development of glacial llyn teifi west wales evidence for lake level fluctuations at the margins of the irish sea ice sheet a thick sequence of quaternary laminated silt and clay sand gravel and diamict has recently been proven at llandudoch st dogmaels west wales most of these deposits accumulated in a tributary valley of afon river teifi that formed prior to the last glaciation the laminated silt and clay occur up to 103 m above present sea level and are considered to have been deposited in llyn lake teifi a large ice dammed lake that developed in the teifi valley as the irish sea ice sheet impinged onto the welsh mainland during the late devensian rhythmic units are interpreted as annual varves whose composition was determined by the distance from the sediment discharge point short term climate fluctuations during the summer months are evident in some of the varve units stratigraphic variations within the laminated deposits are considered to reflect different levels of llyn teifi which varied according to the position of the irish sea ice sheet in the teifi valley and the elevations of three overspill channels the overlying diamict sand and gravel deposits are thought to have accumulated close to the ice front as it encroached into llyn teifi during the final retreat of the irish sea ice sheet a series of kamiform sand and gravel deposits formed along the margins of the glacier

prediction of alluvial channel pattern of perennial rivers abstract purely braided meandering and straight channels can be considered as end members of a continuum of alluvial channel patterns several researchers have succeeded in separating channel patterns in fields defined by flow related parameters however the discriminators of the principal channel patterns derived from these diagrams all require some a priori knowledge of the channel geometry in this paper a method is presented which enables prediction of the equilibrium conditions for the occurrence of braided and high sinuosity meandering rivers in unconfined alluvial floodplains the method is based on two almost channel pattern independent boundary conditions median grain size of the river bed material and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient this can be regarded as a potential maximum of the available flow energy corresponding to the minimum sinuosity condition p 1 based on an analysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that separates the occurrence of braided rivers and meandering rivers with p 1 5 the function applies to equilibrium conditions of rivers that neither incise nor show rapid aggradation with a bankfull or mean annual flood discharge above 10 m3 s and a median bed material grain size between 0 1 and 100 mm

geoarchaeological investigations at the topper and big pine tree sites allendale county south carolina the topper and big pine tree sites are located along the central savannah river in south carolina both sites contain significant clovis horizons and the topper site is reported to contain a pre clovis assemblage characterized by a smashed core and microlithic industry the stratigraphic position of the early assemblage at topper is indeed below clovis and radiocarbon and luminescence ages support its pre clovis age however the human origin of the proposed artifacts has not been conclusively proven the late quaternary stratigraphic sequence developed for this segment of the savannah river provides support for a regional pattern of river metamorphosis over the last 50 000 years in southeastern u s streams

age limits on the late quaternary evolution of the upper loire river abstract the loire river is one of the largest rivers in europe draining a basin area of southern france which exceeds 100 000 km 2 despite its significance the loire remains poorly studied and has a very limited amount of chronological control on the deposited sedimentary record of fluvial activity these factors coupled with the availability of a set of 10 radiocarbon dates on younger c

paleoenvironmental implications and drainage adjustment in the middle reaches of the sabarmati river gujarat implications towards hydrological variability abstract the dryland fluvial sequences exposed in the lower part of the gujarat alluvial plain are investigated for palaeohydrological palaeoclimatic reconstruction using conventional sedimentology grain size analyses supported by optical chronology considering that the study area is cradling large scale constructional activities an attempt has also been made to assess the geotechnical properties of the sediments it has been observed that the lower reaches of the sabarmati valley have preserved record of fluvial aggradation since mis 5 90 ka to mis 3 47 ka whereas the onset of aeolian processes began at around 12 ka based on the sediment texture the alluvial sequences are divided into the lower and upper units the lower fluvial sequence is dated to 90 63 ka whereas the upper fluvial sequence is dated to 47 ka the stratigraphic marker red soil is dated to 63 ka the study indicates that the terrain experienced tectonic perturbations after 12 ka which was responsible for the shifting of the sabarmati river from regional ne sw to n s which is more pronounced towards the upstream of the sabarmati river basin while the landscape stability is observed towards the downstream consisting of the older alluvium dated to 90 ka geotechnical investigation reveals potentially liquefiable sand which however have been compacted due to large scale calcretisation since their deposition

stratigraphic units of the apulian tavoliere plain southern italy chronology correlation with marine isotope stages and implications regarding vertical movements abstract the geologic study of the apulian tavoliere plain apulia region southern italy is extremely difficult due to the scarcity of outcrops and fauna that could be used for dating the survey in progress of the 1 50 000 scale geological sheet no 409 zapponeta including the coastal zone of the apulian tavoliere has prompted us to tackle this problem by using a large set of borehole data and the aar dating method applied to ostracod shells which are capable of colonizing all types of environment as long as there is water this alternative approach has allowed us to recognise nine stratigraphic units or synthems and for the first time in this area to date them and to find a correlation between them and the cycles of sea level variation the recognised stratigraphic units are the coppa nevigata sands nea middle pleistocene mis 17 16 argille subappennine unit asp middle pleistocene mis 15 13 the coppa nevigata synthem nvi middle pleistocene mis 11 the amendola subsynthem mlm1 middle pleistocene mis 11 an undifferentiated continental unit uci middle pleistocene mis 8 7 the foggia synthem tgf middle late pleistocene mis 6 the carapelle and cervaro streams synthem rpl late pleistocene mis 5 3 and the inacquata farm synthem naq holocene within the rpl unit a buried cladocora caespitosa bioherm referable to mis 5 5 lacking in warm fauna and in which the coral is embedded in clay has been found in some boreholes this is the first finding of tyrrhenian deposits with c caespitosa along the italian adriatic coast the presence of this coral in clayey sediments a very uncommon occurrence strengthens the hypothesis that the major fossil reefs grew in coastal waters that were characterised by alluvial inputs of fine sediments higher turbidity and higher temperature than today in addition on the basis of the current evidence some consideration about the fauna of the mis 5 5 layer allows us to hypothesise that the adriatic sea underwent a more moderate warming compared to that of the ionian and tyrrhenian seas instead the finding in the nvi unit of a tropical lagoonal deposit with stromatolites referred to mis 11 proves that the warming in this stage was undoubtedly greater than that of mis 5 5 the mm4 borehole which goes through the mis 5 layers of the rpl unit made it possible to recognise two marine phases during mis 5 the first is referable to the mis 5 5 5 3 interval and the second to mis 5 1 mis 5 2 is marked by land emersion whereas no evidence of land emersion between mis 5 5 and 5 3 has been found also for the first time in this area uplifting and subsiding areas have been recognised and the vertical movements assessed in general the data suggest that the garganic apulian foreland and the amendola highland experienced an uplift while the central southern part of the study area belonging to the apulian tavoliere plain suffered a subsidence with rates increasing from north northwest to south southeast in particular the finding of the mis 5 5 buried layer with c caespitosa has allowed us to fill a gap in the data regarding the recent tectonic movements along the adriatic coast ferranti et al 2006 this feature proves that there has been a recent subsidence event since mis 5 5 in the coastal area of the apulian tavoliere plain

mega meander paleochannels of the southeastern atlantic coastal plain usa abstract paleodischarge estimates based on the slope area method and channel boundaries determined from stratigraphic cross sections indicate that large terminal pleistocene meandering paleochannels mega meanders in river valleys of the southeastern atlantic coastal plain of the united states represent bankfull flows that were at least double the magnitude of those on modern rivers correlation of radiocarbon and luminescence dated paleomeanders with previously reported pollen and eolian sedimentary records suggests that greater discharge was driven by seasonally wetter conditions resulting from dynamic changes to regional precipitation and runoff that occurred in association with global warming at the end of the pleistocene while reflecting larger channel forming flows the exceptionally large widths and radii of curvature of mega meanders were nonetheless maintained by a relatively modest discharge magnitude that was between two and four times larger than modern bankfull flow and within the size range of the present two to five year flood despite their large planform the paleochannels conveyed relatively modest bankfull discharges because a wide shallow shape limited their cross sectional area and hydraulic radius within the late quaternary evolution of fluvial systems in the region scrolled mega meanders constitute a transitional meandering planform that remained influenced by large volumes of sandy bedload following the sand bed braided channels of the late wisconsin interval circa 30 17 ka in addition to greater discharge the large planimetric dimensions of paleochannels reflect a lack of cohesive vertical accretion facies on paleomeander floodplains a sediment regime that transported large quantities of bedload sand and the influence of these factors on channel boundary composition bank stability and channel shape findings underscore the importance of reconstructing channel cross sectional dimensions and slope when estimating discharge for infilled paleomeanders this approach reduces uncertainties surrounding channel cross sectional area gradient and boundary composition inherent to studies lacking subsurface data that rely upon meander geometry to retrodict discharge

sedimentation in ice dammed hazard lake yukon hazard lake located in kluane national park the yukon is an ice dammed lake formed in 1966 by the surge of the steele glacier since 1975 it has drained annually by means of a subglacial tunnel during july 1979 observations were made of lake processes before drainage and of sections described in the lake bottom after drainage three facies associations are believed to represent prelake stable lake and annual draining phases gravel commonly found at the base of sections represents deposition in a braided fluvial system prior to 1966 lake sediments deposited between 1966 and 1975 are dominantly graded laminated silt deposited by turbid underflow from the major inflow stream lamination is probably caused by diurnal underflow events or daily variation in strength of underflow no winter clay component of varved sediments is observed during drainage a regressive sequence is deposited as the lake level drops with sand dominated sediments overlapping laminated silt where the main inflow stream en

late pleistocene braided rivers of the atlantic coastal plain usa abstract infrared landsat imagery band 4 clearly reveals braided river patterns on late pleistocene terraces of unglaciated rivers in the atlantic coastal plain of the southeastern united states a region that presently exhibits meandering patterns that have existed throughout the holocene these pleistocene braided patterns provide a unique global example of river responses to late quaternary climate changes in an unglaciated humid subtropical region at 30 35 north latitude detailed morphological and chronological results are given for the oconee altamaha river valley in georgia and for the pee dee river valley in south carolina including 15 optically stimulated luminescence osl dates and four radiocarbon dates correlative examples are drawn from additional small to large rivers in south and north carolina osl and radiocarbon 14 c dates indicate distinct braiding at 17 30 ka within oxygen isotope stage 2 ois 2 and braiding probably existed at least during parts of ois 3 and possibly ois 4 back to ca 70 ka the chronology suggests that braiding is the more common pattern for the late quaternary in the southeastern united states braided terraces appear to have been graded to lower sea levels and are onlapped by holocene floodplain deposits up to 10 60 km from the coast the braiding probably reflects the response of discharge and sediment yield to generally cooler and drier paleoclimates which may have had a pronounced runoff season sedimentation of eolian dunes on the braid plains is coeval with braiding and supports the conclusion of dry soils and thin vegetation cover during the late pleistocene our chronological data contribute to a body of literature indicating that reliable osl age estimates can be obtained from quartz rich bed load sand from braided rivers based on good correlations with both radiocarbon dates from braided fluvial sediment and osl dates from stratigraphically correlative eolian sand

quaternary coastal lithofacies sequence development and stratigraphy in a passive margin setting north carolina and virginia usa lithofacies analysis is fundamental to unravelling the succession of depositional environments associated with sea level fluctuations these successions and their timing are often poorly understood this report defines lithofacies encountered within the north eastern north carolina and south eastern virginia quaternary section interprets their depositional environments presents a model for coastal depositional sequence development in a passive margin setting and uses this understanding to develop the stratigraphy and quaternary evolutionary history of the region data were obtained from numerous drill cores and outcrops chronology was based on age estimates acquired using optically stimulated luminescence amino acid racemization uranium series and radiocarbon dating techniques geomorphic patterns were identified and interpreted using light detection and ranging imagery since lithofacies occurrence distribution and stratigraphic patterns are different on interfluves than in palaeo valleys this study focused on interfluves to obtain a record of highstand sea level cycles with minimal alteration by fluvial processes during subsequent lowstands nine primary lithofacies and four diagenetic facies were identified in outcrops and cores the uppermost depositional sequence on interfluves exhibits an upward succession from shelly marine lithofacies to tidal estuarine lithofacies and is bounded below by a marine ravinement surface and above by the modern land surface older depositional sequences in the subsurface are typically bounded above and below by marine ravinement surfaces portions of seven depositional sequences were recognized and interpreted to represent deposition from late middle pleistocene to present erosional processes associated with each successive depositional sequence removed portions of older depositional sequences the stratigraphic record of the most recent sea level highstands marine isotope stage 5a and marine isotope stage 3 is best preserved glacio isostatic adjustment has influenced depositional patterns so that deposits associated with late quaternary sea level highstands marine isotope stages 5c 5a and 3 which did not reach as high as present sea level according to equatorial eustatic records are uplifted and emergent within the study area

geochemistry and sedimentology of shelf and upper slope sediments of the south central black sea abstract eighty five surface samples from oxic suboxic and anoxic sites of the south central black sea shelf consist predominantly of clayey silts and silty clays reflecting the moderate to high energy wave dominated hydrological regime grain size data and net sediment transport patterns suggest that the western part of this shelf is an area of east directed active sediment transport with the exception of localized nearshore zones the eastern shelf is by contrast an area of major sediment deposition the sediment transport vectors are correlated with patterns of surface water circulation and storm generated longshore currents the sources of the shelf sediments are indicated by the total concentrations of 30 major minor and trace elements in 59 surface samples factor analysis shows that 99 1 of the total variance can be explained by five factors factor 1 as cu cr fe pb and zn reflects anthropogenic pollution by the etibank copper mine factor 2 mainly total organic carbon and s is linked to anoxia redox as saline conditions factor 3 mainly al si represents aluminosilicates whereas factor 4 sand and silt abundance total carbonate ca and sr represents the carbonate component factor 5 fe mn p cr ni and v tracks primary detrital delivery with strong overprints by redox dependent biogeochemical reactions within the anoxic sediments and the oxic suboxic bottom waters the combined data suggest that the sediments on the south central black sea shelf were largely derived from the north anatolian mountains and supplied to the shoreline by a network of small rivers

testing optically stimulated luminescence dating of sand sized quartz and feldspar from fluvial deposits abstract we apply single aliquot optically stimulated luminescence osl dating to quartz and feldspar rich extracts from fluvial channel deposits of the rhine meuse system in the netherlands the time of deposition of these deposits is tightly constrained by radiocarbon dating or historical sources this allows us to compare osl ages obtained on quartz and infrared osl ir osl ages obtained on potassium rich feldspar with independent ages over the range of 0 3 13 ka we show that the quartz osl ages are in good agreement with the expected age using ir osl dating of feldspar we find a slight age overestimate for the youngest sample whereas for older samples the age is significantly underestimated we also apply osl dating to older fluvial and estuarine channel deposits with limited independent chronological constraints comparison of feldspar ir osl ages with the quartz osl ages up to 200 ka shows a clear trend where the former severely underestimates the latter this trend is similar to that found for the samples with independent age control indicating that the feldspar ir osl ages are erroneously young for the entire age range in the youngest samples incomplete resetting of the ir osl signal prior to deposition probably masks the age underestimation we show that the ir osl age underestimation is partly caused by changes in trapping probability due to preheating correction for this phenomenon improves the ir osl ages slightly but does not provide a complete solution to the discrepancy we suggest that in the light of the problems encountered in the ir osl dating of feldspar quartz is the mineral of choice for osl dating of these deposits however feldspar dating should continue to be investigated because it has potential application to longer time scales

spatial and temporal variability of ice dammed lake sediments in alpine environments abstract the stratigraphic record of ice dammed lakes is the product of a combination of daily intraseasonal seasonal and interseasonal fluctuations in sediment input combined with periods of drawdown or drainage of the lake sedimentation may take place on an ice cored bed which produces deformation structures on melting and eventually results in limited preservation during and after deglaciation the sediments of the contemporary and older ice dammed lakes in the kaskawulsh and dusty glacier basins of the southwest yukon reflect a number of hydrological regimes and lake histories and also demonstrate the complexity of the sedimentary environment the kaskawulsh glacier lake evolved from being semi permanent at the start of deglaciation from the little ice age maximum to annually draining at present the dusty glacier lake was impounded by glacier surges and had a duration of only a few years after each surge a model of the effects of variations in sediment source contrasting hydrological regimes and geomorphological events on sediment accumulation illustrates how spatial and temporal variability is the predominant characteristic of the sediments

riverine dunes on the coastal plain of georgia usa abstract relict eolian dunes on the georgia coastal plain line the north and east sides of many se trending streams and contain important paleoenvironmental information a detailed analysis of four dune fields characterizes dune geomorphology stratigraphy sedimentology and soils georgia s inland dunes range from parabolic to infilled parabolic to irregular in form typically merge to form long chains that parallel source streams and can occur as distinct bands typically the dunes are composed of 95 quartz sand grains with more than half the sand falling in the medium sand fraction dunes overlie flood plain and pointbar sands backswamp and peat deposits fluvial terraces and other dunes in places organic deposits occur on top of dunes cross bedding is observable in dunes more than about 4 m thick and indicates eastward dune migration paleosols found within some dunes indicate holocene reworking conditions favoring dune formation likely included at least seasonal aridity postdepositional modification of the dunes includes a smoothing of the dune surface a clay increase in the c horizon spodic horizon development bioturbation removal of weatherable minerals and fluvial incision

fluvial responses to late quaternary climate change in the shiyang river drainage system western china abstract as a drainage system located in arid western china the shiyang river combined with considerable fluvial strata and landform information provides an environmental context within which to investigate fluvial responses to late quaternary climate change sedimentological analysis and optically stimulated luminescence osl dating enabled us to reconstruct the processes and fluvial styles of three sedimentary sequences of the shagou and hongshui rivers in the shiyang drainage system our results present a variety of river behaviors during the late quaternary in these areas in the upstream shiyang river zhangjiadazhuang zjdz profile of the shagou was dominated by aggradation and a meandering channel pattern at 10 6 4 2 ka while a noticeable channel incision occurred at 4 2 ka followed by lateral channel migration in the downstream shiyang river datugou dtg profile of the hongshui was an aggrading meandering river from 39 7 to 7 2 ka while channel incision occurred at 7 2 ka another downstream profile wudunwan wdw of the hongshui was also characterized by aggradation from 22 4 to 4 8 ka however its channel pattern shifted from braided to meandering at 13 ka a discernable downcutting event occurred at 4 8 ka followed by three channel aggradation and incision episodes prior to 1 8 ka the last 1 8 ka has been characterized by modern channel and floodplain development the fluvial processes and styles investigated have a close correlation with late quaternary climate change in the shiyang river drainage during cold phases the wdw reach was dominated by aggradation with a braided channel pattern during warm phases the rivers that we investigated were also characterized by aggradation but with meandering channel patterns channel incision events and changes of fluvial style occurred mainly during climate transitions

luminescence chronology of river adjustment and incision of quaternary sediments in the alluvial plain of the sabarmati river north gujarat india river adjustment and incision in the sabarmati basin gujarat india have been examined at a site near mahudi towards this the morphostratigraphy and depositional chronometry of the middle alluvial plains were investigated the upper fluvial sequence along with the overlying aeolian sand and riverbed scroll plains provide clues to the evolution of the present sabarmati river sedimentological analyses of the upper fluvial sequence indicate its deposition by a meandering river system during what is believed to be a persistent wetter phase luminescence chronology bracketed this sequence to between 54 and 30 ka which corresponds to oxygen isotope stage 3 during which the sw monsoon was enhanced the overlying aeolian sand has been dated to 12 ka indicating that dune accretion occurred simultaneously with the strengthening of the sw monsoon during the early holocene adjustment of the sabarmati along a n s transect is placed around 12 ka and the incision is bracketed between 12 and 4 5 ka river adjustment could have been tectonic however the incision was facilitated by the availability of continuous flow in the river caused by the sw monsoon the basin experienced two tectonic events at about 3 and 0 3 ka as demonstrated by the morphology of the scroll plains

the braided milk river northern montana fails the leopold wolman discharge gradient test abstract the milk river the northernmost tributary to the missouri mississippi river system exhibits an anomalous sand bed braiding reach in an otherwise meandering system shortly after leaving alberta and entering montana the river suddenly changes to braiding and maintains this pattern for 47 km before entering fresno reservoir measured stream gradient and bankfull discharge in the braiding reach severely fail the leopold and wolman u s geol surv prof pap 282b 1957 39 slope discharge test for differentiating channel patterns while channel slope has long been regarded as one of the primary variables associated with braiding our data from the sand bed milk river do not support this relationship instead the data show that the braiding reach has a lower channel slope 0 00047 than the meandering reach 0 00055 coupled with a constant discharge the unit length stream power is comparable between the two reaches at the morphologic transition between meandering and braiding a dramatic reduction in channel bank strength occurs where the sampled silt clay content declines from 65 in the meandering reach to 18 in the braiding this enables channel widening which is reflected in a 60 reduction in unit area stream power in the braiding reach thus sediment transport capacity declines and channel bars are deposited during waning flows these bars are dissected producing a braiding morphology we suggest that for sand bed braiding rivers the silt clay percentage in the channel banks may be more important than slope a review of the original leopold and wolman u s geol surv prof pap 282b 1957 39 dataset and many subsequent analyses reveals that most braided rivers studied were gravel bed as a result causal variables associated with braiding in sand bed environments may need a thorough evaluation

late pleistocene evolution of the lower mississippi river valley southern missouri to arkansas the mississippi river served as the principal conduit for meltwaters discharging from the southern margins of north american ice sheets the northern half of the mississippi river alluvial valley in missouri and arkansas can be subdivided into two distinct channel courses the western and eastern lowlands which are separated by crowleys ridge the eastern lowlands contain two entry points the bell city oran and thebes gaps the latter is a narrow bedrock gorge that contains the modern river this paper summarizes a model for evolution of channel courses in the western and eastern lowlands during the illinoian and wisconsin glacial stages for the western lowlands stratigraphic relations between loess units and subjacent fluvial deposits show that major continuous terrace surfaces or valley trains are illinoian or late wisconsin in age investigations of tributary valley fills further show the western lowlands were deeply incised during the early to middle wisconsin stage then aggraded during the late wisconsin stage to such an extent that tributary valleys were backfilled with slackwater deposits moreover analysis of loess thinning and fining trends shows that early to middle wisconsin roxana silt and the late wisconsin peoria loess covers on western lowlands valley trains were derived from deflation of valley trains in the eastern lowlands we conclude that the western lowlands were the primary mississippi river course during illinoian deglaciation but were abandoned shortly thereafter then episodically reoccupied during the late wisconsin stage for the eastern lowlands course valley trains of early to middle wisconsin age are not preserved with the exception of a small remnant where the mississippi river broke through a gap in the southern margins of crowleys ridge and reentered the western lowlands all valley trains in the eastern lowlands are late wisconsin age a series of discontinuous terrace surfaces in the bell city oran gap represent dissected remnants of the primary late wisconsin full glacial and early late glacial course of the mississippi river or combined mississippi and ohio rivers whereas younger continuous braided stream surfaces in the bell city oran and thebes gap courses represent valley trains of latest wisconsin and earliest holocene age hence the bell city oran gap was the primary course during the entire wisconsin stage and the thebes gap was permanently occupied in earliest holocene time as much as 5 m difference in elevation between successive late wisconsin terrace surfaces of the eastern lowlands indicates that valley trains were rapidly constructed incised and abandoned in response to fluctuations in the delivery of meltwater and outwash from the former ice margin moreover a variety of data indicates that deglacial meltwater floods were commonly of sufficient magnitude to overflow from the primary course in the bell city oran gap throughout the late wisconsin substage floodwaters overflowed into the western lowlands constructed a series of secondary valley trains and filled tributary valleys with slackwater deposits during the latest wisconsin stage perhaps in association with the drainage of glacial lake agassiz floodwaters overflowed into the western lowlands and broke through the thebes gap the charleston fan represents the initial deposits of the thebes gap course following deposition of a large crevasse splay at the western lowlands entrance that course was no longer active but flow was routed through the thebes gap during periods of high magnitude flooding until the bell city oran gap was abandoned and the thebes gap course was permanently occupied during earliest holocene time

late glacial to early holocene climate changes from a central appalachian pollen and macrofossil record abstract a late glacial to early holocene record of pollen plant macrofossils and charcoal has been obtained from two cores from browns pond in the central appalachians of virginia an ams radiocarbon chronology defines the timing of moist and cold excursions superimposed on the overall warming trend from 14 200 to 7500 14 c yr b p this site had cold moist conditions from ca 14 200 to 12 700 14 c yr b p with warming at 12 730 11 280 and 10 050 14 c yr b p a decrease in deciduous broad leaved tree taxa and pinus strobus haploxylon pollen simultaneous with a reexpansion of abies denotes a brief cold reversal from 12 260 to 12 200 14 c yr b p a second cold reversal inferred from increases in montane conifers is centered at 7500 14 c yr b p the cold reversals at browns pond may be synchronous with climate change in greenland and northwestern europe warming at 11 280 14 c yr b p shows the complexity of regional climate responses during the younger dryas chronozone

fluvial activity in major river basins of the eastern united states during the holocene in the eastern united states existing paleo reconstructions in fluvial environments consist primarily of site specific investigations of climate and human impacts on riverine processes this paper

quaternary eolian dunes in the savannah river valley jasper county south carolina usa sand hills in the savannah river valley in jasper county south carolina usa are interpreted as the remnants of parabolic eolian dunes composed of sand derived from the savannah river and stabilized by vegetation under prevailing climate conditions optically stimulated luminescence ages reveal that most of the dunes were active ca 40 to 19 ka ago coincident with the last glacial maximum lgm through early deglaciation modern surface winds are not sufficient for sustained eolian sand transport when the dunes were active winds blew at velocities of at least 4 m s from west to east and some vegetation was present the ratio of annual precipitation to potential evapotranspiration p pe was less than the modern ratio of 1 23 and may have been 0 30 caused by stronger winds which would have resulted in greater evaporation and or reduced precipitation the savannah river dunes are part of a larger assemblage of eolian dunes that were active in the eastern united states during and immediately after the lgm suggesting that eolian sediment behavior in this region has been controlled by regional forcing mechanisms during the quaternary

soil morphology of an alluvial chronosequence from the little river north carolina coastal plain usa abstract a soil chronosequence on terraces of the little river in the north carolina coastal plain was characterized to evaluate age related trends in pedogenesis five representative pedons per landform were studied from six late quaternary fluvial surfaces and temporal trends were assessed by regression of morphological parameters against previously reported terrace optical age estimates solum b horizon and bt horizon thickness subsoil clay content and buntley westin index rubification have strong positive correlations with age and together distinguish between soils of the floodplain 200 yr bp the first terrace 9 9 2 0 ka intermediate surfaces t2 t3b t4 17 4 4 2 74 6 10 4 ka and the oldest terrace t5b 94 0 15 9 ka over time soils develop from entisols with respective a c and a e bw c profiles on the floodplain and first terrace to ultisols with increasing argillic horizon thickness rubification and clay content on t2 t5b solum thickness bt horizon thickness and clay content display linear increases through time with soil thickening reflective of downward pedogenesis through permeable coarse grained alluvium increasing argillic horizon clay content is attributable to illuviation and possibly also to a combined bioturbation translocation process whereby clays scattered throughout sandy parent sediments are delivered to the surface by bioturbation then concentrated in b horizons by eluviation illuviation rubification increases with age and reflects transformation and subsoil concentration of inherited free iron rather than iron oxide formation from primary mineral weathering t5b pedons display morphologies comparable to those of 200 ka to 1 ma soils along coastal plain rivers that also drain the appalachian piedmont probably because sandy coastal plain derived little river alluvium has a higher hydraulic conductivity that promotes faster rates of downward weathering clay translocation and rubification than the more finely grained sediments of piedmont draining rivers thus textural differences related to sedimentary provenance should be recognized when interpreting chronosequences from the region although rates of pedogenesis differ among coastal plain alluvial soils linear trends in the 100 ka little river chronosequence may nonetheless correspond to the early more linear phases of development in studies from the region that span much longer intervals of time

paleochannels indicating wet climate and lack of response to lower sea level southeast georgia large meandering paleochannels on the flood plain of the middle ogeechee river in southeast georgia represent wet paleoclimate during late pleistocene and early holocene time and show no indication of downcutting in response to eustatically lower sea level radiocarbon dates indicate that the paleomeanders were active at 31 28 ka and 8 5 4 5 ka bivariate regression models that correlate modern channel dimensions to the discharge of low magnitude floods 1 5 yr recurrence interval indicate that paleodischarge of floods during those times was at least double that of modern floods thus suggesting a wetter paleoclimate these data corroborate independent studies of pollen and paleoclimate simulations that indicate wet early to middle holocene 9 3 ka conditions that were characterized by intensified monsoonal circulation paleoclimate conditions at 31 28 ka are less well known our analysis of the middle ogeechee river flood plain indicates the absence of base level response downcutting to eustatic sea level lowering because the beds of the paleochannels are at approximately the same elevation as the bed of the modern channel this supports recent arguments that the geomorphic response of coastal plain streams to sea level lowering is most apparent in deltaic and shelf environments and may not be recognized very far upstream from the coast

late pleistocene and holocene environments of the southeastern united states from the stratigraphy and pollen content of a peat deposit on the georgia coastal plain abstract a 5 4 m peat core from the sandy run creek src valley in the upper coastal plain of georgia shows that before 30 ka the valley had an aggradational sandy floor with shallow swales and low ridges of 1 2 m amplitude suggesting a braided stream pattern and a low water table the climate from 30 25 ka was cool and dry and the vegetation open grassland with stands of pine and spruce that produced few fires at ca 16 ka a warmer wetter climate caused src to meander and incise the valley fill removing some previously deposited sediment at the site of our peat core so that sediments of 13 ka rest directly on sediments deposited at 25 ka after ca 13 ka higher groundwater levels initiated vertical accretion of floodplains allowing peat accumulation in shallow depressions across the valley pollen from the younger dryas period ca 13 11 ka indicates a cool moist environment of open oak woodland mesic trees riparian populations of alder and reduced levels of pine by the early to mid holocene tupelo and oak dominated over pine indicating wetter conditions while sand stringers in peat record periodic heavy rains an elevated water table and intervals of substantial runoff cooling after ca 4 5 ka brought drier and more variable conditions fires increased and southern pine replaced tupelo and oak the absence of sand stringers in peat younger than 4 5 ka indicates fewer intense rainfall events

channel bifurcation and adjustment on the upper yadkin river north carolina usa abstract the bifurcation of river flow around large stable islands also known as anabranching represents a distinctive form of river adjustment that is uncommon in the appalachian piedmont province of the eastern u s within this province highly localized river branching similar to classical anabranching forms exists in one area near the foot of the blue ridge escarpment this paper examines channel form and processes along a reach of the upper yadkin river in north carolina usa before and after a flood induced division of its flow into two subparallel branches both of which remain active 35 years later the research draws on aerial photograph analyses channel surveying and observations of inset channel benches flood frequency analysis and discharge monitoring and modeling to analyze planform history and to track and explain changes in newly excised and losing channels along the bifurcated reach the characterization of this branched reach resembles some descriptions of gravel dominated laterally active anabranching although the match is imperfect reductions in valley slope and confinement and the presence of local valley constrictions near the base of the escarpment steeplands have been conducive to long term sedimentation and a greater likelihood of branching a period of relatively rapid cross section adjustment occurred on both branches soon after bifurcation and this may have permitted the losing branch to remain open well stratified benches currently observed along the losing branch are interpreted to be largely the late product of a waning early major adjustment phase and moderate recent and perhaps ongoing variations in flow division and appear to be not fully adjusted to prevailing discharges coarse benches along the newly excised branch are better adjusted inset floodplain fragments created primarily by lateral migration and point accretion patterns of benchfull flow frequency variation are interpreted to indicate that the flow bifurcation ratio has been neither static nor monotonically changing in recent decades further exploration of branching in this environment otherwise dominated by single thread meandering patterns is of importance for a variety of management and ecological concerns

universal and local controls of avulsions in southeast texas rivers this study addresses the relative importance of universal and local factors in river avulsions from the perspective of the configurational complexity of the fluvial system as it relates to the potential for avulsions because local factors cannot be addressed without a specific context several rivers of the southeast texas coastal plain brazos navasota trinity neches and sabine rivers are studied based on field observations and surveys digital elevation models and geographical information system gis analysis avulsions are influenced by a combination of universal factors relevant to any alluvial river and local factors at least partly contingent on the environmental setting and history of the study rivers the universal controls are factors that create conditions under which avulsions can occur channel aggradation banktop discharge and cross valley slope advantages a rate of channel aggradation greater than that of floodplain accretion is an important setup factor but superelevation channel bed elevation greater than or equal to floodplain elevation behind the natural levee is not required slope advantages are necessary but not sufficient for avulsions to occur local factors include abandoned channels on the floodplain and basins or depressions associated with higher discharge pleistocene conditions the local controls also include deflection factors that divert flow from the main channel during high discharges and levee weaknesses relationships among the universal and local factors were represented as directed graphs and the configurational complexity determined using connectance entropy results show that the relative importance of universal and local factors varies with the scale or scope of analysis in the broadest context universal factors contribute more than 75 of the connectance entropy signifying the importance of identifying the key setup factors within a given aggradation or valley filling context however local factors account for more than 80 of the connectance entropy indicating that knowledge of the trigger factors and local floodplain morphology is the key to understanding and predicting avulsions this study suggests a three stage process for predicting avulsions first the universal factors can be used to identify reaches with the potential to avulse second superelevation a sufficient but not necessary condition can be used to identify specific locations where avulsions are imminent and as a necessary but not sufficient condition the absence of cross valley slope advantages can be used to identify locations where avulsions cannot occur the final stage predicting avulsions at other locations within systems or reaches where the setup factors are present requires specific consideration of local factors

optical resetting in large drainage basins tests of zeroing assumptions using single aliquot procedures abstract optical resetting of previously accumulated charge populations at the time of transportation and burial of sediments remains a critical assumption in luminescence dating this is particularly the case for fluvial sediments we have tested the extent of bleaching in fluvial environments by applying the single aliquot regeneration sar equivalent dose d e determination technique coupled with tests for partial bleaching in the majority of cases samples collected from a point bar complex on the colorado river texas exhibit evidence of incomplete bleaching use of the minimum sar d e in these cases resulted in estimated residual ages of c 100 300 years in a similar examination of sar d e s for bed load samples collected along the loire river we observe a monotonic decrease in effective equivalent dose d e from values of 14 10 2 and 3 2 mean median and minimum gy at source down to 3 3 3 6 and 1 6 gy in the first kilometre of transportation down to levels of 0 3 0 2 and 0 0 gy for transportation distances exceeding 300 km we observed virtually no effect on the d e in the bed load of the introduction of trunk tributary streams and conclude that the likelihood of resetting of osl in large fluvial systems is somewhat more effective that previously considered when the recycling of sediments down the system are borne in mind

a spatially lumped model to investigate downstream sediment flux propagation within a fluvial catchment abstract a spatially lumped process response model pacmod is presented which calculates long time series 103 106 years of fluvial water discharge and sediment load at the river catchment outlet based on climatic data drainage basin characteristics and user defined parameters key aspects of the model are i the lumped approach allowing for fast simulations and preserving the same resolution from palaeoclimatic conditions and geomorphological reconstructions ii the parameterization of sediment routing and storage within the catchment pacmod was successfully tested on observed data from three present day fluvial systems the meuse the waipaoa and the po rivers moreover the simulated sediment flux for the meuse and for the waipaoa rivers in the late quaternary is in agreement with published field and modelling work pacmod experiments show how the downstream propagation of the original climatic signal is hampered by sediment routing and storage within the catchment

continental shelf landscapes of the southeastern united states since the last interglacial abstract the wide sediment starved continental shelf and modern coastal areas of the southeastern united states retain well preserved but scattered remnants of a submerged paleolandscape this paper presents a conceptual model of stratigraphic deposition and landscape formation since the last interglacial on the continental shelf of south carolina with portions of north carolina georgia and florida usa data for this study include multibeam bathymetry surveys sidescan sonar mosaics high resolution subbottom profiles and ground truth surveys from 250 m to the modern tidewater region four bathymetric zones are recognized with eleven landforms and landform indicators the described zones range in depths from the modern shoreline across the shelf and over the shelf edge to 250 m msl relative sea level curves are presented for the area and discussed in conjunction with cultural and climatic events the potential for preservation of paleoamerican sites is high at the shelf edge between 130 m and 45 m with archaic and later occupations likely in depths of less than 25 m prominent vantage points for paleoamericans 11 kya would have existed at the shelf edge and tidewater resources would have been available nearby for a period of almost 6 ka rapid transgression rates 60 km ka after the sea level rose over the shelf edge make preservation of tidewater sites less likely on the outer and middle shelf searches for the earliest paleoamericans should focus on promontories at the edge of the shelf and along future discoveries of paleoincisions on the shelf mapping and delineating this paleolandscape and associated unconsolidated sedimentary deposits interspersed with rocky plains and ledges will continue to be a priority to marine archeologists coastal managers fishery scientists and marine spatial planners over the next several decades

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

predicting channel patterns brewer paul lewin j 2001 predicting channel patterns geomorphology 40 pp 329 339 rae2008

chronology of inland eolian dunes on the coastal plain of georgia usa most inland eolian dunes associated with rivers on the georgia coastal plain probably date to glacial periods direct dating of the dune sand by optically stimulated luminescence dating combined with limiting ages from radiocarbon dating shows that dunes formed during isotope stage 2 stage 3 the transition between stages 4 and 5 and isotope stage 6 or earlier most of the dates indicate dune activity between 30 000 and 15 000 years ago holocene activity included limited and local reworking of the crests of some thick dunes along streams that flow from the piedmont

atmospheric re organization during marine isotope stage 3 over the north american continent sedimentological and mineralogical evidence from the gulf of mexico abstract mineralogical and sedimentological records from the gulf of mexico gom reveal major changes in the terrigenous particles provenance during the marine isotopic stage 3 mis3 that likely resulted from modifications of the environmental conditions including glacial activity and precipitation distribution over the north american continent the southeastern margin of the laurentide ice sheet lis was active throughout the entire mis3 whereas the southwestern margin contributed to short term meltwater events only during late mis3 some of the major mineralogical changes cannot be attributed to glacial activity but rather result from the changes in precipitation distribution combining sedimentological records from the gom with previously published climate related archives from the north american continent allows the reconstruction of two main schematic patterns of moisture inflow and precipitation distribution that may have prevailed during mis3 meltwater discharges contribute to modifying the lis configuration and the gom hydrological properties ultimately affecting large scale oceanic circulation and may have influenced atmospheric re organizations although the insolation variation rate appears to be the main driver of the system

late quaternary climates and river channels of the atlantic coastal plain southeastern usa abstract late quaternary river patterns and sedimentation styles reflect past climate changes in atlantic drainages of eastern georgia and the carolinas past climate episodes for the region are summarized from pollen and eolian sedimentary records that exhibit correlation to major changes in river channel patterns records of past river responses are derived from luminescence and radiocarbon dated landforms and strata slow tectonic uplift does not explain temporal changes in channel patterns drainage networks have not received meltwater from continental or mountain glaciers eustatic influence would have been most pronounced on the now submerged continental shelf prior to 6 ka and currently manifests only within 60 80 km of the present highstand shoreline human impact overshadows climatic changes during historic time but was negligible during prehistoric time the late quaternary fluvial system primarily responded to climatic fluctuations that drove changes in vegetation precipitation and runoff patterns prehistoric meandering paleochannels of the holocene stand as important references to guide natural channel rehabilitation efforts during the coldest climate phases of the late wisconsin stage ca 30 16 ka when forest vegetation was sparse and interspersed with grasses and herbs many rivers and streams were braided with eolian dunes on the floodplains the terminal wisconsin stage ca 16 11 ka exhibited rapid warming and forest expansion characterized by pronounced change from braided to meandering patterns with intermediate forms of sandy scroll bar patterns the younger dryas cold excursion is not readily apparent in the regional fluvial record unusually large meandering channels of the terminal wisconsin stage continue into the first half of the holocene and indicate significantly larger bankfull flood discharges during those times than during the last half of the holocene bankfull channels during the last half of the holocene retained meandering patterns but decreased to modern like dimensions suggesting more modern like flood regimes no clear fluvial response occurs to the presumed middle holocene climatic optimum hypsithermal the medieval warm period and little ice age or to recent instrumentally observed fluctuations in climate but little research has been done in these realms

avulsion regimes in southeast texas rivers avulsions relatively sudden changes in course or establishment of new anabranches are an important process in alluvial rivers their key role in floodplain construction and alluvial architecture and the general conditions favouring avulsions are well known however avulsion processes and evolution and the factors controlling avulsion regimes are poorly understood in the southeast texas coastal plain where avulsions are common features of the river valleys avulsions were studied on the lower brazos navasota trinity neches and sabine rivers using a combination of aerial imagery digital elevation models and field surveys avulsions have important influences on the surface morphology and contemporary processes in all five rivers features associated with avulsions are active and distinct throughout the study area and all the rivers have experienced geologically if not historically recent avulsions however no two of the study rivers have the same contemporary avulsion regime first order differences in avulsion style are controlled by the stage of valley filling and within the three rivers characterized by an unfilled incised valley antecedent morphology associated with late quaternary and holocene coastal and fluvial deltaic processes accounts for the major differences in the navasota 27 avulsions in 185 km and neches 21 in 340 km rivers subchannels associated with avulsions exist in all stages of development from active to infilled and some have occurred in recent decades the other rivers have fewer avulsions but both the sabine and trinity have experienced historic channel shifts only the brazos river has experienced no avulsions within the past c 300 years results show that even within a region of similar environmental controls and geological history local variations in inherited morphology can result in different avulsion regimes copyright 2008 john wiley sons ltd

late quaternary records of vegetation and fire in southeastern north carolina from jones lake and singletary lake abstract we conducted fossil pollen charcoal and geochemical analyses of sediment cores from jones lake and singletary lake spanning the last 50 000 cal yr b p to examine the linkages between climate vegetation and fire activity on the atlantic coastal plain and particularly emphasize changes since the last glacial maximum application of the modern analog technique mat to fossil pollen data allowed for quantitative estimates of holocene climate but pleistocene assemblages had no modern analogues preempting their use for quantitative reconstructions the mat data indicate markedly lower mean annual precipitation and temperatures during the late pleistocene relative to the holocene increased charcoal accumulation during interstadials indicates increased fire activity during these warm intervals geochemical data 13c 15n c n and pollen concentrations indicate a sparsely vegetated pleistocene landscape that produced few fires followed by an increase in biomass and fire activity around the lakes during the holocene transition a quercus spp maximum in the early holocene is associated with low charcoal abundances while increased dominance of pinus spp during the middle holocene is associated with dramatic increases in charcoal it is unclear if the quercus pinus transition was the result of changing fire regimes or if the fire regime changed in response to vegetation the regional asynchronicity of the quercus pinus transition may indicate another forcing mechanism besides climate change such as prehistoric human activity is responsible for the ecological change macroscopic charcoal and c n ratios reach unprecedented values during the late holocene possibly as a result of deforestation by both prehistoric native americans and later immigrant populations

depositional environment and luminescence chronology of the hoarusib river clay castles sediments northern namib desert namibia abstract the clay castles in the hoarusib river valley are fine grained deposits in a tributary immediately upstream of a narrow gorge sedimentological analysis reveals three lithofacies associations 1 channel facies association near the mouth of the tributary 2 back flow facies association in the middle section and 3 silt and massive sand facies association in the head of the tributary overall sedimentary architecture shows that aggradation of the main hoarusib channel led to back flooding into the tributary and the deposition of massive fine grained deposits decreased discharge competency increased sediment load and the presence of narrow gorges within the main valley are suggested as reasons for the aggradation inter fingering of desert derived sediments channeled down the tributary and backflow sediments from the main river indicate an increase in both upland and desert rainfall during the course of sedimentation optically stimulated luminescence osl dating of these deposits indicates formation between 44 and 20 ka with the possibility that deposition occurred during two phases of rapid sedimentation at ca 42 and 25 ka

terminal pleistocene braided to meandering transition in rivers of the southeastern usa abstract thirteen paleomeanders on the oldest parts of meander belts on floodplains in the coastal plain of georgia and the carolinas southeastern usa were selected for radiocarbon dating to determine the onset of meandering following braiding during the late pleistocene during oxygen isotope stage 2 the radiocarbon ages were compared to previously reported late pleistocene ages for braid bars and eolian dunes results indicate that meandering commenced at circa 15 000 to 16 000 cal years bp and continued throughout the terminal pleistocene and holocene correlation with other paleoenvironmental records indicates that this shift to meandering was associated with global warming and moister conditions in the southeastern united states that led to a denser vegetation cover and a reduction in sediment yield the shift to meandering was also associated with some incision and terracing of the late pleistocene braided fluvial surfaces paleodischarge of the bankfull condition of early holocene meandering channels was apparently greater than under modern conditions suggesting wetter conditions at that time than at present this braided to meandering transition in the southeastern united states provides an example of river response to global climate change in a relatively low latitude region of the world that was not influenced by glacial or periglacial landscape conditions

the relationship between flow shear stress and stream pattern based on simple hydraulic reasoning a discharge q slope s diagram for streams is given a physical interpretation permitting the assignment of a relative shear stress value to each stream a sample of 359 streams is used ranging in mean annual discharge from 900 000 to 0 05 ft 3s 1 varying in pattern from highly sinuous p 3 1 to straight and braided sorted according to their relative shear stress values 0 avg streams of high sinuosity p 1 5 are characterized by low relative shear stress median 0 56 which is significantly lower than that characterizing braided streams median 1 70 it is concluded that for natural stream populations the passage from one pattern to another is gradual and the geomorphic thresholds defined by relative shear stress are fuzzy ones

continental record of the southwest monsoon during the last 130 ka evidence from the southern margin of the thar desert india abstract field stratigraphy sedimentology and luminescence dating of the exposed fluvial and aeolian sequences from the southern desert margin were used to discern the pattern of southwest monsoon variability during the last 130 ka the sedimentary architecture and textural attributes of the sediments belonging to the period 130 120 ka suggests the existence of a meandering river system consequent to enhanced southwest monsoon conditions a shift from a meandering to a braided pattern during 120 100 ka indicates a phase of reduced precipitation presence of flood plain fines and bedded calcretes during 100 70 ka suggest a period of enhanced monsoon with seasonality following this a phase of weak monsoon activity was observed during 70 60 ka regional flood plain aggradation and pedogenesis during the period termination of a regional fluvial phase around 30 ka and incision of dunes dated to 20 11 ka suggest that the present rivers occupied their course between 11 ka drowned valleys in the estuarine zones suggest that the incision began during the low sea stand around 20 ka when the rivers were graded to the exposed shelf the incision intensified with the re establishment of monsoon during the early holocene

anastamosing channels in the lower neches river valley texas active and semi active anastomosing holocene channels upstream of the delta in the lower valley of the meandering neches river in southeast texas represent several morphologically distinct and hydrologically independent channel systems these appear to have a common origin as multi thread crevasse channels strongly influenced by antecedent morphology levee breaching leads to steeper cross valley flows toward floodplain basins associated with pleistocene meander scars creating multi thread channels that persist due to additional tributary contributions and ground water inputs results are consistent with the notion of plural systems where main channels tributaries and sub channels may have different morphologies and hydrogeomorphic functions the adjacent trinity and sabine rivers have similar environmental controls yet the trinity lacks evidence of extensive anastomosing channels on its floodplain and those of the sabine appear to be of different origin the paper highlights the effects of geographical and historical contingency and hydrological idiosyncrasy copyright 2014 john wiley sons ltd

channel braiding and stability of the brahmaputra river bangladesh since 1967 gis and remote sensing analyses spatial and temporal changes in channel distribution in the large sandy braided system of the brahmaputra river bangladesh were analyzed using satellite images and gis supervised classification of the images within the braided belt i e channels and bars between the bank lines provided raster land cover data for 14 different years between 1967 and 2002 the width of the braided belt the number and width of channels the distribution of land cover attributes and land stability change were examined from the data the results indicate that the recent history of the dynamics of the brahmaputra can be divided into four phases 1 the late 1960s to early 1970s 2 the mid 1970s to early 1980s 3 the mid 1980s to early 1990s and 4 the mid 1990s to early 2000s spatial distributions of the land cover and channels in phase 4 were the least complex suggesting a state of dynamic equilibrium land cover and channel distributions during phase 2 were partly less complex indicating quasi dynamic equilibrium phases 1 and 3 can be regarded as transitional phases with more complex conditions frequent large floods may have triggered significant changes in the river system during phases 1 and 3

river morphology and thresholds the regime geometry and channel patterns of alluvial rivers are analyzed wing an energy approach together with physical relationships of flow continuity flow resistance and sediment transport because of the discontinuity in flow resistance and thus in power expenditure between lower and upper flow regimes the adjustment in river regime consists of sudden changes in channel geometry channel pattern and sometimes silt clay content when such a discontinuity is crossed thresholds or discontinuities in river morphology are obtained in the analysis in accordance with such thresholds rivers of distinct morphological features are classified into four regions based upon the bankfull discharge channel slope and median size of bed sediment their respective features are described and certain regime relationships for channel width and depth are established the predicted channel geometries are compared with river data

regional variation in the terminal pleistocene and early holocene radiocarbon record of eastern north america in this paper we use radiocarbon dates to evaluate the signature of the younger dryas chronozone ydc in eastern north america using an approach that examines radiocarbon dates by region we argue that the northeastern united states shows a better overall representation of radiocarbon dates when compared to the mid atlantic and southeast these data result in a peak in summed probability distributions during the ydc which is often interpreted as evidence of population growth further examination of these distributions however illustrates that differential standard deviations varying sample size and the effect of taphonomic and research biases likely overwhelm any demographic signatures in our study sample consequently the frequency of radiocarbon dates by itself is insufficient for understanding the relationship between climate culture and demography in eastern north america

controls on late quaternary incised valley dimension along passive margins evaluated using empirical data incised valleys are canyon like features that initially form near the highstand shoreline and evolve over geological time as rivers erode into coastal plains and continental shelves to maintain equilibrium gradient profiles in response to sea level fall most of these valleys flood during sea level rise to form estuaries incised valley morphology strongly controls the rate of creation of sediment accommodation valley fill facies architecture and the preservation potential of coastal lithosomes on continental shelves and affects coastal physical processes nonetheless little is known about what dictates incised valley size and shape and whether these metrics can be used to explain principal formation processes the main control on alluvial channel morphology over human time scales is discharge this is based on numerous empirical studies and is well constrained because all variables are easily measured at this short time scale knowledge of long term river evolution over a complete glacio eustatic cycle on the contrary remains largely conceptual experimental and based on individual systems because variables that are thought to drive morphological change are not easily quantified in spite of this difficulty existing models of incised valley formation at the coast suggest that valley evolution is driven largely by downstream forcing mechanisms highlighting sea level and shelf gradient morphology as the dominant controls on valley incision although valleys are cut by rivers whose channels are a direct reflection of discharge little empirical data exist in coastal areas to address the degree to which valley evolution is governed by upstream controls the late quaternary is the best time period to examine because it provides the most complete sedimentary record and many variables including sea level tectonics substrate lithology and drainage network characteristics are accurately constrained here 38 late quaternary valleys along the coast of two different passive continental margins are compared which suggests that valley shape and size are governed primarily by upstream intrinsic controls such as discharge valley width depth and cross sectional area are found to be predictable at the highstand shoreline and are scaled with the size of their drainage basin which has important implications for estimating sediment discharge to continental shelves and deep water environments during periods of low sea level

late quaternary hydroclimatology of a hyper arid andean watershed climate change floods and hydrologic responses to the el nino southern oscillation in the atacama desert abstract although certain characteristics of the el nino southern oscillation enso are well known on contemporary timescales less is known about the magnitude frequency relationships of this atmospheric phenomenon on longer timescales or its relationship to widespread flooding especially in its core zone along the sub tropical andes where la nina or el nino episodes control regional hydroclimatology using a combination of stratigraphic evidence geochronologic dating 14c and osl stable isotope analyses and water geochemistry along the rio moquegua in the northern fringes of the atacama desert we assemble a paleoflood chronology for mainstem and tributary sections for the past ca 20 ka and ascertain the variation in enso frequency and magnitude because of the inherent watershed structure and regional hydroclimatology mid valley tributaries of the rio moquegua only flood during el nino episodes and thus provide an important proxy of extreme el ninos while mainstem stratigraphy records both la nina and el nino episodes el nino floods appear to have been pronounced during the late pleistocene and up to at least the younger dryas 12 000 cal yr bp while stratigraphic evidence of large el nino floods is lacking in tributary systems during the mid holocene flood stratigraphy in a 2 ka 7 m high terrace along the mainstem indicates an increased frequency and magnitude of large floods between ca 700 and 1610 ad as compared to the period from ca 160 bce to 700 ad with mega ninos occurring ca 1330 ad and ca 1650 ad water geochemistry and radiocarbon dating indicate that at least two major aquifers exist with wells and springs in the mid valley dating to 710 and 3100 14c yr bp respectively while water from a spring in the headwaters dates to 10 320 14c yr bp this range in dates suggests that groundwater flow in the mid valley is neither fossil water nor exclusively recharged from local precipitation while the older date for headwater sections suggests a more fossil groundwater source and lack of contemporary recharge the 18o similarity between groundwater in the mid valley and the regional meteoric water line mwl suggests a pacific moisture source and the role of el nino precipitation in recharging local aquifers thus el ninos and pacific sourced moisture are an important component of the regional hydroclimatology and the variation in enso frequency and intensity has significant social and hydrologic repercussions in these hyper arid settings

patterns of alluvial rivers the pattern planform of a river can be considered at vastly different scales depending upon both the size of the river and the part of the fluvial system that is under consideration figure 1 for example in the broadest sense river patterns comprise a drainage network dendritic parallel trellis etc figure la the type of pattern is of interest to geomorphologists and geologists who interpret geologic conditions from aerial photographs at another scale a river reach which in figure lb is meandering is of interest to the geomorphologist who is interested in what that pattern reveals about river history and behavior and to the engineer who is charged with maintaining navigation and preventing major instability when a single meander is examined figure 1 c the hydraulics offtow the sediment transport and the potential for bank erosion are of concern in addition the sedimentologist is interested in the distribution of sediment within the bend bed forms within the channel figure ld and sedimentary structures figure ie which also establish a component of roughness for the hydraulic engineer finally the individual grains figure if provide geologic information on the sediment sources the nature of sediment loads and the feasibility of dredging for gravel there is an interaction of hydrology hydraulics geology and geomorphology at all scales which emphasizes the point that the fluvial system as a whole cannot be ignored even though only a component of the system is to be studied in this review only the patterns or planforms of alluvial rivers are discussed although it is apparent that the hydrologic and sediment yield characteristics of the drainage basin figure la as well as its geologic history cannot be ignored in the explanation of the pattern of any river

the effect of a submarine canyon on the river sediment dispersal and inner shelf sediment movements in southern taiwan abstract this study examines the influence of a submarine canyon on the dispersal of sediments discharged by a nearby river and on the sediment movement on the inner shelf the study area includes the head region of the kao ping submarine canyon whose landward terminus is located approximately 1 km seaward from the mouth of the kao ping river in southern taiwan within the study area 143 surficial sediment samples were taken from the seafloor six hydrographic surveys along the axis of the submarine canyon were also conducted over the span of 1 yr three different approaches were used in the analysis of grain size distribution pattern they include 1 a combination of filtering and the empirical orthogonal eigen function eof analysis technique 2 the mclaren model and 3 the transport vector technique the results of the three methods not only agree with one another they also complement one another this study reveals that the kao ping submarine canyon is relatively a stratified and statically stable environment the hydrographic characteristics of the canyon display seasonal variability controlled primarily by the temperature field and the effluent of the kao ping river the hydrographic condition and the bottom topography in the canyon suggest the propagation of internal tides during the flood season summer of the kao ping river the submarine canyon acts as a trap and conduit for mud exchange between the kao ping river and offshore near the head of the canyon there is a region of sediment transport convergence this region is also characterized by high mud abundance on the seafloor that coincides with the presence of high suspended sediment concentration ssc spots in the bottom nepheloid layer outside the submarine canyon on the shelf where the evidence of wave reworking is strong the northwestward alongshore transport dominates over the southeastward transport which is a common theme on the west coast in southern taiwan

an optical age chronology of late pleistocene fluvial deposits in the northern lower mississippi valley the lower mississippi valley lmv contains many large braided channel belts that are preserved west of the holocene floodplain previous efforts to establish geochronologic control on channel belt construction have been hindered by the lack of organic material for radiocarbon dating luminescence techniques provide a burial date for the sediment itself and may prove useful in this context samples from three channel belts in the northern lmv were analyzed using the single aliquot regenerative technique on 90 125mm quartz optical ages 19 7 17 8 16 1 15 0 and 12 5 12 1 ka are consistent with geomorphic relationships and indicate that channel belts were formed in the late pleistocene under glacial conditions these optical ages provide the first detailed chronology of lmv channel belt formation and are the first step towards developing a chronology for the entire lmv r 2003 elsevier science ltd all rights reserved

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

influence of glacial isostatic adjustment on river evolution along the u s mid atlantic coast abstract long term river evolution depends partly on crustal deformation which shapes the topography crossed by rivers on glacial timescales ice sheet growth and decay can produce crustal vertical motion of 10 mm yr resulting from the solid earth s adjustment to variations in ice and water loads comparable to tectonically driven rates in the most rapidly uplifting mountains on earth this process of glacial isostatic adjustment gia can influence river courses and drainage basins substantially particularly near former ice margins we explore the extent to which gia influenced the evolution of rivers along the united states east coast during the last glacial cycle we compute gravitationally self consistent gia responses that incorporate recent constraints on the laurentide ice sheet history through the last glacial build up phase and we connect the predicted variations in topography to abrupt changes in river dynamics recorded in the hudson delaware susquehanna and potomac rivers from 40 ka to present to the extent that increases in sediment transport capacity imply increases in river incision rate the gia driven changes in slope and drainage area are consistent with episodes of erosion and sedimentation observed in the hudson delaware and potomac rivers but inconsistent with the observed accelerated river incision in the susquehanna river at 30 14 ka these analyses add to a growing body of evidence showing that gia strongly influences river evolution over millennial timescales

lacustrine sedimentary record of ice dammed neoglacial lake alsek neoglacial lake alsek is an ice dammed lake in the southwest yukon that forms when lowell glacier rapidly advances from a side valley to block the alsek river a sedimentary record of past fillings and catastrophic drainages is preserved in small lakes lying within the lake alsek basin sediment cores from some of these small lakes were retrieved and studied the cores were subjected to facies analysis involving description classification and interpretation of depositional processes leading to assessment of depositional environment despite a relatively sparse set of sedimentary data five distinctive deposits and associated environments can be recognized 1 matrix supported diamicton interpreted as a deposit of iceberg rafted sediment 2 sand and coarse silt interpreted as tractive current deposits 3 massive silt and clay interpreted as rapidly deposited lake margin derived sediment 4 laminated silt and clay interpreted as glaciolacustrine deposits and 5 carbonaceous muds interpreted as

net sediment transport patterns inferred from grain size trends based upon definition of transport vectors reply abstract a new approach to the analysis of the grain size trends associated with net sediment transport directions in shallow marine environments is developed here two specific trends modified from mclaren and bowles 1985 on the basis of a literature review are used to define a grid of trend vectors such vectors are filtered and transformed into transport vectors it is suggested that an ordered pattern of the transport vectors represents net transport paths the orderliness of the derived pattern is examined on the basis of a significance test using the average length of the transport vectors as a criterion both the filtering operation and the significance test procedure are based upon the assumption that the trend vectors which are not associated with net transport have the same probability of being in any direction the technique is applied to data from yangpu harbour southern china the technique can be applied to inner continental shelf and coastal environments for such an analysis the area under investigation should be sampled at an interval large enough to reflect the real grain size trends resulting from net sediment transport but small compared with the dimensions of the sedimentary environment the time scale of the results depends upon the sampling depth applicability of the technique is likely to be somewhat limited where the environment is highly variable over short distances furthermore due to its statistical character the analysis may fail to identify net transport patterns

sedimentation in proglacial sunwapta lake alberta the hydrologic and limnologic conditions of sunwapta lake a small proglacial lake in the canadian rocky mountains were investigated with special reference to the sedimentology of this lake discharge and suspended sediment concentrations of the inflowing streams were measured to give estimates of sediment input distribution of large loads of fine glacial sediment is largely by an inflow and wind controlled circulation which commonly fluctuates diurnally the spatial distribution of sedimentation was determined by use of sediment collecting pans placed on the lake bed turbidity currents are rare with only one event monitored in 2 years this event was caused by a burst of highly sediment charged inflow water the rarity of turbidity currents is attributed to the high sediment concentration in the lake water which results from the small size of the lake in relation to the inflow wind generated water movement at the lake floor ranges from 0 0 0 03 m s while the maximum recorded velocity of the turbid

subglacial meltwater origin and subaerial meltwater modifications of drumlins near morley alberta canada abstract drumlins in the bow valley west of calgary alberta are interpreted as the product of subglacial and subaerial meltwater erosion on the sides of the bow valley highly elongated streamlined first generation drumlins are aligned in an en echelon fashion and are not significantly modified by post glacial processes in the valley bottom scalloped stubby irregularly spaced second generation drumlins are found in close association with valley fill the drumlins are composed of bedrock and diamicton and some are overlain by a thin gravel veneer stratified gravel is found on the leeward flanks of some second generation drumlins meltwater erosional forms s forms found on the limestone bedrock up flow of the drumlins and crescentic furrows around their proximal ends indicate that subglacial meltwater beneath the bow valley ice was probably the main erosive agent responsible for the shaping of the drumlins the second generation drumlins are believed to be the remnants of the first generation drumlins that were dissected and reworked by postglacial subaerial meltwater flow s meltwater drainage from ice dammed glacial lake kananaskis and possibly other glacially dammed tributary valley lakes resulted in the deposition of megaripples 3 5 m high 40 m wavelength 8 km down flow from the drumlins and reverse eddy deposits on the flanks of the drumlins post glacial bow river incision and terrace development has continued to further sculpt these forms

william river an outstanding example of channel widening and braiding caused by bed load addition the lower william river in northwestern saskatchewan canada presents an excellent and unambiguous example of rapid channel adjustment to abrupt additions of sandy bed load a relatively narrow and deep single channel stream as it flows northward to lake athabasca the river picks up a 40 fold increase of bed load over a 27 km reach as it encounters a large dune field just south of the lake as a result of the large infusion of eolian sand the channel develops a thoroughly braided pattern while undergoing a 5 fold increase in width and a 10 fold increase in width depth ratio

sedimentology and origin of deposits from a small ice dammed lake leirbreen norway this paper describes recent proglacial lacustrine sediments exposed by the drainage of a small probably never more than 0 03 km2 ice dammed lake basin at leirbreen central jotunheimen norway the dominant facies include ripple laminated massive and horizontally stratified sands massive and horizontally laminated silts and irregularly laminated fine sands and silts the major control on lake circulation and the nature and distribution of these facies was an underflow driven by a subglacial meltwater stream which formed the major lake input although much of the sedimentary sequence indicates a pulsatory input the proximal character of this small lake prevented the development of classic varved silts compressional deformation of shoreline sediments was due to winter lake ice push other deformational processes included the grounding of icebergs water escape and syn sedimentary downslope collapse observations from an adjacent small ice marginal lake at leirbreen provide support for several of the inferences drawn from the sediments of the former ice dammed lake

was the laurentide ice sheet significantly reduced during marine isotope stage 3 accurately reconstructing the paleogeography of the laurentide ice sheet lis during marine isotope stage 3 mis 3 ca 57 000 to ca 29 000 yr b p is critical for understanding glacial growth toward the last glacial maximum lgm refining sea level histories and studying the earth system response to rapid climate change events here we present a geochronological data set useful for testing hypotheses of global sea level and refining ice sheet configuration through this interval data n 735 span the entire mis 3 interval and consist of 14c determinations n 651 cosmogenic exposure ages n 52 and optically stimulated luminescence dates n 32 on that basis we hypothesize that the central region of the lis underwent a dramatic reduction in ice from ca 52 to 40 ka key to this hypothesis are geological records at sites in the hudson bay lowlands east central canada that suggest a marine incursion and development of terrestrial landscapes we show that these landscapes are consistent with recently published glacial isostatic adjustment predictions that include widespread deglaciation of the eastern labrador sector of the lis with ice buildup over the western keewatin sector at 42 ka ice growth from this minimum toward the lgm is likely to have been rapid the agreement between this data set and modeling predictions prompts the reassessment of key late pleistocene records including heinrich events loess deposition in the continental united states and sedimentological records from the gulf of mexico

characteristics and osl minimum ages of relict fluvial deposits near sossus vlei tsauchab river namibia and a regional climate record for the last 30 ka the present end point of the tsauchab river is at sossus vlei 30 km into the namib sand sea interdune deposits in three depressions west and southwest of the vlei include channel and interdune lithofacies associations but no deposits typical of river end points or of groundwater seepage into interdune areas the two lithofacies associations show that the tsauchab river extended further into the sand sea in the past it had a well developed channel and a higher flow than today that caused flooding of adjacent interdune areas osl 4 mm aliquot minimum ages indicate that the tsauchab river reached 2 3 km beyond its present end point at ca 25 ka and ca 9 7 ka and that the river was more active from 0 9 0 3 ka the eastward migration of the river end point since ca 7 ka suggests a reduction in flood magnitude accompanied by the gradual invasion of the sossus vlei area by dunes the regional data indicate an additional wet interval at ca 15 ka that is so far not recorded in the sossus area copyright 2006 john wiley sons ltd

fluvial terrace formation in the northern upper rhine graben during the last 20 000 years as a result of allogenic controls and autogenic evolution abstract the northern upper rhine graben hosts a well preserved late weichselian and holocene fluvial terrace sequence terraces differ in elevation morphology and overbank sediment characteristics the purpose of this study was to determine the relative importance of allogenic controlling factors versus autogenic evolution on the successive formation of these terraces for a representative valley segment the gernsheim region results from previous research were integrated with newly obtained borehole data and digitized elevation maps to construct palaeogeographic maps and cross sections coarse grained channel deposits below terrace surfaces were dated using optically stimulated luminescence and fine grained abandoned channel fill deposits were dated using pollen stratigraphy and radiocarbon analysis initiation of terrace formation was caused by climatic change in the late pleniglacial after 20 ka but fluvial response was complex and slow and continued locally until the middle boreal 9 ka early to middle holocene 6 ka changes in fluvial style and associated overbank lithofacies are not necessarily controlled by climatic change as was previously proposed instead autogenic processes combined with river reach specific factors explain the observed terrace development continuous incision autogenic evolution and high preservation potential provide an alternative explanation for the presence of a terrace sequence in this subsiding area