the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

paleosol stratigraphy of the eskridge formation early permian pedogenesis and climate in southeastern nebraska abstract at least five aridisol and vertisol like paleosols are developed within the eskridge formation lower permian in richardson county nebraska these soils are recognized by their prominent soil structure peds nodules and filled cracks micromorphology oriented clay fabrics and iron cutans and well developed carbonate enriched horizons eskridge paleosols represent significant decreases or cessations in terrestrial sedimentation during long term subaerial exposure direct evidence for drowning of three out of the five paleosols by subsequent marine transgressions indicates strong marine influence on the duration of pedogenesis stratigraphic fluctuations in the 13c and 18o values of eskridge pedogenic micrites are potentially compatible with climatic fluctuations between wetter and drier conditions during the permian based on comparisons with isotope values from cenozoic paleosols occurrence of fossil plants and coals along with evaporites as well as the different paleosol types tends to support an interpretation of varying climate recognition of paleosols within the eskridge improves the understanding of cyclic sedimentation and sea level change by recording several episodes of low terrestrial sedimentation and geomorphic stability these episodes probably correspond to peak marine regressions

cybertectonic earth and gaia s weak hand sedimentary geology sediment cycling and the earth system tectonics climate and sea level are dominant controls on the nature and distribution of sedimentary environments by inverse logic recognition of influences on sedimentation from the stratigraphic record as a result of perturbations in these variables leads to clarification of past environmental and structural change the succession of sedimentary environments in time and place is determined by a wider combination of variables namely sediment flux biological evolution atmosphere and water body productivity and chemistry the feedbacks and interrelationships between all variables cause the complexity seen in sedimentation processes over geological time the processes of global tectonics that cause widespread mountain belt and continental plateau uplift have produced numerous severe events during earth history these often random workings out of the plate tectonic cycle define the state of cybertectonic earth from cyber after the greek kubernan to steer or govern this has worked within a usually zonally arranged series of climatic belts and within the framework provided by biological evolution at certain times in the geological past a combination of factors arose as a response to continental uplift and have acted to cause certain earth surface conditions and variables notably mean global surface temperature atmospheric p co 2 p o 2 to have varied by very large amounts 2 10 compared with present values these large fluctuations such as those responsible for the neoproterozoic late palaeozoic and late tertiary glaciations lead one to doubt the reality of homeostatic control of surface conditions as proposed in lovelock9s gaia hypothesis the gaian kuberne0te0s steersman had a weak hand on the helm frequently unable to prevent vast areas of the globe experiencing rapid fluctuations in environmental conditions and inimical conditions to life for very long periods during neoproterozoic and phanerozoic times at the same time biogenic and abiogenic processes have proved capable of returning earth to states of mean stability although biogeochemical cycling models seem alarmingly ad hoc and largely untestable as scientific hypotheses in any true geological sense

chemostratigraphic age model for the tornillo group a possible link between fluvial stratigraphy and climate abstract the expression of global climate trends 10 6 to 10 7 years and events 10 5 years in terrestrial sedimentary sections can only be assessed from long continuous continental records such records are rare due to the paucity of well dated terrestrial deposits covering millions of years this study uses isotope chemostratigraphy to develop an age model for fluvial sedimentary rocks of the tornillo group tornillo basin tx and to decipher the potential expression of global climate variations in this sub tropical paleo fluvial system the carbon isotope ratio 13 c of tornillo group pedogenic carbonate correlates well with 13 c variations from benthic foraminifera and suggests deposition between 69 ma and 52 ma for the studied stratigraphic interval higher sediment accumulation rates occurred in the greenhouse period of the early eocene than during the cooler middle paleocene carbon isotope excursions associated with eocene hyperthermals were not identified but their predicted stratigraphic positions coincide with thick sand bodies we interpret the long term sediment accumulation rates and rapid shifts in facies distribution as reflecting change in sediment supply in the basin possibly driven by fluctuations in precipitation seasonality and intensity driven associated with global temperature changes carbon and oxygen isotope ratios from pedogenic carbonates display a strong correlation throughout the section interpreted as an expression of coupling between the hydrological cycle and soil processes those observations suggest that global climate variations along with tectonic and eustatic sea level changes may be an important control of stratigraphic variations of the tornillo group at multiple timescales

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

carbon isotopes in continental weathering environments and variations in ancient atmospheric co2 pressure abstract abundance and carbon isotope data from an fe co3 oh component in apparent solid solution in oolitic goethites have been used to infer ancient atmospheric co2 pressures a test of the validity of these estimates might be comparisons of the carbon isotope compositions of fe co3 oh in oolitic goethites with time equivalent pedogenic calcites temporal trends of the oolitic goethite and pedogenic calcite 13c values are generally similar but time equivalent samples from each of these two groups are not common in the existing data to facilitate discussion of the concept comparisons were made of available goethite and calcite samples even though ages of the compared samples in each pair were not identical in four out of the five comparisons fe co3 oh abundance and 13c data were combined with pedogenic calcite 13c data to calculate physically reasonable soil co2 concentrations for the ancient calcitic soids this suggests that the compared oolitic goethite and pedogenic calcite systems were responding to the same global scale phenomenon i e atmospheric co2 atmospheric pco2 as determined from the goethites in these four well behaved cases ranged from values indistinguishable from modern within analytical uncertainty to values up to approximately 16 time modern modern atmospheric pco2 was taken to be 10 3 5 atm one interpretation of the fifth anomalous comparison is that atmospheric co2 levels increased from about 3 times modern to about 18 times modern from the triassic into the early jurassic this inferred value for the pco2 of the early jurassic atmosphere is not uniquely constrained by the existing data and needs to be substantiated however even considerably lower early jurassic atmospheric pco2 values of 6 to 9 times modern i e 1 3 to 1 2 of the estimated value of 18 times modern would still indicate significant differences between the global carbon cycles then and now these results highlight the need for more research on the behavior of the atmosphere during and after the triassic jurassic transition

carbon isotopic evidence for organic matter oxidation in soils of the old red sandstone silurian to devonian south wales uk petrographic and calcrete carbon isotope data from seasonally waterlogged upper silurian p idoli to lower devonian pragian palaeo vertisols of the old red sandstone south wales uk are presented the 13 c values mostly range from 9 to 12 vpdb suggesting that the soils were inhabited by abundant vegetation that when oxidized perhaps with microbial assistance resulted in co 2 rich soils such soils would favour calcrete precipitation through equilibration of soil zone co 2 with the relatively lower atmospheric p co 2 however reliably estimating palaeoatmospheric p co 2 using these carbon isotope data is a challenge supplementary material detailed information on stable isotope measurement methods descriptions of the samples and carbon and oxygen isotope data are available at www geolsoc org uk sup18754

stable isotopic evidence for a pedogenic origin of carbonates in trench 14 near yucca mountain nevada layered carbonate and silica encrust fault fractures exposed in trench 14 near yucca mountain site of the proposed high level nuclear waste repository in southern nevada comparison of the stable carbon and oxygen isotopic compositions of the fracture carbonates with those of modern soil carbonates in the area shows that the fracture carbonates are pedogenic in origin and that they likely formed in the presence of vegetation and rainfall typical of a glacial climate their isotopic composition differs markedly from that of carbonate associated with nearby springs the regional water table therefore remained below the level of trench 14 during the time that the carbonates and silica precipitated a period probably covering parts of at least the last 300 000 years

simulating late pliocene northern hemisphere climate with the lln 2 d model deep sea sediment records suggest northern hemisphere glaciation intensified at approximately 2 75 ma in this paper we simulate the fluctuations of the late pliocene northern hemisphere ice sheets volume using the lln 2 d model forced by the astronomically derived insolation and by scenarios of co2 concentrations the model simulates the waxing and waning of the northern hemisphere ice volume in an acceptable agreement with geological reconstructions and in particular supports the geological evidence that the development of significant northern hemisphere ice sheets started between 2 75 and 2 55 ma a time interval accompanied by quite high and stable eccentricity values and increased obliquity amplitude when the co2 concentration is lower than a threshold value the milankovitch forcing explains the suddenness and specific timing of this entrance into the ice age during the late pliocene

lower eocene alluvial paleosols willwood formation northwest wyoming u s a and their significance for paleoecology paleoclimatology and basin analysis abstract the lower eocene willwood formation of northwest wyoming is a 700 m thick accumulation of alluvial floodplain and channel mudstones and sandstones nearly all of which show paleopedogenic modifications pedogenesis of willwood sandstones is indicated by taproot and vertebrate and invertebrate bioturbation early local cementation by calcium carbonate and thin illuviation cutans on clastic grains pedogenesis in willwood mudstones is indicated by plant bioturbation insect and other invertebrate burrow casts and lebensspuren free iron aluminum and manganese mobilization including hydromorphic gleying sesquioxide and calcareous glaebule formation in lower parts of the solum presence of clay rich and organic carbon rich zones and well differentiated epipedons and albic and spodic horizons probable a horizons are also locally well developed occurrence of variegated paleosol units in thick floodplain mudstone deposits and their association with thin lenticular and unconnected fluvial sandstones in the willwood formation of the central and southeast bighorn basin suggest that these soils formed during times of rapid sediment accumulation the tabular geometry and lateral persistence of soil units as well as the absence of catenization indicate that willwood floodplains were broad and essentially featureless all willwood paleosols were developed on alluvial parent materials and are complex in that b horizons of younger paleosols were commonly superimposed upon and mask properties of suspected a and b horizons of the next older paleosols the soils appear to be wet varieties of the spodosol and entisol groups aquods and ferrods and aquents respectively though thick superposed and less mottled red purple and yellow paleosols resemble some ultisols most willwood paleosols resemble warm temperate to subtropical alluvial soils that form today under alternating wet and dry conditions and or fluctuating water tables the up section decrease in frequency of gley mottles increase in numerical proportion and thickness of red versus orange coloration and increase in abundance of calcrete glaebules indicate better drained soils and probably drier climate in late willwood time this drying is believed to be related to creation of rain shadows and spacing of rainfall but not necessarily decrease in absolute rainfall due to progressive tectonic structural elevation of the mountainous margins of the bighorn basin

a method for computing infiltration and redistribution in a discretized moisture content domain 1 a new one dimensional infiltration and redistribution method is proposed as an alternative to the richards equation re for coupled surface and subsurface models the proposed method discretizes soil water content into hypothetical hydraulically interacting bins the entry and propagation of displacement fronts in each bin are simulated by means of explicit infiltration and drainage approximations based on capillary and gravitational driving forces wetting front advances within bins create water deficits that are satisfied by capillary driven interbin flow the method inherently provides numerical stability by precluding the need to directly estimate nonlinear gradients through numerical schemes comparisons of the performance of this method against re solutions for theoretical laboratory and field data in both well drained and high water table conditions are presented the new method produces infiltration flux estimates with errors less than 10 compared to a widely used re solution in tests on multiple soil textures with and without high water table conditions while providing unconditionally guaranteed conservation of mass

relation of paleovegetation to geometry and cyclicity of some fluvial carbonaceous deposits abstract the fluvial lower eocene willwood formation bighorn basin wyoming is composed largely of red oxidized overbank sediment that has been extensively altered by soil formation within this matrix are two different types of dominantly fine grained drab to dark colored deposits that contain abundant plant remains the first are areally restricted lenticular bodies that truncate underlying mudstone layers these are interpreted as having formed in abandoned sections of channels deposits of the second type are tabular as much as 10 km in lateral extent and rest conformably on other floodplain sediment these units show a cyclic arrangement of sedimentary subunits sedimentologic and paleobotanic evidence suggests that these tabular deposits accumulated under a sequence of vegetatio al types including in succession a floodplain marsh a swamp forest and a drier ground floodplain forest these interpretations stress the interaction of vegetational succession soil characteristics and fluvial morphology in creating the chemical conditions that led to the preservation of organic matter the stratigraphic distribution of the two types of deposits within the willwood formation suggests that in the bighorn basin tectonism exerted a greater influence on the geometry of carbonaceous deposits than did climate

a study on the hydrogeology and hydrogeochemistry of groundwater from different depths in a coastal aquifer annamalai nagar tamilnadu india chemical characterization of groundwater is essential to bring out its nature and utility samples from shallow and deep ground water of the same location were collected and studied for their geochemical characteristics following standard procedures apha 1998 sediment samples from different depths were collected and analysed for minerals using ftir and sem resisitivity logging was carried out in the bore well to understand the variations in depth to fresh water potential the shallow ground water is dominated by na cl hco3 so4 and deeper groundwater by na hco3 so4 cl types it is observed that there is a significant ionic variation with depth the ionic strength of the deeper samples is lesser than in the shallower samples wide ph variations in the shallow water samples are due to ion exchange process thermodynamic stability plot was used to identify the state of stability it is inferred that there is no major significant difference in the thermodynamic state of stability in the shallow and the deeper aquifers as the aquifer matrix for the shallow and deeper aquifers are almost similar saturation index of gibbsite kaolinite calcite dolomite and anhydrite were studied for shallow and deep aquifers to identify the difference in hydro chemical signatures the si al ratios of shallow samples are less when compared with the deeper samples leaching of secondary salts was the chief mechanism controlling the ground water chemistry of the region

moving multi front mmf a generalized green ampt approach for vertical unsaturated flows abstract a moving multi front mmf method is developed and tested for solving the richards equation governing unsaturated flow in vertical homogeneous porous columns the mmf model is a gridless method it can be viewed as a generalization of the green ampt piston flow approach which models flow as a single abrupt moving front separating saturated and dry regions during infiltration the mmf model further generalizes this concept using a parametrization of unsaturated water retention and conductivity pressure curves it reduces the richards pde to an ode system governing m moving front positions different tests are developed to validate this approach for 1d transient downwards upwards flows submitted to constant and time varying pressure boundary conditions they include i infiltration to deep water tables ii infiltration to shallow water tables iii capillary rise from fixed water tables iv gradual water table rise partially saturated column with evolving pressure condition at bottom the mmf results are compared favorably to finely discretized fixed grid solutions of richards pde analyses of error and accuracy show satisfactory results in terms of water content profiles and boundary fluxes e g infiltration rate

biogeochemical constraints on the triassic jurassic boundary carbon cycle event 1 the end triassic mass extinctions represent one of the five most severe biotic crises in earth history yet remain one of the most enigmatic ongoing debate concerns the environmental effects of the central atlantic magmatic province camp eruptions and their linkage with the mass extinction event across the triassic jurassic boundary there is conflicting paleo evidence for changes in atmospheric pco2 during the extrusion of the camp basalts studies on sediments from european and pacific localities have however identified a substantial negative isotopic anomaly up to 3 5 across the tr j boundary providing an important indicator of changes in the operation of the ancient global carbon cycle we sought to explain the paleo evidence by utilizing a carbon cycle model for the hothouse world of the end triassic that emphasizes the chemical weathering of silicate and carbonate rocks and the ocean carbonate chemistry we find that volcanic co2 outgassing fails to fully account for either a sufficient rise in atmospheric pco2 indicated by the stomata of fossil leaves or the sedimentary isotopic fingerprint instead the scenario that best fits all of the geologic evidence is a positive feedback loop in which warming due to a buildup of volcanically derived co2 triggers destabilization of seafloor methane hydrates and the catastrophic release of ch4 palfy et al 2001 we calculate that this carbon cycle perturbation was huge involving the release of 8000 9000 gt c as co2 during the camp basaltic eruptions and 5000 gt c as ch4 in the model the initial isotopic excursion is assumed to take place over 70 kyr while complete reequilibration of the ocean atmosphere system with respect to co2 is accomplished over 700 1000 kyr our results thus provide a preliminary theoretical explanation for the bioevents estimated pco2 changes and isotopic excursions observed in marine and continental sediments at this time

use of carbon isotopes in paleosols as an indicator of the p co2 of the paleoatmosphere measurements of carbon isotopic composition of coexisting paleosol organic matter and carbonate results in improved estimates of the paleo p co2 content of the paleoatmosphere measurements from tertiary paleosols indicate that the levels of co2 in the early eocene middle and late miocene and pliocene were less than 1000 ppmv early cretaceous levels of p co2 were significantly higher of the order of 1500 to 3000 ppmv

morphology and stable and radiogenic isotope composition of pedogenic carbonates in late quaternary relict soils new mexico u s a an integrated record of pedogenic overprinting abstract this petrographic and stable 13c and 18o and radiogenic 14c isotope study of pedogenic carbonates from late quaternary soils in the rio grande rift region of new mexico documents that carbonate formation in semiarid to arid soils aridisols occurs principally by overprinting and can result in a complex petrographic and isotopic record with increasing duration of exposure 7 to 900 ky of the four studied profiles pedogenic carbonates exhibit 1 an increase in the degree of intraprofile 13c and 18o heterogeneity 2 increased development of down profile 13c and 18o trends 3 an increase in the degree of intermorphologic and intramorphologic stable isotope variation commonly in samples distributed laterally within narrow depth intervals and 4 development of covariation between 13c and 18o values radiocarbon ages of the carbonates permit assessment of the degree of isotope heterogeneity in contemporaneous carbonates and recognition of temporal isotopic trends the range of exposure times recorded by the studied soils are analogous to those associated with the formation of fossil soils this makes the studied soils ideal for evaluating the origin of stable isotope heterogeneity in paleosol carbonates and the implications of those heterogeneities for the use of stable isotopes as paleoenvironmental proxies specific implications of this study include the following 1 pedogenic carbonates that form by overprinting are a cumulative record of the soil conditions present during their accumulation thus isotope analysis of overprinted carbonates can result in time averaging of changing climatic paleoenvironmental and paleoecologic conditions 2 carbonates may record only a fraction of the duration of development of their host profile 3 there is a high level of uncertainty associated with using the sequence of morphologic development of carbonate as a function of time or maturity in paleosols 4 an exponential decrease in carbonate 13c values with depth in a paleosol does not imply that the carbonates are contemporaneous or accumulated under invariant soil conditions 5 shifts in soil and paleoclimatic conditions may be recorded by the 13c and 18o values of carbonates distributed within narrow depth intervals of a given soil in addition to those distributed down profile or even from within individual carbonate samples

co2 drawdown and cooling at the onset of the great oxidation event recorded in 2 45 ga paleoweathering crust abstract the archean atmosphere is thought to have been devoid of oxygen but instead containing high concentrations of greenhouse gases such as co2 and possibly ch4 that were required to keep the earth surface environments warm enough for maintenance of liquid water under faint young sun conditions earlier studies have suggested that the co2 concentrations must have been as high as over 1000 times present atmospheric levels pal to overcome the effects of weaker solar luminosity however more recent studies of precambrian paleosols imply existence of at least tenfold lower but still high pco2 levels the appearance of minute amounts of atmospheric o2 at the transition of archean and proterozoic is well documented however the bulk composition of the atmosphere and its dynamics at this crucial time is still widely debated different paleoclimate proxies of the 2 45 ga kuksha paleoweathering crust suggest its formation in a cool temperate climate paleoatmospheric pco2 estimates by geochemical and isotopic mass balance models suggest remarkably low paleoatmospheric co2 levels with the best guess estimates of atmospheric co2 between 1 and 10 pal we speculate that the kuksha paleoweathering crust either predates or partly overlaps with the onset of huronian glaciation and corresponds to a time interval of low co2 level during the first recorded large glaciation in earth history

fossil plants record an atmospheric 12co2 and temperature spike across the palaeocene eocene transition in nw europe the large negative excursion of carbon isotope composition 13 c recorded from foraminifera and bulk carbonates indicates a major anomaly in the operation of the global carbon cycle across the palaeocene eocene boundary therefore we sought terrestrial evidence for the transfer of isotopically light carbon 12 co 2 from the ocean to the atmosphere by making systematic 13 c measurements or well dated sequences of fossil pollen from nw europe the results indicate an atmospheric 12 co 2 spike of c 2 between 58 and 55 ma coincident with the ocean isotopic anomalies pollen spectra from these sequences suggest a marked shift in dominance from mixed mesophytic to paratropical forests synchronous with the terrestrial isotope excursion

stable isotopic composition of calcic paleosols of the early cretaceous hasandong formation southeastern korea abundant pedogenic carbonate nodules are present in the cretaceous non marine hasandong formation southeastern korea the oxygen isotope compositions of these pedogenic carbonates range from 14 2 to 18 0 pdb 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 previous estimate this suggests that the oxygen isotope compositions of the hasandong pedogenic carbonates were modified during diagenesis the carbon isotopic compositions of the hasandong carbonates range from 2 4 to 9 3 pdb with an average of 5 6 pdb suggesting carbonate formation in soils dominated by c3 type of vegetation the estimated average composition of the vegetation is about 6 pdb enriched compared with the present day c3 vegetation this is probably due to atmospheric influence contributing about 35 of the total co2 in the soil an analysis of this contribution using the model of cerling 1991 indicates that the partial pressure of co2 in the early cretaceous hasandong atmosphere was about 2300 ppmv

hydro geophysical techniques for safe exploitation of the fresh groundwater resources in coastal area vertical disposition of the freshwater aquifer lens and their progressive change on lateral scale are relevant to understand the short circuiting of fresh and saline water at coastal areas since half of the world population dwells within 50 km of coast line the freshwater aquifers at coast are deteriorating at alarming rate there are well defined water well construction plans for coastal aquifer management but mostly fails while execution due to lack of precise knowledge of subsurface lithological layer setup in the present study an attempt has been made to investigate such precise information about subsurface lithological layer setup to protect the freshwater resources at coastal area applying noninvasive hydro geophysical technique integrated electrical parameters hydrochemistry topography and water table assessment have been applied to decipher the geometry of freshwater lens at cuddalore coast india results show in this study 1 the electrical resistivity 1 10 m of subsurface formation electrical conductivity 30 891 s cm of groundwater and water table 1 55 m above mean sea level msl confirms the zone of effluent contamination 2 the zone showing 1 10 m 6172 s cm water table 6 46 m below msl is attributed to the saline water intrusion 3 freshwater formations are identified in beach ridges underlain by clay layers with 30 60 m 453 s cm and water table above msl and 4 water well design is proposed to tap the freshwater aquifers avoiding vertical short circuiting of saline and freshwater

fossil horses and carbon isotopes new evidence for cenozoic dietary habitat and ecosystem changes in north america abstract the transformation from low crowned to high crowned horse teeth during the miocene has traditionally been interpreted as an adaptive response to the spread of savanna grasslands during the middle miocene by about 15 m y ago carbon isotope data from 50 north american horse teeth spanning eocene to pleistocene age indicate that savanna grasslands presumably dominated by c 4 grasses as they are today first became widespread much later than do horses with high crowned teeth prior to 7 m y horses had a c 3 based diet and after 7 m y horses started eating c 4 grasses this change in diet occurred when the major drop in the diversity of horses occurs during the late miocene the change in vegetation reflected in horses diet may be related to a significant reduction in atmospheric co 2 level toward the end of the miocene which provided the c 4 grasses with an adaptive advantage and led to their expansion at the expense of c 3 plants

green and ampt infiltration into soils of variable pore size with depth most expressions for infiltration rely upon the assumption of vertical uniformity in soil texture and hydraulic properties we present an extension of the results of beven 1982 1984 for infiltration and lateral flow in soils with decreasing permeability with depth unlike beven we base the derivations upon joint changes in soil properties based on an overall change in characteristic pore size via miller scaling a set of very simple expressions for the time rate of infiltration are obtained using a green and ampt approach for soils with permeability that decreases with depth following linear power law and exponential relationships

stable isotope geochemistry of vertisols formed on marine limestone and implications for deep time paleoenvironmental reconstructions abstract carbon and oxygen isotope compositions of pedogenic carbonate preserved in paleosols have been used extensively to reconstruct ancient environmental conditions one concern is that pedogenic carbonate precipitated in association with a limestone parent material may include a contribution from inherited detrital lithogenic marine calcite thus compromising interpretations of stable isotope compositions to investigate the impact of lithogenic calcite on environmental interpretations using paleosols we measured stable isotope ratios in pedogenic carbonates and coexisting soil organic matter som in modern vertisols fine smectitic thermic udic haplusterts from riesel texas heiden series and zabcikville texas houston black series forming on cretaceous chalk deposits the pedogenic and lithogenic components in the heiden series soil at riesel were identified using micromorphology and cathodoluminescence cl which showed incorporation of luminescent marine allochems i e foraminifera mollusks into hard nodules and soft powdery pedogenic masses additionally micromorphology showed evidence of meteoric recrystallization of the allochems despite the presence of these inherited carbonates into hard nodules and soft powdery masses the stable isotope compositions recorded a partial pedogenic signal recrystallization of the marine allochems resulted in overprinting of primary marine isotope ratios with ratios that are more similar to those expected for pedogenic carbonates in these soils this study demonstrates that incorporation of parent material into pedogenic carbonates does not necessarily compromise the pedogenic signal that is useful for paleoenvironmental reconstructions however overprinting of marine allochems if present can be important and needs to be identified using micromorphology and cathodoluminescence before using stable isotope ratios of pedogenic carbonates for paleoenvironmental reconstructions

carbon and oxygen isotopic signatures in albian danian limestones of cauvery basin southeastern india abstract the albian danian limestones of cauvery basin show a wide range of d13c and d18o values 13 2 to 1 1 and 9 0 to 2 5 respectively the cement samples show negative carbon and oxygen isotope values 18 9 to 3 9 and 9 0 to 4 3 respectively the petrographic study reveals the presence of algae molluscs bryozoans foraminifers and ostracods as major framework constituents the limestones have microspar and equant sparry calcite cements the pore spaces and vugs are filled with sparry calcite cement the bivariate plot of d13c and d18o suggests that most of the samples fall in the freshwater limestone and meteoric field while few samples fall in the marine limestone and soil calcite fields the presence of sparry calcite cement together with negative carbon and oxygen isotope values indicates that these limestones have undergone meteoric diagenesis

isotopic reconstruction of past continental environments abstract vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments to interpret these records a greater understanding of isotopic sources as well as fractionations associated with animal physiology soil geochemistry and diagenesis has been essential tooth enamel and fish otoliths yield subannual records of surface environments whereas soil minerals may integrate signals over many thousands of years carbon isotope variations in fossil vertebrates and soils record changes in the structure of vegetation and the isotope composition and concentration of atmospheric co2 oxygen isotope variations may be indirectly related to climate through reconstruction of the oxygen isotope composition of meteoric water or directly related to temperature through application of oxygen isotope paleothermometry to soil minerals or otoliths in africa nitrogen isotope variations show promise as a proxy for rainfall abundance though the gen

an isotopic study of paleosol carbonates from olduvai gorge the isotopic composition of paleosol carbonates from olduvai gorge can be used to give estimates of the paleoclimatic history of east africa during the plio pleistocene oxygen isotopes are indicative of major changes in the isotopic composition of meteoric water while carbon isotopes are indicative of major changes in the fraction of biomass using the hatch slack c4 photosynthetic pathway three major periods of climatic change in this terrestrial setting occurred at about 1 67 1 3 and 0 6 myr these involved major changes in flora as well as major changes in the isotopic composition of meteoric water overall the climate has become warmer and more arid over the past 2 2 myr

plants and the palaeoatmosphere the effects of the development of terrestrial vegetation during devonian and carboniferous times is considered and it is concluded that the maximum possible global biomass in carboniferous times was equivalent to about 1 148 10 15 g c which is in excess of the current earth9s biomass 560 860 10 i5 g c global primary productivity however estimated at about 73 10 15 g c a 1 is of the same order as that of the present day the amount of carbon actually becoming stored as 9fossil fuel9 was a very small proportion of this productivity estimated here at only 0 00002 over 65 10 6 a thus the vegetation of carboniferous times cannot be regarded as a significant carbon sink the atmosphere of the mesozoic is discussed in relation to the evolution of angiosperms in particular the photosynthetic modifications in so called c 4 and cam plants are considered in relation to atmospheric and other environmental stresses taxonomic evidence indicates that the c 3 system is primitive in the angiosperms and that the modified systems have a polyphyletic origin physiological considerations suggest that their development relates more clearly to the demands of water balance rather than to lowered atmospheric co 2 or high atmospheric levels of oxygen it is not considered likely that the evolution of these mechanisms or of the angiosperms in general has had any profound effect upon the carbon content of the atmosphere

a complete holocene climate and environment record for the western carpathians slovakia derived from a tufa deposit calcareous tufas are great archives of geochemical information for the reconstruction of past climate their importance increases in the regions where other proxies are rare such as western carpathians here we present the first whole holocene palaeoclimatic reconstruction for this region based on geochemical proxies we analysed o 18 c 13 and mg ca ratio on tufa calcite of the mituchovci site white carpathian mountains w slovakia and compared these with pollen plant macrofossil and mollusc data according to o 18 two distinct thermal maxima occurred in the region around 11 4 ka and between 7 3 and 6 9 ka bp according to c 13 and mg ca ratio a steep increase in moisture and rainfall took place around 8 5 ka cal bp preceded by a cold and dry event these events are well reflected in the biotic proxies and are suggested also by other palaeoenvironmental studies from the carpathians we found some later fluctuations with dry and warm bronze age ca 3 6 ka cal bp cold and wet urnfield period ca 2 8 ka cal bp warm roman period ca 2 ka cal bp and cold but humid migration period ca 1 5 ka cal bp we observed extreme abruptness and amplitude of the variation in all geochemical proxies in the last 500 years when biotic proxies imply a very intense human deforestation land use changes may have altered both the temperature regime in the studied fen and the carbon cycle in the recharge area

a 20 million year record of planktic foraminiferal b ca ratios systematics and uncertainties in pco2 reconstructions we use new and published data representing a 20 million long record to discuss the systematics of interpreting planktic foraminiferal b ca ratios b ca based reconstructions of seawater carbonate chemistry and atmospheric pco 2 assume that the incorporation of boron into foraminiferal tests can be empirically described by an apparent partition coefficient k d b ca caco 3 b oh 4 hco 3 seawater hemming and hanson 1992 it has also been proposed that there is a species specific relationship between k d and temperature yu et al 2007 as we discuss although these relationships may be robust there remain significant uncertainties over the controls on boron incorporation into foraminifera it is difficult to be certain that the empirically defined correlation between temperature and k d is not simply a result of covariance of temperature and other hydrographic variables in the ocean including carbonate system parameters there is also some evidence that k d may be affected by solution hco 3 co 2 3 ratios i e ph or by co 2 3 in addition the theoretical basis for the definition of kd and for a temperature control on k d is of debate we also discuss the sensitivity of pco 2 reconstructions to different k d temperature calibrations and seawater b ca if a k d temperature calibration is estimated using ice core pco 2 values between 0 and 200 ka b ca ratios can be used to reasonably approximate atmospheric pco 2 between 200 and 800 ka however the absolute values of pco 2 calculated are sensitive to the choice of k d temperature relationship for older time periods the absolute values of pco 2 are also dependent on the evolution of seawater b concentrations however we find that over the last 20 ma reconstructed changes in declining pco 2 across the mid pleistocene transition pliocene glacial intensification and the middle miocene climate transition are supported by the b ca record even if a constant coretop k d is used or different k d temperature calibrations and models of seawater b evolution are applied to the data the inferred influence of temperature on k d from coretop data therefore cannot itself explain the structure of a published pco 2 reconstruction tripati et al 2009 we conclude the raw b ca data supports a coupling between pco 2 and climate over the past 20 ma finally we explore possible implications of b ca based pco 2 estimates for the interpretation of other marine pco 2 proxies

an isotopic study of a fluvial lacustrine sequence the plio pleistocene koobi fora sequence east africa stable isotopic analyses of plio pleistocene and modern sediments in the fluvial lacustrine system occupying the turkana basin east africa provide constraints on the paleoenvironmental and diagenetic histories of the pliocene through the recent sediments in the basin the 13c values for carbonates in lacustrine sediments range from 15 to 22 relative to pdb depending on the varying proportions of co2 from the atmospheric reservoir and from various metabolic sources the 18o values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10 from the pliocene to the present the 13c values for pedogenic carbonates record paleoccologic variations and suggest that c4 plants did not become well established in the preserved depositional parts of the basin until about 1 8 myr ago the 18o values pedogenic carbonates suggest a range of over 10 for the isotopic composition of soil water during this interval they also suggest a period of major climatic instability from about 3 4 to 3 1 myr and at about 1 8 myr together the 13c and 18o values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these plio pleistocene sediments

stable isotope signatures associated with palaeosols pennsylvanian holder formation new mexico the holder formation pennsylvanian virgilian of southern new mexico usa consists of limestones interbedded with siliciclastics it was deposited during times of glacio eustatic sea level change and was exposed subaerially during multiple sea level lowstands microcomponents and whole rock samples of limestones were analysed for 13c and 18o values to examine the method of whole rock isotopic analysis for detecting subaerial exposure events and to determine the diagenetic processes acting during subaerial exposure whole rock isotopic shifts are not consistently present across petrographically identified subaerial exposure surfaces apparently whole rock isotopic shifts do not result from wholesale replacement of the host sediment during soil formation however the isotopic shifts are present in calcareous soil precipitated microcomponents such as rhizoliths laminated crusts and soil precipitated cements the components are heterogeneous in isotopic composition but converge on a meteoric calcite line at about 18o 5 5 these microcomponents are heterogeneous in distribution and may either dominate or be a minor constituent of the whole rock at a single stratigraphic horizon without petrographic selection of palaeosol components the detection of whole rock isotopic shifts may depend on the selection or chance sampling of a rock containing abundant microcomponents precipitated in a soil environment only minor whole rock isotopic shifts come from those rocks bearing no evidence of exposure and bearing lithological characteristics suggesting subaerial exposure was unlikely

examining the spatial consistency of palaeosol proxies implications for palaeoclimatic and palaeoenvironmental reconstructions in terrestrial sedimentary basins terrestrial sediments are a significant archive of past conditions and the critical zone in particular is important for understanding past and ongoing interactions between the atmosphere biosphere and lithosphere understanding the details of a palaeolandscape or palaeocatena record can greatly improve palaeoenvironmental descriptions and palaeoclimate reconstructions during crucial time periods in the past this article presents multi proxy data including palaeosol descriptions major element geochemistry magnetic composition and stable isotope geochemistry from an early eocene palaeosol transect which show distinct trends in palaeosol features and geochemistry across the landscape particularly in terms of the differences between a horizon and b horizon samples a horizon geochemical and physical features are highly variable and reflect other not strictly pedogenic controls whereas b horizon composition is extremely consistent given that most palaeoclimatic or palaeoenvironmental proxies based on palaeosols use b horizon features these results highlight the robustness of those proxies at the same time the difference between a horizons and b horizons and the variability within a horizons of the same palaeosol in different geomorphic settings underscores the importance of palaeosol description detailed sampling and a multi proxy approach to produce both precise and accurate reconstructions of past environments and climates using terrestrial sedimentary records

fossil leaves effective bioindicators of ancient co2 levels 1 past variations in the concentration of the greenhouse gas co2 are thought to have played a major role in controlling earth s climate on prequaternary and quaternary timescales to identify the contribution of co2 to past climatic change requires accurate quantification of its content in the ancient atmosphere and a number of proxies have been developed for this purpose for a review see royer et al 2001a for the late quaternary there is the unique opportunity to measure directly the composition of fossil air samples trapped in bubbles preserved in the polar ice sheets results from antarctic ice cores reveal that the glacialinterglacial changes characterizing quaternary climate were accompanied by variations in the atmospheric concentration of co2 petit et al 1999 although detection of phase relations between isotope derived temperature estimates and trace gas concentration values is hampered by the difference in age of ice and air from the same ice sample it is believed that co2 lags glacial interglacial temperature change and has acted as an amplifier of orbitally forced changes in temperature petit et al 1999 shackleton 2000 mudelsee 2001

carbon dioxide in the paleozoic atmosphere evidence from carbon isotope compositions of pedogenic carbonate stable carbon isotope compositions of pedogenic carbonate occurring in three clay rich vertic paleosols within paleozoic red bed successions in central pennsylvania provide a record of past pedogenic environments and can be used to estimate co sub 2 pressure p sub co sub 2 of the paleozoic atmosphere the delta sup 13 c values of carbonate nodules from paleosols in the deltaic lower bloomsburg formation upper silurian reflect the contribution of carbon from marine groundwater or fossils coupled with low biological activity the delta sup 13 c values of carbonate rhizocretions from stratigraphically high paleosols in the bloomsburg formation and in the alluvial catskill upper devonian and mauch chunk upper mississippian formations suggest an extensive c sub 3 flora and significant contribution of atmospheric co sub 2 paleozoic atmospheric co sub 2 levels inferred from delta sup 13 c of pedogenic carbonate are significantly higher than present levels

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

chemical evolution of groundwater in a drainage basin of holocene age east central alberta canada abstract wallick e i 1981 chemical evolution of groundwater in a drainage basin of holocene age east central alberta canada in w back and r letolle guest editors symposium of geochemistry of groundwater 26th international geological congress j hydrol 54 245ndash 283 chemical evolution of groundwater in a small drainage basin of glacial origin 10 250 yr b p based on radiocarbon age dating of gyttja from a closed saline lake in the basin was studied in order to understand the generation of salts in surface mined areas on the interior plains of alberta the basin was considered to be a natural analogue of a surface disturbed area because of the large volumes of rock that had been redistributed by glaciers with the resulting change in topography and drainage the distributions of hydraulic head total dissolved solids tds and environmental isotopes essentially reflect the superimposition of groundwater flow systems associated with the post glacial topography upon a regional bedrock flow system of older but undetermined age in the glacial drift aquifers and aquitards sands and till the groundwater composition was typically ca mg bicarbonate type at depths less than 30 m but at depths of 30ndash 100 m the composition was na bicarbonate sulfate type in the deeper bedrock aquifers 100m na bicarbonate sulfate and na bicarbonate chloride types were present tds was as low as 400 mg l in the shallow drift aquifer generally constant at 1000 mg l in the deep drift and shallow bedrock aquifer and over 1700 mg l in the deep bedrock aquifer system chemical evolution of groundwater in the area appears to be dominated by two depth zones having different types of water rock interaction in the shallow drift zone the dissolution of soil co 2 in infiltrating groundwater oxidation of organic carbon sulfur and pyrite result in the formation of carbonic and sulfuric acids that attack carbonate and silicate minerals on the basis of x ray diffraction analysis these minerals were calcite dolomite plagioclase feldspar and smectite clays however in the deep regional bedrock aquifer conditions are reducing presence of methane groundwater is alkaline ph 8 6 10 3 and the na bicarbonate chloride composition of groundwater is believed to result from the hydrolysis of volcanic glass or feldspar crystals of oligoclase andesine composition under conditions of very slow leaching of reaction products and low partial pressure of co 2 under such conditions calcite and possibly ca zeolite are sinks for ca ion but na can accumulate in the pore water as a result of groundwater movement induced by the postglacial hummocky topography water from the drift aquifers mixes with water from the deep bedrock aquifers in the groundwater discharge area yielding a range of intermediate compositions that may be explained by dilution and calcite precipitation using the mix2 chemical equilibrium model chemical diffusion was shown to be of negligible importance in comparison with mechanical dispersion to explain the mixing effect

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

hydrogeochemical evaluation of groundwater of bhaktapur municipality nepal the present study aims to evaluate groundwater hydrogeochemistry of bhaktapur municipality nepal with respect to water types chemical elements and their statistical variability samples were collected in pre monsoon april june monsoon july august and post monsoon october november seasons in 2007 laboratory analysis of samples revealed inter seasonal variability primarily attributed to hydrogeochemical processes all or most of the samples exceeded the world health organization who guideline value glv for iron conductivity and turbidity while none of the samples exceeded who glv for hardness and arsenic with minor fraction exceeding glv for chloride content higher ammonia content in well water and highest phosphate concentration occurred for stone spout in pre monsoon season principle component analysis highlighted three principle components while the dendrogram divided the sampling sites into four and two clusters respectively for well water and stone spout water sampling sites saturation index computed through wateq4f model revealed that ferrihydrite siderite strengite and vivianite minerals were in under saturated state while goethite was in supersaturated condition for each type of samples well water and stone spout water in both pre and post monsoon seasons depicting their tendency to precipitate high degree of supersaturation in goethite mineral indicated response to temperature gradient of the reactions while under saturation for other minerals indicated the effect of dilution

green ampt infiltration model for sloping surfaces 1 this work quantifies and explains the direct physical effects of slope angle on infiltration and runoff generation by extending the green ampt equation onto sloping surfaces a new extended solution using identical precipitation hydrographs was compared to the original formulation and then used to calculate the infiltration and runoff generation for different slope angles but for identical horizontal projection lengths homogeneous and isotropic soil is assumed and two different boundary conditions for vertical rainfall are studied ponded infiltration and infiltration under steady rainfall infiltration under unsteady rainfall was found to be similar to cases with steady rainfall both theoretical and numerical results show that infiltration increases with increasing slope angle for cases with ponded infiltration the slope effect was generally not significant for mild to moderate slopes but the slope effect became more important for low intensity and short duration rainfall events especially as it delayed the time for ponding it was also found that the cumulative vertical infiltration depth ihp at ponding or the initial loss increases with increasing slope angle the model was compared to richards equation on horizontal and sloping surfaces and found to perform well the model s applicability for nonuniform slopes was discussed and it was found that the model is generally applicable for isotropic and mildly anisotropic soils except for some small scale topographic elements finally the occurrence of nonvertical rainfall could increase runoff with increasing slope angle when rainfall deflects a large angle to upslope

modeling local infiltration for a two layered soil under complex rainfall patterns abstract a general model for local infiltration redistribution reinfiltration in a two layered soil profile is proposed as an extension and generalization of a formulation we developed earlier for infiltration and redistribution in crusted soils it is of analytical conceptual type and involves a runge kutta verner numerical solution of a system of two ordinary differential equations given the basic hydraulic properties of soils there are practically no parameters to estimate by calibration the wetting profile during infiltration is represented by a single similarity curve while in the reinfiltration stage which occurs for rewetting after a period of redistribution the profile of soil water content in each horizontal layer may be composed of two similarity profiles which evolve in time the model is tested by comparison with numerical solution of richards equation carried out for a variety of synthetic experiments upon the combination of three soil types of contrasting hydraulic characteristics it simulates particularly well the entire cycle infiltration redistribution reinfiltration in all cases where either layer may be less permeable the water content at the surface and the interface as well as the infiltration rates are very accurately estimated the usefulness of compound profiles of water content in the reinfiltration stage is also shown by comparison with the simple approach which relies on a single similarity curve

assessing the carbon dioxide content of ancient atmospheres using palaeocalcretes theoretical and empirical contraints recent suggestions that the 13 c composition of calcretes can be used to determine the p co 2 of ancient atmospheres is critically evaluated the problem of differentiating pedogenic calcretes from groundwater ones which could not be used for p co 2 determinations is considered a critical problem a basic tenet of the use of calcretes for assessing p co 2 is that plants using c 4 or cras sulacean acid metabolism photosynthetic pathways were unimportant until the miocene this view is questioned and evidence is presented from carboniferous calcified root mats that non c 3 plants were probably present at this time confirming speculations by palaeobotanists that crassulacean acid metabolism or c 4 photosynthesis may have arisen numerous times during the evolution of higher plants

dinosaur eggshell isotope geochemistry as tools of palaeoenvironmental reconstruction for the upper cretaceous from the tremp formation southern pyrenees abstract the isotopic compositions 13 c and 18 o of dinosaur eggshells have been widely used in palaeoenvironmental studies although the geochemical signatures of eggshells are not usually contrasted with other proxies in this work the isotopic signatures of eggshells from a large maastrichtian succession from the tremp formation southern pyrenees spain are compared to those of carbonate pedogenic nodules occurring in the same levels the isotopic signatures of eggshells vary according to the stratigraphic unit and geographical location a group of samples from several localities corresponding to eggshells without significant diagenetic imprints has isotopic values differing from the associated nodules the late cretaceous isotopic composition record from the tremp fm is consistent that is the eggshells have distinct primary signatures preserved however the eggshells from another locality which exhibit neomorphed textures display isotopic signatures similar to the associated pedogenic carbonate which suggests a diagenetic isotopic signature and confirms alteration in the eggshells both microscopic and geochemical data suggest that an early meteoric diagenesis pedogenesis is responsible for the secondary signatures the 13 c values in the carbonate pedogenic nodules indicate a carbon isotopic composition typical of c3 plants although the slight difference in 13 c between the palaeosol carbonate of coeval successions may be due to slightly different palaeoenvironmental conditions the small discrepancy in the 13 c calculated for c3 plants from carbonate nodules and from eggshells may be because the palaeosol carbonate gives the isotopic composition of the vegetation grown at a local site whereas the 13 c from eggshells is a proxy for the ingested food in the area in which the dinosaurs lived the oxygen isotopic compositions from palaeosol carbonate nodules have been used for calculation of the air temperature and we may conclude that the mean air temperature in the studied area during the late cretaceous was approximately 21 c the use of this temperature gives rational results in the calculation of the oxygen isotopic composition of palaeosol carbonate by means of the isotopic composition of the eggshell carbonate additionally a relatively continuous isotopic record of nodules shows an overall vertical trend towards negative 13 c values and a high relative and steady 18 o content throughout the maastrichtian the k pg boundary was recorded by a negative excursion in 13 c in the carbonate nodules

pedogenic carbonates archive modern and past precipitation change a transect study from soils and loess paleosol sequences from northern iran abstract stable carbon and oxygen isotope compositions in soil carbonates and in soil organic matter provide insights into paleo climatic conditions especially in arid and semiarid regions where carbonate is abundant in soils we here investigate 13c and 18o isotope composition of bulk carbonate pedogenic carbonate nodules and organic carbon from modern soils developed along a precipitation gradient entisol inceptisol mollisol and alfisol and paleosols formed within loess units in northern iran 13c values of organic carbon in the modern soils ranged from 19 5 in the arid and semiarid regions to 24 in the more humid regions with forest vegetation 13c values of bulk carbonate in the modern soils ranged from 12 1 at the wettest sites to 0 8 at the drier sites and thus a 550 mm increase in precipitation leads to a 11 decrease in 13c values of bulk carbonate in the modern soils 13c values of pedogenic carbonate nodules in the semiarid areas show higher values by 3 4 more than the regions with forest vegetation unlike 13c values of pedogenic carbonate nodules the 18o values of pedogenic carbonate nodules of modern soils in this study did not display pronounced changes across the sections the change in 13c of carbonates and organic carbon is consistent with the present above ground vegetation consisting of a mosaic of habitats with differences in the proportion of c3 and c4 vegetation tending to larger c4 contribution with increasing aridity the 13c values of carbonates coupled with climate data of the region confirm seasonal bias in the formation of carbonate nodules in the modern soils seen in studies elsewhere the 13c values of pedogenic carbonate nodules in the paleosols range from 10 in humid areas to 7 2 in semiarid areas the trends in 13c composition in modern soils are also visible in the 13c composition in the paleosols suggesting that in the foothills of the alborz and iranian loess plateau a precipitation gradient existed also in the last interglacial

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

low atmospheric co 2 levels during the permo carboniferous glaciation inferred from fossil lycopsids earth history was punctuated during the permo carboniferous 300 250 million years myr ago by the longest and most severe glaciation of the entire phanerozoic eon but significant uncertainty surrounds the concentration of co2 in the atmosphere through this time interval and therefore its role in the evolution of this major prepleistocene glaciation here i derive 24 late paleozoic co2 estimates from the fossil cuticle record of arborsecent lycopsids of the equatorial carboniferous and permian swamp communities quantitative calibration of late carboniferous 330 300 myr ago and permian 270 260 myr ago lycopsid stomatal indices yield average atmospheric co2 concentrations of 344 ppm and 313 ppm respectively the reconstructions show a high degree of self consistency and a degree of precision an order of magnitude greater than other approaches low co2 levels during the permo carboniferous glaciation are in agreement with glaciological evidence for the presence of continental ice and coupled models of climate and ice sheet growth on pangea moreover the permian data indicate atmospheric co2 levels were low 260 myr ago by which time continental deglaciation was already underway positive biotic feedbacks on climate and geotectonic events therefore are implicated as mechanisms underlying deglaciation

an attempt to understand the behavior of dissolved organic carbon in coastal aquifers of pondicherry region south india groundwaters of the coastal region are significant and serve as a fragile ecosystem in the sedimentary terrain the pondicherry region is characterized by different geological formations of distinct geological epochs cretaceous tertiary and quaternary ninety three samples were collected from specific aquifers with respect to spatial distribution alluvium 31 upper cuddalore 13 lower cuddalore 13 other tertiary 7 cretaceous 24 and mixed multiple completion aquifer 5 the collected samples were analyzed for major ions ca2 mg2 na k hco3 cl po42 so42 f and doc stables isotopes of 18o d and 13c were also analyzed along with heavy metals like al ba fe sr cd and zn the 18o ranges between 6 85 and 2 15 and d ranges between 43 94 and 19 41 the distribution of these environmental isotopes in groundwater of this layered aquifer sequence was also attempted a comparison of the isotopic data with the rainfall local meteoric water line with a equation of d 7 398 18o 5 067 indian meteoric water line and global meteoric water line was performed the 13c values for groundwater ranges from 5 3 to 18 1 the result indicates that the groundwater in the study area is mainly meteoric in origin and few samples show evidence of evaporation the dissolved organic carbon doc is a very important component in biogeochemical cycling of elements characterized by high susceptibility to leaching the range of the doc in the study area is 0 16 mg l factor analysis was applied to classify the groundwater samples and to identify geochemical processes controlling groundwater geochemistry the alluvium aquifers show a complex hydrogeochemistry than the older aquifers the major factor influencing the hydrogeochemistry of the region is rock water interaction and anthropogenic processes hence metal mobility of the groundwater shows the correlation of metal bonding and doc the relation between the doc and heavy metal concentration in the aquifers was also identified

δ13c values of carbonate nodules across the permian triassic boundary in the karoo supergroup south africa reflect a stinking sulfurous swamp not atmospheric co2 abstract paleosol macromorphology petrography and stable isotope geochemistry of carbonate nodules from permo triassic p t boundary strata of the central karoo basin south africa are presented in order to evaluate their utility as geochemical archives of permian triassic paleoatmospheric chemistry and their potential to provide a terrestrial carbon isotope chemostratigraphy for correlation with contemporaneous global marine 13 c records paleosol morphologies across p t boundary strata of the central karoo basin indicate the region was a poorly drained seasonally to continuously flooded bottomland radiaxial calcite microspar and micrite microtextures are observed in the calcite nodules associated with p t paleosol profiles micritic calcite is typical of soil carbonate that forms in well drained soils characterized by open system gaseous diffusion between the soil and global atmosphere whereas more coarsely crystalline textures and radiaxial calcite are more typical of crystallization in phreatic environments with limited gaseous diffusion between the soil and global atmosphere in this regard only those nodules composed of micritic calcite can be considered as a potentially reliable source of proxy information for paleoatmospheric 13 c values across the p t boundary the 13 c values of all carbonate nodules from two overlapping measured sections near carlton heights south africa range from 24 4 to 1 8 whereas micritic calcite nodule 13 c values range from 7 0 to 21 3 comparison of calcite 13 c values with penecontemporaneous organic matter 13 c values indicate that calcite 13 c values 13 c values rather these more negative carbonate nodule 13 c values likely reflect calcite crystallization under poorly drained swampy conditions characterized by a semi closed chemical system that evolved independently of earth s troposphere therefore previously reported negative carbon isotope shift s measured from carbonate nodules in the karoo basin p t strata do not provide a record of atmospheric 13 c and probably do not provide a viable carbon isotope stratigraphy that can be realistically correlated with global p t marine carbon isotope stratigraphies