acid and basic late neogene volcanism in central aegean sea its nature and geotectonic significance local eruptions of acid volcanic rocks occurred in the central aegean region around the miocene pliocene boundary rhyolites outcrop on the island of antiparos located in the central part of the attic cycladic massif the age of these volcanic rocks ranges from 4 0 to 5 4 m y and chemical and sr isotopic data suggest they were generated by partial melting of the continental crust at the same time along the border of the attic cycladic massif i e on the island of patmos and caloyeri local eruptions of naalkaline basalts occurred the whole of the eruptive activity is interpreted as an expression of the marked tensional tectonic phase which has affected the central aegean area since middle miocene the contrasting nature of the erupted volcanic rocks crustal and sub crustal is attributed to the different thermal state of the lithosphere beneath the two areas as emphasized also by the presence of a wide granitic belt of mainly miocene age which developed in the median sector of the attic cycladic massif

decoding downstream trends in stratigraphic grain size as a function of tectonic subsidence and sediment supply downstream grain size fining in stratigraphy is driven primarily by selective deposition of sediment and the long term efficiency of this process is determined by 1 the magnitude and characteristics of the input sediment supply 2 the spatial distribution of subsidence rate which creates accommodation for sediment preservation and 3 the dynamics of sediment transport and deposition a key challenge is to determine how these first two factors control the caliber and spatial distribution of deposits over time scales of 10 4 10 6 yr without incorporating sediment transport details that are largely unknowable for time averaged stratigraphy in the geological past we address this using grain size data collected from fluvial conglomerates in the eocene pobla basin spanish pyrenees a synorogenic basin where the timing of sediment deposition is well constrained the sediment budget is closed and good exposure enables time lines within stratigraphy to be picked out unambiguously for successive stratigraphic horizons downstream trends in grain size and composition are derived for basin filling sediment routing systems with length scales of 6 and 40 km respectively our data show that the rate of grain size fining varies over time and with system length and can be linked to changes in source area these results are contrasted with grain size data from the antist group a 60 km long oligocene system that mantles the southern pyrenees where very slow rates of grain size fining on the wedge top of this fold and thrust belt are observed we apply a self similarity based selective deposition model to quantify the competing controls of tectonic subsidence and sediment supply on derived grain size trends and model results are compared with independent constraints on the eocene oligocene evolution of the pyrenees our results suggest that it is now possible to invert time averaged grain size trends in stratigraphy to gain quantitative information on the geological boundary conditions governing the evolution of sedimentary basins

neogene ignimbrites of the nevsehir plateau central turkey stratigraphy distribution and source constraints abstract in anatolia turkey extensive calc alkaline volcanism has developed along discontinuous provinces from neogene to quaternary times as a consequence of plate convergence and continental collision in the nevsehir plateau which is located in the central anatolian volcanic province volcanism consists of numerous monogenetic centres several large stratovolcanoes and an extensive mainly neogene rhyolitic ignimbrite field vent and caldera locations for the neogene ignimbrites were not well known based on previous studies in the neogene ignimbrite sequence of the nevsehir plateau we have identified an old group of ignimbrites kavak ignimbrites followed by five major ignimbrite units zelve sarimaden tepe cemilkoy gordeles kizilkaya and two smaller less extensive ones tahar sofular other ignimbrite units at the margin of the plateau occur as outliers of larger ignimbrites whose main distributions are beyond the plateau excellent exposure and physical continuity of the units over large areas have allowed establishment of the stratigraphic succession of the ignimbrites as from bottom to top kavak zelve sarimaden tepe cemilkoy tahar gordeles sofular kizilkaya our stratigraphic scheme refines previous ones by the identification of the zelve ignimbrite and the correlation of the previously defined akkoy ignimbrite with the sarimaden tepe ignimbrite correlations of distant ignimbrite remnants have been achieved by using a combination a field criteria 1 sedimentological characterisitics 2 phenocryst assemblage 3 pumice vesiculation texture 4 presence and characteristics of associated plinian fallout deposits and 5 lithic types the correlations significantly enlarge the estimates of the original extent and volume of most ignimbrites volumes range between 80 km 3 and 300 km 3 for the major ignimbrites corresponding to 2500 10 000 km 3 in areal extent the major ignimbrites of the nevsehir plateau have an inferred source area in the derinkuyu tectonic basin which extends mainly between nevsehir and the melendiz dag volcanic complex the kavak ignimbrites and the zelve ignimbrite have inferred sources located between nevsehir and derinkuyu coincident with a negative gravity anomaly the younger ignimbrites sarimaden tepe cemilkoy gordeles kizilkaya have inferred sources clustered to the south between the erdas dag and the melendiz dag volcanic complex we found evidence of collapse structures on the northern and southern flanks of the erdas dag volcanic massif and of a large updoming structure in the sahinkalesi tepe massif the present day derinkuyu tectonic basin is mostly covered with quaternary sediments and volcanics the fault system which bounds the basin to the east provides evidence that the ignimbrite volcanism and inferred caldera formation took place in a locally extensional environment while the basin was already subsiding drilling and geophysical prospecting are necessary to decipher in detail the presently unknown internal structure of the basin and the inferred probably coalesced or nested calderas within it

measuring alluvial fan sensitivity to past climate changes using a self similarity approach to grain size fining death valley california the effects of climate change on eroding landscapes and the terrestrial sedimentary record are poorly understood using mountain catchment alluvial fan systems as simple analogues for larger landscapes a wide range of theoretical studies numerical models and physical experiments have hypothesised that a change in precipitation rate could leave a characteristic signal in alluvial fan sediment flux grain size and down system fining rate however this hypothesis remains largely untested in real landscapes this study measures grain size fining rates from apex to toe on two alluvial fan systems in northern death valley california usa which each have well exposed modern and ca 70 ka surfaces and where the long term tectonic boundary conditions can be constrained between them these surfaces capture a well constrained temporal gradient in climate a grain size fining model is adapted based on self similarity and selective deposition for application to these alluvial fans this model is then integrated with cosmogenic nuclide constraints on catchment erosion rates and observed grain size fining data from two catchment fan systems to estimate the change in sediment flux from canyon to alluvial fan that occurred between mid glacial and modern interglacial conditions in a fan system with negligible sediment recycling an approximately 30 decrease in precipitation rate led to a 20 decrease in sediment flux and a clear increase in the down fan rate of fining supporting existing landscape evolution models consequently this study shows that small mountain catchments and their alluvial fan stratigraphy can be highly sensitive to orbital climate changes over 105 year timescales however in the second fan system it is observed that this sensitivity is completely lost when sediment is remobilised and recycled over a time period longer than the duration of the climatic perturbation these analyses offer a new approach to quantitatively reconstructing the effects of past climate changes on sedimentation using simple grain size data measured in the field this article is protected by copyright all rights reserved

temperature depth curves and heat flow in central part of anatolia turkey abstract the objective of this study is to determine the crustal thermal regime of central anatolia province and its relationship with regional tectonics investigations include new temperature depth measurements in wells calculations of geothermal gradients from new and previously measured temperature logs and determinations of heat flow with terrain corrections if necessary the results provide us with a better understanding of the regional distribution of subsurface temperatures and heat flow within the study area although central anatolia province is bordered with tectonically active areas moderate heat flow values 64 16 mw m 2 are generally observed within the region in accordance with the relatively less tectonic activity two thermally anomalous zones are indicated in the vicinity of kirsehir and kizilcahamam with heat flow values of higher than 100 mw m 2 anomalous heat flow in these areas can best be explained by high radioactivity of basement rocks although this is not directly confirmed for the kizilcahamam anomaly the high elevation and recent volcanic activity in the region indicate that thermal activity may be present at lithospheric levels but have not yet reached up to crustal levels also no surface heat flow anomaly due to fault activity was observed at the section of the north anatolia fault within the study area

fluvial landscape response time how plausible is steady state denudation whether or not steady state topography and denudation are probable states depends on the timescale of system response to tectonic and climatic perturba tions relative to the frequency of those perturbations this paper presents analytical derivations of algebraic relations for the response time of detachment limited fluvial bedrock channel systems both to tectonic and climatic perturbations detachment limited fluvial erosion is described by the stream power incision model and the derivations are limited to the applicability of that model all factors likely to influence system response time that are not adequately captured by the stream power incision model will tend to increase the response time the calculations presented thus provide minimum estimates of landscape response time and therefore over predict the prob ability of attaining and sustaining steady state topography and denudation the central range of taiwan is used as a case study to estimate response times in a landscape often argued to be in steady state model parameters are fit to modern stream profiles by assuming that the topography represents a quasi steady state form estimated response times generally range from 0 25 to 2 5 ma depending on the non linearity of the incision rule and the magnitude and type of perturbation thus it may be reasonably argued that steady state topography and denudation are likely to prevail during periods of climatic stability response time is sufficiently short compared with plate tectonic timescales however rapid climatic fluctuation in the quaternary appears to preclude the attainment of steady state conditions in modern orogens motivation

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

evaluating major controls on basinal stratigraphy pine valley nevada implications for syntectonic deposition the interpretation of prograded gravel as an indicator of tectonic uplift that is syntectonic deposition is not necessarily correct increases in sediment supply induced by tectonic uplifting did not control the progradation of gravel in the pine valley basin an actively subsiding half graben in northeastern nevada rather the distribution of lithofacies in the pine valley basin is primarily controlled by the uneven distribution of subsidence within the basin differences in subsidence along the axis of the basin indicate a strong inverse relationship between the long term subsidence rate since late miocene time and the distance of gravel transport out into the basin differential progradation of alluvial gravel into the basin from various drainages along the footwall is not related to uplift or lithology of the source area size of the catchment area or climate in addition the relatively fixed location of the topographic low within the basin through time as indicated by the distribution of lacustrine deposits and the position of the modern axial drainage suggests that a balance between basin subsidence and sediment supply to the basin has been generally maintained through time thus if subsidence rates are a measure of tectonic activity gravel progradation may record times of reduced not increased tectonism

hidden calderas evidenced by multisource geophysical data example of cappadocian calderas central anatolia abstract the cappadocian volcanic field in central anatolia turkey is characterised by a sequence of 10 neogene ignimbrites the associated calderas have been partly dismantled and buried by subsequent tectonic and sedimentary processes and therefore cannot be readily recognized in the field recent progress in the understanding of the stratigraphic correlations and flow patterns has identified two main probable source areas for the ignimbrites detailed study of these areas based on gravity surveys remote sensing data spot and ers1 images and digital elevation models dem has provided evidence for two major caldera complexes and their relationship to old stratovolcanoes and neogene tectonics the older nevsehir acigol caldera complex located between the towns of acigol nevsehir and cardak is inferred to be the source of the kavak and zelve ignimbrites the nevsehir acigol caldera complex is defined mainly by a 35 mgal circular gravimetry anomaly about 15 km in diameter the boundaries of this now buried caldera complex are shown by high gradients on the bouguer gravity anomaly map the younger derinkuyu caldera complex located between the erdas stratovolcano and the ciftlik basin is inferred to be the source of the sarimaden cemilkoy gordeles and kizilkaya ignimbrites it is well defined by a rectangular 35 23 km gravity low 30 mgal with a positive high 20 mgal in the center gravity remote sensing data and the dem provide evidence that the erdas stratovolcano on the northern margin of the derinkuyu caldera complex represents the remnants of a large stratovolcano partly cut by one or more caldera collapses the positive anomaly within the derinkuyu caldera complex is centered on the 15 km wide sahin kalesi volcanic massif field evidence and structural features inferred from the dem and remote sensing data strongly suggest that this massif is a resurgent doming associated with the gordeles ignimbrite eruption high resolution ers1 spot and dem images reveal that the transtensive regime active at least since the miocene influenced the location of eruptive centers and caldera complexes in cappadocia the two caldera complexes are located in transtensive grabens the subsidence of these grabens continuing after the caldera collapse events most likely resulted in the burying of the calderas and could explain the difficulties in identifying them in the field

the geomorphic and paleoenvironmental record in the sediments of atlin lake northern british columbia atlin lake in northern british columbia and southern yukon territory is the largest natural lake in the north american cordillera 791km 2 inflow from the juneau ice field delivers large volumes of sediment to the proximal basins of willison bay and llewellyn inlet sediment is distributed by interflow and underflow through these basins based on acoustic data each of these basins contain holocene deposits about 120m thick representing mean annual accumulation since deglaciation of more than 1cm a cores confirm this except that the formation of a small lake at the toe of llewellyn glacier during about the past 50 years is trapping sediment and has reduced accumulation in llewellyn inlet by an order of magnitude sills separate these basins from the main body of atlin lake and torres channel where accumulation is much less averaging about 1 4mm a during the history of the lake late pleistocene glacilacustrine sediment occurs as a thin patchy deposit and is overlain by up to 10m of holocene lacustrine deposits unlike other large lakes in the cordillera with thick late pleistocene deposits indicating large volumes of sediment contributed by glaciers in the lakes and their basins the pattern in atlin lake documents rapid retreat of glaciers from the lake and much of the drainage basin

on two dimensional interpretation of magnetotelluric soundings summary the paper presents the views of the 2 d interpretation of magnetotelluric mt data that are characteristic of the russian magnetotelluric school discussing the strategy of 2 d interpretation of mt data we have to answer three questions in decreasing order of importance these questions are as follows 1 which field mode is more sensitive to the near surface and deep structures that are the targets of mt surveys 2 which field mode is more robust to the 3 d evects caused by real geological bodies 3 which field mode is more susceptible to the static shift induced by nearsurface inhomogeneities we examine the transverse magnetic tm and transverse electric te modes of the 2 d magnetotelluric field and show that they satisfy the principle of information complementarity 1 while the tm mode is more sensitive to the near surface structures the te mode may be more sensitive to the deep structures 2 while the tm mode is more robust to the 3 d evects caused by conductive structures the te mode may be more robust to the 3 d evects caused by resistive structures and 3 while the tm mode is more susceptible to the static shift the te mode may be almost undistorted thus the gaps left by one mode can be filled by another mode if so the most comprehensive and reliable information on the conductivity of the earth s interior can be obtained using both modes i e the transverse and longitudinal mt curves the general scheme of this bimodal mt inversion is rather simple the transverse curves provide details of near surface structures e g in the sediments and allow one to evaluate the lithosphere resistance and outline the deep conductive faults while the longitudinal curves help one to detect the conductive zones in deep layers of the lithosphere and in the asthenosphere an eycient two level algorithm for the bimodal mt inversion realizing this scheme is suggested as an illustration the paper presents the geoelectrical model of the kirghiz tien shan constructed by means of the bimodal mt inversion

neoglaciation in the southern coast mountains of british columbia chronology prior to the late neoglacial maximum moraine stratigraphy and morphology radiocarbon dates from klinaklini franklin tiedemann gilbert and bridge glaciers and related information from elsewhere in the coast mountains are used to construct a chronology for glacier fluctuations the garibaldi phase of glacier expansion 6000 5000 14c years bp at the end of the early holocene xerothermic interval is indicated by overridden tree stumps the mid neoglacial tiedemann advance 3300 1900 14c years bp is represented by moraines till and meltwater sediments at three glaciers but only tiedemann glacier attained its greatest holocene extent at this time late neoglacial expansion commenced before 900 14c years bp and continued without notable interruption until glaciers achieved their maximum post pleistocene expansion during the eighteenth and nineteenth centuries evidence for the garibaldi and tiedemann events is scarce within the coast mountains because of the more extensive late neoglacial advance however correlative advances have been

electrical properties of granite with implications for the lower crust the electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure structurally bound water oxygen fugacity and other parameters the effect of sulfur fugacity may be important but is experimentally unconfirmed in addition to changing the magnitude of electrical properties the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties with increasing temperature changes in water content retain large but lessened effects on electrical properties near room temperature a monolayer of water will decrease the electrical resistivity by an order of magnitude several weight percent water may decrease the electrical resistivity by as much as 9 orders of magnitude and decrease the thermal activation energy by a factor of 5 at elevated temperatures just below granitic melting a few weight percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of 2 above the melting temperature 650 to 1100 c depending upon water pressure a few weight percent water will decrease the resistivity by less than an order of magnitude and will barely change the activation energy remarkably the few weight percent water must be present as free water experiments with hydrated hornblende schist with structural water indicate an electrical resistivity very similar to that for dry granite the implications of these results together with the findings of deep magnetic sounding and magnetotelluric surveys suggest much more free water than is commonly associated with the lower crust and possibly into the upper mantle

time scales of tectonic landscapes and their sediment routing systems abstract in regions undergoing active tectonics the coupling between the tectonic displacement field the overlying landscape and the redistribution of mass at the earth9s surface in the form of sediment routing systems is particularly marked and variable coupling between deformation and surface processes takes place at a range of scales from the whole orogen to individual extensional fault blocks or contractional anticlines at the large scale the attainment of a steady state between the overlying topography and the prevailing tectonic conditions in active contractional orogens requires an efficient erosional system with a time scale dependent on the vigour of the erosional system generally in the range 10 6 10 7 years the catchment fan systems associated with extensional fault blocks and basins of the western usa are valuable natural examples to study the coupling between tectonic deformation landscape and sediment routing systems even relatively simple coupled systems such as an extensional fault block and its associated basin margin fans have a range of time scales in response to a tectonic perturbation these response times originate from the development of uniform steady state relief during the accumulation of displacement on a normal fault c 10 6 years the upstream propagation of a bedrock knickpoint in transverse catchments following a change in tectonic uplift rate c 10 6 years or the relaxation times of the integrated catchment fan system in response to changes in climatic and tectonic boundary conditions 10 5 10 6 years the presence of extensive bedrock or alluvial piedmonts increases response times significantly the sediment efflux of a mountain catchment is a boundary condition for far field fluvial transport but the fluvial system is much more than a simple transmitter of the sediment supply signal to a neighbouring depocentre fluvial systems appear to act as buffers to incoming sediment supply signals with a diffusive time scale c 10 5 10 6 years dependent on the length of the system and the extent of its floodplains stream channels and proximal gravel fans the vocabulary for explaining landscapes would benefit from a greater recognition of the importance of the repeat time and magnitude of perturbations in relation to the response and relaxation times of the landscape and its sediment routing systems landscapes are best differentiated as buffered or reactive depending on the ratio of the response time to the repeat time of the perturbation furthermore landscapes may be regarded as steady or transient depending on the ratio of the response time to the time elapsed since the most recent change in boundary conditions the response of tectonically and climatically perturbed landscapes has profound implications for the interpretation of stratigraphic architecture

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

footwall topographic development during continental extension 1 we examine the progressive development of footwall topography associated with a set of active normal faults in the northeastern basin and range province of the western united states fault length and displacement increase monotonically from northeast to southwest in the study area allowing us to track both variations in footwall morphology with increasing displacement and along strike changes in morphology on a single fault we show that patterns of catchment area footwall relief and catchment outlet spacing vary predictably and are related to the growth of the range bounding normal fault array in this semiarid region full parsing of footwall drainage area and removal of antecedent topography do not occur until fault arrays grow beyond two crustal scale segments multiple segment faults with lengths of up to 150 km have footwall relief that is limited to 1000 m in the center of the footwall and that decays to zero at the fault tips over a length scale of 15 km we hypothesize that this relatively uniform footwall relief is erosionally limited and reflects the efficacy of surface processes in removing footwall material in the center of the footwall if the fault array grows by relatively steady propagation of the tips we suggest that the 15 km length scale required to reach uniform relief is related to a timescale of relief generation by the fault tip propagation rate while such propagation rates are poorly known an average rate of 10 mm yr 1 would imply footwall relief generation over a timescale of 1 myr

timescales of alluvial fan development by precipitation on mars 1 dozens of large low gradient alluvial fans are present within impact crater basins on the cratered highlands of mars the timescales and climate conditions that were required to generate such fans are unknown but testable through our understanding of terrestrial hill slope erosion in the presence of precipitation previous estimates of fan formation time vary from years to millions of years here we use an idealised physical model of 2 d catchment fan evolution to present a framework within which the development of martian alluvial fans should be considered we simplify the erosional and depositional system so that there are only three variables erodibility due to gravity amount of water runoff due to precipitation and catchment fan boundary elevation within this framework to generate large low gradient 108 yr if the substrate is extremely erodible relative to terrestrial examples

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

natural oscillations in coupled geomorphic systems an alternative origin for cyclic sedimentation internally oscillating cycles of cutting and filling occur naturally in many coupled geomorphic systems as a demonstration we have modeled stream entrenchment and backfilling where alluvial systems couple to uplifting mountain blocks this simple model tracksbedrockstreamerosionandtransportofalluviumtobaselevel internaloscillations arise from coupling of a kinematic wave model for mountain erosion to a diffusion model for the alluvial basin decaying periodic cutting andfilling occur on time scales of 10 5 yr the largest magnitudes are found at the coupling point model results suggest that cyclic sedimentation may result from the tintinnabulation of single perturbations applied to natural systems and need not record cyclic changes in climate tectonics or base level

sedimentary record of harrison lake implications for deglaciation in southwestern british columbia a sedimentary record from 60 km long harrison lake was constructed by using 3 5 khz subbottom acoustic profiles and gravity cores of surface sediments in places the glaciolacustrine sediments exceed 70 m in thickness and represent the entire deglacial and postglacial accumulation record an upper acoustically transparent layer decreases in thickness from 12 to 4 m southward from the upper lake cores from the upper metre of this layer demonstrate that deposition is dominated by settling of suspended sediment transported in a laterally mixed wind driven surface plume from the north depositional rates inferred from 14c dating of organic macrofossils and counting of probable annual laminated couplets in the cores are almost 2 mm a in the north and decline to less than 0 1 mm a in the south hence the upper acoustic layer accounts for all postglacial last 10 500 years bp lacustrine deposition with most of the sediment derived from lillooet river a lower thicker 12 22 m acoustically stratified

assessment of geothermal energy potential by geophysical methods nevsehir region central anatolia abstract in this study geothermal potential of the nevsehir region central anatolia was assessed by using vertical electrical sounding ves self potential sp magnetotelluric mt gravity and gravity 3d euler deconvolution structure analysis methods extensive volcanic activity occurred in this region from upper miocene to holocene time due to the young volcanic activity nevsehir region can be viewed as a potential geothermal area we collected data from 54 ves points along 5 profiles from 28 mt measurement points along 2 profiles at frequency range between 320 and 0 0001 hz and from 4 sp profiles total 19 km long the obtained results based on different geophysical methods are consistent with each other joint interpretation of all geological and geophysical data suggests that this region has geothermal potential and an exploration well validated this assessment beyond doubt

curie point depth geothermal gradient and heat flow estimation and geothermal anomaly exploration from integrated analysis of aeromagnetic and gravity data on the sabalan area nw iran prospecting the geothermal resources in northwest of iran conducted in 1975 revealed several promising areas and introduced the sabalan geothermal field as a priority for further studies the sabalan mt representing the sabalan geothermal field is a large stratovolcano which consists of an extensive central edifice built on a probable tectonic horst of underlying intrusive and effusive volcanic rocks in this study curie point depth cpd geothermal gradient and heat flow map were constituted from spectral analysis of the aeromagnetic data for the nw of iran the top of the geothermal resource i e the thickness of the overburden was evaluated by applying the euler deconvolution method on the residual gravity data the thickness of the geothermal resource was calculated by subtracting the euler depths obtained from the cpds in the geothermal anomalous region the geothermal anomalous region was defined by the heat flow value greater than 150 mw m2 cpds in the investigated area are found between 8 8 km in the sabalan geothermal field and 14 1 in the northeast the results showed that the geothermal gradient is higher than 62 c km and the heat flow is higher than 152 mw m2 for the geothermal manifestation region the thickness of the geothermal resource was also estimated to vary between 5 4 and 9 1 km these results are consistent with the drilling and other geological information findings indicate that the cdps agree with earthquake distribution and the type of thermal spring is related to the depth of the top of the geothermal resource

glacial interglacial climate changes recorded by debris flow fan deposits owens valley california abstract it is hotly debated whether and how climate changes are recorded by terrestrial stratigraphy basin sediments produced by catchment alluvial fan systems may record past climate over a variety of timescales and could offer unique information about how climate controls sedimentation unfortunately there are fundamental uncertainties about how climatic variables such as rainfall and temperature translate into sedimentological signals here we examine 35 debris flow fan surfaces in owens valley california that record deposition throughout the past 125 000 years during which climate has varied significantly we show that the last full glacial interglacial cycle is recorded with high fidelity by the grain size distributions of the debris flow deposits these flows transported finer sediment during the cooler glacial climate and became systematically coarser grained as the climate warmed and dried we explore the physical mechanisms that might explain this signal and rule out changes in sediment supply through time instead we propose that grain size records past changes in storm intensity which is responsible for debris flow initiation in this area and is decoupled from average rainfall rates this is supported by an exponential clausius clapeyron style scaling between grain size and temperature and also reconciles with climate dynamics and the initiation of debris flows the fact that these alluvial fans exhibit a strong sustained sensitivity to orbital climate changes sheds new light on how eroding landscapes and their sedimentary products respond to climatic forcing finally our findings highlight the importance of threshold controlled events such as storms and debris flows in driving erosion and sedimentation at the earth s surface in response to climate change

structural and geomorphological constraints on active normal faulting and landscape evolution in calabria italy calabria is one of the fastest uplifting and most seismically active regions in the mediterranean yet the time averaged c 10 6 years rates of normal faulting remain poorly constrained here we use digital elevation model analysis geological cross sections and a compilation of published data to quantify systematically along strike the fault throws and time averaged throw rates of the serre cittanova armo east crati and west crati faults we show that regional uplift has uplifted both their hanging wall and footwall blocks by c 200 400 m and the aspromonte massif by up to c 1150 1300 m we find that these faults have throws between c 640 and 1430 m and throw rates between c 0 6 and 1 4 mm a 1 their footwall ranges have variable proportions of inherited relief up to c 300 800 m the channels draining these ranges reflect the active normal faulting and relief in their steepness indices becoming c 5 8 m 0 9 steeper for each 0 1 mm a 1 throw rate increment and each 100 m relief increase finally the presence of knickpoints suggests that these channels are transiently responding to changes in relative base level which could be due to fault linkage or regional strain rate increases for the southern calabrian faults and to regional uplift acceleration in the case of the crati faults supplementary material topographic profiles of the marine terraces and long profiles of rivers are available at https doi org 10 6084 m9 figshare c 3689464

curie point depth investigation of central anatolia turkey the residual aeromagnetic total field intensity anomalies in central anatolia were calculated from the regional aeromagnetic anomalies surveyed by the mineral research and exploration mta of turkey the residual aeromagnetic data were analyzed to produce curie point estimates by the method of okubo et al 1985 the curie point depth of central anatolia varies from 7 9 km and 22 6 km the shallowest curie point depths were observed around the cappadocia and erciyes volcanic complexes in central anatolia a good correlation was deduced between the curie point depths and the heat flow data measured previously which is most certainly important for the geothermal resources of the region the shallow curie point depths also correlate well with the hot spring locations in central anatolia

topographic evolution and morphology of surfaces evolving in response to coupled fluvial and hillslope sediment transport 1 this paper quantifies how the ratio of sediment transport on hillslopes to sediment transport in channels influences surface and channel network morphologies and the dynamics of topographic evolution this problem is investigated by development and investigation of a simple deterministic model incorporating mass balance of sediment and runoff coupled with a law combining dispersive and concentrative sediment transport processes our analysis includes the identification of a new nondimensional parameter de that is a function of rainfall system size rock type and hydraulic regime and that is a measure of the relative importance of fluvial and hillslope sediment transport we show that de has an important influence on the surface morphology e g total exposed surface area and interface width which reflects surface roughness and relief channel network form e g channel sinuosity channel spacing and timescale of surface evolution surface and channel network morphologies are also strongly influenced by the overall surface slope relative to the magnitude of initial topographic roughness topographic evolution occurs in distinct phases of relief growth and decay the transition between which is controlled by a saturation phenomenon related to the growth of spatial correlations the scaling behavior of simulated topography with respect to both time and space is obtained and is shown to be independent of de roughness exponents are found to be independent of de but dependent on the magnitude of initial roughness interface width is shown to grow and decay as a logarithm of time

the influence of debris flow rheology on fan morphology owens valley california we have investigated factors controlling the surface morphology of debris flow fans comprising the bajada along the western slope of owens valley california these fans have average slopes of 4 an extensive network of abandoned boulder lined channels rough undulatory surfaces near the range front and smooth distal surfaces field relationships and mechanical considerations indicate that the channels of the bajada are products of fluvial incision and not debris flow scour this is significant because detailed geomorphic maps indicate that the channels strongly influence the pattern of debris flow deposition the locus of debris flow deposition on a channelized fan surface is set by the interaction of debris flows with the channel system and is controlled by channel size channel gradient flow volume flow hydrograph and flow rheology debris flow behavior is most directly controlled by variations in bulk sediment concentration and its influence on flow rheology whereas low sediment concentration debris flows tend to smooth the surface of the lower fan spreading into thin sheets and filling channels and surface undulations repeated deposition of high sediment concentration debris flows produces the rugged topography of the upper fan the texture of the fan surface rough or smooth is determined by the relative volumetric importance of these two types of debris flow in addition channel avulsions and the associated long term shifting of depositional loci are driven by in channel deposition of debris flows with the highest sediment concentrations these debris flows therefore play a critical role in determining both the structure of the channel network and the long term pattern of deposition on the fan surface as a whole we infer that the frequency distribution of debris flow rheologies set by source terrain geology and hydrology is an important control on fan morphology

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

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

detecting the limit of slab break off in central turkey new high resolution pn tomography results summary inversion of pn traveltime residuals from a 39 station broad band array provides a highresolution image of the velocity structure in the uppermost mantle beneath central turkey individually picked pn phase arrivals from events recorded by the north anatolian fault passive seismic experiment and the kandilli observatory were combined with additional events associated with the eastern turkey seismic experiment tomography results show no change in pn velocity across the north anatolian fault although longitudinal variations are evident a region of very low pn velocities 8 1 km s 1 w est of the fault the sharp transition along the cafz which follows the palaeotectonic inner tauride suture may represent the location of the edge of the slab window created when the oceanic slab broke off along the bitlis zagros suture around 11 ma as the arabian plate collided with the eurasian plate

self organization of river networks to threshold states numerical models in which grid cells self organize so that the shear stress in each cell equals a predetermined threshold value are remarkably successful in producing the fundamental structure of river networks such models are a reasonable approximation of networks characterized by near constant dimensionless shear stress bed shear stress7sol bed grain size with each cell s threshold value being proportional to median bed grain size previous work has shown that this is the case for channels cut into alluvium and that the characteristic narrow range of is different for gravel and sand bed channels channels in the italian apennines that are slowly incising into weak bedrock but which are covered by a veneer of gravel for most of the time are shown to be characterized by the same as alluvial gravel bed channels thus threshold models capture the fundamental behavior of many river networks even in areas of long term bedrock incision

development and response of a coupled catchment fan system under changing tectonic and climatic forcing sediment fans are a potentially useful and underexploited recorder of earth s climatic and tectonic history but historical observations have led to conflicting views on the importance of tectonic climatic and lithologic variables in controlling fan morphology and deposition a one dimensional model of a sediment fan and its associated catchment is used to explore the sensitivity of such simple sediment routing systems to perturbations in fault slip and precipitation rates a transport limited catchment is coupled to a fan whose surface slope is set by the balance between catchment sediment efflux and the available tectonically generated basin accommodation rock uplift rate is spatially variable across the model space increasing the fault slip rate or decreasing the precipitation rate leads to an increase in fan slope temporary back stepping of the fan toe and a pronounced angular unconformity conversely a decrease in slip rate or an increase in precipitation rate results in a decrease in fan slope and progradation and eventual stabilization of the fan toe once perturbed the system evolves toward a new equilibrium state with time constants of 0 5 to 2 myr these response times are insensitive to slip rate but are strongly dependent on precipitation rate variations in fan slope are well described by a dimensionless parameter that expresses equilibrium slope as a function of slip rate precipitation rate system size and catchment lithology this parameter holds promise as a predictive tool in inverting the morphology of natural fans for environmental variables

energy dispersive x ray fluorescence analysis as a rapid method for identifying tephras abstract the use of energy dispersive x ray fluorescence analysis xes for the routine identification of three tephras mazama bridge river mount st helens yn commonly found in archeological sites in british columbia has been investigated researchers have often assumed that chemical analysis of bulk samples of glass separates would be hampered by contamination and weathering effects our results indicate that xes of bulk glass separates provides a very reliable method for rapidly identifying the three tephras in question even with a very simple sample preparation this should enable persons not skilled in geology or in tephrochronology to collect and to identify samples of these tephras finally as a part of the study similar measurements were made on the separated glass portions of these three tephras and of three others glacier peak b and g white river from northwest north america the results suggest that this method may provide tephrochronologists with a useful additional tool for studying tephras in other regions

sedimentology of the debris flow dominated warm spring canyon alluvial fan death valley california facies analysis of widely distributed exposures of the 32 6 km2 and 8 1 km long warm spring canyon fan central death valley shows that it has been built principally by debris flow deposits these deposits were derived from a mature panamint range catchment mostly underlain by precambrian mudrock quartzite and dolomite stacked clast rich and matrix supported debris flow lobes of slightly bouldery muddy pebble cobble gravel in beds 20 150 cm thick dominate the fan from apex to toe accounting for 75 98 of most exposures interstratified with the debris flows are less abundant 2 25 of cuts thinner 5 30 cm and more discontinuous beds of clast supported and imbricated pebble cobble gravel deposited by overland flows and gully flows this facies formed by the surficial fine fraction water winnowing of the debris flows primarily during recessional flood stage of the debris flow events two other facies associations make up a small part of the fan the incised channel tract consists of a 250 m wide clast supported ribbon of irregularly to thickly bedded boulder pebble cobble gravel nested within debris flow deposits this channel fill is oriented generally perpendicular to the panamint range front it formed by extensive erosion and winnowing of debris flows deposited within the incised channel into which all water discharge from the catchment is funnelled the limited presence of this facies only straddling the present incised channel indicates that this channel overall has maintained a consistent position on the fan except for slight lateral shifts some caused by strike slip offset fault offset temporarily closed the upper incised channel causing recessional debris flow mud to be ponded behind the dam the other local facies assemblage consists of subrounded to rounded moderately sorted pebble gravel in low angle cross beds that slope both basinwards and fanwards this gravel was deposited in beachface backshore and shoreface barrier spit environments that developed where lake manly impinged on the warm spring fan during late pleistocene time these deposits straddle headcuts into and were derived from erosion of the debris flow deposits wave energy sorted finer sediment from the shore zone concentrated coarser sediment and rounded the coarse to very coarse pebble fraction by selective reworking

dating the northern deposits of the ebro foreland basin implications for the kinematics of the sw pyrenean front abstract dating the sedimentary infill of the northern margin of the ebro foreland basin informs about the orogen basin evolution a magnetostratigraphic section of 5 km thick combines new magnetostratigraphic results from the syntectonic alluvial uncastillo fm upper oligocene lower miocene 1 km thick the fuencalderas section with previous 3 3 km thick and new 0 7 km thick magnetostratigraphic data from the underlying fluvial campodarbe fm luesia and san marzal sections eocene oligocene this composite section allows dating the entire basin infill in this sector therefore bracketing the timing of the deformation in the southern margin of the pyrenees after considering previous kinematic studies deformation recorded by the continental deposits spans from syn gavarnie nappe activity broto and fiscal basement thrust sheets from 31 3 to 24 55 ma rupelian chattian oligocene to the syn guarga thrust activity from 24 55 to 21 2 ma chattian aquitanian oligocene miocene the accumulation rates vary from ca 22 to ca 39 cm kyr between the genetic stratigraphic units in the uncastillo fm through the section these rates are close to those of the underlying deposits of the campodarbe fm average of ca 36 cm kyr deformation for the latest pyrenean front syn guarga thrust is younger than previously assigned in 5 4 1 5 and 1 1 myr of the beginning of the punta comun thrust sheet from 29 4 ma to 24 ma lower riglos thrust sheet system from 24 to 22 5 ma and the upper riglos thrust system 22 5 to 21 4 ma respectively other significant changes in accumulation rate and its derivative also indicate variations in the tectonic activity ca 33 and 28 ma

fluvial fan deltas linking channel processes with large scale morphodynamics 1 alluvial fan deltas are built by aggrading and avulsing river channels a numerical model of flow and sediment transport in channels is combined with a condition for channel avulsion to describe evolution of the fan surface the model combines elements of two recent approaches 1 diffusional models of depositional basin filling which describe the evolution of overall morphology and 2 cellular models of channel evolution which provide simplified descriptions of channel dynamics here the cellular formulation is used simply as a template for discretizing a standard set of equations describing flow and sediment transport within channels the basic formulation is thus grid invariant and the results are in actual rather than arbitrary time and length scales the model captures the interaction between microscale channel morphodynamics including converging and diverging flow and avulsion and morphodynamics at the macroscale fan it provides a starting point for the study of a wide range of topics including the three dimensional stratigraphy of fan delta deposits and the response of fan deltas to engineering activities

transformation of tectonic and climatic signals from source to sedimentary archive sedimentary rocks reflect past tectonic and climatic events numerical simulations suggest that changes in precipitation and in the rate of tectonic uplift affect the grain size and the distribution of sediments deposited downstream

how plausible are high frequency sediment supply driven cycles in the stratigraphic record abstract this paper is an attempt to quantify the plausible time scales of clastic sediment supply variations at the entrance of sedimentary basins our approach is based on the sedimentary system concept which simplifies natural systems by dividing them into three zones of dominant processes the erosion the transfer and the sedimentation subsystems we examine recent results from geomorphology which show that frequent climate changes can induce high frequency sediment flux variations at the outlet of the source area we put forward the crucial role of the transfer subsystem which conveys sediment from the erosion zone to the basin by applying a diffusive model to a number of worldwide rivers we extend from large 1000 km to intermediate 300 km rivers the previous finding that the transfer subsystem acts as a buffer for short periods sediment pulses tens to hundreds of kiloyears this implies that high frequency stratigraphic cycles in clastic accumulations fed by large drainage systems are unlikely to reflect sediment supply cycles of tens to hundreds of thousands of years of periodicities

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

recent debris flow processes and resultant form and facies of the dolomite alluvial fan owens valley california abstract a multiphase debris flow triggered by an afternoon thunderstorm was deposited 22 august 1984 on the dolomite alluvial fan of owens valley california two tracts 10 300 cm thick accumulated during this event together covering 68 000 m2 26 of the fan with 50 000 m3 of sediment both tracts consist of numerous paired boulder rich levees 100 300 cm high on the proximal fan and multiple attached lobes 20 100 cm thick on the distal fan each levee lobe pathway was built by an individual surge with flow path switching caused by clogging of the frontal bouldery snout of the ensuing surge the levees consist of clast supported to matrix supported muddy pebbly cobbly boulder gravel displaying a well developed radially aligned a axis clast fabric the lobes mostly consist of matrix supported muddy pebbly cobble gravel the clast supported lobe margins are enriched in cobbles displaying a strongly preferred slope parallel a axis fabric along the sides that changes to a slope perpendicular fabric at the snout the distal ends of most of the clast rich lobes are overlain and offlapped by clast poor debris flow lobes of granular mud 10 30 cm thick the central zones of the levees and most lobes were surficially washed by recessional stage water flows that moved winnowed granules sand and mud off the fan the radial change from levees in the proximal fan to lobes distally is morphologically expressed as two intersecting slope segments the upper one sloping 9 12 and the lower one 3 5 this direct relationship between the constituent forms and slope values also is characteristic of pre 1984 deposits suggesting that the 1984 event is typical of the primary processes constructing the dolomite fan the pronounced radial change from levees to lobes and its manifestation as a slope inflection was caused by the selective loss on the upper fan of most of the boulders from the passing debris flow surges boulders were sorted from the surges because of their greater buoyancy which caused them to be preferentially concentrated in the part of the flow that subsequently was sheared off as levees this selective boulder removal depleted the flow of the clasts that provided lateral support facilitating flow expansion and the onset of lobe development thus the resultant facies assemblage is a function of the specific sediment grain size suite available in the catchment colluvium and the transport characteristics of this mix when transformed into a debris flow by the rapid addition of heavy rainfall during infrequent thunderstorms

earthquake clustering inferred from pliocene gilbert type fan deltas in the loreto basin baja california sur mexico a stacked sequence of pliocene gilbert type fan deltas in the loreto basin was shed from the footwall of the dextral normal loreto fault and deposited at the margin of a marine basin during rapid fault controlled subsidence fan delta parasequences coarsen upward from marine siltstone and sandstone at the base through sandy bottomsets and gravelly foresets to gravelly nonmarine topsets each topset unit is capped by a thin shell bed that records marine flooding of the delta plain several mechanisms may have produced repetitive vertical stacking of gilbert deltas 1 autocyclic delta lobe switching 2 eustatic sea level fluctuations 3 climatically controlled fluctuations in sediment input and 4 episodic subsidence produced by temporal clustering of earthquakes we favor hypothesis 4 for several reasons but hypotheses 2 and 3 cannot be rejected at this time earthquake clustering can readily produce episodic subsidence at spatial and temporal scales consistent with stratigraphic trends observed in the loreto basin this model is supported by comparison with paleoseismological studies that document clustering on active faults over a wide range of time scales earthquake clustering is a new concept in basin analysis that may be helpful for understanding repetitive stratigraphy in tectonically active basins

younger dryas readvance in squamish river valley southern coast mountains british columbia abstract stratigraphy and landforms in the brohm creek basin and lowermost mamquam river valley provide evidence for a readvance of a valley glacier in the southern coast mountains of british columbia during the younger dryas interval at brohm creek till containing wood 10 500 and 10 700 14 c yr old ca 12 500 12 900 cal yr old overlies an ice contact terrace that is correlative with similar terraces at the mouth of mamquam river 11 km to the south and 900 m lower in elevation a line linking the two sites has a slope of 5 which is similar to slopes of termini of present day valley glaciers in the southern coast mountains we used these observations to reconstruct the younger dryas glacier in squamish valley at the head of howe sound the glacier deflected landslide debris derived from steep slopes at the head of cheekye river basin on the west flank of mt garibaldi southward to an ice marginal lake at the mouth of mamquam river foreset bedded sediments in the core of a large fan at the mouth of cheekye river indicate the glacier terminus had retreated up squamish valley beyond cheekye and mamquam rivers by 10 200 14 c yr bp 11 900 cal yr old radiocarbon ages on the oldest postglacial sediments in a kettle on the landslide debris show that stagnant ice in the study area had melted before 10 000 14 c yr bp 11 500 cal yr bp the readvance of the squamish valley glacier during the younger dryas chronozone was probably driven by a regional climate reversal

two phase stratigraphic model of foreland basin sequences application of flexural models to nonmarine foreland basin evolution indicates that two different stratigraphic styles of basin fill may develop over time basin subsidence is most rapid during times of thrust load emplacement associated sedimentation is coarse grained immediately adjacent to the thrust front and grades rapidly into fine grained deposits that cover most of the basin the distal part of the basin may also contain deposits derived from streams that flow from beyond the basin toward the thrust belt subsequent removal of the thrust load by erosion and other processes results in flexural rebound of the thrust belt and adjacent foreland basin during this postorogenic phase of adjustment a regional unconformity develops in the proximal part of the foreland basin proximal deposits along with thrust derived sediment are redeposited in the distal foreland basin and beyond this two phase model of foreland sedimentation predicts that coarsening upward sequences in the proximal and distal parts of the basin have reciprocal significance the proximal sequence represents thrust belt advance whereas the distal sequence represents thrust belt cessation

cenozoic river profile development in the upper lachlan catchment se australia as a test of quantitative fluvial incision models 1 we have used early miocene valley filling basalts to reconstruct fluvial long profiles in the upper lachlan catchment se australia in order to use these as well constrained initial conditions in a forward model of fluvial incision many different fluvial incision algorithms have been proposed and it is not clear at present which one of these best captures the behavior of bedrock rivers we test five different formulations the ability of these models to reproduce the observed present day stream profiles and amounts of incision is assessed using a weighted mean misfit criterion as well as the structure of the misfit function the results show that for all models parameter combinations can be found that reproduce the amounts of incision reasonably well however for some models these best fit parameter combinations do not seem to have a physical significance whereas for some others best fit parameter combinations are such that the models tend to mimic the behavior of other models overall best fit model predictions are obtained for a detachment limited stream power model or an undercapacity model that includes a river width term that varies as a function of drainage area the uncertainty in initial conditions does not have a strong impact on model outcomes the model results suggest however that lithological variation may be responsible for variations in parameter values of a factor of 3 5

advance of alpine glaciers during final retreat of the cordilleran ice sheet in the finlay river area northern british columbia canada abstract sharp crested moraines up to 120 m high and 9 km beyond little ice age glacier limits record a late pleistocene advance of alpine glaciers in the finlay river area in northern british columbia the moraines are regional in extent and record climatic deterioration near the end of the last glaciation several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern cordilleran ice sheet other lateral moraines merge with ice stagnation deposits in trunk valleys these relationships confirm the interaction of advancing alpine glaciers with the regionally decaying cordilleran ice sheet and verify a late glacial age for the moraines sediment cores were collected from eight lakes dammed by the moraines two tephras occur in basal sediments of five lakes demonstrating that the moraines are the same age plant macrofossils from sediment cores provide a minimum limiting age of 10 550 10 250 cal yr bp 9230 50 14c yr bp for abandonment of the moraines the advance that left the moraines may date to the younger dryas period the finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late glacial glacier advances

new radiocarbon dates for early deglaciation from the southeastern coast mountains of british columbia basal dates obtained on organic material from postglacial lacustrine sediments from four lakes in the kwoiek creek watershed southern coast mountains of british columbia provide minimum dates of deglaciation the dates obtained 12 255 770 11 485 185 10 385 595 and 9640 380 bp at elevations 835 1120 m suggest that extensive areas of the mountains of southern british columbia were ice free prior to 11 500 years ago this has implications for models of the regional deglaciation of the southern portion of the province

sedimentary processes and facies of the waterlaid anvil spring canyon alluvial fan death valley california the anvil spring canyon fan of the panamint range piedmont in central death valley was built entirely by water flow processes as revealed by an analysis of widespread 2 to 12 m high stratigraphic cuts spanning the 9 7 km radial length of this 2 5 5 0 sloping fan two facies deposited from fan sheetfloods dominate the fan from apex to toe the main one 60 95 of cuts consists of sandy granular fine to medium pebble gravel that regularly and sharply alternates with cobbly coarse to very coarse pebble gravel in planar couplets 5 25 cm thick oriented parallel to the fan surface the other facies 0 25 of cuts comprises 10 to 60 cm thick wedge planar and wedge trough beds of pebbly sand and sandy pebble gravel in backsets sloping 3 28 both facies are interpreted as resulting from rare sediment charged flash floods from the catchment and were deposited by supercritical standing waves of expanding sheetfloods on the fan standing waves were repeatedly initiated enlarged migrated and then terminated either by gradually rejoining the flood or by more violent breakage and washout the frequent autocyclic growth and destruction of standing waves during an individual sheetflood resulted in the deposition of multiple coarse and fine couplet and backset sequences 50 250 cm thick across the active depositional lobe of the fan erosional intensity during washout of the standing wave determined whether early phase backset bed deposits or washout phase sheetflood couplet deposits were selectively preserved in a given cycle two minor facies are also found in the anvil fan pebble cobble gravel lags 0 20 of cuts are present above erosional scours into the sheetflood couplet and backset deposits they consist of coarse gravel concentrated through fine fraction winnowing of the host sheetflood facies by sediment deficient water flows this reworking occurred during recessional flood stage or from non catastrophic discharge during the long intervals between major flash floods this facies is common at the surface giving rise to a braided stream appearance however it is stratigraphically limited present as thin continuous to discontinuous beds or lenses that bound 50 to 250 cm thick sheetflood sequences the other minor facies of the anvil fan consists of clast supported and imbricated thickly stratified pebbly cobbly boulder gravel present in narrow radially aligned ribbons nested within sheetflood deposits this facies is interpreted as representing deposition in the incised channel of the fan a subenvironment characterized by greater flow competence resulting from maintained depth from channel wall confinement and by more frequent water flows and winnowing events caused by its direct connection with the catchment feeder channel

alluvial fan slope as a function of sediment transport efficiency abstract the nature of slope acquisition by alluvial fans was studied by comparing the slope evolution of 37 tributary fans to the san juan river in an arid region of western argentina each of these fans is characterized by truncation of the distal end as a result of incision by the san juan river the alluvial fan slope prior to incision and the slope of the active channel for each fan was measured river accumulation terraces indicate that fan incision was probably synchronous along the valley incised channels in each fan evolved over the same interval but they show different degrees of advance of erosion values of old fan slope fit well with known power laws relating them to drainage area r 0 865 slopes of incised channels also fit with power laws but with a lower regression coefficient r 0 741 the regression lines in each case have almost the same slope 0 218 sd 0 02 and 0 215 sd 0 03 respectively which suggests that although the incised channel slope is not an equilibrium feature both the original and the secondary fans follow the same law of variation an explanation for this phenomenon is that the transport efficiency of the fans may be related to the size of the basin if mean runoff and peak floods are roughly regulated by drainage area fan slopes of larger drainage basins will evolve faster than those of smaller basins apparently as a group of fans approach an equilibrated state their slopes become distributed along successive parallel regression lines progressively displaced upward in the diagram as long as climatic conditions remain constant to see the effects of water availability on fan slope we also compared slopes and drainage basin areas of fans located in settings with different specific runoff which is approximately a function of annual rainfall the regression lines for each set of alluvial fans are roughly parallel the smaller intercept value for humid fans indicates that for a given drainage area fans in arid settings are steeper than those in more humid settings fans dominated by mud flows and dilute flash floods were plotted together but no major differences were observed in this general behavior this suggests that the steepness of a fan is not primarily related to compositional factors or to the sediment transport process but to transport efficiency episodic flood fans of argentina show slopes comparable to the mudflow fans of death valley because water supply and therefore transport efficiency are similar drainage basin area combined with mean annual rainfall may largely determine transport efficiency by controlling mean runoff across the fan as a result transport efficiency may define not only alluvial fan slope but also the rate at which the alluvial fan slope reestablishes equilibrium after some external change

the influence of piedmont deposition on the time scale of mountain belt denudation 1 the linear correlation between modern sediment yields and mean drainage basin elevation suggests that mountain belt topography is denuded exponentially with a time scale of approximately 50 myr following the cessation of active uplift some paleozoic orogens however still exist as high elevation terrain here i explore this paradox within the broader question of what variables control the denudational time scales of mountain belts using a two dimensional model that couples the stream power law for bedrock channel erosion with the diffusion equation for alluvial piedmonts i determined the time scale of mountain belt denudation using numerical and analytic techniques the piedmont plays an important role in mountain belt denudation because it sets the base level for bedrock erosion substantially reducing bedrock relief in mountain belts with broad or steep piedmonts the persistence of the appalachian and ural mountains may be understood within the model framework as largely the result of resistant bedrock and a broad piedmont respectively

alluvial fans formed by channelized fluvial and sheet flow i theory alluvial fans and fan deltas are of three basic types those built up primarily by the action of constantly avulsing river and stream channels those constructed by sheet flows and those resulting from the successive deposition of debris flows the present analysis is directed toward the first two types a mechanistic formulation of flow and sediment transport through river channels is combined with a simple quantification of the overall effect of frequent avulsion to derive relations describing the temporal and spatial evolution of mean i e averaged over many avulsions bed slope and elevation in an axially symmetric fan an example of a fan formed predominantly by the deposition of sand is compared to a similar one formed predominantly by the deposition of gravel in each example the case of channelized flow is compared to the case of sheet flow the model is applied to the tailings basin of a mine in the companion paper

abraded rock landforms whalebacks developed under ice streams in mountain areas like many mountain ranges the coast mountains of british columbia canada have undergone both local and ice sheet glaciation effects of ice sheets are concentrated along major valleys and on adjacent spurs and passes which carried strong flows of diffluent ice the major valleys are broad glacial troughs with frequent rock basins their slopes are broken into rounded steep sided bosses whalebacks abraded on all sides they are of the order of 100 m to 1 km long and 10 m high in the southern coast mountains the distribution of these whalebacks is consistent with a proposed pattern of former ice streams 1 0 2 1 km thick within the cordilleran ice sheet they are best developed where geological structures parallel the valley and thus the former ice flow direction but they are found on a range of lithologies and some are transverse to structure the whalebacks provide an impression of glacial streamlining and occasionally grade into rock drumlins roches moutonnees are rare in the major troughs it is hypothesised that these whalebacks and rock drumlins develop under ice streams of greenland or east antarctic type sliding rapidly over bedrock and exploiting rock weaknesses to produce streamlined features lee slopes are abraded when thick ice suppresses bed separation even with rapid flow basal ice of low viscosity would aid this suppression water pressures under the ice streams may have remained high so that lee side plucking was rare such plucking is most likely where pressure fluctuates dramatically and especially when lee cavities under active ice reach atmospheric pressure

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

continental arc volcanism and tectonic setting in central anatolia turkey abstract the neogene and quaternary volcanism of central anatolia represents the central sector of the anatolian volcanic arc related to continental collision between the afro arabian and eurasian plates it is closely associated with a complex system of tectonic depressions related to brittle deformations of transtentional type and which commenced in the late miocene the volcanism here considered can be divided into three main periods of activity separated by important deformative and erosive events the first period is represented by a mostly andesitic effusive activity the second period is characterized by the emplacement of a thick ignimbritic sequence and shows an areal distribution up to 11 000 km 2 seven ignimbrite units have been recognized the three main units were found at a distance of more than 100 km from the presumed source area geological and sedimentological data lead us to recognize the melendiz dag volcanic complex and the ciftlik caldera as the probable ignimbrites source vent during the third period great andesitic basaltic stratovolcanoes and a number of prevalently acid monogenic centres developed the relationship between the volcanic activity is clearly conditioned by the main transcurrent fault systems present in central anatolia the neogene quaternary volcanic activity prevalently developed along the ene wsw karaman sivas lineament most of the great central volcanoes developed at the intersection between the ene wsw trends and the ecemis and tuz golu transcurrent faults the structural interpretation of the quaternary monogenic centres is more difficult probably they are related to the very recent n s fault swarms which cross the anatolides and the taurus range