structure of chlorella fusca algaenan relationships with ultralaminae in lacustrine kerogens species and environment dependent variations in the composition of fossil ultralaminae numerous kerogens from marine and lacustrine source rocks and oils shales previously considered as amorphous were recently shown to comprise very thin 10 30 nm thick lamellar structures termed ultralaminae comparative morphological and chemical studies of a lacustrine ultralaminae rich kerogen and of the non hydrolysable biopolymer algaenan isolated from the thin resistant outer walls of a freshwater microalga scenedesmus quadricauda established a close relationship between these two materials chemical correlation was mainly based on the production upon pyrolysis of a series of n alkylnitriles with a bimodal distribution the non hydrolysable biopolymer isolated from the outer walls of the ubiquitous freshwater microalga chlorella fusca exhibits the same morphologicalfeatures as those observed in s quadricauda and in fossil ultralaminae the investigation of c fusca algaenan by solid state 13c nmr and analysis of pyrolysis products revealed that the correlation previously established between s quadricauda and lacustrine ultralaminae also holds for c fusca since the same series of n alkylnitriles with the same distribution is formed upon pyrolysis probably via cleavage of amide functions this confirms that fossil ultralaminae in lacustrine kerogens derive from the algaenans building up the thin outer walls of freshwater microalgae via the selective preservation pathway in addition the analysis of the 2 n alkanones generated on pyrolysis indicates that their distribution depends on the algal species considered accordingly variations in ketone distributions in the pyrolysates of lacustrine ultralaminae rich kerogens may reflect differences in populations of the source microalgae on the contrary changes in n alkylnitrile distribution would not be species dependent but would reflect the lacustrine or marine origin of the considered material

structural geology and regional tectonic significance of the ramgarh thrust himalayan fold thrust belt of nepal 1 the ramgarh thrust is one of the major fault systems of the himalayan thrust belt in nepal and northern india the ramgarh thrust sheet is 0 2 2 0 km thick and can be traced along strike the entire length of the himalaya in nepal the fault generally places the oldest paleoproterozoic rocks in the lesser himalayan series upon younger lesser himalayan rocks or lower miocene foreland basin deposits regional balanced cross sections suggest that the ramgarh thrust had at least 120 km of initial south vergent displacement subsequently the frontal part of the thrust experienced further slip as the roof thrust for a large duplex in underlying lesser himalayan rocks ramgarh hanging wall strata are greenschist grade phyllite quartzite and augen gneiss all of which locally exhibit phyllonitic and mylonitic fabrics that indicate a top to the south sense of shear structural fabrics in the ramgarh thrust sheet are generally parallel to the fabrics in rocks above and below the thrust sheet regional and local mapping of the ramgarh thrust in nepal demonstrates that the fault always places a hanging wall flat upon a footwall flat except where local lateral ramps complicate its geometry similarly the structurally overlying main central thrust always places a hanging wall flat in greater himalayan series rocks upon the regionally flat ramgarh thrust sheet these geometric relationships preclude kinematic and thermal models that elevate greater himalayan and lower lesser himalayan rocks along high angle thrust ramps in the vicinity of the present traces of the ramgarh and main central thrust faults instead the corresponding footwall ramps for these thrusts must be located more than 100 km north of the current trace of the main central thrust the present steep dips of the ramgarh and main central thrust sheets can be attributed to tilting during emplacement of structurally lower thrust sheets within a large antiformal duplex that occupies most of the lesser himalayan zone the ramgarh thrust sheet overlaps a bed length of at least 100 km in lower miocene foreland basin deposits indicating that a significant amount of displacement on the thrust must have occurred after 15 ma growth of the lesser himalayan duplex and additional slip on the frontal part of the ramgarh thrust occurred from 12 to 5 ma the presence of a major greenschist grade metasedimentary thrust sheet composed of lesser himalayan rocks directly below the main central thrust suggests that the famous inverted metamorphism in this region is a result of structural inversion similarly the concept of a broad zone of intense shear strain related exclusively to emplacement of the main central thrust sheet is probably invalid in nepal

retrograde net transfer reaction insurance for pressure temperature estimates retrograde net transfer reactions significantly affect compositions of metamorphic minerals yet are rarely considered when determining pressure temperature p t conditions two natural amphibolite facies metapelites from the central himalaya of nepal exhibit extremely common compositional patterns including increases in mn and fe fe mg at the rims of garnets which are the result of retrograde garnet dissolution and fe mg exchange with biotite however typical thermobarometric approaches for these rocks result in errors of hundreds of degrees and 3 6 kbar compared with thermobarometry of nearby rocks and petrogenetic grids these large errors result because dissolution of high fe garnet has strongly affected the fe mg ratio of matrix biotite x ray maps help evaluate the extent and chemical effects of retrograde reactions in these samples by identifying mineral regions that retain highest t compositions or through a new data processing approach by permitting correction of mineral compositions to original high t values these approaches ensure against retrograde net transfer reactions and should be applied routinely in thermobarometric studies they ultimately yield p t estimates that are more petrologically reasonable and permit rapid screening of samples for those least affected by retrograde reactions reconsideration of thermobarometry in the central and eastern himalaya indicates that retrograde net transfer reactions are extremely common therefore previous thermobarometric studies based on garnet major element compositions from that region should be reevaluated

comparative studies of the kinetic parameters of various algaenans and kerogens via open system pyrolyses abstract kinetic parameters were determined for the first time via open system pyrolyses on algaenans highly resistant biomacromolecules that are selectively preserved during kerogen formation isolated from extant microalgae parallel studies were also carried out on 10 kerogens exhibiting with one exception a low level of maturity these kerogens included samples chiefly derived from the selective preservation of the above algaenans and samples mainly or almost exclusively derived from the natural vulcanization pathway important differences in activation energy e a distributions were observed between the four algaenans investigated and correlated with their chemical structures the kerogens predominantly derived from algaenan selective preservation pula alginite ne 70 and bj 248 torbanites rundle oil shale also exhibited pronounced differences in e a distributions these distributions provided i information on the diversity of the source materials and ii reflected the occurrence of important differences in chemical structures and thermal behaviour between three of the tested kerogens even though they are all classified as low maturity type i the kimmeridge clay samples and the lorca oil shale showed broad e a distributions shifted to low energies when compared with the above algaenans and kerogens such shifts reflect an important or even almost exclusive for some of these kerogens contribution of materials originating from sulphur incorporation into various lipids during early diagenesis finally the kinetic data derived for the nine low maturity fossil samples were extrapolated to a very low geological heating rate of 3 c ma 1 and the generation rate curves and cumulative yield curves thus obtained were compared

tethyan and indian subduction viewed from the himalayan high to ultrahigh pressure metamorphic rocks abstract the himalayan range is one of the best documented continent collisional belts and provides a natural laboratory for studying subduction processes high pressure and ultrahigh pressure rocks with origins in a variety of protoliths occur in various settings accretionary wedge oceanic subduction zone subducted continental margin and continental collisional zone ages and locations of these high pressure and ultrahigh pressure rocks along the himalayan belt allow us to evaluate the evolution of this major convergent zone 1 cretaceous 80 100 ma blueschists and possibly amphibolites in the indus tsangpo suture zone represent an accretionary wedge developed during the northward subduction of the tethys ocean beneath the asian margin their exhumation occurred during the subduction of the tethys prior to the collision between the indian and asian continents 2 eclogitic rocks with unknown age are reported at one location in the indus tsangpo suture zone east of the nanga parbat syntaxis they may represent subducted tethyan oceanic lithosphere 3 ultrahigh pressure rocks on both sides of the western syntaxis kaghan and tso morari massifs formed during the early stage of subduction exhumation of the indian northern margin at the time of the paleocene eocene boundary 4 granulitized eclogites in the lesser himalaya sequence in southern tibet formed during the paleogene underthrusting of the indian margin beneath southern tibet and were exhumed in the miocene these metamorphic rocks provide important constraints on the geometry and evolution of the india asia convergent zone during the closure of the tethys ocean the timing of the ultrahigh pressure metamorphism in the tso morari massif indicates that the initial contact between the indian and asian continents likely occurred in the western syntaxis at 57 1 ma west of the western syntaxis the higher himalayan crystallines were thinned rocks equivalent to the lesser himalayan sequence are present north of the main central thrust moreover the pressure metamorphism in the kaghan massif in the western part of the syntaxis took place later 7 m y after the metamorphism in the eastern part suggesting that the geometry of the initial contact between the indian and asian continents was not linear the northern edge of the indian continent in the western part was 300 to 350 km farther south than the area east of the nanga parbat syntaxis such en baionnette geometry is probably produced by north trending transform faults that initially formed during the late paleozoic to cretaceous gondwana rifting farther east in the southern tibet the collision occurred before 50 6 0 2 ma finally high pressure to ultrahigh pressure rocks in the western himalaya formed and exhumed in steep subduction compared to what is now shown in tomographic images and seismologic data

oil oil correlation and potential source rocks for oils in paleozoic reservoir rocks in the tataria and perm basins russia abstract we present a study of 45 oil samples from the tataria and perm basins in the volgo ural region russia crude samples were obtained from 30 oil fields across the two basins samples are from variable carbonate and sandstone reservoir rocks ranging in age between givetian devonian and kazanian permian at various present day depths oil oil correlation suggests that despite the diversity of the reservoir rocks and vast geographic distribution all oils studied are classified in general into a singular genetic oil family with possible indication for secondary subdivision into two subgroups the major characteristics of the oils i e low pr ph ratio cpi 1 relatively high c 27 sterane low proportions of rearranged steranes c 29 c 30 hopane low ratio of ts to tm hopanes high sulfur content and high ratio of v to ni all suggest a reducing and probably hypersaline depositional environment for the source rock which was likely carbonate rich thermal maturity indicated for all the oils is in the upper range of the main phase of oil generation furthermore the characteristics obtained for the light end normal alkanes and mono aromatics indicate no significant degradation for most of the samples hence the relatively high specific gravity of the oil samples is not attributed to either maturity or degradation effects difference recorded in pr ph ratio between samples from perm basin are tentatively attributed to spatial variations in depositional environment conditions differences in tricyclic terpanes content in samples from both basins possibly indicate some variations in input of specific tasmanites algae to their source rock preliminary examination of an extract of devonian domanic formation sample corroborates the possibility that this formation is a major source rock for the oils in both the tataria and perm basins

evidence for gloeocapsomorpha prisca in late devonian source rocks from southern alberta canada abstract organic rich intervals within the late devonian camrose member of southern alberta canada show optical and chemical characteristics very similar to those of ordovician samples whose organic matter is dominated by gloeocapsomorpha prisca derived alginite this includes saturate fraction gas chromatograms dominated by n alkanes with a pronounced odd carbon number up to c19 and much lower abundances of c19 n alkanes acyclic isoprenoids and biomarkers microscopy reveals these samples contain g prisca like alginite with a morphology that previously has been suggested for the growth of this organism under higher salinity conditions which is in agreement with the depositional environment of the camrose member one unusual feature of the g prisca rich samples is the very high concentration of c21 and c23n alkylnaphthalenes and n alkylbenzenes in the aromatic fractions of their extracts the origin of these compounds is not known but their occurrence could be related to the high concentrations of c21 and c23n alkyl phenols that have been noted in pyrolysates of estonian kukersites by previous workers other camrose member extracts show very different distributions that are more typical for carbonates deposited under anoxic higher salinity conditions many oils that occur in nisku formation reservoirs in the enchant hays field in southern alberta show saturate fraction gas chromatograms and other evidence that indicate an important contribution to these oils from the g prisca rich intervals these are thought to have a contribution from camrose member source rocks hence caution should be used in only attributing g prisca geochemical characteristics to cambro ordovician oils as on rare occasions they can also occur in younger source rocks and their derived oils

a reappraisal of kerogen formation abstract comparative microscopical and chemical studies of recognizable entities in kerogen and their extant counterparts suggest a new and simple mechanism of kerogen formation which clarifies the interrelationships between extant biomass kerogen and fossil fuels

modification of the petroleum system concept origins of alkanes and isoprenoids in crude oils discussion in their recent paper collister et al 2004 presented a statistical analysis of c10 c28 n alkane and c16 c21 regular isoprenoid distributions of oils and rock extracts from the timan pechora basin they found that all unaltered to moderately biodegraded samples could be described as mixtures of six end member compositions that were assigned to five unique biological sources and to one reservoir process biodegradation because the end members appeared to yield no indications of thermal maturation collister et al surmised that these hydrocarbons were generated not from the thermal cracking of kerogen but from the liquefaction of biopolymers if this theory is true our current paradigms of oil generation and source rock potential need to be changed drastically because it suggests that a significant quantity of liquid hydrocarbons can be generated directly from unaltered biological precursors instead of the thermal cracking of kerogen we respectfully disagree with the conclusions and hypotheses reached by collister et al we regard their interpretation of the statistical analysis of the hydrocarbon distribution data to be flawed and their hypotheses concerning the generation of c10 n alkanes and isoprenoids during diagenesis from biopolymers to be incorrect the mathematical procedure polytopic vector analysis used by collister et al has the ability to extract end member spectra from mixed systems they found that six end members were needed to explain most of the variance in the data this is not a unique solution however because the inclusion of additional end members will always improve the overall goodness of fit whether these six end member fluids truly are representative of specific biological precursors geologic processes or are merely mathematical constructs cannot be resolved from the statistical analysis alone although collister et al claim that five of the end members bear the signature of specific biological sources and

himalayan metamorphism and its tectonic implications the himalayan range exposes a spectacular assemblage of metamorphic rocks from the mid and deep crust that have fostered numerous models of how the crust responds to continental collisions recent petrogenetically based petrologic and geochronologic studies elucidate processes with unprecedented resolution and critically test models that range from continuum processes to one time events the pronounced metamorphic inversion across the main central thrust reflects continuum thrusting between ca 15 and 20 ma whereas exposure of ultrahigh pressure rocks in northwestern massifs and syntaxis granulites reflects singular early 45 ma and late 10 ma exhumation events multiple mechanisms including wedge collapse and flow of melt weakened midcrust are debated to explain pressure temperature trajectories patterns of thinning and thermal overprinting a geochronologic revolution is under way in which spatially resolved compositions and ages of accessory minerals are combined in a petrogenetically valid co

dependence of the annular mode in the troposphere and stratosphere on orography and land sea heating contrasts 1 using an idealized general circulation model we explore the influence of orography and land sea heating contrasts on the development of annular modes am under perpetual january conditions in the troposphere model experiments with different stationary wave forcing all show an internally induced am but with significantly different amplitudes only the combined forcing of orography and land sea heating contrast leads to a localization of the am similar to the north atlantic oscillation and additionally to a stratospheric am and its downward propagation a tropospheric feedback mechanism between the anomalies of zonal mean wind and stationary waves applies in the simulation with the combined forcing only where the coupling of orographically and thermally forced waves reproduces the observed stationary waves and where the simulated diabatic heating supports the feedback mechanism in contrast transient forcing dominates the variability in the experiments without orography comparable to the southern am

biochemical evolutionary significance of ordovician oils and their sources abstract geochemical data from several ordovician oils and kerogens from distinct basins in canada united states estonia and australia show some unique compositional characteristics the oils analyzed by gas chromatography and gas chromatography mass spectrometry are characterized by an odd dominance in the c9 c19 molecular weight range of normal paraffins and an odd dominated homologous series of cyclohexyl substituted normal paraffins the oils contain an unusually small amount of c20 components and pristane and phytane are conspicuous by their virtual absence the compositions of the oils and kerogens correlate closely and display characteristics that have not been observed in younger sediments the predominant organism found in the source kerogens for these unique oils is gloeocapsamorpha prisca a primitive prokaryotic organism data from the analysis of gloeocapsamorpha rich kerogens and the association of this organism with ordovician source rocks indicate a genetic relationship exists between the organism and the unusual oil chemistry the chemistry of the oils and kerogens suggests that gloeocapsamorpha was either non photosynthetic or that it fixed light using a chlorophyll that did not contain a phytyl side chain e g a bacteriochlorophyll the widespread occurrence of oils and kerogens possessing such a uniform composition appears unique to the ordovician certainly to the early paleozoic this suggests that paleocological conditions of ordovician anoxic environments were very similar and g prisca was particularly well adapted to these conditions

oscillatory and sector zoned garnets record cyclic rapid thrusting in central nepal 1 garnets with oscillatory zoning repeated compositional reversals and sector zoning crystallographically controlled compositional differences were discovered in rocks from near the main central thrust in the langtang region central nepal this zoning results from crystal growth kinetic effects related to extraordinarily rapid possibly cyclic thrusting if cyclic thrusting occurred then timescales of thrust rate inhomogeneities are 25 kyr implying that satellite determination of modern fault movement rates may not accurately reflect slip rates or strain partitioning in orogens on timescales exceeding thousands of years sector zoning in ca but not y mn or mg implies maximum intracrystalline diffusion rates for ca of 10 21 cm2 s at 550 c but faster rates for other elements

formation and exhumation of ultra high pressure rocks during continental collision role of detachment in the subduction channel 1 uhp rocks commonly form and exhume during the transition from oceanic subduction to continental collision their exhumation in subduction channels depends on the balance between down channel shear traction and up channel buoyancy thermal mechanical upper mantle scale numerical models are used to investigate how variations in material properties of the subducting continental margin affect this balance changes in shear traction leading to crustal decoupling detachment are investigated by varying the onset of strain weakening thermal parameters and convergence velocity variations in buoyancy force are investigated by modifying subducted material density and volume the model results are interpreted in terms of the exhumation number e which expresses the role of the pressure gradient channel thickness effective viscosity and subduction velocity peak metamorphic conditions exhumation velocity and timing of exhumation are temporally and spatially variable and are sensitive to the evolution of e the models reproduce natural ptt constraints and indicate that neither slab breakoff nor surface erosion is required for uhp exhumation

relationship between stationary planetary wave activity and the east asian winter monsoon 1 the variability of both the stationary planetary wave activity and the east asian winter monsoon is strongly associated with the thermal contrast between oceans and landmasses in this study we explore the interannual relationship between the monsoon and the wave activity defined by an index of the difference in the divergence of eliassenpalm flux between 50 n at 500 hpa and 40 n at 300 hpa it is found that compared to the winters of low wave activity the equatorward propagation of planetary waves in the middle and upper troposphere is stronger in the high wave activity winters during these high activity winters the upward wave propagation from the troposphere into the stratosphere becomes weaker this is accompanied by a smaller perturbation in the polar vortex which tends to be colder and stronger in the meantime the east asian westerly jet stream the east asian trough the siberian high and the aleutian low all become weaker apparently in particular the weakening of the siberian high and the aleutian low decreases the northeasterly wind over east asia leading to a warming condition in the region especially in northeastern asia a further analysis reveals that the zonal wavenumber 2 pattern of planetary waves contributes dominantly to the variability of the east asian winter monsoon

middle ordovician organic matter assemblages and their effect on ordovician derived oils two distinct middle ordovician oil prone organic matter assemblages occur in thermally immature to marginally mature petroleum source rocks from iowa the substantially more oil prone assemblage a generates the unique ordovician oil fingerprint which has been associated with the organic walled microfossil gloeocapsamorpha prisca the second assemblage b generates a more ordinary signature the two assemblages which are mixed or interbedded in many ordovician sediments of north america explain the variations in oils derived from ordovician source rocks these mixtures also aid in interpretation of the chemistry of g prisca core samples examined are from three wells in iowa penetrating the primarily carbonate sequence from the guttenberg member of the decorah formation down to the st peter sandstone microscopy rock eval pyrolysis and capillary gas chromatography on source rock bitumen extracts and nearby oils were used to evaluate the two assemblages solvent extracts from rocks containing predominantly assemblage a have the diagnostic ordovician gas chromatographic signatures with an odd preference in c11 c19 normal alkanes low amounts of heavier normal alkanes and virtual absence of isoprenoids including pristane and phytane although assemblage a occurs only in very thin beds it is potentially so oil generative that thicknesses in inches may be significant extracts from r cks containing predominantly assemblage b show reduced odd preference a full profile of normal alkanes and conspicuous occurrence of isoprenoids including pristane and phytane these samples from iowa are representative of middle ordovician source rocks found in most paleozoic basins of north america as well as baltic europe and australia therefore the conclusions drawn from these middle ordovician rock samples from iowa provide a basis to explain variations in ordovician derived oils found in many other areas

wave driven zonal flow vacillation in the southern hemisphere the variability of the zonal mean flow in the southern hemisphere during the period 1985 94 is studied using european centre for medium range forecasts analyses the dominant mode of variability has approximately equivalent barotropic variations of opposite signs centered at 40 8 and 608s this structure is dominant in all seasons and has similar variance in all seasons the temporal variance of the amplitude of this mode is well modeled as gaussian red noise with a correlation e folding time of about 10 days zonal wind anomalies are maintained against frictional drag by variations in the zonal flow accelerations driven by transient eddies and associated mean meridional circulations the eddy structures suggest that equatorward propagation is favored when the jet is displaced poleward and zonal propagation is favored when the jet is displaced equatorward

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

modulation of northern hemisphere wintertime stationary planetary wave activity east asian climate relationships by the quasi biennial oscillation 1 the modulation of the relationship between the tropospheric stationary planetary wave activity and the east asian winter climate by the tropical quasi biennial oscillation qbo wind in the stratosphere is investigated in the qbo easterly phase a significant warming appears in northeastern asia in the presence of high wave activities this corresponds to a weakened east asian trough at 500 hpa which determines the extent to which cold waves penetrate into east asia however in the qbo westerly phase both the surface warming and the weakening of the east asian trough become insignificant in response to high wave activities the possible mechanism for this qbo modulation on the tropospheric wave activities may be attributed to the indirect influence of the qbo induced polar and extratropical stratospheric circulation changes under the qbo easterly phase conditions the tropospheric wave activity flux divergence in the higher latitude region is enhanced due to enhanced upward eliassen palm ep flux into the stratosphere while the wave flux convergence in the subtropical troposphere is increased due to the decrease in the equatorward flux this leads to an enhanced wave activity difference and thus the associated east asian climate anomalies become larger and robust an opposite effect i e reduced wave activity difference appears in the qbo westerly phase further analyses reveal that the qbo significantly modulates both the zonal wave number 1 and 2 in the sea level pressure field but not for wave number 3 the combination of wave number 1 and 2 patterns leads to the strongest surface temperature anomalies in northern asia

chemical and isotopic properties of kukersites from iowa and estonia abstract kukersite samples from estonia and iowa were analyzed for elemental composition functional group distribution and carbon and hydrogen stable isotope ratios the elemental and hydrogen isotope values together with other analytical data suggest a higher thermal maturity for the iowa kukersite the wide carbon isotopic range of 9 3 among kukersites with unusually negative 13c values reaching 33 2 indicates isotopically variable carbon sources for production of biomass and thus major paleoceanographic differences between the environments supporting biosynthesis

cause and effect among thrust and normal faulting anatectic melting and exhumation in the himalaya the transition from compression to extension in a regime of overall convergence in a narrow mountain belt requires a change with time in at least one of the following horizontal normal stress applied to the belt by its surroundings the distribution of shear traction on the base of the belt the constitutive relation between stress and strain rate of material in the belt itself the surface height of the belt the following processes could have caused one or other of these changes in the himalaya in miocene time and thus could have triggered the onset of extension by normal faulting on planes parallel to thrust faults that were active at the same time the shear stress on the thrust fault at the base of the himalaya could have decreased for instance because of melting on the fault plane alternatively the creation of a new deeper thrust fault and hence a new locus of convergence could have initiated extensional faulting if the distribution of shear stress on the new thrust fault were unable to support the himalaya above it the himalaya could have been weakened by an increase in pore fluid pressure for instance owing to metamorphic dehydration reactions within the wedge the himalaya could have been elevated for instance following the detachment of a tongue of mantle lithosphere from beneath it or by the underthrusting of a lens of material beneath its base the apparent simultaneity of thrust and normal faulting on nearly parallel planes of anatexis and of exhumation in the himalaya in miocene time can be explained if normal faulting was responsible for most of the exhumation and through decompression melting for anatexis existing data suggest that the most probable cause for miocene normal faulting was either uplift of the himalaya or the cessation of slip on the main central thrust at the base of the orogenic wedge and the creation of a new deeper thrust fault and a new base to the deforming himalaya 1993 the geological society

the south tibetan detachment system facilitates ultra rapid cooling of granulite facies rocks in sikkim himalaya 1 the eastern himalaya is characterized by a region of granulites and local granulitized eclogites that have been exhumed via isothermal decompression from lower crustal depths during the india asia collision spatially most of these regions are proximal to the south tibetan detachment system an orogen parallel normal sense detachment system that operated during the miocene suggesting that it played a role in their exhumation here we use geo and thermochronological methods to study the deformation and cooling history of footwall rocks of the south tibetan detachment system in northern sikkim india these data demonstrate that the south tibetan detachment system was active in sikkim between 23 6 and 13 ma and that footwall rocks cooled rapidly from 700 to 120 c between 15 13 ma while active the south tibetan detachment system exhumed rocks from mid crustal depths but an additional heat source such as strain heating advected melt and or crustal thinning is required to explain the observed isothermal decompression cessation of movement on the south tibetan detachment system produced rapid cooling of the footwall as isotherms relaxed a regional comparison of temperature time data for the eastern south tibetan detachment system indicates a lack of synchronicity between the sa er sikkim yadong section and the nw bhutan section to accommodate this requires either strike slip tear faulting or local out of sequence thrusting in the younger segment of the orogen

similar morphological and chemical variations of gloeocapsomorpha prisca in ordovician sediments and cultured botryococcus braunii as a response to changes in salinity abstract most ordovician source rocks consist of accumulation of a colonial marine microorganism gloeocapsomorpha prisca g prisca whose nature ecology and affinity with extant organisms have been in dispute for years furthermore recent studies have shown major differences in phenol moieties between two g prisca rich samples examination of five g prisca rich kerogens by electron microscopy and pyrolysis studies revealed i the occurrence of two markedly distinct morpho chemical types a closed phenol rich type baltic samples and an open phenol poor one north american samples and ii the selective preservation of the resistant micromolecular material building up the thick cell walls in the original organism comparison with extant botryococcus braunii a widespread green microalga grown on media of increasing salinity suggests that g prisca is likely to be a planktonic green microalga related to b braunii which can adapt to large salinity variations which in turn control its polymorphism the large differences in colony morphology and in the content of phenol moieties observed in fossil g prisca and the resulting occurrence of two morpho chemical types should therefore reflect depositional environments with different salinities the presence of thick highly aliphatic resistant walls in g prisca selectively preserved during fossilization accounts for the major contribution of this organism to ordovician organic rich sediments and for the resulting typical signature of ordovician oils

exhumation of the main central thrust from lower crustal depths eastern bhutan himalaya geothermometry and mineral assemblages show an increase of temperature structurally upwards across the main central thrust mct however peak metamorphic pressures are similar across the boundary and correspond to depths of 35 45 km garnet bearing samples from the uppermost lesser himalayan sequence lhs yield metamorphic conditions of 650 675 c and 9 13 kbar staurolite kyanite schists about 30 m above the mct yield p t conditions near 650 c 8 10 kbar kyanite bearing migmatites from the greater himalayan sequence ghs yield pressures of 10 14 kbar at 750 800 c top to the south shearing is synchronous with and postdates peak metamorphic mineral growth metamorphic monazite from a deformed and metamorphosed proterozoic gneiss within the upper lhs yield u pb ages of 20 18 ma staurolite kyanite schists within the ghs a few metres above the mct yield monazite ages of c 22 1 ma we interpret these ages to reflect that prograde meta morphism and deformation within the main central thrust zone mctz was underway by c 23 ma u pb crystallization ages of monazite and xenotime in a deformed kyanite bearing leucogranite and kyanite garnet migmatites about 2 km above the mct suggest crystallization of partial melts at 18 16 ma higher in the hanging wall south verging shear bands filled with leucogranite and pegmatite yield u pb crystallization ages for monazite and xenotime of 14 15 ma and a 1 2 km thick leuco granite sill is 13 4 0 2 ma thus metamorphism plutonism and deformation within the ghs con tinued until at least 13 ma p t conditions at this time are estimated to be 500 600 c and near 5 kbar from these data we infer that the exhumation of the mct zone from 35 to 45 km to around 18 km occurred from 18 to 16 to c 13 ma yielding an average exhumation rate of 3 9 mm year 1 this process of exhumation may reflect the ductile extrusion by channel flow of the mctz from between the overlying tibetan plateau and the underthrusting indian plate coupled with rapid erosion

pressure temperature time path discontinuity in the main central thrust zone central nepal metapelites collected in central nepal reveal a discontinuity in metamorphic pressuretemperature time p t t paths near the base of the main central thrust zone despite an absence of obvious structural breaks garnets in the structurally lowest rocks grew with increasing t and p loading whereas garnets 1 3 km upsection grew with increasing t but decreasing p exhumation monazite grains in structurally lower rocks yield ionmicroprobe th pb ages of 8 9 ma structurally higher monazite grains range from 10 to 22 ma the p t t paths confirm previous interpretations that footwall metamorphism in part resulted from thrust reactivation ca 8 ma but also reflect thermal relaxation following older 20 ma or older thrust movement the main central thrust zone formed during pulses of movement that resulted in progressive transfer of material from the lower to upper plate

thermal model for the zanskar himalaya abstract crustal thickening along the northern margin of the indian plate following the 50 ma collision along the indus suture zone in ladakh caused widespread high temperature medium pressure barrovian facies series metamorphism and anatexis in the zanskar himalaya metamorphic isograds are inverted and structurally telescoped along the main central thrust mct zone at the base of the high himalayan slab along the zanskar valley at the top of the slab isograds are the right way up and are also telescoped along northeast dipping normal faults of the zanskar shear zone zsz which are related to culmination collapse behind the miocene himalayan thrust front between the mct and the zsz a metamorphic anatectic core within sillimanite grade rocks contains abundant leucogranite granite crustal melts of probable himalayan age a thermal model based on a crustal scale cross section across the zanskar himalaya suggests that m1 isograds developed during early himalayan barrovian metamorphism were overprinted during high grade mct related anatexis and folded around a large scale recumbent fold developed in the hanging wall of the mct

chemical characterization of lower devonian vascular plants vegetative remains of three coalified lower devonian vascular plants zosterophyllum psilophyton renalia were analyzed using flash pyrolysis gas chromatography mass spectrometry the distributions of pyrolysis products are compared with those from younger vascular plant fossil xylem cordaixylon callixylon and cuticle pachypteris the likelihood of the chemical preservation of characteristic higher plant macromolecules e g lignin and cutan in the lower devonian plant fossils is considered in light of this comparison and associated thermal maturity assessments reflectance values from vitrinite like macerals which may not be vitrinite sensu stricto in the lower devonian host rocks for the fossils selected for this study are shown to provide a reasonable assessment of the thermal maturity of these early vascular plant fossils although lignin altered through burial maturation is the most likely source of the prominent alkylphenols and aromatic hydrocarbons in the lower devonian tracheophyte flash pyrolysates a contribution from thermally modified tannins cannot be ruled out comparison of the highly aliphatic pyrolysates from the zosterophyllum and psilophyton axes with that of a thermally mature fossil gymnosperm leaf revealed that cutan was an important component in the devonian plant remains this is the earliest chemical evidence for the presence of cutan in vascular plants

preserved zr temperatures and u pb ages in high grade metamorphic titanite evidence for a static hot channel in the himalayan orogen abstract titanite grains from 800 c gneisses of the c 6 km thick greater himalayan sequence of central nepal were analyzed for zr in titanite temperatures and u pb ages to investigate the formation and evolution of a former weak mid crustal channel in the himalaya laser ablation icp ms depth profiles and spot analyses of titanite zr and u pb isotopic compositions are inconsistent with diffusional reequilibration on scales greater than 1 2 m and instead data appear to faithfully record both temperature and age titanite records protracted heating from 700 750 c at 37 ma to 775 c at 24 ma and possibly slight cooling to 765 c at 20 ma such temperatures exceed partial melting reactions in associated metapelites and imply profoundly weak rheologies i e a hot channel yet predate initiation of the bounding main central thrust and south tibetan detachment systems by as much as 15 myr evidently thick but weak crustal channels may remain stationary with respect to the convergence direction for 10 myr even during one of earth s biggest continent continent collisions

kinematics and dynamics of the namche barwa syntaxis eastern himalaya constraints from deformation fabrics and geochronology abstract field observations deformation and fabric analyses and precise age data acquired by zircon shrimp la icp ms u pb and 40 ar 39 ar dating methods have yielded new constraints on the kinematics and dynamics of the namche barwa syntaxis nbs which is the eastern corner of the himalaya a two stage model has been established to explain the formation and evolution of the nbs the northward indentation of the indian plate beneath the lhasa terrane began at 55 40 ma and crustal materials at this corner were subducted to depths 70 km where they experienced hp uhp metamorphism since 40 ma large scale right lateral strike slip along the sagaing fault has accommodated the rapid northward movement of the eastern indian plate corner with respect to the indochina block this caused significant and progressive bending of the indus yarlung suture zone iysz such that it became the dongjiu milin left lateral strike slip shear zone dmsz in the west and the aniqiao motuo right lateral strike slip shear zone amsz in the east both zones underwent strong mylonitization meanwhile the hp uhp metamorphic rocks were rapidly exhumed first into the deep crust at 22 18 ma and then to the shallow crust to form an antiformal dome at 6 2 ma our model provides new insight into the processes of post collisional crustal thickening related to the formation of the himalayan orogenic belt

the effects of accretion erosion and radiogenic heat on the metamorphic evolution of collisional orogens petrological and thermochronological data provide our best record of the thermal structure of deeply eroded orogens and in principle might be used to relate the metamorphic structure of an orogen to its deformational history in this paper we present a two dimensional thermal model of collisional orogens that includes the processes of accretion and erosion to examine the p t evolution of rocks advected through the orogen calculated metamorphic patterns are similar to those observed in the field metamor phic temperatures depths and ages generally increase with distance from the toe of the orogen p t paths are anti clockwise with rocks heating during burial and early stages of unroofing followed by cooling during late stage unroofing the results indicate that peak metamorphic temperatures within the core of a collisional orogen and the distance from the toe of an orogen to the metamorphic core can be related to the relative rates of accretion erosion and plate convergence model orogens displaying high metamorphic temperatures 600 c are associated with low ratios of accretion rate to plate convergence velocity and with high heat flow through the foreland model orogens with metamorphic cores far from the toe of the orogen are associated with high ratios of accretion rate to erosion rate calculated metamor phic gradients mimic steady state geotherms and inverted thermal gradients can be preserved in the metamorphic record suggesting reconsideration of the concept that the metamorphic record does not closely reflect geothermal gradients within an orogen

interannual variations of stationary planetary wave activity in the northern winter troposphere and stratosphere and their relations to nam and sst 1 with the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data from 1958 to 1998 two teleconnection patterns in the eliassen palm ep flux divergence field due to stationary planetary waves with wavenumbers wns 1 to 3 are studied in the northern hemisphere winter both patterns appear as dipole structures with divergence of ep flux in the north and convergence in the south or vice versa one dipole evolves mainly in the stratosphere and is referred to as the stratospheric interannual oscillation sio the other evolves mostly in the troposphere and is referred to as the tropospheric interannual oscillation tio the tio and the sio are shown to be associated with anomalous meridional planetary wave propagation in the troposphere and stratosphere respectively the upward and poleward refraction of planetary waves into the polar waveguide across the tropopause is closely linked to the tio examination of individual waves indicates that the tropospheric dipole ofep flux divergence comes basically from wn 3 whereas the stratospheric one comes totally from wns 1 and 2 the reduced refraction of planetary waves into the polar waveguide across the tropopause associated with positive tio index is dominantly contributed from both wns 1 and 2 regression and correlation analyses suggest that the tio is closely related to the northern annular mode nam its relation to the sea surface temperature sst is consistent with previous studies on the relation of nam to sst on the other hand the sio is shown to be closely associated with anomalous zonal mean winds in the subtropics of the midstratosphere and has a moderate correlation with an augmented pacific north american pna pattern in 500 hpa geopotential height for the leading eof of stratospheric u variability the sio accounts for a smaller fraction than the tio however with the teleconnectivity in stratospheric ep flux divergence one can distinguish a stratospheric variation of anomalous north south planetary wave propagation from the total amount of wave activity entering the stratosphere which may help us to understand the variability of transport circulation in the stratosphere significant correlation of sio with tropical sst reveals that tropical sst is leading the sio by up to around 9 months which suggests a strong impact of el nino southern oscillation enso on the sio planetary waves tend to be bent poleward in the midstratosphere when there is a warm event the situation tends to be reverse during a cold event

petrochronology of himalayan ultrahigh pressure eclogite the timing and nature of the india asia collision earth s largest ongoing continent continent collisional orogen are unclear ultrahigh pressure metamorphism of indian continental margin rocks is used as a proxy for initial collision because it indicates subduction of india records of this metamorphism are preserved only at kaghan valley pakistan and tso morari ladakh india separated by 500 km and having published ages of peak pressure of 46 2 0 7 ma and 53 51 ma respectively the apparent 6 m y age difference may refl ect multiple subduction events a large promontory along the former indian margin or inadequate constraints on the time of peak pressure recrystallization at tso morari we present 108 coupled in situ u th pb and rare earth element ree analyses of zircons in two tso morari eclogites to obtain age and petrologic information the ages range from ca 53 ma to 37 ma and peak at ca 47 43 ma flat heavy ree slopes and the absence of an eu anomaly are compatible with eclogite facies zircon re crystallization this re crystallization probably occurred at ultrahigh pressure because 64 of the analyses are from zircon included in ultrahigh pressure garnet and omphacite these results are consistent with those from kaghan valley and suggest that a single protracted ultrahigh pressure metamorphic event occurred contemporaneously across much of the orogen following initial contact of the indian and asian continents at ca 51 ma or later

the mechanism of growth of the low frequency east asia pacific teleconnection and the triggering role of tropical intraseasonal oscillation the east asia pacific eap pattern is a well known meridional teleconnection over east asia during boreal summer in this study the mechanism for growth of the eap on intraseasonal timescale is investigated through a vorticity budget it is found that the beta effect and high frequency transient eddies have primary contributions to the growth of the low frequency eap the former leads to a westward shift of disturbances associated with the low frequency eap and the latter favors an amplification of disturbances respectively the interaction between low frequency disturbances and zonal flow has a damping effect by dragging disturbances eastward the impact of boreal summer intraseasonal oscillation bsiso on the triggering of the low frequency eap is also examined in this study based on observational analysis and a linear model experiment it is shown that an elongated anomalous convection band located in the vicinity of philippines associated with the dominant mode of bsiso has a significant impact on the initiation of low frequency eap via rossby wave propagation whereas anomalous convection located over the north indian ocean has a limited impact based on the results of present study the low frequency eap could be a self sustained mode and the bsiso plays a substantial role in triggering the low frequency eap

the interpretation of inverted metamorphic isograds using simple physical calculations several zones of major thrust faulting exhibit a juxtaposition of rocks of higher metamorphic grade over rocks of lower grade this configuration may indicate but does not require that temperature gradients were temporarily inverted near the fault we examine the physical conditions under which such a temperature inversion could occur the overthrusting of hotter rock on colder rock can cause a temporarily inverted gradient both above and below the fault only if the time taken to underthrust rock from the land surface to a given depth z on the fault is less than times the characteristic time for diffusion of heat through the block above the fault where is thermal diffusivity an inverted gradient cannot form without heat generation in the fault zone unless v z sin 100 where v is the rate of underthrusting in millimeters per year z is in kilometers and is the dip of the fault this simple criterion is sufficient to demonstrate that several examples of inverted metamorphic gradients cannot be explained simply by the thrusting of hot on cold rock without heat sources in the fault zone dissipative heating accompanying deformation can cause an inverted temperature gradient within and beneath the thrust zone but whereas the overthrusting of hot upon cold rocks cools the fault zone dissipation heats it thus the overthrusting of hot on cold rock and dissipative heating affect the temperature gradient and the maximum temperatures differently we show that the magnitudes of the inverted temperature gradient and of the maximum temperature above the inverted gradient yield independent estimates of the rate of dissipative heating discrepancy between these estimates implies that some additional process must have occurred such as the post thrusting disruption of the isograds if there is such a discrepancy the maximum temperature probably provides the more reliable estimate of the rate of heating at the fault we illustrate this analysis by applying it to reported inverted metamorphic zonation in the pelona schist the st anthony complex the mt everest region of the main central thrust and the olympos thrust petrological inferences of maximum temperatures depths of metamorphism and magnitudes of apparent inverted gradients imply that shear stresses of about 100 mpa accompanied thrust faulting in some of these regions and that some zones of inverted metamorphism have been tectonically thinned after the metamorphism occured

exhumation of the ultrahigh pressure tso morari unit in eastern ladakh nw himalaya a case study exhumation processes of the ultra high pressure uhp tso morari dome nw himalaya are investigated using structural petrological and geochronological data the uhp tso morari unit is bounded by the low grade metamorphic indus suture zone to the ne and mata unit to the sw three deformation phases d1 d2 and d3 are observed only d3 is common to the uhp unit and the surrounding units in the uhp unit the first deformation phase d1 produced upright folds under eclogitic conditions 20 kbar 580 60 c d1 is overprinted by d2 structures related to a nw se trending open anticline this phase is characterized by blueschist mineral associations and corresponds to the quasi isothermal decompression from a depth of 90 km eclogitic conditions up to 30 40 km the final exhumation phase of the tso morari unit is dominated by tectonic denudation and erosion d3 associated with a slight temperature increase radiochronological analyses indicate that the uhp exhumation process began during the eocene exhumation was fast during d1 d2 and slowed down through d3 in oligocene time the change in the deformation style from d1 d2 to d3 in the tso morari unit coincides with changes in the exhumation rates and in the metamorphic conditions these changes may reflect the transition from an exhumation along the subduction plane in a serpentinized wedge to the vertical uplift of the tso morari unit across the upper crust

influence of orography on the extratropical response to el nino events abstract the contribution of the interaction between tropically forced circulation anomalies and the extratropicalmountains in the generation of extratropical circulation anomalies during the 1987 88 and 1988 89 winter seasons is diagnosed using a divergent barotropic model that solves for both the zonal mean and eddy components of the 200 mb rotational anomalies barotropic modeling shows that the orographic modulation of the rotational response to the 200 mb tropical divergence anomaly can be substantial over the pacific north american region the modulation consists of a large scale wave pattern with a ridge in the central subtropical pacific a trough over the gulf of alaska and a weak ridge extending across north america from baja california to greenland these features have an amplitude of 40 gpm and the orographic modulation is thus about one third as strong as the primary wave pattern the associated 200 mb zonal wind is strongest 5 m s 1 in the vicinity of the eastern end of the east asian

geochemical characterisation of organic matter in keg river formation elk point group middle devonian la crete basin western canada carbonates from the keg river formation la crete basin alberta western canada were examined in order to define a oil source rock potential b bulk maceral composition c extract yield and finally d facies variations using py gc ms thirty samples from 6 different wells were examined from the lower keg river member and 4 from the upper keg river member using conventional geochemical methods as maturity differences are absent within the sample set variations in toc tmax hydrogen index organic petrography and extract yields are caused by variability in organic matter input which is revealed by molecular characterisation using py gc ms lower keg river member bituminous wackestones are excellent potential source rocks containing types i ii and type ii organic matter types i ii organic matter contains large well preserved up to 200 m in diameter thick walled tasmanites 10 15 of sample and akinete algal cells indicative of algal blooms within an amorphous bituminite type ii organic matter contains a higher proportion of degraded alginites bituminite relative to well preserved alginites extract yields mg g toc were seen to increase from types i ii to type ii organic matter py gc ms revealed that 1 2 3 4 tetramethylbenzene was a major peak in most samples this is a pyrolysis product arising from cleavage of c40 diaromatic carotenoids incorporated within the kerogen during diagenesis the source of this compound is thought to be from an unknown diaromatic compound with a 2 3 6 3 4 5 trimethyl substitution pattern and isorenieratene which is specific to photosynthetic green sulphur bacteria chlorobiaceae suggesting that the photic zone was at least partially anoxic during deposition of these samples the relative abundance of this compound n c11 alkene and organic sulphur calculated from the thiophene ratio both increase from types i ii to type ii organic matter this trend was grossly similar to the trend seen in the variability of extract yield with hydrogen index a similar trend for hi and tmax indicates samples containing a higher proportion of degraded alginites bituminite relative to well preserved alginite are more labile than type i ii organic matter upper keg river member marls contain type ii organic matter which is characterised by heavily degraded algal material within a bituminous groundmass pyrolysates of two of the marl samples contain only low amounts of 1 2 3 4 tetramethylbenzene in contrast to the bituminous wackestones indicating that the depositional environment source input was different during deposition of the marl samples although both marls contain similar organic matter their pyrolysates were significantly different one marl 1141 9 m was highly paraffinic containing dominantly short chain alkene alkane doublets while the other marl 1137 6 m contained a bimodal n alkane alkene distribution and high amounts of alkylphenols which may be derived from preservation of resistant algal polyphenolic molecules or suggest a terrestrial input

molecular indicators of redox and marine photoautotroph composition in the late middle ordovician of iowa u s a abstract saturated and aromatic hydrocarbons were used to evaluate depositional redox conditions and marine photoautotroph contributions to middle caradocian strata of the central united states ia at the base of the spechts ferry member of the decorah formation 13c enriched aryl isoprenoids derivatives of green sulfur bacteria become abundant indicating the development of photic zone anoxia this is coincident with the disappearance of the organic walled microfossil gloeocapsomorpha prisca and a marked decrease in the relative abundances of cyanobacterial biomarkers the development of dysoxic to anoxic conditions and or associated changes in basin circulation potentially affected the distributions and abundances of these organisms in the overlying guttenberg member g prisca derived organic matter becomes dominant but relative cyanobacteria abundances remain low in addition the percentage total organic carbon is greater than 20 even though selected biomarker ratios pristane phytane ratios greater than 3 and homohopane indices less than 0 5 and the presence of bioturbation indicate that bottom waters were oxygenated it is suggested that deposition of g prisca affected both organic matter preservation and depositional redox conditions observed variations in redox indicators and marine photoautotroph contributions are associated with changes in siliciclastic deposition reported macrofauna turnover and with evidence for oceanic cooling and a change in circulation patterns documented in the eastern united states

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

possible late middle ordovician organic carbon isotope excursion evidence from ordovician oils and hydrocarbon source rocks mid continent and east central united states oils generated by middle ordovician rocks are found throughout the mid continent and east central regions of the united states gas chromatographic characteristics of these oils include a relatively high abundance of n alkanes with carbon numbers less than 20 a strong predominance of odd numbered n alkanes between c10 and c20 and relatively small amounts of branched and cyclic alkanes saturated and aromatic hydrocarbon fractions of 43 ordovician oils from the anadarko ardmore forest city illinois michigan salina sedgwick and williston basins and the iowa shelf demonstrate a wide range in carbon isotope composition dgr13csat 24 9 pmil to 33 9 pmil dgr13carom 24 3 pmil to 33 7 pmil saturated and aromatic hydrocarbons extracted from late middle ordovician shales 17 core samples show ranges in dgr13c similar to that of the oils the wide ranges in dgr13c for oils and rock extracts reflect a major positive excursion s 6 9 per pmil in organic matter dgr13c in late middle ordovician rocks this excursion has at least a regional significance in that it can be documented in sections 480 mi 770 km apart in south central kansas and eastern iowa the distance may be as much as 930 mi 1 500 km if the carbon isotope variations observed in michigan basin ordovician oils and in organic matter from late middle ordovician rocks in southwestern ontario are related to the same carbon isotope excursion organic matter dgr13c in core samples from south central kansas and eastern iowa is not directly related to variations in quantity or quality of organic matter or maceral compositi n the positive excursion in organic matter dgr13c is a possible result of increased organic matter productivity and or preservation the parallel shifts in organic and carbonate dgr13c in core samples from 1 e m greene well washington county iowa imply changes in the isotope composition of the ocean atmosphere carbon reservoir differences in the magnitude of the carbon isotope shifts between organic matter 8 8 pmil and carbonate 4 2 pmil in this core suggest a decrease either locally or regionally in available dissolved co2 possibly a result of high organic matter productivity and or limited circulation in the late middle ordovician seas

the relationship between zonal mean flow and quasi stationary waves in the midtroposphere abstract the degree to which quasi stationary midtropospheric flow is consistent with linear potential vorticity conservation is investigated the linear theory suggests there should be a well defined relationship between the zonal mean component of steady flow and departures from the zonal mean a set of 45 monthly mean winter states is examined to determine if there is a zonal eddy relationship month to month variations in zonal mean winds are represented in terms of an eof analysis correlation and compositing techniques isolate two dimensional patterns which appear to be associated with each zonal eof solutions to the nondivergent barotropic vorticity equation linearized about a zonal mean state suggest that the two dimensional flow patterns associated with several of the leading zonal mean eofs are consistent with the dynamical mechanism rossby first proposed as an explanation for a zonal eddy relationship it is suggested that the zonal eddy relationship examined here may in fact play a role in l

timing of india asia collision geological biostratigraphic and palaeomagnetic constraints 1 a range of ages have been proposed for the timing of india asia collision the range to some extent reflects different definitions of collision and methods used to date it in this paper we discuss three approaches that have been used to constrain the time of collision the time of cessation of marine facies the time of the first arrival of asian detritus on the indian plate and the determination of the relative positions of india and asia through time in the qumiba sedimentary section located south of the yarlung tsangpo suture in tibet a previous work has dated marine facies at middle to late eocene by far the youngest marine sediments recorded in the region by contrast our biostratigraphic data indicate the youngest marine facies preserved at this locality are 50 6 52 8 ma in broad agreement with the timing of cessation of marine facies elsewhere throughout the region double dating of detrital zircons from this formation by u pb and fission track methods indicates an asian contribution to the rocks thus documenting the time of arrival of asian material onto the indian plate at this time and hence constraining the time of india asia collision our reconstruction of the positions of india and asia by using a compilation of published palaeomagnetic data indicates initial contact between the continents in the early eocene we conclude the paper with a discussion on the viability of a recent assertion that collision between india and asia could not have occurred prior to 35 ma

exhumation history of a section of the sikkim himalayas india records in the metamorphic mineral equilibria and compositional zoning of garnet the exhumation history of pelitic migmatite samples from the high himalayan crystalline complex hhc near the south tibetian detachment system in the sikkim darjeeling section has been determined on the basis of thermo barometric analyses retrograde breakdown reactions and compositional zoning of garnet the peak metamorphic condition is estimated to be 10 4 kbar 800 c from thermo barometric and phase equilibrium constraints the observed retrograde breakdown of garnet to spinel and cordierite requires near isothermal and hence extremely rapid 15 mm yr exhumation up to the depth of 15 km numerical modeling suggests that the initial rapid exhumation must have been followed by a much slower process 2 mm yr up to at least 5 km depth to lead to the development of the observed compositional zoning of garnet the dramatic change of the exhumation velocity vz might reflect a process of tectonic thinning followed by erosion and or horizontal flow at shallow depth assuming that the vz did not change significantly below 5 km depth these results suggest that the hhc samples studied in this work exhumed from a depth of 34 km within 8 ma

modification of the petroleum system concept origins of alkanes and isoprenoids in crude oils kerogen the source material for petroleum can have a long history of alteration and diagenesis before crude oil forms a common assumption is that the bulk composition of the expressed oil reflects so much of these progressive alterations that most of the primary biological information of the original fixed carbon has been lost exceptions are trace constituents the biomarkers that comprise only a fraction of the organic material in most pristine crude oils analysis of the alkane acyclic isoprenoid fraction of a large number of crude oils and rock extracts from the timan pechora basin russia suggest that this fraction the main constituent of most crude oils is a direct product of liquefaction of biological debris that was preserved essentially unaltered to the point of oil generation therefore the primary biological provenance of this fraction is preserved in the oil fraction a set of gas chromatographic analyses of 242 crude oils as well as 83 solvent extracts from upper to middle paleozoic putative source rocks from the timan pechora basin russia were analyzed by a multivariate data analytical procedure new to organic geochemistry the distributions of n alkanes and acyclic isoprenoids 24 in all in the 325 samples could be reproduced by linear combinations of six end member compositions attributed to distinct biological inputs four of the six are assigned to primary producers waxes from higher plants cyanobacteria microalgae and the microorganism gloeocapsomorpha prisca these end members account for most of the n alkanes and acyclic isoprenoids in our samples the other two represent the products of secondary bacterial alteration of primary organics during sedimentation and low level bacterial alteration in the reservoir biodegradation each end member is composed of a spectrum of analytes whose abundances are related to one another by fixed ratios we surmise that each primary end member represents the breakdown of a resistant biopolymer that forms cell walls and partitions of a given biological group the n alkanes and acyclic isoprenoids in crude oils represent the weighted signatures of their various ancestors i e their primary organic inputs if the precursors of most oils are the products of a small set of chemically simple biopolymers then many of our assumptions concerning the importance of total organic carbon and the nature of the oil window must be reexamined

characterization of estonian kukersite by spectroscopy and pyrolysis evidence for abundant alkyl phenolic moieties in an ordovician marine type ii i kerogen abstract the kerogen of a sample of estonian kukersite ordovician was examined by spectroscopic solid state 13c nmr ftir and pyrolytic off line flash methods this revealed an important contribution of long linear alkyl chains in kukersite kerogen the hydrocarbons formed upon pyrolysis are dominated by n alkanes and n alk 1 enes and probably reflect a major contribution of selectivity preserved highly aliphatic resistant biomacromolecules from the outer cell walls of gloeocapsomorpha prisca this is consistent with the abundant presence of this fossilized organism in kukersite kerogen in addition high amounts of phenolic compounds were identified in the pyrolysates series of non methylated mono di and trimethylated 3 n alkylphenols 5 n alkyl 1 3 benzenediols and n alkylhydroxybenzofurans were identified all series of phenolic compounds contain long up to c19 linear alkyl side chains kukersite kerogen is therefore an aliphatic type ii i kerogen despite the abundance of free phenolic moieties this study shows that phenol derived moieties are not necessarily associated with higher plant derived organic matter the flash pyrolysate of kukersite kerogen was also compared with that of the kerogen of the guttenberg oil rock ordovician which is also composed of accumulations of fossilized g prisca similarities in the distributions of hydrocarbons and sulphur compounds were noted especially for the c1 c6 alkylbenzene and alkylthiophene distributions however no phenolic compounds were detected in the flash pyrolysate of the guttenberg kerogen possible explanations for the observed similarities and differences are discussed

the cordierite bearing anatectic rocks of the higher himalayan crystallines eastern nepal low pressure anatexis melt productivity melt loss and the preservation of cordierite cordierite bearing anatectic rocks inform our understanding of low pressure anatectic processes in the continental crust this article focuses on cordierite bearing lithologies occurring at the upper structural levels of the higher himalayan crystallines eastern nepal himalaya three cordierite bearing gneisses from different geological transects from mt everest to kangchenjunga have been studied in which cordierite is spectacularly well preserved the three samples differ in terms of bulk composition likely reflecting different sedimentary protoliths although they all consist of quartz alkali feldspar plagioclase biotite cordierite and sillimanite in different modal percentages analysis of the microstructures related to melt production and or melt consumption allows the distinction to be made between peritectic and cotectic cordierite the melt productivity of different prograde assemblages from two mica metapelite metagreywacke to biotite metapelite has been investigated at low pressure conditions evaluating the effects of muscovite v biotite dehydration melting on both mineral assemblages and microstructures the results of the thermodynamic modelling suggest that the mode and type of the micaceous minerals in the prograde assemblage is a very important parameter controlling the melt productivity at low pressure conditions the two mica protoliths being significantly more fertile at any given temperature than biotite gneisses over the same temperature interval furthermore the cordierite preservation is promoted by melt crystallization at a dry solidus and by exhumation along p t paths with a peculiar dp dt slope of about 15 18 bar c 1 overall our results provide a key for the interpretation of cordierite petrogenesis in migmatites from any low p regional anatectic terrane the cordierite bearing migmatites may well represent the source rocks for the miocene andalusite bearing leucogranites occurring at the upper structural levels of the himalayan belt and low p isobaric heating rather than decompression melting may be the triggering process of this peculiar peraluminous magmatism

rock eval pyrolysis and vitrinite reflectance trends in the cleveland shale member of the ohio shale eastern kentucky within eastern kentucky organic petrographic and geochemical data indicate a southeastwards increase in maturation of the cleveland shale member of the ohio shale devonian mississippian reflectance levels of dispersed organic material in the cleveland shale increase from 0 5 in the outcrop belt in central kentucky to slightly over 1 0 in pike county eastern kentucky a decrease in fluorescence intensity of liptinitic components such as tasmanites accompanies this reflectance increase as does a shift in fluorescence color of the alginite towards the red in the highest rank areas fluorescence is almost absent groundmass fluorescence is observed also and follows trends similar to those shown by the alginite kerogen in the cleveland shale is primarily type ii as indicated by petrographic observations and rock eval data total organic carbon contents of this shale decrease from over 12 in the outcrop belt to less than 2 in the eastern most part of the study area source rock potential ranges from good to very good with the highest potentials occurring in the outcrop belt tmax values for this unit increase from under 430 c in the outcrop belt to over 450 c in the southeast confirming the increase in maturation trends indicated by vitrinite reflectance data both petrographic and geochemical maturation parameters place the cleveland shale of eastern kentucky within the oil window comparison with maturation data for pennsylvanian age coals upsection suggests that maturation indices are retarded or suppressed in the devonian shales the level of maturation indicated for the cleveland may be problematical considering that the ohio shale is a major gas producer in this area

dating the indian continental subduction and collisional thickening in the northwest himalaya multichronology of the tso morari eclogites multichronometric studies of the low temperature eclogitic tso morari unit ladakh india place timing constraints on the early evolution of the northwest himalayan belt several isotopic systems have been used to date the eclogitization and the exhumation of the tso morari unit lu hf sm nd rb sr and ar ar a ca 55 ma age for the eclogitization has been obtained by lu hf on garnet omphacite and whole rock from mafic eclogite and by sm nd on garnet glaucophane and whole rock from high pressure metapelites these results agree with a previously reported u pb age on allanite and together these ages constrain the subduction of the indian continental margin at the paleocene eocene boundary during exhumation the tso morari rocks underwent thermal relaxation at about 9 3 kbar characterized by partial recrystallization under amphibolite facies conditions ca 47 ma as dated by sm nd on garnet calcic amphibole and whole rock from metabasalt rb sr on phengite apatite and whole rock and ar ar on medium si phengite from metapelites ar ar analyses of biotite and low si muscovite from metapelites which recrystallized at 5 kbar toward the end of the exhumation show that the tso morari unit was at upper crustal levels ca 30 ma these results indicate variable exhumation rates for the tso morari unit beginning with rapid exhumation while the indian margin subduction was still active and later proceeding at a slower pace during the crustal thickening associated with the himalayan collision

metamorphism and melting of the lithosphere due to rapid denudation nanga parbat massif himalaya the nanga parbat haramosh massif of the western himalaya has undergone a complex metamorphic and denudational history over the past 1 8 ga metamorphism in the tato region is characterized by a barrovian type metamorphism followed by partial melting and recrystallization along shear zones during nearly isothermal decompression while the massif was still at temperatures 550 c mineralogical and textural evidence for this path includes garnet zoning patterns late stage migmatization abundant cordierite both in schists and leucogranite dikes replacement of high pressure assemblages by low pressure assemblages and abundant low density inclusions thermobarometry on the nonmigmatized gneisses reveals conditions of 540 740 c at 7 1 13 1 kbar thermobarometry in the migmat ized rocks reveals final equilibration at 608 675 c at 3 9 6 8 kbar early fluid inclusions occur in quartz inclusions within garnet porphyroblasts that grew during decompression the last fluid inclusions to be trapped occur in microfrac

zonal eddy dynamics of the north atlantic oscillation abstract this research is an attempt to understand the dynamical mechanisms that drive the wintertime north atlantic oscillation nao on monthly and longer timescales in an earlier work by deweaver and nigam the authors showed that momentum fluxes from stationary waves play a large role in maintaining the zonal mean zonal wind u perturbations associated with the nao in this paper a linear stationary wave model is used to show that zonal mean flow anomalies in turn play a large role in maintaining the nao stationary waves a strong two way coupling thus exists between u and the stationary waves in which each is both a source of and a response to the other when forced by zonal eddy coupling terms terms that represent the interaction between nao covariant zonal mean zonal wind anomalies and the climatological eddy flow together with heating and transient fluxes the model produces a realistic simulation of the observed stationary wave pattern zonal eddy coupling terms make the largest contribution

additional evidence of an upper tropospheric zonal eddy relationship during winter abstract a zonal wind oscillation with a period of about 15 35 days is isolated over the middle latitudes of the northern hemisphere during winter a systematic relationship between the zonal winds and wind departures from zonal symmetry eddies is found for nine prominent zonal wind oscillation cycles taken from six 120 day winters this zonal eddy relationship consists of an oscillation between anomalous zonal flow and anomalous meridional flow which is strongest across north america from 150 w to 0

a thermal model for the distribution in space and time of the himalayan granites abstract in southern tibet crustal thickening due to the india asia collision has led to the formation of two granite belts one is located at the southern edge of the accretionary wedge of tethyan sedimentary rocks close to the contact with basement gneisses of the tibetan slab the other is found within the wedge itself close to the kangmar thrust trace available ages suggest that the granites appeared first in the southern belt and then in the kangmar belt this sequence seems to violate the chronology of thrusting another feature of the himalayas is that melting started only about 20 ma after the onset of thickening which is much less than the thermal time constant of thick crust we give a thermal model based on the assumption of conductive heat transfer which explains these features the model relies on the geometry of a sedimentary accretionary wedge bounded by low angle thrust faults and on the existence of a thermal conductivity contrast between old basement and young sedimentary rocks the wedge of sedimentary rocks acts as an insulating cap and its southern edge heats up along the contact with basement rocks on a horizontal cross section there is a temperature maximum along this southern edge which explains why melting starts there the early thermal evolution is sensitive to local conditions and granites first appear in the vicinity of the most radiogenic parts of the basement the distribution of granites in space and time is seemingly random reflecting different melting events in different radiogenic environments in the heterogeneous basement this model predicts a relationship between radioactivity and age which is compatible with available data the results emphasize that there are large horizontal temperature variations across a thickened region and that granite ages are not related simply to the timing of tectonic phases