the use of oxygen and carbon isotope composition of pedogenic carbonates from pleistocene palaeosols in nw bangladesh as palaeoclimatic indicators abstract 13c and 18o values of pedogenic carbonate concretions from pleistocene palaeosol sequences of the northwestern part of bangladesh are presented the major goal of this study is to test 1 the reproducibility of the 13c and 18o signals within palaeosols and 2 their variation from one palaeosol to the other the palaeosols that are expected to have formed under different palaeoenvironmental palaeoclimatic or diagenetic conditions provide isotopic signatures 13c and z 18o that can be clearly distinguished in other words the differences between analytical results from the same palaeosol are much smaller than between samples from different palaeosols this would mean that climatic or environmental changes are recorded as significant differences in isotopic signature carbon isotopic compositions vary between 11 5 and 2 0 the relatively larger 13c variations may be explained by climatically induced changes in floral composition changes in humidity are translated into variations of c3 and c4 plant proportions resulting in changes in soil co2 13c values the extreme 13c values found would correspond to nearly single phase c3 13c 11 5 or c4 13c 2 0 variations in the oxygen isotopic composition are much smaller and range between 6 5 and 3 5 these smaller differences can be induced by temperature changes

alluvial fan carbonate facies with evaporites eocene guarga formation southern pyrenees spain continental carbonates of the basal part of the guarga formation upper eocene have been studied in the field and in the laboratory both geographic pattern and vertical sequences served as a basis for sedimentary models the pattern reveals that carbonate deposition was greater in the western part of the tremp graus basin than in the eastern part studies of slabs and thin sections suggest high energy deposition in the eastern part of the basin and low energy deposition in the western part gross lithology petrography and faunal floral associations indicate sedimentary environments which include calcimorphic palaeosoils caliche nodule zones solid caliche nodule zones caliche crusts fluvial carbonates paludal carbonates and pond lake carbonates distribution pattern of the carbonate bodies and lithologies seem to be controlled by alluvial fan processes they are typical fining upward sequences in the sense of collinson 1978 which furthermore can be assigned to a channel bound group and a succession independent of fluvial channels referring to fan physiography the sequences can be subdivided into fluvial proximal interchannel fluvial distal interchannel lacustrine distal interchannel nearshore lacustrine paludine and lacustrine offshore carbonate facies the two last categories are distal alluvial plain and or fan edge associations the presence of especially charophyte oogonia adjacent to pseudomorphs of lenticular gypsum in the lacustrine carbonates of the western tremp graus basin indicates that their depositional environment was that of shallow lakes with alternating salinities diagenetic alterations consist of three major phenomena a general cementation of the carbonates by low mg calcite b pseudomorphs of lenticular gypsum and c silification the relationship of gypsum and silica diagenesis to the regional distribution of lacustrine carbonates suggests early diagenetic processes for their formation gypsum pseudomorphs are small and are found to be replaced by fe calcite throughout the whole area or are large and replaced preferentially by silica in the west only there is experimental evidence cody 1979 that distribution of gypsum morphology and crystal sizes can be related to increased salinities and increased organic production in the west chert gypsum fabrics from that area resemble the silex nectique of cayeux 1929 the occurrence of this noteworthy type of chert together with length slow chalcedony is an indication of relatively early silification of the gypsum it is suggested that the sediments containing the silicified lenticular gypsum hosted brines of partly marine origin which alternately became brackish or fresh an attempt was made to check the influence of evaporation during carbonate deposition by determining the stable isotope composition of the carbonates and of the chert the data show no distinct variations with respect to the presumed palaeoenvironments the ranges in the carbonates 13c 5 0 to 7 9 18 o 4 5 to 7 7 fit among the data given in the literature the values derived from chert 18o 26 9 to 31 smow support a concept of alternating salinities distribution of carbonate lithofacies indicate a systematic change in sedimentation from fluvial ephemeral to permanent lacustrine from east to west diagenetic alterations suggest an increase of salinities of pore waters in the same direction in addition the lacustrine limestones in the west were due to frequent changes in pore water salinity similar sequences lacking subtidal and or lagoonal fossil associations but including pseudomorphs of carbonate and chert after lenticular gypsum were described from the lower purbeckian of dorset west 1964 1975 1979 and from the tertiary of the paris basin fontes 1968 guarga limestone environments of especially the western tremp graus basin probably resembled the modern semi arid ephemeral saline lakes in australia burne bauld de dekker 1980 gypsum precipitation in these environments can be compared to the one in modern sabkhas from the mediterranean coast of egypt west ali hilmy 1979 ali west hilmy 1980

carbonate deposition physical limnology and environmentally controlled chert formation in paleocene eocene lake flagstaff central utah abstract lake flagstaff paleocene eocene of central utah owed its existence large size shallowness and low clastic content to its tectonic setting but the climate controlled its mostly autochthonous sediments during the first and most humid of the three lake phases the lake was fresh calcareous large and highly productive with abundant vegetation and snails the first deposits were limestones with gradually increasing detrital dolomite eroded from lake marginal carbonate mudflats that were undergoing penecontemporaneous dolomitization continuous fluctuation in lake level produced many secondary dewatering and pedogenic paludine fabrics the lake developed into a playa lake during the very arid second phase becoming restricted in area and fauna the water was saline and alkaline and twice became a gypsum precipitating brine frequent exposure of the lake beds resulted in much calichification and in rapid and complete dolomitization under the intermediate climate of the third phase the lake reexpanded and freshened snails returned and many limestones escaped dolomitization each phase defines a member of the flagstaff formation chert absent in the oldest beds increases up section the lowest chert forms minor small spheres and linings in voids near the top of the lowest member suggesting limited silica input and post dolomitization precipitation in areas of greatest groundwater movement the base of the middle member contains horizons of atextural chert mudcrack fillings and nodules that appear to have been an inorganically precipitated gel most of the middle member however contains abundant chert nodules that replaced limestone prior to dolomitization the nodules grew prior to burial some even prior to mudcrack formation by the movement of dissolved silica to areas of relatively low ph in the upper member chert is even more prevalent entire thin beds were pervasively but incompletely silicified prior to dolomitization probably by vertical evaporative pumping of siliceous groundwater moving under mudflats toward the lake

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

oxygen and carbon isotope trends and sedimentological evolution of a meromictic and saline lacustrine system the holocene medicine lake basin north american great plains usa abstract the succession of sedimentary subfacies in the medicine lake basin south dakota usa documents numerous changes in total dissolved solids tds lake level and the nature and stability of meromixis during the holocene the lake formed about 10 6 ka b p when coarse clastics and massive fine grained muds were deposited in a well mixed freshwater system subsequently the lake became saline and meromictic depositing a finely laminated unit composed of variegated and gray muds organic facies gypsum and aragonite laminae phototrophic bacterial plate communities bpc at the chemocline were significant producers of pelagic organic matter relatively high lake levels at least 10 m higher than today but saline and meromictic conditions predominated through the early to mid holocene at the end of this phase lake level dropped and stable meromixis was disrupted sands and massive or banded muds were deposited in sublittoral areas and benthic microbial communities bmc spread over the lake replacing bpcs as the predominant microbial producers when lake level rose again massive and laminated units were deposited under less saline conditions another pronounced episode of low lake level and high salinity followed the most recent sediments are sapropels massive or banded muds and littoral sands the 18o record from authigenic aragonite shows more positive values during the arid mid holocene interval with an abrupt increase at the end of this period followed by generally more negative values during the cooler and wetter late holocene the small range of 18o values 3 suggests that the lake was well buffered against high frequency climatic cycles probably as a result of groundwater modulation we postulate that meromixis and the type of photosynthetic microbial communities dominating the basinal region of the lake system either bpcs or bmcs exerted major controls on the carbon cycle and consequently on the development of isotopic trends linking 13c and 18o values more negative 13c values during the early and mid holocene are interpreted as a consequence of the predominance of 12c enriched microbial carbon from bpcs examples of both covariant and inverse covariant isotope trends between 13c and 18o values occur in the medicine lake record inverse covariant trends characterize long periods of stable meromixis when bpcs predominate over bmcs we hypothesize that well developed water stratification caused by greater influx of relatively 18o depleted freshwater induces higher productivity at the chemocline and consequently more positive 13c values in the precipitated carbonates unstable phases of meromixis or holomictic conditions are characterized by a predominance of bmcs or other biogenic producers over bpcs and a number of other factors combine to promote covariant trends the medicine lake record is consistent with the paleoclimatic interpretation for the northern great plains of a more arid early and middle holocene followed by an abrupt transition to a relatively cooler and wetter late holocene the sedimentary succesion in medicine lake documents a much more fluctuating and abrupt climate behavior than suggested by the vegetation paleorecord and suggest a late holocene climate punctuated by arid episodes

calcretes at sequence boundaries in upper carboniferous cyclothems of the sydney basin atlantic canada abstract nodular and associated groundwater calcretes in coal bearing cyclothems of the sydney basin mark the boundary between underlying marginal marine and overlying alluvial deposits they are inferred to represent lowstand surfaces sequence boundaries the host sediments include both sand siltstones and palustrine limestones microfabrics of calcretes with detrital hosts show evidence of replacement displacement and shrinkage alpha fabrics suggesting that the calcretes formed under relatively arid conditions in contrast microfabrics of nodular calcretes with limestone hosts exhibit predominantly beta fabrics with root induced brecciation and subordinate shrinkage fabrics the calcretes and host limestones are inferred to have formed in topographic lows thick alluvial sediments with red calcic vertisols overlie the calcretes and formed within the transgressive systems tract under conditions of abundant sediment supply coals and associated hydromorphic palaeosols lie near the transgressive maximum and in the highstand systems tract the presence of calcareous palaeosols on lowstand surfaces suggests that the lowstands were times of relative climatic aridity

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

depth to pedogenic carbonate horizon as a paleoprecipitation indicator comment and reply royer 1999 1 has recently used a large data set from the u s natural resources conservation service nrcs to reexamine the relationship between mean annual precipitation and depth to the calcic horizon in soils the extremely poor correlation between these variables in his nrcs data r2 0

paleosols spanning the cretaceous paleogene transition eastern montana and western north dakota paleosols occur in exposures of the latest cretaceous hell creek and paleocene tullock ludlow formations in montana and western north dakota these units are composed mainly of interbedded siltstones and sandstones of meandering fluvial origin the paleosols indicate that changes in ancient soil development occurred concomitantly with the better known faunal transition in order of decreasing abundance silty soils sandy soils organic soils and volcanic soils are preserved pedogenic features present in these soils include roots microscopic segregations of amorphous material birefringence fabric and soil structures the features suggest that throughout the cretaceous paleogene transition pedogenic processes in the region produced immature profiles an observation consistent with the unstable fluvial setting in which the ancient soils formed gleization was a dominant process in this setting and podzolization modified some sandy soils the association of the features enables recognition of o a e btg bhs bg bc cg and c horizons during middle hell creek time soils formed in a poorly drained setting that was only stable enough to permit incipient pedogenesis the bulk of the pedogenesis occurred in levee and flood plain deposits soils also occurred on point bar and crevasse splay deposits in topographically depressed regions organic accumulations formed with minimal soil development matted plant debris is the product of this environment gley features and segregations of iron oxides around voids suggest fluctuation of the water table by latest hell creek time the mean level of the water table rose and in the lowest tullock ludlow exposures extensive ponded deposits are preserved vegetation accumulated at a rate sufficient for coal formation the amount of fluctuation apparently was reduced and pedogenesis was further inhibited as indicated by the virtual absence of illuviated clays in the sediments

geochemical evolution and paleoenvironments of the eocene continental deposits in the paris basin abstract the continental and lacustrine deposits of eocene age in the paris basin form a geochemical sequence extending from clastic sediments characterized by aluminous clay minerals to chemical sediments with dolomite gypsum and magnesian clay minerals during the early eocene flood plains and lakes with large deltas extended across the southern margin of the paris basin the clays were derived from the weathered mesozoic rocks calcretes and smectitic vertisols developed within the flood plain deposits indicating that the climate was warm with an alternation of wet and dry seasons during the middle eocene lacustrine limestones and palygorskite clays developed in small lakes subject to periodic desiccation and pedogenesis landwards pedogenetic silcretes developed on the early eocenc pediments palygorskite is indicative of environments with high concentrations of silica and magnesium and the presence of opal in silcretes confirms a high silica concentration in the soils solutions the paleoclimate was warm with distinct dry seasons or periods during the late eocene gypsum was deposited in the basin center surrounded by a marly deposit in which dolomite and sepiolite are the characteristic minerals lacustrine limestone with alumino magnesian smectite and palygorskite formed on the margin of the basin the development of the evaporitic sequence was favored by the flatness of the palaeolandscape and its silcrete capping which restricted erosion and detrital input to the basin the climate was warm with a tendency to aridity thus the continental deposits of eocene age in the paris basin reflect a progressively more aric climate moreover each depositional pedogenetic and encrusting phase modified the palaeolandscape and thus influenced the next sedimentary episode

pedostratigraphic models for alluvial fan deposits a tool for interpreting ancient sequences this paper reviews the scattered literature on quaternary arid type alluvial fan soil sequences and presents a series of model stratigraphies these are primarily influenced by the degree of entrenchment and by climatic controls these models are used to interpret well exposed miocene fan deposits from the madrid basin central spain

soil landscape and climatic relationships in the middle miocene of the madrid basin the miocene alluvial lacustrine sequences of the madrid basin spain formed in highly varied landscapes the presence of various types of palaeosols allows assessment of the effects of local and external factors on sedimentation pedogenesis and geomorphological development in the northern more arid tectonically active area soils were weakly developed in aggrading alluvial fans dominated by mass flows reflecting high sedimentation rates in more distal parts of the fans and in playa lakes calcretes and dolocretes developed the former were associated with mg poor fan sediments while the latter formed on mg rich lake clays exposed during minor lake lowstands the north east part of the basin had a less arid climate alluvial fans in this area were dominated by stream flood deposits sourced by carbonate terrains floodplain and freshwater lake deposits formed in distal areas the high local supply of calcium carbonate may have contributed to the preferential development of calcretes on the fans both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources palaeosols also developed on pond and lake margin carbonates and led to the formation of palustrine limestones the spatial distributions and stratigraphies of palaeosols in the madrid basin alluvial fans suggest that soil formation was controlled by local factors these palaeosols differ from those seen in quaternary fans which are characterized by climatically induced periods of stability and instability

do stable isotope data from calcrete record late pleistocene monsoonal climate variation in the thar desert of india late pleistocene terrestrial climate records in india may be preserved in oxygen and carbon stable isotopes in pedogenic calcrete petrography shows that calcrete nodules in quaternary sediments of the thar desert in rajasthan are pedogenic with little evidence for postpedogenic alteration the calcrete occurs in four laterally persistent and one nonpersistent eolian units separated by colluvial gravel thermoluminescence and infrared and green light stimulated luminescence of host quartz and feldspar grains gave age brackets for persistent eolian units i iv of ca 70 000 60 000 ca 60 000 55 000 ca 55 000 43 000 and ca 43 000 25 000 yr respectively the youngest eolian unit v is 10 000 yr old and contains no calcrete stable oxygen isotope compositions of calcretes in most of eolian unit i in the upper part of eolian unit iv and in the nonpersistent eolian unit range between 4 6 and 2 1 pdb these values up to 4 4 greater than values from eolian units ii and iii are interpreted as representing nonmonsoonal18o enriched normal continental waters during climatic phases when the monsoon weakened or failed conversely 25 000 60 000 yr old calcretes eolian units ii and iii probably formed under monsoonal conditions the two periods of weakened monsoon are consistent with other paleoclimatic data from india and may represent widespread aridity on the indian subcontinent during isotope stages 2 and 4 the total variation in 13c is 1 7 0 0 1 7 and 13c covaries positively and linearly with 18o 13c values are highest when 18o values indicate the most arid climatic conditions this is best explained by expansion of c4grasses at the expense of c3plants at low latitudes during glacial periods when atmosphericpco2was lowered c4dominance was overridingly influenced by global change in atmosphericpco2despite the lowered summer rainfall

dynamics of iron and calcium carbonate redistribution and palaeohydrology in middle eocene alluvial paleosols of the southeast ebro basin margin catalonia northeast spain abstract paleosols in the alluvial middle eocene of the ebro basin exhibit both the redistribution of iron groundwater and surface water gley and calcium carbonate the hydrological dynamics are reconstructed through gley features and location of carbonate accumulation together these allow a sophisticated analysis of the seasonal palaeohydrology of ancient sedimentary environments this analysis is performed on paleosols developed in marginal and distal floodplain and delta plain deposits derived from the southeast ebro basin margin the most proximal part of the floodplain sediments had moderate mainly vadose calcite redistribution with surface water gleying and fairly deep groundwater the more distal sediments have stronger calcite redistribution both of vadose and surface water gley environments these were frequently overprinted by groundwater related calcite indicating shallow and fluctuating groundwater in the most distal alluvial sediments both calcite redistribution and further soil formation were weak while groundwater was shallow

a calcrete based u th chronology for landform evolution in the sorbas basin southeast spain nodular and massive calcretes from alluvial terraces in the sorbas area of southeast spain have been dated by the u th isochron method to between 8 350 ka alternative approaches have been used to generate the multiple samples for the isochron method for several of the calcretes dates agreed closely when obtained by total dissolution of a number of nodules or by the sequential dissolution in different acids of a single nodule however fractional dissolution of a single nodule in the same acid revealed two stages of precipitation of different age it is considered that the calcretes may not be strictly pedogenic in origin and that groundwater processes linked to the alluvial environment may have been involved also nevertheless their dates provide minimum ages for a chronostratigraphic framework for terrace evolution

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

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

use of charophyte carbonates as proxy indicators of subtle hydrological and chemical changes in marl lakes example from the miocene bicorb basin eastern spain abstract the lower alluvial unit in the miocene bicorb basin contains several metric scale limestone intervals which record episodic shallow lacustrine environments in an alluvial setting developed during the early stage of the basin s evolution five main carbonate facies have been differentiated in the lacustrine limestones although calcite charophyte incrustations predominate and constitute the most striking features of these deposits the thinnest limestone intervals correspond to deposits from charophyte meadows in ponded shallow depressions in floodplains the thickest limestone intervals are mainly formed by banded limestones and usually correspond to diverse types of regressive sequences that have been interpreted as resulting from the infill of shallow lakes the sedimentological features and sequences show noticeable differences in the gradient of the littoral zones and the amount of palustrine deposits with models proposed for marl lakes charophytic carbonates from the best preserved facies show similar microtextures to those from recent charophyte incrustations the variations in stable isotopes 13 c 18 o for these primary carbonates occur in parallel with luminescence variations and correspond to hydrological changes and variations in solute composition and eh ph status in the lake waters the carbonates that display moderate to strong diagenetic modifications show a diverse degree of compaction aggrading neomorphism strong cementation and nodulization the isotopic values for these are arranged in diverse clusters there is a correlation between the degree of luminescence and the 13 c this suggests that hydrological and hydrochemical variations both in the lacustrine and diagenetic environments are being recorded in parallel we emphasize the need for further comparative studies between recent and ancient charophytic carbonates as these carbonates have been used in palaeoenvironmental reconstructions special attention must be paid to the diagenetic changes in ancient charophytic marls

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

paleosol classification problems and solutions abstract paleosols are soils that formed on landscapes of the geologic past three kinds exist buried exhumed and relict to help reconstruct paleoenvironments and for ease of comparison we suggest a property based classification system linked to genetic processes we use enduring properties because alteration of paleosols following burial is common morphological properties such as horizonation soil fabric root and worm casts and redoximorphic features are resistant to alteration and thus are valuable as criteria field observable and micromorphological properties degree of weathering and proportion of resistant minerals are also useful as criteria for paleosol orders total chemical analysis provides a proxy measure for base saturation and clay mineralogy we use proxy criteria to help classify paleosols that have changed markedly or have been lithified during or after burial to an earlier version of the system we add two new orders and include buried relict lithified and exhumed units at the suborder level our system clearly separates paleosol taxon names from those of all ground soils we use the prescript paleo at the order level and kryptic to designate the buried enduric to designate the relict lithic to designate the lithified and emergent to designate the exhumed paleosol suborders we use prescript modifiers to describe the physical characteristics of the paleosols and postscripts for parent material origin and the extensiveness of the paleosol landscape we present data and classify a number of paleosols as examples of the system

facies relationships and sedimentation in large rift lakes and implications for hydrocarbon exploration examples from lakes turkana and tanganyika abstract two african lakes turkana and tanganyika illustrate a spectrum of sediments and facies architectures which can occur in large rift lacustrine basins they demonstrate contrasts between sediments deposited in a semi arid moderately deep mainly volcanic basin turkana and a semi humid extremely deep basin without significant volcanism tanganyika turkana deposits are dominated by rapidly accumulating organic poor terrigenous muds coarse clastic input is in part limited by ponding in marginal subbasins due to volcanic barriers profundal coarse clastic deposition is rare sediments contain little biogenic components except in the sediment starved south basin sediments are also poor in cartonates tanganyika deposits are dominated by organic rich biogenic muds steep fault escarpments and uniform slopes along shelf platform and rift axis lake margins promote the efficient transport of sands into profundal settings total clastic sediment supply into the basin is severely restricted by basin morphology with steep relief backslopping a limited drainage basin area and presettling in upstream lake kivu sediment ponding along margins is rare littoral carbonates are common a consequence of low net clastic sedimentation rates many of the differences between facies in the two lakes can be explained by contrasts in basin margin slope and relief volcanic activity and climate between the two lakes the results of this study suggest that lake deposits formed in tanganyika type rift basins are more appropriate exploration target for hydrocarbon exploration than those from turkana type basins

displacive calcite and grain breakage in sandstones abstract many calcrete profiles contain evidence of heterogeneous growth of displacive calcite which includes 1 cathode luminescence defined zones in crystals indicating both linear unidirectional and polyhedral multidirectional growth vectors 2 expanded micaceous grains 3 broken quartz grains and 4 the dispersal of clastic grains in a carbonate matrix these features reflect the influence of the changing character of the growth environment consequent upon changes in the sediment itself in the vadose zone of arid areas rapid evaporation leads to supersaturation and thus crystallization during drying water withdraws from grain surfaces to capillary pores within micaceous grains and at grain to grain contacts these form the primary sites for precipitation of calcite kinetic barriers to nucleation ensure that growth is initially restricted to a few stressed sites and since no other nucleation sites are available continued growth of crystals is displacive with the retention of greater volumes of pore water there is a change from linear growth of a few faces to a polyhedral expansion of packed groups of crystals the resulting dilation creates additional stresses within the sediment which are transmitted between grains and which focussed by smaller areas of poi t contacts break quartz grains as permeability is reduced larger volumes of saturated water are retained within the sediment more nuclei form in pore throats and subsequent growth promotes further expansion and dispersal of framework grains this is primarily by growth of individual displacive crystals but may include the deposition of some micrite reflecting high nucleation and low growth rates later oversized pores formed by expansion are filled by unstressed grains growing as a coarse cement continued post burial diagenesis is reflected in neomorphism of displacive crystals of micrite and of cements indicating a general trend towards chemical homogeneity and structural stability

a classification of rhizogenic root formed calcretes with examples from the upper jurassic lower cretaceous of spain and upper cretaceous of southern france reply abstract studies of fluvial sequences from the upper jurassic and lower cretaceous of the cameros basin spain and the upper cretaceous of the aquitaine basin france have revealed large numbers of calcrete profiles which have formed wholly or largely through the action of plant root calcification those from spain have formed by the calcification of root mats whereas those from france resulted from the accumulation of calcified root cells microcodium these root related rhizogenic calcretes developed in stages allowing developmental time series chronosequences to be identified contrasting with existing models for calcrete profile growth they provide unique examples where vegetation has been the dominant control on profile development and probably indicate specific vegetation types and palaeoecological settings the role of root activity in forming some quaternary calcretes is also discussed

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

fan surface dynamics and biogenic calcrete development interactions during ultimate phases of fan evolution in the semiarid se spain murcia abstract pleistocene alluvial fan surfaces of the campo de cartagena mar menor basin murcia se spain are capped by thick mature calcretes calcrete profiles consist mainly of six different horizons prismatic chalky nodular massive laminar and coated gravels petrographic study of the calcretes has shown the occurrence of features such as alveolar septal structures calcified filaments coated grains spherulites calcified root cells and calcispheres that indicate the biogenic origin of the calcretes mainly induced by plant root related microbial activity the calcretes studied were formed initially in the soil and represented the k horizon development of the calcrete profiles took place in six main stages and was driven by multiple phases of soil formation erosion and reworking the relationships between these processes caused the formation of different calcrete profiles in proximal and distal fan areas in the distal areas which are controlled by limited distal fan aggradation episodic sediment input buried previously developed calcretes and generated new space for calcrete growth by plants growing in the overlying unconsolidated materials this allowed the renewal of calcrete formation and it led to the development of complex composite profiles which are thicker than in proximal areas where surface stabilisation and or dissection enabled calcrete reworking and brecciation these processes of erosion sedimentation reworking and renewed calcrete formation initiated by vegetation were repeated through time they explain the complex macro and microstructures of these calcretes and indicate that calcrete development even reaching mature stages can start before the fan surface is completely abandoned but it requires episodic sedimentation eventually distal fan aggradation and continuous calcrete development throughout the entire fan surface led to the ultimate fan surface induration controlling subsequent landscape evolution so fan surface calcretes cannot be envisaged as simple top surface carbonate accumulations but as complex feedback systems in which pedogenic biogenic and sedimentary processes interact in response to the evolving fan surface dynamics during the terminal phases of fan development in semiarid environments

lacustrine carbonates and pedogenesis sedimentology and origin of palustrine deposits from the early cretaceous rupelo formation w cameros basin n spain the berriasian rupelo formation of the w cameros basin consists of a 2 200 m thickness of marginal and open lacustrine carbonate and associated deposits open lacustrine facies contain a non marine biota with abundant charophytes both stems and gyrogonites ostracods gastropods and rare vertebrates carbonate production was mainly biogenic the associated marginal lacustrine palustrine facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history the succession was laid down in a low gradient shallow lake complex characterized by wide fluctuations of the shoreline carbon and oxygen stable isotope analyses from the carbonates show non marine values with ranges of 13 from 7 to 11 and 18 from 3 to 7 5 differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake analyses from the entire sample suite plot on a linear trend isotopic compositions become lighter with increasing evidence of pedogenic modification this suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil derived co2 the stable isotope data thus support evidence from petrography and facies relations that palustrine limestones form through pedogenic modification of lake carbonates

diagenesis of late miocene micritic lacustrine carbonates madrid basin spain mud grade lacustrine limestones of miocene age from the madrid basin spain reveal varied and complex diagenetic histories microporous micrites occur as well as micrites with anhedral mosaics the micrites have recrystallized from a metastable precursor in part under sub oxic meteoric diagenetic conditions probably before extensive karstification in the pliocene the absence of aragonite relics their mainly micritic microfabric low sr content and covariant trend of sr and mg suggest that the micrites formed from mainly high magnesian calcite muds lacustrine micrites can be compared to marine forms and criteria used to assess the composition of the marine precursor muds can be applied to lacustrine limestones to complement other techniques to identify original lake water compositions

pennsylvanian continental cyclothem development no evidence of direct climatic control in the upper freeport formation allegheny group of pennsylvania northern appalachian basin abstract the occurrence of lacustrine carbonates in the allegheny group upper middle pennsylvanian continental cyclothems of the northern appalachian basin has been attributed to climatic alternation of wet coal deposition and dry carbonate deposition periods however we present evidence from facies associations coal and carbonate petrography and carbonate stable isotope geochemistry for a uniformly wet climate throughout deposition of one of the earliest continental cyclothems the upper freeport formation uff we propose a depositional model comprising a large wetland complex drained by an anastomosed fluvial system containing a mosaic of channels freshwater siliciclastic and carbonate lakes and peat bogs swamps on a siliciclastic floodplain carbonate phases represent bio induced precipitates modified by lake dynamics and not evaporative deposits absence of covariant isotopic trends between 18o and 13c and a relatively small range of 18o values 1 9 to 6 4 pdb that are close to or lighter than predicted paleoprecipitation for the pennsylvanian equatorial regions indicate hydrologically open short residence time lake systems in support of our sedimentary model combined sedimentologic and isotopic data do not indicate reduced effective moisture precipitation evaporation during intervals of limestone deposition the uff lakes developed in a relatively wet climate zone without significant episodic closure due to climatically induced water deficit lithologic patterns within the uff cyclothem are primarily attributed to the evolution of anastomosed fluvial systems controlled by subsidence in an active foreland basin rather than to short term climatic change or eustacy

pedogenic phreatic carbonates on a middle devonian givetian terrigenous alluvial deltaic plain gilwood member watt mountain formation northcentral alberta canada in the muskeg trough of northcentral alberta the gilwood member contains widespread carbonate deposits that formed within terrigenous mudstone and sandstone hosts stratigraphic depositional and petrographic relationships indicate that these carbonates represent calcretes and dolocretes calcretes observed best with cathodoluminescence display microcrystalline alpha fabrics circumgranular cracks root networks displacive growth fabrics elongate channel voids and rare coloform growths with flower spar similarly dolocretes have microcrystalline alpha fabrics brecciation gradational contacts with host mudstones extensive layered nodular horizons and are associated with anhydrite and pyrite 13c values range between 7 to 1 and 6 to 3 for calcretes and dolocretes respectively oxygen isotopes are more variable and differ with host lithologies 18o of calcretes ranges between 11 to 8 for sandstones and 8 to 3 for mudstones whereas 18o of dolocretes ranges between 3 to 1 for marine mudstones and 6 to 2 for pedogenic mudstones regional mapping indicates that calcretes thicken towards the deepest parts of the muskeg trough widespread dolocretes extend beyond the eastern and western limits of muskeg trough and are useful marker intervals for regional correlations dolocretes of restricted lateral extent are found within gleyed palaeosol mudstones next to calcretized channel sandstones calcrete isotopic values are interpreted as indicative of carbonate precipitation from waters with meteoric water input however the higher 18o values in dolocretes are indicative of a contribution from an isotopically heavier source such as seawater stratigraphically calcretes are most common along the western and northern edges of muskeg trough thus calcrete accumulation was further controlled by meteoric water in flow from the highland to the west and sluggish groundwater flow in muskeg trough in contrast regionally widespread dolocrete horizons appear to have formed from mixing of fresh waters derived from the highland to the west and seawaters introduced from the east regionally restricted dolocretes which are found next to channel sandstones formed from groundwater out flow from the permeable channel sandstones which resulted in calcretization in channel proximal mudstones and dolomitization in channel distal mudstones

physical compaction of vertic palaeosols implications for burial diagenesis and palaeo precipitation estimates burial compaction is one of several major obstacles to estimating palaeoprecipitation from depth to pedogenic carbonate in favourably preserved palaeosols palaeosols must be decompacted and the preburial depth to the pedogenic carbonate obtained vertic palaeosols may be particularly good candidates for palaeoprecipitation estimates because of their increased likelihood of preserving clastic dykes one of the best features for estimating burial compaction compaction estimates from clastic dykes and literature based depth of burial estimates suggest vertic palaeosols undergo significantly less burial compaction than may be commonly assumed late carboniferous vertic palaeosols buried to 2 5 3 0 km compacted to 93 of their original thickness in contrast clastic dykes in a nonpedogenic shale directly underlying one of the late carboniferous palaeosols records compaction to 70 of original thickness similarly obtained burial compaction and burial depth estimates for early carboniferous ordovician and proterozoic vertic palaeosols were used to test a burial compaction curve and equation specific to vertic palaeosols results suggest this vertic calibrated curve and equation can be used to estimate burial compaction for vertic palaeosols lacking clastic dykes but additional testing is needed naturally high bulk densities may have limited the compactibility of vertic palaeosols likewise high initial bulk density and an abundance of swelling clays may have severely limited the transmissivity of some vertic palaeosols as they passed from pedogenic to burial environments upon burial these vertic palaeosols may have behaved as closed systems which has implications for understanding their diagenetic modification additional efforts to understand burial compaction of vertic palaeosols also promises to improve our understanding of aquifer aquiclude and hydrocarbon reservoir seal relationships in sedimentary basins containing intercalated palaeosols

stable isotope characterization of the miocene lacustrine systems of los monegros ebro basin spain palaeogeographic and palaeoclimatic implications the lacustrine carbonate facies from three allostratigraphic units n1 n2 and n3 of miocene age in the los monegros region ebro basin are characterized isotopically the dominant facies are marls laminated limestones stromatolitic limestones massive limestones and bioturbated limestones these are associated with lacustrine sulphate deposits and distal alluvial facies palaeohydrological reconstructions of the study area are supported by the isotopic and the mineralogical composition of the carbonates massive and bioturbated limestones occupy a very similar compositional domain and have the lowest isotopic compositions of all the facies 9 18opdb 4 5 and 6 4 13cpdb 0 4 reflecting a short residence time of the water and variable commonly high influence of biogenic co2 laminated limestones and stromatolites define a comparatively enriched domain with 18o values ranging from 6 to 0 and 13c values ranging from 3 5 to 0 these values indicate stronger evaporation and enhanced 12c assimilation due to intense biological activity during periods of longer water residence time marls have isotopic values intermediate between these two domains and correspond to periods of lacustrine dilution dolomite bearing samples mainly laminated and stromatolitic facies show a 18odol cal 7 5 with respect to calcite from the same facies while 13c values show very little enrichment up to 1 the positive correlation r 0 85 between 18o and dolomite contents suggests that dolomite resulted from the progressive evaporative concentration of a single water mass and not from the mixing of waters of different compositions the dolomite is thought to be primary or at most the product of very early diagenetic processes the isotopic composition of the facies and their spatial and temporal variations depend on the depositional environment and were constrained by changing regional paleogeography isotopic trends from units n1 to n3 upper agenian vallesian period display a regular depletion in heavy isotopes that indicates a climatic change towards wetter conditions

use of micromorphology for palaeoenvironmental interpretation of complex alluvial palaeosols an example from the mill creek formation albian southwestern alberta canada abstract field observations are often not sufficient for process based interpretations of palaeosols particularly where they form parts of thick aggradational pedocomplexes within alluvial successions under such conditions micromorphology provides genetic temporal and spatial information on soil forming processes that is critical to an understanding of past environmental conditions thick alluvial successions of the albian mill creek formation contain abundant evidence of pedogenesis but few well developed palaeosol profiles and therefore provide an ideal case study in which to demonstrate the usefulness of micromorphological data for palaeoenvironmental interpretation the micromorphological features of greatest interpretive value are types of clay coatings and ferruginous segregations structure and fabric papules evidence of bioactivity and ferruginous concretions provide information on geomorphic surface stability and assist in reconstructing temporal changes in drainage conditions while individual features can provide some palaeoenvironmental information the relationships of features to one another and assemblages of features provides additional information when analysed hierarchically to establish a sequence of sedimentologic and pedogenic events a common recurring sequence of palaeoenvironmental events subject to local variations can be recognized throughout the mill creek formation the presence of illuvial clay requires that water percolated through the soil and that the soil periodically dried out so that the translocated clay was retained dark reddish clay coatings indicate clay illuviation under freely drained conditions while pale yellow and silty clay coatings suggest that phases of free drainage alternated with phases of poorly drained or saturated soil conditions the presence of iron depletion coatings iron nodules and quasiferrans indicates that these units were at least periodically saturated and the occurrence of multiple overlapping phases within single thin sections demonstrates that redox conditions fluctuated strongly suggesting development in the vadose zone recent soils containing similar assemblages of features develop under warm temperate seasonal climates alternating phases of well drained and saturated conditions on the mill creek floodplains are attributed to changing sediment supply and local palaeogeomorphology rather than to any major regional climate change this type of process based micromorphological analysis should have broad application in other complex pedogenically modified alluvial successions and similar studies would lead to a more detailed understanding of ancient palaeoenvironments

terrestrial stromatolites and laminar calcretes a review abstract laminated carbonates are prominent features of subaerial exposure profiles and many types of calcareous soils including calcretes previously much attention was given to differentiating these laminites from marine or lacustrine microbial stromatolites and oncoids however recent research has shown that many subaerial laminated carbonates are biogenically formed mainly but not wholly by microbial activity this paper reviews the criteria for distinguishing terrestrial carbonate laminites from non terrestrial stromatolites and oncoids and for differentiating biogenic from abiogenic terrestrial laminites

evolution of an ancient coastal plain palaeosols interfluves and alluvial architecture in a sequence stratigraphic framework cenomanian dunvegan formation ne british columbia canada to date discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on floodplains has primarily been from a conceptual standpoint few case studies are available against which to test ideas one hundred and thirty metres of non marine strata of the dunvegan formation were examined in 14 closely spaced sections in the canyon of the kiskatinaw river ne british columbia canada this site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments fluvial channels in the kiskatinaw river section are of two types small single storey very fine to fine grained sandstone ribbons with w t ratios 30 are interpreted as the deposits of meandering rivers filling incised valleys interchannel facies include the deposits of crevasse channels and splays lakes floodplains and palaeosols floodplain palaeosols consist of laterally heterogeneous simple palaeosol profiles and pedocomplexes similar to modern entisols inceptisols and hydromorphic soils interfluve sequence bounding palaeosols adjacent to incised valleys are laterally continuous up to 3 m thick and can be reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure colour degree of rooting and 3 micromorphological features such as evidence of bioturbation clay coatings ferruginous features and sphaerosiderite interfluve palaeosols are similar to modern alfisols and ultisols correlation of the local stratigraphic succession with the regional sequence stratigraphic framework based on 2340 well logs and 60 outcrop sections shows that the vertical changes in coastal plain character more coals and lakes vs more pedogenesis can be related to relatively high frequency base level cycles eustatic that are expressed as transgressive regressive marine cycles in downdip areas regional isopach maps show that these cycles were progressively overprinted and modified by an increasing rate of tectonic subsidence in the north and west the character of palaeosols developed on aggrading floodplains primarily reflects local sediment supply and drainage in contrast well developed interfluve palaeosols record pedogenesis during periods of reduced or negative accommodation base level fall vertical changes in floodplain palaeoenvironments and palaeosol types reflect changes in accommodation rate the detailed micromorphological analysis of interfluve palaeosols represents a powerful application of an under used technique for the recognition of key surfaces in the geological record this has broad implications for non marine sequence stratigraphy

recognition of interfluve sequence boundaries integrating paleopedology and sequence stratigraphy in shallow marine and coastal plain strata sequence boundaries are easily recognized at the base of incised valley fills between valleys however it is more difficult to recognize sequence boundaries where they are expressed as interfluve paleosols we suggest that interfluve paleosols can be most reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure color and degree of rooting and 3 micromorphological features such as bioturbation fabric clay coatings ferruginous features and siderite and barite only micromorphology permits recognition of temporal changes in drainage surface stability and protracted pauses in sedimentation that typify these surfaces this three part approach has been successfully employed to identify interfluve sequence bounding paleosols in the cenomanian dunvegan formation in alberta and british columbia canada

a hydrogeological model for the early diagenesis of late triassic alluvial sediments the late triassic mercia mudstone group of southwest britain a problematic complex arid playa floodplain aeolian deposit contains a variety of mg clays and carbonates recent interpretations have invoked marine waters as a source of mg in clays however both the mg rich clays and other early diagenetic features seen in the late triassic in europe are directly analogous to those found in the inland drainage basins of australia a simple hydrogeological model is offered based on these basins where shallow groundwater evolution takes place within the basin producing a range of early diagenetic products including groundwater dolocretes and mg clays such a model as developed in australia is probably widely applicable to ancient arid alluvial systems the mercia mudstone group is a problematic sequence of predominantly red siltstones and mudstones with minor sand dolomite and limestone intercalations ruffell 1991 it has been extensively studied in outcrops in southwest and southern britain particularly in the bristol channel area the siltstones and mudstones of late triassic age are the distal equivalents to alluvial fan deposits and are associated at least locally with lake margin and spring travertine deposits leslie et al 1992 some workers have favoured a marine influenced setting for the deposition of the mudrocks or playa lakes see review in taylor 1983 most recently they have been interpreted as the deposits of complex floodplain playa systems with a signficant aeolian input talbot et al 1994 extensive evaporites occur locally in the unit including thick halite deposits and have been interpreted as evidence of marine

syngenetic formation of grainstones and pisolites from fenestral carbonates in peritidal settings abstract experiments with unconsolidated muds and petrofabric studies of some ancient peritidal carbonate rocks suggest that intense fenestral alteration of micritic sediments can lead to the in situ formation of grainstones of diagenetic origin intermediate stages in this process have been recognized in many ancient rocks the contemporaneous diagenetic modification of such grainstones commonly results in the formation of pisoliths and associated features that mimic those found in marine pisolites as well as in pisolitic caliche deposits of either marine or meteoric origin

lacustrine and palustrine facies in the bembridge limestone late eocene hampshire basin of the isle of wight southern england abstract the carbonate lake system represented by the late eocene bembridge limestone formation isle of wight southern england comprises two main facies lacustrine and palustrine these facies are arranged vertically in transgressive regressive cycles corresponding to a model of carbonate lakes of low gradient and fluctuating margins with extensive palustrine fringes these lakes developed in a coastal plain of limited relief where two paleogeographical domains predominate a lacustrine domain is represented in northern and eastern sections in the isle of wight by cycles representing upward passage from central lacustrine sub facies marl marly limestone through marginal lacustrine sub facies biomicrite to sub facies indicative of exposure brecciated nodular limestone a palustrine domain predominant in west wight is represented by a predominantly pedogenic palustrine facies with clotted peloidal to ooidal textures and some intercalated laminated laminar calcrete horizons within the pedogenic facies textures have evolved from those of unaltered biomicrites through clotted peloidal to dense ooidal to open ooidal textures a third domain developed in close geographical proximity to more saline waters is represented by gypsiferous lake margin facies found in north wight in which microlenticular gypsum developed post depositionally as a result of evaporation following subaerial sediment exposure in the lacustrine domain there appears to be an association between cyclicity and changes in base sea level reflecting a likelihood that the lakes were part of a paralic coastal plain complex with distal marine connections alternatively the cyclicity might have developed as a result of the alternation of wetter and drier climatic periods

calcrete conglomerate case hardened conglomerate and cornstone a comparative account of pedogenic and non pedogenic carbonates from the continental siwalik group punjab india the occurrence of authigenic carbonates formed in three different environmental situations within the continental siwalik group has been used to compare the lithological and petrographic characters of the contrasted lithofacies the three lithofacies are 1 calcrete conglomerate 2 case hardened conglomerate 3 cornstone pedogenic nodular calcrete the calcrete conglomerate facies laterally intertongues with the channel conglomerates it consists of pisolites which are interpreted to have formed from carbonate rich spring waters emerging on to the gravelly substrate of dry abandoned channels the laminae characteristics of these pisolites are distinctly different from those of marine origin and also from comparable biogenic materials case hardened conglomerate occurs in the youngest part of the siwalik stratigraphic column in boulder conglomerates having limestone as the principal clast component this lithofacies has resulted from cementation of the conglomerate through continued dissolution and re precipitation of calcite by meteoric water downwards from the surface it displays a coarsely crystalline sparry calcite cement with no evidence for displacive growth or replacement by calcite cornstones nodular calcrete occur in several sedimentary cycles of the middle siwalik sub group these are immature and commonly associated with thinly bedded sandstones levee and red shales overbank this lithofacies is a result of concentration of carbonate through capillary action associated with pedogenic activity ooids developed in cornstone are essentially micritic in nature and usually composed of less than five indistinct laminae

carbonate deposition in an ephemeral siliciclastic alluvial system jurassic shuttle meadow formation newark supergroup hartford basin usa abstract nonmarine carbonate accumulation from a sedimentologic perspective has multiple possible origins clastic load springs groundwater discharge soil development biochemical seasonal changes cave speleothems and eolian influx many of these carbonates contain diagnostic textures from which origin is easy to ascertain however differentiating between clastic and spring groundwater carbonates especially in depositional systems dominated by siliciclastics is not always simple here criteria for recognition are developed subsurface hydrology and tectonic origin of the depositional basin source rocks surrounding the basin sedimentologic packaging and extent of the carbonates in question as well as their sedimentary structures and fossil content and stable isotopic analyses of the carbonates can all aid in determining carbonate origin and correctly assessing sedimentary and basin evolution the present study focuses on a nonmarine carbonate deposit found within the jurassic shuttle meadow formation of the hartford basin one of many rift basins which formed as a result of the opening of the north atlantic ocean during the late triassic to early jurassic the upper 50 m of the formation at plainville connecticut is interpreted as continental in origin and is composed of five facies red ripple cross laminated muddy siltstones to sandstones fr sr massive red siliciclastic mudstones fm buff fine to medium grained horizontally laminated sandstones sh red to white disrupted calcareous shales fl3 and rare micritic carbonates pm facies fr sr sh and fm are interpreted as an alluvial plain system in an ephemeral setting with bedload sheetflooding as the dominant depositional mechanism similar to the channel country drainage system of central australia in addition preservation of lateral accretion sandstone sheets accretionary benches indicate that the shuttle meadow alluvial system was rapidly accreting the anomalous existence of carbonate beds in facies fl3 and pm in the smf bedload dominated siliciclastic sequence is attributed mainly to the unique nature of the clastic sediment load in the basin no direct evidence for a spring groundwater input is apparent the shallow carbonate lake margin or a pond with vegetation and periodic exposure is envisioned as the depositional environment the intraclastic texture of the micrites with rare primary relict lamination indicates early diagenetic alteration from root penetration desiccation cracks and burrowing

the role of fungal biomineralization in the formation of early carboniferous soil fabrics paleosols in the lower carboniferous limestones of south wales commonly contain needle fibre calcite which is an unusual form of calcite recently shown to form by the calcification of fungal hyphae in present day soils the needle fibre calcite occurs in two associations in the paleosols as coatings on sediment grains and as rhizocretions the former can be compared with the microbial grain coatings of quaternary calcretes the latter represent the sites of fungal coats on roots and are interpreted as probable ectomycorrhizae a symbiotic fungal sheath root association these findings suggest that biomineralization was important in the formation of soil fabrics during the carboniferous as it is in present day soils

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

lateral relations of deltaic palaeosols from the lower jurassic ronne formation on the island of bornholm denmark abstract the ronne formation which crops out on the southern coast of the danish island of bornholm consists of coal bearing siliciclastic strata a major feature in these sediments is successions of different types of stacked palaeosol profiles beneath coal seams of varying thickness the most obvious and diagnostic properties of these palaeosols are the occurrence of fossil roots and the colour of the horizons penetrated by roots three types of palaeosol profiles represent an association of soils that developed on the ancient tidally influenced lower deltaic plains low relief areas were characterized by hydromorphic conditions due to poor drainage this resulted in the development of waterlogged gleysols in backswamp areas and less acid histosols in closed bays of coastal swamps in the latter case peat bogs were formed in topographically higher areas as levee banks and crevasse splays freely drained podzols developed this soil type was dominated by kaolinite in the clay fraction promoted by acid leaching the morphology and geochemistry of all palaeosols were controlled by the position of the ground water table topography climate and rate of subsidence in the podzol profiles occasional flooding resulted in the formation of spodic b horizons accumulated close to the contemporaneous water table of that time the organic rich top horizons of the podzol and histosols profiles acted as a geochemical barrier and trapped various elements litter decomposition by microorganisms in these soils resulted in a concentration of potassium at the surface thus giving an opportunity to form illite the presence of siderite in the peat bogs suggests that reducing conditions prevailed here at the time of their formation the soils were formed in a humid tropical climate this is indicated by the overall leaching pattern on cations in the podzols and histosols the accumulation of peat in the histosols and the fossil flora

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

penetrative calcretes and their stratigraphic implications multiple calcrete horizons previously considered representative of true subaerial exposures may in fact be false penetrative calcretes related to only one subaerial exposure event individual subaerial exposure periods can produce a true surficial calcrete plus a series of penetrative calcretes although penetrative calcrete horizons are not laterally traceable over long distances they are very similar to surficial calcretes are commonly found at sequence and or lithologic boundaries permeability anomalies and can be easily misinterpreted in core borings as representing individual exposure events recent penetrative calcretes are common on elevated limestone ridges of the caicos islands where roots penetrate downward seeking ground water moisture in glacial times penetrative calcretes may have been present throughout carbonate platforms as ground water levels were much lower penetrative and surficial calcretes can be differentiated by the lower concentrations of insoluble al and fe in penetrative calcretes

lacustrine deposition and related volcanism in a transtensional tectonic setting upper stephanian lower autunian in the aragon bearn basin western pyrenees spain france abstract stephanian to early autunian lacustrine series are exposed in the aragon bearn basin western pyrenees and comprise two main lithostratigraphic units that represent the unfilling of a closed lake located in a transtensional setting accompanied by extensive pyroclastic deposition the lower lacustrine unit overlies epiclastic conglomerates sandstones and siltstones and it is mainly formed of massive and laminated grey limestones laminated carbonates and grey organic rich tuffaceous siltstones a freshwater probably stratified lake with frequent depth fluctuations is proposed for this first stage limestones show very light 18 o values 10 to 14 pdb believed torepresent a primary isotopic signal which is consistent with an intracontinental setting of the basin and the influx of 18 o depleted meteoric waters derived from the adjacent hercynian mountains a wide spread pyroclastic flow deposit marks the limit with the upper lacustrine unit which comprises the following lithofacies pisolitic dolostones stromatolites massive and laminated dolostones and limestones and variegated siltstones this final stage of the lake infilling is interpreted as a shallow brackish environment the transition between both units is marked by nodular limestones and dolomitization of some limestone layers but the stable isotopic composition remains similar to the lower unit strong evaporative concentration shallow well mixed waters and re equilibration with the atmospheric reservoir are suggested by the heavier 18 o 2to 10 and 13 c 0 to 4 values in the dolomites and the heavier 13 c values in the limestones 1 5 to 2 the lacustrine episode ended with the progradation of an alluvial plain because many documented lacustrine deposits in volcanic settings are poor in carbonates the stephanian autunian series provide a case study for concomitant carbonate and pyroclastic deposition high volcanic inputs are implied by the tuffaceous facies the ubiquitous presence of volcanic and pyroclastic components in both detrital and carbonatic facies and by the numerous intercalated pyroclastic layers several criteria are applied to discriminate subaerial and sublacustrine pyroclastic fall out and flow deposits similar lake sequences are found in other stephanian autunian basins in western europe suggesting that sedimentation in the variscan continental basins reflects the dominant climate of the time

models of miocene marginal lacustrine sedimentation in response to varied depositional regimes and source areas in the madrid basin central spain abstract a succession of lake complexes formed through miocene times in the madrid basin central spain the complex formed during the aragonian stage provides an outstanding opportunity to evaluate the role of source areas and depositional regimes in the construction of coeval marginal lacustrine deposits sedimentary facies of the aragonian lake indicate a shallow lake that was fringed to the nw and s by arkosic alluvium to the n by litharenitic alluvial fans and to the ne and e by alluvial fans distally dominated by large floodplains marginal lacustrine deposits in the arkosic realm mostly consist of mg smectites and dolomite sequences that laterally interfinger with sepiolite beds which were deposited in small discontinuous ponds in the distal alluvial fan areas occasionally micaceous rich sandy streams entered the lake forming sheets at their entry points in contrast the northern margin of the lake was formed by muddy flats which were influenced by fluctuation in the water table in this setting illitic mudstones are commonly interbedded with biotite rich flood sands showing a sheet like geometry meandering channels occasionally cut into the mud flats facies assemblages on this side of the lake were mainly derived from low grade metamorphic areas to the northeast the marginal lacustrine facies consist of silty clays carbonate paleosols and paludal to lacustrine limestones these facies reflect an interfingering between the lake and a wide stream floodplain system derived from a carbonate source area the mosaic of marginal lacustrine facies in the madrid basin during the aragonian is discussed in the light of lithological and geochemical factors related to variations in source areas

nonpropagating form drag and turbulence due to stratified flow over large scale abyssal hill topography abstractdrag and turbulence in steady stratified flows over abyssal hills have been parameterized using linear theory and rates of energy cascade due to wave wave interactions linear theory has

initial stages of laminar calcrete formation by roots examples from the neogene of central spain thin carbonate laminae formed by root activity are common within miocene detrital deposits of the duero and madrid basins the laminae are about 3 cm thick extending several metres laterally and displace the original detrital sediment which ranges in grain size from fine gravel to sandy clay the thickness morphology microstructure and stable isotope compositions of the laminae indicate that they formed by the activities of roots and associated microorganisms within the soil the laminae are similar to those commonly recognised in thick laminar calcrete profiles three types of laminae are recognised differences in the micromorphology of the laminae are explained as reflecting the different organisms involved and whether calcification occurred when the root was alive or decaying the first type occurs in a profile at paracuellos the jarama where the laminae consist of a mosaic of 20 mm calcite crystals whose arrangement indicates that calcification took place in the medulla of the root and probably occurred while the plant was alive in a second type in the villacadima profile laminae comprise calcified root mats whose formation indicates the interplay of roots and fungi calcification of the cell walls and intracellular spaces took place in the cortices of the roots and not in the medullas as revealed by the presence of central pores in every calcified root a third type of lamina is recognised in profiles at vin egra de moran a and consists of mucilaginous sheets coated by needle fibre calcite crystals the occurrence of associated small root casts indicates that formation of the laminae occurred while the root was decaying and was also influenced by fungal activity these laminae occur within poorly developed soils and their formation was controlled by the relationship between sedimentation erosion and soil formation processes thus the occurrence of these laminae interbedded with detrital sediments reflects environments where sedimentation was relatively low and episodic so after the detrital sediment input surfaces were stable and root mats were able to develop renewed sedimentation accounted for the death of the root mats and the development of new ones on the new surfaces where the sedimentation rate is lower the laminae tend to amalgamate and thicker laminar calcrete profiles form with little or no interbedded detrital sediment

characterization of a double mesospheric bore over europe observations of a pair of mesospheric bore disturbances that propagated through the nighttime mesosphere over europe are presented the observations were made at the padua observatory asiago 45 9 n 11 5 e by the boston university all sky imager on 11 march 2013 the bores appeared over the north west horizon approximately 30 minutes apart and propagated towards the south east using additional satellite and radar data we present evidence indicating the bores originated in the mesosphere from a single larger scale mesospheric disturbance propagating through the mesopause region furthermore the large scale mesospheric disturbance appeared to be associated with an intense weather disturbance that moved southeastwards over the united kingdom and western europe during 10 and 11 march

carbonates in alluvial fan systems an approach to physiography sedimentology and diagenesis abstract this paper deals with the modes of accumulation and distribution of terrestrial carbonates in semi arid alluvial fluvial generally clastic sedimentary environments it is shown that composition and distribution of the carbonate phases are controlled by physical transportation energy morphological slope gradient chemical precipitation evaporization processes and biochemical interaction with the respective subenvironment of mainly cyanophytes evaluation of recent and fossil examples from semi arid alluvial settings indicate that the physical processes produce carbonate sequences which like the clastic ones are fining upward corresponding to the intermittently active sedimentation on an alluvial fan the mineralogy of the carbonates seems to depend upon disproportioning of dissolved compounds in subsurface waters in down fan directions there is obviously a shift towards more evaporitic minerals in the distal parts in favour of high mg calcite dolomite or even gypsum biochemical carbonate production is in direct correspondence with the respective sedimentary subenvironment in terms of transport energy and sediment supply there is evidence that high energy proximal regimes are producing isolated biosedimentary structures whereas low energy areas distal interchannel floodplains are favourable for continuous structures like algal stromatolites and algal mats a newly proposed classification system based upon transport precipitation mode and sediment type is thought to be more useful for environmental analysis and reconstructions than purely descriptive ones neglecting the process of formation this is especially the case for the non active phases of alluvial fans when the area of deposition is sediment starved referring to the clastics the system takes into account that there are two general carbonate groups detrital allochthonous and chemical biochemical autochthonous ones the latter may be formed within the pores of the clastic sediments or may be due to sedimentation in open water pedogenic processes may themselves be the carbonate forming factor or they may superprint non pedogenic processes

a classification of rhizogenic root formed calcretes with examples from the upper jurassic lower cretaceous of spain and upper cretaceous of southern france discussion

paleosols in shallow marine carbonate sequences abstract shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations some ancient platform sequences contain hundreds of such surfaces associated with paleosols fossil soils typically calcretes a wide range of macro and microstructures are associated with these calcretes which are reviewed profile types and stages in profile development can be defined the nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate although hydromorphic effects related to marine flooding of the platforms can modify the paleosols a potentially important use of paleosols is to define the nature of sequence boundaries several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls

trace fossils and rhizoliths as a tool for sedimentological and palaeoenvironmental analysis of ancient continental evaporite successions abstract recognition of evaporite formations from continental tertiary basins of spain provides evidence that trace fossils including rhizoliths can be abundant in some saline lake systems and their study helps in palaeoenvironmental interpretation of ancient continental evaporite sequences six main types of trace fossils have been distinguished and include 1 networks of small rhizoliths 2 large rhizoliths 3 tangle patterned small burrows 4 isolated large burrows 5 l shaped traces and 6 vertebrate tracks rhizoliths were related to both marginal areas of hypersaline lakes and lakes of moderately high saline waters in these settings pedoturbation resulted from colonization by grasses and bushes of distinct lake subenvironments the activity of burrowing invertebrate faunas was especially intense in lakes of moderately concentrated brines from which gypsum was the main evaporite mineral deposited a specific gypsum lithofacies bioturbated gypsum deposits forming thick massive beds has a widespread occurrence in many of the basins tangle patterned small burrows and minor isolated large burrows constitute the typical trace fossil types within the gypsum the traces are interpreted as having been caused by burrowing insect larvae probably chironomids coleopterans and annelids the behaviour of these organisms in recent lake environments yields information about the salinity range of lake waters from which gypsum precipitated concentration values averaging 100 150 g l may be thus deduced though some organisms involved in the formation of the traces can tolerate higher salinities the combined analysis of lithofacies and trace fossils from the lacustrine evaporite sequences contributes to the study of distinct saline lake subenvironments as well as changes in the sedimentary evolution of the lake systems consequently trace fossils can provide valuable insight for palaeoenvironmental analysis of at least some evaporite formations that accumulated in continental settings

paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks climate is a primary control on sediment flux from continental sources into sedimentary systems in warm climates siliciclastic input is greatest under highly seasonal rainfall nonseasonal conditions favor formation of end member chemical rocks perennially wet climates are conducive to coal formation whereas dry climates produce carbonates and or evaporites stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive regressive events and tectonics

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

palaeosols and late pleistocene rainfall fluctuations in the negev desert the existence of a series of palaeosols in the present day desert region of southern israel the northern negev desert 1 2 indicates recurring periods of wetter climate in the past up to seven well developed palaeosols occur within a section and each has a horizon containing soft calcium carbonate nodules 3 15 mm in diameter the palaeosols are developed within loess or fluvially redeposited loess consisting of silty clay or clayey silt the 14c ages of the uppermost three calcic horizons average 13 000 yr bp calcic horizon ch i 28 000 yr bp ch ii and 37 000 yr bp ch iii drier phases occurred between these periods of pedogenesis especially during the last glacial maximum centred at 18 000 yr bp when extensive erosion occurred analysis of the 13c content of nodule carbonates points to the occurrence of strong north south rainfall gradients during each period of calcic horizon formation which excludes the possibility of monsoonal rains contributing to the increased rainfall during these periods the palaeosols correspond to global warm phases of the last glacial period

multiple calcrete profiles in the tabernas basin southeast spain their origins and geomorphic implications the paper describes a sequence of pliocene to quaternary age calcretes developed within alluvial fan and fluvial gravels in the tabernas basin almeria province southeast spain calcrete profiles are described from sites adjacent to major tributaries of the rambla de tabernas six distinct calcrete units are identified within the basin these have variable distributions but have developed in an identifiable evolutionary sequence two pairs of calcrete units are widely present across the basin preserving two former land surfaces each of the former land surfaces has been planated and subsequently buried by alluvial fan or fluvial gravels a massive calcrete unit is present at the base of each gravel sequence immediately in contact with the underlying bedrock with a less well developed calcrete unit situated at the top of the gravel sequence the lowest two calcrete units within the basin are more spatially restricted and are confined to the floors and flanks of incised drainage lines the geochemistry macro and micromorphological properties and geomorphological positions of the calcrete units are outlined and on the basis of this information their mode of origin identified two main modes of calcrete genesis appear to be present massive calcretes situated in direct contact with bedrock are suggested to have formed by groundwater processes whilst calcretes situated at the top of gravel sequences are likely to have developed by pedogenic processes calcrete genesis is subsequently considered in the context of the reconstruction of the early phases of landscape development and is suggested to have been controlled by phases of uplift and stability within the tabernas basin 1998 john wiley sons ltd

groundwater dolocretes from the upper triassic of the paris basin france a case study of an arid continental diagenetic facies thick dolomite cemented horizons dolocretes occur within a fluvial sandstone mudstone sequence of late triassic age in the western part of the paris basin france two types of dolomites can be distinguished a nodular dolomitic beds less than a few metres thick which formed within mottled overbank siltstones and mudstones and b massive dolomite up to 16 m thick which occurs in coarse grained channel sandstones and conglomerates the majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and less commonly dolomicrite glaebules irregular spar filled cracks spheroidal dolomite silicification and vuggy porosity are locally abundant in the massive dolomite in contrast biologically induced micromorphological features such as rhizocretions and alveolar septal fabrics were observed in the thin nodular dolomite beds the dolomite is near stoichiometric well ordered and non ferroan 18o values range from 7 7 to 0 4 o pdb and 18o values range from 5 1 to 1 8 0 pdb and no obvious difference in the stable isotopic composition between both types of dolomites was observed sr isotope ratios range from 0 7101 to 0 7126 and are invariably higher than the contemporary triassic sea water a vadose pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures several features however argue against a pedogenic origin for the massive carbonates most notably the absence of biologically induced structures the occurrence in coarse grained channel and not overbank deposits and the great thickness these units are thus interpreted as groundwater in origin phreatic calcretes of quaternary age widespread in inland australia are regarded as a modern analogue for the triassic paris basin dolocretes petrographic observations argue in favour of primary proto dolomite precipitation although early diagenetic replacement of calcite by proto dolomite cannot be ruled out strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non marine continental origin for the groundwaters the poorly ordered and non stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near stoichiometric well ordered dolomite that clearly lacks evidence for pervasive recrystallization

quaternary laminar calcretes with bee nests evidences of small scale climatic fluctuations eastern canary islands spain thick laminar calcrete profiles are common on the surface of the eastern canary islands of lanzarote and fuerteventura this paper reports the study of one profile from lanzarote macher profile and one from fuerteventura tef a profile these profiles are about 2 m thick the macher profile is developed on basaltic host rocks and consists of two main horizons a lower horizon in which white veins of laminated micrite penetrate cracks and an upper laminar horizon the tef a profile is cumulative and consists from base to top of massive laminar and massive and laminar brecciated horizons highlighted in the study of these profiles are the presence of ooids the complex structure of the laminar horizons and the occurrence of fossil bee nests celliforma ooids consist of a nucleus of clay micrite and etched grains coated with envelopes of micrite and clay mainly palygorskite organic films favoured both the precipitation of carbonate and the adhesion of clays when the ooids formed in the soil the laminar horizons consist of a centimetre scale alternation of massive micrite with varied amounts of ooids and detrital grains with laminated micrite this alternation indicates the small scale periods of sedimentation erosion and soil formation in the upper part of a relatively stable surface these small scale alternations may reflect climatic vegetation changes in which arid periods are represented by micrite with ooids while laminated micrite reflects a better developed vegetation of the wet periods celliforma occur as ovoid larval cells with more or less rounded bases and a flat top the cells are about 3 cm long and 1 5 cm in diameter their wall is about 5 mm thick and is commonly laminated celliforma is interpreted as fossil nests of solitary bees their presence in the laminar horizon is evidence for the existence of a vegetation cover containing angiosperms

a holocene calcrete from north yorkshire england implications for interpreting palaeoclimates using calcretes glacial gravels of late devensian dimlington stadial age 26 000 13 000 years bp at west tanfield north yorkshire england have been cemented by carbonate rich solutions to produce a strongly indurated calcrete horizon the low mg cements occur as drusy spar needle fibres alveolar septal structures micrite and micropinnacles indicative of vadose zone cementation some complex pore partition structures attributed to precipitation along meniscus films also occur these partitions separate air dominated and water dominated microenvironments of the vadose zone the abundance of vadose fabrics shows that the accumulation is not a groundwater calcrete in addition much of the carbonate appears to have been precipitated by biological mediation carbon and oxygen isotopic data suggest that the carbonate did not form as a result of freezing as has been suggested for some arctic soil carbonates the pollen history of the area since the devensian suggests that this calcrete precipitated at low temperatures this contrasts with widely reported occurrences of calcrete in soils of hot arid or semi arid regions and suggests that palaeo calcretes should not be used as absolute palaeoclimatic indicators the unusual occurrence albeit localized of a thick calcrete under a cool and wet climate probably reflects the well drained nature of the gravels the abundance of caco3 as limestone clasts in the gravel and a high degree of biological activity beneath a forest cover which created a local environment favouring carbonate precipitation

evolution of calcrete in palaeodrainages of the lake napperby area central australia abstract carbonate lithofacies developed along the trunk valley of palaeodrainage channels as well as those adjacent to gypsite facies in the lake napperby drainage basin in central australia show wide ranges of sedimentary characteristics reflecting significant variation in depositional environments sedimentological and geochemical characterization of the calcrete lithofacies in this drainage area indicate that whereas variations in bedrock morphology are important in overall distribution of the phreatic and vadose calcrete varieties faulting and basin adjustments since the early quaternary may also have played a significant role in redistribution of the hydrologic zones and hence the evolution of these calcretes accordingly phreatic calcretes which initially precipitated from laterally moving groundwaters along the palaeodrainage channels undergo systematic mineralogical changes due to direct evaporative precipitation and diagenetic displacement replacement processes mainly dolomitization and silicification under present hydro chemical conditions within the zone of grounwater fluctuations however lateral and downward shifts in groundwater flow due to excessive volumetric expansion and reduction in effective permeability of calcrete may ultimately result in isolation of the calcrete like those observed from the eastern margins of the lake the evolution of the vadose calcretes is thereafter topographically controlled and relates to mobilization and redistribution of earlier deposited calcretes under present meteorological conditions