palaeoclimate perturbations before the sheinwoodian glaciation a trigger for extinctiond during the ireviken event telychian to sheinwoodian conodonts pterospathodus eopennatus ssp n 1 zone through the ozarkodina sagitta rhenana superzone were studied in detail for their oxygen isotope composition the upper kockelella ranuliformis and ozarkodina sagitta rhenana zones represent the peak interval of the sheinwoodian positive 18oapatite excursion reflecting the coolest conditions with marine sea water temperatures decreased by more than 6 c in the subtropics the 18oapatite data cover pre through post ireviken event strata the study includes also material from younger levels up to the late wenlock ctenognathodus murchisoni zone however this record is incomplete with one major hiatus reflecting the regression associated with the middle silurian mulde event the stratigraphic levels of the analyzed conodont samples from estonia can be correlated with high precision to the datum points of the ireviken event strata in the lower and upper visby formations on gotland sweden inferred short term climatic changes in the upper telychian part of the studied interval may have been caused by phases of major volcanic activity along the caledonian front across the ireviken event we observe variations in oxygen isotope ratios which allow a direct comparison to the stepwise extinctions and faunal reorganisations in different groups our data suggest that faunal extinctions are connected to time intervals of warming before the establishment of more stable and cooler conditions during the main sheinwoodian glacial the most severe extinctions and faunal turnovers at datum points 2 and 4 occurred during the early warmer interval of the event after the shift into the sheinwoodian icehouse in the lower kockelella ranuliformis zone reflected by rapidly decreasing sea water temperatures faunas restabilized and reefal communities started to flourish sedimentary evidence for the glaciation is discussed for different palaeolatitudes less

carbon and oxygen isotope stratigraphy of the lower mississippian kinderhookian lower osagean western united states implications for seawater chemistry and glaciation a positive carbon isotope 1 3 c excursion has been recognized in upper kinderhookian and early osagean carbonates in three sections in southeast idaho and nevada the oldest 1 3 c peak 7 is dated to the isostichaconodont zone and a younger peak occurs in the typicus zone the shifts are recorded in a range of carbonate lithofacies representing various water depths along the shelf lithofacies sampled for 1 3 c and 1 8 o at the samaria mountain section in southeast idaho record the shallowest water conditions indicated by cross bedded skeletal and peloidal grainstones the deepest water conditions are present in the pahranagat range section in eastern nevada which consists mainly of bioturbated lime mudstone and skeletal wackestone the 1 3 c values from these widely separated sedimentary basins show a consistent trend that correlates with early mississippian curves generated from brachiopod calcite in western europe and the midcontinent of north america as well as dolomites in utah and wyoming 1 8 o values become more positive up section generally paralleling the positive trend in 1 3 c during the late kinderhookian no subaerial exposure surfaces are recognized in the sections examined in southeast idaho and nevada and at least the 1 3 c trends are interpreted as primary seawater fluctuations sea level changes occurred near the beginning of the late kinderhookian 1 3 c shift early to middle parts of the isosticha zone and within the peak of the 1 3 c excursion kinderhookian osagean boundary although tectonic changes associated with the antler orogeny have likely modified the eustatic signature

widespread prolonged late middle to late ordovician upwelling in north america a proxy record of glaciation late middle to late ordovician subtidal ramp carbonates of new mexico texas and oklahoma contain abundant spiculitic chert to 70 chert by volume and phosphate 1 5 wt indicating that these rocks formed in an extensive upwelling zone upwelling began in the late middle ordovician ca 454 ma and persisted until the end of the ordovician late ordovician cherty carbonates also occur along the u s cordilleran margin in board of organic rich graptolitic shale and chert the widespread occurrence of late ordovician cherty and phosphatic carbonates on southern and western laurentia in addition to phosphate rich cool water carbonates over much of the north american midcontinent suggests vigorous thermohaline circulation related to prolonged 10 14 ma gondwana glaciation

sst anomalies of enso and the madden julian oscillation in the equatorial pacific this study explores whether anomalies of sea surface temperature sst in the equatorial pacific during warm events of el nino southern oscillation enso are related to the madden julian oscillation mjo an index is derived from surface wind data of a global model reanalysis to measure forcing of oceanic kelvin waves by wind stress associated with the mjo this kelvin wave forcing index of the mjo is used to relate interannual anomalies in seasonal activity of the mjo to interannual anomalies in equatorial sst for the 1980 99 time period evidence is found showing that during enso warm events stronger kelvin wave forcing in the western pacific precedes greater sst anomalies in the eastern pacific by 6 12 months no such evidence however can be found for the period of 1950 79 the result suggests that during enso warm events amplitudes of sst anomalies in the eastern pacific can be affected by the mjo at least for the 1980 99 period through its seasonal activity of kelvin wave forcing a possible mechanism for such an mjo enso relationship is described how enso prediction can be benefited from the precursory signals of the mjo is discussed

nutrient and temperature controls on modern carbonate production an example from the gulf of california mexico in addition to salinity and temperature nutrient concentrations in surface waters are known to have a significant impact on distribution of carbonate producing biota but have never been quantitatively evaluated against different temperatures along a latitudinal transect the western coast of the gulf of california mexico presents a natural laboratory for investigating the influence of oceanographic parameters such as salinity temperature and chlorophyll a a proxy for nutrients on the composition of a range of modern heterozoan and photozoan carbonate environments along a north south latitudinal gradient spanning the entire warm temperate realm 29 n 23 n chlorophyll a measured in situ at half hour resolution is highly variable throughout the year due to short term upwelling and increases significantly from the southern to northern gulf of california salinity in contrast fluctuates little and remains at an average of 35 from south to north carbonate production ranges from oligotrophic mesotrophic coral reef dominated shallow water areas minimum temperature 18 6 c through mesotrophic eutrophic red algal dominated inner shelf carbonate production in the central gulf minimum temperature 16 c and to molluscan bryozoan eutrophic inner to outer shelf environments minimum temperature 13 7 c the gulf of california data supplemented with oceanographic and compositional information from a database compiled from a spectrum of modern carbonate systems worldwide demonstrates the significance of nutrient control in the formation of heterozoan photozoan and transitional heterozoan photozoan carbonate systems and serves as a basis for more accurately interpreting fossil carbonates

magnetotelluric interpretation of the geothermal system of the kuju volcano southwest japan abstract a magnetotelluric study was carried out in the kuju volcanic area southwest japan to clarify the geothermal structure of the volcanic body as part of a fundamental study of the utilization of volcano energy conducted by the geothermal research institute of kyushu university two dimensional 2 d resistivity models based on mt data of the kuju volcano and a three dimensional 3 d model of the kuju iwoyama area have been constructed by a finite element modeling technique the 2 d models have shown some low resistivity zones less than 10 ohm m corresponding to fracture zones in the volcanic body the 3 d model of the kuju iwoyama area with the most intense geothermal activity has revealed a very low resistivity zone beneath the fumarolic area with a resistivity of the order of 1 ohm m temperature porosity and deposition of alteration minerals are considered as the causes of this low resistivity zone

exploration and assessment of the geothermal resources in the hammam faraun hot spring sinai peninsula egypt abstract the tectonic position of egypt in the northeastern corner of the african continent suggests that it may possess significant geothermal resources especially along its eastern margin the most promising areas for geothermal development in the northwest red sea gulf of suez rift system are located where the eastern shore of the gulf of suez is characterized by superficial thermal manifestations including a cluster of hot springs with varied temperatures magnetotelluric and gravity reconnaissance surveys were carried out over the geothermal region of hammam faraun to determine the subsurface electric resistivity and the densities that are related to rock units these surveys were conducted along profiles one dimensional 1d and two dimensional 2d inversion model techniques were applied on the mt data integrating the 2d inversion of gravity data the objectives of these surveys were to determine and parameterize the subsurface source of the hammam faraun hot spring and to determine the origin of this spring based on this data a conceptual model and numerical simulation were made of the geothermal area of hammam faraun the numerical simulation succeeded in determining the characteristics of the heat sources beneath the hammam faraun hot spring and showed that the hot spring originates from a high heat flow and deep ground water circulation in the subsurface reservoir that are controlled by faults these studies were followed by an assessment of the geothermal potential for electric generation from the hammam faraun hot spring the value of the estimated potential is 28 34 mw as the reservoir is assumed to be only 500 m thick this value would be enough for the desalination of water for both human and agricultural consumption

carbonate systems along nutrient and temperature gradients some sedimentological and geochemical constraints research over the past several decades has clearly demonstrated that changes in the ocean environment have had major impacts on carbonate systems changes in climate ocean circulation and seafloor spreading rates have influenced temperature and seawater chemistry including carbonate saturation state and nutrient availability and thereby have determined boundary conditions for the biota that form carbonate platforms in turn the biota determine accumulation rates and facies zonations thus controlling platform geometry and facies dynamics in the first section of this paper we examine how nutrient availability influences carbonate facies associations we first discuss the role of temperature and nutrient gradients in the modern ocean and their influence on biotic associations then we discuss how carbonate sedimentation can be characterized along nutrient gradients in the second section we review proxies currently used to reconstruct paleoproductivity in open ocean environments and discuss their applicability to neritic carbonate systems we highlight the variety of existing proxies and their limitations and suggest that multiple lines of evidence are needed for valid interpretations our short review discusses sedimentological biogenic and geochemical proxies that can be used to reconstruct past nutrient fluxes and to constrain paleoceanographic controls over the distribution of carbonate associations however it also reveals that more data and case studies are needed that integrate shallow and deep water carbonate sequences and elucidate the links between temperature vs nutrient supplies changes and facies in ancient carbonate sequences

growth and linkage of the east tanka fault zone suez rift structural style and syn rift stratigraphic response abstract an integrated tectono stratigraphic analysis of the east tanka fault zone suez rift indicates fault growth by linkage of initially isolated fault segments that is consistent with fault growth models based on displacement length d l scaling laws during the initial 2 4 ma of rifting the east tanka fault zone was composed of two en echelon fault segments c 1 1 5 km long separated by a hanging wall intrabasin high that controlled the geometry of depocentres filled with continental deposits alluvial fan conglomerates were fed through the region between the two fault segments and form a discrete coarse grained body preserved in the immediate hanging wall of the fault zone subsequent stratigraphic patterns indicate that the two faults hard linked to form a single fault zone c 3 5 km long hard linkage of the segments resulted in migration of the zone of maximum displacement and subsidence into the zone of linkage uplift due to the migration of activity caused modification of drainage in the footwall of the fault zone that terminated the growth of the alluvial fan this study demonstrates the need to integrate structural and stratigraphic data when attempting to reconstruct the temporal and spatial evolution of normal fault zones additionally the fault dynamics illustrated have implications for tectono stratigraphic models of rift basins and syn rift stratigraphic evolution

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

fault propagation folding in extensional settings examples of structural style and synrift sedimentary response from the suez rift sinai egypt field data from the oligocene miocene gulf of suez rift demonstrate that coeval growth faults folds and transfer zones exerted a major control on synrift stratigraphic sequence development growth folds in the suez rift are related to steeply dipping normal faults that propagated upward resulting in broad upward widening monoclines in overlying strata folding during fault propagation was accommodated by layer parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault the eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall this evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments synrift sediments display onlap and intraformational unconformities toward the growth monoclines and buried faults whereas they diverge into broadly synclinal expanded sections away from the growth monocline continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments each successively younger sequence dipping basinward at a shallower angle than the previous one the resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults along strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low relief transfer zones data from other rift basins indicate that fault propagation folds are not unique to the gulf of suez

surface fluxes and ocean coupling in the tropical intraseasonal oscillation abstract sensitivity of tropical intraseasonal variability to mixed layer depth is examined in the modified national center for atmospheric research community atmosphere model 2 0 1 cam with relaxed arakawa schubert convection coupled to a slab ocean model som whose mixed layer depth is fixed and geographically uniform but varies from one experiment to the next intraseasonal west pacific precipitation variations during boreal winter are enhanced relative to a fixed sst infinite mixed layer depth simulation for mixed layer depths from 5 to 50 m with a maximum at 20 m interestingly near the observed value in the regions where the madden julian oscillation mjo is active but are strongly diminished in the 2 m depth simulation this nonmonotonicity of intraseasonal precipitation variance with respect to mixed layer depth was predicted by sobel and gildor using a highly idealized model further experiments with the same idealized model help to interpret results derived from the modified ncar c

correlation of aerogravity and bht data to develop a geothermal gradient map of the northern western desert of egypt using an artificial neural network the northern part of the western desert of egypt represents the second most promising area of hydrocarbon potential after the gulf of suez province an artificial neural network ann approach was used to develop a new predictive model for calculation of the geothermal gradients in this region based on gravity and corrected bottom hole temperature bht data the best training data set was obtained with an ann architecture composed of seven neurons in the hidden layer which made it possible to predict the geothermal gradient with satisfactory efficiency the bht records of 116 deep oil wells 2 000 4 500 m were used to evaluate the geothermal resources in the northern western desert corrections were applied to the bht data to obtain the true formation equilibrium temperatures which can provide useful constraints on the subsurface thermal regime on the basis of these corrected data the thermal gradient was computed for the linear sections of the temperature versus depth data at each well the calculated geothermal gradient using temperature log data was generally 30 c km with a few local high geothermal gradients in the northwestern parts of the study area explained by potential local geothermal fields the bouguer gravity values from the study area ranged from 60 mgal in the southern parts to 120 mgal in the northern areas and exhibited ne sw and e w trends associated with geological structures although the northern western desert of egypt has low regional temperature gradients 30 c km several potential local geothermal fields were found 40 c km the heat flow at each well was also computed by combining sets of temperature gradients and thermal conductivity data aerogravity data were used to delineate the subsurface structures and tectonic framework of the region the result of this study is a new geothermal gradient map of the northern western desert developed from gravity and bht log data

episodic growth of normal faults as recorded by syntectonic sediments july oil field suez rift egypt the july oil field is a major normal fault bounded structural block in the suez rift basin egypt it is adjacent to a major structural transfer zone which has controlled sediment influx to the rift basin center for the past 20 m y the lower to middle miocene upper rudeis formation part of the synrift stratigraphic sequence records deformation of the july structural block the formation contains abrupt lateral changes in thickness and facies which record earlier phases of fault movement and deformation in the july field area that do not conform to the present day structural configuration the upper rudeis formation was deposited as turbidites in a submarine fan system sourced from the western rift shoulder it was deposited over and around bathymetric highs created by coeval fault displacement in the july field area by studying thickness and facies patterns we have determined that the present day main bounding fault to the july block consisted of a series of unlinked fault segments which linked after upper rudeis deposition a subsidiary fault west of the block exerted the most control on thickness patterns not the present day main bounding fault thus commonly used models of deposition in active half grabens are difficult to apply at july field

integrated biostratigraphy of the lower silurian of the aizpute 41 core latvia integrated graptolite conodont and chitinozoan biostratigraphical data is presented from the rhuddanian through to lower sheinwoodian of the aizpute 41 core latvia correlation of the biozonation schemes based upon the three groups is achieved from the cyphus through to lowermost riccartonensis graptolite biozones except for the upper aeronian and lower telychian which lack both chitinozoans and graptolites and upper lapworthi through to approximately base murchisoni graptolite biozone where there is interpreted to be an unconformity datum 2 of the ireviken event is correlated with a level at the base of or within the murchisoni biozone it is possible that the changes in conodont assemblages at datum 2 on gotland are the result of an unconformity here streptograptus kaljoi sp nov from the lower spiralis graptolite biozone is described

emerging role of indian ocean on indian northeast monsoon this study examines the emerging role of indian ocean sea surface temperature sst on the inter annual variability iav of indian north east monsoon rainfall nemr the iav of nemr is associated with the warm sst anomaly over east bay of bengal bob 88 5oe 98 5oe 8 5on 15 5on and cool sst anomaly over east equatorial indian ocean 80 5oe 103 5oe 6 5os 3 5on the gradient of sst between these boxes i e northern box minus southern box shows strong and robust association with the indian nemr variability in the recent decades for establishing the teleconnections sst mean sea level pressure north indian ocean tropical storm track and circulation data have been used the study reveals that during the positive sst gradient years the inter tropical convergence zone itcz shifts northwards over the east indian ocean the tropical depressions storms and cyclones formed in the north indian ocean moves more zonally and strike the southern peninsular india and hence excess nemr while during the negative sst gradient years the itcz shifts southwards over the indian ocean the tropical depressions storms and cyclones formed in the north indian ocean moves more northwestward direction and after crossing 15on latitude re curve to north east direction towards head bob and misses southern peninsular india and hence deficient nemr

bioproductivity rise in the east baltic epicontinental sea in the aeronian early silurian abstract the occurrence of black shale in deep shelf environments chertification in shoreward carbonate facies barite occurrences positive 13 c excursions in carbonate sections and enhanced micritic limestone accumulation give evidence of a primary bioproductivity rise suggesting upwelling in the aeronian of the east baltic the end rhuddanian onset of the rise in primary bioproductivity corresponds to the beginning of black shale formation on the deep shelf and micritic limestone formation on the shallower shelf the bioproductivity maximum was in the mid aeronian judging from the highest values of 13 c upwelling ceased and primary productivity decreased at the end of aeronian

sequestration of 12c in the deep ocean during the early wenlock silurian positive carbon isotope excursion abstract marine carbonates from three biostratigraphically well dated silurian sections from the mid continent of north america were analyzed for carbon isotopic 13 c carb study the early wenlock positive carbon isotope excursion ireviken excursion is recorded in three sections from tennessee iowa and ohio with values of 4 5 this global shift in the carbon isotopic ratio of marine waters began during a protracted extinction event ireviken event that spanned the llandovery wenlock boundary although several oceanographic models have been developed to account for the coincident changes in lithology biology and carbon isotope stratigraphy during this interval of the silurian their proposed causal connections among glaciation oceanography primary productivity and the global carbon cycle remain a matter of debate this investigation provides carbon isotopic and lithologic evidence that the ireviken excursion occurred during a time of relatively oligotrophic conditions a third order transgressive regressive cycle and increased carbonate production throughout the mid continent of north america the ireviken excursion is recorded in relatively pure carbonate sequences and is immediately preceded by a significant unconformity in each of the measured sections it is proposed that the ireviken excursion was the product of sequestration and burial of 12 c in deep water as a result of altered deep ocean circulation

the effectiveness of the paleoproterozoic biological pump a δ13c gradient from platform carbonates of the pethei group great slave lake supergroup nwt samples of carbonate cements collected along a depth transect of the pethei platform a 1 9 ga stromatolitic reef reveal a small 0 5 carbon isotope gradient between shallow and basinal facies the magnitude of this gradient would conventionally be interpreted as indicating low export of organic matter from ocean surface waters but steady state simulations using a two box model of the paleoproterozoic ocean suggest that the small carbon isotope gradient could instead be due to high partial pressures of carbon dioxide in the paleoproterozoic atmosphere which would increase the ocean9s dissolved inorganic carbon content and damp the effects of biological pumping if the paleoproterozoic atmosphere were indeed enriched in atmospheric co 2 in compensation for a less luminous sun these results indicate that the planktonic biota was a significant component of the precambrian global carbon and nutrient cycles affecting if not regulating as today the composition of both surface and deep ocean waters

geothermal resources in egypt integrated with gis based analysis abstract the energy of egypt is generally derived from petroleum products however advancements in the development of the generation capacity using sustainable and renewable resources for example solar wind and geothermal resources and investment in nuclear power plants are planned the geology and structure setting of egypt affirms that reasonable geothermal resources are available particularly along the gulf of suez the red sea the western desert and parts of the nile valley the main objective of this research is to develop a geothermal favourability map of egypt which may be considered as a screening tool for the assessment of optimal areas for geothermal development digital data layers and maps were employed in a gis model to select the most promising areas for geothermal potentiality the arcgis model includes six thematic layers distance to faults bouguer anomaly distance to seismic activity curie depth heat flow and temperatures at different depths the validation of the generated geothermal favourability map was performed by a comparison with thermal water wells and hot springs generally the most encouraging zones for geothermal probability in egypt are located near the shorelines of the gulf of suez and the red sea

high resolution correlations between gotland and estonia near the base of the wenlock the strata of the ireviken event can be correlated between gotland sweden and the viki core on saaremaa estonia with a high degree of precision most of the ten datum planes are found with a precision of better than 0 1 m in the lower and upper visby beds on gotland and high in the mustjala member of the jaani formation on saaremaa five of the latest llandovery early wenlock units defined by these datum planes are between c 0 12 and 1 77 m thick on gotland and 0 12 and 0 67 m in estonia the duration of each was between a few thousand and c 31 000 years the stratigraphic resolution achieved in the interval of the ireviken event is 10 000 years ultimate range ends are lacking within a preceding slightly longer interval but the pattern of intermittent presence of some taxa agrees well with an unchanged relative rate of sedimentation their coeval presence in different places indicates ecological regional or more widespread changes

geochemistry of telichian silurian k bentonites in estonia and latvia in the telychian section of estonia and latvia k bentonites from 45 volcanic eruptions were discovered the thickness of k bentonite interbeds varies from a few millimetres to 20 cm the sodium component concentration in sanidine phenocrysts measured by xrd ranges from 20 to 48 mol and was used for establishing correlations the ti zr nb th and sr concentrations and ratios show temporal trends indicating fractional crystallization in magma chambers the analysis of biotite phenocrysts revealed magnesium and iron rich biotites in bentonites synthesis of these geochemical data enabled a classification of bentonites into seven geochemical types which probably originate from seven different volcanic sources isopach schemes indicate ash transport from the west and north west directions

subsurface structural features of the basement complex and geothermal resources using aeromagnetic data in the bahariya oasis western desert egypt egypt gives priority to western desert in land reclamation and sustainable development projects the bahariya oasis a northernmost oasis of egypt is closer to the capital compared to other remote oases and represents the most interesting potential candidates for the sustainable development many researches provide insight into the hydrogeology and structural geology of the bahariya oasis however very few attempts have been done to investigate its geothermal potentiality the aim of present study is to reflect the geothermal resources of the bahariya oasis encountered with the predominant structures utilizing aeromagnetic and borehole data the main subsurface structures and the depth to basement map were retrieved from the 2d modelling of the aeromagnetic data the results of the 2d models were verified by well stratigraphic data spectral analysis of the aeromagnetic data was applied to estimate the curie point depth cpd and to produce geothermal gradient and heat flow maps for the bahariya oasis the results of the study indicated that the depth to the basement rocks in the area ranges from 0 6 to 4 0 km the cpd is 15 km in the central parts and increases to 24 km eastward the geothermal gradient varies from 20 to 35 c km with an average 30 c km however the heat flow changes from 60 to 100 m w m2 with an average of 90 m w m2 these results in addition to basement structures imply a high temperature gradient and heat flow correlating with shallow curie depths the results are in agreement with previous work in the same region

active displacement field in the suez sinai area the role of postseismic deformation abstract by means of a spherical viscoelastic model of co and postseismic deformation we compute the postseismic displacement associated with the november 1995 m w 7 2 aqaba jordan earthquake we compare our results with the observational data obtained by a gps campaign performed in a wide portion of sinai between november 1997 and may 1998 though the original purpose of the campaign was to explain the tectonic features of the region the displacement values deduced from the gps observations are hardly reconcilable with any of the proposed tectonic models of sinai our hypothesis is that the detected deformation field could be due more to the postseismic relaxation following the aqaba earthquake rather than to tectonic movements our results show that both gps observational data and the postseismic simulations predict a compressional regime in the gulf of suez though the contraction detected by gps is generally larger the best agreement with the data is obtained for an asthenospheric and lower crust viscosity of 10 18 pa s and an absence of aseismic afterslip on the fault plane we conclude that the contribution coming from the postseismic viscoelastic relaxation of the ductile shallow layers following the 1995 aqaba earthquake is likely to play an important role in determining the present deformation field in sinai the transient postseismic relaxation seems to play a more important role than the secular tectonic deformation

composition and correlation of volcanic ash beds of silurian age from the eastern baltic sanidine composition and bulk geochemistry of volcanic ash beds from the east baltic indicate the subalkaline nature of the volcanism near the margins of the baltica plate during the silurian several bentonites in the wenlock include a previously unknown sanidine with 48 to 58 mol of the na ca component in contrast to the earlier telychian volcanism sodium rich sanidine occurs in ash beds which originate from relatively moderately evolved dacitic magma the studied material from two drill cores integrated with previous research enables production of a more complete list of 49 volcanic eruption layers for the lower to middle wenlock in the east baltic this updated list of bentonites characterized by their sanidine compositions forms a good basis for future integrated bio and chemostratigraphic correlations in northern europe

carbon and sulfur isotope anomalies across the frasnian famennian extinction boundary alberta canada stable isotopes of carbonate and organic carbon from two upper devonian sections in alberta canada indicate a heavy carbon event across the frasnian famennian f f boundary and a negative 13 c shift at the boundary at cinquefoil mountain 13 c values in carbonate are anomalously high 3 5 to 4 5 pdb peedee belemnite within an interval 10 m below to 23 m above the f f boundary representing about 1 m y two standard conodont zones compared to background values of 1 above and below this interval superimposed on this positive excursion is a marked 13 c decrease of about 1 at precisely the f f boundary at medicine lake a similar 13 c excursion in organic carbon from a background of 29 to a high of 26 5 is recorded across the f f boundary the 34 s data for iron sulfide in these sections show unusually high values as much as 15 to 20 cdt canon diablo troilite in the f f boundary interval these data together with those from other areas indicate a period of major global changes e g greenhouse and marine anoxia that took place well before and after the sudden biomass killing event at the f f boundary existing evidence suggests that the f f mass extinction was probably caused by a large extraterrestrial impact on earth at a time when the global ecosystem was already severely stressed

middle palaeozoic extinction events faunal and isotopic data abstract at least 9 and possibly as many as 12 extinction events of global or near global impact can be discriminated in the mid palaeozoic earliest silurian to early carboniferous on the basis of brachiopod coral conodont and ammonoid data and the history of carbonate build ups isotopic data from whole rock samples are presented for three of these events based on australian carbonate sequences constrained by conodont data these data represent the initial phase of a more extensive investigation using c o s sr and nd isotopic signatures derived from conodonts articulate and inarticulate brachiopod shell and fish remains from numerous australian and european sequences the aim of the project is to identify isotopic responses to extinction events and address causes for these changes in limestone sections analysed so far variations in carbon isotope compositions on a whole rock scale are most marked at horizons that can be correlated with times of significant reduction in biomass and diversity this is despite the fact that the whole rocks are in fact multicomponent systems with respect to carbon in part arising from diagenetic rearrangements of carbon distribution within the scale of the whole rock thus the carbon isotope data do provide evidence on a whole rock scale for fundamental changes in the global carbon cycle that are correlative with extinction events it is however unlikely that the magnitude of the isotopic shift will be precisely documented from such whole rock analyses the oxygen isotope results are less obviously related to the times of carbon isotope excursion this contrast in apparent resilience to post depositional modification of pristine isotope compositions exemplifies the extreme caution needed in evaluating isotopic data from carbonates

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

early silurian glaciations in brazil abstract the opening of the brazilian paleozoic basins during the late ordovician was followed by a tectonic stabilization in the silurian at the time of the early silurian glaciations deposition of continental sandstones prevailed in the basins offshore environments were present in the amazonas basin and to a smaller extent in the parana basin the ice sheets advanced over fluviatile and littoral sediments except for the south margin of the amazonas basin where the glacial diamictites immediately overlie marine facies the ice produced much meltwater even when advancing and this was probably climatically controlled the ice movements were from the northwest at the northern margin of the amazonas basin and towards the northeast at the southern margin in the parnaiba basin and its outliers the jatoba basin and cariri valley the ice came from southeast and probably also from east further to the south in the parana basin it came from the north and northeast four glaciations have been dated to the early silurian the oldest is dated as latest ashgill and or earliest llandovery in the parana basin as evidenced from tillites in the upper rio ivai and lower vila maria formations including the former iapo formation it is contemporaneous with a glaciation in the cape basin south africa the next glaciation is dated as early middle llandovery gregarius graptolite zone and is present in the amazonas basin and the andean belt and probably also in the parnaiba basin and its outliers the two youngest tillites were widespread in the northern brazilian basins amazonas parnaiba and jatoba basins and cariri valley as well as in the andean belt and are dated as early late llandovery possibly starting already in the late middle llandovery and latest llandovery to earliest wenlock the latter tillite is the most widespread one assuming these glaciations are related to polar positions the apparent migration of the south pole ice cap must have been quite rapid from central north africa in late ashgill towards central brazil in the middle late llandovery the glaciation in the parana basin took place up to 45 from the late ashgillian south pole the cool climate continued during the silurian but no new glaciations are known before latest devonian

improved interpretation of wireline pressure data modern wireline pressure data can have resolution and reproducibility sufficient to detect small fluid density changes and pressure barriers yet these features are commonly overlooked on conventional pressure depth plots the large pressure variation caused by weight of subsurface fluids hides these subtle features excess pressure is the pressure left after subtracting the weight of a fluid from the total pressure this concept is applied to wireline pressure data to remove effects of weight and emphasize subtle pressure differences caused by density variations and pressure barriers fluid density changes of 0 02 g cm3 or less can be resolved and within well pressure barriers in the order of 5 kpa 0 7 psi can be detected using good quality data effects of reservoir capillary displacement pressure can be detected by offset of the free water level from the petroleum water contact this effect can be used to estimate reservoir wettability subsurface fluid density measurements can also be used to evaluate oil or gas quality on a bed by bed scale in traps having variable oil or gas composition to detect compartmentalization by small petroleum density differences to verify quality of samples for pvt pressure volume temperature analysis and estimate salinity or temperature of unsampled water zones data quality limits barrier and fluid contact resolution thus quality control is essential pressure measurement errors on the 3 kpa 0 5 psi scale can be detected from behavior of the buildup pressure tests having the potential for small amounts of supercharge are identified from the overbalance and formation mobility examples illustrate identification of free water levels and fluid contacts fluid identification supercharge identification and water zone compartmentalization

evaluating mjo event initiation and decay in the skeleton model using an rmm like index the madden julian oscillation mjo skeleton model is a low order dynamic model that is capable of simulating many of the observed features of the mjo this study develops a model based mjo index that is similar to the well known real time multivariate mjo rmm index to better facilitate comparison between the skeleton model and observational data multivariate and univariate empirical orthogonal function eof analyses were performed on the convective heating and zonal wind data taken from the skeleton model for simulations forced with an idealized warm pool and observed sea surface temperatures ssts the leading eof modes indicated a wave number 1 convectively coupled circulation anomaly with zonal asymmetries that closely resembled the observed rmm eofs especially when the model was forced with observed ssts the rmm like index was used to compute an mjo climatology and document the occurrence of primary continuing and terminating mjo events in the skeleton model the overall amount of mjo activity and event lengths compared reasonably well to observations for such a simple model attempts at reconciling the observed geographic distribution of individual mjo initiation and termination events were not successful for the stochastic simulations though stochasticity is necessary in order to produce composite mjos that initiate and decay with time scales similar to observations finally analysis indicates that the existence of slow moving eastward traveling waves with higher wave numbers k 12 embedded within the large scale flow often precedes mjo termination in the skeleton model

a weathering hypothesis for glaciation at high atmospheric pco2 during the late ordovician new paired carbonate and organic carbon isotope analyses from nevada usa together with a consideration of the effects of mountain building and ice sheet coverage of the continents on atmospheric pco2 lead to a new hypothesis for the cause of the late ordovician glaciation we suggest that the taconic orogeny which commenced in the late middle ordovician caused a long term decline in atmospheric pco2 through increased weatherability of silicate rocks ice sheet growth was triggered when pco2 decreased to a threshold of 10 present atmospheric level and proceeded by positive ice albedo feedback in the midst of glaciation atmospheric pco2 began to rise as continental silicate weathering rates declined in response to coverage of weathering terrains by ice sheets at first this enhanced greenhouse effect was overcompensated for by ice albedo effects ultimately however atmospheric pco2 reached a level which overwhelmed the cooling effects of ice albedo and the glaciation ended the isotope results can be interpreted to indicate that atmospheric pco2 rose during the glaciation consistent with other proxy information although alternative interpretations are possible the large positive carbonate isotope excursion observed in late ordovician rocks around the world is explained as the expected response to increased carbonate platform weathering during glacioeustatic sea level lowstand rather than as a response to increased organic carbon burial

paleoenvironmental changes in the silurian indicated by stable isotopes in brachiopod shells from gotland sweden ratios of stable carbon and oxygen isotopes in brachiopod shells more than 370 specimens esp atrypa reticularis from the silurian of gotland sweden have been analysed preservation of biological skeletal ultrastructures observed in sem micrographs and cathodoluminescence analyses indicate that usually no diagenetical alteration occurs the silurian of gotland consists of 440 m carbonate deposits spanning the late llandovery to late ludlow epochs 431 411 m y repeatedly uniform sequences of micritic limestones and marks are interrupted by complex structured reefs and adjacent platform sediments previously the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the silurian sequence of gotland exhibits principally parallel carbon and oxygen isotope records corresponding closely to the topostratigraphic units lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the isotope ratios are influenced by local as well as global factors the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than changes in paleotemperature consequently the facies distribution of gotland is interpreted as resulting from changes in terrigenous input caused by different rates of continental weathering and freshwater runoff rather than by sea level fluctuations periods of arid climate and therefore anti estuarine downwelling of oxygenated surface water appear as short episodes of reef growing 1 5 m y in an epoche characterized by a tropic humid climate which causes an estuarine circulation and the upwelling of co2 rich deep water carbon isotope ratios are obviously connected to these changes in circulation by the advection of 13c rich surface water arid episodes or upwelling of 13c depleted deep water humid episodes of a silurian ocean which itself reveals generally euxinic deep water conditions due to the burial of organic carbon in black shales

the silurian of gotland sweden facies interpretation based on stable isotopes in brachiopod shells the silurian of gotland sweden consists of 440 m of carbonate deposits repeatedly uniform sequences of micritic limestones and marls are interrupted by complex structured reefs and by adjacent platform sediments generally the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the purpose of this study is a facies interpretation based on both field observations and stable isotope measurements of brachiopod shells approximately 700 samples from stratigraphically arranged localities in different facies areas have been investigated the carbon and oxygen isotopes show principally parallel curves and a close relationship to the stratigraphic sequence lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than to paleotemperature carbon isotope ratios are believed to have been connected to global changes in the burial of organic carbon in black shales during periods of euxinic deep water conditions consequently the facies succession on gotland results from global paleoclimatic conditions changes in terrigenous input due to different rates of weathering and freshwater runoff rather than sea level fluctuations control the carbonate formation of the silurian on gotland

correlation of silurian bentonites from gotland and the eastern baltic using sanidine phenocryst composition and biostratigraphical consequences silurian bentonites from sweden and the eastern baltic are correlated using xrd analysis of sanidine composition identifying the same bentonite in different sections has constrained correlations between the conodont graptolite and chitinozoan zonations three bentonites correlate the cyrtograptus murchisoni zone with the upper part of the pterospathodus amorphognathoides zone and both the lower and the upper pseudooneotodus bicornis conodont biozones at their type locality thus the base of the llandovery wenlock boundary stratotype can be correlated with a level in the upper part of the cyrtograptus murchisoni graptolite biozone identifying the y bentonite gotland sweden in eastern baltic drill cores shows that the base of the eisenackitina lagena chitinozoan biozone is close to the base of the k patula conodont biozone which is coeval with an upper part of the c rigidus graptolite zone sanidine data from the grotlingbo bentonite fit well with previous correlations some bentonites from gotland with distinct sanidine compositions and bulk geochemistries have not yet been identified elsewhere

extinction and migration in silurian trilobites and conodonts of northwestern canada appearances and disappearances lineage turnover of trilobite and conodont evolutionary species clades in silurian shelf marginal sections of the mackenzie mountains are concentrated at particular stratigraphical levels a depth energy curve generated for this region shows three major and several minor transgressive regressive cycles in the llandovery and wenlock series a comparison of this curve with conodont and trilobite distributional data supports the thesis that there are cause effect relationships between changes in sea level and migration evolution and extinction events of these marine organisms the rate amount and direction of change in depth were important factors in the migration and extinction of clades the depth energy curve for the region fits the pattern expected for a passive downdropping shelf responding to global eustatic sea level changes emigrations and extinctions are associated with rapid transgressive episodes and concentrated at three levels lower llandovery lower wenlock and middle or lower part of the upper wenlock the early wenlock event was the most impressive a further concentration of extinctions and or migrations not considered here occurred later in the ludlow associated with a regional regression phyletic evolution is most convincingly demonstrated in fossil collections from intervals of gradual regression a model is proposed that predicts that a similar pattern of extinctions occurred around the silurian world in regions of similar palaeotectonic regime and that global extinction patterns of clades between episodes of mass extinction were not random episodes of high extinction turnover pulses were caused by perturbations of the environment foremost of which were rapid changes in the depth of the seas on the continental shelves because taxonomic loss during these extinction emigration episodes was generally at low below generic levels resolution of silurian turnover patterns requires data collected at the evolutionary species level

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

combined effect of mjo enso and iod on the intraseasonal variability of northeast monsoon rainfall over south peninsular india the present study has examined the combined effect of mjo enso and iod on the intraseasonal and interannual variability of northeast monsoon rainfall over south peninsular india the study has revealed that the intraseasonal variation of daily rainfall over south peninsular india during nem season is associated with various phases of eastward propagating mjo life cycle positive rainfall anomaly over south peninsular india and surrounding indian ocean io is observed during the strong mjo phases 2 3 and 4 and negative rainfall anomaly during the strong mjo phases 5 6 7 8 and 1 above normal below normal convection over south peninsular india and suppressed convection over east indian and west pacific ocean high pressure low pressure anomaly over west pacific ocean positive negative sst anomalies over equatorial east and central pacific ocean and easterly wind anomaly westerly anomaly over equatorial indian ocean are the observed features during the first three mjo 5 6 7 phases and all these features are observed in the excess drought nemr composite this suggests that a similar mode of physical mechanism is responsible for the intraseasonal and interannual variability of northeast monsoon rainfall the number of days during the first three phases last four phases of mjo where the enhanced convection and positive rainfall anomaly is over indian ocean east indian ocean and west pacific ocean is more less during el nino and iod years and less during la nina and niod years and vice versa the observed excess deficit rainfall anomaly over west io and south peninsular india and deficit excess rainfall anomaly over east io including bay of bengal and west pacific ocean suggest that the more less number of first three phases during el nino and iod la nina and negative iod is due to the interaction between eastward moving mjo and strong easterlies over equatorial io present during el nino and iod years this interaction would inhibit the development of long duration mjo and would result in short duration high frequency mjo type which confined over indian ocean and south peninsular india and hence make all the el nino and iod years to be excess rainfall years for nem season

simultaneous changes in carbon isotopes sea level and conodont biozones within the cambrian ordovician boundary interval at black mountain australia carbon isotope profiles of marine carbonate units within the cambrian ordovician boundary section at black mountain western queensland australia reveal cyclical changes in 13c within the georgina basin during the boundary interval minimum values in the 13c profile are found in strata bearing lithostratigraphic evidence for sea level drop and also correlate strongly with conodont assemblage zone boundaries these relations indicate that direct mechanistic links existed between carbon cycles changes in sea level and conodont evolution

a search for shocked quartz grains and impact ejecta in early silurian sediments on gotland sweden all bentonite and bentonite resembling layers thicker than a few millimetres from a 120m thick early silurian sequence on gotland sweden were searched for shocked quartz grains of comet or asteroid impact origin although more than 200000 quartz grains from 86 bentonite samples were studied not one single grain with multiple planar shock features was found the studied sequence represents sedimentation during a period of about 2 million years impact frequencies estimated from the cratering record and astronomical observations indicate that during a 2 myr period on average 20 comet or asteroid bodies larger than 0 5 km in diameter strike the earth the number of smaller impacting bodies is many times higher in the light of this high frequency of impacts the absence of any shocked quartz bearing fallout layer in our sequence indicates that lateral spreading of such ejecta is relatively restricted during small and medium scale impact events the results also show that shocked quartz in general is absent or extremely rare in volcanic ash this strengthens the case for an impact related origin of shocked quartz grains in the cretaceous tertiary boundary days

sediment thicknesses of the western anatolia graben structures determined by 2d and 3d analysis using gravity data abstract western turkey is tectonically one of the most active and rapidly deforming regions of continental crust in the world the most pronounced structural and morphological features of this region are defined by normal faulting in an e w direction which creates the boundaries of the buyuk menderes kucuk menderes and gediz grabens the graben systems may have become active between 11 7 ma and are now deeper than the surrounding topography the gediz and buyuk menderes grabens exhibit negative bouguer gravity anomalies the bouguer gravity anomalies increase towards the center of the aegean sea in a regional sense the grabens are filled with recent sediments giving rise to relative negative gravity anomalies these anomalies were interpreted using 2d and 3d gravity inversion techniques in order to determine the depth to the metamorphic basement inversion of geophysical anomalies implies fitting the observed data to theoretical anomalies possibly produced by subsurface bodies inversion of gravity anomalies is a non linear problem in the sense that body parameters are not linearly related to the anomalies gravity anomalies caused by structures are mostly determined by a 2d model which has an n sided polygonal cross section for non linear problems theoretically it is more suitable to determine the parameters of the structure by a series of juxtaposing prisms or vertical dykes extending to infinity rather than using a single n side polygonal model the depths to the top surfaces of a rectangular prisms with infinite depth represent the relief of the basement the basement relief can be computed on the basis of density contrast if the reference depth is assessed as a result of 3d analysis of the bouguer gravity map the maximum thickness of sedimentary cover appears to be more than 2 0 and 1 5 km for the gediz and buyuk menderes grabens respectively towards the saraykoy kizildere area the sedimentary thickness cover thickens to more than 2 0 km 2d analysis of the bouguer gravity profiles indicate that the maximum thickness of the sedimentary cover is between 2 5 and 3 5 km in the buyuk menderes graben and between 0 5 and 2 0 km in the gediz graben

u pb zircon age constraints on the timing and duration of wenlock silurian paleocommunity collapse and recovery during the big crisis high precision isotope dilution u pb zircon dating was conducted on three volcanic ash fall bentonite samples from the swedish island of gotland and on a fourth bentonite from the west midlands england zircons from the ireviken grotlingbo djupvik gotland and wren s nest hill 15 west midlands bentonites yielded weighted mean pb 206 u 238 ages of 431 83 0 23 0 67 ma 428 45 035 0 73 ma 428 06 0 2110 66 ma and 427 86 032 0 71 ma respectively analytical total uncertainties these biostratigraphically well controlled age dates effectively bracket the wenlock epoch of the silurian period and provide control for the duration of one of the major paleozoic biotic events and associated perturbations to the global carbon cycle the big crisis or lundgreni event graptolites the niulde event conodonts the mulde excursion carbon isotopes these new data suggest an older and shorter duration for the recalibration of the wenlock series and demonstrate that the cascade of biological and chemical events that took place during the big crisis happened on time scales of tens to hundreds of thousands of years less

coupling geophysical investigation with hydrothermal modeling to constrain the enthalpy classification of a potential geothermal resource abstract an appreciable challenge in volcanology and geothermal resource development is to understand the relationships between volcanic systems and low enthalpy geothermal resources the enthalpy of an undeveloped geothermal resource in the karckar region of armenia is investigated by coupling geophysical and hydrothermal modeling the results of 3 dimensional inversion of gravity data provide key inputs into a hydrothermal circulation model of the system and associated hot springs which is used to evaluate possible geothermal system configurations hydraulic and thermal properties are specified using maximum a priori estimates limited constraints provided by temperature data collected from an existing down gradient borehole indicate that the geothermal system can most likely be classified as low enthalpy and liquid dominated we find the heat source for the system is likely cooling quartz monzonite intrusions in the shallow subsurface and that meteoric recharge in the pull apart basin circulates to depth rises along basin bounding faults and discharges at the hot springs while other combinations of subsurface properties and geothermal system configurations may fit the temperature distribution equally well we demonstrate that the low enthalpy system is reasonably explained based largely on interpretation of surface geophysical data and relatively simple models

intraseasonal behavior of clouds temperature and motion in the tropics abstract the spectral character of tropical convection is investigated in an 11 yr record of outgoing longwave radiation from the advanced very high resolution radiometer to identify interaction with the tropical circulation along the equator in the eastern hemisphere the space time spectrum of convection possesses a broad peak at wave numbers 1 3 and eastward periods of 35 95 days significantly broader than the dynamical signal of the madden julian oscillation mjo this quasi discrete convective signal is associated with a large scale anomaly that propagates across and modulates time mean or climatological convection over the equatorial indian ocean and western pacific outside that region the convective signal is small even though under amplified conditions coherence can be found east of the date line and in the subtropics having a zonal scale of approximately wavenumber 2 anomalous convection propagates eastward at some 5 m s 1 and suppresses as well as reinforces climatological convection

regional geothermal exploration in egypt although egypt is not characterized by abundant cenozoic igneous activity its location in the northeastern corner of the african plate suggests that it may possess geothermal resources especially along its eastern margin regional geothermal exploration has been carried out in egypt using the thermal gradient heat flow technique and groundwater temperature chemistry technique in the thermal gradient heat flow study existing oil well bottom hole temperature data as well as subsurface temperature measurements in existing boreholes were utilized before special thermal gradient holes were drilled groundwater temperature and chemistry data were used to extend the geographic range of the direct subsurface thermal measurements on a very modest budget a regional thermal high has been discovered along the eastern margin of egypt and a local thermal anomaly has been discovered in this zone published geological information suggests that the sandstones of the nubian formation may be a suitable reservoir for geothermal fluids the new data indicate that temperatures of 150 sup 0 c or higher may be found in this reservoir in the gulf of suez and red sea coastal zone where it lies at a depth of 4 km and deeper

composition and origin of thermal waters in the gulf of suez area egypt abstract thermal waters with discharge temperatures ranging from 32 to 70 c are being discharged along the gulf of suez egypt from springs and shallow artesian wells a comprehensive chemical and isotopic study of these waters supports previous suggestions that the waters are paleometeoric waters from the nubian sandstone aquifer the chemical and isotopic compositions of solutes indicate possible contributions from tertiary sedimentary aquifer rocks and windblown deposits marine aerosols and or evaporite dust in the recharge area there is no chemical or isotopic evidence for mixing with red sea water gas effervescence from the hammam faraoun thermal water contains about 4 ch4 13c 32 6 and 0 03 he having an isotopic ratio consistent with a mixture of crustal and magmatic he 3he 4he 0 26 re geothermometers for the thermal waters indicate maximum equilibration temperatures near 100 c the waters could have been heated by percolation to a depth of several km along the regional geothermal gradient

impact of mjo on the intraseasonal variation of summer monsoon rainfall over india the summer monsoon rainfall over india exhibits strong intraseasonal variability earlier studies have identified madden julian oscillation mjo as one of the most influencing factors of the intraseasonal variability of the monsoon rainfall in this study using india meteorological department imd high resolution daily gridded rainfall data and wheeler hendon mjo indices the intra seasonal variation of daily rainfall distribution over india associated with various phases of eastward propagating mjo life cycle was examined to understand the mechanism linking the mjo to the intraseasonal variability during mjo phases of 1 and 2 formation of mjo associated positive convective anomaly over the equatorial indian ocean activated the oceanic tropical convergence zone otcz and the resultant changes in the monsoon circulation caused break monsoon type rainfall distribution associated with this negative convective anomalies over monsoon trough zone region extended eastwards to date line indicating weaker than normal northern hemisphere inter tropical convergence zone itcz the positive convective anomalies over otcz and negative convective anomalies over itcz formed a dipole like pattern subsequently as the mjo propagated eastwards to west equatorial pacific through the maritime continent a gradual northward shift of the otcz was observed and negative convective anomalies started appearing over equatorial indian ocean during phase 4 while the eastwards propagating mjo linked positive convective anomalies activated the eastern part of the itcz the northward propagating otcz merged with monsoon trough western part of the itcz and induced positive convective anomalies over the region during phases 5 and 6 the dipole pattern in convective anomalies was reversed compared to that during phases 1 and 2 this resulted active monsoon type rainfall distribution over india during the subsequent phases 7 and 8 the convective and lower tropospheric anomaly patterns were very similar to that during phase 1 and 2 except for above normal convective anomalies over equatorial indian ocean a general decrease in the rainfall was also observed over most parts of the country the associated dry conditions extended up to northwest pacific thus the impact of the mjo on the monsoon was not limited to the indian region the impact was rather felt over larger spatial scale extending up to pacific this study also revealed that the onset of break and active events over india and the duration of these events are strongly related to the phase and strength of the mjo the break events were relatively better associated with the strong mjo phases than the active events about 83 of the break events were found to be set in during the phases 7 8 1 and 2 of mjo with maximum during phase 1 40 on the other hand about 70 of the active events were set in during the mjo phases of 3 to 6 with maximum during phase 4 21 the results of this study indicate an opportunity for using the real time information and skillful prediction of mjo phases for the prediction of break and active conditions which are very crucial for agriculture decisions

preliminary study on the occurrence of geothermal systems in the tectonic compressional regions an example from the derman geothermal field in the biga peninsula turkey abstract there are numerous hot springs with temperatures ranging from 30 to 100 c in biga peninsula and they occur throughout the peninsula the result of this study shows that the region is under a tectonic compressional regime the investigation of the faults and fractures in the region indicates that the region has been affected first by n s and then e w compression since the middle miocene opening fractures and antithetic and synthetic faults due to the compressional movements provide paths for the deep circulation of water in addition the tectonic movements granitic intrusion and volcanic activity have also played important roles as heat sources for the geothermal systems

influence of volcanic eruptions on helium isotope ratios in hydrothermal systems induced by volcanic eruptions temporal variations of 3he4he and 4he20ne ratios occur in high temperature gases from a steam well located about 3 km north of the central cone of mt mihara an active volcano in oshima island japan the 3he4he ratio gradually increased from 1 71ratm 1 71 times the atmospheric ratio of 1 40 10 6 in october 1986 to 5 02 ratm in november 1987 taking into account a similar 4he20ne change the magmatic he component in the steam has increased since the violent eruptions of oshima volcano from november 15 to december 18 1986 this confirms a direct relationship between magmatic activity and elevated 3he4he ratios in groundwater hydrothermal systems based on the distance from the craters to the steam well the time lag between the eruptions and the increase of 3he4he we estimate the magmatic component velocity in the fluid flow the calculated value several tens of m per day is significantly higher than typical groundwater flow in deep sedimentary basins of japan

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

the ireviken event in the lower silurian of gotland sweden relation to similar palaeozoic and proterozoic events abstract for a long time the silurian was thought to represent a time of stable environmental conditions in the greenhouse period that followed the late ordovician glaciation during the past decade knowledge about the silurian has increased markedly and today it is known that the conditions in the silurian were much more variable than previously assumed detailed isotopic investigations have revealed several distinct positive excursions in both carbon and oxygen isotope values in low latitudes these periods of high c and o isotope values are in many cases characterised by the growth of reefs and the formation of extended carbonate platforms the sediments deposited during these excursions contain impoverished fossil assemblages especially with respect to conodonts graptolites and trilobites a conspicuous isotope excursion coincident with facies changes and a marked mass extinction is observed near the llandovery wenlock boundary this event is called the ireviken event after its type locality on the island of gotland sweden jeppsson l 1987 in palaeobiology of conodonts ellis horwood ltd chichester pp 129 145 here isotope data from nine sections at the nw coast of gotland are presented that cover the time interval of the ireviken event the 13c mean values rise from 1 4 to 4 5 and the 18o values increase from 5 6 to 5 0 the relative timing of stable isotope development extinctions and facies development is discussed it is shown that first extinctions precede the isotope excursion this indicates that extinction events and stable isotope development are only indirectly connected but might reflect the same causes other events characterised by similar relationships between positive isotope excursions mass extinctions and facies development are found in younger parts of the silurian late wenlock and ludlow in the late ordovician the late cambrian and with some reservations in the proterozoic the similarities between these events indicate analogous controlling mechanisms for the silurian climatic changes between humid and arid conditions in low latitudes were postulated in an earlier study of the authors a palaeoceanographic climatic model was postulated which is consistent with most of the sedimentological palaeontological and geochemical data here we demonstrate that this model may be applicable also for the older events

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana