fingerprinting geological materials using ssms comment commentaire sur l article de kronberg b i murray f h daddar r brown j r 1988 fingerprinting geological materials using ssms chem geol 68 351 359

peculiar features of the low latitude and midlatitude ionospheric response to the st patrick s day geomagnetic storm of 17 march 2015 the current study aims at investigating and identifying the ionospheric effects of the geomagnetic storm that occurred during 17 19 march 2015 incidentally with sym h hitting a minimum of 232 nt this was the strongest storm of the current solar cycle 24 the study investigates how the storm has affected the equatorial low latitude and midlatitude ionosphere in the american and the european sectors using available ground based ionosonde and gps tec total electron content data the possible effects of prompt electric field penetration is observed in both sectors during the main phase of the storm in the american sector the coexistence of both positive and negative ionospheric storm phases are observed at low latitudes and midlatitudes to high latitudes respectively the positive storm phase is mainly due to the prompt penetration electric fields the negative storm phase in the midlatitude region is a combined effect of disturbance dynamo electric fields the equatorward shift of the midlatitude density trough and the equatorward compression of the plasmapause in combination with chemical compositional changes strong negative ionospheric storm phase is observed in both ionosonde and tec observations during the recovery phase which also shows a strong hemispherical asymmetry additionally the variation of equatorial ionization anomaly as seen through the swarm constellation plasma measurements across different longitudes has been discussed we also take a look at the performance of the iri real time assimilative mapping during this storm as an ionospheric space weather tool

carbonate deposition physical limnology and environmentally controlled chert formation in paleocene eocene lake flagstaff central utah abstract lake flagstaff paleocene eocene of central utah owed its existence large size shallowness and low clastic content to its tectonic setting but the climate controlled its mostly autochthonous sediments during the first and most humid of the three lake phases the lake was fresh calcareous large and highly productive with abundant vegetation and snails the first deposits were limestones with gradually increasing detrital dolomite eroded from lake marginal carbonate mudflats that were undergoing penecontemporaneous dolomitization continuous fluctuation in lake level produced many secondary dewatering and pedogenic paludine fabrics the lake developed into a playa lake during the very arid second phase becoming restricted in area and fauna the water was saline and alkaline and twice became a gypsum precipitating brine frequent exposure of the lake beds resulted in much calichification and in rapid and complete dolomitization under the intermediate climate of the third phase the lake reexpanded and freshened snails returned and many limestones escaped dolomitization each phase defines a member of the flagstaff formation chert absent in the oldest beds increases up section the lowest chert forms minor small spheres and linings in voids near the top of the lowest member suggesting limited silica input and post dolomitization precipitation in areas of greatest groundwater movement the base of the middle member contains horizons of atextural chert mudcrack fillings and nodules that appear to have been an inorganically precipitated gel most of the middle member however contains abundant chert nodules that replaced limestone prior to dolomitization the nodules grew prior to burial some even prior to mudcrack formation by the movement of dissolved silica to areas of relatively low ph in the upper member chert is even more prevalent entire thin beds were pervasively but incompletely silicified prior to dolomitization probably by vertical evaporative pumping of siliceous groundwater moving under mudflats toward the lake

magnetospheric substorms and nighttime height changes of the f2 region at middle and low latitudes using the published plots of 15 min interval values of h f2 the minimum virtual height of the ionospheric f2 region at five japanese stations spread over 26 45 n 15 35 n geomagnetic and 128 142 e it is shown that there are frequent rapid increases and less frequent decreases of h f2 by 100 200 km in about 2 hours with near simultaneous start and end at all five stations in the postmidnight hours and at three to five stations in the premidnight hours in the months of september and december 1988 and march 1989 about 80 h f2 perturbations of the above type are identified the near simultaneity of the h f2 disturbances at the five stations suggests that an plasma drift due to an east west electric field is the cause of the h f2 disturbances this interpretation is validated by showing that there is a simultaneous presence of bay disturbances in auroral latitude magnetograms over a wide longitude range during almost all the h f2 increases it is shown that neutral wave disturbances propagating equatorward even with a speed of 750 m s cannot account for the h f2 disturbances the study reveals two categories of h f2 perturbations 1 h f2 increases starting near the beginning of the geomagnetic negative bays at auroral latitudes and 2 rapid h f2 increases starting near the maximum intensity phase of the auroral bays and preceded by h f2 decreases starting at the onset time of the bay disturbance or a little earlier using the vast amount of h f2 data collected all over the globe it is possible to quantify and characterize the substorm related electric fields and their variabilities such characterization is very useful in understanding the magnetospheric and the magnetosphere ionosphere interaction processes involved in the generation of magnetospheric substorms it is also pointed out that the understanding of f2 region changes during magnetic storms may improve greatly if the large f2 region changes caused by electric fields on the substorm time scale are taken into account the h f2 disturbances reported in this study are similar in time scale and appearance to the h f2 disturbances caused by long period atmospheric waves and this suggests the possibility of a mixup of the two effects and the consequent wrong identification on some occasions

relative contribution of ionospheric conductivity and electric field to the auroral electrojets data from continuous scans of the chatanika radar beam along the magnetic meridian plane are used to determine the latitudinal profile of height integrated ionospheric conductivities and horizontal electric fields from which the latitudinal distribution of ionospheric currents is deduced the observations cover invariant latitudes between 62 and 68 where the ims alaska meridian chain of magnetometers was also in operation although the conductivities and the electric fields are interrelated the relative importance of the two in driving the eastward and westward auroral electrojet currents can be assessed it is found that for moderate and large current densities i e 0 2 a m the northward electric field strength increases as the magnitude of the eastward electrojet in the evening sector increases the height integrated hall conductivity stays generally at the level of 10 mhos even when the current density becomes as large as 1 a m however when the eastward electrojet is small substantial electric fields of 10 20 mv m may still exist as if the magnetosphere has a persistent voltage source there appear to be two distinct components to the westward electrojet in the midnight and early morning sestors 0300 mlt is dominated by a strong southward electric field

green river laminites does the playa lake model really invalidate the stratified lake model proponents of the playa lake model have proposed deposition of most of the green river formation microlaminated carbonates including oil shales in lakes that were not perennially stratified meromictic however there is a variety of evidence favoring a meromictic depositional environment 1 close similarity of much of the lamination to varves in modern meromictic lakes 2 evidence that hydrologic events favoring development of meromixis chemical stratification occurred prior to deposition of major accumulations of oil shale 3 mutually exclusive distribution of fossil nekton especially fish and normal lacustrine benthos including mollusks and 4 analogy with a quaternary playa that became a meromictic lake following increased inflow the playa lake model is untenable for the typical fish bearing kerogen rich microlaminated sediments these laminites were probably deposited in a large ectogenic meromictic lake a chemically stratified lake that formed when increased fresh water inflow drowned a saline playa complex

diastasis cracks mechanically generated synaeresis like cracks in upper cambrian shallow water oolite and ribbon carbonates upper cambrian limestones and dolostones of western newfoundland canada display conspicuous synsedimentary mud cracks cracks occur in carbonate mudstone interbedded with ooid and peloid grainstone unwashed oolite and ribbon rock lithofacies the traditional interpretation is that these are desiccation cracks the weight of evidence supports an alternative e explanation cracks resulted from the differential mechanical behaviour under stress of stiff mud interlayered with loose ooid peloid sand the processes envisaged to cause such diastasis cracks may be applicabl e to a wide variety of both carbonate and terrigenous clastic deposits composed of interlayered sediments of contrasting material properties and may be a viable alternative to synaeresis

the shoreline distribution and degradation of tilapia carcasses salton sea california taphonomic implications abstract the salton sea is a hypersaline closed lake system in southern california usa episodic fish kills led to bloating and floating fish bodies that were driven onto the shoreline by wind shear the documented taphonomic destruction of the stranded fish carcasses includes the distribution of the fish parts after desiccation and disarticulation mainly by wave induced transport with possible minor component of wind transport on the upper shoreface carcass decay is divided into five taphonomic categories 1 through 5 category 1 represents whole pliable fish recently washed onto the shoreline while category 5 incorporates longer term destruction into ultimately single isolated skeletal elements high water strand line deposits are delineated by the presence of categories 3 through 5 mixtures the general trend in 2012 was observed to be considerable bone disarticulation away from the shoreline because categories 1 and 2 were present in the swash zone the influx of fresh fish carcasses recharged the shoreline during 2013 the absence of new 1 and 2 categories arriving to the shoreline enhanced wave action to further break down categories 3 and 4 ultimately into category 5 in addition isolated bone elements segregate according to density differences typically on low gradient beaches wave and wave induced current action coupled with beach topography controls distribution of the various fish bones as an actualistic model the salton sea implies that shore parallel complete to partial fish carcass concentrations are more shoreward and isolated skeletal elements more distal

sedimentology taphonomy and palaeoecology of a laminated plattenkalk from the kimmeridgian of the northern franconian alb southern germany abstract at wattendorf in the northern franconian alb southern germany centimetre to decimetre thick packages of finely laminated limestones plattenkalk occur intercalated between well bedded graded grainstones and rudstones that blanket a relief produced by now dolomitized microbialite sponge reefs these beds reach their greatest thickness in depressions between topographic highs and thin towards and finally disappear on the crests the early late kimmeridgian graded packstone bindstone alternations represent the earliest plattenkalk occurrence in southern germany the undisturbed lamination of the sediment strongly points to oxygen free conditions on the seafloor and within the sediment inimical to higher forms of life the plattenkalk contains a diverse biota of benthic and nektonic organisms excavation of a 13 cm thick plattenkalk unit across an area of 80 m2 produced 3500 fossils which with the exception of the bivalve aulacomyella exhibit a random stratigraphic distribution two thirds of the individuals had a benthic mode of life attached to hard substrate this seems to contradict the evidence of oxygen free conditions on the sea floor such as undisturbed lamination presence of articulated skeletons and preservation of soft parts however palaeoecological and taphonomic analyses indicate that the benthic faunal elements are allochthonous having settled out of suspension and thus must have been derived from hard substrate areas of neighbouring topographic highs solely the bivalve aulacomyella which occurs concentrated on a single bedding plane may have colonised the plattenkalk depression during brief periods of oxygenation alternatively a pseudoplanktonic mode of life attached to floating sea weed is envisaged for the bivalve the formation of the plattenkalk is related to local and global factors a drop in relative sea level caused the death of the microbialite sponge reefs restricted circulation in depressions between the crests of the former reefs led to anoxic conditions and the formation of finely laminated sediments stabilised by microbial mats the small depressions received sediment and skeletal elements of benthic organisms that were swept off neighbouring topographic highs by storms and that entered the depressions partly as turbidity currents partly as suspension clouds a rise in the relative sea level finally terminated the restricted circulation in the depressions and closed the taphonomic window that led to the preservation of the plattenkalk biota

cyclicity in the green river formation lacustrine eocene of wyoming abstract basinal facies of the green river formation have two main modes lacustrine and playa the lacustrine mode tipton and laney members accumulated mainly varved oil shale here annual cycles are recorded as varves variations in verve thickness demonstrate el nino enso type and sunspot cycles ripepe et al this volume milankovitch scale cycles are not obvious in lithic variations but gamma ray logs record 1 precessional variations with a mean period varve timed of 19 5 ka and 2 a bundling of these in the ca 100 ka eccentricity cycle in the playa mode wilkins peak member the lithic succession oil shale trona dolomitic marlstone records the precessional drying up of a lake and is again bundled in sets of 5 by the 100 ka eccentricity rhythm the tipton member persisted f r 450 ka the wilkins peak member for ca 1 ma

taphonomic variations in eocene fish bearing varves at horsefly british columbia reveal 10 000 years of environmental change the eocene horsefly locality in british columbia has yielded many fossil fishes insects and plants its varved sediments make it ideal for study of temporal changes in environment and fish morphology several intervals of diatomaceous varves indicate a deep stratified lake setting earlier studies focused on morphological and taphonomic change during the 700 year h2 interval and morphological change during the 10 000 year h3 interval the present study uses taphonomy as an index for environmental change during the ten millennia represented by h3 comparing taphonomic changes with the morphologic changes found earlier the h3 interval records deposition in deep water indicated by dominance of the fish genera amyzon and eohiodon quiet water conditions are indicated by minimal fin disarticulation hypoxia at the time of fish death is confirmed by open mouths of most fish specimens while cool water on the lake floor prevented full flotation of fish carcasses water depth temperature and oxygenation fl

fish taphonomy and environmental inference in paleolimnology abstract the contribution of fish studies to palaeoecology generally takes the form of 1 inference from analogies in modern fish faunas and 2 fish taphonomy the pattern of death and dispersal of bones 1 modern fish faunas and associated organisms provide taxonomic ecological or functional analogues for interpretation of ancient limiting factors and behaviors these inferences presume taxonomic conservatism they also presume functional relationships between morphological form and feeding mode or habitat they become weak with increased geologic age or phyletic distance between ancient subject and modern anaogue 2 fish taphonomy may contribute information about limnology community composition life history mortality depositional environment and preservation taphonomic reconstruction of ecology and preservation depends on the applicability of analogous processes in modern ecology and l limnology in aquatic taphonomy temperature is the most important factor in determining the fate of a carcass above about 16 c depending on depth and pressure most carcasses are made buoyant by bacterial decay gases and are transported to the surface where they may decay further and fall piecemeal into deepwater environments or drift to beach environments where wave energy disarticulates abrades and scatters the bones below about 16 c most carcasses remain on the bottom until buried they may be disturbed by scavengers depending on oxygen concentration in the hypolimnion

biofilms microbial mats and microbe particle interactions electron microscope observations from diatomaceous sediments sediments and diatoms from the mudflats of the bay of bourgneuf in western france were examined in an electron microscope study of biofilms and microbial mats the sediments were kept in an aquarium for study and a diatom culture was made of the benthic diatoms the sediment biofilm was composed of exopolymeric substances eps incorporated clay particles and rarely bacteria this film coated all particles at the sediment water interface its surface morphology reflected its composition and internal structure thin films were smooth whilst a lumpy structure or incorporated fibrils produced either a mammillated or ropy surface and clays in the structure gave rise to a flaky morphology at shallow depths in the sediment column 0 5 cm the biofilm was already degraded the biofilm coating degraded diatom frustules in the benthic diatom culture consisted of eps and bacteria and presented a ragged appearance microbial mats occurred on the surface of the fresh littoral sediments as well as those in the aquarium and on the wall of the aquarium the mat on the surface of the aquarium sediments had an open structure with webs of fibrils and bacteria in the pore space it formed in a relatively quiet environment pore space was more limited in the mat from the surface of the fresh littoral sediments in which direct contact between biofilm coated particles was common in the exposed environment of the aquarium wall there was a thick resistant coating of eps in addition to binding particles together the presence of mats and biofilms in sediments affects sediment physical properties such as porosity and permeability the flux of dissolved substances in pore waters and the dissolution of particles and can therefore influence early diagenesis mats and biofilms seem to be more readily preserved in the geological record than the micro organisms such as bacteria which produce them their identification in the sedimentary record would greatly aid interpretation of sediment genesis and evaluation of the microbial role in sediment formation

sequence stratigraphy in lacustrine basins a model for part of the green river formation eocene southwest uinta basin utah u s a abstract in the middle green river formation of central nine mile canyon uinta basin utah several lacustrine dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences these lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences two types of sequence boundary are identified type a sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or rarely parallel unconformity and they typically juxtapose amalgamated braided fluvial channel sandstone late lowstand systems tract onto the profundal oil shale they also bound depositional sequences that show a distinct asymmetry being dominated by transgressive systems tracts 5 80 m thick highstand systems tracts are less than 4 m thick and may be removed completely by erosion on overlying sequence boundaries other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type b sequence boundaries type a sequence boundaries mark pronounced base level falls following times when the uinta lake had merged with a lake in an adjacent basin to form a much deeper lake such merging permitted the establishment of a new threshold at higher elevation following lake level balancing type b sequence boundaries are interpreted as marking base level falls from a barely merged lake or a lake that had an outflow over a 200 m stratigraphic thickness type a sequence boundaries are more common upsection indicating that with time a pluvial climate became more pronounced or that the adjacent lake was more easily filled type a sequence boundaries also become angular rather than parallel unconformities upsection suggesting increased tilting of the basin margin over time

nearshore carbonate deposits in lake tanganyika an exceptionally wide variety of carbonate fades dominated by high magnesian calcite occurs along the littoral and shallow sublittoral zones 50 m of lake tanganyika in central africa these facies include exposed and submerged calcite cemented ridges of nearshore terrigenous sand ooid sand shoals and lithified oolite ridges chara meadows of bioturbated calcareous silts gastropod shell blankets and related coquinas and extensive thrombolitic microbial reefs though texturally and compositionally similar to many modern and ancient shallow water marine facies these deposits record carbonate deposition and cementation in a large tropical deep water lake of tectonic origin lithofacies along lake tanganyika represent the broadest spectrum of carbonate deposits yet reported from any modern lake and serve as important analogues for lacustrine carbonate sequences in the stratigraphic record

controlled excavations in the romualdo member of the santana formation early cretaceous araripe basin northeastern brazil stratigraphic palaeoenvironmental and palaeoecological implications abstract the romualdo member of the santana formation araripe basin northeastern brazil is famous for the abundance and the exceptional preservation of the fossils found in its early diagenetic carbonate concretions however a vast majority of these early cretaceous fossils lack precise geographical and stratigraphic data the absence of such contextual proxies hinders our understanding of the apparent variations in faunal composition and abundance patterns across the araripe basin we conducted controlled excavations in the romualdo member in order to provide a detailed account of its main stratigraphic sedimentological and palaeontological features near santana do cariri ceara state we provide the first fine scale stratigraphic sequence ever established for the romualdo member and we distinguish at least seven concretion bearing horizons notably a 60 cm thick group of layers matracao located in the middle part of the member is virtually barren of fossiliferous concretions moreover a sample of 233 concretions shows that i the stratigraphic distribution of the concretions is very heterogeneous and their density varies from 0 8 to 15 concretions m3 ii concretions have a preferential bimodal orientation pattern major nw se axis and secondary n s axis throughout the section suggestive of permanent palaeocurrents of low energy iii few concretions yield the well preserved vertebrates that have made the romualdo member so famous and those are mainly restricted to four stratigraphic horizons iv only six fish taxa were recovered the most common being vinctifer and tharrhias followed by cladocyclus whereas brannerion calamopleurus enneles and notelops are rare no tetrapod was found in the sample v there is a strong stratigraphic control in the distribution of these taxa and one can distinguish at least three major assemblages at the same locus these are from older to younger a tharrhias dominated assemblage an assemblage dominated by tharrhias and by cladocyclus and a vinctifer dominated assemblage the stratigraphic sequence of these assemblages also corresponds to their ranking in terms of diversity richness and evenness vi previous accounts on the taxonomic composition and relative abundance of fossils from the romualdo member were severely biased toward well preserved and exotic fossils they are therefore inappropriate for drawing palaeoecological inferences the factors responsible for the variations in faunal composition and abundance patterns across the araripe basin remain largely unknown and we hypothesize that climate and or palaeogeography might be the major forcing agents only fine scale stratigraphic and palaeontological investigations have the potential to solve this issue in turn this work marks the first step of an expanded research program that aims at explaining the spatio temporal relationships between palaeocommunities and their palaeoenvironment in the araripe basin during aptian albian times

common origin of positive ionospheric storms at middle latitudes and the geomagnetic activity effect at low latitudes anomalous increases of the ionization density at middle latitudes positive ionospheric storms and anomalous increases of the neutral gas density at low latitudes the geomagnetic activity effect are prominent features of upper atmospheric storms the present study investigates the idea that both phenomena are caused by traveling atmospheric disturbances tads according to theory such tads are generated during magnetic substorm activity and propagate with high velocity from polar to equatorial latitudes to examine the above hypothesis magnetic ionospheric and neutral atmospheric data are compared for five different disturbance events these case studies demonstrate that 1 there is a good temporal correlation between magnetic substorm activity at high latitudes daytime positive ionospheric storms at middle latitudes and the geomagnetic activity effect at low latitudes 2 the initial phase of positive ionospheric storms propagates with high velocity toward lower latitudes 3 this velocity is roughly consistent with the time lag of the geomagnetic activity effect at low latitudes 4 the ionospheric disturbance is a conjugate phenomenon of global extent and 5 it cannot be explained as an electric field effect in summary our data are fully consistent with the idea that tads are responsible for both positive ionospheric storms at middle latitudes and the geomagnetic activity effect at low latitudes

ionosphere disturbances observed throughout southeast asia of the superstorm of 20 22 november 2003 1 ionospheric disturbances in the southeast asian region during the super magnetic storm of 20 22 november 2003 were investigated through an ionosonde chain and a gps network assisted by the space borne instruments at early stage of the storm in the postsunset sector large enhancements in the critical frequency of f2 layer and total electron content were observed at northern crest region of the equatorial ionization anomaly eia which might be produced by both the storm meridional wind superimposed with traveling atmospheric disturbances and prompt penetration electric field ppe during the main phase of the storm when interplanetary magnetic field started a 12 h southward turning equatorial ionosphere was elevated to a very high level which should be most probably caused by a long duration ppe event meanwhile at mid low latitudes ionosphere witnessed an initial simultaneous decrease then followed by drastic increases which is very different from the past observations in this region reddy and nishida 1992 combined analysis of the data from the ionosonde and other space based measurement shows that for the present case the penetration efficiency of the interplanetary electric field ief to the equatorial ionosphere was larger at night than in the daytime which agrees with the results of fejer et al 2007 showing the ratios of ppe and ief changes were highly variable with the local time during the recovery phase eia was severely inhibited owing to a wind convergence and possibly because of the westward disturbance dynamo electric field

taphonomy of insects in carbonates and amber abstract the major taphonomic processes that control insect preservation in carbonate rocks limestones travertines and nodules are biological insect size and wingspan degree of decomposition presence of microbial mats predation and scavenging environmental water surface tension water temperature density and salinity current activity and diagenetic authigenic mineralisation flattening deformation carbonisation the major taphonomic processes that control the preservation of insects in fossil resins amber and copal are different but can be considered under the same headings biological presence of resin producers size and behaviour of insects environmental latitude climate seasonality resin viscosity effects of storms and fires soil composition and diagenetic resin composition insect dehydration pressure carbonisation thermal maturation reworking oxidation these taphonomic processes are geographically and temporally restricted and generate biases in the fossil record nevertheless where insects occur they may be abundant and very diverse taphonomic processes may impact on phylogenetic and palaeobiogeographic studies in determining the timing of the origin and extinction of insect groups and in identifying radiations and major extinctions taphonomic studies are an essential prerequisite to the reconstruction of fossil insect assemblages to interpreting the sedimentary and environmental conditions where insects lived and died and to the investigation of interactions between insects and other organisms

paleocene lakes of the central rocky mountains western united states abstract lacustrine environments are well developed in the paleocene to early eocene sedimentary sequences in the intermontane basins of the central rocky mountains the available evidence points toward a widespread episode of lake formation in the middle late paleocene torrejonian tiffanian followed by a second major period during the latest paleocene to early eocene clarkforkian wasatchian the earlier period of lake formation is dominated by relatively shallow although often areally extensive freshwater lakes associated with fluvial and paludal environments in basins in northern wyoming and montana a high clastic input prevailed thich mudstone often structureless marks the deep water facies of these lakes with tabular sandstone lenticular carbonate and lignite occurring along the fluviodeltaic margins farther south and west in colorado and wyoming alkaline lakes dominated by carbonate deposition were prevalent the appearance and disappearance of standing water in both northern and southern basins may be more closely controlled by tectonics than by climate most evidence points toward prevailing humid sub tropical conditions until the very end of the paleocene

taphonomic analysis of fish in rift lacustrine systems environmental indicators and implications for fish speciation abstract two rift basin lacustrine successions cacheuta and los rastros formations in the middle triassic of argentina were studied to test two different hypotheses 1 fish taphonomy is useful as an indicator of environmental conditions for these two paleolakes and 2 fish taphonomy is useful for understanding environmental effects on speciation the fish fossils are found in two lacustrine deposits as isolated and disarticulated scales and cranial bones clumps and stringers of scales articulated body segments and complete specimens four taphofacies are defined for cacheuta specimens ca a to ca d and three taphofacies are defined for los rastros fish assemblages lr a to lr c a principal components analysis was performed with the taphonomic features supporting the seven taphofacies defined a taphonomic model is proposed that characterizes a lacustrine deltaic environment developed in the rift basin and identifies three sub environments each one with its particular fossil assemblages the fish assemblages in the los rastros formation suggest that the fishes preserved in delta front and turbidity current deposits lr b and lr c taphofacies were allochthonous to the lake and probably inhabited the delta plains and affluent fluvial system in contrast the isolated fish remains preserved in open lake deposits lr a taphofacies likely represent both autochthonous and or allochthonous specimens in the cacheuta formation articulated and isolated fish remains preserved in open lake deposits ca a and ca d tafofacies might represent autochthonous lacustrine specimens based on the good preservation of the material the fish remains preserved in underflow and turbidity current deposits ca b and ca c taphofacies were allochthonous to the lake and probably inhabited the delta plain and affluent fluvial system the fish taphonomic study of two different rift basin lacustrine successions allows test of the two proposed hypotheses fish taphonomy was useful as an indicator of environmental conditions beacuse the differences in fish preservation allowed differentiation of the sub environments and reconstruction of the environmental conditions and dynamics of the rift lake basins also fish taphonomy was useful for understanding environmental effects on speciation by characterizing the environments and dynamics that promote the development of new fish species recognizing fish inhabited environments and identifying the generalist and specialist species

climate record in varved sediments of the eocene green river formation three time series of varves from the eocene green river formation in colorado consisting of 1469 1869 and 4158 annual thickness measurements were analyzed by a variety of statistical techniques to characterize climate variations the analyses reveal that the time series are lognormal after adjustment for a trend moreover the analyses suggest that the time series are generally nonstationary and are noiselike in structure fourier spectra and maximum entropy spectra of the time series are reddish indicating the importance of nonoscillatory changes in varve thickness at time scales ranging from tens to hundreds of years there are no statistically significant peaks in fourier spectra for the entire time series however one segment of one of the three time series displays statistically significant peaks corresponding to periods of 10 8 and 5 4 years overall the time series are suggestive of a nonperiodic and weakly predictive climate during the time periods corresponding to deposition of the varves

storm time penetration to low latitudes of magnetospheric ionospheric convection and convection driven thermospheric winds from de 2 satellite measurements during two magnetic storms we show that i the magnetospheric convection driven east west ion flows of high velocities 1400 m s penetrate to magnetic latitudes as low as 30 with larger velocities 2000 3000 m s appearing at 45 50 latitudes and ii high velocity 300 640 m s thermospheric winds appear in association with the above ion flows the similarity of the latitude structures and time evolutions of the ion and neutral motions indicates that the zonal winds are driven by magnetospheric ionospheric convection through ion drag these velocities of the convection driven ion flows and winds at such low latitudes are much larger than those reported from observations or predicted by current models

response of the equatorial ionosphere in the indian midnight sector to the severe magnetic storm of july 15 2000 1 during the severe magnetic storm of july 15 2000 an impulsive and remarkably large downward movement of f region occurred simultaneously at locations throughout the equatorial region dip 0 3 20 n in the indian sector in close association with episodes of rapid ring current intensification the abnormal midnight descent of equatorial f region maximum amplitude close to the magnetic equator 215 km hr indicative of a short lived westward electric field disturbance peak amplitude 4 6 mv m is interpreted as the signature of prompt penetration electric fields associated primarily with impulsive ring current injections the westward electric field disturbance in the indian midnight sector occurred near simultaneous with the eastward electric field disturbances in the dusk sector reported by basu et al 2001a moreover the prompt electric field penetration to the magnetic equator both in the dusk and midnight sectors occurred in an environment already under the influence of ionospheric disturbance dynamo idd electric fields illustrating the profound manner in which the equatorial f region plasma dynamics can get modified globally during the main phase of severe magnetic storms

organic geochemistry and paleoenvironment of the early eocene pesciara di bolca konservat lagerstatte italy abstract exceptional preservation of fossils in so called konservat lagerstatten requires specific depositional regimes excluding disturbance of bottom sediments by either wave actions and currents or by benthic fauna we here describe a depositional model for the eocene pesciara di bolca konservat lagerstatte based on sedimentological paleoecological and detailed organic geochemical results sediments were deposited in a lagoonal like basin with stagnant bottom waters located on an extended carbonate platform that was sheltered from open marine waters by a submarine threshold run off from nearby land areas provided nutrients to support an algal community dominated by diatoms no fossil diatom shells have been identified but evidence for their presence is given by the high abundance of highly branched isoprenoids in extractable bitumens influx of terrigenous organic matter into the lagoon occurred in particular during deposition of the basal fish bearing level l1 here not only plant macrofossils amber spores and pollen but also the lipid composition indicated notable input of land plants via the presence of n c 24 to n c 32 carboxylic acids long chain n alkanes n c 27 n c 29 n c 31 and angiosperm wax triterpenoids the redox regime in general was strongly reducing as evidenced by the high concentration of sulfur vs organic carbon excellent kerogen preservation as shown by high hydrogen indices and low pristane phytane but high phytane n c 18 ratios the water column was highly stratified with anoxic saline bottom and fresh surface waters euxinic conditions with free reduced sulfur present in the photic zone could only be detected in sediments from the l1 horizon via traces of aromatic carotenoids derived from green sulfur bacteria chlorobiaceae which utilize h 2 s in anoxygenic photosynthesis the depositional regime is thus comparable to the lithographic limestones of solnhofen but based on biomarker evidence lacks the high salinities postulated for the latter biomarker composition indicates that best preservation conditions prevailed in the basal part of the studied section 0 7 m above datum but declined upon deposition of the upper part we interpret the body of the pesciara as a parasequence of the 4th order 0 01 0 5 ma with the lower part representing a relative sea level lowstand and the upper part a relative sea level highstand

paleolimnology and taphonomy of some fish deposits in fossil and uinta lakes of the eocene green river formation utah and wyoming abstract in four sections in the lacustrine eocene green river formation in utah lake uinta fish are preserved on carbonate mudflats along high energy carbonate shorelines in the littoral zone and in deeper profundal areas scattered bones and scales are found throughout dropped from disintegrating floating carcasses gar scales typify shallow water deposits partly due to habitat preference beach concentrations of greatly abraded bones and scales grade offshore into storm lag layers and lenses which grade to loosely packed horizons or patches of unworn remains littoral fish fossils range from dropped bones to good skeletons with much floating lifting and scavenging preservation improves away from the waterline not only into deep and cold profundal waters where the carcasses are protected from scavenging by anoxia and prevented from floating by temperature and pressure but also onto mudflats where stranding and burial of carcasses can also protect them a section through an isolated part of the green river formation in wyoming fossil lake also ranged from profundal to littoral with minor emergence dropped body parts were found throughout but preservation quality of the best specimens improved with presumed depth the beds with the best specimens seem to have accumulated at the bottom of a deep stratified warm monomictic lake our lake uinta sections were generally shallower and suggest more fluctuations in water level but this is not relevant to broad paleolimnological interpretations because they represent marginal zones which are necessarily more sensitive to changes in depth overall fish fossils are especially informative in deeper waters where sedimentary distinctions fail

positive and negative ionospheric disturbances at middle latitudes during geomagnetic storms the morphology of middle latitude ionospheric disturbances in response to geomagnetic storms has been investigated to determine the phenomenological differences between positive and negative ionospheric storm effects using fof2 observations from azimuthal chain of stations to better organize the disturbance signatures two ionospheric indices were introduced to describe the maximum positive dfu index and negative dfl index deviation observed during an ionospheric storm a systematic appearance of nighttime positive effects was determined with a 24 hour recurrence the thermospheric ionospheric view associated with positive and negative storm effects proposed by prolss 1993 was extended to encompass our observations this test clearly demonstrates that such a model can capture most of the basic aspects of ionospheric storms nevertheless the prominent feature of large nighttime enhancements in the ionization density have yet to be explained

a new fossil lagerstatte from the lower eocene of lessini mountains northern italy a multidisciplinary approach hemipelagic dark limestones within calciturbiditic deposits at monte solane in the western lessini mountains of northern italy yield a fish fauna dominated by stomiiforms a minor component of the fossil assemblage is represented by a macroalgal non calcareous flora associated with rarer terrestrial components including few angiosperm leaves and seeds micropaleontological foraminifera dinoflagellate cysts sedimentological and geochemical proxies tex86 indicate a deposition of the fossil bearing bed in a hypoxic to possibly anoxic warm restricted basin high precision dating based on rich foraminiferal and calcareous nannoplankton content allows ascribing the site to the upper part of the ypresian lower eocene the site is slightly older than the ypresian worldwide famous shallow water bolca konservat lagerstatte located in the same region convergent paleoenvironmental clues based on both microfossils and ichthyofauna indicate that the sediments were deposited in the upper bathyal zone probably between 300 and 600 m solane is therefore one of the rare and precious eocene lagerstatte to have fossilized in a deep marine setting the site contains the oldest cenozoic record of an ichthyofauna dominated by meso bathypelagic taxa

daytime additional f layer stratification over low midlatitude station of the indian sector under geomagnetic disturbed conditions 1 in this paper the observations of additional f layer stratification are presented in a region which is situated at the outer edge of equatorial ionization anomaly eia zone the digital ionosonde data observed over delhi 28 6 n 77 2 e dip 42 44 n during march april 2001 has been used to carry out the present work the observational period was geomagnetically disturbed and represents the high solar activity phase of 23rd solar cycle the additional transient cusp is frequently observed in the considered months before the noon hours however in this paper only five prominent cases are presented from the analysis of ionograms it is observed that the transient additional cusp is formed between the pre existing f1 and f2 layer hence named as the cusp of f1 5 study reveals that the traveling atmospheric disturbances tads along with the vertical expansion of f layer provides the necessary condition for the existence of this transient feature the intensification of f1 layer along with increased altitude immediately after the disappearance of additional stratification remains one of the fascinating features of the present results the present investigation demonstrates that the daytime f1 and f2 region over low midlatitude station is strongly modulated by the passage of tids originating at high latitudes or by atmospheric disturbances of local origin during the high solar activity period the concurrent presence of tads and the associated disturbance composition appears to be plausible reason behind the present observations

seasonal and magnetic activity variations of ionospheric electric fields over millstone hill incoherent scatter observations of e and f region drifts over millstone hill 42 6 n were made routinely from may 1976 to november 1977 at monthly intervals some 667 hours of data gathered over this 19 month period have been analyzed to yield the ionospheric polarization electric field in the magnetic south and magnetic east directions for three seasons during quiet magnetic conditions as well as the annual average during magnetically disturbed conditions kp 3o the results for the quiet days are compared with earlier results obtained at millstone hill kirchhoff and carpenter 1976 and with those reported from st santin 44 6 n by blanc and amayenc 1979 we find that there is best agreement between millstone and st santin for the east west component of the field which exhibits a roughly 12 hour period variation during the daytime in all seasons the north south field exhibits a predominantly diurnal variation that in winter and equinox is almost identically opposite at the two stations this component shows substantial changes in summer at both stations and at millstone appears to exhibit a significant 1mv m average northward component not seen at st santin we attribute the differences in the quiet time behavior observed at millstone and st santin to the very large difference in the latitude of their conjugate points where presumably the tides and hence the dynamo effects are dissimilar there are marked differences in the electric field patterns between disturbed and quiet times which mainly are evident in the nighttime period commencing after noon there is a gradual enhancement of both the northward and eastward fields on disturbed days the eastward field reverses near midnight and becomes westward until dawn while the other component remains northward for most of the night these changes are thought to result from the penetration of auroral electric fields inside the plasmasphere

low latitude ionospheric disturbances results for march 22 1979 and their general characteristics low latitude ionospheric disturbances which were characterized by severe scintillations in the c band range accompanied by complex dynamical behavior of the low latitude ionosphere were examined taking into consideration previous results from the analyses of fof2 and h f data these disturbance events are found to be characterized by a two stage process during the first stage which starts during the magnetospheric energy storage process before the onset of substorms h f begins to increase simultaneously at all observing stations due to eastward electric fields penetrating from the magnetosphere at subequatorial stations increases of fof2 follow as a signature of enhancements of the equatorial anomaly during the second stage values of h f increase again indicating a motion from north to south with no increase of fof2 in this stage dynamical effects including neutral winds become important as well as electric fields in addition it is shown from the analysis of one year s data for 1978 that the occurrence of disturbance events as presented in this paper is a general feature in the evening section under the condition of ring current developments

the bolca lagerstatten shallow marine life in the eocene the eocene limestones around the italian village of bolca occur in a series of distinct localities providing a unique snapshot of marine life in the early cenozoic famous for its fishes the localities of bolca also yield diverse invertebrate faunas and a rich but relatively understudied flora most fossils from bolca derive from the pesciara and monte postale sites which bear similar fossils but are characterized by slightly different taphonomic and environmental profiles although not precisely contemporaneous the age of these principal localities is well constrained to a narrow interval within the ypresian stage c 50 49 ma this places bolca at a critical time in the evolutionary assembly of modern marine fish diversity and of reef communities more generally

biological and sedimentary facies of australian salt lakes abstract four main types of salt lakes are recognized in australian 1 large playa lakes 2 small closed lakes or pans 3 crater lakes and 4 coastal lakes not connected to the sea basically all have an nacl chemistry biological and sedimentary facies characteristic of these salt lakes can be arranged into three basic groups which relate to particular phases in lake regimes these phases are 1 wet phases of ephemeral shallow lakes 2 dry lakes and 3 deep water lakes all elements of the salt lake biota with fossilizable remains are discussed with a detailed account of the palaeo ecological information they offer elements of the nonaquatic biota associated with salt lake sediments are also analysed sedimentary features of australian salt lakes pertinent to palaeoecology are discussed in the context of their association with the biota using numerous illustrations the distribution of the biota on lake floors for example its concentration in particular areas of the lake or its destruction during particular episodes such as lake filling and drying is mentioned in the context of recognizing different facies three major lake regime phases are presented with emphasis on the biological and sedimentary facies which characterize them the paper concludes with a brief discussion of the relevance of recognizing particular salt lake facies and changes in lake histories for the study of palaeoclimates and for mineral and oil exploration

fingerprinting geological materials using ssms abstract spark source mass spectrometry ssms was used to investigate a wide range of geological materials using a semiquantitative method the uncertainties in the method were assessed using u s g s standards and in a study of mount st helens yakima ash in which ssms data were compared to those from other techniques in the method described here the uncertainties for most minor and trace element concentrations are considered to reflect their natural distributions in geological materials the principal advantages of ssms are the simplicity of sample preparation a minimum sample size of 0 1 g and the capacity to survey simultaneously a wide range of elements 50 60 down to ng g 1 levels

controlled excavations in the pesciara and monte postale sites provide new insights about the palaeoecology and taphonomy of the fish assemblages of the eocene bolca konservat lagerstatte italy abstract the eocene konservat lagerstatte of bolca italy is famous for the abundance and exquisite preservation of its fossils although the bolca sites have provided one of the most studied ichthyofaunistic fossil assemblages of the world several aspects about the community structure and the biostratinomic processes that led to the accumulation of its fish remains have been neglected or underestimated in order to improve our knowledge concerning the palaeoecology and palaeoenvironment of bolca a quantitative palaeoecological and taphonomic analysis of the fish remains collected during controlled excavations at the pesciara and monte postale sites is presented herein the results of these analyses concur to suggest that these two sites have different speciose fish assemblages and different depositional contexts the high quality preservation of the fishes from the pesciara site has allowed for the species level identification of most of its specimens providing a good resolution of its palaeoecological spectrum the pesciara fish assemblage is defined by a sharp oligarchic structure clearly dominated by planktivorous taxa the taphonomic features confirm that the sediments were deposited in an intraplatform basin in which anoxic conditions at the bottom and the development of the biofilm acted as promoters of high quality fossil preservation on the other hand the moderate preservation quality of the fishes from monte postale does not allow for most of the specimens to be identified at the genus or species level making it difficult to interpret the ecological and trophic relationships within this assemblage nevertheless the abundance of marine and terrestrial plants coupled with the large number of invertebrates including abundant corals concur to suggest that the sediments of monte postale were likely deposited close to an emerged coastal area characterized by mangroves seagrass and coral reefs the prominent disgregation of fish skeletons coupled with the unimodal dispersion of the elements and bioturbations clearly indicate a high degree of disturbance in the monte postale palaeoenvironment suggesting at least periodic aerobic conditions at the bottom

geochemical application of spark source mass spectrography abstract the abundance of tin has been generally underestimated due to the difficulty of dissolving cassiterite and to the subsequent calibrations of instrumental techniques with standard samples whose sn values were determined by chemical techniques using a spark source mass spectrometric calibration procedure which is independent of standard samples we conclude that the abundance of sn in international rock standards is higher than earlier determinations by factors of 1 5 2 sn abundance values in the continental crust based on these earlier values have been revised as follows upper crust 5 5 ppm total crust 2 5 ppm and lower crust 1 0 ppm

facies analysis palaeoenvironmental reconstruction and biostratigraphy of the pesciara di bolca verona northern italy an early eocene fossil lagerstatte abstract the world famous pesciara di bolca fossil lagerstatte has been examined in its palaeontological and sedimentological aspects a re examination of the co occurring age diagnostic larger foraminifers alveolina and nummulites indicates a sbz 11 late ypresian age sedimentological characters allowed us to distinguish between autochthonous micritic limestones and allochthonous biocalcarenites biocalcirudites the latter are the product of penecontemporaneous transport from nearby areas the depositional model here proposed involves a basin with restricted circulation and a prevailing micrite sedimentation this basin was affected by relative sea level oscillations and coarser grained storm induced deposition the palaeoenvironmental reconstruction suggests neighbouring emerged land and very shallow sea bottoms inhabited by large foraminifers such as alveolina and nummulites as yet it is unclear whether a true coral reef was present nearby the bottom on which the pesciara deposits accumulated is interpreted as poorly oxygenated possibly with stromatolite like bacterial mats thus allowing the exceptional preservation of the fish and plants

a mu radar based study of mid latitude f region response to a geomagnetic disturbance during the night of january 20 21 1989 ionospheric incoherent scatter power measurements were made with the mu middle and upper atmosphere radar at shigaraki geographic latitude 34 85 n longitude 136 10 e geomagnetic latitude 24 9 longitude 204 3 japan and the electron density profiles in the 180 to 1000 km height range were derived at 8 min intervals the observations showed the presence of three f region disturbances during the night during the very large first disturbance which lasted from 2300 to 0240 lt approximately the height of maximum electron density nm increased by 220 km in 2 hours to reach an altitude of 600 km the other two smaller disturbances occurred during 0300 0500 lt and 0530 0700 lt approximately a detailed interpretation of the above f region disturbances is given examination of some high and middle latitude magnetograms showed the beginning of an intense geomagnetic substorm at auroral latitudes at the start of the first f region disturbance and a less intense substorm around the starting time of the second f region disturbance on the basis of this evidence the first two f region disturbances are interpreted as the result of large vertical drifts of f region ionization due to the substorm generated east west electric fields appearing at mid latitudes the patterns of h f variations during this night at five ionospheric stations in japan support the above interpretation additionally during the second disturbance the possible presence of a wind perturbation due to the equatorward propagation of a wave disturbance generated probably by the first major substorm is indicated by the mu radar data and the ionosonde data the third f region disturbance is attributed to a neutral wind perturbation associated with a gravity wave traveling equatorward the wave being generated most plausibly by the joule heating during the first major substorm the brief unusual distortions of the f layer shape as revealed by mu radar observations are also interpreted as the consequence of an unusually large convergence of ionization in the bottomside of the f layer due to the unusually large electric field and wind perturbations theoretical calculations are made using the mu radar data and f region continuity equation and the east west electric field values during the disturbances are quantified during the first major rise of the f layer during 2300 0115 lt the inferred eastward electric field in the ionosphere at shigaraki is found to be as large as 6 1 mv m and after this disturbance a westward electric field and or a poleward meridional wind is found to occur for some time an eastward electric field of about 3 0 mv m is found to occur during the second f region disturbance along with a possible meridional wind perturbation the large eastward electric field around local midnight is most unusual in both magnitude and direction because the theoretical models of disturbance electric fields predict a strong westward electric field in this lt sector this result has important implications for understanding the physics of disturbance electric fields at middle and low latitudes during substorms

on the latitudinal variations of the ionospheric electric field during magnetospheric disturbances a joint alert campaign was organized during the month of october 1980 by the incoherent scatter radars in the american sector namely jicamarca arecibo millstone hill and chatanika the campaign which met with success was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions the arecibo data in this campaign support present and previous observations at jicamarca that suggest that when the convection e field suddenly decreases the alfven layer shielding field becomes unbalanced and penetrates the plasmasphere while this type of observation is reasonably convincing others are more difficult to categorize we suggest that beside the high latitude electric fields time varying auroral conductivity models will have to be considered in order to understand the morphology of the low latitude e field disturbances we present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30 geometric latitude arecibo to the field at 0 jicamarca other highlights of the paper are a discussion of dp2 which may help clarify the controversy surrounding it and a discussion of the sensitivity of low and mid latitude radars to disturbances of magnetospheric origin we show that this sensitivity maximizes at the magnetic equator

depositional subenvironments in an arid closed basin the wilkins peak member of the green river formation eocene wyoming u s a the wilkins peak member of the green river formation is a non marine dolomitic deposit that formed in an arid hydrologically closed basin a transect from the margin to the centre of the wilkins peak basin was examined in outcrop exposures in the south eastern corner of the basin and was supplemented with published core descriptions the rocks were divided into seven facies based upon lithology layering style and sedimentary fabrics 1 af facies quartzose conglomerates and sandstones representing sandy alluvial fans coming from the uinta mountains 2 sf facies quartzose peloidal dolomitic sandstones which represent sheet flood deposits extending basinward from the alluvial fans 3 dm facies irregularly laminated dolomitic mudstones with abundant mudcracks which represent sheet flood deposits on a subaerially exposed mudflat 4 el facies dolomitic mudstones with regular lamination and fewer but larger mudcracks representing sporadically exposed lake margins or shallow ponds 5 pl facies finely laminated oil shales and dolomitic mudstones with rare mudcracks which represent shallow perennial lakes 6 sm facies trona or halite deposits with dolomitic mudstone partings or dolomitic mudstones and sandstones disrupted by evaporites of varied morphology these represent a central salt pan and the surrounding saline mudflat 7 as facies arkosic sandstones siltstones and mudstones which represent braided river and more basinal deltaic plain deposits the five dolomitic facies form poorly defined cycles representing the intersection of sheet floods with a lake which transgressed and regressed in response to climatic variations there are at least forty 3 4 m thick cycles in the wilkins peak and one large scale cycle comprising the whole member which mimics the facies changes of the smaller cycles this is compatible with the transitions of the wilkins peak member to the tipton and laney members as climatic responses and not shifts in drainage the sheet flood sandstones actively aggrading subaerial mudflats and bedded evaporites of the wilkins peak are apparently unique within the green river formation they reflect the unusual provenance and hydrology of the wilkins peak and suggest chemical and sedimentary models established for the other green river members will not be applicable