evaporite hosted native sulfur in trans pecos texas relations to late phase basin and range deformation major deposits of biogenic native sulfur are associated with narrow northeast trending grabens and normal faults that disrupt the gently tilted east dipping upper permian evaporite succession of the western delaware basin in trans pecos texas orebodies are restricted to geologic traps in the fractured and dissolution modified downfaulted blocks of the grabens other parallel regionally distributed grabens and normal faults are commonly the sites of noncommercial sulfur deposits and genetically related secondary replacement diagenetic limestone bodies the sulfur bearing structures probably formed during the later of two episodes of basin and range extension that have not previously been differentiated in texas but are well defined elsewhere in the western united states in texas several lines of evidence collectively support the existence of late phase northwest directed extension that was initiated in the middle miocene

bacterially mediated formation of diagenetic aragonite and native sulfur in zechstein carbonates upper permian central germany abstract neoformed diagenetic aragonite associated with organic rich aggregations and native sulfur occur within cavities of the ca2 and ca3 zechstein carbonates in central germany the cavities were formerly filled with gypsum bacterial sulfate reduction favored the precipitation of the carbonate phase this can be attributed to an increase in alkalinity accompanied with sulfate reduction the high sr concentrations of the neoformed aragonites compared to the low concentrations in the carbonate host rocks point to sulfate dissolution as the cation supplying process for the precipitation of aragonite low 13c values 10 pdb of the aragonite indicate that some of its carbon is derived from organic matter that has been oxidized by bacterial sulfate reduction aragonite inclusions bear rhomb shaped crystals of calcite replacing former dolomite elevated mg ca ratios due to this dedolomitization may have promoted the precipitation of aragonite instead of calcite the aragonite precipitated in the near surface meteoric vadose zone in recent times aragonite crystals display a platy habit sem analyses show that two types of micro rods are associated with these plates the mineralized micro rods are interpreted to be fossilized bacteria aragonite inclusions most of which contain organic rich aggregations yield a distinctive biomarker pattern high concentrations of specific unsaturated fatty acids are clearly indicative of newly produced organic matter and reflect the presence of a discrete microbial community being associated with the formation of the aragonite at one of the studied localities the aragonite is accompanied by native sulfur the formation of sulfur was mediated by h2s oxidizing bacteria this is corroborated by the presence of densely packed curved rods representing permineralized bacterial cells on and within the sulfur

genesis and evolution of the fumaroles of vulcano aeolian islands italy a geochemical model a geochemical model explaining the presence of fumaroles having different gas composition and temperature at the top of the crater and along the northeastern coast of vulcano island is proposed a pressurized biphase liquid vapor reservoir at the depth of about 2 km is hypothesized energy and mass balance sheets controlp t conditions in the system p t must vary along a boiling curve of brine as liquid is present the co2 content in the steam is governed by the thermodynamic properties of the fluids in the h2 nacl co2 system on the assumption that oxygen fugacity in the system is between the hm fmq oxygen buffers observed so2 h2s co2 co co ch4 ratios in the fumarolic gases at the fossa crater appear in equilibrium with a temperature higher than that observed such as may exist at depth the more reduced gas phases present on the sea side may result from re equilibrium processes in shallower aquifers the suggested model would help in monitoring changes in volcanic activity by analyzing fumarolic gases

helium 3 anomalies and crust mantle interaction in italy abstract the distribution of primordial 3he in the crust of italy has been investigated through a survey of groundwaters hot springs exploration and production geothermal wells the mantle derived component varies from 0 to 60 and reaches a maximum at vulcano in the eolian islands 3he anomalies occur where the conductive heat flow is relatively high but the relationships between heat flow and anomaly are uncertain the distribution of 3he in the main reservoir and cap rock to the larderello geothermal system shows that the mantle derived 3he varies from 5 to 40 of total he and reaches a maximum in fluids extracted from a depth of ca 3 km within the basement bomb produced tritiogenic 3he appears to make a near negligible contribution well 107 at larderello has been monitored over a period of 17 months and the 3 he 4 he ratio r varies from 1 4 to 1 6 times the atmospheric ratio ra whilst he ne varies from 9 to 160 a model is proposed for the larderello geothermal system whereby mantle derived heat and volatiles are advected to shallow 6 8 km depths in association with melts and released into the main geothermal reservoir at larderello in a non uniform manner possibly associated with fracturing isotopic and elemental equilibrium of gaseous species c o h appears to have taken place in the basement to the main reservoir from where fluid with r ra 3 2 has been extracted

formation of secondary carbonates and native sulphur in sulphate rich messinian strata sicily abstract microbially formed authigenic carbonates accompanied by native sulphur are present in the calcare solfifero below a thick succession of gypsum deposited during the messinian salinity crisis in sicily we sampled these carbonates and associated sulphur in five former sulphur mines to subject them to a detailed petrographic and geochemical study in order to explore their different modes of formation native sulphur formed in conjunction with microbial sulphate reduction which is reflected in its depletion in 34s 34s values as low as 2 vs v cdt and an enrichment of 34s in the residual sulphate 34s values as high as 61 the oxidation of organic matter by sulphate reduction increased alkalinity inducing precipitation of secondary carbonate minerals a set of authigenic limestones lacking sulphate minerals but characterized by pseudomorphs after gypsum and high 18o values as high as 9 vs v pdb reflects syngenetic mineral formation within evaporitic settings low 13c values as low as 52 vs v pdb reveal that these carbonate phases were formed by microbial sulphate reduction coupled to the oxidation of biogenic methane another set of authigenic carbonates that replaced sulphate minerals is typified by low 18o values as low as 4 these carbonates formed epigenetically during later diagenesis following compaction dissolution of gypsum or anhydrite by meteoric waters delivered the sulphate for microbial sulphate reduction low carbon isotope values of these carbonates 29 to 5 indicate that carbonate was derived from the oxidation of crude oil and possibly minor methane partly involving different degrees of admixture of dissolved carbonate from other sources although the studied rocks with their vast amounts of secondary carbonate minerals and sulphur seem to indicate a similar genesis at first glance having formed by biogeochemical transformations of sulphate and hydrocarbons this study reveals that these processes can occur at different times in variable geological environments

stable isotope mapping in messinian evaporative carbonates of central sicily mapping stable isotope isolines in both modern and ancient evaporative carbonate formations demonstrates that regional variations of 18 o values exist in the case of the messinian central sicilian basin an ancient evaporite basin the distribution pattern of the 18 o isolines can be related to the paleogeometry and paleohydrology of the basin isolines of equal 13 c values also show large regional variations possibly reflecting the domination of different bacterial processes oxidation sulfate reduction or methanogenesis in different regions the potential application for stable isotope mapping in evaporative carbonate formations deposited in both marine and lacustrine environments lies in its ability to predict the location of depositional centers in ancient evaporite basins

carbonate replacement of lacustrine gypsum deposits in two neogene continental basins eastern spain abstract bedded nonmarine gypsum deposits in the miocene teruel and cabriel basins eastern spain are partly replaced by carbonate the libros gypsum teruel graben is associated with fossiliferous carbonate wackestones and finely laminated organic matter rich mudstones which accumulated under anoxic conditions in a meromictic permanent lake the gypsum is locally pseudomorphed by aragonite or less commonly replaced by calcite low 13c values indicate that sulphate replacement resulted from bacterial sulphate reduction processes that were favoured by anacrobic conditions and abundant labile organic matter in the sediments petrographic evidence and oxygen isotopic composition suggest that gypsum replacement by aragonite occurred soon after deposition a subsequent return to oxidising conditions caused some aragonite to be replaced by diagenetic gypsum native sulphur is associated with some of these secondary gypsum occurrences the los ruices sulphate deposits cabriel basin contain beds of clastic and selenitic gypsum which are associated with limestones and red beds indicating accumulation in a shallow lake calcite is the principal replacement mineral bacterial sulphate reduction was insignificant in this basin because of a scarcity of organic matter stable isotope composition of diagenetic carbonate indicates that gypsum replacement occurred at shallow burial depths due to contact with dilute groundwaters of meteoric origin depositional environment evidently has a major influence upon the diagenetic history of primary sulphate deposits the quantity of preserved organic matter degradable by sulphate reducing bacteria is of particular importance and along with groundwater composition is the main factor controlling the mechanism of gypsum replacement by carbonate

late stage calcites in the permian capitan formation and its equivalents delaware basin margin west texas and new mexico evidence for replacement of precursor evaporites comparison of upper guadalupian fore reef reef and back reef strata from outcrops in the guadalupe mountains with equivalent subsurface cores from the northern and eastern margins of the delaware basin indicates that extensive evaporite diagenesis has occurred in both areas in both surface and subsurface sections the original sediments were extensively dolomitized and most primary and secondary porosity was filled with anhydrite these evaporites were emplaced by reflux of evaporitic fluids from shelf settings through solution enlarged fractures and karstic sink holes into the underlying strata outcrop areas today however contain no preserved evaporites in reef and fore reef sections and only partial remnants of evaporites are retained in back reef settings in their place these rocks contain minor silica very large volumes of coarse sparry calcite and some secondary porosity the replacement minerals locally form pseudomorphs of their evaporite precursors and less commonly contain solid anhydrite inclusions some silicification dissolution of anhydrite and conversion of anhydrite to gypsum have occurred in these strata where they are still buried at depths in excess of 1 km however no calcite replacements were noted from any subsurface core samples subsurface alteration has also led to the widespread late stage development of large and small scale dissolution breccias the restriction of calcite cements to very near surface sections petrographic evidence that the calcites post date hydrocarbon emplacement and the highly variable but generally light carbon and oxygen isotopic signatures of the spars all indicate that calcite precipitation is a very late diagenetic telogenetic phenomenon evaporite dissolution and calcitization reactions have only taken place where permian strata were flushed with meteoric fluids as a consequence of tertiary uplift tilting and breaching of regional hydrological seals a typical sequence of alteration involves initial corrosion of anhydrite one or more stages of hydration dehydration during conversion to gypsum dissolution of gypsum and precipitation of sparry calcite such evaporite dissolution and replacement processes are probably continuing today in near outcrop as well as deeper settings this study emphasizes the potential importance of telogenetic processes in evaporite diagenesis and in the precipitation of carbonate cements the extensive mineralogical and petrophysical transformations which these strata have undergone during their uplift indicates that considerable caution must be exercised in using surface exposures to interpret subsurface reservoir parameters in evaporitic carbonate rocks

geology and genesis of sulfur deposits at ras gemsa area red sea coast egypt field petrographic and geochemical analyses indicate that the native sulfur at ras gemsa is off diagenetic origin the sulfur formed together with megacrystalline dolomite biogenic dolomite and biogenic calcite by bacterial action on sulfate in the presence of organic matter hydrocarbons the sulfur occurs in an uplifted horst block consisting of evaporite carbonate rocks overlying the middle miocene oil and gas bearing strata the evaporite deposits are interpreted to be a composite sequence that includes deposits of shallow lagoonal subaqueous and supratidal sabkha environments two types of dolomite microcrystalline and megacrystalline are recognized in the studied sequence stable isotope data showed that the microcrystalline dolomite has high 18 o values mean 1 05 pdb and relatively low 13 c values mean 3 2 pdb these results indicate that the microcrystalline dolomite was deposited mainly under marine evaporitic conditions the megacrystalline dolomite is characterized by negative 18 o values mean 6 8 pdb and strongly negative 13 c values mean 24 05 pdb the negative 18 o values are probably due to the effect of hot conditions or depleted meteoric water and or biological effects during dolomite crystallization the negative 13 c values signify the important role played by the sulfate reducing bacteria in the presence of organic matter

biological influences on modern sulfates textures and composition of gypsum deposits from guerrero negro baja california sur mexico abstract gypsum caso 4 2h 2 o deposits from a range of sedimentary environments at guerrero negro baja california sur mexico were investigated for microscale texture and composition in order to differentiate features formed under substantial microbial influence from those for which microbial effects were relatively minor or absent gypsum deposits were classified according to their sedimentary environment textures crystal habit brine composition and other geochemical factors the environments studied included subaqueous sediments in anchialine pools and in solar salterns as well as subsurface sediments of mudflats and saltpans gypsum that developed in the apparent absence of biofilms included crystals precipitated in the water column and subsedimentary discs that precipitated from phreatic brines subsedimentary gypsum developed in sabkha environments exhibited a sinuous microtexture and poikilitically enclosed detrital particles water column precipitates had euhedral prismatic habits and extensive penetrative twinning gypsum deposits influenced by biofilms included bottom nucleated crusts and gypsolites developing in anchialine pools and saltern ponds gypsum precipitating within benthic biofilms and in biofilms within subaerial sediment surfaces provided compelling evidence of biological influences on crystal textures and habits this evidence included irregular high relief surface textures accessory minerals s ca carbonate sr ca sulfate and mg hydroxide and distinctive crystal habits such as equant forms and crystals having distorted prism faces

use of charophyte carbonates as proxy indicators of subtle hydrological and chemical changes in marl lakes example from the miocene bicorb basin eastern spain abstract the lower alluvial unit in the miocene bicorb basin contains several metric scale limestone intervals which record episodic shallow lacustrine environments in an alluvial setting developed during the early stage of the basin s evolution five main carbonate facies have been differentiated in the lacustrine limestones although calcite charophyte incrustations predominate and constitute the most striking features of these deposits the thinnest limestone intervals correspond to deposits from charophyte meadows in ponded shallow depressions in floodplains the thickest limestone intervals are mainly formed by banded limestones and usually correspond to diverse types of regressive sequences that have been interpreted as resulting from the infill of shallow lakes the sedimentological features and sequences show noticeable differences in the gradient of the littoral zones and the amount of palustrine deposits with models proposed for marl lakes charophytic carbonates from the best preserved facies show similar microtextures to those from recent charophyte incrustations the variations in stable isotopes 13 c 18 o for these primary carbonates occur in parallel with luminescence variations and correspond to hydrological changes and variations in solute composition and eh ph status in the lake waters the carbonates that display moderate to strong diagenetic modifications show a diverse degree of compaction aggrading neomorphism strong cementation and nodulization the isotopic values for these are arranged in diverse clusters there is a correlation between the degree of luminescence and the 13 c this suggests that hydrological and hydrochemical variations both in the lacustrine and diagenetic environments are being recorded in parallel we emphasize the need for further comparative studies between recent and ancient charophytic carbonates as these carbonates have been used in palaeoenvironmental reconstructions special attention must be paid to the diagenetic changes in ancient charophytic marls

helium isotopes and tectonics in southern italy geodynamic evolution of southern italy can be understood within the framework of the mediterranean alpine system subduction of a plate along the sicily calabrian forearc under the tyrrhenian sea has been suggested by many geophysicists although it is not yet confirmed and remains somewhat controversial helium isotope ratios provide useful information on the geotectonic structure of the region the authors report here the sup 3 h sup 4 he ratios of terrestrial gas samples from southern italy the observed sup 3 he sup 4 he ratios are relatively high in the eolian volcanic arc region and low in the other areas dichotomous explanations are presented firstly volcanic arc forearc hypothesis suggests the subduction along the sicily calabrian forearc secondly horizontal transport hypothesis is described based on the relationship between the ratios and radial distance from the recent spreading basin in southern tyrrhenian sea

upper triassic to lower cretaceous continental and coastal saline lake evaporites inthe atacama region of northern chile evaporites within upper triassic to lower cretaceous sequences in the atacama region of northern chile are interpreted as the deposits of continental and coastal saline lakes halite casts and finely laminated calcareous evaporites intercalated with alluvial and fluvial sediments are probably playa lake deposits these continental evaporites have been recognized in upper triassic alluvial sediments cifuncho formation in upper triassic lower jurassic braided river deposits basal unit of the pan de azucar formation and within a sequence of lower cretaceous aeolian alluvial and playa lake mudflat sediments quebrada monardes formation lower cretaceous evaporites between marine limestones lautaro formation and continental redbeds quebrada monardes formation were probably deposited in coastal saline lagoons produced during a regionally extensive marine regression these sequences and other similar successions in northern chile provide a record of almost continuous evaporite deposition and hence of arid to semi arid conditions since upper triassic times these conditions were primarily the result of a constant latitudinal position within the subtropical zone a contributary factor was the geographical position of the area initially on the west coast of gondwanaland and subsequently on the coast of south america with cold northward flowing ocean currents and offshore winds

isotopic composition of natural thermal discharges on vulcano island southern italy this paper reviews the isotopic 18o16o and d h ratios reported in the literature for phreatic waters in the plain of vulcano island off sicily and condensates from high temperature fumaroles at the top of the summit crater the vulcano phreatic waters have a rather high average annual temperature greater than 30 dgc but do not seem to be heated directly by mixture with condensates of fumarolic steam they seem to originate from rainwater and to undergo high evaporation particularly in summer owing to high conductive heat flow in the island by comparing the 18o16o and d h ratios with cl as hcl content it is estimated that 75 of the steam from the high temperature fumaroles comes from seawater and 25 from low salinity waters the latter however do not seem to come directly from the shallow aquifer of vulcano because the steam from the fumaroles does not contain radiogenic tritium this mixing model and the lack of steam condensation in the vulcano aquifer implies indirectly that there are no steam losses during the rise of deep fluids and that some observed variations in the outlet temperatures without accompanying variations in the composition of the associated gas phase may be due to increased or decreased extent of fracturation in the volcanic edifice as a result for instance of tectonic movements which cause more or less vaporization of low salinity fresh water into the volcanic ducts as well as faster or slower outflow of deep gases

enhanced carbonate petrography using fluorescence microscopy abstract fluorescence microscopy can recognize depositional facies and delineate diagenetic fabrics and porosity relationships in certain highly dolomitized or recrystallized limestones previously uninterpretable using standard petrographic techniques this tool has other valuable applications in the study of carbonate rocks these other applications include differentiating carbonate cements from neomorphic spar enhancing depositional and diagenetic fabrics rapidly evaluating mineralogical stabilization and recrystallization in holocene and pleistocene deposits and improving delineation of porosity and pore geometries in sedimentary rocks fluorescence microscopy is a rapid easily used and nondestructive technique that can be applied to unpolished thin sections or rock slabs by itself or in conjunction with other petrographic and geochemical tools it has the potential to expand our understanding of carbonate diagenetic processes and products in particular dolomitization and neomorphism and carbonate porosity evolution we strongly encourage routine usage of fluorescence microscopy in future carbonate petrographic studies

astronomical forcing in upper miocene continental sequences implications for the geomagnetic polarity time scale abstract we present an integrated stratigraphic study of cyclically bedded distal alluvial fan to lacustrine deposits in the late miocene continental sections of cascante and canizar teruel basin ne spain the cyclostratigraphic analysis reveals that different scales of sedimentary cyclicity are present with a thickness ratio of about 1 2 5 spectral analysis of colour records in the depth domain indicates the presence of a significant peak at 2 2 m which corresponds to the average thickness of the basic mudstone carbonate cycle other peaks correspond to the large scale cycle which consists of clusters of five basic cycles and to a cycle twice the average thickness of the basic cycle magnetostratigraphic results in combination with small mammal biostratigraphy indicate that the three normal polarity intervals recorded in our sections correspond to c5n 2n c5n 1n and c4ar 2n assigning the ages of ck95 to the polarity reversals implies significant changes in sedimentation rate which is not in agreement with the regularity of the sedimentary cyclicity thus spectral analysis of high resolution colour records in the time domain only produce a spectrum that is consistent with milankovitch climate forcing if several of the assigned age tie points are excluded this indicates that the sedimentary cyclicity in these sections is related to astronomical variations in climate and that the ages of reversal boundaries are in error hence we have calculated the astronomical durations for c4ar 2n 87 ky c4ar 3r 54 ky c5n 1n 141 ky and c5n 1r 33 ky which indeed show significant discrepancies with ck95 the duration pattern of our polarity intervals is confirmed by seafloor anomaly profiles and magnetostratigraphic records of deep sea cores consequently this study demonstrates that astronomically forcing in continental sequences can be a powerful tool to improve the fundamental dating of the geological record

biotic and abiotic processes in the formation and diagenesis of permian dolomitic stromatolites zechstein group ne england abstract the crinkly bed of the upper permian zechstein group succession roker formation hauptdolomit z2c in northeast england is a distinctive 1 4 meter thick unit that has been interpreted as a stromatolite of microbial origin or alternatively as the result of purely abiotic precipitation close examination of this stratigraphically significant unit shows that it is the result of both physical and microbial processes and was deposited in hypersaline shallow water immediately following lowstand evaporite deposition within the zechstein basin the internal structure of the crinkly bed consists of fine millimeter scale laminae of alternating clotted peloidal or aphanitic micritic layers and granular laminae composed of silt size peloids with rare hollow spheroids the lamination is extremely regular in thickness and laterally persistent for up to 4 meters a microbial community composed of coccoid and filamentous microorganisms inferred from fossil evidence colonized the original sediment surface it is suggested that this biofilm was responsible for the precipitation of both the micrite laminae and most of the peloids of the granular laminae the peloids are consequently interpreted as autochthonous this interpretation of a microbial origin is consistent with the microstructure and geochemical signatures of the micritic dolomite which constitutes both the continuous micritic laminae and the peloids themselves primary dolomite precipitation is hypothesized to have taken place from marine to slightly hypersaline waters mediated by bacterial metabolism similar to the process that operates in modern intertidal microbial mats the crinkly bed shows macro structures that vary along a continuum from symmetrical to asymmetrical centimeter scale ripple like structures some showing interference patterns through to domical and conical structures more typical of stromatolites the more ripple like structures have a lamination of microbial origin identical to that within the domal conical stromatolites there is no internal cross lamination their origin is equivocal they could be the result of physical current or wave induced deformation of a surficial biofilm or their form could be inherited from true mechanically deposited ripples not observed that provided a template for biofilm growth changes in the nature and strength of the wave and or current regime and possibly in the community structure of the microbial mat produced this array of microbially induced macrostructures miss the latter plus the absence of desiccation features indicative of intertidal to supratidal deposition suggest subtidal sedimentation at a depth of several meters intergranular gypsum cement precipitated during early diagenesis and ferroan sparry dolomite precipitated during burial tertiary uplift and the consequent exposure to meteoric waters resulted in the precipitation of calcite cements that replaced gypsum and pre existing dolomite probably via the biological mediation of heterotrophic bacteria the interpretation of this distinctive stratigraphic unit illustrates the difficulty in distinguishing between biotic and abiotic processes in the sedimentary record

testing reproducibility of vitrinite and solid bitumen reflectance measurements in north american unconventional source rock reservoir petroleum systems abstract an interlaboratory study ils was conducted to test reproducibility of vitrinite and solid bitumen reflectance measurements in six mudrock samples from united states unconventional source rock reservoir petroleum systems samples selected from the marcellus haynesville eagle ford barnett bakken and woodford are representative of resource plays currently under exploitation in north america all samples are from marine depositional environments are thermally mature tmax 445 c and have moderate to high organic matter content 2 9 11 6 wt toc their organic matter is dominated by solid bitumen which contains intraparticle nano porosity visual evaluation of organic nano porosity pore sizes 1 0 produced lowest r values generally 0 5 absolute reflectance similar to a prior ils for similar samples other traditional approaches to outlier removal outside mean 1 5 interquartile range and outside f10 to f90 percentile range also produced similar r values standard deviation values

geothermal resources within carbonate reservoirs in western sicily italy a review abstract low to medium temperature fluid reservoirs hosted in carbonate rocks are some of the most promising and unknown geothermal systems western sicily is considered a key exploration area this paper illustrate a multidisciplinary and integrated review of the existing geological geochemical and geophysical data mainly acquired during oil and gas explorations since the 1950s specifically re analyzed for geothermal purposes has led to understanding the western sicily geothermal system as a whole and to reconstructing the modalities and particular features of the deep fluid circulation within the regional reservoir the data review suggests the presence of wide groundwater flow systems in the reservoir beneath impervious cap rocks we identified the main recharge areas reconstructed the temperature distribution at depth recognized zones of convective geothermal flow and depicted the main geothermal fluid flow paths within the reservoir we believe that our reconstruction of geothermal fluid circulation is an example of the general behavior of low to medium enthalpy geothermal systems hosted in carbonate units on a regional scale due to the recent technological developments of binary plants these systems have become more profitable not only for geothermal direct uses but also for power production

bacterial and algal markers in sedimentary organic matter deposited under natural sulphurization conditions lorca basin murcia spain abstract free lipids sulphur bound lipids present in macromolecular fractions and kerogen pyrolysis products have been studied in shales and early diagenetic carbonates replacing gypsum from a messinian sequence of lorca basin the high abundance of phytane 2 3 dimethyl 5 2 6 10 trimethylundecyl thiophene mid chain c 20 isoprenoid thiophenes and bithiophenes and bis o phytanyl and o phytanyl o sesterterpanyl glycerol ethers indicates that the organic matter in all these samples was deposited under hypersaline conditions the isopranyl glycerol ethers are essentially found in the sulphur bound macromolecular matter which contrasts with the low concentrations of these compounds as free lipids however the distributions of these isopranyl glycerols is paralleled by the occurrence of free phytanic acid shales and laminated carbonate and 3 7 11 15 19 pentamethyleicosanoic acid only in the laminated carbonate the bacterial inputs are represented by 2 hydroxytetracosanoic acid n octadec 11 enoic acid hopanoic acids and the distributions of iso and anteiso c 15 and c 17 homologues and minor amounts of iso c 16 and anteiso c 14 these branched fatty acids are characteristic of sulphate reducing bacteria the relative proportions of the iso and anteiso compounds in the total fatty acid distributions are correlated with the proportion of reduced sulphur in the sediments

cathodoluminescent bimineralic ooids from the pleistocene of the florida continental shelf a bored and encrusted late pleistocene ooid grainstone was recovered from the seafloor at a depth of approximately 40 m on the outer continental shelf of eastern florida ooid cortices are dominantly bimineralic generally consisting of inner layers of radial magnesian calcite and outer layers of tangential aragonite ooid nuclei are dominantly rounded cryptocrystalline grains although quartz grains and a variety of skeletal grains also occur as nuclei ooids are partially cemented by blocky calcite and interparticle porosity is partially filled by micrite radial cortex layers are composed of brightly cathodoluminescent magnesian calcite having a composition of approximately 12 mol mgco3 and 1000 ppm strontium the iron and manganese concentrations in radial cortex layers are generally in the range of 500 1000 ppm and 100 250 ppm respectively tangential cortex layers are composed of noncathodoluminescent aragonite containing approximately 11 500 ppm strontium and less than 0 5 mol mgco3 iron concentrations in tangential cortex layers are generally in the range of 150 400 ppm and manganese concentrations are generally below the detection limit of 100 ppm echinoderm skeletal fragments which are present as accessory grains are composed of brightly cathodoluminescent magnesian calcite some ooid nuclei and the thin outer edges of some blocky calcite cement are cathodoluminescent micrite matrix and the bulk of blocky calcite cement are noncathodoluminescent ooids do not exhibit textural evidence of recrystallization the ooid grainstone underwent an episode of meteoric diagenesis but ooid cortices were not affected by the event we propose a previously unrecognized process by which the magnesian calcite cortex layers underwent diagenetic alteration in oxygen depleted seawater during this diagenesis magnesium was lost and manganese was incorporated without apparent textural alteration and without mineralogical stabilization thus we suggest that cathodoluminescence may result from diagenetic alteration on the sea floor

evolution of fumarolic gases boundary conditions set by measured parameters case study at vulcano italy physical chemical and isotopic parameters were measured in fumaroles at the vulcano crater and in drowned fumaroles near the beach the data were used to define boundary conditions for possible conceptual models of the system crater fumaroles time variations of co2 and so2 concentrations indicate mixing of saline gas rich water with local fresh water cl br ratios of 300 400 favour sea water as a major source for cl brand part of the water in the fumaroles cl concentrations and d values revealed independently amixing of 0 75 sea water with 0 25 local freshwaterin furmarole f 5 during september 1982 patterns of parameter correlation and mass balances reveal that co2 s nh3 and b originate from sources other than sea water the co2 value of 13c 2 o favours at least partial origin from decomposition of sedimentary rocks rather than mantle derived material radiogenic4he 1 3 lo 3 ccstp g water and radiogenic40ar 10 6 10 4 ccstp g water are observed 4he 40ar radiogenic 1 2 well in the range of values observed in geothermal systems drowned fumaroles strongly bubbling gas at a pond and at the beachappears to have the same origin and initial compositionas the crater fumaroles 2 km away the fumarolic gas is modified by depletion of the reactive gases caused by dissolution in shallow water atmospheric ne ar kr and xe are addeden route some radiogenic he and ar are maintained the vulcano system seems to be strongly influenced by the contribution of sea water and decomposition of sedimentary rocks evidence of magmatic contributions is mainly derived from heat

lacustrine oil shale basins in tertiary grabens from ne spain western european rift system abstract in the ne iberian plate the convergent motion and collision of the european iberian and african plates resulted in the development of paleogene compressional features strike slip systems thrust fold belts and late oligocene to mainly neogene extensional structures which are superimposed on the former these extensional structures are represented by horsts half grabens and tilted blocks often developed in connection with preexisting inherited faults from the late oligocene and during the neogene both strike slip and extensional regimes alternated and coexisted giving rise to a number of fault bounded basins the deposition of organic rich facies and in particular oil shales took place in the lacustrine complexes developed in some of these basins campins basin late oligocene ribesalbes and rubielos de mora basins early middle miocene libros basin late miocene and cerdanya basin late miocene deep lacustrine sequences ranging from 100 up to 250 m thick were deposited in all the above mentioned basins the organic rich sequences are characterized by thin lamination absence of bioturbation rare benthonic fauna if present it is supplied from other parts of the basin and excellent preservation of exotic fossils plant leaves insects amphibians the suitable depth conditions needed for permanent stratification in the water bodies and anoxia in the deeper parts of the lakes were due essentially to increasing subsidence outstripping deposition intense tectonic activity is recorded by the occurrence of olisthostromes and slumps affecting the lacustrine deposits as well as by the syntectonic structures recorded in the basin fill successions the late oligocene late miocene paleoclimatic regimes ranging from warm tropical to subtropical conditions were favourable for the development of permanently stratified lakes moreover chemical ectogenic meromixis may have contributed in some cases to the establishment of permanent stratification the eastern iberian rift system makes up the southernmost part of the larger western european rift system the occurrence of lacustrine sediments ranging from the late eocene to late miocene is frequent in the fault bounded basins of this complex rift system and lacustrine oil shale deposits have been recorded in several of these basins thus the western european rift system presents an interesting model of intracontinental rifting in a foreland platform setting where favourable conditions for organic rich deposits often took place the high potential of this kind of tectonic settings for lacustrine oil shale exploration must be stressed

late diagenetic calcitization of anhydrite from the mississippian of saskatchewan western canada mississippian nodular anhydrites beneath an unconformity in the subsurface of southern saskatchewan are locally replaced by calcite pyrite and celestite triassic clastics above the unconformity are green rather than red and a usually developed subunconformity alteration zone where carbonates are dolomitized and porosity is filled with anhydrite is absent the unconformity lacks karstic features unlike in the usa and probably formed in a hyperarid climate mississippian anhydrites near the unconformity are not preferentially dissolved nor were they extensively hydrated anhydrite calcitization occurred only after the unconformity was shallowly buried by redbeds and it probably involved sulphate reducing bacteria hydrogen sulphide generated by bacteria reduced redbed pigments the replacement calcite contains pseudomorphs and relicts of anhydrite and pseudomorphs of secondary gypsum these indicate calcitization occurred only after original mississippian gypsum was altered to anhydrite and this in turn was partially converted back to secondary gypsum beneath the unconformity replacement occurred concurrently with the formation elsewhere of the dolomitized zone beneath the unconformity sulphur isotopic ratios of replacement pyrite are depleted relative to mississippian sulphate values consistent with the activities of sulphate reducing bacteria carbon isotopic ratios of replacive calcites however do not support this interpretation and are identical to those of mississippian limestones simple replacement of sulphate by pore water bicarbonate in equilibrium with host limestones is unlikely because protons generated during the reaction should have created acidic conditions in which calcite would have dissolved a full explanation of the calcitization remains elusive but may involve replacement occurring in an active groundwater system and or bacterial sulphate reduction occurring upstream of the site of calcitization

coastal sabkha dolomites and calcitised sulphates preserving the lomagundi jatuli carbon isotope signal palaeoproterozoic tulomozero formation carbonates of the onega basin were targeted by icdp far deep hole 10b the recovered rocks contain abundant evidence for palaeoproterozoic gypsum and anhydrite particularly in the form of pseudomorphs of inclusion containing nodules swallow tail twinned crystals and evaporite dissolution breccias similarly sand patch fabric indicates the former presence of surface covering salt crusts in the palaeoproterozoic atmospheric oxygen and seawater sulphate levels at that time must have been sufficient to allow such sulphates to form carbonate 13c values are considered sedimentary or early diagenetic predating greenschist facies metamorphism associated with the svecofennian orogeny these carbonate 13c values range from 7 7 to 15 7 with the highest and lowest values found in dolostones the dolostones as well as calcitised calcium sulphates record the lomagundi jatuli signal however evidence for activity of sulphate reducing and or methanogenic bacteria seems to be lacking dolomite precipitation or dolomitisation calcium sulphate calcitisation and production of the high 13c values processes which typically involve such bacteria in the phanerozoic are thus inferred to have proceeded without the direct influence of sulphate reducers and methanogens the most plausible explanation for the lomagundi jatuli excursion seems to remain significant sequestration of organic carbon in a location yet to be identified

an isotopic study of a fluvial lacustrine sequence the plio pleistocene koobi fora sequence east africa stable isotopic analyses of plio pleistocene and modern sediments in the fluvial lacustrine system occupying the turkana basin east africa provide constraints on the paleoenvironmental and diagenetic histories of the pliocene through the recent sediments in the basin the 13c values for carbonates in lacustrine sediments range from 15 to 22 relative to pdb depending on the varying proportions of co2 from the atmospheric reservoir and from various metabolic sources the 18o values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10 from the pliocene to the present the 13c values for pedogenic carbonates record paleoccologic variations and suggest that c4 plants did not become well established in the preserved depositional parts of the basin until about 1 8 myr ago the 18o values pedogenic carbonates suggest a range of over 10 for the isotopic composition of soil water during this interval they also suggest a period of major climatic instability from about 3 4 to 3 1 myr and at about 1 8 myr together the 13c and 18o values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these plio pleistocene sediments

late miocene to plio pleistocene fluvio lacustrine system in the karacasu basin sw anatolia turkey depositional paleogeographic and paleoclimatic implications abstract the sedimentary record of the late cenozoic karacasu basin a long lived continental half graben from southwestern turkey is characterized by siliciclastic and carbonate deposits sedimentation was controlled by an active nw se trending major normal fault along the basin s southern margin and by climatically induced lake level changes detailed facies analysis subdivides the entire neogene quaternary basin fill into three distinct litostratigraphic units representing paleogeographic changes and sedimentation patterns throughout the basin evolution sedimentation commenced in the late miocene with the deposition of proximal medial alluvial fan and fluvial facies damdere formation fa1 at this stage alluvial fans developed in elevated areas to the south prograding towards the basin center at the beginning of the pliocene fresh to slightly alkaline shallow lake deposits fa2a of the karacaoren formation formed the lake became open and meromictic conditions developed fa2b pollen data from the fa2b facies show that climate was arid to humid climate probably changed cyclically through time producing alternation of artemisia steppe cold and dry periods and more forested vegetation warm and wet the open lake facies passes upwards into lake margin facies fa2c but it was still dominated by alkaline to slightly saline lake conditions sedimentation was almost continuous from the late miocene to pleistocene in the early quaternary the basin was dissected by the re activation of basin bounding faults the unconformable base of the overlying quaternary deposits karacasu formation fa3 reflected the basin s transformation from a half graben into a full graben system oxygen isotope data from carbonates show an alternation of humid climatic periods when freshwater settings predominated and semiarid arid periods in which the basin hosted alkaline and saline water lakes neotectonic activity has rejuvenated many of the basin bounding faults causing development of talus aprons and local alluvial fans the basin was progressively incised by modern rivers that have largely smoothed out the topographic relief of the graben margins

application of bib sem technology to characterize macropore morphology in coal abstract we use broad ion beam bib milling to prepare low relief polished surfaces of coal samples for high resolution sem imaging in a study of the morphology and distribution of macro and mesopores results show that the bib sections of a few square millimeters are not large enough to be statistically representative so that porosity was investigated as a function of maceral type for a vitrinite maceral type we found comparably little visible macroporosity within the resolution limits of the se detector less than 2 of all the meso and macropores studied were found in vitrinites pore morphology in an inertinite maceral is dependent on the original maceral fusinite yields large elongated pores often filled with mineral phases while macrinite shows comparatively smaller rounder pores the distribution of pore sizes follows a similar power law at different magnifications our results show that micropores and macropores in coal belong to different populations with different size distributions and morphologies bib sem imaging is a useful tool to study meso and macropore morphology especially in the size range between 10 nm and 10 m but more maceral types should be characterized for a better characterization of maceral porosity at different stages of coalification

comparative study of major element geochemistry of gypsum ghost limestones and selenite lithofacies from the miocene of northern carpathian foredeep implication to the model of massive replacement of solid sulphates by calcium carbonates abstract gypsum ghost limestones and selenite gypsum facies commonly believed to be as lithological equivalents caused by massive replacement of selenites by limestones occur in the same miocene evaporitic series of the northern carpathian foredeep southern poland and differ considerably with regard to their sedimentological features and major element compositions the differences dealing with variation of contents ranges means patterns of distribution correlations and interelement ratios of the major elements clearly do not indicate any geochemical similarities between the gypsum ghost limestones and the selenite gypsum lithofacies mass balance chemistry shows a deficit of calcium and sulphur contents in the limestones compared to the composition of the selenitic gypsum and implies that the gypsum ghost limestones system was open to mass transfer and cannot be related to simple and regionally extended replacement of solid sulphate rocks by limestones plus native sulphur the major element geochemistry of the gypsum ghost limestones and the selenites represent their original compositions which in turn reflect original depositional settings rather than pore water chemistry during replacive diagenesis both the lithological units developed in co eval depositional domains carbonate and sulphate constituting an evaporitic system but corresponding to different sedimentary settings of the system the gypsum ghost limestones reflect the unique situation of simultaneous formation of carbonate and selenites in a sedimentary transitional milieu between the carbonate and gypsum domains where bottom calcium carbonate deposition was alternating with the growth of selenite crystals the results are clearly inconsistent with the epigenetic model of formation of the polish sulphur deposits which assumes massive and regionally extended replacement of sulphate deposits by carbonates

carbonate replacements after sulfate evaporites in the middle miocene of egypt abstract massive zones of diagenetic carbonate which replace sulfate deposits are observed in the middle miocene evaporites in several outcrops along the egyptian coast of the gulf of suez these carbonates display marked similarities of morphology lithofacies and stable isotope composition to diagenetic carbonates described in some portions of messinian gessoso solfifera formation of sicily and in the castiles of the upper permian castile formation of the delaware basin the mechanism of mineral transformation is basically bacterial sulfate reduction because the low 13c values of these carbonates argue for the organic origin of carbon the 18o values fall i to two distinct groupings indicating that the carbonates were crystallized during two different diagenetic stages the early diagenetic stage occurred soon after deposition in pore waters of marine origin and at different levels of evaporation organic matter used by bacteria was produced in situ the late diagenetic stage occurred when the tectonic or halokinetic uplift of the sequence caused flushing of the sediments by groundwaters of the phreatic aquifer and hydrocarbon migration furthermore to explain the very low 18o values of these carbonates it is inferred that locally ambient temperatures reached more than 35 c due to the large quantities of energy released during the bacterial sulfate reduction

diagenetic gypsum related to sulfur deposits in evaporites libros gypsum miocene ne spain abstract the libros gypsum is the thickest evaporite unit of the miocene infill of the teruel basin in ne spain during the deposition of this unit intense bacterial sulfate reducing bsr activity in the lake depocenter generated a native sulfur deposit diagenetic gypsum resulted from subsequent sulfur oxidation the different processes involved in these transformations were first investigated by anadon et al 1992 the present paper is concerned with this diagenetic gypsum from the stratigraphic petrographic isotopic and genetic points of view diagenetic gypsum occurs mainly as continuous or discontinuous layers individual levels or lenses irregular masses nodules and micronodules and veins its main textures are coarse crystalline anhedral and fine grained alabastrine both of which can replace any former lithology carbonate gypsum and sulfur the following sequence of processes and mineral textural transformations is deduced primary gypsum deposition bsr and biodiagenetic carbonate h 2 s production growth of native sulfur growth of diagenetic gypsum partial recrystallization of the diagenetic gypsum textures the gypsification of the native sulfur generated two types of banded structures in the diagenetic gypsum 1 concentric structures of centripetal growth and 2 expansive roughly concentric structures in the first type the gypsification operated from the outer boundaries towards the inner parts in the second type part of the carbonate hosting the sulfur was also gypsified replaced cemented in the diagenetic gypsum the 34 s values are in agreement with a native sulfur and h 2 s provenance the 18 o sulfate values however enable us to differentiate two main groups of values one with positive values and the other with negative values in the group of positive values interstitial evaporated solutions participated in the sulfur oxidation this process presumably occurred in a first oxidation stage during shallow to deeper burial of the libros gypsum unit in the group of negative values however only meteoric waters participated in the oxidation which presumably occurred in a second oxidation stage during the final exhumation of the unit a third group of values is characterized by very high sulfur and oxygen values suggesting that bsr residual solutions also participated in the oxidation processes locally during the two oxidation stages both the textural characteristics and the isotopic composition of the diagenetic gypsum indicate that gypsification operated as a multistadic process

authigenesis of native sulphur and dolomite in a lacustrine evaporitic setting hellin basin late miocene se spain abundant sulphur is present in the late miocene evaporitic sequence of the lacustrine hellin basin in se spain weathering of triassic evaporites controlled the chemical composition of the miocene lake the lacustrine deposits comprise gypsum marlstones diatomites and carbonate beds sulphur bearing carbonate deposits predominantly consist of early diagenetic dolomite abundant dolomite crystals with a spheroidal habit are in accordance with an early formation and point to a microbial origin the carbon isotopic composition of the dolomite 13 c values between 10 and 4 indicates mixing of lake water carbonate and carbonate derived from the remineralization of organic matter by heterotrophic bacteria dolomite precipitated syngenetically under evaporitic conditions as indicated by high oxygen isotope values 18 o between 6 and 11 nodules of native sulphur are found in gypsum carbonate beds and marlstone layers sulphur formed in the course of microbial sulphate reduction as reflected by its strong depletion in 34 s 34 s values as low as 17 near to the surface many of the sulphur nodules were in part or completely substituted by secondary gypsum which still reflects the sulphur isotopic composition of native sulphur 18 to 10 this study exemplifies the role of bacterial sulphate reduction in the formation of dolomite and native sulphur in a semi enclosed lacustrine basin during late miocene time

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

modern and holocene carbonate sedimentology of two saline volcanic maar lakes southern australia the basin lakes are two adjacent maar lakes located in the centre of the western volcanic plains district of victoria australia both lakes are saline and alkaline west basin lake is meromictic whereas east basin is a warm monomictic lake the carbonate mineral suite of the modern offshore bottom sediments of these basins consists mainly of dolomite and calcite with smaller amounts of hydromagnesite and magnesite in west basin and monohydrocalcite in east basin the dolomite hydromagnesite magnesite and monohydrocalcite are endogenic in origin being derived by primary inorganic precipitation within the water columns of the lakes or at the sediment water interface the calcite is biologically precipitated as ostracod valves in addition to the carbonates in the modern offshore deep water sediments the lakes also contain a girdle of nearshore carbonate hardgrounds both beachrock and microbialites algal boundstones are present these modern lithified carbonate units exhibit a wide range of depositional and diagenetic fabrics morphologies and compositions in west basin the hardgrounds are composed mainly of dolomite hydromagnesite and magnesite whereas dolomite and monohydrocalcite dominate the east basin sediments aragonite high mg calcite kutnahorite siderite and protohydromagnesite also occur in these lithified carbonate units stratigraphic variations in the carbonate mineralogy of the holocene sediment record in the lakes were used to help decipher the palaeochemistry and palaeohydrology of the basins these changes in conjunction with fluctuations in organic remains and fossil content indicate a pattern of lake level histories similar to that deciphered from other maar lakes in western victoria

saline lake carbonates within an upper jurassic lower cretaceous continental red bed sequence in the atacama region of northern chile the codocedo limestone member is a thin but laterally persistent lacustrine sequence within the red beds of the upper jurassic lower cretaceous quebrada monardes formation in the atacama region of northern chile the thick succession of clastic terrigenous sediments of the quebrada monardes formation was deposited in an arid to semi arid environment sedimentary facies are indicative of deposition of aeolian dunes alluvial fans and braided streams playa lake mudflats and saline lakes and coastal lagoons the strata accumulated in a n s elongated extensional back arc basin on the landward side of an active volcanic arc the 3 m thick codocedo limestone member marks striking facies changes within the quebrada monardes formation it is underlain by a thick sequence of conglomerates and sandstones deposited on alluvial fans the limestone itself is characterized by evaporite minerals and laterally continuous laminations indicative of deposition by vertical accretion in a perennial saline lake the overlying siltstones and fine sandstones contain geodes and gypsum pseudomorphs and were deposited on playa lake mudflats the limestone therefore represents a relatively short period of lacustrine deposition within an essentially terrigenous succession the lake was possibly formed quite suddenly for example by damming of the basin by a lava flow sedimentation in the perennial lake was predominantly cyclical seasonal planktonic algal blooms produced millimetre scale laminations interbedded with these laminites are centimetre scale beds of evaporitic gypsum anhydrite and minor halite the evaporite minerals have been largely replaced by calcite chalcedony and quartz the centimetre scale cycles may have resulted from periodic freshwater input into the lake after a period of about 3000 yr the lake dried up to be replaced by extensive playa lake mudflats the codocedo limestone member possibly formed a plane of detachment during an early tertiary phase of e w directed regional compression the limestones and evaporites were folded and extensively brecciated this deformation probably resulted from simple shear along the bedding plane of the relatively weak evaporite minerals prior to their replacement by calcite and quartz

shallow lacustrine carbonate microfacies document orbitally paced lake level history in the miocene teruel basin north east spain results are presented of a detailed carbonate petrographic study of an upper miocene lacustrine mixed carbonate siliciclastic succession in the teruel basin spain with the aim of constraining lake level variability at different stratigraphic scales regular alternations of red to green mudstone and lacustrine limestone termed the basic cycle reflect lake level variations at the metre scale in an earlier study the basic cycle was shown to be controlled by the climatic precession cycle petrographic analysis made it possible to distinguish two main carbonate microfacies groups characteristic of very shallow transient and shallow permanent lake environments respectively in addition to the basic cyclicity the microfacies analysis reveals lake level variations on a larger scale as a consequence the astronomical forcing hypothesis of the cyclicity in the cascante section is explored further a climate modelling study of orbital extremes indicates that high lake levels could relate to enhanced net winter precipitation and runoff during precession minima consistent with mediterranean geological data using this phase relationship an astronomical tuning of the cycles is established starting from astronomical ages of magnetic reversal boundaries subsequently successive basic cycles are correlated to precession minima the tuning reveals an identical number of basic cycles in the cascante section as precession related sapropel cycles in the deep marine succession at monte dei corvi italy corroborating the precessional control of the basic cycles at cascante lake level highstands in the large scale cycle identified by the microfacies analysis relate to maxima in both the ca 100 and 405kyr eccentricity cycles again consistent with mediterranean geological data subtraction of the identified astronomically related lake level variations from the palaeoenvironmental record at cascante indicates a shift to deeper and more permanent lacustrine environments in the upper half of the section the cause of this shift remains unclear but it may be linked to tectonics non astronomical climate long period astronomical cycles or autogenic processes 2008 the authors journal compilation 2008 international association of sedimentologists

calcitization of mg ca carbonate and ca sulphate deposits in a continental tertiary basin calatayud basin ne spain diagenetic carbonates formed through early calcitization of evaporite gypsum anhydrite and or magnesium carbonate dolomite magnesite deposits have been identified throughout the tertiary calatayud basin ne spain the diagenetic carbonates consist in all cases of low magnesian calcite and are related to main sedimentary discontinuities which record episodes of significant subaerial exposure in the basin early calcite replacements predominate in sediments of the intermediate unit in central areas of the basin two types of diagenetic carbonates have been distinguished 1 laminated diagenetic carbonates in which the original structure of sequences formed of laminated magnesite dolomite and primary gypsum is preserved though transformed in calcite 2 brecciated diagenetic carbonates which resulted from extensive dissolution of lenticular gypsum macrocrystals accompanied by dedolomitization processes of dolomite host rock the replacement by calcite resulted from rapid transformation of evaporite deposits either at the contact of these deposits with overlying freshwaters or by percolating freshwater at very shallow burial depth stable isotope carbon and oxygen analyses of the diagenetic carbonates support influence of meteoric derived carbonate rich groundwater for their formation the meteoric isotope signature is supported by its comparison with the stable isotope values determined from diagenetic calcites formed after magnesite in evaporite sequences during the late pleistocene and holocene the diagenetic carbonate bodies formed as a result of a progressive change from highly to moderately concentrated saline lake waters this gradual evolution was related to a climatic shift from dry and hot to cooler and more humid conditions throughout the miocene a trend that has been also recognized in other large tertiary basins of the iberian peninsula in this period

primary and diagenetic carbonates in the anoxic sediments of lake bosumtwi ghana cores of organic rich muds from the tropical meteorite crater lake bosumtwi ghana contain laminae of authigenic calcite polyhedra and aragonite needles as well as scattered diagenetic calcite mg calcite spherulites and aggregates of dolomite crystals their respective origins are traced by analyses of oxygen and carbon stable isotopes anoxic dolomite and mg calcite formed in pore waters reflecting highest degrees of evaporative concentration and high rates of methanogenesis carbon dioxide reduction must have been the dominant methanogenic pathway producing diagenetic carbonates with delta sup 13 c values up to 27 pdb this example shows the inherent problems of interpreting bulk samples with progressive mineralogical sequences of calcite to mg calcite to aragonite to dolomite merely in terms of mg sup 2 ca sup 2 in lake waters it provides a model for the interpretation of ancient lacustrine carbonates from organic rich environments

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

organic and inorganic geochemistry of low temperature gas discharges at the baia di levante beach vulcano island italy abstract discharge from subaereal and submarine gas vents of the baia di levante beach gases from the vulcano island were sampled for major and trace gas components in may and november 1995 chemical compositions and equilibrium calculations suggest three different groups of co 2 rich gas emissions depending on their distance from the la fossa crater 1 gas vents close to the faraglione area are characterised by high h 2 s contents high calculated equilibrium temperatures based on inorganic species and relatively high proportion of alkene compounds 2 gas vents close to vulcanello are characterised by low calculated equilibrium temperatures and low amounts of alkenes and 3 pontile sample has the highest equilibrium co 2 pressure up to 68 bars which may account for the observed absence of benzene the relative large variability of h 2 s in the baia di levante beach gas discharge may be attributed to either different interactions between iron sulphides and weakly acid waters or catalytic effect of elemental sulphur on the de hydrogenation of cyclo hexane thermodynamic calculations suggest that the main inorganic species and ch 4 may have re equilibrated at relatively shallow depth 10 200 m b s l and 30 600 m b s l for a lithostatic and hydrostatic pressure respectively the slow kinetics of reactions in the c n h 2 n c n h 2 n 2 systems with respect to that of ch 4 co co 2 may explain the observed propene propane ratios which can only be reached at reaction temperatures of 300 350 c this low speed of reactions can also explain the observed disequilibrium of c1 c4 alkanes

kinematic evolution of the eastern chalk draw fault during basin and range extension evaluating the role played by preexisting structural fabrics in along strike displacement patterns abstractbasin and range extensional structures in trans pecos texas have been interpreted to be strongly influenced by preexisting structures including igneous centers in the big bend region these igneous centers are interpreted to have deflected propagating faults as they are rheologically strong relative to the surrounding rocks we conducted detailed field mapping and analysis of fracture and fault data along the eastern segment of the chalk draw fault in big bend national park to evaluate its kinematic evolution and interaction with paleogene plutons our primary results document the following key relationships 1 the rosillos laccolith and other paleogene plutons in the study area are pervasively fractured dominantly by northwest striking mode i fractures which generally do not extend into adjacent sedimentary rock sequences 2 throw on the eastern chalk draw fault is strongly asymmetric decreasing rapidly as it enters the rosillos laccolith and 3 analysis of fault slip data in the regio

a dry polishing technique for the petrographic examination of mudrocks discussion abstract after the paper a dry polishing technique for the petrographic examination of mudrocks by gorbanenko 2017 it is important to stress some differences between the proposed polishing procedure and the existing standards for sample preparation for microscopic examination of organic matter which may lead to less bright surfaces than required for measuring vitrinite reflectance by the most widely used standards 7404 5 iso 2009 or astm d7708 2014