the three dimensional morphology of arrays of echelon and sigmoidal mineral filled fractures data from north cornwall arrays of mineral filled echelon sigmoidal fractures in cobbles of sandstone from the crackington formation of north cornwall were examined by cutting serial sections in three dimensions each array consists of a set of blade like mineral filled fractures these blades project as a fringe from the single but composite fracture that forms through their linkage linkage takes place as the strips of rock bridges between blades fail through cross fracture cross fractures give rise to the steps that mark the margins of the composite fractures so formed bridges show little penetrative deformation arrays are not zones of high ductile strain displacement is a consequence of dilatation echelon fractures were formed and opened by intruding hydrothermal fluid

reply to the comments of d l pinti r mineau and v clement and of a o marshall and c p marshall on biogenicity of earth s earliest fossils a resolution of the controversy by j william schopf and anatoliy b kudryavtsev gondwana research 22 2012 761 771 abstract the abundant and diverse assemblage of filamentous microbial fossils permineralized in the 3465 ma apex chert of northwestern australia among the oldest records of life are arguably the best studied by the most workers using the most advanced techniques in the history of science despite the extensive body of data establishing the biogenicity of the demonstrably cellular carbonaceous apex fossils pinti et al 2013 and marshall and marshall 2013 have raised issues regarding the interpretation of their studies of the apex chert presented in our recent review article schopf and kudryavtsev 2012 we agree with the assessment of both of the relevant papers by pinti et al 2009 2013 the observations they report do not apply to the bona fide microscopic fossils of the apex chert similarly like the minute objects reported by pinti et al 2009 2013 the quartz and haematite filled fractures discussed by marshall and marshall 2013 are mineralic pseudofossils that are not relevant to interpretation of the apex fossil microbes and their suggestion that multiple populations of carbonaceous material may be a wide spread issue through out the precambrian is without merit

effects of grand cycle cessation on the diagenesis of upper cambrian carbonate deposits in the southern appalachians u s a abstract the vertical transition from the mainly subtidal alternating shale and carbonate units or grand cycles of the conasauga group middle to upper cambrian to the peritidal dolostone of the knox group upper cambrian to lower ordovician marks a major change in the early paleozoic passive margin sedimentation of the southern appalachians the grand cycles represent an interplay between intrashelf shale basin and carbonate platform deposition the end of grand cycle deposition occurred in response to carbonate platform progradation over the infilled intrashelf basin and is associated with a prominent change in diagenetic patterns observed in the uppermost conasauga group strata the maynardville formation the maynardville records upward shallowing from subtidal shale and limestone into peritidal dolostone this change from a subtidal into a peritidal depositional regime influenced the early diagenesis of the maynardville and in conjunction with the changes in the regional facies distribution at the end of grand cycle deposition extended its influence upon the burial diagenesis of these deposits the subtidal deposits of the maynardville contain a variety of calcite cements dolomite is not abundant in these deposits where it occurs mainly as a fine crystalline ferroan phase associated with argillaceous layers and pressure dissolution features the local source for this dolomite during burial was provided by expulsion of pore fluids from interbedded shale deposits diagenesis of clay minerals and pressure dissolution of carbonates ferruginous coatings on hardgrounds in the subtidal deposits provided an additional local source of iron for the formation of replacement saddle dolomite the subtidal deposits also contain saddle dolomite cement associated with mississippi valley type mvt minerals which indicate the involvement of externally derived fluids during late burial diagenesis of these strata the peritidal deposits on the other hand are extensively dolomitized fine crystalline dolomite most likely represents early diagenetic replacement of tidal flat carbonate sediment coarse crystalline replacement dolomite formed during burial by recrystallization of early dolomite and dolomitization by warm burial brines fenestrae desiccation cracks and evaporite dissolution voids are occluded with dolomite cement which is commonly complexly zoned zoned dolomite precipitated during shallow to intermediate burial and is postdated by saddle dolomite cement saddle dolomite in pore centers dissolutional voids and tectonic fractures formed during late burial from warm fluids associated with the migration of mvt brines the effects of changes in the depositional setting on diagenesis are reflected in similar early diagenesis between the subtidal maynardville and the underlying conasauga group carbonate deposits and between the peritidal deposits of the upper maynardville and the rest of the overlying knox group the depositional environments and early diagenesis also affected the burial diagenesis the changes in regional facies distribution caused by carbonate platform progradation at the end of grand cycle deposition resulted in a decrease in the proportion of siliciclastic components this decrease was accompanied by a decline in the amount of ferroan carbonate in the peritidal deposits the maynardville is conformably overlain by carbonate deposits of the knox group this allowed the maynardville knox succession to behave as a single hydrologic unit for the migration of burial fluids in response to the formation of the ordovician foreland sevier basin to the southeast during the conversion from a passive into a convergent continental margin the nolichucky shale separates the maynardville knox succession from the carbonate deposits of the underlying conasauga group which were in contrast affected by the migration of burial fluids from the cambrian intrashelf shale basin to the west

mediterranean sea surface radiocarbon reservoir age changes since the last glacial maximum sea surface reservoir ages must be known to establish a common chronological framework for marine continental and cryospheric paleoproxies and are crucial for understanding ocean continent climatic relationships and the paleoventilation of the ocean radiocarbon dates of planktonic foraminifera and tephra contemporaneously deposited over mediterranean marine and terrestrial regions reveal that the reservoir ages were similar to the modern one 400 years during most of the past 18 000 carbon 14 years however reservoir ages increased by a factor of 2 at the beginning of the last deglaciation this is attributed to changes of the north atlantic thermohaline circulation during the massive ice discharge event heinrich 1

sedimentary responses to sea level rise and kuroshio current intrusion since the last glacial maximum grain size and clay mineral evidence from the northern south china sea slope abstract we analyzed the terrigenous fraction of a sediment core from the northern slope of the south china sea to better understand the depositional history of the region since the last glacial maximum lgm temporal variations in the grain size and clay mineral composition revealed a complex set of overlapping controls approximately 90 of terrigenous sediment throughout the core ranged in size from 5 5 to 8 5 with the 5 25 6 25 size class being particularly sensitive to environmental changes the proportion of this fraction decreased during deglacial indicating a reduction in the supply of coarser grains due to coastline retreat as the sea level rose toward its present position the relative proportion of clay derived from taiwan increased however the mass accumulation rate of taiwan derived clay decreased suggesting a reduction in the westward bottom current intensity in contrast the relative contribution of clay from the pearl river decreased from 40 during the lgm to 5 when the sea level reached 70 m below its present position the pearl river contribution has remained consistently low throughout the holocene indicating that shore parallel circulation patterns on the shelf resembled their present configuration by 13 ka compared to taiwan and the pearl river the proportion of clay derived from the area east of pearl river epr was relatively minor and less variable a local peak in the relative contribution from this area occurred during a melt water pulse event mwp 1a suggesting that a reservoir of smectite rich clays residing in coastal bays was remobilized by this marine transgression spectral analysis of the relative contributions of the three major clay sources revealed a significant periodicity of 380 years which may reflect changes in solar insolation modulating the flux of clay minerals from taiwan and the pearl river to the deposition site on a centennial scale

paleoceanographic change during the last deglaciation east sea of korea foraminiferal assemblage and stable isotopic data are presented for three quaternary piston cores from ulleung basin east sea of korea esk japan sea near the korean peninsula major changes in both temperature and salinity strongly affected surface and deep waters of the esk during the transition from the last glacial maximum lgm to the middle holocene local environmental effects dominated during the lgm and the bolling allerod b a when the esk became semi isolated from the pacific ocean regional global influences dominated following the b a after sufficient reconnection with the pacific this is reflected in the foraminiferal 18o record which was largely salinity controlled before the younger dryas yd and temperature controlled after the yd paleoceanographic changes in the esk during the last deglaciation reflect sequential reconnection with the pacific ocean through gateways first b a in the north tsugaru strait and later holocene in the south korea strait

recent developments in dating ancient crustal fluid flow several isotopic techniques have recently been developed or substantially improved allowing the accurate determination of the timing of fluid related processes these include k ar rb sr and sm nd dating of diagenetic minerals in clastic rocks u pb dating of carbonates sm nd dating of fluorite and uraninite re os and rb sr dating of sulfides 40ar 39ar and rb sr dating of fluid inclusions and u pb dating of ilmenite magnetite sphene and rutile while many of these techniques require further evaluation some have already resulted in new constraints on a variety of crustal fluid flow models

microfossils and possible microfossils from the early archean onverwacht group barberton mountain land south africa there is widespread textural evidence for microbial activity in the cherts of the early archean onverwacht group layers with fine carbonaceous laminations resembling fossil microbial mats are abundant in the cherty metasediments of the predominantly basaltic hooggenoeg and kromberg formations in rare cases filamentous microfossils are associated with the laminae the morphologies of the fossils as well as the texture of the encompassing laminae suggest an affinity to modern mat dwelling cyanobacteria or bacteria a variety of spheroidal and ellipsoidal structures present in cherts of the hooggenoeg and kromberg formations resemble modern coccoidal bacteria and bacterial structures including spores the development of spores may have enabled early microorganisms to survive the relatively harsh surficial conditions including the effects of very large meteorite impacts on the young earth

new 230th u and 14c ages from lake lahontan carbonates nevada usa and a discussion of the origin of initial thorium five sets of coeval lacustrine carbonate samples from pleistocene lake lahontan in western nevada were dated by both the ams 14c and 230th u isochron methods all five groups of samples were analyzed for u th isotopes by alpha spectrometry and one of the groups was additionally measured by thermal and secondary ionization mass spectrometry tims and sims for comparison the 14c ages were corrected to calendar years using the calibration curve recommended by bard et al 1992 without local reservoir correction on the 14c ages mean 230th u isochron ages of some sets are apparently older than their calendar corrected 14c ages by up to 2300 years modern carbon contamination of these carbonate samples through recrystallization or deposition of secondary calcite is likely to be responsible for part of the age discrepancies we explored additional biases associated with the isochron ages maybe produced by the presence of initial th coprecipitated from the lake water it can be shown that if dissolved hydrogenous th is directly incorporated into the pure carbonates then the three component mixing among 1 detrital th 2 hydrogenous th adsorbed on detritus and 3 hydrogenous th incorporated by the carbonate can introduce a positive age bias we have developed an approach to estimate the magnitude of this bias of the lake lahontan carbonates the preliminary estimates suggest a positive age bias of 1000 to 2000 years for two sets of the samples

new insight into the origin of manganese oxide ore deposits in the appalachian valley and ridge of northeastern tennessee and northern virginia usa manganese oxide deposits have long been observed in association with carbonates within the appalachian mountains but their origin has remained enigmatic for well over a century ore deposits of mn oxides from several productive sites located in eastern tennessee and northern virginia display morphologies that include botryoidal and branching forms massive nodules breccia matrix cements and fracture fills the primary ore minerals include hollandite cryptomelane and romanechite samples of mn oxides from multiple localities in these regions were analyzed using electron microscopy x ray analysis fourier transform infrared spectroscopy and trace rare earth element geochemistry the samples from eastern tennessee have biological morphologies contain residual biopolymers and exhibit ree signatures that suggest the ore formation was due to supergene enrichment likely coupled with microbial activity in contrast several northern virginia ores hosted within quartz sandstone breccias exhibit petrographic relations mineral morphologies and ree signatures indicating inorganic precipitation and a likely hydrothermal origin with supergene overprinting nodular accumulations of mn oxides within weathered alluvial deposits that occur near to breccia hosted mn deposits in virginia show geochemical signatures that are distinct from the breccia matrices and appear to reflect remobilization of earlier emplaced mn and concentration within supergene traps based on the proximity of all of the productive ore deposits to mapped faults or other zones of deformation we suggest that the primary source of all of the mn may have been deep seated and that mn oxides with supergene and or biological characteristics result from the local remobilization and concentration of this primary mn

strontium isotopic geochemistry of mississippi valley type deposits east tennesse implications for age and source of mineralizing brines strontium isotopic ratios of wall rock ore and gangue minerals from the mascot jefferson city copper ridge and sweetwater mississippi valley type mvt districts and from the lost creek barite deposit in east tennessee were measured in an effort to determine the age of this mineralization and its relation to the tectonic evolution of the appalachian orogen the lower ordovician knox group which hosts the mvt mineralization contains limestones and dolomite karst breccias with 87sr 86sr ratios of 0 70900 to 0 70916 that are similar to those of early ordovician sea water primary diagenetic knox dolomite as well as recrystal line dolomite which formed by later alteration of limestone exhibits 87sr 86sr ratios of 0 70930 to 0 71024 reflecting varying degrees of contamination by solutions with more radiogenic strontium 87sr 86sr isotopic ratios of mineralization in the districts increase in the order lost creek sweetwater copper ridge mascot jefferson city and extend to values significantly higher than those of the enclosing rocks of the three possible source basins for the mvt brines the late proterozoic ocoee cambrian luttrell and ordovician sevier basins the sevier basin appears to be the only one that could have supplied brines of the appropriate composition at geologically reasonable times estimates of the change with time in the isotopic composition of sevier basin brines indicate that the maximum ages of the lost creek sweetwater copper ridge and mascot jefferson city mineralization are 520 460 405 and 395 m y respectively comparison of fluid inclusion temperatures for the sweetwater and mascot jefferson city minerlization with the thermal evolution curve for the sevier basin supports these estimates these ages suggest that the lost creek barite minerlization formed as an exhaltive deposit in the sevier basin and that the sweetwater fluorite barite mineralization formed during the later part of taconic orogeny the copper ridge and mascot jefferson city minerlization could have formed either prior to or during the alleghanian orogeny but prior to deformation of the enclosing rocks depending on the rate of istopic evolution of the sevier basin brines

26al and10be production in iron meteorites abstract we have measured by accelerator mass spectrometry the 26 al contents of 20 and the 10 be contents of 14 iron meteorites the 26 al contents are typically 30 or more lower than values obtained by counting techniques the 10 be contents are 10 15 lower the production rates p of these nuclides decrease by more than a factor of two as the 4 he 21 ne ratio increases with increasing shielding from 200 to 400 for the lighter shielding conditions expected in stony meteorites we estimate p 26 fe as 3 4 dpm kg and p 10 fe as 4 5 dpm kg the average p 10 p 26 activity ratio is close to 1 5 exposure ages calculated from 21 ne 26 al ratios cannot be calibrated so as to agree with both 40 kk ages and ages based on the shorter lived nuclides 39 ar and 36 cl if agreement with the latter is forced then the disagreement with 40 kk ages may signal a 35 increase in the cosmic ray intensity during the last 10 7 a

pumice from the 3460ma apex basalt western australia a natural laboratory for the early biosphere abstract it has recently been hypothesised that pumice a low density vesicular volcanic rock could have acted as a natural floating laboratory for the accumulation and concentration of chemical reactants needed for the origin of life to test the plausibility of his hypothesis we here turn to the earliest rock record for evidence of pumice deposits and their associated mineralogy and biogeochemistry we report abundant clasts of pumice from within a volcaniclastic breccia bed immediately above the 3460 ma apex chert unit of the apex basalt pilbara region western australia textural and geochemical analyses reveal that the body of these pumice clasts was deeply permeated by intimate associations of c o n p and s pumice and scoria vesicles were also lined with carbon or with catalysts such as titanium oxide or potential biominerals such as iron sulfide while many were infilled with aluminosilicate minerals the latter may be the metamorphosed remains of potentially catalytic clay and zeolite minerals it is not yet possible to distinguish between chemical signals left by prokaryote biology from those left by prebiology that being so then early prokaryotes may well have colonised and modified these apex pumice clasts prior to burial nevertheless our data provide the first geological evidence that the catalysts and molecules needed for the earliest stages of life may be found within pumice rafts from the earliest oceans on earth

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

strontium isotopic constraints on the origin of ore forming fluids of the viburnum trend southeast missouri abstract we have measured 87 sr 86 sr and rb and sr concentrations in several minerals primarily sulfides spanning the paragenesis of hydrothermal mineralization in the viburnum trend in southeast missouri separate measurements were made for fluid inclusions opened by crushing or thermal decrepitation and for the solids for comparison measurements were also made on samples of probable local aquifers the bonneterre formation and the lamotte sandstone for some of the samples concentrations of k ca cl na and mg are also reported in several cases 87 sr 86 sr ratios are different higher in the solids than in the fluid inclusions we have investigated the possibility that either type of sample gives spurious results e g that the fluid inclusions are secondary or contaminated by host dolomite or that sr in the solids reflects a detrital rather than an authigenic source consideration of mass balance overall solute chemistry and examination of non sulfide dissolution residue however suggests that both types of sample reflect primary fluid sr composition we thus adopt the working hypothesis that sr isotopic composition in fluids at the time of hydrothermal mineralization was highly variable the observed results for the viburnum trend do not conform well to expected trends for mississippi valley type mvt mineralization based primarily on analyses of gangue carbonates barite and fluorite fluid inclusion sr in some of the viburnum trend samples is more radiogenic than in the host dolomite but only moderately so in other samples notably main stage octahedral galena fluid inclusion sr composition is within the range observed for the host dolomite in contrast sr in some of the sulfides is very radiogenic much more so than previously reported for mvt minerals and is very radiogenic early in the paragenesis pyrite chalcopyrite sphalerite less radiogenic during main stage ore deposition and again more radiogenic in later paragenetic stages

the significance of rb sr glauconite ages bonneterre formation missouri late devonian early mississippian brine migration in the midcontinent rb sr mean model ages of 370 plus minus 10 ma for glauconites from the cambrian lower bonneterre formation in southern and central missouri are in excellent agreement with a rb sr isochron age of 359 plus minus 22 ma for glauconites from the magmont mine viburnum trend in the southeast missouri lead district the lower bonneterre and magmont mines ages probably reflect isotopic resetting most likely associated with dolomitization and or mississippi valley type ore formation in the southeast missouri lead district the temporal relation between widespread dolomitization and ore formation in missouri is unclear but mounting evidence for two devonian disturbances permits the following interpretation 1 a devonian timing 380 400 ma for widespread dolomitization and 2 a late devonian early mississippian timing 360 370 ma for ore formation in southeast missouri late devonian early mississippian fluids associated with the earliest stages of collisional tectonics and metamorphism to the south and southeast may have been important in the formation of southeast missouri ore deposits these tectonically driven waters may themselves have been the mississippi valley type ore fluids entering missouri by way of the black warrior basin and reelfoot rift and or the arkoma basin alternatively the movement of orogenic fluids hundreds of kilometers distant may have initiatedmore and distally influenced the migration of more locally derived mississippi valley type ore fluids broad regions of missouri and adjacent areas experienced heating and crustal flexing in the late devonian and consequently preservation of elevated temperatures in mississippi valley type fluids as they move great lateral distances may not be necessary for ore formation in southeast missouri less

biogenic origin for earth s oldest putative microfossils carbonaceous microbe like features preserved within a local chert unit of the 3 5 ga old apex basalt in western australia may represent some of the oldest evidence of life on earth however the biogenicity of these putative microfossils has been called into question primarily because the sample collection locality is a black carbon rich brecciated chert dike representing an archean submarine hydrothermal spring suggesting a formation via an abiotic organic synthesis mechanism here we describe the macromolecular hydrocarbon structure carbon bonding functional group chemistry and biotic element abundance of carbonaceous matter associated with these filamentous features these characteristics are similar to those of biogenic kerogen from the ca 1 9 ga old gunflint formation although an abiotic origin cannot be entirely ruled out it is unlikely that known abiotic synthesis mechanisms could recreate both the structural and compositional complexity of this ancient carbonaceous matter thus we find that a biogenic origin for this material is more likely implying that the apex microbe like features represent authentic biogenic organic matter

highly resolved beryllium 10 record from odp site 1089 a global signal abstract in this study a highly resolved beryllium 10 record from a rapidly accumulating sediment core located in the southern cape basin odp leg 177 site 1089 is presented to extract the global 10 be production signal from the sedimentary record a dedicated correction procedure is applied first sediment redistribution is quantified by applying thorium 230 normalization then lateral transport of 10 be and 230 th is assessed using simple box model calculations the model results indicate that only minor transport corrections have to be applied thus site 1089 combines the advantage of good time resolution with nearly negligible oceanic transport of 10 be leading to a favored site for the reconstruction of global 10 be production changes from marine sediments our results suggest that the transport corrected 10 be record at site 1089 reflects long term variations of the global 10 be production rate over the past 300 kyr the absolute values of the youngest holocene samples are in good agreement with the estimated recent long term averaged global 10 be production rate deduced from observations the variability of the 10 be flux over the past 300 kyr corresponds well to the expected range deduced from model calculations the comparison with other reconstructions of geomagnetic paleointensity and with records of cosmogenic nuclides further emphasizes the global character of this 10 be record therefore our results show that it is possible to quantitatively extract the global 10 be production rate from a single marine record if transport processes are corrected for since the error of a single reconstruction is large a combination of several highly resolved and transport corrected 10 be records may lead to a significantly improved reconstruction of geomagnetic variability and of global cosmic ray flux and over the past 300 kyr

advanced analytical techniques for studying the morphology and chemistry of proterozoic microfossils this paper outlines the suite of advanced multi scalar techniques currently available in the toolkit of the modern proterozoic palaeobiologist these include non intrusive and non destructive optical laser and x ray techniques plus more destructive ion beam and electron beam methods together these provide morphological mineralogical and biochemical data at flexible spatial scales from that of an individual atom to the largest proterozoic microfossils an overview is given of each technique and a case study from the exceptionally well preserved torridonian biota of nw scotland is presented this microfossil assemblage was first recognized over a century ago but its great diversity and evolutionary importance has only recently come to light due in no small part to the research efforts of martin brasier

evidence for regional stream aggradation in the central oregon coast range during the pleistocene holocene transition abstract low nearly continuous terraces of similar age are present along streams in drainage basins that range in size from drift creek 190 km 2 to the umpqua river 11 800 km 2 in the oregon coast range radiocarbon ages from near the bose of fluvial sediments underlying these terraces are clustered at about 9000 11 000 14 c yr b p beveled bedrock surfaces straths that underlie the fluvial sediments are 1 8 m above summer stream levels and are present along most of the nontidal reaches of the rivers that we studied where exposed the bedrock straths are overlain by 2 11 m of fluvial sediment that consists of a bottom stratum channel facies of sandy pebble cobble gravel and a top stratum overbank facies of sandy silt or silt eight radiocarbon ages from the fluvial sediments allow correlation of the lowest continuous terrace over a wide area and thus indicate that a regional aggradation episode occurred in coast range drainage basins during the pleistocene holocene transition the cause of such widespread aggradation is unknown but may be related to climate induced changes in the frequency of evacuation of colluvium from hollows which are common in all drainage basins in the region

atmospheric14c changes resulting from fossil fuel co2 release and cosmic ray flux variability a high precision tree ring record of the atmospheric14c levels between 1820 and 1954 is presented good agreement is obtained between measured and model calculated 19th and 20th century atmospheric 14c levels when both fossil fuel co2 release and predicted natural variations in14c production are taken into account the best fit is obtained by using a diffusion model with an oceanic eddy diffusion coefficient of 3 cm2 s a co2 atmosphere ocean gas exchange rate of 21 moles m 2 yr 1 and biospheric residence time of 60 years for trees in the state of washington the measured 1949 1951 atmospheric 14c level was20 0 1 2 below the 1855 1864 level model calculations indicate that in 1950 industrial co2 emissions are responsible for at least 85 of the 14c decline whereas natural variability accounts for the remaining 15

biogenicity of earth s earliest fossils a resolution of the controversy abstract the abundant and diverse assemblage of filamentous microbial fossils and associated organic matter permineralized in the 3465 ma apex chert of northwestern australia widely regarded as among the oldest records of life have been investigated intensively first reported in 1987 and formally described in 1992 and 1993 the biogenicity of the apex fossils was questioned in 2002 and in three subsequent reports however as is shown here by use of analytical techniques unavailable twenty years ago the apex filaments are now established to be bona fide fossil microbes composed of three dimensionally cylindrical organic kerogenous walled cells backed by a large body of supporting evidence of similar age other microfossils stromatolites and carbon isotopic data it seems clear that microbial life was present and flourishing on the early earth 3500 ma ago

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

hydrothermal alteration and microfossil artefacts of the 3 465 million year old apex chert the earliest fossils of cyanobacteria have been controversially reported from the 3 465 million year old apex chert in western australia mineralogical analyses of the rock near the fossil site indicate that the site experienced repeated alterations at low and medium temperatures and is therefore unlikely to have preserved any early forms of life the 3 465 million year old apex chert of the pilbara craton in western australia has been controversially reported to contain some of the oldest fossil evidence for life tiny carbonaceous filaments interpreted as cyanobacteria1 yet on the basis of the presence of barite and native metals it has been suggested that the chert formed from hydrothermal fluids at temperatures greater than 250 c refs 2 3 an unlikely environment for cyanobacteria here we use scanning electron microscopy to assess the mineralogy and depositional setting of the chert veins surrounding the nodes that contain the microfossils in addition to rare native metals we find an assemblage of iron oxides and clay minerals which we interpret to have formed during repeated pulses of hydrothermal alteration at low to medium temperatures we also find micrometre sized silica structures that resemble microbial exopolymers4 and textures formed by the partial dissolution of tubular minerals that look similar to fossilized microbial mats5 other branched microstructures suggest post depositional colonization of microcracks and fissures by microbes5 these observations are not directly applicable to the carbonaceous filaments purported to be the earliest fossil evidence of life as we did not recover any in our sample however because of the observed hydrothermal and groundwater alteration we conclude that the apex chert is unlikely to have preserved any early forms of life

paleomagnetic dating of alleghanian orogenesis and mineralisation in the mascot jefferson city zinc district of east tennessee usa abstract the mascot jefferson city m jc mississippi valley type mvt deposits are in the valley and ridge province of the appalachian orogen in east tennessee they have been a major source of zinc for the usa but their age is uncertain and thus their genesis controversial about 10 specimens from each of 37 sites have been analysed paleomagnetically using alternating field and thermal step demagnetisation methods and saturation isothermal remanence methods the sites sample limestones dolostones breccia clasts and sphalerite dolomite mvt mineralisation from mines in the lower ordovician kingsport and mascot formations of the knox group the characteristic remanent magnetisation chrm is carried by magnetite in the limestones by both magnetite and pyrrhotite in the dolostones and by pyrrhotite preferentially to magnetite in the mineralisation mineralized sites have a more intense chrm than non mineralised indicating that the mineralising and magnetisation event are coeval paleomagnetic breccia tests on clasts at the three sites are negative indicating that their chrm is post depositional remagnetisation and a paleomagnetic fold test is negative indicating that the chrm is a remagnetisation and a post dates peak alleghanian deformation the unit mean chrm direction for the a limestones gives a paleopole at 129 e 12 n d p 18 d m 26 n 3 indicating diagenesis formed a secondary chemical remanent magnetisation during the late ordovician early silurian b dolomitic limestones and dolostone host rocks gives a paleopole at 125 3 e 31 9 n d p 5 3 d m 9 4 n 7 recording regional dolomitisation at 334 14 ma 1 and c mvt mineralisation gives a paleopole at 128 7 e 34 0 n d p 2 4 d m 4 4 n 25 showing that it acquired its primary chemical remanence at 316 8 ma 1 the mineralisation is interpreted to have formed from hydrothermal fluid flow either gravity or tectonically driven after peak alleghanian deformation in eastern tennessee with regional dolomitisation of the host rocks occurring as part of a continuum during the 20 ma prior to and during peak deformation

carbonate hosted zinc lead deposits in the lower cambrian of hunan south china a radiogenic pb sr isotope study zinc lead deposits hosted by lower cambrian carbonate rocks near huayuan in the hunan guizhou orogenic belt southern china have been studied by means of pb and sr isotopes the deposits are characterized by two mineralization stages 1 a main economic stage comprising cockade style sphalerite galena pyrite marcasite fluorite barite and calcite and 2 a subsequent noneconomic stage with nodular rosette sphalerite saddle dolomite and bitumen both ore stages are postdated by a generation of late calcite main stage sulfides 206pb 204pb 18 162 18 225 display a steep linear trend on conventional pb pb diagrams which indicates binary mixing of lead components bearing the imprint of ancient 207pb dominated crustal rocks and reservoirs with elevated th u ratios possibly located in the lower crust nodular rosette sphalerites fall outside this line but reflect a second mixing trend between mineralizing fluids characterized by 206pb 204pb 18 3 and lead isotopically similar to specific main stage cockade sphalerites suggesting either remobilization of pb from main stage ores or contemporaneous mixing of three distinct lead components in the course of an evolving hydrothermal event the 87sr 86sr ratios of diagenetic and hydrothermal carbonate cements and barites range from 0 70905 to 0 71006 and increase systematically with the paragenetic sequence indicating progressive mixing of marine sr derived from the lower cambrian carbonate host rocks with radiogenic sr supplied by external mineralizing fluids in order to identify possible local metal sources u pb and rb sr analyses were performed on six whole rock samples from the lower cambrian sequence and their time integrated pb and sr isotope evolution was compared to the isotopic signature of the mineralization whereas shales and black shales of the cambrian balang and niutitang formations underlying the ore bearing qingxudong carbonate unit appear to be possible external sources for the radiogenic sr found in hydrothermal carbonates the u pb data do not permit these shales to be considered as primary source rocks for the ore lead both the pb and the sr isotopes indicate mineralizing fluids that had interacted with various external metal sources some of them most probably being located in sedimentary or crystalline basement rocks this refutes prevailing genetic models favoring the hydrocarbon and metal rich lower cambrian niutitang black shales as the most likely source reservoir for the zn and pb in the deposits of the huayuan district the pb and sr isotope mixing trends observed for the ore and gangue preciptates reflect small scale heterogeneous fluid systems that were not capable of producing large deposits this may indicate that the huayuan district is not a favorable target for future exploration of economic ore deposits it also limits the prospects of successful radiometric dating of the mineralization since conventional geochronologic models require initial isotopic homogeneity

mineral microbial structures in a bone of the late cretaceous dinosaur saurolophus angustirostris from the gobi desert mongolia a raman spectroscopy study abstract bones while buried undergo diagenetic transformations the intensity of which depends on a variety of geochemical factors microbial degradation is one of the main processes acting on bones during early diagenesis we present mineral microspheres formed during bone diagenesis from the inner walls of the left tibia of the late cretaceous dinosaur saurolophus angustirostris from the gobi desert mongolia the microspheres occur either as individual bodies from a few micrometers to about 70 m in diameter or aggregated in clusters micro raman analysis shows that the microspheres are composed of various fe oxides mostly hematite and goethite that form regular reddish brown rings with organic matter at their cores the bone itself is composed for the most part of diagenetically transformed carbonate fluorapatite calcite cement was identified around the spheres and at points of contact with bone tissue negative ce anomalies indicative of ce iv in the diagenetic environment indicate oxic burial conditions all the size distribution of the microspheres their mode of occurrence and the presence of organic matter in cores surrounded by concentric fe oxide envelopes indicate early diagenetic microbially mediated mineralization in aerobic conditions the presence of microspheres and other mineral phases in the studied bone gives evidence of at least two mineralization episodes 1 fe oxide formation during an early diagenetic microbial attack on the bone and 2 later calcite barite gypsum cementation

diatom evidence for late holocene climatic events in granite harbor antarctica downcore diatom data from a deep basin in granite harbor antarctica provide new high resolution information concerning changes in oceanographic and depositional processes that have occurred during approximately the last 1250 years the influence of global scale climatic change during the time of the medieval warm period and possibly the little ice age is revealed by long term changes in floral assemblages as recorded by changes in the relative concentration of nitzschia cylindrus the diatom data suggest that granite harbor experienced less annual ice and pack ice cover during both these periods possibly because of higher temperatures during the medieval warm period and stronger offshore winds during the little ice age the sedimentary record reveals several distinct short lived events in which nearly monospecific blooms of corethron criophilum and chaetoceros spp occurred possibly the result of strong stabilization of the upper water column and were most likely a response to regional rather than global conditions although short lived these events may play a significant role in the delivery of organic carbon and biogenic silica to the seafloor

constraints on the age and genesis of the llanrwst and llanfair talhaiarn orefields north wales from k ar and rb sr studies the llanrwst pb zn and llanfair talhaiarn cu pb zn orefields contain vein mineralization similar to lower palaeozoic hosted base metal deposits elsewhere in the british isles which are believed to have formed in the late palaeozoic k ar and rb sr data on intensely sericitized wallrock material indicate that the main phase of mineralization at both orefields occurred between the mid devonian and thetournasian 386 350 ma the latest veins at llanrwst formed in visean westphalian times gangue mineral sr isotope compositions indicate a mixture of radiogenic wallrock derived sr with less radiogenic sr with a poorly defined trend to more radiogenic compositions with time the age of the main mineralization precludes dewatering of carboniferous basins as a source of ore fluid more generally sr isotopes rule out unmodified basinal brines or metamorphic fluids as mineralizing agents since their sr content would be too radiogenic local sources of unradiogenic sr are available at llanrwst in metadolerites and calcareous sandstones and at llanfair talhaiarn in thin ludlow limestone beds

climatic solar oceanic and geomagnetic influences on late glacial and holocene atmospheric 14c 12c change late glacial and holocene 14c12c ratios of atmospheric co2 vary in magnitude from a few per mil for annual decadal pertubations to more than 10 for events lasting millennia a data set illuminating 10 to 104 yr variability refines our understanding of oceanic climatic versus geomagnetic or solar forcing of atmospheric 14c12c ratios most of the variance in the holocene atmospheric 14c12c record can be attributed to the geomagnetic millennia time scale and solar century time scale influence on the flux of primary cosmic rays entering the atmosphere attributing the observed atmospheric 14c12c changes to climate alone leads to ocean circulation and or global wind speed changes incompatible with proxy records climate ocean related 14c redistribution between carbon reservoirs while evidently playing a minor role during the holocene may have perturbed atmospheric 14c12c ratios measurably during the late glacial younger dryas event first order corrections to the radiocarbon time scale 12 000 30 000 14c yr b p are calculated from adjusted lake sediment and tree ring records and from geomagnetically defined model 14c histories paleosunspot numbers 100 9700 cal yr b p are derived from the relationship of model 14c production rates to sunspot observations the spectral interpretation of the 14c12c atmospheric record favors higher than average solar activity levels for the next century minimal evidence was found for a sun weather relationship

strontium boron oxygen and hydrogen isotope geochemistry of brines from basal strata of the gulf coast sedimentary basin usa abstract significant spatial heterogeneities exist in the stable isotopic composition of saline formation waters from reservoirs of the smackover formation upper jurassic we focused on the southwest arkansas shelf a structurally simple portion of one of the interior basins of the northern gulf coast sedimentary basin here faulting and facies changes juxtapose dominantly oolitic carbonate strata against basal evaporites red beds and siliciclastics as well as metamorphosed basement rocks brines from this area have exceptionally high br and alkali element concentrations and have spatially heterogeneous hydrogen sulfide concentrations strontium boron oxygen and hydrogen isotope compositions exhibit coherent relations with other aspects of brine geochemistry sr isotope compositions range from those expected for carbonates and evaporites deposited from jurassic seawater 0 7071 to radiogenic ratios as high as 0 7107 generally most radiogenic sr isotope values are associated with h 2 s rich waters which also have elevated alkali element li b k rb concentrations these alkali element rich waters are associated with portions of the south arkansas fault system which reach basement boron isotope compositions are similarly heterogeneous ranging from values of 26 to 50 brines with highest b contents are most depleted in 11 b consistent with boron input from brines generated from high temperature siliciclastic diagenetic reactions normalizing b contents to br in the brines reveals a reasonable mixing trend between a dead sea type composition and texas gulf coast type shale sand reservoir waters oxygen and hydrogen isotope data exhibit regional variations which are controlled by meteoric water invasion along the northern limb of the southwest arkansas fault which has surface expression although oxygen isotope compositions are often near equilibrium with respect to reservoir carbonate it is more difficult to ascribe trends in d values to local water rock interaction the stable isotope trends can be explained either in terms of an evolved marine evaporite brine or a water evolved via water rock interaction and mixing with meteoric water in the vicinity of the southwest arkansas fault spatial heterogeneity in isotopic composition of formation waters from this relatively restricted study area suggests that assumptions of a homogeneous sr reservoir in dating regional mineralization events require careful assessment in ancient systems

limits on the ventilation rate for the deep ocean over the last 12000 years in this paper we present accelerator radiocarbon measurements on hand picked benthic and planktonic foraminifera separated from two deep sea cores raised from the south china sea from the benthic planktonic age differences we are able to place limits on the extent to which the ventilation rate of the deep pacific ocean has changed over the last 12000 years while much work remains to be done before any definitive answers for the global oceans can be given these results on cores with sedimentation rates suitably high to avoid major corrections for bioturbation effects suggest that the ventilation rate of the deep pacific ocean has remained nearly the same throughout holocene time further there is no suggestion that the rate was slower during the period of major glacial retreat these results confirm that the changes in atmospheric14c c ratio over the last 10000 years owe their origin to radiocarbon production rate changes

radiocarbon reservoir age of high latitude north atlantic surface water during the last deglacial the radiocarbon reservoir age of high latitude north atlantic ocean surface water is essential for linking the continental and marine climate records and is expected to vary according to changes in north atlantic deep water nadw production measurements from this region also provide important input and or tests of oceanic radiocarbon using 3 d global ocean circulation models here we present a surface water radiocarbon reservoir age record of the high latitude western north atlantic for the deglacial period via the use of fossil cold water corals growing in waters that are rapidly exchanged with nearby surface waters the reservoir age of high latitude north atlantic surface waters was computed from the radiocarbon age difference between our radiocarbon calibration record http radiocarbon ldeo columbia edu and our marine radiocarbon data 230th 234u 238u dates provide the absolute coral ages our high latitude north atlantic ocean reservoir age data combined with recalculated reservoir ages based on published coexisting terrestrial and marine material and vedde ash radiocarbon dates from central and eastern north atlantic show modern values 380 140 year n 14 during the bolling and allerod warm period and a 200 year increase in reservoir age 590 130 year n 10 during the entire younger dryas yd cold episode the reservoir age then decreased to 270 20 year n 2 at the preboreal yd transition although the dates are too sparse for us to be confident in this estimate we are not able to resolve the timing of the transition to increased reservoir ages from the mid allerod to the yd due to the relatively small change and correspondingly large uncertainty in the estimates the atmospheric 14c record derived from our atmospheric radiocarbon record displays a 40 per mil increase from 12 900 to 12 650 cal years bp coincident with the shift to high reservoir ages in the early yd cold event intrusion of 14c depleted antarctic intermediate water aaiw to the high latitude north atlantic and reduction of nadw formation are possible causes for the coincident shift to high reservoir ages in the north atlantic surface ocean and increased atmospheric 14c during the beginning of the yd event

abyssal water carbon 14 distribution and the age of the world oceans the carbon 14 distribution in the abyssal waters of the world oceans indicates replacement times for pacific indian and atlantic ocean deep waters more than 1500 meters deep of approximately 510 250 and 275 years respectively the deep waters of the entire world ocean are replaced on average every 500 years

rb sr dating of sphalerites from tennessee and the genesis of mississippi valley type ore deposits mississippi valley type mvt ore deposits commonly consist of some combination of lead zinc and iron sulphides accompanied by barite fluorite dolomite and calcite they are thought to form by fluid expulsion from sedimentary successions1 3 but their exact origin has remained controversial because of the scarcity of reliable geochronological data in a recent and widely quoted model the mvt deposits of the central and eastern united states formed as a result of large scale lateral fluid flow driven by the tectonic squeezing of sedimentary successions during the late palaeozoic alleghenian orogeny 330 250 myr 4 here we report the first direct rb sr dating of sphalerites from an mvt deposit and propose this as a useful geochronological technique for sulphide mineralization with poor age control rb sr data for sphalerites from coy mine east tennessee define an isochron age of 377 29 myr ruling out any genetic connection with the alleghenian orogeny instead mvt mineralization in the eastern united states was apparently generated from fluids expelled during thrusting associated with the older acadian orogeny 380 350 myr

multiple generations of carbonaceous material deposited in apex chert by basin scale pervasive hydrothermal fluid flow abstract the pilbara craton in western australia contains the best preserved and most complete record of archean rocks in the world as such they are some of the most studied rocks in the world paleontologists isotopic geochemists geologists and geobiologists have all investigated these rocks for clues about the early biosphere and atmosphere here we show using high resolution transmission electron microscopy that the carbonaceous material found in the apex chert and potentially in other associated units was formed by multiple processes such as abiotic catalytic synthesis and or biological synthesis we use these data as well as the geological history of the craton to demonstrate that when the rocks of the pilbara craton experienced a high degree of post depositional hydrothermal alteration carbonaceous material could have been remobilized and redeposited as the carbonaceous material within the apex chert samples was formed over nearly a billion years bulk chemistry even at the micron level will be unable to unambiguously delineate the presence of life in these ancient rocks although nanoscale observations may provide a way forward in the search for ancient life

re evaluation of greek archaeomagnitudes a new technique is used to determine the secular variation of the geomagnetic ancient field in athens the results indicate that published greek archaeomagnitudes were seriously affected by alteration it is shown that all intensities obtained using modifications of the thellier method may be affected by alteration and are therefore suspect

changing the picture of earth s earliest fossils 3 5 1 9 ga with new approaches and new discoveries new analytical approaches and discoveries are demanding fresh thinking about the early fossil record the 1 88 ga gunflint chert provides an important benchmark for the analysis of early fossil preservation high resolution analysis of gunflintia shows that microtaphonomy can help to resolve long standing paleobiological questions novel 3d nanoscale reconstructions of the most ancient complex fossil eosphaera reveal features hitherto unmatched in any crown group microbe while eosphaera may preserve a symbiotic consortium a stronger conclusion is that multicellular morphospace was differently occupied in the paleoproterozoic the 3 46 ga apex chert provides a test bed for claims of biogenicity of cell like structures mapping plus focused ion beam milling combined with transmission electron microscopy data demonstrate that microfossil like taxa including species of archaeoscillatoriopsis and primaevifilum are pseudofossils formed from vermiform phyllosilicate grains during hydrothermal alteration events the 3 43 ga strelley pool formation shows that plausible early fossil candidates are turning up in unexpected environmental settings our data reveal how cellular clusters of unexpectedly large coccoids and tubular sheath like envelopes were trapped between sand grains and entombed within coatings of dripstone beach rock silica cement these fossils come from earth s earliest known intertidal to supratidal shoreline deposit accumulated under aerated but oxygen poor conditions

an estimate of late pleistocene geomagnetic intensity variation from sulu sea sediments abstract sediments from site 769 of the ocean drilling program s leg 124 provide a record of geomagnetic intensity variation over the past 110 ky using continous shipboard measurements exclusively i estimate the variation in the geomagnetic field strength by employing low field magnetic susceptibility as a normalization parameter for the measured remanence intensity by calibrating the resultant relative paleointensity record against previously available holocene age estimates of absolute paleointensity i derive an estimate of virtual dipole moment since 110 ka the record obtained from these sulu sea sediments is strikingly like that previously obtained from sediments of a similar age in the mediterranean basin with distinct intervals of low intensity near 15 20 40 and 65 70 ka the sulu sediments also indicate a low intensity feature near 108 ka important differences in paleointensity estimates obtained from these different regions for the interval between 30 and 20 ka suggest that a relatively large non dipolar component of the geomagnetic field might have been present at that time

biofilm microfacies in phosphoritic units of the neoproterozoic halkal shale bhima basin south india abstract the phosphatic bands of the halkal shale of the neoproterozoic bhima basin record an anoxic paleoenvironment where only a few episodic depositional events introduced oxygen in thin sections five distinct microfacies caused by biofilms colonizing the ancient sea floor can be distinguished the microfacies document that low sedimentation rate allowed growth of biomass rich laminae sets whereas episodic influx of sand led to stacks of organic laminae alternating with fine sandy interlayers such depositional events may have also caused local rupture of biofilms and the release of small biofilm roll ups and clasts the ancient biofilms led to precipitation of phosphorous and iron rich minerals and likely contributed to phosphorite formation in modern equivalent environments sea floor colonizing biofilms include a high abundance of sulfide oxidizing and sulphate reducing bacteria

variations of upwelling intensity recorded in varved sediment from the gulf of california during the past 3 000 years circulation in the pacific ocean is periodically affected by el nino events which are a direct response to intensity changes in trade winds1 2 the appearance of anomalously warm surface water in the eastern equatorial pacific ocean is one of the most spectacular manifestations of this event warm surface water anomalies are also observed in the northern hemisphere along the californian coast and in the gulf of california in the gulf strengthened trade winds induce upwelling during the winter whereas in the summer prevailing southerly winds provoke an input of warm water from the south3 we have sampled laminated sediments from the slopes of guaymas basin to reconstruct with high resolution variations of the hydrology of surface waters in the central part of the gulf of california sedimentation rate is of the order of 4 mm yr 1 at the top and 1 2 mm yr 1 down core by analysing the oxygen isotope ratio of biogenic silica of diatoms4 we have recorded the surface water temperature variations in the guaymas basin the comparison of these fluctuations and variations of silicoflagellate abundance has allowed us to reconstruct changes in upwelling intensity during the past three thousand years the present conditions of low upwelling activity are seen to be abnormal in comparison with those prevailing in the past

critical testing of earth s oldest putative fossil assemblage from the 3 5ga apex chert chinaman creek western australia abstract structures resembling cyanobacterial microfossils from the ca 3465 ma old apex chert of the warrawoona group in western australia have until recently been accepted as providing the oldest morphological evidence for life on earth and have been taken to support an early beginning for oxygen releasing photosynthesis eleven species of filamentous prokaryote principally distinguished by shape and geometry have been put forward as meeting the criteria required of authentic archaean microfossils they were contrasted with other microfossils that were dismissed as either unreliable or irreproducible the aim of this paper is to provide a detailed account of research recently reported by us on the type and recollected material involving optical and electron microscopy digital image analysis and other techniques all previously figured holotype materials are illustrated here and the context for all the published materials is re evaluated the apex chert microfossils occur near the top of a 1 5 km long chert dyke complex associated with major synsedimentary growth faults highly localised glassy felsic tuffs erupted explosively from this and other fissures during the early stages of volcanism and were followed by the deposition of essentially hydrothermal black and white baso4 rich cherts that infiltrated the feeder dykes underplating and dilating adjacent stratiform cherts before the start of the next volcanic cycle the apex chert microfossils occur within multiple generations of these metalliferous hydrothermal vein cherts some 100 m down the dyke system comparable structures occur in associated volcanic vent glass and in hydrothermal cherts at least 1 km deep we find no supporting evidence for a primary biological origin we reinterpret the purported microfossil like structures as pseudofossils that formed from the reorganization of carbonaceous matter mainly during recrystallization from amorphous to spherulitic silica

evidence of archean life stromatolites and microfossils abstract fossil evidence of the existence of life during the archean eon of earth history 2500 ma is summarized data are outlined for 48 archean deposits reported to contain biogenic stromatolites and for 14 such units that contain a total of 40 morphotypes of described microfossils among the oldest of these putatively microfossiliferous units is a brecciated chert of the 3465 ma apex basalt of western australia the paleoenvironment carbonaceous composition mode of preservation and morphology of the apex microbe like filaments backed by new evidence of their cellular structure provided by two and three dimensional raman imagery support their biogenic interpretation such data together with the presence of stromatolites microfossils and carbon isotopic evidence of biological activity in similarly aged deposits indicate that the antiquity of life on earth extends to at least 3500 ma

accelerator mass spectrometry radiocarbon stratigraphies in deep labrador sea cores paleoceanographic implications foraminiferal accelerator mass spectrometry ams 14c ages and benthic planktonic age differences in surface layer sediments of labrador sea are influenced by bioturbation and by changes in the relative abundance of foraminiferal species carrying the 14c signal using benthic mixing models we demonstrate that inverse benthic planktonic age differences can be generated when the effect of benthic mixing and abundance change exceeds apparent age differences between surface water and deep water ams 14c ages obtained put constraints on the timing of major paleoceanographic changes in the basin notably on the history of the western boundary undercurrent which was clearly reinitiated during the mid deglaciation and intensified during the last 2 3 ka

radiocarbon age of last glacial pacific deep water one of the most important projects envisaged ever since the possibility emerged of making tandem accelerator mass spectrometric radiocarbon determinations has been that of investigating changes in the radiocarbon age of the deep ocean1 initial attempts to achieve this2 were thwarted by difficulties imposed by bioturbation because these workers used core v28 238 with an accumulation rate of only 1 5 cm kyr 1 thus emphasizing the need to work in a core with a higher accumulation rate working in the glacial section of core tr163 31b with an accumulation of 10 cm kyr 1 we show here that the ventilation age of pacific deep water was about 500 years greater in last glacial times than it is today

sedimentary phosphate and associated fossil bacteria in a paleoproterozoic tidal flat in the 1 85 ga michigamme formation michigan usa abstract phosphorus is a nutrient fundamental to life and when it precipitates in modern environments bacteria are intimately involved in its release concentration and mineralization preserved fossil bacteria in phosphate crusts and grains from the ca 1850 million year old bijiki iron formation member of the michigamme formation michigan provide insight into the longevity and nature of this relationship the michigamme formation accumulated near the end of the earth s initial phosphogenic episode ca 2 2 and 1 8 ga to produce one of the first granular phosphorites phosphatic lithofacies consist of fine to medium sand sized francolite peloids concentrated on bedding surfaces in peritidal facies granular beds are up to 2 cm thick and peloids are often partially to completely replaced by dolomite and chert the grains contain organic matter and pyrite framboids that suggest bacterial breakdown of organic matter and bacterial sulfate reduction the peritidal nature of phosphorite in the michigamme formation is in sharp contrast to phanerozoic phosphogenic environments in deeper coastal upwelling settings peritidal settings were well suited for phosphogenesis under the very low oxygen and low dissolved sulfate levels of the paleoproterozoic as cyanobacteria produced oxygen in shallow water and evaporation led to increased sulfate concentrations such concomitant processes helped establish focused redox interfaces in the sediment that chemosynthetic bacterial communities sulfur oxidizers reducers forms that concentrate p and possibly iron oxidizers could exploit phosphate released from organic matter by heterotrophic bacteria and fe redox pumping was further concentrated by these chemotrophs a process that forms late neoproterozoic to phanerozoic phosphorites but on a much larger scale this early example of a granular phosphorite demonstrates that like their phanerozoic counterparts paleoproterozoic phosphorites are the concentrated indirectly biomineralized products of bacterial communities but unlike younger analogs which accumulated across subtidal shelves and shelf margins these ancient deposits formed only in tidal flat settings where phosphogenic redox processes could be established in the sediment from this early beginning the zone of phosphogenesis likely migrated into deeper water settings as oxygen and sulfate levels rose expanding the zone of chemosynthetic bacterial and associated phosphogenesis across the shelf

reduced solar activity as a trigger for the start of the younger dryas it is generally assumed that changes in ocean circulation forced the abrupt climate changes during the late pleistocene including the younger dryas event recently however it was proposed that variations in solar irradiance could have played a much more prominent role in forcing pleistocene climate changes furthermore two physical mechanisms were recently published that explain how relatively small changes in solar irradiance could have had a strong impact on the climate system we discuss the possibility that an abrupt reduction in solar irradiance triggered the start of the younger dryas and we argue that this is indeed supported by three observations 1 the abrupt and strong increase in residual c 14 at the start of the younger dryas that seems to be too sharp to be caused by ocean circulation changes alone 2 the younger dryas being part of an similar to 2500 year quasi cycle also found in the c 14 record that is supposedly of solar origin 3 the registration of the younger dryas in geological records in the tropics and the mid latitudes of the southern hemisphere moreover the proposed two physical mechanisms could possibly explain how the north atlantic thermohaline circulation was perturbed through an increase in precipitation together with iceberg influxes in addition the full magnitude of the younger dryas cooling as evidenced by terrestrial records in europe could be explained we conclude that a solar triggering of the younger dryas is a valid option that should be studied in detail with climate models c 2000 elsevier science ltd and inqua all rights reserved

chemically oscillating reactions during the diagenetic oxidation of organic matter and in the formation of granules in late palaeoproterozoic chert from lake superior abstract filamentous and coccoidal microfossils have been reported since the 1950 s from a range of granular cherts from the late palaeoproterozoic southwestern superior craton canada united states however the chemical and mineral compositions of granules the presence of microfossils in granules and the common presence of granules in intercolumnar space of stromatolitic chert are poorly documented and explained furthermore the depositional model for the origin of granules in wave agitated waters does not entirely explain their mineral diversity nor their characteristic morphologies and patterns we report on the crystallinity of organic matter mineral diversity and compositions of microfossils in granules from three different kinds of late palaeoproterozoic cherts namely phosphatic organic and haematitic stromatolitic organic rich chert from the gunflint fm contains granules with euhedral carbonate and equidistant concentric laminations of organic matter akin to fractal patterns from the belousov zhabotinsky b z chemically oscillating reaction these granules also contain authigenic anatase ferric ferrous silicates and fe oxides filamentous and coccoidal microfossils similar to those of the gunflint occur in chert from the biwabik formation and share morphology and co occur with mn siderite and apatite granules in phosphatic chert in the michigamme formation often contain filamentous and coccoidal microfossils composed of organic matter sericite and apatite bulk carbonate associated with these michigamme granular phosphatic chert beds has systematically negative 13ccarb values around 3 1 0 9 1 and 18ocarb smow between 20 8 and 30 7 which suggest some contribution from the diagenetic oxidation of organic matter notably residual carboxylic acid is detectable in c xanes spectra of organic matter from granular phosphatic chert which is a residual reactant of b z type reactions along with previously reported observations of pyritised microfossils from the gunflint formation these distinct mineralogies indicate variable modes of preservation for the products of chemically oscillating reactions that likely relate to the availability of different oxidants in the diagenetic environment we conclude that the late palaeoproterozoic shallow marine environments of the lake superior area were populated by morphologically similar micro organisms and that the diagenetic oxidation of organic matter through chemically oscillating reactions contributed to the formation of spheroidal rosettes granules and concretions during a late palaeoproterozoic great putrefaction event granules in chert that contain organic matter or microfossils thus provide a reliable petrographic context to search for a record of putrefaction of microbial life on the early earth and on other ancient planetary surfaces

precambrian microbe like pseudofossils a promising solution to the problem of various problems that have hindered progress in documenting the precambrian history of life the difficulty in distinguishing between bona fide microbial fossils and nonbiological microscopic pseudofossils has been among the most serious though errors in the interpretation of putative precambrian fossil microbes have diminished greatly over recent years mistakes continue to be made we suggest that such errors can be avoided by the use of a multifaceted strategy based on a specified series of biologically definitive characteristics that document the presence of interrelated biological morphology and biologically derived chemistry to illustrate this promising approach we use optical microscopy confocal laser scanning microscopy and raman spectroscopy together to distinguish between authentic microbial fossils and microscopic look alikes both coccoidal and filamentous rock embedded in five proterozoic and two archean geological units bona fide fossils of the 800 ma bitter springs formation of central australia and 3050 ma farrel quartzite of northwestern australia and objects we regard to be pseudofossils from the 770 ma chanda limestone of southern india 800 ma myrtle springs formation of south australia 1020 ma lakhanda formation of southeastern siberia 1700 ma vempalle formation of central india and 2629 ma marra mamba iron formation of northwestern australia the results demonstrate that no single criterion by itself is sufficient to establish the biological origin of such objects instead as shown here this problem appears solvable by the use of an interdisciplinary approach that combines the data and techniques of geology biology and chemistry

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

the strontium isotopic composition of ordovician and silurian brachiopods and conodonts relationships to geological events and implications for coeval seawater utilized for strontium isotope measurements the results document a gradual decrease in 87 sr 86 sr from 0 7091 to 0 7087 from tremadoc to llandeilo a sharp decline to 0 7078 during the late llandeilo early caradoc little change during caradoc and the ashgil and a steady rise to 0 7087 through the silurian these long term 10 7 yr variations with magnitudes in the range of 10 23 are interpreted to be controlled primarily by continental collisional tectonics and its associated erosion and weathering the gradual decrease in 87 sr 86 sr ratio during the early ordovician may record the reduction in uplift and weathering rates due to waning of the pan african orogenies the rapid decline near the llandeilo caradoc boundary suggests a strong hydrothermal flux likely due to increased sea floor spreading and a possible superplume event the latter may have caused the prominent transgressive phase the largest in the phanerozoic which would have muted continental flux input although the caradoc was the main interval for the taconic orogeny its impact on the sr continental flux may have been delayed until the early llandovery this effect complemented by reworking of glacial deposits near the ordovician silurian boundary and enhanced by phases of the silurian salinic orogeny may have combined to give the progressive increase in the strontium isotope ratio through the silurian the scale and directionality of these changes makes the strontium isotope curve valuable for dating and correlation purposes copyright 1998 elsevier science ltd

the palaeobiology and geochemistry of precambrian hydrocarbon source rocks abstract organic carbon productivity and formation of hydrocarbon source rocks during the early precambrian was almost exclusively the product of the growth of microbial mats indirect evidence of microbial mats can be traced back to at least 2 6 2 7 ga neoarchaean with the earliest evidence of mat development in siliciclastic sediments coming from the 2 9 ga mesoarchaean predominantly marine sedimentary rocks of the mozaan group in south africa the earliest direct evidence for terrestrial microbial mats in siliciclastic sediments comes from the 2 75 ga palaeoproterozoic fluviolacustrine sediments of the hardey formation of the pilbara craton in western australia well preserved proterozoic hydrocarbons provide valuable information about the early evolution of the biosphere eukaryotic steranes biomarker for eukaryotic cells and therefore evolved forms of life are present in the geological record from about 2 7 ga but they are not abundant or diverse within archaean communities which tend to be dominated by archaea isoprenoids some hydrocarbons have been generated and migrated from archaean organic rich shales but they were probably not of sufficient volume to be of commercial interest the world s oldest significant hydrocarbon source rocks are palaeoproterozoic in age and include the shungite deposits 2 0 ga in the lake onega region of arctic russia there is strong evidence of a global biospheric oxygenation event at c 1300 1250 ma mesoproterozoic in conjunction with a first order positive shift in the marine carbon isotope record this is supported by the appearance of the oldest bedded marine gypsum deposits and of the earliest unambiguously multicellular eukaryotes at this time this oxygenation event probably played a significant role in supporting the more diverse eukaryotic communities preserved in the neoproterozoic molecular record and provided the volume of organic material required to generate commercial volumes of hydrocarbons hydrocarbon source rocks of late mesoproterozoic and early neoproterozoic age are widespread and include highly organic rich shales deposited in restricted basinal settings adjacent to stromatolitic carbonate banks by c 850 ma the neoproterozoic molecular record is dominated by hopanes from cyanobacteria with a significant abundance and diversity of eukaryotic steranes including those of multicellular eukaryotes red and green algae as well as molecular evidence for heterotrophic protists the most widespread hydrocarbon source rocks of mid to late neoproterozoic age are commonly transgressive organic rich black shales associated with inter glacial and post glacial phases of the neoproterozoic global scale glaciations the relative dominance of microbial mats in the contribution of organic matter as a source for hydrocarbon generation probably decreased significantly during the late neoproterozoic and earliest cambrian perhaps as a result of the rapid growth of grazing metazoan communities or possibly as a result of changes in seawater chemistry and or nutrient supply precambrian and infracambrian petroleum systems are relatively abundant and widespread the oldest live oil recovered to date is sourced from mesoproterozoic rocks within the velkerri formation roper group of the mcarthur basin of northern australia dated at 1361 21 ma and 1417 29 ma re os dates with at least the initial phase of oil generation and migration having taken place before 1280 ma however the geologically oldest commercial production is currently from the somewhat younger mid to late neoproterozoic cryogenian ediacaran petroleum systems of the lena tunguska province in east siberia and in southern china from the latest neoproterozoic to early cambrian huqf supergroup in oman and potentially in the near future from the age equivalent mawar supergroup in western india

microparticle concentration variations linked with climatic change evidence from polar ice cores the microparticle concentrations in three deep ice cores reveal a substantial increase in the concentration of insoluble particles in the global atmosphere during the latter part of the last major glaciation the ratio of the average particle concentration in the late glacial strata to that in the holocene strata is 6 1 for the core from dome c antarctica 3 1 for the core from byrd station antarctica and 12 1 for the core from camp century greenland whether this temporal correlation between increased atmospheric particle load and the lower surface temperatures is directly causal is unknown however the variations in these two parameters must be satisfactorily resolved in any successful hypothesis that addresses the causes of climatic change

large variations of surface ocean radiocarbon evidence of circulation changes in the southwestern pacific radiocarbon 14c and stable isotope 18o and 13c records are presented for biannual samples from a 323 year banded coral series collected from the southern great barrier reef australia the high precision 14c record contains variations on an interannual timescale that are particularly large between a d 1680 and 1730 by comparison with tree ring 14c records stuiver and quay 1980 m stuiver personal communication 1992 it is clear that these shifts were not caused by changes in the 14c of atmospheric co2 changes in vertical mixing and large scale advective changes involving source waters to the western coral sea region are likely processes that could account for these large 14c variations most low 14c values for the period a d 1635 1875 coincide with el nino southern oscillation enso events as reported by quinn et al 1987 for the eastern tropical pacific however enso does not explain all of the variations especially during 1875 1920 when 14c values remained high cross spectral analysis of the early half of the 14c and 18o records a d 1635 1795 reveals that the 6 year period is coherent this coherency is not present in the latter half a d 1797 1957 of the isotope records these data support the concept of century timescale changes in the nature of enso as it is manifest in the southwestern pacific our coral record shows no evidence of a suess effect the lowering of 14c from late 1800s through 1955 due mainly to co2 input from fossil fuel burning this is coincident with the change we observe in the nature of enso and is further evidence that a long term change in mixing of upper waters occurred in this region

confocal laser scanning microscopy and raman imagery of ancient microscopic fossils abstract among all problems confronting the study of ancient permineralized petrified microscopic fossils two stand out the need for 1 accurate documentation of their three dimensional morphology and 2 direct analysis of their chemical composition and that of their surrounding mineral matrices to address these problems we demonstrate the use of two techniques that we have recently introduced to precambrian paleobiology confocal laser scanning microscopy and raman imagery these techniques both of which are non intrusive and non destructive can provide data by which to characterize in situ and at micron scale resolution the cellular and organismal morphology of thin section embedded organic walled fossils in addition raman imagery provides direct analyses of the molecular structural composition of the kerogenous components of such fossils and of their surrounding matrices and a means to assess quantitatively the geochemical maturity of the preserved organics use of these techniques for studies of ancient microscopic fossils can provide information in three dimensions at high spatial resolution about their morphology and cellular anatomy taphonomy and fidelity of preservation composition and mode of preservation and their biogenicity and syngenetic origin with the rocks in which they occur

ore mineralogy of the applachian caledonian stratabound sulfide deposits abstract the diverse ore mineralogies of more than 100 stratabound sulfide deposits that occur along the length of the appalachian caledonian orogen have been tabulated the minerals reflect the varying cu zn pb ratios that have been used as a means to separate the ore deposits into six distinct types following the igcp project 60 guidelines the ore deposits each containing at least one million metric tons of ore are typical of massive sulfide deposits throughout the world and provide a basis for contrasting and comparing this orogen with others differing grades of metamorphism have significantly modified the ore mineral grain sizes and textures but do not seem to have effectively influenced the number or variety of mineral species present

a model for solar constant secular changes although the direct influences of sunspots upon the solar constant leads to short term decreases an opposite nearly in phase 11 year variation in the solar constant can be modelled this opposite behavior results primarily from global faculae polar network and active region the model attributes the observed variations in the solar constant entirely to magnetic features in the solar atmosphere hence the model does not require any indirect effect of the magnetic cycle on the brightness of non magnetic areas of the sun the model uses the well studied active region influences upon the solar constant together with the influences of global faculae associated with polar and general solar magnetism studied by sheeley using the present model together with the sunspot prediction of schatten and sofia 1987 we predict the average solar constant to the year 1997 normalized to the mean active cavity radiometer acrim and earth radiation budget erb observations the model also provides a relation so 0 007 rm max for the very long term solar constant variations due to the secular changes in solar activity we obtain a change of 1 w m for the difference between the late twentieth century solar constant and the 17th century solar constant this supports eddy s view that this difference could give rise to the glacial increase during the little ice age of the 17th century

age and origin of the well preserved organic matter in internal sediments from the silesian cracow lead zinc deposits southern poland the molecular and petrographic characteristics of organic matter in internal sediments from the mississippi valley type lead zinc deposits in southern poland reveal immature and well preserved organic matter huminite reflectance values of organic matter in all internal sediments are low with a mean value of 0 29 corresponding to a lignite range of coalification most organic compounds in the organic matter e g cadalene retene simonellite perylene and sitosterol and its transformation products stigmastanol and stigmasta 3 5 dien one as well as lignin degradation compound products e g benzoic acid vanillin 4 benzaldehyde benzenedicarboxilic acids and hydroxybenzoic acids are of terrestrial origin monosaccharides with dominant and glucose were identified as possible remnants of cellulose degradation products suggesting an excellent state of organic matter preservation given that monosaccharides are preserved only under conditions of limited oxygen after sedimentation resulting from the rapid accumulation of internal sediments in meteoric paleokarst cavities followed by insignificant diagenesis petrologic and palynological data on internal sediments clearly indicate a middle triassic age for organic matter and for the development of a triassic meteoric karst system immediately after anisian carbonate sedimentation

eighty eight year periodicity in solar terrestrial phenomena confirmed the existence of a 60 100 year periodic variation in solar and or solar terrestrial phenomena has been a matter of dispute for many years a wide variety of data sets previously have been analyzed and the results of the analyses have been interpreted as showing evidence either for or against such a variation however all data sets that are proxy for solar wind in the ecliptic at 1 au show variations consistent with a period of about 88 years here we report that a maximum entropy spectral analysis of the number of aurora reported per decade in europe and the orient from 450 a d to 1450 a d shows a strong stable line at a 88 4 0 7 years since the data set contains 11 cycles this analysis establishes the reality of the long cycle for 1000 years the mean amplitude and phase are then estimated from a superposed epoch analysis the mean amplitude was 2 2 auroral reports per decade and the last minimum phase in these data occurred between 1403 a d and 1413 a d

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

constraints on the sources of ore metals in mississippi valley type deposits in central and east tennessee usa using pb isotopes abstract the mississippi valley type mvt central and east tennessee tn districts contain lead zinc deposits that occur in the early ordovician carbonates of the knox group although both districts share similar host rock have similar temperatures of formation and typically fill open spaces of collapse breccias or replace their host carbonates previous studies may suggest that these ores did not form from the same mineralizing fluids and may have different pb sources nu plasma mc icp ms pb isotopic analyses on sulfides from central and east tn were conducted and the metal sources evaluated pb isotope ratios from the young mine in the east tn district plot within ranges defined by other east tn district samples from previous studies generally pb isotope ratios or ores from the elmwood mine in the central tn district are more radiogenic and plot between samples from the southern appalachians and illinois kentucky districts it appears that the thick black metal rich shales of the appalachian basin have been the source of the pb zn and ore fluids of mvt deposits that formed the east tn deposits when east tn pb data from this study are compared to central tn pb data central tn pb is commonly more radiogenic suggestive of a mineralizing fluid with different compositions lead isotopic signature of central tn ores may imply potential mixing between end member sources originating from the southern appalachians and illinois basins lead isotopes in mvt and carbonate hosted base metal deposits in us south america and europe display two basic types of pb isotopic signatures the classic mvt deposits in the mid continent us se and central missouri illinois kentucky and upper mississippi valley districts have highly radiogenic pb isotopic compositions and they generally display linear pb isotopic arrays in contrast deposits from europe irish type silesian type alpine type and cevennes region the appalachians and andean type deposits have lower pb isotopic values the european deposits except for the irish type have a restricted range of isotopic ratios which suggest a single mineralizing event of relatively short duration it appears that basement rocks or sedimentary rocks derived from the basement contributed pb to many mvt and carbonate hosted base metal deposits worldwide hydrothermal leaching of radiogenic pb from the crystalline basement rocks may have occurred during formation of these ore deposits high 238u 204pb values for several districts also suggest a supracrustal origin of pb

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

carbonaceous microstructures from sedimentary laminated chert within the 3 46 ga apex basalt chinaman creek locality pilbara western australia abstract hydrothermal black chert veins intruding the 3 46 ga apex basalt contain some of earth s oldest microfossil like objects whose biogenicity has been questioned whilst these black chert veins have been studied in great detail relatively little is known about the stratiform seafloor sedimentary cherts that are conformably interbedded with volcanic rocks of the apex basalt herein we document and assess the biogenicity of carbonaceous microstructures present in the lowermost of the stratiform chert units informally known as the apex chert at the chinaman creek locality in the marble bar greenstone belt pilbara craton western australia carbonaceous material mostly occurs within clotted grey black cherts and microgranular grainstone like cherts within the stratiform unit the latter being the major focus of this study in the clotted cherts carbon occurs as lobate fluffy grains rare compressed flakes and as a grain boundary phase around spherulitic silica there is no morphological evidence to support the biogenicity of these microstructures in contrast the microgranular chert contains fluffy and flaky carbonaceous grains plus laminated grains comprising multiple non isopachous wrinkled carbonaceous laminae with noted thickening towards some ridge crests as determined by confocal laser scanning microscopy roll up structures provide evidence of an initial plasticity interpreted to have formed via the tearing up and current induced plastic deformation of microbial mat fragments geochemical mapping using laser raman micro spectroscopy and nanosims respectively demonstrates the antiquity of the carbon and reveals a close correlation between carbon nitrogen and sometimes sulphur concentrated within dark brown to black laminae adjacent to microgranular zones are zones of more persistent carbonaceous undulose filament like laminae that entrain relict sediment grains these microstructures are directly comparable to a sub type of microbially induced sedimentary structure miss widely reported from younger siliciclastic sediments colonised by microbial biofilms the morphology and chemical composition of both the non isopachous laminated grains and the filament like laminae are consistent with a biological interpretation suggesting microscopic miss were present in the microgranular stratiform apex chert however the fact that neither macroscopic miss nor bona fide microfossils have yet been reported from this unit coupled with the proximity of these structures to active hydrothermal vents potentially discharging hot carbon rich fluids urges caution in such an interpretation the chinaman creek apex chert investigated here is one of at least five sedimentary laminated cherts within the apex basalt these horizons are promising targets in the search for biological activity within a dominantly volcanic archaean environment

the distribution of bomb radiocarbon in the ocean water column inventories are calculated for bomb radiocarbon at all the stations occupied during the geosecs and norpax expeditions and for the available tto stations the pattern of global inventories obtained in this way suggests that a sizable portion of the bomb radiocarbon that entered the antarctic the northern pacific and the tropical ocean has been transported to the adjacent temperate zones a strategy for utilizing these inventory anomalies as constraints on global ocean circulation models is presented essential to this strategy are the improvement of our knowledge of the pattern of wind speed over the ocean the establishment of the wind speed dependence of the rate of gas exchange between the atmosphere and sea and the continued mapping of the distribution of bomb produced radiocarbon in the sea

possible connection between surface winds solar activity and the earth s magnetic field records of 14c in tree rings provide a proxy for changes in solar activity on timescales of decades to centuries1 2 here i report an association between maunder type solar cycles recorded in tree rings and fluctuations in surface wind intensity on a roughly 200 year timescale over a period of about 2 000 years in the mid holocene the wind record is preserved as changes in the thickness of varved sediments in elk lake minnesota which contain a large aeolian component changes in cyclonic activity and tropospheric winds have been reported1 5 to occur in this region a few days after strong coronal mass ejections cmes increases of up to 7 in zonal flow have been reported5 at an altitude of 300 m after strong cmes in winter the implication of this association is that century scale changes in surface winds over minnesota were the long term maunder scale counterpart of short term daily changes in winds after cmes the weak magnetic field strength of the earth at this time6 7 might be relevant to a possible mechanism for the association

organic carbon accumulation rates in the holocene and glacial arabian sea implications for o2 consumption in the deep sea and atmospheric co2 variations variations in the deep sea carbon reservoir have been invoked to explain the observed atmospheric carbon dioxide co2 changes during glacial interglacial cycles in order to distinguish between the quantity of organic matter remineralized in the deep sea and that permanently removed into sediments we compared the bulk and organic carbon accumulation rates in holocene and glacial sediments deposited below the oxygen minimum layer with total and organic carbon fluxes to the deep arabian sea from continuous sediment trap deployments this comparison shows that the mass of organic carbon remineralized at the sediment water interface is mainly a function of the bulk sediment flux the oxygen consumed by the organic carbon remineralization is of the order of the observed oxygen deficiency of the modern deep arabian sea water we use the evidence from the northern indian ocean to speculate on the possible effect of abiogenic mineral flux on the removal of organic carbon from upper layers of the world ocean to the deep sea we assume that if the bulk accumulation rate not primary productivity influences the flux of organic carbon that is fixed from the atmosphere by marine organisms then mineral matter flux will exert a significant control over atmospheric co2 contents model calculations incorporating transient changes in global bulk flux caused by natural or anthropogenic changes show that significant proportions of the observed changes in atmospheric co2 contents can be explained by this mechanism

microbiological processes in banded iron formation deposition banded iron formations have been studied for decades particularly regarding their potential as archives of the precambrian environment in spite of this effort the mechanism of their deposition and specifically the role that microbes played in the precipitation of banded iron formation minerals remains unresolved evidence of an anoxic earth with only localized oxic areas until the great oxidation event ca 2 45 to 2 32 ga makes the investigation of o2 independent mechanisms for banded iron formation deposition relevant recent studies have explored the long standing proposition that archean banded iron formations may have been formed and diagenetically modified by anaerobic microbial metabolisms these efforts encompass a wide array of approaches including isotope ecophysiological and phylogeny studies molecular and mineral marker analysis and sedimentological reconstructions herein the current theories of microbial processes in banded iron formation mineral deposition with particular regard to the mechanisms of chemical sedimentation and post depositional alteration are described the main findings of recent years are summarized and compared here and suggestions are made regarding cross disciplinary information still required to constrain the role of the biosphere in banded iron formation deposition

haematite pseudomicrofossils present in the 3 5 billion year old apex chert microstructures from the 3 5 billion year old apex chert have been interpreted as the remains of ancient cyanobacteria geochemical analyses suggest similar structures at the same location are instead haematite filled fractures although carbonaceous material in the surrounding matrix is consistent with the presence of microbes at this time

data model comparison of the younger dryas event the younger dryas cooling event is well established in the north atlantic region through numerous climate proxy records although the climatological controls vary from site to site it is considered to have taken place between about 10 000 and 11 000 bp radiocarbon years 11 500 13 000 calendar years ago outside the north atlantic region climate proxy records and chronology commonly become problematic because of weaker signals and less dating control in addition to this evidence oceanic records reveal conflicting evidence for younger dryas forcing mechanisms and the timing of events we compare proxy evidence with the results from an ocean general circulation model coupled to the energy moisture balance atmospheric model the model results reveal a global pattern and regional magnitude which generally agree with temperature changes interpreted from paleoclimate reconstructions the model also supports the general duration of global cooling of the younger dryas although proxy data can be controversial outside of the north atlantic region the authors believe that there is enough evidence to support the younger dryas event on a global scale they also recognize however that more concrete evidence is needed before the question can be unequivocally answered

structural characterization by raman hyperspectral mapping of organic carbon in the 3 46 billion year old apex chert western australia abstract the 3 46 billion years old apex chert pilbara craton western australia is well known for hosting the oldest highly disputed microfossils on earth this rock has a complex history of thermal alteration that includes circulation of hydrothermal fluids lower greenschist facies regional metamorphism and post metamorphic weathering by meteoric fluids carbonaceous material occurs in the sedimentary stratiform part of the chert as well as the underlying intruding hydrothermal black chert veins in order to identify a least altered remnant of early life it is necessary to develop a method that enables rapid evaluation of cm structural order on a small spatial scale here we present the detailed characterization of cm in the apex chert by raman hyperspectral mapping it is shown that this approach gives better estimates of average raman band ratios than individual point analyses and it is demonstrated that significant differences in structure exist between cm in the stratiform part of the apex chert and cm in an underlying black chert vein the large raman map based datasets also reveal that significant mixing took place between these two end members cm s indicating that the apex chert has been thoroughly altered by hydrothermal fluid circulation at the brecciated intersection between the stratiform chert and the intrusive hydrothermal chert vein very poorly ordered cm was found that is not in line with lower greenschist facies regional metamorphism it is speculated here that this cm represents an organic fraction that was introduced or thoroughly altered by late stage meteoric fluids alternatively the ubiquitous presence of hematite in this sample caused a perturbation in the raman spectra of the cm leading to an artifact in the calculated raman based band ratios overall it can be concluded that the best preserved cm occurs in the stratiform parts of the apex chert while earlier discussions on organic microfossils in this rock often focused on parts of the chert that either represented the hydrothermal veins or the brecciated intersection between the veins and the stratiform part

information on past solar activity and geomagnetism from 10 be in the camp century ice core a nearly continuous record of the concentration of 10be from ice core data is compared with the tree ring derived record for 14c over the same period and it is found that short term trends in these data sets provide a record of solar activity no definitive relationship between the long term trends and the geomagnetic dipole moment is found

relative paleointensity of the earth s magnetic field from marine sedimentary records a global perspective abstract to assess the potential of marine sediments as a source of relative paleointensity information we have undertaken an investigation of selected box cores stored in the scripps core repository we present here new results from two north atlantic box cores magnetic remanence in the sediments is carried by magnetite and is univectorial during alternating field and thermal demagnetization the median destructive field is 25 30 mt normalization by anhysteretic remanent magnetization yields relative paleointensity data that are highly concordant within and between cores age control provided by oxygen isotope data from both cores allows comparison of these relative paleointensity data with contemporaneous archeomagnetic data from czechoslavakia both data sets indicate a peak in paleofield intensity at around 8 10 ka this peak is less prominent in box core data from the western pacific and global averages of archeomagnetic and lava flow data however the peak is evident in data estimating changes in production of radiocarbon which is controlled in part by changes in the dipole moment of the geomagnetic field the excellent agreement between production variations predicted by the changes in dipole moment and those observed suggests that long term variations in atmospheric radiocarbon are dominated by geomagnetic field variations

filamentous microfossils from the 3 500 myr old onverwacht group barberton mountain land south africa the swaziland supergroup barberton mountain land south africa has long been regarded as a promising location for the earth s oldest fossils because it includes some of the most ancient well preserved sedimentary rocks many of which contain carbonaceous matter although there have been numerous reports of microfossils from swaziland group rocks1 7 the biogenicity of most of the structures has been questioned8 10 although some of the organic spheroids are probably biogenic10 11 the best early archaean simple spheroids are generally regarded as possible microfossils 10 because organic spheroids may form abiotically in several ways12 the discovery of less simple biological morphologies is therefore important in establishing the existence of early life forms in the early archaean uniformly sized curving filaments especially tubular ones are difficult to explain as anything other than the fossil remains of filamentous organisms here we report the discovery of numerous filaments from two different stratigraphical positions in the 3 500 myr old onverwacht group of the swaziland supergroup their morphologies and abundance provide convincing evidence for the existence of bacteria or cyanobacteria like organisms on the earth during the early archaean this supports recent reports of similar filamentous microfossils from 3 500 myr old rocks from western australia13

seawater circulation through the flank of the florida platform evidence and implications dense biological communities at the base of the florida escarpment depend on energy provided by reduced compounds for bacterial chemosynthetic production sharp gradients in the concentrations of ch4 h2s nh4 so42 cl na mg2 sr2 i and seabed 226ra2 exist in the sediments underlying these communities the compositions of this fluid departs from that of normal seawater indicating the importance of microbial and diagenetic reactions within the escarpment before it is advected to the seafloor the 87sr 86sr ratios in the seep fluids range from 0 70920 seawater to 0 70773 which requires addition of light mesozoic strontium 18o values 0 3 to 0 1 smow and d values 2 6 smov of these waters are similar to normal seawater values and do not indicate that either meteoric processes or gas hydrates are involved in the genesis of the seeping fluid concentrations of cl ca2 and na suggest that the fluids which arrive at the seafloor are a mixture of mostly seawater with 4 7 formation brine from within the florida bahama platform mesozoic brines within the florida platform occupy levels above the scarp base a density driven flow system in implied which involves mesozoic platform brines that are greatly diluted by seawater entrained through the flanks of the platform the observed depletion of sulfate in the seeping fluids requires that sulfate reduction must occur in the platform within the zone where the recharging seawater and platform brines mix in order to produce the high concentrations of biogenic methane observed methanogenesis is inferred to be occuring within the platform in a zone where sulfate reduction has gone to completion the zone where the mixing of brine and seawater occurs should be cooled by the flushing seawater and heavily corroded by under saturation occurring as a result of the mixing the platform interior mixing is non conservative because of the addition of light mesozoic sr2 and the relative depletion in mg2 with espect to cl ca2 and na2 concentrations the inferred uptake of mg2 and concurrent depletion of so42 on the flanks of this margin