characteristics of equatorial plasma bubble zonal drift velocity and tilt based on hong kong gps cors network from 2001 to 2012 hong kong 22 3 n 114 2 e dip 30 5 n geomagnetic 15 7 n 173 4 w declination 2 7 w is a low latitude area and the hong kong continuously operating reference station cors network has been developed and maintained by lands department of hong kong government since 2001 based on the collected gps observations of a whole solar cycle from 2001 to 2012 a method is proposed to estimate the zonal drift velocity as well as the tilt of the observed plasma bubbles and the estimated results are statistically analyzed it is found that although the plasma bubbles are basically vertical within the equatorial plane the tilt can be as big as more than 60 eastward or westward sometimes and the tilt and the zonal drift velocity are correlated when the velocity is large the tilt is also large generally another finding is that large velocity and tilt generally occur in spring and autumn and in solar active years

additional records of ichnogenus rhizocorallium from the lower and middle triassic south china implications for biotic recovery after the end permian mass extinction

ichnology of a restricted epicontinental sea arapien shale middle jurassic utah usa abstract three trace fossil assemblages associated with different lithofacies have been recognized in the arapien shale middle jurassic near nephi ut usa the planolites montanus assemblage occurs in thinly laminated micrites and it is characterized by low ichnotaxonomic diversity shallow burrow penetration depth small size of the traces and low intensity of bioturbation the lockeia siliquaria assemblage is restricted to few millimeters thick grainstone layers and it exhibits low ichnodiversity small size and shallow burrow penetration of the traces as well the gyrochorte comosa assemblage is associated with 1 5 cm thick grainstone storm beds and it shows higher ichnodiversity and higher intensity of bioturbation the trace fossil assemblages suggest unfavorable environmental conditions for benthic life during fair weather periods which partly improved after storm disturbances the possible stress factors are related to the paleogeographic restriction and arid paleoclimate of the epicontinental sea where the arapien shale was deposited in this particular setting salinities would have reached values above normal marine producing thermohaline stratification of the body of water and consequently low oxygen levels in the bottom hence hypersalinity and poor bottom oxygenation are proposed here as the main controls on the trace fossil assemblages of the arapien shale

evidence for rapid precipitation of calcium carbonate in south china at the beginning of early triassic abstract anachronistic facies are sedimentary features and fabrics that are very common in the early history of the earth but mainly occur following mass extinctions during the phanerozoic anachronistic facies are typically found in carbonates commonly have a microbial origin and reflect an unusual oceanic chemistry the aftermath of the end permian mass extinction is one of the periods when anachronistic facies were common and occur in sedimentary rocks from around the world in south china different types of anachronistic facies appear in an orderly succession over time microbialites are often the first anachronistic sediments that formed after the end permian mass extinction in shallow platform settings and are subsequently followed by oolites and oncolites which are sometimes intercalated with vermicular limestones because different types of anachronistic facies represent different depositional environments this succession pattern in the strata records the evolution of marine environments following the end permian mass extinction based on sedimentological analysis of the yangjiawan section hunan province south china this study suggests that the transition from microbialite to oolitic limestone was associated with a rise of sea level and an increase in hydrodynamic energy the shift from oolite to oncolite reflects a sustained rapid rise of sea level the occurrence of vermicular limestone is considered to be the product of an ephemeral restricted environment anachronistic facies reach a thickness of 75 m at the yangjiawan section while over nearly the same time interval argillaceous limestone reaches a thickness of only 40 cm of beds 27 29 at the global stratotype section and point gssp section at meishan in zhejiang province this difference in thickness indicates strongly elevated sedimentation rates in shallow water platform settings after the end permian mass extinction high rates of carbonate precipitation are indicative of calcium carbonate supersaturation within shallow watermasses which may have resulted from the upwelling of alkaline anoxic deep waters accompanied by high rates of evaporation as a consequence of extremely high temperatures at the time nevertheless it is the global sea level rise in the early triassic that provided the accommodation space necessary for the precipitation of the great thickness of anachronistic carbonate sediments at the yangjiawan section

distribution characteristics of topside ionospheric density irregularities equatorial versus midlatitude regions 1 the global distribution of the occurrence rate for density irregularities at 600 km topside ionosphere between 35 geographic latitudes has been studied with the rocsat data during moderate to high solar activity years of 1999 to 2004 the result indicates that the global occurrence distribution of the intermediate scale 0 1 to 50 km density irregularities can be grouped into two different populations one in the equatorial region and the other in the middle to subauroral latitude region the global seasonal longitudinal s l distribution of equatorial irregularities in the current report reproduces the result of mcclure et al 1998 obtained with the ae e observations of the mesoscale 50 to 1000 km plasma bubble structures during high solar activity years of 1978 to 1980 two solar cycles ago this implies that the density irregularities of different scales from multistage cascading process of the large scale 1000 km gravitational rayleigh taylor instability have manifested in same global s l distribution pattern furthermore global variation in seeding mechanism and growth condition of the instability process that results in major features in global irregularity pattern seems to persist for past 25 years in addition the current result further indicates that an upper latitudinal limit of the equatorial irregularity distribution is located at about 30 a different kind of midlatitude irregularity distribution starts to fill in from this dip latitude in other words the equatorial density irregularity inside a depleted flux tube can only rise on statistical average to an apex height of 2000 km different magnetic and solar variability effects as well as the local time dependence are noted for the occurrences of density irregularities in the equatorial region versus that at midlatitudes the occurrence frequency of equatorial density irregularities increases with solar flux intensity whereas the midlatitude density irregularity is more likely to occur during low solar activity period the equatorial density irregularities are more likely to occur during periods of low magnetic activity than during magnetic disturbed times on the other hand the occurrence of midlatitude density irregularities indicates little dependence on geomagnetic activity the local time distribution of equatorial irregularity peaks before midnight while the midlatitude irregularity indicates a plateau of high occurrence rate after midnight such opposite characteristics in the occurrence pattern between these two spatially separated distributions suggest that different instability mechanisms are operated in two different latitude regions for the occurrence of intermediate scale density irregularities

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

ionospheric conditions affecting the evolution of equatorial plasma depletions model studies have been carried out to specify the ionospheric conditions and electrodynamical processes required to describe the geometry of westward tilting and bifurcating equatorial plasma depletions inferred from airglow imaging measurements taken on ascension island in early 1981 the results indicate that if the westward tilts are to be associated with eastward plasma drifts that decrease with altitude above the f peak this shear must be set up by a zonal wind pattern of decreasing speed at increasing distances from the equator below the peak calculations of flux tube integrated pedersen conductivity including both e and f region contributions are in agreement with the simulations of zalesak et al 1982 that show bifurcated depletions to be associated with a mild gradient in the bottomside conductivity profile

equatorial spread f related airglow depletions at arecibo and conjugate observations 1 we present evidence of the incursion into the caribbean region of airglow depletions associated with the equatorial rayleigh taylor instability data from the boston university all sky imager located at arecibo puerto rico 18 3 n 66 7 w 28 n magnetic latitude have been used to identify several nights with 630 0 nm airglow patterns that are typical signatures of equatorial spread f and distinctly different from the more common airglow bands frequently observed there two case studies 2 november 2002 and 26 february 2003 show the occurrence of simultaneous airglow depletions observed with another all sky imager located at el leoncito argentina 31 8 s 69 3 w 18 s magnetic latitude relatively close to the arecibo conjugate point supporting information is obtained from defense meteorological satellite program rocsat 1 and gps data all of them showing the presence of strong ionospheric irregularities collocated with the airglow depletions mapping the circular field of view from arecibo into the southern hemisphere reveals a distorted pattern due to the differences in the magnetic field characteristics in both hemispheres this adds an interesting spatial complexity to the formulation of conjugate point observing programs in the latin american longitude sector

ichnological analysis of pleistocene sediments from the iodp site u1385 shackleton site on the iberian margin approaching paleoenvironmental conditions ichnological analysis focused on trace fossil assemblages and an ichnofabric approach with special attention to cross cutting relationships tiering relative abundances and bioturbation degrees has been used to assess environmental parameters affecting the pleistocene macrobenthic tracemaker community at the iodp expedition 339 site u1385 shackleton site on the iberian margin the trace fossil assemblage consists of abundant planolites frequent yet sparsely distributed palaeophycus thalassinoides and thalassinoides like structures and taenidium and localized zoophycos and chondrites other ichnotaxa such as phycosiphon and scolicia are rare this assemblage is typical of the zoophycos ichnofacies though the distal expression of the cruziana ichnofacies has a similar composition ichnofabrics reveal variable substrate colonization with well defined cross cutting relationships and tiering distribution differentiated ichnofabrics are green mottled ichnofabric planolites ichnofabric taenidium and planolites ichnofabric thalassinoides like and palaeophycus ichnofabric planolites and thalassinoides thalassinoides like ichnofabric zoophycos ichnofabric and chondrites ichnofabric usually showing gradual transitions a multi tiered assemblage can be envisaged with differentiation of the shallowest biodeformational structures shallow planolites palaeophycus and even taenidium middle thalassinoides thalassinoides like structures and lower zoophycos and chondrites tiers according to the ichnological data a general context of good bottom and pore water oxygen conditions and organic matter availability can be interpreted but localized dysaerobic intervals might be related with the record of zoophycos and chondrites a constant rate of sedimentation shows only minor variations as revealed by ichnofabric succession soupy soft and stiffgrounds are interpreted as inducing changes in ichnological features salinity and temperature have a minor incidence on the macrobenthic tracemaker community causing only small changes in the trace fossils

early diagenetic celestite replacement of demosponges in upper cretaceous campanian maastrichtian chalk stevns denmark celestite nodules with subordinate amounts of chalcedony are common in upper cretaceous chalk in two cores drilled at stevns denmark the nodules occur throughout the cores indicating that the environmental conditions that led to their formation were an integral part of the biogeochemical cycle in the chalk sea petrographic evidence indicates that the celestite nodules were formed by replacement of lithistid demosponges in localized reduced environments prior to sediment compaction and chert formation the 87 sr 86 sr values of the celestite nodules indicate that the sr is mainly sourced from seawater and the 34 s values indicate activity of sulfate reducing bacteria this unusual occurrence of celestite is interpreted as a result of rapid burial of the sponges and following decomposition of the organic tissue by sulfate reducing and sulfide oxidizing bacteria forming an anoxic microenvironment the decomposition produced hydrogen sulfide which was oxidized to sulfate by sulfide oxidizing bacteria resulting in decreasing ph strontium precipitated as celestite in dysoxic microenvironments and at the anoxic dysoxic interface within the sponge the crystallization of celestite apparently created an sr gradient that drove sr into the site of crystallization this geochemical environment in dead demosponges represents an unknown celestite forming process

sedimentological and ichnological analyses of the continental to marginal marine centenario formation cretaceous neuquen basin argentina reservoir implications abstract the upper valanginian lower aptian centenario formation is a significant producer of oil and gas in the neuquen basin western argentina this formation is located exclusively in the subsurface of the eastern and northeastern neuquen basin and is 450 1000 m thick the centenario formation laterally interfingers with the agrio formation previous studies addressing the paleogeographic history of the centenario formation are scarce and a comprehensive geological model has yet to be put forward the current study scrutinizes the centenario formation especially its lower member within the northeastern neuquen basin the study area includes the cerro hamaca oeste senal cerro bayo and volcan auca mahuida oilfields operated by yacimientos petroliferos fiscales ypf sedimentological and ichnological core data geophysical well logs and petrographic thin sections have been utilized to construct a geological model eleven sedimentary facies and three facies associations have been identified from the core dataset providing insights into the paleoenvironmental settings and their stresses on infaunal colonization basin margin deposits from the northeastern part of the study region were formed in continental environments comprising ephemeral fluvial channel complexes and floodplains and are ichnologically represented by rare skolithos and common rhizoliths the central part of the study area is interpreted as recording deposition in ephemeral lakes river dominated lake deltas and coastal lagoons and sabkhas and is represented by a combination of stressed expressions of both the skolithos and scoyenia ichnofacies river dominated storm influenced delta deposits are located towards the southwestern limit of the study area and are ichnologically represented by the skolithos and depauperate cruziana ichnofacies deltaic deposits gradually transition into the basinal facies of the agrio formation to the west overall sedimentologic characteristics suggest semi arid to arid climatic conditions during deposition

significance of pot and gutter casts in a middle triassic carbonate platform betic cordillera southern spain pot casts and gutter casts are described for the first time in the lower part of the majanillos formation a middle triassic carbonate unit located in the external zones of the betic cordillera southern spain their identification as well as their relation to tempestites enables the better interpretation of the depositional environments and the shoreline to offshore facies transition on the anisian muddy carbonate ramp of the southern iberian massif the majanillos formation contains three members which become progressively more marly towards the top well preserved pot and gutter casts and thin intercalations of calcarenite which are interpreted as tempestites are abundant in the lowest member above the pot and gutter casts thicker calcarenite beds which locally contain hummocky cross stratification predominate bioturbated nodular limestones are prevalent at the top of the member the remaining succession which records a long term triassic transgressive cycle consists mostly of fine grained limestones deposited in very shallow marine environments calcarenitic sediments only accumulated within potholes and gutters in the nearshore they developed during storms when strong currents transported sediment to the outer shelf where it was deposited as tempestite beds pot and gutter casts characterize sedimentation in the bypass zone it is concluded that storm deposits provide important constraints for the interpretation of palaeobathymetry it is proposed that gutter casts display a trend of increasing width thickness ratios towards the outer shelf the identification of these structures in marine successions elsewhere should prove useful in the interpretation of depositional environments

the ichnogenus rhizocorallium classification trace makers palaeoenvironments and evolution rhizocorallium is one of the oldest known trace fossils with wide distribution through the phanerozoic and all over the world originally introduced from the epicontinental triassic of central germany its high morphological lability gave reason for the subsequent erection of about twenty ichnospecies the study of newly collected material from the type area and many specimens from various collections permits the conclusion that rhizocorallium jenense and rhizocorallium commune are the only valid ichnospecies of rhizocorallium the type ichnospecies r jenense is a comparatively small inclined and heavily scratched firmground burrow with passive fill while r commune consists of extensive more or less horizontal burrows with occasionally scratched marginal tubes and an actively filled spreite between the tubes the faecal pellets coprulus oblongus are typically associated with r commune morphological variations of r commune are captured in ichnosubspecies and varieties of this ichnospecies and can aid a refined reconstruction of palaeoenvironments a review of more than 180 records from the literature reveals the common confusion of both ichnospecies which has consequences for the application of rhizocorallium in facies interpretations the end members of both ichnospecies may be linked by transitional forms which suggests the same kind of trace maker polychaetes are the most likely producers of marine rhizocorallium based on their long ranging occurrence morphological features appearance of faecal pellets associated soft body remains and modern analogues r commune occurs from early cambrian to holocene while r jenense just appears after the end permian mass extinction probably as a consequence of an adapted firmground burrowing lifestyle of its producer fluvial r jenense are probably produced by mayfly larvae in homology to marine polychaete burrows a consequent application of the newly established classification scheme allows for a more rigorous application of rhizocorallium in the reconstruction of palaeoenvironments thus palaeozoic and mesozoic r commune are restricted to the cruziana ichnofacies of shallow marine environments while in cenozoic time similar forms are also found in deep marine deposits r jenense on the other hand is a constituent of the widespread glossifungites ichnofacies and aside from continental environments occurs in peritidal to deep marine deposits several studies have demonstrated the value of rhizocorallium for interpreting sequence stratigraphical surfaces current directions and fluctuations in salinity and oxygen

direct observational evidence for the merging of equatorial plasma bubbles in this work we present direct ground based observational evidence for the merging of individual epbs obtained through the imaging of oi 630 0 nm airglow three potential mechanisms have been identified 1 one of the epbs tilts and reaches location of the adjacent growing epb finally merging with it 2 some of the branches of an epb arising from secondary instabilities reaches out to adjacent epb and merge with it 3 the eastward zonal drift of the epb on the eastern side slows down while the adjacent epb on the western side drifts relatively faster and catches up in one of the cases a branch of an epb was observed to get interchanged with another epb as a result of merging and consequent pinching off from the parent epb

geometry of depleted plasma regions in the equatorial ionosphere an image intensified all sky 6300 a airglow imaging system operating on ascension island is early 1981 has been used to assemble a photographic data base of several hundred airglow depletion patterns by mapping the airglow depletion features along geomagnetic field lines to the equatorial plane the geometrical characteristics of plasma depleted regions may be described over the 400 to 1200 km altitude region above the equator such an analysis revealed that single or linear depletions tilted toward the west with an average skewness of 0 6 longitude west 100 km altitude corresponding to a zenith angle tilt of 40 at a height of 800 km the tilts increased with local time during the evening hours showing that an effective velocity shear of 0 05 m s km is required to account for the observed evolution in several cases the depletion geometry showed a wishbone or bifurcated pattern such features had a mean height of bifurcation of 740 km and tilt factors very similar to those found for linear depletions observed during the same local time periods

evidence for recurrent changes in lower triassic oceanic circulation of the tethys the δ13c record from marine sections in iran abstract stable carbon isotope curves derived from lower triassic carbonate rocks from three iranian sections are established to investigate changes in the carbon cycle during the early triassic in this area the sections are located in the south center abadeh north amol and northwest zal of iran all three curves show a similar pattern starting out with high 13 c values in the uppermost permian decreasing across the permian triassic boundary an increase toward more positive values during the griesbachian that slowly increase further up during the dienerian followed by a positive excursion to values as high as 8 near the dienerian smithian boundary during the smithian values return to below 0 whereas second positive excursion to values higher than 3 is recorded at the smithian spathian boundary again followed by a drop in 13 c into the spathian and a final excursion to positive values at the spathian anisian boundary the results from these iranian sections are consistent with previous studies from italy and china thus strongly suggesting that the recorded 13 c variability represents at least tethys wide geochemical signals moreover the new curves reveal evidence of high amplitude frequent oscillations pointing toward rapid and profound changes in the global carbon cycle during the lower triassic stratification of the ocean interrupted by episodic overturning transporting deep water to the ocean surface is a viable mechanism to account for the recorded isotope variations provided that the 13 c curve is representative of the global lower triassic ocean it has high potential for accurately dating sedimentary successions via chemostratigraphy

ichnology and sedimentology of the triassic carbonates of north west sardinia italy the classical middle to upper triassic carbonate sections at monte santa giusta and punta del lavatoio north west sardinia italy referred to the muschelkalk and keuper lithofacies group are revisited and their trace fossil content is investigated for the first time a combined ichnological and sedimentological study reveals insights into the depositional environments regional context palaeogeography and sequence stratigraphy the results indicate deposition on a homoclinal carbonate ramp with broad facies belts all recognized trace fossils are also known from time equivalent deposits of germany and thus indicate a close affinity between the north west sardinian triassic and the germanic basin only a few trace fossils are particularly abundant and these indicate opportunistic colonization by their producers which is probably related to restricted endobenthic conditions due to reduced oxygen and or increased salinity the trace fossil association can be grouped into a softground suite belonging to the cruziana ichnofacies and a firmground suite of the glossifungites ichnofacies this discrimination enables an interpretation of the northern monte santa giusta section as a carbonate ramp with extensive tidal flats and abundant carbonate accumulation in a relatively proximal position whereas the southern punta del lavatoio section exhibits broad lagoonal environments with reduced sedimentation in a deeper and more tethys influenced area the sardinian sections are ichnologically similar to the anisian ladinian succession known from the tatra mountains but differ from it by having a slightly higher ichnodiversity which again can be attributed to a less restricted lagoonal environment this study demonstrates the importance of integrating trace fossil analysis in sedimentological and palaeontological investigations of carbonate systems

facies pattern of western tethyan middle triassic black carbonates the example of gutenstein formation in silica nappe carpathians hungary and its correlation to formations of adjoining areas during the middle triassic a broad carbonate ramp developed at the western end of the tethys ocean in the early phase of the ramp evolution dark grey or black finely crystalline carbonates were deposited over a considerable part of the ramp in the aggtelek karst northeastern hungary carbonates of the aggtelek facies of the silica nappe are exposed in the latest early triassic bioturbated mudstones wackestones and occasionally packstones were formed in the outer ramp zone below the storm wave base during the early anisian oxygen depleted bottom conditions evolved gradual changes took place in the sedimentary features of mud dominated deposits that is attributed to increasing oxygen depletion as a result of density stratification of seawater in the deeper ramp areas remarkable ecological and sedimentary changes began with the colonisation by sponges and microbes in the aggtelek facies area that occurred coevally with a relative sea level fall the appearance of the foraminifer glomospira densa points to late early anisian age for these changes this unit is very variable in lithology and facies compared to the monotonous development of the lower units massive limestones and dolomites of microbial origin are ubiquitous additionally oolites with micro oncoids cross bedded and cross laminated bioclastic peloidal packstones grainstones thin bedded bioclastic wackestones mudstones laminated and brecciated dolomites with evaporite pseudomorphs and dolocretes are also present specific microfacies types i e automicrite varicoloured micrite microspar groundmass and cuneiform spongy microfabric preserved by cryptic microbial films are recognised and interpreted as sponge microbe mud mound deposits the microfacies of pilot samples from northern calcareous alps inner western carpathians and dinarides exhibit similar sedimentary features tectonic setting biota evolution after the end permian mass extinction relative sea level changes and hypersalinity may have been the most important controlling factors of the non skeletal carbonate factory which produced dark grey mud dominated deposits

non tetrapod trace fossils from the middle devonian tetrapod tracksite at zachelmie quarry holy cross mountains poland abstract the middle devonian eifelian dolomites exposed in the zachelmie quarry holy cross mountains southern poland contain the earliest fossil record of tetrapods low diversity but unique assemblages of trace fossils characterize the track bearing interval within the lower complex of the wojciechowice formation the reconstructed environment of the trace fossil rich beds includes ephemeral lakes and or shallow water lagoons separated from an open marine area by sparsely vegetated islands and spits the most abundant non tetrapod trace fossils from these beds are large horizontal to vertical burrows and dish circular to oval shaped shallow depressions the burrows are abundant on the upper surfaces of thick dolomicritic beds especially in some palaeosol levels but they are also associated with tetrapod trackways large semi aquatic or terrestrial animals e g arthropods or vertebrates most likely produced these burrows the circular to oval shaped depressions observed on a large surface and other smaller isolated blocks from the same stratigraphical level are interpreted as fish feeding nesting resting traces piscichnus sanctacrucensis isp nov is proposed as a new ichnospecies of the oval shaped fish trace fossil from the middle devonian of poland a single medium sized undichnia specimen a fish swimming trace is associated with the piscichnus traces the described trace fossils provide new insight into the palaeoecology and taphonomy of the middle devonian tetrapod tracksite from poland and clarify remaining controversies regarding the interpretation of some poorly preserved trace fossils from the zachelmie quarry

gps phase fluctuations in the equatorial region during the miseta 1994 campaign in this paper we present the first coordinated use of global positioning system gps multisite and multisatellite observations with ground based radar and optical diagnostics to investigate equatorial irregularity patterns thirty second samples of total electron content tec obtained from gps phase differences between 1 2 and 1 6 ghz signals are used to study phase fluctuations at several stations comparisons were made with various types of ground measurements during the multi instrument studies of the equatorial thermosphere aeronomy miseta period depletions of 6300a airglow emission from arequipa peru correlated with phase fluctuations recorded at the same site phase fluctuations at arequipa occurred at the times when the jicamarca radar backscatter returns from plumes were noted but were also seen on other nights when there were no radar returns from plumes levels of phase fluctuations noted at arequipa varied considerably on nights when only thin layers of irregularities were observed by the jicamarca radar differences of ionospheric conditions between the two sites separated by only 5 5 geographic longitude may account for the different behavior patterns of irregularities noted similar differences in the general behavior pattern of phase fluctuations were shown when data from arequipa and fortaleza brazil were compared these stations 33 apart but at the same dip latitude had different patterns for some days during a magnetic storm a very high altitude plume was observed by the radar and by phase fluctuations noted at santiago at 18 dip latitude this correlation of high plume altitude during some periods of magnetic activity was validated by additional examples of phase fluctuations from three other magnetic storms in the solar minimum years of 1994 and 1995

lower triassic storm dominated ramp sequence in northern hungary an example of evolution from homoclinal through distally steepened ramp to middle triassic flat topped platform

behavioural responses of rhizocorallium to storm events evidence from the middle triassic of sw china abstract large numbers of densely distributed rhizocorallium provide a window to understanding the behavioural and functional changes of the trace maker after extreme environmental events this study focuses on the analysis of rhizocorallium from the middle triassic anisian limestones in the boyun section yunnan province southwest china to investigate the ecological strategies and ethological signatures of its producers before and after storm events based on its morphological features the studied rhizocorallium is attributed to two ichnospecies rhizocorallium jenense and r commune the latter showing two varieties r commune var auriforme and r commune var irregulare in addition to rhizocorallium the trace fossil assemblage consists of arenicolites palaeophycus planolites and thalassinoides which allows assignation to the cruziana ichnofacies associated with the shallow marine environment the studied ichnofossil bearing intervals in the boyun section are usually high bioturbated with bpbi bedding plane bioturbation index around 5 the ichnoassemblage has a relatively low ichnodiversity and shows high density of rhizocorallium which is interpreted as the result of the opportunist strategy when the rhizocorallium trace makers exploited the quiet nutrient rich substrates after storm events crosscutting relationships between multiple levels of rhizocorallium indicate that earlier burrows were reworked by later ones due to successive storm events and erosion of the shallow tier burrows orientation of the marginal tubes of rhizocorallium jenense shows a bidirectional pattern at 295 nw and 160 se which may record the changes of the main flow direction diameter measurements support the total recovery of the macrobenthic trace makers during the middle triassic anisian

nodular celestite in the chihsia formation middle permian of south china the middle permian chihsia formation of south china accumulated on a shallow shelf and consists mainly of black to dark grey micritic limestone rich in chert nodules and organic matter a unique type of nodular crystal cluster is distributed widely in the carbonate succession most crystal clusters consist of calcite some however are composed of celestite and geochemical microscopic and crystal morphological data suggest that celestite was the precursor of the calcite the celestite developed displacively within the sediments during early diagenesis before compaction and before local dolomitization of the host rock similar strontium isotopic values were obtained from the celestite clusters replacement calcite vein calcite and host rock the values are within the range of middle permian sea water the strontium in the celestite was furnished chiefly by either diagenetic alteration of strontium rich marine aragonite to strontium poor calcite or aragonite dissolution induced by aerobic oxidation of organic matter or both the sulphur isotopic values of the celestite are about 6 11 heavier than the sulphur isotopic value of sulphate in coeval sea water based on geological context this difference is attributed to microbial reduction of porewater sulphate in the chihsia sediments

turbulent upwelling of the mid latitude ionosphere 2 theoretical framework in a companion paper data from the mu radar have been presented which show that during sunspot minimum conditions in japan the mid latitude ionosphere is sometimes characterized by regions of rapid and turbulent upwelling in this paper we explore possible mechanisms for these events the most likely process seems to be the instability of the equilibrium which occurs when the mid latitude plasma is supported against gravity either by an eastward electric field component or by a southward neutral wind as was proposed by perkins 1973 we show for example that the growth rate determined by perkins is considerably higher in sunspot minimum conditions than at sunspot maximum for comparable altitudes of the ionospheric f layer the growth rate is not very large however and we argue here that the observed structures must evolve from preexisting undulations of the bottomside of the f region which are generated by gravity waves that is the gravity waves create finite amplitude structures which are amplified by the plasma instability an intriguing feature of the gravity wave role in this process is that the echoing patches detected by the mu radar and the height bands detected by the arecibo radar which we believe to be related phenomena all seem to propagate to the west this is the same direction reported for the angle of arrival measurements of classic mid latitude spread f by a number of researchers using ionosonde techniques since the mu radar detects the upwelling regions from nonthermal 3 m irregularities there must be mechanism to create such tracers we propose that secondary structures are created at intermediate scales via the e b instability operating on the dome of the upwelling structure and by the neutral wind driven process on either the west or the east wall of the structure depending on the direction of the zonal wind the 3 m waves are then created in a cascade process which brings energy into a range of k space in which the structures are linearly damped finally we discuss the fine structure of the echoing patches and suggest several plausible mechanisms two of which involve e region coupling and one which deals with the vertical structure of the gravity wave seeding process

thalassinoides phycodes compound burrow systems in paleocene deep water limestone southern alps of italy abstract compound burrow systems consisting of branching horizontal tunnels in the core areas of the systems intergrading with fan like tunnels in distal areas are common in the paleocene scaglia cinerea limestone if preserved as isolated elements the cores would be identified as thalassinoides suevicus and the distal elements as phycodes cf palmatus these complex trace fossils are probably combination dwelling deposit feeding structures produced by endobenthic crustaceans that occupied and operated the systems for relatively long intervals of time compounds such as these may be more common than supposed and represent an important but essentially unexploited source of biologic information on marine invertebrate trace producers

ichnology and depositional environments of the upper ordovician stony mountain formation in the williston basin canada refining ichnofacies and ichnofabric models for epeiric sea carbonates abstract ordovician epeiric sea carbonates in intracratonic basins of laurentia are enigmatic due to their unique depositional settings and the absence of modern analogs integrated ichnologic and sedimentologic analysis of the upper ordovician stony mountain formation in the williston basin of canada allows recognition of neritic marine nearshore marine open lagoon restricted lagoon peritidal sand shoal and peritidal flat subenvironments the cruziana ichnofacies occurs in neritic between fair weather and storm wave bases and nearshore around fair weather wave base marine environments the depauperate cruziana ichnofacies is present in open and restricted lagoon environments indicating a shift from fully marine to stressed conditions in the open lagoon composite ichnofabrics related to omission surfaces illustrate the low rates of background sedimentation interrupted by event deposition and early cementation illustrating the glossifungites and trypanites ichnofacies the decreased size of discrete burrows in the restricted lagoon is attributed to reduced oxygenation under stagnation rather than hypersalinity the peritidal complex includes high energy sand shoals and low energy tidal flats only monospecific colonization took place sporadically in associated subtidal environments within the peritidal complex deposits

the characteristics of carbonate system recovery during a relatively dry event in a mixed carbonate siliciclastic environment in the pelsonian middle triassic proximal marginal marine basins a case study from the tropical tethyan northwest gondwana margins abstract eight early mid pelsonian middle triassic marine sedimentary successions an outcrop and subsurface sections of the ra af formation from the northwest gondwana margins facing the southeast corner of the tropical western tethyan seaway assigned to the southern intertropical convergence zone itcz south israel levant basin north arabian plate are the focus of this work the successions especially with the exclusive outcrop at har arief are a golden opportunity to observe the still connected transitional zone between the huge siliciclastic domains derived from gondwana hinterland parts north arabian plate and the open tropical tethyan marine carbonate domain and their mutual relationships this multidiscipline research tracks a carbonate recovery attempt in a dominant siliciclastic system the recovery effort was characterized by starved sedimentary conditions basin constrained oxygen stressed environments and low diverse autochthonous burrowed sediments barren of other faunal remains low diverse fossiliferous allochthonous beds transported from higher sites on the slopes revealed differential distributions of echinoids mollusks and especially foraminifera large pilammina pilamminella versus small glomospirids these variances were attributed to different environmental conditions on the slopes of each basin type and illuminate some constraints on their distribution pattern and climate affinity in the triassic southern itcz mixed carbonate siliciclastic sedimentary system the carbonate recovery phase is ascribed to a relatively dry period in the hinterland rather than to sea level rise this dry period which interrupted the relatively humid climate in the northern tropical gondwana during the pelsonian is represented by the constant although with some perturbations siliciclastic sedimentary system that prevailed in the southeastern corner of the tethys seaway during the anisian insights from the symmetric and asymmetric correlation of climate fluctuations in the hinterlands of the southeastern european basins northern hemisphere and this work from the southern hemisphere both embracing basins ascribed to the western tropical tethyan seaway illuminate the possible effects of the ictz behavior pattern and possible extra tropical forces on the climate variations

chondrites a trace fossil indicator of anoxia in sediments the trace fossil chondrites a highly branched burrow system of unknown endobenthic deposit feeders occurs in all types of sediment including those deposited under anaerobic conditions in some cases such as the jurassic posidonienschiefer formation of germany chondrites occurs in black laminated carbonaceous sediment that was deposited in chemically reducing conditions in other cases such as numerous oxic clastic and carbonate units throughout the geologic column chondrites typically represents the last trace fossil in a biotutbation sequence this indicates that the burrow system was produced deep within the sediment in the anaerobic zone below the surficial oxidized zone that was characterized by freely circulating and oxidizing pore waters

interesting equatorial plasma bubbles observed by all sky imagers in the equatorial region of china this paper reports some interesting equatorial plasma bubbles epbs on 04 05 october 2013 and 29 30 september 2013 observed by two all sky imagers located in the magnetically equatorial region of hainan 19 5 n 9 5 geomagnetic latitude and guiping 23 8 n 13 9 geomagnetic latitude china the case of 04 05 october 2013 shows that 1 epbs had planar wave like structures and their wavefronts were parallel to each other before midnight 2 the angle between the wavefronts of those epbs and the geomagnetic meridian were 30 3 near midnight the higher latitude part of one epb suddenly began to rotate with a large eastward zonal drift resulting in an unusual c shaped epb that was observed for the first time by an all sky imager 4 after midnight one epb merged into another epb and formed an integrated epb the other epb case on 29 30 sept 2013 shows that 1 the images captured the full evolution processes of an i shaped epb with an angle of 30 with respect to the geomagnetic meridian the imagers also observed s and y shaped epbs 2 the change of epbs shape was directly related to the change of epbs zonal drift velocities 3 the angle between the i shaped epbs and the geomagnetic meridian was likely caused by the change of the latitudinal gradient of zonal neutral wind velocities and ionospheric conductivity 4 the zonal velocity of each branch of the y shape epb was different which could be related to the polarization electric fields within each branch

unusually well preserved casts of halite crystals a case from the upper frasnian of northern lithuania abstract upper frasnian carbonate siliciclastics of the stipinai formation northern lithuania comprise a bed of calcareous silty arenite with casts of halite crystals including hopper crystals unusually well preserved casts occur on the lower surface of the bed while poorly preserved casts are present on the upper bedding surface the casts originated as the result of the dissolution of halite crystals which grew in the sediment the dissolution took place during early stages of diagenesis when host sediment was soft unstable cavities after crystal dissolution were filled by overlying sediment forming their casts the collapsing sediment form sink hole deformation structures which disturb wave ripple cross lamination from the upper part of the bed dewatering pipe structures are also present the casts and accompanying sink hole and dewatering pipes are classified as the postdepositional deformation structures caused by haloturbation

trace fossils as indicators of environmental change in holocene sediments of the archipelago sea northern baltic sea abstract biogenic structures in holocene sediments from the archipelago sea northern baltic sea were characterized through the analysis of x ray images of four cores collected from water depths between 32 and 66 m in the area initial colonization of endobenthic invertebrates occurred at 7800 80 calendar years bp the trace assemblage at this level is low diversity small diameter shallowly tiered and palaeophycus dominated rare arenicolites are also observed early colonization coincides with increasing marine influence in the post glacial lacustrine setting just before the dramatic onset of brackish water conditions established after 7600 bp the post incursion brackish water assemblage possesses a higher diversity of traces planolites arenicolites lockeia teichichnus which is taken to reflect the enhanced salinity and trophic state of the basin the shift from palaeophycus mottling to a planolites dominated fabric represents changed behavioural patterns in the endobenthic community due to changed substrate properties the ethology of the succeeding trace assemblage also represents a switch from domicile based activities such as predation scavenging and interface dominated deposit feeding to shallow tier deposit feeding finally traces are excluded from thinly laminated intervals demonstrating that seafloor oxygen deficiency commonly reached levels that were detrimental to colonization of the sediment substrate

field aligned observations of transequatorial bubbles from rarotonga in 1969 70 a raster scanning photometer with 0 5 field of view was used in 1969 70 to make images in 6300 a and 5577 a emission from rarotonga of tropical f region trans equatorial bubbles or depletions from this site the f region plasma structures in the emission layer can be viewed in a magnetic field aligned configuration a spatial resolution of approximately 15 km was achieved and revealed a variety of shapes in the bubble cross sections including bifurcations and pinched off bubbles eastward drift velocities averaged 125 ms 1 tilts were usually westward at about 45 in the equatorial plane but some were near zero and some were eastward the tops reached apex heights of over 800 km the structures appeared a little less diffuse in 5577 a emission than in 6300 a owing to less diffusion of o s with its 0 75 sec lifetime than o d with its 150 sec lifetime

observations and modeling of the coupled latitude altitude patterns of equatorial plasma depletions 1 the equatorial ionosphere is host to the most dramatic and enigmatic plasma instability mechanism in the geospace environment equatorial spread f esf was discovered in early ionosonde measurements and interpreted theoretically using rayleigh taylor theory subsequent diagnostic and modeling advances have improved substantially our understanding of esf onset and evolution and its associated effects on the ionosphere throughout the low latitude domain the degree to which esf mechanisms penetrate into the lower midlatitudes is a topic of current study a reverse of the familiar concept of high to low latitude coupling for space weather phenomena optical diagnostic systems first ground based and now space based reveal the presence of esf structures via images of airglow depletions that are aligned in the approximately north south direction spanning the geomagnetic equator ground based all sky camera systems used to capture the two dimensional horizontal patterns of airglow depletions are the main source of observations showing that esf processes intrude to midlatitudes in the l 1 5 domain in this paper we review the process of mapping airglow depletions along geomagnetic field lines to the equatorial plane hence defining the maximum apex heights achieved a case study comparison of simultaneous radar backscatter data from kwajalein with optical data from wake island sites that share common magnetic meridians in the pacific section confirms the utility of the approach and its applicability to sites at other longitudes modeling studies based on buoyancy arguments using flux tube integrated mean density values versus l shell apex heights show that instability induced plasma depletions starting at f layer bottomside heights easily reach altitudes above 2000 km in the equatorial plane implying that esf intrusions to lower midlatitudes should be a relatively frequent occurrence

a review of the origin and setting of tepees and their associated fabrics carbonate hardgrounds often occur at the surface of shallow subtidal to supratidal lacustrine and subaerial carbonate shelf sediments these are commonly disrupted and brecciated when the surface area of these crusts increases in the subtidal environment megapolygons form when cementation of the matrix causes the surface area of the hardgrounds to expand similar megapolygons form in the supratidal lacustrine and subaerial settings when repeated incremental fracturing and fracture fill by sediment and or cement also causes the area of the hardgrounds to expand the arched up antiform margins of expansion megapolygons are known as tepees the types of tepees found in the geological record include 1 submarine tepees which form in shallow carbonate saturated waters where fractured and bedded marine grainstones are bound by isopachous marine phreatic acicular and micritic cements the surfaces of these brecciated crusts have undergone diagenesis and are bored unlike tepees listed below they contain no vadose pisolites or gravity cements 2 peritidal and lacustrine tepees are formed of crusts characterized by fenestral pisolitic and laminar algal fabrics this similarity in fabric makes these tepees of different origins difficult to separate peritidal tepees occur where the marine phreatic lens is close to the sediment surface and the climate is tropical they are associated with fractured and bedded tidal flat carbonates their fracture fills contain geopetal asymmetric travertines of marine vadose origin and or marine phreatic travertines and or terra rossa sediments the senile form of these peritidal tepees are cut by labyrinthic dissolution cavities filled by the same material lacustrine tepees form in the margins of shallow salinas where periodic groundwater resurgence is common they include groundwater tepees which form over evaporitic boxwork carbonates and extrusion tepees which also form where periodic groundwater resurgence occurs at the margins of shallow salinas but the dominant sediment type is carbonate mud these latter tepee crusts are coated and crosscut by laminated micrite the laminae extend from the fractures downward into the underlying dolomitic micrite below the crust both peritidal and lacustrine tepees form where crusts experience alternating phreatic and vadose conditions in time intervals of days to years cement morphologies reflect this and the crusts often contain gravitational meniscus vadose cements as well as phreatic isopachous cement rinds 3 caliche tepees which are developed within soil profiles in a continental setting they are formed by laminar crusts which contain pisolites and fractures filled by micritic laminae microspar spar and terra rossa most of the cements are gravitational and or meniscoid in ancient carbonates when their cementation and diagenetic fabric can be interpreted tepee structures can be used as environmental indicators they can also be used to trace the evolution of the depositional and hydrological setting

a triassic homoclinal ramp from the western tethyan realm western balkanides bulgaria integrated insight with special emphasis on the anisian outer to inner ramp facies transition abstract the triassic carbonate succession exposed in the western balkanides is analyzed in terms of depositional evolution sequence stratigraphy sedimentation rate environmental constraints and biota distribution deposition took place on a storm dominated ramp which existed at the nw end of the tethys ocean from late olenekian to early carnian time subtidal intertidal and supratidal sediments were accumulated in three zones of the ramp profile inner ramp mid ramp and outer ramp the calculated average sedimentation rate is typical for other ancient marine shallow water carbonates including those deposited on ramps newly accomplished sedimentological study on part of the anisian interval reveals a homoclinal ramp model with episodic initial distal steepening two main phases of the ramp evolution are distinguished on the basis of changing relative paleobathymetry transgressive e g retrogradational depositional trend and regressive e g progradational depositional trend the maximum flooding zone is marked by the terebratula beds having late pelsonian age the inferred environmental constraints of the ramp system comprise normal marine to hypersalinity warm well illuminated water aerobic and rarely dysaerobic bottom conditions dominantly soft lime mud substrate intensive storm activity temporal seismic influence presumably related to early triassic rifting the vertical distribution of marine fauna indicates shifting from germanic peri tethyan affinity to alpine tethyan affinity in anisian time the sedimentation was not characterized by formation of large buildups because of the paucity or lack of metazoan and other reef builders the studied rocks are well correlated with the triassic ramp succession outcropping in the tizsa meagunit of southern hungary similarities to the german polish and spanish muschelkalk are also clearly outlined and some parallel can be drawn with other platform carbonates from the nw tethys shelf area and peri tethys basins

the condor equatorial spread f campaign overview and results of the large scale measurements during the condor campaign a number of instruments were set up in peru to support the rocket experiments in this series of papers we report on the results of the experiments designed to study the equatorial f region in this overview paper we summarize the main results as well as report upon the macroscopic developments of spread f as evidenced by data from backscatter radas from scintillation observations and from digital ionosonde meaurements in this latter regard we argue here that at least two factors other than the classical gravitational rayleigh taylor plasma instability process must operate to yield the longest scale horizontal organization of spread f structures the horizontal scale typical of plume separation distances can be explained by invoking the effect of a shear in the plasma flow although detailed comparison with theory seems to require shear frequencies a bit higher than observa tions indicate on the other hand the largest scale organization or modulation of the scattering layer cannot be explained by the shear theory and must be due to local time variations in the ionospheric drift or to gravity wave induced vertical motions using simultaneous rocket and radar data we were also able to confirm the oft quoted hypothesis that rapid overhead height variations in the scattering region over jicamarca are primarily spatial structures advecting overhead the detailed rocket radar compari son verified several other earlier results and speculations particularly those made in the plumex experiments in particular companion papers discuss and extend some of the plumex results to include the role of anomalous diffusion labelle et al this issue in the theory of equatorial spread f and to shed light upon the shallow spectral form often observed in the intermediate scale regime labelle and kelley this issue

equatorial plasma bubble zonal velocity using 630 0 nm airglow observations and plasma drift modeling over ascension island 1 we present oi 630 0 nm airglow image data from ascension island geographic 7 9 s 14 4 w dip latitude 16 s in the southern atlantic ocean taken with the utah state university all sky ccd camera during 20 march to 7 april 1997 in order to study plasma bubbles occurring in the low latitude nighttime ionosphere the initial plasma bubble onset occurs in the early evening hours at 19 15 20 00 lst and is followed by eastward propagation with an average speed of 90 120 m s prior to local midnight rapidly decreasing around the midnight and postmidnight periods the ascension results are compared with similar observations from christmas island in order to examine the longitudinal variations of epb development and propagation the observed epb velocities from ascension island are also compared with the results of a plasma drift model in a case study during the night of 4 5 april the velocity reveals unusual latitudinal shear up to 0 12 m s km with a reversal to westward flow at low latitudes while eastward flow is maintained at higher latitudes consequently the bubble rotates counterclockwise and tilts eastward significantly away from alignment with the geomagnetic field lines the westward reversal of the drift motion near the geomagnetic equator is most likely the result of a reversal in the f region dynamo or from a large increase in the altitude of the shear node in the f region plasma drift at the geomagnetic equator

trace fossil model for reconstruction of paleo oxygenation in bottom waters recognition of fluctuations in the degree of paleo oxygenation of bottom waters recorded in fine grained pelagic strata is important for interpretation of paleoceanographic and paleoclimatologic conditions general sedimentary fabric composition of trace fossil assemblages and burrow size and crosscutting relationships have been incorporated into a trace fossil tiering model that permits detailed reconstruction of changes in paleo oxygenation of bottom waters applications of this model to the miocene monterey formation california and the cretaceous niobrara formation colorado indicate that the ichnologic approach is more sensitive to both magnitude and rates of change in oxygenation levels compared to macrobenthic body fossil information

mapping a bubble at dip equator and anomaly with oblique ionospheric soundings of range spread f multiple ionospheric sounders are employed in the first attempt to detect and map remotely an equatorial bubble near the dip equator and simultaneously near the appleton anomaly crest the sounders also provide latitudinal profiles of electron density through 30 degrees dip latitude diplat conditions are solar maximum and low kp using oblique range spread f rsf echoes from the bubble boundaries four sounders located near the dip equator detect a single isolated bubble at ranges as great as a 1020 km and track it for 2 25 hours at 5 min intervals as it drifts eastward through 15 degrees geomagnetic longitude mlong maximum velocity is 185 m s and width is 375 km near the northern anomaly crest a sounder at 20 3 degrees diplat observes the western boundary for a duration of 1 hour concurrently with and magnetically conjugate to the equatorial observations the boundary here has nearly the same drift velocity and mlong as at the equator implying that the boundary location and velocity are nearly independent of altitude above the dip equator subsequently in the south a sounder at 19 9 degrees diplat observes the bubble to have a velocity approximately half that seen by other stations and a mlong that is at least 3 degrees more west of the others this difference may be related to the north south asymmetry of the anomaly crest which is at the location of the northern sounder but equatorward of the southern sounder although the two are at the same diplat the onset of the bubble is recorded in the first appearance of rsf at 1915 local mean time 20 min later the bubble boundary appears and begins accelerating eastward the movement occurring within about 5 min of electric field reversal as inferred from f layer vertical motion 30 refs 8 figs less

on the interpretation of resistivity soundings by the least squares method an interactive least squares method for the interpretation of ves curves was proposed by johansen 1977 the method permits one to select some parameters thicknesses and or resistivities of individual layers and to change the rest in such a way that the interpreted model approaches the measured data this note suggests a modification of johansen s method in which not only the individual parameters can be selected but also linear combinations of parameters in particular the sum of thicknesses of several layers

a statistical analysis of equatorial plasma bubble structures based on an all sky airglow imager network in china this paper investigates the statistical features of equatorial plasma bubbles epbs using airglow images from 2012 to 2014 from a ground based network of four imagers in the equatorial region of china it is found that 1 epbs mainly occur during 21 00 00 00 local time lt in equinoxes there is an asymmetry in occurrence rates between march june and september equinoxes december solstices 2 most epbs occur in groups of two to six depletions the distance between adjacent epb depletions is 100 700 km and the average is 200 300 km the zonal extension of an epb group is usually less than 1500 km but can reach 3000 km 3 epbs usually have a maximum drift velocity near 100 m s at 21 00 22 00 lt in 9 5 1 5 geomagnetic latitude and then decrease to 50 70 m s toward sunrise 4 the averaged westward tilt angle of most epbs with respect to the geographic north south increased from 5 10 to 23 30 with lt between 20 00 and 03 00 lt then decreasing to 10 20 toward sunrise 5 when 90 140 the maximum pmle increases by 3 4 5 5 when f10 7 changes from 90 to 190 6 the epb occurrence patterns and zonal drift velocities are significantly different from those at kolhapur india which locates west to our stations by 20 0 32 0 in longitude

airglow characteristics of equatorial plasma depletions a new low light level all sky 6300 a airglow imaging system has been developed for ground based studies of the optical signatures of equatorial plasma depletions the system was designed for narrowband interference filters 6 a full width at half power with interchangeable all sky 180 and narrow field 60 lenses and records images photographically by using a standard 35 mm camera a field test of the apparatus was conducted on ascension island 8 0 s 14 4 w from january 24 to february 10 1981 the photographs were analyzed for broad morphological characteristics by using simple overlay techniques augmented by digital image processing methods to extract more quantitative detail the initial results to come from these observations show that airglow depletions occur most often during the 2030 2330 lt period often covering one fourth of the visible sky they extend from the magnetic equator to beyond the crest of the equatorial anomaly with east west cross sections of 100 km to several hundred kilometers they are usually not aligned with magnetic meridians showing a progressive skewness to the west at further distances from the equator several cases of apparently twisting overlapping and bifurcating depletions were observed the depletions drifted to the east with speeds that decreased from 190 m s at 2100 lt to 80 m s at 0100 lt the airglow intensities within depletions were typically 40 50 of the background levels and the western walls of the depletions usually had a steeper gradient than the corresponding eastern walls

lateral variations in sediment composition and bedding in middle triassic interplatform basins buchenstein formation southern alps italy hemipelagic deposits are widespread in triassic sequences of the alpine belt and provide important data for stratigraphy and the study of bedding rhythms the area of the western and central dolomites of northern italy escaped strong alpidic deformation and preserves such deposits in their original palaeogeographic setting the buchenstein formation the object of this study was deposited in up to 1000 m deep middle triassic interplatform basins which extend over an area of 500 km 2 within the dolomites excellent outcrops and volcaniclastic markers allow a detailed correlation of the formation in both laminated anoxic and bioturbated facies down to a bed scale and show its relationship to coeval carbonate platforms correlation of lithostratigraphically well constrained intervals in the bioturbated facies reveal that lateral thickening and thinning of the deposits depends on the amount of shallow water debris in the succession and is a function of the distance to coeval carbonate platform sources in the laminated background deposit thickness variations in limestones and marls parallel the thickness variations in ash layers and were caused by local redeposition of sediment on the basin floor lateral persistence of laminae indicates that bottom currents were weak in the buchenstein basin but were able to redeposit mud in a significant way in the area around seceda and geisler western dolomites a lateral transition from dark grey laminated to grey bioturbated to red bioturbated facies is observed which is probably linked to local relief with different oxygenation conditions on the sea floor a comparison shows that decimetre scale bedding is preserved in all facies types and that the bedding rhythm is partly the result of different cementation of the sediment during early diagenesis correlation of individual layers in the bioturbated facies reveals that beds are thicker and enriched in lime mud in the western part of the basin and decrease in thickness and contain less micrite towards the east further away from the main shallow water areas nearslope calciturbidites change gradually from distinct layers into lateral arrays of micrite nodules and bands further out in the basin these observations point to a platform source of lime mud in the buchenstein basin

a hypersaline ichnoassemblage from the middle triassic carbonate ramp of the tatricum domain in the tatra mountains southern poland abstract the middle triassic of the tethyan domain contains heavily bioturbated carbonates known as vermicular limestones in the tatricum domain in the tatra mountains western carpathians these were deposited on a restricted carbonate ramp below the fair weather wave base sedimentological and geochemical evidence points to a hypersaline depositional environment the vermicular limestones contain an impoverished ichnoassemblage of the cruziana ichnofacies dominated by planolites small size thalassinoides is less common balanoglossites and rhizocorallium are rare and helminthopsis phycosiphon and taenidium are very rare the ichnoassemblage points to environmental stress related foremost to hypersaline conditions and less so to lowered oxygenation trace fossil diversity and abundance diminishes from totally bioturbated limestones to dolomitic limestone and dolostones and disappears in the dolostones probably due to an increase in salinity to values in which burrowing fauna is eliminated the repetitive occurrence of the vermicular limestones and associated facies reflects partly fluctuations of salinity which were probably climatically controlled

an empirical model of the drift velocity of equatorial plasma depletions 1 the far ultraviolet imager on the image spacecraft image fuv has been used to observe o plasma depletions in the post sunset equatorial ionosphere small scale density irregularities associated with such depletions are believed to adversely affect trans ionospheric radio signals such as gps prediction of the motion of these plasma depletions is a necessary component of the ability to forecast the occurrence of such radio signal interference an automated method has recently been developed to identify and track the position and zonal drift velocity of these depletions here we use this method to create a large database of the zonal drift velocities of these depletions we present an empirical model based on these observations that describes the observed drift velocities as a function of both local time and magnetic latitude which is essential to represent their behavior a comparison of the observed drift velocities with zonal winds from both an empirical model horizontal wind model hwm07 and a first principles model the tiegcm reveals that the plasma depletions drift velocities have a latitudinal gradient that cannot be explained solely by the f region dynamo in the post sunset period at least by these climatological models this suggests that these plasma depletions may not simply drift with the background f region plasma it has previously been suggested that vertical polarization electric fields associated with the plasma depletions are responsible for their zonal drifts exceeding the background flow which may explain the previously observed discrepancy in the drift velocities and the discrepancy in their gradients reported here

hummocky cross stratified deposits and turbidites in some sequences of the umbria marche area central italy during the toarcian abstract some sections of the umbria marche basin central italy were characterized during the toarcian by alternately thicker and thinner organic rich marls and well oxygenated red and nodular marly limestones these sequences exhibit sharp based hummocky cross stratified hcs deposits and turbidites ranging in thickness from several centimetres to 200 cm palaeocurrent measurements of hcs beds and turbidites indicate the same se nw direction hcs deposits that show wavelengths mostly from 70 to 140 cm are grainstones and matrix poor packstones a complete sequence consists of three divisions a a lower coarse grained bivalve and echinoderm lag from 0 5 to 40 cm thick the lag is generally erosive and discontinuous and probably represents a proximal material deposited during a high energy phase of a storm event b a middle well sorted calcarenite calcisiltite division from 20 to 100 cm thick that exhibits well preserved hummocky cross stratification bioclastic calcareous sands transported by offshore currents from storm surges were organized into hcs beds under an oscillatory unidirectional flow regime near the bottom c an upper oscillatory ripple bedded calcisiltite division from 0 5 to 25 cm thickness ripples were probably formed during a dominant oscillatory regime wave action after the sand sedimentation had stopped locally a pervasive bioturbation is common in the upper part of this bed turbidites 10 200 cm thick are packstones and rudstones with abundant muddy matrix and generally show the classical bouma bc sequence the lower and middle interval of the studied sequences from the late domerian to the early toarcian is dominated by fining upward turbidites on the contrary the upper part of the sequence middle late toarcian in age is dominated by sharp based hcs beds the vertical transition from turbidites to sharp based hcs deposits is indicative of a general regressive trend the causes of the sea bottom depth changes can be related respectively to a sea level rise documented for the early toarcian and to the sea level fall of the middle toarcian lateral and vertical distribution frequency grain size structures and composition of detritic beds and microfaunal assemblages confirm the differentiated topography of the umbria marche basin during toarcian time

field aligned 777 4 nm composite airglow images of equatorial plasma depletions 1 we present a powerful tool to analyze two dimensional field aligned images of equatorial plasma depletions taken from mid latitudes by shifting each individual image by the sum of the longitudinal offsets obtained by performing a cross correlation between successive images a single composite image can be formed for the entire night it is shown that these field aligned composite images give information on the observation times of the depletions associated with spread f as they pass by hawaii in addition they can be used to estimate the formation time and location of the depletions to the west of the observing site this technique also yields estimates of the eastward velocity and velocity shear of the depletions we suggest that the information gained by using these images can be used to predict satellite scintillations at stations to the east of the observing station

time evolution and dynamics of equatorial backscatter plumes 1 growth phase much of our understanding of equatorial spread f phenomena has resulted from vhf radar studies of backscatter plumes i e patterns of backscatter that appear to extend from the bottomside into the topside of the f layer by using altair a fully steerable backscatter radar to map selected plumes repeatedly it was found that the dynamic behavior of plumes can be characterized by a growth and a decay phase the growth phase characteristics described in this paper are found to be generally consistent with equatorial irregularity generation as predicted by the rayleigh taylor and gradient drift instabilities in particular 1 plumes are generated primarily in the local time around f layer sunset 2 plumes develop from local perturbations in plasma density in the bottomside of the f layer 3 plumes develop upward with growth velocities ranging from 125 to 350 m s and 4 backscatter strength increases during upward plume development and decreases when upward plume growth slows or ceases however certain characteristics namely an east west asymmetry in backscatter strength found in the bottomside f layer have been found that suggest key roles played by the eastward neutral wind and by altitude modulation of the bottomside f layer in establishing the initial conditions for plume growth

first observation of interhemispheric asymmetry in the epbs during the st patrick s day geomagnetic storm of 2015 in this work we have studied the characteristics of epbs such as their zonal drift and tilt from the low latitude and dip equatorial region in the indian longitude sector during the main phase of the 17 march 2015 storm all sky airglow imaging observations from tirunelveli 8 7on 77 8oe geographic 1 7on dip latitude and kolhapur 16 7on 74 3oe geographic 11 5on dip latitude are utilized here on 17 march 2015 epbs were observed to drift eastward during 14 30 16 30 ut between 3os and 15on dip latitudes a westward drift presumably under the influence of the disturbance dynamo electric field ddef initially appeared at higher dip latitudes almost 10 hours after the storm onset and subsequently the same was observed at lower dip latitudes the epbs attained a peak westward drift at 17 00 ut followed by a gradual decrease in their speed till 18 30 ut after regaining their westward speed the epbs continued to drift westward till 22 00 ut moreover a latitudinal gradient in the drift motion of the epbs was also observed on this night another interesting observation made from the images obtained from tirunelveli was the presence of a large westward tilt of the epbs the most intriguing finding of this study however was the asymmetry in the tilt of the epbs at conjugate points during the pre midnight hours on 17 march 2015 in this study the possible mechanisms that can explain these observations are discussed in the light of the current understanding of the equatorial electrodynamics and epbs

assessing early triassic paleoceanographic conditions via unusual sedimentary fabrics and features article i nfo analysis of the lower triassic sedimentary rock record has revealed a variety of unusual sedimentary fabrics and features many of which were more common in the proterozoic than the phanerozoic these so called anachro nistic facies developed across lower triassic carbonate platforms from shallow subtidal environments to deep basinal environments and include features associated with the enhanced precipitation of calcium carbonate e g synsedimentary seafloor cements microbialites and fabrics that formed due to a reduction in the intensity and depth of bioturbation e g vermicular limestones three interacting factors controlled the development of anachronistic facies during the early triassic including 1 environmental conditions i e the unusual chemistry of early triassic oceans 2 biotic factors e g bioturbation and grazing pressures and 3 actualistic sedimen tologic processes e g waves and currents sedimentation because these three factors typically acted in concert with each other it is important to consider the role of each when using anachronistic facies to reconstruct early triassic paleoceanographic conditions overall anachronistic facies are indicative of enhanced calcium carbonate precipitation during the early triassic but do not necessarily indicate the former presence of anoxic or suboxic conditions where they were deposited the influence of seawater chemistry on the deposition of anachronistic facies was most pronounced in deeper water environments where anomalous paleoceanographic conditions heightened calcium carbonate precipitation and caused a decrease in bioturbation and grazing pressures via the upwelling of anoxic alkaline waters the degree of environmental influence lessened shorewards where biotic factors and actualistic processes were more important and slight modification of seawater by microbial activity shallow burial or co2 degassing was necessary for calcium carbonate precipitation to occur anachronistic facies are a useful tool for reconstructing paleoceanographic conditions and examining shifts in the distribution of environmental stress during the recovery from the permian triassic mass extinction but only when the biologic sedimentologic and geochemical factors that led to their growth are carefully considered

optical observations of the development of secondary instabilities on the eastern wall of an equatorial plasma bubble 1 optical evidence is presented for the growth of a local secondary plasma instability on the eastern wall of an equatorial plasma bubble observed from the haleakala volcano hawaii geographic 20 71 n 203 83 e geomagnetic 21 31 n 271 45 e typically only the western wall of depletions at tropical latitudes are susceptible to secondary structuring this event occurs during a minor geomagnetic storm when the plasma bubble is observed to be drifting to the west rather than with the typical eastward drift velocity the data are interpreted in terms of the generalized e b instability with an anomalous wind directed westward and toward the equator this wind drives the eastern wall of the depletion region unstable the anomalous wind is associated with an equatorward propagating neutral wind surge caused by an ongoing geomagnetic storm the observations of the growth of these instabilities in the local tropical ionosphere are in stark contrast to the typical development of secondary instabilities on equatorial plasma bubbles which grow near the equatorial plane on the western wall of the primary depletion and map along the magnetic field lines to off equatorial latitudes