cenozoic lateritic weathering and erosion history of peninsular india from 40 ar 39 ar dating of supergene k mn oxides since deccan traps extrusion 65 ma ago thick weathering mantles have developed over peninsular india on both the western coastal lowland and adjacent plateau separated by the western ghats escarpment manganiferous lateritic profiles formed by supergene weathering of late archean manganiferous protores are exposed on paleolandsurface remnants on both sides of the escarpment petrological and geochemical characterizations of samples from those mn lateritic profiles allowed identifying cryptomelane k mn oxide dated by 40ar 39ar geochronology the ages obtained document major weathering periods ca 53 50 ma and ca 37 23 ma in the highland and ca 47 45 ma ca 24 19 ma and discrete weathering pulses at 9 ma and 2 5 ma in the lowland old ages of the highland 53 50 ma and the lowland 47 45 ma indicate synchronous lateritic weathering across the escarpment at a time the peninsula started to drift across the equatorial belt intense weathering periods at ca 53 45 and ca 37 23 ma are interpreted to reflect the early eocene climatic optimum and the onset of asian monsoon regimes respectively the ages further indicate that most of the dissection of the highland must have taken place after 23 ma whereas the lowland was weakly incised essentially after 19 ma our results also document divergent erosion and weathering histories of the lowland and the highland after the eocene suggesting installation of a dual climatic regime across the western ghats escarpment

the dissolution kinetics of a granite and its minerals implications for comparison between laboratory and field dissolution rates the present study compares the dissolution rates of plagioclase microcline and biotite chlorite from a bulk granite to the dissolution rates of the same minerals in mineral rich fractions that were separated from the granite sample the dissolution rate of plagioclase is enhanced with time as a result of exposure of its surface sites due to the removal of an iron oxide coating removal of the iron coating was slower in the experiment with the bulk granite than in the mineral rich fractions due to a higher fe concentration from biotite dissolution as a result the increase in plagioclase dissolution rate was initially slower in the experiment with the bulk granite the measured steady state dissolution rates of both plagioclase 6 2 1 2 10 11 mol g 1 s 1 and microcline 1 6 0 3 10 11 mol g 1 s 1 were the same in experiments conducted with the plagioclase rich fraction the alkali feldspar rich fraction and the bulk granite based on the observed release rates of the major elements we suggest that the biotite chlorite rich fraction dissolved non congruently under near equilibrium conditions in contrast the biotite and chlorite within the bulk granite sample dissolved congruently under far from equilibrium conditions these differences result from variations in the degree of saturation of the solutions with respect to both the dissolving biotite chlorite and to nontronite which probably was precipitating during dissolution of the biotite and chlorite rich fraction following drying of the bulk granite the dissolution rate of biotite was significantly enhanced whereas the dissolution rate of plagioclase decreased the presence of coatings wetting and drying cycles and near equilibrium conditions all significantly affect mineral dissolution rates in the field in comparison to the dissolution rate of fully wetted clean minerals under far from equilibrium laboratory conditions to bridge the gap between the field and the laboratory mineral dissolution rates these effects on dissolution rate should be further studied

10be and 26al evidence for exceptionally low rates of australian bedrock erosion and the likely existence of pre pleistocene landscapes analysis of in situ produced 10be and 26al demonstrate that some australian inselbergs granitic domes are among the most stable geomorphic surfaces in the world eroding at rates as low as 0 6 m myr twenty isotopic analyses of ten samples suggest that the bare bedrock tops of these isolated granitic domes have been exposed to cosmic radiation for at least 0 5 myr and are eroding at a mean model rate less than 0 7 0 1 m myr n 6 isotopic analyses of samples collected from the top of mt wudinna little wudinna and yarwondutta rock are most consistent with continuous exposure during erosion on the other hand samples collected from the flanks of some domes and the tops of other domes have isotopic abundances suggestive of complex exposure histories including burial and reexposure these unique isotopic data provide the first quantitative information for evaluating longstanding but previously untested hypotheses regarding the antiquity and development of these enigmatic landforms and indicate that some eyre peninsula inselbergs are probably relict features of pre pleistocene landscapes

temporally and spatially uniform rates of erosion in the southern appalachian great smoky mountains we measured 1 0 be in fluvial sediment samples n 27 from eight great smoky mountain drainages 1 330 km 2 results suggest spatially homogeneous sediment generation on the 10 4 10 5 yr time scale and 100 km 2 spatial scale at 73 11 t km 2 yr 1 equivalent to 27 4 m m y of bedrock erosion this rate is consistent with rates derived from fission track long term sediment budget and sediment yield data all of which indicate that the great smoky mountains and the southern appalachians eroded during the mesozoic and cenozoic at 30 m m y in contrast unroofing rates during the paleozoic orogenic events that formed the appalachian mountains were higher 10 2 m m y erosion rates decreased after termination of tectonically driven uplift enabling the survival of this ancient mountain belt with its deep crustal root as an isostatically maintained feature in the contemporary landscape

strain accumulation in the santa barbara channel 1970 1988 geodetic observations between 1970 and 1988 indicate appreciable strain accumulation in the santa barbara channel california eleven line length changes from a six station geodetic network spanning the eastern two thirds of the channel were determined from electronic distance measurements in 1970 1971 and global positioning system observations in 1987 1988 within this network the strains observed are spatially nonuniform in the easternmost channel the strain is nearly uniaxial with convergence of 6 4 0 9 mm yr oriented n25 e 5 this direction is consistent with the seismicity which is dominated by thrust mechanisms with p axes directed to the northeast in the central channel the strain is less well determined but appears to include a significant component of shear that is left lateral when resolved on an east west plane

subsidence compaction and gravity sliding implications for 3d geometry dynamic rupture and seismic hazard of active basin bounding faults in southern california in southern california high rates of measured geodetic shortening occur where active basin bounding faults thrust early cenozoic rocks over young uncon solidated sediments this implies that compaction subsidence and other nonelastic processes of footwall deformation may play an important role in contributing to the high rates of observed crustal strain even in the absence of active tectonic short ening sediment compaction alone can produce surficial motions that mimic deep fault slip or elastic strain accumulation differential compaction and subsidence of footwall sediments relative to hanging wall rocks can lead to increased vertical sep aration basinward collapse and fault rotation about horizontal axes such effects contribute to net horizontal and vertical motions in both geologic and geodetic data and if not properly accounted for result in incorrect estimates of the inferred seismic hazard subsidence and compaction also increase the potential for gravity sliding toward the basin and the development of significant nonplanar 3d fault geometry a prime example occurs along the san cayetano fault that bounds the eastern ventura basin at shallow levels a large thrust sheet the modelo lobe with low dip extends out in front of the more steeply dipping planar fault segment by over 4 km is nearly 2 km thick and occupies over 60 cubic km this geometry is strongly indicative of gravity driven failure resulting from hanging wall uplift basinward tilt and collapse enhanced by footwall subsidence and compaction failure of this mega slide off the hanging wall block most likely occurred within the rincon formation a thick ductile shale sequence that often accommodates detachment slip this 3d geometry has significant implications for how the fault may behave during dynamic rupture and implies that additional care should be taken in extrapolating near surface measure ments or estimates of fault slip and dip to seismogenic depths

scales of stress heterogeneity near active faults in the santa barbara channel southern california the santa barbara channel represents the offshore portion of the ventura basin in southern california ongoing transpression related to a regional left step in the san andreas fault has led to the formation of e w trending en echelon fault systems that accommodate localized shortening across the basin recent studies have suggested that faults within the channel could be capable of a multisegment rupture and producing a m w 7 7 8 1 tsunamigenic earthquake however dynamic rupture models producing these results do not account for stress heterogeneity with only sparse information available on the stress field in this region further borehole derived stress constraints are essential for obtaining a more comprehensive understanding of the hazards related to the complex fault systems we used caliper logs from 19 wells obtained from industry to identify stress induced borehole breakouts beneath the holly and gail oil platforms in the channel our newly developed forward modeling technique provides constraints on the orientations and relative magnitudes of the three principal stresses at gail we determine a reverse faulting stress regime s hmax 1 7 s hmin 1 6 sv 1 0 and an s hmax azimuth of n45 e our results are consistent with local structures which reflect deeper regional scale trends and with similar studies onshore nearby at holly an s hmax rotation from n36 w to n57 e occurs across 100 m depth in a single well and differs from nearby results indicating that short length scale 10 km laterally and 1 km in depth stress heterogeneity is associated with complex changes in fault geometry

engineering and geological characteristics of granite weathering profiles in south china granite weathering profiles are widely distributed in south china their engineering and geological characteristics are major geotechnical subjects that are important in the design and construction of civil engineering projects this paper presents a summary of the weathering characteristics and zoning of granite weathering profiles in south china and discusses their engineering and geological properties a five grade scheme has been adopted in the zoning of a granite weathering profile studies have shown that the completely weathered granites cwg in south china have the following characteristics low moisture content low to medium plasticity w l 22 5 39 0 i p 6 5 11 8 medium void ratio 0 36 1 29 weak shrinkage and medium compressibility a 1 2 0 24 0 8 mpa 1 and high shear strength phi 20 30degrees c 20 40 kpa the cwgs are usually at a low or high plastic state and most of them are over consolidated soils a majority of the physical and mechanical properties have good statistical correlations with the degree of weathering the data presented in the paper are important in geotechnical engineering projects such as slope stability evaluation in china c 2002 elsevier science ltd all rights reserved

measuring vertical tectonic motion at the intersection of the santa cruz catalina ridge and northern channel islands platform california continental borderland using submerged paleoshorelines we used submerged paleoshorelines as strain markers to investigate holocene and late pleistocene vertical tectonic movement at the intersection of the offshore santa cruz catalina ridge with the southern boundary of the western transverse ranges within the california continental borderland past submerged shoreline positions were identified using high resolution multibeam bathymetry side scan sonar submersible observations and the presence of intertidal and subtidal invertebrate fossils numerous accelerator mass spectrometry ams 14 c ages of shells from these paleoshorelines were found to be between 27 000 yr radiocarbon rc and 11 500 yr before present indicative of shoreline colonization during and following the last glacial maximum lgm establishing these paleoshorelines as a usable datum for measuring vertical change since this time removal of the nontectonic component of vertical change using an ice volume equivalent eustatic sea level compilation indicates between 20 and 45 m of uplift of the eastern part of the northern channel islands block since the lgm lowstand resulting in an uplift rate of 1 50 0 59 mm yr over the last 23 k y this rate closely matches uplift predicted by published slip rates for the channel islands thrust which underlies the northern channel islands platform results from post lgm shoreline features on pilgrim banks are somewhat more ambiguous submarine paleoshoreline uplift together with the extensive upper crustal fold thrust style of deformation illustrates the transpressional interaction of the borderland and the western transverse ranges blocks where the santa cruz catalina ridge and northern channel islands intersect

re assessment of chemical weathering indices case study on pyroclastic rocks of hong kong abstract quantitative and objective characterization of weathered states of rock by means of chemical weathering indices has significant potential in ground investigation practice this paper reviews more than thirty different chemical indices and re assesses their variations along a weathered profile developed over pyroclastic rocks under subtropical conditions chemical weathering indices are principally based on the basic assumption that distributions of chemical elements as well as loss on ignition loi content along the profile are mainly regulated by the degree of weathering however this study clearly demonstrates that the behavior of chemical elements and loi during weathering depend not only on the degree of weathering but also on microenvironmental conditions that control the type and abundance of clay minerals and sesquioxides and thus determine the level of heterogeneity of the profile it is suggested that signatures of chemical weathering should be used to establish a framework for the interpretation of the heterogeneity level and the prediction of variability in engineering properties rather than for quick classifications using chemical weathering indices

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

relative dating of quaternary deposits based on p wave velocities in weathered granitic clasts abstract a new quantitative reproducible method for determining relative ages of unconsolidated quaternary deposits containing granitic clasts has been developed and tested the technique makes use of a microseismic timer to determine the compressional wave velocity clast sound velocity in each clast of a group chosen from a single deposit from these data a group mean velocity is determined that is proportional to the age of the deposit the youngest deposits having the highest velocities the clast sound velocity method was used to study quaternary deposits in the san gabriel valley and san gabriel mountains california using a previously proposed four part age classification for the deposits the clast sound velocity group means for the four age groups were found to be statistically separable at better than 99 confidence a velocity age correlation curve was determined for these deposits using two radiocarbon dates and one paleomagnetic determination this curve suggests that the clast sound velocity method may be used to determine ages of deposits up to one million years old when calibrated with sufficient radiometric dates and may also be used as a tool for correlating undated deposits

regolith production and chemical weathering of granitic rocks in central chile abstract we have evaluated the long term chemical and physical weathering mass balance of an anomalously thick saprolite profile 30 m thickness developed in granitic rocks near curacavi coastal range of central chile the results of geochemical mass balance calculations for the regolith profile point to a moderate depletion for na and sr due to the plagioclase dissolution and precipitation of kaolinite furthermore silicon shows a predominantly constant behaviour along the profile that is indicative of incongruent weathering of plagioclase strongly suggesting that quartz dissolution conditions are not reached in addition low depletion of k mg ca rb and ba in the saprolite indicates a low degree of k feldspar biotite and hornblende weathering denudation rates calculated using cosmogenic 10be data range from 20 to 70 m ma if the saprolite thickness has reached a steady state condition the reported denudation rates lead to mineral residence times in the upper part of the saprolite profile of about 0 5 to 1 8 ma with such duration a higher weathering degree than observed at curacavi would be expected this apparent contradiction might be explained if all of the weatherable plagioclase has been dissolved under the present day precipitation and temperature conditions of the curacavi region therefore we propose that the curacavi profile could be in local equilibrium with respect to the weatherable fraction of plagioclase a local equilibrium regime may be reached when the overall degree of depletion is small in a weathering profile uniform elemental distribution and low weathering degree in the thick weathering profile at curacavi defy the traditional notion of weathering regimes and reveal the importance of exploratory studies in order to better understand weathering process in mediterranean and semi arid climate regions

the santa barbara california earthquake of 13 august 1978 the 5 1 m l santa barbara earthquake of 13 august 1978 occurred at 22h54m 52 8s utc the epicenter was located 3 km southeast of santa barbara at 34 23 9 n latitude and 119 40 9 w longitude with a focal depth of 12 7 km the main shock was followed between 13 august and 30 september by 373 aftershocks that were located with the caltech usgs array the aftershock zone extended 12 km wnw from the epicenter and was 6 km wide in the n s direction and it had a very clear temporal development during the first 20 min of activity all the aftershocks were located in a cluster 7 km wnw of the main shock epicenter during the next 24 hr the aftershock zone grew to 11 km in the wnw direction and 4 km in the n s direction during succeeding weeks the zone extended to 12 by 6 km this temporal spatial development relative to the main shock epicenter may indicate that the initial rupture propagated 7 km unilaterally to the wnw and the initial rupture plane may have been considerably smaller than the eventual aftershock zone this smaller area suggests that the stress drop may have been significantly greater than that derived from the final aftershock zone in cross section the aftershock hypocenters outline a nearly horizontal plane dipping 15 or less at 13 km depth the main shock focal mechanism indicates nne ssw compression and vertical extension the preferred fault plane strikes n80 w and dips 26 nne indicating north over south thrusting with a component of left lateral movement focal mechanisms for 40 aftershocks also indicate compression in the general n s direction for most of these events the north dipping nodal plane dips between 7 and 45 with most dipping 25 or more which is significantly steeper than the plane delineated by the hypocenters themselves these observations are consistent with a tectonic model in which much of the slip during the santa barbara earthquake occurred on a nearly horizontal plane the after shocks then might represent movement on a complex series of imbricate thrust faults that flatten into the plane of primary slip hence the santa barbara earthquake may be taken as evidence for mid crustal horizontal shearing in the western transverse ranges

map restoration of folded and faulted late cenozoic strata across the oak ridge fault onshore and offshore ventura basin california the ventura basin lies within the east west trending active fold and thrust belt of the western transverse ranges california this basin has been the site of significant earthquakes on structures within it and bordering it the purpose of our study is to identify the main structures in the basin and its borders and to quantify their rate of deformation our study includes the onshore and offshore ventura basin the arcuate basin bounding oak ridge reverse fault and the oxnard shelf to the south shortening fault slip and crustal block motions were studied using a three dimensional map restoration technique structure contour maps on the 6 ma surface and other horizons were digitized and restored to the initial horizontal state by unfolding them using the computer program unfold and then fitting the unfolded surfaces across faults comparing the restored and present configuration allows us to estimate total net finite displacements relative to a fixed horizontal reference line average post 5 ma shortening rates estimated from our restoration are slower than both post 1 ma rates and present rates determined by global positioning systems most shortening due to folding in the onshore basin is post 1 ma although slip on the oak ridge fault has occurred both before and after 1 ma displacement due to faulting and folding includes left lateral strike slip motion on the northeast southwest coastal segment of the oak ridge fault and associated clockwise rotation of the adjacent ventura basin the oxnard shelf is bordered to the south by mountains and islands that have been previously interpreted as folds above thrust fault ramps this onshore offshore block moves as one continuous thrust sheet similarly beyond the well studied onshore fault a kinematically continuous offshore oak ridge mid channel left oblique fault system is interpreted to continue at least an additional 100 km westward beneath the santa barbara channel

calibrating a long term meteoric 10be accumulation rate in soil 1 using 13 samples collected from a 4 1 meter profile in a well dated and stable new zealand fluvial terrace we present the first long term accumulation rate for meteoric 10 be in soil 1 68 to 1 72 10 6 at cm 2 yr integrated over the past 18 ka site specific accumulation data such as these are prerequisite to the application of meteoric 10 be in surface process studies our data begin the process of calibrating long term meteoric 10 be delivery rates across latitude and precipitation gradients our integrated rate is lower than contemporary meteoric 10 be fluxes measured in new zealand rainfall suggesting that long term average precipitation dust flux or both at this site were less than modern values with accurately calibrated long term delivery rates such as this meteoric 10 be will be a powerful tool for studying rates of landscape change in environments where other cosmogenic nuclides such as in situ 10 be cannot be used

strain accumulation in southern california 1973 1980 frequent surveys of seven trilateration networks in southern california over the interval 1973 1980 suggest that a regional increment in strain may have occurred in 1978 1979 prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north south compression this secular trend was interrupted sometime in 1978 1979 by an increment in both north south and east west extension in five of the seven networks the onset of this change appears to have occurred first in the networks farthest south the changes occurred without any unusual seismicity within the networks but the overall seismicity in southern california was unusually low prior to and has been unusually high since the occurrence the average principal strain rates for the seven networks in the 1973 1980 interval are 0 17 mu strain yr north south contraction and 0 08 mu strain yr east west extension although the observed increment in strain could be related to unidentifed systematic error in the measuring system a careful review of the measurements and comparison with three other measuring systems reveal no appreciable cumulative systematic error

10be distribution in soils from merced river terraces california abstract the distribution and residence time of cosmogenic 10 be in clay rich soil horizons is fundamental to understanding and modelling the migration of 10 be on terrestrial sediments and in groundwater solutions we have analyzed seven profiles of clay rich soils developed from terrace sediments of the merced river california the terraces and soils of increasing age are used to compare the 10 be inventory with a simple model of accumulation decay and erosion the data show that the distribution of 10 be varies with soil horizon clay content that the residence time of 10 be in these horizons exceeds 10 5 years and that to a rough approximation the inventory of 10 be in a thoroughly sampled soil profile fits the equation n q em 1 e where q is delivery rate e is erosion rate m is the concentration of 10 be in the eroding surface layer is the decay constant and t is the age of the depositional unit from which the soil has developed the general applicability of this model is uncertain and warrants further testing in well calibrated terrace sequences

the dependence of dissolution rates on grain size for some fresh and weathered feldspars abstract ground samples from naturally weathered mineral fragments can still contain substantial proportions of weathered bet surface area if the freshly ground and naturally weathered surfaces in such samples have different dissolution rates data must be interpreted by a kinetic model in terms of both types of surface such a kinetic model is presented the model was used to reexamine literature data for ground size fractions from nine different naturally weathered feldspars ratios of dissolution reactive bet to measured bet surface area were analyzed as a function of the grain size both for the fresh and weathered surfaces in the samples for the naturally weathered surfaces the model strongly suggests that the ratio of reactive bet to measured bet surface area is either independent of the grain size or alternatively increases with decreasing grain size if so grinding does not destroy and possibly creates weathered reactive surface area relative to weathered surface area for the freshly ground surfaces the ratio of reactive bet to measured bet surface area was approximately directly proportional to the grain size thus grinding destroys fresh reactive surface area relative to fresh surface area at all grain sizes additional dissolution experiments on samples essentially containing fresh bet surfaces only have confirmed this finding in the literature ground samples from large naturally weathered fragments are frequently implied to contain fresh bet surface only observed dissolution rates can then be explained if dissolution rates per unit of fresh bet surface area are approximately independent of the grain size in fact however two partly counteracting processes appear to be active during grinding of naturally weathered mineral fragments these are 1 1 increase of the ratio of freshly ground bet to measured freshly ground plus naturally weathered bet surface area and 2 2 decrease of the dissolution rate per unit of fresh bet surface area these observations demonstrate that rate constants and dissolution rates when normalized to fresh bet surface are valid at one grain size only tentative calculations further suggest that dissolution rates normalized to dissolution reactive bet surface are approximately two orders of magnitude higher for fresh feldspar surfaces than for naturally weathered feldspar surfaces

structural transect of the western transverse ranges california implications for lithospheric kinematics and seismic risk evaluation a retrodeformable cross section that integrates surface and subsurface data across the western transverse ranges california illustrates an actively developing fold and thrust belt that began forming at 2 3 ma high level thrusts are interpreted to root in a mid crustal detachment at 12 15 km depth which coincides with the maximum depth of earthquakes the cross section documents 53 km of convergence above the mid crustal detachment dividing this by the time since onset of deformation yields convergence rates of 17 6 26 5 mm yr the high density lithospheric anomaly beneath the transverse ranges is related to subduction of lower crust and lithosphere below the mid crustal detachment to balance the shallow crustal shortening thrust ramps coincide with zones of high seismicity in the transverse ranges this suggests that ramp regions have the highest potential for compressive earthquake events e g the recent whittier narrows earthquake of october 1 1987 m sub l 5 9 occurred along the eastern part of a ramp zone

trapped charge thermochronometry and thermometry a status review abstract trapped charge dating methods including luminescence and electron spin resonance dating have high potential as low temperature 200 c ma 1 or elevated temperature underground settings 30 c despite this limitation trapped charge thermochronometry comprises a diverse suite of versatile methods and we explore potential future applications and research directions

active faulting and block rotations in the western transverse ranges california the geometry of faulting slip vectors of major earthquakes and results of very long baseline interferometry vbli are consistent with active clockwise rotation of crustal blocks in the western transverse ranges about vertical axes oblique left lateral thrust faults trending roughly east west across the western transverse ranges apparently separate long east west blocks of upper crust and the large components of lea lateral shear on east striking planes suggest that the blocks rotate with respect to the san andreas fault in the mojave region between the western transverse ranges and the mojave desert paleomagnetic declinations indicate some 35 and possibly 60 of clockwise rotation since about 10 ma and more importantly the relative velocity between the only two frequently measured vbli sites in the western transverse ranges is consistent with a rotation rate of 6 ma 3 ma during a 5 year period in the 1980s azimuths of slip vectors of major earthquakes are essentially orthogonal to the segment of the san andreas fault across the western mojave desert indicating that crustal shortening across the region is absorbed by crustal thickening and not by lateral translation extension of material parallel to that segment of the fault plate motions late quaternary offsets on the san andreas and san jacinto faults and geodetic measurements in the mojave region yield a calculated direction of relative motion between the san gabriel mountains and the pacific plate across the western transverse ranges that also is perpendicular to the san andreas fault in the mojave region rotation rates associated with simple mechanisms for applying essentially normal tractions to the lateral margins of blocks are not consistent with the observed geometry of faulting and with average rotation rates the rotation rate of 2 8 5 3 ma calculated assuming that the long east west blocks rotate in response to a uniform compression of a viscous substratum to the western transverse ranges however overlaps the range of observed average rotation rates thus the hypothesis that blocks of continental crust move as if carried passively by a substratum undergoing continuous deformation passes one test that can be made of it

regolith evolution on the millennial timescale from combined u th ra isotopes and in situ cosmogenic 10be analysis in a weathering profile strengbach catchment france abstract u th ra disequilibria cosmogenic in situ 10be concentrations and major and trace element concentrations have been analyzed in a 2 m deep weathering profile sampled at the summit of the granitic strengbach catchment france the data have been used to independently estimate both the long term regolith production and denudation rates and the weathering and erosion rates modeling of the 238u 234u 230th 226ra disequilibrium variations in the lower part of the profile yields a regolith production rate of 12 4 mm kyr 30 10 t km2 yr while modeling of the high resolution 10be concentration profile leads to an exposure age of 19 7 2 2 kyr an inherited concentration of 15 000 1 000 at g in quartz and a mean denudation rate of 22 10 mm kyr 37 15 t km2 yr the consistency between production and denudation rates suggests that on a millennial timescale the regolith mass balance at the summit of the catchment is close to a steady state even if the watershed may have been impacted by quaternary climatic changes and by recent anthropogenic perturbations e g 20th century acid rain and recent afforestation efforts the results also indicate that physical erosion is likely the dominant long term process of regolith denudation in the catchment furthermore the comparison of the long term production and denudation rates and of weathering and erosion rates determined from the depth profile analyses with the current weathering and erosion rates estimated at the outlet of the watershed based on monitoring of the water chemistry and sediment fluxes suggests that physical erosion may have varied more than the chemical weathering flux during the last 150 kyr although very few other sites with u series in situ 10be and stream monitoring data are available for comparison the current data suggest that 1 the mass balance steady state of regolith might be commonly achieved in soil mantled landscapes and 2 physical erosion has varied much more than chemical weathering in mid mountain catchments over the last 10 150 kyr these results highlight the importance of the combined analysis of u series nuclides and in situ 10be in the same weathering profile for the determination of key geomorphic parameters which are important to constraining landscape stability and the responses of landscapes to natural or anthropogenic forcing

goethite u th he geochronology and precipitation mechanisms during weathering of basalts u th he geochronology of 33 goethite grains from in situ ferruginous duricrusts overlying the parana flood basalt in the guarapuava region parana brazil reveals ages ranging from 3 6 0 4 to 0 4 0 1 ma thirty one grains from detrital fragments of ferruginous duricrust yield ages in the 6 2 0 6 to 0 7 0 1 ma range the results show that goethites from detrital blocks are generally older than those from the in situ ferruginous layers and that all the goethites from the guarapuava sites are relatively young 6 2 0 6 ma goethites show variable u and th contents depending on the mode of precipitation goethite that forms by progressive ferrugization and pseudomorphic replacement of basalts are rich in th u poor contain various mineral inclusions e g kaolinite rutile ilmenite and display a distinct checkered appearance colloform goethite precipitated within cavities and desiccation cracks contain higher u show low th u values and are free of mineral contaminants suggesting direct precipitation from solution the geochronological results reveal a dynamic evolution for the soils overlying the parana basalt where recurrent duricrust formation and dismantling lead to the evolution of regional colluvial soil profiles while simultaneously preventing the evolution of chemically stratified lateritic weathering profiles the modes of formation and u th and he contents of goethite at guarapuava provide useful constraints on the expected compositions and modes of formation of goethite formed on basaltic soils on mars

discrepancy between geological and geodetic deformation rates in the ventura basin space geodesy provides a new tool for measuring neotectonic deformation which when combined with geological and geophysical observations and models can be used to infer rates and styles of deformation in the ventnra basin region of southern california the geodetically measured convergence rates of 7 10 mm yr 1 ref 1 are significantly lower than the 20 25 mm yr 1 estimated from geological data2 3 here we investigate the possible implications of this discrepancy it might be for example that temporal variations cause the short and long term convergence rates to differ but if this were the case we would expect to observe the long term rate by extending the geodetic measurements over a broader region yet only 11 3 mm yr 1 of regional convergence is observed4 our preferred explanation of the discrepancy is that the geological models require revision and to this end we present two deformation models that satisfy both the geological and geodetic constraints our modelling suggests that the faults bounding the basin are locked at the surface but are slipping at depths below 2 5 km

mechanical modeling of compressional basins origin and interaction of faults erosion and subsidence in the ventura basin california using geophysical observations and some basic geological ideas on the present structure of the ventura basin we model its possible mechanical evolution during the last 4 million years we use a two dimensional finite element model with frictional and elastoviscoplastic rheologies that allow strain localization this allows us to study the mechanical origin of the san cayetano thrust fault scf and its interaction with the oak ridge fault orf the results of our modeling indicate that the geometry and activity of a shear zone which mimics the san cayetano fault are conditioned both by the preexistence of the oak ridge fault and by the shape of the brittle ductile transition furthermore the presence of a decollement level is shown to favor the development of the san cayetano fault shear zone as a low angle structure the value of the effective friction on the oak ridge fault is evaluated from this model possible values of the viscosity of the sediments are also estimated it is shown that low sediment viscosity may completely hinder the activity of such a fault at the surface while slip at depth continues the stratigraphic profile of the basin is also shown to depend on the relative strengths of the orf and scf which also provide an explanation for the shortening and rapid subsidence of the basin

centroid moment tensor solutions for 35 earthquakes in western north america 1977 1983 abstract seismic records from the gdsn sro asro dwwssn rstn and ida networks were used to obtain long period t 45 sec focal mechanisms for 35 earthquakes in western north america longitude 140 to 110 latitude 30 to 60 employing the centroid moment tensor method of dziewonski et al 1981 and dziewonski and woodhouse 1983 the same algorithm was applied to all events the smallest m 0 6 4 10 23 dyne cm being an aftershock to the 1979 imperial valley california earthquake and the largest m 0 8 5 10 26 dyne cm the 1980 eureka california earthquake all events were analyzed with and without the constraint m r m r 0 on the moment tensor an ad hoc criterion on the relative variance reduction was employed to determine a favored solution our solutions show general agreement with other published results as well as with tectonic structures agreement with results obtained using the abundant local and regional data confirms the adequacy of the method in determining long period source parameters and verifies its applicability in regions where local and regional data are scarce or nonexistent in some cases disagreement between our solution and results from first motion studies appears to be related to source complexities our moment tensor represents the total stress release of the composite event a consistent westward movement of the centroid locations reflects lateral heterogeneities in the crust and mantle

an introduction to the global positioning system and some geological applications receivers equipped to measure dual frequency carrier phase signals from satellites of the global positioning system gps have been capable under special conditions of determining relative horizontal positions among stations separated by one to a few hundred kilometers with a precision of one to several millimeters since the early 1980s the major obstacles to making this capability routine extending it to all parts of the globe and extending it to longer station separations have been equipment cost limitations in the gps satellite constellation arduous data analysis uncertainties in satellite orbits uncertainties in propagation delays associated with variable tropospheric water vapor and difficulties in resolving carrier phase cycle ambiguities recent improvements have occurred in all these areas the increasing ease and reduced cost of gps data acquisition and analysis are having a significant impact on studies of near fault crustal deformation and earthquake processes until recently the province of conventional terrestrial geodetic techniques the enhanced satellite constellation improved models and establishment of global tracking networks have extended several millimeters horizontal positioning capability to station separations of 1000 km or more in virtually all parts of the world this enables study of new classes of tectonic problems that previously were difficult to attack with any geodetic technique examples include a complete kinematic description of ongoing crustal deformation in broad complex continental plate boundary zones and measurement of relative plate motion at convergent boundaries where global models may be poorly constrained

statistical description of slope dependent soil transport and the diffusion like coefficient 1 for hillslopes undergoing diffusive soil transport it is often assumed that the soil flux is proportional to the local land surface gradient where the coefficient of proportionality is like a diffusion coefficient inasmuch as transport involves quasi random soil particle motions related to biomechanical mixing and similar dilational processes a slope dependent relation arises from a balance between particle fluxes that tend to loft a soil and gravitational settling of particles into available pore space a specialized form of the fokker planck equation adapted to such particle motions clarifies how the particle flux involves advective and diffusive parts this in turn contributes to a kinematic description of the diffusion like coefficient ingredients of this coefficient include an active soil thickness a characteristic particle size the porosity in excess of a consolidated porosity and the rate of particle activation as a function of depth these last two ingredients vertical porosity structure and activation rate in effect characterize the magnitude and frequency of settling particle motions related to biological activity and thereby set the rate constant of the transport process the significance of land surface slope is that it is a measure of the downslope component of slope normal lofting that is balanced by settling because the diffusion like coefficient contains the soil thickness the analysis suggests that the soil flux is proportional to the depth slope product the analysis is consistent with published profiles of soil creep displacement and with published estimates of soil flux obtained by downslope integration of soil production rates for hillslopes in california and australia

rare earth elements dynamics along pedogenesis in a chronosequence of podzolic soils rare earth elements ree total concentration and signature in soils are known to be impacted by successive soil forming processes so it can be used as probe of soil processes however few studies focus on their behavior in podzols podzols result from the combination of two main pedogenic processes 1 the strong weathering in the surface eluvial horizon 2 the downward transfer of dissolved organic matter om and mobile al and fe and their accumulation in the illuvial horizon beneath iron oxides and om are known to have strong affinities with ree and to play an important role in transfer and immobilization of ree in order to decipher the relative importance of fe oxide and om in ree fate during podzolization and to investigate whether ree can trace podzol formation we study here the evolution of ree signatures along five pedons aged from 120 to 530 years in a cambisol podzol chronosequence located in the cox bay of vancouver island our results show that the ree content is strongly correlated to the general loss of elements and mineral weathering furthermore the accumulation of secondary om al and fe bearing phases does not impact the ree signature of the bulk soil both our results and the ones available in the literature indicate that the release of ree induced by weathering and subsequent leaching in percolating water are the main pathways determining the ree fate in podzols furthermore we show that ree can be released and mobilized in very short periods of time during podzolization 330 years

kinematics of present crust and mantle flow in southern california in the southern california region published geologic studies of prehistoric fault offsets yield at least 81 rates of slip covering various periods of time chiefly since the opening of the gulf of california these rates together with the known geometries of active faults are used to constrain a hand fit block model for present horizontal velocity of the crust the assumptions employed are that these rates apply to the present that the blocks are internally rigid down to the greatest depth of earthquakes and that the over all pacific north american plate motion is correctly given by global models the resulting model fits 67 data within their uncertainties 10 more with a small discrepancy 1 mm yr and fails to accommodate only 4 data 2 of which are inconsistent with other data nominal precision is good 3 mm yr but accuracy and uniqueness are both suspect because many block boundaries are questionable despite its many local defects this model suggests four reliable regional conclusions first the rate of shortening on the south side of the transverse ranges varies from 6 to 14 mm yr increasing eastward which implies an unrecognized seismic hazard unless the motion is taken up by folding or fault creep second the pattern of block rotation rates is quite different from the pattern of rotations shown by tertiary paleomagnetic declinations which implies some major pliocene reorganization of blocks third the great bend left step of the plate boundary fault system in the transverse ranges appears to be straightening gradually by a 3 m y clockwise rotation relative to both plates finally if it is assumed that plate shortening has been occurring at this bend since the early pliocene and that crust and upper mantle velocities are similar then this model predicts mantle lithosphere downwelling to at least 250 km depth beneath the transverse ranges this prediction is consistent with upper mantle seismic velocity structure

the assessment of weathering stages in granites using an ec ph meter the weathering of granite encompasses a wide range extending from slightly weathered rock to saprolite to soil although many different methods are available for quantifying the amount of chemical or physical weathering in granites dissolution rate as a method for estimating the degree of chemical weathering in these rocks was not thoroughly investigated this study sought to identify a method for quantifying weathering stages in granite based on both the chemical and physical properties of the rock using the weathering profile of granites from two quarries in the chugoku region of western japan a simple dissolution experiment measured with an electrical conductivity meter for 10 min recorded the differences in dissolution rates which reflects the chemical weathering stages in granites the combination of the dissolution rate and the p wave velocity produces a diagram that gives the chemical and physical properties of the weathered rock body in a single chart

global positioning system network analysis with phase ambiguity resolution applied to crustal deformation studies in california a 5 year campaign is in progress in central and southern california to monitor tectonic motions using observations of the global positioning system gps satellites evidence from geological and space geodetic data indicates that significant horizontal deformations of order 10 mm yr are occurring west of the san andreas fault along the california margin we demonstrate using data from initial epoch measurements in january 1987 that the goal of measuring horizontal deformations with an accuracy of 5 mm yr over the duration of the campaign should be readily achievable the gps network was designed to span a wide range of baseline lengths within california and across north america to aid in phase ambiguity resolution an important factor in achieving highest accuracy baseline determinations we present an efficient algorithm for multisession network analysis of gps data with simultaneous orbit determination and ambiguity resolution using this algorithm with the california data we demonstrate the improvement obtained in station position and satellite orbit estimation when the phase ambiguities are resolved we demonstrate several millimeters 1 part in 108 short term repeatability over five single session daily analyses for horizontal baseline components and length and several tens of millimeters for the vertical comparison with the independently determined very long baseline interferometry baseline between mojave and owens valley suggests that the accuracy is at the same level as the repeatability we show that simultaneous multisession analyses with ambiguity resolution improve the baseline and satellite orbit estimates compared to the single session analyses with the single session analyses we were able to resolve all phase ambiguities on baselines within california with the multisession analyses we were able to resolve the phase ambiguities for most of the network over regional and continental scales

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

coupling uranium series and 10be cosmogenic radionuclides to evaluate steady state soil thickness in the betic cordillera abstract on earth the critical zone is the near surface environment where interactions between the atmosphere lithosphere hydrosphere and biosphere take place the development of the regolith mantle is controlled by the downwards propagation of the weathering front into the bedrock and denudation at the surface of the regolith by mass movements water and wind erosion when the removal of surface material is approximately balanced by the production of weatherable material at the bottom of the regolith profile the soil system is assumed to be in steady state although recent literature on chemical weathering often assumes that soils have a steady state thickness the concept has rarely been validated with empirical field data in this study we present and compare analytical data from two independent isotopic techniques in situ produced cosmogenic nuclides and u series disequilibria to constrain soil development under semi arid climatic conditions three soil profiles were sampled across the betic ranges at the ridge crest of zero order catchments with distinct topographic relief hillslope gradient and 10be derived denudation rate soil production rates determined based on u series isotopes 238u 234u 230th and 226ra are of the same order of magnitude as 10be derived denudation rates suggesting steady state soil thickness in two out of three sampling sites our results show the potential of a combined u series disequilibria and in situ 10be isotope approach to evaluate steady state soil thickness our study also illustrates the frontiers in applying u series disequilibria to track soil production in environments characterized by weak soil development

assessment of global positioning system measurements for studies of crustal deformation the u s geological survey has been using the global positioning system gps to perform repeated surveys of networks of different sizes since january 1986 the intersite distances from these various networks are 223 km for a single line connecting the palos verdes and vandenberg sites in southern california 30 50 km for a network of three sites south of the san francisco bay near loma prieta 9 30 km for a network located near hebgen lake montana 7 12 km for a network of sites in the vicinity of parkfield california and 240 m for a line located at the goldstone antenna complex in the mojave desert the lengths quoted do not include the intersite distances for the fiducial sites included in the solutions for orbit determination which can be up to 8000 km we have attempted to assess the long term precision and accuracy of determinations of relative site position for a range of line lengths this assessment has consisted of several different studies in assessing precision we have generally investigated repeatability usually about a best fit linear temporal trend the smallest fractional repeatability was yielded by the measurements on the palos verdes to vandenberg line the root mean square rms residual about the best fit line for these determinations was 6 mm 0 03 parts per million or ppm for the north component 11 mm 0 05 ppm for the east component and 40 mm 0 18 ppm for the vertical component for these determinations gps data from 3 4 consecutive days were combined to produce a single estimate of the vector separation we also used the day to day scatter from these measurements to perform an analysis of variance and found that these multiday determinations can be significantly more precise than estimates determined from a single observing session the worst results were obtained for the loma prieta network where we obtained rms residuals of 11 12 mm 0 3 0 4 ppm for north 14 18 mm 0 3 0 6 ppm for east and 18 21 mm 0 4 0 7 ppm for vertical we cannot definitely explain these poor results but we have evidence to indicate that this poor scatter is due to the short observing session 4 5 hours compared to 6 5 hours for the palos verdes to vandenberg results in assessing accuracy we compared the gps results to those from independent techniques at parkfield we compared the gps estimates of fault parallel motion to those from creep meters and alignment arrays and found excellent agreement within 1 2 mm yr 1 not only for the slip but also for the variation of slip along the san andreas fault we compared the loma prieta and hebgen lake line length estimates to those obtained from a geodolite a high precision laser distance measurement device that the u s geological survey has used for 20 years for studies of crustal deformation if we model the geodolite minus gps line length differences l as l l where l is the line length then we find 0 6 0 5 mm and 0 1 0 1 mm km 1 the uncertainties quoted are one standard deviation from this comparison we conclude that at this level of significance there is no detectable difference between lengths determined from geodolite and gps data finally we compared the gps estimates of the palos verdes to vandenberg line length to those obtained from very long baseline interferometry vlbi the mean difference between the six gps estimates of line length and a best fit line through the vlbi estimates was 1 mm and the rms difference was 12 mm 0 05 ppm close to the standard deviation of the gps measurements for this predominantly east west line

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

geodetic measurement of deformation in the ventura basin region southern california we have measured the deformation in the ventura basin region southern california with global positioning system gps measurements carried out over 4 6 years between 1987 and 1992 the deformation within our network is spatically variable on scales of tens of kilometers with strain rates reaching 0 6 1 micro rad yr in the east central basin blocklike rotations are observed south and northwest of the basin where the maximum shear strain rates are an order of magnitude lower 0 06 1 micro rad yr to the south we also observed clockwise rotations of 1 deg 7 deg m y shear strain rates determined by comparing angle changes from historical triangulation spanning several decades and gps measurements give consistent though less precise results the geodetic rates of shortening across the basin and western transverse ranges are lower than those estimated from geological observations but the patterns of deformation from the two methods agree qualitatively

integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes 1 we developed a process oriented hillslope soil mass balance model that integrates chemical and physical processes within hillslope soils the model explicitly factors that soil chemical weathering at any hillslope position is related to the flux of soil eroded from upslope as well as soil production from underlying bedrock the model was merged with measurements of soil elemental chemistry and cosmogenic radionuclide based saprolite to soil conversion rates along a 50 m transect of a semiarid granodiorite hillslope in the southeastern australian highlands inverse modeling results in the simultaneous quantification of the rates of soil chemical weathering and soil transport as a function of hillslope position soil chemical weathering rates per land surface area systematically varied along the transect from losses of 0 035 kg m 2 yr 1 on the ridge to gains of 0 035 kg m 2 yr 1 at the lowest slope position the mass loss via soil chemical weathering would have been overestimated by 40 if the impact of soil transport on soil chemistry was ignored the chemical mobility of elements combined with biological nutrient demand controlled the spatial redistribution of individual elements p and ca were preferentially retained relative to si al and fe within the hillslope base the calculated soil transport rate is linearly related to the product of soil thickness and slope gradient instead of slope alone soil residence time was determined by calculating the time length for a 3 dimensional box volume 1 m2 surface area soil thickness to be entirely removed by mass flux of soil transport 4 ka on the ridge to 0 9 ka at the hillslope base these soil residence times combined with soil chemical weathering rates indicate that a 1 m2 area of soil loses 1 800 kg via chemical weathering while passing through the upslope portion of the hillslope but that it regains 90 kg probably via clay precipitation and biological retention of cations during its passage through the lower segments of the transect this study provides a previously unrecognized linkage between physical soil transport and soil chemical weathering that have implications for hillslope evolution as well as biogeochemistry

carrier phase ambiguity resolution for the global positioning system applied to geodetic baselines up to 2000 km the global positioning system gps carrier phase data are biased by an integer number of cycles a successful strategy has been developed and demonstrated for resolving these integer ambiguities for geodetic baselines of up to 2000 km in length resulting in a factor of 3 improvement in baseline accuracy and giving centimeter level agreement with coordinates inferred by very long baseline interferometry in the western united states for this experiment a method using pseudorange data is shown to be more reliable than one using ionospheric constraints for baselines longer than 200 km an automated algorithm exploits the correlations between the many phase biases of a gps receiver network to enable the resolution of ambiguities for very long baselines a method called bias optimizing has been developed which unlike traditional bias fixing does not require an arbitrary confidence test bias optimizing is expected to be preferable to bias fixing for poorly configured networks in order to enable ambiguity resolution for long baselines it is recommended that future gps networks have a wide spectrum of baseline lengths ranging from 1000 km and that gps receivers be used which can acquire dual frequency p code data

deformation near the junction of the creeping and locked segments of the san andreas fault cholame valley california 1970 1980 we have constructed a simple dislocation model of the san andreas fault near cholame california that reproduces the observed deformation of nearby geodetic networks as well as the transition from quasi continuous slip fault creep to a no slip locked condition on the surface trace the model is specified by the slip rates imposed on the fault surface slip on the surface trace is given by the observed fault creep rates and slip at depths greater than 12 6 km is taken to 30 mm yr along the entire length of the fault i e beneath creeping and locked sections alike slip at intermediate depths is assigned by a rather arbitrary extrapolation of the surface creep values this postulated distribution of slip on the fault is tested by using it in a dislocation model to predict the deformation in two geodetic networks a trilateration network 20 km aperture and a 20 km long level line the calculated deformation of the trilateration network agrees with the observed deformation within the observational error agreement between the predicted and observed elevation changes along the level line was satisfactory in the sense that the predicted values were below the level of detection and the observed changes were not significant

assessing the effect of sequential extraction on the uranium series isotopic composition of a basaltic weathering profile abstract soil sustainability implies maintaining the balance between soil erosion and production while it is known how to assess soil erosion only recently we have been able to estimate rates of soil and saprolite namely regolith production using uranium series isotopes this method assesses the time elapsed since rock forming minerals start fractionating the u series isotopes in this study we assess a sample pre treatment protocol that has the potential to improve the method used to estimate regolith production rates we propose that removal or partial removal of secondary phases precipitated from solution during pedogenesis solution derived phases and organic matter from regolith may improve the accuracy of this method this is tested using sequential extraction followed by etching as sample pre treatment here we assess their effect on the u series isotopic composition of regolith and infer whether they minimize the presence of solution derived phases and organic matter we applied sequential extraction and etching to a basaltic weathering profile bedrock saprolite and soil and compared the u series isotopic composition before and after treatment we also measured major elements concentrations and assessed mineralogy the bedrock was in secular equilibrium and sequential extraction resulted in unchanged 234u 238u activity ratios while increased 230th 238u in contrast etching resulted in increased 234u 238u and 230th 238u activity ratios which is attributed to the removal of primary minerals relative to the untreated bedrock the untreated saprolite showed no changes in u and th concentrations and activity ratios we hypothesise that during the conversion of bedrock into saprolite u and th budgets are unaffected moreover major element and mineralogical analyses suggest that during this process rock forming minerals are converted into secondary phases clays we hypothesise that during this conversion the u series isotopes are not fractionated therefore the removal of these secondary phases is not necessary relative to the saprolite the soil showed gains of u and th 234u 238u 1 and 230th 238u 1 to minimize the presence of solution derived phases and organic matter in basaltic weathering profiles we suggest that only soil samples should undergo sequential extraction because only these are significantly affected by solution derived phases and organic matter additionally our experiments show the existence of fractionation processes that are often overlooked in u series isotopic studies i e implantation of 234u and 230th recoiled from u rich mineral i e glass into adjacent u poor phases e g pyroxene and feldspar

systematics of u th disequilibrium in calcrete profiles lessons from southwest india pedogenic carbonates calcretes have often been proposed as possible markers of the pedogenetic processes in soils under semi arid climate however precise chronological constraints on their formation are required in order to investigate the climatic and paleo environmental conditions that prevailed during and after their formation and to improve our understanding of the physical and chemical conditions that promoted their development and preservation moreover these authigenic calcium carbonate precipitates provide us with an interesting test of the u th radioactive disequilibrium dating method the reliability of which has been demonstrated extensively in aragonitic corals and calcitic continental speleothems but which remains much more questionable in highly porous chemically and mineralogically complex media such as soil profiles we report here 238u 234u 230th radioactive disequilibrium analyses measured by thermo ionization mass spectrometry in calcretes from two sites in southwest india since calcretes are impure carbonates mixed with various amounts of parent rock and weathered minerals all ages must be computed using the isochron technique involving the extraction of several coeval subsamples from the same soil horizon and u th analyses after total dissolution tsd method in order to correct for the detrital component 232th is usually used as index of the detrital contamination and the isochron age is derived from the isotopic composition 230th 238u 234u 238u of the pure authigenic carbonate end member of the mixing line our results show that each set of samples taken from decimetric blocks is characterized by a well defined isochron line in a 3 d osmond diagram 232th 238u 230th 238u 234u 238u the regression lines obtained for most of the samples show probabilities of fit satisfying the mathematical assumptions of the isochron model in most cases 0 05 and mean square weighted deviations mswd values around 1 the compositions of the end members are highly variable between the different isochrons both for the carbonate phase indicating various ages of cristallisation and for the detrital phase indicating various origins and compositions notably our data demonstrate that the detrital component is in all cases out of secular equilibrium by contrast with the standard paradigm of dirty carbonate dating which is based on the assumption of average continental crust th u elemental ratio and secular equilibrium values of the 230th 238u and 234u 238u ratios at the first site coimbatore we obtain u th ages between 304 38 ka and 44 2 9 ka 2 from the base to the top of the profile these suggest discontinuous precipitation of the different facies in good agreement with micromorphological observations at the second study site gundlupet the carbonate nodules sampled from two different profiles yield consistent ages of 200 ka which suggests that precipitation of nodular carbonate occurred across the entire pediment toposequence during a single event surprisingly in mere contradiction with the standard model of impure carbonate dating two puzzling samples display vertical isochrons i e variable 232th 238u without any variation of the 230th 238u and 234u 238u ratios such patterns require extremely high 232th 238u ratios in an as yet unidentified detrital phase taken at face value these results suggest that no clear correlation can be inferred between the precipitation of these pedogenic carbonates and major orbitally driven climate variations recorded in other archives during the last glacial interglacial cycles

regolith production and transport at the susquehanna shale hills critical zone observatory part 2 insights from meteoric 10be 1 regolith mantled hillslopes are ubiquitous features of most temperate landscapes and their morphology reflects the climatically biologically and tectonically mediated interplay between regolith production and downslope transport despite intensive research few studies have quantified both of these mass fluxes in the same field site here we present an analysis of 87 meteoric 10be measurements from regolith and bedrock within the susquehanna shale hills critical zone observatory ssho in central pennsylvania meteoric 10be concentrations in bulk regolith samples n 73 decrease with regolith depth comparison of hillslope meteoric 10be inventories with analyses of rock chip samples n 14 from a 24 m bedrock core confirms that 80 of the total inventory is retained in the regolith the systematic downslope increase of meteoric 10be inventories observed at ssho is consistent with 10be accumulation in slowly creeping regolith 0 2 cm yr 1 regolith flux inferred from meteoric 10be varies linearly with topographic gradient determined from high resolution light detection and ranging based topography along the upper portions of hillslopes at ssho however regolith flux appears to depend on the product of gradient and regolith depth where regolith is thick near the base of hillslopes meteoric 10be inventories at the north and south ridgetops indicate minimum regolith residence times of 10 5 3 7 and 9 1 2 9 ky respectively similar to residence times inferred from u series isotopes in ma et al 2013 the combination of our results with u series derived regolith production rates implies that regolith production and erosion rates are similar to within a factor of two on ssho hillcrests

rock surface roughness as an indicator of degree of rock surface weathering rock surface weathering often leads to increased rock surface roughness but roughness has proved difficult to quantify several instruments are available for micro mapping and recording rock surface profiles but the most appropriate for most purposes is the simple profile gauge short profiles can be recorded quickly and accurately a range of roughness indices has been proposed in other areas of geomorphology and their efficacy as measures of roughness at scales of interest in studies of weathering is assessed some are too complex or labour intensive and others are too sensitive to the scale of roughness to provide reliable measures of magnitude the most appropriate indicator of both the scale and magnitude of roughness is the standard deviation of the differences between height values at a range of set horizontal intervals along a profile the deviogram varying the measurement interval records roughness at different scales a regression approach root mean square roughness provides a reliable measure of the magnitude of roughness at the maximum scale present three case studies confirm the efficacy of these approaches to studies of weathering of different rocks in different environments software is supplied which automates the calculation of roughness indices from gauge profiles

a kinematic model of southern california we propose a kinematic model for southern california based on late quaternary slip rates and orientations of major faults in the region internally consistent motions are determined assuming that these faults bound rigid blocks relative to north america most of california west of the san andreas fault is moving parallel to the san andreas fault through the transverse ranges and not parallel to the motion of the pacific plate this is accomplished by counterclockwise rotation of california south of the san andreas fault and by the westward movement of central california north of the gar lock fault the velocities of the blocks are calculated along several paths in southern california that begin in the mojave desert and end off the california coast a path that crosses the western transverse ranges accumulates the accepted relative north america pacific plate velocity whereas paths to the north and south result in a significant missing component of motion this implies the existence of a zone of active deformation in southern california that is interpreted to include the western transverse ranges and northwest trending predominately strike slip faults close to the coast both north and south of the transverse ranges strain on this system accounts for about a third of the total north america pacific plate motion

late quaternary slip rate on the oak ridge fault transverse ranges california implications for seismic risk abstract the slip rate on the oak ridge fault at south mountain in the densely populated lower santa clara valley california is estimated as 6 15 to 12 3 mm yr since the end of saugus deposition at 0 4 to 0 2 ma slightly lower slip rate estimates result from a different projection of the top of the saugus in the hanging wall block of the fault an assumed displacement of 3 m per event gives an average recurrence interval of 250 to 500 yr with the major uncertainty being the age of the top of the saugus displacement of 2460 m of the top of the saugus at south mountain includes piercing point displacement and distributed displacement from drag folds near the fault both are the near surface expression of faulting at potential mainshock depths beneath well control slip rates for the nearby san cayetano and red mountain faults are not well constrained because post miocene strata are absent in their hanging wall blocks but available evidence suggests that their slip rates are about the same as that for the oak ridge fault earthquake return times measured in hundreds of years have been shown by others for the 1971 san fernando fault and a small fault near the red mountain fault and comparable return times are suggested for a normal fault in the hanging wall block of the oak ridge fault a trench on the harmon alluvial fan near the ventura county government center revealed evidence of cracks filled with sediments from below suggesting liquefaction during an earthquake the lower santa clara valley has not had a large damaging earthquake in 200 years of record keeping but one is expected there in the near future the december 21 1812 earthquake may have occurred on the offshore continuation of the oak ridge or red mountain fault

evolution of the stress field in southern california and triggering of moderate size earthquakes a 200 year perspective changes in stress in southern california are modeled from 1812 to 2025 using as input 1 stress drops associated with six large 7 0 7 5 earthquakes through 1995 and 2 stress buildup associated with major faults with slip rates 3 mm yr as constrained by geodetic paleoseismic and seismic measurements evolution of stress and the triggering of moderate to large earthquakes are treated in a tensoffal rather than a scalar manner we present snapshots of the cumulative coulomb failure function acff as a function of time for faults of various strike dip and rake throughout southern california we take acff to be zero everywhere just prior to the great shock of 1812 we find that about 95 of those well located m 6 earthquakes whose mechanisms involve either strike slip or reverse faulting are consistent with the coulomb stress evolutionary model that is they occurred in areas of positive acff the interaction between slow moving faults and stresses generated by faster moving faults significantly advanced the occurrence of the 1933 long beach and 1992 landers events in their earthquake cycles coulomb stresses near major thrust faults of the western and central transverse ranges have been accumulating for a long time future great earthquakes along the san andreas fault especially if the san bernardino and coachella valley segments rupture together can trigger moderate to large earthquakes in the transverse ranges as appears to have happened in the santa barbara earthquake that occurred 13 days after the great san andreas shock of 1812 maps of current acff provide additional guides to long term earthquake prediction

a broadband study of the 13 august 1978 santa barbara earthquake the santa barbara earthquake of 13 august 1978 provides an opportunity to perform a broadband investigation of body waves for a well recorded moderate size m l 5 1 event the long and short period teleseismic body waves are modeled in the time domain to construct a source time function which is consistent in the period range of 1 to 20 sec the long period records indicate an overall duration of 6 sec while the short period records reveal the fine scale character of the slip history consisting of two sharp pulses separated by about 1 sec the source mechanism determined from this analysis is a moderately dipping 30 ne thrust with significant left lateral slip the moment was determined to be 1 1 10 25 dyne cm the earthquake was also reasonably well recorded on accelerographs in the near field the modeling of the strong motion displacements was a two step procedure 1 the displacements were modeled alone and 2 in an attempt to achieve consistency between the local and far field time functions the qualitative features of the teleseismic short period time function were used to predict the displacements if the two sources in the short period time function are allowed to have different mechanisms the displacements can be modeled quite well this suggests that the overall faulting process was rough and the multiple source character suggested at high frequencies is due to high stress drop asperities the two sources are modeled as asperities separated by 1 5 km the first source has a mechanism consistent with the teleseismic solution while the second source is more steeply dipping the total moment determined from the strong motion data is 3 5 10 24 dyne cm or one third the long period moment this is consistent with other recent studies which suggest that the high frequency strong ground motion is controlled by the distribution of asperities even though the sum of their moments may be small compared to the overall moment this study also shows the importance of teleseismic short periods in predicting the local displacements

geodetic measurements near parkfield california 1959 1984 trilateration measurements have been made by various agencies since 1959 near parkfield california in the transition zone between the central creeping section and the southern locked section of the san andreas fault within the transition zone there are several creep meters and alignment arrays four small aperture trilateration networks and a broad trilateration network extending 70 km southwest from the san andreas fault to the pacific coast line length changes observed after the 1966 ml 5 6 parkfield earthquake indicate a geodetic moment of 4 5 1 0 1025 dyn cm the data are consistent with either 91 8 cm slip on a rupture zone which is 30 km long and extends from 3 to 8 km below the surface or 59 5 cm on a 30 km long zone 2 10 km deep this moment estimate includes some postseismic slip and is a factor of 2 4 greater than the moment determined from seismic surface waves the post 1966 data set is well suited to discriminate between the effects of surface and deep slip surface slip rates determined by creep meters alinement arrays and small aperture trilateration networks decrease from 29 mm yr at slack canyon to zero south of highway 46 a gradient of roughly 0 48 0 01 mm yr km deformation of a subset of the trilateration network between cholame and san luis obispo is consistent with shallow slip of 2 9 1 2 mm yr from the surface to a depth of 16 km and 33 4 5 5 mm yr below 16 km the trilateration data alone do not uniquely constrain both the transition depth from shallow to deep slip and the deep slip rate a transition depth near 16 km is preferred because it provides the best fit to the data and because the predicted slip rate is consistent with independent estimates of the total slip rate across the san andreas fault this simple two dimensional model neglects along strike variations in the deformation the data show no evidence for significant strike slip deformation across faults between the san andreas and the pacific coast

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

deep weathering along a granite ridgeline in a subtropical climate abstract bulk chemical composition and mineralogy were examined in three soil profiles and a deeper 11 meter profile weathering on a granite ridgeline under subtropical climate conditions in south china the weathering sequence is delineated by mineralogy and major element variations apatite biotite hornblende and plagioclase dissolve early during weathering resulting in nearly 100 ca and na loss and significant mg fe and p depletion at depth the k feldspar reaction front begins at the depth of depletion of plagioclase leading to a loss of 80 of the k at the land surface near the bottom of the ridgeline and almost 100 at the top dissolution of quartz and other silicates releases about 60 of si in the profiles kaolinite is the dominant clay mineral and it transforms to gibbsite in the uppermost layer the soil horizon upper 100 cm is the zone dominated by pedogenic processes including active biological activity physical erosion and influx of high concentrations of atmospheric components especially co2 and o2 the pedogenic processes are characterized by low ph 4 54 to 5 85 high clay content kaolinite 6 16 wt gibbsite 2 8 wt and total organic carbon content 0 13 3 93 and intensive fracturing and dissolution of quartz and k feldspar compared with the lower horizons accumulation of organic material and resistant minerals downslope is attributed to down ridge movement of water termed here interflow and weathering products in the uppermost 100 cm down the ridgeline using a mass balance model calculation for the catena that assumes steady state soil thickness at all sites the bottom profile shows the highest apparent total chemical weathering loss rate 14 g m 2 y 1 whereas the middle position shows the highest physical erosion loss rate 44 g m 2 y 1 sio2 accounts for about 84 of the chemical weathering outflux from the soil horizons along the ridgeline hillslope chemical weathering rates at the bottom of the hillslope may be accelerated by high concentrations of organic material and by dissolution of kaolinite this study demonstrates that mineral reaction fronts in granite become separated over depth intervals of meters and that elemental fluxes and release mechanisms vary with position along a ridgeline catena

large scale quaternary detachments in ventura basin southern california the ventura basin is an east north east trending trough in the california transverse ranges which records major quaternary detachment faulting at three levels the earliest thrusting occurred along weak siltstone interbeds in a sequence dominated by competent basin plain turbidite sandstone because sedimentation continued during thrusting the age rate and direction of thrusting can be worked out faulting began 1 3 m y ago and ceased 0 65 m y ago with a maximum slip rate of 2 8 mm yr to the southeast the fault set moved up a 45 ramp and ended as a blind thrust the ramp had topographic expression on the seafloor diverting turbidites around the ramp and preserving ash beds along with other hemipelagic sediments on its crest following the end of deposition 0 2 m y ago the competent basin plain turbidites underwent flexural slip folding over an incompetent miocene sequence dominated by shale underlying competent paleogene strata were not folded the south flank of the ventura avenue anticline tilted at 3 4 rad yr the anticlinal crest rose at a rate of 15 16 mm yr decelerating to 4 3 5 2 mm yr and the anticline and an adjacent syncline shortened at a rate of 20 mm yr the high rate of folding in the ventura avenue oil field resulted in overpressured sandstone reservoirs and oil water interfaces which have not had time to reach gravity equilibrium the red mountain san cayetano and santa susana faults mark the surface expression of a seismically active midcrustal detachment which produced convergence across the ventura basin at rates as high as 23 mm yr total convergence across the eastern san cayetano fault near fillmore is 11 600 2000 m in the last million years

fully coupled approach to modeling shallow water flow sediment transport and bed evolution in rivers 1 our ability to predict complex environmental fluid flow and transport hinges on accurate and efficient simulations of multiple physical phenomenon operating simultaneously over a wide range of spatial and temporal scales including overbank floods coastal storm surge events drying and wetting bed conditions and simultaneous bed form evolution this research implements a fully coupled strategy for solving shallow water hydrodynamics sediment transport and morphological bed evolution in rivers and floodplains pihm hydro and applies the model to field and laboratory experiments that cover a wide range of spatial and temporal scales the model uses a standard upwind finite volume method and roe s approximate riemann solver for unstructured grids a multidimensional linear reconstruction and slope limiter are implemented achieving second order spatial accuracy model efficiency and stability are treated using an explicit implicit method for temporal discretization with operator splitting laboratory and field scale experiments were compiled where coupled processes across a range of scales were observed and where higher order spatial and temporal accuracy might be needed for accurate and efficient solutions these experiments demonstrate the ability of the fully coupled strategy in capturing dynamics of field scale flood waves and small scale drying wetting processes

surface ages and weathering rates from 10be meteoric and 10be 9be insights from differential mass balance and reactive transport modeling abstract to reconstruct the dynamic evolution of weathered material at the earth s surface requires techniques that record the fluxes of material into and out of the weathering zone cosmogenic isotopes formed in situ within the earth s surface or in the atmosphere meteoric are important chronometers for both time and fluxes meteoric 10 be has been used to evaluate surface ages soil residence times and rates of sediment transport however the meteoric 10 be dating tool relies on complete retention of 10 be on mineral surfaces within the weathered regolith an assumption that will not be valid where soil ph is low or mineral surface area available for sorption is lacking here we evaluate whether the stable isotope of 9 be that is released upon weathering reactive be can be used to correct for 10 be mobility this approach relies on the inventory of reactive 9 be in the weathering zone as a measure of the mass depletion whereas the 10 be inventory is a function of age to explore the spatial and temporal relationship between the be isotopes we use a multi component reactive transport model framework to evaluate a set of differential mass balance equations for the 10 be 9 be composition of the bulk solid and sorbed reservoirs on non eroding surfaces we first find that the 10 be 9 be reac is inversely proportional to the long term chemical weathering rate even in cases of incomplete be retention second we find that coupling 10 be and 9 be to provide a tool for surface age dating 10 be is complex because incomplete retention affects each isotope to a different extent beryllium 10 is supplied at the surface of soil where sorption onto secondary minerals is more extensive while 9 be is released from primary minerals at the weathering front where secondary minerals are less abundant if 9 be loss is less than about 15 we find 9 be inventories can be used to reliably correct 10 be inventories to within 10 the error associated with the correction also increases with increasing age and thus the correction is more favorable for younger surfaces over longer timescales the error on the age introduced by the loss correction using 9 be is magnified whereas the error associated with uncorrected ages decreases because the 10 be is more strongly retained as chemical weathering progresses we also find that the reactive transport model confirms a set of simple mass balance descriptions providing guidance for future data collection collectively the modeling results suggest that measurement of be isotopes in weathered regolith provides a unique approach to determine both surface ages and chemical weathering rates

geochemical behaviors of different element groups during shale weathering at the susquehanna shale hills critical zone observatory major and trace element concentrations were measured in bedrock regolith and stream sediments from a first order catchment developed entirely on grey shale in central pennsylvania usa these elements can be classified into five major groups based on statistical data analysis the presence of different elemental groups is due to the mineralogical origin cycling processes and geochemical properties of these elements during soil formation a better understanding of the behaviors of these elements during chemical weathering would allow for their possible use as natural tracers in critical zone processes

the time scale of river sediment source to sink processes in east asia abstract knowledge of river sediment recycling provides important constraints on continent weathering and earth surface processes in this study we estimate the comminution age of sediments from the changjiang yangtze river and two small mountainous rivers in taiwan based on their lithogenic 234u 238u ratio the 234u 238u distributions in the changjiang catchment are overall related to sediment grain size and chemical weathering regime while 234u 238u ratios in taiwan rivers mainly depend on erosion denudation processes the comminution age constrains the time scale of sediment source to sink processes in catchments from sediment weathering denudation to transportation and finally deposition our results indicate that the comminution ages vary from 250 to 600 kyr for the changjiang sediments and 110 kyr for the taiwan sediments different comminution ages are associated with contrasting erosion and weathering regimes and diverse topography between the large changjiang catchment and small mountainous taiwan basins the longer comminution age of the changjiang sediment is an interacting effect of a longer erosion weathering history and sediment trapping effect and thus slow transfer rate created by broad floodplains and lakes in the middle and lower reaches the shorter comminution age of the taiwan sediment results from fast sediment denudation and transport associated with strong tectonic uplift typhoon climate and steep topography as these two major river systems dominate the sedimentology in east asia continent margin the distinct geological and topographical settings between the changjiang and taiwan river systems result in different sediment source to sink transport processes this work presents a systematic and quantitative constraint on the time scale of river sediment transfer process in east asia and also provides new insight into weathering regimes and sediment transport in monsoon climate dominated continent and island

strain accommodated by brittle failure in adjacent units of the monterey formation u s a scale effects and evidence for uniform displacement boundary conditions abstract extensional strain accommodated by brittle deformation was measured in adjacent mudstone and dolostone units at arroyo burro beach california the dolostone failed in effective tension whereas the mudstone failed in shear both in response to the same extensional tectonic event in the mudstone unit initial bed length and fault displacement methods document extensional strains of 6 6 0 3 and 6 0 0 3 respectively upon adjusting the displacement estimates according to theoretical fault displacement population analysis the corrected strain becomes 9 7 0 3 for the mudstone measurements of vein apertures in the dolostone document extensional strain that varies according to scale with outcrop vein scanlines indicating a strain of 3 4 0 1 and thin section scanlines yielding a strain of 5 8 0 2 applying theoretical fault displacement population analysis to vein apertures in dolostone shows that small veins below the detection limit of outcrop surveys contribute significantly to fracture related strain within the dolostone this difference in extensional strain may arise because veins measured in outcrop extend across the entire bed height and thus are controlled by the dolostone mechanical layer thickness whereas microscopic veins measured in thin section terminate without regard to a bounding layer the corrected dolostone strain becomes 10 2 1 0 matching the revised strain calculated in the adjacent mudstone unit and indicating uniform displacement boundary conditions for the two markedly different lithologies the 10 extensional strain at arroyo burro indicates significant strike parallel nw se extension accommodated by brittle failure during development of the western transverse ranges fold and thrust belt

uranium series isotopes in river materials insights into the timescales of erosion and sediment transport abstract the uranium series isotope signatures of the suspended and dissolved load of rivers have emerged as an important tool for understanding the processes of erosion and chemical weathering at the scale of a watershed these signatures are a function of both time and weathering induced fractionation between the different nuclides provided appropriate models can be developed they can be used to constrain the residence time of river sediment this chronometer is triggered as the bedrock starts weathering and the inferred timescale encompasses the residence time in the weathering profile storage in temporary sediment deposits e g floodplain and transport in the river this approach has been applied to various catchments over the past five years showing that river sediments can reside in a watershed for timescales ranging from a few hundreds of years iceland to several hundreds of thousands of years lowlands of the amazon various factors control how long sediment resides in the watershed the longest residence times are observed on stable cratons unaffected by glacial cycles or more generally climate variability and human disturbance shorter residence times are observed in active orogens andes or fast eroding recently glaciated catchments iceland in several cases the residence time of suspended sediments also corresponds to the time since the last major climate change the u series isotope composition of rivers can also be used to predict the river sediment yield assuming steady state erosion is reached by comparing this estimate with the modern sediment yield obtained by multi year sediment gauging it is clear that steady state is seldom reached this can be explained by climate variability and or human disturbance steady state is reached in those catchments where sediment transport is rapid iceland or where the region has been unaffected by climate change and or human disturbance u series are thus becoming an important tool to study the dynamics of erosion

carbonate and elemental accumulation rates in arid soils of mid to late pleistocene outwash terraces southeastern wind river range wyoming usa an important result of the past few decades of soil geomorphic research is the awareness of the major role of dust and related carbonate precipitates in arid soils the temporal evolution of soils developed on outwash terraces is still a matter of debate particularly regarding the type of evolution progressive evolution and constant rates vs complex and or interval accumulation rates progressive or regressive evolution possible soils on a chronosequence of outwash terraces just outside and downstream of canyon mouths of the wind river range usa were analysed for carbonate accumulation organic carbon and poorly crystalline pedogenetic oxyhydroxides stocks and pathways of chemical weathering the soils and their carbonate stocks in the fine earth fraction 2 mm can be used as a relative dating tool and appear to correlate with regional glacial chronostratigraphy pinedale c 20 ky bull lake with two different units around 160 and 260 ky and sacagawea ridge c 660 ky carbonate stocks of soils on these terraces increase with increasing soil age but at generally decreasing rates a quasi steady state situation however was not reached before 1 my the time split approach showed that caco3 accumulation rates were the highest during marine isotope mis cold stages 2 13 g caco3 m2 y presumably due to a sparse vegetation cover during mis2 pinedale and 8 lower bull lake compared to organic carbon c 8 10 kg corg m2 the inorganic carbon stocks of the fine earth fraction were much higher c 60 kg cinorg m2 although the dominant pedogenic process here appears to be carbonate accumulation chemical weathering and elemental leaching also are significant weathering data were obtained using immobile elements and rare earth elements ree as tracers chemical weathering and related leaching were particularly notable for na originating from plagioclase in addition pedogenetic al and mn oxyhydroxides accumulate 220 and 32 g m2 respectively after 660 ky these form at relatively low rates however when compared to moister and cooler conditions at higher altitudes in the wind river range due to the dry climate under which the terrace soils formed annual precipitation 32 cm yr 1 weakly crystalline and amorphous fe oxyhydroxide is rapidly transformed into crystalline forms hematite over time consequently the stocks of weakly crystalline and amorphous fe oxyhydroxide was significantly lower in the 660 ky soils 50 g m2 than in the holocene soils 1000 g m2 the development of soils on quaternary outwash terraces in this region is controlled through the rates of aeolian influx over time as modified by glacial interglacial climate variations rather than by moisture availability consequently carbonate accumulation rates in these soils are influx limited rather than moisture limited

recent crustal deformation in southern california deduced from the restoration of folded and faulted strata a rigid element method of restoration unfold is used to restore competent folded and faulted layers of the ventura and los angeles basins to their initial horizontal state comparison of initial undeformed state with present deformed state allows one to estimate both the finite crustal deformation and its associated horizontal displacement field relative to an arbitrary fixed line including data from the santa barbara channel basin the total finite displacement field for the western transverse ranges and vicinity within the pacific plate is inferred from this map restoration and is modeled as a double fan closure this model implies a 10 clockwise rotation of the northeen boundary of the western transverse ranges and a 5 counterclockwise rotation of its northeast boundary lateral variation of the deformation reveals the heterogeneity of the subsurface deformation most of the major thrusts appear to initiate as en echelon structures along the left lateral northern margin and the right lateral northeastern margin of the studied area the resulting deformation and displacement values closely match those derived by other geological methods section balancing techniques or fault slip measurements and by geophysical methods geodetic paleomagnetic and focal mechanism data map restoration thus is a method that can independently quantify both local and regional deformation including folds and faults this method also reveals the zones where problems of compatibility appear with the available geological and geophysical data and thus where the next studies might be focused

the illusion of diffusion field evidence for depth dependent sediment transport soil covered upland landscapes are common in much of the habitable world and our understanding of their evolution as a function of different climatic tectonic and geologic regimes is important across a wide range of disciplines erosion laws direct quantitative study of the processes shaping earth s surface and form the basis of landscape evolution modeling but are based on limited field data here we use in situ produced cosmogenic 1 0 be and 2 6 al concentrations from granitic saprolite to quantify an exponential decline in soil production with increasing soil thickness for a new field site in point reyes california results are similar to soil production functions from two different previously studied field sites and are used with extensive measurements of soil thickness to quantify depth integrated sediment transport flux plots of calculated sediment fluxes against the product of soil depth and hillslope gradient provide the first field based evidence that soil transport is a nonlinear depth dependent function data from all sites suggest that the widely used linear diffusion equation is only appropriate for shallow gradient convex up regions while the depth dependent transport law is more broadly applicable quantifying both the mobile soil thickness and landscape morphology is therefore critical to understanding how landscapes evolve

geodetic measurement of tectonic deformation in the santa maria fold and thrust belt california we have analyzed geodetic observations to resolve tectonic deformation across the santa maria fold and thrust belt northwest of santa barbara california the geodetic network forms a braced quadrilateral with 40 km sides whose southwest corner is the vandenberg very long baseline interferometry station the data include 1 historical triangulation from the 1880s 1920s and 1950s 2 electronic distance measurement trilateration from 1971 and 1985 and 3 global positioning system observations from 1986 and 1987 we combine the three different types of data to estimate two dimensional station positions and strain rate parameters simultaneously using a model which constrains the relative velocity field to be linear in space and constant in time we find significant strain rates the maximum compressive strain is oriented n17 e 5 e and the compressive strain rate in this direction is 0 13 0 03 strain yr under the assumption that the unresolved rotational component of the velocity field is zero we estimate that the integrated rate of deformation across the basin is 7 1 mm yr oriented at n03 e 13 this vector can be decomposed into 6 2 mm yr of crustal shortening on the general structural trend of n30 e and 3 1 mm yr of right lateral shear across this axis on the basis of these values and earthquake focal mechanisms in the area we infer that the deformation occurs on northwest trending folds and thrusts within the belt these results are consistent with the rate and direction of deformation across the central california coast ranges inferred by balancing pacific north america plate motion against san andreas slip and basin and range extension they imply that the santa maria fold and thrust belt is the primary active element in transforming motion from the coast ranges to the western transverse ranges and the santa barbara channel