calcareous duricrust al qasim province saudi arabia occurrence and origin in al qasim province saudi arabia calcareous pedogenic duricrust overlies the upper permian carbonates and clays of the khuff formation and ranges in thickness from 60 cm to 2 m it consists of white sandy duricrust capped by brown nodular porous duricrust petrographic investigation led to recognition of three lithofacies that show spatial distribution 1 structureless sandy calcareous mudstone 2 brecciated nodular calcareous mudstone and 3 pisolitic calcareous mudstone the diagenetic changes in duricrust are aggrading neomorphism and formation of calcite rims around quartz grains microprobe chemical analysis was performed on the diagenetically altered material the development of the duricrust is controlled by four factors the climate changes the type of underlying rocks source of carbonate and biological effects the repeated changes from semi arid climate with alternating wet and dry seasons are the main controlling factor in generation of duricrust development during humid periods descending water carries the dissolved carbonates downward as bicarbonates whereas dry and interpluvial period the carbonate rich solutions are carried upwards by capillary or evaporation the claystone and sandstone interbeds possibly affect the development of calcareous duricrust more than the sandstones and dolostones because the former have the ability to attach calcium carbonate to form the duricrust the development of calcareous duricrust is mainly attributed to the pleistocene and early holocene alternating humid and arid periods that prevailed over the arabian peninsula during this time

behavior of rare earth elements in a paleoweathering profile on granodiorite in the front range colorado usa abstract a paleoweathering profile on the boulder granodiorite in northern colorado provides an opportunity to trace the behavior of rees from parent rock through a weathering profile into unconformably overlying permian sediments with progressive upward weathering of the granodiorite na2o cao sio2 ta hf co th cr sc cr th zr hf la sc zr y and la th decrease al2o3 and fe2o3t increase and tio2 mgo k2o p2o5 rb zr sc cr co hf nb ta y th u ree ti nb and zr nb increase to maximum values and then either level off or decrease lree enrichment is less in the weathering profile than in the parent granodiorite and although the parent does not have an eu anomaly or only a slight positive anomaly all samples from the weathering profile and overlying sediments have significant negative eu anomalies this observation is especially important in that it shows conclusively that a negative eu anomaly can be produced during chemical weathering of granitoids we suggest these eu anomalies are due to relative enrichment of the other rees and partial loss of eu during the breakdown of plagioclase the boulder weathering profile also has a very minor negative ce anomaly that is within error of a ce anomaly in the parent in the unweathered parent 50 of the ree are contained in sphene and in the case of la also in allanite from 10 20 of the ree are contained in apatite and biotite hornblende and from 7 10 of the hrees are in zircon with exception of eu for which feldspars contribute about 8 negligible amounts of rees occur in the feldspars in weathered samples 75 of the rees are contained in clay minerals the crossover between sphene and clay control of rees occurs over a distance of 1 m near the contact with fresh rock except for their small negative eu anomalies the clay minerals have ree patterns very similar to those of the parent rock isocon plots suggest apparent enrichments of many elements in the boulder weathering profile result from losses of na ca and si during plagioclase weathering in addition variable amounts of sr eu ta nb p and ba were lost during weathering although th u zr y th sc zr hf lu hf and ti zr may have been transferred relatively unchanged from granodiorite parent to the bulk weathering profile most other element ratios and ree distributions were significantly changed during weathering this observation implies that caution needs to be exercised when using ree patterns and element ratios to trace sediment provenance the fact that most element ratios and ree distributions also differ between fountain sediments and the bulk weathering profile may be related to one or a combination of four factors listed in order of probable decreasing importance contribution of other sources to the fountain sediments sorting of minerals during sediment deposition remobilization of elements during diagenesis and leaching of elements by water flow through the upper meter of the weathering profile

genesis of calcretes in the devonian wood bay group dicksonland spitsbergen abstract a continuous pedogenic calcrete and numerous glaebular calcretes are exposed over approximately 150 km 2 in the devonian wood bay group dicksonland spitsbergen the prominent continuous calcrete horizon is up to 4 m thick and exhibits both prismatic and knobby weathering outcrops the prismatic calcrete outcrop of approximately hexagonally arranged vertical fractures usually shows gradational contacts with the underlying sediment the calcrete and clastic sediments immediately below the gradational contact show petrographic evidence for both replacive and displacive carbonate crystallization in contrast knobby calcrete is generally lenticular and probably represents an intra formational conglomerate both the knobby and prismatic calcretes have a brecciated fabric in which low ferroan calcite fragments are cemented and bound by dolomite some of the calcite fragments are coated by concentric laminae of dolomite the glaebular calcretes are composed of low ferroan calcite nodules ranging in size from a few millimeters to approximately 6 cm and show elongation ratios of approximately 1 5 normal to bedding these nodular zones are most common in floodbasin or levee sediments in both the stjordalen formation and the upper part of the keltiefjellet formation nodular horizons occur singly and in groups and vary from a single layer of nodules to beds several meters thick calcretes are common in the old red sandstone of great britain and rare in equivalent strata in spitsbergen suggesting differences in climate or other aspects of the depositional environment

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

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

measuring stream discharge by non contact methods a proof of concept experiment this report describes an experiment to make a completely non contact open channel discharge measurement a van mounted pulsed doppler 10ghz radar collected surface velocity data across the 183 m wide skagit river washington at a usgs streamgaging station using bragg scattering from short waves produced by turbulent boils on the surface of the river surface velocities were converted to mean velocities for 25 sub sections by assuming a normal open channel velocity profile surface velocity times 0 85 channel cross sectional area was measured using a 100 mhz ground penetrating radar antenna suspended from a cableway car over the river seven acoustic doppler current profiler discharge measurements and a conventional current meter discharge measurement were also made three non contact discharge measurements completed in about a 1 hour period were within 1 of the gaging station rating curve discharge values with further refinements it is thought that open channel flow can be measured reliably by non contact methods

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

the karoo sediments late palaeozoic to early jurassic of the ogaden basin ethiopia abstract the ogaden basin is a major sedimentary basin in east africa located in the south and southeast of ethiopia covering an area of about 350 000 km 2 it contains over 5 000 m of phanerozoic sediments as evidenced by recent drilling and seismic surveying a sedimentological investigation has been carried out on cored sections of the karoo these are the oldest sediments in the basin and occur only in the subsurface karoo sediments permian to lower jurassic in the ogaden basin have an average thickness of about 800 to 1 200 m the sequence is divided into four formations from oldest to youngest the calub sandstone the bokh shale the gumburo sandstone and the adigrat sandstone continental karoo sedimentation was ended by a progressive mesozoic marine transgression which initiated the deposition of the overlying hamanlei limestone the basal calub sandstone consists of arkosic and lithic conglomerate and sandstone of alluvial fan origin it is overlain by lacustrine shale siltstone and minor sandstone of the bokh shale the remaining two formations have a transitional boundary the gumburo and adigrat sandstones are fluviatile quartzitic sandstone deposited by braided and meandering rivers respectively initially karoo sedimentation took place within an extensional rift before becoming progressively more widespread during the deposition of the gumburo and adigrat sandstone

mineralogical composition and potential sources of dust fallout deposits in kuwait northern arabian gulf abstract detailed mineralogical investigations of dust fallout deposits collected at eleven locations in kuwait during april 1979 march 1980 were carried out the mineralogy of five size fractions medium sand fine sand very fine sand coarse silt and clay was determined occurrence frequency and potential sources of the mineral grains that form the various size fractions are discussed and the gross mineralogical composition of the dust fallout calculated it was found that dust fallout deposited in kuwait is quartzitic calcareous sandy silt and is mostly derived from the dry mesopotamian flood plain in the middle and south of iraq the occurrence of sand size particles is attributed to pick up from local recent surface deposits

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

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

new geochemical and palaeontological data from the permian triassic boundary in the south african karoo basin test the synchronicity of terrestrial and marine extinctions abstract the end permian mass extinction epme is widely recognised as the largest mass extinction in phanerozoic history in marine strata the main extinction event is well constrained and has been radiometrically dated to an interval of some 60 kyr approximately 251 9 million years ago however the age and duration of the epme in the terrestrial realm as well as its possible synchronicity with that of the marine realm is debated here we shed light on issues pertaining to the identification and position of the terrestrial epme in southern africa using recently collected sedimentological facies sequences palaeontological biostratigraphic ranges geochemical stable isotope analyses and detrital zircon id tims data from a new site in the xhariep district of the south african karoo basin we demonstrate that the permian triassic boundary sequence containing evidence for phased tetrapod extinctions is time equivalent with the marine extinction we conclude that the terrestrial epme recorded in the karoo may be regarded as essentially synchronous with the epme currently defined in the marine realm and was likely the result of the same volcanically induced atmospheric disturbances this study describes the first single vertical succession of vertebrate and plant fossils that span the terrestrial permian triassic boundary that are also well constrained both by relative stable isotopes and absolute detrital zircon geochronology dating methods

calibration of a 3d hydrodynamic meandering river model using fully spatially distributed 3d adcp velocity data abstractthis study used fully spatially distributed three dimensional 3d velocity data for the improved calibration of a 3d hydrodynamic model the conventional calibration methods do not account

geochemistry of calcic horizons in relation to hillslope processes southern india abstract the study concerns chemical and mineralogical properties of calcic horizons in relation to their physical environment such as position in the soil profile and the terrain the carbonates were calcitic in upslope positions but dolomite was abundant in valley sites the content of fluorine increased downslope the distribution of the composition in the terrain indicates a sequential precipitation of calcite dolomite and fluorite from soil water and groundwater as the water flows downslope to discharge areas carbonates in vertisols formed from the more basic charnockites were of the low mg calcite type while dolomite occurred only in entisols and alfisols formed from biotite hornblende gneisses manganese in calcic horizons increased as the groundwater level was approached black intercalations in laminated petrocalcic horizons contained elevated concentrations of mn k al and si this may indicate periods of higher soil moisture and clay formation the presence of low mg calcitic carbonates overlying dolomitic ones in valley sites is likely to be due to deposition of calcite rich material from upslope the amount of soil eroded from upslope positions was between 0 2 and 2 m in four investigated profiles

alluvial sandstone composition and paleoclimate ii authigenic mineralogy abstract various empirical and theoretical arguments suggest that early formed cement in sandstone is a product of meteoric water whose chemistry is controlled by climate the nature and distribution of early silicate cement in gondwana fountain and cutler sandstone support this supposition sandstones from all three units have experienced a broadly similar diagenetic history characterized by two stages of authigenesis stage i was typified by neomorphic development of kaolinite chlorite smectite quartz and additionally in the cutler formation laumontite stage ii was dominated by replacement reactions involving the production mostly of illite iron oxide carbonate minerals and mostly in the gondwana sandstone a second generation of quartz thermodynamic relations hydrologic constraints and radiometric dating of the late stage illite indicate that early authigenesis took place within a few million years of deposition at burial depths measured in hundreds of meters consequently the nature of the silicate cement was a function of the groundwater chemistry as controlled by climate during times of relative aridity ionic concentration of the groundwater was high and high proportions of smectite chlorite and more rarely laumontite formed such was the case in petrofacies i iv v of the gondwana supergroup for a definition of gondwana petrofacies see part i of this study in the cutler fm and in the upper 150 m of the fountain fm during times of high precipitation pore water was dilute which promoted authigen c formation of kaolinite and quartz this is represented by sandstones in petrofacies ii and vi of the gondwana and by sandstones in the lower 200 m of the fountain fm illite is especially abundant as a pseudomorphic replacement of kaolinite in the older gondwana sandstones illitization apparently began at burial depths of about 1 600 m at a temperature of about 75 c illite is not common in the cutler formation and is present only in subordinate amounts in the fountain formation from the study area the 18o values of early clay cement in the gondwana sandstones range systematically from base to top from 5 00 to 13 20 the systematic variation in 18o value of gondwana clay reflects the gradual migratory drift of the gondwana harm toward lower latitudes through time average 18o values for cutler cement 13 23 and fountain cement 19 82 are greater than the analogous values for gondwana cements this is consistent with the lower latitude setting of deposition for the cutler and fountain relative to the latitudinal location of the gondwana basins however the values are anomalously lower than what have been observed in modern day neoformed clays in weathering profiles from low latitudes

biogenic β fabric features in the hard laminated crusts of the mersin and adana regions southern turkey and the role of soil organisms in the formation of the calcrete profiles abstract this paper describes fabric features and their distribution in the calcretes and emphasizes the role of soil organisms in the formation of the calcrete profiles quaternary calcretes are common in the mersin and adana provinces occurring as powdery nodular tubular fracture infill and various forms of crusts the stable isotope values indicate calcrete development under semi arid climatic conditions and a pedogenic origin biogenic or fabric constituents are abundant in the hard laminated crust these are the rhizoliths alveolar septal structures needle fiber calcites calcified filaments spherical calcite bodies microcodium and vadose calcrete pisoliths rhizoliths have mainly formed by the petrification of roots and often contain cellular cortex structures the alveolar septal structure comprises root voids separated by a micritic wall or a bundle of tangentially oriented calcite needles needle fiber calcite is common in the hard laminated crust as monocrystalline rods and polycrystalline needles monocrystalline rods are smooth and small

record of late mississippian tectonics in the new perce group visean of eastern gaspesie quebec visean clastic units and structures at the northwest margin of the upper paleozoic maritimes basin provide information on tectonic events that are only poorly recorded in more central parts of the basin these continental units are time equivalent to marine sediments of the windsor group of nova scotia they are herein assigned to the new perce group which includes the la coulee and bonaventure formations as well as a new unit the cap d espoir for mation the latter unit unconformably underlies the bonaventure formation in a small but thick sub basin of the ristigouche basin in eastern quebec it is characterized by a succession of sandstone and mudstone rhythmites that contrast with the coarse alluvial fan deposits of the overlying bonaventure formation the cap d espoir formation was sourced from a broad area of subdued topography occupied by the visean la coulee formation and underlying units erosional remnants of the la coulee formation are unconformably overlain by the bonaventure formation in marginal parts of the ristigouche basin whereas these units are separated by the cap d espoir formation in more central areas of the basin the la coulee and cap d espoir formations underwent tilting and erosion during a normal faulting event that preceded deposition of the fault controlled bonaventure formation this series of events is interpreted to represent different steps in the reactivation of a pre carboniferous dextral strike slip system in response to northwest southeast compression during the visean in gaspesie resume des unites clastiques viseennes et leurs structures intrinseques dans la marge nord ouest du bassin des mari times paleozoique superieur illustrent des evenements tectoniques qui ne sont que pauvrement enregistres dans les parties plus centrales du bassin ces unites continentales sont chronologiquement equivalentes aux sediments marins du groupe de windsor en nouvelle ecosse elles sont ici assignees au nouveau groupe de perce lequel inclut les forma tions de la coulee et de bonaventure ainsi qu une nouvelle unite la formation de cap d espoir cette derniere est re couverte en discordance par la formation de bonaventure a l interieur d un petit mais relativement epais sous bassin du bassin de ristigouche dans l est du quebec elle est caracterisee par une succession de depots rythmiques de gres et de mudstone qui contraste avec les depots grossiers de cones alluviaux de la formation de bonaventure sus jacente la formation de cap d espoir est le produit de l erosion d une region source de grande etendue et a faible gradient topo graphique laquelle etait occupee par la formation de la coulee et les unites qui lui sont sous jacentes les reliques d erosion de la formation de la coulee sont recouvertes de facon discordante par la formation de bonaventure dans les parties marginales du bassin de ristigouche alors que ces unites sont separees par la formation de cap d espoir dans les parties plus centrales du bassin les formations de la coulee et de cap d espoir ont ete basculees et partiel lement erodees a l interieur d un evenement de fracturation ayant precede le depot de la formation de bonaventure dont les facies ont ete controles par des escarpements de failles cette serie d evenements est consideree comme etant le resultat de differentes etapes dans la reactivation d un systeme de coulissage dextre pre carbonifere en reponse a des contraintes orientees nw se durant le viseen en gaspesie

calcrete and near surface geology of kuwait city and suburbs kuwait arabian gulf abstract near surface accumulation of pedogenic carbonate calcrete is a common and characteristic feature of the landscape of kuwait city and its suburbs the principal host material for these calcretes is a thick sequence of unconsolidated quartzose sand a typical fully developed soil profile can be divided into five zones in descending order these are 1 a top calcareous aeolian soil 2 a zone of friable sand with powdery or tightly cemented calcrete lumps nodules 3 a massive calcrete zone 4 a mottled calcrete zone and 5 unaltered parent material episodic formation of calcrete is indicated by the occurrence of multiple profiles in which zones are repeated calcrete ooids and pseudo ooids of accretionary origin are characteristic of the upper calcrete zone the carbonate fraction in the upper calcrete zone consists dominantly of low mg calcite with minor amounts of dolomite replacement was a major process in formation of the massive calcrete and the dominant cementing material is largely low mg calcite and or microcrystalline dolomite aeolian dust is considered to be the major source of ions for calcrete formation in kuwait city and suburbs an earlier introduced model is applied to explain the mechanisms of formation and precipitation of low mg calcite and dolomite the calcrete thickness in the study area is explained by episodic deposition of fluviatile sand and calcrete formation during the oligocene through lower miocene period

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

geochemistry and hydrodynamics in the hutt and leeman evaporitic lagoons western australia a comparative study abstract hutt and leeman lagoons in the perth basin are shallow m evaporitic basins developed as a result of ponding in a pleistocene dune terrain the contemporary lagoons are playa surfaces in which sedimentation is related to distribution and interaction of hydrologic units groundwaters seawater and lagoonal brines precipitation is restricted to ephemeral halite in ponded waters and diagenetic emplacement of caco3 and caso4 minerals in playa sediments playa surfaces predominantly below sealevel fundamentally control the lagoonal circulation system a net influx of seawater impelled by a hydrostatic head of up to 4 m is seasonally balanced by evaporative reflux

petrology of caliche derived peloidal calcirudite calcarenite in the late triassic maleri formation of the pranhita godavari valley south india abstract the maleri formation late triassic of the pranhita godavari valley south india is a continental red bed sequence represented mainly by red clays with a few sheet like bodies of channel fill sandstone crudely bedded and cross bedded peloidal calcirudite calcarenite occurs at the base of fining upward sequences in multistorey sand bodies and also as discrete solitary lenses within red clay the calcirudite calcarenite consists mainly of calcite cemented spherical peloids which are made up of micrite and microspary calcite with microfabrics characteristic of caliche pure calcitic peloids are often reddened and those having a quartzose component are generally not red the paucity of broken and abraded peloids close association with intraformational materials and other evidence indicate a local source of the peloids the microfabric of the peloids suggest their derivation from caliches available evidence favours a pedogenic origin for the peloids which mostly developed by displacive precipitation in a set up of alternate wetting and drying the lack of in situ caliche profiles in the maleri sequence and the rarity of compound grains imply that the peloids were derived from incipient caliche profiles which were localized at or near the surface and were completely stripped off by subsequent erosion the ghost caliche profiles suggest the presence of periodically stable levels in the maleri alluvial plain and low to moderate rates of alluviation the residence intervals of channels were long enough to allow incipient pedogenesis in the temporarily stable inactive areas in the present context the predominance of smectite in fines the poor floral content the maleri faunal assemblage and the paucity of evaporites point to a low seasonal rainfall in a semi arid climatic environment

geotechnical properties of calcrete soil gatch in kuwait abstract this paper presents the results of a comprehensive laboratory testing program carried out to study the geotechnical properties of gatch calcrete soil samples a total of 17 samples collected from 17 different sites in kuwait city and its suburbs were used for the study the testing program included determination of physical index and engineering properties of gatch samples the sensitivity of various geotechnical properties of compacted gatch was examined by testing specimens at various moisture contents and also at different soaking periods

characteristics evolution and distribution of quaternary channel calcretes southern jordan cemented and calcretized conglomerates of quaternary age are found within ancient river channels exposed at various heights between 1 and 125 m above the current bed of the wadi dana in southern jordan in cross section the calcrete deposits are typically lensoid in shape and are found in lling palaeochannels cut into the bedrock the fossilized channel sediments preserve evidence of past river conditions sediment loads source areas phases of river down cutting and sediment accretion as well as post depositional alteration processes samples have been analysed in thin section and under the scanning electron microscope in order to determine the calcrete micromorphology cement types and crystal sizes the results show that the river deposits have undergone signi cant displacement and replacement of the detrital grains by caco3 and this has resulted in the cementation in places of over 4 m of river material the cements display an alpha type fabric with no evidence of biogenic activity the nature of the cement fabric within and between deposits differs as a function of two key variables i the speci c location within the channel and ii height above the modern wadi oor firstly in many of the deposits cement crystal size varies with sparite dominating at depth within impermeable palaeowadi channels whereas on the anks of the channels and near the top of the channels micrite is the main type of cement these variations are thought to be a result of differences in the length of residence time of calcium carbonate rich uids in different parts of the channel and the spatially varying in uence of evaporation secondly distinct changes in cement fabric can be seen in channels of different ages with a reduction in the amount of micrite and an increase in the amount of secondary recrystallized pore lling spar over time copyright 2004 john wiley sons ltd

genesis of calcrete in quaternary soil profiles hutt and leeman lagoons western australia abstract soil profiles exposed along the margins of hutt and leeman lagoons contain a succession of calcrete horizons that exhibit oolitic pisolitic grainstone lithoclast breccia and pelloidal wackestone mudstone stone lithologies the typical coastal profile consists of an upper laminar calcrete horizon which is usually overlain by a transitional pisolitic loose soil horizon underlying the laminar calcrete is breccia and or massive calcrete downward gradation into the host is through a mottled calcrete horizon structure textures and fabrics are utilized to classify the following different calcrete types pisolitic loose soil is composed of sandy soils calcrete ooids and pisolites eolianite clasts and shell fragments laminar calcrete is composed of parallel laminated sheets of micritic carbonate that develop by segregation processes massive calcrete is dense relatively structureless calcrete with a secondary mudstone fabric resulting from diagenetic alteration of primary constituents calcrete mottles form in response to localized diagenesis in the host sediment breccia calcrete develops as a result of prolonged weathering involving repeated episodes of calcretization dissolution and brecciation diminution of permeability of the host sediment by development of massive calcrete is a major process in genesis of the profile and occurs in the lowermost part of the zone of alternate wetting and drying where the effect of water input overcomes the cumulative effects of evapotranspiration profile development is thereafter topographically controlled and restricted to horizons overlying the massive calcrete redevelopment of zones of alternate wetting and drying in older deposits may produce multiple soil profiles

river discharge measurements by using helicopter mounted radar 1 the united states geological survey and the university of washington collaborated on a series of initial experiments on the lewis toutle and cowlitz rivers during september 2000 and a detailed experiment on the cowlitz river during may 2001 to determine the feasibility of using helicopter mounted radar to measure river discharge surface velocities were measured using a pulsed doppler radar and river depth was measured using ground penetrating radar surface velocities were converted to mean velocities and horizontal registration of both velocity and depth measurements enabled the calculation of river discharge the magnitude of the uncertainty in velocity and depth indicate that the method error is in the range of 5 percent the results of this experiment indicate that helicopter mounted radar can make the rapid accurate discharge measurements that are needed in remote locations and during regional floods

diagenesis of carbonate cements in permo triassic sandstones from the iberian range spain evidence from chemical composition and stable isotopes petrographic chemical and stable isotope investigations have been made on calcite dolomite and fe dolomite ankerite from permian triassic clastic sequences from the iberian range spain calcite and dolomite cements have precipitated before the fe dolomite ankerite calcite however has also formed by calcitization of dolomite due to uplift the negative 13cpdb values 9 51 to 2 13 in these carbonates suggest derivation of carbon from oxidation of organic matter in the early carbonates and from decarboxylation of organic matter in the late fe dolomite ankerite early diagenetic dolomitic cements have heavier 13c 3 54 higher mn mn fe and mn mn mg and lower fe fe mg ratios than later diagenetic dolomitic cements the latters are also characterized by lighter 18opdb 10 64 than the early cements due to increase in temperature and to pore water mineral reactions

surficial calcareous crust of caliche type along the red sea coast egypt karstified features and surficial calcareous crust caliche develop on the upper most surfaces of the middle miocene rocks in the area between quseir and mersa alam along the red sea coast egypt detailed studies of the caliche profile revealed various textures and fabrics denoting a cyclicity in deposition as well as diagenetic differentiation crystallization and deformation the occurrence of these caliche deposits suggest that the middle miocene rocks in the study area have been subjected to alternating periods of rainfall and intense evaporation

an overview of the surface and near surface geology geomorphology and natural resources of kuwait abstract the surface and near surface geology geomorphology and natural resources of kuwait have been reviewed based on the published work the stratigraphy and structure of the near surface sediments of kuwait have been mainly controlled by the tertiary tectonic activity of the arabian shield the shield started separating from the african mainland by the close of the eocene and drifted northeastward towards the asian plate giving rise to the folding and thrusting of the zagros mountains of iran the tectonic activity superimposed a northwest southeast trend over an earlier north south structural trend and gave rise to parallel ridges and valleys trending northwest southeast through differential erosion it has been possible to identify 15 geomorphic zones and 11 morphostructures from analysis of the surface features of kuwait seven of these morphostructures can be attributed to tectonic processes and two to fluvial processes it has not been possible however to explain satisfactorily the origin of the jal az zor escarpment or the ad dalmaniyah cliff the whole of kuwait can be divided into seven drainage zones of these the internal drainage systems of the ar raudhatain umm al aish drainage system and the ad dibdibba drainage system are hydrogeologically most important the clastic deposits of kuwait group sediments often affected by low temperature carbonate calcite and dolomite and sulfate gypsum precipitation form the surface rock of kuwait these are covered by recent aeolian and residual deposits playa deposits in the enclosed basins and near the coast oolitic sediments beach sands and sabkha deposits the surface and near surface deposits of kuwait contain important reserves of construction sand and gravel as well as the only naturally occurring freshwater reserves of the country an understanding of the nature of these surface deposits is required for the management of environmental issues like sand encroachment land use planning and soil and groundwater pollution

anatomy of a mass extinction sedimentological and taphonomic evidence for drought induced die offs at the permo triassic boundary in the main karoo basin south africa abstract the southern part of the karoo basin of south africa contains a near complete stratigraphic record of the permo triassic boundary ptb isotope and magneto stratigraphy confirm that these predominantly fluvial strata are approximately the same age as zircon dated marine ptb sections 252 mya by august 2013 our team had found 579 in situ vertebrate fossils mostly of the clade therapsida in ptb exposures at three widely separated locations in the southern karoo basin biostratigraphic ranges of the various taxa found in each of the sections reveal three separate phases of die off within the same roughly 75 metre thick stratigraphic interval displaying the same sequence of sedimentary facies interpreted as indicative of climatic drying increased seasonality and the onset of an unpredictable monsoon type rainfall regime the three phases of an inferred ecologically stepped mass extinction are phase 1 45 m 30 m below ptb datum brought on by lowered watertables which led to loss of shallow rooting groundcover in the more elevated proximal floodplain areas and the disappearance of the smaller groundcover grazing herbivorous dicynodonts and their attendant small carnivores phase 2 20 0 m below ptb datum is the main extinction that occurs in massive maroon grey mudrock culminating in an event bed of laminated reddish brown siltstone mudstone couplets this facies reflects progressively unreliable rainfall leading to vegetation loss in proximal and distal floodplain areas the larger tree browsing herbivores and their attendant carnivores are confined to watercourses before finally disappearing phase 3 25 30 m above ptb datum occurs in massive maroon siltstone facies with evidence of climatic aridity including the accumulation of mummified carcasses buried by windblown dust all of the surviving permian taxa disappear within 30 m of the ptb temporal resolution based on accretion rates and pedogenic maturity of each stratigraphic section reveals that phase 1 and phase 2 die offs lasted 21 000 and 33 000 years separated by a short period of 7000 years where no disappearances are recorded and this was followed by 50 000 years of stasis for the final extinction phase lasting only 8000 years that removed all the permian survivor taxa we propose that the recorded disappearances are real rather than preferential preservation failure and that they represent drought induced die offs moving progressively up the food chain as the terrestrial ecosystem collapsed the latter mostly likely caused by volcanogenic greenhouse gas emissions and rapid global warming

pliocene pleistocene sedimentary and geomorphologic development of the vasilikos river catchment s cyprus in relation to uplift of the troodos ophiolite and climate related changes the pleistocene development of the vasilikos river exemplifies the interaction of focused tectonically induced surface uplift and climate influenced changes the resulting sediments are well exposed in vasilikos quarry and in the main river catchment further east an important erosional surface incises the highest level oldest fluvial conglomerates down into late pliocene early pleistocene open marine mudrocks nicosia formation allowing integration with the circum cyprus sedimentary geomorphic development f1 f4 stages to determine where the quarry deposits lie in relation to the vasilikos river catchment the fluvial deposits were mapped and valley profiles were constructed revealing four main episodes each associated with incision and distinctive fluvial deposition source lithology strongly influenced channel morphology infill and adjacent slope sediment colluvium composition palaeosols particularly red brown terra rossa developed on abandoned fluvial terraces and adjacent hillslopes especially overlying f3 surfaces the combined evidence allows close correlation of the vasilikos river and quarry deposits relatively coarse chalky conglomerate breccia and fine grained colluvium calcareous silt cyprus harvara developed especially on lower hillslopes following incision mainly above f2 and f3 surfaces based on regional comparisons overall sediment aggregation ended during the early pleistocene the f1 f2 surfaces and deposits are inferred to be middle pleistocene the f3 ones later middle pleistocene and the f4 ones near the middle late pleistocene boundary geomorphology and deposition were tectonically forced during strong focused early middle pleistocene surface uplift coarse clastic ruff off and palaeosol development terra rossa and related sediment aggradation are inferred to have increased during warm humid periods late pleistocene geomorphology and deposition were more influenced by climatic change with semi perennial streamflow rapid sediment aggradation and palaeosol terra rossa development during warm humid periods interglacials cooler glacial periods enhanced fluvial incision sediment bypassing and hillslope colluvial processes e g frost shattering downslope creep and mass flow when sediment transport bypassing exceeded sediment supply neotectonic faulting affected the catchment but did not greatly affect geomorphology or sediment supply although climate climate change and eustatic sea level change had an important influence tectonics is interpreted as the fundamental driver of geomorphological development and fluvial sedimentation with implications for other areas regionally to globally

calcareous crusts on exposed pleistocene limestones a case study from grand cayman british west indies abstract calcareous crusts which include laminar up to 6 cm thick and non laminar calcretes have developed on ooid grainstones and skeletal wacke pack grain floatstone in the pleistocene ironshore formation exposed at morgan s harbour tarpon springs and rogers wreck point on grand cayman british west indies non laminar calcretes which consist largely of micrite with variably altered skeletal fragments and lithoclasts derived from the host limestone contain peloids in their basal parts in contrast the laminar calcretes are formed of porous laminae and low porosity laminae calcified roots are common in the porous laminae but rare in the low porosity laminae the 18o values of calcretes from 5 22 to 0 16 have a positive correlation with the 13c values that vary from 10 03 to 6 41 at tarpon springs from 11 57 to 5 43 at morgan s harbour and from 9 89 to 8 68 at rogers wreck point the non laminar calcretes reflect progressive micritization of the bedrock with a basal peloidal zone that passes upward into the micrite zone in contrast laminar calcretes are attributed to accretionary build up dictated by microscale processes that were controlled largely by the interplay of plant roots and their associated microorganisms the positive correlation between the 18o and 13c values from the calcareous crusts indicates that evaporation influenced calcite precipitation the 13c values of the laminar calcretes record a change from vegetation dominated by c3 plants that grew in a cool wet climate to a c3 c4 vegetation that grew in a hotter drier climate the cayman calcretes resemble those found on the pleistocene miami limestone in florida and highlight the possibility that these calcareous crusts may reflect regional climates and may therefore enable regional stratigraphic correlation

hydrochemistry of surficial brines in hutt lagoon western australia abstract major elemental compositions in surficial waters collected systematically since 1981 from selected monitoring sites along the landward and seaward margins of the evaporitic hutt lagoon in western australia indicate a predictable annual concentration cycle imposed by strong seasonally defined climatic factors the amount of surface water in the lagoon is determined by a balance between influxes and evaporative reflux of solution influxes are from the sea direct precipitation subsurface input of fresh brackish groundwaters from the lagoon marginal aquifers and evaporative pumping of the concentrated brines interstitial intrastratal to lagoonal evaporitic units this balance between influx reflux budgets together with the topographic relief in the lagoon basically control the surface water circulation system in such a way that the lagoon changes from an essentially playa environment in the dry seasons to one which accomodates large ponds several decimeters in depth comparison of the chemistry of the surficial solutions in adjacent ponds indicate that the ionic concentrations in individual samples are greatly influenced by 1 the physiographic setting of the pond 2 the influx reflux relationship and 3 the types and the extent of selective ionic segregation due to processes including the common ion effect adsorption onto clayey flocculates and variation in p co 2 conditions variation in crystal habits fabrics and structural features of contemporary gypsite deposits can be directly related to seasonal changes in hydrogeochemical conditions at depositional sites therefore characterization of cyclic changes in hydrologic settings should form an integral part of the identification of formative processes and hence interpretation of palaeoenvironmental conditions

the role of detrital composition and climate on the diagenetic evolution of continental molasses evidence from the cambro ordovician guaritas sequence southern brazil abstract the cambro ordovician molassic guaritas sequence camaqua basin southern brazil comprises alluvial fan and braided fluvial sandstones and conglomerates with intercalated aeolian and lacustrine deltaic deposits and andesitic lava flows the sediments display a complex detrital composition derived from plutonic gneissic acidic volcanic and low grade metamorphic source rocks this detrital assemblage was strongly modified by semi arid continental near surface diagenesis early cementation by hematite smectite quartz and calcite and the relatively limited burial prevented strong compaction and preserved some primary macroporosity in most of the sandstones whereas the absence of early cements and or abundance of ductile grains promoted substantial porosity destruction by compaction and the inhibition of further diagenetic modifications the diagenetic dissolution and replacement of volcanic rock fragments and detrital feldspars by clays and albite changed the original framework composition as well as the tectonic provenance classification of the sandstones detailed quantitative petrographic study allowed the reconstruction of the original detrital compositions and the distinction of six different pathways of diagenetic evolution of the sandstones attesting to the efficiency of this method for diagenetic modelling and provenance analyses of ancient sandstones

two dimensional velocity distribution modeling for natural river based on uhf radar surface current abstract non contact flow measurement method plays an increasingly important role in river discharge measurement however most channel cross section velocity distribution models proposed by researchers have certain limitations in application underwater velocities are always necessary when applied in narrow channels which makes it challenging to calculate natural river discharge using water surface velocities measured by remote sensing instruments this letter takes water surface velocities detected by uhf radar as boundary conditions and a new velocity distribution model is derived based on the reynolds averaged navier stokes rans equations uhf radar measures surface velocities of the cross section and velocities on the river bed of the cross section are considered to be 0 the rans equations are simplified to be a two dimensional poisson equation and the cross section velocity distribution is solved by using the closed boundary conditions some field experiments were conducted in the hanjiang river at xiantao hubei china in september 2017 and april july 2018 the processing results of which show that the proposed model is superior to the power law and the log law models especially near the side wall narrow channel region river discharges calculated by this method are highly consistent with those provided by hubei xiantao hydrologic station which verifies the reliability of the model and the feasibility of using uhf radar to measure natural river discharge continuously and automatically

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

carboniferous calcretes in the canadian arctic calcrete palaeosols have been found in the upper carboniferous canyon fiord formation of southwestern ellesmere island canadian arctic these calcretes were developed in fluvial and shallow marine sediments that accumulated within two adjacent subbasins in which the tectono sedimentary environment led to the deposition of five different sedimentary facies i floodbasin sandstones ii alluvial fan sandstones iii alluvial fan conglomerates iv braided fluvial sandstones and v shallow marine limestones nodular massive palaeosol profiles consisting of cryptic nodular massive and laminar horizons occur within the floodbasin sandstone and alluvial fan sandstone facies plugged palaeosol profiles consisting of cryptic plugged and laminar horizons are restricted to the alluvial fan conglomerate facies massive brecciated palaeosol profiles consisting of cryptic massive brecciated and laminar horizons occur essentially within the shallow marine limestone facies the relationships between calcrete profiles and sedimentary facies suggest that profile types were controlled mainly by the texture and composition of the parent material nodular massive profiles are restricted to silicate rich sandstone hosts plugged profiles are restricted to carbonate rich conglomerate hosts and massive brecciated profiles are restricted to limestone hosts important relationships also exist between the maturity levels of nodular massive profiles and sedimentary facies profiles are generally mature in the floodbasin sandstones invariably immature in the alluvial fan sandstones and absent from the braided fluvial sandstones these different maturity levels were probably controlled mainly by exposure time vegetation and substrate composition

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

discussion of behavior of pile groups subject to excavation induced soil movement in very soft clay by d e l ong c f leung and y k chow

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

degassing water around air bubbles entrapped in the vadose zone as a mechanism of carbonate precipitation a hypothesis abstract irreversible water degassing connected with periodic entrapment of pore air and formation of bubbles after the wetting of unsaturated sediments followed by the subsequent release of air from the bubbles after the sediments dry is proposed as a possible mechanism for the precipitation of calcium carbonate in the vadose zone the process involves an initial stage during rainy periods when pore air may be entrapped due to preferential water flow in large pores equilibration of the water air system causes pressure in the entrapped air bubbles to decrease to a value close to the sum of atmospheric and capillary pressure 40 95 of atmospheric pressure this pressure decrease leads to degassing of pore water adjacent to the bubbles bubble expansion and a shift in the equilibrium of all aqueous reactions involving dissolved gases in particular the degassing must accelerate carbonate precipitation a second stage develops when entrapped air is released during lowering of the groundwater table and or drying of sediment release of entrapped air that has been subjected to a pressure lower than atmospheric should draw in a portion of free pore air towards the water air interface that free pore air has a lower gas concentration compared to that in the released air which causes fast mixing between the two in addition transfer of a portion of the degassed water towards the groundwater occurs in combination these processes cause the degassing and corresponding geochemical processes in the zone of air entrapment and release to be irreversible the proposed degassing mechanism of carbonate precipitation may take place in the wetting front zone that passes through unsaturated sediments from the land surface downwards after rainy periods this mechanism may also occur at the upper boundary of the fluctuating capillary fringe of phreatic aquifers including perched groundwater periodically formed within unsaturated sediments that lie upon more clayey less permeable layers for a sandy capillary fringe the minimum rate of carbonate precipitation by this mechanism is estimated in a wide range of 120 to 175 200 mg m 2 yr 1 at these rates within a 1 m zone of capillary fringe fluctuations sand might become cemented until pourability is lost for from 800 to 1 170 000 years

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

estimating rates of calcrete formation and sediment accretion in ancient alluvial deposits the use of calcrete horizons as a means of assessing rates of sediment accretion in ancient alluvial sequences is reviewed any attempt to use such horizons in quantifying ancient alluvial deposition must appreciate that accurate data on rates of formation of quaternary calcretes are limited such data show considerable variations in the rates and no reliable data exist at all for some calcrete types the abundance of calcretes in the geological record warrants a new initiative to improve our understanding oftheir origins and rates of formation

dolomitized calcrete in the middle devonian winnipegosis carbonate mounds subsurface of south central saskatchewan canada dolomitized calcrete is a widespread diagenetic feature in the uppermost portions of the middle devonian winnipegosis mud mounds in the subsurface of south central saskatchewan individual calcrete profiles are composed of 2 to 5 horizons including in descending order laminar crust massive pisolitic breccia chalky and transitional horizons the calcrete profiles are interpreted to be pedogenic in origin formed by diagenetic alteration of the host carbonate deposits during subaerial exposure of the mud mounds this interpretation is based on the occurrence of an orderly set of well differentiated horizons disconformities vadose pisoids micritic stringers circumgranular cracks linkage coatings and gradational contacts between the calcrete and underlying host carbonate rocks lack of root related structures such as rhizoconcretion and alveolar septal fabric in the winnipegosis calcrete suggests a limited influence of macrophytes on the formation of calcrete the occurrence of up to three discrete pedogenic calcrete profiles in a single winnipegosis calcrete succession indicates the mounds underwent three periods of subaerial exposure that resulted from drops of water level in the elk point basin of saskatchewan during middle devonian time d 2004 elsevier b v all rights reserved

a sedimentological and stable isotopic study of travertines and associated sediments within upper triassic lacustrine limestones south wales uk the upper triassic in south wales is composed of up to 100 m of red dolomitic mudstones of the mercia mudstone group which overlie and are laterally equivalent to basin margin coarse clastic deposits in the sully island and dinas powys areas a series of carbonate deposits was laid down within small basins adjacent to the main bristol channel basin the rocks consist of dolomites containing replaced evaporites overlain by perilittoral freshwater limestones the limestones are fenestral intrasparites and contain abundant pedogenic and stromatolitic horizons as well as locally developed travertines evidence for vadose diagenesis within the limestones is common the travertines consist of sheets of fibrous calcite flowstone associated with pisoids and floe calcite most of the travertines consist of single sheets several millimetres in thickness although mounds up to 1 m in height and 5 m in diameter are also present the topmost metre of the limestones which has been dolomitized is deformed into tepee and megapolygonal structures the carbon and oxygen stable isotopic composition of the limestones suggests that they were precipitated in low salinity waters successive samples from individual bands of flowstone show a covariance of 18c and 13c which is consistent with the mixing of resurgent groundwaters with pools of more evolved waters at the surface the sedimentological and geochemical evidence suggests that the limestones were deposited in a small enclosed basin fed by upwelling meteoric groundwaters in an environment distinct from that in which the laterally equivalent gypsiferous red mudstones were formed

multiple episodes of aggradation and calcrete formation in late quaternary aeolian sands central thar desert rajasthan india abstract a 12 m thick section in a dune sandy plain terrain of the central thar in rajasthan has provided a near continuous record of environmental change for the past 160 ka the site presently receives 280 mm rainfall almost entirely from the summer monsoon the base of this section comprises a gravel bed of an ephemeral stream and the overlying six litho units each with discrete boundaries comprise a succession of aeolian sands luminescence dating provided an estimate of the timing of the sand aggradation periods to 160 90 60 27 and 17 14 ka and helped constrain the timing of calcrete formation periods in each aggradation unit discrete nodular calcretes formed by the leaching of carbonate from the overlying solum this is analogous to present day conditions in sandy plains during periods of increased rainfall and landscape stability several of these calcretes are however devoid of their donor solum suggesting solum removal during a subsequent period of decreased rainfall and resultant surface instability this is supported by the presence of reworked nodules on the surfaces of some calcretes a prominent phase of calcrete development followed the aeolian sand aggradation at 60 ka suggesting climate amelioration that also caused the formation of groundwater related calcrete and mottling the study suggests that stage ii calcrete nodules form in a time frame of 10 20 ka and confirms limited data on the duration and stage of calcrete development in the literature the 13c values of calcrete carbonate lie in a narrow range 0 5 to 1 1 suggesting formation under soils with c4 vegetation this implies that even during phases of climatic amelioration the high temperatures and increased seasonality of rainfall did not permit significant development of c3 plants in the central thar

stratigraphy depositional setting and diagenetic history of the saint jules formation upper devonian or mississippian a newly identified post acadian red clastic unit in the southern gaspe peninsula quebec the saint jules formation a post acadian continental clastic unit previously mapped as part of the bonaventure formation pre namurian unit was recently identified in the southern gaspe peninsula of quebec the saint jules formation in the study area is confined to a small post sedimentary graben the unit is characterized by fault controlled oxidized and poorly sorted detritus that underwent short transportation by fluvial processes the saint jules formation is locally overlain by a massive groundwater calcrete several metres in thickness which is tenta tively correlated with the calcretization event that has affected the base of the la coulee formation grey clastics pre namurian unit the calcrete has developed within the karstified upper beds of the saint jules formation which brings new insights into the potential hosts of such calcretes and on the potential stratigraphic confusion that such diagenetic overprints can create partial erosion of both the la coulee and saint jules clastic rocks as well as the mas sive groundwater calcretes occurred prior to deposition of the bonaventure formation like the la coulee and bonaventure formations the saint jules is undated but unconformably overlies acadian structures middle devonian and predates mabou group units namurian

petrographic and geochemical features of sinkhole filling deposits associated with an erosional unconformity on grand cayman abstract on grand cayman exposures of dolostones belonging to the cayman formation miocene represent an erosional unconformity that has been developing since the late pliocene 3 6 ma sinkholes that developed during this time have remained open or become partly to fully filled with various combinations of rootcrete breccias loose limestone and dolostone lithoclasts and white red and orange limestones these sinkhole filling deposits have different geochemical attributes to the neogene and pleistocene marine carbonates that form the bedrock of the island the deposits in the sinkholes formed in response to the variations of sea level climate exposure and vegetation that developed during the period when the erosional unconformity was developing the rootcrete oncoids red and orange limestones are terrestrial in origin whereas the limestone and dolostone lithoclasts and white limestones are derived from marine deposits on the erosional unconformity intense root activity led to the formation of rootcrete and terrestrial oncoids but also selectively blackening reworked marine carbonates the red and orange limestone matrices which formed under more arid conditions contrast with the other sinkhole filling deposits that formed during periods when the climate was semi arid to humid the distinctive ree signatures of the sinkhole filling deposits which are different from those of the bedrock limestones and dolostones can probably be attributed to trace amount of terra rossa and or airborne saharan derived dust that are present in those deposits

polygenetic development of the mormon mesa nv petrocalcic horizons geomorphic and paleoenvironmental interpretations abstract mormon mesa nevada usa is of one of earth s rare and unique landforms regionally mormon mesa is important because of its relationship to the lower colorado river and its connection to stream incision petrocalcic horizons at mormon mesa developed from multiple exposure erosion and sedimentation events driven by variations in paleoclimate since the early pliocene this study utilizes pedogenic features at mormon mesa to construct a sequence of development for the soil profile we sampled and described seven profiles at mormon mesa to determine the soil and geomorphic processes that have influenced the development of this geomorphically important soil the mormon mesa soil profile generally consists of four petrocalcic soil horizons from the base upward transitional laminar massive and brecciated and an additional set of horizons that formed in unconsolidated surficial eolian sediments the transitional horizon formed after cessation of muddy creek fm deposition 5 to 4 ma and accumulated calcium carbonate to a stage ii iii morphology maybe iv in some locations after a period of landform stability the upper portion of the transitional horizon was exposed and eroded 2 8 ma petrocalcic fragments and stage ii pendants that formed in the transitional horizon were exposed on the surface and later mixed with aggrading eolian sediments after the surface re stabilized calcium carbonate accumulated along the underlying discontinuity with the transitional horizon and formed a laminar horizon shallower accumulations of calcium carbonate formed pendants on the undersides of the rotated petrocalcic fragments and pendants that had previously been eroded from the transitional horizon continued rooting and bioturbation caused rotation and multiple directions of pendant formation today in plan view these pendants appear concentric and are the pisoliths described by bachman and machette bachman g o machette m n 1977 calcic soils and calcretes in the southwestern united states usgs open file report 77 797 continued calcium carbonate precipitation eventually plugged the horizon massive horizon after the massive horizon became indurated the upper portion was exposed fractured eroded and mixed with aggrading eolian sediments these brecciated fragments experienced erosion brecciation and soil stabilization cementation with pedogenic calcite multiple times probably as a result of the pleistocene glacial interglacial climate cycles all of the features described in this study are interpreted to have formed in response to climatic changes that caused either soil erosion with concurrent eolian deposition or soil development and pedogenic carbonate accumulation it is important to understand the development of the mormon mesa soil because it can provide an understanding of the pedogenic and geologic processes that effect the development of stages v and vi soil horizons this study provides a relative sequence of events for the formation of pedogenic features at mormon mesa that can be used for future dating applications more precise dates for the development of the mormon mesa soil will contribute to our understanding of the geomorphic tectonic and climatic processes that have affected this region

newly identified carboniferous units the pointe sawyer and chemin des pecheurs formations in the gaspe peninsula quebec implications regarding the evolution of the northwestern sector of the maritimes basin the upper member of the cannes de roches formation was recently recognized overlying the bonaventure formation in the new carlisle area over 100 km southwest of the previously documented exposures of this unit moreover remnants of the la coulee formation which are unconformably overlain by the bonaventure formation have also been recognized underlying with a similar type of contact the lower member of the cannes de roches for mation from this and from facies similarities the lower and middle members of the cannes de roches formation are now considered to be equivalent to the bonaventure formation it is proposed to abandon these two member designa tions and to only keep the bonaventure formation the remaining upper member of the cannes de roches formation is renamed the pointe sawyer formation a late visean to early namurian age is attributed to this grey clastic forma tion from spore analysis dark reddish brown sandstone conformably overlie the pointe sawyer formation in the mal bay area they correspond to the beginning of sedimentation from more distant sources within the regional carbonifer ous stratigraphic succession which was until then characterized by sedimentation from proximal sources this previ ously unidentified unit is here referred to as the chemin des pecheurs formation

biogenic laminar calcretes evidence of calcified root mat horizons in paleosols laminar calcretes are described from the lower carboniferous of south wales the upper jurassic of southern england and the upper jurassic lower cretaceous of northern spain they are interpreted as calcified root mats horizontal root systems and are compared with other examples in the geological record and with possible modern analogues all three occurrences consist of virtually identical centimetre to decimetre thick locally organic carbon rich laminar micrites containing up to 50 by volume of millimetre sized typically calcite filled tubular fenestrae set in an irregular but very finely laminated matrix it is suggested that root mat calcretes are probably very common in the geological record in peritidal lacustrine margin and floodplain deposits but owing to their crudely biogenic microstructure they more closely resemble cryptalgal laminites than do other laminar calcretes the recognition of such root mat calcretes in sedimentary sequences not only provides evidence of subaerial exposure and vegetation cover but can also indicate positions of palaeo water tables in certain circumstances

kuwaiti dolocrete petrology geochemistry and groundwater origin abstract near surface sediments in southern kuwait show extensive development of duricrusts the host materials are siliciclastic sandstones of the post eocene kuwait group inland the duricrusts are dominantly pedogenic calcrete with some silcrete and gypcrete whereas within 10 20 km of the coast dolomite is the dominant duricrust mineral both these dolocretes and the inland calcretes display a similar maturation sequence in which carbonate rich nodules develop and coalesce carbonate progressively replacing and displacing detrital grains the dolomite of the dolocretes forms mosaics of crystals typically 10 70 m in size varying from simple rhombs to spherulites an intermediate morphology named artichoke dolomite from its appearance in sem is particularly abundant authigenic palygorskite is associated with the dolomite dissolution of cores or zones within dolomite crystals has occurred calcite is present as sparry crystals always post dating dolomite and is the expected precipitate from present day soil and groundwaters chemical analyses of dolomite show highly negative values of 13 c to 10 7 pdb and 18 o varying from 0 6 to 3 3 pdb the oxygen isotope values are interpreted as reflecting evaporation of a marine based fluid manganese values of around 1000 ppm show that this fluid was reducing strontium data show variability reflecting mineral fluid reactions the general absence of metastable carbonates and presence of zoning in dolomite crystals suggests that meteoric dilution of seawater also occurred given that the duricrusts lack biogenic features the light carbon isotope values are taken to indicate oxidation of seeping hydrocarbons the dolocretes are interpreted as groundwater precipitates near the water table of a brackish water body formed at a time of higher relative sea level than today

geomorphological analysis of paleo drainage systems and their environmental implications in the desert of kuwait a well developed drainage network is carved in the hard calcretized and gypcretized gravelly sand of the pleistocene dibdibba formation in northern kuwait the present day aridity suggests that these drainages were developed during pluvial episodes that took place in the post pleistocene time and therefore are considered as paleo drainage detailed morphometrical analysis of the endoeric drainage systems was performed and the degree of correlation among their different morphometric parameters was investigated based on these parameters the studied drainage basins are statistically grouped into three groups such grouping was confirmed by discriminant analysis the categorical data analysis demonstrated the dependence of these groupings on the surface geology regional topography and local geomorphological settings infiltration measurements revealed that the drainage bedrocks have a low infiltration rate 20 cm h 1 whereas the drainage fill deposits have a relatively high infiltration rate 67 30 cm h 1 the impact of the drainage system pattern and morphometry on the hydrological conditions is discussed and potential near surface low salinity to freshwater aquifers is delineated the role of the studied drainage systems in the occurrence of mobile sand and sand dunes rainwater harvesting and land capability are discussed

pleistocene terrace deposition related to tectonically controlled surface uplift an example of the kyrenia range lineament in the northern part of cyprus abstract in this study we consider how surface uplift of a narrow mountain range has interacted with glacial related sea level cyclicity and climatic change to produce a series of marine and non marine terrace systems the terrace deposits of the kyrenia range record rapid surface uplift of a long lived tectonic lineament during the early pleistocene followed by continued surface uplift at a reduced rate during mid late pleistocene six terrace depositional systems are distinguished and correlated along the northern and southern flanks of the range termed k0 to k5 the oldest and highest k0 terrace system is present only within the central part of the range the k2 k5 terrace systems formed later at sequentially lower levels away from the range the earliest stage of surface uplift k0 terrace system comprises lacustrine carbonates interbedded with mass flow facies early pleistocene the subsequent terrace system k1 is made up of colluvial conglomerate and aeolian dune facies on both flanks of the range the later terrace systems k2 to k5 each begin with a basal marine deposit interpreted as a marine transgression deltaic conglomerates prograded during inferred global interglacial stages overlying aeolian dune facies represent marine regressions probably related to global glacial stages each terrace depositional system was uplifted and preserved followed by subsequent deposits at progressively lower topographic levels climatic variation during interglacial glacial cycles and autocyclic processes also exerted an influence on deposition particularly on short period fluvial and aeolian deposition

geochemical and organic carbon isotope studies across the continental permo triassic boundary of raniganj basin eastern india abstract organic carbon isotope and geochemical changes across a continental interior permo triassic boundary section from the raniganj basin india indicate a 9 drop in organic carbon 13c in the early triassic and synchroneity of this event throughout the pangea the study demands a common causative mechanism for the perturbation of the global carbon reservoir and not a combination of multiple causes a global sea level fall and oxidation of marine gas hydrates possibly increased the 12co2 input in the ocean atmosphere system which caused a climatic shift from humid to warm semi arid type and consequent extinction of land plants simultaneous increase in erosion from near barren lands change in the erosional base level and provenance deposited the boundary sandstone with positive europium anomaly and debris flow type matrix rich conglomerate no extraterrestrial source therefore is needed to explain this eu anomaly the response of the terrestrial plant community to this perturbation of the carbon reservoir was however sluggish and the 13c drop took place slowly being maximal in the early triassic only

late pleistocene unconformity in the gulf of kavalla northern aegean greece abstract a 147 cm core from the gulf of kavalla on the northern aegean shelf displays two different lithologies separated by an erosional contact the upper part 0 128 cm consists of clayey silt to silty clay grading into silty sand and represents a neritic to nearshore marine environment the lower section 128 147 cm is a stiff calcareous mudstone with scattered microcrystalline calcite nodules and probably represents part of a subaerial soil horizon b ca seismic data indicate that at this location the unconformity between the late glacial subaerial surface and the overlying post glacial transgressive deposits occurs at a depth of 150 cm and has apparently been sampled by the core

calcretes related to phreatophytic vegetation from the middle triassic otter sandstone of south west england carbonate cementation in the triassic otter sandstone of budleigh salterton sw england occurs in two distinct forms large vertical concentrically zoned cyclinders and thin subhorizontal sheets the former represent rhizocretions of the tap roots of phreatophytic plants which colonized bars and abandoned channels on a large braidplain the sheets represent cementation around ancient water tables the precipitation of the rhizocretions took place at least in part during the life of the plants and 13c and 18o values support the view that evapo transpiration induced carbonate precipitation palaeosol profiles are rare in the otter sandstone reflecting the geomorphological instability of the braidplain surfaces in contrast rhizocretionary and sheet calcretes which formed several metres below the active depositional surface are abundant because they had a high preservation potential

pedogenetic and diagenetic fabrics in the upper proterozoic sarnyere formation gourma mali abstract several diagenetic fabrics are described in the uppermost member of the sarnyere formation an upper proterozoic dolomite 700 600 ma micronodular micrite micro sparite showing nodulisation processes orbicular crusts and oncoids are thought to be due to the pedogenetic alteration of an algal porostromata boundstone further evolution in a vadose zone creates a network of cavities which are later filled by cave stromatolites micropopcorn micrite and multilayered cements a rhythmical repetition of facies evidences a polyphased pedogenetic history leading to a 30 m thick highly complex section such numerous and diversified structures are rarely preserved especially in proterozoic rocks but each of them have equivalents in recent examples of caliche soil profiles

sedimentological characteristics of the surficial deposits of the jal az zor area kuwait abstract the purpose of this article is to discuss the nature and characteristics of the surface geology of the jal az zor escarpment and the adjacent area to better understand the sedimentology of desert landforms and the main factors controlling depositional and diagenetic processes active in this environment the oldest outcrops along the face of the escarpment are the sand and sandstone sequences of the mutla and jal az zor formations of the kuwait group neogene gravelly deposits of the upper member of the kuwait group dibdibba formation pleistocene are restricted to a few hillocks and ridges in the summit area of the escarpment the neogene deposits in most of the study area are overlain by a veneer of unconsolidated holocene sediments these were classified according to their morphological setting and field occurrence into coastal deposits intertidal mud sabkha deposits and sand dunes and inland deposits sand drifts slope deposits wadi fills residual deposits and playa deposits wind born quartzitic sand is the most common holocene sediment in the study area indicating the dominance of the aeolian processes gypsum and carbonate present as cementing materials or in the form of gypcrete and calcrete respectively are characteristic sedimentological features of the pre holocene deposits gypcrete and gypsum cement are abundant in the upper section of the escarpment and decreases downward whereas the carbonate calcrete shows a reverse pattern i e it becomes more dominant in the lower section of the escarpment the source of sulphate ions in the groundwater that is responsible for the development of gypcrete is believed to be the evaporites in the lower section of the neogene sequence the source of ions for the formation of calcrete and calcite cement is less understood due to the lack of significant primary carbonates in the near surface deposits it is believed that the nature and distribution of the chemically precipitated material gypsum and carbonates are controlled by the chemistry and hydrodynamics of the groundwater which in turn are controlled mostly by the climatic conditions during their development and the lithology of the host sediments arid and semi arid climatic and paleoclimatic conditions are considered the most critical factors affecting the depositional and diagenetic processes impacting surficial deposits of the jal az zor area

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

an overview of the tertiary geology and hydrogeology of the northern part of the arabian gulf region with special reference to kuwait abstract tertiary sediments constitute the main source of usable groundwater in kuwait tectonics depositional environment lithology and the hydrogeology of these sediments have been reviewed on a regional scale with special reference to kuwait the review showed that kuwait was situated at the boundary of the stable shelf towards southwest and the unstable shelf towards northeast throughout the tertiary period the tertiary sedimentation started in this area with a marine transgression in the palaeocene shallow marine to sabkha conditions prevailed in the area until the end of the eocene a carbonate evaporite sequence umm er radhuma rus and dammam formation was deposited during this period the sea regressed at the end of eocene and a widespread unconformity causing the absence of oligocene deposits over most of the area marked the event the karstification of the dammam limestone formation that provides localized easier pathways for ground water took place during this period the deposition of the clastic sediments of the kuwait group and its equivalents on the stable shelf under mostly continental conditions started in the early miocene the tertiary aquifers of the area are recharged by occasional rainstorms in the outcrops of saudi arabia and iraq the water flows towards the north and east in the direction of the regional dip and discharges along the present day coast of the gulf the water quality deteriorates in the same direction being more mineralized as it flows through the aquifers the aquifers are presently being exploited at a comparatively high rate since the aquifers extend beyond the political boundaries cooperation among the countries of the region is recommended to ensure the optimum utilization of the scarce water resources of this desert environment

discussion of axial compression of footings in cohesionless soils i load settlement behavior by sami o akbas and fred h kulhawy the discussers would like to commend the authors for their investigation of the characterization and parameterization of the load settlement behavior of axially loaded footings on cohesionless soils because of its importance in geotechnical practice in this discussion the discussers would like to 1 provide the results of a comparative assessment of the performance of loaddisplacement models in approximating the results of a set of fullscale load tests on large footings 2 stress the importance of investigating load displacement uncertainty by addressing quantitatively not only second moment statistics of model parameters but also the correlation between the parameters themselves and 3 examine the adequateness of load displacement models for the generation of multivariate distributions for simulation purposes a database of 30 footings on 12 different sands that were subjected to vertical loading in the field was used for these purposes the origins of these sands included natural marine deposits alluvial sediments aeolian dune sands and compacted sand fills the footings included 18 square 7 rectangular and 5 circular shallow foundations with the equivalent footing width b varying from 0 5 to 6 m only full scale foundations were considered to avert difficulties associated with 1 g model tests and scaling problems e g cerato and lutenegger 2007 a summary of the sand sites test locations sand origin index number in the database footing sizes embedment depth groundwater depth median grain size and cptu net cone tip resistance qnet representative of capacity is given in uzielli and mayne 2010 the applied stress was normalized by qnet settlement s was normalized by foundation width b three load displacement model types were considered

regional to global correlation of lower cretaceous hauterivian barremian shallow water carbonates of the southern apennines italy and dinarides montenegro southern tethyan margin abstract we propose a high resolution regional to global scale correlation of two hauterivian barremian shallow water carbonate platform sections belonging to different palaeogeographic domains of the southern margin of the tethys these successions are now located more than 500 km apart and are represented by 137 m of core drilled at monte raggeto southern apennines italy and by 80 m of well stratified rocks cropping out in the podgorica mountains dinarides montenegro they display three superimposed orders of stratigraphic cyclicity defined by elementary cycles grouped into bundles and superbundles and attributed to orbitally induced composite sea level fluctuations elementary cycles are interpreted as the precession and the obliquity periodicities 20 40 ky while bundles and superbundles correspond to the short 100 ky and long 400 ky eccentricity cycles respectively as both the ratios between the elementary cycles and the bundles and between the bundles and the superbundles do not always reflect the classical 5 1 and 4 1 relationship the sedimentary record of both the studied sections is likely to include omission of bundles or their portion the general evolution of depositional and diagenetic facies the vertical change in thickness of the cyclic units and the interpretation of superbundles as small scale depositional sequences suggest that elementary cycles and their groups are superimposed on lower frequency environmental oscillations these display an upward transgressive regressive trend t rt of the facies and testify to larger scale variations of accommodation potential on the shelf t rts sequence stratigraphic interpretation of the superbundles as well as the common occurrence of the biostratigraphic dated hauterivian barremian boundary in the studied sections support the long distance regional correlation between the successions to be carried out on the 100 ky scale moreover by assuming the maximum flooding intervals of time equivalent superbundles as virtually isochronous intervals we have detected stratigraphic gaps of 1200 and 600 ky in the monte raggeto and in the podgorica mountains sections respectively both sections are formed of 10 complete superbundles each of them testifying to the 400 ky long eccentricity hence the monte raggeto and podgorica mountains successions represent a duration of at least 4 0 my in terms of elapsed time regardless of gaps within the stratigraphic record finally a correlation between the orbitally induced compared sections and both the 3rd order tethyan stratigraphic cycles and the global cycle chart is suggested our study confirms that cyclically organized shallow marine carbonate platform deposits controlled by orbitally induced sea level fluctuations represent a powerful tool for high precision regional and global correlations this can be of fundamental importance for quantification of sedimentary diagenetic and evolutionary processes as well as for the understanding of autocyclic versus allocyclic control on sequence development

carnotite mineralization in inland drainage areas of australia abstract calcrete deposits developed adjacent to gypsite facies in arid inland drainage areas of australia contain several economic carnotite deposits major prospects and numerous minor occurrences the calcareous lithofacies located in the ponded sections of internal drainage systems are not only the main host for localization and concentration of uranium but they also offer the greatest number and variety of depositional environments for carnotite ore development factors identified as fundamental in carnotite mineralization include the physiographic and hydrologic setting of the individual uraniferous drainage systems and the solution chemistry pco2 co 3 hco 3 u v k concentrations eh ph however variation in several basic ore characteristics mineralogic textural and chemical variations radiometric disequilibrium and or distribution in some of the mineralized areas suggest that a major factor controlling the presence and ultimate extent of carnotite mineralization relates to the nature and extent of post depositional modification of earlier deposits due to changing chemical physical processes variation in the modes of carnotite precipitation relates directly to the textural and compositional characteristics of the host in different groundwater hydrologic zones hence the chemical modifications may be directly attributed to the contemporary hydrologic circulation pattern in individual drainage systems the physical processes mainly relate to the downward gradation of vadose modification into mineralized calcretes which may ultimately result in redistribution of ore zones within the drainages

the association of gold with calcrete abstract the discovery that au accumulates in calcrete pedogenic carbonate or caliche was made in 1987 by csiro calcrete is a general term describing accumulation of alkaline earth metals in soils of arid and semi arid terrains around the world the principal constituent of calcrete is calcite while au is a noble metal calcrete has been a significant tool in a number of au deposit discoveries so understanding the mechanisms by which these diametrically different components come together is valuable for enhancing future discovery numerous laboratory experiments case histories and exploration models have been published most from australia yet we do not fully understand the mechanisms involved it is timely therefore twenty five years on since the first publication of this phenomenon to review this highly unusual but economically important association critical to any review on au in calcrete is to first consider calcretes themselves the nature of a particular calcrete where it has formed and mode of formation is relevant to how where and why au accumulates within it this review commences with a background nomenclature history classification and some examples of calcrete types found near au deposits how calcretes form their origins and the role of biota is considered their locations in the regolith and landscape as well as exploration models for au in calcrete are discussed a section on the chemistry of au in calcretes details what we know about possible mechanisms of formation and considers what laboratory experiments on microorganisms and abiotic experiments tell us following on is a summary of practical aspects of identifying collecting and analysing samples for exploration purposes selected mineral exploration case histories are described and how they fit into models of exploration and different regolith settings concluding sections include a summary and implications of this accumulated knowledge to discovering au deposits

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