nd isotopic and geochemical constraints on the provenance and tectonic setting of the low grade meta sedimentary rocks from the trans north china orogen north china craton abstract in the trans north china orogen tnco of the north china craton low grade supracrustal successions extensively occur in the wutai luliang zanhuang zhongtiao and dengfeng complexes from north to south meta sedimentary samples from the wutai and zhongtiao complexes were collected for geochemical and nd isotopic studies and several samples from the zanhuang and dengfeng complexes were also analyzed for nd isotopic studies for comparative purpose most of the meta siltstones and meta sandstones from the wutai and zhongtiao complexes are characterized by depletions in mobile elements like cao sr and na2o high chemical index of weathering ciw values and strong positive correlation between al2o3 and tio2 indicating intense weathering conditions significant post depositional k metasomatism is indicated in the a cn k diagrams for most of the analyzed samples and the relatively high pre metasomatized chemical index of alteration cia values 43 87 also imply a high degree of source weathering depleted transitional trace elements ni cr co and sc fractionated light rare earth elements patterns mild negative eu anomalies in the majority of these meta sedimentary samples point toward felsic source rocks including the 2 5 ga granitics ttg gneisses and the paleoproterozoic granitics in the tnco minor contribution from mafic rocks is evidenced from relative high contents of mgo fe 2 o 3 t sc and lower la ybn ratios in some older sequence set samples from the zhongtiao complex our geochemical and nd isotopic data combined with previous studies in the lithostratigraphic sequence provenance and depositional age suggest that the older and younger sequence sets of the low grade supracrustal successions in the tnco were deposited in the different depositional environments the older sequence set was deposited in a back arc basin between the andean type continental margin arc and the eastern block after 2 1 ga whereas the younger sequence set formed in a foreland basin between 1 88 and 1 80 ga which is consistent with the model that the collision between the eastern and western blocks to form the trans north china orogen occurred at 1 85 ga

provenance and tectonic setting of the paleoproterozoic metasedimentary rocks from the liaohe group jiao liao ji belt north china craton insights from detrital zircon u pb geochronology whole rock sm nd isotopes and geochemistry abstract geochronological geochemical and isotopic studies were carried out on the paleoproterozoic metasedimentary rocks from the jiao liao ji belt north china craton to constrain their provenance and tectonic setting as well as to evaluate the effects of weathering and sedimentary processes on the source rock signature u pb isotopic dating using the la icp ms method on zircons from the paleoproterozoic metasedimentary rocks reveals that the depositional age can be constrained in the period between 1 98 and 1 9 ga geochemical data reveal low intermediate degrees of weathering of the source compositionally immature and poorly sorted detailed analysis of detrital zircon u pb geochronology whole rock sm nd isotope and geochemistry show that these metasedimentary rocks are derived from a mixed provenance the predominant derivation is from metavolcanic rocks of the liaohe group and paleoproterozoic gneissic granitoids there is also an input of archean continental crust the metasedimentary rocks were probably deposited in a back arc basin within an arc system thus supporting the paleoproterozoic arc continent collision model as already proposed by some authors

geochemistry of the holocene sediments of lake chenghai sw china and its implications for paleoenvironmental reconstruction abstract analysis of lake sediment geochemistry is valuable for understanding past hydroclimatic changes via the reconstruction of changes in catchment erosion chemical weathering redox processes and the intensity of evaporation in this study we analyzed the geochemical composition magnetic susceptibility and carbonate content of the holocene sediments of lake chenghai in the jinsha river valley southwest china our aims were to determine the influence of holocene hydroclimate evolution and geo hazards on lacustrine sedimentation the results show that the hydroclimate was generally humid during 7 57 4 65 cal ka bp and that subsequently it became relatively dry during 4 65 1 37 cal ka bp our results also reveal that the centennial scale variability of the lake level during the holocene is forced by changes in solar activity and oceanic atmospheric feedback in addition the interval of 3 31 1 95 cal ka bp was the driest due to highly variable and intense el nino events and the southward migration of the intertropical convergence zone furthermore three large landslide events occurred at 7 30 6 36 and 0 76 cal ka bp around lake chenghai which are correlated with unusually large floods during the period of weakened monsoon activity and or with earthquake events

intensified aridity in the qaidam basin during the middle miocene constraints from ostracod stable isotope and weathering records the thick and continuous cenozoic successions in the qaidam basin provide an excellent paleoclimate archive here we focus on the ostracod fauna stable isotope records and paleoweathering indice

the geochemistry of major and selected trace elements in a forested peat bog kalimantan se asia and its implications for past atmospheric dust deposition abstract biogeochemical processes in a forested tropical peat deposit and its record of past atmospheric dust deposition were assessed using the vertical distribution of lithophilic and plant essential elements in a dated core profile from borneo se asia peat formation started 22 120 14c yr before present bp and ca mg mass ratios of the solid peat and very low ash contents indicate a strongly ombrotrophic character throughout the deposit implying that most of the inorganic fraction has been supplied exclusively by atmospheric inputs concentration profiles of mn sr and ca suggest a very minor influence of chemical diagenesis in the underlying sediments silicon ca mg p s and k show a strong and extended zone of enrichment in the top 200 cm of the profile indicating that biological accumulation mechanisms are much more extensive than in temperate peat bogs in the lower core sections where the element distribution is dominated solely by past atmospheric deposition average al ti ratios are similar to the upper continental crust ucc whereas fe is slightly enriched and si is strongly depleted this condition favors highly weathered tropical soil dust as the main inorganic mineral source significant correlation of al fe si s ca and ti with the lithophilic elements y and zr suggests that the distribution of these elements is controlled by sources of atmospheric mineral dust the ca mg ca k and mg k ratios of the collected rainwater samples are similar to the global average of continental rainwater and suggest a continental character for the site this is supported by the similarity of the average concentration of br mg ca and s to that in temperate continental and maritime bogs in switzerland and scotland the concentration profiles of si fe al and ti show distinct peaks within the profile implying enhanced dust deposition reduced rates of peat accumulation or possibly both owing to climatic changes during the holocene enhanced dust deposition between 10 830 and 9060 14c yr bp is tentatively interpreted as a younger dryas like event with dust fluxes of 10 8 mg m2 yr the variations in al ti and fe ti profiles suggest that mineral dust sources have been changing constantly during the holocene with local sources being dominant between 7820 and 9500 14c yr bp and long range transport derived most likely from china being important during the late pleistocene and early holocene and from 7820 14c yr bp to the present

the metamorphic aureole of the nisa alburquerque batholith sw iberia implications for deep structure and emplacement mode the nisa alburquerque granitic batholith southern variscan belt iberian peninsula has been studied by petrological structural and geophysical approaches obtaining contrasting models for its deep structure and emplacement sequence in order to test these models and gain knowledge on the thermal increase induced by the intrusion we have studied its contact aureole which was developed in similar country rock lithologies mica schists alternating with metasandstones and feldespatic schists all along the northern external contact of the batholith our results indicate no change in metamorphic grade and some variations in aureole width which narrows toward the western sectors of the batholith cordierite is the only contact metamorphic mineral developed together with a high temperature biotite probably related to the granite thermal input by considering these new data together with zircon saturation temperatures within the granite and previous petrological and geophysical studies we propose a model in which the feeder zones of the granitic magmas were an eastern main one and a western secondary one we have also made comparisons of the metamorphic grade in the country rocks and the xenoliths within the granite most of the xenoliths have the same metamorphic facies as the country rocks crd zone though some of them contain slightly different assemblages and crd which could be explained in different ways 1 differences in the primary schist compositions 2 increased time span of xenoliths in contact with the melt and 3 xenolith incorporation at slightly higher depths during final granite ascent

linkage between lake xingkai sediment geochemistry and asian summer monsoon since the last interglacial period in this study we present the element geochemical data of core xk08 a2 drilled from lake xingkai khanka northeast china the study aims to examine the changes of sediment provenance and geochemical composition in response to asian summer monsoon variability since the last interglacial period major elemental analyses on lacustrine samples and sand samples from lake xingkai and the surrounding sandy ridges in northeast china indicate that their abundance varied in relatively narrow ranges the samples had only undergone the primary stage of chemical weathering similar ti al and k al ratios between the lacustrine samples from lake xingkai and the loess paleosol samples in north china were observed which suggests that they come from broadly similar desert sources due to the significant dependence on grain size and influence of sediments recycling chemical index of alteration of the lacustrine sediments could not be regarded as sensitive indicators of source regions weathering on the glacial interglacial timescale alternatively the geochemical proxies of the lacustrine sediments could be linked to the asian summer monsoon through the development of runoff and physical erosion in the catchment weakened asian summer monsoon caused more fine particles transported to the lake basin by reduced runoff in the last glacial period in contrast coarser and less weathered detritus are transported into the lake accompanying strengthened asian summer monsoon during the warm periods

al2o3 tio2 ratio of the clay fraction of late ordovician silurian carbonate rocks as an indicator of paleoclimate of the fennoscandian shield abstract in the fennoscandian shield the fluctuations in arid humid climate conditions are inferred from the al2o3 tio2 ratio of the clay fraction of estonian carbonate rocks of the baltoscandian sedimentary basin the late ordovician climate of the fennoscandian shield was mainly semi humid with several humid pulses in the sandbian mid katian and hirnantian the post hirnantian climate was fluctuating between humid and arid until stable humid conditions were established in the middle and early late llandovery starting from the latest llandovery the climate turned semi arid and arid the ordovician silurian long term trend toward aridity was caused by the equator ward drift of the baltica plate shorter term fluctuations of al2o3 tio2 reflect climate changes of the global extent

geochemical characteristics of the eolian deposits in the zoige basin and their implications for provenance and weathering intensity abstract eolian deposits in the zoige basin at the northeastern region of the tibetan plateau tp were analyzed for their major trace elements and sm nd isotopic compositions to explore the provenance and weathering intensity the results are compared with the data from the lingtai section lt in the chinese loess plateau clp eolian deposits from different sections in the zoige basin have resembling geochemical compositions reflecting similar provenance their major element compositions are close to those of the ucc and their ucc normalized major trace element abundances and chondrite normalized rare earth element ree abundances are similar to the lt samples however the sio2 al2o3 tio2 zr hf sc co v ni concentrations and sio2 tio2 tio2 al2o3 co th la sc th sc end 0 147sm 144nd ratios of the zoige sections are quite different from those of the lt section which suggests different provenances for the eolian deposits in these two regions the relatively high abundances of sio2 zr hf and low abundances of trace elements indicate that local sediments on the tp are the major contributors to the eolian deposits in the zoige basin eolian deposits from the zoige basin have experienced the early na and ca removal stage and chemical weathering parameters suggest a moderate weathering condition in the source and deposition regions

element mobilization and redistribution under extreme tropical weathering of basalts from the hainan island south china abstract chemical weathering of rocks has substantial influence on the global geochemical cycle in this paper the geochemical profile of a well developed basalt weathering profile 15 m thick including soil saprolite semi weathered rock and fresh basalt on the island of hainan south china was presented the soil and saprolite samples from this profile are characterized by high al2o3 and fe2o3 concentrations up to 32 3 and 28 5 respectively the mineral assemblage is dominated by kaolinite fe oxides hydroxides and gibbsite or boehmite indicating extensive desilicate and ferrallitic weathering the acidic and organic rich environment in the soil horizon may have promoted elemental remobilization and leaching the strongest sio2 depletion and al2o3 enrichment at about 2 4 m deep indicate that the main kaolinite hydrolysis and gibbsite formation occurred near the soil saprolite interface the mild sr reconcentration at about 3 9 m and 7 1 m deep may be attributed to secondary carbonate precipitation mn oxides hydroxides precipitated at 6 1 m deep accompanied by the strongest enrichment of ba and co uranium is mildly enriched in the middle part about 7 1 m and 9 1 m deep of the weathering profile and the enrichment may have been caused by the decomposition of uranyl carbonates or the accumulation of zircon immobile element i e zr hf nb ta th and ti distributions at different depths are mainly controlled by secondary fe oxides hydroxides and follow the stability sequence of nb ta th zr hf ti the limited thickness 15 cm of the semi weathered basalt horizon at the rock regolith interface 15 28 m deep suggests that plagioclase and pyroxene are readily altered to kaolinite smectite and fe oxides under tropical climate the marked enrichment of transitional metals such as cu zn ni and sc along the rock regolith interface may have associated mainly with increasing ph values as well as the dissolution of primary apatite and formation of secondary phosphates our findings highlight the importance of secondary phosphates in the redistribution of transition metals and in the possible mg cu and ni isotopic fractionation under extreme weathering of basalt in tropic climate

geochemistry and origin of ferruginous nodules in weathered granodioritic gneisses mysore plateau southern india fe nodules occur within saprolites formed from weathering of granodioritic gneisses in the rain shadow region of the mysore plateau adjacent to the sahyadri mountains in southern india these nodules and their host saprolites were studied for their geochemistry including chemical speciation to understand nodule formation and chemical redistribution processes during rock weathering from their mode of occurrence and mineralogical and geochemical data we infer that the nodules originated by a two stage process in which the initial extensive weathering of gneisses likely facilitated subsequent ferrolysis weathering and nodule formation nodules originated by precipitation of goethite hematite and gibbsite along with several amorphous phases within the matrix of weathered gneisses this is possible only under hydromorphic conditions suggesting that parts of the plateau must have gone through a humid phase prior to the present aridity in the saprolites al fe and ti become enriched because of the removal of si ca na and k however within the nodule fe ti cr and ni are deposited after their chemical transport from the saprolite titanium known for its immobile nature was also mobilized and concentrated under the conditions of nodule formation the most important elements in the nodule constitution are fe al ti and mn each having both crystalline and amorphous phases fe ti and mn oxyhydroxides grain coatings in the saprolites and discrete amorphous mn and ti phases in the nodules seem to have scavenged trace elements from the weathering profile ree were mobilized during weathering and nodule genesis in which ce and ti show a strong geochemical coherence the enrichment of only hree in saprolite and both hree and lree with significant ce in the nodule indicate the control of evolving secondary minerals in the ree redistribution during rock weathering strong enrichment of ce in the weathering profile and in nodules has important implications to the ree chemistry of river waters

geochemical characteristics of organic rich shale upper yangtze basin implications for the late ordovician early silurian orogeny in south china abstract the tectonic sedimentary environment of the upper yangtze basin in china underwent significant changes from the late ordovician to early silurian the widely distributed shale formed during this interval has recorded key information about paleo ocean conditions analysis of major trace and rare earth elements was conducted on 135 shale samples collected from five wells in the study area the covariation of the mo u enrichment factors indicates that the upper yangtze basin in the wufeng stage was characterized by sedimentary differentiation the southern basin was dominated by a reducing bottom water environment under euxinic conditions the northern and central basins were dominated by a suboxic anoxic environment up to the early longmaxi stage the upper yangtze basin formed a relatively uniform sedimentary environment with gradually increasing oxygen content in the bottom water the paleoproductivity index indicates that marine organisms flourished in the wufeng to early longmaxi stages making an important contribution to the siliceous content in organic rich shale subsequently terrestrial siliciclastics gradually dominated analysis of paleogeography rare earth elements and weathering indicates that chuanzhong and qianzhong uplifts in the wufeng stage were the provenance area of the upper yangtze basin with a relatively high weathering degree weathering decreased in the beginning of the longmaxi stage and then gradually increased with the xuefeng uplift becoming the main provenance areas after the early longmaxi stage controlled by stress transfer from the continuous syn caledonian kwangsian orogeny in eastern south china the upper yangtze basin and xiangzhong basin were squeezed and pushed up successively the uplift separated the open shallow sea and formed a relatively limited deep water shelf environment resulting in a relatively euxinic bottom water environment which was favorable for organic matter accumulation the tectonic sedimentary evolution of the upper yangtze basin in the late ordovician to early silurian proposed in this study indicates that the formation of organic enriched shale was not only related to glacio eustatic change but also strongly controlled by tectonic activities in south china

diagenetic mobilization of ti and formation of brookite anatase in early cambrian black shales south china abstract titanium ti is typically hosted in detrital minerals in marine sediments and has long been considered to be immobile during diagenesis in this study the authigenic titania minerals brookite and anatase are observed in early cambrian carbonaceous shales from the meishucun and zhajin sections of south china respectively black shales in the meishucun section have total organic carbon toc contents from 1 6 to 3 9 wt and hi hydrogen index values from 3 8 to 20 mg hc g toc whereas black shales in the zhajin section have much higher toc 7 1 15 6 wt but lower hi

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

tracking the onset of phanerozoic style redox sensitive trace metal enrichments new results from basal ediacaran post glacial strata in nw canada abstract a global rise in oxygen levels has been proposed to coincide with the ediacaran to cambrian radiation of animals yet the precise timing and nature of this change remains unresolved one hypothesis is that the ocean atmosphere system became temporarily well oxygenated in the earliest ediacaran directly following the marinoan snowball earth glaciation 635 ma the evidence for oxygenation is based on large enrichments of redox sensitive trace elements in black shale from south china presumably deposited under a euxinic water column these enrichments meet or exceed the bulk concentrations of redox sensitive trace elements found in phanerozoic shale deposited under euxinic water columns here we test the early ediacaran post snowball oxygenation hypothesis with new data from a high resolution multi proxy geochemical and sedimentological study of three stratigraphic sections in the earliest ediacaran sheepbed formation of the mackenzie and wernecke mountains nw canada iron speciation data from all sections suggest that the local water column was dominantly ferruginous with a notable exception of probable euxinic conditions recorded in part of one section redox sensitive elements show no appreciable enrichments in the basal sheepbed formation with maximum concentrations of molybdenum vanadium uranium and chromium only slightly above world average shale values the lack of substantial elemental enrichments within the sheepbed formation is consistent with results from coeval ferruginous strata in svalbard the dominance of local ferruginous conditions in nw canada cannot alone account for the muted redox sensitive element enrichments as v u and cr are thought to be enriched under these conditions and samples deposited under euxinic conditions also lack phanerozoic style enrichments these contrasting results from different localities highlight a need to further investigate the veracity of trace metal enrichments in all localities as representing global redox conditions as the results have important implications for the timing of oxygenation with respect to early animal evolution

origin of deep sea clastics of the magura basin eocene makovica sandstones in the outer western carpathians with constraints of framework petrography heavy mineral analysis and zircon geochronology abstract petrographic examination heavy mineral analysis and detrital zircon u pb dating were performed on the eocene siliciclastic rocks in the raca unit of the outer western carpathians in order to reveal their origin and establish the development of the magura basin during the eocene the medium to fine grained sublitharenites and quartzarenites were mainly derived from extra basinal sources and the deposits predominantly contain minerals from metamorphic rocks the terrigenous material was derived from low to medium grade metapelites and granitoids the sedimentation was also controlled by a sediment supply from the mafic source the basic and metabasic rocks contain pyrope rich garnets and cr spinels palaeo currents document that the sedimentary material was supplied from the south east the first detrital zircon u pb ages confirm zircon producing events occurring in the proterozoic from approximately 2200 to 590 ma but predominantly in the paleozoic between 550 and 60 ma the palaeocurrent indicators petrographic data heavy mineral spectra and zircon geochronology strongly suggest that the tisza mega unit variscan crystalline basement erosion with accompanying sedimentary cover supplied the magura basin from the south the mecsek zone is also suggested to support the villani bihor and part of the bekes codru zones in supplying the magura basin during the eocene to oligocene the eocene transport of significant detrital material to the magura basin is also related to erosion of the marmarosh massif proterozoic ordovician low to medium grade crystalline basement therefore it is most likely that magura basin sedimentation was dominated by supply from the sub ophiolitic fore marmarosh suture zone of the eastern carpathians

origin of enigmatic structures field and geochemical investigation of columnar joints in sandstones island of bute scotland abstract columnar joints resembling those in igneous rocks are present in devonian and early carboniferous sandstones at two localities on the island of bute in southwestern scotland new data concerning field relations and geochemical changes constrain processes responsible for generation of columnar fracture patterns in sedimentary rocks the columns are mostly normal to bedding and occur at several discrete stratigraphic levels the host rocks are cut by early carboniferous volcanic necks or plugs which acted as heat sources but development of columnar jointing was strongly controlled by small sills and dikes of a recessive purple fine grained rock geochemistry of these rocks points to an igneous origin where contacts are exposed columnar joints appear above subconcordant intrusions and disappear upward the lowest parts of the columnar jointed sandstones are si depleted and enriched in ca mg fe al rare earth elements rees and some base metals ree patterns from columnar jointed sandsto

a multiproxy micro xrf pollen chironomid and stable isotope lake sediment record for the lateglacial to holocene transition from thomastown bog ireland a multiproxy lateglacial environmental record is presented for a ca 3 5 m lacustrine sequence retrieved from a small basin ca 2 km2 at thomastown bog in county meath ireland sediment chemistry pollen chironomid and stable isotope data provide a detailed picture of catchment and lake system changes from the end of the last glacial gs 2a to the early holocene that correspond closely to existing local and regional models of climate change concomitant adjustments in independent proxy records are matched to the ngrip oxygen isotope curve giving 12 event episodes ranging from major climatic shifts to lower amplitude centennial to sub centennial scale adjustments including a previously unreported regressive period of landscape instability during the north west european rammelbeek phase the study emphasizes the potential of palaeoenvironmental reconstruction from sediment chemistry where the sediment mixing system reflects autochthonous versus allochthonous inputs the investigation also indicates problems of interpreting isotope data derived from bulk marl due to possible lag effects controlling the delivery of soil and groundwater and multiple sources of hco3 aq these research findings have implications for core site selection and for studies attempting to use stable isotopes for correlation purposes

assessing changes in elemental mass as a result of chemical weathering of granodiorite in a mediterranean hot summer climate abstract in ascending order relatively unweathered granodiorite 1 97 m of friable granodiorite and 0 91 m of very coarse loamy sand make up a well developed weathering profile that developed on a cretaceous granodiorite lying within a mediterranean hot summer climatic belt in the peninsular ranges of southern california u s a textural modal and chemical data indicate that in the friable granodiorite and in the very coarse loamy sand plagioclase was leached at a rate faster than was k feldspar while quartz remained little changed in addition molecular ca and na were probably leached at a faster rate from plagioclase and titanite than k was leached from k feldspar and biotite mass balance calculations show that 3 4 2 0 of the original bulk mass of the friable granodiorite was removed during its development this loss of bulk mass was accommodated through the removal of 4 9 18 11 17 29 and 14 of the masses of si ca k na p ba and sr respectively in addition the masses of fe and y were increased by 12 and 52 respectively of the 3 4 loss of original bulk mass 99 is due to the loss of si ca k and na mass the severity of chemical alteration is greatest in samples analyzed from very coarse loamy sand this conclusion is supported not only by textural relationships but also by mass balance relationships that show that 11 2 2 1 of the original bulk mass of the very coarse loamy sand was removed during its development this loss in mass was accommodated through the removal of 12 12 42 14 41 80 21 14 10 and 40 of the masses of si mn ca k na p ba zn rb and sr respectively in contrast during development of the very coarse loamy sand the masses of ti and fe were increased by 17 and 22 respectively of the 11 2 loss of original bulk mass 99 is attributable to the removal of si ca k and na mass data summarized above and in work by others imply that plutoniclastic sediment derived from sources lying within a wide range of climatic conditions do not reflect directly the bedrock from which they were derived but instead will mirror the compositions of the weathering profile

fracture control on type morphology and distribution of parasitic volcanic cones an example from mt etna italy abstract this paper uses a coupled morphometric and stratigraphic analysis of several tens of parasitic pyroclastic cones of the se flank of mt etna volcano italy to explain the structure of a poorly understood actively deforming zone of the volcano moreover we present a new general classification of pyroclastic cones based on the parameterisation of coeval eruption points along the same magma feeding fracture each cone has been studied in detail in order to define its stratigraphic position morphometric characteristics growth evolution in relation to fracture distribution and orientation stress field and morphology of the substratum end members of this classification are at one side a simple circular or elongated edifice that grew around a single eruption point and can be related to a magma feeding fracture constrained by a relatively high confining stress in the substratum or a low magma pressure the other end member is a multiple rifted strongly elongated cone formed along multiple eruption points of a magma feeding fracture constrained by a relatively low confining stress or a high magma pressure lithostratigraphic and historical analyses demonstrate that the cones in this area developed between 15 ka bp and historical times the most recent one in 1669 ad testifying to a high rate of lateral eruption occurrence in the area these cones show n s elongated maximum crater axes n s trending axis of the depressed points of the crater rim and southward and southeastward breaching directions while coeval cones are n s aligned these morphometric characteristics reflect the geometry of n s magma feeding fractures the area can be regarded as a transitional weakness zone between the n s rift and the releasing system represented by the transtensional trecastagni and mascalucia faults indicating an e w oriented local component of extension possibly related to the interplay between the regional timpe fault system and the eastward gravitational spreading of the volcano the azimuth of breaching is controlled by magma feeding fracture orientation and substrate morphology especially in the eastern part of the area where it is influenced by the scarps related to the timpe regional fault system but it is also sensitive to cone development

a 40 000 yr record of clay mineralogy at lake towuti indonesia paleoclimate reconstruction from reflectance spectroscopy and perspectives on paleolakes on mars sediment deposited within lake basins can preserve detailed records of past environmental conditions on planetary surfaces including both earth and mars establishing how to best characterize these paleoclimate records is thus critical for understanding the evolution of past planetary climates here we present an 40 k y lake sediment record from lake towuti indonesia developed using visible to near infrared vnir reflectance spectroscopy source sediment from the main river input to lake towuti the mahalona river is spectrally dominated by mg rich serpentine however we also identify a distinct al phyllosilicate component which we interpret as kaolinite that increases in relative proportion to serpentine with decreasing grain size sink sediment from two cores collected at the distal margins of the mahalona river delta has similar spectral signatures to the input source sediment the cores capture systematic variations in the proportion of al phyllosilicate to serpentine over time which is also expressed in changes in bulk elemental chemistry of the sediment we show that the abundance of serpentine relative to al phyllosilicate increases dramatically during the globally cooler regionally drier climate of the last glacial maximum this change records the grain size dependent mineralogy of deltaic sediment which is ultimately driven by forced delta progradation and river incision during lake lowstands our analyses show that vnir reflectance spectroscopy offers a rapid nondestructive and effective method for developing paleoenvironmental records from sedimentary phyllosilicate mineralogy exposed paleolake deposits on mars should preserve similar paleoenvironmental information that can be accessed through detailed remote sensing observations of stratigraphy and vnir reflectance spectroscopy in a source to sink framework

oligocene miocene antarctic continental weathering record and paleoclimatic implications cape roberts drilling project ross sea antarctica abstract the bulk chemistry of mudrocks in ross sea drillcores on the antarctic inner shelf is re evaluated to extract records of continental paleotemperatures and ice extent the chemical index of alteration cia of the sedimentary sequence derived from the composite of the cape roberts cores changes in accordance with pco 2 pagani m zachos j c freeman k h tipple b bohaty s 2005 marked change in atmospheric carbon dioxide concentrations during the paleogene science 309 600 603 the k 2 o na 2 o al 2 o 3 molar ratio of the mudrocks is used as a mean summer temperature proxy for continental antarctica and it shows similarities with benthic mg ca temperatures for the southern ocean billups k schrag d p 2002 paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and stable isotope measurements on benthic foraminifera paleoceanography 17 doi 10 1029 2000pa000567 the ratio is calibrated using intervals with significant pollen assemblages and the temperature proxy enables extrapolation of the paleoclimatic data over a larger portion of the drilled record the cia and k na al ratios support a persistent cooling and drying of climate through the oligocene miocene transition the results reinforce the strong coupling between east antarctic continental temperatures and ice volume with deep sea temperatures and concentrations of atmospheric carbon over long timescales

pedogenesis of spatially associated red and black soils in purna valley from semi arid region of central india abstract eight representatives spatially associated red and black soils in purna valley from the semi arid region of central india were studied through mineralogical micromorphological and geochemical investigations to infer pedogenic transformations during changing climatic phase the morphology of soils showed that dissected alluvial plains over the basaltic landforms consists predominantly of dark reddish brown to dark yellowish brown soils with iron calcium carbonate nodules typic haplustepts and lithological discontinuities typic ustifluvents whereas pediplains and alluvial plains have clayey dark brown sodic slickensided bss horizons enriched with caco3 nodules typic haplusterts buried natrustalf on alluvial fans and floodplains has strong brown natric btn horizons with distinct ferriargillans and abundant caco3 nodules ferriargillans in alfisols indicates prevalence of humid climatic phase in the past during which alteration of plagioclase feldspars to smectites could have occurred thereafter termination of humid phase and an onset of semi arid climatic phase had favored drier non leaching environment which has resulted in the preservation of smectites in vertisols the randomness in soils are expressed as entropy index which showed that physical mixing in subgroups of vertisols and sodium enriched argrillic horizons in alfisols were the indicators of altered pedogenesis at steady state the formation of caco3 pedogenic carbonates and the concomitant development of sodicity during arid climatic phase were indicators of strong alkalinity and base accumulation in soils as a mark of aridity in red and black soils of the valley the chemical index of alteration weathering index and entropy index were served as good indicators for assessing intensity of chemical weathering rate with respect to hydrology and topography the study demonstrates that how the morphological physical chemical mineralogical and micromorphological data were useful in assessing pedogenetic processes in spatially associated red and black soils of purna valley

late quaternary tectonic switching of siliciclastic provenance in the strike slip dominated foreland of the western carpathians upper morava basin bohemian massif abstract this study is focused on the lithology and provenance of late quaternary fluvial deposits of the upper morava basin a pull apart basin situated at the contact of the bohemian massif and western carpathians late cenozoic tectonic convergence between these two units caused differential subsidence along strike slip faults of the elbe odra zone leading to a distinct horst and graben morphology of the upper morava basin the pleistocene fluvial deposits are preserved in several terrace levels and partly buried under the present day floodplain of the morava river this study is based on four cores 11 25 m deep drilled in the floodplain of two major depocentres of the basin the lutin graben and the upper morava basin sensu stricto the drill cores were analysed for grain size pebble and heavy mineral composition chemical composition of detrital garnets bulk magnetic susceptibility sediment colour visible light spectral reflectance and bulk element geochemistry age interpretations are based on eight optically stimulated luminescence osl analyses the upper pleistocene sediments were deposited in a gravelly braided to transitional braided meandering river in both the upper morava basin s s and the lutin graben the oldest osl age is 161 5 ka corresponding to the late saalian between the end of the saalian and late weichselian glaciations the morava river abandoned the lutin graben for the upper morava basin s s where it flows up to the present day the pleistocene fluvial style contrasts with the present day meandering to anastomosing fluvial style of the morava river the pleistocene deposits were sourced from areas corresponding to the present day morava river catchment including crystalline units of the eastern bohemian massif and the moravo silesian carboniferous basin they also contain a considerable input from the bohemian cretaceous basin the composition of late weichselian deposits from the dub nad moravou core 34 53 3 42 ka and younger differs from the older fluvial deposits representing the other cores it indicates that a major provenance change occurred between the latest saalian and the late weichselian in the late weichselian the morava river started to recycle loess deposits which cover large areas of its catchment based on osl dating it may be assumed that the morava river turned from degrading between 92 6 8 03 and 34 53 3 42 ka to aggrading in style from 34 53 3 42 ka to the present day due to coeval tectonic movements in the umb which are indirectly indicated by present day seismicity geomorphic faults and palaeoseismic evidence both the tectonic context and fluvial deposition styles of the upper morava basin show similar features to the upper rhine graben of the alpine foreland

authigenesis of titania minerals and the mobility of ti new evidence from pro deltaic sandstones cretaceous scotian basin canada titania tio2 minerals are minor diagenetic phases in many sandstone shale successions but the conditions of ti mobility and titania authigenesis are poorly known here new modes of occurrence of authigenic titania minerals filling pores and replacing phytodetritus are documented from lower cretaceous prodeltaic sandstones in the offshore scotian basin of southeastern canada textural relationships suggest that titania minerals formed at the same time as kaolinite most commonly below lowstand sequence boundaries related to flux of meteoric water such authigenic titania is most abundant in thin bedded sandstones interbedded with thick prodeltaic mudstone in which fine grained detrital ti rich minerals are concentrated textures in titania that has replaced uncompacted phytodetritus suggest microbial mediation in near surface eodiagenesis eogenetic titania is enriched in phosphorus 0 6 p2o5 and may co occur with authigenic fluorapatite and crandallite crystals such titania resulted from prolonged flow of meteoric water that dissolved p from apatite and feldspar thereby enhancing ti solubility in basins with supply of immature sediment from granitic terranes and important diagenesis by meteoric water the assumption that ti is an immobile element and that rutile or other titania minerals are exclusively of detrital origin may not be valid probable mesodiagenetic titania has low p content suggesting that ti mobility under these conditions was facilitated by some other agent probably organic acids the results of this study illustrate that even in cases where titania minerals are volumetrically insignificant their microtextures and trace element chemistry can provide important insights into the character of fluid flow during diagenesis of siliciclastic rocks

the chemical index of alteration cia as a proxy for climate change during glacial interglacial transitions in earth history abstract the glacial interglacial transitions of ice ages are associated with large rapid changes in climate which potentially can be reconstructed from stratigraphic profiles of the chemical index of alteration cia here we present a case study based on high resolution cia profiles of neoproterozoic glacial deposits from south china paleolatitude 30 n as a record of the climate transition at the termination of the sturtian glaciation 663 ma drillcore zk2115 gaodi deposit exhibits a progressive upsection increase in mean cia over a 50 m interval from 58 range 52 65 note all ranges are given as 16th 84th percentiles in the synglacial upper tiesi ao formation to 67 range 64 69 in the deglacial basal datangpo formation cap carbonates and to 68 range 66 70 in the postglacial datangpo formation black shales a coeval section from the lijiawan deposit also exhibits an increasing cia trend upsection within shallow water mn carbonate facies these cia patterns show no relationship to lithology and are interpreted to reflect climatic warming and intensified chemical weathering during the sturtian deglaciation similar large increases in postglacial cia values are seen in paleoproterozoic and late paleozoic successions and at least moderate increases in cia values are recorded during warm stages of the late quaternary e g the bolling allerod and holocene relative to the cold stages e g the last glacial maximum and younger dryas the rapidity of cia changes in quaternary systems 1 to 10 kyr suggests that weathering intensity may have changed at similarly rapid rates in more poorly dated deep time glacial successions with potential implications for snowball versus slushball models of cryogenian glaciations these examples show that cia can be a robust proxy for climate changes i e enhanced chemical weathering intensity during glacial interglacial transitions of both ancient and recent ice ages

a model to estimate the depositional brine depths of ancient halite rocks implications for ancient subaqueous evaporite depositional environments a model is derived which allows a more general approach to the interpretation of bromine profiles in halite rocks than is possible with the models of kuhn or holser allowing for an open system with influx and reflux reduces the depth of brine necessary to generate a given salt deposit even very small and regular bromine gradients which historically have been interpreted as the result of deposition from deep brine bodies can be generated in an open system from brine no more than a few tens of metres deep the bromine gradient produced from a given depth of brine is strongly dependent on the composition and amount of influx but less so on the composition of brine already in the basin a zechstein profile is analysed which in a closed basin would require brine 2665 m deep it can equally be modelled by influx of normal seawater which fully replenishes a basin no more than 140 m deep a somewhat irregular profile from the paradox basin instead of requiring a basin 100 400 m deep can be modelled as being produced by deposition from brines only 10 m deep reflux in both cases can only be a few per cent of influx at a maximum

recognizing metasedimentary sequences potentially hosting concealed massive sulfide accumulations in the iberian pyrite belt using geochemical fingerprints abstract promising advances in the development of new greenfield and brownfield exploration methods and methodologies for massive sulfide ore systems in the iberian pyrite belt ipb have been made over the last two decades however the effects of lateral and vertical facies variations in metasedimentary piles forming the two main lithostratigraphic units that potentially host massive sulfide deposits the phyllite quartzite group pqg and the volcanic sedimentary complex vsc on mineral exploration remain unknown herein we report on results of a multi element geochemical study of 133 samples representing pqg and vsc metasedimentary rocks from the albernoa area 713 km2 this dataset is complemented by whole rock sr nd and pb isotopic data for a subset of 12 vsc metasedimentary rock samples the prevalent siliciclastic component in the analyzed rocks derives from an evolved felsic source as suggested by the zr sc th sc eu eu relationships that according to cia values should have been affected by significant weathering before they were deposited in the basin from middle devonian to visean time the siliciclastic component comprises clay and fine grained sand whose relative abundance can be distinguished on the basis of al2o3 tio2 sc tio2 ga tio2 zr tio2 and sio2 al2o3 ratios these terrigenous components are in places variably mixed with volcanic derived fractions leading to the formation of tuffaceous metapelites typical of the vsc sequences but also present in the upper stratigraphic sections of the pqg in general vsc samples display the following parameters 2 5 sio2 al2o3 6 5 0 02 tio2 al2o3 0 06 and 0 2 cao na2o k2o al2o3 0 25 whereas pqg samples display 2 5 sio2 al2o3 12 0 08 tio2 al2o3 0 58 and cao na2o k2o al2o3 0 3 fe2o3 tio2 ratios 10 and al2o3 al2o3 fe2o3 mno ratios 0 6 indicate the strong influence of an early developed prior to variscan metamorphism and deformation hydrothermal component on the prevalent siliciclastic component sometimes mixed with a variable volcanic derived fraction moreover values of as sb sc cu zn pb sc and 5 fe2o3 mgo mno al2o3 ratios between 1 and 10 indicate the influence of seafloor metasomatism processes and ratios 10 indicate close proximity to hydrothermal discharge potentially associated with massive sulfide mineralization the sr nd pb isotopic data show that vsc metasedimentary rocks are mostly derived from old reworked upper continental crust isotope ratios characterizing the main siliciclastic component are somewhat disturbed by the significant presence of volcanic derived components and or mineral changes due to early hydrothermal alteration mineralization processes which should have involved isotopically distinct fluids

weathering and paleosol formation in the 1 1 ga keweenawan rift abstract at 1 1 ga the north american craton began to rift resulting in flood style basaltic volcanism during the phase of active tectonism some of that basalt was weathered and redistributed by fluvial processes new observations near the northwestern shore of lake superior have also revealed the presence of seven paleosols formed on weathered immature sediments derived from the basalt that are described here for the first time only three other paleosols have previously been described from this part of the geologic record so these new paleosols represent a significant new discovery the paleosols are weakly developed and exhibit physical and chemical characteristics similar to phanerozoic entisols in contrast to many precambrian paleosols the keweenawen paleosols have been subject to minimal post burial alteration among the paleosols three distinct pedofacies are recognized 1 waterlogged gleyed fluvial proximal paleosols 2 dry fluvial distal paleosols and 3 cumulative fluvial proximal paleosols despite these facies differences using a combination of physical and chemical measures of weathering it is found that the paleosols are all derived from the same parental basalt with one of the paleosols showing an additional extra basinal rhyolitic component by considering the mass balance behaviour of a variety of alkali and alkaline earth elements it is possible to rule out significant potassium metasomatism suggesting that these paleosols may be particularly useful for paleoatmospheric and paleobiologic reconstructions and that they form an important new source of data about mesoproterozoic weathering

modelling the joint variability of grain size and chemical composition in sediments abstract the geochemical composition of siliciclastic sediments correlates strongly with grain size hence geochemical composition may serve as a grain size proxy in the absence of grain size variations geochemical data of siliciclastic sediments may be used to characterise size independent processes i e sediment provenance weathering mixing shape density sorting and diagenesis in general however geochemical data sets contain both types of information in order to formalise interpretation of geochemical data we propose a mathematical method to decompose the total geochemical variability of a series of genetically related specimens into a grain size dependent the shared signal and a grain size independent part the residual signal the former may serve as a proxy for grain size whereas the latter represents geochemical variability that would have been observed if all sediments would have had the same grain size distribution the two data sets are jointly decomposed by means of partial least squares pls and orthogonal projection subsequently the presence of significant grain size independent geochemical variability in the residual signal is determined in a statistically rigorous manner using a 2 test using a synthetic example we show that the residual record effectively reveals an imposed provenance signal which could not have been resolved from the geochemical or grain size data sets individually we analysed the relation between grain size and geochemical composition in three quaternary marine sediment cores located offshore west africa and south america geob7920 2 geob9508 5 and geob7139 2 both sites are characterised by biogenic sediment input in addition to fluvial and aeolian sediment input from the continent it was found that all cores show a strong but different correlation between the mean grain size and the bulk geochemical composition these results demonstrate that geochemical grain size proxies are empirical and site specific it was also found that the geochemical and grain size data in cores geob7920 2 and geob7139 2 do not contain unique information whereas in core geob9508 5 ti varies independently from the grain size this residual ti signal correlates with the transport mechanism as demonstrated by statistically different values of aeolian and fluvial dominated sediments however a unique interpretation of this residual signal in terms of the postulated grain size independent mechanisms could not be provided without additional information we conclude that the proposed model facilitates identification and validation of different element ratios as grain size proxies and more importantly as proxies for size independent processes for this reason the model paves the way for rigorous analysis of multi proxy data which are widely used in palaeoceanographic and palaeoclimatic research

middle miocene pedological record of monsoonal climate from nw himalaya jammu kashmir state india abstract the lower siwalik subgroup represented by the dodenal kamlial formation and ramnagar members chinji formation is well exposed at ramnagar district udhampur jammu kashmir state the ramnagar member consists of an alternating sequence of silt and mudstone formed under crevasse splay and flood plain environments of deposition argillisol and gleysol soils are developed on the ramnagar member deposits argillisols formed under well drained conditions at high levels whereas gleysols formed under poorly drained conditions at low levels of the palaeo landscape geochemical and micromorphological studies of the ramnagar member palaeosols suggest formation under wet and humid climatic conditions early uplift of the tibetan plateau himalaya resulted in a contemporaneous change in precipitation and monsoonal climate conditions within the indian region beginning in middle miocene

chronostratigraphy of two late pleistocene loess palaeosol sequences in the rhone valley southeast france abstract a sedimentological and chronostratigraphical investigation was carried out on two loess sections located in the mediterranean area in southeast france along the rhone river lautagne and the lower reach of a tributary of the rhone river collias high resolution sampling 5 20 cm for magnetic susceptibility grain size distribution including non parametric end member modelling colour reflectance and geochemistry was performed the chronology was based on luminescence dating of quartz grains and radiocarbon dating of small gastropod shells coupled with hierarchical bayesian modelling the collias section 8 m thick records the whole last climatic cycle it comprises a thick red basal pedocomplex s1 developed during the last interglacial and the early glacial similar to that observed elsewhere in southern and southeastern europe loess deposition occurred during the lower l1l2 and the upper pleniglacial l1l1 it was interrupted by soil formation during the middle pleniglacial of which a brown bwk horizon has been preserved l1s1 by contrast the 5 m thick lautagne section provides a detailed record of the upper pleniglacial weakly developed hydromorphic soils are correlated with the greenland interstadials gi 4 to gi 2 while the main period of coarse loess sedimentation corresponds to the greenland stadials gs 5 to gs 2 at a regional scale the time of loess deposition ranges between 38 5 ka and 12 ka with a peak at 28 24 ka overlapping with the maximal advance of the alpine ice sheet ais this strongly suggests that regional glacier dynamics was the main driver of loess sedimentation

cenomanian to santonian radiolarian biostratigraphy carbon isotope stratigraphy and paleoenvironments of the sverdrup basin ellef ringnes island nunavut canada abstract an upper albian to santonian sedimentary record on ellef ringnes island canadian arctic archipelago records variable paleoenvironmental conditions within the cretaceous polar sea and sverdrup basin the upper albian to lower cenomanian uppermost christopher and hassel formations represent a regressive system tract from offshore to shoreface terrestrial paleoenvironments the upper cenomanian to santonian shales of the kanguk formation signify a distal offshore basin setting controlled by increased subsidence and high global sea levels siliceous pelagic faunas and floras dominate the basin and herein three informal radiolarian partial range zones are proposed for the polar sea alternating diversity and abundance patterns are interpreted as a response to sea level controlled productivity systems transgressive phases correspond to low diversity shallow dwelling radiolarian taxa with an expanded oxygen minimum zone omz regressive phases are coupled with radiolarian radiations of deeper dwelling species and a depressed omz the upper cenomanian to turonian was marked by increased preservation of marine type organic matter and organic carbon isotope excursions indicate the presence of the oceanic anoxic event 2 oae 2 at the base of the kanguk formation rock eval data suggest that an increasing terrestrial influence prevailed during the coniacian to campanian time covering the oae 3 benthic environments are dominated by anoxic conditions as suggested by the near lack of benthic foraminifera and extensive intervals of fine platy shale lacking bioturbation only the upper coniacian records a return to dysoxic benthic conditions radiolarian faunal comparisons to more southern localities suggest migration routes from the east through a narrow north atlantic pathway and from the pacific through the alaskan asian pathway

anomalous cold in the pangaean tropics the late paleozoic archives the greatest glaciation of the phanerozoic whereas high latitude gondwanan strata preserve widespread evidence for continental ice the permo carboniferous tropics have long been considered analogous to today9s warm and shielded from the high latitude cold here we report on glacial and periglacial indicators that record episodes of freezing continental temperatures in western equatorial pangaea an exhumed glacial valley and associated deposits record direct evidence for glaciation that extended to low paleoelevations in the ancestral rocky mountains furthermore the permo carboniferous archives the only known occurrence of widespread tropical loess in earth9s history the volume chemistry and provenance of this loess ite is most consistent with glacial derivation together with emerging indicators for cold elsewhere in low latitude pangaea these results suggest that tropical climate was not buffered from the high latitudes and may record glacial interglacial climate shifts of very large magnitude coupled climate ice sheet model simulations demonstrate that low atmospheric co 2 and solar luminosity alone cannot account for such cold and that other factors must be considered in attempting to explain this best known analogue to our present earth

mobilization and re distribution of major and trace elements during extreme weathering of basalt in hainan island south china major trace and organic elements of a laterite profile developed on neogene basalts in northern hainan island south china were reported in this paper the aim of which was to investigate element mobilization and re distribution during extreme weathering the results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution organic matter om can significantly improve the transport of insoluble elements among all the elements th is the least mobile as for the general conservative elements during incipient chemical weathering such as fe ti zr hf nb and ta the removals are up to 20 40 in the upper profile however these elements behave as conservatively as th in the lower profile in the middle profile oxic environment occurs accompanied with significant om decomposition the mn and ce transferred downward are readily oxidized into insoluble mn iv and ce iv and precipitate in the oxic front important om decomposition decreases the capacity of transfer of insoluble elements in aqueous solution consequently al significantly precipitates in the oxic front and rees with the exception of ce precipitate largely in the omdepleted layers co and u are also concentrated in the oxic front in association with mn and ce respectively however cr shows a negative correlation with mn because its response to redox condition changes is reversed from that of mn mn oxides hydroxides fe oxides hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for rees except for ce in the profile rees with high concentrations in the profile seem closely associated with mn oxides hydroxides remarkable highly correlated ce and gd anomalies are observed in the profile ce anomalies are caused by ce precipitation in the oxic environment and successive decomposition of organic matter gd anomalies are likely to have resulted from lower stability constants of gd om complexes compared to those of neighboring rees the overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re distribution of the elements during extreme weathering

anomalous geochemical provenance and weathering history of plio pleistocene glaciomarine fjord strata bardin bluffs formation east antarctica major and trace element chemical analyses of the plio pleistocene bardin bluffs formation on the margin of a major ice stream of the east antarctic ice sheet yield an anomalous chemically altered sediment composition the bardin bluffs formation of the pagodroma group is one of the key deposits on the antarctic continent recording glaciomarine sedimentation under open marine fjord conditions as recently as the plio pleistocene in modern fjords occupied by outlet glaciers of ice sheets the composition of fine grained terrigenous sediments approaches that of unweathered rock types exposed upstream in the bardin bluffs formation average abundances of stable elements ti al zr approach average upper crustal compositions and the element ratios are consistent with sediments with a cratonic source implying glacial dispersal from a large shield area through the lambert glacier drainage system interestingly the chemical index of alteration cia of these sediments has values similar to those of average shales formed under conditions of chemical weathering the sediments are particularly depleted in silicate ca which has been observed elsewhere in glacial muds sourced from pre glacial saprolites the anomalous chemistry of the bardin bluffs formation can be explained by a sequence of events involving chemical weathering prior to glacial expansion and erosion the presence of a remnant 1 5 m deep late neogene weathering profile at the base of the bardin bluffs sequence corroborates this conclusion supply of large quantities of chemically weathered materials to antarctic marginal basins requires at least partial deglaciation of the continent and was previously regarded as uncharacteristic for late neogene antarctica

provenance and paleoweathering reconstruction of the mesoproterozoic hongshuizhuang formation 1 4 ga northern north china this is the first study presenting major and trace elemental data from the mesoproterozoic hongshuizhuang formation shales in yanshan basin north china in order to reconstruct its provenance and chemical weathering history the shales are strongly depleted in na2o and sr and enriched in y and transition metal elements relative to upper continental crust low zr concentrations and various discriminant plots e g th sc zr sc and al2o3 tio2 zr indicate insignificant mineral sorting or recycling of these shales the rocks show light rare earth element ree enrichment la ybcn 3 99 6 92 flat heavy ree and significantly negative eu anomalies euan 0 57 0 68 in chondrite normalized ree patterns similar to post archean australian average shales the fairly uniform ree patterns and trace element ratios indicate that the hongshuizhuang formation shales were derived from a felsic source area with granodiorite as the dominant contributor mixing calculations suggest a mixture of 30 granite porphyry 5 basalt and 65 granodiorite as the possible source of the shales also supporting that granodiorite was the predominant source intense chemical weathering of the source terrain is indicated by high values of the premetasomatized chemical index of alteration plagioclase index of alteration rb sr a strong positive correlation between tio2 and al2o3 depletion of cao na2o and sr and mineral compositions such strong chemical weathering suggests a warm and wet paleoclimate perhaps due to high atmospheric co2 and ch4 concentrations and a near equatorial location of the north china craton in the columbia supercontinent at 1 4 ga

processes controlling the distribution of ti and al in weathering profiles siliciclastic sediments and sedimentary rocks abstract the ratio of ti to al varies greatly in primary igneous source rocks these elements are considered to be relatively immobile in most weathering regimes so that tio2 al2o3 ratios have been used to investigate the provenance of sediments and sedimentary rocks in modern weathering profiles that have undergone moderate weathering ti al ratios remain fairly constant so that siliciclastic sediments derived from them should have ti al ratios like that of the source materials under extreme weathering conditions however the upper most weathered parts of profiles commonly show a marked increase in ti al ratio that is thought to be due to preferential translocation of al rich phases under steady state weathering conditions one particular level of the profile may act as the main source of detrital material and may thus control the ti al ratio of sediments produced from it in a glacio fluvial setting minimum weathering moderate sorting there is considerable variation in ti content but al is nearly constant this is due to concentration of ti bearing mafic minerals such as biotite in the fine fraction in modern sediments derived from moderately weathered and sorted material the ti al distribution reflects mixing of al and ti enriched fine grained materials with sands that are depleted in these elements when a plot of tio2 vs al2o3 is constructed for a suite of such sands and muds the resultant trend differs significantly from that shown by a similar suite of unweathered glacio fluvial sediments comparison of these results with data from sedimentary rock suites suggests that trends shown by plots of tio2 vs al2o3 may provide insight into weathering and depositional history in addition to their use as provenance indicators

geology and geochemistry of arenite quartzwacke from the late archaean sandur schist belt implications for provenance and accretion processes abstract detailed geological petrological and geochemical studies have been carried out on an arenite quartzwacke suite of rocks constituting a part of the late archaean sandur schist belt in dharwar craton southern india for understanding the nature of provenance for these sedimentary rocks the arenite quartzwacke consists of rounded to sub rounded and angular fragments of monocrystalline polycrystalline quartz quartzite and chert embedded in a fine grained matrix of quartz and sericite while arenites are more siliceous sio 2 80 92 wt the quartzwacke have relatively lower silica content ca 69 78 wt the arenites and quartzwackes have cia values ranging from 76 to 96 which suggest intense chemical weathering this is further corroborated by the positive correlation between al 2 o 3 and tio 2 in both these rock types the a cn k modeling of arenites and quartzwackes show evidence for addition of k 2 o during later metasomatic alteration in the a cnk fm ternary diagram all the samples plot along a mixing line between chlorite and sericite indicating alteration during k metasomatism and the presence of mafic rocks in the source the high concentration of hfse such as zr hf nb and ta and the trace element ratios th sc la sc th u and ce th in the arenite quartzwacke indicate a mixed provenance the rare earth element modeling of quartzwackes considering tonalite granite and amphibolite end members in the provenance suggests equal proportions of mafic and felsic end members a composition comprising of 25 tonalite 25 granite 50 amphibolite in the provenance appears to match with the observed range of ree patterns of quartzwackes the presence of higher proportions of granite in the provenance is evidenced by the large negative eu anomalies in these sediments field evidence and structural discordance suggest that the arenite quartzwacke suite is an allochthonous part of the sandur schist belt

soil mineralogy at the mars exploration rover landing sites an assessment of the competing roles of physical sorting and chemical weathering 1 soils in gusev crater and meridiani planum derive primarily from a surface dominated by basalt the modal mineralogy of primary igneous and secondary alteration phases in the soils is estimated using mossbauer minites and apxs spectra primary minerals include plagioclase pyroxene and olivine with less common apatite magnetite and chromite secondary phases are dominated by sulfates and include nanophase oxides chlorides hematite and are assumed to include amorphous silica and phyllosilicates most soil chemical compositions overlap with basalts indicating that despite the presence of a secondary component in the soils they have not been significantly chemically weathered we modeled the significance of olivine dissolution by acid s by iteratively removing the molar feot mgo component olivine proxy from the mean bulk compositions of the gusev rock classes adirondack algonquin and irvine until none remained regardless of modeling conditions acid s alteration cannot account for many soils in gusev crater that are either depleted or enriched in molar feot mgo although it is a process capable of explaining some soil compositions based on a rock and mineral mixing model supports our hypothesis for soil formation that consists of surface comminution by impact gardening followed by compositional modification by hydrodynamic sorting and admixing of secondary components including phyllosilicates and sulfates such a physical process can produce the range of molar feot mgo in soils by concentrating or depleting specific minerals for example dust and fine sands are enriched in molar feot mgo relative to coarse sand which suggests accumulation of more mafic phases in finer grain fractions

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

weathering patterns in high latitude regolith 1 large areas distributed on the earth s surface are covered by regolith an unconsolidated heterogeneous material overlying bedrock in high latitude areas most of the land surface has been reworked and eroded by both glacial and fluvial processes leaving only remnants of formerly extensive regolith covers in an effort to further the understanding of weathering patterns and processes in old regolith covers a comprehensive study of localities spread across norway was carried out on the basis of the distribution of minerals and elements within regolith as well as its internal structure and geomorphologic setting we ascertained that it was formed in situ and originated in pre quaternary times there are similarities between the study sites with respect to regolith thickness zonation and composition the chemical index of alteration cia and the weathering index of parker wip suggests that the degree of chemical weathering in the regolith is advanced compared to the parental bedrock with a maximum change of over 80 which indicates a substantial increase in the proportion of secondary versus primary minerals mineral analysis identified kaolinite and gibbsite which are considered indicative of advanced weathering and therefore support this observation on the basis of statistical relationships between different grain size fractions 125 m we observed a consistent pattern which revealed that physical weathering becomes progressively less important in the production of grains smaller than 32 m on the basis of this finding we infer that chemical weathering progressively dominates the production of fine silt very fine silt and clay whereas physical weathering primarily controls the production of grain size fractions larger than 32 m this particular pattern is suggested to be an intrinsic feature in the formation of weathered high latitude regolith

geochemical compositional changes at the pliocene pleistocene transition in fluviodeltaic deposits in the tegelen reuver area southeastern netherlands o contents which can be attributed to the alpine source supplying fresh sodic plagioclase rich material instead of the local strongly weathered sediments increasing k2o al2o3 can be attributed to a similar decrease in degree of weathering however this trend is disturbed by the loss of k from clay minerals during weathering in organic rich layers local high tio2 anomalies caused by preferential sorting and concentration are found in most pliocene sections but they are absent in the upper pliocene and lower pleistocene alpine derived deposits this change is probably due to a change in the energy of the fluvial system finally pyrite s contents drop siderite fe contents rise micromorphological observations indicate that the pliocene pyrite was formed when freshwater deposits were flooded with seawater during short term events the decrease in s and the increase in siderite fe can be attributed to decreasing marine influence as a result of the marine regression at the pliocene pleistocene transition

whole rock geochemistry of upper paleozoic loessite western pangaea implications for paleo atmospheric circulation abstract average bulk major and trace element chemical composition of upper paleozoic loessite lithified loess from several widely scattered sites in western equatorial pangaea western north america approximates upper continental crust ucc but is more similar to the bulk composition of precambrian basement coring uplifts of the ancestral rocky mountains however distinct compositional signatures occur among the various loessite deposits controlled primarily by differences in al 2 o 3 mgo na 2 o k 2 o and rb furthermore values of the chemical index of alteration cia of these loessites are low 55 63 skewed toward lower values closely matching values for north american loess and precambrian basement although diagenesis can account for some of the compositional differences e g local sio 2 or k 2 o enrichment it fails to explain the major differences among the sites rather these differences are best explained as a result of variations in regional basement that sourced the loess coupled with transport wind pathways which varied from zonal easterlies to monsoonal westerlies in this region of tropical pangaea from late carboniferous to early permian time the low cia values generally reflect first cycle derivation from regional basement uplifts of the arm and for younger deposits a variable contribution from the suture zone uplifts and volcanism of the appalachian ouachita marathon collisional belt the variations in bulk chemical composition of the loessite coupled with previously collected detrital zircon geochronology suggest that these low latitude loessites are not simply the result of deflation of mid latitude erg deposits or coastal alluvial plain sediments these data represent a first attempt at geochemical characterization of pre quaternary loess and demonstrate the utility of loess geochemistry as a proxy for paleoatmospheric circulation in earth s deep time past

late glacial erosion and pedogenesis dynamics evidence from high resolution lacustrine archives and paleosols in south bohemia czech republic abstract sediments from three paleolakes and two paleosol horizons in south bohemia czech republic provide evidence of climate change and landscape evolution in central eastern europe on millennial to centennial timescales over the late glacial 16 11 5 ky based on a combination of geochemical sedimentological and geophysical proxy indicators along with the pollen record and soil micromorphology we propose a relationship between vegetation cover soil development and erosional processes four major and two minor environmental stages identified in all investigated paleo lakes were broadly correlated with the late glacial climatostratigraphy short term decadal to centennial climatic deteriorations between the bolling and allerod and within the allerod have been correlated with the older dryas and the intra allerod cold period iacp respectively b horizons of two gleyic podzols discovered under aeolian sand dunes in the lake catchments were dated to the allerod interstadial and were parallelized with usselo soils pedostratigraphical marker horizons of west and northern central europe the upper parts of these soils have signs of colluvial processes according to the radiocarbon dating the erosion occurred at 13 155 150 cal yr bp and can be associated with the iacp event which is marked by a significant input of allogenic material into the lake basins we attribute the significant increase in the iron and consequent phosphorus content in the lake sediments during the allerod to the podzolization that occurred with the humid interstadial conditions

an effective geochemical method to identify provenance from sources with similar geology a case study from ordos basin china abstract rare earth elements as the most resistant elements have been widely used to determine sediment provenance however yin mountains and qinling orogen the two main source terrains of the ordos basin both dominated by felsic rocks and experienced passive continental margin settings and active margin setting from the middle proterozoic to the tertiary without strongly contrasting geological settings rees distribution pattern alone and these related discrimination diagrams are inadequate to distinguish both nevertheless the rees abundance of mudstones solely supplied by each source terrain vary distinctly moreover the total rees contents of shales with the same provenance increase roughly with increasing cia indices mudstones supplied by yin mountains are significantly more enriched in rees average 309 4 ppm but yield lower cia indices average 79 6 while those sourced from qinling orogen yield lower rees content average 135 6 ppm but higher cia value average 90 1 considering the particular situation we combine cia with the total ree content rees to provide new insights into sediment provenance identification and effectively distinguish the two source regions in ordos basin

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

carbonate to biosilica transition at the norian rhaetian boundary controlled by rift related subsidence in the western tethyan lagonegro basin southern italy abstract the lagonegro basin located in the southern apennines italy records a transition from carbonate sediments of the calcari con selce fm cherty limestone to biosiliceous sediments of the scisti silicei fm siliceous shale around the norian rhaetian boundary nrb upper triassic sedimentologic and chemostratigraphic analysis of three sections pignola abriola monte volturino and madonna del sirino representing a proximal to distal transect across the basin document marine productivity redox and chemical weathering conditions the basin was characterized by low to moderate productivity and mainly oxic deep waters with no systematic secular variation throughout the 10 myr long study interval a weathering proxy the chemical index of alteration cia shifts toward higher values from 0 70 to 0 80 in all three study sections suggesting development of warmer and or more humid conditions just before the nrb the lack of evidence for changes in marine productivity or redox conditions and the time transgressive nature of the carbonate biosilica transition suggests that the latter was caused not by changes in planktonic communities but rather by a rise in the ccd the most likely cause of which was seafloor subsidence within the actively rifting ionian ocean i e the westernmost branch of the tethys ocean the tectonically active character of the lagonegro basin is also reflected in evidence of synsedimentary paleoseismic activity e g numerous debris flows around the basin margins the present study thus documents sedimentologic changes within a marginal basin in a geologically young ocean

discriminating sediment archives and sedimentary processes in the arid endorheic ejina basin nw china using a robust geochemical approach abstract geochemical characteristics have been intensively used to assign sediment properties to paleoclimate and provenance nonetheless in particular concerning the arid context bulk geochemistry of different sediment archives and corresponding process interpretations are hitherto elusive the ejina basin with its suite of different sediment archives is known as one of the main sources for the loess accumulation on the chinese loess plateau in order to understand mechanisms along this supra regional sediment cascade it is crucial to decipher the archive characteristics and formation processes to address these issues five profiles in different geomorphological contexts were selected analyses of x ray fluorescence and diffraction grain size optically stimulated luminescence and radiocarbon dating were performed robust factor analysis was applied to reduce the attribute space to the process space of sedimentation history five sediment archives from three lithologic units exhibit geochemical characteristics as follows i aeolian sands have high contents of zr and hf whereas only hf can be regarded as a valuable indicator to discriminate the coarse sand proportion ii sandy loess has high ca and sr contents which both exhibit broad correlations with the medium to coarse silt proportions iii lacustrine clays have high contents of felsic ferromagnesian and mica source elements e g k fe ti v and ni iv fluvial sands have high contents of mg cl and na which may be enriched in evaporite minerals v alluvial gravels have high contents of cr which may originate from nearby cr rich bedrock temporal variations can be illustrated by four robust factors weathering intensity silicate bearing mineral abundance saline alkaline magnitude and quasi constant aeolian input in summary the bulk composition of the late quaternary sediments in this arid context is governed by the nature of the source terrain weak chemical weathering authigenic minerals aeolian sand input whereas pedogenesis and diagenesis exert only limited influences hence this study demonstrates a practical geochemical strategy supplemented by grain size and mineralogical data to discriminate sediment archives and thereafter enhance our ability to offer more intriguing information about the sedimentary processes in the arid central asia

petrology of sapphirine granulite and associated sodic gneisses from the indian head range newfoundland migmatitic granulites from the indian head range ihr are dominated by granoblastic opx bearing quartz dioritic gneiss with subordinate garnet orthopyroxene biotite albite quartz microcline cordierite sillimanite gneiss and comparatively biotite rich sapphirine cordierite orthopyroxene albite microcline sillimanite corundum gneiss the latter contains at least two generations of sapphirine and cordierite one apparently predating migmatization the other associated with or following this event mineral thermobarometers yield temperatures up to 800 c at 8 kbar the ihr granulites have very high 18o values 10 8 to 14 5 which most likely indicate a sedimentary precursor their ree and hfse contents resemble the trace element signature of post archean australian shale paas lithological analogues from other grenvillian inliers in western newfoundland have similar oxygen isotopic and immobile element signatures they too are interpreted as metasedimentary rocks the ihr rocks however have unusually sodic compositions e g na2o cao and na2o k2o 2 1 22 5 and 0 93 13 8 respectively and contain albite or sodic oligoclase despite their high metamorphic grade the geochemical data indicate that these rocks were albitized prior to high grade metamorphism no counterpart of this event is recorded in granulites from the other inliers indicating that the ihr may be highly allochthonous with respect to these other grenvillian terranes