petrology and textural classification of the jericho kimberlite northern slave province nunavut canada the paper presents data on petrology bulk rock and mineral compositions and textural classification of the middle jurassic jericho kimberlite slave craton canada the kimberlite was emplaced as three steep sided pipes in granite that was overlain by limestones and minor soft sediments the pipes are infilled with hypabyssal and pyroclastic kimberlites and connected to a satellite pipe by a dyke the jericho kimberlite is classified as a group ia lacking groundmass tetraferriphlogopite and containing monticellite pseudomorphs the kimberlite formed during several consecutive emplacement events of compositionally different batches of kimberlite magma core logging and thin section observations identified at least two phases of hypabyssal kimberlites and three phases of pyroclastic kimberlites hypabyssal kimberlites intruded as a main dyke hk1 and as late small volume aphanitic and vesicular dykes massive pyroclastic kimberlite mpk1 predominantly filled the northern and southern lobes of the pipe

tectono sedimentary evolution of the bowland basin n england during the dinantian the bowland basin is a ne sw trending sedimentary basin lying between the askrigg bowland high to the n and nw and the central pennine high to the se the basin was initiated in late devonian tournaisian times sediment thickness and facies variations within the dinantian succession show marked asymmetry on both a basin wide and intra basin scale as a result of approximate nw se to n s extension across normal faults thickening of the sedimentary sequence from ne to sw over much of the basin resulted from fault controlled extension along the se margin of the basin with downthrow to the nw giving the basin a half graben character extension occurred in two distinct episodes marked by basin wide debris flow and sedimentary slide slump deposits during the late chadian early arundian the simple half graben became modified by a series of ne sw trending antithetic and nw se trending transfer faults associated with local unconformities and marked lateral thickness and facies variations this interval marks the transition from carbonate ramp to slope sedimentation and a temporary halt in carbonate supply to the basin the second episode of extension the late asbian early brigantian marks the break up of the northern basin margin ending major carbonate deposition within the basin reactivation of these structures at the end of the carboniferous created the ribblesdale fold belt as a result of nw se to n s compression transpression application of this research to areas surrounding the bowland basin has led to the recognition of additional shelf basins the orientation of which suggests control by normal and transfer fault systems discussion and

coarse grained deep water sedimentation along a border fault margin of lake malawi africa seismic stratigraphic analysis lake malawi africa serves as an important modern analog for understanding depositional processes in an active rift setting this paper explores the depositional processes and stacking patterns of coarse grained facies across a large fan delta and associated sub lacustrine fan system offshore of the south rukuru river using single channel seismic data coupled with deep water vibracores and gravity cores a companion paper wells et al 1999 discusses the details of the depositional processes of the system inferred from core data using 2900 km of single channel seismic data eight genetic facies were defined based on seismic reflection character external geometry accompanying core data and location within the modern geomorphic system five sand dominated facies include 1 mouth of canyon fan facies 2 progradational fan delta facies 3 channel fill facies 4 canyon fill facies and 5 basin plain fill facies these facies occur as surficial deposits in water depths of more than 600 m suggesting that coarse grained sedimentation characterizes certain localities in even the deepest parts of lake malawi climatically driven lake level changes influenced the internal character of these facies their thickness and to some extent their location within the south rukuru study area however climate was generally subordinate to tectonism in controlling the temporal and spatial distribution of the facies tectonic controls can be categorized as 1 orientation of the first order border fault and intrabasinal faults 2 syndepositional footwall uplift and rotation and 3 temporal changes in the rate and location of maximum subsidence these controls affect the location and stacking of the mouth of canyon fans and the presence and orientation of sub lacustrine canyons and the zone of maximum sediment accumulation and depositional gradients

development and flow structures of sand injectites the hind sandstone member injectite complex carboniferous uk abstract the hind sandstone member of the carboniferous craven basin occurs within a thick succession of marine mudstone and is here interpreted as a sandstone injectite complex injectites take the form of i sills ii upwards emplaced dykes iii downwards emplaced dykes iv a sedimentary laccolith and v sandstone bodies remobilised in situ the remobilised and injected sand originated from small turbidite scour fills and potentially a more significant sand body such as a submarine slope gully fill the sedimentary laccolith appears to jack up the units it injects and is filled by sandstone with a chaotic fabric suggestive of brecciation of partly cemented sand the laccolith and sill dominated nature are suggestive of relatively shallow remobilisation sills are commonly laterally gradational with upwards emplaced dykes and in some cases these feed apparently downwards emplaced dykes a series of flow structures are preserved within some of the injectites and these provide clues to the emplacement history crack propagation direction is inferred from the orientation of undulating crests developed on the upper and lower surfaces of injectites peak flow is indicated by scour marks resembling flute and tool marks which are superimposed onto these undulating surfaces internal flow structures highlighted by pyrite mineralistion record the waning stage of injection the observed flow structures suggest that the apparent crack propagation direction was generally oblique to the peak flow and nearly perpendicular to the direction of late stage fluidised sediment flow crack propagation relates to the local stress field whilst injection flow may be related to the local pore pressure distribution recognition of this suite of structures may provide a useful interpretational tool for other injectites in both core and outcrop pore fluid overpressure which drove injection developed through the migration of petroleum and mineralising fluids from the underlying bowland shales and older limestones a complex brecciated fracture network within the mudstones underlying the injectites records fluid migration pathways sliced blocks and thin sections from injectites reveal flow structures defined by iron pyrite mineralisation the trigger is here related to growth of compressional structures and associated syn sedimentary slumps which occur at the same stratigraphic level as the injectites

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

geometry of submarine slides in the bowland basin dinantian and their relation to debris flows sedimentary slide deformation structures in the lower carboniferous dinantian sediments of the bowland basin show a spoon shaped morphology with extension in the head region and compression in the toe the particular structures developed depend on the rheological properties of the sediment involved slides in soft sediment have deformation distributed throughout the slide mass with folding being the dominant deformation style slides within more lithified sediment have deformation concentrated along slip planes both types of deformation may be present within a particular slide depending on diagenetic factors and the depth to which slide planes cut down disaggregation of slides to yield material for sediment gravity flows is explained by processes operating within the slide unit

topographic controls on the development of contemporaneous but contrasting basin floor depositional architectures abstract sediment laden gravity driven flow deposits on the basin floor are typically considered to form either discrete lobes that stack compensationally or packages of laterally extensive beds commonly termed sheets these end member stacking patterns are documented in several basinfills however whether they can coexist in a single basin or there are intermediate or transitional stacking patterns is poorly understood an analysis of depositional architecture and stacking patterns along a 70 km dip oriented transect in the upper broto turbidite system jaca basin south central pyrenees spain which displays disparate stacking patterns in contemporaneous strata is presented proximal and medial deposits are characterized by discrete packages of clean sandstones with sharp bed tops which exhibit predictable lateral and longitudinal facies changes and are interpreted as lobes distal deposits comprise both relatively clean sandstones and hybrid beds that do not stack to form lobes instead localized relatively thick hybrid beds are inferred to have inhibited the development of lobes hybrid beds developed under flows which were deflected and entrained carbonate mud substrate off a carbonate slope that bounded the basin to the south evidence for this interpretation includes 1 divergent paleoflow indicators and hummock like features in individual beds 2 a decrease in hybrid bed thickness and abundance away from the lateral confining slope 3 a carbonate rich upper division not seen in more proximal turbidites the study demonstrates the co occurrence of different styles of basin floor stacking patterns in the same stratigraphic interval and suggests that characterization of deep water systems as either lobes or sheets is a false dichotomy

on the periodicity and magnitude of late carboniferous glacio eustatie sea level changes data from sedimentary cycles in basins from northern england the appalachians and midcontinent us afford an insight into periodicities and controls of late carboniferous glacio eustatic sea level changes lithofacies with identifiable palaeobathymetry are used to assess the magnitude of sea level change in the pennine basin of northern england the method yields a minimum value of 42m walsh power spectral analysis is employed to resolve periodicities of about 120ka within the pennine basin of northern england 212 140 and 93 ka within the midcontinent us succession and 109 84 67 63 ka within the appalachian basin within the pennine basin periodicities and magnitudes are found to be independent of their position within the basin thus any tectonism can be assumed to have had a negligible effect on the transgressions a simplified modelled climatic curve is derived from milankovitch parameters and pleistocene 18 o data this is used in a basin fill model that simulates the thermally subsiding pennine basin the resulting distribution of marine deposits is seen to depend upon both the steady regional subsidence and the magnitude and extent of glacio eustatic transgressions

linked debrites in sand rich turbidite systems origin and significance abstract the outer parts of a number of small late jurassic sandy deep water fans in the northern north sea are dominated by the stacked deposits of co genetic sandy and muddy gravity flows sharp based structureless and dewatered sandstone beds are directly overlain by mudclast breccias that are often rich in terrestrial plant fragments and capped by thin laminated sandstones pseudonodular siltstones and mudstones the contacts between the clast rich breccias and the underlying sandstones are typically highly irregular with evidence for liquefaction and upward sand injection the breccias contain fragments up to metre scale of exotic lithologies surrounded by a matrix that is extremely heterogeneous and strewn with multiphase and variably sheared sand injections and scattered coarse and very coarse sand grains often coarser than in the immediately underlying sand bed markov chain analysis establishes that the breccias consistently overlie sandstones and the character of the breccias and their external contacts rule out a post depositional origin via in situ liquefaction intrastratal flowage or bed amalgamation and disruption the breccias are interpreted as debrites that rode on a water rich sand bed just deposited by a co genetic concentrated gravity current as such they are referred to as linked debrites to distinguish them from debrites emplaced in the absence of a precursor sand bed the distinction is important because these linked debris flows can achieve significant mobility through entrainment of both water and sediment from beneath and they ride on a low friction carpet of liquefied sand this explains the paradox presented by fan fringes in which there are common debrites when conventional thinking might predict that deposits of low concentration gravity currents should be more important here in fact evidence for transport by low concentration turbidity currents is rare in these systems several possible mechanisms might explain the formation of linked flows but the ultimate source of both sandy and clast rich flow components must be in shallower water on the basin margin the debrites are not triggered from distal slopes flow partitioning may have occurred by upslope erosion and retardation of the mudclast charged portion of an erosional sandy density current partial flow transformation of a precursor debris flow and or hydraulic segregation and reconcentration of the flaky clasts and carbonaceous matter during transport linked debrites are not restricted to small sand rich fans and similar mechanisms may be responsible for the long runout of debris flows in other systems the recognition of a distinct class of linked debrites is of wider importance for facies prediction reservoir heterogeneity and even carbon fluxes and sequestration on continental margins

the origin and tectonic significance of asymmetrical meander belts in the hebgen lake area of sw montana the madison and south fork rivers occupy the northeast sides of their respective meander belts the form of the abandoned meander loops within these asymmetric meander belts indicates that they were produced by gradual northeast migration of the active channels this progressive migration can be related to tectonic tilting produced by regional extensional faulting at a high angle to the original channel belt axis which ran down a gently sloping outwash cone asymmetric channel sandstone bodies in the rock record can be recognized by the preferred dip of successive lateral accretion units in meander loops together with soft sediment deformation facies and thickness variations they may indicate tectonic deformation of the sedimentary surface

three dimensional model of alluvial stratigraphy theory and applications abstract a three dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution proportion and connectedness of coarse grained channel belt deposits in alluvial strata as a function of channel belt width floodplain width bankfull channel depth channel belt and overbank sedimentation rates avulsion location and period compaction and tectonism tilting and faulting in this model a floodplain surface of variable width and length is occupied by a single channel belt changes in floodplain topography are produced by spatial and temporal variation of channel belt and floodplain deposition rates and by compaction and local or regional tectonism the location and timing of avulsions are determined by local changes in floodplain slope relative to channel b lt slope and by flood magnitude and frequency the diverted channel belt follows the locus of maximum floodplain slope at the end of each simulation architectural parameters are calculated including channel deposit proportion and connectedness and the dimensions of channel belt sandstone bodies three dimensional perspective diagrams mesh surfaces and two dimensional stratigraphic sections can be plotted to illustrate depositional surfaces time planes and the location and geometry of coarse grained channel belt deposits within finer grained overbank deposits the model predicts that channel belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross section orientation upstream from avulsion points sandstone bodies have low width thickness ratios because of aggradation in a fixed channel belt immediately downstream from avulsion points channel belts tend to be connected resulting in sandstone bodies with high width thickness ratios avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period such sequences may produce successions in which channel belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years down valley increases in aggradation rate or down valley decreases in floodplain slope for example associated with a rise in base level may result in an increase in channel belt proportion and connectedness because of high avulsion frequencies in down valley regions of the floodplain down valley decreases in aggradation rate as in alluvial fans foreland basins and during base level fall may result in high avulsion frequencies in up valley parts of the floodplain tectonic tilting and faulting locally increase avulsion probabilities and channel belts generally shift toward areas of maximum subsidence under certain conditions however depositional topography may cause channels to shift away from areas of maximum subsidence channel deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain but distribution clustering of channel belts may not be a reliable indicator of fault geometry or displacement models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified the three dimensional model presented here predicts many of the features of channel behavior observed in modern rivers but there is a pressing need for better models and adequate natural data to test them

tectonic and sediment supply control of deep rift lake turbidite systems lake baikal russia tectonically influenced half graben morphology controls the amount and type of sediment supply and consequent type of late quaternary turbidite systems developed in the active rift basins of lake baikal russia steep border fault slopes footwall on the northwest sides of half graben basins provide a limited supply of coarser grained clastic material to multiple small fan deltas these multiple sediment sources in turn laterally feed small 65 km axially fed elongate mud rich fans sourced by regional exterior drainage of the selenga river that supplies large quantities of silt basin plain turbidites in the center of the linear basins and axial channels that are controlled by rift parallel faults are fed from and interfinger with aprons and fans the predictability of the turbidite systems in lake baikal provides the best example yet studied of how tectonics and sediment supply interact to control the development of a wide variety of coeval turbidite systems on a single basin floor

interpreting complex fluvial channel and barform architecture carboniferous central pennine province northern england the bashkirian lower brimham grit of north yorkshire england is a fluvio deltaic sandstone succession that crops out as a complex series of pinnacles the three dimensional arrangement of which allows high resolution architectural analysis of genetically related lithofacies assemblages combined analysis of sedimentary graphic log profiles architectural panels and palaeocurrent data have enabled three dimensional geometrical relationships to be established for a suite of architectural elements so as to develop a comprehensive depositional model small scale observations of facies have been related to larger scale architectural elements to facilitate interpretation of the palaeoenvironment of deposition to a level of detail that has rarely been attempted previously thereby allowing interpretation of formative processes detailed architectural panels form the basis of a semi quantitative technique for recording the variety and complexity of the sedimentary lithofacies present their association within recognizable architectural elements and thus the inferred spatio temporal relationship of neighbouring elements fluvial channel fill elements bounded by erosional surfaces are characterized internally by a hierarchy of sets and cosets with subtly varying compositions textures and structures simple cross bedded sets represent in channel migration of isolated mesoforms dunes cosets of both trough and planar tabular cross bedded facies represent lateral accreting and downstream accreting macroforms bars characterized by highly variable yet predictable patterns of palaeocurrent indicators relationships between sandstone dominated strata bounded by third order and fifth order surfaces which represent in channel bar deposits and incised channel bases respectively chronicle the origin of the preserved succession in response to autocyclic barform development and abandonment major episodes of incision probably influenced by episodic tectonic subsidence differential tilting and fluvial incision associated with slip on the nearby north craven fault system overall the succession represents the preserved product of an upper delta plain system that was traversed by a migratory fluvial braid belt system comprising a poorly confined network of fluvial channels developed between major sandy barforms that evolved via combined lateral accretion and downstream accretion

early miocene sedimentary processes and their hydrocarbon implications in the baiyun sag of pearl river mouth basin northern south china sea abstract the shelf slope zone has received considerable attention for hydrocarbon exploration due to its unique location where the sediments are delivered to deep water environment and deposited as hydrocarbon reservoirs that have been discovered around the world however it is realized that the sedimentary processes are very complex and various depositional bodies develop in the shelf slope zone constrained by 3d seismic core and well log data numerical simulations can be applied to better understand the sedimentary processes and predict the distribution and characteristics of deposits as hydrocarbon reservoirs based on core log seismic integration the early miocene shelf margin delta and channelized submarine fan systems along the northern slope of baiyun sag in the pearl river mouth basin are distinguished and they are mainly composed of debris turbidites and slumps the numerical model is built based on early miocene topography acquired by back stripped well tied seismic profiles and the initial boundary conditions including sediment concentration velocity and grain size and so on behaviors and structures of slope system are set according to the results of marine surveys around the world the computational fluid dynamic software ansys fluent was applied for the modelling as a results the distributions and geometries of the simulated deposits are compared with the depositional bodies interpreted from seismic data the hydrodynamic simulations of the two sedimentary systems indicate that depositional bodies converge to the downstream of the slope and the basin floor and turn tractive current into turbidity current during the sedimentary processes which result in obviously various sedimentary characteristics in different locations the identification of sedimentary processes in the shelf margin delta and channelized submarine fan systems has been beneficial for predicting reservoirs and exploring hydrocarbons in the baiyun sag pearl river mouth basin which is also contributing to the understanding of sedimentary process and reservoir prediction in deep water areas around the world

submarine channel response to intrabasinal tectonics the influence of lateral tilt lateral tilting is a common deformation style in extensional basins its influence on subaerial channels is to a degree understood and may be significant controlling the style of channel development and the resultant sand body architecture growth faulting and lateral tilting in turbidite channel systems have been demonstrated from three dimensional seismic data but the resultant architecture of channels within these settings has not yet been documented in the carboniferous of northern england a sand rich slope channel developed within a basin undergoing late stage extension underwent progressive and unidirectional migration toward a topographic low on a laterally tilting block the resultant sandstone body is wedge shaped in cross section and composed dominantly of sigmoidal lateral accretion deposits the channel returned to an axial course before undergoing lateral migration in the same direction creating a multistory multilateral channel sandstone body the repeated unidirectional migration combined with evidence of syndepositional deformation suggests that active tectonism strongly influenced channel evolution and deposition a model of submarine channel evolution in extensional basins is presented in systems where large displacements occur the channel system may avulse creating isolated sand ribbons which are connected updip where the lateral dip is always more influential than the regional dip the system may pond in the hanging wall syncline the model is compared to a subsurface channel within the pliocene of the nile delta slope which was influenced by syndepositional fault movement application of the outcrop derived model allows some simple architectural interpretations to be made

allogenic vs autogenic controls on megaflute formation abstract megaflutes are large concave up erosional scours within turbidite successions and have been described from modern and ancient settings they are interpreted to represent the passage of erosive largely bypassing turbidity currents here two categories of megaflute are distinguished 1 allogenic corresponding to the case above where erosion is associated with sediment bypass leading to deposition farther into the basin e g the classical megaflutes of the ross formation 2 autogenic where the erosion occurs during aggradation of the host bed both types are illustrated with examples from the carboniferous succession of northern england the distinction is important because the formative processes are different leading to distinct facies associations for each group for example allogenic flutes are interpreted to form in systems with large variations in flow magnitude and imply significant down dip sediment accumulation whereas autogenic megaflutes are thought to be formed by unsteady flows and imply less significant bypass autogenic megaflutes occur above inversely graded poorly sorted sandstones which improve in sorting and decrease in mud content upwards to the megaflute surface which is overlain by a well sorted mantle of the coarsest sediment found within the bed detailed grain size profiles suggest that autogenic megaflutes develop in response to waxing of flows from a depositional to an erosional state cannibalizing the already deposited sand bed as the flow wanes reverting to a depositional state the coarsest grained fraction of its remaining load is deposited first forming the basal part of a variably well developed normally graded and overall finer grained interval thus it is interpreted that flow unsteadiness promotes the formation of these features which has implications for the reconstruction of paleoenvironmental conditions specifically the generation mechanisms return periods flow routing into the basin and the resultant flow characteristics of turbidity currents

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

variation in syn subduction sedimentation patterns from inner to outer portions of deep water fold and thrust belts examples from the hikurangi subduction margin of new zealand

seismic modeling in the analysis of deep water sandstone termination styles innovative seismic forward modeling is used to illustrate the sensitivity within seismic data and its application in the interpretation of onlap and pinch out of terminating deep water sandstones two critical components in deep water exploration and production sandstone quality net to gross estimates volume calculations vertical connectivity and stratigraphic trapping are all dependent on the sandstone extent and their seismic characteristics in these settings however seismic resolution is commonly insufficient to resolve the critical reservoir parameters seismic modeling of termination styles based on integrated outcrop and subsurface properties allows for depth and resolution focused predictive models to be built for improved subsurface analysis this technique is currently underused as a method to better understand the sensitivity of seismic data to the target lithologies and their geometries the gres d annot formation is a well studied sand prone deep water system of paleogene age deposited in a bathymetrically complex setting six end member termination styles are discussed including three sand prone styles simple onlap o s draping onlap o d and bed thickening o t and three heterolithic styles advancing pinch out p a convergent pinch out p c and convergent thickening and pinch out p ct local thickening close to the system margins is common in both sand prone and heterolithic terminating strata and plays an important function in the appropriate distribution of sandstone the outcrops are interpreted as potential process analogs for the complex sandstone distribution and termination patterns observed in plays like the paleogene of the gulf of mexico and the jurassic of the northern north sea

fluvial response to active extension evidence from 3d seismic data from the frio formation oligo miocene of the texas gulf of mexico coast usa tectonic deformation of the land surface is known to influence the gradient water and sediment discharge and the grain size of modern fluvial systems any change in these variables alters the equilibrium of a fluvial system potentially causing a change in channel morphology 3d seismic data from the tertiary miocene age upper frio formation kelsey field south texas in the us are used to examine changing fluvial channel morphology through time during a period of active growth of a rollover anticline in the hangingwall of a normal fault the vicksburg fault the studied interval varies between 22 and 47 m thick and spans several hundred thousand years it consists of an alternation of fluvial sandstones overbank mudstones and coal seismic extractions show the evolution of sinuous fluvial channels during a phase of growth fault activity prior to growth a single sinuous channel is imaged during growth the fluvial system became decapitated by a developing rollover anticline and a highly sinuous drainage network formed with frequent avulsion events headward propagation of streams and related stream capture increased channel sinuosity was spatially associated with increased avulsion frequency in the area down dip to the east of the rollover anticline more than 10 km from the active fault more than 25 m of relative accommodation developed on the flank of the growing rollover anticline compared with on the crest the increased channel sinuosity is interpreted as reflecting an increase in longitudinal valley slope analogous to observations made in flume experiments and modern river systems the increase in avulsion frequency is attributed to increased aggradation as the rivers adjusted back to equilibrium grade following the increase in slope

climate and tectonic effects on holocene development of an alpine lake muge co se margin of tibet south west china is an important area for determining variability of the sw asian monsoon it is however also tectonically very active palaeolimnological studies in this region generally focus on climate as a direct driver of ecological change rarely considering the effects of tectonic activity and catchment ontogeny we present diatom and organic matter data from a holocene sediment record from muge co an alpine lake located on an active fault zone in the southeast margin of tibet and explore the possible drivers of ecological change a major change occurred at 9000 cal bp when the diatom assemblage switched from benthic to predominantly planktonic forms and organic matter content decreased rapidly comparison of the holocene diatom record with a regional data set of lake surface sediments using detrended canonical correspondence analysis dcca suggests that this change in diatom development was mainly associated with changing water depth most likely linked to a seismically triggered landslide

geomorphic and sedimentary response of rivers to tectonic deformation a brief review and critique of a tool for recognizing subtle epeirogenic deformation in modern and ancient settings abstract rivers are extremely sensitive to subtle changes in their grade caused by tectonic tilting as such recognition of tectonic tilting effects on rivers and their resultant sediments can be a useful tool for identifying the often cryptic warping associated with incipient and smaller scale epeirogenic deformation in both modern and ancient settings tectonic warping may result in either longitudinal parallel to floodplain orientation or lateral normal to floodplain orientation tilting of alluvial river profiles alluvial rivers may respond to deformation of longitudinal profile by 1 deflection around zones of uplift and into zones of subsidence 2 aggradation in backtilted and degradation in foretilted reaches 3 compensation of slope alteration by shifts in channel pattern 4 increase in frequency of overbank flooding for foretilted and decrease for backtilted reaches and 5 increased bedload grain size in foretilted reaches and decreased bedload grain size in backtilted reaches lateral tilting causes down tilt avulsion of streams where tilt rates are high and steady down tilt migration combing where tilt rates are lower each of the above effects may have profound impacts on lithofacies geometry and distribution that may potentially be preserved in the rock record fluvial sedimentary evidence for past tilting is traditionally based on the assumption that depositional features reminiscent of modern fluvial tectonic effects are evidence for past tectonic effects where it is closely associated with historically active structures or where non tectonic causes cannot be invoked however caution must be exercised when using these effects as criteria for past or current tectonic warping as these effects may be caused by non tectonic factors these non tectonic causes must be eliminated before tectonic interpretations are made

parallel lamination formed by high density turbidity currents experiments were conducted in order to investigate processes of sediment transport and deposition from sustained turbidity currents with initial volume fraction sediment concentration of 0 20 0 25 and 0 35 parallel lamination was formed at bed aggradation rates up to 4 mm s 1 and bedload layer sediment concentration up to 0 36 this observation contradicts the generally held assumption that parallel lamination forms only from low density flows and at low bed aggradation rates this misconception illustrates a poor understanding of threshold values of grain support mechanisms in the bedload layer the present results bring new insight into understanding sediment transport in the deep sea and interpreting the sedimentary record

axial river evolution in response to half graben faulting carson river nevada u s a abstract the holocene history of faulting and river channel movement for the carson valley nevada allows the tectonic alluvial interactions of an active half graben to be studied topographic surveys maps cores radiocarbon dates and paleohydrology are used to study the temporal and spatial patterns of carson river channel change the influence of faulting and associated ground tilting on channel movement is determined by comparing the pattern and timing of river movements with the published event history of the basin bounding fault inverse modeling of the fault history assuming rigid block motion suggests that surface gradients perpendicular to the channel and basin axis have progressively increased through the holocene from an initially horizontal surface the greater part of this movement occurred during and immediately after faulting channel avulsion in response to this increased tectonic ground tilting appears to be the most important factor controlling alluvial architecture although intrinsic fluvial processes and regional climate change may have triggered individual avulsions channel belts avulsed towards the fault onlap after each tectonic event during periods of tectonic quiescence they migrated away from the fault offlap taking the path of maximum overall gradient lag times between faulting and channel avulsion are very short instantaneous to hundreds of years the observed holocene history of the carson river is consistent with positions of channel belts predicted by half graben stratigraphic models and therefore this study provides the first confirmation that the underlying alluvial tectonic assumptions of these models are broadly correct