geothermobarometry of basaltic glasses from the tamu massif shatsky rise oceanic plateau 1 we present the results of a petrological study of core samples from tamu massif site u1347 recovered during the shatsky rise integrated ocean drilling program iodp expedition 324 the basaltic glasses from site u1347 are evolved tholeiitic basalts containing 5 2 6 8 wt mgo and are principally located within the compositional field of mid ocean ridge basalts morbs but they have systematically higher feo lower al2o3 sio2 and na2o concentrations and the cao al2o3 ratios are among the highest known for morbs in this sense glasses from site u1347 more closely resemble basaltic magmas from the ontong java plateau ojp although they still have lower sio2 concentrations in contrast to morb and similar to ojp our fractionation corrected values of na2o and cao al2o3 indicate more than 20 of partial melting of the mantle during the generation of the parental magmas of tamu massif the water contents in the glasses determined by midinfrared fourier transform infrared ftir spectroscopy are morb like and vary between 0 18 and 0 6 wt h2o the calculated pressure p temperature t conditions at which the natural glasses represent cotectic olivine plagioclase clinopyroxene compositions range from 0 1 to 240 mpa and 1100 to 1150 c reflecting magma storage at shallow depth the variation of the glass compositions and the modeled p t conditions in correlation with the relative ages indicate that there were at least two different magmatic cycles characterized by variations in eruptive styles massive flows or pillow lavas chemical compositions volatile contents and preeruptive p t conditions each magmatic cycle represents the progressive differentiation in course of polybaric crystallization after the injection of a more primitive magma batch magma crystallization and eruption episodes are followed by magmatic inactivity reflected in the core sequence by a sedimentary layer our data for tamu massif demonstrate that similar to ontong java ocean plateau the crystallization beneath shatsky rise occurs at different crustal levels

amphibole sponge in arc crust pressure temperature time paths followed by arc magmas ascending through the lithosphere dictate the phase assemblage that crystallizes and hence the compositions of liquid fractionates here we use la yb and dy yb versus sio 2 relationships from selected volcanoes to show that amphibole is an important mineral during differentiation of arc magma production of intermediate and silicic arc magmas occurs as magmas stall and cool in the mid lower crust where amphibole is stable because amphibole is rarely a phenocryst phase we term this cryptic amphibole fractionation if this process is as widespread as our investigation suggests then 1 amphibole cumulates may act as an effective filter for water dissolved in mantle derived magmas 2 amphibole cumulates may act as a fertile source of intracrustal melts and fluids and 3 recycling of amphibole cumulates has the potential to return incompatible trace elements and water to the mantle

forest soil paludification and mid holocene retreat of jack pine in easternmost north america evidence for a climatic shift from fire prone to peat prone conditions soil paludification is the main ecosystem process initiating the formation and development of most peatlands in the northern hemisphere sandy podzolic soils developed on coarse deposits are among

the tolbachik volcanic massif a review of the petrology volcanology and eruption history prior to the 2012 2013 eruption abstract the primary goal of this paper is to summarize all of the published data on the tolbachik volcanic massif in order to provide a clear framework for the geochronologic petrologic geochemical and to a lesser extent the geophysical and tectonic characteristics of the tolbachik system established prior to the 2012 2013 eruption the tolbachik massif forms the southwestern part of the voluminous klyuchevskoy volcanic group in kamchatka the massif includes two large stratovolcanoes ostry sharp tolbachik and plosky flat tolbachik and a 70 km long zone of the basaltic monogenetic cones that form an arcuate rift like structure running across the plosky tolbachik summit the tolbachik massif gained international attention after the 1975 1976 great tolbachik fissure eruption gtfe which was one of the largest eruptions of the 20th century and one of the six largest basaltic fissure eruptions in historical time by the end of the gtfe 2 2 km 3 of volcanic products of variable basaltic compositions with morb like isotopic characteristics covered an area of 1000 km 2 during the following three decades more than 700 papers on various aspects of this eruption have been published both in national and international journals although the recent 2012 2013 eruption which is the main topic of this volume was not as long as the gtfe in duration or as large in area and volume of the erupted deposits it brought to the surface a unique volcanic material never found before in order to understand the data from new eruptions and make significant progress towards a better understanding of the tolbachik magmatic system it is important to be able to put the new results into the historic context of previous research

reactive transport modelling of reflux dolomitization in the arab d reservoir ghawar field saudi arabia it has long been recognized that the arab d reservoir in ghawar field has been significantly dolomitized and that the distribution of dolomites is highly heterogeneous across this reservoir previous studies indicated that dolomite occurs with either a stratigraphic or non stratigraphic distribution when mapped dolomite tends to form several parallel linear trends across the field although stratigraphic dolomite was suggested to be formed early from highly evaporated pore fluids sourced from overlying evaporite deposits non stratigraphic dolomite was thought to be generated primarily from hydrothermal fluids sourced from below this study focuses primarily on these non stratigraphic dolomites and proposes that i these dolomites initially formed via seepage reflux but were reinforced by late stage hydrothermal dolomitization and ii reflux is also responsible for the formation of parallel linear trends of dolomite the reflux model hypothesizes that an evaporative lagoon which is the source of dolomitizing fluids formed during the falling stage systems tract of a depositional sequence and that with continuing sea level fall this lagoon migrated progressively towards deeper parts of an intrashelf basin adjacent to the ghawar field leaving behind lines of dolomite bodies along a series of temporary coastlines two dimensional reactive transport models have been built to test this hypothesis and have resulted in a predicted pattern of dolomite bodies that agrees with both the observed vertical distribution of non stratigraphic dolomite as well as the mapped lateral distribution of the dolomite trends in addition the major ion compositions of late jurassic seawater are calculated based on fluid inclusion data in the literature using jurassic seawater in current models leads to the absence of anhydrite cements and less potential of over dolomitization than using modern seawater

a comparison of khuff and arab reservoir potential throughout the middle east a compilation of average porosity and permeability data for petroleum reservoirs in the permian triassic khuff formation and the jurassic arab formation shows that most khuff reservoirs have an average porosity of less than 12 whereas most arab reservoirs have an average porosity of 12 26 higher porosity correlates with shallower depth suggesting that burial diagenesis is the main cause of the overall porosity difference between these units deeper burial of khuff reservoirs is inferred to have resulted in greater porosity loss by chemical compaction and associated cementation a broad correlation also exists between average porosity and average permeability suggesting that deeper burial and the resulting porosity decrease are also a primary cause of the lower permeabilities of the khuff reservoirs in addition to greater burial depth however a combination of depositional and early diagenetic factors is also reflected in the lower average porosity and permeability values of the khuff reservoirs khuff strata were deposited on an extensive poorly circulated very low relief shelf and consist in large part of interbedded mudstones and grainstones having relatively fine grain size with major amounts of depositional calcium sulfate present arab reservoirs were deposited under better circulated conditions near platform margins facing deep intracratonic basins and thus have coarser more grain dominated fabrics and lesser overall content of chemically precipitated grains calcium sulfate and dolomite khuff deposits were likely composed of less stable mineralogy than arab sediments because the late permian was a time of aragonite seas whereas the late jurassic was a time of calcite seas the combined result of these factors is that arab reservoirs are characterized by greater preservation of primary depositional pore types more coarsely crystalline dolomite fabrics and lesser plugging by anhydrite finally a possible factor affecting the average porosity and permeability values is petroleum composition which is gas in most khuff reservoirs and oil in arab reservoirs lower economic cutoff values for gas production would favor inclusion of low permeability zones in khuff reservoirs thus reducing average reservoir values two main aspects of these results are innovative this is the first time that porosity and permeability values for either khuff or arab reservoirs have been examined regionally second the conclusion that thermal exposure is the primary control on average porosity and permeability in these units is consistent with previous work from other carbonates but is new for the middle east

holocene carbon accumulation rates from three ombrotrophic peatlands in boreal quebec canada impact of climate driven ecohydrological change understanding the processes controlling peatland carbon c sequestration is critical to anticipate potential changes in the global c cycle in response to climate change although identification of these factors may be relatively straightforward on seasonal timescales at centennial to millennial timescales complexities arise because of interactions between climate vegetation hydrology and long term ecological processes to better understand the factors controlling long term c accumulation holocene rates of c sequestration were quantified from three pristine ombrotrophic peatlands in boreal quebec northeastern canada 52 n 75 76 w bulk density and loss on ignition analyses combined with radiocarbon dating and age depth modelling were used to estimate long term apparent rates of carbon accumulation past changes in vegetation and water table depth were obtained from plant macrofossil and testate amoeba analysis earliest regional peat accumulation started 7520 cal bp with long term rates of c s

chemistry and environments of dolomitization a reappraisal abstract dolomitization of calcium carbonate can best be expressed by mass transfer reactions that allow for volume gain preservation or loss during the replacement process experimental data as well as textures and porosities of natural dolomites indicate that these reactions must include co 3 2 and or hco 3 supplied by the solution to the reaction site since dolomite formation is thermodynamically favoured in solutions of a low ca 2 mg 2 ratios b low ca 2 co 3 2 or ca 2 hco 3 ratios and c high temperatures the thermodynamic stability for the system calcite dolomite water is best represented in a diagram with these three parameters as axes kinetic considerations favour dolomitization under the same conditions and additionally at low as well as at high salinities if thermodynamic and kinetic considerations are combined the following conditions and environments are considered chemically conducive to dolomitization 1 environments of any salinity above thermodynamic and kinetic saturation with respect to dolomite i e freshwater seawater mixing zones normal saline to hypersaline subtidal environments hypersaline supratidal environments schizohaline environments 2 alkaline environments i e those under the influence of bacterial reduction and or fermentation processes or with high input of alkaline continental groundwaters and 3 many environments with temperatures greater than about 50 c subsurface and hydrothermal environments whether or not massive replacive dolostones are formed in these environments depends on a sufficient supply of magnesium and thus on hydrologic parameters most massive dolostones particularly those consisting of shallowing upward cycles and capped by regional unconformities have been interpreted to be formed according to either the freshwater seawater mixing model or the sabkha with reflux model however close examination of natural mixing zones and exposed evaporitic environments reveals that the amounts of dolomite formed are small and texturally different from the massive replacive dolostones commonly inferred to have been formed in these environments many shallowing upward sequences are devoid of dolomite it is therefore suggested that massive replacive dolomitization during exposure is rare if not impossible rather only small quantities of dolomite cement or replacement are formed which may act as nuclei for later subsurface dolomitization alternatively large scale dolomitization may take place in shallow subtidal environments of moderate to strong hypersalinity the integration of stratigraphic petrographic geochemical and hydrological parameters suggests that the only environments capable of forming massive replacive dolostones on a large scale are shallow hypersaline subtidal environments and certain subsurface environments

partial dolomitization of a pennsylvanian limestone buildup by hydrothermal fluids and its effect on reservoir quality and performance dolomite was studied in the reinecke field in west texas to determine its origin reservoir characteristics and effect on oil production the reinecke reservoir includes approximately 25 dolomite in an upper pennsylvanian to lowest permian limestone buildup dolomites are fine to coarsely crystalline with undulose extinction petrography indicates that dolomite formed diagenetically late dolomites overgrow stylolites indicating precipitation during deep burial low 18o values are consistent with primary fluid inclusions that indicate dolomite precipitation or recrystallization at 92 to 118 c these temperatures are much higher than those in the existing reservoir or what should have been encountered during regional burial two types of dolomite are observed one type is stratiform replaced micrite rich facies and is interpreted as early dolomite that recrystallized in hydrothermal brines the second type crosscuts stratigraphy and depositional facies and has vertically continuous morphologies that trend northwest southeast the latter dolomite is interpreted as forming in hydrothermal brines derived from latest permian aged highly evaporated seawater these brines descended deep into the basin because of their greater density and then ascended because of heating and thermal convection reinecke dolomites have lower porosity but higher permeability than the surrounding limestones as a result dolomites provide raceways for fluids moving through the reservoir these dolomites helped an artificially enhanced bottom water drive to recover approximately 50 of the original oil in place the dolomite has complicated a crestal co2 flood these hydrothermal reinecke dolomites have lower porosity but much higher permeability than most nearby permian dolomites formed in evaporated seawater during shallow burial arthur h saller is a stratigrapher with chevron energy technology company in houston texas he has worked in the petroleum industry for 27 yr helping with exploration and production projects in west texas canada angola and southeast asia he received his b s degree from the university of kansas m s degree from stanford university and ph d from louisiana state university 1984 john a tony d dickson received his ph d from queen mary college london university in 1967 he has had academic positions in cardiff nottingham and cambridge universities he has worked on smackover andrews horseshoe atoll shu iaba tengiz and other oil reservoirs he retired from academia in 2007 and is now consulting and conducting courses in carbonate diagenesis

statistical evaluation of elemental concentrations in shallow marine deposits cretaceous lusitanian basin abstract the elemental geochemistry of ancient shallow marine carbonates represents an often underexplored archive of paleoenvironmental change and diagenetic pathways complex multi parameter datasets from a lithologically heterogeneous sedimentary succession in the southern part of the lusitanian basin ericeira portugal are presented and interpreted the section comprises marly carbonate and sandstone rich coastal marine deposits of early albian to early cenomanian age principal component analysis of bulk elemental abundance ca mg sr fe and mn lead to define four geochemical clusters based on common elemental attributes siliciclastics and dolomitized limestones facies yield evidence for significant diagenetic alteration but still preserve information on paleoshoreline position mixed carbonate siliciclastics and limestone facies bear evidence for relative sea level position and relevant paleoclimatic information in their elemental record accordingly mid albian mixed carbonate siliciclastic deposits present variable degrees of continental influx specifically a sharp increase of fe and mn concentrations in relation to continental input is in agreement with periods of enhanced hydrological cycling and increased weathering on adjacent emerged lands the progressive transition towards more marine conditions is accompanied by higher ca and sr content and represented by limestone facies corresponding to a higher sea level position during late albian to early cenomanian times moreover this facies records a trend towards warmer and more arid conditions early diagenetic stabilization and or dissolution of aragonite into low mg calcite can account for major elemental variations including higher sr content strongly coupled with ca content along with lower mg fe and mn concentrations data shown here provide solid evidence that the statistical analysis of the elemental record of ancient marine deposits when combined with conventional sedimentology and thin section petrography allow for elaborate conclusions on their depositional environment and diagenetic pathways cored wells and facies specific reservoir properties can be addressed by these methodologies able to detect and quantify changes in patterns both industry and academy can therefore benefit from approaching such a complex interplay

an experimental investigation of the influence of water and oxygen fugacity on differentiation of morb at 200 mpa crystallization experiments were performed at 200mpa in the temperature range 1150 950 c at oxygen fugacities corresponding to the quartz fayalite magnetite qfm and mno mn3o4 buffers to assess the role of water and fo2 on phase relations and differentiation trends in mid ocean ridge basalt morb systems starting from a primitive mgo 9 8 wt and an evolved morb mgo 6 49 wt crystallization paths with four different water contents 0 35 4 7 wt h2o have been investigated in primitive morb olivine is the liquidus phase followed by plagioclase clinopyroxene amphibole is present only at water saturated conditions below 1000 c but not all fluid saturated runs contain amphibole magnetite and orthopyroxene are not stable at low fo2 qfm buffer residual liquids obtained at low fo2 show a tholeiitic differentiation trend the crystallization of magnetite at high fo2 mno mn3o4 buffer results in a decrease of melt feo mgo ratio causing a calc alkaline differentiation trend because the magnetite crystallization temperature is nearly independent of the h2o content in contrast to silicate minerals the calc alkaline differentiation trend is more pronounced at high water contents residual melts at 950 c in a primitive morb system have compositions approaching those of oceanic plagiogranites in terms of sio2 and k2o but have ca na ratios and feo contents that are too high compared with the natural rocks implying that fractionation processes are necessary to reach typical compositions of natural oceanic plagiogranites

holocene pool formation in oligotrophic fens from boreal quebec in northeastern canada at the biogeographical limit between the boreal and the subarctic domain in northeastern canada peatlands are mainly oligotrophic fens characterized by a dominance of aquatic microforms such as pools and wet hollows these peatlands present similar features as the appa mires in scandinavia they show evidence for recent water table rise indicated by tree mortality physical degradation of strings and pool expansion this study aims to evaluate the timing of pool inception and their impact on the long term dynamics of these microforms within two patterned oligotrophic fens in the laforge region northern quebec plant macrofossil and testate amoeba analyses from sediment underneath pools were used along with radiocarbon dating to reconstruct peatland pool dynamics over the holocene our data indicate that wet hollows or shallow pools developed at minimal ages between 4200 and 2500 cal a bp pool initiation in the peatlands of the laforge region corresponds to the climate shift toward cooler and wetter

global boundary stratotype section and point gssp for the anthropocene series where and how to look for potential candidates abstract the anthropocene as a potential new unit of the international chronostratigraphic chart which serves as the basis of the geological time scale is assessed in terms of the stratigraphic markers and approximate boundary levels available to define the base of the unit the task of assessing and selecting potential global boundary stratotype section and point gssp candidate sections a required part of the process in seeking formalisation of the term is now being actively pursued here we review the suitability of different stratified palaeoenvironmental settings and facies as potential hosts for a candidate gssp and auxiliary sections and the relevant stratigraphical markers for correlation published examples are evaluated for their strengths and weaknesses in this respect a marked upturn in abundance of radioisotopes of 239pu or 14c approximately in 1952 and 1954 ce respectively broadly coincident with a downturn in 13c values is applicable across most environments principal palaeoenvironments examined include settings associated with accumulations of anthropogenic material marine anoxic basins coral reefs estuaries and deltas lakes at various latitudes peat bogs snow ice layers speleothems and trees together many of these geographically diverse palaeoenvironments offer annual subannual laminae that can be counted and independently dated radiometrically e g by 210pb examples of possible sections offer the possibility of correlation with annual seasonal resolution from among such examples a small number of potentially representative sites require the acquisition of more systematic and comprehensive datasets with correlation established between sections to allow selection of a candidate gssp and auxiliary stratotypes the assessments in this paper will help find the optimal locations for these sections

cenozoic dolomites of carbonate islands their attributes and origin abstract dolomites found on and below carbonate islands atolls and oceanic platforms provide useful insights into the origin of dolomite insights that may not be attainable from the study of more ancient cratonic dolomites for this reason they have been the subject of study for decades a critical mass of case studies now exist and some significant conclusions can be drawn from the cumulative data in most cases the association with an island is causal and not genetic nevertheless these dolomite occurrences are referred to herein as island dolomites one type of dolomite on carbonate islands is penecontemporaneous dolomite a phase that forms while the host sediment is in its original depositional setting island examples are holocene in age occur in holocene sediments and originate as a direct precipitate from either normal or evaporated seawater these are microcrystalline poorly ordered ca rich 18o enriched and geochemically unstable phases that are susceptible to recrystallization in the setting in which they formed post depositional dolomite is the other type of dolomite associated with carbonate islands this type of dolomite replaces older precursors and forms as cement distinctive characteristics include a dominance of fabric preserving texture pore lining cement rims that may exhibit micron scale banding with low mg calcite and formation in association with precursor dissolution sr isotopic dating indicates that all examples are neogene or quaternary in age those formed during the middle miocene through pliocene are massive laterally continuous and often multigenerational in contrast younger examples tend to be localized partial replacements of a single generation sr isotope ages also suggest global synchroneity in many dolomitization events which suggests a connection between dolomitization global eustacy and or global climatic factors geochemical attributes of post depositional island dolomites are ca enrichment positive 18o and 13c low sr contents 150 300 ppm and low fe global similarity in petrography and geochemistry of replacive island dolomites argues for a similar origin inferred origins however depend primarily on how 18o and sr data are interpreted values for 18o and dsr must be assumed due to uncertainties in oxygen isotope fractionation and sr partitioning there is no consensus or uniformity in those assumptions thus interpretations can vary and be biased to a desired result covariant trends in 13c and 18o some negative 13c values and high sr all favor a mixing zone origin but examples with these attributes are few lack of covariance in the isotopes mean 18o of 2 0 to 3 5 and low sr future studies should standardize the type of data collected and the analytical techniques employed multiple geochemical attributes should be measured on microsampled components and quantitative modeling should be employed in order to constraint interpretations as much as possible also needed are a better understanding of the kinetic processes that form these dolomites more careful assessment of their recrystallization status and an improved understanding of dsr and 18o at low temperature

occurrence and formation of dolomite in organic rich continental margin sediments dolomite is presently forming throughout a large part of the oceans in continental margin marine sediments accumulating at rates less than 500 m m y and having organic carbon contents greater than 0 5 wt at higher sedimentation rates the dolomite content of the sediments is greatly diluted at lower organic carbon content the porewater chemistry precludes dolomite formation the reactants for dolomite formation have the following sources magnesium supplied from overlying seawater calcium supplied by the dissolution of calcium carbonate and carbon supplied from carbonate dissolution and organic carbon oxidation the rate of dolomite formation appears to be limited by the rate of calcium carbonate dissolution this rate can be quantitatively calculated from the magnesium diffusional and advective fluxes conversely in ancient sediments the depth and timing of dolomite formation can be calculated from the amount of dolomite and the sedimentation rate in dolomite rich sediments these calculations demonstrate that most of the dolomite formed within a few tens of meters of the sea floor within the zone of microbial sulfate reduction such dolomites have ne ative values of dgr13c dolomite in dolomite poor sediments may form at greater burial depth below the zone of sulfate reduction resulting in positive values of dgr13c the distribution coefficient of strontium in dolomite has been determined to have an average value of 0 06 using this value predicted strontium contents for submarine dolomites range from 150 ppm in dolomite rich sections to 1 290 ppm in dolomite poor sections

holocene development of a peatland southern quebec a spatio temporal reconstruction based on pachymetry sedimentology microfossils and macrofossils this study examines the relationships between allogenic and autogenic processes during the holocene development of a southern quebec bog local vegetation surface moisture and peat accumulation were independently reconstructed from palaeoecological data microfossils macrofossils loss on ignition and radiocarbon dating and sedimentological analyses conducted on seven profiles the observed successional stages from pond to marsh rich fen poor fen then bog represents a typical hydrosere the early wetland development provides an obvious illustration of the facilitation model each community modified the hydrological conditions by means of peat accumulation which then favoured the onset of the succeeding stage no direct link is evidenced between vegetation moisture and peat accumulation while all of them clearly reveal the initial influence of minerotrophic groundwater supply notably the decrease in this allogenic influence is reflected by the increasing asynchrony of local vegetation change th

textural and geochemical alternations in late cenozoic bahamian dolomites dolomitized intervals of a core from san salvador island bahamas exhibit variations of two texturally and geochemically distinct end members in the pliocene section of the dolomitized interval the two end members alternate in a pattern that may reflect originally and or diagenetically modified depositional facies formerly mud free intervals locally capped by exposure surfaces are massive crystalline mimetic dolomites cm muddier sediments are replaced by friable microsucrosic dolomites ms cm and ms dolomites also differ in porosity 30 permeability 100 md mol mgco3 44 9 vs 47 7 mol oxygen isotopic composition 1 7 vs 2 7 and strontium content 241 vs 106 ppm these data indicate that depositional and diagenetic fabric are the principal controls governing the distribution of dolomite types differences in texture and geochemistry are suggested as arising through differential rates of crystallization produced as a result of variations in permeability and reactivity of the precursor sediments and rocks

depths of partial crystallization of h2o bearing morb phase equilibria simulations of basalts at the mar near ascension island 7 11 s phase equilibria simulations were performed on naturally quenched basaltic glasses to determine crystallization conditions prior to eruption of magmas at the mid atlantic ridge mar east of ascension island 7 11 s the results indicate that mid ocean ridge basalt morb magmas beneath different segments of the mar have crystallized over a wide range of pressures 100 900 mpa however each segment seems to have a specific crystallization history nearly isobaric crystallization conditions 100 300 mpa were obtained for the geochemically enriched morb magmas of the central segments whereas normal n morb magmas of the bounding segments are characterized by polybaric crystallization conditions 200 900 mpa in addition our results demonstrate close to anhydrous crystallization conditions of n morbs whereas geochemically enriched morbs were successfully modeled in the presence of 0 4 1 wt h2o in the parental melts these estimates are in agreement with direct fourier transform ir measurements of h2o abundances in basaltic glasses and melt inclusions for selected samples water contents determined in the parental melts are in the range 0 04 0 09 and 0 30 0 55 wt h2o for depleted and enriched morbs respectively our results are in general agreement within 200 mpa with previous approaches used to evaluate pressure estimates in morb however the determination of pre eruptive conditions of morbs including temperature and water content in addition to pressure requires the improvement of magma crystallization models to simulate liquid lines of descent in the presence of small amounts of water

evaluating long term regional climate variability in the maritime region of the st lawrence north shore eastern canada using a multi site comparison of peat based paleohydrological records this study presents paleohydrological reconstructions from ombrotrophic peatlands bogs along the north shore of the estuary and the gulf of st lawrence in eastern canada past water table depths were reconstructed based on testate amoebae analyses within four peatlands from two maritime ecoclimatic regions boreal and subarctic using a new transfer function the comparison of multiple peat based paleohydrological records was used to distinguish climate driven changes from variations related to site specific factors coherence between the water table reconstructions at the regional scale suggests a common climatic influence on bog paleohydrology but there are inconsistencies which also suggest an influence of non climatic factors e g internal peatland processes and feedbacks the surface drying and increased hydrological variability after 3000 cal a bp in the studied bogs coincide with the transition from the holocene climatic optimum to the neoglacial cooling documented by proxy climate records in eastern canada the bogs of havre st pierre have experienced major drying during the late holocene indicating important annual to centennial water deficits at the peatland surface regional differences in the magnitude of the hydrological fluctuations may result from distinctive climatic conditions or could indicate that bog surface wetness in the gulf of st lawrence was more sensitive to past climate changes copyright 2014 john wiley sons ltd

controls on formation and alteration of early diagenetic dolomite a multi proxy δ44 40ca δ26mg δ18o and δ13c approach abstract the full potential of the dolomite ca isotope proxy only unfolds when combined with data of the other main elements c o mg in the crystal lattice of mg carbonates data presented here reveal the level of complexity inherent to dolomite precipitation and alteration environments and add new constraints to the understanding of early diagenetic dolomite formation well constrained precambrian to pleistocene dolomites were investigated representing three characteristic formation and alteration environments i sabkha ii altered marine and iii lacustrine palustrine dolomites primary sabkha dolomites with typically low cation ordering degree cod high 13c and low 44 40ca values contrast with recrystallized sabkha dolomites with relatively high cod low 13c and high 44 40ca values both 13c and 44 40ca values of sabkha dolomite bear witness to the relative effects of kinetic and equilibrium ca isotope fractionation conditions primary sabkha dolomites display 44 40cadolomite fluid ranging from 0 4 to 1 3 whereas recrystallized dolomite is approaching isotopic equilibrium 44 40cadolomite fluid 0 using the fractionation factor deduced from the sabkha dolomite data set recrystallized precambrian dolomite points to a 44 40caseawater pore fluid of about 1 2 srm 915a a value that is distinctively lower compared to previously suggested ones and modern seawater altered marine dolomites display evidence for meteoric overprint indicated by 18o values as low as 4 62 both mg and ca isotope signatures correlate with 18o values of altered marine dolomites whereas 13c values lack correlation with the other isotope systems we propose that freshwater circulated through silicate aquifers prior to reaching the dolostone units and ca mg and o isotopes of altered marine dolomites reflect variable degrees of this meteoric overprint lacustrine palustrine dolomites display a correlation between the isotope values of c mg and ca these dolomites are formed during pulses of marine ingression in swamp playa and lake environments and are thus characterized by water logged conditions anaerobic and saline sulfate rich fluids bacterial sulfate reduction induces dolomite formation and leads to lower 13c and 44 40ca as well as to higher 26mg values the ca isotope proxy acts as a benchmark against which other proxy data can be calibrated or processes tested taking cod and dolomite stoichiometry into consideration the here documented multi proxy isotope approach is promising and provides benchmarks against which proxy signals can be calibrated and tested interestingly even the limited data sets shown here point to patterns that can be interpreted in a meaningful manner that is of relevance for dolomite research

multistage dolomitization in late jurassic early cretaceous platform carbonates berdiga formation basoba yayla trabzon ne turkey implications of the generation of magmatic arc on dolomitization abstract late jurassic early cretaceous berdiga formation which is widely distributed in an e w trending belt in the eastern pontides ne turkey is composed of platform carbonates the formation shows varying lithofacies changing from supratidal to platform margin reef both laterally and vertically the studied basoba yayla trabzon ne turkey area comprises one of the typical exposures of formation in the northern zone of eastern pontides in this area the lower parts of the formation are pervasively dolomitized by fabric destructive and fabric preserving replacive dolomites that are ca rich and nonstoichiometric ca56 60mg40 44 replacement dolomites rd are represented by 18o values of 15 3 to 4 2 vpdb 13c values of 3 7 1 5 vpdb and 87sr 86sr ratios of 0 70675 0 70731 petrographic and geochemical evidence implies that rd dolomites are formed before compaction at shallow moderate burial depths from late jurassic early cretaceous seawater and or partly modified seawater as a consequence of rock water interaction and they are recrystallized at elevated temperatures during subsequent burial during subsequent late cretaceous diagenetic process when the region became a magmatic arc rd1a and rd3 dolomite were recrystallized by hydrothermal fluids of marine origin the dolomite cements cd overlying the low amplitude stylolites have similar geochemical charasteristics than rd1a and rd3 dolomite and are characterized by high homogenization temperatures th this might indicate that cd dolomite was precipitated from hydrothermal fluids of marine origin that recrystallized the rd1a and rd3 dolomite the fact that cd dolomite comprising the latest phase of dolomitization is overlain by coarsely crystalline mosaic calcite and silica cements may indicate that diagenetic fluids were undersaturated with respect to dolomite and oversaturated with respect to calcite and silica

palaeoecology of a palsa and a filled thermokarst pond in a permafrost peatland subarctic quebec canada radiocarbon dating and macrofossil data from a palsa and a filled thermokarst pond within a subarctic permafrost peatland were used to reconstruct their evolution and to distinguish between allogenic and autogenic processes that had been involved in their development peat began to accumulate in the peatland basin shortly after 6000 cal bp the initial stage was a shallow bay or a salty marsh followed by a wet marsh triggered by a relatively rapid drop in sea level related to a rapid isostatic uplift of land by 5640 cal bp the site had transformed into a rich fen a high rate of peat accumulation led to the establishment of a short lived intermediate fen by 4610 cal bp and to a poor fen from 4200 cal bp until 1760 cal bp low water tables associated with decreased precipitation occurred between 5170 and 4610 cal bp and 3100 and 1760 cal bp between 1760 and the little ice age there was ombrotrophication of the site largely as a result of a thick peat accumulation during this period autogenic processes had controlled the general hydrosere while allogenic processes mainly precipitation had influenced species composition permafrost established during the little ice age leading to palsa formation and it has been melting in response to recent climate warming and precipitation increases macrofossil results from the filled thermokarst pond show that plant succession used the followed hydrosere calliergon giganteum and sphagnum riparium when the pond s depth was at a maximum s riparium and c giganteum when the pond was partly filled in and s lindbergii and s riparium since the pond has been completely filled in

an 8500 cal year multi proxy climate record from a bog in eastern newfoundland contributions of meltwater discharge and solar forcing analyses of plant macrofossils testate amoebae and the degree of peat humification have been combined into a single composite reconstruction of bog surface wetness bsw on a coastal plateau bog in eastern newfoundland the reconstruction reveals 14 distinctive phases of near surface water tables commencing at 8270 7500 6800 5700 5200 4900 4400 4000 3100 2500 2050 1700 600 and 200 cal bp which may be used to infer changes in the atmospheric water balance of eastern newfoundland the first two major phases of pool development follow the final drainage of glacial lake agassiz at 8400 cal bp and the ungava lakes between ca 7500 6900 cal bp respectively from 7500 cal bp to the present there appears to be a strong correlation within dating errors between reconstructed bsw and the stacked ice rafted debris ird record in the north atlantic ocean both records may reflect long term changes in air masses comparisons of the bsw reconstruction with records of cosmogenic isotope flux also suggest a persistent link between reduced solar irradiance and increased bsw during the holocene

holocene hydro climatic change and effects on carbon accumulation inferred from a peat bog in the attawapiskat river watershed hudson bay lowlands canada abstract multiple proxies from a 319 cm peat core collected from the hudson bay lowlands northern ontario canada were analyzed to determine how carbon accumulation has varied as a function of paleohydrology and paleoclimate testate amoeba assemblages analysis of peat composition and humification and a pollen record from a nearby lake suggest that isostatic rebound and climate may have influenced peatland growth and carbon dynamics over the past 6700 cal yr bp long term apparent rates of carbon accumulation ranged between 8 1 and 36 7 g c m 2 yr 1 average 18 9 g c m 2 yr 1 the highest carbon accumulation estimates were recorded prior to 5400 cal yr bp when a fen existed at this site however following the fen to bog transition carbon accumulation stabilized carbon accumulation remained relatively constant through the neoglacial period after 2400 cal yr bp when pollen based paleoclimate reconstructions from a nearby lake mcandrews et al 1982 and reconstructions of the depth to the water table derived from testate amoeba data suggest a wetter climate more carbon accumulated per unit time between 1000 and 600 cal yr bp coinciding in part with the medieval climate anomaly

application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium this wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid rock interaction careful consideration of the uncertainties associated with trace element partitioning sample heterogeneity and fluid rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis goundwater evolution ancient seawater chemistry and isotope stratigraphy a principal uncertainty involved in the application of sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of sr between mineral and solution this variation may be a function of precipitation rate mineral stoichiometry crystal growth mechanism fluid composition and temperature calcite and dolomite in ancient limestones commonly have significantly lower sr concentrations 20 70 p p m than would be expected from published trace element distribution coefficient values and sr ca ratios of most modern sedimentary pore waters this discrepancy probably reflects the uncertainties associated with determining distribution coefficient values as techniques improve for the analytical measurement and theoretical modelling of sr concentration and isotopic variations the petrological analysis of carbonate samples becomes increasingly important the presence of even small percentages of non carbonate phases with high rb concentrations and high 87 sr86 sr values such as clay minerals can have significant effects on the measured 87 sr 86 sr values of carbonate rocks due to the decay of 87rb to 87 sr for example a permian marine limestone with 50 p p m sr and 1 p p m rb will have a present day 87 sr 86 sr value that is 2 10 4 higher than its original value this difference is an order of magnitude greater than the analytical uncertainty and illustrates the importance of assessing the need for and accuracy of such corrections a quantitative evaluation of the effects of water rock interaction on sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water rock interaction including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals quantitative modelling may also be used to construct diagnostic fluid rock interaction trends that are independent of distribution coefficient values and to distinguish between mixing of mineral end members and fluid rock interaction

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

a study of rare earth element ree sio 2 variations in felsic liquids generated by basalt fractionation and amphibolite melting a potential test for discriminating between the two different processes the origin of felsic magmas 63 sio2 in intra oceanic arc settings is still a matter of debate two very different processes are currently invoked to explain their origin these include fractional crystallization of basaltic magma and partial melting of lower crustal amphibolite because both fractionation and melting can lead to similar major element trace element and isotopic characteristics in felsic magmas such lines of evidence have been generally unsuccessful in discriminating between the two processes a commonly under appreciated aspect of rare earth element ree solid liquid partitioning behavior is that d ree for most common igneous minerals especially hornblende increase significantly with increasing liquid sio2 contents for some minerals e g hornblende and augite ree partitioning can change from incomptatible d 1 at high liquid sio2 when this behavior is incorporated into carefully constrained mass balance models for mafic basaltic amphibolite melting intermediate andesitic amphibolite melting lower or mid to upper crustal hornblende present basalt fractionation and mid to upper crustal hornblende absent basalt fractionation the following general predictions emerge for felsic magmas e g 63 to 76 sio2 partial melting of either mafic or intermediate amphibolite should regardless of the type of melting equilibrium fractional accumulated fractional yield ree abundances that remain essentially constant and then decrease or steadily decrease with increasing liquid sio2 content at high liquid sio2 contents lree abundances should be slightly enriched to slightly depleted i e c l c o 2 to 0 2 while hree abundances should be slightly depleted c l c o 1 to 0 2 lower crustal hornblende bearing basalt fractionation should yield roughly constant ree abundances with increasing liquid sio2 and exhibit only slight enrichment c l c o 1 2 mid to upper crustal hornblende bearing basalt fractionation should yield steadily increasing lree abundances but constant and then decreasing hree abundances at high liquid sio2 contents lree abundances may range from non enriched to highly enriched c l c o 1 to 5 while hree abundances are generally non enriched to only slightly enriched c l c o 1 to 2 hornblende absent basalt fractionation should yield steadily increasing ree abundances with increasing liquid sio2 contents at high sio2 contents both lree and hree are highly enriched c l c o 3 to 4 it is proposed that these model predictions constitute a viable test for determining a fractionation or amphibolite melting origin for felsic magmas in intra oceanic arc environments where continental crust is absent

peatland development at the arctic tree line quebec canada influenced by flooding and permafrost in this study we documented the holocene history of a peat plateau at the arctic tree line in northern quebec using stratigraphic and macrofossil analyses to highlight the effects of geomorphic setting in peatland development paludification of the site began about 6800 cal yr bp from 6390 to 4120 cal yr bp the peatland experienced a series of flooding events the location of the peatland in a depression bounded by two small lakes likely explains its sensitivity to runoff the proximity of a large hill bordering the peatland to the south possibly favored the inflow of mineral laden water the onset of permafrost aggradation in several parts of the peatland occurred after 3670 cal yr bp uplifting of the peatland surface caused by permafrost stopped the flooding according to radiocarbon dating of the uppermost peat layers permafrost distribution progressed from the east to the west of the peatland indicating differential timing for the initiation of permafrost throughout the peatland most of the peatland was affected by permafrost growth during the little ice age picea mariana macroremains at 6450 cal yr bp indicate that the species was present during the early stages of peatland development which occurred soon after the sea regression

late pleistocene mixing zone dolomitization southeastern barbados west indies field geochemical and petrographic data for late pleistocene dolomites from southeastern barbados suggest that the dolomite precipitated in the zone of mixing between a coastal meteoric phreatic lens and normal marine waters the dolomite is localized in packstones and wackestones from the algalamphistegina fore reef calcarenite facies stable isotopic evidence suggests that meteoric water dominated the diagenetic fluids responsible for dolomitization carbon isotopes in pure dolomite phases average about 15 0 pdb this light carbon is attributed to the influence of soil gas co2 and precludes substantial mixing with seawater a narrow range of oxygen isotopic compositions coupled with a wide range of carbon compositions attest to the meteoric diagenetic overprint dolomitization likely occurred with as little as a five per cent admixture of seawater strontium compositions of the dolomites indicate probable replacement dolomitization of original unstable mineralogy the dolomite is characterized by low sodium values low concentrations of divalent manganese and iron suggest oxidizing conditions at the time of dolomitization a sequence of petrographic features suggests a progression of diagenetic fluids from more marine to more meteoric early marine diagenesis was followed by replacement dolomitization of skeletal grains and matrix limpid euhedral dolomite cements precipitated in primary intra and interparticle porosity subsequent to replacement dolomitization as waters became progressively less saline dolomite cements alternated with thin bands of syntaxial calcite cement the final diagenetic phase precipitated was a blocky calcite spar cement representing diagenesis in a fresh water lens this sequence of diagenetic features arose as the result of a single fall in eustatic sea level following deposition a stratigraphic eustatic diagenetic model constrains both the timing and rate of dolomitization in southeastern barbados dolomitization initiated as sea level began to fall immediately following the oxygen isotope stage 7 3 high stand some 216 000 yr bp due to the rapidity of late pleistocene glacio eustasy dolomitization locally complete is constrained to have occurred within about 5000 yr

early dolomitization and recrystallization in shallow marine carbonates mississippian alida beds williston basin canada evidence from petrography and isotope geochemistry abstract the mississippian lower carboniferous alida beds of the northern williston basin canada are carbonate rocks that contain a number of significant hydrocarbon reservoirs these shallow marine carbonate platform deposits consist of abundant very finely to finely crystalline dolomite that occurs mainly in mud dominated sediments dolomite crystals are 4 to 30 m in length subhedral to anhedral in shape and typically replace the matrix but also occur as thin lamellae within ooid cortices textural relations indicate that the dolomite predates all other diagenetic phases including coarse calcite cement anhydrite and bitumen dolomite 18o values 9 3 to 4 5 pdb are depleted relative to that expected for precipitation from osagean late tournaisian seawater 0 5 to 1 5 pdb while 13c values 2 3 to 3 4 pdb are within the range of osagean seawater values 1 8 to 4 8 pdb dolomite 87sr 86sr values 0 70816 to 0 70921 are somewhat elevated with respect to osagean seawater 0 70768 to 0 70817 a trend of increasing average dolomite crystal size with decreasing 18o is observed in matrix replacive dolomite based on petrographic relations 13c compositions and the pervasive occurrence of finely crystalline dolomite initial dolomitization is interpreted to have taken place in the presence of slightly evaporated seawater the absence of depositional evaporites in dolomitized intervals suggests that dolomitization was driven by reflux of slightly evaporated seawater that had not reached gypsum saturation depleted 18o values elevated 87sr 86sr ratios and correlation of dolomite crystal sizes and 18o values suggest that the early formed dolomite was variably recrystallized during burial

the role of polybaric crystallization in genesis of andesitic magmas phase equilibria simulations of the bezymianny volcanic subseries abstract using the updated comagmat model the crystallization sequences of a bezymianny volcano basaltic andesite kamchatka russia are simulated in a wide range of thermodynamic conditions p t f o 2 as a function of h 2 o concentration comparison of the modeled liquid lines of descent with petrochemical trends of the volcanic suite indicates the parental melts contain 1 5 2 wt h 2 o stored under 490 520 mpa pressure in the magma plumbing system beneath bezymianny volcano the initial magma originates as a result of the polybaric evolution of mantle derived high mg basaltic magmas of the adjacent kliuchevskoi volcano the subsequent evolution of derivative hydrous and alumina rich basaltic andesite magmas may proceed under polybaric conditions with an average decompression of 12 mpa per 1 of crystallization in the course of polybaric crystallization compositions of pyroxene bearing andesites can be numerically reproduced and the modeled liquid compositions follow the natural liquid line of descent however hornblende bearing magmas cannot be produced as a result of continued crystallization from parental basaltic andesite through the stage of pyroxene bearing andesite formation they require high water contents and high pressures of crystallization in this case liquid composition should deviate from the chemical trend defined by the whole rock compositions

phase relations and liquid lines of descent in hydrous ferrobasalt implications for the skaergaard intrusion and columbia river flood basalts crystallization experiments using a hydrous ferrobasalt as starting material conducted at 200mpa 940 12008c at a wide range of water activities 0 1 1 and redox conditions qfm 3 to qfm 4 where qfm is the quartz fayalite magnetite oxygen buffer show that h2o influences significantly the differentiation history of ferrobasaltic magmas a combination of our data with published experiments on dry ferrobasalt at 1atm provides an extensive experimental database for modeling and quantifying crystallization and differentiation processes within a typical fe rich tholeiitic system under both dry and hydrous conditions the addition of h2o decreases liquidus temperatures and changes significantly the proportions temperature range and sequence of crystallizing mineral phases the dry liquidus is at about 11708c whereas the liquidus for h2o saturated melts is at 10608c the main phases crystallizing from h2o bearing ferrobasalt at the investigated conditions are olivine ol clinopyroxene cpx plagioclase pl magnetite mt hematite hm ilmenite ilm and amphibole am the phase assemblage is similar to that of the dry system except for the presence of hm at extremely oxidizing conditions and am at low temperatures 59508c and h2o saturated conditions the important observation made in this study is that the stability of fe ti oxides and in particular mt as well as the simultaneous coprecipitation of mtand ilm are almost independent of the activity of h2o ah2o in the system whereas the liquidus temperatures of the silicate minerals are dramatically depressed by increasing ah2o the stabilities of oxides are controlled mainly by the redox conditions prevailing in the system the most pronounced effect of ah2o on the liquidus temperatures of silicates is observed for pl which shows a considerable delay in crystallization with progressive magma differentiation early crystallization of fe ti oxides in h2o bearing ferrobasaltic compositions precludes any significant fe enrichment during differentiation as fe enrichment is a characteristic feature of the skaergaard intrusion it implies that the skaergaard parental magma did not contain considerable amounts of water on the other hand our experiments indicate that the differentiation of some ferrobasaltic series from the columbia river flood basalt province might have occurred in magmatic systems containing significant amounts of volatiles 0 5 3 wt h2o

holocene palaeoecological reconstruction of three boreal peatlands in the la grande riviere region quebec canada pollen and macrofossil analyses from central peat cores along with 23 radiocarbon dates were used in palaeoecological reconstructions for three peatlands lg1 lg2 and lg3 within the lower la grande riviere watershed in northern boreal quebec basal ages from lg3 and lg2 indicate up to an 1100 years later and possibly more abrupt tyrrell sea retreat in the lg3 area compared with the timeline for the region both autogenic and allogenic factors were found to have influenced local vegetation succession and rates of peat accumulation internal autogenic factors such as peat accumulation were key elements for the general peatland developmental pathway that followed the classic hydrosere sequence pond fen bog regional climate and hydrography are the main external factors associated with changes in vegetation assemblages surface wetness and consequently rates of peat accumulation the lg2 and lg3 peatlands began developing shortly after 7000 cal bp as shallow ponds with herbaceous freshwater aquatic and e

impact of geodynamics on fluid circulation and diagenesis of carbonate reservoirs in a foreland basin example of the upper lacq reservoir aquitaine basin sw france abstract orogeny driven fluids that circulate in foreland basins can have strong impacts on petroleum systems and reservoir properties this applies to the upper cretaceous lacq reservoir of the aquitaine basin in southwestern france located north of the pyrenean mountains we study a drillcore from a 650 m deep oil reservoir to document how the evolution of a foreland basin which formed after a hyperextension phase affected fluid circulation and eventually reservoir diagenesis using drillcore samples petrographic observations fluid inclusion studies coupled with thermodynamic modeling isotopic and rare earth element geochemistry as well as basin modeling were performed to investigate and describe the fluid types and sources the pressure temperature evolution and the timing of diagenetic fluid flow early diagenesis involves some bacterial activity represented by micrite rims and framboidal pyrites as well as early dolomitization involving a mixture of meteoric and formation fluids during burial dolomite overgrowth saddle dolomites coarse blocky calcites and anhydrites precipitate the last products consist of iron oxide precipitation and meteoric recharge of the reservoir with groundwater our results indicate that after the deposition of the paleocene flysch formation mg rich low salinity hot and relatively deep clay released fluids migrated along thrust faults from deeper parts of the basin during the climax of the compressional pyrenean phase eocene they acted as dolomitizing hydrothermal fluids with a thermal disequilibrium in the order of 30 40 c hotter than the ambient host rocks another orogeny driven hydrothermal and mg poor fluid mixed with oil generated by jurassic barremian source rocks and precipitated calcites and anhydrites finally during uplift oxidizing fluids were laterally introduced as the present day groundwater hence by combining different petrographic geochemical and modeling proxies we document how the eocene orogenic phase played a crucial role in basin scale fluid flow and carbonate diagenesis

late holocene atmospheric dust deposition in eastern canada st lawrence north shore dust deposition in two ombrotrophic peatlands baie and ile du havre peatland idh bogs of the estuary and gulf of the st lawrence in eastern canada was reconstructed using elemental geochemistry the rare earth elements rees and other lithogenic element concentrations were measured by icp oes and q icp ms along two peat cores spanning the last 4000 years principal component analyses on the geochemical profiles show that rees display the same behavior as al ti sc and zr all conservative elements which suggests that rees are immobile in the studied peat bogs and can be used as tracers of dust deposition plant macrofossils were also used to infer past environmental and humidity changes the dust fluxes were reconstructed using the sum of rees ree the range of dust deposition varies from 0 2 to 3 8 g m 2 yr 1 in the baie bog while the idh bog shows lower fluxes ranging between 0 1 and 1 2 g m 2 yr 1 the highest dust fluxes in the baie bog were recorded from 1750 1000 cal bp to 600 100 cal

the origin of dolomites in tertiary sediments from the margin of great bahama bank abstract based on an integrated geochemical and petrographic investigation of dolomites from two cores drilled on great bahama bank we have determined three different environments of formation for the dolomites that are common throughout the pliocene and miocene parts of these cores the first environment of dolomitization occurs in association with development of nondepositional surfaces dolomite typically forms below each of these surfaces the concentration and extent of which is governed by the length of the period of nondeposition these dolomites are recognized by their association with the nondepositional surfaces characteristic positive 18o values indicative of formation from cold bottom waters and 18o and sr profiles with depth that suggest formation in the presence of diffusive temperature and sr gradients the second environment of dolomitization occurs in pore fluids where the cation and anion profiles are governed by diffusive processes the dolomite forming here is termed background dolomite this is a microsucrosic dolomite and forms both by recrystallization of the existing sediment and precipitation directly into void space dolomitization by this mechanism uses a local source of mg2 and consequently the dolomite never constitutes more than between 5 and 10 of the sediment this type of dolomite is characterized by extremely high sr concentrations which reflect concentrations of sr2 in the pore fluids from which it formed the high concentrations of sr2 in the pore fluids arise through the continued recrystallization of metastable aragonite and high mg calcite to dolomite and low magnesium calcite driven by oxidation of organic material by sulfate not only does sulfate reduction provide an additional thermodynamic drive for recrystallization but because the absolute concentration of sr2 in the pore fluids is governed by the solubility of celestite srso4 removal of sulfate allows the sr2 ca2 ratio of the interstitial fluid to become much higher than normally encountered the final type of environment of dolomitization is associated with coarse grained reefal sediments the pervasive nature of the dolomitization and the relatively normal sr concentrations suggest the circulation of normal marine water in a relatively open system

magma source beneath the bezymianny volcano and its interconnection with klyuchevskoy inferred from local earthquake seismic tomography abstract we present a new 3d model of p and s wave velocities and vp vs ratio to 20 km depth beneath the active klyuchevskoy and bezymianny volcanoes kamchatka russia in this study we use travel time data from local seismicity recorded by temporary stations of the pire experiment from october 24 to december 15 2009 and permanent stations operated by the kamchatkan branch of geophysical survey kbgs the calculations were performed using the lotos code koulakov 2009 the resolution limitations were explored using a series of synthetic tests with checkerboard patterns in the horizontal and vertical sections at shallow depths the resulting vp and vs anomalies tend to alternate on opposite sides of the lineation connecting the most active volcanic centers of the klyuchevskoy volcanic group kvg this prominent lineation suggests the presence of a large fault zone passing throughout the kvg consistent with regional tectonics we suggest that this fault zone weakens the crust creating a natural pathway for magmas to reach the upper crust beneath bezymianny volcano we observe a shallow anomaly of high vp vs ratio extending to 5 6 km depth beneath klyuchevskoy another high vp vs anomaly is observed at deeper depths of 7 and 15 km these findings are consistent with the regional scale model of koulakov et al 2013a and provide some explanation for how very different eruption styles can be maintained at two volcanoes in close proximity over numerous eruption cycles

penetrative calcretes and their stratigraphic implications multiple calcrete horizons previously considered representative of true subaerial exposures may in fact be false penetrative calcretes related to only one subaerial exposure event individual subaerial exposure periods can produce a true surficial calcrete plus a series of penetrative calcretes although penetrative calcrete horizons are not laterally traceable over long distances they are very similar to surficial calcretes are commonly found at sequence and or lithologic boundaries permeability anomalies and can be easily misinterpreted in core borings as representing individual exposure events recent penetrative calcretes are common on elevated limestone ridges of the caicos islands where roots penetrate downward seeking ground water moisture in glacial times penetrative calcretes may have been present throughout carbonate platforms as ground water levels were much lower penetrative and surficial calcretes can be differentiated by the lower concentrations of insoluble al and fe in penetrative calcretes

a 9600 year record of water table depth vegetation and fire inferred from a raised peat bog prince edward island canadian maritimes a 582 cm long peat core was collected from baltic bog an ombrotrophic peatland in north eastern prince edward island canada the core was studied for testate amoebae plant macrofossils macrocharcoal peat humification and organic matter content the results show that baltic bog first developed 9600 cal a bp as a minerotrophic peatland fen dominated by cyperaceae at 8200 cal a bp the fen transitioned into a peat bog dominated by sphagnum between 8200 and 4000 cal a bp water table depth wtd was generally low and the bog surface supported trees such as picea mariana from 4000 to 1700 cal a bp wtd rose and the bog became more open the macrocharcoal results show that the period 2000 1000 cal a bp was characterized by several fire events that may have occurred on the bog surface at the core site the results presented in this paper correspond closely with previous fossil pollen research done at baltic bog and suggest that regional climate change was a key factor in controlling long term wtd variability and vegetation change at the site

examining the role of allogenous and autogenous factors in the long term dynamics of a temperate headwater peatland southern quebec canada abstract plant macrofossil and testate amoebae analyses were conducted on a sedimentary core taken from a headwater peatland located near the summit of a hill at the northern extension of the adirondack mountains quebec canada the aims were to reconstruct the developmental stages of the peatland and to examine the allogenous and autogenous factors associated with its long term dynamics results were compared with a quantitative paleoclimatic reconstruction based on the modern analog technique using pollen data from the same core the long term development of the peatland pond rich fen intermediate fen poor fen bog mainly reflects an autogenous hydroseral succession active peat accumulation under the relatively dry climate of the early holocene suggests that summer temperature was a critical factor in peat accumulation through enhanced biomass production a major long term decrease in net peat accumulation rates and a progressive decline of mean water table depth occurred during the mid to late holocene 7900 500 cal yr bp even though annual precipitation was abundant at the time the high summer temperature associated to the highest evapotranspiration rates maintained a low water table which in turn led to strong humification of the peat a similar synchronous pattern in vertical peat accumulation dynamics characterized another nearby peatland based on these results we suggest that small peatlands situated atop a watershed and or within a small watershed are ecosystems sensitive to changes in precipitation and or evapotranspiration due to their limited water supply

limitation of laboratory measurements in evaluating rock properties of bioturbated strata a case study of the upper jubaila member in central saudi arabia abstract to understand the limitations of laboratory measurements in evaluating the rock properties of bioturbated reservoirs this study integrates field investigations computed tomography ct scanning image analysis spot permeability measurements and geostatistical modeling with previously published porosity and permeability results of upper jurassic bioturbated carbonate strata in central saudi arabia upper jubaila member the porosity and permeability measurements from previous studies have indicated that the studied strata are very tight with porosity ranging from 0 3 to 4 8 mean 1 2 1 4 and permeability ranging from 0 0 to 2 0 md 0 01 0 03 md the field investigation results from this study showed that these strata were extensively bioturbated 10 to 50 burrow intensity and dominated by thalassinoides burrows these thalassinoides burrows had either open or partially filled shafts with diameters ranging from 2 to 5 cm in 2d outcrop faces the results from ct scanning of a boulder sized rock sample 68 cm 27 cm 15 cm with 20 bioturbated intensity from the studied strata showed that the thalassinoides burrows developed a connected burrow porosity network within a tight matrix spot permeabilities of the matrix ranging from 0 05 to 0 22 md with 0 07 0 05 md interestingly however in cropped volumes of the ct scans with core plug and whole core sizes the entire connected pore network of the thalassinoides burrows is not represented instead these volumes show isolated pores erroneously indicating the absence of a connected permeability pathway for thalassinoides burrows in the ct scanned sample in 2d slices of the ct scans however thalassinoides burrows show connected porous pore network from one end to the opposite end suggesting a permeable pathway the visual porosity estimated from these 2d slices has a value of 18 4 8 which is significantly larger than what was estimated for the upper jubaila strata in previous studies geostatistical models of the ct scanned sample estimated that the bulk permeability permeability of a homogenized sample with a steady state flow was at least 1200 md this value is also significantly higher than previous estimates for the studied strata this study highlights the inability of core plugs and full diameter cores to capture the complete burrow porosity network a limitation that can be problematic in the characterization of rock properties of bioturbated hydrocarbon reservoirs

geophysical source conditions for basaltic lava from santorini volcano based on geochemical modeling abstract santorini volcano sits 145 km above the aegean wadati benioff zone where the african plate subducts northward beneath eurasia there are only a few localities in the whole aegean where basaltic lavas primitive enough to constrain mantle processes beneath the aegean arc can be found in this work we analyzed one such locality a basalt lava from the southern part of santorini we apply a suite of petrological tools primacalc2 and abs5 in sequence to estimate magma chamber conditions primary magma composition mantle melting conditions and slab dehydration conditions back calculation modeling based on major element chemistry yields shallow magma chamber conditions of p 0 02 gpa fo 2 qfm 2 and 1 wt h 2 o in the primary magma the estimated major element composition of this primary magma then leads to estimated mantle melting conditions of 2 1 gpa 1353 c and f 8 whereas a more precise estimate derived from trace element modeling implies 1 7 gpa 1323 c and f 18 furthermore the trace element model implies a slab flux derived from 4 6 gpa 150 km slab depth the estimated slab depth magma segregation conditions and magma chamber depth are all consistent with seismic observations supporting slab dehydration in the seismically imaged steep slab interval and flux melting in a relatively hot mantle wedge

ages of calderas large explosive craters and active volcanoes in the kuril kamchatka region russia the ages of most of calderas large explosive craters and active volcanoes in the kuril kamchatka region have been determined by extensive geological geomorphological tephrochronological and isotopic geochronological studies including more than 600 14c dates eight krakatoa type and three hawaiian type calderas and no less than three large explosive craters formed here during the holocene most of the late pleistocene krakatoa type calderas were established around 30 000 40 000 years ago the active volcanoes are geologically very young with maximum ages of about 40 000 50 000 years the overwhelming majority of recently active volcanic cones originated at the very end of the late pleistocene or in the holocene these studies show that all holocene stratovolcanoes in kamchatka were emplaced in the holocene only in the eastern volcanic belt periods of synchronous intensified holocene volcanic activity occurred within the time intervals of 7500 7800 and 1300 1800 14c years bp

shallow burial dolomite cement a major component of many ancient sucrosic dolomites dolomite cement is a significant and widespread component of phanerozoic sucrosic dolomites cements in dolomites that were never deeply buried are limpid have planar faces non saddle forms often distinct zonation in cathodoluminescence and form syntaxial overgrowths on crystals facing pores five samples of sucrosic dolomites interpreted as having had mostly limemudstone or wackestone precursors in four carbonate aquifers provide insights into the abundance of planar cements in sucrosic dolomites such cement comprises 11 to 45 32 mean of peritidal to sub tidal dolomites on an outcrop in the edwards aquifer early cretaceous of central texas 19 to 33 25 mean of ramp dolomites in the hawthorn group oligomiocene and 50 to 70 in shelf dolomites of the avon park formation eocene in the upper floridan aquifer of sub surface peninsular florida 18 to 45 32 mean of sub tidal shelf dolomites in quarry sections of the burlington keokuk formation early mississippian in south eastern iowa and 18 to 76 50 mean in shallow cores and outcrops of outer shelf dolomites from the gambier limestone oligo miocene of south australia backstripping the cement phases revealed by cathodoluminescence colour photomicrographs documents the effects of cements on textural coarsening pore space reduction induration and general maturation of these dolomites most pre holocene dolomites are multiphase crystalline rocks composed of i seed crystals or cores ii crystal cortices that concentrically enlarged the cores and iii free space syntaxial precipitates of limpid cement around the crystals remaining caco3 grains and micrite can be replaced by dolomite but typically they are dissolved between stages ii and iii creating systems of intercrystal and mouldic pores typical of sucrosic dolomites networks of cement overgrowths aided by water filled pore systems under hydrostatic to lithostatic pressure are judged to slow or prevent compaction in sucrosic dolomites it can be argued that cortex growth involves both replacement of caco3 particles and microcementation of their interparticle pores this interpretation and the abundance of cements in so many dolomites would obviate the controversy over the volumetrics of replacement dolomitization limpid planar and syntaxial dolomite cements of early diagenetic origin are interpreted to have precipitated from clear pore waters at low temperatures 30 to 35 c and shallow burial depths 100 m in water saturated networks of dolomite silt and sand cements in many dolomites in island and continental aquifer systems appear to result from event driven processes related to sea level highstands cementation events can follow replacement

holocene development of maritime ombrotrophic peatlands of the st lawrence north shore in eastern canada article i nfo article history received 13 august 2013 available online 27 may 2014 macrofossil analyses were used to reconstruct long term vegetation successions within ombrotrophic peatlands bogs from the northern shorelines of the st lawrence estuary baie comeau and the gulf of st lawrence havre st pierre over the holocene the timing and the ecological context of peatland inception were similar in both regions and were mainly influenced by fluctuations in relative sea level peat accumulation started over deltaic sands after the withdrawal of the goldthwait sea from 7500 cal yr bp and above silt clay deposits leftby the laurentian marinetransgression after 4200 cal yr bp in each region the early vegetation communities were similar within these two edaphic contexts where poor fens with cyperaceae and eastern larch larix laricina established after land emergence the rapid transitions to ombrotrophy in the peatlands of baie comeau are associated with particularly high rates of peat accumulation during the early developmental stage the results suggest that climate was more propitious to sphagnum growth after land emergence in the baie comeau area macrofossil data show that treeless sphagnum dominated bogs have persisted over millennia and that fires had few impacts on the vegetation dynamics this study provides insight into peatland vegetation responses to climate in a poorly documented region of northeastern america

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

diffusion and mass balance of mg during early dolomite formation monterey formation abstract diffusion from overlying seawater is capable of supplying enough mg to account for all of the early diagenetic dolomite observed in the monterey formation 0 5 20 vol the amount formed depends on the mg flux magnitude into the sediment which is proportional to the rate of dolomite precipitation and inversely proportional to the sediment accumulation rate the amount of dolomite formed is calculated for accumulation rates of 50 and 600 m ma using reaction rate constants obtained from the mg concentration profile of dsdp sites 479 533 and 147 and proposed profiles that assume significant dolomite formation in the uppermost tens of meters of sediment advective pore water flow from compaction decreases the mg flux and becomes increasingly significant as the accumulation rate increases and the reaction rate decreases advection alone during compaction supplies sufficient mg to account for a realistic maximum of 2 vol dolostone within a compacted section an approximate evaluation of the rayleigh number suggests that the low permeability of siliceous ooze prevents convective fluid flow at shallow burial depths the mg mass balance is calculated from dolomite abundance in monterey formation sections santa maria basin area california pore water and solid particle velocities are calculated as a function of sediment depth using a porosity depth relation for average siliceous sediment based on a composite of dsdp data the bulk sediment diffusion coefficient increases with sediment depth at a rate proportional to the geothermal gradient at shallow burial depths seawater is probably the only significant source of mg dolomite volcanic ash and clay minerals are the only significant sinks clay mineral organic matter and silica diagenesis may provide additional mg at deeper burial depths the more or less regular spacing of dolomitic layers may be controlled by the residence time of the dolomite forming layer within the uppermost sediment where the mg flux is a maximum

quantifying spatial and temporal holocene carbon accumulation in ombrotrophic peatlands of the eastmain region quebec canada 1 northern peatlands represent important stocks of organic carbon c peatland c dynamics have the potential to influence atmospheric greenhouse gas concentrations and are therefore of interest concerning future climate change quantification of holocene variations in peat c accumulation rates is often based on a single deep core however deep cores may overestimate accumulation rates when extrapolated to the ecosystem scale we propose a reconstruction of c sequestration patterns based on multiple cores from three ombrotrophic peatlands in boreal quebec canada both total c accumulation and temporal variations herein were quantified radiocarbon dated stratigraphies from different sections resulted in peatland specific age depth models peatland initiation started rapidly after deglaciation around 7500 cal bp vertical accumulation slowed down in the course of the holocene whereas lateral expansion was rapid in the early stages but slowed down near mid holocene total c accumulation showed maximum rates between 5250 and 3500 cal bp with a regional mean holocene apparent rate of 16 2 g m 2 yr 1 the eastmain peatlands have been modest sinks of organic c compared to those of alaska western canada and western siberia although differences in calculation methods hamper direct comparisons considering within peatland dynamics maximum total c sequestration coincided with a period of slowing down in both lateral expansion and vertical accumulation late holocene diminishing peatland c sink functions have been attributed to autogenic as well as allogenic factors height induced surface drying and or neoglacial cooling effects may have forced the slowing down of c sequestration in the studied bogs results further show that in order to obtain an accurate quantification of past c sequestration reconstructions of peatland expansion are essential

inside out dolomite abstract inside out dolomite crystals are unusual because their cores are younger than their encasing cortices in the cayman formation middle miocene of grand cayman they developed diagenetically from zoned dolomite crystals that have cores formed of high ca calcian dolomite hcd 55 mol caco3 and outer cortical zones formed of low ca calcian dolomite lcd 3 or oscillatory zoned lcd hcd the cores of these crystals labeled as type i have a euhedral rhombic outline with no embayments or angular reentrants and commonly contain calcite inclusions and or micropores hollow dolomite crystals evolved from these crystals as preferential dissolution removed all or part of the hcd core later calcite or dolomite cement was precipitated inside the hollow crystals the former produced dolomite crystals with a calcitic core i e dedolomite whereas the latter produced inside out dolomite crystals that have a dolomite core lcd or hcd encased by a dolomite cortex the cores of the inside out dolomite crystals labeled as type ii have an irregular outline characterized by angular reentrants and or embayments micropores that are usually larger than those in the type i cores but few calcite inclusions the cortical zones have a euhedral rhombic motif irrespective of the type of core development of insideout dolomite crystals may significantly alter the average ca of the dolostones as hcd is lost to dissolution and lcd or hcd cement is precipitated in its place the 18o may also change inasmuch as it is thought to covary with ca in some tertiary dolostones the genesis of inside out dolomite crystal may offer an alternative explanation for the textures e g clotted cathodoluminescence patterns in some ancient dolomite crystals that have been attributed to replacement and or recrystallization

origin of dolomite in the arab d reservoir from the ghawar field saudi arabia evidence from petrographic and geochemical constraints a significant proportion of oil production from the kim meridgian arab d strata in the ghawar field saudi arabia originates from dolomitized rocks stratigraphic petrographic and geochemical data suggest that at least four episodes of dolomitization affected these sediments the lower portion of the arab d zone 3 is only partially dolomitized with the dolomite frequently being associated with firm grounds we propose that these dolomites were formed on an outer ramp setting with a maximum water depth of 50 m during a period of nondeposition with the dolomitization process being promoted by the oxidation of organic material and the diffusion of mg 21 from the overlying seawater the dolomites in zone 2b are geochemically dis tinct compared to those in zone 3 in that they have relatively positive oxygen isotope compositions 2 1t o22 compared to 26 5 the relatively positive oxygen isotope composition and the geochemical sim ilarity of zone 2b to the dolomites in zone 1 which are intimately associated with the overlying evaporites has led us to conclude that the zone 2 dolomites probably formed by the reflux of hypersaline fluids through the sediments these hypersaline fluids bypassed zone 2a by moving through the grain dominated sediments early cemen tation and dolomite formation made these units more susceptible to later fracturing that affected the entire arab d formation this frac turing allowed higher temperature fluids to leach the dolostones there by removing any remaining calcite and partially resetting the oxygen isotope composition of some of the dolomites as a result of this later dolomitization event rocks that were only partially dolomitized were leached creating units with extremely high permeability and porosity super k intervals dolomites in the lower zone 3 were recrystallized during burial by the normal geothermal gradient leading to the pre sent negative oxygen isotope values zone 1 dolomites are petrograph ically distinct from zone 2 dolomite in that they are mimetic and fabric preserving although they are geochemically similar this mimetic style of dolomitization occurs immediately adjacent to the overlying anhy drite and is interpreted to have formed very shortly after deposition from hypersaline brines recovery and their presence is inferred from a combination of production data and the diameter of the bore hole as measured using the caliper log as a result of the importance of dolomite in the formation of the super k intervals within the arab d an understanding of the paragenesis of these zones is important not only in predicting super k formation within the arab d but also as an analogue for understanding other dolomitized res ervoirs with high permeability and porosity previous characterization work of dolostones from the arab d in the ghawar field cantrell et al 2004 has identified three types of dolomite with distinctive petrographic stratigraphic and geochemical characteristics fabric preserving non fabric preserving and baroque dolomite fabric pre serving dolomite is very finely crystalline in which petrographic details of the original limestone fabric are usually well preserved fabric preserving dolomite contains low concentrations of fe average 247 ppm fe and relatively positive oxygen isotope values average

dolomitization of the late cretaceous paleocene platform carbonates golkoy ordu eastern pontides ne turkey abstract late cretaceous paleocene agillar formation in the eastern pontide zone ne turkey is composed of shallow marine platform carbonates that were buried until uplift in late paleocene time the formation which is represented by 100 m thick reefal limestones around golkoy is completely dolomitized on the basis of petrographic and geochemical features four different replacive and cement dolomite phases are present the replacive dolomites which are cut by low amplitude stylolites include 1 fine crystalline planar s dolomite rd1 and 2 coarsely crystalline planar s e dolomite rd2 two types of dolomite cements were developed in minor amounts 1 a coarse dolomite cement cd1 that mostly fills molds vugs and fractures in rd1 dolomites and 2 rim dolomite cement cd2 that commonly develops on the space facing surfaces of rd2 dolomite the replacive dolomites are nearly stoichiometric ca 49 51 mg 48 50 and have 18 o values of 3 5 to 1 6 vpdb 13 c values of 1 1 to 0 8 vpdb and 87 sr 86 sr ratios of 0 707104 to 707458 sr na mn and fe concentrations of replacive dolomites are 102 171 ppm bdl 371 ppm 244 9941 ppm and 2643 8951 ppm respectively petrographic and geochemical data indicate that the replacive dolomites were formed prior to chemical compaction at shallow to intermediate burial depths from late cretaceous paleocene seawater and or seawater slightly modified by water rock interaction process and then recrystallized by meteoric waters at increasing burial depths and temperatures compared with replacement dolomites cd1 dolomites yield lower 18 o values 4 9 to 5 3 vpdb similar 13 c values 1 2 to 0 5 vpdb and higher 87 sr 86 sr ratios 0 707660 0 707609 the cd1 dolomites overlie the low amplitude stylolites and have homogenization temperatures between 94 and 112 c indicating that they were deposited from basinal brines although replacive dolomites and dolomite cements have similar na bdl 413 ppm mn 259 6990 ppm and fe 2184 6690 ppm concentrations the cements have lower sr contents 63 114 ppm like replacive dolomites cd1 dolomite is nearly stoichiometric ca 49 50 mg 47 49 but cd2 dolomite is slightly ca rich ca 51 52 mg 47 48 the cd2 dolomite is overlain by coarsely crystalline mosaic calcite cement indicates that diagenetic fluids eventually evolved to undersaturation with respect to dolomite and oversaturation with respect to calcite

microfacies diagenesis and oil emplacement of the upper jurassic arab d carbonate reservoir in an oil field in central saudi arabia khurais complex abstract the upper jurassic kimmeridgian arab d reservoir of the arab formation in the arabian peninsula is considered to be the largest hydrocarbon carbonate reservoir in the world despite a relative large number of studies dealing with lithofacies and depositional sequences there are still few studies dealing with diagenesis of this supergiant reservoir in this study petrographic cathodoluminescence and ultra violet light fluorescence microscopy analyses of the arab d reservoir in an oil field of saudi arabia khurais complex have been combined with isotope geochemistry 13c 18o and 87sr 86sr to decipher the sequence of diagenetic events affecting the reservoir before and during oil emplacements and the impact of depositional mineralogies and their modifications during the diagenesis on the reservoir quality and heterogeneity all the analyzed samples correspond to lithofacies that can be ascribed to nine microfacies types mft 1 to mft 9 three stages of carbonate dissolution d1 to d3 four stages of calcite cements c1 to c4 and 5 zones of replacive dolomite and dolomite cement d1 to d5 have been documented from diagenetic environments ranging from marine to late burial abundant oil fluid inclusions have been recognized in calcite c3 and c4 and dolomite d5 from wells located in the flanks of the structure group 2 of cements cements from wells located in the center of the structure are largely oil inclusions free group 1 of cements this distribution suggests that group 2 of cements formed within the oil water transition zone of the reservoir during the oil infilling of the structure allowing to constrain the timing of oil emplacement and suggesting at least two phases of oil charging porosity enhancement by corrosive dissolution d3 occurred during late burial and took place just before precipitation of dolomite d5 and calcite c4 and just before the second stage of hydrocarbon arrival suggesting the presence of aggressive fluids preceding the late phase of hydrocarbon migration cross plot of carbon vs oxygen stable isotopes shows a general trend toward decreasing 18o values with increasing burial depth whereas all 13c values remain positive except for group 2 of c3 and c4 calcites which exhibit negative up to 4 6 13c values the later suggest precipitation from pore waters with increased volumes of 12c as a by product of hydrocarbon maturation except for c4 all the 87sr 86sr values are within the range of the late jurassic seawater suggesting precipitation from jurassic marine or evolved marine pore waters in contrast the more radiogenic calcite c4 suggests a source from fluids that interacted with siliciclastics or clay rich sequences depositional mineralogy of the grainy lithofacies is interpreted to have had an impact on the effectiveness of cementation and dissolution controlling the reservoir heterogeneity due to excess of cementation reservoir quality is worse in grainstone microfacies rich in aragonitic components and better in grainstone and packstone microfacies poorer in aragonitic grains but affected by late dissolution of micrite the integration of all these data resulted in a more precise understanding of the reservoir quality and heterogeneity

early diagenetic dolomite cements examples from the permian lower magnesian limestone of england and the pleistocene carbonates of the bahamas abstract early diagenetic dolomite cements are found in the permian lower magnesian limestone of eastern england and the pleistocene carbonates of great abaco island bahamas in the lower magnesian limestone the dolospar occurs as isopachous rinds that have grown both centripetally and centrifugally on the dolomitized micrite envelopes of hollow centered allochems because compactional fractures penetrate both the allochem walls and the cement rinds dolomite cementation is inferred to have predated any significant sediment accumulation in the great abaco carbonates limpid dolomite forms isopachous rinds around inter and intragranular porosity and is postdated by meteoric calcite cement both examples of early diagenetic dolomite cement textures developed as a consequence of changes in pore fluid chemistry from marine to mixed meteoric marine to meteoric waters therefore the presence of this cement type may point toward aliagenetic environments resulting from marine regressions

predicting rock mechanical properties of carbonates from wireline logs a case study arab d reservoir ghawar field saudi arabia abstract four hundred plug samples from the arab d carbonate reservoir ghawar field were tested for acoustic and mechanical properties at increasing triaxial stress the results show that the rock mechanical parameters are primarily functions of porosity and to a lesser degree of mineralogy texture and pore fabric in order of degree of impact from higher to lower the rock mechanical parameters of the intact matrix rock show no significant changes with stress under reservoir condition the study enabled the generation of general and layer specific correlation formulae of porosity with p wave velocity s wave velocity static and dynamic constants and the angle of internal friction the formulae were then applied to a key well in the ghawar using the compressional wave slowness from a multipole array acoustic log mac baker atlas to derive rock mechanical pseudo logs on reservoir scale referred to here as general and on individual reservoir zone scale referred to here as layer specific comparison made between the general and the layer specific pseudo logs shows good agreement for each of the elastic constants with matching peaks and troughs throughout the logs in addition the laboratory derived rock mechanical constants show a good agreement with the pseudo logs where there is some difference between the general and layer specific pseudo logs the layer specific log shows better correlation with the laboratory derived constants it can be concluded that the porosity correlation is an accurate representative and cost effective method of obtaining a rock mechanical profile of the arab d reservoir the derived formulae have been implemented as predictive tools in reservoir development and management e g hydrofracturing and underbalanced drilling and new prospect evaluation the rock mechanical layering scheme shows higher resolution in the prolific part of the arab d reservoir than the saudi aramco conventionally used zonation each of zones 2b and 3a consists of two rock mechanical layers furthermore the least prolific zones lower part of 3a the whole of 3b and 4 form one rock mechanical layer

new distribution coefficient for the incorporation of strontium into dolomite and its implications for the formation of ancient dolomites late tertiary dolomites form the bahamas exhibit a strong inverse correlation between sr and mol mgco sub 3 it is proposed that this relation is a result of a distribution coefficient dependent on the concentration of ca in dolomite because these dolomites precipitated from water with a sr sup 2 ca sup 2 ratio similar to that of seawater a distribution coefficient d sub sr sup dolomite of 0 0118 is calculated for sr in stoichiometric dolomite this coefficient increases by about 0 0039 for every additional mol caco sub 3 in nonstoichiometric dolomite these data have three important implication first the new d sub sr sup dolomite is substantially lower than previously suggested second a relation has been established among the sr sup 2 ca sup 2 ratio of dolomite forming waters the major element composition of dolomites and the sr content of dolomites allowing the determination of the sr sup 2 ca sup 2 ratio of fluids involved in the formation of ancient dolomites third some published data sets on dolomites show a similar relation between sr content and major element composition suggesting that these dolomites may also have formed from seawater other data sets deviate from the correlation defined by little bahama bank dolomites indicating either dolomitization in fluids other than seawater or changes ofmore the sr sup 2 ca sup 2 ratio of seawater through time less