properties of multilayered cloud systems from satellite imagery the spatial coherence method for obtaining fractional cloud cover from satellite imagery is extended to the case of multilayered cloud systems examples are presented in which simultaneous observations at 3 7 m and 11 m are used to solve a system of linear equations for the nonoverlapped fractional cover contributed by each of two layers the retrieval relies on the assumption that the clouds reside in distinct well defined layers and are optically thick at the wavelengths of observation simultaneous observations at 3 7 m and 11 m of the separate layers indicate that the assumptions are generally valid owing to the reflection of solar radiation at 3 7 m by low level water clouds the method is limited to nighttime observations

a bistable organic rich atmosphere on the neoarchaean earth it has been hypothesized that before widespread oxygenation about 2 45 billion years ago the earth s atmosphere contained an organic haze similar to that on titan however these theoretical predictions have not been substantiated by geological evidence here we use multiproxy geochemical analyses of sediments from the 2 65 2 5 billion year old ghaap group in south africa to reconstruct ocean and atmospheric chemistry during this time we find evidence for oxygen production in microbial mats and localized oxygenation of surface waters carbon and sulphur isotopes indicate that this oxygen production occurred under a reduced atmosphere that was periodically rich in methane consistent with the prediction of a hydrocarbon haze we use a photochemical model to corroborate our geochemical data our simulations predict transitions between two stable atmospheric states one with organic haze and the other haze free the transitions are presumably governed by variations in the amount of biological methane production during the archaean eon we find that the isotopic signatures we observe are evident in other data sets from this period and conclude that methane was an important component of the atmosphere throughout the archaean before the rise of oxygen the atmosphere of the early earth may have consisted of an organic haze geochemical data and modelling suggest that from 2 65 to 2 5 gyr ago several transitions between hazy and haze free atmospheric conditions occurred potentially linked to variations in biogenic methane production

an ocean floor carbonaceous sedimentary sequence in the 3 2 ga dixon island formation coastal pilbara terrane western australia abstract the dixon island formation of the pilbara terrane western australia extends from cleaverville beach to the dixon island coast and is the only example worldwide of a coastal outcrop of a 3 2 3 1 ga low grade greenstone belt the dixon island formation was situated in an immature island arc setting and comprises siliceous carbonaceous deep water sediments that contain evidence for hydrothermal and microbial activity the extensive outcrop along the coastline makes it possible to examine in detail the characteristics of mesoarchean sedimentation in a hydrothermal environment this study focuses on a continuously exposed carbonaceous black chert succession in the central part of the northern coastline outcrop on dixon island at this site a 20 m thick carbonaceous black chert sequence conformably overlies basement rocks of highly altered komatiite rhyolite tuffs the black chert sequence formed well bedded black chert with carbonaceous peloidal matter and fragmented grains and the sequence is homogeneous and finely laminated in this sequence evidence of low temperature hydrothermal fluid sediments and alteration stractures are well preserved in the lowermost section indicating that high levels of hydrothermal activity occurred on the ocean floor during deposition in particular swarms of black chert veins provide evidence of post volcanic hydrothermal activity that released organic matter and silica to the ocean the carbonaceous peloidal textures and 13 c org values of sediments located just above the basement which hosts the vein swarms suggest that the veins were the conduits for hydrothermal fluid which contained organic rich silica material and that flowed onto the seafloor to form the homogeneous carbonaceous cherts along with hydrothermal related sediment the 13 c org values of organic matter in the black cherts range from 42 to 22 average 31 9 n 313 lighter 13 c values 35 to 42 characterize carbonaceous laminated black chert located 5 m above the basement where biogenic structures e g biomat bed microfossil structures are found the lighter 13 c values might be related to methanotrophic micro organic activity within the sediments during hydrothermal activity in summary we reconstructed the sedimentary environment upon a mesoarchean hydrothermal ocean floor that was a site of microbial activity and local methanogenesis

a giant late archean lake system the meentheena member tumbiana formation fortescue group western australia abstract the 2720 ma old meentheena member of the tumbiana formation fortescue group is a 30 50 m thick succession of alternating siliciclastic and limestone beds that crop out intermittently over a distance of 680 km across the pilbara craton western australia limestones of the member consist of flat pebble intraformational conglomerate oolite grainstone calcisiltite and calcilutite siliciclastics consist of shale siltstone and sandstone and many of these are tuffaceous sedimentary structures include abundant symmetrical ripples ripple cross stratification desiccation cracks teepee structures and planar to wavy lamination the member is superficially similar in appearance wherever it crops out however the correlation of individual beds and units over distances greater than 15 km is problematic there are no regional marker beds radiometric ages from tuffaceous units young to the west by a few million years four lithofacies are defined a flat pebble conglomerate b ripple cross laminated oolite grainstone c planar to wavy laminated calcilutite calcisiltite and d shale siltstone stromatolites are found in all three of the limestone facies evaporites are rare and include halite pseudomorphs the four lithofacies are generally found in a vertical succession that characterizes a lithofacies association and reflects a deepening upward succession associations may not have all four lithofacies but do reflect the same deepening upward pattern the uppermost portions of shale siltstone facies commonly contain symmetrical ripples and desiccation cracks indicating subaerial exposure measured sections contain as many as 25 of these parasequences indicating fluctuating water levels limestone lithology and facies commonly change abruptly laterally at the meter and greater scale and vertically centimeter to meter scale the sedimentary structures differences and abrupt changes in lithofacies patterns the inability to correlate confidently between regions and the differences in age from east to west suggest a complex diachronous depositional system of fluctuating water levels in separate bodies of water the limestone is dominated by sedimentary structures indicative of shallow water within wave base however it is devoid of evidence of any tidal influence possibilities for depositional environments include a tideless sea or a lacustrine system 87sr 86sr values from limestone differ from known archean marine carbonates ree patterns are decidedly non marine as well a lacustrine system is favored for the meentheena member based on sedimentary structures the abruptness of lithologic and facies changes the facies association lateral gradation into fluvial deposits the inability to correlate many units and beds for more than a few to several kilometers geochemical data stromatolites and comparisons with younger lacustrine basins as well as marine successions there is no single line of evidence that unequivocally establishes a lacustrine origin however multiple lines of evidence are collectively consistent with a lacustrine origin the meentheena member would therefore represent the oldest known carbonate rich lacustrine system which we call the meentheena lakes system

uv induced mass independent sulfur isotope fractionation in stratospheric volcanic sulfate 1 sulfuric acid aerosols produced in the stratosphere following massive volcanic eruptions possess a mass independent sulfur isotopic signature acquired when volcanic so2 experiences uv photooxidation the volcanic data are consistent with laboratory so2 photooxidation experiments using uv light at 248 nm maximum absorption of ozone whereas sulfur isotopic anomalies previously observed in archean samples are consistent with photodissociation at 190 220 nm a mechanism of so2 photooxidation occurring in the early stage of a stratospheric volcanic plume in the range of 220 320 nm weak band absorption of so2 is also proposed since mass independent sulfur isotope anomalies in stratospheric volcanic sulfate appear to depend on the exposure of so2 to uv radiation their measurements might therefore offer the possibility to determine the degree of uv penetration in the ozone absorption window for the present and past atmospheres they can also be used to determine the stratospheric or tropospheric nature of volcanic eruptions preserved in glaciological records offering the possibility to reassess the climatic impact of past volcanic eruptions

the chemical conditions of the late archean hamersley basin inferred from whole rock and pyrite geochemistry with δ33s and δ34s isotope analyses the well preserved late archean sedimentary rocks of the fortescue and hamersley basins in western australia offer fascinating insights into early earth ocean chemistry prior to the great oxidation event goe in this study we use a combination of whole rock geochemistry la icpms trace element analysis of sedimentary pyrite and pyrrhotite and shrimp si sulfur isotope analyses to elucidate the chemical changes in these sedimentary rocks these proxies are used to examine chemical conditions of the ocean during the late archean two to three periods of oxygen enrichment prior to the deposition of banded iron formations bif can be identified one minor stage of general increase in whole rock enrichment factors and trace element content of pyrite is observed up stratigraphy in the jeerinah formation fortescue basin and a more substantial stage is present in the paraburdoo and bee gorge members of the wittenoom formation hamersley basin some of the trace element enrichments indicate organic matter burial flux ni cr zn co and cu which suggests an increase in biological productivity if the increased biological activity reflects an increase in cyanobacteria activity then an associated increase in oxygen is likely to have occurred during the deposition of the bee gorge member an increase in atmospheric oxygen would result in continental weathering of sulfide and other minerals increasing the trace element content of the water column via erosion and avoiding excessive depletion of trace elements due to drawdown in seawater since some of these trace elements may also be limiting nutrients such as mo and se for the cyanobacteria the degree of biological productivity may have further increased due to the increasing amount of trace elements introduced by oxygenation in a positive feedback loop these periods of increased productivity and oxygen rise stopped prior to the onset of bif deposition in the hamersley basin this may be due to the ocean reaching an oxidation threshold enabling the precipitation of hematite and magnetite bif the bif deposition caused depletion of ocean nutrients such as phosphate severely limiting the growth of cyanobacteria and thus limiting further oxygen production

middle archean volcano hydrothermal sequence bacterial microfossil bearing 3 2 ga dixon island formation coastal pilbara terrane australia the 3 2 ga dixon island formation in the cleaverville group of the coastal pilbara terrane australia is one of the most complete and best preserved examples of middle archean oceanic stratigraphy and contains possible microbial material field observations and geochemical evidence suggest that this formation contains a low temperature hydrothermal vent system with a biogenic microbial colony from the archean ocean the dixon island formation is 350 m thick and consists of the rhyolite tuff black chert and varicolored chert members in ascending order the rhyolite tuff member contains many vein swarms such as quartz and black chert veins and highly altered rhyolite tuff layers which are identified as an underground bypass zone for circulating hydrothermal fluid many black chert vein swarms in the rhyolite tuff member imply intensive low temperature hydrothermal activity during deposition of the black chert member which is 10 15 m thick the black chert member is composed of massive black chert laminated black chert dark greenish siliceous shale and tuffaceous laminated chert which are mainly composed of very fine quartz abundant pseudomorphs of silica after aragonite barite and gypsum and a distinctly continuous stromatolite like biomat layer 10 20 cm thick are preserved within the laminated black chert bed the stromatolite like biomat bed is formed of fine iron or iron coated quartz pisolite within fine grained silica the absence of detrital sediment of continental origin and the many vein injections imply that this sedimentary facies represents a pelagic hydrothermal environment at 500 2000 m paleodepth and may have been on the slope of an immature island arc microbial material has been preserved well in the lower part of black chert member the massive black chert has carbonaceous peloids 0 3 2 0 mm in diameter which are similar to those in the black chert veins the massive black chert contains spiral rod and dendrite shaped bacterial material the total organic carbon toc value of massive black chert in the lower part of the black chert member is higher toc 0 15 0 45 than that of the overlying laminated chert section toc 0 02 0 15 and the black chert vein toc 0 1 0 13 and the carbon isotope 13 c values of this lithology 33 to 27 are also lighter than for the black chert veins 29 to 26 and the laminated black chert in the upper part of the black chert member and the varicolored chert member 27 to 13 this evidence suggests that the carbonaceous grains and bacteria shaped material in the lower part of the black chert member are of bio genic origin and were formed close to a low temperature hydrothermal vent system the microbial colony may have been rapidly fossilized by silicification related to hydrothermal activity laminated black chert in the upper part of the black chert and the varicolored chert members may have formed by cyanobacterial sedimentation from the ocean surface

pyrite paragenesis and multiple sulfur isotope distribution in late archean and early paleoproterozoic hamersley basin sediments abstract the sulfur isotope record in late archean and early paleoproterozoic rocks is of considerable importance because it provides evidence for changes in early earth atmospheric oxygen levels and potentially constrains the origin and relative impact of various microbial metabolisms during the transition from an anoxic to oxic atmosphere mass independently fractionated mif sulfur isotopes reveal late archean and early paleoproterozoic sulfur sources in different pyrite morphologies in western australia s hamersley basin multiple sulfur isotope values in late archean pyrite vary according to morphology fine grained pyrite has positive sulfur mif indicating a reduced elemental sulfur source whereas pyrite nodules have negative sulfur mif potentially derived from soluble sulfate via microbial sulfate reduction the hamersley basin 34 s 33 s record suggests that the extent of oxygenation of the surface ocean fluctuated through the late archean from at least 2 6 ga more than 150 million yr before the great oxidation event in the early paleoproterozoic there is less distinction between pyrite morphologies with respect to sulfur isotope fractionation and pyrite from the brockman iron formation trends toward modern sulfur isotope values an important exception to this is the strong negative mif recorded in layer parallel pyrite in paleoproterozoic carbonate facies iron formation this may suggest that deeper water hydrothermal environments remained anoxic while shallower water environments became more oxidised by the early paleoproterozoic the results of the current study indicate that sulfide paragenesis is highly significant when investigating archean and early paleoproterozoic multiple sulfur isotope compositions and sulfur sources

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

a multiple sulfur and organic carbon isotope record from non conglomeratic sedimentary rocks of the mesoarchean witwatersrand supergroup south africa abstract multiple sulfur isotope ratios 36 s 34 s 33 s 32 s and organic carbon isotope ratios 13 c 12 c were measured from 198 non conglomeratic sedimentary samples that were collected from five deep diamond drill cores that cover the majority of the ca 2 96 2 82 ga witwatersrand supergroup 13 c org 34 s py and 33 s py values of the sample set range from 44 3 to 21 9 3 7 to 16 5 and 4 0 to 1 9 respectively these geochemical data vary relative to depositional facies proximal marine distal marine and fluvial dominated and tectonic setting trailing margin and foreland basin in the trailing margin setting of the 2 96 ga hospital hill subgroup the proximal marine depofacies is characterized by relatively high organic carbon contents up to 0 9 wt and 13 c org values around 28 in contrast to the distal marine depofacies that yields low organic carbon contents 0 01 wt and high 13 c org values up to 22 both depofacies yield low sulfur contents 0 02 wt a narrow range of 34 s values 3 2 and positive 33 s values up to 1 9 this data is consistent with photoautotrophic carbon fixation in shallow marine environments and limited organic carbon production preservation in deeper water settings due to longer transport distances and effective biological degradation e g fe reducing microbes positive 33 s values imply that sulfur was largely derived from a photochemical elemental sulfur reservoir in the foreland basin tectonic setting of the 2 94 ga government and 2 92 ga jeppestown subgroups shelf deposits associated with fluvial braidplain depofacies are characterized by 13 c depleted organic carbon 44 to 38 relatively high sulfur contents 0 2 1 3 wt variable 34 s values 3 7 to 16 5 and small negative 33 s values 0 4 these data suggest that the microbial community in the fluvial dominated depofacies may have consisted of photoautotrophs methanogens anaerobic methanotrophs and sulfate reducers sulfate was derived from a variety of sources that include photochemical crustal and marine sulfur reservoirs the occurrence of three regionally persistent diamictite deposits in the government subgroup coincides with the onset of compressional tectonics and development of pyritic shales with highly 13 c depleted organic carbon suggesting that an increase in continental sulfur flux and methane oxidation may have triggered the mesoarchean glaciations drawdown of h 2 and ch 4 however the link between large 33 s anomalies 4 0 to 1 2 and diamictite suggests low levels of atmospheric oxygen and minimal dilution of photochemical signatures

in situ quadruple sulfur isotopic compositions of pyrites in the ca 3 2 2 72 ga metasedimentary rocks from the pilbara craton western australia abstract the sulfur mass independent fractionation s mif of mesoarchean is distinct from the other archean periods by the dampened magnitudes of 33s and a steeper slope of 36s 33s compared with the archean reference array ara according to previous studies however samples available of this interval are limited owing to poor or no preservation additionally the majority of the data were obtained by analysis of bulk rocks thus are essentially the sulfur isotopic compositions of mixed sulfur components due to multiple stages of post diagenesis overprints and modifications this study systematically measured the multiple sulfur isotopic compositions of pyrites nodular disseminated in ca 3 2 2 72 ga metasedimentary rocks from the pilbara craton western australia where one of the best preserved archean records occur using the upgraded shrimp si after detailed pyrite generation and genesis investigation by bse imaging and naocl etching the results show that 33s values of the diagenetic pyrites in these metasedimentary rocks range from 2 4 to 0 8 such a range is inconsistent with the other archean intervals and any experiment producing s mif so far where the magnitude of the maximum positive 33s value is considerably larger than the corresponding minimum negative 33s value the dampened positive 33s is explained in several ways from the perspective of production and preservation including original photochemical products with larger magnitudes of negative 33s than positive 33s in a different atmospheric composition non zero 33s of initial so2 different mechanism producing s mif chain formation and destruction of positive 33s by subduction the downward 36s 33s deviations from ara in the diagenetic pyrites of 2 72 ga tumbiana formation can be attributed to modifications induced by microbial activities this is based on the negative 0 9 33s 36s values similar to biological products and the large range of negative 34s values the downward 36s 33s offsets in the hydrothermally altered diagenetic pyrites of 2 78 ga mt roe basalt are most likely mixing of primary sulfur on ara with later sulfur disobeying ara the upward 36s 33s deviations in the diagenetic pyrites of 2 93 ga mosquito creek formation likely reflect different atmospheric composition

facies architecture and sequence stratigraphic features of the tumbiana formation in the pilbara craton northwestern australia implications for depositional environments of oxygenic stromatolites during the late archean abstract the tumbiana formation ca 2 7 ga is a succession developed in response to late archean crustal extension in the pilbara craton northwestern australia the formation is characterized by intercalations of stromatolitic carbonates and provides a perspective of the evolution of photosynthetic organisms which are interpreted to have been responsible for the oxygenation of earth surface environments in early earth here we investigated the depositional setting of the stromatolitic carbonates for the better understand of the environments which may have controlled the massive development of oxygenic photosynthesis we studied lithofacies and sequence stratigraphic features of the tumbiana formation in the redmont area a southern margin of the northern pilbara craton on the basis of three dimensional analyses of onshore outcrops the tumbiana formation as much as 170 m thick unconformably overlies the early to middle archean basement rocks and is unconformably overlain by the maddina formation that consists of mafic tuffaceous sediments and basalt lavas the lower part of the tumbiana formation is characterized by planar and trough cross stratified conglomerates which are interpreted to be an alluvial fan deposit shed from the northern hinterlands and developed mainly in local depressions of the basement rocks during late lowstand and early transgressive stages the base of the middle part is defined by a transgressive surface of erosion overlain by conglomerates and or breccias that pass upward to mafic tuffaceous mudstones and sandstones intercalated with accretionary lapillis breccias and basalt pillow lavas mudstones are commonly laminated and sandstones contain current and wave ripple lamination parallel lamination hummocky cross stratification and trough cross stratification in general the middle part exhibits an overall fining and coarsening upward pattern and is interpreted to indicate transgressive and regressive shelf to coastal lithofacies successions in particular the uppermost horizon of the middle part is characterized by sandstone beds with herringbone structures and desiccation cracks and is interpreted to indicate an intertidal deposit developed during late highstand and or following falling stages the middle part of the formation in general thickens to the northern proximal area and eventually flattened out the topographic irregularity of the basement rocks the upper part is characterized by stromatolitic carbonates associated with minor mudstones and wave and current rippled sandstones and does not exhibit distinct lateral variation in thickness and vertical lithofacies organization the base of the upper part is characterized by a transgressive lag deposit the ensuing transgression over the intertidal deposits of the uppermost middle part is interpreted to have developed a new accommodation space for the vertical stacking of stromatolites with different external shapes from elongated small domal and columnar types associated with desiccation cracks to stratiform and large domal types these changes may have responded to the increase in paleowater depth possibly from intertidal to subtidal environments in conclusion stromatolites in the upper tumbiana formation in the redmont area are interpreted to have developed in coastal and shallow marine environments in response to the rise in relative sea level rather than in ephemeral saline lakes as proposed by previous studies however the outcome of the present research does not necessarily deny the previously proposed interpretation but suggests spatial variations in depositional environments of the tumbiana formation from the north to south

the mesoarchean emergence of modern style subduction abstract well preserved volcanic sequences span the paleoarchean to neoarchean evolution of the pilbara craton in northwestern australia this region provides the best physical evidence bearing on the stage of earth s history when modern style tectonic processes began paleoarchean assemblages in the eastern nucleus of the craton the 3 51 3 24 ga pilbara supergroup show few features that can reasonably be interpreted as evidence for modern style subduction processes incompatible trace element enriched felsic volcanic horizons show geochemical evidence for the interaction between mafic magmas and crust but this evidence on its own can equally well be interpreted in terms of either a subduction enriched mantle source or local and limited assimilation of felsic crust into the voluminous tholeiitic magmas that dominate the pilbara supergroup viewed in context within the thick autochthonous and consistently upward younging pilbara supergroup these felsic units are most likely related to the same plume dominated processes that formed the basalts that dominate the supergroup it is very unlikely that modern style plate tectonic processes played any role in the paleoarchean evolution of the pilbara craton although some form of non uniformitarian e g flat subduction process may have operated in stark contrast the mesoarchean units of the west pilbara terrane and the late tectonic basins that cover that boundary between the west and east pilbara terranes show clear evidence for modern style convergent margin processes igneous rocks in this belt which flanks the old eastern cratonic nuclei have enriched geochemical signatures that cannot be accounted for by crustal contamination this region is also characterised by a linear magmatic and structural fabric by the presence of lithologically and geochronologically exotic belts and by the presence of a broad belt of isotopically more juvenile crust the collective strength of these arguments provides compelling evidence that a modern style oceanic arc fringed the east pilbara terrane at 3 12 ga and accreted to that terrane by 2 97 ga these assemblages mark the minimum age for the birth of modern style plate subduction process

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

a new method of seismic site classification using hvsr curves a case study of the 12 november 2017 mw 7 3 ezgeleh earthquake in iran abstract on the 12th of november 2017 a strong earthquake with a moment magnitude of 7 3 struck the west of iran causing massive damage in sarpolezahab and surrounding areas in this study the horizontal to vertical spectral ratio hvsr or h v technique of strong ground motion recorded at 60 stations is used for identifying of site response and subsequent site classification very clear amplification is observed at stiff and soft soil sites empirical equations from the literature relating frequency of hvsr peak to average shear wave velocity in the upper 30m vs30 commonly used as a proxy for site classification were found to be unreliable making site classification difficult to overcome this problem a soft computing method based on the generalized regression neural networks grnn algorithm is used this algorithm relies on hvsr curves at the recording stations and uses pattern recognition against a set of pre defined curves for different site types in this approach site characterization is based on the overall features of the hvsr curves rather than just the peak frequency the stations are classified into four different site classes and the results are consistent with local geotechnical information where available rather than relying on vs30 which has been found deficient in many studies and is known to have difficulty in reliably estimating when geotechnical data is lacking site classification proposed in this study uses the overall characteristics of hvsr curves of response spectra of recorded strong motion data this method is proposed as a more reliable and direct method for site characterization in seismically hazardous regions

the information content of high frequency seismograms and the near surface geologic structure of hard rock recording sites due to hardware developments in the last decade the high frequency end of the frequency band of seismic waves analyzed for source mechanisms has been extended into the audio frequency range 20 hz in principle the short wavelengths corresponding to these frequencies can provide information about the details of seismic sources but in fact much of the signal is the site response of the nearsurface several examples of waveform data recorded at hard rock sites which are generally assumed to have a flat transfer function are presented to demonstrate the severe signal distortions includingfmax produced by near surface structures analysis of the geology of a number of sites indicates that the overall attenuation of high frequency 1 hz seismic waves is controlled by the whole path q between source and receiver but the presence of distinctfmax site resonance peaks is controlled by the nature of the surface layer and the underlying near surface structure models of vertical decoupling of the surface and nearsurface and horizontal decoupling of adjacent sites on hard rock outcrops are proposed and their behaviour is compared to the observations of hard rock site response the upper bound to the frequency band of the seismic waves that contain significant source information which can be deconvolved from a site response or an array response is discussed in terms offmax and the correlation of waveform distortion with the outcrop scale geologic structure of hard rock sites it is concluded that although the velocity structures of hard rock sites unlike those of alluvium sites allow some audio frequency seismic energy to propagate to the surface the resulting signals are a highly distorted limited subset of the source spectra

review secular tectonic evolution of archean continental crust interplay between horizontal and vertical processes in the formation of the pilbara craton australia the archean pilbara craton contains five geologically distinct terranes the east pilbara karratha sholl regal and kurrana terranes all of which are unconformably overlain by the 3 02 to 2 93 ga de grey superbasin the 3 53 3 17 ga east pilbara terrane ep represents the ancient nucleus of the craton that formed through three distinct mantle plume events at 3 53 3 43 3 35 3 29 and 3 27 3 24 ga each plume event resulted in eruption of thick dominantly basaltic volcanic successions on older crust to 3 72 ga and melting of crust to generate first tonalite trondhjemite granodiorite ttg and then progressively more evolved granitic magmas in each case plume magmatism was accompanied by uplift and crustal extension the combination of conductive heating from below thermal blanketing from above and internal heating of buried granitoids during these events led to episodes of partial convective overturn of upper and middle crust these mantle melting events caused severe depletion of the subcontinental lithospheric mantle making the ep a stable buoyant unsubductable continent by c 3 2 ga extension accompanying the latest event led to rifting of the protocontinent margins at between 3 2 and 3 17 ga after 3 2 ga horizontal tectonic forces dominated over vertical forces as revealed by the geology of the three terranes karratha sholl and regal of the west pilbara superterrane the c 3 12 ga whundo group of the sholl terrane is a fault bounded 10 km thick volcanic succession with geochemical characteristics of modern oceanic arcs including boninites and evidence for flux melting that indicate steep archean subduction at 3 07 ga the 3 12 ga sholl terrane 3 27 ga karratha terrane and c 3 2 ga regal terrane accreted together and onto the ep during the prinsep orogeny this was followed by development of the de grey superbasin an intracontinental sag basin and widespread plutonism 2 99 2 93 ga as a result of orogenic relaxation and slab break off craton wide compressional deformation at 2 95 2 93 ga culminated with 2 91 ga accretion of the 3 18 ga kurrana terrane with the ep this compression caused amplification of the dome and keel structure in the ep final cratonization was effected by emplacement of 2 89 2 83 ga post tectonic granites

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

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

lithofacies control on multiple sulfur isotope records and neoarchean sulfur cycles abstract triple sulfur isotope ratios 32 s 33 s 34 s were measured for 141 bulk rock samples from two agouron scientific drill cores gkp01 and gkf01 that recovered neoarchean successions of the transvaal supergroup south africa these two deep time cores are correlated to each other with 14 tie lines using volcanic and impact spherule layers in a sequence stratigraphic framework allowing us to evaluate both lithofacies and temporal controls over multiple sulfur isotope systematics the ca 2 5 ga giga annum before present basinal klein naute formation and the ca 2 6 ga peritidal boomplaas and vryburg formations yield an array of data characterized by 33 s 1 4 34 s these linear trends are found in both shallow water and deepwater facies but are characteristic to rocks with high iron content suggesting these may reflect isotopic compositions of aqueous sulfide elemental sulfur reservoirs in the neoarchean oceans data that deviate from this linear array are interpreted as resulting from additional inputs of sulfide from microbial sulfate reduction with or without contribution from sulfur disproportionation sulfate derived sulfur evolved to be either enriched or depleted in 34 s depending on the local depositional environment for example the reivilo formation in core gkf01 is characterized by abundant microbialite textures and shows an isotopic signature of closed system sulfate reduction rapid cementation of these carbonate fabrics may have attenuated the supply of sulfate to pore waters resulting in the progressive 34 s enrichments during bacterial sulfate reduction below the sediment water interface in contrast signatures of open system sulfate reduction are associated with slope facies dominated by granular dolostones preserved in the upper nauga formations in gkf01 and gkp01 the two different sulfur isotope patterns interpreted to reflect closed versus open system sulfate reduction are both found in the lower reivilo formation in both cores this lateral variation of isotope signals documents that observed 34 s shifts can be controlled locally and may not have temporal significance this study demonstrates critical importance of recovering sulfur isotope data from stratigraphically correlated drill cores to evaluate both geographical and temporal shifts of sulfur cycles and their links to the great oxidation event at the end of the archean eon

quaternary negative tectonic inversion along the sibillini mts thrust zone the arquata del tronto case history central italy geological and geophysical investigations have been carried out in the surroundings of the villages of pretare and piedilama in the central apennines this area located at the footwall of the prominent nne ssw oriented sibillini thrust front was struck by the august 24th 2016 mw 6 earthquake the results of the geological field survey combined with geological and geophysical subsurface investigations are here illustrated by a detailed geological map and by two significant cross sections the studied area is crossed by the fosso di morricone valley that entrenched within the messinian pelitic arenaceous succession of the laga formation hosts a late pleistocene palaeo landslide the study evidences the occurrence of a n 10 oriented west dipping normal fault here named pretare piedilama fault that controlled the left side of the fosso di morricone valley producing a vertical displacement of the palaeo landslide deposits of about 50 m the geological geomorphological and geophysical data indicate that the fault was active during the late pleistocene and part of the holocene thus constraining a minimum vertical displacement rate of 0 4 mm a in the last 125 ka the geometry of the deformed laga formation cut by the fault suggests to relate it to the late quaternary negative tectonic inversion of a previous thrust plane located in the footwall of the sibillini thrust front the pretare piedilama fault would represent the easternmost tectonic expression of this main potentially active structure future researches could be addressed to detail the age and the actual motion rate of the structure and to define its seismic hazard assessment

atmospheric sulfur rearrangement 2 7 billion years ago evidence for oxygenic photosynthesis mass independently fractionated sulfur isotopes mif s provide strong evidence for an anoxic atmosphere during the archean moreover the temporal evolution of mif s shows increasing magnitudes between 2 7 and 2 5 ga until the start of the great oxidation event g o e at around 2 4 ga the conclusion of a completely anoxic atmosphere up to the g o e is in contrast to recent studies on redox sensitive elements which suggest slightly oxidizing conditions during continental weathering already several hundred million years prior to the g o e in order to investigate this apparent inconsistency we present multiple sulfur isotopes for 2 71 ga pyritic black shales derived from the kidd creek area ontario canada these samples display high positive 33s values up to 3 8 and the typical late archean slope in 36s 33s of 0 9 in contrast the time period before 3 2 2 73 ga is characterized by greatly attenuated mif s magnitudes and a slope in 36s 33s of 1 5 we attribute the increase in 33s magnitude as well as the contemporaneous change in the slope of 36s 33s to changes in the relative reaction rate of different mif s source reactions and changes in atmospheric sulfur exit channels both of these are dependent on atmospheric ch4 co2 and o2 mixing ratios we propose a distinct change in atmospheric composition at 2 7 ga resulting from increased fluxes of oxygen and methane as the best explanation for the observed neoarchean mif s record our data and modeling results suggest that oxygenic photosynthesis was a major contributor to primary productivity 2 7 billion years ago

a change in the geodynamics of continental growth 3 billion years ago models for the growth of continental crust rely on knowing the balance between the generation of new crust and the reworking of old crust throughout earth s history the oxygen isotopic composition of zircons for which uranium lead and hafnium isotopic data provide age constraints is a key archive of crustal reworking we identified systematic variations in hafnium and oxygen isotopes in zircons of different ages that reveal the relative proportions of reworked crust and of new crust through time growth of continental crust appears to have been a continuous process albeit at variable rates a marked decrease in the rate of crustal growth at 3 billion years ago may be linked to the onset of subduction driven plate tectonics

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

structural evolution of the middle archean coastal pilbara terrane western australia 1 the middle archean coastal pilbara terrane is composed of two lithotectonic units the karratha and cleaverville roebourne supercomplexes the karratha supercomplex lies tectonically beneath the cleaverville roebourne supercomplex and consists of 3270 3250 ma granitic batholiths and metamorphosed terrigenous sediments it is identified as a juvenile continental crust with tonalite trondhjemite granodiorite type granites the cleaverville roebourne supercomplex is interpreted as a dismembered immature island arc which has a restored crustal thickness of 20 km this supercomplex consists of 3195 ma bimodal volcanic chemical sedimentary sequences metabasite low k granitic gneiss and peridotite regionally distributed granite porphyries circa 3020 3000 ma have intruded all of the coastal pilbara terrane detailed structural analyses and zircon u pb dating suggest that the coastal pilbara terrane records two phases of deformation the first phase is an immature island arc and micro continental crust collision and is represented by top to the northwest thrusting d1 circa 3100 3020 ma this phase of deformation an arc continent collision appears to represent an important transition in the formation of continental crust the 3020 ma granite porphyry event may be related to syn post collision igneous activity and may reflect a second crustal thickening associated with magmatic underplating the second phase of deformation is characterized by regional scale left lateral strike slip faulting d2 circa 3020 2925 ma and by more localized right lateral strike slip faulting d3 circa 2925 2770 ma this phase of craton scale strike slip faulting may represent stabilization of the newly formed continental crust

site effects close to structural lineaments in eastern sicily italy abstract this paper analyses site effects that are applied to compute the h v spectral ratio close to structural lineaments aseismic creep and seismic creep have been examined the lineaments are located in different types of volcanic soil the aim of the work is to verify the possibility of fault guided seismic waves within the structures which behave as a waveguide for trapped waves the measurements of ambient noise were carried out along profiles crossing the structures and the standard nakamura technique was applied to calculate the spectral h v ratio it was observed that horizontal components of ground motion were found to be significantly amplified within the shear zone

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