exceptional fossil record distribution of soft tissue preservation through the phanerozoic preservation of soft bodied fossil biotas konservat lagerstaten that preserve traces of volatile nonmineralized tissues readily degraded by bacteria are not evenly spaced through geologic time when compared to outcrop area exceptional faunas appear to be over represented in the cambrian and jurassic these concentrations in time correspond to particular environments indicating that controls on the distribution of exceptional faunas may have operated on a global scale the reduction in the number of exceptional faunas after the cambrian may reflect the evolution and diversification of deep bio turbators specific conditions favoring stagnation and episodic burial were required to ensure preservation in younger rocks

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

synoptic reconstruction of a major ancient lake system eocene green river formation western united states numerous 40ar 39ar experiments on sanidine and biotite from 22 ash beds and 3 volcaniclastic sand beds from the greater green river piceance creek and uinta basins of wyoming colorado and utah constrain 8 m y of the eocene epoch multiple analyses were conducted per sample using laser fusion and incremental heating techniques to differentiate inheritance 40ar loss and 39ar recoil when considered in conjunction with existing radioisotopic ages and lithostratigraphy biostratigraphy and magnetostratigraphy these new age determinations facilitate temporal correlation of linked eocene lake basins in the laramide rocky mountain region at a significantly increased level of precision to compare our results to the geomagnetic polarity time scale and the regional volcanic record the ages of eocene magnetic anomalies c24 through c20 were recalibrated using seven 40ar 39ar ages overall the ages obtained for this study are consistent with the isochroneity of north american land mammal ages throughout the study area and provide precise radioisotopic constraints on several important biostratigraphic boundaries applying these new ages average sediment accumulation rates in the greater green river basin wyoming were approximately three times faster at the center of the basin versus its ramp like northern margin during deposition of the underfilled wilkins peak member in contrast sediment accumulation occurred faster at the edge of the basin during deposition of the balanced filled to overfilled tipton and laney members sediment accumulation patterns thus reflect basin center focused accumulation rates when the basin was underfilled and supply limited accumulation when the basin was balanced filled to overfilled sediment accumulation in the uinta basin at indian canyon utah was relatively constant at 150 mm k y during deposition of over 5 m y of both evaporative and fluctuating profundal facies which likely reflects the basin margin position of the measured section the most rapid sediment accumulation for the entire system 1 m k y occurred between 49 0 and 47 5 ma when volcaniclastic materials from the absaroka and or challis volcanic fields entered the green river formation lakes from the north our new ages combined with existing paleomagnetic and biostratigraphic control permit the first detailed synoptic comparison of lacustrine depositional environments in all the green river formation basins coupled with previously published paleocurrent observations our detailed correlations show that relatively freshwater lakes commonly drained into more saline downstream lakes the overall character of eocene lake deposits was therefore governed in part by the geomorphic evolution of drainage patterns in the surrounding laramide landscape freshwater overfilled lakes were initially dominant 53 5 52 0 ma possibly related to high erosion rates of remnant cretaceous strata on adjacent uplifts expansion of balanced fill lakes first occurred in all green river formation basins at 52 0 51 3 ma and again between 49 6 and 48 5 ma evaporative underfilled lakes occurred in various basins between 51 3 and 45 1 ma coincident with the end of the early eocene climatic optima and subsequent onset of global cooling defined from marine record however evaporite intervals in the different depocenters were deposited at different times rather than being confined to a single episode of arid climate evaporative terminal sinks were initially located in the greater green river and piceance creek basins 51 3 48 9 ma then gradually migrated southward to the uinta basin 47 1 45 2 ma this history is likely related to progressive southward construction of the absaroka volcanic province which constituted a major topographic and thermal anomaly that contributed to a regional north to south hydrologic gradient the greater green river and piceance creek basins were eventually filled from north to south with absarokaderived detritus at sedimentation rates 1 2 orders of magnitude greater than the underlying lake deposits

results of a stratified snow emissivity model based on the wave approach application to the antarctic ice sheet the results from a snow emissivity model are used to help with the interpretation of the scanning multichannel microwave radiometer data aboard the satellite nimbus 7 1978 1986 over antarctica the model is based on the solution of maxwell s equations through strong fluctuation theory stogryn 1986 the snow is considered isothermal with horizontal stratification isotropic inside each stratum and with smooth interfaces to wipe out the interference pattern created by plane stratification and in order to take into account the spatial variability of the snow characteristics the final result is a mean value of many computations done with many stratigraphies randomly distributed around a mean profile the spatial distribution of the microwave signatures over antarctica reveals three areas with typical spectral signatures these areas are identified from the point of view of snow characteristics through a ground data set surdyk and fiiy 1993 the model reproduces well the effect of the stratification on the polarization differences as observed the strong gradient of emissivity versus frequency observed on one of the test sites is not completely understood depth hoar layers characterized by faceted and cup shaped coarse snow grains seem to have a particular scattering behavior compared with that of the usual grains when those coarse grains are replaced by fine grains the model results are closer to the measured data the presence of crusts the roughness at the snow ice interfaces and crystal orientation may also have significant effects

characteristics of the flank magnetopause cluster observations the magnetopause is a current sheet forming the boundary between the geomagnetic field on one side and the shocked solar wind on the other side this paper discusses properties of the low latitude dawn and dusk flanks of the magnetopause the reported results are based on a large number of measurements obtained by the cluster satellites during magnetopause traversals using a combination of single spacecraft and multispacecraft techniques we calculated macroscopic features such as thickness location and motion of the magnetopause the results show that the typical flank magnetopause is significantly thicker than the dayside magnetopause and also possesses a pronounced and persistent dawn dusk asymmetry thicknesses vary from 150 to 5000 km with an median thickness of around 1400 km at dawn and around 1150 km at dusk current densities are on average higher on dusk suggesting that the total current at dawn and dusk are similar solar wind conditions and the interplanetary magnetic field cannot fully explain the observed dawn dusk asymmetry for a number of crossings we were also able to derive detailed current density profiles the profiles show that the magnetopause often consists of two or more adjacent current sheets each current sheet typically several ion gyroradii thick and often with different current direction this demonstrates that the flank magnetopause has a structure that is more complex than the thin one dimensional current sheet described by a chapman ferraro layer

reconnaissance of upper jurassic morrison formation ichnofossils rocky mountain region usa paleoenvironmental stratigraphic and paleoclimatic significance of terrestrial and freshwater ichnocoenoses seventy five types of ichnofossils documented during a four year reconnaissance study in the upper jurassic morrison formation demonstrate that highly diverse and abundant plants invertebrates and vertebrates occur throughout most of the morrison or equivalent strata invertebrate ichnofossils preserving the most environmentally and climatically sensitive in situ behavior of morrison organisms are in nearly all outcrops terrestrial ichnofossils record biotic processes in soil formation indicating soil moisture and water table levels freshwater ichnofossils preserve evidence of water depth salinity and seasonality of water bodies ichnofossils categorized as epiterraphilic terraphilic hygrophilic and hydrophilic new terms reflect the moisture regime where they were constructed the ichnofossils are vertically zoned with respect to physical chemical and biological factors in the environment that controlled their distribution and abundance and are expressed as surficial shallow intermediate and deep the sedimentologic stratigraphic and geographic distribution of morrison ichnofossils reflects the environmental and climatic variations across the basin through time marginal marine tidal to brackish water ichnofossils are mainly restricted to the windy hill member very large to small termite nests dominate the salt wash member similar size ranges of ant nests dominate the brushy basin member soil bee nests dominate in the salt wash decreasing in abundance through the brushy basin deeper and larger insect nests indicate more seasonal distribution of precipitation and rainfall shallower and smaller insect nests indicate either dry or wet substrate conditions depending on the nest architecture and paleopedogenic and sedimentologic character of the substrate trace fossil indicators of flowing or standing water conditions are dominant in the tidwell member and in fluvial sandstones of the salt wash and brushy basin members large communities of perennial freshwater bivalve traces are abundant in the tidwell and brushy basin members but to a lesser extent in the salt wash member shallow crayfish burrows indicating a water table level close to the surface 1 m are restricted to channel bank and proximal alluvial deposits in the salt wash recapture and brushy basin members sauropod theropod pterosaur and other vertebrate tracks occur throughout the morrison formation associated with alluvial lacustrine and transitional marine shoreline deposits ichnofossils and co occurring paleosols in the morrison reflect the local and regional paleohydrologic settings which record the annual soil moisture budget and were largely controlled by the climate in the basin contributions to near surface biologic systems by groundwater from distant sources were minor except where the water table perennially seasonally or ephemerally intersected the ground surface the jurassic morrison formation in the southern portion of the basin experienced a mosaic of seasonal climates that varied from a drier tidwell windy hill deposition to a wetter lower and middle salt wash deposition and slightly drier upper salt wash deposition tropical wet dry climate returning to a wetter tropical wet dry climate near the end of morrison deposition brushy basin deposition the northern part of the basin experienced similar trends across a mosaic of mediterranean climate types the range and mosaic pattern of wet dry morrison climates is analogous to the range of climates and their seasonal variability that dominates the african savanna today

organic matter composition and distribution through the aptian albian lacustrine sequences of the araripe basin northeastern brazil abstract the main characteristics and distribution of organic matter have been studied through several aptian albian lacustrine units rio da batateira crato and ipubi formations araripe basin ne brazil six main facies have been distinguished on the basis of their lithological sedimentological characteristics and the type and amount of organic matter 1 marginal lacustrine deltaic massive to coarsely laminated mudstones and sandstones found as lenticular sheet and channel infills 2 oxic marginal lacustrine massive to poorly laminated mudstones 3 oxic suboxic inner lacustrine mudstones and laminated bioclastic mudstones 4 anoxic inner lacustrine dark mudstones 5 anoxic inner lacustrine dark clay carbonate rhythmites and 6 anoxic inner lacustrine finely laminated dark micritic limestones these facies make up decimeter to several meter thick parasequences which stack up in several tens of meters thick successions water level changes and variations of the detritic sediment contribution in the basin controlled the evolution of the depositional system palynomorph associations showed that the lacustrine system evolved in an arid semiarid tropical area where the most characteristic flora consisted of conifers gnetales bennettitales and early angiosperms in facies 1 to 3 organic matter was scarce poorly preserved and mainly derived from higher land plants facies 4 is characterised by containing abundant algal bacterial derived well preserved organic matter facies 5 and 6 contained mainly branchlets and pollen debris blown by the wind or fed by lacustrine underflows the pattern of organic matter accumulation and preservation corresponds well with cyclical palaeoenvironmental changes from anoxic to oxic bottom conditions and from a fresh to saline upper water layer which affected the shallow lacustrine system the deposition of thin organic matter rich mudstones facies 4 probably occurred during higher water levels which resulted in relatively low salinity waters and low detrital contribution to the inner lacustrine zones less significant organic matter accumulation is recorded in the clay carbonate rhythmites and in the limestones facies 5 and 6 due to scarce autochthonous aquatic organic matter deposition and pervasive intense bacterial degradation caused by persistent meromictic conditions large differences in the degree and path of evolution of the humic material derived from higher land plants have been detected depending on the depositional conditions the humic material in the oxic facies underwent humification and gelification and had the highest huminite reflectances whereas it showed suppressed reflectance values in the oil shales facies 4 and in the carbonate dominated facies in the latter extensive bacterial reworking of humic material is also observed these differences are considered significant and applicable to other case studies in terms of evaluating the maturity of organic matter in ancient lacustrine systems

2d plasma sheet ion density and temperature profiles for northward and southward imf 1 we previously developed a method for inferring plasma sheet ion temperature and density from ionospheric observations using this method and dmsp observations for 1992 we present 2d profiles of the equatorial plasma sheet ion density and temperature for southward and northward imf for b2i 64 or kp 3 during periods of northward imf cold dense ions can be found plentifully along the plasma sheet flanks however during periods of southward imf the presence of these cold dense ions is noticeably diminished especially at the dusk flank where the density peak is less discernable these cold dense ions have been previously interpreted in terms of magnetosheath ion entry into the plasma sheet our result suggests that any mechanism proposed to transport magnetosheath ions from dusk llbl to the plasma sheet along the dusk flank during periods of northward imf would have to be able to do so efficiently over a large spatial scale

characteristics of the flank magnetopause themis observations the terrestrial magnetopause is the boundary that shields the earth s magnetosphere on one side from the shocked solar wind and its embedded interplanetary magnetic field on the other side in this paper we show observations from two of the time history of events and macroscales interactions during substorms themis satellites comparing dayside magnetopause crossings with flank crossings near the terminator macroscopic properties such as current sheet thickness motion and current density are examined for a large number of magnetopause crossings the results show that the flank magnetopause is typically thicker than the dayside magnetopause and has a lower current density consistent with earlier results from cluster observations we also find a persistent dawn dusk asymmetry with a thicker and more dynamic magnetopause at dawn than at dusk

major episodes of quaternary activity in the lower neales river northwest of lake eyre central australia abstract the lake eyre basin australia s largest internal drainage system represents a key site in unravelling the complexities of terrestrial climate change the basin covering one sixth of the australian continent spans a number of climatic zones including the tropical monsoon system to the north and the mid latitude westerly circulation to the south this study describes four major episodes of quaternary fluvial lacustrine and aeolian activity in the neales river a western catchment of lake eyre the first phase is represented by coarse grained fluvial aggradation which dates to at least 170 ka the depocentre of lake eyre is believed to have been located further to the east during this phase the second episode is a phase of high lake level lacustrine deposition which occurred before 103 ka the deltaic margin of the lake at this time was approximately 20 km west of the present playa the third phase was characterised by significant base level lowering and channel incision after 50 ka but before 31 ka lake level lowering induced fluvial incision of up to 9 m scouring several metres into the basal silicified miocene sediments some time after 50 ka the final phase was a period of aeolian and ephemeral fluvial deposition which peaked between 20 ka and 18 ka coincident with the last glacial maximum these episodes are compared with chronostratigraphic data from the monsoon dominated catchments of the cooper and diamantina rivers the nature and record of fluvial and lacustrine deposition are correlated throughout the basin during the penultimate and last interglacial cycles the late quaternary record is more ambiguous and further studies are required to elucidate the precise nature of climate change in the basin over the last 30 ka

new oceanic proxies for paleoclimate environmental variables such as temperature and salinity cannot be directly measured for the past such variables do however influence the chemistry and biology of the marine sedimentary record in a measurable way reconstructing the past environment is therefore possible by proxy such proxy reconstruction uses chemical and biological observations to assess two aspects of earth s climate system the physics of ocean atmosphere circulation and the chemistry of the carbon cycle early proxies made use of faunal assemblages stable isotope fractionation of oxygen and carbon and the degree of saturation of biogenically produced organic molecules these well established tools have been complemented by many new proxies for reconstruction of the physical environment these include proxies for ocean temperature mg ca sr ca 44ca and ocean circulation cd ca radiogenic isotopes 14c sortable silt for reconstruction of the carbon cycle they include proxies for ocean productivity 231pa 230th u concentration nutrient utilization cd ca 15n 30si alkalinity ba ca ph 11b carbonate ion concentration foraminiferal weight zn ca and atmospheric co2 11b 13c these proxies provide a better understanding of past climate and allow climate model sensitivity to be tested thereby improving our ability to predict future climate change proxy research still faces challenges however as some environmental variables cannot be reconstructed and as the underlying chemistry and biology of most proxies is not well understood few proxies have been applied to pre pleistocene times another challenge for future research only by solving such challenges will proxies provide a full understanding of the range of possible climate variability on earth and of the mechanisms causing this variability

flux transfer events on the magnetopause spatial distribution and controlling factors magnetic field profiles across the dayside magnetopause obtained during the first five years 1977 1981 of the isee mission have been examined in boundary normal coordinates to determine the spatial distribution and controlling factors of flux transfer events fte s owing to the natural evolution of the orbital plane of the spacecraft the dayside magnetopause region is eventually sampled both above and below the magnetic equator nevertheless at the end of the period surveyed the satellites still had not yet reached latitudes as far south of the equator as they were initially north of the equator two types of magnetic signature in the component normal to the magnetopause are regularly observed when an fte passes the spacecraft in the northern dawn quadrant the perturbation along the normal direction is usually first outward and then inward whereas in the southern dusk quadrant the reverse behavior occurs the dividing line between the two signatures is tilted somewhat with respect to the equator along a south dawn north dusk direction however deviations from this simple pattern are observed in both hemispheres examination of simultaneous imp 8 and isee 3 interplanetary data reveals that fte s occur almost exclusively during southward interplanetary magnetic field imf conditions fte s occur about 45 of the time when the imf has a southward component with the highest rates of occurrence for due southward imf the sign of the east west component of the imf does not exert control on the rate of fte occurrence

spider leg flexure as an indicator for estimating salinity in lacustrine paleoenvironments abstract spider fossils are rare outside of amber but do occur in lacustrine fossil lagerstatten in general spiders preserved in lacustrine beds show splayed legs however those in the crato formation of brazil are commonly curled up it is hypothesized that the post mortem flexure of spider legs is related to the salinity of the lake water to investigate this we measured the flexure at the two main leg joints femur patella and tibia metatarsus of spider legs in three fossil lagerstatten the crato formation of brazil cretaceous the green river formation of the western usa eocene and the florissant formation of colorado eocene in addition we drowned living spiders in water of three salinities fresh

deciphering the depositional environment of the laminated crato fossil beds early cretaceous araripe basin north eastern brazil the laminated limestones of the early cretaceous crato formation of the araripe basin north eastern brazil are world famous for their exceptionally well preserved and taxonomically diverse fossil fauna and flora whereas the fossil biota has received considerable attention only a few studies have focused on the sedimentary characteristics and palaeoenvironmental conditions which prevailed during formation of the crato fossil lagerstatte the nova olinda member represents the lowermost and thickest unit up to 10 m of the crato formation and is characterized by a pronounced rhythmically bedded pale to dark lamination to obtain information on palaeoenvironmental conditions sample slabs derived from three local stratigraphic sections within the araripe basin were studied using high resolution multiproxy techniques including detailed logging petrography xrf scanning and stable isotope geochemistry integration of lithological and petrographic evidence indicates that the bulk of the nova olinda limestone formed via authigenic precipitation of calcite from within the upper water column most probably induced and or mediated by phytoplankton and picoplankton activity a significant contribution from a benthonic carbonate secreting microbial mat community is not supported by these results deposition took place under anoxic and at least during certain episodes hypersaline bottom water conditions as evidenced by the virtually undisturbed lamination pattern the absence of a benthonic fauna and by the occurrence of halite pseudomorphs input of allochthonous catchment derived siliciclastics to the basin during times of laminite formation was strongly reduced the 18o values of authigenic carbonate precipitates between 7 1 and 5 1 point to a 18o poor meteoric water source and support a continental freshwater setting for the nova olinda member the 13c values which are comparatively rich in 13c between 0 1 and 1 9 are interpreted to reflect reduced throughflow of water in a restricted basin promoting equilibration with atmospheric co2 probably in concert with stagnant conditions and low input of soil derived carbon integration of lithological and isotopic evidence indicates a shift from closed to semi closed conditions towards a more open lake system during the onset of laminite deposition in the crato formation

the role of decay and mineralization in the preservation of soft bodied fossils abstract fossil deposits that preserve soft bodied organisms provide critical evidence of the history of life usually only more decay resistant materials e g cuticles survive as organic remains as a result of selective preservation and subsequent diagenesis to more resistant biopolymers permineralization the permeation of tissues by mineralizing fluids may preserve remarkable detail particularly of plants however evidence of more labile tissues e g muscle normally requires the replication of their morphology by rapid in situ growth of minerals i e authigenic mineralization this process relies on the steep geochemical gradients generated by decay microbes the minerals involved and the level of detail preserved which may be subcellular depend on a number of factors including the nature of microbial activity and amount of decay availability of ions and the type of organism that is fossilized understanding these controls is essential to determining the conditions that favor exce

use of snow cover derived from satellite passive microwave data as an indicator of climate change to assess future global change monitoring of the climate system through observation and analysis of seasonal and interannual fluctuations of climate variables is necessary cryospheric elements such as snow cover are often seen as sensitive indicators and integrators of basic climate conditions and hence an indicator of regional and global change snow cover elements which may serve as signals of variability and change are discussed with respect to the effective use of conventional and remotely sensed information conventional data are shown to be effective for assessing questions of temporal variability but are limited for spatial variability passive microwave satellite data make an important contribution by providing spatial and temporal information on snow water equivalent swe and the regional distribution of snowpack extent and state use of nimbus 7 smmr scanning multichannel microwave radiometer data to develop a time series of swe is assessed as a complement to conventional data limitations of smmr coverage compared to dmsp ssm i special sensor microwave imager coverage for production of swe maps for climate change analysis are discussed although there are limitations during early season snow cover information derived from passive microwave data is shown to be able to map and compute the areal coverage of swe allowing interannual comparison of the amount of water available the date of peak accumulation and the associated spatial distribution however the satellite data record is still too short to establish any definitive trend in snow cover variability

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic

the use of land snail shells in paleoenvironmental reconstruction fossil land snail shells constitute a valuable source of paleoenvironmental information for the quaternary they can be dated by a variety of methods including radiocarbon amino acid racemization and epimerization and perhaps also thu and esr the vast majority of paleoenvironmental studies based on land snail shells have examined the faunal composition of fossil assemblages from which a variety of paleoenvironmental characteristics such as biome temperature and moisture conditions have been reconstructed still there are a number of problems involved in using this approach and these are discussed shell morphology has occasionally been used to reconstruct such factors as rainfall and temperature stable isotope studies on quaternary land snails include analysis of 18o values of organic matter in the shells to reconstruct c4 plant distributions from which rainfall amounts can be inferred and analysis of 18o values of shell carbonate from which trends in the oxygen isotope composition of rainfall can be reconstructed stable carbon isotopes of shell carbonate have also been studied but their interpretation is not clear amino acid epimerization analysis dalloisoleucinel isoleucine ratios of land snail shells has been used for estimation of paleotemperatures some potential uses of land snail shells for paleoenvironmental reconstruction include the study of stable isotopes of h and n periodic growth lines and deposits of pedogenic carbonates on the shells