early diagenetic silica deposition in algal cysts and spores a source of sand in black shales abstract devonian black shales deposited on the north american craton contain abundant tasmanites cysts although these are typically flattened because of compaction a small proportion are filled with diagenetic silica the latter are spherical to ellipsoidal 0 1 0 5 mm and filled with chalcedony microquartz and megaquartz and single quartz crystals chalcedonic cyst fillings are preserved best in cheat and phosphate nodules whereas megaquartz and single quartz crystals are most common in shale matrix together with colloform textures this suggests that the various silica types originated from recrystallization of early diagenetic silica deposits thin sandstone beds in the chattanooga shale e g bransford sandstone contain abundant quartz sand that is much coarser than the detrital quartz component of the underlying black shales because of this their quartz component is thought to have been transported over considerable distances from the basin margin however because certain shale horizons contain as much as 10 silicified cysts that upon reworking could have yielded quartz grains of fine to coarse sand size the quartz component of these sandstone beds may actually have formed in situ indeed petrographic examination of the sandstone beds shows them to contain quartz grains with morphological and textural features of cyst quartz e g rounding sphericity chalcedony pyrite inclusions lobate grain margins thus silica deposition in algal cysts may provide a significant component of intrabasinal quartz sand in shale sequences distinction of this type of quartz from extrabasinal detrital quartz is important to the reconstruction of the depositional history of shale sequences

diagenesis of the lower eocene thebes formation gebel rewagen area eastern desert egypt abstract the diagenesis of lower eocene shallow water carbonates with flint was studied in the gebel rewagen area eastern desert egypt the carbonates are mainly wackestones to packstones with benthic bioclasts embedded in a dark red luminescent micrite matrix the studied succession displays a complex diagenetic history that involves syngenetic and late diagenetic processes silica which exists either as persistent bands nodules and or silicified benthic bioclasts shows a distinctive pattern regarding its distribution source depositional environments and timing three lines of evidence support a syngenetic origin of the chert bands 1 they alternate in a cyclic manner within the host carbonates and 2 they exhibit noticeable lateral persistence throughout the investigated area following the strata boundaries and 3 there is a lack of any carbonate dissolution in limestone adjacent to chert bands the deposition of silica bands in association with shallow water carbonates is possibly related to eustatic sea level changes which were accompanied by episodic variations in silica and carbonate productivities with a relative sea level fall and the establishment of a lowstand period at the end of the early eocene a basinward shift of the groundwater zones is expected within the carbonate platform during this period some late diagenetic processes took place which involve 1 the formation of siliceous and carbonate concretionary growths 2 partial silicification of bioclasts 3 neomorphic stabilization of the caco3 bioclasts and 4 the formation of equant calcite cement siliceous and carbonate concretions are believed to have taken place within microenvironments created and controlled by sulphate reducing bacteria and physico chemical and kinetic factors near a marine meteoric water mixing zone this is inferred from the distribution of iron sulphides the non ferroan nature of all concretions and the depleted 13c 5 4 to 6 0 pdb and 18o 5 8 to 6 8 pdb values of the carbonate concretions the silica fabrics of all the partly silicified benthic bioclasts with abundant pyrite cubes argue for a delayed silicification process within the sulphate reduction zone the close and relatively depleted 18o values of the low mg calcite micrite matrix 3 0 to 4 4 pdb and benthic bioclasts 3 4 to 4 8 pdb indicate that both matrix and bioclasts have probably suffered neomorphic stabilization from freshwater dominated solutions the initial marine 13c values of both low mg calcite matrix 0 2 to 2 2 pdb and altered benthic bioclasts 0 2 to 0 9 pdb are retained and not affected by diagenesis the luminescence character and the extremely depleted oxygen values 8 3 to 10 1 pdb of the equant void filling calcite mosaics are consistent with their formation within a meteoric phreatic realm

tropical intraseasonal oscillation at monthly time scale during boreal summer and winter this study describes the space time structure of an intraseasonal oscillation with the time scale of a month over the south asian monsoon region and the tropical pacific for the boreal summer and winter seasons these nonlinear oscillations were extracted by applying multichannel singular spectrum analysis on daily anomalies of three dimensional diabatic heating separately during the summer and winter the monthly oscillations mos are distinct from the leading monsoon intraseasonal oscillation with a period of 45 days during the summer and the madden julian oscillation during the winter the summer mo exhibits horizontal quadrupole structure predominantly in the northern hemisphere and propagates eastward over the indian region and westward over the pacific along with northward movement the winter mo is confined to the equatorial region in the southern hemisphere and propagates eastward and southward both the summer and winter mos consist of propagating deep vertical columns of heating and cooling anomalies the associated fields of convection precipitation and three dimensional circulation show similar patterns and propagation the corresponding specific humidity has revealed moisture preconditioning for horizontal propagation and co located vertical advection however there is no clear pattern of ocean atmosphere interaction associated with the mo as seen in the examination of sea surface temperature and latent heat flux

preservation of larval bivalve shells in a radiolarian chert in the late triassic early norian interval of the malampaya sound group calamian island western philippines abstract silicified thin larval bivalve shells occur in upper triassic radiolarian chert early norian in the liminangcong formation of the malampaya sound group part of a late jurassic to early cretaceous subduction related accretionary complex in the north palawan block western philippines the bivalve bearing radiolarian chert which we term bivalve chert is considered to be a deep sea sediment that accumulated in an open ocean realm of the panthalassa ocean radiolarian and conodont biostratigraphies indicate an early norian deposition of the thin shelled bivalves the bivalve morphology thin shells less than 30 m thick smooth ornamentation and small size less than 1 3 mm long suggests they represent larval shells although their taxonomic identity cannot be established with certainty halobiid bivalves that lived in norian times apparently had such a planktonic larval mode of life

space time structure of diabatic heating in monsoon intraseasonal oscillation abstractthe space time structure of the leading monsoon intraseasonal oscillation miso in three dimensional diabatic heating is studied using the era interim data of the european centre for medium range weather forecasts the diabatic heating data were constructed by the residual method of the thermodynamic equation the miso was extracted by applying multichannel singular spectrum analysis on the daily anomalies of three dimensional diabatic heating over the south asian monsoon region for the period 1979 2011 the diabatic heating miso has a period of 45 days and exhibits eastward propagation in the equatorial indian and pacific oceans and northward propagation over the entire monsoon region the horizontal structure shows a long tilted band of heating anomalies propagating northeastward the period horizontal pattern and propagation properties of the diabatic heating miso are similar to those found in precipitation outgoing longwave radiation and circulation in earlier studies the vertical struc

diagenesis of bivalves from jurassic and lower cretaceous lacustrine deposits of northeastern china in contrast to the numerous excellently preserved arthropods vertebrates and plants from the mesozoic lacustrine fossil lagerstatten of northeastern china which have calcium phosphate or organic skeletons the preservation of taxa with a calcareous skeleton is fairly poor here we investigate using a scanning electron microscope and energy dispersive x ray spectrometer the preservational modes of bivalves from the jurassic daohugou fossil beds of inner mongolia and the lower cretaceous yixian formation of eastern liaoning the jurassic bivalve ferganoconcha sibirica is preserved as strongly compressed composite moulds which contain remains of the organic periostracum in the yixian formation the bivalves sphaerium anderssoni and arguniella ventricosa occur as compacted internal external or composite moulds or are preserved with a silicified shell and rarely with a shell consisting of iron hydroxides which had replaced pyrite during late diagenesis weathering silicification produced partly fabric replacive microcrystalline quartz and partly void filling megaquartz crystals after the carbonate shell had been dissolved films of authigenic aluminosilicate minerals partly secondarily silicified cover the exterior and interior shell surfaces occasionally early diagenetic pyrite crystals now oxidized to iron hydroxides filled shell cavities forming internal moulds and rarely replaced the bivalve shell the poor preservation of the bivalves reflects the environment and water chemistry of these lakes which were heavily influenced by volcanic processes frequent ash deposition and decomposition of volcanic glass particles created acidic and alkaline lake and interstitial waters which led to early diagenetic formation of authigenic aluminosilicate minerals ferruginous internal moulds dissolution of shell carbonate and silicification of shells

interactions between dissolved silica and carbonate minerals an experimental study at 25 50 c abstract replacement of carbonate minerals by silica polymorphs in marine and meteoric environments is a common early diagenetic feature of sedimentary rocks although relatively few experimental investigations have been made of interactions between carbonate minerals and dissolved sio 2 at moderate temperatures available data suggest that silica uptake onto carbonate surfaces can be significant we present results of experiments conducted between 25 and 50 c of the uptake of aqueous sio 2 from artificial seawater mg na cl ca hco 3 i 0 7 and meteoric type cacl 2 na 2 co 3 i m a reasonable upper limit for natural diagenetic waters dissolved silica carbonate mineral interactions were investigated under three experimental conditions 1 in solutions near equilibrium with respect to calcite 2 in calcite seeded precipitation experiments at fixed degrees of calcite supersaturation and 3 during closed system dissolution precipitation of metastable carbonate minerals aragonite and 18 mole mg calcite to low mg calcite lmc in artificial seawater asw maintained near equilibrium with respect to calcite at various p co2 values silica uptake from solution onto calcite surfaces 1 15 mol si gram seed was irreversible and strongly time and ph dependent the rate of uptake was greatest in the first 5 hr and in solutions of lower ph higher p co2 silica uptake was only nominally dependent on solution mg and temperature over the range studied silica uptake was greater in asw than in otherwise comparable experiments conducted in low ionic strength solutions controlled calcite precipitation rates were unaffected by the adsorption of silica during recrystallization of aragonite and mg calcite in low ionic strength solutions silica uptake 1 6 mol g was similar to values frorn near equilibrium experiments for synthetic calcite in asw experimental si adsorption values were comparable to si adsorption values determined for modem metastable sediments 3 4 mol g 1 despite considerable variation in the experimental carbonate equilibrium disequilibrium mineralogy and solution chemistry si uptake at near surface and moderate burial conditions 25 50 c was limited to 15 mol g 1 si even in solutions maintained near opal ct saturation over a period of days to weeks

influences of northward propagating 25 90 day and quasi biweekly oscillations on eastern china summer rainfall the present study reveals that rainfall anomalies associated with the 25 90 day quasi biweekly tropical convective activity propagates northward northwestward into northern china the yangtze river enhanced rainfall over southern china results directly from enhanced convection propagating northward from the south china sea scs western north pacific wnp strengthened northward water vapor transport and intensified upper level divergence the anomalous anticyclone over scs wnp which is induced by local lower sea surface temperature provides a favorable condition for transporting more moisture to southern china stronger subtropical westerly jet and south asia high strengthen upper level divergence the northward propagating 25 90 day oscillation over eastern china reaches farther north than the quasi biweekly oscillation qbwo the intensity of qbwo in summer rainfall has significantly strengthened over southern china after 1993 but not for the 25 90 day oscillation this is mainly contributed by an interdecadal increase in rainfall over southern china and the yangtze river basin in the wet phases of qbwo the interdecadal enhancement of rainfall associated with the qbwo is attributed to three factors one is lower tropospheric convergence caused by anomalous anticyclone over the wnp and anomalous cyclone over korean peninsula and japan the second is upper tropospheric divergence resulting from strengthening of subtropical westerly jet and the south asia high the last is enhanced ascent over south china through meridional vertical circulation

intraseasonal periodicities in indian rainfall abstract spectral analysis of a 70 year 1901 70 record of daily precipitation from 3700 stations in the country of india is carried out to search for periodicities on subseasonal time scales during the summer monsoon two statistically significant spectral peaks are found a 40 50 day spectral peak corresponding to the madden julian oscillation is found over most of the portion of india south of 23 n the phase of the oscillation is such that the precipitation maximum appears first over the relatively dry southeastern portion of the peninsula ten to 12 days later the precipitation peaks simultaneously all along the coast west of the western ghats and along a line running across india between 20 and 25 n the precipitation maximum then spreads slowly northward and loses significance cross spectral analysis shows strong coherence between the precipitation patterns and wind oscillations the zonal wind oscillations at 850 and 200 mb am about 180 degrees out of phase equatorward of about 20 n but in pha

intraseasonal oscillations of the monsoon circulation over south asia the space time structure of the three dimensional circulation over the south asian monsoon region has been studied using the era 40 reanalysis of the european centre for medium range weather forecasts applying multi channel singular spectrum analysis on combined daily values of horizontal winds and pressure vertical velocity at ten vertical levels for the period 1958 2001 two leading intraseasonal nonlinear oscillations were extracted the first oscillation has an average period of 50 days and propagates northeastward from the indian ocean to the indian subcontinent the second oscillation has a period of 30 days and propagates northwestward from the west pacific to the indian region both the oscillations exhibit the oscillatory and propagation features at all vertical levels from 1 000 to 100 hpa the two oscillations correspond well with similar oscillations found in outgoing longwave radiation and precipitation in earlier studies the wind oscillations also account for the active and break phases of the indian monsoon the vertical structures and propagation of specific humidity and temperature are found to be consistent with those of the winds in each oscillation the structure and movement of regional hadley and walker circulations have also been described the analyses provide further strong evidence for the existence of two distinct monsoon intraseasonal oscillations

mechanism and controls of silicification of fossils in limestones silicification of calcitic fossils occurs along thin solution films at which calcite dissolves and silica precipitates the mechanism is replacement controlled by force of crystallization whereby the growth of the silica phase exerts pressure across the silica carbonate contact increasing the gibbs free energy and hence solubility of shell calcite physical evidence for force of crystallization controlled replacement includes restriction of carbonate dissolution to the silica carbonate contact and euhedral quartz terminations at some quartz calcite contacts correlations among some replacement quartz types and fossil taxa indicate that shell microstructure and bulk pore water silica concentration control replacement quartz type

too low δ18o of paleo meteoric low latitude water do paleo tropical cyclones explain it abstract isotopic analysis of rock samples showed anomalously 18 o depleted reconstructed isotopic composition of paleo meteoric water over southern israel between the late cretaceous and the early miocene with 18 o w as low as 14 smow this range is significantly lighter than the expected values for rain at the relevant paleo latitudes 8 n to 25 n it is similar or lighter than areas with meteoric water at the present climate in which rainfall contribution from tropical cyclone tc is significant rainfall from tcs is 18 o depleted because of the recirculation of the vapor into repeated precipitation or distillation cycles a paleo geographic reconstruction of the region shows that throughout the period there was a warm ocean to the east and southeast of the relevant area thus tcs formed over the ocean and made landfall on the coastline at a distance of 300 to 400 km to the east the reconstructed composition of the rainwater implies dominance of tcs at these times furthermore the combination of warmer seas and lighter rainwater than at present suggests that the tcs were more dominant than in the most tc prone coastal areas at the present climate the results of the present study suggest that climate during the relevant time periods was very different from the present with tc activity similar or exceeding the most tc prone locations in the world at the present climate this might also hint that warmer sea waters in the geological past were conducive to greater tc activity than in the present climate answering this question requires additional research

seasonal persistence and propagation of intraseasonal patterns over the indian monsoon region the space time evolution of convection over the monsoon region containing the indian subcontinent the indian ocean and the west pacific has been studied a multi channel singular spectrum analysis of the daily outgoing longwave radiation has yielded two intraseasonal oscillatory patterns and two large scale standing patterns as the most dominant modes of intraseasonal variability the oscillatory modes vary on time scales of about 45 and 28 days and their average cycles of variability are shown to correspond to the life cycles of active and break periods of monsoon rainfall over india during an active break cycle a convection dry anomaly zone first appears in the equatorial indian ocean subsequently expands to cover the indian subcontinent and finally contracts to disappear in the northern part of india some eastward and northward movements are found to be associated with both oscillatory modes while westward movement may also be associated with the 28 day mode the oscillatory modes are shown to have a large spatial scale extending to the west pacific one of the standing modes has anomalies of uniform sign covering the entire region and is related to el nino and southern oscillation enso pattern the other standing mode has a dipole structure in the equatorial indian ocean associated with large scale anomalies over india with the same sign as those over the western part of the dipole these two standing modes persist throughout the monsoon season each maintaining its respective pattern the seasonal mean monsoon is mainly determined by the two standing patterns without much contribution from the oscillatory modes the relative role of the standing patterns enso mode and dipole mode seems to be important in determining the seasonal mean during certain years

geological factors for hazardous debris flows in hoser central taiwan by means of an onsite investigation the largest debris flow in taiwan s history is analyzed in this paper a heavy rainfall of 1 748 mm day occurred during typhoon herb in the hoser area at the end of july 1996 aerial photographic assessment and observations of geological and geomorphological features have contributed to our understanding of this massive destruction mechanisms of the hazardous debris flow are explored and discussed data revealed that the rock discontinuities were a major factor in the voluminous loose materials in the debris flows the heavy and rapid rainfall instantly transported massive amounts of debris flow materials into the center and then quickly funneled them to the lower parts of gullies the heavy slurry became an effective cutting device to erode the side walls and move large quantities of the debris materials to the end of the gullies

late cretaceous quartz geodes after anhydrite from burgos spain quartz geodes cauliflower like appear in a specific level of the late cretaceous north of burgos due to their anhydrite relicts and spherulitic quartz length slow chalcedony they are considered as pseudomorphs of anhydrite nodules formed during early diagenesis at the same level compact chert nodules sporadically appear presenting a considerable amount of sponge spicules with fibrous texture length fast chalcedony the silicification of the anhydrite nodules took place before total compaction and cementation of the sediment the source of silica is principally biogenic sponge spicules there is no link between the depositional environment and the existence in itself of anhydrite nodules indirectly it is possible to see the effects of an arid climate which have not been recorded in the lithologic column here described modified journal abstract

splash detachment runoff depth and soil cohesion summary a set of laboratory experiments has been carried out in order to investigate the importance of soil cohesion and the interference due to the depth of the surface runoff on the detachment rate of soil particles and aggregates experimental data show that the soil detachment rate decreases as the runoff depth increases this indicates that the detachment power of the raindrops is partially dispersed by the water layer an inverse relationship between soil detachment and soil cohesion has been confirmed nevertheless the grain size distribution must also be used in order to define soil detachability

trends interdecadal and interannual oscillations in global sea surface temperatures this study aims at a global description of climatic phenomena that exhibit some regularity during the twentieth century multi channel singular spectrum analysis is used to extract long term trends and quasi regular oscillations of global sea surface temperature sst fields since 1901 regional analyses are also performed on the pacific northern and southern atlantic and indian ocean basins the strongest climatic signal is the irregular long term trend characterized by overall warming during 1910 1940 and since 1975 with cooling especially of the northern hemisphere between these two warming intervals substantial cooling prevailed in the north pacific between 1950 and 1980 and continues in the north atlantic today both cooling and warming are preceded by sst anomalies of the same sign in the subpolar north atlantic near decadal oscillations are present primarily over the north atlantic but also over the south atlantic and the indian ocean a 13 15 y oscillation exhibits a seesaw pattern between the gulf stream region and the north atlantic drift and affects also the tropical atlantic another 7 8 y oscillation involves the entire double gyre circulation of the north atlantic being mostly of one sign across the basin with a minor maximum of opposite sign in the subpolar gyre and the major maximum in the northwestern part of the subtropical gyre three distinct interannual signals are found with periods of about 60 65 45 and 24 30 months all three are strongest in the tropical eastern pacific the first two extend throughout the whole pacific and still exhibit some consistent albeit weak patterns in other ocean basins the latter is weaker overall and has no consistent signature outside the pacific the 60 month oscillation obtains primarily before the 1960s and the 45 month oscillation afterwards

petrology and diagenetic evolution of neoproterozoic ooids libby formation western montana u s a abstract radial concentric and twinned sparry ooids from the upper belt supergroup originally formed as mixed mg calcite and aragonite and aragonite textural evidence suggests that mg calcite ooids may have formed along with the ooids having an original aragonite mineralogy strontium concentrations of 2400 to 2900 ppm support an aragonitic precursor to the twinned sparry ooids and sr values of 2500 ppm strongly suggest that the radial concentric ooids had an aragonitic component in addition to the mg calcite suggested by the preserved fabric trace element mn mg fe and sr values of ooids and early carbonate cements suggest that diagenetic trends for these proterozoic carbonates are similar to those established for their phanerozoic and archean counterparts mg fe and mn increase and sr decreases with successively later carbonate phases

relation between indian monsoon variability and sst abstract the relation between the intraseasonal modes of the south asian monsoon and the sea surface temperature sst in the tropical oceans on a daily time scale has been investigated long lead lag relations of the daily sst anomalies with the dominant monsoon modes obtained from a multichannel singular spectrum analysis mssa of the daily outgoing longwave radiation olr over the south asian monsoon region are presented the dominant mssa monsoon modes consisting of two oscillatory modes at 45 and 28 day time scales and two seasonally persistent modes are found to have varying degrees of lead lag relation with the ssts in the indian and pacific oceans while the 45 day oscillatory mode has weak correlations with the ssts in the pacific and indian ocean it also reveals a possible 45 day oscillation in the sst in the northwestern pacific and northern indian ocean the 28 day oscillatory mode has negligible correlation with the tropical sst one of the persistent monsoon modes has a very strong r

silicification of carbonate clasts in a marine environment upper miocene vera basin se spain abstract upper miocene marine sediments in the vera basin se spain contain abundant silicified marble pebbles and bivalves the silicification of these marble pebbles and bivalves represents one of the stages of their sedimentary history associated with small fluctuations in relative sea level during the late tortonian alluvial fan deposits containing the marble pebbles were invaded by the sea which caused reworking of the pebbles and the establishment of a marine biota in the environment after shallow burial numerous marble pebbles and bivalve remains were silicified both types of clasts were partially replaced by opal ct or quartz from opaline silica derived from dissolution of skeletal debris the silicified zones rinds now consist of quartzine or quartz silicification of the clasts must have taken place under shallow burial conditions during early diagenesis while pyrite formed in favourable anoxic sites iron oxides also precipitated during early diagenesis but after silicification finally part of the deposits containing the silicified clasts were transported by gravitational mass flows and redeposited in deeper areas of the basin if the hypothesis proposed for the diagenetic process is correct it indicates that the uncommon silicification of carbonate clasts does not only occur in continental environments in which it has previously been described

patterns of silicification in permian pelecypods and brachiopods from wyoming abstract silicified pelecypods and brachiopods are common in the ervay franson and grandeur members of the permian park city formation of central and western wyoming study of hundreds of these fossils has resulted in recognition of five patterns of silicification pattern i is characterized by megaquartz crystals projecting inward from and perpendicular to the skeletal boundary whereas fossils exemplifying pattern ii consist of concentric laminae of chalcedonic quartz in pattern iii an outer lamina of microcrystalline quartz grades abruptly inward to laminated chalcedonic quartz which in turn grades abruptly inward to megaquartz shells demonstrating pattern iv involve megaquartz crystals aligned parallel to the skeletal boundary and lying adjacent to beekite discs pattern v consists of megaquartz crystals aligned parallel to the skeletal boundary in brachiopods these crystals typically exhibit relict skeletal microstruture pelecypod wall layers constructed originally of aragonite are characterized by patterns i ii iii and iv pattern v characterizes all brachiopods and originally calcitic layers of pelecypods patterns i ii iii and iv are interpreted to result from filling of voids created by dissolution of skeletal carbonate pattern v results from concurrent carbonate dissolution and silica precipitation

role of north indian ocean air sea interaction in summer monsoon intraseasonal oscillation abstractair sea coupling processes over the north indian ocean associated with the indian summer monsoon intraseasonal oscillation miso are investigated observations show that miso convection an