large scale traveling ionospheric disturbances observed by gps total electron content during the magnetic storm of 29 30 october 2003 1 we have investigated the propagation of large scale traveling ionospheric disturbances lstids during the super magnetic storm of 29 30 october 2003 two dimensional total electron content tec perturbation maps over north america were built using tec data provided by the american gps network and the international gnss service three lstid events were observed in the range of 30 degrees n 50 degrees n 60 degrees w 110 degrees w during this period the first two lstids occurred consecutively during 0620 0800 ut on 29 october at the local time of midnight right after the onset of the big substorm the third one was found at noon during the expansion phase of another substorm on 30 october the phase fronts of these lstids passed over the united states and traveled southwestward to the distance of similar to 2000 km with the maximum front width of similar to 4000 km and the duration of less than 2 hours the maximum amplitude of tec perturbations attained 3 total electron content units tecus the results differ from the former observation of afraimovich and voeykov 2004 and afraimovich et al 2006 who reported a solitary lstid propagating southwestward over the united states with the amplitudes of up to 14 tecu on 30 october 2003 we have checked the magnetic h component observed at the geomagnetic observatories in north america and found it is most likely that the auroral westward electrojet was the cause of the lstids on 29 october the source region for these tids was likely to be located several hundred kilometers north of 50 degrees n cross spectral analysis was conducted to obtain the global propagation characteristics of lstids during this superstorm equatorward lstids were found in all the three sectors of north america europe and asia showing high correlation with the occurrence of auroral substorms

rayleigh wave tomography at coronation field canada the topography effect within reflection seismology surface waves or ground roll are often considered a form of unwanted source generated noise unlike body waves surface waves propagate exclusively in the lateral direction and are virtually insensitive to structure deeper than one wavelength for a nominal frequency of 5 hz and phase velocity of 500 m s this means that a surface wave of the rayleigh or love type only feels the upper 100 m of the subsurface as a result surface waves cannot be used for imaging deep reflectors however they can be used to estimate near surface properties xia et al 1999 ross et al 2008 in particular the shear wave velocity knowledge of near surface velocity structure in turn can be used to estimate shear wave statics in reflection seismology estimating statics in the presence of laterally varying structure i e obtaining the long wavelength static component can be challenging

evidence in pre 2 2 ga paleosols for the early evolution of atmospheric oxygen and terrestrial biota the loss of fe from some pre 2 2 ga paleosols has been considered by previous investigators as the best evidence for a reduced atmosphere prior to 2 2 ga i have examined the behavior of fe in both pre and post 2 2 ga paleosols from depth profiles of fe 3 ti fe 2 ti and fe ti ratios and fe 3 ti vs fe 2 ti plots this new approach reveals a previously unrecognized history of paleosols essentially all paleosols regardless of age retain some characteristics of soils formed under an oxic atmosphere such as increased fe 3 ti ratios from their parental rocks the minimum oxygen pressure p o 2 for the 3 0 2 2 ga atmosphere is calculated to be about 1 5 of the present atmospheric level which is the same as that for the post 1 9 ga atmosphere the loss of fe common in paleosol sections of all ages was not due to a reducing atmosphere but to reductive dissolution of ferric hydroxides formed under an oxic atmosphere this reductive dissolution of ferric hydroxides occurred either 1 after soil formation by hydrothermal fluids or 2 during and or after soil formation by organic acids generated from the decay of terrestrial organic matter terrestrial biomass on the early continents may have been more extensive than previously recognized

geomagnetic conjugate observation of nighttime medium scale and large scale traveling ionospheric disturbances front3 campaign 1 the third front f region radio and optical measurement of nighttime tid campaign was carried out during the new moon period of may june 2003 in order to investigate the geomagnetic conjugacy of medium scale and large scale traveling ionospheric disturbances mstids lstids at midlatitudes seven all sky airglow imagers were operated in japan and australia for almost all clear sky nights we observed mstids in the 630 nm airglow images with horizontal wavelengths of 100 400 km propagating southwestward in japan and northwestward in australia all of them show a one to one correspondence of wave structures between the northern and southern hemispheres indicating strong electrodynamic coupling between the two hemispheres through the geomagnetic field line we also found that airglow intensity variations with a timescale longer than that of mstids often show a good correlation between the two hemispheres on 28 may we succeeded in detecting an equatorward propagating lstid spatial scale 1000 km as airglow enhancements at the conjugate stations the airglow peak of the lstid in the northern hemisphere was 20 min earlier than that in the southern hemisphere indicating that the observed lstid is caused by a wave in the neutral atmosphere rather than by an electric field structure

well preserved late precambrian paleosols from northwest scotland abstract two paleosol profiles were developed side by side on gneiss sheigra clay paleosol and amphibolite staca clay paleosol along the same unconformable contact of lewisian metamorphic rocks 2 7 1 7 ga overlain by torridonian sandstones 0 8 ga in northwestern scotland although altered during burial by compaction and illitization these profiles are well preserved compared with most other precambrian paleosols that are metamorphosed to at least greenschist facies in addition deformation of pegmatite veins in a manner similar to soil creep can be taken as an indication that upper horizons of these paleosols have been preserved soil development in both profiles was characterized by the oxidation of iron in biotite and magnetite and by hydrolysis of plagioclase orthoclase and hornblende clay skins soil like microfabrics and pedogenic smectite have been preserved in the profiles alteration of silicate grains other than quartz microcline and biotite has been intense but chemical analyses failed to show dramatic removal of alkalis and alkaline earths from the profiles microscopic concretions similar to pedogenic carbonate were found in subsurface horizons of the staca clay rare earth elements are more abundant within the paleosols than in their parent materials these paleosols developed on a well drained landscape that was buried by torridonian alluvial fans atmospheric oxidation was greater than revealed by studies of archean paleosols but probably still short of modern levels paleoclimate was subhumid and probably seasonal organic carbon and its light isotopic composition in the paleosol is evidence for photosynthetic microbial crusts paleosols of such great antiquity do not fit comfortably within modern soil taxonomies and are for the moment assigned to the informal category of green clays

seismic ground roll absorption and reemission by sand dunes this work was performed at schlumberger cambridge research where m i arran was a case student intern and e muyzert is a senior research scientist

integrating sandstone petrology and nonmarine sequence stratigraphy application to the late cretaceous fluvial systems of southwestern utah u s a abstract petrographic and dispersal data are essential to correct interpretation of mechanisms that create continental sequence stratigraphic architecture a case study from southern utah demonstrates that upper cretaceous upper santonian campanian alluvial successions in the southernmost part of the cordilleran foreland basin were deposited by fluvial systems of contrasting drainage directions and provenance and suggests that different mechanisms governed their sequence architecture most of the rivers flowed northeast subparallel to the basin foredeep less common fluvial systems flowed to the east southeast the fluvial sandstones fall naturally into four petrofacies 1 quartzofeldspatholithic mean qt61f19l20 2 feldspatholithic qt29f19l52 3 quartzolithic qt75f6l20 and 4 quartzose qt99f1l1 petrofacies 1 and 2 were derived from mixed supracrustal and basement sources to the southwest and south respectively whereas petrofacies 3 and 4 were derived from uplifted thrust sheets of the sevier orogenic belt to the southwest and west respectively only the east southeast flowing rivers transported the quartzose petrofacies the fluvial strata which include the uppermost straight cliffs wahweap and kaiparowits formations form two large scale stratigraphic successions typically interpreted as continental stratigraphic sequences hundreds of meters thick each succession begins with an amalgamated braided fluvial deposit grades to mudstone rich strata with low sandstone body connectivity and culminates in highly connected sandstone bodies with multistory stacking the basal amalgamated deposits of each succession are architecturally similar but their compositional and dispersal characteristics are different quartzofeldspatholithic quartzolithic and quartzose sandstones above the lower base level shift are variable but generally similar in compositional and dispersal characteristics to both underlying and overlying strata a phenomenon termed here congruence in contrast quartzose amalgamated fluvial sandstone above the upper base level shift differs sharply in composition and dispersal direction from underlying and overlying lithic rich strata the foredeep axis controlled the progradation direction of the congruent shift which was likely driven by climatically induced sediment influx a eustatic fall or both in the case of the incongruent shift increased sediment supply permitted the rivers to cross the foredeep temporal association of the upper amalgamated deposit with active structures in the thrust belt and foreland basin indicates that syntectonic thrust uplift not isostatic uplift or climate caused the influx of quartz

recovery rates of microbiotic crusts within a dune ecosystem in the negev desert abstract despite the important role played by microbiotic crusts in desert ecosystems data concerning their recovery rates are scarce and are mainly based on estimates that fluctuate between several years to a few hundred years in order to study the recovery rates of microbiotic crusts inhabiting sand dunes in the western negev desert israel annual measurements of chlorophyll protein carbohydrates and moss counts were carried out during 1990 1995 measurements were taken in two pairs of plots 1 5 6 3 m2 established in each north and south facing aspect from which the upper 10 cm surface from one plot of each pair was removed recovery of the crusts was fast with surface removed plots showing a complete recovery of chlorophyll a within 6 7 years of protein within 6 8 years and of carbohydrates within 8 9 years recovery of the mosses was slightly longer at 17 22 years the data are higher than the lower estimates of recovery but much lower than the higher estimates proposed in the literature the data also suggest that upon prohibition of goat and sheep grazing and consequently trampling a relatively rapid stabilization process may take place in the north eastern sinai dune field

microbenthic distribution of proterozoic tidal flats environmental and taphonomic considerations silicified carbonates of the late mesoproterozoic to early neoproterozoic society cliffs formation baffin island contain distinctive microfabrics and microbenthic assemblages whose paleo environmental distribution within the formation parallels the distribution of these elements through proterozoic time in the society cliffs formation restricted carbonates including microdigitate stromatolites laminated tufa and tufted microbial mats consist predominantly of synsedimentary cements these facies and the cyanobacterial fossils they contain are common in paleoproterozoic successions but rare in neoproterozoic and younger rocks less restricted tidal flat facies in the formation are composed of laminated microbialites dominated by micritic carbonate lithified early yet demonstrably after compaction these strata contain cyanobacteria that are characteristic in neoproterozoic rocks within the formation the facies dependent distribution of microbial populations reflects both the style and timing of carbonate deposition because of the strong substrate specificity of benthic cyanobacteria a reasonable conclusion is that secular changes in microbenthic assemblages through proterozoic time reflect a decrease in the overall representation of rapidly lithified carbonate substrates in younger peritidal environments as well as concomitant changes in the taphonomic window of silicification through which early life is observed

wrinkle structures microbially mediated sedimentary structures common in subtidal siliciclastic settings at the proterozoic phanerozoic transition sedimentary structures produced by microbial activity are well known from ancient carbonate facies but little is known about equivalent microbial structures in ancient siliciclastic facies wrinkle marks and kinneyia ripples are closely related sedimentary structures that are commonly found in ancient siliciclastics and they may represent microbial activity to evaluate this possibility these structures were studied in vendian cambrian strata of north america and compared to structures formed by modern microbial mat communities in redfish bay texas striking similarities in sedimentologic petrographic and morphologic characteristics of modern and ancient occurrences suggest that the enigmatic but widespread ancient structures could have been formed by microbial processes the relative abundance of these structures in siliciclastic facies of this interval further suggests that prior to the onset of relatively intense bioturbation in the ordovician microbial mats could have played a significant role in the evolution and diversification of early life in a broad variety of sea floor environments

ediacaran life on land a new interpretation of fossilized soils palaeosols suggests that at least some ediacaran 625 542 million years ago organisms lived on land thus these ediacaran fossils were not animals but a fungus dominated terrestrial biota that predated vascular plants by about 100 million years ediacaran fossils 542 to 635 million years old occur worldwide in a variety of sedimentary deposits generally interpreted as shallow to deep marine origin they have been regarded as early animal ancestors of the cambrian evolutionary explosion of marine invertebrate phyla as giant marine protists and as lichenized fungi here gregory retallack raises doubts over the assumption that ediacaran organisms were marine a new interpretation of fossilized soils palaeosols from south australia suggests that at least some lived on land retallack s suggestion that some ediacaran fossils were large sessile organisms of cool dry soils is compatible with observations that ediacaran fossils are similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts rather than marine animals or protists ediacaran 635 542 million years ago fossils have been regarded as early animal ancestors of the cambrian evolutionary explosion of marine invertebrate phyla1 as giant marine protists2 and as lichenized fungi3 recent documentation of palaeosols in the ediacara member of the rawnsley quartzite of south australia4 confirms past interpretations of lagoonal aeolian deposition based on synsedimentary ferruginization and loessic texture5 6 further evidence for palaeosols comes from non marine facies dilation cracks soil nodules sand crystals stable isotopic data and mass balance geochemistry4 here i show that the uppermost surfaces of the palaeosols have a variety of fossils in growth position including charniodiscus dickinsonia hallidaya parvancorina phyllozoon praecambridium rugoconites tribrachidium and old elephant skin ichnogenus rivularites7 these fossils were preserved as ferruginous impressions like plant fossils8 and biological soil crusts9 10 of phanerozoic eon sandy palaeosols sand crystals after gypsum11 and nodules of carbonate12 are shallow within the palaeosols4 even after correcting for burial compaction13 periglacial involutions and modest geochemical differentiation of the palaeosols are evidence of a dry cold temperate ediacaran palaeoclimate in south australia4 this new interpretation of some ediacaran fossils as large sessile organisms of cool dry soils is compatible with observations that ediacaran fossils were similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts3 rather than marine animals1 or protists2

biogenic soil crusts and soil depth a long term case study from the central negev desert highland wind blown soil degradation is a major problem in arid regions biogenic soil crust consists of a dense growth of many small organisms covering bare desert soil surfaces in arid regions worldwide these organisms perform essential services in the ecosystem for example soil surface stabilization and carbon and nitrogen fixation a unique service provided by biogenic crusts is the incorporation of large quantities of deposited atmospheric particles leading to a significantly enhanced rate of increase in soil depth in windy and arid environments a long term study over 42 months was conducted to investigate the contribution of a biogenic crust to the accumulation of atmospheric particles in an arid zone undisturbed and treated biogenic crusts were studied for their capacity to incorporate deposited particles atmospheric particles were found to accumulate on marble dust collectors at a rate of 120 g m 2 year 1 and on sterilized crust at a rate of 208 g m 2 year 1 while the accumulation rate on live intact crusts was 277 g m 2 year 1 suggesting a soil depth accretion rate on an undisturbed biogenic crust of 10 mm every 33 years maintenance of a healthy biogenic crust in dry land environments should therefore be a major consideration for improving soil quality and increasing soil depth in arid regions

observation of f region irregularities near a northern equatorial anomaly crest during solar minimum using ionosonde gps receiver and satellites 1 for solar minimum the spread f gps phase fluctuations and plasma bubbles near the crest of equatorial ionization anomaly eia are simultaneously analyzed to investigate f region irregularities for the first time the data were observed using the chungli ionosonde ymsm gps receiver and dmsp satellites during 1996 it is found that in the observed ionograms the frequency spread f fsf usually comes after the range spread f rsf in a series of nighttime spread f events this results in that the maximum occurrence of rsf appears before that of fsf in the nighttime variations in occurrence probabilities moreover the seasonal variation for rsf is close to that for fsf both have a board maximum in the j months and a secondary maximum in december these indicate that rsf and fsf should be regarded as one type of spread f which is the all spread f asf in this study because the equatorial plasma bubbles occur infrequently during solar minimum the f region irregularities forming asf are not related to the equatorial spread f on the other hand the similarity in seasonal occurrence between asf and medium scale traveling ionospheric disturbances mstids demonstrates that the f region irregularities near the eia crest are mainly generated by the gradient drift instability driven by mstids the irregularities generated by mstids mostly occur in the bottom side of the f region consequently the events of significant gps phase fluctuations and plasma bubble near the eia crest are rare during 1996

removal of scattered surface waves using multicomponent seismic data in many exploration areas the shallow subsurface is strongly heterogeneous the heterogeneities can give rise to scattering of surface waves these scattered waves can depreciate the quality of land seismic data when they mask the body wave reflections from the deeper part of the subsurface surface waves scattered near a line of receivers inline scattered waves can be removed by well known filtering techniques see e g yilmaz 1987 section 1 6 2 however surface waves scattered far from the receiver line crossline scattered waves are left intact partially by filtering because these waves can resemble body wave reflections in previous papers we have discussed an inverse scattering method for removing scattered surface waves from simulated data blonk and herman 1994 as well as from field data blonk et al 1995 so far we have limited our attention to the vertical components of the particle velocity which implies that surface waves and body wave reflections can be distinguished on the basis of their respective differences in phase velocity

interferometric ground roll removal attenuation of scattered surface waves in single sensor data land seismic data are contaminated by surface waves or ground roll these surface waves are a form of source generated noise and can be strongly scattered by near surface heterogeneities the resulting scattered ground roll can be particularly difficult to separate from the desired reflection data especially when this scattered ground roll propagates in the crossline direction we have used seismic interferometry to estimate scattered surface waves recorded during an exploration seismic survey between pairs of receiver locations where sources and receivers coincide these interreceiver surface wave estimates were adaptively subtracted from the data this predictive subtraction process can successfully attenuate scattered surface waves while preserving the valuable reflected arrivals forming a new method of scattered ground roll attenuation we refer to this as interferometric ground roll removal

traveling ionospheric disturbances detected in the front campaign the f region radio and optical measurement of nighttime tid front campaign was conducted to clarify the non classical features of traveling ionospheric disturbances tids at mid latitudes in may 1998 and august 1999 a cluster of all sky ccd cameras and a gps receiver network observed a wide area of the ionosphere over japan to detect the spatial structure and temporal evolution of tids the propagation direction of the nighttime tid detected during the front campaign periods is restricted to the southwest the time evolution of their amplitude indicates that the tid structure is intensified as it travels from high latitudes to low latitudes the significant coincidence between the structures of 630 nm band airglow and total electron content indicates that the perturbations take place in the bottomside of the ionospheric f region coherent echoes from the field aligned irregularities were observed by the mu radar in the nights when the tid activity was high

traveling ionospheric disturbances observed in the oi 630 nm nightglow images over japan by using a multipoint imager network during the front campaign pilot observations using a network of five all sky imagers asis were conducted during the new moon period of may 19 22 1998 as part of the f region radio and optical measurement of nighttime tid front campaign the network observation enabled us to track propagation of medium scale traveling ionospheric disturbances tids in the oi 630 nm nightglow over a distance of more than 2500 km the tids were observed every night during the campaign period but occurrence was limited from evening to midnight they have horizontal wavelengths of 200 600 km travel a horizontal distance of more than 1000 km and last for more than three hours in every case the tids moved southwestward with a velocity of 83 137 m s using dual site tid images the altitude of the tid structures in the 630 nm nightglow was calculated to be 260 km which corresponds to the bottom side of the mid latitude ionospheric f layer

wind velocity and algal crusts in dune blowouts abstract in two saucer shaped blowouts wind velocity was measured at 0 18 m height and compared to the wind velocity data from the nearest standard meteorological station at valkenburg about 3 5 km to the northeast in blowout 1 relative velocities are highest when the wind blows from directions between e and sse in blowout 2 winds blowing from directions between s and wsw are relatively stronger in general the wind speed increases as its moves along the surface inside the blowout because the aerodynamic roughness of the blowout surface is less than that of the surrounding area less important are the influence of the configuration of the terrain surrounding the blowout and the influence of the slopes within the blowout the frequency distribution of the general wind at valkenburg is analysed and combined with the horizontal wind velocity pattern within blowouts a simulation model producing the spatial distribution of the wind power shows that the prevalence of algal crusts at the sw side of blowouts agrees well with the location which reaches the lowest wind power values in other parts of the blowouts algal crusts are damaged by moving sand at times of high wind velocity

surface wave methods for anomaly detection abstractperimeter defense operations geohazard assessment and engineering characterization require the detection and localization of subsurface anomalies seismic waves incident upon these discontinuities generate a scattered wavefield we have developed various surface wave techniques currently being fielded that have consistently delivered accurate and precise results across a wide range of survey parameters and geographical locations we use the multichannel analysis of surface waves approach to study the multimode rayleigh wave the backscatter analysis of surface waves basw method to detect anomalies 3d visualization for efficient seismic interpretation basw correlation for attribute analysis and instantaneous amplitude integration in the complex basw method discrete linear moveout functions and f k filter designs are optimized for basw considering the fundamental and higher mode dispersion trends of the rayleigh wave synthetic and field data were used to demonstrate multimode basw and mod

high resolution mapping of tec perturbations with the gsi gps network over japan two dimensional total electron content tec perturbations over japan are mapped with the geographical survey institute gsi gps network geonet gps earth observation network its spatial resolution is 0 15 latitude 0 15 longitude and temporal resolution is 30 seconds two dimensional tec observations with these high resolutions revealed spatial structures and temporal evolutions of traveling ionospheric disturbances tids in the nighttime mid latitude ionosphere on july 03 1997 a preliminary result of the tec perturbation mapping indicates that it would be a strong tool to investigate the ionospheric structures in detail coordinated observations with other ionospheric observation techniques such as incoherent scatter is radars airglow imagers and ionosondes are needed to clarify the vertical structure of the ionosphere

earliest laterites and possible evidence for terrestrial vegetation in the early proterozoic paleosols preserve information about the composition of the atmosphere and paleoclimatic conditions here we report the discovery of the first pisolitic laterites of precambrian age the laterites are immediately above the regional unconformity at the base of the early proterozoic gamagara formation in paleokarst depressions on the campbellrand dolomite transvaal supergroup south africa the paleosol profiles are very well preserved and show zoning relict soil textures and chemical composition virtually identical to those of modern laterites the pisolitic laterites provide not only evidence for a highly oxygenated atmosphere and possible hot and humid climatic conditions in early proterozoic time but also indicate the presence of terrestrial life on the kaapvaal craton 2 0 2 2 b y ago

underestimation of body waves and feasibility of surface wave reconstruction by seismic interferometry interferometry is an approach to extract the green s function between two receivers as if the virtual source is at one of the receiver locations the green s function which is the response to an impulsive source accounts for the wave propagation in the medium between the two receivers it is commonly thought that green s function estimates obtained from interferometry accurately represent the full green s function but this is not always the case in fact the accuracy of the retrieved green s function which consists of the surface and body waves is in practice restricted by the limited distribution of the sources of field fluctuations we demonstrate the importance of adequate source distribution for the accuracy of the retrieved green s function using examples from interferometry applications in these examples sources are controlled as in exploration seismology or uncontrolled as in crustal seismology

life on land in the proterozoic evidence from the torridonian rocks of northwest scotland the stoer group and diabaig formation of the torridonian succession in northwest scotland are late mesoproterozoic to early neoproterozoic ca 1200 1000 ma features preserved on the top surfaces of fine to medium grained sandstone beds in a number of stratigraphically and geographically separated localities are attributable to microbially induced sedimentary structures these include wrinkle structures remnants of apparent microbial crusts and indications of original cohesiveness and pliancy in sand sized sediment the surfaces on which the microbial structures formed were exposed subaerially abundant deep desiccation cracks and locally pedogenic structures in alluvial interfluve and lacustrine margin settings and many of the structures developed in areas well away from the perennially wetted regions adjacent to shorelines and fluvial channels thus these features indicate that earth9s biosphere had adapted to and colonized land surfaces many hundreds of millions of years before the dawn of the phanerozoic

nighttime medium scale traveling ionospheric disturbances detected by network gps receivers in taiwan 1 the nighttime medium scale traveling ionospheric disturbances mstids are detected by the network gps receivers in taiwan for the first time the two dimensional mapping technique a spatial resolution of 0 05 0 05 in latitude and longitude with 5 5 pixels smoothing is applied on the data of tec perturbations tecp and gps phase fluctuations tec min the results show that the mstids move southwestward to latitude of 20 5 n with a horizontal velocity between 100 and 160 m s and a wavelength of about 500 km the wavefronts of the mstids are aligned along the northwest southeast direction furthermore the greater tec min values are corresponding to the wave peak and trough of tecp this coincidence indicates that the mstids play an important role for the generation of f region irregularities in the low latitude ionosphere

scattered ground roll attenuation using model driven interferometry scattered ground roll is a type of noise observed in land seismic data that can be particularly difficult to suppress typically this type of noise cannot be removed using conventional velocity based filters in this paper we discuss a model driven form of seismic interferometry that allows suppression of scattered ground roll noise in land seismic data the conventional cross correlate and stack interferometry approach results in scattered noise estimates between two receiver locations i e as if one of the receivers had been replaced by a source for noise suppression this requires that each source we wish to attenuate the noise from is co located with a receiver the model driven form differs as the use of a simple model in place of one of the inputs for interferometry allows the scattered noise estimate to be made between a source and a receiver this allows the method to be more flexible as co location of sources and receivers is not required and the method can be applied to data sets with a variety of different acquisition geometries a simple plane wave model is used allowing the method to remain relatively data driven with weighting factors for the plane waves determined using a least squares solution using a number of both synthetic and real two dimensional 2d and three dimensional 3d land seismic data sets we show that this model driven approach provides effective results allowing suppression of scattered ground roll noise without having an adverse effect on the underlying signal

a preserved late cretaceous biological soil crust in the capping sandstone member wahweap formation grand staircase escalante national monument utah paleoclimatic implications abstract modern biological soil crusts develop under semiarid to arid conditions and are characterized by diverse communities of micro and macro organisms the upper meter of the upper cretaceous capping sandstone member of the wahweap formation in grand staircase escalante national monument utah contains an outcrop of an ancient biological soil crust preserved in matrix rich quartz sandstone the interpretation is based in comparison with modern biological soil crust analogs specifically similarities in morphological expression sorting and proximity to associated eolianites this study reports on this rarely recognized type of paleosol a biological soil crust and discusses the sedimentologic and paleoclimatic implications

statistical analysis of nighttime medium scale traveling ionospheric disturbances using airglow images and gps observations over central china statistical analyses were conducted to investigate the nighttime medium scale traveling ionospheric disturbances mstids for the first time by using airglow images and global positioning system gps data over central china during 2013 2015 our results show that the phase fronts of perturbations are aligned from northwest to southeast direction and propagate toward the southwest direction the characteristics of the nighttime mstids observed by oi 630 0 nm images are consistent with those of the nighttime mstids obtained from the gps data the phase velocity period wavelength and amplitude of nighttime mstids are 50 150 m s 0 5 1 5 h 150 400 km and 2 15 respectively as measured from 630 0 nm images and gps data in addition we utilized the simultaneous observations from oi 630 0 nm and oi 557 7 nm images to explore the relationship between nighttime mstids and gravity waves 100 km in the mesopause it is found that the nighttime mstids frequently occurred in the summer solstice which was not consistent with the occurrence of gravity wave observed in the mesopause our results indicate that the nighttime mstids may be generated by the coupling of electrodynamic processes rather than be trigged by gravity waves from the lower atmosphere

horizontal velocities and propagation directions of gravity waves in the ionosphere over the czech republic 1 using a five point continuous doppler sounding system operating at 3 59 mhz developed at the institute of atmospheric physics as cr iap we investigate propagation directions and velocities of gravity waves gws at altitudes from 150 to 250 km over the western part of the czech republic the velocities and directions are computed from the time delays between the observations of corresponding gws at different reflection points that correspond to various sounding paths we focused on the gws that produce an s shaped trace in doppler shift spectrograms and are observed close to sunrise and sunset we have selected about 100 of such events our results show that the analyzed gws propagate with typical horizontal velocities from 100 to 200 m s the north south component of gw velocities depends on the season it is directed northward in the summer and southward in the winter at the same time the north south component of the neutral winds calculated by the horizontal wind model hwm07 has the opposite sign typical observed periods of the analyzed waves range from 10 to 30 min

medium scale traveling ionospheric disturbances affecting gps measurements spatial and temporal analysis 1 in this work we present a simple technique to estimate the medium scale traveling ionospheric disturbances mstids characteristics such as occurrence velocity vertical propagation with periods lower than 20 min and its application to a set of gps data both temporally and spatially representative near one solar cycle and four local networks in the northern and southern hemispheres respectively some of the main results presented in this paper are the mstids which occur at daytime in local winter and nighttime in local summer related to the solar terminator and modulated by the solar cycle they present equatorward from 100 to 400 m s and westward 50 to 200 m s horizontal propagation velocities respectively the corresponding periods are compatible higher with the theoretical prediction which is given by the neutral atmosphere

evidence for 2 0 ga continental microbial mats in a paleodesert setting abstract early evolved microbial communities characterized the initial biological invasion of precambrian continental landscapes in modern arid settings microbial mats and biological soil crusts are well developed and stabilize sediment the paleoproterozoic makgabeng formation in south africa is one of the oldest and best preserved dryland systems on earth six types of microbial mat related structures are now recognized within these depositional systems this paper presents three newly discovered structures that include tufted microbial mat biological soil crusts and gas escape features in addition to three previously documented structures that include roll up features sand cracks and wrinkled features these discoveries demonstrate that microbial communities were well established and inhabited diverse continental settings by 2 0 ga approximately 200 million years after the onset of the great oxidation event

stable isotope variations in the neoproterozoic beck spring dolomite and mesoproterozoic mescal limestone paleokarst implications for life on land in the precambrian proterozoic karst events lowered 13c values by as much as 11 for the 800 ma beck spring dolomite california and as much as 8 5 for the 1 1 ga mescal limestone central arizona relative to the originally deposited carbonate the 13c changes are attributed to input of 13c depleted organic co2 derived from photosynthetic organisms that colonized the ancient land surface the large isotopic shift and its presence at two separate localities suggest that proterozoic karst surfaces were colonized by significant photosynthetic communities with phytomasses possibly approaching those of today

adaptive interferometry for ground roll suppression generally seismic interferometry refers to a method of extracting the wavefield responses between two receivers as if we had replaced one of those receivers by a source van manen et al 2005 wapenaar and fokkema 2006 this is done by a process of cross correlation and summation of wavefields observed at those receivers these recorded wavefields can be excited by active sources earthquakes dynamite air guns vibroseis and others or passive sources oceanic microseisms traffic on roads industrial machinery and others when applying seismic interferometry using surface sources and surface receivers the recovered inter receiver response is dominated by surface waves this phenomenon is observed in both global and regional seismology where passive seismic energy is used and in exploration seismology where active sources are used

removal of scattered guided waves from seismic data near surface scattered waves form a major source of coherent noise in seismic land data most current methods for removing these waves do not attenuate them adequately if they come from other than the inline direction we present a wave theory based method for removing scattered guided waves by a prediction and removal algorithm we assume that the near surface consists of a laterally varying medium in which heterogeneities are embedded that act as scatterers we first estimate the dispersive and laterally varying phase slowness field by applying a phase based tomography algorithm on the direct groundroll wave subsequently the near surface heterogeneities are imaged using a least squares criterium finally the scattered guided waves are modeled and subtracted adaptively from the seismic data we have applied this method to seismic land data and found that near surface scattering effects are attenuated

all sky imaging observations of conjugate medium scale traveling ionospheric disturbances in the american sector 1 all sky imaging systems at arecibo puerto rico 18 3 n 66 7 w 28 mag lat and mercedes argentina 34 6 s 59 4 w 24 6 mag lat are used to study ionospheric conjugate processes at lower midlatitudes for the first time in the american sector the simultaneous occurrence in both hemispheres of medium scale traveling ionospheric disturbances has been observed the first year of observations yielded 43 nights 40 with simultaneous occurrence of airglow bands supporting information from gps receivers indicate the presence of vertical total electron content variations that correlate with the airglow structures observed with the imagers weak phase fluctuations have been measured indicating that these structures do not produce severe large scale ionospheric irregularities

climatology of medium scale traveling ionospheric disturbances observed by a gps network in central china 1 the 15 month climatology of medium scale traveling ionospheric disturbances mstids during a solar minimum period has been constructed from observations of a dense gps receiver array in central china in total 793 mstid events are identified with peaks in occurrence at 1500 lt and 0100 lt the occurrence of mstids decreases following an increase in geomagnetic activity with 46 of the mstids occurring in the daytime daytime mstids are characterized by a major occurrence maximum around the winter solstice and by an equatorward propagation direction the period phase velocity azimuth and amplitude of daytime mstids are 20 60 min 100 400 m s 130 270 and 0 8 1 5 respectively the remaining 54 of the mstids occurred at night and were characterized by a peak in occurrence at the summer solstice and by a southwestward propagation direction the period phase velocity azimuth and amplitude of nighttime mstids are 20 70 min 50 230 m s 170 300 and 2 7 respectively the propagation directions and the seasonal behaviors support the view that daytime mstids are an ionospheric manifestation of atmospheric gravity waves from the lower atmosphere while a possible excitation mechanism of nighttime mstids is the electrodynamics process caused by plasma instability in the f layer

statistical investigation of horizontal propagation of gravity waves in the ionosphere over europe and south africa 1 a statistical investigation into the horizontal propagation of 8 30 min gravity waves gws in the ionosphere over a 1 year period from june 2010 to may 2011 is presented the gws were observed by multipoint continuous doppler sounding systems installed in the czech republic and in the western cape south africa measurements of gw propagation in the ionosphere over south africa have never been presented before simultaneous measurements from nearby ionosondes made it possible to estimate the height of the gw observations and show that the analyzed gws propagated at altitudes from 150 to 250 km the analyzed waves were mainly observed after sunrise and around sunset our statistical study shows that the analyzed gws propagated with horizontal velocities from 70 to 250 m s the average observed horizontal velocities were 100 m s in the local summer and 125 150 m s in the local winter the waves propagated approximately poleward in the local summer whereas roughly equatorward propagation was observed in the local winter westward propagation was rarely observed in the czech republic and eastward southeast propagation was seldom observed in south africa a comparison with neutral wind velocities shows that the analyzed gws propagated approximately against the neutral winds calculated by the hwm07 model the estimated horizontal wavelengths of the analyzed waves were 100 300 km

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

tufted microbial cyanobacterial mats from the proterozoic stoer group scotland upward thinning stellate and polygonal carbonate structures are described and compared to modern and ancient stromatolites although tufted microbial mats are common in modern settings they have rarely been described from ancient rocks owing to their poor preservation potential the preservation of these from the stoer group is due to early replacement by calcite before their original tufted relief could be obliterated by compaction associated limestones with some similar features are interpreted as flat to mamillated microbial mats

predictive removal of scattered noise land seismic data can be severely contaminated with coherent noise we discuss a deterministic technique to predict and remove scattered coherent noise from land seismic data based on a mathematical model of near surface wave propagation we test the method on a unique data set recorded by petroleum development of oman in the qarn alam area with shots and receivers on the same grid and we conclude that it effectively reduces scattered noise without smearing reflection energy

the interaction of aeolian and fluvial processes during deposition of the upper cretaceous capping sandstone member wahweap formation kaiparowits basin utah u s a abstract detailed examination of the upper cretaceous capping sandstone member of the wahweap formation in the kaiparowits basin utah reveals the presence of aeolian stratification deposition by aeolian processes is recognized and distinguished from subaqueous deposition by the presence of centimeter scale inversely graded wind ripple stratification the aeolian stratification in the wahweap formation is the first occurrence reported from upper cretaceous strata on the colorado plateau of the western u s a aeolian stratification occurs as thin wind reworked caps of fluvial bar sandstones deposited within low sinuosity braided streams and as more extensive deposits of small scale dunes that developed in geographically restricted dune fields aeolian reworking of bars took place during low stage flow and was possibly controlled by intermittent seasonal discharge variations prolonged aridity led to increased sand supply entering the aeolian system dunes nucleated and grew rapidly between the braided stream systems these small scale dunes rarely developed extensive or tall slip faces as evidenced by the rare preservation of grain flow strata and the dominance of wind ripple stratification the dune field was characterized by sinuous crested dunes probably barchans amid and linked to the extensive braided stream systems based on modern analogs the resulting change in sand storage supply probably is related to a short term shift to a more semi arid arid climate possibly seasonally however a longer term climate change to semi arid arid may be indicated for the dune complex near the boundary with the overlying kaiparowits formation

micromorphology and significance of the surface crusts of soils in rangelands near cobar australia abstract micromorphological observations were made on thin sections of surface crusts from the uppermost 50 mm of red earths near cobar new south wales samples were collected to represent six classes of surface conditions important to plant growth the crusts consisted of an upper zone comprising cryptogamic mats litter and transported soil aggregates and a lower zone of layers of generally laminated sands silts and clays crusts from class 1 surfaces which showed little evidence of erosion were loosely structured bioturbated and lacked sealing properties crusts from classes 2 to 4 in which erosion was increasingly evident contained decreasing proportions of cryptogams exhibited decreasing evidence of bioturbation and increasing proportions of platy and sealing structures crusts from class 5 found in areas of marked colluvial deposition had a wide range of properties whereas crusts from class 6 consisted primarily of litter deposited under trees the major processes responsible for crust formation are considered to be a combination of erosion by raindrop impact redeposition by rainwash and colonisation by cryptogams micromorphological properties of the crusts are believed to affect lodgement and germination of seeds and the infiltration and runoff of water thereby influencing plant growth dry matter production ranged from 2 3 t ha 1 on soils with class 1 surfaces to 0 1 t ha 1 on soils with class 4 surfaces cryptogam mats also afford protection of the underlying materials from erosion and also promote aggregation cryptogams are therefore considered highly desirable components of the crusts

statistical study of nighttime medium scale traveling ionospheric disturbances using midlatitude airglow images 1 we have investigated statistical characteristics of the nighttime medium scale traveling ionospheric disturbances mstids observed in 630 nm airglow images at two stations rikubetsu 43 5 n 34 8 mlat and shigaraki 34 9 n 25 4 mlat in japan for 1998 2000 near the solar maximum period most of the observed mstids propagate southwestward in the images the typical wavelength velocity period and amplitude are 100 300 km 50 100 m s 0 5 1 5 h and 5 15 respectively seasonal variations in these parameters are not clear the occurrence rate has a major peak 50 60 in summer that appears 2 months earlier at lower latitudes and a minor peak in winter similar occurrence characteristics are obtained from midlatitude spread f signatures using multipoint ionosonde data in japan though the coincidence of the spread f and the mstids in airglow images is only 10 15

medium scale traveling ionospheric disturbances detected with dense and wide tec maps over north america 1 nighttime and daytime medium scale traveling ionospheric disturbances mstids are detected with dense and wide detrended total electron content tec maps over north america using multiple gps receiver networks the tec maps cover a wide region of 60 130 w and 24 54 n 30 65 n in geomagnetic latitude and have a spatial resolution of 1 05 1 05 in latitude and longitude 0 15 0 15 with 7 7 pixel smoothing and a temporal resolution of 30 seconds the tec maps reveal for the first time that the nighttime mstids propagate southwestward with 200 500 km wavelengths over north america and have wavefronts longer than 2 000 km we also observe that daytime mstids with 300 1 000 km wavelengths propagate southeastward until mid afternoon and southwestward in the late afternoon in the mid to late afternoon these mstids propagating in the different directions are superimposed the tec maps can be a new powerful tool to investigate the mstids

life on land in the precambrian microfossils have been discovered in cavity fill and replacement silica that occurs between chert breccia clasts in 1200 million year old paleokarst at the top of the mescal limestone central arizona and in 800 million year old paleokarst at the top of the beck spring dolomite southeastern california microbial communities on precambrian g550 million years ago land may have been extensive enough to affect weathering erosion sedimentation and geochemical processes

digisonde spread f and gps phase fluctuations in the equatorial ionosphere during solar maximum 1 the jicamarca 11 95 s 76 87 w digisonde and the arequipa 16 47 s 71 49 w gps receiver observed the equatorial f region irregularities on the western south america from april 1999 to march 2000 the spread f measured by the digisonde were classified into four types and the gps phase fluctuations derived from the temporal variation of total electron content were divided into three levels to represent the irregularity strength the observation shows that the occurrences of all four types of spread f are higher in the d months january february november and december than in the e months march april september and october for the gps phase fluctuations both seasonal and nighttime variations show that the occurrences of strong level irregularities are higher than moderate level irregularities in the e months but the situation is reversed in the d months moreover the occurrence sequences of four types of spread f and three levels of gps phase fluctuations all can be explained by the e b drift variations and the generalized rayleigh taylor instability for the comparisons between the gps phase fluctuations and the digisonde spread f plasma bubbles results show that the gps phase fluctuations can represent the appearances of the digisonde spread f and the strong level of gps phase fluctuations are associated with the occurrence of topside plasma bubbles these results imply that the greater gps phase fluctuation is related to the larger altitudinal range distribution of irregularities

nighttime medium scale traveling ionospheric disturbances at low geomagnetic latitudes 1 nighttime medium scale traveling ionospheric disturbances mstids are a commonly observed structure in the middle latitude ionosphere during the months surrounding the solstices and low solar flux conditions mstids consist of one or more narrow bands exhibiting uplift in f region electron density which are elongated from northwest to southeast in the northern hemisphere and southwest to northeast in the southern hemisphere these electrified structures propagate westward and toward the equator in a direction perpendicular to their long dimension previously this type of mstid was not thought to occur at magnetic latitudes equatorward of the equatorial anomalies or approximately 15 geomagnetic latitude here we present observational evidence from a field aligned narrowfield imaging system of mstids existing very close to the magnetic equator we discuss the implications of this observation in terms of the development and propagation of mstids