isotopic test of a thermally driven intraplate orogenic model australia a recently proposed model for intraplate orogenesis couples long term self heating of basement rocks by radioactive decay with thermal blanketing by overlying sedimentary deposits this model has been tested in one of the type areas in central australia the proterozoic musgrave complex which was reworked in an early cambrian orogeny we have determined the source of the pre orogenic and postorogenic sediments in the amadeus basin immediately to the north of the reworked basement including the fan deposits associated with uplift comprising uluru ayers rock and kata tjuta olgas detrital zircon age populations indicate that all basin sediments were derived from the musgrave complex which was therefore emergent rather than covered by sediments as required by the model in the basement the preservation of mesoproterozoic mica ages during transpressive burial to depths of 40 km ca 550 ma indicates that the associated thermal pulse was short lived not long lived as envisaged in the model we conclude therefore that the thermal blanketing model is inconsistent with the isotopic data and that the localization of deformation in intracratonic settings is associated with regions of contrasting strengths in central australia these are along the margins of the amadeus basin with the musgrave complex and arunta inlier

meteoric sphaerosiderite lines and their use for paleohydrology and paleoclimatology sphaerosiderite a morphologically distinct millimeter scale spherulitic siderite feco 3 forms predominantly in wetland soils and sediments and is common in the geologic record ancient sphaerosiderites are found in paleosol horizons within coal bearing stratigraphic intervals and like their modern counterparts are interpreted as having formed in water saturated environments here we report on sphaerosiderites from four different stratigraphic units each of which has highly variable 13 c and relatively stable 18 o compositions the unique isotopic trends are analogous to well documented meteoric calcite lines which we define here as meteoric sphaerosiderite lines meteoric sphaerosiderite lines provide a new means of constraining ground water 18 o and thus allow evaluation of paleohydrology and paleoclimate in humid

lower cambrian paleosols from the cantabrian mountains northern spain a comparison with neogene quaternary estuarine analogues abstract the lower cambrian barrios beds cantabrian mountains consist of a siliciclastic succession deposited in deltaic environments punctuated by intertidal and fluvial systems in the barrios de luna area this succession displays a progradational depositional systems tract that contains linkages between upper offshore tidal sand bars fluvial channels and floodplain environments the uppermost fluvial channels are encased within floodplain or interfluvial deposits some of which develop muddy paleosols the detailed micromorphological scanning electron microscopy sem geochemical and mineralogical studies of their pedogenic profiles indicate the presence of three well differentiated horizons fragmentation and shrinking of the upper horizons originated a network of channel like to vuggy porosity occluded by microlaminated clays cyclically emplaced by tidal floods and seasonal oxidation the middle horizons have concretionary to vermicular textures associated with microbioturbation and bacterial colonization and the lower ones are mottled containing numerous preserved lithorelics the barrios sulfidic ustifluvent paleosols represent short time pedogenic events under semiarid subtropical conditions and support previous studies of cambrian microbial life on subaerially exposed microenvironments

the mass balance of soil evolution on late quaternary marine terraces northern california mass balance interpretation of a soil chronosequence provides a means of quantifying elemental addition removal and transformation that occur in soils from a flight of marine terraces in northern california six soil profiles that range in age from several to 240 000 yr are developed in unconsolidated sandy marine and eolian parent material deposited on bedrock marine platforms soil evolution is dominated by 1 open system depletion of si ca mg k and na 2 open system enrichment of p in surface soil horizons 3 relative immobility of fe and al and 4 transformation of fe si and al in the parent material to secondary clay minerals and sesquioxides net mass losses of bases and si are generally uniform with depth and substantial in some cases approaching 100 however the rate of loss of each element differs markedly causing the ranking of each by relative abundance to shift with time loss of si from the sand fraction by dissolution and particle size diminution from 100 to 80 to 90 to 10 concurrently with an increase of ai in the organic sesquioxide and clay phases to 10 and 50 respectively while only minor increases occur in the nonorganic sesquioxide phases

high resolution gravity model of venus the anomalous gravity field of venus shows high correlation with surface features revealed by radar we extract gravity models from the doppler tracking data from the pioneer venus orbiter pvo by means of a two step process in the first step we solve the nonlinear spacecraft state estimation problem using a kalman filter smoother the kalman filter has been evaluated through simulations this evaluation and some unusual features of the filter are discussed in the second step we perform a geophysical inversion using a linear bayesian estimator to allow an unbiased comparison between gravity and topography we use a simulation technique to smooth and distort the radar topographic data so as to yield maps having the same characteristics as our gravity maps the maps presented cover 2 3 of the surface of venus and display the strong topography gravity correlation previously reported the topography gravity scatter plots show two distinct trends

environmental interpretation and a sequence stratigraphic framework for the terminal proterozoic ediacara member within the rawnsley quartzite south australia abstract fossils of the ediacara biota are confined to preservational windows in the ediacara member of the rawnsley quartzite pound subgroup from the flinders ranges south australia the base of the ediacara member is a type 1 sequence boundary incised into the partly lithified chace quartzite member of the rawnsley quartzite the ediacara member and the upper half of the rawnsley quartzite comprise the rawnsley depositional sequence bounded above by the early cambrian uratanna depositional sequence the rawnsley sequence developed over an erosional surface cut into the chace quartzite member with some 250 m of relief southeasterly directed palaeovalleys are filled with a sequence of massive sandstone and laminated siltstone passing up into well bedded sandstone at lowstand local channels were filled by massive sand the highstand systems tract consists of several parasequence sets of laminated siltstone and channelized amalgamated massive sandstone overlain by interbedded siltstone and sandstone grading up into well bedded clean sandstone impressions of soft bodied ediacaran organisms are preserved above the valley fill facies on sandstone partings within upward shoaling delta front environments between storm and fairweather wavebase the ediacara member is in places conformably overlain by up to 500 m of sandstone of the same lithofacies as those underlying the member distinctive microbial mat bound sand laminae described as petee structures are characteristic of the rawnsley quartzite above and below the ediacara member during deposition of the ediacara member colonization of the deeper substrates by microbial mat communities enabled preservation of the ediacara biota the erosional surface at the base of the ediacara member is one of at least four incision events recorded in the terminal proterozoic and early cambrian succession of the adelaide geosyncline the similarity of incision filling lithofacies of the rawnsley and uratanna sequences has in condensed sections led to confusion between the depositional sequences characteristic trace and body fossil assemblages provide the only clear distinction between depositional cycles spanning the proterozoic cambrian boundary

venus gravity a harmonic analysis an improved model of venusian global gravity has been obtained by fitting an eighteenth degree and eighteenth order spherical harmonic series to 78 orbital arcs of high altitude 950 1350 km at periapsis tracking data and 351 orbital arcs of lower altitude 150 200 km at periapsis data from the pioneer venus orbiter pvo compared to a recently published tenth degree model mottinger et al 1985 which is based on the 78 high altitude arcs only the current model provides a significant improvement in resolution and fidelity as a measure of this improvement we note that for the low altitude arcs alone the variance of the residuals for the present model is reduced to 19 of the data variance compared to 51 for the tenth degree model venus differs significantly from the earth in that it exhibits a significant correlation between long wavelength topography and gravity the gravity topography spectral admittances are inconsistent with either airy or pratt isostasy but they are consistent with dynamic support by mantle convection

formation of secondary carbonates and native sulphur in sulphate rich messinian strata sicily abstract microbially formed authigenic carbonates accompanied by native sulphur are present in the calcare solfifero below a thick succession of gypsum deposited during the messinian salinity crisis in sicily we sampled these carbonates and associated sulphur in five former sulphur mines to subject them to a detailed petrographic and geochemical study in order to explore their different modes of formation native sulphur formed in conjunction with microbial sulphate reduction which is reflected in its depletion in 34s 34s values as low as 2 vs v cdt and an enrichment of 34s in the residual sulphate 34s values as high as 61 the oxidation of organic matter by sulphate reduction increased alkalinity inducing precipitation of secondary carbonate minerals a set of authigenic limestones lacking sulphate minerals but characterized by pseudomorphs after gypsum and high 18o values as high as 9 vs v pdb reflects syngenetic mineral formation within evaporitic settings low 13c values as low as 52 vs v pdb reveal that these carbonate phases were formed by microbial sulphate reduction coupled to the oxidation of biogenic methane another set of authigenic carbonates that replaced sulphate minerals is typified by low 18o values as low as 4 these carbonates formed epigenetically during later diagenesis following compaction dissolution of gypsum or anhydrite by meteoric waters delivered the sulphate for microbial sulphate reduction low carbon isotope values of these carbonates 29 to 5 indicate that carbonate was derived from the oxidation of crude oil and possibly minor methane partly involving different degrees of admixture of dissolved carbonate from other sources although the studied rocks with their vast amounts of secondary carbonate minerals and sulphur seem to indicate a similar genesis at first glance having formed by biogeochemical transformations of sulphate and hydrocarbons this study reveals that these processes can occur at different times in variable geological environments

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

shallow marine sedimentary processes in the late devonian catskill sea new york state shallow marine strata of the upper devonian west falls group in south central new york comprise centimetre to decimetre thick sheetlike to lenticular beds of sandstone and siltstone interbedded with mudstone unidirectional current scour marks and tool marks occur on the basal erosion surfaces of the sandstones their internal structures are hummocky cross strata of various styles planar laminae and wave ripple cross laminae with characteristic vertical and lateral transitions among them vertical burrows of the skolithos ichnofacies dominate upper portions of sandstone beds whereas mudstones and silt stones contain mainly horizontal burrows of the cruziana ichnofacies transported and in situ shelly fossils occur throughout in places concentrated in coquinite lenses large scale 15 to 30 in bedding sequences are characterized by upward thickening and coarsening of sandstone beds increase in amalgamated hummocky cross strata coquinites plant debris and bivalves followed by abrupt fining and thinning of beds the depositional environment is interpreted as a shallow marine shelf episodically influenced by intense tropical storms hurricanes individual sandstone beds were deposited by spatially decelerating combined flows where an initially strong offshore directed flow component decreased in time relative to the oscillatory flow component large scale bedding sequences reflect changes in storm combined current intensity and deposition rate strong eustatic control is unlikely and there is no evidence of changing wave climate instead these sequences may be associated with delta lobe progradation and or offshore bar development

evolution of polygonal patterns in stratified mud during desiccation the role of flaw distribution and layer boundaries detailed analysis of diagnostic surface morphologies of fractures in natural mud indicates that mud cracks systematically nucleate at the bottom of the mud and propagate vertically upward toward the free surface and laterally outward toward adjacent cracks earlier generations of mud cracks rupture the set of desiccated layers altogether forming polygonal patterns that are similar throughout the mud sequence later generations of mud cracks subdivide each layer separately forming markedly different polygonal patterns within individual mud layers a simple mechanical model draws an analog between cooling of granular materials and drying of mud it shows that subfact defects at grain boundaries near the base may become critical before defects associated with fine particles at the top even though the stress profile due to drying is usually more tensile at the top thin section analysis and sieving method indicate that grain boundaries at the bottom are several times longer than at the top of the mud due to the natural sorting of grains illustrating the validity of the model this study suggests that stress variations with depth are less important for pattern evolution of mud cracks than previously theorized however nonuniform flaw distribution and surface discontinuities play a fundamental role during mud crack nucleation and growth these results have significance for several subjects including experimental studies of cracking induced by desiccation the previously suggested analogy between natural mud fracturing and basalt fracturing and the use of mud cracks in stratigraphic interpretation

response of benthos to stress factors in holocene arctic fjord settings maktak coronation and north pangnirtung fjords baffin island canada maktak coronation and north pangnirtung fjords are situated on cumberland peninsula baffin island canada having a common freshwater source from the penny ice cap bottom photographs were examined to identify epifaunal trails and shallow endobenthic burrow openings exposed on the seafloor surface these were compared to biogenic sedimentary structures revealed through x radiograph images and direct observations of lehigh gravity core samples intermediate and deep tier structures characterize the ichnofabrics of the glaciomarine sediments extensive bioturbation by the shallow tier and epibenthic tracemakers most notably ophiuroid echinoderms brittlestars and other organisms has destroyed much of the primary sedimentary fabric i e lamination resulting in homogenous silty clay sediments the dominant deep tier structure consisting of an open three dimensional boxwork burrow system is the most pervasive biogenic structure observed within the core samples interestingly although proximal distal trends in benthic macrofaunal composition are evident in the bottom photographs ichnofabrics remain relatively constant along the length of the fjords environmental factors influencing the biological community in these modern high latitude fjords differ from conditions described in paleozoic and cenozoic fjord environments an increasing number of recent studies are expanding significantly on the fjord ichnology database and provide the basis for the revision of the currently proposed fjord trace fossil model accommodating the complexity and diversity of fjord settings

venus gravity anomalies and their correlations with topography this report provides a summary of the high resolution gravity data obtained from the pioneer venus orbiter radio tracking data gravity maps covering a 70 latitude band through 360 of longitude are displayed as line of sight and vertical gravity topography converted to gravity and bouguer gravity maps are also shown in both systems topography to gravity ratios are made over several regions of the planet there are markedly different ratios for the aphrodite area as compared to the beta and atla areas

late neoproterozoic baltic paleosol intense weathering at high latitude the neoproterozoic was a time when repeated global cooling events interrupted by supergreenhouse phases preceded environmental change toward a modern oxygen rich atmosphere and the eventual emergence of animal life cyclically increased atmospheric co2 levels intensified weathering of continental silicates but little is known about the influence of neoproterozoic climates on soil morphogenesis which acts as a direct proxy of conditions at the time of formation however being typically fragmented in time and space these mineralic soils paleosols had a low preservation potential an exceptionally well preserved neoproterozoic deeply weathered paleosol on the baltica paleocontinent provides new information on weathering during the precambrian the kaolinite fe oxyhydroxide composition of this paleosol is indicative of intense weathering in a stable landscape at a time when baltica was positioned between intermediate to high southern latitudes it is plausible that this paleosol developed over long steady state weathering under temperate climatic conditions or alternatively during an intensified weathering event triggered by elevated co2 levels and transient greenhouse climatic conditions at the termination of ediacaran glaciations or possibly the ediacaran shuram wonoka isotope event

equation for compaction of paleosols due to burial existing empirically derived compaction curves for marine sediments fail to estimate the compaction of paleosols flood plain sediments and peats as indicated by deformation of clastic dikes dinosaur footprints and sandstone paleochannels yet compaction estimates are vital to reconstructing paleoclimate and geochemical profiles of paleosols to modeling sediment accumulation rates of nonmarine rocks and to tectonic flexural modeling of molasse facies this paper presents a compaction equation and physically derived constants that make geologically realistic estimates of compaction of paleosols and other nonmarine sediments a protocol for the application of the equation is suggested that would allow the following equation to solve for burial compaction c as a fraction of original thickness given depth of burial d in km as c s i f e d k 1 this equation can be applied to nonmarine sedimentary rocks or paleosols given appropriate empirical data on the physical constants in the equation such as initial solidity s i initial porosity f and the corresponding curve fitting constant k data on physical constants useful for this equation are compiled here for a range of paleosol and nonmarine sediment types

mixing zone diagenesis in the subsurface of florida and the bahamas abstract three cores from great bahama bank and southern florida contain examples of mixing zone diagenesis where typical shallow water aragonite rich sediments were altered to low mg calcite the 40 50 m thick mixing zones are identified on the basis of downcore covariant trends from depleted meteoric 18o 3 2 0 7 13c 1 6 1 8 to enriched marine isotopic values 18o 1 0 0 3 13c 1 9 0 7 the age of the mixing zones varies from late pliocene to pleistocene so these cores provide three independent examples of mixing zone diagenesis mixing zone diagenesis produced a limestone composed of low mg calcite with petrographic fabrics including moldic porosity blocky to dogtooth calcite cementation and recrystallization of lime mud to micrite and microspar the mixing zone diagenetic model predicts alteration in only part of the mixing zone because the alteration recorded in these cores shows continuous alteration through the entire mixing zone we consider the mixing of waters itself to be largely irrelevant rather diagenesis was probably driven by the difference in solubility between aragonite and calcite with some additional dissolution of aragonite driven by the microbial oxidation of buried organic matter the mixing zone has been proposed as a likely location for dolomitization with the exception of some clearly sea floor dolomite in one core unda the mixing zones in these cores lack dolomite despite the sediment clearly having been altered in the mixing zone the lack of dolomite in these mixing zones combined with the extensive literature questioning the chemical reasoning for mixing zone dolomite supports rejection of the mixing zone dolomite model

potassium metasomatism of precambrian paleosols abstract independent of substratum composition ancient regoliths formed by subaerial weathering are characterized by accumulation of k and other alkaline elements potassium enrichment due to the formation of clay minerals is a trend typically observed in regoliths developed by modern hypergene processes however the k content in precambrian paleosols is much higher than in modern weathering profiles k metasomatism affecting buried hypergen targets is a possible mechanism for k accumulation a novel reaction transport dissolution precipitation model designed as part of this work proved able to reproduce many essential features of post burial alterations of a subaerial weathering profile formed on basaltic rocks including potassium enrichment dehydration compaction and pore filling that impacted the buried regolith the phenomena of preservation of the primary basaltic structure the apparent selective alteration of soil levels and immobility of al ti and p could be explained by the model

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

geochemical petrographic and grain size variations within single turbidite beds pronounced changes in chemical composition were detected upwards within single turbidite beds with sio2 contents deceasing by as much as 20 all other major elements and eighteen trace elements increase in abundance upwards enrichment factors from bed base to top range from 1 2 na2o to 5 7 cu these changes are related to textural and mineralogical grading that in turn were the result of turbidity current action before and during the deposition of the bed we found only slight changes in the modal petrographic composition of the sandstone fractions although this technique is operator dependent and only semi quantitative in nature chemical analysis appears to be a more sensitive more rapid and less subjective method of determining provenance and the compositional contrasts within beds chemical anomalies produced by dilution effects from quartz overgrowths and intrabasinal material however show the need for utilisation of a combination of techniques and for an appreciation of the interdependence of texture framework modes and bulk chemistry the chemical variations we detect in single beds also reflect the variation in a suite of representative samples collected from within a confined several km2 geographic area hence either sampling over a given area or specific sampling of individual beds provided that the bed is typical of the succession as a whole can be used to determine the compositional variations within a succession as a whole

syneresis cracks subaqueous shrinkage in argillaceous sediments caused by earthquake induced dewatering abstract syneresis cracks often confused with subaerial desiccation phenomena are traditionally ascribed to subaqueous shrinkage whereby salinity changes caused deflocculation of clay this and other previously proposed mechanisms fail to account for their occurrence in low energy typically non evaporitic facies stratigraphically sporadic distribution intrastratal formation under shallow burial depths variation in morphology degree of contraction generation of sedimentary dikelets as crack fills and deformation of dikelets and enclosing layers instead it is suggested that ground motion from strong synsedimentary earthquakes caused argillaceous sediments to dewater interbedded sands and silts to be almost simultaneously liquefied and injected into the resulting fissures and then these dikelets to be distorted comparative rarity of syneresis cracks in phanerozoic versus precambrian marine strata is considered to be primarily an evolutionary consequence of theological changes caused by increased organic binding of clay flocs in the water column greater input of organic matter into the sediment and the diversification of sediment dwelling bacteria and meiofauna in phanerozoic deposits

greenhouse crises of the past 300 million years proxies of past co 2 and climate over the past 300 m y now reveal multiple global climate change events in unprecedented detail evidence for past co 2 spikes comes from expanded and refined data on stomatal index of fossil ginkgo and related leaves new evidence for synchronous climatic change comes from paleosols in montana utah and neighboring states each co 2 spike was coeval with unusually clayey red and decalcified paleosols which can be traced throughout the colorado plateau spikes in atmospheric co 2 also were coeval with increases in paleosol alkali depletion as an indication of high temperature and spikes in paleosol base depletion and depth to calcic horizons as indications of high precipitation in the colorado plateau times of warmer climate were also more humid perhaps due to greater moisture potential of warmer air seasonality of climate did not increase during warm wet spikes the mesozoic greenhouse was not persistently hot with cool spells but warm with hot flashes these data furnish power laws predicting the sensitivity and magnitude of change in mean annual temperature mat and mean annual precipitation map due to rising co 2 in a mid latitude mid continental region the magnitude of the coming anthropogenic greenhouse pales in comparison with past greenhouse spikes at times of global mass extinctions

the nature of the proterozoic cambrian transition in the northern amadeus basin central australia abstract the nature and completeness of the rock record is vital in determining whether evolution across the proterozoic cambrian boundary was episodic or explosive this study documents the nature of the neoproterozoic cambrian transition within the arumbera sandstone of the northern amadeus basin central australia and demonstrates an erosional surface close to this major stratigraphic boundary we are not able to recognise major facies differences between the largely unfossiliferous lower units i and ii and the rich trace fossil bearing beds of units iii iv horizons above and below the purported neoproterozoic cambrian transition were traced laterally and searched for both trace and body fossils in an attempt to locate a local boundary between the neoproterozoic and cambrian a single nonconformity bound sedimentary cycle above the major erosional surface dividing arumbera ii and iii is recognised the lowest sedimentary cycle of arumbera iii is devoid of trace fossils but at correlative levels in the ooraminna sub basin this horizon bears elements of the ediacara fauna reported for the first time herein we therefore suggest that contrary to previous studies the neoproterozoic cambrian transition is not coincident with the widespread seismic reflector but in areas of more complete sedimentation actually lies above it this study also presents new stratigraphic ichnological and palaeontological information from the neoproterozoic cambrian transition in central australia identifies areas of potentially continuous sedimentation and provides a basis for correlation of the arumbera sandstone with other neoproterozoic cambrian successions within australia and beyond

late eocene detrital laterites in central oregon mass balance geochemistry depositional setting and landscape evolution detrital laterites interbedded with clayey ultisol like paleosols in the late eocene strata of central oregon record periods of soil erosion colluvial concentration of iron cemented soil nodules and deposition of these weathered products in hillslope settings two sets of lateritic paleosols are extensively exposed in the painted hills area of oregon and span the transition from eocene clarno formation andesitic volcanism to the initiation of late eocene miocene pyroclastic volcanism of the john day formation these late eocene lateritic paleosols developed along the margins of several different lava flows where they formed local accumulations of iron rich strata which are now exposed in deep red and ocher colored badlands along the exhumed flow margins stratigraphically the lateritic paleosols are above upper clarno formation rhyodacite flows below the thick tuffaceous oligocene early miocene part of the john day formation and sandwich the welded tuff of member a that defines the base of the john day formation in each of several cases from different lava flows studied a similar sequence of detrital laterites and clayey paleosols rest on weathered lava flow breccia the basal paleosol of these sequences consists of a thick 5 10 m very strongly weathered saprolite zone developed in lava flow breccia and an overlying clayey b horizon this paleosol is overlain by 8 12 m of alternating clayey kaolinite rich paleosols ultisol like paleosols and weakly developed paleosols with iron rich claystone breccia fragments detrital laterites the iron cemented claystone fragments are up to 35 fe 2 o 3 very base poor and weather resistant and they contain abundant cross cutting clay skins and clay filled pedotubules indicative of polycyclic weathering the lower of the two sets of detrital laterites is associated with a thick rhyodacite flow in the upper clarno formation and has an up section increase in the degree of weathering and concentration of resistate constituents as determined by mass balance geochemical analysis the time span represented by this well developed weathering trend is estimated to be between 2 and 4 m y based on estimates of the time of formation of interbedded paleosols this long lasting weathering trend is probably the result of a lack of soil rejuvenation resulting from the late eocene hiatus between clarno and john day volcanism a developmental model for the formation of the detrital laterites and ultisol like paleosols involves alternating episodes of soil formation and soil erosion in which iron rich soil nodules are concentrated as a colluvial lag deposit on the toe slope of hills subsequent colluvial pulses of iron cemented gravel were increasingly weathered and rich in resistate constituents because of longer residence time in up slope soils during periods of landscape stability slow vertical accretion of soils by small additions of volcanic ash and dust produced the strongly developed but nonlateritic ultisol like paleosols the episodes of soil erosion probably correspond to periods of climatic change during the late eocene climatic deterioration the john day formation detrital laterites and clayey paleosols are very similar to the clarno formation laterites except for the presence throughout the section of 1 3 pyrogenic feldspar crystals no up section increase in weathering is observed in the john day detrital laterites perhaps because of rejuvenation of soils by volcanic ash the similar textures and chemistries of the two groups of detrital laterites despite the onset of john day pyroclastic volcanism indicate that climate remained subtropical and humid up to the oligocene eocene boundary

carbon isotopic evidence for photosynthesis in early cambrian oceans were the first metazoan reefs ecologically similar to modern tropical reefs enabling them to persist under oligotrophic conditions we tested the hypothesis of ecological similarity by employing a geochemical approach petrography cathodoluminescence trace elements and stable isotope analyses of primary precipitates of the lower cambrian ajax limestone south australia indicate preservation of original c isotopic composition all primary carbonate components exhibit c isotopic values similar to the composition of inorganically precipitated fibrous marine cements suggesting that archaeocyaths and the calcimicrobe epiphyton precipitated skeletal carbonate in equilibrium with ambient seawater in the absence of vital effects such data do not support the contention that archaeocyaths possessed photosymbionts however a 0 55 shift in 13 c occurs in reefs developed under shallower water conditions relative to deeper reefs this shift suggests the stratification of primary production in early cambrian oceans the pattern is similar to that seen in the modern ocean whereby significant photosynthesis modulates the c isotopic composition of the photic zone

venus comparison of gravity and topography in the vicinity of beta regio the doppler tracking data obtained from the pioneer venus orbiter when it passed near beta regio yielded a peak vertical anomaly of 150 mgal when analyzed by our two stage procedure a comparison of maps of the gravity and topography at comparable resolution shows a striking correlation a scatter plot shows that the observed gravity anomaly is approximately 0 4 of that expected from uncompensated topography of half the mean density of venus however the spectral admittance shows that the gravity anomalies can not be explained either by airy compensation at fixed depth or by a model comprising an elastic plate atop an inviscid fluid the gravity and topography variations may signify deep compensation or dynamic support for beta regio and more shallow compensation for other features

ediacaran fossil preservation taphonomy and diagenesis of a discoid biota from the amadeus basin central australia abstract aspects of the preservation of the enigmatic soft bodied ediacara biota in relatively coarse grained siliciclastic sediments remain unresolved the taphonomic model proposed by gehling in 1999 is here validated through examination of previously unpublished discoid fossils from the shallow marine deltaic arumbera sandstone in the amadeus basin within the flinders style preservation the model predicts stalked frondose organisms attached by a discoid holdfast to a microbial mat encrusted sea bed with sedimentation as periodic storm event beds during a terminal neoproterozoic taphonomic window a pyrite sole veneer provided critical fossil rigidity during burial the sequence of sedimentation events presented here advances a slightly modified gehling model no direct evidence of pyrite is detected instead a thin haematite clay coating covers fossil hyporelief surfaces nevertheless an original pyrite sole veneer is indirectly validated by tracing its diagenetic history through to today s haematite detailed petrography demonstrates reducing conditions during eodiagenesis that remained anoxic mildly alkaline through mesodiagenesis thus the pyrite sole veneer survived deepest burial meteoric water penetrated the deep regolith during prolonged telodiagenesis creating oxic mildly acidic pore water so pyrite oxidised and hydrolised to haematite the applicability of gehling s model is higher where marine shelf sediments subsided continuously in shallower or eroded areas that experienced intermittent meteoric eodiagenesis diagenetic history was different and ediacaran fossil preservation unlikely diagenetic history therefore has crucial implications for ediacaran fossil preservation

comment on trace fossil evidence for ediacaran bilaterian animals with complex behaviors by chen et al precambrian res 224 2013 690 701 a b s t r a c t trace fossils from the shibantan member of the denying formation 551 541 ma of south china interpreted by chen and colleagues as evidence of undermat feeding epibenthic locomotion and temporary dwelling of a small worm like animal metazoa bilateria show four features incompatible with that interpretation 1 bulbous ends 2 interruptions 3 variable width 4 narrow ends and 5 beaded levees these features are better explained as due to formation of a sorocarp base looping upward shape changing cell aggregation and slime nodules respectively of the slug grex or pseudoplasmodium phase of a cellular slime mold comparable with living dictyostelium discoideum amoebozoa mycetozoa another three features are found in worm as well as slime mold trails 6 transverse markings 7 central ridge and 8 small size similar observations can be made and mycetozoan affinities considered for comparable trace fossils from the 550 ma ediacaran member of south australia 558 ma ust pinega formation of russia 585 600 ma tacuari formation of uruguay 1100 ma chorhat sandstone of india and 2000 1800 ma stirling range sandstone of western australia slime molds are terrestrial eucaryotic protists and may have a fossil record extending back as far as the likely 1900 ma age of aquatic metazoans

trace fossil evidence for ediacaran bilaterian animals with complex behaviors abstract distinguishing ediacaran trace fossils from tubular body fossils can be a challenge and several ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils nonetheless true ediacaran trace fossils are present but they are relatively few and morphologically simple dominated by horizontal trails and shallow burrows such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the cambrian explosion here we report three types of trace fossils horizontal tunnels surface tracks trails and vertical traces from the latest ediacaran dengying formation 551 541 ma in the yangtze gorges area of south china cross cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils instead these three types of traces likely represent animal activities related to under mat feeding epibenthic locomotion and temporary dwelling respectively we show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and o 2 resources these animals heralded a new age in ecosystem engineering animal sediment interaction and biogeochemical cycling

trace fossils in the ediacaran cambrian transition behavioral diversification ecological turnover and environmental shift abstract after taxonomic revision trace fossils show a similarly explosive diversification in the ediacaran cambrian transition as metazoan body fossils in shallow marine deposits of ediacaran age trace fossils are horizontal simple and rare and display feeding strategies related to exploitation of microbial matgrounds equally notable is the absence of arthropod tracks and sinusoidal nematode trails this situation changed in the early cambrian when a dramatic increase in the diversity of distinct ichnotaxa is associated was followed by the onset of vertical bioturbation and the disappearance of a matground based ecology agronomic revolution on deep sea bottoms animals have been present already in the ediacaran but ichnofaunas were poorly diverse and dominated by the horizontal burrows of undermat miners as shown by the ichnogenus oldhamia this life style continued to be predominant into the early and to a lesser extent middle cambrian nevertheless there was an explosive radiation of behavioral programs during the early cambrian when exactly the bioturbational revolution arrived in the deep sea is uncertain in any case the nereites ichnofacies was firmly established in the early ordovician the rich ichnofauna in the early cambrian guachos formation of northwest argentina probably marks a first step in this ecological onshore offshore shift

assessing pedogenic calcite stable isotope values can positive linear covariant trends be used to quantify palaeo evaporation rates abstract palaeoclimate models suggest enhanced evaporation rates in subtropical regions 15 30 latitude during greenhouse world conditions however there are no empirical data to support these estimates laboratory evaporation experiments have shown that calcites precipitated from variably saturated solutions yield a positive linear covariant trend plct in 18 o calcite versus 13 c calcite values the goal of the present controlled laboratory experiments is to develop a method to quantify regional palaeo evaporation rates from palaeosol calcrete plcts samples of powdered caco 3 were dissolved in de ionized water in pressure sealed containers with a range of elevated atmospheric p co 2 concentrations for 24 h the solution was then allowed to evaporate completely from an open container within an incubator with the time of calcite crystallization noted and aliquots removed for analysis every 24 h the precipitated calcite produced an array of 18 o calcite versus 13 c calcite values that fall upon a plct projected from a theoretical meteoric calcite line mcl water analyses yielded 18 o water enrichments from an initial value of 4 75 vsmow ranging up to between 10 0 and 14 8 the experimental results show that solutions formed under higher p co 2 conditions precipitated calcite very early on during evaporation and thus have 18 o calcite and 13 c calcite values that are slightly enriched relative to the mcl the solutions that formed under low p co 2 conditions precipitated calcite after much of the fluid had evaporated and thus yield more enriched 18 o calcite and 13 c calcite values repeat trials with varying temperature and relative humidity show that the plct is steeper under both higher temperature and low relative humidity the wide range of p co 2 temperature and relative humidity conditions used simulate meteoric phreatic and meteoric vadose conditions that may affect a calcrete horizon over time during numerous dissolution precipitation reactions the results of these experiments show that a dominant factor in the precipitation of vadose calcite is the saturation state of the fluid with respect to caco 3 while the primary factors affecting the magnitude and steepness of the plct are vadose zone temperature relative humidity the starting 18 o water value and saturation state of the fluid with respect to caco 3 since the p co 2 of the rooting zone is cross controlled by the local soil and surface ecology the magnitude of the plct enrichment may not be a direct proxy for palaeo evaporation rates

climate dependent chemical weathering of volcanic soils in iceland abstract the major element mobility within soil profiles of brown to gleyic andosols that developed under diverse climatic conditions in iceland is assessed the volcanic soils were selected from areas with good monitoring of annual temperature and precipitation and the degree of weathering and elemental behavior is compared icelandic soils are subject to high fluxes of aeolian dust and at times to tephra ejecta from volcanic eruptions the source of dust input is assessed for each profile based on comparison of the chemical signatures found in the less weathered upper horizons with those of volcanic systems supplying material to source areas results show that tio 2 al 2 o 3 and fe 2 o 3 t and mno are the least mobile species and generally found enriched within more mature horizons the mobile base cations mgo cao and na 2 o are depleted in these horizons as a result of chemical weathering during pedogenesis soils developed in colder climatic conditions with mean annual temperature mat 1 c give values for the chemical index of weathering ciw of 37 45 that reflect only weak chemical weathering soils developed in milder climates mat 2 4 c are more strongly affected by weathering ciw 50 77 the parent material has ciw values of 37 temperature is demonstrated as the dominant variable exerting control on the extent of weathering with only minor mobilization following the incipient near surface weathering stage a robust linear relationship is found between ciw and model mat mat 0 21ciw 8 93 r 2 0 81 this climofunction can deliver proxy climate estimations from volcanic soils and paleosols of basaltic origin in cool to subarctic conditions 2 to 6 c

a high resolution gravity model for venus gvm 1 a spherical harmonic model of the gravitational field of venus complete to degree and order 50 has been developed using the s band doppler tracking data of the pioneer venus orbiter pvo collected between 1979 and 1982 the short wavelengths of this model could only be resolved near the pvo periapse location 14 n latitude therefore a priori constraints were applied to the model to bias poorly observed coefficients towards zero the resulting model has a half wavelength resolution of 400 km near the pvo periapse location but the resolution degrades to greater than 1000 km near the poles this gravity model correlates well with a degree 50 spherical harmonic expansion of the venus topography derived from a combination of magellan and pvo data new tracking data from magellan s gravity mission should provide some improvement to this model although a complete model of the venusian gravity field will depend on tracking of magellan after the circularization of it s orbit using aerobraking

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

fossils and matgrounds from the neoproterozoic longmyndian supergroup shropshire uk body and trace fossils of ediacaran affinity are described from strata of the late neoproterozoic longmyndian supergroup exposed near church stretton shropshire uk the almost spherical soft bodied ediacaran fossil beltanelliformis brunsae menner occurs rarely in the burway formation but much smaller simpler discoidal structures are common in both the burway and synalds formations and are referred to beltanelliformis minutae sp nov similar discoidal structures but with a distinct central depression are included in intrites punctatus fedonkin and are common at several horizons two blocks with numerous examples of medusinites aff asteroides sprigg glaessner wade were recovered from the burway formation the purported ediacaran body fossil arumberia glaessner walter is common at several horizons but its biogenicity is not accepted herein arumberia is thus treated along with evidence for microbially bound sediment surfaces or matgrounds that have been suggested by several authors to be necessary for some types of ediacaran preservation the assemblage of simple trace and body fossils along with matgrounds is typical of latest neoproterozoic time though some elements range into the phanerozoic

venus gravity west of beta regio abstract doppler tracking data from the pioneer venus orbiter pvo have been used to estimate the anomalous gravity field in the region of venus west of beta regio the analysis invokes a kalman filter smoother to solve the nonlinear spacecraft state estimation problem and a linear bayesian estimator to perform the geophysical inversion the topographic map for this region derived from the pvo radar has been filtered to have the same distortions and degree of smoothing as the gravity map the undulations of the gravity are about 0 2 times as large as expected from the topography on the assumption that the latter is uncompensated a comparison of the gravity and topography by means of the spectral admittance is consistent with airy compensation at a depth of 50 km if the surface material has a density of 2 6 g cm 3 however this is not a unique interpretation

interactions between ediacaran animals and microbial mats insights from lamonte trevallis a new trace fossil from the dengying formation of south china abstract a new ichnogenus and ichnospecies lamonte trevallis is formally described from the shibantan member limestone of the upper ediacaran dengying formation yangtze gorges area south china it is characterized by horizontal tunnels connected with short vertical burrows and surface trails the horizontal burrows are elliptical or bilobed in transverse cross section preserved in full relief and filled with carbonate intraclasts micrites as well as calcite and silica cements they occur exclusively in silty crinkled and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats no burrows have been found in intraclastic layers adjacent to the microlaminated layers the vertical traces are filled with the same material as the burrows but they typically project through the crinkled microlaminae and are exposed on the bedding surface the surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs the burrow infill has 18ocarb and 13ccarb values distinct from but intermediate between microlaminated and intraclastic layers consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements intraclasts and micrites bedding plane bioturbation intensity 20 40 measured as percentage of bedding plane area covered by l trevallis traces is comparable to similar measurements in pre trilobite cambrian carbonates the exclusive occurrence of l trevallis within microbial mats may have both taphonomic and ecological significance these mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows and they may have also facilitated early diagenetic cementation of burrow infill thus facilitating burrow preservation the close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources the trace makers of l trevallis were better able to utilize the resources around them than many other ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late ediacaran oceans at the dawn of the agronomic revolution

glacial cold water coral growth in the gulf of cadiz implications of increased palaeo productivity a set of 40 uranium series datings obtained on the reef forming scleractinian cold water corals lophelia pertusa and madrepora oculata revealed that during the past 400 kyr their occurrence in the gulf of cadiz goc was almost exclusively restricted to glacial periods this result strengthens the outcomes of former studies that coral growth in the temperate ne atlantic encompassing the french iberian and moroccan margins dominated during glacial periods whereas in the higher latitudes irish and norwegian margins extended coral growth prevailed during interglacial periods thus it appears that the biogeographical limits for sustained cold water coral growth along the ne atlantic margin are strongly related to climate change by focussing on the last glacial interglacial cycle this study shows that palaeo productivity was increased during the last glacial this was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling after the younger dryas cold event the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the goc this primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems moreover these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern ne atlantic where more suitable environmental conditions established with the onset of the holocene

venus gravity a high resolution map the doppler data from the radio tracking of the pioneer venus orbiter pv0 have been used in a two stage analysis to develop a high resolution map of the gravitational potential of venus represented by a central mass and a surface mass density the two stage procedure invokes a kalman filter smoother to determine the orbit of the spacecraft and a stabilized linear inverter to estimate the surface mass density the resultant gravity map is highly correlated with the topographic map derived from the pv0 radar altimeter data however the magnitudes of the gravity variations are smaller than would be expected if the topography were uncompensated indicating that at least partial compensation has taken place

a comprehensive approach to the study of methane seep deposits from the lincoln creek formation western washington state usa a comprehensive approach using palaeontology petrography stable isotope geochemistry and biomarker analyses was applied to the study of seven small methane seep carbonate deposits these deposits are in the oligocene part of the lincoln creek formation exposed along the canyon and satsop rivers in western washington each deposit preserves invertebrate fossils many representing typical seep biota authigenic carbonates with 1 3 c values as low as 51 pdb reveal that the carbon is predominately methane derived carbonates contain the irregular isoprenoid hydrocarbons 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi lipid biomarkers diagnostic for archaea these lipids are strongly depleted in 1 3 c 1 3 c values as low as 120 pdb indicating that archaea were involved in the anaerobic oxidation of methane small filaments preserved in the carbonate may represent methanotrophic archaea archaeal methanogenesis induced the formation of a late diagenetic phase brownish calcite consisting of dumbbell shaped crystal aggregates that exhibit 1 3 c values as high as 7 pdb clotted microfabrics of primary origin point to microbial mediation of carbonate precipitation downward directed carbonate aggregation in the seeps produced inverted stromatactoid cavities large filaments interpreted as green algae based on their size shape arrangement and biomarkers imply that deposition occurred in places in water no deeper than 210 m

element mobility patterns record organic ligands in soils on early earth considerable mobilization of fe without mobilization of al in precambrian paleosols has been documented and attributed to either anoxic or ligand promoted dissolution to elucidate these mechanisms basalt was dissolved under oxic and anoxic conditions with and without citrate and the mobility of several elements was analyzed the extent of release of fe and p was minor in citrate free conditions or considerable with citrate regardless of oxygen pressure release of al was minor in all cases whereas release of cu was minor in anoxic conditions or considerable in oxic conditions release of cu was enhanced by citrate in comparison in the weathered surface of two of the oldest known basalt derived paleosols the mount roe 2 76 ga and the hekpoort 2 25 ga fe and p were considerably depleted and al retained consistent with the presence of organic ligands cu retained in the mount roe paleosol but considerably mobilized in the hekpoort paleosol documents formation under an anoxic atmosphere and an oxic atmosphere respectively as inferred by others on the basis of fe mobility the immobility of al in both paleosols is consistent with formation under conditions in which the annual volume of rainwater was lower than the topsoil pore volume mobilization of p in such paleosols developed under low rainfall conditions provides a new proxy for identification of ligands secreted by terrestrial organisms on early earth

venus ishtar gravity anomaly ishtar has been detected as a positive gravity anomaly verification of this result has been made with two independent data sets isostatic compensation of the ishtar topography using an airy model is achieved at approximately 150km

confirmation of carboniferous clastic swamp communities tropical lowlands dominated by arborescent lycophytes are the principal foci for our understanding of carboniferous peat and non peat accumulating coastal swamps1 2 suggested palaeoeco logical interpretations of various lycophytes and accessory vegetation have been based on transported compression assemblages3 4 and palynomorphs5 6 or in situ permineralized peats7 where transported macrodetritus resulting in compression assemblages is used to reconstruct past vegetational patterns taphonomic factors tend to bias the preserved flora8 11 taken alone or out of depositional context the heterogeneity of an assemblage most probably bears little or no relationship to that of the original contributing communities gastaldo9 suggests that reconstructions should be based on the autecology of erect in situ plants because with peats permineralized in situ precise resolution in time of laterally equivalent vegetation is difficult here i document an erect in situ early pennsylvanian lycophyte swamp which provides the first confirmatory evidence for previously hypothetical ecological amplitudes

neoichnology of a barrier island system the mula di muggia grado lagoon italy abstract barrier islands are common landforms and biodiverse habitats yet they received scarce neoichnological attention this gap is tackled by studying the mula di muggia barrier island system grado lagoon italy focusing on morphology ecology and ethology of individual traces the following incipient ichnotaxa are identified archaeonassa arenicolites bergaueria diverging shafts helminthoidichnites lockeia macanopsis monocraterion nereites parmaichnus polykladichnus skolithos thalassinoides and squat burrows vertebrate avipeda ardeipeda like canipeda and invertebrate tracks parallel furrows are also described for each ichnotaxon tracemaker and behavior are discussed together with their position with respect to sediment barriers results suggest that sediment barriers impose a sharp contrast in terms of ichnological composition back barrier is dominated by branched burrows i e thalassinoides parmaichnus while the fore barrier presents vertical and u shaped burrows arenicolites skolithos the environmental conditions of the back barrier show that low oxygen substrates favor intense bioturbation provided that the water column is sufficiently oxygenated

constraints from diffusion profiles on the duration of high strain deformation in thickened crust diffusion profiles in garnet are used to determine the duration of movement on shear zones in the musgrave block central australia grenville age granulites were overprinted at depths of 40 km by high strain zones during the intracratonic petermann orogeny ca 550 ma ago in these zones quartzofeldspathic mylonites contain garnet from the early granulite facies event that developed compositional gradients during the high pressure overprint the diffusion of ca into garnet is linked with the release of ca in plagioclase the only calcic mineral in the rock during neocrystallization of sodic feldspar during high strain deformation available diffusion data on garnet directly define the duration of high strain deformation at eclogite facies our results indicate that the integrated time scales of movement in individual high strain zones were short lived between 0 07 ma and 1 4 ma and that wide shear zones were active longer than narrow ones in addition we find that relict k feldspar in one of the narrow eclogite facies shear zones yields a 40 ar 39 ar age that is partially reset indicating that the thermal event was also short lived these short time scales support the hypothesis that shear heating was the dominant source of heat for the eclogite facies overprint

point counting pores and illuvial clay in thin section abstract six soil thin sections containing various amounts of illuvial clay previously estimated by ten operators were point counted four times by an additional experienced operator the results indicate that a count of 6000 points over a section area of 25 25 mm is sufficient to quantify satisfactorily the pore space of the section replicated results for illuvial clay however differed widely for some sections these differences are attributed both to difficulties in recognising illuvial clay and to orientation and variability of soil components variability of results for illuvial clay in this study was less than that reported for ten operators but nonetheless it is evident that for most sections the amount of illuvial clay cannot be estimated precisely by a single count of 6000 points suggestions are made for improving the reliability of estimates of illuvial clay in soil thin sections and an improved basis for reporting results is proposed

application of sedimentary structure interpretation to geoarchaeological investigations in the colorado river corridor grand canyon arizona usa abstract we present a detailed geoarchaeological study of landscape processes that affected prehistoric formation and modern preservation of archaeological sites in three areas of the colorado river corridor in grand canyon arizona usa the methods used in this case study can be applied to any locality containing unaltered non pedogenic sediments and thus are particularly relevant to geoarchaeology in arid regions resolving the interaction of fluvial aeolian and local runoff processes in an arid land river corridor is important because the archaeological record in arid lands tends to be concentrated along river corridors this study uses sedimentary structures and particle size distributions to interpret landscape processes these methods are commonplace in sedimentology but prove also to be valuable though less utilized in geoarchaeology and geomorphology in this bedrock canyon the proportion of fluvial sediment generally decreases with distance away from the river as aeolian slope wash colluvial and debris flow sediments become more dominant we describe a new facies consisting of flood couplets that include a lower fine grained fluvial component and an upper coarser unit that reflects subaerial reworking at the land surface between flood events grain size distributions of strata that lack original sedimentary structures are useful within this river corridor to distinguish aeolian deposits from finer grained fluvial deposits that pre date the influence of the upstream glen canyon dam on the colorado river identification of past geomorphic settings is critical for understanding the history and preservation of archaeologically significant areas and for determining the sensitivity of archaeological sites to dam operations most archaeological sites in the areas studied were formed on fluvial deposits with aeolian deposition acting as an important preservation agent during the past millennium therefore the absence of sediment rich floods in this regulated river which formerly deposited large fluvial sandbars from which aeolian sediment was derived has substantially altered processes by which the prehistoric inhabited landscape formed and has also reduced the preservation potential of many significant cultural sites

revised wonoka isotopic anomaly in south australia and late ediacaran mass extinction the global late ediacaran shuram wonoka carbon isotope anomaly has been regarded as the largest and longest known isotopic anomaly in the ocean assuming that all ediacaran carbonate is marine disregarding carbonate in south australia shown here to be palaeosol or palaeokarst the synchronous marine organic carbonate excursion is only 8 for 13 c organic and 6 for 13 c carbonate and lasted less than a million years this revised magnitude and duration is comparable with perturbations across the permian triassic boundary and correlative with a global late ediacaran acritarch mass extinction like permian triassic isotopic excursions the revised organic carbonate wonoka excursion may also have been a greenhouse palaeoclimatic warm spike which terminated valley incision and glacioeustatic drawdown during the mid ediacaran fauquier glaciation and preceded chill of the late ediacaran billy springs glaciation supplementary material measured sections and tables of mineral and grain size proportions major element and stable isotope analyses are available at www geolsoc org uk sup18756

a dynamic model of venus s gravity field unlike earth long wavelength gravity anomalies and topography correlate well on venus venus s admittance curve from spherical harmonic degree 2 to 18 is inconsistent with either airy or pratt isostasy but is consistent with dynamic support from mantle convection a model using whole mantle flow and a high viscosity near surface layer overlying a constant viscosity mantle reproduces this admittance curve on earth the effective viscosity deduced from geoid modeling increases by a factor of 300 from the asthenosphere to the lower mantle these viscosity estimates may be biased by the neglect of lateral variations in mantle viscosity associated with hot plumes and cold subducted slabs the different effective viscosity profiles for earth and venus may reflect their convective styles with tectonism and mantle heat transport dominated by hot plumes on venus and by subducted slabs on earth convection at degree 2 appears much stronger on earth than on venus a degree 2 convective structure may be unstable on venus but may have been stabilized on earth by the insulating effects of the pangean supercontinental assemblage

terrestrial and planetary gravity fields the determination of the gravity field together with knowledge of the surface topography provides one of the primary means of inferring the density structure and dynamics of planetary interiors phillips and lambeck 1980 hager 1985 after removing the topographic gravity signal the distribution of internal density anomalies caused by thermal or compositional differences can be studied gravity field models can also be used to study the compensation of surface topography which can provide information on the mechanical properties and state of stress of the lithosphere the determination of these models has been accomplished using a wide variety of different measurement types and solution techniques the near earth measurement types can be divided into satellite tracking measurements surface gravity measurements and satellite altimeter measurements in both near earth and interplanetary contexts tracking data are used to measure gravitational perturbations affecting satellites with the accuracy and spatial temporal distribution of the data being the most important factors in the resulting field accuracy and resolution surface gravity data provide a more direct measurement of the gravity field but acquiring data uniformly over the earth has always been difficult satellite altimetry provides precise measurements of the marine gravity field provided that satellite orbit errors and non geoidal sea surface height variations can be adequately modeled comprehensive gravity field solutions must incorporate these disparate data types in order to estimate mathematical parameters describing the gravity field such as spherical harmonic coefficients the proper combination of these data along with the desire to acquire an accurate representation of the model errors require that complex procedures be developed for computing these solutions

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

late oligocene bunch grassland and early miocene sod grassland paleosols from central oregon usa abstract fossil soils burrows and mammals of the upper john day formation in central oregon are evidence of bunch grasses and open semiarid vegetation as old as late oligocene earliest arikareean 30 ma root traces in these paleosols include both stout tapering tubes like roots of trees as well as sinuous filamentous tubes similar to roots of grasses paleosol structure is fine subangular blocky with patchy distribution of grass like roots as in wooded grassland and sagebrush steppe with bunch grasses cursoriality in horses mesohippus miohippus and hypsodonty in rhinos diceratherium is also evidence for open grassy vegetation trace fossils of pallichnus dung beetle boli and edaphichnium earthworm chimneys are characteristic of wooded grassland paleosols whereas taenidium cicada burrows dominates desert shrubland paleosols as has also been found in quaternary paleosols and soils of eastern washington in both oligocene and quaternary paleosol sequences arid shrubland and semiarid grassland paleosols alternate on milankovitch frequencies 23 41 100 ka the oldest known paleosols in oregon with crumb structure and abundant fine fossil root traces characteristic of sod grasslands are dated by mammalian biostratigraphy as hemingfordian early miocene ca 19 ma wooded grassland habitats are indicated by scattered chalcedony calcite rhizoconcretions from large woody plants and by fossil chalicotheres moropus camels gentilicamelus paratylopus and horses parahippus silty texture and silcrete horizons are evidence of semiarid to arid paleoclimate and are in striking contrast to highly calcareous and clayey underlying paleosols of the john day formation these silcrete paleosols may represent the miocene onset of summer dry mediterranean seasonality as opposed to a summer wet monsoonal pattern of seasonality found in this region during the oligocene oregon s early rangelands can be compared with those in the north american great plains granular structured calcareous paleosols of the brule formation of south dakota are evidence of dry bunch grasslands as old as 33 ma early orellan early oligocene and crumb structured paleosols of the anderson ranch formation of nebraska are evidence of sod grasslands as old as 19 ma late arikareean early miocene although grasses were a conspicuous part of dry rangelands well back into the oligocene early and middle miocene sod grasslands in north america were restricted to regions estimated to have had less than 400 mm mean annual precipitation

the record and stratigraphie implications of organic walled microfossils from the ediacaran terminal proterozoic of south australia two assemblages of organic walled microfossils have been recognized in drillcore samples from the late proterozoic rodda beds in the eastern officer basin south australia the fossils include tube like remains and large simple and sculptured acritarchs lithostratigraphic studies and seismic information in conjunction with previous albeit limited acritarch finds allow local correlation of the rodda beds with ediacaran or terminal proterozoic sequences in the northern adelaide fold belt site of the nominated ediacaran stratotype the new palynofloras are comparable with acritarch assemblages in the amadeus basin of central australia and suggest tentative correlations with sequences in china and the u s s r the presence of isotopically heavy marine carbonate in the lower fossiliferous horizons of the rodda beds pcpdb 3 to 6 0 is consistent with isotopic data from the equivalent interval in china in contrast the upper fossiliferous strata occur higher in the rodda beds where carbonate is significantly lighter 13 cpdb 1 to 3 o

gravity topography and crustal evolution of venus abstract the gravity anomalies of venus although small by comparison with those on mars and the moon are still much larger than those on earth for large features on venus even the low degree spherical harmonic terms for venus gravity field indicate a close association of broad positive gravity anomalies with major topographic highs this is striking contrast to the situation on earth where the broad regional gravity anomalies show little correlation with continental masses or plate tectonic features but instead appear to be caused by deep mass anomalies a method for estimating radial gravity anomalies from line of sight acceleration data their interpolation and use of iteration for improved radial anomaly estimates is outlined a preliminary gravity anomaly map of venus at spacecraft altitude prepared using first estimate values is presented a profile across the western part of aphrodite along longitude 85 e was analyzed using time series techniques an elastic plate model would require a plate thickness of about 180 to 200 km to match the general amplitude of the observed gravity anomaly about 33 mgal a thickness much greater than that found for earth structures and because of high surface temperatures unlikely for venus an airy isostatic model convolved with the topography across aphrodite however provides a better match between the predicted and observed gravity anomalies if the nominal crustal thickness is about 70 to 80 km this thickness is over twice that for continental crust on the earth and considerably greater than that of the earth s basaltic ocean crust only 5 km a different differentiation history for venus than that of the earth thus is anticipated high gravity anomalies 110 mgal occur over beta regio and over the topographic high in eastern aphrodite both highs are associated with regions where detected lightning is clustered and thus the topographic features may be active volcanic constructs the large gravity anomalies at these two sites of volcanic activity require an explanation different than that indicated for western aphrodite

neoarchaean c 2 58 ga halite casts implications for palaeoceanic chemistry possibly the most extensive and best preserved archaean halite casts yet discovered occur in the c 2 58 ga upper black reef and basal oaktree formations transvaal supergroup in mpumalanga province south africa halite casts are isolated on bedding planes range in size from c 1 mm to 20 mm and have cubic dumbbell and triangular shapes as well as hopper like pyramidal hollows on cube faces some of the casts display distinct hopper shapes characteristic of halite crystals the halite cast bearing pavements are developed within silicified mudstone interbedded with siltstone or stromatolitic dolomite associated sedimentary structures pointing to subaerial exposure include adhesion ripples and warts desiccation and prism cracks rill marks and tepee structures halite cast bearing beds are interpreted as supratidal flat or sabkha deposits the presence of isolated casts and hopper shaped crystals suggests that halite resulted from displacive growth within the sediment from supersaturated residual brines after mudstone deposition absence of any indication of the former presence of gypsum or anhydrite supports previous contentions that the neoarchaean ocean was deficient in sulphate or contained a high bicarbonate to calcium ratio such that with progressive evaporation most calcium was consumed before the gypsum stability field was reached the association of halite and carbonate in the upper black reef and basal oaktree formations constrains the palaeolatitude of the transvaal basin at 2 58 ga to subequatorial 10 30

isotope geochemistry of caliche developed on basalt enormous variations in oxygen and carbon isotopes occur in caliche developed on 3 ma basalts in 3 volcanic fields in arizona significantly extending the range of 18o and 13c observed in terrestrial caliche within each volcanic field 18o is broadly co variant with 13c and increases as 13c increases the most 18o and 13c enriched samples are for subaerial calcite developed on pinnacles knobs and flow lobes that protrude above tephra and soil the most 18o and 13c depleted samples are for pedogenic carbonate developed in soil atmospheres the pedogenic caliche has 18o fixed by normal precipitation in local meteoric waters at ambient temperatures and has low 13c characteristic of microbial soil co2 subaerial caliche has formed from 18o rich evapoconcentrated meteoric waters that dried out on surfaces after local rains the associated 13c enrichment is due either to removal of 12c by photosynthesizers in the evaporating drops or to kinetic isotope effects associated with evaporation caliche on basalt lava flows thus initially forms with the isotopic signature of evaporation and is subsequently over layered during burial by calcite carrying the isotopic signature of the soil environment the large change in carbon isotope composition in subsequent soil calcite defines an isotopic biosignature that should have developed in martian examples if mars had a warm wet early period and photosynthesizing microbes were present in the early soils the approach can be similarly applied to terrestrial precambrian paleocaliche in the search for the earliest record of life on land large variations reported for 18o of carbonate in martian meteorite alh84001 do not necessarily require high temperatures playa lakes or flood runoff if the carbonate is an example of altered martian caliche

ediacaran and cambrian paleosols from central australia abstract ediacaran to cambrian red sandstones of the northern territory including arumbera sandstone and grant bluff and central mount stuart formations have been reexamined and sampled in order to reconstruct paleoenvironments from sedimentary facies and paleosols sedimentary facies include green gray calcareous sandstone member iii of arumbera sandstone only red siltstone with calcareous nodules also only member iii and also non calcareous red green siltstone interbedded red siltstone and sandstone and trough bedded sandstone the green gray facies has diverse and distinctive cambrian marine trace fossils not found in the red beds which have instead an assemblage of problematic body fossils including arumberia noffkarkys hallidaya ernietta trepassia and dickinsonia the red facies are interpreted as fluvial paleochannels trough cross bedded fluvial levees interbedded siltstone and sandstone poorly drained floodplain red green siltstone and well drained floodplain or low terrace calcareous nodular the carbonate nodules have micritic replacive fabrics and a significant positive correlation of 13c and 18o characteristic of pedogenic carbonate of calcid soils other red beds have pseudomorphous sand crystals after gypsum like those of gypsid soils individual red beds show negative strain and mass transfer for cationic bases typical of soils as well as gradational alteration down from fossiliferous tops characteristic of soils their varied degree of pedogenic differentiation is identified as psamment aquent and ochrept paleosols phosphorus depletion in the paleosols is evidence that organisms lived in the paleosols and were not introduced by transient marine incursions the problematic quilted fossils arumberia noffkarkys and hallidaya formed a distinctive inland terrestrial polsterland during the ediacaran and early cambrian

a new paleothermometer for forest paleosols and its implications for cenozoic climate climate is a primary control on the chemical composition of paleosols making them a potentially extensive archive applicable to problems ranging from paleoclimate reconstruction to paleoaltimetry however the development of an effective widely applicable paleosol temperature proxy has remained elusive this is attributable to the fact that various soil orders behave differently due to their respective physical and chemical properties therefore by focusing on an individual order or a subset of the 12 soil orders whose members exhibit similar process behavior a better constrained paleothermometer can be constructed soil chemistry data were compiled for 158 modern soils in order to derive a new paleosol paleothermometry relationship between mean annual temperature and a paleosol weathering index pwi that is based on the relative loss of major cations na mg k ca from soil b horizons the new paleothermometer can be applied to clay rich paleosols that originally formed under forest vegetation including inceptisols alfisols and ultisols and halves the uncertainty relative to previous approaches a case study using cenozoic paleosols from oregon united states shows that paleotemperatures produced with this new proxy compare favorably with paleobotanical temperature estimates global climatic events are also evident in the oregon paleosol record including a 2 8 c drop across the eocene oligocene transition comparable to marine records and a neogene peak temperature during the mid miocene climatic optimum

how well do fossil assemblages of the ediacara biota tell time patterns of origination evolution and extinction of early animal life on this planet are largely interpreted from the fossils of the precambrian soft bodied ediacara biota spanning nearly 40 m y of the terminal ediacaran period localities containing these fossils are loosely considered as part of either the avalon white sea or nama associations these associations have been interpreted to have temporal paleobiogeographic preservational and or paleoenvironmental significance surprisingly elements of all three associations occur within the ediacara member of the rawnsley quartzite of south australia an analysis of over 5000 specimens demonstrates that fossil distribution is strongly controlled by facies and taphonomy rather than time or biogeography and that individual taxa vary considerably in their environmental tolerance and taphonomic integrity the recognition that these taxa represent organisms living in various distinct environments both juxtaposed and shared holds strong implications for our interpretation of the record of early animal life on this planet and questions the biostratigraphic utility of the three associations furthermore although in situ soft bodied preservation provides a unique perspective on composition of benthic fossil assemblages the record should not be interpreted as a simple snapshot fossil beds represent a range of preservational modifications varying from current winnowed census samples of benthic communities at different depths and ecological maturity to entirely transported assemblages unless the appropriate environments and taphonomic conditions are present for certain taxa the absence of a particular taxon may or may not indicate its extinction in space or time