petrographic and geochemical analysis of caliche profiles in a bahamian pleistocene dune two caliche profiles from a pleistocene carbonate dune on san salvador island bahamas were examined by petrographic and geochemical analysis profile a is an immature buried caliche profile characterized by caliche pisolites a friable crust and abundant cerion profile b is a more well developed caliche profile at the top of the dune which contains abundant pisolites rhizomorphs laminated calcrete a breccia and abundant cerion geochemical changes in caliche profiles relative to the host rock are an increase in al2o3 fe2o3 and total organic carbon a decrease in mg and sr and a decrease in 13ccarb 18ocarb and 13corg the magnitude of these changes is probably a function of the duration of subaerial exposure and resultant colonization by dune plants and associated microflora abundance of calcified filaments and needle fibre crystals in profile a attests to the importance of microbial processes in the early development of caliche profiles biogenic structures are largely destroyed in profile b due to recrystallization but indirect evidence of biological activity is retained in the form of carbon isotope values

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

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

inversion of p wave vsp data for local anisotropy theory and case study we discuss improve and apply the slowness polarization method for estimating local anisotropy from vsp data although the idea of fitting a given anisotropic model to the apparent slownesses measured along a well and polarization vectors recorded by three component downhole geophones is hardly new we extend the area of applicability of the technique and make the anisotropic inversion more robust by eliminating the most operationally difficult and noisy portion of the data the shear waves we show that the shear wave velocity is actually unnecessary for fitting the slowness of polarization dependence of p wave vsp data for the most common geometry of a vertical borehole in a vertically transversely isotropic subsurface such data are governed by the p wave vertical velocity vp0 and two quantities vsp and vsp that describe the influence of anisotropy these quantities depend on conventional anisotropic coefficients and and absorb the s wave velocity we apply the developed theory to a 2d walka

the application of cathodoluminescence to interpreting the diagenesis of an ancient calcrete profile a laterally extensive calcrete profile has been identified in the late asbian lower carboniferous shallow marine shelf limestones of the llangollen area north wales the upper surface of the profile is defined by a laterally discontinuous palaeokarstic surface and by laminated calcareous crusts which developed within the underlying limestone the profile contains a unique series of early pore filling vadose cements which only occur down to 1 m below the palaeokarstic surface cathodoluminescence reveals that these cements pre date the late pore filling meteoric phreatic cements which occur throughout local asbian lithologies a spar cement stratigraphy has been established for the calcrete profile subaerial vadose cements comprise two generations of non luminescent cement followed by a brightly luminescent generation which occasionally shows an acicular habit this needle fibre calcite represents the final stage of vadose cementation precipitation of vadose cements was contemporary with subaerial alteration and micritization of the limestone textures visible only with cathodoluminescence provide evidence of recurrent periods of fabric dissolution the most extensive phase of dissolution occurred immediately after the precipitation of the non luminescent subaerial vadose cements several different textures have been recorded each reflecting the morphology of a partially dissolved substrate dissolution textures are generally confined to the walls of the larger pores and to early brecciation fractures these probably acted as fluid pathways in the calcrete during early subaerial diagenesis much of the non marine micrite in the calcrete profile appears as needle fibre calcite under cathodoluminescence this acicular calcite was probably formed in response to localized supersaturation of meteoric pore fluids caused by periods of near surface evaporation since needle fibre luminescence is strongly variable these ambient conditions are not believed to have directly controlled the activator ion concentrations of cementing pore waters needle fibre calcite is considered to be a cement precipitate which has almost completely recrystallized to micrite probably during the late stages of subaerial diagenesis two generations of subaerial micrite which define a micrite stratigraphy have been distinguished under cathodoluminescence reconstructing the diagenetic history of this ancient calcrete profile has revealed that subaerial alteration was multistaged with many diagenetic processes acting simultaneously during a single phase of emergence

kalahari valley calcretes their nature origins and environmental significance abstract calcretes that form in non pedogenic settings have been widely reported in the geomorphological and geological literature yet they are still poorly understood in comparison with pedogenic varieties this may be because there are assorted types of non pedogenic calcretes often loosely referred to as groundwater calcretes but encompassing groundwater phreatic open valley or confined channel calcrete types forming within vadose and phreatic environments in different geomorphological settings relatively few studies have described the detailed petrological characteristics of such calcretes leading wright and tucker calcretes international association of sedimentologists reprint series 1991 vol 2 blackwell scientific publications oxford p 10 to suggest that much more work is needed to define the groundwater calcrete facies and to devise criteria for its recognition so that the various non pedogenic calcretes can be identified within the quaternary as well as further back in the geological record most descriptions of groundwater calcretes are highly generalistic and do not take into account the variability that may occur as a result of calcretes forming in different positions within a landscape and affected by separate controls thus the range of groundwater calcretes that exists now needs to be studied individually to identify patterns within the distinct types as a step towards expanding our knowledge of the variety of non pedogenic calcretes this paper describes the petrology micromorphology and mode of development of one of these types of calcrete namely that which forms within valley locations but not in definite fluvial channels late quaternary to holocene valley calcretes are described from various dry valleys mekgacha across the kalahari region of central botswana with the majority of samples collected from trunk and tributary valleys of the okwa samples have been analysed in thin section and under scanning electron microscope in order to determine the carbonate matrix type and calcrete micromorphology in general most samples consist of grains of quartzose kalahari sand cemented by fine crystalline often glaebular grain coating and pore filling micrite cement types are fairly consistent and not as micromorphologically variable as has been noted for other kalahari calcretes biological inputs are prevalent in many samples and include networks of calcified rootlets these characteristics reflect the fact that the calcretes formed in a relatively near surface environment with relatively high rates of evaporation

building tilted transversely isotropic depth models using localized anisotropic tomography with well information tilted transverse isotropytti is increasingly recognized as a more geologically plausible description of anisotropy in sedimentary formations than vertical transverse isotropy vti a lthough model building approaches for vti media are well understood similar approaches for tti media are in their infancy even when the symmetry axis direction is assumed known we describe a tomographic approach that builds localized anisotropic models by jointly inverting surface seismic and well data we present a synthetic data example of anisotropic tomography applied to a layered tti model with a symmetry axis tilt of 45 degrees we demonstrate three scenarios for constraining the solution in the first scenario velocity along the symmetry axis is known and tomography inverts for thomsen s and parameters in the second scenario tomography inverts for and velocity using surface seismic data and vertical check shot traveltimes in contrast to the vti case both these inversions are nonunique to combat nonuniqueness in the third scenario we supplement check shot and seismic data with the profile from an offset well this allows recovery of the correct profiles for velocity along the symmetry axis and we conclude that tti is more ambiguous than vti for model building additional well data or rock physics assumptions may be required to constrain the tomography and arrive at geologically plausible tti models furthermore we demonstrate that vti models with atypical thomsen parameters can also fit the same joint seismic and check shot data set in this case although imaging with vti models can focus the tti data and match vertical event depths it leads to substantial lateral mispositioning of the reflections

early carbonate diagenetic fabrics in the rhizosphere of late pleistocene aeolian sediments analysis of a range of aeolianite deposits from the western mediterranean roquetas in southern spain and campo de tiro in mallorca and the bahamas crab cay on san salvador island has shown that biota can be important in the diagenesis of deposits in the vadose zone and this may aid in the interpretation of palaeoenvironments particularly where pedogenic calcretes are absent this paper looks at how the growth of roots into dune sediments and the associated profusion of micro fauna and micro flora can have on a local scale a profound affect on the early diagenetic and sediment fabric these fabrics are affected at three levels 1 at the site of the former root 2 directly surrounding the root the peritrophic zone and 3 from the peritrophic zone to a few tens of centimetres from the former root

human induced calcretisation in anthropogenic soils and sediments field observations and micromorphology in a mediterranean climatic zone israel abstract for over a century the study of pedogenic calcrete and its formation focuses on natural processes disregarding the possible role of humans in its formation here we present field and micromorphological evidence from archaeological and modern sites in the eastern mediterranean region israel that indicate that some specific calcretes are human induced we demonstrate that anthropogenic affected calcrete differs from natural non human induced calcrete we show that the occurrence of the human induced calcrete is spatially limited and is associated with both macro and micro scale remnants and occasionally high content of organic material we propose an operative definition for anthropogenic calcretisation as the interference of humans with a component s that influence the formation of calcrete we assume that if present day calcretised environments will retain their calcretisation prone conditions for the next 5 10 millennia a distinct calcretic morphology could become a significant terrestrial formation this discovery can be particularly useful for evaluating past human impact on the environment adding a new archaeological set of research tools that should further be developed

stable carbon and oxygen isotope signatures of pedogenic needle fibre calcite abstract carbon and oxygen isotope compositions of the needle fibre calcite nfc from two soils observed in quarries villiers and savagnier in the swiss jura mountains are used to investigate the processes involved in the formation of these calcite crystals in pedogenic environments nfc occurs in soils with different macroscopic and microscopic morphologies three groups of microscopic morphologies are distinguished simple needles sn simple needles with overgrowths sno and simple needles with nanofibres snn nanofibres being either organic or mineral in nature these groups correspond to different stages in the formation and evolution of nfc evaluation of the 13c and 18o values of nfc and late calcite cements lcc in relationship to the composition of the carbonate host rock chr and 13cdic from the soil waters indicate that both nfc and lcc are precipitated in isotopic equilibrium with the soil waters similar 13c and 18o values of the elongated nfc and the rhombohedral calcite crystals of the lcc suggest that the precipitation of these different calcite habits is not due to changes in physicochemical conditions the growth of nfc crystals inside an organic mould formed by the fungal hyphae could explain the formation of calcite crystals in the shape of a needle in isotopic equilibrium with the local environment the comparison of the 13c and 18o signatures of the various nfc morphological groups suggests that they likely evolve in the soil solution from calcite crystals liberated during the degradation of fungal hyphae walls the nfc may be a proxy of the soil conditions temperature and vegetation during its precipitation and also an indicator of biogenic fungal activity

interpretation of late quaternary climate and landscape variability based upon buried soil macro and micromorphology geochemistry and stable isotopes of soil organic matter owl creek central texas usa abstract small basin floodplain buried soils formed in association with low order tributary streams are valuable archives of past climates but have not been studied extensively in central texas usa four buried soils exposed along owl creek within the larger brazos river drainage basin were examined using soil morphology and micromorphology optically stimulated luminescence osl dating soil characterization whole soil geochemical and stable isotope analyses of soil organic matter and pedogenic carbonate these buried soils provide a record of changes in paleoecological and paleo alluvial conditions spanning 14 ky morphological and geochemical differences between buried soils reflect changes in landscape attributable to climate with a distinct 5 increase in 13 c values of soil organic matter corresponding to the holocene onset and drier conditions paleoecological reconstructions coupled with depth to bk suggest possible amounts of erosion of 1 m for each of the buried soils compilation of the proxies presented shows evidence for a cooler and wetter late pleistocene climate followed by a warmer and drier climate dominating during the holocene

oxygen and carbon isotopic composition of quaternary meteoric carbonates from western and southern europe their role in palaoenvironmental reconstruction abstract the relationship between environmental conditions and the 18 o and 13 c values of soil and groundwater carbonates in europe is poorly understood consequently the use of the isotopic composition of these carbonate palaeoclimatic indicators in european sedimentary sequences is restricted in this study we examine the 18 o and 13 c values of soil and groundwater carbonates from western and southern europe in western europe there is no relationship between carbonate 18 o values and carbonate 13 c values the 18 o values of soil carbonate appears to be driven by temperature whilst the 13 c value of soil and groundwater carbonate reflects the persistent dominance of c 3 vegetation in this region during the quaternary the 18 o and 13 c values of soil carbonates from spain and crete show a strong degree of co variance suggesting that they are being controlled by the same environmental factor this is suggested to be aridity 18 o values are controlled by soil moisture evaporation whilst 13 c value is controlled by soil moisture degassing vegetation abundance and possible c 3 c 4 vegetation inputs the paper concludes by highlighting the fact that although currently under utilised the 18 o and 13 c values of soil and groundwater carbonates have a huge potential for providing important palaeoenvironmental information from sites across europe

seismicity and faulting in the charlevoix zone of the st lawrence valley abstract continuous monitoring of the seismically active charlevoix zone since late 1977 has delineated the boundaries of the earthquake zone under the north shore and has enabled an association to be made with surface mapped faults that strike along the st lawrence valley and dip to the southeast within the active zone aseismic volumes are found under parts of the st lawrence river and another elongated zone of activity is found to the southeast on unmapped faults dipping under the river the previous suggestions that the activity is related to old rift faults which have been later weakened by a meteor impact would seem to be upheld

evaluation and joint inversion of tti velocity models with walkaway vsp in deep water offshore angola we present a case study where a multitude of walkaway vertical seismic profiling wvsp data was employed in evaluating the accuracy of anisotropic velocity models used in a prestack depth migration psdm project we integrated the wvsp traveltimes with surface seismic psdm residual moveout on migrated common image gathers cig in a joint inversion that determined the anisotropic model parameters the resulting anisotropic model significantly reduces the mis ties between the modeled and observed first arrivals in the various wvsp lines in addition to the enhancement in cig flatness and significant im provement in imaging

pedogenic carbonates on precambrian silicate rocks in south india origin and paleoclimatic significance abstract calcrete in alfisols on precambrian silicate rocks is studied here in an attempt to reconstruct paleorainfall trends in semiarid south india facies of observed carbonate accumulation are pseudomycelium calcrete nodules nodular horizons hardpan and laminar horizons based on geochemical and sr isotope tracing we relate the presence of calcrete to local geologic conditions within the precambrian basement notably discrete ca rich metamorphic outcrops and rule out eolian input micromorphologic analysis reveals a multi stage origin of the calcretes involving soil colluvial geochemical and biologic processes mostly in vadose environments preliminary u th ages of 190 200 ka obtained on calcrete nodules suggest a major phase of ca release rock weathering and precipitation during marine oxygen isotope stage 7 the calcrete thus indicates fairly stable semiarid conditions at the 200 ky time scale despite fluctuations around an annual rainfall average close to current values 700 mm the stability of the western ghats barrier as a shield to the southwest monsoon explains the long term average stability of the pedoclimatic environment in the rainshadow zone the radiometric ages suggest that weathering may occur massively at discrete intervals of geologic history during spikes of humidity in the paleoclimatic record the rest of the time is spent recycling and redistributing the products of weathering incrementally at landscape scale within seasonal cycles of a relatively stable semi arid climate dating the calcrete therefore does not equate with dating the soil but instead the residence times of nodules in a dynamic soil system in which different constituents have different turnover rates

calcretes from a palaeosinkhole in jurassic palaeokarst subbetic southern spain abstract calcretes have been recognized in the bottom of a palaeokarstic sinkhole etched into early jurassic carbonates from the subbetic southern spain these are 3 to 10 cm thick and they show an internal structure in which three units can be distinguished the lower unit is composed of alternate irregular bands of unfossiliferous micrite and sparry calcite in the micrite several features point out the activity of endolithic microorganisms as fungi and bacteria the middle unit which has a laminated structure with palisade calcite spar and some vadose silt is interpreted as a speleothem and finally the upper unit shows calcrete pisoids and rhizocretions the isotope ratio analysis gives results in which 13 c ranges from 10 1 to 10 9 and 18 o ranges from 5 7 to 7 0 these values are very similar to those from palaeosols of other ages and localities which is an important argument favouring emersion stages with continental deposition in an island with an arid or semi arid climate nevertheless these calcretes outcrop in association with a palaeokarstic relief reflecting wet climate before the calcrete formation

mineralogical geochemical and isotopic characteristics of quaternary calcretes in the adana region southern turkey implications on their origin abstract calcretes are widespread and form as nodular columnar tubular fracture infill laminated hardpan and conglomeratic crust in the adana region x ray powder diffractometry xrd scanning electron microscopy and energy dispersive analyses sem edx and differential thermal analysis thermal gravimetry dta tg reveal that calcretes and their host rock mudstones are composed predominantly of calcite and smectite respectively the other minerals determined in the samples are palygorskite quartz and feldspar palygorskite is a minor component of the calcretes the inductively coupled plasma atomic emission spectroscopy icp aes analyses reveal that the calcrete samples are characterized by high cao and loi values whereas the host rock mudstones contain relatively high values of sio 2 al 2 o 3 fe 2 o 3 and mgo the cross plots of sio 2 al 2 o 3 cao sio 2 cao mgo and cao fe 2 o 3 show positive and negative correlations their gradual change is due to the degree of the progressive calcretization causing mudstone replacement the 18 o and 13 c values range from 3 8 to 5 7 mean 4 4 and from 7 7 to 10 0 mean 8 6 pdb respectively which are consistent with values of pedogenic calcretes reported in the literature from worldwide sites the 18 o values indicate formation from meteoric water either by replacement or precipitation at estimated temperatures from 21 to 23 c the 13 c values are typical for pedogenic calcretes reflecting development under the c3 dominated vegetation cover and semiarid or seasonally arid climatic conditions

genesis of palygorskite and calcretes in pliocene eskisehir basin west central anatolia turkey abstract calcretes are common in the eskisehir province and occur as powder nodules tubes fracture infills and hard laminated crusts they are white in color and developed in the near surface setting of the pliocene reddish brown mudstones calcrete profiles consist mainly of isolated calcrete occurrences within mudstone palygorskite occurs generally as a beige colored layer in the mudstone and also as a minor component in the calcretes the calcrete nodules are roughly spherical to ellipsoidal in shape with diameters of 3 to 20 cm and are composed mainly of micrite locally recrystallized to microsparite and sparite detrital quartz and feldspar float in the micritic groundmass circumgranular cracks crumbly fractures and rhizoliths are also present xrd analyses indicate that calcrete samples are comprised mainly of calcite accompanied by small amounts of palygorskite quartz feldspar smectite chlorite and locally accessory illite and amphibole the sem tem images indicate that palygorskite fibers formed singly as bundles knitted and or matted aggregates either covering calcite crystals or smectite aggregates or as a meniscus cement between smectite flakes the latter are precipitated from meteoric water flushed through the open pore system of the sediments close to the surface based on the sem images palygorskite is presumed to have formed authigenically by direct precipitation in the vadose zone of a lacustrine environment following precipitation of calcite the 13c and 18o values of calcite indicate calcretization from meteoric soil water in an arid environment enrichment of ba sr ni and lree relative to mree hree and a negative eu anomaly reflect the fractionation of feldspar and amphibole in the parent mudstone the palygorskite associated with calcretes and mudstone was precipitated from alkaline water rich in si al fe and mg having mg rich character with a structural formula of si7 94al0 06o20mg2 96al0 99fe0 31 oh 2 oh2 4ca0 12k0 01 nh2o the required elements were derived from ophiolitic melange and volcanic units

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

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

instrumental group delay for high frequency and teleseismic p waves the instrumental group delay d d is considered here first these delays were calculated for three different recording systems that were used in a precise travel time monitoring experiment where the delays varied between 10 and 40 msec for the high frequencies of the seismograms involved a technique is demonstrated by which these delays may be readily accounted for and by which instrumental malfunctions can be readily detected second two of these systems are also currently used for the recording of short period teleseisms at the 1 sec period the group delays are from 0 3 to 0 4 sec which is significant and must be accounted for this is particularly important when these systems are used in connection with data from other systems that have different delays such as the world wide seismograph station network and canadian seismograph network stations neglecting these delays will create serious problems in seismological tomography and earthquake catalogs third for long period phases recorded by the sro type instruments the delays for the 10 to 20 sec periods are 6 to 12 sec again these are significant and must be accounted for

p wave deflection or off azimuth arrivals in the charlevoix seismic zone abstract during the months of august 1984 and october 1985 experiments were undertaken in the charlevoix seismic zone to record high frequency body waves from earthquakes the seismograms were recorded by digital three component seismographs the experiments were conducted on the north shore of the st lawrence river only and covered nine sites all but the two most northeasterly recording sites exhibited p wave arrivals that arrived from azimuths that differed from the theoretical azimuth based on the computed hypocenter station relationship these differences amounted to several tens of degrees neither the errors in hypocenter location nor in the orientation of the horizontal seismometers are believed to be the cause of this difference theoretical computations based on a two dimensional model with strong lateral velocity gradients or a discontinuity in velocity produce deviations of the direction of arrival of the p wave in a horizontal plane normal to the anomaly that can amount to several tens of degrees both the lateral gradient and discontinuity models satisfy the observed deviation of azimuth versus azimuth deflection however only the discontinuity satisfies the deflection versus hypocentral distance distribution at least for distances to 20 km comparing the observed data with the theoretical values suggests that the anomaly in velocity occurs in a near vertical plane striking parallel to the st lawrence river this is also the direction of ancient extension faults in the region other structures were introduced 350 m y ago when the charlevoix impact structure was formed a number of anorthosite bodies with very high seismic velocities also outcrop in the region because of the high frequencies involved the scale of the anomaly may well be only a few hundred meters and the anomaly may most likely be located very close to even directly beneath the station

azimuthal variations in p wave travel times and shear wave splitting in the charlevoix seismic zone abstract a significant drop of up to 1 in the seismic p travel times recorded from controlled explosions occurred in the charlevoix seismic zone csz between 1979 and 1980 the travel time data exhibited variations not only with distance but also with azimuth these variations are interpreted in terms of extensive dilatancy anisotropy eda in 1984 and 1985 shear wave splitting was observed in the csz on micro earthquake seismograms under the assumption of eda the observations are interpreted in terms of a dominant crack orientation of about 36 and a crack density of around 0 05 to 0 02 the observations from the p and s waves are not incompatible with one another

petrography micromorphology and genesis of holocene pedogenic calcrete in al jabal al akhdar sultanate of oman abstract holocene pedogenic calcrete nodules occur within quaternary terra rossa soil that fills shallow phytokarst cavities in the permian triassic carbonate sequence of al jabal al akhdar in the sultanate of oman they are preferentially clustered around plant roots and are almost wholly formed of calcite holocene pedogenic calcrete nodules developed within a mediterranean like climate that is characterized by intermittent wet and dry seasons petrographic examination revealed that the host terra rossa soil is partially calcitized and that the calcrete nodules consist of smaller coalesced diffused and or discrete granular nodules the latter consist of several types of rhizoliths floating in a groundmass formed of micrite and microspar as well as spar to a lesser extent several textures of calcrete groundmass are recognized the most common is partially neomorphosed micrite three types of rhizoliths are recognized root moulds root casts and petrified calcified root tissues the latter were developed by mimic replacement of the tissue cells by cytomorphic calcite sem investigation of the calcite forming the calcrete nodules revealed that it consists of closely stacked sheets formed of calcareous nanoglobules agglutinated by eps and entombed calcareous microbial fossils which indicate a biogenic origin the calcareous nature of the bedrock climatic conditions and prevalence of biological activities of microorganisms associated with the plant root system in the host soil have significantly controlled the development and texture of these nodules the relative abundance of scalenohedral calcite within the calcrete groundmass is attributed to the impact of mg ions and organic compounds it has been concluded that the studied pedogenic calcrete is a type of freshwater terrestrial thrombolitic microbialite this study may help improve the understanding of the palaeoenvironmental conditions of analogue fossil calcretes

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

a new form of needle fiber calcite produced by physical weathering of shells needle fiber calcite is a common crystal form in soils and sediments from diverse environmental settings and it has been used as evidence of a specific soil development either past or present however it can have either a physicochemical or a biological origin and its ubiquity prevents straightforward use as an environmental proxy in this paper we present a new form of needle fiber calcite derived neither from biologically mediated mineralization in the soil nor from physicochemical precipitation this needle fiber calcite is monocrystalline and prismatic and is associated with the physical weathering of mytilus edulis linnaeus bivalve shells found in soils from anthropic shell middens located on the northern coast of the beagle channel argentina the effects of freeze thaw cycles can be observed in the local soils and would be responsible for the release of the calcite crystals that make up the outer layer of the shell in this respect the new form of needle fiber calcite would be specific for this process in anthropogenic soils in cold climates and could provide information on past climatic conditions

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

paleosols of late pennsylvanian cyclic strata new mexico cyclically deposited siliciclastic and carbonate rocks of the late pennsylvanian virgilian holder formation of south central new mexico were deposited on a narrow shelf between the pedernal uplift and the orogrande basin in the dry canyon area sacramento mountains shelf to basin palaeotopography is indicated by onlapping beds and primary dips calcareous alteration zones are developed on the tops of major carbonate units these detailed studies confirm earlier interpretations that alteration zones represent subaerial exposure events and provide new evidence for and further documentation of a paleosol environment the paleosols contain 1 rhizoliths 2 tangential needle fibres of calcite 3 five types of alveolar texture 4 upward oriented ribbon spar 5 brownish and clear isopachous spar 6 blackened grains 7 random needle fibres of calcite 8 coated grains 9 micritized grains 10 glaebules 11 desiccation cracks 12 possible microcodium and 13 well developed laminated crusts isopachous cements upward oriented cements which mark the former tops of capillary fringes dark colour and shallow depth of penetration of rhizoliths less than 1 m indicate significant paleosol formation in waterlogged hydromorphic and drier conditions pennsylvanian palaeohydrogeology of the system is reflected in the type of paleosol alteration paleosols developed on subtidal strata and paleosols which drape tens of metres of palaeotopography indicate cyclic sedimentation was not controlled by delta lobe switching local tectonic up and down movement would be an unlikely mechanism to explain the repeated tens of metres of relative sea level fluctuation eustatic sea level fluctuations induced by late pennsylvanian gondwana glaciation probably were of the correct magnitude and frequency to have caused the holder cycles

geochemical constraints on the origin of enigmatic cemented chalks norfolk uk very hard cemented chalk stacks and crusts found locally in the upper part of the cretaceous chalk of north norfolk uk are related to solution features the solution features mainly pipes and caves formed after deposition of the overlying middle pleistocene wroxham crag probably by routing of sub glacial or glacial melt waters derived from late pleistocene glaciers new geochemical particularly stable isotope data shows that cementation of the chalks although related spatially to the solution features was not caused by glacier derived waters the carbon isotope composition of the chalk cements is typically around 9 5 indicative of biologically active soils moreover the oxygen isotope compositions of the cements around 5 are incompatible with water 18 o values much below 9 to 10 which probably precludes isotopically negative glacier derived water as resulting palaeo temperatures are below zero taken together the isotope data suggest chalk cementation occurred under interglacial conditions similar to the present dissolved calcium carbonate for cementation came from dissolution of reworked chalk in overlying mis 12 glacial tills

optically stimulated luminescence osl dating of loessic sediments and cemented scree in northwest england optically stimulated luminescence osl dates are reported for silts and very fine sands believed to be loessic sediments from northwest england at three sites loessic sediments were initially interpreted as primary aeolian deposits and at two other sites as loess incorporated into the matrix of cemented scree however the results of osl dating indicate a more complex pattern of accumulation than originally hypothesized and have prompted reconsideration of these materials whatever the process es and underlying cause s it is evident that significant amounts of soil erosion occurred on the limestone uplands earlier than previously thought all but one of the ages fall entirely within the holocene period and suggest that these deposits contain reworked rather than primary loess four of the five sites are characterized by non gaussian dose distributions and consequently equivalent doses have been estimated using a range of appropriate age models the implications of differences in the ages derived f

wettability decay in an oil contaminated waste mineral mixture with dry wet cycles the dependency of soil particle wettability on soil water content implies that soils subjected to drying wetting cycles become wettable with wetting and water repellent with drying while this has been demonstrated widely the results are contradictory when water repellent soils are subjected to a sequence of cycles added to this past wettability measurements were seldom done in batches of samples collected from the field at natural or dry water contents with little appreciation that slight particle size variations different drying wetting histories and fabric as required by different wettability measurement methods may alter the results this note presents soil particle wettability soil water content relations by means of an index test following staged drying and wetting paths over a period of 8 months for an untreated oil contaminated anthropogenic soil a mixture of slag coal particles fly ash and mineral particles from barry docks uk a site formally used for oil storage which is to be remediated and redeveloped for housing the results revealed a decrease in the water repellency and increasing mineralization and bacterial activity with the wetting and drying cycles

localized anisotropic tomography with well information in vti media we develop a concept of localized seismic grid tomography constrainedbywellinformationandapplyittobuildingvertically transversely isotropic vti velocity models in depth the goal is to use a highly automated migration velocity analysis to build anisotropic models that combine optimal image focusing withaccuratedepthpositioninginonestep welocalizetomographytoalimitedvolumearoundthewellandjointlyinvertthesurface seismic and well data well information is propagated into thelocalvolumebyusingthemethodofpreconditioning whereby model updates are shaped to follow geologic layers with spatial smoothing constraints we analyze our concept with a synthetic data example of anisotropic tomography applied to a 1d vti model we demonstrate four cases of introducing additional information in the first case vertical velocity is assumed to be known and the tomography inverts only for thomsen s and profiles using surface seismic data alone in the second case tomography simultaneously inverts for all three vti parameters including vertical velocity using a joint data set that consists of surface seismic data and vertical check shot traveltimes in the thirdandfourthcases sparsedepthmarkersandwalkawayverticalseismicprofilingvspareused respectively tosupplement the seismic data for all four examples tomography reliably recovers the anisotropic velocity field up to a vertical resolution comparable to that of the well data even though walkawayvsp hastheadditionaldimensionofangleoroffset itoffersnofurther increase in this resolution limit anisotropic tomography with well constraints has multiple advantages over other approaches anddeservesaplaceintheportfolioofmodel buildingtools

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

twelve years of geophysical research in the charlevoix seismic zone abstract various and extensive geophysical monitoring began in 1974 in the charlevoix seismic zone csz the historical record and a major earthquake in 1925 characterize this zone as the likely site of a future damaging earthquake i e m 5 5 or larger and the aim of the monitoring was to develop the capability of predicting such earthquakes the parameters studied included microseismicity seismic travel times electrical impedance vertical movement horizontal movement tilt gravity change and strain through water well level changes although no clear precursor was detected in the months before the largest seismic event that occurred during the observation period m 5 0 the multiparameter experiment provided new insights into the structure and the mechanics of this active region observations of several hundred well located microearthquakes have permitted the delineation of ancient rift faults that are now being activated by high horizontal compression the geographical extent of the zone is sharply defined by the microseismicity which occurs in an area of 35 km 80 km straddling the st lawrence river observation of p waves from accurately timed explosions and s waves from earthquakes support the hypothesis of extensive dilatancy anisotropy eda involving saturated parallel cracks in the crust the data have permitted an estimate of both crack density and the direction for the principal compressive stress in the region n 30 e changes in electrical parameters with periods of months to years were detected at five of the six magnetotelluric stations installed in the region changes in the polarization angle of the earth s electrical telluric field correlated well for seven years with calculated groundwater accumulation levels at one site electric impedance changes showed no clear correlation from station to station but changes at one station appear to correlate with a seismic p wave travel time change anomaly and with the disappearance of a negative gravity anomaly at the time of an unusual number of earthquakes in the range m 2 to 3 from mid 1976 to mid 1977 it is suggested that these correlated changes could be related to aseismic stress redistribution and fluid flow along one of the ne striking rift faults about two years before the m 5 0 earthquake in 1979 continuous monitoring of tilt surface and borehole and well water levels was carried out at a single site charlevoix geophysical observatory although there were unexplained near surface tilts of the order of the earth tide amplitude within two or three days before some earthquakes they were either not spatially coherent or were related to small unexplained temperature changes in the tiltmeter vault no intermediate term one week to one year precursors were seen against a noise level of 1 3 rad rms for near surface tilt observations and a noise level of 0 2 0 3 rad rms for borehole tilt measurements at a depth of 50 100 m the threshold of detectable tidal tilt admittance changes for the borehole tiltmeters was lowered to 2 but no significant changes were seen four coseismic changes in the levels of water in boreholes were observed all were drops in water level which were much larger than expected on the basis of elastic dislocation theory it is suggested that these could be explained either by the collapse of a dilatant zone around the respective hypocentres or by triggered aseisnuc movement on a nearby active fault borehole water level tides observed from 1980 to 1986 exhibit significant variations in amplitude and phase which are thought to be the result of time varying elastic properties in a nearby structure some constraints can now be placed on the long term deformation of the csz as a whole from tiltmeter levelling and horizontal surveys data from a levelling array observed from 1976 to 1986 puts a limit of 0 54 rad yr on the secular tilt rate at the observatory a further limit of 0 1 rad yr is provided by borehole tilt measurements over the period 1983 1986 a limit of 2 cm is placed on vertical movements northwest of the st lawrence river by levelling surveys in 1965 1978 1980 and 1982 no significant 90 confidence deviatoric strain has been detected across the csz from horizontal control surveys carried out in 1912 1919 1965 1978 and 1983 the maximum allowable long term strain rate across the csz from 1919 to 1983 is 0 16 strain yr

paleoclimatic implications of pedogenic carbonates in holocene soils of the gangetic plains india abstract this study attempts to reconstruct the holocene climatic history of the indo gangetic plains based on micromorphological characteristics and stable isotope composition of calcretes in a soil chronoassociation between the ramganga and rapti rivers the calcrete from the b2 horizon of older soils qgh4 qgh5 6500 13 500 year bp consists of septaric and irregularly shaped nodules of dense micrite and diffused needles associated with the illuvial clay pedofeatures fabric of the calcretes of older soils show inclusion of soil constituents and precipitation of carbonates in between weathered layers of micas formation of this calcrete took place during the pedogenesis in an arid to semi arid climate that also influenced vegetation and c4 type biomass such as chenopodium and typha angustata spread in the area a change to warm and humid phase at 6500 year bp led to dissolution and reprecipitation of the calcretes this led to the formation of blocky crystals and needles of calcite in voids and coarsening of the fabric in the lower horizons the vegetation pattern also changed to woodland with anogeissus and tecomella spp the younger soils bp show secondary carbonate accumulation associated mainly along the voids in lower parts of the profiles these are relatively coarse textured with little or no inclusion of soil constituents this coarse grained calcrete results from capillary rise from a fluctuating water table in a sub humid climate similar to present carbon and oxygen isotope data suggest that the formation of pedogenic carbonate in old soils qgh4 and qgh5 by evapotranspiration during arid to semi arid climate in the upper horizons the carbonates are depleted in 13c as their formation was influenced by the sparse vegetation and low soil respiration rate in the lower horizons the carbonates show enrichment of 13c due its extensive dissolution reprecipitation during the humid climate the younger soils showed the enrichment of 13c in their calcretes and support their formation from fluctuating shallow groundwater table the oxygen isotope values similar to that of meteoric water of the area indicate calcrete precipitation in equilibrium with the soil water

the biogenic origin of needle fibre calcite needle fibre calcite is one of the most ubiquitous habits of calcite in vadose environments caves deposits soil pores etc its origin either through inorganic indirect or direct biological processes has long been debated in this study investigations at 11 sites in europe africa and central america support arguments for its biogenic origin the wide range of needle morphologies is the result of a gradual evolution of the simplest type a rod this rod is the elementary brick which by aggregation and welding builds more complex needles the absence of cross welded needles implies that they are welded in a mould or under a longitudinal and unidirectional constraint before being released inside the soil pores the difference between the lengthening of the needles and the c axis can be explained by the existence of needles observed under a scanning electron microscope in organic sleeves which can act as a mould during rod growth complex morphologies with epitaxial outgrowths on straight rods cannot have grown entirely inside organic microtubes they must result from soil diagenesis after the release of straight rods in a soil free medium whisker crystals are interpreted as the result of growth and coalescence of euhedral crystals on a rod rhomb chains are considered to be the consequence of successive epitaxial growth steps on a needle during variations in growth conditions isotopic signatures for needle fibre calcite vary from 16 63 to 1 10 and from 8 63 to 2 25 for 13c and 18o respectively the absence of high 18o values for needle fibre calcite precludes a purely physicochemical origin evaporative for this particular habit of calcite as epitaxial growth cannot precipitate in the same conditions as initial needles needle fibre calcite stable isotopic signatures should be used with caution as a proxy for palaeoenvironmental reconstructions in addition it is suggested that the term needle fibre calcite should be kept for the original biogenic form the other habit should be referred to as epitaxial forms of needle fibre calcite

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