porosity and permeability in volcanic rocks a case study on the serie tobifera south patagonia argentina the middle to late jurassic serie tobifera belongs to the chon aike province and extends all over patagonia and the antarctic peninsula it consists largely of ignimbrites epiclastics and rhyolitic lavas and was considered only a minor reservoir rock for oil with fracture permeability petrographic and petrophysical data in selected core samples from the austral basin were collected to determine the processes controlling the porosity and permeability of these volcanic rocks the sequence of processes occurring during cooling and in the post cooling stages can modify sometimes substantially their original petrophysic characteristics the results show that the highest porosity and permeability occur in rocks with quench fractured glasses and in non welded ignimbrites with gas pipe structures followed by autobrecciated rhyolites welded ignimbrites massive glasses and fresh rhyolites have the lowest permeabilities the new data indicate that tectonic fracturing is not as significant as was considered before and application of these concepts are relevant in the assesment of volcanic reservoir quality

tropical sea surface temperatures for the past four centuries reconstructed from coral archives most annually resolved climate reconstructions of the common era are based on terrestrial data making it a challenge to independently assess how recent climate changes have affected the oceans here as part of the past global changes ocean2k project we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives validation exercises suggest that our reconstructions are interpretable for much of the past 400 years depending on the availability of paleoclimate data within and the reconstruction validation statistics for each target region analysis of the trends in the data suggests that the indian western pacific and western atlantic ocean regions were cooling until modern warming began around the 1830s the early 1800s were an exceptionally cool period in the indo pacific region likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century decadal scale variability is a quasi persistent feature of all basins twentieth century warming associated with greenhouse gas emissions is apparent in the indian west pacific and western atlantic oceans but we find no evidence that either natural or anthropogenic forcings have altered el nino southern oscillation related variance in tropical sea surface temperatures our marine based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change

cementation and porosity evolution of tight sandstone reservoirs in the permian sulige gas field ordos basin central china abstract tight sandstone gas reservoirs constitute an important type of unconventional gas resources and may be of crucial significance as environment friendly source of energy in the world however the dynamics of densification and evolution of the low porosity and low permeability sandstone reservoirs are intensively debated in literature recently the question of sequence of reservoir densification and hydrocarbon accumulation has arisen a typical tight sandstone reservoir the first member of the shanxi formation and the eighth member of shihezi formation in the permian sulige gas field in central china provides an excellent case study to probe these questions by using a variety of different methodologies such as scanning electron microscopy sem x ray diffraction xrd cathodoluminescence fluid inclusion analysis and confocal raman spectrometer analysis we identified different authigenic minerals such as illite kaolinite dickite chlorite and smectite illitization coexisting with siliceous and calcitic cements these authigenic minerals precipitated at different diagenetic stages related to the changing conditions during compaction and lithification and therefore changed the porosities of the host rocks during each of these stages the types of pores in the sulige gas field are dominated by illite and kaolinite intercrystalline pores matrix solution pores and primary intergranular pores the results of this study suggest that compaction and cementation are the reasons for the most distinct loss in porosity on the other hand kaolinite and illite preserve their intercrystalline pores which could be identified as the main reserve space of the tight gas reservoirs therefore the secondary porosity of the sandstone reservoirs forms the most important contributor to the gas reservoir potential in the sulige gas field in addition it could be inferred that the tight gas accumulation took place during the densification of the reservoirs the implications of the presented results may also help to understand the formation of other tight reservoirs world wide

distinct modes of east asian winter monsoon documented by a southern red sea coral record the large scale boreal winter climatic patterns associated with interannual variability in a coral oxygen isotope 18o record from the southern red sea covering most of the last century are investigated from the early 1930s to the early 1960s the winter coral 18o record reflecting temperature and salinity variations in southern red sea surface waters is associated with global or large scale sea surface temperature sst and 850 mb geopotential height z850 anomalies which project on the corresponding patterns associated with the el nino southern oscillation enso in contrast since the early 1960s the winter coral 18o record is related to a z850 pattern that reflects the enso independent part of the east asian winter monsoon eawm which includes the siberian high the east asian through and the east asian upper tropospheric jet our results indicate a weakening of the enso control on interannual temperature salinity variations in southern red sea surface waters in the early 1960s due to the warming of the indian ocean and suggest that information about the nonstationarity in the relationship between enso and two distinct modes of eawm can be documented in southern red sea coral 18o records

volcanic rocks as prolific gas reservoir a case study from the qingshen gas field in the songliao basin ne china abstract the qingshen gas field with over 100 billion cubic meters bcms of proven gas reserves was discovered recently in the upper jurassic lower cretaceous strata of the songliao basin northeastern china the stratigraphic relationships and gas chemical compositions indicate mixed gas sources dominantly from the upper jurassic lower cretaceous coals and associated dark mudstones underlying the gas reservoirs with minor contribution from deep inorganic sources the gas reservoirs consist mainly of volcanic rocks rhyolite and tuff with some production also from the conglomerate gas charge into these largely volcanic rock reservoirs appears to coincide with the peak gas generation in the deep upper jurassic lower cretaceous coal measures the presence of several thick lacustrine mudstone beds in the upper cretaceous strata as regional caprocks and relatively mild structural deformation since the late cretaceous are among the favorable conditions for the preservation of large volume of natural gases in these relatively deep gas reservoirs the gas yields are the highest in the paleomorphological highs where fractures and secondary porosity are well developed in the gas reservoirs

modal distribution of pore throat size in sandy conglomerates from an alluvial fan environment lower karamay formation junggar basin west china abstract alluvial fan exhibits various modal distribution of pore throat size which effectively control the oil displacement efficiency and fluid movement however the genetic mechanism of the modal distribution of the pore throat size and its macroscopic distribution within alluvial fan is poorly understood based on core analysis this paper which take the sandy conglomerate reservoir within the alluvial fan in junggar basin as an example aims to study the variations in modal distribution of pore throat size and controlling mechanisms the results reveal that 1 the modal distribution types of the pore throat size are complicated and can be classified into six subtypes including unimodal type uni unimodal type uni unimodal type uni bimodal type bi bimodal type bi and multimodal type multi uni uni and uni is dominated by intergranular pores intragranular dissolved pores and micropores respectively bi bi and multi are characterized by the combination of several pore types 2 diagenesis including compaction cementation and dissolution rock composition the mudstone fragment content and rock texture the clay content control the volume of each pore throat type which significantly influences the modal distribution of the pore throat size lithofacies with low mudstone fragment and clay content and great grain sorting tend to have experienced weak compaction thereby retaining a large volume of intergranular pores and have been subjected to strong dissolution when adequate acidic ions occur in the porewater resulting in a large volume of intragranular dissolved pores strong dissolution reduced the rock compressive strength and further enhanced the degree of mechanical compaction during the burial process cementation occurred later than compaction and dissolution and its intensity is controlled by the supply of co2 and ca2 and compaction intensity thus reducing the volume of intergranular pores the content of mudstone fragment and clay varies among different lithofacies of different origins for traction current deposits lithofacies with smaller median grain size contain fewer mudstone fragments resulting in fewer micropores the clay content decreased first and then increased with decreasing median grain size and lithofacies with lower clay content cause less volume of micropores 3 lithofacies types combined with porewater condition for dissolution and lithofacies location affect the diagenetic intensity rock composition and rock texture variations thus resulting in various modal distribution of pore throat size within the alluvial fan moreover the rock texture especially grain sorting is very important for compaction and facilitates percolation of meteoric water and dissolution

near infrared spectral mapping of titan s mountains and channels 1 we investigate the spectral reflectance properties of channels and mountain ranges on titan using data from cassini s visual and infrared mapping spectrometer vims obtained during the t9 encounter 26 december 2005 we identify the location of channels and mountains using synthetic aperture radar maps obtained from cassini s radar instrument during the t13 30 april 2006 flyby channels are evident even in vims imaging with spatial resolution coarser than the channel size the channels share spectral characteristics with titan s dark blue terrain e g the huygens landing site that is consistent with an enhancement in water ice content relative to the rest of titan we use this fact to measure widths of 1 km for the largest channels comparison of the data sets shows that in our study area within the equatorial bright spectral unit east of xanadu mountains are darker and bluer than surrounding smooth terrain these results are consistent with the equatorial bright terrain possessing a veneer of material that is thinner in the regions where there are mountains and streambeds that have likely undergone more recent and extensive erosion we suggest a model for the geographic relationship of the dark blue dark brown and equatorial bright spectral units based on our findings

interaction between the enso and the asian monsoon in a coral record of tropical climate the oxygen isotopic composition of a banded coral from the western equatorial indian ocean provides a 150 year long history of the relation between the el nino southern oscillation enso phenomenon and the asian monsoon interannual cycles in the coral time series were found to correlate with pacific coral and instrumental climate records suggesting a consistent linkage across ocean basins despite the changing frequency and amplitude of the enso however decadal variability that is characteristic of the monsoon system also dominates the coral record which implies important interactions between tropical and midlatitude climate variability one prominent manifestation of this interaction is the strong amplitude modulation of the quasi biennial cycle

characteristics and petroleum origin of the carboniferous volcanic rock reservoirs in the shixi bulge of junggar basin western china abstract shixi bulge of the central junggar basin in western china is a unique region that provides insight into the geological and geochemical characteristics of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks in the shixi bulge mainly consist of striped lava and agglomerate as well as breccia lava and tight tuff volcanic rocks differ in porosity and permeability striped lava exhibits the highest porosity average 14 2 but the lowest permeability average 0 67 10 15 m among the rock types primary gas pores are widely developed and mostly filled secondary dissolution pores and fractures are two major reservoir storage spaces capillary pressure curves suggest the existence of four pore structure types of reservoir rocks several factors namely lithology pore structure and various diagenesis govern the physical properties of volcanic rocks the oil is characterized by a high concentration of tricyclic terpane a terpane distribution of c 23 21 c 20 and sterane distributions of c 27 28 29 and c 27 c 28 29 oil and gas geochemistry revealed that the oil is a mixture derived primarily from p 2 w source rock and secondarily from p 1 j source rock in the sag west of pen 1 well the gases are likely gas mixtures of humic and sapropelic organic origins with the sapropelic gas type dominant in the mixture the gas mixture is most likely cracked from kerogen rather than oils the carboniferous volcanic reservoirs in shixi bulge share some unique characteristics that may provide useful insights into the various roles of different volcanic reservoir types in old volcanic provinces the presence of these reservoirs will undoubtedly encourage future petroleum exploration in volcanic rocks up to the deep parts of sedimentary basins

direct observations of basin wide acidification of the north pacific ocean 1 global ocean acidification is a prominent inexorable change associated with rising levels of atmospheric co 2 here we present the first basin wide direct observations of recently declining ph along with estimates of anthropogenic and non anthropogenic contributions to that signal along 152 w in the north pacific ocean 22 56 n ph changes between 1991 and 2006 were essentially zero below about 800 m depth however in the upper 500 m significant ph changes as large as 0 06 were observed anthropogenic and non anthropogenic contributions over the upper 800 m are estimated to be of similar magnitude in the surface mixed layer depths to 100 m the extent of ph change is consistent with that expected under conditions of seawater atmosphere equilibration with an average rate of change of 0 0017 yr future mixed layer changes can be expected to closely mirror changes in atmospheric co 2 with surface seawater ph continuing to fall as atmospheric co 2 rises

geology of the selk crater region on titan from cassini vims observations abstract observations of titan obtained by the cassini visual and infrared mapping spectrometer vims have revealed selk crater a geologically young bright rimmed impact crater located 800 km north northwest of the huygens landing site the crater rim crest diameter is 90 km its floor diameter is 60 km a central pit peak 20 30 km in diameter is seen the ratio of the size of this feature to the crater diameter is consistent with similarly sized craters on ganymede and callisto all of which are dome craters the vims data unfortunately are not of sufficient resolution to detect such a dome the inner rim of selk crater is fluted probably by eolian erosion while the outer flank and presumed ejecta blanket appear dissected by drainages particularly to the east likely the result of fluvial erosion terracing is observed on the northern and western walls of selk crater within a 10 15 km wide terrace zone identified in vims data the terrace zone is bright in sar data consistent with it being a rough surface the terrace zone is slightly wider than those observed on ganymede and callisto and may reflect differences in thermal structure and or composition of the lithosphere the polygonal appearance of the crater likely results from two preexisting planes of weakness oriented at azimuths of 21 and 122 east of north a unit of generally bright terrain that exhibits similar infrared color variation and contrast to selk crater extends east southeast from the crater several hundred kilometers we informally refer to this terrain as the selk bench both selk and the bench are surrounded by the infrared dark belet dune field hypotheses for the genesis of the optically bright terrain of the bench include wind shadowing in the lee of selk crater preventing the encroachment of dunes impact induced cryovolcanism flow of a fluidized ejecta blanket similar to the bright crater outflows observed on venus and erosion of a streamlined upland formed in the lee of selk crater by fluid flow vestigial circular outlines in this feature just east of selk s ejecta blanket suggest that this might be a remnant of an ancient cratered crust evidently the southern margin of the feature has sufficient relief to prevent the encroachment of dunes from the belet dune field we conclude that this feature either represents a relatively high viscosity fluidized ejecta flow a class intermediate to ejecta blankets and long venusian style ejecta flows or a streamlined upland remnant that formed downstream from the crater by erosive fluid flow from the west northwest

fine grained volcanic hydrothermal sedimentary rocks in permian lucaogou formation santanghu basin nw china implications on hydrocarbon source rocks and accumulation in lacustrine rift basins abstract subaqueous volcanic hydrothermal field is a complex hybrid geological system where sediments originated from volcanic hydrothermal lacustrine terrestrial and biotic sources are mixed recent petrological studies on such sediments have indicated a potential relationship between volcanic hydrothermal activities and oil generation and accumulation here we explore the mechanisms of sedimentation and oil accumulation in well laminated organic rich fine grained sedimentary rocks in permian lucaogou formation deposited in the lacustrine santanghu rift basin nw china we conducted petrographic carbon and oxygen isotopic and organic geochemical analyses of fifty four core samples from three wells forty eight samples from well w1 two from w2 four from w3 designed for tight oil exploration four main observations and interpretations are 1 the fine grained sediments are a mixture of volcanic hydrothermal detrital feldspar grains authigenic quartz crystals and primary lacustrine dolomite forming interbedded tuffaceous shale and dolostone 2 authigenic quartz crystals were precipitated from acidic hydrothermal fluids whereas fine grained angular alkaline feldspars were derived from subaqueous volcanic eruption 3 the toc content and oil generation potential increase with increased mixing of feldspars and carbonate minerals hence the dolomite bearing tuffaceous shale and tuffaceous dolostone are the best source rocks and 4 the fine grained sedimentary rocks are interpreted as a subaqueous volcanic hydrothermal deposit that controls the source potential the sedimentary processes of an ancient sediment hosted geothermal system and its implications on hydrocarbon source rocks and accumulation were first identified algal bloom induced by subaqueous eruptions is the main cause for episodic deposition of organic matter and extreme heterogeneity in both lithofacies and source rock distribution the results suggest that cone shaped buildups on seismic sections which were formed by volcanic hydrothermal deposits and contain highly mixed feldspar and carbonate sediments are the best hydrocarbon reservoirs and demonstrate a strong relationship between volcanic hydrothermal activities and hydrocarbon accumulation in an extensional tectonic setting

origin and accumulation mechanisms of petroleum in the carboniferous volcanic rocks of the kebai fault zone western junggar basin china abstract the kebai fault zone of the west junggar basin in northwestern china is a unique region to gain insights on the formation of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks are widespread in the kebai fault zone and consist of basalt basaltic andesite andesite tuff volcanic breccia sandy conglomerate and metamorphic rocks the volcanic oil reservoirs are characterized by multiple sources and multi stage charge and filling history characteristic of a complex petroleum system geochemical analysis of the reservoir oil hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source the petroleum filling history and the dominant mechanisms controlling the petroleum accumulation reservoir oil geochemistry indicates that the oil contained in the carboniferous volcanic rocks of the kebai fault zone is a mixture the oil is primarily derived from the source rock of the permian fengcheng formation p 1 f and secondarily from the permian lower wuerhe formation p 2 w compared with the p 2 w source rock p 1 f exhibits lower values of c 19 tt c 23 tt c 19 20 tt tt ts ts tm and 20r sterane c 27 c 28 ratios but higher values of tt c 23 c 21 hhi gammacerane c 30 hopane hopane 20s c 34 c 33 c 29 and c 29 20s 20s 20r ratios three major stages of oil charge occurred in the carboniferous in the middle triassic late triassic to early jurassic and in the middle jurassic to late jurassic periods respectively most of the oil charged during the first stage was lost while moderately and highly mature oils were generated and accumulated during the second and third stages oil migration and accumulation in the large scale stratigraphic reservoir was primarily controlled by the top carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity secondary dissolution pores and fractures are the two major reservoir storage space types in the reservoirs structural highs and reservoirs near the unconformity are two favorable oil accumulation places the recognition of the large scale carboniferous volcanic reservoirs in the kebai fault zone and understanding of the associated petroleum accumulation mechanisms provide new insights for exploring various types of volcanic reservoir plays in old volcanic provinces and will undoubtedly encourage future oil and gas exploration of deeper strata in the region and basins elsewhere with similar settings

characterization of the paleocrusts of weathered carboniferous volcanics from the junggar basin western china significance as gas reservoirs abstract volcanic reservoirs comprise reservoir spaces made up of pores and cracks with secondary solution pores and tectonic induced cracks being the most dominant various volcanic lithologies and lithofacies show differences in porosity and permeability because resistance to weathering differs among volcanic rock types this study shows that among volcaniclastic rocks volcanic breccia shows higher porosity and permeability as well as poor pore radius sorting and connectivity compared with volcanic tuff basalt and monzonitic porphyry show higher porosity and permeability compared with other volcanic lava and subvolcanic rocks the level of porosity of different facies is in the order of effusive facies explosive facies subvolcanic rock facies volcanic sedimentary facies eruptive facies reservoirs show relatively high porosity and permeability near the top surface of the weathered crust porosity and permeability generally decrease with an increase in the distance from the carboniferous top weathered crust this condition indicates that weathering controls the properties of volcanic reservoirs the distribution pattern of porosity and permeability in the weathered crust of volcanic facies differs strong weathering contributes to a decrease in porosity and permeability at the top part of the weathered crust various weathering effects on volcanic rocks control porosity and permeability vertically and the gas accumulates mainly in the range of 0 m 200 m from the top of the weathered crust gas accumulation in subvolcanic and volcaniclastic rocks is better than that in volcanic lava the log curve in geophysical exploration can help determine the vertical structure of weathered crust the strong weathering belt shows high gamma low electrical resistivity low density high neutron porosity and high interval transit time

global scale surface spectral variations on titan seen from cassini vims we present global scale maps of titan from the visual and infrared mapping spectrometer vims instrument on cassini we map at 64 near infrared wavelengths simultaneously covering the atmospheric windows at 0 94 1 08 1 28 1 6 2 0 2 8 and 5 m with a typical resolution of 50 km pixel or a typical total integration time of 1 s our maps have five to ten times the resolution of ground based maps better spectral resolution across most windows coverage in multiple atmospheric windows and represent the first spatially resolved maps of titan at 5 m the vims maps provide context and surface spectral information in support of other cassini instruments we note a strong latitudinal dependence in the spectral character of titan s surface and partition the surface into 9 spectral units that we describe in terms of spectral and spatial characteristics

processes controlling porosity and permeability in volcanic reservoirs from the austral and neuquen basins argentina volcanic rocks develop primary and secondary porosity and permeability depending on both their lithology and the sequence of processes involved in their formation primary processes welding deuteric crystal dissolution gas release flow fragmentation and crystal shattering may lead to high porosity and permeability the best example of which is a nonwelded ignimbrite with well developed gas pipe zones secondary processes different types of alteration however tend to decrease primary porosity however certain secondary processes such as dissolution and hydraulic fracturing may contribute to enhance total porosity and permeability these conclusions were developed through a systematic review of reservoir quality in volcanic rocks integrating lithology and process interpretation with petrophysical data the said information was taken from selected cores of volcanic rocks from the serie tobfera unit in the austral basin and the precuyano unit in the neuqun basin argentina a clear understanding of both primary and secondary processes may serve to predict the quality of volcanic reservoirs and could be used as a guide for oil and gas exploration and development in many parts of the world

modes of climate variability synthesis and review of proxy based reconstructions through the holocene abstract modes of climate variability affect global and regional climates on different spatio temporal scales and they have important impacts on human activities and ecosystems as these modes are a useful tool for simplifying the understanding of the climate system it is crucial that we gain improved knowledge of their long term past evolution and interactions over time to contextualise their present and future behaviour we review the literature focused on proxy based reconstructions of modes of climate variability during the holocene i e the last 11 7 thousand years with a special emphasis on i proxy based reconstruction methods ii available proxy based reconstructions of the main modes of variability i e el nino southern oscillation pacific decadal variability atlantic multidecadal variability the north atlantic oscillation the southern annular mode and the indian ocean dipole iii major interactions between these modes and iv external forcing mechanisms related to the evolution of these modes this review shows that modes of variability can be reconstructed using proxy based records from a wide range of natural archives but these reconstructions are scarce beyond the last millennium partly due to the lack of robust chronologies with reduced dating uncertainties technical issues related to proxy calibration and difficulty elucidating their stationary impact or not on regional climates over time while for each mode the available reconstructions tend to agree at mutidecadal timescales they show notable disagreement on shorter timescales beyond the instrumental period the reviewed evidence suggests that the intrinsic variability of modes can be modulated by external forcing such as orbital solar volcanic and anthropogenic forcing the review also highlights some modes experience higher variability over the instrumental period which is partly ascribed to anthropogenic forcing these features stress the paramount importance of further studying their past variations using long climate proxy records for the progress of climate science

dunes on titan observed by cassini radar thousands of longitudinal dunes have recently been discovered by the titan radar mapper on the surface of titan these are found mainly within 30 of the equator in optically near infrared and radar dark regions indicating a strong proportion of organics and cover well over 5 of titan s surface their longitudinal duneform interactions with topography and correlation with other aeolian forms indicate a single dominant wind direction aligned with the dune axis plus lesser off axis or seasonally alternating winds global compilations of dune orientations reveal the mean wind direction is dominantly eastwards with regional and local variations where winds are diverted around topographically high features such as mountain blocks or broad landforms global winds may carry sediments from high latitude regions to equatorial regions where relatively drier conditions prevail and the particles are reworked into dunes perhaps on timescales of thousands to tens of thousands of years on titan adequate sediment supply sufficient wind and the absence of sediment carriage and trapping by fluids are the dominant factors in the presence of dunes

geochemistry and origin of a black mudstone in a volcaniclastic environment ordovician lower rhyolitic tuff formation north wales uk black mudstones in marine volcaniclastic environments have been interpreted both as non volcanic background sedimentation and as fine grained vitric dust from the waning stages of primary volcanism although difficult to distinguish by standard petrographic techniques differentiation between the two is crucial when attempting to determine sedimentation rates or to infer periods of volcanic quiescence in the ordovician lower rhyolitic tuff formation of north wales such a fine grained black unit at cwm idwal is geochemically similar to an underlying rhyolite ash flow tuff its chemical index of alteration cia is identical to that of the tuff these data suggest that the black mudstone unit is a vitric tuff related to the underlying ash flow tuff use of a cia in addition to trace element geochemistry should in most cases serve to distinguish tuffs from silicified mudstones

artificial neural network assisted prediction of dissolution spatial distribution in the volcanic weathered crust a case study from chepaizi bulge of junggar basin northwestern china abstract the reservoir rocks in the volcanic weathered crust are characterized by plentiful dissolution pores caverns and fractures however as an essential control factor of the reservoir distribution volcanic dissolution is often ignored in quantitative studies in this paper we propose a complete artificial intelligence workflow to model and predict the volcanic dissolution distribution by integrating the image logging semi quantitative analysis with seismic prediction a synthetic reservoir property named dcv dissolution comprehensive values is generated as logging curves from xrmi resistivity pseudo pictures to indicate the intensity of dissolution these curves are then used as the target for the seismic based prediction in an artificial intelligence framework a multi layer artificial neural network ann model is constructed in order to map the seismic attributes into the dcv the methodology is demonstrated on a real case study from the junggar basin in northwestern china the maps and profiles from the prediction represent the dissolution values in the volcanic weathered crust the predictions are consistent with the geological volcanic dissolution model provided by geological knowledge it is concluded that the spatial dissolution distribution in volcanic weathered crust can be reliably predicted by this integrated method

volcanic settings and their reservoir potential an outcrop analog study on the miocene tepoztlan formation central mexico abstract the reservoir potential of volcanic and associated sedimentary rocks is less documented in regard to groundwater resources and oil and gas storage compared to siliciclastic and carbonate systems outcrop analog studies within a volcanic setting enable to identify spatio temporal architectural elements and geometric features of different rock units and their petrophysical properties such as porosity and permeability which are important information for reservoir characterization despite the wide distribution of volcanic rocks in mexico their reservoir potential has been little studied in the past in the valley of mexico situated 4000 m above the neogene volcanic rocks groundwater is a matter of major importance as more than 20 million people and 42 of the industrial capacity of the mexican nation depend on it for most of their water supply here we present porosity and permeability data of 108 rock samples representing five different lithofacies types of the miocene tepoztlan formation this 800 m thick formation mainly consists of pyroclastic rocks mass flow and fluvial deposits and is part of the southern transmexican volcanic belt cropping out south of the valley of mexico and within the two states of morelos and mexico state porosities range from 1 4 to 56 7 average porosity is 24 8 generally permeabilities are low to median 0 2 933 3 md with an average permeability of 88 5 md the lavas are characterized by the highest porosity values followed by tuffs conglomerates sandstones and tuffaceous breccias on the contrary the highest permeabilities can be found in the conglomerates followed by tuffs tuffaceous breccias sandstones and lavas the knowledge of these petrophysical rock properties provides important information on the reservoir potential of volcanic settings to be integrated to 3d subsurface models

characteristics controls and geological models of hydrocarbon accumulation in the carboniferous volcanic reservoirs of the chunfeng oilfield junggar basin northwestern china the national natural science foundation of china grant no 41672120 and no 41402120 and shandong university of science and technology research fund grant no 2015tdjh101

fracture permeability and water rock interaction in a shallow volcanic groundwater reservoir and the concern of its interaction with the deep geothermal reservoir of mt amiata italy abstract the study of core samples and in hole data of a 545 m deep well drilled in mt amiata extinct volcano allowed a better characterization of the shallow volcanic reservoir which is exploited for domestic utilization the new discovery is that 1 the water table level is at a depth of 302 m b g l 783 m a s l in agreement with recent magnetotelluric surveys and in disagreement with previous hydrogeological models 2 there is no evidence of present or past interaction with geothermal fluids the alteration minerals being present only in fractures within the volcanic rocks and indicating fluids of low temperature and relatively low ph due to gas inlets in the volcanic reservoir and 3 the volcanic reservoir is characterized by fracture permeability as shown by the fracture system along the well on the base of these new data the previous geological and hydrogeological models of mt amiata should be revised in particular the hypothesis of a catastrophic lowering of the water table in a short time span is unlikely

global pattern of titan s dunes radar survey from the cassini prime mission 1 we present a map of the orientation and extent of titan s sand dunes derived from the complete radar imaging dataset from the cassini prime mission the 16 000 dune segments we have mapped cover 8 of the titan s surface suggesting a total coverage of 20 are confined within 30 of the equator and show local and regional deviations of dune orientation of up to about 40 from due eastwards there is no obvious global longitudinal pattern although some divergence with latitude is apparent the most striking pattern is one of collimation by and divergence around bright and or high terrain obstacles 100 300 m high obstruct dunes when the local slope is 1 50 or steeper while slopes 1 200 or shallower cause dunes to thin out as they climb or to deviate around the obstacles

mode shift in the indian ocean climate under global warming stress 1 a 115 year coral record from kenya has been found to preserve the history of rainfall anomalies in east africa in relation to global warming induced indian ocean dipole iod variability the coral iod index demonstrates a dominantly decadal periodicity in the early part of the 20th century this low frequency iod occurred more frequently before 1924 with mostly quasi biennial ranging from 18 months to 3 years events since 1960 the mode shift has also coincided with an intensified coupling with indian summer monsoon rainfall we suggest that a warming of the western indian ocean which has attenuated and replaced the el nino southern oscillation effect over the indian ocean has driven the observed shift

formation mechanism of volcanic reservoirs within a volcanostratigraphic framework the case of the wangfu fault depression in the songliao basin china abstract we discuss the reservoir formation mechanisms in volcanic gas reservoirs within a volcanostratigraphic framework with a focus on the huoshiling formation of the wangfu fault depression in the songliao basin china the volcanic sequences are divided from large to small into the volcanic cycle vc cooling unit set cus and cooling unit cu the cu is the basic volcanogenic stratigraphic unit and the cus is a superposition of cooling units which may be recognized on seismic profiles the huoshiling formation consists of two volcanic cycles and one volcanic sedimentary cycle the formation mechanisms of volcanic reservoirs include three processes based on the strata s evolution first cus formed and primary pore spaces developed near cooling surfaces second cuss and vcs formed and parasyngenetic and secondary pore spaces developed around the crater or caldera especially near the weathering surface lastly numerous dissolved pores and structural fractures formed during burial and concentrated near the fault belt cus volcanic edifices and structural systems controlled the formation of volcanic reservoirs the overlapping crater proximal crater region and the faulted area were centres of reservoir formation in the huoshiling formation cus 6 cus 8 and cus 13 are the major horizons where volcanic reservoirs developed forming dissolution reservoirs and structurally fractured reservoirs for natural gas accumulation

central pit and dome craters exposing the interiors of ganymede and callisto central pit craters on the large icy satellites ganymede and callisto are an unusual crater class perhaps related to the unusual properties of water ice the detailed morphology and dimensions of pit crater features differ from those of smaller normal complex craters on these two satellites pit crater depths appear to be constant regardless of diameter rim collapse is also restricted relative to that in lunar craters or smaller ganymede craters the floors of pits in craters larger than 60 km are occupied by smooth bright domes pit to crater and dome to crater diameter ratios increase linearly with crater diameter and are indistinguishable on ganymede and callisto and with terrain type or surface longitude the floors and central structures of young bright rayed pit craters such as osiris are covered by a thin uniformly bright impact melt or frost deposit thus domes and pits form rapidly on the time scale of the impact itself rather than by long term postimpact intrusion or extrusion the bright domes in pit craters are most simply explained as the uplift and exposure of relatively ice rich material from depths of 3 5 to 5 km during impact this process is almost directly analogous to the uplift and exposure of anamolous deep seated material observed in terrestrial and lunar craters the unusual pit morphology on icy satellites may be the result of impact into crust that is mechanically much weaker at shallow depth than on rocky bodies such as the moon because crater morphology is strongly dependent on ice rock composition the similarity of pit and dome dimensions on ganymede and callisto indicates that the structure and rheology of the crusts of these bodies down to depths of 10 km are very similar and have been for several b y pit crater morphology indicates that the crusts of both satellites are probably ice rich and differentiated

the geology of hotei regio titan correlation of cassini vims and radar abstract joint cassini vims and radar sar data of 700 km wide hotei regio reveal a rich collection of geological features that correlate between the two sets of images the degree of correlation is greater than anywhere else seen on titan central to hotei regio is a basin filled with cryovolcanic flows that are anomalously bright in vims data in particular at 5 m and quite variable in roughness in sar the edges of the flows are dark in sar data and appear to overrun a vims bright substrate sar stereo topography shows the flows to be viscous 100 200 m thick on its southern edge the basin is ringed by higher 1 km mountainous terrain the mountains show mixed texture in sar data some regions are extremely rough exhibit low and spectrally neutral albedo in vims data and may be partly coated with darker hydrocarbons around the southern margin of hotei regio the sar image shows several large dendritic radar bright channels that flow down from the mountainous terrain and terminate in dark blue patches seen in vims images whose infrared color is consistent with enrichment in water ice the patches are in depressions that we interpret to be filled with fluvial deposits eroded and transported by liquid methane in the channels in the vims images the dark blue patches are encased in a latticework of lighter bands that we suggest to demark a set of circumferential and radial fault systems bounding structural depressions conceivably the circular features are tectonic structures that are remnant from an ancient impact structure we suggest that impact generated structures may have simply served as zones of weakness no direct causal connection such as impact induced volcanism is implied we also speculate that two large dark features lying on the northern margin of hotei regio could be calderas in summary the preservation of such a broad suite of vims infrared color variations and the detailed correlation with features in the sar image and sar topography evidence a complex set of geological processes pluvial fluvial tectonic cryovolcanic impact that have likely remained active up to very recent geological time

enhanced multidecadal climate variability in the seventeenth century from coral isotope records in the western indian ocean 1 the slowly growing coral diploastreaheliopora affords a novel opportunity to obtain multicentury records of paleoclimate including details of the interannual rhythms associated with the el nino southern oscillation enso system we examine climate variability in an enso teleconnected region using new oxygen isotope records from d heliopora spanning most of the twentieth 1896 1998 and seventeenth 1622 1722 centuries from the mafia archipelago tanzania the modern record demonstrates coherency with relevant instrumental and proxy time series documents twentieth century warming and displays significant power at enso periodicities the seventeenth century record lacks any trend exhibits interannual variance comparable to the modern record and displays a pronounced interdecadal signal not evident in the twentieth century that correlates with other tropical and hemispheric climate records we find no clear evidence of solar irradiance influence on interannual variability in the western indian ocean during these intervals although the mean sea surface temperature appears to vary inversely with insolation

recognition classification and mechanical description of debris flows abstract various types of flow or mass movement involving water and sediments occur on steep slopes in mountainous areas among them debris flows are peculiar events during which a large volume of a highly concentrated viscous water debris mixture flows through a stream channel throughout the world these phenomena cause considerable damage but remain poorly understood although a basic knowledge is already available concerning their recognition and propagation firstly a synthesis of the useful practical criteria of recognition is proposed debris flows must be seen as intermediate phenomena between hyperconcentrated flows intense bed load transport and landslides separated from them by sharp transitions of some characteristics celerity deposit nature and flow type two parameters solid fraction and material type thought to be appropriate for a sound and practical classification are brought out and the corresponding complete classification of flow and mass movements in mountain areas is presented two extreme debris flow types are thus distinguished muddy debris flows and granular debris flows a critical review of recent advances in debris flow dynamic is then proposed it is pointed out that adequate work must be carried out in the field of non newtonian fluid mechanics in particular one fundamental rheological property of debris flow materials is the yield stress which explains thick deposits on steep slopes and can be inferred from field measurements furthermore it can be used to estimate viscous dissipation within the bulk during flow relevant models predicting muddy debris flow dynamics are already available whereas further progress is needed concerning granular flows

optimized coral reconstructions of the indian ocean dipole an assessment of location and length considerations the indian ocean dipole iod or indian ocean zonal mode is a coupled ocean atmosphere climate oscillation that has profound impacts on rainfall distribution across the indian ocean region instrumental records provide a reliable representation of iod behavior since 1958 while coral reconstructions currently extend the iod history back to 1846 large fluctuations in the number and intensity of positive iod events over time are evident in these records but it is unclear to what extent this represents multidecadal modulation of the iod or an anthropogenically forced change in iod behavior in this study we explore the suitability of coral records from single site locations in the equatorial indian ocean for capturing information about the occurrence and magnitude of positive iod piod events we find that the optimum location for coral reconstructions of the iod occurs in the southeastern equatorial indian ocean along the coast of java and sumatra between 3 and 7 s here the strong ocean cooling and atmospheric drying during piod events are unambiguously recorded in coral oxygen isotope records which capture up to 50 of iod variance unforced experiments with coupled climate models suggest that potential biases in coral estimates of piod frequency are skewed toward overestimating piod recurrence intervals and become larger with shorter reconstruction windows and longer piod recurrence times model output also supports the assumption of stationarity in sea surface temperature relationships in the optimum iod location that is necessary for paleoclimate reconstructions this study provides a targeted framework for the future generation of paleoclimate records including optimized coral reconstructions of past iod variability

impact craters on titan five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22 of titan s surface imaged by cassini s high resolution radar through december 2007 the certain craters have morphologies similar to impact craters on rocky planets as well as two with radar bright jagged rims the less certain craters often appear to be eroded versions of the certain ones titan s craters are modified by a variety of processes including fluvial erosion mass wasting burial by dunes and submergence in seas but there is no compelling evidence of isostatic adjustments as on other icy moons nor draping by thick atmospheric deposits the paucity of craters implies that titan s surface is quite young but the modeled age depends on which published crater production rate is assumed using the model of artemieva and lunine 2005 suggests that craters with diameters smaller than about 35 km are younger than 200 million years old and larger craters are older craters are not distributed uniformly xanadu has a crater density 2 9 times greater than the rest of titan and the density on equatorial dune areas is much lower than average there is a small excess of craters on the leading hemisphere and craters are deficient in the north polar region compared to the rest of the world the youthful age of titan overall and the various erosional states of its likely impact craters demonstrate that dynamic processes have destroyed most of the early history of the moon and that multiple processes continue to strongly modify its surface the existence of 24 possible impact craters with diameters less than 20 km appears consistent with the ivanov basilevsky and neukum 1997 model of the effectiveness of titan s atmosphere in destroying most but not all small projectiles

origin and migration pathway of biodegraded oils pooled in multiple reservoirs of the chepaizi uplift junggar basin nw china insights from geochemical characterization and chemometrics methods abstract the chepaizi uplift possesses three sets of oil bearing reservoirs six sets of source intervals multiple episodes of hydrocarbon charging and variable physical properties of crude oils in this study based on geochemical characterization source intervals and the biodegradation rank of the crude oils four oil populations named as group a b c and d d1 d2 were defined the combined results of q cluster analysis qca and discriminant analysis da indicate that group a occurred mainly in lower neogene shawan formation n1s in the western chepaizi uplift and were primarily derived from the middle lower jurassic xishanyao badaowan sangonghe formations j2x j1b j1s and a little of paleogene anjihaihe formation e2 3a of the sikeshu sag group b occurred essentially in upper carboniferous xibeikulasi formation c2x of the western chepaizi and originated mainly from the j1b mudstone of the shawan sag in addition the crude oils of group c occurred mainly in the lower cretaceous tugulu group k1tg of the eastern chepaizi and were primarily derived from carboniferous sourced oil from the chepaizi uplift the crude oils of groups d d1 and d2 are mixed with permian p1f and p2w of shawan sag and carboniferous sourced oil from the chepaizi uplift based on the reconstruction of the migration history the oils of group a in the n1s formation of western chepaizi migrated predominantly from the south sikeshu sag to the north and northeast with wells su1 2 and c27 as the initial filling points the oils of group b in the n1s formation of the western chepaizi travelled predominantly from the southeast shawan sag to the north and northwest the oils of group d1 in the c2x formation of eastern chepaizi migrated mainly from the northeast and southeast shawan sag to the west with well p661 as the initial filling point wells sm011 and c64 are the initial filling points of the k1tg group in the hongche fault belt crude oils of group c in the k1tg group travelled predominantly from the southeast shawan sag and northeast to the west into the eastern chepaizi and from well p68 to the southwest according to the paleo oil preferential filling orientations and paleogeomorphology some favourable targets for petroleum exploration of the chepaizi uplift are forecast in this study

mapping and interpretation of sinlap crater on titan using cassini vims and radar data 1 only a few impact craters have been unambiguously detected on titan by the cassini huygens mission among these sinlap is the only one that has been observed both by the radar and vims instruments this paper describes observations at centimeter and infrared wavelengths which provide complementary information about the composition topography and surface roughness several units appear in vims false color composites of band ratios in the sinlap area suggesting compositional heterogeneities a bright pixel possibly related to a central peak does not show significant spectral variations indicating either that the impact site was vertically homogeneous or that this area has been recovered by homogeneous deposits both vims ratio images and dielectric constant measurements suggest the presence of an area enriched in water ice around the main ejecta blanket since the ku band sar may see subsurface structures at the meter scale the difference between infrared and sar observations can be explained by the presence of a thin layer transparent to the radar an analogy with terrestrial craters in libya supports this interpretation finally a tentative model describes the geological history of this area prior during and after the impact it involves mainly the creation of ballistic ejecta and an expanding plume of vapor triggered by the impact followed by the redeposition of icy spherules recondensed from this vapor plume blown downwind subsequent evolution is then driven by erosional processes and aeolian deposition

hemispherically in phase precipitation variability over the last 1700 years in a madagascar speleothem record paleoclimate studies of tropical rainfall have led to a recognition of a predominant pattern of anti phase behavior between the northern and southern hemispheres at both orbital and millennial timescales less certain is how regional tropical rainfall patterns have changed in the late holocene under boundary conditions and on timescales which are most relevant to the tropics response to a warming world several high resolution southern hemisphere rainfall records are at odds with meridional movement of the mean inter tropical convergence zone location as the major driver of holocene tropical rainfall variability with regional precipitation patterns resembling modern day el nino southern oscillation end members to test emerging ideas on sub millennial tropical rainfall variability additional records from the southern hemisphere are required we present a new speleothem 18o record from anjohibe cave northwestern madagascar which provides a quasi annual record of monsoonal strength and precipitation amount for the last 1700 years the majority of 18o variability in the record is at the decadal scale and shows little to no correlation with major climate indices or cyclical climate drivers at lower frequencies changes in mean speleothem 18o show good correlation with other regional precipitation records both north and south of the equator the regional coherency of tropical rainfall across the west indian ocean resembles expansion and contraction of the tropical rain belt and positive indian ocean dipole like conditions at different timescales the cause of this coherency could be related to symmetrical changes in continental sensible heating or to a low frequency sea surface temperature climate mode

tectonic and paleogeographic controls on development of the early middle ordovician shanganning carbonate platform ordos basin north china lower middle ordovician platform carbonates are important oil and gas reservoir rocks in the ordos basin of the north china craton ncc in recent years numerous cores have been recovered from these units but the depositional environments and facies architecture of this large carbonate platform system have not yet been reported in detail this study integrates sedimentological and magnetic fabric data collected from outcrops and cores to document variation in microfacies and facies associations within the shanganning carbonate platform scp infer paleowind directions and the paleogeographic location of the scp and evaluate tectonic and paleogeographic controls on platform development this analysis documented 25 microfacies belonging to 7 microfacies fabric and sediment types carbonate mudstone wackestone packstone grainstone evaporite bindstone framestone siliciclastics and dolostone microfacies can be grouped into facies associations that represent tidal flat open platform restricted platform evaporite platform platform margin slope and deep basinal depositional environments these environments are mainly distributed zonally around the l shaped qingyang paleo uplift on the western and southern margins of the scp anisotropy of magnetic susceptibility measurements at five platform margin locales yielded paleocurrent directions of all approximately 318 348 51 81 42 72 80 110 and 54 84 from paleo north after correction for a 120 150 clockwise rotation of the ncc since the ordovician the depositional architecture of the scp depended on a combination of tectonic and paleogeographic wind influences local tectonic movements controlled the spatial distribution of facies associations around the qingyang paleo uplift which was characterized by open restricted and evaporite platform facies in the platform interior and mainly slope and basinal facies on the outer platform margin to the west and south of the qingyang paleo uplift vertical tectonic movements resulted in cyclic submergence and emergence of the platform over its approximately 20 m y long formation history paleo trade winds influenced aspects of facies zonation across the platform including growth of metazoan reefs on the windward platform margin and formation of oolitic grainstone and microbial reefs on the leeward platform margin the facies model for the scp developed in this study should provide a useful reference framework for future carbonate oil and gas exploration in lower middle ordovician units of the ordos basin furthermore this study makes innovative use of magnetic anisotropy data in combination with standard petrographic core and field data to discern facies patterns and controls on a paleo carbonate platform which is an integrated methodology that may serve as a model for future studies of other carbonate platforms

mapping of titan results from the first titan radar passes the first two swaths collected by cassini s titan radar mapper were obtained in october of 2004 ta and february of 2005 t3 the ta swath provides evidence for cryovolcanic processes the possible occurrence of fluvial channels and lakes and some tectonic activity the t3 swath has extensive areas of dunes and two large impact craters we interpret the brightness variations in much of the swaths to result from roughness variations caused by fracturing and erosion of titan s icy surface with additional contributions from a combination of volume scattering and compositional variations despite the small amount of titan mapped to date the significant differences between the terrains of the two swaths suggest that titan is geologically complex the overall scarcity of impact craters provides evidence that the surface imaged to date is relatively young with resurfacing by cryovolcanism fluvial erosion aeolian erosion and likely atmospheric deposition of materials future radar swaths will help to further define the nature of and extent to which internal and external processes have shaped titan s surface

improved prediction of the indian ocean dipole mode by use of subsurface ocean observations abstractthe numerical seasonal prediction system using the scale interaction experiment frontier version 1 sintex f ocean atmosphere coupled model has so far demonstrated a good performance for prediction of the indian ocean dipole mode iod despite the fact that the system adopts a relatively simple initialization scheme based on nudging only the sea surface temperature sst however it is to be expected that the system is not sufficient to capture in detail the subsurface oceanic precondition therefore the authors have introduced a new three dimensional variational ocean data assimilation 3dvar method that takes three dimensional observed ocean temperature and salinity into account since the new system has successfully improved iod predictions the present study is showing that the ocean observational efforts in the tropical indian ocean are decisive for improvement of the iod predictions and may have a large impact on important socioeconomic activities particularly in the indian ocean rim co

shapes of streamlined islands on earth and mars experiments and analyses of the minimum drag form streamlined islands in rivers and comparable landforms in the channeled scabland of washington and in the outflow channels on mars have shapes that are closely similar to symmetrical airfoils with length width ratios averaging 3 to 4 a review of measurements of drag on airfoils demonstrates that a minimum total drag is achieved at such length width ratios supporting the hypothesis that these islands acquired shapes that minimized the drag or resistance to the flowing fluid when they were formed this minimum drag is achieved by the reduction of the wake while maintaining a small skin friction flume experiments were undertaken with model islands to examine how they achieve their streamlined form when the island is not fully submerged a combined bow wave and hydraulic drop play a major role in their erosion but most of the streamlining is brought about by deposition filling the wake region when the island is submerged the flow over the top can become supercritical producing a hydraulic jump in the island lee and focusing the erosion in that region rapidly eroding the island to a streamlined shape these experiments are consistent with the prototype streamlined islands duplicating many of their features

on the weakening relationship between the indian monsoon and enso analysis of the 140 year historical record suggests that the inverse relationship between the el nino southern oscillation enso and the indian summer monsoon weak monsoon arising from warm enso event has broken down in recent decades two possible reasons emerge from the analyses a southeastward shift in the walker circulation anomalies associated with enso events may lead to a reduced subsidence over the indian region thus favoring normal monsoon conditions additionally increased surface temperatures over eurasia in winter and spring which are a part of the midlatitude continental warming trend may favor the enhanced land ocean thermal gradient conducive to a strong monsoon these observations raise the possibility that the eurasian warming in recent decades helps to sustain the monsoon rainfall at a normal level despite strong enso events

impacts do not initiate volcanic eruptions eruptions close to the crater many papers on meteorite impact suggest that large impacts can induce volcanic eruptions through decompression melting of the underlying rocks we perform numerical simulations of the impact of an asteroid with a diameter of 20 km striking at 15 km s 1 into a target with a near surface temperature gradient of 13 k km 1 cold case or 30 k km 1 hot case the impact creates a 250 300 km diameter crater with 10 000 km3 of impact melt however the crater collapses almost flat and the pressure field returns almost to the initial lithostat even an impact this large cannot raise mantle material above the peridotite solidus by decompression statistical considerations also suggest that impacts cannot be the common initiator of large igneous provinces any time in post heavy bombardment earth history

build up and depositional dynamics of an arc front volcaniclastic complex the miocene tepoztlan formation transmexican volcanic belt central mexico volcanic terrains such as magmatic arcs are thought to display the most complex surface environments on earth ancient volcaniclastics are notoriously difficult to interpret as they describe the interplay between a single or several volcanoes and the environment the early miocene tepoztlan formation at the southern edge of the transmexican volcanic belt belongs to the few remnants of this ancestral magmatic arc and therefore is thought to represent an example of the initial phase of evolution of the transmexican volcanic belt based on geological mapping detailed logging of lithostratigraphic sections palaeocurrent data of sedimentary features and anisotropy of magnetic susceptibility mapping of two dimensional panels from outcrop to field scale and geochronological data in an area of ca 1000 km 2 three periods in the evolution of the tepoztlan formation were distinguished which lasted around 4 myr and are representative of a volcanic cycle edifice growth phases followed by collapse in a magmatic arc setting the volcaniclastic sediments accumulated in proximal to medial distances on partly coalescing aprons similar to volcanic ring plains around at least three different stratovolcanoes these volcanoes resulted from various eruptions separated by repose periods during the first phase of the evolution of the tepoztlan formation 22ae 8t o 22 ae2 ma deposition was dominated by fluvial sediments in a braided river setting pyroclastic material from small andesitic dacitic composite volcanoes in the near vicinity was mostly eroded and reworked by fluvial processes resulting in sediments ranging from cross bedded sand to an aggradational series of river gravels the second phase 22ae 2t o 21 ae3 ma was characterized by periods of strong volcanic activity resulting in voluminous accumulations of lava and tuff which temporarily overloaded and buried the original fluvial system with its detritus continuous build up of at least three major volcanic centres further accentuated the topography and in the third phase 21ae 3t o 18 ae8 ma mass flow processes represented by an increase of debris flow deposits became dominant marking a period of edifice destruction and flank failures

diagenesis and reservoir potential of permian triassic fluvial lacustrine sandstones in the southern junggar basin northwestern china the junggar basin is one of the largest oil producing areas in china and contains upper permian lacustrine oil shales with some of the greatest hydrocarbon potental in the world in this study we present the diagenetic characteristics of permian triassic sandstones from the southern junggar basin and evaluate their reservoir potential the uppermost permian and lower triassic cangfanggou group in the southern junggar basin is characterized by alternating fluvial and lacustrine deposits whereas the middle upper triassic xiaoquangou group was deposited predominantly in a lacustrine environment fluvial and deltaic sedimentation was subordinate the sandstones of the cangfanggou and xiaoquangou groups are volcanic litharenites their detrital modes and textures of volcanic fragments suggest a primarily andesitic basaltic volcanic arc provenance early diagenesis of the sandstones is characterized by nonferroan calcite cementation grain coating pore lining clay minerals and the initial dissolution of detrital grains authigenic quartz pore filling phyllosilicates pore filling grain replacive zeolites albitized detrital plagioclase authigenic k feldspar copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received april 15 1996 revised manuscript received november 4 1996 final acceptance may 2 1997 2department of earth sciences university of western ontario london ontario n6a 5b7 canada 3school of geosciences queen s university of belfast belfast bt7 1nn united kingdom this work was done at the queen s university of belfast with funding from exxon bhp mobil and itotal which we gratefully acknowledge the karamay institute of petroleum exploration and development generously provided borehole samples geng ansong at the institute of geochemistry guangzhou academia sinica and zhou yisheng at the xinjiang institute of petroleum are thanked for assistance with field work and for valuable discussions special thanks go to the staff of the electron microscopy unit at the queen s university of belfast we also thank a h ruffell and s r lawrence for their constructive comments on an earlier version of the manuscript stable isotope analysis and ongoing research concerning the junggar basin at the university of western ontario have been supported by the natural science and engineering research council of canada the manuscript benefited substantially from critical commentary by kevin t biddle suzanne kairo w r kaiser and an anonymous reviewer

variations in water level for lake turkana in the past 8500 years near mt porr kenya and the transition from the african humid period to holocene aridity abstract a stratigraphic and geomorphic study of relict beaches up to 80 m above current water level of lake turkana reveal four major lake level fluctuations of 50 m between ca 8 5 and 4 5 ka during the transition from the african humid period to holocene aridity we hypothesize that high stands of lake turkana reflect complex hydrological processes with variability in atlantic and indian ocean derived moisture into east africa ultimately linked to changes in sea surface temperatures ssts lake level rise was also amplified regionally by increased precipitation causing overflow from the adjacent suguta and chew bahir basins particularly during high stands at ca 8 5 ka and at 6 4 ka the timing of transgressive and regressive events is constrained by 14c dating of carefully selected lacustrine mollusks incorporation of previous shell ages with sufficient elevational control and osl dating of quartz grains from littoral and sublittoral deposits by a multiple aliquot regeneration mar approach there was a high water level up to at least 70 m at 8 5 ka that probably reached the spillover limit 100 m a brief