meteoric like fabrics forming in marine waters implications for the use of petrography to identify diagenetic environments petrographic fabrics have long been used to identify meteoric diagenesis of carbonate sediments however on the basis of oxygen isotopic data we document similar fabrics forming in marine pore fluids in the shallow subsurface of great bahama bank therefore petrographic fabrics alone are not reliable indicators of diagenetic environments even for shallow water sediments in our study skeletal grainstones show two distinct diagenetic assemblages either dissolution of aragonitic grains and minimal cementation high permeability intervals or abundant blocky spar cement and neomorphism of aragonitic skeletal grains low permeability intervals these marine burial fabrics are present as shallow as 110 m below sea level well above the aragonite compensation depth a feature that must be considered for models of diagenesis in ancient carbonate sediments marine burial diagenesis may be important in ancient carbonate sediments deposited in moderate water depths or in shallow water during rising sea level where meteoric diagenesis is suppressed

peculiar phenomena regarding climatic and glacial variations on the tibetan plateau in contrast to the worldwide intensive warming and consequent glacier shrinkage during the last 30 years two peculiar phenomena have been observed on the tibetan plateau 1 the temperature has decreased about 0 68c on the northern tibetan plateau with smaller than average glacier retreat and meltwater discharge and 2 a number of glaciers have been advancing on the southeast tibetan plateau in response to increased precipitation these observations indicate the complex nature of the response of glaciers to climate changes the main part of the northern tibetan plateau includes the western and central kunlun shan and the northern qiangtang plateau roughly 32 378 n 75 958 e fig 1 the kunlun shan are known as the backbone of asia extending from west to east with wide mountain ranges mostly higher than 6000 m a s l and the highest peak at 7167 m a s l the high and broad mountains and prevailing climate provide favorable conditions for glacier develop ment at present according to the china glacier inventory cgi glaciers in the western and central kunlun shan cover 12 136 km 2 and the equilibrium line altitude ela ranges between 480 and 6200 m there are several isolated mountains in the northern qiangtang plateau with eroded surfaces above 6000 m a s l and some isolated interior lake basins in this region glaciers cover an area of about 1500 km 2 with the ela ranging from 5300 to 6100 m

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

missing aragonitic biota and the diagenetic evolution of heterozoan carbonates a case study from the oligo miocene of the central mediterranean abstract several previous studies have addressed the diagenetic evolution of heterozoan carbonate assemblages generally it is assumed that early diagenetic processes in heterozoan settings are mainly destructive including abrasion and dissolution on the sea floor constructive diagenesis cementation is delayed to later stages in the burial environment with pressure solution of calcitic grains acting as a cement source this paper presents a study of oligo miocene inner to outer ramp heterozoan carbonates from the central mediterranean maltese islands and sicily indicating that early diagenetic processes are more important than previously assumed four to five different cement types including fibrous two types of epitaxial bladed and blocky cement are distinguished based on transmitted light microscopy cathodoluminescence microscopy allowed a differentiation between primary high mg calcitic fibrous and epitaxial cement i and primary low mg calcitic epitaxial cement ii bladed and blocky cements stable isotope data indicate cement precipitation from marine marine derived and meteoric waters trace element analyses point to cementation in an open system maltese islands and a closed system sicily our investigations show that the majority of constructive diagenetic processes in these rocks occurs rather early in the shallow marine burial environment which is transitional between the marine seafloor and the deep burial diagenetic environment the main cement source in this environment is assumed to be aragonite we suggest careful consideration of the importance of aragonitic components in fossil heterozoan settings which seem to be more abundant than previously assumed and can act as a major early cement source due to the low preservation potential of these components detailed geochemical studies are necessary to detect aragonite as the cement source our findings also have implications when considering the reservoir qualities of these rocks because primary porosity can be occluded early and secondary porosity is not preserved

submarine hydrothermal activity along the mid kermadec arc new zealand large scale effects on venting 1 the 2 500 km kermadec tonga arc is the longest submarine arc on the planet here we report on the second of a series of cruises designed to investigate large scale controls on active hydrothermal venting on this arc the 2002 nzaplume ii cruise surveyed 12 submarine volcanic centers along 580 km of the middle kermadec arc mka extending a 1999 cruise that surveyed 260 km of the southern kermadec arc ska average spacing between volcanic centers increases northward from 30 km on backarc crust along the ska to 45 km on backarc crust along the southern mka to 58 km where the mka joins the kermadec ridge volcanic cones dominate in the backarc and calderas dominate the kermadec ridge the incidence of venting is higher along the mka 83 10 of 12 volcanic centers than the ska 67 8 of 12 but the relative intensity of venting as given by plume thickness areal extent and concentration of dissolved gases and ionic species is generally weaker in the mka this pattern may reflect subduction of the 17 km thick oceanic hikurangi plateau beneath the ska subduction of this basaltic mass should greatly increase fluid loss from the downgoing slab initiating extensive melting in the upper mantle wedge and invigorating the hydrothermal systems of the ska conversely volcanic centers in the southern mka are starved of magma replenishment and so their hydrothermal systems are waning farther north where the mka centers merge with the kermadec ridge fewer but larger magma bodies accumulate in the thicker older crust ensuring more widely separated caldera dominated volcanic centers

controls on stylolite development morphologic lithologic and temporal evidence from bedding parallel and transverse stylolites from the u s appalachians quantification of morphology of bedding parallel and transverse or tectonic stylolites from the southern appalachians reveals that regardless of tectonic setting or stylolite orientation lithologic heterogeneity controls stylolite development for example stylolites in more heterogeneous carbonate lithologies packstones and grainstones are more serrate than those in wackestones and mudstones similarly early forming stylolites are more serrate than late forming stylolites and computer simulations suggest that decreases in porosity or other lithologic heterogeneity cause the less serrate nature of late forming stylolites the linkage of a stylolite s morphology to its time of development should allow field estimation of timing of stylolitization and thus of timing of loading or compression although bedding parallel and transverse stylolites generally result from different kinds of compression morphological relations indicate that their development follows the same fundamental patterns bedding

development of microporosity in a micritic limestone reservoir lower cretaceous middle east abstract abundant intercrystalline microporosity is developed within the matrix of micritic limestones over several hundreds of meters of section in the thamama group lower cretaceous at sajaa field eastern u a e sediments in the upper shuaiba formation uppermost tamama group include muddy rudist algal coralgal and orbitolina dominated lithofacies matrix is composed of euhedral to subhedral micro rhombic low mg calcite crystals with average diameters of about 5 m microporosity development was not related to leaching chalkification of lithified micrite during post depositional emergence of the shuaiba formation features diagnostic of emergence are lacking in core below the upper contact of the unit matrix microporosity is believed to have been an early developed property of micritic limestones trace element compositions of matrix reflect a diagenetic process that involved conversion of a calcitic lime mud into micro rhombic micrite and microspar using a closed system geochemical model the observed matrix oxygen isotope compositions 18 o of 4 to 5 pdb are compatible with dissolution of aptian lime mud 18 o of 2 pdb and reprecipitation of calcite in fluids of marine composition under conditions corresponding to burial depths of 550 800 m porosity of 30 50 at 40 50 c closed system conditions are consistent with textural constraints for limited or arrested cementation in the matrix chemical compaction was responsible for partial occlusion of matrix microporosity as microporosity is decreased in zones of intense stylolitization slight corrosion of matrix crystals and leaching of peloids and orbitolina postdated cementation and chemical compaction during deep burial

neomorphism and cementation in ancient deep water limestones cow head group cambro ordovician western newfoundland canada abstract lithification of thinly bedded lime mudstones and grainstones in the cow head group resulted mainly from precipitation of calcite cement and neomorphic spar at shallow burial depths below the sea floor these crystals are predominantly non ferroan although the iron content and the size of neomorphic spar commonly increase near the margins of nodular and continuous beds of lime mudstone displacive fringes of ferroan fibrous calcite represent the last stage of carbonate precipitation in some limestones most calcite 13c values range between 0 and 3 pdb but 13c values as negative as 15 indicate that bacterial degradation of orgnaic matter variably influenced pore water composition serial analyses from the centres to the margins of nodular and continuously bedded lime mudstones suggest that many of the limestones in this sequence were lithified prior to the precipitation of calcite having the prominent negative 13c values typical of concretionary carbonate calcite 18o values range from 5 to 8 pdb indicating precipitation from 18o depleted pore waters of uncertian origin cathodoluminescence shows that aggrading neomorphism in the lime mudstones did not take place by porphyroid or coalescive consumption of a more finely crystalline mosaic to yield a more coarsely crystalline mosaic instead scattered crystals enlarged by precipitation of progressively younger and eventually ferroan calcite especially at the margins of nodular and continuous limestone beds the cathodoluminescence zoning in calcite crystals is similar to that observed in meteorically altered limestones where pore waters were initially oxidizing but became progressively more reducing with time the preservation of trace element zoning crystal growth microfabrics and 13c values in authigenic calcite suggest collectively that recrystallization did not occur during subsequent burial

missing molluscs as evidence of large scale early skeletal aragonite dissolution in a silurian sea in the silurian carbonate platform succession of gotland sweden interreef limestone and marl sequences have shallow marine shelly assemblages dominated by brachiopods typical of many paleozoic benthic faunas locally from similar facies where early skeletal silicification occurred associated with bentonites there are rich and diverse assemblages of originally aragonitic molluscs quantitative faunal analysis suggests that massive depletion of skeletal aragonite chiefly molluscs took place and the entire molluscan fauna may generally be underrepresented by at least 100 fold previous workers on the gotland succession have already shown that abundant diagenetic limestones were sourced by early aragonitic remobilization our findings indicate molluscs as the probable source of this diagenetic calcite not aragonite mud as was previously thought the taphonomic window represented by the silicified faunas illustrates the importance of aragonitic shells among the original silurian shelf benthos and raises the possibility that the paucity of such shells among many fossil faunas may be largely an early taphonomic effect

a review of the nature and origin of limestone microporosity abstract limestone microporosity is ubiquitous and extensively developed in most phanerozoic limestones from an economic perspective microporosity is important because it contributes substantially to the carbonate pore system which can host significant volumes of water and hydrocarbons therefore determining the presence and distribution of limestone micropores is necessary for accurate hydrocarbon estimations reservoir characterization and fluid flow simulations from an academic standpoint microporosity is important because its genesis is intimately linked with the mineralogical stabilization of metastable sediments a fundamental process in carbonate diagenesis many types of micropores contribute to what has been referred to as microporosity but the vast majority is hosted among low magnesium calcite lmc microcrystals that are present in limestone matrix and allochems geochemical textural and mineralogical data from natural settings and laboratory experiments indicate that lmc microcrystals are diagenetic in origin more specifically these data support a diagenetic model of mineralogical stabilization that involves dissolution of precursor sediments dominated by aragonite and high magnesium calcite hmc minerals and precipitation of lmc microcrystal cements the stabilization process is inferred to take place in the meteoric marine and burial diagenetic realms although it has not been directly observed carbon and oxygen isotopes as well as trace element data suggest that lmc microcrystals form during burial diagenesis in marine like fluids evidence suggests that porosity is not generated during this dissolution precipitation process but rather inherited from the precursor sediments the final arrangement of the micropores in a limestone however depends on the precise diagenetic pathway lmc microcrystals exhibit a range of microcrystalline textures that are classified on the basis of crystal morphology and size the three main textural classes granular framework fitted mosaic and clustered have been recognized across a wide range of ages depositional settings burial depths and precursor types and are characterized by distinct petrophysical properties such as porosity permeability and pore throat size observations from modern sediments also support the hypothesis that lmc microcrystals develop from aragonite and hmc dominated lime mud the origin of lime mud has been extensively studied but still highly debated of particular interest to the discussion of microporosity are proposed secular variations in the dominant mineralogy of carbonate sediments through the phanerozoic microporous limestones comprised of lmc microcrystals are equally abundant during times of aragonite seas and calcite seas which suggests that no special mineral precursor is required microporous textures are also observed in deep marine chalks where micropores are hosted between chalk constituents unlike shallow marine limestones deep marine sediments start out as mostly lmc therefore mineralogical stabilization is not a significant process in chalk diagenesis

diagenesis and evolution of microporosity of middle upper devonian kee scarp reefs norman wells northwest territories canada petrographic and chemical evidence the middle upper devonian kee scarp reef complexes of norman wells northwest territories canada are oil producing stromatoporoid dominated carbonates episodic increases in the rate of sea level rise produced multiple cycles of reef growth that exhibit backstepping characteristics these carbonates composed of invariably altered limestones have original interskeletal intraskeletal and intergranular porosity mostly occluded by nonferroan dull luminescent cements secondary porosity represented by micropores of various types developed during diagenesis by aggrading neomorphism and dissolution the micropores represent the main reservoir porosity in the kee scarp limestone micropores in the kee scarp limestone can be classified into four categories based on thei shapes 1 stepwise rhombic about 1 m to 2 m in diameter developed mainly in stromatoporoids 2 intercrystalline rhombic about 1 m in diameter developed mainly in algal aggregates 3 microvugs 4 m to 10 m in diameter developed mainly in algal aggregates and 4 microchannels about 12 m in length and 0 5 m in width developed in algal aggregates and stromatoporoids the stepwise rhombic and microvugs are developed mainly at the kee scarp reef margin and constitute the best type of reservoir porosity petrographic chemical and isotopic studies of kee scarp reef components reveal a complex diagenetic history involving marine fluids modified by increasing water rock interaction and burial early diagenetic processes include marine cementation and micritization followed by neomorphic replacement of high mg calcite and aragonite reef components resulting in the creation of the first generation of microporosity via dissolution on a micron scale later diagenesis represented by microfracturing and cementation with two generations of equant calcite and stylolitization was responsible for the second generation of microporosity very minor silicification dolomitization and vertical fracturing occurred at variable depths portions of well preserved marine cements stromatoporoids an rare crinoids of postulated high mg calcite precursor mineralogy have escaped diagenetic alteration and preserve the original marine dgr18o and dgr13c signatures 4 7 0 3 pmil pdb for oxygen 1 0 0 4 pmil pdb for carbon minor and trace element data show less preservation of the postulated original marine composition neomorphic stabilization of skeletal components caused further depletion in dgr18o but very little change in dgr13c an argument for modification of the original marine fluids with increasing burial variations in magnitude of water rock interaction with depth facies changes and porosity modifications probably exerted some control on fractionation and distribution of stable isotopes and trace elements in ree components

transformation of aragonite dominated lime muds to microcrystalline limestones scanning electron microscopy of textures in several well lithified pleistocene micrites mixed micrite and microspar from south florida and the bahamas shows significant diagenetic alteration of the lime mud precursors the dominance of aragonite in those precursor muds is supported by the surprising presence of abundant aragonite relics in the neomorphic calcite crystals confirmed by feigl stain x ray and electron diffraction polished very lightly etched surfaces of neomorphic calcite crystals even in the microspar show aragonite relics and pits both absent in coexisting void fill cements similarities between micrite and microspar crystals indicate their common origin through a one step neomorphic process of calcitization that is the mud did not first calcitize to micrite and then alter to microspar by aggrading neomorphism this conclusion has more general implications for the interpretation of the origins of other older microsparitic carbonates both early calcitization and concurrent early meteoric cementation were significant in producing the florida bahamas micrites studied which have low porosities similar to those found in most ancient fine grained limestones these low porosities despite the absence of significant overburden indicate that major porosity reduction without compaction can occur in calcitized aragonite dominated muds

carbonate apron models alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration sediment gravity flow deposition along the deep water flanks of carbonate platforms typically does not produce submarine fans rather wedge shaped carbonate aprons develop parallel to the adjacent shelf slope break the major difference between submarine fans and carbonate aprons is a point source with channelized sedimentation on fans versus a line source with sheet flow sedimentation on aprons two types of carbonate aprons may develop along relatively gentle 4 platform margin slopes aprons form immediately adjacent to the shallow water platform and are referred to as carbonate slope aprons along relatively steep 4 15 platform margin slopes redeposited limestones accumulate in a base of slope setting by passing an upper slope via a multitude of small submarine canyons and are referred to as carbonate base of slope aprons both apron types are further subdivided into inner and outer facies belts inner apron sediments consist of thick mud supported conglomerates and megabreccias facies f as well as thick coarse grained turbidites facies a interbedded with subordinate amounts of fine grained peri platform ooze facies g outer apron sediments consist of thinner grain supported conglomerates and turbidites facies a as well as classical turbidites facies c with recognizable bouma divisions interbedded with approximately equal proportions of peri platform ooze facies g seaward aprons grade laterally into basinal facies of thin base cut out carbonate turbidites facies d that are subordinate to peri platform oozes facies g carbonate base of slope aprons grade shelfward into an upper slope facies of fine grained peri platform ooze facies g cut by numerous small canyons that are filled with coarse debris as well as intraformational truncation surfaces which result from submarine sliding in contrast slope aprons grade shelfward immediately into shoal water platform margin facies without an intervening by pass slope the two carbonate apron models presented here offer alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration for mass transported carbonate facies

questioning carbonate diagenetic paradigms evidence from the neogene of the bahamas carbonate diagenetic models have been heavily influenced by numerous studies of exposed quaternary limestones as a result meteoric diagenesis is often assumed to be the principle means of altering aragonite rich sediments into calcitic limestones however these models are limited by the scarcity of examples of aragonite rich sediments buried in seawater that have never been influenced by meteoric fluids the bahamas transect cores recovered originally aragonite rich sediments deposited in deep water beyond the easy reach of meteoric waters and provide an opportunity to test current diagenetic paradigms the bahamas transect consists of seven cores drilled in the prograding western margin of great bahama bank the two proximal cores clino and unda were drilled on the platform top and recovered shallow water platform to reef facies overlying deeper margin and proximal slope facies the five distal cores were drilled by odp leg 166 in up to 660 m of water and recovered carbonate slope facies all studied sections are neogene to pleistocene in age diagenetic environments were identified based on petrographic and scanning electron microscopy sem observations xrd mineralogy carbon and oxygen stable isotopic data and trace elements the upper 100 150 m of the two proximal cores were altered in meteoric to mixing zone diagenetic environments but all other intervals were altered exclusively in marine pore fluids during seafloor marineburial and deep burial diagenesis several of the findings of this study question current carbonate diagenetic paradigms these include 1 large scale sea level lowstands may not have chemically active meteoric lenses as we found no meteoric alteration at the 3120 m elevation of the latest pleistocene lowstand rather phreatic meteoric diagenesis appears restricted to within w10 m of the land surface 2 mixing zone diagenesis includes aragonite dissolution and minor lmc cementation but does not show the cavernous porosity or dolomitization predicted by mixing zone diagenetic models current models are based on coastal mixing zones which do not appear to be applicable to these more inland and perhaps more typical locations 3 marine burial diagenesis produces a mature limestone with fabrics formerly considered diagnostic for meteoric diagenesis such as moldic porosity aragonite neomorphism blocky calcite spar and calcite microspar however oxygen stable isotopic data average n 18 o 1x indicate alteration in marine pore fluids only the character of marine burial diagenesis is partially controlled by the nature of the sediment being altered we have identified two end member styles an open system style characterized by dissolution of aragonite without significant cementation and a more closed system style with aragonite dissolution

discrimination of effective from ineffective porosity in heterogeneous cretaceous carbonates al ghubar field oman the natih e heavy oil reservoir 21 api at al ghubar field oman has produced less than 5 of the calculated oil in place porosity logs used to calculate reserves show high porosity throughout the reservoir but further analysis of the only continuous core taken from the field indicates that much of the porosity is ineffective there are four heavily oil stained high permeability skeletal pelletal grainstone units with interparticle porosity in the core that probably contributed most of the production the four permeable grainstone units occur at the top of small scale accommodation cycles that have wackestone and packstone bases these grainstones make up about 20 of the total thickness of the porous natih e reservoir the other 80 is composed of packstone and wackestone with ineffective microporosity interparticle porosity in burrows and isolated moldic and intraskeletal porosity the small scale reservoir bearing cycles can be correlated across the field using the separation between the medium and deep induction curves as a guide resistivity logs are the most reliable tool to distinguish effective from ineffective porosity most high permeability grainstone units have deep induction values more than 100 ohm m and separation of more than 10 ohm m between the medium and deep induction curves the ineffective intervals with microporosity burrow porosity and moldic porosity have lower resistivity and little separation between the medium and deep induction curves

where has all the aragonite gone mineralogy of holocene neritic cool water carbonates southern australia abstract surficial carbonate sediments on the southern continental shelf of australia are cool water in aspect and composed of biogenic particles produced largely during the late quaternary current understanding is that such sediments are calcite dominated as were their older cenozoic counterparts the holocene fraction of these sediments in modern open shelf neritic environments between 30 and 350 meters water depth is however 50 to 80 aragonite scant evidence of significant former aragonite in many cool water carbonate sedimentary rocks implies that most aragonite is lost before such sediments exit the marine diagenetic environment although marine dissolution must be taking place in such settings the conundrum is exacerbated because seawater over the shelf in southern australia is saturated with respect to aragonite it is proposed that the aragonite from skeletons of gastropods infaunal bivalves and certain bryozoans is dissolved in the shallow subsurface probably as the byproduct of bacterial degradation of sedimentary organic matter as a consequence the geological and paleontological record of many cool water carbonates is strongly biased and the inferred original calcitic composition of such sediments is the product of early diagenetic taphonomic loss not selective biogenic productivity the net result is not only dissolution of aragonite but also neomorphism of mg calcite to calcite with a marine geochemical signature synsedimentary aragonite loss by removing caco3 that is usually available for calcite cementation during meteoric diagenesis leads to retarded lithification of these cool water carbonates until deeply buried such removal of a significant carbonate fraction during deposition likely contributes to the low rates of cool water sediment accumulation

the influence of organic matter diagenesis on caco3 dissolution at the deep sea floor abstract in situ benthic flux chamber measurements were performed at seafloor locations in the atlantic and pacific oceans where the bottomwaters were supersaturated approximately saturated and undersaturated with respect to calcite there was no evidence of significant dissolution at or above the saturation horizon below the saturation horizon however significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution where observed the rate of dissolution is consistent with a rate expression of reaction order 4 5 and a rate constant in the range of 0 05 to 0 5 per day a numerical simulation was constructed to represent organic matter and caco3 diagenesis at the seafloor at the supersaturated and near saturation sites the model over predicts the influence of metabolically produced co2 on the extent of caco3 dissolution it is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments the primary factors to be considered include 1 the oxidation state of the carbon being oxidized 2 the vertical distribution of oxidation rates including the role of doc in sediment remineralization 3 the influence of nondiffusive transport of near surface porewaters and 4 the influence of episodic depositional events on organic and inorganic carbon cycling

multiple hydrothermal sources along the south tonga arc and valu fa ridge 1 quantifying hydrothermal venting at the boundaries of tectonic plates is an outstanding geoscience problem considerable progress has been made by detailed surveys along mid ocean ridges mors but until recently little was known about fluid venting along volcanic arcs we present the first systematic survey for hydrothermal venting along the 425 km long south tonga arc and new chemistry data for particle and thermal plumes previously reported along an adjacent 88 km long section of the back arc valu fa ridge vfr eleven hydrothermal plumes recognized by their anomalous light backscattering eh temperature ph dissolved he 3 ch4 and total dissolvable fe and mn were identified arising from seven volcanic centers along the arc five plumes on the vfr were characterized chemically vent field density for the south tonga arc was 2 6 sites 100 km of arc front comparable to that found by surveys of the kermadec arc 1 9 to 3 8 sites 100 km and to mors in the eastern pacific average value for 2280 km of surveyed ridgecrest 3 2 sites 100 km a vent gap occurs along a 190 km section of the arc closest to the vfr and a site density twice the average for mors on the eastern edge of the pacific plate was found on this part of the vfr 6 6 sites 100 km we suggest magmas ascending under the adjacent south tonga arc have been captured by the vfr while chemical enrichments of plumes on the south tonga arc were in general slightly less than those on the kermadec arc several instances of excessive anomalies in ph suggest a similar presence of fluids enriched in magmatic volatiles co2 so2 h2s locally venting on the vfr has contributed to accumulations of 3 he fe and mn within the southern lau basin on a broader scale our results provide considerable support for the notion that venting from intraoceanic arcs on the convergent margin of the pacific plate adds significantly to the total hydrothermal input into the pacific ocean

venting of a separate co2 rich gas phase from submarine arc volcanoes examples from the mariana and tonga kermadec arcs submersible dives on 22 active submarine volcanoes on the mariana and tonga kermadec arcs have discovered systems on six of these volcanoes that in addition to discharging hot vent fluid are also venting a separate co2 rich phase either in the form of gas bubbles or liquid co2 droplets one of the most impressive is the champagne vent site on nw eifuku in the northern mariana arc which is discharging cold droplets of liquid co2 at an estimated rate of 23 mol co2 s about 0 1 of the global mid ocean ridge mor carbon flux three other mariana arc submarine volcanoes nw rota 1 nikko and daikoku and two volcanoes on the tonga kermadec arc giggenbach and volcano 1 also have vent fields discharging co2 rich gas bubbles the vent fluids at these volcanoes have very high co2 concentrations and elevated c 3he and 13c co2 ratios compared to mor systems indicating a contribution to the carbon flux from subducted marine carbonates and organic material analysis of the co2 concentrations shows that most of the fluids are undersaturated with co2 this deviation from equilibrium would not be expected for pressure release degassing of an ascending fluid saturated with co2 mechanisms to produce a separate co2 rich gas phase at the seafloor require direct injection of magmatic co2 rich gas the ascending co2 rich gas could then partially dissolve into seawater circulating within the volcano edifice without reaching equilibrium alternatively an ascending high temperature co2 rich aqueous fluid could boil to produce a co2 rich gas phase and a co2 depleted liquid these findings indicate that carbon fluxes from submarine arcs may be higher than previously estimated and that experiments to estimate carbon fluxes at submarine arc volcanoes are merited hydrothermal sites such as these with a separate gas phase are valuable natural laboratories for studying the effects of high co2 concentrations on marine ecosystems

syndepositional diagenesis of modern platform carbonates evidence from isotopic and minor element data physical elemental and stable isotopic evidence documents significant syndepositional diagenesis off biogenic carbonate in modern sediment pore water halimeda aragonite and neogoniolithon high mg calcite fragments from sediment cores and experimental substrates were compared with fresh samples to determine the magnitude of minor element sr mg and stable isotopic c and o compositional shifts although no significant shift in bulk sediment mineralogy is apparent experimental substrates and natural biogenic grains exhibit significant diagenetic changes these changes include dissolution textures net loss of mass changes in minor element composition and progressive evolution toward carbon and oxygen isotopic equilibrium with p ore water our results demonstrate that carbonate sediment can undergo rapid syndepositional dissolution and reprecipitation pore waters likely are buffered chemically and isotopically by most abundant carbonate grain types in turn compositions of less abundant carbonate grains may shift toward equilibrium with respect to pore water therefore many components of shelf limestone have compositions controlled by chemically evolved pore waters rather than by seawater from which the biotic carbonate originally precipitated

estimation of glacier runoff and future trends in the yangtze river source region china glacier runoff from the yangtze river source region yrsr china is estimated for the period 1961 2000 using a degree day approach in the investigation area glacier runoff accounts for 11 0 of the total river runoff during the period 1961 2000 in the 1990s its contribution to river runoff rises to 17 0 due to the current rate of glacier decline the impact of glacier runoff on river runoff has recently increased in the source region based on two different climate change scenarios derived from echam5 mpi om future glacier runoff is assessed for the period 2001 50 in all climate change scenarios annual glacier runoff shows a significant increase due to intensified ice melting there is an increase in glacier runoff during spring and early summer yet a significant decrease in late summer this study highlights the current and future impact of glacier runoff on river runoff in the yrsr

zebra dolomitization as a result of focused fluid flow in the rocky mountains fold and thrust belt canada discordant zebra dolomite bodies occur locally in the middle cambrian cathedral and eldon formations of the main ranges of the canadian rocky mountains fold and thrust belt they are characterized by alternating dark grey a and white b bands forming an abba diagenetic cyclicity these bands developed parallel to both bedding and cleavage dark grey a bands consist of fine 300 m non planar crystalline impure dolomite the white b bands are composed of coarse up to several millimetres milky white pure saddle dolomites b1 which are often covered by pore lining zoned dolomite b2 the b phases often possess a saddle shaped morphology in contrast to the replacement origin of the a dolomite the zoned b2 dolomite rims are interpreted as a cement formed in open cavities the b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non carbonate components all the zebra dolomites studied are nearly stoichiometric and are characterized by enriched na and depleted sr concentrations fe and mn concentrations in these dolomites differ depending on the sample locality fluid inclusion data indicate that the dolomites formed from relatively hot th 130 200 c saline 20 23 wt cacl2 eq fluids a diagenetic high temperature origin is also supported by depleted 18o values 20 to 14 vpdb a contribution of 87sr enriched fluids is reflected in the 87sr 86sr values 0 7091 0 7123 zebra dolomite development is explained by focused fluid flow which exploited areas of structural weaknesses e g basin platform rim areas faults etc expulsion of hot basinal brines in a tectonically active regime generated overpressures which explains the development of secondary porosity during zebra dolomitization as well as the intra zebra fracturing at decimetre to micrometre scale

diagenesis and porosity preservation in eocene microporous limestones south florida usa abstract microporous limestones may contain immobile capillary bound irreducible water that is only in diffusional contact with mobile pore waters or in some reservoirs may contain producible hydrocarbons the preservation and distribution of microporosity impact both subsurface fluid flow and solute transport the diagenesis of microporous limestones has received relatively little attention because their very fine grains and cements are not amenable to standard analytical methods the ocala limestone upper eocene and upper avon park formation middle eocene in south florida contain microporous micritic limestones mudstones to packstones that are at an intermediate stage of diagenesis the limestones have been exposed to the active near surface environment but have not yet reached a burial depth sufficient for intense chemical compaction and associated porosity reduction nuclear magnetic resonance nmr logging allowed for the quantification of total porosity pore size distribution and permeability the ocala limestone and avon park formation have different predominant microfacies and porosity size distributions but yet both retain total porosities predominantly between 35 and 37 estimated microporosities range mostly between 12 and 45 the mudstones and wackestones of the ocala limestone have significantly lower permeabilities mostly 3 to 12 md than the wackestones to grainstones of the avon park formation commonly in the 100 to 3000 md range which have more mixed and overall coarser pore sizes computer modeling using carbon and oxygen stable data indicates that the studied microporous limestones underwent only a low degree of chemical diagenetic alteration despite likely experiencing episodes of freshwater flushing associated with post depositional sea level lowstands the ocala limestone and avon park formation limestones illustrate the general concept that total porosity is often largely preserved through early diagenesis although may undergo intra formational redistribution and that confined aquifers are diagenetic quiescent environments

sedimentological and marine eogenetic control on porosity distribution in upper cretaceous carbonate turbidites central albania results of a detailed petrographic and stable isotope study illustrate that sedimentological differences and eogenetic dissolution precipitation processes controlled porosity distribution within carbonate turbidites of the ionian basin central albania based on lithology characteristics and porosity distribution observed in outcrop individual turbidite beds can be subdivided into four distinct intervals i e from base to top a a non porous wackestone floatstone or packstone followed by b porous packstone grainstone that grades into c wackestone and d non porous mudstone with pelagic foraminifera wackestone interval c is characterized by an alternation of porous and non porous laminae changes in turbidity current flow regime controlled the initial presence of matrix micrite giving rise to both matrix and grain supported lithologies within turbidite sequences these are non porous and porous respectively four eogenetic diagenetic processes dissolution cementation neomorphism and compaction acted shortly after deposition and modified primary porosity characteristics and distribution alteration by meteoric water is excluded based on the continuous burial until the oligocene of the studied deep marine carbonates moreover the stable isotope data with values between 2ae1 and 0ae7 for d 18 ov pdb and between 1 and 3 for d 13 cv pdb favour alteration by marine derived pore waters compaction and aggrading neomorphism occurred dominantly in intervals characterized by higher matrix micrite content i e the floatstone base and the wackestone mudstone upper turbidite part framework stabilizing cementation occurred dominantly in the packstone grainstone middle part of the turbidite beds in the latter porous lithologies matrix micrite was not compacted because of the grain fabric and the framework stabilizing cements here neomorphism of micrite into microrhombic euhedral calcite occurred and microporosity was preserved

recent glacier and glacial lake changes and their interactions in the bugyai kangri southeast tibet glaciers in the bugyai kangri are located in a transition zone from southeast tibet where monsoonal temperate glaciers dominate to inner tibet where continental glaciers dominate here we analyze glacier and glacial lake changes in this region using multi year inventories based on landsat images from 1981 2013 results show that the total area of 141 glaciers in the region decreased by 30 44 0 89 km 2 from 198 35 9 54km 2 1980s to 167 93 4 52 km 2 2010s the annual area shrinkage rate 0 48 a 1 is lower than that reported for southeastern tibet but higher than that of inner tibet both the number and total area of glacial lakes increased between 1981 and 2013 among all lakes proglacial lakes contribute most similar to 81 to the expansion the total area of ten proglacial lakes increased by 150 3 13 17 and of these ten lakes the four that expanded most sharply showed increased calving at their upper margins resulting in more rapid retreat of lake terminating glaciers than land terminating glaciers owing to rapid calving several lakes may undergo further growth in the near future increasing the potential risk of glacial lake outburst floods

influences of temperature and mg ca ratio on caco3 precipitates from seawater the mg ca ratio at which the calcium carbonate mineral that has pseudohomogeneously precipitated from seawater changes from calcite to aragonite was experimentally determined as a function of temperature results indicate a dramatic change in the critical mg ca ratio over a relatively small temperature range for example in normal seawater with a mg ca of 5 1 the critical temperature is 6 3 c at a temperature of 25 c however mg ca must be less than 1 4 0 1 for calcite to form these data indicate that paleoclimatic conditions at the time of carbonate deposition must be considered when attempting to make inferences about variation in other factors such as paleo p co 2 p pressure and paleo mg ca ratios that may control carbonate mineral formation by abiotic processes however the inverse relation between inferred global paleoclimatic conditions and the dominant type of caco 3 polymorph being abiotically deposited i e warm conditions and low mg calcite versus cool conditions and aragonite suggest that substantial changes must have taken place in ocean chemistry over phanerozoic time

a revised classification of limestones abstract the most widely used classifications of limestones are now thirty years old and our appreciation of the diagenetic effects on limestone textures is now much greater a revision of the classifications of dunham 1962 and embry and klovan 1971 is offered and new diagenetic categories are proposed the confusing term lime mudstone is replaced by calcimudstone two categories of diagenetic textures are recognized non obliterative and obliterative the former contains limestones which are almost wholly composed of diagenetic cement cementstones and those whose fabric is the result of intergranular pressure solution condensed and fitted grainstones obliterative categories include limestones and dolomites whose original fabric has been destroyed sub categories include sparstones or dolosparstones crystals 10 m in size and microsparstones dolomicrosparstones crystals 4 10 m in size and dolomicrostones crystals m in size many diagenetic processes can produce fabrics which mimic depositional ones and these are reviewed

depletion of 13c in seawater σc02 on modern carbonate platforms significance for the carbon isotopic record of carbonates seawater co2 from modern carbonate platforms bahama banks and florida is depleted in 13c by as much as 4 relative to open ocean water depletion in 13c is caused by isotopically light co2 input from respiration of marine and terrestrial organic matter during water mass residence on the bank as such depletion in 13c is related to changes in water chemistry driven by evaporation freshwater discharge and caco3 withdrawal deviation of modern platform seawater 13c values away from those of surface seawater suggests that 13c values of ancient cratonic carbonate must be cautiously interpreted initial depositional environment as well as alteration during diagenesis must be considered in extracting valid secular trends for oceanic 13c variation

plate tectonic evolution of the mediterranean middle east region abstract an interpretive model for the mesozoic cenozoic plate tectonic evolution of the mediterranean and adjacent areas is illustrated by a series of paleoposition maps at selected intervals between the late triassic and recent this interval witnessed an important period of tensional development during the triassic and jurassic that fragmented pangea after its late paleozoic consolidation a number of oceanic areas evolved through jurassic time all of which have since been consumed during the alpine orogeny during the cretaceous and tertiary sea floor spreading geometry in the north and south atlantic resulted in convergence between africa and eurasia that controlled the evolution of the mediterranean and adjacent middle east areas from the late mesozoic to recent the interpretation departs from several previous ones in the following respects 1 1 the eastern mediterranean and adjacent middle east area are interpreted to have developed as two seaways with an intervening continental sliver derived from africa that now comprises central turkey and west iran these seaways persisted from the late triassic to late cretaceous by which time they were largely consumed by northward subduction 2 2 spreading that produced the present eastern mediterranean sea developed during the late cretaceous driving the tripolitza eratosthenes iskenderun continental fragments northward from africa to collision with central turkey as the preceding southern arm of the mesozoic tethys sea floor was entirely consumed initial block faulting in this zone occurred during the jurassic and early cretaceous but without subsidence reaching clearly bathyal depths until the cenomanian turonian this differs from the timing of events in the ionian sequence of the pindic nappe of crete which shows a change from shallow carbonate shelf in the triassic to deep basin in the liassic to the north of equivalent platform facies of the tripolitza nappe 3 3 moesia and rhodope are concluded to have been a single plate until a rifting event that started during the late jurassic the balkan mountains are interpreted to represent an alpine inversion of this mesozoic rift system that extended west from the black sea basin 4 4 the eastern carpathian microcontinental sliver is concluded as continuing southward as the serbo macedonian massif that separates rhodope from the vardar zone rather than as rhodope itself 5 5 the scutari pec lineament is considered as representing a major discontinuity between the apulia pannonian plate and adjacent greece and turkey ophiolites to the northwest of this lineament originated in a single oceanic area the vardar zone ophiolites to the southeast of this lineament evolved from two oceanic areas those of interior greece and northern anatolia and the associated ankara melange relating to the vardar zone the former north arm of tethys and the pindos southern anatolia zagros oman ophiolites relating to a former south arm of mesozoic tethys 6 6 based on the history of development of various elements of the alpine system there is a strong suggestion that important dextral movement took place along a major strike slip fault system reaching from the middle east to the central alps between late cretaceous and middle eocene times

sedimentary carbonates through phanerozoic time plate tectonic processes play a critical role in the origin and distribution of sedimentary carbonates through phanerozoic time the phanerozoic age distribution of sedimentary properties like calcite dolomite ratio inferred ooid and cement mineralogy and survival rate of continental carbonates is cyclic the cycles appear to be coupled to plate tectonic processes that give rise to global sea level change and changes in the properties of the ocean atmosphere system first order changes in sea level are driven by the accretion of mid ocean ridges high accretion rate high sea level low accretion rate low sea level although correlations between sea level and sedimentary carbonate properties are not strong high sea level over an extended period of time appears to be correlated with low calcite dolomite ratios lack of inferred aragonite ooids and cements and maxima in the survival rate of continental carbonates the opposite is true for extended periods of low mid ocean ridge accretion rates and global sea levels the lack of strong correlations may reflect an insufficient data base and the possibility of lags between sea level change and change in carbonate properties furthermore the survival rate of continental carbonates appears to be affected by differential cycling and therefore may not be directly related to accumulation rate it appears that the environmental conditions for early dolomitization and calcite ooid and cement formation are best met during extended times of high sea level when atmospheric co2 levels are high and the saturation state of seawater with respect to carbonate minerals relatively low during low sea levels early dolomitization is less favored and aragonite precipitates are more abundant because of low atmospheric co2 levels and enhanced seawater carbonate saturation states differential cycling has modified the phanerozoic sedimentary carbonate mass age distribution because of erosion of younger units within continental carbonate cycles it may be difficult to derive an unequivocal record of the partitioning of carbonate between the deep sea and shallow water realms of deposition during the phanerozoic this difficulty must be considered in further quantification of geochemical models describing the geologic history of atmospheric co2 and climate change

tectonic forcings of maastrichtian ocean climate evolution a global compilation of deep sea isotopic records suggests that maastrichtian ocean climate evolution tvas tectonically driven during the early maastrichtian the atlantic intermediate deep ocean was isolated from the pacific indian and southern oceans deep water formed in the high latitude north atlantic and north pacific at the early late maastrichtian boundary a major reorganization of oceanic circulation patterns occurred resulting in the development of a thermohaline circulation system similar to that of the modem oceans a combination of isotopic and plate kinematic data suggests that this event was triggered by the final breaching of tectonic sills in the south atlantic and the initiation of north south flow of intermediate and deep water in the atlantic the onset of laramide tectonism during the mid maastrichtian led to the concurrent draining of major epicontinental seaways together these events caused cooling increased latitudinal temperature gradients increased ventilation of the deep ocean and affected a range of marine biota

microspar development during early marine burial diagenesis a comparison of pliocene carbonates from the bahamas with silurian limestones from gotland sweden comparison of ultrastructures in pliocene periplatform carbonates from the bahamas with silurian limestones from gotland sweden reveals that despite the differences in primary sediment composition and age they reflect a similar mechanism of lithification in both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis neither significant compression nor meteoric influence are necessary for the formation of calcite microspar a model is proposed for the process of microsparitic cementation of fine grained aragonite needle muds comprising four stages 1 unconsolidated aragonite dominated carbonate mud 2 precipitation of microspar that engulfs aragonite needles 3 dissolution of aragonite resulting in pitted surfaces of the microspar crystals and 4 slight recrystallization our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite

contribution to the understanding of the ionian basin sedimentary evolution along the eastern edge of apulia during the late cretaceous in albania abstract integrated in the peri adriatic domain the ionian basin extended along a nw se direction during the late cretaceous limited on its sides by the apulian and the kruja platforms the basinal slope succession was studied in seven outcrops exposed in the albanian fold and thrust belt sedimentological investigations supported by bio and chronostratigraphy were performed on calcareous upper cretaceous hemipelagites gravity flow deposits and slumps the western part of the basin was studied revealing a strong influence of the apulian margin alternatively shedding sediment basinward by means of a tectonically controlled edge the late albian to cenomanian period is characterized by the settling of muddy debrites along the margin a deep basinal environment characterizes this period which prolongs until the santonian with no significant influx of the platform basinward this sedimentary setting abruptly changed at the end of the santonian with an important influx derived from both platforms coarsening and thickening upward sequences show a progressive increase in sediment shedding during the campanian the late campanian early maastrichtian period points out a major change on the resedimentation processes with the settling of several slumped units reworking thick sediment packages the latter can be traced along the apulian margin testifying of instabilities along the edge of apulia

observed changes of cryosphere in china over the second half of the 20th century an overview during approximately the past five decades changes in snow cover mountain glaciers frozen ground including permafrost sea ice and river ice have been observed in china however most data were published in chinese and thus unknown to the international communities here we review these published results to show an overview of cryospheric changes in china for the last 50 years long term variability of snow cover over the qinghai xizang tibetan plateau qxp is characterized by large interannual variability superimposed on a continuously increasing trend glacier changes in western china vary remarkably in different regions although in most mountains the glaciers display a retreating trend 80 or have even vanished some glaciers 20 are still advancing frozen ground including permafrost has experienced a rapid decay since the 1980s and these changes are occurring both in the qxp and in the cold regions of north china sea ice areas in the bohai and north yellow seas have been shrinking since the 1970s interannual variations possibly relate to the solar cyles and sea ice extent extremes relate to el nino southern oscillation enso events the freeze up and break up dates of river ice in north china in the 1990s are on average 1 6 days later and 1 3 days earlier respectively than the 1950s 1990 mean frozen duration and the maximum thickness of river ice are respectively 4 10 days shorter and 0 06 0 21 cm thinner in the 1990s than the average cryosphere the cryosphere in china is mainly located in the qinghai xizang tibetan plateau hereafter qxp the eastern tien shan the altai shan the east pamirs and northeast china the total number of glaciers in china is 46 298 with a total area of 59 406 km 2 and an ice volume of 5590 km 3 the permafrost and the seasonally frozen ground sfg cover an area of 1 49 10 6 and 5 28 10 6 km 2 accounting for 11 5 and 55 of chinese land territory respectively the snow covered area in china is around 9 0 10 6 km 2 and of this an area over 4 8 10 6 km 2 consists of unstable snow cover duration 60 days is mainly located in the qxp north xinjiang including the tien shan and the inner mongolia northeast china hereafter im nec regions the mean snow cover areas of these three regions are 2 3 10 6 0 5 10 6 and 1 4 10 6 km 2 respectively seasonal sea ice forms in the bohai sea and in the northern yellow sea of china sea ice forms in mid to late november reaches its

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

carbonate turbidite sequences deposited in rift basins of the jurassic tethys ocean eastern alps switzerland syn rift sediments in basins formed along the future southern continental margin of the jurassic tethys ocean comprise in the eastern alps of switzerland up to 500 m thick carbonate turbidite sequences interbedded with bioturbated marls and limestones in the fault bounded troughs no submarine fans developed in contrast the fault scarps acted as a line source and the asymmetric geometry as well as the evolution of the basin determined the distribution of redeposited carbonates the most abundant redeposits are bio and lithoclastic grainstones and packstones with sedimentary structures indicating a wide range of transport mechanisms from grain flow to high and low density turbidity currents huge chaotic megabreccias record catastrophic depositional events their main detrital components are upper triassic shallow water carbonates and skeletal debris from nearby submarine highs after an event of extensional tectonism sedimentary prisms accumulated in the basins along the faults each prism is wedge shaped with a horizontal upper boundary and consists of a thinning and fining upward megacycle within each megacycle six facies associations are distinguished at the base of the fault scarp an association of breccias was first deposited by submarine rockfall and rockfall avalanches a narrow approximately 4000 m wide depression along the fault was subsequently filled by the megabreccia association in which huge megabreccias interfinger with thin bedded turbidites and hemipelagic limestones the thick bedded turbidite association covered the megabreccias or formed farther basinward the base of the sedimentary column within the thick bedded turbidites thinning and fining upward cycles are common the overlying thin bedded turbidite association shows nearly no cyclicity and the monotonous sequence of fine grained calciturbidites covers most of the basin area with continuous filling and diminishing sediment supply a basin plain association developed comprising fine grained and thin bedded turbidites intercalated with bioturbated marls and limestones on the gentle slopes opposite the fault escarpment redeposited beds are scarce and marl limestone alternations as well as weakly nodular limestones prevail

glacier change and glacier runoff variation in the tuotuo river basin the source region of yangtze river in western china glaciers in the tuotuo river basin western china have been monitored in recent decades by applying topographical maps and high resolution satellite images results indicate that most of glaciers in the tuotuo river basin have retreated in the period from 1968 1971 to 2001 2002 and their shrinkage area is 3 2 of the total area in the late 1960s to assess the influence of glacier runoff on river runoff a modified degree day model including potential clear sky direct solar radiation has been applied to the glaciated regions of the river basin over the period 1961 2004 it was found that glacier runoff has increased in the last 44 years especially in the 1990s when a two thirds increase in river runoff was derived from the increase in glacier runoff caused by loss of ice mass in the entire tuotuo river basin

palaeoecological evidence for early aragonite dissolution in ancient calcite seas it has been proposed that shallow carbonate seas of upper ordovician and jurassic ages precipitated calcite as the primary calcium carbonate phase1 3 unlike such settings today it is expected that such seas were undersaturated with respect to the more soluble aragonite so that aragonitic invertebrate skeletons would have tended to dissolve here we describe examples in which this seems to have been the case our evidence consists of submarine cemented horizons in which aragonite fossils have been dissolved out to leave open moulds the walls of the moulds are encrusted by contemporaneous organisms confirming the early timing of the aragonite dissolution

isotopic signature of burial diagenesis and primary lithological contrasts in periplatform carbonates miocene great bahama bank the stable isotope geochemistry of miocene sediments from the leeward margin of the great bahama bank was examined to investigate burial diagenetic processes in periplatform carbonates data indicate that in addition to differences in bulk proportions of neritic and pelagic carbonate along the slope rhythmic variation in primary carbonate content has controlled patterns of burial diagenesis and associated geochemical signatures throughout much of the succession examined the present study focuses on ocean drilling program sites 1006 and 1007 the most distal of five sites drilled from marginal to deep basin environments during leg 166 these miocene sections are characterized by their cyclic appearance manifest as decimeter to meter scale alternations between light colored ooze chalk limestone and dark colored marl marlstone the section at site 1006 contains a high proportion of pelagic carbonate and is unlithified to a subbottom depth of 675 m fluctuations in 18 o and 13 c values at this site are independent of lithological variation and reflect primary conditions at site 1007 located at the toe of slope and composed of a mixture of bank derived and pelagic carbonate limestones are densely cemented show little evidence of compaction and have 18 o values up to 2 higher than coeval sediments at site 1006 marlstones at site 1007 are poorly cemented exhibit an increase in compaction related features with depth and have lower and more variable 18 o values that are similar to those of coeval sediments at site 1006 isotopic and petrographic characteristics of limestone interbeds result from cement precipitation from cold sea water during the first 100 m of burial higher proportions of insoluble materials and pelagic carbonate seem to have inhibited diagenetic alteration in adjacent marlstones in spite of significant compaction and pressure solution during burial original isoto pic compositions appear to be best preserved in these intervals at site 1007 the documented contrasts in petrographic and isotopic patterns illustrate the role of primary sediment composition in controlling lithification processes in periplatform carbonates and stress the importance of consid ering such factors when interpreting geochemical data from ancient shelf and slope limestones

micro rhombic calcite and microporosity in limestones a geochemical study of the lower cretaceous thamama group u a e abstract euhedral micro rhombic calcite forms a microporosity network in limestones of the lower cretaceous thamama group u a e isotopic and trace element data indicate that micro rhomb formation was a two step process associated with diagenesis in meteoric waters the micro rhombic calcite and the micropores are both products of the second event sr fe mn and mg contents of the micro rhombs are all relatively low ranging from 108 to 310 ppm 34 to 308 ppm 3 to 32 ppm and 0 42 to 0 68 mole respectively the low sr and mg contents indicate extensive flushing of these constituents from the rock the low fe and mn contents are probably inherited from the original sediments and indicate the lack of any fe or mn in the pore fluids during micro rhomb formation the 13c of the micro rhombs 3 1 to 4 5 pdm are also primary unaltered by diagenesis the 13o of the micro rhombs 4 5 to 6 0 pdb reflect alteration by mateoric waters a large number of pore volumes and an open water buffered system would be necessary to flush sr and mg yet decreasing 18o with increasing porosity indicates that 18o values in non porous intervals are partially rock buffered two diagenetic events are thus implicated the first flushing sr and mg and lowering 18o in all rocks and the second event actually forming the micro rhombs and further altering 18o as a function of porosity the first diagenetic event was most likely mineralogical stabilization in an unconfined meteoric aquifer immediately after shuaiba deposition if mineralogical stabilization was completed in the first event then calcite to calcite recrystallization is implicated for the second event the second event may have occurred in the unconfined meteoric aquifer or it may have occurred in a confined meteoric aquifer during the early late cretaceous

low mg calcite marine cement in cretaceous turbidites origin spatial distribution and relationship to seawater chemistry lower cretaceous hauterivian bioclastic sandstone turbidites in the scapa member north sea basin were extensively cemented by low mg calcite spars initially as rim cements and subsequently as concretions five petrographically distinct cement stages form a consistent paragenetic sequence across the scapa field the dominant and pervasive second cement stage accounts for the majority of concretions and is the focus of this study stable isotope characterization of the cement is hampered by the presence of calcitic bioclasts and of later cements in sponge spicule moulds throughout the concretions nevertheless trends from whole rock data augmented by cement separates from synlithification fractures indicate an early calcite 18o value of 0 5 to 1 5 pdb as such the calcite probably precipitated from marine pore fluids shortly after turbidite deposition carbon isotopes 13c 0 to 2 pdb and petrographic data indicate that calcite formed as a consequence of bioclastic aragonite dissolution textural integrity of calcitic nannoplankton in the sandstones demonstrates that pore fluids remained at or above calcite saturation as expected for a mineral controlled transformation electron probe microanalyses demonstrate that early calcite cement contains 2 mol mgco3 despite its marine parentage production of this cement is ascribed to a combination of an elevated aragonite saturation depth and a lowered marine mg2 ca2 ratio in early cretaceous calcite seas relative to modern oceans scapa cement compositions concur with published models in suggesting that hauterivian ocean water had a mg2 ca2 ratio of 1 this is also supported by consideration of the spatial distribution of early calcite cement in terms of concretion growth kinetics in contrast to the dominant early cement late stage ferroan 18o depleted calcites were sourced outwith the scapa member and precipitated after 1 2 km of burial our results emphasize that bioclast dissolution and low mg calcite cementation in sandstone reservoirs should not automatically be regarded as evidence for uplift and meteoric diagenesis

glacier mass balance and length variation observed in china during the periods 1959 2015 and 1930 2014 abstract the importance of glaciers for providing runoff is reflected in the extensive glacier measurement record for china in this paper we summarized the mass balance and front variation data of glaciers in china that have long term records mass balance has been measured for 22 glaciers length or front position records exist for 96 glaciers we found that the mean rate of glacial mass balance decreased by 0 015 m w e water equivalent per year during the period 1959 2015 which was lower than that for glaciers globally 0 013 m w e per year it was indicated that the rate of glacial melting mass loss increased in china which was higher than that in glaciers worldwide however glacial frontal positions varied among mountains in time and space glaciers in the karakoram mountains mean advanced 379 m during the 1968 2000 period while glaciers in the pamir mountains remained relatively stable from the 1960s through the 2000s i e retreated 28 m glaciers in hengduan mountains retreated farthest 1250 m maximum from 1930 to 2005

glacier surface velocities in alpine terrain from optical satellite imagery accuracy improvement and quality assessment the worldwide retreat of mountain glaciers has important consequences for the water food and power supply of large and densely populated areas in south and central asia successful mitigation of the hydrological impacts on societies as well as assessing glacier related hazards require large scale monitoring of glacier dynamics however detailed glaciological data from the asian highlands are lacking due to its size and difficult accessibility we have applied a novel technique for precise orthorectification co registration and sub pixel correlation of advanced spaceborne thermal emission and reflection radiometer aster satellite imagery to derive surface velocities of himalayan glaciers our approach allows for the correction of offsets due to attitude effects and sensor distortions as well as elevation errors if a digital elevation model dem from the shuttle radar topography mission srtm was used for orthorectification after post processing the error on the displacements is on the order of 2 4 m per correlation translated into annual velocities this error is reduced increased when the correlated images are more less than a year apart through application of a filtering procedure and several quality tests the consistency of the results is validated to provide confidence in the remotely sensed velocity measurements despite the lack of ground control this novel approach allows fast easy and economically viable acquisition of detailed glaciological data in areas of difficult access and provides a means for large scale monitoring of glaciers in high mountainous terrain

missing molluscs field testing taphonomic loss in the mesozoic through early large scale aragonite dissolution as a field test for cherns and wright9s previously published hypothesis based on paleozoic faunas that the paucity of certain molluscan groups in the fossil record may be largely a taphonomic not ecologic effect a typical mesozoic molluscan dominated fauna is compared with its early silicified lagerstatten equivalent from a similar depositional setting a lower jurassic offshore carbonate ramp facies in south wales comprises alternating thin limestones and organic rich shales the former are largely diagenetic and carry marine isotopic signatures their typical fauna is mainly well preserved calcitic and bimineralic calcite aragonite epifaunal and semiinfaunal bivalves evidence of aragonitic shells is normally restricted to molds common in inner ramp settings in high energy skeletal grainstones but mostly poorly preserved and restricted to deep burrowing bivalves in offshore deposits however locally early silicification in offshore facies has preserved much more diverse faunas with abundant formerly aragonitic molluscs including many more infaunal burrowers it appears that major aragonite dissolution normally distorted both apparent diversity 65 decrease in bivalve diversity and the trophic structure of the offshore facies providing aragonite that probably sourced the diagenetic carbonates we suggest that aragonitic shells were selectively dissolved in the upper sediment column in lower energy settings where high organic contents favored microbial decay and acidity such early dissolution was absent from the higher energy facies that originally had low organic contents taphonomic loss through early skeletal aragonite dissolution was an equally important process in mesozoic offshore shelf environments and although still leaving depleted molluscan dominated faunas resulted in a massive distortion of diversity

paragenesis of cretaceous to eocene carbonate reservoirs in the ionian fold and thrust belt albania relation between tectonism and fluid flow this paper examines the diagenetic history of dual i e matrix and fracture porosity reservoir lithologies in cretaceous to eocene carbonate turbidites of the ionian fold and thrust belt close to the oil producing centre of fier ballsh central albania the first major diagenetic event controlling reservoir quality was early cementation by isopachous and syntaxial low mg calcite these cements formed primarily around crinoid and rudist fragments which acted as nucleation sites in sediments in which these bioclasts are the major rock constituent this cement can make up 30 of the rock volume resulting in low effective porosity in strata in which these bioclasts are mixed with reworkedmicrite isopachous syntaxial cements stabilized the framework and matrixporosity is around 15 the volumetric importance of these cements their optical and luminescence character distribution and dull orange luminescence and stable isotopic signal 18o and 13c averaging respectively 0 5 vpdb and 2 vpdb all support a marine phreatic origin within these turbidites and debris flows several generations of fractures alternated with episodes of cementation a detailed reconstruction of this history was based on cross cutting relationships of fractures and compactional and layer parallel shortening lps stylolites the prefolding calcite veins possess orange cathodoluminescence similar to that of the host rock their stable isotope signatures 18o of 3 86 to 0 85 vpdb and 13c of 0 14 to 2 98 vpdb support a closed diagenetic rock buffered system a similar closed system accounts for the selectively reopened and subsequently calcite cemented lps stylolites 18o of 1 81 to 1 14 vpdb and 13c of 1 52 to 2 56 vpdb within the prefolding veins brecciated host rock fragments and complex textures such as crack and seal features resulted from hydraulic fracturing they reflect expulsion of overpressured fluids within the footwall of the frontal thrusts after folding and thrust sheet emplacement some calcite veins are still rock buffered 18o of 0 96 to 0 2 vpdb and 13c of 0 79 to 1 37 vpdb whereas others reflect external i e extraformational and thus large scale fluid fluxes some of these veins are linked to basement derived fluid circulation or originated from fluid flow along evaporitic decollement horizons 18o around 3 0 vpdb and 13c around 1 5 vpdb others are related to the maturation of hydrocarbons in the system 18o around 7 1 vpdb and 13c around 9 3 vpdb an open joint system reflecting an extensional stress regime developed during or after the final folding stage this joint system enhanced vertical connectivity this open joint network can be explained by the high palaeotopographical position and the folding of the reservoir analogue within the deformational front the joint system is pre burdigalian in age based upon a dated karstified discordance contact sediment filled karst cavity development is linked to meteoric water infiltration during emergence of some of the structures despite its sediment fill the karst network is locally an important contributor to reservoir matrix porosity in otherwise tight lithologies development of secondary porosity along bed parallel and bed perpendicular i e layer parallel shortening stylolites is interpreted as a late stage diagenetic event associated with migration of acidic fluids during hydrocarbon maturation development of porosity along the lps system enhanced the vertical reservoir connectivity

geometry and petrophysical parameters of a calcarenitic turbidite lobe barremian aptian pas de la cluse france abstract several bioclastic resedimentation systems late barremian to early aptian in age outcrop in southeastern france the upslope portion of a calcarenitic turbidite lobe outcrops as a cliff 2 3 km wide and up to 45 m high oriented roughly perpendicular to the direction of palaeoflow it has been studied through 31 sections the studied body is point sourced and corresponds to a channel lobe transition located at the toe of slope of a urgonian carbonate platform on the western edge of the vocontian trough french subalpine chains the internal geometry of the lobe is the result of repeated erosion and filling of channels creating well defined stacked units filling phases result in lobe shaped morphology units evolve from base to top in an ordered way first the sediments exported from the platform and deposited in the basin are represented by decimetre thick sheet like and fine grained bouma a e and ab e sequences in this first unit erosion is limited and represented by shallow and symmetrical channels this initial phase of deposition corresponds to the formation of a lobe with a positive morphology the next phase of system development is more erosional and this is dominated by migrating sinuous channels several metres deep filled with coarse grained poorly graded turbidites these channels are first filled through lateral accretion and then sediment spills over to create a sub lobe the mixture of channel and lobe features could be considered as a carbonate equivalent of the channel levee system of siliciclastic deposits finally the system ends with the deposition of a flat based unit this unit extends for more than 2 km and is composed of the southwards lateral accretion of hundreds of metres wide sequences each composed of a debris flow deposit capped by a coarse grained calcarenite bed these sigmoidal bodies could be the ultimate forms of a spreading out phenomenon of the lobe overall the pas de la cluse system is a coarsening upward body as the grain size is related to the nature of the material this coarsening upward implies either an evolution in the nature of the carbonate material produced on the platform from grainy to bioconstructed a displacement of the source sediment from inner platform to margin or a displacement of the channel head through time from distal to proximal the upward evolution from classic turbidites to debris flow deposits can be explained either by the way the platform facies evolved with time in a depositional sequence or through retrogressive erosion by successive slope failures that cut deeper and deeper into the platform slope although its present day porosity is low the size of the system and the fact that it is encased in marls make it an interesting outcrop analogue for hydrocarbon exploration

glacier changes during the past century in the gangrigabu mountains southeast qinghai xizang tibetan plateau china the present research focuses on glacier changes in the southeast of the qinghai xizang tibetan plateau where most of the temperate glaciers in china are located our results show that the 102 measured glaciers in the region have all retreated between 1915 and 1980 with total area and volume decreases of 47 9 km 2 and 6 95 km 3 respectively the extrapolated mass loss of all glaciers in the gangrigabu mountains amounted to 27 km 3 9 8 of the ice mass in 1915 between 1980 and 2001 glaciers in the region have also experienced a general retreat however up to 40 of the glaciers were advancing our analysis demonstrates that precipitation in the studied area has increased substantially since the mid 1980s this precipitation increase is likely to bring about a positive mass balance for glaciers in the region so that the retreat of retreating glaciers might slow down or even turn into advance considering the sensitivity of the temperate glaciers in the region and the uncertainty in climate projections more attention must be paid to glacier changes in the southeast tibetan plateau region

facies variation diagenesis and exploration potential of the cretaceous rudist bearing carbonates of the arabian gulf the cretaceous rudist bearing carbonates of the arabian gulf region are proven exploration targets for hydrocarbons and form the reservoirs of a number of giant fields including bu hasa fateh fahud idd el shargi rumaila shaybah and shah rudist buildups occur in three principal formations 1 aptian shuaiba 2 cenomanian mishrif and 3 maastrichtian simsima a regional subaerial unconformity marks the upper boundary of each of these formations associated with the rudists that dominate the shuaiba formation are calcareous algal crusts foraminifera and echinoid plates which accumulated in mudstone packstone and carbonate sands these rudists are mainly caprinids with a lesser number of caprotinids monopleurids and requienids deposited in a normal marine shallow shelf setting the mishrif formation contains mollusk fragments bioclastic packstones to grainstones miliolid and nonrudist bivalves in muddy limestones and rudist mainly radiolitids and caprinids conglomeratic floatstones with fragmented rudists mixed with wackestone lithoclasts the mishrif sediments accumulated as a progradational low energy leeward margin formed in marginal slope shoal backshoal and lagoonal settings the simsima formation consists of bioclastic grainstone to packstone and dolomitic lime mudstones to wackestone these are rich in bioclastic grains loftusia rudist and rudist debris coral and foraminifera deposited on a restricted to semirestricted shallow marine shelf that was exposed to moderate energy conditions the excellent reservoir porosity and permeability of the rudist deposits and their associated sediments are the products of primary and secondary diagenesis freshwater leaching during post aptian post cenomanian and post maastrichtian erosion enhanced the secondary moldic porosity fracturing locally improved porosity and permeability other porosity types that occur include interparticle intraparticle vuggy growth framework shelter intercrystalline and karstic because of their favorable depositional and postdepositional conditions the cretaceous succession of rudists in this region contains many giant oil fields

glacier changes since the little ice age maximum in the western qilian shan northwest china and consequences of glacier runoff for water supply based on aerial photographs topographical maps and the landsat 5 imidge data we have analyzed fluctuations of glaciers in the western qilian shan northwest china from the little ice age lia to 1990 the areas and volumes of glaciers in the whole considered region decreased 15 and 18 respectively from the lia maximum to 1956 this trend of glacier shrinkage continued and accelerated between 1956 and 1990 these latest decreases in area and volume were about 10 in 34 years the recent shrinkage may be due either to a combination of higher temperatures and lower precipitation during the period 1956 66 or to continuous warming in the high glacicrized mountains from 1956 to 1990 as a consequence glacier runoff from ice wastage between 1956 and 1990 has increased river runoff by 6 2 km 3 in the four river basins under consideration besides the equilibrium line altitude ela rise estimated from the mean terminus retreat of small glaciers 1 km long is 46 m which corresponds to a 0 3 c increase of mean temperatures in warm seasons from the lia to the 1950s

late cretaceous campanian carbon isotope events sea level change and correlation of the tethyan and boreal realms abstract carbon stable isotope stratigraphy provides unique insights into environmental change during the campanian the longest 83 5 71 3 ma but least well understood stage of the late cretaceous a new carbon isotope 13c profile for a 500 m thick campanian basal maastrichtian tethyan pelagic hemipelagic section near el kef northern tunisia is calibrated using data from a biostratigraphically well constrained succession at kalaat senan the general shapes of the tunisian 13c reference curve and published tethyan 13c profiles from elles tunisia and bidart sw france and a boreal curve for the trunch borehole eastern england are remarkably similar in all three areas a positive carbon isotope event of 0 2 13c in the mid campanian dated at 78 7 ma and a negative excursion of 0 4 in the upper campanian at 74 8 ma can be correlated between tunisia and england a positive excursion of 0 3 at 83 7 ma spans the santonian campanian boundary these isotope events enable precise inter regional correlations that are consistent with published nannofossil data review of campanian sea level data from north africa the middle east and northern europe indicates that major shifts in 13c profiles coincide with changes in eustatic sea level relatively stable 13c values in the lower campanian and their long term fall through the upper campanian reflect high and then falling eustatic sea levels and increased carbonate production short term 600 kyr positive excursions record greater organic productivity and or organic matter preservation and decreased carbonate fluxes during periods of rapid sea level rise and the drowning of carbonate platforms excursions were terminated by falling nutrient supply and increased carbonate deposition associated with epicontinental sea expansion and renewed carbonate platform growth during the late transgression and highstand negative excursions are linked principally to reworking of marine and terrestrial organic matter during rapid sea level fall carbon isotope stratigraphy is a powerful tool for correlation which can be used to test the validity of campanian global biostratigraphic frameworks and improve our understanding of the nature and timing of late cretaceous sea level change

oxygen and carbon isotope compositions of upper cretaceous chalk from the danish sub basin and the north sea central graben the oxygen and carbon isotopic compositions of upper cretaceous chalk have been studied from a large number of outcrops and boreholes in the danish sub basin and the north sea central graben the carbon isotopic compositions vary from 0 50 o to 3 00 o 13c which correspond to the expected carbon isotopic composition of carbonate precipitated from normal sea water the oxygen isotopic compositions of samples from outcrops and near surface drilled sections fall in the range from 0 50 o to 2 00 o 18o which is close to the expected values for carbonate produced by coccoliths in the late cretaceous sea a geographic distribution exists in the danish sub basin showing relatively heavy oxygen isotope values in the centre of the basin and slightly more negative values in the eastern part of the basin primarily the phenomenon is thought to reflect minor variations in the oceanographic parameters in the late cretaceous sea the deep subsurface sections represent a depth interval of 0 3100 m mechanical compaction in the uppermost part of the sequences apparently has no influence on the isotopic composition chemical compaction dominates at greater depth leading to temperature induced isotopic re equilibration in the water rock system in these sequences the oxygen isotope values range from 1 50 o to 7 50 o 18o and are significantly correlated with depth of burial cementation and porosity the data indicate that pressure dissolution recrystallization reprecipitation and ion exchange between solid carbonate phase and pore water are all actively involved in the oxygen isotope re equilibration process this process is believed to take place in a diagenetically closed system and is tentatively divided into two phases 1 an early diagenetic phase which takes place at porosities down to approximately 20 in which the chalk possesses a pore water controlled isotopic re equilibration system and 2 a late diagenetic phase at porosities below 20 in which the re equilibration process increasingly becomes influenced by the rock introduced isotopic change in the composition of the formation water

depositional sequences diagenesis and structural control of the albian to turonian carbonate platform systems in coastal fars sw iran abstract this study covers a 300 km long ne sw oriented transect including five outcrop sections and provides new biostratigraphic data and a sequence stratigraphic interpretation of the albian cenomanian and turonian sediments kazhdumi and sarvak formations present in coastal fars sw iran two different carbonate depositional systems are distinguished one for the albian and one for the cenomanian turonian during the albian eustatic control was the dominant factor influencing sedimentation while during the cenomanian and turonian large and small scale tectonics were dominant this resulted in significant thickness variations and local diagenetic overprint of the sequence boundaries regional correlations were established constrained by ammonite data as well as sedimentological and sequence stratigraphic considerations in the albian interval including the kazhdumi formation and re dated mauddud member three 3rd order sequences have been distinguished the depositional system consists of muddy carbonate ramps rich in orbitolinid benthic foraminifers which laterally interfinger with green marls albian deposits are present throughout the area and vary in thickness from 100 to 160 m subaerial exposure has only been observed on top of the albian 3 sequence top mauddud member in the upper part of the succession which is of cenomanian turonian age the depositional system changed to rudist rimmed carbonate platforms surrounding local organic rich intra shelf basins the thickness in this interval varies greatly from 0 to 300 m which was controlled by both large scale qatar fars high and local scale salt domes tectonic processes in this tectonically active setting three cenomanian and one turonian 3rd order sequences have been distinguished several sequence boundaries show evidences for long lasted subaerial exposures up to 13 ma with the local preservation of soil sequences and continental deposits the expression of these exposures varies laterally considerably and macroscopic evidences are sometimes lacking petrographic and c o stable isotope investigations supplement classic sedimentology to reveal the record of these exposures

rapid burial diagenesis of deep water carbonates exuma sound bahamas well lithified deep water periplatform limestones of late miocene age occur at subsurface depths from 113 m to total depth of 283 m at ocean drilling program odp site 632 in exuma sound bahamas this occurrence marked by a dramatic increase in compressional wave velocities up to 5 0 km s represents the most rapid transformation of ooze to limestone yet discovered in either periplatform or open ocean settings the burial diagenetic pathway is similar to those for meteoric and deep burial diagenetic environments aragonite dissolves magnesian calcites exsolve or dissolve low mg calcite precipitates as cement and secondary moldic vuggy porosity develops stable isotope ratios suggest precipitation of low mg calcite from cold marine derived pore waters accelerated diagenesis is a response to the influx of large quantities up to 80 of bank derived metastable carbonates and rapid burial via high accumulation rates up to 210 m m y our findings 1 document carbonate mineral stabilization and lithification in a seawater mediated shallow burial diagenetic environment 2 highlight the very high diagenetic potential of periplatform carbonates and 3 call into question the use of seismic velocities as support for the bahama megabank hypothesis

signature and hydrologic consequences of climate change within the upper middle brahmaputra basin a prevailing perception is that the glaciers and perennial snow and ice covered areas scap or in the himalayan region are fast contracting however systematic studies providing the quantitative estimates of scap as a function of time within individual river basins are lacking the importance of meltwater in river flows varies greatly from one river basin to another yet the actual estimates of those contributions are largely unknown this study bridges such knowledge gaps for the upper middle brahmaputra basin by using best available digital cartographic and remotely sensed snow cover data we find that when the entire basin is considered scap decreased from 7637 764 in 1980 to 4298 1422 km2 in 1992 however it has increased to 7160 2248 km2 in 2000 from 2000 to 2010 the scap has remained nearly constant around a mean of 10 052 1468 km2 the same trend is observed within individual physiographic zones of the basin such increase in scap is due to the increase in the precipitation over the middle brahmaputra basin and the nyainquentanglha mountains as observed in station records the incursion of moist air through the brahmaputra valley to the higher elevations within the nyainquentanglha mountains causes snowfall during pre monsoonal and post monsoonal seasons and an expansion of the scap glacial expansions in the nyainquentanglha mountains have also been observed in other recent studies in addition to the increase in precipitation and scap another manifestation of climate change observed in this basin is the increasing temperature with a mean annual trend of 0 28 c decade the hydrologic consequences of the observed effects of climate change are expected to be an insignificant change in streamflows in the watersheds drained by the upper brahmaputra river but a perceptible increase in river discharges in the watersheds drained by the middle brahmaputra river and its tributaries particularly within the upper and lower catchments of the middle brahmaputra basin copyright 2012 john wiley sons ltd

fluid flow evolution in the albanide fold thrust belt insights from hydrogen and oxygen isotope ratios of fluid inclusions tectonic forces generated during thrust emplacement along active margins may drive complex fluid flow patterns in fold thrust belts and foreland basins isotope data 2h and 18o of fluid inclusions hosted in calcite vein cements are used to reconstruct regional fluid migration pathways in the albanide fold thrust system the calcite veins used in this study developed in a sequence of naturally fractured cretaceous eocene carbonate rocks as a result of episodic throughput of fluids from the early stages of burial onward the acquired fluid inclusion isotope data demonstrate that fluids circulating in the carbonates were derived from an underlying reservoir that consisted of a mixture of meteoric water and evolved marine fluids probably derived from deep seated evaporites the meteoric fluids infiltrated in the hinterland before being driven outward into the foreland basin and ascended as soon as fracturing induced a sufficient increase in permeability structural and petrographic observations provide time constraints for the various phases of fracture infilling and reveal an increasing dominance of meteoric water in the system through time as migration pathways shortened and marine formation fluids were progressively flushed out similar fluid flow evolutions have previously been recorded in various fold thrust belt settings elsewhere in the world