hydrochemical characteristics of shallow groundwater in aquifer containing uranyl phosphate minerals in the koprubasi manisa area turkey the concentrations of uranium iron and the major constituents were determined in groundwater samples from aquifer containing uranyl phosphate minerals meta autunite meta torbernite and torbernite in the koprubasi area groundwater samples from wells located at shallow depths 0 5 6 m show usually near neutral ph values 6 2 7 1 and oxidizing conditions eh 119 275 mv electrical conductivity ec values of samples are between 87 and 329 s cm 1 they are mostly characterized by mixed cationic ca dominating bicarbonate types the main hydrogeochemical process is weathering of the silicates in the shallow groundwater system all groundwater in the study area are considered undersaturated with respect to torbernite and autunite phreeqc predicted uo2 hpo4 22 as the unique species the excellent positive correlation coefficient r 0 99 between u and po4 indicates the dissolved uranium in groundwater would be associated with the dissolution of uranyl phosphate minerals the groundwater show u content in the range 1 71 70 45 g l but they are mostly lower than us epa 2003 maximum contaminant level of 30 g l this low u concentrations in oxic groundwater samples is attributed to the low solubility of u vi phosphate minerals under near neutral ph and low bicarbonate conditions iron closely associated with studied sediments were also detected in groundwater the maximum concentration of fe in groundwater samples was 2837 g l while the drinking water guidelines of turkish tse 1997 and us epa 2003 were suggested 200 and 300 g l respectively furthermore iron and uranium showed a significant correlation to each other with a correlation coefficient r of 0 94 this high correlation is probably related to the iron rich sediments which contain also significant amounts of uranium mineralization in addition to ph and bicarbonate controlling dissolution of uranyl phosphates association of uranyl phosphates with iron hydr oxides seems to play important role in the amount of dissolved u in shallow groundwater

uranyl phosphates and associated minerals in the koprubasi manisa uranium deposit turkey abstract the koprubasi uranium deposit is the largest known uranium deposits in turkey uranium mineralization is hosted in neogene fluvial sediments that consist of predominantly sandstone and conglomerate interlayered with siltstone claystone and mudstone sediments were primarily derived from metamorphic rocks adjacent to the basins of deposition with some volcanic contribution in the form of tuffs the sandstones and conglomerates are the most widespread sediments within the study area and host the majority of the u ore x ray diffraction xrd and scanning electron microscopy sem with energy dispersive x ray spectroscopy edx analysis were used to identify the ore and associated minerals the uranium ore minerals of the host sedimentary rocks are torbernite meta torbernite and meta autunite these coexist with jarosite various clays chlorite kaolinite illite and smectite and fe and mn hydr oxides with minor titanium oxide additionally quartz feldspars and a minor amount of mica muscovite and biotite are the main primary minerals in the sedimentary rocks the uranyl phosphates coat the surfaces of pebbles and some mineral grains fill cracks and are disseminated within the pores of the host sedimentary rocks uranyl phosphates are commonly associated with fe hydr oxides and clays although some were observed in millimeter or centimeter wide gaps within koprubasi sediments oxides of manganese are also locally abundant and associated with uranyl phosphates the uranyl phosphates in the sediments of the koprubasi area most likely formed when oxidizing groundwater moved through the host rock the common association of uranyl phosphates with fe hydr oxides and clays suggests that the precipitation of uranyl phosphate minerals is mainly due to adsorption of the uranyl and phosphate to the surface of fe hydr oxides and clays

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

climatic variability in the northern sector of the american tropics since the latest mis 3 abstract we inferred millennial scale climate variations and paleohydrological conditions in the northern sector of the american tropics for 30 3 5 5 cal ka bp using geochemical characteristics of sediments from lake chalco in central mexico the sediment sequence is chronologically constrained with three tephra and nine radiocarbon dates temporal variations in titanium total inorganic carbon total organic carbon titanium ratio carbon nitrogen ratio and silica titanium ratio indicate changes in runoff salinity productivity and sources higher concentrations of ti indicate more runoff during latest marine isotope stage mis 3 30 3 28 6 cal ka bp runoff was lower during the last glacial maximum lgm 23 19 cal ka bp than during the heinrich 2 event 26 24 cal ka bp the interval of reduced runoff continued up to 17 5 cal ka bp but increased during the bolling allerod trends of decreasing runoff and increasing salinity are observed throughout mis 1 lake chalco received less runoff during the lgm compared to deglaciation opposite the trend of other north american tropical records different amounts of rainfall at different sites are possibly due to shifts in the position of the intertropical convergence zone changes in the size of the altlantic warm pool and varying sea surface temperatures of the atlantic and pacific oceans

late pleistocene and holocene paleoenvironments of chalco lake central mexico abstract in order to establish paleoenvironmental conditions during the late quaternary four cores from the basin of mexico central mexico were drilled in chalco lake located in the southeastern part of the basin the upper 8 m of two parallel cores were studied using paleomagnetic loss on ignition pollen and diatom analyses based on 11 14c ages the analyzed record spans the last 19 000 14c yr b p volcanic activity has affected microfossil abundances both directly and indirectly resulting in absence or reduction of pollen and diatom assemblages important volcanic activity took place between 19 000 and 15 000 yr b p when the lake was a shallow alkaline marsh and an increase of grassland pollen suggests a dry cold climate during this interval abrupt environmental changes with increasing moisture occurred from 15 000 until 12 500 yr b p the lake level increased and the pollen indicates wetter conditions the highest lake level is registered from 12 500 to ca 9000 yr b p the end of the pleistocene is characterized by an increase in humidity from 9000 until ca 3000 yr b p chalco lake was a saline marsh and the pollen record indicates warmer conditions after 3000 yr b p the lake level increased and human disturbance dominates the lacustrine record

seismic interpretation below tuning with multiattribute analysis the tuning bed thickness or vertical resolution of seismic data traditionally is based on the frequency content of the data and the associated wavelet seismic interpretation of thin beds routinely involves estimation of tuning thickness and the subsequent scaling of amplitude or inversion information below tuning these traditional below tuning thickness estimation approaches have limitations and require assumptions that limit accuracy the below tuning effects are a result of the interference of wavelets which are a function of the geology as it changes vertically and laterally however numerous instantaneous attributes exhibit effects at and below tuning but these are seldom incorporated in thin bed analyses a seismic multiattribute approach employs self organizing maps to identify natural clusters from combinations of attributes that exhibit below tuning effects these results may exhibit changes as thin as a single sample interval in thickness self organizing maps employed in this fashion analyz

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

the dynamic history of the trans mexican volcanic belt and the mexico subduction zone abstract the trans mexican volcanic belt tmvb is a 1000 km long neogene continental arc showing a large variation in composition and volcanic style and an intra arc extensional tectonics it overlies the rivera and cocos slabs which display marked changes in geometry geophysical studies indicate that lithospheric mantle is very thin or absent beneath the forearc and arc the fluids from the slab are released in a 40 to 100 km wide belt beneath the frontal part of the arc and the lower crust beneath the arc is partially molten east of 101 w the tmvb is built on a precambrian to paleozoic crust with thickness of 50 55 km west of 101 w the tmvb is underlain by jurassic to cenozoic marine and continental arcs with a 35 40 km thick crust the evolution of the tmvb occurred in four stages 1 from 20 to 10 ma the initial andesitic arc moved inland showing progressively drier melting and eventually slab melting suggesting flattening of the subducted slab 2 since 11 ma a pulse of mafic volcanism migrated from west to east reaching the gulf of mexico by 7 ma this mafic lavas marks the lateral propagation of a slab tear triggered by cessation of subduction beneath baja california 3 thereafter the volcanic front started moving trenchward with a marked phase of silicic volcanism between 7 5 and 3 ma local emplacement of small volume intraplate like basalts since 5 ma and development of extensional faulting these features are related to slab rollback enhancing asthenophere flux into the mantle wedge and promoting partial melting of the crust 4 the modern arc consists of a frontal belt dominated by flux and slab melting and a rear belt characterized by more differentiated rocks or by mafic lavas with little or no evidence of subduction fluids but higher asthenosphere fingerprint

a tutorial on complex seismic trace analysis complex seismic trace analysis treats a seismic trace as the product of two independent and separable functions instantaneous amplitude and cosine of the instantaneous phase at any given time instantaneous amplitude is the maximum value the seismic trace can attain under a constant phase rotation and instantaneous phase is the phase angle required to rotate the trace to the maximum defining these two attributes in this way permits complex seismic trace analysis to be founded without reference to the complex trace all other complex seismic trace attributes derive from amplitude and phase through differentiation averaging combination or transformation the chief derived attributes are frequency relative amplitude change wavelength dip and azimuth at any point on a seismic trace the instantaneous attributes describe a sinusoid that locally matches the trace most instantaneous attributes are improved through filtering or weighted averaging the phase wavenumber vector provides a convenient basis for quantifying 3d seismic properties such as reflection parallelism

biogenic mn oxide minerals coating in a subsurface granite environment abstract this paper reports the results of a study of biogenic mn oxide minerals coating in a subsurface granite environment this subterranean environment corresponds to galleries of a 16th century spring water tunnel dug throughout the granite bedrock located in porto city nw portugal several techniques xrd ftir raman icp ms tem eds fesem eds stem eds and stxm nexafs were used to assess the mechanisms involved in the formation of manganese oxides specifically birnessite and todorokite these manganese oxides presented peculiar shapes nano dimensions low degree of crystallinity and high levels of some trace elements such as p ca c al si ba and zn they were associated with large amounts of extracellular polymeric substances exuded by filamentous bacterial communities which serve as nuclei for preferential precipitation of manganese oxides on the extracellular sheaths scientific assessment revealed that biological activity played a major role in the development of these manganese oxides

orbital pacing and ocean circulation induced collapses of the mesoamerican monsoon over the past 22 000 y the dominant controls on global paleomonsoon strength include summer insolation driven by precession cycles ocean circulation through its influence on atmospheric circulation and sea surface temperatures however few records from the summer north american monsoon system are available to test for a synchronous response with other global monsoons to shared forcings in particular the monsoon response to widespread atmospheric reorganizations associated with disruptions of the atlantic meridional overturning circulation amoc during the deglacial period remains unconstrained here we present a high resolution and radiometrically dated monsoon rainfall reconstruction over the past 22 000 y from speleothems of tropical southwestern mexico the data document an active last glacial maximum 18 24 cal ka b p monsoon with similar 18o values to the modern and that the monsoon collapsed during periods of weakened amoc during heinrich stadial 1 ca 17 ka and the younger dryas 12 9 11 5 ka the holocene was marked by a trend to a weaker monsoon that was paced by orbital insolation we conclude that the mesoamerican monsoon responded in concert with other global monsoon regions and that monsoon strength was driven by variations in the strength and latitudinal position of the intertropical convergence zone which was forced by amoc variations in the north atlantic ocean the surprising observation of an active last glacial maximum monsoon is attributed to an active but shallow amoc and proximity to the intertropical convergence zone the emergence of agriculture in southwestern mexico was likely only possible after monsoon strengthening in the early holocene at ca 11 ka

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

play analysis and leading edge oil reservoir development methods in the permian basin increased recovery through advanced technologies the permian basin of west texas and southeast new mexico remains an important oil producing province accounting for 17 of united states production 327 million bbl in 2002 with a resource base of such size increased understanding of reservoir geology and improved use of enhanced recovery practices in the basin can have a substantial impact on united states oil production thirty two oil plays covering both the texas and new mexico portions of the permian basin were defined on the basis of reservoir stratigraphy lithology depositional environment and structural and tectonic setting one thousand three hundred and thirty nine significant sized reservoirs cumulative production of 1 million bbl 1 59 105 m3 of oil through 2000 were assigned to a geologic play cumulative production from these reservoirs was 28 9 billion bbl 4 59 109 m3 or 95 of the basin s total examples of successful reservoir development practices are listed by play because methods demonstrated to work well in one reservoir should be applicable to other reservoirs in the play the permian basin is dominantly a carbonate province carbonate reservoirs account for 75 of total oil production clastics 14 mixed clastics and carbonates 8 and chert 3 the plays having the largest cumulative production are the northwest shelf san andres platform carbonate play 4 0 billion bbl 6 31 108 m3 the leonard restricted platform carbonate play 3 3 billion bbl 5 25 108 m3 the pennsylvanian and lower permian horseshoe atoll carbonate play 2 7 billion bbl 4 29 108 m3 and the san andres platform carbonate play 2 2 billion bbl 3 42 108 m3 the permian system dominates production accounting for 73 of cumulative production followed by the pennsylvanian 13 and the ordovician 6 the estimated remaining reserves from that component of the resource base that is already discovered and producing is 3 25 billion bbl 5 17 108 m3

last glacial droughts and fire regimes in the central mexican highlands over the last glacial cycle climate variations in the neotropics were related to diverse forcing mechanisms whose understanding has been limited because of the scarcity of continuous long records here we use high resolution charcoal particle accumulation inorganic carbon precipitation and magnetic susceptibility data from lake chalco located in high altitude tropical central mexico to assess the fire regimes and drought periods between 85 and 10 8k cal a bp overall drought intervals were characterized by high carbonate deposition and were contemporary with high spring insolation most of the high fire activity periods were coupled with droughts whereas some of them seem to have responded to volcanic activity in the basin periods of more fire activity during the latest part of marine isotope stage 3 were associated with a long interval of higher spring insolation increase in drought frequency during 47 27k cal a bp were possibly linked to a more active laurentide ice sheet influencing the oceanic and atmospheric controls of the tropical climatic system in fact chalco and cariaco records show similar millennial scale trends suggesting a role of the intertropical convergence zone in modulating moisture availability in the region

3 d seismic imaging and interpretation of brushy canyon slope and basin thin bed reservoirs northwest delaware basin a study was done at nash draw field eddy county new mexico to demonstrate how engineering drilling geologic geophysical and petrophysical technologies should be integrated to improve oil recovery from brushy canyon reservoirs at depths of approximately 6600 ft 2000 m on the northwest slope of the delaware basin these thin bed reservoirs were deposited in a slope basin environment by a mechanism debated by researchers a common model being turbidite deposition in this paper we describe how state of the art 3 d seismic data were acquired interpreted integrated with other reservoir data and then used to improve the sitting of in field wells and to provide facies parameters for reservoir simulation across this complex depositional system the 3 d seismic field program was an onshore subsalt imaging effort because the ochoan rustler salado a high velocity salt anhydrite section extended from the surface to a depth of approximately 3000 ft 900 m across the entire study area the primary imagi

stable isotope geochemistry of alteration associated with the key lake uranium deposit canada the key lake uranium deposit occurs within a shear zone that intersects the unconformity between early proterozoic basement gneiss and overlying middle proterozoic athabasca group sandstone uranium is concentrated near the unconformity and is associated with intense illite chlorite and kaolinite alteration the delta d and delta 18 o values of the clay minerals suggest that several different fluids have affected the ores and surrounding host rocks alteration of the basement gneisses associated with the uranium mineralization consists mainly of mg chlorite that equilibrated about 200 degrees c with a fluid having a delta d value near 20 per mil and a delta 18 o value near 5 per mil an illite rich sandstone alteration halo preserved only locally above the deposit equilibrated about 200 degrees c with a basinal brine having a delta d value near 65 per mil and a delta 18 o value near 5 per mil the uranium was concentrated near the unconformity by the mixing of these two distinct fluids the delta 18 o values of coexisting quartz and illite sampled from the shear zone hosting the uranium mineralization yield equilibration temperatures of 190 degrees to 230 degrees c which is postulated to be the temperature of the ore forming event fracturing in the sandstone above the deposit controlled late low temperature 50 degrees c kaolinitization of preexisting hydrothermal illite and chlorite by meteoric waters having delta d values of 50 or 30 per mil and delta 18 o values of 7 or 3 per mil the youngest event to affect the key lake deposit is related to the influx of modern meteoric waters that have lowered the delta d values but not greatly affected the delta 18 o values of some of the clay minerals associated with the shear and breccia zones this latest event has recrystallized much of the hydrothermal mg chlorite associated with the uranium to produce an fe mg chlorite with delta d values as low as 170 per mil

clay alteration associated with proterozoic unconformity type uranium deposits in the east alligator rivers uranium field northern territory australia clay minerals associated with the unconformity type uranium deposits of the east alligator rivers uranium field have been used to determine the spatial distribution of hydrothermal alteration and the conditions of uranium deposition within the altered basement underlying the kombolgie unconformity alteration develops a similar pattern at regional and smaller scales with a close relationship between the degree of alteration and the amount of structural discontinuities observed on both sides of the unconformity e g faults fractures breccias these discontinuities were mechanically active during the hydrothermal activity the hydrothermal clay minerals partly to totally replace diagenetic dickite and illite in the kombolgie sandstones and metamorphic phengite and chlorite in the basement rocks the time space alteration sequence established in this study can be summarized as follows 1 early crystallization of illite illite smectite i s mixed layer minerals lree sr bearing aluminum phosphate sulfates aps in sandstones above the unconformity illite i s mixed layer minerals sudoite aps on both sides of the unconformity and in fault gouges and illite i s mixed layer minerals chlorite apatite deeper in the basement and 2 late precipitation of chlorite in the open fracture network mainly centered below the unconformity the main stage of uranium deposition was associated with chloritization in the basement rocks smaller particle size lath shaped or flaky morphology common interstratification with expandable layers lower crystallinity and mg rich chemical compositions can be used to distinguish the hydrothermal clays from the other diagenetic and metamorphic illite and or chlorite hydrothermal illite can be distinguished from diagenetic and metamorphic illite phengite by its poor crystallinity along the c axis interstratification with minor amounts of smectite layers and a 1m polytype in which trans vacant octahedral sites predominate 1 mt chemically the hydrothermal illite differs from diagenetic illite by a lower interlayer charge and a higher mg content the hydrothermal chlorite is distinguished from the metamorphic chlorite by its smaller particle size spherulitic habit poor crystallinity along the c axis and common association with corrensite and or chlorite corrensite mixed layers most of the hydrothermal chlorite is mg rich and has a structural formula close to that of clinochlore xfe 0 20 near the uranium deposits the spherules of hydrothermal chlorite are chemically zoned from xfe 0 10 to xfe 0 40 which is interpreted as the result of a change in the oxidation state of the hydrothermal solution during the chlorite crystallization the space time alteration sequence established for clay minerals and the observed transition of aps to apatite are interpreted as the result of an increasing degree of interaction of the basement rocks with infiltrating acidic and oxidizing sub basinal brines in turn these fluids tend to be neutralized and reduced by their ongoing interaction with ferrous iron bearing phyllosilicates fe chlorite and biotite and iron sulfides of metamorphic origin the ore deposits are surrounded by zones in which the degree of fluid rock interaction was very high and chloritization is most abundant the octahedral mg content of the associated hydrothermal illite from the sandstone can be used as a guide to indicate the possible presence of uranium orebodies in the basement rocks tens to hundreds of meters below the crystal structures of the hydrothermal illite and chlorite suggest that these minerals crystallized at temperatures approximatively 30 to 50 c lower than those expected at the peak diagenesis of the kombolgie sandstones near the unconformity

seismic attributes a historical perspective a seismic attribute is a quantitative measure of a seismic characteristic of interest analysis of attributes has been integral to reflection seismic interpretation since the 1930s when geophysicists started to pick traveltimes to coherent reflections on seismic field records there are now more than 50 distinct seismic attributes calculated from seismic data and applied to the interpretation of geologic structure stratigraphy and rock pore fluid properties the evolution of seismic attributes is closely linked to advances in computer technology as examples the advent of digital recording in the 1960s produced improved measurements of seismic amplitude and pointed out the correlation between hydrocarbon pore fluids and strong amplitudes bright spots the introduction of color printers in the early 1970s allowed color displays of reflection strength frequency phase and interval velocity to be overlain routinely on black and white seismic records interpretation workstations in the 1980s provided

mobility of uranium during weathering mineralogical and geochemical mechanisms of u fixation under oxidizing conditions in the vicinity of the secondary u ore deposit at koongarra australia were examined using transmission and scanning electron microscopy and thermodynamic calculations the formation of saleeite mg uo 2 2 po 4 2 1oh 2 o is the predominant mechanism for u fixation upstream from the deposit where saleeite replaces sklodowskite and granular apatite within the deposit and further downstream u is fixed in microcrystals 10 50 nm of saleeite and meta torbernite scattered within veins of fine grained 2 50 nm fe super 3 minerals primarily goethite and hematite thermodynamic calculations indicate the groundwater is undersaturated with respect to saleeite and metatorbernite and that these minerals should precipitate at higher u or p concentrations than observed this suggests that the upstream saleeite precipitated at the reaction interfaces of dissolving sklodowskite and apatite under local saturation conditions observed textural relationships of saleeite and meta torbernite microcrystals with the fe minerals combined with thermodynamic calculations suggest surface precipitation as the formation mechanism for saleeite and meta torbernite microcrystals within and downstream from the secondary ore deposit phosphorous released during the aging of ferrihydrite and u adsorbed onto fe minerals are probably the sources of the major components of the microcrystals downstream the microcrystals exist where groundwater u concentrations are as low as 10 30 mu g l once released from the ore deposit u is fixed in uranyl phosphates even where measured groundwater is undersaturated with respect to uranyl phosphates the surface precipitation is an important example of long term post adsorption u fixation in a natural system the fully crystalline and radiation damaged microstructures of saleeite indicate uranyl phosphates have formed continuously or intermittently for the last few million years

diatom based transfer functions for inferring past hydrochemical characteristics of african lakes abstract a new dataset of 282 modern diatom samples and associated environmental information has been created by merging existing regional datasets from north and east africa and niger the relationships between diatom species distributions and hydrochemistry are examined using canonical correspondence analysis cca and partial cca variables reflecting water conductivity ph and cation and anion composition account for significant and independent components of the total variation in the diatom data predictive models transfer functions are developed using the method of weighted averaging for conductivity r 2 0 87 ph r 2 0 77 and ratios between alkali and alkaline earth metals r 2 0 81 and carbonate bicarbonate and sulphate chloride ions r 2 0 82 prediction errors are estimated using the computer intensive method of jackknifing these transfer functions enlarge the potential domain for reconstruction of past hydrochemistry from fossil diatoms preserved in lake sediments

reconstruction of the volcanic history of the tacambaro puruaran area michoacan mexico reveals high frequency of holocene monogenetic eruptions the 690 km2 tacambaro puruaran area located at the arc front part of the michoacan guanajuato volcanic field in the trans mexican volcanic belt tmvb records a protracted history of volcanism that culminated with intense monogenetic activity in the holocene geologic mapping 40ar 39ar and 14c radiometric dating and whole rock chemical analyses of volcanic products provide insights to that history eocene volcanics 55 40 ma exposed at uplifted blocks are related to a magmatic arc that preceded the tmvb early tmvb products are represented by poorly exposed pliocene silicic domes 5 2 ma quaternary 30 km may be related to high rates of magma production at depth and a favorable tectonic setting

palynological and magnetic susceptibility records of lake chalco central mexico abstract pollen and magnetic susceptibility data from a 11 27 m long core drilled in the central part of lake chalco 99 00 w 19 15 n located at the southeastern part of the basin of mexico are interpreted in terms of paleoenvironmental changes the record of this subtropical highland lake dated by radiocarbon methods spans approximately 24 000 yr b p and documents changes in climate vegetation lake level and volcanic activity seven palynozones were established by using the method of cluster analysis for correlation purposes zones 7 6 and 5 between 20 600 and 18 300 yr b p indicate reduced forests with extensive grasslands relatively high input of sediments by water discharge of surface streams and high lake level the evidences obtained in zone 4 between 18 300 and 17 500 yr b p suggest a dry and warm climate with xerophytic vegetation lower lake level and erosion rates zone 3 between 17 500 and 10 000 yr b p shows a trend to increasing moisture and cooler temperatures volcanic activity during this period is intense and strongly influences the natural environments at around 12 000 yr b p a clear expansion of forests and fulfillment of the lake recorded at the beginning of the holocene an oak forest expansion and a lowering of lake levels are initiated and by the mid holocene zone 2 subhumid temperate conditions are detected although lake level continues to be low the human impact is recorded in the last 4000 yr

geologic significance of anomalous instantaneous frequency anomalous frequency spikes derived from complex trace analysis have long been considered more as a flaw of algorithms than a valuable seismic attribute however synthetic models and field data show that instantaneous frequency spikes are clearly linked to physical models that could help geologic interpretations of seismic data frequency spikes are related to relative amplitude minima along a seismic trace that occur either at the merging point of the top and base reflections of a wedge type i or at the tip of the wedge type ii a type ii spike is indicative of a seismically thin bed average 0 2 or thinner in this study denotes wavelength although the bed thickness tends to decrease with the data frequency and bed spacing in a multibed acoustic impedance profile in the range of 16 to 2 in this study interpretive values of instantaneous frequency include recognizing thin reservoirs that are otherwise difficult to detect mapping relative thickness changes of lithofacies detecting lithof

quantitative estimates of orbital and millennial scale climatic variability in central mexico during the last 40 000 years abstract diatom based transfer functions for salinity precipitation and temperature were developed using a training set that included data from 40 sites along central mexico these transfer functions showed good performance parameters and were subsequently applied to the previously published diatom record from lake chalco southern basin of mexico heinrich stadials hs 3 to hs 0 were reconstructed as cold and dry events with hs 2 representing the coldest and driest conditions while hs 1 shows a complex bimodal cooling pattern orbital scale variability is also recorded high and variable lake salinities from 34 to 29 ka bp marine isotope stage 3 mis 3 corresponded with times of maximum summer insolation and evidences of frequent fires mis 2 was identified as a cold period with low lake salinity associated with low evaporation with two cold intervals during the minima in spring 25 5 ka bp and summer 20 ka bp insolation the 20 ka bp cold event together with hs 2 24 23 ka bp defined a bimodal maximum cooling during the last glacial maximum lgm 24 5 19 5 ka bp within the range of pollen based estimates further supporting a maximum tropical cooling of 4 5 c for the lgm the deglacial 19 5 11 5 ka bp showed the highest precipitation anomalies with three peaks that closely correlated with glacier advances in the nearby mountains iztaccihuatl the early holocene marked a change towards high lake salinities and the highest positive temperature anomalies 3 5 c during a peak in summer insolation even though at orbital scale chalco showed a nearly opposite trend to the record from the more southerly lake peten itza guatemala at millennial scale it showed a common pattern of cold and dry conditions during hss comparable to other tropical latitude sites in the northern hemisphere and further supporting the idea that there is a strong coupling between tropical and higher latitudes climates in particular with the north atlantic

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

3 d instantaneous frequency used as a coherency continuity parameter to interpret reservoir compartment boundaries across an area of complex turbidite deposition in previous unpublished work we found that anomalous values of instantaneous frequency that is frequency values that are negative or that have positive magnitudes greater than nyquist limit are valuable indicators of alterations in reflection waveshape that occur commonly at stratigraphic terminations inspection of 3 d seismic data across nash draw field on the northwest slope of the delaware basin showed that appreciable wavelet alterations occurred at the boundaries of distinct seismic facies within the targeted brushy canyon reservoirs that are being produced in this field based on this observation we used instantaneous frequency as the fundamental database to define the edge positions and areal shapes of individual reservoir facies within this complex slope basin distribution of siltstones and sandstones commonly thought to be a succession of turbidite depositions we compared the compartmentalization detail derived from this frequency based approach with compartmentalization models provided

genetic model of uranium mineralization in the permo triassic sedimentary rocks of the stara planina eastern serbia abstract one deposit and four occurrences of uranium minerals in the permo triassic sedimentary rocks of the stara planina in eastern serbia were ascertained using data from years of multidisciplinary geological research the minerals are the fissure filling type and were assigned to the exogenic mineralization group being mostly epigene in nature relevant geological information was used to derive a genetic model of uranium mineralization in the permo triassic sedimentary rocks of the stara planina the model explains the formation of permo triassic rocks and three stages of the complex process of u mineralization the genetic model treats 1 the primary sources of the uranium 2 the mobility of uranium and 3 accessory metals from the parent rocks to their deposition in host rocks and the postmineral change in ore bodies a geochemical barrier zone was identified in the sedimentary rocks that contained uranium mineral ore this geochemical barrier area included crescent shaped flat lens or vein like ore bodies the u containing mineral described is comparable with those from the relatively common fissure filling uranium minerals found around the world

a high elevation holocene pollen record from iztaccihuatl volcano central mexico pollen data from 3860 m in the agua el marrano valley on the northwest side of iztaccihuatl volcano southeastern part of the basin of mexico 198n combined with data on the glacial chronology and tephrochronology document holocene climatic and vegetation changes near the present timberline glacial advances occurred between 12 000 and 10 500 cal yr bp milpulco 1 and between 8300 and 7300 cal yr bp milpulco 2 a 450 cm core was drilled in sediments accumulated in a milpulco 1 moraine depression the sequence covers the last 11 000 cal yr bp according to three 14 c dates and the presence of a distinctive pumice deposit dated elsewhere at 5700 cal yr bp the pollen record of agua el marrano shows barren conditions after glacier retreat followed by a gradual colonization by elements of the alpine grasslands around 10 900 cal yr bp this plant community remained until c 7200 cal yr bp between c 7200 cal yr bp and 6500 cal yr bp coniferous forest grew close to or at the site but alpine grasslands were re established between 6500 cal yr bp and c 5000 cal yr bp apparently in connection with mid holocene dry conditions recorded in central mexico the upper timberline attained its modern altitude 4000 m in the last 3000 years during this period no significant changes are observed in the pollen spectra comparison with other palaeoecological records from central mexico suggests that the timberline fluctuated in response to both temperature and precipitation changes during the holocene