pancakelike domes on venus the shape of seven large domes on the plains of venus with volumes between 100 and 1000 km3 is compared with that of an axisymmetric gravity current spreading over a rigid horizontal surface both the altimetric profiles and the horizontal projection of the line of intersection of domes on the synthetic aperture radar images agree well with the theoretical similarity solution for a newtonian fluid but not with the shape calculated for a rigid plastic rheology nor with that for a static model with a strong skin as a viscous current spreads it generates an isotropic strain rate tensor whose magnitude is independent of radius such a flow can account for the randomly oriented cracks that are uniformly distributed on the surface of the domes the stress induced by the flow in the plains material below is obtained and is probably large enough to produce the short radial cracks in the surface of the plains beyond the domes the viscosity of the domes can be estimated from their thermal time constants if spreading is possible only when the fluid is hot and lies between 1014 and 1017 pa s laboratory experiments show that such viscosities correspond to temperatures of 610 to 700 c in dry rhyolitic magmas these temperatures agree with laboratory measurements of the solidus temperature of wet rhyolite these results show that the development of the domes can be understood using simple fluid dynamical ideas and that the magmas involved can be produced by wet melting at depths below 10 km followed by eruption and degassing

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

petrographic characterization and evolution of the permian coal deposits of the rajmahal basin bihar india abstract lower gondwana rocks are exposed as narrow bands and discontinuous patches along the western edges of the rajmahal hills covering a large area of the bengal basin north bengal and pumea two coalfields hura and chuperbhita have productive coal mines pillar coal samples from the working coal seams of hura and chuperbhita coalfields were collected and subjected to a detailed petrographic and geochemical study using refined procedures on a large number of samples the results of the micropetrographic study reveal that the rajmahal coals are rich in liptinite and inertinite contents the fluorescence microscopy indicates that a major part identified as argillaceous mineral matter under white incident light is composed of liptinite macerals such as bituminite fluorinite and exsudatinite the volatile matter and reflectance suggest these coals are subbituminous to high volatile bituminous b c in rank the quantitative relationships among maceral and microlithotype suggest that these coals were deposited in limnic to limno telmatic conditions under very wet conditions that resulted from undisturbed peat that developed in situ along with subaquatic limnic sedimentation in swampy lakes further the gi and tpi values indicate that the hura coals were formed under oxic moor conditions with sudden episodes of flooding while the chuperbhita coals have originated in wet moors with intermittent moderate to high flooding in addition g i values suggest the formation of these coals in an upper delta alluvial valley with braided plains

steep sided domes on venus characteristics geologic setting and eruption conditions from magellan data a survey of more than 95 percent of the venus surface reveals 145 steep sided domes which can be subdivided into a variety of morphologic forms the most common being shaped like inverted bowls or flat topped domes results of a preliminary analysis of the distribution and geologic setting of the domes are presented the relation of the domes to analogous terrestrial features is examined and possible models for their mode of emplacement are outlined

cryovolcanic features on titan s surface as revealed by the cassini titan radar mapper abstract the cassini titan radar mapper obtained synthetic aperture radar images of titan s surface during four fly bys during the mission s first year these images show that titan s surface is very complex geologically showing evidence of major planetary geologic processes including cryovolcanism this paper discusses the variety of cryovolcanic features identified from sar images their possible origin and their geologic context the features which we identify as cryovolcanic in origin include a large 180 km diameter volcanic construct dome or shield several extensive flows and three calderas which appear to be the source of flows the composition of the cryomagma on titan is still unknown but constraints on rheological properties can be estimated using flow thickness rheological properties of one flow were estimated and appear inconsistent with ammonia water slurries and possibly more consistent with ammonia water methanol slurries the extent of cryovolcanism on titan is still not known as only a small fraction of the surface has been imaged at sufficient resolution energetic considerations suggest that cryovolcanism may have been a dominant process in the resurfacing of titan

shapes of venusian pancake domes imply episodic emplacement and silicic composition the main evidence available for constraining the composition of the large circular pancake domes on venus is their gross morphology laboratory simulations using polyethylene glycol show that the height to diameter aspect ratios of domes of a given total volume depend critically on whether their extrusion was continuous or episodic with more episodes leading to greater cooling and taller domes thus without observations of their emplacement the compositions of venusian domes cannot be uniquely constrained by their morphology however by considering a population of 51 venusian domes to represent a sampling of many stages during the growth of domes with comparable histories and by plotting aspect ratio versus total volume we find that the shapes of the domes are most consistent with episodic emplacement on earth this mode of dome growth is found almost exclusively in lavas of dacite to rhyolite composition strengthening earlier inferences about the presence of evolved magmas on venus

effects of eruption history and cooling rate on lava dome growth to better understand the factors controlling the shapes of lava domes laboratory simulations measurements from active and prehistoric flows and dimensional analysis were used to explore how effusion history and cooling rate affect the final geometry of a dome fifty experiments were conducted in which a fixed volume of polyethylene glycol wax was injected into a tank of cold sucrose solution either as one continuous event or as a series of shorter pulses separated by repose periods when the wax cooling rates exceeded a critical minimum value the dome aspect ratios height diameter increased steadily with erupted volume over the course of a single experiment and the rate at which height increased with volume depended linearly on the time averaged effusion rate thus the average effusion rate could be estimated from observations of how the dome shape changed with time our experimental results and dimensional analyses were compared with several groups of natural lava flows the recently emplaced mount st helens and soufriere domes which had been carefully monitored while active three sets of prehistoric rhyolite domes that varied in eruptive style and shape and two sets of holocene domes with similar shapes but different compositions geometric measurements suggest that dome morphology can be directly correlated with effusion rate for domes of similar composition from the same locality and that shape alone can be related to a dimensionless number comparing effusion rate and cooling rate extrapolation to the venusian pancake domes suggests that they formed from relatively viscous lavas extruded either episodically or at average effusion rates low enough to allow solidified surface crust to exert a dominating influence on the final morphology

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

the fold illusion the origins and implications of ogives on silicic lavas abstract folds on the surfaces of mafic lavas are among the most readily recognized geological structures and are used as first order criteria for identifying ancient lavas on earth and other planetary bodies however the presence of surface folds on the surface of silicic lavas is contested in this study and we challenge the widely accepted interpretation that silicic lava surfaces contain folds using examples from the western united states and sardinia italy we interpret the ridges and troughs on their upper surfaces typically referred to as ogives or pressure ridges as fracture bound structures rather than folds we report on the absence of large scale buckle style folds and note instead the ubiquitous presence of multiple generations and scales of tensile fractures comparable to crevasses in glaciers and formed in ways similar to already recognized crease structures we report viscosity data and results of stress analyses that preclude folding ductile deformation in compression of the upper surface of silicic lavas at timescales of emplacement weeks to months therefore analysis of fold geometry wavelength amplitude etc is erroneous and instead the signal produced reflects the strength and thickness of the brittle upper surface stretching over a ductile interior the presence of ogives on the surfaces of lavas on other planetary bodies may help to elucidate their rheological properties and crustal thicknesses but relating to their tensile strength not viscosity

the genesis of coal from the viewpoint of coal petrology abstract the genesis of the microscopic constituents of coal macerals and of maceral associations microlithotypes representing various coal facies is discussed in the light of recent advances that have been made in the study of coals and modern peats peat microscopy especially promoted the understanding of humification and biological gelification both of which are decisive for the genesis of huminites vitrinites in brown coals and hard coals respectively microbial activity during peatification has been documented by chemists microbiologists and petrologists and recently by electron microscopical observations in coals this activity leads to the incorporation of lipid substances into the humic matter and later influences the chemical physical and technological properties of vitrinites geochemical gelification transforms the huminites of brown coals into the vitrinites of bituminous coals and is probably caused by the onset of bitumen generation in coal in this process the hydrogel brown coal is transformed to the bitumogel bituminous coal coal as a source rock for oil has become an important research subject for coal petrologists and oil exploration the formation of more or less liquid bitumen and its later cracking to gaseous hydrocarbons leads to the coalification jumps of the macerals especially liptinites and vitrinites and to the generation of secondary macerals like exsudatinite bitumen and micrinite dead carbon bituminization in coal has been revealed by the use of fluorescence microscopy which also found the presence of new liptinite macerals bituminite fluorinite and exsudatinite and suggests a higher proportion of algal material in coals than was thought earlier the genesis of various types of inertinite macerals will probably become an increasingly important subject of research especially with regard to rank inertinites that seem to attain their high inertinitic reflectance initially during coalification besides the origin of macerals the origin of various coal facies in terms of maceral associations is considered in relation to the palaeogeographic depositional milieu the peat forming vegetation palaeoclimate water and nutrient supply acidity marine and calcareous influence and fire with examples from euramerican carboniferous coals gondwana coals and tertiary brown coals vegetation water and oxygen supply eh conditions are most important for the generation of coal facies vegetation has been reconstructed with the help of palaeobotany including palynology cuticular analysis and wood anatomy in brown coals and with the study of petrified permineralized peats preserved in coal balls the microscopical investigations of botanically recognizable plant remains isolated from coals or accompanying rocks has been especially informative however the results of palynological and cuticular analyses should be evaluated with caution considering the varying resistance of palynomorphs and cuticles and in the case of palynomorphs their possible extrapaludal origin microscopical studies of modern peats that were derived from different types of vegetation growing in different hydrological environments have been very helpful in interpreting coal facies especially in brown coals the much disputed origin of brown coal lithotypes is considered in detail for hard coals there seems to be agreement that coal layers rich in vitrites and liptinite poor clarite were deposited in wet forest swamps that microlayered liptinite rich clarites are sub aquatic humic muds and that inertinite rich durites represent oxidized peats the origin of liptinite rich durites is controversial either subaquatic muds or oxidized peats the latter perhaps from raised bogs a recent trend in the literature is the assumption that many if not all mineable coal seams have been deposited in raised bogs under ombrogenous oligotrophic conditions although raised bogs with a dense arborescent vegetation are known from borneo it seems not probable that most seams which were deposited in foredeeps or steadily sinking graben zones are of ombrogenous origin although a succession from relatively wet and eutrophic to relatively dry and oligotrophic conditions may be true for occasional seams but as in modern peats striking changes of coal facies are commonly caused by hydrological events e g inundations as a consequences of crevasses or of fires that burned the peat the origin of the inertinite rich gondwana coals is discussed in relation to their specific climatic conditions and a comparison with sub arctic peats is recommended coals influenced by marine and calcareous conditions are characterized by high contents of sulfur and pyrite as well as by hydrogen rich vitrinites with a relatively low reflectance and high fluorescence all due to a strong bacterial activity in peats of low acidity proposals for further research are made in the conclusions

how do deep water volcanoes grow abstract deep water volcanoes are emplaced in water depths 1 0 km and are widespread along continental margins and in ocean basins whilst the external morphology of deep water volcanoes can be mapped using bathymetric surveys their internal structure and true volume remain enigmatic it is thus difficult to determine how deep water volcanoes grow we investigate 13 late miocene to quaternary deep water volcanoes that are imaged in 3d by seismic reflection data from the northern south china sea which allow us to quantify their external morphology and examine their internal structure these deep water volcanoes were emplaced in water depths 1 5 km are relatively small 15 mpa which are typical of water depths 1 5 km inhibited degassing and fragmentation of ascending magma and thus erupted lava this lack of degassing and fragmentation permitted effusive eruptions during the latter stages of volcanism our models for volcano growth in the deep submarine realm demonstrate the power of using 3d seismic data when investigating the internal structure and total volume of deep water volcanoes

atmospheric carbon dioxide and early eocene climate a general circulation modeling sensitivity study abstract the early eocene was the warmest time interval of the past 65 million years we have investigated the hypothesis that the warm climate of the early eocene may have been caused by higher than present levels of atmospheric carbon dioxide co2 we have used an atmospheric general circulation model the ncar genesis model coupled to a land surface model and a mixed layer ocean to examine the sensitivity of early eocene climate to varying levels of atmospheric co2 model cases contained a description of the early eocene earth and included either 300 560 or 1680 ppm atmospheric co2 climate responses to increased atmospheric co2 include 1 increased mean annual global temperature by 2 6 c and decreased latitudinal surface temperature gradients 2 maximum warming at high latitudes especially in the winter season 3 increased mean global precipitation 4 increased high latitude clouds in comparison with geological paleoclimate data the climate response to increased co2 does not appear to explain completely the early eocene latitudinal surface temperature gradient for example with the 1680 ppm co2 case high latitude oceans and continents are minimally warm enough to match paleoclimate data while low latitude regions are overly warm when compared to sea surface temperature reconstructions we conclude that co2 was very likely at least double the present level during the early eocene and contributed to the overall character of early eocene climate however consideration of increased poleward oceanic heat transport and or other factors may be required to produce model results that more closely agree with marine and terrestrial paleoclimate data especially at low latitudes

sequence stratigraphy of paralic coal bearing strata an overview abstract sequence stratigraphy arose in the late 1980s to fundamentally change the science of stratigraphy former practice of labeling formations and erecting stratigraphic columns gave place to a dynamic genetic stratigraphic analysis where the main concern is about understanding the history of sedimentation and to establish models able to predict facies born and mainly applied to an environment of petroleum prospecting and exploration sequence stratigraphy has gained entrance to other branches of sedimentary geology the present paper gives a short introduction to sequence stratigraphic concepts and shows an overview of its application on coal bearing strata two case studies one from the early permian coals of the parana basin brazil and one from the lower cretaceous coals of the western canada sedimentary basin illustrate the concepts

ambient effects on basalt and rhyolite lavas under venusian subaerial and subaqueous conditions both subaerial and subaqueous environments have been used as analog settings for venus volcanism to assess the merits of this the effects of ambient conditions on the physical properties of lava on venus the seafloor and land on earth are evaluated rhyolites on venus and on the surface of earth solidify before basalts do because of their lower eruption temperatures rhyolite crust is thinner than basalt crust at times less than about an hour especially on venus at later times rhyolite crust is thicker because of its lower latent heat relative to basalt the high pressure on the seafloor and venus inhibits the exsolution of volatiles in lavas vesicularity and bulk density are proportional so that lavas of the same composition should be more dense on the seafloor and less dense on land because viscosity depends partly upon the fraction of unvesiculated water in a melt basalts with the same initial volatile abundance will be least viscous on the seafloor and most viscous on land assuming the same preemptive h2o contents molten rhyolites on venus will have viscosities 10 that of rhyolites on land despite lower expected viscosities underwater flows are more buoyant and should have heights like subaerial and venusian lavas of the same composition and extrusive history in cases where the influence of crust is insignificant a volume of rhyolite will have a higher aspect ratio than the same volume of basalt no matter what the environment if flow rheology is dominated by the presence of strong crust aspect ratios differ little among environments or between compositions these analyses support a rhyolitic interpretation for the composition of venusian festooned flows and a basaltic interpretation for the composition of venusian steep sided domes although ambient effects are significant extrusion rate and eruption history must also be considered to explain analogous volcanic landforms on earth and venus

crystallization of mount st helens 1980 1986 dacite a quantitative textural approach quantitative measurements of crystal size distributions csds have been used to obtain kinetic information on crystallization of industrial compounds randolph and larson 1971 and more recently on hawaiian basalts cashman and marsh 1988 the technique is based on a population balance resulting in a differential equation relating the population densityn of crystals to crystal sizel i e at steady staten no exp l itg whereno is nucleation density g is the average crystal growth rate is the average growth time and the nucleation ratej nog csd inn vsl plots of plagioclase phenocrysts in 12 samples of mount st helens blast dacite and 14 samples of dacite from the 1980 1986 mount st helens dome are similar and averageg 9 6 1 1 10 3 cm andno 1 2 106 cm 4 reproducibility of the measurements was tested by measuring csds of 12 sections cut from a single sample in three mutually perpendicular directions precision of the size distributions is good in terms of relative but not necessarily absolute values 10 growth and nucleation rates for plagioclase have been calculated from these measurements using time brackets of 30 150 years growth ratesg are 3 10 10 12cm s and nucleation ratesj are 5 21 10 6 cm3 s g andj for fe ti oxides calculated from csd data areg 2 13 10 13 cm sec andj 7 33 10 5 cm3 s respectively the higher nucleation rate and lower growth rate of oxides resulted in a smaller average crystal size than for plagioclase sizes of plagioclase microlites 0 01 mm in the blast dacite groundmass have been measured from backscatter sem photographs nucleation of these microlites was probably triggered by intrusion of material into the cone of mount st helens in spring 1980 this residence time of 52 days gives minimum crystallization estimates ofg 1 3 10 11 cm s andj 9 16 1o3 cm3 s the skeletal form of the microlites provides evidence for nucleation and growth at high values of undercooling t relative to the phenocrysts a comparison of nucleation and growth rates for the two crystal populations phenocrysts vs microlites suggests that while growth rate seems to be only slightly affected by changes in t nucleation rate is a very strong function of undercooling a comparison of plagioclase nucleation and growth rates measured in the mount st helens dacite and in basalt from makaopuhi lava lake in hawaii suggests that plagioclase nucleation rates are not as dependent on composition groundmass textures suggest that plagioclase microphenocrysts crystallized at depth rather than in the conduit in the dome or after extrusion onto the surface most of this crystallization appears to be in the form of crystal growth coarsening of groundmass microphenocrysts at small degrees of undercooling rather than extensive nucleation of new crystals this continuous crystallization in a shallow magmatic reservoir may provide the overpressurization needed to drive the continuing periodic domebuilding extrusions which have been the pattern of activity at mount st helens since december 1980

the influence of topographic roughness on lava flow emplacement a quantitative understanding of the factors controlling lava flow emplacement is critical for both hazard assessment and mitigation and for the interpretation of past flow emplacement conditions the influence of topography with a vertical amplitude smaller than flow thickness i e substrate roughness is currently not accounted for in most flow emplacement models and hazard estimates here we measure the effect of substrate roughness on flow emplacement through experiments using analog fluids and molten basalt complementing recent work on the interaction of lava flows with obstacles taller than flow thickness we present results from three sets of analog experiments in which corn syrup polyethylene glycol and molten basalt were each extruded onto a sloping plane covered with a series of beds of varying grain sizes we find that flow front advance rates are impacted by bed roughness for all materials with decreases in average velocities by up to 50 with increases of substrate grain sizes by 5 100 times ranges analogous with topographic variations found in nature these decreases in flow front advance velocities are equivalent to up to an order of magnitude increase in fluid viscosity we interpret this velocity decrease to be caused by the movement of material into void spaces between substrate grains and by enhanced cooling through heat conduction to the substrate due to increased surface contact area the difference in advance velocity with increasing grain size diminishes with time after initial emplacement as a basal boundary layer is established additionally the experimental flow geometry measured by the complexity of the flow external perimeter became increasingly complex with increasing substrate grain size this effect will act to both slow the forward advance of lava flows and to create irregular emplacement paths of flows moving over rough surfaces we propose that flow emplacement models should be modified possibly through a calibrated effective viscosity term to account for bed roughness to increase accuracy in flow prediction and hazard estimation models

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

the implications of basalt in the formation and evolution of mountains on venus abstract the highland region of ishtar terra on venus has mountains that reach up to 11 km in height and are thought to be basaltic in composition assuming that dynamic uplift of crust to this height is unlikely we examine the topography produced by an isostatically supported thickening basaltic crust it is found that regardless of whether the crust thickens by crustal shortening or by volcanic construction the high density basalt eclogite phase transition is the limiting factor for producing significant elevation of the mountains the maximum height attained by basaltic mountains depends on the nature of the basalt eclogite phase transition without a phase transition a basaltic crust must thicken to greater than 100 km to reach heights over 10 km an instantaneous phase transition of basalt to eclogite allows a maximum topographic height of less than about 2 km however with a time lag of 100 ma owing to slow rates of solid state diffusion our calculations show that the mountains can reach elevations greater than 10 km only if they are less than 25 ma old higher temperatures within the venusian crust may decrease the extent of the stability fields of high density basalt phases and allow high topography if the thickening crust melts this can occur if the radioactive element concentrations measured on the surface of venus are uniformly distributed throughout the crust the crust thickens to greater than 65 km and the thickened crust is older than about 400 ma the conflicting results of a young age predicted for high basaltic mountains and an almost uniform surface age of 500 ma from crater populations coupled with similarities in bulk physical properties of venus and earth suggest that the basaltic surface composition found at several landing sites on the planet may not be representative of the entire crust we suggest that ishtar terra formed from the collision of continent like highly silicic cratons over a region of mantle downwelling lakshmi planum resulted from the thickening of a basaltic crust and the peripheral mountain belts formed from the collision of granitic cratons that were pulled toward a downwelling region of mantle

radar topography of domes on planetary surfaces abstract we investigate the possibility of measuring the heights and morphology of viscously emplaced domes using radar imagery we accurately reproduce the known height and shape of a terrestrial salt dome and estimate the heights of several venusian pancake domes to within a factor of two the terrestrial salt dome is consistent with a bingham flow while the much larger venusian pancake domes are consistent with a newtonian flow applying the same techniques to ganesa macula a potential cryovolcanic dome on titan we estimate a height between 2 0 4 9 km additional factors such as variable roughness and composition might account for some of the discrepancies observed

analysis of venusian steep sided domes utilizing stereo derived topography 1 the morphology and topography of 23 venusian steep sided domes are analyzed to examine possible emplacement mechanisms stereo radargrammetric techniques are used with magellan synthetic aperture radar image data 100 m resolution to generate digital elevation models for the domes 1 km horizontal resolution heights of the domes range from 390 to 1590 m aspect ratios height diameter range from 0 01 to 0 07 and volumes range from 73 to 1790 km 3 dome morphology varies along a continuous trend that is directly related to the aspect ratio domes with a low aspect ratio tend to be sunken in their centers whereas domes with higher aspect ratios have flat to convex surfaces domes with the highest aspect ratios have central peaks these trends are likely due to slight variations in the thickness of the crust and possibly effusion rates episodic emplacement is also inferred to be a significant process for the formation and growth of some of the domes in this sample

the role of unsteady effusion rates on inflation in long lived lava flow fields abstract the emission of volcanic gases and particles can have global and lasting environmental effects but their timing tempo and duration can be problematic to quantify for ancient eruptions where real time measurements are absent lava flows for example may be long lasting and their impact is controlled by the rate tempo and vigor of effusion these factors are currently difficult to derive from the geologic record but can have large implications for the atmospheric impact of an eruption we conducted a set of analogue experiments on lava flow inflation aiming at connecting lava morphologies preserved in the rock record to eruption tempo and dynamics through pulsating effusion rates inflation a process where molten material is injected beneath the crust of an active lava flow and lifts it upwards is a common phenomenon in basaltic volcanic systems this mechanism requires three components a a coherent insulating crust b a wide spread molten core and c pressure built up beneath the crust from a sustained supply of molten material inflation can result in a lava flow growing tens of meters thick even in flow fields that expand hundreds of square kilometers it has been documented that rapid effusion rates tend to create channels and tubes isolating the active part of the flow from the stagnant part while slow effusion rates may cause crust to form quickly and seize up forcing lava to overtop the crust however the conditions that allow for inflation of large flow fields have not previously been evaluated in terms of effusion rate by using peg 600 wax and a programmable pump we observe how by pulsating effusion rate inflation occurs even in very low viscosity basaltic eruptions we show that observations from inflating hawaiian lava flows correlate well with experimental data and indicate that instantaneous effusion rates may have been 3 times higher than average effusion rates during the emplacement of the 23 january 1988 flow at k lauea hawai i the identification of a causal relationship between pulsating effusion rates and inflation may have implications for eruption tempo in the largest inflated flows flood basalts

petrology palynology and organic geochemistry of eocene lignite of matanomadh kutch basin western india implications to depositional environment and hydrocarbon source potential abstract petrological palynological and organic geochemical investigations were undertaken to determine the source vegetation depositional conditions and hydrocarbon source potential of eocene matanomadh lignites from kutch basin western india the maceral study reveals that studied lignites are rich in huminite av 63 with sub ordinate amount of liptinite av 19 and low inertinite av 3 along with low to moderately high associated mineral matters av 15 the overall petrographic composition points to a lagoonal condition for the formation of these lignites the mean huminite reflectance values r r 0 28 0 34 av 0 31 as well as low rock eval t max av 417 c values for the seams suggest brown coal or lignitic stage rank for the studied lignites the palynological assemblages dominated by tropical angiospermic pollen suggest prevalence of warm humid tropical climate during the deposition of these lignites the total organic carbon toc content of lignites ranges between 26 and 58 wt whereas the toc content of the associated carbonaceous shales is around 4 wt the hydrogen index hi ranging from 23 to 452 mg hc g toc indicates that the lignite sequence has the potential to produce mixed oil and gaseous hydrocarbons on maturation the major pyrolysis products of lignites derived from curie point pyrolysis gc ms are straight chain aliphatics phenols and cadalene based c 15 bicyclic sesquiterpenoids the exclusive occurrence of c 15 bicyclic sesquiterpenoids suggests that these compounds are derived from dammar resin of angiosperm plants belonging to family dipterocarpaceae

maceral and geochemical characteristics of coal seam 1 and oil shale 1 in fault controlled huangxian basin china abstract seven samples of coal seam 1 and oil shale 1 from the fault controlled hangxiang basin have been analysed by coal petrographic and geochemical methods high huminite ratios and high contents of sesquiterpenoids and diterpenoids indicate that coal seam 1 and oil shale 1 are predominantly composed of terrestrial higher plant material two ternary diagrams of facies diagnostic macerals and biomarkers were used to interpret the depositional environments of organic matter in coal seam 1 and oil shale 1 in both diagrams coal seam 1 is plotted in the forest moor zone but the top sample of coal seam 1 shows an influence of transgressed sea water oil shale 1 is plotted in a transition zone from forest moor to open moor this indicates an increased abundance of lower plants and algal derived organic matter in oil shale 1 relative to coal seam 1 the boundary faults controlled the sedimentation in huangxian basin when the faults ceased to move the peat of coal seam 1 was formed when the faults became active again and the basin began to sink sea water flowed into the swamps at which time oil shale 1 was deposited

eruption of crystal mush and the formation of steep sided volcanic domes on venus insight from picritic bodies near marki cyprus abstract steep sided domes are one of the most striking volcanic landforms on venus they may also be key to determining the range of magmatic processes operating on venus as in contrast to all other volcanic landforms they likely represent eruption of viscous lava although there have been various explanations for the presence of high viscosity lavas on a planet dominated by effusive basaltic volcanism it is often assumed that they are silica rich this would necessitate either periodic large scale extensive fractionation of basaltic magma in the venusian crust or a mechanism for re melting an already silica enriched lower crust as such determining the origin of steep sided domes is important in constraining magmatic processes on venus and for understanding geological evolution of stagnant lid regime planets generally here we use observations from the marki region of the troodos ophiolite cyprus to propose an alternative model where steep sided domes form by eruption of crystal mush from the same magmatic systems which fed extensive basaltic terrains with which domes are associated steep sided volcanic landforms near marki represent extrusion of un eruptible extremely olivine rich mush onto the palaeo seafloor following cessation of widespread basaltic volcanism field relations suggest that these bodies formed by localised repeated extrusion of crystal mush fed by extensional faults tapping crustal magma chambers differential stress enabled eruption of viscous non newtonian magmas with crystal contents 50 vol which then built up volcanic edifices on the seafloor a similar much larger scale mechanism can explain many features of steep sided volcanic domes on venus including their intimate relationship with extensive basaltic terrains general morphology and dome spatial and temporal clustering this implies that domes share a common magmatic origin with the venusian basaltic crust rather than representing a discrete magmatic process and that they represent periods of magmatic quiescence it also implies that the contrasting morphology of these domes arises from a fundamental difference in eruptive style from widespread effusive basaltic magmatism to localised extensional fault controlled extrusion of crystal mush if correct this mechanism might also explain formation of steep sided volcanic edifices on other large stagnant lid regime planetary bodies

a laboratory investigation into the effects of slope on lava flow morphology abstract in an attempt to model the effect of slope on the dynamics of lava flow emplacement four distinct morphologies were repeatedly produced in a series of laboratory simulations where polyethylene glycol peg was extruded at a constant rate beneath cold sucrose solution onto a uniform slope which could be varied from 1 through 60 the lowest extrusion rates and slopes and highest cooling rates produced flows that rapidly crusted over and advanced through bulbous toes or pillows similar to subaerial toey pahoehoe flows and to submarine pillowed flows as extrusion rate and slope increased and cooling rate decreased pillowed flows gave way to rifted flows linear zones of liquid wax separated by plates of solid crust similar to what is observed on the surface of convecting lava lakes then to folded flows with surface crusts buckled transversely to the flow direction and at the highest extrusion rates and slopes and lowest cooling rates to leveed flows which solidified only at their margins a dimensionless parameter primarily controlled by effusion rate cooling rate and flow viscosity quantifies these flow types increasing the underlying slope up to 30 allows the liquid wax to advance further before solidifying with an effect similar to that of increasing the effusion rate for example conditions that produce rifted flows on a 10 slope result in folded flows on a 30 slope for underlying slopes of 40 however this trend reverses slightly owing to increased gravitational forces relative to the strength of the solid wax because of its significant influence on heat advection and the disruption of a solid crust slope must be incorporated into any quantitative attempt to correlate eruption parameters and lava flow morphologies these experiments and subsequent scaling incorporate key physical parameters of both an extrusion and its environment allowing their results to be used to interpret lava flow morphologies on land on the sea floor and on other planets

the lunar gruithuisen silicic extrusive domes topographic configuration morphology ages and internal structure abstract the gruithuisen domes situated on the western portion of the imbrium basin rim form three tall mountains nw gamma delta totaling 780 km3 in volume the shapes of the domes are significantly different from that of mare type domes elsewhere on the moon we use data from the lunar reconnaissance orbiter lro and kaguya missions lro lunar orbiter laser altimeter lunar reconnaissance orbiter camera diviner and the kaguya imager to characterize the domes and assess models for their origin the configuration of the domes steep slopes up to 18 20 and their specific remote sensing characteristics strong downturn in the uv and results from the m3 and diviner instruments suggest that the domes formed by eruptions of highly viscous lava the estimated surface volumes of the domes vary from 20 km3 nw dome to 290 km3 gamma dome to 470 km3 delta dome the domes occur on the portion of the imbrium basin rim that is overlain by ejecta from the post imbrium iridum crater in some areas relatively high albedo smooth volcanic plains are seen within the iridum ejecta near the gruithuisen domes and low albedo mare deposits surround and embay the domes and iridum crater dating of different units and features by crater counts indicates that impact melts from the iridum basin are 3 9 ga old the domes gamma and delta are 3 8 ga and the ages of the plains near the domes vary from 2 3 to 3 6 ga a fresh impact crater exposes the internal structure of the gamma dome the most prominent features on the wall of the crater are rough blocky layers that are typical of volcanic plains in the highlands and maria around the domes the layers are interleaved with fine grained materials of higher and lower albedo and the visible orientation of the layers changes over short a few hundred meters distances these characteristics of the internal structure of the dome are consistent with eruptions of high viscosity lava rough layers that alternated with possible explosive activity fine grained materials the spatial association of the gruithuisen domes with the highland lava plains resembles the situation in which bimodal volcanism occur on earth the terrestrial association can be due to either fractional crystallization in basaltic magma reservoirs or remelting of high silica crustal materials in the first case the evolved melts appear in later stages of volcanic activity and in the second case these melts are formed near the beginning of evolution of the magmatic systems the age estimates of the gruithuisen domes and the surrounding volcanic plains are more consistent with the crustal remelting scenario however remelting of primary anorthositic crust cannot readily produce the silica rich melts and requires the presence of pre existing granite like materials formation of the domes by fractional crystallization avoids this difficulty but requires explanation of the older age of the domes relative to the volcanic plains in the surroundings a third option is that the domes are unrelated genetically to the mare deposits

testing the silica leakage hypothesis with sedimentary opal records from the eastern equatorial pacific over the last 150 kyrs 1 we have measured 230th normalized opal fluxes in several cores from the eastern equatorial pacific eep to test the validity of the silica leakage hypothesis which purports that redistribution of silicic acid from the southern ocean to the low latitudes was responsible for a significant portion of the reduction in atmospheric carbon dioxide co2 during the last glacial period the silica leakage hypothesis predicts higher opal fluxes in the eep and lower opal fluxes in the southern ocean during periods of low atmospheric co2 these predictions are not borne by the sedimentary record during glacial oxygen isotope stage 2 ois 2 13 27 kyrs b p however we find a prominent opal flux maximum in the eep in the middle of ois 3 ca 40 60 kyrs bp coinciding with low opal fluxes in several cores from the subantarctic zone this observation is consistent with silica leakage from the southern ocean to the equatorial upwelling region during ois 3 when both low dust flux and extended sea ice could have contributed to limiting diatom productivity in the southern ocean since this event is not associated with a clear minimum in the vostok ice record of co2 its impact on atmospheric co2 appears to be small

reconstructing lava flow emplacement processes at the hot spot affected galapagos spreading center 95 w and 92 w 1 volcanic eruptions at mid ocean ridges mors control the permeability internal structure and architecture of oceanic crust thus establishing the foundation for the evolution of the ocean basins to better understand the emplacement of submarine lava flows at mors we have integrated submersible based geologic mapping with remote sensing techniques to characterize the lava flow morphology within previously mapped lava flow fields produced during single eruptive episodes at the galapagos spreading center gsc detailed attributes describing the surface geometry and texture of the lava flows have been extracted from high resolution sonar data and combined with georeferenced visual observations from submersible dives and camera tows based on signatures contained in these data a fuzzy logic based classification algorithm categorized lava flow morphology as pillows lobates or sheets the resulting digital thematic maps offer an unprecedented view of gsc lava morphology collectively covering 77 km2 of ridge axis terrain at a resolution of 2 m 2 m error assessments with independent visual reference data indicate approximately 90 agreement comparable to subaerial classification studies the digital lava morphology maps enable quantitative spatially comprehensive measurements of the abundance and distribution of lava morphologies over large areas of seafloor and within individual eruptive units a comparison of lava flow fields mapped at lower and higher magma supply settings 95 and 92 w respectively indicates that effusion rates increase along with magma supply and independent of spreading rate at the gsc although a complete range of eruptive behavior exists at each setting

arctic late paleocene early eocene paleoenvironments with special emphasis on the paleocene eocene thermal maximum lomonosov ridge integrated ocean drilling program expedition 302 we reconstruct the latest paleocene and early eocene 57 50 ma environmental trends in the arctic ocean and focus on the paleocene eocene thermal maximum petm 55 ma using strata recovered from the lomonosov ridge by the integrated ocean drilling program expedition 302 the lomonosov ridge was still partially subaerial during the latest paleocene and earliest eocene and gradually subsided during the early eocene organic dinoflagellate cyst dinocyst assemblages point to brackish and productive surface waters throughout the latest paleocene and early eocene dinocyst assemblages are cosmopolitan during this time interval suggesting warm conditions which is corroborated by tex86 reconstructed temperatures of 15 18 c inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower eocene spectral analysis reveals that the cyclicity recorded in x ray fluorescence scanning fe data from close to eocene thermal maximum 2 53 ma presence confirmed by dinocyst stratigraphy is related to precession within the lower part of the petm proxy records indicate enhanced weathering runoff anoxia and productivity along with sea level rise on the basis of total organic carbon content and variations in sediment accumulation rates excess organic carbon burial in the arctic ocean appears to have contributed significantly to the sequestration of injected carbon during the petm

magellan radar performance and data products the magellan venus orbiter carries only one scientific instrument a 12 6 centimeter wavelength radar system shared among three data taking modes the synthetic aperture mode images radar echoes from the venus surface at a resolution of between 120 and 300 meters depending on spacecraft altitude in the altimetric mode relative height measurement accuracies may approach 5 meters depending on the terrain9s roughness although orbital uncertainties place a floor of about 50 meters on the absolute uncertainty in areas of extremely rough topography accuracy is limited by the inherent line of sight radar resolution of about 88 meters the maximum elevation observed to date corresponding to a planetary radius of 6062 kilometers lies within maxwell mons when used as a thermal emission radiometer the system can determine surface emissivities to an absolute accuracy of about 0 02 mosaicked and archival digital data products will be released in compact disk cdrom format

comparison of the shapes and sizes of seafloor volcanoes on earth and pancake domes on venus the fact that flat topped pancake domes observed on venus resemble flat topped volcanoes on earth s seafloor suggests that volcanic processes on the seafloor and on venus may operate to construct volcanic forms with similar characteristics to test this the shapes and size distributions of terrestrial submarine volcanoes seamounts from several magmatic and tectonic provinces are quantitatively compared with those of venusian pancake domes seamount heights and diameters are highly correlated suggesting that there may be a universal mechanism for their growth the 2014 point sample mean of the height to diameter ratio is d 0 10 0 04 in contrast heights and diameters of 52 pancake domes exhibit no obvious trend and values of d are as much as three orders of magnitude smaller with a 52 point sample mean of d 0 02 0 03 seamounts with basal diameters db 10 km have flatness values ratio of top to bottom diameter that span the entire range between 0 pointed cone and 1 truncated cone larger sized seamounts tend to have small values of flatness and more pointed tops this is not true for pancake domes which show large flatnesses at all sizes additionally seamounts have distinctive profiles with their flank slopes increasing in gradient toward the summit flank slopes of pancake domes however commonly increase in gradient toward the base with respect to sizes the diameter distributions of the different seamount populations are consistent with a model in which the number of seamounts decreases exponentially with increasing diameter the diameter distribution of 126 pancake domes by contrast is more uniform its mean is db 22 13 km this size is at least an order of magnitude larger than the estimated characteristic diameters of the seamount populations based on the above results i conclude that seamounts have significantly different shapes and size distributions than venusian pancake domes that have been identified and measured to date this suggests that one or more of the variables e g magma composition crystallinity magma volume effusion rate cooling rate pre existing topography governing their formation differs in terms of shapes and size distributions the small db 20 km volcanic edifices first identified from venera data are good morphologic matches to seamounts and should be the focus of future work investigating the formation of comparable volcanic features in these two different planetary environments

early palaeogene in the south shillong plateau ne india local biostratigraphic signals of global tectonic and oceanic changes abstract the early palaeogene in the history of the earth is noted for large scale plate reorganisation believed to be associated with a changeover from the laramide tectonic regime old crustal configuration to the himalayan tectonic regime new crustal configuration this tectonic change possibly proved to be a turning point in the evolution of lithosphere and ushered in drastic changes in the physical environment and evolutionary course of biosphere in the cenozoic the consequent changes in the sedimentary environment and biotic development during early palaeogene have been pointed out for the indian ocean region this paper examines the biostratigraphic data of the early palaeogene late palaeocene middle eocene succession of the south shillong plateau in the light of climatic and oceanic changes and explores the possible role the regional tectonic changes may have played in shaping the course of environmental and biotic development preserved in the rock record of the sylhet limestone group an attempt has also been made to propose a model to explain the underlying tectonic changes in the shillong plateau the biostratigraphic data from the area of investigation indicate that the major stratigraphic sequences recognised in the sylhet limestone group can be broadly correlated with the stratigraphic succession of the early palaeogene identified in the indian ocean region the succession of the sedimentary facies in this region seems to be the result of sea level and climatic changes controlled by major tectonic reshuffling from this correlation it appears that the litho and biostratigraphic markers of the sylhet limestone were created by sea level and climatic events related to tectonic changes occurring in the adjoining indo burmese orogen as part of the large scale global plate reorganisation mentioned as above

mid atlantic ridge volcanism from deep towed side scan sonar images 25 29 n abstract we present deep towed side scan sonar mosaics of the inner valley floor of eight spreading segments at the slow spreading mid atlantic ridge between 25 and 29 n an analysis of these images which well resolve features a few tens of meters in size confirms that the multitude of small seamounts with diameters between 0 5 and 3 km identified on the inner valley floor from previously collected multibeam bathymetry data are volcanically constructed moreover these images reveal that these volcanoes have distinct surface morphologies not evident in the coarser resolution multibeam bathymetry maps 83 of the seamounts have a hummocky bulbous morphology the other 17 have a smooth morphology in addition to near circular seamounts small 1 2 km long volcanic ridges are abundant in our study regions and are not in general seen in the bathymetry maps we combine these new morphological data with existing models for the construction of the shallow oceanic crust to obtain a better understanding of the melt delivery system that builds the distinctive seafloor topography at the slow spreading mid atlantic ridge

tectonically driven late paleocene 57 9 54 7 ma transgression and climatically forced latest middle eocene 41 3 38 0 ma regression on the indian subcontinent abstract cenozoic era was the turning point in the geological history of the indian subcontinent when india experienced maximum isolation before it collided with asia and there occurred a great mountain building activity shaping the himalaya in the cenozoic era the sedimentation commenced in the late paleocene 57 9 ma in the pericratonic basins of the western india as well as the foreland basins of the himalaya that marks the beginning of a major transgression on the indian subcontinent till now it is not sure whether this transgression was forced by tectonics or climate we have interpreted that the primary driver for this transgression was the tectonics that marks the beginning of the india asia convergence a major regression of similar magnitude occurred during latest middle eocene 41 3 38 0 ma that corresponds to global sea level fall this regression is global and can be identified even in the cenozoic basins developed within the african plate it is interpreted that this regression was driven by the global cooling during latest middle eocene late eocene possibly associated with the nucleation of the antarctica ice sheets coupled with the uplift of the himalaya

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

hydrogen isotope evidence for extrusion mechanisms of the mount st helens lava dome from october 1980 to october 1986 the dacite lava dome at mount st helens grew through the accumulation of more than 15 separate lobes during extrusive episodes that lasted from 1 to 24 days except for an anomalous period of continuous growth throughout most of 19831 over these six years the growth rate was generally volume predictable that is the amount of lava added to the dome in a given eruption was roughly proportional to the time since the preceding extrusion2 these well documented eruptions were separated by repose intervals lasting from several months to more than a year2 in an attempt to identify the triggering mechanisms for these periodic eruptions we have used hydrogen isotope analyses to determine water content and deuterium content for 18 samples of the mount st helens dome dacite these isotope data the first ever collected from an active lava dome suggest a steady state process of magma evolution combining crystallization induced volatile production in the chamber with three different degassing mechanisms closed system volatile loss in the magma chamber open system volatile release during ascent and kinetically controlled degassing upon eruption at the surface the data suggest that future dome building eruptions may require a new influx of volatile rich magma into the chamber

petrographic characteristics of coal from the lati formation tarakan basin east kalimantan indonesia the present paper entails the petrographic characterization on limited coal samples drawn from the tarakan basin eastern kalimantan indonesia these coals contain a high concentration of huminite which in turn is dominated by telohuminite as a result of telohuminite content they have high gi and tpi values they contain low concentrations of liptinite and inertinite macerals the dominant microlithotype is vitrite based on the macerals and microlithotypes of these coals their paleodepositional environment has been reconstructed accordingly it is deciphered that these coals have originated under telmatic condition there was predominance of wood derived tissues and increased subsidence rate prevailed in the basin moreover during the time of their evolution there were alternate phases of oxic and anoxic moor conditions with intermittent moderate to high flooding in the basin

petrographic characteristics and carbon isotopic composition of permian coal implications on depositional environment of sattupalli coalfield godavari valley india abstract the present paper entails a study carried out on selected samples of coal and carbonaceous shales of permian age from the sattupalli open cast coal mine of godavari valley andhra pradesh to know their petrographic and chemical characteristics based on these characteristics the depositional environment has also been discussed the study reveals that these coals are sub bituminous in rank and are chemically characterized by low to medium moisture 4 3 to 8 6 wt and volatile matter 24 5 to 32 6 wt while the ash yield varies between 16 4 and 35 3 wt petrographically these coals are rich in inertinite liptinites occur in very small concentration collotelinite collodetrinite and vitrodetrinite are the main vitrinite macerals whereas fusinite inertodetrinite and semi fusinite constitute the major proportion of inertinites mean 13c value measured for coal is 22 58 0 20 and for carbonaceous shale it is 23 64 0 57 while in the organic matter of barakar sandstones the 13c is 25 2 2 1 dry periods are reflected by the abundance of inertinite in some samples while more anoxic conditions are indicated by high concentration of vitrinite in some samples seam ii of sattupalli coalfield initially formed in dry condition and gradually flooding took place due to rise in the water table during the formation of the upper part of the seam again a relatively dry phase prevailed moreover a positive correlation of 13corg with toc and a negative one with tic indicate that 13corg is being modified by 13cdic

granite a planetary point of view the telluric planets and the asteroid belt display the same internal structure with a metallic inner core and a silicate outer shell experimental data and petrological evidence in silicate systems show that granite can be produced through all types of magmatic processes on moon 4 4 3 9 ga granite clasts displaying dry mineral assemblages correspond to discrete intrusive events large k ca enrichment and low ree abundances in granite relative to kreep are consistent with silicate liquid immiscibility a process observed in melt inclusions within olivine of lunar basalts on mars black and white rhythmic layers observed on the tharsis rise along the flanks of valles marineris and the peripheral scarps of the tharsis montes giant volcanoes suggest the eruption of possibly felsic pyroclastites samples analysed in the mars pathfinder landing site yield basic to intermediate 45 to 62 wt sio2 compositions though no granites were found so far in the martian snc meteorites a component close to terrestrial continental granitic crust is inferred from trace element and isotope systematics like the martian northern hemisphere venus has suffered extensive volcanic resurfacing whereas folded and faulted areas resemble terrestrial continents the hypothesis of a granitic component is again tantalizing finally extra terrestrial granite is also found as enclaves within iron meteorites and ordinary chondrites granite a major component of the earth s crust can be generated in all geodynamic settings the low density of granite favours continental accretion thus the occurrence or absence of granite and of associated silicic volcanism within the other telluric planets is not a trivial question granite is generally thought to be produced through wet processes lunar evidence shows that dry conditions may apply as well in venus a large planet with high rates of magma production it is speculated that significant volumes of granite can develop

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

the unique radar properties of silicic lava domes 1 silicic lava domes exhibit distinct morphologic characteristics at scales of centimeters to kilometers multiparameter radar observations capture the unique geometric signatures of silicic domes in a set of radar scattering properties that are unlike any other natural geologic surfaces backscatter cross section values are among the highest observed on terrestrial lava flows and show only a weak decrease with incidence angle cross polarization backscatter hv shows a unique behavior increasing with increasing wavelength circular polarization ratios are relatively high in the 0 3 0 95 range and increase with increasing wavelength field measurements of boulder size frequency distributions and microtopography indicate that silicic dome surfaces are among the roughest ever measured rms heights at a 1 m lateral scale range from 13 cm to 50 cm rms slopes at 1 m spacing range from 12 to 43 degrees modeling of the scattering behavior suggests it results from a combination of rough surface facet scattering and scattering from block edges that act as a random collection of dipoles the unusual wavelength dependence of the radar parameters appears to result from a higher component of edge scattering at large wavelengths producing for example higher cross polarized backscatter at p band 68 cm steep sided volcanic domes on venus superficially resemble terrestrial silicic domes in plan view gross morphology but few similarities remain when the radar scattering and three dimensional shapes of the features are compared the unique radar scattering properties suggest that such volcanic surfaces can be identified with multiparameter radar observations in future planetary radar missions and in active terrestrial volcanoes where dome development can represent serious hazards

geomorphology of the central red sea rift determining spreading processes highlights the red sea rift overall morphology is typical for ultra slow spreading ridges distribution of various volcanic morphotypes correlates with mantle temperatures spreading perpendicular ridges indicate stable magma focusing over 8 12 my warm mantle under the rsr prohibits the occurrence of oceanic core complexes specific characteristics of the rsr morphology are related to its young age abstract continental rifting and ocean basin formation is occurring today in the red sea providing a possible modern analogue for the creation of mid ocean ridges yet many of the seafloor features observed along the axis of the red sea appear anomalous compared to ancient and modern examples of mid ocean ridges in other parts of the world making it unclear until recently whether the red sea is truly analogous recent work suggests that the main morphological differences between the red sea rift rsr and other mid ocean ridges are due to the presence and movement of giant submarine salt flows which blanket large portions of the rift valley and thereby the oceanic crust using ship based high resolution multibeam bathymetry of the central rsr between 16 5 n and 23 n we focus here on the rsr volcanic terrains not covered by salt and sediments and compare their morphologies to those observed along slow and ultra slow spreading ridges elsewhere regional variations in style and intensity of volcanism can be related to variations in volcanic activity and mantle heat flow the red sea oceanic seafloor shows typical features of mature ultra slow spreading mid ocean ridges such as 2nd order discontinuities overlapping spreading centres and magma focussing in the segment centres forming spreading perpendicular volcanic ridges of thick oceanic crust the occurrence of melt salt interaction at locations where salt glaciers blanket the neovolcanic zone and the absence of large detachment faults are unique features of the central rsr these features can be related to the young character of the red sea and may be applicable to all young oceanic rifts associated with plumes and or evaporites thus the rsr falls in line with ultra slow spreading mid ocean ridges globally which makes the red sea a unique but highly important type example for initiation of slow rifting and seafloor spreading and one of the most interesting targets for future ocean research

a pyroclastic flow deposit on venus explosive volcanism on venus is severely inhibited by its high atmospheric pressure and lack of water this paper shows that a deposit located near 16 s 144 e here referred to as scathach fluctus displays a number of morphological characteristics consistent with a pyroclastic flow deposit these characteristics particularly its lack of channelisation and evidence for momentum rather than cooling limited flow length contrast with fissure fed lava flow deposits the total erupted volume is estimated to have been between 225 km3 and 875 km3 but this may have been emplaced in more than one event interaction between scathach fluctus and a small volcanic cone constrain the flow velocity to 48 m s 1 and plausible volatile concentrations to at least 1 8 wt h2o 4 3 wt co2 or 6 1 wt so2 the latter two implying magma sourced directly from the mantle the deposit has radar characteristics particularly an exponential backscatter function that are similar to those of nearly half the planetary surface implying that pyroclastic deposits may be much more common on venus than has been recognised to date and suggesting both a relatively volatile rich mantle and a volcanic source for atmospheric so2

multiple early eocene hyperthermals their sedimentary expression on the new zealand continental margin and in the deep sea the paleocene eocene thermal maximum petm ca 55 5 ma was a geologically brief interval characterized by massive influx of isotopically light carbon extreme changes in global climate and profound variations in earth system processes an outstanding issue is whether it was an isolated event or the most prominent example of a recurring phenomenon recent studies of condensed deep sea sections support the latter but this finding remains uncertain here we present and discuss lithologic and carbon isotope records across two lower eocene outcrops on south island new zealand the petm manifests as a marl rich horizon with a significant negative carbon isotope excursion cie above in sediment deposited between 54 and 53 ma are four horizons with similar though less pronounced expressions marl beds of all five horizons represent increased terrigenous sedimentation presumably linked to an accelerated hydrological cycle five corresponding clay rich horizons and cies are found in deep sea records although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution the presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of 13 c depleted carbon during the early eocene

cool equatorial terrestrial temperatures and the south asian monsoon in the early eocene evidence from the gurha mine rajasthan india abstract early eocene 55 52 ma laminated lacustrine sediments overlying lignites in the gurha mine 27 87398 n 72 86709 e rajasthan india yield a diversity of fossil leaves flowers fruits seeds and insects clamp multivariate foliar physiognomic analysis of two horizons separated by an estimated several tens of thousands of years of deposition indicates cool equatorial 10 n temperatures and a pronounced monsoon signature a lower assemblage consisting of 54 leaf morphotypes and an upper assemblage of 57 leaf forms yielded mean annual temperatures mat of 24 7 and 23 9 c respectively the uncertainty 2 82 c means these temperature regimes are identical despite few similarities in the morphotypes between the two assemblages the mean annual range of temperature mart was approximately 9 7 c for both assemblages when corrected for evapotranspirational cooling these temperature regimes are similar to those experienced today at 10 n on the west coast of india and surprisingly cool for the tropics at a time of extreme global warmth growth was year round the tropical to paratropical fossil floras also suggest a moist regime 80 annual relative humidity and high mean annual precipitation of 1800 mm for both assemblages but with a pronounced wet dry seasonality indicative of a pronounced monsoonal regime the lower assemblage has a stronger monsoon index 11 8 than the upper assemblage 8 8 the two assemblages seem to have been deposited less than 100 ka apart this suggests that not only a pronounced south asian monsoon existed when india and asia first made contact but also a variation in monsoon strength existed that cannot be ascribed to tectonic drivers

terrestrial carbon isotope excursions and biotic change during palaeogene hyperthermals the earth s climate between 60 and 50 million years ago was punctuated by several abrupt warming events the largest of these being the palaeocene eocene thermal maximum carbon isotope records from the bighorn basin wyoming document these events in the terrestrial realm and show a consistent scaling between marine and terrestrial records across the three main events

petrographic characteristics and depositional conditions of eocene coals of platform basins meghalaya india abstract the coal deposits of meghalaya occur in the lakadong sandstone 25 250 m thick of eocene age the coal bearing formations are understood to have been deposited over platform areas in estuarine and lagoonal environments and subjected to recurrent marine transgressions and regressions during the eocene period there are three major groups of coalfields in meghalaya viz garo hills west daranggiri and siju coalfields khasi hills langrin and mawlong shella coalfields and minor coalfields laitryngew cherrapunji and bapung coalfields pillar coal samples have been collected from 10 seams at 15 locations and have been subjected to a detailed petrographic examination for their characterization an effort has been made to trace the path of their evolution based on coal petrography based models the quantitative petrographic analysis shows that these coals are vitrinite rich 45 0 92 9 mean 73 4 mmf basis with low concentration of inertinite 0 0 13 8 mean 3 0 mmf basis whereas the liptinite occurs in appreciable concentration 5 5 53 1 mean 22 5 mmf basis further these coals are rich in vitrite 51 6 100 mean 78 3 mmf basis the volatile matter from 38 5 to 70 0 d a f and vitrinite reflectance rom from 0 37 to 0 68 characterize these coals as per german din and north american classification approximately as sub bituminous c to high volatile c bituminous the occurrence of teleutospore single double and triple celled suggests that these coals have originated from a characteristic tertiary flora the maceral and microlithotype composition in the coal petrography based depositional models suggest that the coals of garo hills were formed in reed to open water swamps in telmatic to limnic conditions the coals of khasi hills were dominated by forest swamps and telmatic to limno telmatic conditions in addition the occurrence of large size resins suggests prolific growth of conifers in the swamps

progressive growth of the cerro bayo cryptodome chachahuen volcano argentina implications for viscous magma emplacement cryptodome and dome collapse is associated with volcanic hazards such as explosive eruptions pyroclastic flows and volcanic edifice collapse study of the growth and evolution of volcanic domes

comparison of flat topped stellate seamounts on earth s seafloor with stellate domes on venus using side scan sonar and magellan synthetic aperture radar abstract the diameters of many domes on venus imaged by the magellan synthetic aperture radar sar are an order of magnitude larger than terrestrial subaerial domes however surveys of the seafloor using sonar imaging systems such as gloria geological long range inclined asdic and seabeam have revealed flat topped volcanic features with similar diameters volumes and slope angles suggested analogies between domes on venus and seamounts on the northern east pacific rise and off hawaii have been tested by d k smith j volcanol geotherm res 73 1996 47 64 using comparisons of size and shape and significant differences identified gloria images of flat topped seamounts near hawaii show them to have stellate planforms over half of the total population of 375 domes on venus have been modified and many have stellate planforms we have focused on the similarities in stellate planforms between flat topped seamounts and modified domes on venus we have used gloria sonar and magellan radar data to constrain the formation and evolution of both flat topped seamounts on the ocean floor and volcanic domes on venus to see if the processes that formed them are similar we propose that flat topped seamounts on the hawaiian ridge are built on sediments overlying the oceanic crust and that available evidence supports three processes that can form stellate margins 1 radial dike intrusions related to flank rift zones 2 dike intrusions which cause slope failures and 3 gravitational slope failures unrelated to intrusions for venus where low erosion rates and the absence of a sediment layer results in lavas being emplaced directly onto the crust the available evidence supports stellate margins originating by gravitational slope failures unrelated to diking though intrusions cannot be ruled out with existing data

venus volcanism initial analysis from magellan data magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of venus high resolution imaging data reveal evidence for intrusion dike formation and cryptodomes and extrusion a wide range of lava flows also observed are thousands of small shield volcanoes larger edifices up to several hundred kilometers in diameter massive outpourings of lavas and local pyroclastic deposits although most features are consistent with basaltic compositions a number of large pancake like domes are morphologically similar to rhyolite dacite domes on earth flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas perhaps komatiites may be present volcanism is evident in various tectonic settings coronae linear extensional and compressional zones mountain belts upland rises highland plateaus and tesserae volcanic resurfacing rates appear to be low less than 2 km 3 yr but the significance of dike formation and intrusions and the mode of crustal formation and loss remain to be established

stratigraphic and geographic distribution of steep sided domes on venus preliminary results from regional geological mapping and implications for their origin analysis of the stratigraphic position of 44 steep sided domes in a global band of c1 midrs at 30 n latitude shows that in a region representing over 11 of the surface of venus the vast majority of steep sided domes are closely associated stratigraphically with shield plains psh a unit characterized by a very high abundance of small shields of apparent basaltic extrusive origin previously reported heterogeneities in areal and altitude distribution are now more plausibly interpreted in terms of formation in association with this unit and burial by subsequent regional plains units measurement of abundances of steep sided domes presently exposed in shield plains and extrapolation to areas below younger units suggest that over a thousand of these features may have formed originally interpretation of the mode of formation of the steep sided domes in the context of these new data favors hypotheses for their origin which call on remelting of basaltic crust to produce more silica rich magmas occurrences of some steep sided domes in association with summits of large shields e g tepev mons and sapas mons indicate that other mechanisms of dome formation e g evolution of magma reservoirs have also operated at other times in the history of venus

optical properties of some tertiary coals from northeastern india their depositional environment and hydrocarbon potential abstract in northeastern india the coalfields of arunachal pradesh assam and nagaland are disposed along a linear belt of overthrusts known as the belt of schuppen where tertiary strata have been folded and dispersed into a number of thrust slices the coal bearing sediments in this belt are associated with the baragolai and tikak parbat formations of the barail group oligocene in meghalaya the tertiary sediments were deposited on a stable shelf along the periphery of the shillong plateau they are almost undisturbed and sub horizontal in attitude the coal seams are associated with the sylhet tura formations palaeocene of the jaintia group the chemical properties of these coals show characteristics of both low on volatile matter content and high on moisture and calorific value ranks the coals have a low softening temperature and a high swelling index volatile matter hydrogen and sulphur contents besides having the highest tar yield among indian coals the syncrude produced from these coals shows similarities with the identical fraction of crude oil from nahorkatiya oilfield assam the coals from the belt of schuppen and meghalaya are non banded and bright in nature microscopically their humic components are strongly decomposed with a common to frequent association of framboidal pyrite and calcite concretions the coals are vitrinite rich 52 0 80 0 with moderate amounts of liptinite macerals 5 8 16 2 the inertinite content is low 4 6 11 0 to occasionally high 30 0 fluorescing vitrinite and liptinite macerals constitute 46 5 to 83 5 by volume m m f perhydrous vitrinite liptodetrinite and resinite are the most common fluorescing macerals the rank of the coal samples r 0 max 0 57 0 74 ranges between high volatile bituminous c and b stages the assam coals are higher in rank than those of nagaland and meghalaya in northeastern india during the palaeocene and oligocene epochs peat swamps formed in situ from tropical mangrove rich angiospermous forest vegetation the palaeocene coals in meghalaya were formed in estuaries or lagoons however the coal forming phase ceased shortly due to prolonged marine transgression the oligocene coals in the belt of schuppen were formed during a regressive phase in back water lagoons or brackish water swamps on a prograding delta complex the hydrocarbon potential mg ch g c org of the coal samples from northeastern india has been theoretically deduced on the basis of their kerogen types following mukhopadhyay et al 1985 the presumed hydrogen index varies from 250 to 430 and 300 to 470 mg ch g c org respectively for coals in the belt of schuppen and meghalaya evidence indicates that in arunachal pradesh assam and nagaland oil has been generated from kerogen types ii b and ii a in the oligocene mudstone siltstone shale association of the coal measures of barail group in meghalaya no oil is known so far nevertheless the predominance of kerogen types ii a and ii b in coals indicates a good oil potential in the palaeocene sediments of the jaintia group

production preservation and prediction of source rock facies in deltaic settings abstract this article hypothesizes that production and preservation of source rock type facies in deltaic systems both landward and seaward of a coastline is mutually exclusive time successive and related to the dynamics of relative sea level sedimentologic research in the holocene mississippi and rhone delta complexes suggests that rheotrophic peats and associated organic rich beds preferably accumulate in the accommodation space created behind landward stepping shorelines in a transgressive systems tract tst such a setting also allows for a sufficient supply of recharging fresh nutrient rich groundwater into the peat forming mires kosters e c suter j r 1993 facies relationships and systems tracts in the late holocene mississippi delta plain journal of sedimentary petrology 63 4 727 733 independently carried out quantitative paleoecological studies in the same delta systems and in addition in the orinoco and po deltas suggest that in a progradational setting highstand systems tract hst seasonally discharged nutrient and sediment laden river waters on the shelf may give rise to anoxia or dysoxia subsequent overfertilization of the shelf leads to accumulation of organic rich mud belts on the shelf vanderzwaan g j jorissen f j 1991 biofacial patterns in river induced anoxia in tyson r v pearson t h eds modern and ancient continental shelf anoxia geological society of london special publication no 58 pp 65 82 thus production and preservation of source rock type facies landward of a shoreline as peats and related sediments is preferred in a tst when accommodation space and nutrient supply are landward of the shoreline vice versa production and preservation of such facies seaward of a shoreline as organic rich shelf muds occurs preferentially in a highstand systems tract in that situation accommodation space is on the shelf where river fed nutrients are supplied as well this hypothesis suggests further potential for application of sequence stratigraphic concepts for improved understanding of the occurrence of source rock type facies

palynofacies characterization for evaluation of hydrocarbon source rock potential of lower paleogene thanetian ypresian sub surface sediments of barmer basin western rajasthan india abstract this paper deals with the hydrocarbon source rock evaluation and depositional environment of lower paleogene sub surface sediments from borehole mmk 26 of barmer basin rajasthan hydrocarbon potential of these sediments are estimated on the basis of plant derived sedimentary organic matter som analysis the palynofacies analysis indicate that the sediments are rich in organic matter with amorphous organic matter constituting the majority of the som in the lower part of the borehole where as the phytoclasts dominate in the upper part the dominance of sapropelic facies amorphous organic matter at a depth of 152 m and below suggests that these sediments are a good source for hydrocarbon generation further the categorized palynofacies components are plotted on tyson s amorphous organic matter phytoclast palynomorph diagram which reveal that the studied sediments are characterized by type ii oil generating and type iii kerogen deposited in a dysoxic anoxic shelf thermal alteration index tai values were determined to asses the organic maturity of the sediments and a maturation value of 2 80 3 0 for the lower part of the bore core suggest that the sediments have attained an optimum maturation level to produce hydrocarbons the increasing frequency of marine palynomorphs in association with continental components indicates a transgressive phase of sea level during the deposition of the studied sediments

submarine analogs to venusian pancake domes abstract the morphology and dimensions of the largediameter steep sided flat topped pancake domes on venusmake them unlike any type of terrestrial subaerial volcano comparisons between images of hawaiian seamounts andpancake domes show similarities in shapes and secondaryfeatures the morphometry of pancake domes is closer to thatof pacific seamounts than subaerial lava domes consideringboth morphology and morphometry seamounts seem a betteranalog to the pancake domes the control of volatileexsolution by pressure on venus and the seafloor can causelavas to have similar viscosities and densities although thelatter will be counteracted by high buoyancy underwater however analogous effects of the venusian and seafloorenvironments alone are probably not sufficient to producesimilar volcanoes rather venusian lavas of variouscompositions may behave like basalt on the seafloor ifappropriate rates and modes of extrusion and planetary thermalstructure are a so considered introduction

formation of submarine flat topped volcanic cones in hawai i high resolution bathymetric mapping has shown that submarine flat topped volcanic cones morphologically similar to ones on the deep sea floor and near mid ocean ridges are common on or near submarine rift zones of kilauea kohala or mauna kea mahukona and haleakala volcanoes four flat topped cones on kohala were explored and sampled with the pisces v submersible in october 1998 samples show that flat topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage similarly shaped flat topped cones on the northwest submarine flank of ni ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage submarine postshield stage eruptions on hilo ridge mahukona hana ridge and offshore ni ihau form pointed cones of alkalic basalt and hawaiite the shield stage flat topped cones have steep 25 sides remarkably flat horizontal tops basal diameters of 1 3 km and heights 300 m the flat tops commonly have either a low mound or a deep crater in the center the rejuvenated stage flat topped cones have the same shape with steep sides and flat horizontal tops but are much larger with basal diameters up to 5 5 km and heights commonly greater than 200 m the flat tops have a central low mound shallow crater or levees that surrounded lava ponds as large as 1 km across most of the rejuvenated stage flat topped cones formed on slopes 10 and formed adjacent semicircular steps down the flank of ni ihau rather than circular structures all the flat topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades these and other submarine volcanic cones of similar size and shape apparently form as continuously overflowing submarine lava ponds a lava pond surrounded by a levee forms above a sea floor vent as lava continues to flow into the pond the lava flow surface rises and overflows the lowest point on the levee forming elongate pillow lava flows that simultaneously build the rim outward and upward but also dam and fill in the low point on the rim the process repeats at the new lowest point forming a circular structure with a flat horizontal top and steep pillowed margins there is a delicate balance between lava heat supply to the pond and cooling and thickening of the floating crust factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents moderate to high confining pressure at moderate to great ocean depth long lived steady eruption years to decades moderate effusion rates probably ca 0 1 km3 year and low but not necessarily flat slopes with higher effusion rates sheet flows flood the slope with lower effusion rates pillow mounds form hawaiian shield stage eruptions begin as fissure eruptions if the eruption is too brief it will not consolidate activity at a point and fissure fed flows will form a pond with irregular levees the pond will solidify between eruptive pulses if the eruption is not steady lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones as occurs during the post shield stage the steady effusion of lava on land constructs lava shields which are probably the subaerial analogs to submarine flat topped cones but formed under different cooling conditions

early eocene equatorial vegetation and depositional environment biomarker and palynological evidences from a lignite bearing sequence of cambay basin western india abstract an investigation of palaeofloral distribution with depositional environment and palaeoclimatic condition of western indian subcontinent during early eocene period has been carried out from a lignite bearing succession of cambay basin western india the study of biomarkers palynological remains and petrography is taken as proxies for providing supportive evidence for our inference the petrographic results reveal that the sediments are thermally immature and coalification was extended up to the lignitic stage low rank b the palynological results show the dominance of angiosperms mainly members belonging to the arecaceae family throughout the studied section triterpenoids with oleanane ursane and lupane structure in extractable organic matter are derived from angiosperm wax pollen grains spinizonocolpites proxapertites dipterocarpuspollenites albertipollenites retipollenites arengapollenites lakiapollis and longapertites with pteridophyte spores and fungal fruiting bodies confirm the prevalence of tropical to subtropical climate during the deposition of the sediments sesquiterpenoids like longifolene 12 methanoazulene cadinane and selinene together with amyrin derivatives are the indicator of dipterocarpaceae family that grows in the extant tropical rain forests in se asia appearance of dinoflagellate cysts and the predominance of lower molecular weight part in n alkane series with the signature of submerged floating vegetation in the shale horizon indicate marine influence in the younger part of the mine section the presence of mangrove pollen such as spinizonocolpites proxapertites and acanthotricolpites further suggests that the lignite bearing sequence was deposited in marshy marginal marine environment

petrographyof some fraser river delta peat deposits coal maceral and microlithotype precursors in temperate climate peats abstract peat deposits on the recent lobe of the fraser river delta british columbia have accumulated in a variety of depositional settings the study of the decomposition of the plant components associated with each depositional area has enabled prediction of the occurrence and distribution of the precursors of the loal macerals and microlithotypes on inactive portions of the distal lower delta plain thin sedge grass peats ave developed these peats were influenced by marine conditions near the base and freshwater conditions higher in the section a high ratio of cellulose to lignin in marsh plants and limited exposure of these tissues to desiccation and oxidation prodcue primarily desmocollinite smaller amounts of cernite cutinite and alganite origginate from algal and sedge lipids in the transition to freshwater peats oxyfusinite pyrofusinite and micrinite partially replace former exinite and vitrinite group maceral precursors subsequent transgression by marine waters has further promoted decomposition of the peat laterally extensive but thin and discontinouus coal seams which would develop from such peat will contain vitrite bands near the base and grade upsection into interlamlaminated durite and vitrinertite peats deposited between the upper and lowerdelta plain originate from brackish water as such earliest peat horizons contain similar maceral compositions to thoce encountered in distal delta plain deposits crevasse and fire splays disrupt gradational changes in fabric upsection and along channel margins flooding by oxygenated neutral ph waters followed by extended periods of desicaation result in increases of inertodetrinite macrinite sclerotinite and oxyfusinite interlaminated durites and vitrinertites will form common microlithotypes interbedded bands of telinite cutinite and cerinite are produced by later freshwater sedge grass peat accumulations in this biofacies clarite replaces durite after colonization by sphagnum lignin rich tissues from ericaceous shrubs and pinus contorta provide precurssors for subernnite telocollinite and telinite stumps of massive telinite interrupt these banded macerals coal seams originating from such peats would be thick laterally extensive and characterized by vitrite with laminae of liptite and lenses of clarite in the upper part

volcanic constructs on ganymede and enceladus topographic evidence from stereo images and photoclinometry paul m schenklunar and planetary institute houston texasjeffrey m moorespace sciences division and the seti institute nasa ames research center moffett field californiaabstract the morphology of volcanic features on ganymede differs significantly from that onthe terrestrial planets few if any major volcanic landforms such as thick flows or shieldvolcanoes have been identified to date using new stereo voyager images we have searchedganymede for relief generating volcanic constructs we observed seven major types of volcanicstructures including several not previously recognized the oldest are broad flat topped domespartially filling many older craters in dark terrain similar domes occur on enceladus togetherwith smooth dark deposits these domes indicate that the volcanic history of the dark terrain iscomplex bright terrain covers vast areas although the style of emplacement remains unclear smooth bright materials embay and flood older terrains and may have been emplaced as low viscosity fluids associated with smooth bright material are a number of scalloped shaped semi enclosed scarps that cut into preexisting terrain in planform these structures resemble terrestrialcalderas the youngest volcanic materials identified are a series of small flows that may haveflooded the floor of the multiring impact structure gilgamesh forming a broad dome theidentification of volcanic constructs up to 1 km thick is the first evidence for extrusion ofmoderate to high viscosity material on ganymede viscosity and yield strength estimates for thesematerials span several orders of magnitude indicating that volcanic materials on ganymede have arange of compositions and or were extruded under a wide range of conditions and or eruptive styles introductionthe voyager survey of the outer solar system has revealedan astonishing variety of endogenic landforms on the surfacesof icy satellites despite extensive endogenic resurfacing ofsomc satellites for example ganymede enceladus andtriton volcanism on these surfaces has little topographicexpression we do not see massive volcanic edifices similarto olympus mons or mauna kea even the best putativeexamples of volcanic landforms seen on ariel miranda triton and enceladus exhibit rarely more than 1 2 km ofrelief jankowski and squyres 1988 pozio and kargel 1989 schenk 1991a croft et al 1995 this may berelated to the soft theology of ice see poirier 1982 durham et al 1983 and kirby et al 1987 or torheology and volcanic styles peculiar to icy petrologicsystems e g kargel 1991 kargel et al 1991 well over half of the surface of ganymede radius 2634 kin has been covered by endogenic effusions it is now consideredlikely that ganymede experienced one or more episodes ofchaotic orbital behavior malhotra 1991 possiblyresulting in tidal heating volcanic resurfacing constitutes arecord of ganymede s compositional and thermal evolution andmay record some of these putative tidal heating events yetthis satellite has been the subject of morphological study for15 years without the unambiguous detection of relief copyright 1995 by the american geophysical union paper number 95je01854 0148 0227 95 95je 01854505 00generating volcanic constructions on its landscape the styleof emplacement and composition of those volcanic depositsthat have been identified remains unclear on any planetary surface volcanic and other nonimpactconstructs can be difficult to recognize in spacecraft images particularly those obtained under high sun conditions e g malin 1978 topography is especially low on the galileansatellites and imaging resolution is at best 500 m pixel major local albedo variations on ganymede further complicategeologic and topographic mapping with these problems inmind we have undertaken the production of stereo pairs ofvoyager images where coverage permits to aid in the searchfor and characterization of volcanic landforms on ganymede ssurface in addition to an examination of previously identifiedvolcanic materials we report the discovery of severalpreviously unrecognized volcanic landforms and at least twotypes with substantial relief and describe their morphologyand geologic setting morphology of volcanic depositsindicates that ganymede extrusions probably had a range oftheologies and may be compositionally variable we concludewith speculations and predictions regarding their mode ofemplacement and the implications of volcanic landforms forthe geologic evolution of ganymede stereo imaging with voyagerthis study was motivated by the recognition that asignificant fraction of the surfaces of most of the outer planetsatellites were imaged by voyager in stereo e g croft andsoderblom 1991 schenk and moore 1993 we can usestereo imaging to detect subtle topographic features that were19 009

the late paleozoic felsic lava dominated large igneous province in northeast germany volcanic facies analysis based on drill cores in the deep subsurface of the northeast german basin products of extensive volcanism are present that formed during the waning phase of the variscan orogeny permian carboniferous boundary large volumes 48 000 km3 of dominantly felsic magma were emplaced in the northern foreland of the variscan mountains in a terrestrial semi arid environment most of these units were inferred by previous authors to represent the products of explosive volcanic eruptions such as ignimbrites however a detailed analysis of the volcanic texture and lithofacies association shows that most units are best interpreted as coherent lavas emplaced either as extrusive units or as shallow intrusions with important implications for the reconstruction of the paleo environment this study shows that detailed textural examination of drill cores provide important observations which can be applied as criteria for the interpretation of the mode of volcanic eruptions furthermore phenocryst logging and geochemical fingerprinting based on immobile element ratios can be employed for the classification and discrimination of individual emplacement units

on lava dome growth with application to the 1979 lava extrusion of the soufriere of st vincent abstract a theoretical analysis is presented for the spread of a viscous liquid flowing under its own hydrostatic pressure on a horizontal surface in order to model lava dome formation two situations are considered in detail the spreading of a constant volume of liquid and the case where the amount of liquid is continually increased experiments with silicone liquids show close agreement with theory the formation of a basaltic andesite lava extrusion in 1979 on the crater floor of the soufriere of st vincent west indies provided the motivation for and an application of the model the extrusion reached a diameter of 868 m and a height of 133 m over a period of 150 days over the first 90 days the growth relationships were consistent with those predicted by theory application of the theory to the soufriere dome suggests an effective viscosity of 2 x 10 12 poise for the basaltic andesite lava the large effective viscosity calculated for the lava may be attributed to the dominant influence of a high viscosity skin which forms at the margins of the flow as it cools after 70 days the rate of growth of the extrusion markedly decreased because a substantial collar of rubble accumulated at the flow front due to this collar the growth of the extrusion ceased after 150 days from approximately two weeks after the initiation of the extrusion the discharge rate of lava decreased approximately linearly with increasing dome height this observation suggests that the lava ascended under a decreasing hydrostatic driving pressure and that extrusion ceased when the lava column reached hydrostatic equilibrium

the spreading of variable viscosity axisymmetric radial gravity currents applications to the emplacement of venusian pancake domes the magellan images of venus have revealed a number of intriguing volcanic features including the steep sided or pancake domes these volcanic domes or flows have morphologies that suggest formation by a single continuous emplacement of lava with a higher viscosity than that of the surrounding basaltic plains numerous investigators have suggested that such high viscosity is due to high silica content leading to the conclusion that the domes are evidence of evolved magmatic products on venus however viscosity depends on crystallinity as well as on silica content high viscosity could therefore also be due to a cooler and therefore higher crystal content lava models of dome emplacement which include both cooling and composition factors are thus necessary in order to determine the ranges of crystallinity and silica content which might lead to the observed gross dome morphologies accordingly in this study domes are modelled as radial viscous gravity currents with an assumed cooling induced viscosity increase to include both effects analytical and numerical results indicate that pancake dome formation is feasible with compositions ranging from basaltic to rhyolitic therefore observations of gross dome morphology alone are insufficient for determining composition and the domes do not necessarily represent strong evidence for evolved magmatism on venus

revisiting the paleomires of western india an insight into the early paleogene lignite corridor abstract the paleocene eocene lignite sequences of western india occur in the bikaner nagaur barsingsar gurha and kasnau matasukh lignite seams and barmer kapurdi and giral lignite seams basins of rajasthan whereas those in the cambay vastan rajpardi and tadkeshwar lignite seams saurashtra bhavnagar upper and lower lignite seams and kachchh matanomadh and panandhro lignite seams basins are located in gujarat the position of the cambay basin gujarat being closer to the equator during the early eocene period makes it pertinent to understand the variations in petrographic and geochemical constituents of gujarat and rajasthan lignites in space and time floral growth which largely depends on the climate of the region and its geographical location has an important role in the formation of mire nevertheless the peat forming plant communities nutrient supply bacterial activity types of deposition temperature ph and redox potential impart various characteristics to coal and are reflected in macerals black bands in gujarat and rajasthan lignites are strongly gelified compared to brownish bands and are stratified in nature they are dominantly composed of huminite maceral group while liptinites and inertinites occur in subordinated amount these lignites of gujarat and rajasthan have high values of gelification index gi and low tissue preservation index tpi indicating thereby a continuous presence of wet condition in the basin and slow subsidence rate however due to fluctuating water level in the basins few sections experienced relatively oxic episodes indicated by relatively high inertinite content study of the ground water index gwi and vegetation index vi of these lignites indicates rheotrophic to mesotrophic hydrological condition the study revealed that the lignites of rajasthan and gujarat were formed during the transgressive phase under coastal marshy setting however there were intermittent episodes of fluvial activities which gave rise to supratidal flood plains

petrographic composition and depositional environments of the pliocene velenje lignite seam slovenia abstract a pliocene lignite seam up to 160 m thick occurs in the velenje depression in northern slovenia it forms part of a non marine transgressive sequence petrographic data together with ash and sulphur content of samples from two boreholes one located in the central and the other in the marginal part of the seam have been used to study vertical and lateral coal facies variations in the central part the lignite seam overlies fluvial sediments facies critical macerals and petrographic indices suggest that the lower ash rich part of the seam unit i accumulated in a wet forest swamp in an alluvial plain setting later this environment was replaced by a dry telmatic forest swamp unit iia according to our interpretation a decrease in tree density in units iib and iic reflects a change to a bush moor the transition from unit ii to unit iii is characterized by a rapid water table rise which resulted in the establishment of a wet limnotelmatic forest swamp within unit iii the tree density decreases and the degree of gelification increases towards the top of the seam suggesting a transition to a fen type environment another rapid water table rise ended peat formation in the eutrophic topogenous mire and established open lacustrine conditions a calcium rich environment resulted in high ph values and is responsible for high sulphur lignites up to 4 on a dry basis in the upper part of the seam the ph values were controlled by the amount of the inflowing lacustrine water only thin ash rich topotelmites accumulated along the northern margin of the mire there the seam originated in a wet forest swamp and was separated by limnic and fluvial sediments from other organic rich horizons due to its closer vicinity to the pre tertiary carbonates the depositional environment was probably even more alkaline therefore the lignite shows a higher degree of gelification and is even more sulphur rich up to 5 5 on a dry basis

petrological evolution of the paleogene coal deposits of jammu jammu and kashmir india abstract a detailed macro and micro petrological investigation of 8 coal seam profiles of eocene age from the sub himalayan zone of jammu was undertaken in order to characterize them petrographically and to focus on their evolution the quantitative data suggest that these coals are vitrinite rich with low concentrations of inertinite and rare occurrences of liptinite according to microlithotype concentration these coals may be characterized as vitrinite rich with minor amounts of clarite vitrinertite and trimacerite the dominant minerals are clays siderite and pyrite occurring mostly as disseminations cavity filling and in framboidal state these coals are vitric in type low volatile bituminous in rank and ashy in grade the petrographic character and the presence of teleutospores suggest that similar to other tertiary coal deposits in the world the angiosperm flora contributed chiefly to the development of coal facies in the area the maceral and microlithotype composition shows that these coals originated from the low forest and undisturbed in situ peat in foreland basins under limno telmatic depositional conditions the water was brackish with regular influxes of fresh water

pulsating continents on venus an explanation for crustal plateaus and tessera terrains we propose that tessera terrains on venus represent continental crust that does not participate in the periodic recycling of the lithosphere through global subduction events we have studied the force balance on the boundary of a continental area that survives a global subduction event using an analytical model in the proposed model the ratio between the crustal and lithospheric mantle thicknesses controls the force balance if the crust thickness is less than 2 5 of the lithospheric mantle thickness the continental area will be compressed but if the crustal thickness is higher than 2 5 of the lithospheric mantle thickness the continental area will spread out and collapse consequently if the lithospheric mantle beneath a continental region is delaminated during a global subduction event the continent will collapse generating tessera inliers dominated by extensional tectonics but if a significant portion of lithospheric mantle remains then the continental area will be compressed generating a plateau by crustal shortening the observed plateau heights can be explained by this model a 2 km height plateau can be generated by a lithospheric mantle thickness of 40 km while a 4 km height plateau can be generated by a 90 km thick lithospheric mantle we have modelled this crustal thickening of a continental area by tectonic contraction using a thin viscous sheet approach with a newtonian viscosity for the crust the force from a hot mantle elevated during a global subduction event is enough to build up a plateau by compression in 50 ma using a viscosity for the continental crust of 1021 pa s and 200 ma for 5 1021 pa s during this compressional stage concentric fold and thrust belts are generated in the plateau continent erasing any impact craters that were present the subsequent stabilization of a new crust and lithosphere in the surrounding mantle changes the force balance allowing a moderate gravitational collapse of the plateau continent accommodated by radial grabens the pulsating continent model links for the first time the generation of crustal plateaus and the origin of the volcanic plains predicting the observed equivalent effective crater density for both terrains

evolution of pennsylvanian late carboniferous peat swamps of the ruhr basin germany comparison of palynological coal petrographical and organic geochemical data abstract this study focuses on the reconstruction of the environment during peat swamp development eight coal and sedimentary organic rock bearing seam successions were examined all belonging to the duckmantian pennsylvanian late carboniferous 410 samples were analysed with coal petrographical methods 155 of these also by palynological methods in addition on 55 samples organic geochemical investigations were carried out with respect to n alkanes and iso alkanes the established coal petrographical parameters gelification index gi tissue preservation index tpi groundwater index gwi and vegetation index vi were used to characterize different periods of peat swamp development furthermore the new index wci water cover index was introduced to reflect water level conditions by using the ratio between hydrophilous hygrophilous and mesophilous plants in this study the index is based on palynological data but can be equally applied when quantitative macrofloral counts are available gi versus tpi values show two general trends of peat swamp evolution low gi and tpi values as indicator for drier swamp conditions like ombrogenous mires and high gi and tpi values which show a trend to water covered environments like topogenous mires in addition ash yields and gwi versus vi data also emphasize a general trend from topogenous to ombrogenous mires a decrease in water level towards the top of the seams and thus resulting in the development of domed mires is reflected by the newly introduced wci hence these parameters show recurrent peat swamp successions characterized by mineral and vitrinite rich coals typical for topogenous swamps and an evolution towards inertinite liptinite rich coals with low ash yield typical for ombrogenous swamps n alkane ratios like the carbon preference index cpi pristane n c17 phytane n c18 pristane phytane and the n c17 n c27 relationship indicate a strong correlation of these parameters with thermal maturity e g cpi values correlate with vitrinite reflectance sulphur organic carbon s toc ratios are quite uniform in clastic rocks with low to moderate toc contents but highly variable in coals probably reflecting variable sulphate availability during deposition of peats sphenophyll rich floral assemblages are restricted to low sulphur environments