biomarkers from huronian oil bearing fluid inclusions an uncontaminated record of life before the great oxidation event we report detailed molecular geochemistry of oil bearing fluid inclusions from a ca 2 45 ga fluvial metaconglomerate of the matinenda formation at elliot lake canada the oil most likely derived from the conformably overlying mckim formation was trapped in quartz and feldspar during diagenesis and early metamorphism of the host rock probably before ca 2 2 ga the presence of abundant biomarkers for cyanobacteria and eukaryotes derived from and trapped in rocks deposited before the great oxidation event is consistent with an earlier evolution of oxygenic photosynthesis than previously thought and suggests that some aquatic settings had become sufficiently oxygenated for sterol biosynthesis by this time it also implies that eukaryotes survived several extreme climatic events including the paleoproterozoic snowball earth glaciations the extraction of biomarker molecules from paleoproterozoic oil bearing fluid inclusions thus establishes a new method using low detection limits and system blank levels to trace evolution of life through earth s early history that avoids the potential contamination problems affecting shale hosted hydrocarbons

reduced reused and recycled detrital zircons define a maximum age for the eoarchean ca 3750 3780 ma nuvvuagittuq supracrustal belt quebec canada abstract a key discovery from the hadean pre 3850 ma detrital zircon record has been that the dichotomy of granitic and basaltic crust was established within about 160 myr of earth s formation harrison 2009 understanding the origin and fate of this primordial crust would greatly add to what we know about the geodynamics of the hadean earth insights emerge from 147 146sm 143 142nd isotope data reported from different eoarchean terranes worldwide including the nuvvuagittuq supracrustal belt nsb in northern quebec some ca poor cummingtonite rich amphibolites and granitoid gneisses of the nsb preserve lower 142nd 144nd than bulk silicate earth bse these also show positive correlations against 147sm 144nd that were used by o neil et al 2008 o neil et al 2012 to assign a ca 4400 ma age alternatively the compositions were inherited during the formation of the nsb at around 3800 ma roth et al 2013 guitreau et al 2013 to resolve this discrepancy ion microprobe u pb ages are reported for detrital zircons from nsb meta sediments from within the same supracrustal successions that preserve low 142nd 144nd the youngest detrital zircon cores of igneous derivation define a maximum age for the nsb of ca 3780 ma this age is about 600 myr younger than that obtained from 142nd 144nd vs 147sm 143nd regressions thus just like the variable 142nd 144nd ratios reported for other eoarchean terranes non bse 142nd 144nd values of the nsb were inherited from an older component

the paleoproterozoic snowball earth a climate disaster triggered by the evolution of oxygenic photosynthesis although biomarker trace element and isotopic evidence have been used to claim that oxygenic photosynthesis evolved by 2 8 giga annum before present ga and perhaps as early as 3 7 ga a skeptical examination raises considerable doubt about the presence of oxygen producers at these times geological features suggestive of oxygen such as red beds lateritic paleosols and the return of sedimentary sulfate deposits after a 900 million year hiatus occur shortly before the 2 3 2 2 ga makganyene snowball earth global glaciation the massive deposition of mn which has a high redox potential practically requires the presence of environmental oxygen after the snowball new age constraints from the transvaal supergroup of south africa suggest that all three glaciations in the huronian supergroup of canada predate the snowball event a simple cyanobacterial growth model incorporating the range of c fe and p fluxes expected during a partial glaciation in an anoxic world with high fe oceans indicates that oxygenic photosynthesis could have destroyed a methane greenhouse and triggered a snowball event on timescales as short as 1 million years as the geological evidence requiring oxygen does not appear during the pongola glaciation at 2 9 ga or during the huronian glaciations we argue that oxygenic cyanobacteria evolved and radiated shortly before the makganyene snowball

weathering model for the quantification of atmospheric oxygen evolution during the paleoproterozoic abstract a weathering model has been developed to quantify atmospheric oxygen evolution during the paleoproterozoic the weathering model calculates the concentrations of fe2 dissolved from fe2 bearing primary minerals and oxidized fe3 out of the dissolved fe2 at a given partial pressure of atmospheric oxygen p o 2 during weathering and establishes the relationships between p o 2 and where is the ratio of oxidized and then precipitated fe3 out of the fe2 dissolved from primary minerals to the dissolved fe2 in a whole weathering profile the weathering model considers controlling factors of the redistribution of fe during weathering that is the dissolution rate of fe2 bearing primary minerals the oxidation rate of fe2 and the groundwater flow rate the validity of the model was confirmed by applying the model to the experimental data of olivine dissolution carried out under low o2 conditions the sensitivity analysis of the model has revealed that the formation time of weathering the mineral dissolution rate and the diffusion of o2 into a weathering profile have no or slight influence on resulting in 0 0 and 0 3 changes in log p o 2 caused by four orders of magnitude change of the formation time more than 10 orders change of the mineral dissolution rate and assumed change of the o2 diffusion respectively on the other hand the temperature the ph and the groundwater flow rate have moderate to large effects on 0 6 1 4 and 1 5 changes in log p o 2 for changes of 5 c in temperature 0 5 in ph and one order of magnitude in groundwater flow rate respectively using possible surface temperature ph and groundwater flow rate estimated from the literature we calculated the p o 2 relationships which were then applied to the values of paleosols fossil weathering profiles formed between 2 5 and 1 8 ga taking account of the constraints given by the records of mass independent fractionation in sulfur isotopes and other geological proxies i e 10 6 atm at 2 32 ga and 10 3 atm at 2 0 ga our model implies that the p o 2 levels were 10 9 atm at 2 46 ga 10 4 5 10 2 atm at 2 25 2 0 ga and 10 2 atm at 1 85 ga the present weathering model can constrain p o 2 levels during the possible paleoproterozoic hot periods but not those during the glacial periods when temperature was

evidence from early proterozoic anhydrite for sulphur isotopic partitioning in precambrian oceans relative to meteoritic sulphur sulphur in the contemporary exogenic cycle is marked by a depletion of 34s in biogenic sulphide that is balanced by excess 34s in sulphate of the oceans and evaporites1 2 the onset of this isotopic partitioning during the precambrian required sulphate in the ocean in sufficient concentration to permit significant isotopic fractionation during biogenic reduction3 4 and the evolution of sulphate reducing bacteria5 7 the conclusion that partitioning existed at 2 300 myr has been derived from strongly 34s depleted sedimentary sulphide of this age from south africa4 i report here on 34s enriched stratiform nodular anhydrite of similar age from canada which supports partitioning at this time strontium isotope data on these samples indicate that the anhydrite was derived from continental brines possibly in the inland portion of a continental sabkha this requires that the reported enrichment in 34s be considered a minimum for seawater sulphate at 2 300 myr

in situ sulfur isotope analysis of sulfide minerals by sims precision and accuracy with application to thermometry of 3 5 ga pilbara cherts abstract secondary ion mass spectrometry sims measurement of sulfur isotope ratios is a potentially powerful technique for in situ studies in many areas of earth and planetary science tests were performed to evaluate the accuracy and precision of sulfur isotope analysis by sims in a set of seven well characterized isotopically homogeneous natural sulfide standards the spot to spot and grain to grain precision for 34 s is 0 3 for chalcopyrite and pyrrhotite and 0 2 for pyrite 2sd using a 1 6 na primary beam that was focused to 10 m diameter with a gaussian beam density distribution likewise multiple 34 s measurements within single grains of sphalerite are within 0 3 however between individual sphalerite grains 34 s varies by up to 3 4 and the grain to grain precision is poor 1 7 n 20 measured values of 34 s correspond with analysis pit microstructures ranging from smooth surfaces for grains with high 34 s values to pronounced ripples and terraces in analysis pits from grains featuring low 34 s values electron backscatter diffraction ebsd shows that individual sphalerite grains are single crystals whereas crystal orientation varies from grain to grain the 3 4 variation in measured 34 s between individual grains of sphalerite is attributed to changes in instrumental bias caused by different crystal orientations with respect to the incident primary cs beam high 34 s values in sphalerite correlate to when the cs beam is parallel to the set of directions uuw from 111 to 110 which are preferred directions for channeling and focusing in diamond centered cubic crystals crystal orientation effects on instrumental bias were further detected in galena however as a result of the perfect cleavage along 100 crushed chips of galena are typically cube shaped and likely to be preferentially oriented thus crystal orientation effects on instrumental bias may be obscured test were made to improve the analytical precision of 34 s in sphalerite and the best results were achieved by either reducing the depth of the analysis pits using a kohler illuminated primary beam or by lowering the total impact energy from 20 kev to 13 kev the resulting grain to grain precision in 34 s improves from 1 7 to better than 0 6 2sd in both procedures with careful use of appropriate analytical conditions the accuracy of sims analysis for 34 s approaches 0 3 2sd for chalcopyrite pyrite and pyrrhotite and 0 6 for sphalerite measurements of 34 s in sub 20 m grains of pyrite and sphalerite in 3 5 ga cherts from the pilbara craton western australia show that this analytical technique is suitable for in situ sulfur isotope thermometry with 50 c accuracy in appropriate samples however sulfides are not isotopically equilibrated in analyzed samples

multiple sulfur isotopes from paleoproterozoic huronian interglacial sediments and the rise of atmospheric oxygen mass dependently fractionated mdf sulfur isotopes in sedimentary sulfides and sulfates can provide information on the past activity of microbial metabolisms and serve as a proxy for the concentration of seawater sulfate in conjunction with these proxies mass independently fractionated mif sulfur isotopes can be used to track the rise of atmospheric oxygen the anoxic oxic transition of the surface environment in the paleoproterozoic has been constrained by mif sulfur in 2 47 ga sulfides from western australian banded iron formations and the absence of mif in diagenetic sulfides from 2 32 ga black shales in the transvaal supergroup south africa we report new multicollector ion microprobe data for individual sulfides from water lain sedimentary units in the 2 45 2 22 ga huronian supergroup ontario canada the authigenecity of sulfides in these units is interpreted on the basis of host lithology mode of distribution sulfide chemistry and mdf sulfur isotopes sulfides interpreted to have an authigenicsedimentary origin from the mckim fm have a range of 0 7 in 33 s values and those in the pecors fm preserve small magnitude mif 33 s values up to 0 88 which we propose represents the last remnants of an anoxic atmosphere high 34 s values up to 31 2 and near zero 33 s values in authigenic sulfides from the stratigraphically higher espanola and gordon lake fms suggest local variations of seawater sulfate concentrations and or 34 ssulfate consistent with increased atmospheric o2 levels mif sulfur is absent from the marine record after the second huronian glaciation which is analogous to the record of the transvaal supergroup where mif is absent from the upper part of the interglacial sequence our results suggest that the possible simultaneous demise of mif sulfur isotopes at these two localities may serve as a useful global geochemical marker to correlate paleoproterozoic supergroups we propose a new biogeochemical model where enhanced weathering rates during paleoproterozoic post glacial thawing served as a critical stimulus for interglacial blooms of oxygenic photosynthesis the demise of methane and ultimately to the irreversible rise in atmospheric oxygen

proterozoic plate tectonics glaciation and iron formations abstract glacigenic diamictites and associated rocks are common in early and late proterozoic sequences most of the preserved proterozoic glacigenic rocks formed in marine basins in an extensional tectonic regime at or close to the rift drift transition the reasons for glaciation in this tectonic setting are not known but two possible contributing factors given an initially cool climatic regime are the formation of new seaways by continental fragmentation and uplift of the rift shoulders during early stages of breakup the absence of such glacigenic deposits in the classical miogeoclines of the peri atlantic region may be due to an anomalously warm global climatic regime in the late mesozoic iron formations in the archean and early proterozoic formed in many different environments the critical factor was a dearth of siliciclastic deposition starved basins commonly developed during the transition from miogeocline to foreland basin in the wilson cycle of ocean opening and closure when drainage from the craton was replaced by that from a rising orogen early proterozoic iron rich sediments in the great lakes region in southeast wyoming and in the northwest territories of canada are interpreted as the earliest deposits of such foreland basins they are considered to be chemical precipitates from iron rich sea water late proterozoic iron formations formed under an extensional regime possibly in small red sea type ocean basins where hydrothermal circulation produced metal rich brines these brines were displaced by movement of cold waters derived from sea going glaciers leading to dilution and precipitation of fe and si thus in the late proterozoic there was a critical association of continental rifting glaciation and hydrothermal circulation this combination of environmental parameters led to the production of the unique late proterozoic class of hydrothermal iron formations

evidence for paleoproterozoic cap carbonates in north america the early paleoproterozoic snowy pass supergroup of the medicine bow mountains and sierra madre wyoming usa and huronian supergroup ontario canada were deposited along the present day southern flank of the wyoming and superior cratons whereas three discrete levels of glacial diamictite are developed in both successions carbonate strata are known only directly above the middle diamictite vagner and bottle creek formations in medicine bow mountains and sierra madre respectively and espanola formation in southern ontario in these thick correlative siliciclastics dominated strata the carbonates from each succession record negative 13 c values 4 0 to 0 8 v pdb and attenuated carbon isotopic difference between organic and inorganic phases oxygen in carbonates is strongly depleted in 18 o suggesting exchange with hot fluids which is consistent with pervasive recrystallization of carbonates and remobilization of elements however the stratigraphic coherence of carbon isotopic compositions and the general lack of correlation between 13 c and either 18 o values or trace element concentrations supports a primary origin for 13 c depleted carbonates which are interpreted here to reflect anomalous oceanic compositions the intimate association of thick carbonate units containing abundant carbonate debris flows with immediately underlying glacial strata indicates that chemical precipitation resulted from a rapid flux of carbonate alkalinity onto ocean margins during post glacial transgression although these early paleoproterozoic carbonates are similar to neoproterozoic cap dolomites in stratigraphic position and carbon isotopic compositions the older post glacial accumulations begin with limestone and lack many of the sedimentary structures typical of neoproterozoic deposits furthermore it is not understood why carbonates only occur above the middle of the three glacial horizons whereas these deposits are ubiquitous above neoproterozoic diamictites the differences might reflect lower overall carbonate saturation in early paleoproterozoic oceans which contrasts sharply with archean and later paleoproterozoic intervals and higher siliciclastic inputs in rift environments which shut down carbonate deposition geological and geochemical indicators suggest a stepwise increase in atmospheric oxygen across the paleoproterozoic glacial epoch the tempo and mode of atmospheric oxygen rise has significant consequences for the abundance of the important greenhouse gases ch4 and co2 and hence for oceanic acidity if we accept that atmospheric oxidation of methane to carbon

a negative fold test on the lorrain formation of the huronian supergroup uncertainty on the paleolatitude of the paleoproterozoic gowganda glaciation and implications for the great oxygenation event previous paleomagnetic studies of the glaciogenic gowganda and lorrain formations have identified several low inclination magnetic components of high thermal stability which suggest low latitude glaciation during deposition of the huronian supergroup canada while extraordinary claims demand extraordinary proof prior authors have been unable to support their interpretations of these components conclusively with any of the classic field stability tests e g conglomerate fold and baked contact capable of demonstrating that the magnetization was acquired at or soon enough after the time of deposition to be used to constrain the paleolatitude of the gowganda or lorrain formations we report here the results of a fold test from the purple siltstone member of the lorrain formation near the town of desbarats ontario which indicate that none of the reported components dates to the time of deposition hence the paleolatitude of the gowganda glaciation is uncertain comparison of the lithostratigraphic paleomagnetic and radiometric constraints on the huronian sequence and the transvaal supergroup of southern africa implies that the one verified low latitude paleoproterozoic glacial event the makganyene glaciation transvaal supergroup south africa is younger than the three glacial units of canada with this correlation the physical rock record indicates that the great oxygenation event began in the time interval between the gowganda and makganyene glaciations these data are consistent with the sudden evolution of oxygenic photosynthesis destroying a methane greenhouse and thereby triggering the first snowball earth event in earth history

potassic and sodic metasomatism in the southern province of the canadian shield evidence from the paleoproterozoic serpent formation huronian supergroup canada abstract major element geochemistry petrographic observations and microprobe analyses of the paleoproterozoic serpent formation huronian supergroup canada suggest that these strata experienced both potassium and sodium metasomatism major element data plotted in al2o3 cao na2o k2o compositional space form an array nearly identical to data from sub huronian paleosols reported elsewhere suggesting that serpent fluvial systems captured materials from entire weathering profiles potassium metasomatism was concentrated in shales and represents the illitization of kaolinite which is a residual product of plagioclase weathering sodium metasomatism principally affected silt and sand sized particles microprobe analyses of plagioclase grains indicate that they are nearly pure albite ab96 corresponding whole rock major element data plot in bulk albite space on an al2o3 k2o cao na2o ternary diagram whereas basement rocks plot in bulk andesine and oligoclase space end member compositions and the absence of luminescence when bombarded with an electron beam indicate that the albites are of secondary origin extremely pure albite cements ab99 commonly fringe detrital grains there has been little replacement of detrital k feldspars despite the complete albitization of plagioclase grains the timing of metasomatism at least the last stage is constrained to the period between 1700 and 1750 ma based on geochronologic data reported elsewhere when the southern province of the canadian shield experienced considerable felsic plutonism possibly related to arc collision this plutonism may have resulted in the heating of deep basinal brines stresses associated with orogenic build up or gravity driven groundwater circulation working in concert with the plutonism expelled these brines through the serpent formation and the entire huronian supergroup thoroughly metasomatizing the region such processes associated with collisional tectonics are akin to the development of mississippi valley type pb zn mineralization in the mid continent of the united states

rise of atmospheric oxygen and the upside down archean mantle 1 the establishment of an oxygen rich atmosphere dramatically altered the evolution of life on earth most of the recent discussion of the topic has been focused on the timing of the event rather than on its mechanism here we draw upon recent developments in the understanding of earth s interior to propose that the rise of oxygen followed a geologically abrupt period of mantle overturn and or intense plume activity near the archean proterozoic transition 2470 2450 million years ago the magmatic event has already been linked to the widespread deposition of oxide facies banded iron formation and the rise of oxygen has been implicated as the trigger for iron deposition and earth s first major glaciation we argue that these events are all related to a change in redox state of volcanic gases brought about by deep seated late archean and earliest paleoproterozoic magmatism

primitive os and 2316 ma age for marine shale implications for paleoproterozoic glacial events and the rise of atmospheric oxygen abstract re os dating of synsedimentary to early diagenetic pyrite from carbonaceous shale that straddles the boundary between the rooihoogte and timeball hill formations transvaal supergroup south africa provides a precise isochron age of 2316 7 ma 4 statistical uncertainty if error on decay constant is excluded and a chondritic initial 187os 188os ratio of 0 1121 0 0012 these units were deposited between what are interpreted as the second and third of three paleoproterozoic global glacial events and thus provide minimum and maximum ages respectively for these events the rooihoogte formation is correlative with the duitschland formation which records previously undated carbon isotope excursions because the pyrite samples show no evidence of mass independent fractionation of sulfur and have highly negative 34s values the rise of atmospheric oxygen most likely began prior to 2 32 ga the chondritic initial 187os 188os ratio requires that primitive hydrothermal sources of os dominated the os budget of seawater at 2 32 ga os is mobile only under oxidizing conditions therefore the chondritic initial 187os 188os ratio may reflect atmospheric oxygen levels too low to introduce sufficient riverine flux of dissolved radiogenic os to offset the primitive hydrothermal magmatic flux even if atmospheric oxygen levels had increased significantly by 2 32 ga anoxic conditions throughout the archean most likely limited os enrichment in archean marine shales so that their subsequent exposure and weathering was unable to provide a significant amount of radiogenic os to paleoproterozoic seawater

depositional environments of the early proterozoic espanola formation ontario canada the carbonate rich espanola formation forms part of the huronian supergroup deposited in early proterozoic time between about 2 5 and 2 1 ga ago the espanola formation overlies glacigenic diamict

a ca 200 ma hiatus between the lower and upper transvaal groups of southern africa shrimp u pb detrital zircon evidence from the segwagwa group botswana implications for palaeoproterozoic glaciations abstract the segwagwa group of southeastern botswana a correlate of the pretoria group of the transvaal supergroup of south africa consists of a major sequence of siliciclastic sedimentary rocks minor carbonates and basaltic to andesitic lavas and tuffs straddling the western and central domains of the kaapvaal craton the segwagwa group unconformably overlies the taupone dolomite group a correlative of the south african chuniespoort ghaap groups of the transvaal supergroup shrimp u pb analyses of 123 detrital zircons from the top middle and bottom of the segwagwa group sedimentary rocks include 96 concordant to near concordant zircons defining three main age groups 3 0 2 9 ga n 12 2 8 2 5 ga n 27 and 2 45 2 20 ga n 57 the 2 90 ga zircons were sourced from granitoids emplaced before and around 2915 12 ma and are related to the amalgamation of the western northern and central domains of the kaapvaal craton concordant zircons with a mean age of 2781 8 ma originate from the gaborone igneous complex the detrital zircons in the range 2 7 2 5 ga were likely sourced from the kalahari continental fragment made up of the kaapvaal craton limpopo belt and the zimbabwe craton specifically from the limpopo belt and or the zimbabwe craton where igneous rocks in this age range are widespread the igneous sources for the palaeoproterozoic ca 2 45 2 20 ga zircons are difficult to identify since igneous rocks in that age are not widely known or documented by reliable dates in the kalahari craton the youngest zircons of ca 2 2 ga occur in all the sandstones and form the main group 90 in the sample from the top of the segwagwa group the youngest detrital zircon of 2193 20 ma sets the maximum time of deposition of the segwagwa group published data suggest that the minimum deposition age of chuniespoort ghaap group sedimentary rocks is 2431 31 ma d r nelson compilation of shrimp u pb zircon geochronological data 1996 record 1997 2 pp 189 western australia geological survey 1997 therefore the unconformity between the lower and upper transvaal represents a 200 ma hiatus and the lithostratigraphic units on the two sides of the unconformity should not be grouped in the same supergroup detrital zircon ages suggest that the time of deposition of the segwagwa pretoria group which ranges from ca 2 40 to 2 20 ga is coeval with the palaeoproterozoic global glacial deposits in north america australia and fennoscandia and with sedimentary rocks from the palaeoproterozoic magondi belt therefore the segwagwa pretoria group and the magondi metasedimentary succession were deposited during the first global glacial period are possibly related to the same geodynamic cycle and should be part of the same supergroup

high δ13c paleoproterozoic carbonates from the transvaal supergroup south africa marbles from the transvaal supergroup kaapvaal craton south africa record two positive carbon isotope excursions to average 13 c carbonate values of 6 to 8 relative to v pdb separated by carbonates with normal marine 13 c values 0 2 these elevated values have been preserved through metamorphic devolatilization together with an already documented high 13 c excursion in overlying rocks three separate positive carbon isotope excursions occurred on the kaapvaal craton in the interval 2 43 to 1 93 ga it is not yet clear how many of these excursions reflect global rather than local processes

low latitude glaciation in the palaeoproterozoic era one of the most fundamental enigmas of the earth s palaeoclimate concerns the temporal and spatial distributions of precambrian glaciations through four billion years of precambrian history unequivocally glacial deposits have been found only in the palaeoproterozoic and neoproterozoic record nonetheless some of these deposits are closely associated with tropical rather than just polar palaeolatitudinal indicators such as carbonate rocks red beds and evaporites these observations are quantitatively supported by palaeomagnetic results indicating a 5 latitude for neoproterozoic glaciogenic rocks in australia similarly reliable palaeolatitudes for the older palaeoproterozoic glaciogenic rocks have not yet been obtained as such deposits commonly suffer from poor preservation and secondary magnetic overprinting the archaean palaeoproterozoic transvaal supergroup on the kaapvaal craton in south africa is however exceptionally well preserved and is thus amenable to the palaeomagnetic determination of depositional palaeolatitudes within this supergroup the 2 2 billion year old ongeluk lavas are a regionally extensive largely undeformed and unmetamorphosed extrusive volcanic succession which conformably overlies glaciogenic deposits the makganyene diamictite here we report a palaeomagnetic estimate of 11 5 depositional latitude for the lavas and hence for the underlying contemporaneous glacial rocks the palaeoclimate enigma is thus deepened a largely ice free precambrian world was apparently punctuated by two long ice ages both yielding glacial deposits well within tropical latitudes

isotopic composition of pb in ore deposits of the betic cordillera spain origin and relationship to other european deposits the betic cordillera in southern spain is a complex alpine fold belt that resulted from the cretaceous through cenozoic collision of africa with europe the region is illustrative of one of the characteristics of the alpine mediterranean orogen the occurrence over a limited area of mineral deposits with a wide variety of host rocks mineralization ages and styles the metamorphic basement in the betic zone is characterized by a nappe structure of superimposed tectonostratigraphic units and consists of lower paleozoic to lower triassic clastic metasedimentary rocks this is overlain by middle to upper triassic platform carbonate rocks with abundant strata bound f pb zn ba deposits e g sierra de gador sierra alhamilla cretaceous to paleogene subduction related compression in southeastern spain was followed by miocene postcollisional extension and resulted in the formation of the almeria cartagena volcanic belt and widespread hydrothermal activity and associated polymetallic mineralization typical miocene hydrothermal deposits include volcanic hosted au e g rodalquilar and ag rich base metal e g cabo de gata mazarron deposits as well as complex polymetallic veins mantos and irregular replacement bodies which are hosted by paleozoic and mesozoic metamorphic rocks and neogene sedimentary and volcanic rocks e g cartagena sierra almagrera sierra del aguilon loma de bas lead isotope compositions were measured on sulfide samples from nine ore districts and from representative fresh samples of volcanic and basement rock types of the region the results have been used to evaluate ore forming processes in southeastern spain with emphasis on the sources of metals during a late triassic mineralizing event pb was leached from paleozoic clastic metasedimentary rocks and incorporated in galena in strata bound f pb zn ba deposits 206 pb 204 pb 18 332 or 12 207 pb 204 pb 15 672 or 12 208 pb 204 pb 38 523 or 46 the second episode of mineralization was essentially contemporaneous late miocene throughout the region and did not involve remobilization of less radiogenic triassic ore pb lead isotope data indicate a dominantly paleozoic metasedimentary source for polymetallic vein and manto type deposits that formed by hydrothermal circulation through the betic basement driven by miocene intrusions 206 pb 204 pb 18 747 or 20 207 pb 204 pb 15 685 or 9 208 pb 204 pb 39 026 or 37 lead in au cu te sn ores is isotopically indistinguishable from that of the calc alkalic volcanic host 206 pb 204 pb 18 860 or 9 207 pb 204 pb 15 686 or 8 208 pb 204 pb 38 940 or 27 in contrast the pb in volcanic hosted pb zn cu ag au veins was derived from paleozoic metamorphic and miocene volcanic rocks 206 pb 204 pb 18 786 or 5 207 pb 204 pb 15 686 or 2 208 pb 204 pb 38 967 or 9 a comparison of the pb isotope data from southeastern spain with published data from selected pb zn deposits in southern europe including les malines l argentiere and the alpine iglesiente sulcis and montagne noire districts indicates the importance of a metasedimentary basement as a common source of ore pb

carbon isotopes and the rise of atmospheric oxygen new data for the isotopic composition of carbon in carbonate sediments deposited between 2 6 and 1 6 ga indicate that the value of 13c in these sediments underwent a very large positive excursion between 2 22 and 2 06 ga a reassessment of the earlier 13c data for carbonate sediments shows that this excursion was probably worldwide and that it was preceded and followed by several hundred million years during which the 13c of carbonate sediments differed little from that of modern carbonates the large 13c excursion between 2 22 and 2 06 ga was probably related to an abnormally high rate of organic carbon deposition which generated an abnormally high rate of o2 production we estimate that the total excess o2 produced during the excursion was between 12 and 22 times the present atmospheric o2 inventory the 13c data therefore suggest that the o2 content of the atmosphere increased very significantly between 2 22 and 2 06 ga this inference is supported strongly by several other lines of evidence

isotopic composition of disseminated sulfur in precambrian sedimentary rocks abstract isotopic analyses of trace sulfur in precambrian carbonates and clastic sedimentary rocks support the results of previous studies which have shown that 34s measurements of archean sedimentary sulfur cluster mostly around mantle like values and that a significant overall dispersion of 34 s 32 s ratios commenced at about 2 7 ga ago the outstanding feature of the proterozoic record is the predominance of heavy 34ssulfide values mostly in excess of 0 cdm consideration of these data in combination with the sparse 534s record for proterozoic sulfates suggests that 34ssulfide sulfide may have been smaller than was the case during the phanerozoic a possible scenario that is compatible with the above data is based on a proposition that the terrestrial exogenic sulfur cycle evolved in a tripartite manner in the archean it was coupled to and controlled by the magmatic endogenic cycle the proterozoic for the most part represents a transitional stage into a phanerozoic like exogenic cycle the latter essentially decoupled from its endogenic counterpart and its redox balance maintained and mediated by the biosphere the indication that the mean combined 34s of proterozoic sulfate and sulfide may have significantly exceeded the phanerozoic mean value of 2 cdm is enigmatic and poses problems for balance considerations

did global tectonics drive early biosphere evolution carbon isotope record from 2 6 to 1 9 ga carbonates of western australian basins the 13 ccarb record of well preserved carbonates in outcrop and core is here examined from the 2 6 to 1 9 ga old basins of western australia these data which are constrained by a well defined stratigraphic and tectonic framework and by u pb zircon ages provide an insight into the variables coincident with the evolution of an oxidative atmosphere and the evolution of the early biosphere in the latest archaean ca 2 6 ga the secular 13 ccarb curve is flat much like that seen in the later palaeoproterozoic basins of northern australia 1 8 ga this implies that photosynthesis was a major component of the biosphere at that time and that the carbon mass balance was stable in the early palaeoproterozoic beginning after 2 5 ga and continuing until at least 1 9 ga the 13 ccarb the curve is much more dynamic with significant positive and negative excursions including a major positive excursion 9 pdb close to 2 2 ga these excursions can be correlated with the lomagundi event identified in africa europe and north america previously published studies of the overlying meso to palaeoproterozoic bangemall basin and of 1 8 1 5 ga old basins in northern australia suggest that the 13 ccarb curve became relatively monotonic again after ca 1 8 ga and remained so for most of the following mesoproterozoic comparisons with data from other ancient cratons especially africa suggest that the secular carbon curve may be even more complex than presently understood and probably comparable to the major excursions seen in the neoproterozoic when the western australian data are placed in their stratigraphic and tectonic framework we find that the monotonic latest archaean curve coincides with a tectonically quiescent period in which carbonates formed in an basinal setting on a craton surrounded by passive margins the data are consistent with an earth in which the carbon mass balance was in equilibrium the 13 ccarb curve began to oscillate following the onset of glaciation as the pilbara and yilgarn cratons began to converge during the capricorn orogeny suggesting periods of rapid carbon burial during continental dispersal however the major positive excursion is preserved in carbonates from back arc basins formed as the ocean closed and subduction began since similar tectonic processes can be recognised not only in northern australia but also on other early cratons it can be argued that the carbon excursions relate to supercontinent cycles and to major periods of mantle overturn and superplume development we explain this coincidence of carbon isotopic excursions

neoproterozoic sulfur isotope variation in australia and global implications abstract seven sulfur isotope stages are apparent in australian neoproterozoic sections 1 from 840 ma to the sturtian glaciation 700 ma 34ssulfate varied little 19 to 17 5 and 34ssulfide ranged from 20 to 23 2 the sturtian glaciation was followed by 3 a rise in 34ssulfide to an average of 30 seen also in china namibia and canada and in 34ssulfate at least to 26 and possibly to 45 the sharp rise in 34s of all sulfur fractions sulfate sulfide and organic leads us to speculate that sulfide depleted in 34s was deposited on the abyssal plain and that residual sulfate enriched in 34s remained beneath a stagnant ice covered ocean during the sturtian glaciation and was brought to the shallow continental margin during the post glacial transgression 4 34ssulfide and 34ssulfate fall from 640 to 607 ma 34ssulfate down to 17 probably from oxygen excess through massive organic carbon burial which causes weathering of sulfide depleted in 34s continental sulfide and previously deposited sulfide on the abyssal plain 5 the oxic environment of the marinoan 605 595 ma glaciation minimises sulfate reduction unlike the sturtian so that 34ssulfate is unvarying 6 the post glacial environment has sulfide depleted in 34s average 34ssulfide

evidence of anoxic to oxic atmospheric change during 2 45 2 22 ga from lower and upper sub huronian paleosols canada paleoweathered zones in four underground drill holes in quirke ii mine and one drill hole by denison mines in elliot lake area ontario canada were studied for petrography mineralogy and whole rock chemistry these paleosols formed beneath 2 45 ga old lower huronian formations are characterized by upward depletion of fetotal and fe3 in the whole rock by upward depletion of fetotal fe mg ratios in chlorites and fine grained muscovite and by the presence of fe2 minerals e g pyrite pyrrhotite ilmenite in contrast the paleosols underlying upper huronian strata 2 22 ga old exhibit an upward increase in fe3 and fetotal and contain hematite and goethite uraninite and pyrite bearing paleoplacers occur in lower huronian strata whereas the upper huronian formations contain red beds and are devoid of detrital uraninite and pyrite these differences between the sub huronian paleoweathering profiles and mineralogical characteristics of the lower huronian strata overlying the paleosols support the previously postulated oxyatmoversion theory and restricts the time interval for its occurrence to between 2 45 and 2 22 ga assuming that few tens of millions of years were required for the deposition of lower huronian groups oxyatmoversion likely occurred at about 2 4 ga

sedimentology of the lower huronian supergroup early proterozoic elliot lake area ontario canada abstract the early proterozoic huronian supergroup is a slightly metamorphosed sedimentary succession locally 10 km thick exposed to the north of lake huron ontario canada the lower part of the supergroup comprising the matinenda mckim ramsay lake and pecors formations was studied in the quirke syncline area elliot lake and regions immediately to the west and south thirteen lithofacies are present trough and planar cross stratified sandstone quartz pebble conglomerate clay rich sandstone lenticular bedded sandstone siltstone mudstone laminated sandstone siltstone mudstone massive sandstone massive pebbly sandstone massive diamictite stratified matrix supported diamictite stratified clast supported diamictite graded diamictite and massive siltstone the lithofacies may be grouped into associations which correspond approximately to the mapped formations the crossbedded sandstones and conglomerates comprise a fluvial association matinenda formation which was formed mainly in shallow braided channels clay rich sandstone and the lenticular and laminated lithofacies constituting portions of the mckim and pecors formations were deposited on the strand and offshore areas of braid deltas interfingering laterally and vertically with the matinenda fluvial deposits four glacigenic subassociations are present in the ramsay lake formation an ice proximal subassociation i consists of massive pebbly sandstone and diamictite which progressively truncates the matinenda and mckim formations to the north the massive sandstone may be an ice override deposit formed by erosion and reworking of the underlying matinenda formation or a sub ice shelf rain out accumulation of locally eroded glacial debris subassociations ii and iii consist mainly of subaqueous sediment gravity flow and ice rain out deposits subassociation iv is interpreted as an ice proximal fluvial outwash deposit containing resedimented blocks of moraine material stratigraphic and paleocurrent data indicate a south dipping paleoslope that tilted southeast during the deposition of the fluvial and deltaic units a trough of relatively deep water extended nw se across the region transverse to the e w divergent continental margin hinge line that is assumed to have existed to the south of the project area analogies are suggested to mesozoic recent basins on the atlantic margin of canada where transverse paleogeographic trends reflect either landward extension of active oceanic fracture zones or reactivation of earlier structural lineaments

paleomagnetism of the paleoproterozoic gowganda and lorrain formations ontario low paleolatitude for huronian glaciation abstract to further our understanding of the paleolatitudes of precambrian glaciations a paleomagnetic study has been conducted on the glaciomarine coleman member of the gowganda formation and the conformably overlying deltaic firstbrook member and lorrain formation huronian supergroup 2 4 2 3 ga in ontario canada many of the rocks notably the gray and grayish red argillic facies display unstable magnetization or overprints carried by magnetite and or hematite that give negative fold tests some red sandstones however have stable high temperature 690 c components marked by very shallow northerly or southwesterly directions five sites in pale red sandstone from the coleman member near elliot lake give a dip corrected a direction of d 216 3 i 5 5 95 6 7 n 30 and 17 sites in lorrain red sandstone near desbarats give a dip corrected a direction of d 5 4 i 5 5 95 5 9 n 75 unfavorable structural attitudes rendered fold tests inconclusive these very shallow directions may be ascribed to early chemical remanent magnetization crm because a some specimens display polarity reversals b such directions are unknown either as original or as overprint components in post huronian rocks of the region and c a prior site in coleman red beds gave a high temperature shallow nnw direction that is not significantly different from lorrain a and which a positive conglomerate test suggested is not an overprint the very shallow directions are near primary directions for the slightly older 2 45 ga matachewan dyke swarm in the region lorrain argillic rocks at five sites give a normal component b t 670 c d 18 6 i 59 6 95 6 1 n 16 dip corrected and a reverse component e t 500 c d 190 9 i 60 9 95 7 3 n 14 in situ which are close to a prefolding direction carried by magnetite previously identified in coleman gray argillites morris a however a primary origin for morris a is dubious because of the widespread occurrence of overprints carried by magnetite in coleman gray argillites and because the fold test employed folds formed during the penokean orogeny at 1900 1800 ma our results suggest that morris a lorrain b and lorrain e may data from immediately before and just after penokean folding respectively hence coleman sandstone a and lorrain a may be better estimates of original directions those components and matachewan paleomagnetic data constrain huronian paleolatitudes and suggest that huronian glaciation occurred within 11 and possibly within 4 of the paleoequator

a u pb age for mineralized nipissing diabase gowganda ontario concordant baddeleyite and rutile analyses from mineralized nipissing diabase at gowganda s castle mine yield a u pb age of baddeleyite is a primary phase of the diabase therefore the age dates the magmatic emplacement the genesis of rutile is less certain rutile could have formed during an episode of alteration veining and ag mineralization in which case the u pb age would also date the secondary event and demonstrate that ag mineralization was related to the nipissing magmatism however a primary magmatic origin of the rutile cannot be completely excluded for now thus the u pb age may not constrain the time of ag mineralization further research is needed to clarify this point

uranium bearing stratiform organic matter in paleoplacers of the lower huronian supergroup elliot lake blind river region canada the elliot lake blind river ontario paleoplacer deposits in the basal matineda formation lowermost member of the 2 25 2 45 ga old huronian supergroup contain organic matter chemically consistent with kerogen this substance is also referred to as thucholite uranium ores and some gold occur here and these minerals may be in close association with the kerogen two uraniferous and auriferous stratiform kerogens obtained from the denison mines limited s denison mine and rio algom limited s stanleigh mine have been analyzed by combined high vacuum pyrolysis gas chromatography mass spectrometry and by neutron activation the reflectances of these samples have also been determined related samples containing dispersed kerogen have been examined by backscattered scanning electron microscopy the polymer like matrix of the two stratiform kerogens consists of aromatic alkyl aromatic hydrocarbon and sulphur moieties and contains 20 and 32 uranium with gold abundances in the parts per billion range

chronology and sources of trace elements accumulation in the rhone pro delta sediments northwestern mediterranean during the last 400years abstract the rhone pro delta sediments receive the particulate inputs from the rhone river the largest freshwater discharge of the western mediterranean sea trace element tes ag cd co cr cu ni pb and zn concentrations and stable pb isotope ratios were determined along a 7 7 m long sediment core collected from the rhone prodeltaic lobe archiving the deposits of the last 400 years trace element mean concentrations during the pre industrialized era before 1850 ce were no different from the average composition of earth s upper crust except for cr principal component analysis performed on tes and tracers suggests three origins for tes that we identified as i marine biogenic material ag cd ii ultramafic rocks li cr ni and iii other clay minerals co cu pb and zn during the pre industrial period several changes in the te al ratios coincided with flood events or and modifications in the channelization of the rhone river mouth some frequencies in the tes temporal variations allow us to hypothesize some influence of climate variation sediments deposited after 1850 ce exhibited concentrations of certain tes exceeding 1 3 3 5 times the concentrations of the pre industrial era ag cd pb cu zn principal component analysis performed on post 1850 ce data allows to distinguish pristine and anthropogenically impacted tes pristine tes such as co cr and ni are linked with clay markers al li and fe co and ni are associated with mn enrichment whereas cr is correlated with fe anthropogenically impacted elements consist of ag cd cu pb and zn vertical profiles show that te contamination has increased dramatically after the iind world war and reached a maximum between 1970 and 1980 consistently with anthropogenic atmospheric emissions changes sediment deposited on the rhone prodelta at the beginning of xviith century have 206 207pb ratios close to values of natural pb 1 200 whereas sediments deposited after 1850 ce are clearly contaminated by european gasoline and industrial pb pools

chronological correlations between the pilbara and kaapvaal cratons abstract the early geological development of the pilbara and kaapvaal cratons has many features in common attempts have been made to correlate geologically similar features of the two cratons and it has been postulated that they originated as contiguous components of a single continent vaalbara during this time the early geological histories of the pilbara and kaapvaal cratons are here compared in detail and the evidence that they were initially contiguous is assessed these comparisons indicate significant differences in the chronologies of magmatic events within the granite greenstone crusts of the pilbara and kaapvaal cratons in addition igneous correlatives emplaced during ca 2985 and 2782 ma magmatic events on the kaapvaal craton have not been identified on the pilbara craton and a well defined 2760 ma magmatic event manifest as widespread emplacement of granitic rocks into the pilbara granite greenstone basement and eruption of flood basalts of the lower part of the fortescue group is absent from the kaapvaal craton furthermore similarities in first and second order transgression regression cycles within the sedimentary supracrustal sequences may be attributable to global sea level fluctuations and thus may be irrevelant to the question of former contiguity however similarities in some aspects of the geological development of the pilbara and kaapvaal cratons imply that there were periods extending for between 60 and 200 ma of the archaean era during which the style of crust formation intensity of volcanism and subaerial erosion and magnitude of sea level fluctuations may have varied on a global scale such similarities include the overall duration of formation of the granite greenstone crusts from ca 3650 to 3100 ma the onset of craton wide erosion in the interval ca 3125 to 3000 ma the major episodes of flood basaltic volcanism between 2760 and 2680 ma the predominance of chemical carbonate and banded iron formation sedimentation between ca 2630 and 2440 ma and the transition to widespread clastic sedimentation within the interval 2440 to 2200 ma

chemostratigraphy of the paleoproterozoic duitschland formation south africa implications for coupled climate change and carbon cycling the paleoproterozoic duitschland formation lies stratigraphically beneath the timeball hill formation which contains the only unequivocal glacial unit of this era in the transvaal basin south africa lithologic evidence in paleoproterozoic successions of north america however indicates the existence of three discrete and potentially global ice ages within this 300 my interval carbonates of the duitschland formation are significantly enriched in 13c up to 10 1 permil in the upper part of the succession above a notable sequence boundary in contrast the lower part of this unit contains carbonates with consistently negative 13c values trace and major element compositions of these carbonates as well as carbon isotopic compositions of coexisting organic matter support a primary origin for the markedly positive carbon isotope anomaly the stratigraphic constraints indicate that 13c enriched carbonates were deposited prior to paleoproterozoic glaciation in southern africa similar to carbonates stratigraphically beneath neoproterozoic glacial diamictites worldwide also mirroring the neoproterozoic record are strongly negative 13c values in cap carbonates atop glacial diamictites in paleoproterozoic strata of wyoming and ontario the litho and chemostratigraphic constraints indicate that the interval of negative carbon isotope values in well preserved carbonates of the lower duitschland formation may reflect a second paleoproterozoic ice age in the transvaal succession this interpretation is further supported by recently discovered bullet shaped clasts with striations in diamictite from the basal part of the succession thus the emerging temporal pattern of carbon isotope variations and glaciation in the paleoproterozoic has a close analogue to neoproterozoic events suggesting a coupling of climatic and biogeochemical changes at both ends of the eon

mass independent isotope effects in archean 2 5 to 3 8 ga sedimentary sulfides determined by ion microprobe analysis we report sulfur isotope anomalies with 33 s the deviation from a mass dependent fractionation line for the three isotope system 34 s 32 s vs 33 s 32 s ranging up to 2 within individual archean sedimentary sulfides from a variety of localities our measurements which are made in situ by multicollector secondary ion mass spectrometry unequivocally corroborate prior bulk measurements of mass independent fractionations mif in sulfur and provide additional evidence for an anoxic atmosphere on the earth before 2 ga this technique also offers new opportunities for exploring ancient sulfur metabolisms preserved in the rock record the presence of mif sulfur in sulfides from a 3 8 ga fe rich quartzite from akilia island west greenland is consistent with a marine sedimentary origin for this rock copyright 2003 elsevier science ltd

oil bearing co2 ch4 h2o fluid inclusions oil survival since the palaeoproterozoic after high temperature entrapment the 2 45 ga fluvial quartz arenites and conglomerates of the matinenda formation at elliot lake canada contain evidence for two episodes of oil migration with entrapment of oil bearing fluid inclusions the first episode was during diagenesis the second during a subsequent sub greenschist facies metamorphic event at ca 2 2 ga at temperatures exceeding 250 c remnants of the migrating hydrocarbon fluids are preserved as radiogenic pyrobitumen nodules occupying former inter granular pore spaces and as complex fluorescing oil bearing fluid inclusions the latter include two dominant types 1 aqueous oil inclusions with a minor oil phase located within original detrital grains and clasts and within rare quartz overgrowths and 2 aqueous carbonic inclusions with a minor oil phase light hydrocarbons and solids located within microfractures in detrital quartz grains and clasts the majority of type 1 inclusions were trapped with a high salinity fluid up to 25 wt nacl equivalent at relatively low temperatures between 80 and 200 c and pressures of less than 2 kbar early in the burial history of the matinenda formation type 2 inclusions were trapped during metamorphism with a much lower salinity aqueous carbonic fluid 1 2 to 17 wt nacl equivalent at temperatures between 280 and 350 c and pressures between 1 and 1 5 kbar under these conditions oil may have been miscible in the mixed fluid 13c of 25 5 and 24 9 for the pyrobitumen nodules and fluid inclusion hydrocarbon gas indicate a biogenic origin for the petroleum 13c of 16 2 for the bulk inclusion gas suggests a value of 12 for the carbonic phase hence a mix of inorganic co2 and organic co2 from either thermal alteration of organic matter or in situ chemical oxidation of hydrocarbons this study has implications for the depth and temperature at which oil may be present suggesting that deep old reservoirs may not be completely barren of petroleum the fact that hydrocarbons in the matinenda formation fluoresce indicates that aromatic compounds are able to survive temperatures of up to 350 c in a suitable geological environment

geochemistry of precambrian carbonates iv early paleoproterozoic 2 25 0 25 ga seawater in an effort to narrow down the first and second order variations in isotopic composition of the early paleoproterozoic 2 25 0 25 ga seawater we report a comprehensive study of mineralogy chemistry and isotopic composition of the malmani dolomite transvaal supergroup south africa duck creek dolomite wyloo group australia and bruce limestone member of the espanola formation huronian supergroup canada based on trace element data their diagenetic rank increases in the order duck creek bruce malmani the interpolation of alteration trends to best values yields an estimate of 0 70550 for 87sr86sr comparable to our previously published value of 0 70496 for 13c the measured range of 0 1 5 pdb is similar to that observed for phanerozoic marine carbonates in contrast the best 18o value for dolostones is 5 pdb depleted in 18o relative to phanerozoic counterparts but comparable to the estimates obtained by similar approach for archean facies the isotope geochemistry and mineralogy of bruce limestone member is consistent with the proposition that the sequence may have been deposited in a lacustrine environment possibly related to the recession of the brace glaciers if such interpretation proves unacceptable from a sedimentological standpoint the origin of the unusual isotopic signatures must be sought despite the above trace element interpretation in as yet unspecified post depositional alteration phenomena in contrast to phanerozoic carbonates the early paleoproterozoic as well as the previously described archean counterparts are enriched in mn and fe

the gowganda formation in the southern part of the huronian outcrop belt ontario canada stratigraphy depositional environments and regional tectonic significance abstract the early proterozoic huronian supergroup of the north shore of lake huron comprises a lower part that is largely of continental origin and a more widespread dominantly marine upper succession the gowganda is the lowest formation of the upper huronian in the southern part of the huronian outcrop belt it is in conformable but commonly erosional contact with the underlying serpent formation the basal part of the gowganda formation unit 1 is stratified diamictites boulder and cobble orthoconglomerates and subordinate thin turbiditic sandstones these rocks are largely resedimented but glaciogenic the basal diamictite complex is overlain by unit 2 a thick argillite formed in deep water during a period of glacial retreat unit 3 begins with a discontinuous glaciomarinite this is overlain by resedimented boulder and cobble conglomerates that pass up into sandy turbidites down to basin movements on syn sedimentary north trending normal faults led to deposition of coarsening upward wedges of eastward transported debris there is a thick stratified diamictite complex at the top of unit 3 in the eastern part of the study area it includes a 50 m thick argillite the diamictite complex is overlain by a series of coarsening upward sequences formed by prograding deltas these comprise unit 4 of the gowganda formation the lowest deltaic sequence includes a thick diamictite in the east and a more widespread thin diamictite in its upper part the glaciogenic and resedimented nature of the rocks at the base of the gowganda formation suggests that basin deepening was tectonic rather than due to eustatic sea level rise glaciation in the huronian supergroup may have been initiated by uplift of rift shoulders and propagated by influx of marine waters into the interior of the continent the regional extent of the gowganda formation its unconformable relationship with older huronian rocks in the north and its largely resedimented nature all indicate an episode of regional subsidence possibly after continental separation similar tectonic and climatic events have been postulated for early proterozoic rocks of southeastern wyoming and possibly elsewhere lending support to earlier correlations based mainly on stratigraphic similarities glaciogenic diamictites are present above the breakup unconformity in many early and late proterozoic successions suggesting a possible causative relationship

methanotrophs regulated atmospheric sulfur isotope anomalies during the mesoarchean tumbiana formation western australia abstract the 2 73 billion year old tumbiana formation of the fortescue group in the pilbara craton western australia preserves one of the best records of the fortescue negative carbon isotope excursion with organic 13 c values as low as 60 the prevailing environmental conditions at this biological excursion are not well understood here we present an integrated carbon 12 c 13 c and multiple sulfur 32 s 33 s 34 s 36 s isotopes study of a pristine diamond drill core through the tumbiana formation collected at meentheena by the pilbara drilling project our results show centimeter to meter scale heterogeneities in sulfur and carbon contents and isotope compositions organic 13 c values vary at the meter scale and display a bimodal distribution with peaks at about 44 and 34 this bimodal distribution is interpreted to reflect variations in the contribution of methanotrophic metabolism to the biomass the 34 s v cdt values of sedimentary pyrite vary from 5 73 to 2 75 sulfur isotopes sulfur contents and s c ratios are variable suggesting a complex local biotic sulfur cycling sedimentary pyrite preserves mass independent fractionation of sulfur mif s with 33 s v cdt ranging between 0 25 and 1 64 average 0 47 corresponding to the characteristic dampened mesoarchean anomalies positive correlation between sulfide mif s and a 13 c depletion of organic matter argues for a causal link between methanotrophs activity and the preservation of mif s anomalies in the rock record

the reappearance of the huronian in wyoming rifting and drifting of ancient continents striking stratigraphic and sedimentological similarities between the early proterozoic huronian supergroup of the canadian shield and the snowy pass supergroup of wyoming suggest that they were deposited in a single broad epicratonic basin developed atop a large archean continent that included the superior and wyoming geological provinces breakup of the continent after the 2 2 ga intrusion of widespread gabbro sheets and dykes resulted in the separation of the archean superior and wyoming cratons and their early proterozoic covers these crustal fragments were subsequently reassembled during early proterozoic 1 85 ga orogenesis the end result being the present 2000 km separation of the huronian and snowy pass supergroups and their archean basements

carbon isotope record for the onset of the lomagundi carbon isotope excursion in the great lakes area north america carbonate units of the chocolay group in the lake superior area usa and the gordon lake formation of the correlative upper huronian supergroup ontario canada were deposited after the last paleoproterozoic glacial event and an episode of intense chemical weathering the huronian supergroup contains at the base 2 45 ga volcanics and is intruded by the 2 22 ga nipissing diabase dykes and sills while the chocolay group is bracketed in age between 2 29 and 2 20 ga the lomagundi 2 22 2 1 ga carbon isotope excursion started after the paleoproterozoic glacial epoch and before a plume breakout event at 2 22 ga therefore the chocolay and upper huronian carbonates were deposited either before or during the onset of the lomagundi event notably thin carbonates of the basal gordon lake formation and thick carbonate succession of the kona dolomite in the northeastern exposures of the chocolay group record 13 c values as high as 9 5 versus v pdb similar to other successions deposited during the lomagundi event both units contain pseudomorphs and molds after sulfates this observation suggests that seawater sulfate contents rose dramatically in association with the onset of the lomagundi event and the rise of atmospheric oxygen carbonates in the western and southern exposures of the chocolay group randville and bad river dolomites and saunders formation previously assumed to be equivalent to the gordon lake formation and kona dolomite have carbon isotope values close to 0 based on basin analysis we infer that these carbonate units were deposited during a negative carbon isotope excursion after the lomagundi event started and are slightly younger than the kona dolomite and gordon lake formation this interpretation implies that the carbonate platform in the great lakes area transgressed to the west over shallow marine and fluvial deposits the negative carbon isotope excursion in the lake superior area might correspond to similar 13 c values of the mooidraai dolomite in the griqualand west basin south africa supporting correlation between paleoproterozoic successions of north america and south africa and the notion of three global glaciations in the paleoproterozoic era carbonates of the mille lacs group trout lake glen township and denham formations in minnesota have 13 c values ranging from 1 2 to 2 5 combined with geochronologic constraints these data suggest that these units were deposited after the lomagundi excursion and are related to the rifting event that led to development of the so far unrecognized 2 0 ga passive margin in the lake superior area 2006 elsevier b v all rights reserved

chemostratigraphy of paleoproterozoic carbonate successions of the wyoming craton tectonic forcing of biogeochemical change the archean wyoming craton is flanked on the south and east by belts of paleoproterozoic supracrustal successions whose correlation is complicated by lack of geochronologic constraints and continuous outcrop however carbonate units in these successions may be correlated by integrating carbon isotope stratigraphy with lithostratigraphy the 10 km thick paleoproterozoic snowy pass supergroup in the medicine bow mountains was deposited on the present day southern flank of the wyoming craton it contains three discrete levels of glacial diamictite correlative with those in the huronian supergroup on the southern margin of the superior craton the nash fork formation of the upper snowy pass supergroup is significantly younger than the uppermost diamictite and was deposited after the end of the paleoproterozoic glacial epoch carbonates at the base of the nash fork formation record remarkable 13 cenrichment up to 28 v pdb whereas those from overlying members of the lower nash fork formation have d 13 c values between 6 and 8 carbonates from the upper nash fork formation above the carbonaceous shale have carbon isotope values ranging between 0 and 2 5 the transition from high carbon isotope values to those near 0 in the nash fork formation is similar to that at the end of the ca 2 2 2 1 ga carbon isotope excursion in fennoscandia this chemostratigraphic trend and deposition of bifs mn rich lithologies carbonaceous shales and phosphorites at the end of the global ca 2 2 2 1 ga carbon isotope excursion are likely related to ocean overturn associated with the final breakup of the kenorland supercontinent correlative carbonates from the slaughterhouse formation in the sierra madre wy and from the whalen group in the rawhide creek area in the hartville uplift wy have highly positive carbon isotope values in contrast carbonates from other exposures of the whalen group in the hartville uplift and all carbonate units in the black hills sd have carbon isotope values close to 0 combined with existing geochronologic and stratigraphic constraints these data suggest that the slaughterhouse formation and the succession exposed in the rawhide creek area of the hartville uplift are correlative with the lower and middle nash fork formation and were deposited during the ca 2 2 2 1 ga carbon isotope excursion the estes and roberts draw formations in the black hills and carbonates from other exposures in the hartville uplift postdate the ca 2 2 2 1 ga

methane and climate during the precambrian era abstract the sun was substantially less bright in the distant past yet earth s surface temperature remained above freezing higher concentrations of the greenhouse gases co 2 and ch 4 were likely responsible for keeping the early climate warm ch 4 concentrations of 1000 ppm or higher are predicted for the late archean paleoproterozoic atmosphere prior to the rise of o 2 photolysis of this ch 4 may have created an optically thin organic haze during much of this time the rise of o 2 at 2 3 ga eliminated most of the methane and probably triggered the paleoproterozoic glaciations ch 4 concentrations could have remained elevated throughout much of the proterozoic however as a consequence of low concentrations of dissolved o 2 and sulfate in the deep oceans and a corresponding increase in organic matter recycling by fermentation and methanogenesis

multiple sulfur isotopes of sulfides from sediments in the aftermath of paleoproterozoic glaciations geochemical evidence reported from paleoproterozoic sediments has long been used to evaluate the transition from the anoxic archean atmosphere to an oxygenated atmosphere sulfur isotopes 32s 33s 34s and 36s in sedimentary sulfides and sulfates are an especially sensitive means to monitor this transition such that the timing of the paleoproterozoic great oxidation event can be investigated using mass independently fractionated mif sulfur isotope systematics expressed as 33s here we report data from 83 individual analyses of pyrite pyrrhotite and chalcopyrite on a new suite of 30 different samples from finland south africa wyoming and ontario that span 600 my and follow one or several snowball earth events in the paleoproterozoic the samples were measured using a high resolution secondary ion mass spectrometry technique in multicollection mode that investigates multiple sulfur isotopes in microdomains 30 m within individual sulfide grains while preserving petrographic context we focused on sediments deposited in the aftermath of the paleoproterozoic glaciations between 1 9 and 2 2 ga to trace fluctuations in atmospheric o2 concentrations that were likely affected by an interplay of o2 sinks in the atmosphere and the upper ocean and continental crust and by the emergence and diversification of aerobic organisms our results demonstrate that mif sulfur isotopes are absent in sediments deposited after the period of protracted global cooling in the paleoproterozoic and independently confirm observations that mif ceased during this time we interpret our results by integrating 33s and 34s data in sulfides 13c data in carbonates and the estimated timing of glaciation events in the paleoproterozoic data strongly hint at the presence of microbial sulfate reduction and fluctuations in the concentration of dissolved seawater sulfate and or in 34ssulfate in the aftermath of glaciations and likely were affected by changing erosion rates and nutrient delivery to the oceans these changes modulated the population of primary producers especially oxygenic photosynthesizers and led to fluctuations in the abundance of atmospheric o2 co2 and ch4 our results support the interpretation that the world wide 13ccarb excursion observed between 2 25 and 2 05 ga karhu and holland 1996 was a period of significant accumulation of o2 in the atmosphere

multiple sulfur isotopes and the evolution of the atmosphere interest in multiple sulfur isotope analyses has been fueled by recent reports of mass independent sulfur isotope signatures in the geologic record a non zero multiple isotopic signature of sulfur 33s and 36s is produced primarily through photochemical reactions and it is an almost perfect tracer of the source of sulfur once the signature is passed on to a given sulfur reservoir it will be preserved unless there is addition of sulfur with a different 33s or 36s in the geological record this signature has been used to study the evolution of the earth s atmosphere and to trace movement of sulfur through geological systems early in earth s history recently small but significant mass independent signatures have been reported for some younger samples raising the possibility of additional applications of multiple isotope studies the purpose of this review is to introduce and discuss the implications of multiple isotope studies and to focus attention on these anomalous but not uncommon isotopic signatures

regional cross section of the southern province adjacent to lake huron ontario implications for the tectonic significance of the murray fault zone the southern province in the lake huron area of ontario and the penokean fold belt of minnesota wisconsin and michigan have the earmarks of a collisional orogen the huronian supergroup a southerly facing passive margin sequence was deposited during early aphebian early proterozoic crustal stretching and ocean basin formation along the southern margin of the superior province archean craton it accumulated as four unconformity bounded northerly tapering onlapping clastic wedges megacycles the thickness and facies variations reflect syndepositional down to the basin south normal faulting that controlled the accumulation and preservation of the lower three huronian megacycles these are overlapped northward by the youngest megacycle an extensive sheet of clastic sediments recording post stretching regional subsidence of the cratonic margin due to cooling and thermal contraction soft sediment folds in the rocks of the youngest megaycycle to the extreme south probably indicate southward slu

mass dependent fractionation of quadruple stable sulfur isotope system as a new tracer of sulfur biogeochemical cycles abstract sulfur isotope studies of post archean terrestrial materials have focused on the ratio 34s 32s because additional isotopes 33s and 36s were thought to carry little information beyond the well known mass dependent relationship among multiple isotope ratios we report high precision analyses of 33s and 36s values defined as deviations of 33s and 36s from ideal mass dependent relationships for international reference materials and sedimentary sulfides of phanerozoic age by using a fluorination technique with a dual inlet isotope ratio mass spectrometer measured variations in 33s and 36s are explained as resulting from processes involve branching reactions two or more reservoirs formed or mixing irreversible processes in closed systems rayleigh distillation amplify the isotope effect we outline how this new isotope proxy can be used to gain new insights into fundamental aspects of the sulfur biogeochemical cycle including additional constraints on seawater sulfate budget and processes in sedimentary sulfide formation the isotope systematics discussed here cannot explain the much larger variation of 33s and 36s observed in archean rock records furthermore phanerozoic samples we have studied show a characteristic 33s and 36s relationship that differs from those measured in archean rocks and laboratory photolysis experiments thus high precision analysis of 33s and 36s can be used to distinguish small non zero 33s and 36s produced by mass dependent processes from those produced by mass independent processes in archean rocks and extraterrestrial materials