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

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

precambrian alluvial fan and braidplain sedimentation patterns example from the mesoproterozoic rjukan rift basin southern norway abstract an integrated approach of facies analysis geochemistry and paleohydrology provides new insight into the sedimentology and paleogeography of alluvial sediments in the precambrian here alluvial fan and braidplain sedimentation patterns are documented in a mesoproterozoic rift basin called known as the rjukan rift basin in southern norway the studied formation heddersvatnet formation consists of volcanoclastic breccias and conglomerates cross bedded sandstones with associated mudstones and subaerial basaltic lava beds deposited in a rift basin during the syn rifting phase based on genetically related major lithofacies associations and individual minor lithofacies the sedimentation is characterized by colluvial and screen apron deposits subaerial debris flows hyperconcentrated or sheet flood deposits in the proximal part representing waning flood cycles the distal part contains shallow water traction current deposits and associated subaerial continental flood basalts that flowed down the rift valleys the synsedimentary intra rift faulting formed seasonal or climatically controlled intrafan ponded lake with playa lake type cycles and shrinkage cracks the geochemical composition of the of the studied sandstones and mudstones suggests a passive rifted continental margin with minor to moderate chemical weathering possible in a semi arid arid paleoclimate clastic petrofacies of the sandstones indicate a locally uplifted and syn rift paleotectonic setting during the main sedimentation stage passing toward a post rifting stage of the depositional basin small scale structures within the sedimentary basin affected the depositional patterns of the heddersvatnet formation by creating local sites of uplift and erosion controlling the sediment transport and defining the accommodation space for deposition the sedimentation of the heddersvatnet formation reflects a tectonic base level fall which resulted in an accumulation of thick alluvial fan or braidplain sediments near uplifted flank s of the sedimentary basin this was combined with intensive erosion of the basement in the pre vegetation landscape which resulted in changes in the hydraulic geometry of flow and sediment discharge of stream channels the following criteria observed from the heddersvatnet formation are suggestive of an ancient alluvial fan and associated braidplain sedimentation 1 deposition close to the source area 2 slightly divergent paleoflows 3 high energy flows with waning flood cycles 4 abundance of poorly sorted and laterally extensive subaerial debris flows and related streamflows possible sheetfloods hyperconcentrated flows and their associations 5 great distribution of grain size and lithofacies changes in proximal vs distal parts 6 limited suite of sedimentary structures cross stratification ripple marks and desiccanation cracks 7 fault bounded basin graben with hanging wall close to uplifted flank s 8 paleoslope estimation indicating at least moderate paleotopographic highs 9 colluvial and scree apron breccias 10 lack of any typical braided stream channel fill conglomerates and floodplains and 11 channelized sediment bodies lacking extensive lateral continuity

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

element geochemistry and neodymium isotope systematics of the neoarchean banded iron formations in the qingyuan greenstone belt north china craton abstract pure marine chemical sediments such as banded iron formations bif are excellent archives of ancient seawater and may also provide constraints on the coeval hydrosphere atmosphere system however on the bases of interpreted depositional settings it has long been argued that algoma type bif merely recorded the intrabasinal volcanic or hydrothermal conditions here we couple systematic major and trace elements data with samarium sm neodymium nd isotopic analyses of 2 56 ga old algoma type bifs and associated schists from different stratigraphic horizons of the qingyuan greenstone belt qgb in the north china craton ncc to characterize the source and depositional environment over a short period 30 ma meanwhile we also compare our results with data for other archean to paleoproterozoic superior and algoma type bifs especially those near contemporaneous counterparts in the ncc to further evaluate the reliability of qgb bifs as proxies for the neoarchean seawater low al2o3

measuring and adjusting the weathering and hydraulic sorting effects for rigorous provenance analysis of sedimentary rocks a case study from the jurassic ashikita group south west japan the present study examines the provenance of the jurassic ashikita group distributed in south west japan which is composed of the idenohana kyodomari and sakamoto formations two geochemical diagrams for provenance analysis were utilized which incorporate full consideration of compositional modifications resulting from weathering mfw diagram and hydraulic sorting processes sio2 al2o3 na2o k2o diagram the mfw diagram delineates weathering trends of sedimentary rocks and allows estimation of the original source rock composition by tracing the weathering trends backwards to an unweathered domain weathering trends of the idenohana and kyodomari formations extend backward to the domain of intermediate and felsic igneous rocks in contrast sediments of the sakamoto formation do not fit into a linear weathering trend indicating that the source rock cannot be approximated to igneous rocks on the sio2 al2o3 na2o k2o diagram sediments are organized into compositional trends in which the range reflects compositional variations induced by the hydraulic sorting effect on this diagram sediments derived from the igneous and recycled sedimentary provenances can be distinguished by reading the inclination of the trend by utilizing this principle source rocks of the idenohana and kyodomari formations are interpreted as igneous rocks and those of the sakamoto formation are interpreted as recycled sedimentary rocks therefore these diagrams concurrently estimate the source rock composition through quantifying and adjusting the weathering and sorting effects and reveal a systematic transition in the provenance of the ashikita group the idenohana and kyodomari formations were supplied chiefly from an igneous provenance which shifted from intermediate to felsic compositions in stratigraphic order whereas sediments of the sakamoto formation were sourced primarily from a recycled sedimentary provenance

geochemistry of the mesoproterozoic lakhanda shales in southeastern yakutia russia implications for mineralogical and provenance control and recycling abstract shales of the lakhanda group of late mezoproterozoic age 1050 1000 ma from the southeastern siberian craton in russia have been analyzed for major elements and a number of trace elements including the ree s shales along the maya river formed as platform sediments in a deeper shelf facies whereas shales along the belaya river formed in more active and open environments of an upper shelf carbonate ramp the log of most elemental compositions to al2o3 ratios are the same in the maya and belaya river samples suggesting a similar source rock composition for rocks in the two areas the log of sio2 mgo na2o k2o rb ba and ni to al2o3 ratios are significantly higher and the log of tio2 to al2o3 ratios are significantly lower in shales from the belaya river than the maya river sections the cia chemical index of alteration is thus significantly lower in the belaya shales than the maya shales suggesting less weathering of the in the belaya shales than the maya shales the icvs index of compositional variability fe2o3 k2o na2o cao mgo tio2 al2o3 of the lakhanda shales are less than 1 suggesting that they are compositionally mature and were likely dominated by recycling several samples have icv 1 suggesting some first cycle input the low k2o al2o3 ratios of these shales suggest that minimal first cycle alkali feldspar was present in the initial source most shales of the lakhanda plot parallel and along the a k line in a cn k plots suggestive of intense chemical weathering high cia and do not indicate any clear cut evidence of k metasomatism or direct weathering back to the original source if k metasomatism produced these rocks then they could have formed from tonalites to basalts if weathering produced these rocks then they could have been produced from varied amounts of mostly granodiorite to granite elemental ratios critical of provenance la sc la cr la co th sc th cr th co and eu eu are not significantly different between the maya river and belaya river shales and the ratios are similar to fine fractions derived from the weathering of mostly granitoids and not basic rocks the eu eu th sc and low k2o al2o3 ratios of most shales suggest weathering from mostly a granodiorite source rather than a granite source consistent with a source from old upper continental crust some samples at the bottom of the belaya river section contain very low eu eu 0 35 suggesting significant input of first cycle detritus from highly differentiated granitoids similar to those from the aldan shield

inferring tectonic provenance of siliciclastic rocks from their chemical compositions a dissent abstract chemical compositions of siliciclastic sedimentary rocks are commonly used to infer their tectonic provenance we have tested the universal applicability of the underlying principle in a small but controlled study expecting 100 confirmation of the practice a comparison is made between the chemical composition of the 1480 ma butler hill granite in an uplifted cratonic block of the st francois mountain igneous complex and that of a small 1 m thick regolith body a weathered granite sample and the basal quartz arenites of the 520 ma lamotte formation immediately above the regolith the results show that in plots of k 2 o na 2 o vs sio 2 al 2 o 3 the regolith and sandstone samples correctly plot in the passive margin field although the weathered granite plots in the arc field in plots of th sc zr 10 and la th sc the results plot in the passive and active continental margins and their extensions in other common plots to discriminate tectonic provenance e g sio 2 vs k 2 o na 2 o fe 2 o 3 mgo vs al 2 o 3 sio 2 fe 2 o 3 mgo vs tio 2 sc cr vs la y a few points plot in the passive margin field but scatter into and outside of other fields of tectonic provenances the chondrite normalized ree distributions show variable degrees of negative eu anomalies with flat hree conforming to a felsic source the lree distributions show both positive and negative ce anomalies that can be ascribed to the variability of redox conditions during weathering and diagenesis of the original siliciclastic sediments the variability of the eu anomaly was likely affected by post erosion processes in addition to whatever was inherited from the parent rocks we conclude that chemical compositions can provide good clues but are neither strong indicators nor unique identifiers of their tectonic provenance rather they indicate a dominantly felsic or dominantly mafic or a mixed set of source rocks

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

geochemistry of the upper triassic black mudstones in the qiangtang basin tibet implications for paleoenvironment provenance and tectonic setting abstract the qiangtang basin is the largest mesozoic marine basin in the tibetan plateau the upper triassic black mudstones are among the most significant hydrocarbon source rocks in this basin here we present geochemical data for the upper triassic black mudstones to determine their paleoenvironment conditions provenance and tectonic setting to achieve these 30 black mudstones formed in various sedimentary environments were collected from the zangxiahe zana and bagong formations the results show that the total ree concentrations of mudstones from these formations range from 169 to 214 ppm 204 to 220 ppm and 141 to 194 ppm respectively all samples have chondrite normalized ree patterns with enrichment of lree depletion of hree and negative eu and ce anomalies specifically mudstones from the bagong formation exhibit higher negative eu anomalies and lower ree contents than those from the zangxiahe and zana formations mudstones from the zangxiahe and zana formations with low sr ba and sr cu ratios indicate the humid climate whereas the high sr ba and sr cu ratios of rocks from the bagong formation suggest the arid climate the low u th cu mo zn v cr and ni co ratios of rocks from the zangxiahe zana and bagong formations are indicators of oxidized conditions the bivariate diagrams tio2 vs al2o3 tio2 vs zr la th vs hf and co th vs la sc reveal that mudstones from the zangxiahe and zana formations were potentially derived from intermediate igneous rocks whereas mudstones from the bagong formation were probably sourced from felsic igneous rocks their source rocks are mostly deposited in the collisional setting ree of mudstones from the zangxiahe zana and bagong formations were possibly originated from terrigenous detritus with minor non terrigenous contributions into the zana samples the ree contents of these mudstones are controlled mainly by terrigenous detrital minerals rather than by the paleoclimate paleoredox conditions or organic matter however calcite minerals could dilute ree therefore the ree contents of the bagong formation mudstones are significant lower than those of the zangxiahe and zana formations mudstones

provenance diagenesis tectonic setting and geochemistry of tawil sandstone lower devonian in central saudi arabia abstract the tawil sandstone lower devonian in central saudi arabia overlies the sharwara member of the tayyarat formation silurian and succeeded conformly by the shaiba member of the jauf formation petrographical data reveal that the tawil sandstone comprises 96 quartz 3 feldspar and 1 rock fragments and all samples are classified as quartz arenites the presence of well sorted altered to fresh feldspar and discriminate function analysis suggests that the sediments have been subjected to substartial reworking resulting in a high level of maturity modal analysis data q f l suggest a stable cratonic provenance for the sediments and accumulation in a passive margin basin is indicated binary plot of sio2 vs k2o na2o diagenetic features include dissolution of feldspar and rock fragments compaction reduction of the existing pore space through rearrangements and rotation and fragmentation of grains resulting in dissolution of quartz grains and cementation

controls of the altyn tagh fault on the early middle miocene sedimentation in the honggouzi area qaidam basin western china abstract the altyn tagh fault atf has important controls on the sedimentation in the qiadam basin in this study detailed sedimentological and geochemical analyses were presented to deduce the impact of the atf on deposition in the honggouzi area during the early middle miocene which is a significant period for atf strike slip movements the early middle miocene strata of the honggouzi area are deposits of a fan delta and show retrogradation by sedimentary characteristic of drilled wells the elementary geochemical analysis indicates that the early middle miocene deposits of the honggouzi area was mainly composed of felsic rocks formed in the continental island arc or active continental margin setting and derived from a segment of the altyn tagh mountains atm in addition the seismic data suggests that 1 the nearly nw se directed anticlines which were caused by the flexural deformation and uplift of the piedmont area in the northwestern qaidam basin occurred simultaneously during the early middle miocene and 2 retrogradational sedimentation was caused by greatly increased accommodation during the early middle miocene when the subsidence amount of flexural deformation was larger than the uplift amount the flexural deformation uplift of the piedmont area of the northwestern basin and uplift of the atm were all controlled by the atf strike slip movements and therefore were the ways in which the atf strike slip movements affected the early middle miocene deposition of the honggouzi area

on the relationship between sst gradients boundary layer winds and convergence over the tropical oceans a linear mixed layer model that skillfully reproduces observed surface winds and convergence over the tropicaloceans is used to examine the relative influenceof boundarylayer and free tropospheric processes on the distribution of climatological surface winds and convergence the semiempirical model assumes a subcloud layer momentum force balance between pressure gradients coriolis acceleration linearized friction and downward momentum mixing and it utilizes boundary conditions from the 40 yr ecmwf re analysis era 40 observed pressure gradients are linearly decomposed into boundary layer defined as the region below 850 hpa and free tropospheric components and the surface winds and convergence associated with these components are computed results show that surface zonal winds are predominantly associated with a combination of free tropospheric pressure gradients and downward momentum mixing whereas the distribution of convergence is primarily due to boundary layer temperature gradients which are closely related to sst gradients the authors conclude that the climatological distribution of boundary layer convergence is primarily a function of the pattern of sst gradients and is better regarded as a cause rather than a consequence of deep convection

influence of provenance weathering and sedimentary processes on the elemental ratios of the fine grained fraction of the bedload sediments from the vembanad lake and the adjoining continental shelf southwest coast of india abstract geochemical studies comprising twelve major elements and twenty four trace elements including the rare earth elements ree have been carried out on the concentrations normalized to the average upper continental crust ucc show that the sediments studied are depleted in rb k ba ta hf na and ca and enriched in cs u th rees sc fe co and cr ucc normalized patterns are strikingly similar for all the three sediment types probably because of efficient mixing of sedimentary material during weathering transport and deposition the depletion of na k ca and ba in sediments relative to ucc could be attributed to their mobility during weathering the depletion of ta and hf and enrichment of th ree and sc are probably related to provenance characteristics and enrichment of u is attributed to oxidation reduction processes shale normalized ree values reveal steep hree patterns tbsample tbshale ybsample ybshale lasample lashale smsample smshale and flat lree patterns the shale normalized patterns for all the three types of sediments are remarkably similar with variations in the magnitude of lree enrichment lan ybn varies between 1 72 to 2 57 times that of paas lree enrichment and steep hree patterns are attributed to felsic source rock characteristics other geochemical characteristics such as high la th and low la sc and th sc ratios compared to ucc also support a felsic provenance eu eu values for all the three types are little more than 1 which is also a characteristic feature of archean crust furthermore data plotted on discrimination diagrams of la th vs hf and la th sc cluster closer to granite and away from basalt and komatiite and are consistent with source rock geology geochemical data have also helped in ascertaining the weathering trends the chemical index of alteration cia has been used to quantify the degree of weathering cia values range between 81 and 94 on a scale of 40 100 indicating a high degree of alteration fluvial sediments seem to be more altered on an a cn k diagram the data fall closer to the compositional fields of highly weathered minerals kaolinite gibbsite and chlorite a high degree of weathering is also indicated by other plots such as k2o fe2o3 al2o3 and log k vs log rb the geochemical data are consistent with the studies on clay mineralogy higher kaolinite carried out by other authors on the sediments of the same area secondary processes seem to affect other geochemical discriminants such as co cr ni and u as revealed by plots of 1 la sc vs co th and 2 th hf co and co th cr th ratios and makes them unsuitable for determining provenance and tectonic setting

composition provenance and tectonic setting of eze aku sandstone facies in the afikpo synclinorium southern benue trough nigeria field study petrographic and major element geochemical composition of the eze aku sandstone facies outcropping in the afikpo synclinorium southeastern nigeria were utilized in this study the aim is to interpret the provenance and tectonic setting for sandstones in the sedimentary basin field observation shows alternating sequence of parallel sandstone ridges trending ne sw and shales which represent the low lying plains in the area four major sandstone facies were identified massive conglomeritic sandstone facies laminated sandstone facies bioturbated sandstone facies and cross bedded sandstone facies ternary plots for framework elements quartz feldspar and rock fragments from petrography of the sandstones indicate the sandstones as arkosic and subarkosic arenites tectonic setting discrimination diagrams plotted based on major element oxides revealed continental block provenance dominantly in a passive continental margin petrographic and geochemical results indicate large amounts of detritus were derived principally from plutonic igneous rocks with minor contribution from metamorphic source region probably from obudu plateau oban and cameroon massifs

the provenance of garnet constraints provided by studies of coastal sediments from southern india abstract the provenance of sediment with heavy mineral suites containing garnets with low grossular and high pyrope contents is enigmatic such garnet assemblages characterise sediments in many basins worldwide they are especially common in the sedimentary basins around northern britain but their source cannot be identified in adjacent basement rocks this paper documents garnet populations in beach dune and river sands from southern india which almost exclusively comprise low grossular high pyrope garnets these are derived from the high grade granulite facies metasedimentary and charnockitic rocks that form the basement in this area by analogy similar lithologies are inferred to source sediments with low grossular high pyrope garnet assemblages seen elsewhere in the case of the sandstones of northern britain the most likely location of such material is considered to be greenland

provenance and tectonic setting of the proterozoic turbidites in hunan south china geochemical evidence the geochemical composition of the middle upper proterozoic turbidites in hunan south china is related to provenance and tectonic setting of the sedimentary basin the turbidites are characterized by moderate sio 2 contents al 2 o 3 sio 2 typically 0 1 0 3 and moderate k 2 o na 2 o ratios generally 0 1 0 3 but relatively high fe 2 o 3 mgo contents 5 10 wt and unusually low contents of cao typically 1 wt abundances of ferromagnesian trace elements and incompatible elements are moderate the ree patterns are uniform and similar to the upper continental crust and typical post archean shales with lree enrichment flat hree and significant negative eu anomalies in general the slates show higher contents of fe 2 o 3 mgo and ferromagnesian trace elements and lower ratios of la sc and th sc than the associated graywackes suggesting that more mafic materials were incorporated into the clay size fraction compared to the upper proterozoic banxi group the middle proterozoic lengjiaxi group has higher concentrations for most ferromagnesian trace elements and lower la sc ratios implying more mafic components in the provenance of the latter the relationship among alkali and alkaline earth elements the chemical index of alteration cia and the th u ratios indicate that the source area was affected by a moderate weathering history the main source was old continental crust the yangtze craton dominated by felsic rocks of magmatic origin with a variable admixture of mafic components from continental island arcs e g the fangjingshan dayong and the sibao yiyang island arc chains the flysch deposition took place in a back arc basin rather than a failed intracontinental rift as proposed by some workers we suggest that suturing between the yangtze and cathaysia blocks did not occur until late proterozoic time and that the final assembly of the supercontinent rodinia in south china was probably marked by the jingning orogeny at 0 8 ga

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

geochemistry of high grade supracrustal rocks from the kerala khondalite belt and adjacent massif charnockites south india abstract the kerala khondalite belt kkb comprises a suite of supracrustal rocks of probable proterozoic age that was metamorphosed to the granulite facies the kkb consists of an interlayered sequence of 1 garnet biotite orthopyroxene graphite gneisses 2 khondalites graphite garnet biotite sillimanite cordierite gneisses and 3 cordierite gneisses garnet biotite cordierite orthopyroxene as well as less abundant mafic granulites calc silicates and quartzites petrologic and geochemical data suggest that these rocks were originally arkosic and argillaceous sediments possibly accompanied by felsic volcanic rocks along with minor intercalations of basalts carbonates and quartz rich sandstones the ree patterns of the metasediments are typically lree enriched with large negative eu anomalies indicating a continental provenance the major and trace element compositions of some of the arkosic rocks of the kkb resemble those of the massif charnockites that bound the kkb to the north which suggests that the massif charnockites may have been the source of some of the kkb sediments modern day analogues of the pelite arkose lithologic association observed in the kkb occur in intracratonic rifts and rifted continental margins this association is clearly distinct from the graywacke mafic volcanic association found in the southern indian greenstone belts and many other lower grade archean sedimentary sequences the kkb supracrustals show both lithologic and chemical similarities to many proterozoic supracrustal successions

archaean plate tectonics revisited 1 heat flow spreading rate and the age of subducting oceanic lithosphere and their effects on the origin and evolution of continents a simple model which relates the rate of seafloor creation and the age of the oceanic lithosphere at subduction to the rate of continental accretion can successfully explain the apparent differences between archaean and phanerozoic terrains in terms of plate tectonics the model has been derived using the following parameters 1 the spreading rate at mid ocean ridges 2 the age of the oceanic lithosphere at the time of subduction 3 the area age distribution of the seafloor 4 the continental surface area as a fraction of the total surface area of the earth and 5 the erosion rate of continents as a function of continental surface area and the total number of continental masses observations in phanerozoic terranes suggest that there are profound differences in the nature and volume of subduction zone igneous activity depending upon the age of the oceanic lithosphere being subducted and the nature of the overriding plate that is either continental or oceanic the subduction of young oceanic lithosphere less than 50 m y old which is thermally buoyant appears to result in a reduced volume of igneous activity most of the igneous activity caused by subduction of young oceanic lithosphere is either siliceous plutonism or bimodal tholeiitic rhyolitic volcanism when very young lithosphere is being subducted 50 m y old appears to result in greater volumes of igneous activity including the eruption of andesitic magmas thus andesites could only begin to be abundant in the rock record when older oceanic lithosphere began to be subducted our model predicts that as the earth aged and as heat flow from the interior of the earth diminished the proportion of old oceanic lithosphere being subducted increased fundamentally changing the nature of subduction zone igneous activity and the rate of continental accretion if the subduction of old oceanic lithosphere results in an 8 10 times greater volume of subduction zone magmatism our model predicts or explains all of the following observed features of earth history 1 archaean terranes appear to record two periods of rapid continental accretion between 3 8 and 3 5 b y ago and between 3 1 and 2 6 b y ago 2 there are very few differences and many marked similarities between rocks from archaean terranes and equivalent rocks from phanerozoic terranes 3 the total continental area appears to have remained essentially constant for the past 2 b y 4 archaean andesites are comparatively rare and the relative abundances of mafic and siliceous rocks appear to change during the archaean and the proterozoic with siliceous volcanics becoming proportionately more abundant in the geologic record with time 5 plutonic tonalites and trondhjemites appear to have been relatively much more abundant during the archaean plate tectonics is thus shown to have evolved over time due to a gradually decreasing rate of creation of oceanic lithosphere meaning that archaean tectonics and phanerozoic tectonics are but two points on an evolutionary continuum

geochemical signatures of bedded cherts of the upper la luna formation in tachira state western venezuela assessing material provenance and paleodepositional setting abstract here we undertook an inorganic geochemical study of cenomanian campanian bedded cherts the tachira ftanita member of the la luna formation in the western region of the tachira state venezuela the aim of this study was to determine the paleo oceanographic and paleo environmental conditions that governed the deposition of chert beds and put forward a sedimentation model for the tachira ftanita member in the study area seventy two chert samples were collected and trace rare earth elements la ce pr nd sm eu gd tb dy ho er tm yb lu rb cs th u y co and sc and major trace elements sio2 tio2 al2o3 fe2o3 mgo cao na2o k2o p2o5 mn ba sr cr ni and v were determined by icp ms and icp oes respectively on the basis of the stratigraphic abundance and distribution of relatively immobile elements as well as the distribution of rare earth elements we established that the detrital sediments associated with the sequences studied have matching characteristics with distinct continental materials with an intermediate composition thus pointing to the guayana massif as the main source of sediments in addition we also determined the influence of hydrothermal input on the chemical composition of some cherts from la molina mine on the basis of geochemistry we found a biological influence regarding the uptake of dissolved silica for forming chert beds the application of parameters for relatively immobile elements allowed us to establish a still proximal continental margin hemipelagic for most samples from the zorca river and a continental margin for almost all the cherts from the delicias villa paez section and the remaining samples from la molina mine finally we propose that the rhythmicity that accompanies the sequence of bedded cherts is related to changes in the intensity of upwelling patterns of water and or to variability in the supply of silica dissolved in the tachira sub basin

mechanism and effect of chemical weathering of sedimentary rocks the mineralogy geochemistry and physical and mechanical properties of rocks from four weathering profiles of miocene to pleistocene mudstones and sandstones in japan showed that chemical weathering of sedimentary rocks is characterized by sequential reaction between percolating groundwater and rock forming minerals pyrite a common mineral contained in sedimentary rocks is especially important in these sequential reactions pyrite is oxidized by oxygen coming from the ground surface and sulfuric acid is generated at the base of the oxidized zone the sulfuric acid in turn dissolves rock forming materials to make a dissolved zone if the fluxes of oxygen and water are in the same direction sulfuric acid generated at the oxidation front migrates farther and forms a dissolved zone if these fluxes are in opposite directions the oxidized and dissolved zones are not differentiated rocks in the dissolved zone are caused to deteriorate by the acid leaching and are acidic if buffering minerals such as calcite and zeolite are absent in the oxidized zone sandstone is strengthened because of cementation by iron oxide or hydroxide while mudstone is weakened because it has greater clay fractions and larger specific surface areas than sandstone

geochemical study of the cambrian ordovician meta sedimentary rocks from the northern altai mongolian terrane northwestern central asian orogenic belt implications on the provenance and tectonic setting abstract the altai mongolian terrane am is a key component of the central asian orogenic belt caob but its tectonic nature has been poorly constrained this paper reports geochemical compositions of cambrian ordovician meta sedimentary rocks from the northern am to trace their source nature and depositional setting which in turn place constraints on the geodynamic evolution of the am the cambrian ordovician meta sedimentary rocks from the northern am show variable major element compositions with negative correlation between sio2 and tio2 al2o3 fe2o3t mgo and k2o their high icv values 1 18 2 53 and relatively low cia values 37 9 76 3 indicate that the sediments were immature and probably underwent mild to moderate chemical weathering the low sio2 samples are characterized by relatively restricted sio2 al2o3 mostly 2 60 6 07 and low rb sr ratios 0 02 1 89 implying their proximal deposition without obvious sedimentary sorting and recycling in contrast the high sio2 samples show much higher sio2 al2o3 ratios 15 4 19 9 possibly due to sedimentary sorting and or silicification all these samples yield relatively high al2o3 tio2 ratios 15 6 22 8 strong lrees hrees differentiation la yb n 4 86 10 7 and obvious negative eu anomalies eu 0 61 0 83 combined with their th sc zr sc la th and co th ratios comparable with intermediate acidic magmatic rocks we infer that these kinds of magmatic rocks served as a major source for the investigated meta sedimentary rocks the tio2 al2o3 and fe2o3t mgo concentrations are mostly higher than typical sediments from passive margin and the th u la sc th sc eu eu zr hf zr th and la th ratios are quite similar to sediments from continental arcs these data suggest that the cambrian ordovician meta sedimentary rocks from the northern am were most likely deposited in an environment related to a continental arc setting rather than a passive regime these rocks show strong similarities to their counterparts in the chinese altai ca southern am and tseel terrane southeastern extension of the ca in western mongolia in terms of geochemical compositions and depositional setting with combination of recent isotopic studies for detrital zircons our data suggest that the am probably represented a coherent accretionary prism along a continental arc in the early paleozoic

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

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

geochemistry of the floodplain sediments of the kaveri river southern india abstract the floodplain sediments of the kaveri river southern india derived from archean gneissic and charnockitic source regions show interbedding of silty 4 4 7 and sandy units 1 4 3 7 the geochemistry of silty beds is remarkably uniform at a given location and over a lateral distance of nearly 250 km the sandy beds have more variable chemical compositions yet are comparable to those of silty beds except for the diluting effect of quartz silty sediments retain the geochemical signature of prominently exposed source rocks for almost all elements and provide evidence of tectonic instability in the source region the floodplain sediments contain all size grades sand silt and clay which may have resulted in minimizing the biases imposed on suspended and bedload sediments due to sorting the low chemical index of alteration cia the dominance of unweathered primary minerals and the minor proportion of smectitic clay all suggest that the region has been subjected to little chemical weathering this is possible if the region has undergone recent uplift exposing fresh archean rock to surface denudation the formation of fertile farmland along the kaveri river course and its delta is related to these recent geological processes

geochemistry of fine grained clastic sediments in the archean abitibi greenstone belt canada implications for provenance and tectonic setting abstract archean sandstone and shale samples from turbiditic tf and alluvial facies af in the southern volcanic zone of the abitibi greenstone belt canada have been analyzed for major and trace elements the sandstones from tf are mainly greywackes whereas those from af are lithic arenite sio 2 ranges from 51 to 68 geochemically the clastic sediments cluster into mafic element mep and low mafic element lmep populations the mep sediments which include turbiditic facies sediment samples from the larder lake group in the kirkland lake area are characterized by elevated abundances of mgo 5 ni 200 ppm cr 400 ppm sc 22 ppm and feo 7 5 abundances lower contents of incompatible elements such as th u ta hf zr and total rees n ratios are 4 5 with eu eu 1 the lmep sediments which include samples from the beatty dome and three nations lake formations in timmins the kewagama group noranda area and timiskaming group in the kirkland lake area however show reverse abundance distributions the geochemical gaps shown by the major and trace elements define two populations of sediments suggesting contrasting provenances for them the mep sediments require a dominantly mafic and ultramafic 90 source with 10 felsic contribution whereas the lmep sediments require a mixture of felsic 75 and mafic 25 rocks this compositional distribution of the sediments is closely related to their tectonic environments the mep was formed in basins proximal to or within an active oceanic rift consequently having ultramafic and mafic rocks as the major source for the lmep calc alkaline volcanic sequences formed in an island arc like setting were the major source these two contrasting volcanic plutonic terranes were tectonically juxtaposed during late archean collisional tectonics

dehydration melting phenomena in leptynitic gneisses and the generation of leucogranites a case study from the kerala khondalite belt southern india

petrography and geochemistry of cretaceous to quaternary siliciclastic rocks in the tarfaya basin sw morocco implications for tectonic setting weathering and provenance the petrography heavy mineral analysis major element geochemical compositions and mineral chemistry of early cretaceous to miocene pliocene rocks and recent sediments of the tarfaya basin sw morocco have been studied to reveal their depositional tectonic setting weathering history and provenance bulk sediment compositional and mineral chemical data suggest that these rocks were derived from heterogeneous sources in the reguibat shield west african craton including the mauritanides and the western anti atlas which likely form the basement in this area the early cretaceous sandstones are subarkosic in composition while the miocene pliocene sandstones and the recent sediments from wadis are generally carbonate rich feldspathic or lithic arenites which is also reflected in their major element geochemical compositions the studied samples are characterized by moderate sio2 contents and variable abundances of al2o3 k2o na2o and ferromagnesian elements binary tectonic discrimination diagrams demonstrate that most samples can be characterized as passive continental marginal deposits al2o3 na2o ratios indicate more intense chemical weathering during the early cretaceous and a variable intensity of weathering during the late cretaceous early eocene oligocene early miocene miocene pliocene and recent times moreover weathered marls of the late cretaceous and miocene pliocene horizons also exhibit relatively low but variable intensity of chemical weathering our results indicate that siliciclastics of the early cretaceous were primarily derived from the reguibat shield and the mauritanides in the sw of the basin whereas those of the miocene pliocene had varying sources that probably included western anti atlas ne part of the basin in addition to the reguibat shield and the mauritanides

on the geochemistry of the late quaternary loess deposits of dobrogea romania abstract ten samples of loess and palaeosols collected from the costinesti dobrogea romania loess deposit and covering a time span of about 690 90 ka were analyzed by x ray diffraction instrumental neutron activation analysis and x ray fluorescence in order to determine the origin as well as the climatic conditions during loess deposition the presence of illite and calcite suggests reduced weathering confirmed by climate proxies chemical index of alteration 54 6 64 0 chemical index of weathering 65 7 71 7 and rb sr 0 26 0 47 were lower than the neighboring hungarian loess but closer to the average loess the content of 28 trace elements including 10 ree confirmed an average rock composition close to the upper continental crust the elevated content of cr and ni indicated the presence of a certain amount of felsic rock material zr and hf whose content was more than twice that of the upper continental crust indicate significant sediment sorting the low values of climatic proxies as well as the absence of any statistical significant difference between loess and palaeosol material confirmed rather limited weathering during the formation of the south eastern dobrogea loess deposits

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

geochemistry of sandstones from the upper miocene kudankulam formation southern india implications for provenance weathering and tectonic setting abstract petrographic major trace and rare earth element compositions of sandstones from the upper miocene kudankulam formation southern india have been investigated to determine their provenance tectonic setting and weathering conditions all sandstone samples are highly enriched in quartz q but poor in feldspar f and lithic fragments l the major element concentrations of these sandstones reveal the relative homogeneity of their source geochemically the kudankulam sandstones are classified as arkose subarkose litharenite and sublitharenite the cia values chemical index of alteration mean value 44 5 for these sandstones and the a cn k diagram suggest their low weathering nature similarly their fe2o3 mgo mean 2 7 al2o3 sio2 0 09 k2o na2o 2 2 ratios and tio2 contents 0 3 are consistent with a passive margin setting the eu eu 0 5 la lu cn 21 la sc 5 9 th sc 1 9 la co 5 7 th co 1 8 and cr th 5 3 ratios support a felsic source for these sandstones chondrite normalized ree patterns with lree enrichment flat hree and negative eu anomaly also are attributed to felsic source rock characteristics for kudankulam sandstones total ree concentrations of these sandstones reflect the variations in their grain size fractions the source rocks are probably identified to be proterozoic gneisses charnockites and granites of the kerala khondalite belt which must have been exposed at least since the late miocene finally the unusual ni enrichment in the kudankulam sandstones unaccompanied by a similar enrichment in cr co and v may be related to either the presence of pyrite in the sandstones or more likely the fractionation of garnet from the source rocks during transportation

the cr th ratio in precambrian pelites from the kaapvaal craton as an index of craton evolution the cr th ratio in precambrian pelites from the kaapvaal craton in southern africa correlates with pelite th sc and co th ratios and appears to monitor changes in source composition it is a more sensitive indicator of provenance than other commonly used ratios including eu eu la yb and th u pelite cr th ratios are controlled most strongly by the effects of local provenance and local tectonics secular decreases in this ratio the most prominent of which occurred at 2 4 2 3 ga in pelites of the kaapvaal craton record rapid uplift exposing granite decreases in the ratio reflect increases in the abundance of komatiite basalt in sediment sources in response to arc collisions rift hotspot volcanism or intracratonic uplift of older greenstones relatively constant cr th ratios appear to require widespread uplift or and efficient sediment mixing during tectonic stability changes in cr th ratio of kaapvaal pelites reflect a complex tectonic history of the craton from about 3 3 ga to 1 8 ga and do not favor single stage cratonization in the late archean

geochemistry of cumulus peridotites and gabbros from the marum ophiolite complex northern papua new guinea the layered cumulus rocks of the marum ophiolite complex in northern papua new guinea range from highly magnesian dunite wehrlite and lherzolite through pyroxenite to norite gabbro with minor anorthosite and ferronorite gabbro near the top of the sequence most of the cumulates particularly the gabbroic rocks are characterised by recrystallised adcumulus textures and all intercumulus melt mesostasis has been expelled trends in the cumulate sequence from mg rich to more fe ca and al rich compositions are consistent with the formation of the layered sequence by magmatic accumulation from mafic tholeiitic magmas with varying degrees of differentiation the cumulates are characterised by extremely low levels of incompatible elements k ba rb p zr nb hf y and ree at all levels of differentiation ree patterns are strongly depleted in lree hree abundances range from 0 3 chondrites in peridotite to 3 x chondrites in the norite gabbros

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

reversal of the middle upper songhua river in the late early pleistocene northeast china abstract the study of drainage evolution in the songnen plain northeast china is essential for understanding the interactions between tectonics topography climate drainage evolution in the region despite this it remains unclear whether the paleo songhua river upper middle reaches of the songhua river once flowed westward into the songnen plain and what forcings influenced the drainage development of the songnen plain in this contribution we provide insight into drainage development on the songnen plain using an integrated approach of magnetic susceptibility geochemical elemental and sr nd isotopic and heavy mineral composition recovered from a 102 m sediment core sediments extracted from the eastern edge of the songnen plain with sedimentological and topographic archives our results show that a dramatic provenance shift occurred at the depth of 62 2 m 0 94 ma in the core sediments it is proposed that the songhua river was separated by the jia yi jiamushi yilan divide into two segments before 0 94 ma the west flowing proto songhua river and the east flowing proto sanjiang river lower reach of the songhua river however the proto songhua river reversed direction at 0 94 ma when the jia yi divide was cut through by headward erosion of the proto sanjiang river marking the birth of the songhua river as a single eastward flowing river system tectonics is suggested as the first order control on the evolution of the songhua river before 1 20 ma whereas climate changes may be responsible after 1 20 ma

geology and geochemical constrains on the origin and depositional setting of the kpwa atog boga banded iron formations bifs northwestern congo craton southern cameroon abstract the kpwa atog boga kab area lies within the paleoproterozoic nyong unit which defines the northwestern edge of the archean congo craton in southern cameroon rock types in the area are mainly comprises of garnet gneiss associated with banded iron formations bifs the bifs and its host rocks were subjected to amphibolite facies metamorphism the rare earth elements ree patterns and the discrimination ratios e g al2o3 tio2 cr th th sc la sc of the garnet gneiss suggest that they are metasedimentary rocks derived from a felsic parent sources that have undergone intensive weathering the kab bifs exhibit significant concentration of tfe2o3 sio2 93 wt and lower al2o3 and tio2 contents and high field strength elements e g hf nb ta and zr this involves little contamination with continental detritus at their depositional environment the post archean australian shale paas normalized ree patterns of the kab bifs show enrichment in heavy ree and the depletion in light ree with positive la anomalies which imply that these bifs precipitated in ambient seawater moreover the contribution of low temperature hydrothermal fluids during the deposition of the studied bifs were highlighted through their high superchondritic y ho ratio mean 31 48 weak positive eu eu sn ratio mean 1 83 and the low contents of transition metals this suggests that the geochemical characteristics of the kab bifs and those of the paleoproterozoic superior type bifs are almost similar in summary low temperature hydrothermal fluids mixed with seawater contributed to the deposition of the kab bifs on the continental margin this depositional setting similar to its host rocks is consistent with the paleoproterozoic geological history recorded within the nyong unit this preliminary study reveals that the kab bifs are associated with low grade gold

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

ophiolitic source rocks for taconic age flysch trace element evidence flysch generated along the appalachian orogen during the ordovician taconic orogeny ranges in age from late arenig to early caradoc allochthonous flysch and from late llanvirn to ashgill autochthonous flysch sandstones in these units are dominantly lithic arenites with a heavy mineral suite containing common to abundant mg rich chromite north of the canada united states border the only reasonable sources for the chromite were the lower ultramafic units of obducted ophiolites trace element analyses cr ni v cu ti zr y of flysch sandstones indicate a striking increase in cr and ni concentrations from the united states appalachians to the canadian appalachians in the united states units cr is in the range of 10 to 50 ppm canadian flysch units average an order of magnitude more cr these results suggest that ophiolite obduction either did not occur or was of minor importance during the taconic orogeny in the united states appalachians the difference in ophiolite abundance between the canadian and united states appalachians suggests a fundamental difference in tectonic style along the orogen a feature that must be accommodated by plate tectonic models new models will probably need to consider both obliquity of subduction and geological complexity of the ordovician collision zone in order to explain the spatial distribution of obducted ophiolite sheets

elemental distributions and neodymium isotopic compositions of silurian metasediments western maine usa redistribution of the rare earth elements abstract pelitic schists from the lower garnet to lower staurolite zones from the rangeley perry mountain and smalls falls formations of western maine were analyzed for major elements trace elements and neodymium isotopes these formations were derived from highlands created during the taconian orogeny deposited into a trough and metamorphosed during subsequent orogenic events most major and trace element abundances relative to al 2 o 3 were statistically identical between zones of the same formation as well as between formations although the average major element composition of these formations are the same there are systematic variations in some elements notably plots of sio 2 vs al 2 o 3 and k 2 o vs al 2 o 3 suggest that most of the variation could be produced by mixing of a fairly constant ratio of clay minerals and feldspar with varied amounts of quartz due to sorting in the sedimentary system different amounts of these minerals should not influence the shape of the ree patterns of the metapelites but higher amounts of quartz and feldspar may dilute the rees and most elemental abundances of the clay minerals and lead to lower elemental abundances the major difference between the samples within the perry mountain formation are different lree and mree abundances relative to al 2 o 3 which are not correlated to differences in major element or other trace element abundances relative to al 2 o 3 the samples in the perry mountain with higher lree and mree abundances have for example 42 3 8 3 ppm and those with low abundances have 5 6 3 6 ppm the samples with the high ree abundances of the perry mountain formation are similar in abundances and ree patterns to those of the rangeley and smalls falls formations typical of mudstones derived from granitoids another difference between the low and high ree abundance samples are the calculated t dm model ages the high ree abundance samples of the perry mountain formation show t dm similar to the samples of the rangeley formation with ages of about 1 7 1 8 ga the perry mountain samples with low ree abundances however give unrealistically old t dm s between 2 5 and 5 3 ga these unrealistically old t dm s are due to the relatively high sm nd ratios compared to crustal values which are characteristic of samples of the perry mountain formation with lower ree abundances we therefore suggest that these samples may be indicators for open system behavior of the neodymium isotopic system the timing of this disturbance of the neodymium isotope system is difficult to determine and cannot be tied to weathering or a definite postdepositional event the complexities of the data suggest more than one resetting event the most likely event that could have produced much of the movement of the lrees and mrees could have been due to small scale migration between anoxic hemipelagites and turbidite mudstones during diagenesis but some migration may have continued during metamorphism in order to reconcile the neodymium isotopic data

the negative eu anomaly in archean sedimentary rocks implications for decomposition age and importance of their granitic sources abstract a negative correlation between eu anomaly eu eu and chemical index of weathering ciw is found for archean pelites in both greenstone belts and high grade terrains from southern africa western greenland north america western australia and china a similar negative correlation betweeneu eu and chemical index of alteration cia is also found for worldwide young deep sea sediments from various tectonic settings the increase in the indices of weathering and alteration coincide with both shifts in mineral composition and mineral decomposition from plagioclase k feldspar to mica kaolinite and from amphibole to chlorite smectite juvenile crustal materials from local sources are only slightly decomposed due to little or no transport they are characterized by low ciw cia and negligible eu anomalies in contrast crustal materials from large provenance areas have usually suffered long transport and recycling which results in decomposition of high temperature minerals and large ciw cia values that are negatively correlated with significant negative eu anomalies thus the observed trends are interpreted as mainly reflecting increasing contributions of recycled and decomposed materials from large provenances relative to juvenile crustal additions through arc magmatism at local sources in this context there is no obvious distinction between archean greenstone and high grade metasediments and young deep sea sediments the large provenance areas have contained a significant proportion of granitic and rhyolitic materials which in part have not resisted decomposition and erosion due to their occurrence in shallow crustal layers granites received their distinctive negative eu anomaly from equilibration with a feldspar rich residuum the negative eu anomaly of archean metaclastic sediments apparently increased with decreasing age trends of minimum and averageeu eu values of metaclastic sediments evolving with time are calculated for the archean and lead us to infer that the negative eu anormaly eu eu

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

geochemical characteristics and depositional environment of kalpakkam southeast coast of india sediments from kalpakkam southeast coast of india were geochemically analyzed to document the provenance tectonic setting and role of chemical weathering the sediments are dominated by quartz si and the higher concentration of si suggests the presence of quartz feldspar dominated terrigenous sands the study demonstrates that the sediments are derived from the granitic to gneissic or from a sedimentary source beach sediments are deposited in a passive continental margin setting and seabed sediments are deposited in active continental margin in the a cn k diagram most of the samples fall in the lower part i e below the plagioclase feldspar joint which indicates a low degree of alteration only s6 falls just above the plagioclase feldspar joint close to the ak boundary suggesting a slightly advanced weathering of sediment and source beach and seabed sediments lie close to cnk and fm region suggesting the presence of ferromagnesian minerals likely to be pyroxene except s6 which falls in the inner triangle of the minerals feldspar garnet and biotite in a cnk fm diagram both cia and ciw values depict the unweathered nature of the sediments under humid to semi humid climatic conditions

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

sediment chemistry and detrital zircon record in the bosque and paseo del mar coastal areas from the southwestern gulf of mexico abstract in this study we analyzed the mineralogy and bulk chemical composition of 20 sediment samples as well as trace rare earth element ree concentrations and u pb ages of 400 detrital zircons retrieved from the bosque pb and paseo del mar pm coastal sediments southwestern gulf of mexico to investigate the provenance the xrd study revealed that the pb sediments are associated with quartz muscovite cordierite albite and anorthite the pm sediments are associated with calcite aragonite and biogenic materials which derived probably within the coastal environment the weathering indices like chemical index of alteration cia chemical index of weathering ciw and plagioclase index of alteration pia revealed a moderate intensity of weathering for the pb sediments the chondrite normalized ree patterns of the pb and pm sediments are with negative and positive europium anomalies eu eu suggesting that the sediments were derived by the combination of felsic and mafic source rocks the th u ratios 0 3 of the pb and pm zircons indicated an igneous origin the chondrite normalized ree patterns of the pb and pm zircons are depleted in low ree lree and enriched in heavy ree hree with positive cerium and negative europium anomalies a wide variation in chondrite normalized ree patterns of zircons with respect to ages was observed the pb is dominated by proterozoic 551 2500 ma and paleozoic zircons 445 480 ma ordovician whereas pm is dominated by cenozoic zircons 5 21 ma miocene indicating that the zircons were derived from different source terranes the chiapas massif cmc and chuacus complexes are identified as the potential source areas which contributed proterozoic zircons to pb on the other hand cuicateco terrane cui and tuxtla volcanic field tvf are considered as the potential source areas which supplied significant number of cenozoic zircons to the pm coastal area the zircon u pb ages and the bulk sediment geochemistry together indicate that the source terranes which supplied sediments to the pb and pm coastal areas consist of mafic and felsic rocks the results of this study further illustrated the importance of littoral currents in distributing sediments although rivers are considered as a carrier and agent of distributing sediments along the coastal areas

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

detecting syn orogenic extension and sediment provenance of the cilento wedge top basin southern apennines italy mineralogy and geochemistry of fine grained sediments and petrography of dispersed organic matter abstract wedge top basins can provide highly sensitive information on the uplift and erosion history of an evolving collisional belt but their burial and thermal history has generally been neglected because their siliciclastic infill records the very low temperature history which is difficult to detect this paper provides an integrated approach for defining the first order tectonic events shaping the southern apennines in neogene times through the study of a wedge top basin a new dataset of temperature dependent clay minerals and vitrinite reflectance alongside whole rock geochemistry of the fine grained sediments is provided for the uppermost burdigalian lower tortonian succession of the cilento group deposited in one of the largest wedge top basins of the southern apennines italy and its substratum the distribution of paleothermal indicators allowed us to model a detailed burial and thermal history of the basin whereas whole rock geochemistry allowed us to trace the provenance and alteration of sediments through time geochemical data on the fine grained fraction of sediments suggest a source area mainly characterized by felsic rocks with a modest mafic contribution reflecting a prevalent upper crust composition chemical paleoweathering processes played a minor role consistent with medium cia and cia values and sediments subdued poor sorting and rapid deposition the dataset from clay minerals and vitrinite reflectance analyses indicates a basin evolution marked by two phases of intense subsidence interpreted as the result of syn orogenic extension at shallow crustal levels intermitted with periods of low sedimentation rates linked to gravitational instability of a vertically growing orogen

the geochemistry of the sedimentary rocks from the huadi no 1 well in the wufeng longmaxi formations upper ordovician lower silurian south china with implications for paleoweathering provenance tectonic setting and paleoclimate abstract the late ordovician early silurian transition was a critical interval in earth s history marked by mass extinction the gondwana glaciation and volcanic events here we present mineralogical and geochemical characteristics across the ordovician silurian boundary wufeng guanyinqiao and longmaxi formations from the huadi no 1 well in the sichuan basin in order to explore the paleoweathering provenance tectonic setting and paleoclimatic conditions of the source area thin sections xrd x ray diffraction data and major element results reveal that the rocks were abundant in clay minerals quartz minor feldspar pyrite and carbonate minerals the samples have similar chondrite normalized ree patterns to those of paas which are characterized by slight lree enrichments and accompanied by flat hree trends with weakly negative eu anomalies paleoweathering indices cia and pia suggest that the sediments experienced weak to moderate chemical weathering in the source area cia values in the lower wufeng formation range from 67 11 to 72 17 indicating a warm and humid climate the cia values in the upper wufeng formation decrease from 70 35 to 66 15 and the cia values in the guanyinqiao and lower longmaxi formation are persistently low 56 64 62 87 suggesting a cold and dry climate which is consistent with the widespread presence of glaciation in the hirnantian period further upward in the upper longmaxi formation the cia returns to a high value 65 59 which may reflect that the climate started getting warm and glaciation had finished fluctuations in cia values reflect that the climate shifted from warm to cold and then to warm again during the end ordovician early silurian time period the a cn k triangular diagram and sio2 al2o3 tio2 tio2 zr and la th hf bivariate diagrams indicate that the provenance of the rocks from the three formations was primarily felsic igneous rocks discriminant function diagrams and la th sc th co zr 10 and th sc zr 10 triangular diagrams show that the clastic sediments of the wufeng longmaxi formations were derived most likely from an active continental margin finally across the late ordovician early silurian tectonic activity and the end of the ordovician glaciation dominantly controlled the deposition of black shales and siltstones in the wufeng longmaxi formations of south china

geochemistry and provenance of sediments from the pongola supergroup south africa evidence for a 3 0 ga old continental craton abstract the 3 0 ga pongola supergroup of south africa is one of the oldest well preserved supracrustal successions the sequence is divided into the nsuze chiefly volcanics quartzites and pelites and the overlying mozaan groups chiefly quartzites and pelites relative to north american shale composite nasc most pongola pelites have similar la yb and eu eu ratios and large ion lithophile elements lile high field strength elements hfse ree v and sc contents ni 30 300 ppm and cr 100 800 ppm contents are greater than those of nasc while cr ni ratios are generally higher than shales and pelites of all ages these trends may reflect residual cr enrichment during intense chemical weathering of komatiitic source rocks local populations of nsuze pelites based on major and trace element data may result from source heterogeneities and or contemporaneous volcanic input into the sedimentary basin pongola quartzite compositions and detrital modes are similar to those of sandstones from phanerozoic passive margin and basement uplift tectonic settings ree lile and hfse contents in pelites suggest that pongola source rocks were remarkably similar in composition to average phanerozoic upper continental crust trace element geographic and isotopic constraints favor 3 2 to 3 0 ga hood granites as a major source for pongola detritus moderate contributions from mafic sources are also required whereas relatively minor contributions from tonalite and komatiite are allowed these results indicate the existence of a chemically evolved felsic craton in southern africa by 3 0 ga this craton appears to have been more evolved than sources for either older moodies 3 3 ga or most of the younger witwatersrand sediments 2 8 2 7 ga pelites from the kaapvaal craton record at least two mafic to felsic source area compositional cycles in pelites deposited from the mid to late archean additional cycles may be masked by a depositional or erosional hiatus between the moodies and pongola sequences these sedimentary patterns suggest that crustal development in southern africa was episodic in nature during the early precambrian

minerals and potentially hazardous trace elements in the late triassic coals from the qiangtang basin china abstract the tumen coal mine has the largest coal resources in tibet which have been developed and utilized as an important energy source in the last decades it has raised some health problems during the coal exploration and utilization in tibet fifty late triassic coal or coaly samples were picked up from the qiangtang basin tumen mine woruoshan and hongshuihe areas to determine the minerals potentially hazardous elements and their mode of occurrence and possible sources coal samples from the qiangtang basin have medium and high ash yields 15 20 47 88 with low or medium high total sulfur content 0 04 4 86 minerals in qiangtang basin coal include clay minerals dolomite quartz pyrite siderite and hematite and trace amounts of halite feldspar anhydrite barite chromite and galena potentially hazardous trace elements in coal samples include as hg pb and se arsenic is controlled mainly by aluminosilicate minerals mercury occurs mainly as an organic bound form the organically bound pb is dominant selenium is controlled mainly by fe bearing probably pyrite a proportion of the elevated concentrations of as hg pb and se in qiangtang basin coal may be related to underlying shale bed these elements might have been eroded or leached from the shale bed which were subsequently transported and accumulated syngenetically in the coal forming peat swamps the enrichment of as hg pb and se in qiangtang basin coal however is also partly to be related to magmatic hydrothermal fluids

the formation and evolution of the paleo pearl river and its influence on the source of the northern south china sea abstract the paleo pearl river has been suggested as one of the major source terrains for the northern south china sea which headstreams in the hinterland of the tibetan plateau and flows through the south china block eventually discharges into the pearl river mouth basin prmb of the south china sea scs however the drainage history of the paleo pearl river remains a matter of debate detrital zircon u pb ages trace elements nd and sr isotopes and clay minerals from the eocene to miocene sediments in the pearl river mouth basin of the south china sea have been used to investigate the sedimentary provenance and reconstruct the drainage history of the paleo pearl river the eu eu la sc la co th sc and th co ratios the hf la th and la sc co th diagrams and the chondrite normalized ree patterns of the samples suggested that the eocene to miocene sediments were mainly derived from felsic source rock the lower eocene sediments were mainly provided by the intrabasinal uplift regions the dong river and bei river initiated since upper eocene supplied large amounts of felsic detritus from the southern china coast to zhu depression and then transported sediments into the zhu depression during the upper early oligocene the nd and sr isotopes of the sediments suggested that the liu river may not provide sediments for the prmb however the gui river may have made a very small contribution the nd and sr isotopes of the sediments also suggested that the paleo pearl river began to extend westward to form xi river and eventually the hongshui river in the late oligocene the trace element ratios of the samples also suggested that the miocene sediments may have received more input from an intermediate rock area indicating the main provenance switch from the coast of south china to a northern source during this time this conclusion has been supported by the detrital zircon u pb ages nd and sr isotopes and clay minerals data of the samples which show that the provenance of the sediments supplied by the paleo pearl river had an abrupt shift in the middle miocene the southeastern tibetan plateau rapid uplifted and experienced erosion in the middle miocene leading to the progressive headward erosion of the pearl river system into the continental interior

tectonic setting and provenance of the neoproterozoic uinta mountain and big cottonwood groups northern utah constraints from geochemistry nd isotopes and detrital modes abstract the neoproterozoic uinta mountain group was deposited in an east trending intracratonic rift bounded on the north by an active fault system and opening into a shallow sea on the west where the big cottonwood group was deposited in an estuary although this rift may have been associated with the early stages in the breakup of rodinia it was not an aulacogen geochemical nd isotope and detrital mode studies indicate that uinta mountain group sediments were derived from mixed archean and paleoproterozoic sources with the former dominating big cottonwood group sediments appear to have been derived predominantly from paleoproterozoic sources the archean sediment source is the wyoming craton and source rocks comprised dominantly granites enriched in th u y zr hf and ree the relative abundance of enriched granite implied by sedimentary rocks of the uinta mountain group indicates that the wyoming craton is anomalous compared to other archean cratons cia values and a cn k relationships in shales of the uinta mountain and big cottonwood groups indicate high degrees of weathering of sources probably in subtropical to tropical climates supporting a near equatorial location for southwestern laurentia at about 800 ma differences in the nd isotopic composition between the big cottonwood group and neoproterozoic sedimentary rocks in western utah and northeast nevada suggest a northwest striking uplift in northwest utah possibly ancestral to the paleozoic toole uinta arch

ground truthing chemostratigraphic correlations in fluvial systems changes in elemental chemistry have been used to define stratigraphic correlations between wellbores in petroleum basins few publications however relate defined chemical stratigraphy to physical correlations and none have been found that do so in fluvial systems here chemostratigraphy is applied to permian fluvial sediments within the beaufort group of the karoo basin in south africa and a correlation between three logged sections is defined this correlation is tested against physically determined chronostratigraphic correlations achieved using heli lidar data to provide a high resolution correlation between two sections 7 km 4 4 mi apart and mapping of strata using google earth to produce a correlation between sections 25 5 km 15 8 mi apart the chemostratigraphic characterization that is defined using data from fine grained lithologies resulted in the recognition of eight chemostratigraphic packages with thicknesses between 50 and 250 m 164 and 820 ft over a stratigraphic interval of approximately 900 m 2953 ft two distinctive changes in geochemical composition of the coarser lithologies fluvial channel belts were seen over this interval in the two sections that are 7 km 4 4 mi apart higher resolution subdivision of chemostratigraphic packages was achieved to produce four correlative geochemical units 30 60 m 98 197 ft in thickness that provide a high resolution correlation the chemostratigraphic and chronostratigraphic correlations are in close agreement in both the 7 km 4 4 mi and the 25 5 km 15 8 mi spaced sections the thickness of the study interval and spacing of sections is analogous to published chemostratigraphy studies on subsurface sequences thereby ground truthing the use of chemostratigraphy for correlation in subsurface fluvial systems that are to some degree analogous to the beaufort group sediments of this paper

petrography and major element geochemistry of the permo triassic sandstones central india implications for provenance in an intracratonic pull apart basin abstract detrital mode composition of feldspars and heavy minerals and major element chemistry of sandstones from the permo triassic succession in the intracratonic satpura gondwana basin central india have been used to investigate provenance the talchir formation the lowermost unit of the succession comprises glacio marine and glacio fluvial deposits the rest of the succession base to top comprising the barakar motur bijori pachmarhi and denwa formations largely represent variety of fluvial depositional systems with minor fluvio deltaic and fluvio lacustrine sedimentation under a variety of climatic conditions including cold warm arid sub humid and semi arid qfl compositions of the sandstones indicate a predominantly continental block provenance and stable cratonic to fault bounded basement uplift tectonic setting compositional maturity of sandstones gradually increases upwards from the early permian talchir to the middle triassic denwa but is punctuated by a sharp peak of increased maturity in the barakar sandstones this temporal change in maturity was primarily controlled by temporal variation in fault induced basement uplift in the craton and was also influenced by climatic factors plots of different quartz types suggest plutonic source rocks for the talchir sandstones and medium to high rank metamorphic plus plutonic source rocks for the younger sandstones composition of alkali feldspars in the permo triassic sandstones and in different precambrian rocks suggests sediment derivation from felsic igneous and metasedimentary rocks compositions of plagioclase in the talchir and bijori sandstones are comparable with those of granite acid volcanic and metasedimentary rocks of the precambrian basement suggesting the latter as possible source rare presence of high k plagioclase in the talchir sandstones however indicates minor contribution from volcanic source rock exclusively plagioclase bearing metasedimentary rock tonalite gneiss and mafic rocks are the probable sources of plagioclase in the upper denwa sandstones quartz rich nature of the sandstones predominance of k feldspar over plagioclase and albite rich character of plagioclase in the sandstones is consistent with deposition in an intracratonic pull apart basin like the satpura gondwana basin composition of garnet and its comparison with that from the precambrian basement rocks suggests mica schist and amphibolite as possible sources predominance of dravite variety of tourmaline in the permian sandstones suggests sediment supply from metasedimentary rocks presence of both dravite and schorl variety of tourmaline in subequal amount in the triassic sandstones indicates sediment derivation from granitic and metasedimentary rocks however schorl bearing rocks are absent in the basement complex of the study area a cn k plot suggests granites acid volcanic rock and meta sediments of the basement as possible sources of the talchir sandstones and metasedimentary rocks for the barakar to pachmarhi sandstones the denwa sandstones were possibly derived from k feldspar free plagioclase bearing metasediments mafic rocks and tonalite gneiss chemical index of alteration cia values suggest low intensity source rock weathering for the talchir sandstones and higher intensity source rock weathering for the others various bivariate plots of major oxides composition of the sandstones suggest passive to active continental margin setting and even arc tectonic setting for a few samples

mineralogical composition of and trace element accumulation in lower toarcian anoxic sediments a case study from the bilong co oil shale eastern tethys the sediments of organic rich oil shales in the bilong co area can be correlated with those of the early toarcian anoxic black shale events in europe the bilong co sediments are rich in trace elements se mo cd as and ni and to a lesser extent li f v co cu cs hg and bi in comparison to the upper continental crust thirty two oil shale samples were collected from the bilong co oil shale to evaluate the controlling factors of trace element enrichment in the lower toarcian anoxic sediments minerals identified in the bilong co oil shale include calcite quartz illite feldspar and dolomite and trace amounts of siderite magnesite halite haematite zeolite amphibole gypsum anhydrite apatite pyrite sphalerite barite and mixed layer illite smectite mineralogical and geochemical data show that seawater and hydrothermal activities are the dominant influences on the mineralogical composition and elevated trace element concentrations in the oil shale the clay minerals quartz and feldspar in the bilong co oil shale were derived from the nadi kangri volcanic rocks input of sediment from this source may have led to enrichment of trace elements li cr and cs in the oil shale carbonate minerals and nodular and framboidal pyrite are authigenic phases formed from seawater the enrichment of v co ni cu mo as se bi and u in the oil shale was owing to marine influence barite sphalerite and fracture filling pyrites were derived from hydrothermal solutions high concentrations of f zn and cd were probably derived from hydrothermal fluids

minerals and potentially hazardous trace elements in marine oil shale new insights from the shengli river north surface mine northern tibet china the shengli river changshe mountain oil shale zone including the changliang mountain shengli river oil shale the shengli river north oil shale and the changshe mountain oil shale represents potentially the largest marine oil shale resource in china new geochemical data from the shengli river north oil shale are presented to evaluate potentially hazardous trace elements in oil shale and to discuss possible factors controlling the geochemical anomalies oil shale samples from the shengli river north area are characterized by high ash yield 59 25 66 27 and toc content 4 77 9 35 with low total sulfur content 0 1 1 56 and intermediate shale oil content 3 60 16 30 minerals in the shengli river north oil shale include calcite clay minerals quartz dolomite and fe bearing minerals e g pyrite limonite and hematite and trace amounts of zeolite apatite and barite potentially hazardous trace elements in oil shale samples include as se mo f ni cd and hg arsenic is present probably in both organic and inorganic matter selenium is controlled mainly by fe bearing probably pyrite while f and cd occur mainly as apatite the organically bound mo and ni are dominant and hg probably occurs as a substitution in the structure of pyrite apatite and calcite the elevated concentrations of f and cd in the shengli river north oil shale may be related to sediment source water chemistry may have played an important role for ni and mo enrichments while the enrichment of se in the oil shale samples is possibly related to hydrothermal fluids other elements including hg and as are probably related to several factors

water level and redox fluctuations in a sichuan basin lacustrine system coincident with the toarcian oae abstract increasing cases have indicated that oceanic anoxic events oaes appear to have records in terrestrial sediments which provide valuably high resolution materials for the debated and challenging issues of oaes however the current works are preliminary and need more geological analyses to test here we present a case study in the lower jurassic da anzhai member of the toarcian ca 180 ma sichuan basin sw china the petrology and sedimentary facies of the da anzhai member were used to reconstruct the relative water level fluctuations in the sichuan basin which are revealed to be consistent with coeval changes in global sea levels the da anzhai member was deposited during a period of lake shallowing with enhanced salinities corroborated by the sr ba and s toc ratios when sea level was generally high after global transgression during the lake shallowing there were four complete secondary lacustrine deepening shallowing cycles over shorter time scales the total organic carbon contents and organic carbon isotopic stratigraphy show there was a basin wide terrestrial response to the t oae as recorded by the da anzhai member the enrichment factors of mo relative to paas moef and corg p values imply a dysoxic redox condition the terrestrial response of oaes is likely caused by changes in hydrological conditions which were related to the global warming triggered by the karoo ferrar large igneous province the associated organic carbon accumulation mechanism is a combined effect of elevated primary productivity and oxygen depleted preservation conditions our data suggest that oaes do have terrestrial response and induce organic carbon accumulation but the mechanisms are still not much clear and need further studies

petrography and geochemistry of lower carboniferous greywacke and mudstones in northeast junggar china implications for provenance source weathering and tectonic setting abstract northeast junggar occupies an important position that links east junggar and chinese altai numerous magmatic and sedimentary rocks of the paleozoic in this area recorded the final amalgamation processes of east junggar and chinese altai this study analyzes the petrological and geochemical characteristics of sandstones and mudstones from the early carboniferous nanmingshui formation in northeast junggar the provenance and tectonic setting of these clastic rocks are discussed petrography indicates that the composition and texture maturity of the sandstones are low the components of the sandstones are mainly volcanic fragments 61 87 feldspars 9 30 and monocrystalline quartz 2 18 with a few polycrystalline quartz and other minerals slice observation indicates that the majority of the volcanic fragments of sandstones are basic intermediate volcanic rocks with a few dacite and felsic plutonic fragments the detrital modes of the sandstones reflect that these sandstones are derived from undissected arcs a low to moderate chemical index of alteration and the al2o3 cao na2o k2o diagram reflect a low to moderate weathering degree in the source area trace and rare earth element e g la th hf sc cr co and eu contents and their ratios suggest that the source rocks of the clastic rocks are intermediate basic rocks with some felsic rocks compared with sandstones the source rocks for mudstones are more felsic the petrography and geochemistry characteristics of the clastic rocks suggest that the proximal dulate arc should be the primary source area mixing calculations based on ree data suggest that approximately two thirds of the sandstone fragments are intermediate basic volcanic rocks the contents of the major and trace elements as well as the stratum features of the clastic rocks manifest that these clastic rocks resemble sedimentary rocks in a back arc basin the formation of this back arc basin is caused by the southward subduction of the zaysan erqis ocean

quantification of the effects of secondary matrix on the analysis of sandstone composition and a petrographic chemical technique for retrieving original framework grain modes of altered sandstones abstract most studies of sandstone provenance involve modal analysis of framework grains using techniques that exclude the fine grained breakdown products of labile mineral grains and rock fragments usually termed secondary matrix or pseudomatrix however the data presented here demonstrate that when the proportion of pseudomatrix in a sandstone exceeds 10 standard petrographic analysis can lead to incorrect provenance interpretation petrographic schemes for provenance analysis such as qfl and qfr should not therefore be applied to sandstones containing more than 10 secondary matrix pseudomatrix is commonly abundant in sandstones and this is therefore a problem for provenance analysis the difficulty can be alleviated by the use of whole rock chemistry in addition to petrographic analysis combination of chemical and point count data permits the construction of normative compositions that approximate original framework grain compositions provenance analysis is also complicated in many cases by fundamental compositional alteration during weathering and transport many sandstones particularly shallow marine deposits have undergone vigorous reworking which may destroy unstable mineral grains and rock fragments in such cases it may not be possible to retrieve provenance information by either petrographic or chemical means because of this pseudomatrix rich sandstones should be routinely included in chemical petrological provenance analysis because of the many factors both pre and post depositional that operate to increase the compositional maturity of sandstones petrologic studies must include a complete inventory of matrix proportions grain size and sorting parameters and an assessment of depositional setting

provenance evolution of oligocene pliocene foreland deposits in the dezful embayment to constrain central zagros exhumation history this paper presents a detailed provenance analysis of the 6 5 km thick oligocene pliocene foreland succession in the north dezful embayment in zagros iran using petrography geochemistry and palaeoflow analysis we determined three provenance shifts during the exhumation of the zagros orogen above the ahwaz sandstones sourced from the arabian craton a sharp decrease in sio2 al2o3 zr sc th sc th co and th cr within the gachsaran fm and the appearance of first cycle sands derived from metamorphic and volcanic rocks at the base of the aghajari fm characterize the onset of exhumation rising topography and denudation of the zagros orogenic system during the latest oligocene and constitute the first shift the second shift in the middle aghajari fm is marked by a distinct increase in radiolarian cherts and compatible incompatible elements indicating the exhumation of neotethyan radiolarite ophiolite allochthonous slices in the high zagros zone during the tortonian c 9 ma large quantities of carbonate clasts derived from the nearby growing izeh zone anticlines characterize the messinian c 7 ma bakhtyari conglomerates marking the third shift in conclusion a detailed hands on provenance analysis of the clastic sedimentary sequences in the north dezful embayment enabled us to determine catchment areas and shifts hitherto unstudied thus contributing to the exhumation history of the central zagros orogenic system supplementary material details of the petrography and geochemistry results are available at https doi org 10 6084 m9 figshare c 4905558

chromium and nickel in shale of the taconic foreland a case study for the provenance of fine grained sediments with an ultramafic source abstract to test the suitability of using shale geochemistry as a provenance indicator of a source with an ultramafic component we used i c p mass spectrometry to analyze 130 samples from seven localities from newfoundland to new york these samples represent mud from the foreland basin produced during the collision of the taconic are with north america in the ordovician the sandstones in the flysch contain detrital chromite and other detritus that indicate that the source contained ultramafic rocks presumably from ophiolites emplaced during collision this setting is an ideal test case for examining the spatial and temporal variation in cr and ni geochemistry of shale derived from ophiolite bearing highlands shale samples with high concentrations of cr and ni have a cr ni ratio of 1 4 which is approximately the cr ni ratio for ultramafic rocks 1 6 suggesting only minor geochemical partitioning but sandstones have a cr ni ratio of 3 0 suggesting significant sedimentary fractionation analyses of samples taken upsection in a single stratigraphic section suggest that proximity to the source influences cr and ni concentrations a decrease in cr and ni concentrations through time suggests that uplift and erosion of the thrust complex non ophiolitic diluted the ultramafic signal we attribute significant along strike variation in cr and ni concentrations to the relative proportion of ultramafic rocks in the source region this case study shows that cr and ni geoch mistry of shale from basin strata can be used to determine the lateral and temporal variability of ultramafic rocks in an active orogenic setting