importance of clay in iron transport and sediment reddening evidence from reduction features of the abo formation new mexico u s a abstract petrographic and geochemical data from reduction features in the abo formation permian of central new mexico provide insight into the source of iron for hematite precipitation in red beds reduction features in the abo formation include isolated reduction spots as well as zones of reduction associated with fractures and coarser grained beds the reduction features contain less iron and more copper than the host rock mean values in ppm host rock fe 6456 cu 9 reduced fe 3730 cu 113 hematite relics are present in reduced areas associated with fractures and reduced bedding but are absent in reduction spots hematite apparently never formed in the reduction spots because of localized reducing conditions present at the time of pervasive reddening reduced fractures and bedding most likely result from migration of reducing pore fluids flowing through more permeable areas and postdate hematite precipitation iron bearing sand and silt grains which are typically regarded to be the principal source of iron for hematite precipitation in red beds are uncommon average 1 in the abo formation where present these grains are not significantly altered in either red host rock or in the white reduction features therefore detrital iron bearing clay size material is the primary source of iron in the abo formation although compositionally variable the clay rich areas contain a mean of 8 4 feo total in the host rock and a mean of 4 6 feo total in reduction spots chemical and mineralogical data from clay rich areas suggest that ferric oxyhydroxides associated with the clays are a more important iron source than iron from the clay crystal structure low whole rock iron content of the abo formation relative to other red bed units is consistent with clay and associated ferric oxyhydroxides being the principal iron source the abo formation may represent a clay dominated end member in a continuum of red beds in which the iron needed for reddening is derived from clays and coarser iron bearing framework grains

stable isotopic investigation of clay minerals and pedogenesis in an interfluve paleosol from the cenomanian dunvegan formation n e british columbia canada abstract mineralogical and stable hydrogen and oxygen isotopic compositions have been obtained for clay minerals comprising an interfluve paleosol clayhurst ch 2 from the early to middle cenomanian dunvegan formation british columbia canada this paleosol provides a special opportunity to determine the stable isotopic composition of early late cretaceous paleoprecipitation on the western coast of the western interior seaway at a very northerly paleolatitude 65 detrital kaolinite and illite and complex dioctahedral mixed layer clay minerals of pedogenic origin are abundant throughout the paleosol in the d values of 93 to 81 and 18 o values of 12 9 to 11 6 were generally obtained for the ancient soil water and hence paleoprecipitation for one thin interval near the top of the paleosol higher values are indicated for the ancient soil water these results may indicate processes arising from a westward transgression of the western interior seaway

plant architecture and spatial structure of an early permian woodland buried by flood waters sangre de cristo formation new mexico abstract natural molds of 165 stems were found in life position in a 1 m thick sandstone bed lower permian wolfcampian sangre de cristo formation northern new mexico the sandstone represents a single flood event of a river sourced in the ancestral rocky mountains most of the flood buried plants survived and resumed growth the stem affinities are uncertain but they resemble coniferophytic gymnosperms possibly dicranophylls stem diameters n 135 vary from 1 to 21 cm with three strongly overlapping size classes modern forest studies predict a monotonically decreasing number inverse square law of individuals per size class as diameter increases this is not seen for fossil stems 6 cm diameter reflecting biases against preservation exposure and observation of smaller individuals stems 6 cm diameter obey the predicted inverse square law of diameter distribution height estimates calculated from diameter to height relationships of modern gymnosperms yielded heights varying from 0 9 m to 8 m mean of 3 m mean stand density is approximately 2 stems m 2 20 000 stems hectare for all stems 1 cm diameter for stems 7 5 cm or 10 cm diameter density is approximately 0 24 stems m 2 2400 stems hectare and 0 14 stems m 2 1400 stems hectare stem spatial distribution is random poisson mean all stem nearest neighbor distance nnd averages 36 cm mean nnd between stems 7 5 cm and 10 cm diameter is approximately 1 02 m and 1 36 m nnd increases in approximate isometry with stem diameter indicating conformation to the same spatial packing rules found in extant forests and other fossil forests of varying ages nearest neighbor distance distribution passes statistical testing for normality but with positive skew as often seen in extant nnd distributions the size frequency distribution of the stems is similar to those of jurassic early tertiary and extant woodlands the early permian woodland distribution line has the same slope but differs in that the overall size range increases over time cope s rule the early permian woodland is self thinning its volume versus density relationship shows a self thinning exponent between 1 25 and 1 5 within the range seen in some extant plant stands 1 21 to 1 7

origin distribution and significance of carbonate cements in the albert formation reservoir sandstones new brunswick canada abstract carbonate cements in the fluvio lacustrine reservoir sandstones of the albert formation mainly occur in three phases pre compaction calcite post compaction calcite and ankerite the precompaction calcite cement 25 to 40 is characterised by bright luminescence high concentrations of fe mn and sr means of 1 56 wt 1 42 wt and 0 25 wt respectively slightly heavy 13c and 18o values mean 1 79 pdb mean 14 99 pdb respectively and its selective occurrence in lacustrine sandstones suggestive of cementation at shallow depths from lacustrine connate water dull luminescence variable concentrations of fe mn and sr variable but slightly heavy 13c and 18o values mean of 2 97 pdb and 11 05 pdb respectively of the post compaction calcite as well as its occurrence in alluvial fan sandstones exhibiting high pressure solution of detrital grains suggest cementation from pore waters modified by water rock interactions we suggest that the ankerite cement was formed from upwardly migrating formation water based on the following evidence i ankerite cement filling the secondary pores created in the deep subsurface ii an absence of unconformity during ankerite cementation precluding involvement of meteoric water iii ankerite cementation in brecciated veins synchronous with ankerite precipitation in host sandstones iv occurrences of significant volumes of ankerite 20 to 30 in the shales indicating that the fe and mg ions expelled during smectite to illite transformation reactions were consumed within the shales and v the heavy 13c and 18o isotope values of the ankerite cements means of 2 2090 pdb and 11 05 pdb respectively

oxygen isotope ratios in holocene carbonates across a climatic gradient eastern washington state usa evidence for seasonal effects on pedogenic mineral isotopic composition oxygen isotope ratios of pedogenic carbonates were analyzed along a climatic gradient in the palouse region of eastern washington state to evaluate changes in their isotopic composition with changing climate a modern analog approach was used to assess the relationship between the istotope ratios in the pedogenic carbonates with those in soil water measured in june when we anticipated carbonate formation might occur because of low soil water content and meteoric water from two national atmospheric deposition program nadp sites adjacent to our sequence mean annual meteoric water 18o values wrt vsmow from the two nadp sites varied slightly with elevation 13 9 at the starkey site elevation 1253 m and 13 0 at the palouse site elevation 766 m but showed distinct seasonal trends with weighted means ranging from 11 9 during autumn to 15 0 during the winter carbonate 18o wrt vpdb varied significantly with map ranging from 14 1 at the most arid site to 11 4 at the wettest site but d

diagenetic control on secondary porosity in flood plain deposits an example of the lower triassic of northeastern belgium abstract the lower triassic sandstones of northeastern belgium were deposited in channels and by sheet floods introduction of clays formation of iron oxides and alteration of feldspars in these sediments occurred at near surface conditions subsequent calcite precipitation and the replacement of feldspars and quartz occurred at low temperatures 21 26 c in meteoric waters with a 18 o 5 8 smow characteristic is the bleaching of the originally red coloured sediments red coloration was caused by iron oxide pigments in clay coatings around quartz grains the bleaching is the result of the reduction of these iron oxides most likely by organic acids the oxidation reduction reaction produced carbon dioxide and protons which altered the feldspars the underlying upper carboniferous strata are a potential source for organic acids released by thermocatalytic degradation of its kerogen the bleaching took place before a period of important authigenic quartz growth which occurred after compaction feldspars quartz and calcites have been replaced by dolomite and ankerite these carbonates could have formed from meteoric waters at relatively low temperatures e g 50 c as well as from brines at higher temperatures e g 120 c following dolomite ankerite cementation an intensive dissolution of feldspar took place the secondary pores have been filled with kaolinite barite and illite primary and secondary porosity is now significantly lower in clay rich sandstones than in pure sandstones early diagenetic replacive calcites have a negative effect on late diagenetic porosity creation feldspar grains which have been replaced by calcites were either slightly or not affected by late diagenetic dissolution

an oxygen isotope study of illite and calcite in three appalachian paleozoic vertic paleosols abstract the oxygen isotope compositions of pedogenic calcite and illite in three paleozoic vertic red bed paleosols record a complex history of pedogenic and diagenetic processes the paleosols are preserved in the upper mississippian chesterian mauch chunk pennsylvania hinton west virginia and pennington tennessee formations in the appalachian basin and were buried to 7 8 km 230 260 c 3 4 km 100 145 c and 1 5 3 km 70 100 c respectively the submicron size clay fractions of the paleosols are presently composed of r3 ordered illite smectite i s inferred from k ar dates and soil morphology to have been authigenically produced by the reaction of smectite to illite oxygen isotope fractionations calculated pore fluid compositions and k ar dates were used to constrain the conditions and timing of i s and pedogenic calcite re crystallization in each of the paleosols the data were interpreted in light of three possible end member environments for formation and recrystallization 1 the pedogenic environment 2 the burial diagenetic environment and 3 a burial environment dominated by hot tectonically driven fluid the 18o values of pedogenic calcite and authigenic i s in vertic red bed paleosols generally reflect recrystallization and exchange during burial diagenesis and are thus not suitable for interpretation of paleoenvironment or paleoclimate the involvement of orogenic fluids during burial cannot be ruled out but it is not required by any of the paleosols in the coastal margin pennington formation paleosol i s formation may have been initiated in the pedogenic environment in response to cyclical wetting and drying of the soil clay matrix continued smectite transformation and coarsening and ordering of i s during a long period of shallow burial led to its isotopic reequilibration with pore fluids at slightly elevated temperature but oxygen isotope compositions of pedogenic calcite in the paleosol are preserved

diagenetic and porosity evolution of conglomerate sandstones in bayingebi formation of the lower cretaceous chagan sag china mongolia frontier area abstract the fan delta conglomerate sandstones of bayingebi formation including conglomerates and pebbly sandstones in the chagan sag are reservoir for large accumulations of hydrocarbons based on observation of cores thin sections sem and cl combined with application of fluid inclusion and carbon and oxygen isotopes it indicates that the conglomerate sandstones are mainly feldspathic litharenites with immature texture it has considerable heterogeneity with a wide range of porosity from 0 3 to 15 3 and the permeability from 0 004 md to 1168 md this study discusses conglomerate sandstones diagenesis and its controls on reservoir quality its eodiagenesis is primary compaction and the minor of calcite cementation the subsequent mesodiagenesis includes weak compaction precipitation of quartz overgrowth and feldspar overgrowth albitization dissolution of early carbonate cement and metastable framework grains late carbonate cementation and illitization a comparison between porosity depth data and normal compaction curve of conglomerate sandstones shows two groups group a is mainly composed of tight conglomerate sandstones with permeability less than 1 md and porosity less than 10 petrology studies show that two types of the tight conglomerate sandstones developed in this group one type mainly depositing in the thinly bedded subaqueous channels of fan delta front is characterized by abundant clay minerals occluding intergranular pores the other type mainly depositing in the thinly bedded subaqueous channels or along sandstone mudstone interface of thickly bedded subaqueous channels is characterized by abundant carbonate cements occluding intergranular and intragranular pores group b is mainly composed of conglomerate sandstones with higher permeability more than 1 md and porosity ranging from 5 to 16 corresponding to the burial depth from 2200 to 3400 m it mainly deposited within the thickly bedded subaqueous channels of fan delta front significant dissolution of carbonate cement feldspars and other metastable framework grains by organic acids and co 2 generated from organic maturation are the major cause of abnormally high porosity

stable isotopic composition of an evaporite dissolution breccia in the lower visean limestones of se belgium an evaporitic dissolution breccia occurs in the lower visean limestones of southeastern belgium three periods of brecciation have been recognized the first of which took place early in the diagenetic history the breccia matrix consists of infiltrated marine sediments the fragments and the sedimentary matrix subsequently neomorphosed and lithified in meteoric waters multiple water rock interactions in an open system caused an oxygen isotopic composition of the limestones in equilibrium with meteoric water this composition varies between 8 9 and 5 5 depending on the palaeogeographical position the early diagenetic interaction led also to a spread in the carbon isotopic composition which ranges between an early visean marine 13c 4 pbd and a palaeosol 13c 3 pdb isotopic composition due to the migration of fluids along fractures in the subsurface a second dissolution brecciation and cementation period occurred during this period breccia fragments and the early diagenetic matrix locally neomorphosed a second time the oxygen isotopic composition of the limestone constituents decreased due to the interaction with burial fluids the 18o composition of the breccia fragments and matrix moved towards those of dull orange brown luminescent calcite cements 18o 20 to 11 pdb filling the secondary cavities a third period of brecciation and neomorphism caused the development of orange yellow zoned and bright luminescent microsparites to sparites and of granular to blocky calcites

superlakes megafloods and abrupt climate change about 8200 years ago the climate of much of the northern hemisphere cooled abruptly for a period of about 200 years in their perspective clarke et al examine the most likely culprit for this cooling an outburst of fresh water from a vast ice dammed glacial lake in north america the superlake had formed when the kilometers thick ice sheet covering much of north america disintegrated when the ice dam became unstable fresh water flooded from the lake into the north atlantic it remains unclear how this fresh water affected ocean circulation or whether the outburst occurred in more than one stage but the timing points strongly to the outburst flood as the trigger of the 8200 year climate event

physico chemical environment of pedogenic carbonate formation in devonian vertic palaeosols central appalachians usa the morphology and geochemistry of pedogenic carbonate found in vertic claystone palaeosols in the devonian catskill formation in central pennsylvania preserve a record of the physical and chemical environment of carbonate precipitation the carbonate is characterized by three distinct petrographic generations pedogenic rhizoliths and nodules are the earliest precipitated generation and typically consist of dull red brown luminescent micrite clear equant calcite spar cement fills voids in the centres of rhizoliths as well as circumgranular cracks and septarian voids in nodules early spar cements are nonluminescent to dull luminescent whereas later spar cements exhibit bright yellow orange luminescence late stage pedogenic fractures are always occluded with very bright yellow orange luminescent spar cements the incorporation of progressively higher concentrations of mn up to 34 000 ppm into successively younger calcite spar cements without concomitant increases in fe suggests carbonate precipitation from an evolving meteoric water in which mn2 became increasingly mobile over time the increased mobility is possibly due to decreasing eh resulting from oxidation of organic matter after rapid soil burial on the floodplain the amount of fe2 available for incorporation into calcite was limited because most iron was immobile having been earlier oxidized and bound to the palaeosol clay matrix as a poorly crystallized ferric oxide or oxyhydroxide mineral carbon isotope compositions of pedogenic carbonate correlate with the inferred depth of carbonate precipitation rhizoliths preserved below the lowest stratigraphic occurrences of pedogenic slickensides are consistently depleted in 3c relative to nodules which formed stratigraphically higher within the zone of active soil shrink and swell processes nodular carbonate precipitated in proximity to deep cracks in the soil is enriched due to increased gas exchange with isotopically heavy atmospheric c02 accordingly rhizolith compositions will most accurately estimate palaeoatmospheric levels of c02 the use of nodule compositions may result in overestimation of pco by as much as 30

outburst flood evolution at russell glacier western greenland effects of a bedrock channel cascade with intermediary lakes abstract glacial lake outburst floods have produced a distinctive and widespread quaternary record both onshore and offshore via widespread and intense geomorphological impacts yet these impacts remain poorly understood due to a lack of modern analogues this study therefore makes a systematic quantification of the evolution of a bedrock channelled outburst flood channel topography was obtained from digitised aerial photographs a 5 m grid resolution dem and bathymetric surveys flood inundation was measured in the field from dgps measurements flood evolution was analysed with application of a numerical model novel flood metrics including rate of rise to peak and persistence above a value of hydraulics were calculated the key findings were that outburst floods i that enter intermediary lakes are dramatically attenuated in terms of propagation whilst basin filling proceeds to the outlet level dissipated of energy due to considerable flow recirculation during the rising stage of the flood and after overtopping of the outlet are moderated in terms of peak discharge ii can have kinematic waves that are introduced to a flood via hydraulic ponding iii may develop a partitioning of flow regimes for instantaneous peak discharge bed shear stress and froude number due to time transgressive changes in channel cross section specifically between inner channel and overbank regions furthermore normalised change in cross sectional area and normalised change in channel slope can be used to suggest the relative magnitude of instantaneous peak discharge net erosion along a reach can be related to hydraulic persistence above a marker value and net deposition can be related to a time to peak value reconstructions of quaternary outburst floods should consider the importance of including intermediary lakes modern hazard mitigation studies could usefully note the potential use of reservoirs as an outburst flood alleviation resource

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

coastal plain origin of trace fossil bearing red beds in the early permian of southern new mexico u s a abstract the early permian robledo mountains formation of the hueco group in the robledo mountains south central new mexico u s a is a world class ichnofossil lagerstatte of supposed peritidal origin abundant and diverse invertebrate and vertebrate trace fossils occur in several thin horizons of siliciclastic red beds that are intercalated with thick successions of shallow marine limestone and shale the depositional environment of the red beds has been discussed for decades but without any detailed sedimentary facies analysis a recently completed systematic excavation shows that the majority of trace fossils is related to mud draped surfaces within distal crevasse splay siltstone to fine grained sandstone interbedded mudstone with well preserved macrofloral remains and a lungfish aestivation burrow represents a hitherto disregarded facies in overbank fines both environmental subzones were at least loosely covered with low growing plants and experienced common periods of subaerial exposure none of the physical and biological structures recorded in the measured section indicates tidal influence but instead they support the reconstruction of a freshwater ecosystem dominated by arthropods and tetrapods given their proximity to carbonates of unambiguous subtidal origin we propose that the trace fossil bearing red beds of the robledo mountains formation formed in distal parts of an extensive coastal floodplain during alternating wet and dry conditions if this interpretation is correct it provides an impetus to continue ichnological and sedimentological field research in the study area because the true tidal flat ichnoguilds still await elucidation

braided river deposits in a muddy depositional setting the molina member of the wasatch formation paleogene west central colorado u s a the molina member is a paleogene sand rich interval up to 125 meters thick found within the otherwise mud dominated nonmarine wasatch formation of west central colorado sandstone beds of the molina member form sheet like units interbedded with subordinate volumes of mudstone the sandstones contain a low diversity assemblage of sedimentary structures that is commonly dominated by horizontal planar laminae and bedding is locally contorted by large scale soft sediment deformation a braided fluvial model best explains the characteristics of these strata yet the existing braided river models do not fully account for the assemblage of sedimentary structures or the relatively high volumes up to half of the section of interbedded mudstones two modern braided rivers medano creek colorado and the prairie dog town fork of the red river texas have rapid shallow flows that form horizontal planar bedding in both systems the presence of large volumes of easily mobilized sandy sediment a flashy discharge regime and a lack of reworking between flood stages lead to the development of high energy shallow water bedforms and the preservation of the resulting high energy sedimentary structures similar conditions and processes are suggested to have controlled deposition of the sand dominated molina member which is a depositional anomaly within the otherwise muddy wasatch formation short term availability of readily eroded second cycle sandstones from a newly elevated source area to the southeast is the most likely reason for the abrupt change from a mud dominated fluvial system to the sandy molina system

palaeosols and sequence stratigraphy of the lower permian abo member south central new mexico usa the relationship between palaeosols and sequence stratigraphy is tested in the lower permian abo member south central new mexico by comparing interfluve and fluvial terrace palaeosols with palaeosols that developed within lowstand fluvial deposits interfluve and fluvial terrace palaeosols consist of primary pedogenic features including vertical root traces vertic structures stage ii and iii pedogenic calcite and translocated clay argillans which are cross cut or replaced by low aluminium goethite gley colour mottling sparry calcite veins and ankerite the polygenetic character of the palaeosols is consistent with initial development for several thousand to tens of thousands of years on well drained interfluves or fluvial terraces followed by waterlogging due to invasion by a rising water table that locally may have been brackish in contrast lowstand fluvial sediment that filled incised valleys contains only rooted and vertic palaeosols whose immaturity resulted from high aggradation rates palaeosols similar to those in the abo member have been recognized in other ancient strata and when combined with highresolution correlation provide evidence for interpretation of sequencestratigraphic surfaces and systems tracts

paleoclimatic controls on stable oxygen and carbon isotopes in caliche of the abo formation permian south central new mexico u s a abstract the stable oxygen and carbon isotopic composition of caliche in fluvial and supratidal rocks of the abo formation permian south central new mexico is controlled by paleoclimate and depositional environment fluvial caliche consists of low mg calcite nodules and vertically oriented tubules that display stage ii texture micrite matrix support brecciation ooids pisoliths aveolar septal texture and peloids are common in the fluvial caliche and along with red color and slickensides in the host shale indicate pedogenesis in a well oxidized vadose zone in contrast periodic waterlogging of the supratidal paleosols probably due to high water table is indicated by drab colors carbonaceous flecks horizontal rhizoliths and the paucity of vadose textures in the stage ii caliche n dules stable oxygen isotopes are similar in the fluvial and supratidal caliches and range from 21 6 to 30 5 smow the data exhibit a crude bimodality and 18o enrichment with a decrease in age higher in the section consideration of these data in the context or temperature relations suggests that 1 surface waters responsible for caliche formation increased in 18o from roughly 8 to 1 over the 18 m y time interval that separated the lowest stratigraphic nodule horizon from the highest 2 the inc easing 18o values also reflect a warming trend approximately 15 to nearly 3 c in the mean monthly temperature over this same time period with perhaps an associated increase in permian ocean temperatures and 3 the significant variation in 18o from oldest to youngest caliche was probably enhanced by the amount effect such that as the temperature increased the amount of precipitation decreased resulting in high 18o values caliches in the abo are enriched in heavy carbon 7 2 to 1 5 pdb compared to that of soil carbonate derived exclusively from c plants 12 pdb and the supratidal caliches contain somewhat heavier carbon compared to the fluvial caliche the 13c values for both environments increase with a decrease in caliche age these results indicate that as the temperature increased and rainfall decreased with time the level of c3 plant productivity apparently declined allowing a greater influx of atmospheric co2 into the soil this can only occur when soil respiration rates are quite low or at very sha low depths less than 10 cm or both atmospheric co2 seems to have invaded the supratidal soils to a somewhat greater extent than the fluvial soils

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

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

photosynthetic community responses to upwelling in mesoscale eddies in the subtropical north atlantic and pacific oceans in this paper we summarise the photo physiological responses of phytoplankton to upwelling of macronutrients in mesoscale eddies in the subtropical north atlantic eddies project sargasso sea and subtropical north pacific e flux project hawaii the observations obtained on two sets of cruises over 2 years occupied six cyclonic eddies and two mode water eddies the photosynthetic physiological parameters were measured using a bench top fluorescence induction and relaxation fire system and a submersible in situ fast repetition rate fluorometer frrf deployed on an undulating towed vehicle both of these instruments were used to provide highly sensitive and well resolved data on community responses the responses are dependent on both the type of eddy and its stage of development our results indicate that while cyclonic eddies in the atlantic and pacific can increase primary photosynthetic production early in their development mode water eddies in the subtropical north atlantic can support patchy blooms of large diatoms for long periods of time more than 3 months

pedogenic carbonates in texas stable isotope distributions and their implications for reconstructing region wide paleoenvironments abstract pedogenic carbonates are ubiquitous in paleosols through geologic history and have been widely used to speculate on paleoclimatic conditions during their formation they are widespread and well developed in large areas of texas a majority are of late quaternary age and have formed across a range of climatic conditions on various types of substrates to evaluate the usefulness of pedogenic carbonates as environmental indicators this study investigates regional scale trends in stable isotope compositions of pedogenic carbonates across approximately 900 km of texas the 13c values of 49 pedogenic carbonate profiles 182 analyses on various host strata e g limestone igneous rocks range from 10 6 to 0 7 v pdb most 13c values are evenly distributed between 9 and 1 and the 18o values range from 9 1 to 0 2 v pdb mainly between 6 and 2 there is no correlation between carbon and oxygen isotopic values r2 0 0002 pedogenic carbonates in the texas gulf coastal plains southern high plains and west texas exhibit higher 13c values than those in south and central texas which corresponds to the spatial change in vegetation between c4 dominated and c3 dominated plants the marked increase in 13c values of the pedogenic carbonates from the tertiary strata into the overlying quaternary strata confirms the invasion of a c4 biomass into the southern high plains since the early pliocene from east to west the 18o values of late quaternary pedogenic carbonates decrease gradually a trend that mimics the spatial variation of 18o values of modern meteoric water primarily due to the increased distance from the gulf of mexico source of most of the meteoric water in contrast to the regional trends the stable isotope values of some pedogenic carbonates developed on marine limestone and calcareous alluvium in central texas and south texas have isotopic signatures inherited from the host strata in addition some of the 13c values of pedogenic carbonate nodules in the gulf coastal plains have been affected by saline groundwater soil carbonates formed in the shallow parts of the profile such as petrocalcic horizons may have also been influenced by the atmospheric co2 nevertheless climatic trends are readily apparent in the isotopic data thus demonstrating their potential value in region wide paleoclimatic analyses

carbon isotopic subsets of soil carbonate a particle size comparison of limestone and igneous parent materials abstract the c isotopic analysis of pedogenic carbonate is an important method for investigating paleoclimatic conditions and carbon sequestration however a calcic soil sample may contain multiple types of carbonate especially in soils formed in limestone parent material to evaluate isotopic values of the different soil carbonate types stable c isotopic analysis was applied to an array of particle size classes in bulk soil that was collected from soils formed in limestone parent material and neighboring soils formed in igneous parent material a pronounced trend of decreasing 13 c with progressively decreasing soil particle size was revealed in soils of both parent materials ranging from about 2 to 6 for limestone soils and 1 to 5 for igneous soils thin section microscopy and radiocarbon dating also indicated multiple subsets of calcium carbonate types in soils thin section analysis disclosed the presence of limestone detritus calcitans aggregates of carbonate crystals and calcified root hairs radiocarbon dating revealed different 13 c values of carbonate crystals of different ages ranging from about 2620 to 40 290 years for limestone soils and 1660 to 5830 years for igneous soils these results indicate 1 limestone particles in soil may contribute to a complex mixture of 13 c values that is absent from soils formed in igneous parent material and 2 it is necessary to recognize that isotopic values of bulk soil represent a mixture of different 13 c values from different size fractions and ages in both limestone and igneous soils

lithofacies and palaeosol analysis of the middle and upper siwalik groups plio pleistocene haripur kolar section himachal pradesh india abstract the middle upper siwalik groups plio pleistocene are exposed at haripur kolar himachal pradesh india the succession is 2800 m thick and has been subdivided into unit m1 of the middle siwalik and four units u1 u4 of the upper siwalik group on the basis of facies associations and type and degree of development of palaeosols the available magnetostratigraphic ages for bases of units u1 u3 and u4 are 5 5 2 6 and 1 77 ma respectively the top of the section has been dated as 19 ka lithofacies association and palaeocurrent analysis indicates that the middle and upper siwalik groups were formed mainly by a basin transverse fluvial system two types of river systems which differ in their size can be documented in unit m1 unit u1 and unit u2 one trunk river system similar to the modern kosi and the other smaller river system which formed tributaries to the former the large rivers were mainly braided in nature the unit u3 and lower part of unit u4 were deposited in the piedmont depositional system mainly by small braided streams and the upper part of the unit u4 was deposited during a period of arid climate by sediment gravity flows integration of fluvial lithofacies and pedofacies helps to identify two fluvial depositional systems from the modern indo gangetic plains the lowland system involved deposition on alluvial megafans and interfan areas which resulted in sand rich and mud rich sequences with weekly developed soils the upland system allowed large tracts to act as high ground for thousands of years thereby giving rise to sandstone poor intervals with moderately to strongly developed soils occurrence of moderately to strongly developed soils was controlled by uplifting and tilting of large tectonic blocks without any relation to distance from the main channels rate of subsidence apparently controlled the occurrence of lowland and upland systems deposition of the unit m1 unit u1 and unit u2 took place under upland and lowland systems very similar to those identified from the modern indo gangetic plains the warm and humid climate between 5 3 and 2 6 ma led to the formation of red alfisols with calcrete nodules at places slightly cooler and drier climate starting at about 2 6 ma and approximately coinciding with the onset of global scale glaciation produced poorly developed yellow soil with common development of nodular calcretic horizon and calcitc material disseminated in the groundmass at ca 0 9 ma a probable significant change to still drier and cooler climate produced typical sediment gravity flows in the piedmont system that continued until at least up to 19 ka

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

evidence of past environmental conditions during the evolution of a calcretised wadi system in southern jordan using stable isotopes abstract a stratigraphically and temporally ordered sequence of channel calcretes preserved along the wadi dana southern jordan records the quaternary evolution of the formation and infilling of rock cut channels and their subsequent incision in a tectonically subsiding basin it is currently unknown under what palaeoenvironmental conditions these non pedogenic calcretes formed stable isotope analyses have been used to investigate whether any past topographical hydrological vegetational diagenetic and or temporal signatures can be identified from the channel calcretes the results of this research indicate that channel calcrete development is influenced by altitudinal variation affecting vegetation and hydrology within the landscape as well as location within individual wadi channels which has an affect on diagenetic processes the lack of calcretisation of a terrace that is between 1 and 1 5 m above the modern wadi floor supports the idea that the environment is currently too arid for calcrete to develop thus the presence of older wadi dana channel duricrusts suggests wetter conditions when they formed the 18o data of the calcrete implies cooler conditions than today as there is little evidence of a strong evaporative effect any temporal control is limited and mainly a function of stratigraphic position with some numeric dating

isotopic approach to soil carbonate dynamics and implications for paleoclimatic interpretations the radiocarbon content and stable isotope composition of soil carbonate are best described by a dynamic system in which isotopic reequilibration occurs as a result of recurrent dissolution and reprecipitation depth of water penetration into the soil profile as well as soil age determines the degree of carbonate isotope reequilibration we measured 13c 18o and radiocarbon content of gravel rinds and fine 2 mm carbonate in soils of 3 different ages 1000 3800 and 6300 14 c yr b p to assess the degree to which they record and preserve a climatic signal in soils developing in deposits independently dated at 3800 and 6300 radiocarbon yr b p carbonate radiocarbon content above 40 cm depth suggests continual dissolution and reprecipitation presumably due to frequent wetting events between 40 and 90 cm depth fine carbonate is dissolved and precipitated as rinds that are not redissolved subsequently below 90 cm depth in these soils radiocarbon content indicates that inherited fine carbonate undergoes little dissolution and reprecipitation in the 3800 and 6300 yr old soils 13c in rind and fine carbonate follows a decreasing trend with depth apparently in equilibrium with modern soil gas as predicted by a diffusive model for soil co2 18o also decreases with depth due to greater evaporative enrichment above 50 cm depth in contrast carbonate isotopes in a 1000 yr old deposit do not reflect modern conditions even in surficial horizons this soil has not undergone significant pedogenesis there appears to be a lag of at least 1000 but less than 3800 yr before carbonate inherited with parent material is modified by ambient climatic conditions although small amounts of carbonate are inherited with the parent material the rate of pedogenic carbonate accumulation indicates that ca is derived primarily from eolian and rainfall sources a model describing carbonate input and radiocarbon decay suggests that fine carbonate below 90 cm is mostly detrital inherited and that carbonate rinds have been forming pedogenically at a constant rate since alluvial fans were deposited

geology mineralogy and geochemistry of late miocene paleosol and calcrete in the western part of the central anatolian volcanic province cavp turkey abstract the late miocene was characterized by high global temperatures and partly to nearly complete desiccation of the mediterranean sea throughout the latter part of the messinian age the messinian salinity crisis the non marine paleoenvironmental and paleoclimatic records from the mediterranean area are highly limited in their spatial range late miocene river flood plain sediments in the central anatolian volcanic province cavp of central turkey consist of siliciclastic and pyroclastic sediments with paleosols and calcrete five lithofacies were identified as a massive conglomerate b trough cross bedded sandstone c massive mudstone d disrupted mud e and disrupted matrix supported conglomerate the paleosols were composed predominantly of smectite and illite with smaller amounts of feldspar quartz opal a pyroxene and amphibole and the calcretes were composed mainly of calcite with smaller amounts of feldspar quartz and opal a and minor amounts of smectite chlorite and illite authigenic clay minerals and micritic calcite coating on the detrital grains and soil peds and pendant cement in the calcrete and paleosol horizons were evidence of a vadose zone in contrast the large equant spar drusy mosaics were formed in phreatic environments the weathering of ignimbrite and marble led to the depletion of sio2 cao al2o3 fe2o3 tio2 and k2o through the precipitation of smectite and illite in the paleosols and cao in the form of micrite and calcite in the calcrete horizons field observations mineralogy geochemistry and the results of 18o and 13c isotopic analysis reveal that alternating wet and dry periods resulted in an upward increase in precipitation of authigenic smectite and illite within the late miocene sections under the influence of geochemical and ph fluctuations in phreatic or vadose water within the river flood plain paleoenvironment

a comparison of two recent jokulhlaups from an ice dammed lake sondre stromfjord west greenland the hydro graphs of two jokulhl aups resulting from the sudden drainage of an ice d ammed lake in west greenland in 1984 and 1987 are compared the first flood had a similar peak discharge to the second but drained only two thi rds of the total volume of the 1987 event which amounted to 32 36 x 106 m3 in 36 h calcula tions based on the lake refill time suggest that it drains every 2 3 years but that peak flows may be variable from flood to flood the timing of the joku lhlaups in relation to the melt season may reflect variations of water pressure within the subglacial drainage networks and changes in the

hydrodynamic characteristics of the tam pokhari glacial lake outburst flood in the mt everest region nepal the tam pokhari glacial lake outburst flood glof which occurred in 1998 in the mt everest region of nepal was evaluated using hydrodynamic models to gain a better understanding of the flow behaviour the flood wave was analysed separately under rigid and erodible boundary conditions in both cases the calculated dam breach hydrograph which had a peak discharge of about 10 000 m3 s was routed through the inkhu river which originates from the lake the morphologic changes along the river were also analysed and the results were compared with satellite images field observations and recorded data in the case of rigid boundaries the routing procedure gradually attenuated the peaks of the hydrographs to account for hydraulic pooling in narrow gorges and storage in the channel in the case of erodible boundaries such effects were minimized due to the increment in channel capacity associated with erosion by debris flow the study revealed that the glof event produced a large scale debris flow additionally the results revealed that erosion and deposition took place intermittently but that approximately 440 000 m3 of sediment was deposited about 14 km downstream from the lake mouth the calculated peak of the water and sediment mixture at 14 4 km was found to be 30 000 m3 s which is almost 6 times as large as that observed when the rigid boundary conditions were used further the increase in the peaks of the hydrographs due to sediment transport was the primary reason for the destruction associated with the glof these findings suggest that the local sedimentology and topography as well as other geo hazard conditions in the area should be carefully evaluated before recommending any control measures against glofs in the himalayan region copyright 2009 john wiley sons ltd

paleoclimate and the global distribution of paleosols a theoretical model is developed for the relationship between paleoclimate and paleosols for the time interval following the widespread appearance of vascular land plants the model defines four paleoclimatic zones 1 a wet equatorial zone primarily characterized by oxisols and secondarily by argillisols and histosols 2 a subtropical dry zone containing calcisols and less commonly gypsisols and vertisols 3 a moist mid latitude zone with argillisols spodosols gleysols and histosols and 4 a polar zone featuring protosols and gleysols the model is general in nature and its application to the geologic past will be affected by variability through time in paleogeography and paleoclimatic parameters

isotopic tracers of the origin of ca in a carbonate crust from the middle atlas morocco abstract carbonate crusts developed on basalt were studied at tazouta in the moroccan middle atlas the chosen representative weathering profile is 2 8 m thick and is composed from base to top of a fresh basalt overlain by a coherent saprolite a friable saprolite and a surface soil carbonate crust genesis occurs by replacement of primary and secondary clay minerals by low mg calcite the 14 c dates of the calcite range from 15 to 14 ka in the coherent saprolite and from 12 to 8 5 ka in the friable saprolite smectitic weathering and replacement of si bearing minerals by carbonate are coupled processes leading to a strong calcium net gain 300 kg m 3 within the friable saprolite the low weathering rate of basalt compared to the calcrete genesis rate and the high mobility of calcium in supergene weathering mantles limit the basaltic ca contribution to calcrete genesis the contribution of the triassic sediment is also limited by the mineralogical unavailability of ca the 87 sr 86 sr ratios confirm the low contribution of basalt and indicate an external origin of ca the sr isotope ratios of calcrete are different from those of the adjacent liassic carbonates and are close to rainfall values the carbon isotope compositions of carbonates 8 to 9 vs pdb imply a significant contribution of c3 dominated organic carbon during carbonate precipitation oxygen isotopic compositions of carbonates average 5 24 vs pdb show that carbonates are 18 o enriched compared to meteoric waters 4 to 3 5 vs smow

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