cyclostratigraphy of lower triassic terrestrial successions in the junggar basin northwestern china abstract the astrochronology for the early triassic has been constructed from well preserved marine successions however astronomical analyses of terrestrial strata have continued to be rare and problematic physical logs natural gamma ray logging data from two wells in the junggar basin northwestern china cover the entire lower triassic terrestrial baikouquan formation and have been shown to be a powerful tool in cycle analysis therefore these logs offer an excellent opportunity to detect astronomically forced sedimentation in a terrestrial setting from mid to high latitudes power spectral analysis revealed that the sedimentary cycles had wavelengths of 31 3 35 9 m 8 4 10 0 m 4 0 4 6 m and 4 0 m these are interpreted to correspond to the orbital eccentricity cycles of 405 kyr and 100 kyr and to the obliquity cycles of 51 kyr and 34 kyr respectively we thus established an astronomical time scale for the studied interval assuming that the 31 3 35 9 m cycles represent the 405 kyr eccentricity cycles this astrochronology indicated that the duration of the baikouquan formation was 2 0 0 1 myr statistical evaluations of optimal sediment accumulation rates using the correlation coefficient approach showed that the rates of the investigated successions were approximately 6 0 12 0 cm kyr orbitally controlled climate change was the major dynamic mechanism for the formation of early triassic fan delta successions in the junggar basin

a climatic trigger for catastrophic pleistocene holocene debris flows in the eastern andean cordillera of colombia the geomorphology and stratigraphy of massive debris flows on the eastern andean cordillera colombia indicate two distinct deposits can be recognized the lower chinauta deposit covers 14 km2 and has a thickness of 60 m whereas the upper fusagasuga deposit covers 20 km2 and has a thickness of 20 m the lower chinauta section consists of matrix supported gravels with isolated boulders and massive to moderately bedded structure and local inverse grading the upper section displays sequences of inversely graded clast supported gravels with boulders 2 m in axial length capped by massive matrix supported fine gravels the latter are dissected by coarse channelized gravels we interpret these facies as a series of debris and hyper concentrated flows dissected by river channels the fusagasuga deposit is dominated by massive to inversely graded matrix supported gravels with isolated boulders single grain optically stimulated luminescence dates of the sandy silty matrix of debris and hyper concentrated flows constrain the timing of deposition of the chinauta debris flow deposits between 38 9 and 8 7 ka we postulate that millennial scale climate variability is responsible for causing these massive debris flows through a combination of elevated temperatures and increased rainfall that triggered runoff and sediment transport

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

alignment of stone pavement clasts by unconcentrated overland flow implications of numerical and physical modelling the crucial role of stone pavements in arid environments for aeolian or alluvial processes and as numerical dating tools is increasingly acknowledged this role is based on the assumption that stone pavements are stable landforms formed gradually over time and predominantly by vertical processes however this is challenged by evidence of stone pavement clast reworking or burial bimodal mostly slope aspect symmetrical clast orientation is a frequent phenomenon in various study areas it implies that stone pavements may be influenced by unidirectional lateral processes besides vertical ones here the finding of lateral processes contributing to stone pavement evolution is supported by numerical modelling and physical experiments these unequivocally show that unconcentrated overland flow can transport clasts to form a closely packed stone mosaic with characteristics similar to those of natural stone pavements the commonly observed length axes orientation angle of 40 14 for natural stone pavement clasts is consistently reproduced by angle dependent force equilibrium monte carlo runs confirm the natural scatter and allow characterization of the control parameters of clast orientation the model explains up to 70 of the natural variance it is further validated by flume experiments which confirm model predictions of single object orientation angles experiments with multiple objects yield artificial stone pavements with properties similar to those found in the field the unidirectional lateral process acting on natural stone pavements requires the presence of a vesicular horizon this underlines the tight genetic coupling of this common epipedon feature and the clast cover the presented findings highlight the role of stone pavements as process and environment proxies however stone pavements represent information since the last surface disturbance only this has to be considered when using them as age indicators copyright 2013 john wiley sons ltd

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

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

range front fault scarps of the sierra el mayor baja california formed above an active low angle normal fault the canada david detachment a west dipping low angle normal fault juxtaposes pliocene and pleistocene sedimentary units over sheared bedrock in the sierra el mayor baja california along the west central range front the detachment is overlapped by quaternary alluvial fans that are in turn cut by fault scarps up to 7 m high map relationships suggest that scarp forming faults may sole into the detachment at very shallow depth 200 300 m palinspastic restoration of a topographic profile across 15 north striking scarps suggests that the ratio of net heave to net throw along scarp forming faults is 2 consistent with them soling into a low angle 30 fault these 15 scarps may have all formed in one earthquake with rupture propagation from depth to the near surface aided by clay gouge along the detachment the detachment is abandoned in the footwall east of the scarps

analysis of scarp profiles evaluation of errors in morphologic dating morphologic analysis of scarp degradation can be used quantitatively to determine relative ages of different scarps formed in cohesionless materials under the same climatic conditions scarps of tectonic origin as well as wavecut or rivercut terraces can be treated as topographic impulses that are attenuated by surface erosional processes this morphological evolution can be modelled as the convolution of the initial shape with erosion or degradation function whose width increases with time such modeling applies well to scarps less than 10m high formed in unconsolidated fanglomerates to a good approximation the degradation function is gaussian with a variance measuring the degree of rounding of the initial shape this geometric parameter can be called the degradation coefficient a synthetic experiment shows that the degradation coefficient can be obtained by least squares fitting of profiles levelled perpendicular to the scarp gravitational collapse of the free face is accounted for by assuming initial scarp slopes at the angle of repose of the cohesionless materials 30 35 uncertainties in the measured profiles result in an uncertainty in degradation coefficient that can be evaluated graphically because the degradation coefficient is sensitive to the regional slope and to three dimensional processes gullying loess accumulation stream incision etc a reliable and accurate determination of degradation coefficient requires several long profiles across the same scarp the linear diffusion model of scarp degradation is a gaussian model in which the degradation coefficient is proportional to numerical age in that case absolute dating requires only determination of the propotionality constant called the mass diffusivity constant for holocene scarps a few meters high in loose alluvium under arid climatic conditions mass diffusivity constants generally range between 1 and 6 m 2 kyr morphologic analysis is a reliable method to compare ages of different scarps in a given area and it can provide approximate absolute ages of holocene scarplike landforms

morphological analysis of the lake lahontan shoreline and beachfront fault scarps pershing county nevada abstract with the diffusion equation representation of landform evolution providing reference calculations quantitative comparisons between profiles of the high stand of lake lahontan presented here and profiles of the lake bonneville shoreline scarps analyzed elsewhere reveal that the two sets of scarps are nearly identical morphologically when care is exercised in the selection of profiles the lahontan high stand scarps are remarkably reproducible from one profile to the next highly suggestive evidence that the processes that have shaped and changed the shape of these landforms are correspondingly regular slope angle differences of only 2 are both discernible and interpretable features of these late quaternary landforms cut in weakly consolidated alluvium at a level of uncertainty of no more than 50 per cent the mass diffusivity of the lahontan high stand is the same as the lake bonneville shoreline 1 1 gkg 1 gkg 1 m 2 ka this result suggests that much can be learned about the ages of late quaternary fault scarps cut in weakly consolidated alluvium throughout the basin and range province from their morphology alone the beachfront fault scarps themselves truncated by lake lahontan in our study area are morphologically only slightly older 15 to 18 ka bp than the lahontan high stand 12 ka bp

global climate change and active tectonics effective tools for teaching and research abstract multidisciplinary student teams foster innovative research projects that can discern the locations times and styles of late quaternary faulting field studies in the area of the 1992 landers magnitude 7 3 earthquake in southeastern california provide excellent opportunities for teaching and research in climatic and tectonic geomorphology graduate student work begins with descriptions of type sections for mappable units of quaternary alluvium climate change induced aggradation events these are stair stepped flights of alluvial fan and terrace surfaces topographic profiles along faulted stream channels and fans provide estimates of vertical tectonic deformation and insight into the responses of fluvial systems to wrench fault tectonics time lines in this tectonically deforming landscape are the result of global climate changes that caused synchronous pulses of alluviation in the mojave desert at about 125 55 and 10 12 and 8 ka these dated alluvial surfaces record tectonic deformation resulting from cumulative late quaternary surface ruptures tectonic geomorphologic analyses use topographic pedogenic stratigraphic and structural data but do not require expensive and time consuming trenching projects ages of faulted and unfaulted alluvium constrain the dates of two pre 1992 earthquakes the 1992 landers event is not characteristic of earlier faulting because it ruptured through adjacent segments of the emerson fault that previously ruptured in separate events one at 3 1 2 ka and the other before 8 ka styles of tectonic deformation and locations of active faults however may not have changed during the past 125 ka

upper neogene stratigraphy and tectonics of death valley a review abstract new tephrochronologic soil stratigraphic and radiometric dating studies over the last 10 years have generated a robust numerical stratigraphy for upper neogene sedimentary deposits throughout death valley critical to this improved stratigraphy are correlated or radiometrically dated tephra beds and tuffs that range in age from 3 58 ma to

the impact of quaternary sea level and climatic change on coastal alluvial fans in the cabo de gata ranges southeast spain conventionally a fall in base level is seen as stimulating incision into the distal zones of alluvial fans in the cabo de gata ranges of southeast spain evidence exists to the contrary two sets of quaternary coastal alluvial fans demonstrate the interaction between climatically driven variations in the supply of sediment and eustatically driven changes in base level the fans are supplied from miocene volcanic terrain within which no evidence can be found for major tectonic deformation during the period of fan development the evolution of the east coast fans has been affected by variations in sediment supply and changes in sea level the west coast fans were buffered from the effects of changes in sea level by coastal barriers three phases of past sedimentation can be identified on the fans these can be differentiated on the basis of field observations of soil profiles particularly colour of the b horizons and accumulation of caco3 and laboratory analyses of sequential iron oxide extractions and magnetic mineral properties the two earlier major sedimentation phases were coincident with global glacials ca 135 ka and ca 85 10 ka based on the stratigraphy and uranium thorium dating of the coastal sediments high sea levels during the intervening interglacial and during the holocene caused erosion of the distal zones of the east coast fans which led to channel incision into the fan surfaces on the west coast fans no such incision occurred simply proximal incision by small fanhead trenches the youngest relatively minor phase of fan sedimentation has occurred during the holocene these contrasting contexts have produced differing styles of fans with telescopic fan morphology on the east coast and stacked morphology on the west coast fans the differences are reflected in the fan profiles with steeper gradients dominating the east coast fans and extensive lower gradient distal surfaces on the west coast fans fan morphometry based on analysis of the residuals from drainage area to fan area and gradient regressions also differentiates between the fan contexts the fan building phases appear to be controlled proximally by climatically driven pulses of sediment supplied to the fans these occurred during global glacials coincident with low sea levels and caused fan progradation onto the exposed foreshore the intervening global interglacials were times of little fan sedimentation and on the east coast where high sea levels were able to erode the fan toes deep through fan dissection ensued

geomorphic constraints on landscape sensitivity to climate in tectonically active areas abstract the geomorphology of fluvial landscapes is known to record information about uplift rate spatial patterns of faulting and tectonic history data is far less available when addressing the sensitivity of common geomorphological metrics such as channel steepness to climatic boundary conditions we test the relationship between channel steepness and precipitation rate by measuring a large number of channels in different mountainous areas these regions exhibit a tenfold variation in precipitation rate between them 100 1000 mm y 1 but have similar uplift rates allowing the tectonic variable to be controlled by accounting for the orographic coupling of rainfall with uplifted topography we find that channel steepness is significantly suppressed by higher precipitation rates in a measurable way that conforms to simple stream power erosion laws and empirical constraints on their parameters we demonstrate this using modern and estimated glacial precipitation rates and climate emerges as an important quantifiable control on channel geometry these findings help to explain why highly variable measurements of channel steepness are reported from different locations and provide important empirical constraints on how climate shapes tectonically active landscapes

luminescence ages for alluvial fan deposits in southern death valley implications for climate driven sedimentation along a tectonically active mountain front abstract controversy exists over whether alluvial fan sedimentation along tectonically active mountain fronts is driven by climatic changes or tectonics knowing the age of sedimentation is the key to understanding the relationship between sedimentation and its cause alluvial fan deposits in death valley and throughout the arid southwestern united states have long been the subjects of study but their ages have generally eluded researchers until recently most mapping efforts have recognized at least four major relative age groupings q1 oldest q2 q3 and q4 youngest using observed changes in surface soils and morphology relation to the drainage net and development of desert pavement obtaining numerical age determinations for these morphologic stages has proven challenging we report the first optically stimulated luminescence osl ages for three of these four stages deposited within alluvial fans along the tectonically active black mountains of death valley deposits showing distinct remnant bar and swale topography q3b have osl ages from 7 to 4 ka whereas those with moderate to poorly developed desert pavement and located farther above the active channel q3a have osl ages from 17 to 11 ka geomorphically older deposits with well developed desert pavement q2d have osl ages 25 ka using this osl based chronology we note that alluvial fan deposition along this tectonically active mountain front corresponds to both wet to dry and dry to wet climate changes recorded globally and regionally these findings underscore the influence of climate change on alluvial fan deposition in arid and semi arid regions

pleistocene lake outburst floods and fan formation along the eastern sierra nevada california implications for the interpretation of intermontane lacustrine records berin d i owen l a finkel r c clemmens s 2006 pleistocene lake outburst floods and fan formation along the eastern sierra nevada california implications for the interpretation of intermontane lacustrine records quaternary science reviews 25 2729 2748 sponsorship national science foundation grant ear 0207245

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

morphologic dating of scarps formed by repeated slip events along the san andreas fault carrizo plain california morphologic dating of fault scarps determines late cenozoic fault activity by comparing observed topographic profiles with those determined using a calibrated hillslope development model we postulate that the material transport rate along the profile is a function only of local slope and is transport limited morphologic dating of hillslopes bounded by continuously dropping boundaries or cut by continuously slipping faults is used to determine the material transport rate constant the time since the downdrop was initiated or the fault began to slip we calibrated the hillslope development model on the southwest facing scarp southeast of wallace creek along the san andreas fault saf in the carrizo plain california the scarp has been exposed by right lateral offset of a southeast sloping shutter ridge located on the southwest side of the saf and by vertical offset related to secondary deformation we assume that all the observed offset occurs after initial exposure of the scarp by passage of the shutter ridge forward modeling of profile development yielded a mass diffusivity of 8 6 0 8 m2 kyr 1 normal fault slip rates were determined for two graben bounding faults in the northern elkhorn hills in the southeastern carrizo plain by applying the calibrated to the degradation of the scarps to determine the scarp age one fault scarp began to form about 12 kyr ago and the other about 63 kyr ago those ages and estimates of the dip slip along the faults result in slip rates of 1 2 mm yr 1

ages estimated from a diffusion equation model for scarp degradation the diffusion equation derived from the continuity equation for hillslopes is applied to scarp erosion in unconsolidated materials solutions to this equation allow direct calculation of the product of the rate coefficient and the age of the scarp from measurements of scarp morphology where the rate coefficient can be estimated or can be derived from scarps of known age this method allows direct calculation of unknown ages of scarps

quaternary alluvial fan development climate and morphologic dating of fault scarps in laguna salada baja california mexico article i nfo late quaternary slip across the canada david detachment has produced an extensive array of quaternary scarps cutting alluvial fans along nearly the entire length 60 km of the range bounding detachment eight regional alluvial fan surfaces q1 youngest to q8 oldest are defined and mapped along the entire sierra el mayor range front terrestrial cosmogenic nuclide 10 be concentrations from individual boulders on alluvial fan surfaces q4 and q7 yield surface exposure ages of 15 5 2 2 ka and 204 11 ka respectively formation of the fans is probably tectonic but their evolution is strongly moderated by climate with surfaces developing as the hydrological conditions have changed in response to climate change on milankovitch timescales systematic mapping reveals that the fault scarp array along active range bounding faults in sierras cucapa and el mayor can be divided into individual rupture zones based on cross cutting relationships with alluvial fans quantitative morphological ages of the laguna salada fault scarps derived from linear diffusive degradation modeling are consistent with the age of the scarps based on cross cutting relationships the weighted means of the maximum mass diffusivity constant for all scarps with offsets b 4 m is 0 051 and 0 066 m 2 ka for the infinite and finite slope solutions of the diffusion equation respectively this estimate is approximately an order of magnitude smaller than the lowest diffusivity constants documented in other regions and it probably reflects the extreme aridity and other microclimatic conditions that characterize the eastern margin of laguna salada

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

late quaternary activity of the laguna salada fault in northern baja california mexico faulted alluvial fans and bajadas along the central laguna salada fault zone in northernbajacaliforniarecordarecurrent history of oblique slip holocene earthquakes alluvialsurfaces whichrangefrom late pleistocene to historic in age have been progressively displaced along the base of the crystalline rangefront as well as along more basinward fault splays in alluvium the recurrence interval determined from displacedalluvialdepositsthataredatedby soil profile development is in the range of 1 2 ka with a corresponding right lateral slip rate of 2 3 mm yr similar to that of thesouthernelsinorefaultinsoutherncalifornia the most recent event along the fault zone is probably the widely felt earthquake of february 23 1892 at least 22 km ofthefaultzonerupturedduringthisevent along both an oblique dextral section of the northwest strikinglagunasaladafaultand

development and maintenance of a telescoping debris flow fan in response to human induced fan surface channelization chalk creek valley natural debris flow laboratory colorado usa abstract channel change has been a constant theme throughout william l graf s research career graf s work has examined channel changes in the context of natural environmental fluctuations but more often has focused on quantifying channel change in the context of anthropogenic modifications here we consider how channelization of a debris flows along a bajada has perpetuated and sustained the development of telescoping alluvial fan two dimensional debris flow modeling shows the importance of the deeply entrenched channelized flow in the development of a telescoping alluvial fan gis analyses of repeat five different debris flows high resolution 5 cm digital elevation models dems generated from repeat terrestrial laser scanning tls data elucidate sediment and topographic dynamics of the new telescoping portion of the alluvial fan the embryonic fan flow constriction from channelization helps to perpetuate debris flow runout and to maintain the embryonic fan and telescoping nature of the alluvial fan complex embryonic fan development in response to five debris flows proceeds with a major portion of the flows depositing on the southern portion of the embryonic fan the third through the fifth debris flows also begin to shift some deposition to the northern portion of the embryonic the transfer of sediment from a higher portion of the embryonic fan to a lower portion continues currently on the embryonic fan while channelized flow has been shown to be critical to the maintenance of the telescoping fan the flow constriction has led to higher than background levels of sediment deposition in chalk creek a tributary of the arkansas river a majority of the sediment from each debris flow is incorporated into chalk creek as opposed to being stored on the embryonic fan

response of alluvial fan systems to the late pleistocene to holocene climatic transition contrasts between the margins of pluvial lakes lahontan and mojave nevada and california usa abstract dated shorelines of late pleistocene pluvial lakes lahontan great basin desert northwest nevada and mojave mojave desert eastern california provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late pleistocene to early holocene two sets of alluvial fan systems have been mapped the stillwater fans feeding lake lahontan and the zzyzx fans feeding lake mojave their contrasting morphologies suggest different responses of the two fan systems to late pleistocene to early holocene climatic change at the time the stillwater fan systems underwent minimal sedimentation with the catchment hillslopes apparently stable the zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes there was a major phase of hillslope debris flow activity followed by fanhead trenching and distal fan progradation both areas were wetter and colder in the late pleistocene than they are today but during the transition to the holocene the zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the southwest vegetation reconstructions for the late pleistocene to the early holocene suggest that catchment hillslopes in the mojave supported a desert shrub vegetation but those in the stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the pleistocene to holocene climatic transition after the falls in lake levels of lakes lahontan and mojave in the early holocene both areas underwent aridification resulting in reductions in hillslope vegetation cover increased storm runoff led to fanhead trenching and distal progradation of the alluvial fans variations in fan style at that time may relate primarily to base level conditions resulting from different gradients on the exposed lake shores

cosmogenic 10be and 36cl geochronology of offset alluvial fans along the northern death valley fault zone implications for transient strain in the eastern california shear zone the northern death valley fault zone ndvfz has long been recognized as a major right lateral strike slip fault in the eastern california shear zone ecsz however its geologic slip rate has been difficult to determine using high resolution digital topographic imagery and terrestrial cosmogenic nuclide dating we present the first geochronologically determined slip rate for the ndvfz our study focuses on the red wall canyon alluvial fan which exposes clean dextral offsets of seven channels analysis of airborne laser swath mapping data indicates 297 9 m of right lateral displacement on the fault system since the late pleistocene in situ terrestrial cosmogenic 10 be and 36 cl geochronology was used to date the red wall canyon fan and a second correlative fan also cut by the fault beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 22 20 ka for the offset landforms the minimum age of the alluvial fan deposits based on 36 cl depth profiles is 63 8 ka combining the offset measurement with the cosmogenic 10 be date yields a geologic fault slip rate of 4 2 1 9 1 1 mm yr 1 whereas the 36 cl data indicate 4 7 0 9 0 6 mm yr 1 of slip summing these slip rates with known rates on the owens valley hunter mountain and stateline faults at similar latitudes suggests a total geologic slip rate across the northern ecsz of 8 5 to 10 mm yr 1 this rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the mojave section of the ecsz does not extend north of the garlock fault although the overall geodetic rates are similar the best estimates based on geology predict higher strain rates in the eastern part of the ecsz than to the west whereas the observed geodetic strain is relatively constant

thermal evolution of monte blanco dome low angle normal faulting during gulf of california rifting and late eocene denudation of the eastern peninsular ranges footwall rocks of the canada david detachment fault northeastern baja california record late eocene earliest oligocene and late neogene cooling events previously unrecognized in the region biotite 40 ar 39 ar ages of 65 ma reflect slow cooling through 350 c 5 to 10 m y later than is typical in the region multiple diffusion domain modeling of k feldspar 40 ar 39 ar release spectra shows very slow cooling 1 c m y from 65 to 45 ma accelerated cooling from 315 c to 215 c between 45 and 33 ma records at least 3 4 km of denudation that we relate to east side up reactivation of late cretaceous structures that generally follow the oceanic continental suture previously established rivers flowing west from mainland mexico apparently became further entrenched during this uplift and continued to supply distinctive rhyolitic detritus to the coast ultimately surface uplift disrupted and rerouted the extraregional rivers some 2 to 6 m y before the cooling event ended footwall rocks remained nearly isothermal from 30 to 15 10 ma when renewed rapid cooling 33 17 c m y began in response to footwall exhumation by top to the west low angle normal faulting that accommodated rift related extension in what finally became the gulf of california apatite fission track and u th he ages of 5 ma and 4 ma respectively record final detachment related cooling through 110 c to 70 c thermal kinematic modeling suggests that 5 7 km of late neogene tectonic denudation and 10 12 km of horizontal extension were necessary in order to unroof the samples by 2 ma additional extension of unknown magnitude has probably occurred subsequently geodetically measured horizontal extension rates are considerably higher than the long term extension rate that can be attributed to detachment faulting

the vesicular layer and carbonate collars of desert soils and pavements formation age and relation to climate change abstract the vesicular fine grained a horizon av is the widespread ubiquitous surficial horizon of desert soils in diverse landforms and parent materials of varying ages now known to form mostly through accumulation of eolian dust recent studies show that dust accumulation and concomitant soil development are genetically linked to stone pavement formation changes in the magnitude of eolian activity and effective leaching related to quaternary climatic changes are also hypothesized to have influenced the evolution of the av horizon numerical modeling geochronologic and field laboratory studies elucidate the nature of pedogenic processes controlling compositional evolution of av how the changing av horizon increasingly influences soil infiltration and carbonate translocation and accumulation and the control that clasts of the evolving pavement exert on pedogenic processes results of a model that determines soil bulk chemical composition based on mixing of estimated proportions of externally derived eolian material and parent materials imply that the evolution of the soil bulk composition is strongly influenced by av horizon formation the early development of a weakly to moderately developed av horizon directly over gravelly parent material in late and middle holocene soils moderately influences soil infiltration but significant leaching of very soluble materials and some carbonate in dust are permitted in older pleistocene soils however the texturally more mature av and underlying cumulic nongravelly horizons more strongly limit the rate and depth of leaching and soil bulk composition therefore more closely approximates a simple mixture of dust and parent material other aspects of av horizon development and its relations to the pavement are evaluated through studies of pavement clasts with coatings of soil carbonate referred to as carbonate collars development of a numerical model that integrates soil hydrology a co2 production diffusion model calcite kinetics and thermodynamic considerations composition and thermal characteristics of pavement clasts and the textural and structural properties of the surface horizon provides the basis for testing a hypothesis of collar formation model results combined with results of 13c and 18o analyses of collar carbonate demonstrate how precipitation of calcite on pavement clasts and within the av is favored at a depth much shallower than that indicated by the classic carbonate depth climate relationship of jenny and leonard jenny h j leonard c d 1935 functional relationships between soil properties and rainfall soil science 38 363 381 and arkley arkley r j 1963 calculations of carbonate and water movement in soil from climatic data soil science 96 239 248 or simulated by numerical models of carbonate accumulation simultaneous development of thick carbonate collars and the av horizon requires the sustained pavement clast av horizon coupling for at least centuries to possibly millennia new thermoluminescence ages also indicate that much of the av horizon formed in the holocene and that it is certainly much younger than the older pleistocene pavements this supports the previously proposed hypothesis that increased dust flux during the pleistocene to holocene transition triggered and or greatly accelerated av horizon development an understanding of the genesis of collars provides not just an understanding of how carbonate can accumulate in surface environments but it also provides important clues into processes of pavement evolution and preservation of av horizons during long glacial periods the av horizon is not merely an insignificant surficial zone of recent dust accretion instead its development profoundly influences the genesis of desert soils and pavements

volcano core collapse triggered by regional faulting it has been proposed recently that large scale caldera like structures may result from the viscous lateral spreading of a hydrothermal system located in the central part of volcanic edifices for this to occur an unbutressed boundary resulting in reduced lateral stresses must exist or be created not far from the hydrothermal system different ways to achieve such a weak lateral confinement may be proposed in this paper we show that regional tectonics may provide an unconfined boundary if a normal fault lowers part of the volcanic edifice a natural example is the island of nuku hiva in the marquesas archipelago french polynesia for which geological data strongly suggest that a regional fault oriented n75 e is responsible for the present day shape of the island i e an ellipse cut in the middle by a straight side along which two nested calderas are breached analogue modelling shows the mechanical consistency of the model and reveals that very low velocity faulting is needed for the formation of a caldera like structure

estimating the ages of fault scarps in the arava israel abstract systematic age estimations for the numerous fault scarps that rupture the alluvial fans in the southern arava valley israel are rare or nonexistent here we estimate the morphologic ages of several of these faults by the fault scarp degradation method and show that the ages agree well with ages estimated by the independent earlier soil geomorphic studies the values we use for the coefficient of diffusion for the fault scarp degradation process are calibrated by a few numerical ages these ages were determined by the infrared stimulated luminescence irsl method on one of the fault scarps and are the only numerical ages in the region the morphologic ages are all in a correct stratigraphic order and in agreement with field stratigraphic relationships determined by earlier studies they indicate that the studied fault scarps range in age from the latest pleistocene to very recent times the most recent fault scarps which were analyzed are less than 2000 years old and perhaps much younger they indicate that at least two earthquakes with magnitude 6 5 have affected southern israel and jordan during that period it is emphasized that so far we have studied only a limited number of fault scarps and therefore the number of large earthquakes during the last one to two millennia is a minimum

evidence for late hesperian lacustrine activity in shalbatana vallis mars 1 an intravalley paleolake more than 400 m deep was detected along the course of shalbatana vallis from the evidence of shorelines and the occurrence of a few fan delta deposits including a gilbert type delta the fronts of all the sedimentary deposits strikingly match the same topographic contours 2800 and 3000 m below the martian datum indicating the paleolake water levels under which they formed also the corresponding shorelines are visible along the shalbatana vallis walls the peculiar settings of the lake suggest that shalbatana vallis was impounded during its final hydrological activity and that ponding of water lasted enough time to allow the formation and evolution of the lacustrine system water source is uncertain but a composite sapping mechanism is hypothesized in order to take into account the amount of water required to excavate transport and deposit the materials found in the deposits previous works and new crater counting computations indicate that the paleolake was active during the hesperian epoch therefore at that time surface conditions were different from those of modern mars and supportive of flow and ponding of water it is unclear whether the hydrological activity was sustained entirely by a favorable climatic regime and secondary regional factors like volcanism impact cratering and tectonism could have also triggered accelerated the local groundwater activity implying that the system could have evolved relatively independent from climatic conditions the latter eventuality and the regional importance of this research advised against an extrapolation of its results to the overall debate about martian climatic geomorphological evolution

dating quaternary fault scarps formed in alluvium using morphologic parameters abstract ages of fault scarps as well as those other types of transport limited slopes can be estimated by comparing their morphology with the morphology of scarps of known age age estimates are derived by fitting the scarp profiles to synthetic profiles generated using a diffusion equation or alternatively by classification using a linear discriminant function the usefulness of morphology derived age estimates depends on the relative importance of non age related morphologic variation data from more than 200 scarp profiles demonstrate that morphologic variation not related to scarp age can introduce significant uncertainties into morphology derived age estimates

the egiin davaa prehistoric rupture central mongolia a large magnitude normal faulting earthquake on a reactivated fault with little cumulative slip located in a slowly deforming intraplate setting the prehistoric egiin davaa earthquake rupture is well preserved in late quaternary deposits within the hangay mountains of central mongolia the rupture is expressed by a semicontinuous 80 km long topographic scarp geomorphological reconstructions reveal a relatively constant scarp height of 4 4 5 m and a nw directed slip vector previous researchers have suggested that the scarp s exceptional geomorphological preservation indicates that it may correspond to an earthquake that occurred in the region c 500 years ago however we constrain the last rupture to have been at least 4 ka ago from morphological dating and 7 4 ka ago based on radiocarbon dating from one of two palaeoseismic trenches our study shows that discrete earthquake ruptures along with details such as the locations of partially infilled fissures can be preserved for periods well in excess of 1000 years in the interior of asia providing an archive of fault movements that can be directly read from the earth s surface over a timescale appropriate for the study of slowly deforming continental interiors the egiin davaa rupture involved c 8 m of slip which along with the observations that it is largely unsegmented along its length and that the ratio of cumulative slip c 250 m to fault length c 80 km is small suggests relatively recent reactivation of a pre existing geological structure

isotopic evidence for climatic influence on alluvial fan development in death valley california at least three semiarid to arid cycles are recorded by delta sup 13 c values of organic matter in layers of rock varnishes on surfaces of hanaupah canyon and johnson canyon alluvial fans death valley california these isotopic paleoenvironmental signals are interpreted as indicating major periods of fan aggradation during relatively more humid periods and fan entrenchment during subsequent lengthy arid periods

timing and nature of alluvial fan and strath terrace formation in the eastern precordillera of argentina abstract sixty eight 10 be terrestrial cosmogenic nuclide tcn surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper arid san juan region of the argentine precordillera this region is tectonically active and numerous fault scarps traverse quaternary landforms the three study sites marquesado strath complex loma negra alluvial fan and carpinteria strath complex reveal a history of alluvial fan and strath terrace development over the past 225 ka the marquesado complex q3 m surface dates to 17 3 ka whereas the loma negra q1 ln q2 ln q3 ln q4 ln and q5 ln surfaces date to 24 3 ka 48 2 ka 65 13 ka 105 21 ka and 181 29 ka respectively the carpinteria complex comprises eight surfaces that have been dated and include the q1 c 23 3 ka q2 c 5 5 ka q3a c 25 12 ka q3b c 29 15 ka q4 c 61 12 ka q5 c 98 18 ka q6 c 93 18 ka and q7 c 212 37 ka 10 be tcn depth profile data for the loma negra alluvial fan complex and carpinteria strath terrace complex as well as osl ages on some carpinteria deposits aid in refining surface ages for comparison with local and global climate proxies and additionally offer insights into inheritance and erosion rate values for tcns 10 10 4 10 be atoms g of sio 2 and 5 m ma 1 respectively comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the carpinteria and loma negra areas with only younger alluvial fan surfaces preserved both to the north and south these data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region

active tectonics in southern xinjiang china analysis of terrace riser and normal fault scarp degradation along the hotan qira fault system the northern piedmont of the western kunlun mountains xinjiang china is marked at its easternmost extremity south of the hotan qira oases by a set of normal faults trending n50e for nearly 70 km conspicuous on landsat and spot images these faults follow the southeastern border of a deep flexural basin and may be related to the subsidence of the tarim platform loaded by the western kunlun northward overthrust the hotan qira normal fault system vertically offsets the piedmont slope by 70 m highest fault scarps reach 20 m and often display evidence for recent reactivations about 2 m high successive stream entrenchments in uplifted footwalls have formed inset terraces we have leveled topographic profiles across fault scarps and transverse abandoned terrace risers the state of degradation of each terrace edge has been characterized by a degradation coefficient derived by comparison with analytical erosion models edges of highest abandoned terraces yield a degradation coefficient of 33 4 m 2 profiles of cumulative fault scarps have been analyzed in a similar way using synthetic profiles generated with a simple incremental fault scarp model the analysis shows that 1 rate of fault slip remained essentially constant since the aggradation of the piedmont surface and 2 the occurrence of inset terraces was synchronous at all studied sites suggesting a climate driven terrace formation observation of glacial and periglacial geomorphic features along the northern front of the western kunlun range indicates that the qira glaciofluvial fan emplaced after the last glacial maximum during the retreat of the kunlun glaciers 12 22 ka the age of the most developed inset terrace in uplifted valleys is inferred to be 10 3 ka coeval with humid climate pulses of the last deglaciation the mass diffusivity constant k t being time b p in the hotan region is determined to be 3 3 1 4 m 2 10 3 years consistent with other estimates in similar climatic and geologic environments of western china these results imply a minimum rate for the tarim subsidence of 3 5 2 mm yr if western kunlun overthrusts the tarim platform on a crustal ramp dipping 40 45 to the south it would absorb at least 4 5 3 mm yr of convergence between western tibet and tarim

late quaternary slip rates along the sierra nevada frontal fault zone california slip partitioning across the western margin of the eastern california shear zone basin and range province new geologic mapping tectonic geomorphologic and cosmogenic radionuclide geochronologic data provide the fi rst numerical constraints on late quaternary vertical slip and horizontal extension rates across the southern sierra nevada frontal fault zone california this fault zone exposes numerous nnw striking east facing normal fault scarps that offset seven distinct quaternary alluvial surfaces and a rockslide deposit beryllium 10 cosmogenic radionuclide surface exposure dating of these surfaces provides surface abandonment model ages of 123 7 16 6 ka 60 9 6 6 ka 25 8 7 5 ka 4 4 1 1 ka and 4 1 1 0 ka on alluvial fan surfaces and 18 7 3 9 ka on the rockslide deposit these age constraints combined with measurements of vertical surface offset across fault scarps yield preferred late pleistocene to holocene vertical and horizontal extensional slip rates of 0 2 0 3 mm yr and 0 1 0 2 mm yr vertical slip rate estimates in this study are comparable to late pleistocene vertical slip rate estimates across other prominent range front normal faults within the basin and range province these geologic and geochronologic results indicate that the eastern escarpment of the southern sierra nevada has remained tectonically active throughout the late quaternary combining our data with slip data from the owens valley and lone pine faults implies that slip along the eastern escarpment of the sierra nevada block is partitioned into three components dominantly dextral slip along the owens valley fault intermediate oblique slip along the lone pine fault and subordinate normal slip along the sierra nevada frontal fault zone these observations are consistent with global positioning system gps data which indicate that dextral shear strain accumulation dominates today along the western boundary of the eastern california shear zone and basin and range province

outburst flood sedimentation on the proglacial tuttle canyon alluvial fan owens valley california u s a abstract surface deposits of the tuttle canyon alluvial fan eastern sierra nevada piedmont california mainly accumulated during a catastrophic outburst flood probably triggered by the failure of a moraine dammed lake in the steep 16 4 high relief 2361 m and high elevation to 4275 m catchment moraines of the catchment and upper fan facies a comprise unsorted sand to blocks derived from the granitic bedrock the main flood facies b is texturally like the moraine consisting of unsorted matrix supported sandy pebbly cobbly blocky boulder gravel in a single unit 3 to 8 m thick distributed across most of the 10 5 km long and 28 1 km2 fan facies b was deposited during the initial outburst flood phase as a high volume noncohesive sediment gravity flow ncsgf instigated by water rapidly descending over moraine it differs from the moraine by a planar unit geometry and a slope transverse long axis alignment of boulders ncsgf deposition was followed by a water flood phase caused by continued lake drainage subsequent to removal of loose sediment in the flood path this discharge carved channels 2 22 m deep and 5 60 m wide around and across fan ncsgf deposits with channels departing from various points along tuttle creek horseshoe separation scours also formed around bedrock spurs and laminated pebbly sand accumulated on the channel beds facies d flood discharge expanded on the distal fan into a sheetflood that first deposited a boulder unit facies e and then 4 m of cobbly sandy pebble gravel in planar beds 5 20 cm thick facies f the final flood phase entailed incision of tuttle creek wherein bouldery cobble gravel facies c was concentrated post flood modification of these deposits has been limited to secondary processes such as eolian deposition facies g and bioturbation outburst floods on fans of the sierra nevada piedmont ultimately are caused by the glacial transfer of colluvium from the upper catchment slopes into moraines on the valley floors that dam drainage to form lakes outburst floods differ from meteorological floods in the valley by the high water and sediment discharge achieved during a single event by deposition of massive ncsgf beds and by causing major changes to the landscape such as the carving of channels these differences produce fans with distinctive facies and hazards the former allowing their recognition in either modern or ancient settings

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

timing and nature of alluvial fan development along the chajnantor plateau northern chile abstract alluvial systems in the atacama desert provide a unique opportunity to elucidate the sedimentary response to climate variability particularly changes in precipitation in hyperarid environments alluvial fans along the eastern margin of the salar de atacama adjacent to the chajnantor plateau in the atacama desert of northern chile provide an archive of climate modulated sediment transfer and erosion at an extreme of earth s climate three regional alluvial fan surfaces qf1 oldest to qf3 youngest were mapped along the western flank of the chajnantor plateau the alluvial fans were examined with geomorphic and terrestrial cosmogenic 36 cl surface exposure dating methods to define the timing of alluvial fan formation and to determine the role of climatic processes on fan development in a hyperarid environment alluvial fans in the study area are comprised of hyperconcentrated flow and boulder rich debris flow deposits that reflect deposition transitioning between cohesive and noncohesive regimes alluvial fan surfaces yield exposure ages that range from 49 6 4 4 to 194 12 ka while debris flow boulders yield exposure ages ranging from 12 4 2 1 to 229 53 ka cosmogenic 36 cl exposure ages indicate that abandonment of alluvial fan surfaces qf1 qf2 and qf3 date to 175 22 6 ka mis 6 134 5 9 18 ka mis 6 and 20 07 6 26 ka mis 2 respectively a 36 cl concentration depth profile through alluvial fan qf1 suggests a simple depositional history with minimal nuclide inheritance implying relatively rapid aggradation 6 m in ca 25 kyr followed by surface abandonment ca 180 200 ka our data support a strong climatic control on alluvial fan evolution in the region and we propose that the alluvial fans along the margins of the salar de atacama form according to the humid model of fan formation

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

alluvial fan aggradation incision history of the eastern tibetan plateau margin and implications for debris flow debris charged flood hazard abstract this paper reconstructs the quaternary aggradation and incision history of a debris flow debris charged flood affected valley in order to detect the impact of climate on alluvial fan dynamics we used optically stimulated luminescence osl dating of quartz to determine the ages of alluvial fan terraces comparison between the aggradation and incision history and regional climatic records suggests that aggradation occurred in cold and or dry climates whereas incision is a feature of warm and wet climates cold climates lead to enhanced frost shattering and dry climates cause deteriorated vegetation both effects caused surplus sediment which was transported by infrequent flood discharges to form alluvial fan terrace deposits incision during wet and warm climates is due to increased vegetation cover and an increase in the frequency of flood discharges this relationship between climate and valley evolution is applied to assess future changes in the present active channel by considering recent climatic records the results show that the valley channel is expected to experience net incision if the average temperature continues increasing while precipitation maintains at a constant level

influence of lithology on hillslope morphology and response to tectonic forcing in the northern sierra nevada of california 1 many geomorphic studies assume that bedrock geology is not a first order control on landscape form in order to isolate drivers of geomorphic change e g climate or tectonics yet underlying geology may influence the efficacy of soil production and sediment transport on hillslopes we performed quantitative analysis of lidar digital terrain models to examine the topographic form of hillslopes in two distinct lithologies in the feather river catchment in northern california a granodiorite pluton and metamorphosed volcanics the two sites separated by 2 km and spanning similar elevations were assumed to have similar climatic histories and are experiencing a transience in landscape evolution characterized by a propagating incision wave in response to accelerated surface uplift c 5 ma responding to increased incision rates hillslopes in granodiorite tend to have morphology similar to model predictions for steady state hillslopes suggesting that they adjust rapidly to keep pace with the incision wave by contrast hillslopes in metavolcanics exhibit high gradients but lower hilltop curvature indicative of ongoing transient adjustment to incision we used existing erosion rate data and the curvature of hilltops proximal to the main channels where hillslopes have most likely adjusted to accelerated erosion rates to demonstrate that the sediment transport coefficient is higher in granodiorite 8 8 m2 ka 1 than in metavolcanics 4 8 m2 ka 1 hillslopes in both lithologies get shorter i e drainage density increases with increasing erosion rates

effect of height and orientation microclimate on geomorphic degradation rates and processes late glacial terrace scarps in central idaho terrace scarps can serve as a nearly ideal natural laboratory for the study of the evolution of slopes this paper examines the effects of scarp size height and orientation microclimate by keeping constant variables such as age lithology and regional climate if a scarp degrades as a closed system and downslope movement is directly proportional to surface gradient the evolution of the scarp is modeled by the diffusion equation for a group of scarps of same age and known starting angle the diffusion equation model predicts the relation between maximum scarp angle and scarp height h late pleistocene terrace scarps now as steep as 33 25 as well as measured angles of repose for sand and gravel require a starting angle as steep as 33 5 for latest pleistocene idaho and utah scarps as h increases is gentler more degraded than modeled by the diffusion equation with a constant rate coefficient the degradation rate coefficient c increases tenfold with scarp height it should not change with scarp height if downslope movement is solely determined by surface gradient to the first power soil wash appears to be responsible for this departure from the diffusion equation model for transport rate by soil wash is a function of scarp size height south facing scarps are less vegetated and more degraded than north facing scarps for scarps 2 m high the degradation rate c on s facing scarps is 2 times that on n facing scarps for 10 m scarps it is 5 times the observed dependence of the rate coefficient c on scarp height can be removed by normalizing c to values for west facing scarps of the same height the residual c values calculated by this method correlate well with differences in incident solar radiation resulting from the different scarp orientations and maximum gradients this correlation demonstrates the importance of orientation on slope processes and their rates through the differences in freeze thaw cycles soil moisture and vegetative cover scarp morphology may be used to estimate age if one accounts for the effects of climate and for scarp height orientation and lithology for example using the dated bonneville shoreline scarps for calibration and comparing only scarps of equal height we estimate the drum mountains fault scarps to be 9 000 yr old this age is about twice that produced by previous diffusion equation calculations that have not accounted for the height as we have here but it is the same as independent geologic estimates of their age

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

an analysis of the factors that control fault zone architecture and the importance of fault orientation relative to regional stress the moment magnitude 7 2 el mayor cucapah emc earthquake of 2010 in northern baja california mexico produced a cascading rupture that propagated through a geometrically diverse network of intersecting faults these faults have been exhumed from depths of 6 10 km since the late miocene based on low temperature thermochronology synkinematic alteration and deformational fabrics coseismic slip of 1 6 m of the emc event was accommodated by fault zones that displayed the full spectrum of architectural styles from simple narrow fault zones 100 m in width that have multiple anastomosing high strain cores as fault zone complexity and width increase the full spectrum of observed widths 20 200 m coseismic slip becomes more broadly distributed on a greater number of scarps that form wider arrays thus the infinitesimal slip of the surface rupture of a single earthquake strongly replicates many of the fabric elements that were developed during the long term history of slip on the faults at deeper levels of the seismogenic crust we find that factors such as protolith normal stress and displacement which control gouge production in laboratory experiments also affect the architectural complexity of natural faults fault zones developed in phyllosilicate rich metasedimentary gneiss are generally wider and more complex than those developed in quartzo feldspathic granitoid rocks we hypothesize that the overall weakness and low strength contrast of faults developed in phyllosilicate rich host rocks leads to strain hardening and formation of broad multi stranded fault zones fault orientation also strongly affects fault zone complexity which we find to increase with decreasing fault dip we attribute this to the higher resolved normal stresses on gently dipping faults assuming a uniform stress field compatible with this extensional tectonic setting the conditions that permit slip on misoriented surfaces with high normal stress should also produce failure of more optimally oriented slip systems in the fault zone promoting complex branching and development of multiple high strain cores overall we find that fault zone architecture need not be strongly affected by differences in the amount of cumulative slip and instead is more strongly controlled by protolith and relative normal stress

scarp degraded by linear diffusion inverse solution for age under the assumption that landforms unaffected by drainage channels are degraded according to the linear diffusion equation a procedure is developed to invert a scarp profile to find its diffusion age diffusion age having dimension length 2 is the product of diffusivity times chronological age the second moment of scarp slope grows linearly with age this fact together with an assumption about initial scarp shape allows the inverse determination of diffusion age age found assuming a vertical initial scarp is termed apparent age any nonvertical initial scarp profile has a nonzero initial apparent age true diffusion age differs from apparent age by a fraction of scarp offset squared the inverse procedure applied to synthetic data yields the following rules of thumb evidence of initial scarp shape has been lost when apparent age reaches twice its initial value if a scarp is formed by two events the inversion gives their offset weighted mean age with an error that is a fraction of offset squared a scarp that appears to have been formed by one event may have been formed by two with an interval between them as large as apparent age after scarps of two fault traces have diffused to appear as one the error in inferred age may be as large as half the apparent age variation of apparent age along strike would indicate multiple fault traces the simplicity of scarp profile measurement and this inversion makes profile analysis attractive if linearity of the flow law time for a free face to be reduced to the angle of repose and variation of diffusivity with climate and material could be established profile analysis would become a reliable dating technique

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

effect of far field slope on morphologic dating of scarplike landforms the principal finding of this paper is that the far field slope has a first order effect on model age determinations of scarplike landforms in weakly consolidated terrains observationally this can be demonstrated in two ways using the lake bonneville and lahontan shoreline scarps as separate and combined data sets use of the reduced scarp slope tan theta sub s minus b where theta sub s is the maximum scarp angle and b is the far field or fan slope instead of tan theta sub s alone as the measure of scarp slope measurably reduces separation between the two data sets induced by different average fan slopes for the two data sets and significantly reduces scatter in the slope offset plot for both the separate and combined data sets theoretically the argument can be put even more strongly at least within the range of linear and nonlinear diffusion models that the authors consider here together with a mathematical transformation of the empirical approach of r c bucknam and r e anderson when one correctly takes into account the far field slope one will basically get the same age determination no matter which of these models one uses conversely without accounting properly for the effect of far field slope one is virtuallymore guaranteed to get an erroneous age determination no matter which model is used less

initiation of the southern elsinore fault at 1 2 ma evidence from the fish creek vallecito basin southern california 1 strike slip faults west of the san andreas fault saf accommodate more than half of the modern pacific north america plate motion in southern california yet their age kinematic evolution and long term slip rates are incompletely understood the southern elsinore fault is part of this zone and occupies the boundary between mesozoic crystalline rocks of the peninsular ranges and late cenozoic sedimentary rocks of the salton trough depocenter the fish creek vallecito basin a recently inverted western sub basin of the salton trough contains a thick succession of plio pleistocene sedimentary rocks that preserve a record of crustal subsidence and uplift in response to evolving tectonic controls deposits older than 1 2 ma accumulated during transtension and subsidence in the hanging wall of the low angle west salton detachment fault a fanning dip interval high in the section dated at 1 2 1 0 ma accumulated during tilting caused by earliest motion on the elsinore and earthquake valley faults total offset of 1 2 km yields a lifetime slip rate of about 1 2 mm yr for the southern elsinore fault similar to a late pleistocene rate in the coyote mountains but slower than published estimates for the northern elsinore fault this difference likely results from long term transfer of slip from the northern elsinore fault to the san felipe and san jacinto fault zones farther east initiation of the elsinore fault at 1 2 ma coincides with a major tectonic reorganization that terminated slip on the detachment fault and formed the modern network of strike slip faults west of the saf

isotopic insights into smoothening of abandoned fan surfaces southern california cosmogenic nuclide concentrations measured on abandoned fan surfaces along the mojave section of the san andreas fault suggest that sediment is generated transported and removed from the fans on the order of 30 40 kyr we measured in situ produced cosmogenic 10 be and in some cases 26 al in boulders n 15 surface sediment n 15 and one depth profile n 9 nuclide concentrations in surface sediments and boulders underestimate fan ages suggesting that 10 be accumulation is largely controlled by the geomorphic processes that operate on the surfaces of the fans and not by their ages field observations grain size distribution and cosmogenic nuclide data suggest that over time boulders weather into grus and the bar sediments diffuse into the adjacent swales as fans grow older the relief between bars and swales decreases the sediment transport rate from bars to swales decreases and the surface processes that erode the fan become uniform over the entire fan surface the nuclide data therefore suggest that over time the difference in 10 be concentration between bars and swales increases to a maximum until the topographic relief between bars and swales is minimized resulting in a common surface lowering rate and common 10 be concentrations across the fan during this phase the entire fan is lowered homogeneously at a rate of 10 15 mm kyr 1

miocene pliocene exhumation along the west salton detachment fault southern california from u th he thermochronometry of apatite and zircon 1 the salton trough is the northernmost segment of the active gulf of california oblique rift system the main rift related structure in the western salton trough is the low angle west salton detachment fault wsdf footwall and hanging wall apatite and zircon u th he ages record a significant contrast in thermal history across the wsdf confirming pliocene normal slip along the fault apatite u th he ages record rapid exhumational cooling from 5 to 2 ma consistent with the timing of accelerated tectonic subsidence recorded in wsdf hanging wall sedimentary strata and consistent with the initiation age of dextral plate boundary slip on the southern san andreas fault in the salton trough our results indicate that the wsdf caused at least 2 3 4 km of exhumation and 8 10 km of approximately e directed horizontal extension since 5 ma slip rate of the wsdf at yaqui ridge was likely in the range of 2 3 5 km ma from 7 to 2 ma the wsdf may have been active well before 5 ma middle miocene apatite u th he ages from samples at high elevations have steep age elevation gradients and suggest that exhumation may have initiated by 12 ma about when subduction ceased along a large segment of the baja california margin and consistent with the age of onset of extension in northeastern baja california

late neogene stratigraphy and tectonic control on facies evolution in the laguna salada basin northern baja california mexico abstract the laguna salada basin lsb in northeastern baja california records late neogene marine incursions in the salton trough and progradation of the colorado river delta early subsidence and subsequent tectonic erosion are related to evolution of the sierra el mayor detachment fault during late miocene time

late quaternary weathering erosion and deposition in nahal yael israel an impact of climatic change on an arid watershed in their seminal paper in 1979 bull and schick proposed a conceptual model for the geomorphic response to pleistocene to holocene climate change based on the hyperarid nahal yael watershed in the southern negev desert in this model the change from semiarid late pleistocene to hyperarid early holocene climates reduced vegetation cover increased the yield of sediment from slopes and accelerated aggradation of terraces and alluvial fans the model is now over 30 yr old and during this time chronologic paleoenvironmental and hydrogeomorphic research has advanced here we reevaluate the model using data acquired in nahal yael over the 30yr since the original model was proposed recent studies indicate that the late pleistocene climate was hyperarid and a transition from semiarid to hyperarid climates did not occur the revised chronology reveals a major 35 20 ka episode of accelerated late pleistocene sediment production on slopes with lower rates probably already at ca 50ka due to increased frequency of wetting drying cycles caused by frequent extreme storms and floods between 35 and 27 ka without lag time these sediments were transported and aggraded in depositional landscape components fluvial terraces and alluvial fans this intensified sediment production and delivery phase is unrelated to the pleistocene holocene transition the depositional landforms were rapidly incised between 20 and 18 ka since and or soon after this last glacial maximum lgm incision most material leaving the basin originated from sediments stored in depositional landforms and was not produced from bedrock using these new data we propose a revision to the bull and schick model in this hyperarid environment our revision suggests that the model should include the frequent storms and floods responsible for a late pleistocene pulse of intense weathering due to numerous cycles of wetting and drying on slopes and coeval sediment transport to fluvial terraces and alluvial fans we also discuss the common use and pitfalls of using the bull and schick conceptual model to explain observations in diverse arid environments usually without sufficient data on basin specific stratigraphic chronologic paleoenvironmental and paleoclimatic information

morphology of the latest quaternary surface faulting in the gulf of elat region eastern sinai abstract a variety of morphotectonic features bear evidence of neotectonic activity along the gulf of elat these include stepped topography deflected channels fault line grabens sag pond depressions backtilted fan segments faulted gravel bars and debris flow deposits the age of the fault scarps is estimated on the basis of the extent of dissection the amount of rounding of the crest of the scarps the scarp gradient the stage of clast weathering the intensity of the micro relief and the stage of soil and desert pavement development the field data are interpreted and related to the geomorphic time curves suggested by wallace by bucknam and anderson and by nash and the seismic hazard implications are discussed some criteria suggest a recent age with 10 000 yrs b p as a frequently recurrent estimate from the data it is concluded that the gulf of elat has definitely been tectonically highly active during the holocene

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr