compositional variability in oils and formation waters from the ayoluengo and hontomin fields burgos spain implications for assessing biodegradation and reservoir compartmentalization abstract the main scope of this work is the geochemical characterization of 12 crude oils and formation waters of the ayoluengo oilfield basque cantabrian basin nw spain to delineate its reservoir compartmentalization the ayoluengo oil characteristics were also compared with data obtained from crude oil and formation water of the hontomin 2 well located 25 km to the se of ayoluengo the 13 ayoluengo and hontomin oil samples are very similar in composition bulk properties and isotopic signature indicating that these oils are genetically related however the hontomin oil is more mature and it is slightly biodegraded which suggests some differences in the reservoir environments the molecular parameters of both oils confirm a marine origin related to a liassic source rock coincident with the occurrence of lateral facies changes along the sedano sub basin on the other hand the connate waters are analogous and both classified as chloride calcium type given the complex nature of the sedimentology and structures of the reservoir gas chromatographic fingerprints of the analyzed crude oils have been used to detect minor variations in composition that are indicative of reservoir compartmentalization

quantifying climatic change through the last glacial interglacial transition based on lake isotope palaeohydrology from central turkey questions remain as to the nature of climatic change through the last glacial interglacial transition in the eastern mediterranean region particularly the relative contribution of evaporation and precipitation to regional water balance here changes in oxygen isotope values through this time period from eski acigol a crater lake in central turkey are investigated using hydrological and isotope mass balance models these allow changes in evaporation and precipitation to be quantified and their relative importance evaluated we show that it is the volumetric flux rate of water passing through the lake system and not the precipitation to evaporation ratio per se which controlled the stable isotope record in eski acigol early holocene precipitation is shown to be much greater than that during both the latter part of the last glaciation and the present day we test these calculated values against other records in the same region firstly with other lake records in anatolia the konya basin and lake van and secondly with isotope inferred palaeo precipitation data from soreq cave in israel this reveals a contrast between pre and post lgm precipitation values in turkey wetter and drier respectively and also suggests that during the last glacial interglacial transition there was a more marked precipitation gradient than at present between northern interior and southern coastal parts of the eastern mediterranean region

drimane type compounds in source rocks and fluids from fluvial deltaic depositional settings in the north west shelf of australia abstract fluvial deltaic petroleum systems with gas prone source rocks are difficult to assess because the released fluids generally lack biomarkers and this limits the implementation of traditional organic geochemistry screening however there are a number of compound classes yet to be investigated in order to establish novel parameters for correlation studies in fluvial deltaic geological settings in this study we have focused on drimane skeleton molecules c15 decalins particularly the compounds 1 2 2 5 5 pentamethyl trans decalin and 1 1 2 5 5 pentamethyl trans decalin termed herein as rearranged drimanes rd1 and rd2 respectively and drimane d in source rock extracts and fluids from fluvial deltaic petroleum systems in the carnarvon basin north west shelf of australia nws we have calculated the ratio rd1 rd2 d as proposed by ji et al ji l he c zhang m wu y li x 2016 bicyclic alkanes in source rocks of the triassic yanchang formation in the ordos basin and their inconsistency in oil source correlation marine and petroleum geology 72 359 373 and compared their results with samples from the nws our compilation of rearranged drimane ratios for a variety of lithologies suggests clay catalysed rearrangement of c15 decalins in siliciclastic source rocks from fluvial deltaic depositional environments therefore the mineral content seems to be a key factor controlling the isomerisation of decalins samples with higher clay content such as claystone from the brigadier formation have higher rd1 rd2 d ratios 6 and higher c29 diasterane c29 sterane 1 1 compared to silty claystone from the legendre formation 2 and 0 8 respectively the effects exerted by thermal maturity of the source rock and redox conditions of the depositional environment require further investigation although samples from the yanchang fomation and la luna formation where deposition occurred under more reducing conditions exhibit lower rearranged drimane ratios

the effect of clay minerals on diasterane sterane ratios to examine the effect of clay minerals on diasterane sterane ratios the mineral compositions of three sample sets of sedimentary rocks displaying a wide range of diasterane sterane ratios were analysed quantitatively diasterane sterane ratios do not to correlate with clay content but depend on the amount of clay relative to the amount of organic matter clay toc ratios this correlation may explain the high diasterane sterane ratios in crude oils and extracts derived from certain carbonate source rocks based on the concentrations of regular and rearranged steroids in the sample sets it is proposed that diasterenes are partly reduced to diasteranes and partly degraded during diagenesis in a ratio largely determined by the availability of clay minerals it is suggested that the hydrogen atoms required for reduction of the diasterenes originate from the water in the interlayers of clay minerals

stable isotope records of late quaternary climate and hydrology from mediterranean lakes the isomed synthesis lake isotope records can be used to assess the spatial coherency of late quaternary climate change across the circum mediterranean region we place modern and palaeo data within a simple conceptual lake response model to show that the isotope hydrology of most mediterranean lakes has been influenced strongly by water balance even in those systems that are chemically dilute i e freshwater 18o data on biogenic and endogenic carbonates from 24 lake basins are used to reconstruct multi millennial scale trends since the lgm while it is difficult to make direct comparisons between lake records in terms of single climatic parameters coherent regional isotopic trends can be identified during glacial times mediterranean lakes deposited carbonates isotopically heavier in 18o compared to the holocene partly due to source area effects isotopic enrichment was most marked during intervals corresponding to the h1 and younger dryas events confirming that late pleistocene cold stages in the north atlantic region were marked by aridity around much of the mediterranean almost all mediterranean lake records shifted to more depleted isotopic values during the last glacial interglacial transition lgit this shift is the reverse of the trend which characterised the same transition in lakes from northern and central europe and suggests that temperature changes were not an important direct driver of mediterranean lake isotopic records over glacial interglacial timescales in the early holocene many lakes in the eastern part of the region were more depleted isotopically than in recent millennia this corresponds with marine sapropel formation both chronologically and geographically and implies that increases in local rainfall contributed significantly to the creation of a freshwater lid and anoxia in the east mediterranean sea in contrast no such pattern is currently apparent from lake isotope records from the west mediterranean suggesting a possible nw se contrast in climate history during the holocene

migration of brines in the basement rocks of the athabasca basin through microfracture networks p patch u deposit canada abstract the unconformity type uranium deposits of the athabasca basin saskatchewan canada are hosted near the unconformity between a middle proterozoic intracratonic sedimentary basin and an archean to paleo proterozoic metamorphic and plutonic basement these deposits which are considered to be the richest u deposits in the world are the result of massive basinal fluid migrations in the basement rocks this study shows that basinal brines have strongly penetrated into the basement not only through faults and major pathways but also by way of dense networks of microfractures which favoured the percolation of fluids down to considerable depths hundred metres below the unconformity and their chemical modification salinity increase by interaction with basement lithologies these processes are one of the major causes of uranium mobility within the basement rocks and the formation of unconformity type mineralization microfracture networks which opened during the basinal brine stage ca 1600 1400 ma are interpreted as sets of mode i cracks corresponding to a specific stage of deformation and occur as fluid inclusion planes after healing the stress field at that stage 1 n130 150 e subvertical partly reopened the earlier microcrack networks 1 n80 110 e and n130 150 e subvertical issued from the trans hudson orogeny late retrograde metamorphic stage ca 1795 1720 ma the circulation of the two types of fluids carbonic and brines occurs thus at two distinct events trans hudson orogeny late retrograde metamorphism for carbonic fluids and maximal burial diagenesis for brines but the same main microfissure geometry was used by the fluids this demonstrates the existence of a similar stress field direction acting before and after the basin formation moreover the brine circulations in the basement acted in a wider volume than the clay rich alteration halo surrounding the u ores generally considered as the main envelope of fluid percolation outside the fault systems the data on the chemistry of the fluids and on the geometry of their migration at various scales emphasise the fundamental role of the basement in the chemical evolution of highly saline brines linked to unconformity related uranium mineralization in the athabasca basin

ocean atmosphere forcing of centennial hydroclimate variability in the pacific northwest reconstructing centennial timescale hydroclimate variability during the late holocene is critically important for understanding large scale patterns of drought and their relationship with climate dynamics we present sediment oxygen isotope records spanning the last two millennia from 10 lakes as well as climate model simulations indicating that the little ice age was dry relative to the medieval climate anomaly in much of the pacific northwest of north america this pattern is consistent with observed associations between the el nino southern oscillation enso the northern annular mode and drought as well as with proxy based reconstructions of pacific and atlantic ocean atmosphere variations over the past 1000 years the large amplitude of centennial variability indicated by the lake data suggests that regional hydroclimate is characterized by longer term shifts in enso like dynamics and that an improved understanding of the centennial timescale relationship between external forcing and drought is necessary for projecting future hydroclimatic conditions in western north america

the microbial input in carbonate anhydrite facies of a sabkha palaeoenvironment from guatemala a molecular approach abstract nine representative rock samplesincluding four anhydrites an oil stained dolomite and a laminated mudstone source rock from a sabkha type palaeoenvironment la felicidad 1 well guatemala have been compared in order to tentatively characterize each facies by a geochemical signature each sample has been studied by using basic parameters toc rock eval pyrolysis yields and analyses of alkanes and aromatics by computerized gc ms the following families of compounds have been reviewed n alkanes branched and cyclic alkanes n alkylbenzenes benzohopanes monoaromatic steroids d ring aromatic 8 14 secohopanoids alkylnaphthalenes alkylphenanthrenes alkyldibenzothiophenes and triaromatic steroids despite close geochemical relationships of all the sample a more in depth investigation taking into account molecular patterns and semi quantitative data reveals significant differences among the samples anhydrites may be differentiated from carbonates which illustrates the efficiency of organic geochemistry in environmental palaeoreconstruction even in organiccarbon lean sediments toc 0 04 0 08 in anhydrites in these anoxic marginally mature sediments the strong predominance of triterpanes over steranes tt to st 20 associated with other molecular features leads to the conclusion that the main contribution to the organic matter of all facies is by bacteria several prominent components including novel families iso c23 and iso c27 alkanes tetracyclic terpanes d ring aromatic 8 14 secohopanoids 1 phenylpentadecane undecylnaphathalene and their mono and dimethylated counterparts have been interpreted as derived from halophilic bacteria these conclusions may be extended to all crude oils from the same area which may be considered as true bacterially derived petroleums the la felicidad 1 well data are discussed with reference to other palaeosabkha type sequences from the sw aquitaine basin france in which the bacterial input is less important however in these sabkha sequences 1 phenylpentadecane undecylnaphthalene and related structures have also been identified

the isotopic and hydrologic response of small closed basin lakes to climate forcing from predictive models application to paleoclimate studies in the upper columbia river basin simulations conducted using a coupled lake catchment hydrologic and isotope mass balance model indicate that small closed basin lakes in north central washington are isotopically sensitive to changes in precipitation relative humidity and temperature most notably model simulations predicted inconsistent lake responses to precipitation changes due to differences in lake outseepage rates and surface area to volume sa v ratios greater outseepage within model experiments resulted in increased sensitivity to changes in mean precipitation moreover simulations suggest that in lakes with appreciable outseepage sa v ratio changes resulting from lake level variations control the direction of changes in lake water oxygen isotope composition 18o specifically in lakes with a sa v ratio that increases at higher lake levels steady state 18o values will increase in response to greater long term average precipitation these results suggest that closed basin lakes with low outseepage rates will exhibit a transient isotopic response to stochastic variability in hydrologic forcing but will not strongly respond at steady state to variation in mean hydrologic conditions conversely closed basin lakes with appreciable outseepage will exhibit strong isotopic responses to both stochastic variability and variation in mean hydrologic conditions i e mean precipitation relative humidity and temperature control of catchment hydrologic inputs to the lake these relationships provide a mechanism for explaining inconsistencies in the isotopic responses of lakes within a given region to hydrologic forcing and demonstrate that semiquantitative models for describing the relationship between lake hydrologic and isotopic responses to climate variability are not appropriate for all closed basin lakes

geochronology of the narakay volcanic complex implications for the age of the coppermine homocline and mackenzie igneous events u pb isotope analysis of four zircon separates from a rhyolite porphyry that is part of the bimodal narakay volcanic complex dease arm great bear lake yields an age of 1663 8 ma east trending feldspar phyric dykes that cut the complex yield zircons that are within analytical error the same age as the porphyry the narakay volcanic complex occurs in the upper part of the hornby bay group the lowermost group of the coppermine homocline and the stratigraphic position of the dated rocks indicates that 1663 ma is the depositional age of the upper hornby bay group this is the first u pb zircon age determined from rocks of the coppermine homocline and has important implications for previous geochronology and extrabasinal correlation earlier rb sr dates from the conformably overlying coppermine river group basalts of ca 1200 ma when taken together with the new data suggest that the dismal lakes group which conformably overlies the hornby bay group was deposited during a period of more than 400 ma

paleomagnetism of rocks from burin peninsula newfoundland hypothesis of late paleozoic displacement of acadia criticized the posttectonic st lawrence granite 360 5 ma and associated subvertical dikes have two magnetizations n and h n points north with an intermediate upward inclination declination 005 inclination 50 alpha 95 10 paleopole 12 n 120 e we consider n to have been acquired close to the time of initial cooling the h magnetization points south with low inclination h is also the dominant magnetization in the nearby permo carboniferous spanish room formation h is considered to be an overprint acquired chemically during the kiaman reversed superchron late carboniferous and permian the n magnetization corresponds to a paleolatitude of 31 7 s very different from the near equatorial values expected from the commonly accepted late devonian and earliest carboniferous tournaisian reference paleofields for cratonic north america this is generally consistent with the hypothesis of a southerly displaced acadia proposed by kent and opdyke although the displacement is much greater 30 rather than 15 however we show that all inclinations observed from middle to upper devonian and tournaisian rocks from the craton are not significantly different either from the kiaman paleofield or from the h overprints observed from newfoundland some of these cratonic studies are not very detailed but it is noteworthy that the declination observed in the most comprehensive of them catskill red beds also agrees with the kiaman paleofield and with the h overprints from newfoundland declinations in some other cratonic studies show small departures of only a few degrees with one exception based on limited sampling and two from the colorado plateau which may have been rotated which could be caused by experimental inaccuracies moreover the directions obtained from cratonic studies are 97 reversed as they are in rocks with kiaman magnetizations we suggest therefore that the commonly accepted late devonian to earliest carboniferous reference paleofield for north america is either entirely kiaman in age or has been seriously affected by kiaman overprinting consequently the 30 of southerly displacement which the n magnetization of the st lawrence granite apears to indicate and the 15 invoked by kent and opdyke we consider to be illusory three late precambrian rock units 623 to 606 ma have scattered declinations but similar inclinations yielding paleolatitudes of about 35 the scattered declinations presumable were caused by local pre carboniferous relative rotations there is little or no evidence of kiaman overprinting in precambrian rocks indicating that overprinting is comparatively superficial and is probably related to late paleozoic groundwater circulation

a lake sediment stable isotope record of late middle to late holocene hydroclimate variability in the western guatemala highlands abstract long term perspectives on past hydroclimate variability provide context for evaluating the potential future impacts of changes in northern hemisphere temperatures and oceanic atmospheric circulation on the timing and distribution of precipitation in central america here we use the isotopic composition of fine grained 18 ocalcite and 13 ccalcite from lake kail located in the western highlands of guatemala to infer multi decadal to multi centennial scale variability in the balance between precipitation and evaporation p e over the last 6000 years the sediment age model is based on 210pb and 41 14c ages with chronological uncertainty estimated using bayesian methods a model that couples lake hydrology and isotope mass balance is applied to characterize the isotopic responses of lake water and calcite to changes in drought controlling climate variables such as precipitation temperature and relative humidity the 18 ocalcite variations indicate intermediate to dry p e conditions during the late middle holocene from 6000 to 4100 cal yr bp there was then a shift to drier conditions at the start of the late holocene until 3050 cal yr bp followed by a trend to wetter conditions until 1500 cal yr bp the most recent 1500 years is characterized by high and relatively stable p e with particularly wet intervals from 1500 to 1170 cal yr bp and from 470 to 260 cal yr bp comparisons of the lake kail 18 ocalcite record with central american circum caribbean proxy datasets spanning the late middle and late holocene indicate northern tropical hydroclimate changes were highly variable across space and time and were likely driven by regional oceanic atmospheric responses with a secondary influence by insolation forcing

regional trends in the timing of alleghanian remagnetization in the appalachians pole positions related to remagnetized components isolated in appalachian limestone and redbed rock units range over about 60 m y of the permian carboniferous apparent polar wander path for north america apparent ages of remagnetization are older in the southern appalachians and younger to the north if the remagnetizations are associated with fluids expelled during the alleghany orogeny then the apparent remagnetization age trend could describe the timing of thrust sheet emplacement

the uranium mineralization potential of the paleoproterozoic sioux basin and its relationship to other basins in the southern lake superior region abstract the paleoproterozoic sioux basin and the baraboo barron flambeau mccaslin and waterloo quartzites in northcentral usa are all supermature quartz arenites that are among the world s oldest redbeds these quartzites were deposited on a stable craton at ca 1750 ma following exhumation and uplift of penokean crust and major orogenic activity related to the amalgamation of archean microcontinents at ca 2 0 1 8 ga to form laurentia 40ar 39ar ages of 1615 1543 ma from diagenetic muscovite in the sioux basin provide the first geochronological evidence for mazatzal related deformation and low grade metamorphism of the quartzites during subsequent convergence on the southern margin of laurentia one muscovite sample from the sioux basin has a 40ar 39ar age of 1465 ma that likely corresponds with fluid and thermal resetting due to felsic magmatism in the region and is similar to 40ar 39ar ages for muscovite from the baraboo and waterloo quartzites thus the sioux basin and other quartzites in the region have experienced a similar tectonic and fluid history the sioux basin has similar sedimentologic characteristics as other paleoproterozoic basins in north america including the uranium rich athabasca basin canada that is host to some of the world s largest and highest grade unconformity type uranium deposits we compared key characteristics such as the stratigraphy character of diagenetic fluids paleoaquifer characteristics and composition of leachable pb in the sandstones from the sioux basin with the athabasca basin in order to evaluate the fluid history of the basin and the potential of the sioux basin to host unconformity type uranium mineralization based on the hydrogen and oxygen isotopic composition of muscovite m1 that formed during diagenesis at 150 200 c the pore fluids that were present during peak diagenesis in the sioux basin had 18o and d values of 0 5 to 5 2 and 32 to 46 respectively similar to those of the fluids associated with uranium mineralization and alteration in the athabasca basin however fluid flow in the sioux basin was likely restricted to relatively thin and discontinous proximal fluvial facies that could have been diagenetic paleoaquifers in contrast to the extensive paleoaquifers in the athabasca basin that promoted large scale diagenetic reactions and alteration that led to the formation of unconformity type uranium mineralization in addition the non radiogenic isotopic composition of leachable pb in the sioux basin sandstones indicates that the majority of the pb is from a normal crustal source inconsistent with mobilization of radiogenic pb from a uranium rich source such as a uranium deposit although the sioux basin shares similar general characteristics to the athabasca basin the results of this study suggest that it has a lower potential than the athabasca basin to host significant high grade unconformity type deposits

petrogenesis of the proterozoic athabasca basin northern saskatchewan canada and its relation to diagenesis hydrothermal uranium mineralization and paleohydrogeology abstract in the athabasca basin proterozoic sandstones unconformably overlie archean and aphebian rocks multiple fluid events involving isotopically and chemically distinct fluids which have migrated laterally for considerable distances and along fault zones have produced a paragenetically identifiable assemblage of clay silicate and oxide minerals in the basin and basement rocks altered sandstones and the underlying metasedimentary rocks proximal to fault zones host high grade u ni co unconformity type uranium ore deposits and contain an alteration assemblage of highly crystalline 2m 3t illite 1m kaolinite clinochlore and sudoite hematite dravite and euhedral quartz in the sandstones 18o values of coeval quartz hematite quartz illite quartz dravite illite hematite and kaolinite hematite fluid inclusion temperatures in diagenetic quartz and d values of 1m kaolinite 2m 3t illite dravite and in fluid inclusions in the quartz indicate formation from a basinal fluid that had d values of 60 10 and which underwent salinity temperature and 18o increases from 5 to 34 wt nacl 120 to 240 c and 5 to 3 respectively as a result of increasing burial depth and sustained water rock interactions with the basinal sediments over substantial time periods 18 o 16 o and d h ratios of sudoite and clinochlore in meta sedimentary basement rocks within the alteration haloes indicate formation from a basement derived fluid with 18o and d values of 4 4 and 30 10 respectively that was isotopically distinct from the basinal fluids 18o and d values of late kaolinites in reactivated fault zones indicate formation mainly from low temperature 50 25 c fluids having 18o and d values of 16 and 130 respectively similar to relatively modern meteoric waters in the area some kaolinites have 18o and d values which suggest they formed from meteoric waters at mid latitudes and have experienced varying degrees of oxygen and hydrogen isotope exchange with relatively modern meteoric waters in the re activated faults illite sudoite and dravite have d values that vary by 100 without concurrent changes to their 18o values indicating preferential hydrogen isotope exchange with relatively modern meteoric waters at low temperatures and under conditions of high integrated water rock ratios rb sr isochron and model ages of 1477 57 and 952 ma respectively for the crystalline 2m 3t illites indicate the timing of the high temperature basinal fluid events associated with fluid mixing rb sr and k ar ages on illites with the lowest d values are as young as 300 ma and indicate late stage resetting of their radiogenic isotope systematics as a result of substantial interactions with relatively modern meteoric waters the evolution of sr isotopic compositions of fluids in the basin and basement rocks as reflected by the 87 sr 86 sr ratios of chlorite illite and dravite indicates that mixing of two isotopically distinct fluids in the vicinity of faults was the process by which uranium was precipitated similar to that suggested by oxygen and hydrogen isotope systematics in the clays and silicate minerals nd ratios in the high temperature diagenetic and hydrothermal clay and silicate minerals and the cogenetic uranium ores suggest they all have formed from similar fluids which have interacted substantially with the basin sediments in general the isotopic chemical microthermometric and petrologic data indicate that the athabasca basin has had a protracted fluid history comparable to that documented for more modern sedimentary basins the data clearly show that the major sandstone aquifers have been affected by widespread lateral flow of diagenetic fluids over distances of hundreds of kilometers and also that these fluid migration paths have been modified by cross formational fluid flow near active fault zones

palaeomagnetism of the early carboniferous deer lake group western newfoundland no evidence for mid carboniferous displacement of acadia early carboniferous visean to possibly earliest namurian sedimentary rocks of the deer lake group of western newfoundland rest unconformably on grenvillian basement rocks of the canadian shield which form the western border of the early palaeozoic appalachian orogen in addition to magnetically soft magnetizations directed along the present field three families of magnetization directions are found two of them referred to as n north and s south are antiparallel and prefolding and were probably acquired during the depositional process n and s are roughly of equal frequency they have a mean direction irrespective of sign of 0 7 35 2 k 40 95 8 9 and a palaeopole 21 5 n 121 8 e 10 3 6 0 corresponding to a palaeolatitude of 20 6 s this agrees with the palaeolatitude 17 5 s determined from the somewhat older early carboniferous tournaisian terenceville formation of the avalon platform on the eastern side of the appalachian orogen in newfoundland the third magnetization referred to as h roughly horizontal has a mean direction 156 8 13 3 k 37 95 10 1 and a palaeopole 45 4 n 140 3 e 10 3 5 3 corresponding to a palaeolatitude of 7 4 n we interpret this to be an early kiaman latest carboniferous to early permian overprint probably acquired chemically the palaeolatitude determined from the h overprint agrees with that determined from early carboniferous rocks of cratonic north america west of the appalachians therefore we argue early carboniferous palaeofield determinations for cratonic north america have been strongly biased by unremoved kiaman overprints because of this and because of the good agreement between early carboniferous palaeolatitudes obtained from opposite margins of the appalachian orogen we suggest that there is at present no palaeomagnetic evidence for the previously proposed 1500 km displacement from the south of an eastern portion of the appalachians acadia relative to cratonic north america during the carboniferous

paleomagnetic and isotopic evidence for the diagenesis and alteration of evaporites in the paleozoic elk point basin saskatchewan canada in the paleozoic elk point basin saskatchewan canada hematite in evaporite rocks of the middle devonian prairie formation records two magnetizations that are very different from those expected when the evaporites were originally deposited the first x magnetization corresponds to cretaceous or cenozoic paleofield directions and contains both normal and reversed polarities the second y magnetization appears to be a composite of cretaceous cenozoic and late paleozoic kiaman reversed polarity directions the x magnetization occurs in anomalous ores and is associated with fine grained hematite occurring predominantly along grain boundaries the y magnetization occurs in normal ore and is associated with sylvite that has hematite both along grain boundaries and within sylvite crystals the latter inferred to be of kiaman age k ar ages of the host sylvites are also composite and are consistent with those inferred from paleomagnetic directions stable isotopic compositions of fluid inclusions in hali

geochemistry and geochronology of the kiggavik uranium deposit nunavut canada the thelon basin nunavut canada is similar in age size and geology to the u producing athabasca basin in saskatchewan the kiggavik project area located immediately south of the aberdeen sub basin of the thelon basin contains u deposits and showings along a 30 km long ne sw structural trend the basement hosted kiggavik deposit comprising three separate mineralized zones main centre and east is located at the northern end of this trend multiple styles of u mineralization and alteration were identified at the kiggavik deposit disseminated euhedral uraninite u1 1284 53 ma has elevated pb contents up to 14 wt pbo and is associated with illite and hematite alteration vein style uraninite u2 284 19 ma forms along fractures contains lower pb contents 3 9 wt pbo and is partly altered to ca si rich 4 5 wt cao and 3 3 wt sio2 uraninite highly altered u2 is associated with galena late u minerals u3 have biogenic textures and are pb free indicating that they formed recently 1 ma based on sims in situ u pb geochronology the minimum age of uraninite at the kiggavik deposit is 1284 53 ma however this is likely a reset age associated with the mackenzie dyke event 1267 ma oxygen and hydrogen stable isotope compositions of illite and muscovite suggest that the kiggavik deposit has been overprinted by high latitude surficial fluids derived from snowmelt

numerical investigation of lake bed seepage patterns effects of porous medium and lake properties abstract three dimensional steady state numerical models were used to investigate the relative significance of several factors controlling lake bed seepage patterns lake depth lake bed slope orientation of an asymmetric lake with respect to a regional hydraulic gradient lake bed sediments and heterogeneity and anisotropy of the porous medium we considered both inflow and flow through lakes and our focus was on the details of seepage flux at the lake bed not on the surrounding porous medium while porous medium factors anisotropy and heterogeneity are important we found several conditions where lake bed factors were nearly as important in controlling the distribution of seepage varying lake bed slope from 0 013 to 0 04 in different simulations had a significant effect on shoreline seepage rates were 10 40 higher for lakes of low slope than lakes of steep slope also significantly elevated seepage in some cases a local maximum was observed offshore at the break in bed slope between the sloping side and flat central portions of the lake bed whenever the surrounding porous medium had a high anisotropy 1000 or 100 for flow through lakes in media of high anisotropy the annual volume of groundwater inseepage was significantly higher about 20 in lakes with steep bed slope compared to those with low slope this effect of slope was smaller at lower anisotropy for an asymmetric flow through lake a lake with a steep bed slope on one side moderate slope on the other the percentage of lake bed experiencing inseepage was greatest when the steep side was downgradient and the effect was larger at higher anisotropy these effects illustrate the complex interaction between lake bed slope and the anisotropy of the surrounding porous medium in controlling lake groundwater exchange adding low conductivity lake sediments and decreasing their conductivity shifted groundwater seepage further offshore in inflow lakes increasing the anisotropy of the surrounding porous medium had the same effect adding sediments and increasing anisotropy also decreased nearshore seepage in flow through lakes but without increasing offshore seepage in this case the net effect was a smaller annual volume of lake groundwater exchange at the same time the percentage of the lake bed experiencing inseepage increased in flow through lakes even as the annual volume of inseepage was decreasing thus for flow through lakes a larger area of inseepage may not be a good indicator of a greater volume of inseepage lake depth did not have a significant effect on the quantity or distribution of seepage to inflow or flow through lakes many of the physical factors investigated here influence the amount of lake groundwater exchange and the proportions of nearshore and offshore seepage therefore they are potentially significant to lake water quality and ecology in addition to hydrology

metal rich fluid inclusions provide new insights into unconformity related u deposits athabasca basin and basement canada the paleoproterozoic athabasca basin canada hosts numerous giant unconformity related uranium deposits the scope of this study is to establish the pressure temperature and composition p t x conditions of the brines that circulated at the base of the athabasca basin and in its crystalline basement before during and after uo2 deposition these brines are commonly sampled as fluid inclusions in quartz and dolomite cementing veins and breccias associated with alteration and u mineralization microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms data from five deposits rabbit lake p patch eagle point millennium and shea creek complement previously published data for the mcarthur river deposit in all of the deposits investigated fluid inclusion salinity is between 25 and 40 wt nacl equiv with compositions displaying a continuum between a nacl rich brine end member cl na ca mg k and a cacl2 rich brine end member cl ca mg na k the cacl2 rich brine has the highest salinity and shows evidence for halite saturation at the time of trapping the continuum of compositions between the nacl rich brine and the cacl2 rich brine end members combined with p t reconstructions suggest anisothermal mixing of the two brines nacl rich brine 180 30 c and 800 400 bars cacl2 rich brine 120 30 c and 600 300 bars that occurred under fluctuating pressure conditions hydrostatic to supra hydrostatic however because the two brines were u bearing and therefore oxidized brine mixing was probably not the driving force for uo2 deposition several scenarios are put forward to account for the cl na ca mg k composition of the brines involving combinations of seawater evaporation halite dissolution mixing with a halite dissolution brine mg ca exchange by dolomitization na ca exchange by albitization of plagioclase na k exchange by albitization of k feldspar and mg loss by mg rich alteration finally the metal concentrations in the nacl rich and cacl2 rich brines are among the highest recorded compared to present day sedimentary formation waters and fluid inclusions from basin hosted base metal deposits up to 600 ppm u 3000 ppm mn 4000 ppm zn 6000 ppm cu 8000 ppm pb and 10 000 ppm fe the cacl2 rich brine carries up to one order of magnitude more metal than the nacl rich brine though the exact origin of major cations and metals of the two brines remains uncertain their contrasting compositions indicate that the two brines had distinct flow paths and fluid rock interactions large scale circulation of the brines in the athabasca basin and basement was therefore a key parameter for metal mobility including u and formation of unconformity related u deposits

sr isotopic study of helikian sediment and diabase dikes in the athabasca basin northern saskatchewan the athabasca group overlies 1 8 ga or older basement of the churchill province and predates uranium mineralization at 1 3 ga cross cutting diabase dikes have been dated by rb sr mineral isochrons

late paleozoic remagnetization of the trenton limestone samples of the middle ordovician trenton limestone were collected from 8 sites in quebec ontario and new york state for paleomagnetic study stepwise thermal demagnetization reveals a very well defined characteristic magnetization that has a corresponding paleomagnetic pole at 53 0 n 126 9 e k 97 7 a 95 2 7 this pole is not at all close to other ordovician poles from cratonic north america but is near late carboniferous and early permian ones indicating that the trenton was remagnetized in the late paleozoic an earlier paleomagnetic investigation of the trenton gave a pole that did not appear to be late paleozoic in age however we demonstrate that this earlier study failed to isolate the ancient characteristic magnetization rock magnetic experiments and analyses of magnetic extracts show that the carrier of magnetization is fe3o4 that does not contain ti or other elements in solid solution that would indicate a detrital source the magnetite and its associated remanence appear to have a diagenetic origin

a giant oil seep at a salt induced escarpment of the sao paulo plateau espirito santo basin off brazil host rock characteristics and geochemistry abstract an international research cruise named iata piuna took place on the sao paulo plateau on may 2013 in the campos and espirito santo basins off brazil the cruise was carried ou on board the research vessel r v yokosuka that hosts the human operated vehicle hov shinkai 6500 it aimed at finding chemosynthetic communities composed of organisms capable of generating their own vital energy by metabolizing organic and inorganic compounds related to seeps identification of these organisms could provide information for understanding the origin of life since they may resemble primitive organisms that existed in the initial stages of life on earth during leg 2 may 10 24 2013 however dives on the northern part of the sao paulo plateau at the espirito santo basin led to the discovery of a giant oil seep the seep ca 3 nautical miles ca 5 6 km in length is located along an outcrop of eocene rocks on a salt induced escarpment of the plateau and at a water depth of ca 2700 m the 200 m relief of the seafloor suggests that the seep takes place along an active fault system driven by salt diapirism the oil was analyzed and identified as a severely biodegraded marine oil generated by carbonate rocks within a minibasin located to the east of the escarpment this represents valuable exploratory information because it proves that an active petroleum system is present in the context of minibasins associated with salt diapirism in the area

early quartz cements and evolution of paleohydraulic properties of basal sandstones in three paleoproterozoic continental basins evidence from in situ δ18o analysis of quartz cements quartz cement microstratigraphy and high precision in situ 18 o values obtained by secondary ion mass spectrometry sims from m size quartz cement zones have been used here to determine the timing of cementation and to evaluate precipitation mechanisms within the basal sandstones of three economically significant paleoproterozoic basins the athabasca and thelon basins canada and the mcarthur basin australia in these examples the earliest quartz cements have the highest 18 o values up to 33 mean 26 0 v smow indicative of low temperature precipitation at depths of 0 to 1 1 km some paragenetically early cement phases however have lighter isotopic values that suggest either precipitation from isotopically depleted water or precipitation at higher temperatures subsequent generations of quartz cements have progressively lower 18 o values mean 16 1 3 consistent with precipitation at higher temperatures these data combined with petrographic observations indicate quartz cementation began in near surface vadose and phreatic zones the next stage of cementation is characterized by syntaxial burial cement overgrowths regionally and stratigraphically well sorted sandstone facies that were initially aquifers preferentially experienced early quartz cementation which resulted in cement bridged pore throats at relatively shallow depths of 0 2 km and very early in their burial history transforming these units into diagenetic aquitards as a result these units did not experience mineralization compositionally and texturally immature braided fluvial facies did not experience early addition of quartz cement but are instead marked by minor syntaxial overgrowth cement that make upb5 of the intergranular volume formed at depths of 3 5 km and were variably replaced by illite and chlorite during burial these lithologies were still open to fluid movement at critical times in the basin when u and

evaporation and transport of water isotopologues from greenland lakes the lake size effect abstract isotopic compositions of evaporative flux from a lake are used in many hydrological and paleoclimate studies that help constrain the water budget of a lake and or to infer changes in climate conditions the isotopic fluxes of evaporation from a water surface are typically computed using a zero dimensional 0 d model originally conceptualized by craig and gordon 1965 such models generally have laminar and turbulent layers assume a steady state condition and neglect horizontal variations in particular the effect of advection on isotopic variations is not considered while this classical treatment can be used for some sections of large open surface water bodies such as an ocean or a large lake it may not apply to relatively small water bodies where limited fetch does not allow full equilibration between air from land and the water surface both horizontal and vertical gradients in water vapor concentration and isotopic ratios may develop over a lake these gradients in turn affect the evaporative fluxes of water vapor and its isotopic ratios which is not adequately predicted by a 0 d model we observed for the first time the vertical as well as horizontal components of vapor and isotopic gradients as relatively dry and isotopically depleted air advected over the surfaces of several lakes up to a 5 km fetch under winds of 1 5 m s in kangerlussuaq greenland we modeled the vapor and isotopic distribution in air above the lake using a steady state 2 d model in which vertical diffusive transport balances horizontal advection the model was verified by our observations and then used to calculate evaporative fluxes of vapor and its isotopic ratios in the special case of zero wind speed the model reduces to 1 d results from this 1 d model are compared with those from the 2 d model to assess the discrepancy in isotopic fluxes between advection and no advection conditions since wind advection above a lake alters the concentrations gradients and evaporative fluxes of water isotopes it alters the water balance and isotope ratios of the lake and the relationship between them these effects are greatest for small lakes if wind advection is neglected in the inference of water balance from lake isotopes an error is thus introduced the magnitude of which depends on lake size we refer to this as the lake size effect for lakes less than 500 m in length along the wind direction the average 18o and d of vapor flux are at least 2 lower than the corresponding flux values from the 1 d model the magnitude of the resulting relative error in water balance calculations is much greater if using 18o than d in mass balance calculations the former is about eight times the latter this result argues that water balance calculated with d is less sensitive to the difference in lake size and or its change over time the 1 d model result is also compared with that from a comparable 0 d model since vertical vapor and isotope gradients always exist even under no advection conditions one may not obtain correct flux values if the relative humidity and isotopic ratios in ambient air measured at an arbitrary height are used for the 0 d model calculation typically the standard meteorological measurements at 2 or 10 m would result in an underestimate of the 18o and d values of the vapor flux this work has provided the first quantification on the effect of advection on isotopic fluxes of evaporation the method of mobile vapor analysis combined with 2 d modeling can be applied to other environmental settings in which the size of advection effect on isotopic fluxes depends upon relationships among local meteorological and hydrological variables our results also suggest that incorporating isotopic vapor measurements can help constrain modeled evaporation rates which is worth exploring further in future studies

early proterozoic geomagnetic field in western laurentia implications for paleolatitudes local rotations and stratigraphy abstract the east west trending post orogenic subvertical cleaver dykes from the great bear magmatic arc are dated by the u pb baddeleyite method to be 1740 5 4 ma they have a mean direction of magnetization of d i 136 5 and 57 4 k 64 95 4 5 based on samples from 17 diabase dykes a mean location 65 7 n 118 03 w and a corresponding paleopole at 19 4 n 83 3 w a95 6 1 studies of baked contacts country rocks distant from dykes and later intrusions that cut them show that the dykes became magnetized soon after intrusion the paleopole is not significantly different from that obtained from the 1759 1 ma post orogenic jan lake granite from the hudsonian orogen in southeast saskatchewan these paleopoles fall among a cluster previously determined from post orogenic overprints in a wide variety of rocks and geological settings across laurentia their mean is 20 8 n 94 5 w a95 5 2 collectively they record a widespread remagnetization episode following the hudsonian orogeny during which the polarity of the field remained constant this single polarity interval the cleaver superchron has a mean age of approximately 1747 ma and its duration is at least 13 million years but is probably much longer with further refinement it could become a global statigraphical marker there are 18 paleopoles from red beds and igneous rocks which record the paleofield in western laurentia mainly over an extended interval we estimate to be at least 100 million years between about 1960 and 1830 ma during the hudsonian orogeny over this interval western laurentia remained at a low and essentially constant latitude reversals of the geomagnetic field occurred opposed magnetizations being of approximately equal frequency there are numerous magnetochrons which could in future assist in regional stratigraphic correlations on the basis of six studies we estimate that the reference paleopole for this interval is at 1 1 s 71 7 w a95 12 1 n 6 paleopoles from the other 12 studies are spread over a 100 arc indicating large variable rotations about local vertical axes which probably resulted from transcurrent faulting caused by indentation of the bordering archean slave and superior cratons during the hudsonian orogeny these reference paleopoles show that during the hudsonian orogeny western laurentia was in paleolatitudes of 15 30 during post hudsonian time ca 1750 ma paleolatitudes were about 20 higher paleowind directions inferred by others indicate that laurentia during these intervals was in the northern hemisphere

reconstruction of late quaternary paleohydrologic conditions in southeastern british columbia using visible derivative spectroscopy of cleland lake sediment abstract visible derivative spectroscopy vds analysis of sediment from cleland lake southeastern british columbia provides a reconstruction of paleolimnological productivity and hydrologic change during the past 14 000 calibrated 14 c years before present cal yr bp the first five principal components pc of the vds data explain 97 of the variance in the vds data set four pcs correlate with standard reflectance derivative spectra for diatom dinoflagellate algae and cyanophyte pigments that record ecological change while two pcs are paleohydrologic indicators dinoflagellate algae are predominant from 11 600 to 8600 cal yr bp then decrease to low levels after 8500 cal yr bp pcs 3 5 represent variations in cyanophyte abundance and exhibit peaks from 14 000 to 11 600 14 000 to 9500 and 6100 to 5400 cal yr bp respectively conditions shifted toward favoring diatoms around 9400 and lasted until 170 cal yr bp higher dinoflagellate related pigment concentrations suggest a lower lake level from 11 600 to 8600 cal yr bp followed by higher water levels and wetter conditions after 8500 cal yr bp we propose that drier conditions transitioning from the late glacial into the holocene were caused by summer insolation driven non linear feedbacks between the northern hemisphere subtropical high pressure systems vegetation and soil moisture

tracing of variabilities within a geological barrier by molecular organic geochemistry case of the callovo oxfordian sedimentary series in the east of the paris basin france abstract the callovo oxfordian claystones located at 500 m depth at bure meuse france are currently being investigated by andra the french national radioactive waste management agency for testing the feasibility of long term and deep geological nuclear waste disposal in order to evaluate its potential as a geological barrier it is very important to study assess and describe its physico chemical variability the molecular biomarker composition of 150 samples of these claystones and their surrounding limestones carry diverse information on the sources of the sedimentary organic matter the chemistry of the depositional environment the preservation and diagenesis conditions it also allows assessing the degree of lateral and vertical variability of the organic matter within these sedimentary series the abundance of unsaturated biomarkers the distribution of steroids and hopanoids and cpi values 2 prove the thermal immaturity of the organic matter the co occurrence of plankton bacteria and land plant biomarkers indicate that the organic matter is a mixture of marine and continental contributions the data also reveal that the organic matter was deposited under oxic and open sea conditions except for a brief event of photic zone anoxia at the beginning of the middle callovian in the claystones the geosynthesis of diasterenes is favored to the detriment of the formation of steranes especially in smectite rich levels and the organic matter is rapidly isolated from oxidizing then reducing conditions after the deposition due to the protective effect of clays on the scale investigated the claystones are characterized by a unique molecular facies and are thus homogenous from their organic content point of view yet detailed investigation of specific molecular families indicates changes related to major claystone limestone transitions the homogeneity of these claystones can be explained by the paleogeographic position of their depositional setting and the plane and sub horizontal paleotopography on which they were deposited this study demonstrates the efficiency of organic geochemistry in the assessment of the variability of geological barriers

paleomagnetism of the komatiitic basalts of the ottawa islands n w t the komatiitic basalts of the ottawa islands in eastern hudson bay are on strike with and believed to form a continuation of similar units of the cape smith belt 150 km to the northeast units sampled in the ottawa islands all dip gently to the west and hence are not suitable for an internal fold test of their age of magnetization however before correcting for the tilt of the lavas the dominant magnetization direction d 207 6 i 61 9 k 168 95 3 7 does not differ significantly from the uncorrected magnetization direction reported from the steeply dipping northwest facing units at cape smith d 218 i 60 k 47 95 4 this negative fold test suggests that the remanence at both locations was acquired after folding comparison with the north american precambrian apparent polar wander path implies that overprinting is related to the hudsonian orogeny a second stable magnetization directed to the west with a shallow inclination is superimposed on the dominant component at a numbe

drought variability in the pacific northwest from a 6 000 yr lake sediment record we present a 6 000 yr record of changing water balance in the pacific northwest inferred from measurements of carbonate 18o and grayscale on a sediment core collected from castor lake washington this subdecadally resolved drought record tracks the 1 500 yr tree ring based palmer drought severity index reconstructions of cook et al cook er woodhouse ca eakin cm meko dm stahle dw 2004 science 306 1015 1018 in the pacific northwest and extends our knowledge back to 6 000 yr b p the results demonstrate that low frequency drought pluvial cycles with occasional long duration multidecadal events are a persistent feature of regional climate furthermore the average duration of multidecadal wet dry cycles has increased since the middle holocene which has acted to increase the amplitude and impact of these events this is especially apparent during the last 1 000 yr we suggest these transitions were driven by changes in the tropical and extratropical pacific and are related to apparent intensification of the el nino southern oscillation over this interval and its related effects on the pacific decadal oscillation the castor lake record also corroborates the notion that the 20th century prior to recent aridity was a relatively wet period compared to the last 6 000 yr our findings suggest that the hydroclimate response in the pacific northwest to future warming will be intimately tied to the impact of warming on the el nino southern oscillation

hydrogen isotope systematics of submarine basalts the d h ratios and water contents in fresh submarine basalts from the mid atlantic ridge the east pacific rise and hawaii indicate that the primary d h ratios of many submarine lavas have been altered by processes including 1 outgassing 2 addition of seawater at magmatic temperature and 3 low temperature hydration of glass decreases in d and h2o from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between d and h2o in basalts from the galapagos rise and the famous area are attributed to outgassing of ch4 and h2 a good correlation between d values and h2o is observed in a suite of submarine tholeiites dredged from the kilauea east rift zone where seawater added directly to the magma affected only the isotopic compositions of hydrogen and argon analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having d values as low as 100 d values vary with h2o contents of subaerial transitional basalts from molokai hawaii and subaerial alkali basalts from the society islands indicating that the primary d values were similar to those of submarine lavas extrapolations to possible unaltered d values and h2o contents indicate that the primary d values of most thoteiite and alkali basalts are near 80 5 the weight percentages of water are variable 0 15 0 35 for mor tholeiites about 0 25 for hawaiian tholeiites and up to 1 1 for alkali basalts the primary d values of 80 for most basalts are comparable to those measured for deep seated phlogopites these results indicate that hydrogen in marked contrast to other elements such as sr nd pb and o has a uniform isotopic composition in the mantle this uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the earth

quantifying closed basin lake temperature and hydrology by inversion of oxygen isotope and trace element paleoclimate records lake systems are important paleoclimate archives that preserve ecosystem and hydrologic responses to critical periods in earth history such as carbon cycle perturbations and glacial interglacial cycles geochemical measurements of biogenic carbonate for example 18o 13c 87sr 86sr li u sr and mg are indicators of hydrologic variability in lake systems throughout the geologic record in this study we present a new closed basin lake modeling approach hybim the hydrologic balance inverse model that employs a system of total differential equations and uses the measured 18o sr ca and mg ca of biogenic carbonate to determine changes in temperature runoff and lake evaporation using equally spaced time steps these equations are simultaneously solved to constrain the hydrologic parameters of the lake as recorded in biogenic carbonate we use a monte carlo approach to account for uncertainty in the input parameters such as 18o temperature relationships partition coefficient uncertainty and watershed solute chemistry for illustrative purposes we apply the model to two ostracod valve datasets covering different timescales 1 the cretaceous songliao basin northeast china and 2 holocene lake miragoane haiti modern water measurements of water isotopes and cation concentrations from each location are required as model inputs we compare our modeling results with author interpretations and geologic observations the modeling approach presented in this study can be applied to other closed basin lake records can be modified for other calcifying species for example gastropods or mollusks or with calibration to inorganic lacustrine carbonate in addition this approach holds promise for extension with additional proxy measurements that is d u ca or li ca and changing source area on tectonic timescales using proxies that reflect changing source lithology that is sr and pb isotopes future incorporation of age model uncertainty in the monte carlo approach will also provide utility by quantifying temporal uncertainty on the hydrologic response recorded by lake sediments

implications of ash dispersal for tectonic models with an example from wopmay orogen the coronation supergroup a 1 9 ga west facing continental margin prism in the wopmay orogen represents the opening and closing of a basin but was this an open ocean or a back arc basin the 10 m y life span of the basin suggests a korean type margin but geological arguments have been raised against a back arc interpretation the most serious argument is the lack of ash beds in lagoonal facies of the shelf despite prevailing onshore winds on the basis of combined paleomagnetic data stromatolite elongation starved fore slope and other sedimentological evidence the margin faced east and deposition occurred in the belt of trade winds at fat 10 20 n however ash is generally not distributed by low level winds such as trades but by winds in the troposphere ash erupted from an offshore arc located near lat 15 n would probably have been transported away from the margin not toward it this nullifies the strongest geological argument against a back arc origin for the coronation supergroup which is supported by many independent lines of evidence the method described has potential for determining whether other ancient basins represent back arc basin fill or continental margin deposits of an open ocean

carbonate deposition pyramid lake subbasin nevada 4 comparison of the stable isotope values of carbonate deposits tufas and the lahontan lake level record abstract in this paper the fundamental importance of changes in hydrologic balance and hydrologic state on the 18o and 13c values of water and dissolved inorganic carbon dic in lakes of the lahontan basin is illustrated abrupt changes in 18o and 13c values of carbonate deposits tufas from the pyramid lake subbasin nevada coincide with abrupt changes in lake level and hydrologic state minima in lake level at 26 000 15 500 and 12 000 yr b p are associated with relatively heavy 18o and 13c values maxima in the lake level record at 14 000 and 10 500 yr b p are associated with relatively light 18o and 13c values we believe that the correlation between maxima and minima in the lake level and 18o records reflect the fundamental effect of lake level dynamics on the 18o value of lake water evaporation increases the 18o value of lake water whereas streamflow discharge and on lake precipitation decrease the 18o value variation in the 18o value of lake water therefore indicates change in the hydrologic balance increases in 18o accompany decreases in lake volume and decreases in 18o accompany increases in lake volume covariance of 13c and 18o indicates that change in 13c values of dic also accompany change in lake volume we offer the hypothesis first put forward by j a mckenzie that change in the productivity photosynthesis respiration balance is responsible for much of the observed variation in 13c most great basin lakes including lake lahontan experienced changes in hydrologic state during the late wisconsin when a lake becomes hydrologically open the residence time of water decreases the greater the rate of spill the greater the volume of evaporated 18o enriched water removed from the spilling lake and the more negative the 18o value of water remaining in the spilling lake the concentration of dic as well as the concentrations of photosynthesis limiting nutrients e g phosphorus nitrogen silica molybdenum decrease as spill increases increasing rates of spill therefore lead to overall decreases in photosynthetic rates relative to respiration rates and as a consequence the 13c values of dic become more negative

paleozoic oil source rock correlations in the tarim basin nw china we studied a suite of 40 oils and extracts of purported source rocks from the tarim basin in nw china the main group of oils comes from tazhong and tabei wells which sample the largest known petroleum accumulations in the basin these oils can be statistically correlated with extracts of ordovician rocks based upon high relative concentrations of 24 isopropylcholestanes and low relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes in contrast extracts from cambrian rocks have low relative concentrations of 24 isopropylcholestanes with high relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes although some tarim basin cambrian rocks yield high total organic carbon contents we see little evidence in the analyzed oil samples to suggest that they came from cambrian source rocks

vascular plant biomarker distributions and stable carbon isotopic signatures from the middle and upper jurassic callovian kimmeridgian strata of staffin bay isle of skye northwest scotland the molecular and stable carbon isotopic composition of higher plant biomarkers was investigated in middle to upper jurassic strata of the isle of skye northwest scotland aromatic hydrocarbons diagnostic of vascular plants were detected in each of nineteen sedimentary rock samples from the early callovian to early kimmeridgian interval a succession rich in fossil fauna including ammonites that define its constituent chronozones the higher plant parameter hpp and higher plant fingerprint hpf calculated from the relative abundance of retene cadalene and 6 isopropyl 1 isohexyl 2 methylnaphthalene ip ihmn exhibit several large fluctuations throughout the skye succession studied these molecular profiles contrast with both 1 the more uniform profiles previously observed in jurassic successions putatively of the same age from other palaeogeographical settings including the carnarvon basin western australia and 2 the steady rise in global sea level during this interval this suggests that the hpf profiles of jurassic marine successions may not be reliable indicators of global climate change our results indicate that other factors such as local tectonism resulting in changes to the relief and landscape of the hinterland likely influenced the palaeoflora and the mode of transport of its detritus into adjacent marine depocentres however the skye succession showed similar 13c profiles of total organic carbon toc comprising mainly fossil wood the vascular plant biomarker retene and a predominant phytoplanktonic biomarker phytane the apparent isotopic relationship between terrigenous and marine derived biomarkers supports a strong coupling of the atmosphere and ocean the maximum isotopic excursion occurs in the cardioceras cordatum ammonite biozone of the early to middle oxfordian which may be indicative of changes in atmospheric and oceanic levels of co2

isotopic and hydrologic responses of small closed lakes to climate variability comparison of measured and modeled lake level and sediment core oxygen isotope records abstract simulations conducted using a coupled lake catchment isotope mass balance model forced with continuous precipitation temperature and relative humidity data successfully reproduce within uncertainty limits long term i e multidecadal trends in reconstructed lake surface elevations and sediment core oxygen isotope 18 o values at castor lake and scanlon lake north central washington error inherent in sediment core dating methods and uncertainty in climate data contribute to differences in model reconstructed and measured short term i e sub decadal sediment i e endogenic and or biogenic carbonate 18 o values suggesting that model isotopic performance over sub decadal time periods cannot be successfully investigated without better constrained climate data and sediment core chronologies model reconstructions of past lake surface elevations are consistent with estimates obtained from aerial photography simulation results suggest that precipitation is the strongest control on lake isotopic and hydrologic dynamics with secondary influence by temperature and relative humidity this model validation exercise demonstrates that lake catchment oxygen isotope mass balance models forced with instrumental climate data can reproduce lake hydrologic and isotopic variability over multidecadal or longer timescales and therefore that such models could potentially be used for quantitative investigations of paleo lake responses to hydroclimatic change

precise maturity assessment over a broad dynamic range using polycyclic and heterocyclic aromatic compounds abstract the construction and reliable application of maturation indices is extremely important in deep earth exploration yet predicting levels of maturation on a molecular level especially at overmature stages is still a major challenge here we report robust broad ranging and precise maturity parameters that were developed using a continuous core of thermally overmature lacustrine deposits shahezi fm from the deep songke 2 well sk 2 songliao basin china augmented by shallow cores of lower maturity marine deposits posidonia shale from the hils syncline germany the novel indices presented here are based on the general process of thermally induced cyclization aromatization and aliphatic chain cracking of hundreds to thousands of compounds during maturation the newly developed parameters with an extremely broad dynamic range extending from catagenesis and into metagenesis vitrinite reflectances ro range from 0 9 to 2 2 are based on polycyclic and heterocyclic aromatic compounds measured using fourier transform ion cyclotron resonance mass spectrometry ft icr ms the high coefficient of correlations between the new maturity parameters with ro and tmax demonstrate their utility for assessing precisely the thermal maturity of overmature shales

o and pb isotopic analyses of uranium minerals by ion microprobe and u pb ages from the cigar lake deposit we apply a rapid and accurate in situ technique to make u pb isotopic measurements of complexly intergrown uranium minerals and oxygen isotopic analyes of uraninite from the unconformity type cigar lake uranium deposit secondary uranium minerals intergrown with uraninite such as coffinite usio4 nh2o and calciouranoite cau2o7 5h2o were identified by highresolution transmission electron microscopy hrtem in situ u pb results from three stages of uraninite and coffinite define well correlated arrays on concordia with upper intercepts of 1461f47 1176f9 and 876f14 ma f1r these ages are interpreted as the minimum ages of mineralization correlate with the timing of clay mineral alteration f1477 ma associated with these unconformity type uranium deposits the ages of magnetization events at 1600 1450 and 900 ma from the athabasca basin and the grenvillian orogeny at f1100 ma in situ u pb isotopic analyses of uraninite and coffinite can document the pb u heterogeneities that occur on the scale of 15 30 am thus providing relatively accurate information regarding the timing of fluid interactions associated with the evolution of these deposits the high spatial resolution and precision of the ion microprobe allow us to measure d 18 o values of 20 100 am unaltered portions of uraninites from cigar lake the range of d 18 o values 33 9 to 20 4x are among the lowest reported for unconformity type deposits confirming that conventional fluorination analyses of material sampled at the mm scale are insufficient to avoid contamination from isotopically heavier coffinite and calciouranoite d 2002 elsevier science b v all rights reserved

quantitative reconstruction of early holocene and last glacial climate on the balkan peninsula using coupled hydrological and isotope mass balance modelling abstract we investigate the modern hydrology of lake ohrid macedonia albania using a combined hydrological and isotope based modelling approach and present a new evaluation of contemporary water balance and palaeoclimate estimates the combined model is able to estimate hydrological components that cannot be directly measured and indicates that sublacustrine spring inflow is in the order of 50 higher than previous estimates and groundwater outflow comprises approximately a third of overall water outflow in combination with sediment core oxygen isotope data we used the combined model to quantitatively reconstruct past climate in particular precipitation during the early holocene and last glacial period calculated precipitation in the early holocene was higher than the value for present day and was approximately 44 lower than present during the last glacial assuming the majority of precipitation fell as snow the estimated amount of precipitation in the last glacial would have been high enough to provide refugial conditions at lake ohrid and to support the continuous existence of arboreal vegetation in the catchment the improved understanding of the modern isotope hydrology of lake ohrid is fundamental for explaining the systematics of past isotope variation and providing context for extended sediment records from the lake which will provide longer term palaeoclimate reconstructions covering multiple glacial interglacial cycles

origin of low molecular weight alkylthiophenes in pyrolysates of sulphur rich kerogens as revealed by micro scale sealed vessel pyrolysis abstract micro scale sealed vessel mssv pyrolysis experiments have been conducted at temperatures of 150 200 250 300 330 and 350 c for various times on a thermally immature type ii s kerogen from the maastrichtian jurf ed darawish oil shale jordan in order to study the origin of low molecular weight lmw alkylthiophenes these experiments indicated that the lmw alkylthiophenes usually encountered in the flash pyrolysates of sulphur rich kerogens are also produced at much lower pyrolysis temperatures i e as low as 150 c as the major apart from hydrogen sulfide sulphur containing pyrolysis products mssv pyrolysis of a long chain alkylthiophene and an alkylbenzene indicated that at 300 c for 72 h no cleavage leading to generation of lmw alkylated thiophenes and benzene occurs in combination with the substantial production of lmw alkylthiophenes with a linear carbon skeleton at these conditions this indicated that these thiophenes are predominantly formed by thermal degradation of multiple poly sulfide bound linear c 5 c 7 skeletons which probably mainly originate from sulphurisation of carbohydrates during early diagenesis lmw alkylthiophenes with linear carbon skeletons seem to be unstable at mssv pyrolysis temperatures of 330 c either due to thermal degradation or to methyl transfer reactions lmw alkylthiophenes with a branched carbon skeleton most likely derive from both multiple poly sulfide bound branched c 5 c 7 skeletons and alkylthiophene units present in the kerogen

estimating the regional climate signal in a late pleistocene and early holocene lake sediment δ18o record from vermont usa abstract we present a new oxygen isotope 18o record from carbonate rich lake sediments from central vermont the record from twin ponds spans from 13 5 cal ka bp 1950 ad to present but contains a 6 ka long hiatus starting shortly after 7 5 cal ka bp we compare the record for ca 13 5 7 5 cal ka bp with published 18o data from the region after using a bayesian approach to produce many possible chronologies for each site principal component analysis then identified chronologically robust multi site oxygen isotope signals including negative values during the younger dryas but no significant deviations from the early holocene mean of the regional records however differences among sites indicate significant trends that likely relate to interacting changes in the regional gradients of seasonal temperatures and precipitation as well as moisture sources moisture pathways and aridity that were controlled by large scale climatic controls such as insolation the progressive decline of the laurentide ice sheet and changes in oceanic circulation centennial shifts punctuate these trends at ca 9 3 and 8 2 cal ka bp and reveal that the local character of these short lived features requires a detailed understanding of lake hydrology and regional isotopic gradients to yield reliable information for regional climate reconstructions

low long term erosion rates and extreme continental stability documented by ancient u th he dates zircon and apatite crystals from the western canadian shield yield u th he dates that are the oldest yet reported for terrestrial rocks zircon dates from 1 73 to 1 58 ga are consistent with independent geological and thermochronological constraints and indicate that the rocks were at temperatures 180 c and crustal depths 7 10 km since ca 1 7 ga apatite dates from 0 95 to 0 55 ga suggest residence of rocks at temperatures 40 50 c and crustal depths 1 5 2 km for 1 0 0 6 b y when interpreted using conventionally accepted apatite he diffusion kinetics and considering the proposed effect of radiation damage on apatite he retentivity our analysis implies long term integrated unroofing rates of 2 5 m yr since ca 1 7 ga these rates are significantly lower than the long term rates suggested by previous thermochronological data sets in continental interiors but are within the range of short term erosional estimates the results are consistent with the extreme stability of this region since the proterozoic

comparison of diagenetic fluids in the proterozoic thelon and athabasca basins canada implications for protracted fluid histories in stable intracratonic basins the paleoproterozoic thelon basin located on the border between nunavut and the northwest territories of canada is a contemporaneous analog of the uranium rich paleoproterozoic athabasca basin in canada early diagenesis resulted in precipitation of extensive hematite on the surfaces of detrital quartz grains throughout the thelon formation and minor hydroxy phosphate in veins locally continued diagenesis then resulted in syntaxial quartz cementation of detrital quartz at 130 c from fluids having ca 17 wt equivalent nacl similar to the athabasca basin cementation of this type is most pronounced in fine grained sequences in the thelon basin a period of extensive desilicification during continued burial was followed by formation at ca 200 c of peak diagenetic illite having ar ar ages of ca 1400 1690 ma in the thelon formation this illite was associated with fluids with 18 oa nd d values of ca 6 and 50 respectively similar to those during peak diagenesis of the athabasca basin although the timing salinity and isotopic composition of the peak diagenetic fluids in the thelon and athabasca basins are similar the peak diagenetic mineral assemblage in the athabasca formation is dickite and illite with minor dravite and goyasite rather than simply illite consequently the fluids at peak diagenesis which in the athabasca basin are synchronous with formation of world class unconformity type uranium deposits had different compositions in each basin post peak diagenesis in the thelon basin was quite distinct from that in the athabasca basin in that illite was replaced in the central portion of the basin by k feld spar and then sudoite which crystallized from saline brines at ca 1000 ma and 100 c evidence for later infiltration of these brines is absent in the athabasca basin although uranium mobilization at ca 900 ma from fluids having the same characteristics as those at peak diagenesis was pronounced in the athabasca basin recent incursion of meteoric waters along reactivated structures into the athabasca basin has variably affected hydrous and uraniferous minerals but evidence for this is lacking in the thelon basin the thelon basin reflects less intensive fluid rock interaction in its early history than that recorded in the basal units of the athabasca basin 132

paleomagnetism and the evolution of fluids in the proterozoic athabasca basin northern saskatchewan canada in the athabasca basin diagenetic hematite of variable paragenesis occurs throughout the sandstones and underlying paleoregolith this hematite carries three distinct single component magnetizations a d 158 i 62 95 5 n 21 b d 11 i 36 95 7 n 6 and c d 18 i 79 95 3 n 27 in some areas of the sandstones such as near reactivated fault zones the diagenetic hematite has been altered to goethite which yields a very low intensity incoherent d magnetization ages for the a b and c magnetizations inferred from comparisons with paleomagnetic directions in precambrian rocks whose ages are known approximately are 1750 1600 1600 1450 and about 900 ma respectively the a magnetization is carried by the earliest formed hematite and its estimated age compares well with u pb ages of 1650 1700 ma for early diagenetic apatite u pb and rb sr ages of approximately 1500 and 900 ma for uraninite and illite coeval with hematite that carries the b and c magnetiza

accretion history of the trans hudson orogen in manitoba and saskatchewan from paleomagnetism lithoprobe s sponsorship has led to the acquisition of paleomagnetic data from 20 units throughout the paleoproterozoic trans hudson orogen tho of saskatchewan and manitoba essentially the first such data for the region discussed summarily in this paper they provide an initial framework for the tho s tectonic evolution they show that the archean hearne and superior cratons were at subtropical and subpolar paleolatitudes respectively at 1875 ma with the lynn lake laronge arc midway between them in the manikewan ocean by 1855 ma this ocean was still 5500 700 km wide and its seafloor was subducting northwestward under the hearne craton and pericratonic peter lake domain margin with the coeval development of an andean type continental magmatic arc the wathaman chipewyan batholith between 1855 and 1810 ma coalescing apparent polar wander path apwp segments record closing of the ocean at a rate of 12 cm a trapping and accreting the several separate intervening terranes flin flon hanson lake lynn lake laronge rottenstone and presumably also other tho terranes from 1815 to 1775 ma the assembled terranes drifted as a coherent craton yielding a stillstand and hairpin in the apwp

source rock lithology prediction based on oil diacholestane abundance in the siliceous clastic akita sedimentary basin japan in an effort to predict the source rock lithology from oil biomarkers in the akita basin the relationship of diacholestane abundance to clay mineral content thermal maturation and the oxic anoxic depositional conditions of representative mudstone samples has been investigated the relative diacholestane abundance of samples with similar maturity levels increases with increasing clay mineral content the oxic anoxic depositional conditions of the samples estimated by c35 homohopane index are less influential for diacholestane formation in the case of the yabase oil field samples a crossplot of the diacholestane abundance versus ethylcholestanes 20s 20s 20r and clay mineral content was applied to evaluate the source rock lithology of the yabase oils the source of this oil is consequently predicted to be the clay poor siliceous rocks of the miocene onnagawa formation although this study did not achieve quantitative clay content prediction the results demonstrate that this approach is useful for the characterization of source rock lithology especially for moderately mature oils

depositional environment and hydrocarbon source potential of the permian gondwana coals from the barapukuria basin northwest bangladesh article barapukuria coal basin is situated in dinajpur district of the northwestern part of bangladesh a total of eight coal samples have been collected from two different locations of the basin and analyzed using organic geo chemical and organic petrological methods the extracted organic matter of the studied samples is a mixture of type iii and type ii kerogen as evaluated by the source rock analyzer sra and pygc pyrograms the measured total organic carbon toc ranges from 61 to 74 wt and the recovered extractable organic matter eom varies from 27 561 to 41 389 ppm these results suggest that the coals are ranked as good quality source rock the hydrocarbon yield has been calculated which is also high and it ranges from 12 192 to 20 799 ppm the organic matter is thermally mature for hydrocarbon generation considering their tmax and measured mean vitrinite reflec tance values of 431 to 435 c and 0 72 to 0 81 ro respectively the hopane 22s 22s 22r moretane hopane ratio and sterane parameters are also in support of these thermal maturity assessment

biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of opalinus clay and posidonia shale in northern switzerland abstract samples from two argillaceous formations opalinus clay and posidonia shale of near identical maturity from northern switzerland were subjected to a geochemical characterisation of organic matter and to confined system pyrolysis experiments throughout the study area the characteristics of organic matter are similar indicating a spatially homogeneous sedimentary facies posidonia shale contains marine organic matter deposited in a reducing environment while a predominantly terrigenous source and a more oxidising environment of deposition was identified for opalinus clay in the western and central parts of the study area organic maturity is close to the onset of oil generation in the easternmost part a higher maturity has been reached due to a deeper burial below thick tertiary molasse deposits isothermal pyrolysis experiments were conducted at temperatures between 250 and 390 c over 24 h bitumen yields increase along similar pathways for both opalinus clay and posidonia shale but the maximum values are displaced by 10 20 c data pertaining to maturity were determined from gc ms analyses of saturated hydrocarbons and specific attention was given to c 29 sterane and c 32 hopane isomerisation ratios the evolution of these parameters with rising temperature is slightly different in the two formations which is attributed to the contrasting organic facies the pyrolysis data together with literature data from natural basins were used to calculate kinetic parameters for c 29 sterane and c 32 hopane assuming a single step isomerisation scheme according to the arrhenius law the resulting values based on pyrolysis data alone are very similar to those based on the combination of pyrolysis and natural data activation energies are similar in both formations while the frequency factors are up to one order of magnitude higher for posidonia shale when compared to opalinus clay for the benken site maximum temperature during cretaceous burial was calculated on the basis of the kinetic data using the tti approach the resulting temperatures of 75 80 c are 5 10 c below those derived in the literature from apatite fission track analysis vitrinite reflectance and basin modelling

u redox fronts and kaolinisation in basement hosted unconformity related u ores of the athabasca basin canada late u remobilisation by meteoric fluids proterozoic basement hosted unconformity related uranium deposits of the athabasca basin saskatchewan canada were affected by significant uranium redistribution along oxidation reduction redox fronts related to cold and late meteoric fluid infiltration these redox fronts exhibit the same mineralogical and geochemical features as the well studied uranium roll front deposits in siliclastic rocks the primary hydrothermal uranium mineralisation 1 6 1 3 ga of basement hosted deposits is strongly reworked to new disseminated ores comprising three distinctly coloured zones a white green zone corresponding to the previous clay rich alteration halo contemporaneous with hydrothermal ores a uranium front corresponding to the uranium deposition zone of the redox front brownish zone rich in goethite and a hematite rich red zone marking the front progression the three zones directly reflect the mineralogical zonation related to uranium oxides pitchblende sulphides iron minerals hematite and goethite and alumino phosphate sulphate aps minerals the zoning can be explained by processes of dissolution precipitation along a redox interface and was produced by the infiltration of cold 50 c meteoric fluids to the hydrothermally altered areas u fe ca pb s ree v y w mo and se were the main mobile elements in this process and their distribution within the three zones was for most of them directly dependent on their redox potential the elements concentrated in the redox fronts were sourced by the alteration of previously crystallised hydrothermal minerals such as uranium oxides and light rare earth element lree rich aps the uranium oxides from the redox front are characterised by lree enriched patterns which differ from those of unconformity related ores and clearly demonstrate their distinct conditions of formation uranium redox front formation is thought to be linked to fluid circulation episodes initiated during the 400 300 ma period during uplift and erosion of the athabasca basin when it was near the equator and to have been still active during the last million years a major kaolinisation event was caused by changes in the fluid circulation regime reworking the primary uranium redox fronts and causing the redistribution of elements originally concentrated in the uranium enriched meteoric related redox fronts

paleomagnetic dating of the transformation of oolitic goethite to hematite in iron ore we show that the oolitic hematite ores of birmingham alabama carry a remanence direction stable enough to have survived major folding nevertheless this remanence was very likely acquired in the

oxygenation of the earth s atmosphere ocean system a review of physical and chemical sedimentologic responses abstract the great oxidation event goe is one of the most significant changes in seawater and atmospheric chemistry in earth history this rise in oxygen occurred between ca 2 4 and 2 3 ga and set the stage for oxidative chemical weathering wholesale changes in ocean chemistry and the evolution of multicelluar life most of what is known about this important event and the subsequent oxygenation history of the precambrian earth is based on either geochemistry or data mining published literature to understand the temporal abundance of bioelemental sediments bioelemental sediments include iron formation chert and phosphorite which are precipitates of the nutrient elements fe si and p respectively because biological processes leading to their accumulation often produce organic rich sediment black shale can also be included in the bioelemental spectrum thus chemistry of bioelemental sediments potentially holds clues to the oxygenation of the earth because they are not simply recorders of geologic processes but intimately involved in earth system evolution chemical proxies such as redox sensitive trace elements cu cr v cd mo u y zn and ree s and the ratio of stable isotopes 56fe 53cr 97 95mo 98 95mo 34s 33s in bioelemental sediments are now routinely used to infer the oxygenation history of paleo seawater the most robust of these is the mass independent fractionation of sulfur isotopes mif which is thought to have persisted under essentially anoxic conditions until the onset of the goe at ca 2 4 ga since most of these proxies are derived from authigenic minerals reflecting pore water composition extrapolating the chemistry of seawater from synsedimentary precipitates must be done cautiously paleoenvironmental context is critical to understanding whether geochemical trends during earth s oxygenation represent truly global or merely local environmental conditions to make this determination it is important to appreciate chemical data are primarily from authigenic minerals that are diagenetically altered and often metamorphosed because relatively few studies consider alteration in detail our ability to measure geochemical anomalies through the goe now surpasses our capacity to adequately understand them in this review we highlight the need for careful consideration of the role sedimentology stratigraphy alteration and basin geology play in controlling the geochemistry of bioelemental sediments such an approach will fine tune what is known about the goe because it permits the systematic evaluation of basin type and oceanography on geochemistry this technique also provides information on how basin hydrology and post depositional fluid movement alters bioelemental sediments thus a primary aim of any investigation focused on prominent intervals of earth history should be the integration of geochemistry with sedimentology and basin evolution to provide a more robust explanation of geochemical proxies and ocean atmosphere evolution

the isotopic response of lake chenghai sw china to hydrologic modification from human activity the human modification of lake hydrology is widespread in the industrial era however anthropogenic impacts have occurred for thousands of years in regions of the world with long histories of human occupation here we use geochemical analyses of lake sediment to document the isotopic and geochemical response of cheng lake chenghai in southwestern china to catchment modification including the construction of a downstream dam the chenghai record indicates that land use changes affected the lake catchment by at least ad 1150 as evidenced by an increased flux of terrestrial organic matter sediment with high concentrations of sorbed metals and variations in stable isotopes of oxygen in precipitated aragonite decreases in magnetic susceptibility and metal concentrations after ad 1360 indicate a change in sediment basin dynamics the construction of a downstream dam between ad 1573 and 1620 caused positive shifts in the isotopic composition of aragonite indicative of increased evaporative loss and a lo

organic geochemical study and genetic correlation of natural gas oil and menilite source rocks in the area between san and stryi rivers polish and ukrainian carpathians abstract we studied the source rocks and petroleum accumulations in the carpathian mountains of the polish ukrainian border area between the san and stryi rivers a total of 108 oligocene menilite formation rock samples 12 oil and 15 gas samples accumulated in the oligocene reservoirs and one oil and gas sample from an upper cretaceous reservoir were analysed the aim of this study was to evaluate the petroleum potential of the menilite formation in this area and to evaluate potential genetic correlations between source rock and petroleum the menilite formation represents a prolific source rock with toc content ranging from 2 to 7 wt locally exceeding 20 wt algal type ii and mixed type ii iii kerogens dominate but sometimes type iii kerogen and rarely type i kerogen occur thermal maturity of the oligocene menilite formation increases from outer to inner tectonic units from the immature in the boryslav pokuttya and skole units to the overmature in the southern parts of silesian and dukla units as a consequence petroleum potential decreases in the same order geochemical analyses reveal that oil and gas generation and migration processes within the carpathian flysch succession are complicated all analysed oils were generated from the menilite formation during early and peak stages of the oil window associated gas is of low temperature thermogenic origin sometimes containing an admixture of microbial gas high temperature thermogenic gas occurs only in the polish part of the silesian unit

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

a molecular and carbon isotope biogeochemical study of biomarkers and kerogen pyrolysates of the kimmeridge clay facies palaeoenvironmental implications abstract structures and carbon isotopic compositions of biomarkers and kerogen pyrolysis products of a dolomite a bituminous shale and an oil shale of the kimmeridge clay formation kcf in dorset were studied in order to gain insight into i the type and extent of water column anoxia and ii changes in the concentration and isotopic composition of dissolved inorganic carbon dic in the palaeowater column the samples studied fit into the curve of increasing 13 c of the kerogen 13 c toc with increasing toc reported by huc et al 1992 their hypothesis that the positive correlation between toc and 13 c toc is the result of differing degrees of organic matter om mineralisation in the water column was tested by measuring the 13 c values of primary production markers these 13 c values were found to differ on average by only 1 among the samples implying that differences in the extent of om mineralisation cannot fully account for the 3 difference in 13 c toc the extractable om in the oil shale differs from that in the other sediments due to both differences in maturity and differences in the planktonic community these differences however are not likely to have significantly influenced 13 c toc either all three sediments contain abundant derivatives of isorenieratene indicating that periodically euxinia was extending into the photic zone the sediments are rich in organic sulfur as revealed by the abundant sulfur compounds in the pyrolysates the prominence of c 1 c 3 alkylated thiophenes over n alkanes and n alkenes is most pronounced in the pyrolysate of the sediment richest in toc this suggests that sulfurisation of om may have played an important role in determining the toc 13 c toc relationship reported by huc et al 1992

lacustrine stable isotope record of precipitation changes in nicaragua during the little ice age and medieval climate anomaly discerning the infl uences of the el nino southern oscillation enso and the north atlantic oscillation nao on drought variability in the tropics during the medieval climate anomaly mca and little ice age lia will help to improve our understanding of climate system responses to internal and external forcing sediments from lago el gancho nicaragua provide an 1400 yr record of water balance precipitation and evaporation changes from a region that is sensitive to teleconnected pacifi c and atlantic ocean atmosphere dynamics oxygen isotope values of ostracod carapaces 18 o ostracod are consistently low in el gancho sediments between ca a d 950 and 1250 indicating that wetter conditions prevailed during the mca a period of la nina like mean state conditions in the tropical pacifi c and a positive mean state of the nao the 150 yr period between the mca and lia was marked by an abrupt shift to persistently drier conditions at a time of highly variable pacifi c sea surface temperatures and a transition toward a more negative nao phase in sediment from ca a d 1450 to the present 18 o ostracod values increase suggesting that drier conditions persisted through most of the lia a time of a relatively negative nao phase and el nino like mean state conditions in the tropical pacifi c the long term precipitation trends inferred from the el gancho data are not entirely consistent with modern associations between precipitation in the circum caribbean region and the nao suggesting that present day hydroclimatic shifts resulting from variability in synoptic climate patterns are dissimilar to changes resulting from teleconnected ocean atmosphere dynamics that operated during the mca and lia

paleomagnetism of the mississippi valley type ores and host rocks in the northern arkansas and tri state districts a paleomagnetic study has been done on 452 specimens from the early ordovician cotter and middle ordovician everton formations in the northern arkansas mississippi valley type mvt lead zinc ore d

late paleoproterozoic climate tectonics and metamorphism in the southern lake superior region and proto north america evidence from baraboo interval quartzites abstract red supermature quartzites of the baraboo interval of the lake superior region contain detrital zircon that ranges in age from 1782 to 1712 ma deposition clearly occurred after the geon 18 penokean orogeny these late paleoproterozoic sedimentary rocks consist largely of quartz kaolinite or pyrophyllite and hematite detrital feldspar and muscovite are rare or absent their chemical index of alteration ranges from 96 8 to 98 6 among the most chemically mature clastic sediments in the geological record the quartzites are underlain by mature feldspar free paleosols accounting for the absence of feldspar in the overlying sediments and indicating the presence of first cycle quartzose detritus such physical and chemical characteristics imply that late paleoproterozoic deposition in the lake superior region occurred in a stable tectonic setting with subdued topographic relief in a warm humid climate folding and low grade metamorphism of the quartzites is thought to reflect 1630 ma foreland

an evaporated seawater origin for the ore forming brines in unconformity related uranium deposits athabasca basin canada cl br and δ37cl analysis of fluid inclusions abstract analyses of halogen concentration and stable chlorine isotope composition of fluid inclusions from hydrothermal quartz and carbonate veins spatially and temporally associated with giant unconformity related uranium deposits from the paleoproterozoic athabasca basin canada were performed in order to determine the origin of chloride in the ore forming brines microthermometric analyses show that samples contain variable amounts of a nacl rich brine cl concentration between 120 000 and 180 000 ppm and a cacl2 rich brine cl concentration between 160 000 and 220 000 ppm molar cl br ratios of fluid inclusion leachates range from 100 to 900 with most values between 150 and 350 cl br ratios below 650 seawater value indicate that the high salinities were acquired by evaporation of seawater most 37cl values are between 0 6 and 0 seawater value which is also compatible with a common evaporated seawater origin for both nacl and cacl2 rich brines slight discrepancies between the cl concentration cl br 37cl data and seawater evaporation trends indicate that the evaporated seawater underwent secondary minor modification of its composition by i mixing with a minor amount of halite dissolution brine or re equilibration with halite during burial ii dilution in a maximum of 30 of connate and or formation waters during its migration towards the base of the athabasca sandstones iii leaching of chloride from biotites within basement rocks and iv water loss by hydration reactions in alteration haloes linked to uranium deposition the chloride in uranium ore forming brines of the athabasca basin has an unambiguous dominantly marine origin and has required large scale seawater evaporation and evaporite deposition although the direct evidence for evaporative environments in the athabasca basin are lacking due to the erosion of 80 of the sedimentary pile cl br ratios and 37cl values of brines have behaved conservatively at the basin scale and throughout basin history

exploiting radiation damage control on apatite u th he dates in cratonic regions abstract apatites from four pairs of samples of precambrian basement from the western canadian shield were analyzed by u th he thermochronometry to test for the influence of radiation damage on apatite u th he dates in this cratonic region recent studies have demonstrated that the accumulation of radiation damage increases the apatite he retentivity so that apatites with a span of effective u concentrations eu that experienced the same thermal history may be characterized by a range of closure temperatures in this investigation each sample pair consisted of a mafic dike cross cutting felsic gneisses from a single outcrop or nearby outcrops that contained apatites with a span of eu the apatites yielded u th he dates from 846 to 123 ma and were positively correlated with eu within each sample pair these results can be explained using a model that tracks the evolution of he mobility in response to the accumulation of radiation damage when coupled with regional geological constraints the data appear to require partial to complete he loss due to burial and reheating in phanerozoic time new apatite fission track dates and length data were obtained for five of these samples the apatite fission track dates are proterozoic regardless of apatite eu thermal history simulations indicate that the apatite fission track data are compatible with the u th he results although the thermal histories are not identical in detail and the fission track results alone do not require phanerozoic heating together the data are consistent with burial of this region by 1 km of phanerozoic strata that were subsequently denuded thus pointing toward significant phanerozoic deposition in the north american cratonic interior hundreds of kilometers east of where previously documented the results suggest that exploiting radiation damage control on apatite u th he dates through investigation of surface sample apatites with a span of closure temperatures can impose tighter restrictions on thermal histories in low relief cratonic landscapes than was previously possible

deuterium excess determination of evaporation to inflow ratios of an alpine lake implications for water balance and modeling the numerous lakes on the tibetan plateau tp play an important role in the regional hydrological cycle and water resources but systematic observations of the lake water balance are scarce on the tp here we present a detailed study on the water cycle of cona lake at the headwater of nujiang salween river based on three years 2011 2013 of observations of 18o and 2h including samples from precipitation upper lake water and outlet surface water short term atmospheric water vapor was also sampled for isotope analyses the 2h 18o relationship in lake water 2h 6 67 18o 20 37 differed from that of local precipitation 2h 8 29 18o 12 50 and the deuterium excess d excess in the lake water 7 5 was significantly lower than in local precipitation 10 7 indicating an evaporative isotope enrichment in lake water the ratio of evaporation to inflow e i of the lake water was calculated using both d excess and 18o the e i ratios of cona lake ranged from 0 24 to 0 27 during the three years observations of atmospheric water vapor isotopic composition a improved the accuracy in e i ratio estimate over a simple precipitation equilibrium model though a correction factor method provided nearly identical estimates of e i ratio the work demonstrates the feasibility of d excess in the study of the water cycle for lakes in other regions of the world and provides recommendations on sampling strategies for accurate calculations of e i ratio this article is protected by copyright all rights reserved

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

characteristics of magnetic carriers responsible for late paleozoic remagnetization in carbonate strata of the mid continent u s a magnetic analysis of carbonate strata of the mid continent region of the united states indicates that the late paleozoic remagnetization already recognized in the appalachians also affects almost the entire mid continent magnetic intensity is regionally variable with more intense magnetizations occurring on intracratonic arches magnetization is carried predominately by magnetite which often occurs in tiny hollow spheroids composed of well formed octahedral microcrysts spheroid chemistry and morphology suggests that the magnetite is authigenic composed of iron extracted from pre existing pyrite or clay the timing of the remagnetization the character of the magnetite and the regional variation in magnetic intensity support the idea that the remagnetization is a diagenetic consequence of tectonically driven brine migration

the werra cyclotheme upper permian fore sudetic monocline poland insights into fluctuations of the sedimentary environment from organic geochemical studies abstract a study of the extracts of samples recording a transgressive regressive succession of the werra cyclothem zechstein upper permian from the southern margin of the european permian basin the fore sudetic monocline poland provides an insight into major sources of organic matter and diagenetic processes the studied cross section comprises all lithologies representative for the european basin including transgressive sandstones weissliegend and organic rich shales kupferschiefer followed by carbonates as well as regressive anhydrites with intercalations of rock salt due to the variable influence of overlapping diagenetic processes that affected the organic matter i e maturation and late diagenetic oxidation related to base metal mineralisation a reliable comparison of the biomarker results is only possible for the major upper part of the section ca 38 m including carbonates and evaporites but not for the oxidised first 2 3 m from the base of the kupferschiefer the transition from carbonate to evaporate sedimentation is associated with a shift to predominant even c numbered n alkanes increased abundance of carotanes and high homohopane index reflecting enhanced reducing conditions the presence of the c25 regular isoprenoid squalane biphytane and the rapid decrease in the pristane phytane ratio in the evaporites are mainly controlled by the important contribution from both halophilic and methanogenic archaea the occurrence of gammacerane in the anhydrites suggests development of water column stratification at some stages of the sea regression this is associated with appearance of specific aryl isoprenoids with a lycopane carbon skeleton most likely related to botrycoccus braunii race l algae lycopane derivative occurrence suggests that such an algal race could have occurred since permian currently known recent eocene the presence of the abundant freshwater brackish algal biomarkers in evaporititic deposits can be envisaged in the costal part of the zechstein basin with temporary salt wedge estuary water stratification the algae bloomed in the top fertile fresh brackish water layer fed by rivers and the algal biomass was deposited on the sea floor covered with evaporitic brine the stratification periodically broke down during precipitation of the rock salt presumably due to a decrease in riverine water input as revealed by characteristic disappearance of gammacerane and hopane distributions similar to those observed for the carbonate rocks the methylphenanthrenes phenanthrene ratio was used together with methyldibenzothiophenes dibenzothiophene ratio to assess maturity these maturity estimations indicate that the peak of oil window has been reached which is confirmed by other biomarker maturity parameters based on sterane and hopane distributions the maturity stage of oil generation and expulsion was further confirmed by the presence of solid bitumen as cements in the sandstone underlying kupferschiefer and bitumen veins and lenses in the carbonates

organic geochemistry of the lower toarcian posidonia shale in nw europe abstract a suite of core and outcrop samples of the lower toarcian posidonia shale and time equivalent deposits was collected from multiple locations including southern germany swabian alb and franconian alb northern germany the east coast of great britain the netherlands and luxembourg in order to study major differences and similarities with respect to depositional environment and redox potential based on molecular geochemical data all samples are immature or in the early oil window with the highest thermal maturity occurring in the profile from great britain about 0 7 vitrinite reflectance molecular geochemical maturity parameters were used to quantify maturation in detail during shale deposition in the west cleveland basin great britain h 2 s was immediately consumed in the water column by terrigenous input supplying abundant reactive iron to form pyrite these samples are characterized by low dibenzothiophene phenanthrene ratios 95 of 2 and h 2 s in contrast sulfidic euxinic bottom waters possibly with enhanced salinity and stratified water column prevailed due to a more restricted iron supply in luxembourg northern germany and the franconian alb of southern germany a more oxygenated dysoxic bottom water column associated with anoxic sediments i e anoxic dysoxic boundary close to the sediment water interface prevailed in the swabian alb of southern germany despite observed changes within each vertical profile at each site large scale regional trends in depositional conditions can be clearly identified for the early toarcian

isotopic and hydrologic responses of small closed lakes to climate variability hydroclimate reconstructions from lake sediment oxygen isotope records and mass balance models abstract hydroclimate sensitivity simulations were conducted with a lake catchment hydrologic and isotope mass balance model adapted to two small closed lakes castor and scanlon located in the pacific northwest model simulations were designed to investigate the combined influences of persistent disequilibrium reddening and equifinality on lake water and sediment i e biogenic and endogenic carbonate mineral oxygen isotope 18 o values and to provide a basis for quantitative probabilistic climate reconstructions using lake sediment 18 o records simulation results indicate that within closed basin lakes changes in long term i e multi decadal precipitation amounts produce inconsistent responses in lake water and sediment 18 o values that are strongly influenced by lake basin outseepage and morphometry simulations of variable initial conditions in which randomly generated monthly climate data i e precipitation temperature and relative humidity were used to force the model during the equilibration period which precedes the application of instrumental climate data demonstrate that castor lake and scanlon lake have a somewhat limited isotopic memory of 10 years additional tests conducted using a monte carlo ensemble in which random climate data were used to force the model combined with 18 o analyses of water samples collected from 2003 to 2011 ad indicate that within small closed lakes in the pacific northwest november february precipitation is the strongest seasonal climatic control on sediment oxygen isotope values further a monte carlo based reconstruction of 20 year average november february precipitation amounts strongly correlates r 2 0 66 to instrumental values from the 20th century with all observed values falling within modeled 95 prediction limits indicating that probabilistic quantitative paleoclimate interpretations of lake sediment 18 o records are attainable

mixing of sodic and calcic brines and uranium deposition at mcarthur river saskatchewan canada a raman and laser induced breakdown spectroscopic study of fluid inclusions the richest u deposit in saskatchewan canada occurs in the mcarthur river area in the vicinity of the unconformity between the athabasaca sandstones and an archean to lower proterozoic basement paleofluids related to the silicification of the sandstones and the formation of pre and postore cements in breccias were studied using microthermometry raman microspectroscopy and laser induced breakdown spectroscopy libs on individual fluid inclusions a detailed reconstruction of the fluid composition in the system na ca mg cl shows that two types of brines are responsible for the main quartz cements an nacl rich brine 25 wt nacl up to 14 wt cacl 2 and up to 1 wt mgcl 2 which is interpreted as a primary formation water that was expelled from bedded evaporites and a cacl 2 rich brine 5 8 wt nacl 20 wt cacl 2 and up to 11 wt mgcl 2 which is considered to have formed during the interaction between the nacl rich brine and ca rich minerals in the basement and was introduced into the fault system and mixed with the nacl rich brine during the critical stage of u deposition the pressure temperature conditions of formation of the quartz cements are estimated to be 1 200 to1 400 bars and 190 to 235 c for the silicification events during the preore stage and 500 to 900 bars after a pressure decrease from lithostatic conditions and slightly lower temperatures due to the mixing of the nacl rich brine with the cooler approx 140 c cacl 2 rich brine during the main stage of breccia sealing temperature and pressure drops combined with the effects of brine mixing appear to be key factors for the main stages of quartz cementation and u deposition at the mcarthur deposit

u pb pb pb and k ar isotopic study and petrography of uraniferous phosphate bearing rocks in the thelon formation dubawnt group northwest territories canada the thelon formation uppermost unit of the dubawnt group overlies a regionally extensive paleoweathered zone developed on a wide range of lithochronological units including formations in the lower dubawnt group authigenic uraniferous phosphate minerals fluorapatite and goyazite cementing thelon conglomerate sandstone and filling fractures in the underlying paleoweathered zone were dated in an attempt to better constrain the age of thelon sedimentation and diagenesis the oldest age 1720 6 ma derived from phosphate cemented sediments is interpreted as a minimum age for diagenesis and therefore brackets initial thelon sedimentation between emplacement of fluorite bearing granites at 1753 ma and authigenic phosphate cementation at 1720 ma additional ages of 1685 4 and 1647 ma are interpreted as remobilization or subsequent cementation events k ar ages on illite 1386 37 and 1266 31 ma from the paleoweathered zone and basal conglomerate respectively are significantly younger than ages de

oxygen isotope records of holocene climate variability in the pacific northwest abstract oxygen isotope 18o measurements of authigenic carbonate from cleland lake southeastern british columbia paradise lake central british columbia and lime lake eastern washington provide a 9000 year holocene record of precipitation evaporation balance variations in the pacific northwest both cleland lake and paradise lake are small surficially closed basin systems with no active inflows or outflows lime lake is surficially open with a seasonally active overflow water isotope values from cleland and paradise plot along the local evaporation line indicating that precipitation evaporation balance is a strong influence on lake hydrology in contrast lime lake water isotope values plot on the local meteoric water line signifying minimal influence by evaporation to infer past hydrologic balance variations at a high temporal resolution we sampled the cleland paradise and lime lake sediment cores at 1 60 mm intervals 3 33 years per sample on average and measured the isotopic composition of fine grained

sequence stratigraphy provenance c and o isotopic composition and correlation of the late paleoproterozoic early mesoproterozoic upper hornby bay and lower dismal lakes groups nwt and nunavut abstract late paleoproterozoic basins of canada s north including the thelon athabasca and hornby bay basins can be broadly correlated based on similarities in age sequence stratigraphy paleocurrents and detrital zircon provenance but their detailed evolution is poorly understood and their age and lateral equivalencies are poorly constrained this study contributes to the understanding of sedimentary basins during a critical interval of time representing the latest stages of amalgamation of the supercontinent laurentia nuna through a detailed study of the hornby bay basin the hornby bay basin strata have been divided into four unconformity bounded subsequences a1 a2 a3 a4 that belong to the first of three unconformity bounded post hudsonian proterozoic stratigraphic packages in northwestern canada subsequences a2 1600 ma and a3 analysis of sm nd isotopes on mudrocks yielded isotopic compositions in the range 8 2 to 2 3 nd 1600 ma in subsequence a2 and 9 8 to 5 0 nd 1400 ma in subsequence a3 an nd versus time graph illustrates two distinct groupings that plot within known isotopic evolution fields of the taltson thelon tectonic zone and the great bear magmatic zone sediment provenance was strongly influenced by the paleoproterozoic forward orogeny but there are no significant changes in sedimentary provenance across the a2 a3 sequence boundary stable isotope analyses of c and o in the dolomitic east river formation of subsequence a2 reveal a relatively monotonous signal with an average of 0 5 13 c and 8 76 18 o which is consistent with global values of other late paleoproterozoic carbonate successions enriched mn values and depleted sr values however suggest that the east river carbonate rocks experienced some degree of meteoric alteration it is unknown how much this alteration affected stable isotope compositions based on similarities in sedimentary provenance age and sequence stratigraphy subsequence a2 of the hornby bay group is correlated with the wernecke supergroup yukon the latter is interpreted to represent the deep water distal equivalent of the upper hornby bay group in a westward deepening basin deposition of subsequence a2 is recorded across north america and is mirrored by deep water sedimentation along the eastern margin of the north australian craton the tectonic evolution of subsequence a2 in laurentia is therefore remarkably similar to that of the north australian craton up to 1600 ma the age of the forward orogeny and this has implications for interpretation of the latest stages of accretion of the supercontinent nuna

lake sediment records of holocene hydroclimate and impacts of the mount mazama eruption north central washington usa abstract multi proxy sediment records from castor lake and scanlon lake north central washington provide a late quaternary perspective on lake catchment hydrologic and ecosystem responses to climate change and the mazama volcanic ashfall event analyses of authigenic carbonate mineral oxygen and carbon isotope values organic carbon and nitrogen content and sedimentological facies were conducted on sediment from castor lake in order to reconstruct lake catchment hydrologic balance the source and abundance of organic matter and variations in lake level sedimentary facies characterization was conducted on the scanlon lake sediment in order to provide supporting evidence for the lake level shifts inferred from the castor lake data marked changes in castor lake proxy values occur from 12 860 to 11 440 calendar years before present yr bp suggesting lake catchment responses to the younger dryas cold reversal including higher lake levels substantial variability in productivity and increased catchment erosion high 18o values at 9630 yr bp indicate that lake levels were lower than at present and that the early holocene was dry sedimentological analyses and 18o data demonstrate that subsequent to the mazama climactic eruption 7600 yr bp a transition to the lowest lake levels of the holocene occurred over several centuries with maximum 18o values at 7290 90 uncertainty range 7020 7500 yr bp and low lake levels persisting until 6190 5960 6410 yr bp lithological changes in the scanlon lake record support these inferences the lowest 18o values of the holocene occur in sediment from 5000 yr bp indicating high lake levels at this time after which a secular trend toward higher 18o values and lower lake levels occurred the prolonged lowstand in the centuries following the mazama eruption suggests that catchment hydrologic characteristics were strongly impacted by the ashfall through effects on soil water retention capacity that similar responses may have occurred in comparable settings within the mazama ashfall zone and that such volcanic events have the potential confound the climate signal in lake sediment records were a similar event to happen in the future catchment hydrology stream river discharge and lake catchment ecosystem dynamics could be affected for centuries

isomerisation rearrangement and aromatisation of steroids in distinguishing early stages of diagenesis abstract the distributions of proposed reactants and products of stages of early diagenesis of steroid hydrocarbons have been studied by gc and gc ms in a variety of downhole sequences of dsdp cores of various ages which include the san miguel gap walvis ridge gulf of california and falkland plateau the compounds comprise aliphatic and aromatic hydrocarbons such as diasterenes monoaromatic anthrasteroids and spirosterenes from the study of the progress of proposed reactions and of presumed product reactant relationships a pattern emerges that extractable lipid distributions can provide a means of distinguishing levels of early diagenesis which cannot be recognised readily from other methods a number of diagentic trends are evident such as progressive isomerisation at c 20 in diasterenes which occurs at different relative rates and temperature ranges in sediment sequences with different heat fluxes such studies allow investigation of the changes in biological marker compounds in the part of the continuum between changes during sediment deposition and the advent of catagenesis

effects of an oceanic anoxic event on the stable carbon isotopic composition of early toarcian carbon the early toarcian transgression is marked by the occurrence of organic carbon rich shales in large parts of western europe and in other parts of the world as well based on the positive carbon isotope excursion of pelagic limestones in the middle to upper part of the falciferum zone in several of the tethyan sections the widespread occurrence of the early toarcian shales was explained by an oceanic anoxic event oae jenkyns 1988 jenkyns and clayton 1997 the rapid burial of large amounts of organic carbon which is rich in 12 c would have led to a relative enrichment in 13 c of the global carbon reservoir and hence to an increase in delta 13 c of the limestones in southwest germany and a number of other locations both organic and inorganic carbon display a negative isotope excursion in the upper part of the tenuicostatum zone and the lower part of the falciferum zone synchronous to black shale deposition and predating the positive isotopic excursion kuspert 1982 1983 it is presently unclear what the exact cause for this widespread negative isotopic excursion is jenkyns and clayton 1997 the objective of our study was to examine if the negative carbon isotope excursion of organic matter om in the southwest german toarcian shales can be attributed to compositional changes of the om or if the excursion is related to variations in delta 13 c sub co2 aq in the photic zone to this end we analyzed the molecular and stable carbon isotope composition of om in ten samples spanning the early toarcian toc 2 5 10 5 percent hi 350 700 biomarker distributions and kerogen pyrolysates differ only slightly among the samples and delta 13 c values of primary production markers follow closely those of associated carbonate and kerogen delta 13 c sub carb toc this strongly suggests that differences in delta 13 c toc are related to differences in delta 13 c of co 2 aq in the photic zone supporting kuspert9s model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters evidence for euxinic conditions extending into the photic zone was found by the presence of derivatives of carotenoids such as isorenieratane from anoxygenic phototrophic sulfur bacteria their concentrations are extremely low in black shales from the tenuicostatum zone but are significant in the falciferum and bifrons zone with a maximum in the exaratum subzone suggesting that photic zone euxinia pze was a common feature of the early toarcian sea in southwest germany our data therefore support the kuspert model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters to the upper part of the photic zone resulting in a negative isotope spike the enrichment in 13 c in the middle of the falciferum zone which followed the negative spike may be attributed to the burial of isotopically light organic matter through worldwide black shale deposition