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

echinoderm stabilization associated with a paleokarst surface at the mississippian pennsylvanian boundary in tennessee u s a abstract pennington formation limestone deposits in tennessee immediately underlie a paleokarst surface that straddles the mississippian pennsylvanian unconformity vertic paleosols with significant gleying and coal seams overlie the paleokarst surface this study quantifies the fe loss associated with paleosol gleying and subsequent incorporation of fe into echinoderm grains that underwent stabilization echinoderm grains immediately below the paleokarst surface have lower mg and 13c values and higher fe concentrations compared to echinoderm grains meters below the paleokarst surface additionally echinoderm grains have variable 13c and invariant 18o values characteristic of alteration in a meteoric setting paleosols draping the paleokarst surface and coal seams that were deposited immediately above the mississippian pennsylvanian unconformity provided ample organic matter that could have driven heterotrophic microbial activity additionally the paleosols were an ample source of oxidized fe that could have been used as a terminal electron acceptor by an anaerobic microbial community therefore we suggest that fe reduction transferred fe from the paleosol to the limestone during meteoric stabilization of echinoderm grains fluid rock modeling constrains the magnitude of fe transfer that occurred during echinoderm stabilization stabilization can account for only a fraction 8 to 14 of the total quantity of fe lost from the gleyed paleosol thus supporting the premise of continued transfer of fe from the paleosol to limestone during burial diagenesis additionally this study constrains the timescale associated with echinoderm stabilization which was likely 12 ky finally stabilization timescale is consistent with echinoderm alteration associated with organic diagenetic conditions with elevated dissolved inorganic carbon in stabilizing pore fluids that were localized immediately below the paleokarst surface

paleosols associated with miocene basalts porcupine river northeastern alaska implications for regional paleoclimates abstract paleosols of middle miocene age consisting of wood peat organic matter rich mineral soil and weathered basalt are described from the upper ramparts of the porcupine river in northeastern alaska a highly acidic soil representing a floodplain wetland swamp forest environment underlies the basalts of the upper ramparts and is composed of 1 m of compressed peat and interbedded fluvial sediments wetland soils from between basalt flows were also observed in depressional sites on basalt surfaces palynological investigations indicate that these wetland peat profiles developed in association with temperate mixed hardwood conifer flora correlative to the early middle miocene seldovian floristic stage previously defined for southcentral alaska three well preserved types of basalt saprolites residual soils were identified in the study area depending on the drainage condition at the time of formation the greatest degree of basalt weathering occurred under apparent well drained conditions where a red clay rich soil with a solum depth greater than 1 m was observed between basalt flows the colour of this well drained paleosol and the presence of iron oxides including possible hematite is interpreted to reflect soil development under warm temperate climatic conditions

modeling influence of stratification on lateral circulation in a stratified estuary abstract the dynamics of lateral circulation in the passaic river estuary is examined in this modeling study the pattern of lateral circulation varies significantly over a tidal cycle as a result of the temporal variation of stratification induced by tidal straining during highly stratified ebb tides the lateral circulation exhibits a vertical two cell structure strong stratification suppresses vertical mixing in the deep channel whereas the shoal above the halocline remains relatively well mixed as a result in the upper layer the lateral asymmetry of vertical mixing produces denser water on the shoal and fresher water over the thalweg this density gradient drives a circulation with surface currents directed toward the shoal and the currents at the base of the pycnocline are directed toward the thalweg in the lower layer the lateral circulation tends to reduce the tilting of isopycnals and gradually diminishes at the end of the ebb tide a lateral baroclinic pressure gradient is a dominant dri

geochemistry and origin of ferruginous nodules in weathered granodioritic gneisses mysore plateau southern india fe nodules occur within saprolites formed from weathering of granodioritic gneisses in the rain shadow region of the mysore plateau adjacent to the sahyadri mountains in southern india these nodules and their host saprolites were studied for their geochemistry including chemical speciation to understand nodule formation and chemical redistribution processes during rock weathering from their mode of occurrence and mineralogical and geochemical data we infer that the nodules originated by a two stage process in which the initial extensive weathering of gneisses likely facilitated subsequent ferrolysis weathering and nodule formation nodules originated by precipitation of goethite hematite and gibbsite along with several amorphous phases within the matrix of weathered gneisses this is possible only under hydromorphic conditions suggesting that parts of the plateau must have gone through a humid phase prior to the present aridity in the saprolites al fe and ti become enriched because of the removal of si ca na and k however within the nodule fe ti cr and ni are deposited after their chemical transport from the saprolite titanium known for its immobile nature was also mobilized and concentrated under the conditions of nodule formation the most important elements in the nodule constitution are fe al ti and mn each having both crystalline and amorphous phases fe ti and mn oxyhydroxides grain coatings in the saprolites and discrete amorphous mn and ti phases in the nodules seem to have scavenged trace elements from the weathering profile ree were mobilized during weathering and nodule genesis in which ce and ti show a strong geochemical coherence the enrichment of only hree in saprolite and both hree and lree with significant ce in the nodule indicate the control of evolving secondary minerals in the ree redistribution during rock weathering strong enrichment of ce in the weathering profile and in nodules has important implications to the ree chemistry of river waters

hematite spherules at meridiani results from mi mini tes and pancam 1 we report on observations of hematite bearing spherules at meridiani planum made using the microscopic imager mi mini thermal emission spectrometer mini tes and panoramic camera pancam instruments on the mars exploration rover opportunity spherules were observed on soil surfaces and in outcrop rocks both on undisturbed surfaces and in abraded surfaces ground using the rock abrasion tool rat spherule size and shape change little along the 850 m eastward traverse from eagle crater to endurance crater but spherules decrease and then slightly increase in size along the 6 km traverse from endurance south to victoria crater local populations range from submillimeters to several millimeters in diameter an additional small diameter 100 m size population is possible an increase in irregular shapes is found near victoria crater this combined with the size decrease south of endurance suggests either a changing depositional environment or variation in the duration and timing of diagenetic events the dominant smaller size population observed early in the mission in aeolian areas and ripple crests is observed as the primary size population in abraded outcrop farther south this suggests that successively younger beds are exposed at the surface along the southward traverse stratigraphically higher units removed by erosion could be recorded by the present surface lag deposit coordinated systematic observations are used to determine optical and infrared hematite indices of the surface soils in pancam and mini tes in spite of the systematic variation seen in mi both pancam and mini tes indices are highly variable based on the local surface and neither show systematic trends south of endurance the lack of a 390 cm 1 feature in mini tes spectra suggests concentric or radial interior structure within the spherules at scales too fine for mi to observe mini tes does not detect any silicate component in the spherules a bound water component in soils or in exchange with the atmosphere is observed these spherules have been previously interpreted as concretions formed within what were once water saturated diagenetically altered dirty evaporate sandstone sediments our observations support this interpretation however no single terrestrial analog provides a model that can account for all attributes of the spherules on mars

depth to pedogenic carbonate horizon as a paleoprecipitation indicator an analysis of 1168 modern soil profiles from the u s natural resources conservation service yields no correlation between mean annual precipitation and depth to the top of the carbonate horizon r 2 0 03 p 0 001 parent material and soil texture both play negligible roles in this regression when combined with similar published studies n 1481 r 2 improves slightly r 2 0 31 p 0 001 caution is therefore advised in using this or any previously published regression for inferring paleoprecipitation from paleosols however in the combined data set carbonate horizon bearing soils correlate with a mean annual precipitation of 760 mm p 0 05 thus the presence vs absence of pedogenic calcium carbonate is a good indicator of paleoprecipitation above or below this value

geochemistry and palaeoclimatic reconstruction of a palaeosol sequence at langebaanweg south africa abstract neogene langebaanweg lbw palaeosol sediment sequences at the west coast of south africa are well known for their well preserved rich palaeontological heritage the palaeosols developed on estuarine marine coastal alluvial deposits stacked on each other ranging in age from the mid miocene to quaternary elemental mobility and redistribution based on major and minor element geochemistry of 11 horizons of the 18 m sequences were studied to evaluate the degree of chemical weathering a major process of soil formation and to reveal important palaeoenvironments in which the palaeosols developed elemental geochemistry was carried out on 2 50 mean wt two wi 1 and wi 2 of the four weathering indices applied to evaluate weathering intensity proved unsuitable for use in an alluvial palaeosol sediment sequences such as lbw chemical index of alteration cia and chemical index of weathering ciw values were relatively more consistent in distribution pattern across the pedocomplex but caution should be applied when using them in similar cases the pedogenic carbonate horizons on average had the lowest values for both cia and ciw 1 12 2 60 suggesting more advanced weathering plots of geochemical ratios quantifying pedogenic processes against depth show striking variations among and within the palaeosol and sediment sections soil formation was more advanced in the mid miocene and pliocene than in the quaternary suggesting a more humid and warmer climate than present we evaluated selected geochemical climofunctions and conclude that more data are obviously needed for a more robust calibration of the models in langebaanweg palaeosols

pedogenic and diagenetic influences on void coating formation in lower cretaceous paleosols of the mill creek formation southwestern alberta canada abstract pedogenic and diagenetic influences on void coating formation were studied in two paleosols from the lower cretaceous albian mill creek formation in southwestern alberta canada using detailed micromorphological mineralogical and geochemical methods the paleosols consist of alternating decimetre scale beds of red grey green and variegated mudstone intermediate horizons red and grey green variegated mudstones contain associations of pale yellow clay coatings dark red clay coatings fe depletion hypo coatings and fe oxide quasi coatings sem edx ray analyses indicate that the dark reddish coatings are dominated by si al and fe with subordinate amounts of k na ca mg and ti pale yellow clay coatings have a higher si content and lower al k na ca and fe contents relative to reddish coatings within the paleosol profiles the distribution of clay minerals indicates 1 an increase in discrete clay minerals downward 2 a decrease in mixed layer illite smectite downward and 3 an increase in chlorite upward x ray diffraction indicates that the pale yellow and dark red clay void coatings are polymineralic pale yellow clay coatings have a higher proportion of mixed layer illite smectite and kaolinite less chlorite and are less crystalline than dark reddish coatings despite a diagenetic overprint including development of diffusion gleyans degradation of organic matter burial reddening and probably some smectite illitization both compositional and morphological gradients exist in the paleosol profiles and void coatings these gradients are most likely related to depositional variations and to pedogenic development in the original soils under variable eh ph conditions in the presence of organic matter therefore although the void coatings are altered diagenetic features their morphology mineralogy and perhaps even some of their microchemistry is attributable to the presence of pedogenic precursors initially formed in soils similar to modern temperate alfisols and glossic soils

mass balance reconstruction of a modern vertisol implications for interpreting the geochemistry and burial alteration of paleo vertisols abstract utilizing identical sampling and analytical techniques the morphological and chemical characteristics of a modern vertisol houston black series central texas can be directly compared with an upper mississippian paleo vertisol from the appalachian basin pennington formation east central tennessee mass balance reconstructions suggest retention of primary pedochemical patterns in the paleo vertisol including patterns of soil volume change strain and transport functions translocations of many major and trace elements retention of primary pedochemical patterns suggests that vertisols constitute nearly closed systems during burial diagenesis chemical and mineralogical changes associated with burial diagenesis of the paleo vertisol include oxidation of organic carbon oc illitization of smectites dehydration and recrystallization of fe mn oxyhydroxides and dolomitization of pedogenic calcite significant differences in the chemical behavior of gilgai microhigh and microlow pedons in modern vertisols have implications for interpretation of geochemical data obtained from paleo vertisols overall wetter soil conditions and variable redox potential under gilgai microlows promote greater depths of leaching and mobility of redox sensitive trace elements including co cr cu mn ni and v gilgai microhighs behave as evaporative wicks that draw moisture and soluble phases towards the soil surface resulting in precipitation of metal hydrosylate complexes and sulfates gypsum at the capillary fringe and shallower depths of leaching and fixation of trace elements paleoprecipitation estimates from paleosols based on the depth to the top of the pedogenic carbonate horizon should therefore utilize field petrographic and geochemical data for characterizing maximum depths of leaching loss or gain of exchangeable bases and calcification rather than relying solely upon field data

sensitivity of northern hemispheric continental ice sheets to tropical sst during deglaciation a thermomechanical ice sheet model ism is used to investigate the sensitivity of the laurentide and fennoscandian ice sheets to tropical sea surface temperature sst perturbations during deglaciation the ism is driven by surface temperature and precipitation fields from three different atmospheric general circulation models agcms for each agcm the responses in temperature and precipitation over the ice sheets nearly compensate such that ice sheet mass balance is not strongly sensitive to tropical sst boundary conditions it was also found that there is significant variation in the response of the ism to the different agcm output fields

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

palaeosol stratigraphy across the permian triassic boundary bogda mountains nw china implications for palaeoenvironmental transition through earth s largest mass extinction abstract upper permian and lower triassic palaeosols from northeastern tethyan localities exposed within the bogda mountains nw china provide a wealth of information regarding long term palaeoclimatic and palaeoenvironmental variations wuchiapingian palaeosols are characterized by intense redoximorphy accumulation of vascular plant matter accumulation of clay minerals and fe oxides slickensides and clastic dikes suggesting a soil moisture regime that ranged from perennially wet to distinctly seasonal in soil moisture budget changsinghian to early induan palaeosols include subsurface accumulations of clay and carbonate as well as surficial accumulations of organic matter indicative of sub humid to sub arid soil moisture and variable soil moisture regimes induan to olenekian palaeosols contain pedogenic caco 3 accumulations and gypsum pseudomorphs indicating a drier environment characterized by net soil moisture deficiency elemental composition of palaeosol matrix was used to estimate palaeoprecipitation through the chemical index of alteration minus potassium cia k proxy estimates from various wuchiapingian strata indicate relatively stable palaeoprecipitation during the late changsinghian and early induan palaeoprecipitation appears to have decreased from 1100 to 230 180 mm year over less than 100 m of vertical stratigraphic section in the induan and olenekian palaeoprecipitation appears much less stable than in wuchiapingian with values vacillating from 290 to 1014 mm year the transition to a relatively unstable precipitation state coincides generally with the permian triassic boundary and may reflect climatic disturbances associated with the end permian extinction event in addition to altered atmospheric circulation patterns resulting from regional tectonics moisture availability and expansion of the subtropical high pressure belt

preservation of a paleo vertisol and an estimate of late mississippian paleoprecipitation abstract a late mississippian paleosol satisfying all of the morphological criteria required for classification of holocene vertisols provides quantitative paleoclimate information in addition to the now commonplace interpretation of precipitation seasonality based on the presence of vertic features paleoprecipitation was estimated using the empirical relationship between depth to pedogenic carbonate horizon in quaternary soils burial compaction erosional truncation and high paleoatmospheric co2 concentration all factors that complicate paleoprecipitation estimates are unusually well constrained for this paleosol allowing for 10 compaction the paleosol had a pre burial depth of 100 cm for the pedogenic carbonate horizon yielding a mean annual paleo precipitation estimate f 648 141 mm this is comparable to the mean annual precipitation for brownsville texas where similar soils are found today a dolomicrite crust developed in gilgai microlows is well preserved in the paleo vertisol higher late mississippian paleotemperatures and rates of evapotranspiration associated with a lower latitude paleogeography for central tennessee during the late mississippian may explain in part why holocene coastal vertisols in the brownsville region lack surficial crusts similar to that of the paleo vertisol we qualitatively define the late mississippian climate of central tennessee as semiarid

evidence for an early sagebrush ecosystem in the latest eocene of montana abstract late eocene strata at little pipestone montana preserve paleosols and an undiverse but abundant trace fossil assemblage dominated by adhesive meniscate burrows placed into the ichnogenera taenidium the assemblage as a whole is most consistent with the scoyenia ichnofacies the reconstructed paleohydrological and paleoenvironmental setting that results from the combination of sedimentological paleopedological and ichnological data is of a seasonally desiccated well aerated floodplain characterized by low flood frequency and intensity slow sediment accumulation rates and an overall subhumid semiarid climate very similar to a modern sagebrush steppe this would represent the oldest documented sagebrush steppe ecosystem in montana

neoichnology at lake margins implications for paleo lake systems abstract neoichnological studies provide significant information that can aid in the interpretation of ancient ichnological assemblages here we examine for the first time the pattern in both vertebrate and invertebrate trace distribution and abundance that can be seen in two geographically separate but broadly analogous contemporary semi arid climate lake margin settings in an effort to describe taphonomic processes relevant to paleo lake systems lake margin to supralittoral zone transects were made at ruby reservoir montana usa and la sotonera spain and vegetation cover trace cover trace diversity and substrate characteristics were recorded similar patterns in trace distribution were seen through the eulittoral to supralittoral zones with the majority of traces identified within a single transect present at both sites however a few traces attributed to larger organisms were found to be unique to each and in some instances could to be assigned to a specific trace maker the eulittoral zone was considered to have characteristics attributable to the scoyenia ichnofacies however analysis of the supralittoral zone shows some characteristics of both the coprinisphaera and the mermia ichnofacies in addition a transitional zone between a scoyenia like ichnofacies and a fully terrestrial assemblage was found which may enable continental ichnofacies to be further refined for application to paleo lake systems study of the distribution of traces with distance along the transects also suggests taphonomic biases against the preservation of certain types of traces e g avian due to seasonal fluctuations of the lake level and the subsequent reduced preservation potential for lake proximal traces

pedogenic iron manganese nodules in vertisols a new proxy for paleoprecipitation the total fe content of pedogenic iron manganese fe mn nodules taken from a vertisol climosequence on the texas gulf coastal plain correlates with mean annual precipitation map r 2 0 92 no significant trend of total fe fetot with depth was noted in profiles using the regression developed from modern vertisol data fetot contents of paleozoic paleo vertisol fe mn nodules yielded map regimes comparable to previously inferred paleoenvironmental interpretations paleoprecipitation estimates derived from fe mn nodules for an uneroded late mississippian paleo vertisol are very close to estimates determined from a depth to pedogenic carbonate horizon dch proxy determined from the modern vertisol climosequence the lack of soil depth dependence of the fe mn nodule proxy provides a consistent paleoprecipitation estimate even in eroded paleo vertisols and in combination with the dch may be useful in determining original paleosol thickness

distinguishing climate in the soil record using chemical trends in a vertisol climosequence from the texas coast prairie and application to interpreting paleozoic paleosols in the appalachian basin u s a a suite of vertisols clay rich soils with high shrink swell potential were examined across a climosequence climatic transect in twelve soil pits from the coast prairie of texas in order to determine if mean annual precipitation map exerts a control on the chemistry of these soils and if the observed chemical trends are useful for interpreting paleoclimate records of paleovertisols in the geologic record the precipitation regime of the climosequence spans a range between 144 and 86 cm year with moisture regimes classified as udic udic ustic ustic and aridic ustic in a general northeast to southwest direction other soil forming factors such as soil age 35 40 ka parent material fluviodeltaic beaumont formation of late pleistocene age landscape low relief coastal plain and vegetation prairie or mixed woody shrubs are relatively constant across the climosequence climate sensitive chemical proxies of map identified include dithionite citrate extractable fe fedith acid oxalate extractable fe feoxal caco3 equivalent caco3equiv s and ammonium acetate extractable na k and mg naacet kacet and mgacet respectively which vary across the climosequence because of differences in effective depths of leaching and intensity of wetting and drying cycles these standard usda wet chemical climate proxies are related to bulk oxide or element chemistry of soils and paleosols measured using xrf which supports the use of geochemical climate proxies for interpreting the paleoclimate records of paleovertisols application of the chemical index of alteration minus potash cia k geochemical climofunction to late mississippian paleosols from the appalachian basin of the eastern u s demonstrates evidence for a shift from a lower to a higher map paleoclimate that is consistent with previous paleoclimate models and with observed morphological changes in the paleosols we advocate actualistic research using bulk chemistry of soils and paleosols as a means of obtaining soil information useful for interpreting paleosols in the geological record

paleoenvironmental analysis of the neotropical fossil mammal site of cerdas bolivia middle miocene based on ichnofossils and paleopedology abstract the early middle miocene langhian age site of cerdas in the southern bolivian altiplano has produced a diverse fauna of extinct mammals 15 species in seven orders and 11 families in this study we use paleosols and ichnofossils to reconstruct its paleoenvironment and the conditions in which its fossils were preserved the described paleosols represent three pedotypes and three distinct landscape surfaces in an alluvial system type 1 paleosols are interpreted as haplusteps inceptisols that formed on a proximal floodplain in a subhumid to humid patchy shrubland with seasonal variation in precipitation and associated changes in soil moisture conditions landscape 1 type 2 paleosols are interpreted as dystrudepts that formed on a well vegetated distal floodplain in a seasonal humid climate with ground covering shrubland vegetation landscape 2 type 3 paleosols are interpreted as calciustolls mollisols that formed in a shifting alluvial environment in a seasonal sub humid to semi arid open environment landscape 3 ichnofossil assemblages of cerdas include skolithos planolites macanopsis parowanichnus rhizohaloes and rhizotubules these were produced by detritivorous herbivorous and faunivorous soil arthropods as well as plant roots and represent soil communities not normally preserved as body fossils that were living within a heterogeneous alluvial environment the physical and geochemical properties of the paleosols and associated ichnofossil assemblages indicate that the paleolandscapes were composed of shrublands and open environments that experienced changes in moisture regimes due to seasonal precipitation and flooding events and had varying degrees of temporal stability our analysis is the first detailed study of pre pleistocene cenozoic paleosols and trace fossils from the southern tropics mid latitudes of south america and one of the few focused on important fossil mammal bearing sediments

micromorphological and sem analysis of cretaceous paleogene petrosols from eastern montana and western north dakota abstract microscopy is used to distinguish pedogenic features from those associated with primary sedimentary fabric and non pedogenic diagenesis in a suite of 65 million year old sediments sand to clay sized material was deposited in meandering river systems over a broad coastal alluvial plain and pedogenesis occurred in all lithologies a variety of petrosol lithified soil horizons which exhibit both syndepositional bedding and pedogenic and non pedogenic diagenetic features remains today features attributable to the in situ interaction between root and soil provide the most convincing evidence of pedogenesis in addition features such as illuvial clay and iron oxide accumulations around voids which are commonly but not exclusively associated with soil environments provide accessory evidence of pedogenesis stress related void and ground mass birefringence fabrics are evident in the petrosols and some purely sedimentary deposits and thus cannot be used as diagnostic indicators of pedogenesis in this fluvial setting erosion and transport of soil material occurred which is indicated by the presence of pedorelicts in petrosol horizons and purely sedimentary deposits detailed study both by petrographic and by scanning electron microscope elucidates pedogenic indicators not visible in hand samples such tools are useful in resolving ambiguities between pedogenesis and non pedogenic diagenesis