what is diatomite different types of biogenic remains ranging from siliceous algae to carbonate precipitates accumulate in the sediments of lakes and other aquatic ecosystems unicellular algae called diatoms which form a siliceous test or frustule are an ecologically and biogeochemically important group of organisms in aquatic environments and are often preserved in lake or marine sediments when diatoms accumulate in large numbers in sediments the fossilized remains can form diatomite in sedimentological literature diatomite is defined as a friable light coloured sedimentary rock with a diatom content of at least 50 however in the quaternary science literature diatomite is commonly used as a description of a sediment type that contains a large quantity of diatom frustules without a precise description of diatom abundance here we pose the question what is diatomite what quantity of diatoms define a sediment as diatomite is it an uncompacted sediment or a compacted sediment we provide a short overview of prior practices and suggest that sediment with more than 50 of sediment weight comprised of diatom sio2 and having high 70 porosity is diatomaceous ooze if unconsolidated and diatomite if consolidated greater burial depth and higher temperatures result in porosity loss and recrystallization into porcelanite chert and pure quartz less

oyu tolgoi mongolia siluro devonian porphyry cu au mo and high sulfidation cu mineralization with a cretaceous chalcocite blanket the oyu tolgoi porphyry cu au mo deposit is located in the gobi desert of southern mongolia the deposit consists of three main mineralized zones north central and south oyu interpreted to constitute at least two separate porphyry copper centers oyu tolgoi is associated with a series of small structurally controlled stocks and dikes of monzonitic and dioritic composition which intrude a sequence of siluro devonian volcanic and sedimentary rocks country rocks consist of pillow basalt and basaltic andesite interbedded with fine grained clastic sedimentary horizons the sequence is interpreted to have formed in a subaqueous island arc volcanic environment which formed part of the extensive paleozoic tuva mongol arc these island arc rocks are covered by carboniferous terrigenous sequences and are intruded by carboniferous syenite and granite and permian alkaline granite much of the area is covered by poorly consolidated cretaceous sedimentary sequences central oyu consists of a multiple phase hydrothermal breccia crosscutting an altered fine grained feldspar porphyry containing porphyry type alteration and mineralization the breccia underwent texture destructive advanced argillic alteration characterized by several associations of quartz alunite dickite pyrophyllite sericite and zunyite plus lesser svanbergite and fluorite these associations overprint earlier formed k silicate and quartz sericite illite assemblages copper mineralization at central oyu is present in a supergene chalcocite blanket that formed at the expense of a pyrite rich hypogene chalcocite covellite tennantite arsenosul vanite sulvanite chalcopyrite bornite sulfide suite that accompanied the advanced argillic alteration event at south oyu a feldspar hornblende porphyry of monzonitic composition intrudes a sequence of fine grained andesite and basaltic andesite hypogene copper gold mineralization occurs as early magnetite rich pyrite poor quartz chalcopyrite bornite stockworks and sheeted veinlets hydrothermal alteration is composed of biotite and k feldspar with apatite and minor albite magnetite averages 7 to 10 vol percent and copper and gold grades vary sympathetically these early assemblages are overprinted by a sericite chlorite event with ore grade copper and erratic gold and molybdenum values and also by structurally controlled pyrite rich advanced argillic alteration k ar ages show that the hypogene copper gold mineralization at south oyu is latest silurian earliest devonian 411 3 ma and that the entire district was intruded by postmineralization syenite during the carboniferous 307 4 ma the supergene chalcocite blanket at central oyu formed in the early cretaceous earliest late cretaceous based on ages for supergene alunite of 117 1 and 93 1 ma which makes central oyu one of the oldest preserved chalcocite blankets in the world chalcocite blanket preservation was favored by climatic desiccation into the late cretaceous and the tertiary it is inferred that significant regional uplift took place at the silurian devonian boundary this synmineral ization uplift and erosion may have been in part responsible for the telescoping of the hydrothermal systems at oyu tolgoi including the superposition of epithermal style associations over higher temperature deeper seated assemblages typical of the porphyry environment

u pb zircon and geochemical constraints on the age origin and evolution of paleozoic arc magmas in the oyu tolgoi porphyry cu au district southern mongolia abstract uranium pb zircon ages are linked with geochemical data for porphyry intrusions associated with giant porphyry cu au systems at oyu tolgoi to place those rocks within the petrochemical framework of devonian and carboniferous rocks of southern mongolia in this part of the gurvansayhan terrane within the central asian orogenic belt the transition from devonian tholeiitic marine rocks to unconformably overlying carboniferous calc alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation radiogenic nd and pb isotopic compositions e nd t range from 3 1 to 7 5 and 206 pb 204 pb values for feldspars range from 17 97 to 18 72 as well as low high field strength element hfse contents of most rocks mafic rocks typically have 2 are consistent with magma derivation from depleted mantle in an intra oceanic volcanic arc the late devonian and carboniferous felsic rocks are dominantly medium to high k calc alkaline and characterized by a decrease in sr y ratios through time with the carboniferous rocks being more felsic than those of devonian age porphyry cu au related intrusions were emplaced in the late devonian during the transition from tholeiitic to calc alkaline arc magmatism uranium pb zircon geochronology indicates that the late devonian pre to syn mineral quartz monzodiorite intrusions associated with the porphyry cu au deposits are 372 ma whereas granodiorite intrusions that post date major shortening and are associated with less well developed porphyry cu au mineralization are 366 ma trace element geochemistry of zircons in the late devonian intrusions associated with the porphyry cu au systems contain distinct th u and yb gd ratios as well as hf and y concentrations that reflect mixing of magma of distinct compositions these characteristics are missing in the unmineralized carboniferous intrusions high sr y and evidence for magma mixing in syn to late mineral intrusions distinguish the late devonian rocks associated with giant cu au deposits from younger magmatic suites in the district

the benthic boundary biofacies model hartland shale member greenhorn formation cenomanian western interior north america abstract well laminated predominantly non burrowed strata of the mid cretaceous western interior basin contain in situ epifaunal body fossils indicative of dysaerobic benthic oxygen levels a gradient of increasing ecological complexity in these dysaerobic faunas is identifiable and reflects improvements in benthic conditions using these faunal assemblages a benthic boundary biofacies model is developed in which the critical redox boundary is in dynamic equilibrium at the sediment water interface variations in bottom water oxygenation as well as substrate characteristics are cited as the controlling factors in the position of this boundary and thus control benthic colonization the model describes a background of low oxygen tolerant flat clam communities which were predominant during deposition of the late cenomanian hartland shale member superimposed on this background a history of brief episodic colonization and sedimentation events reveals a dynamic climate ocean system in the western interior sea which maintained a delicate balance of oxygen deficiency at the sediment water interface

an indicator of water column anoxia resolution of biofacies variations in the kimmeridge clay upper jurassic u k abstract an indicator of anoxicity ia defined as the ratio pyrite fe oxide fe total fe can be used to recognize sediments deposited under an anoxic water column modern marine sediments deposited under oxygenated bottom waters mainly have ia values 0 5 ia values in the central kimmeridge clay upper jurassic uk for fissile organic rich shales indicate that deposition occurred principally from anoxic bottom waters with infrequent oxygenation events

chronology of warm core ring 82b a chronology constructed from satellite derived thermal imagery is presented to describe the formation and life history of warm core ring 82b this overview provides insight into a classification of features and discrete events associated with gulf stream warm core rings and allows these events as well as our limited shipboard observations to be placed in a broader spatial and temporal context than would otherwise be possible without the satellite data events influencing the evolution of 82b include environmental factors such as meteorological influences and gulf stream interactions as well as those stimulated by encounters with changes in bottom topography the interactions of the ring with surrounding waters are especially noteworthy and the existence of vortex vortex interactions is shown to be a significant cause of local water advection through streamer activity ring events are documented by following changes in ring size shape translation and surface thermal structure our satellite observations are supported by extensive contemporaneous shipboard observations including xbt ctd bops biooptical profiling system temperature profiles and along track sea surface temperature measurements in addition acoustic velocity profiling and drifter trajectories have been used to corroborate hydrographic features of the ring and environs these ship and satellite data form a coherent space time overview of the ring and its environment and show them to be closely related and continually interacting

exhumation and preservation of porphyry cu au deposits at oyu tolgoi south gobi region mongolia field relationships and u pb data zircon are used to constrain the timing of tectonomagmatic events that occurred shortly after the formation of late devonian 372 ma porphyry cu au deposits at oyu tolgoi mongolia in the two northernmost of the several discrete porphyry centers hugo dummett deposits upper devonian rocks positioned stratigraphically above copper gold mineralization preserve a record of uplift exhumation and subsequent burial shortly after mineralization strongly altered and mineralized quartz monzodiorite and volcanic rocks at hugo dummett are overlain by an unmineralized dacite sequence 369 2 ma the basal breccia and conglomerate of the dacite sequence contain mineralized porphyry clasts derived from erosion of the porphyry deposits two zircon grains recovered from one of these mineralized porphyry clasts yielded chemical abrasion thermal ionization mass spectrometry ca tims 206 pb 238 u dates of 374 0 1 9 and 371 4 1 6 ma which are consistent with previously published ages for mineralized intrusions this implies that oyu tolgoi or other nearby porphyry deposits were exhumed shortly after the main mineralization event weakly mineralized granodiorite dikes intruded the postmineralization dacite sequence as well as devonian sedimentary and volcaniclastic rocks that structurally overlie the dacite a weighted mean 206 pb 238 u age of 370 6 0 5 ma for this rock is based on the three youngest grains analyzed by the ca tims technique mswd 1 14 burial of the cu au deposits at oyu tolgoi soon after their exhumation was critical to their preservation exhumation and subsequent burial occurred at 371 ma during a short time frame within the overlapping u pb zircon ages for the quartz monzodiorite mineralized porphyry clast unmineralized dacite sequence and granodiorite unit

interpreting benthic oxygen levels in mudrocks a new approach quantified paleoecology and gamma ray spectrometry have been applied in the analysis of the kimmeridge clay a highly organic rich british jurassic mudrock decreasing benthic oxygen trends are reflected in decreasing species richness and dominance diversity values similarly the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen the calculation of authigenic uranium values from data gathered by gamma ray spectrometry shows enrichment in more oxygen deficient environments the good correlation between the independently derived paleoecological and authigenic u data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks

observations of gulf stream ring 83 e and their interpretation using feature models analysis techniques were developed to track and estimate the propagation velocity size shape orientation and swirl velocity of gulf stream warm core rings the methods involve fitting idealized warm core ring feature models to observed surface fronts in the satellite imagery to expendable bathythermograph survey data and to satellite tracked drifting buoy data the ring feature models are analytic structure functions with adjustable parameters in this case the ring is modeled as an isolated translating elliptic paraboloid with a swirl velocity that increases linearly with distance from the center use of the feature models is illustrated with data collected from warm core ring 83 e gradient currents based on the bathythermograph survey of ring 83 e and the feature model agree well with currents measured by expendable current profilers a comparison of the time series of ring 83 e feature model parameters indicates that not only is the feature model analysis of the buoy track an effective method for tracking and monitoring the evolution of gulf stream rings it also provides useful forecasts of ring locations based simply on a persisted propagation velocity these techniques were used to provide real time support for exploratory deepwater drilling operations off the u s east coast

anoxic events during sedimentation of a palaeogene diatomite in denmark a diatomite about 60 m thick of late palaeocene early eocene age crops out in northern jutland denmark the diatomite is locally termed moler frustules of marine diatoms constitute c 65 by weight of the diatomite and clay minerals chiefly montmorillonite make up the remainder slight variations in the relative supply of diatom frustules and clay minerals are preserved undisturbed in laminated diatomite while lamination is partly destroyed by burrowing organisms in weakly laminated diatomite and obliterated by total bioturbation in structureless diatomite these three facies alternate throughout the sequence the presence or absence of infaunal burrowing organisms is interpreted as a record of the content of dissolved oxygen in the water above the sediment water interface and hence of the position of the redox potential discontinuity interspaced in the diatomite are 179 identifiable layers of volcanic ash these ash layers provide a means of precise lateral correlation they show that levels of laminated diatomite may be followed throughout the basin and therefore that changes between anoxic and oxic conditions occurred simultaneously across the area the laminated diatomites may consequently be interpreted as representing short term anoxic events of which twelve have been recognized

organic matter apatite pyrite relationships in the botneheia formation middle triassic of eastern svalbard relevance to the formation of petroleum source rocks in the nw barents sea shelf abstract the middle triassic botneheia formation of eastern svalbard edgeoya and barentsoya comprises an organic carbon rich fine grained clastic succession 100 m thick that makes the best petroleum source rock horizon in the nw barents sea shelf the succession records a transgressive regressive interplay between the prodelta depositional system sourced in the southern barents sea shelf black shale facies of the lower and middle parts of the muen member and the open shelf phosphogenic system related to upwelling and nutrient supply from the panthalassic ocean phosphogenic black shale facies of the upper part of the muen member and the blanknuten member the relationships between organic matter authigenic apatite and pyrite in these facies allow to characterize the relative roles of redox conditions and oceanic productivity in the organic carbon preservation the accumulation of terrestrial and autochthonous marine organic matter in the black shale facies occurred under dominating oxic conditions and increasing upward productivity related to early transgressive phase and retrogradation of the prodelta system the phosphogenic black shale facies deposited in an oxygen minimum zone omz of the open shelf environment during the late transgressive to regressive phases under conditions of high biological productivity suppressed sedimentation rates and changing bottom redox the phosphatic black shales occurring in the lower and upper parts of the phosphogenic succession reveal depositional conditions indicative of the shallower part of omz including high input of autochthonous organic matter into sediment oxic to dysoxic episodically suboxic and or anoxic conditions intense phosphogenesis and recurrent reworking of the seabed the massive phosphatic mudstone occurring in the middle of the phosphogenic succession reflects the development of euxinia in the deeper part of omz during high stand of the sea high input of autochthonous organic matter in this environment was coupled with mineral starvation and intermittent phosphogenesis in mature sections in eastern svalbard the petroleum potential of the botneheia formation rises from moderate to good in the black shale facies and from good to very good in the phosphogenic black shale facies attaining maximum in the massive phosphatic mudstone

concepts and methods of high resolution event stratigraphy modern geological analyses involving sedimentary rocks require a high resolution system of dating integrating and correlating diverse strati graphic geochemical and paleontological data that also takes into account the possibility that short term phenomena 100 kyr or less exercise a strong control on sedimentation such phenomena may be extraterrestrial tectonic volcanic oceanographic climatic sedimentologic and or bio logic in origin some reflect unpredictable perturbations of local to global scale but most short term phenomena are predictable and may be either autocyclic locally regulated with limited stratigraphic continuity or allo cyclic in nature regionally to globally regulated with extensive strati graphic continuity beerbower 1964 a stratigraphic system based on short term phenomena would ideally be chronostratigraphic involving the identification and regional tracing of time lines isochronous surfaces or very thin event deposits and easily integrated with refined independently derived biostratigraphic and geochronologic systems an intensive search for such a new and revolutionary system of stratig raphy has been prompted in many parts of the phanerozoic by attain ment of plateaus in stratigraphic resolution utilizing the more standard tools of magnetostratigraphy biostratigraphy and geochronology most magnetic reversals have been identified biostratigraphic systems can be no more refined than the maximum evolutionary rates of component taxa and their major structures known for many favored groups and geo chronology is regulated by the analytical confidence limits of radiometric

tracing bottom water redox conditions during deposition of lower and upper jurassic organic rich sedimentary rocks in the lusitanian basin portugal insights from inorganic geochemistry abstract the lower jurassic agua de madeiros am fm and vale das fontes vf fm formations and the upper jurassic cabacos formation cab fm are considered the most important units with petroleum source rock potential in the lusitanian basin and the likely sources for its widespread hydrocarbon occurrences nonetheless the bottom water redox conditions during their deposition remain debatable to resolve this controversy we investigated whole rock inorganic geochemical data of the most significant organic rich levels of the am vf and cab fms cropping out at basin scale significant variations in toc ts and redox sensitive elements contents and their ratios are evident within and between the organic rich levels of the studied units a positive covariation between primary productivity proxies toc enrichment and paleo redox proxies for the lower jurassic units clearly suggest an interdependence between enhanced primary productivity organic matter accumulation and bottom water redox conditions for the am fm the paleo redox proxies indicate that the black shales deposition took place beneath bottom waters that ranged from suboxic to strongly euxinic conditions with a clear predominance of the latter a toc threshold of 6 7 wt clearly separates samples deposited under suboxic to anoxic conditions from those deposited under true euxinic conditions and is interpreted as the minimum amount of organic matter om accumulation within sediments required to sustain h2s production at rates that outpaced its consumption through precipitation of sulphides and or om sulphurization allowing the diffusion of h2s to the bottom waters for the vale das fontes fm the paleo redox proxies suggest a prevalence of suboxic to anoxic bottom waters despite all black shales displaying toc contents greater than the above threshold the less reducing conditions relative to the am fm euxinic black shales are attributed to i a larger proportion of continental om ii lower reactivity of the om reaching the sediment water interface decreasing oxygen consumption and iii higher availability of reactive iron increasing the buffer effect to h2s produced through om remineralization by sulphate reducing bacteria both units display mo ef vs u ef covariation patterns that deviate from the field of sediments deposited under unrestricted open marine conditions towards higher mo enrichment relative to that of u indicating an accelerated transport of aqueous mo to the sediments consistent with the operation of a metal oxyhydroxide particulate shuttle linked to mn and fe redox cycling within the water column in a weakly restricted basin the mo cot regression line slope indicates a moderate degree of bottom water mass restriction with mo aq concentration of 60 70 of the present day seawater value and bottom water renewal times of 10 20 years akin to the present day cariaco basin the redox conditions of the cab fm organic rich levels are dependent on the location of the depositional environment in the basin with deposition taking place beneath oxygenated bottom waters at cabo mondego and under suboxic conditions at vale de ventos and pedrogao the latter denoting a larger degree of oxygen depletion than the former in this context the overall potential for om preservation should increase from cabo mondego to vale de ventos and pedrogao

mineralogy textures and whole rock geochemistry of advanced argillic alteration hugo dummett porphyry cu au deposit oyu tolgoi mineral district mongolia advanced argillic aa alteration is developed over a vertical interval of 500 m above and enclosing late devonian quartz monzodiorite intrusions that accompany porphyry style cu au mineralization at the hugo dummett deposit the aa alteration is mainly in basaltic rocks and locally extends into the overlying dacitic ash flow tuff for about 100 m the aa zone overprints porphyry style quartz veins associated with quartz monzodiorite intrusions but at least partly precedes high grade porphyry style bornite mineralization mineralogically it consists of andalusite corundum residual quartz titanium oxides diaspore alunite aluminum phosphate sulfate aps minerals zunyite pyrophyllite topaz kaolinite and dickite as well as anhydrite and gypsum but is dominated by residual quartz and pyrophyllite alteration zonation is not apparent except for an alunite bearing zone that occurs approximately at the limit of strong quartz veining whole rock geochemistry shows that the aa alteration removes most major elements except si al ti and p and removes the trace elements sc cs and rb v zr hf nb ta u and th are relatively immobile whilst light rees la to nd sr ba and ga can be enriched middle rees sm to gd are moderately depleted y and heavy rees tb to lu are strongly depleted except in two unusual samples where middle to heavy rees are enriched

organic petrology and geochemistry of tournaisian age albert formation oil shales new brunswick canada abstract lacustrine oil shale and shale samples of the tournaisian age albert formation in new brunswick canada taken from six locations were analyzed by organic petrology using reflected white and fluorescence light microscopy and by rock eval pyrolysis to determine their depositional environment and hydrocarbon generating potential calcium th and ca contents of the samples were also determined using icpms the results were compared to the big marsh lacustrine oil shale of carboniferous age in nova scotia organic matter consists mostly of filamentous alginite bacterial remains and matrix bituminite which fluoresce green to dark yellow organic matter was deposited in a lake basin the regular layering of algal remains and wrapping around mineral particles indicate deposition in a low energy setting below wave base which resulted in the stratification of the organic matter and the enclosing mineral matrix there are also fluorescing to non fluorescing bitumens present in parts of the albert oil shale the bitumens were incorporated as a result of hydrocarbon migration during deposition of the oil shales the two are considered to be syn sedimentary because the bitumens are part of the regular rock layering and the fact that the organic matter is wrapped around mineral grains the bitumens in the albert oil shales consist of fluorescing wurtzilite and non fluorescing albertite the albert oil shales have lower input of terrestrial sediments containing th and are carbonate rich the variation of th u ratio and toc wt indicates that the albert oil shales have different mineralogy than those from the big marsh ones there are two types of carbonates particles in the albert oil shale a syngenetic angular particles which are suspended in the organic matter but may also occur as micrite and b rounded to angular and possibly transported particles containing oil inclusions as a result variations in th u and calcium divided the oil shales into a low calcium lacustrine type which includes the big marsh oil shale the albert oil shale and shale deposited far from the albert mine and few samples from a deposit close to the albert mine that have high calcium content and some of them contained oil inclusions the higher toc of samples collected from the bitumen mining area in the albert mine is related to bitumen impregnation due to hydrocarbon migration variation of hi mg hc g toc and authigenic uranium in the albert oil shale indicates that depositional environment was more anoxic than most of the oil shales in the big marsh deposit rock eval pyrolysis data and accompanying organic petrology analysis indicate that the samples are mostly immature to marginally mature as indicated by ro ran of 0 60 0 68 and variation in the fluorescence red green and blue green and blue r g b g b quotients variations in maturity indicators such as hi and tmax are caused by other factors such as quantity of organic matter in the samples the hydrogen index hi vs tmax plot of the oil shales displays a wide range of hi within a narrow tmax range of 438 442 c indicating immature to marginally mature type i kerogen there is a slight trend of increasing tmax into the oil window with increasing hi likely due to the extreme mass of hydrocarbons in these samples which requires higher energy to breakdown rather than burial related thermal maturity maturity of the albert oil shale increases from east to west within the study area as indicated by the westward increase of all three fluorescent quotients of both filamentous algae and matrix bituminite and in the ro the reflectance of the albert oil shales measured on vitrinite is mostly suppressed compared to the nearby mapleton organic lean shale in new brunswick there is also a correlation between hi and ro ran in the oil shale samples studied the higher is the hi the lower is the ro the majority of the oil shale samples have a very high potential for hydrocarbon extraction using the ex situ methodology at 30 l t and the upper 20 of the samples have the potential for in situ extraction at 60 l t

fluid and metal sources of the wenquan porphyry molybdenum deposit western qinling nw china the wenquan porphyry moybdenium deposit western qinling nw china with a resource of 247 million tonnes at 0 048 mo formed during triassic collision between south china and north china blocks ore fluids at wenquan vary widely in composition from single phase low salinity aqueous to low salinity vapor and hypersaline inclusions fluid inclusion assemblages in a quartz molybdenite vein contain 60 vol vapor are equant to negative crystal shaped and form clusters or distinct inclusion trails they yield homogenization temperatures of 285 295 c with an estimated trapping temperature of 425 c suggesting a paleodepth of about 5 km calculated at a pressure correction of 100 150 mpa hydrothermal k feldspar from early stockwork veins related to potassic alteration have calculated 18ofluid values of 1 9 to 1 9 hydrothermal sericite from an overprinting phyllic alteration associated with late quartz pyrite veins has calculated dfluid values between 68 and 60 and 18ofluid values from 3 7 to 1 4 these isotopic data suggest that both early and late stage fluids are dominated by magmatic fluids with influx of meteoric water during the late stage exsolution of volatiles from magma in a late stage open system results in more variable d values than an earlier closed system molybdenite and pyrite have 34s values ranging from 1 1 to 6 6 indicating that sulfur at wenquan had a magmatic source a linear relationship between 34s values of sulfides separated from early potassic alteration and late phyllic alteration could reflect incorporation of isotopically heavy evaporate sulfate into source magmas from underlying devonian sedimentary rocks during late alteration the 56fe whole rock values of altered porphyries range from 0 08 to 0 26 similar to 56fe values of 0 15 0 32 for pyrite from quartz veins related to both the potassic and phyllic alteration assemblages the 56fe values of pyrite are positively correlated to but in general slightly lighter than those of altered porphyries indicating similar metal sources moreover both altered porphyries and the pyrite are progressively enriched in heavy fe isotopes from biotite through potassic to late phyllic alteration consistent with isotopic evolution from an early lithostatic load to a late hydrostatic load the triassic intrusive rocks and fluids responsible for mineralization were derived from a deeply sourced hybrid mantle crustal magma crystallizing at a paleodepth of 5 km under lithostatic load external late triassic meteoric or devonian formational fluids became a part of the hydrothermal system during the post fracturing final stage of ore formation under a hydrostatic regime the formation of the wenquan magmatic hydrothermal systems spans the ductile brittle transition based on a normal thermal gradient as constrained by the temperature range of 550 300 c the early high temperature potassic alteration developed under a ductile regime whereas the later low temperature phyllic alteration correlates to a brittle environment where hydraulic rock fracturing enhances permeability and fluid circulation most sulfur and metals were precipitated from vapor rich fluids resulting from cooling and expansion of a single phase fluid exsolved from a hybrid magma

the late cretaceous western interior seaway as a model for oxygenation change in epicontinental restricted basins abstract deoxygenation is a critical problem facing the ocean as the world warms and has the potential to effect coastal upwelling zones shelf areas influenced by high runoff and nutrification and restricted and semi restricted basins the mechanisms that drive deoxygenation in these diverse environments are still not fully understood in part because the modern record of redox change is short and anoxia is still relatively rare in the modern ocean here we address this problem of scale by studying deoxygenation in the geologic past we summarize decades of individual studies of benthic foraminifera to generate a record of bottom water oxygen change in the cretaceous western interior sea wis of north america over 13 myr cenomanian campanian spanning two major sea level cycles the wis was prone to major changes in dissolved oxygen content throughout its long history sometimes directly antiphase to trends in the global ocean presented as maps our data show that bottom water oxygen within the wis was controlled by a combination of water mass source and mixing moderated by sea level and basin restriction areas flooded by cool boreal northern sourced waters in the northern and western parts of the seaway were better oxygenated than the eastern and southern portions of the seaway which were flooded by warmer tethyan southern sourced waters beyond east west differences explained by water mass the entire seaway was better oxygenated during periods of transgression and more poorly oxygenated to anoxic during periods of peak transgression highstand and regression we suggest that this pattern was due to the formation and downwelling of western interior intermediate water by the mixing of tethyan and boreal waters during transgressions an increasing volume of these watermasses entered the seaway mixed and downwelled well oxygenated surface water to the seafloor during late transgression highstand partial stratification and the encroachment of low oxygen waters from the open ocean caused dissolved oxygen levels to drop at the seafloor but continued downwelling prevented anoxia during the subsequent regression a decline in the volume of outside watermasses entering the seaway caused a reduction in mixing and weakened downwelling which led to stratification and seafloor anoxia as a model for other semi restricted basins the trends observed in the wis show that local changes in relative sea level mixing and circulation are critical in controlling oceanic deoxygenation in these environments in clear contrast to continental margins impinged by oxygen minimum zones like the contemporaneous demerara rise in the southern caribbean although the wis is larger than most semi restricted basins it is characterized by quasi estuarine circulation driving the interaction of normal marine and brackish watermasses and thus serves a model for similar shallow epicontinental basins of any size understanding how these processes vary in different environments is key to predicting susceptibility of regional water bodies to deoxygenation in the future with a warming world

organic rich biolaminated facies from a kimmeridgian lagoonal environment in the french southern jura mountains a way of estimating accumulation rate variations abstract during kimmeridgian times the present day southern jura was a carbonate platform in the palaeolagoon at the village of orbagnoux organic matter was deposited giving birth to calcareous laminites with organic carbon reaching 12 three facies may be distinguished two types of laminites are encountered one made of parallel laminae and the other made of undulating laminae the laminites alternate with massive limestone beds in which no internal structure may be seen the lithology sedimentology and the faunal floral and organic content of laminites and of massive limestones was thoroughly investigated at different scales using various methods field observation transmitted light and scanning electron microscopy rock eval pyrolysis biomarkers infrared study of kerogen palynofacies observation it is suggested that the different types of laminites parallel or undulating may reflect variations in the accumulation rates linked with the carbonate and organic matter productions undulating laminae would correspond to periods of lack of sedimentation whereas parallel laminae would reflect alternations of periods of sedimentation and periods of non sedimentation these variations might in turn reflect climatic changes affecting the emerged lands supplying the lagoon with detrital products organic or inorganic the accumulation and preservation of organic matter were made possible by the development of microbial mats building oxygen tight barriers at the water sediment interface these barriers separated overlying oxygenated water from anaerobic sediments these phenomena may explain one way in which potential hydrocarbon source rocks can form under a poorly oxygenated water column

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

organic facies of the early albian niveau paquier a key black shales horizon of the marnes bleues formation in the vocontian trough subalpine ranges se france abstract the marnes bleues formation was deposited in the central hemipelagic part of the vocontian trough during aptian albian times it contains several levels of black shales which are characterized by abundant organic matter of both continental and marine origin as well as by some qualitative and quantitative variations in planktonic and benthic foraminifera contents we concentrate here upon the most striking of these horizons the niveau paquier early albian the niveau paquier has a laminated paper shale facies varying in thickness from a few decimeters to 5 m it can be traced over a large part of the alpine tethys it is one of the most organic rich levels in the marnes bleues formation it displays a subtly fluctuating organic content of both marine dinocysts algae foraminifera linings amorphous organic matter or aom and terrestrial origins inertinite vitrinite cutinite spores and pollen many characteristics of the niveau paquier lithology microfauna organic matter presence of resident dysaerobic faunas etc suggest frequent oscillations between anaerobic dysaerobic and aerobic conditions a model involving subtle modifications in the water stratification can be suggested the fluctuating position of the redox potential discontinuity layer rpd layer or of the pycnocline would have affected epi meso planktonic nectonic and epi endo benthic life and the nature and preservation of organic matter mainly of aom organic parameters palynofacies and rock eval data of the niveau paquier seem to have recorded some four ca 100 000 yr long cycles these cycles may be related to climatic variations affecting both the emerged lands supplying the vocontian trough in clay minerals organic residues and nutrients and the conditions in the marine milieu these variations seem to be in the milankovitch frequency band

magmatic oxidation state of the baogutu porphyry copper deposit in the west junggar of china implication for ore formation abstract the ore forming processes in the baogutu porphyry copper deposit are spatially and temporally related to the late carboniferous intrusions in the west junggar of china the mineralized intrusions consisting of granodiorite quartz diorite and diorite are characterized by moderate zircon ce4 ce3 ratios 15 9 163 and eu eu ratios 0 25 0 57 eu eu eun smn gdn 1 2 estimated magmatic oxidation state based on amphibole crystallized in the deep magma chamber logfo2 fmq 1 7 is lower comparing with that based on amphibole crystallized in the shallow magma chamber logfo2 fmq 3 5 the baogutu ore forming magmas were moderately oxidized with an average logfo2 value of fmq 2 5 based on amphibole oxygen barometer or fmq 2 7 based on magnetite ilmenite oxygen barometer these data indicate that the baogutu ore forming magmas were moderately oxidized

the significance of palynofacies fluctuations in the greenhorn formation cenomanian turonian of the western interior basin usa abstract in the greenhorn limestone formation of the pueblo section colorado the palynofacies in the hartland shale member is remarkably homogeneous this is in marked contrast to that of the overlying bridge creek limestone member in which the alternating limestones and marlstones are characterized by rhythmic variations in the terrestrial phytoclasts such variations appear to be related to milankovitch cycles as well as to both the dilution and productivity models the marine palynofacies includes three dinocyst associations and scytinascia foraminiferal linings changes in the marine palynofacies do not appear to be related to the cyclical limestone marlstone deposits however the alternating dinocyst associations suggest mesotrophic oligotrophic rhythms in the surface waters the discrepancy between the dinocyst cycles and the lithological couplets could reflect the modulation of the sea level rises in the milankovitch frequency band by a barrier during deposition of the hartland shale member within the second order t6 transgression of kauffman the discrepancies between the foraminifer nannofossil and dinocyst fluctuations are interpreted as reflecting specific responses by each planktic group to global oceanographic changes and diagenesis

use of multi proxy approaches to determine the origin and depositional processes in modern lacustrine sediments carajas plateau southeastern amazon brazil abstract geochemical and isotopic compositions of surficial sediments from a plateau lake in carajas southeastern amazon region were investigated to understand the spatial distribution of major and trace elements 13 c 15 n and c n ratio depositional processes and the origin of inorganic and organic fractions the 13 c 15 n and c n ratio indicate mainly an autochthonous source with siliceous sponge spicules and algae being the major source of organic matter in the center of the lake sector 3 while an allochthonous source mainly derived from c3 vascular forest plants dominates in the shallowest portion of the lake sector 1 consequently there was an apparent dilution of c4 plants montane savanna in the sediment water interface among major elements fe 2 o 3 is highly enriched in sector 3 which is controlled by the erosion of catchment laterites and underwater topography while al 2 o 3 and p 2 o 5 enrichment near the northern border of the lake is controlled by the weathering of mafic rocks similar spatial distribution of sio 2 with total organic carbon toc and isotopic evidence indicate that si distribution is partially controlled by organic components such as siliceous sponge spicules and algae the occurrence of most of the trace and rare earth elements ree is independent of fe 2 o 3 and toc but controlled by detrital aluminum silicates and heavy minerals indicating a lack of post depositional diagenetic control on their distribution the distribution of as and mo are possibly controlled by organic matter mineralization during early diagenesis and subsequently precipitation of fe phases the values of the chemical index of alteration cia in the sediments are very high 94 99 and similar to those of the source rocks suggesting that sediment composition is mainly controlled by mechanical weathering rather than chemical weathering geochemical indices al k ti k al ti la th ti zr zr hf hf nb la al co th ba sr and th sc together with the a cn k plot suggest that the provenance of the inorganic sediments remained relatively uniform or constant during the depositional period and that they were mainly derived from laterite crusts and subordinately from mafic soils this inference was further substantiated by the chondrite normalized ree patterns and discrimination plots geochemical indices such as u th authigenic u mo al and v cr indicate that the sediments were deposited under an oxic environment

faunal replacement in the early jurassic of northern chile implications for the evolution in mesozoic benthic shelf ecosystems abstract long term within habitat species replacement is either evolutionary or ecological in nature ecological replacement of dominant species by unrelated species which share essentially the same niche requirements is a very characteristic feature of early jurassic benthic shelf faunas from northern chile more than that an examination of the relevant literature reveals that the process was significant in mesozoic benthic shelf ecosystems on the whole it occurred among all important guilds and in a broad range of environmental subdivisions salinity controlled environments coarse grained and fine grained shallow shelf mid to outer shelf and oxygen controlled environments in contrast evolutionary replacement of dominant faunal elements appears to have been limited to restricted basins faunal replacement was the underlying process of several distinctive patterns in the temporal distribution of mesozoic benthic shelf faunas that is the evolutionary stability of dominant morphoptypes the widespread occurrence of parallel associations and the persistence of guild assemblages through time fluctuations of relative sea level are regarded as a substantial controlling factor of within habitat species replacement

thin fine grained storm layers in a muddy shelf sequence an example from the lower jurassic in the stenlille 1 well denmark thin storm sand layers are a characteristic feature of many sandy shelf sequences while little evidence of storm layers is preserved in muddy shelf deposits where bioturbation is often total the present study shows that storm generated depositional processes governed sedimentation in a muddy shelf environment the studied sequence is dominated by blackish mudshale and silt streaked mudshale with thinner intervals of pale fine grained heterolithic sandstone it represents the lower jurassic fjerritslev formation in the eastern part of the danish basin and has been studied in four cores from the stenlille 1 well within the muddy outer shelf association four sedimentary facies and 14 types of laminae 0 5 10 mm thick may be distinguished most of the laminae share the characteristics of graded bedding erosive bases and occasional fading ripples with storm layers of sand grade the structures indicate that the mudshale laminae formed by settling of the suspension load carried by storm generated currents this kind of episodic deposition of fine grained storm layers may be common though rarely preserved in outer shelf environments

new aspects on the formation of hydrocarbon source rocks episodic volcanism favors as shown by examples from europe the usa and brazil the formation of organic rich sediments hydrocarbon source rocks the examples examined from europe comprise the lower carboniferous oil shale group scotland upper carboniferous coal measures western germany upper jurassic kimmeridge shale north sea area lower cretaceous blattertonstein northwest germany and eocene messel oil shale rheingraben examples from the usa are devonian mississippian gas shales permian phosphoria shale middle cretaceous mowry shale eocene green river shale and miocene monterey shale examples from brazil are permian irati oil shale and oligocene paraiba valley oil shale volcanism is reflected during sedimentation 1 by exhalation of so2 and or co2 2 volcanic ashfalls 3 by generation of anoxia and preservation of organic matter and 4 by halmyrolytic alteration of volcanic ashes into highly surface active clay minerals montmorillonite

sulfur poor intense acid hydrothermal alteration a distinctive hydrothermal environment abstract a fundamentally distinct sulfide poor variant of intense acid advanced argillic alteration occurs at the highest structural levels in iron oxide rich hydrothermal systems understanding the mineralogy and geochemical conditions of formation in these sulfide poor mineral assemblages have both genetic and environmental implications new field observations and compilation of global occurrences of low sulfur advanced argillic alteration demonstrates that in common with the sulfide rich variants of advanced argillic alteration sulfide poor examples exhibit nearly complete removal of alkalis leaving a residuum of aluminum silicate quartz in contrast the sulfur poor variants lack the abundant pyrite other sulfides hypogene alunite al leached rocks residual vuggy quartz as well as the au cu ag as rich mineralization of some sulfur rich occurrences associated mineralization is dominated by magnetite and or hematite with accessory elements such as cu au ree and p these observations presented here indicate there must be distinct geologic processes that result in the formation of low sulfur advanced argillic styles of alteration hydrolysis of magmatic so 2 to sulfuric acid is the most commonly recognized mechanism for generating hypogene advanced argillic alteration but is not requisite for its formation low sulfur iron oxide copper gold systems are known to contain abundant acid styles of alteration e g sericitic chloritic which locally reaches advanced argillic assemblages a compilation of mapping in four districts in northern chile and reconnaissance observations elsewhere show systematic zoning from near surface low sulfide advanced argillic alteration through chlorite sericite albite and locally potassic alteration the latter is commonly associated with specular hematite chalcopyrite mineralization present at deeper structural levels are higher temperature styles of sodic calcic oligoclase scapolite actinolite alteration associated with magnetite chalcopyrite mineralization these patterns are in contrast to the more sulfur rich examples which generally zone to higher pyrite and locally alunite bearing alteration fluid inclusion evidence from the systems in northern chile shows that many fluids contain 25 to 50 wt nacl eq with appreciable ca fe and k contents with trapping temperatures 300 c these geological and geochemical observations are consistent with the origin of the low sulfur advanced argillic assemblages from hcl generated by precipitation of iron oxides from iron chloride complexes from a high salinity fluid by reactions such as 3fecl 2 4h 2 o fe 3 o 4 6hcl h 2 such hcl rich and relatively hso 4 poor fluids can then account for the intense acid al silicate rich styles of alteration observed at high levels in some iron oxide coppe gold iocg systems the geochemical differences between the presence of sulfide rich and sulfur poor examples of advanced argillic alteration are important to distinguishing between system types and the acid producing capacity of the system including in the modern weathering environment they have fundamental implications for effective mineral exploration in low sulfur systems and provide yet another vector of exposed alteration in the enigmatic iocg clan of mineral deposits furthermore understanding the geochemistry and mineralogy of this distinct geologic environment has applications to understanding the acid generating capacity and deleterious heavy metals associated with advanced argillic alteration

dynamics of the slope water off new england and its influence on the gulf stream as inferred from satellite ir data abstract the movements of warm core rings and the gulf stream front were studied in the new england slope water region by using both satellite ir data and available in situ sea surface temperature data it is found that 1 the rotating speed of the rings exhibits a marked seasonal variation with the maximum speed occurring in the winter and the minimum in the late fall 2 the surface area of the rings increases monotonically with time and 3 the gulf stream front at the north wall migrates seasonally and attains its northernmost position in the late fall based on these findings we calculated the horizontal eddy viscosity for the rings as 4 10 8 cm 2 5 furthermore by comparing the seasonal variations of the rotational velocity of the rings and the total mass transport of the gulf stream we suggest that the seasonal variation of the slope water hydrography through local air sea interactions could play an important role in the dynamics of the gulf stream system

source rock quality determination from oil biomarkers i a new geochemical technique biomarker analyses of the aspen shale mowry shale equivalent skully s gap wyoming suggest that vital source rock properties e g kerogen hydrogen to carbon h c ratio rock eval hydrogen index hi and maceral composition may be indirectly yet quantitatively predicted from the biomarker parameters measured in oils a strong correlation exists between the homohopane index of aspen source rock extracts and both the h c ratio and hi of the associated kerogen r2 0 93 and 0 83 respectively the percentages of c30 and c28 4 desmethyl steranes relative to total extracted 4 desmethyl steranes correlate with the percentage of marine derived amorphous type ii organic matter in the kerogen r2 0 80 and 0 73 respecti ely and with kerogen h c ratio and hi r2 0 89 and 0 88 respectively for c30 steranes r2 0 89 and 0 83 respectively for c28 steranes the ratio of 4 agr methyl 24 ethylcholestanes to 3s methyl 24 ethylcholestanes in the extracts also correlates with kerogen h c ratio and hi r2 0 93 and 0 92 respectively in contrast the percentage of c29 steranes in the extracts correlates with the percentage of higher plant derived vitrinite in the kerogen r2 0 69 and shows a negative correlation with h c ratio and hi r2 0 81 and 0 66 respectively these relationships were used to determine indirectly the source rock kerogen properties of several mowry derived oils the correlations etween biomarkers and source rock properties observed in the aspen shale probably apply to many deltaic and nearshore marine source rocks that were deposited after the evolution of vascular plants therefore prediction of source rock properties from oils in vertically drained basins could prove extremely useful to explorationists seeking to identify the most oil prone areas in regions such as the u s gulf coast the north sea the beaufort sea and the mahakam and niger deltas an example from the beaufort sea is given in this same issue mccaffrey et al 1994

trace fossil model for reconstructing oxygenation histories of ancient marine bottom waters application to upper cretaceous niobrara formation colorado abstract trends of decreasing trace fossil diversity burrow size and penetration depth with diminishing oxygen availability in contemporary marine settings have been incorporated with the concept of trace fossil tiering to develop a model for reconstructing the oxygenation history of ancient basin bottom waters more sensitive than traditionally employed criteria the model permits detailed evaluation of relative degree of oxygenation through the recognition of oxygen related ichnocoenosis ori units or units of strata deposited under similar levels of bottom water oxygenation when employed in detailed vertical sequence analyses the model may also be used to construct interpreted oxygenation curves that reflect rates and magnitudes of temporal change in redox conditions the utility of the model is demonstrated by its application to rhythmically bedded calcareous strata of the niobrara formation upper cretaceous exposed in colorado non laminated strata of the niobrara are characterized by four recurring trace fossil suites referred to as the 1 chondrites 2 zoophycos teichichnus 3 planolites and 4 thalassinoides assemblages on the basis of trends in trace fossil diversity burrow diameter and penetration depth these assemblages are recognized as oxygen related ichnocoenoses interpreted oxygenation curves for the basal fort hays member reflect high magnitude redox cycles characterized by rapid deoxygenation events followed by gradual reoxygenation phases curves for the overlying smoky hill member reflect an overall lower degree of oxygenation with more irregular lower magnitude redox fluctuations significant correlation between interpreted levels of paleooxygenation and organic carbon content illustrate the model s potential for evaluating the distribution of organic rich fine grained strata co interpretation of these variables with carbonate content supports the premise that deposition was controlled by paleoceanographic perturbations modulated by milankovitch like climatic cycles comparison with traditionally emphasized macroinvertebrate body fossil criteria clearly demonstrates the greater utility of the trace fossil approach for evaluating paleo oxygenation

genesis of acid sulfate alteration and au cu ag mineralization at summitville colorado the summitville au cu ag deposit occurs within a porphyritic quartz latite primarily in a zone of vuggy silica alteration characterized by leaching of all major elements except silica and iron vuggy silica is best developed between an elevation of 3 700 and 3 500 m where it occurs in irregular pipes and lenticular pods up to 70 m wide and is enclosed by up to 30 m of intense quartz alunite alteration the vuggy silica zones diminish in size with decreasing elevation and rarely exceed a width of 2 m below an elevation of 3 400 m these deep vuggy silica zones are enclosed by quartz kaolinite alteration with little or no alunite sulfide mineralization occurs primarily within the vuggy silica the sulfide assemblage changes with decreasing elevation from covellite luzonite or native gold to chalcopyrite tennantite sulfides occur lining voids or in microveinlets and are accompanied by minor kaolinitc but not by alunite gold also occurs in a near surface barite goethite jarosite assemblage that crosscuts the vuggy silica consideration of alunite kaolinitc and pyrite stability relations and of aluminum speciation at 250 degrees c indicates that a ph of 2 or below and a log f sub o 2 of 31 or 1 at 250 degrees c were necessary to produce vuggy silica alteration the chalcopyrite tennantite mineralization occurring at depth in the vuggy silica zone is indicative of less oxidizing and less acidic conditions the covellite luzonite or gold assemblage requires conditions intermediate between those necessary for vuggy silica alteration and for deep sulfide mineralization barite gold mineralization is interpreted as a near surface assemblage produced under highly acidic oxidizing conditions these textural and geochemical relationships indicate that sulfide and gold mineralization postdate the formation of vuggy silica alteration in the deposit and are not directly related to the highly acidic solutions necessary for this early acid leaching event the change from extreme acid leaching to copper sulfide and precious metal deposition may represent a transition from a magmatic vapor dominated to a liquid dominated system leading to more reducing and less acidic conditions during sulfide deposition

cretaceous climate a comparison of atmospheric simulations with the geologic record abstract atmospheric simulations using realistic cretaceous geography 100 million years ago suggest that paleography is an important factor governing the nature of the circulation the simulated cretaceous atmospheric circulations are markedly different both from the present day atmospheric circulation and from the classical hypotheses of a weaker circulation and poleward displacement of circulation features e g the subtropical high therefore they pose specific questions which can be tested against the geologic record aspects of the cretaceous simulations are verified in comparisons with the geologic record the simulations serve to guide areas of future paleoclimatic research and to formulate better the nature of the problem of warm equable climates

palaeoenvironmental turnover across the cenomanian turonian transition in oued bahloul tunisia foraminifera and geochemical proxies abstract the integrated analysis of foraminiferal assemblages geochemical proxies and stable isotopes in the oued bahloul section tunisia allowed us to reconstruct the environmental turnover across the cenomanian turonian boundary an increase in palaeoproductivity proxies p ti u al sr al and in 13 c values and a decrease in foraminiferal diversity and 18 o values mark the beginning of the oceanic anoxic event 2 oae2 at the rotalipora cushmani and whiteinella archaeocretacea biozones boundary eutrophic conditions at the seafloor and in the water column are evidenced by high proportions of buliminids and the replacement of planktic oligotrophic specialist rotalipora by eutrophic opportunist hedbergella the enrichment in organic matter and redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicate dysoxic conditions in the deep water column and at the seafloor higher u aut than mo aut among planktic foraminifera deep and intermediate dwellers disappear rotalipora and globigerinelloides and surface dwellers proliferate hedbergella the persistency of the poorly oxygenated conditions during the w archaeocretacea biozone locally produced euxinic conditions where mo ef and mo aut reach high values diversity presents minimum values and benthic foraminifera temporarily disappear the maximum percentage of heterohelicids indicates a stratified water column with a well developed oxygen minimum zone improved oxygen conditions returned in the upper part of the w archaeocretacea biozone and helvetoglobotruncana helvetica biozone with a slow recovery of foraminiferal assemblages decrease in eutrophic genera heterohelix and increase in mesotrophic genera whiteinella a gradual increase in 18 o values suggests decreased temperatures in surface waters the oae2 has been attributed to global temperature changes and palaeoceanographic reorganization the poor mixing of surface and deep waters and enhanced primary productivity related to global warming associated with increasing continental weathering and nutrient runoff may have favored the eutrophication of the ocean and the expansion of the oxygen minimum zone

geochemical evidence from bio apatite for multiple oceanic anoxic events during permian triassic transition and the link with end permian extinction and recovery abstract a detailed 20 myr redox history of permian to triassic oceans changhsingian to carnian stages has been constructed using ce anomaly ce and th u ratios from conodont albid crown apatite material the results show that the well established phenomenon of intense ocean anoxia coincident with the end permian mass extinction is faithfully recorded in conodont ce and th u data extending this conodont redox record shows that end permian anoxia persisted possibly into the earliest dienerian stage and that two intense oceanic anoxic events also occurred later in the early triassic earliest smithian earliest spathian and middle spathian followed by a weaker manifestation of anoxia in the anisian stage seen in ce data marine benthic radiation following the end permian mass extinction began after the smithian earliest spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions the failure of the middle spathian anoxic event to retard the evolutionary rebound implies shallow shelf seas remained well ventilated at this time even if the oceans did not other attributes of the early triassic record also closely coincide with redox fluctuations phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope swings that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light remineralised carbon and or indicate a trigger meachnaims related to increased fluxes of light c from siberian volcanic sources

chondrites a trace fossil indicator of anoxia in sediments the trace fossil chondrites a highly branched burrow system of unknown endobenthic deposit feeders occurs in all types of sediment including those deposited under anaerobic conditions in some cases such as the jurassic posidonienschiefer formation of germany chondrites occurs in black laminated carbonaceous sediment that was deposited in chemically reducing conditions in other cases such as numerous oxic clastic and carbonate units throughout the geologic column chondrites typically represents the last trace fossil in a biotutbation sequence this indicates that the burrow system was produced deep within the sediment in the anaerobic zone below the surficial oxidized zone that was characterized by freely circulating and oxidizing pore waters

geology and reconnaissance stable isotope study of the oyu tolgoi porphyry cu au system south gobi mongolia the oyu tolgoi porphyry cu au system in the south gobi desert mongolia comprises five deposits that extend over 6 km in a north northeast oriented zone they occur in a middle to late paleozoic arc terrane and are related to late devonian quartz monzodiorite intrusions the hugo dummett deposits are the northernmost and deepest with up to 1 000 m of premineral sedimentary and volcanic cover rock remaining they are the largest deposits discovered to date and characterized by high grade copper 2 5 cu and gold 0 5 2 g t mineralization associated with intense quartz veining and several phases of quartz monzodiorite intruded into basaltic volcanic host rocks sulfide minerals in these deposits are zoned outward from a bornite dominated core to chalcopyrite upward to pyrite enargite and covellite at shallower depth the latter high sulfidation state sulfides are hosted by advanced argillic alteration mineral associations this alteration is restricted mainly to dacitic ash flow tuff that overlies the basaltic volcanic rock and includes ubiquitous quartz and pyrophyllite kaolinite plus late dickite veins as well as k alunite al phosphate sulfate minerals zunyite diaspore topaz corundum and andalusite a reconnaissance oxygen hydrogen and sulfur isotope study was undertaken to investigate the origin of several characteristic alteration minerals in the oyu tolgoi system with particular emphasis on the hugo dummett deposits based on the isotopic composition of o h and s 18o so4 8 8 20 1 d 73 to 43 34s 9 8 17 9 the alunite formed from condensation of magmatic vapor that ascended to the upper parts of the porphyry hydrothermal system without involvement of significant amounts of meteoric water the isotopic data indicate that pyrophyllite 18o 6 5 10 9 d 90 to 106 formed from a magmatic fluid with a component of meteoric water muscovite associated with quartz monzodiorite intrusions occurs in the core of the hugo dummett deposits and isotopic data 18o 3 0 9 0 d 101 to 116 show it formed from a magmatic fluid with water similar in composition to that which formed the pyrophyllite mg chlorite 18o 5 5 d 126 is a widespread mineral retrograde after hydrothermal biotite and may have formed from fluids similar to those related to the muscovite during cooling of the porphyry system by contrast paragenetically later and postmineralization alteration fluid which produced dickite 18o 4 1 to 3 3 d 130 to 140 shows clear evidence for mixing with substantial amounts of meteoric water relatively low d values 140 for this meteoric water component may indicate that its source was at high elevations the geologic structure nature of alteration styles of mineralization and stable isotope data indicate that the oyu tolgoi deposits constitute a typical porphyry system formed in an island arc setting the outward zonation of sulfide minerals for the hugo dummett deposits from a bornite dominated core to chalcopyrite and pyriteenargite can be interpreted to be related to a cooling magmatic hydrothermal system which transgressed outward over enclosing advanced argillic alteration this resulted in some unusual alteration and sulfide parageneses such as topaz or pyrite enargite and tennantite entrained by high grade bornite

a model for the analysis of drifter data with an application to a warm core ring in the gulf of mexico a model developed primarily for the analysis of drifter data is discussed the model is based on a parametric representation of the drifter velocity in terms of monge potentials two of which are constants following the motion of the fluid in the application presented here one of the potentials is taken as the frequency of rotation about a ring by a parcel a more restricted interpretation of the velocity gradient in variant for horizontal flow is also discussed the other potential is taken as the streamline of a parcel that is locally approximated as a conic section for the restricted interpretation solutions to the model equations are critically dependent on the relative sizes of the squares of the vertical vorticity and the total deformation rate this model differs from drifter cluster models in that each drifter provides independent estimates of the vorticity and deformation rates application is made to path data from three drifters that were seeded in a warm core ring in the gulf of mexico in november 1980 the model provided estimates of the ring translation and swirl velocities along with the ring geometry the analysis showed that the ring was persistently elliptical with the major axis aligned in the east west direction a satellite infrared photo on january 21 1981 confirmed this orientation

regional mineral mapping of island arc terranes in southeastern mongolia using multi spectral remote sensing data abstract over the last few decades many porphyry cu deposits have been discovered in southeastern se mongolia in particular the gurvansayhan and mandalovoo island arc terranes have high potential for ore deposits regional mineral mapping of these terranes using data from the landsat enhanced thematic mapper plus etm and the advanced spaceborne thermal emission and reflection radiometer aster have provided new geological information on the metallogenic province revealing potential mineral deposits for future explorations iron oxides hydroxides with high etm band 1 3 ratio values occur extensively in quaternary deposits located at the boundary between the gurvansayhan and mandalovoo island arcs terranes and basins the high average band ratios 1 35 registered for the porphyry cu and au deposits and their occurrences are associated with iron oxidation which originates from the erosion and weathering of ore zones regional mapping of the island arc terranes using the aster shortwave infrared swir logical operators showed circular or semicircular alteration patterns which usually cluster along faults the mineral assemblages mapped by the aster swir analysis in five major porphyry cu districts can be divided into two types the first type includes argillic phyllic and propylitic mineral assemblages as exemplified by the shuteen ikh shankhai and oyu tolgoi deposits the second type of assemblage includes phyllic and propylitic mineral assemblages as exemplified by the kharmagtai and tsagaan suvarga deposits within the deposits of the first type quartz was also mapped using the aster thermal infrared tir mineral index the difference between the two types may be related to the presence of a lithocap the results of a field survey including spectral reflectance measurements in the ikh shankhai porphyry cu district showed a good correlation with the image analysis results

molecular and petrographic indicators of redox conditions and bacterial communities after the f f mass extinction kowala holy cross mountains poland abstract pyrite framboid diameter analysis and organic geochemistry of the triangularis crepida boundary section at kowala holy cross mountains poland imply suboxic to oxic and sporadically euxinic bottom waters during the lower famennian in addition morphological web like structures typical for microbial mats as well as the recognition of 2 methylhopanes and monomethyl alkane cyanobacteria biomarkers is evidenced of microbial activity after the global frasnian famennian f f extinction event the presence of cyanobacterial mats also suggests suboxic to oxic environments and at the same time photic bottom water conditions however isorenieratane and its derivatives were detected in almost all samples the presence of this well known biomarker of green sulfur bacteria implies that euxinic conditions were present in the upper part of the water column at least intermittently or that temporal euxinia occurred in the water column presence of euxinic conditions is confirmed by the occurrence of small sized pyrite framboids which were particularly dominant in the lower part of the section the shift towards low 13 c values in both micritic limestones and in sedimentary organic matter seen at the beginning of the period of diminished photic zone might reflect an influx of newly respired co 2 to surface waters caused by enhanced respiration at depth after the f f transition in the checiny zbrza basin

the genesis of glaucony in the oligo miocene torquay group southeastern australia petrographic and geochemical evidence abstract the oligo miocene torquay group at bird rock in southeastern australia comprises a sequence of fine grained skeletal carbonates and argillaceous and glauconitic sandstones which were deposited in a cool water mid shelf environment the bird rock glaucony consists predominantly of randomly interstratified glauconitic smectite which constitutes bioclast infills and faecal pellet replacements petrographic and geochemical evidence indicates that the glaucony is autochthonous and comprises chemical components derived primarily from argillaceous matrix material seawater is unlikely to be a significant source of ions the glauconitization of the bird rock sediments occurred under sub oxic partially reducing conditions in the very shallow burial environment and involved local iron redistribution sub oxic conditions favour glauconitization because iron is stable in the soluble ferrous state and can be fixed in authigenic silicates due to the negligible concentrations of hydrogen sulphide it is likely that localised acidic conditions were initiated during the glauconitization process this acidity appears to have been buffered by the dissolution of bioclastic carbonate the fact that glaucony predominantly occurs as bioclast infills and faecal pellet replacements implies that the physico chemical conditions appropriate for glauconitization develop preferentially in such biogenic detritus the development of appropriate micro environments within such sediments probably relates to their physical confinement and or high organic matter content the bird rock glaucony developed during intervals of slow sedimentation and environmental quiescence associated with marine flooding events these conditions facilitated glauconitization by allowing the favoured clay rich sediments to accumulate and remain in the appropriate physico chemical regime sufficiently long for the complex glauconitic structures to form

satellite and hydrographic observations of low frequency wave motions associated with a cold core gulf stream ring thermal infrared data from the noaa polar orbiting satellite and hydrographic observations from surface ships are used to estimate the eccentricity and the rotation rate of wavelike perturbations around the circumference of a gulf stream cyclonic eddy in april 1977 from the satellite data the rotation rate is estimated at 4 4 0 1 10 6 s 1 for the period april 8 16 estimates of are obtained from the trajectory of satellite tracked drifters and from changes in the sea surface temperature fields determined from expendable bathythermograph trace xbt surveys a simple eady model suggests the perturbations are stable modes of azimuthal wave number 2

production and preservation of organic matter the significance of iron 1 iron fertilization has been previously recognized as a potential mechanism for enhanced organic matter burial in marine sediments however the singular view of iron as a control on primary production overlooks its role in sedimentary diagenesis a factor that must be evaluated when considering organic matter accumulation this study examines the role of iron as a buffer of pore water sulfide and its implications for marine organic matter burial biogeochemical model experiments indicate that dissolved sulfide buildup in surficial marine sediments is highly sensitive to reactive iron concentration a reduction in reactive iron concentration can initiate dissolved sulfide accumulation the consequences of which include inhibition of bioturbation bioirrigation a decrease in oxygen exposure time and enhanced organic matter burial alternatively an increase in reactive iron concentration can serve to decrease organic matter burial the coupling of iron and phosphorous cycling within marine sediments provides an important positive feedback and therefore this mechanism is designated the sulfide buffer phosphorous trap hypothesis given sufficient organic carbon supply carbonate rich and opal rich sediments should be especially prone to the development of sulfidic conditions because of a deficiency in terrigenous iron widespread chalk and marl deposition during the cretaceous in association with the evolutionary expansion of calcareous plankton may have predisposed many benthic marine environments to the accumulation of toxic hydrogen sulfide and fostered the development of oceanic anoxic events comparison of model results with proxy data from oceanic anoxic event ii middle cretaceous suggests a complex role of iron as a control on both organic matter production and preservation

trace elements and cathodoluminescence of quartz in stockwork veins of mongolian porphyry style deposits the combination of scanning electron microscope cathodoluminescence cl fluid inclusion analysis and high resolution electron probe microanalysis of al ti k and fe in vein quartz has yielded results permitting a greater understanding of the complex mineralisation of the central oyu tolgoi and zesen uul porphyry style deposits southern mongolia these data demonstrate the relationship between quartz precipitation dissolution and ore deposition as the mineralising fluid chemistry changed through time four major quartz generations are identified in the a type veins from the stockworks of both the central oyu tolgoi oti to otiv and zesen uul deposits zui to zuiv despite differences in the associated alteration and mineralisation style the observed cl textures and trace element signatures of the quartz generations are comparable between deposits the oti and zui stage formed both the primary network of a type veins and pervasive silicification of the host rock using the ti in quartz geothermometer crystallisation temperatures for oti and zui of between 598 c and 880 c are indicated the main stage of sulphide mineralisation was accompanied by the dissolution of pre existing quartz oti and zui and precipitation of a weakly luminescent generation of quartz otii and zuii with a low ti content reflected in a calculated temperature drop from approximately 700 c to 340 c in central oyu tolgoi and 445 c in zesen uul otii and zuii stage quartzes show high and variable al concentrations the next stage of quartz in both deposits otiii and zuiii forms a fine network of veins in cracks formed in pre existing quartz otiii and zuiii quartz contain measurable fluid inclusions of moderate salinity 3 17 1 wt nacl eq entrapped in the temperature range 256 c to 385 c otiii and zuiii are not related to any sulphide mineralisation the final otiv and zuiv stages are characterised by quartz calcite micro breccias that penetrate the a type veins based on the calculated entrapment temperatures the otiv zuiv stage crystallised between 212 c and 335 c and the quartz is characterised by elevated but variable al and fe contents the cl and trace element signatures of the oti to otiii and zui to zuiii stages of the two mongolian porphyries show similar features to those observed in porphyry style deposits from other regions this suggests that a common sequence of quartz crystallisation occurs during the formation of early veins in many porphyry copper systems

constraints on magma degassing beneath the far southeast porphyry cu au deposit philippines k silicate alteration in the far southeast fse porphyry cu au introduction deposit formed at 1 4 ma concentric to dikes of quartz diorite magmas become saturated with volatile components as porphyry at 2 km paleodepth the hydrothermal system consisted they ascend in the crust and either erupt or crystallize of magmatic hypersaline liquid and vapor at 550 c and 50 at depth saturated magmas that remain at depth exsolve mpa lithostatic pressure advanced argillic alteration formed at an aqueous fluid that forms a hydrothermal system on the same time over the deposit at 1 km paleodepth from acidic separation from the magma chamber burnham 1979 condensates of the vapor at 1 3 ma k silicate alteration was although part of the exsolved fluid a low density vapor overprinted by 350 c magmatic liquid 5 wt nacl equiv may discharge to the surface from passively degassing at hydrostatic pressure sericite alteration and much of the cu au volcanoes hedenquist 1995 part will remain at depth mineralization formed at this later stage evolution of the magmatic and this dense residual magmatic liquid may be asfluid composition was simulated with a magma chamber cryssociated with hydrothermal mineralization in the portallization model homogeneous crystallization during early stage phyry ore environment hedenquist lowenstern convection is assumed whereas at 50 vol crystals the chamber 1994 becomes stagnant and crystallizes from rim to core over a narrow in this paper we use evidence from a porphyry ore crystallization interval the model calculation based on a magma deposit in the philippines to determine the composition chamber with 2 km thickness at 6 km depth 150 mpa and of the fluid that exsolved from the deeper parent magma 800 c saturated melt composition at 30 vol crystals 5 the evolving composition of the magmatic fluid at the wt h2o 0 2 wt cl and dd of 40 can reproduce the depth of the ore body can then be used to place constraints chemical and isotopic compositions of the early and late magmatic on the nature of the evolved magma chamber far below fluids the most critical factor controlling the compositional evolution the porphyry ore body this approach differs from that of the model hydrothermal system is the transition from convective of other studies where a portion of the parent magma to stagnant magma chamber crystallization there is also a sharp chamber is available to study directly e g at yerington decrease in the rate of fluid exsolution associated with this transition nevada dilles 1987 which can account for the thermal collapse of the fse porphyry the far southeast fse porphyry cu au deposit system from k silicate to sericite alteration and overlying lepanto epithermal cu au ore body are

trace fossil model for reconstruction of paleo oxygenation in bottom waters recognition of fluctuations in the degree of paleo oxygenation of bottom waters recorded in fine grained pelagic strata is important for interpretation of paleoceanographic and paleoclimatologic conditions general sedimentary fabric composition of trace fossil assemblages and burrow size and crosscutting relationships have been incorporated into a trace fossil tiering model that permits detailed reconstruction of changes in paleo oxygenation of bottom waters applications of this model to the miocene monterey formation california and the cretaceous niobrara formation colorado indicate that the ichnologic approach is more sensitive to both magnitude and rates of change in oxygenation levels compared to macrobenthic body fossil information

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

warming and environmental changes in the eastern north sea basin during the palaeocene eocene thermal maximum as revealed by biomarker lipids analysis of sediments deposited at different latitudes around the world during the palaeocene eocene thermal maximum petm 56 ma have revealed a globally profound warming phase regionally varying from 5 8 c such records from europe have not yet been obtained we studied the variations in sea surface and continental mean annual air temperatures sst and mat respectively and the distribution patterns and stable carbon isotopes of higher plant derived n alkanes in two proximal petm sections fur and store baelt denmark from the epicontinental north sea basin a negative carbon isotope excursion cie of 4 7 was recorded in land plant derived n alkanes similar to what has been observed for other petm sections however differences observed between the two proximal sites suggest that local factors such as regional vegetation and precipitation patterns also influenced the cie the presence of s bound isorenieratene derivatives at the onset of the petm and increased organic carbon contents points to a rapid shift in depositional environment from well oxygenated to anoxic and sulfidic these euxinic conditions are comparable with those during the petm in the arctic ocean ssts inferred from tex86 show relatively low temperatures followed by an increase of 7 c across the petm at the fur section a remarkably similar temperature record was obtained for mat using the mbt cbt proxy however the mat record of the store baelt section did not reveal this warming

do marine faunas track lithofacies faunal dynamics in the upper cretaceous pierre shale western interior usa abstract most studies examining faunal assemblages use their sedimentary context as a critical element in constraining and reconstructing their underlying environmental controls this has resulted in the assumption that an absence of lithofacies change in a section should be reflected in a lack of environmental variation this inference however has been placed into question by evidence that marine species are influenced by a broader range of environmental dynamics than just change in lithofacies in this study we examine the sensitivity of marine faunas to broadly defined environmental change within lithologically homogenous strata by examining concretionary fossil assemblages of the baculites eliasi through b clinolobatus biozones in monotonous clay rich strata of the campanian maastrichtian pierre shale in wyoming we recognize five biofacies which reflect different environmental conditions related to benthic oxygenation substrate firmness and water depth analyses of abundance patterns raw species richness trends and life habit patterns display recurrent switching upsection between low and high diversity intervals our data reveal that samples with lower diversity show a strong relationship with intervals when water conditions were deepest whereas higher diversity samples are associated with periods when shallow water conditions prevailed in the study area the distribution of taxa and diversity of the assemblages most likely reflect migrating oxygen and substrate controlled biofacies that were responding to changes in depth this study shows that substantial changes in biofacies diversity and life habits can arise in response to variations in water depth with limited to no apparent change in lithofacies supporting the hypothesis that fossil taxa are much more sensitive indicators of environmental change than lithofacies

organic matter accumulation of the wufeng longmaxi shales in southern sichuan basin evidence and insight from volcanism abstract the wufeng longmaxi formations wf lm fms in the sichuan basin are sets of graptolite bearing shale strata containing high frequency bentonite layers in order to investigate the influence of volcanism on the organic matter om accumulation in shales detailed observations of several typical profiles and wells were performed also analyses including total organic carbon toc contents and mineral compositions were conducted on 126 shale and 5 bentonite core samples major and trace element analyses were conducted on the selected 25 shale and 5 bentonite samples in the wf lm fms of well lu a results show that wf and lm1 4 members are the bentonites concentrated sections while lm5 6 are the bentonites relatively concentrated sections and no bentonite is found in lm7 9 members the high potassium k content of bentonites have the typical characteristics of intermediate acid calcium alkaline volcanic rocks such as andesite and dacite which probably originated from intraplate collision or volcanic arc structural backgrounds related to the collision belt of the cathaysia block to the yangtze block productivity indicators p content excess si p al cu al and ni al in the wf and lm1 3 members are all significantly higher than those in the lingxiang lx and lm4 5 members the higher biological productivity during the ordovician silurian o s transition was attributed to the massive and intensive volcanism the fertilization by volcanic ash brought abundant biologically relevant nutrient elements n p si fe and al into the ocean thus triggering the phytoplankton bloom and enhancing primary biological productivity all the redox condition indexes moef uef nief vef mo toc corg p and u th positively correlate with toc content during the o s transition the intensive and massive volcanic eruptions triggered global cooling sea level changes late ordovician mass extinction and primary productivity increases thus promoting anoxic and possibly intermittently euxinic bottom conditions in addition the deposited bentonite layers had a strong capacity for oxygen isolation volcanism should be considered when modeling the om accumulation of the wf lm shales

paleoenvironmental and paleoceanographic changes across the cenomanian turonian boundary event oceanic anoxic event 2 as indicated by foraminiferal assemblages from the eastern margin of the cretaceous western interior sea abstract two sites near the eastern margin of the cretaceous western interior sea wis were investigated the section at cuba kansas ck is 630 km east of the gssp for the cenomanian turonian boundary at rock canyon colorado rc and the section near sioux city iowa sci is 315 km northeast of the cuba site surprisingly planktic foraminifera dominate all the studied samples despite the relative proximity of the sites to the paleo shoreline and presumed neritic water depths such dominance suggests inhospitable benthic environments and benthic foraminiferal assemblages indicate that seafloor oxygen in the wis decreased eastward therefore the hypothesis of an influx of freshwater into the wis from the western margin forming a fresh water cap that diminished eastward is not supported benthic foraminifera are scarce in most studied samples and species diversity is low in the ck section diversity and abundance increase abruptly in the uppermost cenomanian benthonic zone at the initiation of the 13corg positive excursion marking the onset of oceanic anoxic event oae 2 in the sci section however the benthonic zone is recognized only by presence of nodosaria bighornensis that has a stratigraphic range restricted to this interval other benthic taxa are very rare or absent the favorable conditions of the benthonic zone were short lived while relatively diverse planktic foraminiferal assemblages including keeled species characterize the initial 13c excursion at the ck site dwarfed specimens of heterohelix and hedbergella dominate the assemblages at the more proximal sioux city site furthermore most of the biostratigraphic events recognized in the basin center rc section can be traced into the ck section but not into the sci section including the rotalipora spp and globigerinelloides bentonensis extinctions the heterohelix shift event and the brief benthic recovery event correlation between eastern wis sites shows that the sci section is thicker suggesting a major sediment source to the east this may explain the inhospitable benthic conditions and development of a dead zone seasonal hypoxia analogous to the modern shelf of the northern gulf of mexico proximal to active discharge of the mississippi river development of estuarine circulation in the wis provided the eastern part of the basin with input of calcareous plankton from the south including planktic foraminifera foraminiferal assemblages total organic carbon toc and 13c data of the studied sections suggest a two fold history of greenhorn transgression and oae 2 development the initial phase is a global signal characterized by a positive 13c excursion low toc values and high foraminiferal species diversity the second phase is characterized by overprinting by local conditions in the wis including high fluvial input relatively high toc values and low foraminiferal species diversity these findings suggest that the eastern margin records unique depositional and biotic environments further revealing the dynamic and complex nature of the wis and its sedimentary cycles

characteristics and 40ar 39ar geochronology of the erdenet cu mo deposit mongolia the early to middle triassic erdenet porphyry cu mo deposit in northern mongolia developed in a continent continent arc collision zone within the central asian orogenic belt the porphyry system is related to multiple intrusions of crystal crowded biotite granodiorite porphyry which formed a composite stock about 900 m in diameter with multiple porphyritic microgranodiorite dikes wall rocks are late permian to early triassic medium grained granodiorite with similar whole rock geochemistry mineralogy and composition to the granodiorite porphyry whole rock analysis of the granodiorite porphyry and wall rocks shows that these rocks cannot be discriminated but both have depleted middle heavy rare earth elements and y typical of fertile porphyry magmatic suites at the current pit level 1 250 m elev early porphyry style quartz veins a and b type are locally infilled by pyrite chalcopyrite with subordinate bornite but most of the chalcopyrite occurs in d veins that constitute more than 50 of the cu grade 0 5 wt cu the 0 3 wt cu shell resembles a molar tooth enveloping the granodiorite porphyry with deeper roots extending down the wal rock contacts molybdenite occurs in monomineralic veins and in finely laminated to massive quartz molybdenite veins the most important alteration is quartz muscovite which occurs as relatively coarse 100 500 m alteration selvages 1 5 cm that envelop d veins the d veins cut illite kaolinite smectite or intermediate argillic alteration intermediate argillic alteration together with abundant pink anhydrite commonly hydrated to gypsum extends from at least 1 300 to 900 m elevation in the deepest drill holes and has overprinted early potassic alteration or relatively unaltered red granodiorite meter wide zones of kaolinite cut the anhydrite gypsum at all levels there is an abrupt transition outward from the intermediate argillic alteration to chlorite epidote propylitic alteration at 50 to 200 m from the granodiorite porphyry contact although d veins and chalcopyrite extend outward to the propylitic zone the erdenet porphyry system was overprinted by advanced argillic alteration which outcrops 2 km northwest of the pit and forms a lithocap that extends over 10 2 5 km it is characterized by residual quartz andalusite na ca and k alunite diaspore pyrophyllite zunyite topaz dickite and kaolinite the upper part of the porphyry cu mo deposit removed by mining comprised a bornite chalcocite enriched zone up to 300 m thick with an average grade of 0 7 wt cu and up to 5 wt cu locally based on hypogene bornite chalcocite mineral textures and high sulfidation state mineralogy the enriched zone is inferred to be of hypogene origin but modified by supergene processes consequently it may be related to formation of the lithocap previous re os dates of 240 4 and 240 7 0 8 ma for molybdenite in quartz veins are comparable to new 40 ar 39 ar dates of 239 7 1 6 and 240 2 ma for muscovite that envelops d veins one 40 ar 39 ar date on k alunite from the lithocap of 223 5 1 9 ma suggests that it may be about 16 m y younger than erdenet but this result needs to be verified by further dating

an intense cyclonic eddy east of the mozambique ridge data from cruises of the meiring naude in 1978 delineated an intense cyclonic eddy in the vicinity of 30 s 38 e and extending to a depth of more than 1800 m between may and june 1978 the eddy advected to the southeast at 5 cm s 1 the eddy was elliptical 90 240 km and the volume transport varied between 20 and 48 106 m3 s 1

undiscovered porphyry copper resources in the urals a probabilistic mineral resource assessment abstract a probabilistic mineral resource assessment of metal resources in undiscovered porphyry copper deposits of the ural mountains in russia and kazakhstan was done using a quantitative form of mineral resource assessment permissive tracts were delineated on the basis of mapped and inferred subsurface distributions of igneous rocks assigned to tectonic zones that include magmatic arcs where the occurrence of porphyry copper deposits within 1 km of the earth s surface are possible these permissive tracts outline four north south trending volcano plutonic belts in major structural zones of the urals from west to east these include permissive lithologies for porphyry copper deposits associated with paleozoic subduction related island arc complexes preserved in the tagil and magnitogorsk arcs paleozoic island arc fragments and associated tonalite granodiorite intrusions in the east uralian zone and carboniferous continental margin arcs developed on the kazakh craton in the transuralian zone the tracts range from about 50 000 to 130 000 km 2 in area the urals host 8 known porphyry copper deposits with total identified resources of about 6 4 million metric tons of copper at least 20 additional porphyry copper prospect areas and numerous copper bearing skarns and copper occurrences probabilistic estimates predict a mean of 22 undiscovered porphyry copper deposits within the four permissive tracts delineated in the urals combining estimates with established grade and tonnage models predicts a mean of 82 million metric tons of undiscovered copper application of an economic filter suggests that about half of that amount could be economically recoverable based on assumed depth distributions availability of infrastructure recovery rates current metals prices and investment environment

bedding rhythms and cyclic sequences as documented in organic carbon carbonate patterns upper cretaceous western interior u s abstract a three component sedimentation model is introduced for estimating the relative effects of major changes in sediment flux coupled organic carbon carbonate changes reflecting different dilution concentration styles are utilized to detect the changing flux between the carbonate siliciclastic and organic matter components the three component model is then applied to upper cretaceous rhythmically bedded units of the greenhorn and niobrara cycles of the western interior seaway the cycles are related to third order sea level changes the western interior seaway was sensitive to small scale climatic cycles only during periods of maximum flooding due to combined variations in carbonate productivity redox conditions and siliciclastic supply from continental sources rhythmic deposition is different for different parts within the periods of maximum flooding for each of the two investigated third order sea level cycles section intervals reflecting peak flooding show variations in carbonate productivity and variations in redox conditions slightly more regressive intervals show variations in calcareous productivity and siliciclastic dilution with stagnant dysaerobic bottom waters for most of the investigated bedding rhythms persistent dysaerobic bottom waters are largely uninfluenced by variations in pelagic carbonate productivity except for section intervals representing peak flooding this suggests the existence of a circulation pattern in which a mixed surface water zone was underlain by more stratified oxygen depleted water masses with slow circulation

zircon u pb geochronology geochemistry and sr nd hf isotopes of granitoids in the yulekenhalasu copper ore district northern junggar china petrogenesis and tectonic implications abstract the yulekenhalasu porphyry copper deposit is located in the kalaxiange er metallogenic belt in northern junggar china we present the results from zircon u pb geochronology and geochemical and sr nd hf isotope analyses of the granitoids associated with the ore deposits with a view to constrain their petrogenesis and tectonic setting the granitoids consist of quartz diorite diorite porphyry porphyritic monzonite and quartz porphyry emplaced at 382 379 375 374 and 348 ma respectively which span late devonian to early carboniferous ages the ore bearing intrusion is mainly diorite porphyry with subordinate porphyritic monzonite the late devonian intrusions are characterized by sio2 contents of 54 5 64 79 wt na2o contents of 3 82 8 24 wt enrichment in na light rare earth elements lrees and large ion lithophile elements they also display relative depletion in y ba p nb ta and ti and weak negative eu anomalies eu 0 6 0 87 the early carboniferous quartz porphyry is characterized by high sio2 content 72 26 73 35 wt enrichment in lrees k and sr and relative depletion in y 10 82 12 52 ppm and yb 1 06 1 15 ppm the late devonian and early carboniferous granitoids are characterized by positive end t values 5 2 10 1 one sample at 1 9 positive ehf t values 7 46 18 45 low 87sr 86sr i values 0 70363 0 70476 and young crustal residence ages these data indicate that the sources of the granitoids were mainly mantle derived juvenile rocks geochemical and nd sr hf isotopic data demonstrate that the late devonian granitoids formed in an oceanic island arc and they were formed from different sources among which the mineralized diorite porphyry might have originated from a mixed slab derived and mantle wedge melt source the early carboniferous quartz porphyry was likely emplaced in a mature island arc environment and was probably derived from juvenile crust

the palaeoecological and palaeoclimatic significance of miocene freshwater diatomite deposits from southern new south wales australia abstract the bonnie doon member of the bunyan formation is a relatively extensive diatomite deposited over about 100 ka during the mid to late miocene the diatomite was deposited in a shallow eutrophic slightly alkaline lake with low salinity and turbidity the deposit consists of well laminated massive and bioturbated and dark organic rich diatomine facies which are dominated by melosira granulata the deposit is cyclic at three scales 1 paired laminae of diatomite and diatomite plus clay the thickness of which varies with a period of 11 6 23 2 and 51 2 yr 2 packets of varves variable thickness composed of 10 25 paired laminae each and 3 megascopic cycles about 1 m thick of laminated diatomite grading up into massive and or brecciated diatomite and thence into bioturbated dark coloured diatomite these cycles are interpreted as 1 strong annually seasonal variations in temperature and or light availability 2 packets reflecting wide variations in solar activity and 3 longer term climatic instability with a period less than or equal to 8 ka which produced cycles we interpret as shallowing upwards variations in the lake levels on this basis we conclude that strong climatic seasonality existed at this locality during the late miocene as well as longer term climatic cycles

redox controlled preservation of organic matter during oae 3 within the western interior seaway during the cretaceous widespread black shale deposition occurred during a series of oceanic anoxic events oaes multiple processes are known to control the deposition of marine black shales including changes in primary productivity organic matter preservation and dilution oaes offer an opportunity to evaluate the relative roles of these forcing factors the youngest of these events the coniacian to santonian oae 3 resulted in a prolonged organic carbon burial event in shallow and restricted marine environments including the western interior seaway new high resolution isotope organic and trace metal records from the latest turonian to early santonian niobrara formation are used to characterize the amount and composition of organic matter preserved as well as the geochemical conditions under which it accumulated redox sensitive metals mo mn and re indicate a gradual drawdown of oxygen leading into the abrupt onset of organic carbon rich up to 8 deposition high hydrogen indices hi and organic carbon to total nitrogen ratios c n demonstrate that the elemental composition of preserved marine organic matter is distinct under different redox conditions local changes in 13c indicate that redox controlled early diagenesis can also significantly alter 13corg records these results demonstrate that the development of anoxia is of primary importance in triggering the prolonged carbon burial in the niobrara formation sea level reconstructions 18o results and mo total organic carbon ratios suggest that stratification and enhanced bottom water restriction caused the drawdown of bottom water oxygen increased nutrients from benthic regeneration and or continental runoff may have sustained primary productivity

pliocene holocene evolution of depositional conditions in the eastern mediterranean role of anoxia vs productivity at time of sapropel deposition a multiproxy geochemical study of nine sapropel layers from odp hole 964a odp leg 160 in the eastern mediterranean spanning the pliocene holocene time interval provides new insights into the evolution of sapropel deposition paleoenvironmental proxies were used for reconstruction of productivity ba derived from marine barite oxygen conditions trace metal ratios and sedimentary regime clay minerals detrital elements these proxies reveal a significant increase in river runoff relative to decreasing aeolian input during sapropel deposition over the whole time interval ba excess supports the argument that a significant increase in export productivity is the main triggering mechanism for sapropel deposition although preservation also played an important role furthermore major differences exist in depositional conditions including both oxygenation and productivity since the pliocene productivity fluctuated substantially and was higher during the pliocene and pleistocene than during the holocene at the same time decreasing oxygen availability parallels the enhanced productivity dysoxic to anoxic conditions appear to coincide with marine productivity maxima thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation this correspondence supports the hypothesis that productivity fluctuations resulting from climate oscillations were the main cause of enhanced organic matter contents and also a main controlling factor for reduced oxygen availability