sample scale carbon isotopic variability and diverse biomass in the paleoproterozoic zaonega formation russia abstract the stratigraphic record of organic matter in the c 1 97 ga zaonega formation zf onega basin northwestern russia exhibits a distinct negative 13c excursion 13corg from 25 to 40 vpdb which was previously interpreted either to reflect a disturbance in the global carbon cycle after the great oxidation event or to have been caused by an increase in basinal methanotrophic activity in order to assess the nature of primary biomass and the effects of post depositional alteration we here report the sample scale carbon isotopic characteristics of organic matter in two drill cores from the zf covering 500 m of stratigraphy by using secondary ion mass spectrometry sims the results confirm that the organic matter has to a large extent preserved the primary isotopic signatures whereas secondary effects are limited

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

a short term post lomagundi positive c isotope excursion at c 2 03 ga recorded by the wooly dolomite western australia it is generally accepted that carbon isotope variations in seawater were muted between c 2 06 ga after the end of the lomagundi carbon isotope excursion lcie and c 1 3 ga evidence is presented here that c 30 myr after the end of the lcie the biogeochemical cycle of carbon experienced a short term c 2 myr high amplitude up to 8 4 v pdb perturbation recorded in the horseshoe rift basin western australia the basin was initiated at c 2 03 ga with deposition of fluvial and shallow marine sandstones followed by the eruption of flood basalt and culminated with the deposition of platform carbonates and accompanying volcaniclastic and siliciclastic sediments wooly dolomite the horseshoe rift basin during deposition of the wooly dolomite was fault compartmentalized but connected to an ocean six depositional sequences make up the wooly dolomite sequence 1 records establishment of a carbonate platform conformably on basalt and coevally with volcaniclastic sedimentation all other sequences have dominant carbonate platform deposits and are unconformity bounded sequence 3 contains a c 57 m thick section with 13 c enriched carbonates bracketed between carbonates with close to 0 carbon isotope values further high resolution chemostratigraphic studies may reveal a more complex pattern of carbon isotope variations during the boring billion years but without precise geochronology similar short term carbon isotope excursions in carbonate successions could be incorrectly correlated to the lcie supplementary material table 2 including chemical and isotopic data sample locations and their position in figure 8 is available at https doi org 10 6084 m9 figshare c 2868055

u pb and sm nd isotopic constraints on the evolution of the paleoproterozoic perapohja belt northern finland ten localities representing metasedimentary and igneous rocks from the northern part of the paleoproterozoic perapohja belt fennoscandian shield were sampled for zircon u pb dating by la mc icp ms and sm nd analysis by tims the results revealed two phases of granitic magmatism that took place at 1 99 ga and 1 79 1 77 ga the former age 1989 6 ma was given by the kierovaara granite pluton representing the first example of felsic plutonism of this age in northern finland though a type felsic volcanic rocks of the same age have previously been recognized the strongly negative initial nd values obtained for granitoids ranging from 3 9 to 11 4 are compatible with the previous sm nd data indicating the presence of archean basement in northern finland at the time of granite emplacement a garnet whole rock sm nd age of 1752 14 ma was measured for a mica gneiss constraining the time of metamorphic cooling down to the closure temperature of garnet detrital zircon grains from quartzite samples belonging to the jatulian palokivalo formation and a stratigraphically unassigned lithodemic unit the mellajoki suite yielded solely archean zircon populations in contrast our sample from the martimo formation representing kalevian sedimentation revealed a 66 paleoproterozoic detrital zircon component with the youngest zircon grains showing an age of ca 1 91 ga the new age data allow us to constrain the depositional time of this sedimentary unit between ca 1 91 and 1 88 ga the latter being the time of the synorogenic plutonism our geochronological data coupled with recent data from other karelian belts suggest that the depositional time period for rocks assigned to the kaleva spans ca 150 ma and the simple division of these rocks into two non coeval units the lower and upper kaleva has become problematic

upb geochronology of layered mafic intrusions in the eastern baltic shield implications for the timing and duration of paleoproterozoic continental rifting abstract paleoproterozoic layered mafic ultramafic intrusions are widespread in the eastern baltic fennoscandian shield and mark the initial stages of continental rifting and outpouring of voluminous flood basalts u pb zircon baddeleyite ages have been determined for seven layered mafic intrusions and a subvolcanic felsic unit associated with two paleoproterozoic volcanic sedimentary belts the pechenga imandra varzuga belt in the kola peninsula and the sumi sariola belt in karelia the layered intrusions in the sumi sariola belt show an age progression from 2449 0 1 1 ma for the burakovka complex located at the southeastern edge of the belt to 2442 1 1 4 ma and 2441 3 1 2 ma for the lukkulaisvaara and tsipringa intrusions of the olanga complex in northern karelia northeastern part of the belt these age results indicate a total duration of mafic magmatism along the ca 800 km belt in karelia to be less than 10 m y the pechenga imandra varzuga belt kola peninsula contains two distinct age groups of layered mafic intrusions and related rocks the younger of these overlaps with the ages obtained for the olanga intrusions and includes the 2441 0 1 6 ma imandra lopolith and a spatially associated felsic subvolcanic unit dated at 2442 2 1 7 ma the older group of mafic layered intrusions in the kola peninsula includes the 2501 5 1 7 ma pana tundra intrusion the 2504 4 1 5 ma monche pluton and the 2505 1 1 6 ma general skaya mountain intrusion the temporal and spatial distribution of the 2 50 2 44 ga rift related igneous activity in the baltic shield is consistent both with the model of starting mantle plume and with the model of passive rifting controlled by pre existing lithospheric weaknesses

new age constraints for the proterozoic aravalli delhi successions of india and their implications abstract proterozoic sedimentary successions of india are important archives of both the tectonic history of the indian subcontinent and the geochemical evolution of earth surface processes however the lack of firm age constraints on many of these stratigraphic units limits their current utility here we present new detrital zircon age data from strata of the southern aravalli delhi orogenic belt adob and the rajasthan vindhyan successions the alwar group of the southern delhi supergroup yielded a large population of 1 2 ga detrital zircon grains which refutes the 1 9 1 7 ga age assertion for this unit detrital zircon age distributions from the southern alwar group differ strongly from the alwar group of the north delhi belt demonstrating miscorrelation between these two regions the jhamarkotra formation of the lower aravalli group contains a large population of 1 9 1 7 ga detrital zircon grains therefore the unit cannot be 2 1 ga as traditionally assumed age distributions of the aravalli and delhi supergroups are similar to those of the lower and upper vindhyan successions and we postulate contiguous sediment sources for both regions with strata of the tectonically deformed adob representing the distal margin equivalents of the vindhyan successions additionally a late paleoproterozoic age for the jhamarkotra formation nullifies the hypothesis that the markedly positive carbonate 13c values in this unit are linked to the 2 3 2 0 ga lomagundi jatuli positive isotope excursion the potential of a large late paleoproterozoic ca 1 7 ga positive 13c excursion contrasts with the long held view of a prolonged period of carbon isotope stasis during the so called boring billion

the lomagundi jatuli carbon isotopic event recorded in the marble of the tandilia system basement rio de la plata craton argentina abstract the lomagundi jatuli event corresponds to the most important 13c positive anomaly 5 globally reported in palaeoproterozoic marine carbonates between 2 30 and 2 06 ga in the tandilia system argentina rio de la plata craton this event was recorded in the basement marble of the san miguel area the calcite diopside marble hosted by biotite gneiss and intruded by 2 12 ga garnet leucogranite was metamorphosed in amphibolite facies during the transamazonian cycle paas normalised rare earth elements ree and y for the carbonate rocks are hree enriched and display positive eu and y anomalies typical of primary precipitates from a mixed hydrothermal marine environment carbonate additionally a truly negative ce anomaly for all the samples indicates that the depositional environment was oxidising positive 13c values ranging from 5 90 to 4 30 v pdb and 18o from 17 45 to 13 84 v smow were determined in this marble both gradually decreasing towards the contact with the leucogranites these values indicate that devolatilization reactions took place during the crystallisation of a wollastonite vesuvianite grossular diopside skarn generated by the leucogranite intrusions into the marble 18o values obtained from diopside and calcite crystals in the marble sectors furthest from the contacts with leucogranite allowed a 663 623 c formation temperature to be calculated considering oxygen in a calcite diopside geothermometric pair these temperatures are consistent with the metamorphic degree amphibolite facies reached in this portion of the basement although the san miguel marble shows petrographic and mineralogical evidence of regional and contact metamorphism important geochemical and isotopic characteristics together with its estimated palaeoproterozoic age indicate that the marble protolith was a marine carbonate deposited during the lomagundi jatuli event

a high resolution14c dated sediment sequence from southwest sweden age comparisons between different components of the sediment a macrofossil rich glaciomarine marine lacustrine sediment from a soft water lake in southwestern sweden has provided an opportunity to 14c date different components of its sediments bulk sediment dates are 100 to 500 yr older than fragile terrestrial macrofossils of corresponding levels with a mean age difference of ca 300 yr this is explained by the presence of old and reworked organic material in the sediment five age comparisons between terrestrial macrofossils and periostraca of marine bivalves probably arctica islandica of allerod age give a mean age difference of 380 yr i e slightly greater than the present reservoir age of 340 30 yr for the swedish west coast this difference is roughly the same as for the marine macroalga desmarestia aculeata a date from shell carbonate fragments of mytilus edulis yields an age that is more than 1000 yr older than corresponding periostraca and terrestrial macrofossils and 500 1000 yr older than the age of the supposed deglaciation of the site altogether this indicates a larger marine reservoir effect during the allerod than at present 1998 john wiley sons ltd

travertine precipitation in the paleoproterozoic kuetsjarvi sedimentary formation pechenga greenstone belt ne fennoscandian shield abstract precambrian travertines tufas and speleothems either formed rarely or they have not been identified in previous studies in the absence of high pco2 soils in paleoproterozoic karst solution and speleothem formation occurred by processes distinct from those commonly found in present day low temperature karst environments however the high pco2 atmosphere could itself have encouraged karst formation the paleoproterozoic kuetsjarvi sedimentary formation of the pechenga greenstone belt nw russia includes abundant terrestrial carbonate precipitates these precipitates were sampled from a drillcore representing a complete section of the ca 120 m thick formation and were investigated for c and o isotopes acid soluble elemental contents and petrography the newly obtained results were used to constrain the origins of the precipitates and to illuminate different terrestrial carbonate types the investigated drillcore includes abundant small scale cavities and veins which are commonly filled with dolomite and quartz dolomite crusts are found both in the cavities and on bedding erosional surfaces dolomite cements coat uneven surfaces and surficial rock fragments the surficial dolomite crusts form distinct and discrete layers whereas the cements do not the cavity and vein fills are likely post depositional in origin whereas the surficial dolomite crusts and dolomite cements are likely syn depositional precipitates the investigated precipitates often show 13c values lower than those reported from their host rocks suggesting the influence of an external carbon source petrographic features and geochemical data suggest dissolution and precipitation of carbonate material originating from deep sourced co2 bearing fluids likely at high earth surface temperatures

dating the termination of the palaeoproterozoic lomagundi jatuli carbon isotopic event in the north transfennoscandian greenstone belt abstract existing radio isotopic age constraints indicate that the global palaeoproterozoic lomagundi jatuli large positive carbonate carbon isotopic excursion with 13 c values 5 occurred between 2 2 and 2 06 ga in the north transfennoscandian greenstone belt of the kola peninsula nw russia northern norway and finland the lomagundi jatuli event is recorded in the carbonate rocks of the umba and kuetsjarvi sedimentary formations in the imandra varzuga and pechenga greenstone belts in both areas thick mafic volcanic units umba and kuetsjarvi volcanic formations overlie the carbon isotopic excursion bearing sedimentary units overlying and younger sedimentary units contain carbonate rocks with 13 c values typically ranging between c 1 and 3 signalling the termination of the lomagundi jatuli excursion two new u pb id tims isotope dilution thermal ionisation mass spectrometry zircon dates constrain this termination in both successions the lower unit of the il mozero sedimentary formation is a cross and parallel bedded volcaniclastic greywacke derived largely from erosion of the underlying umba volcanic formation it has yielded detrital zircons with 207 pb 206 pb dates as young as 2055 5 2 3 ma which is a maximum age for deposition and is inferred to date part of the underlying umba volcanics in pechenga the kolosjoki sedimentary formation was intersected by a drill hole obtained by the icdp international continental scientific drilling program supported far deep fennoscandian arctic russia drilling early earth project drilling programme zircons from a mafic fine tuff in this drill core have yielded a 207 pb 206 pb age of 2056 6 0 8 ma this age is interpreted as an eruption age contemporaneous with sedimentation the new age determinations overlap each other within uncertainty and is within error of previously published detrital zircon ages of 2058 2 ma from the kolosjoki sedimentary formation and 2049 28 ma from the kuetsjarvi volcanic formation combined these indicate that the lomagundi jatuli excursion terminated across fennoscandia by 2056 6 0 8 ma and may correlate with similar termination ages in fennoscandia and the transvaal south africa

extreme 13ccarb enrichment in ca 2 0 ga magnesite stromatolite dolomite red beds association in a global context a case for the world wide signal enhanced by a local environment abstract the palaeoproterozoic positive excursion of 13 c carb is now considered as three positive shifts of 13 c carb separated by returns to 0 which all occurred between 2 40 and 2 06 ma this isotopic event is unique in terms of both duration 300 ma and 13 c enrichment up to 18 the mechanism responsible for one of the most significant carbon isotopic shifts in earth history remains highly debatable to date 13 c of 10 to 15 cannot be balanced by organic carbon burial forg as there is no geological evidence for an enhanced corg accumulation prior to or synchronous with the excursion instead termination of these excursions is followed by formation of a vast reservoir of 13 c depleted organic material 45 at shunga and by one of the earliest known oil generation episodes at 2 0 ga none of the three positive excursions of 13 c carb is followed by a negative isotopic shift significantly below 0 as has always been observed in younger isotopic events reflecting an overturn of a major marine carbon reservoirs this may indicate that forg was constant implying that the mechanism involved in the production of corg was different onset of intensive methane cycling resulting in c change is another possibility the majority of sampled 13 c carb rich localities represents shallow water stromatolitic dolostones red beds and evaporites formed in restricted intracratonic basins and may not reflect global 13 c carb values closely spaced drill core samples n 73 of stromatolitic dolostones from the 1980 27 ma tulomozerskaya formation in the onega palaeobasin russian karelia have been analysed for 13 c carb and 18 o carb in order to demonstrate that different processes were involved in the formation of 13 c carb rich carbonates the 800 m thick magnesite stromatolite dolomite red beds succession formed in a complex combination of environments on the karelian craton peritidal shallow marine low energy protected bights barred basins evaporative ephemeral ponds coastal sabkhas and playa lakes the carbonate rocks exhibit extreme 13 c enrichment with 13 c values ranging from 5 7 to 17 2 vs v pdb mean 9 9 2 3 and 18 o from 18 6 to 26 0 vs v smow mean 22 0 1 6 the tulomozerskaya isotopic excursion is characteristic of the global 2 4 2 06 ga positive shifts of carbonate 13 c 12 c although it reveals the greatest enrichment in 13 c known from this interval an external basin s is considered to have provided an enhanced corg burial and global seawater enrichment in 13 c the global background value for the isotopic shift at tulomozero time ca 2 0 ga is roughly estimated at around 5 an explosion of stromatolite forming microbial communities in shallow water basins evaporative and partly restricted environments high bioproductivity enhanced uptake of 12 c and pene contemporaneous recycling of organic material in cyanobacterial mats with the production and consequent loss of co2 and ch4 are believed to be additional local factors which may have enhanced 13 c from 5 up to 17 such factors should be taken into account when interpreting carbon isotopic data and attempting to discriminate between the local enrichment in 13 c and globally enhanced 13 c values we propose that many previously reported 13 c values from other localities where environmental interpretations are not available or have not been taken into account may not represent the global 13 c values

secular change in the precambrian silica cycle insights from chert petrology chert deposits preserve a record of secular change in the oceanic silica cycle the evolutionary radiation of silica secreting organisms resulted in a transition from abiological silica deposition characteristic of the archean and proterozoic eons to the predominantly biologically controlled silica deposition of the phanerozoic comparative petrography of phanerozoic and precambrian cherts indicates that an earlier change in chert deposition occurred toward the end of the paleoproterozoic era ca 1 8 ga in neoproterozoic and mesoproterozoic strata early diagenetic chertification is largely restricted to peritidal environments these early diagenetic cherts typically occur as nodules or discontinuous beds within carbonate deposits that have similar depositional textures the cherts formed primarily by carbonate replacement with subsidiary direct silica precipitation some of the paleoproterozoic cherts associated with iron formations however are distinctly different from younger cherts and appear to have formed largely by direct silica precipitation at or just below the seabed these primary cherts lack ghosts or inclusions of carbonate precursors have fine scale grain fracturing possibly from syneresis exhibit low grain packing densities and are not associated with unsilicified carbonate deposits of similar depositional composition cherts in some paleoproterozoic iron formations e g the gunflint formation northwestern lake superior region are composed of silica types similar to those in phanerozoic sinters e g the devonian rhynie and windyfield cherts scotland such cherts may provide evidence that basinal and perhaps global oceanic silica concentrations were higher during the paleoproterozoic era than at later times

potential influence of sulphur bacteria on palaeoproterozoic phosphogenesis all known forms of life require phosphorus and biological processes strongly influence the global phosphorus cycle1 although the record of life on earth extends back to 3 8 billion years ago2 and the advent of biological phosphate processing can be tracked to at least 3 5 billion years ago3 the earliest known p rich deposits appeared only 2 billion years ago4 5 the onset of p deposition has been attributed to the rise of atmospheric oxygen 2 4 2 3 billion years ago and the related profound biogeochemical shifts6 7 8 9 which increased the riverine input of phosphate to the ocean and boosted biological productivity and phosphogenesis5 10 however the p rich deposits post date the rise of oxygen by about 300 million years here we use microfabric trace element and carbon isotope analyses to assess the environmental setting and redox conditions of the 2 billion year old p rich deposits of the vent or seep influenced zaonega formation northwest russia we identify phosphatized microorganism fossils that resemble modern methanotrophic archaea and sulphur oxidizing bacteria analogous to organisms found in modern seep settings and upwelling zones with a sharp redoxcline11 12 we therefore propose that the p rich deposits in the zaonega formation were formed by phosphogenesis mediated by sulphur bacteria similar to modern sites13 and by the precipitation of calcium phosphate minerals on microbial templates during early diagenesis

an early holocene greenland whale from melville bugt greenland abstract radiocarbon age determination of a greenland whale balaena mysticetus vertebra from melville bugt in northwestern greenland yields an age of 9259 8989 cal yr bp the margin of the greenland ice sheet in melville bugt was situated behind its ad 1950 2000 position in the early holocene at a similar position to that being reached following rapid retreat in recent years such an early deglaciation of areas close to the greenland ice sheet is unusual this probably reflects the unique glaciological setting resulting from the narrow fringe of ice free islands and peninsulas and offshore waters with deep areas that characterize this part of greenland the timing of greenland ice sheet retreat to its present margin varies significantly around greenland

global nature of the paleoproterozoic lomagundi carbon isotope excursion a review of occurrences in brazil india and uruguay abstract positive carbon isotope excursion is reported from paleoproterozoic carbonates of the aravalli supergroup northwestern india the minas supergroup brazil and new sections of the paso severino formation uruguay the 2 42 ga gandarela formation minas gerais brazil contains red carbonate facies bif grading into dolostones and limestones and yielding 13 c values ranging from 1 6 to 0 4 v pdb the positive c isotope excursion up to 11 v pdb in marine shallow water carbonates in india and brazil jhamarkotra formation in northwestern india and cercadinho and fecho do funil formations in minas gerais state brazil is comparable to that observed in 2 22 2 1 ga carbonate successions worldwide that were deposited during the lomagundi excursion in uruguay 13 c values up to 11 6 v pdb in the deep water paso severino formation of the piedra alta terrane are compatible with deposition at ca 2 15 ga as indicated by the 2146 7 ma u pb age of dacites occurring at the top of the unit negative 13 c values are also present in carbonates of the paso severino formation but an origin related to organic matter remineralization cannot be ruled out thin carbonate beds in the rio itapicuru greenstone belt bahia state brazil are associated as in the paso severino formation with deep water black shales and have carbon isotope values up to 9 v pdb high metamorphic grade carbonates of the jacurici terrane in the medrado ipueira area bahia brazil have carbon isotope values up to 6 9 v pdb consistent with their minimum age of 2085 5 ma inferred from the intrusive contact with and the age of the medrado norite no evidence was found in india brazil or uruguay for paleoproterozoic glacial events recognized in the 2 45 2 22 ga sedimentary successions worldwide unconformities between the gandarela and cercadinho formations in brazil and the banded gneissic complex and the lower aravalli supergroup in india might explain the absence of glacial record compositional and isotopic data presented here for studied paleoproterozoic carbonate successions allow their integration into the global record of the paleoproterozoic evolution as well as correlation with other successions of similar age the study highlights the global nature of the lomagundi excursion furthermore it indicates that the lomagundi excursion is recorded in both shallow water aravalli and minas supergroups and deep water carbonates paso severino formation and rio itapicuru greenstone belt negating a significant impact of stromatolite productivity and hypersaline conditions on carbon isotope values of carbonates deposited in shallow water open marine and isolated basins

palaeoproterozoic evaporites in fennoscandia implications for seawater sulphate the rise of atmospheric oxygen and local amplification of the δ13c excursion this paper addresses global oxygenation and establishment of a marine sulphate reservoir in the palaeoproterozoic we report syn depositional marine anhydrite containing pseudomorphs after ca sulphates as widespread throughout the tulomozero formation in the se fennoscandian shield implying that surface waters were oxidized and a large so42 marine reservoir was developed as early as 2100 ma the ca sulphates and associated magnesite and halite precipitated syn depositionally from oxidized evolved and modified seawater in coastal playa sabkha and intertidal flat settings sr 87 sr 86 and delta 13 c of associated c 13 rich stromatolitic dolostones were environmentally controlled with the highest ratios occurring in playa and sabkha carbonates the results imply that the palaeoproterozoic delta 13 c carb excursion was amplified by 8 by local environmental factors and calls into question many observations of putative delta 13 c global signals reported previously from similar palaeoproterozoic evaporitic dolostones the local environmental amplification can explain a large regional and intercontinental delta 13 c discrepancy observed in synchronous carbonates

paleoecological studies of a holocene lacustrine record from the kangerlussuaq sondre stromfjord region of west greenland abstract a lacustrine sediment record from the kangerlussuaq region west greenland has resulted in a pollen macrofossil and sediment stratigraphy that encompasses the last 5000 14 c yr deglaciation of the area and subsequent development of a nearby floodplain occurred before 5000 yr b p since that time eolian sand and silt deposition appear to have been continuous with a significant increase ca 1000 14 c yr b p pollen analysis shows little change in the character of the vegetation throughout the record fluctuations in herb pollen taxa indicate changes in the extent and development of eolian sand sheets the oldest pollen zone records relatively little pollen accumulation and low taxa diversity this is followed by a zone of high pollen accumulation presumably a phase of highest vegetation density from 4400 to 3400 14 c yr b p thereafter declining pollen accumulation rates reveal a gradual environmental deterioration macrofossil analyses record significant limnological changes with an early eutrophic phase followed by a masotrophic phase and a reversal to more eutrophic conditions in the final phase the preserved record illustrates the interactions of deglaciation eolian activity regional vegetation and limnological change

multiple palaeoproterozoic carbon burial episodes and excursions organic rich rocks averaging 2 5 total organic carbon and positive carbonate carbon isotope excursions view the mathml source and locally much higher i e the lomagundi jatuli event are hallmark features of palaeoproterozoic successions and are assumed to archive a global event of unique environmental conditions following the c 2 3 ga great oxidation event here we combine new and published geochronology that shows that the main palaeoproterozoic carbon burial episodes cbes preserved in russia gabon and australia were temporally discrete depositional events between c 2 10 and 1 85 ga in northwest russia we can also show that timing of the termination of the lomagundi jatuli event may have differed by up to 50 ma between localities and that ni mineralisation occurred at c 1920 ma further cbes have traits in common with mesozoic oceanic anoxic events oaes both are exceptionally organic rich relative to encasing strata associated with contemporaneous igneous activity and marked by organic carbon isotope profiles that exhibit a stepped decrease followed by a stabilisation period and recovery although cbe strata are thicker and of greater duration than oaes 100 s of metres versus metres 106 years versus 105 years their shared characteristics hint at a commonality of cause s and feedbacks this suggests that cbes represent processes that can be either basin specific or global in nature and a combination of circumstances that are not unique to the palaeoproterozoic our findings urge circumspection and re consideration of models that assume cbes are a deep time singularity

the goias massif implications for a pre columbia 2 2 2 0 ga continent wide amalgamation cycle in central brazil abstract the goias massif is a collage of archean paleoproterozoic terranes that crop out in the central brazil northern brasilia belt and acted as the continental margin onto which neoproterozoic brasiliano orogenic events took place most belts in the massif formed from 2 2 to 2 0 ga a widespread age bracket in the sao francisco congo craton pericratonic areas and other terranes associated with the formation of the atlantica supercontinent however the genesis of the goias massif has always been a matter of debate due to a sharp crustal thickness contrast marked on surface by the trace of the rio maranhao thrust and widely hypothesized as a suture zone the hypothesis that this suture would have been formed when a microcontinent was accreted to the rest of the massif during the neoproterozoic brasiliano orogeny is tested in this paper through mapping and zircon geochronology of rocks along the rio maranhao thrust our study indicates that units contain paleoproterozoic ages have similar geological features to other goias massif 2 2 2 0 ga terranes and show no evidence of syn collisional neoproterozoic magmatism we therefore reinterpret the available data to propose instead that the amalgamation of the massif occurred fully in the paleoproterozoic first the gravimetric contrast marked by the rio maranhao thrust represents in fact a neoproterozoic lower crust delamination event that affected both the brasiliano orogen and the terrane it was accreted against the campinorte arc second serra da mesa suite mesoproterozoic granites intruded both sides of the rio maranhao thrust and thus indicate the two domains were amalgamated prior to the mesoproterozoic finally mesoproterozoic volcanic and plutonic rocks follow the trace of the rio maranhao thrust suggesting a reactivated intracontinental structure rather than an original product of brasiliano collision the goias massif also show important similarities to the sao francisco craton a orogen building and magmatism from 2 2 to 2 0 ga b metamorphic peaks from 2 11 to 2 08 ga c zircon age peaks at 1 76 ga 1 58 ga and 1 2 ga largely attributed to crustal extension events and d contiguous seismic signature from massif to craton these common features allied to our reassessment of central brazil geochronology and the nature of central brazil sharp crustal thickness contrast indicate that the goias massif was fully assembled during a 2 2 2 0 ga orogeny as part of the western border of the sao francisco congo paleocontinent a comprehensive understanding of this orogeny is vital to test the validity of atlantica and to infer the landmasses later involved in the assembly of columbia

temporal constraints on the paleoproterozoic lomagundi jatuli carbon isotopic event the paleoproterozoic lomagundi jatuli positive 13c excursion in sedimentary carbonates represents an event whose magnitude and duration is unique in earth history although precise absolute chronology of this event remains poorly constrained in northeastern fennoscandia an 1300 m thick sedimentary volcanic succession of the pechenga greenstone belt records decline of this isotopic excursion zircons from sedimentary rocks that occur within the decline have yielded 207pb 206pb dates at 2058 2 ma 6 ma including u decay constant uncertainties and provide the first maximum age constraint on the termination of the lomagundi jatuli event combined with existing constraints these data indicate an 140 m y interval characterized by 13c rich carbonate accumulation

palaeoecological studies of holocene lake sediments from west greenland abstract colonisation by plants and animals and subsequent biotic development in west greenland was studied by analyses of macrofossils in four holocene lake sequences one of the lake basins located near the outer coast was deglaciated shortly after the transition from the last glacial stage to the holocene and a basal date of 12 100 11 300 cal years bp was obtained two of the lake basins located near the margin of the greenland ice sheet were deglaciated several millennia later the oldest sediments contain low diversity floras and faunas some of the first immigrants were chironomidae and daphnia pulex soon followed by other insects crustaceans and other invertebrates water mosses ranunculus confervoides hippuris vulgaris and potamogeton filiformis were among the first plants that colonised the lakes the earliest holocene terrestrial flora in west greenland was probably entirely herbaceous with salix herbacea and empetrum nigrum being some of the first woody plants to arrive a number of invertebrates are new to the fossil fauna of greenland and the ostracod ilyocypris bradyi that was found in one sequence from 7000 to 6500 cal years bp has not been recorded from greenland before

depositional setting of the 2 1 ga francevillian macrobiota gabon rapid mud settling in a shallow basin swept by high density sand flows the depositional setting of the 2 1 ga fill to the franceville basin of gabon is important for understanding the habitat energy and availability of light and oxygen and taphonomy of recently discovered early macro organisms buried in black shales in unit fb the available data bearing on the stratigraphy and sedimentology of unit fb provide new insight into processes acting on the palaeo seafloor the shales are interpreted to have formed as fluid mud deposits interstratified with structureless sands the latter poubara sandstones were emplaced during a forced regression during the terminal infill of fault bounded sub basins following a stage characterised by a ferruginous to anoxic water column the structureless sandstones were deposited from high density gravity currents along with a locally strong bottom oscillation of the water column tuft structures preserved in cyanobacterial mats together with the position of the macro organisms at the top of the sandstone beds within associated black shales point to a water depth of less than 80 m the relative sea level fall that drove deposition of the poubara sandstones controlled the rise of a phototrophic ecosystem and also possibly favoured the supply of oxygen and nutrients via density flows this article is protected by copyright all rights reserved

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

holocene environmental variability in southern greenland inferred from lake sediments abstract sediments from qipisarqo lake provide a continuous holocene paleoenvironmental record from southern greenland following deglaciation and glacio isostatic emergence of the basin from the sea 9100 cal yr b p proxies of lake paleoproductivity including biogenic silica and organic matter increased markedly until 6000 cal yr b p and thereafter remained stable over the ensuing warm three millennia subsequent decreases in these proxies most dramatically between 3000 and 2000 cal yr b p show the lake s responses to initial neoglacial cooling intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr b p briefly interrupting the decreasing trend in productivity that culminated in the little ice age increased lake productivity during the latter half of the 20th century which reflects the limnological response to circum arctic warming still has not reached peak holocene values the neoglacial climate of the last 2000 yr includes the most rapid high amplitude environmental changes of the past nine millennia the norse thus migrated around the north atlantic ocean region in the most environmentally unstable period since deglaciation lacustrine sediment records provide a context with which to consider future environmental changes in the labrador sea region in particular any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales

a widespread positive 13ccarbanomaly at around 2 33 2 06 ga on the fennoscandian shield a paradox carbon isotope measurements carried out on 201 carbonate samples from the early proterozoic of the kola peninsula n karelia and norway yield 13c pdb spanning 20 5 to 11 a general 13c secular trend shows that prior to 2 33 ga values are typically normal marine averaging around 3 0 between 2 33 and 2 06 ga in jatulian time there follows a rapid excursion to positive 13c of around 6 post jatulian time is characterized by 13c of sedimentary carbonates fluctuating between 5 and 3 also it is remarkable for the first pronounced development of diagenetic carbonates which have 13c between 14 and 6 the c 6 positive 13c shift with a duration of about 270 myr coincides with a maximum in the diversity and abundance of stromatolites and with widespread development of red beds but does not coincide with the maximum of buried corg mass the fennoscandian shield represents the largest isotoically anomalous carbonate province yet reported and the positive 13c excursion together with a series of major global palaeoenviromental changes seems to be more intense than the precambrian cambrian transition events however it is still not clear what kind of mechanism this phenomenon could be attributed to an increase of the ronov ratio and or broecker ratio and other possible models are discussed as the target for future investigations

sedimentary and volcanic facies recording the neoarchaean continent breakup and decline of the positive δc excursion abstract the palaeoproterozoic kalix greenstone belt at the northern end of the bothnian bay in sweden comprises three groups the lower group a ca 3000 m thick unit of subaerially erupted tholeiitic intraplate basalts interbedded with fluviatile conglomerates represents the volcano sedimentary succession deposited in a rift setting these units are truncated by a break up unconformity above which is the middle group an 800 m thick succession of dolograinstones stromatolitic dolostones arenites volcanoclastic and mafic volcanic rocks stromatolite morphologies and the occurrence of distinctive sedimentary structures including planar and herringbone cross bedding hummocky cross stratification symmetrical and asymmetrical ripples desiccation cracks and tepees indicate markedly variable depositional environments associated with transition from a marine influenced rifted margin to a rimmed carbonate shelf sedimentation was accompanied by subaerial mafic volcanism and syndepositional tectonics the upper group a more than 2000 m thick unit of deep water shales was deposited on the drowned carbonate platform of the middle group in response to tectonically enhanced subsidence this study provides a detailed palaeoproterozoic depositional history of the fennoscandian shield from rifting to passive margin development associated with both dispersal of the neoarchaean supercontinent and decline of the proterozoic positive isotopic excursion of 13 c 12 c in sedimentary carbonates in contrast to many previously reported 13 c rich palaeoproterozoic carbonates which were deposited in non marine to restricted or partly restricted settings the carbonate facies reported herein were well connected to the oceanic realm and thereby represent a good opportunity to test restricted marine versus open marine models for how the carbon cycle functioned in deep time

oxygenated conditions in the aftermath of the lomagundi jatuli event the carbon isotope and rare earth element signatures of the paleoproterozoic zaonega formation russia abstract the c 2 0 ga zaonega formation of the onega basin nw russia has been central in efforts to understand what led to the initial rise great oxidation event goe and postulated fall in free atmospheric oxygen and associated high amplitude carbon cycle excursions the lomagundi jatuli event lje and subsequent shunga event during paleoproterozoic time the formation accumulated shortly after the lje and encompasses both the recovery in the carbon cycle and hypothesised contraction of the oceanic oxidant pool however interpreting the correct environmental context recorded by geochemical signatures in the zaonega rocks is difficult due to a complex depositional and diagenetic history in order to robustly constrain that history we undertook a multiproxy study mineralogy petrography carbon isotope and rare earth element composition of carbonate beds in the upper part of the zaonega formation recovered in the 102 m composite section of the onzap drill cores our findings differentiate primary environmental signatures from secondary overprinting and show that i the best preserved carbonate beds define an upwards increasing 13ccarb trend from c 5 4 to near 0 and that ii large intra bed 13ccarb variations reflect varying contributions of methanotrophic dissolved inorganic carbon dic to the basinal dic pool rare earth element and yttrium reysn patterns confirm a marine origin of the carbonate beds whereas a consistent positive eusn anomaly suggests a strong high temperature hydrothermal input during accumulation of the zaonega formation importantly the presence of a negative cesn anomaly in the reysn pattern indicates an oxygenated atmosphere ocean system shortly after the lje and indicates that models invoking a fall in oxygen at that time require reassessment

reos isotopes and major and trace element geochemistry of carbonaceous shales aravalli supergroup india impact of post depositional processes abstract this study presents re os isotopes and major and trace elemental geochemistry of carbonaceous black shales and a weathering profile developed on them from the paleoproterozoic deposits of the jhamarkotra formation lower aravalli group india these measurements provide information on the impact of post depositional processes particularly hydrothermal fluid interactions on the 187re 187os geochronology and element mobility in shales in contrast to previously reported compositions for black shales the re concentrations of the jhamarkotra shales are in general lower than their corresponding os concentrations the 187os 188os ratios of the black shales vary widely from 3 5 to 10 5 without any discernible systematic trend with 187re 188os range 0 4 to 17 7 excluding an outlier these 187re 188os ratios are lower by a few orders of magnitude than those generally reported for fresh black shales these observations indicate that the jhamarkotra shales though they seem visually well preserved have undergone post depositional modification resulting in open system behavior of re and os with re more mobile than os higher sio2 tio2 and k2o na2o ratios of the jhamarkotra shales compared to their sediment provenance suggest interaction of the shales with hydrothermal possibly si and k rich fluids the sio2 tio2 ratios an index for hydrothermal alteration show negative correlation with re corg and positive correlation with corg n ratios 42 154 indicating loss of re and nitrogen during hydrothermal fluid interaction earlier studies have shown the presence of re porphyrins n containing organic compounds in black shales thus the observed co variations of sio2 tio2 with re corg and corg n ratios suggest mobilization of re from the porphyrins in the shales further positive correlation between sio2 tio2 and 187os 188os ratios indicates that significant amounts of radiogenic os component were re distributed throughout the jhamarkotra shales during the post depositional processes in the weathering profile developed on black shales the al2o3 normalized abundance ratios of mobile major elements are in general lower in the upper layers relative to those in deeper sections attesting to their preferential mobility during chemical weathering on the contrary the al2o3 normalized ratios of trace elements mostly showed insignificant depth variations in the weathering profile suggesting limited mobility over the depth of the profile the depth profiles of re al2o3 and 188os al2o3 and 187os 188os ratios in the weathering profile by and large reflect compositions of their presumed parent shales which have gone through significant post depositional changes

palaeoecology of two lake basins from disko west greenland the macrofossils lithology and chronology of two lake basins on disko in central west greenland have been investigated both lakes were isolated from the sea in the mid holocene as a result of relative land uplift a marine brackish limnic sequence was recovered from the qivittut lake the marine fauna is unusually diverse whereas the brackish water fauna consists only of few species immediately after isolation the lake passed through a short lived eutrophic phase after which stable mesotrophic conditions were established from the second lake basin the fortunebay lake only limnic sediments were recovered this lake record demonstrates that rather stable conditions have persisted since mid holocene times both lakes show anomalously high accumulation rates

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

insights from isotope stratigraphy a symposium on precambrian isotope stratigraphy was heldwithintheframeofthe33rdigcheldatoslo norway august2008 this symposium spawned the idea for a special issue on this themeand ultimately to the ten papers assembled here this special issueprovides the results of some of the latest cutting edge research ontraditional c sr s isotopechemostratigraphyandintroducesomenewer isotope systems ree ca and hg chemostratigraphy as apotential tracer for glacial events and estimate of the buildup ofvolcanicgases includingco

holocene records of effective precipitation in west greenland holocene changes in effective precipitation precipitation evaporation p e were reconstructed for the sondre stromfjord region of southwest greenland using the sediment records of two neighbourin

archean proterozoic collision boundary in central fennoscandia revisited abstract archean proterozoic ap collision boundary in central fennoscandia is a complex collage of archean basement rocks its paleoproterozoic supracrustal cover rocks and svecofennian 1 93 1 78 ga supracrustal and plutonic rocks the apparent steep nature and complexity of the ap boundary has led to contradictory tectonic models varying from arc continent collision via back arc closure to accretion of arc terranes along a strike slip shear zone we present new geochronology data from detrital zircons combined with whole rock geochemical and sm nd isotopic data on paleoproterozoic sedimentary and volcanic rocks across the boundary to revise its nature the 2 06 ga siilinjarvi volcanic complex and associated turbidites with an inferred deposition age at 2 1 2 06 ga are part of the cover sequence the siilinjarvi volcanic rocks derive from both plume oib and sub continental lithospheric mantle sclm magma sources and are often contaminated by the archean crust the sahara suite sedimentary cover rocks are derived from local 1 95 1 92 ga bimodal volcano plutonic source which source also explains the common age population found in younger sedimentary rocks the nalantojarvi suite psammites with maximum depositional ages of 1 97 1 93 ga are continental slope to deep water sediments deposited at the continental margin contemporaneous mafic magmatism seen as lavas and dykes show a change from sclm dominated present east to asthenospheric depleted mantle dm dominated present west melts the interpretation of the nalantojarvi suite as cover rocks of the lower plate indicates that the archean crust continues at least 50 km more to the west than thought earlier parautochthonous sedimentary rocks from salahmi eastern kansanneva and loutemaki with maximum depositional ages at 1 92 1 91 ga are inferred as collision related foredeep deposits from local sources both the lampaanjarvi suite and pyhajarvi suite sedimentary rocks have deposited at 1 89 1 88 ga or later whereas the lampaanjarvi suite rocks are dominated by a local source and the pyhajarvi suite rocks derive from a mixture of older sediments and 1 89 1 88 ga granitoids at least two tectono metamorphic stages separated with a major unconformity can be differentiated in the study area the early deformation and metamorphic stage in the nalantojarvi suite has occurred before the intrusion of the late to post collisional pyroxene granitoids at 1 88 ga the pyhajarvi suite sedimentary rocks have been deposited after the intrusion of these granitoids between 1880 and 1875 ma and then subsequently deformed and metamorphosed at 1875 ma we propose a tectonic model where the continental breakup occurred at 2 1 2 06 ga followed by a new spreading within the pre existing passive margin at 1 98 1 93 ga during initial continent arc collision the subducted slab steepened strongly at high angle subduction ceased rapidly and finally detached and shallow slab breakoff occurred at 1 92 1 91 ga followed subsequently by ophiolite obduction and a formation of a foreland fold and thrust belt mantle crust decoupling of the archean lithosphere occurred and a crocodile jaw formed where the arc rocks are partly buried beneath the bounding archean continent similar features have been recorded in other ap collision zones which could indicate that the buoyant nature of the archean lithosphere combined with denser paleoproterozoic lithosphere may be a general cause for decoupling of archean crust and mantle during arc continent collision in paleoproterozoic

postglacial uplift and relative sea level changes in finnmark northern norway abstract the outer coast of finnmark in northern norway is where the former fennoscandian and barents sea ice sheets coalesced this key area for isostatic modelling and deglaciation history of the ice sheets has abundant raised shorelines but only a few existing radiocarbon dates constrain their chronology here we present three holocene sea level curves based on radiocarbon dated deposits from isolation basins at the outermost coast of finnmark located at the islands soroya and rolvsoya and at the nordkinn peninsula we analysed animal and plant remains in the basin deposits to identify the transitions between marine and lacustrine sediments terrestrial plant fragments from these transitions were then radiocarbon dated radiocarbon dated mollusk shells and marine macroalgae from the lowermost deposits in several basins suggest that the first land at the outer coast became ice free around 14 600 cal yr bp we find that the gradients of the shorelines are much lower than elsewhere along the norwegian coast because of substantial uplift of the barents sea also the anomalously high elevation of the marine limit in the region can be attributed to uplift of the adjacent seafloor after the younger dryas the coast emerged 1 6 1 0 cm per year until about 9500 9000 cal yr bp between 9000 and 7000 cal yr bp relative sea level rose 2 4 m and several of the studied lakes became submerged at the outermost locality rolvsoya relative sea level was stable at the transgression highstand for more than 3000 years between ca 8000 and 5000 cal yr bp deposits in five of the studied lakes were disturbed by the storegga tsunami ca 8200 8100 cal yr bp

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

paleomagnetism and u pb geochronology of the lac de gras diabase dyke swarm slave province canada implications for relative drift of slave and superior provinces in the paleoproterozoicgeological survey of canada contribution 20080350 lac de gras diabase dykes trend north to nne across the central slave province of the canadian shield u pb baddeleyite ages of 2023 2 and 2027 4 ma are interpreted as dyke emplacement ages th

ams radiocarbon dating of organic poor lake sediment an example from linnevatnet spitsbergen svalbard ams radiocarbon dating of specific organic fractions is used to evaluate sources of errors in dating of organic poor lake sediment from linnevatnet a proglacial arctic lake dates on un differentiated bulk organic matter are much too old because of contamination from detrital coal attempts to remove coal from other organic matter were only partially successful a consequence of the wide grain size distribution of the coal even if coal contamination is fully removed the bulk of the remaining organic matter is of aquatic origin and is unsuitable for 14c dating because the lake waters are depleted in 14 c due to dissolution of carbonate minerals terrestrial plant macrofossils provide the only reliable material to date the lake sediment however this material is present in sufficient quantity for ams radiocarbon dating only in cores proximal to the main inlet streams paired dates on terrestrial plants and aquatic insects from the same core level and paired dates on modern aquatic and terrestrial vege

holocene boreal molluscs in greenland palaeoceanographic implications abstract boreal molluscs now extinct in greenland waters occur as subfossils in west greenland between lat 65 30 and 68 30 n a number of new localities for these warmth demanding molluscs are described and the list of species now comprises the gastropod emarqinula fissura and the bivalvalves heteranomia squamula modiolus arctica islandica panopea norvegica and zirphaea crispata during their time the molluscs formed an isolated northern outpost located in the area which as a result of the complex oceanic circulation today has greenland s highest ocean surface temperatures the occurrences are 14c dated to the interval 8400 4900 yr b p and summer surface temperatures were 1 3 c higher than now for its beginning this period coincides with similar marine optimal periods in east greenland and on the baffin island shelf whereas it took 1000 years before the beginning of warmer than present temperatures on land on the basis of this evidence it is concluded that the rise of sea surface temperatures was afforded by a decrease in inflow of cold polar water and or increase in inflow of warm atlantic water into davis strait rather than climatic change

long lived lree mobility in the cratonic rift and foredeep to foreland sedimentary cover at the western margin of the karelia province abstract the western margin of the karelia province of the fennoscandian shield consists of archean crust covered by remnants of paleoproterozoic c 2 5 1 9 ga metasedimentary rocks the study area in the eastern part of the margin shows 2 3 2 1 ga cratonic sedimentation followed by 2 1 2 05 ga rift sedimentation and c 1 91 1 92 ga foredeep to foreland sedimentation related to continent arc continent collision extreme lree mobility loss up 95 of la is recorded by many samples from these units monazite bastnasite and in some cases allanite have been the prealteration lree host phases in the lree depleted samples monazite was altered to th silicates with variable loss of the lree the remaining part of which was incorporated in th poor monazite the depositional age of the sedimentary units was studied by dating la mc icpms detrital zircon grains and the age of lree mobility by dating monazite and xenotime and by whole rock sm nd modeling the maximum deposition age of the foredeep to foreland basin is 1 91 1 92 ga based on detrital zircon data and the minimum age of the main foliation in the study area is 1 87 1 86 ga based on the younger age limit of late to post tectonic xenotime and the ages of few probable metamorphic zircons coeval bastnasite with xenotime in a lree enriched sample suggests that this was also one important stage of lree mobility monazite crystallizations have occurred 1 76 1 78 ga ago while the rb sr whole rock data suggest that the closure of this isotope system took place 1732 21 ma ago the sm nd modeling gives ages at 0 4 1 0 ga for lree depletion the sm nd age of 412 27 ma can be considered as the age of the latest major lree depletion event we propose that alkali bearing oxidizing fluids started to form in the cratonic sequences due to diagenetic reactions maybe as early as 2 3 2 1 ga alkalinity of fluids was later increased by interaction with alkaline 2 05 ga source materials before and during the c 1 91 1 92 ga foredeep to foreland basin stage basin inversion and metamorphic crystallization occurred at 1 91 1 87 ga episodes of fluid migration at 1 78 1 73 ga and afterwards were focused along fracture zones and in microfracture networks the 0 4 ga stage is the most prominent of the

paleomagnetic and geochronological studies on paleoproterozoic diabase dykes of karelia east finland key for testing the superia supercraton paleomagnetic results are presented for two paleoproterozoic mafic dykes in the taivalkoski area in northern karelia province of the fennoscandian shield where based on k ar data the crust has seen minimal effects of the otherwise pervasive 1 8 1 9 ga svecofennian orogeny within this study a new u pb baddeleyite age of 2339 18 ma has been determined for one of the e w trending dykes dyke ad13 the paleomagnetic results show that a strong svecofennian overprinting is pervasive in the area upon thermal or af demagnetization four remanence directions were obtained most typical are the secondary svecofennian remanence direction a intermediate down to the nnw and remanence direction b intermediate down to the nne component d d 115 4 degrees 1 50 5 degrees alpha 95 2 6 degrees yielding a virtual geomagnetic pole vgp d plat 19 5 degrees n plon 263 3 degrees a95 3 1 degrees is obtained from baked rocks for dyke wd and based on a positive baked contact test is interpreted to represent the primary magnetization dating from about 2 4 ga dyke ad13 carries only secondary a and b components its unbaked host migmatites carry reversed a a r component and the baked host rock carries a component d d 134 5 degrees 1 7 3 degrees alpha 95 8 8 degrees which yields a vgp pole d plat 20 4 degrees n plon 257 3 degrees a 95 7 6 degrees possibly representing magnetization at 2 3 ga the new paleomagnetic data from the karelia province compared to similar aged paleomagnetic data from the superior province does not support the recently proposed superia configuration based upon dyke swarm trajectories c 2013 elsevier b v all rights reserved

a paleoproterozoic drowned carbonate platform on the southeastern margin of the wyoming craton a record of the kenorland breakup abstract the nash fork formation in the upper part of the early paleoproterozoic snowy pass supergroup medicine bow mountains of wyoming was deposited on a mature passive margin along the southern flank of the wyoming craton and straddles the end of the ca 2 2 2 1 ga carbon isotope excursion two drowning events marked by black shales subdivide the carbonate platform into three parts the lower nash fork formation consists of outer shelf to supratidal deposits represented by massive and stromatolitic dolomites heterolithic siliciclastics carbonates large silicified domal digitate stromatolites nodular dolomites and stromatolitic dolomites molds after evaporite crystals are pervasive in the heterolithic siliciclastics carbonates large silicified domal digitate stromatolites formed biostromes and bioherms following flooding events the middle nash fork formation comprises two intervals of black shale separated by inner shelf heterolithic siliciclastics nodular carbonates black shales are organic and pyrite rich contain turbidites and developed in response to drowning of the platform overlying massive dolomite of the upper nash fork formation was deposited in an unprotected intertidal setting and displays an upward shallowing trend terminated by a prominent karstic surface in the middle of the unit the nash fork formation is open marine with no evidence for restricted circulation on the carbonate platform the two drowning events on the carbonate platform are likely related to dissection of the mature passive margin associated with the breakup of kenorland the younger drowning event is associated with the end of the carbon isotope excursion the main building elements of the lower and middle nash fork carbonate platform are dolomitic mudstones and stromatolites macroscopic seafloor precipitates are volumetrically negligible with the exception of tufa deposits and domes in the massive and stromatolitic dolomites and possibly digitate stromatolites within domal digitate stromatolites the upper nash fork formation comprises dolomitic mudstones relatively rare stromatolites and inorganic precipitates that are more common than in the underlying carbonates styles of carbonate deposition on this early paleoproterozoic platform differ from those documented on late archean carbonate platforms there are fewer macroscopic seafloor precipitates and more dolomitic mudstones this pattern is considered to be related to a rise of the atmospheric oxygen level that led to a decrease in bicarbonate saturation in the ocean

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

new isotopic and geochemical data from the palaeoproterozoic pechenga greenstone belt nw russia implication for basin development and duration of the volcanism abstract the north pechenga group of the pechenga greenstone belt comprises a thick supracrustal succession developed within a time interval of ca 500 ma in the early part of the palaeoproterozoic era it records several important global events leading to the onset of modern style earth system but the temporal evolution of the belt is still insufficiently established new nd isotope data clearly indicate an abrupt change from a strong crustal signature in the lower two volcanic units to a depleted mantle like signature in the upper two volcanic units which conforms with the coeval shift of the volcanism from subaerial to submarine indicating a significant thinning of the lithosphere due to continental rifting the timing of the change in the geotectonic regime can be bracketed between 2058 6 ma u pb data and 2018 54 ma sm nd data in situ ion microprobe analyses of zircon grains from a thin felsic tuff member in the upper part of the succession pilgujarvi volcanic formation produced an age of 1988 3 ma which is within error the same as has been reported previously for the ferropicritic magmatism that produced the pechenga ni cu ores it is concluded that the upper 3 km thick volcanic pile dominated by tholeiitic basalts and minor ferropicrites was generated within a short time span unresolvable with current geochronological tools geochemical and isotopic data suggest that the felsic tuffs were generated from a ferropicritic parental magma via extensive fractional crystallisation and the presence of gneiss xenoliths in the tuffs reveals that this happened in a magma chamber located in the underlying archaean basement thus although the mafic subaqueous volcanism of the upper part of the belt does not bear nd isotopic or trace element evidence for contamination with ancient crustal material the rifting of the basement did not yet proceed to a total break up of the archaean craton

rock magnetic and paleomagnetic study of the keurusselka impact structure central finland abstract there are 31 proven impact structures in fennoscandia one of the most densely crater populated areas of the earth the recently discovered keurusselka impact structure 62 08 n 24 37 e is located within the central finland granitoid complex which formed 1890 1860 ma ago during the svecofennian orogeny it is a deeply eroded complex crater that yields in situ shatter cones with evidence of shock metamorphism e g planar deformation features in quartz new petrophysical and rock magnetic results of shocked and unshocked target rocks of various lithologies combined with paleomagnetic studies are presented the suggested central uplift with shatter cones is characterized by increased magnetization and susceptibility the presence of magnetite and pyrrhotite was observed as carriers for the remanent magnetization four different remanent magnetization directions were isolated 1 a characteristic svecofennian target rock component a with a mean direction of d 334 8 i 45 6 95 14 9 yielding a pole plat 51 1 plon 241 9 a95 15 1 2 component b d 42 4 i 64 1 95 8 4 yielding a pole plat 61 0 plon 129 1 a95 10 6 3 component c d 159 5 i 65 4 95 10 7 yielding a pole plat 21 0 plon 39 3 a95 15 6 and 4 component e d 275 5 i 62 0 95 14 4 yielding a pole plat 39 7 plon 314 3 a95 19 7 components c and e are considered much younger possibly neoproterozoic overprints compared with the components a and b the pole of component b corresponds with the 1120 ma pole of salla diabase dyke and is in agreement with the 40ar 39ar age of 1140 ma from a pseudotachylitic breccia vein in a central part of the structure therefore component b could be related to the impact and thus represent the impact age

chemostratigraphy of carbonates from the minas supergroup quadrilatero ferryifero iron quadrangle brazil a stratigraphic record of early proterozoic atmospheric biogeochemical and climactic change the ca 2 42 ga old gandarela formation overlies the finely laminated caue banded iron formation bif of the itabira group minas supergroup brazil and consists of red carbonate facies bif grading upsection into buff dolomites and limestones which are locally stromatolitic carbonates of the gandarela formation have 1 3 c values ranging narrowly from 1 6 to 0 4 permil versus pdb n 93 the cercadinho formation at the base of the overlying piracicaba group is a thick arenaceous succession with rare thin carbonates that have 1 3 c values ranging from 3 3 to 5 4 permil n 12 stromatolitic dolomites of the overlying fecho do funil formation have pb pb carbonate age 2 11 0 11 ga babinski and others 1995 that provide the minimum age for this unit and 1 3 c values ranging from 5 6 to 7 4 permil n 69 at present we find no evidence in brazil for the any of the three early paleoproterozoic glacial events recognized in 2 45 to 2 22 ga sedimentary successions in north america given the radiometric constraints however it is possible that geological and geochemical traces of these ice ages are missing along the unconformity between the gandarela and cercadinho formations if correct carbonates of the gandarela formation may provide a record of the carbon isotope composition of the seawater prior to any of the paleoproterozoic ice ages combined with other available 1 3 c data results from the gandarela formation suggest that seawater preceding the ice ages was not significantly enriched in 1 3 c on the other hand the carbon isotopic signature of the cercadinho carbonates and chemical composition of the cercadinho arenites are consistent with deposition after the end of the glacial epoch and likely during the early stage of ca 2 22 to 2 1 ga carbon isotope excursion the 1 3 c values of marine carbonates of the fecho do funil formation are consistent with carbon isotope record of contemporaneous carbonate successions worldwide providing additional evidence for a global biogeochemical anomaly at ca 2 22 to 2 1 ga these compositional and isotopic changes allow integration of the minas supergroup into the global record of the paleoproterozoic evolution as well as correlation with other successions of similar age

stratified interglacial lacustrine sediments from baffin island arctic canada chronology and paleoenvironmental implications abstract thirteen of 18 piston cores recovered from robinson lake in the mid arctic vegetation zone of baffin island arctic canada penetrated stratified lacustrine sediment beneath a thin over consolidated diamict till and postglacial lacustrine sediment the sub till lacustrine units are up to 120 cm thick of which the upper several decimeters frequently contain thick layered mats of aquatic moss pollen and diatoms are common throughout both lacustrine units a series of 23 ams 14c dates defines the chronology of the postglacial sequence which records a succession from a pioneer grass and oxyria dominated tundra between 10 4 and 8 ka bp to a sedge dominated tundra after 8 ka bp limiting 14c dates place the sub till lacustrine sediments more than 40 ka bp 10 luminescence dates centered on 85 ka indicate they were deposited late in oxygen isotope stage ois 5 the dominance of shrub and tree pollen especially shrub birch and alder in sub till lacustrine samples indicates low arctic tundra farther north than at any time during the holocene pollen concentrations are comparable to or higher than in the holocene units cooling late in the interglacial is indicated by declining birch and alder pollen percentages in the upper part of the section diatom floras in both the sub till and postglacial lacustrine sequences indicate similar development of lake water chemistry but input of silica and weathering products was greater in the older lake cycle suggesting more vigorous catchment processes macrofossils in the sub till units are characteristic of lakes ice free in summer based on pollen assemblages indicating local and regional vegetation diagnostic of summer temperatures higher than the holocene we interpret the sub till lacustrine units to be of interglacial character by analogy with holocene plant succession in central and eastern canada all of keewatin and labrador ungava must have been ice free throughout this interval suggesting essentially complete deglaciation of the laurentide ice sheet at the time

on the lomagundi jatuli carbon isotopic event the evidence from the kalix greenstone belt sweden we report a significant new database on the carbon and oxygen isotopic analyses 233 whole rock and 43 microcored samples obtained from sedimentary dolostones in the kalix greenstone belt from the fennoscandian shield of sweden this characterises the second half of the prominent palaeoproterozoic lomagundi jatuli positive carbon isotope excursion within a 600 m thick succession of alternating volcanic volcaniclastic siliciclastic and dolomitic rocks from greenschist epidote amphibolite metamorphic facies the least altered dolostone samples show a gentle oscillation between 2 and 4 throughout stratigraphy with a second order positive excursion from 4 through 8 and gradually back again to 4 in the c 150 m thick unit in the middle and upper parts of the succession this second order excursion is superimposed on the general relatively rapid 13c decline at the second half of the lomagundi jatuli isotopic event and coincides with the transition from a marine influenced rift to a passive margin setting if the excursion is global it would reveal internal fine structure of the lomagundi jatuli isotopic excursion if not basinal local factors are the main players lithostratigraphic and c isotope correlation between kalix and neighbouring perapohja schist belt successions 40 km apart suggest an incomplete geological record in both successions despite the absence of obvious non depositional unconformities

identifying global vs basinal controls on paleoproterozoic organic carbon and sulfur isotope records abstract paleoproterozoic sedimentary successions are important archives of the redox evolution of earth s atmosphere and oceans efforts to unravel the dynamics of our planet s early oxygenation from this archive rely on various geochemical proxies including stable carbon and sulfur isotopes however ancient metasedimentary rocks often experienced early and late stage bio geochemical processes making it difficult to discern primary environmental signals from bulk rock 13corg and 34s values such complexity in carbon and sulfur isotope systematics contributes to uncertainty about the redox structure of paleoproterozoic oceans a currently popular idea is that following the great oxidation event global changes led to low oxygen environments and temporally fluctuating ocean redox conditions that lasted until the neoproterozoic the volcano sedimentary rocks of the onega basin have figured prominently in this concept particularly the exceptionally organic rich rocks of the 1 98 ga zaonega formation however a growing body of evidence shows that local depositional processes acted to form the 13corg and pyrite 34s records of the zaonega formation thus calling for careful assessment of the global significance of these isotope records placing new and existing organic carbon and sulfur isotope data from the zaonega formation into the context of basin history and by comparing those results with key paleoproterozoic successions of the francevillian basin gabon the pechenga greenstone belt nw russia and the animikie basin canada we show that the stratigraphic 13corg and pyrite 34s trends can be explained by local perturbations in biogeochemical carbon and sulfur cycling without requiring global drivers despite their temporal disparity we also demonstrate that individual successions share certain geological traits e g magmatic and or tectonic activity hydrocarbon generation basin restriction suggesting that their pyrite 34s and 13corg trends were governed by common underlying mechanisms e g similar basinal evolution and biogeochemical feedbacks and are not necessarily unique to certain time intervals we further show that pyrites in these successions that are most likely to capture ambient seawater sulfate isotopic composition have consistent 34s values of 15 18 which hints at remarkable stability in the marine sulfur cycle over most of the paleoproterozoic era

redox stratification and anoxia of the early precambrian oceans implications for carbon isotope excursions and oxidation events abstract an updated compendium of 13c data offer compelling evidence that 13c positive excursions of unsurpassed magnitude in the recorded earth history 8 and up to 18 pdb occurred in the early proterozoic the lomagundi event questions whether or not these unprecedented positive 13c shifts were contemporaneous in various basins and represent local or global events remain unresolved the framework of major geologic events that occurred in the paleoproterozoic argues against a snowball earth scenario as a backdrop to these exceptional 13c enrichments substantial increases of carbon flux ratio fo fc eight times the phanerozoic average and organic carbon burial rate fo three times the phanerozoic average are required to account for the observed 13c enrichments under steady state and dynamic equilibrium modes respectively these enhanced ratios and rates are conditional on the availability of a flux of nutrients to the contemporaneous biota producers in excess of the riverine flux and a decoupling of the p and c cycles it is argued that these two conditions were met between 2 25 and 2 11 ga in a redox stratified ocean with weak upwelling and sluggish meridional surface circulation the alternative that the major disturbance in the terrestrial carbon cycle occurred in a rapidly ventilated ocean is assessed as being unlikely a large pulse of o2 equivalent to six to seven times the present terrestrial oxygen budget was rapidly scavenged and spent in the oxidation of reduced fe and s transported to the shelves by rivers this contention is consistent with data inferring low oxygen levels 10 5 to 10 2 pal in the paleoproterozoic atmosphere and the occurrence of ocean anoxia until the late precambrian

kolosjoki sedimentary formation a record in the aftermath of the paleoproterozoic global positive δ13c excursion in sedimentary carbonates abstract the kolosjoki sedimentary formation of the pechenga greenstone belt north eastern fennoscandia records the aftermath of the paleoproterozoic global positive 13 c excursion in sedimentary carbonates the lomagundi jatuli isotope excursion the goals of this research were to provide detailed new data on the 13 c trend in the kolosjoki sedimentary formation and generate a secular 13 c curve for the time period immediately succeeding the lomagundi jatuli isotope excursion for these purposes sedimentary carbonate samples from two new drillcores representing the kolosjoki sedimentary formation were collected in total 88 whole rock samples and 67 micro drilled subsamples ca 1 3 mg were analyzed for the isotope composition of c and o the whole rock elemental abundances and for the composition of the acid soluble fraction the kolosjoki carbonate rocks are dolostone or calcitic dolostone mg ca 0 50 0 67 with minor limestone mg ca 0 04 0 06 only weak correlation was observed between the mn sr ratios and the 13 c and 18 o values and the carbonate samples have likely retained their near primary 13 c values the sedimentary carbonate rocks show first low 13 c values at 2 to 1 and then a subtle upward increasing 13 c trend from ca 1 to 3 the increasing 13 c trend is interpreted to record a recovery from a 13 c minimum following the lomagundi jatuli isotope excursion

holocene development of the fauna of lake boeckella northern antarctic peninsula the origins of the freshwater fauna that inhabits antarctic lakes are poorly known the species present today could be relict species that have survived quaternary glaciations on the continent or holocene migrants from more temperate regions one approach to investigating these questions is to study faunal microfossils in lake sediment this approach was applied to a 293 cm sediment core from lake boeckella located at the northern tip of the antarctic peninsula the microfossils indicated that most of the metazoan species that occur in the lake today have been present since soon after the lake s formation c 5 5 ka ago in particular the centropagid copepod boeckella poppei mra zek has been present throughout the lake s history suggesting a local source for this species the development of biodiversity in the lake with time was in general more consistent with local antarctic rather than distant south american sources though an alternative explanation is that dispersal to antarctica was more efficient in the mid holocene evidence of dispersal from extra continental sites comes from the scattered occurrence throughout the core of eubosmina chilensis daday a south american species that does not reach the antarctic or the sub antarctic islands at present and which failed to establish a permanent population in the lake

paleomagnetism and rock magnetic cyclostratigraphy of the ediacaran doushantuo formation south china constraints on the remagnetization mechanism and the encoding process of milankovitch cycles abstract south china provides exceptional and unique sedimentary archives of earth s fundamental changes in ediacaran time however the lack of robust geochronological constraints renders a poorly defined chronostratigraphic framework for ediacaran aged strata in south china thus making it difficult to understand earth s critical changes during this time interval magnetostratigraphy and rock magnetic cyclostratigraphy turn out to be a few reliable methods in chronostratigraphic studies especially in the precambrian here we present a detailed paleomagnetic and rock magnetic study of the ediacaran doushantuo formation in the huanglianba section guizhou province south china the section consists of 75 m thick carbonate succession and has a record of one of the largest carbon isotope excursions in the earth history known as the shuram excursion stepwise thermal demagnetization of doushantuo carbonates reveals single component magnetizations that yield a paleomagnetic pole consistent with the late triassic segment of the apparent polar wander path of south china the secondary origin of doushantuo carbonates magnetization is supported by their magnetic mineralogy based on various rock magnetic experiments and scanning electron microscopic analyses we interpret that the secondary magnetization resides mainly in authigenic pyrrhotite that likely precipitated from the reducing fluids during the late stage of indosinian orogeny in the triassic interestingly the companion high resolution cyclostratigraphic study of a 4 m thick succession at the upper layers of the doushantuo formation in the huanglianba section indicates that the milankovitch cycles were encoded in the variation of magnetic susceptibility immune from the influence of remagnetization variation of magnetic susceptibility is attributed to changes in the abundance of paramagnetic minerals which by implication means that the amount of terrestrial materials transported from the continent was regulated by milankovitch cycles during the deposition of doushantuo carbonates therefore our results suggest that even though carbonates are prone to remagnetization astronomical modulation of deposition could be encoded in rock magnetics of the remagnetized carbonates as a result rock magnetic cyclostratigraphy has potential in remagnetized carbonates for providing a floating astronomical timescale that can be applied to constrain sediment accumulation rates estimate the duration of geological events and construct high resolution chronostratigraphies

hydrothermal dedolomitisation of carbonate rocks of the paleoproterozoic zaonega formation nw russia implications for the preservation of primary c isotope signals abstract the paleoproterozoic zaonega formation in karelia nw russia has played a key role in understanding the environmental conditions postdating the great oxidation and lomagundi jatuli events its carbonate and organic rich rocks shungite define the postulated shunga event representing an accumulation of very organic rich sediments at c 2 ga and are central in ideas about changing ocean atmosphere composition in the wake of those worldwide biogeochemical phenomena our work focussed on a key interval of carbonate rocks in the upper part of the formation to i obtain new high resolution carbon oxygen and strontium isotope data complemented by detailed petrography and mineralogical characterisation and ii expand upon previous studies by using our data to constrain geochemical modelling and show in greater detail how magmatic hydrothermal fluids induced dedolomitisation and altered geochemical signals our findings show that the 13ccarb of calcite rich intervals are the most altered with values between 16 9 to 0 6 whereas the dolomite dominated parts retain the best preserved i e most original values those define a trend of steadily increasing 13ccarb from 6 to 0 5 which we interpret as a return to normal marine conditions and carbonate carbon values following the lomagundi jatuli event

hydrothermal circulation and oil migration at the root of the heterogeneous micro structure of carbonaceous material in the 2 0 ga zaonega formation onega basin russia abstract organic rich rocks of the 2 0 ga zaonega formation karelia russia have been studied extensively to gain understanding of the global carbon cycle and reconstruction of paleo environments directly after the great oxidation event goe this formation has a complex history of alteration involving pervasive hydrothermal circulation hydrocarbon generation migration and mineral authigenesis several previous studies have focused on the description of these secondary effects and the identification of primary geochemical signals in the carbonaceous phases migration and infiltration of organic rich fluids appear to have had only limited effect on the primary carbon isotope record 13corg however the structural variability of carbonaceous material cm appears to have been strongly affected with a range of reported structures including carbon onion shaped nanostructures and mineral templated graphite films here we present a systematic raman spectroscopy based study of the structural variability of cm in a drill core representing the middle and upper strata of the zaonega formation the raman spectra of cm show a systematic difference in structural order between the bulk carbonaceous matrix matrix cm and the cm occurring near mineral contacts contact cm indicating that mineral templating was an important process affecting structural order in the formation the templating effect was observed on the surface of a wide range of minerals the difference in structural order between matrix cm and contact cm can be traced throughout the ca 400 m stratigraphy the structural order varied with the degree of alteration and hydrothermal circulation from highly ordered structures directly above a large gabbro intrusion at the bottom of the stratigraphy to less ordered structures higher up in the sequence this trend directly correlates with the 18o trend of secondary calcite and can be attributed to the decreasing influence and temperature regime of hydrothermal circulation upward in the stratigraphy the results presented here suggest that organic rich hydrothermal fluids can locally strongly enhance graphitization of carbonaceous materials and cause sample scale heterogeneities in the structural order of organic materials this has implications for the interpretation of carbonaceous materials in other ancient rocks experiencing circulation of organic rich hydrothermal fluids

isotopic evidence for massive oxidation of organic matter following the great oxidation event the stable isotope record of marine carbon indicates that the proterozoic eon began and ended with extreme fluctuations in the carbon cycle in both the paleoproterozoic 2500 to 1600 million years ago ma and neoproterozoic 1000 to 542 ma extended intervals of anomalously high carbon isotope ratios 13c indicate high rates of organic matter burial and release of oxygen to the atmosphere in the neoproterozoic the high 13c interval was punctuated by abrupt swings to low 13c indicating massive oxidation of organic matter we report a paleoproterozoic negative 13c excursion that is similar in magnitude and apparent duration to the neoproterozoic anomaly this shunga francevillian anomaly may reflect intense oxidative weathering of rocks as the result of the initial establishment of an oxygen rich atmosphere

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

petrography and geochemistry of carbonate rocks of the paleoproterozoic zaonega formation russia documentation of 13c depleted non primary calcite the norwegian research council grant 191530 v30 to v a melezhik fully funded the work of aec vam and al atb was supported by nerc grant ne g00398x 1 to aef and arp we are grateful for sample preparation and analyses to all the personnel at ngu lab we appreciate the work on carbon and oxygen isotope analyses by julie dougans and chris taylor bojan otonicar organized and helped with the cl work at the karst research institute at postojna arrangement of toc ic and tc analyses at university of munster is acknowledged to harald strauss

the ree composition and petrography of apatite in 2ga zaonega formation russia the environmental setting for phosphogenesis the first significant p rich deposits appear in the global rock record during the paleoproterozoic around 2 ga however the specific triggers that led to apatite precipitation are still under debate the ca 2 ga zaonega formation karelia russia contains p rich intervals in its upper part with abundantly occurring apatite these apatites have been studied for their rare earth element ree composition using laser ablation inductively coupled plasma mass spectrometry la icp ms with an emphasis on the environmental condition during phosphogenesis petrographic observations by scanning electron microscopy sem integrated with la icp ms results allow recognition of variously recrystallized apatite and distinction of best preserved diagenetic apatite which presumably records syn depositional ree characteristics diagenetic apatite exhibits moderately negative ce anomalies that indicate an at least partially oxygenated water column a variable but typically positive eu anomaly is consistent with geologic evidence suggesting intensive magmatic activity and hydrothermal influence during apatite precipitation we conclude that phosphatic sediments in the paleoproterozoic zaonega formation record phosphogenesis in a vent seep influenced setting that experienced fluctuating redox conditions at the sediment water interface

sr isotopic composition of paleoproterozoic 13c rich carbonate rocks the tulomozero formation se fennoscandian shield abstract rb sr systematics has been studied in 13c rich carbonate rocks of the paleoproterozoic 2 09 0 07 ga tulomozero formation in the northern onega lake area the se fennoscandian shield the formation is divided into eight members a f consisting of greenschist facies grade variegated sandstones siltstones mudstones stromatolitic dolostones and subordinate crystalline limestones samples of carbonate rocks were obtained from two overlapping drillholes intersecting the entire thickness of the tulomozero formation prior to isotope analysis the rocks powders were treated with 1n ammonium acetate for partial removal of the late epigenetic carbonate phases major resetting of the rb sr systems in the tulomozero carbonate rocks appears to take place during the svecofennian regional metamorphic event and it was screened by using mn sr fe sr mg ca and 18o 16o ratios high sr content up to 2080 g g in limestones and 530 g g in dolostones coupled with low fe mn 0 40 in dolostones of the upper part of member b and of members g and h is indicative of seawater influxes sea transgression into the tulomozero basin the 87sr 86sr values in the least altered mn sr

a review of temporal constraints for the palaeoproterozoic large positive carbonate carbon isotope excursion the lomagundi jatuli event abstract the palaeoproterozoic lomagundi jatuli event is one of the largest magnitude and earliest known positive carbonate carbon isotope excursions preserving 13 c values between 5 and 16 and even higher it is recorded in sedimentary rocks on all continents bar antarctica and spans stratigraphic thicknesses ranging from several to many tens of metres this unique positive 13 c interval signals fundamental changes in the global carbon cycle and is a key event in earth system evolution following oxygenation of earth s atmosphere here we present a comprehensive review of the age constraints on the lomagundi jatuli event the first such effort in two decades this new chronology compilation focuses on the u pb and re os chronometers and demonstrates that global synchronicity of the lomagundi jatuli event is permissible an interpretation supported by the apparent wide dispersion of lomagundi jatuli event bearing successions in the most recent palaeoproterozoic plate reconstructions assuming the lomagundi jatuli event is synchronous worldwide then the bounds on its duration range from a maximum of 249 9 myr 2306 9 ma to 2057 1 ma to a minimum of 128 9 4 myr 2221 5 ma to 2106 8 ma

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

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

weathering during the great oxidation event fennoscandia arctic russia 2 06 ga ago abstract the establishment of an oxygen rich atmosphere between 2 4 and 2 0 billion years ago ga is one of the defining events in earth history however the nature of the transition from an anoxic atmosphere is poorly resolved with interpretations relying heavily on empirical evidence that is poorly calibrated and not supported by numerical modeling in an attempt to characterize the nature timing and impact the great oxidation event goe had on earth s surface the fennoscandian arctic russia drilling early earth project far deep targeted the archean proterozoic transition exposed in the eastern part of the fennoscandian shield far deep recovered more than 400 m of the highly oxidized 2 06 ga kuetsjarvi volcanic formation kvf which is potentially a manifestation of when atmospheric oxygen levels exceeded the ultimate proterozoic steady state identifying the timing and extent of oxidation within the kvf are the primary objectives of this study the presence of secondary hematite within fractures and amygdales indicates that the elevated oxidation state of the kvf is not a primary feature of the rocks immediately below the erosional surface marking the top of the kvf the degree of iron oxidation scales with the degree of chemical weathering implying that oxidation of the kvf is the result of interaction with oxygen charged groundwaters during subaerial exposure the incorporation of rounded clasts with conspicuous hematite rinds into the overlying kolosjoki sedimentary formation indicates that the oxidation of the kvf occurred prior to its deposition the oxidized regolith recovered in the far deep drill cores is more oxidized for the degree of weathering observed compared to older precambrian and archean aged paleosols but not anomalously so compared to younger proterozoic paleosols this observation suggests that the kuetsjarvi regolith was created during the progressive increase of po2 towards the proterozoic steady state using a previously published mass balance model to infer paleoatmospheric pco2 and po2 we are unable to provide any useful constraint on the paleoatmospheric pco2 and po2 levels we estimate that the paleoatmospheric pco2 and po2 levels ca 2 06 ga ago in fennoscandia were between 0 4 and 6 500 times present atmospheric level pal and 1 10 3 and 12 times pal respectively the wide range in the calculated pco2 and po2 levels is the result of the pco2 model calculations being extremely sensitive to key parameters that are nearly impossible to estimate accurately for ancient paleosols e g the annual precipitation rate depth to the groundwater table and the amount of time it took the soil to form

sedimentation patterns during the precambrian a unique record abstract although the similarities between depositional processes and products as well as the analogous controls on basin filling and evolution appear to have enjoyed great uniformity throughout the sedimentary rock record a noticeable distinction exists in the rates and intensities of a broad range of geological processes in the precambrian epoch this paper searches for distinctiveness in the precambrian sedimentary record both siliciclastic and carbonate through an extensive though not exhaustive review of the relevant literature augmented by new observations while differences in precambrian deltaic aeolian glacial and possibly also lacustrine deposits and settings appear to have been small their large scale development was controlled largely by a combination of temporal and geodynamic influences essentially of global compass in this regard the onset of the supercontinent cycle and major perturbations in palaeo atmospheric composition appear to have been significant marine environments provide a poor platform for precambrian phanerozoic comparisons of sedimentation patterns as those from the former period are preserved almost exclusively in epeiric settings an environment essentially lacking on modern earth for the shallow marine carbonates biological mediation of chemical sediment deposition changed radically from dominance by microbial biota in the precambrian to a combination of metazons protozoans and algae for the skeletal carbonates of the phanerozoic despite it being widely recognized that precambrian channel systems were braided in all environments deltaic tidal alluvial fluvial as a consequence of the lack of vegetation and poor development of soils the fluvial setting has some enigmatic aspects amongst these is evidence for ponding of muddy detritus in apparently sandstone bed load dominated braided systems with effects on local palaeoslopes which have resulted in unusual palaeohydraulic parameters for precambrian fluvial systems this is perhaps a field of research which holds greater promise when investigating sedimentation patterns prior to the phanerozoic

tracking lateral δ13ccarb variation in the paleoproterozoic pechenga greenstone belt the north eastern fennoscandian shield abstract the kuetsjarvi sedimentary formation ksf records the global paleoproterozoic ca 2200 2100 ma positive 13 c excursion of sedimentary carbonates this event is here called as the lomagundi jatuli isotopic excursion in this study lateral 13 c carb variation in the ksf and local basinal factors amplifying global 13 c carb value were investigated and a secular 13 c curve for the ksf was constructed sedimentary carbonate samples from a new drillcore drillcore 5a from the ksf were analysed for 13 c 18 o and selected major and trace elements the 13 c values of the samples vary from 5 to 8 vpdb and the 18 o values from 18 to 10 vpdb most of the samples have retained their primary c isotopic composition as they do not show correlation between the mn sr ratios and the 13 c and 18 o values the new results were compared to those previously obtained from another drillcore drillcore x from the ksf ca 25 km along strike from drillcore 5a both cores show a similar kind of generally upward decreasing trend in 13 c excluding some negative and positive spikes in drillcore x and samples close to a contact with a fe picrite dyke in drillcore 5a a secular 13 c curve of the ksf was constructed based on the least altered 13 c data from the cores 5a and x the secular 13 c curve of the ksf may represent the latest part of the lomagundi jatuli isotopic excursion

fractionation between inorganic and organic carbon during the lomagundi 2 22 2 1 ga carbon isotope excursion article i nfo the lomagundi 2 22 2 1 ga positive carbon isotope excursion in shallow marine sedimentary carbonates has been associated with the rise in atmospheric oxygen but subsequent studies have demonstrated that the carbon isotope excursion was preceded by the rise in atmospheric oxygen the amount of oxygen released to the exosphere during the lomagundi excursion is constrained by the average global fractionation between inorganic and organic carbon which is poorly characterized because dissolved inorganic and organic carbon reservoirs were arguably larger in the paleoproterozoic ocean at a time of lower solar luminosity and lower ocean redox state decoupling between these two variables might be expected we determined carbon isotope values of carbonate and organic matter in carbonates and shales of the silverton formation south africa and in the correlative sengoma argillite formation near the border in botswana these units were deposited between 2 22 and 2 06 ga along the margin of the kaapvaal craton in an open marine deltaic setting and experienced lower greenschist facies metamorphism the prodelta to offshore marine shales are overlain by a subtidal carbonate sequence carbonates exhibit elevated 13 c values ranging from 8 3 to 11 2 vs vpdb consistent with deposition during the lomagundi positive excursion the total organic carbon toc contents range from 0 01 to 0 6 and 13 c values range from 24 8 to 13 9 thus the isotopic fractionation between organic and carbonate carbon was on average 30 3 2 8 n 32 in the shallow marine environment the underlying sengoma shales have highly variable toc contents 0 14 to 21 94 and 13 c values 33 7 to 20 8 with an average of 27 0 3 0 n 50 considering that the shales were also deposited during the lomagundi excursion and taking 13 c values of the overlying carbonates as representative of the 13 c value of dissolved inorganic carbon during shale deposition a carbon isotope fractionation as large as 37 appears to characterize the production of bulk organic matter in the deeper part of the pretoria basin at that time this enhanced fractionation relative to that observed in shallow water environments likely reflects heterotrophic secondary and chemotrophic productivity at and below a pronounced redoxcline consistent with the euxinic conditions inferred from independent evidence for the deeper part of the pretoria basin greater variability in organic carbon vs carbonate carbon isotopic values on the shallow marine carbonate platform suggests that the carbon cycling was dominated by a large dissolved inorganic carbon reservoir during the lomagundi excursion our study suggests that in contrast to the late neoproterozoic and phanerozoic when carbon isotope fractionation between carbonate and organic carbon in the open ocean was mostly controlled by primary producers in the paleoproterozoic redox stratified ocean heterotrophic and chemotrophic productivity overprinted a signal of primary productivity below the redoxcline this strong imprint of heterotrophic and chemotrophic productivity on organic carbon isotope records complicates the reconstruction of spatial patterns and secular trends in the 13 c values of dissolved inorganic carbon in the paleoproterozoic seawater

exceptional preservation of expandable clay minerals in the ca 2 1 ga black shales of the francevillian basin gabon and its implication for atmospheric oxygen accumulation abstract clay minerals are exceptionally well preserved in marine black shale of the ca 2 1 ga francevillian group in southeastern gabon the fb formation of the francevillian group is characterized by smectite rich clay minerals including randomly ordered r0 type and ordered r1 type mixed layer illite smectite i s the preservation of r0 type clay minerals suggests unexpectedly slow mineral transformation and a moderate degree of diagenesis which is unique considering the paleoproterozoic age of the sedimentary rocks r0 and r1 type smectite rich particles occur in stratigraphic intervals with high organic carbon content and are associated with carbonaceous filamentous structures suggesting formation of clay organic matter complexes our data suggests that clay minerals may have enhanced organic matter preservation providing the oldest example where a link between clay minerals and organic matter sequestration can be established our findings are consistent with the hypothesis that clay minerals enhanced organic carbon burial and aided in atmospheric oxygen accumulation through time

synsedimentary diagenetic and metamorphic pyrite pyrrhotite and marcasite at the homestake bif hosted gold deposit south dakota usa insights on au as ore genesis from textural and la icp ms trace element studies the paleoproterozoic homestake deposit northern black hills south dakota is the largest banded iron formation bif hosted gold deposit in the world and one of the largest single gold deposits globally 1 300 t au mined at an average grade of 8 4 g t the origin of the deposit has remained in dispute from its discovery with views broadly falling into two groups 1 the gold and associated elements were externally sourced and deposited in a suitable structural and or chemical trap e g iron formation and 2 gold was indigenous to the host iron formation from which it was remobilized into dilatant structural zones during deformation and metamorphism in recent times most workers have favored the former model appealing to the broad synchroneity of paleoproterozoic metamorphism felsic magmatic activity and gold event timing la icp ms analysis of synsedimentary to early diagenetic sulfides at homestake and surrounding area indicates that the au in the orebodies may have originally had a significant syngenetic component in particular la icp ms mapping of multistage pyrites from carbonaceous shale in the upper poorman formation shows that au and a suite of trace elements co ni cu zn se mo ag sb te au hg tl pb and bi similar to those in diagenetic pyrite from around the globe are contained in anhedral sponge textured cores and nodules surrounded by relatively trace element barren au poor euhedral pyrite rims furthermore interelement ratios e g co ni ni ag of the trace element rich spongy and nodular pyrites are also similar to those of typical diagenetic pyrite la icp ms imaging of pyrrhotite in the same rocks reveals multistage growth in this mineral as well with the earlier generation having higher concentrations of ag sb pb tl and bi than its presumed metamorphic counterpart imaging of marcasite in the shales of the upper poorman formation demonstrates this mineral s high abundance of w and tl relative to all generations of pyrite and pyrrhotite mass balance calculations indicate that the volume of upper poorman formation in the mine area approx 12 km3 could potentially yield 4 500 t of au a value greater than the total mined resource by more than a factor of three these geochemical data and calculations suggest that a significant portion of the gold at homestake may have been sourced from the relatively thick carbonaceous and sulfidic black shale facies in the stratigraphic footwall to the host iron formation in a manner similar to other sediment hosted gold districts

oxygen overshoot and recovery during the early paleoproterozoic abstract during the lomagundi event ca 2 22 to 2 06 ga marine carbonates recorded the largest and longest uninterrupted positive carbon isotope excursion the earliest extensive marine sulfate evaporites were deposited and the average ferric iron to total iron expressed as fe 2 o 3 fe fe2o3 ratio of shales increased dramatically at the end of the lomagundi event the first economic sedimentary phosphorites were deposited and the carbon isotope values of marine carbonates returned to 0 vpdb thereafter marine sulfate evaporites and phosphorites again became scarce while the average fe 2 o 3 fe fe2o3 ratio of shales decreased to values intermediate between those of the archean and lomagundi age shales we propose that the large isotopic and chemical excursions during the lomagundi event were caused by a positive feedback between the rise of atmospheric o 2 the weathering of sulfides in the pre 2 3 ga continental crust and the flux of phosphate to the oceans cf holland 2002 the rise in the terrestrial phosphate flux led to an increase in the burial rate of organic carbon and a major transfer of oxygen from the carbon to the sulfur cycle the end of the lomagundi event was probably caused by a decrease in the terrestrial phosphate flux related to the weathering of low pyrite sediments that were deposited during the lomagundi event the rate of deposition of organic matter and the precipitation of sulfate evaporites decreased the isotopic and chemical excesses of the lomagundi event were eliminated and the ocean atmosphere system entered the period frequently called the boring billion