quantitative integration of sedimentological core descriptions and petrophysical data using high resolution xrf core scans abstract in light of the huge investments needed to acquire sediment cores and the growing need of energy providing companies to predict reservoir quality it is remarkable that the standard workflow in core analysis has not been optimized to extract as much information from cores as possible the integrated core analysis ica protocol presented in this study provides a statistical framework for multivariate calibration and prediction of a wide range of properties measured in core based on integration of high resolution x ray fluorescence core scanning xrf cs proxy records with records of sparsely sampled petrophysical data and sedimentological core descriptions the downscaling of numerical data involves the application of invertible transformations to remove range constraints on data followed by calibration with partial least squares regression through cross validation categorical data i e lithofacies are downscaled by associating each class with a statistical model based on the xrf cs data all data points are reassigned to their most likely class by applying quadratic discriminant analysis the result of the ica is a multivariate data set in which all properties are specified at the same high resolution along the core with their prediction uncertainties downscaling of all variables to 1 cm vertical resolution permits investigation of the variability among petrophysical properties geochemical proxies and lithofacies memberships petrographic analysis is fundamental for interpretation of the xrf cs records element mineral affinity and for understanding the sedimentological controls on predicted petrophysical properties application of the ica protocol to a 32 m thick heterogeneous upper carboniferous fluvial sandstone interval resulted in a near 30 fold increase of the petrophysical data base which allowed identification of the main depositional and diagenetic controls on the spatial distribution of reservoir quality successful implementation of the novel ica protocol will greatly increase the economic value of legacy core data in studies that aim to re use depleted hydrocarbon reservoirs

enhanced turbulence and energy dissipation at ocean fronts the ocean surface boundary layer mediates air sea exchange in the classical paradigm and in current climate models its turbulence is driven by atmospheric forcing observations at a 1 kilometer wide front within the kuroshio current indicate that the rate of energy dissipation within the boundary layer is enhanced by one to two orders of magnitude suggesting that the front rather than the atmospheric forcing supplied the energy for the turbulence the data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence the resulting boundary layer is stratified in contrast to the classically well mixed layer these effects will be strongest at the intense fronts found in the kuroshio current the gulf stream and the antarctic circumpolar current all of which are key players in the climate system

first cycle quartz arenites in the orinoco river basin venezuela and colombia modern first cycle quartz arenites are forming in the orinoco drainage basin by at least two distinct mechanisms common to both mechanisms is an environment of intense chemical weathering and extended time over which weathering can occur in the llanos andean foreland basin extended time is provided by temporary storage of orogenically derived sediments on extensive alluvial plains in lowland portions of the guayana shield long soil mineral residence times are produced by very low erosion and transport rates resulting from low relief and tectonic quiescence both weathering intensity and the duration of weathering are important in the modification of sand composition first cycle quartz arenites are produced in diverse tectonic settings and cannot be used by themselves to infer paleotectonic settings of ancient sequences furthermore although tectonic setting is of great importance in determining sand composition modifications during transport and deposition can overprint the effects of the tecto

sedimentology stratigraphy and geochronology of the proterozoic mazatzal group central arizona quartzite conglomerate and shale of the mazatzal group record the filling of a prot erozoic intra arc basin in central arizona u pb ages of zircons from rhyolite ash flow tuff indicate that deposition began at 1701 2 ma basal deposits of the newly defined pine creek conglomerate formed in an alluvial fan setting synchronous with the final phase of extrusive rhyolite volcanism and active faulting after volcanic activity ceased shallower slope braided stream environments developed in early deadman quartzite time subsequent marine transgression produced shallow subaqueous deposits of the upper part of the deadman quartzite these were overlain by prodelta sediments of the maverick shale indicating a phase of basin deepening finally the mazatzal peak quartzite was deposited as the basin shoaled again first to shallow marine and subsequently to fluvial conditions the quartzite is diagenetic quartz arenite originally deposited as lithic arenite and lithic arkose the provenance was initially restricted and earliest sediment was derived mainly from the subjacent red rock group when tectonic activity ceased how ever the surrounding highlands were planed down by erosion and detritus from a wider variety of source rocks was funneled into the basin this included contributions from arc related supracrustal rocks of the payson ophiolite and east verde river formation and finally a granitic basement input detrital quartz in the lower part of the mazatzal group is largely monocrystalline and volcanic in origin polycrystalline quartz associated with detrital feldspar and of probable continental affinity is concentrated in the uppermost parts of the sequence the life span of the intra arc basin was on the order of 30 m y from the formation of the payson ophiolite at 1 73 ga to the deposition of the upper mazatzal peak quartzite sometime after 1 70 ga the pre mazatzal red rock group represents the last stages of volcanic arc activity and the mazatzal group records the transition from orogenic to nonorogenic sedimentation in central arizona

fluid dynamics of oceanic thermocline ventilation abstract a flux form of the potential vorticity pv equation is applied to study the creation and transport of potential vorticity in an ocean gyre generalized pv fluxes j vectors and the associated pv flux fines are used to map the creation by buoyancy forcing of pv in the mixed layer and its transport as fluid is subducted through the base of the mixed layer into the thermocline the pv flux lines can either close on themselves recirculation or begin and end on the boundaries ventilation idealized thermocline solutions are diagnosed using j vectors which vividly illustrate the competing process of recirculation through western boundary currants and subduction from the surface potential vorticity flux vectors are then used to quantify the flux of mass passing invisidly through a surface across which potential vorticity changes discontinuously but at which potential density and velocity are continuous such a surface might be the base of the oceanic mixed layer or in a meteorological context

the spatial distribution of grains and crystals in rocks characterisation and analysis of the spatial distribution pattern sdp of grains or crystals in rocks is potentially a powerful technique which can be used to constrain the processes which operate in the formation of rocks a method to quantify the sdp of grains in thin section is presented the distance betwen the centre of a grain and the centre of its nearest neighbour is calculated for all the grains in the sample area to produce a distribution of distances that characterises the spatial pattern of grains in the rock this distribution is then normalised to a random distribution of points with the same population density to give a descriptive value r values of r for rock samples are plotted against porosity modal abundance of other phases in igneous and metamorphic rocks to characterise the sdp the sdp of randomly packed distributions of equal size spheres varies systematically with porosity producing a line on a porosity versus r plot termed the random sphere distribution line rsdl rocks which plot above the rsdl have an ordered sdp and those that plot below a clustered sdp the effects of variation in grain packing order grain sorting compaction and random crystallisation overgrowth on determined r values were investigated using a combination of 3 d sphere models and 2 d texture models the maximum possible value of r is 2 148 corresponding to a perfect section through hexagonal cubic close packing of grains the minimum value of r is dependent on the proportion of grains in the sample volume and may be as low as 1 2 for a sample volume with 30 grains which are clustered variations in size sorting can cause r to vary by approximately 0 25 mechanical compaction of a loose framework of grains results in a higher packing order and an increase in r continued compaction creates a fabric in the texture and r decreases as cluster patterns are developed perpendicular to the principal stress the overgrowth of grains in a touching framework alters the location of the geometric grain centre as the crystal shape changes leading to an increase in r as porosity decreases results reveal that grain sorting compaction and grain overgrowth produce different r versus porosity relationships which can be identified in and therefore used to constrain the relative importance of these processes in rock samples

south america and a few grains of sand part 1 beach sands to study correlations between petrography and provenance of modern sands and thus contribute to improved interpretation of ancient sandstones this study reports on the petrography of 218 modern south american beach sands obtained from a shoreline of 25 300 km judged by quartz feldspar rock fragment ratios there are five major associations pacific 24 16 60 argentina 28 14 58 brazil 91 4 5 caribbean east 59 8 23 and caribbean west 54 17 29 study of potash feldspar volcanic rock fragments and the sio 2 al 2 o 3 ratio supplement q f rf ratios tectonics are the dominant control on the mineralogy both the pacific and brazilian associations which form 75 of south america s coastline identify correctly tectonic setting that is active margin composition for the pacific and passive margin for the brazilian however the argentine association would yield a serious error because sand with active margin composition overprints a passive margin variation of total quartz and feld

subsurface dissolution of heavy minerals frio formation sandstones of the ancestral rio grande province south texas abstract oligocene sandstones frio formation of south texas deposited by the ancestral rio grande contain a heavy mineral assemblage that is markedly altered even in the shallowest sample examined approximately 1 km depth the weight fraction of detrital heavy minerals in the modern rio grande is approximately 1 whereas subsurface frio sandstones contain as little as 0 1 or less heavy minerals modern rio grande sand contains a diverse and unstable heavy mineral assemblage dominated by pyroxenes amphiboles and an assortment of iron titanium oxides minor components include apatite garnet sphene epidote and zircon heavy minerals in subsurface oligocene sandstones include abundant apatite zircon and titanium oxide among detrital components minor iron rich garnet also survives in the subsurface to depths of about 3 km other very stable but also very minor heavy minerals include tourmaline chromite spinel and monazite locally the heavy mineral fraction in the frio is dominated by authigenic components such as siderite pyrite or barite authigenic sphalerite is also observed among the heavy minerals feldspars and rock fragments suggest that sediment deposited by the ancestral rio grande was more strongly dominated by volcanic detritus than is the modern river it is reasonable to infer that the initial heavy mineral assemblage of the frio formation was likewise more unstable than that which appears today in the rio grande thus heavy mineral loss determined by comparing subsurface frio sandstones with the sand in the modern rio grande is conservative comparison of sr and nd concentrations in modern rio grande sands and subsurface frio sandstones suggests that heavy mineral destruction in the subsurface does not cause major perturbations of whole rock isotopic systems involving these elements

poleward coastal jets induced by westerlies in the bay of biscay 1 two hydrodynamic surveys based on acoustic doppler current profiler adcp and drift buoys measurements taken in summer 2008 and 2009 revealed poleward coastal jets of up to 32 cm s 1 that lasted up to 22 d along the aquitaine shelf in the southeastern area of the bay of biscay a strong increase in bottom temperature was associated with these currents up to 4 c in 5 d at 54 m depth these observations occurred after a few days of westerlies cross shore winds which were thought to have only a limited impact on longshore circulation here the mars3d hydrodynamic model was used with a schematic bathymetry of the southeastern area of the bay of biscay to reproduce and analyze these coastal jets simulations revealed that the triggering mechanism of the poleward currents is unequivocally due to downwelling circulation induced along the spanish coast this downwelling induces an external longshore pressure gradient which generates a high speed coastal trapped wave that propagates along the french coast with a phase velocity of about 3 to 4 m s 1 and an internal baroclinic kelvin wave with a phase velocity of about 1 m s 1 a sensitivity study of the role of stratification conditions wind strength and duration was then carried out to determine the periods that are the most sensitive to this wind induced circulation

the use of mineral interfaces in sand sized rock fragments to infer ancient climate the kinds of mineral interfaces preserved in rock fragments of modern plutoniclastic sand are closely correlated with climate and topography in the source area stepwise linear regression analysis of the relationship among environmental and petrographic parameters for sand collected from 16 drainages of varying morphology developed on five granodiorite plutons demonstrates that sand composition varies systematically with temperature and precipitation and drainage steepness and area for small drainages in temperate climates the durability of each kind of mineral interface in sand sized rock fragments derived from the plutons depends on mechanical chemical and textural factors interfaces are mechanically stressed by differential expansion of minerals during unroofing interfaces between minerals of similar expansibility compressibility are more likely to remain uncracked and thus survive weathering the rate and extent of chemical dissolution of interfaces depends on the crystallography and chemistry of adjoining minerals interfaces between minerals of similar structure that have short atomicbond lengths are more likely to survive mineral inclusions are texturally isolated from rock disaggregating processes and thus more likely to survive interfaces of opaque with tectosilicate minerals are enriched relative to other interfaces by progressive disaggregation the rate and extent of which increase with increasing temperature interfaces of biotite with tectosilicates are depleted relative to other interfaces with increasing precipitation regression analysis yields statistically plausible testable models of the dependence of modem sand composition on modern climate such models can be used to quantitatively estimate ancient mean annual air temperature and precipitation based on ancient sand composition

influence of granitoid textural parameters on sediment composition implications for sediment generation the aim of this study is to determine and characterise the control exerted by parent rock texture on sand composition as a function of grain size the sands investigated were generated from granitoid parent rocks by the rhone damma and sidelen glaciers which drain the aar massif in the central alps switzerland and were deposited in glacial and fluvio glacial settings mechanical erosion comminution crystal breakdown and abrasion and hydraulic sorting are the most important processes controlling the generation of sediments in this environment whereas chemical and or biochemical weathering plays a negligible role by using a gis based microscopic information system mis five samples from the glacier drained portions of the aar basement have been analysed to determine textural parameters such as modal composition crystal size distribution and mineral interfaces types and lengths petrographic data of analysed sands include traditional point counts gazzi dickinson method minimum of 300 points as well as textural counts to determine interface types frequency and polycrystallinity in phaneritic rock fragments according to pettijohn s classification grain size dependent compositions vary from feldspathic litharenite 0 fraction via lithic arkose 1 and 2 to arkose 3 and 4 compositional differences among our data set were compared to modern plutoniclastic sands from the iberian massif spain and the st gabriel mts california usa which allowed us to assess the role exerted by glaciers in generating sediments by combining data from the mis with those from petrographic analysis we outlined the evolution of mineral interfaces from the parent rocks to the sediments

friction frontogenesis and the stratification of the surface mixed layer the generation and destruction of stratification in the surface mixed layer of the ocean is understood to result from vertical turbulent transport of buoyancy and momentum driven by air sea fluxes and stresses in this paper it is shown that the magnitude and penetration of vertical fluxes are strongly modified by horizontal gradients in buoyancy and momentum a classic example is the strong restratification resulting from frontogenesis in regions of confluent flow frictional forces acting on a baroclinic current either imposed externally by a wind stress or caused by the spindown of the current itself also modify the stratification by driving ekman flows that differentially advect density ekman flow induced during spindown always tends to restratify the fluid while wind driven ekman currents will restratify or destratify the mixed layer if the wind stress has a component up or down front i e directed against or with the geostrophic shear respectively scalings are constructed for the relative importance of friction versus frontogenesis in the restratification of the mixed layer and are tested using numerical experiments of mixed layer fronts forced by both winds and a strain field the scalings suggest and the numerical experiments confirm that for wind stress magnitudes mixed layer depths and cross front density gradients typical of the ocean wind induced friction often dominates frontogenesis in the modification of the stratification of the upper ocean the experiments reveal that wind induced destratification is weaker in magnitude than restratification because the stratification generated by up front winds confines the turbulent stress to a depth shallower than the ekman layer which enhances the frictional force ekman flow and differential advection of density frictional destratification is further reduced over restratification because the stress associated with the geostrophic shear at the surface tends to compensate a down front wind stress

rare earth element and mineralogic changes in holocene soil and stream sediment a case study in the wet mountains colorado u s a size fractions of soil and stream sediment developed on plutonic metamorphic or mixed plutonic metamorphic sources in the wet mountains colorado have been analyzed for ree rare earth elements and mineralogy the clay sized fractions 0 5 m and 0 5 2 m or 2 m have ree contents that are similar to more enriched than the source eu sm ratios that are similar to the source and la lu ratios that are higher than their corresponding source the 0 5 m fractions have lower ree contents than the corresponding 0 5 2 m fraction in every stream sediment for example unweathered san isabel batholith near the sampled stream sediment contains ree 511 712 ppm and eusmratio 0 17 0 19 and lalu cn 9 8 10 3 the corresponding 0 5 and 0 5 2 m fractions of sediment formed from san isabel batholith are enriched in the ree ree 1135 and 2225 ppm respec are slightly lower in eu sm ratios 0 16 and 0 14 respec and are higher in la lu ratios 12 2 and 16 3 respec than the unweathered rocks the silts have lree light ree contents and eu sm ratios very similar to the source due to similar mineralogy but silts have hree heavy ree contents higher than the source due to high zircon for example silt sized fractions in stream sediment draining the san isabel batholith contain ree 808 ppm eusmratio 0 18 and lalu cn 7 4 in contrast the sands contain lower ree contents similar to higher eu sm ratios and lower la lu ratios than the corresponding source due to depletion in heavy minerals concentrated in the ree and containing lower eu sm ratios relative to quartz and feldspar depleted in the ree and containing higher eu sm ratios for example the sand fraction from stream sediment from the san isabel batholith has ree 206 ppm eusmratio 0 17 and lalu cn 5 6 small variations of accessory minerals concentrated in the ree like allanite or sphene may cause drastic variation in ree content in the sand fraction clays and silts derived only from the plutonic rocks have higher ree and similar to lower eu sm ratios than corresponding fractions derived only from migmatites e g ree of silt fractions from migmatites 224 ppm and from plutons 375 808 ppm eu sm ratios from migmatites 0 17 and from plutons 0 11 0 18 the ree content and the eu sm ratio of clays and silts derived from migmatites are much more similar to the average of mcps mid continent platform sediment than corresponding fractions derived from the plutons mcps has ree 192 ppm eusm 0 19 lalu 8 0 the eusm ratio of sands derived from plutons and migmatite are lower to mostly higher than the mcps the ree content of sands from plutons are not necessarily higher than the mcps due to variation in heavy minerals like allanite or sphene concentrated in the ree sediments derived from mixed sources have ree contents in fine fractions that may not necessarily reflect the ree content of the nearest source for example 0 5 2 m and silt fractions developed on the san isabel batholith with a migmatite upstream have the high ree content of the batholith ree in 0 5 2 m fraction 1100 ppm silt 573 ppm while the corresponding 0 5 m fraction has the very low ree content of the migmatites ree 110 ppm these results suggest fine grained material near the source may sample a much larger area than coarser material near the source thus analysis of fine grained sediment associated with coarse grained material near the source may give a much different impression of the source than would determination of the source using classic petrographic examination of the sand or gravels

granular disintegration of gneiss and migmatites summary weathering of precambrian gneiss and granitoid migmatites in the kora area of central kenya is essentially a two stage process in the first stage the rocks experience granular disintegration due to the widening of grain boundary microcracks and loosening of the rock structure sem and microprobe data indicate that during this stage chemical alteration of biotite and feldspars is limited and occurs mainly on grain margins and along microcracks no evidence has been found to suggest that stresses created by extensive alteration and expansion of biotite are primarily responsible for granular disintegration the second stage of weathering involves development of intragranular microcracks and progressive chemical decomposition with leaching of ca mg na and k from biotite and feldspars

eddy saturation of equilibrated circumpolar currents abstractthis study uses a sector configuration of an ocean general circulation model to examine the sensitivity of circumpolar transport and meridional overturning to changes in southern ocean wind stress and global diapycnal mixing at eddy permitting and finer resolution the sensitivity of circumpolar transport to forcing magnitude is drastically reduced at sufficiently high resolution there is little or no sensitivity of circumpolar transport to wind stress even in the limit of no wind in contrast the meridional overturning circulation continues to vary with southern ocean wind stress but with reduced sensitivity in the limit of high wind stress both the circumpolar transport and meridional overturning continue to vary with diapycnal diffusivity at all model resolutions the circumpolar transport becomes less sensitive to changes in diapycnal diffusivity at higher resolution although sensitivity always remains in contrast the overturning circulation is more sensitive to change in diapycnal

downfront winds over buoyant coastal plumes abstractdownfront or downwelling favorable winds are commonly found over buoyant coastal plumes it is known that these winds can result in mixing of the plume with the ambient water and that the winds influence the transport spatial extent and stability of the plumes in the present study the interaction of the ekman velocity in the surface layer and baroclinic instability supported by the strong horizontal density gradient of the plume is explored with the objective of understanding the potential vorticity and buoyancy budgets the approach makes use of an idealized numerical model and scaling theory it is shown that when winds are present the weak stratification resulting from vertical mixing and the strong baroclinicity of the front results in near zero average potential vorticity q for weak to moderate winds the reduction of q by diapycnal mixing is balanced by the generation of q through the geostrophic stress term in the regions of strong horizontal density gradients and stable stratificati

on the response of a buoyant plume to downwelling favorable wind stress here the responseof a coastallytrappedbuoyantplume to downwelling favorablewind forcingis explored using a simplified two dimensional numerical model and a prognostic theory for the resulting width depth and density anomaly and along shelf transport of the plume consistent with the numerical simulations the analytical model shows that the wind causes mixing of the plume water and that the forced cross shelf circulation can also generate significant deepening and surface narrowing as well as increased along shelf transport the response is due to a combination of the purely advective process that leads to the steepeningof the isopycnals and the entrainment of ambient water into the plume the advective component depends on the initial plume geometry plumes that have a large fraction of their total width in contact with the bottom bottom trapped suffer relatively small depth and width changes compared to plumes that have a large fraction of their total width detached from the bottom surface trapped key theoretical parameters are wg wa theratioofthewidthoftheplumedetachedfromthebottomtothewidthoftheplumein contactwith it and the ratio of the wind generated mixed layer de to the initial plume depth hp which determines the amountofwaterinitiallyentrainedintotheplume themodelresultsalsoshowthatthecross shelfcirculation can be strongly influenced by the wind driven response in combination with the geostrophic shear of the plume the continuous entrainment into the plume as well as transient events is also discussed

quantitative provenance analysis of sediments review and outlook provenance analysis of sediments is aimed at reconstructing the parent rock assemblages of sediments and the climaticphysiographic conditions under which sediments formed inferring sediment provenance from the final product a basin fill is anything but straightforward because the detrital spectrum evolves as the sediment is transported along the pathway from source to basin successful provenance analysis requires that the nature and extent of compositional and textural modifications to the detrital spectrum be recognised if not quantified the history of quantification in sediment provenance studies is summarised and illustrated by tracking two fundamental ideas the concept of the sediment petrological province or petrofacies and the relation between sandstone composition and plate tectonic environment progress in sedimentary provenance analysis has been closely linked with advancements in measurement technology a brief survey of modern data acquisition tools illustrates the possibilities and limitations of modern provenance research an operational definition of quantitative provenance analysis qpa is presented in which the central role of mass balance is acknowledged extension of this definition to include quantitative predictions obtained by forward modelling computer simulation of sediment production as well as methodological improvements in data acquisition and processing is needed to cover likely future developments in qpa the contributions to the special issue quantitative provenance analysis of sediments illustrate the intrinsic multidisciplinarity and rapid expansion of qpa d 2004 elsevier b v all rights reserved

geochemistry of footwall alteration associated with the early proterozoic united verde massive sulfide deposit arizona three zones of progressively increasing alteration occur in the deception rhyolite associated with the united verde massive sulfide deposit of early proterozoic age near jerome arizona zone 1 most intense alteration is comprised chiefly of chlorite and exhibits apparent losses of sio 2 na 2 o cao and k 2 o enrichments in mgo fe 2 o sub 3 total 1 al 2 o 3 volatile constituents chiefly h 2 o and relatively unchanged tio 2 which is used to monitor changes in other major elements sio 2 and k 2 o losses are most prominent in zone 1 quartz chlorite and sericite are the dominant secondary minerals in zones 2 and 3 these zones also show major losses of na 2 o and cao and variable but small enrichments in mgo fe 2 o sub 3 total 1 sio 2 and locally in k 2 o zone 1 is characterized by major decreases in k rb sr and ba and increases in cs u th mn sc co rare earth elements and high field strength elements zr nb y ta hf increases in cu zn and pb occur in all zones but are greatest in zone 1 with the exception of light rare earth elements nb and y in zone 1 ratios of high field strength elements viz ti zr ta hf hf th and rare earth element distribution patterns are relatively unchanged during alteration and provide a means of identifying protoliths alteration at jerome is complex involving both submarine diagenetic hydrothermal and possibly metamorphic processes zone 1 formed at the highest temperatures and at high water rock ratios the geochemical character and lithologic association of the volcanic host rocks are consistent with a back are basin tectonic setting for the united verde deposit 1 fe 2 o sub 3 total total fe expressed as fe 2 o 3

statistical analysis of bubble and crystal size distributions application to colorado plateau basalts abstract a new analytical technique for the statistical analysis of bubble populations in volcanic rocks proussevitch a a sahagian d l and tsentalovich e p 2007 this issue statistical analysis of bubble and crystal size distributions formulations and procedures j volc geotherm res has been applied to a collection of colorado plateau basalts 96 samples a variety of mono and polymodal distributions has been found in the samples all of which belong to the logarithmic family of statistical functions most samples have bimodal log normal distributions while the others are represented by mono or bimodal log logistic and weibull distributions we have grouped the observed distributions into 11 groups depending on distribution types mode location and intensity the nature of the curves within these groups can be interpreted as evolution of vesiculation processes we conclude that within bimodal log normal distributions the mode of smaller bubbles is the result of a second nucleation and growth event in a lava flow after eruption in the case of log logistic distributions the larger mode results from coalescence of bubbles coalescence processes are reflected in growth of a larger mode and decreasing bubble number density another style of population evolution leads to a monomodal weibull or exponential distribution as a result of superposition of multiple log normal distributions in which the modes are comparable in size and intensity these various population distribution styles can be interpreted with an understanding of vesiculation processes that can be gained through appropriate numerical models of coalescence and population evolution the applicable vesiculation processes include a a single nucleation growth event b continuous multiple nucleation growth events c coalescence and d ostwald ripening

the relation between magnetite and silicate fabric in granitoids of the adamello batholith abstract the link between the macroscopic silicate fabric and the magnetite controlled ams anisotropy of magnetic susceptibility fabric in ferromagnetic rocks was investigated through a comprehensive comparison between different fabric measurement techniques sample lithologies include tonalites and granodiorites from the lago della vacca complex adamello batholith italy the datasets used to assess the link between subfabrics and the coherence between methods include 1 macroscopic silicate fabric measured directly in the field 2 macroscopic silicate fabric derived from image analysis ia of outcrop pictures and sample pictures 3 shape preferred orientations spo of mafic silicates 4 spo of magnetite and 5 calculated distribution of magnetite grains from computer assisted high resolution x ray tomography x ray ct images 6 fabrics derived from the ams macroscopic mineral fabrics measured in the field agree with the ia results and with the spo of mafic silicates obtained from the x ray ct imaging the x ray ct results show that the spo of the magnetite grains are consistent with the ams data whereas the spatial distribution of the magnetite grains is less compatible with the ams fabric this implies that the ams signal is mainly controlled by the shape of the magnetic carrier mineral rather than by the spatial arrangement of the magnetite grains an exception is the presence of magnetite clusters furthermore the spo of mafic silicates and the spo of the magnetite grains are consistent with the ams data another finding of this study is that the magnetic susceptibility correlates linearly with the amount of magnetite in the samples the coherent results obtained from a variety of methods reinforce the application of both ams measurements and ia as robust tools to analyse fabrics in granitic intrusions

lead isotopic evidence for the origin of paleo and mesoproterozoic rocks of the colorado province u s a abstract lead isotopic ratios of k feldspars and whole rocks from 1 7 and 1 4 ga plutonic rocks of the colorado province are relatively non radiogenic for 207 pb 204 pb plotting below the average crust model curve of stacey and kramers 1975 indicating that the terrane was derived primarily from juvenile mantle material slightly more radiogenic ratios in the northern part of the terrane near the archean wyoming province suggest minor inclusion of an older component the data from 1 7 ga plutons plot in a broad field suggesting two episodes of re equilibration with whole rock pb probably related to heating events in the mesoproterozoic 1 4 ga and cretaceous 70 ma possible differences in calculated whole rock th u coupled with slight pb isotopic variations along the north south transect suggest either a terrane boundary through central colorado near salida and gunnison or fundamental differences in source rocks metasedimentary vs metavolcanic u pb analyses of multigrain splits of detrital zircons from quartzites throughout the colorado province have failed to identify archean detritus the oldest 207 pb 206 pb ages found in two samples of quartzite from northern colorado are about 2 0 ga perhaps derived from rocks of the trans hudson orogen in contrast to 2 75 ga detrital zircon in a paleoproterozoic quartzite from the southern part of the wyoming province while we are not yet able to discern if these ages are true provenance ages or mixtures of archean and paleoproterozoic components the absence of easily recognizable archean zircons supports other isotopic data and a conclusion that most of the paleoproterozoic crust of the colorado province was ultimately derived from a juvenile at 1 8 ga mantle reservoir

geochemistry and tectonic setting of lower proterozoic supracrustal rocks of the pinal schist southeastern arizona two lithologic assemblages are identified in the early proterozoic 1700 ma supracrustal rocks of the pinal schist in southeastern arizona a western assemblage is composed largely of quartz wacke turbidites and an eastern assemblage includes bimodal volcanics and variable amounts of sediment chiefly feldspathic quartzite and conglomerate basalts from the eastern assemblage have incompatible element distributions similar to those found in basalts from continental margin arcs or evolved oceanic arcs whereas those from the western assemblage have distributions similar to within plate or back arc basin basalts felsic volcanics range in composition from rhyodacite to rhyolite and exhibit incompatible element distributions similar to those found in felsic volcanics from continental rifts and back arc basins near continents provenance studies of sediments from both assemblages indicate sources rich in granite and felsic volcanics the quartz wackes are similar in composition to sediments from continental margin arcs and associated back arc basins an increase in mafic components in these rocks from north to south in the pinal basin may reflect compositional polarity in an arc system the eastern assemblage may represent remnants of a major northeast trending continental margin arc system and the western assemblage may have been deposited in an intra arc basin or a northwest trending aulacogen which opened on the southwest

generation of upwelling circulation under downwelling favorable wind within bottom attached buoyant coastal currents abstracta two dimensional modeling study by moffat and lentz recently reported that downwelling favorable wind can induce cross shore upwelling circulation within a bottom attached buoyant coastal current here we extend the problem to three dimensions the driving mechanism and the sensitivity for the upwelling circulation are studied using a primitive equation ocean model and an analytical model after the initial downwelling adjustment that steepens the isopycnals and compresses the coastal current the cross shore flow can switch to steady upwelling circulation this reverse circulation coincides with a vertically well mixed water column and persists until interrupted by the arrival of river plume bulge from upstream during the upwelling phase the ageostrophic cross shore flow follows the ekman balance the sense of cross shore circulation is governed by a dimensionless parameter the shear ratio which measures the relative size of geostrophic shear and velocity shear supported by the wind in th

ekman layers and two dimensional frontogenesis in the upper ocean a two dimensional modified semi geostrophic model is used to study the evolution of oceanic fronts in the presence of vertical mixing the parameterization used for mixing is an elevated constant value of vertical viscosity and friction hence the ekman layer acts as a surrogate mixed layer with however vertical shear allowed everywhere an initial condition representative of the observed fields in frontal air sea interaction experiment fasinex is used and its modification in the presence of vertical mixing alone is investigated without external forcing an ekman layer results because of the presence of vertical geostrophic shear at the surface the maximum density gradient moves toward the dense side of the front driven by this flow convergence of ekman flow results in downward bowing of the isopycnals beneath the surface expression of the front a feature reminiscent of density sections taken during fasinex this feature is not evident when a barotropic convergence field is applied in the absence of mixing or in fully nonlinear simulations of the evolution of fronts with baroclinic instability an analytic theory suggests that the maximum density gradient will increase over time when vertical mixing alone is present in the presence of negative uniform wind stress in the direction opposite to the surface geostrophic flow the front moves toward the denser water and the jet uniformly decreases in strength in the presence of a positive uniform wind in the direction of the surface geostrophic flow the surface jet initially weakens but then strengthens again as the wind driven ekman flow opposes the frictionally driven ekman flow and the cross front density gradient increases

chronologic and isotopic framework for early proterozoic crustal evolution in the eastern mojave desert region se california the early proterozoic geologic evolution of the eastern mojave desert region as defined by characteristics of its supracrustal rocks granitoids metamorphism structural history and pb and nd isotopic signature contrasts sharply with other proterozoic provinces of the southwestern united states the oldest supracrustal rocks of the mojave desert region contain zircons over 2 0 ga corroborating nd isotopic evidence for a much older crust here than elsewhere in the southwestern united states granitoids widely emplaced within these supracrustal rocks range from 1 76 to 1 64 ga the earlier plutons and surrounding supracrustal rocks were metamorphosed to granulite and high amphibolite facies throughout the province at about 1705 ma in a migmatite producing event that we term informally the ivanpah orogeny subsequent granitoids emplaced from 1 69 to 1 67 ga were voluminous along a north trending belt in the middle of the mojave province younger plutons were emplaced at about 1 66 ga in several places and at about 1 64 ga along the extreme southern part of the province commonalities between the proterozoic evolutions of the mojave and arizona crustal provinces do not conclusively establish the time that the provinces were juxtaposed the data only suggest that the juxtaposition occurred between about 1 76 and 1 64 ga

quartz grain size reduction in a granitoid rock and the transition from dislocation to diffusion creep abstract in the gran paradiso metagranodiorite western alps small scale lower amphibolite facies shear zones record the transition from a mylonite composed of polycrystalline mineral aggregates to a homogeneous ultramylonite with a grain scale phase mixture polycrystalline quartz aggregates in the mylonite deform by dislocation creep developing a crystallographic preferred orientation cpo and a monoclinic surface orientation distribution function odf the polymineralic matrix of the mylonite and the ultramylonite deform by diffusion creep in the ultramylonite the quartz cpo is randomized and the surface odf becomes orthorhombic the transition from mylonite to ultramylonite is accompanied by a grain size decrease and a disintegration of quartz aggregates concomitant with the precipitation of k feldspar biotite between quartz grains in quartz reduction from the dynamically recrystallized grain size in the aggregates 110 m to the size of the dispersed grains in the ultramylonite 25 m occurs through the following processes k feldspar precipitates at opening sites along grain boundaries strain incompatibility pinning the grain size in quartz aggregates coalescence of k feldspar leads to enhanced grain boundary sliding and disintegration of the quartz aggregates solution precipitation reduces the size of the dispersed grains to less than subgrain size 45 m

a refined technique for measuring crystal size distributions in thin section log normal size distributions are of the form n noe l where n number density l crystal length and is a constant a method for measuring three dimensional log normal crystal or grain size distributions csds in thin section has been deduced from computer experiments in which 2d sections were cut through assemblages of 3d solids the size ranges and distributions studied were appropriate for igneous microphenocryst to megacryst populations conversion from 2d to 3d is based on an exact correction for spheres of uniform diameter cumulate numbers of polygons with length l n2d are converted to n3d by the equation ln n3d ln n2d l s ln l s the number density is then obtained as n dn dl the parameters s and correct the measured lengths and no no number density at l 0 respectively and are functions of crystal shape the parameter is a weak function of the degree of spatial orientation of the crystals highly symmetrical shapes such as cubes octahedra and elongated prisms can be accurately measured when randomly oriented however rectangular solids with a b c cannot be accurately measured because they produce bimodal length distributions in cross section strongly oriented textures trachytic or lineated can be accurately measured regardless of crystal shape new csd data from alkaline rocks and a kimberlite give examples of csds modified by megacryst retention xenocryst addition phenocryst accumulation and groundmass nucleation

geochemistry nd and sr isotopes and u pb zircon ages of granitoid and metasedimentary xenoliths from the navajo volcanic field four corners area southwestern united states abstract proterozoic granitoid xenoliths from the navajo volcanic field nvf in the southwestern united states range in composition from tonalite diorite to granite with the latter greatly dominating there is no apparent relationship between chemical or isotopic composition and age geographic location or degree of alteration or deformation of the xenoliths two of the major ages of proterozoic plutonism recognized in the southwest 1 75 1 70 yavapai and 1 45 1 41 ga anorogenic are represented by the nvf xenoliths in some instances within a single diatreme we did not find any xenoliths in the 1 65 1 62 ma mazatzal range the xenoliths are dominantly i types and both nd and sr isotopes and trace element distributions indicate juvenile arc sources approximately 1 8 ga the granite magmas may have been produced by either vapor absent partial melting or fractional crystallization of a tonalite parent juvenile sources must have been available for melting in each of the three periods of magma production and hence some juvenile 1 8 ga crust in this region must have escaped melting in the first two episodes of magmatism and deformation metasedimentary xenoliths are chiefly biotite sillimanite schists garnet biotite schists and garnet paragneisses these three groups are strikingly similar in chemical and isotopic composition suggesting similar graywacke pelite protoliths the schists appear to be limited to the far northern part of the volcanic field consistent with a possible crustal boundary in the basement compositional and thermobarometric results suggest that the biotite schist xenoliths are not restites but that the paragneisses may be mixtures of melt and restite sedimentary protoliths may have been deposited in a forearc basin and later tectonically transported to the deep crust during one or more arc continent collisions in the late paleoproterozoic

the influence of source rock type chemical weathering and sorting on the geochemistry of clastic sediments from the quetico metasedimentary belt superior province canada abstract the geochemistry of clastic sediments is controlled by at least four factors source rock composition weathering of the source rocks sorting of the weathered detritus and post depositional alteration during diagenesis and metamorphism in order to evaluate the relative importance of these factors major trace and rare earth element contents were determined for distal and proximal clastic turbidites from the archaean quetico metasedimentary belt the degree of metamorphism of the samples ranges from middle greenschist to upper amphibolite facies simple mixing of archaean mafic and acidic rocks of similar composition to those found in the adjacent granite greenstone terrains will account for the tio2 feot mgo cr sc y and hree contents of the clastic turbidites the metasediments are enriched in lree relative to the mafic acidic rock mixing line indicating that the acidic source was enriched in the lree compared to archaean terrains from other parts of the world some quetico turbidites have an additional fe rich source component possibly a chemical sediment incorporated at the time of turbidite slumping cao na2o k2o rb and sr form trends on bivariant plots that are oblique to the mafic acidic rock mixing line and hence cannot be accounted for by simple mixing of the source rocks chemical weathering of feldspars prior to deposition can account for cao na2o k2o rb and sr trends since cao na2o and sr are lost to the weathering solutions and k2o and rb are retained on the product clays the higher na 2 o cao k 2 o na 2 o rb k 2 o and sr cao ratios but lower cao content of the distal samples suggest that they were derived from a bulk sediment that had experienced a greater degree of chemical weathering than the proximal sediments sorting is the factor that most strongly influences the composition of individual samples within the proximal sample group the coarse grained metagraywackes with their higher quartz feldspar and heavy mineral contents are enriched in sio2 cao na2o sr lree zr and hf relative to the fine grained clay rich metapelites metapelites are enriched in tio2 al2o3 feot mgo k2o cr zn sc y hree cs and rb as a result of their higher clay contents thus the use of clastic sediment compositions in determining average crustal compositions e g for the ree can only give satisfactory results when all grain size fractions are sampled in their correct relative proportions the chemical differences observed between the high and low grade samples can be accounted for by source rock type chemical weathering of the source rocks or sorting post depositional element mobility does not appear to be an important factor in determining the composition of the quetico metasediments

two dimensional ageostrophic secondary circulation at ocean fronts due to vertical mixing and large scale deformation 1 ageostrophic secondary circulation asc in frontal data sets have been previously diagnosed using only adiabatic versions of omega equations this study includes the effect of vertical mixing on such diagnostics modified quasi geostrophic and semigeostrophic balance equations are examined for the existing azores front data sets and idealized fronts in the presence of diabatic vertical mixing as well as a large scale deformation field the relevant dimensionless parameter representing the relative importance of large scale deformation and vertical mixing is the inverse of the ekman number based on the deformation rate h2 ao where is large scale deformation rate h is vertical scale of the front and ao is the maximum vertical eddy viscosity when this parameter is smaller than o 102 the influence of vertical mixing may be important other relevant parameters include burger number bu and prandtl number pr the vertical velocity in ascs caused by diabatic mixing in all diagnostics solutions except for large bu cases shows good agreement with the garrett loder scaling the structure of ascs is found to be sensitive to pr the diagnostics of ascs for the azores front data set indicates that the vertical mixing intensifies the asc in the upper ocean 100 m and should not be neglected when the large scale deformation rate is o 10 6 s 1 or smaller the magnitude of vertical velocity in ascs due to mixing contributions reaches o 10 m d 1 with downwelling on the dense side and upwelling on the less dense side of azores front

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

alluvial sandstone composition and paleoclimate i framework mineralogy abstract systematic variations in compositional maturity of first cycle fluvial sandstones are found in the cutler formation permian and fountain formation permian pennsylvanian in colorado and in the gondwana supergroup permian triassic of peninsular india these variations reflect changing climate during deposition climate is considered to be the critical factor affecting maturity because source rocks granite granite gneiss and tectono environmental setting alluvial systems associated with basement cored block uplifts were similar and remained relatively unchanged throughout deposition of all three of the units the roughly 3 200 m thick gondwana succession consisting of five sandstone petrofacies is characterized by the following sequence of change oldest to youngest in compositional maturity expressed in q f r percentages 54 42 4 88 10 2 62 34 4 82 16 2 99 1 0 this sequence is a function of the changing paleoclimate glacial arid temperate humid warm semiarid warm semihumid warm humid associated with the overall global limatic change and the changing latitudinal location of india as it moved from a location close to the south pole northward during the interval of time represented by gondwana deposition lithologic and fossil evidence indicates that during deposition of the fountain formation climate gradually changed from relatively wet and warm to at least semiarid and warm this climatic change is the main factor responsible for the difference in compositional maturity of the older fountain sandstone q f r 65 26 9 relative to the younger q f r 54 36 10 cutler sandstone was deposited in an arid climate and has maximum compositional immaturity q f r 49 44 7 a log log plot of the ratio of total quartz to total feldspar plus rock fragments against the ratio of total polycrystalline quartz to to al feldspar plus rock fragments is a sensitive discriminator of first cycle sandstones with differing climatic heritage bulk chemical composition data support interpretation of climate from framework mineralogy but by themselves are not sensitive enough to be unequivocal indicators the same is true for the ztr index and observations of degree and abundance of solution pits embayments on detrital quartz results of this study support the conclusion of earlier empirical and theoretical analyses which suggest that the optimum conditions for the production and preservation of a distinctive climatic signature on sand composition are met in extensional plate tectonic settings such settings are characterized by coarse grained crystalline parent rocks short transport distances in low order streams deposition in nonroutine environments and shallow burial diagenesis however even in such optimum settings only rarely will climate be a more important determinant of sandstone composition than the tectonic setting itself

verification of ideal semi logarithmic lognormal or fractal crystal size distributions from 2d datasets crystal size distributions can follow any function provided the total crystal content is less than 100 however many theories suggest that they approximate a number of ideal distribution models the most widely adopted model for igneous rocks produces a straight line on a classic csd diagram of ln population density versus size lognormal by size distributions have been proposed for igneous and metamorphic rocks and materials that crystallise at low temperatures lognormal models are difficult to prove with simple linear frequency histograms or on a classic csd diagram instead it is better to use a normalized cumulative distribution function diagram which gives a straight line for lognormal distributions similarly fractal size distributions can best be verified simply by using a bi logarithmic diagram statistical measures can be used to invalidate a null hypothesis but with much caution for real data especially those derived from two dimensional measurements and with a limited range in sizes these methods are applied to csds of plagioclase in three igneous rock samples to illustrate the pitfalls of model fitting a simple nomenclature is proposed for ideal csd shapes

destruction of potential vorticity by winds the destruction of potential vorticity pv at ocean fronts by wind stress driven frictional forces is examined using pv flux formalism and numerical simulations when a front is forced by downfront winds that is winds blowing in the direction of the frontal jet a nonadvective frictional pv flux that is upward at the sea surface is induced the flux extracts pv out of the ocean leading to the formation of a boundary layer thicker than the ekman layer with nearly zero pv and nonzero stratification the pv reduction is not only active in the ekman layer but is transmitted through the boundary layer via secondary circulations that exchange low pv from the ekman layer with high pv from the pycnocline extraction of pv from the pycnocline by the secondary circulations results in an upward advective pv flux at the base of the boundary layer that scales with the surface nonadvective frictional pv flux and that leads to the deepening of the layer at fronts forced by both downfront winds and a destabilizing atmospheric buoyancy flux f b the critical parameter that determines whether the wind or the buoyancy flux is the dominant cause for pv

geostatistical modelling of compositional variability across granitoid complexes its relevance to petrogenetic interpretations and specification of parent rock properties in sediment generation models abstract sediment generation models need an accurate specification of the fundamental properties of parent rocks and their variability at the scale of first order mono lithologic drainage basins georeferenced point count data of five extensively surveyed plutons were extracted from the literature to examine the spatial variability of modal composition in granitoids point count data must be considered inherently noisy from the point of view of geospatial analysis because sampled areas thin sections are small compared to the average crystal size of granitoids geostatistical modelling of such data is further complicated by the fact that crucial information on short range variability is unavailable because sampling was carried out according to more or less regular patterns to achieve an equal density of data coverage across plutons geostatistical modelling of compositional data was carried out by transforming the data to centred log ratios and calculating their principal components pcs the pc scores were used as input for a geostatistical workflow based on ordinary kriging coupled with cross validation and stochastic simulation to assess the predictive capabilities of the models sets of omnidirectional exponential variogram models with fixed range and sill and variable nugget were used for each pluton the local neighbourhood search radius for geostatistical interpolation was set equal to the range variogram modelling was formulated as an optimisation problem aimed at estimating the nugget for which the mean squared cross validation prediction error reaches its minimum the best model of each pluton was selected from all possible combinations of models obtained from the pcs results of a permutation test indicate that the residuals of observed and predicted compositions do not exhibit significant cross covariance within the search radius adopted and may be interpreted as stationary random errors which suggests that little may be gained by application of co kriging random sampling from the geostatistical models indicates that up to several hundreds of specimens must be analysed to successfully predict the area weighted mean modal composition of plutons and its spatial covariance structure as depicted in single component and qapf streckeisen maps an illustration of the internal consistency of the log ratio approach and petrogenetic models is provided by the analysis of the compositional pattern in one of the granite complexes which can be explained by the combined effects of mixing and fractionation the volumes sampled by bulk geochemical analysis are equivalent to the areas of thin sections and geochemical data of coarse crystalline rocks are thus subject to the same limitations as modal analyses the combined data reduction and geostatistical modelling strategy outlined in this study is expected to be particularly efficient for the modelling of such high dimensional data the advent of quick non destructive measurement techniques such as xrf and nir is expected to play a crucial role in future attempts at rigorous quantitative mapping of lithosomes if sediment generation can be simulated the uncertainties associated with the initial conditions area weighted means of parent rock properties can be propagated all the way through to uncertainties of predicted sediment properties

sediment dispersal patterns in part of a deformed mesozoic back arc basin on south georgia south atlantic abstract the cumberland bay formation south georgia is a deformed late jurassic early cretaceous volcaniclastic turbidite formation several kilometers thick it has been interpreted as the fill of a back arc basin which was active on the southwest margin of gondwana during the mesozoic the cumberland bay formation was derived entirely from the volcanic arc and was deformed when the basin closed in midcretaceous times sole marks n 510 oriented fossil wood n 64 and small channels n 9 identified the paleocurrent directions and slump folds n 95 indicated the paleoslope in most areas sole marks show a southeast northwest trend roughly parallel to the axis of the island unambiguous current direction indicators show that the axial dispersal was towards the northwest along the southwest coast paleocurrent distributions are bimodal and there is a lateral mode at a high angle to the axial mode in most areas beds bearing lateral mode sole marks are thicker than those with only axial mode sole marks fossil wood and channel orientations provide further evidence of a major axial dispersal pattern slump folds show that over much of the outcrop paleoslopes were roughly northerly a though there was a topographic high some 40 km across on the southwest coast that may have been a small depositional lobe due to lateral input this lobe appears not to have inhibited the axial flow the overall paleocurrent pattern defines a curve concave to the southwest which parallels the shape of the island this pattern may reflect original basin shape the modern grenada basin lesser antilles provides an analogue which can be used to model depositional patterns within the cumberland bay formation

sediment generation in humid mediterranean setting grain size and source rock control on sediment geochemistry and mineralogy sila massif calabria abstract grain size control on sediment composition is investigated in modern proximal sediment from the sila massif where basic to felsic intrusive rocks are exposed in a mediterranean humid temperate upland climate samples were taken from small creeks and weathering profiles from three areas reflecting different bed rock compositions samples were separated into eleven grain size fractions from very coarse sand to clay and analyzed by i x ray fluorescence for chemical composition and ii x ray diffraction and mineral liberation analysis for mineralogical composition the chemical composition vs grain size relations were modeled by compositional linear regression mineralogical composition of selected samples is used to substantiate the interpretations based on geochemistry results reveal a high degree of chemical weathering with chemical index of alteration cia up to 92 high cia values are restricted to the fine grained fractions while sand sized sediment average at low to moderate cia values 60 although strongly weathered the three sample suites reflecting basic to felsic plutonic bed rock can be effectively discriminated across all grain size classes using trace elements such as v rb and sr linear trend modeling and mineralogical data reflect similar patterns for all sample suites implying similar processes independent of source rock composition this includes overall decrease of quartz and k feldspar over the full grain size range from very coarse sand to clay which is contrasted by overall increase of sheet silicates from coarse to fine among the latter increase of clay minerals strongly outpaces the increase of micas in silt to clay fractions a more complex behavior is shown by plagioclase which is most abundant in intermediate grain size fractions for all sample suites this is likely caused by initial hydrolysis along cleavage and twinning planes and subsequent breakage of plagioclase crystals into smaller fragments towards finer grain size intense hydrolysis has destroyed most feldspars

another look at rare earth elements in shales linear correlation and mass balance considerations indicate that clays are more important than zircon or other heavy minerals in hosting both light and heavy ree in cratonic shales considering the uniformity of the eu anomaly and ree distributions in cratonic shales it seems likely that detritus is thoroughly mixed during weathering and sediment transport and that the ree patterns in shales reflect the average ree pattern of the sources regardless of the ratio of clays to heavy minerals in the shales shales suspended river loads and near shore marine sediments all have broadly similar ree patterns and reported hree depletions in the latter two groups may reflect incomplete dissolution of heavy minerals during sample preparation ree distributions in shales and suspended river loads determined by inna are similar to those in average upper continent crust and ree distributions in shale averages nasc and paas seem to be reasonably representative of the average composition of post archean upper continental crust

grain size distribution of volcaniclastic rocks 1 a new technique based on functional stereology the power of explosive volcanic eruptions is reflected in the grain size distribution and dispersal of their pyroclastic deposits grain size also forms part of lithofacies characteristics that are necessary to determine transport and depositional mechanisms responsible for producing pyroclastic deposits however the common process of welding and rock lithification prevents quantification of grain size by traditional sieving methods for deposits in the rock record here we show that functional stereology can be used to obtain actual 3d volume fractions of clast populations from 2d cross sectional images tests made on artificially consolidated rocks demonstrate successful correlations with traditional sieving method we show that the true grain size distribution is finer grained than its representation on a random 2d section our method allows the original size of vesicular pumice clasts to be estimated from their compacted shapes we anticipate that the original grain size distribution of welded ignimbrites can also be characterized by this method our method using functional stereology can be universally applied to any type of consolidated weakly to non deformed clastic material regardless of grain size or age and therefore has a wide application in geology

early proterozoic assembly of tectonostratigraphic terranes in southwestern north america a 500 km wide early proterozoic orogenic belt in arizona and adjacent areas is divided into lithotectonic blocks by northeast and north trending shear zones structural and u pb zircon studies suggest that these blocks may have experienced different tectonic histories prior to their juxtaposition by thrust and strike slip movements on shear zones a northwestern province here called the yavapai province is composed of at least five tectonic blocks and was assembled at about 1700 ma a southeastern province here called the mazatzal province is composed of at least three blocks and was assembled and juxtaposed with the northwestern province during the mazatzal orogeny between 1695 and 1630 ma the diversity of seemingly incompatible 1700 ma tectonic regimes now in close proximity to each other and the absence of systematic cross strike changes in age and character of deformation plutonism and metamorphism suggest a model whereby the orogenic belt developed and north america grew by assembly of d

detrital zircon evidence for non laurentian provenance mesoproterozoic ca 1490 1450 ma deposition and orogenesis in a reconstructed orogenic belt northern new mexico usa defining the picuris orogeny detrital zircon and igneous zircon u pb ages are reported from proterozoic metamorphic rocks in northern new mexico these data give new insight into the provenance and depositional age of a 3 km thick metasedimentary succession and help resolve the timing of orogenesis within an area of overlapping accretionary orogens and thermal events related to the proterozoic tectonic evolution of southwest laurentia three samples from the paleoproterozoic vadito group yield narrow unimodal detrital zircon age spectra with peak ages near 1710 ma igneous rocks that intrude the vadito group include the cerro alto metadacite the picuris pueblo granite and the penasco quartz monzonite and yield crystallization ages of 1710 10 ma 1699 3 ma and 1450 10 ma respectively within the overlying hondo group a metamorphosed tuff layer from the pilar formation yields an age of 1488 6 ma and represents the first direct depositional age constraint on any part of the proterozoic metasedimentary succession in northern new mexico detrital zircon from the overlying piedra lumbre formation yield a minimum age peak of 1475 ma and 60 grains 25 yield ages between 1500 ma and 1600 ma possibly representing non laurentian detritus originating from australia and or antarctica detrital zircons from the basal metaconglomerate and the middle quartzite member of the marquenas formation yield minimum age peaks of 1472 ma and 1471 ma consistent with earlier results we interpret the onset of ca 1490 1450 ma deposition followed by tectonic burial regional al 2 sio 5 triple point metamorphism and ductile deformation at depths of 12 18 km to reflect a mesoproterozoic contractional orogenic event possibly related to the final suturing of the mazatzal crustal province to the southern margin of laurentia we propose to call this event the picuris orogeny

submesoscale cold filaments in the gulf stream abstracta set of realistic very high resolution simulations is made for the gulf stream region using the oceanic model regional oceanic modeling system roms to study the life cycle of the intense submesoscale cold filaments that form on the subtropical gyre interior wall of the gulf stream the surface buoyancy gradients and ageostrophic secondary circulations intensify in response to the mesoscale strain field as predicted by the theory of filamentogenesis it can be understood in terms of a dual frontogenetic process along the lines understood for a single front there is however a stronger secondary circulation due to the amplification at the center of a cold filament filament dynamics in the presence of a mixed layer are not adequately described by the classical thermal wind balance the effect of vertical mixing of momentum due to turbulence in the surface layer is of the same order of magnitude as the pressure gradient and coriolis force and contributes equally to a so called turbulent therm

3d particle size distributions from 2d observations stereology for natural applications abstract we have developed a general formulation for stereological analysis of particle distributions which is applicable to any particle size or size distribution not limited to log normal unimodal etc we have applied numerical techniques to define intersection probability distributions for any shapes previously only known for spheres and quantified the errors involved in using spherical coefficients for various non spherical particles this stereological technique is based on knowing the probability distribution of random cross sections through various particles so that small circle cross sections can be subtracted from an observed population to provide the 3d size distribution of particles the results indicate that the most important parameter controlling calculated size distribution is particle aspect ratio for a distribution of particles with a specific aspect ratio or range of aspect ratios variations of particle form spherical vs cubic rectangular vs elliptical do not alter the results so the technique can be applied to a range of particle shapes applications can be made in a petrology volcanology and other fields only a few of which can also be treated using expensive x ray techniques

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

the archean proterozoic transition evidence from the geochemistry of metasedimentary rocks of guyana and montana abstract chemical and isotopic compositions of ancient sedimentary rocks have in some cases provided evidence of first order changes yin the composition and extent of continental crust from the archean to the proterozoic we reversed the typical sampling pattern comparing metapelites and carbonates from proterozoic greenstone belts with those from an archean continental margin sequence and found the reverse of the typical age composition relations metapelites and volcaniclastic metagreywackes from the early proterozoic greenstone belts of northern guyana resemble those of many archean greenstone belts in ree trace and major element compositions mean ratios la sm 5 0 la th 5 1 eu eu 0 80 th u 3 4 median k 2 o na 2 o 0 8 schists from an archean continental marginal sequence in montana have compositions like many post archean metapelites derived from continental sources mean ratios la sm 6 8 la th 2 7 eu eu 0 67 th u 5 2 median k 2 o na 2 o 1 7 other archean continental basin sediments also resemble their post archean counterparts implying that upper continental crusts of these eras may not have differed significantly in these respects however temporal change may have occurred in upper crustal contents of ni and cr many archean clastic metasedimentary rocks of both continental and greenstone belt provenance have contents of these compatible elements higher than in their post archean equivalents dolomitic limestone from a greenstone belt of northern guyana has a very low 87 sr 86 sr ratio of 0 7007 such low values may reflect the local influence of mantle derived volcanic rocks during carbonate deposition diagenesis or metamorphism and they may not be reliable indicators of the evolution of sr in seawater archean dolomitic marbles from the continental marginal sequence of montana have 87 sr 86 sr ratios of 0 7065 and higher significantly more radiogenic than many accepted values for carbonates of archean greenstone belts

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

primary to re equilibrated fluids and geochemical signatures for the evolution of the nagthat siliciclastics in the tons valley lesser himalaya india abstract medium to coarse grained neo proterozoic nagthat siliciclastic rocks form a part of the krol formation in the lesser himalayan geotectonic zone fluid inclusion and geochemical studies have been carried out on the nagthat siliciclastics from the tons valley to determine their provenance during the proterozoic and their recrystallisation during maximum burial to uplift fluid inclusion studies have been carried out on detrital recrystallised quartz grains and quartz overgrowths major and trace element analyses of the siliciclastics the relationships of sio 2 with various trace elements and the association of various trace elements with mineral species suggest a granitic source for these siliciclastics primary q1 aqueous brine inclusions and q3 h 2 o co 2 fluid with 0 9 gm cm 3 co 2 density in detrital quartz grains characterised the protolith of the sandstone as granite or metamorphic rocks h 2 o nacl fluids participated in the cementation history temperatures of quartz overgrowth from 198 to 232 c show the effect of maximum burial the re equilibration of the primary fluid due to elevated internal pressure confining pressure is evident from features like c shaped cavities stretching of the inclusions their migration decrepitation clusters etc during recrystallisation these inclusions were equilibrated at 187 and 235 c in a restricted fluid of aqueous moderately saline composition the observed inclusion morphology is attributed to a decrease in external pressure related to isothermal decompression uplift

rapid changes in mixed layer stratification driven by submesoscale instabilities and winds 1 submesoscale eddies generated by baroclinic instability of upper ocean fronts lead to rapid restratification of the mixed layer on a time scale of days this restratification can be opposed by a down front wind stress acting in the direction of the geostrophic velocity that drives a surface ekman flow from the dense side to the light side of the front to arrest the slumping of isopycnals a scaling diagnostic is suggested to determine whether the effect of eddies or wind dominates under different conditions using a numerical model we investigate the juxtaposition of submesoscale eddies and down front winds acting on the mixed layer by estimating the eddy induced overturning stream function in the mixed layer we separate the along and cross isopycnal fluxes of buoyancy associated with submesoscale mixed layer eddies and demonstrate the need for parameterization of the advective along isopycnal flux though the cross front transport of buoyancy induced by the down front component of the wind opposes restratification by mixed layer eddies it becomes diminished as the eddies and growth of the frontal instability disrupt alignment between the wind and frontal axis

on baroclinic instability over continental shelves testing the utility of eady type models abstractthis study examines the utility of eady type theories as applied to understanding baroclinic instability in coastal flows where depth variations and bottom drag are important the focus is

mineralogical and chemical changes of soil and stream sediment formed by intense weathering of the danburg granite georgia u s a abstract a series of soil and stream sediments developed during intense weathering on the metaluminous danburg granite northeastern georgia u s a have been analyzed mineralogically and chemically the concentrations of ba na rb and cs in the silt and coarser fractions are controlled mainly by feldspars and biotite hf is controlled by zircon and the ree rare earth elements and th are largely controlled by sphene variations in feldspar sphene and zircon may produce small variations in eu sm and la lu ratios ferromagnesian minerals control ta fe co sc and cr concentrations the mineralogical and chemical composition of the danburg granite is more closely reflected in the silt than in the sand or gravel fractions of stream sediments in the silt the contents of rb ree th ta fe co and sc and the ratios of la sc th sc la co th co eu sm and la lu are similar to those in the unweathered granite in contrast these element contents or ratios in the sands and gravels are 0 05 3 the concentration in the unweathered granite ta and ba contents are an exception to the above the ta and ba contents of the sands and gravels are similar to those of the granite in the kaolinite halloysite clays the content of na is depleted relative to the source rb cs ba hf and ta are depleted or enriched in the clays relative to the source while the ree th fe co sc and cr are enriched the eu sm eu anomaly size and la lu ratios and the ree patterns of the clays are similar to those of the source thus the mineralogy and element contents of a siltstone developed from metaluminous granitic sources during intense weathering would be expected to be more similar to the source rock than the sandstones and conglomerates claystones should contain similar ree patterns and eu sm ratios as the source rock but such fine grained sediments might represent much larger areas of source rocks than the more locally derived sandstones or conglomerates

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

how round is round a new approach to the topic roundness by fourier grain shape analysis numerous methods for roundness measurement have been developed none however has been generally accepted because of conceptual and practical deficiencies modern image processing and fourier grain shape analysis have eliminated the practical shortcomings but the conceptual ones remained single higher harmonics of the fourier series for example fail to serve as reliable equivalents for roundness evaluation the concept outlined in this paper recognizes three criteria for the evaluation of roundness 1 all curvatures convex as well as concave or plane elements must be considered 2 the positions of morphological elements are significant because salient parts of a particle are more easily abraded than protected ones consequently the curvatures have to be weighted by their relative position on the particle 3 positions and curvatures of morphological elements have to be compared with the particle s ultimate abraded shape which is assumed to be an ellipsoid the ellipsoid reflects the aspect of form or sphericity the distinction between sphericity and roundness is retained because there is no evidence that sphericity changes significantly during transport the measurement is based on the outline of a particle s maximum projection plane which is transformed to a fourier series roundness data are derived from the complete amplitude spectrum the aspect of sphericity is eliminated by subtracting the amplitude spectrum of the best approximating ellipse from the spectrum of the empirical shape the residual amplitudes are normalized and summed in a final step the resulting values are rescaled this guarantees reasonable boundaries and a normal distribution of roundness values the procedure is automated and its efficiency permits the calculation of large samples tests on fluvial and coastal gravel populations demonstrate that the method is sensitive to abrasional wear during all stages of roundness

quantitative models of sediment generation and provenance state of the art and future developments abstract an overview of quantitative approaches to analysis and modelling of sediment generation and provenance is presented with an emphasis on major framework components as determined by means of petrographic techniques conceptual models of sediment provenance are shown to be consistent with two classes of numerical statistical models i e linear mixing models and compositional linear models these cannot be placed within a common mathematical framework because the former requires that sediment composition is expressed in terms of proportions whereas the latter requires that sediment composition is expressed in terms of log ratios of proportions additivity of proportions a fundamental assumption in linear mixing models cannot be readily expressed in log ratio terms linear mixing models may be used to describe compositional variability in terms of physical and conceptual un mixing models of physical un mixing are appropriate for describing compositional variation within transport invariant subpopulations of grains as a result of varying rates of supply of detritus from multiple sources conceptual un mixing governs the relations among chemical mineralogical and petrographic characteristics of sediments which represent different descriptive levels within a compositional hierarchy compositional linear process models may be used to describe compositional and or textural evolution resulting from selective modifications induced by sediment transport as well as chemical and mechanical weathering current approaches to modelling of surface processes treat the coupled evolution of source areas and sedimentary basins in terms of bulk mass transfer only and do not take into account compositional and textural sediment properties moving from the inverse modelling approach embodied in provenance research to process based forward models of sediment generation which provide detailed predictions of sediment properties meets with considerable albeit not insurmountable problems strategies for developing more advanced parameterizations of sediment properties and for simulating their evolution are proposed and expansion of current data acquisition protocols is discussed in the light of data requirements for such advanced sediment generation models inclusion of sediment generation modules in models of landscape evolution and basin filling will mark a significant step towards full fledged source to sink simulations of earth surface processes

a new statistical description of the spatial distribution of minerals in rocks we propose a new method to describe quantitatively rock textures with a special emphasis on the spatial distributions of minerals the method employs a statistical approach and examines probabilities for particular mineral pairs to occur for variable interpoint distances the probability is measured by counting the number of point pairs on digitized images of rock textures that are obtained with a computer aided digital image processor several problems in obtaining textural images and processing the data that were encountered in the actual procedures are reviewed the method is applied to two rock samples granite and contact metamorphic hornfels the method is useful in examining the extent of homogeneity and randomness of mineral distributions and spatial correlations among minerals of different kinds

quantitative analysis of crystal grain sizes and their distributions in 2d and 3d abstract we review methods to estimate the average crystal grain size and the crystal grain size distribution in solid rocks average grain sizes often provide the base for stress estimates or rheological calculations requiring the quantification of grain sizes in a rock s microstructure the primary data for grain size data are either 1d i e line intercept methods 2d area analysis or 3d e g computed tomography serial sectioning these data have been used for different data treatments over the years whereas several studies assume a certain probability function e g logarithm square root to calculate statistical parameters as the mean median mode or the skewness of a crystal size distribution the finally calculated average grain sizes have to be compatible between the different grain size estimation approaches in order to be properly applied for example in paleo piezometers or grain size sensitive flow laws such compatibility is tested for different data treatments using one and two dimensional measurements we propose an empirical conversion matrix for different datasets these conversion factors provide the option to make different datasets compatible with each other although the primary calculations were obtained in different ways in order to present an average grain size we propose to use the area weighted and volume weighted mean in the case of unimodal grain size distributions respectively for 2d and 3d measurements the shape of the crystal size distribution is important for studies of nucleation and growth of minerals the shape of the crystal size distribution of garnet populations is compared between different 2d and 3d measurements which are serial sectioning and computed tomography the comparison of different direct measured 3d data stereological data and direct presented 2d data show the problems of the quality of the smallest grain sizes and the overestimation of small grain sizes in stereological tools depending on the type of csd

mineralogical and textural controls on the weathering of granitoid rocks summary the results obtained in several recent studies provide convincing evidence that potassium rich granitoid rocks are relatively more resistant to weathering than their less potassic counterparts this reflects the fact that microcline and orthoclase are more stable in most weathering environments than calcic plagioclase and biotite relatively slight differences in bulk rock chemical composition can lead to differential rates of weathering in areas of inhomogeneous granitoid terrain thereby leading to the development of topographic features such as inselbergs a second major control on the rate of weathering is rock permeability this is largely a function of degree of microfracturing and jointing in most circumstances grain size and other textural differences probably exert a minor influence on rates of chemical weathering although laboratory tests have shown they may profoundly affect physical strength parameters

stratigraphic control of rare earth pattern types in mid proterozoic sediments of the belt supergroup montana u s a implications for basin analysis abstract within sediments of the helena embayment an eastern extension of the mid proterozoic belt basin montana u s a three different types of ree patterns were identified the lower part of the investigated sequence chamberlain shale and lower newland formation is a uniform shale interval which accumulated during a period of tectonic quiescence the ree patterns of these shales normalized to nasc are either flat or lree enriched lacking eu deficiencies the superjacent unit newland transition zone contains variable amounts of feldspathic sandstone it indicates rejuvenation of the hinterland and regression the uppermost unit upper newland formation consists of alternating packages of carbonates and shales ree patterns in shales of the newland transition zone and upper newland formation have negative eu anomalies this drastic change of ree patterns was observed in all stratigraphic sections the source rocks of the beltian sequence were probably dominated by granitoid gneisses and migmatites and rocks of this composition show negative eu anomalies against nasc in many other places the observed negative eu anomalies in the shales were probably inherited from the source rocks however the patterns of the chamberlain shale and the lower newland formation are not as easy to explain because the source rocks seem not to have changed during deposition of the beltian sequence perhaps more intense chemical weathering during chamberlain shale lower newland time obscured the negative eu anomalies in the residual clays adsorption of lree s on clays during transport may have caused the lree enriched patterns a change in tectonic regime and weathering intensity coincides with the stratigraphic distribution of the different ree pattern types thus stratigraphically controlled ree pattern distribution in a sedimentary basin may help to establish quasi time lines and may allow monitoring of tectonic pulses and of weathering conditions in the hinterland

quantitative analysis of crystal interface frequencies in granitoids implications for modelling of parent rock texture and its influence on the properties of plutoniclastic sands abstract generation of sediments from crystalline rocks is the result of a complex and incompletely understood suite of processes the time evolution of the rock fragment assemblage in sands derived from granitoids is determined by the relative strengths of crystal interfaces and their abundances in the parent rock in this study we highlight the role of crystal interface frequencies in granitoids strong evidence for non random texture with significant implications for predicted interface frequencies have been reported in previous studies we analysed available interface frequency data from granitoids using methods of compositional data analysis and connected our results to existing texture classifications on average granitoids display a high degree of ordering with significant depletion of isomineralic interfaces relative to expectations based on random texture analysis of 210 normalized interface frequency distributions from nine different granitoids reveals a consistent pattern of variation among interface frequencies which suggests a single underlying petrogenetic process related to the combined effects of nucleation and textural equilibration coarsening in view of the large scatter of relative interface frequencies within and among granitoids we propose to model their distribution empirically for the purpose of calibrating sediment generation studies multivariate normal distributions of centred log ratio transformed relative frequencies are capable of capturing 95 of the observed variability with a limited number of dimensions as a rule of thumb the number of dimensions needed to approximate interface frequency counts can be taken equal to the number of mineral classes which is much smaller than the number of interface classes mathematical analysis shows that the joint variability of rock texture and composition may be factorized into three statistically independent measures modal composition crystal size probability density functions and normalized interface frequencies the potential independence of these measures permits objective identification of petrogenetically significant correlations among them which will be indicated by statistically significant cross covariances at this stage inferences from microscopic texture analysis cannot be extrapolated to the scale of entire drainage basins in which sediments are generated because insufficient data are available on the large scale spatial heterogeneity of texture and composition of granitoid parent rocks

quantitative analysis of the joint variability of rock texture and composition in thin section the generalized griffiths descriptor and its application to sediment generation from granitoids abstract the general protocol for quantitative petrographic description of clastic sediments envisioned by j c griffiths approximately 60 years ago is built on specification of the following five statistically independent fundamental properties of aggregates modal composition spatial arrangement size distributions shape distributions and orientation distributions of the elements each element is represented by a grain falling into one of an exhaustive set of petrographic classes we introduce the so called generalized griffiths descriptor ggd which extends this protocol to igneous and metamorphic rocks statistical independence of the fundamental properties permits rigorous testing of petrogenetic hypotheses as well as simulation of rocks based on any conceivable combination of them the benefits of a unifying scheme for description of crystalline parent rocks and their weathering products are illustrated by exploratory analysis of a petrographic data set derived from five granodiorites from across north america comprising the parent rocks and three size fractions coarse medium and fine of their detritus compositional data analysis is used to estimate sediment generation and evolution sge trajectories for each of the plutons sampled the bulk mineral composition and the mineral composition of the rock fragment assemblage display a common trend of relative depletion of quartz and k feldspar with decreasing grain size compensated for by relative enrichment of biotite and accessory minerals the evolution of crystal interface composition suggests that the balance between chemical and mechanical weathering may be reflected in relative stabilities of crystal interfaces we propose a computationally efficient stereological inversion procedure for estimating the parameters of crystal size probability distributions in rocks based on the assumption of lognormality the lognormal distribution is an acceptable default model for crystal size in granitoids at the level of individual thin sections about 87 passes the tests for lognormality but less so at the level of entire plutons only 62 success ratio the current implementation of the ggd is not yet complete because it deals explicitly with the first three fundamental properties only as a consequence of adopting the simplifying assumption that all elements which make up a rock are spherical shape and orientation distributions may be included in future implementations of the ggd dedicated data sets comprising sediments generated from a single parent rock under different conditions will be needed to advance sge studies by shedding more light on the balance between chemical and mechanical weathering

nd sr isotopic provenance and trace element geochemistry of amazonian foreland basin fluvial sands bolivia and peru implications for ensialic andean orogeny nd and sr isotopes and the trace element contents including the rare earths were determined for fluvial sands of lithic arenite composition from the madre de dios foreland basin of bolivia and peru on standard petrologic ternary diagrams the sands fall in the recycled orogen provenance field and thus are similar to typical ancient foreland basin composition the average rare earth elemental pattern of the sands is identical to the upper continental crustal average as estimated from post archean composite shales of different continents ratios ofth u co th la sc and th sc of the fluvial sands are intermediate between an average magmatic arc and an upper crustal average compositions the dispersion of some trace elemental patterns in the sands can be attributed to fractionation of dense minerals including zircon during the sedimentation process the variations of nd isotopes in conjunction with the petrographic parameters of lithic metamorphic lm and volcanic lv fragments allow a two fold classification of the sands these two sand types can be interpreted in terms of mixing among three different provenances one volcanic rock suite with less negativeend o parameter than the other volcanic suite and a third metasedimentary source withend o value of around 12 which is considered to be similar to the average western brazilian shield composition thus the overall compositions of the sands has been modeled as mechanical mixtures of two components an andean magmatic arc and the brazilian shield derived metasediments the model is strongly supported by a plot ofend o versusesr o of the sands in this plot the type 1 and 2 sands define two coherent hyperbolic trends contiguous with two different portions of the andean magmatic trend this relationship has been interpreted to indicate that the observed andean magmatic trend in anesr o end o diagram is the result of varying degrees of contamination of a primitive arc type magma by the precambrian continental crust of the western brazilian shield the depleted mantle average nd model age of 1 46 ga for the fluvial sands reflects the average age of the brazilian continental crustal source the development of the andean orogenic belt has been discussed schematically with the isotopic data of the sands the model describes a trailing edge prism of sediments derived from the brazilian shield during the late paleozoic early mesozoic the prism becomes part of the fold thrust belt during the andean orogeny in the neogene when the foreland basin develops with the basin fill partly derived from the fold thrust belt the sedimentary rocks in the fold thrust belt are also a major source of contaminants for the andean magmas the contiguous nature of the andean magmatic trend and the fluvial sand data in theesr o end o diagram suggests that the ensialic andean magmatic arc has remained connected to its parent continent the western brazilian shield throughout the development of the andean orogeny

3d quantification of mineral components and porosity distribution in westphalian c sandstone by microfocus x ray computed tomography abstract microfocus x ray computed tomography ct measurements were performed on deltaic sandstone samples from the diagenetically altered westphalian c strata campine basin north east belgium in order to collect three dimensional data on mineral quartz kaolinite ankerite etc and porosity distribution the acquired ct data were compared with point counting results of stained impregnated thin sections to qualify the sensitivity of ct comparison between techniques shows positive results with regard to the quantification of main mineral phases such as quartz and ankerite and porosity distribution however major discrepancies exist when studying the clay minerals this can be explained by the influence of microporosity associated with these clay minerals resulting in partial volume effects

geochemical and detrital mode evidence for two sources of early proterozoic sedimentary rocks from the tonto basin supergroup central arizona the tonto basin supergroup includes up to 6 5 km of early proterozoic sedimentary and volcanic rocks that were deposited in a relatively short period of time at about 1 7 ga in central arizona moderate correlations of rare earth elements ree and ti with al2o3 and ree distributions in detrital sediments of this supergroup suggest that these elements are contained chiefly in clay mica and or zircon fractions ree distributions including negative eu anomalies in most tonto basin sediments are similar to those in phanerozoic shales weak to moderate correlations of fe sc ni and co to al2o3 also suggest a clay mica control of these elements detrital modes and geochemical characteristics of sediments indicate two dominant sources for sedimentary rocks of the tonto basin supergroup a granitoid source and a volcanic source the granitoid source was important during deposition of the upper part of the succession the mazatzal group as shown by increases in k2o al2o3 and th in pelites with stratigraphic height and increases in zr and hf and decreases in eu eu cr and ni in in pelites of the maverick shale sediment provenance characteristics and paleocurrent indicators are consistent with deposition of the supergroup in a continental margin back arc basin the granitoid sediment source appears to have been the north american craton on the north and the volcanic source a more local source from an arc on the south

geochemistry of mansar lake sediments jammu india implication for source area weathering provenance and tectonic setting abstract the sediment geochemistry including ree of surface and core samples from mansar lake along with mineralogical investigations have been carried out in order to understand the provenance source area weathering hydrolic sorting and tectonic setting of the basin the geochemical signatures preserved in these sediments have been exploited as proxies in order to delineate these different parameters the major element log values fe 2 o 3 k 2 o vs sio 2 al 2 o 3 and na 2 o k 2 o vs sio 2 al 2 o 3 demarcate a lithology remarkably similar to that exposed in the catchment area the chondrite normalized ree patterns of lake samples are similar to post archaean australian shale paas with lree enrichment a negative eu anomaly and almost flat hree pattern similar to a felsic and or cratonic sedimentary source however the la th sc plot of samples fall in a mixed sedimentary domain close to upper continental crust ucc and paas suggesting sedimentary source rocks for the mansar detritus it also indicates that these elements remained immobile during weathering and transportation the mineralogical characteristic rees and high field strength elements hfse together with the high percentage of metamorphic rock fragments in the siwalik sandstone support a metamorphic source for lower siwalik sediments a very weak positive correlation between zr and sio 2 poor negative correlation with al 2 o 3 negative correlation of la yb n and gd yb n ratios with sio 2 and positive correlation with al 2 o 3 suggest that zr does not dominantly control the ree distribution in mansar sediments the petrographic character and textural immaturity indicate a short distance transport for the detritus the distribution of elements in core samples reflect fractionation the higher zr th and zr yb ratios in coarse sediments and paas compared to finer grained detritus indicate sedimentary sorting plots of the geochemical data on tectonic discrimination diagrams suggest that the sediments derived from the lower siwalik were originated within a cratonic interior and later deposited along a passive margin basinal setting it therefore reveals lower siwalik depositional history

geochemistry and origin of early proterozoic supracrustal rocks dos cabezas mountains southeastern arizona early proterozoic supracrustal rocks in the dos cabezas mountains in southeastern arizona include felsic volcanic and hypabyssal rocks amphibolite feldspathic quartzite arkose and conglomerate quartzite and phyllite felsic volcanics are chiefly water laid tuff and associated volcaniclastic sediments feldspathic quartzites arkoses and conglomerates are derived from granitic and felsic volcanic sources felsic and basaltic igneous rocks define a bimodal suite and felsic rocks can be divided into three populations rhyodacites quartz latites and rhyolites volcanics share major and trace element distributions in common with modern volcanics from continental rift systems and few in common with arc or oceanic volcanics dos cabezas basalts can be produced by 20 melting of an incompatible element enriched iherzolite source in the mantle followed by as much as 40 fractional crystallization of olivine rhyodacites can be produced by partial melting of an undepleted granulite source in the middle crust and quartz latites and rhyolites by fractional crystallization of rhyodacite magma the proterozoic succession in the dos cabezas mountains appears to have formed in a continental rift system similar to or part of early proterozoic rift systems in central and southern new mexico and perhaps in central arizona

sr nd isotopic characteristics of the northeast sandy land china and their implications for tracing sources of regional dust abstract the sr nd isotopic study of the northeast sandy land nesl china is of great significance for a thorough understanding of the dust system in this area the 162 bulk

early proterozoic ophiolite central arizona the 1 73 ga payson ophiolite is a pseudostratigraphic sequence of mafic plutons dike swarms sheeted dikes and submarine basalts that intruded and erupted upon a 1 75 1 76 ga magmatic arc complex the composition of the sheeted dikes is tholeiitic basalt minor andesite with island arc affinities the submarine basalts are overlain by dacitic breccias and a thick section of turbidites with ca 1 72 ga ash beds the entire sequence was deformed intruded by ca 1 70 ga granites and unconformably overlain by fluvial to shallow shelf sediments although most of the 1 8 1 6 ga juvenile crust of arizona consists of magmatic arc rocks the payson ophiolite is unique and is interpreted to have formed the floor of an intra arc basin the ophiolite developed in situ on the older arc basement as opposed to being thrust over it the basin was accreted to the continent by ca 1 70 ga

will greenland melting halt the thermohaline circulation 1 climate projections for the 21st century indicate a gradual decrease of the atlantic meridional overturning circulation amoc the weakening could be accelerated substantially by meltwater input from the greenland ice sheet gis here we repeat recent experiments conducted for the intergovernmental panel of climate change providing an idealized additional source of freshwater along greenland s coast for conservative and high melting estimates the amoc reduction is 35 and 42 respectively compared to a weakening of 30 for the original a1b scenario even for the high meltwater estimate the amoc recovers in the 22nd century the impact of the additional fresh water is limited to further enhancing the static stability in the irminger and labrador seas whereas the backbone of the overturning is maintained by the overflows across the greenland scotland ridge our results suggest that abrupt climate change initiated by gis melting is not a realistic scenario for the 21st century citation jungclaus j h h haak m esch e roeckner and j marotzke 2006 will greenland melting halt the thermohaline circulation geophys res lett 33 l17708 doi 10 1029 2006gl026815

formulas for sediment porosity and settling velocity several existing formulas for the initial porosity and settling velocity of sediment have been tested by using extensive data collected from different countries and regions and modified to achieve better reliability or convenience in use

quantifying the three dimensional shapes of spheroidal objects in rocks imaged by tomography abstract the shapes of objects in rocks are sometimes measured through tomographic sections either physical sections or virtual x ray computed tomography approximation of these objects as ellipsoids is often sufficient in these analyses here we present an easily implemented algorithm to best fit an ellipsoid to a set of n points n 9 distributed on the surface of a spheroidal object observed in tomographic sections the method is demonstrated on x ray computed tomography data of 90 chondrules in a cr2 chondrite by averaging the ellipsoids for all the objects measured in a rock one can then readily describe its fabric by an average ellipsoid and if that average ellipsoid is interpreted as a strain ellipsoid and assuming all objects have undergone the same strain each object can be retro deformed and the inferred initial population of objects studied