explosive volcanic eruptions on mercury eruption conditions magma volatile content and implications for interior volatile abundances images obtained by the messenger spacecraft have revealed evidence for pyroclastic volcanism on mercury because of the importance of this inference for understanding the interior volatile inventory of mercury we focus on one of the best examples determined to date a shield volcano like feature just inside the southwestern rim of the caloris impact basin characterized by a near central irregularly shaped depression surrounded by a bright deposit interpreted to have a pyroclastic origin this candidate pyroclastic deposit has a mean radius of 24 km greater in size than the third largest lunar pyroclastic deposit when scaled to lunar gravity conditions from the extent of the candidate pyroclastic deposit we characterize the eruption parameters of the event that emplaced it including vent speed and candidate volatile content the minimum vent speed is 300 m s and the volatile content required to emplace the pyroclasts to this distance is hundreds to several thousands of parts per million ppm of the volatiles typically associated with pyroclastic eruptions on other bodies e g co co2 h2o so2 h2s for comparison measurements of the exsolution of volatiles h2o co2 s from basaltic eruptive episodes at kilauea volcano hawaii indicate values of 1300 6500 ppm for the terrestrial mantle source evidence for the presence of significant amounts of volatiles in partial melts derived from the interior of mercury is an unexpected result and provides a new constraint on models for the planet s formation and early evolution

a molecular organic carbon isotope record of miocene climate changes the difference in carbon 13 13c contents of hopane and sterane biomarkers in the monterey formation naples beach california parallels the miocene inorganic record of the change in 18o 18o reflecting the miocene evolution from a well mixed to a highly stratified photic zone upper 100 meters in the pacific steranes 13c 25 4 0 7 per mil versus the pee dee belemnite standard from shallow photic zone organisms do not change isotopically throughout the miocene in contrast sulfur bound c35 hopanes likely derived from bacterial plankton living at the base of the photic zone have systematically decreasing 13c concentrations in middle and late miocene samples 13c 29 5 to 31 5 per mil consistent with the middle miocene formation of a carbon dioxide rich cold water mass at the base of the photic zone

sources and occurrence of c12c22n alkane distributions with even carbon number preference in sedimentary environments abstract the occurrence of c12 c22n alkanes with a strong even carbon number preference is reported in recent and miocene sediments encompassing marine and freshwater systems deposited under oxic and anoxic conditions it is therefore shown that these n alkanes can be found in a wider type of sedimentary environment than those previously described the occurrence in some cases of a parallel distribution of c14 c20n alk 1 enes is also illustrated a variety of biological sources including both marine and freshwater bacteria as well as fungi and yeast species is suggested to account for such distributions

lacustrine basin dynamics and organosulphur compound origin in a carbonate rich lacustrine system late oligocene mequinenza formation se ebro basin ne spain abstract the late oligocene mequinenza formation se ebro basin ne spain records the development of extensive shallow low gradient lacustrine zones which evolved under a subtropical warm climatic regime affected by humidity aridity cycles carbonate dominated inner lacustrine sequences which include thin coal seams are laterally related to muddy carbonate and siliciclastic marginal lacustrine assemblages where evaporites occur water solute concentration of the lacustrine zones changed during the alternative high and low stand episodes with lacustrine waters ranging mainly from fresh to oligosaline nonsulphurised nsc and sulphurised osc organic compounds occur in the inner lacustrine facies and record significant contributions from aquatic and terrestrial higher plants bacteria cyanobacteria photosynthetic anaerobic bacteria and algae these biomarkers show that the lacustrine system was eutrophic and the water column was poorly oxygenated and sometimes stratified as evidenced by occasional finely laminated facies and gammacerane organic matter s c ratio lower in carbonate than in coal and coal related facies suggests significant variations in the lacustrine autotrophic production and or the allochthonous organic matter contribution higher plant biomarkers were recorded mainly as normal nonsulphurised lipids by contrast bacterial and algal lipids hopanoids steroids and isoprenoids under intense sulphate reduction conditions incorporated sulphur in their hydrocarbon skeleton and gave rise to osc with distributions of thienyl and thiolanylhopanoids epithiosteranes and polyprenoids linear thiols are new biomarkers which probably were generated by the early incorporation of sulphur into funtionalised precursors e g alkanols intense methanogenesis was enhanced in some lacustrine zones owing to high organic matter input and as a consequence biomarkers of methanotrophic and methylotrophic bacteria related to methane emission are also found

occurrence of two novel benzothiophene hopanoid families in sediments abstract two novel families of c 34 c 35 benzothiophene hopanoids have been identified in laminated marlstones and limestones of hauptdolomit germany upper triassic calcaires en plaquettes france upper jurassic and ghareb jordan upper cretaceous formations structures were assigned on the basis of raney nickel desulphurization deuteriated nickel boride desulphurization mass spectral data and gc behaviour based on quantitative analysis a precursor product relationship between thiophene hopanoids and benzothiophene hopanoids seems likely this means that the novel hopanoids are not formed by sulphur incorporation into benzohopanes but instead cyclization and aromatization of the hopanoid side chain occur after sulphur incorporation

the geological nature of dark material on vesta and implications for the subsurface structure abstract deposits of dark material appear on vesta s surface as features of relatively low albedo in the visible wavelength range of dawn s camera and spectrometer mixed with the regolith and partially excavated by younger impacts the material is exposed as individual layered outcrops in crater walls or ejecta patches having been uncovered and broken up by the impact dark fans on crater walls and dark deposits on crater floors are the result of gravity driven mass wasting triggered by steep slopes and impact seismicity the fact that dark material is mixed with impact ejecta indicates that it has been processed together with the ejected material some small craters display continuous dark ejecta similar to lunar dark halo impact craters indicating that the impact excavated the material from beneath a higher albedo surface the asymmetric distribution of dark material in impact craters and ejecta suggests non continuous distribution in the local subsurface some positive relief dark edifices appear to be impact sculpted hills with dark material distributed over the hill slopes dark features inside and outside of craters are in some places arranged as linear outcrops along scarps or as dark streaks perpendicular to the local topography the spectral characteristics of the dark material resemble that of vesta s regolith dark material is distributed unevenly across vesta s surface with clusters of all types of dark material exposures on a local scale some craters expose or are associated with dark material while others in the immediate vicinity do not show evidence for dark material while the variety of surface exposures of dark material and their different geological correlations with surface features as well as their uneven distribution indicate a globally inhomogeneous distribution in the subsurface the dark material seems to be correlated with the rim and ejecta of the older veneneia south polar basin structure the origin of the dark material is still being debated however the geological analysis suggests that it is exogenic from carbon rich low velocity impactors rather than endogenic from freshly exposed mafic material or melt exposed or created by impacts

eruption conditions of pele volcano on io inferred from chemistry of its volcanic plume we use thermodynamic models and published 1996 hubble space telescope hst observations of so2 so and monatomic sulfur gas in the pele volcanic plume on jupiter s moon io to evaluate the temperature 1440 k and oxidation state 3 3 log fo2 units below the ni nio buffer of pele s magma and exsolved volcanic gas combination of these results with 1999 hst data on the so2 s2 ratio in the pele plume allows us to calculate pressures 10 4 7 10 5 4 bar in the vicinity of volcanic vent and to present a detailed chemical model for the plume our model indicates that the pele plume represents volcanic gas which last equilibrated at magmatic temperature and was not significantly altered in the plume finally the redox state of pele plume indicates that io is differentiated and has an oxidized fe metal free mantle

explosive volcanism and the compositions of cores of differentiated asteroids eleven iron meteorite groups show correlations between ni and siderophile trace elements that are predictable by distribution coefficients between liquid and solid metal in fractionally crystallizing metal magmas these meteorites are interpreted to be fragments of the fractionally crystallized cores of eleven differentiated asteroids many of these groups crystallized from s depleted magmas which we propose resulted from removal of the first partial melt the fe nifes cotectic melt by explosive pyroclastic volcanism of the type envisaged by wilson and keil 8 we show that these dense negatively buoyant melts can be driven to asteroidal surfaces due to the presence of excess pressure in the melt and the presence of buoyant bubbles of gas which decrease the density of the melt we also show that in typical asteroidal materials veins will form which grow into dikes and serve as pathways for migration of melt and gas to asteroidal surfaces since cotectic fe nifes melt consists of about 85 wt fes and 15 wt fe ni removal of small volumes of eutectic melts results in major loss of s but only minor loss of fe ni thus leaving sufficient fe ni to form sizeable asteroidal cores

organic sulfur compounds formed during early diagenesis in black sea sediments abstract sediments from units i and ii of the black sea were analyzed to assess the early diagenetic formation of organic sulfur compounds osc a series of isomeric c28 2 4 dialkylthiophenes was found at low concentrations in surface sediments osc with c25 highly branched isoprenoid rbi skeletons were not found in surface sediments even though there was a rapid decrease in the concentrations of c25 hbi alkenes in the same sediments nor were osc found which contained carbon skeletons derived from c37 c39 alkenes which are also abundant in the sediment as depth increased in unit i concentrations of the c28 2 4 dialkylthiophenes decreased while c25 and c30 hbi thiolanes appeared at the bottom of unit i and increased in concentration into unit ii treatment of macromolecular material from sediment extracts with raney nickel yielded phytane as the dominant hydrocarbon as well as series of c25 and c30 hbi hydrocarbons carotane and isorenieratane these latter two components were generally absent from the free hydrocarbon fractions these results indicate that sulfur incorporation into functionalized lipids can occur during the very early stages of sedimentary diagenesis even at the sediment water interface on the other hand the rapid loss of c25 hbi alkenes in surface sediments could not be accounted for by sulfur quenching and other potential osc precursors such as c37 c39 alkenes also apparently did not incorporate sulfur into readily analyzable material

vesta s shape and morphology vesta s surface is characterized by abundant impact craters some with preserved ejecta blankets large troughs extending around the equatorial region enigmatic dark material and widespread mass wasting but as yet an absence of volcanic features abundant steep slopes indicate that impact generated surface regolith is underlain by bedrock dawn observations confirm the large impact basin rheasilvia at vesta s south pole and reveal evidence for an earlier underlying large basin veneneia vesta s geology displays morphological features characteristic of the moon and terrestrial planets as well as those of other asteroids underscoring vesta s unique role as a transitional solar system body

volatile degassing of basaltic achondrite parent bodies evidence from alkali elements and phosphorus abstract the volatile alkali element na k rb cs and p abundances in eucrites diogenites and basaltic clasts from polymict eucrites howardites and mesosiderites were compared with an average of highly incompatible refractory ahir elements ba la ce nd sm hf th u normalized to cosmic abundances ratios of e g rb ahir remain constant during normal magmatic differentiation because the very low and approximately equal mineral melt partition coefficients for these elements are inefficient in causing fractionation in the melt the na ahir ratio in eucrites is essentially constant at 0 050 cosmic basaltic eucrites and basaltic clasts show a positive correlation between k rb and cs and alkali element ahir ratios the averages for basaltic eucrites are k ahir 0 043 rb ahir 0 0088 cs ahir 0 0040 cosmic the positive correlations between alkali elements and alkali ahir are due to progressive volatile loss of the alkali elements from the basalts and not to source region heterogeneities this process probably had a minor effect on the parent body inventory of volatile elements in diogenites the alkali ahir ratios are systematically greater than in basaltic eucrites and are more variable the lower values are 1 4 2 the means for basaltic eucrites while the higher values are similar to those of cv and co chondrites for k rb and cs the highest alkali ahir ratios were obtained on the most incompatible poor of the diogenites and indicate minimum ratios for the parent body of na ahir 0 24 k ahir 0 49 rb ahir 0 55 and cs ahir 0 14 cosmic there are well defined negative correlations between k rb cs and alkali ahir ratio in the diogenites the data are consistent with progressive alkali loss through volatile outgassing during crystallization of one or more parent magmas this process resulted in 90 loss of the volatile element inventory from the parent body phosphorus also shows evidence for volatile loss from the basaltic eucrites and elevated p ahir ratios in diogenites the low p ahir ratio in eucrites is largely controlled by volatile loss rather than through equilibration with a metallic liquid as previously suggested the parent body of the basaltic achondrites appears to have initially contained alkali element and presumably other volatile element abundances comparable to those in co and cv chondrites and perhaps higher

volcanic gas composition metal dispersion and deposition during explosive volcanic eruptions on the moon abstract the transport of metals in volcanic gases on the moon differs greatly from their transport on the earth because metal speciation depends largely on gas composition temperature pressure and oxidation state we present a new thermochemical model for the major and trace element composition of lunar volcanic gas during pyroclastic eruptions of picritic magmas calculated at 200 1500 c and over 10 9 10 3 bar using published volatile component concentrations in picritic lunar glasses we have calculated the speciation of major elements h o c cl s and f in the coexisting volcanic gas as the eruption proceeds the most abundant gases are co h 2 h 2 s cos and s 2 with a transition from predominantly triatomic gases to diatomic gases with increasing temperatures and decreasing pressures hydrogen occurs as h 2 h 2 s h 2 s 2 hcl and hf with h 2 making up 0 5 0 8 mol fractions of the total h water h 2 o concentrations are at trace levels which implies that h species other than h 2 o need to be considered in lunar melts and estimates of the bulk lunar composition the cl and s contents of the gas control metal chloride gas species and sulfide gas and precipitated solid species we calculate the speciation of trace metals zn ga cu pb ni fe in the gas phase and also the pressure and temperature conditions at which solids form from the gas during initial stages of the eruption elemental gases are the dominant metal species as the gas loses heat chloride and sulfide species become more abundant our chemical speciation model is applied to a lunar pyroclastic eruption model with isentropic gas decompression the relative abundances of the deposited metal bearing solids with distance from the vent are predicted for slow cooling rates 2 o co 2 and cl rich volcanic gas from erta ale volcano ethiopia as an analogy for more oxidized planetary eruptions in the terrestrial cl rich gas the metals are predominantly transported as chlorides as opposed to metallic vapors and sulfides in the lunar gas due to the presence of cl species metal transport is more efficient in the volcanic gas from erta ale compared to the moon

environmental conditions in the south atlantic angola basin during the early cretaceous abstract the south atlantic has experienced periods of intense anoxia and black shale deposition that form an important hydrocarbon source here we have investigated the depositional environment during the initial opening phase of the south atlantic during the early cretaceous the period is crucial as it is characterized by extensive source rock deposition and because it sets the stage for subsequent periods of anoxia within the northern sub basin of the south atlantic within an aptian sequence of organic rich sediments up to 40 total organic carbon toc from deep sea drilling project dsdp site 364 we found a distinct biomarker distribution including the presence of isorenieratane and an array of thiophenic s containing compounds our results indicate that during the time of deposition corresponding to the initial phase of opening of the south atlantic most of the water column in the angola basin was hypersaline 40 and euxinic with euxinia episodically reaching the photic zone the low relative abundance of marine biomarkers in the samples suggests that these extreme conditions were unfavourable for typical marine organisms stratigraphically up section the biomarker distribution changed as the toc content gradually decreased

geochemical and biological marker assessment of depositional environments using brazilian offshore oils abstract a combined geochemical and molecular characterization of a wide selection of oils from the major brazilian offshore basins has been undertaken the elemental sulphur nickel and vanadium and bulk oapi and 13c properties of each sample been considered together with its molecular composition determined using liquid and gas chromatography and quantitative biological marker investigations using gas chromatography mass spectrometry for alkanes the results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups the distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils each group is correlated tentatively with source rocks laid down in a specific depositional regime namely lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate or marine deltaic the diagnostic features that allow this classification are the relative abundance and carbon number distributions of n alkanes pristane phytane ratios sulphur nickel and vanadium contents carbon isotope data the absolute concentrations of hopanes and steranes and their abundance relative to 4 methylsteranes and also the occurrence and abundance of several specific biological markers including 18 h oleanane gammacerane carotane tricyclic terpanes higher acyclic isoprenoids 28 30 bisnorhopane and 25 28 30 trisnorhopane this investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils

an igneous fragment from cluster idp l2011 21 an analog for the source of pyrrhotite and taenite in comet 81p wild 2 captured in stardust aerogel

volcanic eruptions and intrusions on the asteroid 4 vesta we use basic principles of fluid mechanics to explore the intrusive and eruptive consequences of early large scale silicate melting within the asteroid 4 vesta and relate our findings to the properties of the howardite eucrite diogenite meteorites surface lava flows on vesta would commonly have had widths ranging from a few hundred meters to a few kilometers and lengths lying between a few kilometers and at least several tens of kilometers flow thicknesses would have occupied a much narrower range lying between about 5 and 20 m these thicknesses imply cooling rates and plagioclase crystal growth rates which are extremely similar to those measured in the eucrite meteorites intrusions may have formed at very shallow depths as cooling dikes failed to erupt their contents completely to the surface or at the base of the crust where rising magmas would have been neutrally buoyant as the density structure of vesta s crust evolved deep intrusions would have had lateral extents up to 30 km and thicknesses up to 3 m shallow intrusions would have had vertical extents less than 10 km and widths of 1 m none of these intrusions and surface flows would have been thick enough or have formed frequently enough at a given location to have caused extensive thermal alteration of earlier eruptives lending support to the idea that burial and subsequent long term exposure to the rising geothermal gradient was the main mechanism of thermal metamorphism

identification of a novel c25 highly branched isoprenoid thiophene in sediments a novel c25 highly branched isoprenoid hbi thiophene 2 2 methylpropyl 4 9 2 6 12 trimethyltetradecyl thiophene has been identified in three sediment samples by isolation followed by characterization by 1h nmr gc ms and raney ni desulphurization this component is probably formed by incorporation of inorganic sulphur species into a specific sedimentary c25 hbi alkadiene this latter compound is probably derived from diatoms

clast sizes of ejecta from explosive eruptions on asteroids implications for the fate of the basaltic products of differentiation we use a simple model of the formation growth coalescence and migration of veins of basaltic melt generated by partial melting in chondritic asteroids to deduce the sizes of and pressures within the fluid filled dikes reaching the surfaces of such bodies the gas contents 1000 ppm of mainly co and n2 of the asteroids were high enough that bubbles of free gas trapped in the melt veins gave the basaltic melts significant buoyancy expansion of these gases as a dike opened to the vacuum at the surface led to fragmentation of the melts into liquid droplets which were transported upwards by the accelerating gases to the surface the sizes of these droplets and hence of the pyroclastic glass beads into which they cooled are calculated to lie in the range 30 m to 4 mm this range is essentially independent of the size or gas content of the asteroid parent and only weakly dependent on the internal pressure of the erupting fluid the fate of the pyroclasts however does depend on all of these factors at very low internal pressures significant separation of the gas and liquid in a rising dike may take place and not all of the liquid will be expelled from the dike when it opens to the surface for relatively large 100 km radius asteroids with relatively low 300 ppm gas contents the larger clasts are too heavy to be lifted from the level at which magma fragmentation takes place by the gas flow and so would also remain behind to form basaltic veins the apparent absence of basaltic veins in meteorites then implies both that internal pressures in near surface dikes were generally greater than 0 3 mpa and that low gas contents were not common finally as long as pyroclasts are lofted from the magma fragmentation level they will be accelerated to at least 90 of the final gas speed if this speed exceeds the escape speed from the asteroid as happens readily for high gas contents and small asteroids the pyroclasts will be expelled into space and lost from the meteorite record otherwise low gas contents or large asteroids they will eventually fall back to be incorporated into the surface regolith modifying the chemical and physical properties of meteorites subsequently derived from it

high temperature mass spectrometric degassing of enstatite chondrites implications for pyroclastic volcanism on the aubrite parent body wilson and keil 1991 argued that a few hundred ppm of expanding volatiles present in early partial basaltic melts on the aubrite parent body or on other differentiated asteroids 925 c principally co 1580 2830 ppm n2 110 430 ppm cl 120 450 ppm s see discussion for abundance are indigenous the precise host phases and host sites of the indigeneous volatiles are uncertain 2 2 n2 release appears to be associated with the melting of the fe ni sulfide cotectic at 950 c the amounts of gas released are not unlike those previously measured for iron meteorites and sulfides in irons but exceed by several orders of magnitude the equilibrium n2 solubility in metallic fe ni for solar nebula pressures this suggests that either partial pressures during n2 incorporation were much higher than solar values or n2 is trapped in lattice defects and microcracks possibly in sulfides 3 3 co release over a narrow temperature interval of 1025 1255 c is violent and results in pronounced vesiculation of the residue co may be trapped in microvesicles and cracks in silicates or less likely may form by a reduction reaction during heating between carbon graphite and the minor ferrosilite in the enstatite 4 4 cl release beginning at 950 eh s and 1025 c el s appears not to be associated with lawrencite which should sublime at t as low as 325 c in eh s some may be released from djerfisherite 5 5 gas release and textural studies suggest that metamorphic reheating of eh s and el s was to less than about 950 c el s did not form during metamorphic reheating of eh s by draining of cotectic fe ni sulfide liquid 6 6 sinoite present in some el6 s did not form by condensation from the solar nebula but during parent body metamorphism at t 950 c via the reaction of sio2 gaseous n2 and si in solid solution in the metallic fe ni 7 7 as little as 1 by volume partial melting in an asteroid of any size will generate excess pressures in the melt much greater 10 s of mpa than the tensile strength of silicate materials and will initiate formation of cracks this process will be enhanced by expansion of any exsolved or trapped gas phase in the asteroid and will lead to the formation of pathways cracks growing into dikes for melt migration 8 8 the pressure gradients implied when these pathways intersect the asteroid surface coupled with the observed amounts of indigenous volatiles released from eh s and el s are easily sufficient to drive the pyroclastic volcanic eruptions envisaged by wilson and keil 1991

a comparison of volcanic eruption processes on earth moon mars io and venus the silicate planets and satellites display a wide range of physical chemical and atmospheric characteristics which may influence the nature of volcanism a major geological process common to the evolution of the surfaces of these bodies consideration of the process of magma ascent and eruption from first principles allows predictions to be made concerning volcanic eruption styles and expected landforms and deposits on each planetary body examination of actual land forms and deposits in light of these predictions leads to a better understanding of the nature of volcanic eruption processes and outlines outstanding problems

the influence of geometry on the ascent of magma in open fissures during steady eruption the flow conditions emitted mass flux exit velocity and exit pressure depend on the geometry of the conduit in which the eruption occurs this dependence is examined for the onedimensional isothermal ascent of a homogeneous basaltic magma with an aqueous volatile phase and newtonian rheology by fixing the geometry of the feeding fissure the mass flux flowing in steady conditions can be determined at any depth as well the magma pressure and vertical velocity flow behaviour is analysed for three fissure shapes constant width slowly upward narrowing and lenticular in all the cases examined the magma arrives at the earth s surface with a pressure greater than atmospheric the results are compared with those obtained when a lithostatic pressure gradient is assumed for the magma column some speculations are made moreover about the change in eruption style if conduit geometry varies during a non steady phase

characterization of model evaporitic environments through the study of lipid components abstract a saline circuit has been studied as a model of coastal evaporite system the lipid composition of diverse salt ponds encompassing calcite gypsum and halite domains has been determined most of the lipid materials has been found in the carbonate samples and is related to algal cyanobacterial debris lipids in the gypsum domain are of heterotropic microbialorigin and extreme halophilic bacteria constitute the main lipid contribution in the halite samples n alkane distributions with high predominance of n docosane constitute a previously described feature of sedimentary evaporitic conditions that is charateristics of the intermediate calcite gypsum samples in the calcite domain the presence of c20 highly branched isoprenid olephines tetrahymanol and the large amounts of phytol constitute likely precursors of lipids usually found in evaporitic environments i e c20 highly branched isoprenoid alkanes gammacerane and high phytane pristane ratios their occurence point to dehydration and hydrogenations as two main diagenetic processes leading to the formation of evaporitic molecular markers

consequences of explosive eruptions on small solar system bodies the case of the missing basalts on the aubrite parent body aubrite meteorites are composed of constituents which are almost certainly of igneous origin if they were generated by the melting and fractionation of enstatite chondrite like parental material as seems very likely then plagioclase rich basaltic complements to the aubrites should have formed however such materials are not known as individual meteorites and the compositions of two plagioclase silica clasts and one albite silica diopside anorthite clast probably an impact melt in the norton county aubrite breccia suggest that they are not the putative enstatite plagioclase basalts we propose a new mechanism that explains the absence of these materials showing that the expansion of even very small amounts of volatiles present in a melt approaching the surface of a small low gravity body will be enough to disrupt the melt into a spray of droplets moving faster than the local escape velocity this explosive volcanic process of melt removal requires larger melt volatile contents on larger bodies and data on the solubility of volatiles in basaltic melts suggest that the process was limited to bodies smaller than about 100 km in radius

origin and diagenetic transformations of c25 and c30 highly branched isoprenoid sulphur compounds further evidence for the formation of organically bound sulphur during early diagenesis abstract a number of c25 and c30 highly branched isoprenoid hbi sulphur compounds e g thiolanes 1 oxo thiolanes thiophenes and benzo b thiophenes with 2 6 10 14 tetramethyl 7 3 methylpentyl pentadecane and 2 6 10 14 18 pentamethyl 7 3 methylpentyl nonadecane carbon skeletons were identified in sediments ranging from holocene to upper cretaceous these identifications are based on mass spectral characterisation desulphurisation and in some cases by comparison of mass spectral and relative retention time data with those of authentic standards the presence of unsaturated c25 and c30 hbi thiolanes in a recent sediment from the black sea age 3 6 10 3 a strongly supports their formation during early diagenesis the co occurrence of hbi polyenes c25 and c30 and unsaturated hbi thiolanes c25 and c30 possessing two double bonds less than the corresponding hbi polyenes in this recent sediment testifies to the formation of unsaturated hbi thiolanes by a reaction of inorganic sulphur species with double bonds of the hbi polyenes furthermore a diagenetic scheme for hbi sulphur compounds is proposed based on the identification of hbi sulphur compounds in sediment samples with different maturity levels

free and sulphurized hopanoids and highly branched isoprenoids in immature lacustrine oil shales abstract a study of the solvent extracts of four samples from two immature oil shales from tertiary lacustrine basins ribesalbes and campins southern european rift system deposited under reducing conditions has allowed the identification of s containing hopanoids and novel highly branched isoprenoids hbi hbi derivatives occur only in the ribesalbes shales where two new structural types of c 25 s containing hbi isomers have been identified these compounds probably have different precursor organisms from those in recent marine systems they are present as thiophenes thiolanes and thiolane sulphoxides in one case and only as thiolanes in the other 17 21 h 17 21 h and 17 21 h thienyl and methylthienylhopanes have been found in the shales from the two basins in the campins samples these compounds occur together with thiolanyl and methylthiolanylhopanes distributions of 17 21 h and 17 21 h hopanes hop 17 21 enes and 2 methylhop 17 21 enes ribesalbes only are also encountered comparison of the hopane distributions from both solvent extractable aliphatic and thiophene fractions and the sulphur and oxygen bound macromolecular matter in ribesalbes basin shows a remarkable similarity between all fractions this resemblance points to rather uniform inputs and depositional processes for the accumulation of these compounds both as small molecules or bound to macromolecules e g early bonding of bacteriohopanepolyols to sulphur and to the macromolecular organic matter the good correlation among the macromolecular fractions in ribesalbes basin is reinforced when comparing the 13 c composition of phytane c 20 and c 25 hbi and the c 35 hopane homologues in the different fractions

eruption of magmatic foams on the moon formation in the waning stages of dike emplacement events as an explanation of irregular mare patches abstract volcanic eruptions on the moon take place in conditions of low gravity and negligible atmospheric pressure very different from those on earth these differences lead to characteristic lunar versions of hawaiian and strombolian explosive activity and to the production of unusual eruption products neither predicted nor observed on earth in the terminal stages of eruptions these include the unusual mounds and rough hummocky blocky floors of some small shield summit pit crater floors elongate depressions and mare flows similar to those named irregular mare patches imps by braden et al 2014 we examine the ascent and eruption of magma in the waning stages of the eruptive process in small shield summit pit crater floors and show that many imp characteristics can be plausibly explained by basaltic magma behavior as the rise rate of the ascending magma slows to zero volatiles exsolve in the dike and lava lake to form a very vesicular foam and the dike begins to close stresses in the very vesicular and porous lava lake crust produce fractures through which the foam extrudes at a rate determined by its non newtonian rheology waning stage extrusion of viscous magmatic foams to the surface produces convex mounds whose physical properties inhibit typical impact crater formation and regolith development creating an artificially young crater retention age this mechanism for the production and extrusion of very vesicular magmatic foams is also applicable to waning stage dike closure associated with pit craters atop dikes and fissure eruptions in the lunar maria providing an explanation for many irregular mare patches this mechanism implies that imps and associated mare structures small shields pit craters and fissure flows formed synchronously billions of years ago in contrast to very young ages less than 100 million years proposed for imps by some workers

application of biological markers in the recognition of palaeohypersaline environments the hydrocarbon fractions of a marl sample from a messinian basin in the northern appenines and four oils rozel point oil utah and three seep oils from sicily were studied

formation of vesicles in asteroidal basaltic meteorites rare asteroidal vesicular basalts have previously been thought to form in surficial lava flows with co as the vesicle forming gas however vesicular lava flows are unlikely on small airless bodies such as asteroids to unravel the origin of these rocks we analyzed vesicle sizes and abundances for two angrites and two eucrites using high resolution x ray computed tomography and conducted numerical modeling of bubble formation in a dike of ascending magma modeling results indicate that thin 30 cm wide dikes are trapped at 5 km depth where 75 ppm of co and co2 contribute equally to vesicle formation vesicular eucrites were metamorphosed in this deep seated environment the gas was lost and they were excavated by impacts

sedimentation distribution and diagenesis of organic matter in a recent carbonate environment abu dhabi u a e abstract in the modern hypersaline carbonate lagoon and sabkha sedimentary environments of abu dhabi united arab emirates three types of organic matter originate respectively from microbial mat avicennia mangrove and halodule lagoonal seagrass the study of recent sedimentary processes and cross sections through the sabkha sediments lead to the definition of organo sedimentary facies based on geochemical and sedimentological criteria this permits the construction of an organo sedimentary sequence which expresses the holocene sedimentary record involving a transgressive and a regressive sequence the various organic facies occur in both sequences heterogeneity within the individual organic facies reflects several factors including sedimentation dynamics mineral matrix oxidation and reduction and selective organic and mineral diagenesis these parameters are discussed in terms of depositional environment and location within the organo sedimentary sequence changes in distribution quantity and preservation potential of the buried organic matter are discussed in terms of sea level changes and sedimentary accretion rates

dark ring in southwestern orientale basin origin as a single pyroclastic eruption 1 a large 154 km diameter dark annular ring located in the southwestern part of the orientale basin along the montes rook ring was first discovered and documented in soviet zond 8 images clementine uv visible multispectral data indicate that the dark ring consists of material similar to the pyroclastic glasses collected by the apollo astronauts with the glasses being more closely related to the orange glass beads that comprise the aristarchus plateau than to the crystallized black beads typical of taurus littrow this implies relatively rapid cooling times for the eruption products we propose that the dark ring is the manifestation of a pyroclastic eruption originating at a fissure vent an elongate 7 5 km by 16 km depression located near the center of the ring the event producing the eruption began with a dike rapidly emplaced from subcrustal depths to within 3 4 km of the surface the dike stabilized and degassed over 1 7 years to form an upper foam layer which then penetrated to the surface to cause an eruption lasting 1 2 weeks the eruption produced a 38 km high symmetrical spray of pyroclasts into the lunar vacuum at velocities of 350 to 420 m s and the pyroclastic material accumulated in a symmetrical ring around the vent the geometry of eruption caused the deposits to accumulate preferentially in a ring representing the material ejected at 45 the paucity of pyroclastic rings of this type on the moon can be attributed to the low probability of a dike stalling at just the right depth 3 4 km to create these eruption conditions the detailed characteristics of this ring provide important new insight into the emplacement of pyroclastics in the more regionally continuous lunar dark mantle deposits suggesting that their sources are dominated by effusive and hawaiian style eruptions the orientale dark ring deposit has similarities to the pyroclastic rings on the galilean satellite io both the orientale dark ring and ionian eruptions involve acceleration of small particles to a high velocity in an expanding gas stream silicate pyroclasts derived from the disrupted foam layer in the lunar case and a mixture of silicate pyroclasts and snowflakes of condensing so2 solids on io in both cases the silicate pyroclasts ejected from the vent are accelerated by the gas until they become decoupled and continue on ballistic trajectories controlled only by gravity differences in mass flux and cloud opacity between the moon and io are the direct result of the origin and mass fraction of the volatile phase the accumulation of a magmatic foam layer on top of a silicate intrusion in the lunar case and the intimate mixing on io of a steadily erupting magma and liquid so2 the interpretation of the orientale dark mantle ring as a pyroclastic eruption provides an alternative to the hypothesis that the dark ring represents the presence of an ancient pre orientale impact structure and that the orientale basin cavity of excavation must therefore lie within the outer rook mountain ring

thermal stability of thiophene biomarkers as studied by hydrous pyrolysis abstract an immature r o 0 25 sulphur rich calcareous shale from the gessoso solfifera formation messinian in the vena del gesso basin northern italy was artificially matured by hydrous pyrolysis at constant temperatures ranging from 160 to 330 c for 72 h to study the applicability of alkylthiophenes as molecular indicators during progressive diagenesis and early catagenesis artificial maturation at temperatures up to 330 c generated large amounts of alkylthiophenes from the thermal degradation of kerogen the importance of the kerogen in the production of alkylthiophenes is supported by the observation that the isomer distributions of alkylthiophenes at high temperatures coincide with the isomer distributions of alkylthiophenes in the curie point pyrolysate of the isolated kerogen of the original sample the generation profiles of the thiophenes with a phytane carbon skeleton and the 3 4 di n alkylthiophenes suggest that continuous degradation of alkylthiophenes is also taking place so that the overall effect is alkylthiophene concentrations with intermediate values the structural isomer distribution of linear alkylthiophenes does not change significantly when these compounds are generated at different temperatures this implies that important information regarding the original positions of functionalities in the precursor molecules is retained and thus that alkylthiophenes are useful biomarkers at relatively high levels of thermal maturity up to r o 0 95 1 1

near vertical supersonic and shock free gas magma flow at ionian volcanoes application to pillan in 1997 the pillan volcano on io was home to a fierce volcanic eruption that emplaced extensive lava flows and a circular plume deposit the gas magma flow issuing from the unresolved vent region appeared to form an almost vertical jet we consider steady eruptions of gas and magma and take the vent to be either a fissure or a point source in the fissure scenario the upper conduit flow must reach mach 1 in the 25 75 m depth range to produce the vent velocities of 550 600 m s that are required to explain the observed plume heights conduit wall deflections in the range 20 30 degrees from vertical values referring to the upper meter of the conduit and similar to 26 30 by mass of incorporated crustal so2 are also needed in the point source scenario sonic flow conditions and similar velocities are achieved in the depth range 350 500 m for similar conduit wall deflections and gas mass proportions in the erupting mixture probably the source of the 140 km high plume imaged in 1997 was either a similar to 6 11 m wide fissure active for similar to 14 40 km along strike or a circular vent similar to 125 216 m in diameter the former scenario being preferred finally a shock free conduit flow is more likely to sustain a tall lava fountain in a near vacuum

the fate of pyroclasts produced in explosive eruptions on the asteroid 4 vesta we evaluate the consequences of explosive activity having taken place during volcanic eruptions on the differentiated asteroid 4 vesta which is the likely parent body of the howardite eucrite diogenite hed meteorites for a wide range of magma volatile contents we calculate the eruption speeds and subsequent trajectories of the pyroclastic magma droplets produced by considering the size distribution and eruption speeds of the droplets and the mass fluxes at which they are ejected we show that under all realistic circumstances the droplets will have formed lava fountains that were extremely optically dense as a result virtually all of the droplets will have reached the surface having suffered a negligible amount of radiative cooling and will have coalesced into lava ponds feeding lava flows typically 1 of the pyroclasts will have undergone enough cooling to allow them to accumulate into a recognizable fall deposit consisting of unwelded or partly welded volcanic glass beads this result is consistent with the apparent absence of identifiable pyroclastic material in the hed and other types of differentiated meteorites

lacustrine oil shale basins in tertiary grabens from ne spain western european rift system abstract in the ne iberian plate the convergent motion and collision of the european iberian and african plates resulted in the development of paleogene compressional features strike slip systems thrust fold belts and late oligocene to mainly neogene extensional structures which are superimposed on the former these extensional structures are represented by horsts half grabens and tilted blocks often developed in connection with preexisting inherited faults from the late oligocene and during the neogene both strike slip and extensional regimes alternated and coexisted giving rise to a number of fault bounded basins the deposition of organic rich facies and in particular oil shales took place in the lacustrine complexes developed in some of these basins campins basin late oligocene ribesalbes and rubielos de mora basins early middle miocene libros basin late miocene and cerdanya basin late miocene deep lacustrine sequences ranging from 100 up to 250 m thick were deposited in all the above mentioned basins the organic rich sequences are characterized by thin lamination absence of bioturbation rare benthonic fauna if present it is supplied from other parts of the basin and excellent preservation of exotic fossils plant leaves insects amphibians the suitable depth conditions needed for permanent stratification in the water bodies and anoxia in the deeper parts of the lakes were due essentially to increasing subsidence outstripping deposition intense tectonic activity is recorded by the occurrence of olisthostromes and slumps affecting the lacustrine deposits as well as by the syntectonic structures recorded in the basin fill successions the late oligocene late miocene paleoclimatic regimes ranging from warm tropical to subtropical conditions were favourable for the development of permanently stratified lakes moreover chemical ectogenic meromixis may have contributed in some cases to the establishment of permanent stratification the eastern iberian rift system makes up the southernmost part of the larger western european rift system the occurrence of lacustrine sediments ranging from the late eocene to late miocene is frequent in the fault bounded basins of this complex rift system and lacustrine oil shale deposits have been recorded in several of these basins thus the western european rift system presents an interesting model of intracontinental rifting in a foreland platform setting where favourable conditions for organic rich deposits often took place the high potential of this kind of tectonic settings for lacustrine oil shale exploration must be stressed

recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach study of organic matter in immature sediments from a messinian evaporitic basin shows that consideration of structures modes of occurrence and carbon isotopic compositions of free and sulfur bound carbon skeletons allow identification of biochemical precursors detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way moreover unprecedented biochemicals were recognized these extend the horizon of biomarker geochemistry

hydrocarbons of the hypersaline basins of shark bay western australia shark bay is an 8000 sq km shallow marine embayment on the western coast of western australia the waters exhibit a well established salinity gradient from oceanic to hypersaline the chemical assemblage of sediment hydrocarbons along the salinity gradient may be classified into two distinct chemogeographic types firstly oceanic sediments contain n alkanes and a suite of highly branched and branched cyclic c25 alkenes hypersaline sediments are characterised by a high relative abundance of a c25h50 alkene together with an analogous c20h40 alkene and its parent c20h42 alkene 2 6 10 trimethyl 7 3 methylbutyl dodecane a pair of alkanes c21h42 and c22h44 increase in concentration and relative abundance with depth the hydrocarbons of the hypersaline basins are found in only trace amounts in oceanic sediments these chemical signals are overlain by further input indicative of the immediate biotic community

a model for large scale volcanic plumes on io implications for eruption rates and interactions between magmas and near surface volatiles 1 volcanic plumes deposit magmatic pyroclasts and so2 frost on the surface of io we model the plume activity detected by galileo at the pillan and pele sites from 1996 to 1997 assuming that magmatic eruptions incorporate liquid so2 from near surface aquifers intersecting the conduit system and that the so2 eventually forms a solid condensate on the ground the temperature and pressure at which deposition of solid so2 commences in the ionian environment and the radial distance from the volcanic vent at which this process appears to occur on the surface are used together with observed vertical heights of plumes to constrain eruption conditions the temperature pressure and density of the gas magma mixtures are related to distance from the vent using continuity and conservation of energy similar eruption mass fluxes of order 5 107 kg s 1 are found for both the pillan and the pele plumes the pele plume requires a larger amount of incorporated so2 29 34 mass than the pillan plume up to 6 mass implied vent diameters range from 90 m at pillan to 500 m at pele the radial extents of the optically dense isothermal incandescent parts of the eruption plumes immediately above the vents are 100 m at pillan and 1300 m at pele gas pressures in the vents are 20 kpa at pillan and 2 kpa at pele and the eruption conditions appear to be supersonic in both cases though only just so at pele

possible origin of n alkanes with a remarkable even to odd predominance in recent marine sediments abstract n alkane distributions with a remarkable even to odd predominance c16 c24 were found in marine surface sediments the previously proposed diagenetic reduction of the corresponding n fatty acids could not be considered as a source for these n alkane based on a comparison of compositional features of n alkane n fatty acid and n alcohol distributions carbon isotope analyses and other geochemical parameters the data indicate that the even predominant n alkanes were derived directly from marine bacteria

the role of rift zone storage in controlling the site and timing of eruptions and intrusions of kilauea volcano hawaii repeated eruptive and intrusive activity on the east rift zone of kilauea volcano allows dikes to exist within the rift zone for extended periods of time leakage of magma from the summit storage region into the rift zone can cause inflation of a rift zone dike inflation raises the excess pressure at the dike centre and increases the stress intensity at the dike edges if the inflation is sufficiently large the stress intensity may exceed the fracture toughness of the country rocks and allow vertical or lateral dike emplacement to occur theoretical modelling can be used to predict the conditions under which vertical or lateral dike propagation and hence eruptive or intrusive activity may occur over typical ranges of dike half height and regional tension gradient vertical propagation and hence eruption are favored by high fracture toughness relatively low dike half heights and low regional tension gradients lateral propagation can occur when the fracture toughness is low when dike half height is higher and when the regional tension gradient is high the results of from the model constrain the fracture toughness within the east rift zone to be 100 110 mpa m and the regional tension gradient to be 1000 pa m

volcanism and the dynamics of open magma chambers the repeated eruption of many volcanoes is now accounted for by events taking place in a subterranean magma chamber which is open in the sense that the inflow of material to the chamber from below leads to a magma pressure p which exceeds the lithostatic pressure pl by an amount greater than the tensile strength of the chamber walls before the contents of the magma chamber have reached thermodynamic and geochemical equilibrium this is the condition which must be satisfied when an eruption occurs we have now derived a relationship giving the critical volume of added material v required to cause an eruption as a function of magma compressibility and the volume by which the chamber expands

pyroclast loss or retention during explosive volcanism on asteroids influence of asteroid size and gas content of melt we review the conditions under which explosive volcanism took place on early forming differentiated asteroids the pressure dependent solubility of typical asteroid volatiles in melts implies that the gas driving explosive volcanism on asteroids less than approximately 100 km in diameter was probably present mainly as a free phase capable of accumulating into large gas bodies and thus causing slug flow in melts approaching the surface in contrast in asteroids larger than approximately 100 km the gas was probably present largely as a dispersion of small bubbles we show that these gas distributions have implications for the size distribution of the pyroclastic droplets produced in explosive eruptions at the surface all pyroclastic melt droplets are accelerated by the expanding gases but their speeds lag the gas speed by a finite amount that is a function of the droplet size and density and the asteroid size and hence acceleration due to gravity we compute pyroclast speeds and by comparing them with escape velocities we identify the critical pyroclast diameter on a given size asteroid that distinguishes droplets lost to space from droplets that return to the surface identification of asteroidal pyroclasts and measurements of their sizes could throw light on the amounts of gas driving eruptions

glasses in howardites impact melts or pyroclasts we have analyzed glasses in eight howardites with the aim of distinguishing their origins as impact melts or pyroclasts although theoretical calculations predict that pyroclastic eruptions could have taken place on vesta the occurrence of pyroclastic glasses in hed meteorites has not been documented this study involved petrographic examination of textures electron microprobe analysis of major and minor elements and la icp ms analysis for selected trace elements previously documented textural and compositional differences between lunar impact melt and pyroclastic glasses partly guided this study this work yielded no positive identification of pyroclastic glasses the most likely explanation is that pyroclastic glasses never formed either because vesta contains insufficient volatiles to have powered explosive eruptions or because eruptive conditions produced optically dense fire fountains that allowed melt drops to collect as lava ponds the impact melt glasses were grouped low alkali ca rich and k rich based on compositions we suggest that these glasses are the result of impacts onto known hed lithologies the low alkali glasses are impact melts of bulk hed lithologies we hypothesize that the ca rich and k rich glasses result from oversampling of plagioclase and of mesostasis that experienced liquid immiscibility respectively during micrometeorite impacts into eucrite targets

determination of gross kinetic parameters for petroleum formation from jurassic source rocks of different maturity levels by means of laboratory experiments abstract solvent extracted core samples of lower toarcian carbonate rich shales posidonia shale lias of the hils syncline area lower saxony basin northern germany covering a wide maturity range vitrinite reflectance rr 0 48 0 88 and 1 45 and a kimmeridge mudstone rr 0 45 are pyrolyzed at three different heating rates 0 1 0 7 and 5 0 k min by application of non isothermal first order reaction kinetics to the resulting hydrocarbon evolution curves activation energy distributions between 46 and 70 kcal mol and pre exponential arrhenius factors are obtained by an iteration method hypothetical hydrocarbon generation curves are calculated for the lias assuming three geological heating rates 0 5 5 and 50 k 106a peak hydrocarbon generation temperatures range from 135 to 165 c

volcanism in the solar system the myriad bodies that occur in the solar system show a wide range of physical properties exploration by spacecraft during the past four decades has shown that volcanism a major mechanism by which internal heat is transported to the surface is common on many of these bodies

origin of hydrocarbons in triassic serpiano oil shales hopanoids abstract the hydrocarbons in the sapropelic serpiano oil shales have been examined the hopanoids are the most predominant hydrocarbons present in the bitumen with hopanes hopenes benzohopanes and monoaromatic secohopanoids being detected the novelty of the serpiano hopanoid assemblages lies in the occurrence of high concentrations of methylhopanoids the distributions of the hopanoids and of their corresponding methylhopanoids are remarkably similar this similarity was also observed for the hopanes and methylhopanes which were generated from the asphaltene and kerogen by hydrous pyrolysis and is indicative of a common biosynthetic pathway

lava fountains from the 1999 tvashtar catena fissure eruption on io implications for dike emplacement mechanisms eruption rates and crustal structure the first direct evidence that patterns of basaltic eruptive activity may be very similar on io and earth was seen on november 26 1999 when the solid state imaging system on board the galileo spacecraft obtained high resolution images of a fissure eruption taking place in one of the calderas of the tvashtar catena complex we analyzed the dynamics of the fissure eruption from the morphology of the lava fountains and pyroclastic deposits and derived an estimate of the eruption rate our best estimate of the volume eruption rate per unit length of fissure lies in the range 0 7 to 7 m3 s 1 m 1 and multiplying this rate by the fissure length of 25 km yields a total volume eruption rate of magma of 2 104 to 2 105 m3 s 1 the upper end of the inferred eruption rate is very close to the upper end of the range of eruption rates observed or inferred for fissure eruptions on earth theoretical models of the possible dike systems feeding the fissure show that for eruptions of positively buoyant magma the elastic properties of rocks are such that a magma flux of 6 to 7 m3 s 1 m 1 is the largest value that can ever be realized in such eruptions this limiting value being independent of planetary gravity and thus the same on all silicate bodies the eruption rate inferred for tvashtar can also be achieved by a negatively buoyant magma but in that case the source depth cannot be much greater than a few tens of kilometers we find that some eruptive events are consistent with the effusion of magmas which are buoyant relative to the crust whereas others appear to involve magmas which are not this implies that the distribution of crustal volatiles is laterally very inhomogeneous our analyses suggest that the depths from which magmas make their final ascent to the surface of io are generally of order tens rather than hundreds of kilometers

evidence for sulphide links in a crude oil asphaltene and kerogens from reductive cleavage by lithium in ethylamine abstract reduction of a sulphur rich asphaltene from a crude oil rozel point with lithium in ethylamine li etnh2 affords an alkane fraction similar to that obtained from desulphurisation with raney nickel but in higher yield using li etnd2 deuterium labelled alkanes were obtained thereby confirming the presence of sulphide linkages in the asphaltene fraction reduction of two sulphur rich kerogens with similar sulphur contents serpiano shale m triassic and jurf ed darawish jed u cretaceous afforded significant quantities of polar solvent extractable material both kerogens also yielded low amounts of hydrocarbons although the amount released from jed kerogen was significantly higher the results indicate that whereas the kerogens contain hydrocarbon moieties intermolecularly linked by sulphide bridges the distributions of the precursors lipids which were incorporated were different for example gc ms analysis of the labelled products from jed kerogen revealed them to be dominated by steranes of algal origin with the position s of deuterium labelling providing evidence of sulphide linking and cross linking on the other hand the labelled products from serpiano kerogen were dominated by hopanes of bacterial origin which were linked terminally via the side chain

geochemical characterization of malm zeta laminated carbonates from the franconian alb sw germany ii abstract during jurassic times especially within the malm stage local depressions formed on the eastern bavarian carbonate platform that were surrounded by wall reefs this created a unique depositional environment where in an open marine setting stagnant and anoxic bottom waters developed in an intra reef depression anoxic conditions were stabilized below wave base by enhanced salinity in the bottom waters and establishment of a density stratification biomarker analysis was applied to characterize palaeosalinity and redox conditions utilizing organic sulfur compound methylated chroman hopanoid and saturated isoprenoid distributions prevention of terrigenous influx by protecting reef walls lead to iron deficiency in intra reefal sediments causing early diagenetic sulfurization of functionalized lipids absence of clay mineral catalysts and early sulfurization favored an unusual steroid distribution lacking rearranged analogues but providing coexistence of saturated steranes with and configuration 13 17 spirosterenes unknown sterenes and steradienes as well as mono di and triaromatic steroids desulfurization of the polar fraction was carried out for two samples to verify that palaeoenvironment reconstruction based on free hydrocarbon and heterocompound distribution was not invalidated by sulfur quenching of selected compounds gammacerane was found to be the only component to occur exclusively in the sulfur bound fraction only minor amounts of hydrocarbons were released upon desulfurization implying that free bitumen analysis was applicable for organofacies characterization organic petrological investigation of organic mats revealed the presence of two different types of such structures comparison of organoclast fluorescence spectra with those of extracted porphyrin fractions indicate an origin of porphyrins exclusively from cyanobacterial mats whereas algal dominated mats yield no porphyrins this aims towards a better localization of specific biomarker origin in geological samples

silicate glass micro and nanospherules generated in explosive eruptions of ultrabasic magmas implications for the origin of pelletal lapilli abstract the genesis of spherical ash to lapilli sized clasts with a central phenocryst or lithic fragment mantled by a rim of fine grained juvenile material that includes abundant concentrically arranged prismatic crystals is interpreted as either i the result of the spinning of a magma bleb with a crystalline kernel in a fluidized system or ii the accretion of small melt droplets to a previously crystallized nucleus in a gas jet we demonstrate that the rims of pelletal lapilli within tephras of the cabezo segura volcano calatrava spain are clastic and were formed by the progressive welding of juvenile crystals and silicate glass droplets and to a lesser extent filaments both melt in origin around a large crystalline nucleus our results support the accretion hypothesis and offer explicit and new images of the melt droplets that were so far considered hypothetical particles these results indicate also that nanometre scale juvenile pyroclasts melt droplets and crystals can be generated in explosive eruptions of ultrabasic magmas those pyroclasts can be subsequently welded together inside a dense gas jet generating pelletal lapilli and ash

petroleum geocghemistry of the tarragona basin spanish mediterranean off shore abstract nine oils obtained from the tarragona basin spanish mediterranean off shore have been characterized geochemically in order to asses their source and maturity histories miocene deposits constitute the only known rock with hydrocarbon source potential of the area the sterane distributions indicate a common marine source for all of them except for amposta crude the occurrence in this oil of a series of unique biological markers and distributions methylsteranes and hopanes gammacerane etc enables us to postulate that marginal hypersalline carbonate evaporite episodes may have occurred in the basin during highly restricted deposition in the miocene thus determining a different oil composition analysis of formation waters supports the restricted marine depositional environment of the tarragona basin as well as the observed biodegradation of the oils recovered on the tarragona platform the oils belong to a maturity sequence that has been defined by new indices based on the isomerization of methyl substituted aromatic hydrocarbons dibenzothiophenes and long chain alkyltoluenes furthermore a series of long chain isoalkylbenzenes have been tentatively identified and assigned as archaebacterial markers

chondrites as samples of differentiated planetesimals abstract chondritic meteorites are unmelted and variably metamorphosed aggregates of the earliest solids of the solar system the variety of metamorphic textures in chondrites motivated the onion shell model in which chondrites originated at varying depths within a parent body heated primarily by the short lived radioisotope 26 al with the highest metamorphic grade originating nearest the center allende and a few other chondrites possess a unidirectional magnetization that can be best explained by a core dynamo on their parent body indicating internal melting and differentiation here we show that a parent body that accreted to 200 km in radius by 1 5 ma after the formation of calcium aluminum rich inclusions cais would have a differentiated interior and ongoing accretion would add a solid undifferentiated crust overlying a differentiated interior consistent with formational and evolutionary constraints inferred for the cv parent body this body could have produced a magnetic field lasting more than 10 ma this hypothesis represents a new model for the origin of some chondrites presenting them as the unprocessed crusts of internally differentiated early planetesimals such bodies may exist in the asteroid belt today the shapes and masses of the two largest asteroids 1 ceres and 2 pallas can be consistent with differentiated interiors conceivably with small iron cores with hydrated silicate or ice silicate mantles covered with undifferentiated crusts

petrology and geochemistry of d orbigny geochemistry of sahara 99555 and the origin of angrites petrology and geochemistry of d orbigny geochemistry of sahara 99555 and the origin of angrites

thiophenic biomarkers for palaeoenvironmental assessment and molecular stratigraphy reconstruction of ancient depositional environments is an important objective in the earth sciences the complex assemblages of organic molecules in sediments include compounds that can be related to known biochemicals produced by specific biota from well defined habitats1 3 and these chemical fossils are applied frequently to reconstruct palaeoenvironments especially in studies of organic and petroleum geochemistry and in chemical oceanography most of the compounds used in this way are hydro carbons2 4 although oxygenated for example alcohols acids and ketones and nitrogen containing for example porphyrins compounds have also been applied successfully1 2 here we report on the use of organic sulphur compounds as geochemical tools for palaeoenvironmental and stratigraphic assessment depth profiles of specific sulphur compounds related to certain organisms show significant variations reflecting changes both in sources of organic matter and in physical conditions such as salinity of the depositional environment in a number of cases these variations are not otherwise revealed by changes in lithology geochemical bulk data and or absolute and relative amounts of hydrocarbon biological markers moreover several organic sulphur compounds reveal the presence of unprecedented biochemicals in these palaeoenvironments

organic geochemical studies of a messinian evaporitic basin northern apennines italy ii isoprenoid and n alkyl thiophenes and thiolanes abstract series of n alkyl and isoprenoid thiophenes and thiolanes most of which have not been previously reported have been identified in an extract from a messinian upper miocene marl layer deposited under hypersaline euxinic conditions the identifications were based on mass spectra and chromatographic data of synthesized reference compounds and on comparison of mass spectra relative retention times and response on the fpd their specific structures and their distribution patterns show similarities with those of the alkanes inorganic sulphur is therefore considered to be incorporated into specific lipid moieties from archae bacterial and or algal input during diagenesis a biosynthetic origin of these compounds is also possible however the organic sulphur compounds encountered are thought to be indicators of a hypersaline depositional environment

structure and kinematics of a sinistral transpressive suture between the ossa morena and the south portuguese zones south iberian massif the ossa morena zone and the south portuguese zone represent the southernmost hercynian domains of the iberian massif lithostratigraphic petrographic and structural differences exist between both zones the boundary between the ossa morena and the south portuguese zones is marked by a narrow belt of amphibolites of tholeiitic affinity and related oceanic sequences the beja acebuches ophiolites the southernmost area of the ossa morena zone which bounds the acebuches amphibolites is composed of medium to high grade metamorphic rocks the ossa morena zone south portuguese zone suture preserves a complex story of middle to upper devonian to upper stephanian sinistral transpression the resulting structures were generated in a ductile to brittle regime transpressive shear zones affect the ophiolitic remnants and the high grade rocks of the southernmost area of the ossa morena zone the late hercynian faulting combines sinistral strike slip movements and some thrusting component which cut the suture to produce fish like megaboudins the transpressive regime can be explained by the oblique collision of the two plates now represented by the ossa morena zone and the south portuguese zone during the continental accretion on the scale of the hercynian belt this sinistral transpression belongs to a network of comparable structures explained by the impingement of the ibero armorican terranes