the effects of rock uplift and rock resistance on river morphology in a subduction zone forearc oregon usa relationships between riverbed morphology concavity rock type and rock uplift rate are examined to independently unravel the contribution of along strike variations in lithology and rates of vertical deformation to the topographic relief of the oregon coastal mountains lithologic control on river profile form is reflected by convexities and knickpoints in a number of longitudinal profiles and by general trends of concavity as a function of lithology volcanic and sedimentary rocks are the principal rock types underlying the northern oregon coast ranges between 46 30 and 45 n where mixed bedrock alluvial channels dominate average concavity is 0 57 in this region in the alluviated central oregon coast ranges between 45 and 44 n values of concavity are on average the highest 0 82 south of 44 n however bedrock channels are common and 0 73 mixed bedrock alluvial channels characterize rivers in the klamath mountains from 43 n south 0 64 rock uplift rates of 0 5 mm a 1 mixed bedrock alluvial channels and concavities of 0 53 0 70 occur within the northernmost coast ranges and klamath mountains for rivers flowing over volcanic rocks 0 53 and 0 72 for reaches crossing sedimentary rocks whereas channel type and concavity generally co vary with lithology along much of the range rivers between 44 5 and 43 n do not follow these trends concavities are generally greater than 0 70 alluvial channels are common and river profiles lack knickpoints between 44 5 and 44 n despite the fact that lithology is arguably invariant moreover rock uplift rates in this region vary from low 0 5 mm a 1 to subsidence 0 mm a 1 these observations are consistent with models of transient river response to a decrease in uplift rate conversely the rivers between 44 and 43 n have similar concavities and flow on the same mapped bedrock unit as the central region but have bedrock channels and irregular longitudinal profiles suggesting the river profiles reflect a transient response to an increase in uplift rate if changes in rock uplift rate explain the differences in river profile form and morphology it is unlikely that rock uplift and erosion are in steady state in the oregon coastal mountains copyright 2006 john wiley sons ltd

importance of a stochastic distribution of floods and erosion thresholds in the bedrock river incision problem 1 fluvial erosion of bedrock occurs during occasional flood events when boundary shear stress exceeds a critical threshold to initiate incision therefore efforts to model the evolution of topography over long timescales should include an erosion threshold and should be driven by a stochastic distribution of erosive events however most bedrock incision models ignore the threshold as a second order detail in addition climate is poorly represented in most landscape evolution models so the quantitative relationship between erosion rate and measurable climatic variables has been elusive here we show that the presence of an erosion threshold when combined with a well constrained probabilistic model of storm and flood occurrence has first order implications for the dynamics of river incision in tectonically active areas first we make a direct calculation of the critical shear stress required to pluck bedrock blocks for a field site in new york second we apply a recently proposed stochastic threshold bedrock incision model to a series of streams in california with known tectonic and climatic forcing previous work in the area has identified a weak relationship between channel gradient or relief and rock uplift rate that is not easily explained by simpler detachment limited models the results with the stochastic threshold model show that even low erosion thresholds which are exceeded in steep channels during high frequency flood events fundamentally affect the predicted relationship between gradient and uplift rate in steady state rivers in a manner consistent with the observed topography this correspondence between theory and data is however nonunique models in which a thin alluvial cover may act to inhibit channel incision in the low uplift rate zone also provide plausible explanations for the observed topography third we explore the broader implications of the stochastic threshold model to the development of fluvial topography in active tectonic settings we suggest that continued field applications of geomorphic models including physically meaningful thresholds and stochastic climate distributions are required to advance our knowledge of interactions among surficial climatic and crustal processes

the frequency and distribution of recent landslides in three montane tropical regions of puerto rico landslides are common in steep mountainous areas of puerto rico where mean annual rainfall and the frequency of intense storms are high each year landslides cause extensive damage to property and occasionally result in loss of life average population density is high 422 people km2 and is increasing this increase in population density is accompanied by growing stress on the natural environment and physical infrastructure as a result human populations are more vulnerable to landslide hazards the blanco cibuco and coamo study areas range in surface area from 276 to 350 km2 and represent the climatologic geographic and geologic conditions that typify puerto rico maps of recent landslides developed from 1 20 000 scale aerial photographs in combination with a computerized geographic information system were used to evaluate the frequency and distribution of shallow landslides in these areas several types of landslides were documented rainfall triggered debris flows shallow soil slips and slumps were most abundant hillslopes in the study area that have been anthropogenically modified exceed 12 in gradient are greater than 300 m in elevation and face the east northeast are most prone to landsliding a set of simplified matrices representing geographic conditions in the three study areas was developed and provides a basis for the estimation of the spatial controls on the frequency of landslides in puerto rico this approach is an example of an analysis of the frequency of landslides that is computationally simple and therefore may be easily transferable to other settings

stochastic dynamics of damage evolution in brittle rocks development of defects in brittle rocks is analysed in terms of continuous damage mechanics with an emphasis on a shear damage evolution necessity to account for an effect of stochastic action leads to an introduction of kinetic relations for damage accumlation in a form of stochastic differential equations numerical algorithms for their solution for three types of noise are proposed results of simulation are compared with analytical solutions for a determiistic case absence of stochastic action effect of various types of noise on damage accumulation and on time to fracture distributions is investigated the study is limited to the case of temporal stochasticity ways for unification of approach and schemes with spatial randomness are discussed

grain size sediment transport regime and channel slope in alluvial rivers the general relationship between channel morphology and the grain size of sediment in the channel bed is an important but poorly known aspect of alluvial rivers an analysis of an equation for total sediment flux in the limits of suspension bedload and mixed modes of transport indicates distinct steady state regimes of channel morphology such regimes are readily seen in published data for modern alluvial rivers by way of a conventional shields plot or a plot of channel slope as a function of relative grain size d h and the ratio ws u where d and ws are respectively mean diameter and fall speed of bed sediments and h and u are respectively mean depth and friction velocity of the flow with slope and mode of transport in an alluvial river constrained by grain size and channel depth alone estimates of discharge and sediment flux follow directly introduction of the sediment flux relationship into conventional diffusion models for the evolution of an alluvial system provides nominal estimates of

epicontinental permian cretaceous seaways in central india the debate for the narmada versus godavari rifts for the cretaceous tertiary incursion abstract this study presents an overview of mesozoic transgressions that influenced the palaeogeography of central india and offers an analysis of the existing evidence for the interpretation of the depositional record of infra and inter trappean sequences these data are then used to understand the respective palaeogeographic settings of the narmada and the godavari master valleys leading to a reappraisal of the paths suggested thus far for a cretaceous tertiary k t seaway major rift related discontinuities have been subjected to reactivation episodes during the mesozoic these tectonic events caused the initiation of several pericratonic basins the riftogenic valley systems have been affected by transgressions from the western margin of india through the narmada valley and or from the eastern margin through the godavari valley however for the most part these continent scale valley systems have hosted mainly mesozoic fluviatile and lacustrine sediment successions besides a marine incursion from the west in the lower reaches of narmada valley is widely recognised on the basis of the late cretaceous bagh beds additionally the maastrichtian palaeogeography of these valley systems of central india have been strongly influenced by the uplift resulting from the thermo magmatic flux associated with the deccan volcanism this resulted in major topographic readjustments within the godavari and narmada tapti palaeovalleys resulting in turn in major basinal depressions as revealed from the reconstruction of the palaeo digital elevation model significantly removed from the eastern and western coastal margins of india isolated occurrences of marine biota such as foraminifera marine algae and palm fossils have been found in infra and inter trappean maastrichtian and danian sequences of central india their presence in these inland basins is enigmatic and three hypotheses have been proposed to explain the presence of marine environments in these basins a trans deccan strait connecting both the margins of india through pre existing rift systems b an 800 km long seaway through the narmada valley and c a marine incursion through the godavari valley this palaeogeographic analysis supports a marine incursion through the godavari rift and presents arguments against the other two

coarse sediment distribution as evidence of an elevation limit for flash flooding bear creek colorado bear creek is a tributary of the south platte river in central colorado the stream flows east from an elevation of 4348 m at the continental divide to the mountain front at 1670 m it thus encompasses the 2300 m elevation limit for substantial rainfall flooding in the colorado front range proposed by jarrett maximum paleoflood discharges estimated from flood deposits at four sites along bear creek demonstrate a consistent decrease in unit discharge with increasing elevation and support the hypothesis of an upper elevation limit for rainfall floods the unit discharge values were used to explain coarse sediment distribution along bear creek measurements of coarse grained channel sediment at 19 sites along the creek indicate a decrease in particle size in flood deposits with increasing elevation as well as a decrease in the size of clasts introduced to the main channel along tributaries these changes in grain size are hypothesized to reflect changes in the competence of channel transport as a result of snowmelt dominated versus rainfall dominated discharge regimes above and below 2100 m elevation calculations of flow competence versus entrainment thresholds for the deposits may support this interpretation one of the geomorphic implications of the elevation limit on flash flooding is a reversal of the usual downstream fining trend in coarse channel sediments

slopewash surface runoff and fine litter transport in forest and landslide scars in humid tropical steeplands luquillo experimental forest puerto rico rainfall slopewash the erosion of soil particles surface runoff and fine litter transport at humid tropical steepland sites in the luquillo experimental forest puerto rico 188 20 n 658 45 w were measured from 1991 to 1995 hillslopes underlain by 1 cretaceous tuffaceous sandstone and siltstone in subtropical rain tabonuco forest with vegetation recovering from hurricane hugo 1989 and 2 tertiary quartz diorite in subtropical lower montane wet colorado and dwarf forest with undisturbed forest canopy were compared to recent landslide scars monthly surface runoff on these very steep hillslopes 248 to 438 was only 0 2 to 0 5 per cent of monthly rainfall slopewash was higher in sandy loam soils whose parent material is quartz diorite averaging 46 g m 2 a 1 than in silty clay loam soils derived from tuffaceous sandstone and siltstone where the average was 9gm 2 a 1 annual slopewash of 100 to 349 gm 2 on the surfaces of two recent small landslide scars was measured initially but slopewash decreased to only 3 to 4 g m 2 a 1 by the end of the study the mean annual mass of fine litter mainly leaves and twigs transported downslope at the forested sites ranged from 5 to 8 g m 2 and was lower at the tabonuco forest site where post hurricane hugo recovery is still in progress mean annual fine litter transport was 2 5gm 2 on the two landslide scars copyright 1999 john wiley sons ltd

erosion of steepland valleys by debris flows episodic debris flows scour the rock beds of many steepland valleys along recent debris flow runout paths in the western united states we have observed evidence for bedrock lowering primarily by the impact of large particles entrained in debris flows this evidence may persist to the point at which debris flow deposition occurs commonly at slopes of less than 0 03 0 10 we find that debris flow scoured valleys have a topographic signature that is fundamentally different from that predicted by bedrock river incision models much of this difference results from the fact that local valley slope shows a tendency to decrease abruptly downstream of tributaries that contribute throughgoing debris flows the degree of weathering of valley floor bedrock may also decrease abruptly downstream of such junctions on the basis of these observations we hypothesize that valley slope is adjusted to the long term frequency of debris flows and that valleys scoured by debris flows should not be modeled using conventional bedrock river incision laws we use field observations to justify one possible debris flow incision model whose lowering rate is proportional to the integral of solid inertial normal stresses from particle impacts along the flow and the number of upvalley debris flow sources the model predicts that increases in incision rate caused by increases in flow event frequency and length as flows gain material downvalley are balanced by rate reductions from reduced inertial normal stress at lower slopes and stronger less weathered bedrock these adjustments lead to a spatially uniform lowering rate although the proposed expression leads to equilibrium long profiles with the correct topographic signature the crudeness with which the debris flow dynamics are parameterized reveals that we are far from a validated debris flow incision law however the vast extent of steepland valley networks above slopes of 0 03 0 10 illustrates the need to understand debris flow incision if we hope to understand the evolution of steep topography around the world

trends of grain sizes on gravel bars in the rio chagres panama abstract we examined the trends of grain sizes along the upper 414 km 2 of the mountainous rio chagres drainage basin in panama gravel bars were sampled along 40 km of the rio chagres and five major tributary streams using a transect pebble count of median diameter lithology and clast rounding although previous investigators have found that downstream fining can be obscured by inputs of colluvial sediment and other local controls in mountain drainages we decided to examine the trends of grain sizes along a tropical mountain river where rapid weathering and high capability of transport might be capable of overriding the input effects of colluvium specifically we tested the hypotheses that downstream fining would be present as a result of selective sorting and that weak felsic particles would decrease in size preferentially to strong mafic particles because of abrasion statistical analyses reveal a weak downstream decrease of sediment size on gravel bars along the study reach of the rio chagres with a sternberg diminution coefficient for felsic and mafic grains of 0 013 and 0 017 respectively felsic clasts have thicker weathering rinds and become rounded downstream faster than mafic particles but tumbling mill tests of abrasion show no significant differences in rate of mass loss in relation to lithology and downstream decreases in grain size are similar between lithologies dividing the study reach into six sub reaches bounded by major tributary junctions we further tested the hypothesis that downstream trends in fining might be obscured at the basin scale by sediment input from tributaries but that trends in grain sizes might be more visible at the reach scale between tributaries we did not find any consistent trends in grain size between tributaries stream width appears to assert a local control on grain size coarse particles are associated with narrow channel reaches whereas smaller particles are associated with wide channel reaches

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

channel geometry median grain size and stream power in small mountain streams abstract small mountain streams are typically affected by the same variables as larger counterparts but small headwater channels are also coupled with hillslopes the added degree of system complexity limits extension of existing conceptual and quantitative models of stream response to small mountain streams our objective is to determine how the presence of multiple lithologies on channel beds and coarse sediments affect relationships between channel geometry and driving and resisting variables in small mountain streams when the variables are examined at the landscape scale we test for systematic scaling of channel geometry stream power indices and median bed grain size d 50 in headwater streams draining 2 and overlying multiple strata on a passive continental margin field data were collected from 157 reaches in 32 watersheds local strata can be divided into a thick sequence of resistant sandstones and a thick sequence of low resistance calcareous siltstones and shales with interbedded limestones both stratigraphic units are present in every watershed and all streams carry abundant coarse bed load derived from the resistant unit mean widths and gradients of the channels are correlated with upstream drainage area unit stream power is not statistically different as a function of rock unit but channel gradients are lower atop the low resistance unit d 50 is not correlated with drainage area but is positively correlated with unit stream power the correlation between unit stream power and d 50 is evidence for mutual adjustments among gradients widths and d 50 as a function of the primary driving force in the drainage area discharge the small effect of bed lithology on stream processes and strong relationship between channel geometry unit stream power and d 50 implies that available driving forces and grain size are the primary controls on stream processes in the study area we conclude that future research into system response in this and similar settings should focus on sediment characteristics production and flux

first record of marine bivalves from the talchir formation of the satpura gondwana basin india palaeobiogeographic implications abstract marine invertebrate fossils are rarely reported from the permian talchir formation of the intracontinental gondwana basins of peninsular india they are known to occur in umaria and manendragarh rewa basin daltonganj and rajhara daltonganj basin and dudhi nala bokaro basin the fossil assemblages include bivalves brachiopods gastropods polyplacophora crinoids bryozoans foraminifers ostracods conulariids etc the fossil localities define a roughly e w trending linear belt along the present day river valleys of son narmada damodar accordingly the existence of a marine embayment within the indian peninsula along this belt during permian time was inferred which extended westward up to the rewa basin this study reveals for the first time occurrence of marine invertebrate fossils within the hlchir formation of the satpura basin which is located further west of the presently known belt of marine fossils the fossil assemblage of the satpura basin includes bivalves ostracods and foraminifers along with floral remains in this present endeavor i describe two bivalve species praeundolornya subelongata dickins 1963 and eurydesrna sp juv this finding implies that the permian marine embayment of the indian peninsula extended further west than that was so far thought to be

geochemistry of permo triassic mudstone of the satpura gondwana basin central india clues for provenance abstract major and trace element data of the permo triassic mudstones from the intracratonic satpura gondwana basin central india have been used to investigate provenance the satpura succession 5 km thick unconformably overlies the precambrian basement sediment dispersal pattern suggests that the precambrian rocks straddling the southern margin of the satpura basin were the most probable source for the sediments the lowermost unit of the satpura succession comprises glacio marine and glacio fluvial deposits the rest of the succession largely represents a variety of fluvial depositional systems with some records of fluvio deltaic and fluvio lacustrine sedimentation under a climatic spectrum of temperate humid to warm semi arid the present study is confined to the lower six formations namely talchir barakar motur bijori pachmarhi and denwa arranged in that order from bottom to top the oldest rocks of this sequence the talchir formation are enriched in mobile elements such as na ca and mg depleted in alumina and have high icv 0 93 1 29 and lower cia values 61 82 74 89 compared to those of the younger mudstones k 2 o al 2 o 3 ratios of the talchir mudstones 0 24 0 28 are higher than the younger mudstones in this sequence these results suggest that the talchir mudstones were weathered less intensely and are thus more immature than the younger mudstones this is consistent with the prevailing cold climate and relatively higher rate of basin subsidence in contrast the majority of the mudstones from the younger formations are depleted in mobile elements have relatively low icv 0 18 0 87 and k 2 o al 2 o 3 values 0 07 0 26 higher cia values 76 99 92 86 and appear compositionally more mature reflecting moderate to high intensity source rock weathering among them the barakar mudstones likely have been more intensely weathered than mudstones from any of the other formations the trace element compositions and ratios are consistent with most mudstones being derived from a felsic source with some mudstones being derived from a more mafic source for example la sc 0 805 and 0 114 la th 6 245 5 072 7 418 6 245 and 5 072 and eu eu 1 431 0 868 and 0 805 of some mudstones indicate mafic source bivariate plot of th sc and zr sc indicates considerable enrichment of zircon that suggests recycling from meta sedimentary rocks prominent negative eu anomaly high lree hree and flat hree pattern reflect sediment derivation from predominantly felsic rocks of the old upper continental crust sio 2 al 2 o 3 versus k 2 o na 2 o plot for the mudstones suggests that they formed in a passive margin also total ree content of most of the mudstones is conformable with passive margin tectonic setting and craton interior type of provenance plotting in la th sc th sc zr 10 and la sc versus ti zr diagrams largely indicates continental margin settings for majority of the mudstones but fails to differentiate between active and passive continental margins

controls on bedrock channel incision along nahal paran israel nahal paran drains 3600 km2 of egypt s sinai peninsula and israel s negev desert much of the channel is alluvial but a canyon 10 5 km long has been incised into late cretaceous chert and dolomite in the lower portion of the basin slackwater deposits and paleostage indicators preserved within the canyon record approximately 10 floods of 200 to 2500 m3 s 1 over a period of at least 350 years step backwater simulations of flood flow hydraulics indicate extreme variations in stream power per unit area along the length of the canyon and associated variability in energy expenditure and sediment transport these variations reflect channel cross sectional morphology the greatest values of stream power occur along the lower half of the study reach in association with three pronounced knickpoints and an inner channel the locations of these features reflect the exposure of thick resistant chert layers along the channel the presence of several similar but buried and inactive knickpoints along the upper study reach indicates that the locus of most active channel incision has shifted with time probably in response to baselevel changes associated with tectonic activity along the dead sea rift thus the rate and manner of channel incision along the canyon of nahal paran are controlled by lithologic variability and tectonic uplift as they influence channel morphology and gradient which in turn influence hydraulics and sediment transport

reach scale channel geometry of a mountain river mountain rivers can be subject to strong constraints imposed by changes in gradient and grain size supplied by processes such as glaciation and rockfall nonetheless adjustments in the channel geometry and hydraulics of mountain rivers at the reach scale can produce discernible patterns analogous to those in fully alluvial rivers mountain rivers can differ in that imposed reach scale gradient is an especially important control on reach scale channel characteristics as indicated by examination of north st vrain creek in colorado north st vrain creek drains 250 km2 of the rocky mountains we used 25 study reaches within the basin to examine controls on reach scale channel geometry variables measured included channel geometry large woody debris grain size and mean velocity drainage area at the study reaches ranged from 2 2 to 245 km2 and gradient from 0 013 to 0 147 m m 1 we examined correlations among 1 potential reach scale response variables describing channel bankfull dimension and shape hydraulics bedform wavelength and amplitude grain size ow resistance standard deviation of hydraulic radius and volume of large woody debris and 2 potential control variables that change progressively downstream drainage area discharge or that are likely to re ect a reach speci c control bed gradient we tested the hypothesis that response variables correlate most strongly with local bed gradient because of the segmented nature of mountain channels results from simple linear regression analyses indicate that most response variables correlate best with gradient although channel width and width depth ratio correlate best with discharge multiple regression analyses using mallow s cp selection criterion and log transformation of all variables produced similar results in that most response variables correlate strongly with gradient these results suggest that the hypothesis is partially supported channel bed gradient is likely to be a good predictor for many reach scale response variables along mountain rivers but discharge is also an important predictor for some response variables copyright 2004 john wiley sons ltd

depositional record of tidal flat sedimentation in the permian coal measures of central india barakar formation mohpani coalfield satpura gondwana basin abstract the permian barakar formation in the mohpani coalfield satpura gondwana basin is composed of three broad lithologies that occur repetitively and are iterdigitated 1 several metres thick coarse to medium grained sandstone bodies with scoured bases 2 5 20 m thick medium to fine grained sandstone bodies and 3 5 20 m thick mudstone dominated packages with variable proportions of centimetre to decimetre scale fine to medium grained sandstone carbonaceous shale and coal the barakar strata were previously interpreted as deposits of braided rivers and associated inter channel flood basin in a continental setting however this study recognizes signatures of tidal current from the mudstone dominated packages implying marine influence during barakar sedimentation the mudstone dominated sediment bodies are the focus of this paper and comprise of three lithofacies that bear imprints of tidal processes during barakar sedimentation 1 heterolith 2 sandstone and 3 coal carbonaceous shale which alternate with one another within individual bodies the heterolithic facies show interlayering of sandstone and claystone resembling flaser wavy and lenticular bedding as well as pinstripe stratification successive sandstone mudstone couplets indicate periodic waxing and waning of flows within individual heterolithic packages the sandstone claystone ratio along with the bedding style varies cyclically upwards giving rise to alternate sandstone dominated and claystone dominated intervals suggesting tidal velocity fluctuation reflective of spring neap lunar cycle thickness plots of successive sand mud couplets also reveal cyclic variation with a conspicuous periodicity of around 12 couplets per cycle which corroborates the spring neap spring or neap spring neap lunar cycle presence of abundant desiccation cracks indicates periodic emergence and points towards an intertidal setting the sandstone facies is characterized by a variety of wave generated features such as bundled and chevron upbuilding of lamina bi directional foreset orientations offshooting and draping laminae scour and drape feature swollen lens like geometries suggesting their emplacement under storm induced combined flow on the tidal flat the coal carbonaceous shale facies represent supratidal marsh environment

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

limits of downstream hydraulic geometry adjustments to flow width depth and velocity in response to changes in discharge are commonly characterized by using downstream hydraulic geometry relationships the spatial limits of these relationships within a drainage basin have not been systematically quantified where the erosional resistance of the channel substrate is sufficiently large hydraulic driving forces presumably will be unable to adjust channel form data sets from 10 mountain rivers in the united states panama nepal and new zealand are used in this study to explore the limits of downstream hydraulic geometry relationships where the ratio of stream power to sediment size d 84 exceeds 10 000 kg s3 downstream hydraulic geometry is well developed where the ratio falls below 10 000 kg s3 downstream hydraulic geometry relationships are poorly developed these limitations on downstream hydraulic geometry have important implications for channel engineering and simulations of landscape change

effects of land use change on channel morphology in northeastern puerto rico between 1830 and 1950 much of northeastern puerto rico was cleared for agriculture runoff increased by 50 and sediment supply to the river channels increased by more than an order of magnitude much of the land clearance extended to steep valley slopes resulting in widespread gullying and landslides and a large load of coarse sediments delivered to the stream channels a shift from agriculture to industrial and residential land uses over the past 50 yr has maintained the elevated runoff while sediment supply has decreased allowing the rivers to begin removing coarse sediment stored within their channels the size abundance and stratigraphic elevation of in channel gravel bar deposits increases channel depth decreases and the frequency of overbank flooding increases downstream along these channels this is presumed to be a transient state and continued transport will lead to degradation of the bed in downstream sections as the channel adjusts to the modern supply of water and sediment a downstream decrease in channel size is contrary to the expected geometry of self adjusted channels but is consistent with the presence of partially evacuated sediment remaining from the earlier agricultural period reverse downstream decreasing channel morphology is not often cited in the literature although consistent observations are available from areas with similar land use history identification of reverse channel morphology along individual watercourses may be obscured in multiwatershed compilations in which other factors produce a consistent but scattered downstream trend identification of reverse channel morphology along individual streams in areas with similar land use history would be useful for identifying channel disequilibrium and anticipating future channel adjustments

a review of the palynostratigraphy of gondwana sediments from the godavari graben india global comparison and correlation of the permian triassic palynoflora abstract the continental sequences of gondwana deposits from the chintalapudi sub basin of the godavari graben south india have been palynologically investigated to explore the permian triassic palynoflora total 11 distinct palynoassemblages belonging to the asselian sakmarian i ii artinskian iii iv guadalupian v vi lopingian vii viii ix induan x and olenekian xi age have been documented the palynological studies support the existence of the two coal bearing horizons in the chintalapudi sub basin one in the karharbari and barakar formations sakmarian artinskian while other in the raniganj formation guadalupian lopingian the lack of the upper barakar and barren measures roadian palynoflora indicates apparent discordance in stratigraphic sequence in this sub basin presently studied the permian triassic palynofloral transition has been found akin to the palynoflora of the salt range madagascar antarctica australia and south africa the palynofloral correlation supports the presence of guttulapollenites palaeophytogeographic province in the gondwana during the guadalupian lopingian the guttulapollenites palaeophytogeographic province co exists with the glossopteris megafloral province and extends from the salt range in the north to amery basin in the south mid zambesi luangwa basin in the west to satpura wardha godavari basin in the east

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

downstream variation in stream power abstract stream power has a significant influence on many form and process attributes of the fluvial system using a similar approach to that suggested by d m lawler in 1992 and 1995 a model is developed to explore how stream power might vary in the downstream direction based on the assumption that the longitudinal profile of the river has an exponential form no particular discharge is necessarily specified but near bankfull flows are regarded as significant morphologically and one such discharge is the focus here total stream power per unit channel length qs is predicted to peak at an intermediate location the position of which depends on the ratio b where b and are the downstream rates of change of discharge and slope respectively if b is a relatively conservative quantity then the form of the longitudinal profile and in particular its degree of concavity will have the major influence on the position of maximum stream power specific stream power w is even more sensitive to and is expected to peak closer to the headwaters about half way between source and the location of the stream power maximum although this will depend on how channel width w varies with distance from source the model is tested along three connected streams of different size in the catchment of the river trent taking advantage of a relationship between mean annual flood and link magnitude which enables this near bankfull discharge to be estimated at any point within the network the model is verified in so far as stream power does attain a mid basin maximum but the observed and predicted locations of the maxima do not always correspond largely because of the distinctive variation in discharge and especially slope along individual pathways for example maximum power lies far downstream along the trent because of the large increase in mid basin discharge associated with a series of large closely spaced tributaries the importance of slope is borne out by the near headwater locations for specific power maxima which tend to be further upstream than predicted along all three rivers as a result of the steepness of upper reaches the variety of geomorphic settings produces deviations from expectation which has implications for the movement and storage of material in the fluvial system

lithological and fluvial controls on the geomorphology of tropical montane stream channels in puerto rico an extensive survey and topographic analysis of five watersheds draining the luquillo mountains in north eastern puerto rico was conducted to decouple the relative influences of lithologic and hydraulic forces in shaping the morphology of tropical montane stream channels the luquillo mountains are a steep landscape composed of volcaniclastic and igneous rocks that exert a localized lithologic influence on the stream channels however the stream channels also experience strong hydraulic forcing due to high unit discharge in the humid rainforest environment gis based topographic analysis was used to examine channel profiles and survey data were used to analyze downstream changes in channel geometry grain sizes stream power and shear stresses results indicate that the longitudinal profiles are generally well graded but have concavities that reflect the influence of multiple rock types and colluvial alluvial transitions non fluvial processes such as landslides deliver coarse boulder sized sediment to the channels and may locally determine channel gradient and geometry median grain size is strongly related to drainage area and slope and coarsens in the headwaters before fining in the downstream reaches a pattern associated with a mid basin transition between colluvial and fluvial processes downstream hydraulic geometry relationships between discharge width and velocity although not depth are well developed for all watersheds stream power displays a mid basin maximum in all basins although the ratio of stream power to coarse grain size indicative of hydraulic forcing increases downstream excess dimensionless shear stress at bankfull flow wavers around the threshold for sediment mobility of the median grain size and does not vary systematically with bankfull discharge a common characteristic in self forming threshold alluvial channels the results suggest that although there is apparent bedrock and lithologic control on local reach scale channel morphology strong fluvial forces acting over time have been sufficient to override boundary resistance and give rise to systematic basin scale patterns copyright 2010 john wiley and sons ltd

downstream coarsening in headwater channels 1 field data from four mountain drainage basins in western washington document systematic downstream coarsening of median bed surface grain size d50 and a subsequent shift to downstream fining at a drainage area of about 10 km2 analyses of network wide patterns of unit stream power derived from both channel surveys and digital elevation models reveal maximum unit stream power that in all four study areas roughly corresponds with both the grain size maxima and an inflection in the drainage area slope relation thought to represent the transition from debris flow dominated channels to fluvially dominated channels our results support the hypothesis that basin wide trends in d50 are hydraulically controlled by systematic variations in unit stream power in addition to lag deposits forced by mass wasting processes the similar relations found in our four study areas suggest that the tendency for downstream coarsening may be ubiquitous in headwater reaches of mountain drainage basins where debris flow processes set the channel gradient

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

ichnology of a late palaeozoic ice marginal shallow marine succession talchir formation satpura gondwana basin central india abstract the late palaeozoic glaciomarine talchir formation in the satpura gondwana basin central india hosts sparse to profuse trace fossils of various kinds although sporadically among the three principal depositional systems that gave rise to the talchir succession deposits of the ice contact fan delta system and the glacial outwash braidplain delta system lack trace fossils of any kind on the other hand within the deposits of the storm wave dominated shoreface shelf system a variety of animal traces is present including simple locomotion traces and non descript bioturbation three trace fossil assemblages could be recognized within these deposits assemblage i is dominated by cylindrichnus of the skolithos ichnofacies that occurs in storm laid medium to fine sandstones deposited in shoreface and transitional shoreface inner shelf environments in contrast assemblage ii comprising dominantly horizontal grazing cum deposit feeding traces cochlichnus helminthopsis phycosiphon planolites archaeonassa and psammichnites occurs on decimeter thick sandstone beds interlayered with mudstones deposited in lower shoreface to inner shelf environments trace fossil assemblage iii is known from a 6 9 m thick outer shelf to lower shoreface progradational succession showing a vertical transition from dark gray mudstone to fine sandstone the middle part of this particular section shows rhizocorallium and flat type zoophycos whereas the upper part hosts profuse cylindrichnus along with rosselia and teichichnus in lesser proportions this assemblage is comparable to the marine ichnofacies succession combining elements of both skolithos and cruziana ichnofacies the characteristic features of the talchir trace fossil assemblages are i low ichnodiversity ii presence of forms typically found the in marine environment iii co occurrences of vertical and horizontal traces of skolithos and cruziana ichnofacies iv presence of simple structures formed by trophic generalists v abundance of certain forms and vi presence of monospecific suites these characters are akin to those of brackish water ichnofaunas in the talchir succession the transition from an ice contact fan delta system to a relatively ice free open marine system indicates an enormous flux of fresh water into the sea reducing its overall salinity predominance of annelid and worm traces and the rarity of crustacean burrows in the talchir strata also suggest a stressful environment due to the prevailing cold climate and a lower than normal marine salinity it thus appears that mixing of fresh water during deglaciation might be a key controlling factor in shaping the characters of ichnofaunas in glacially influenced shallow marine environments

statistical physics of fault patterns self organized by repeated earthquakes this work presents at attempt to model brittle ruptures and slips in a continental plate and its spontaneous organization by repeated earthquakes in terms of coarse grained properties of the mechanical plate a statistical physics model which simulates anti plane shear deformation of a thin plate with inhomogeneous elastic properties is thus analyzed theoretically and numerically in order to study the spatio temporal evolution of rupture patterns in response to a constant applied strain rate at its borders mimicking the effect of neighboring plates rupture occurs when the local stress reaches a threshold value broken elements are instantaneously healed and retain the original material properties enabling the occurrence of recurrent earthquakes extending previous works cowieet al 1993 miltenbergeret al 1993 we present a study of the most startling feature of this model which is that ruptures become strongly correlated in space and time leading to the spontaneous development of multifractal structures and gradually accumulate large displacements the formation of the structures and the temporal variation of rupture activity is due to a complex interplay between the random structure long range elastic interactions and the threshold nature of rupture physics the spontaneous formation of fractal fault structures by repeated earthquakes is mirrored at short times by the spatio temporal chaotic dynamics of earthquakes well described by a gutenberg richter power law we also show that the fault structures can be understood as pure geometrical objects namely minimal manifolds which in two dimensions correspond to the random directed polymer rdp problem this mapping allows us to use the results of many studies on the rdp in the field of statistical physics where it is an exact result that the minimal random manifolds in 2d systems are self affine with a roughness exponent 2 3 we also present results pertaining to the influence of the degree of stress release per earthquake on the competition between faults our results provide a rigorous framework from which to initiate rationalization of many reported fractal fault studies

relationships between hydraulic variables and bedload transport in a subalpine channel colorado rocky mountains u s a abstract this study used three cross sections along a subalpine channel to examine associations between flow and sand and gravel bedload transport in a cobble bed channel at each section velocity was measured at 0 2 0 4 0 6 and 0 8 of flow depth for ten increments across the section at each increment velocity measurements were immediately followed by 10 min bedload samples with a 7 6 cm helley smith sampler linear regressions between bedload and flow variables suggest that grain shear stress stream power near bed velocity average velocity and the froude number are the most relevant indicators of bedload transport particularly when regressed against the d max or d 84 of the bedload grain size distribution no significant relationships however were constant at all three cross sections inconsistency in relationships between bedload discharge and hydraulic variables is at least in part the result of the extreme temporal and spatial variability present in east st louis creek photographs and observations made throughout the field season suggest the importance of random events such as tree fall and log jam formation in regulating bedload discharge the data from east st louis creek suggest equal mobility for sand and gravel transport

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

the nature and controls on downstream fining within sedimentary links abstract at scales of 100 to 102 km grain size change in gravelly alluvial systems is characterized by punctuated downstream fining significant lateral sediment inputs define a sequence of sedimentary links within which fluvial processes produce fining trends using a new set of surface grain size data eighteen such links along two canadian gravel bed rivers are examined negative exponential functions are found to be most appropriate for describing within link grain size changes development of a pragmatic means of predicting grain size is then pursued by searching for a means to relate model diminution coefficients to link attributes consideration of lithologically differentiated fining trends indicates that lithology plays an insignificant role in controlling fining rate examination of within link longitudinal profiles indicates a reasonable relation between fining rate and the rate of change of channel slope the predictive value of this relation is limited by the regional nature of the data upon which it is based and the relative difficulty of obtaining accurate gradient information however as previously noted for alluvial fans although for different reasons channel gradient is correlated with link length and a reasonable predictive tool is apparent in a relation between link length and diminution rate the validity of the derived relation cannot be tested for want of a suitable data set several lines of evidence indicate that abrasion is unimportant as a fining mechanism on these rivers and it is argued that this may be typical of sedimentary links fining rate must then be a function of the efficiency with which sorting processes operate and it is suggested that this efficiency is dependent on aggradation rates associated with the lateral sediment influxes at the head and terminus of individual links

eurydesma lyonia fauna early permian from the itarare group parana basin brazil a paleobiogeographic w e trans gondwanan marine connection abstract here the biocorrelation of the marine invertebrate assemblages of the post glacial succession in the uppermost portion of the late paleozoic itarare group parana basin brazil is for the first time firmly constrained with other well dated gondwanan faunas the correlation and ages of these marine assemblages are among the main controversial issues related to brazilian gondwana geology in total 118 brachiopod specimens were analyzed and at least seven species were identified lyonia rochacamposi sp nov langella imbituvensis oliveira streptorhynchus sp cyrtella sp tomiopsis sp cf t harringtoni archbold and thomas quinquenella rionegrensis oliveira and biconvexiella roxoi oliveira the presence of tomiopsis sp cf t harringtoni and the bivalve atomodesma aphanaia orbirugata harrington in the teixeira soares beds plus myonia argentinensis harrington and heteropecten paranaensis neves et al both of which recorded in deposits in the teixeira soares and mafra beds butia suggests a biocorrelation with the eurydesma fauna from the bonete formation sauce grande colorado basin argentina furthermore the presence of lyonia archbold and praeundulomya cf subelongata dickins in the taciba formation indicates affinities with deposits in the lyons group carnarvon basin and the fossil cliff member perth basin western australia suggesting a late asselian early sakmarian age even more importantly the collected data suggest the existence of an w e trans gondwanan marine seaway between the parana brazil sauce grande colorado argentina huab hardap shale of the dwyka group aranos area namibia southwest africa the carnavon western australia basins and beyond eastward to the cimmerian region a v proto rift system through two major axes of extensional basin development facilitated the w e marine connection main axes formed by a north northwesterly trending axis paralleling the future south atlantic and a broadly north northeasterly trending line of separation related to the future indian ocean this proto rift system coupled with a sea level rise of at least 100 m favored the establishment of a long narrow shallow seaway allowing the exchange of eurydesma fauna between eastern and western gondwana

downstream variations in the width of bedrock channels field surveys of channel width w and drainage area a in bedrock channel reaches reveal relationships where w 5 ca b similar to the classic hydraulic geometry of alluvial channels data from five mountain channel networks support the assumption used in many landscape evolution models that an alluvial hydraulic geometry relationship where b 5 0 3 0 5 holds for bedrock channel systems although there is substantial local variability in channel width in bedrock channel systems there is no systematic difference in width versus drainage area relations for the surveyed bedrock and alluvial reaches in sedimentary lithologies in coastal oregon and washington in contrast bedrock channels were narrower and therefore had deeper flow than alluvial channels with equal drainage areas in the granite and limestone terrain of the yuba river california in addition data from the mokelumne river show that bedrock channel width decreases substantially downstream at the contact between relatively weak limestone and more erosion resistant granite but that channel slope does not change appreciably across contacts between these two lithologies data from coastal oregon drainage basins further show systematic channel widening after flood flows and debris flow impacts we conclude that downstream variations in the width of bedrock channels generally follow traditional hydraulic geometry relations but also reflect the local influence of longitudinal patterns of bedrock erosivity and disturbance history

kinematics of the gondwana basins of peninsular india abstract the gondwana successions 1 4 km thick of peninsular india accumulated in a number of discrete basins during permo triassic period the basins are typically bounded by faults that developed along precambrian lineaments during deposition as well as affected by intrabasinal faults indicating fault controlled synsedimentary subsidence the patterns of the intrabasinal faults and their relationships with the respective basin bounding faults represent both extensional and strike slip regimes field evidence suggests that preferential subsidence in locales of differently oriented discontinuities in the precambrian basement led to development of gondwana basins with varying but mutually compatible kinematics during a bulk motion grossly along the present day e w direction the kinematic disparity of the individual basins resulted due to different relative orientations of the basement discontinuities and is illustrated with the help of a simple sandbox model the regional e w motion was accommodated by strike slip motion on the transcontinental fault in the north

petrography and major element geochemistry of the permo triassic sandstones central india implications for provenance in an intracratonic pull apart basin abstract detrital mode composition of feldspars and heavy minerals and major element chemistry of sandstones from the permo triassic succession in the intracratonic satpura gondwana basin central india have been used to investigate provenance the talchir formation the lowermost unit of the succession comprises glacio marine and glacio fluvial deposits the rest of the succession base to top comprising the barakar motur bijori pachmarhi and denwa formations largely represent variety of fluvial depositional systems with minor fluvio deltaic and fluvio lacustrine sedimentation under a variety of climatic conditions including cold warm arid sub humid and semi arid qfl compositions of the sandstones indicate a predominantly continental block provenance and stable cratonic to fault bounded basement uplift tectonic setting compositional maturity of sandstones gradually increases upwards from the early permian talchir to the middle triassic denwa but is punctuated by a sharp peak of increased maturity in the barakar sandstones this temporal change in maturity was primarily controlled by temporal variation in fault induced basement uplift in the craton and was also influenced by climatic factors plots of different quartz types suggest plutonic source rocks for the talchir sandstones and medium to high rank metamorphic plus plutonic source rocks for the younger sandstones composition of alkali feldspars in the permo triassic sandstones and in different precambrian rocks suggests sediment derivation from felsic igneous and metasedimentary rocks compositions of plagioclase in the talchir and bijori sandstones are comparable with those of granite acid volcanic and metasedimentary rocks of the precambrian basement suggesting the latter as possible source rare presence of high k plagioclase in the talchir sandstones however indicates minor contribution from volcanic source rock exclusively plagioclase bearing metasedimentary rock tonalite gneiss and mafic rocks are the probable sources of plagioclase in the upper denwa sandstones quartz rich nature of the sandstones predominance of k feldspar over plagioclase and albite rich character of plagioclase in the sandstones is consistent with deposition in an intracratonic pull apart basin like the satpura gondwana basin composition of garnet and its comparison with that from the precambrian basement rocks suggests mica schist and amphibolite as possible sources predominance of dravite variety of tourmaline in the permian sandstones suggests sediment supply from metasedimentary rocks presence of both dravite and schorl variety of tourmaline in subequal amount in the triassic sandstones indicates sediment derivation from granitic and metasedimentary rocks however schorl bearing rocks are absent in the basement complex of the study area a cn k plot suggests granites acid volcanic rock and meta sediments of the basement as possible sources of the talchir sandstones and metasedimentary rocks for the barakar to pachmarhi sandstones the denwa sandstones were possibly derived from k feldspar free plagioclase bearing metasediments mafic rocks and tonalite gneiss chemical index of alteration cia values suggest low intensity source rock weathering for the talchir sandstones and higher intensity source rock weathering for the others various bivariate plots of major oxides composition of the sandstones suggest passive to active continental margin setting and even arc tectonic setting for a few samples

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

grain size sediment transport and alluvial channel pattern abstract the shields parameter a dimensionless bed shear stress which can be expressed as a ratio of the slope depth and characteristic properties of bed material in an alluvial channel has been observed in natural rivers to take on modal values for the regimes of bedload mixed load and suspension transport dade w b friend p f 1998 grain size sediment transport regime and channel slope in alluvial rivers j geology 106 661 675 such conditions correspond to channel geometries associated with conserved sediment flux and thus to a state of approximate equilibrium in which the channels are neither aggrading nor degrading to a significant degree these findings are extended here to accommodate the effects of channel width in the context of a comprehensive data set on stable perennial rivers the new analysis reconciles existing empirical and theoretical approaches to predict alluvial channel geometry

combined tide and wave influence on sedimentation of lower gondwana coal measures of central india barakar formation permian satpura basin the coal bearing barakar succession of the satpura basin is typical of the gondwanan coal basins of peninsular india in that it has previously been interpreted as continental in origin the succession comprises three main facies associations which are documented within this paper medium to fine grained muddy sandstone deposits of 5 75 m thickness are reinterpreted as tidally influenced delta deposits mudstone deposits of 3 20 m thickness with subordinate sandstones coals and carbonaceous shales are reinterpreted as delta top deposits and medium to coarse sandstones of 3 38 m thickness are interpreted as braided delta top channels the evidence for tidal influence arises from documentation of bidirectional cross strata tidal bundles tidal rhythmites and periodic variation in foreset thickness the recognition of tidal deposits indicates marine depositional conditions and significantly changes existing palaeogeographical models this in turn has important implications for our understanding of the depositional setting and distribution of the permian coals that occur across much of the southern supercontinent furthermore to the best of the authors9 knowledge coal bearing tidal delta deposits have not previously been described from continental interior basins

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out