins peak and one large scale cycle comprising the whole member which mimics the facies changes of the smaller cycles this is compatible with the transitions of the wilkins peak member to the tipton and laney members as climatic responses and not shifts in drainage the sheet flood sandstones actively aggrading subaerial mudflats and bedded evaporites of the wilkins peak are apparently unique within the green river formation they reflect the unusual provenance and hydrology of the wilkins peak and suggest chemical and sedimentary models established for the other green river members will not be applicable

morphology of the latest quaternary surface faulting in the gulf of elat region eastern sinai abstract a variety of morphotectonic features bear evidence of neotectonic activity along the gulf of elat these include stepped topography deflected channels fault line grabens sag pond depressions backtilted fan segments faulted gravel bars and debris flow deposits the age of the fault scarps is estimated on the basis of the extent of dissection the amount of rounding of the crest of the scarps the scarp gradient the stage of clast weathering the intensity of the micro relief and the stage of soil and desert pavement development the field data are interpreted and related to the geomorphic time curves suggested by wallace by bucknam and anderson and by nash and the seismic hazard implications are discussed some criteria suggest a recent age with 10 000 yrs b p as a frequently recurrent estimate from the data it is concluded that the gulf of elat has definitely been tectonically highly active during the holocene

spatial characteristics of the pliocene to modern alluvial fan successions in the uplifted sedimentary basins of almeria se spain review and regional synthesis

holocene seismic and tectonic activity in the dead sea area abstract the dead sea is a large active graben within the dead sea rift which is bounded by two major strike slip faults the jericho and the arava faults we investigated the young tectonic activity along the jericho fault by excavating trenches up to 3 5 m deep across its trace the trenches penetrate through late pleistocene and holocene sediments we found that a zone up to 15 m wide of disturbed sediments exists along the fault these disturbed sediments provide evidence for two periods of intensive activity or more likely for two major earthquakes that occurred during the last 2000 years the earthquakes are evident in small faults vertical throw of a few layers cracks unconformities and wide fissures we further documented evidence for recent sinistral shear along the jericho fault in deformed sediments and damage to an 8th century palace on a subsidiary fault we suggest that the two earthquakes may be correlated with the 31 b c earthquake and the 748 a d earthquake reported by the ancients