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

influence of neotectonism on geomorphology and depositional architecture of the gandak megafan middle ganga plain india abstract the gandak megafan formed by episodic tilting of tectonic block followed by an eastward shift of the gandak river the study area has been identified with 5 distinct depositional units which were chronologically named as oldest gandak plain osgp old gandak plain olgp gandak terminal fan gtfn i ii and iii an integrated approach including morphometry pedology gpr study and osl dating was adopted to study morphotectonics of the megafan dem of the megafan and anomalies in drainage of the area helped to delineate ne sw trending normal faults which divide the megafan block into 3 tectonic sub blocks present day channels reciprocate the fault movements through anomalies in drainage and change in sinuosity around the faults sinuosity of the gandak chhoti gandak and other small streams daha gandaki and rohini varies from 1 6 4 5 and 3 5 respectively which suddenly increases across faults the concurred variations in longitudinal river profiles and sl index appear to be attributable to the tectonic controls the development of these faults and subsequent tilting of the sub blocks influenced the sedimentary architecture and fluvial geomorphology of the megafan a linear arrangement of natural waterlogs and paleochannels observed in satellite images imply lateral shifting of the gandak river older depositional units osgp and olgp show well developed thick solum formation 2 2 m and 1 9 m respectively comparatively the younger units i e terminal fans show poor to no development of soil with 1 2 m to 0 8 m thick successions osl dates indicate that older and younger units were deposited between 10 7 and 8 5 ka and 5 7 and 1 4 ka respectively the tectonically stable period of 3 ka is also exhibited by non depositional surfaces in soil successions

sone megafan a non himalayan megafan of craton origin on the southern margin of the middle ganga basin india abstract researchers in the last few decades have focused on the fluvial megafans at the base of himalayan foothills in the ganga basin no major effort has so far been made to delineate any such large depositional environment at the base of the northern indian peninsular craton at the distal parts of the basin in this work for the first time we document a megafan unusually created by the cratonic sone river in the marginal plains south of the ganga the geomorphology of the megafan surface distribution of palaeochannels sedimentology and areal extent of the megafan are described the study also reconstructs the tectonic and palaeoclimatic conditions which might have helped in sediment supply from the cratonic catchment areas of the sone we suggest tectonic control over the sone river channel dynamics and development of the megafan the oval and fan shaped craton derived sediment body covers an area of around 12 000 km2 in the marginal plains and about 9000 km2 in the central alluvium north of the ganga river the megafan is around 190 km long and 240 km wide the mean slope of the megafan surface is 0 03 an onlap of himalayan sediments has occurred over the megafan at its toe parts caused by southward encroachment of the ganga during the holocene the megafan sediments comprise brownish yellow fine to coarse sand and gravels with an admixture of carbonaceous nodules kankars the thickness of the megafan sediment which directly overlies the precambrian basement varies from only a few meters in the south near the peninsular craton to 1000 m at the north in the central alluvial plain the granular zones form prolific aquifer systems in an otherwise poor hydrogeological setting of the marginal plains

facies analysis of the kosi megafan deposits abstract the kosi river shows distinct changes in its channel pattern from chatra where the river enters the indogangetic plains to kursela where it joins the ganga river i e gravelly sandy braided zone 1 sandy braided zone 2 and straight zone 3 to meandering zone 4 facies analysis of the kosi channel deposits suggests that in zones 1 and 2 mid channel bars islands side bars 3 d dunes and various types of linguoid dunes are the most common features large linguoid dunes with lengths of up to 1 km and with superimposed smaller 3 d dunes are also common the deeper parts of the channel are probably characterized by longitudinal bars in zone 1 and sandwaves in zone 2 lateral accretion of sandy bars is a significant process in these zones zone 3 is characterized by side bars with deposition by lateral accretion as on point bars linguoid dunes may migrate up a side bar or move across it subparallel to the main channel thalweg the uppermost sedimentary sequence 8 10 m thick of the kosi megafan consists of mainly sands and minor gravels in the proximal northern half and sand and mud 45 vol in the distal southern half of the megafan this downfan trend reflects the change from braided to straight channel pattern numerous spring fed streams rework the surficial sediments of the megafan and produce a fining upward sequence up to 4 7 m thick on top of braided straight channel deposits of the megafan

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

response of the ganges dispersal system to climate change a source to sink view since the last interstade the forcing of sediment dispersal systems by climate is widely accepted but there remains disagreement on the general responses to climate change such as how resulting signals propagate downstream and ultimately how they are preserved in the stratigraphic record towards a better understanding of these issues this paper presents a comprehensive overview of ganges dispersal system behavior since the last interstade which reveals major coeval responses to changes in the south asian monsoon at 3000 km from its mountain headwaters to deep sea fan the ganges dispersal system is immense and yet shows tight coupling between source area catchment basin and coastal and marine depocenters furthermore system wide responses and downstream transfer of the signal appear to occur at least as fast as current temporal resolution of 1 2 ky this tight linkage of source to sink components is considered a function of the southwest summer monsoon s overwhelming control on regional hydrology about 80 of the ganges discharge and 95 of its sediment load are delivered to the margin during only 4 months making the system extremely sensitive to this seasonal forcing in addition the regional scale and distribution of the monsoon weather system means that changes in atmospheric circulation affect the entire drainage basin rather than local subcomponents finally despite its present intensity strength of the summer monsoon has varied significantly over the past 150 ky under orbitally driven changes in insolation and global glacial boundary conditions the resulting changes in precipitation both well above and below modern values have forced system wide responses ranging from glacier advance retreat to sediment fluxes to the margin and deep sea fan the overall conclusions are 1 that this immense dispersal system responds to multimillennial scale 104 years climate change in a system wide and largely contemporaneous manner and 2 that major sedimentary signals can be transferred rapidly from source to sink with little apparent attenuation furthermore these acute responses to climate change have produced sedimentary stratigraphic features that diverge from traditional sequence models in their nature and timing

sandstone body variability in the medial distal part of an ancient distributive fluvial system salt wash member of the morrison formation utah u s a abstract plan view exposures of the salt wash member of the morrison formation in central utah provide unique insights into the characteristics of fluvial sandstone bodies associated with ancient distributive fluvial systems dfs here we use field based observations and data from an unmanned aerial vehicle and structure from motion photogrammetry to document and interpret sandstone bodies across a 10 km2 area from the medial distal portion of the salt wash dfs we divide the fluvial sandstone bodies into four distinct groups very narrow narrow and medium width sandstone bodies as well as an additional classification of other sandstones very narrow sandstone bodies are 100 m and poorly exposed the sandstone bodies record a portion of the dfs that was occupied by fluvial channels with multiple orientations sizes and plan view morphologies similar to the variety of channels observed on modern dfs because the fluvial deposits are composed of distinct sandstone body types mean values from the combined data set tend to obscure important aspects of the depositional history cyclical deposits in the salt wash member suggest that autogenic processes were important in this region consistent with modern dfs overall dfs depositional models derived from regional scale studies provide an excellent framework for interpreting dfs strata however smaller scale details of these deposits particularly the variability in sandstone body orientations are not addressed by existing models

quaternary fluvial systems of tropics major issues and status of research abstract fluvial systems in tropical regions are not only the lifeline for modern civilizations there but also form an important continental archive for reconstructing quaternary palaeoclimates and palaeoenvironments tropical rivers drain through a variety of geological and geomorphological settings across the world and have been studied for their hydrology sediment transport characteristics facies models stratigraphic development and flood hazards this paper presents an overview of the research on tropical rivers globally and identifies major gaps and unanswered research questions as a part of the igcp 582 on tropical rivers the participants of this project are continuing to tackle many of these issues the collection of papers in this special issue is an outcome of this activity and presents new data on processes and alluvial stratigraphy of the tropical rivers from china india south america and northern australia

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

luminescence chronometry and late quaternary geomorphic history of the ganga plain india abstract flexing of the indian lithosphere due to the continent continent collision and thrust fold loading produced the gangetic foreland basin during the middle miocene the basin attained its present configuration during the late quaternary neotectonics and climate change since the last interglacial influenced the evolution of the present landscape of the gangetic ganga plains the regional geomorphic surfaces in these plains are 1 upland interfluve surface t2 2 marginal plain upland surface mp 3 megafan surface mf 4 piedmont fan surface pf 5 river valley terrace surface t1 6 active flood plain surface t0 minor geomorphic features comprise ponds alluvial ridges and small channels which occur on the upland interfluve surfaces the present contribution reviews geomorphic processes that sculpted the basin landscape and then using the blue green stimulated luminescence bgsl and infrared stimulated luminescence irsl ages provides a first order chronological framework for the relationship of major and minor geomorphic features to climate and tectonics luminescence dating of the upland interfluve surface t2 shows that formation of this surface started before 51 ka and continued at least up to 7 ka deposition in the marginal plain mp began at least at 76 ka and continued after 32 ka bracketing the evidence of a more humid climate during 50 40 ka sedimentation on the t2 and mp surfaces was synchronous the top of these surfaces gives variable ages ranging from 48 to 7 ka due to differential erosion of an undulatory topography caused by tectonic activity age upper bound for the initiation and termination of the final building phase of ganga megafan can be placed at 26 ka and 22 ka respectively deposition on piedmont fan surface continued between 8 and 3 ka the river valley terrace surface t1 of ganga river shows the activity of yazoo type channels during 3 1 1 ka the last phase of active accretion on the narrow poorly developed youngest active flood plain surface t0 was after 1 5 ka the ponds of t2 surface formed due to cessation of fluvial activity sometime during 8 6 ka a prominent tectonic activity at 7 5 ka and dry climate at 5 ka produced undulatory topography and high siltation rates in the lakes and ponds the peripheral bulge southern ganga plain has been tectonically active causing deep incision of rivers and a 40 ka seismic event and mid late holocene tectonic activity can be inferred

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

basin scale stratigraphic architecture and potential paleocene distributive fluvial systems of the cordilleran foreland basin alberta canada abstract the paleocene paskapoo formation in western canada is composed of several hundred meters of fluvial strata that were deposited in an actively subsiding retro arc foreland basin adjacent to the southern canadian cordillera here we utilize newly available subsurface data from down hole gamma ray well logs to reconstruct the large scale fluvial stratigraphy and depositional history of the paskapoo formation in the central portion of the cordilleran foreland basin in alberta paleocene fluvial strata in this region contain several notable characteristics including variable degrees of channel sandstone amalgamation regionally variable stratigraphic architecture and a large fan shaped sandstone unit that emanated from the adjacent fold thrust belt fluvial channel sandstone bodies are abundant and amalgamated near the base of the formation in the southern portion of the basin but become less apparent in the northernmost 100 km of the basin the middle interval of the paskapoo formation characterized by abundant mudstone with isolated channel sandstone bodies is prevalent across the entire study area the upper portion of paskapoo formation is dominated by a large 5000 km2 north northwest trending laterally continuous sandstone in the northern portion of the basin that abuts against the fold thrust belt and fans outward into the basin this feature is interpreted as either a distributive fluvial system or a fixed outlet river system that experienced repeated avulsions this area of the fold thrust belt may be the site of a long lived fluvial outlet the variable degree of sandstone amalgamation in the paskapoo formation suggests two different modes in the relative ratio of accommodation to sediment supply periods of rapid subsidence likely associated with thrust emplacement in the adjacent fold thrust belt resulted in mudstone dominated successions with isolated sandstone bodies whereas tectonically inactive periods associated with less subsidence resulted in amalgamated sandstone units the principal stratigraphic features reconstructed from the data in this area can be used to better understand and predict fluvial stratigraphy within other foreland basins

late cretaceous fluvial megafan and axial river systems in the southern cordilleran foreland basin drip tank member of straight cliffs formation and adjacent strata southern utah u s a abstract the upper cretaceous lower campanian drip tank member of the straight cliffs formation in the grand staircase region of southern utah is an upward coarsening sandstone rich low sinuosity fluvial deposit in the cordilleran foreland basin the drip tank member thins from 75 m to 30 m eastward across the basin foredeep approximately parallel to its dominant eastward sediment dispersal direction and thins southward along the foredeep to as little as 17 m near its southern outcrop extent along modern cliff lines it overlies and underlies mudstone rich fluvial strata of the john henry member of the straight cliffs formation and lower member of the wahweap formation respectively both of which were deposited by northeast flowing rivers the john henry drip tank contact lies in an interfingering progradational stratigraphic transition from medium grained lenticular sandstone bodies to tabular coarse grained amalgamated sandstone bodies the contact with the overlying wahweap formation is locally a prominent surface of erosion or sediment reworking sandstone petrography and detrital zircon age populations of the strata indicate detrital sources in basement south of the foreland basin thrust sheets to the west and magmatic arc rocks to the southwest the uppermost part of the john henry member contains as much as 10 feldspar and abundant 1 84 1 60 ga detrital zircons derived from yavapai mazatzal basement rocks in the mogollon highlands the drip tank member ranges from quartzarenite to chert bearing sublitharenite with grenville 1 2 1 1 ga neoproterozoic and early paleozoic detrital zircons derived from proterozoic through jurassic strata exposed in the sevier orogenic belt lower member wahweap litharenites contain abundant thrust belt derived detrital carbonate grains absent from compositionally mature drip tank sandstones as well as a broad range of zircon ages the drip tank member constitutes deposits of a sand rich fluvial megafan or distributive fluvial system that displaced a subjacent but partly time equivalent axial fluvial system eastward as the megafan driven in part by seasonally high discharge fed by monsoonal precipitation prograded across the basin foredeep a thick amalgamated fan axis succession present in northern exposures contrasts with a thinner fan flank succession in southern localities tabular sixth order lithosomes each containing channels on the order of 7 m deep define three individual fluvial fans or fan lobes in the megafan system younger wahweap fluvial channels eroded uppermost drip tank deposits of the fan axis and fan flank transverse fan progradation across the foredeep recorded falling accommodation sediment supply in an aggradational to progradational systems tract erosion and reworking of the upper fan surface record decreased accommodation sediment bypass and erosion prior to reoccupation of the foredeep by the wahweap axial fluvial system the upper contact of the drip tank member is thus the primary sequence boundary in this multi component fluvial system and the lower wahweap represents transitional systems tract deposits accumulated as accommodation sediment supply increased

eddy kuroshio interaction processes revealed by mooring observations off taiwan and luzon the influence and fate of westward propagating eddies that impinge on the kuroshio were observed with pressure sensor equipped inverted echo sounders piess deployed east of taiwan and northeast of luzon zero lag correlations between pies measured acoustic travel times and satellite measured sea surface height anomalies ssha which are normally negative have lower magnitude toward the west suggesting the eddy influence is weakened across the kuroshio the observational data reveal that impinging eddies lead to seesaw like ssha and pycnocline depth changes across the kuroshio east of taiwan whereas analogous responses are not found in the kuroshio northeast of luzon anticyclones intensify sea surface and pycnocline slopes across the kuroshio while cyclones weaken these slopes particularly east of taiwan during the 6 month period of overlap between the two pies arrays only one anticyclone affected the pycnocline depth first at the array northeast of luzon and 21 days later in the downstream kuroshio east of taiwan

basin scale hydrology and sediment dynamics of the kosi river in the himalayan foreland abstract hydrological and sediment transport characteristics for the kosi basin which covers parts of nepal and india were analysed to understand the spatiotemporal variability of the hydrology and sediment dynamics of the kosi basin and its implications for flood hazard and sediment dynamics the study revealed that 56 of the discharge at chatara where all major tributaries of the kosi meet is contributed from the western part of the basin even though this constitutes only 34 of the total basin area in contrast the central and eastern parts of the basin constitute 57 and 8 of the basin area but contribute 38 and 16 of the discharge at chatara respectively the contribution of sediment load at chatara from the different tributaries of the kosi river also shows a similar pattern of a total of 100 million tonnes of the annual sediment load at chatara 56 is transported from four tributaries the indrawati bhote kosi tama kosi all draining from the west and tamor the remaining 44 is transported by other tributaries upstream of chatara the most important being the arun dudh kosi and sun kosi sediment budgeting in this study based on annual sediment load data suggested that 20 million tonnes of sediments are deposited between chatara and birpur annually this study also found that 53 million tonnes of sediments are being accommodated between birpur and baltara annually sediment dynamics in the kosi basin emerges as the most important river management issue and this is closely linked to channel instability and frequent flooding in the alluvial plains

historical geomorphology and pedology of the gandak megafan middle gangetic plains india the gandak megafan of eastern uttar pradesh and northwestern bihar lies in the middle gangetic plains the gandak river has shifted about 80 km to the east due to tilting in the last 5000 years this has created a soil chronoassociation similar to the chronosequences found on some flights of river terraces this chronoassociation has five members qgd1 5 they are distinguished on the basis of profile development clay mineralogy and calcium carbonate content chlorite transforms to vermiculite on a large scale from qgd1 to qgd3 and decreases drastically in member qgd4 kaolinite and interstratified kaolinite smectite are abundant in the older members of the chronoassociation the youngest soils qgd1 500 b p while qgd3 soils like those on the older gandak plain and old rapti plains date back to 2500 b p qgd4 soils like those on the oldest gandak plain are dated as 5000 years b p whilst the oldest qgd5 soils as on the old ghaghra plain and ganga ghaghra interfluve date back to 10000 b p these soils which include pedogenic calcite and a saline epipedon indicate a dry climatic spell during the period 9000 11000 b p faults developed on the megafan are not related to the basement structures

kosi megafan historical records geomorphology and the recent avulsion of the kosi river abstract it has been proposed that the kosi river continuously migrated 113 km westward across the surface of the megafan over the last two centuries examination of a number of old maps published between 1760 and 1960 shows that during most of this period the kosi river occupied a position slightly east of the megafan axis the apparent channel movement shown in these maps is oscillating in nature and not unidirectional instead of encountering deposits left behind by a sweeping braided kosi like stream a preliminary study of the uppermost 2 5 m succession in the north central part of the megafan reveals overwhelming dominance of meandering stream deposits assuming the existing notion of kosi river migration the rate of deposition averaged over 100 200 years for the uppermost 5 10 m of megafan deposits works out to be unusually high 50 mm y all these observations question the soundness of the hypothesis of rapid westward migration of the kosi river over the last two centuries the existing facies model for the uppermost 8 10 m of the megafan deposits also appears untenable the three dimensional geometry of the kosi megafan is similar to those of typical alluvial fans but with much gentler gradient 0 05 0 01 and with larger area 10 000 km 2 based mainly on the patterns of paleo and modern channels recognised in the satellite images three major accretionary lobes can be identified on the kosi megafan relative age of the lobes determined from the truncating relationship of the paleochannels indicates a random shift of the trunk channel forming these lobes similar multilobate form and evidences of random switching of the loci of lobe aggradation are also found to be common in the tista and taquari megafans the factors known to favour avulsion and the results of the recent simulation studies of alluvial deposits are inconsistent with the notion of unidirectional shift of the channels for more than 100 km across the entire megafan surface this study suggests that the relocation of the kosi river in the past was through random nodal avulsion rather than systematic unidirectional shift the recent avulsion of the kosi channel by a large distance to the east follows this expected pattern further study and age dating is required for a comprehensive understanding of the depositional dynamics of the megafan and the pattern of channel movement on it future flood predictions and disaster management plans should be based on such comprehensive understanding

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

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

late pleistocene holocene development of the tista megafan west bengal india 10 be cosmogenic and irsl age constraints abstract the himalayan proximal foreland is characterized by quaternary megafans of which the formational mechanisms remain debated the tista megafan spreads over more than 16 000 km2 from the mountain front where it is strongly incised to the confluence of the tista river with the jamuna brahmaputra river and stores sediments produced in the sikkim himalaya we propose a scenario for the late pleistocene holocene development of the tista megafan based on new 10be cosmogenic and infra red stimulated luminescence irsl age constraints and discuss the main potential controls on its evolution we suggest that two distal lobes developed successively downstream from a common proximal lobe deposition in the proximal lobe took place since at least 135 ka and incision began at 3 7 0 7 1 0 ka the western distal lobe of the megafan was deposited early in the history of the megafan when the sikkim himalaya catchment was drained by a tributary of the ganga river and was abandoned in the early holocene 10 11 ka the eastern recent

large scale structure of calamus river deposits nebraska usa revealed using ground penetrating radar the large scale i e bar scale structure of channel deposits of the braided low sinuosity calamus river nebraska is described using ground penetrating radar gpr profiles combined with vibracores basal erosion surfaces are generally overlain by medium scale trough cross stratified sets 3 25 cm thick very coarse to medium sands that are associated with relatively high amplitude discontinuous gpr reflectors overlying deposits are bioturbated small scale cross stratified sets 3 cm thick and vegetation rich fine to very fine sands that are associated with low amplitude discontinuous reflectors near surface peat and turf have no associated gpr reflectors in along stream profiles through braid and point bars most gpr reflectors dip downstream at up to 2 relative to the basal erosion surface but some reflectors in the upstream parts of bars are parallel to the basal erosion surface or dip upstream in cross stream profiles through bars gpr reflectors are either approximately parallel to bar surfaces or have low angle inclinations up to 6 towards cut banks of adjacent curved channels basal erosion surfaces become deeper towards cut banks of curved channels these structures can be explained by lateral and downstream growth of bars combined with vertical accretion convex upwards forms up to 0 5 m high several metres across and tens of metres long represent episodic accretion of unit bars scroll bars and bar heads stratal patterns in channel fills record a complicated history of erosion and deposition during filling including migration of relatively small bars a revised facies model for this type of sandy braided river has been constructed based on this new information on large scale bedding structure

fluvial and lacustrine palaeoenvironments of the miocene siwalik group khaur area northern pakistan the miocene siwalik group upsection the chinji nagri and dhok pathan formations in northern pakistan records fluvial and lacustrine environments within the himalayan foreland basin thick 5 m to tens of metres sandstones are composed of channel bar and fill deposits of low sinuousity 1 08 1 19 single channel meandering and braided rivers which formed large low gradient sediment fans or megafans river flow was dominantly toward the south east and likely perennial palaeohydraulic reconstructions indicate that chinji and dhok pathan rivers were small relative to nagri rivers bankfull channel depths of chinji and dhok pathan rivers were generally 15 m and up to 33 m for nagri rivers widths of channel segments including single channels of meandering rivers and individual channels around braid bars were 320 710 m for chinji rivers 320 1050 m for nagri rivers and 270 340 m for dhok pathan rivers mean channel bed slopes were on the order of 0 000056 0 00011 bankfull discharges of channel segments for chinji and dhok pathan rivers were generally 700 800 m3s 1 with full river discharges possibly up to 2400 m3s 1 bankfull discharges of channel segments for nagri rivers were generally 1800 3500 m3s 1 with discharges of some larger channel segments possibly on the order of 9000 32 000 m3s 1 full river discharges of some of the largest nagri braided rivers may have been twice these values thin decimetres to a few metres sandstones represent deposits of levees crevasse channels and splays floodplain channels and large sheet floods laminated mudstones represent floodplain and lacustrine deposits lakes were both perennial and short lived and likely less than 10 m deep with maximum fetches on the order of a few tens of kilometres trace fossils and body fossils within all facies indicate the former existence of terrestrial vertebrates molluscs bivalves and gastropods arthropods including insects worms aquatic fauna e g fish turtles crocodiles trees bushes grasses and aquatic flora palaeoenvironmental reconstructions are consistent with previous palaeoclimatic interpretations of monsoonal conditions

soft sediment deformation associated with the east patna fault south of the ganga river northern india influence of the himalayan tectonics on the southern ganga plain abstract the geomorphic tectonic and seismic aspects of the ganga plain have been studied by several workers in the recent decades however the northern part of this tectonically active plain has been the prime focus in most of the studies the region to the south of the ganga river requires necessary attention especially regarding the seismic activities the region lying immediately south of the outer himalayas i e the ganga plain responds to the stress regime of the himalayan frontal thrust zone by movement along the existing basement faults extending from the indian peninsula and creating new surface faults within the sediment cover as well as a result several earthquakes have been recorded along these basement faults such as the great earthquakes of 1934 and 1988 associated with the east patna fault large zones of ground failure and liquefaction in north bihar close to the himalayan front have been recorded associated with these earthquakes the present study reports the soft sediment deformation structures from the south bihar associated with the prehistoric earthquakes near the east patna fault for the first time the seismites have been observed in the riverine sand bed of the dardha river close to the east patna fault several types of liquefaction induced deformation structures such as pillar and pocket structure thixotropic wedge liquefaction cusps and other water escape structures have been identified the location of the observed seismites within the deformed zone of the east patna fault clearly indicates their formation due to activities along this fault however the distance of the liquefaction site from the recorded epicenters suggests its dissociation with the recorded earthquakes so far and hence possibly relates to any prehistoric seismic event the occurrence of the earthquakes of a magnitude capable of forming liquefaction structure in the southern ganga plain indicates the transfer of stress regime far from the himalayan front into the peninsular region through these basement faults northward extension of the east patna fault coincides with the region of the himalayan front which corresponds to a less slip potential therefore an association of frequent earthquakes in this region indicates strain release along the east patna fault

multi scale classification of fluvial architecture an example from the palaeocene eocene bighorn basin wyoming this work was supported by phase 2 of the fluvial systems research group bp bg chevron conocophillips and total mgms thanks the sao paulo research foundation fapesp 2014 13937 3 the authors also wish to thank numerous residents of the bighorn basin for their kind hospitality and access to land we also thank john howell for discussions on fluvial geometries and nomenclature and isobel buchanan and alistair swan for assistance in the field comments from reviewers andrew miall luca colombera and an anonymous reviewer greatly improved this manuscript

evolution of miocene fluvial environments eastern potwar plateau northern pakistan the miocene pliocene siwalik group records changing fluvial environments in the himalayan foreland basin the nagri and dhok pathan formations of this group in the eastern potwar plateau northern pakistan comprise relatively thick tens of metres sandstone bodies and mudstones that contain thinner sandstone bodies metres thick and palaeosols thick sandstone bodies extend for kilometres normal to palaeoflow and are composed of large scale stratasets storeys stacked laterally and vertically adjacent to each other sandstone bodies represent single or superimposed braided channel belts and large scale stratasets represent channel bars and fills channel belts had widths of km bankfull discharges on the order of 103 cumecs and braiding parameter up to about 3 individual channel segments had bankfull widths maximum depths and slopes on the order of 102 m 101 m and 10 4 respectively and sinuosities around 1 1 these rivers are comparable to many of those flowing over the megafans of the modern indo gangetic basin and a similar depositional setting is likely thin sandstone bodies within mudstone sequences extend laterally for on the order of 102 m and have lobe wedge sheet and channel form geometries they represent crevasse splays levees and floodplain channels mudstones are relatively bioturbated disrupted and represent mainly floodbasin and lacustrine deposition mudstones and sandstones are extremely disrupted in places showing evidence of prolonged pedogenesis these mature palaeosols are m thick and extend laterally for km lateral and vertical variations in the nature of their horizons apparently depend mainly on deposition rate the 500 m thick nagri formation has a greater proportion and thicker sandstone bodies than the overlying 700 m thick dhok pathan formation the thick sandstone bodies and their large scale stratasets thicken and coarsen through the nagri formation then thin and fine at the base of the dhok pathan formation compacted deposition rates increase with sandstone proportion 0 53 mm year for nagri 0 24 mm year for dhok pathan and palaeosols are not as well developed where deposition rates are high within both formations there are 100 m scale variations representing on the order of 105 years in the proportion and thickness of thick sandstone bodies and tens of m scale alternations of thick sandstone bodies and mudstone sandstone strata that represent on the order of 104 years formation scale stratal variations extend across the potwar plateau for at least 100 km although they may be diachronous however 100 m and smaller scale variations can only be traced laterally for up to tens of km alluvial architecture models indicate that increases in the proportion and thickness of thick sandstone bodies can be explained by increasing channel belt sizes mainly average deposition rate and avulsion frequency on a megafan comparable in size to modern examples 100 m scale variations in thick sandstone body proportion and thickness could result from regional shifts in the position of major channels possibly associated with fan lobes on a single megafan or with separate megafans however such variations could also be related to local changes in subsidence rate or changes in sediment supply to the megafan system formation scale and 100 m scale stratal variations are probably associated with interelated changes in tectonic uplift sediment supply and basin subsidence increased rates of hinterland uplift sediment supply and basin subsidence recorded by the nagri formation may have resulted in diversion of a relatively large river to the area alternatively changing river sizes and sediment supply rates may be related to climate changes affecting the hinterland possibly linked to tectonic uplift climate during deposition of the siwalik group was monsoonal although the deposits contain no direct evidence for climate change independent evidence indicates global cooling throughout the miocene and the possibility of glacial periods e g around 10 8 ma corresponding to base of nagri formation if the higher himalayas were periodically glaciated a mechanism would exist for varying sediment supply to megafans on time scales of 104 105 years although eustatic sea level changes are related to global climatic change they are not directly related to siwalik stratigraphic changes because the shoreline was many 100 km away during the miocene

river systems and their sediment flux indo gangetic plains northern bihar india river systems of part of the himalayan foreland northern bihar plains india are described in terms of their channel morphology hydrology and suspended sediment characteristics a simple classification of the river systems based mainly on the source area characteristics is proposed i mountain fed ii foothills fed iii plains fed and iv mixed fed rivers distinct differences are noted between these classes of river systems most rivers show evidence of channel movement mainly by avulsion but cut offs also occur locally the mountain fed rivers are characterized by very high discharge and low suspended sediment concentration and the plains fed rivers have relatively low discharge and high suspended sediment concentration the foothill fed rivers have moderate values of discharge and suspended sediment concentration the mountain fed rivers have built megafans of large extent whereas the foothills fed and plains fed rivers have formed muddy interfan areas semi quantitative estimates of water and sediment flux suggest that about 99 9 of the mass transfer into the plains is water with the remaining 0 1 being sediment and that 10 s of the latter 0 01 of the total is retained in the basin the remainder being transferred to the bengal fan

shallow subsurface stratigraphy and alluvial architecture of the kosi and gandak megafans in the himalayan foreland basin india abstract the kosi and the gandak are two major himalayan tributaries of the ganga river in the north bihar plains india with a large hinterland in the nepal himalaya both these rivers have generated megafans in the plains over the quaternary time scale both these rivers are known to be highly dynamic and sediment charged a few conceptual models and limited field data suggested that these megafans have produced thick sand sheets over late quaternary period but these ideas have remained speculative and there is no data on the size and dimension of these sand bodies this paper attempts to reconstruct the subsurface stratigraphy and alluvial architecture for the upper 100 m of the megafans based on electrical resistivity soundings borehole data and drill cores alluvial architecture of the kosi megafan shows significant variability from proximal to medial parts of the fan in terms of sediment grain size and layer thicknesses while the medial part shows 20 30 m thick medium to coarse sand sheets which are laterally stacked the proximal part of the fan has a dominantly gravel unit below 15 m depth that is underlain and overlain by medium to coarse sand units further the medial fan also shows significant vertical and lateral variability in alluvial stratigraphy the near surface

subsidence control on river morphology and grain size in the ganga plain the ganga plain represents a large proportion of the current foreland basin to the himalaya the himalayan sourced waters irrigate the plain via major river networks that support approximately 10 percent of the global population however some of these rivers are also the source of devastating floods the tendency for some of these rivers to flood is directly linked to their large scale morphology in general the rivers that drain the east ganga plain have channels that are perched at a higher elevation relative to their floodplain leading to more frequent channel avulsion and flooding in contrast those further west have channels that are incised into the floodplain and are historically less prone to flooding understanding the controls on these contrasting river forms is fundamental to determining the sensitivity of these systems to projected climate change and the growing water resource demands across the plain here we present a new basin scale approach to quantifying floodplain and channel topography that identifies areas where channels are super elevated or entrenched relative to their adjacent floodplain we explore the probable controls on these observations through an analysis of basin subsidence rates sediment grain size data and sediment supply from the main river systems that traverse the plain yamuna ganga karnali gandak and kosi rivers subsidence rates are approximated by combining basement profiles derived from seismic data with known convergence velocities results suggest a more slowly subsiding basin in the west than the east grain size fining rates are also used as a proxy for relative subsidence rates along the strike of the basin the results also indicate higher fining rates and hence subsidence rates for given sediment supply in the east by integrating these observations we propose that higher subsidence rates are responsible for a deeper basin in the east with perched low gradient river systems that are relatively insensitive to climatically driven changes in base level in contrast the lower subsidence rates in the west are associated with a higher elevation basin topography and entrenched river systems recording climatically induced lowering of river base levels during the holocene

late cenozoic fluvial successions in northern and western india an overview and synthesis abstract late cenozoic fluvial successions are widespread in india they include the deposits of the siwalik basin which represent the accumulations of the ancient river systems of the himalayan foreland basin palaeomagnetic studies reveal that fluvial architecture and styles of deposition were controlled by himalayan tectonics as well as by major climatic fluctuations during the long 13 ma span of formation the indo gangetic plains form the world s most extensive quaternary alluvial plains and display spatially variable controls on sedimentation himalayan tectonics in the frontal parts climate in the middle reaches and eustasy in the lower reaches close to the ganga brahmaputra delta climatic effects were mediated by strong fluctuations in the sw indian monsoon and himalayan rivers occupy deep valleys in the western ganga plains where stream power is high cut in part during early holocene monsoon intensification the broad interfluves record the simultaneous aggradation of plains fed rivers since 100 ka the eastward increase in precipitation across the ganga plains results in rivers with low stream power and a very high sediment flux resulting in an aggradational mode and little incision the river deposits of semi arid to arid western india form important archives of quaternary climate change through their intercalation with the eolian deposits of the thar desert although the synthesis documents strong variability both spatial and temporal in fluvial stratigraphy climatic events such as the decline in precipitation during the last glacial maximum and monsoon intensification in the early holocene have influenced fluvial dynamics throughout the region

soils of the indo gangetic plains a pedogenic response to landscape stability climatic variability and anthropogenic activity during the holocene abstract bound by the himalaya in the north and the craton in the south the indo gangetic plains igp is one of the largest fluvial plains of the world the igp is monotonously flat with a spread of surface soils in hot arid conditions of rajasthan in west to per humid conditions in west bengal the soil geomorphology of the igp detailed during the last few decades is useful in determining the interrelationship among the pedogenesis the climate and the landscape evolution during the holocene these studies demonstrate that the igp soils developed on five geomorphic surfaces with varying degree of development soils occurring on older geomorphic surfaces 2 5 ka are polygenetic with a distinct record of climatic changes and neotectonics the present synthesis is based on recent developments in pedology achieved through macro and micromorphology clay mineralogy pedogenic calcrete and polygenetic pedogenic features of the igp soils a critical evaluation of the igp soils has helped to comprehend the subtle nuances of the pedogenic processes that were also influenced by anthropogenic activities and cultivation over this vast agricultural tract during the holocene we provide state of the art information on the pedology polygenesis and soil degradation natural and anthropogenic over the last 10 ka the review has potential as a reference for critical assessment of the pedosphere for health and quality in different parts of the world in addition it facilitates developing a suitable management practices for the food security in the 21st century

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

river avulsions and sedimentary evolution of the luanhe fan delta system north china since the late pleistocene abstract the luanhe fan delta lfd is one of the most important coastal deltas in north china numerous investigations on the late quaternary evolution of this fan delta system have been implemented during the 1980s however few detailed sedimentologic studies have been undertaken based on comprehensive analysis of sedimentary facies grain size microfossils radiocarbon dates ams14c and optically stimulated luminescence osl ages from three 30 m long cores along with recent reports from a series of cores and seismic profiles from the coastal areas we reconstructed the detailed late quaternary sedimentary evolution of the northern bohai coast which evolved from a coastal barrier lagoon system during mis5 to an alluvial plain with river channels and floodplains between mis4 and the early holocene a variety of transgressive coastal depositional environments freshwater marshes beach ridges sandy barriers shallow seas developed during the early holocene these environments were followed by delta progradation the delta system then gradually turned into a coastal barrier lagoon system under the combined impact of prevailing wave driven currents and local subsidence two dramatic 90 degree diversions of the lower luanhe river course likely influenced the sedimentary evolution of the lfd in its inner portion the first avulsion took place in qianxi probably at the end of the late pleistocene 15 000 cal a bp it led to the abandonment of the luanhe alluvial fan in the western part of the northern bohai coastal plain nbcp and to the formation of a new alluvial fan in the eastern nbcp this alluvial fan evolved into a fan delta system 7000 3500 cal a bp during the holocene transgression the second avulsion occurred at zhuacun during the late holocene probably at 3600 100 cal a bp following this latter avulsion the luanhe river shifted toward the east and formed a new fan delta system 3700 cal a bp present with its apex in luanzhou abrupt tectonic uplift in this highly seismic region likely controlled the two avulsions and the dramatic shift of the alluvial fan complexes climate and sea level changes may also have partly influenced the development of the lfd

facies and architectural analysis of channel sandy macroforms in the upper parana river abstract the upper parana river in the area under analysis has a multichanneled pattern with many islands and channel bars channel bars are sandy macroforms classified as central and lateral bars this paper presents a sedimentological analysis of these bars according to their textures facies and facies architecture central bars are unstable deposits situated in the highest flow energy sites of the main channel with intensive processes of deposition and erosion they are composed of cross stratified medium to coarse sand sp and st facies lateral bars are very stable macroforms situated in the lower flow energy areas with no or very few erosional processes where flaser and climbing rippled fine sand to mud sr so fl and fm facies are the most common sediments

the influence of valley aggradation and listric normal faulting on styles of river avulsion a case study of the brazos river texas usa abstract the holocene avulsion history of the lower brazos alluvial valley of east texas usa was studied using 10 drill cores 26 radiocarbon dates aerial photos and a digital elevation model this study shows that two long term processes aggradation and localized valley tilting along a normal listric fault are responsible for generating two styles of avulsion the first process precedes avulsion by progradation while the second process precedes avulsion by annexation as valley aggradation migrated updip over the last 7 5 ka three regional backstepping avulsions occurred along the lower 140 km of the valley and each generated sizable deposits a pattern emerges of landward stepping progradational avulsions tracking the locus of valley aggradation and of valley aggradation migrating inland even after the rate of sea level rise diminishes at the same time several local nodal avulsions occurred between 50 and 55 km updip of the current highstand shoreline but generated no observable deposits geomorphic evidence indicates that since the late pleistocene active movement along a previously undocumented normal listric fault has occurred at the location of the nodal avulsion these two long term processes do not operate mutually exclusive of each other to promote avulsions rather they operate concurrently only aggradation promotes avulsions that affect floodplain alluviation although the total volume of these deposits comprises a small portion of the valley fill

lithofacies and palaeosol analysis of the middle and upper siwalik groups plio pleistocene haripur kolar section himachal pradesh india abstract the middle upper siwalik groups plio pleistocene are exposed at haripur kolar himachal pradesh india the succession is 2800 m thick and has been subdivided into unit m1 of the middle siwalik and four units u1 u4 of the upper siwalik group on the basis of facies associations and type and degree of development of palaeosols the available magnetostratigraphic ages for bases of units u1 u3 and u4 are 5 5 2 6 and 1 77 ma respectively the top of the section has been dated as 19 ka lithofacies association and palaeocurrent analysis indicates that the middle and upper siwalik groups were formed mainly by a basin transverse fluvial system two types of river systems which differ in their size can be documented in unit m1 unit u1 and unit u2 one trunk river system similar to the modern kosi and the other smaller river system which formed tributaries to the former the large rivers were mainly braided in nature the unit u3 and lower part of unit u4 were deposited in the piedmont depositional system mainly by small braided streams and the upper part of the unit u4 was deposited during a period of arid climate by sediment gravity flows integration of fluvial lithofacies and pedofacies helps to identify two fluvial depositional systems from the modern indo gangetic plains the lowland system involved deposition on alluvial megafans and interfan areas which resulted in sand rich and mud rich sequences with weekly developed soils the upland system allowed large tracts to act as high ground for thousands of years thereby giving rise to sandstone poor intervals with moderately to strongly developed soils occurrence of moderately to strongly developed soils was controlled by uplifting and tilting of large tectonic blocks without any relation to distance from the main channels rate of subsidence apparently controlled the occurrence of lowland and upland systems deposition of the unit m1 unit u1 and unit u2 took place under upland and lowland systems very similar to those identified from the modern indo gangetic plains the warm and humid climate between 5 3 and 2 6 ma led to the formation of red alfisols with calcrete nodules at places slightly cooler and drier climate starting at about 2 6 ma and approximately coinciding with the onset of global scale glaciation produced poorly developed yellow soil with common development of nodular calcretic horizon and calcitc material disseminated in the groundmass at ca 0 9 ma a probable significant change to still drier and cooler climate produced typical sediment gravity flows in the piedmont system that continued until at least up to 19 ka

a three dimensional numerical model of sediment transport erosion and deposition within a network of channel belts floodplain and hill slope extrinsic and intrinsic controls on floodplain dynamics and alluvial architecture a three dimensional numerical model of sediment transport erosion and deposition within a network of channel belts and associated floodplain is described sediment and water supply are defined at the upstream entry point and base level is defined at the downstream edge of the model sediment and water are transported through a network of channels according to the diffusion equation and each channel has a channel belt with a width that increases in time the network of channels evolves as a result of channel bifurcation and abandonment avulsion the timing and location of channel bifurcation is controlled stochastically as a function of the cross valley slope of the floodplain adjacent to the channel belt relative to the down valley slope and of annual flood discharge a bifurcation develops into an avulsion when the discharge of one of the distributaries falls below a threshold value the floodplain aggradation rate decreases with distance from the nearest active channel belt channel belt degradation results in floodplain incision extrinsic extrabasinal allogenic and intrinsic intrabasinal autogenic controls on floodplain dynamics and alluvial architecture were modelled and sequence stratigraphy models were assessed input parameters were chosen based on data from the rhine meuse delta to examine how the model responds to extrinsic controls the model was run under conditions of changing base level and increasing sediment supply rises and falls in base level and increases in sediment supply occurred over 10 000 years rising base level caused a wave of aggradation to move up valley until aggradation occurred over the entire valley frequency of bifurcations and avulsions increased with rate of base level rise and aggradation rate channel belt width varied with water discharge and the lifespan of the channel belt wide connected channel belts and high channel deposit proportion occurred around the upstream inflow point because of their high discharge and longevity less connected smaller channel belts occurred further down valley such alluvial behaviour and architecture is also found in the rhine meuse delta during base level fall valley erosion occurred and the incised valley contained a single wide channel belt during subsequent base level rise a wave of aggradation moved up valley filling the incised valley bifurcation and avulsion sites progressively moved upstream relatively thin narrow channel belts bordered and cut into the valley fill these results differ substantially from existing sequence stratigraphy models the increase in sediment supply from upstream resulted in an alluvial fan most bifurcations and avulsions occurred at the fan apex nodal avulsion and channel belts were the widest and the thickest here giving high channel deposit proportion due to their high discharge and longevity the width and thickness of channel belts decreased down valley due to decreased discharge longevity and aggradation rate this behaviour occurs in modern alluvial fans intrinsic controls also affect floodplain dynamics and alluvial architecture variation of aggradation rate bifurcation frequency and number of coexisting channel belts occurred over periods of 500 to 2000 years compared with 10 000 years for extrinsic controls this variation is partly related to local aggradation and degradation of channel belts around bifurcation points channel belts were preferentially clustered near floodplain margins because of low floodplain aggradation rate and topography there

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

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

diverse tetrapod trackways in the lower pennsylvanian tynemouth creek formation near st martins southern new brunswick canada abstract newly discovered tetrapod trackways are reported from eight sites in the lower pennsylvanian tynemouth creek formation of southern new brunswick canada by far the most abundant and well preserved tracks comprise pentadactyl footprints of medium size 32 53 mm long with slender digits and a narrow splay mostly

an allostratigraphic approach to a non marine basin the north western part of cretaceous kyongsang basin se korea the north western part of the cretaceous kyongsang basin south east korea comprises alluvial deposits of conglomerate gravelly sandstone sandstone and mudstone which can be grouped into four allomembers bounded by stratigraphic discontinuities the discontinuities trend nw se and are marked by distinct facies transitions abrupt emplacement of conglomerate and thin but persistent mudstone beds sedimentary facies and architectural analyses reveal that each allomember formed a depositional system of fluvial channel networks draining toward the south east with alluvial fans on the northern margin each allomember can be characterized by distinctive architecture of channel fills clast composition of conglomerate and sandstone mudstone ratio successive units show an eastward shift in the locus of deposition suggesting basinward relocations of alluvial systems such variations with time and space are interpreted to reflect changes in accommodation space and sediment supply during basin evolution probably caused by fault movements this study shows that detailed mapping combined with architectural analysis and the establishment of alluvial allostratigraphy can help assess changes in alluvial systems and structural development of the basin

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

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

geomorphic characterization and diversity of the fluvial systems of the gangetic plains the extensive gangetic alluvial plains are drained by rivers which differ strongly in terms of hydrological and sediment transport characteristics these differences are manifested in the geomorphic diversity of the plains the western gangetic plains wgp are marked by a degradational topography with incised channels and extensive badland development in some parts while the eastern gangetic plains egp are characterized by shallow aggrading channels with frequent avulsions and extensive flooding we interpret such geomorphic diversity in terms of differences in stream power and sediment supply from the catchment areas the rivers draining the western plains are marked by higher stream power and lower sediment yield that result in degradation in comparison the rivers draining the eastern gangetic plains have lower stream power and higher sediment yield that result in aggradation the variation of stream power a function of channel slope and high sediment yield is attributed to differences in rainfall and rate of uplift in the hinterland it is suggested that such differences have resulted in a marked geomorphic diversity across the plains it is also suggested that such diversity has existed for a fairly long time because of climatic and tectonic variance

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

radiocarbon dating and sedimentation rates in the holocene alluvial sediments of the northern bihar plains india seven radtocarbon dates of carbonate shells and charcoal from the upper two metres ofsedrment in the indo gangetrc plarns of northem brhar eastern indra can be drvrded rnto three groups with the follow ing approxrmate ages 2400 45 a bp two samples ll00r45 a bp four samples and 765t45 a bp one sample thrs evtdence for at least three eprsodes of sedrmentatron rn the last 22100 a contrasts with evidence of greater ages from srmrlarly near surface sedrments rn the mrddle gangetic plains of uttar pradesh further west in these more westerly areas greater ages and well developed nver terraces polnt to much more restncted late flolocene sedtmentatron rates of net sedrment accumulatron calculated using our bihar ages spannrngapenodof theorderof l0 loaa aresrmr lartothosecalcul atedforperiodsof theorderof l0 106 a for the hrmalayan foreland basrn thrs uggests that in the whole basin case short period rates hrgher than the brhar rates have been compensated by longer than brhar periods of non deposrtion or eroston

the table rocks sandstone a fluvial friction dominated lobate mouth bar sandbody in the westphalian b coal measures ne england abstract westphalian b duckmantian alluvial coal measures along the northumberland coast ne england comprise coal capped coarsening upward crevasse splay sequences of shale siltstone and sandstone interbedded with a number of major distributary channel sandbodies including the table rocks sandstone lithofacies architectural analysis and outcrop geometries divide the table rocks sandstone into flaggy sandstone massive sandstone heterolithic and mudstone facies associations each comprising up to 7 lithofacies types the three sandy facies associations are characterised by lenticular bed geometries on different scales producing a hierarchy of lensoid packages and associated bounding surfaces all showing typical offset stacking patterns 1 lenses represent individual lenticular cross bed sets bounded by 1st order surfaces 2 packages of lenses called lens clusters are bounded by 2nd order surfaces and are the basic architectural building block of the sandy facies associations and 3 vertically stacked lens clusters called amalgamated lens clusters bounded by 3rd order surfaces the table rocks sandbody has a laterally extensive irregular lobate subsurface plan geometry it displays a radial palaeocurrent pattern with 180 dispersion and it forms part of a 14 m thick coarsening upward regressive sequence it is interpreted as a composite lobate crevasse splay delta system that prograded into a shallow interdistributary fresh to brackish water lake up to 14 m deep the shallow lake water fluvial input and extensive development of traction structures such as cross bedding and ripple cross lamination suggests a friction dominated delta in which the four facies associations can be interpreted in terms of discrete elements of the mouth bar environment the flaggy sandstone facies association represents the main axial part of the mouth bar system the erosively based massive sandstone facies association major subaqeous distributary channels the lithologically more variable heterolithic facies association the medial mouth bar and the mudstone facies association the distal mouth bar fringe and prodelta within this environmental setting amalgamated lens clusters are interpreted as small discrete mouth bar sand lobes whose offset imbricate stacking pattern reflects channel spacing and bifurcation the rate of channel shifting or shallow depths and lack of accommodation space thus lens clusters are interpreted as discrete growth elements of the mouth bar sand lobes and lenses as individual bedforms making up these growth elements because of the high rate of channel shifting lack of extensive erosion of the mouth bar lobes and deposition of low discharge fines the lobes retained much of their original depositional geometry thereby providing advantageous gradients for offset deposition and stacking of adjacent sand lobes although the delta complex was maintained by frequent crevassing from the feeder channel and by subsidence due to contemporaneous compaction and or local tectonism it was deeply incised on two occasions by subaqeous channels in response to high magnitude floods or falling lake level

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

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

avulsion frequency avulsion duration and interavulsion period of holocene channel belts in the rhine meuse delta the netherlands abstract avulsion parameters greatly influence alluvial architecture because they determine channel density and interconnectedness reliable data on avulsion parameters is still scarce from a detailed reconstruction of the holocene avulsion history of the whole rhine meuse delta we determined quantitative values for the avulsion parameters avulsion frequency avulsion duration and interavulsion period in the rhine meuse delta the number of coeval channels is related to the avulsion frequency calibrated 14c intensity histograms are used to analyze 14c dates of beginning and ending river activity the histograms show that instantaneous and gradual avulsions were almost equally important in the rhine meuse delta a high avulsion frequency occurred from 8000 to 7300 cal yr bp a total of 17 avulsions i e 2 43 avulsions 100 years during this period the avulsion frequency was related to the high rate of sea level rise which induced fluvial sedimentation in the present near coastal area after 7300 cal yr bp avulsion frequency decreased as a result of a continuously decreasing rate of sea level rise from 7300 to 3200 cal yr bp avulsion frequency was low 35 avulsions took place within 4100 years 0 85 avulsions 100 years approximately 5000 cal yr bp the coastal barriers became closed and large scale peat formation occurred this resulted in fixation of the river channels and low cross valley gradients reducing the chances for avulsion between 3200 and 1400 cal yr bp avulsion frequency was high again a total of 34 avulsions i e 1 89 avulsions 100 years as a result of increased discharge and or within channel sedimentation which enhanced chances for avulsion the period of activity of channel belts shows no significant trend on the time scale of the holocene it is highly variable and averages 1280 820 cal yr the avulsion duration fluctuates between less than 200 and 1250 cal years and averages 335 cal years the avulsion duration shows no significant trend through time and remained constant until at least 1900 cal yr bp avulsion duration seems not to be influenced by aggradation rate average interavulsion period is shorter than the period of activity of channel belts and is approximately 945 cal years in the rhine meuse delta on the time scale of the holocene interavulsion period and avulsion duration are on average constant therefore the number of coeval channels is directly related to avulsion frequency available evidence from other rivers and deltas around the world however suggests that the relationship between these avulsion parameters is not everywhere the same

facies and palaeosol analysis in a progradational distributive fluvial system from the campanian maastrichtian bauru group brazil

late glacial and holocene avulsions of the rio pastaza megafan ecuador peru frequency and controlling factors the geomorphological study by means of remote sensing imagery of the rio pastaza megafan ecuador and northern peru reveals the traces of numerous avulsions one hundred and eight avulsion sites have been defined the location of these sites the available radiocarbon ages as well as historical maps of the seventeenth century enable us to propose an evolution history of the migration and avulsions of the rio pastaza since the last glacial maximum the first avulsions of the rio pastaza occurred after the lgm in a zone close to and roughly parallel to the sudandean front where the developed avulsion gave a distributive pattern to the ancient stream of the rio pastaza in an area located between the modern rio morona and pastaza where they caused the rio pastaza to develop a fan like distributary pattern this is interpreted as a response to thrust related forelimb tilt progressively shifting eastward the rio pastaza and the apex of the megafan this sequence of events ended with the great diversion of the rio pastaza towards the modern rios corrientes and tigre avulsions occurred in the tigre corrientes area between 9200 and 8 500 years cal bp afterwards the rio pastaza was diverted to its present day north south course this last significant avulsion occurred before ad 1691 in the area located between the modern rio morona and pastaza avulsion frequency probably overestimated ranges between 100 and 200 years in the rios tigre and corrientes area avulsion frequency probably underestimated ranges from 300 to 400 years regional tectonics is likely to have triggered most of the avulsions in the morona pastaza area but its influence is restricted to this area the factors controlling the avulsions in the tigre corrientes area are less clear because the frequently described hydrologic driven avulsion as observed in areas characterized by contrasted hydrologic cycles are inconsistent with the characteristics of the hydrologic cycles of the rio pastaza

connectivity structure of the kosi megafan and role of rail road transport network abstract movement of biophysical fluxes and resultant processes are governed by among other things the dis connectivity structure of a landform hence the quantification of connectivity structure of a landform is important in order to analyze water and sediment fluxes over a surface two dimensional connectivity structure through analysis of lateral and longitudinal connectivity for water and sediment flux has been quantitatively defined for the well known kosi megafan in north india the avulsive behavior of the kosi river has resulted in various paleochannels over the megafan and they guide the flux transfer over the surface and also control the local topography of the megafan as dis connectivity structure of landform is governed by its physical characteristics and also affected by anthropogenic disturbances both these factors have been considered to quantitatively analyze the connectivity structure of the kosi megafan for sediment and water fluxes megafan surface characteristics have been defined through local slope variability land use land cover map and flow length these surface parameters have been used to map buffers in the area the distribution pattern of buffers on the megafan surface has been used to define the natural dis connectivity structure further the megafan surface has also been affected by progressive development of the rail road transport network which is mostly east west aligned and intersects the south flowing paleochannels these rail road network acts as an anthropogenic barrier for water and sediment fluxes across the megafan surface a detailed mapping of rail and road network in different years 1955 1983 and 2010 has been used to characterize anthropogenic disturbance on the connectivity structure the spatio temporal variation in connectivity structure is attributed to density of the transport network finally natural and anthropogenic disturbances on connectivity structure have also been integrated to quantitatively define the present day connectivity structure of the kosi megafan for water as well as for sediment flux further the dis connectivity structure has been used to explain the spatial variability of waterlogging over the megafan surface which is presently a serious hazard in the region

paleoceanographic implications and cyclostratigraphy of variations in well log data from the western slope of the ulleung basin east sea cyclic variations of density and gamma ray logs achieved from the two drill sites of ubgh2 1 1 and ubgh2 1 2 in the western slope of the ulleung basin were investigated to reveal their paleoceanographic implications and establish cyclostratigraphy of the well logs integration of the core log and seismic data from the two sites indicates that the sediments of the drilled intervals mostly consist of hemipelagic muds with a few sporadic mass transport deposits intercalated only in the downslope site of ubgh2 1 1 comparison with variations in sediment composition suggests that ratios of terrigeneous to biogenic materials which were modulated by orbital scale climate changes should be responsible to the well log variations the established cyclostratigraphy of the well logs based on correlation with marine oxygen isotope records indicates such climatic modulation of the sedimentation in the western slope of the ulleung basin has persisted at least since 2 6 ma consistent with the variation reported from the oki ridge

a model of alluvial megafan sedimentation ganga megafan abstract ganga megafan is one of several megafans developed in the northern and central part of the ganga plain that formed during the middle late pleistocene under conditions of higher sediment water discharge and higher regional slopes than today incision by the ganga river exposes 15 30 m thick megafan deposits in the valley walls and cliffs ganga megafan deposits can be separated into four zones zone i gravelly braided streams zone ii sandy braid plain zone iii anastomosing channel plain and zone iv meandering channels with broad interfluve areas deposits of each zone show distinct facies associations palaeocurrents fan from sw to se and e while the grain size decreases from proximal to distal fan at present fan building activity is highly subdued and is restricted only to the northernmost 5 10 km wide belt of piedmont plain