erosion rates over millennial and decadal timescales at caspar creek and redwood creek northern california coast ranges comparing millennial scale denudation rates from cosmogenic nuclides with decadal scale sediment yields can shed light on erosional processes and on the effects of land use on sediment delivery to streams detailed measurements of sediment fluxes in the northern california coast ranges at caspar creek and redwood creek have provided estimates of physical erosion rates since 1963 and 1971 respectively we used cosmogenic 10 be to measure

tectonic control of erosion in the southern central andes abstract landscape evolution modeling and global compilations of exhumation data indicate that a wetter climate mainly through orographic rainfall can govern the spatial distribution of erosion rates and crustal strain across an orogenic wedge however detecting this link is not straightforward since these relationships can be modulated by tectonic forcing and or obscured by heavy tailed frequencies of catchment discharge this study combines new and published along strike average rates of catchment erosion constrained by 10be and river gauge data in the central andes between 28 s and 36 s these data reveal a nearly identical latitudinal pattern in erosion rates on both sides of the range reaching a maximum of 0 27 mm a near 34 s collectively data on topographic and fluvial relief variability of rainfall and discharge and crustal seismicity suggest that the along strike pattern of erosion rates in the southern central andes is largely independent of climate but closely relates to the n s distribution of shallow crustal seismicity and diachronous surface uplift the consistently high erosion rates on either side of the orogen near 34 s imply that climate plays a secondary role in the mass flux through an orogenic wedge where the perturbation to base level is similar on both sides

soil genesis and mineralogy across a volcanic lithosequence abstract lithology is a principle state factor of soil formation interacting with climate organisms topography and time to define pedogenesis a lithosequence of extrusive igneous lithologies rhyolite obsidian dacite andesite and basalt was identified in the clear lake volcanic field in the coast range of northern california to determine the effects of lithology on pedogenesis clay mineralogy and soil physiochemical properties based on regional landscape erosion rates 0 2 0 5 mm yr 1 the soil residence times for the investigated pedons 150 cm deep were of the order of 3000 to 7500 years indicating that the soils developed under the relatively stable holocene mesic xeric climate regime soils from all lithologies developed to a similar xeralf taxonomy with remarkably consistent physiochemical properties although total fet and dithionite citrate extractable fed iron concentrations diverged across lithologies the degree of weathering as assessed by the fed fet ratio was similar across the lithosequence in spite of large differences in silica content of the parent materials the clay mineralogical assemblage of all lithologies was dominated by kaolin minerals kaolinite and or halloysite all pedons displayed an increase in halloysite and the degree of halloysite hydration with increasing depth except the basalt pedon which was dominated by kaolinite with only trace halloysite we attribute this lack of halloysite in the basalt pedon to the lower silica activities associated with this silica poor lithology there was a lack of nanocrystalline minerals across all lithologies as inferred from selective dissolution the dominance of crystalline materials is a function of the xeric soil moisture regime whereby summer soil profile desiccation promotes dehydration and crystallization of metastable nanocrystalline precursors further the pronounced summer dry period results in dehydration of halloysite 1 0 nm to halloysite 0 7 nm also referred to as meta halloysite in some literature together with transformation to kaolinite in the upper soil profile in spite of the relatively young soil residence times of these soils holocene age the effects of lithology persisted only in differences in fe oxide concentrations fed as well as a lack of significant halloysite in basalt pedons the overwhelming effect of climate in these highly weatherable parent materials narrowed the trajectory of pedogenesis resulting in soils from contrasting lithologies converging on kaolin mineralogy a lack of nanocrystalline constituents and similar soil physiochemical properties

structure and contents of a new geomorphological gis database linked to a geomorphological map with an example from liden central sweden this paper presents the structure and contents of a standardised geomorphological gis database that stores comprehensive scientific geomorphological data and constitutes the basis for processing and extracting spatial thematic data the geodatabase contains spatial information on morphography morphometry hydrography lithology genesis processes and age a unique characteristic of the gis geodatabase is that it is constructed in parallel with a new comprehensive geomorphological mapping system designed with gis applications in mind this close coupling enables easy digitalisation of the information from the geomorphological map into the gis database for use in both scientific and practical applications the selected platform in which the geomorphological vector raster and tabular data are stored is the esri personal geodatabase additional data such as an image of the original geomorphological map dems or aerial orthographic images are also included in the database the structure of the geomorphological database presented in this paper is exemplified for a study site around liden central sweden

sandstone diagenesis and reservoir quality prediction models myths and reality models and concepts of sandstone diagenesis developed over the past two decades are currently employed with variable success to predict reservoir quality in hydrocarbon exploration not all of these are equally supported by quantitative data observations and rigorous hypothesis testing simple plots of sandstone porosity versus extrinsic parameters such as current subsurface depth or temperature are commonly extrapolated but rarely yield accurate predictions for lithified sandstones calibrated numerical models that simulate compaction and quartz cementation when linked to basin models have proven successful in predicting sandstone porosity and permeability where sufficient analog information regarding sandstone texture composition and quartz surface area is available analysis of global regional and local data sets indicates the following regarding contemporary diagenetic models used to predict reservoir quality 1 the effectiveness of grain coatings on quartz grains e g chlorite microquartz as an inhibitor of quartz cementation is supported by abundant empirical data and recent experimental results 2 vertical effective stress although a fundamental factor in compaction cannot be used alone as an accurate predictor of porosity for lithified sandstones 3 secondary porosity related to dissolution of framework grains and or cements is most commonly volumetrically minor 2 exceptions are rare and not easily predicted with current models 4 the hypothesis and widely held belief that hydrocarbon pore fluids suppress porosity loss due to quartz cementation is not supported by detailed data and does not represent a viable predictive model 5 heat flow perturbations associated with allochthonous salt bodies can result in suppressed thermal exposure thereby slowing the rate of quartz cementation in some subsalt sands

beyond threshold hillslopes channel adjustment to base level fall in tectonically active mountain ranges numerous empirical and model based studies argue that in general hillslopes and river channels increase their gradients to accommodate high rates of base level fall to date however few data sets show the dynamic range of both these relationships needed to test theoretical models of hillslope evolution and river incision here we utilize concentrations of 10 be in quartz extracted from river sand on the eastern margin of the tibetan plateau to explore relationships among short term 10 2 10 5 a erosion rate hillslope gradient and channel steepness our data illustrate nonlinear behavior and a threshold in the relationship between erosion rate and mean hillslope gradient confi rming the generalization that hillslopes around the world are limited by slope stability and cease to provide a metric for erosion at high rates 0 2 mm a the relationship between channel steepness index and erosion rate is also nonlinear but channels continue to steepen beyond the point where threshold hillslopes emerge up to at least 0 6 mm a demonstrating that channel steepness is a more reliable topographic metric than mean hillslope gradient for erosion rate and that channels ultimately drive landscape adjustment to increasing rates of base level fall in tectonically active settings

landscape form and millennial erosion rates in the san gabriel mountains ca abstract it has been long hypothesized that topography as well as climate and rock strength exert first order controls on erosion rates here we use detrital cosmogenic 10 be from 50 basins ranging in size from 1 to 150 km 2 to measure millennial erosion rates across the san gabriel mountains in southern california where a strong e w gradient in relief compared to weak variation in precipitation and lithology allow us to isolate the relationship between topographic form and erosion rate our erosion rates range from 35 to 1100 m ma and generally agree with both decadal sediment fluxes and long term exhumation rates inferred from low temperature thermochronometry catchment mean hillslope angle increases with erosion rate until 300 m ma at which point slopes become invariant with erosion rate although this sort of relation has been offered as support for non linear models of soil transport we use 1 d analytical hillslope profiles derived from existing soil transport laws to show that a model with soil flux linear in slope but including a slope stability threshold is indistinguishable from a non linear law within the scatter of our data catchment mean normalized channel steepness index increases monotonically though non linearly with erosion rate throughout the san gabriel mountains even where catchment mean hillslope angles have reached a threshold this non linearity can be mostly accounted for by a stochastic threshold incision model though additional factors likely contribute to the observed relationship between channel steepness and erosion rate these findings substantiate the claim that the normalized channel steepness index is an important topographic metric in active ranges

the control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment the study of a sample of river sediment enables the determination of spatially averaged denudation rates that provide an exceptional perspective on erosion and weathering processes that have taken place within a landscape these measurements are done with in situ produced cosmogenic nuclides e g 10be 26al mostly in quartz from alluvial sediment cosmogenic nuclides are produced when secondary cosmic rays interact with the very uppermost layer of the earth s surface they are produced within a characteristic depth scale of about 1 m which means that the measured concentrations record an integrated denudation history while material passed through this depth interval depending on the denudation rate the resulting integration time scales are 103 to 105 years and one obtains a robust long term estimate of natural denudation that is relatively insensitive to short term changes the last 10 years have seen significant research activity using these methods and an array of fascinating tectono geomorphologic and geochemical insights are emerging amongst these is the ability to identify the physical and chemical processes with which a landscape responds to tectonic activity or climate change a compilation of world wide denudation rates in non glaciated areas that however does not yet include some of the world s most active mountain belts has resulted in the following findings some of which have been unexpected 1 no obvious relationship between precipitation or mean annual temperature and total denudation is apparent 2 topographic relief alone does not result in high rates of denudation 3 denudation rates are high in areas of landscape rejuvenation that is triggered and controlled by tectonic activity faulting escarpment formation and retreat rifting surface uplift 4 rates of weathering using a combination of cosmogenic nuclides and zirconium normalised cation loss balances co vary primarily with physical erosion rates and much less with temperature or precipitation 5 in some areas of high land use short term rates from river load gauging exceed those from cosmogenic nuclides by several orders of magnitude which serves to highlight the severity of geomorphic change caused by human action in the future the control mechanisms over denudation will be determined on all spatial scales ranging from the single soil section to entire river basins the same analysis can be done back through time on well dated terraces lake records and marine sediment cores which is possible with 10be for the past 1 2 my the rates obtained will be used to develop a quantitative understanding of tectonic geomorphologic and geochemical landscape processes which in turn is a prerequisite to design and calibrate models of the response of landscapes to tectonic climate and anthropogenic forcing

remote sensing technology and geographic information system modeling an integrated approach towards the mapping of groundwater potential zones in hardrock terrain mamundiyar basin in this paper remote sensing evaluation of digital elevation models dem geographic information systems gis and fieldwork techniques were combined to study the groundwater conditions in mamundiyar basin tamilnadu several digital image processing techniques including standard color composites intensity hue saturation ihs transformation and decorrelation stretch ds were applied to map rock types remote sensing data were interpreted to produce lithological and lineament maps dem was used for lineament and geomorphologic mapping all thematic layers were integrated and analyzed in a gis the overall results demonstrate that the use of remote sensing and gis provide potentially powerful tools to study groundwater resources and design a suitable exploration plan

formation of inner gorges abstract under certain conditions a distinctive type of landform the inner gorge evolves in drainage basins undergoing persistent base level lowering inner gorges are typical of basins in north coastal california u s a and one such basin was selected for detailed study based on analysis of along channel distribution of rock types streamside land sliding and stored sediment as well as computation of stream power the following set of conditions appears to accompany the formation of an inner gorge 1 inner gorge parent materials are relatively competent homogenous rock types 2 in inner gorge reaches there is an absence of any base level control that would prevent downcutting 3 continued downcutting occurs due to continued base level fall and this fall is most likely induced by tectonic uplift 4 mass slope failures that form steep straight slopes debris slides are the main denudational hillslope process in the inner gorge 5 sufficient stream power is available to transport landslide derived material out of the inner gorge reach such that alluvial sediment does accumulate in the reach over time and 6 the initial condition of the landscape is a low relief erosionally mature land surface into which the inner gorge is cut this initial condition implies that inner gorges develop in tectonically rejuvenated landscapes the processes of denudation on inner gorge slopes acting over a time scale of 105 years result in a style of landform evolution that approximates parallel slope retreat this type of slope retreat maintains the distinct inner gorge morphology during sustained downcutting though the analysis is confined to one basin in northern california so as to provide a detailed framework to understand inner gorge landform inner gorges appear to be commonplace in areas of moderate to high uplift where lithologic and tectonic conditions are appropriate for their formation a global search for this landform yet to be undertaken is needed to confirm whether it indeed occurs where the above conditions are met

slope distributions threshold hillslopes and steady state topography digital elevation models of two steady state mountain ranges the olympic mountains om and oregon coast range ocr are used to examine relationships between slope distributions the development of threshold hillslopes and steady state topography plots of drainage area versus slope for these mountain ranges exhibit substantial scatter that complicates comparison of range form to analytical theories and landscape evolution models contour plots of the density of such data reveal an attractor at the scale of the transition from hillslope processes to channel processes and log bin averaging reveals trends that parallel predictions of steady state erosion laws but with different rate laws for five distinct process domains hillslopes valley heads and colluvial bedrock and alluvial valley segments slope histograms computed for 100 km2 areas defined by a 10 10 km grid throughout the om exhibit approximately normal or exponential distributions in areas of active rock uplift and depositional topography respectively local slope distributions in the ocr also tend to be normally distributed but some are left skewed in areas with gentler slopes mean slopes determined both over the above referenced grid and a 10 km diam moving window are relatively invariant in the core of the om in spite of strong contrasts in bedrock erodibility and gradients in long term rock uplift rates in contrast the mean slopes in the ocr parallel latitudinal gradients in rock uplift rates and bedrock erodibility hence the slope distributions in the om and ocr reflect distinct relationships between development of threshold bedrock and soil mantled hillslopes and steady state topography

the role of fluid pressure and diagenetic cements for porosity preservation in triassic fluvial reservoirs of the central graben north sea anomalously high porosities and permeabilities are commonly found in the fluvial channel sandstone facies of the triassic skagerrak formation in the central north sea at burial depths greater than 3200 m 10 499 ft from which hydrocarbons are currently being produced the aim of our study was to improve understanding of sandstone diagenesis in the skagerrak formation to help predict whether the facies with high porosity may be found at even greater depths the skagerrak sandstones comprise fine to medium grained arkosic to lithic arkosic arenites we have used scanning electron microscopy petrographic analysis pressure history modeling and core analysis to assess the timing of growth and origin of mineral cements with generation and the impact of high fluid pressure on reservoir quality our interpretation is that the anomalously high porosities in the skagerrak sandstones were maintained by a history of overpressure generation and maintenance from the late triassic onward in combination with early microquartz cementation and subsequent precipitation of robust chlorite grain coats increasing salinity of pore fluids during burial diagenesis led to pore filling halite cements in sustained phreatic conditions the halite pore filling cements removed most of the remaining porosity and limited the precipitation of other diagenetic phases fluid flow associated with the migration of hydrocarbons during the neogene is inferred to have dissolved the halite locally dissolution of halite cements in the channel sands has given rise to megapores and porosities of as much as 35 at current production depths

late neogene and quaternary landscape evolution of the northern california coast ranges evidence for mendocino triple junction tectonics a landscape records the surface response to tectonics at time scales intermediate between short time scale information derived from seismic imaging and global positioning systems and the long term geologic record we link late neogene and quaternary deposits and landforms in the northern california coast ranges to the tectonics of the mendocino triple junction in the northern california coast ranges the mendocino crustal conveyor geodynamic model describes crustal thickening thinning and dynamic topography that produce a double humped pattern of uplift that migrates northward with the mendocino triple junction the tectonics are manifest in the drainage system and elevation pattern of the coast ranges at long wavelengths the elevation pattern closely matches the predicted double peaked shape of mendocino crustal conveyor topography and the high points of uplift control the location of drainage divides presently the divide between the russian and eel rivers and the divide between the eel and van duzen rivers approximately correspond to the peaks of uplift predicted by the mendocino crustal conveyor model as the triple junction migrates northward the double humped pattern of uplift and subsidence migrates and the coast ranges emerge smaller drainages develop and evolve by stream capture and flow reversal and the two main divides migrate in concert with the triple junction in contrast to the systematic development of the small streams the largest trunk streams can maintain grade through regions of high uplift and coastal river mouths remain stationary despite the uplift moving north before ca 2 ma the majority of the coast range drainage flowed to a southern coastal outlet near the present mouth of the russian river at 2 ma facilitated by headwater stream capture at key locations the drainage direction reversed and the majority of coast range rivers now drain into the north flowing eel river the major drainage reorganization at 2 ma highlights the potential for complexity in geomorphic response to tectonics

asthenospheric buoyancy and the origin of high relief topography along the cascadia forearc abstract the forearc topography of the cascadia subduction zone varies systematically along strike with high relief in the north and south the olympic and klamath ranges separated by relatively low relief in its central region this systematic topographic variability reflects the long term pattern of uplift and erosion however the underlying cause of uplift and the mechanisms by which current topography is supported are unclear here we synthesize results from seismic imaging geodetic decadal and geomorphic millennial uplift rates erosion rates topographic analysis and characteristics of the megathrust interface with a mechanical model to infer that buoyancy in the subslab asthenosphere influences the development and longevity of cascadia s forearc topography the cascadia margin can be divided into three broad segments with the northern and southern segments characterized by rapid geodetic and geomorphic uplift rates rapid erosion rates high coseismic subsidence of great megathrust ruptures shallower slab dip angles and increased plate locking compared to the central segment tomographic images show low velocity anomalies beneath the slab in the northern and southern segments which are inferred to be regions of partial melt resulting from localized upwellings and regions of positive mantle buoyancy modeling suggests that these buoyant regions can locally increase the total shear force at the megathrust by either shallowing the slab dip thereby increasing the area of the seismogenic zone or increasing mechanical plate coupling along the megathrust by increasing normal stress and or the effective coefficient of friction we propose that 1 sub slab buoyancy influences topographic development by modulating along strike patterns of strain within the over riding plate during the seismic cycle 2 permanent development of surface topography occurs due to unrecovered strain over thousands of seismic cycles and 3 variations in cascadia s forearc topography are laterally supported by changes in the total shear force at the megathrust interface using independent estimates for slab dip and plate locking we predict the first order variations in cascadia forearc topography with local maxima in the north and south as observed given our results variations in subslab buoyancy may be critical to explaining forearc topography in other subduction systems

prediction of deep reservoir quality using early diagenetic process models in the jurassic norphlet formation gulf of mexico we have developed process based models for early grain coats and their impact on deep reservoir quality in the jurassic eolian norphlet formation alabama with implications for exploration and development in other conventional and tight gas continental reservoirs the norphlet a major gas reservoir to depths of 21 800 ft 6645 m and temperatures of 419f 215c displays contrasting intervals of high and low reservoir quality within compositionally similar cross bedded eolian sands study results show that grain coats formed soon after deposition are responsible for differences in deep norphlet porosity of up to 20 and permeability up to 200 md three types of grain coats were identified in norphlet dune sands each formed in a different part of a shallow groundwater system and each with distinctive impact on deep reservoir quality diagenetic chlorite coats formed where dunes subsided into shallow hypersaline groundwater preserve good deep porosity to 20 and permeability to 200 md continuous tangential illitic coats formed in the vadose zone of stabilized dunes exposed to periodic fresh water influx preserve good deep porosity to 15 associated with poor permeability 1 md due to linked formation of later high temperature diagenetic illite discontinuous grain coats formed in active dunes where grains were abraded by eolian transport are associated at depth with tight zones of pervasive quartz cement low porosity 8 and low permeability 1 md these concepts plus data from 60 wells were used to derive bay wide predictive tight and porous zone isopachs that can be used for well placement geologic models and field development

geodetic constraint on the motion of a slab window implication for the mendocino crustal conveyor model the migration of the slab window in the northern california coast ranges provides a unique setting to study the viscous coupling between crust and asthenosphere flow the mechanisms of these dynamic processes are explained by the mendocino crustal conveyor model which predicts a 2 d double humped surface uplift rate pattern on a 400 km long profile to evaluate the mendocino crustal conveyor mcc model using accurate geodetic measurements we derive the vertical velocity field from 43 continuous gps cgps stations in the coast ranges region and project it onto the profile along three possible orientations of the slab window the cgps measured uplift rates are in good agreement with the mcc prediction when the slab window orientation is parallel to the symmetry axis of the region of thickened crust thus the cgps solutions not only provide a complementary means to diagnose the mcc model but also provide an effective way to constrain the orientation of the slab window

holocene strath terraces climate change and active tectonics the clearwater river basin olympic peninsula washington state the 400 km 2 clearwater river basin located on the pacific flank of the actively uplifting olympic mountains of western washington state contains a well preserved flight of holocene fluvial terraces we have collected a large data set of numeric ages from these terraces that is used to elucidate the geomorphic fluvial active tectonic and climatic processes that operate at holocene spatial and temporal scales detailed field mapping reveals three prominent holocene straths and their overlying terrace deposits terrace ages fall into three broad ranges ca 9000 11 000 yr b p qt4 4000 8000 yr b p qt5 and 0 3000 yr b p qt6 terrace deposit stratigraphy sedimentology and age distributions allow us to consider two alternative models for their genesis the favored model states that the terrace ages are coincident with lateral incision of the clearwater channel emplacement of the terrace alluvium and the carving of the straths vertical incision of the clearwater channel was primarily relegated to the brief 1000 yr intervals when we have no record of terraces alternatively the straths were carved as the channel incised vertically during the brief time periods between dated terrace deposits and the terrace ages record a subsequent long time of alluviation atop the straths and concomitant termination of vertical incision in both models we envision a clearwater river channel at or near capacity with a temporally variable rate of both lateral and vertical incision small deviations from this at capacity condition are driven by variations in the liberation and delivery of hillslope sediment to the channel we consider several causes for variable hillslope sediment flux in this tectonically active setting including holocene climate change and ground accelerations related to earthquakes holocene rates of vertical incision are reconstructed along nearly the entire clearwater valley from the wide distribution of dated terraces incision rates clearly increase upstream mimicking a pattern documented for pleistocene terraces in the same basin however the rates are 2 3 times those determined for the pleistocene terraces the faster holocene incision rates may be interpreted in terms of an increase in the rates of rock uplift however we favor an alternative explanation in which the holocene rates represent a channel rapidly reacquiring its stable graded concavity following protracted periods of time in the pleistocene when it could not accomplish any vertical incision into tectonically uplifted bedrock because the channel was raised above the bedrock valley bottom by climatically induced alluviation these results illustrate how even in tectonically active settings representative rates of rock uplift inferred from studies of river incision should be integrated over at least one glacial interglacial cycle

late quaternary climatic controls on erosion rates and geomorphic processes in western oregon usa climate regulation of erosion in unglaciated landscapes remains difficult to decipher while climate may disrupt process feedbacks that would otherwise steer landscapes toward steady erosion sediment transport processes tend to erase past climate landforms and thus bias landscape evolution interpretations here we couple a 50 k y paleoenvironmental record with 24 10be derived paleo erosion rates from a 63 m thick sediment archive in the unglaciated soil mantled oregon coast range our results span the forested marine oxygen isotope stage mis 3 50 29 ka the subalpine mis 2 29 14 ka and the forested mis 1 14 ka to present from 46 ka through 28 5 ka erosion rates increased from 0 06 mm yr 1 to 0 23 mm yr 1 coincident with declining temperatures mean mis 2 erosion rates remained at 0 21 mm yr 1 and declined with increasing mis 1 temperatures to the modern mean rate of 0 08 mm yr 1 paleoclimate reconstructions and a frost weathering model suggest periglacial processes were vigorous between 35 and 17 ka while steady erosion is often assumed our results suggest that climate strongly modulates soil production and transport on glacial interglacial time scales by applying a cosmogenic paleo erosion model to evaluate 10be concentrations in our sedimentary archive we demonstrate that the depth of soil mixing which is climate dependent controls the lag time required for cosmogenic erosion rates to track actual values our results challenge the widely held assumption that climate has minimal impact on erosion rates in unglaciated midlatitude terrain which invites reconsideration of the extent to which past climate regimes manifest in modern landscapes

sediment supply controls equilibrium channel geometry in gravel rivers in many gravel bedded rivers floods that fill the channel banks create just enough shear stress to move the median sized gravel particles on the bed surface d50 because this observation is common and is supported by theory the coincidence of bankfull flow and the incipient motion of d50 has become a commonly used assumption however not all natural gravel channels actually conform to this simple relationship some channels maintain bankfull stresses far in excess of the critical stress required to initiate sediment transport we use a database of 300 gravel bedded rivers and 600 10be derived erosion rates from across north america to explore the hypothesis that sediment supply drives the magnitude of bankfull shear stress relative to the critical stress required to mobilize the median bed surface grain size formula see text we find that formula see text is significantly higher in west coast river reaches 2 35 n 96 than in river reaches elsewhere on the continent 1 03 n 245 this pattern parallels patterns in erosion rates and hence sediment supplies supporting our hypothesis we find a significant correlation between upstream erosion rate and local formula see text at sites where this comparison is possible our analysis reveals a decrease in bed surface armoring with increasing formula see text suggesting channels accommodate changes in sediment supply through adjustments in bed surface grain size as also shown through numerical modeling our findings demonstrate that sediment supply is encoded in the bankfull hydraulic geometry of gravel bedded channels through its control on bed surface grain size

evaluation of multispectral fine scale digital imagery as a tool for mapping stream morphology abstract multispectral digital imagery acquired from soda butte and cache creeks montana and wyoming was used in conjunction with field data to classify and map hydrogeomorphic stream units on four stream reaches the morphologic units that were field mapped were eddy drop zones glides low gradient riffles high gradient riffles lateral scour pools attached bars detached bars and large woody debris unsupervised and supervised classifications of the imagery were used to develop a maximum joint probability classification and an alternative joint probability classification of the stream reaches the maximum joint probability classification allowed only one of the image classes to represent each hydrogeomorphic unit on the field map and resulted in relatively low overall accuracies for identification of these units of 10 to 50 the alternative joint probability classification allowed each image class to represent any geomorphic unit where the probability of a correct classification was greater than random in this technique two or three image classes were assigned to represent each hydrogeomorphic unit resulting in higher overall accuracies of 28 to 80 accurate classification of hydrogeomorphic units was hampered by poor rectification of imagery with the field maps because of inadequate ground control points in general the largest hydrogeomorphic units were most accurately classified whereas units that were small in area or spatially linear were least likely to be accurately classified the results of this study demonstrated that multispectral digital imagery has the potential to be a useful tool for mapping hydrogeomorphic stream units at fine scales imagery to be an effective tool however careful measures such as accurate documentation of ground control points must be taken to ensure accurate rectification of the imagery with field maps

influence of the mendocino triple junction on the tectonics of coastal california abstract the migration of the mendocino triple junction through central and northern california over the past 25 30 million years has led to a profound change in plate interactions along coastal california the tectonic consequences of the abrupt change from subduction plate interactions north of the triple junction to the development of the san andreas transform system south of the triple junction can be seen in the geologic record and geophysical observations the primary driver of this tectonism is a coupling among the subducting juan de fuca gorda north american and pacific plates that migrates with the triple junction this coupling leads to ephemeral thickening of the overlying north american crust associated uplift and subsequent subsidence and a distinctive sequence of fault development and volcanism

erosion rates in the southern oregon coast range evidence for an equilibrium between hillslope erosion and sediment yield the relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes in landscapes containing hillslopes crenulated by alternating topographic noses and hollows estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows hollows act as local traps for a portion of the colluvium transported down hillslopes and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area analysis of colluvial deposits in nine oregon coast range hollows has yielded average colluvial transport rates into the hollows of about 35 cm3cm 1yr 1 and average bedrock lowering rates of about 007 mm yr for the last 4000 to 15000 yr these rates are consistent with maximum bedrock exfoliation rates of about 0 09 mm yr calculated from six of the hollows supporting the interpretation that exfoliation rates limit erosion rates on these slopes sediment yield measurements from nine coast range streams provide similar basin wide denudation rates of between 0 05 and 0 08 mm yr 1 suggesting an approximate steady state between sediment production on hillslopes and sediment yield in addition modern sediment yields are similar in basins varying in size from 1 to 1500 km2 suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

anomalously high porosity and permeability in deeply buried sandstone reservoirs origin and predictability porosity and permeability generally decrease with increasing depth thermal exposure and effective pressure however a significant number of deep 4 km approximately 13 000 ft sandstone reservoirs worldwide are characterized by anomalously high porosity and permeability anomalous porosity and permeability can be defined as being statistically higher than the porosity and permeability values occurring in typical sandstone reservoirs of a given lithology composition and texture age and burial temperature history in sandstones containing anomalously high porosities such porosities exceed the maximum porosity of the typical sandstone subpopulation major causes of anomalous porosity and permeability were identified decades ago however quantification of the effect of processes responsible for anomalous porosity and permeability and the assessment of the predictability of anomalous porosity and permeability occurrence in subsurface sandstones have rarely been addressed in published literature the focus of this article is on quantification and predictability of three major causes of anomalously high porosity 1 grain coats and grain rims 2 early emplacement of hydrocarbons and 3 shallow development of fluid overpressure grain coats and grain rims retard quartz cementation and concomitant porosity and permeability reduction by inhibiting precipitation of quartz overgrowths on detrital quartz grains currently prediction of anomalous porosity associated with grain coats and grain rims is dependent on the availability of empirical data sets in the absence of adequate empirical data sedimentologic and diagenetic models can be helpful in assessing risk due to reservoir quality such models provide a means to evaluate the effect of geologic constraints on coating occurrence and coating completeness required to preserve economically viable porosity and permeability begin page 302 in a given play or prospect these constraints include thermal history and sandstone grain size and composition the overall effect of hydrocarbon emplacement on reservoir quality is controversial it appears that at least some cements quartz and illite may continue to precipitate following emplacement of hydrocarbons into the reservoir our work indicates that integration of basin modeling with reservoir quality modeling can be used to quantify prior to drilling the potential impact of hydrocarbon emplacement on porosity and permeability the best case scenario for significant reservoir quality preservation due to fluid overpressure development is in rapidly deposited tertiary or quaternary sandstones our models suggest that significant porosity can be preserved in sandstones that have experienced continuous high fluid overpressures from shallow burial depths the models also indicate that the potential for porosity preservation is greatest in ductile grain rich sandstones because compaction tends to be the dominant control on reservoir quality in such rocks the case for significant porosity preservation associated with fluid overpressures in pre tertiary basins however is more problematic because of the complexities in the history of fluid overpressure and the greater significance of quartz cementation as a potential mechanism of porosity loss

topographic form of the coast ranges of the cascadia margin in relation to coastal uplift rates and plate subduction the coast ranges of the cascadia margin are overriding the subducted juan de fuca gorda plate we investigate the extent to which the latitudinal trend in average topography of the coast ranges is a function of the latitudinal change in attributes related to the subduction process these attributes include the variable age of the subducted slab that underlies the coast ranges and average vertical crustal velocities of the western margin of the coast ranges for two markedly different time periods the last 45 years and the last 100 kyr these vertical crustal velocities are computed from the resurveying of highway bench marks and from the present elevation of shore platforms that have been uplifted in the late quaternary respectively topography of the coast ranges is in part a function of the age and buoyancy of the underlying subducted plate this is evident in the fact that the two highest topographic elements of the coast ranges the klamath mountains and the olympic mountains are underlain by youngest subducted oceanic crust the subducted blanco fracture zone in southernmost oregon is responsible for an age discontinuity of subducted crust under the klamath mountains the northern terminus of the topographically higher klamaths is offset to the north relative to the position of the underlying blanco fracture zone the offset being in the direction of migration of the fracture zone as dictated by relative plate motions vertical crustal velocities at the coast derived from bench mark surveys are as much as an order of magnitude greater than vertical crustal velocities derived from uplifted shore platforms this uplift rate discrepancy indicates that strain is accumulating on the plate margin to be released during the next interplate earthquake in a latitudinal sense average coast range topography is relatively high where bench mark derived short term vertical crustal velocites are highest because the shore platform vertical crustal velocites reflect longer term permanent uplift we infer that a small percentage of the interseismic strain that accumulates as rapid short term uplift is not recovered by subduction earthquakes but rather contributes to rock uplift of the coast ranges the conjecture that permanent rock uplift is related to interseismic uplift is consistent with the observation that those segments of the subduction zone subject to greater interseismic uplift rates are at approximately the same latitudes as those segments of the coast ranges that have higher magnitudes of rock uplift over the long term

regional diagenetic variation in norphlet sandstone implications for reservoir quality and the origin of porosity abstract although deeply buried 18 000 20 000 feet eolian and reworked marine norphlet arkose and subarkose in mississippi alabama and florida have been intensely studied by several workers fundamental questions remain regarding diagenetic controls on reservoir quality and the origin of porosity in spite of a regionally uniform framework composition of quartz albite and potassium feldspar the diagenetic character of the unit is variable on a scale ranging from individual laminations to single hydrocarbon producing fields to areas encompassing several fields or offshore blocks the presence or absence of clay minerals in various forms clearly is a dominant control on porosity permeability trends in deep reservoirs in mobile bay and offshore alabama and florida petrographic evidence for dissolution of pervasive authigenic carbonate and or evaporite minerals to produce high secondary porosity values is equivocal or absent although evidence exists for some secondary porosity much porosity appears to be relict primary porosity on a regional scale including both onshore and offshore areas sandstones with radial authigenic chlorite coats consistently have high porosity and permeability in mobile bay and offshore alabama the distribution of this form of chlorite may be controlled by the presence of precursor clay iron oxide grain coats the occurrence of these coats likely is related to environment of deposition for example reworked marine sands which constitute much of the tight zone in the upper norphlet in mobile bay and offshore alabama were deposited in an environment hostile to formation or preservation of syndepositional grain coats as also may have been the case in some subenvironments of the eolian system although chlorite is the dominant authigenic clay mineral in offshore areas illite is dominant in onshore areas sandstones with authigenic illite fibers and flakes typically have permeability values lower by an order of magnitude or more than those with authigenic chlorite in general chlorite is dominant in eastern areas of norphlet exploration and production and illite is dominant in western areas it is unlikely that provenance variations are of sufficient magnitude to account for the distribution of the two clay minerals particularly since illite or chlorite may dominate in different wells within the same onshore field variations in types of authigenic carbonate minerals and in degree and type of feldspar alteration suggest that differences in fluid composition and fluid flow paths relative to sub basins structural highs salt structures fault systems and depositional texture are important the occurrence of authigenic magnesium rich chlorite zeolites and an unusual ferroan magnesite cement indicates that fluids associated with evaporites and variations in the composition of evaporites or residual fluids may be responsible for variation in diagenetic character of the norphlet evaporites associated with these fluids include the underlying louann salt and evaporite systems within the norphlet

erosional response to northward propagating crustal thickening in the coastal ranges of the u s pacific northwest we measured basin scale erosion rates using cosmogenic 10 be concen trations in quartz from fluvial sediment in rivers draining the coastal mountain ranges of the u s pacific northwest between 40 and 47 n apparent erosion rates are 0 1 to 0 2 mm yr 1 throughout the oregon coast ranges north of 43 n and increase to the south to 0 6 to 1 1 mm yr 1 in the northern california coast ranges near 40 n we propose that these observations display the erosional response to northward migrating crustal thickening associated with subduction of the mendocino triple junction north south variations in erosion rate range elevation and metrics of landscape relief and steepness are consistent with the hypotheses that i their primary cause is northward migrating crustal thickening ii erosion rates are strongly controlled by topographic relief and weakly if at all controlled by climate and iii the dependence of erosion on relief is nonlinear and obeys a threshold relief relationship

how clay grain coats inhibit quartz cement and preserve porosity in deeply buried sandstones observations and experiments observations and hydrothermal experiments were used to derive new information about how clay grain coats inhibit quartz cement and preserve porosity in deeply buried sandstones samples of deeply buried porous sandstones with different types of clay coats were split in two coats removed from one of each pair of splits and grain surfaces inspected with scanning electron microscopy quartz grains in a fluvial deltaic sandstone buried to 115c had no visible authigenic quartz on grain surfaces cleaned of diagenetic chlorite coats though well developed overgrowths occurred on nearby naturally uncoated grains however in similar sandstones buried to 164c quartz grain surfaces exposed by chlorite coat removal were covered with small 5 m mainly anhedral syntaxial quartz overgrowths similar overgrowths were observed under various detrital and diagenetic clay coats in porous eolian sandstones buried to temperatures up to 215c we conclude that clay coats may retard quartz nucleation at moderate temperatures but at high temperatures many coats permit quartz nucleation and preserve porosity by limiting cement growth to investigate cement growth limitation mechanisms samples with coats removed were subjected to quartz cementing conditions in a hydrothermal reactor during experiments the naturally occurring small overgrowths on clay cleaned grains coalesced and grew suggesting that clay particles in coats inhibit cement growth by forming barriers to early overgrowth coalescence although the fraction of grain surface coverage is the primary control on cement inhibition by coats cement growth interference textures vary with coat type providing a mechanism by which coat composition may be a secondary control on inhibitory effectiveness in deeply buried sandstones quartz cement can fill significant microporosity within diagenetic chlorite coats potentially affecting mechanical and petrophysical rock properties

rock to sediment slope to sea with 10be rates of landscape change abstract measurements of cosmogenic nuclides predominately 10be allow new insights into the ways in which and the rates at which sediment is generated transported and deposited over timescales ranging from 103 to 106 years samples from rock exposures are used to estimate erosion rates at points on the landscape whereas samples of fluvial sediment provide estimates of basin scale rates of denudation integrated over 104 km2 nuclide data show that hilltop bare rock outcrops erode more slowly than basins as a whole suggesting the potential for relief to increase over time as well drained outcrops grow higher more elaborate experiments and interpretive models provide insight into the distribution of hillslope processes including the bedrock to soil conversion rate which appears to increase under shallow soil cover and then decrease under deeper soils changes in average nuclide activity down slopes can be used to estimate grain speed over millennia suggesting for example that sediment o

landslides threshold slopes and the survival of relict terrain in the wake of the mendocino triple junction establishing landscape response to uplift is critical for interpreting sediment fluxes hazard potential and topographic evolution we assess how landslides shape terrain in response to a wave of uplift traversing the northern california coast ranges united states in the wake of the mendocino triple junction we extracted knickpoints landslide erosion rates and topographic metrics across the region modified by mendocino triple junction migration landslide erosion rates mapped from aerial imagery are consistent with modeled uplift and exhumation while hillslope gradient is invariant across the region suggesting that landslides accommodate uplift as predicted by the threshold slope model landslides are concentrated along steepened channel reaches downstream of knickpoints generated by base level fall at channel outlets and limit slope angles and relief we find evidence that landslide derived coarse sediment delivery may suppress catchment wide channel incision and landscape denudation over the time required for the uplift wave to traverse the region we conclude that a landslide cover effect may provide a mechanism for the survival of relict terrain and orogenic relief in the northern californian coast ranges and elsewhere over millennial time scales

a 30 000 yr record of erosion rates from cosmogenic 10be in middle european river terraces abstract cosmogenic 10 be in river borne quartz sand records a time integrated erosion rate representative of an entire drainage basin when sequestered in a terrace of known age paleo erosion rates may be recovered from the nuclide content of the terrace material paleo erosion rates between 30 and 80 mm kyr are determined from terrace sediments 200 to 30 000 yr in age of the allier and dore rivers france and the meuse maas river the netherlands erosion rates determined from cosmogenic nuclides on terraces from the allier river are consistent with rates derived from the sedimentary fill of a lake in the allier catchment a strong decrease in cosmogenic nuclide derived erosion rates from terraces of the meuse river with late pleistocene to holocene age is observed the paleo erosion signal from cosmogenic nuclides records projection of the elevated late pleistocene erosion rate into the time integrated rates derived from middle european rivers

detecting the intertidal morphologic change using satellite data abstract the objectives of this study were a to generate an intertidal digital elevation model dem using waterlines extracted from landsat tm and in situ ground levelling data b to quantitatively estimate morphologic change from the generated dems for the years 1991 and 2000 and c to evaluate the chenier migration in the tidal flats of gomso bay korea on extracting the waterlines we considered the tidal flat environments such as tidal conditions remnant surface water suspended sediment and exposure time ground levelling was carried out along one line in 1991 and two lines in 2000 from the extracted waterlines and ground levelling data we succeeded in generating intertidal dems with an accuracy of 10 9 cm r m s overall and 7 3 cm r m s in the lower tidal flats the morphologic changes estimated by subtracting the two dems showed an erosion rate of 9 0 cm over 9 yr that corresponds to an annual mean morphologic change budget of 309 865 m 3 yr overall the gomso tidal flats can be defined as an erosion dominant environment the changes with respect to the sedimentary facies were also evaluated as a the sandy silt flat had a sedimentation rate of 3 4 cm over 9 yr that corresponds to an annual mean budget of 52 552 m 3 yr b the silty sand flat had a sedimentation rate of 14 3 cm over 9 yr that corresponds to a mean erosion of 197 927 m 3 yr and c the sand flat had a sedimentation rate of 11 8 cm over 9 yr that corresponds to a mean change of 58 808 m 3 yr the results comply with the general rules of sedimentology we also investigated the chenier migration which is the most dynamic geomorphologic change in the tidal flats chenier is usually composed by sand and shell as a result of coastal progradation in sand and it is dominantly fed by sediments transported by long shore currents the chenier was found to have migrated about 148 m landward over 6 yr the results demonstrate that satellite remote sensing is an efficient and effective tool for a long term morphologic change estimation in tidal flats

ephemeral crustal thickening at a triple junction the mendocino crustal conveyor as the north american crust interacts with the migrating mendocino triple junction the crust is first significantly thickened and then equivalently thinned over a distance of a few hundred kilometers within a time frame of 5 m y or less this process of ephemeral crustal thickening is proposed to result from viscous coupling between the northward migrating gorda slab and the base of north america south of the triple junction a time dependent thermal mechanical finite element model is developed to test this hypothesis of plate boundary tectonics results of the numerical simulations show patterns of crustal deformation consistent with the mapped sequence of folding and faulting in the area the observed crustal structure and triple junction regional seismicity and localized regions of crustal extension coincident with the position of a hypothesized lower crustal melt zone

arrested development erosional equilibrium in the southern sierra nevada california maintained by feedbacks between channel incision and hillslope sediment production tributary creeks of the southern sierra nevada have pronounced knickpoints that separate the landscape into an alternating sequence of gently sloped treads and steeply sloped risers these knickpoints and the surrounding stepped topography suggest that the landscape is still responding to pleistocene changes in base level on main stem rivers we tested this hypothesis using cosmogenic nuclides and uranium isotopes measured in stream sediment from widely distributed locations catchment scale erosion rates from the cosmogenic nuclides suggest that the treads are relict surfaces that have adjusted to a previous base level nevertheless erosion rates of relict interfluves are similar to canyon incision rates implying that relief is unchanging in the lower kings and san joaquin rivers in addition our results suggest that much of the southern sierra nevada is in a state of arrested development the landscape is not fully adjusted to and moreover is not responding to changes in base level lowering in the canyons we propose that this can be explained by a paucity of coarse sediment supply which fails to provide sufficient tools for bedrock channel incision at knickpoints we hypothesize that the lack of coarse sediment in channels is driven by intense weathering of the local granitic bedrock which reduces the size of sediment supplied from hillslopes to the channels our analysis highlights a feedback in which sediment size reduction due to weathering on hillslopes and transport in channels is both a key response to and control of bedrock channel incision and landscape adjustment to base level change

the influence of climate and microclimate aspect on soil creep efficiency cinder cone morphology and evolution along the eastern mediterranean golan heights although hillslope evolution has been subject to much investigation for more than a century the effect of climate on the morphology of soil mantled hillslopes remains poorly constrained in this study we perform numerical simulations of volcanic cinder cones in the golan heights eastern mediterranean to estimate soil transport efficiency across a significant north south gradient in mean annual precipitation 1100 to 500 mm we use the initial cinder cone morphology constrained by stratigraphy the modern hillslope form surveyed with sub meter accuracy and the eruption age based on 40ar 39ar chronology to predict the best fit value of the soil transport coefficient diffusivity based on a nonlinear transport model our results indicate that the best fit diffusivity k varies from 1 to 6 m2 ka 1 among the five cinder cones in our field area diffusivity k values vary systematically with precipitation and hillslope aspect specifically k is higher on south facing drier hillslopes and decreases with mean annual precipitation we interpret this climate dependency to reflect vegetation driven variations in apparent soil cohesion which increases with root network density and attenuation of rain splash and overland flow erosion which increases with vegetative ground cover to assess how vegetative root mass and ground cover vary with precipitation and aspect we quantified the spatial distribution of ndvi normalized difference vegetation index from aster satellite images and observed spatial variations that correlate with our calibrated values of k analysis of previously studied cinder cones in the usa can be used to extend our framework to arid domains this endeavor suggests a humped relationship between k and precipitation with maximum diffusivity at mean annual precipitation of 400 600 mm copyright 2017 john wiley sons ltd

pre requisites processes and prediction of chlorite grain coatings in petroleum reservoirs a review of subsurface examples abstract deeply buried reservoirs containing chlorite coated quartz sand grains commonly have higher than expected porosity and permeability although prediction of such positive anomalies still remains elusive a total of 54 published examples based on information and data from 62 scientific papers was collated quantification of some of the most common parameters including depositional environment age and latitude of sand deposition effect on reservoir quality and chemical composition of chlorite is presented the dataset indicates that chlorite coats are found in sandstones deposited in a range of depositional environments but most commonly occur in delta related environments 44 with fluvial environments the second most common 19 age relationships indicate that there is an overall exploration bias in published examples with chlorite coats becoming increasingly common through time the latitude at the time of deposition of sands with chlorite coats is wide 60 n 60 s and indicates that temperate and tropical climates are important for the generation of this clay mineral chlorite can have a variable effect on reservoir quality but is typically positive iron rich chlorites occur overwhelmingly in coastal environments while mixed iron and magnesium rich chlorites are principally found in marine and terrestrial sandstones analysis of these factors suggests that hinterland geology basinal soil development and geochemical weathering and proximity to river systems are essential to the formation of chlorite precursor phases these characteristics have been combined to define situations where chlorite coats were more likely or more unlikely to form these parameters will provide insights into the formation of chlorite and to further refine predictive models for the presence or absence of chlorite coated sandstones

interpreting quaternary uplift rates at the mendocino triple junction northern california from uplifted marine terraces analysis of the altitudinal spacing of 14 flights of marine terraces indicates a spatial pattern of varying uplift rates that agrees with that determined from previously dated terraces for the past 3 81 ka and temporal changes in uplift rates from 1 m ka to 3 5 m ka that may reflect response to changes in tectonic regime during passage of the mendocino triple junction mtj a possible mechanism for regional uplift is growth of a slab window south of the mtj the region of most rapid uplift is 25 43 km south of the mtj immediately south of the northern boundary of the slab window the coastline is tilted upward to the south in the region directly above the southern edge of the subducted gorda plate at point delgada 55 km south of the present mtj where the northern edge of the slab window passes approximately 300 ka uplift rates have been 1 2 m ka for at least 330 ka more than 1 4 m y after passage of the southern edge of the subducted slab at the mendocino coast uplift rates have been less than 0 4 m ka for at least 330 ka

tectonic uplift threshold hillslopes and denudation rates in a developing mountain range studies across a broad range of drainage basins have established a positive correlation between mean slope gradient and denudation rates it has been suggested however that this relationship breaks down for catchments where slopes are at their threshold angle of stability because in such cases denudation is controlled by the rate of tectonic uplift through the rate of channel incision and frequency of slope failure this mechanism is evaluated for the san bernardino mountains california a nascent range that incorporates both threshold hillslopes and remnants of pre uplift topography concentrations of in situ produced cosmogenic 10 be in alluvial sediments are used to quantify catchment wide denudation rates and show a broadly linear relationship with mean slope gradient up to 30 above this value denudation rates vary substantially for similar mean slope gradients we propose that this decoupling in the slope gradient denudation rate relationship marks the emergence of threshold topography and coincides with the transition from transport limited to detachment limited denudation the survival in the san bernardino mountains of surfaces formed prior to uplift provides information on the topographic evolution of the range in particular the transition from slope gradient dependent rates of denudation to a regime where denudation rates are controlled by rates of tectonic uplift this type of transition may represent a general model for the denudational response to orogenic uplift and topographic evolution during the early stages of mountain building

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

diagenesis of an overmature gas reservoir the spiro sand of the arkoma basin usa abstract the spiro sand is a laterally extensive thin sandstone of earliest atokan pennsylvanian age that forms a major natural gas reservoir in the western arkoma basin oklahoma petrographic analysis revelas a variety of diagenetic alterations the majority of which occurred during moderate to deep burial early diagenetic processes include calcite cementation and the formation of fe clay mineral peloids and coatings around quartz framework grains these clays which underwent transformation to well crystallized chamosite polytype lb 90 c these clays are particularly abundant in medium grained channel sandstones whereas illitic clays are predominant in fine grained interchannel sandstones subsequent to mechanical compaction saddle ankerite precipitated in the reservoir at temperatures in excess of 70 c crude oil collected in favourable structural locations during and after ankeritization whereas hydrocarbons apparently halted inorganic diagenesis in oil saturated zones cementation continued in the underlying water saturated zones as reservoir temperatures increased further hydrocarbons were cracked and a solid pyrobitumen residue remained in the reservoir at temperatures exceeding 140 150 c non syntaxial quartz cement ferroan calcite and traces of dickite locally reduced the reservoir quality local secondary porosity was created by carbonate cement dissolution this alteration post dated hydrocarbon emplacement and is probably related to late stage infiltration of freshwater along leaky faults the study shows that the spiro sandstone locally retained excellent porosites despite deep burial and thermal conditions that correspond to the zone of incipient very low grade metamorphism

stochastic processes of soil production and transport erosion rates topographic variation and cosmogenic nuclides in the oregon coast range landscapes in areas of active uplift and erosion can only remain soil mantled if the local production of soil equals or exceeds the local erosion rate the soil production rate varies with soil depth hence local variation in soil depth may provide clues about spatial variation in erosion rates if uplift and the consequent erosion rates are sufficiently uniform in space and time then there will be tendency toward equilibrium landforms shaped by the erosional processes soil mantle thickness would adjust such that soil production matched the erosion previous work in the oregon coast range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported we quantify how soil production varies with soil thickness in the southern oregon coast range and explore further the issue of landscape equilibrium apparent soil production is determined to be an inverse exponential function of soil depth with a maximum inferred production rate of 268 m ma 1 occurring under zero soil depth this rate depends however on the degree of weathering of the underlying bedrock the stochastic and large scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth the spatial variation of soil depth neither supports nor rejects equilibrium morphology our observed catchment averaged erosion rate of 117 m ma 1 is however similar to that estimated for the region by others and to soil production rates under thin and intermediate soils typical for the steep ridges we suggest that portions of the oregon coast range may be eroding at roughly the same rate but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle copyright 2001 john wiley sons ltd

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

timing of hydrocarbon generation and accumulation in fault bounded compartments in the norphlet formation offshore alabama abstract analysis of the variation in depth of the gas water contacts in the bon secour bay and lower mobile bay mary ann fields of offshore mobile bay alabama together with fault seal analysis implies that some of the pre cretaceous faults in these fields must be sealing it is also likely that the large post cretaceous lower mobile bay fault is dip leaking the gas currently reservoired in the norphlet formation has most likely been produced by thermal degradation of oils generated in the overlying jurassic lower smackover formation for a range of heat flow models appropriate for this area of the gulf coast the onset of gas generation defined as the time at which 10 of the maximum possible amount of gas has been generated occurs at 104 5 10 ma the error bounds in this estimate are the 90 confidence limits which were calculated by assuming that the times of onset of gas generation are log normally distributed the time of onset of gas generation is younger than the age of the sealing faults in the area hence it is likely that gas generation occurred in situ in the norphlet formation with re migration occurring during the development of the post cretaceous lower mobile bay fault

paleoerosion rates from cosmogenic 10be in a 1 3 ma terrace sequence response of the river meuse to changes in climate and rock uplift abstract river borne quartz carries a cosmogenic nuclide memory that is a function of the catchment wide erosion rate this record may be preserved in fluvial deposits such as river terraces if the age of a terrace is independently known and transport time in the river system is relatively short then the upstream erosion rate at the time of terrace deposition can be determined we have used cosmogenic nuclides to date river terraces in the lower meuse catchment the netherlands and to obtain a 1 3 ma record of paleoerosion rates in a 104 km2 drainage basin comprising the ardennes mountains paleoerosion rates were uniform within the range of 25 35 mm ka from 1 3 to 0 7 ma after 0 7 ma erosion rates have increased progressively to late pleistocene values of around 80 mm ka around 0 7 ma both climatic and tectonic boundary conditions changed the amplitude and duration of climate cycles increased significantly resulting in long periods of sustained low temperatures in the meuse catchment in additio

estimating rates of denudation using cosmogenic isotope abundances in sediment we propose as a testable hypothesis a basin scale approach for interpreting the abundance of in situ produced cosmogenic isotopes an approach which considers explicitly both the isotope and sediment flux through a drainage basin unlike most existing models which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on earth s surface our model is designed for interpreting isotope abundance in sediment because sediment is a mixture of materials in favourable cases derived from throughout a drainage basin we suggest that measured isotope abundances may reflect spatially averaged rates of erosion we investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed

geomorphic response to uplift along the dragon s back pressure ridge carrizo plain california we used high resolution topography geomorphic mapping of active surface processes and geologic mapping to study the topographic and erosional response of small drainage basins to rock uplift along the dragon s back pressure ridge along the san andreas fault in the carrizo plain california we infer the history of deformation experienced by 40 small drainage basins formed in poorly consolidated sedimentary rocks a space for time substitution directly images the erosional and topographic responses to deformation progressive deformation and rock uplift are accompanied by increases in channel steepness and basin relief as uplift ceases channel concavity rapidly increases causing channels to undercut hillslopes this undercutting promotes the consumption of hillslopes by landsliding this undercutting also causes basin relief to be greatest after uplift has stopped this analysis indicates that channels of the dragon s back pressure ridge respond to changes in rock uplift rates over thousands of years whereas hillslope processes may take more than an order of magnitude longer to adjust to changes in rock uplift rates our study directly measures changes in erosional processes due to the initiation and cessation of rock uplift which can typically only be inferred using numerical models by direct field observations

controls on the seasonal deformation of slow moving landslides article history precipitation drives seasonal velocity changes in slow moving landslides by increasing pore water pressure and reducing the effective normal stress along basal shear zones this pressure change is often modeled as a pore water pressure wave that diffuses through the landslide body such that the minimum time required for landslides to respond to rainfall should vary as the square of landslide depth which often approximates the saturated thickness and inversely with hydraulic diffusivity here we assess this model with new observations from the landslide prone eel river catchment northern california using satellite radar interferometry insar time series precipitation data and high resolution topographic data from airborne lidar we quantify the seasonal dynamics of 10 slow moving landslides which share the same lithologic tectonic and mediterranean climate conditions these slope failures have areas ranging from 0 16 to 3 1 km 2

tectonic uplift of a middle wisconsin marine platform near the mendocino triple junction california an uplifted wave cut marine platform eroded across bedrock of the franciscan complex at point delgada northern california is overlain by 0 5 to 5 m of wave worked pea gravel which is in turn directly overlain by fluvial gravel and silt deposited as alluvial fans woody plant debris at the base of the fluvial deposits includes cones of brewer spruce picea breweriana which today are found only at higher elevations and latitudes fossil wood debris from this horizon yields a 14c date of 44 800 1 300 yr the 44 800 yr radiocarbon age for the base of the fluvial deposits establishes an approximate age for the immediately underlying marine gravels and wave cut platform we tentatively correlate this terrace with the middle wisconsin high sea level stand at 37 m dated at about 45 000 yr b p if this age is correct the tectonic uplift since middle wisconsin time has been 44 m and the average rate of uplift has been at least 1 0 m 1 000 yr this relatively high rate is probably related to interaction among the pacific gorda and north american plates at the mendocino triple junction

implications from sulfur isotopes of the nakhla meteorite for the origin of sulfate on mars abstract the isotope geochemistry of sulfur in the snc shergottite nakhlite chassignite meteorites may carry important implications for the origin and chemistry of sulfates and sulfides in the martian surface and subsurface we report measurements of the sulfur isotope composition for three sulfur bearing components of the nakhla meteorite these results yield a negative 33 s signal of 1 25 and a near zero 36 s signal for total sulfate as well as a small nonzero 33 s of 0 09 for sulfide phases the 33 s of total sulfate measured here is more negative than the 33 s reported previously for water soluble sulfate and points to sulfur isotopic heterogeneity in the sulfate of nakhla current understanding of mass independent isotope effects associated with sulfur oxidation reactions rules out hydrothermal oxidation mechanisms for producing nonzero 33 s and points to a significant role for photochemical effects including hyperfine chemistry likely located in the martian atmosphere the near zero 36 s signal allows for the possibility of hyperfine chemistry because of the relationship between snc sulfate and the sulfate deposits seen on mars these results place constraints on the generation of sulfur vi at the martian surface and provide a case for future direct measurements of 33 s and 36 s of martian sulfate

geochemical and tectonic uplift controls on rock nitrogen inputs across terrestrial ecosystems rock contains 99 of earth s reactive nitrogen n but questions remain over the direct importance of rock n weathering inputs to terrestrial biogeochemical cycling here we investigate the factors that regulate rock n abundance and develop a new model for quantifying rock n mobilization fluxes across desert to temperate rainforest ecosystems in california usa we analyzed the n content of 968 rock samples from 531 locations and compiled 178 cosmogenically derived denudation estimates from across the region to identify landscapes and ecosystems where rocks account for a significant fraction of terrestrial n inputs strong coherence between rock n content and geophysical factors such as protolith i e parent rock grain size and thermal history are observed a spatial model that combines rock geochemistry with lithology and topography demonstrates that average rock n reservoirs range from 0 18 to 1 2 kg n m 3 80 to 534 mg n kg 1 across the nine geomorphic provinces of california and estimates a rock n denudation flux of 20 92 gg yr 1 across the entire study area natural atmospheric inputs 140 gg yr 1 the model highlights regional differences in rock n mobilization and points to the coast ranges transverse ranges and the klamath mountains as regions where rock n could contribute meaningfully to ecosystem n cycling contrasting these data to global compilations suggests that our findings are broadly applicable beyond california and that the n abundance and variability in rock are well constrained across most of the earth system

combining digital elevation data srtm aster high resolution satellite imagery quickbird and gis for geomorphological mapping a multi component case study on mediterranean karst in central crete abstract remote sensing data have become more and more popular for geomorphological investigations because their steadily increasing level of detail and accessibility opens up new potentials in this context this paper examines the application and quality of digital elevation models srtm and aster dems high resolution satellite imagery quickbird and gis techniques for the detection and mapping of karst landforms mainly enclosed depressions at different scales in the ida mountains of central crete besides discussing methodological issues and evaluating suitability potentials we conducted an exemplary case study based on spatial analysis of the regional karst morphology different input datasets and processing methods are applied gis based analysis land cover classification raster calculations etc in order to carry out an area wide surveying and mapping of karst depressions the findings are supported and validated by auxiliary field studies due to the level of detail and occasional data errors an exclusive use of satellite imagery or digital elevation models for automatic karst landform detection performs insufficiently our results demonstrate that mapping karst features through remote sensing is significantly dependent on scale of interest existing environmental conditions and data quality a semi automatic data integration approach on the basis of digital datasets generated by combined satellite image processing and dem analysis yields the best results especially when indirect karst indicating variables like iron oxide rich sediments are included as detection criteria the multi component application presented in this paper provides a time saving and effective tool for meso to macro scale object detection and extensive study areas however the potential of fully automated karst feature mapping still needs to be explored in future work concerning the spatial dimension of karstification in central crete the gis based results allow differentiating further geomorphological characteristics e g by indicating a significant altitudinal change of karst forms within the study area size and shape of depressions dolines uvalas and poljes vary considerably due to the geological setting climatic impacts neotectonics and elevation

late quaternary stream incision and uplift in the forearc of the cascadia subduction zone western oregon documentation of a latest pleistocene earliest holocene episode of strath formation and fluvial aggradation in the oregon coast range provides a datum from which long term bedrock stream incision rates are determined variations in long term incision rates probably reflect cumulative differential uplift in the forearc of the cascadia subduction zone although factors such as bedrock and climatic controls and isostatic adjustments to erosion obscure the precise relationship between surface uplift and stream incision patterns of differential incision are most striking near the latitude of newport where a steep gradient divides a region of higher rates 0 6 0 9 mm yr in the northern coast range from a region of lower rates 0 1 0 3 mm yr in the central coast range the steep incision gradient is nearly coincident with abrupt changes in marine terrace 80 125 kyr uplift rates the locations of quaternary faults and the southern flank of a saddle of low historic 40 70 years uplift the exact causes of these variable patterns of incision uplift are unknown analogies with uplift patterns in other subduction zones and comparisons with other neotectonic data in the region indicate that patterns of differential incision probably are caused by variations in permanent strain accumulation along the cascadia subduction zone such variations may be related to differences in seismic moment release during individual earthquakes to changes in plate geometry or rates of wedge accretion to segmentation of earthquake ruptures and or to deformation on active structures in the north american plate and accretionary wedge

kinematics of earthflows in the northern california coast ranges using satellite interferometry abstract slow moving landslides exhibit persistent downslope motion with variations in velocity driven by transient stress perturbations along the sliding surface here we use satellite insar and high resolution topographic data to identify 50 slow moving landslides in the northern california coast ranges and monitor their seasonal kinematics over 4 years these landslides have similar mechanical properties and are subject to the same external forcings which allows us to explore geometrical controls on kinematics to overcome errors associated with large deformation gradients we incorporate a deformation model in the insar processing that enables us to generate deformation time series we test our novel methodology using a synthetic deformation time series confirming our ability to resolve seasonal velocity patterns time series analysis of four representative landslides reveals that seasonal velocity changes are characterized by comparatively rapid acceleration and gradual deceleration each slide displays distinct kinematic zones with different mean velocities although velocity changes appear to occur synchronously along the landslide body over seasonal timescales because these deformation patterns are sensitive to subsurface geometry we employ a commonly used non newtonian viscous flow law to infer slide thickness and find that these slides likely exhibit a highly variable thickness and an irregular i e rough and non planar basal sliding surface our results suggest that slide geometry controls long term motion but does not strongly regulate their response to seasonal stress perturbations