rare earth elements in the sediments of the north atlantic ocean amazon delta and east china sea reinterpretation of terrigenous input patterns to the oceans

geochemistry and provenance of the middle ordovician austin glen member normanskill formation and the taconian orogeny in new england the austin glen member of the upper middle ordovician normanskill formation is a sandstone shale ysch succession deposited in the foreland of the taconian orogen petrographic major and trace element and nd pb isotopic data provide substantial constraints on its provenance lack of k feldspar and paucity of plagioclase in addition to the dominance of sedimentary rock fragments indicate that the source was dominated by recycled sedimentary components major and trace element data support this conclusion and indicate that the provenance of both shales and sandstones was the same no evidence of an ophiolitic or volcanic component was observed interpretation of nd isotopic characteristics are complicated by a partial resetting of the nd isotope system at about the time of sedimentation but indicate that the provenance of the austin glen member had a long term history of light rare earth element lree enrichment average tdm 1a8 ga furthermore nd isotopic compositions are extremely homogeneous end 8a1 0a6 1 s d n 23 at 450 ma the approximate depositional age indicating either a single source or very well mixed sources 207pb 204pb ratios are variable but within the range of pb isotopic compositions typically described as grenvillian the range of 207pb 204pb is greater than expected for the range of 206pb 204pb and suggests an additional component of pb possibly introduced during diagenesis the immediate source of the austin glen member may have been the accretionary prism that developed as older sediments of the laurentian margin were scraped off the basin oor incorporated within the accretionary prism and shed into the basin no evidence indicating the arrival of an undifferentiated island arc or continental fragment during the taconian orogeny has been found the data acquired during this study can be explained almost exclusively by grenville province source components but with possible additional contributions from older laurentian terranes and late proterozoic rift volcanics that are not readily quanti ed but likely to have been minor accordingly we conclude that the taconian orogeny in new england involved either 1 a continental arc that involved exclusively laurentia 2 collision of a continental block with identical geochemical characteristics as laurentia or 3 essentially no detritus from any exotic colliding block island arc or continental fragment reached the foreland basin at the time of austin glen deposition

post fire induced soil water repellency modeling short and long term processes soil water repellency has direct implications to hydrological as well as geomorphological processes especially in fire prone ecosystems five predominant mechanisms have been described as generating water repellency in soils fungal and microbial activity growth of particular vegetation species organic matter heating of the soils by wildfires and soil characteristics herein we synthesize among these mechanisms and propose a general model describing the long term properties of water repellency in soils using non linear regression analysis methods we compare among different variants of the model in order to assess the relative role of vegetation on water repellency dynamics we suggest that following a wildfire event hydrophobic peak soil properties are dictated by vegetation properties but that the rapid decrease is not associated with the vegetation following wildfires the recovery of the ecosystem commences and water repellency is characterized by increased predominance of the biotic activity thus the general pattern of a rapid decrease and a long term increase in water repellency can be described by a mathematical model presented herein

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

stratigraphic responses to a major tectonic event in a foreland basin the ecuadorian oriente basin from eocene to oligocene times the eocene to oligocene sediments of the ecuadorian oriente basin record two kinds of second order stratigraphic response to the tectonic evolution lower eocene shows evidences of local scale syntectonic deposits this tectonic activity can be related to right lateral convergent movements inverting pre cretaceous extensional structures upper eocene and oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition this response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations these data have allowed us to propose a new geodynamic model for the paleogene evolution of the oriente basin

andean tectonics as a cause for changing drainage patterns in miocene northern south america newdatafromneogenestratainnorthernsouthamericasuggestthatmiocenetectonisminthenortheasternandeswasresponsible for the genesis of the amazon river and changes in the drainage patterns of other major rivers such as the magdalena and the orinoco here we present a new model for the paleogeographic evolution of northern south america during the miocene in the early miocene a large part of the drainage of northwest amazonia was directed northward along the paleo orinoco river system to a deltainlakemaracaibo upliftoftheeasterncordillerainthelate middle miocene caused thefirst development of the amazon river however no connection with the atlantic was established and the amazon fed the paleo orinoco river system which drained toward the caribbean substantial andean uplift in the late miocene resultedinmajorchangesinpaleogeography theorinocochangedits course the amazon established a connection to the atlantic causing the drowning of carbonate platforms and the amazon caribbeanconnectionwasclosed thusthedrainageandpaleogeography ofnorthernsouthamericainthemiocenewerestronglycontrolled by tectonic movements in the northeastern andes

modern sands of south america composition provenance and global significance standard petrographic methods were used to study 604 modern sands from south america of which 351 came from rivers and 253 from beaches in spite of the wide geomorphic contrasts these sands belong to only three great families 1 an immature andean family of lithic arenites rich in volcanic and metamorphic grains that covers about 30 of south america 2 a cratonic association rich in quartz that covers about 62 of the continent and 3 a transitional molasse association which occurs between these two and covers only about 8 of the continent the grand arithmetic average q f rf ratio for the entire continent is 60 11 29 and the area weighted carbonate free average qa fa rfa is 68 10 22 a superior continental estimate and the first ever for an entire continent

geochemistry of shales from the archean 3 0 ga buhwa greenstone belt zimbabwe implications for provenance and source area weathering abstract phyllites from the archean 3 0 ga buhwa greenstone belt zimbabwe were deposited on a stable cratonic platform analyses of the phyllites generally define a single geochemical group based on major and trace element abundances the phyllites are strongly depleted in cao na2o and sr with respect to average archean upper crust by contrast k2o ba and rb are enriched several times relative to average archean upper crust reflecting basin scale k metasomatism transition metals are somewhat depleted whereas high field strength elements are typically enriched relative to average archean upper crust samples generally have fractionated lree patterns average cen smn 2 4 with small negative eu anomalies average eu eu 0 78 and generally flat hrees average gdn ybn 1 3 such geochemical characteristics suggest that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite mixing calculations which massbalance the rees and th sc suggest 70 tonalite 15 mafic volcanic rocks and 15 granite as possible proportions for the source of the phyllites a nearby early archean 3 5 ga continental nucleus preserves similar lithologies and is the probable source intense chemical weathering of the source terrane is indicated by premetasomatized chemical index of alteration values of 95 100 nearly complete depletion of cao and na2o and high al2o3 na2o ratios fine grained sediments of comparable age and presumed tectonic setting elsewhere in southern africa show similar geochemical characteristics implying that source area compositions and weathering intensities were similar these mature platformal deposits suggest a tectonically stable environment where intense chemical weathering took place at 3 0 ga across southern africa

provenance derived from the geochemistry of late paleozoic early mesozoic mudrocks of the pyeongan supergroup korea late carboniferous early triassic pyeongan supergroup korea was deposited in paralic to nonmarine environments developed disconformably on a lower paleozoic platformal sequence pyeongan supergroup mudrocks show progressive upsection changes in major trace and rare earth element compositions mudrocks in the lower and middle parts of the pyeongan supergroup are strongly depleted in cao and na2o while those in the upper part are enriched in these elements in parallel with cao and na2o the ratio of k2o al2o3 in the lower and middle sections is less than 0 3 while uppermost strata are enriched in k2o having k2o al2o3 ratios greater than 0 3 the index of compositional variability a measure of compositional maturity is less than 0 6 in the lower to middle section whereas in the uppermost strata it is greater than 0 7 similar trends are reflected in a cn k space compared to paas mudrocks of the pyeongan supergroup except for those in uppermost units they are depleted in mn ca and na and are slightly depleted in mg and p contrasting major oxide trends between the lower and middle parts of the pyeongan and the uppermost units are due to decreasing proportions of clay minerals and a concomitant increase in the proportion of nonclay silicate minerals due to increasing input of first cycle detritus excursions marked by increases in mgo na2o and cao reflect large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift incompatible elements are generally enriched in mudrocks of the pyeongan supergroup relative to paas while transition metals co ni cr and v are progressively depleted in younger parts of the section total rare earth element concentrations are higher than paas but chondrite normalized patterns display the typical lree enriched pattern of paas eu anomalies for most mudrocks are close to that of paas the youngest mudrocks in the pyeongan supergroup have the most negative values these trends can be explained by a sedimentary system dominated by detritus derived from recycled highly weathered granitic materials in the lower to middle pyeongan section with an increased proportion of less weathered detritus derived from fractionated granitic materials in uppermost strata such an interpretation is consistent with the results of studies on coarse grained sediments of the pyeongan supergroup

petrology chemistry and texture of modern river sands amazon river system key idea following the spirit of p d krynine the sands of the world s largest tropical river system are studied to reveal much about the general origin of sand and sandstone thin section and chemical study of 95 sand samples from the amazon river system in brazil peru ecuador and colombia a river system with great contrasts in climate and rock types reveals that sands derived from the andes are lithic arenites whereas sands derived from precambrian terrains are much richer in quartz as are sands in rivers draining tertiary molasse sand becomes more mature downstream along the main stem of the amazon solimoes maranon so that a sample analyzed at the mouth does not accurately reflect headwater composition dilution by quartz rich tributaries and quartz rich tertiary outcrops possible differential elimination of rock fragments and even possible weathering on the modern flood plain of the amazon contribute to enhanced maturity downstream we speculate that although data on modern large subarti

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

ichnology and sedimentology reveal depositional characteristics of bay margin parasequences in the miocene amazonian foreland basin abstract proposed depositional models for miocene amazon foreland basin strata pebas formation peru are controversial recent depositional models include lacustrine and tidally influenced brackish water embayment this paper presents data that support tidally influenced brackish water deposition for at least part of pebas time 10 14 ma two parasequences are presented santa julia and tamshiyacu both crop out along the amazon river in upper amazonia near iquitos peru at these locations abundant evidence of brackish water tidally influenced deposition is documented including marginal marine bioturbation sedimentary couplets semidiurnal couplets preserved in burrows and pinstripe lamination the deposits are locally highly bioturbated at both locations ichnogenera normally associated with marine to brackish water depositional environments are common three normally marginal marine ichnofabrics are reported 1 a chondrites reburrowed planolites ichnofabric resident only in massive appearing muds 2 a scolicia laminites thalassinoides ophiomorpha ichnofabric that is manifested as intensely bioturbated silty sands and 3 a thalassinoides generated ichnofabric that is interpreted to have descended into consolidated substrates and is thus representative of the glossifungites ichnofacies several trace fossils contain laminated infills organized into distinct sedimentary couplets that are best interpreted as resulting from semidiurnal processes six conclusions are arrived at 1 sedimentological and ichnological data consistently indicate that sediment accumulation dominantly occurred in sporadically dysaerobic marine to brackish water under a tidal influence 2 sediment accumulation occurred in bay margin environments that prograded into a shallow quiescent bay 3 a stratified water column is indicated by the ichnofauna 4 low accommodation space repetitive and rapid adjustments of relative sea level shallow wave base and a stratified water column combined to generate an atypical parasequence architecture 5 previously published isotopic data are consistent with sediment accumulation in brackish to marine water and 6 marine incursion into amazonia occurred during the middle miocene

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

geochemistry of permian triassic shales in the salt range pakistan implications for provenance and tectonism at the gondwana margin abstract upper permian and lower triassic griesbachian dienerian smithian and spathian shales in the salt range pakistan were deposited at the margin of gondwana during a time of active rifting xrf and inaa major element trace element and rare earth element ree analyses of shales exhibit progressive change in chemistry from upper permian to spathian sio 2 al 2 o 3 decreases upsection and k 2 o na 2 o increases together with an increase in the chemical index of alteration cia hfs elements are enriched relative to paas at the base of the sequence but are progressively depleted upward most compatible elements are depleted throughout relative to paas sc however is relatively enriched producing a general decline in th sc upward with the exception of a single sample at the base of the sequence ree shows little variation from upper permian to smithian ranging from 159 to 146 but increases to 206 in the spathian chondrite normalised la n yb n also increases upsection from 9 0 to 12 8 eu eu values are 0 48 0 54 in the upper permian dienerian sequence but anomalies become smaller 0 53 0 65 and more similar to paas 0 66 in the smithian and spathian such values are typical of continentally derived sediments but the slight decrease upward suggests a small influx of more mafic material this and decreasing th sc contrasts with increasing la n yb n and ree which imply an increasingly felsic source these anomalies may be resolved by modeling potential sources using the ree and th sc the modeling suggests that the permian dienerian sediments could have been derived from a source of upper proterozoic crust upc phanerozoic granite pg and amphibolite amp in ratios around 60 38 2 in the smithian and spathian proportions change to 76 20 4 and 68 28 4 respectively although the increase in the amp component is small when combined with increase in upc at the expense of pg it is sufficient to approximate the changes in th sc and eu eu la n yb n ratios in the permian dienerian may be influenced by concentrations of hree enriched garnet and zircon cia indices and a cn k relations show that source weathering conditions oscillated between non steady state permian dienerian smithian and steady state griesbachian spathian indicative of episodic uplift at the gondwana margin cia ratios in the spathian are greatest in the spathian indicative of more intense weathering at that time however a cn k relations ree contents and the modeled upc pg amp mix in the spathian could also have been produced by recycling of smithian sediments

controls on weathering and provenance in the amazonian foreland basin insights from major and trace element geochemistry of neogene amazonian sediments abstract miocene and pliocene deposits from the ecuadorian bolivian and peruvian amazonian foreland basin north and south amazonian foreland basin nafb and safb were analyzed for major and trace element geochemistry 97 and 104 samples respectively neogene deposits are well homogenized and have an overall paas like composition they are mainly derived from a granodioritic crust in the nafb chemical weathering increases from miocene to pliocene to cia values 100 physical sorting seems to have played a minor role in the chemical composition of these sediments chemical ratios such as cr th and th u and eu anomaly vary within each formation and from one formation to another in the safb sediments have a paas like composition with recycling increasing toward the distal part of the foreland basin in the nafb the neogene formations have various provenances basic andesitic sediments originated from the ecuadorian andes these sediments were trapped in the subsiding ecuadorian foredeep during the miocene and reached the iquitos forebulge to join the paleo amazon near iquitos amazon formation during the pliocene other miocene formations have paas like affinities but are enriched in zr and hf relative to the paas suggesting that they are derived from a recycled and differentiated upper continental crust uplift of the iquitos forebulge may have been responsible for dividing drainage networks originating from the andes and the craton the quaternary floodplain deposits of the amazon river resemble paas with depletion in trace elements and enrichment in zr and hf which indicate that they are derived from a recycled differentiated upper continental crust overall the transition from tidal sedimentation in the miocene to fluvial sedimentation in the late miocene pliocene related to a change with foreland basin dynamics have caused increasing silicate weathering that could have had consequences on climate and global carbon cycle during the neogene

sedimentary rocks and crustal evolution tectonic setting and secular trends a significant change in the composition of turbidites deposited at active tectonic settings is seen at the archean post archean transition in comparison to post archean active margin turbidites archean greenstone turbidites exhibit more uniform th sc ratios but with a similar average greater hree depletion gd n yb n 2 less eu depletion eu eu mostly 0 85 and an absence of low th u ratios th u 3 these data indicate that differing mantle sources and or conditions of mantle melting existed during the archean and that intracrustally differentiated rocks older cratons or young differentiated arcs were relatively unimportant as provenance components for archean turbidites in contrast some sedimentary rocks preserved in archean platformal sequences of high grade terranes display significant negative eu anomalies similar to the majority of post archean shales indicating that the general process of cratonization including intracrustal differentiation has taken place since at least 3

rare earth elements in river waters we measured rare earth element ree concentrations in river waters to characterize the suspended and dissolved river flux of the ree to the oceans the ree pattern of river suspended materials is sensitive to drainage basin geology a positive correlation is observed between la yb ratios and nd model ages for the rivers studied major rivers have light ree enriched patterns relative to the north american shale composite nasc with la yb n 1 6 2 7 river water dissolved material 0 2 m is heavy ree enriched relative to suspended material and the most pronounced negative ce anomalies occur in rivers of high ph light ree concentrations vary by approximately 3 orders of magnitude and are inversely related to ph and major cation concentrations from these data we estimate that typical major river runoff has heavy ree depleted suspended material with la yb n 1 9 we conclude that the terrigenous input to the oceans from major rivers is heavy ree depleted relative to shales from the available data average river water dissolved material appears to be heavy ree enriched with la yb n 0 4 estuarine removal processes lower the dissolved ree river flux by approximately 60 and result in a flux that is more heavy ree enriched with la yb n 0 2 calculated oceanic residence times with respect to river input range from 2300 to 21 000 years are shortest for ce and greatest for the heavy ree and la such long residence times may suggest the presence of additional sources of ree in seawater

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

ree geochemistry of recent clastic sediments from the kaveri floodplains southern india implication to source area weathering and sedimentary processes abstract the kaveri river drains through archean gneissic and charnockitic terranes in south india the rare earth element ree chemistry of the floodplain sediments along with their major and trace element composition in different size fractions are discussed we observe a strong coherence between ree and tio2 contents in the sediments which is suggestive of strong control by titanite or its weathered products on the ree chemistry ree concentrations also show a general increase with decreasing size of bulk sediments different size fractions and of light and heavy mineral fractions this suggests the presence of ree in the fe oxy hydroxide surface coatings on clastic grains formed by the weathering of hornblende and titanite in the granodioritic to dioritic protoliths we also interpret the data as showing that ree patterns of clastic sediments notably eu anomaly are affected by the degree of source rock weathering as well as by the fluvial processes of sorting and mineral differentiation therefore for provenance study sediments having all granulometric grades such as the floodplain sediments are preferable because they most closely represent the source particularly when the source region suffered little chemical weathering in the present case the sediments were derived from the high standing hills of archean charnockites because of their recent uplift and physical denudation

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

modal and geochemical compositions of the lower silurian clastic rocks in north qilian nw china implications for provenance chemical weathering and tectonic setting abstract the north qilian orogenic belt records the transition from ordovician marine back arc basin to early devonian terrestrial molasse basin as the central qilian block was sutured to the north china craton the detrital framework and geochemical composition of lower silurian sedimentary rocks within the north qilian belt record the provenance tectonic setting and a variety of sedimentary processes that operated during transport from source to sink the petrological and geochemical characteristics of sandstones siltstones and shales in the western segment of the north qilian belt indicate a generally low degree of chemical weathering of source area s and limited sorting prior to deposition these characteristics suggest an active tectonic setting in contrast samples studied from the eastern part of the north qilian belt indicate low to moderate chemical weathering and low to moderate hydraulic sorting such characteristics imply a more stable tectonic setting geochemical data including eu eu ti nb th sc and co th ratios suggest contrasting source regions for the western and eastern segments of the north qilian belt sources in the west included basement rocks of the central qilian block and the north china craton in addition western sources may have included mafic rocks located within the north qilian arc in contrast data derived from eastern samples suggest a felsic provenance that probably formed part of the basement complex in the central qilian block and the north china craton overall detrital and geochemical data combined with the regional geology suggest a foreland basin setting that formed during collision of the central qilian block with the north china craton

sediment sources and dispersion as revealed by single grain 40ar 39ar ages of detrital muscovite from carboniferous and cretaceous rocks in mainland nova scotiageological survey of canada contribution 20090289 single grain ages of detrital muscovite from 15 sand stone samples from the lower carboniferous horton group and the lower cretaceous chaswood formation of central nova scotia were used to infer the nature of the early carboniferous unroofing of the meguma terrane and the reworking of carboniferous rocks in the early cretaceous in the western windsor basin a sample from the oldest horton group rocks yielded ages principally between ca 400 and 380 ma suggesting that most of the muscovite present came from the metamorphic rocks of the meguma terrane but was variably reset by the intrusion of the south mountain batholith at ca 380 ma other samples in this part of the basin show partial post depositional resetting younger horton group metamorphic rocks in the eastern windsor basin contain many grains with ages of ca 370 360 ma suggesting derivation from the central core of the south mountain batholith or the musquodoboit pluton horton group sandstones from the western part of the st marys basin co

amazon deep sea fan muds light ree enriched products of extreme chemical weathering abstract pleistocene muds collected over a wide area of the amazon deep sea fan display light rare earth element lree enrichment patterns when normalized to the north american shale composite nasc the patterns appear to reflect the results of extreme in situ weathering combined with particle size sorting rather than source rock composition or diagenetic processes this explanation is supported by the mineralogical and major element compositions of the muds they are highly aluminous 20 26 al2o3 and contain large amounts of kaolinite

geochemical records of qionghai lake sediments in southwestern china linked to late quaternary climate changes abstract knowledge of the chemical weathering history under the subtropical monsoonal climate will help to resolve the discrepancies regarding how climate conditions constrain chemical weathering major element and rare earth element ree compositions of the qionghai lake sediments in sichuan province southwestern china were analyzed aiming to provide information on sediment source discrimination and history of chemical weathering intensities and its responses to variations of indian summer monsoon ism and paleoclimate conditions as revealed by the a cn k diagram and other provenance proxies including tio2 zr ratio th sc vs zr sc and la th vs hf diagrams as well as the ree characteristics the source of qionghai lake sediments was felsic rocks additionally these sediments were subjected to small changes in provenance sedimentary sorting and recycling and weak diagenesis after deposition and or metasomatism indicating original signals were maintained on the intensity of chemical weathering of source area the chemical weathering intensities inferred from cia chemical index of alteration values have significantly fluctuated over the past 28 kyr reflecting three stages of paleoclimate evolution which is consistent with grain size characteristics carbonate contents low frequency magnetic susceptibilities toc and biomarker proxy paq the cia values changed significantly during the typical warm and cold climate events including the last glacial maximum heinrich 1 cold event younger dryas and holocene climatic optimum and generally exhibited an increasing trend in amplitude correspondingly in concert with the climate shifting from cold and dry to warm and humid conditions generally warm and humid climate conditions suggest enhanced chemical weathering intensity whereas weak chemical weathering denotes cold and dry climate in the ism region in addition sequential variations of the cia values during the past 28 kyr may reflect changing chemical weathering processes in responses to the varying intensities of indian summer monsoon and the climate conditions forced by the northern hemisphere solar insolation

the geochemistry of archaean shales derived from a mafic volcanic sequence belingwe greenstone belt zimbabwe provenance source area unroofing and submarine versus subaerial weathering shales of the 2 7 ga zeederbergs formation belingwe greenstone belt zimbabwe form thin 0 2 2 m horizons intercalated with submarine lava plain basalts shales of the overlying cheshire formation a foreland basin sedimentary sequence form 1 100 m thick units intercalated with shallow water carbonates and deep water resedimented basalt pebble conglomerates zeederbergs shale is characterized by high contents of mgo and transition metals and low concentrations of k2o and lile as compared to average phanerozoic shale indicative of an ultramafic to mafic source terrain cheshire shales have similar major and trace element contents but mgo and transition metals are less enriched and the lile are less depleted zeederbergs shales have smoothly fractionated ree patterns lan ybn 2 84 4 45 and no significant eu anomaly eu eu 0 93 0 96 ree patterns are identical to those of the surrounding basaltic rocks indicating local derivation from submarine reworking cheshire shales have rather flat ree patterns lan ybn 0 69 2 19 and a small negative eu anomaly average eu eu 0 85 indicative of a mafic provenance with minor contributions of felsic detritus a systematic change in ree patterns and concentrations of transition metals and hfse upwards in the sedimentary succession indicates erosion of progressively more lree depleted basalts and ultramafic volcanic rocks followed by unroofing of granitoid crust weathering indices confirm the submarine nature of zeederbergs shale whereas cheshire shale was derived from a source terrain subjected to intense chemical weathering

major and trace elements of stream sediments from the lowermost amazon river geochemical results from river bottom sediments taken from the lowermost amazon river are presented bedload sediments were analyzed for 10 major and 38 minor elements mud bulk sediments exhibit a tendency to a slight enrichment in cr mn rb sr zr cs ba and hf pointing to the importance of these elements in the silt fraction generally cu zn rb cs ba and sn are clearly associated with clay minerals while y zr hf th and u are associated with heavy minerals the location of this area in an intensive chemical weathering environment results in the strong modification of sediment composition chemical weathering processes strongly modify original sediment composition and can be recognized apart from provenance processes on the basis of their geochemical signature discriminant analysis makes the detection of less marked differences in sediment characteristics possible thus improving the accuracy of distinctions between groups the amazon mouth and xingu mouth xm are discriminated principally by the textural maturity of their sediments the jari mouth jm shows highest co and fe2o3 contents despite similarities between the amazon north branch anb and amazon south branch asb the anb can be differentiated on the basis of its higher sr p2o5 and na2o contents the asb on the basis of its higher zn mno and cao contents and the estreitos de breves est based on its higher abundance of ni and cu higher contents in p2o5 fe and mn are related to laterite covers

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

solid liquid ree fractionation in the lateritic system of goyoum east cameroon the implication for the present dynamics of the soil covers of the humid tropical regions the ree th weathering geochemistry and mineralogy has been investigated in a lateritic soil cover in relation to the close hydrographical system at goyoum east cameroon the stutied area composed of gneissic hills covered by humid tropical forest belongs to the sanaga river basin and corresponds to a transition vegetation zone between rainforest and savannah a representative soil catena was taken as a reference zone close to the sanaga river the gneissic parent rock soil and groundwater samples have been cut off in pits in the lower part of the catena waters were also sampled both in brooks rich in organic matter and in the sanaga river all the waters were sampled seasonally during the rainy and dry periods the water rock interactions and the exportation of ree and th have been discussed as a function of the evolution of specific ratios considering th as the less mobile element during laterization variation of parent rock pr normalized ratios ln th pr vs depth show that the upper ferruginous horizons are depleted in ree while the basal saprolite presents accumulation zones which are differently located for ce and the other lrees the hrees are also depleted the la accumulations are located near the saprolite gneiss weathering front associated with negative ce anomalies ce ce 0 4 the ce accumulations inducing strong positive ce anomalies ce ce 4 are located in the upper saprolite beneath the ferruginous horizons all along the soil catena the secondary lree bearing minerals which reflect lree fractionation during incipient weathering of the gneiss are hydrous phosphates rhabdophane lreepo4 nh2o and cerianite ceo2 whose precipitation depends on the eh ph changes in the soil profiles on the other hand hree depletion is controlled by the dissolution of xenotime the major hree bearer in the parent gneiss in the 0 45 m filtered acidic groundwater ph 5 5 which have flooded the saprolite for a long residence time th contents are extremely low 0 th 10 ppt while lree contents are high 90 la 450 ppt in these filtered waters th seems to be strongly controlled by minerals i e thorianite which lead to its immobilization in the soil while lree remain in the soluble and or colloidal pools moreover the groundwaters show significant negative ce anomalies throughout the year 0 1 ce ce 0 4 the mobilization of lree except redox active ce results from the dissolution and or the mobilization in colloidal form of the secondary phosphates which may present major negative ce anomalies as indicated by the bulk soil analyses at the saprolite gneiss weathering front therefore the groundwaters have the signature of saprolitic materials we propose that the strong positive ce anomalies of the upper saprolite result from ancient weathering processes these processes would have led to much stronger ce iii ce iv dissolution reprecipitation conditions than those occurring at the present time in the saprolite in the 0 45 m filtered brook acidic blackwaters lree and th contents are high 100 th 400 ppt 400 la 1700 ppt in this organic matter rich environment lree and th are highly mobilized the colloial pool controls half of the whole lree th load the geochemical signature of these waters is independent of the gneissic parent rock and soil lree contents there is no ce anomaly this signature is similar to those of other organic rich rivers draining humid tropical ecosystems in the world in the 0 45 m filtered sanaga waters lree and th contents are lower than in the brooks 15 th 40 ppt 40 la 300 ppt these concentrations are dependent on the time and on the colloidal composition however 90 of these elements are mainly controlled by the suspended pool

geochemistry and mineralogy of sediments from the ventersdorp and transvaal supergroups south africa cratonic evolution during the early proterozoic approximately 100 pelite and 12 quartzite samples from the ventersdorp 2 7 ga and transvaal supergroups 2 6 2 1 ga have been analyzed to monitor the early proterozoic evolution of the kaapvaal craton southern africa from oldest to youngest pelites were sampled from the ventersdorp bothaville bot transvaal selati sel black reef br timeball hill th strubenkop str and silverton sil formations paleocurrent measurements in transvaal quartzites indicate sources lying predominantly to the north and east relative to the bot sel br pelites from the th str sil are enriched in heavy ree lile zr hf nb and ta depleted in k2o mgo ni and cr and have lower cr zr sc th k2o na2o and k rb ratios compared to sel br bot th str sil pelites have higher light ree contents and la yb ratios and lower eu eu ratios 0 61 0 66 relative to nasc north american shale composite thstr sil pelites are enriched in light ree th u ta nb sc cs have higher la yb ratios and are depleted in k2o and mgo bot sel br pelites are enriched in k2o mgo cr and ni have higher k2o na2o sc th and eu eu ratios and are depleted in th u heavy ree and high field strength elements hfse relative to nasc compositions of th str sil pelites suggest a provenance similar to average phanerozoic uppercontinental crust this source is more evolved than that of bot sel br pelites indicating a transformation from primitive mafic rich to evolved felsic rich upper crust at 2 2 ga this transition follows earlier primitive to evolved trends in moodies pongola 3 3 3 0 ga and witwatersrand 2 8 ga successions these data suggest that several cycles of changing upper continental crust occurred in the kaapvaal craton between 3 3 2 1 ga

the controls on the major and trace element variation of shales siltstones and sandstones of pennsylvanian permian age from uplifted continental blocks in colorado to platform sediment in kansas usa shales siltstones and sandstones of pennsylvanian permian age from near the source in colorado to those in the platform in eastern colorado and kansas have been analyzed for major elements and a number of trace elements including the rees the near source sandstones are significantly more enriched student t test at better than the 99 confidence level in sio2 and na2o concentrations and more depleted in al2o3 fe2o3 total tio2 th hf sc cr cs rees y and ni concentrations and laco and lani ratios than the near source shales and siltstones most likely due to more plagioclase and quartz and less clay minerals in the sandstones than in the shales and siltstones there are no significant differences in k2o and sr concentrations and eueu lalu lase thsc thco and crth ratios between the near source sandstones and the near source shales and siltstones samples of the molas hermosa and cutler formations near the source that were formed in different environments in the same area contain no significant difference in eueu lalu lasc thsc thco and crth ratios so a generally silicic source and not the environment of deposition was most important in producing these elemental ratios for example crth ratios of near source shales siltstones and sandstones range from 2 5 to 17 5 and eueu range from 0 48 to 0 78 which are in the range of sources of sediments derived from mainly silicic and not basic sources near source shales and siltstones contain significantly higher student t test and more varied concentrations of most elements al2o3 fe2o3 mno tio2 ba th hf ta co sc rees nb y but significantly lower concentrations of na2o and eueu than platform shales and siltstones in kansas e g la 65 7 40 and eueu 0 55 0 07 in near source shales and siltstones and la 23 7 8 7 and eueu 0 64 0 08 in platform shales and siltstones the sio2 and cao concentrations are not significantly different in platform shales and siltstones compared to the near source shales and siltstones so dilution of other minerals by quartz and calcite is not the main reason for the lower concentration of most elements in the platform relative to the near source shales and siltstones rather the lesser concentrations of most elements in clay minerals of the platform shales and siltstones can account for the lower concentration of most elements compared to corresponding near source shales and siltstones the lower concentrations of many elements in clay minerals in the platform shales and siltstones may be a result of having been derived from recycling of clay minerals from older rocks the greater homogeneity of elemental concentrations of the platform shales and siltstones compared to those in the source is also consistent with homogeneous mixing of such recycled material also there is no significant difference in thsc laco thco lani and crth ratios of the near source sedimentary rocks in colorado to the platform shales and siltstones in kansas and the latter are also consistent with derivation from mostly silicic source rocks

terrigenous sediment on ceara rise a cenozoic record of south american orogeny and erosion abstract ceara rise located east the amazon river mouth is covered with a thick blanket of pelagic carbonate and hemipelagic terrigenous sediment the terrigenous component has been extracted from 57 bulk sediment samples at ocean drilling program odp sites 925 and 929 on ceara rise to obtain a cenozoic record of riverine discharge from northern south america from the early eocene to early miocene 55 20 ma terrigenous accumulation was dominated by moderate amounts of generally large grained gray to green sediment especially depleted in elements that are enriched in post archaean shale e g cs th yb however pulsed inputs of relatively small grained gray to green terrigenous sediment less depleted in the above elements occurred in the late eocene and oligocene the accumulation of terrigenous sediment decreased significantly until 16 5 ma in the middle miocene 16 5 13 ma terrigenous accumulation was dominated by small amounts of small grained tan sediment notably depleted in na and heavy rare earth elements the accumulation rate of terrigenous sediment increased markedly from the latest miocene 10 ma to the present day a change characterized by deposition of gray green sediment enriched in elements that are enriched in post archaean shale observed changes in terrigenous sediment at ceara rise record tectonism and erosion in northern south america the brazil and guyana shields supplied sediment to the eastern south american margin until the middle miocene 20 16 5 ma when a period of thrusting shortening and uplift changed the source region probably first to highly weathered and proximal phanerozoic sediments by the late miocene 9 ma there was a transcontinental connection between the andes and eastern south america weathering products derived from the andes have increasingly dominated terrigenous deposition at ceara rise since the late miocene and especially since the late pliocene

the chemical signature of source rocks in size fractions of holocene stream sediment derived from metamorphic rocks in the wet mountains region colorado u s a eight stream sediments draining primarily mixed silica rich and silica poor metamorphic rocks in the wet mountains colorado were analyzed at their source for their mineralogic and selected elemental composition the low silica source rocks include amphibolite hornblende schist and muscovite biotite schist the high silica source rocks include granodioritic to leucocratic granitic gneisses the high silica source rocks tend to contain higher concentrations of ree th hf and ba lower concentrations of fe sc and cr higher la sc and thsc ratios and more negative eu anomalies than the low silica source rocks especially those low silica source rocks derived from basic sources rather than weathered silicic sources the stream sediments draining this mixed metamorphic rock terrain are dominated by sands and gravels and they are composed of feldspar quartz and 25 heavy minerals the silts contain more total biotite hornblende pyroxene and opaque minerals and less quartz and feldspar than the sands and gravels sediment especially the silts derived from mixed low and high silica sources tends to be intermediate in elemental composition between those of the end member sources so there is some hope that source rock signatures may be preserved in the sediment elemental ratios of la sc th sc la co th co and ba co and th la sc plots most clearly distinguish sediment derived from the most silicic and most basic source rocks in addition finer sediment near the source can potentially distinguish silicic sources higher ree and more negative eu anomalies from those of basic sources the clay and silt fractions contain negative eu anomalies normalized to the mcps north american mid continent platform sediment and the sands and gravels have positive eu anomalies normalized to the mcps most size fractions are similar to more enriched in la sc th sc la co and th co ratios than the mcps this suggests local sources in the wet mountains are on the average more silica rich than those that formed the mcps

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

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

multi element chemistry of some amazonian waters and soils abstract the rivers flowing through the amazon basin are both physically and chemically heterogeneous through detailed geochemical analyses variability is shown to be primarily controlled by both substrate lithology in the source region and soil geochemistry in the erosional regime the solute rich waters of the rio solimoes reflect the drainage from the andes mountains and the fertility of the varzea in contrast the solute deficient waters of the rio negro reflect the infertility of the lateritic and podsolitic terrains of the central amazon rivers flowing through the precambrian shield have an intermediate composition such observations suggest that it is possible to classify the chemical composition of amazonian rivers according to the soil types in their catchment regions and vice versa these findings have profound implications for using water chemistry as an indicator of the agricultural and mineral potential of a region results from this study also confirm that precipitation is a significant source of major cations and trace metals to solute deficient river systems such as the rio negro

geochemistry of precambrian and paleozoic siliciclastic rocks from the iberian range ne spain implications for source area weathering sorting provenance and tectonic setting abstract the major and trace element chemical composition of precambrian and paleozoic shales and sandstones from the iberian range spain has been investigated to determine the provenance and tectonic setting of these rocks as well as to appraise the influence of the weathering hydraulic sorting and recycling processes upon source rock signature the samples studied belong to a prograde sequence from diagenesis to anchizonal grade and are mainly composed of quartz illite mica phases and or kaolinite with chlorite feldspars and carbonates as minor components the major element distribution chemical index of alteration cia indices reflects that recycling processes have been important in homogenizing the composition of shales and sandstones the higher cia indices observed in the silurian and devonian shales 80 and 85 respectively compared with those of precambrian to ordovician and the carboniferous age about 70 indicate that their source area underwent more intense chemical weathering processes possibly due to climatic and or tectonic variations alternatively the source area of the silurian and devonian shales may have been composed of recycled sedimentary materials mineral fractionation is mainly observed in coarser rocks through zircon apatite and xenotime accumulation although the shales are not free of these phases the zircon content of the fine grained rocks is not high enough to affect rare earth element ree contents but phosphate minerals apatite and xenotime at least partially control the ree distribution the influence of apatite and xenotime are slightly higher in the precambrian shales as the phosphate concentration produces a decrease in the la sm ratios chondrite normalized ree patterns and negative eu anomaly size of the studied rocks are similar to that of post archean australian shales paas indicating that they originally come from a differentiated silicic source the higher ree contents in the studied shales in relation to paas indicate that recycling processes in the iberian range sources were probably more intense than that of paas the slight differences among the ree patterns of the different groups of shales probably do not reflect changes in source area composition but instead suggest variations in mineral sorting chemical weathering and or sediment recycling the th sc co th cr th cr v v ni ratios support a primitive silicic source for these rocks with the higher th sc and lower co th in cambrian and ordovician shales indicating a higher proportion of felsic material in their primitive source area the compositional maturity of analyzed sandstones is typical of cratonic environments and their la sc th and zr contents reflect their passive continental margin setting

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

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

upper pleistocene amazon deep sea fan muds reflect intense chemical weathering of their mountainous source lands abstract upper pleistocene muds of the amazon deep sea fan contain an abundance of residual weathering products as indicated by their bulk chemical and mineralogical compositions the muds are chemically more mature than average shale average pelagic mud or the surrounding demerara abyssal sediments they are however very similar to the bulk chemical compositions of contemporary suspended sediments of both the amazon estuary and those carried by the major andean tributaries the modern sediment compositions reflect the rapid weathering now occurring in the andean source regions of the basin the major element geochemical signature of the upper pleistocene deep sea fan sediments suggests that intense chemical weathering in the mountainous source lands has controlled the chemistry of amazon river suspended sediments since at least the upper pleistocene minor and trace element signatures appear uniform throughout the fan and element concentrations are in general higher than in the intensely weathered amazon lowland soils but lower than in deep sea sediments

petrology of fluvial sands from the amazonian foreland basin peru and bolivia modal sand compositions in nine rivers draining the proximal part of the amazonian retroarc foreland basin in peru and bolivia provide support for the recycled orogen provenance model of dickinson and suczek average compositions of 52 sand samples from the rio madre de dios and its tributaries are qfl 74 5 21 qmflt 60 5 35 qplvmlsm 44 10 46 lmlvls 69 18 13 and qmpk 91 4 5 these compositions accurately reflect the predominance of sedimentary and metasedimentary rocks in the cordillera oriental of the andean orogen the ultimate source terrane for the sands of the modern foreland basin rivers of the madre de dios basin can be classified in one of three ways 1 rivers that head in the subandean fold thrust belt 2 rivers that are actively incising a subtle intraforeland uplift overlain by quaternary and upper tertiary foreland basin fill and 3 trunk rivers that collect both type 1 and type 2 rivers the rivers that drain the fold thrust belt carry sands that are slightly more lithic than those carried by rivers that drain the intraforeland uplift the intraforeland derived sands are relatively enriched in volcanic rock fragments lmlvls 70 22 8 whereas sands derived from the fold thrust belt are relatively enriched in sedimentary rock fragments lmlvls 66 9 24 the overriding control on sand composition is the relative area of bedrock type exposed in the fold thrust belt sands reworked from tertiary and quaternary foreland basin fill are relatively enriched in quartz possibly owing to intense weathering of sediments in the soil profile the preservation of predictable and systematic mixing patterns in sand compositions from different rivers suggests that sandstone petrologic data may be augmented by paleocurrent isopach and textural data to facilitate detailed reconstruction of drainage patterns in ancient nonmarine foreland basins