long term atmospheric deposition as the source of nitrate and other salts in the atacama desert chile new evidence from mass independent oxygen isotopic compositions abstract isotopic analysis of nitrate and sulfate minerals from the nitrate ore fields of the atacama desert in northern chile has shown anomalous 17 o enrichments in both minerals 17 o values of 14 21 in nitrate and 0 4 to 4 in sulfate are the most positive found in terrestrial minerals to date modeling of atmospheric processes indicates that the 17 o signatures are the result of photochemical reactions in the troposphere and stratosphere we conclude that the bulk of the nitrate sulfate and other soluble salts in some parts of the atacama desert must be the result of atmospheric deposition of particles produced by gas to particle conversion with minor but varying amounts from sea spray and local terrestrial sources flux calculations indicate that the major salt deposits could have accumulated from atmospheric deposition in a period of 200 000 to 2 0 m years during hyper arid conditions similar to those currently found in the atacama desert correlations between 17 o and 18 o in nitrate salts from the atacama desert and mojave desert california indicate varying fractions of microbial and photochemical end member sources the photochemical nitrate isotope signature is well preserved in the driest surficial environments that are almost lifeless whereas the microbial nitrate isotope signature becomes dominant rapidly with increasing moisture biologic activity and nitrogen cycling these isotopic signatures have important implications for paleoclimate astrobiology and n cycling studies

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

airborne dust and its significance to soils abstract movement of mineral dust by the atmosphere has been underway for ages but efforts to assess its magnitude and significance have come largely in the last century attempts to identify and understand effects of the dust on soils are even more recent mostly in the last 30 years airborne movements have several forms dust is transported by large storms that can be spectacular dust is also moved by smaller pulses and in a rather continuous flux most movement is within continents or from continents to nearby oceans but fine dust fine silt and clay is carried from one continent to another prime sources of the dust are the deserts and semi arid regions of the world for example large quantities of dust are carried out of the sahara every year quantities of dust carried by individual pulses from the small ones to the massive storms extend from a few thousand to 150 million metric tons during the course of a year the total quantities can be large one example is an estimate that on the average 770 million metric tons originating in the western united states are carried 2300 km each year that amount would add roughly 3000 kg ha 1 yr 1 to soils between the rocky mountains and the mississippi river small pulses and the near continuous flux add between 100 and 200 kg ha 1 yr 1 to soils of the eastern united states on the average comparable quantities are being added to soils in other parts of the world as well airborne accessions of dust have a variety of effects in soil development and on soils after they have been formed dust dominates processes of genesis in a few soils affects horizon differentiation appreciably in many more is a primary source of constituents essential to some horizons and layers in a number of soils provides the bulk of the material for silty surface horizons in many soils and can contribute supplies of nutrient elements for plants examples of all such effects are covered in this review first among these effects to be recognized even though not understood were the silty surface layers that failed to match underlying horizons later recognized was airborne dust as a source of calcium carbonate for calcic horizons that the dust could add significant quantities of nutrient elements as for example south of the sahara came into the picture even later the beneficial effects of airborne dust to many soils raises an interesting question is the dust more or less useful in its new location than it was in its source area an adequate answer to that question would provide an improved basis for assessing the effects of wind erosion

genesis of marine terrace soils barbados west indies evidence from mineralogy and geochemistry well developed clay rich soils dominated by interstratified kaolinite smectite are found on the uplifted coral reef terraces on the island of barbados the reef limestone is unlikely to have been the soil parent material however because it is 98 per cent caco3 and geomorphic evidence argues against the 20 m of reef solution required to produce the soils by this process the mineralogy of the sand silt and clay fractions of the soils and trace element geochemistry suggest that aeolian materials carried on the trade winds from africa volcanic ash from the island of st vincent and quartz from tertiary bedrock on the island itself are the parent materials for the soils

formation and preservation of pedogenic carbonates in south india links with paleo monsoon and pedological conditions clues from sr isotopes u th series and rees the influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the western ghats karnataka plateau south west india has been studied along the climosequence the current mean annual rainfall mar varies within a 80 km transect from 6000 mm at the edge of the plateau to 500 mm inland pedogenic carbonates occur in the mar range of 500 1200 mm in the semi arid zone mar 500 900 mm carbonates occur i as rhick hardpan calcretes on pediment slopes and ii as nodular horizons in polygenic black soils i e vertisols in the sub humid zone mar 900 1500 mm pedogenic carbonates are disseminated in the black soil matrices either as loose irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size they also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate cemented lumps of centimetric to decimetric size chemical and isotopic sr 87 sr 86 compositions of the carbonate fraction were determined after leaching with 0 25 n hcl the corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed the trend defined by the sr 87 sr 86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition considering the residual fraction of each sample as the most likely lithogenic source of ca in carbonates it is estimated that from 24 to 82 55 on average of ca is derived from local bedrock weathering leading to a consumption of an equivalent proportion of atmospheric co2 these values indicate that climatic conditions were humid enough to allow silicate weathering mar at the time of carbonate formation likely ranged from 400 to 700 mm which is 2 to 3 fold less than the current mar at these locations the sr u and mg contents and the u 234 u 238 activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation the relatively high concentrations of sr u and mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite possibly due to a better confinement of the pore waters which is supported by their high u 234 u 238 signatures and or to higher content of dissolved carbonates in the pore waters the occurrence of ce mn and fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation the carbonate ages determined by the u th method range from 1 33 0 84 kyr to 7 5 2 7 kyr and to a cluster of five ages around 20 kyr i e the last glacial maximum period the young occurrences are only located in the black soils which therefore constitute sensitive environments for trapping and retaining atmospheric co2 even on short time scales the maximum age of carbonates depends on their location in the climatic gradient from about 20 kyr for centimetric nodules at mule hole mar 1100 mm yr to 200 kyr for the calcrete at gundlupet mar 700 mm yr durand et al 2007 the intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils c 2010 elsevier ltd all rights reserved

isotopic evidence for the source of ca and s in soil gypsum anhydrite and calcite in the atacama desert chile abstract the origin of pedogenic salts in the atacama desert has long been debated possible salt sources include in situ weathering at the soil site local sources such as aerosols from the adjacent pacific ocean or salt encrusted playas salars and extra local atmospheric dust to identify the origin of ca and s in atacama soil salts we determined 34 s and 87 sr 86 sr values of soil gypsum anhydrite and 87 sr 86 sr values of soil calcite along three east west trending transects our results demonstrate the strong influence of marine aerosols on soil gypsum anhydrite development in areas where marine fog penetrates inland results from an east west transect located along a breach in the coastal cordillera show that most soils within 90 km of the coast and below 1300 m in elevation are influenced by marine aerosols and that soils within 50 km and below 800 m in elevation receive 50 of ca and s from marine aerosols 34 s values 14 and 87 sr 86 sr values 0 7083 in areas where the coastal cordillera is 1200 m in elevation however coastal fog cannot penetrate inland and the contribution of marine aerosols to soils is greatly reduced most pedogenic salts from inland soils have 34 s values between 5 0 to 8 0 and 87 sr 86 sr ratios between 0 7070 and 0 7076 these values are similar to average 34 s and 87 sr 86 sr values of salts from local streams lakes and salars 5 4 2 34 s and 0 70749 0 00045 87 sr 86 sr in the andes and atacama suggesting extensive eolian reworking of salar salts onto the surrounding landscape ultimately salar salts are precipitated from evaporated ground water which has acquired its dissolved solutes from water rock interactions both high and low temperature along flowpaths from recharge areas in the andes therefore the main source for ca and s in gypsum anhydrite in non coastal soils is indirect and involves bedrock alteration not surficially on the hyperarid landscape but in the subsurface by ground water followed by eolian redistribution of ground water derived salar salts to soils the spatial distribution of high grade nitrate deposits appears to correspond with areas that receive the lowest fluxes of local marine and salar salt supporting arguments for tropospheric nitrogen as the main source for soil nitrate

strontium and carbon isotope tracers and the origins of soil carbonate in south australia and victoria abstract calcium carbonate occurs in soils in association with a variety of rock types in coastal and inland south australia and victoria the 87 sr 86 sr ratios of the coastal soil carbonates fall between 0 7094 and 0 7098 showing that the ocean is the principal source of calcium to nearly all soils near the coast and that contributions from bedrock are generally small an exception is the soil formed on the young volcano at mt gambier in which the average ratio for carbonate is about 0 7070 compared to 0 7041 for the volcanic ash the basaltic ash of the volcano is readily weathered and rich in calcium roughly 40 of strontium and 10 to 20 of the calcium in the soil carbonate derives from the ash and the balance from marine sources the 87 sr 86 sr ratios from soil carbonate gradually increase inland reaching values of 0 7152 these higher ratios reflect at least in part the increasing 87 sr 86 sr ratio of inland dust in contrast the ocean does not contribute significantly to the carbon pool of the soils we studied the 13 c pdb values of soil carbonates on kangaroo island and the higher rainfall areas of eastern victoria fall between 11 0 and 8 7 indicating that the carbonate formed in equilibrium with the c3 dominated vegetation typical of the region in the warmer inland areas to the north such as the eyre peninsula the 13 c value of soil carbonate averages 5 3 reflecting the higher proportion of c4 plants in the local biomass mixing with marine sources of carbonate cannot account for the observed carbon isotopic patterns the flux of carbon into soils from the ocean therefore must be small compared to that derived from plant respiration and decay

the effect of dust deposition on the soils of the land of israel abstract loess and aeolian dust affected soil formation to different degrees in most parts of the land of israel in the arid desert the loess was re eroded from slopes and sedimented as fluvial loess in along the valleys by flood water in areas with slight precipitation loess remains on slopes sedimentation rates are slower and loessial serosems are formed in the mildly arid areas in the northern negev the loess covers most of the landscape and occurs in thick sequences intercalated with several superimposed strongly developed loessial brown soils sedimentary and weathering processes occurred simultaneously and sediment palaeosols profiles up to 12 m thick were formed in areas further away from the desert aeolian deposition decreased as a result loessial brown soils grade into dark brown grumic soils and grumusols aeolian dust input also affected soils of the sand dunes of the coastal plain and in the terra rossa soils of the mountainous region

soil forming intervals caused by eolian sediment pulses in the lahontan basin northwestern nevada we have studied a series of toyeh post isotope stage 2 eolian dust fall was the source of fines and salts in these soils apparently this influx was concentrated during two brief intervals or pulses one during the holocene and one during the previous isotope stage 5 interpluvial leaching during the sehoo pluvial removed salts from churchill soils carbonate and soluble salts now observed in the churchill soils represent a toyeh overprint on the churchill profile these pulses of fine sediment and accompanying salts are tantamount to the soil forming intervals that morrison described in the lahontan area episodic eolian dustfall provides fine particles of silicates calcite and soluble salts that infiltrate into the clast supported alluvial piedmont sediments several hundred playas exist in the basin and range each providing directional dust contributions that influence local and regional soil development we counsel caution in assuming constant gradual development of soil properties without due consideration of paleoenvironmental influences on soil forming factors

water chemistry and isotope study of streams and springs in northern chile abstract the relationship between the stable isotopic and chemical composition of rain spring and stream water was studied in the high andes of northern chile the isotopic pattern of the springs is mainly a reflection of the altitude of their recharge areas however processes that occur during snow melting seem to play a major role in the high altitude springs the streams show patterns similar to the springs in the higher part of the basins but their isotopic composition is modified along the river course due mainly to evaporation the difference in chemical composition between the springs at high and intermediate elevations reflects the duration of water rock interaction the best parameter to trace this length of travelling time is the na k ratio which increases as a result of removal of k into alteration minerals k silicates the na cl ratio increases with salinity in springs and decreases in stream water this reflects the different sources of salt whereas the main source of salts in spring water is the dissolution of silicate and sulfide minerals halite accumulations close to the surface is the main salt source in the streams during floods the stream water chemical characteristics change na cl increases with decreased salinity and na k decreases

extensional tectonics in convergent margin basins an example from the salar de atacama chilean andes the salar de atacama basin of northern chile preserves stratigraphic evidence for the evolution of the andean cycle it has evolved from a non arc related rift through back arc and inter arc stages to a neogene fore arc basin accumulation of the sedimentary succession was mainly due to extensional faulting important but short duration contractional episodes do link to known fast order plate margin changes but their stratigraphic effect appears to be restricted to uplift erosion rather than creation of significant flexural subsidence the salar de atacama basin originated as part of a regional rift system during permian time and contains 2 km of permo triassic continental detritus and volcanic rocks the area remained above depositional base level throughout late triassic to late cretaceous time syn rift continental red beds were deposited to a thickness of at least 2 km on a parallel rift segment in the domeyko area to the west continued triassic jurassic extension in the domeyko basin resulted in a classic continental to marine transition with deposition of a 2 km jurassic mixed carbonate clastic sequence in latest cretaceous eocene time the salar basin was an arc related basin and accommo dated some 4 km of continental detritus purilactis group due to back arc extension sediment being derived from the domeyko cordillera and arc rocks to the west late eocene right lateral strike slip faulting and associated restraining bend uplift were driven by a high rate of oblique convergence between the farallon and south american plates this deformation complicated the stratigraphy of the purilactis group and inverted the western basin margin which formed the dominant provenance area for a 2 km thick oligocene continental basin fill component paciencia group the oligocene basin was an extensional to trans tensional basin the miocene holocene salar basin is a continental fore arc basin this latest segment of the basin fill comprises pyroclastic and continental sedimentary rocks thrust over quaternary gravels in many places the cordillera de la sal is an intrabasinal uplift initiated as a thin skinned contractional feature thus the superposed basin fill components represent responses to distinctly different geodynamic settings

geochemistry of bolivian salars lipez southern altiplano origin of solutes and brine evolution abstract the southern bolivian altiplano is a volcanic area which contains numerous undrained basins occupied by playas and saline lakes locally named salars solutes carried by springs and rivers into the salars originate mostly from the alteration of the volcanic rocks and the re solution of ancient buried evaporites both weathering and hydrothermal alteration lead to na hco 3 inflow waters of similar composition high contents of lithium and boron are not specifically related to hydrothermal activity evaporite leaching leads to na cl inflow waters of higher salinity atmospheric precipitation contributes only a small amount of ca and so 4 and very little na or cl the calculated evaporative evolution of the inflow waters shows that about half of them should become highly alkaline brines and the other half should end as near neutral brines however alkaline soda lakes are rare in this region most lake brines are of the na cl and na cl so 4 types to understand this anomaly one characteristic sequence of evaporating waters was studied in detail precipitation of calcite and mg smectites accounts only partially for the reduction of alkalinity a further loss of alkalinity is probably related to the oxidation of wind blown native sulfur in peripheral ponds wind blown sulfur is also deposited around the lakes on the drainage basins in the rainy season ephemeral streams carry along sulfur particles in permanent pools of the preconcentration areas a hydrologic control of brine chemistry is suspected inflow waters that should become alkaline appear to evolve to neutral brines if they remain in contact with atmospheric dust and peripheral colluvium for a long time on the contrary inflow waters to soda lakes are generally close to the shore and have only minimal contact with atmospheric dust and peripheral sediments presently all lakes are at relatively low levels and inflow waters often drain an important area of the drainage basin before reaching the topographic low in the past lakes were at higher levels and less interaction occurred between inflow waters atmospheric dust and peripheral sediments as a result the chemistry of some lakes may have changed during the quaternary

isotopic evidence for eolian recycling of pedogenic carbonate and variations in carbonate dust sources throughout the southwest united states using isotopic ratios of sr c and o we trace calcium carbonate through surface systems across a wide region of semi arid terrain in arizona southwestern usa in order to evaluate the contribution of cations from silicate weathering to soil carbonate we present 87sr 86sr ratios of soil carbonate parent rock dry river course silts floodplain playa dust and rain samples as well as 18o and 13c values of selected samples results show that both parent rock and dust are important sources of cations for soil carbonate in this inland setting where bedrock is dominated by silicate lithologies dust in southeast arizona has higher 87sr 86sr ratios 0 7100 0 7123 than phanerozoic sea water 0 7070 0 7096 these high ratios derive ultimately from silicate rocks our 18o and 13c data show clearly that the dominant source of carbonate dust is eroded older soil carbonate not bedrock limestone because dust contributes significantly to newly forming soil carbonate some products of silicate weathering may reside in soil carbonate two or more times before being removed from the region and this recycling retards the rate at which the products of silicate weathering enter the sedimentary system comparison of the 87sr 86sr ratios of carbonate dust from southeast arizona with those from surrounding regions shows that dust 87sr 86sr ratios and by inference carbonate dust sources vary on a scale of 200 300 km in the southwest united states

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

a preliminary petrographic study of the chilean nitrates the nitrate deposits of the northern atacama desert occurin a narrow zone between the low lying pampa del tamarugal to the east and the hills of the coastal range to the west high purity nitrate ore occurs as stratiform seams about 20 cm thick present at depths of 3 7 m below thedesert surface the ore is hosted by a variety of lithologies and overlain by salt cemented regolith the ore is largely composed of nitratite sodanitre or chilean salt peter and halite with locally abundant humberstonite polyhalite and mirabilite other salts present include ca iodates and a variety of sulphate borate and chromate minerals textural relationships can be used to deduce paragenetic sequences for individual salt samples and these combined to produce a generalized paragenetic web for the nitrate ore these textural data can be combined with published solubility data to investigate the course of fluid evolution during ore genesis the multiplicity of paragenetic relationships within the ore reflects the derivation of precipitating fluids from a variety of sources westwards flowing andean groundwater coastal fogs occasional rainfall and andean derived surface floodwaters the unusual mineralogy of the nitrate ore reflects the extreme chemical evolution of the precipitating brines through multiple episodes of salt precipitation and remobilization during transport to the nitrate horizons the formation of high purity nitrate ore appears to be the result of multiple phases of dissolution reprecipitation and recrystallization that have separated the highly soluble nitrate salts from less soluble salts in the overlying profile salts have largely accumulated through displacive growth but some of the host silicate and carbonate lithologies have also undergonea small degree of salt replacement

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

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

polygenetic development of the mormon mesa nv petrocalcic horizons geomorphic and paleoenvironmental interpretations abstract mormon mesa nevada usa is of one of earth s rare and unique landforms regionally mormon mesa is important because of its relationship to the lower colorado river and its connection to stream incision petrocalcic horizons at mormon mesa developed from multiple exposure erosion and sedimentation events driven by variations in paleoclimate since the early pliocene this study utilizes pedogenic features at mormon mesa to construct a sequence of development for the soil profile we sampled and described seven profiles at mormon mesa to determine the soil and geomorphic processes that have influenced the development of this geomorphically important soil the mormon mesa soil profile generally consists of four petrocalcic soil horizons from the base upward transitional laminar massive and brecciated and an additional set of horizons that formed in unconsolidated surficial eolian sediments the transitional horizon formed after cessation of muddy creek fm deposition 5 to 4 ma and accumulated calcium carbonate to a stage ii iii morphology maybe iv in some locations after a period of landform stability the upper portion of the transitional horizon was exposed and eroded 2 8 ma petrocalcic fragments and stage ii pendants that formed in the transitional horizon were exposed on the surface and later mixed with aggrading eolian sediments after the surface re stabilized calcium carbonate accumulated along the underlying discontinuity with the transitional horizon and formed a laminar horizon shallower accumulations of calcium carbonate formed pendants on the undersides of the rotated petrocalcic fragments and pendants that had previously been eroded from the transitional horizon continued rooting and bioturbation caused rotation and multiple directions of pendant formation today in plan view these pendants appear concentric and are the pisoliths described by bachman and machette bachman g o machette m n 1977 calcic soils and calcretes in the southwestern united states usgs open file report 77 797 continued calcium carbonate precipitation eventually plugged the horizon massive horizon after the massive horizon became indurated the upper portion was exposed fractured eroded and mixed with aggrading eolian sediments these brecciated fragments experienced erosion brecciation and soil stabilization cementation with pedogenic calcite multiple times probably as a result of the pleistocene glacial interglacial climate cycles all of the features described in this study are interpreted to have formed in response to climatic changes that caused either soil erosion with concurrent eolian deposition or soil development and pedogenic carbonate accumulation it is important to understand the development of the mormon mesa soil because it can provide an understanding of the pedogenic and geologic processes that effect the development of stages v and vi soil horizons this study provides a relative sequence of events for the formation of pedogenic features at mormon mesa that can be used for future dating applications more precise dates for the development of the mormon mesa soil will contribute to our understanding of the geomorphic tectonic and climatic processes that have affected this region

a 106ka paleoclimate record from drill core of the salar de atacama northern chile abstract a 100 m long salt core sqm 2005 from the salar de atacama northern chile 23 s 68 w a dry lake bed contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central andes of south america six u series disequilibrium dates range sequentially from 106 1 6 4 to 5 4 2 7 ka based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods saline lakes and expanded mudflats existed in the salar de atacama from 75 7 to 60 7 ka and from 53 4 to 15 3 ka with the wettest perennial lake interval from 26 7 to 16 5 ka short relatively wet periods also occurred in the holocene from 11 4 to 10 2 ka and from 6 2 to 3 5 ka these wet periods at salar de atacama correspond well with other late pleistocene climate records from the central andes that are a function of the net hydrologic budget the minchin tauca lake sequence from salar de uyuni bolivia is synchronous with the 53 4 15 3 ka saline lake wet period at salar de atacama the tauca phase coincided with the wettest perennial lake interval at salar de atacama from 26 7 to 16 5 ka the coipasa lake phase from uyuni was probably contemporaneous with the early holocene wet period at salar de atacama from 11 4 to 10 2 ka the early holocene wet interval at salar de atacama was also synchronous with the maximum holocene lake levels of the chilean altiplano lakes to the east and with grass rich rodent middens between 11 8 and 10 5 ka in age from the atacama basin the lake period at salar de atacama between 26 7 and 15 3 ka compares closely with low 18o values low anion concentrations and high accumulation rates from the sajama glacial ice core southwestern bolivia between 25 and 15 5 ka it is concluded that wet and dry phases were synchronous in the central andean plateau of southwestern bolivia and along the western flank of the andes of northern chile over the past 50 kyr this region which today receives its moisture from the amazon basin to the east probably also did so in the past the wet periods at salar de atacama are in phase with january insolation maxima at 15 s at 70 45 and 20 ka which suggests that past changes in summer insolation influenced precipitation patterns in the central andes however there are no major wet periods linked to the january insolation maximum at 93 ka and the present day extremely dry climate in the atacama desert is associated with a peak in summer insolation therefore there must be other important influences over precipitation in the central andes which modify the first order insolation controls

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

middle miocene climatic change in the atacama desert northern chile evidence from supergene mineralization at la escondida geochronology and paleotopographic reconstruction of the porphyry copper deposit at la escondida chile are used to calculate long term erosion rates and to deduce the timing of tertiary climatic change for a portion of the atacama desert region hypogene hydrothermal alteration and protore mineralization at la escondida took place between 33 7 1 4 and 31 0 1 4 ma based on k ar dating of hydrothermal biotite and sericite supergene weathering and copper sulfide en richment processes were active from 18 0 0 7 to 14 7 0 6 ma based on k ar dating of supergene alunite distinguished from hypogene alunite by grain size color and sulfur isotopic composition reworked lenses of volcanic ash in the vicinity of la escondida provide useful time stratigraphic markers at 8 7 0 4 6 5 0 2 and 4 2 0 2 ma within present soil profiles long term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at la escondida using mass balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid inclusion geobarometry at similar deposits the observed trend of decreasing long term average erosion rates with time is consistent with arid to semiarid conditions in the early miocene changing to hyperarid conditions during the middle miocene this climatic desiccation caused termination of significant supergene copper suffide enrichment at la escondida and elsewhere in the atacama region and preservation of surficial features including the ash horizons and the leached capping middle miocene climatic desiccation in northern chile and southern peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral humboldt current and an increase in upwelling intensity as the antarctic ice cap became established at approximately 15 to 13 ma the central andes cordillera which now provides a rain shadow protecting the atacama region from precipitation from the east must have attained at least half its present elevation prior to about 15 ma to have played a similar role in the middle miocene

rates and geochemical processes of soil and salt crust formation in salars of the atacama desert chile abstract the hyperarid atacama desert contains numerous local basins with surficial salt crusts known as salars where evaporation of shallow groundwater drives the major soil processes we examine chemical and isotopic profiles in two soils of differing ages from the salar llamara to determine the geochemical processes involved in their formation evaporation which provides salts to the soils through mineral precipitation decreases with increasing salt crust thickness and average 0 03 mm m 2 d 1 over geological time frames salt distribution varies predictably with depth and soil age with the most soluble compounds concentrated nearest to the land surface indicating the direction of fluid flow 34s values of mineral sulfate tend to decrease with decreasing soil depth following a pattern indicative of rayleigh like fractionation as solute rich waters migrate toward the land surface 13c and 18o values of carbonate suggest that the uppermost halite layers which contain very small amounts of carbonate have a strong biological signature in contrast carbonate rich layers deeper in the profiles consist of largely unmodified lacustrine carbonate that formed in highly evaporitic lake conditions the continuous upward evaporation of water and dissolved solutes creates a rugged and physically dynamic halite crust composed of rounded salt nodules the crust undergoes deliquescence as atmospheric relative humidity rises from marine air intrusions and we found that the halite nodules on the surface of the salar llamara are nearly always at or above deliquescence relative humidity the interiors of these nodules are therefore able to buffer the large diurnal changes in atmospheric relative humidity allowing for the survival of halophilic microbial communities in an otherwise very dry environment radiocarbon measurements of occluded organic c in the surface crusts indicate that c cycling occurs at differing rates depending on local micrometeorological conditions and that a given salt crust feature may persist for thousands of years once formed

more than ten million years of hyper aridity recorded in the atacama gravels abstract the atacama desert s hyper aridity is closely linked to the development of world class copper and nitrate iodine ores and to regional tectonics and global paleoclimate changes in the cenozoic era the timing when the hyper aridity commenced remains controversial with proposed ages ranging from late oligocene to pleistocene in this study we provide an independent constraint on the initiation of atacama hyper aridity utilizing a 100 m deep profile within the atacama gravels and underneath porphyry copper deposit in spence northern chile the overall high concentration of sulfate up to 10 wt and a multimodal distribution of water soluble salt sulfates chlorides and nitrates indicate multiple generations of sedimentation and salt accumulation events under semi arid to hyper arid climate conditions the multiple sulfate isotope compositions 17o 18o 34s of the upper section 15 0 to 34 5 m are close to those of modern hyperarid surface sulfates while the lower section 34 5 to 65 m displays a depth dependent isotope trend that is best interpreted as marking a period of climate change from semi arid to hyper arid when these data are combined with new chronological 40ar 39ar dates obtained from a volcanic ash layer at depth of 28 0 m our results show that hyper arid condition in the atacama desert was prevailing at least prior to 9 47 ma and may go back as old as the middle miocene

isotopic evolution of river water in the northern chile region two main northern chilean rivers the loa and tarapaca were investigated regarding their isotopic characteristics groundwater associated with various recharge zones and the input of tributaries along their courses mainly control their 180 2h isotopic composition of the rivers in the loa river carbon isotopic exchange between dissolved inorganic carbon dic and atmospheric coplays a minor role in the inorganic carbon cycle of the loa river the carbon isotopic composition 4 c 13 c of this river is probably controlled by carbon source associated with volcanic and geothermal activities and by the deposition of travertines for the tarapaca river the carbon isotope content of the dic reflects the input of recirculated water from irrigated areas along the river course and carbon isotopic exchange these findings imply that the input of volcanic and or geothermal co2 into the dic pool has to be evaluated in order to use carbon isotopes as a dating tool for groundwater in the loa basin and that modern conditions are not analogous to the paleohydrology of the tarapaca river

the stable isotope composition of halite and sulfate of hyperarid soils and its relation to aqueous transport halite nacl and gypsum or anhydrite caso4 are water soluble minerals found in soils of the driest regions of earth and only modest attention has been given to the hydrological processes that distribute these salts vertically in soil profiles the two most notable chloride and sulfate rich deserts on earth are the dry valleys of antarctica and the atacama desert of chile while each is hyperarid they possess very different hydrological regimes we first show using previously published s and o isotope data for sulfate minerals that downward migration of water and sulfate is the primary mechanism responsible for depth profiles of sulfate concentration and s and o isotopes in both deserts in contrast we found quite different soluble cl concentration and cl isotope profiles between the two deserts for antarctic soils with an ice layer near the soil surface the cl concentrations increase with decreasing soil depth whereas the ratio of 37 cl 35 cl increases based on previous field observations by others we found that thermally driven upward movement of brine during the winter described by an advection diffusion model qualitatively mimics the observed profiles in contrast in the atacama desert where rare but relatively large rains drive cl downward through the profiles cl concentrations and 37 cl 35 cl ratios increased with depth the depth trends in cl isotopes are more closely explained by a rayleigh like model of downward fluid flow the isotope profiles and our modeling reveal the similarities and differences between these two very arid regions on earth and are relevant for constraining models of fluid flow in arid zone soil and vadose zone hydrology 2012 elsevier ltd all rights reserved

the origin and distribution of salts on alluvial fans in the atacama desert northern chile the atacama desert has been predominantly hyperarid since the middle miocene combined ionic and x ray diffraction analysis shows that calcium sulphate is prevalent on three similar alluvial fans in salar basins across a transect of different environments in antofagasta province northern chile differences between the fans were largely due to the effect of local factors on salt input secondary redistribution and deposit preservation thus carbonate was notable in the high andes fan c and pre cordillera fan b whereas in the central valley fan a greater qualities of the more soluble salts chlorides and nitrates probably reflect the higher level of aridity and an oceanic source the camanchaca calcium sulphate distribution on the alluvial fans and on adjacent hilltops indicates an aeolian origin evidence from the pre cordillera fan b however suggests that salt input may have been episodic related to changes in conditions within the general aridity and possibly to stone pavement and soil development calcium sulphate sources range from an input in andean precipitation and the camanchaca to abundant regional evaporite deposits it is probable however that products of andean volcanism constitute the dominant primary source of calcium sulphate and that the salt has subsequently been distributed widely within the endoreic basins of the region by a combination of groundwater surface flow and the wind 1997 john wiley sons ltd

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

hydrogeochemistry and stable isotopes of ground and surface waters from two adjacent closed basins atacama desert northern chile the geochemistry and stable isotopes of groundwaters surface waters and precipitation indicate different sources of some dissolved constituents but a common source of recharge and other constituents in two adjacent closed basins in the atacama desert region of northern chile 24 15 24 45 s waters from artesian wells trenches and ephemeral streams in the punta negra basin are characterized by concentrations of na ca mg and cl so4 with tds mg ca and so4 cl with tds also mg ca and so4 cl but with tds up to 40 g l the deep mine waters have ph between 3 2 and 3 9 and are high in dissolved co2 13c 4 8 pdb indicating probable interaction with oxidizing sulfides the deep mine waters have 18o values of 1 8 compared with values 3 5 for other hamburgo basin waters thus the mine waters may represent a mixture of meteoric waters with deeper metamorphic waters which had interacted with rocks and exchanged oxygen isotopes at elevated temperatures alternatively the deep mine waters may represent fossil meteoric waters which evolved isotopically along an evaporative trend starting from values quite depleted in 18o and dd relative to either precipitation or shallow groundwaters high i br ratios in the hamburgo basin waters and la escondida mine waters are consistent with regionally high i in surficial deposits in the atacama desert region and may represent dissolution of a wind blown evaporite component rain and snow collected during june 1984 indicate systematic 18o and d fractionation with increasing elevation between 3150 and 4180 m a s l 0 21 18o and 1 7 d per 100 m excluding the deep mine waters from la escondida the waters from the hamburgo and punta negra basins have similar d and 18o values and together show a distinct evaporative trend d 5 0 18o 20 2 snowmelt from the central andes cordillera to the east is the most likely source of recharge to both basins some of the waters in the hamburgo basin may have been recharged during late pleistocene when the climate was wetter and a lake filled the intervening punta negra basin as suggested by recent archaeological and geomorphological studies

anatomy of recent and peatified calluna vulgaris stems implications for coal maceral formation abstract anatomical characteristics of peatified calluna vulgaris stems isolated from a selection of northwest european raised bog peat deposits were compared with intact stems in order to reveal anatomical modifications caused by the peatification process four main decomposition processed were discerned 1 loss of structural integrity of cell walls and cell inclusions 2 gelification and swelling of cell walls 3 discolouration of cell walls and 4 deposition of matter in cell lumina fibre tracheids and wood parenchyma appear to be the most affected cell types the two main decomposition trends discerned in these were related to different fungal types precipitation of decay products was mainly observed in vessels bark tissues primary xylem and medullary parenchyma were characterized by an excellent anatomical preservation in the first stages of peatification a rapid decrease in cell contents was observed in bark tissues swelling and gelification was mainly seen in cell walls of the cambium and vessels we conclude that different types of cell walls respond differently to decay conditions this is probably related to differences in the original cell wall chemistry a high intra and intracellular variability in degree of preservation was sometimes observed in identical tissues the microscopic variability arising during peatification of wood and bark testifies to the heterogeneity of coal macerals derived from these tissues