relationship between deep diagenetic quartz cementation and sedimentary facies in a late ordovician glacial environment sbaa basin algeria abstract production of hydrocarbons from sandstone reservoirs is complicated by their diagenetic history although many aspects of sandstone diagenesis are well studied the character and processes of glacial associated diagenesis remain unknown to address this problem the origin conditions and timing of quartz cementation in glacial ordovician sandstones of the sbaa basin algeria were constrained on the basis of fluid inclusion microthermometry electron microprobe data and quantification by image analysis combined with optical and cathodoluminescence microscopic studies samples of the cambro ordovician formations in the sbaa basin were investigated from four wells at burial depths between 2 0 and 2 5 km and at ambient temperatures between 110 and 130 c quartz cements range in abundance from 1 to 27 of bulk rock volume in all wells three separate phases of quartz cementation are readily distinguished by cathodoluminescence microscopy the main silica sources are interpreted to be dissolution of feldspar grains intergranular quartz dissolution stylolitization and illitization of smectite fluid inclusion data depths indicate that quartz overgrowths precipitated between 100 to 160 c this range of temperature corresponds to the visean namurian burial phase according to the basin thermal history image analysis demonstrates intergranular quartz dissolution also called pressure dissolution in the presence of thin illite coatings around detrital quartz grains these clay coatings were mechanically emplaced below the ordovician ice sheet by pressurized meltwater circulation and subsequent fluid expulsion within sandy subglacial soft bedrock that was initially porous and permeable therefore the subglacial bedrock lithology directly influenced quartz diagenesis because an increase in the content of clay matrix or the presence of an argillaceous layer can block the circulation of fluids flowing below the ice sheet which prevents the formation of clay coatings quartz cements in this environment are favored in less compacted areas without clay coatings and with high porosity the results of this study clearly illustrate the relationships among sedimentary facies ice dynamics and diagenetic architecture of the formation these types of processes may control the porosity permeability distribution in other glacial sandstone successions through quartz cementation and chemical compaction

a review of the intracontinental porphyry deposits in the middle lower yangtze river valley metallogenic belt eastern china abstract the middle lower yangtze river valley metallogenic belt mlyb is one of the most important metallogenic belts in eastern china and contains many important porphyry deposits these deposits include the tongshankou cu mo jiguanzui cu au chengmengshan cu mo wushan cu mo fengshandong cu au dingjiashan cu yangjishan au shaxi cu au dongguashan cu au shujiadian cu and anjishan cu deposits etc in this review we summarize the geological characteristics including the stratigraphy structure ore bearing porphyry types vein characteristics and wall rock alteration metallogenic ages and petro geochemistry of representative porphyry deposits in the mlyb we conclude that porphyritic magmatism and metallogeny have occurred in three stages the early ca 149 135 ma and late ca 123 105 ma stages comprise mainly porphyry skarn mineralization whereas the middle ca 133 125 ma stage comprises porphyry mineralization ore bearing porphyries in the mlyb are the high k calc alkaline to calc alkaline series with the majority possess adakitic geochemical signature the ore bearing porphyries with adakitic signature may have originated from magma mixing produced by the delamination of enriched lithospheric mantle and partial melting of the thickened lower crust the enriched mantle derived mafic melts component are very important for generating fertile magma and the 34s and 18o values suggest that ore forming materials were magma derived compared with porphyry deposits in typical magmatic arc settings porphyry deposits in the mlyb do not contain advanced argillic lithocaps or high to intermediate sulfidation systems and the magmatic and ore forming material sources are also very different

kaolinitic meniscus bridges as an indicator of early diagenesis in nubian sandstones sinai egypt discussion j marcelo ketzer l fernando de ros and norberto daniuniversidade federal do rio grande do sul instituto de geocie ncias avenue bento gonc alves 9500 91501 970 porto alegre brazil e mail jm ketzer com br lfderos inf ufrgs br norberto dani ufrgs br keywords clay in ltration diagenesis kaolinite microtexture sandstone introductionthe recently published paper by du bernard c moraes de ros 1990 weibel 1998 salem et al 2000 fig 1a this is becausemechanical in ltration is most effective andextensive in semi arid climatic conditions kess ler 1978 walker et al 1978 moraes de ros 1990 under which smectitic clays are the mostcommon weathering products conversely kaoli nite is characteristically formed in humidclimatic conditions under which in ltration isuncommon or volumetrically insigni cant ketzer et al 2003a despite nding the occurrence described by dubernard carrio schaffhauser 2003 interesting we identi ed problems in their methodology anddiscussion the present discussion aims to com ment on these points and to suggest an alter native interpretation of the origin timing andeffects on compaction and reservoir quality of thedescribed clays in the nubian sandstones origin of kaolinitedu bernard carrio schaffhauser 2003 de scribed two types of kaolinite occurrence in thenubian sandstones i nely crystalline 1 5lm and ii coarsely crystalline aggregates 50lm the nely crystalline kaolinite consists of brown under uncrossed polarizers colour pore llingaggregates with meniscus shape a close inspec tion of the backscattered bse scanning elec tronic microscope sem images provided by dubernard and carrio schaffhauser their g 5cand d suggests that the meniscus aggregates arecomposed of several kaolinite booklets g 1b this morphology is typical of diagenetic authi genic kaolinite such evidence indicates an au thigenic origin for the nely crystalline kaolinite as opposed to the in ltrated origin proposed bydu bernard and carrio schaffhauser hence thiskaolinite most probably resulted from the in situreplacement of mechanically in ltrated possiblysmectitic clay minerals owing to active circula tion of meteoric water through the sandstones the origin of the uids responsible for thekaolinitization of the precursor in ltrated claysshould be constrained by o and h isotopicanalyses of the kaolinite morad et al 2003 the preservation of the meniscus morphology ofthe in ltrated clay aggregates after kaolinitizationresulted from the inheritance of the texture of theprecursor clay mineral by the kaolinite it is nosurprise that such preservation occurs as pseudo morphic replacement is rather common amongclay minerals e g in the chloritization or illiti zation of kaolinite morad et al 1998 de ros 1998 the variable in places random orientationof some kaolinite booklets is typical of authigenicaggregates and thus has no direct relationshipwith differences in water volume within themeniscus as suggested by du bernard andcarrio schaffhauser p 1227 additionally therelevance of the theoretical discussion on theaspects of the menisci geometry pp 1225 1227 to the interpretations of the authors is not clear x ray diffraction analysis from the 2 lmfraction revealed that kaolinite is the single claymineral present in the samples as shown in theprovided x ray diffractogram their g 4 thissedimentology 2005 52 213 217

geochronology and zircon hf isotope geochemistry of granites in the giant chalukou mo deposit ne china implications for tectonic setting abstract in this contribution the largest porphyry mo deposit in ne china chalukou is selected to provide insights into the tectonic evolution of ne china the deposit was considered to be rift related or climax type porphyry mo deposit developed in an extensional setting while other researchers attributed its formation to the subduction of the paleo pacific ocean in view of different granite petrogenesis between rift type and subduction type porphyry mo deposits geochronological and zircon lu hf isotope studies have been carried out on granitic rocks associated with the chalukou deposit zircon grains from the ore host monzogranite and ore causative granite porphyry yield weighted mean 206pb 238u ages of 166 2 ma and 152 2 ma with molybdenite samples yielding a re os isochron age of 150 2 ma indicating a jurassic age for both granitic intrusion and mo mineralization zircon ehf t values of monzogranite and granite porphyry range from 0 9 to 3 0 and from 1 4 to 0 5 respectively when integrated with published zircon lu hf isotopic data our data suggest that the barren granites both pre and post ore were mainly derived from mantle derived juvenile rocks whereas the syn ore granite requires additional involvement of old continental crust thus a contribution of continental crust to mo mineralization is suggested the petrogenesis and geochemical data reveal that the chalukou deposit is a subduction related porphyry mo deposits and not rift related integrated evidence links its formation to the southeastward subduction of the mongol okhotsk ocean instead of the westward subduction of the paleo pacific ocean

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

provenance signatures recorded in transgressive sandstones of the upper cretaceous iberian seaway abstract maximum mesozoic transgressions flooded many continental areas worldwide forming a wide and shallow seaway on the iberian microplate during the late cretaceous several siliciclastic and mixed siliciclastic carbonate units developed along the iberian massif cratonic area while at the same time epeiric carbonate platforms spanned iberia these siliciclastic deposits unconformably cover the variscan basement as well as the permian and triassic deposits this study focuses on sandstone provenance in central spain in a transgressive relatively quiet tectonic setting with a wide rock variety in the potential source areas results shown in this paper can be applied in analogue systems transgressive sandstones often form important hydrocarbon reservoirs due to their high primary porosity the cretaceous siliciclastic deposits are included in four formations ranging in age from the cenomanian to the early coniacian the deposits were initially of fluvial origin followed by a coastal tidal setting quantitative petrographic analysis of sandstones from these formations reveals compositional variations related to provenance and weathering degree the oldest formation utrillas fm was deposited on a paleorelief surface sandstone composition changes from arkosic sandstones in the depressed area petrofacies p1a to younger quartzarenites when sediments were deposited on top of the paleotopographic high petrofacies p1b quartz grains in both sub petrofacies are angular to subangular and the framework is poorly sorted intense weathering conditions are deduced for petrofacies p1b manifested by grain infiltration clay coatings and the absence of plagioclase grains and alteration features on k feldspars all these observations have been related to wetter conditions during p1b deposition main source areas of the utrillas fm were ordovician metasediments and orthogneisses permian volcanic rocks and triassic buntsandstein facies petrofacies 2 encompasses the three coastal tidal formations constituted mainly by subarkoses generally showing a subangular and poorly sorted framework the deduced source areas are mainly associated with variscan granitoids pre ordovician schists and paragneisses and ordovician metasediments glauconite and carbonate grains support intrabasinal inputs the low degree of sorting of this petrofacies related to a low energy sedimentary environment produced lower values of original porosity compared to transgressive sandstone hydrocarbon reservoirs also intrabasinal inputs promoted carbonate cementation and contribute to almost occlude the porosity

diagenesis and reservoir quality evolution of incised valley sandstones evidence from the abu madi gas reservoirs upper miocene the nile delta basin egypt abstract elucidation of the distribution of diagenetic alterations in incised valley sandstones within a sequence stratigraphic framework allows a better understanding of their reservoir quality evolution during burial gas reservoirs of the upper miocene abu madi formation present day depth 3350 m temperature 116 the nile delta basin egypt consist of lowstand systems tract lst fluvial and transgressive systems tract tst estuarine sandstones deposited in an incised valley these sandstones have a wide range of porosity 2 to 29 and permeability 0 01 to 6071 md which reflect both depositional facies and diagenetic controls diagenetic events that influenced the reservoir quality evolution include mainly the formation of extensive grain rimming fe mg chlorite mechanical compaction of ductile grains pressure dissolution of quartz and quartz cementation the chlorite rims distributions of which are not clearly related to sequence stratigraphy have preserved reservoir quality by inhibiting quartz cementation but have increased microporosity values in the reservoirs calcite cementation 18o 13 5 to 6 0 13c 14 3 to 1 0 and 87sr 86sr 0 707124 to 0 708181 has not influenced the overall reservoir quality evolution of the sandstones because of its localized occurrence other diagenetic events that have little influence on reservoir quality include the more frequent formation of kaolin in the lst fluvial sandstones and formation of pyrite in the tst estuarine sandstones this study demonstrates the possibility of constraining and evaluating the impact of diagenetic alterations on reservoir quality evolution in incised valley deposits and their sequence stratigraphic distribution and thus has an important impact on hydrocarbon exploration in such settings

diagenesis provenance and reservoir quality of triassic tagi sandstones from ourhoud field berkine ghadames basin algeria the triassic tagi trias argilo greseux inferieur fluvial sandstones are the main oil reservoirs in the berkine basin algeria nonetheless their provenance and diagenesis and their impact on reservoir quality are virtually unknown samples from the ourhoud field representing the lower middle and upper tagi subunits were studied using a combination of petrographic mineralogical and geochemical techniques the lower tagi sandstones have an average framework composition of q98 3f0 6r1 1 and 95 of the quartz grains are monocrystalline by contrast the middle upper tagi sandstones have an average framework composition of q88 3f9 8r1 9 and 79 7 of the quartz grains are monocrystalline the lower tagi quartz arenites derived from paleozoic siliciclastic rocks whereas the middle upper tagi subarkoses originated mainly from metamorphic terrains this change in provenance is a potential criterion for correlation within the tagi also this change has contributed to the significantly different diagenetic paths followed by the lower tagi quartz arenites and the middle upper tagi subarkoses grain coating illitic clays are abundant in the lower tagi where they exert a critical control on reservoir quality these clays are interpreted as pedogenic and or infiltrated in origin and to have had in part smectitic precursors shallow burial fe dolomite cementation was favored in the downthrown block of the field bounding fault where it contributed to the poor reservoir quality magnesite siderite cements are multiphase the earliest generation is composed of fe rich magnesite that precipitated during shallow burial from hypersaline fluids with high mg ca ratios probably refluxed residual brines associated with the liassic evaporites later magnesite siderite generations precipitated during deeper burial from waters with progressively higher fe mg ratios authigenic vermicular kaolin largely consists of dickite that replaced previously formed kaolinite dickitization was followed by late stage illitization related to the dissolution of detrital and authigenic k feldspar quartz the most abundant cement was mainly sourced by the pressure or clay induced dissolution of detrital quartz and is a critical factor controlling the reservoir quality overall quartz cement is more abundant in the lower tagi than in the middle upper tagi and this increase correlates with a decrease in average porosity within the lower tagi quartz cement abundance is stratigraphically very variable which is in part related to facies controlled variations in grain coating clay resulting in major vertical variations in reservoir quality anhydrite and barite cements postdate quartz overgrowth the sulfate necessary for their formation was likely sourced by deep subsurface dissolution of late triassic liassic evaporites

diagenetic heterogeneity and reservoir quality fluvial deltaic and turbiditic sandstone reservoirs potiguar and reconcavo rift basins brazil fluvial and lacustrine deltaic and turbiditic sandstones are major hydrocarbon reservoirs in the onshore lower cretaceous potiguar and reconcavo rift basins in northeastern brazil diagenetic elements including mechanically infiltrated mi clay calcite dolomite and chlorite show distinct distribution patterns at interwell and field wide reservoir scales such distributions and thereby diagenetic heterogeneity have been modeled based on thin section core well log and petrophysical data at the interwell scale relationships between sandstone body geometry and the distribution of diagenetic elements are a critical aspect of reservoir heterogeneity at this level 1 mi clay concentrations occur in fluvial reservoirs following the orientation of paleochannels generating strong compartmentalization of the reservoirs 2 calcite cement appears either concentrated near sand shale contacts peripheral distribution or dispersed in the interior of the sandstone layers scattered distribution 3 dolomite cement may appear concentrated along laminations in cross stratified sandstones causing a decrease of one order of magnitude in the effective horizontal permeability and 4 authigenic chlorite is observed to reduce more significantly the permeability in fine grained sandstones than in coarse grained sandstones an effect that may cause important modifications in the permeability structure of the reservoirs at the field wide scale diagenetic heterogeneity includes 1 stratigraphic zonation of diagenetic properties in fluvial reservoirs 2 increasing carbonate cementation toward the border of the hydrocarbon accumulations in deltaic reservoirs and 3 distinct patterns of carbonate cementation observed in channel fills and lobes in turbiditic reservoirs incorporating the distribution and effects of diagenetic elements into the interwell and field wide geological modeling is essential to achieve a realistic reservoir representation such incorporation is performed by the integration of diagenetic properties with other geological attributes including nature and distribution of depositional facies structural elements and stratigraphic framework this procedure improves reservoir quality evaluation and leads to more precise prediction of reservoir performance

effects of soil and vegetation on runoff along a catena in semi arid spain runoff and infiltration were investigated on abandoned fields of patchy vegetation in semi arid spain during 15 months of natural rainfall and by rainfall simulations the aim was to ascertain sources and sinks of runoff and the effects of soils and plant cover soils of the catena developed from mica schists of the upper hillslopes fan deposits of the lower hillslopes and an alluvial terrace at the bottom runoff from natural events were from three sets of three pairs each of 10 2 m runoff plots the pairs of each set had different densities of plant cover the sets were vegetated with tussock grass stipa tenacissima a shrub anthyllis cytisoides and a bush retama sphaerocarpa nineteen natural rainfall events of intensities up to 18 mm h produced 400 mm of rain during the study period because the rainfall threshold for runoff production was about 20 mm only eight events produced runoff the rainfall simulations used a sprinkler that produced 50 mm h of rain for 30 minutes runoff was recorded each minute in 0 24 m2 bounded plots the depth and structure of the soil mantle provide the main controls on runoff rates which are lowest on the lower fan deposits and highest on the thin upslope soils the river bank terrace with a surface covered by crusts and mosses also yields relatively high runoff in general vegetation density varies inversely with runoff nevertheless shrub and bush litter favor runoff as does a particular spatial distribution of individual plants on the hillslope settling of the upper few centimeters of soils of the alluvial fan following cessation of cultivation 15 to 40 years ago has produced a near surface compacted layer favoring shallow subsurface runoff apparently contradictory results between runoff plots and rainfall simulations are the result of differing processes

contribution of mantle components within juvenile lower crust to collisional zone porphyry cu systems in tibet most porphyry cu mo au deposits are found in magmatic arcs worldwide and are associated with hydrous high fo2 calc alkaline magmas derived from a mantle wedge that was metasomatized by the fluids from a subducted oceanic slab recently such deposits have been documented as occurring widely in collisional settings where they are associated with potassic magmas generated during the collisional process but the genesis of the fertile magmas and the mechanism of metallic enrichment remain controversial here we present new geochemical and sr nd hf isotopic data from the post collisional fertile and barren porphyries of the miocene gangdese porphyry belt in the tibetan orogen an orogen formed by the collision of india and asia in the early cenozoic both types of porphyry are characterized by high k2o contents and have geochemical affinities with adakite but the fertile magmas were most likely derived from the melting of a thickened juvenile mafic lower crust formed by the underplating of earlier asthenospheric melts at the base of crust whereas the derivation of the barren magmas involved variable amounts of old lower crust in tibet the melting of sulfide bearing phases in the juvenile mantle components of the tibetan lower crust probably provided cu au and s to the fertile magmas the breakdown of amphibole during melting at the source released the fluids necessary for the formation of the porphyry cu deposits in tibet the thickened crust up to 70 80 km due to collision is thought to be responsible for a decrease in the fo2 of the fertile magmas during their ascent to the upper crust thus preventing the generation of more porphyry cu au and epithermal au deposits in this collisional zone

nari calcrete outcrop contribution to ancient agricultural terraces in the southern shephelah israel insights from digital terrain analysis and a geoarchaeological field survey a field survey revealed that byzantine and early arab ca 5th to 8th century c e agricultural systems in the semi arid region of the shephelah central israel were similar to runoff agricultural systems in the arid region of the negev southern israel this similarity led to the hypothesis that systems in the shephelah also function as runoff farms this hypothesis is not trivial since runoff values in semi arid regions are generally low due to intensive but short rainfall events and due to the presence of sink patches that absorb runoff on slope surface the aim of the current research is to examine whether runoff potential in a representative agricultural system in the shephelah is sufficient for sustaining runoff farming a geoarchaeological field survey and digital terrain analysis show that large nari calcrete outcrops on the footslopes generate high runoff values that improve water potential hydrological simulations and calculations show that 230 mm of direct rainfall generates a water potential equivalent to 300 mm of direct rainfall in view of these results it is reasonable to conclude that the presence of nari enabled runoff agricultural farming in the shephelah region even in drought years

diagenesis and reservoir quality evolution of fluvial sandstones during progressive burial and uplift evidence from the upper jurassic boipeba member reconcavo basin northeastern brazil the reservoir quality of fluvial sandstones of the upper jurassic boipeba member reconcavo basin northeastern brazil is highly heterogeneous and controlled by eodiagenesis under semiarid climate mesodiagenesis during burial to a depth of 3500 m and telodiagenesis due to local uplift eodiagenesis resulted in mechanical compaction calcite cementation clay infiltration and limited grain dissolution whereas mesodiagenesis resulted in the precipitation of calcite cement and quartz over growths intergranular quartz grain dissolution chloritization and illitization of smectite and albitization of feldspars sandstones continuously buried at maximum burial depths of about 1600 m t 65 c since 125 ma display a relatively greater degree of mesogenetic modifications and on average poorer reservoir quality than sandstones that were buried deeper 2100 m t 75 c prior to uplift but only since 13 ma uplift which affected the sequence along the western border of the basin has resulted in telogenetic dissolution of framework silicates and formation of kaolinite relatively good reservoir quality in the deeply buried sandstones occurs when 1 the grains are coated with a thin layer of chloritized infiltrated smectite 2 there is little or no pseudomatrix and 3 there are widely scattered patches of eogenetic calcite cement that supported the framework of sandstones against compaction

clay illuviation and mechanical clay infiltration is there a difference abstract soil scientists attribute the presence of coatings of oriented clay in soils and sediments to the process of clay illuviation which is a process that occurs at the earth s surface and may penetrate to a depth of several metres geologists attribute coatings of oriented clay in coarse sediments to a process of mechanical infiltration of muddy river water or muddy overland flow clay illuviation is a climate dependent process seasonal climate which is restricted to the vadose zone the source of the translocated material is internal i e material from upper soil layers is transported to deeper layers the resulting accumulation horizons are up to 2 m thick and continuous in clayey deposits but in sandy deposits they are discontinuous and may reach a depth of several metres the process of mechanical infiltration is not climate related and its effect is not restricted to the vadose zone but may reach far below the ground water table the source of the transported material is external it is provided by muddy water entering the soil the accumulations are supposed to be deep and continuous the environment of muddy waters with higher electrolyte concentrations than water that percolates the soil upon first rain and a gradient of particles coarser than clay should however preclude mechanical infiltration because 1 clays will tend to flocculate 2 both coarser suspended material and flocculated clay will tend to clog the pore system and 3 below ground water transport of suspended material will be virtually impossible because of low percolation velocity in addition flocculated clay will not produce oriented coatings upon desiccation the model of mechanical infiltration is not supported by theory or observations we suggest that the process of mechanical infiltration of clay needs further study to prove whether it is different from clay illuviation in soils the distinction between the two is of utmost importance for the interpretation of paleosols

diagenetic history and provenance of devonian terrestrial sandstones at the margin of gondwana padeha formation eastern alborz iran abstract the northern margin of gondwana in iran rifted in the devonian forming a passive continental margin to the paleotethys ocean the details of which are obscured by later collision a record of the early phase of opening of paleotethys is preserved in the 600 m thick padeha formation a middle devonian terrestrial rift basin succession the sandstones are quartz arenite sub arkose and arkose and contain minimal detrital matrix 1 bulk rock geochemistry according to major elements suggests a source to the sandstones that was dominated by i type granite but also based on trace elements included small amounts of intermediate or mafic rocks low zr and hree contents suggest little or no sandstone in the source area and thus low abundance of fine grained heavy minerals

the ediacaran sedimentary architecture and carbonate productivity in the atar cliffs adrar mauritania palaeoenvironments chemostratigraphy and diagenesis abstract the neoproterozoic strata of the taoudeni basin west african craton display a single glaciogenic deposit late cryogenian in age and included within a stratigraphic marker triad of tillite carbonate and bedded chert this work is focused on the analysis of the sedimentary architecture and episodic carbonate productivity related to its transgressive deglaciation recorded in the atar cliffs of adrar mauritania it offers a joint chemo event and sequence stratigraphic analysis that allows us to control problems of stratigraphic completeness and time resolution necessary for regional and worldwide stratigraphic correlation in the atar cliffs the cap carbonate sequence is underlain by a composite unconformity that comprises the pan african i discordance and an inherited palaeorelief associated with the glaciation the transgressive sequence began with accumulation of a sheet like apron onlapped by a toe of slope to basin transition with cap carbonates bedded cherts and distal turbidites tichilit el beida shales the carbonate strata of the atar cap carbonate sequence have recorded both dolomitization and dedolomitization processes destroying the original cement textures carbon isotope values from the sheet like apron range from 0 to 0 6 were directly controlled by the reworking of the underlying atar strata and do not reflect primary variations in seawater composition the general pattern of 13 c fluctuations within the overlying incomplete cap carbonate sequence is consistent with other post late cryogenian strata except in the initial shift from slightly to moderately negative values recognized elsewhere that is not preserved in the study area carbon isotope values in the preserved upper part of the cap carbonate record a pronounced rise in 13 c from 6 2 to highly enriched values 3 7 followed by the final demise of carbonate productivity the cap carbonate sequence is topped by an erosive unconformity succeeded by the recovery of carbonate accumulation represented by an onlapping dolostone deposited in coastal to foreshore environments there the carbon isotope values reflect the return to moderately negative values ranging from 0 9 to 2 0 the palaeogeographic development of a palaeorelief associated with the end of glacial conditions and deposition of the onlapping atar cap carbonate is related to the presence of interbedded felsic bentonites and phenocrysts and reflects the intermittent influence of a neighbouring explosive volcanism

zircon dating sr and nd isotopes and element geochemistry of the khalifan pluton nw iran evidence for variscan magmatism in a supposedly cimmerian superterrane abstract the khalifan pluton of the sanandaj sirjan zone is composed of a type peraluminous leucogranites with nd model ages around 1 2 ga it intrudes an unfossiliferous sedimentary sequence previously considered as cretaceous by analogy with neighboring areas however zircon u pb shrimp and pb pb sequential evaporation dating have revealed that khalifan granites are carboniferous with a precise age of 315 2 ma this is the first reliable variscan age obtained so far in this area but there are geological indicators that other small plutonic bodies might also be variscan the existence of carboniferous granite rocks in the sanandaj sirjan zone casts doubts on whether it was a part of the cimmerian superterrane detached from east gondwanide terranes because these characteristically lack variscan magmatism the age chemical features and nd isotopes of khalifan granites are similar to those of the southernmost urals and tien shan so that we tentatively suggest that this area bears a middle asian instead of cimmerian linkage

lateral moisture flow beneath a sandy hillslope without an apparent impeding layer part of a small drainage basin on the sevilleta national wildlife refuge about 25 km north of socorro nm was intensively instrumented with soil monitoring equipment to estimate natural ground water recharge soil moisture data were analysed with special attention to characterizing the influence of topography on the direction of vadose water flow paths in fine to medium aeolian sand moisture content data were obtained by the neutron scattering technique and hydraulic head data were obtained using tensiometers in addition tracer experiments were conducted on a sandy hillslope to delineate the flow paths of vadose water the results indicate that there is a strong lateral component to unsaturated flow on a hillslope even in the absence of apparent sublayers of much lower permeability darcian calculations estimate the long term steady deep flux beneath a concave location to be about 4 per cent of an assumed mean annual precipitation of 20 cm the deep soil water flux downward varied by several orders of magnitude during the 17 month period of record

infiltrated clays in fluvial jurassic sandstones of reconcavo basin northeastern brazil abstract fluvial sandstones and conglomerates of the sergi formation a jurassic unit of reconcavo basin northeastern brazil contain significant amounts of interstitial detrital clays which are interpreted as the product of early mechanical infiltration developed in an arid semi arid environment within such an environment the lowered water table allowed muddy waters of episodic runoff to infiltrate through the coarse alluvium concentrating the clays in the upper phreatic zone near the sources of influent seepage petrographic textures considered to be typical of mechanically infiltrated mi clays are herein presented using examples from the sergi formation these textures include 1 ridges and bridges 2 geopetal fabrics 3 loose aggregates 4 anisopachous coatings of tangentially accreted lamellae cutans 5 massive aggregates and 6 shrinkage patterns developed during diagenesis in addition their detrital aspect as revealed by sem observations and the presence of impurities in the interior of the clay aggregates were also used as evidence for the interpreted origin of the clays in most hydrocarbon reservoirs in the sergi formation the clays described in this paper are among the main controls on porosity and permeability distribution commonly zones with maximum clay concentration are the main internal permeability barriers within the sergi formation reservoirs

genesis and magmatic hydrothermal evolution of the yangla skarn cu deposit southwest china the yangla skarn cu deposit 150 mt at 1 03 cu is located in the central segment of the jinshajiang metallogenic belt within the sanjiang three rivers region southwest china skarn orebodies are mainly developed between different units of devonian carbonate and quartz sandstone rocks with stratiform like shapes or within the contact zone between granitoids and marbles re os dating of molybdenite intergrowth with chalcopyrite yielded a well constrained 187re 187os isochron age of 232 0 1 5 ma with a weighted average age of 231 8 1 3 ma both coeval with the related intrusions 233 1 1 4 and 231 0 1 6 ma at 2 by zircon u pb dating from our previously published work field and textural relationships indicate three hydrothermal stages characterized by assemblages of prograde skarn pre ore stage retrograde skarn and cu fe mo bi sulfides main ore stage and pb zn sulfides associated with calcite and quartz late ore stage as well as one supergene stage marked by secondary cu mineralization malachite and azurite skarns contain garnets with andraditic compositions ad96 gr2 3py0 1 and clinopyroxene two series hd6di94 and hd86di13jo1 with low mn fe ratios 0 1 typical of cu skarn deposits worldwide three stages of fluid evolution were observed by a detailed fluid inclusion study 1 early fluids were trapped under two phase conditions as evidenced by the coexistence of brine homogenization temperatures 560 600 c average salinity 49 4 1 7 wt nacl equiv n 33 and vapor rich inclusions in pre ore stage andradite and diopside trapped at 600 bars or a depth of approximately 2 km assuming lithostatic pressure conditions 2 main ore stage fluid inclusions in quartz were also trapped under two phase conditions boiling as identified by the coexistence of vapor and liquid rich fluid inclusions liquid rich inclusions homogenized between 312 and 389 c average 350 24 7 c n 20 with salinities of 2 4 to 5 6 wt nacl equiv average 4 2 0 9 wt nacl equiv n 13 and a depth of 2 km 200 bars hydrostatic pressure conditions 3 late ore stage fluids are represented by inclusions in calcite characterized by homogenization temperatures ranging from 220 to 290 c average 249 27 c n 14 and salinities between 2 1 and 8 0 wt nacl equiv average 4 6 1 5 wt nacl equiv n 11 sulfur isotope compositions of sulfide minerals pyrite chalcopyrite pyrrhotite and molybdenite from the main and late ore stage have a narrow range of 34s values from 1 9 to 2 6 consistent with a magmatic origin calcite in the late ore stage has 13c values ranging from 3 2 to 5 9 and 18o from 7 2 to 18 0 distinct from the host rock marble compositions 13c 1 2 4 3 18o 10 8 23 9 when corrected for temperature 250 c estimated from fluid inclusion analysis in calcites these calcite data correspond to ore fluid 13cfluid values of 2 0 to 4 6 and 18ofluid values of 0 5 to 11 2 clustering at 10 which are consistent with a magmatic origin lead isotope compositions of sulfides 206pb 204pb 18 273 18 369 207pb 204pb 15 627 15 677 and 208pb 204pb 38 445 39 611 are similar to those of the granitic intrusions and sedimentary wall rocks but distinct from those of basalts 206pb 204pb 18 282 19 133 207pb 204pb 15 564 15 665 and 208pb 204pb 38 367 38 942 in the mining area taken together these geologic geochemical and isotopic data confirm that yangla is a typical cu skarn deposit

genesis of poikilotopic zeolite in aeolianites an example from the parnaiba basin ne brazil abstract zeolite cement is one of the main components of the jurassic to lower cretaceous fluvial aeolian succession in the parnaiba basin northeastern brazil core and outcrop based stratigraphic analyses permitted the paleo environmental and diagenetic interpretation of aeolian sandstone and showed the influence of the volcanic substrate in the origin of the zeolite cement the substrate is represented by an extensive volcanic plain developed in the last stages of the central atlantic magmatic province camp in west gondwana the siliciclastic deposits consist of dune field sand sheet and wadi deposit facies associations the zeolite cement of the aeolian succession forms poikilotopic crystals with anomalous up to 50 modal content x ray diffraction and sem eds cl analyses showed laumontite and ca stilbite exhibiting respectively massive and radial textures during eodiagenesis the main processes included clay infiltration linked to water table fluctuations and flash flood events producing clay coatings and displacive stilbite cementation massive laumontite cementation and smectite chlorite conversion occurred in the mesodiagenesis while in the final stages the zeolite was partially replaced by calcite cement telodiagenesis is recorded by iron exsudation and the corrosion of clay films several processes can be inferred to explain the origin of the zeolite cement in the jurassic lower cretaceous sandstone of the parnaiba basin after the first magmatic pulse triassic magmatism the zeolite bearing basalts were submitted to chemical weathering causing cation leaching afterwards the deposition of aeolian sands related to a wet desert system occurred above this weathered substrate fractured basaltic substrate favored the release of ions to the surface with fluids enriched in sodium and calcium that percolated the permeable aeolian sandstone beds during the diagenesis furthermore zeolite cement is geographically associated with the volcanic substrate in the western parnaiba basin however it is absent in the eastern part where the aeolianites overlie sedimentary rocks we suggest that the system was thermally reactivated by the last thermal camp phase with basalt emplacement in the eastern parnaiba basin linked to the opening of the equatorial atlantic ocean cretaceous magmatism the progressive heating towards the western part of the basin triggered fluids convection and the enrichment in ions such as ca2 si4 na al3 hco 3 and so42 promoting optimal conditions for zeolite crystal growth 100 c 300 c sandstone textural aspects as well as extensional faults and fractures allowed fluids migration resulting in the massive poikilotopic zeolite cementation characterizing one of the most singular features of the diagenetic history of the west gondwana record

detrital clay grain coats in estuarine clastic deposits origin and spatial distribution within a modern sedimentary system the gironde estuary south west france

abrasion of detrital grain coating clays during sediment transport implications for diagenetic clay coats abstract detrital grain coating clay minerals have been identified as precursors of diagenetic grain coating clay minerals that inhibit quartz cementation and preserve good reservoir quality properties in deeply buried sandstone reservoirs between initial and final deposition detrital grain coats are likely to be affected by sediment transport processes to date it has not been demonstrated that detrital grain coating clays are able to survive sediment transport flume experiments simulating open channel flow conditions were performed using sediments from the ravenglass estuary cumbria uk where the distribution and characteristics of modern detrital grain coating clays is well established scanning electron microscopy and automated mineralogy techniques were employed to study the sediment before and after transport to determine the stability of the detrital grain coating clays the experimental results show that detrital grain coating clays are still present after sediment transport in turbulent flows with velocities up to 0 5 m s 1 the stability of the detrital grain coating clays was enhanced by 1 high initial clay coat coverage 2 turbulence characteristics of the flow and 3 entrapment of the detrital grain coating clays in bedforms this work documents the first quantifiable evidence that estuary derived detrital clay coats are routinely preserved after sediment transport clay coat rich estuarine sediments can therefore act as the source of clay coated grains found in cleaner estuarine sandstones and may even survive transport out into open marine settings

impact of structural setting on diagenesis of fluvial and tidal sandstones the bahi formation upper cretaceous nw sirt basin north central libya abstract this petrographic mineral chemical fluid inclusion and stable isotopic study shows that the distribution of diagenetic modifications and their influence on reservoir quality and heterogeneity in tidal and fluvial sandstones of the upper cretaceous bahi sandstones in the rift sirt basin nw libya varies systematically along a series of closely spaced dominantly normal faults between the basin margin and more basinward located areas shallow eogenetic modifications resulting from the percolation of meteoric waters include infiltration of grain coating clays kaolinitization of detrital silicates and cementation by dolomite and k feldspar overgrowths mesogenetic alterations 70 c 2 km include feldspar albitization illitization of infiltrated clay and kaolinite conversion of kaolinite into dickite and cementation by quartz overgrowths t h 112 c 134 c barite t h 145 c 158 c and fe carbonates the restriction of barite and fe carbonate cements to the basinward located sandstones suggests formation by hydrothermal fluids along the faults extensive feldspar dissolution and formation of moldic pores in sandstones from the basin margin were probably caused by deep percolation of meteoric waters results from this study regarding the structural control on the spatial distribution of diagenetic alterations have implications for constraining the flux of pore fluids and by extension reservoir quality in analogous epicratonic rift basins

diagenetic patterns in eolian coastal sabkha reservoirs of the solimoes basin northern brazil abstract the jurua formation carboniferous solimoes basin is the largest gas reservoir in brazil a petrologic study of the jurua sandstones from the urucu area revealed the diagenetic evolution and controls on the quality of the main reservoirs as well as the relationships among diagenetic patterns depositional facies and stratigraphic unit boundaries the sandstones mudrocks evaporites and dolostones were deposited within a coastal sabkha environment with pervasive eolian reworking under increasing marine influence and a hot and dry climate eolian dune and sandsheet sandstones are the best reservoirs four stacked drying wetting upward cycles were identified with sabkha facies at the base overlain by eolian sandsheet and dune deposits which in turn are overlain again by sabkha deposits commonly eroded by the next cycle the sandstones are mostly subarkoses and arkoses blocky dolomite is the most abundant diagenetic constituent in the non eolian sandstones its distribution shows no relationship with depositional cycle limits microcrystalline pore filling and pore lining dolomite is more abundant in the eolian sandstones stable o and c dolomite isotope values presented by these dolomite cements indicate initial precipitation from a dominantly marine fluid at low temperatures 18ovpdb values mostly between 1 and 5 13cvpdb values from 3 to 2 with increasing contribution of organic matter decarboxylation at higher temperatures during burial 18ovpdb values between 12 and 6 13cvpdb from 3 5 to 8 9 chemical compaction through intergranular and stylolitic pressure dissolution and cementation by quartz overgrowths are more intense in the non eolian sandstones poikilotopic patchy post compactional anhydrite cementation is more abundant in the eolian sandstones but pervasive only close to the contacts with interbedded sabkha evaporites abundant anhydrite and quartz cementation along the base of depositional cycles contributed to the strong compartmentalization among the reservoir sub units but not to introduce internal heterogeneity to the reservoirs conversely dolomite cementation substantially affected the internal porosity and permeability heterogeneity by generating laterally extensive barriers to fluid flow

impact of depositional facies on the distribution of diagenetic alterations in the devonian shoreface sandstone reservoirs southern ghadamis basin libya abstract the middle devonian shoreface quartz arenites present day burial depths 2833 2786 m are important oil and gas reservoirs in the ghadamis basin western libya this integrated petrographic and geochemical study aims to unravel the impact of depositional facies on distribution of diagenetic alterations and consequently related reservoir quality and heterogeneity of the sandstones eogenetic alterations include the formation of kaolinite pseudomatrix and pyrite the mesogenetic alterations include cementation by quartz overgrowths fe dolomite ankerite and illite transformation of kaolinite to dickite illitization of smectite intergranular quartz dissolution and stylolitization and albitization of feldspar the higher energy of deposition of the coarser grained upper shoreface sandstones combined with less extensive chemical compaction and smaller amounts of quartz overgrowths account for their better primary reservoir quality compared to the finer grained middle lower shoreface sandstones the formation of kaolin in the upper and middle shoreface sandstones is attributed to a greater flux of meteoric water more abundant quartz overgrowths in the middle and lower shoreface is attributed to a greater extent of stylolitization which was promoted by more abundant illitic clays this study demonstrated that linking the distribution of diagenetic alterations to depositional facies of shoreface sandstones leads to a better understanding of the impact of these alterations on the spatial and temporal variation in quality and heterogeneity of the reservoirs

ecogeomorphology in the australian drylands and the role of biota in mediating the effects of climate change on landscape processes and evolution

a diagenetic study of intrabasaltic siliciclastics sandstones from the rosebank field abstract the rosebank field contains producible hydrocarbons from paleocene eocene intrabasaltic fluvial and shallow marine siliciclastic sandstone reservoirs despite close proximity to volcanic lithologies the siliciclastic sandstones display very good reservoirs properties with permeability in the darcy range and porosity values ranging from 19 to 23 preservation of high quality reservoir properties is the result of low quantities of volcanic minerals in the siliciclastic sandstones and limited element diffusion e g fe and mg from adjacent basalts into siliciclastic reservoir sandstones the low content of volcanic derived detritus is most likely a result of the main sediment source being situated outside the volcanic terrain the effect is that formation of clay minerals smectites and or chlorites reducing permeability and porosity is low in contrast to the siliciclastic sandstones the pore space of the volcaniclastics is occupied by authigenic clays chlorite smectite and carbonates calcite and mg calcite resulting in poor reservoir quality this paper demonstrates that high quality reservoirs can be found in intrabasaltic siliciclastic reservoirs in depth analyses of core samples show that authigenic phases formed during progressive burial with temperatures up to 120 c the suite of diagenetic phases in siliciclastic sandstones between wells and the different colsay units vary and are interpreted to result from differences in pore water chemistry and or detrital mineralogy laumontite was formed as a late stage authigenic mineral restricted to cored colsay 1 and 3 units in well 213 26 1z and has not been observed in the neighbouring 213 27 2 core which may be explained by differences in pore water ph or co2 partial pressure the occurrence of laumontite is often associated with poor reservoir quality but due to the patchy distribution of this mineral in the rosebank reservoir sands it appears not to have affected reservoir quality

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

effect of burial history on diagenetic and reservoir forming process of the oligocene sandstone in xihu sag east china sea basin abstract porosity evolution history hydrocarbon charging periods diagenetic and reservoir forming characteristics of low permeability and tight sandstone are presented in this study the interpretation is based on information including thin section scanning electron microscope homogenization temperature of fluid inclusion bulk rock x ray diffraction analysis clay x ray diffraction analysis and stable isotopic composition these sandstones are located in the oligocene e3h formation in the xihu sag east china sea basin east china five diagenetic events in the h3 h4 and h5 members were determined including connate alkaline pore water of the oligocene sandstone meteoric water leaching in late miocene organic acids and co2 acidic fluids in early middle miocene reservoir temperature decrease induced by tectonic uplift and alkaline diagenetic environment from late miocene to present day porosity evolution history of different grain size lithology were evaluated by basin modelling and test data the medium sandstone and coarse sandstone of the h3 member and medium sandstone of the h4 member not reached the tight state in the geologic time the fine sandstone of the h4 member entered the tight state at 12 ma suffered acidic fluids to improve the tight state in late stage and entered the tight state again since 6 5 ma the medium sandstone fine sandstone and siltstone in the h5 member entered the tight state at 13 5ma 16ma and 19ma respectively three hydrocarbon charging periods were determined including 15 5 ma 10 4 ma in the middle miocene 9 6 ma 7 0 ma in the late miocene and 6 2 ma 0 0 ma from the late miocene to present day three diagenetic and reservoir forming patterns were proposed including accumulation without tightness accumulation after tightness improving reservoir quality with acidic fluid accumulation while tightness accumulation after tightness the burial history cannot be ignored in the diagenetic events porosity evolution history and hydrocarbon charging periods of similar low permeability and tight sandstone in sedimentary basins

kaolinitic meniscus bridges as an indicator of early diagenesis in nubian sandstones sinai egypt abstract characteristic meniscus geometries formed by kaolinitic in ltration areobserved in nubian sandstones collected on the western coast of the sinaipeninsula egypt based on petrographic and scanning electron microscope sem observations the kaolinite forming the menisci consists of mixed sizediscrete platelets that gather into the corners around the framework grain to grain contacts speci cally the internal fabric of menisci indicates a generalorganizing trend from 1 the centre where the platelets coat the frameworkgrains 2 to the peripheral zone where they are oriented tangentially to grainsurfaces 3 to the pore linings with curvatures that are consistent withtheoretical considerations of air water interfaces this typical arrangementsuggests a detrital origin of kaolinite platelets by mechanical in ltration intosediments lying above the tablewater in vadose conditions this type of claycementation occurring during early diagenesis can prevent delay deep burialdiagenetic processes and therefore preserve excellent reservoir properties keywords clay minerals kaolinite nubian sandstone sandstone diagenesis introductionearly diagenesis of sediment can occur shortlyafter deposition depending on depositional envi ronment the early lithi cation i e the rstdeveloped bonding agent occurs as carbonateprecipitation or particle in ltration that linksframework grains by forming meniscus bridges such grain to grain bridges grow preferentially inthe corners of pore space close to grain contacts dunham 1971 speci cally by developing inconformity to the water air interface the menis cus as a result of differential capillarity pres sures these cements or in ltrating material areassumed to be related to vadose environments dunham 1971 the meniscus geometry forming pore roundinghabit has been described frequently in modernsedimentary environments where carbonate pre cipitation produces beachrocks from carbonatesands meyers 1987 hillga rtner et al 2001 these types of precipitated meniscus cementsconsist mainly of crypto to microcrystallinecalcite or aragonite that display laments whichgenerally grow perpendicular to grain rim miller 1988 rao et al 1994 hillga rtner et al 2001 incontrast precipitated menisci of goethitic ferru ginous material have been reported for a lateriticpro le in basalt horva th et al 1999 several studies have also dealt with the men iscus shape displayed by mechanically in ltratedclay particles in clastic sediments walker 1976 kessler 1978 meyers 1987 matlack et al 1989 moraes de ros 1990 owing to the micro metre scale size of particles the detrital clays aretransported along connected pores by uidscirculating between skeleton grains walker 1976 during a drying period the detrital claysgather where the capillarity pressure preserves uids therefore the accumulated clays exhibitgrain coatings and meniscus shaped bridgeslinking neighbouring grains thus the meniscuscements typically indicate vadose conditionswhere pore spaces are not permanently saturated i e water table level uctuates walker 1976 matlack et al 1989 moraes de ros 1990 sedimentology 2003 50 1221 1229

coalescence megafan multistorey sandstone complex of the late orogenic mio pliocene sub himalayan belt dehra dun india in the himalayan foreland basin a prominent multistorey sandstone complex in the middle siwalik subgroup is exposed along the southern flank of the dehra dun valley in the mohand anticline extending laterally for 40 km the middle siwalik subgroup consists of sandstone mudstone couplets 300 450 m thick in the lower part and the multistorey sandstone complex 900 1200 m thick in the upper which forms a gross coarsening upward sequence the major lithofacies are trough cross stratified sandstone planar cross stratified sandstone ripple drift laminated sandstone horizontal laminated sandstone and massive sandstone with subordinate amounts 20 of mudstone and conglomerate the multistorey sandstone complex is punctuated by several erosional surfaces over which abundant mud clasts are present the trough cross stratification exhibits a dominantly southward palaeoflow with much variation in the southeast and southwest quadrants however at outcrop level the palaeoflow data reveal internal consistency this spatial and temporal variability in palaeoflow direction indicates the existence of two major drainage systems of coalescing alluvial megafan type the estimated palaeochannel sinuosity is of the order of 1 04 to 1 23 with a return period of 4 to 8 103 years palaeoflow variability facies distribution frequent avulsion and the coarsening upward sequence collectively suggest the progradation of coalescing alluvial fans towards the south and southwest this was principally controlled by thrust movements and differential basin subsidence at the margin of the himalayan orogen

subduction and accretionary tectonics of the east kunlun orogen western segment of the central china orogenic system abstract the kunlun orogen is generally divided into the east kunlun orogenic belt e kob and the west kunlun orogenic belt w kob by the altyn tagh fault the e kob forms part of the western segment of the central china orogenic system ccos and is considered to have formed by the collision between the qaidam block and qiangtang or bayanhar terrane as a consequence of the closure of the kunlun ocean branch of the paleo tethyan ocean based on a compilation recently published high quality data this contribution provides an overview of the composition nature and ages of the principal tectonic elements including ophiolitic melanges and related volcanic rocks intrusive plutons and sedimentary cover sequences in the e kob according to multiple lines of evidence from these tectonic elements we proposed herewith a paleozoic triassic subduction and accretionary tectonic model to interpret the spatiotemporal tectonic framework plate subduction polarity and tectonic processes from accretion to collision of the e kob three main ophiolitic melange zones are identified in the e kob from north to south they are the qimantagh xiangride ophiolitic melange zone qxm the aqikekulehu kunzhong ophiolitic melange zone akm and the muztagh buqingshan anemaqen ophiolitic melange zone mbam according to these ophiolitic melange zones the e kob is divided into four major tectonic units the north qimantagh belt the central kunlun belt the south kunlun belt and the bayanhar terrane based on several lines of evidence from geology geochemistry and geochronology the south kunlun belt is interpreted as a paleozoic to triassic fore arc and accretionary complex related to northward subduction of the kunlun ocean during the ordovician triassic time the akm mabm and the south kunlun belt constitute a wide accretionary complex along the kunlun suture zone that marks final closure of the major paleo tethyan ocean while the qxm represents the best expression of another suture that records final closure of the qimantagh back arc basin the central kunlun belt as a long lived island arc terrane from ordovician to triassic times rifted from the qaidam block due to the spreading of the qimantagh back arc basin during the period of ca 485 425 ma taken into all the geological geochemical and geochronological lines of evidence together a trench arc back arc basin tectonic system in the e kob was built up and evolved into a protracted and long lived northward subduction and accretion along the kunlun suture during paleozoic and triassic time

the role of detrital composition and climate on the diagenetic evolution of continental molasses evidence from the cambro ordovician guaritas sequence southern brazil abstract the cambro ordovician molassic guaritas sequence camaqua basin southern brazil comprises alluvial fan and braided fluvial sandstones and conglomerates with intercalated aeolian and lacustrine deltaic deposits and andesitic lava flows the sediments display a complex detrital composition derived from plutonic gneissic acidic volcanic and low grade metamorphic source rocks this detrital assemblage was strongly modified by semi arid continental near surface diagenesis early cementation by hematite smectite quartz and calcite and the relatively limited burial prevented strong compaction and preserved some primary macroporosity in most of the sandstones whereas the absence of early cements and or abundance of ductile grains promoted substantial porosity destruction by compaction and the inhibition of further diagenetic modifications the diagenetic dissolution and replacement of volcanic rock fragments and detrital feldspars by clays and albite changed the original framework composition as well as the tectonic provenance classification of the sandstones detailed quantitative petrographic study allowed the reconstruction of the original detrital compositions and the distinction of six different pathways of diagenetic evolution of the sandstones attesting to the efficiency of this method for diagenetic modelling and provenance analyses of ancient sandstones

ophiolites of the kunlun mountains china and their tectonic implications abstract three ophiolite belts ranging in age from cambrian to triassic provide valuable data on the tectonic evolution of the kunlun mountains which lie along the northern margin of the tibetan plateau all of the ophiolites contain dismembered but nearly complete assemblages of peridotite mafic and ultramafic cumulates pillow and massive lavas and radiolarian cherts 1 the oldest belt contains ophiolites of cambrian age but the initial spreading of the ocean basin most likely began in the late proterozoic these ophiolites outcrop in the central part of the eastern kunlun extend for at least a few hundred kilometers and are believed to reflect a small ocean basin closure of this ocean led the accretion of south kunlun block to the north kunlun block and tarim craton ophiolitic lavas in this belt have island are affinities 2 a second belt of early carboniferous ophiolites extends nearly 600 km along the northern margin of the western kunlun lavas in this belt are basalt basaltic andesite and andesite all of which have compositions characteristic of volcanic arcs this ocean basin possibly developed on the basis of the early paleozoic oceanic basin closure of this ocean basin by southward subduction in the early permian produced a suite of calc alkaline volcanic rocks in what is now the central part of the western kunlun 3 the third belt extends nearly 1200 km along the southern margin of the eastern kunlun and contains numerous ophiolites of early permian to middle triassic age these ophiolites are highly tectonized containing volcanic rocks with the geochemical characteristics of mid ocean ridges oceanic islands and volcanic arcs this belt is tentatively interpreted as the suture zone between gondwana and eurasia

the diagenetic destruction of porosity in plutoniclastic petrofacies the miocene diligencia and eocene maniobra formations orocopia mountains southern california usa

how clay grain coats inhibit quartz cement and preserve porosity in deeply buried sandstones observations and experiments observations and hydrothermal experiments were used to derive new information about how clay grain coats inhibit quartz cement and preserve porosity in deeply buried sandstones samples of deeply buried porous sandstones with different types of clay coats were split in two coats removed from one of each pair of splits and grain surfaces inspected with scanning electron microscopy quartz grains in a fluvial deltaic sandstone buried to 115c had no visible authigenic quartz on grain surfaces cleaned of diagenetic chlorite coats though well developed overgrowths occurred on nearby naturally uncoated grains however in similar sandstones buried to 164c quartz grain surfaces exposed by chlorite coat removal were covered with small 5 m mainly anhedral syntaxial quartz overgrowths similar overgrowths were observed under various detrital and diagenetic clay coats in porous eolian sandstones buried to temperatures up to 215c we conclude that clay coats may retard quartz nucleation at moderate temperatures but at high temperatures many coats permit quartz nucleation and preserve porosity by limiting cement growth to investigate cement growth limitation mechanisms samples with coats removed were subjected to quartz cementing conditions in a hydrothermal reactor during experiments the naturally occurring small overgrowths on clay cleaned grains coalesced and grew suggesting that clay particles in coats inhibit cement growth by forming barriers to early overgrowth coalescence although the fraction of grain surface coverage is the primary control on cement inhibition by coats cement growth interference textures vary with coat type providing a mechanism by which coat composition may be a secondary control on inhibitory effectiveness in deeply buried sandstones quartz cement can fill significant microporosity within diagenetic chlorite coats potentially affecting mechanical and petrophysical rock properties

dolomite diagenesis and porosity preservation in lithic reservoirs carmopolis member sergipe alagoas basin northeastern brazil the lithic sandstones and conglomerates of the carmopolis member of the muribeca formation aptian were deposited bp fan deltas alluvial fans and braid deltas that prograded from low grade metamorphic terrains into the sergipe alagoas rift basin during

aridisols in the southern permian basin of lithuania a key to understanding clay cement distribution the change from fossil to geothermal energy supply includes the necessity to re evaluate gas reservoirs in the southern permian basin of nw europe as higher permeability reservoirs are needed for the exploitation of geothermal energy than natural gas a key reservoir risk in permian sandstones in the southern permian basin is the presence of clay cement the distribution of the clay cement is not properly understood the negative effect can be attributed to complex grain coatings formed by tangential clay directly around the detrital grains followed by authigenic clay rim cement both being genetically related this study presents new results on the origin of the tangential and the authigenic clay the southern permian basin in lithuania was a marginal area of the basin with low accommodation rates and extensive aridisol development here sandstones of the perloja formation contain abundant clayey matrix in the form of grain and void coatings the limited burial depth of a few hundreds of metres ensured that the original internal fabric and mineralogy of the clay coatings remained well preserved thin section microscopy revealed that the clay coatings are cutans that formed by post depositional mechanical infiltration illuviation of suspensions of clay minerals iron hydroxides and some clay to silt sized quartz other pedogenic features are the development of nodular calcrete rootlets and of infiltrated clay aridisols were recurrently eroded by fluvial or aeolian activity causing wide scale dispersion of siliciclastic grains with more or less complete clay cutans and also carbonate calcrete clasts in certain stratigraphic intervals

diagenetic history of fluvial and lacustrine sandstones of the hartford basin triassic jurassic newark supergroup usa abstract the early introduction of clays into continental sandstones has been attributed to mechanical infiltration by percolation of clay rich surface waters into grain framework or cutans formed from pedogenic processes the discovery of pedogenic mud aggregates as traction load mud in ancient fluvial deposits suggests that permeability and porosity of terrigenous sandstones can be influenced at deposition and control early diagenetic patterns this study compares diagenesis in fluvial subaerially exposed sandstones with lacustrine subaqueous sandstones in a triassic jurassic continental rift basin hartford basin newark supergroup diversity of diagenetic minerals and sequence of diagenetic alteration can be directly related to depositional environment the fluvial sandstones in the new haven arkose east berlin formation and shuttle meadow formation of the hartford basin are dominated by concretionary calcite and early calcite cement infiltrated clays illite smectite pedogenic mud aggregates smectite and illite smectite grain coating clays illite hematite illite chlorite hematite quartz overgrowths late stage carbonate cements calcite ferroan calcite pore filling clays illite kaolinite with minor amounts of smectite smectite chlorite illite smectite and hematite however pedogenic processes in these fluvial sandstones retarded the development of quartz and feldspar overgrowths and carbonate authigenesis as well as the quality of diagenetically enhanced porosity dark gray black lacustrine subaqueous sandstones and mudrocks in the east berlin and shuttle meadow formations are dominated by pyrite concretionary dolomite and early dolomite cement radial grain coating clays smectite chlorite illite smectite late stage carbonate cements dolomite ferroan dolomite ankerite albite and pore filling clays smectite chlorite illite smectite illite chlorite clay minerals exist as detrital mechanically infiltrated and neoformed clay the fluvial sandstones in the new haven arkose are dominated by illite the east berlin and shuttle meadow formations are dominated by illite in the fluvial sequences and smectite chlorite and illite smectite in the lacustrine sandstones dolomite ferroan dolomite and ankerite are restricted to lacustrine sandstones whereas calcite and ferroan calcite to fluvial sandstones albite predominantly precipitated in lacustrine rather than fluvial environments through intergranular dissolution of plagioclase by acidic meteoric water dissolution of unstable mafic minerals and sodium rich brines and evaporites developed from groundwater albitization and carbonate cementation are the most pronounced late stage diagenetic processes affecting both types of hartford sandstones

distribution of diagenetic alterations in glaciogenic sandstones within a depositional facies and sequence stratigraphic framework evidence from the upper ordovician of the murzuq basin sw libya abstract the spatial and temporal distribution of diagenetic alterations has been constrained in relationship to depositional facies and sequence stratigraphy of the upper ordovician glaciogenic quartzarenite sandstones in the murzuq basin sw libya which were deposited during the haritanian glaciation when the basin was laying along the continental margin of gondwana eogenetic alterations encountered include i replacement of detrital silicates mud matrix and pseudomatrix by kaolinite in paraglacial tide dominated deltaic in foreshore to shoreface highstand systems tract hst and in post glacial gilbert type deltaic lowstand systems tract lst sandstones particularly below the sequence boundaries sb kaolinite formation is attributed to the influx of meteoric water during relative sea level fall and basinward shift of the shoreline ii cementation by calcite 18 o vpdb 3 1 to 1 1 and 13 c vpdb 1 7 to 3 5 and mg rich siderite in the paraglacial tide dominated deltaic and foreshore to shoreface hst sandstones in the glacial tide dominated estuarine transgressive systems tract tst sandstones and in the post glacial shoreface tst sandstones is interpreted to have occurred from marine pore waters iii cementation by mg poor siderite which occurs in the post glacial gilbert type deltaic lst sandstones and in the paraglacial tide dominated deltaic and foreshore to shoreface hst sandstones is interpreted to have occurred from meteoric waters during relative sea level fall and basinward shift of the shoreline iv pervasive cementation by iron oxides has occurred in the glacial shoreface offshore tst sandstones and post glacial shoreface tst sandstones immediately below the maximum flooding surfaces mfs which was presumably enhanced by prolonged residence time of the sediments under oxic diagenetic conditions at the seafloor v formation of grain coating infiltrated clays mainly in the glacial fluvial incised valley lst sandstones and in the post glacial gilbert type deltaic lst sandstones as well as less commonly in the paraglacial foreshore to shoreface hst sandstones and in the tide dominated deltaic hst sandstones below the sbs mesogenetic alterations include mainly the formation of abundant quartz overgrowths in the glacial fluvial incised valley lst sandstones post glacial gilbert type deltaic lst sandstones and glacial shoreface tst sandstones in which early carbonate cements are lacking illite chlorite and albitized feldspars which occur in small amounts are most common in the glacial tide dominated estuarine tst sandstones and paraglacial shoreface hst sandstones this study demonstrates that the spatial and temporal distribution of diagenetic alterations and their impact on reservoir quality evolution in glacial paraglacial and post glacial sandstones can be better elucidated when linked to the depositional facies and sequence stratigraphic framework

diagenetic influence on reservoir quality evolution examples from triassic conglomerates arenites in the edvard grieg field norwegian north sea abstract the utsira high southern norwegian north sea has been a petroleum exploration target since the late 1960s the southwestern part of the utsira high complex haugaland high attracted new interest when in 2007 lundin norway as and partners revus energy asa and rwe dea norge as discovered commercial hydrocarbon reservoirs in triassic to early cretaceous formations edvard grieg field in the present study four siliciclastic cores from the edvard grieg field have been investigated sedimentologically including core logging optical mineralogy x ray powder diffraction xrd and scanning electron microscope sem quantification and characterization of the different mineralogical phases in thin section have been executed to better understand porosity evolution through time intergranular volume igv and cement volume were also compared in order to estimate the most important factors effecting porosity loss within the studied samples the results show that through time the various diagenetic events and phases such as dissolution of unstable grains and precipitation of clay minerals and cements strongly influenced reservoir quality in the edvard grieg field two main lithology groups are identified within the cored intervals conglomerates and sandstones these two groups can further be sub divided into four units 1 sandy conglomerate 2 silty conglomerate 3 interbedded sandstone 4 large scale cross bedded sandstone most of the reservoir quality reduction in the conglomerate matrix can be related to poor sorting carbonate cement and pore filling pore lining authigenic clay minerals better reservoir quality characterizes the sandstone dominated alluvial fan intervals which generally are associated with a greater degree of sorting that led to higher intergranular porosities large scale cross stratified sandstone units interpreted to be of aeolian origin have the highest reservoir quality these deposits are moderately to well sorted with only minor occurrences of patchy carbonate cement and generally low proportions of authigenic minerals however locally abundant kaolinite has been observed filling the pore space and reducing the porosity predominantly by blocking interconnected primary pores

u pb dating geochemistry and sr nd isotopic composition of a granodiorite porphyry from the jiadanggen cu mo deposit in the eastern kunlun metallogenic belt qinghai province china abstract the jiadanggen porphyry cu mo deposit is newly discovered and located in the eastern kunlun metallogenic belt of qinghai province china here we present a detailed study of the petrogenesis magma source and tectonic setting of the mineralization causative granodiorite porphyry the new data indicate that the granodiorite porphyry is characterized by high sio 2 68 21 70 41 wt and al 2 o 3 relatively high k 2 o low na 2 o and low mgo and cao concentrations and is high k calc alkaline and peraluminous the granodiorite porphyry has low mg 38 46 values that are indicative of no interaction between the magmas and the mantle the samples that we have examined have low nb ta 9 17 10 3 and rb sr 0 28 0 39 ratios which are indicative of crustal derived magmas source region discrimination diagrams indicate that the magmas that formed the granodiorite porphyry were derived from melting of a mixed amphibolite source in the lower crust the samples have i sr values of 0 70954 0 70979 e nd t values of 8 3 to 7 9 and t 2dm ages ranging from 1644 to 1677 ma these indicate that the magmas that formed this intrusion were generated by melting of mesoproterozoic lower crustal material higher k rb contents of the samples indicate that the magma source is high potassium basaltic material in the lower crust which could be derived from an enriched mantle source la icp ms zircon u pb dating of the granodiorite porphyry yields a late indosinian age concordia age of 227 1 ma mswd 0 31 which is close to the molybdenite re os isochron age 227 2 1 9 ma indicating further the close relationship between the granodiorite porphyry and the cu mo mineralization these samples are lree and lile e g rb k ba and sr enriched and hfse e g nb ta p and ti depleted especially in p and ti similar to the characteristics of volcanic arc magmas this intrusion most likely formed during the later stage of indosinian deep subduction of oceanic slab this was associated with underplating of mantle derived magmas which provided heat for crustal melting similar to the jiadanggen granodiorite porphyry indosinian hypabyssal intermediate felsic intrusive rocks formed under subduction tectonism or a transitional regime from subduction to syn collision make up the most important targets for porphyry cu mo deposits in the eastern kunlun metallogenic belt

clay cutans and the origin of illite rim cement an example from the siliciclastic rotliegend sandstone in the dutch southern permian basin

formation of anhydrous and hydrous skarn in cu au ore deposits by magmatic fluids most skarn ore deposits are characterized by two distinctly different alteration styles an early prograde stage with anhydrous minerals such as garnet and pyroxene forms from relatively high temperature hypersaline liquid a later retrograde stage with hydrous minerals such as epidote amphibole and chlorite plus sulfide ore minerals forms from lower temperature lower salinity fluids these two alteration stages commonly have been thought to reflect a dominance of magmatic and meteoric water respectively with relevance to the source of ore metals we report data from two different skarn systems one being part of the world s largest cu au resource stable isotope compositions of anhydrous and hydrous alteration minerals from both deposits indicate a magmatic source for both the prograde and retrograde stages 18o averages 5 0 per mil for garnet range 3 4 7 2 6 5 per mil for pyroxene 4 3 8 2 and 7 1 per mil for amphibole 4 3 8 7 the d values of late amphibole are more complex with magmatic values 77 to 78 for one deposit and both magmatic and lighter values for another deposit that could be explained either by magmatic degassing or by limited mixing with meteoric water we conclude that the differences in fluid composition prograde versus retrograde stages resulted from a magmatic fluid that intersected its solvus during the early stage creating vapor and hypersaline liquid whereas in the later stage this magmatic fluid did not intersect its solvus because it followed a different cooling path this late low salinity liquid only boiled once its vapor pressure curve was reached causing sulfide ore to precipitate during the retrograde stage

palaeo climate controlled diagenesis of the westphalian c d fluvial sandstones in the campine basin north east belgium the westphalian c and d fluvial sandstones in the campine basin north east belgium are potential reservoirs for the sequestration of co2 and interesting analogues of the hydrocarbon reservoirs in the southern north sea although these sandstones were deposited in a relatively short period of time their reservoir properties and mineralogical compositions are very different a petrographic study complemented with stable isotope analyses fluid inclusion microthermometry and x ray diffraction analyses of the clay fractions of the sandstones which were sampled from deep boreholes 1000 m in the campine basin revealed that these differences are related mainly to the climate at the time of deposition the most important eogenetic processes affecting the westphalian sandstones were the generation of a pseudomatrix by physical compaction of al silicates and lithic fragments that were strongly altered by extensive meteoric leaching kaolinitization of unstable silicates and precipitation of siderite these processes had a detrimental influence on the reservoir properties of westphalian c sandstones but their impact on the westphalian d sandstones was minimal the difference is assumed to be related to the climate at the time of deposition which changed from tropical humid in the westphalian c to semi arid arid during the late westphalian d both the westphalian c and d sandstones were affected by similar mesogenetic processes mesogenetic quartz cementation resulted from chemical compaction and illitization of kaolinite k feldspar and smectitic clays illitization of kaolinite was controlled by the available quantities of co existing kaolinite and k feldspar and mainly affected the westphalian d sandstones illitization of k feldspar was controlled by the k feldspar content it had a much larger impact on the reservoir properties of the westphalian d as in these sandstones k feldspar was less affected by eogenetic alteration the illitization of smectitic clays resulted in illite quartz and ankerite cementation in both reservoirs this process had a more important impact on the westphalian c reservoir since cementation here also resulted from smectite to illite conversion in the interbedded and underlying shales the effect of mesogenetic alterations on the reservoir properties was much less drastic than the impact of eodiagenesis mesogenetic alterations do exert a significant control on the properties of the westphalian d the vast impact of eodiagenesis on the westphalian c sandstones made them less susceptible to mesogenetic alteration the effect of telogenetic processes on the porosity and permeability of the westphalian sandstones was small and restricted to the top reservoir intervals that directly underlie the cimmerian unconformity no significant telogenetic alterations related to the variscan unconformity were observed

pre requisites processes and prediction of chlorite grain coatings in petroleum reservoirs a review of subsurface examples abstract deeply buried reservoirs containing chlorite coated quartz sand grains commonly have higher than expected porosity and permeability although prediction of such positive anomalies still remains elusive a total of 54 published examples based on information and data from 62 scientific papers was collated quantification of some of the most common parameters including depositional environment age and latitude of sand deposition effect on reservoir quality and chemical composition of chlorite is presented the dataset indicates that chlorite coats are found in sandstones deposited in a range of depositional environments but most commonly occur in delta related environments 44 with fluvial environments the second most common 19 age relationships indicate that there is an overall exploration bias in published examples with chlorite coats becoming increasingly common through time the latitude at the time of deposition of sands with chlorite coats is wide 60 n 60 s and indicates that temperate and tropical climates are important for the generation of this clay mineral chlorite can have a variable effect on reservoir quality but is typically positive iron rich chlorites occur overwhelmingly in coastal environments while mixed iron and magnesium rich chlorites are principally found in marine and terrestrial sandstones analysis of these factors suggests that hinterland geology basinal soil development and geochemical weathering and proximity to river systems are essential to the formation of chlorite precursor phases these characteristics have been combined to define situations where chlorite coats were more likely or more unlikely to form these parameters will provide insights into the formation of chlorite and to further refine predictive models for the presence or absence of chlorite coated sandstones

the role of crust thickness in runoff generation from microbiotic crusts contrary to humid areas where runoff takes place following the saturation of the soil column runoff in arid and semiarid zones takes place when rain intensities exceed the infiltration capability of the upper soil crust whether physical crust or microbiotic crust mc this type of overland flow known as hortonian overland flow hof is not fully understood especially in the case of mc in particular little is known regarding the effect of crust thickness and its fine silt and clay content on runoff generation with some scholars claiming that runoff generation is positively correlated with crust thickness and fine content in an attempt to determine the effect of crust thickness and to assess the role played by the silt and clay on runoff generation a set of field and lab experiments were undertaken on mcs inhabiting sand dunes in the negev desert israel these included sprinkling experiments coupled with measurements of the physical thickness silt and clay and biological chlorophyll protein total carbohydrates properties of 0 5 10 mm thick crusts the data showed that runoff generation took place on surfaces as thin as 0 5 0 7 mm only and was not correlated with the fine silt and clay content the implications for hof and for arid ecosystems are discussed copyright 2014 john wiley sons ltd

intracontinental porphyry and porphyry skarn mineral systems in eastern china scrutiny of a special case made in china in this contribution we discuss a series of porphyry and porphyry skarn mineral systems which constitute important metallogenic belts along major lithospheric breaks and or collision zones that form the margins of the north china craton and the yangtze craton we describe a selection of porphyry and porphyry skarn deposits in the great xing an range in northeast china the yanshan liaoning xilamulum belts along the northern margin of the north china craton the qinling orogen and the middle lower yangtze river valley along the bonudaries between the north china and the yangtze cratons the occurrence of platform carbonate successions may have played some role in the evolution of ore fluids that resulted in the formation of porphyry skarn deposits the porphyry deposits of eastern china although sharing some common features with classic porphyry systems that are related to convergent margins do exhibit unusual features particularly in terms of ore fluid compositions the common presence of fluorite hydrothermal alteration assemblages which tend to be less hydrous than the porphyry at convergent margins on the other hand the porphyry mineral systems of eastern china have some similarities with the climax type porphyry a major tectonothermal event yanshanian which took place in the jurassic cretaceous affected eastern china and most of the eastern margin of asia this yanshanian event was responsible for the magmatism and associated mineral systems in the region the granitoid intrusions and accompanying porphyry and porphyry skarn deposits were developed along orogenic belts and major structural discontinuities mostly along the tectonic boundaries between the north china and yangtze cratons and between the northern margin of the north china craton and the mongolia siberia plate the porphyry and porphyry skarn deposits herein described include chalukou in the great xing an range orogen jiguanshan in the xilamulun metallogenic belt xiaojiayingzi lanjiagou chehugou yuanbaoshan in the yanshan liaoning belt nanninhu yuchiling jinduicheng lemeingou in the east qinling orogen tongchakoou shaxi from the middle lower yangtze river valley the role of mantle lithosphere dynamics in eastern china which led to the formation of these porphyry and porphyry skarn mineral systems is discussed and reviewed

geology geochronology and geochemistry of the saishitang cu deposit east kunlun mountains nw china constraints on ore genesis and tectonic setting abstract the saishitang cu deposit located on the eastern area of the eastern kunlun orogenic belt ekob and on the northern margin of the tibetan plateau is one of the most important copper deposits in qinghai province china skarn and cu orebodies mainly occur as stratoids or lenses along the contact zone between the quartz diorite and lower to middle triassic metamorphosed tuff and marble in this study we use new zircon u pb ages molybdenite re os ages granitoid geochemical compositions and zircon hf isotope data to constrain the ore genesis and the tectonic setting of the saishitang cu deposit the quartz diorite is composed of inner medium to fine grained quartz diorite phase and an outer porphyritic quartz diorite phase u pb dating of zircons by laser ablation inductively coupled plasma mass spectrometry la icp ms yield ages of 222 7 2 3 ma and 222 6 2 4 ma for the inner and outer phase of quartz diorite respectively molybdenite separated from ore bearing quartz veins yields a re os isochron age of 223 4 1 5 ma indicating a close temporal link between magmatism and mineralization geochemically the quartz diorite shows high contents of sio 2 59 63 68 21 wt al 2 o 3 15 57 18 13 wt and na 2 o 3 07 3 56 wt with a cnk values between 0 90 and 1 01 and mg between 46 and 52 classified as the calc alkaline i type granite the trace element patterns are characterized by high lree lree hree 7 36 13 03 weak negative eu anomalies eu 0 69 0 86 relative enrichment of rb th k and pb and depletion of nb ta p and ti the quartz diorite has variable e hf t values 2 5 to 4 87 and mesoproterozoic two stage model ages 997 to 1387 ma based on petrological and geochemical features we infer that the quartz diorite is derived from the partial melting of thickened lower crust with an additional input of mantle components according to the geological geochemical and mineralogical features we propose that the saishitang cu deposit is a skarn deposit with minor porphyry type mineralization and the porphyry skarn mineral system is related to the crust mantle interaction based on the tectonic evolution of the paleo tethys ocean during the late triassic we infer that the intrusions and associated cu mineralization were related to regional extension of the ekob in a post collision environment the results also show that most porphyry skarn cu deposits in the ekob have similar mineralization ages 240 220 ma and the late triassic granitoids in the ekob present significant potential for the prospecting of porphyry skarn cu deposits

petrogenesis and tectonic significance of the late permian middle triassic calc alkaline granites in the balong region eastern kunlun orogen china numerous calc alkaline granitoid intrusions in the eastern kunlun orogen provide a valuable opportunity to constrain the evolution of the orogen the age and genesis of these intrusions however remain poorly understood the granitoid intrusions near the balong region eastern kunlun orogen consist of granodiorite diorite and syenogranite the granodiorite contains crystallized segregations abundant mafic microgranular enclaves mmes and small quartz diorite stocks in situ zircon u pb dating reveals that the granodiorites and quartz diorites were emplaced between 263 and 241 ma whereas the syenogranite was produced at c 231 ma the granodiorite and quartz diorite have a calc alkaline affinity and are metaluminous and na rich with slightly enriched sr nd isotope compositions the granodiorite is characterized by fractionated ree patterns whereas the quartz diorite displays a relatively flat ree pattern the mmes are consistent with the granodiorite in terms of incompatible elements and sr nd isotope composition compared to the granodiorite and diorite the syenogranite has higher sio 2 k rb th and sr contents and a lower rb sr ratio the results presented here when combined with regional geological data indicate that the granodiorite and quartz diorite were derived from dehydration melting of mafic lower crustal rocks during the n directed subduction of the anyemaqen ocean lithosphere in late permian middle triassic times whereas the syenogranite was produced at a higher crustal level in a syn collisional setting compared to the granodiorite

geochemical variability induced by entrainment sorting quantified signals for provenance analysis abstract a substantial part of the mineralogical and chemical heterogeneity of clay poor sands at the bed scale results from tractive redistribution of the grains in the bedload since coarse and light particles are more easily entrained than denser and smaller heavy minerals the latter commonly concentrate in grain scale lags that alternate with sand depleted in these minerals when sampled and analysed at the centimetre scale this primary heterogeneity translates into nice geochemical covariations between the minor trace elements that concentrate in some heavy minerals zr ti p cr v y ce among others regressing these variations allow us to derive two chemical fingerprints of the sand one records the proportions between some heavy minerals the other the average composition of framework grains i e a sand composition corrected from the contribution of heavy minerals both relate to provenance and allow different sand beds to be compared in appropriate spider diagrams the construction of these diagrams their potential use and their limitations are discussed using two contrasting examples continental channel sandstones from the ravenscar group middle jurassic yorkshire uk illustrate how these geochemical fingerprints vary from the local to the group scales and how robust they are against diagenetic overprint at ravenscar the zr vs ti v cr covariations record the presence of ti oxides and magnetite together with zircon and of volcanic lithoclasts at the deposition stage despite a high degree of diagenetic alteration overbank sandstones lateral to channels from the deep marine gres d annot formation eocene oligocene alps illustrates how apatite and monazite delivered by a dominantly granitic source generate covariations between zr and p y ce and th contents with characteristically steep slopes

petrology and isotopic geochemistry of dawsonite bearing sandstones in hailaer basin northeastern china abstract the co2 gas reservoir sandstones in the hailaer basin contain abundant dawsonite and provide an ideal laboratory to study whether any genetic relationship exists between dawsonite and the modern gas phase of co2 the origins of dawsonite and co2 in these sandstones were studied by petrographic and isotopic analysis according to the paragenetic sequence of the sandstones dawsonite grew later than co2 charging at 110 85 ma the dawsonite 18o value is 7 4 smow and the calculated 18o values of the water present during dawsonite growth are from 11 4 to 9 2 smow this combined with the nahco3 dominated water linked to dawsonite growth suggests meteoric water being responsible for dawsonite growth the 13c values of gas phase co2 and the ratios of 3he 4he of the associated he suggest a mantle magmatic origin of co2 rich natural gas in hailaer basin dawsonite 13c values are 5 3 to 1 5 average 3 4 and the calculated 13c values of co2 gas in isotopic equilibrium with dawsonite are 11 4 to 7 3 these c isotopic values are ambiguous for the dawsonite c source from the geological context the timing of events together with formation water conditions for dawsonite growth dawsonite possibly grew in meteoric derived water atmospherically derived co2 maybe or at least the dominant c source for dawsonite it seems that there are few relationships between dawsonite and the modern gas phase of co2 in the hailaer basin

differential responses of hillslope and channel elements to rainfall events in a semi arid area the degree of hydrological connectivity of hillslope elements in a semi arid climate was studied at the season and event timescales field data were obtained in rambla honda a medalus project field site situated in se spain on micaschist bedrock and with 300 mm annual rainfall the season timescale was assessed using correlation analysis between soil moisture and topographic indices the event timescale was studied by a quasi continuous monitoring of rainfall soil moisture runoff and piezometric levels results show that widespread transfers of water along the hillslope are unusual because potential conditions for producing overland flow or throughflow are spatially discontinuous and extremely short lived during extreme events runoff coefficients may be locally high ca 40 on slope lengths of 10 m but decrease dramatically at the hillslope scale 10 on slope lengths of 50 m two mechanisms of overland flow generation have been identified infiltration excess and local subsurface saturation from upper layers the former occurs during the initial stages of the event while the latter which is quantitatively more important takes place later and requires a certain time structure of rainfall intensities that allow saturation of the topsoil and the subsequent production of runoff hillslopes and alluvial fans function as runoff sources and sinks respectively permanent aquifers are lacking in rambla honda variable proportions of hillslope areas may contribute to flash floods in the main channel but their contribution to the formation of saturated layers within the sediment fill is very limited

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

isotopic evidence on the diagenetic evolution of coastal sabkha reservoirs from the solimoes basin northern brazil abstract the isotopic composition of diagenetic carbonates sulfates illites and associated diagenetic constituents of the carboniferous jurua sandstones solimoes basin largest hydrocarbon reservoirs of northern brazil was analyzed in conjunction with petrographic characterization and chemical composition eolian jurua sandstones deposited in a coastal sabkha of a wide cratonic sag are the best reservoirs but diagenetic processes introduced strong and complex heterogeneities which affect hydrocarbon production dolomite and anhydrite cementation together with compaction exerts the main control on the quality of the reservoirs early dolomite cements precipitated under strong evaporation while late dolomites are related to thermal decarboxylation late anhydrite cements are related to the interbedded evaporites and possibly to the oxidation of dissolved sulfide authigenic illite k ar ages are related to the voluminous triassic basic magmatism around 200 ma and to the jurassic cretaceous tectonism around 150 ma which may have also affected the late anhydrite and dolomite ankerite cementation this isotopic study revealed the major conditions of the diagenetic processes that strongly affected the jurua reservoirs which are essential for the development of models that will optimize the production as well as decrease the risks in the exploration for new jurua reservoirs

crustal structure of the paleozoic kunlun orogeny from an active source seismic profile between moba and guide in east tibet china abstract we herein present a new seismic refraction wide angle reflection profile that crosses the songpan ganzi terrane the animaqing suture zone and the eastern kunlun mountains comprised of the south kunlun and middle kunlun blocks separated by the middle kunlun fault the profile is 380 km long and extends from moba to guide in eastern tibet the crustal thickness is about 62 km under the songpan ganzi terrane 62 64 km under the south kunlun and 60 km under the middle kunlun block the songpan ganzi flysch seems to be present up to a depth of 15 km south of the animaqing suture zone and up to a depth of 10 km in the middle kunlun block with thicknesses elsewhere that depend on assumptions about the likely lithologies the profile exhibits clear lateral variations both in the upper and lower crust which are indicative of different crustal blocks juxtaposed by the kunlun fault system whether or not the songpan ganzi flysch was originally deposited on oceanic crust at the longitude of our profile 100 e it is now underlain by continental crust and the presence of continental crust beneath the songpan ganzi terrane and of a continental arc under the south kunlun block suggest paleozoic continent continent arc collision in the eastern kunlun mountains comparison of crustal velocity columns from all wide angle seismic profiles across the eastern kunlun mountains indicates a remarkable west to east change in the moho topography across the kunlun fault system 15 20 km moho step at 95 e but only 2 5 km along our profile at 100 e lower crustal thickness of the kunlun terranes is rather uniform about 35 km from 80 95 e which suggests that similar thrust thickening processes have played a role where the qaidam basin abuts the kunlun fault but thins to 20 25 km at 100 e east of the qaidam basin the increased crustal thickness from 93 to 98 e compared to that at 100 e may be due to the differences in the thickness of the crust of the two plates before their collision and or largely achieved by thickening of the lower crust perhaps indicating a crustal flow mechanism operating more strongly in the western region

3d characterization of porosity and authigenic cementation in triassic conglomerates arenites in the edvard grieg field using 3d micro ct imaging abstract x ray computed tomography ct is well known especially in medical applications but more recently also in geosciences in this study we present a model for characterizing the distribution and texture of pores and pore throats in siliciclastic rocks using multi scale 3d micro ct imaging and apply this to reservoir rocks of the edvard grieg field comprising conglomerates and arenites the conglomerates are highly heterogeneous and rich in clays which are carrying the majority of the porosity microporosity the sandstones display better sorting permeabilities and porosities in particular the aeolian samples compared to the conglomerate matrix the sandstones also have less clay and carbonate cement in order to resolve porosity distribution below image resolution the dry wet method was applied this method not only resolves porosity distribution below image resolution but also the pore throats and connectivities in this study we also investigate the effect carbonate cementation has had on the porosity and pore throat characteristics low reservoir quality conglomerates very tight conglomerates are highly carbonate cemented which has reduced the pore throat connectivity significantly in the sandstone samples the pore filling carbonate cement is less abundant and has had a much smaller effect on the porosity reduction and pore throat geometries and hence permeabilities

multiple authigenesis of k feldspar in sandstones evidence from the cretaceous areado formation sao francisco basin central brazil abstract abundant authigenic k feldspar is present in continental sandstones of the lower cretaceous areado formation in sao francisco basin central brazil feldspar authigenesis occurred in two major episodes 1 in the early cretaceous k feldspar precipitated as overgrowths healing of microfractures and replacement of detrital k feldspar and plagioclase at very shallow depths authigenesis was related to meteoric dissolution of detrital volcanic feldspars volcanic vitric rock fragments and micas in a hot semiarid climate 2 in the late cretaceous while still at shallow depths k feldspar precipitated as abundant fine crystals associated with opal ct hematite and mixed layer illite smectite the feldspar has extensively filled the intergranular and to a lesser extent intragranular pores and replaced mud intraclasts and volcanic rock fragments the authigenesis in this second episode was related to percolation of meteoric waters through the overlying upper cretaceous alkaline volcanic rocks of the mata da corda formation as indicated by the 18osmow of k feldspars from 19 4 to 21 8

depositional facies diagenesis and their impact on the reservoir quality of silurian sandstones from tazhong area in central tarim basin western china abstract the silurian sandstones of the tazhong area are an important oil exploration target in the tarim basin western china this study deals with the lower silurian of the kalpingtag formation which was deposited in a braided delta system four major depositional microfacies are identified consisting of distributary channel interdistributary bay front bar and sand sheet in spite of their large lateral extent exploration of these sandstones is complicated by variation of sediment facies and intense diagenesis which strongly affected reservoir quality depositional environment exerted an essential control on the reservoir quality higher energy well sorted and relatively coarser grained sandstones have better quality than low energy fine grained clay rich sandstones diagenesis was mainly composed of mechanical and chemical compaction and cementation by quartz overgrowths carbonates and various clay minerals mechanical compaction was a significant porosity reducing agent in the silurian sandstones the presence of carbonate cement exerts a dominant influence on porosity and permeability in tazhong area other cements are less important but quartz cement is significant the third significant element is clay minerals the porosity reduction by compaction and cementation and the relative timing of them indicates that compaction was much more important than cementation in reducing porosity

preservation and exhumation history of the harizha halongxiuma mining area in the east kunlun range northeastern tibetan plateau china abstract the extent to which ore bodies are preserved in orogenic belts remains a poorly understood area of ore deposit research using zircon and apatite fission track analysis together with apatite u th he dating we constrained the erosion history of the ore bodies in the harizha halongxiuma mining area of the east kunlun range northern tibetan plateau china apatite fission track ages range from 114 8 to 87 6 ma with mean track lengths varying from 11 4 1 9 to 12 9 2 0 m zircon fission track ages vary from 205 14 to 142 7 ma in addition apatite u th he dating yielded ages of 60 56 ma the thermal history of jiapigou was modelled based on the apatite fission track data including ages and track lengths with constraints of zircon fission track ages and u th he ages the exhumation history of the harizha halongxiuma mining area was reconstructed with these age data revealing that since the early mesozoic the area has undergone three cooling stages 1 rapid cooling from 175 30 ma to 100 10 ma with a cooling rate and inferred exhumation of 2 0 0 8 c myr and 4 3 1 7 km respectively 2 a relatively stable stage from 100 10 ma to 40 10 ma with a cooling rate and inferred exhumation of 0 3 0 1 c myr and 0 5 0 2 km respectively and 3 rapid cooling since 40 10 ma with a cooling rate and inferred exhumation of 1 2 0 6 c myr and 1 4 0 4 km respectively this exhumation history is consistent with the subduction process of pacific plate and the strike slip movements of dunmi fault the total exhumation after main mineralization is calculated to be 7 6 3 2 km suggesting that ore bodies in the harizha halongxiuma mining area remain partially preserved

gravel washing wastes from jarama river deposits spain an undervalued natural raw material this work presents the main characteristics of 97 quarry wastes collected in 23 gravel pits from the jarama river area madrid province spain in this area more than 2 5 106 ton of silty clay waste are generated every year and no applications have as yet been defined for them this work is the first systematic study of the fine fractions generated from the jarama river quaternary deposits playing part in the comprehension of this complex terrace systems quartz potassium feldspar plagioclase calcite and complex mixtures of phyllosilicates such as smectite illite kaolinite chlorite and illite smectite mixed layer have been detected two sets of waste which are recognized according to the calcite content have been directly related with the terrace level beneficed in the jarama river and the position along the valley calcite concentrates in the wastes produced in the lower course where henares and tajuna tributaries promote an extensive change in the geochemistry of underground water and locally in the petrology of quarried conglomerates this clear distinction by location between calcite bearing and calcite free wastes is essential for potential applications such as soil conditioning raw materials for brick or tiles etc the wastes studied can be considered as a potential source of industrial raw materials because of their uniformity and large volume this suggestion is now being carried out with an attempt at assessing the possibilities of using these mining wastes as ceramic raw materials

nuclear magnetic resonance characterization of porosity preserving microcrystalline quartz coatings in fontainebleau sandstones the almost pure quartz cemented fontainebleau formation paris basin france sandstones are known to preserve their porosity because of microcrystalline quartz coatings here we use nuclear magnetic resonance nmr techniques petrography scanning electron microscopy porosity and permeability measurements hysteresis and mercury injection capillary pressure curves to identify and analyze their porosity structure nuclear magnetic resonance experiments include transverse relaxation time t2 distributions and t2 filtered t2 t2 exchange t2f trex a technique that provides estimates on the diffusion coupling by comparing the evolution of families of pores in t2 distributions at different exchange times samples were divided according to their texture composition and abundance of microcrystalline quartz crystals comprising group 1 samples with very low amounts of coatings and group 2 samples with entire grains coated by microquartz both groups show three or four peaks in nmr 2 mhz t2 distribution at approximately 1 peak a 10 1 peak b and 10 2 s peak c group 2 samples present a slight shift to shorter t2 times in comparison with other samples the longest t2 peak a is because of intergranular macropores whereas the shortest peak c is because of the microporosity associated with the microcrystalline quartz coating at the surface of the pores peak b is also because of microporosity associated with microcrystalline quartz but with a different surface volume ratio being likely related to flat shaped pores within the microcrystalline coating the t2f trex indicates the proton exchange is higher between macropores and the pore surface micropores peak c than between macropores and the internal flat shaped micropores no exchange between the two sets of micropores can be observed our results show the potential of nmr techniques in characterizing the microporosity in fontainebleau sandstones which is key for the mechanism of porosity preservation in these rocks

the impact of diagenesis on the heterogeneity of sandstone reservoirs a review of the role of depositional facies and sequence stratigraphy diagenesis exerts a strong control on the quality and heterogeneity of most clastic reservoirs variations in the distribution of diagenetic alterations usually accentuate the variations in depositional porosity and permeability linking the types and distribution of diagenetic processes to the depositional facies and sequence stratigraphic framework of clastic successions provides a powerful tool to predict the distribution of diagenetic alterations controlling quality and heterogeneity the heterogeneity patterns of sandstone reservoirs which determine the volumes flow rates and recovery of hydrocarbons are controlled by geometry and internal structures of sand bodies grain size sorting degree of bioturbation provenance and by the types volumes and distribution of diagenetic alterations variations in the pathways of diagenetic evolution are linked to 1 depositional facies hence pore water chemistry depositional porosity and permeability types and amounts of intrabasinal grains and extent of bioturbation 2 detrital sand composition 3 rate of deposition controlling residence time of sediments at specific near surface geochemical conditions and 4 burial thermal history of the basin the amounts and types of intrabasinal grains are also controlled by changes in the relative sea level and therefore can be predicted in the context of sequence stratigraphy particularly in paralic and shallow marine environments changes in the relative sea level exert significant control on the types and extent of near surface shallow burial diagenetic alterations which in turn influence the pathways of burial diagenetic and reservoir quality evolution of clastic reservoirs carbonate cementation is more extensive in transgressive systems tract tst sandstones particularly below parasequence boundaries transgressive surface and maximum flooding surface because of the abundance of carbonate bioclasts and organic matter bioturbation and prolonged residence time of the sediments at and immediately below the sea floor caused by low sedimentation rates which also enhance the formation of glaucony eogenetic grain coating berthierine odinite and smectite formed mostly in tst and early highstand systems tract deltaic and estuarine sandstones are transformed into ferrous chlorite during mesodiagenesis helping preserve reservoir quality through the inhibition of quartz cementation the infiltration of grain coating smectitic clays is more extensive in braided than in meandering fluvial sandstones forming flow barriers in braided amalgamated reservoirs and may either help preserve porosity during burial because of quartz overgrowth inhibition or reduce it by enhancing intergranular pressure dissolution diagenetic modifications along sequence boundaries are characterized by considerable dissolution and kaolinization of feldspars micas and mud intraclasts under wet and warm climates whereas a semiarid climate may lead to the formation of calcrete dolocrete cemented layers turbidite sandstones are typically cemented by carbonate along the contacts with interbedded mudrocks or carbonate mudstones and marls as well as along layers of concentration of carbonate bioclasts and intraclasts commonly hybrid carbonate turbidite arenites are pervasively cemented proximal massive turbidites normally show only scattered spherical or ovoid carbonate concretions improved geologic models based on the connections among diagenesis depositional facies and sequence stratigraphic surfaces and intervals may not only contribute to optimized production through the design of appropriate simulation models for improved or enhanced oil recovery strategies as well as for co2 geologic sequestration but also support more effective hydrocarbon exploration through reservoir quality prediction

molybdenite re os zircon u pb dating and hf isotopic analysis of the shuangqing fe pb zn cu skarn deposit east kunlun mountains qinghai province china the shuangqing fe pb zn cu deposit is located in the xiangride county of qinghai province china and is a typical example of skarn deposits in the east kunlun mountains skarnization and mineralization took place along the contact zone between carboniferous carbonates and the concealed triassic plagiogranite la icp ms u pb dating of zircons from the plagiogranite has yielded ages of 227 2 1 0 and 226 54 0 97 ma which are interpreted as the emplacement age of the plagiogranite molybdenites separated from ore bearing quartz veins yielded a re os isochron age of 226 5 5 1 ma these age data confirm that both intrusion and related skarn mineralization initiated at 227 ma re contents of molybdenite zircon ehf t and 176 hf 177 hf values fall into the ranges 3 31 to 6 58 g g 8 6 to 0 0 and 0 282403 to 0 28263850 respectively the timing of the shuangqing fe pb zn cu mineralization coincided with a major change in the stress field in east kunlun from transpression to extension related to the partial melting of thickening crustal materials in a post collisional tectonic setting

sedimentary controls on modern sand grain coat formation abstract coated sand grains can influence reservoir quality evolution during sandstone diagenesis porosity can be reduced and fluid flow restricted where grain coats encroach into pore space conversely pore lining grain coats can restrict the growth of pore filling quartz cement in deeply buried sandstones and thus can result in unusually high porosity in deeply buried sandstones being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality here we report a modern analogue study of 12 sediment cores from the anllons estuary galicia nw spain collected from a range of sub environments to help develop an understanding of the occurrence and distribution of coated grains the cores were described for grain size bioturbation and sedimentary structures and then sub sampled for electron and light microscopy laser granulometry and x ray diffraction analysis the anllons estuary is sand dominated with intertidal sand flats and saltmarsh environments at the margins there is a shallowing fining upwards trend in the estuary fill succession grain coats are present in nearly every sample analysed they are between 1 m and 100 m thick and typically lack internal organisation the extent of grain coat coverage can exceed 25 in some samples with coverage highest in the top 20 cm of cores samples from muddy intertidal flat and the muddy saltmarsh environments close to the margins of the estuary have the highest coat coverage mean coat coverage of 20 2 and 21 3 respectively the lowest mean coat coverage occurs in the sandy saltmarsh 10 4 beyond the upper tidal limit and sandy intertidal flat environments 8 4 close to the main estuary channel mean coat coverage correlates with the concentration of clay fraction the primary controls on the distribution of fine grained sediment and therefore grain coat distribution are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary bioturbation and clay illuviation mechanical infiltration are secondary processes that may redistribute fine grained sediment and produce grain coats here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary fills which are typically found in the fining upward part of progradational successions

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

desert aeolian origin of late cenozoic regolith in arid and semi arid southwestern australia abstract using a sedimentary geology approach the late cenozoic regolith of southwestern australia is interpreted as basement saprock and saprolite unconformably overlain by sequences of continental sedimentary deposits the sedimentary deposits which overlie saprock and saprolite are allochthonous variously altered and mainly partly to wholly desert aeolian sediments they include aeolian and fluvial sandy clayrock facies e g deposits which resemble the pallid and mottled zones of weathered precambrian bedrock of the traditional laterite profile altered aeolian sand and sandy dust facies e g hardpan lower parts of duplex soils red sandy silt claystone and calcrete valley fills altered sandy duststones e g bauxite laterite and ferricrete of the traditional laterite profile and bioturbated aeolian sand sheets e g sandplain soils lateritic sandplains of the traditional laterite profile and upper parts of duplex soils the allochthonous and desert aeolian views proposed here differ fundamentally from the traditional residual colluvial and erosional views consequently there is a need for both traditional and alternative views to be critically appraised from the perspective of sedimentary geology

diagenesis and its impact on the reservoir quality of miocene sandstones surma group from the bengal basin bangladesh abstract rapid supply and deposition of 1000 s of meters of miocene and pliocene sediment tend to lead to a different set of controls on reservoir quality than older more slowly buried sandstones here we have studied miocene fluvial deltaic bhuban formation sandstones from the surma group bengal basin buried to 3 000 m and 110 c using a combination of petrographic geochemical and petrophysical methods in order to understand the controls on miocene sandstone reservoir quality to facilitate improved prediction of porosity and permeability the main conclusions of the study are that mechanical compaction processes are the dominant control on porosity loss although early calcite growth has led to locally negligible porosity in some sandstones mechanical compaction occurred by grain rearrangement ductile grain compaction and brittle grain fracturing calcite cement occupying up to 41 intergranular volume was derived from a combination of dissolved and recrystallized bioclasts an influx of organic derived carbon dioxide and plagioclase alteration clay minerals present include smectite illite kaolinite and chlorite the smectitic clay was probably restricted to low energy depositional environments and it locally diminishes permeability disproportionate to the degree of porosity loss kaolinite is probably the result of feldspar alteration resulting from the influx of organic derived carbon dioxide quartz cement is present in small amounts despite the relatively high temperature due to a combination of limited time available in these young sandstones grain coating chlorite and low water saturations in these gas bearing reservoir sandstones reservoir quality can now be predicted by considering primary sediment supply and primary depositional environment the magnitude of the detrital bioclast fraction and the influx of organic derived carbon dioxide

geodynamic settings of mineral deposit systems mineral deposits represent extraordinary metal concentrations that form by magmatic magmatic hydrothermal or hydrothermal processes in geodynamic environments typified by anomalously high thermal and or mechanical energy near plate boundaries as they require the conjunction of specific environmental conditions to form particular mineral deposit types tend to occupy specific geodynamic niches the temporal distributions of mineral deposit types reflect both formational and preservational processes in the archaean and palaeoproterozoic these were linked because of preservation in continental crust connected to thick buoyant subcontinental lithospheric mantle sclm but were decoupled by the neoproterozoic and phanerozoic as a result of evolution to thinner increasingly dense sclm the transition marks a change from mantle plume influenced plate tectonics to modern style plate tectonics with broadly coincident environmental changes and a major impact on the nature and abundance of preserved mineral deposit types as mineral deposits represent an integral part of tectonic process they are essential indicators of that process and geodynamic settings and should be incorporated into any holistic tectonic terrane analysis their distribution also provides a particularly critical test on ancient continental reconstructions derived from palaeomagnetic data conversely such reconstructions provide a first order targeting tool for the conceptual exploration required to discover new mineral provinces and deposits under cover

channel network extent in the context of historical land use flow generation processes and landscape evolution in the north carolina piedmont intensive agricultural land use in the 18th to early 20th centuries on the southeastern piedmont resulted in substantial soil erosion and gully development today many historically farmed areas have been abandoned and afforested and such landscapes are an opportunity to study channel network recovery from disturbance by gullying channel initiation mapping watershed area slope relationships and field monitoring of flow generation processes are used to identify channel network extent and place it in hydrologic historical and landscape evolution context in six study areas in the north carolina piedmont 100 channel heads were mapped in fully forested watersheds revealing a channel initiation relationship of 380 as1 27 where a is contributing area m2 and s is local slope m m flow in these channels is generated by subsurface and overland flow the measured relative slope exponent is lower than expected based on literature values of 2 for forested watersheds with subsurface and overland flow suggesting that the channel network extent may reflect a former hydrological regime however geomorphic evidence of recovery in channel heads within fully forested watersheds is greater than those with present day pasture present day channel heads lie within hollows or downslope of unchanneled valleys which may be remnants of historical gullies and area slope relationships provide evidence of colluvial aggradation within the valleys channel network extent appears to be sensitive to land use change with recovery beginning within decades of afforestation channel initiation mapping and area slope relationships are shown to be useful tools for interpreting geomorphic effects of land use change copyright 2012 john wiley sons ltd

depositional and diagenetic controls on the reservoir quality of lower cretaceous pendencia sandstones potiguar rift basin brazil the quality of the reservoirs of the lower cretaceous pendencia formation of the potiguar basin northeastern brazil is directly controlled by depositional facies related carbonate cementation and compaction the study of the interplay of these processes in the reservoirs offers an opportunity to unravel the diagenetic patterns of clastic sequences in interior rifts and in particular the role of carbonate cementation in poorly understood continental systems the pendencia formation is a thick sequence of fan deltaic fluvial deltaic turbiditic and lacustrine sandstones conglomerates and shales deposited during the rift stage of the basin the sandstones are predominantly arkoses average q49f40l11 with subordinate plutonic and volcaniclastic feldspathic litharenites compaction and cementation had similar importance in the destruction of porosity with a dominance of cementation in the turbidites and of compaction in the fluvial deposits carbonate cementation in pendencia reservoirs increases progressively with depth and is facies controlled eodiagenetic nonferroan calcite i d18opdb 10 7 to 4 0 d13cpdb 17 5 to 8 5 mesodiagenetic rhombohedral ferroan dolomite ankerite d18opdb 9 3 to 3 9 d13cpdb 1 7 to 1 1 and ferroan calcite ii d18opdb 17 2 to 6 8 d13cpdb 13 6 to 2 3 were precipitated at three distinct temperature intervals calculated from the d18o values 21 to 58 c 70 to 79 c and 85 to 150 c respectively according to the d13c values dissolved carbonate for calcite i was derived from oxidation and methanogenic fermentation of organic matter and from methane oxidation ferroan mesogenetic cements were derived from thermal decarboxylation of organic matter the shales were a major source of dissolved begin page 1720 carbonate as indicated by the isotopic similarity between their calcite d13cpdb 0 2 to 1 8 87sr 86sr 0 719 and most cements in the sandstones and by the peripheral cementation along the contacts of interbedded sandstones as a result of this cementation pattern thin turbiditic and deltaic sandstone beds are pervasively cemented the best reservoir quality potential is encountered in the partially cemented fluvial sandstones at moderate depths deltaic and turbiditic sandstones are more pervasively cemented by carbonate derived from the interbedded shales alluvial fan conglomerates and sandstones were flushed by telogenetic meteoric waters close to the borders of the basin and to the proximity to the postrift unconformity however porosity enhancement was very limited due to the precipitation of kaolinite and the intense compaction related to the compositionally immature detrital framework

geochemical characteristics of harizha granite diorite porphyry in east kunlun and their geological implications the harizha cu mo poly metallic deposit is one of the typical large size porphyry deposits in the eastern kunlun metallogenic belt with the la icp ms u pb age of its mother rock granite diorite porphyry being 234 5 4 8 ma mswd 0 24 detailed petrographic and geochemical studies show that the granite diorite porphyry in harizha belongs to high k calc alkaline series rich in sio2 70 94 76 08 and k2o 4 91 6 07 and poor in cao 0 16 2 01 and na2o 0 24 0 78 the granite diorite porphyry is characterized by total content of ree varying greatly from 124 69 10 6 to 178 68 10 6 rich in lree and low hree with eu values from 0 26 0 30 trace elements show enrichment of lile such as rb u la and nd and depletion of hfse like ba sr nb and y granite diorite porphyry resulted from the syn collisional tectonic setting