steryl ethers in a valanginian claystone molecular evidence for cooler waters in the central pacific during the early cretaceous abstract coring on shatsky rise by ocean drilling project leg 198 recovered sediments rich in organic matter 2 0 corg from three time intervals the early aptian corresponding to oceanic anoxic event oae 1a the valanginian and the berriasian episodes of enhanced sequestration of organic matter during the valanginian are well documented in the tethyan realm notably those associated with a positive 13c isotopic excursion and with changes in plankton assemblages including a demise in nannoconids the 13c excursion has been previously reported in the pacific but the occurrence of valanginian sediments rich in organic matter 1 corg is unprecedented a distinctive feature of the biomarker composition of these valanginian sediments at shatsky rise is the presence of a suite of steryl ethers which extends the temporal record of these compounds from the neogene to the early cretaceous the biological source of steryl ethers remains enigmatic although the sedimentary occurrences of these compounds in quaternary and neogene environments characterized by cool water high seasonal productivity and or nutrient enrichment by upwelling in combination with their liquid crystal properties raise the possibility that they may represent storage lipids akin to wax esters and triacylglycerols prior occurrences of steryl ethers suggest that their presence in the valanginian may reflect an oceanic environment characterized by upwelling consistent with the likely position of shatsky rise within the equatorial divergence zone of the pacific during the early cretaceous alternatively or in addition the appearance of these compounds may represent a biological response to cooler temperatures and thereby augment evidence for global cooling during the early valanginian consistent with independent paleontological evidence for contemporaneous upwelling induced increases in productivity in the western atlantic

iron oxide copper gold iocg deposits through earth history implications for origin lithospheric setting and distinction from other epigenetic iron oxide deposits the iron oxide copper gold iocg group of deposits initially defined following discovery of the giant olympic dam cu u au deposit has progressively become too embracing when associated deposits and potential end members or analogs are included the broader group includes several low ti iron oxide associated deposits that include iron oxide p rich iron oxide f and ree rich fe or cu au skarn high grade iron oxide hosted au cu carbonatite hosted cu ree and f rich and iocg sensu stricto deposits consideration of this broad group as a whole obscures the critical features of the iocg sensu stricto deposits such as their temporal distribution and tectonic environment thus leading to difficulties in developing a robust exploration model the iocg sensu stricto deposits are magmatic hydrothermal deposits that contain economic cu and au grades are structurally controlled commonly contain significant volumes of breccia are commonly associated with presulfide sodic or sodic calcic alteration have alteration and or brecciation zones on a large commonly regional scale relative to economic mineralization have abundant low ti iron oxides and or iron silicates intimately associated with but generally paragenetically older than fe cu sulfides have lree enrichment and low s sulfides lack of abundant pyrite lack widespread quartz veins or silicification and show a clear temporal but not close spatial relationship to major magmatic intrusions these intrusions where identified are commonly alkaline to subalkaline mixed mafic even ultramafic to felsic in composition with evidence for mantle derivation of at least the mafic end members of the suite the giant size of many of the deposits and surrounding alteration zones the highly saline ore fluids and the available stable and radiogenic isotope data indicate release of deep volatile rich magmatic fluids through devolatization of causative mantle derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional scale fluid flow paths precambrian deposits are the dominant members of the iocg group in terms of both copper and gold resources the 12 iocg deposits with 100 tonnes t resources are located in intracratonic settings within about 100 km of the margins of archean or paleoproterozoic cratons or other lithospheric boundaries and formed 100 to 200 m y after supercontinent assembly their tectonic setting at formation was most likely anorogenic with magmatism and associated hydrothermal activity driven by mantle underplating and or plumes limited amounts of partial melting of volatile rich and possibly metal enriched metasomatized early precambrian subcontinental lithospheric mantle sclm fertilized during earlier subduction probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the iocg deposits preservation of near surface deposits such as olympic dam is probably due to their formation above buoyant and refractory sclm which resisted delamination and associated uplift most precambrian iron oxide p rich or magnetite apatite kiruna type deposits have a different temporal distribution apparently forming in convergent margin settings prior to or following supercontinent assembly it is only in the phanerozoic that iocg and magnetite apatite deposits are roughly penecontemporaneous in convergent margin settings the phanerozoic iocg deposits such as candelaria chile occur in anomalous extensional to transtensional zones in the coastal cordillera which are also the sites of mantle derived mafic to felsic intrusions that are anomalous in an andean context this implies that special conditions possibly detached slabs of metasomatized sclm may be required in convergent margin settings to generate world class iocg deposits it is likely that formation of giant iocg deposits was mainly a precambrian phenomenon related to the extensive mantle underplating that impacted on buoyant metasomatized sclm generally smaller and rarer phanerozoic iocg deposits formed in tectonic settings where conditions similar to those in the precambrian were replicated

organic carbon and sedimentation rate further evidence for anoxic deep water conditions in the cenomanian turonian atlantic ocean abstract the relationship between organic carbon content and sedimentation rate based on data derived from recent to miocene sediments deposited under oxic and anoxic sea water conditions is used to characterize the different depositional environments these data are compared with data of cenomanian turonian dsdp sediments from the atlantic ocean the results may support deposition in anoxic environments due to extremely reduced deep water circulation as the main cause for the formation of cenomanian turonian black shales in the north atlantic rather than increased supply of organic matter due to higher oceanic productivity

halogen and ar ar age determinations of inclusions within quartz veins from porphyry copper deposits using complementary noble gas extraction techniques abstract extension of ar ar methodology has been used to determine mineralisation ages from mica inclusions and to simultaneously evaluate the noble gas and halogen composition of inclusion fluids within irradiated quartz vein samples from five porphyry copper deposits samples have been collected from the potassic and propylitic zones of bingham canyon utah and four arizonan deposits silverbell globe miami pinto valley and ray data obtained using three noble gas extraction techniques laser ablation in vacuo crushing and stepped heating are compared with each other laser ablation provides a means for the analysis of individual fluid inclusions but is limited by blank levels and detection limits stepped heating and in vacuo crushing are bulk extraction techniques that preferentially release gases from solid and fluid inclusion phases respectively and can be used in combination to obtain accurate and meaningful ages of mineralisation ages obtained for porphyry copper deposits are as follows bingham canyon 37 1 0 5 ray 65 3 1 5 globe miami 61 7 3 4 pinto valley 63 2 8 0 and silverbell 55 8 1 8 the age of mineralisation at ray is of particular interest as it enables a reported discrepancy in k ar ages to be understood halogen data for the bingham canyon samples gives insight into the partitioning of the heavy halogens br and i between solid and liquid phases

mineral composition of sedimentary formations in the north atlantic ocean sedimentary formations established in the western north atlantic basin byjansa et al 1979 and their coeval counterparts from the eastern north atlantic were studied for their mineral composition using x ray powder diffractometry more than thousand samples from different legs of the deep sea drilling project were analysed semiquantitatively the results are presented as diagrams of about thirty five different mineral phases versus depth stratigraphy in the single boreholes sites 105 106 386 387 391 417 and 418 were studied from the western north atlantic and sites 367 369 370 415 and 416 from the eastern north atlantic off w africa specific mineral spectra were found from most of the formations which can thus be additionally characterized the change of mineral composition along the formation boundaries is in most cases sharp but along some of the boundaries it is transitional local variations of mineral spectra within the same formation can mainly be referred to distance from source areas the sedimentary section studied from the western north atlantic basin ranges in age from oxfordian to quaternary it consists of argillaceous limestones cat gap formation limestones blake bahama formation claystones and shales hatteras formation zeolitic claystones plantagenet formation nanno marls crescent peaks member siliceous oozes clays and cherts bermuda rise formation and hemipelagic muds blake ridge formation with locally redeposited shallow water carbonates great abaco member a corresponding section in the eastern north atlantic is only developed at site 367 where similar mineral assemblages could be found at sites 369 370 415 and 416 the sediment sequence is dominated by turbiditic influx of terrigenous components alternating with pelagic sediments this can clearly be depicted from the mineral suites but it is not possible to establish sedimentary formations which can be paralleled to those within the western north atlantic seismically mappable reflectors which were calibrated at the sediment sequence of the drillsites are in most cases related to lithological changes and mineral composition these acoustic horizons are very often coincident with formation boundaries besides different mineral composition changes in grain size and diagenesis but also erosional unconformities are responsible for the impedance contrasts leading to the reflectors as already pointed out bytucholke 1979

aquifer protection during longwall mining of shallow coal seams a case study in the shendong coalfield of china large scale underground mining of shallow coal seams can have significant impacts on ground surface and potentially leads to incidental damage to the overlying aquifer with subsequent environmental hazards in order to deal with the apparent conflict between water protection and high production in underground mining an aquifer protection mining technique was trialed in panel 51201 in the shangwan colliery the shendong coalfield china overburden failure water level of the unconsolidated aquifer surface cracks and ground subsidence were monitored in a series of boreholes using borescope and also by observations in a nearby water well and by surface surveys monitoring results indicate that the aquifer protection mining technique can be successfully applied by modifying a few mining parameters such as mining height or advance rate under some suitable geological conditions the critical zone in the stratigraphy appears to be the weathered bedrock located immediately below the aquifer the weathered bedrock will remain impermeable after mining as long as its thickness is greater than the mining height the development of the mining induced overburden failure is affected by the key strata but ultimately controlled by the soft aquiclude such as the weathered zone it was observed respectively that the height of the caved zone was observed to be 5 to 6 times the mining height whilst the height of the fractured zone is about 10 to 11 times the mining height

ore genesis constraints on the idaho cobalt belt from fluid inclusion gas noble gas isotope and ion ratio analyses a reply the idaho cobalt belt is a 60 km long alignment of deposits composed of cobaltite co pyrite chalcopyrite and gold with anomalous nb y be and rare earth elements rees in a quartz biotite tourmaline gangue hosted in mesoproterozoic metasedimentary rocks of the lemhi group it is the largest cobalt resource in the united states with historic production from the blackbird mine all of the deposits were deformed and metamorphosed to upper greenschist lower amphibolite grade in the cretaceous they occur near a 1377 ma anorogenic bimodal plutonic complex the enhanced solubility of fe co cu and au as chloride complexes together with gangue biotite rich in fe and cl and gangue quartz containing hypersaline inclusions allows that hot saline fluids were involved the isotopes of b in gangue tourmaline are suggestive of a marine source whereas those of pb in ore suggest a u th enriched source the ore and gangue minerals in this belt may have trapped components in fluid inclusions that are distinct from those in post ore minerals and metamorphic minerals such components can potentially be identified and distinguished by their relative abundances in contrasting samples therefore we obtained samples of co and cu sulfides gangue quartz biotite and tourmaline and post ore quartz veins as well as cretaceous metamorphic garnet and determined the gas noble gas isotope and ion ratios of fluid inclusion extracts by mass spectrometry and ion chromatography the most abundant gases present in extracts from each sample type are biased toward the gas rich population of inclusions trapped during maximum burial and metamorphism all have co 2 ch 4 and n 2 ar ratios of evolved crustal fluids and many yield a range of h 2 ch 4 co 2 h 2 s equilibration temperatures consistent with the metamorphic grade cretaceous garnet and post ore minerals have high r h and r s values suggestive of reduced sulfidic conditions most extracts have anomalous 4 he produced by decay of u and th and 38 ar produced by nucleogenic production from 41 k in contrast some ore and gangue minerals yield significant so 2 and have low r h and r s values of a more oxidized fluid three extracts from gangue quartz have high helium r r a values indicative of a mantle source and neon isotope compositions that require nucleogenic production of 22 ne in fluorite from u th decay two extracts from gangue quartz have estimated 40 k 40 ar that permit a precambrian age extracts from gangue quartz in three different ore zones are biased toward the hypersaline population of inclusions and have a tight range of ion ratios na k nh 4 cl br f suggestive of a single fluid their na cl br ratios suggest this fluid was a mixture of magmatic and basinal brine na k ca temperatures 279 347 c are similar to homogenization temperatures of hypersaline inclusions the high k na of the brine may be due to albitization of k silicate minerals in country rocks influx of k rich brines is consistent with the k metasomatism necessary to form gangue biotite with high cl an extract from a post ore quartz vein is distinct and has na cl br ratios that resemble metamorphic fluids in cretaceous silver veins of the coeur d alene district in the belt basin the results show that in some samples for certain components it is possible to see through the cretaceous metamorphic overprint of great import for genetic models the volatiles trapped in gangue quartz have 3 he derived from a mantle source and 22 ne derived from fluorite both of which may be attributed to nearby 1377 ma basalt rhyolite magmatism the brine trapped in gangue quartz is a mixture of magmatic fluid and evaporated seawater the former requires a granitic intrusion that is present in the bimodal intrusive complex and the latter equatorial paleolatitudes that existed in the mesoproterozoic the results permit genetic models involving heat and fluids from the neighboring bimodal plutonic complex and convection of basinal brine in the lemhi group while the inferred fluid sources in the idaho cobalt belt are similar in many respects to those in iron oxide copper gold deposits the fluids were more reduced such that iron was fixed in biotite and tourmaline instead of iron oxides

the primordial noble gases in the earth a key constraint on earth evolution models abstract we made an extensive compilation of noble gas data obtained from morb oceanic island basalts oib and diamonds on the basis of this data base we discuss the primordial noble gases in the earth and its implications on mantle evolution we conclude that in the contrary to a common assumption the primordial ne ar kr and xe in the earth are distinctly different from the solar noble gases the primordial noble gases were derived from the solar noble gas through rayleigh distillation like mass dependent fractionation the primordial ar kr xe are identical with the atmospheric components but ne observed in the mantle derived materials differs significantly from the atmospheric ne we suggest that ne was further fractionated in the atmosphere while the abundances of ar kr and xe in the mantle derived materials are well correlated to each other he and ne in morb is totally uncorrelated with the heavier noble gases this indicates that he and ne in morb is decoupled from the heavier noble gases in the mantle source he ne ar systematics indicate that he was open to the morb and oib mantle sources and ne in the morb mantle source while he is excess in the morb mantle source it is deficient in the oib mantle source relative to the closed system values however it is not known whether this apparent complementary characteristic corresponds to some fundamental mantle dynamics or accidental coincidence

stress relief coalbed methane drainage by surface vertical wells in china abstract this paper summarizes the status of engineering practice technology and research related to stress relief coalbed methane cbm drainage using surface wells in china during the past 10 years comments are provided on the theory and technical progress of this method in high gas mining areas such as the huainan huaibei and tiefa mining areas characterized by heavily sheared coals with relatively low permeability stress relief cbm surface well drainage has been successfully implemented and has broad acceptance as a cbm exploitation technology the fundamental theories underpinning stress relief cbm surface well drainage were established in china and include elements relating to 1 rock layer deformation theory vertical zoning and horizontal partitioning and the change in the stress condition in mining stopes 2 a theory regarding an abscission circle in the development of mining horizontal abscission fracture and vertical broken fracture in overlaying rocks and 3 the theory of stress relief inducing permeability increase in protected coal seams during mining and the gas migration accumulation theory of stress relief cbm surface well drainage three kinds of technical drainage modes are described protected seam surface well drainage in areas influenced by mining represented mainly in the huainan mining area gob surface well drainage most prominently in the tiefa mining areas and the multipurpose surface well drainage used in the huaibei mining areas serial well allocation in which wells are used for different purposes as extraction and mining proceeds and well bore configurations and designs suitable for this purpose are described the development and utilization of cbm is significant to energy saving emission reduction and to ensure safety in coal production

u th pb and rb sr geochronology of middle proterozoic granite and augen gneiss salmon river mountains east central idaho coarsely porphyritic granite and augen gneiss in east central idaho have been dated by the u th pb zircon method when plotted on concordia diagrams the results give nonlinear data arrays that indicate the presence of at least one component of inherited radiogenic lead as well as postcrystallization probably recent episodic lead loss nevertheless a systematic relationship between zircon size and convergence of the 207 pb 206 pb ages for the 100 and 100 150 mesh fractions from several samples are interpreted to provide a valid age of about 1 370 m y for these plutons a single sample which is free of inheritance for all size fractions confirms this conclusion rb sr whole rock samples are highly enriched in radiogenic strontium but do not define an isochron probably because the system did not remain closed following crystallization of the plutons intrusive contacts of the granitic rocks indicate that deformation and regional metamorphism of the host yellowjacket formation occurred prior to 1370 ma rather than prior to 1500 ma as previously suggested by others this refinement of the geochronology 1 removes the necessity that the yellowjacket formation and overlying proterozoic metasedimentary rocks of central and east central idaho be pre belt in age 2 permits the traditional age correlation of the east central idaho metasedimentary sequence yellowjacket through lawson creek formations with the belt supergroup and 3 suggests that a re evaluation is in order for paleogeographic models of central idaho especially the proposed topographic high known as the salmon river arch

fluid inclusion gas compositions from an active magmatic hydrothermal system a case study of the geysers geothermal field usa abstract hydrothermal alteration and the active vapor dominated geothermal system at the geysers ca are related to a composite hypabyssal granitic pluton emplaced beneath the field 1 1 to 1 2 million years ago deep drill holes provide a complete transect across the thermal system and samples of the modern day steam the hydrothermal system was liquid dominated prior to formation of the modern vapor dominated regime at 0 25 to 0 28 ma maximum temperatures and salinities ranged from 440 c and 44 wt nacl equivalent in the biotite hornfels adjacent to the pluton to 305 c and 5 wt nacl equivalent at distances of 1730 m from the intrusive contact the major minor and noble gas compositions of fluid inclusions in the hydrothermally altered rocks were integrated with microthermometric and mineralogic data to determine their sources and the effects of mixing and boiling major and minor gaseous species were released from the inclusions by crushing or thermal decrepitation noble gases were released by crushing the samples were analyzed by mass spectrometry the analyses document the presence of magmatic crustal and meteoric components in the trapped fluids hydrothermal fluids present during the liquid dominated phase of the system contained gaseous species derived mainly from crustal and magmatic sources at the geysers n 2 ar ratios greater than 525 and 3 he 4 he ratios of 6 10 7 ra are diagnostic of a magmatic component crustal gas has co 2 ch 4 ratios less than 4 n 2 ar ratios between 45 and 525 and low 3 he 4 he ratios 0 5 ra meteoric fluids have co 2 ch 4 ratios greater than 4 and n 2 ar ratios between 38 air saturated water and 84 air however n 2 ar ratios between 15 and 110 can result from boiling ratios less than 15 reflect the incorporation of n 2 into nh 3 bearing clay minerals in the central geysers the incursion of meteoric fluids occurred during the transition from the liquid to vapor dominated regime variations in the relative ch 4 co 2 and h 2 contents of the gas analyses demonstrate that boiling took place under open system conditions the gas data indicate that the inclusions have remained closed to the diffusion of he and h 2 since their formation

amber and organic matter from the late oligocene deep water deposits of the central western carpathians orava podhale basin abstract the occurrence of amber in the central carpathian paleogene basin is reported here for the first time the amber has been analyzed by means of optical microscopic methods infrared spectroscopy gas chromatography mass spectrometry and pyrolysis gas chromatography mass spectrometry to understand the amber composition origin taphonomy alteration and diagenesis organic petrographic and reflectance analyses of organic matter from amber bearing sediment was carried out to get information about paleoenvironment and maturity of sedimentary rock analyses confirmed polylabdane structure associated with class ib type of amber and its possible origin from the conifer family araucariaceae it is characterized by a high degree of maturity where both temperature and exogenic processes have participated in its conversion heterogeneity of reflectance values in the resinite suggests that amber was not redeposited from an older and more mature sedimentary unit the discrepancy between the maturity of the amber and amber bearing sedimentary rock along with abundant char and inertinite macerals indicates a probability of thermal alteration of the amber under the influence of heat from a wildfire and increased maturity occurring before its ultimate burial in a deep sea environment the assemblage of terrigenous macerals and numerous char and inertinite particles which were found in amber bearing sediment as well as in the amber crust suggest forest swamp type vegetation affected by wildfires the presence of amber and predominantly terrigenous organic matter besides mud rip up clasts derived from freshwater sediments in deep marine deposits indicates a direct connection of terrestrial environments to the deep water depositional system

application of borehole optical televiewing to investigating the 3 d structure of glaciers implications for the formation of longitudinal debris ridges midre lovenbreen svalbard digital optical televiewing optv of hot water drilled boreholes is evaluated as a technique for the investigation of englacial ice and debris structures on the basis of six boreholes drilled in the terminus region of midre lovenbreen svalbard the resulting optv logs successfully reveal several visually distinctive englacial ice properties and deformation structures e g oblique englacial fractures imaged here for the first time combining these optv logs with surface mapping has resulted in the identification of eight separate structural elements several of which can be interpolated onto 3 d grids at a node spacing of 1 m vertically and 10 m horizontally basally derived englacial sediment layers are also found to be intercalated with primary stratification elevated into near vertical planes around a central fold axis by large scale lateral folding the analysis also allows supraglacial longitudinal debris ridges to be subclassified into two types a previously described type i form which are the exposed fold axes of large scale lateral folds and a new type ii form experiencing secondary deformation by small scale horizontal folding in association with vertical displacements across arcuate shear planes in response to longitudinally compressive stresses near the glacier terminus although using boreholes to investigate glacier structure is limited e g by parallelism with vertical planes applying optv to multiple boreholes at midre lovenbreen has successfully revealed a range of 3 d structural elements at high spatial resolution as such interpolating between multiple optv logs overcomes many of the problems associated with interpretations made solely on the basis of surface based structural mapping and combining the two techniques represents a powerful glaciological tool

palynofacies investigation of callovian middle jurassic sediments from dsdp site 534 blake bahama basin western central atlantic abstract during the extension of deep sea drilling project dsdp leg 76 a new and previously unpenetrated lithological unit composed mainly of claystones was cored above basalt basement at site 534 in the blake bahama basin the callovian part of the new unit contains interbedded black shales which were hitherto unexpected in this part of the section this paper presents a brief palynological examination of lithofacies kerogen relationships in these sediments and shows that their organic content is almost entirely a function of the re deposition of terrestial and marine organic matter versus the ambient redox conditions of the depositional environment allochthonous organic matter inputs are highest in the interbedded turbidites and decline progressively toward the pelagic black shales in which marine organic matter is comparatively well preserved the significance of various kerogen and palynomorph indices are discussed the study emphasizes the absolute necessity for sedimentologically aware sampling in all palynological and geochemical work on lithologically heterogeneous sequences

the borehole camera an investigative geophysical tool applied to engineering environmental and mining challenges thousands of shallow holes and wells are drilled each year to assist engineers geologists geophysicists hydrologists and other professionals investigate inspect and evaluate near surface geologic conditions that may impact surface structures and or to gain in situ subsurface information drilling is the litmus test to confirm interpretations made on various scientific data sets applied to petroleum mining engineering and environmental challenges however traditional drilling and logging techniques can yield residual inconclusive data for rational assessments because small fractures washouts thinly laminated layers minor casing damage etc may be too small for standard logging tools to detect to close this uncertainty gap borehole camera bhc systems can be employed to enhance the investigation and inspection of shallow holes the capabilities of this simple optical imaging tool have until now remained underutilized

iron and chlorine as guides to stratiform cu co au deposits idaho cobalt belt usa the cu co au deposits of the idaho cobalt belt are in lithostratigraphic zones of the middle proterozoic yellowjacket formation characterized by distinctive chemical and mineralogical compositions including high concentrations of fe 15 30 wt percent fe2o3 cl 0 1 1 10 wt percent and magnetite or biotite 50 vol percent the cu co au deposits of the blackbird mine are stratabound in fe silicate facies rocks that are rich in biotite fe and cl but stratigraphically equivalent rocks farther than 10 km from ore deposits have similar compositions a lower lithostratigraphic zone containing magnetite and small cu co au deposits extends for more than 40 km the fe rich strata are probably exhalative units related to mafic volcanism and submarine hot springs but the origin of the high cl concentrations is less clear former chlorine rich pore fluids are suggested by the presence of supersaline fluid inclusions by cl rich biotite and scapolite as much as 1 87 percent cl in fe rich biotite and by high cl concentrations in rock samples chlorine is enriched in specific strata and in zones characterized by soft sediment deformation thus probably was introduced during sedimentation or diagenesis unlike some metasedimentary rocks containing scapolite and high cl the yellowjacket formation lacks evidence for evaporitic strata that could have been a source of cl more likely the cl reflects a submarine brine that carried fe k and base metals strata containing anomalous fe k cl are considered to be a guide to sub basins favorable for the occurrence of stratiform base metal deposits

jurassic and mid cretaceous carbonaceous claystones in the western dsdp leg 76 and eastern dsdp leg 79 north atlantic abstract deep sea drilling in the blake bahama basin dsdp leg 76 site 534 and at the mazagan escarpment off morocco dsdp leg 79 site 547 recovered carbonaceous claystones of mid cretaceous and middle late jurassic age although there are differences in the sedimentological and organic geochemical characteristics of these sediments from opposite margins of the north atlantic the preservation of the organic matter in both cases appears to be controlled by the intensity of the terrigenous organic matter supply downslope transport events and local oxygen depletion

n2 ar he compositions in fluid inclusions indicators of fluid source abstract a quadrupole mass spectrometer was used to measure bulk samples of conservative gas species n 2 ar and he in fluid inclusions from a variety of hydrothermal systems analyses of these tracer elements help determine 1 1 if gases extracted by bulk inclusion analyses can provide accurate measurement of n 2 ar he in active and fossil geothermal systems 2 2 if hydrothermal fluids associated with paleogeothermal systems in a continental setting follow n 2 ar he systematics similar to th the western pacific rim active geothermal systems specifically new zealand and 3 3 whether different deposit types systematically vary with regard to n 2 ar he the n 2 ar he ratios of fluid inclusion volatiles released from recently deposited minerals from the valles system are similar to those of present day valles thermal waters those inclusion samples from deep within the valles system below a regional aquitard increase in n 2 compositions for inclusions from the questa and copper flat porphyry deposits are n 2 rich similar to those of arc related volcanic gases whereas those from taylor creek sn deposit appear to be mixtures of magmatic and crustal components n 2 ar he ratios of the precambrian tribag deposit suggest a basalt source but significant levels of self generated he from u and th in the inclusion fluids are also possible inclusions from two epithermal deposits with low salinity inclusions have n 2 ar he ratios trending towards air saturated meteoric waters asw and those inclusions with higher salinities indicate minor to no asw component the n 2 ar he ratios in fresnillo and cochiti inclusions which have magmatic helium isotopic ratios indicate additions of magmatic gases to meteoric fluids inclusions from sediment hosted deposits that contain hydrocarbon bearing brines are he rich as are meteoric waters with a long residence time in the crust at relevant pressure temperature composition conditions henry s law constants of n 2 ar and he are similar and thus the relative amounts of these species trapped under boiling conditions will not vary appreciably from solubility controlled amounts in coexisting liquid furthermore there is no evidence of he loss or gain in inclusions by diffusion process data from the various systems that were examined indicate that fluid inclusion n 2 ar he compositions may be related to magmatic fluid sedimentary brine deep circulating meteoric fluid and shallow circulating meteoric fluid sources which we modified from those proposed by giggenbach 1986 relationships between the n 2 ar he tracer gases and other measurable quantities in fluid inclusions are indicated to be helpful in understanding fluid mixing processes in paleogeothermal systems

organic geochemistry and depositional history of upper albian sediments from the kirchrode i borehole northern germany abstract in the framework of a multidisciplinary research program an organic geochemical study was carried out on a drill core which comprises a 245 m thick sequence of light colored upper albian marlstones that were deposited in the central part of the lower saxony basin northern germany for part of the upper albian sequence high resolution measurements of carbonate contents reveal cycles which can be related to earth orbital forcing based on these data sediment accumulation rates were calculated to be in the order of 15 g m2yr1 these high accumulation rates contrast with very low organic carbon contents and an extremely poor preservation of the autochthonous organic matter most of the sedimentary organic matter is of terrigenous origin and mainly derived from the erosion of older sedimentary rocks organic petrography reveals only a very small fraction of marine organic particles carbon sulphur ratios pristane phytane ratios as well as the predominance of resedimented organic particles over autochthonous organic particles suggest that aerobic degradation processes rather than anaerobic processes sulphate reduction were responsible for the degradation of the organic matter furthermore the scarcity of terrigenous organic particles vitrinite indicates that there was little vegetation on nearby land areas to explain these analytical results a depositional model was developed which could explain the scarcity of organic matter in the upper albian sediments this model is based on downwelling of oxygen rich saline waters of tethyan origin which reduces the nutrient content of surface waters and thus primary bioproductivity while degradation of primary organic matter in the water column is enhanced at the same time these conditions contrast to those which existed in barremian and early aptian times in this basin when limited water exchange with adjacent oceans caused oxygen deficiency and the deposition of numerous organic carbon rich black shales the thick organic matter poor upper albian sequence of northern germany also contrasts with comparatively thin time equivalent deep sea black shales from italy this discrepancy indicates that local and regional oceanographic factors at least in this case have a greater influence on organic matter deposition than global events

ocean wide stagnation episode in the late cretaceous in this paper we report that marine sediment locations spread over a wide area contain evidence of an anoxic interval during the mid cretaceous here called the cenomanian turonian black shale horizon ctbsh the occurrence of laminated carbonaceous shales with marine organic matter in an unoxidized state implies deposition and early diagenesis in anaerobic environments the stratigraphic record above and below the ctbsh in environments as different as the deep north atlantic ocean and marginal and epicontinental seas over enormous areas in north america north africa and northwestern europe is characterized by a stratigraphic gap a disconformity or a continuous but strongly condensed stratigraphic section the anoxic layer coincides in time with the maximum extension of a worldwide marine transgression of eustatic origin recorded on continental margins1 as well as on various cratons2 no simple model has yet been found to explain the occurrence of the ctbsh in such a wide range of depth and palaeoenvironmental conditions

sulfur carbon hydrogen and oxygen isotope geochemistry of the idaho cobalt belt cobalt copper gold deposits of the idaho cobalt belt including the deposits of the blackbird district have been analyzed for their sulfur carbon hydrogen and oxygen isotope compositions to improve the understanding of ore formation previous genetic hypotheses have ranged widely linking the ores to the sedimentary or diagenetic history of the host mesoproterozoic sedimentary rocks to mesoproterozoic or cretaceous magmatism or to metamorphic shearing the 34 s values are nearly uniform throughout the blackbird district with a mean value for cobaltite coass the main cobalt mineral of 8 0 0 4 n 19 the data suggest that 1 sulfur was derived at least partly from sedimentary sources 2 redox reactions involving sulfur were probably unimportant for ore deposition and 3 the sulfur was probably transported to sites of ore formation as h 2 s hydrogen and oxygen isotope compositions of the ore forming fluid which are calculated from analyses of biotite rich wall rocks and tourmaline do not uniquely identify the source of the fluid plausible sources include formation waters metamorphic waters and mixtures of magmatic and isotopically heavy meteoric waters the calculated compositions are a poor match for the modified seawaters that form volcanogenic massive sulfide vms deposits carbon and oxygen isotope compositions of siderite a mineral that is widespread although sparse at blackbird suggest formation from mixtures of sedimentary organic carbon and magmatic metamorphic carbon the isotopic compositions of calcite in alkaline dike rocks of uncertain age are consistent with a magmatic origin several lines of evidence suggest that siderite postdated the emplacement of cobalt and copper so its significance for the ore forming event is uncertain from the stable isotope perspective the mineral deposits of the idaho cobalt belt contrast with typical vms and sedimentary exhalative deposits they show characteristics of deposit types that form in deeper environments and could be related to metamorphic processes or magmatic processes although the isotopic evidence for magmatic components is relatively weak

bicarbonate rich fluid inclusions and hydrogen diffusion in quartz from the libcice orogenic gold deposit bohemian massif abstract unusual paleofluid composition is reported for the libcice orogenic type gold deposit located in the central bohemian plutonic complex cbpc czech republic unexpected bicarbonate rich fluids and their complex chemistry variations characterize primary fluid inclusions from the main gold bearing quartz vein a detailed microthermometry laser raman micro spectroscopy lrms and sem cathodoluminescence study was used to understand the complex chemistry and p t x history the results indicate the presence of h 2 o and h 2 o co 2 ch 4 n 2 h 2 s fluids the latter displaying variations of the co 2 ch 4 ratio in the gaseous phase from 6 8 to 0 06 variation of the ch 4 content across single grains and between different levels of the mine was recorded the presence of nahcolite h 2 up to 6 mol and ethane 0 0 2 mol in the fluids were also discovered by lrms potential models for the formation of different types of fluids present in the deposit are discussed including the genesis of hco 3 rich fluids as well as h 2 and c 2 h 6 presence in the primary fluid inclusions the potential influence of organic matter bearing sediments as well as the impact of the intrusion of cbpc re equilibration and or re speciation of fluid inclusions during the post entrapment history is considered to have the main impact on the complex paleofluid chemistry based on the thermodynamic modeling h 2 diffusion into the fluid inclusions was shown to be the main reason for the ch 4 variation on the scale of a single grain as well as across the whole vein although the exact processes of production formation of hco 3 and h 2 at the libcice deposit remain open to discussion reactions in the c o h system are considered to be a possible formation mechanism this work also contributes to our understanding of the importance of post entrapment modifications and reactions in the c o h system on interpretation deciphering the processes in orogenic type deposits

strata bound fe co cu au bi y ree deposits of the idaho cobalt belt multistage hydrothermal mineralization in a magmatic related iron oxide copper gold system mineralogical and geochemical studies of strata bound fe co cu au bi y rare earth element ree deposits of the idaho cobalt belt in east central idaho provide evidence of multistage epigenetic mineralization by magmatic hydrothermal processes in an iron oxide copper gold iocg system deposits of the idaho cobalt belt comprise three types 1 strata bound sulfide lenses in the blackbird district which are cobaltite and less commonly chalcopyrite rich with locally abundant gold native bismuth bismuthinite xenotime allanite monazite and the be rich silicate gadolinite y with sparse uraninite stannite and bi tellurides in a gangue of quartz chlorite biotite muscovite garnet tourmaline chloritoid and or siderite with locally abundant fluorapatite or magnetite 2 discordant tourmalinized breccias in the blackbird district that in places have concentrations of cobaltite chalcopyrite gold and xenotime and 3 strata bound magnetite rich lenses in the iron creek area which contain cobaltiferous pyrite and locally sparse chalcopyrite or xenotime most sulfide rich deposits in the blackbird district are enclosed by strata bound lenses composed mainly of cl rich fe biotite some deposits have quartz rich envelopes whole rock analyses of 48 co and or cu rich samples show high concentrations of au up to 26 8 ppm bi up to 9 16 wt y up to 0 83 wt rees up to 2 56 wt ni up to 6 780 ppm and be up to 1 180 ppm with locally elevated u up to 124 ppm and sn up to 133 ppm zn and pb contents are uniformly low 821 and 61 ppm respectively varimax factor analysis of bulk compositions of these samples reveals geochemically distinct element groupings that reflect statistical associations of monazite allanite and xenotime biotite and gold detrital minerals chalcopyrite and sparse stannite quartz and cobaltite with sparse selenides and tellurides significantly cu is statistically separate from co and as consistent with the general lack of abundant chalcopyrite in cobaltite rich samples paragenetic relations determined by scanning electron microscopy indicate that the earliest y ree be mineralization preceded deposition of co cu au and bi allanite xenotime and gadolinite y commonly occur as intergrowths with and inclusions in cobaltite the opposite texture is rare monazite in contrast forms a poikiloblastic matrix to cobaltite and thin rims on allanite and xenotime reflecting a later metamorphic paragenesis allanite and xenotime also show evidence of late dissolution and reprecipitation forming discordant rims on older anhedral allanite and xenotime and separate euhedral crystals of each mineral textural data suggest extensive deformation of the deposits by folding and shearing and by pervasive recrystallization all during cretaceous metamorphism sensitive high resolution ion microprobe u pb geochronology by aleinikoff et al 2012 supports these paragenetic interpretations documenting contemporaneous mesoproterozoic growth of early xenotime and crystallization of megacrystic a type granite on the northern border of the district these ages are used together with mineralogical and geochemical data from the present study to support an epigenetic iocg model for fe co cu au bi y ree deposits of the idaho cobalt belt a sulfide facies variant of iocg deposits is proposed for the blackbird district in which reducing hydrothermal conditions favored deposition of sulfide minerals over iron oxides this new model includes mesoproterozoic vein mineralization and related fe cl metasomatism that formed the biotite rich lenses a predominantly felsic magmatic source for metals in the deposits given their local abundance of y rees and be and a major sedimentary component in the hydrothermal fluids based on independent sulfur isotope and boron isotope data for sulfides and ore related tourmaline respectively

organic facies of surface sediments in the north sea abstract surface sediments of the north sea were investigated by organic geochemical and sedimentological methods including organic carbon and nitrogen determination rock eval pyrolysis protokerogen microscopy gas chromatography of aliphatic hydrocarbons grain size fractionation and clay mineral analysis the total organic matter was found to be a mixture of mostly reworked or oxidized marine and terrestrial constituents with a generally strong influence of the latter throughout the platform locally improved hydrodynamic conditions yielded an incorporation of more freshly produced marine organic matter differences in water current velocities and turbulence also appeared to determine whether this supplement is incorporated into the fine or coarse fractions of the sediments a general constancy of the organic carbon contents within the individual size fractions was recognized independently of sediment type and age i e in recent and pre recent deposits this suggested that the latter have been effectively overprinted by the shelf processes operating at present or that these processes have been of comparable intensity since about the beginning of the holocene transgression the major factors controlling the spatial variations in the organic facies are the sediment grain size and the present day hydraulic regime

in situ study of intensity of weathering induced fractures and methane emission to the atmosphere through these fractures abstract the width and length of weathering induced fractures horizontal distances between through channels formed due to weathering number of through channels in a very weak sandy shale surface layer and methane emission through these fractures to the atmosphere are studied sampling from the studied weathered sandy shale exhibiting very low rock quality rqd in situ directly in the walls of five surface vertical boreholes 1 5 m deep using an original measurement device the radial expansion of measurement devise due to air pressure is used to press wet gypsum into the fractures in borehole surface in order to make gypsum casts of the fractures semi empirical relations between methane volumetric flow rate into the atmosphere through weathering induced fractures and dimensions area and number of weathering induced fractures and gas pressure difference are obtained the comparison between the values of gas seepage through the fractures and rock matrix is performed

application of borehole logging core imaging and tomography to geotechnical exploration lithological structural and rock mechanical information has been derived from geophysical methods classification and characterisation of rock structures have been defined by a combined interpretation of core images and acoustic images of borehole wall geophysical well logs also provide an efficient tool for determination of lithology by a combined evaluation of the log responses seismic velocities and reflectivity measured in full wave sonic and between seismic tomography boreholes are very important for the derivation of rock strength and the determination of weakness zones in solid formations several examples show the benefits of the combined use of geophysical methods in geotechnical studies

organic matter variations in transgressive and regressive shales abstract organic matter in the upper cretaceous mancos shale adjacent to the tocito sandstone in the san juan basin of new mexico was characterized using organic petrology and organic geochemistry differences in the organic matter found in these regressive and transgressive offshore marine sediments have been documented and assessed within a sequence stratigraphic framework the regressive lower mancos shale below the tocito sandstone contains abundant well preserved phytoclasts and correspondingly low hydrogen indices total organic carbon values for the regressive shale are low sediments from the transgressive systems tract tocito sandstone and overlying upper mancos shale contain less terrestrially derived organic matter more amorphous non structured protistoclasts higher hydrogen indices and more total organic carbon advanced stages of degradation are characteristic of the phytoclasts found in the transgressive shale amorphous material in the transgressive shale fluoresces strongly while that found in the regressive shale is typically non fluorescent data from pyrolysis gas chromatography confirm these observations these differences are apparently related to the contrasting depositional styles that were active on the shelf during regression and subsequent transgression it is suggested that data from organic petrology and organic geochemistry provide greater resolution in sedimentologic and stratigraphic interpretations particularly when working with basinward fine grained sediments petroleum source potential for the regressive lower mancos shale below the tocito sandstone is poor based on abundant fluorescent amorphous material high hydrogen indices and high total organic carbon the transgressive upper mancos shale above the tocito sandstone possesses excellent source potential this suggests that appreciable source potential can be found in offshore fine grained sediments of the transgressive systems tract below the condensed section and associated downlap surface organic petrology can be used to accurately predict petroleum source potential the addition of simple fluorescence microscopy greatly enhances this predictive ability because non generative amorphous material is generally non fluorescent organic petrology must also be used to properly evaluate the utility of t max from programmed pyrolysis as a thermal maturity indicator organic matter dominated by autochthonous amorphous protistoclasts exhibits lower t max values than that which is composed of mostly phytoclasts

structural controls and evolution of gold silver and ree bearing copper cobalt ore deposits blackbird district east central idaho epigenetic origins the cu co au ag ni ree ore deposits of the blackbird district east central idaho have previously been classified as besshi type vms sedex and iocg deposits within an intact stratigraphic section new studies indicate that across the district mineralization was introduced into the country rocks as a series of structurally controlled vein and alteration systems quartz rich and biotite rich veins and alteration zones and minor albite and siderite veinlets maintain consistent order and sulfide mineral associations across the district both early and late quartz veins contain chalcopyrite and pyrite whereas intermediate stage tourmaline biotite veins host the cobaltite barren early and late albite and late carbonate generally siderite form veins or are included in the quartz veins ree minerals principally monazite allanite and xenotime are associated with both tourmaline biotite and late quartz veins the veins are in mineralized intervals along axial planar cleavage intrafolial foliation and shears mineralized intervals are hosted by a variety of metasedimentary rocks including three phyllitic units of mesoproterozoic age and two schistose units all of these units are s tectonites in the footwall of a regional thrust fault specifically the district lies within an oblique thrust ramp containing a series of structural horses three domains in a duplex system the deposits span the three domains and are hosted by metamorphic rocks that range from lower amphibolite facies in the structurally upper domain to lower middle greenschist facies in the lower domain an inverted metamorphic sequence early quartz and biotite veins were introduced during progressive folding and prolonged peak metamorphic conditions and they underwent late tectonic retrograde recrystallization and metamorphic mineral growth to the same extent as the country rocks in each domain where little subsequent deformation occurred early veins are discordant to bedding but where folding was polyphase and fabrics are penetrative mineralized zones are concordant with metamorphic compositional layering late quartz veins in the zones are associated with retrograde minerals and textures and are only locally deformed 40 ar 39 ar dating of unoriented muscovite from the selvage of a late quartz vein yields a late cretaceous age of about 83 ma the time of retrograde metamorphism associated with introduction of late quartz veins textural data at all scales indicate that the host sites for veins and the tectonic evolution of both host rocks and mineral deposits were kinematically linked to late cretaceous regional thrust faulting heat fluids and conduits for generation and circulation of fluids were part of the regional crustal thickening the faulting also juxtaposed metaevaporite layers in the mesoproterozoic yellowjacket formation over blackbird district host rocks we conclude that this facilitated chemical exchange between juxtaposed units resulting in leaching of critical elements cl k b na from metaevaporites to produce brines scavenging of metals co cu etc from rocks in the region and finally concentrating metals in the lower plate ramp structures although the ultimate source of the metals remains undetermined the present cu co au ag ni ree blackbird ore deposits formed during late cretaceous compressional deformation

further evidence for the development of photic zone euxinic conditions during mesozoic oceanic anoxic events periods in earth history characterized by extensive organic carbon deposition so called oceanic anoxic events oaes are the subject of considerable scrutiny insight into the extent of anoxic conditions in the water column has been provided by the reported occurrence of derivatives of isorenieratene a carotenoid found only in green sulphur bacteria and thus indicative of photic zone euxinia i e a water column containing free h 2 s in north atlantic deep sea sediments deposited during the cenomanian turonian boundary oae2 bonarelli event in this study we have used the distributions of chlorophyll and bacteriochlorophyll degradation products maleimides 1 h pyrrole 2 5 diones and high molecular weight porphyrins to examine further the cenomanian turonian boundary oae2 as well as other oaes of the early toarcian posidonienschiefer event and early aptian selli event in particular methyl isobutyl me i bu maleimide on structural grounds appears to be diagnostic of green sulphur bacteria this compound occurs in five of seven examined marls that record the early toarcian oae marche umbria italy further expanding the geographical range of toarcian sediments where evidence for photic zone euxinic conditions has been found me i bu maleimide occurs in three of six black shales spanning the livello selli marche umbria italy the type locality for the aptian oae1a providing the first evidence for photic zone euxinic conditions during this event with respect to the cenomanian turonian oae maleimide evidence for photic zone euxinic conditions was found in all the north atlantic sites investigated including those characterized by relatively organic lean sediments several tethyan sites and one site off western australia these data indicate that euxinic conditions were common in the water column during mesozoic oceanic anoxic events

evaporitic source model for igneous related fe oxide ree cu au u mineralization we propose that many igneous related fe oxide rich ree cu au u bearing deposits form by hydrothermal processes involving evaporitic ligand sources either coeval salars or older evaporites these deposits are abundant in both phanerozoic and proterozoic extensional continental and continent margin settings they commonly form in global arid zones but they also occur where magmatism is superimposed upon older evaporites magmatic compositions exert only second order control mainly on alteration mineralogy and on element abundances hot s poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments siderophile lithophile and hydrothermal alteration sodic locally alkaline found in these systems this model contrasts with immiscible oxide melt and magmatic hydrothermal origins commonly proposed for these deposits although all three mechanisms can occur 31 refs 3 figs 1 tab

accumulation of organic carbon rich sediments in the late jurassic and cretaceous atlantic ocean a synthesis abstract organic carbon rich sediments black shales were deposited at some 40 deep sea drilling project dsdp sites in the atlantic ocean during late jurassic and cretaceous times in order to reconstruct the depositional environments of black shale formation we have studied in detail changes in the occurrence of black shales as well as the type and amount of organic matter in relation to changes in paleogeography paleooceanic circulation and paleoclimate we have calculated accumulation rates of marine and terrigenous organic carbon and combined these with organic carbon content sedimentation rate relationships to obtain information about paleoenvironments main factors causing the preservation and accumulation of organic carbon are 1 the supply of terrestrial organic matter 2 the supply of marine organic matter 3 the oxygenation of the deep water and 4 the bulk sedimentation rate changes in the importance of these different factors and changes in the interrelationships among them determine the complex system of black shale formation and their cyclic variations increased supply of terrestrial organic matter due to increased river discharge and humid climate in northeast america southwest europe and south africa were important in the hauterivian albian northwest and northern northeast atlantic and in the late jurassic aptian south atlantic in the latter anoxic deep water conditions due to restricted circulation in the nascent largely isolated basin as well as higher oceanic productivity may have reinforced the high preservation rates of marine organic matter during that time off northwest africa higher flux rates of marine organic matter were recorded in areas of higher productivity which may have been caused by fluvial nutrient supply during the hauterivian and by intensified upwelling during albian turonian times in general the depositional environment was oxygenated and the content of marine organic matter was a function of the sedimentation rate furthermore at some places redeposition by turbidity currents or slumps may have been important for the accumulation of organic matter in the deep sea basins the only episode of widespread anoxia in the western and eastern basins of the north atlantic may have occurred in the cenomanian turonian when high amounts of marine organic matter were also preserved in areas of low productivity and low sedimentation rates

detection of hydraulic pathways in fractured rock masses and estimation of conductivity by a newly developed tv equipped flowmeter abstract we developed a flowmeter well logging system that can detect hydraulic pathways in fractured rock mass and applied it to a site where granitic rock is widely distributed hydraulic pathways were detected by flow velocity measurement using the doppler effect of ultrasonic waves and fractures which acted as hydraulic pathways were specified by a borehole tv camera attached to the system fractures with hydraulic conductivity more than 10 7 m s were detected by the logging system and the accuracy of the measured conductivities was within one order of magnitude the newly developed flowmeter system can provide information on the location and conductivity of hydraulic pathways at the borehole for field employment in the earliest stages of site characterization surveys

the source and significance of argon isotopes in fluid inclusions from areas of mineralization argon isotopes in fluid inclusions in quartz veins associated with granite hosted tungsten mineralization in the southwest and north of england have been investigated in detail by the40ar 39ar technique the natural argon is present as a number of discrete components which can be identified through correlations with39ar 38ar and 37ar induced by neutron bombardment of potassium chlorine and calcium the potassium correlated component arises principally from in situ decay of potassium in solid phases in the inclusions in the case of the hemerdon tungsten deposit of southwest england the phases responsible are small 25 m captive authigenic micas which are shown to have been deposited from a fluid 268 20 ma ago shortly after the emplacement of the host granite the chlorine correlated component is present in the brines which constitute the fluid phase of the inclusions the argon in these hydrothermal fluids is made up in part of parentless or excess 40ar leached from surrounding crustal rocks and in part of dissolved ancient atmospheric argon absolute concentrations of both atmospheric and excess components in the brine can be estimated from 40arcl ratios and independent determinations of the salinity of the inclusions the absolute concentrations of the atmospheric argon are close to those found in modern meteoric water while those of the excess component can be interpreted in terms of the degree of interaction betwen the circulating fluids and country rock a calcium correlated component with a much higher ratio of excess to atmospheric argon than that in the brine was found to be a dominant phase in one sample from the hemerdon deposit indicating the presence of a solid phase probably a caso4 daughter mineral inclusions of this composition represent fluids which have had a more prolonged interaction with crustal rocks the results obtained from this study provide a systematization and a framework for future multi component argon studies of fluid inclusions together with an indication of the wide range of information which can be inferred

fluorite u th he thermochronology constraints on the low temperature history of yucca mountain nevada abstract fluorite is one of the secondary minerals precipitated in pore spaces at the future nuclear waste repository site at yucca mountain nevada the authors have conducted u th he dating of this fluorite in an attempt to constrain the temperature and timing of paleo fluid flux into the site repeated analysis of colourless fluorite yielded a weighted average age of 9 7 0 15 ma 2 younger than previously determined sanidine 40ar 39 ar ages 12 8 ma for deposition of the tuff laboratory he diffusion experiments conducted on the yucca fluorite yield a preliminary he closure temperature tc of 90 10 c cooling rate of 10 c ma and previous studies have determined that the fluorite precipitated from warm fluids 65 80 c at depths of it was observed that the purple coloured outer portion of the fluorite nodule yielded non reproducible and invariably older ages than colourless fluorite several possible reasons are suggested

changes in paleoenvironments in the atlantic ocean during cretaceous times results from black shales studies large parts of the cretaceous atlantic ocean are characterized by the wide spread deposition of organic carbon rich sediments black shales with a maximum occurrence during aptian albian and cenomanian turonian times in order to explain the origin of these black shales changes in the amount and type of organic matter in relation to changes in paleogeography paleoceanic circulation and paleoclimate have been investigated in detail the study is mainly based on calculation of accumulation rates of marine and terrigenous organic carbon organic carbon sedimentation rate relationships and estimates of paleoproductivity