paragenetic and mineral chemical relationships in orthoamphibole bearing gneisses from enderby land east antarctica a record of proterozoic uplift abstract polymetamorphic orthoamphibole bearing gneisses from the vicinity of shear zones in casey bay enderby land antarctica record both the overprinting of archaean granulite lithologies by proterozoic metamorphism and the subsequent evolution of the latter episode during localized deformation mineral chemistry and zoning relationships in orthoamphibole garnet kyanite quartz and later orthoamphibole garnet cordierite quartz assemblages are used together with interpretation of reaction and corona textures to constrain the proterozoic pressure temperature path experienced by the rocks consideration of reaction topologies p t x fe mg a1 relationships in orthoamphibole bearing assemblages and standard geothermobarometry indicate that the gneisses underwent a near isothermal decompression p t history steep positive dp dt from 8 kbar and 700 c to 5 5kbar and 650 c this uplift path is correlated with the general effects of rayner complex metamorphism and deformation which occurred after 1100 ma in a major erogenic belt south of casey bay

paragenetic relations in gedrite cordierite staurolite biotite sillimanite kyanite gneisses at ajitpura rajasthan india aluminous parageneses containing gedrite cordierite garnet staurolite biotite sillimanite kyanite quartz or spinel plus corundum are found as dark colored lenses in the polymetamorphic multideformed archean complex at ajitpura in northwest peninsular india staurolite like kyanite is a relict phase of earlier metamorphism and is excluded as a paragenetic mineral in view of its incompatibility with quartz and gedrite and its lower xmg values than for garnet of the assemblage its stability here is attributed to zinc content of up to 3 wt the xmg in other ferromagnesian minerals decreases in the order cordierite biotite gedrite garnet as found elsewhere in high grade rocks

garnet orthopyroxene bearing granulites from enderby land antarctica metamorphic pressure temperature time evolution of the archaean napier complex

late proterozoic high pressure granulite facies meta morphism in the north east ox inlier north west ireland high pressure granulite facies gneisses in the ne ox inlier in nw ireland have undergone extensive caledonian retrogression in the local area of slishwood however reworking was negligible and the gneisses psammites semipelites pelites metabasites and ultramafites preserve evidence of p t changes at high grade which mainly post date pre caledonian polyphase deformation temperatures reached 850 900 c based on garnet clinopyroxene geothermometry and the presence of mesoperthite during and after decompression from earlier eclogite facies conditions inferred from textural evidence of plagioclase release in sieve textured augite subsequent cooling at high pressure is inferred from the unequivocal replacement of sillimanite by kyanite a sm nd mineral isochron gt cpx plag wr of 605 37 ma is taken to date a point on the cooling path and confirms the hitherto suspected pre caledonian age of the high grade metamorphism geochemical and sm nd isotopic data indicate that the protoliths were probably late proterozoic arkosic sediments and tholeiites following metamorphism they apparently came to reside near the base of the crust where they slowly cooled the eventual exhumation of these gneisses is attributed to caledonian crustal imbrication followed by rapid isostatic recovery

solid phase phosphorus pools in highly organic carbonate sediments of northeastern florida bay currently few studies have investigated sediment phosphorus p pools or identified the chemical processes important in the p cycle of fine grained carbonate sediments particularly in coastal estuaries with high organic matter to determine the role of fine grain calcium carbonate and high organic matter on sedimentary p we investigated the solid phase p pools in seagrass sediments of north eastern ne florida bay at the bay mangrove ecotone sediments were fractionated by sequential extractions into seven chemically defined groups exchangeable inorganic and organic p reducible inorganic and organic p fe bound acid extractable inorganic and organic p ca bound and residual organic p calcium bound p accounted for approximately 56 of total p and 96 of inorganic p our total calcium bound p was in the range 34 151 gpg 1 reported for coarse grained low organic sediments while the organic p associated with this fraction was slightly 10 higher than those reported for other carbonate systems the second dominant p fraction was residual organic p 30 71 gpg 1 accounting for 42 of tp this high residual pool suggests the importance of fringing mangrove and seagrass detritus in long term p storage in contrast to temperate estuaries the iron bound p fraction in ne florida bay sediments was low 70 gg 1 at the surface and undetectable 1 gg 1 below 10 cm based on our findings we hypothesize that carbonate chemisorption reactions along with potential reactive organic surfaces and the sequestering of p into recalcitrant organic pools maintain low exchangeable and pore water p concentrations across the ne florida bay estuary and account for the reported autotrophic p limitation 2001 academic press

comprehensive chemical analyses of natural cordierites implications for exchange mechanisms abstract cordierite samples from pegmatites and metamorphic rocks have been analysed for major electron microprobe analysis empa and trace elements inductively coupled plasma mass spectrometry icp ms secondary ion mass spectrometry analyses sims as well as for h 2 o and co 2 coulometric titration and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant apart from the homovalent substitutions femg 1 and mnmg 1 on the octahedral site some minor kna 1 on the ch0 channel site and fe 3 al 1 on the t 1 1 tetrahedral site the three most important substitution mechanisms are those for the incorporation of li on the octahedral sites nali 1 mg 1 and of be and other divalent cations on the tetrahedral t 1 1 site nabe 1 al 1 and na mg fe 2 1 al 1 the dominant role of the last vector is clearly demonstrated we propose a new generalized formula for cordierite ch na k 0 1 vi mg fe 2 mn li 2 iv si 5 iv al 3 iv al be mg fe 2 fe 3 o 18 x ch h 2 o co 2 our results show that the population of mg fe 2 on the t 1 1 site is limited to about 0 08 a p f u other exchange mechanisms that were encountered in experiments operate only under p t conditions or in bulk compositions that are rarely realized in nature routine analyses by electron microprobe in which li and be are not determined can be plotted as mg fe mn versus si al to assess whether significant amounts of li and be could be present these amounts can be calculated as li a p f u al na 4 and be a p f u 10 2al m 2 na

controls on phosphorus concentration and accumulation in oceanic sediments understanding phosphorus p sedimentation in the ocean is important both for quantifying outputs in the marine phosphorus cycle and for determining the controls on phosphogenesis the authigenic formation of carbonate fluorapatite and phosphorite deposition large accumulations of p rich sediments on continental margins in this study i have compiled literature data on sedimentary p concentrations and sedimentation rates from continental margins phosphogenic continental margins and open ocean environments i have also calculated p accumulation rates the product of p concentration sediment density and sedimentation rate in these settings sedimentary p concentrations exhibit a similar range in a wide variety of oceanic environments and sedimentation rate conditions for example p concentrations in continental margin sediments range from 8 to 108 mol p g 1 with sedimentation rates from 80 to 8 000 m my 1 in open ocean sediments the p concentration range is similar 7 307 mol p g 1 even though sedimentation rates are generally about 100 times lower 2 50 m my 1 the exception to this are phosphogenic environments where p concentrations are exceptionally high 580 3 700 mol p g 1 while sedimentation rates are relatively low 20 310 m my 1 phosphorus accumulation rates appear to be controlled by sedimentation rate in ocean sediments although p concentrations generally exhibit similar ranges the large difference in sedimentation rates between various environments results in p accumulation rates that are several orders of magnitude higher in continental margins 90 8 000 mol p cm 2 kyr 1 compared to open ocean sediments 2 75 mol p cm 2 kyr 1 in the case of phosphogenic environments low sedimentation rates result in p accumulation rates 80 6 300 mol p cm 2 kyr 1 that are surprisingly similar to those of non phosphogenic continental margin sediments

the phosphorus cycle in coastal marine sediments the concentration of dissolved phosphate in sediment box cores from the laurentian trough in the gulf of st lawrence increased sharply across the sediment water interface from 2 0 mol po4 1 in the bottom water to 6 3 mot po4 1 in the top cm remained almost constant at this value down to 5 15 cm depth and then increased rapidly with further depth in the region of constant concentration phosphate is buffered by sorption equilibria with the sediment the production rate of phosphate the sorption capacity of the sediment and the thickness of the diffusive boundary layer at the sediment water interface appear to control the shape of the pore water profile even though the buffering places an upper limit on the concentration gradient across the sediment water interface and hence on the flux the phosphate flux to the overlying water is controlled by the production rate of phosphate within the sediment a model is proposed to relate sediment chemistry to phosphorus fluxes

geochemistry of archean shales from the pilbara supergroup western australia archean clastic sedimentary rocks are well exposed in the pilbara block of western australia shales from turbidites in the gorge creek group ca 3 4 ae and shales from the whim creek group ca 2 7 ae have been examined the gorge creek group samples characterized by muscovite quartzchlorite mineralogy are enriched in incompatible elements k th u lree by factors of about two when compared to younger archean shales from the yilgarn block alkali and alkaline earth elements are depleted in a systematic fashion according to size when compared with an estimate of archean upper crust abundances this depletion is less notable in the whim creek group such a pattern indicates the source of these rocks underwent a rather severe episode of weathering the gorge creek group also has fairly high b content 85 29 ppm which may indicate normal marine conditions during deposition rare earth element ree patterns for the pilbara samples are characterized by light ree enrichment lanybn 7 5 and no or very slight eu depletion eueu 0 82 0 99 a source comprised of about 80 felsic igneous rocks without large negative eu anomalies felsic volcanics tonalites trondhjemites and 20 mafic ultramafic volcanics is indicated by the trace element data very high abundances of cr and ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for

geochemistry of banded iron formation of orissa india major and trace element analyses of representative samples of various types of banded iron formation and its various minerals associated sediments iron ores and volcanic tuff from different localities of orissa india are presented in this paper the orissa banded iron formation is classified as precambrian banded iron formation and is similar to the oxide facies iron formation of lake superior type the orissa iron formation consists only of iron oxide and silica with total absence of iron silicate sulfide and carbonate minerals and is devoid of terrigenous material the trace element content suggests the source of the underlying quartzite to be a continental igneous rock mass while the interbedded tuff are of undoubted volcanic origin the overlying iron formation were chemically precipitated as oxidate sediments in which the principal iron mineral magnetite was formed at low temperature in a shallow marine environment from the overwhelming similarity of major and trace element contents of all the samples from the different localities it is postulated that these detached outcrops originated in the same continous basin

potentially mobile pools of phosphorus and silicon in sediment from the bay of brest interactions and implications for phosphorus dynamics abstract competitive interactions between silicate and phosphate at ligand exchange sites in the sediment surface layer may increase the release of phosphorus p from the sediment into the water column in this study the role of silicon si in the release of p from the sediment surface layer was studied in a marine estuarine environment the bay of brest with the aid of a sequential sediment fractionation procedure developed for p and the addition of inorganic or diatom bound si to surface sediment samples in vitro the potentially mobile pools of p in the surface sediment loosely bound p fe al bound p amounted to 5 0 mol g 1 dry sed 42 of the total extractable and 33 of the total amount of p in the sediment while the similarly extracted pools of si were bigger ca 20 mol g 1 dry sed 50 of the total extractable si additions of inorganic si increased the concentration of dissolved p in the sediment interstitial water in a bottle experiment and the addition of both inorganic si and cultivated diatoms to intact sediment cores increased the outward flux of dissolved p model calculations based on the regression equation from the bottle experiment and si and p water column data showed that the sedimentation of spring diatoms could cause si pulses to the sediment which would produce a p flux to the water column of ca 44 mol m 2 d 1 field data from the bay show that in spring decreases in p and si and an increase in chl a due to diatom production are often followed by a small separate p peak which may be caused by si induced p fluxes from the sediment surface

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

alumina rich rocks from the early precambrian of the kaapvaal craton as indicators of paleosols and as products of other decompositional reactions within early archaean to early proterozoic pelites and volcanics of the kaapvaal craton rocks with above 20 al2o3 are widely distributed the alumina rich nature of these rocks is ascribed to decompositional reactions during which up to about 60 of the original material was leached out of the source rock and removed in solution many of these rocks also show diagenetic enrichment in k2o of up to 10 the decomposition reactions in many cases affected the source rocks without disturbing fine structures such as perlitic devitrification cracks in volcanic glass granules the origin of the majority of these rocks can be ascribed to decomposition during subaerial weathering they represent paleosols for other occurrences the stratigraphic context rules out an explanation as paleosols the origin of this type is ascribed to subaqueous decomposition of lavas or tuffs assisted by hydrothermal exhalations it is shown that alumina rich rocks in greenschist belts almost exclusively formed subaqueously whereas the younger occurrences mostly are of weathering origin geotectonic differences are invoked to explain this contrast rocks of similar chemical composition are described from the canadian shield zimbabwe western australia india and the baltic shield they illustrate that the preservation potential of these rocks is high only the study of the stratigraphic context will allow a conclusion on whether a particular occurrence is the product of weathering or subaqueous decomposition

early proterozoic tectonothermal events in the napier complex east antarctica implications for the formation of east gondwana abstract sm nd internal isochron ages involving retrograde garnet determined from three ultrahigh temperature uht gneisses taken from tonagh island the western part of the napier complex east antarctica gave 1870 82 ma 1897 50 ma and 1557 35 ma these ages are younger than the late archaean timing of uht metamorphism in the napier complex the ca 1900 ma age is considered to reflect an important tectonothermal event in the napier complex including a tholeiite dyke intrusion on the other hand the ca 1600 ma age represents a thermal modification lacking signs of deformational events and separates from the ca 1900 ma event the related east gondwana fragments such as the rayner complex in antarctica and the eastern ghats belt in india record extensive tectonothermal event of ca 1400 1600 ma and rare indications of ca 1900 2000 ma it is stressed that the assembly of east gondwana including the napier complex the rayner complex and the eastern ghats belt if it existed should be before ca 1600 ma and may be traced back to ca 2000 ma of the supercontinent columbia era

distribution patterns of different forms of phosphorus in some surficial sediments of the baltic sea abstract the lateral distribution patterns of different forms of phosphorus p in some baltic sea sediments were investigated by a sequential extraction procedure the distribution and amount are mainly related to redox state grain size organic content and the chemical characteristics of the sediments recalculation from mol p per dry weight d w to mol p per unit area indicates that coarse sediments typical of transportation bottoms contain more total p than the finer sediments found in accumulation areas this is applicable for almost all extracted p fractions the extraction procedure shows that hcl extractable p often referred to as apatite p is the dominating fraction of almost all sediment types oxidized fine grained sediments of the near shore area and the archipelago are enriched in the hydrogen sulfide h 2 s extractable p fraction however also some transportation bottoms dominated by slightly coarser grain size i e silt instead of clay have incorporated large amounts of p a rough estimate indicates that the overall importance of a redox dependent release of p from the sediments is of secondary importance compared to the total annual load a predictive calculation of the importance of a hypothetical oxidation of all accumulation bottoms in the baltic proper indicates that the optimally adsorbed amount of p to these bottoms may represent about twice the annual load however this calculation represents an extreme potential uptake a more realistic adsorption uptake is probably far less than two years supply the sorbing capacities of the archipelago and near shore sediments are today of great importance for the net balance of p in comparison to that of the off shore sediments furthermore the study also implies that other incorporation mechanisms must occur to balance the total annual load entering the baltic proper

thermal and baric evolution of garnet granulites from sri lanka abstract garnet granulites from sri lanka preserve textural and chemical evidence for prograde equilibration at temperatures of at least 700 750 c and pressures in the vicinity of 6 8 kbar associated strain patterns suggest prograde metamorphism occurred during and immediately following an episode of crustal thickening with the prograde p t conditions probably reflecting a combination of the conductive and advective transport of heat at the mid levels of tectonically thickened crust the occurrence of prograde wollastonite provides evidence for internally buffered fluid compositions or fluid absent conditions during peak metamorphism and precludes pervasive advection of a co2 rich fluid the advective heat component is therefore likely to have been provided by the transport of silicate melt intricate symplectitic textures record partial re equilibration of the garnet granulites to lower pressures 4 6 kbar at high temperatures 600 750 c and testify either to the erosional denudation of the overthick crust prior to significant cooling i e quasi isothermal decompression or to a subsequent static heating possibly of early palaeozoic age pan african the metamorphic history of the sri lankan granulites is compared with high grade terrains in the neighbouring fragments of gondwana with the emphasis on similarities with proterozoic granulites of the east antarctic craton

reaction history of garnet sapphirine granulites and conditions of archaean high pressure granulite facies metamorphism in the central limpopo mobile belt zimbabwe sequential reaction textures in archaean garnet corundum sapphirine granulites from the central zone of the limpopo belt document a progression from early coarse grained high pressure p 9 5 kbar granulite facies assemblages m1 to late low pressure p 6 kbar granulite facies sub assemblages m2 the stable m1 assemblage was garnet 57 pyrope mg mg fe 62 sapphirine corundum gedrite phlogopite rutile late m1 boron free kornerupine grew at the expense of garnet and corundum and coexisted with garnet sapphirine and gedrite partial or complete breakdown of coarse garnet and kornerupine during m2 resulted in the development of pseudomorphs and coronas consisting of fine grained symplectic intergrowths of cordierite gedrite and sapphirine later spinel the majority of reaction textures can be explained in terms of a stable reaction sequence and a model time sequence of mineral facies can be constructed when compared with a qualitative petrogenetic grid of fe mg discontinuous reactions in the fmash multisystem sapphirine garnet corundum spinel cordierite gedrite kornerupine the facies sequence indicates decompression at essentially constant t assuming constant a h2o exhumation of m1 corundum inclusions during m2 breakdown of kornerupine resulted in production of metastable spinel by a disequilibrium reaction with gedrite a second disequilibrium reaction of the spinel with cordierite produced sapphirine the operation of such reaction while pressure was decreasing the opposite dp from that implied by the texture if assumed to be the product of an equilibrium reaction has serious implications for the use of reaction textures in the construction of p t vectors garnet biotite thermometry on garnet interiors and phlogopite inclusions in corundum yields temperatures of ca 850 c for the m1 stage a minimum late m1 pressure of ca 7 kbar is indicated by the former association of kornerupine and corundum relict m1 kyanites reported by other workers indicate a minumum early m1 pressure of 9 5 kbar implying metamorphism at depths of at least 33 km probably 38km the high pressure granulite facies metamorphism was followed by an almost isothermal pressure decrease of 5 kbar indicative of rapid uplift the p t path is interpreted as the product of a single metamorphic cycle which probably took place in response to tectonic thickening of the crust such a process contrasts with the extensional origin recently proposed for isobarically cooled granulite facies terranes

two stage decompression in orthopyroxene sillimanite granulites from forefinger point enderby land antarctica implications for the evolution of the archaean napier complex magnesian metapelites of probable archaean age from forefinger point sw enderby land east antarctica contain very high temperature granulite facies mineral assemblages which include orthopyroxene 8 9 5 wt al2o3 sillimanite garnet quartz k feldspar that formed at 10 1 5 kbar and 950 50 c these assemblages are overprinted by symplectite and corona reaction textures involving sapphirine orthopyroxene 6 7 wt al2o3 cordierite and sometimes spinel at the expense of porphyroblastic garnet or earlier orthopyroxene sillimanite these textures mainly pre date the development of coarse biotite at the expense of initial mesoperthite and the subsequent formation of orthopyroxene 4 6 wt al2o3 cordierite plagioclase rinds on late biotite the early reaction textures indicate a period of near isothermal decompression at temperatures above 900 c decompression from 10 1 5 kbar to 7 8 kbar was succeeded by biotite formation at significantly lower temperatures 800 850 c and further decompression to 4 5 1 kbar at 700 800 c the later parts of this p t evolution can be ascribed to the overprinting and reworking of the forefinger point granulites by the late proterozoic c 1000 ma rayner complex metamorphism but the age and timing of the early high temperature decompression is not known it is speculated that this initial decompression is of archaean age and therefore records thinning of the crust of the napier complex following crustal thickening by tectonic or magmatic mechanisms and preceding the generally wellpreserved post deformational near isobaric cooling history of this terrain

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

petrology of cordierite gedrite bearing sodic granulite from the grenvillian long range inlier newfoundland sodium rich potassium poor granulite in the long range inlier contains ab qtz crd bt opx ilm and either gedrite or garnet but rarely both the distribution of garnet in the sodic gneiss was influenced by bulk compositional controls e g higher al2o3 sio2 textural evidence indicates that gedrite was metastable with respect to crd opx during granulite grade metamorphism peak metamorphic conditions are estimated to have been 700 c at 600 mpa the metamorphic fluid was co2 rich the preservation of pelitic sil crd bt grt qtz mc and layers in which k2o na2o suggests a sedimentary precursor for the sodic gneiss but the granulites are more sodic and less magnesian than primary sediments recently identified as possible precursors to cordierite orthoamphibole rocks e g ultramafic derived greywackes evaporitic mudstones leucosomes tend to be more sodic mean na2o k2o 23 5 than mesosomes mean na2o k2o 17 8 m garnet free gneiss and 1 4 m garnetiferous gneiss so unl

first report of sapphirine bearing rocks from the palghat cauvery shear zone system southern india abstract silica deficient mg al granulites from paramati within the palghat cauvery shear system contain sapphirine in association with corundum spinel and sillimanite gedrite which occurs commonly in this locality coexists with cordierite corundum and sillimanite mineral assemblages and reaction textures indicate peak metamorphism at ultrahigh temperature conditions this new locality provides evidence for extreme crustal metamorphism along the archean proterozoic collision boundary in southern india

reappraisal of a 2200 ma old paleosol near waterval onder south africa abstract a fossil soil paleosol about 2200 ma old in a deep roadcut between the towns of waterval boven and waterval onder transvaal here called the waterval onder clay paleosol was formerly reported to have formed on the hekpoort basalt it is here thought to have developed on a thick formerly at least 5 5 m upward fining and thinning sequence of sandstone siltstone and shale derived from pre existing soils on hekpoort basalt within the basal portion of the fluvial dwaal heuvel formation in contrast to paleosols developed on hekpoort basalt the waterval onder clay paleosol is little deformed lacks corestones and shows compositional variation and berthierine rich laminae interpreted as relict bedding the paleosol has a ridge and swale topography linear or wavy gilgai and a subsurface structure mukkara typical of modern vertisols since there is considerable relict bedding it probably formed over a short period of time less than 7000 years and was not self plowing to the extent seen in modern vertisols clastic dikes filled with sandstone from the overlying rocks are evidence that the profile was periodically dry to depths of at least 2 m more drab colored rocks below that may represent the level of permanent water table iron and manganese stain of layers and claystone granules within the surface horizon of the profile have some characteristics of modern rock varnish and could be taken as evidence for life in the soil the high ratio of ferric to ferrous iron near the surface of the paleosol together with evidence from clastic dikes that this horizon was not waterlogged is an indication of an oxidizing atmosphere although probably one in which oxygen was much less abundant than it is today the very low amounts of acid titratable bases in the shaly parent material of this paleosol and surficial loss of these bases within the paleosol appear to have been produced by decarbonation reactions comparable to those found today in soils of vascular land plants a likely source of weathering acid during the precambrian is an elevated abundance of atmospheric carbon dioxide considering these likely atmospheric differences together with the distribution of comparable modern vertisols and other geological evidence the climate under which this soil formed was probably semiarid to subhumid seasonally dry and temperate

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

petrogenesis of cordierite orthoamphibole assemblages from the springton region south australia textural evidence for the partial breakdown of staurolite biotite and andalusite biotite assemblages to cordierite orthoamphibole implies high temperature metasomatic depletion of k2o in semi pelitic rocks from springton south australia the origin of the reaction textures is discussed with reference to k2o t diagrams derived from the topologically equivalent k2o h2o diagram showing both discontinuous and fe mg continuous reactions the involvement of fluids in the metasomatic process is implied by the scale of k2o removal and suggests that the outcrop pattern of cordierite gedrite rocks reflects at least in part a heterogeneous distribution of advecting fluids in the metamorphic pile at high temperatures

geochronology and geological evolution of metamorphic rocks in the field islands area east antarctica detailed geochronological structural and petrological studies reveal that the geological evolution of the field islands area east antarctica was substantially similar to that of the adjacent archaean napier complex though with notable differences in late and post archaean times these differences reflect the area s proximity to the proterozoic rayner complex and consequent vulnerability to tectonic process involved in the formation of the latter distinctive structural features of the field islands are 1 consistent development of a discordant pervasive s3 axial plane foliation 2 re orientation of s3 axial planes to approximate to the subsequent e w tectonic trend of the nearby rayner complex 3 selective retrogression by a post d3 static thermal overprint and 4 relatively common development of retrogressive e w trending mylonitic shear zones peak metamorphic conditions in excess of 800 c at 900 100 m pa 9 kbar were attained at one locality following but probably close to the time of d2 folding d3 took place in late archaean times when metamorphic temperatures were about 650 c and pressures were about 600 mpa 6 kbar later temperatures of 600 50 c and pressures of 700 mpa 7kbar were attained in an amphibolite facies event presumably associated with the widespread granulite to amphibolite facies metamorphism and intense deformation involved in the formation of the rayner complex at about 1100 ma the area was subsequently subjected to near isothermal uplift rb sr isotopic data indicate that the pervasive d3 fabric developed at about 2400 2500 ma and this age can be further refined to 2456 8 5 ma by concordant zircon analyses from a syn d3 pegmatite all zircons were affected by only minor 7 10 pb loss and or new zircon growth during the rayner event at about 1100ma thus the 450 850 g gu concentrations of these zircons were too low to cause sufficient lattice damage over the 1350 ma from 2450 ma for excessive pb to be lost during the 1100 ma event the emplacement of pegmatite at 522 10 ma substantially changed the rb sr systematics of the only analysed rock that developed a penetrative fabric during the 1100 ma event monazite in this pegmatite contains an inherited pb component which probably resides in small opaque inclusions a good correlation is found between rb sr total rock ages and rock fabric u pb zircon intercepts with concordia also mostly correspond to known events however in one example a near perfect alignment of zircon analyses probably developed by mixing of unrelated components produced concordia intercepts that appear to have no direct geochronological significance

sapphirine kornenipine bearing rocks and crustal uplift history of the limpopo belt southern africa sapphirine kornerupine bearing rocks occur within the anorthosites of the messina layered intrusion in the limpopo mobile belt of zimbabwe the xmg range of the major minerals is as follows cordierite 0 98 0 93 enstatite 0 97 0 86 chlorite 0 98 0 92 phlogopite 0 98 0 90 sapphirine 0 98 0 86 kornerupine 0 94 0 88 gedrite 0 96 0 85 spinel 0 92 0 78 there are four rock types the constituent minerals of which have different x m g values which decrease in the above mineral order other minerals are corundum sillimanite and relict kyanite we recognise twenty reactions without phlogopite and nine reactions involving phlogopite the textural relations and the plots of the microprobe data of coexisting minerals in the mgo al2o3 sio2 h2o system are consistent with the following sequence of main reactions 1 enstatite corundum cordierite sapphirine 4 sapphirine sillimanite cordierite corundum 8 kornerupine corundum cordierite sapphirine 13 kornerupine cordierite sapphirine enstatite 15 enstatite spinel chlorite sapphirine 18 cordierite sapphirine chlorite corundum 20 sapphirine chlorite corundum spinel the early reactions are shown by coarse grained reaction intergrowths kornerupine and gedrite breakdown is shown by finer grained symplectites and the latest reactions by very fine grained products in micro fractures these selected reactions illustrate a remarkably steep trajectory from thept peak close to 10 kbar and 800 c to the minimum observable at 3 5 4 5 kbar and 700 c as indicated by the pure mash system very rapid uplift took place under nearly isothermal conditions the protolith of this material was possibly sedimentary derived from altered volcanic rocks the bulk composition is close to the composition of kornerupine or to a mixture of alunite chlorite and pyrophyllite these texturally and mineralogically complex rocks contain a wealth of relevant data for documenting crustal uplift history

metamorphic evolution of the bunger hills east antarctica evidence for substantial post metamorphic peak compression with minimal cooling in a proterozoic orogenic event the bunger hills east antarctica experienced a low pressure granulite facies orogenic event during the proterozoic the stable coexistence of the s1 foliation parallel m1 assemblages garnet cordierite spinel ilmenite and garnet sillimanite spinel ilmenite rutile in quartz bearing pelitic gneisses is evidence for metamorphic peak pressures of around 4 kbar during m1 at temperatures of about 800 c the growth of massive reaction coronas of garnet and cordierite around hercynitic spinel and iron titanium oxides during m2 is evidence for the destabilization of the m1 assemblages during compression thermodynamic calculations on the m2 assemblages indicate formation pressures of 6 7 kbar at temperatures of about 750 c thus the gneisses from the bunger hills indicate about 2 kbar or more of compression during minimal cooling such a p t path is different from that of many other proterozoic terranes which are characterized by isobaric cooling or decompression a large charnockite body which is undeformed was intruded at 950 c towards the end of compression the low pressures during m1 can be best explained by metamorphism at mid crustal levels in thin continental crust in thin lithosphere above a thermal perturbation in the underlying asthenosphere we suggest that the compression during cooling was a result of gravitational backflow in which the action of body forces between adjacent normal thickness crust and the thin crust of the bunger hills is switched on by the thermal perturbation within such a model the timing of intrusion of the charnockite exposed in the bunger hills is consistent with its generation by partial melting during the metamorphic maximum of the lowermost crust

preservation of oxygen isotope compositions in granulites from northwestern canada and enderby land antarctica implications for high temperature isotopic thermometry preservation of high temperature mineral isotopic compositions is necessary for successful high temperature isotopic thermometry other requirements include large fractionations between constituent minerals well calibrated equilibria carefully designed sampling strategies and data handling techniques that quantitatively account for retrograde exchange here we apply isotopic thermometry and data handling techniques to calculate and contrast mineral pair apparent temperature data and observed closure temperature data tc observed cf farquhar et al 1993 for the very high temperature 900 c dry granulites of the taltson magmatic zone of northwestern canada and the napier complex of enderby land antarctica the isotopic compositions of garnet grains from both terrains reflect high temperature conditions 950 c and point to this mineral as an excellent candidate for isotopic thermometry the isotopic compositions of quartz pyroxene ilmenite and magnetite indicate that they equilibrated to lower temperature conditions 900 c due to faster rates of oxygen diffusion in these minerals possibly enhanced by exsolution and ductile deformation compared with garnet our temperature data for garnet and pyroxene are 200 c higher than is possible to explain by existing wet diffusion data but is consistent with dry diffusion data suggesting that the extremely dry nature of these rocks may have played a significant role in the preservation of high temperature isotopic compositions both quartz and magnetite exhibit subgrain features indicative of ductile deformation quartz magnetite temperatures from the napier complex are similar to those inferred for a late d3 deformation and are lower than those predicted by dry diffusion data we infer that the quartz magnetite isotopic fractionations reflect deformation enhanced exchange that accompanied d3 garnet in these same samples did not undergo ductile deformation and did not exchange oxygen with coexisiting phases during cooling this may reflect strain partitioning between less easily deformed low abundance garnet and more easily deformed matrix quartz and magnetite the resistance of garnet to ductile deformation in these rocks is a second reason why garnet is suitable for isotopic thermometry

archean chemical weathering at three localities on the canadian shield abstract sapropelite developed on a granodiorite basement below the archean steeprock group in the western superior structural province of canada weathered materials from a 3 15 ga granitic basement to the archean yellowknife supergroup in the slave structural province and weathered detritus from contemporaneous komatiites and gneissic basement of the archean prince albert group in northern churchill structural province have been analysed the deviation of the weakly metamorphosed weathered material from the chemical composition of their precursors is comparable to that seen in more recent weathered profiles from similar source materials this includes the enhancement of ferric to ferrous iron ratios and potash to soda lime and magnesia ratios there is also an increase in lighter ree and a depletion of heavier ree quartz rich sediments immediately above the unconformity derived from the basement granitoids may be enriched in aluminum and iron and yield chloritoid under proper metamorphic conditions sediments formed from mixed sources such as weathered gneissic basement and contemporaneous komatiitic volcanics yield anomalous resistate sedimentary mixtures such as chromiferous quartzites based on the data given here there is no need to postulate that different weathering and or ground water systems were operative during the archean compared to more recent times on the other hand the complicated weathering and diagenetic history that altered material undergoes below a subsiding unconformity relies as much or more on the buffering capacity of the enclosed rock mass as on the atmospheric conditions prevalent at the time of weathering hence weathering profiles old and new are more a response to local environmental conditions within the rock than the composition of the atmosphere

corona textures between kyanite garnet and gedrite in gneisses from errabiddy western australia corona textures which developed in alternating layers in rocks in a supracrustal belt at errabiddy western australia involved a the production of staurolite cordierite and quartz or sapphirine between kyanite and or sillimanite and gedrite and b the production of cordierite between garnet and gedrite these textures are inconsistent with development along the same pressure temperature path in the system feo mgo al2o3 sio2 h2o but can be accounted for if cao mainly in garnet is taken into account the sapphirine bearing kyanite gedrite textures are explained by lower a sio2 during their development the assemblages indicate a consistent pressure temperature p t trajectory involving substantial uplift with only a slight decrease in temperature the history of these rocks includes reheating of originally high grade rocks that had cooled to a stable conductive geotherm followed by substantial essentially isothermal uplift the tectonic environment for this was presumably the one responsible for emplacement of the high grade terrain in the upper crust

aluminous reaction textures in orthoamphibole bearing rocks the pressure temperature evolution of the high grade proterozoic of the bamble sector south norway aluminous reaction textures in orthoamphibole bearing rocks from the froland area bamble south norway record the prograde pressure temperature path of the high grade kongsbergian orogeny c 1600 1500 ma and the low mid amphibolite facies overprint during the sveconorwegian orogeny c 1100 1000 ma the rocks contain anthophyllite gedrite garnet cordierite biotite quartz andalusite kyanite cr rich staurolite tourmaline ilmenite rutile and corundum in a variety of parageneses the p t path is deduced from petrographic observations mineral chemistry and zoning geothermometry and n fmash equilibria the results indicate the sequence of metamorphic stages outlined below a an m1 phase characterized by the presence of strongly deformed andalusite gedrite and tourmaline b an m2 phase with the development of kyanite after andalusite and the growth of staurolite associated with strong na al mg zoning in orthoamphibole indicating an increase in pressure 4 8 kbar and temperature 500 650 c c pressure decrease at high p 6 7 kbar and high t 600 700 c during m3a with the production of cordierite corundum between kyanite staurolite and orthoamphibole and cordierite growth between corundum and orthoamphibole d temperature increase to 740 60 c and 7 kbar static growth of garnet m3b at the metamorphic climax peak t the heat supply necessary to explain the temperature increase between the m3a and m3b phases is correlated with synkinematic enderbitic charnockitic and basic intrusions in the arendal granulite facies terrain e m3b metamorphic conditions were followed by an initial isobaric cooling path early m4 and late stage pressure decrease late m4 early m4 conditions of 6 7 kbar and 550 600 c assuming ph2o ptotal are indicated by a retrograde talc kyanite quartz assemblage in late quartz cordierite veins late m4 conditions of 3 4 kbar and 420 530 c are inferred from a kyanite andalusite chlorite quartz assemblage in vein cordierite the m1 m3 stages are interpreted as being the result of the same metamorphic p t path which was caused by both tectonic and magmatic thickening a prolonged crustal residence time is proposed for the bamble sector before uplift during the later stages of m4 occurred

geochemistry of precambrian gneisses relevance for the evolution of the east antarctic shield archaean granulite facies orthogneisses of the napier complex in enderby land metamorphosed 3070 maago comprise two chemically distinct suites the more abundant mainly of tonalitic to granodioritic composition shows strong y depletion explicable by hydrous partial melting of a garnet bearing source garnet amphibolite or possibly eclogite it apparently represents new continental crust other gneisses predominantly of trondhjemitic to granitic s s composition do not show y depletion and have higher tio2 zr nb la ce and ga al and lower cao sr and mg mg total fe they probably originated by relatively dry melting of predominantly felsic crystal rocks both suites show evidence for loss of rb relative to k th and u during metamorphism late archaean 2800 ma amphibolite facies gneisses of macrobertson land are of undepleted type and may be representative of a higher crustal level than those of enderby land late proterozoic 1000 ma granulite facies gneisses of enderby land rayner complex are to a large extent remetamorphosed napier complex rocks of igneous derivation in contrast gneisses of similar age in macrobertson land include a much higher proportion derived either directly or by partial melting from sedimentary protoliths

phosphorus distribution in the estuarine sediments of the daliao river china abstract the objective of this study was to investigate the phosphorus distribution in the estuarine sediments of the daliao river intensively affected by municipal effluent and agricultural activity for about 50 years surface sediment samples were taken at 35 sites in the estuarine area and phosphorus species and contents of total p al fe and ca in the sediments were measured results showed that the content of total p in the sediments ranged from 230 to 841 mg kg 1 with an average of 549 mg kg 1 ca bound p residual p al bound p reductant soluble p fe bound p and soluble and loosely bound p were averagely 44 5 21 6 13 6 11 7 8 9 and 0 2 of total p respectively with the gradual increase of total p content al bound p reductant soluble p and fe bound p generally increased while the rest species of p did not this might indicate that anthropogenic p is bound to al and fe oxides regression analysis showed that al bound p and sum of fe bound p and reductant soluble p were correlated to the contents of total al and fe respectively on the other hand ca bound p was not correlated to the content of total ca in the sediment probably suggesting that ca p was mainly from authigenic marine origin whereas the content of total p in the estuarine sediments of the daliao river was within the range of total p content for chinese and worldwide river estuaries as well as coastal sediments non calcium apatite phosphorus content in the estuarine sediments of the daliao river was relatively higher indicating higher release risk and bioavailability of p in the sediment on the other hand the molar ratio of total fe to total p was 16 34 in the estuarine sediments of the daliao river suggesting that iron oxides hydroxides in the sediments might be able to sequester more phosphorus therefore the accumulation or release of p in from the estuarine sediments might be dependent on the external loading of p and the estuarine eutrophication may be sustained by the internal bioavailable p pools following the decrease of the external p loading

the stability and origin of sodicgedrite in ultrahigh temperature mg al granulites a case study from the gondwana suture in southern india mg al rich rocks from the palghat cauvery shear zone system pcsz within the gondwana suture zone in southern india contain sodicgedrite as one of the prograde to peak phases stable during t 900 990 c ultrahigh temperature metamorphism gedrite in these samples is mg rich mg fe mg x mg 0 69 0 80 and shows wide variation in na2o content 1 4 2 3 wt naa 0 33 0 61 pfu gedrite adjacent to kyanite pseudomorph is in part mantled by garnet and cordierite the gedrite proximal to garnet shows an increase in naa and aliv from the core naa 0 40 0 51 pfu aliv 1 6 1 9 pfu to the rim naa 0 49 0 61 pfu aliv 2 0 2 2 pfu suggesting the progress of the following dehydration reaction ged ky na ged grt crd h2o this reaction suggests that as the reactants broke down during the prograde stage the remaining gedrite became enriched in na to form sodicgedrite which is regarded as a unique feature of high grade rocks with mg al rich and k si poor bulk chemistry we carried out high p t experimental studies on natural sodicgedrite and the results indicate that gedrite and melt are stable phases at 12 kbar and 1 000 c however the product gedrite is na poor with only 0 13 wt na2o naa 0 015 0 034 pfu in contrast the matrix glass contains up to 8 5 wt na2o suggesting that with the progressive melting of the starting material na was partitioned into the melt rather than gedrite the results therefore imply that the occurrence of sodicgedrite in the uht rocks of the pcsz is probably due to the low h2o activity during peak p t conditions that restricted extensive partial melting in these rocks leaving na partitioned into the solid phase gedrite the occurrence of abundant primary co2 rich fluid inclusions in this rock which possibly infiltrated along the collisional suture during the final amalgamation of the gondwana supercontinent strengthens the inference of low water activity

experimental determination of the emplacement pressure of proterozoic mafic dikes within portions of the east antarctic shield abstract in order to further constrain previous determinations of the p t pressure time path of two portions of the east antarctic shield the depth pressure under which two proterozoic dike suites were emplaced in the vestfold hills block was determined by experimentally reproducing the equilibrium phenocryst assemblage found in their chilled margins the phenocryst assemblage oliv opx of a high mg tholeiite sample ca 2420 ma could only be experimentally reproduced at 7 5 kbar it was also found that at 7 5 kbar the ca mg fe components of the synthetic orthopyroxene very closely matched the natural phenocryst concentrations based on high pressure experiments the phenocryst assemblage in a sample from the ca 1360 ma fe rich tholeiite suite oliv opx plag opx is only consistent with dike emplacement at pressures 5 5 kbar while the mg values of the natural clinopyroxene phenocrysts match the experimental pyroxene compositions at pressures of 4 5 kbar these results are consistent with pressures of 8 0 and 5 3 kbar obtained for the mg and fe rich tholeiite samples respectively using geobarometry applied to the groundmass assemblages emplacement pressures of compositionally similar dikes from the napier complex were estimated by comparison with previous experimental studies the comparison shows that a napier complex high mg tholeiite suite ca 2350 ma and an fe rich tholeiite suite ca 1190 ma were both emplaced at a pressure 8 kbar

phosphorus burial and diagenesis in the central bering sea bowers ridge iodp site u1341 perspectives on the marine p cycle abstract to reconstruct the cycling of reactive phosphorus p in the bering sea a p speciation record covering the last 4 ma was generated from sediments recovered during integrated ocean drilling program iodp expedition 323 at site u1341 bowers ridge a chemical extraction procedure distinguishing between different operationally defined p fractions provides new insight into reactive p input burial and diagenetic transformations reactive p mass accumulation rates mars are 20 110 mol cm2 ka which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings we find that authigenic carbonate fluorapatite cfa and opal bound p are the dominant p fractions at site u1341 an overall increasing contribution of cfa to total p with sediment depth is consistent with a gradual sink switching from more labile p fractions fish remains fe oxides organic matter to stable authigenic cfa however the positive correlation of cfa with al content implies that a significant portion of the supposedly reactive cfa is non reactive detrital contamination by eolian and or riverine cfa in contrast to cfa opal bound p has rarely been studied in marine sediments we find for the first time that opal bound p directly correlates with excess silica contents this p fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long term sink for reactive p in the ocean despite the likelihood for diagenetic re mobilisation of this p at depth indicated by increasing ratios of excess silica to opal bound p average reactive p mars at site u1341 increase by 25 if opal bound p is accounted for but decrease by 25 if 50 of the extracted cfa fraction based on the lowest cfa value at site u1341 is assumed to be detrital combining our results with literature data we present a qualitative perspective of terrestrial cfa and opal bound p deposition in the modern ocean riverine cfa input has mostly been reported from continental shelves and margins draining p rich lithologies while eolian cfa input is found across wide ocean regions underlying the northern hemispheric dust belt opal bound p burial is important in the southern ocean north pacific and likely in upwelling areas shifts in detrital cfa and opal bound p deposition across ocean basins likely occurred over time responding to changing weathering patterns sea level and biogenic opal deposition

u pb geochronology from tonagh island east antarctica implications for the timing of ultra high temperature metamorphism of the napier complex abstract ion microprobe u pb zircon geochronology of an orthopyroxene bearing felsic orthogneiss from central tonagh island enderby land east antarctica provides insight into the chronological metamorphic evolution of the archaean napier complex the details of which have been the source of debate for over two decades the orthogneiss crystallised at 2626 28 ma predating peak ultra high temperature uht metamorphism and development of an intense regional s1 gneissosity two subsequent episodes of zircon growth resetting can be identified a minor period of zircon growth occurred at 2546 13 ma the regional significance and geological nature of which is unclear this was followed by an episode of abundant zircon growth as mantles on 2626 ma cores and as anhedral grains partly characterised by high th u 1 2 at 2450 2480 ma this age coincides with both lower and upper concordia intercept ages from other u pb zircon studies and several rb sr and sm nd whole rock isochron ages from the napier complex we conclude that uht metamorphism occurred at 2450 2480 ma and find no compelling evidence that uht occurred much earlier as has been postulated the zircon u pb data from this study also indicates a lower intercept age of 500 ma which coincides with the emplacement of early palaeozoic pegmatite swarms and synchronous infiltration of aqueous fluids into the southwestern regions of the napier complex

phosphorus forms related to sediment grain size and geochemical characteristics in french coastal areas abstract phosphorus forms with respect to sediment characteristics such as grain size and major chemical elements were studied in french coastal marine areas the bay of seine and the loire and gironde estuaries in the three areas fe al bound phosphate fe al p and exchangeable phosphate exch p were significantly related to the proportion of fine fraction calcium bound phosphate ca p was found in all grain size classes with comparable concentrations in the bay of seine where there was no correlation between ca p and ca this corresponded to the calcium s marine origin shells in the bay of seine in contrast the correlation of ca p with ca and the fine fraction of the sediment in the loire and gironde estuaries was characteristic of the predominant metamorphic origin of ca p in these areas useful information for interpretation of p forms can be obtained from major sediment characteristics thus for areas where specific relationships have previously been established good estimates of p forms could be predicted from sediment properties

evidence of tidal processes from the lower part of the witwatersrand supergroup south africa abstract a 1600 m succession of quartz arenites and associated shaley deposits comprising the hospital hill subgroup at the base of the witwatersrand supergroup is considered to have been deposited largely under the influence of tidal processes facies analysis indicates that deposition occurred in the following environments 1 marine shalf 2 shallow subtidal to intertidal 3 intertidal flat and 4 tidal inlet the presence of strong tidal currents implies that the witwatersrand basin was open to an ocean basin at least during the early stages of its evolution palaeocurrent trends and isopach data suggest that this probably lay to the southwest an area now occupied by the high grade natal namaqua metamorphic belt the contrast between the supermature quartz arenites of the hospital hill subgroup and the overlying gold bearing immature subgreywackes feldspathic quartzites and conglomerates of fluvial origin is believed to be a function of tidal reworking of sediments