magnetic susceptibility of soils in different slope positions in saskatchewan canada abstract the magnetic susceptibility of soils varies with the slope position due to some factors such as texture and drainage class this study attempts to link to soil profile characteristics soil horizon type organic and inorganic c sand and oxalate feo and dithionite fed extractable iron measured on soil cores collected from the three uncultivated soil catenas in saskatchewan the parent material at all sites consisted of medium textured hummocky glacial till the waitville catena gray luvisol was developed under trees the weyburn catena dark brown chernozem under grass and the oxbow catena black chernozem had trees on the lower slope and grass in the center of the depression and on the upper and middle slopes in all the three catenas a downslope decrease in was correlated with increasing feo fed ratios and decreasing sand content lower slope gleyed profiles in the two chernozemic catenas had high feo fed ratios and low the impact of gleying was most evident in the solum and tended to increase in the c horizons of these profiles the of the sand and silt fractions was positively correlated with that of the bulk soil whereas the of the clay fraction did not vary with the of the bulk soil stable sand sized magnetite grains are believed to be rare in these soils

coupled micromorphological and stable isotope analysis of quaternary calcrete development pedogenic calcretes are widespread in arid and semi arid regions using calcrete profiles from four river terraces of the rio alias in southeast spain this study explores the potential of using detailed micromorphological and stable isotopic analysis to more fully understand the impacts of quaternary environmental change on calcrete development the four profiles increase in carbonate complexity with progressive age reflecting calcretisation over multiple glacial interglacial cycles since mis 9 c 300 ka calcrete profiles contain a mixture of alpha non biogenic and beta biogenic microfabrics alpha fabrics have higher 13c and 18o values the profiles contain a range of crystal textures but there is little difference between the 13c and 18o values of spar microspar and micrite cements strong positive covariance between 13c and 18o suggests that both isotopes are responding to the same environmental parameter which is inferred to be relative aridity the study reveals that the detailed co analysis of calcrete micromorphology and stable isotope signatures can allow patterns of calcrete formation to be placed into a wider palaeoclimatic context this demonstrates the potential of this technique to more reliably constrain the palaeoenvironmental significance of secondary carbonates in dryland settings where other proxy records may be poorly preserved

groundwater dolocretes in a lake marginal environment an alternative model for dolocrete formation in continental settings danian of the provence basin france in the long continental history of the provence basin which extended from santonian to oligocene times a major period of palaeosol development occurred in the danian dolocretes developed within floodplain silts and partly from palustrine limestones dolocretes are overlain by pedogenic facies calcretes and palustrine limestones gradational lower and upper limits of profiles succession of nodular coalescent and massive horizons the epigenesis of quartz by dolomite the unimodal crystal size and the euhedral dolomite fabric as well as the absence of biogenic structures and vadose cements show that dolocretes formed in the phreatic zone the exclusive occurrence of dolocretes around the palaeolake or playa suggests that dolocrete formed by the mixing of groundwaters and lake brines which infiltrated the phreatic zone during periods of strong evaporation and lake level lowering the term halo dolocrete is proposed to describe this type of dolocrete deposit subsequent alteration of the dolocrete includes leaching of the central core of dolomite crystals and calcitization calcitization was either fabric destructive type i or fabric preserving type ii and took place during very early diagenesis i e concomitant with calcrete formation or palustrine limestone deposition fabric destructive calcitization is attributed to a drop in the lake level when the upper part of the dolocrete was subjected to vadose zone processes whereas the fabric preserving calcitization resulted from reactions with dilute lake and groundwaters during rise in lake level

silica diagenesis ii general mechanisms abstract amorphous silica phases opal a precipitate in nature due to the formation of dense colloids in supersaturated alkaline aqueous solutions with low relative concentrations of other ions opal a dissolves and yields solutions of still relatively high silica content in pore waters containing abundant cations open framework polymers form which flocculate to yield opal ct opal ct becomes increasingly ordered primarily due to preferential growth of cristobalite relative to tridymite and crystal size increase opal ct dissolves to yield pore waters of low silica concentration which allows slow growth of quartz crystals from monomeric solution the quartz crystals then slowly increase in size and crystallinity carbonates appear to enhance opal ct formation possibly due to the activity of positively charged hydroxyl complexes hence polymerization in relatively pure systems is involved in opal a formation and polymerization in impure systems is involved in opal ct formation and slow growth from monomeric low silica concentration solutions is involved in precipitation of quartz in sedimentary realms

the occurrence and interpretation of carbonate and sulfate minerals in a sequence of vertisols in new caledonia abstract in the tamoa valley on the western coast of new caledonia a vertisol sequence shows a downslope transition from calcimagnesic vertisols containing gypsum aragonite and magnesium calcite derived from flysch colluvium to hypermagnesic vertisols rich in dolomite and magnesite and derived from peridotite and serpentinite alluvium deposited by the tamoa river gypsum magnesium calcite and magnesite were probably formed during the dry period of the last glaciation between 30 000 and 17 000 yr b p magnesite nodules seem to be allochtonous and were formed upstream by the weathering of serpentinite during the more humid period of last flandrian transgression 5000 yr b p floods of the magnesium rich waters of the tamoa river over the alluvial plain brought magnesium to the soils and lead to fluctuations of the water table these conditions favoured the formation of manganese deposits as mangans calcite pseudomorphs after lenticular gypsum crystallization of authigenic barite in calcimagnesic vertisols and dolomite formation in magnesic and hypermagnesic vertisols during the recent period apparently drier aragonite is forming in the lower part of calcimagnesic vertisols

magnetic susceptibility of soils along a lithotoposequence in southeast iran abstract magnetic susceptibility is a simple and quick technique to determine soil properties and to describe soil forming processes knowledge about factors affecting data helps better interpretation magnetic susceptibility of soils along a lithotoposequence was studied in this research in order to investigate the effects of soil forming factors parent material and relief and processes on the content and its vertical distribution the study area is a transect from jiroft to kahnooj area south kerman province iran rock pediment mantled pediment inselberg alluvial fan alluvial plain and flood plain landforms with igneous parent materials gabbro diorite and granite were selected in the area thirteen representative pedons on different geomorphic positions were studied low frequency lf values ranged from 193 1 10 8 m3 kg 1 to 2704 2 10 8 m3 kg 1 in studied soils and decreased with increasing diamagnetic material contents mean lf values in soils formed on gabbro diorite and granite parent rock were 1700 10 8 m3 kg 1 515 22 10 8 m3 kg 1 and 352 53 10 8 m3 kg 1 respectively frequency dependent of soils in the range of 0 06 to 1 05 showed that coarse multi domain grains inherited from igneous parent material were the main source of lf in the area under study both increasing and decreasing trends of lf with depth were observed decreasing trend of lf with depth was due to illuviation of diamagnetic material into subsurface layers on the other hand increasing lf with depth was attributed to the primary ferrimagnetic material inherited from igneous parent material alluvial plain 320 44 10 8 m3 kg 1 and mantled pediment 328 50 10 8 m3 kg 1 showed low values of lf due to high amounts of soluble salts anhydrite and calcium carbonate investigated in these geomorphic positions a positive significant relationship r2 0 018 r 0 27 p

carbonate accumulation and weathering of the granitic substratum of tanecherfi basin northeastern morocco abstract in the tanecherfi basin a granitic body is partly overlain by a calcrete which only seems superimposed morphologically the profiles consist of three horizons the lowest one corresponds to a filling of carbonates into the weathered granitic rocks microscopically the carbonates cut the primary minerals along open cracks and voids in the second horizon the increased carbonation results in calcite septa that gradually isolate rock cells inclosed in a micritic matrix forming a cortex gradually the rock residues vanish and glaebules appear the upper horizon is characterized by a micritic matrix associated with the disappearance of the nodules these morphologic relations are confirmed by chemical data the primary minerals are weathered silica is locally released and precipitates partly around the glaebules magnesium combines into the carbonate structure but locally combines with the silica of the cortex of the glaebules aluminium seems to be totally removed the granite calcrete relationships indicate a weathering process rather to a simple superposition

micromorphology of calcium carbonate in bauxite processing waste abstract secondary calcium carbonate accumulations were observed in bauxite processing waste a waste product of aluminum production the waste material is saline sodic calcareous and highly alkaline ph 11 8 the waste was packed as a 50 solids slurry into cylindrical acrylic columns and subjected to treatment combinations of differing drainage regimes and gypsum and sulfuric acid additions after eight wetting and drying cycles samples were taken from the columns for analysis of carbonate distribution and thin section analysis micromorphic forms of carbonate found in the waste included infillings calcitic coatings and hypocoatings of voids acicular calcite found in vughs and calcium carbonate replacing gypsum these results suggest that secondary calcite forms commonly found in soils may form very rapidly under certain conditions

magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies a review of magnetic methods and challenges abstract magnetic iron oxide minerals principally magnetite maghemite hematite and goethite are formed in well drained soils in response to a suite of physical chemical and biological factors despite a wide range of complexity in the pedogenic processes that lead to magnetic mineral formation dissolution and transformation there are well documented empirical relationships between various magnetic mineral assemblages in soils with environmental and climatic conditions recently there has been an increase in the number of quantitative magnetic paleoprecipitation proxies that have been developed and there is great potential for magnetic methods to be used in the geologic record to develop reconstructions of past climates magnetic paleoprecipitation proxies have been widely utilized in quaternary or younger loess paleosol systems however they have yet to be utilized in the pre quaternary fossil record future studies of magnetic mineralogy of soils and paleosols should aim to explore non loessic modern soils and pre quaternary paleosols with more focus on understanding the interaction between magnetic mineral assemblages and soil moisture applications of existing and novel magnetic paleoprecipitation proxies in the fossil record should prove to be a valuable resource for paleoclimatologists

small scale secondary caco3 accumulations in selected sections of the european loess belt morphological forms and potential for paleoenvironmental reconstruction eighteen important quaternary loess paleosoil sites have been studied across the european loess belt they included approximately 50 buried soils the over and or underlying loess and the present day surface soils where possible from the numerous types of secondary caco3 accumulations recognized only the small scale accumulations are discussed in this paper including calcified root cells caco3 hypocoatings needle fiber calcite powdery calcite coatings earthworm biospheroliths and calcite pseudomorphs on gypsum most of the features studied are found in the rhizosphere microecosystem each of these features showed a unique relationship with organic matter micro organism and plant distribution moisture and leaching processes for example the exceptional abundance of calcified root cells is an indicator of a long stability of soil surface during favorable climatic conditions needle fiber calcite is related to biomineralization of saprophytes in soils with sufficient moisture and decomposing organic matter the presence of powdery calcite coatings covering clay and mn coatings in non calcareous soils indicates a change from leaching to non leaching soil moisture regimes earthworm biospheroids provide arguments for a relative stability of the soil surface without rapid burial processes or drastic prolonged water stress finally gypsum pseudomorphs are indicators of changes in local climatic parameters in addition to a discussion of the genesis and the dynamics of the various accumulations several examples are given to show how these accumulations can be used as indicators of a changing environment such as renewed loess deposition the extent of drought or varying intensity of leaching during the year to conclude various forms of small scale secondary caco3 accumulations are common in the loess paleosoils and each type has the potential to contribute to a better understanding of the evolution of the paleoenvironment therefore it is proposed that their individual presence or absence throughout the pedostratigraphical levels and throughout the paleo topography should be recorded at all scales of observation

clay coatings formation in tepetates from texcoco mexico abstract tepetates are common in the mexican highlands and are classified as fragipan duripan pedosediments or saprolite a common feature is the abundance of clay coatings three pedons with red tepetate and grey tepetate were selected at different altitudes and slopes in a small watershed in texcoco mexico physical chemical mineralogical and micromorphological analyses were carried out in soil tepetate and separated clay coatings clay illuviation and neoformation indexes were calculated using micromorphometric techniques red tepetate is composed of basic volcanic glass dust andesitic vitric tuff and has a high clay neoformation and illuviation index in contrast grey tepetate is composed of acid volcanic glass acid vitric tuff and only clay neoformation takes place leading to the formation of a clayey soil although all the tepetates were subject to pedogenesis the intensity and variation of the processes increases on the lower slope and different diagnostic horizons are formed due to tepetate erosion the laterally running waters containing suspensions of particles and soluble silica were deposited or precipitated in sediments or tepetates on the lower slopes giving rise to compound coatings these processes must be older than 20 000 years tepetates from texcoco present several variants which were recognised since pre hispanic times

magnetic imprints of pedogenesis in planosols and stagnic alisol from bulgaria iron in its diverse forms in soils is an important indicator of a number of past and or ongoing environmental processes iron oxide mineralogy pertinent to a particular soil type could be obtained with high resolution using magnetic methods planosols are a particular soil type characterized by surface water logging leading to development of great textural differentiation with depth this study presents magnetic investigation on three planosols and a stagnic alisol from bulgaria combined with conventional chemical extraction methods oxalate citrate dithionite and soil property characterization ph grain size fractions and organic carbon content extensive magnetic analyses on high resolution sampled depth profiles have been done for determination of iron oxyhydr oxide minerals their stability and variations of effective magnetic grain size with depth zones of intensive iron oxides dissolution the topmost soil horizons are magnetically depleted in the content of strongly magnetic minerals but the paramagnetic content detected through the ratio 77 293 is enhanced accordingly bleached eluvial horizons however contain stable crystalline magnetite maghemite fraction albeit in a trace amounts we ascribe this to the processes of lessivage and translocation of magnetite maghemite from the topmost humus horizon the main results on iron oxide mineralogy suggest that thin humus horizons are enriched with pedogenic maghemite thermal behavior of magnetic susceptibility suggests that ferrihydrite is present in humus and eluvial horizons of all profiles in illuvial horizons of planosols the common mineral is lepidocrocite while in alisol al substituted hematite planosols and stagnic alisol contain both poorly crystalline and well crystalline iron oxides increasing precipitation and weathering leads to higher proportion of well crystalline pedogenic phases in the alisol profile

origins of some early carboniferous calcrete fabrics revealed by cathodoluminescence implications for interpreting the sites of calcrete formation abstract calcretes from the lower carboniferous marginal marine limestones of south wales germany and belgium exhibit complex calcite microspar fabrics with rhombic irregular and spherical crystals in variable mosaics while many of these fabrics resemble classic recrystallization microspars having irregular crystal forms and non planar crystal boundaries cathodoluminescence microscopy reveals that they result from multiple phases of precipitation and dissolution no evidence for recrystallization by crystal boundary migration or replacement during the transformation of less stable calcite minerals aragonite or high magnesian calcite is seen identical microspar fabrics have been widely described in quaternary calcareous soils which may also be primary fabrics and not due to recrystallization or mineral transformation cathodoluminescence provides a useful tool for interpreting calcrete fabrics and in the case of these carboniferous forms indicates multiple phases of carbonate saturation and leaching reflecting the prominent wetting and drying phases evidenced by associated vertic soils horizons the complex cycles of precipitation and dissolution are characteristic of pedogenic calcretes and the recognition of such features using cathodoluminescence may provide a means of differentiating pedogenic from groundwater calcretes

magnetic fingerprint of southern portuguese speleothems and implications for paleomagnetism and environmental magnetism environmental magnetism of speleothems is still in its early stage of development here we report on our investigation of the environmental and paleomagnetic information that has been recorded in speleothems and what are the factors that control its preservation and reliability to address these issues we used a multidisciplinary approach including rock magnetism petrography scanning electron microscopy stable carbon and oxygen isotope compositions and major and trace element concentrations we applied this to a set of samples from different stages of speleothem evolution present day dripwater glass plates a weathered stalactite a fresh stalagmite cave sediments and terra rossa soils these samples come from the penico and excentricas caves located in two distinct aquifers of the algarve region south portugal our results show that the main magnetic carriers of the speleothems under study are primary detrital and consist of maghemite and magnetite similarities in coercivity and temperature dependence of the studied set of samples suggest that iron oxides are inherited from the terra rossa soils that cap the cave and were transported to the speleothems by dripwater hence they represent a regional environmental signature interestingly a stable and probably detrital remanent magnetization could be isolated in the fresh stalagmite whereas the weathered stalactite yielded chaotic magnetic directions and very low remanent intensities we propose that these low intensities can be the result from i different remanence acquisition mechanisms between stalagmite and stalactite and or ii iron dissolution by fungal activity we also suggest that magnetic properties and color and the content in detrital elements in the fresh speleothem inform about environmental processes acting on the interface of rock soil atmosphere while oxygen isotope composition and alkaline earth element concentrations inform about calcite water interaction processes these results provide a better understanding of how environmental information is recorded in speleothems and what the factors are that control the reliability of the paleomagnetic and paleo environmental signal

a micromorphological view through a namaqualand termitaria heuweltjie a mima like mound heuweltjies occur throughout namaqualand and the western and southern cape coasts broad low relief termitaria of the harvester termite microhodotermes viator which show different vegetation patterns to the surrounding soils distinguishable even in satellite images there is a direct relationship between soil hardpan occurrence and the heuweltjies characteristically in the semi arid areas the hardpans grade outwards from a central sepiolitic petrocalcic horizon laterally through petro sepiolitic palygorskitic variable in the degree of cementation to the petroduric horizon on the edges in a landscape in which these hardpans are otherwise absent the aim of the study was to investigate the genesis of these hardpans associated with the heuweltjie mound with a particular focus on the build up of calcite and sepiolite the micromorphological study examined a transect through a representative sepiolite bearing heuweltjie on the coast near the olifants river mouth and revealed evidence of termite activity in the central petro calcic part of the mound this concentration of calcite and mg rich clay in the centre can be explained by termite foraging as the regionally characteristic ca and mg rich foliage is moved into the centre of the mound facilitating the precipitation of calcite and sepiolite as bacterial decomposition and subsequent leaching modify the soil solution in the mound the increase in coarse fine ratio from the centre outward showed that accumulation of calcite and sepiolite displaced the original sand matrix by a greater degree than the silica accumulation consistent with the topographically raised surface in the centre limpid yellow low birefringent nodules some with pseudo negative uniaxial interference figures showed a fibrous nature under esem and their low ca and molar mg si ratios of 0 64 to 0 68 esem edx were consistent with sepiolite the presence of the sepiolite with its mg rich composition and hydrophilic character together with organic acids generated from the vegetation collected by the termites is considered to be an explanation for the formation of ooids radial calcite crystals associated with a core of sepiolite colourless non calcareous pseudo uniaxial negative spherulites were present in fresh termite excrement from an active heuweltjie near stellenbosch these were either produced in the termite gut itself or had been ingested along with herbivore dung by the termites the presence of faecal spherulites in termite excrement is significant since it shows that faecal spherulites can be distributed over a wider area than that directly associated with mammalian herbivores

palustrine deposits on a late devonian coastal plain sedimentary attributes and implications for concepts of carbonate sequence stratigraphy abstract palustrine deposits in coastal environments can cover thousands of square kilometers and are stratigraphically important palustrine deposits that originated in supratidal marshes can be used to track shifts in the shoreline position whereas palustrine deposits that formed in marshes above the peritidal realm are indicative of subaerial unconformities despite the importance of these deposits there are few documented examples of ancient coastal palustrine deposits and their sedimentary attributes remain poorly understood misinterpretation of coastal palustrine deposits as marine deposits or calcrete may partly explain this situation the upper devonian alexandra formation exposed in the northwest territories of canada is formed of two reef complexes that are separated by a type i sequence boundary at the landward part of the platform this boundary is marked by a succession of coastal plain deposits that is 50 cm thick the most distinct aspect of this succession are palustrine deposits characterized by charophytes skeletal rivularia stromatolites and various pedogenic features including complex crack networks root traces and authigenic kaolinite karst features and calcrete generally regarded as typical indicators of subaerial exposure are not found this study highlights the sedimentary attributes that can be used to identify ancient palustrine deposits in marine coastal regions distinguish these deposits from calcrete and demonstrates their sequence stratigraphic significance when found in marine limestone successions it clearly demonstrates that palustrine deposits like those found in the alexandra formation should be considered indicative of subaerial unconformities and sequence boundaries in the same manner as karst and calcrete

painting altamira cave shell tools for ochre processing in the upper palaeolithic in northern iberia abstract much of our knowledge of the symbolic world of upper palaeolithic hunter gatherers is based on the study of the graphic representations found in western european caves however to date few studies have been conducted on rock art apart from chronological and stylistic characterisation altamira cave northern iberia is characterised by an outstanding rock art ensemble whose representations cover practically the whole upper palaeolithic the site is equally important for the rich upper palaeolithic deposits in the cave entrance which contain large shell assemblages traditionally the presence of shells in hunter fisher gatherer settlements has been interpreted as part of the diet and or the symbolic world through the creation of ornaments of these groups regardless of their possible use as an instrument in this paper we utilise use wear methodology chemical analysis and analytical experimentation to verify the initial hypothesis that shells in the archaeological deposits of altamira were used to obtain the ochre powder utilised to produce the magnificent and diverse rock art ensemble in the cave the results provide new information on the process of obtaining pigments for the realisation of paintings and confirm that the use of shells to obtain ochre was a systematic activity throughout the whole study period finally our conclusions support the explanatory model that highlights the role played by marine resources for upper palaeolithic human populations

the reactivity of carbonates in selected soils of southern spain the properties of many soils of arid and semiarid areas are influenced by the presence of carbonates this study was conducted to characterize the reactivity of carbonates in the surface horizons of 25 soils entisols inceptisols vertisols and alfisols of southern spain the samples were analyzed for calcium carbonate equivalent cce active calcium carbonate equivalent acce predominant carbonate mineralogy mg content particle size distribution psd of carbonates by sedimentation and by a ph stat acid dissolution method and surface area sa of carbonates by n2 adsorption and by 45ca exchange from the differences between intact and decalcified soil samples as well as by estimates from the psd described above the cces ranged from 70 to 778 g kg 1 of soil and the acces ranged from 48 to 285 g kg 1 dolomite was present in only eight samples and in the dolomite free samples calcite generally had mg ca mg ratio 0 03 the carbonate psd as determined by sedimentation differed from the psd calculated from the ph stat data with the latter method giving a much higher proportion of claysize carbonates the average sas of carbonates as estimated from the psd data were 0 49 m2 g 1 soil for the sedimentation method and 3 2 m2 g 1 for the ph state method the average sas determined by the n2 and the 45ca methods were 6 0 and 2 3 m2 g 1 respectively the average specific surface areas ssas of soil carbonate m2 g 1 cce were 1 5 7 5 8 8 and 22 for the sedimentation 45ca exchange ph stat and n2 methods respectively the low sa and ssa values from the sedimentation method were a consequence of the occurrence of porous aggregates which have considerably higher equivalent spherical diameters than the particles of which these aggregates are composed the ph stat and 45ca methods gave sa values of similar magnitude to each other probably because both methods are dependent on actual reactive surface area instead of aggregate size of the carbonate mass the higher values obtained by the n2 method might indicate that n2 is physisorbed on carbonate surfaces that are slowly reactive to acid attack or 45ca exchange the ph stat sa was highly correlated with acce which measures the reactivity of carbonates to oxalate to obtain a rapid estimate of the reactivity of soil carbonate the acce method because of its simplicity may be preferred

magnetite originating from bonfires in a brazilian prehistoric anthrosol a micro raman approach abstract soils within archaeological sites may show magnetic properties due to the presence of magnetic minerals such as magnetite and maghemite which form during deposition of the soil or due to local fires the similarities in the crystallographic structures of magnetite and maghemite lead to difficulties in the identification of these mineral phases this work aims to study the genesis of fe nodules at an archaeological site in a cave in quartzite with a very low fe content and no spinel group minerals the guiding hypotheses of the research are as follows i the abundant fe nodules in all the studied stratigraphic layers are of pedogenic origin and were generated by local bonfires and ii these fe nodules are composed of magnetite maghemite and hematite and the conversion of magnetite to maghemite indicates pedogenic processes micromorphological analysis and raman spectroscopy were used for mineral phase determination the results confirm the in situ pedological nature of the fe nodules associated with anthropogenic fires in the cave

lithological factors affecting magnetic susceptibility of subtropical soils zhejiang province china abstract magnetic susceptibility was measured on subtropical soils formed on a range of parent materials in zhejiang province china to demonstrate the influence of parent material lithologies on the amount and vertical distribution of in the soils we found that the values of soils vary by up to two orders of magnitude with their parent material lithologies soils formed on igneous rocks with high values showed high absolute and distinctly decreased compared with values of parent materials the values of soils formed on basalt andesite and granodiorite were 250 10 8 m 3 kg 1 the values of soils formed on granite and other neutral and acid igneous rocks ranged from 50 10 8 to 120 10 8 m 3 kg 1 in most of the soils formed on sedimentary rocks enhancement in upper horizons of soils was found compared with parent material this enhancement was believed to be pedogenic formation of superparamagnetic sp stable single domain ssd magnetic grains which are characterized by high values of frequency dependent susceptibility fd and anhysteretic remanent magnetization arm soils formed on sedimentary rocks with a very low initial and iron content showed a low value throughout the profile it was found that there is a highly significant relationship between the values of soils and their dithionite citrate bicarbonate solution dcb soluble iron contents fe d the values of soils in chronosequences formed on alluvium and two marine deposits increased as soils became older it is suggested that the values can be used as a tool for determining the relative age in chronosequence studies

mineral magnetic properties of chinese paddy soils and its pedogenic implications abstract magnetic susceptibility ms of paddy soils hydragric anthrosols and their corresponding dryland soils formed on the same parent materials in zhejiang province of eastern china were measured in order to understand better magnetic profile discrimination and pedogenic magnetic minerals in paddy soils magnetic measurements showed that the ms values of paddy soils were much lower than those of dryland soils formed on the same parent materials the higher the ms value of the original dryland soil is the more remarkable the decrease in the ms value is when the soil is put under rice cultivation gleyed paddy soils exhibited very low ms value

palaeoenvironmental and palaeoclimatic reconstruction of the upper cretaceous late campanian early maastrichtian horseshoe canyon formation alberta canada abstract pedogenic features and geochemical signatures of paleosol profiles exposed in the horseshoe canyon formation hcfm were studied to reconstruct the ancient environments and climates that prevailed at high latitude 60 n in the north american western interior during the late campanian to early maastrichtian eight pedotypes representing hydromorphic moderately drained and well drained paleosols were recognized when considered within their stratigraphic context these paleosols show that palaeoenvironmental and palaeoclimatic changes occurred either gradually between major lithological subdivisions of the hcfm or relatively rapidly within subdivisions hydromorphic paleosols predominant in the coal bearing stratigraphic interval at the base of the hcfm were gradually replaced by well drained paleosols in the overlying coal poor interval while climate remained warm and humid during this change in soil drainage conditions mean annual temperature and precipitation dropped rapidly higher in section shortly prior to the campanian maastrichtian boundary without concomitant lithological or pedological changes a brief return of poorly drained paleosols in the middle of the hcfm coincides with a regional marine transgression drumheller marine tongue well drained palaeoenvironments associated with a warm and dry climate persisted through the upper part of the hcfm until a gradual return to poorly drained conditions and to a warm humid climate occurred at the top of the formation an important decline in turtle diversity through the hcfm previously attributed to climate is shown to coincide instead with changes in soil drainage conditions where aridity landscape instability and migratory barriers possibly acted as secondary limiting factors to faunal recovery

the small stone content of mima like mounds in the south african cape region implications for mound origin summary mima type earth mounds known locally as heuweltjies occur in many parts of the western and southern cape province of south africa the active hypotheses of their origin are biological and involve soil translocation by i termites ii bathyergid mole rats or iii both of these animal groups we sampled the small stone composition of mound and intermound soils at two locations robertson and clanwilliam to determine if stones in the size range that mole rats can move are abundant in the mounds gravel 8 15 mm and pebbles 15 50 mm were common in the surface soil of mounds but were only about one fourth to one seventh their concentration in intermound soils the concentration of small stones increased with depth in the mounds however and in the basal strata of mounds these stones became incorporated in calcrete nodules or layers the total abundance of small stones in a column from the surface to the base of the soil system was greater on mound tops than in intermounds as expected if mole rats contribute substantially to mound formation by lateral translocation of soil increase in small stone density with depth is interpreted as resulting from the movement of soil fines to the surface by termites additional data on small stone concentration in deep mound layers are needed to determine if mole rat translocation can fully account for mound formation

using magnetic susceptibility to facilitate more rapid reproducible and precise delineation of hydric soils in the midwestern usa abstract standard field indicators currently used for hydric soil delineations usda nrcs 1998 field indicators of hydric soils in the united states version 4 0 in g w hurt et al ed united states department of agriculture nrcs fort worth tx are useful but in some cases they can be subjective difficult to recognize or time consuming to assess magnetic susceptibility ms measurements acquired rapidly in the field with a portable meter have great potential to help soil scientists delineate and map areas of hydric soils more precisely and objectively at five sites in illinois from 5 to 15 ha in area with contrasting soil types and glacial histories the ms values of surface soils were measured along transects and afterwards mapped and contoured the ms values were found to be consistently higher in well drained soils and lower in hydric soils reflecting anaerobic deterioration of both detrital magnetite and soil formed ferrimagnetics at each site volumetric ms values were statistically compared to field indicators to determine a critical ms value for hydric soil delineation such critical values range between 22 10 5 and 33 10 5 si in silty loessal or alluvial soils in illinois but are as high as 61 10 5 si at a site with fine sandy soil a higher magnetite content and slower dissolution rate in sandy soils may explain the difference among sites with silty parent material the lowest critical value 22 10 5 si occurs in soil with low ph 4 5 5 5 since acidic conditions are less favorable to ferrimagnetic mineral neoformation and enhance magnetite dissolution because of their sensitivity to parent material properties and soil ph critical ms values must be determined on a site specific basis the ms of studied soil samples 0 5 cm depth is mainly controlled by neoformed ultrafine ferrimagnetics and detrital magnetite concentrations with a minor contribution from anthropogenic fly ash neoformed ferrimagnetics are present in all samples but based on high fd 5 to 10 are most prevalent in high ph mollisols of northeastern illinois scanning electron microscope images display significantly more detrital magnetite alteration in hydric soils substantiating that reductive dissolution of magnetite aided by microorganisms is a primary cause for lower ms fly ash comprises 8 50 of the 5 m strongly magnetic particles and typically accounts for 5 15 of the total ms signal the proportion of fly ash in 5 m strongly magnetic fractions is greater in hydric soils because of lower natural magnetite contents possibly combined with historical topsoil accumulation in lower landscapes magnetic fly ash particles are also more altered in low ms soils implying that significant magnetite dissolution can occur in less than 150 years

the hydrological setting occurrence and significance of gypsum in late quaternary salt lakes in south australia well exposed often laminated gypsum sequences occur in many quarternary salt lakes in southern south australia the gypsum in the salt lakes is classified by increasing grain size into gypsite gypsarenite and selenite the salt lakes are classified by age and hydrological setting into coastal salinas which are holocene sea water fed groundwater lakes and continental playas which are late pleistocene endorheic basins a study of the relationships between coastal salina hydrology and the associated gypsum deposition has shown the different types of gypsum form under distinct hydrological regimes as the hydrology above a coastal salina depositional surface changes through time so does the type of gypsum deposited application of a gypsum depositional model derived from a study of the coastal salina gypsum to those portions of a continental playa gypsum unit where deposition is no longer occurring confirms the applicability of the model to non salina gypsum deposits

distribution and diagenesis of microfossils from the lower proterozoic duck creek dolomite western australia two distinct generations of microfossils occur in silicified carbonates from a previously undescribed locality of the lower proterozoic duck creek dolomite western australia the earlier generation occurs in discrete organic rich clasts and clots characterized by microquartz anhedra it contains a variety of filamentous and coccoidal fossils in varying states of preservation second generation microfossils consist almost exclusively of well preserved gunflintia minuta filaments that drape clasts or appear to float in clear chalcedony these filaments appear to represent an ecologically distinct assemblage that colonized a substrate containing the partially degraded remains of the first generation community the two assemblages differ significantly in taxonomic frequency distribution from previously described duck creek florules taken together duck creek microfossils exhibit a range of assemblage variability comparable to that found in other lower proterozoic iron formations and ferruginous carbonates with increasing severity of post mortem alteration duck creek microfossils appear to converge morphologically on assemblages of simple microstructures described from early archean cherts two new species are described oscillatoriopsis majuscula and o cuboides the former is among the largest septate filamentous fossils described from any proterozoic formation

the use of lithic artefacts for making rock art engravings observation and analysis of use wear traces in experimental tools through optical microscopy and sem in this paper we present the results of observations made via optical microscopy and sem of microwear traces on experimental lithic tools used in the replication of rock art engravings the overall aim of this experimental programme is to generate diagnostic microscopic criteria that could subsequently be used a in the identification of archaeological artefacts that have been involved in the production of rock art engravings and b in the inference of the engraving techniques in which they have been used the methods of replication of engraved figures and lines and the observation of the microwear traces on the experimental artefacts used are presented the complementary use of stereomicroscope metallographic microscope with bright field dark field and laser illumination and sem is also discussed the resulting microwear traces observed on the tools used in the experiment are characterized and are linked to the two different engraving techniques with which the rock art replication has been carried out

clay transformation and pedogenic calcite formation on a lithosequence of igneous rocks in northwestern iran abstract knowledge about the pathways of pedogenic calcite formations and clay transformations on igneous rocks in semiarid regions plays a vital role in the commentary of soil development on these rocks the present study was conducted to explore the weathering stages and pathways for the formation of pedogenic calcite in soils developed on selected plutonic and volcanic rocks in a semiarid climate in north western iran the soils developed on plutonic rocks were found to be in the primary stage of weathering with very few pedogenic calcites except for soil developed on alkali granite which contained few calcitic pedofeatures calcitic crystallitic b fabrics and calcitic pedofeatures were found in all soils developed on volcanic rocks in situ weathering of ca bearing minerals such as plagioclases amphiboles and pyroxenes could be the possible explanation for the accumulation of pedogenic calcite in the absence of calcareous parent rocks in the studied area micritic calcite was observed to be the dominant form in most of the soils developed on volcanic rocks indicating a rapid precipitation of calcium carbonate smectite kaolinite and mica illite were present in the soils developed on plutonic rocks and the clay content in these soils was less than that of the volcanic rocks feldspars plus mica were supposed to be the most likely source minerals for the formation of pedogenic illite which could be consequently transformed into smectite in these semi arid environments smectite mica illite and kaolinite were the most abundant clay minerals in the soils developed on dacite and andesite rocks while a minor quantity of vermiculite occurred only in andesite derived soils smectite as the dominant mineral and some kaolinite with fairly constant variation in content with depth were observed in the soils formed on hornblende andesite and pyroxene andesite this could indicate that the smectite had the authigenic origin and was formed most likely from the weathering of plagioclase hornblende and pyroxene in general in situ crystallization of pedogenic carbonates and high quantities of smectite in the clay fraction confirmed that the soils formed on volcanic rocks were more developed than those on plutonic rocks in the studied semiarid region moreover our results showed that releasing calcium from ca bearing minerals in igneous rocks in conjunction with biological activities resulted in pedogenic calcite formation

abiogenic growth of needle fiber calcite in spring towers at shiqiang yunnan province china abstract at shiqiang china there are spring towers up to 4 m high and 3 m in diameter that are formed of porous gray to orange to brown bedded limestones that have a multistage diagenetic history the walls of many cavities in these limestones are covered with hypocoatings and or needle fiber calcite nfc that formed during the last stage of diagenesis where present the hypocoatings are 10 m thick appear homogeneous and typically lie under the nfc mats the nfc is divided into nanofibers rods 1 m long 75 100 nm diameter composite fibers bundles of 2 to 16 rods each rod 300 400 nm in diameter up to 25 m wide and 100 m long pyramid fibers pyramid shape with 4 to 6 sides up to 25 wide at base tapering to point up to 100 m long and ribbon fibers blade shape 2 4 m wide 1 m thick up to 100 m long many crystals are highly ornate with epitaxial overgrowths that display elements of skeletal and or dendritic growth the wall covering nfc mats are formed of one crystal type or any combination of different crystal types with or without epitaxial overgrowths precipitation of needle fiber calcite known from a diverse array of geological settings throughout the world is commonly linked to fungi or other biogenic processes in the shiqiang spring towers however no fungi were found with the nfc and only scattered microbes and minor amounts of exopolysaccharides were associated with some of the nfc in some pores the nfc crystals appear to have been precipitated from fluids that were highly saturated with respect to calcite as a result of evaporation the calcium probably came from rainwater groundwater via capillary action and or dissolution of the calcite framework whereas evaporation was mediated by solar radiation and or the wind available evidence indicates that the nfc found in the spring deposits at shiqiang were a late diagenetic product that probably formed through abiogenic precipitation

sedimentation on the distal reaches of the okavango fan botswana and its bearing on calcrete and silcrete ganister formation the distal reaches or flood plain of the okavango alluvial fan of northern botswana are characterized by gently undulating topography with local relief generally less than two meters the entire area is blanketed by eolian sand although the area is semiarid with evapotranspiration exceeding precipitation the area is subject to seasonal flooding by annual influx of floodwater from subtropical angola to the north distributary channels on the flood plain are poorly defined and consist of sinuous depressions lacking normal fluvial characteristics such as levees bars or incision the flood water has very little suspended load higher ground on the flood plain forms islands during the seasonal flood elevated tracts arise by displacive subsurface crystallization of carbonate and silica which is induced by trees that grow on the higher ground sedimentation on lower lying areas occurs by a combination of 1 accumulation of fine clastic material derived from the flood water and phytolithic silica both of which are mixed into the sandy substrate by illuviation and bioturbation and 2 precipitation of fine grained amorphous silica from the groundwater induced by transpiration by aquatic grasses and sedges accumulation of silica in the soil profile produces a proto silcrete this sequence grades laterally into carbonate dominated island soils the ultimate cause of this association is an abundance of water with low suspended load in an environment with a high evapotranspiration rate ganisters in ancient rocks may have a similar origin

behavior of mexico city clay subjected to undrained repeated loading this note describes a series of cyclic triaxial tests on undisturbed soil samples of mexico city clay obtained near the sct building the site is a silty clay deposit of a very high water content and soft consistency the material exhibits elastic behavior in spite of its very high water content three empirical relationships describing an equivalent young s modulus an equivalent damping ratio and a cyclic stress level associated with cyclic strain level were obtained test results define two different patterns of strength loss

differentiation of pedogenic and lithogenic carbonate forms in texas abstract sixteen pedons representing soils developed from limestone and fluvial deltaic sediments were sampled in central and western texas 300 800 mm annual precipitation to differentiate pedogenic secondary and lithogenic inherited carbonate forms by field and laboratory techniques lithogenic carbonate forms identified in the field included indurated limestone bedrock and coarse limestone fragments lithorelicts field identified pedogenic forms included petrocalcic horizons thin laminar cappings on indurated limestone carbonate joint seams pendants on pebbles and carbonate films and threads on ped faces small

micromorphology submicroscopy and microprobe study of carbonate pedofeatures in a vertisol gilgai soil complex south russia abstract carbonate nodules and soft masses were studied in a gilgai soil complex in the north caucasus south russia microrelief with an amplitude about 30 cm resulted in a wetter environment with stronger leaching in the microlow and a drier pedoenvironment with carbonate accumulation in the microhigh various macroforms of carbonate nodules and soft masses were identified in soil pits and sampled for micromorphology scanning electron microscopy sem and microprobe analyses to better characterize them and elucidate their pedogenesis common and unique attributes were described for carbonate pedofeatures depending on loci in gilgai soil complex the most probable hypothesis for their formation is as follows nodules represent early pedogenic products that were initiated before gilgai formation modern hydrology resulted in variability of dissolution recrystallization of the nodules along the gilgai microtopography the variability in degree of impregnation aggregation into pellets and presence of hard nodular cores reflects several generations of soft masses

provenance and climate changes inferred from magnetic properties of the sediments from the lower yangtze river china during the last 130 years abstract it is essential to have a clear scientific view on paleoclimate change and its potential environmental and socio economic impacts for the prediction of future climate change fluvial sediment is one of the best archives for the investigations of high resolution environmental variability and anthropogenic impacts on catchment over the last hundreds or even thousands years anthropocene in this study we examine magnetic properties of a 130 year fluvial sediment profile from an island in the main channel of the lower yangtze mainstream which aims to determine the connections between modern observational data and paleoclimate signals from sediments sediments from the upper yangtze river is characterized by high concentration of magnetite which is different from the middle reach the difference of magnetic properties allows us to trace particles in the lower reach back to upstream of the yangtze river climate change that reconstructed from physical properties of sediment susceptibility and mean grain size is comparable to those records in historical documents which provides a possible way to obtain precise ages the calibrated sedimentation rate reflects long term variation of flood drought events over the catchment which is dominantly controlled by the climate circulation of pacific the enhanced human impacts since 1950s especially in the mid lower reaches are observed therefore riverine sediment not only contains paleoclimate information but also reflects human activities

sequestration of inorganic carbon in soil and groundwater movement of co 2 from the atmosphere into land via photosynthesis and root respiration the subsequent formation of bicarbonate in soil and its storage in groundwater or precipitation as caco 3 in dryland soils are major processes in the global carbon cycle together inorganic carbon as soil carbonate 940 pgc and as bicarbonate in groundwater 1404 pgc surpass soil organic carbon 1530 pgc as the largest terrestrial pool of carbon yet despite general agreement about its huge size as a carbon pool controversy about the potential of inorganic carbon to sequester atmospheric co 2 remains unresolved we suggest that the controversy stems from the absence of a lexicon and propose a classification scheme that uses 1 calcium source illustrated by two widely recognized chemical reactions and 2 the concept of carbonate generations when calcium is derived from preexisting carbonate an equilibrium reaction occurs that does not sequester carbon in soil carbonate but does sequester carbon in groundwater until bicarbonate precipitates as caco 3 when calcium is derived from silicate minerals a unidirectional reaction occurs that sequesters carbon in both soil carbonate and groundwater the generations concept shows that carbon sequestration occurs only in the first generation when calcium is released directly from silicates this classification not only enhances communication and provides a framework for quantifying amounts of fossil fuel carbon that can be sequestered within a geoengineering context it provides more precise language for discussing the terrestrial carbon cycle through geologic time

stable isotope geochemistry of pedogenic carbonates in loess derived soils of northeastern iran paleoenvironmental implications and correlation across eurasia despite the occurrence of pedogenic carbonates in loess paleosol sequences of northern and northeastern iran there is no information about stable isotope geochemistry of pedogenic carbonates in these regions this paper presents the first stable isotope data on pedogenic carbonates in loess derived soils of northeastern iran southern eurasian loess belt carbon and oxygen stable isotope values of pedogenic carbonates in different landforms were measured using mass spectrometry based on climatic data there is no possibility for soil leaching and pedogenic carbonate formation under the present arid conditions stable oxygen and carbon isotopic data suggest two separate periods of carbonate formation these periods are characterized by either lower or higher temperatures during post glacial than today and paleoecological conditions dominated by c3 and c4 plants respectively hemispheric correlation of loess deposits based on isotopic data of pedogenic carbonates shows a strong positive correlation for the post glacial carbonates nodules of northeastern iran and european russia this suggests a similar mechanism of carbonate formation and also the impact of westerlies in these regions we present the first quantitative isotopic data for paleoenvironment of northeastern iran however more quantitative investigations about the holocene and the last interglacial paleoenvironments of northeastern iran are needed

micromorphological fabrics and developmental stages of carbonate nodular forms related to soil characteristics abstract carbonate nodules often constitute the first stage of calcrete formation micromorphological analysis of carbonate nodules and nodular fabrics in different soil materials shows that their development is a function of several factors nature of the host matrix texture porosity carbonate and non carbonate clay distribution bulk density and the interactions among them different micromorphological stages therefore exist in different soil materials in calcareous medium textured soil materials the stages of nodule formation are related to the increase of the density of the nodule caused by the accumulation of microcalcites in such a soil material the following stages occur 1 microcalcites within the low to moderate density matrix 2 microcalcites of moderate to high density and moderately dense diffuse nodules parallel calcans may occur 3 microcalcites of high density with dense microcalcitic nodules during these stages the amount of non carbonate clay decreases but is homogeneously dispersed and disseminated with the microcalcites in general the size of microcalcites 1 8 m is inversely related to the clay content in non calcareous medium to fine textured soil materials secondary carbonate precipitates in intrapedal and or interpedal voids as large sparry crystals due to pedoturbation processes the nodules thus formed are subjected to recrystallization resulting in a microsparry pattern the development stages are 1 few calcans and crystal chambers 2 crystic nodules mainly of sparry crystals and an increase of calcans and crystic chambers 3 recrystallized nodules composed mainly of microspars in coarse grained materials secondary carbonates precipitate directly in voids as sparry crystals and the resulting nodules are of the crystic type the large crystals are often subjected to recrystallization in partly calcareous coarse grained materials with additions of calcareous dust particular micromorphological carbonate forms occur in the c horizon cutanic calciasepic fabric forms besides zones of crystic fabric which gradually become calciasepic in the b horizon and include the typical nodular forms of the calcareous medium textured soil material together with appreciable amounts of glaebular halos the processes leading to the formation of these stages occur essentially without a significant biogenic influence where carbonate segregation occurs as rhizomorphs surrounding active roots the fabric is always micritic even in coarse textural soil material

origin of cristobalite in soils derived from volcanic ash in temperate and tropical regions abstract cristobalite was isolated from four ando soils and a podzolic soil developed on volcanic ashes in french west indies indonesia and japan by selective chemical dissolution with 6 m hcl 0 5 m naoh and h 2 sif 6 treatments followed by specific gravity separation all the cristobalite isolates give x ray diffractograms with a strong and sharp peak at 4 10 4 11 a and associated peaks at 2 8 and 2 5 a which are characteristic for cristobalite of high temperature origin four out of five isolates show a peak at 4 06 4 07 a ascribed to low temperature cristobalite the oxygen isotopic ratios 18 o smow of cristobalite isolates show a range of 5 3 to 11 0 which suggests a high temperature igneous origin these x ray diffraction and oxygen isotopic data indicate that the cristobalite was inherited from primary volcanic ash rather than formed during pedogenesis

isotopic evidence for dolomite formation in soils abstract dolomite formation in soils constitute a particular challenge because of 1 scant magnesium content in continental environments as opposed to the marine medium 2 the kinetic problem related to the incorporation of magnesium into the carbonate and 3 the unknown role of soil dolomites in the global carbon cycle pedogenic dolomite formed at deeper soil levels subsoil before the development of petrocalcic horizon barriers was investigated in a semiarid region of se spain guadix baza basin mineralogical characterization textural relationships and isotopic data concerning soil dolomite together with the results of a precipitation experiment provided fuller knowledge of the processes and conditions governing neoformation of dolomite in these soils in the study case dolomite enrichment occurs beyond the limit of major biological activity which coincides with the rooting depth of native perennial plants in the semiarid soils studied textural studies reveal the corrosion of inherited dolomite crystals in the upper soil horizons and the formation of dolomite in depth in relation to a clayey material composed mainly of smectites stable isotope distribution in dolomites throughout the profiles indicates a fractionation with depth this is explained by the formation of dolomites after the dissolution of the pedogenic calcite the calcite detected in the subsoil is interpreted here as a precursor of the neoformed dolomites that transport the isotopic signal associated with biological activity of soils to deeper layers dolomite formation appears to be favoured by the presence of clay minerals in the precipitation media clays retain water during evapotranspiration stages which drastically change the transport properties of the media and promote the incorporation of mg into the structure of the neoformed ca mg carbonate as confirmed by laboratory experiments diffusion controlled crystal growth processes lead to the formation a precursory protodolomite with disordered ca mg distribution from a fluid locally supersaturated in dolomite

micromorphology of opaline features in soils on the sediments of the ex lago de texcoco mexico abstract the former texcoco lake ex lago de texcoco is situated in the closed basin in mexico the lake was artificially drained in the 20th century six soil profiles on the eastern border of the former lake were analysed for mineralogical and microfabric characteristics in order to differentiate between sedimentary and pedogenic processes large quantities of silica liberated as a result of weathering of the surrounding volcanic mountains partly precipitated in the lake as a result layers of an exceptional sediment locally called jaboncillo were deposited they are characterised by a high si content and a very high up to 500 water retention in addition several amorphous silica features were formed in these lacustrine conditions in the centre of the lake opaline nodules mainly composed of opal a formed in the jaboncillo near the former coast line concentric silico calcitic nodules ooliths were formed as a result of fluctuations of the input of fresh water and biological activity several superposed layers of in situ silicified roots point to frequent changes in the shore line position after emergence of the sediments about 100 years ago a translocation of silica mainly caused by an alkalisation of the sediment gave rise to the formation of different pedogenic types of opaline coatings and infillings resulting locally in a duripan the micromorphological and mineralogical properties of these silica features are discussed and sedimentary and pedogenic processes considered

characteristics of silica rich pedofeatures in a buried paleosol abstract whitish and whitish light brown milky like textural pedofeatures and impregnations were found in the voids and the matrix of buried paleosols older than 2 7 million years in a site in sardinia italy the pedofeatures were described and analysed using micromorphology x ray diffraction and microprobe techniques and their spatial distribution correlated with field evidence the suite of analyses showed that the main components of the pedofeatures were more or less ordered silica phases as well as forming a matrix cement these pedofeatures also occurred as coatings and infillings in pores significant amounts of alumina and less mg ca and fe were also present in the pedofeatures possibly in the form of silicate coatings and inclusions impurities or alumino silicates of the adjacent soil matrix a number of hypotheses are drawn on the possible mechanisms of formation of these silica rich pedofeatures including the possibility of prolonged weathering of volcanic materials and the resulting formation of colloids and more or less ordered silica phases with successive dehydration and progressive ordering of phases during the at least 2 5 million years

geochemical normalization of magnetic susceptibility for investigation of floodplain sediments magnetic susceptibility ms is commonly used as a proxy for industrial pollution in natural sediments or as a proxy for the percentage of detrital components in peat or carbonates the ms may also reflect the geology of the sediment source and post depositional processes in sediments such as soil development the aim of our research was to test the usefulness of fe normalized mass specific ms and ti normalized fe in a study of floodplain sediments we sampled 27 floodplain sediment cores from several geologically different catchments throughout the czech republic analysed their fe and ti concentrations using x ray fluorescence spectroscopy and determined their to decipher sediment grain size dependence and possible magnetic enrichment background functions for were constructed using similar approach as that used for geochemical background functions of the risk element concentrations with fe concentrations as an independent variable it provides a mechanism to calculate of sediments as it would be pristine i e without post depositional changes and pollution sediments derived from mafic source rocks had fe larger by two orders of magnitude than sediments derived from felsic rocks sediments derived from mafic source rocks also exhibit lower mean fe ti ratio in pristine sediment strata than the average upper continental crust the magnetic carriers inherited from mafic rocks are stepwise destroyed by pedogenesis in the floodplains and thus slowly approach of sediments derived from felsic rocks gleying processes may change fe fe ti ratio allows identifying a past action of those post depositional processes

microfossil populations in the context of synsedimentary micrite deposition and acicular carbonate precipitation mesoproterozoic gaoyuzhuang formation china abstract silicified stratiform stromatolites of the mesoproterozoic gaoyuzhuang formation 1 4 1 5 ga china contain well preserved microfossils the cherts also harbor varied synsedimentary precipitates and void filling cements replaced by early diagenetic silica minerals these precipitates disclose microenvironments characterized by supersaturated solutions in protected shallow depressions within an intertidal setting the precipitates provided surfaces for selective microbial settlement and rigid sediment matrix for microbial growth together with early silicification the frequent precipitation events contributed to preservation of microfossils by reducing sediment compaction and shearing fossiliferous cherts display fine flat and wavy lamination characterized by an alternation of highly silicified thin organic rich layers with thick sediment rich layers organic rich layers are dominated either by coccoid or by filamentous microfossils whereas sediment rich layers contain abundant synsedimentary precipitates within which the microfossils are preserved in their growth position four dominant microfossils coccostratus dispergens n gen et sp eoentophysalis belcherensis eoschizothrix composita and siphonophycus inornatum occur contiguously through several tens of laminae and are identified as main frame building biological components of gaoyuzhuang stromatolites community composition microbial density distribution orientation and developmental patterns of the frame building microfossils are closely correlated with the changing depositional events of gaoyuzhuang cherts contrasting conditions of sedimentary kinetics with those of sedimentary stasis each assemblage of frame building microfossils responded to sedimentation with different mechanisms to escape burial high sedimentation rates correlate with scattered colonies of coccoids and with loose webs of predominantly upright filaments low sedimentation rates correlate with dense laterally connected colonies of coccoids and with a change in filament orientation from vertical to horizontal in multi trichomous microfossil eoschizothrix composita low sedimentation rates are also accompanied with an increase in number of trichomes per filament the observed morphological variability of the frame building microfossils is explained by microbial development reproduction and behavior by interactions between sedimentological and biological controls

genesis of hydromorphic calcisols in wetlands of the northeast yucatan peninsula mexico abstract tropical wetlands are fragile ecosystems controlled by hydrological factors they are less studied than wetlands of the temperate and subtropical areas and limited information is available about soil genesis in such systems here we present a soil study of a wetland in the yalahau region of the northeastern yucatan peninsula in order to assess the properties and understand the genesis of these hydromorphic soils an east west transect was established through the wetland to understand differences in soil processes between shallower deposits at the edge of the wetland and thicker deposits at the center of the wetland contrary to the central image of peaty and gleyic wetland soils the dominant soil unit in the wetland examined in the current study is a calcisol according to their properties we assume that the bk horizons of these soils are the product of neoformation as they consist principally of micritic groundmass shells of terrestrial mollusks are also present and constitute the coarser fractions the micrite in these soils is proposed to have been synthesized through participation of algae when periodic flooding with waters from karstic geosystems rich in dissolved carbonates from limestone dissolution affects the area algae develop intensely on the surface of the flood water forming periphyton the algae consume co 2 dissolved in water through photosynthesis thus displacing the bicarbonate soluble carbonate low solubility equilibrium in favor of carbonate formation profiles near the edge of the open wetland show a carbonate enriched horizon bk overlaying the organic matter enriched horizon ah we conclude that alternation of horizons enriched with organic material and carbonates reflects the duration of floods more prolonged flooding promotes algae productivity and carbonate precipitation while organic matter accumulation is inhibited

amorphous silica materials in soils and sediments of the ex lago de texcoco mexico an explanation for its subsidence abstract mexico city is built on the sediments of the former texcoco lake ex lago de texcoco which are characterised by the presence of a siliceous deposit up to 70 m in thickness called jaboncillo like soap the jaboncillo is composed dominantly of amorphous silica and iron oxides and hydroxides with minor amounts of phyllosilicates and detrital volcanic minerals the mineralogy the micromorphology and physical and chemical properties are discussed the optical isotropic groundmass consists largely of amorphous silica and iron hydroxides the bulk density calculated for the dry material is about 0 26 g cm 3 its water retention capacity is extremely high up to 522 at field capacity but this characteristic is partly lost after drying also the high solubility of si the high cec and cole are irreversibly reduced after drying due to a denser packing of the originally randomly distributed hydrated silica spheres therefore it is evident that drainage will irreversibly change physical characteristics and increase risk of instability and subsidence of the sediments when used for construction

micromorphic record and interpretations of carbonate forms in the rolling plains of texas abstract the rolling plains of texas comprises about 10 million hectares of soils developed in permianage deposits most soils occur on erosional landscape positions soils have ustic moisture regimes and thermic temperature regimes these soils have developed in a wide variety of sediments ranging from red bed shales to sandstones most of the soils have carbonate enriched bk horizons while parent materials are slightly to non calcareous pedogenic calcite usually occurs as nodules calcans neocalcans and crystallaria calcite nodules are the dominant form in upper bk horizons while the other forms occur primarily in lower bk cr horizons additional forms of calcite include pseudomorphs after gypsum and equant anhedral calcite which fill fracture or joint seams and sand calcite crystals poikilotopic these are considered pedogenic although formed under an earlier climatic regime dolomite a post depositional lithogenic mineral occurs as nodules intercalary crystals and clustered to dispersed microsparite crystals micromorphic forms of calcite indicate that the soils have been through several major and minor fluctuations in the soil chemical environment on stable landscape positions carbonate minerals preserve the long term pedogenic record of soil development

archaeology of the continental shelf marine resources submerged landscapes and underwater archaeology we provide a critical review of the evidence for the long term use of marine resources and coastal environments in human evolution and later development we emphasise the importance of the coastal archaeological record in understanding patterns of human settlement and dispersal and draw attention to the large potential biases introduced by the destructive or obscuring effects of pleistocene sea level change we note that lowered sea levels have been the norm for most of the pleistocene and that periods of high sea level have been too short lived to provide other than a fragmentary coastal record and one that is beset with ambiguities and uncertainties we examine the geological processes of coastal uplift and underwater preservation that may help to mitigate these biases coastlines elevated by isostatic and tectonic processes or with very steep offshore drop offs at plate boundaries are important in providing a potential window into coastal landscapes and archaeology formed during periods of lowered sea level however we conclude that the opportunities afforded by these geological factors are too limited to obviate the need for underwater exploration we review the evidence now available from submerged landscapes across the africa eurasia interface from the atlantic coastlines of northwest europe to the southern red sea we show that geomorphological conditions for the preservation of archaeological and palaeoenvironmental data are commonly present that much material has already been discovered and that new techniques technologies and projects are providing the momentum for a rapidly expanding field of investigation the results do not simply add to what we already know from sites on land but are likely to produce qualitatively different evidence for coastal adaptations and landscapes that have no analogue on present day coastlines we note the strong probability that many coastal landscapes exposed at lowered sea level provided relatively fertile and productive refugia for plants land mammals and humans at a time when increased aridity would have reduced or deterred hinterland occupation we conclude that underwater investigation is essential if hypotheses of early human adaptation and dispersal are to be fully tested

the contribution of termites to the microgranular structure of soils on the uasin gishu plateau kenya abstract the structure of many clay soils in tropical africa is composed of microaggregates that range in size from 0 03 to 1 mm these structural units are often very stable and known as pseudo sand or pseudo silt their presence is detected from the loamy feel of the soil this paper tests the hypothesis that termites contribute to a stable microgranular i e finely aggregated soil structure a termite mound was selected on pedologically unaffected clayey weathering material derived from phonolite the fate of microaggregates produced by termites has been followed through the various stages of mound building field evidence was supplemented with microscopic analysis development of the mound begins when lumps of soil are detached from the subsoil by termites and carried as microaggregates up to the surface in the next stage the microaggregates are cemented to form the nest breakdown begins when the nest is abandoned and disintegrates by splash and runoff producing colluvium or is demolished by ants in the final stage this material is integrated in the soil of the mound soil aggregates produced by splash ants and soil forming processes have different size characteristics but the original microaggregates produced by the termites are preserved in the matrix throughout it is assumed that they owe their stability to impregnation with saliva or other body fluid excreted by the termites termites produce also microaggregates in the form of fecal pellets but these appear to be unstable and are found only in the voids of the soil developed during the last stage

mineral magnetic properties of a weathering sequence of soils derived from basalt in eastern china abstract the magnetic properties and magnetic mineralogy of a weathering sequence of soils developed on basalt parent material from eastern china were studied by rock magnetism x ray diffraction and soil chemical analyses to establish the connection between mineral magnetic properties and pedogenic development in a subtropical region the magnetic susceptibility of soils formed on basalt varied greatly and did not increase with the degree of pedogenic development the frequency dependent susceptibility fd values of soils ranged from 1 0 to 11 1 and increased with the pedogenic development highly significant linear relationship was found between the frequency dependent susceptibility and the fed content r2 0 683 and fed fet ratio r2 0 780 in soils indicating that pedogenic sp ferrimagnetic grains were associated with enrichment of the secondary iron oxide minerals in the weathering process of soil rock magnetism analysis showed that the major magnetic carriers in the weakly weathered soil profiles are magnetite and or maghemite and the highly developed soil profiles are generally enriched in magnetite maghemite grains of pedogenic origin and the magnetically hard haematite indicating that the magnetic component was transformed from a ferrimagnetic phase magnetite to antiferromagnetic phase hematite during pedogenic development results indicated that some of the magnetic parameters of soils in this case fd can be useful for pedogenic comparisons and age correlations in the weathering sequence of soil it is thus suggested that multiparameter rock magnetic investigations represent a more powerful approach for pedogenesis

at the land s end marine resources and the importance of fluctuations in the coastline in the prehistoric hunter gatherer economy of portugal abstract this paper focuses on the importance of aquatic resources in economy and subsistence strategies during the middle and upper palaeolithic of portugal modern theoretical biases in archaeology have led to a marginalization of marine resources and a dismissal of their use by palaeolithic hunter gatherers geological and archaeological data show that changes in the position of the coastline had a direct impact on the visibility of marine resources in the archaeological record marine regressions and transgressions have significantly altered the record of pleistocene coastal settlement using recent studies on changes in upwelling intensity during the last glacial we offer a new perspective on palaeolithic hunter gatherer economy that emphasizes the importance of the coast as a focus of subsistence and settlement

spatial variability of environment change in the teotihuacan valley during the late quaternary paleopedological inferences the teotihuacan valley mexico has been the object of considerable interest because of its importance in the context of human history in america although archeological research has been extensively conducted to understand causes of the decline of teotihuacan culture no sufficient scientific evidence has been provided this paper is focused on paleopedological evidence especially properties that constitute soil memory in order to reconstruct the spatial distribution of environment variability during the late pleistocene and holocene three profiles that include modern soils and buried paleosols were studied in different geomorphic positions uplands cerro gordo site cg lower talus slope transition to valley bottom maseca ma and the mouth of the valley at the ancient border of the former texcoco lake this last site is near tepexpan te where some of the oldest human remains in mexico were recovered the oldest paleosol is at cg at 3000 m a s l it is dated at 22 000 yr bp and exhibits a truncated profile with a very well developed bt horizon dominated by kaolinite with phytoliths of c3 plants all of its features are related to a humid probably warm environment it was classified as a luvisol this paleosol is buried by another luvisol dated at 13 000 yr bp with morphological characteristics similar to the previous soil although clay mineralogy consists mostly of halloysite and a higher percentage of c4 plant phytoliths is apparent in ma the oldest paleosol was not recognized it is probable that the two paleosols found in cg merge into one at ma which shows strong redoximorphic features but high percentages of c4 plant phytoliths and halloysitic clays at the te site paleosols are less developed fluvisols modern soil cover also varies in relation to its geomorphic position in cg it is a phaeozem while in ma and te present day soils have carbonate accumulation we interpret prevailing conditions during the last glacial maximum in the teotihuacan valley to be humid with a tendency towards drying at the end of pleistocene dry conditions prevail in the valley today

mineralogy and origin of rhizoliths on the margins of saline alkaline lake bogoria kenya rift valley abstract a wide range of rhizoliths occurs around the margins of lake bogoria kenya these include root casts moulds tubules rhizocretions and permineralised root systems these rhizoliths are variably composed of opaline silica calcite zeolites mainly analcime fluorite and possibly fluorapatite either alone or in combinations some rhizoliths are infilled moulds with detrital silicate grains most rhizoliths are in situ showing both vertical and horizontal orientations reworked rhizoliths have been concentrated locally to form dense rhizolites hot spring fluids concentrated by evapotranspiration and capillary evaporation have provided most of the silica for the permineralisation of the plant tissues precipitation involved the growth of silica nanospheres and microspheres that coalesced into homogeneous masses calcite rhizoliths formed following evaporative concentration evapotranspiration and or co2 degassing of ca bearing runoff water that infiltrated the sediment or by mixing of runoff with saline alkaline groundwater fluorite precipitated in areas where mixing of hot spring and meteoric waters occurred or possibly where hot spring fluids came into contact with pre existing calcite zeolitic rhizoliths formed during a prolonged period of aridity when capillary rise and evaporative pumping brought saline alkaline waters into contact with detrital silicate minerals around roots

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

the genesis and paleoenvironmental records of longji agricultural terraces southern china a pilot study of human environment interaction ancient agricultural terraces distributed over the mountainous areas in southern china can be taken as new objects for studies on human environment interaction in the past however this type of study is rare this study selected longji terraces longsheng guilin one of the famous ancient agricultural terraces to explore its genesis and paleoenvironmental records three soil profiles including an original hillslope woodland soil profile and two terrace profiles were sampled for analyses of physical and geochemical proxies and radiocarbon dating cultivated soil in the terrace profile shows aggradation making the cultivated horizon a bottom up chronological sedimentary sequence two basal samples in the cultivated horizons of two parallel terrace profiles show calibrated ages of 1361 1406 ad and 1335 1384 ad respectively indicating that the genesis of longji terraces occurred during the late yuan dynasty in chinese history strong survival pressure and desire for new living space in the turbulent social situation of the late yuan dynasty might have been the direct factor forcing some people of national minorities to migrate to the longji mountain area where they effectively utilized the hillslope land and water resources for cultivation by building agricultural terraces and constructing a gravity irrigation network multi proxy analyses of the cultivated horizon of one selected terrace profile reveal that human farming activity has experienced a staged strengthening process including four stages since the late 14th century moreover some changes of the intensity of human farming activity found within each stage might reflect the impact of climatic fluctuations on human farming activity during the little ice age and the later warming period

weathering characteristics of interflow volcanic boles from mandla lobe eastern deccan volcanic province abstract the deccan volcanism straddling the cretaceous paleogene boundary resulted into one of the most extensive continental flood basalts in the western and central peninsular india the interflow sedimentary units boles often cited as paleosols are the rare archives of paleoenvironmental conditions existed during successive lava flows a debate on the origin of boles as true paleosols exists therefore in order to trace out regional extent of such conditions pedogenic non pedogenic in the context of their paleoenvironmental significance during the deccan volcanism we studied here mineral magnetic characteristics of 36 color differentiated bole beds from the mandla lobe in the eastern deccan volcanic province edvp classified into four types gray yellow brown and red based on their munsell notations the gray yellow and brown boles show dominantly ferrimagnetic composition chiefly magnetite and titanomagnetite while red boles characterize mixed ferri and antiferromagnetic mainly hematite mineralogy the granulometric domain parameters suggest larger single domain sd and the multidomain md ferrimagnets in the majority of cases whereas superparamagnetic sp particles with frequency dependent susceptibility fd 2 6 to 20 3 10 8 m 3 kg 1 are limited to the few red and brown boles only the significant presence of primary parent magnetic minerals i e coarse sd md titanomagnetite and magnetite in the majority of boles depict incipient to moderate weathering owing to limited time intervals during successive eruptions the combination of hematite and sp particles present only in the few red and brown boles depicts baking effect rather than pedogenesis the comparison of magnetic properties of boles from edvp and western deccan volcanic province wdvp shows significant differences in the concentration of sp ferrimagnetic particles and hematite attributed to variable weathering intensity duration and heating related alterations from the upper flows both edvp and wdvp boles indicate similar first order paleoenvironmental conditions without any major pedogenesis that can be regionally correlated

calcretes from a late quaternary interfluve in the ganga plains india carbonate types and isotopic systems in a monsoonal setting abstract calcretes are abundant in late quaternary channel and floodplain strata of the southern ganga plains in a key section at kalpi pedogenic carbonates nodules rhizoconcretions and powdery carbonate are present within aggradational floodplain deposits where they correspond to relatively high monsoonal precipitation and river discharge in contrast groundwater carbonate has cemented degradational surfaces discontinuities which correspond with periods of relatively low precipitation mixed groundwater and pedogenic calcretes are present in the deposits of small interfluve channels and reworked nodules line degradational surfaces and locally fill channels most carbonates show alpha fabrics that include floating textures shrinkage crack fills and grain coatings the predominance of alpha fabrics is unexpected but is characteristic of calcretes across dryland and seasonal parts of northern india where soil formation led to only weakly developed or poorly preserved beta fabrics interpretation of 13c and 18o values of bulk and microdrilled calcrete samples suggests relatively little variation in precipitation and vegetation types through the sampled interval at kalpi floodplain deposits were vegetated with a mixture of c4 and c3 plants predominantly c4 with a higher proportion of c3 plants associated with channel deposits this apparent lack of variation is surprising because the sampled interval represents at least 60 000 years of marine isotope stages 3 5 during which climate models suggest that asia experienced radical fluctuations in monsoon intensity and precipitation some of the apparent lack of variation may be explained by preferential preservation of aggradational strata that represent relatively active monsoonal periods as well as by the mixing of drier floodplain c4 and riparian c3 vegetation however local departures from the regionally based climate model cannot be ruled out a modest upsection increase in c4 plants may represent increased aridity and lower atmospheric co2 isotopic analysis of organic matter from floodplain pedogenic nodules suggests a higher c3 plant contribution than carbonate based data would suggest the preserved organic matter may reflect the annual average biomass in the soil whereas carbonate formation may have taken place mainly during the drier season when respiration of c4 plants was more important in interfluve settings such as kalpi seasonality may strongly affect the c3 c4 system with preferential preservation of only part of the biomass

magnetic separation and evaluation of magnetization of brazilian soils from different parent materials abstract ten selected brazilian soils representative of oxisols ultisols alfisols and inceptisols and derived from gneiss basalt sandstone diabase and itabirite were sampled and examined to provide insight into the behavior of their magnetic minerals the objective was to measure the magnetization of the sand silt and clay fractions and to submit the clay fraction to variable magnetic fields to obtain the magnetization curves and to study their magnetic behavior as related to their parent material lithology the separation procedure using a magnetic separator was done in two different ways dry separation for the sand and wet separation for the silt and clay fractions x ray diffraction patterns of magnetic and nonmagnetic fractions were obtained and the segregation of ferrimagnetic minerals were shown the magnetization s of the total and the magnetic and nonmagnetic soil fractions was evaluated using a special analytical balance the s values obtained varied from 0 03 to 17 72 j t 1 kg 1 for sand 0 05 to 8 91 j t 1 kg 1 for silt and 0 05 to 2 54 j t 1 kg 1 for the clay fractions the results from the magnetically concentrated fractions varied in the same fashion but reached higher values magnetization curves showed spontaneous magnetization ms values of 0 6 to 3 35 j t 1 kg 1 high field slopes ranging from 0 17 to 0 77 j t 2 kg 1 and clearly the influence of the parent material lithology on the nature of the soil magnetic behavior magnetic measurements suggested pathways for ferrimagnetic minerals transformations in soil systems

chemical physical and micromorphological properties of termite mounds and adjacent soils along a toposequence in zona da mata minas gerais state brazil article i nfo little is known about the effects of neotropical mound building termites in soil chemical and physical properties the influence of soil termite activity on soil characteristics was studied by assessing chemical physical and micromorphological properties of a toposequence of latosols oxisols soil samples were collected from the walls and inner parts of termite mounds and also from adjacent soil a high diversity of termite genera was found in the mounds along the toposequence together with the inquiline termites and other soil dwelling arthropods chemical analyses showed that ph and the contents of organic c and n p ca and mg were significantly higher in termite mounds compared with adjacent areas with an inverse trend for al content significant differences in ph and exchangeable al were observed between soil and mound across the slopes the mound density across the landscape was higher at the upper slope segment followed by the hill top middle slope and lower slope segments considering a lifespan of 30 years and dimensions of termite mounds found in the toposequence we conclude that the textural and chemical uniformity of latosols may be increased following the pedobiological turnover during mound building with local rates varying from 2 1 to 7 5 m 3 ha 1

physical chemical and mineralogical properties of mexico city sediments a geotechnical perspective the authors appreciate the interest of the discussers in the paper and offer the following comments as indicated in the paper the results presented were obtained as part of a comprehensive research program on the microstructure of mexico city sediments being conducted at the national university of mexico a second site has been studied and the corresponding paper has been written in which correlation of the profiles of geotechnical properties of the sediments with their profiles of physical chemical and mineralogical properties has been investigated the discussers compare the mexico city sediments with illitic sensitive clays in canada the united states and norway we believe their discussion estimates in an alternate scenario which did not in our judgement optimally represent the circumstances of the just case the focus of our article principally mexico city sediments are predominant disintegration products of andesitic rocks and fine and ultrafine volcanic ash furthermore the discussers indicate that variations in carbonate content may have only a small influence on observed variations in the engineering behavior of deposits with high water content which is the case for mexico city sediments all of the ramon lopez velarde park core was checked with scanning electron microscopy and we did not find carbonate precipitation except at a depth of 4 m from the surface so the role of carbonate cementation is doubtful phase contacts are developed in highly compacted clays or cemented clays and are distinguished by the presence of direct contacts between the structural elements and by a new phase carbonates developed at the contacts cementing the particles coagulation contacts are widespread in young clays and poorly cemented clays the structural elements do not directly touch each other and structural cohesion is de termined by molecular and possibly magnetic and dipole interaction furthermore the coagulation contacts allowed the soil to reach a restructured form after it was altered which happened in the mexico city sediments the authors agree that the processes by which the amorphous material content is determined are chemically aggressive as suggested by the discussers overall however the authors feel that the role of the amorphous material is mainly responsible for the properties of mexico city sediments the authors will investigate further quantitative interpretations in mexico city sediments

clay illuviation and calcium carbonate accumulation along a precipitation gradient in kansas one of the significant features of loess derived soils in kansas is the occurrence of clay rich subsurface horizons above a layer enriched with pedogenic carbonates in order to examine the extent of clay increase and pedogenic carbonate enrichment in a precipitation gradient ten soil profiles from three different precipitation regions were studied using micromorphological and mineralogical techniques the precipitation gradient was divided into three groups 400 550 mm 550 750 mm and 750 1100 mm regions the objectives were to 1 understand the cause of clay orientation in clay rich horizons 2 investigate the reasons for the clay increase and 3 observe the interaction of clay and pedogenic carbonate accumulation features along a precipitation gradient in kansas although clay films were identified in the field for soils in the 400 550 mm regions illuvial clay films were not observed in thin section analysis the clay accumulations mostly occurred as grain coatings the rest of the clay accumulations observed were very thin striated and mostly associated with voids the argillic horizons had a granostriated b fabric which indicates stress orientation of micromass caused by high shrink swell activity thick and continuous illuvial coatings were observed in the buried horizons of paleosols in the other two regions where precipitation exceeds 550 mm illuvial clay coatings with strong orientation were observed along with thin and striated stress oriented clay both types of clay orientations exceeded 1 of the cross sectional area for the thin section although illuvial clay features and pedogenic carbonates were observed in all soils at approximately the same depth complete obliteration of clay coatings was not observed in these horizons in situ weathering of biotite was one of the reasons for the clay increase in all soil profiles in all soils studied the clay increase and cause of clay orientation cannot be attributed to a single genetic process or event both illuviation and shrink swell activity were involved in the orientation of clay although orientation of clay and pedogenic carbonates were observed in all soils at approximately the same depth the decomposition of clay coatings was not observed in these horizons

the morphology of calcite crystals grown in a porous medium doped with divalent cations calcite crystals were grown in the presence of small concentrations 50 200 and 600 ppm of divalent cations ba2 sr2 co2 and mn2 in a silica hydrogel medium the calcite crystals grown in the presence of cations larger than ca2 ba2 or sr2 developed rhombohedral habits defined by 101 4 form similar to the morphology of calcite grown in a pure gel sem images show that growth on 101 4 occurs by lateral advancement of layers bounded by macroscopic dendritic or jagged steps in the case of calcite crystals grown in a gel doped with cations smaller than ca2 co2 or mn2 a variety of morphologies was obtained ranging from blocky crystals at lower concentrations 50 and 200 ppm to peanut like aggregates spheres and spherulites at 600 ppm the macroscopic morphological characteristics of such doped calcite crystals reflect closely the growth behaviour of calcite 101 4 surface at a nanoscale reported by previous afm studies morphological features have been interpreted on the basis of the modification of growing steps characteristics as a consequence of asymmetrical cation incorporation the use of such morphologies as a criterion of biological activity is therefore unreliable

implications of subfossil coleoptera for the evolution of the mima mounds of southwestern puget lowland washington abstract the origin of washington state s mima mounds has been debated for over a century with numerous mechanisms being postulated subfossil coleopteran beetle remains recovered from the base of a mound at mima prairie consist of species that would be expected in rodent burrows and nests all but one species are obligate burrow inhabitants these results suggest the past presence of fossorial rodents probably pocket gophers thomomys mazama in the mounds although none live there at present whether or not the gophers created the mounds they may well have been instrumental in maintaining mound geometry until very recently