processes regulating the solute concentrations of snowmelt runoff in two subalpine catchments of the sierra nevada california geochemical processes regulating solute concentrations in snowmelt runoff were investigated for the snowmelt periods of 1992 and 1993 in two subalpine catchments in sequoia national park california the catchments 0 5 and 0 2 ha have 10 and 25 soil coverage respectively the remaining area is exposed granodiorite bedrock mineral weathering was the major source of solutes in runoff calcium export in excess of stoichiometric plagioclase weathering was attributed to dry deposition and the weathering of mafic minerals and disseminated calcite cation exchange was important in the regulation of k and increased base cation export in response to rain on snow events and libr tracer sulfate fluxes were attributed to snowpack elution and so4 desorption after the beginning of melt the selective retention of li during tracer experiments suggests that acid neutralizing capacity is linked to soil stocks along convoluted flow paths and is not necessarily compromised in areas of sparse soil cover

silicate weathering and base cation export in granitic watersheds sierra nevada california u s a under certain conditions the composition of runoff from the sierra nevada california can be explained by the stoichiometry of weathering products from a selected suite of primary minerals found in the bedrock in the seminal study of this problem the dissolution of plagioclase feldspars and the formation of kaolinite largely explained typical runoff composition feth et al 1964 garrels and mackenzie 1967 there is no question that primary mineral weathering is the ultimate source of cations in surface waters in the sierra nevada while the compositions of samples collected in the summer at the time of maximum accessibility and minimum flows e g feth et al 1964 clow 1987 can be explained by basin mineralogy waters collected during the period of spring snow melt in alpine and subalpine watersheds are not as easily interpreted brown et al 1990 williams et al 1991 1993 accurate mass balance has required modifications and assumptions in nearly all cases including selective mineral weathering mixing multiple sources of waters and selective cation retention by soils the analysis of cation export from alpine sierra watersheds needs to include some or all of these mechanisms to produce an accurate accounting primary mineral weathering alone is not sufficient to explain intra annual variations in cation export 2 selective mineral weathering

controls on surface water chemistry in the upper merced river basin yosemite national park california surface water draining granitic bedrock in yosemite national park exhibits considerable variability in chemical composition despite the relative homogeneity of bedrock chemistry other geological factors including the jointing and distribution of glacial till appear to exert strong controls on water composition chemical data from three surface water surveys in the upper merced river basin conducted in august 1981 june 1988 and august 1991 were analysed and compared with mapped geological hydrological and topographic features to identify the solute sources and processes that control water chemistry within the basin during baseflow water at most of the sampling sites was dilute with alkalinities ranging from 26 to 77 pequiv i alkalinity was much higher in two subcatchments however ranging from 51 to 302 pequiv 1 base cations and silica were also significantly higher in these two catchments than in the rest of the watershed concentrations of weathering products in surface water were correlated to the fraction of each subcatchment underlain by surficial material which is mostly glacial till silicate mineral weathering is the dominant control on concentrations of alkalinity silica and base cations and ratios of these constituents in surface water reflect the composition of local bedrock chloride concentrations in surface water samples varied widely ranging from 1 to 96 pequiv 1 the annual volume weighted mean chloride concentration in the merced river at the happy isles gauge from 1968 to 1990 was 26 pequiv l which was five times higher than in atmospheric deposition 4 5 pequiv l suggesting that a source of chloride exists within the watershed saline groundwater springs whose locations are probably controlled by vertical jointing in the bedrock are the most likely source of the chloride sulphate concentrations varied much less than most other solutes ranging from 3 to 14 pequiv 1 concentrations of sulphate in quarterly samples collected at the watershed outlet also showed relatively little variation suggesting that sulphate may be regulated to some extent by a within watershed process such as sulphate adsorption

episodic lake acidification in the sierra nevada california seven high altitude headwater catchments were studied from 1990 to 1994 to evaluate susceptibility to episodic acid neutralizing capacity anc depression dilution decreasing base cation concentrations was the primary factor in anc depression during snowmelt accounting for 75 to 97 of the anc reduction in lakes where acidification increasing anion concentrations was noted nitrate and sulfate were equally important during the first half of snowmelt while sulfate dominated the latter half a linear model based on the relationship between minimum and fall overturn anc for the lakes in our study estimated that none of the 114 lakes sampled during the 1985 epa western lakes survey had been episodically acidified anc 0 modifications of the model were used to predict that approximately 6 and 10 of sierran lakes will become episodically acidified with increases in nitrate and sulfate deposition of 50 and 150 respectively no lakes will be chronically acidified with these depositional increases

paleoenvironmental and paleoclimatic interpretations of the late paleocene goler formation southern california u s a based on paleosol geochemistry the paleocene was characterized by high global temperatures and elevated concentrations of atmospheric co2 paleoclimate records of this epoch are of particular interest to understanding the effects of anthropogenic climate forcing as well as linkages between the paleocene climate and major tectonic and evolutionary events however terrestrial paleoclimatic records of the paleocene are limited in their spatial extent and few such records are known from western north america in this study paleosols from two members in the late paleocene goler formation of southern california were used to investigate local paleoclimatic conditions the paleosols were described in detail and analyzed for morphology clay mineralogy and bulk geochemistry carbonate nodules present in paleosols from the upper member member 4a were characterized using petrographic and cathodoluminescence microscopy and were analyzed for carbon and oxygen stable isotope composition enrichment and retention of soluble elements ca mg and na and the mobilization of fe and mn in the paleosol profiles suggest a climate with strongly seasonal precipitation this interpretation is further supported by the presence of pedogenic slickensides and the clay minerals smectite and illite the appearance of pedogenic carbonate nodules in paleosols from the upper member is suggestive of a shift to more arid or more seasonal conditions that is coincident with a prominent change in sediment provenance and an inferred increase in sedimentation rate uplift of the ancestral sierra nevada during the late paleocene was likely an important control on regional paleoclimate due to the effects of elevated topography on mean annual precipitation and seasonal distribution of precipitation the correlation of a shift in pedogenic processes with changes in provenance and sedimentation rate suggests that the evolution of regional tectonic activity was an important control on these processes during the deposition of the goler formation

stratigraphic evidence for late quaternary dune activity near hudson on the piedmont of northern colorado stabilized dune fields are common features near hudson on the piedmont of northern colorado exposures in dune and interdune sites expose a sequence of eolian sediments and paleosols that record a complex history of eolian activity during the late quaternary radiocarbon and thermoluminescence age estimates on a horizons buried by eolian sand indicate that dunes were reactivated sometime between 7 and 9 ka on the basis of morphology of surface soils the dunes were most recently stabilized 3 ka at present there are no data to indicate if there were multiple periods of dune movement and stabilization during the holocene the penultimate pre holocene dune forming episode probably terminated ca 13 ka and may be coincident with the pinedale glaciation the stratigraphy at interdune sites shows at least two eolian depositional events prior to the penultimate event they were separated by periods of pedogenesis one of which may have exceeded 40 ka this analysis indicates that dunes in northern colorado were active during both cold arid and warm arid periods in the late quaternary

neutralization of atmospheric acidity by chemical weathering in an alpine drainage basin in the north cascade mountains the most important weathering reaction that neutralizes incoming atmospheric acidity in the south cascade lake basin is weathering of calcite which occurs in trace amounts in veins on joint surfaces and as a subglacial surficial deposit although the basin is underlain by igneous and high grade metamorphic rocks weathering of plagioclase is quantitatively negligible the principal silicate weathering reaction is alteration of biotite to vermiculite these conclusions are based on mass balance calculations involving runoff compositions and on mineralogical observations for predictive modeling of the effects of increased acid deposition it is essential to identify the relevant weathering reactions feldspar weathering is commonly not an important source of solutes in alpine basins underlain by granitic rocks 30 references 2 figures 1 table

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

alkalinity dynamics in an unacidified alpine lake sierra nevada california gem lake a small unacidificd high elevation lake in the sierra nevada undergoes an annual cycle of low alkalinity between 30 and 40 pcq liter during the ice free season and high alkalinity 240 peq liter in fall and winter both ph and alkalinity decrease drastically up to one unit for ph and 200 peq liter for alkalinity during spring snowmelt but chemistry of the snow snowmelt and runoff indicate that the declines in alkalinity are due to dilution rather than acidification the hydraulic residence time in the lake incrcascs from about 135 d in winter to 7 d during snowmclt high alkalinity water is simply flushed from the lake and replaced by water with an ionic composition very near that of the snowmclt runoff increases in alkalinity in fall and winter can be accounted for by the rates of weathering in the watershed a mass balance approach is used to reconstruct weathering reactions in the basin it suggests that the lake receives both surface runoff with the weathering products of the hydrolysis of granodiorite minerals to kaolinite and deep water from subterranean circulation with the products of granodiorite weathering to both kaolinitc and smectite the relative importances of low alkalinity surface runoff and high alkalinity groundwater to the recharge of the lake are proposed as factors controlling the seasonal bicarbonate concentration of the lake

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

stability of holocene climate regimes in the yellowstone region abstract a 12 500 yr pollen record from loon lake wyoming provides information on the climate history of the southwestern margin of yellowstone national park the environmental reconstruction was used to evaluate hypotheses that address spatial variations in the holocene climate of mountainous regions loon lake lies within the summer dry winter wet climate regime an increase in xerophytic pollen taxa suggests drier than present conditions between ca 9500 and 5500 14 c yr b p this response is consistent with the hypothesis that increased summer radiation and the expansion of the east pacific subtropical high pressure system in the early holocene intensified summer drought at locations within the summer dry winter wet regime this climate history contrasts with that of nearby sites in the summer wet winter dry region which were under the influence of stronger summer monsoonal circulation in the early holocene the loon lake record implies that the location of contrasting climate regimes did not change in the yellowstone region during the holocene the amplitude of the regimes however was determined by the intensity of circulation features and these varied with temporal changes in the seasonal distribution of solar radiation

late holocene dune accretion and episodes of persistent drought in the great plains of northeastern colorado abstract the great plains of the mid west usa contain dunefields which display stratigraphic evidence of episodic sand drift throughout the holocene and in some cases the late pleistocene widespread aeolian activity has been linked to persistent megadroughts caused by a weakening of the tropical moisture laden circulation from the gulf of mexico and equatorial pacific infrared stimulated luminescence irsl dating has been applied to two exposures in the fort morgan dunefield of northeastern colorado where radiocarbon dated buried soils provide ages for land surface stability irsl ages show that sand drift occurred episodically during the late holocene at 4 85 2 37 1 06 0 80 0 6 0 53 and 0 37 ka

middle and late holocene dune reactivation in the nebraska sand hills usa a combination of optical dating of aeolian sand and radiocarbon dating of palaeosols and interdune sediments has allowed some refinements to the chronostratigraphy of the nebraska sand hills our results directly confirm previous inferences that multiple phases of aeolian deposition including megabarchan dune reactivation occurred within the sand hills during the middle and late holocene optical dates on stratified aeolian barchan dune sediments from two localities provide ages ranging from c 6 ka to 300 years ago weakly developed palaeosols intercalated within the dune sediments and other forms of post depositional modification indicate periods of relative stability and reduced dune mobilization optical dates on the upper 12 15 m of two dune exposures indicate repeated possibly regionally correlative reactivations which occurred between c 400 500 and 200 300 years ago comparison of late holocene aeolian activity with local and regional palaeoclimatic proxy records suggests that dune reacti

the role of disseminated calcite in the chemical weathering of granitoid rocks accessory calcite present at concentrations between 300 and 3000 mg kg 1 occurs in fresh granitoid rocks sampled from the merced watershed in yosemite national park ca usa loch vale in rocky mountain national park co usa the panola watershed ga usa and the rio icacos puerto rico calcite occurs as fillings in microfractures as disseminated grains within the silicate matrix and as replacement of calcic cores in plagioclase flow through column experiments using de ionized water saturated with 0 05 atm co2 produced effluents from the fresh granitoid rocks that were dominated by ca and bicarbonate and thermodynamically saturated with calcite during reactions up to 1 7 yr calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates principally biotite mass balance calculations indicate that most calcite had been removed during this time and accounted for 57 98 of the total ca released from these rocks experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution the lack of excess ca and alkalinity indicated that calcite had been previously removed by natural weathering the extent of ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks high ca na ratios relative to plagioclase stoichiometries indicate excess ca in the yosemite loch vale and other alpine watersheds in the sierra nevada and rocky mountains of the western united states this ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains in contrast ca na flux ratios are comparable to or less than the ca na ratios for plagioclase in the subtropical panola and tropical rio icacos watersheds in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport limited weathering these results indicate that the weathering of accessory calcite may strongly influence ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces

mechanisms of petm global change constrained by a new record from central utah catastrophic carbon release and global warming during the paleocene eocene thermal maximum petm profoundly affected continental climate and ecosystems understanding of the details and mechanisms of these effects is limited by the poor geographic coverage of existing continental petm records here we extend the record of this event in north america through identification of the petm carbon isotope excursion within a sequence of paleosols in the north horn formation of central utah some 500 km to the south of previous records from northern wyoming data from the new site suggest that patterns of climatological change were similar across a meridional transect of western north america but that petm climate was relatively more arid in the southern rocky mountains possibly reflecting diversion of precipitation from middle to high latitudes our results are consistent with two proposed mechanisms explaining variation in the amplitude of continental petm carbon isotope records in terms of changes in floral composition or varying environmental wetness and they present opportunities for future tests of proposed north south biotic dispersal during the petm

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

ground water processes controlling a prairie lake s response to middle holocene drought lake response to climate forcing is commonly regarded as being controlled by within lake processes we present a case from the northern great plains in which holocene drought response recorded in lake sediments was determined by changes in chemical characteristics of source ground water middle holocene ostracode assemblages were dominated by halophylic limnocythere staplini indicating increased lake water salinity yet the oxygen isotope values in this period decreased by 2 to 3 contrary to expectations of evaporative dominance we infer from these proxy records and ground water flow model results that the paleoclimatic record in the lake was mediated by changes in ground water catchment area and by reduction in evapotranspiration accompanying desiccation of peripheral lake basins

granite weathering and the sensitivity of alpine lakes to acid deposition lake chemical data from the national surface water survey nsws were corrected for the effects of regional atmospheric deposition and then used to evaluate the role of weathering in supplying base cations silica sulfate and alkalinity to surface waters in alpine vs subalpine and in glaciated vs unglaciated granitic terrane of the western and southeastern united states thermodynamic models idealized reaction stoichiometry and multivariate regression involving solutes and geographic variables indicate that irreversible weathering can largely account for lake chemistry by contrast relatively minor roles are played by reversible ion exchange in soils and sediments terrestrial bioaccumulation and transformations in lakes the regional patterns in lake acidity components no so4 doc co3 and statistical relationships between acidity and base cations demonstrate that rock weathering is limited by acid inputs in many alpine catchments prior to fall overturn the empirical success of the henriksen alkalinity model depends on a high ca na weathering ratio the latter increases with increasing physical disturbance of the catchment iuvenility hence under natural circumstances attains a maximum as a result of on going or recent glaciation the henriksen model fails in geochemically old terrane where cation losses accompanying silicate weathering attain steady state proportions

a solution to anomalous fading and age shortfalls in optical dating of feldspar minerals abstract recent reports of age underestimations for events of interest in both palaeoclimatology and archaeology have led to questioning the validity of using luminescence for dating sediments the commonly designated culprit is anomalous fading of feldspar luminescence we investigated the differential fading rates of single feldspar grains in sediment samples from different geological domains of north america and deduced how one could extrapolate to zero fading this is shown to resolve an extreme case of optical age underestimation documented for the late pleistocene norfolk formation a key palaeoclimate stratigraphic unit exposed along the north american atlantic coast

paleosol geochemistry of the late paleocene goler formation of southern california abstract paleosol fossilized soil geochemistry can provide a record of paleoclimatic conditions due to the relationships between pedogenic processes and climate in this study paleosols from the late paleocene goler formation of southern california were used to determine the paleoclimatic conditions active during pedogenesis the enrichment and retention of soluble elements ca mg and na and the mobilization of fe and mn within the paleosol profiles suggest a climate with strongly seasonal precipitation similarly variations in the mn content and 13c ratio of pedogenic carbonate nodules also reflect seasonal precipitation regional paleotopography was likely an important control on the paleoclimate of the goler formation due to rain shadow effects although the size and location of these ancient mountains are poorly constrained the identification of climatic effects specifically associated with these variables provides new constraints

optical dating of dune sand for the study of sea level change a new widely applicable method to obtain well constrained relative sea level records presented here relies on optical dating of inorganic coastal landforms and sediments eighteen optical ages of basal dune sand from a barrier in massachusetts united states indicate that local relative sea level rose 8 m during the past 5 5 k y a sea level curve drawn from these optical ages shows good agreement with independent evidence from salt marsh peat sampled behind the barrier demonstrating the reliability of the method optical dating will be particularly useful in analyzing coastal records that contain too few organic indicators to allow high resolution 14 c based analyses

paleoelevation estimates for the northern and central proto basin and range from carbonate clumped isotope thermometry 1 quantitative paleoelevation histories can help explain both why and how widespread cenozoic extension occurred in the basin and range province of western north america we present new estimates of preextensional paleoelevations for the northern and central basin and range using clumped isotope 47 thermometry of lacustrine carbonates collected from each region comparison of carbonate 47 derived mean annual air temperature maat estimates 16 c 20 c for the late cretaceous eocene sheep pass basin of east central nevada with published maat estimates for the eocene coastal northern sierra nevada 20 c 25 c suggests that the early paleogene sheep pass basin had a paleoelevation of 2 km such a modest paleoelevation suggests that either 1 the proto northern basin and range did not attain maximum paleoelevations of 3 4 km until the late eocene early oligocene or 2 the sheep pass basin was a local high relief 1 km setting contained within a 3 km orogenic highland nevadaplano similarity of 47 derived maat estimates 17 c 24 c for carbonates from the central basin and range and the near sea level southern sierra nevada bena basin indicate that middle miocene paleoelevations in the death valley region were 1 5 km these fairly low paleoelevations are incompatible with preextensional crustal thicknesses 52 km and indicate that mean elevation change was minor 500 m and lithospheric mass was not conserved during 100 neogene extension of the central basin and range but was instead likely compensated by synextensional magmatic additions to the crust

chemical weathering and cation loss in a base poor watershed weathering of minerals in soils provides important plant nutrients and consumes acidity yet mineral weathering is difficult to observe and quantify we derived present day weathering flux estimates for soil minerals in a forested watershed in central new hampshire using a geochemical mass balance the cone pond watershed is characterized by low alkalinity surface waters and acidic spodosols developed on a thin mantle of locally derived till making it susceptible to continued inputs of acid precipitation weathering reactions were developed on the basis of observed patterns of mineral abundance in the soil profile and measured mineral chemistry the dissolution of approximately 171 mol ha 1 yr 1 of plagioclase feldspar is the predominant weathering reaction at cone pond weathering fluxes of hornblende biotite chlorite and potassium feldspar ranged from 3 to 20 mol ha 1 yr 1 an order of magnitude lower when normalized to their abundances in the soil however hornblende and chlorite had the fastest weathering rates as measured by cation release chemical weathering mainly of plagioclase resulted in the neutralization of only 52 of incoming acidity furthermore silicate weathering could only account for the release of about 53 mol ha 1 yr 1 of ca compared to the observed net output stream loss minus bulk precipitation input of 75 mol ha 1 yr 1 on the basis of these observations and a companion study we conclude that current acid inputs exceed the ability of cone pond soils to neutralize hydrogen ion and that depletion of approximately 22 53 mol ha 1 yr 1 of ca from labile soil pools is occurring in this area the rate of ca depletion is one third to one eighth of the rate estimated for a more base rich watershed nearby