fossil cyclic calcrete in the kuwait group clastic deposits mio pleistocene of kuwait arabian gulf an investigation of the upper kuwait group clastic sequence mio pleistocene exposed along the jal az zor escarpment in north kuwait revealed several horizons of fossil calcrete field occurrences and textural characteristics of the studied sequence indicated that the fossil calcrete was hosted in cyclic fluviatile muddy sandstones and developed through diagenesis during inter fluvial periods depositional and diagenetic features of the calcretized fluviatile sandstone units suggested that each cycle started with the deposition of a fluviatile muddy host sandstone during a humid period this was followed by a period of semi aridity during which calcrete profiles developed the upper part of the calcrete profiles was weathered and terra rosa type soil was formed during wet seasons this was succeeded by a severe arid climate and the deposition of desert aeolian sand sheets fossil nodular calcrete was only developed within the fluviatile muddy sandstones the calcretized sandstones were lithified in two stages of diagenesis an early stage that was responsible for the authigenesis of microcrystalline calcite and the development of calcrete nodules and a later stage during which macrocrystalline calcite cement was precipitated as an intergranular cement displacing and replacing the clay matrix of the host sediments and filling fractures and cavities in the calcrete nodules the findings and conclusions of the present study will help in understanding the lithostratigraphic setting of the kuwait group clastic sequence in the northern arabian gulf region

geomorphology and palaeoclimatology of some upper cretaceous palaeosols in central india abstract the late cretaceous maastrichtian lameta formation exposed around jabalpur in central india comprises a pedogenically modified fluvial succession accumulation of early diagenetic calcite cement during penecontemporaneous pedogenesis has transformed the fluvial sandstones into calcareous sandstones the microscopic features of the palaeosol material include floating grain fabric root traces laminated micrite microspar micrite envelopes and corona structures illuvial clay envelopes poikilotopic spars and minor amounts of siliceous grain and void cutans the palaeosol profiles of the lameta formation can be classified into eleven different types nine of which are comparable to present day mature aridisols and two to inceptisols nine to thirteen palaeosol profiles are present in the individual sections of the lameta formation within the study area each profile comprises two to four distinct pedohorizons arranged in vertical succession there are six types of pedohorizons present in the area of study namely partly altered hosts light coloured and poorly cemented horizons horizons with root traces and root related alterations horizons of subspherical glaebules horizons of platy fused glaebules and subhorizontal root traces and horizons with solution features they show many characteristics similar to the present day soil horizons for example those termed c bk k a and e by pedologists the palaeosol characteristics show correspondence to the nature of fluvial channel migration and the depth of the groundwater table controlled by the geomorphic setting a shallow groundwater table favoured the development of rootmat bearing and gleyed horizons horizons with vertical root traces and glaebules occur where the groundwater table was low mature and thin palaeosols developed in those parts of the lameta fluvial tract that were characterized by stable channels and wide floodplains in contrast thin and comparatively immature soils occurred in the parts where laterally migrating channels were operative the characteristics of the lameta palaeosols suggest that a hot and semiarid climate prevailed for most of the time represented by the lameta formation but short term wet spells occurred during the initial and the terminal phases of the lameta accumulation the low latitudinal palaeoposition of india and the absence of the palaeo monsoon circulation might have produced the hot and semiarid climatic setting during this time

cohesive sediment characterization by combined sedimentation and rheological measurements a laboratory characterization of cohesive sediment has been carried out in which data obtained from standard sedimentation and rheological measurements were combined in a determination of the critical solid concentration for the detection of elasticity in a weakly cohesive suspension the corresponding storage modulus and shear stress are very critical in any in situ rheometry of sediments especially in the study of mud water surface erosion in a flume sedimentation results showed that particle size distribution rather than surface treatment controlled the rheological behavior of the suspension while the critical solid concentration for the appearance of three dimensional space filling network showing some measurable elasticity in the suspension occurred in the region of 0 015 this parallel between the consolidation behavior and shear rheology development for the flocculating system has been established this technique could be an adjunct to the laboratory characterization of cohesive sediments for the estimation of critical shear stress for surface erosion especially in a typical flume experiment under water wave pressure

uv induced mass independent sulfur isotope fractionation in stratospheric volcanic sulfate 1 sulfuric acid aerosols produced in the stratosphere following massive volcanic eruptions possess a mass independent sulfur isotopic signature acquired when volcanic so2 experiences uv photooxidation the volcanic data are consistent with laboratory so2 photooxidation experiments using uv light at 248 nm maximum absorption of ozone whereas sulfur isotopic anomalies previously observed in archean samples are consistent with photodissociation at 190 220 nm a mechanism of so2 photooxidation occurring in the early stage of a stratospheric volcanic plume in the range of 220 320 nm weak band absorption of so2 is also proposed since mass independent sulfur isotope anomalies in stratospheric volcanic sulfate appear to depend on the exposure of so2 to uv radiation their measurements might therefore offer the possibility to determine the degree of uv penetration in the ozone absorption window for the present and past atmospheres they can also be used to determine the stratospheric or tropospheric nature of volcanic eruptions preserved in glaciological records offering the possibility to reassess the climatic impact of past volcanic eruptions

sulfate oxygen 17 anomaly in an oligocene ash bed in mid north america was it the dry fogs 1 the oxygen and sulfur isotope compositions of sulfate particularly the oxygen 17 anomaly provide clues to the origin of sulfate we report a variable oxygen 17 anomaly for water and acid leached sulfate from an oligocene volcanic ash bed in the northern high plains u s a we find no sulfate o 17 anomaly however in freshly collected ashes from recent eruptions around the world the oligocene paleoclimatic and sedimentary evidence argues against a hyperarid condition in the high plains thus a long term background atmospheric sulfate accumulation is less likely the origin combining sulfur isotope data we suggest that the anomalous sulfate was associated with volcanic eruptions in the west but was not directly carried by ash falls extreme dry fog sulfate haze events resulting from tropospheric oxidation of volcanic sulfur gases might provide a viable explanation for the sulfates in the ash bed that carry the oxygen 17 anomaly

calcic paleosols of the plio pleistocene camp rice and palomas formations southern rio grande rift usa abstract seventy four separate paleosols are recognized in the plio pleistocene camp rice and palomas formations of the southern rio grande rift seven types of profiles are present a bw bk c a bt bk c bw bk c bt bk c bt k c bk c and ak calcic and petrocalcic horizons bk and k commonly overlain by argillic horizons bt dominate most paleosol profiles greater pore size and enhanced permeability typical of sandy and silty parent material favored the development of argillic horizons however micrite is the dominant form of calcium carbonate in bk and k horizons regardless of parent material grain size non calcified a horizons are typically lighter in color than adjacent subsurface pedogenic intervals due to their oxidized nature or lower clay content they are only rarely preserved probably due to erosion prior to final burial calcified root mats ak are not directly associated with other pedogenic horizons abundant horizontal roots suggest root mats formed under high water table conditions restriction of ak horizons to the distal piedmont lithofacies supports their development as spring or pond deposits near the toes of alluvial fans individual pedogenic horizons can often be traced hundreds of meters to kilometers normal and parallel to a basin s axis paleosol maturity and preservation potential are greatest for symmetrical basins especially where pedogenesis was far removed from active channels within the axial fluvial system or within distal piedmont settings of asymmetrical basins

settling and consolidation of mud sand mixtures abstract the formation of a cohesive sediment bed is a combination of settling and consolidation processes these processes strongly influence the structure properties and erodibility of the sediment bed at low values of the bed shear stress suspended sediments individual particles or flocs deposit onto the bed subsequently during the consolidation process the flocs and aggregates rearrange themselves to form a denser structure the pore water initially supporting the particles is being expelled in an extensive set of laboratory experiments the influence of sand on the settling and the consolidation of mud has been studied the deposition of mud sand mixtures has been closely followed in settling column experiments for different types of mud at different sand contents during the experiments settling rates density profiles and pore water pressures have been measured the presence of a sand fraction in the initial suspension has a large impact on the bed formation processes the results show that the heavier sand particles settle faster and form a separate layer at the bottom of the column as long as the mud does not form a continuous network structure that prevents this segregation a continuous mud matrix is formed at low sediment supply rates or at high initial suspension concentrations when the concentration of the mud fraction in the mixture exceeds the gel point density the settling rates of the mud sand suspension increase with increasing sand content the local bed densities within the consolidating bed increase with increasing sand content of the initial suspension even for the sand free top layer sand addition also speeds up the consolidation process and permeability increases however these effects seem to be limited to a maximum sand content above which no additional effect is found using the experimental results guidelines for modelling the settling and consolidation of mud sand mixtures have been formulated

lithofacies associations and stable isotopes of palustrine and calcrete carbonates examples from an indian maastrichtian regolith detailed information on semi arid palustrine carbonate calcrete lithofacies associations in a sheetwash dominated regolith setting is sparse this is addressed by studying the lower limestone of the lameta beds a well exposed maastrichtian regolith in central india the general vertical lithofacies assemblage for this unit comprises a basal calcareous siltstones and marls with charophytes ostracods and gastropods b buff micritic limestones associated in their upper parts with calcretized fissure fill sandstones c sheetwash as fissure fill diamictites and thin pebbly sheets locally developed over a few metres and d sandy nodular brecciated and pisolitic calcretes at the top the sequence is regressive with upsection filling of topographic lows by increased sheetwash lateral lithofacies change is marked but there are no permanent open water lake deposits in topographic lows close to the water table marshy palustrine or groundwater calcretes formed whereas on better drained highs brecciation and calcretization occurred prolonged exposure is implied suggesting that shrinkage was the main cause of brecciation evidence for rhizobrecciation and other biological calcrete fabrics is sparse contrasting with the emphasis on root related brecciation in many studies of palustrine lithofacies stable isotope d18o and d13c values are consistent with the palustrine limestones being fed from meteoric derived groundwater with a strong input of soil zone carbon there is overlap of both d18o and d13c values from the various palustrine and calcrete fabrics co occurring at outcrop this suggests that in groundwater supported wetlands conversion from palustrine carbonate to calcrete need not show isotopic expression as the groundwater source and input of soil zone carbon are essentially unchanged cretaceous tertiary d18o and d13c values from palustrine lithofacies and associated calcretes appear to be strongly influenced by the inherited values from lakes and wetlands hydrologically closed lakes and marine influenced water bodies tend to result in low negative palustrine d18o and d13c values during brecciation and calcretization the degree of isotopic inheritance depends on whether or not alteration occurs in waters that are different from those of the original water body or wetland marked biological activity e g rhizobrecciation or root mat development during calcretization may lower d13c values where c3 plants are abundant but in shrinkage dominated systems d13c values will be largely inherited from the palustrine limestones

quantifying sulfate components and their variations in soils of the mcmurdo dry valleys antarctica 1 many soils of the mcmurdo dry valleys mdv antarctica being old hyperarid and frigid have accumulated abundant atmospheric salts over the last several million years this salt repository offers an opportunity to study atmospheric chemistry past and present the origin and transport of ions in soils the weathering activity of soils and postdepositional soil leaching processes within this unique environment in particular soil sulfate in the mdv is known to have multiple origins but the precise proportions of different sulfate components remain elusive here we test a hypothesis that soil sulfate in the mdv is a predictable mixture of three major components sea salt sulfate non sea salt sulfate and background sulfate derived from weathering and volcanic sources that to a large extent varies as a function of elevation and distance from the coast by measuring sulfate s three stable isotope parameters i e 17o 18o and 34s plus estimating independently the end member stable isotope parameters for the three components on the basis of published reports and our measured data we solve explicitly the mixing proportion for each component using a set of three simultaneous linear equations the results from four spatially representative soil profiles show that the sum of such calculated proportions for the three components is very close to unity in most samples suggesting that a simple three component mixing model is a good representation of the soil sulfate budget while significant uncertainties still exist in the isotope compositions of different sulfate end members these data provide important initial constraints on sulfate diversity as well as its spatial and vertical distribution in the mdv

a neogene seawater sulfur isotope age curve from calcareous pelagic microfossils abstract until now our knowledge of the sulfur isotopic composition of seawater through geologic time has depended on stable isotopic analysis of sulfate from evaporites owing to the sporadic occurrence of evaporites through time the secular sulfur isotope age curve contains many gaps with little or no data in order to fill in some of these gaps particularly the neogene we have analyzed the sulfur isotopic composition of carbonate associated sulfate in carbonate tests of planktonic foraminifera other investigators have shown that sulfate may occur in biogenic calcites either lattice bound as micro fluid inclusions in adsorbed phases or as protein polysaccharides whatever the origin the sulfur isotopic composition of this sulfate appears to be representative of that of the water in which the organism lived as shown by results on recent calcareous foraminifera and macrofossils using this approach for study of miocene to recent pelagic marine sediments supplemented by new data for miocene marine evaporites from the gulf of suez we have found that the 34 s of seawater has decreased about 2 5 over the past 25 m y and that most of the decrease has occurred over the past 5 m y parallelling a decrease in the 13 c of dissolved oceanic bicarbonate from the same interval sedimentary redox models based on isotope records suggest that organic carbon and sulfide burial have both decreased over the past 5 m y alternatively an increase in weathering rates over the past 5 m y would not require a decrease in organic carbon or sulfide burial as long as the isotopic effect of the increased river input exceeds the isotopic effect of the burial of the reduced species in either case the net result would be a decrease in atmospheric p o 2

deformation structures and an alteration zone linked to deposition of volcanogenic sulphate in an ancient playa oligocene of nebraska usa historic sulphur rich volcanic eruptions have altered global climate for as much as five years and much larger events are known from the geologic record at scotts bluff nebraska early oligocene strata of the lower arikaree group contain a tephra bed with abundant calcite pseudomorphs after gypsum previous work has shown sulphate from the pseudomorphs in this tephra bears a high 17 o anomaly indicative of oxidation of sulphur gases by ozone or hydrogen peroxide in the atmosphere possible sources of the tephra were caldera eruptions at about 28 ma in the san juan volcanic field of southwestern colorado 500 km sw of the study site and the eastern great basin 1000 km wsw the present sedimentological study shows that tephra and volcanogenic sulphate were deposited and preserved within a small surfacedischarging playa that developed on the irregular upper surface of aeolian siltstones of the subjacent white river group sulphate solutions including perhaps sulphuric acid percolated downward within the vadose zone dissolving early formed smectite cement within underlying volcaniclastic sandstones reddening these rocks along an irregular alteration front preserved fine scale stratification within the sandstones precludes the possibility that reddening took place during pedogenesis displacive growth of gypsum at the playa centre folded tephra beds and forced tephra into underlying sandstones forming elongate cones the large mass fraction of gypsum now replaced by calcite in the playa sediments suggests a huge long distance delivery of sulphate aerosols some of the sulphate and tephra may have come from the same eruption or the fine grained tephra may simply have aided preservation of dry fog sulphate derived from an unrelated effusive eruption of lava

the formation of caliche in soils of the mojave desert california abstract radiocarbon and 230th 234u dates of calcic horizons from calciorthid soil profiles in the mojave desert were used to calculate the rate of deposition of pedogenic caco3 a major period of caco3 deposition appears to have occurred about 20000 ybp forming calcic horizons below 100 cm depth during a climatic regime with greater effective rainfall than in the present the overall rate of deposition has been 1 0 to 3 5 g caco3 m2 yr during soil formation this rate is consistent with present day rates assuming that the atmospheric deposition of ca limits the process stable isotope ratios in calcic horizons indicate that caco3 precipitated from a soil environment with co2 of 15 5 13 c 12 c vs pdb and h2o of 2 0 18 o 16 o vs smow these values suggest that caco3 precipitates when seasonal drought simultaneously lowers soil pore pco2 and enriches soil water 18o by evaporation the role of soil calcic horizons in the global geochemical cycle of carbon is discussed

tectonic and climatic controls on rift escarpments erosion and flexural rebound of the dhofar passive margin gulf of aden oman we investigate the respective roles of climatic parameters and the flexural rigidity of the lithosphere in the erosion history and behavior of two adjacent rift escarpments along the northern coast of the gulf of aden in oman at this 25 myr old passive margin we define a type 1 scarp which is high sharp crested and has retreated 25 30 km inland from its master fault and a type 2 scarp which exhibits a more rounded profile lower relief and still coincides with its mapped normal fault trace since about 15 ma the margin has been seasonally affected by monsoon precipitation but with contrasting effects at the type 1 and type 2 escarpments depending on the position of the intertropical convergence zone in the geologic past during peak monsoon conditions both scarps experienced heavy rainfall and runoff whereas during monsoon starved conditions such as today the type 2 scarp experienced a foggy moist climate while the type 1 scarp remained much drier in order to assess the relative effects of climate and flexural parameters on the present day morphology of the dhofar margin we present onedimensional numerical models of erosion and flexure along two profiles representative of the type 1 and type 2 scarps unlike most surface process models previously published where present day topography is the only criterion by which to evaluate the quality of model outputs model behavior here is additionally constrained by independent estimates of denudation provided by geological cross sections well defined fault traces and other stratigraphic markers the best fitting models indicate that the type 1 escarpment formed under relatively arid climatic conditions and was affected by significant erosion recession and flexural uplift due to a low 7 km effective elastic thickness in contrast the morphology of the type 2 fault scarp was smoothed by a more humid climate but a high effective elastic thickness 15 km prevented it from uplifting or receding in addition we show that the sedimentary load acting at the foot of the escarpments exerts significant influence on their morphological evolution though this parameter is often neglected in other scarp evolution models

palaeoclimate and palaeovegetation in central india during the upper cretaceous based on stable isotope composition of the palaeosol carbonates abstract the oxygen isotope compositions of the pedogenic carbonates formed on the sediments of the lameta formation of central india during the upper cretaceous range from 6 7 to 8 9 estimates of the oxygen isotope composition of the soil water in equilibrium with the carbonates suggest average meteoric water composition of 8 this value is considerably lighter compared to the modern precipitation in central india 3 the lighter oxygen isotope composition can be explained in terms of cumulative effects of highly seasonal monsoon like climatic regime in a rain shadow zone and a more pronounced continental effect due to a bigger size of cretaceous india the carbon isotopic compositions of the lameta carbonates range from 7 1 to 10 7 with an average of 9 1 suggesting pedogenesis in soils dominated by c 3 type of vegetation the estimated average composition of the vegetation is about 3 enriched compared to the modern day c 3 vegetation this is probably due to atmospheric influence contributing about 15 of the total co 2 in the soil an analysis of this contribution using the model of cerling 1991 indicates that the partial pressure of co 2 in the late cretaceous atmosphere was 800 12 000 ppmv

sulfate in modern playa settings and in ash beds in hyperarid deserts implication for the origin of 17o anomalous sulfate in an oligocene ash bed abstract a large amount of calcite pseudomorphs after gypsum were discovered in a volcanic ash bed and its underlying sand siltstone in the gering formation late oligocene northwestern ne usa the highly positive 17o anomalies in the residual sulfate indicate that the sulfate could only have come from the oxidation of sulfur gases by ozone in the atmosphere we previously proposed that it was most likely the result of an extreme tropospheric sulfate haze dry fog event that was associated with volcanic eruptions in the west to test the dry fog hypothesis we examine here two alternative scenarios that also involve atmospheric sulfate deposition but do not imply a dramatic volcanic and dry fog source 1 is it possible that some playas in arid or semiarid regions accumulate the type of atmospheric sulfate deposits as we see in the mid gering bed by the inflow of surface water or groundwater 2 could a period of hyperaridity and stability during the late oligocene have caused a significant accumulation of atmospheric background sulfate onto the mid gering ash bed surface sulfates from a variety of playa settings were collected and measured for their 17o anomalies the sulfate isotope both o and s and concentration profiles of two volcanic ash beds that are currently exposed in the central atacama desert chile and in taylor valley of the antarctica dry valleys were studied along with their sedimentary features these two ash beds were chosen for comparison because of their significant levels of atmospheric sulfate accumulated during prolonged and hyperarid climatic conditions results showed no or minimal 17o anomalies in any of the playa sulfate samples from around the world and none of the parameters in the mid gering ash profile matches those in either of the two volcanic ash profiles in modern hyperarid settings conclusion the observed 17o anomalous gypsum deposit in the mid gering ash bed is most likely the result of a series of extreme dry fogs that resulted in an intense pulse of atmospheric sulfate deposition to a semiarid playa setting

sulfur geochemistry across a terrestrial permian triassic boundary section in the karoo basin south africa concentrations of sulfur and carbon and isotopic compositions of sulfur were determined in sedimentary rocks from a section across the terrestrial permian triassic p tr boundary in the northern karoo basin south africa high concentrations of sulfide produced by sulfate reducing bacteria were found in the sedimentary rocks at and just below the perceived p tr boundary the ratios of organic carbon to sulfide of the sedimentary rocks with high concentrations of sulfide are relatively constant and similar to those of marine environments this means that the enhanced accumulation of sulfide is a result of the enrichment of sulfate in the water as the sulfide concentrations do not correlate with concentrations of any major elements indicative of weathering intensity the supply of sulfate was independent of environmental factors such as temperature and co2 concentrations in the atmosphere which control weathering intensity therefore it is reasonable to consider that the sulfate might have been supplied to the freshwater directly as acid rain by an event such as a bolide impact or a volcanic eruption the absence of evidence for an impact event in the geological record though favors volcanic input as the cause of the acid rain

caliche as a geological repository for atmospheric sulfate 1 recent studies demonstrate that important information on sulfur source oxidation pathway transport pattern and reaction kinetics of atmospheric oxidation of sulfur gases can be uncovered by measuring multiple isotope compositions of the oxidation product secondary atmospheric sulfate sas sas from earth s distant past however is rarely preserved in the rock records because of its high solubility and small quantity we report here from the measurement of 47 modern and fossil caliche samples that caliches contain variable amounts of carbonate associated sulfate cas and the 17o values of the cas range from 0 12 to 2 32 with most values higher than the background value of 0 05 for seawater sulfate indicating the presence of an sas component derived from the oxidation of sulfur gases by atmospheric ozone or related oxidants this study demonstrates that caliche a pedogenic carbonate common in the geologic record could serve as a repository for ancient sas

settling characteristics of calcareous sand this paper provides quantitative comparisons and relationships for the fall velocities and drag coefficients of 998 calcareous sand grains collected on oahu hawaii laboratory analyses of the grains provide the three orthogonal dimensions fall velocity and density from which the nominal diameter drag coefficient reynolds number and shape factor are evaluated for each grain the fall velocity and drag coefficient expressed respectively as functions of nominal diameter and reynolds number show strong correlation over a wide range of corey shape factors the present relationships are validated with published data based on quartz grains analysis of the data by flow regime shows that particle shape has a stronger influence on the settling characteristics when turbulent boundary layers develop around the grains

stable isotopic composition of pedogenic carbonates of the early cretaceous shimonoseki subgroup western honshu japan abstract abundant pedogenic carbonate nodules are present in the shimonoseki subgroup in the kanmon basin of kyushu and honshu japan the oxygen isotope compositions of these pedogenic carbonates range from 20 1 to 22 8 pdb which is 7 lower than those of the septarian crystallaria in the carbonate nodules the meteoric water composition estimated from the oxygen isotope composition of the soil water in equilibrium with the carbonates is much depleted compared with the estimate from other sources this suggests that the oxygen isotope compositions of the shimonoseki pedogenic carbonates were modified during diagenesis the carbon isotopic compositions of the shimonoseki carbonates range from 5 4 to 7 0 pdb with an average of 6 7 pdb suggesting carbonate formation in soils dominated by c 3 type of vegetation an analysis of these values using cerling s model cerling t e wright v p vanstone s d 1992 further comments on using carbon isotopes in paleosols to estimate the co 2 content of the palaeo atmosphere j geol soc london 148 1991 945 947 149 673 676 indicates that the partial pressure of co 2 in the early cretaceous shimonoseki atmosphere was about 1700 3200 ppmv

upper pennsylvanian permian naco group paleosols north central arizona field and isotopic evidence deposits of the upper naco group upper pennsylvanian permian north central arizona include features consistent with multiple episodes of soil formation the preserved paleosols are developed on shallowing upward regressive carbonate cycles that accumulated on the margins of a shallow shelf platform field evidence of paleosols consist of a monopodial taproot like and branching root and rootlet trace fossils b cylindrical carbonate nodules rhizoliths c subspherical carbonate nodules that occur as discrete entities in the paleosol and d an accumulation of red clay and quartz silt petrographic evidence consists of a plasmic fabrics analogous to those found in some modern soils cf brewer 1976 b microscopic carbonate nodule accumulations c soil nodule spar crystallaria and d alveolar septal structures paleosol profiles occur as a lithified in situ partly eroded clay rich horizons that commonly grade into unmodified parent material at depth below the disconformity and b reworked pedogenic carbonate nodule horizons oxygen and carbon stable isotope ratios of pedogenic carbonate are depleted relative to local marine carbonate this suggests that isotopically light soil co2 and meteoric water were present during pedogenic carbonate precipitation the depleted stable isotope ratios are consistent with an interpretation of soil carbonate precipitated under near surface conditions the presence of well developed calcareous rhizoliths and soil nodules in a red bed matrix and desiccation like crystallaria in host rhizoliths may qualitatively signify seasonally dry paleoclimatic conditions alteration of the underlying limestone units and development of multiple albeit truncated paleosols record a cyclical shift between marine and terrestrial paleoenvironmental conditions near the pennsylvanian permian boundary 280 m y ago

a late archaean palaeoproterozoic 2 6 ga palaeosol on ultramafics in the eastern transvaal south africa abstract this article describes a palaeosol developed on archaean 3 4 ga ultramafics and overlain by sedimentary rocks of the chuniespoort group 2 55 ga the palaeosol is thick mature and complex forming carapaces on palaeohills from base to top it comprises four lithological units 1 carbonated serpentinite 2 black talc rock 3 silcrete dolocrete 4 silcrete breccia in mudstone matrix petrographic and geochemical studies major elements plus v cr ni zn ga y zr nb pge and th indicate that units 1 to 3 represent former saprolites and silicified carbonated saprolites with bedrock textures still preserved unit 4 has been more intensely leached with some admixture of allochthonous sialic material collapse of the original texture and concentration of the immobile elements an irregular ni mineralization in the bottom part of the profiles is described and compared with equivalent modern lateritic deposits a high carbon content suggests the presence of a surficial mat of primitive micro organisms which could have contributed to the stability of the palaeosol on the hilly topography and greatly enhanced the weathering rate the presence of silcrete is indicative of a semi arid climate possibly with alternating wet and dry seasons or of a dry period having succeeded a wet one the absence of fe oxides and the general deficiency of this element in the upper part of the profiles taking into account that the soil was well drained and aerated support the model of an atmospheric o2 level much lower than at present by an order of two magnitudes

different sulfate sources and their post depositional migration in atacama soils abstract sulfate is one of the major salts accumulated in the hyperarid atacama desert chile its origin has been attributed to local weathering volcanic source sea salt and atmosphere deposition previous studies concluded that atmospheric sulfate is present in the desert but this term was poorly defined in terms of chemical origin and its contribution to the total sulfate budget in soil is debated the contribution of each potential sulfate source is expected to vary geographically due to different source locations efforts to quantify the contribution from each source have been hampered by the lack of well defined isotopic compositions for its end members in this study we discard the vague term of atmospheric sulfate by recognizing two major sulfate sources on the basis of their formation pathways primary and secondary sulfate primary sulfate including those from rock weathering sea salt and volcanic ash leachates do not have an 17o anomaly secondary sulfate derived from the oxidation of reduced sulfur gases biological or volcanic emissions by atmospheric ozone or hydrogen peroxide however has an 17o anomaly we developed a method to extract water soluble anions sequentially or entirely from bulk soil samples and analyzed the sulfate concentrations and 17o anomalies for four geographically representative soil profiles in the central atacama desert 23 s to 25 5 s we found that sequential sulfate extractions on the same soil sample produce sulfate with decreasing 17o values except for a positive bulge at 20 to 50 cm in depth there is a general increase in the 17o value for total sulfate with soil depth for all the four soil profiles that we examined these findings are consistent with the hypothesis that secondary sulfates 17o anomalous sulfates are more soluble and thus preferentially leached in liquid water than primary sulfate the finding also warns that incomplete sulfate extraction from sulfate rich soils yields unpredictable results we infer a 17o value of 4 6 for secondary sulfate based on data from partial sulfate extraction experiments total contribution of secondary sulfate in the central atacama desert is estimated to range from 9 to 24 with the highest percentage in the central depression

buried carbonate paleosols developed in pliocene pleistocene deposits of the pasco basin south central washington u s a abstract carbonate rich paleosols represent a small volume of material at the hanford site in south central washington state u s a but their position below highly permeable missoula flood deposits and above the water table makes them an important component of contaminant remediation plans previous work indicated that these buried carbonate paleosols constitute a relatively continuous low permeability paleosurface the distribution of the pliocene pleistocene deposits containing the paleosols depends in part on erosion of the underlying miocene pliocene fluvial lacustrine ringold formation and post depositional erosion by the catastrophic missoula floods the character of the caliche layer s as determined from cores varies across the study area from 0 20 m in thickness at depths of 20 m in the south to 65 m in the northwest bounded above and below by irregular surfaces with as much as 25 m relief and in general co varies in number of carbonate layers with the thickness of the deposits these carbonate layers reflect the geomorphology and hydrology existing during the time they developed i interpret these carbonate layers as paleosols but recognize morphologic features that indicate modification may have occurred after initial development at the surface these include the absence of associated soil horizons no apparent decrease in carbonate content with depth in some of the carbonate layers and unusual bk horizon fabrics including crystalline or popcorn like forms these features and fabric differences influence potential flow pathways of waste fluids

isotope geochemistry of caliche developed on basalt enormous variations in oxygen and carbon isotopes occur in caliche developed on 3 ma basalts in 3 volcanic fields in arizona significantly extending the range of 18o and 13c observed in terrestrial caliche within each volcanic field 18o is broadly co variant with 13c and increases as 13c increases the most 18o and 13c enriched samples are for subaerial calcite developed on pinnacles knobs and flow lobes that protrude above tephra and soil the most 18o and 13c depleted samples are for pedogenic carbonate developed in soil atmospheres the pedogenic caliche has 18o fixed by normal precipitation in local meteoric waters at ambient temperatures and has low 13c characteristic of microbial soil co2 subaerial caliche has formed from 18o rich evapoconcentrated meteoric waters that dried out on surfaces after local rains the associated 13c enrichment is due either to removal of 12c by photosynthesizers in the evaporating drops or to kinetic isotope effects associated with evaporation caliche on basalt lava flows thus initially forms with the isotopic signature of evaporation and is subsequently over layered during burial by calcite carrying the isotopic signature of the soil environment the large change in carbon isotope composition in subsequent soil calcite defines an isotopic biosignature that should have developed in martian examples if mars had a warm wet early period and photosynthesizing microbes were present in the early soils the approach can be similarly applied to terrestrial precambrian paleocaliche in the search for the earliest record of life on land large variations reported for 18o of carbonate in martian meteorite alh84001 do not necessarily require high temperatures playa lakes or flood runoff if the carbonate is an example of altered martian caliche

multiple sulfur isotopes and the evolution of the atmosphere interest in multiple sulfur isotope analyses has been fueled by recent reports of mass independent sulfur isotope signatures in the geologic record a non zero multiple isotopic signature of sulfur 33s and 36s is produced primarily through photochemical reactions and it is an almost perfect tracer of the source of sulfur once the signature is passed on to a given sulfur reservoir it will be preserved unless there is addition of sulfur with a different 33s or 36s in the geological record this signature has been used to study the evolution of the earth s atmosphere and to trace movement of sulfur through geological systems early in earth s history recently small but significant mass independent signatures have been reported for some younger samples raising the possibility of additional applications of multiple isotope studies the purpose of this review is to introduce and discuss the implications of multiple isotope studies and to focus attention on these anomalous but not uncommon isotopic signatures

oxygen 17 excesses of the central namib gypcretes spatial distribution abstract we present here sulfate oxygen isotopic data 72 samples with both 18o and 17o systematically collected from the central namib desert surface soils from two shore inland west east transects exhibit a gradual increase in the sulfate oxygen 17 excess 17o 17o 0 52 18o until at ca 70 km inland where no continuous gypcrete deposit is observed further east inland the oxygen isotopic compositions for water soluble sulfates extracted from soils and gypcretes range from 8 3 to 13 3 and 0 06 to 1 11 for 18o and 17o respectively the lateral pattern is similar to what has been seen in the cold deserts of the antarctic dry valleys however unlike the dry valleys no discernible correlation is found between 18o and 17o or between the depth of soil horizon and 17o in the namib possible explanations include a relatively smaller component of dimethylsulfide dms derived sulfate in the total gypsum deposits and or more active surface processes e g flooding and leaching in the central namib desert than in the antarctic cold deserts although current state of knowledge is insufficient to delineate quantitatively the sulfate contributions from different sources and reactions the measurement of sulfate 17o does identify an unmistakable atmospheric sulfate component and provides additional independent information regarding sources and reactions

energy volatile production and climatic effects of the chicxulub cretaceous tertiary impact a comprehensive analysis of volatiles in the chicxulub impact strongly supports the hypothesis that impact generated sulfate aerosols caused over a decade of global cooling acid rain and disruption of ocean circulation which contributed to the mass extinction at the cretaceous tertiary k t boundary the crater size meteoritic content of the k t boundary clay and impact models indicate that the chicxulub crater was formed by a short period comet or an asteroid impact that released 0 7 3 4 x 10 31 ergs of energy impact models and experiments combined with estimates of volatiles in the projectile and target rocks predict that over 200 gigatons gt each of so2 and water vapor and over 500 gt of co2 were globally distributed in the stratosphere by the impact additional volatiles may have been produced on a global or regional scale that formed sulfate aerosols rapidly in cooler parts of the vapor plume causing an early intense pulse of sulfuric acid rain estimates of the conversion rate of stratospheric so2 and water vapor to sulfate aerosol based on volcanic production of sulfate aerosols coupled with calculations of diffusion coagulation and sedimentation demonstrate that the 200 gt stratospheric so2 and water vapor reservoir would produce sulfate aerosols for 12 years these sulfate aerosols caused a second pulse of acid rain that was global radiative transfer modeling of the aerosol clouds demonstrates 1 that if the initial rapid pulse of sulfate aerosols was global photosynthesis may have been shut down for 6 months and 2 that for the second prolonged aerosol cloud solar transmission dropped 80 by the end of first year and remained 50 below normal for 9 years as a result global average surface temperatures probably dropped between 5 degrees and 31 degrees k suggesting that global near freezing conditions may have been reached impact generated co2 caused less than 1 degree k greenhouse warming and therefore was insignificant compare to the sulfate cooling the magnitude of sulfate cooling depends largely upon the rate of ocean mixing as surface waters cool sink and are replaced by upwelling of deep ocean water this upwelling apparently drastically altered ocean stratification and circulation which may explain the global collapse of the delta 13c gradient between surface and deep ocean waters at the k t boundary