a redox stratified ocean 3 2 billion years ago abstract before the great oxidation event goe 2 4 2 2 billion years ago it has been traditionally thought that oceanic water columns were uniformly anoxic due to a lack of oxygen producing microorganisms recently however it has been proposed that transient oxygenation of shallow seawater occurred between 2 8 and 3 0 billion years ago here we present a novel combination of stable fe and radiogenic u th pb isotope data that demonstrate significant oxygen contents in the shallow oceans at 3 2 ga based on analysis of the manzimnyama banded iron formation bif fig tree group south africa this unit is exceptional in that proximal shallow water and distal deep water facies are preserved when compared to the distal deep water facies the proximal samples show elevated u concentrations and moderately positive 56 fe values indicating vertical stratification in dissolved oxygen contents confirmation of oxidizing conditions using u abundances is robustly constrained using samples that have been closed to u and pb mobility using u th pb geochronology although redox sensitive elements have been commonly used in ancient rocks to infer redox conditions post depositional element mobility has been rarely tested and u th pb geochronology can constrain open or closed system behavior the u abundances and 56 fe values of the manzimnyama bif suggest the proximal shallow water samples record precipitation under stronger oxidizing conditions compared to the distal deeper water facies which in turn indicates the existence of a discrete redox boundary between deep and shallow ocean waters at this time this work therefore documents the oldest known preserved marine redox gradient in the rock record the relative enrichment of o 2 in the upper water column is likely due to the existence of oxygen producing microorganisms such as cyanobacteria these results provide a new approach for identifying free oxygen in earth s ancient oceans including confirming the age of redox proxies and indicate that cyanobacteria evolved prior to 3 2 ga

carboniferous floras in siliciclastic rocks of kashmir himalaya india and the evolutionary history of the tethyan basin the fenestella shale formation of jammu and kashmir himalaya comprises latest visean or serpukhovian siliciclastic deposits formed along the southern margins of the palaeotethys ocean a sequence of shallowing upward and deepening upward units indicates changes from shoreface to offshore and deeper shelf conditions probably controlled by eustatic changes in an otherwise passive depositional system some of the finer grained shallow marine deposits have yielded fossil floras dominated by sub arborescent lycopsids sublepidodendron lepidodendropsis sphenophytes archaeocalamites and pteridophylls nothorhacopteris triphyllopteris the assemblage compares with other gondwanan floras of this age that have been assigned to the paraca floral realm and are taken to indicate relatively warm climatic conditions that existed just prior to the onset of the carboniferous permian ice age

floristic migration in south america during the carboniferous phytogeographic and biostratigraphic implications abstract new data on the carboniferous flora of northern south america are combined with existing data for gondwanaland to re examine the floristic evolution of south america during the carboniferous the integration of paleobotanical palynological paleomagnetic paleogeographic and paleoclimatologic data makes it possible to reconstruct the floristic evolution of south america during the carboniferous as a dynamic process that was mainly controlled by the northward movement of the south american plate towards the equator during the carboniferous three carboniferous floras the cold archaeosigillaria lepidodendropsis frenguellia flora the temperate nothorhacopteris flora and the tropical euramerican flora characterize south america intra south american floristic migration is documented by the different age and composition of the nothorhacopteris flora it is of late early carboniferous age in northern south america bolivia northeastern brazil and peru whereas it is of late carboniferous age in southern south america argentina and southern brazil the flora was adapted to warm temperate climatic conditions indicating that southern south america moved into this climatic zone during the late carboniferous this migration explains the different ages recorded for the same taxa e g nothorhacopteris in northern and southern south america taxonomic differences between the northern and southern nothorhacopteris flora reflect visean westphalian evolution

origin and timing of the metasomatic silicification of an early archean komatiite sequence barberton mountain land south africa abstract stratiform units of pervasively silicified early archean ultramafic rocks occur near the boundary between the onverwacht and fig tree groups in the barberton mountain land republic of south africa the origin of these units has been variously ascribed to early archean subaerial weathering or submarine alteration to cataclastic metamorphism and to the alteration of silicic tuffs an exceptionally well exposed example of such an alteration sequence along the skokohla river valley in the central barberton mountain land was studied to determine the nature of the precursor rocks and the timing and nature of the alteration processes well preserved ghosts of spinifex and culmulate textured olivines and pyroxenes establish the komatiitic ancestry of the skokohla rocks rock units of several distinctive lithofacies can be correlated over the entire 1 5 km strike of the sequence and were derived from the metasomatic conversion of a series of ultramafic flow units to rocks dominated by quartz dioctohedral mica and chlorite the original ultramafics have been strongly enriched in si k rb and ba and depleted in fe mg ca na mn sr zn and ni the elements al ti p cr zr y and nb were immobile alteration apparently occurred soon after extrusive activity and before any significant tectonic deformation it is most probable that alteration resulted from the dynamic hydrothermal upwelling of fluids through original fracture porosity in the ultramafic flows

transitional changes in arborescent lignophytes at the devonian carboniferous boundary abstract it is usually considered that after the extinction of the devonian tree archaeopteri s no new arborescent lignophytes were established before the late tournaisian a reassessment of this pattern is presented here based on a three fold approach a re evaluation of the taxic diversity of tournaisian lignophyte trees based on descriptions of new plants from palaeotropical latitudes a study of the patterns of phenotypic changes occurring among early lignophytes using a principal coordinate analysis and a phylogenetic analysis of the affinities of the arborescent taxa the best supported results indicate that a substantial taxonomic and phenotypic diversity of arborescent lignophytes was already established in the first part of the tournaisian including some taxa that persisted until the serpukhovian two genera may have originated in the late devonian and crossed the devonian carboniferous boundary fewer originations and a decrease in phenotypic diversity occurred in the visean the phenotypic distinctiveness of tree stems compared with those of other growth forms in the lignophytes is assessed we propose a scenario in which the presence of lignophyte trees is continuous across the devonian carboniferous boundary with arborescent taxa distinct from archaeopteris already present in the latest devonian possibly in upland floras and diversifying significantly soon after the devonian carboniferous boundary supplementary material a list of taxa characters and matrices used in the principal coordinate analysis and phylogenetic analysis is available at http www geolsoc org uk sup18447

mississippian early permian brachiopods from western argentina tools for middle to high latitude correlation paleobiogeographic and paleoclimatic reconstruction abstract brachiopod faunas from western argentina are reviewed to improve the current understanding of their biostratigraphic and paleobiogeographic value for intercontinental correlation and paleoclimatic reconstruction especially for middle to high paleolatitudes the oldest faunal assemblage the late tournaisian early visean malimanian fauna indicates an incipient biogeographic segregation of southwestern south america from contemporaneous peri gondwana and northern hemisphere regions likely due to the enhanced thermal gradient that predated the pronounced latest visean global cooling and the major latitudinal biotic differentiation on a global scale paleogeographical distribution of key brachiopod taxa provides evidence of faunal interchange along western gondwana during late early carboniferous the paleoclimate of the region by this time has been interpreted as temperate preglacial conditions in a higher paleolatitudinal setting global cooling and strong differentiation between marine biota of circum polar and paleoequatorial regions occurred after late visean the barrealian fauna rugosochonetes bulahdelia and levipustula assemblages represents the oldest faunal record in western argentina of this major latitude related biotic segregation linked with the onset of the mid carboniferous glaciation the barrealian fauna appeared during a major late visean serpukhovian glacial episode with short lived glacial and interglacial stages climatic fluctuations were probably related to local faunal changes and marine biotic exchange between higher and middle paleolatitudes of southwestern and eastern gondwana widespread postglacial deposits bearing bashkirian faunas demonstrate the beginning of a progressive climatic amelioration trend until early permian times barely affected by short lived colder paleoclimatic fluctuations the incoming of the late bashkirian early moscovian marginovatia maemia fauna was linked to a climatic change in the region following the disappearance of glacial conditions in westernmost argentina ocean currents from the north that reached the region bringing boreal brachiopods were warm enough since bashkirian times to build a thermal barrier for the biotic interchange with peri gondwana regions under subpolar settings and a faunal disconnection was established in addition asymmetrical climatic record between western argentina and regions still under strong glacial influence such as patagonia and eastern australia reflect the clockwise rotation of gondwana and consequent migration of western argentina to lower latitudes after a preceding mainly regressive depositional interval the marine incursion bearing the tivertonia streptorhynchus fauna accompanied the most extensive transgression that covered western argentina it was probably linked with the beginning of a thalassocratic regime by the global major sea level rise of late asselian sakmarian times the tivertonia streptorhynchus assemblage represents a middle paleolatitude temperate and mixed fauna which migrated toward southern gondwana regions indicating a marine faunal connection during a climatic amelioration trend the last marine incursion in western argentina brought the costatumulus fauna linked to a brief interruption of the mostly temperate paleoclimatic conditions established since the pennsylvanian a short lived minor glacial pulse associated with the costatumulus fauna reflected local mitigated climatic fluctuations by the paleolatitudinal gradient to circumpolar areas where a major glacial pulse occurred during sakmarian artinskian times

a new serpukhovian mississippian fossil flora from western argentina paleoclimatic paleobiogeographic and stratigraphic implications an uppermost mississippian serpukhovian fossil flora from western argentina is described for the first time its particular composition includes both warm climate plants typical from the pennsylvanian of gondwana namely pteridosperms sphenophytes as well as arboreous lycopsids and small lycopsids characteristic of cooler climates of pre serpukhovian times a warm temperate climate is inferred for this association which fills a time gap between those pennsylvanian and mississippian classic floras previously known the presence of tomiodendron nothorhacopteris kellaybelenensis and paracalamites allow the recognition of the paraca floral realm in argentina supporting the existence of a nonglacial paleoclimate period developed just before of the bashkirian moscovian gondwanan glaciation and after a latest visean glaciation it likewise would indicate the paleogeographic position of south west gondwana which would have acceded to a warm temperature latitudinal belt during serpukhovian times the recognition of this floral assemblage has relevant biostratigraphic and lithostratigraphic implications for the western margin of gondwana it defines a new zone for western argentina herein named frenguellia eximia nothorhacopteris kellaybelenensis cordaicarpus cesarii fnc zone which is recorded in the oldest known lithostratigraphic unit from the paganzo basin the loma de los piojos formation nom nov

depositional settings and evolution of a fjord system during the carboniferous glaciation in northwest argentina abstract fjord systems represented by glacial diamictites and postglacial transgressive shales formed in the basins of western argentina during the late carboniferous gondwana glaciation well exposed fjord deposits of the guandacol formation were studied in the loma de los piojos region protoprecordillera where they fill a 2 9 km wide paleovalley with steep side walls and a relatively flat floor the valley cross cuts lower devonian sandstones and mississippian mudstones and sandstones and provides evidence of glacial abrasion including striated pavements and glacial microtopography grooves ridges and striae based on the analysis of seven sedimentary logs eight sedimentary facies in the valley fill were recognized a massive diamictites b laminated mudstones with dropstones c stratified diamictites d clast supported conglomerates and sandstones e deformed diamictites conglomerates and sandstones f folded diamictites g mudstones interbedded with sandstones and h stacked and amalgamated sandstones these sedimentary facies are grouped into two principal facies assemblages that represent different stages of the paleovalley fill assemblage 1 is composed of diamictites facies a c and f laminated mudstones with dropstones facies b and conglomerates facies d and e which represent glacially influenced sedimentation in the paleovalley assemblage 2 represents the paleovalley fill when glacial influence ceased and comprises laminated mudstones interbedded with sandstones facies g and stacked sandstone beds facies h that mostly record deltaic sedimentation stratigraphic relationships plant fossils found in the paleovalley walls and palynological assemblages recovered in mudstones of facies d help to establish an early pennsylvanian age for both the incision and the filling of the paleovalley the studied paleovalley records an exceptional example of the western gondwanan glacial to postglacial transition due to the continuous stratigraphic succession within the paleovalley as well as palynological megafloristic and radiometric data this example provides a complete framework of the late carboniferous postglacial evolution in western gondwana

paleoarchean sulfur cycle and biogeochemical surface conditions on the early earth barberton south africa abstract this study presents the first multiple sulfur isotope dataset on sulfides from the ca 3 5 3 2 ga onverwacht group in the paleoarchean barberton greenstone belt bgb of south africa in situ 34 scdt and 33 s values of pyrite n 568 are reported from a wide range of hydrothermal volcanic and sedimentary environments and are used to explore mid archean biogeochemical sulfur cycling samples are from fresh drill core collected by the barberton scientific drilling project that intercepted cherts metabasalts and sheared ultramafics of the 3 3 3 35 ga kromberg formation the sedimentary units of the 3 432 ga noisy formation and the unconformably underlying metabasaltic pillow lavas of the 3 472 ga hooggenoeg formation pyrite in quartz carbonate veins in the lower diamictite of the noisy sequence records the largest range and most negative 34 scdt values so far reported from an archean terrain 34 s cdt 55 04 to 27 46 the noisy sediments also contain detrital and diagenetic pyrites with a significant variation in 33 s of between 0 62 to 1 4 and 34 scdt of between 7 00 and 12 6 interpreted to reflect tectonic exposure of these early sediments to atmospheric shallow marine conditions early marine pyrites from the kromberg cherts also display strong positive 33 s values up to 2 50 with narrow range in 34 scdt values 6 00 to 1 50 whereas hydrothermal veins in the basal ultramafic shear zones preserve magmatic values 0 this study reveals a potential proto tectonic control on atmospheric geodynamic and hydrothermal environments available for early sulfate reducing and or methanogenic microbes in the paleoarchean no evidence for microbial sulfate reduction or disproportionation was identified in the kromberg cherts despite previous morphological claims for microbial life highly variable and negative 34 scdt values were found in the noisy turbidites and hooggenoeg pillow lava breccia supporting the presence of microbial sulfate reduction in early tectono sedimentary basins and in the paleoarchean sub seafloor respectively in light of current controversies surrounding sulfur isotope studies in similar aged rocks of the pilbara craton west australia we argue that microbial elemental sulfur disproportionation was not a preferred metabolic pathway on the paleoarchean earth

two coexisting sulfur metabolisms in a ca 3400 ma sandstone a sandstone from the ca 3400 ma strelley pool formation of western australia contains pristine micron sized pyrite intimately associated with organic material coating framework quartz grains a synsedimentary to early diagenetic origin for this pyrite is indicated by its occurrence in black bedded sandstone at the base of the formation and in reworked black clasts higher up in the formation high resolution multiple sulfur isotope analysis 32s 33s 34s using secondary ion mass spectrometry nanosims and large radius ion microprobe reveals 34svcdt vienna canyon diablo troilite values between 12 and 6 and 33s values between 1 65 and 1 43 from pyrite grains within a single thin section a large spread of 34s values over only 5 10 m together with the spatial association of pyrite with carbon and nitrogen indicates biological processing of sulfur the presence of both 33s and 33s signals overprinted by significant mass dependent 34s fractionation in this pyrite population indicates for the first time that both microbial sulfate reduction of aqueous sulfate 33s and microbial disproportionation of elemental sulfur 33s were co occurring in an open marine sedimentary hosted ecosystem in the paleoarchean

palaeoecological and evolutionary significance of anatomically preserved terrestrial plants in upper carboniferous marine goniatite bullions anatomically preserved plants are described from marine goniatite bullions of marsdenian age namurian b upper carboniferous from star wood oakamoor staffordshire england they comprise stems and petioles up to 15 cm long predominantly of cordaites mesoxylon and pteridosperms sutcliffia with rare calamites ferns and lycopsids and are preserved as calcareous permineralizations rare fusainized plant fragments are also found the flora is similar although comprising fewer species to the roof nodule floras of langsettian westphalian a age from lancashire which occur above coal seams yielding calcareous coal balls the plants preserved in these roof nodules probably grew in well drained slightly elevated lowlands not inundated during marine transgression and contrast in botanical composition to the floras of lowland peat forming mires represented in typical coal ball floras the oakamoor assemblage likewise probably represents an assemblage living in well drained elevated areas which drifted into the sea and was preserved in sediment starved carbonates during the height of the marine transgression these species of plants appear not to have become part of lowland mire ecosystems until later in the carboniferous the occurrence of this flora pre dates that previously described from the westphalian coal measures and extends the range of several important upper carboniferous plant taxa

pyrite in a sulfate poor paleoarchean basin was derived predominantly from elemental sulfur evidence from 3 2 ga sediments in the barberton greenstone belt kaapvaal craton abstract multiple sulfur isotope variability in archean sedimentary rocks provides constraints on the composition of the earth s earliest atmosphere the magnitude and sign of mass independent anomalies reflect not only atmospheric processes but also transformations due to the archean marine sulfur cycle prior to preservation into sedimentary pyrite the processes affecting the archean marine sulfur cycle and the role of microbial or abiotic redox reactions during pyrite formation remain unclear here we combine iron fe and multiple sulfur s isotope data in individual pyrite grains with petrographic information and a one dimensional reactive transport model to investigate the sources of fe and s in pyrite formed in a paleoarchean sedimentary basin pyrites were selected from mudstones sandstones and chert obtained from a drill core in the ca 3 2 ga mapepe and mendon formations of the fig tree and onverwacht groups respectively in the barberton greenstone belt kaapvaal craton south africa pyrite textures and 56 fe distinguish early diagenetic pyrite formed with pore water ferrous iron disseminated grains with average 56 fe pyrite 0 from late diagenetic pyrite formed through sulfidation of iron oxide minerals layered and aggregate forms with average 56 fe pyrite 1 mass dependent s isotope variability in pyrite was small 34 s pyrite ranged from 1 1 to 3 3 with a correspondingly minor spread in 33 s pyrite ranging from 0 3 to 2 1 and 36 s pyrite ranging from 3 08 to 0 27 that indicates a lack of post depositional re working with other distinct sulfur sources our combined fe and s isotope data are most readily explained with pyrite sulfide derived from microbial reworking of solid elemental s iron oxide minerals were necessary to buffer sulfide concentrations and provide favorable conditions for microbial sulfur disproportionation to proceed the lack of a negative 33 s signal indicates that pyrite from relatively deep marine diagenetic environments only partially records the products of atmospheric photolysis consistent with low sulfate concentrations in the paleoarchean ocean

an upper paleozoic bio chronostratigraphic scheme for the western margin of gondwana abstract the carboniferous and permian fossiliferous sequences of the central western argentina contain abundant plant remains palynomorphs and invertebrates they include a continuous record of large distribution in the paganzo rio blanco calingasta uspallata and san rafael basins the most recent biostratigraphic schemes recognize a floristic succession represented by the biozones archaeosigillaria frenguellia af biozone frenguellia eximia nothorhacopteris kellaybelenensis cordaicarpus cesarii fnc biozone nothorhacopteris botrychiopsis ginkgophyllum nbg biozone interval biozone and gangamopteris biozone the associated palynological record is represented by the biozones reticulatisporites magnidictyus verrucosisporites quasigobbetti mq biozone raistrickia densa convolutispora muriornata dm biozone pakhapites fusus vittatina subsaccata fs biozone and lueckisporites weylandites lw biozone the precise age of the upper paleozoic western gondwanan biozones has been under discussion and remains controversial to date in some regions the main issue hampering an integrated comparison of the gondwanan biozones was its imprecise chronostratigraphic framework however new studies in some argentinian stratigraphic sections bearing floras and faunas have yielded several radiometric ages from these 206 pb 238 u zircon datings it is possible to determine the chronostratigraphic range of many fossiliferous assemblages in this sector of gondwana in this way the af and mq biozones are restricted to the late mississippian and they would be not younger than 335 ma according to radiometric ages 206 pb 238 u ages suggest that the nbg dma and dmb biozones characterize the late serpukhovian glacial deposits and persisted up to the late bashkirian beds containing the interval and dmc biozones have yielded 206 pb 238 u ages of 312 82 0 11 ma and 310 71 0 1 ma which would indicate that both zones characterize the moscovian the remains of gangamopteris biozone found in the paganzo basin overlie basalt levels ranging between 308 6 and 293 6 ma therefore the incoming of the first glossopterids was closely associated to the carboniferous permian boundary in this part of gondwana the data presented in this paper are used for establishing comparisons with other gondwanan biozones constrained by absolute ages

a greenhouse interval between icehouse times climate change long distance plant dispersal and plate motion in the mississippian late visean earliest serpukhovian of gondwana abstract the late paleozoic ice age lpia is the closest example that can be compared with current climate conditions near the beginning of the lpia fossil plants of mississippian late visean to earliest serpukhovian age indicate a widespread frost free climate in a wide belt on gondwana indicating an interval of greenhouse conditions between the earlier visean and later serpukhovian icehouse times this warm temperate floral belt has been named the paraca floral belt after the locality on the peruvian coast where it was first recognized the origin of this particular zono biome was due to the interplay of 1 climate oscillations 2 several kinds of long distance plant dispersal within between or through zono biomes and 3 plate motion the carboniferous age strata on the paracas peninsula in peru serve as an example for an analysis of these large scale patterns through the analysis of local geology paleobotany and paleoecology the processes observed during this time interval can serve as a model for long distance plant dispersal at other times

evidence of glacial abrasion in the calingasta uspallata and western paganzo basins mid carboniferous of western argentina abstract evidence of glacial abrasion is present in the basal part of the carboniferous section of the calingasta uspallata and paganzo western argentina where subglacial and proximal glacial marine diamictites with pebbly dropstone shales constitute the dominant facies association intraformational striated pavements are exposed in the hoyada verde and leoncito formations of the calingasta uspallata basin marine invertebrate fossils levispustula zone in associated shales indicate a mid carboniferous age for both units a single layer striated boulder pavement is superbly exposed in the hoyada verde formation local a axis clast imbrication in the underlying bouldery diamictite and strong parallel striae on the flattened upper surfaces of boulders indicate a subglacial origin for the pavement paleo ice flow directions have an nne ssw strike the leoncito intraformational pavement is shaped on bioturbated fine grained sandstones with plant remains glacial striations are straight and parallel with subcircular cross sections dome like features are present in the surface which is covered in turn by a sandy bouldery diamictite four striated surfaces are present in the western paganzo basin three of them pavements at the san juan river valley loma de los piojos and agua hedionda are developed on basement rocks they contain parallel to subparallel striations nailhead striations crescentic gouges impact marks and furrows the pavements are overlain by thin up to 1 5 m laterally discontinuous diamictite beds with striated clasts some of them bullet shaped paleo ice flow directions are n ne directed an intraformational pavement is also present at the san juan river valley section it is carved on the top of the basal diamictite and exhibits furrows probably caused by subglacial soft sediment grooving the dispersion of paleo ice flow directions in the calingasta uspallata and paganzo basins indicates i regional slopes toward the north into a brackish water embayment and northwest into the open marine conditions ii glacial erosion by ice grounded below sea level and confined to the margins of the basins

reassessment of mid carboniferous glacial extent in southwestern gondwana rio blanco basin argentina inferred from paleo mass transport of diamictites abstract late paleozoic glacial diamictites occur in many localities in western argentina indicating that the region was strongly affected by glaciation during the mid carboniferous late serpukhovian early bashkirian in most instances these diamictites are found in steeply walled paleovalley settings in the andean precordillera this study presents new data from a locality north of the precordillera that suggests an additional distinct volume of ice existed in the region during the carboniferous the glacigenic diamictites in the rio blanco basin were ultimately emplaced as gravity flows precluding inferences of paleo ice volume fold nose orientation and soft sediment groove orientations within the diamictites indicate that the deposits were emplaced from north to south suggesting that glacial ice was most likely not sourced from the proto precordillera at this locality requiring the need for another ice center to the north of the basin diamictite facies indicates that the sediment was initially supplied to the study area by a warm based glacier

late paleozoic paleoclimatology of central west argentina abstract based on sedimentologic and paleontological characteristics present in the sedimentary record of the calingasta uspallata and paganzo basins a model of paleoclimatic evolution for the late paleozoic of central west argentina is proposed additional evidence is also provided by data from other basins of southern san rafael and tepuel basins and northern tarija basin west argentina five paleoclimatic stages have been defined paleoclimatic stage i tournalism visean early carboniferous is characterized by temperature and humid preglacial conditions as evidencedin the el raton and maliman formations calingasta uspallata basin plant remains of archeosigillaria and lepidodendropsis zone are present in both units the paleoclimatic stage ii namurian early westphalian middle carboniferous comprises widespread glacial deposits including glaciomarine sequence in the westernmost basins calingasta uspallata western paganzo san rafael and tepuel and terrestrial tillites and glaciolacustrine fine clastics in some areas of the paganzo basin fossils of the levipustula fauna are distinctive in the glaciomarine deposits of this stage and in the overlying postglacial fine clastics of the basal portion of stage iii substage iiia the paleoclimatic stage iii of middle carboniferous late westphalian age corresponds to postglacial transgressions that flooded the previously glaciated shelves in the calingasta uspallata and tepuel basins terminal glaciolacustrine deposits substage iiia indicate of the demise of glacial conditions and coal measures of fluvial affinity in the paganzo basin substage iiib probably this postglacial stage was characterized by high humidity and moderate temperatures this stage is paleobiologi defined by a floral assemblage known as nbg nothorhacopteris botrychiopsis and ginkgophyllum the paleoclimatic stage iv late carboniferous stephanian early permian corresponds to a time interval characterized by seasonally dry climates and a progressive amelioration in humidity clear evidence of these climatic conditions is present in several localities in the paganzo basin the first astherothecae and glossopteris leaves are found finally paleoclimatic stage v middle late permian is dominated by red beds thick eolian sequences and saline lake facies deposited under arid to semi arid conditions coeval volcanism derived from the west is expressed by interbedded tuffs and agglomerates calingasta uspallata paganzo and san rafael basins

multiple sulfur isotopes and the evolution of earth s surface sulfur cycle abstract the distribution of sulfur isotopes in geological materials reveals information about earth history and biogeochemical processes research during the last several decades has used sulfur isotope geochemistry as a tool to better understand microbial processes harrison and thode 1958 kaplan 1975 monster et al 1979 peck 1959 peck 1962 rees 1973 and sediment diagenesis berner 1969 berner 1982 canfield et al 1993b earth historians also realized this potential as there exists a rich record of environmental change within the sedimentary records canfield and teske 1996 claypool et al 1980 goodwin et al 1976 habicht et al 2002 kah et al 2004 monster et al 1979 shen et al 2001 strauss 1993 thode and goodwin 1983 these applications have championed the use of the two most abundant sulfur isotopes 32s and 34s and provide a rich introduction to what the sulfur isotope record has to offer see canfield 2004 canfield and raiswell 1999 within the last decade this information has been supplemented by new data derived from the less abundant isotopes 33s and 36s the measurement of all four stable sulfur isotopes multiple sulfur isotope geochemistry has expanded our understanding of biological evolution and activity atmospheric chemistry and transport crustal recycling and many more fields related to earth surface processes see farquhar and wing 2003 here i present a review of recent works in multiple sulfur isotope geochemistry with a focus on results that inform our understanding of biogeochemical processes and earth surface evolution

micro scale quadruple sulfur isotope analysis of pyrite from the 3480 ma dresser formation new insights into sulfur cycling on the early earth abstract we report in situ quadruple sulfur isotope analysis 32s 33s 34s and 36s of a pyritized microbial mat from the 3480 ma dresser formation pilbara craton western australia these data yield positive 34s and 33s indicative of sulfur sourced from a pool with similar character as the putative atmospheric elemental sulfur channel of pavlov and kasting 2002 contrary to previous data from the dresser formation however this pyrite is heavily depleted in 36s with a 36s 33s slope of c 3 6 much steeper than slopes typically seen in other early archean rock successions 36s 33s 1 which suggests either a different atmospheric signature for deposited s or a different pool altogether significant micro scale isotopic heterogeneity is observed within the microbial mat 34s 1 6 to 6 7 33s 0 4 to 2 6 36s 3 1 to 8 1 implying a role for microbial s metabolism while metabolic s cycling has been shown to shift 36s to lower values microbial metabolization of s does not appear sufficient to account for the full range of 36s we conclude that the isotopic composition of the pyrite was controlled by the relative proportions of mass independently fractionated mif s0 and sulfate derived sulfur incorporated into polysulfide pyrite precursors during reactions in the microbial mat the dominance of the mif s0 isotopic signature 34s 33s 36s indicates that contributions from the sulfate derived sulfur pool were relatively small consistent with low concentrations of sulfate in archean seawater and that contributions from a non sulfate pool were significant micro scale isotopic heterogeneity in the pyrite points to mixing between the two sulfur pools in selected micro environments within the microbial mat the particularly negative 36s observed here reveals a 3480 ma sulfur reservoir with novel 36s 33s chemistry whose significance now requires further investigation

engineering geological mapping developed in the fortaleza metropolitan region state of ceara brazil abstract engineering geological mapping was carried out at a scale of 1 100 000 in the fortaleza metropolitan region located in northeastern brazil to provide engineering geological information as an aid in planning land use and occupation in this study eight basic maps were produced drawing urban areas lithology unconsolidated materials in addition to geomorphological map showing slopes water resources engineering geological zoning and distribution of geological geotechnical environmental problems based on information collected through field and laboratory investigations the region was divided into nine engineering geological zones analyzed in terms of geohazard susceptibility and foundation excavation and waste disposal conditions

pyritic event beds and sulfidized fe oxyhydr oxide aggregates in metalliferous black mudstones of the paleoproterozoic talvivaara formation finland the paleoproterozoic 2 0 1 9 ga talvivaara formation of finland was deposited during the shunga event a worldwide episode of enhanced accumulation of organic rich sediments in the aftermath of the lomagundi jatuli carbon isotope excursion sulfidic carbonaceous mudstones in the talvivaara formation contain one of the largest known shale hosted nickel deposits in order to gain new insight into this shungian sedimentary environment sedimentological petrographical and in situ s and fe isotopic microanalyses were carried out on samples representing depositional and early diagenetic conditions the event bedded lithology with tidal signatures in the organic rich mudstones strongly indicates deposition from predominantly river delivered mud on a highly productive coastal area below storm wave base the riverine supply of phosphorus sulfate and iron supported high primary productivity and resulted in strong lateral and vertical chemical gradients in the nearshore waters with a shallow oxic surface layer underlain by euxinic water the stratigraphic upper part of the talvivaara formation contains banded intervals of thin alternating pyrite beds and carbonaceous mudstone beds the pyrite beds were deposited by seaward excursions of the concentrated acidic fe rich river plume subsequent to droughts or dry seasons which led to intense pyrite precipitation upon mixing with euxinic waters s34 and fe56 values of the bedded pyrite median s34 10 3 and fe56 0 79 are consistent with the reaction of dissolved fe ii with h2s from bacterial sulfate reduction organic rich clayey fe monosulfide bearing granules were transported from the muddy estuary and enclosed in fe oxyhydr oxide aggregates that were forming by wave and current reworking in nearshore accumulations of river delivered iron the isotopic composition of these presently pyrrhotitic inclusions median s34 3 3 and fe56 1 6 indicates microbial iron reduction the fe oxyhydr oxide aggregates were transported in muddy debris flows to the distal euxinic seafloor their fe oxyhydr oxide matrix was replaced by pyrite median s34 5 8 and fe56 0 81 at shallow sediment depths with 34s and 56fe enriched porewater wavy crinkly laminae of possible microbial origin developed on the euxinic seafloor during low sedimentation these results indicate episodic deposition at seasonal to multiannual time scales s34 and fe56 values in the studied fe sulfides provide evidence of microbial isotope fractionation processes and syndepositional and early diagenetic origin finding no support for the previously proposed local hydrothermal activity in the talvivaara mudstones

quadruple sulfur isotope analysis of ca 3 5 ga dresser formation new evidence for microbial sulfate reduction in the early archean abstract multiple sulfur isotope system is a powerful new tracer for atmospheric volcanic and biological influences on sulfur cycles in the anoxic early earth here we report high precision quadruple sulfur isotope analyses 32s 33s 34s 36s of barite pyrite in barite and sulfides in related hydrothermal and igneous rocks occurring in the ca 3 5 ga dresser formation western australia our results indicate that observed isotopic variations are mainly controlled by mixing of mass dependently md and non mass dependently fractionated non md sulfur reservoirs based on the quadruple sulfur isotope systematics 34s 33s 36s for these minerals four end member sulfur reservoirs have been recognized 1 non md sulfate 34s 5 2 33s 3 1 2 md sulfate 34s 10 3 3 non md sulfur 34s 6 33s 4 and 4 igneous md sulfur 34s 33s 0 the first and third components show a clear non md signatures thus probably represent sulfate and sulfur aerosol inputs the md sulfate component 2 is enriched in 34s 10 3 and may have originated from microbial and or abiotic disproportionation of volcanic s or so2 our results reconfirm that the dresser barites contain small amounts of pyrite depleted in 34s by 15 22 relative to the host barite these barite pyrite pairs exhibit a mass dependent relationship of 33s 34s with slope less than 0 512 which is consistent with that expected for microbial sulfate reduction and is significantly different from that of equilibrium fractionation 0 515 the barite pyrite pairs also show up to 1 difference in 36s values and steep 36s 33s slopes which deviate from the main archean array 36s 33s 0 9 and are comparable to isotope effects exhibited by sulfate reducing microbes 36s 33s 5 to 11 these new lines of evidence support the existence of sulfate reducers at ca 3 5 ga whereas microbial sulfur disproportionation may have been more limited than recently suggested

paleoarchean sulfur cycling multiple sulfur isotope constraints from the barberton greenstone belt south africa mass dependent and mass independent sulfur isotope fractionation archived in volcanic and sedimentary rocks from the barberton greenstone belt 3550 3215 ma south africa provide constraints for sulfur cycling on the early earth four different sample suites were studied komatiites and tholeiites barite massive and disseminated sulfide ores and non mineralized black shales variable but generally slightly positive 34s values between 0 7 and 5 2 negative 33s values between 0 50 and 0 09 and a negative correlation between 34s and 33s as well as between 33s and 36s for komatiites and tholeiites from the komati formation and from the weltevreden formation are outside the expected range of unfractionated juvenile sulfur instead results suggest alteration of oceanic crustal rock sulfur through interactions with fluids that most likely derived their sulfur from seawater barite from the mapepe formation displays positive 34s values between 3 1 and 8 1 and negative 33s values between 0 77 and 0 34 the mass independent sulfur isotope fractionation indicates an atmospheric sulfur source notably photolytic sulfate whereas the positive 34s values suggest bacterial sulfate reduction of the marine sulfate reservoir non mineralized black shale samples from the presumed stratigraphic equivalent of the mapepe formation show positive 34s values between 0 0 and 1 3 and positive 33s values between 0 59 and 2 45 these results are interpreted to result from the reduction of photolytic elemental sulfur carrying a positive 33s signature positive 34s values ranging from 0 7 to 3 5 and slightly negative 33s values between 0 17 and 0 12 characterize massive and disseminated sulfides from the bien venue prospect results suggest unfractionated juvenile magmatic sulfur source as the primary sulfur source but a contribution from recycled seawater sulfate which would be indicative of submarine hydrothermal activity cannot be ruled out massive and disseminated sulfides from the m hlati prospect are distinctly different from massive and disseminated sulfide from the bien venue prospect they show negative 34s values between 1 2 and 0 1 and positive 33s values between 2 66 and 3 17 thus displaying a sizeable mass independent sulfur isotopic fractionation again these samples clearly exhibit the incorporation of an atmospheric mif s signal the source of sulfur for these samples has positive 33s values suggesting a connection with photolytic elemental sulfur in conclusion the sulfur isotope signatures in paleoarchean rocks from the barberton greenstone belt are diverse and indicate the incorporation of different sources of sulfur for komatiites and tholeiites barite and massive and possibly also disseminated sulfides from bien venue multiple sulfur isotopes are related to ambient seawater sulfate and its photolytic origin while massive and disseminated sulfides from m hlati and non mineralized black shales are related to a second photolytic elemental sulfur end member

migration origination and extinction of southern hemisphere brachiopods during the middle carboniferous abstract the migration patterns and latitudinal diversity gradients of early and middle carboniferous articulate brachiopod genera from the paleoequatorial zone and southern hemisphere are consistent with the paleoclimatic history of these intervals interpreted from the study of paleoequatorial and northern hemisphere forms both poles apparently became warmer between the middle and late visean south polar cooling associated with glaciation probably began in the late visean at this time 44 of 92 southern hemisphere nonequatorial genera migrated toward the equator the north pole remained warm into the namurian a and cooled during the namurian a to b both northern and southern hemisphere non equatorial genera reacted to high latitude warming with significant increases in percent origination genera from all latitudinal zones responded to high latitude cooling with significant increases in percent extinction during the namurian a to b when both poles were cool a small but statistically significant number of equatorial genera 8 out of 70 migrated out of the equatorial zone into the non equatorial northern hemisphere no similar migration into the southern hemisphere occurred at this time perhaps due to the steep latitudinal temperature gradient several lines of evidence suggest that the latitudinal temperature gradient was steeper in the southern hemisphere than in the northern hemisphere whereas percent origination in northern non equatorial latitudes rose significantly following north polar cooling origination rates in southern non equatorial latitudes did not rise significantly following south polar cooling southern hemisphere non equatorial brachiopods suffered a greater loss of diversity during the interval of polar cooling than either equatorial or northern hemisphere non equatorial brachiopods and there may be namurian tillites within 20 s of the paleoequator veevers and powell 1987

stratigraphy and palynology of a late paleozoic glacial paleovalley in the andean precordillera argentina fil limarino carlos oscar consejo nacional de investigaciones cientificas y tecnicas oficina de coordinacion administrativa ciudad universitaria instituto de geociencias basicas aplicadas y ambientales de buenos aires universidad de buenos aires facultad de ciencias exactas y naturales instituto de geociencias basicas aplicadas y ambientales de buenos aires argentina

a paleoclimatic review of southern south america during the late paleozoic a record from icehouse to extreme greenhouse conditions abstract this paper provides a review of the late mississippian to permian paleoclimatic history for southern south america based on lithologic indicators biostratigraphic information and chronostratigraphic data the region is divided into three major types of basins 1 eastern intraplate basins e g parana basin 2 western retroarc basins e g paganzo basin and 3 western arc related basins e g rio blanco basin four major types of paleoclimatic stages are recognized in these basins 1 glacial late visean early bashkirian 2 terminal glacial bashkirian earliest cisuralian 3 postglacial cisuralian early guadalupian and 4 semiarid arid late guadalupian lopingian the glacial stage began in the late visean and continued until the latest serpukhovian or early bashkirian in almost all of the basins in southern south america during the bashkirian earliest cisuralian terminal glacial stage glacial deposits disappeared almost completely in the western retroarc basins e g paganzo basin but glaciation persisted in the eastern basins e g parana and sauce grande basins a gradual climatic amelioration postglacial stage began to occur during the earliest permian when glacial deposits completely disappeared across all of south america during this interval glacial diamictites were replaced by thick coal beds in the parana basin while north south climatic belts began to be delineated in the western basins which were likely controlled by the distribution of mountain belts along the panthalassan margin of south america towards the late permian climatic belts became less evident and semiarid or arid conditions dominated in the southern south america basins eolian dunes playa lake deposits and mixed eolian fluvial sequences occur in the parana basin and in the western retroarc basins volcanism and volcaniclastic sedimentation dominated along the western margin of south america at that time the stratigraphic record obtained in southern south america supports a long duration transition from icehouse to extreme greenhouse conditions

high precision u pb calibration of carboniferous glaciation and climate history paganzo group nw argentina the duration and geographic extent of carboniferous glacial events in southern gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered we report 10 high precision 2 0 1 u pb ages for the permian carboniferous paganzo group nw argentina that redefi ne the chronostratigraphy of the late paleozoic paganzo and rio blanco basins and signifi cantly refi ne the timing of glacial events and climate shifts in the western region of southern gondwana radiometric calibration of the paganzo group indicates three pulses of carboniferous glaciation in the mid visean the late serpukhovian to earliest bashkirian and between the latest bashkirian to early moscovian an abrupt shift in depositional style from high sinuosity single storied fl uvial deposits and clay rich paleosols to low sinuosity multi storied feldspathic fluvial deposits inter calated with eolianites and calcic paleosols is constrained to the latest moscovian and earliest kasimovian these constraints indicate a relatively abrupt climate shift from humid subhumid to nonseasonal semiarid regional climate conditions that occurred signifi cantly earlier than previously inferred early permian this period of high latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the pangean paleotropics in the pennsylvanian

in situ iron isotope analyses of pyrites from 3 5 to 3 2ga sedimentary rocks of the barberton greenstone belt kaapvaal craton abstract the barberton greenstone belt bgb south africa consists of volcano sedimentary and sedimentary successions deposited between 3 5 and 3 2 ga which are subdivided into three groups the onverwacht fig tree and moodies after deposition the barberton greenstone belt underwent relatively low grade tectonothermal events enabling estimation of surface environmental events and biological evolution in the middle archean isotopic studies suggest the activity of methanogen sulfate reducing bacteria and photosynthetic bacteria at 3 4 ga microbial dissimilatory iron reduction dir is also considered one of the earliest expressions of metabolism on earth but the isotopic signal of microbial dir is still uncertain in the archean we performed in situ iron isotope analyses of individual pyrites in sedimentary rocks from the bgb using a femtosecond laser ablation multi collector icp ms technique fs la mc icp ms to find isotopic evidence for the microbial activity we obtained a large variation in 56 fe values ranging from 1 84 to 3 79 most of the 56 fe values of pyrites from the hooggenoeg complex show positive values whereas those from the noisy complex and subsequent sedimentary sequences show a wide variation from negative to positive 56 fe values one of the main differences between these complexes is their depositional depth the hooggenoeg complex was probably deposited in a deep ocean environment whereas the noisy complex was in shallow water the negative 56 fe values of pyrite grains in the noisy complex onverwacht group indicate the occurrence of partial reduction caused by microbial dir in a middle archean shallow sea

sulfur isotope mass independent fractionation in impact deposits of the 3 2 billion year old mapepe formation barberton greenstone belt south africa abstract theoretical and experimental studies have shown that atmospheric so 2 isotopologue self shielding effects in the 190 220 nm region of the solar spectrum are the likely cause for mass independent fractionation of sulfur isotopes s mif the main products of this photochemical reaction so 3 and s 0 typically define a compositional array of ca 33 s 34 s 0 06 0 14 this is at odds with the generally observed trend in archean sulfides which broadly defines an array of ca 33 s 34 s 0 9 various explanations have been proposed including a diminution of 34 s caused by chemical and biogenic mass dependent fractionation of sulfur isotopes s mdf mixing with photolytic products produced during felsic volcanic events or partial blocking of the low wavelength part of the spectrum due to the presence of reduced atmospheric gases or an organic haze early in earth history large meteorite impacts would have ejected dust and gas clouds into the atmosphere that shielded solar radiation and affected global climate it is thus likely that at certain time intervals of high meteorite flux the atmosphere was significantly perturbed having an effect on atmospheric photochemistry and possibly leaving anomalous sulfur isotopic signatures in the rock record here we describe the sulfur isotopic signatures in sulfides of spherule beds s2 s3 and s4 of the barberton greenstone belt south africa in particular in spherule bed s3 and to a lesser extent s4 a trend of ca 33 s 34 s 0 23 is observed that closely follows the expected trend for so 2 photolysis in the 190 220 nm spectral range this suggests that an impact dust cloud deposited as spherule beds which sampled the higher region of the atmosphere specifically incorporated products of so 2 photolysis in the 190 220 nm range and blocked photochemical reactions at higher wavelengths 250 330 nm band by implication the generally observed archean trend appears to be the result of mixing of different mif s sources arising from a variety of photochemical reactions that took place in the lower part of the atmosphere

stratigraphic imprint of the late palaeozoic ice age in eastern australia a record of alternating glacial and nonglacial climate regime stratigraphic and sedimentological data from new south wales and queensland eastern australia indicate that the late palaeozoic ice age comprised at least eight discrete glacial intervals each 1 8 ma in duration here termed glaciations separated by nonglacial intervals of comparable duration these events spanned an interval from mid carboniferous c 327 ma to the early late permian c 260 ma and illustrate a pattern of increasing climatic austerity and increasingly widespread glacial ice from initial onset until an acme in the late early permian followed by an opposite trend towards the final demise of glaciation in the late permian the alternating glacial nonglacial motif suggests that the late palaeozoic ice age was considerably more dynamic than previously thought these patterns are remarkably consistent with recent interpretations of palaeofloral change eustatic sea level fluctuations and co 2 climate glaciation relationships for this interval of time the detailed record of alternating glacial and nonglacial climate mode disclosed herein may facilitate more closely resolved evaluations of stratigraphic records elsewhere notably in far field ice distal northern hemisphere successions

neoarchean carbonate associated sulfate records positive δ s anomalies mass independent fractionation of sulfur isotopes reported as 33s recorded in archean sedimentary rocks helps to constrain the composition of earth s early atmosphere and the timing of the rise of oxygen 2 4 billion years ago although current hypotheses predict uniformly negative 33 s for archean seawater sulfate this remains untested through the vast majority of archean time we applied x ray absorption spectroscopy to investigate the low sulfate content of particularly well preserved neoarchean carbonates and mass spectrometry to measure their 33 s signatures we report unexpected large widespread positive 33 s values from stratigraphic sections capturing over 70 million years and diverse depositional environments combined with the pyrite record these results show that sulfate does not carry the expected negative 33 s from sulfur mass independent fractionation in the neoarchean atmosphere

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

new insights into archean sulfur cycle from mass independent sulfur isotope records from the hamersley basin australia we have measured multiple sulfur isotope ratios 34 s 33 s 32 s for sulfide sulfur in shale and carbonate lithofacies from the hamersley basin western australia the v 33 s values v 33 swn 33 s30 515un 34 s shift from 31 9 to 6 9x over a 22 m core section of the lower mount mcrae shale v2 5 ga likewise sulfide sulfur analyses of the jeerinah formation v2 7 ga yield v 33 s values of 30 1 to 8 1x over a 50 m section of core despite wide variations in v 33 s and n 34 s these two shale units yield a similar positive correlation between v 33 s and n 34 s in contrast pyrite sulfur analyses of the carawine dolomite v2 6 ga yield a broad range in n 34 s 3 2 to 16 2x but a relatively small variation and negative values in v 33 s 32 5 to 31 1x the stratigraphic distribution of n 33 s n 34 s and v 33 s in western australia allows us to speculate on the sulfur isotopic composition of archean sulfur reservoirs and to trace pathways in the archean sulfur cycle our data are explained by a combination of massindependent fractionation mif in the atmosphere and biological mass dependent fractionation in the ocean in the archean volcanic sulfur bearing gas species were photolysed by solar ultraviolet uv radiation in an oxygen free atmosphere resulting in mif of sulfur isotopes aerosols of s8 with v 33 ss 0 and sulfuric acid with v 33 s6 0 formed from the products of uv photolysis and carried mass independently fractionated sulfur into the hydrosphere the signatures of atmospheric photolysis were preserved by precipitation of pyrite in sediments pyrite precipitation was mediated by microbial enzymatic catalysis that superimposed mass dependent fractionation on mass independent atmospheric effects multiple sulfur isotope analyses provide new insights into the early evolution of the atmosphere and the evolution and distribution of early sulfur metabolizing organisms a 2003 elsevier science b v all rights reserved