provenance of jurassic sediments in the hefei basin east central china and the contribution of high pressure and ultrahigh pressure metamorphic rocks from the dabie shan abstract the provenance of the jurassic sediments in the hefei basin is constrained by compositions of the detrital k white micas and garnets and shrimp dating of the detrital zircons which can help to understand the evolution and to reconstruct the paleogeographic distribution of hp uhp rocks in the jurassic dabie shan 1 for the oldest mesozoic sediments at the bottom of the fanghushan formation j 1 the predominance of the early paleozoic and luliang 1700 1900 ma zircons indicates a major source from the north china block however neoproterozoic zircons as the major component in other jurassic sediments indicate that the source rocks were mainly derived from the exhumed yangtze block in the dabie shan 2 the co occurrence of high si phengites and triassic zircons provides stratigraphic evidence that the first exposure of the uhp rocks at the earth s surface in the dabie shan occurred in the early jurassic during deposition of the fanghushan formation 3 from the east to the west of the hefei basin there is a spatial variation in the compositions for detrital micas and garnets and in the u pb ages of detrital zircons evidently hp uhp rocks were widely distributed at outcrop in the eastern dabie shan in contrast they were less important in the western dabie shan during the jurassic

organic molecules formed in a primordial womb primordial organic molecules may have evolved in seafloor hydrothermal systems by mineral catalysis most organic compounds decompose in 300 c vent fluid however we show that smectite type clays can protect and promote development of diverse organic compounds that may be precursors to biomolecules smectite provides a safe haven for the synthesis of organic molecules essentially like a primordial womb our experiments simulated seafloor hydrothermal conditions 300 c 100 mpa and reacted common clays montmorillonite saponite illite with dilute methanol as a source of c montmorillonite reacts under these conditions to illite while the other clays do not change we observed increased organic synthesis over time with montmorillonite during mineralogical reaction approaching equilibrium smectite contracts and organic molecules are expelled organic compounds unstable in hot fluid where the smectite reacts may survive in cooler waters outside the vent

provenance evolution of collapse graben fill in the himalaya the miocene to quaternary thakkhola mustang graben nepal abstract this study focuses on the detailed provenance evolution of young syn to post orogenic extensional grabens in orogens like the himalaya to trace the tectonic history of such late stage basins using the neogene thakkhola mustang graben as a case study the graben is situated within the tibetan tethys zone and is filled with 870 m of continental deposits of miocene to holocene age based on logged sections within the predominantly alluvial to coarse grained fluvial fill of the graben we investigated paleocurrent data and the petrology of sandstones and conglomerates including heavy minerals studies to interpret provenance and source areas in detail significant changes are recorded by slight differences in heavy mineral and pebble compositions the sandstones can be classified as lithic greywackes lithic arkoses and feldspathic litharenites sandstone mudstone quartzite and some granite clasts are dominant in conglomerates of the central part of the graben tetang formation conglomerates of miocene age comprise mostly clasts of mesozoic rocks with an eastern provenance consistent with measured paleocurrent directions all paleocurrent data and compositional analyses of imbricated conglomerates of the miocene pliocene thakkhola formation in the northeast of the graben suggest that clasts were derived from eastern source areas comprising mainly mesozoic rocks whereas paleozoic clasts of a western to northern source area predominate in the centre of the graben heavy mineral analysis indicates that tourmaline staurolite zircon garnet and apatite constitute a significant proportion of the assemblages of all formations through time whereas epidote andalusite kyanite chloritoid hornblende chrome spinel rutile and amphiboles are less common these assemblages reflect in general stable minerals and low to high grade metamorphic source rocks and are principally controlled by reworking of older passive margin sediments of the tibetan tethys zone as indicated by provenance discrimination diagrams three successive stages in provenance evolution were recognized 1 the miocene tetang formation characterized by higher kyanite values corresponding to the himalayan foreland evolution 2 the thakkhola formation characterized by granite clasts and significantly higher amounts of andalusite indicating source area expansion and erosion of the mustang mugu granites to the northwest 3 the upper pleistocene holocene kaligandaki formation bearing higher amounts of epidote klinozoisite and ophiolite and high pressure low temperature detritus as indicated by chrome spinel and blue amphiboles derived from the north lying indus tsangpo suture zone the change in source areas from the miocene pliocene to the late pleistocene holocene is interpreted as a result of the evolution from an initial stage of high angle normal faulting and collapse basin formation to a low angle extensional detachment basin system

longevity of bentonite as buffer material in a nuclear waste repository abstract longevity of bentonite as a nuclear waste barrier depends on mineralogical stability of the smectite component of the clay as well as on its ability to perform as a buffer in the repository for long periods of time processes affecting the stability of smectites under the geochemical and thermal conditions in a high level nuclear waste repository can be construed by examining the geological analogues and the results of the hydrothermal experiments the physical and chemical properties of bentonite seem to be related to the nature of smectites in them smectites represent a range of expandable layer silicates of al mg fe and other transition metals their thermal hydrothermal or solution stabilities vary from one smectite species to another this is also true to a certain extent for the physical properties of bentonites i e swelling permeability plasticity and adsorption swelling ability and permeability of naturally altered metabentonites and steam treated bentonites are badly damaged temperature distribution in a clay barrier that was simulated in situ under the repository conditions showed a sharp drop from 175 c at the clay canister contact to 81 c at a distance 65 mm away microstructures of bentonites were noticeably altered after hydrothermal treatment at 200 c

mesozoic cenozoic tectonic relationships between the kuqa subbasin and tian shan northwest china constraints from depositional records abstract stratigraphic profiles in the kuqa subbasin located along the southern flank of the tian shan northwest china display similar mesozoic cenozoic evolutionary sequences of compositional maturity exist in conglomerate clasts sandstone framework grains and detrital heavy minerals the similarity of these time series profiles resulted from orogenesis and intracontinental deformation of the provenance area the ancestral tian shan mineralogical maturities of conglomerates and sandstones increase from triassic to middle jurassic and decrease from upper jurassic lower cretaceous to tertiary this trend parallels a similar decrease in maturity in detrital heavy minerals zircon rutile and tourmaline dominate in middle upper triassic to middle jurassic sandstone whereas unstable hornblende and pyroxene dominate the heavy mineral suites in the tertiary especially in miocene and pliocene strata these compositional trends are coeval with gradual southward migration of alluvial depositional fronts and depositional depocenters from cretaceous to miocene since the pliocene large scale southward migration of alluvial depositional systems occurred while depositional depocenters migrated northward based on the mesozoic cenozoic depositional records the tectonic evolution of the tian shan kuqa subbasin may be divided into five phases 1 in early triassic following compression and uplift since permian gravelly braided river alluvial plain depositional systems developing in the kuqa subbasin characterized by sands of mixed orogenic provenance type derived from the ancestral tian shan 2 from middle triassic to middle jurassic sediment composition of the kuqa subbasin reflects arc orogen and mixed orogenic sand types with extensive planation of the ancestral tian shan and the development of relatively stable coal bearing depositional environments 3 renewed compression uplift of the tian shan occurred in late mesozoic especially in cretaceous with most detrital modes of the kuqa subbasin indicating provenance attributes akin to the south tian shan 4 further intensive compression uplift and probably southward basinward propagation of the south tian shan occurred during miocene and 5 supracrustal gravity gliding and collapse occurred in the tian shan kuqa subbasin probably due to intensive deep compression with rejuvenated uplift and probable southward basinward structural propagation of the south tian shan developing since pliocene observed changes in sediment composition and depositional environment since pliocene time were also controlled by frequent and abrupt climate changes in addition to intensive uplift of the tian shan moreover all depositional records in the kuqa subbasin seem to reflect west to east differences in provenance along the tian shan probably indicating greater exhumation depth in the western tian shan than that in the eastern tian shan since early cretaceous

light element distributions n b li in baltic basin bentonites record organic sources abstract distributions of nitrogen boron and lithium were studied in illite smectite from ordovician silurian k bentonites in the baltic basin these trace elements are linked to thermal maturation of organic matter creating fluid signatures that are distinct from those in regionally buried sediments the fluid chemistry is ideally recorded in authigenic illite within the k bentonite because b substitutes in tetrahedral sites of illite li in octahedral sites and n is fixed in the interlayers as nh 4 three nanometric size fractions of illite 10 among these size fractions relate mainly to changes in fluid composition during illite growth bentonite volcanic ash layers mark stratigraphic timelines while illitization of the bentonite k bentonite varies as a function of burial and tectonic temperature gradients in the central baltic basin bentonites were deposited across a carbonate platform near estonia grading to deep basin shales near denmark and poland compositional variations in illite reflect fluids from different sources high n illite 2000 ppm in the southwest basin transitions to high b 250 ppm and high li 100 ppm illite to the northeast these trends follow a thermal gradient decreasing from southwest 200 c to northeast 90 c isotope ratios of b and li show opposing trends in samples across this thermal gradient the bisotopes decrease from southwest to northeast 18 to 4 while li isotopes increase from 5 to 32 the cambrian alum shale a regional hydrocarbon source rock was studied as a potential source of b and li as more than 50 of its b and li was associated with organic matter with increasing thermal maturity illite 11b decreased from 0 to 13 while 7li increased from 20 to 5 these opposing trends are similar to those observed in the k bentonites this suggests that organic sources of n b and li dominate fluids in bentonites from the southwestern baltic basin whereas basement derived fluids dominate in the northeastern baltic basin these trace elements record paleofluid changes during illite crystal growth and can identify pathways of chemically distinct oil and gas related fluids

thermochemical effects on the smectite alteration of gmz bentonite for deep geological repository gaomiaozi gmz bentonite has been recognized as the first choice for using as buffer backfill material in deep geological repository for the disposal of high level nuclear waste in china high salinity and high ph of the pore solutions may cause changes in the mineralogical composition and the swelling capacity of the bentonite results in affecting the long term performance of the engineering barrier system in the present work a series of hydrothermal reactivity experiments were performed using batch reactors at 20 35 and 80 c for evaluating the chemical and mineralogical responses of gmz bentonites the results show that the dissolution of smectite releases si and al under the conditions of 1 m koh at 35 and 80 c and the released si and al may work as a cementing agent in gmz bentonite xrd pattern results show that alteration of the gmz bentonite is expected to be insignificant for reaction with nacl kcl and naoh solutions under low temperatures however it is obviously reacted with koh solutions especially at 80 c during which cementitious material was produced leading to kaolinitization when contacted with koh solutions the basal spacing d001 of the main primary diffraction peaks 001 value of gmz bentonite increases with increasing temperature salinity also can influence the smectite stability and accordingly loss of swelling capacity this conclusion could be explained by the diffusing double layer effects induced by salt solutions and ion exchange

garnet provenance studies juxtaposition of laurentian marginal terranes and timing of the grampian orogeny in scotland a study of the composition and zoning patterns of detrital garnets from ordovician greywackes from the northern belt of the southern uplands terrane of scotland reveals characteristics of the metamorphic sources very similar to the dalradian supergroup of the scottish grampian terrane the radiometric cooling and uplift ages of the dalradian metamorphic zones and the depositional ages of the southern uplands greywackes support the hypothesis for local provenance detrital metamorphic garnet identical to dalradian garnet has also been identified in the upper ordovican sandstones of the highland border complex these observations do not support proposals that the grampian midland valley and southern uplands terranes were exotic to each other in the late ordovician time these new results together with a review of published age dates clarify the late ordovician palaeogeography for this part of the laurentian margin the distances between the grampian midland valley and southern uplands terranes may have been similar to the present day it is concluded that large rivers flowed out of the uplifting mountainous grampian terrane and across the midland valley into a southern uplands trench during the late ordovician time the main orogeny i e mountain building in the grampian terrane was therefore post cambrian producing the first high mountains and resultant flysch in the caradoc

compositional variation in lower old red sandstone detrital garnets from the midland valley of scotland and the anglo welsh basin compositional variation in lower old red sandstone ors detrital garnets can be used to evaluate potential source areas and to trace the pattern of early devonian sediment dispersal garnets in northwesterly derived fans along the northern flank of the midland valley appear to duplicate spatial variation in the compositions of garnets in the adjacent dalradian block whilst metamorphic clasts resembling dalradian lithologies occur in these fanglomerates the strike extent of dalradian type crust c 1000 km makes simply matching the clasts a rather imprecise way of constraining source basin displacement the garnet data imply that the ordovician separation inferred for crustal blocks juxtaposed along the highland boundary was removed by early devonian times major silurian displacements are thus invoked along the highland boundary with amalgamation largely achieved prior to the acadian transcurrent deformation seen in the slate belts to the south vertical changes in the composition of garnets in the thick lower ors sequence in the northeast midland valley are slight and it is not known to what extent these reflect migration of a differentiated source block or the involvement of recycled additions which become increasingly important towards the base of the ors succession the axially dispersed sandstones which interdigitate with the northwesterly derived fans are dominated by spessartine rich almandines which resemble garnets fed laterally to the basin in the northwest midland valley although the large scale inferred for the axial fluvial system suggests that its drainage basin extended outside scotland almandine pyropes which might have come from exhumed eclogites in western norway are absent such compositions are widespread in mesozoic sandstones in the northern north sea and it is evident that these sediments do not represent the final repository for the lost sediment stripped from caledonian metamorphic terranes in scotland garnet populations from the anglo welsh basin do not resemble those in the coeval axial sandstones of the midland valley suggesting that the two basins were not linked at this time the scale of the midland valley axial sandbodies are inconsistent with internal drainage of central scotland and a route to the early devonian shoreline must be sought it may be that acadian strike slip motions have displaced the scottish basins from the coastal alluvial plains they originally fed

an application of heavy mineral analysis to lithostratigraphy and reservoir modelling in the oseberg field northern north sea abstract three distinctive detrital garnet associations have been recognized in brent group sandstones of the oseberg area northern north sea by means of electron microprobe analysis these have lithostratigraphical significance with one association occurring in the etive and oseberg formations one in the ness formation and one in the tarbert formation the stratigraphic variation in garnet population reflects changes in provenance and in the pattern of distribution of clastic detritus although a detailed reconstruction of source areas is not possible on the basis of the available information differentiation of ness and etive oseberg formations by means of detrital garnet geochemistry has enabled the recognition of fluvial chanbel sandstones belonging to the ness formation which have cut down into the etive formation shoreline complex this provides direct evidence of communication between ness and etive oseberg adding an extra degree of sophistication to the geological input for reservoir simulation a strong permeability anisotropy can be modelled around the fluvial channels and a net sand volume can be modelled in agreement with channel orientation

provenance study of early and middle bronze age pottery from kaman kalehoyuk turkey by heavy mineral analysis and geochemical analysis of individual hornblende grains the provenance of early bronze age and early middle bronze age pottery produced between 2100 and 1970 b c and excavated from kaman kalehoyuk turkey was studied using mineralogical methods including heavy mineral analysis and geochemical study of individual hornblende grains the relative abundances of heavy minerals in the fabrics of 20 early bronze age eba and early middle bronze age mba pottery sherds together with 27 local sediments collected within a radius of 25 km of the site were studied the heavy mineral distributions in the kaman region were statistically analyzed for consistencies in their occurrence amphibole was found to be the most abundant heavy mineral in most of the analyzed samples followed by titanite and epidote the amounts of other minerals such as garnet clinopyroxene and zircon are subordinate different proportions of heavy minerals in the fabrics allow categorization of the eba and early mba potteries into 5 groups comparative study of heavy mineral assemblages of local sediments and pottery suggests that half of the eba and most of the mba potteries were produced from sediment near the excavation site whereas the other half of the eba potteries were produced from sediment occurring at 25 km east or more east of the site the geochemistry of individual amphibole grains was studied by electron microprobe analysis most of the studied amphibole grains are calcic and aluminous corresponding to hornblende they can be further characterized into four types based on their chemical composition the combination of heavy mineral identity and hornblende geochemistry provides diagnostic evidence for the origins of kaman kalehoyuk pottery these and analogous heavy mineral techniques are effective archaeometric tools for determining pottery provenance

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

modal composition and detrital clinopyroxene geochemistry of lithic sandstones from the new england fold belt east australia a paleozoic forearc terrane the new england fold belt of southeast australia is divided by the peel fault system into two time equivalent zones showing contrasting depositional structural and metamorphic histories these are inferred to represent a western magmatic arc frontal arc succession and an eastern subduction complex assemblage the composition of the early to middle paleozoic clastic rocks from both east and west of the peel fault system indicates derivation from an undissected volcanic arc detrital quartz is absent or present only in minor amounts and always as monocrystalline grains lithic fragments are almost exclusively volcanic and normally dominant over feldspar which is invariably plagioclase now largely albitized to the west of the fault the distribution of lathwork microlitic felsitic and vitric rock fragments as well as variation in the amount of detrital quartz indicates changes in provenance through time and two cycles of basaltic to silicic volcanic activity have been identified the composition of detrital calcic clinopyroxene grains particularly their low ti and al contents and their ti mn na ratios indicates that they crystallized mainly from subalkaline probably calc alkaline volcanic arc magmas the dominantly volcanogenic provenance of sandstone from east of the fault and the low ti content of most detrital clinopyroxene grains indicate that the volcanic chain that lay to the west of the peel fault was the most likely source for the major portion of the clastic debris in the eastern rocks however the presence of ti rich detrital clinopyroxenes identical in composition to those in the metabasalts of the subduction complex indicates that uplifted segments of the complex provided an additional sediment source

the origin of faceted garnets in sandstones dissolution or overgrowth faceted garnets from a wide range of geological ages environments and locations have been studied in polished grain mounts by a combination of backscattered electron microscopy and elemental mapping using energy dispersive x ray analysis in all cases the areas apparently showing positive relief on the faceted garnet surfaces are compositionally identical to the adjacent grain cores despite a wide variation in detrital garnet compositions in one case zoning within the grain core can be traced into the faceted areas on the grain surface thus faceted areas must be considered to form part of the original detrital grains together with previously published studies on experimental garnet etching thermodynamic conditions for garnet growth textural relationships between faceted garnets and authigenic and detrital phases and distribution of faceted garnets in the subsurface this paper provides conclusive proof that faceted garnet surfaces form as a result of dissolution not overgrowth

conversion of diatoms to clays during early diagenesis in tropical continental shelf muds in coastal muds downdrift from the amazon river mouth marine diatom frustules are rapidly converted to various forms of authigenic aluminosilicate phases during burial the dominant neoformed crystalline phases have a composition similar to k smectite yield electron diffraction patterns characteristic of clay minerals and exhibit a range of crystal sizes and morphologies including euhedral pseudohexagonal crystals and anhedral flakes replacing biogenic silica a poorly crystalline or microcrystalline k rich and fe rich aluminosilicate material also replaces the siliceous frustules the conversion process is not always complete leaving relics of the original frustule in the resulting authigenic aluminosilicate phases laboratory incubation experiments with cultured diatoms demonstrate that the conversion process occurs in 20 23 months the conversion of biogenic silica to authigenic clays occurs throughout the amazon deltaic deposits and presumably takes place in other comparable depositional settings biogenic silica alteration provides proof for a direct link between the biogeochemical cycle of silica in nearshore environments and the neoformation of cation rich aluminosilicate phases and it may prove to be important for oceanic geochemical cycles as a sink for si k and other elements incorporated in the authigenic aluminosilicates rapid formation of authigenic k smectite may also represent a reaction stage leading to eventual formation of illitic clays during later diagenesis

a genetic link between remagnetization and potassic metasomatism in the devonian onondaga formation northern appalachian basin whole rock chemical analyses indicate that the onondaga formation along a rochester syracuse new york transect has a marked eastward increasing trend in k al ratio which correlates with an increase in authigenic magnetite content and degree of diagenetic illitization an eastward increase in the content of some authigenic minerals including k feldspar quartz and fe rich chlorite in the rocks is indicated by petrographic and x ray diffraction studies these observations suggest a link between remagnetization and potassic alteration of fe bearing silicates in the onondaga two hypothetical reactions are proposed in which magnetite authigenesis is related to the breakdown of fe bearing smectite in the presence of potassium products of these reactions include authigenic k feldspar illite quartz and chlorite as well as magnetite our results suggest that remagnetization was triggered by a basin wide migration of k rich fluids during the alleghenian orogeny

heavy minerals as a guide to turbidite provenance in the lower palaeozoic southern welsh basin a pilot study a pilot study has demonstrated that heavy mineral analysis is a useful guide to the provenance of silurian turbidites in the southern welsh basin the results confirm the sedimentological evidence for two distinct source areas of coarse clastic detritus one lying to the south and the other to the east they also provide mineralogical criteria by which the two source areas may be distinguished the southern area provided material with relatively low mineral diversity and is characteristic in having low rutile zircon ratios whereas the eastern source provided more diverse assemblages generally with high rutile zircon ratios the southern source shows variations in terms of apatite tourmaline ratio with the older aberystwyth grits group tending to contain relatively low apatite compared with the younger cwmystwyth grits group rhuddnant and pysgotwr grits formations there is evidence for polycyclic material and volcanic detritus in both southerly and easterly derived samples however easterly sourced sandstones apparently tapped a more lithologically diverse terrain

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

hydrothermal synthesis of ammonium illite synthetic gel and glass of illitic composition natural kaolinite and mixed layer illitesmectite were used as starting materials for hydrothermal synthesis of ammonium illite ammonium illite was prepared from synthetic gel by hydrothermal treatment at 300 8c the onset of crystallization began within 3 h and well crystallized ammonium illite appeared at 24 h increasing reaction time up to four weeks led to many illite layers per crystal in the presence of equivalent proportions of potassium and ammonium the gel was transformed to illite with equimolar contents of k and nh4 in contrast synthesis using glass under the same conditions resulted in a mixture of mixed layer ammonium illite smectite with large expandability and discrete illite hydrothermal treatments of the fine fractions of natural kaolinite and illite smectite produced ammonium illite from kaolinite but the illite smectite remained unchanged

using detrital garnet compositions to determine provenance a new compositional database and procedure detrital garnet compositions can be used to help determine the provenance of sedimentary rocks in this study a garnet compositional database consisting of more than 2500 wet chemical and electron microprobe analyses was compiled from the literature for the garnets in the database the six principal garnet end member compositions pyrope almandine spessartine uvarovite grossular and andradite were calculated a multi stage methodology was devised to match garnet compositions to source rocks and a series of garnet provenance fields on ternary plots were identified the method was tested using compositional data from detrital garnet studies in several areas where provenance has already been identified with good results the methodology was then used to assess the provenance of detrital garnets from neogene sandstones of northern sabah borneo for which provenance is unknown and in a region where there are few garnet analyses for comparison comparison of garnet compositions from possible sources on palawan philippines and in borneo combined with the ternary plots excludes some known garnet bearing rocks as potential sources and suggests derivation of metamorphic and igneous garnets from palawan during the early miocene

provenance analysis of lower cretaceous sindong group sandstones in the gyeongsang basin korea using integrated petrography quartz sem cathodoluminescence and zircon zr hf analysis the sindong group aptian albian in southeastern korea is a 2 3 km thick fluvio lacustrine sedimentary package deposited in an elongated basin the nakdong trough which was formed by extension in an active continental margin setting the provenance of the sindong group was studied to understand spatial and temporal variation in composition in three different parts of the basin by using integrated data on petrography quartz sem cathodoluminescence cl analysis and zircon zr hf analysis although sindong group sandstones display wide variation in the composition of framework grains they generally have increasing amounts of feldspar and decreasing amounts of quartz up sequence significant amounts of volcanic rock fragments and volcanic quartz are observed in the late stage sediments metamorphic quartz is predominant in all sindong group sandstones indicative of the exposure of metamorphic rocks in the source terrane mostly from precambrian basement and triassic granites the occurrence of significant amounts of plutonic quartz from early stage sediments suggests that jurassic granites were widely exposed in the source terranes in addition the episodic increase in volume of plutonic quartz content in the sequence especially in the northern part of the basin suggests that episodic tectonic activity occurred in the catchment the increasing feldspar content up sequence could support the occurrence of tectonic activity in the catchments the zr hf analysis of detrital zircons revealed that the majority of zircons are of continental crust origin formed in orogenic settings but zircons in the lowest strata in the northern part of the basin were derived largely from anorogenic magmatic rocks of mantle origin our results demonstrate that source terranes for the sindong group have heterogeneous spatial and temporal distribution and were composed mainly of precambrian basement and triassic to jurassic granitic rocks with minor meta sedimentary rocks and syndepositional volcanic rocks the detritus derived from syndepositional volcanic rocks became significant in the late stage of basin filling representing the transition from extensional tectonism to continental arc magmatism the differences in characteristics of quartz sem cl and zircon zr hf ratios in different parts of the basin are best explained by deposition on different alluvial fans and river systems

variations in mixed layer illite smectite diagenesis in the rift and post rift sediments of the jeanne d arc basin grand banks offshore newfoundland canada mixed layer illite smectite i s clays were analyzed from 22 deep exploration wells from the jeanne d arc basin on the grand banks offshore newfoundland the host of large commercial hydrocarbon accumulations discovered in the last two and a half decades the fine fraction of the clays 0 1 m consists mainly of mixed layer i s with minor amounts of kaolinite illite and chlorite smectite and or smectite rich i s clays were supplied to the jeanne d arc basin from upper jurassic to tertiary times smectite rich i s clays occur only in shallow samples irrespective of geologic age the proportion of illite in i s mixed layers as well as the degree of ordering increase with depth and temperature indicating that smectite rich i s clays have been progressively illitized in both rift and post rift sediments of the jeanne d arc basin during burial the transition from random to r1 ordered i s occurs between subsurface depths of 1940 and 3720 m and crosses major stratigraphic boundaries the transition fr

hydrogen isotope geochemistry of diagenetic clay minerals from cretaceous sandstones alberta canada evidence for exchange abstract the d and 18o values of diagenetic kaolinite and 10aclay minerals illite illite smectite have been determined for lower cretaceous viking formation marine sandstones and conglomerates upper cretaceous basal belly river group shoreline and deltaic sandstones and overlying belly river brazeau groups continental sandstones from the western canada sedimentary basin early and late diagenetic kaolinites have a remarkably small range of d values 132 to 112 viking formation 137 to 128 belly river brazeau groups relative to their d18o compositions 13 8 to 26 9 viking formation 5 9 to 12 7 belly river brazeau groups the d values are also much lower than commonly reported for kaolinite calculations indicate that the diagenetic kaolinite from all units is in or close to hydrogen isotopic equilibrium with present formation waters at present subsurface temperatures within the limits of available fractionation data similar observations can be made for diagenetic 10aclay minerals from these units d 132 to 107 viking formation 138 to 123 belly river brazeau groups by comparison a general state of oxygen isotope equilibrium does not exist between diagenetic kaolinite and present formation waters kaolinite has retained oxygen isotope compositions characteristic of neoformation during earlier stages of diagenesis some diagenetic 10aclay minerals e g belly river brazeau groups may be in oxygen isotope equilibrium with present formation waters because of neoformation from these waters in sandstones or oxygen isotopic exchange during the smectite to illite transformation in shales the results of this study suggest that hydrogen isotope re equilibration between diagenetic kaolinite and formation water in sandstones can occur independent of oxygen isotope exchange at temperatures as low as 40 c interpretation of hydrogen and oxygen isotope compositions for clay minerals from such systems i e high water rock ratio low temperatures should therefore be decoupled

middle miocene denudation of the higher himalayan crystallines revealed by chemical composition of detrital garnets from the siwalik foreland basin sediments western and central nepal abstract the middle miocene to early pleistocene siwalik group is composed of sediments deposited in the himalayan foreland basin in this study the heavy mineral assemblage and chemical composition of detrital garnets from the sandstones in the lower siwalik sub group which are exposed along the karnali river in western nepal and the tinau khola in central nepal are studied and the provenance shift during the middle miocene is discussed the heavy mineral assemblage in the lower section of the lower siwalik sub group is characterized as predominantly zircon tourmaline rutile chemical analysis of the detrital garnets showed a monomodal almandine rich composition with low pyrope prp

hydrothermal alteration in the valles caldera ring fracture zone and core hole vc 1 evidence for multiple hydrothermal systems two types of hydrothermal mineral assemblages kaolinite alunite and sericite chlorite were recognized in outcrop and core samples from the jemez volcanic field new mexico active and fossil acid sulfate hydrothermal activity producing kaolinite alunite alteration occurs along the caldera ring fracture and within the resurgent dome whereas alterations of the chlorite sericite type are mostly confined to subsurface rocks k ar dates on illitic clays 2 m 2 0 25 m and 0 25 m separated from hydrothermally altered samples are used to document hydrothermal episodes in pre caldera rocks of the jemez volcanic field the clay separates are illitic 75 95 illite layers with k2o contents of 8 24 8 95 in the core samples and 4 22 6 67 in the outcrops three episodes of hydrothermal alteration are now recognized in the jemez mountains region based on k ar age dates of illites the earliest event 17 11 ma n 4 occurred within altered and illite rich 90 illite layers lowermost paleozoic rocks in core hole vc 1 and may correlate with the inception of volcanism in the jemez region 16 5 ma illitic clays from altered andesite and rhyolite from the topographic rim of the valles caldera were dated at 8 2 and 6 96 ma suggesting that a hydrothermal event related to the waning stages of the keres group volcanism 13 5 8 ma was responsible for the alteration these dates overlap minimum ages obtained on slightly altered basalt 8 05 ma and andesite lava 7 07 ma from the southern and northwestern topographic rim of the valles caldera respectively ages of 1 21 and 1 34 ma from illite rich 90 illite layers hydrothermally altered paleozoic sandstone at a depth of 479 m in vc 1 suggest hydrothermal activity contemporaneous with the formation of the toledo 1 45 ma and valles 1 12 ma calderas ore minerals of sphalerite chalcopyrite galena barite and molybdenite mineralization occur in the lower half of vc 1 and are related to the toledo and valles caldera forming eruptions

evaluation of sediment provenance using magnetic mineral inclusions in clastic silicates comparison with heavy mineral analysis magnetic fe oxide inclusions within framework clastic grains in sediments provide an indication of the provenance of the enclosing host silicate particles magnetic mineral inclusion characterisation is performed using a variety of magnetic properties that are related to magnetic mineral abundance magnetic grain size domain state oxidation state and magnetic grain interaction the magnetic methodology extends that based on a conventional set of environmental magnetic measurements using a variety of recent sediments transported from known rock sources within the uk and eire it is demonstrated using discriminant function analysis that the magnetic properties of the fe oxide inclusions provide a clear distinction of primary provenance this is both at the large scale in terms of various gneiss schist and granite sources and also at a smaller scale when considering subdivisions of these sources using case studies from the marine upper jurassic piper formation and non marine triassic sediments otter bank sandstone and foula sandstone formations it is shown that provenance differences clearly expressed by the results of heavy mineral analysis are also sensitively displayed by the magnetic mineral inclusion data the provenance classification is based around use of hierarchical cluster analysis and multidimensional scaling simple statistical tools are developed to determine a least noisy subset of magnetic parameters which are most suitable for stratigraphic provenance discrimination the triassic case study has indicated the magnetic mineral inclusion technique is most sensitive when using the sediment fractions larger than 150 m

alteration adsorption and nucleation processes on clay water interfaces mechanisms for the retention of uranium by altered clay surfaces on the nanometer scale abstract nano scale processes on the solid water interface of clay minerals control the mobility of metals in the environment these processes can occur in confined pore spaces of clay buffers and barriers as well as in contaminated sediments and involve a combination of alteration adsorption and nucleation processes of multiple species and phases this study characterizes nano scale processes on the interface between clay minerals and uranyl bearing solution near neutral ph samples of clay minerals with a contact ph of 6 7 are collected from a u mill and mine tailings at key lake saskatchewan canada the tailings material contains cu as co mo ni se bearing polymetallic phases and has been deposited with a surplus of ca oh 2 and na2co3 slaked lime small volumes of mill process solutions containing sulfuric acid and u are occasionally discharged onto the surface of the tailings and are neutralized after discharge by reactions with the slaked lime transmission electron microscopy tem in combination with the focused ion beam fib technique and other analytical methods sem xrd xrf and icp oes are used to characterize the chemical and mineralogical composition of phases within confined pore spaces of the clay minerals montmorillonite and kaolinite and in the surrounding tailings material alteration zones around the clay minerals are characterized by different generations of secondary silicates containing variable proportions of adsorbed uranyl and arsenate species and by the intergrowth of the silicates with the uranyl minerals cuprosklodowskite cu uo2 2 sio3oh 2 h2o 6 and metazeunerite cu uo2 aso4 2 h2o 8 the majority of alteration phases such as illite illite smectite kaolinite and vermiculite have been most likely formed in the sedimentary basin of the u ore deposit and contain low amounts of fe 10 at formed most likely in the limed tailings at high contact ph 10 5 and their structure is characterized by a low degree of long range order adsorption of u and nucleation of metazeunerite and cuprosklodowskite are strongly controlled by the presence of the adsorbed oxy anion species arsenate and silica on the fe enriched silicates heterogeneous nucleation of nano crystals of the uranyl minerals occurs most likely on adsorption sites of binary uranyl arsenate and silica complexes as well as on ternary uranyl arsenate or uranyl silicate complexes the uranyl minerals occur as aggregates of misoriented nano size crystals and are the result of supersaturated solutions and a high number of nucleation sites that prevented the formation of larger crystals through oswald ripening the results of this study provide an understanding of interfacial nano scale processes between uranyl species and altered clay buffers in a potential nuclear waste repository as similar alteration conditions of clays may occur in a multi barrier system

comments on the paper entitled the heavy minerals of the kurnub sandstone early cretaceous of jordan by s nasir and w sadeddin

k ar dates of hydrothermal clays from core hole vc 2b valles caldera new mexico and their relation to alteration in a large hydrothermal system abstract seventeen k ar dates were obtained on illitic clays within valles caldera 1 13 ma to investigate the impact of hydrothermal alteration on quaternary to precambrian intracaldera and pre caldera rocks in a large long lived hydrothermal system 1 0 ma to present clay samples came from scientific core hole vc 2b 295 c at 1762 m which was spudded in the sulphur springs thermal area and drilled into the boundary between the central resurgent dome and the western ring fracture zone six illitic clays within quaternary caldera fill debris flow tuffaceous sediment and ash flow tuff 48 to 587 m depth yield ages from 0 35 to 1 09 ma illite from miocene pre caldera sandstone 765 m gives an age of 6 74 ma two dates on illite from sandstones in permian red beds 1008 and 1187 m are 4 33 and 4 07 ma respectively surprisingly three dates on illites from altered andesite pebbles within the red beds 1010 1014 m are 0 95 to 1 06 ma four illite dates on variably altered precambrian quartz monzonite 1615 1762 m range from 2 90 to 276 ma post valles age illite is not correlated with alteration style argillic to propylitic rather post valles ages are uniformly obtained from illites in highly fractured intensely altered caldera fill rocks and the permian volcanic clasts generally finer clay fractions from identical samples yield younger ages plots of 40 ar 36 ar versus 40 k 36 ar and 40 ar versus 40 k for the illites in caldera fill rocks lie close to a 1 ma isochron most illite dates older than valles caldera are difficult to interpret because they correspond to the ages of pre valles volcanic and hydrothermal episodes in the jemez volcanic field 13 ma in addition older dates may be caused by co mingling of different illites during sample preparation or by inherited argon or lost argon in illites from rocks with potentially complex hydrothermal histories however the range of ages obtained from illites in permian sands and pebbles and from precambrian crystalline rocks indicates that valles hydrothermal activity is overwhelming illite produced by earlier geologic events

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

timing and depositional environments of a middle pleistocene glaciation of northeast england new evidence from warren house gill county durham at various times during the quaternary north eastern england was a zone of confluence between dynamic ice lobes sourced from the pennines northern scotland the cheviots and scandinavia the region thus has some of the most complex exposures of middle to late pleistocene sediments in britain with both interglacial and glacial sediments deposited in terrestrial and marine settings we investigated sedimentary sequences exposed on the coastline of county durham at warren house gill and present a new model of british and fennoscandian ice sheet interaction in the north sea basin during the middle pleistocene the stratigraphy at warren house gill consists of a lower diamicton and upper estuarine sediments both part of the warren house formation they are separated from the overlying weichselian blackhall and horden tills by a substantial unconformity the lower diamicton of the warren house formation is re interpreted here as an mis 8 to 12 glaciomarine deposit containing ice rafted lithics from north eastern scotland and the northeast north sea and is renamed the ash gill member it is dated by lithological comparison to the easington raised beach middle pleistocene amino acid racemisation values and indirectly by optically stimulated luminescence the overlying shallow subaqueous sediments were deposited in an estuarine environment by suspension settling and bottom current activity they are named the whitesides member and form the uppermost member of the warren house formation during glaciation ice rafted material was deposited in a marine embayment there is no evidence of a grounded onshore scandinavian ice sheet in county durham during mis 6 which has long been held as the accepted stratigraphy this has major implications for the currently accepted british quaternary stratigraphy combined with recent work on the middle pleistocene north sea drift from norfolk which is now suggested to have been deposited by a scottish ice sheet the presence of a scandinavian ice sheet in eastern england at any time during the quaternary is becoming increasingly doubtful

stable isotope geochemistry of authigenic clay minerals from late permian coal measures queensland australia implications for the evolution of the bowen basin oxygen and hydrogen isotope analyses were carried out on authigenic clay minerals from late permian coal measures of the bowen basin australia in the northern bowen basin the oxygen isotope compositions of the mixed layer illite smectite show significant irregular variations with respect to depth which parallel the changes in the extent of the illitisation reaction and are interpreted as reflecting changes in water rock ratio in turn related to permeability the o and d values of illite smectite and kaolinite in the northern bowen basin and the calculated fluid isotopic composition o 3 to 1 d 70 to 90 in equilibrium with these clays are considerably lower than those typically reported for deeply buried sedimentary basins these stable isotope data together with relatively high inferred palaeotemperatures up to 235 c and abnormally high geothermal gradients are consistent with a hydrothermal origin for clay mineral formation in the northern bowen basin the hydrothermal system is interpreted to be a result of the late triassic extensional tectonic regime which developed in large parts of eastern australia and affected the northern part of the bowen basin in the southern bowen basin by contrast clays are more enriched in o and deuterium which is explained by lower temperatures in the shallow coal measures and a significant enrichment in the fluid isotopic composition o 3 6 to 5 6 d 66 to 35 under low water rock ratio conditions especially in deeper pelitic rocks c 2000 elsevier science b v all rights reserved

a new palaeogeographic reconstruction for the middle jurassic of the northern north sea an estuarine sequence equivalent in age to the brent group deltaic deposits further north is recognized in the central viking graben it indicates a persistent marine connection southwards from the boreal ocean during deltaic accumulation and suggests that the brent delta did not prograde from the south along the graben as previously suggested evidence from the uk north viking graben indicates the brent delta was probably derived transversely rather than axially as were the other jurassic clastic systems infilling the graben

provenance of the carboniferous hochwipfel formation karawanken mountains austria slovenia geochemistry versus petrography this study focuses on the carboniferous sediments of the karawanken mountains austria slovenia to identify possible source areas and their geotectonic setting provenance analyses have been applied using petrographical and geochemical approaches what also lead to an evaluation of the used methods within the hochwipfel formation five stratigraphic related petrofacies groups can be defined using the sandstone component inventory homogenous provenance results based on major element and trace element data suggest an active continental margin continental island arc with probably an intraplate signature provenance analyses of light minerals point to source areas with basement rocks mainly metamorphic arc material and sedimentary rocks in combination the rapid and highly variable change of provenance signatures within the stratigraphic succession of the petrofacies types excludes a single provenance in the western part of the karawanken mountains additionally changes in composition of the individual petrofacies groups correlate with the stratigraphy in the eastern part varying contents of garnet chromite hornblende and epidote within the sedimentary succession of the hochwipfel sandstones can partly be attributed to geodynamical changes in the hinterland the chemical compositions of garnets tourmalines and chromites confirm the results of both geochemistry and sediment petrography in a quantitative approach based on petrography we can see an equal mixture of all source areas whereas quantification with a geochemical approach results in c 11 of material that can be attributed to a passive continental margin source 28 to 37 to an active continental margin c 44 to a magmatic arc setting and 16 to 19 to an oceanic within plate source area the resulting model for the geodynamical setting of the hochwipfel basin during the late palaeozoic can be best explained by a forearc basin in the eastern part and various pull apart basins in the western part connected through bypasses at the continental margin of gondwana and the palaeotethys as an additional outcome this study clarifies that geochemically derived provenance results based on bulk rock and mineral composition recognize best complex geodynamical settings and a mixture of sources since they incorporate best the provenance significant lithic components on the other hand it points out that an application of additional petrological approaches does not necessarily lead to further information and an elimination of errors but could be essential to define general information of the investigated stratigraphy like the correlation of deposits with stratigraphy petrofacies groups

burial diagenesis of illite smectite in shales and the origins of authigenic quartz and secondary porosity in sandstones several gram size samples of 0 1 mu m nearly monomineralic mixed layer illite smectite i s were isolated from nineteen whole cores of shale of the frio formation from the texas gulf coast between approximately 7 000 ft 2133 m and approximately 15 000 ft 4572 m burial depth i s changes from random interstratification r 0 with low 1 to ordered interstratification r 3 with high i the accompanying chemical changes are loss of si mg and fe sup 3 gain of k al and fe sup 2 and a shift in the ree content of the mineral there is no chemical or mineralogical evidence for a cessation of i s reaction at approximately 80 i as is commonly accepted both chemical and mineralogical changes occur throughout burial continuous change in the oxygen isotopic composition of i s implies that the conversion of smectite layers to illite layers is a dissolution and reprecipitation process mass balance calculations indicate that burial diagenesis of frio formation shales is an open system process that requires addition of k sub 2 o and al sub 2 o sub 3 and results in loss of sio sub 2 the amount of sio sub 2 made available by shale diagenesis is sufficient to be the source of the quartz overgrowth cements in the associated frio sandstones iron reduction in i s is amore significant source of the acid required for the diagenesis of both frio shales and sandstones 68 refs 12 figs 4 tabs less

a new approach to provenance studies electron microprobe analysis of detrital garnets from middle jurassic sandstones of the northern north sea reading provenance from heavy mineral suites is hampered by the depletion of diagnostic but unstable heavy minerals through intrastratal solution a common phenomenon in deep sedimentary basins such as the north sea this paper demonstrates the potential of electron microprobe analysis in overcoming this problem by concentrating on the compositional variations shown by detrital garnets which are relatively resistant to intrastratal solution studies of the garnets from the brent group middle jurassic of the murchison and tern oilfields in the northern north sea reveal that three distinct areas supplied detritus association 1 which characterizes the broom formation in both areas and recurs higher in the sequence in the tern field is ascribed to an orkney shetland source the location of the areas supplying the garnets of association 2 best represented in murchison and association 3 common to both fields is less clear their ultimate sources clearly include high grade metamorphics and therefore probably lie on the norwegian landmass the orkney shetland platform or conceivably the scottish landmass but the possibility of recycling makes it difficult to judge their immediate provenances nevertheless the presence of three garnet associations indicates that the most widely accepted model of brent sedimentation with sands derived from a domal uplift in the outer moray firth and channelled northward along the viking graben is untenable

assessing detrital garnet chemical composition as a quantitative provenance tool a multivariate statistical approach abstract chemical analysis of detrital garnet is a widely utilized quantitative tool for determining the provenance of sediments the goal of this study is to investigate the ability of the compositions of detrital garnet to provide a direct linkage to the specific source rocks from which the garnet was derived to achieve this goal we analyzed detrital garnet isolated from alluvial samples collected from the french broad river and several of its tributaries a watershed that drains portions of the multiply deformed southern appalachian orogen usa to test whether potential linkages between detrital and potential source rock garnet could be achieved garnet crystals were chemically characterized from a wide variety of lithologies that crop out in the french broad watershed and thus are the most likely local sources of detrital garnet mahalanobis distances measured on canonical discriminant functions successfully differentiated garnet compositions among the 18 analyzed source rocks these metrics were then applied to 2 300 detrital garnet compositions to link each grain to its potential source rock approximately 94 of the detrital garnet crystals were linked to their potential source regions thus only 6 of the detrital crystals were treated as unclassified we interpret the unclassified high ca garnets to have been derived from minor sub map scale lenses and boudins of calc silicate or skarns from exposed ocoee or ashe metaclastic units within the french broad river watershed the unclassified high mn detrital garnet grains are interpreted to have been derived from the various felsic granitiods and pegmatites that intrude the region of study

microanalysis of carbonate cement δ18o in a co2 storage system seal insights into the diagenetic history of the eau claire formation upper cambrian illinois basin oxygen isotope 18o zonation in carbonate mineral cements is often employed as a proxy record typically with millimeter scale resolution of changing temperature regimes during different stages of sediment diagenesis recent advances in secondary ion mass spectrometry allow for highly precise and accurate determinations of cement 18o values to be made in situ on a micrometer scale thus significantly increasing the spatial resolution available to studies of diagenesis in sandstone shale and carbonate systems chemo isotopically zoned dolomite ankerite cements within shaly sandstone beds of the predominantly silty shaly eau claire formation cambrian illinois basin were investigated revealing the following with increasing depth of burial from 0 5 to 2 km 1500 to 6500 ft cement 18o values decrease from a high of approximately 24 down to approximately 14 on the vienna standard mean ocean water vsmow scale equivalent to 6 5 to 16 5 on the vienna peedee belemnite vpdb scale the observed cross basin trend is largely consistent with cements having formed in response to progressive sediment burial and heating within the context of independent burial and thermal history models for the illinois basin cementation began soon after deposition and continued intermittently into the mid permian however temperatures in excess of burial model predictions are inferred at the time of latest ankerite cement precipitation which we propose overlapped in time with conductive heating of the eau claire formation a closed system from under and overlying sandstone aquifers that channeled the flow of hot mississippi valley type mineralizing brines during the mid permian ca 270 ma

evolution of paleocene sediment dispersal systems in the foinaven sub basin west of shetland heavy mineral assemblages in deepwater paleocene sandstones of the foinaven sub basin west of shetland reflect the influence of three main provenance and dispersal systems the schiehallion system has relatively uniform characteristics and persisted through much of the early mid paleocene its sphere of influence was centred on the schiehallion field but it progressively encroached into the foinaven area with time its main source was the triassic foula formation with minor supply from lewisian and moine basement rocks the foinaven system shows marked changes in character related to evolution of the source area the earliest sands were derived from a heavily weathered late cretaceous regolith and represent the onset of uplift and exhumation of the shetland platform progressive unroofing led to the incorporation of increasing amounts of lewisianand moine sourced detritus following deposition of the main reservoir sandstones in foinaven and schiehallion there was a progressive change in provenance with a gradual increase in the amount of sediment shed directly from metamorphic basement pulsing of the proto icelandic plume has been proposed as the mechanism for repeated influx of sand to the basins around scotland however on the basis of available geochronological data there does not appear to be a direct link between events in the british tertiary igneous province btip and changes in provenance in the foinaven sub basin the initial influx of sediment from a weathered land surface may have been coeval with the onset of magmatism in the btip but the cessation of supply through the foinaven system at c 59 ma does not appear to be related to magmatic events in the btip the waning of magmatism in the btip around 58 ma is broadly coincident with a gradual increase of first cycle basement detritus please contact us if you would like a copy of this paper

provenance of heavy mineral deposits on the northwestern shelf of the south china sea evidence from single mineral chemistry abstract a study of heavy mineral geochemistry has been carried out in order to examine the potential sources of heavy mineral deposits within surficial sediment on the northwestern shelf of the south china sea tourmaline amphibole and garnet from six samples near the coast and eleven samples on the shelf were analyzed by an electron microprobe chemical varieties of tourmaline and amphibole indicate that the pearl river is the main supplier of sandy sediments on the eastern shelf within a 100 km radius west of the paleo deltas sandy sediments on the western shelf are mainly sourced from the jian river and the wanquan river heavy mineral placers on the middle and outer shelves are mainly derived from reworking of the paleo pearl river deltas heavy mineral placers in the west are mainly sourced from the small rivers and are distributed in the sandy deposits near the coasts this study demonstrates that the occurrence of heavy mineral placers on wide continental shelf is mainly determined by the sediment supply and marine processes during transgressions

faceted garnets from sandstones of the munising formation cambrian northern michigan petrographic evidence for their origin by intrastratal dissolution imbricate wedge marks facets on garnets in sandstones of the cambrian munising formation of northern michigan are associated with mouldic secondary porosity developed at the expense of garnet mouldic pores surrounding faceted garnets indicate that garnets in these sandstones have been affected by intrastratal dissolution retreat of the mineral surface from its original boundaries rather than by grain enlargement which would be expected if garnet overgrowths had formed the association of garnet facets with textural evidence of garnet dissolution proves that garnet facets form by intrastratal dissolution these results confirm similar findings in other recent studies and extend the geographic and stratigraphic range of proven occurrences of facet formation by intrastratal dissolution

heterogeneous reactions of dioctahedral smectites in illite smectite and kaolinite smectite mixed layers applications to clay materials for engineered barriers abstract the clay materials selected for use in the engineered barriers of the french nuclear waste isolation programme are mainly composed of dioctahedral smectite either bentonite of wyoming type or kaolinite smectite mixed layered minerals from the sparnacian deposit of the paris basin these dioctahedral smectites most often consist of randomly stacked layers with low and high charges in the case of the wyoming type bentonite these two differently charged layers do not react in the same way when subjected to hydrothermal alteration overall the low charge smectite layers react to form high charge smectite layers quartz kaolinite then fixing k ions the high charge smectite layers are transformed into iilite smectite mixed layers i s when the temperature conditions increase diagenetic formations geothermal fields or metasomatic environments a symmetrical process is observed in natural or experimental hydrothermal conditions when the high charge smectite layers of i s minerals react with quartz and or kaolinite to produce low charge smectite layers the chemical properties cation exchange capacity irreversible k fixation of the bentonite engineered barriers clearly depend on the low charge high charge smectite layer proportion which is in turn controlled by the temperature dependent reactions in the vicinity of the waste disposal although there are fewer published data on the kaolinite smectite mixed layered minerals k s a similar low charge high charge reaction appears to affect their smectite component the experimental alteration of k s leads to the formation of a low charge beidellite with an increase in the cation exchange capacity and in the expandability of the clay material thus the properties of the engineered barrier seems to be improved after hydrothermal alteration

the hydrothermal transformation rate of kaolinite to muscovite illite batch reactor experiments were performed to measure the rate of the reaction 1 5 kaolinite k muscovite h 1 5 water at temperatures ranging from 250 to 307 c in these experiments the rate of kaolinite conversion to muscovite illite was monitored as the rate of production of h runs were performed in small volume 50 ml titanium hydrothermal reactors charged with well crystallized georgia kaolinite indian ruby muscovite and 25 ml of kcl solution 0 5 2 0 m both solids and solutions were monitored at specific intervals throughout each experiment the determined rate law is dmh dt dmk dt amm k mk k mh where mk and mh are the concentrations of potassium ion and hydrogen ion k and k are the forward and reverse rate constants in kg m 2 sec 1 am is the total surface area of the muscovite in m2 and m is the mass of the solution in kg the initial rate method was used to find k and k was found by fitting data to an integrated rate equation temperature functions for the rate constants are in k 12 90 1 87 104 t r2 0 98 and in k 6 03 1 21 104 t r2 0 95 the activation energies ea for the forward and reverse reaction are 155 15 kj mol 1 and 101 10 kj mol 1 respectively

major and trace elements in pyrope almandine garnets as sediment provenance indicators of the lower carboniferous culm sediments drahany uplands bohemian massif abstract the lower carboniferous culm basin is part of the european variscan foreland basin garnet is an abundant heavy mineral at all stratigraphic levels of the culm sediments the protivanov rozstani and myslejovice formation from base to top this paper compares the major element electron microprobe and trace element la icp ms compositions of garnet for the purpose of studying the provenance of the culm sediments the polymict garnet assemblages ranging from the protivanov to lower part of the myslejovice formation goniatite zones pe go pass into oligomict ones dominated by pyrope almandine garnets uppermost part of the myslejovice formation goniatite zones go go as the predominant low grossular pyrope almandines from oligomict garnet assemblages are very uniform and homogeneous in major element composition we studied their trace element composition and zoning pyrope almandine garnets are poor in lree and show enrichment in hree the chondrite normalized patterns are almost flat from dy to lu and show a significant negative eu anomaly typical for granulite grade garnets major element compositions of detrital low grossular pyrope almandines can only be matched with some granulites and garnetiferous felsic gneisses of the bohemian massif garnets from granulites cropping out at the present day erosion level of the bohemian massif have usually higher ca and or lower mg contents the major and trace element compositions and zoning patterns of pyrope almandine garnets from the upper part of the myslejovice formation compare well with garnets from the miroslav granulites and small moldanubian granulite bodies west of the t ebic massif the moldanubian granulites are commonly associated with mantle derived peridotites and eclogites the presence of detrital cr spinels with high cr and low mg single grains of cr spinels and fine grained kelyphitic intergrowths of cr spinel with chlorite comparable with spinel types from moldanubian peridotites could indicate the joint occurrence of peridotites serpentinized peridotites and granulites at the erosion level of the bohemian massif during the deposition of the uppermost culm sediments 325 ma while the older culm sediments polymict garnet assemblages represent the accumulation of clastic material from the northern and north western areas moravo silesian and lugian zone the uppermost culm sediments oligomict garnet assemblages contain material from western and south western areas moldanubian zone and moravian nappe the general influx of clastic material changed as a result of clockwise rotation of the eastern part of the variscan belt during this time span 340 325 ma

provenance and tectonic setting of carboniferous triassic sandstones from the karaburun peninsula western turkey a multi method approach with implications for the palaeotethys evolution abstract carboniferous triassic siliciclastic sediments of the karaburun peninsula in western turkey were studied to unravel their provenance and the tectonic setting of depositional basins within the palaeotethyan realm a set of complementary techniques including petrography bulk rock geochemistry and single grain analysis of rutile garnet and chrome spinel were applied to provide a diverse dataset for testing existing palaeotectonic models using both established and recently published diagrams we show that tectonic discrimination diagrams of siliciclastic sediments based on major and trace element whole rock geochemical data do yield ambiguous results and are only partly in accordance with regional geological events chondrite normalised ree patterns of upper palaeozoic samples are characterised by enrichment of lree and a flat trend towards hree the degree of fractionation allows for discrimination between sandstones of karaburun lan ybn 8 00 14 79 and adjacent greek islands of chios 5 82 9 23 and inousses 7 40 9 95 petrographic observations and compositional data from single grain analysis indicate significant supply from low to medium grade metamorphic rocks of generally felsic character and minor input of ultra mafic detritus detrital chrome spinels in the lower triassic gerence formation are different in composition and shape compared to chrome spinels in carboniferous permian sandstones they were derived from a very proximal source and exhibit variable but generally high cr and mg numbers consistent with chrome spinels from podiform chromitites that have been formed in an intra oceanic back arc setting above a supra subduction zone we conclude that most of the carboniferous triassic successions were deposited along the southern active margin of eurasia in a continental arc environment during the time period when palaeotethys diminished in size and finally vanished large volumes of detritus were probably derived from rock units located in the present day balkan region and the sakarya zone or equivalent successions that are not present anymore

new geochemical results indicate a non alpine provenance for the alpine spectrum epidote garnet hornblende in quaternary upper rhine sediment abstract the heavy mineral assemblage of late pleistocene to modern rhine river sediment in the upper rhine graben is dominated by garnet green amphibole and epidote this so called alpine spectrum has been taken to indicate an exclusive derivation from the alps and has hitherto been investigated with optical methods only we present the first single grain geochemical data set of garnet and amphibole from the upper rhine river and some of its main tributaries we use the new data to test the alleged alpine provenance in the rhine our results show that the provenance of garnet mostly pyrope rich almandine is grain size dependent particularly the pyrope content indicates that the 0 063 0 25 mm size fraction has an alpine provenance whereas 0 25 0 5 mm grains derived from the black forest and the vosges which flank the upper rhine graben they mainly comprise of paleozoic metamorphic and igneous rocks supplying a suite of heavy minerals similar to the alpine spectrum to the rhine river amphibole mostly mg hornblende has an increasing tio2 content from the south to the north of the graben which also indicates an input from the graben shoulders the new data indicate that the so called alpine spectrum of heavy minerals in rhine river sediment of the upper rhine derived to significant degrees from non alpine sources furthermore our results indicate a relatively uniform provenance for the rhine river system during the past 1 ma

grain size dependence of garnet composition revealed by provenance signatures of modern stream sediments from the western hohe tauern austria abstract heavy minerals are valuable indicators about the geological framework in the source area the heavy mineral garnet is one of the most widespread heavy minerals in orogenic sediments and its geochemistry provides important information about metamorphic conditions the application of heavy minerals and garnet geochemistry for sedimentary provenance analysis is tested for modern stream sediments collected along three rivers draining the eclogite zone and adjacent geological source units of the western hohe tauern area in the central eastern european alps for comparison with the stream sediments rock outcrops exposed in this area were also sampled the chosen area is very well investigated and provides an excellent place to constrain the relations between source rocks and sediment in first order drainages the influence of grain size is studied in detail by considering grain size fractions ranging from coarse silt to coarse sand 32 to 1000 m in all grain size fractions the heavy mineral assemblages are characterised to a variable extent by epidote zoisite garnet and green calcic amphibole in the smaller grain size fraction apatite is more frequent whereas in the coarser grain size fractions an increase of green calcic amphibole and garnet can be observed electron microprobe analysis of detrital garnet shows the dominance of almandine rich garnet stream sediments within and downstream of the eclogite zone show an increase of pyrope rich garnets interestingly in all samples grossular rich garnets are more frequent in the smaller grain sizes and pyrope rich garnets are more frequent in the coarser grain sizes this is controlled by the original finer size distribution of grossular in the source rocks rather than being a hydraulic effect the heavy mineral assemblages and garnet geochemical data reflect the geological setting of the study area hence confirming the general strength of these methods in sedimentary provenance analysis however the data underline strong grain size control on sediment composition including single grain compositional variations

mineralogy of the core yrd 1101 of the yellow river delta implications for sediment origin and environmental evolution during the last 1 9myr abstract in this study we report the high resolution heavy mineral records from a 200 30 m long borehole yrd 1101 on the northern coast of modern yellow river delta yrd covering the last 1 90myr the results show that the heavy mineral assemblages are dominated by epidote followed by hornblende garnet and hematite limonite in the yellow river yr sediments the content of hornblende is higher than the epidote and the epidote to hornblende ratios e h are lower than the core yrd 1101 the e h show two distinct lower values at depositional unit du 4 2 117 9 125 6 m and du 4 1 to du 2 13 5 99 3 m indicating the obvious influence of yr sediments the heavy mineral composition of du 5 is distinct from yr sediments and interpreted as the result from heterogeneous provenance of the adjacent ancient rivers while du 4 to du 1 resemble the upper middle reaches of the yr sediments the different sediment types mud sandy silt and silt of core yrd 1101 do not contain markedly different transparent heavy mineral assemblages in terms of concentration and mineral ratios no matter how sedimentary environment changes the ratios of epidote and hornblende show very stable values in du 4 1 and du 3 due to the influence of yr sediments the transparent heavy minerals such as hornblende epidote and other stable minerals which were relatively stable are controlled primarily by provenance while the sedimentary environment mostly influences the flaky minerals and the authigenic minerals this study provides evidence regarding the history of the lower reaches of the yr and yrd since the early pleistocene highlighting river s important role for the evolution of the western coast of the bohai sea bs

a multivariate discrimination scheme of detrital garnet chemistry for use in sedimentary provenance analysis abstract garnet chemistry provides a well established tool in the discrimination and interpretation of sediment provenance current discrimination approaches however i suffer from using less variables than available ii subjective determination of discrimination fields with strict boundaries suggesting clear separations where in fact probabilities are converging and iii significant overlap of compositional fields of garnet from different host rock groups the new multivariate discrimination scheme is based on a large database a hierarchical discrimination approach involving three steps linear discriminant analysis at each step and the five major host rock groups to be discriminated eclogite a amphibolite b and granulite c facies metamorphic rocks as well as ultramafic d and igneous rocks e the successful application of statistical discrimination approaches requires consideration of the a priori knowledge of the respective geologic setting this is accounted for by the use of prior probabilities three sets of prior probabilities priors are introduced and their advantages and disadvantages are discussed the user is free to choose among these priors which can be further modified according to the specific geologic problem and the level of a priori knowledge the discrimination results are provided as integrated probabilities of belonging to the five major host rock groups for performing calculations and results a supplementary excel spreadsheet is provided the discrimination scheme has been tested for a large variety of examples of crystalline rocks covering all of the five major groups and several subgroups from various geologic settings in most cases garnets are assigned correctly to the respective group exceptions typically reflect the peculiarities of the regional geologic situation evaluation of detrital garnets from modern and ancient sedimentary settings of the western gneiss region norway eastern alps austria and albertine rift uganda demonstrates the power to reflect the respective geologic situations and corroborates previous results as most garnet is derived from metamorphic rocks and many provenance studies aim at reconstructing the tectonic and geodynamic evolution in the source area the approach and the examples emphasize discrimination of metamorphic facies i e temperature pressure conditions rather than protolith composition

stability of detrital heavy minerals on the norwegian continental shelf as a function of depth and temperature abstract petrographic analysis of 1931 thin sections from sandstones of pliocene to devonian age on the norwegian continental shelf indicate that the heavy minerals zircon tourmaline rutile apatite and spinel survive to depths exceeding 5000 m and to temperatures of around 200 c without showing signs of intrastratal dissolution on the other hand the maximum depth and temperature of occurrence for amphibole are 841 m and 40 c around 1500 m and 55 c for sphene when 0 5 km of probable uplift is taken into account 2231 m and 92 c for kyanite 2559 m and 95 c for epidote 2810 m and 109 c for staurolite and 4589 m and 175 c for garnet initial signs of garnet dissolution occur at around 2000 m depth and all garnets are partially dissolved at depths greater than 3500 m monazite is present down to 4858 m and 182 c and chloritoid to 3811 m and 149 c it is however uncertain whether this is due to the low number of samples deeper than 4858 m and to the rare occurrence of chloritoid or to intrastratal dissolution the same sequence of heavy mineral stability is found when volume of quartz cement is used as a proxy for time temperature exposure quartz cement is not found in samples containing amphibole or detrital sphene a maximum of a fraction of a percent quartz cement is found in samples containing kyanite up to 1 together with epidote up to 6 with staurolite up to 24 with chloritoid up to 25 with garnet whereas maximum values of 25 35 are present together with zircon tourmaline rutile patite spinel and monazite the sequence of persistence of heavy minerals versus depth found in this study is very similar to results from several previous studies although unstable heavy minerals survive to greater depths in very young and rapidly buried sandstones and there are some differences regarding the stability of sphene and epidote heavy mineral dissolution has created secondary pores and possibly has contributed to precipitation of kaolinite illite quartz and carbonates in the studied sandstones but these reactions are of very limited volumetric importance

the influence of organic matter on the boron isotope geochemistry of the gulf coast sedimentary basin usa large variations in the boron isotopic composition of sedimentary environments make boron an attractive monitor of fluid rock interactions during diagenesis studies of b in marine sediments have shown that preferential adsorption of 10b on clay minerals leaves pore waters enriched in 11b during diagenesis clay minerals recrystallize and incorporate 10b into the mineral structure spivack a j palmer m r edmond j m 1987 the sedimentary cycle of the boron isotopes geochim cosmochim acta 51 1939 1949 this process should cause a depletion of b in the pore water with an increase in the 11b in the gulf coast sedimentary basin usa however there is a general increase in b content of formation waters land l s macpherson g l 1992 origin of saline formation waters cenozoic section gulf of mexico sedimentary basin geochim cosmochim acta 76 1344 1362 moldovanyi e p walter l m 1992 regional trends in water chemistry smackover formation southwest arkansas geochemical and physical controls aapg bull 76 864 894 and a decrease in 11b with depth this suggests that another source of 10b exists in deep basinal environments we know that oil reservoir brines are commonly enriched in boron collins a g 1975 geochemistry of oilfield waters elsevier new york p 496 therefore this study examines organic matter as a possible source of boron during thermal maturation samples of water oil and cored sediments were collected from three stacked hydrocarbon reservoirs in the gulf of mexico sedimentary basin at a depth of 3500 4350 m extraction of boron from organic matter oil and kerogen was done by parr bomb volatilization with mannitol used as a b complexing agent the isotope ratios were measured using negative thermal ionization and compared to in situ analyses using secondary ion mass spectrometry the 11b values of pore filling clays in sandstone reservoirs is 2 2 the b content of the clay averages 144 ppm oil field waters show a range in b content from 8 85 ppm and 11b values from 28 to 37 increasing from the lowest to the uppermost reservoir there is an apparent 11b enrichment of fluids with progressive migration through clay rich sediments very little b ppb was found in the oil but kerogen extracted from the oil source rock sassen r 1990 lower tertiary and upper cretaceous source rocks in lousiana and mississippi implications to gulf of mexico crude oil aapg bull 74 857 878 contains significant b 140 ppm with a 11b of 2 2 similar to the pore filling clay minerals in the sandstones while kerogen comprises only 2 of the sedimentary basin its influence can be significant if b with distinctly low 11b is released over a specific temperature interval during thermal maturation the release of b from organic compounds could cause the observed regional 10b enrichment in waters deep in the gulf coast basin

argillization processes at the el berrocal analogue granitic system spain mineralogy isotopic study and implications for the performance assessment of radwaste geological disposal abstract the el berrocal granite u bearing quartz vein uqv system has been studied as a natural analogue of a high level radioactive waste repository the main objective was to understand the geochemical behaviour of natural nuclides under different physicochemical conditions within this framework the argillization processes related to fracturing and formation of the uranium quartz vein were studied from a mineralogical and isotopic standpoint in order to establish their temperatures of formation and thus complete the geothermal history of the system for this purpose 18 o values were determined for pure mineral from the unaltered granite and quartz from the uranium quartz vein as well as for mixture samples from the hydrothermally altered granite sericitised granite and clayey samples from fracture fillings including the clayey walls of the uranium quartz vein the isotopic signature of quartz from the uranium quartz vein and the monophasic nature of its fluid inclusions led us to conclude that the isotopic signature of water in equilibrium with quartz was approximately in the range from 8 3 to 5 7 v smov its temperature of formation being around 85 120 c the 18 o values of pure sericite from the hydrothermally altered granite calculated by means of the oxygen fraction molar method indicate that its temperature of formation in equilibrium with the aforementioned waters is also in the range from 70 c to approximately 120 c clays from fracture fillings and clayey walls of the uranium quartz vein are usually mixtures in different proportions of illite approximately formed between 70 and 125 c two generations of kaolinite formed at approximately 90 130 c and at around 25 c respectively smectite formed at 25 c and occasionally palygorskite formed either between 30 and 45 c or 19 and 32 c depending on the fractionation equation used these data suggest that sericite from the hydrothermally altered granite quartz from the uranium quartz vein illite and the first generation of kaolinite from the fracture fillings resulted from the same hydrothermal process affecting the el berrocal granite in relation to fracturing under certain physicochemical conditions t 100 c ph 8 and log h 4 sio 4 between 4 and 3 illite and kaolinite can be paragenetic as a result of weathering processes smectite was formed from hydrothermal illite and inherited albite under alkaline weathering while the second generation of kaolinite was formed from smectite under acid conditions and close to the sulphide rich uranium quartz vein palygorskite is an occasional mineral formed probably either during the thermal tail of the above described hydrothermal process or during weathering processes in both cases palygorskite must have formed from alkaline si mg rich solutions finally these data and processes are discussed in terms of natural analogue processes drawing some implications for the performance assessment of a deep geological radwaste repository dgrr

the potential of detrital garnet as a provenance proxy in the central swiss alps abstract detrital garnet is a promising candidate to reliably fingerprint sediment sources in the alps which has so far been complicated by the wide range and similarity of some of the lithologies garnet is present in most alpine sediments is easy to identify is fairly stable and most importantly reflects the type and the metamorphic grade of its source rock in its chemical composition this study aims to establish fingerprints based on detrital garnet composition for the most important tectonic units of the central alps including european penninic and adriatic basement rocks and their respective metasedimentary covers sediments collected from modern rivers which drain representative portions of the individual tectonic units contain a natural mixture of the various garnet populations present in each unit we selected six catchments in southwestern switzerland draining the external massifs helvetic sediments and the penninic nappe stack at the transition of alpine greenschist to amphibolite facies metamorphism in order to test the variability of alpine garnets and the role of inherited pre alpine garnets extraordinary grossular and spessartine rich garnets of the external massifs which experienced greenschist facies metamorphism are clearly distinguishable from generally almandine rich garnets supplied by the higher grade metamorphic penninic nappe stack the variable pyrope grossular and spessartine components of these almandine rich garnets can be used to further distinguish pre alpine alpine eclogite facies and low grade metasedimentary garnets this provenance proxy has the potential to be used for reconstructing sediment sources transport and dispersal patterns in a variety of settings throughout the alpine sedimentary record

discrimination of density flow deposits using elemental geochemistry implications for subtle provenance differentiation in a narrow submarine canyon palaeogene danish north sea abstract elemental geochemistry of 1131 sandstone samples has been used to characterise five palaeogene sandstone members in a system of density flow deposits within an incised submarine canyon danish north sea diagenetic overprinting has complicated the use of most main and trace elements but a group of heavy mineral bound elements with low mobility ti y zr nb and th has proved highly potential for correlation the individual sandstone members exhibit very consistent relations between the heavy mineral elements along the canyon and based on zr ti plots two families of sandstone members can be distinguished the families are recognised on variations in inclination and intersection of linear regression lines which are related to subtle variations in provenance source area the inclination is believed to be controlled by the detrital heavy mineral hm suite and composition whereas the intersections are controlled by the background contribution such as hm inclusions in detrital rock forming minerals e g quartz and or feldspar as well as substituted and or adhered elements in glauconite the correlation pattern has been used to suggest a re interpretation of the stratigraphic relation of some of the sands

geochemistry and diagenesis of stratabound calcite cement layers within the rannoch formation of the brent group murchison field north viking graben northern north sea abstract up to four calcite cemented horizons doggers form impermeable barriers to fluid flow within the middle jurassic rannoch formation and are correlatable across the murchison field calcite precipitated during early diagenesis within high porosity permeability sandstones at the top of coarsening shoaling upward shoreface cycles calcite 13c and 18o compositions range from 4 1 to 13 4 pdb and 6 6 to 16 7 pdb respectively sr concentrations of up to 1334 ppm are consistent with marine carbonate sources probably shell fragments but no viable intraformational carbonate source has been identified in the murchison field area initial 87sr 86sr compositions 0 71109 0 71266 are higher than middle jurassic seawater 0 7073 and consistent with precipitation from modified porewaters containing significant proportions of continentally derived meteoric fluids enriched in 87sr as a result of basement weathering or percolation through hinterland soils unconsolidated detritus an internal source of 87sr is not considered viable in view of the high proportion up to 25 clastic constituents of unaltered detrital alkali feldspar and mica within the rannoch formation geochemical and isotope data indicate correlations between increasing 18o composition and increasing iron and magnesium content within calcite calcium concentrations decrease with increasing 18o for calcites geochemical data trends can be interpreted differently in terms of either static or evolving 18o porewater models static 18o porewater models using jurassic early cretaceous meteoric water 18 o 6 smow predict cement precipitation temperatures of 17 77 c however 13c compositions are more depleted than those typical of carbon derived from shell debris and correlation between decreasing 18o and decreasing 13c suggests modification of a meteoric derived porewater system during burial via contribution of low 13c carbon derived from a deep basinal source however it is difficult to constrain accurately the degree to which porewater 18o may have evolved during burial the degree to which porewater 18o could have evolved from that of a jurassic early cretaceous meteoric water can be loosely constrained as from 18 o 6 smow to 18 o 2 smow if the temperature at which the most 18o depleted cements precipitated is limited by present day bottom hole temperatures 110 c for wells currently at maximum burial depth

boron lithium and nitrogen isotope geochemistry of nh4 illite clays in the fossil hydrothermal system of harghita bai east carpathians romania abstract coarse 2 0 0 2 m and fine boron in nh4 i s clays ranges from 513 to 1457 ppm and reached 1000 ppm in the k i nh4 k i the 11b measured in nh4 i s ranges from 12 6 to 22 4 0 3 and in k i nh4 k i is consistently 5 5 to 5 1 0 3 boron isotopes systematically become lighter in the nh4 i s series as temperature increased from 90 to 270 c low li content 1 to 8 ppm was found in illitic clay fractions the 7li shows negative values ranging from 8 6 to 12 3 0 8 for the coarser 2 0 0 2 m nh4 i s clays and from 4 3 to 14 1 1 for the finer the 11b of k i nh4 k i clays reflect a magmatic source whereas the nh4 i s series is consistent with the influx of isotopically light b waters derived from hydrothermal leaching of continental evaporites and or organic rich sediments the 7li signature measured on k i nh4 k i clays also support a magmatic fluid enriched in heavy li followed by precipitation of coarser nh4 i s from more recent sedimentary contributions of isotopically light li this interpretation is also supported by the 15n which reflect an influx of waters from an organic sediment origin the 15n of 14 6 0 6 measured on nh4 i s could be attributed to the presence of meteoric waters mixed with hydrothermal fluids the isotopic data obtained trace the mobility of magmatic and organic sedimentary components in the upper continental crust

reliability and application of detrital opaque fe ti oxide minerals in provenance determination a survey of detrital opaque fe ti oxide minerals in holocene sands derived exclusively from known source rocks in the rocky mountains usa semi arid climate high relief and the appalachian mountains usa humid climate low relief shows that despite obvious differences in weathering rates the abundance of detrital ilmenite relative to parent rocks is similar in these two regions because ilmenite is very common in many crystalline rocks ilmenite is considered to be a useful fe ti oxide mineral for varietal studies about 30 to 50 of detrital fe ti oxide minerals are polymineralic grains with intergrowths of two or more phases discriminant function analysis indicates that morphological varieties of detrital fe ti oxide minerals in combination with their chemical compositions are useful guides to provenance an igneous or metamorphic source of 96 of the holocene samples is correctly identified by this method the method is used to determine the relative contribution of igneous and metamorphic source rocks to the sandstones of the part of the tertiary renova formation which was deposited within a dissected magmatic arc in southwestern montana usa a separate discriminant function is calculated using the chemical compositions of detrital ilmenite and morphological properties of detrital fe ti oxide minerals in rocky mountain holocene sands classification of detrital fe ti oxide minerals in renova sandstones using this function suggests that igneous and metamorphic rocks contributed 77 and 23 respect ively to the renova sandstones in this area

role of permeability versus temperature in the distribution of the fine 0 2 μm clay fraction in the chipilapa geothermal system el salvador central america abstract detailed x ray diffraction of clay minerals from the less than 0 2 m fraction of altered rocks has been carried out on cuttings and cores from three boreholes ch7 ch9 and ch7b from the geothermal field of chipilapa el salvador central america in most of the low permeable horizons the vertical distribution of i s and c s mixed layers fairly agrees with the general scheme of di smectite to illite and tri smectite to chlorite conversion series with increasing depth max 2600 m and temperature max 220 c the deepest parts of the wells are characterized by chlorite and illite rich illite smectite mixed layers i sr 1 in close agreement with the measured temperature 170 220 c within fracture controlled permeable horizons the distribution of clay minerals strongly disagrees with the classical pattern of di smectite to illite and tri smectite to chlorite conversions observed in low permeable horizons great amounts of smectites and or smectite rich mixed layers occur at temperatures which strongly exceed the current range of smectite stability in natural systems up to 205 c similar discrepancies may also be viewed from chlorite crystallinity in well ch9 and smectite content in smectite rich chlorite smectite mixed layers in well ch7b these high temperature smectites are considered as present or very recent metastable phases representing the first step of kinetically controlled conversion series toward illite and or chlorite such phenomena are restricted to the levels in which the present hydrodynamic conditions promote the crystallization process boiling and mixing of fluids with contrasting temperatures high temperature smectites and smectite rich mixed layers may be of great interest for the understanding of the very recent evolution of geothermal reservoirs they do not only indicate the present horizons of active fluid circulations in geothermal wells smectite coatings at the wall of fractures but they are also potential guides in the determination of the horizons in which permeability has recently decreased

evaluation of garnet discrimination diagrams using geochemical data of garnets derived from various host rocks abstract this work is an attempt to evaluate six different garnet discrimination diagrams one binary diagram and five ternary diagrams commonly used by many researchers the mineral chemistry of detrital garnet is a useful tool in sedimentary provenance studies yet there is no clear cut understanding of what garnet type originates from which host lithology several discrimination diagrams exist for garnet showing distinct compositional fields separated by strict boundaries that are thought to reflect specific types of source rocks for this study a large dataset was compiled n 3532 encompassing major element compositions of garnets derived from various host lithologies including metamorphic igneous and mantle derived rocks in order to test the applicability of the various discrimination schemes the dataset contains mineral chemical data collected from the literature complemented with some new data n 530 from garnet bearing metamorphic and ultramafic rocks in austria and norway discrimination of the tested diagrams only works for a small group of garnets derived from mantle rocks granulite facies metasedimentary rocks and felsic igneous rocks for other garnet types the assignment to a certain type of host rock remains ambiguous this is considered insufficient and therefore the evaluated diagrams should be used with great care we further apply compositional biplot analysis to derive some hints towards future perspectives in detrital garnet discrimination

patterns of bedrock channel erosion on the boso peninsula japan three channels on the boso peninsula japan were examined to assess how cross sectional to reach scale channel morphology relates to substrate variables and how cross sectional to reach scale erosional patterns relate to basin scale longitudinal profile two of the channels shichiri gawa and torii zawa are deeply incised into interbedded sandstone and mudstone whereas the third channel futama gawa is incised into mudstone reach scale channel morphologies include knickpoints chutes and pools plane beds and both transverse and longitudinal bed erosional features step backwater modeling of a september 1996 typhoon related flood flow along each channel indicated that unit stream power is highly variable downstream stream power minima are associated with bends and with coarse clast deposition magnitude of erosional bed features correlates with hydraulics and flow energy expenditure along futama gawa and with variability in substrate resistance along shichiri gawa and torii zawa thickness and ori