experimental behaviour of compacted marls jurassic marls from abadia portugal were used in the construction of some motorway embankments large fragments of this evolving material remained after the construction process and their degradation was of concern because of the expected change of the engineering properties of the compacted material the material exhibits a very complex behaviour which is difficult to reproduce with existing constitutive models for unsaturated structured materials this paper focuses on understanding and providing data on the interaction between the pure marls rock and the aggregate behaviour it presents the main results of tests performed to characterise the hydro mechanical behaviour of compacted marls in specimens prepared with different grading size distributions and subjected to oedometer tests where both stress and suction changes were applied the experimental data obtained were analysed considering the presence of fragments and their degradation the marl matrix was characterised to complete the existing

isotopic evidence b c o of deep fluid processes in fault rocks from the active woodlark basin detachment zone we report results from boron carbon and oxygen stable isotope analyses of faulted and veined rocks recovered by scientific ocean drilling during odp leg 180 in the western woodlark basin off papua new guinea in this area of active continental extension crustal break up and incipient seafloor spreading a shallow dipping seismically active detachment fault accommodates strain defining a zone of mylonites and cataclasites vein formation and fluid infiltration syntectonic microstructures and vein fill mineralogy suggest frictional heating during slip during extension and exhumation of moresby seamount low carbon and oxygen isotope ratios of calcite veins indicate precipitation from hydrothermal fluids 13cpdb down to 17 18opdb down to 22 formed by both dehydration and decarbonation boron contents are low 7 ppm indicating high grade metamorphic source rock for the fluids some of the 11b signatures 17 35 parent solutions to calcite vein fills are low when compared to deep seated waters in other tectonic environments likely reflecting preferential loss of 11b during low grade metamorphism at depth pervasive devolatilization and flux of co2 rich fluids are evident from similar vein cement geochemistry in the detachment fault zone and splays further updip multiple rupture and healing history of the veins suggests that precipitation may be an important player in fluid pressure evolution and hence seismogenic fault movement

structure degradation and changes in the mechanical behaviour of a stiff clay due to weathering the paper discusses the results of research into the causes of weathering of stiff pleistocene clays located in the montemesola basin ta italy and on the effects of weathering on the clay s mechanical behaviour the weathered clays are yellow brown and overlie the original grey clays in the whole basin the liquidity indexes of both the yellow and the grey clays their fabric as observed by means of scanning electron microscopy as well as the yellow clay oxidation features suggest that drying has been the main weathering process in the basin this is confirmed by the results of drying wetting cycle tests carried out in the laboratory on undisturbed clay samples which show the drying wetting cycles to produce changes in the grey clay similar to those present in situ due to weathering results of oedometer stress path and triaxial tests show that weathering has caused a degradation of the clay bonding and an associated reduction in the size of the clay state boundary surface both one dimensional an

carbonate diagenesis in ice the fine particles created by glacial comminution of carbonate minerals are susceptible to interaction with meltwater and the isotopic composition of fine carbonate in glacial deposits has the potential of recording this interaction here we focus on the carbonate fraction of glacial sediment and debris within basal ice at the tsanfleuron glacier switzerland size separates of basal ice debris and melt out tills show a collinear isotopic trend interpreted as a mixing line between detritus 18 o pdb 5 and 13 o pdb 0 6 and authigenic calcite which in one case had 18 o values as light as 18 7 and 13 c values as light as 5 7 in most cases the finer fractions with calcite crystals as small as 0 1 m are enriched in the isotopically light component which is interpreted to form largely by freezing in basal ice the isotopic compositions of ice and included gases could be influenced by this process melt out tills inherit the authigenic calcite thus carbonate bearing till should no longer be regarded simply as clastic sediment

the origin and timing of multiphase cementation in carbonates impact of regional scale geodynamic events on the middle jurassic limestones diagenesis paris basin france the middle jurassic carbonates of the eastern part of the paris basin display surprisingly low values of porosity and permeability 15 and k 0 5 md the main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs a fate that did not befall their equivalents in deeper central parts of the paris basin using petrographic and geochemical analyses stable o and c isotopes sr isotopes major elements we identify six calcitic spar stages two dolomite stages and several episodes of fracturing and stylolitization ordered in paragenetic sequence cement quantification shows the predominance of two blocky calcite cement stages 75 of total cementation o and sr isotopes from these calcite cements suggest that the parent fluids resulted either from a mixing of trapped jurassic seawater and meteoric water or from buffered meteoric waters in the geological history of the paris basin major meteoric water inputs were possible during the early cretaceous when the middle jurassic carbonates cropped out at its northern and eastern borders lateral meteoric recharge may have occurred as a result of two separate uplift events late cimmerian unconformity and late aptian unconformity and the related exposures of carbonates to the north of the study area this palaeohydrological circulation brought about a significant reduction of porosity from 40 to 10 through calcite cement precipitation the early cretaceous events are of great importance in the diagenetic evolution of the sedimentary basins bordering the london brabant massif across all of northwestern europe a subsequent dolomite and calcite cementation stage accounts for about 5 of the total cement volumes this late cementation may have been caused by hydrothermal fluids ascending along permeable fractures during the late oligocene extension episode

geochemistry of vein and wallrock carbonates from the ediacaran system in south china insights into the origins of depositional and post depositional fluids abstract a combined study of carbon oxygen isotopes and major trace elements was carried out for vein and wallrock carbonates from the lantian formation of the ediacaran system in south china the results provide geochemical constraints on the origins of depositional and post depositional fluids with respect to recognition of the post depositional alteration the lantian formation was subdivided into the upper and lower carbonate units for the upper unit uu petrographic observations indicate that wallrock carbonates only experienced limited post depositional alteration the wallrock exhibits 18 o values of 19 2 to 13 1 and 13 c values of 9 6 to 8 9 both relative to vpdb the vein carbonates are divided into groups a and b based on their 18 o values and ree y patterns group a veins show nearly similar 18 o and 13 c ranges to but different ree y patterns from the wallrock these data indicate that the origin of fluids for group a veins may be similar to that of wallrock which was probably the mixture of continental and marine glacial meltwaters group b veins show both different 18 o values and ree y patterns from but similar 13 c values to the wallrock this indicates that post depositional fluids are different from the depositional fluids and thus of external origin low 18 o values 23 7 to 18 1 for group b veins indicate that the post depositional fluids were derived from continental glacial meltwater there is no correlation between 18 o and 13 c values for these vein and wallrock carbonates suggesting that the wallrock was not extensively altered by the post depositional fluids for the lower unit lu veins exhibit different c o isotope compositions and ree y patterns from wallrock carbonate indicating that post depositional fluids have different geochemical compositions from depositional fluids and thus are of external origin the simultaneous changes in 18 o and 13 c values with different laminations in the wallrock carbonates suggest the preservation of the primary geochemical compositions the 18 o values and ree y patterns for the lu veins indicate that the post depositional fluids were probably the mixtures of continental and marine glacial meltwaters therefore the lantian carbonates record the incorporation of continental glacial meltwater into the marginal sea of ediacaran age nevertheless the geochemical screening can provide constraints on the preservation of primary signatures and thus on the origins of depositional and post depositional fluids in the neoproterozoic marine carbonates

post depositional origin of highly 13c depleted carbonate in the doushantuo cap dolostone in south china insights from petrography and stable carbon isotopes abstract extremely negative carbon isotope values from the doushantuo cap dolostone succession in the yangtze gorges south china were interpreted as direct evidence of the hypothesis of methane hydrate destabilization during the marinoan deglaciation however this suggestion remains uncertain due to the obscurity of the paragenetic sequence of carbonate minerals with diverse carbon isotopic compositions here we conducted macroscopic and microscopic petrographic and carbon isotopic investigations of the cap dolostone succession at the jiulongwan section in the yangtze gorges our results show that extreme 13c values down to 44 exclusively occur in calcite whereas 13c values for the host dolomite range mostly between 4 and 2 and clearly reveal that the host dolomite were locally dissolved and or replaced by the calcite bearing highly 13c depleted signals this finding suggests that methane oxidation activity as indicated by the strongly depleted 13c signals did not occur until after the cap dolostone deposition thus the presence of the extremely negative 13c values could not be taken as evidence for the proposed methane hypothesis nevertheless this conclusion is not contradictory to the scenario that massive releases of methane from permafrost hydrates during deglaciation much prior to methane oxidation documented here could drive substantial negative 13c shifts well exhibited by the doushantuo cap dolostone and others around the world

isotopic approaches for quantifying the rates of marine burial diagenesis 1 diagenetic reactions in marine sediments have the potential to alter geochemical proxy records and affect the global carbon cycle over tens of thousands to millions of years this article describes advances in the use of ca sr and u series isotopes in constraining carbonate recrystallization and silicate dissolution rates in marine systems we specifically focus on recent efforts that interpret isotope variability in marine pore fluids using reactive transport models of varying complexity such studies suggest that calcite recrystallization rates are significant over time scales 1 myr approaching exchange rates of 0 4 1 myr 1 over longer time scales isotopic data point to continued exchange between calcite and coexisting pore fluid though at lower rates than in young sediments extrapolating these recrystallization rates over tens of millions of years we quantify the extent to which geochemical climate proxies such as mg ca in calcite can be altered diagenetically in some cases such diagenetic effects significantly affect the interpretation of long term climatic trends as well as determinations of absolute paleotemperatures silicate dissolution rates in siliclastic marine sediments appear to be similar in magnitude to dissolution rates in terrestrial environments 10 7 10 6 yr 1 such estimates suggest that silicate weathering in marine sediments may play an important role in the carbon cycle at least over time scales approaching 400 500 kyr

evaluation of the application of rare earth elements to paleoceanography anomalous departures of rare earth elements ree from similarity of chemical behaviour are most evident in a comparison of ce with its neighbors under reducing conditions ce3 acts like other ree but oxidized ce4 is adsorbed on mn fe oxyhydroxides or organic particulates and consequently the remaining solution will tend to exhibit a negative ce anomaly in addition more subtle fractionations may emphasize the light or the heavy or the middle ree a pattern of ree may be recorded by immediate diagenesis on a suitable chemical substrate such as apatite fish debris conodonts carbonate or chert this record was originally thought to reflect the paleoredox conditions of primary deposition however any such primary record may be overprinted by late diagenetic alteration early analyses of ree in conodonts from a wide range of sediments suggested a prevalence of reducing conditions no ce anomaly in pre carboniferous oceans and more common oxidation negative ce anomaly in the late paleozoic however recent research by other investigators indicates that variations in cean are more diverse in origin and in particular many are distorted to an unknown extent by late diagenesis in any case it is now clear that geological age does not show a consistent relationship to the level of the ce anomaly the ce anomaly apparently does not play any regular role in the isotopic events that accompany prominent mass extinctions further research is required to understand and thus make useful the controls on the ce anomaly

seasonal variation of momentum flux in the mesosphere observed with the mu radar we have regularly monitored mesospheric winds at 60 85km for three years with the mu radar 35 n 136 e and have found that the variance of wind velocity fluctuations for periods from 5 min to 2 hr shows a semi annual variation with a significant peak in summer centered in july and irregular enhancements in winter the zonal momentum flux induced by gravity waves shows eastward and westward maxima in july august and december february respectively typical eastward accelerations at the 70km altitude range from 7 to 13 m s day and from 8 to 11 m s day in summer and winter respectively which agree fairly well with theoretical predictions

calcite cemented concretions in shallow marine and fluvial sandstones of the birket qarun formation late eocene el faiyum depression egypt field petrographic and geochemical studies implications for formation conditions abstract this work deals with field petrographic stable oxygen and carbon isotopic and elemental composition studies of pervasively calcite cemented concretions within shallow marine and fluvial host sandstones of the upper eocene birket qarun formation of el faiyum depression egypt in order to decipher their conditions of formation the studied concretions have been classified into two types type 1 and type 2 type 1 concretions occur in the fluvial sandstones deposited at the northern scarp of birket qarun some of these concretions are confined within the host sandstones while others appear as erosional remnants of the host sandstones they show oblate spheroidal to flattened ellipsoidal shapes and have variable diameters ranging from 0 5 to 3 m geometrically they are bedding parallel concretions with spacing ranges from 0 3 to 1 m petrographically the rocks of type 1 concretions are attributed to quartzarenite cemented by sparry calcite that exhibits poikilitopic texture these calcite cements are characterized by small ranges of 18o 8 36 to 9 73 pdb and 13c 11 01 to 15 04 pdb values they were originated from light root respired carbon and media of meteoric pore water geometry of these concretions is interpreted to correspond to fluid flow during early diagenetic processes type 2 concretions are recorded in the shallow marine sandstones deposited at gabal el lahun they are confined within the host rocks these concretions exhibit spheroidal to ellipsoidal shapes and range from 0 3 to 1 m in diameter geometrically the individuals of these concretions occur as scattered strata bound and continuously cemented layers microscopically the rocks of type 2 concretions are mainly belonged to quartzarenites cemented by micritic and microsparitic calcites these calcites have small ranges of 18o 3 4 to 4 60 pdb and 13c 0 78 to 1 67 pdb values the calcite cements of type 2 concretions are interpreted to be a result of dissolution of marine carbonate shells at shallow burial depth in slightly modified marine pore water geometry of these concretions was controlled by the spatial distribution of carbonate shells in their host sandstones this study imports an idea that variation of depositional environments of the host clastic rocks of concretions plays an important role in the difference of modes of formation of their concretions also caution should be made to simplify and generalize the conditions of formation of concretions in host clastic rocks deposited in one sedimentary basin of similar age

archean gold mineralization synchronous with the final stages of cratonization yilgarn craton western australia sm nd ages of pegmatite dikes that crosscut gold bearing structures in the southern yilgarn craton western australia provide minimum age constraints of 2640 6 11 ma 2628 6 10 ma and 2620 6 36 ma for gold mineralization at the westonia and nevoria yellowdine terrane and scotia norseman terrane gold deposits respectively similarly a post gold mineralization dike at westonia has a u pb zircon age of 2637 68 ma theseconstraintsareconsistentwith andprovidefurthersupportfor suggestionsthatthe majority of gold deposits in the yilgarn craton formed during a regionally extensive gold mineralization event at ca 2630 ma i e 2630 6 10 ma in combination with recent geochronological results these data also provide further evidence that although mineralization appears to significantly postdate the majority of magmatic and metamorphic activity at higher crustal levels widespread thermal reworking of the lower middle crust involvingpartialmelting amphibolitetogranulitefaciesmetamorphism andlowercrustal granitoid intrusion occurred concurrently with gold mineralization at ca 2630 ma it is probable that the large scale hydrothermalfluidflow that produced widespread gold deposition was also part of this tectonothermal event models developed for other archean terranes whereby gold mineralization postdates formation and cratonization of host granite greenstone terranes and is therefore unrelated to these processes are not required to explain the timing of the majority of gold deposits in the yilgarn craton

conditions for veining in the barrandian basin lower palaeozoic czech republic evidence from fluid inclusion and apatite fission track analysis abstract the interplay between fracture propagation and fluid composition and circulation has been examined by deciphering vein sequences in silurian and devonian limestones and shales at kosov quarry in the barrandian basin three successive vein generations were recognised that can be attributed to different stages of a basinal cycle almost all generations of fracture cements host abundant liquid hydrocarbon inclusions that indicate repeated episodes of petroleum migration through the strata during burial tectonic compression and uplift the earliest veins that propagated prior to folding were displacive fibrous beef calcite veins occurring parallel to the bedding of some shale beds hydrocarbon inclusions within calcite possess homogenisation temperatures between 58 and 68 c and show that the beef calcites originated in the deeper burial environment during early petroleum migration from overpressured shales e w striking extension veins that postdate beef calcite formed in response to variscan orogenic deformations based on apatite fission track analysis afta data and other geological evidence the veins probably formed 380 315 ma ago roughly coinciding with peak burial heating of the strata folding and the intrusion of variscan synorogenic granites the veins that crosscut diagenetic cements and low amplitude stylolites in host limestones are oriented semi vertically to the bedding plane and are filled with cloudy twinned calcite idiomorphic smoky quartz and residues of hardened bitumen calcite and quartz cements contain abundant blue and blue green fluorescing primary inclusions of liquid hydrocarbons that homogenise between 50 and 110 c geochemical characteristics of the fluids as revealed by gas chromatography mass spectrometry particularly the presence of olefins and parent aromatic hydrocarbons phenonthrene suggest that the oil entrapped in the inclusions experienced intense but geologically fast heating that resulted in thermal pyrolysis of its hydrocarbons this implies that the organic fluids in the fractures may have been partly influenced by heating associated with igneous intrusions that are hidden below the surface subvertical n s striking veins represent the most recent fracturing event s some of these veins are only a few millimeters thick and sparsely mineralised with thin leaf like quartz crystals that contain tiny blue and yellow orange fluorescing hydrocarbon inclusions most of the n s veins however occur as thick calcite veins that generally crystallised at 70 c or less from h2o nacl solutions of variable salinity with admixture of petroleum the origin of these fluids is interpreted in terms of deeply circulating meteoric waters that partially mixed with deep basinal fluids wider structural considerations combined with fission track analysis of adjacent host sediments suggest that n s veins formed during post mesozoic uplift of the area probably in response to major tertiary alpine deformations transmitted far into the bohemian massif

mesospheric momentum flux studies at adelaide australia observations and a gravity wave tidal interaction model abstract we present here the results of an analysis of gravity wave momentum fluxes in the mesosphere and lower thermosphere inferred using a dual beam doppler radar near adelaide australia during june 1984 our analysis reveals that over 70 of the momentum flux and of the inferred zonal drag was due to gravity waves with observed periods less than one hour this suggests that it is the gravity waves with high intrinsic frequencies and small horizontal scales that are most effective at transporting momentum into the middle atmosphere the temporal variations in the momentum flux and flux divergence due to high frequency motions were also examined in detail in addition to daily variability a strong diurnal modulation was observed to occur this was found to be correlated with the phase of large amplitude diurnal tidal motions as a result of these observations a gravity wave tidal interaction model was proposed which accounts for all of the major features of the observed data including a reduction i

carbonate oxygen isotope paleoaltimetry evaluating the effect of diagenesis on paleoelevation estimates for the tibetan plateau carbonate oxygen isotope paleoaltimetry is based on analysis of the d 18 o value of carbonate precipitated from surface water deciphering the diagenetic history is important for establishing whether particular carbonates are accurate recorders of paleosurface waters which reflect paleoelevation this study provides examples from southern east central and northeastern tibet of approaches aimed at evaluating the diagenetic history of lacustrine micrites and pedogenic carbonates the most desirable technique for avoiding erroneous interpretations related to diagenetic overprinting is to analyze carbonates that are known to be primary such as aragonitic shell material in rocks that do not contain shell material we have compared lacustrine micrites and pedogenic carbonates to diagenetic carbonate phases to determine the effects of diagenesis on the isotopic composition of primary carbonates where the potential effects of diagenesis are subtle or ambiguous we have evaluated the fidelity of the carbonate record from systematic trends in c and o isotopes that agree with other interpretations of paleoenvironment such as high frequency covariance in c and o that corresponds with changes in the mg concentration of carbonates using these strategies we have determined that diagenesis has not affected the isotopic composition of carbonates in the late miocene pliocene thakkhola graben in southern tibet and the oligocene to pliocene linxia basin in northeastern tibet in the case of paleogene basins in east central tibet however ambiguity in data precludes the determination of diagenetic effects d 2004 elsevier b v all rights reserved

elevation or alteration evaluation of isotopic constraints on paleoaltitudes surrounding the eocene green river basin low oxygen isotope values 16 relative to peedee belemnite standard obtained from microbial carbonates of the green river formation have been interpreted as evidence for snowmelt and high elevations surrounding this early eocene lake basin however low values from microbial precipitates could also represent a diagenetic overprint we investigate these alternate hypotheses by measuring the oxygen isotope composition of altered and unaltered freshwater bivalves from the basin we analyzed subannual samples from 3 individuals and bulk samples from 54 individuals subannual samples exhibit clear seasonal fluctuations in oxygen isotope values these fluctuations are large enough to require seasonal shifts in temperature and or the oxygen isotope value of the lake water however the lowest value of any unaltered sample either bulk or high resolution corresponds to lake water 18 o of 12 relative to standard mean ocean water and is not low enough to require the addition of snowmelt to the lake a few bulk samples exhibit very low oxygen isotope values which would seem to suggest snowmelt however these samples also show clear evidence of calcite in x ray diffraction patterns demonstrating the presence of diagenetic precipitates given that 1 diagenetic alteration is a plausible explanation of very low 18 o values 2 alteration has not been examined in microbial carbonates and 3 unaltered aragonitic bivalves provide no independent evidence for low 18 o values for lake waters we conclude that robust isotopic evidence for high elevations surrounding the green river basin during the eocene is currently lacking

carbon isotope anomaly in marbles associated with eclogites from the dabie mountains high 13c values up to 5 7 pdb were measured in marbles associated with ultrahigh pressure eclogites in the dabie mountains east china such a carbon isotope anomaly is interpreted to represent the carbon isotope composition of premetamorphic limestone i e the protolith of the marbles because there is no known process to enrich carbonate in 13c during regional metamorphism the high 13c also corresponds to high 18o of up to 22 9 smow suggesting that premetamorphic 13c values would be about 5 to 6 for their protolith limestones the carbon isotope anomaly in the protolith of the marbles implies a local change in the redox state of water during deposition of the limestones preservation of the unusually high positive 13c values in the marbles supports the previous conclusion that there was no significant isotopic exchange with the mantle during subduction of supracrustal rocks to mantle depths of greater than 100 km

rare earth element geochemistry of late devonian reefal carbonates canning basin western australia confirmation of a seawater ree proxy in ancient limestones rare earth element and yttrium ree y concentrations were determined in 49 late devonian reefal carbonates from the lennard shelf canning basin western australia shale normalized sn ree y patterns of the late devonian samples display features consistent with the geochemistry of well oxygenated shallow seawater a variety of different ancient limestone components including microbialites some skeletal carbonates stromatoporoids and cements record seawater like ree y signatures contamination associated with phosphate fe oxides and shale was tested quantitatively and can be discounted as the source of the ree y patterns co occurring carbonate components that presumably precipitated from the same seawater have different relative ree concentrations but consistent ree y patterns clean devonian early marine cements n 3 display ree y signatures most like that of modern open ocean seawater and the highest y ho ratios e g 59 and greatest light ree lree depletion average nd sn yb sn 0 413 sd 0 076 however synsedimentary cements have the lowest ree concentrations e g 405 ppb non contaminated devonian microbialite samples containing a mixture of the calcimicrobe renalcis and micritic thrombolite aggregates in early marine cement n 11 have the highest relative ree concentrations of tested carbonates average total ree 11 3 ppm stromatoporoid skeletons unlike modern corals algae and molluscs also contain well developed seawater like ree patterns samples from an estuarine fringing reef have very different ree y patterns with lree enrichment nd sn yb sn 1 possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged lree from a nearby riverine input source hence devonian limestones provide a proxy for marine ree geochemistry and allow the differentiation of co occurring water masses on the ancient lennard shelf although appropriate partition coefficients for quantification of devonian seawater ree concentrations from out data are unknown hypothetical devonian canning basin seawater ree patterns were obtained with coefficients derived from modern natural proxies and experimental values resulting devonian seawater patterns are slightly enriched in lree compared to most modem seawaters and suggest higher overall ree concentrations but are very similar to seawaters from regions with high terrigenous inputs our results suggest that most limestones should record important aspects of the ree geochemistry of the waters in which they precipitated provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high non seawater like ree contents hence we expect that many other ancient limestones will serve as seawater ree proxies and thereby provide information on paleoceanography paleogeography and geochemical evolution of the oceans copyright c 2004 elsevier ltd

oil bearing inclusions in vein quartz and calcite and bitumens in veins testament to multiple phases of hydrocarbon migration in the barrandian basin lower palaeozoic czech republic abstract the petroleum charge history of the barrandian basin was investigated by analysing quartz and calcite and organic phases that occur in veins and fractures cutting dolerite sills within the lite formation silurian the geochemical characteristics of fluid inclusions trapped in vein quartz and calcite vein bitumens and adjacent potential source rocks when combined with burial and thermal history data reflect the presence of at least three separate hydrocarbon charge episodes solid highly reflecting rmax 0 92 1 49 bitumen provides information on the first and oldest episode of oil migration the precursor oil was probably derived relatively early during diagenesis from nearby organic rich sediments and was subsequently thermally altered to form the solid bitumen the liquid oil preserved within the fluid inclusions in vein quartz and calcite cements represents a second hydrocarbon charge that migrated after the cooling of the sill at diagenetic temperatures between 73 and 150 c this migration event probably occurred during the peak burial of the strata during or after the variscan orogeny the inclusion oil is moderately matured non biodegraded and most likely derived from lower palaeozoic source rocks such as the enclosing lite formation and or directly overlying kopanina and p idoli formations the presence of low salinity 0 2 3 2 eq wt nacl aqueous inclusions coexisting with oil inclusions indicates that the hydrocarbon flow had a substantial aqueous component brightly yellow fluorescing low reflecting rr 0 25 wax forming thin coatings on vein minerals herald the third and most recent pulse of hydrocarbons that migrated significantly after the peak heating of the strata indirect evidence suggests that this late stage event may have been associated with the post palaeogene alpine uplift of the basin that stimulated circulation of waxy oils and acid waters through the reactivated fractures

introduction to tectonics of china abstract the continental crust of china is a mosaic of cratonic blocks and orogenic belts containing small cratons and terranes with various tectonic settings they have diverse origins and complex histories of amalgamation and often suffered repeated reworking after multiple episodes of amalgamation in the last three decades extensive geological geochemical and geophysical investigations have been carried out on these cratonic blocks and intervening orogenic belts producing an abundant amount of new data and competing interpretations this provides important insights into understanding the formation and evolution of the chinese continents the papers assembled in this volume present a timely and comprehensive overview on major advancements and controversial issues related to the formation and evolution of continental crust in china complex tectonic histories were experienced not only by the large scale cratonic blocks and orogenic belts but also by small scale terranes and orogens between and inside these blocks nevertheless our understanding of lithotectonic units and geological processes has been greatly advanced by recent studies of zirconology and geochemistry for various rock types from major petrotectonic units in china it has been further advanced from integrated interpretations of geochemical and petrological data for petrogenesis of magmatic rocks an overview of these observations and interpretations provides new insights into understanding the continental plate tectonics and the chemical geodynamics of subduction zones

a burial diagenesis origin for the ediacaran shuram wonoka carbon isotope anomaly marked negative 13c excursions in ediacaran age carbonate sediments have been identified in several sections globally but are not recognized in all sections of similar age the presence of 13ccarb values as low as 12 has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today the 13ccarb anomalies are strongly correlated with 18ocarb values but are not represented in 13corg records while no primary depositional processes have been identified that can produce the correlated 18o 13c arrays simulations show that fluid rock interaction with high pco2 fluids is capable of producing such arrays at geologically reasonable pco2 and water rock ratios variations in the mg ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs calcite and anhydrite in the resulting mineral assemblage incorporation of an initially aragonitic mineralogy demonstrates that high sr low mn sr and modest alteration of 87sr 86sr in ancient carbonates are all compatible with a burial diagenesis mechanism for generation of the 13c anomalies and do not necessarily imply preservation of primary values the profound ediacaran negative 13c anomalies can be adequately explained by well understood diagenetic processes conflated with the difficulty of correlating precambrian sections independently of chemostratigraphy they are not a record of primary seawater variations and need not have independent stratigraphic significance

a ubiquitous hydrothermal episode recorded in the sheet crack cements of a marinoan cap dolostone of south china implication for the origin of the extremely 13 c depleted calcite cement abstract sheet crack primarily filled with chalcedony quartz and calcite is a type of significant sedimentary structure in almost all documented cap carbonates in platform to slope settings which sharply overlie the global marinoan 635 ma glacial tillite the jiulongwan section located in the yangtze gorges areas south china is significant for the first discovery of extremely 13c depleted 13c down to 41 calcite cements in sheet crack structure jiang et al 2003a which provides direct evidence for the methane seep hypothesis kennedy et al 2001 focusing on the calcite cements in the same section bristow et al 2011 proposed a hydrothermal origin based on high temperatures 378 c determined by carbonate clumped isotope thermometry ccit in this study we provide evidence for the hydrothermal model using fluid inclusion technology fit to quartz cements in the jiulongwan section the widespread sheet crack structures in south china have uniform mineral paragenetic assemblages which apparently reflect three stages of a hydrothermal fluid activity including dolomitization at the early stage silicification comprising chalcedony and quartz at the middle stage and calcitization characterized by carbonaceous calcite filling preexisting voids at the late stage primary aqueous fluid inclusions from quartz crystals have homogenization temperatures of approximately 160 220 c mean 192 c n 31 while the salinity histogram contains two peaks at low salinity 6 3 8 3 wt nacl equiv and high salinity 18 0 20 8 wt nacl equiv reflecting precipitation caused by mixing of high and low salinity fluids a modified and detailed hydrothermal model is proposed indicating that the sheet crack structure resulted from successive thermal fluid activity after karstic dissolution due to postglacial isostatic rebound this model is compatible with the unified sequence of glacio eustatic events after the termination of marinoan glaciation zhou et al 2010 and the temperature results determined by ccit bristow et al 2011

multi beam mu radar measurements of advective accelerations in the atmosphere a method is developed to calculate nonlinear zonal sx and meridional sy longitudinal advective accelerations from mu radar observations with antenna beam scanning in eight directions the results of measurements of sx and sy at altitudes of 2 18 km on april 16 18 1997 are presented the values of sx and sy are mainly between 0 01 m s 2 and 0 01 m s 2 with increases up to 0 04 m s 2 during tens of minutes to several hours in regions with vertical scales up to several kilometers such extremes are more frequent at the altitudes of tropo stratospheric jet at 10 15 km and may indicate regions of inclination from geostrophic balance and of increased generation of atmospheric waves

origin of vein hydrothermal carbonates in triassic limestones of the espadan ranges iberian chain e spain dolomitization and hg bearing veins in the lower triassic limestones of the espadan ranges iberian chain e of spain

implications of weathering on the engineering properties of the fuller s earth formation the fuller s earth formation is an overcon solidated jointed randomly assured calcareous mudstone with some thin to medium jointed argillaceous limestone bands south of bath the formation contains the commercial montmorillonite rich fuller s earth bed this paper reviews the effect of the proportion of calcite present on the moisture content atterberg limits particle size and residual shear strength attention is drawn to the importance of appreciating that the calcite percentage and the clay mineralogy are both likely to change with time as a result of weathering processes this will affect the stability of natural slopes and man made cuttings excavations etc la formation de terre a foulon est un limon compact calcaire surconsolide jointe et fissure au hasard qui contient des bandes de chaux argillacee jointees d epaisseur faible ou moderee au sud de bath la formation comprend la couche de terre a foulon commerciale qui est riche en montmorillonite l article examine l influence de la prop

a new old approach for shallow landslide analysis and susceptibility zoning in fine grained weathered soils of southern italy abstract rainfall induced shallow landslides involve several geo environmental contexts and different types of soils in clayey soils they affect the most superficial layer which is generally constituted by physically weathered soils characterised by a diffuse pattern of cracks this type of landslide most commonly occurs in the form of multiple occurrence landslide phenomena simultaneously involving large areas and thus has several consequences in terms of environmental and economic damage indeed landslide susceptibility zoning is a relevant issue for land use planning and or design purposes this study proposes a multi scale approach to reach this goal the proposed approach is tested and validated over an area in southern italy affected by widespread shallow landslides that can be classified as earth slides and earth slide flows specifically by moving from a small 1 100 000 to a medium scale 1 25 000 with the aid of heuristic and statistical methods the approach identifies the main factors leading to landslide occurrence and effectively detects the areas potentially affected by these phenomena finally at a larger scale 1 5000 deterministic methods i e physically based models trigrs and trigrs unsaturated allow quantitative landslide susceptibility assessment starting from sample areas representative of those that can be affected by shallow landslides considering the reliability of the obtained results the proposed approach seems useful for analysing other case studies in similar geological contexts

characteristics of gravity waves in the mesosphere observed with the middle and upper atmosphere radar 1 momentum flux we observed wind motions from 60 to 90 km altitudes with the mu radar 35 n 136 e in the four observation periods october 1986 june 1987 july 1990 and january february 1991 mean wind profiles were fairly consistent with results of kyoto meteor radar observations 35 n 136 e collected in 1983 1985 at 80 to 110 km altitudes and zonal mean winds generally agreed well with cira 1986 except for the profiles below 70 km in january february 1991 although discrepancy of amplitudes sometimes ranged up to 10 to 20 m s characteristics of frequency spectra of radial wind velocities were basically similar among results determined in four observation periods that is oblique spectra had a logarithmic slope of about 5 3 in the frequency range lower than 4 5 10 4 s 1 gravity waves with periods longer than 20 50 min to 5 hours the lowest limit of the spectral analysis were found to carry a large part of the zonal momentum flux while a dominant frequency component was not detected for the meridional flux zonal and meridional drag of mean winds induced by the gravity wave with periods from 5 min to 8 10 hours were 51 m s d and 4 m s d in june at 75 km and 4 0 m s d and 7 4 m s d in october at 70 km respectively the major part of the drag force was also found in the wave component with periods larger than 30 min the day to day variation in the zonal momentum flux showed a good correlation with the vertical shear of the zonal mean wind which suggests effects of the gravity wave activities on mean wind fields or the effect of shear variation on the gravity wave activity

a petrographic and geochemical study of carbonate and silica phases from the ediacaran doushantuo formation in the three gorges area of south china implications for diagenetic conditions abstract the carbonate of the ediacaran doushantuo formation contains various silica phases in the three gorges area of south china to better understand the diagenetic conditions under which these silica phases formed we carried out a petrographic and geochemical study of the silica phases and the coadjacent carbonate phases at the xiaofenghe section xfh in the three gorges area of south china five types of silica phases can be distinguished based on petrographic characteristics s1 and s2 are composed of microcrystalline quartz in chert nodules and disseminated in the host dolostone respectively s3 is composed of the megaquartz while s4 and s5 are microcrystalline quartz and fibrous silica respectively both replacing calcite cement six distinct types of carbonate can be recognized including the host matrix carbonate c1 sparry calcite nodules c2 calcite around chert nodules c3 dispersed calcite cement within chert nodules c4 fine micropeloidal calcite cements c5 and calcite veins c6 sedimentary structures suggest that formation of the s1 through s5 silica phases and c2 through c5 carbonate phases occurred during early burial diagenesis and therefore their formation recorded early diagenetic conditions assuming that ediacaran surface seawater temperature ranged from 28 to 39 c surface seawater 18o values can be calculated based on the oxygen isotopic composition of the host dolostone matrix c1 which range from 6 to 0 4 to 0 and 2 to 0 for the d2 d3 and d4 subunits of the doushantuo formation respectively based on the 18o values of chert nodules and beds mainly phase s1 diagenetic temperatures can be constrained to between 27 and 60 c under such low diagenetic temperatures the primary geochemical signatures of the host dolostone such as ree y patterns 13ccarb and 34spy values are likely to be preserved those silica phases without evidence of contamination of continental silicate detritus show characteristic ree y patterns with minor light ree depletions positive la eu and gd anomalies negative ce anomalies and slightly super chondritic y ho ratios implying that the source of silica may be derived from seawater negative ce anomalies in the silica phases in d2 through d4 subunits indicate that the bottom seawater or early diagenetic porewater was oxic at the time of silica precipitation

dolomitization of the cambrian carbonate platform southern canadian rocky mountains dolomite front geometry fluid inclusion geochemistry isotopic signature and hydrogeologic modelling studies

rare earth element and nd isotopic variations in regionally extensive dolomites from the burlington keokuk formation mississippian implications for ree mobility during carbonate diagenesis abstract marine carbonates of the burlington keokuk fm miss of the midcontinent region have been subject to two major episodes of regionally extensive 100 000 km2 dolomitization previous studies of the cathodoluminescent petrography sr c and o isotopic compositions and sr fe mn and ca concentrations of burlington keokuk dolostones outline a diagenetic history in which lime mud was pervasively dolomitized by a seawater dominated fluid at many localities this early dolomite generation dolomite i was recrystallized by nonmarine diagenetic fluids at shallow burial depths to produce dolomite ii dolomites i and ii have similar rare earth element ree patterns and abundances and a narrow range of initial 143nd 144nd isotope ratios of 0 511906 0 000025 1 this consistency in the nd isotope ratios and ree patterns along with the presence of anomalously low abundances of cerium in the dolomites cherts glauconite pellets fish apatite and crinoids suggests that 1 seawater derived ree dominated the system and 2 the extensive water rock interaction that produced profound textural and compositional changes during the formation of dolomite ii did not significantly alter the ree patterns or nd isotopic signatures of the dolomites the results of quantitative modeling of isotopic and trace lement exchange during water rock interaction in carbonate systems indicate that extremely large water rock ratios are required to alter the ree signatures of diagenetic carbonates such large water rock ratios can reflect either 1 large extents of fluid flow during carbonate recrystallization or 2 minimal interaction between diagenetic fluids and host rocks during carbonate cement crystallization late vug filling calcite and dolomite have low sm nd and high ce nd n ratios relative to the dolostones such distinct ree signatures probably reflect limited interaction between late diagenetic fluids and burlington keokuk host rocks penecontemporaneous clastic sediments have similar initial 143nd 144nd isotope ratios 0 511857 0 511877 and lower sm nd ratios compared to the dolomites suggesting 1 a common crustal source of ree for the clastics and carbonates and 2 ree fractionation during the formation of carbonate apatite glauconite and other authigenic phases in the marine environment

genesis of baddeleyite and high δ18o zircon in impure marble from the tongbai orogen central china insights from petrochronology and hf o isotope compositions coexistence of baddeleyite and zircon is rarely documented in metacarbonate rocks and poorly understood in this study metamorphic baddeleyite and zircon were recognized in marbles from the tongbai orogen central china we carried out high spatial resolution analysis of trace element geochemistry and u pb lu hf o isotope systematics for the zircon and baddeleyite sims secondary ion mass spectroscopy u pb analysis yields weighted average 207pb 206pb ages of 1848 0 3 3 ma msdw 1 2 n 12 for baddeleyite and 1840 13 ma mswd 1 7 n 13 for zircon the baddeleyite grains have relatively low ree rare earth element contents ree 1 30 47 3 ppm with flat chondrite normalized patterns and moderate contents of hfse high field strength element which are ascribed to the nature of its host metacarbonate rock and mineral assemblage the zircon grains have low ti contents 1 63 3 56 ppm positive ce anomalies ce ce 1 91 6 96 and mineral inclusions of hematite calcite dolomite lizardite and h2o these characteristics indicate zircon formation in a relatively low temperature setting under oxidizing and water rich conditions the baddeleyite and zircon have similar ranges of ehf t values of 7 7 to 10 5 and 7 8 to 11 6 respectively which suggest their derivation from a relatively uniform hf source the high 18o values of these zircon grains 20 0 21 0 preclude any percolation of external meteoric fluids during their crystallization therefore a detrital zircon dissolution reaction is preferred to provide the zr for the metamorphic zircon and baddeleyite in this study the o isotope disequilibrium between whole rock 18o 16 2 16 3 and metamorphic zircon is most likely caused by metamorphic devolatilization or interaction with an h2o dominant fluid during later metamorphism on the other hand the baddeleyite grains yield 18o values ranging from 4 5 to 8 7 which is in disequilibrium with metamorphic zircon at the temperature of detrital zircon dissolution reaction ca 660 710 c zircon dolomite baddeleyite forsterite calcite co2 the genesis of metamorphic zircon can be interpreted by a baddeleyite to zircon reaction of zro2 sio2 zrsio4 at a retrograde stage consistent with the low ti in zircon temperatures the results highlight the importance of integrating trace element and multiple isotopic compositions in studying the genesis of metamorphic baddeleyite and zircon additionally the u pb geochronology data also indicate that the protoliths of the marble were deposited in the early paleoproterozoic and experienced a metamorphism at 1 85 ga the ca 1 85 ga high grade metamorphic event might have been induced by the coeval magmatism in an extensional setting

porites corals as recorders of mining and environmental impacts misima island papua new guinea abstract in 1989 open cut gold mining commenced on misima island in papua new guinea png open cut mining by its nature causes a significant increase in sedimentation via the exposure of soils to the erosive forces of rain and runoff this increased sedimentation affected the nearby fringing coral reef to varying degrees ranging from coral mortality smothering to relatively minor short term impacts the sediment associated with the mining operation consists of weathered quartz feldspar greenstone and schist these rocks have distinct chemical characteristics rare earth element patterns and high abundances of manganese zinc and lead and are entering the near shore environment in considerably higher than normal concentrations using laser ablation inductively coupled plasma mass spectrometry la icp ms we analyzed eight colonies two from high sedimentation two transitional two minor and two unaffected control sites for y la ce mn zn and pb all sites show low steady background levels prior to the commencement of mining in 1988 subsequently all sites apart from the control show dramatic increases of y la and ce associated with the increased sedimentation as well as rapid decreases following the cessation of mining the elements zn and pb exhibit a different behavior increasing in concentration after 1989 when ore processing began and one year after initial mining operations elevated levels of zn and pb in corals has continued well after the cessation of mining indicating ongoing transport into the reef of these metals via sulfate rich waters rare earth element ree abundance patterns measured in two corals show significant differences compared to coral sea seawater the corals display enrichments in the light and middle rees while the heavy rees are depleted relative to the seawater pattern this suggests that the nearshore seawater ree pattern is dominated by island sedimentation trace element abundances of misima island corals clearly record the dramatic changes in the environmental conditions at this site and provide a basis for identifying anthropogenic influences on corals reefs

calcium mass transport and sandstone diagenesis during compaction driven flow stevens sandstone san joaquin basin california sediment compaction provides a limited source of fluids for diagenesis and drives fluid flow at average rates of only 1 mm yr nevertheless many geochemical and petrographic studies of diagenesis provide evidence of significant mass transport in systems where fluid flow appears to be compaction driven this apparent discrepancy could arise because diagenetic studies generally are concerned with relatively permeable petroleum reservoirs focused fluid flow through permeable zones could increase local flow rates and allow mixing of fluids from different sources this study uses the stevens sandstone of the san joaquin basin to explore the potential diagenetic effects of fluid focusing during compaction driven flow over a 5 m y period reactive transport simulations incorporate a new kinetic expression for plagioclase dissolution and suggest that rate limited plagioclase dissolution drove calcium enrichment of pore fluids and caused precipitation of calcite kaolinite and albite in spite of the importance of this rate limited reaction simulations show that influx of fluids from compacting shale could limit the distribution of calcite and kaolinite in adjacent sandstones although calcium mass transport is predicted on a scale of kilometers upward flow of calcium rich fluids from deep beds does not significantly increase calcite volume relative to closed system predictions increased transverse dispersivity increases mixing which further limits precipitation of calcite and kaolinite results are consistent with field observations of fluid chemistry although simulations account for

diagenesis of upper jurassic concretions from the antarctic peninsula abstract early diagenetic calcite concretions are widespread in mudstone tuff sequences deposited in late jurassic oxygen deficient basins of the antarctic peninsula although obscured or destroyed in host rocks original components and sedimentary structures are well preserved in concretions in spite of significant mineralogical and geochemical change during growth early diagenesis led to a rapid and almost total variation in the mineralogy within the concretions independently of the original host lithologies siliceous particles were replaced by chlorite and zeolites in suboxic alkaline and moderately reducing conditions on the sea floor and in the first centimeters of burial these conditions also led to localized early formation of phosphate concretions pyrite developed subsequently because of high sulfide abundance in the sulfate reduction zone most calcite precipitation took place in the lower part of the sulfate reduction zone in a strongly alkaline environment where sulfide content had been lowered by pyrite precipitation in this stage the remaining siliceous elements were dissolved or replaced by calcite later diagenetic changes include enlargement of zeolites minor changes in clay minerals and the formation of calcite veins the wide range of 13c values in cement and vein calcite 1 47o oo and 20 23o oo pdb is explained by mixed carbon sources from organic matter oxidation and dissolution of calcareous shells the low 18o of calcite 2 34o oo to 19 72o oo pdb is the result of recrystallization in contact with high temperature diagenetic or hydrothermal fluids flushed through micro fractures in the concretions which also produced extensive vein formation

snowball earth termination by destabilization of equatorial permafrost methane clathrate the recovery from the marinoan snowball ice age of about 635 million years ago is one of the most severe climate change events known to have occurred on earth hypotheses accounting for the abruptness of deglaciation include ice albedo feedback deep ocean out gassing during post glacial oceanic overturn or methane hydrate destabilization martin kennedy and colleagues now report the broadest range of oxygen isotope values yet measured in marine sediments in methane seeps in marinoan deglacial sediments underlying a thin interval of carbonate these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise the range of values is likely the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater their findings suggest that methane released from low latitude permafrost clathrates acted as a trigger and or strong positive feedback for deglaciation and warming this paper reports the broadest range of oxygen isotope values yet measured in marine sediments in methane seeps in marinoan deglacial sediments underlying a thin interval of carbonate these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise the range of values is likely the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater the start of the ediacaran period is defined by one of the most severe climate change events recorded in earth history the recovery from the marinoan snowball ice age 635 myr ago ref 1 marinoan glacial marine deposits occur at equatorial palaeolatitudes2 and are sharply overlain by a thin interval of carbonate that preserves marine carbon and sulphur isotopic excursions of about 5 and 15 parts per thousand respectively3 4 5 these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise1 3 4 this abrupt transition records a climate system in profound disequilibrium3 6 and contrasts sharply with the cyclical stratigraphic signal imparted by the balanced feedbacks modulating phanerozoic deglaciation hypotheses accounting for the abruptness of deglaciation include ice albedo feedback3 deep ocean out gassing during post glacial oceanic overturn7 or methane hydrate destabilization8 9 10 here we report the broadest range of oxygen isotope values yet measured in marine sediments 25 to 12 in methane seeps in marinoan deglacial sediments underlying the cap carbonate this range of values is likely to be the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater the equatorial palaeolatitude implies a highly volatile shelf permafrost pool that is an order of magnitude larger than that of the present day a pool of this size could have provided a massive biogeochemical feedback capable of triggering deglaciation and accounting for the global postglacial marine carbon and sulphur isotopic excursions abrupt unidirectional warming cap carbonate deposition and a marine oxygen crisis our findings suggest that methane released from low latitude permafrost clathrates therefore acted as a trigger and or strong positive feedback for deglaciation and warming methane hydrate destabilization is increasingly suspected as an important positive feedback to climate change11 12 13 that coincides with critical boundaries in the geological record14 15 and may represent one particularly important mechanism active during conditions of strong climate forcing

modification of fracture porosity by multiphase vein mineralization in an oligocene nontropical carbonate reservoir taranaki basin new zealand the nontropical oligocene carbonate rich tikorangi formation is an important oil producer in the taranaki basin new zealand hydrocarbons are hosted and produced from mineralized natural fracture systems petrographic trace element stable isotope 18o and 13c and fluid inclusion data have enabled a complex sequence of eight paragenetic events to be determined the tikorangi formation host rock was cemented by low mg calcite event 1 during burial diagenesis from temperatures of 27c corresponding to 0 5 km burial and continued until 37c 1 km burial depth producing tight pressure dissolved fabrics with essentially no porosity and permeability the host rock was partially dolomitized 5 50 event 2 by ca and fe rich dolomite rhombohedra at burial depths and temperatures of 1 0 1 5 km and 35 50c without secondary porosity development subsequent brittle fracturing formed by neogene compression event 3 is constrained to a period following lithification and dolomitization but before precipitation of first generation vein calcite event 4 this initial ferroan low mg vein calcite formed after a period of burial from fe rich meteorically modified fluids at temperatures of about 50 60c and 1 4 1 9 km burial depth baroque dolomite formed event 5 following a period of mg enriched basinal fluid input precursory to hydrocarbon emplacement per se the dolomite formed mainly as a primary cement but also as a calcite replacement at temperatures following further burial to 2 2 5 km and temperatures of 65 80c formation of celestite and quartzine phases event 6 coincided with or marginally postdated dolomite at similar depths and temperatures to event 6 and formed as both replacements and cements second generation ferroan vein calcite formed event 7 at cooler temperatures 53 65c perhaps resulting from the introduction of cooler meteoric fluids from upsection the presence of petroleum fluid inclusions in the second generation calcite suggests precursory hydrocarbon bearing fluids have migrated along with aqueous fluids from about 10 ma with hydrocarbon emplacement event 8 occurring in the last 6 m y following a period of rapid late miocene burial an improved understanding of the paragenesis of the tikorangi formation may assist in hydrocarbon production from its reservoirs

integrated ediacaran sinian chronostratigraphy of south china abstract the ediacaran period was a critical time in the history of life and earth understanding the complex interactions between geological and biological events during this interval requires high resolution chronostratigraphy thanks to its uniquely favorable palaeogeographic setting south china is an ideal region for constructing a framework for global chronostratigraphic correlation of ediacaran strata here continuous ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles as part of the present study 62 reference sections distributed throughout the yangtze platform were investigated analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies three major sequence boundaries occur respectively in the middle and upper parts of the doushantuo formation and in the middle part of the dengying formation subdivision and correlation of the ediacaran successions of the yangtze platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections 1075 samples the sequence boundary sb2 in the middle part of the doushantuo formation is suggested here as the lower xiadongian upper yangtzean series boundary of the ediacaran which coincides with several globally recognizable events namely 1 the end of the neoproterozoic glaciations 2 the first appearance of animals 3 the sudden increase in the diversity of acanthomorphic acritarchs and 4 a negative 13 c excursion the ediacaran system of south china may be subdivided into five stages furthermore the criteria for defining these stages may be applicable throughout the world also the composite carbon isotope profile of the ediacaran of south china can be used as a global reference for chronostratigraphic subdivision and correlation in addition to the globally recognizable negative 13 c excursion in the cap carbonate at the base of the ediacaran the negative 13 c excursion in the uppermost doushantuo wonoka shuram interval represents another globally correlatable major excursion the positive 13 c excursion immediately following the uppermost doushantuo excursion and ending at 548 ma is also useful for global correlation current ediacaran chronostratigraphy and global correlations indicate that the upper doushantuo wonoka shuram negative 13 c excursion ranges from ca 560 ma to 551 ma and therefore coincides with the evolutionary renovation of life feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative 13 c excursion in earth history our chronostratigraphic correlations also imply that the earliest known metazoan biotas namely the weng an and characteristic ediacaran biotas do not constitute two temporally separate evolutionary lineages as proposed previously but represent two parallel evolutionary pathways preceding the cambrian explosion of animal life

a case study of long gravity wave crests in noctilucent clouds and their origin in the upper tropospheric jet stream atmospheric gravity waves with very long crests of 450 500 km length and short horizontal wavelengths of about 20 km were observed in noctilucent clouds and were studied in detail for the first time the gravity waves were slowly moving in opposite direction to the background wind indicating their forced generation outside the mesopause region a ray tracing analysis using meteorological reanalysis and empirical atmospheric model data shows that a source of such peculiar gravity waves observed in noctilucent clouds was located near the tropopause and could be associated with the jet stream at altitudes 8 10 km two considered examples of very long wave crests confirm a significant role of the upper tropospheric jet stream as a source of gravity waves and reveal that these waves could propagate without critical levels to the mesopause in summertime

was the ediacaran shuram excursion a globally synchronized early diagenetic event insights from methane derived authigenic carbonates in the uppermost doushantuo formation south china abstract the ediacaran period is characterized by the most profound negative carbon isotope 13c excursion in earth history the shuram excursion various hypotheses including the massive oxidation of dissolved organic carbon doc in the oceans the weathering of terrestrial organic carbon or the release and oxidation of methane hydrates and or expelled petroleum from the subsurface have been proposed as sources of the 13c depleted carbon more recently it has been suggested that global scale precipitation of early authigenic carbonates driven by anaerobic microbial metabolism in unconsolidated sediments may have caused the shuram excursion but empirical evidence is lacking here we present a comprehensive analysis of a shuram associated interval from the uppermost doushantuo formation in south china our study reveals petrographic evidence of methane derived authigenic calcite formed as early diagenetic cements and nodules that are remarkably depleted in 13c suggesting a buildup of alkalinity in pore fluids through the anaerobic oxidation of methane aom and systematically depleted in 18o relative to co occurring dolomite early authigenesis of these minerals is likely to be driven by increased microbial sulfate reduction triggered by enhanced continental weathering in the context of a marked rise in atmospheric oxygen levels in light of the finding of methane derived authigenic carbonates at zhongling and based on our basin scale stratigraphic correlation we hypothesize that the marked 13c and 18o depletion including their co variation noted worldwide in the shuram excursion may reflect an episode of authigenesis occurring within a sulfate methane transition zone smtz if true the shuram excursion was then a global biogeochemical response to enhanced seawater sulfate concentration in the ediacaran ocean driven by the neoproterozoic oxidation of surface environments this paleo oceanographic transition may have therefore paved the way for subsequent evolution and diversification of animals our study highlights the significance of an integrated approach that combines petrography mineralogy and texture specific micro drilling geochemistry in chemostratigraphic studies

isotopic constraints of vein carbonates on fluid sources and processes associated with the ongoing brittle deformation within the accretionary wedge of taiwan terra nova 22 251 256 2010 abstract the continuously distributed well preserved fracture filling carbonates were collected from the cores retrieved from the taiwan chelungpu fault drilling program between 400 and 2000 m depth for carbon and oxygen isotope analyses to constrain the fluid compositions and processes associated with brittle deformation within the accretionary wedge the isotope analyses of fracture filling carbonates yielded 18o values steadily increasing with depth the 13c values exhibited a pattern similar to that of 18o values at shallower depths but an opposite trend at greater depths such variations in the isotopic compositions could be best explained by a mixing of shallow meteoric water and deeply rooted fluid carrying isotopic signatures of various microbial processes the notable excursion of 18o values might infer a conduit for the lateral fluid transport along the high vein density zone overall the isotopic patterns preclude the substantial influence of early diagenesis and suggest pervasive fluid percolation through the fracture network

characteristics of gravity waves in the mesosphere observed with the middle and upper atmosphere radar 2 propagation direction we studied the characteristics of dominant component of gravity waves z 10 km in the vertical profile of the wind velocities observed in the mesosphere at around 70 75 km with the middle and upper atmosphere mu radar in the four observation campaigns june 1987 july 1990 october 1986 and january february 1991 and the monthly mesosphere observations carried out 4 5 days a month in december 1985 to december 1988 by assuming linear dispersion relations of gravity waves both vertical and horizontal propagation directions of gravity waves were determined most of the dominant waves propagated upward except that they sometimes propagated downward mainly in summer a typical vertical wavelength and intrinsic period of the dominant gravity waves were 4 15 km and 4 15 hours respectively the mean values of the vertical wavelength horizontal wavelength and intrinsic periods were 8 2 km 1200 km and 10 2 hours respectively which did not show significant seasonal variations most of the waves were found to be dissipated by the eddy diffusion of 15 100 m2 s which does not agree with mf radar observations 10 to 120 min observed periods but is rather consistent with sodium lidar observations 36 300 m2 s the mean horizontal phase velocity was 33 m s the horizontal propagation direction was generally eastward throughout a year except for the westward propagation in early winter november to december this suggests that the dominant gravity waves are less sensitive to a change in the mean zonal wind direction in the middle atmosphere than the short period gravity waves 2 hours to 5 min momentum flux carried by the dominant gravity waves was estimated to be 0 5 1 m2 s2 which was generally smaller than the momentum flux of gravity waves with periods ranging from 8 hours to 5 min the amplitude of the momentum flux of the dominant gravity waves had an autumn maximum while the momentum flux with periods of 8 hours to 5 min had equinoctial minima thus in september and october the momentum flux due to the dominant gravity waves became significant we further pointed out that the possibility that depends on the wave periods and therefore the major frequency component of is not easily determined from simple dispersion relation only

sedimentology and diagenesis of tertiary carbonates on the mangkalihat peninsula borneo implications for subsurface reservoir quality abstract combined field and laboratory studies of surface exposures on the mangkalihat peninsula borneo provide new constraints on the chronostratigraphy sedimentology and diagenesis of tertiary carbonate deposits the reservoir characteristics of carbonate facies are described providing an analogue model for carbonate reservoirs in the subsurface of this region a mixed carbonate siliciclastic shelf with intervening probably fault bounded deeper water areas developed on the eastern part of the mangkalihat peninsula in the late eocene to oligocene during the oligo miocene shallow water platform carbonates accumulated over much of the area of the mangkalihat peninsula this platform had a steep reef rimmed or possibly locally faulted northern margin where high energy conditions prevailed and marine cements were pervasive in contrast the platform interior was a low energy area affected by leaching of aragonitic bioclasts the best reservoir quality on the platform occurs in moderate energy grainstones and packstones tens to hundreds of metres towards the platform interior from the platform margin where a combination of primary intergranular and secondary mouldic porosity results in good porosity and permeability

quartz cementation history of sandstones revealed by high resolution sims oxygen isotope analysis abstract evaluating the timing and origin of quartz cement is central to understanding how porosity is lost in sandstones during burial kinetic models of quartz cementation have been calibrated using large scale datasets but have never been tested at the microscopic level at which cement forms here we use high precision in situ oxygen isotope analyses on sandstone from the jurassic ness formation from the north sea to reveal the growth history of single quartz overgrowths to a resolution of 2 m measured 18o cement range from 28 to 20 v smow in early to late cement and are consistent with quartz cementation models that propose the bulk of quartz precipitates as a continuous process beginning at 60 70 c quantitative x ray diffraction analyses and clay mineralogical analysis of interbedded shales are inconsistent with a silica source from shale implying that silica for the cement is sourced internally to the sand these isotope data are broadly consistent with predictive conceptual quartz cementation models and provide a critical link from micron scale measurements to basin scale predictions and observations

susceptibility and triggering scenarios at a regional scale for shallow landslides abstract the work aims at identifying susceptible areas and pluviometric triggering scenarios at a regional scale in calabria italy with reference to shallow landsliding events the proposed methodology follows a statistical approach and uses a database linked to a gis that has been created to support the various steps of spatial data management and manipulation the shallow landslide predisposing factors taken into account are derived from i the 40 m digital terrain model of the region an 15 075 km2 extension ii outcropping lithology iii soils and iv land use more precisely a map of the slopes has been drawn from the digital terrain model two kinds of covers prevalently coarse grained cg cover or fine grained fg cover were identified referring to the geotechnical characteristics of geomaterial covers and to the lithology map soilscapes were drawn from soil maps and finally the land use map was employed without any prior processing subsequently the inventory maps of some shallow landsliding events totaling more than 30 000 instabilities of the past and detected by field surveys and photo aerial restitution were employed to calibrate the relative importance of these predisposing factors the use of single factors first level analysis therefore provides three different susceptibility maps second level analysis however enables better location of areas susceptible to shallow landsliding events by crossing the single susceptibility maps on the basis of the susceptibility map obtained by the second level analysis five different classes of susceptibility to shallow landsliding events have been outlined over the regional territory 8 9 of the regional territory shows very high susceptibility 14 3 high susceptibility 15 moderate susceptibility 3 6 low susceptibility and finally about 58 very low susceptibility finally the maps of two significant shallow landsliding events of the past and their related rainfalls have been utilized to identify the relevant pluviometric triggering scenarios by using 205 daily rainfall series different triggering pluviometric scenarios have been identified with reference to cg and fg covers a value of 365 mm of the total rainfall of the event and or 170 mm d of the rainfall maximum intensity and a value of 325 mm of the total rainfall of the event and or 158 mm d of the rainfall maximum intensity are able to trigger shallow landsliding events for cg and fg covers respectively the results obtained from this study can help administrative authorities to plan future development activities and mitigation measures in shallow landslide prone areas in addition the proposed methodology can be useful in managing emergency situations at a regional scale for shallow landsliding events triggered by intense rainfalls through this approach the susceptibility and the pluviometric triggering scenario maps will be improved by means of finer calibration of the involved factors

geochemistry of late archaean stromatolites from zimbabwe evidence for microbial life in restricted epicontinental seas we report comprehensive trace element and sr isotope data for microbial carbonates from the archaean mushandike limestone masvingo greenstone belt zimbabwe the stromatolites have very coherent ree y patterns and share the essential shale normalised characteristics of other archaean marine precipitates positive la and gd anomalies absence of a negative cc anomaly and a strongly superchondritic y ho ratio mixing models constrain the maximum amount of shale contamination to 0 25 1 and calculated detritus free carbonate ree y systematics require precipitation from seawater in terms of light ree over heavy ree depletion however the studied samples are very different from all other known archaean marine precipitates in shale normalised plots the mushandike samples yield a negative slope a very restricted regional input source of the dissolved load is indicated because normalisation with locally occurring tonalite gneiss ree y data yields a pattern closely resembling typical shale normalised archaean marine chemical sediments the disappearance of a negative eu anomaly when patterns are normalised with local tonalite gneiss strengthens this interpretation sr isotope ratios are strongly correlated with trace element contents and ratios which explains the modest scatter in sr isotope ratios as representing minor clastic contamination importantly even the least contaminated samples have very radiogenic initial sr 87 sr 86 ratios 0 7184 implying sr input from an ancient high rb sr source such as the early archaean gneisses of south central zimbabwe a local ancient 3 5 3 8 ga source is also indicated by previously published pb isotope datasets for the mushandike stromatolites this is entirely compatible with the occurrence of 3 7 3 8 ga zircons in quartzites and metapelites from comparably old greenstone belts within less than 150 km of the studied locality comparison of the pb isotope ratios of the mushandike stromatolites with 2 7 and 2 6 ga old stromatolites from the neighbouring belingwe greenstone belt demonstrates differences in initial isotope composition that relate to the extent of exchange with the open ocean the development of numerous basins on old continental crust with water masses variably restricted from the open ocean suggests a lack of strong vertical topography on this late archaean craton c 2004 elsevier b v all rights reserved

does burial diagenesis reset pristine isotopic compositions in paleosol carbonates abstract sedimentological study of early oligocene continental carbonates from the fluvial dagshai formation of the himalayan foreland basin india resulted in the recognition of four different types namely soil palustrine pedogenically modified palustrine and groundwater carbonates stable oxygen and carbon isotopic 18 o and 13 c analyses of fabric selective carbonate microsamples show that although the pristine isotopic compositions are largely altered during deep burial diagenesis complete isotopic homogenization does not occur 18 o and 13 c analyses of 200 calcrete and palustrine carbonates from different stratigraphic horizons and comparison with 18 o of more robust bioapatite fossil vertebrate tooth phase show that dense micrites 70 carbonate invariably preserve the pristine 18 o value mean of 9 8 while altered carbonates show much lower 18 o value 13 8 such inhomogeneity causes large intra sample and intra soil profile variability as high as 5 suggesting that soils behave like a closed system where diagenetic overprinting occurs in local domains a simple fluid rock interaction model suggests active participation of clay minerals to enhance the effect of fluid rock ratio in local domains during diagenesis this places an upper limit of 70 micrite concentration above which the effect of diagenetic alteration is minimal careful sampling of dense micritic part of the soil carbonate nodules therefore does provide pristine isotopic composition and it is inappropriate as proposed recently to reject the paleoclimatic potential of all paleosol carbonates affected by burial diagenesis based on pristine 13 c value of 8 8 0 2 in soil carbonates an atmospheric co 2 concentration between 764 and 306 ppmv is estimated for the early oligocene 31 ma dagshai time these data show excellent agreement between two independent proxy records viz soil carbonate and marine alkenone and support early oligocene survival of the antarctic ice sheet

carbon isotope chemostratigraphy and sedimentary facies evolution of the ediacaran doushantuo formation in western hubei south china abstract the doushantuo formation of south china consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies is one of the key sedimentary units in the world for understanding ediacaran geobiological processes however stratigraphic correlation and sedimentary facies evolution of the doushantuo formation remain controversial sedimentary facies analysis of the well known sections of the yangtze gorges area and new sections in northern yichang western hubei indicate that the doushantuo succession in the yangtze gorges area was deposited in an offshore intra shelf basin within the yangtze platform in contrast the doushantuo formation in the northern yichang area which is characterized by one or a few phosphate rich horizons represents deposition on the subtidal or intertidal shelf and so is similar to the succession in the weng an area central guizhou province the carbon isotope profiles of the different sections exhibit significant variation which is interpreted to result from facies differences sequence and high resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the doushantuo formation on the yangtze platform the results confirm that a prominent negative 13ccarb excursion baince nadir down to 5 in the middle portion of the second sequence of the doushantuo formation is a widely traceable event baince together with three other 13ccarb excursions namely cance at the base wance near the first sequence boundary near the middle and dounce at the top of the doushantuo formation constitute a complete carbon isotope profile for the doushantuo formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the ediacaran period

structure and porosity of smectitic mudrocks as affected by experimental wetting drying cycles and freezing thawing cycles abstract the erosion rates in the vallcebre basin pyrenees are controlled predominantly by the physical weathering rate of bare regolith i e mudrocks to obtain information on the influence of thermic and moisture regimes on the weathering dynamics laboratory experiments were carried out to investigate how freezing thawing or wetting drying cycles under controlled conditions affect structure and porosity three different clayey mudrocks were selected to represent materials more susceptible to erosion in the studied area the three lithologies identified as ca1r ca2r carr differed mainly in mineral constituents type and quantity of the clay minerals and cation exchange capacity an automated non contact laser profile meter was used to analyse surface microtopography in order to monitor random roughness variations and to calculate bulk density porosity and pore size distribution were carried out with image analysis freezing thawing cycles were the most active in modifying soil surface and bulk structure roughness of ca1r and ca2r was more than doubled at the end of freezing thawing cycles this variation was mostly associated with the whole surface elevation related to the bulk volume increase roughness variations in carr were less pronounced and related to a modification of the microtopography micromorphological observations revealed a platy structure formation induced by repeated ice lensing also porosity was increased by freezing thawing cycles with the formation of a large number of irregular and rounded pores wetting drying cycles did not affect surface roughness and modified bulk density very little in all samples they increased porosity by the formation of large cracks and fissures overall data from wetting drying cycles showed that changes in water content alone did not produce deep structural modifications a mechanism of alteration of soil structure during freezing thawing cycles is proposed

an experimentally verified model for calcite precipitation in veins calcite is commonly found as a vein filling mineral in rocks however the factors controlling its deposition are complex and not well understood in quantitative terms in order to advance our understanding of the processes involved we have refined the model for calcium carbonate mass transport in subsurface carbonate rocks of morse and mackenzie 1993 and developed a new experimental technique to test it this technique uses a flow through reactor that simulates a vein opening agreement was observed between model predictions and experimental observations for the deposition of calcite in synthetic veins the influences of surface area to solution volume ratio solution saturation state with respect to calcite and flow velocity were well predicted by the model the model predicts that in order to have a fairly uniform deposition of calcite within a vein solution flow must be quite rapid tens to thousands of cm h 1 or the solution must be only slightly supersaturated with respect to calcite a low degree of solution supersaturation demands what may be unreasonably large volumes of solution flow to achieve vein filling for the vein configuration we have studied

effect of weathering on the compressibility and shear strength of a natural clay in situ seasonal changes expose soils to frequent wetting drying freezing thawing cycles such processes can favour and trigger shallow instabilities controlled by the weathering process this paper presents an experimental study carried out to investigate the effects of the weathering process caused by the wetting drying freezing thawing cycles on the compressibility and shear strength of a natural clay several specimens were trimmed from block samples of overconsolidated clays taken from a slope in south calabria italy specimens were subjected to wetting drying freezing thawing cycles of different durations and then tested with standard equipment oedometer and direct shear test results show that the wetting drying freezing thawing cycles caused a change in the initial microstructure that produced a decrease in the compression index and an increase in the swelling index moreover the direct shear test results show a decrease in the peak shear strength and demonstrate that a larger reduction occ