mixing processes in modern estuarine sediments from the gulf of khambhat western india abstract sandy and muddy detritus from two distinctive end member provenance terrains basaltic and granitic are transported to the estuaries of the gulf of khambhat by fluvial discharge and opposing tidal currents making this embayment ideal for investigating the effects of mineralogical and geochemical mixing on sediment composition in estuarine depositional systems rivers flowing predominantly from the north over precambrian metasediments and granites supply a felsic plutoniclastic sand to the gulf whilst a mafic volcaniclastic sand sourced by deccan basalts is transported by rivers draining the western ghats and from the local coastal erosion in the southern part of the gulf sediments from the tapti estuary are rich in basaltic rock fragments 50 and are characterised by a distinctly basaltic source composition la sc 0 25 0 86 th sc 0 12 0 40 cr th 13 121 eu eu 0 93 1 68 and lree hree 2 96 6 57 by contrast the sediments of the sabarmati inner estuary are rich in quartz grains 80 as evident from the major and trace element compositions la sc 1 38 6 63 th sc 0 58 2 98 cr th 0 58 19 39 eu eu 0 46 0 86 and lree hree 2 90 11 40 the detrital compositions of the remaining major estuaries the narmada dhadhar and mahi scatter across a broad range in a qfr diagram and contain varying amounts of quartz feldspar and rock fragments in the narmada estuary the mixed signature characterised by ree values including eu eu 0 42 2 28 and lree hree 4 37 14 80 is caused by the presence of diverse rock types that crop out in the source area in the mahi estuary which largely flows across felsic source terrains the compositional signature is controlled by mixing of felsic detritus from riverine input with mafic sediments from seaward side in the estuary the two end member detrital compositions plutoniclastic and volcaniclastic are mixed in the macro tidal estuaries mixing of sediment takes place where fluvial currents and tidal flows interact and the proportion of mixing varies systematically from outer to central to inner estuary a high degree of mixing of felsic sediments with deccan basalt derived sediments takes place in the outer estuary resulting in felsic mafic ratios of 40 60 sediments in the central estuaries 65 35 and in the fluvial dominated inner estuaries 90 10 are characterised by moderate to minor degrees of mixing the mixing in estuaries is systematic and is reflected in both the mineralogy and geochemistry of the sediments provenances of ancient estuarine successions should therefore be interpreted with great care incorporating awareness of the mixing processes which influence sediment compositions to different degrees in estuaries especially those characterised by strong tidal currents

rates of weathering rind formation on costa rican basalt weathering rind thicknesses were measured on 200 basaltic clasts collected from three regionally extensive alluvial fill terraces qt 1 qt 2 and qt 3 preserved along the pacific coast of costa rica mass balance calculations suggest that conversion of unweathered basaltic core minerals plagioclase and augite to authigenic minerals in the porous rind kaolinite allophane gibbsite fe oxyhydroxides is iso volumetric and ti and zr are relatively immobile the hierarchy of cation mobility ca na k mg si al fe p is similar to other tropical weathering profiles and is indicative of differential rates of mineral weathering anorthite albite hypersthene orthoclase apatite alteration profiles across the cm thick rinds document dissolution of plagioclase and augite and the growth of kaolinite with subsequent dissolution of kaolinite and precipitation of gibbsite as weathering rinds age the rate of weathering rind advance is evaluated using a diffusion limited model which predicts a parabolic rate law for weathering rind thickness rr as a function of time t rr t and an interface limited model which predicts a linear rate law for weathering rind thickness as a function of time rr kappt in these rate laws is a diffusion parameter and kapp is an apparent rate constant the rate of advance is best fit by the interface model terrace exposures are confined to the lower reaches of streams draining the pacific slope near the coast where the stream gradient is less than 3 m km and terrace deposition is influenced by eustatic sea level fluctuations geomorphological evidence is consistent with terrace deposition coincident with sea level maxima when the stream gradient would be lowest assigning the most weathered regionally extensive terrace qt 1 mean rind thickness 6 9 0 6cm to oxygen isotope stage ois 7 ca 240 ka and assuming that at time 0 rind thickness 0 it is inferred that terrace qt 2 rr 2 9 0 1 cm is coincident with stage 5e ca 125 ka and that qt 3 rr 0 9 0 1 cm is consistent with ois 3 ca 37 ka these assignments yield a value of kapp of 8 6 10 13 cm s 1 r 2 0 99 only this value satisfies both the existing age controls and yields ages coincident with sea level maxima using this value elemental weathering release fluxes across a weathering rind from qt 2 range from 6 0 10 9 mol si m 2 s 1 to 2 5 10 11 mol km 2 s 1 the rate of rind advance for the costa rican terraces is 2 8 10 7 my r 1 basalt rind formation rates in lower temperature settings described in the literature are also consistent with interface controlled weathering with an apparent activation energy of about 50 kj mol 1 rates of rind formation in costa rica are an order of magnitude slower than reported for global averages of soil formation rates copyright 2004 elsevier ltd

trace element characteristics ree patterns and partition coefficients of zircons from different geological environments a case study on indian zircons abstract twelve zircon separates from diverse geological settings in peninsular india have been analyzed for their zr hf sc ree th and u contents employing neutron activation techniques the whole rock samples of acid charnockite and a related rock of syenitic composition were also analyzed for these elements after separation of zircons the study reveals that 1 a the zircons exhibit a wide range of variation in elemental abudances and their ratios 2 b their chondritic normalised ree patterns exhibit negative or positive ce and negative eu anomalies in addition to smooth hree enriched patterns without anomalies and 3 c there are significant differences in the ree partition coefficients of zircons from the charnockite and the associated syenite the overall elemental abundances and ree patterns of the zircons could be explained in terms of crystallochemical factors bulk compositional differences of parent melts and paragenetic histories

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

theoretical constraints and chronological evidence of holocene coastal development in central and southern new south wales australia abstract holocene coastal evolution in new south wales has been interpreted essentially as the unfolding of the impact of marine transgression sea level on this coast supposedly reached its present height at 6 6 5 ka and varied

rare earth element complexation behavior in circumneutral ph groundwaters assessing the role of carbonate and phosphate ions rare earth element ree concentrations were determined in circumneutral ph 7 ph 9 groundwaters from south central nevada and the mojave desert in eastern california u s a the inorganic speciation of the rees in these water were evaluated primarily to assess the relative importance of carbonate lnhco32 lnco3 and ln co3 2 and phosphate lnh2po42 lnhpo4 ln hpo4 2 and lnpo40 complexes other ree complexes with sulfate hydroxyl chloride and fluoride ions were also assessed as was the significance of the free metal ion species i e ln3 our speciation calculations indicate that ree carbonate complexes dominate and typically account for more than 99 of each ree in solution moreover carbonato complexes lnco3 were predicted to be the dominant species for the light rees and dicarbonato complexes ln co3 2 were predicted to increase in importance with increasing atomic number all other complexes were predicted to be negligible furthermore the combined percentage of all ree phosphate complexes never accounted for more than 0 1 of the dissolved rees and generally much less than 0 1 phosphate complexes can not compete with carbonate complexes in these groundwaters because of the low po43 concentrations 0 3 1 58 mol kg the much lower concentrations of the free phosphate ion i e po43 f 10 9 10 6 mol kg due to ion pair formation with ca2 and mg2 and the much higher free carbonate ion concentrations co32 f 0 32 87 mol kg

holocene sea level change on the southeast coast of australia a review a revised holocene sea level curve for the southeast coast of new south wales australia is presented based on a review of previously published geochronological results for fossil molluscs organi

aminostratigraphy of quaternary coastal sequences in southern australia an overview abstract since the early 1980s amino acid racemisation reactions have been applied to the dating of quaternary coastal deposits in australia sequences of middle pleistocene age or younger have received the greatest attention amino acid racemisation has been applied as a relative and numeric dating method as well as for identifying remanie fossils and in delineating the spatial distribution of some fossil mollusc species the method has also been used to verify the radiocarbon ages of fossil molluscs from interstadial sediments it has also been used in studies of coastal neotectonics and in comparisons with other dating methods e g electron spin resonance and thermoluminescence the most reliable results are from replicate analyses of the hinge region of well preserved and diagenetically unmodified fossil bivalve molluscs from deeply buried situations i e 1 m molluscs have been dated from a range of sites around the southern australian coastline and include specimens of plio pleistocene age and from middle pleistocene oxygen isotope stage 7 ca 220 ka bp late pleistocene substage 5e ca 125 ka bp interstadial stage 3 45 to 30 ka bp last glacial stage 2 ca 18 ka bp and holocene sequences amino acid racemisation dating of the australian quaternary coastal record has 1 confirmed the widespread occurrence of last interglacial coastal strata and allowed their correlation with sequences of equivalent age from the northern hemisphere 2 identified strata of penultimate interglacial age and 3 confirmed the interstadial age of marine strata stage 3 in gulf st vincent south australia aminostratigraphic studies of the southern australian quaternary coastal record also indicate that sea levels during the penultimate interglacial stage 7 may have been higher than otherwise predicted on the basis of the oxygen isotope record

hotspots mantle plumes flood basalts and true polar wander persistent long lived stationary sites of excessive mantle melting are called hotspots hotspots leave volcanic trails on lithospheric plates passing across them the global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions through the orientations and age distributions of volcanic trails left by these melting anomalies hotspots appear to be maintained by whole mantle convection in the form of upward flow through narrow plumes evidence suggests that plumes are deflected little by horizontal flow of the upper mantle mantle plumes are largely thermal features and arise from a thermal boundary layer most likely the mantle layer just above the core mantle boundary experiments and theory show that gravitational instability drives flow beginning with the formation of diapirs such a diapir will grow as it rises fed by flow through the trailing conduit and entrainment of surrounding mantle the structure thus develops a large spherical plume head and a long narrow tail on arrival at the base of the lithosphere the plume head flattens and melts by decompression producing enormous quantities of magma which erupt in a short period these are flood basalt events that have occurred on continents and in ocean basins and that signal the beginning of major hotspot tracks the plume supported hotspot reference frame is fixed in the steady state convective flow of the mantle and is independent of the core generated axial dipole paleomagnetic reference frame comparison of plate motions measured in the two frames reveals small but systematic differences that indicate whole mantle motion relative to the earth s spin axis this is termed true polar wander and has amounted to some 12 since early tertiary time the direction and magnitude of true polar wander have varied sporadically through the mesozoic probably in response to major changes in plate motions particularly subduction zone location that change the planet s moments of inertia

contrasting facies patterns in subtropical and temperate continental slope sediments inferences from east australian late quaternary records abstract studies of latest quaternary continental slope sediments at two localities on the east australian margin have revealed markedly different responses to late quaternary sea level fluctuations offshore of noosa in the sub tropics the sediment is predominantly a mixture of fine metastable carbonate siliciclastic material and pelagic carbonate important features of the stratigraphy include a siliciclastic dominated facies deposited relatively slowly during the last glacial lowstand sedimentation rate 8 cm ka and a calcareous facies rich in metastable carbonate deposited more rapidly during the late post glacial transgression sedimentation rates 15 24 cm ka highstand and transgressive sedimentation rates are greater than lowstand rates by a factor of 2 5 6 due to increased shelf carbonate productivity after flooding of the mid shelf off sydney in temperate latitudes continental slope sediment is largely a mixture of fine siliciclastic material and pelagic carbonate mean sedimentation rates range from 2 to 5 cm ka over the last four oxygen isotope stages with mean glacial interstadial rates higher than holocene rates by a factor of 1 36 this largely reflects the transfer of siliciclastic mud from the shelf to the slope during sea level regression in both localities facies changes on the slope are not related to specific sea level states e g lowstand facies transgressive facies etc but reflect instead the interaction of changing sea level with shelf morphology

last interglacial and holocene trends in sea level maxima around australia implications for modern rates this paper defines the spatial trend in sea level around australia at 3 timescales namely at the time of the maximum of the last interglacial around 125 000 yr b p during the holocene maximum between 5000 and 6000 yr b p and over the last 20 years last interglacial elevations range from 2 m around the great barrier reef to 32 m in northeast tasmania trend surface analysis shows that over 77 of the noise in these sea level elevations can be accounted for by a pattern evidencing tectonic uplift towards the southern edge of the continent assuming a eustatic sea level at this time of 4 to 6 m most of the east coast of new south wales and the west coast of western australia can be considered tectonically stable while the southern edge of the continent has risen by at least 5 m and the north northeast corner has downwarped by at least 2 m the spatial pattern of the holocene maximum tentatively supports the continuation of this tectonic deformation sea level at this time reached 1 6 and 2 4 m above present high tide limits around the northern and southeastern coastlines of australia respectively this holocene pattern is weak because much of the data is dominated by local variations reflecting differential loading of the continental shelf by water during the holocene transgression the holocene trend surface does not support geophysical modelling implying a southern latitudinal downwarping of the crust produced by the melting of the antarctic ice sheet and the loading of the ocean crust with meltwater however the spatial pattern of modern trends appears to contain a remnant holocene signal fitting this isostatic model rather than the long term pattern of tectonic flexure since the last interglacial sea level is presently rising at a rate of 1 75 mm yr 1 in northern australia compared to only 0 75 mm yr 1 in tasmania these results imply that isostatic factors as well as previously identified climatic variables may be controlling present day variations in the rate of change of sea levels around the australian continent

geothermal fluid chemistry of the orakeikorako field new zealand abstract samples of water and steam from natural discharges in the orakeikorako geothermal area of the taupo volcanic zone have been analyzed for their chemical and stable isotopic components the waters are near neutral with chloride contents less than 400 mg kg a model of the subsurface hydrology based upon well measurements and chemical and isotopic measurements has been developed in which the dilute waters discharged at the surface are considered to result from the dilution of deeper fluids which may have temperatures as high as 280 c in the northern parts of the field waters with relatively lower chloride and higher bicarbonate composition have further diluted the rising fluid there is no evidence that local lake or river waters have changed the field character or water composition significantly since the river water level was raised

multidisciplinary approaches to australian island pasts late pleistocene to historical perspectives on australian island use in this review volume we bring together researchers and institutions involved in australian island research to provide a contemporary synthesis and benchmark on archaeological and palaeoenvironmental research of australian island environments the last major overview of australian islands archaeological research appeared 16 years ago in the volume australian coastal archaeology hall and mcniven 1999 at that time the main geographical areas of dynamic islands research in australia were northwest western australia and central and southeast queensland since 1999 torres strait has developed as the most dynamic region of islands research in australia and this new volume showcases the range of recent research from torres strait and the adjacent region of southern papua new guinea all five inqua commissions coastal and marine processes humans and the biosphere palaeoclimates stratigraphy and chronology terrestrial processes deposits and history are represented in the papers in the volume key environmental themes explored through the volume are geoarchaeology taphonomy impacts of sea level rise and climate change chronology of island formation and colonisation anthropogenic environmental modifications island terrestrial and marine resource management and intra and inter island occupation mobility and exchange relationships key socio cultural themes explored include ritual and ceremonial sites mortuary practices canoe voyaging and responses to colonial impact site types discussed include shell deposits cultural and natural villages long houses gardens rock art ritual shrines artificial reefs and ceremonial stone arrangements the contributions represent diverse multidisciplinary approaches adopting coordinated methodologies to the task of understanding the diversity of human use and modification of islands in the australian context culturally and chronologically the volume surveys the depth and breadth of australian island societies including studies of late pleistocene island use in northwest australia late holocene deltaic island societies of papuan lowland rainforests early to mid holocene tropical island use of torres strait and the great barrier reef and holocene selective occupation and abandonment of bass strait and other southern ocean islands the volume s geographic coverage is thus broadscale spread from the hot and humid tropical north to the cold temperate waters of the southern ocean uniquely the papers in this volume reveal the diversity and complexity of cultural practices e g subsistence mobility technology socio religious institutions cosmology resource manipulation and management and historical contingencies that structure and mediate long term human use engagement and modification of islands

warmer or cooler late holocene marine palaeoenvironments interpreting southeast australian and brazilian sea level changes using fixed biological indicators and their δ18o composition abstract relic inter tidal assemblages of sessile organisms which are referred to as fixed biological indicators fbis are shown to be useful proxies for late holocene climatic and environmental changes as well as direct indicators of short term fluctuations in sea level a detailed comparison of change in the inter tidal assemblages of two southern hemisphere sites at comparable latitudes port hacking new south wales south east australia and the laguna imbituba region of southern brazil indicates periods of marked similarities in the timing and nature of changes at 5200 3800 cal years bp and differences after 2400 cal years bp there is sufficient concurrence of cooling phases and falling sea levels to strongly suggest that in some cases global rather than regional forcing factors are at work the value of inter tidal organisms as indicators of changed environments is developed by identifying the past and present distributions of the common marker species tubeworms barnacles and mussels the 18 o content of these extant specimens at port hacking confirmed changes in ocean water temperature and associated sea level behaviour corresponding to invasion or extinction of temperature sensitive species a similar pattern is repeated although in a less marked fashion in the laguna imbituba region of southern brazil

the chemistry of geothermal waters in iceland iii chemical geothermometry in geothermal investigations abstract new data from geothermal wells in iceland have permitted empirical calibration of the chalcedony and na k geothermometers in the range of 25 180 c and 25 250 c respectively the temperature functions are t c 1112 4 91 log sio 2 273 15 t c 933 0 993 log na k 273 15 concentrations are expressed in ppm these temperature functions correspond well with the chalcedony solubility data of fournier 1973 and the thermodynamic data for low albite microcline solution equilibria of heloeson 1969 a new co2 geothermometer is proposed which is considered to be useful in estimating underground temperatures in fumarolic geothermal fields its application involves analysis of co2 concentrations in the fumarole steam the temperature function which applies in the range 180 300 c is logco2 37 43 73192 t 11829 103 t2 0 18923t 86 187 logt where t is in k and co2 in moles per kg of steam

inter tidal fixed indicators of former holocene sea levels in australia a summary of sites and a review of methods and models abstract the reconstruction of mid to late holocene marine environments using the calcareous remains of inter tidal fixed biological indicators as sea level proxies is reviewed useful palaeo environmental information can be obtained from the fossil evidence of successive invasions and disappearances of tropical and temperate species within the sub fossil inter tidal biological sequences examples illustrating spatially synchronous late holocene sea level fluctuations are described from 3000 km of north south coastline along eastern australia the method uses tightly constrained species such as the tubeworm galeolaria caespitosa which allows for the precise measurement of relative sea level fluctuations by using the differential between emerged sub fossil encrustations and current distributions of the same species the error range can be defined according to the extent of preservation of the relic distributions particularly the extent that diagnostic boundaries between species limited to different inter tidal zones have been preserved the rapidity of sea level fluctuations is inferred by the preservation from erosion of emerged shell layers as well as discontinuities in the relic biological sequences and the relative preservation of fragile species this apparent rapidity of sea level fluctuations as well as evidence of near uniform synchronous sea level heights along the north south span of the entire australian coast and equally consistent variations australia wide in spencer gulf and rottnest island raises questions about the predicted poleward decline of sea level curves derived from hydro isostatic rebound modelling

holocene palaeoecology and formation of the shoalhaven river deltaic estuarine plains southeast australia the shoalhaven river is one of the largest rivers on the south coast of new south wales and the deltaic estuarine plains associated with its mouth represent a mature stage of infill of a barrier estuary the stratigraphy of sediments from more than 60 drillholes from the plains indicates that the area has infilled during the mid holocene as a result of input of marine sands associated with a sand barrier on the high energy coast and fluvial mud and sands from the shoalhaven river molluscan assemblages indicate that marine influence was initially widespread throughout the eastern and southern parts of the embayment and that most of the plains infilled under estuarine conditions prominent levees across the plains surface are interpreted to be part of a birdsfoot delta distributary complex and individual floodbasins accreted progressively as they were encapsulated by distributary extension these former tidal environments mean that there are extensive potential acid sulphate soil conditions beneath the

genetic relationship between the emeishan plume and the bauxite deposits in western guangxi china constraints from u pb and lu hf isotopes of the detrital zircons in bauxite ores abstract the formation processes and alumina sources of the large and super large bauxite deposits that have developed in west guangxi in the yangtze block have been debated for a long time shrimp zircon u pb dates combined with in situ hf isotopic data of the detrital zircons from permian bauxite ores in the western guangxi province china provide new constraints on the genesis of the bauxites in west guangxi u pb dating ages of the detrital zircons cluster around 256 ma and 261 ma this is consistent with the emplacement age of the emeishan plume thus it has been determined that the detrital zircons come from magmatic rocks related to the emeishan plume and that the emeishan plume has significant control on the formation of bauxites in addition this work presents new evidence for the evolution of the emeishan plume most of the e hf t values of the zircons around 256 ma and 261 ma are negative varying widely from 1 3 to 16 1 this data indicates the melting of yangtze block basement rocks and the mixing of magmas generated both from the mantle and from the crust occurred at the periphery of the plume in the main phase of emeishan lip magmatism this study verified that the plume induced uplift exposed carbonates as well as the mafic and felsic rocks generated by the emeishan plume to long periods of intense weathering under humid tropical conditions the weathering remnants of the high alumina magmatic rocks and carbonates were deposited on or transported to the paleokarst surface and converted to bauxites

ce anomalies in the textural components of upper cretaceous karst bauxites from the apulian carbonate platform southern italy the chemical and mineralogical composition of upper cretaceous apulian karst bauxites southern italy and their textural components i e ooids and matrix has been studied the bulk samples are composed of boehmite hematite anatase and kaolinite the samples collected along a vertical profile show a downward enrichment for the elements rb sr ba ni and cr a similar distribution is observed in deposits bauxitized in situ at the expense of matrix like material collected in the karst zone the ooids consist mainly of hematite with minor boehmite and anatase whereas in the matrix boehmite prevails on hematite kaolinite and anatase in the void fillings in the matrix there is a ca fluorocarbonate having a ce ce of 5 8 the ooids with the exception of ce are enriched in ree and show a higher la yb ch ratio relative to the matrix the matrix exhibits a large positive ce anomaly whereas the ooids have negative ce anomaly the ce fractionation between the textural components can be explained assuming 1 ce oxidation and cerianite precipitation in the uppermost part of the deposits 2 scavenging of ree from ce depleted percolating solutions by the iron oxide inducing both ree enrichment and ce negative anomalies in ooids 3 remobilization of cerium as fluoride complex as a consequence of more acidic conditions in the uppermost part of the deposit and precipitation of ce3 as fluorocarbonate mineral toward the carbonate bedrock barrier at alkaline ph alternatively the cerium remobilization possibly as a carbonate fluoride complex could be due to an eh decrease favoured by a rise of the groundwater level

factors controlling the trace element distribution in fine grained rocks the albian kaolinite rich deposits of the oliete basin ne spain abstract this paper combines mineralogical data x ray diffraction petrographic and scanning electron microscopy techniques and geochemical analyses in order to investigate the composition of a set of samples claystones siltstones and sandstones which belong to the albian deposits of the oliete basin in spain the aims of the study are to characterize the distribution of major and trace elements in kaolinite rich rocks to infer the role played by accessory phases and clay minerals on the trace element distribution and to assess the source area composition of these materials mineralogical analyses show that these rocks are mainly composed of different proportions of quartz and clay minerals kaolinite and illite with minor feldspar micron accessory minerals such as monazite zircon pyrite marcasite fe oxides and ti oxides have also been detected the sandstone framework implies that the source area of these sediments was probably a granitoid source which underwent low rank metamorphism the major element distribution reflects the mineralogy of the rocks plots in the a cn k diagram as well as their cia values indicate that these sediments were generated from an intensely weathered source area this produced the development of relatively cation poor clays such as kaolinite and claystones with large rare earth elements ree contents the fact that transition element contents in claystones are greater than in siltstones and sandstones suggests that they are preferentially linked to clay minerals probably by surficial sorption in comparison with other lithologies the high abundances of high field strength elements in siltstones imply that accessory minerals such as zircon and nb bearing phases are mainly concentrated in siltstones it should be noted that siltstones are also the lithology which displays the highest ree abundances the statistical analysis of the geochemical data suggests that ree are mainly controlled by ti and nb bearing phases such as titanite and nb and ti oxides although clay minerals are not the main phases in the ree control they probably also have some influence as the analyses show in addition other accessory phases such as monazite secondary phosphates and zircon also contribute to the ree contents although much less than amorphous fe oxides in some samples according to the ree patterns and elemental ratios such as la sc th sc th co etc the source area of the studied outcrops was probably felsic and with intermediate composition between granite and granodiorite

aeolian accumulation an alternative origin of laterite on the deccan plateau india abstract laterite is ubiquitous in india and has been extensively studied however it is still controversial with respect to its origin definition classification and implications in paleoclimate tectonic history and topography evolution of those the origin of laterite either in situ weathering of protoliths or weathering of allochthonous input is the most critical to address the ca 25 m thick laterite duricrust capping the deccan plateau is conventionally hypothesized to derive from in situ weathering of the topmost basalt however this thick laterite lacks upward progressive weathering which is characteristic of lateritic profile instead it displays 1 homogeneity in weathering intensity through the duricrust 2 a clear unconformable contact of laterite with red clay which together suggests that this thick laterite is genetically unrelated to in situ weathering of the topmost basalt lines of evidence in mineralogy granularity and geochemistry proved the disconnection between this laterite and basalt and in contrast indicated its correlation to aeolian accumulation in this study the laterite together with the red clay was proposed to derive from aeolian dust accumulation and weathering since 65 ma within context of indian plate drifting across the equator from southern to northern hemisphere

major hydrogeochemical processes in the two reservoirs of the yangbajing geothermal field tibet china abstract the yangbajing geothermal field with the highest reservoir temperature in china is located about 90 km northwest to lhasa city capital of tibet where high temperature geothermal fluids occur both in shallow and deep reservoirs the geophysical survey by the indepth international deep profiling of tibet and the himalayas project group proved the existence of magmatic heat source at yangbajing in the study area the hydrochemistry of cold surface waters and groundwaters and that of thermal groundwaters from both reservoirs are distinctively different however analysis of the relationship between enthalpy values and cl concentrations of cold groundwaters and geothermal fluids indicates that the geothermal fluids from the shallow reservoir were formed as a result of mixing of cold groundwaters with geothermal fluids from the deep reservoir in other words the geothermal fluids from the deep reservoir flowed upwards into the shallow reservoir where it was diluted by the shallow cold groundwaters to form the shallow geothermal fluids with much lower temperature a binary mixing model with two endmembers the cold groundwaters and the deep geothermal fluids was proposed and the mixing ratios for the geothermal fluid from each shallow well were estimated using the mixing ratios the concentrations of some constituents in shallow geothermal fluids such as as b sio 2 so 4 2 and f were calculated and their differences with the actual concentrations were estimated the results show that the differences between estimated and actual concentrations of as and b are small the average absolute values being only 1 9 and 7 9 respectively whereas those of sio 2 so 4 2 and f are much bigger indicating that other hydrogeochemical processes are responsible for the concentrations of these constituents it is postulated that sio 2 precipitation due to water temperature decrease h 2 s oxidation and ion exchange between oh in geothermal waters and exchangeable f in fluoride bearing silicate minerals during the geothermal fluid upflow might be the causes for the observed concentration differences

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

the logic of visitation tool use technology and economy on great glennie island southeastern australia abstract archaeological excavation over 30 years ago in a small granite cave on great glennie island 7 km off the southernmost tip of mainland australia revealed five stratigraphically distinct midden units with intermittent occupation over the last 2000 years fluctuations in tool stone quartz and flint abundance and the nature of tool use track a shift in economic focus from one dominant taxon seabird during initial visits to four seal seabird fish and shellfish in the last 500 years an analysis of flint cortex distributions indicates that during the second visit people carried core tools and retouched flint flakes and during later visits they transported unworked flint nodules for knapping flakes as needed on the island these data have been integrated with a functional analysis of all the stone artefacts to evaluate a model of human settlement based on island biogeography formulated by jones 1976 i explore whether island toolkits can be linked with shifts in food procurement and argue that the island was visited infrequently because there was no compelling need to regularly harvest its rich food resources

prehistoric blood residues detection on tool surfaces and identification of species of origin blood residues from several animal species have been discovered on the surfaces of chert basalt and obsidian prehistoric tools 1000 to 6000 years old from open air sites along the western coast and in the northern boreal forest of canada a screening test has been developed to detect residual blood hemoglobin has been crystallized from the residues and the species of origin determined

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

argillite debris converted to bauxite during karst weathering evidence from immobile element geochemistry at the olmedo deposit sardinia the olmedo bauxite deposit occurs in the nurra district of northwest sardinia it forms a stratiform horizon in cretaceous limestone and marl uplift in mid cretaceous had exposed recently deposited limestone to karst weathering and a layer of argillaceous debris accumulated on its surface and was partly converted to bauxite intermediate products were desiccated marl bauxitic argillite and argillaceous bauxite subsidence followed and the bauxite was preserved by the deposition of late cretaceous limestone and other sediments uplift in oligocene miocene time with ensuing erosion exposed the bauxite horizon to its present configuration concentrations of normative minerals illustrate chemical processes and the build up of al in the bauxite horizon plots of chemical data and correlation coefficients show that al ti zr nb th cr and v were immobile during the bauxitization process mass changes point to large net removal of si mg and k from the system although some of this material and slightly mobile al were reprecipitated in the underlying argillite and altered marl immobile element ratios trace the source of the bauxite to the underlying argillaceous limestone al in the bauxite was accumulated from the degradation of 25 to 50 m of the argillaceous limestone

rare earth element mobility during conversion of nepheline syenite into lateritic bauxite at passa quatro minais gerais brazil abstract in a lateritic bauxite formed by weathering of nepheline syenite at passa quatro minas gerais state brazil bauxites on the hill tops directly develop from the syenite bed rock while downslope a kaolinitic layer occurs between bauxite and synetie a petrological investigation was performed on undisturbed weathered rock samples collected from a representative upslope pit the undisturbed weathered rocks were chemically analysed for major trace elements including ree and zr mass balance calculations were applied and the behaviour of the ree in the passa quatro weathering system was established compared to ree reference chondrite and to ree reference parent rock in the lateritic bauxite the results suggest that the first stages of weathering induce a volumetric change of 50 i e collapse with respect to the parent rock and remove ree with a slightly larger loss of the lree except ce compared to the hree in the upper layers where bauxite is more mature a net mass gain in ree is observed relative to the underlying layers this gain takes place during the reduction of the upper layer during the downward progression of the weathering front very significant ree losses occurs during the bauxitization processes throughout the upslope profile in addition the downslope kaolinitic system is demonstrated to be depleted in ree in the same proportions as the upslope bauxite we proposed that the ree exported in solution from the whole weathering mantle have enriched neighbouring watershed sediments

smooth or oscillating late holocene sea level curve evidence from cross regional statistical regressions of fixed biological indicators abstract what if any is the pattern of change of the late holocene sea level curve if a common pattern exists can it be better discerned in the non glaciated tectonically stable regions of the southern hemisphere and is sea level data more reliable from one type of marine sample than another to begin an investigation of these questions we present a review of regressing time elevation plots from the low to mid latitudes of the southern hemisphere based upon the differential between modern and past levels of various fixed biological indicators mainly calcareous tubeworms and corals stranded up to 2 m above present relative sea levels the sample sets come from our work in southeast australia and comparable work from north east australia the pacific islands and brazil we show that using evidence obtained from fixed intertidal tubeworm species there is no statistical exclusivity between the smooth and oscillating polynomials but corals are more problematic in situ tubeworm species with their reduced error bars in comparison to corals fulfil the condition of providing more robust results for statistical analysis regression curves based on these species point to cross regional similarities in the pattern of sea level movement of the last 6000 years across the lower latitudes of the southern hemisphere these statistical exercises while not able to yield definitive conclusions can highlight statistically equally likely alternative patterns of sea level movement which can then be tested by field evidence they can also give useful indications of the quality of sea level data obtained from different biological sources as in the difficulties in the use of corals compared to common intertidal tubeworm species

geochemical study of laterites of the jamnagar district gujarat india implications on parent rock mineralogy and tectonics abstract the laterite deposits occur in a linear stretch along the northern arabian sea coast in the jamnagar and porbandar districts of gujarat state india these deposits are characterised by presence of gibbsite kaoline calcite quartz anatase natroalunite goethite and hematite and relicts of mafic minerals and plagioclase on the basis of petro mineralogy and geochemistry these deposits are grouped as aluminous laterites fe2o3 1 45 3 84 av 3 13 al2o3 39 31 57 24 av 45 80 and laterites fe2o3 9 84 32 21 av 25 13 al2o3 34 74 49 59 av 41 27 the major trace and ree characteristics of laterites indicate that these were formed in situ by the alteration of parent rocks of trachytic andesitic composition and the process of bauxitisation followed the path of destruction of kaolinite and deferruginisation the correlation patterns of several trace and rare earth elements and their preferential enrichment have indicated that there is an influence of precursor rock on the distribution of trace elements the jamnagar laterite deposits occur as capping over the deccan trap basaltic lava flows and pyroclasic deposits lateritisation prevailed during palaeocene age when india was separated from the seychelles and passing over the equator during this time climate morphology and drainage conditions were favourable for lateritisation that result in the formation of jamnagar and other laterite deposits within the deccan province flood basaltic provinces of deccan columbia north australia and hawaii appear good location for hosting laterite deposits due to their wide areal extent small geological time span and uniform chemical composition however comparison of the major flood basaltic provinces of the world has indicated that their palaeopositions along with palaeoclimate morphology and drainage are equally important factors for facilitating lateritisation

aspartic acid racemisation dating of mid holocene to recent estuarine sedimentation in new south wales australia a pilot study abstract the degree of aspartic acid racemisation measured in radiocarbon dated specimens of fossil estuarine molluscs collected from lake illawarra a holocene barrier estuary in new south wales australia is evaluated in the context of results of laboratory induced racemisation established in heating simulated ageing experiments the general kinetic trend of aspartic acid racemisation in both heating experiments and fossil molluscs anadara trapezia and notospisula trigonella conforms to a model of apparent parabolic kinetics using the apparent parabolic kinetic model numeric ages based on the degree of aspartic acid racemisation in the fossil molluscs have been calculated an aminostratigraphy of the lake illawarra holocene basin fill has been established based on the extent of aspartic acid racemisation measured in 29 specimens of fossil molluscs aspartic acid d l ratios in a trapezia and n trigonella range from 0 079 0 005 to 0 436 0 004 representing an age range from

lateritization and bauxitization events laterites and bauxites are produced in tropical soils by weathering which enriches iron of laterites and alu mina of bauxites as well as trace elements such as nickel gold phosphorus and niobium to ore grade la terites and bauxites can be redeposited into sedimentary sequences and remain as ores if not transported far and diluted with other materials the age of redeposited laterites and bauxites and of bauxitic and lateritic pa leosols can be established from the geologic age of overlying rocks an approach especially effective in pale osols within sequences of isotopically datable volcanic rocks lateritic profiles can also be dated by paleomag netic inclination in special cases in which land masses such as in australia and india drifted long distances northward during cenozoic time in addition cryptomelane and other k mn oxides can be dated by k ar and 40ar 39ar techniques to obtain multiple ages from different crystals in a single relict paleosol compilation of new and more accurate laterite and bauxite ages reveals unusually widespread and intense laterite and bauxite formation during events of less than 100 k y duration at 2 12 16 35 48 55 65 and 100 ma such events can also be inferred at times older than 100 ma from paleolatitudinal distribution of laterites and bauxites but these are poorly sampled laterite and bauxite peaks were coeval with times of global high warmth and pre cipitation elevated atmospheric carbon dioxide oceanic anoxia exceptional fossil preservation and mass ex tinction these co2 greenhouse events and attendant titration of carbonic acid with soils are interpreted as transient fluctuations in the atmosphere produced by meteorite impact flood basalt volcanism and methane outbursts concentration of bauxite and laterite resources in particular stratigraphic horizons formed during greenhouse crises suggests the usefulness of an event stratigraphic approach to exploration and exploitation of these and related ores

phase transformation processes in karst type bauxite deposit from yunnan area china abstract bauxite is the only resource of aluminum metal and forms through weathering leaching and deposition i e bauxitization processes here we characterize the bauxite deposit in yunnan area china through mineralogical and textural characteristics using xrd sem edx and micro raman analyses the al oxyhydroxide polymorphs alo oh such as diaspore and boehmite are the dominant phases in most of the samples gibbsite al oh 3 is the main mineral in two samples from quaternary bauxite and these three al rich minerals mixed with goethite hematite kaolinite and small amounts of tio 2 polymorphs anatase and rutile considering the textural characteristics and the stratigraphy of the bauxite deposit some of the al oxyhydroxides and ti oxides are inferred to be products of the bauxitization in the lateritic soil during late permian weathering in the subsequent transgression stage the earlier formed al rich minerals and anatase phases were transformed to diaspore or boehmite as spherulitic form and to rutile respectively with the processes of diagenesis burial metamorphism tectonic movements and magmatic activity following crustal uplift in the yunnan province after the late triassic diaspore was transformed into boehmite and the bauxite deposit formed earlier was exposed again to weathering resulting in the formation of gibbsite hematite goethite kaolinite and anatase with diaspore boehmite and rutile remaining as relics our study provides insights into phase transformation during bauxitization and subsequent processes

trace elements and their relation to the mineral phases in the lateritic bauxites from southeast guinea bissau abstract fourteen trace elements sr ba la ca mg cu zn v ni co mn ga cr zr were determined in 120 auger and core drill samples from one bauxite plateau situated in the se part of guinea bissau following the quantitative determination of minerals identified in the samples all geochemical and mineralogical data were statistically treated the use of several statistical tools enabled us to identify two distinct populations of samples which were found to be related to the shale and dolerite parent rocks respectively the dispersion patterns of the elements mn zr la zn cu cr and ni yield strong contrasts between these two populations bauxites developed on devonian shales were found to contain more cr and ni than bauxites derived from cretaceous dolerites which were richer in cr and ni it is postulated that the difference in duration of the bauxitization processes which affected the two parent bedrocks and or the different resistance to weathering of the primary mineral host phases in the two rock types are responsible for this inversion r mode factor analysis revealed the conspicuous affinity of the mn zn ni cu co mg group and v to goethite gibbsite boehmite and anatase were found to be associated with resistate trace elements like zr and to a lesser extent cr gibbsite also reveals a certain affinity to more mobile strongly depleted elements like sr and ba the study proved the existence of numerous statistically significant correlations between the trace elements like the groups zr ti zn cu ni co mn and sr ba la

geochemical and mineralogical features of karst bauxite deposits from the alborz zone northern iran implications for conditions of formation behavior of trace and rare earth elements and parental affinity abstract the present study focuses on three outcrops of upper permian to lower jurassic karst bauxite deposits in the alborz zone north of iran the deposits occur as sharp semi continuous lenses within the upper permian ruteh formation gheshlagh and the upper triassic elika formation siahrudbar and separdeh carbonate rocks textural characteristics such as pelitomorphic matrix local ooidic pisoidic fluidal and clastic textures indicate authigenic allothigenic origins mineralogically kaolinite boehmite goethite and hematite in the gheshlagh diaspore hematite and kaolinite in the siahrudbar and kaolinite hematite goethite diaspore siderite and chamosite in the separdeh deposits are the main phases the distribution patterns of major elements normalized to the upper continental crust ucc depict enrichments of al fe and ti in all three deposits the three deposits are variably enriched in transition trace elements cr ni co v u th and high field strength elements ga hf zr nb y relative to ucc the studied bauxites have average concentrations of rare earth elements ree la lu between 305 97 and 373 69 ppm geochemical data reveal progressive enrichment of ree and an intense lree hree n fractionation toward the lower parts of the profile in the separdeh deposit due to the alkaline conditions of the carbonate bedrock and irregular distribution patterns at the gheshlagh and siahrudbar deposits due to water level and ph fluctuations the positive ce anomalies at separdeh and siahrudbar suggest oxidizing conditions in the upper parts of the profiles at gheshlagh the negative to nil ce anomalies reflect low intensity of oxidation based on previous geochemical analysis data the upper permian basalts in the gheshlagh and the upper triassic basalts in the separdeh and siahrudbar areas were the most likely source materials the local uplift of the permian upper triassic series led to the formation of karstic topography filled with materials derived from weathering of the basaltic rocks under humid tropical paleoclimate the initial weathering converted the source rocks to kaolinitic soils characterized by the enrichment of al fe and ti then they were transferred to the karstic depressions and sinkholes and underwent in situ leaching and desilicification bringing about a relatively higher ore grade the overall field and petrographic evidence demonstrate that these deposits were formed in shallow and swampy environments in the eastern part of the alborz zone at siahrudbar and gheshlagh better drainage conditions have enhanced the quality of ores