sr s and oso4 isotopes and the depositional environments of the upper miocene evaporites spain abstract upper miocene evaporites in the nijar basin southeastern spain contain thick massive and coarse crystalline selenites of the middle messinian yesares formation on the basis of their sedimentary fabrics and structures such as euhedral terminations of crystals well preserved algal filament inclusions and standing growth orientations these selenites are interpreted to be primary bottom growth deposits most of these selenites have sr concentrations of about 1000 ppm range from 700 to 1800 ppm 87sr 86sr values of yesares selenites vary between 0 70890 and 0 70896 n 18 which are all within the known range of messinian seawater suggesting a marine origin however quantitative modeling of 87sr 86sr vs sr ca of fluids demonstrates that a minor amount of admixed nonmarine fluid e g 20 might have contributed to the yesares marine brines 34s and 18oso4 values of yesares selenites range from 21 to 24 cdt and from 10 to 16 smow respectively these ranges are more variable and most values are heavier than those expected for normal miocene marine gypsum on the basis of quantitative modeling these heavy 34s and 18oso4 values have most likely resulted from reduction and oxidation reactions of sulfur species that occurred in brines rather than from contributions of nonmarine water or from reservoir crystallization effects the use of sr s and o isotopes provides a possible means of distinguishing whether an ancient evaporite was deposited by marine nonmarine or hybrid brines sr isotopes however are insensitive to minor nonmarine contributions on the basis of quantitative modeling and consequently marine sr isotopes for evaporites e g gypsum do not necessarily indicate pure marine depositional environments compared to sr isotopes 34s and 18oso4 of marine gypsum are even more insensitive to minor nonmarine contributions because of much higher so4 concentrations in seawater and seawater evaporated brines than in most freshwaters therefore sr o and s isotopes should be used with caution to interpret depositional environments and to determine parent fluids of ancient evaporites

sr ca mg ca ratios and sr and stable isotopes of biogenic carbonates from the late miocene velona basin central apennines italy provide evidence of unusual non marine messinian conditions abstract the sr ca and mg ca ratios of fossil ostracod and mollusc shells from a late miocene early messinian lacustrine sequence in the velona basin central apennines italy were used to calculate the sr ca and mg ca of waters in which these taxa lived sr ca of these waters were always higher than the sr ca calculated for the messinian seawater despite the broad salinity ranges fresh water oligo mesohaline inferred from the paleontological analyses the estimated mg ca water from the velona samples are below the mg ca value for coeval seawater even though they represent relatively high values when compared with many non marine waters the salinity variations of the velona lacustrine system recorded by changes in faunal assemblages are linked to variable inputs of na cl from deep groundwaters and are not reflected in significant changes in sr ca and mg ca of the waters calculated from shell chemistry the combination of 18 o signatures and sr isotopic ratios from molluscs from the velona basin suggests a non marine environment during some episodes of the lake history given the saline inputs the waters in the lake would attain a large solute concentration oligo to mesohaline although they retained the meteoric 18 o signature we compare the paleohydrochemical inferences from the studied sequence with other messinian records and we show the importance of combining paleoecological and geochemical proxies to obtain consistent paleoenvironmental reconstructions

paratethyan mediterranean connectivity in the sea of marmara region nw turkey during the messinian the sea of marmara region is thought to have been a gateway between paratethys and the mediterranean since the middle miocene and is therefore an important control on water mass exchange between the two realms the miocene successions in the northeastern aegean and northwestern marmara regions indicate that the first mediterranean marine transgression to affect these areas occurred during the late serravallian in the northeastern aegean region frequent marine incursions occurred during the tortonian and messinian stages the messinian stage in this area is represented by a package of brackish to fresh water carbonates with some marine sandstone siltstone interbeds alcitepe formation which conformably overlies the tortonian kirazli formation the messinian sequence is overlain with an erosional contact by a shallow marine siliciclastic sequence goztepe formation of zanclean age with its brackish to fresh water carbonates and broadly constrained age the messinian sequence is interpreted as being coeval with the upper evaporite lago mare sequence observed in western mediterranean basins in the western marmara region the pontian messinian alcitepe formation consists of bioclastic and oolitic limestones with basal clastic rocks it conformably overlies the fluvio lacustrine siliciclastic sediments of the middle to upper miocene kirazli formation and is overlain by fluvio lacustrine sediments of the kimmerian 5 5 3 2 ma truva and tevfikiye formations with an erosional contact the bioclastic limestones of the alcitepe formation in the western marmara region contain a molluscan and ostracod fauna that are endemic to paratethys these fauna indicate deposition in a shallow brackish to fresh water environment faunal and paleomagnetic analyses of a section of the alcitepe formation at yenimahalle canakkale confirm that the formation is of pontian age and represents chron c3r 6 04 5 24 ma the ostracod analysis indicates that during deposition of the alcitepe formation salinity increased from brackish in the lower part to more saline conditions in the upper part ostracod valves have low 87sr 86sr values relative to coeval late miocene ocean water this indicates that exchange between the sea of marmara region and the global ocean was restricted throughout this period fossil and sr isotope evidence suggests however that there was a paratethyan marmara connection during the deposition of the lower part of the alcitepe formation with paratethyan influence reaching the north aegean connection via marmara between paratethys and the mediterranean was not re established until the late aktchagylian late pliocene the re connection was caused by both increased activity on the north anatolian fault and global sea level rise

87sr 86sr ratios in hydrothermal waters and deposits from the east pacific rise at 21 n abstract 87 sr 86 sr ratios of three hydrothermal waters collected on the east pacific rise at 21 n define a mixing line between seawater and a hydrothermal end member at 0 7030 which is derived by seawater basalt interaction at ca 350 c and water rock ratio of about 1 5 sr concentrations are not affected in the process while mg uptake from seawater is almost complete up to2 3 of this hydrothermal component is involved in anhydrite precipitation while the sr isotopic ratio in sulfides chalcopyrite sphalerite cannot be distinguished from that of sulfate it is estimated that ca 1 10 10 moles of strontium are yearly cycled in the hydrothermal systems of mid oceanic ridges thereby affecting the 87 sr 86 sr budget of seawater mass balance between river runoff limestone precipitation and ridge basalt alteration suggests that the 87 sr 86 sr ratios of the river runoff are in the range 0 7097 0 7113 and are largely dominated by limestone alteration

geochemistry and water dynamics of a medium sized watershed the herault southern france abstract the aim of this study of the herault watershed is to constrain the river groundwater relations with a global geochemical investigation major and trace elements radiogenic isotopes sr pb and stable isotopes oxygen deuterium among the six sampling campaigns in high and low flows this paper focuses on the first one march 1995 sampled during a low flow period for major and trace elements and sr isotopes on both dissolved and particulate loads a companion paper will focus on the river karst relations in a dynamical scheme over a complete hydrological cycle the objective of this paper is to constrain the spatial organisation of the different water reservoirs to show the relations between surficial and groundwaters and to assess the mechanical and chemical weathering in this low flow period the herault main stream successively drains a palaeozoic basement a karstified mesozoic cover and a tertiary and quaternary alluvial plain the different tributaries also drain these lithologies this watershed is also impacted by ancient mining and agricultural activities especially in the southern part major element concentrations generally reflect the drained lithologies the chemistry of the herault main stream is mainly controlled by silicate and carbonate endmembers whereas the karstic springs show clearly a mixture of limestones and dolomitic limestones major elements point out some specific characteristics of some karstic springs and sr isotopes are used to check previous underground circulation hypotheses and sometimes reveal strong connections with overlying surface waters mixing phenomena between the herault river and its tributaries can be quantified in the 87 sr 86 sr vs 87 rb 86 sr diagram based on a simple two component scheme and agree within 10 with the real discharge measurements as in large basins the suspended matter presents more variable and more radiogenic 87 sr 86 sr than the dissolved load due to the more important contribution of silicate particles which are less soluble than carbonate dissolved ca fluxes were estimated to be 36 51 and 38 kg km 2 day 1 in the palaeozoic basement the mesozoic cover and the alluvial plain respectively this implies a chemical erosion estimated to be 20 m year in the palaeozoic basement and 58 m year in the mesozoic cover similar to values calculated for large basins

geocatalytic reactions in formation and maturation of petroleum theory and experiments suggest that catalytic reactions are involved in petroleum formation this suggestion is not new but has never gained wide acceptance a model chemical system illustrates that acid catalyzed reactions can explain several key transformations in the generation and maturation of oil it also is shown that such reactions should occur under geologically reasonable conditions and that naturally occurring active catalysts exist in many sediments catalytic principles indicate that the nature and amount of these catalysts in sediments can importantly control the fate of organic substances therein it is suggested that under a given time temperature history organic matter in a sediment may or may not generate petroleum depending on the concentration and a tivity of the geocatalysts stated another way sediments differ in the time temperature histories needed to generate petroleum

the link between surface water and groundwater based drinking water strontium isotope spatial distribution patterns and their relationships to danish sediments abstract the hydrological relationship between surface waters and groundwaters in many regions of the world is well known and the effects of their mutual interaction and interaction with the soils and bedrocks with respect to resulting changes in their chemical composition are well studied in this study we add to this knowledge by comparing the distributional patterns of strontium sr isotopes in previously published 192 surface water samples with those of newly acquainted sr isotope data from groundwater based drinking water samples extracted from 163 of the major waterworks in denmark the aim is to investigate potential compositional changes that might derive from the interaction with the aquifer lithology or overlying sediments and soils the average sr isotope signatures of surface and groundwater based drinking waters define 87sr 86sr values of 0 7096 0 0015 2 and 0 7088 0 0013 2 respectively the skewed distribution of sr isotope compositions in groundwaters towards lower 87sr 86sr values indicates enhanced contribution of natural carbonate derived strontium with depth while slightly elevated 87sr 86sr signatures in surface waters may reflect the diminished contribution of sr from carbonates in the glaciogenic sediments due to their progressive acid dissolution strontium concentrations sr in groundwater based drinking water from the participating major waterworks define a country wide average of 1 17 mg l and the distributional pattern shows an east west decreasing trend lowest concentrations are found in the west jutland glaciogenic province wjgp average sr 0 36 mg l and in the northernmost tip of jutland a corresponding pattern although less pronounced is also depicted by the 87sr 86sr signatures of groundwater based drinking water whereby increasing 87sr 86sr values from zealand through funen into the jutland peninsula correspond with increasing thickness of glaciogenic overburden providing though mass balance wise subordinate radiogenic sr to the natural carbonate dominated groundwaters the highest 87sr 86sr values are recorded in waters from northern jutland possibly reflecting the admixture of radiogenic strontium from late glacial and post glacial glacio isostatic adjustment related marine aquifers generally the surprisingly rather homogeneous and similar distributional patterns of 87sr 86sr signatures of danish aquifers and surface waters implies a strong and dominant control of sr by natural clastic reworked carbonate components in the quaternary miocene and holocene sediments and to lesser degree with the exception of northern central jutland and eastern zealand from the pre quaternary limestone dominated basement directly our results are consistent with a tight hydrological and geochemical interrelationship between surface waters and groundwaters in denmark there is a need for further investigations of the effects of advanced treatment of soft acidic groundwater based drinking water on the concentrations and isotopic signatures of trace elements such as sr however our study lends support for the adequate use of sr isotope signatures of either of these waters to characterize the isotope compositional range of bioavailable fractions relevant for authenticity identification forensic studies and for prehistoric and modern human and animal proveniencing

role of minerals in thermal alteration of organic matter ii a material balance pyrolysis experiments were performed on green river and monterey formation kerogens types i and ii respectively with and without calcite illite or montmorillonite at 300 c for 2 to 1 000 hours under dry and hydrous conditions pyrolysis products were identified and quantified and a material balance of product and reactants resulted significant differences were found in the products generated by pyrolysis of kerogens with and without minerals both illite and montmorillonite adsorb a considerable portion up to 80 of the generated bitumen the adsorbed bitumen is almost exclusively composed of polar compounds and asphaltenes that crack to yield low molecular weight compounds and insoluble pyrobitumen during prolonged heating montmorillonite shows the most pronounced adsorptive and catalytic effects with calcite however the pyrolysis products are similar to those from kerogen heated alone and bitumen adsorption is negligible applying these results to maturation of organic matter in natural environments we suggest that a given type of organic matter associated with different minerals in source rocks will yield different products furthermore the different adsorption capacities of minerals exert a significant influence on the migration of polar and high molecular weight compounds generated from the breakdown of kerogen therefore the overall accumulated products from carbonate source rocks are mainly heavy oils with some gas whereas light oils and gases are the main products from source rocks that contain expandable clays with catalytic and adsorptive properties

the k ar and 40ar 39ar methods revisited for dating fine grained k bearing clay minerals abstract the strengths and weaknesses of the two ar isotopic methods k ar and 40ar 39ar were evaluated on the basis of respective recent applications mainly on low temperature k bearing illite type clay minerals this review includes a presentation of basic analytical and technical aspects for both methods as well as a discussion of varied claims on the two methods and of requests about sample preparation and characterization whenever possible the advantages and weaknesses of each method were compared on coeval results obtained by both methods on the same mineral separates the comparative review examines stratigraphic dating of glauconites indirect dating of low temperature ore deposits dating of burial related illitization and dating of polyphased tectono thermal activity more specifically of fault gouges some pending questions such as the necessary encapsulation due to 39ar recoil and its restoration into step heating patterns are also raised together with the new potential of ar dating of nanometric illite crystals weakness of the k ar method is in its pioneering status that makes many believe that it is no longer accurate because of its traditional analytical aspects and of the k determinations leading to somewhat large uncertainties however precise evaluation of varied applications points to a k ar method having probably larger applicability in sedimentary to diagenetic environments than the 40ar 39ar method the drawbacks become less important if the method is applied to nanometer sized clay minerals in diagenetic to low grade metamorphic environments in this instance the extracted size fractions are generally homogeneous and the relative uncertainty given by the age calculations if mathematically justified can be reduced by duplicate analyses weakness of the 40ar 39ar method is in its basics such as the 39ar recoil the necessary encapsulation the reintegration of the 39ar into the step heating patterns and the meaning of the step heating patterns that are more suggestive of variable 39ar reservoirs created among the clay particles by irradiation than of meaningful geologic ages if the k ar method is the preferred method for dating diagenetic clay processes such as glauconitization illite crystal nucleation and growth or low temperature hydrothermal activities then the 40ar 39ar method has more potential in dating low temperature tectono thermal activities and in detailing mixtures of multi generation illite

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

rare earth elements neodymium and strontium isotopic systematics in mineral waters evidence from the massif central france abstract rare earth elements rees and sr and nd isotope distributions have been studied in mineralized waters from the massif central france the co 2 rich springs are characterized by a neutral ph 6 7 associated with total dissolved solids tds from 1 to 7 g l 1 the waters result from the mixing of very mineralized water pools thought to have equilibrated at a temperature of around 200 c with superficial waters these two mineral water pools evidenced by sr isotopes and dissolved rees could reflect 2 different stages of water rock interaction and an equilibrium with different mineral assemblages the concentrations of individual dissolved rees and total dissolved rees ree in the mineral waters examined vary over several orders of magnitude but are not dependent on the main parameters of the waters tds t c ph total organic c the dissolved ree concentrations presented as upper continental crust normalized patterns show hree enrichment in most of the samples the time evolution of ree patterns does not show significant fluctuations except in 1 borehole located in the limagne d allier area which was sampled on 16 occasions over an 18 month period ten samples are hree enriched whereas 6 samples show flat patterns the aqueous speciation of rees shows that co 2 3 complexes dominate 80 over the free metal f so 2 4 and hco 3 complexes the detailed speciation demonstrates that the fractionation of rees i e the hree enrichment in co 2 rich and ph neutral fluids is due essentially to the predominance of the co 2 3 complexes the sr isotopic composition of the mineral waters in the massif central shows different mixing processes in the cezallier area at least 3 end member water types exist the most dilute end member is likely to originate as poorly mineralized waters with minimal groundwater circulation two other mineralized end members are identified although the link between the geographical location of spring outflow and the mixing proportion between the 2 end members is not systematic the range in nd 0 for mineralized waters in the massif central correlates well with that of the known parent rocks except for 4 springs one way to explain the nd 0 in these instances is a contribution from drainage of volcanic rocks the isotopic systematics help to constrain the hydrogeological models for this area

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

the mediterranean water body in the late messinian interpreting the record from marginal basins on sicily the stratigraphic record of climatic and palaeoceanographic changes in the mediterranean during the late messinian is controversial on sicily sedimentary facies show a steady transgression suggesting that sub basins were hydrodynamically linked to a larger water body here we test this hypothesis using strontium isotope studies from messinian materials collected from a range of sites in the caltanissetta basin of central sicily the strata include a regionally regressive first cycle of early mid messinian age and a younger transgressive second cycle these cycles are separated by an inter regional unconformity which may be correlated with base level low stand in the mediterranean 87 sr 86 sr ratios for all first cycle gypsum fall within the expected global marine composition 0 70891 0 70897 all second cycle analyses fall within a grouping of significantly lower values 0 70868 0 70878 a surprisingly tight but discrepant grouping for data collected from shells of a brackish water fauna and from gypsum analyses from these different second cycle materials are statistically indistinguishable these results indicate that the strontium isotopic composition of waters from different sub basins on sicily are indistinguishable regardless of salinity during the late messinian therefore these basins must have mixed with a larger homogenized reservoir which we infer was the ancestral mediterranean thus circum mediterranean basins may indeed chart regional palaeoceanographic and climatic events by the end of messinian times the base level of the mediterranean was within the range of the world9s oceans but the water body probably had a distinctly different but internally homogeneous strontium isotopic composition

mineralogical chemical and k ar isotopic changes in kreyenhagen shale whole rocks and 2 μm clay fractions during natural burial and hydrous pyrolysis experimental maturation abstract progressive maturation of the eocene kreyenhagen shale from the san joaquin basin of california was studied by combining mineralogical and chemical analyses with k ar dating of whole rocks and hydrous pyrolysis was intended to alleviate the problem of mineral and chemical variations in initially deposited rocks of naturally matured sequences however experiments on aliquots from thermally immature kreyenhagen shale outcrop sample did not mimic the results from naturally buried samples experiments conducted for 72 h at temperatures from 270 to 365 c did not induce significant changes at temperatures above 310 c in the mineralogical composition and k ar ages of the rock and large amounts of smectite layers in the illite smectite mixed layers of the pyrolyzed outcrop

evidence for slowly changing 87sr86sr in runoff from freshwater limestones of southern france abstract 87 sr 86 sr ratios have been determined in modern rivers and freshwater limestones dating from 65 ma to the present over an area extending from the pyrenees to the massif central southern france about 40 ma ago the alpine mountain range of the pyrenees was strongly uplifted by the alpine orogenic activity and its pre hercynian basement dominated by schists gneisses and granites was rapidly exposed from beneath its blanket of mesozoic marine limestones meanwhile the 87 sr 86 sr ratio of the rivers has remained remarkably constant in both space with the exception of the very few northernmost samples and time in this area extreme variations through the orogenic period are small with 87 sr 86 sr lying between 0 7073 and 0 7084 at 55 65 ma and 0 7077 0 7096 for the last 30 ma river sr is controlled by a nearly binary mixing of silicate 3 4 and 1 4 end members with negligible influence of evaporites it is inferred that the silicate sediment contribution ratio of the world average rivers to seawater sr changes at a very slow rate even taking major basaltic events into account does not alter this conclusion as their contribution to the river sr is very subordinated to other components it is inferred that the seawater 87 sr 86 sr secular main trend over the phanerozoic is controlled by hydrothermal alteration of oceanic basalts and slow variation of the limestone silicate contribution ratio to the riverine sr oceanic events changes in organic productivity and carbonate compensation depth ccd may produce intense short term variations but recovery of steady state seawater 87 sr 86 sr is delayed by 40 80 ma through diagenetic sr remobilization in carbonate sediments

reconstructing fluid flow events in lower triassic sandstones of the eastern paris basin by elemental tracing and isotopic dating of nanometric illite crystals lower to middle triassic sandstones from eastern paris basin were buried to a maximum depth of 2500 m at a paleo temperature of about 100 c they contain extensive amounts of authigenic platy and filamentous illite particles similar to those reported in reservoirs generally buried at 3000 to 5000 m and subjected to temperatures of 120 to 150 c to evaluate this unexpected occurrence such sandstones were collected from drill cores between 1825 and 2000 m depth and nanometric sized sub fractions were separated the illite crystals were identified by xrd observed by sem and tem analyzed for their major trace rare earth elements and oxygen isotope compositions and dated by k ar and rb sr illite particles display varied growth features in the rock pore space and on authigenic quartz and adularia that they postdate tem eds crystal chemical in situ data show that the illite lath fiber and platelet morphologies correspond at least to two populations with varied interlayer charges between 0 7 and 0 9 in the former and between 0 8 and 1 0 in the latter the fe fe mg ratio being higher in the platelets except for the deeper conglomerate the paas normalized ree patterns of the illite crystals are bell shaped enriched in middle rees ca carbonates and ca phosphates were detected together with illite in the separates these soluble components yield 87sr 86sr ratios that are not strictly in chemical equilibrium with the illite crystals suggesting successive fluids flows with different chemical compositions the k ar data of finer 0 05 m illite separates confirm two crystallization events at 179 4 4 5 and 149 4 2 5 ma during the early and late jurassic the slightly coarser fractions contain also earlier crystallized or detrital k bearing minerals characterized by lower 18o values the 18o of the finest authigenic illite separates tends to decrease slightly with depth from 18 2 0 2 to 16 3 0 2 suggesting different but contemporaneous crystallization conditions deeper in the section the illite platelets and filaments crystallized in changing physical chemical crystallization conditions induced by fluids flows through the host rock pore system these flow events were probably driven by repetitive rifting episodes of the north atlantic ocean although located several hundreds kilometers away from eastern paris basin and or by fracturing events in the nearby basement of the vosges massif complex relationships between geodynamical events thermal anomalies and advective fluids confirm that remote tectonic activities can impact quiescent basins even if located far from tectono thermal activities by discrete and long distance fluid flows

diagenetic evolution of clay minerals in oil bearing neogene sandstones and associated shales mahakam delta basin kalimantan indonesia the clay fraction of the mahakam delta basin eastern kalimantan indonesia consists of mixed layer illite smectite kaolinite dickite detrital illite and chlorite kaolinite formed early as vermicular particle aggregates and thick dickite booklets formed late in pore spaces the dickite particles probably grew in deeper intervals of the sequence in contact with brines acidified by decarboxylation of organic matter during dissolution of k feldspar and upward migration of potassium in the handil field on the nearshore anticline evolution of the mixed layer illite smectite is characterized by a decrease in expandability with depth in the tunu field located on the next offshore anticline variable amounts of expandable layers suggest a different evolution the conversion process of smectite to illite layers in the mixed layers depends on the lithology of the host rocks transformation in the shales and dissolution precipitation in the sandstones sample location also played a role in the conversion process because the types of illite clays in the two locations differ when they are compared at similar degrees of evolution present day temperatures and paleotemperatures vitrinite reflectance and illitization of the mixed layer illite smectite all suggest that organic matter and clay particles evolved differently in the handil field but similarly in the tunu field integration of the analytical results obtained here and comparison with a two dimensional numerical model suggest that hydrocarbon generation took place in the deeper synclinal zones of the sequence and that oil migrated upward with brines probably inducing most of the illitization in the upper sequence both models emphasize the role of faults in channelizing fluid flow during the final stages of evolution of the basin

a strontium isotopic study of mineral and surface waters from the cezallier massif central france implications for mixing processes in areas of disseminated emergences of mineral waters abstract surface and mineral waters from a geothermal area cezallier in the centre of the massif central france were analysed for sr isotopes sr and major elements in order to use sr isotopes to investigate the discharge of a mineralised water area especially in the case of disseminate mineralised water emergences the 87 sr 86 sr ratios of mineralised waters ranged from 0 715541 to 0 716773 the variation in 87 sr 86 sr values was small for the 5 mineral springs sampled over two periods 5 10 6 14 10 6 regarding the reproductivity of the 87 sr 86 sr ratio measurements no differences can be seen and the 87 sr 86 sr ratio of mineral waters can be considered to be constant with time the 87 sr 86 sr ratios of surface waters collected along the zagat river ranged from 0 705303 to 0 715091 the lowest values were always observed in the headwaters the difference in the 87 sr 86 sr ratios between the two sampling periods was 22 10 4 and can be related to the hydrological situation low or high flow the 87 sr 86 sr ratios of surface waters collected in the drain ranged from 0 715072 to 0 716585 the difference in the 87 sr 86 sr ratios between the two sampling periods is 11 10 4 for the drain headwaters and 13 10 5 at the outlet of this area likewise these variations can also be related to the hydrological situation plots of 87 sr 86 sr vs 1 sr ratios show two distinct binary mixing trends and the existence of at least four end members a mixing parameter f giving the proportions of the two components can be estimated for assumed 87 sr 86 sr ratio and sr content values of the pure end members an estimate of the mineral water discharge can be calculated using the results of the mixing model and the measured flow in the drain area the mixing model gives an estimate 0 5 1 l s 1 or 10 13 of mineral water in the total flow a similar calculation was done for the river where the mineral water flow was 0 96 l s 1 3 5 m3 h 1 100 m downstream from the bridge in april 1994 and 6 m3 h 1 20 m downstream from the bridge in september 1994

late cretaceous to late eocene palaeogeographic evolution of southwest europe abstract a synthesis of personal research concerning the peri pyrenean region and previously published data is presented as a series of palaeogeographic reconstructions subsequent to the progressive regression at the end of the cretaceous the sea invaded three times parts of the earlier senonian marine domain on both sides of the eastern palaeo pyrenees pre cuisian climatic rewarming combined with cuisian continental epeirogenic deformations resulted in major biogeographic modifications during the cuisian local tectonics forced the sea from the northern pyrenean basin whereas in the southern pyrenean basin the sea retreated much later as a consequence of the pyrenean tectonic phase however the pyrenean tectogenesis seems to have affected a much larger region including the alps shoreline migrations are compared and related to the geodynamic behaviour of the meridional and septentrional european provinces in order to distinguish between tectonic and eustatic causes

atomic h c ratio of kerogen as an estimate of thermal maturity and organic matter conversion in recent years the atomic h c hydrogen to carbon ratio of kerogen as a way to assess the quality of organic matter in source rocks has been overlooked in favor of the more easily determined rock eval hydrogen index rock eval pyrolysis provides fast inexpensive quantitative mg hc g rock data without requiring kerogen isolation from the rock because of the general scatter in the data many source rock interpreters consider rock eval pyrolysis to be a screening analysis in this paper i describe the benefits of using h c ratios in source rock evaluations and present new correlations between atomic h c ratios and thermal maturity organic matter conversion and expulsion volumetrics atomic h c ratios of pyrolyzed kerogens have been correlated to the extent of thermal conversion of organic matter for both type i and type ii kerogens the excellent agreement between stoichiometric calculated hydrogen and carbon loss to observed losses from hydrous pyrolysis maturation experiments suggests that kerogen h c ratios are excellent indicators of thermal maturity for end member kerogen types these data also offer a method to estimate percent organic matter conversion provided that both the initial and present h c ratios of the kerogen are known present h c ratios can be measured and initial h c ratios can be reasonably estimated from microscopic organic analysis of kerogen for oil prone source rocks typical immature type i kerogens have h c ratios of 1 35 1 50 whereas type ii kerogens have h c ratios of 1 20 1 35 correlations of the amount of expelled oil in hydrous pyrolysis experiments to atomic h c ratio of the spent kerogen offer exploration geologists a quick estimate of oil expulsion volumes based on hydrous pyrolysis experiments measured h c ratios and calculated original toc total organic carbon values first order volumetric approximations were made on three basins containing mature source rocks results compared favorably with published approximate oil in place estimates for the williston basin bakken shale los angeles basin nodular shale and the illinois basin new albany shale

mineralogical changes in organic rich posidonia shale during natural and experimental maturation abstract the diagenesis of clay minerals and organic matter in posidonia shale has been typically studied independently of each other here the results of an experimental investigation focused on the mineralogical changes of organic rich shales are presented to understand the dissolution and precipitation processes of minerals as a function of thermal maturity three core samples of posidonia shale hils syncline germany with increasing natural thermal maturity wickensen wic 0 53 r0 dohnsen doh 0 73 r0 haddessen had 1 45 r0 were reacted in experimental aliquots of 0 3 m kcl solution rock fluid ratio 1 5 sealed in gold capsules at 300 c and 120 bars for 27 days following treatment the calculated maturities easy r0 values of the two samples with the lowest vitrinite reflectance values indicates thermal enhancement wic 1 14 r0 doh 1 15 r0 whereas the most mature sample remained unchanged had 1 45 r0 the educts and products were analysed by transmission electron microscopy tem combined with energy dispersive x ray spectroscopy edx and x ray diffraction xrd in all experiments kaolinite and carbonates were extensively dissolved whereas quartz underwent partial dissolution reaction products consisted of lath shaped mg2 rich 1md illite together with k feldspar in the form of sanidine trioctahedral saponite precipitated only in the oil producing sample wic along with less sanidine and 1md illite the unexpected formation of metastable 1md illite at 300 c instead of stable 2m1 illite is attributed to low k reactivity due to either depletion of this element by the early formation of sanidine and or the chemical effects of organic acids that shift the stable phase into the k poor stability field the precipitation of saponite and the limited sanidine and 1md illite formation in sample doh is attributed to high dolomite content and hence mg2 availability along with the more extensive release of hydrocarbon compounds and further reduction of k reactivity in this sample it is concluded that the neoformation of metastable phases 1md illite and trioctahedral smectite observed in short term higher temperature experiments may differ significantly from prolonged mineral transformations occurring under natural conditions

carbonate lake deposits associated with distal siliciclastic perennial river systems abstract the genesis of thick accumulations of carbonate lake deposits on the siliciclastic floodplains of perennial rivers situated below the regional spring line requires 1 a significant source for calcium in the watershed and 2 a protected area to accumulate calcite the phanerozoic record of fluvial deposits shows that anastomosing rivers with carbonate rich provenance situated in distal areas below the spring line are the best environments for floodplain accumulation of significant carbonate lake deposits anastomosing rivers exist below the regional spring line and have isolated flood basins generally protected from bedload by high levees receiving suspended and dissolved load during flooding events numerical modeling to test the rate of accumulation for these carbonate sediments was performed using stratigraphic data from the pennsylvanian succession containing floodplain limestones of the stewart quadrangle of athens county in ohio usa limestone volumes for six limestone units upper pittsburgh fishpot sewickley benwood arnoldsburg uniontown and waynesburg limestones were calculated with the assumption of overland input of dissolved calcite from carbonate source areas in comparing the calcium input rate to the amount of calcium calculated from limestone unit volumes overland transport of calcium ions not spring input can supply sufficient ions to accumulate thick carbonates over the short lifetime of floodplain lakes within anastomosing river systems

application of sr isotope stratigraphy and sedimentary analysis to the origin and evolution of the neogene basins in the isparta angle southern turkey abstract four miocene basins are located within the isparta angle in southern turkey one of these the darioren basin is well established as the foreland basin to the adjacent lycian nappes which marks the western margin of the isparta angle the tectonic origin of the other three basins aksu kopru and manavgat has remained enigmatic largely because of the difficulties of dating the lowermost part of the succession continental and shallow marine conglomerates and limestones comparison of carbonate 87 sr 86 sr with the ocean water sr isotope record provides a powerful chronological tool for marine sediments by using sr isotope ratios in this way ages of the neritic limestones have been derived despite the absence of age diagnostic fossils these data constrain the age of the underlying conglomerates as lower to middle burdigalian the timing of deepening and subsidence events suggested by these new dates taken together with palaeocurrent measurements from conglomerates suggest that the basin configuration of the isparta angle was initiated in the lower burdigalian and was directly related to movement on north south oriented faults depocentre development in the north of the aksu basin is consistent with a tectonic origin for all three basins by flexurally induced block faulting of the foreland in front of the lycian nappes along pre existing structural weaknesses

strontium and its isotopes in canadian rivers fluxes and global implications systematic sampling of the 39 largest canadian rivers shows that the weighted average 87sr86sr ratio in the dissolved load is 0 7111 similar to previous measurements on such large rivers as the amazon and mississippi consequently we believe that the above estimate is likely representative of the global average this imposes a limit of 6 5 1011g yr 1 on the amount of sr exchanged with basalts in hydrothermal cells on mid oceanic ridges evaluation of geological information suggests that sr from silicate sources is of considerable importance for all but the largest canadian rivers the latter have chemical and isotopic composition consistent with 4 1 carbonate vs silicate derivation of sr but such interpretation is not unique in terms of their water discharge the 39 canadian rivers studied account for 4 2 of the world total and their weighted average concentrations for other dissolved solutes are tds 176 ppm ca 18 ppm cl 6 8 ppm and sr 84 ppb

pliocene transgression in the western mediterranean sea strontium isotopes from cuevas del almanzora se spain the deposition of marine sediments in the deep mediterranean basins following the messinian salinity crisis zanclean deluge began at 4 9 ma and continued until normal marine conditions prevailed at 4 6 ma the betic strait of southeast spain the rif strait of northern morocco and the strait of gibraltar have been postulated as possible entry ways for the marine waters into the mediterranean two possible explanations have been offered for the timing of the deposition of marine hemipelagic marls in the vera basin cuevas del almanzora section within the betic strait 1 early pliocene representing the zanclean deluge cita et al 1980 2 messinian 5 7 ma representing the last marine stage before the messinian salinity crisis benson and rakic el bied 1991 benson et al 1991 the strontium isotopic ratio on mixed assemblages of foraminifers from these marine marls was determined in order to assess their ages the average 87sr 86sr 0 709033 24 of the seven measured samples is compared to the base of the miocene pliocene boundary stratotype at capo rossello sicily higher by 38 10 6 and yields an age of 4 6 0 5 ma when compared to the established open ocean sr seawater curve the determined age indicates that 1 the first 3 6 m of marine deposits of the cuevas del almanzora section sensu cita et al 1980 including the passage zone are pliocene 2 the earliest marine pliocene might not be represented at cuevas del almanzora indicating that this marginal basin at the edge of the mediterranean sea yet within the former betic strait was filled progressively by a marine transgression originating from the mediterranean sea around 4 6 ma the absence of lowermost pliocene sediments could suggest that the betic strait did not serve as a conduit for the water masses entering the mediterranean basins during the early pliocene and 3 the presence of an early evolutionary stage of globorotalia margaritae in the moroccan bou regreg section approximately 5 8 5 6 ma and in the spanish cuevas del almanzora section later than 4 6 0 5 ma are diachronous suggesting that straightforward correlations of micropaleontological events within the mediterranean area with micropaleontologic events of open marine sections should be tested thoroughly by independent methods like sr isotopes

causes and consequences of the relation between area and age of the ocean floor the distribution of area of the ocean floor with age t is approximately described by da dt c0 1 t tm where c0 is the rate of crustal generation and tm the maximum age a linear differential area versus age relation can be explained by a balance between crustal generation and consumption where consumption is uniformly distributed with age the present distribution of consumption with age was estimated from the isochron map used to derive the area age relation and a recently published set of angular velocity vectors describing present plate motions the rate of consumption per unit age shows considerable scatter about a mean value equal to c0 tm 1 7 10 8 km2 yr2 but consumption is sufficiently close to being uniformly distributed with age to explain the observed degree of approximation to a linear differential area age relation the trenches appear to be distributed randomly with respect to age provinces in the oceans it was not possible to discern any trend of mean subduction velocities with age apart from the smaller velocities observed for the two youngest age provinces 0 9 ma changes in the rate of plate generation and the distribution of consumption with age result in shifts in the area age distribution in turn these shifts produce changes in the plate driving forces which act to restore the rate of plate generation and distribution of consumption to their initial states the ridge pushing force for example decreases as the rate of crustal generation increases this coupling between driving forces and the area age distribution provides a feedback mechanism limiting the extent of any changes a measure of the magnitude of shifts in the area age distribution is given by global changes in sea level if long term changes in sea level are less than 150 m as suggested by recent estimates then only small changes 12 in the rate of plate generation and distribution of consumption with age are required sea level changes as large as 300 m require about a 50 change in the rate of crustal generation the above area age relation can be combined with simple expressions for depth and heat flow versus age to obtain an empirical hypsometric distribution parameterized in terms of age and exact expressions for the heat loss from the ocean floor the latter is estimated to be 2 9 1013 w with 25 of this heat being lost by seafloor younger than 5 ma of the total heat loss from the mantle 26 is estimated to be transported by small scale convection

sr isotopes in interstitial waters of marine sediments from deep sea drilling project cores sr isotopic compositions of interstitial sea waters have been documented in detail with cores from 37 deep sea drilling project sites the 87sr 86sr ratios are sensitive indicators of diagenetic reactions involving alteration of volcanic matter dispersed in sediments and recrystallization of carbonates effects of basalt alteration reactions except possibly for hydrothermal signals and of alteration of continental debris are minimal carbonate recrystallization has a significant effect on the geochemical mass balance of sr but diffusion of unradiogenic strontium from interstitial waters has only a small effect on the 87sr 86sr ratio of ocean water

effects of thermal maturation on stable organic carbon isotopes as determined by hydrous pyrolysis of woodford shale acquiring crude oils that have been expelled from the same rock unit at different levels of thermal maturation is currently not feasible in the natural system this prevents direct correlation of compositional changes between the organic matter retained in a source rock and its expelled crude oil at different levels of thermal maturation alleviation of this deficiency in studying the natural system requires the use of laboratory experiments natural generation of petroleum from amorphous type ii kerogen in the woodford shale may be simulated by hydrous pyrolysis which involves heating crushed rock in contact with water at subcritical temperatures 374 c four distinct stages of petroleum generation are observed from this type of pyrolysis 1 pre oil generation 2 incipient oil generation 3 primary oil generation and 4 post oil generation the effects of thermal maturation on the 13c values of kerogen bitumen and expelled oil like pyrolysate from the woodford shale have been studied through these four stages of petroleum generation similar to the natural system the kerogens isolated from the pyrolyzed rock showed no significant change in 13c this suggests that the 13c value of kerogens may be useful in kerogen typing and oil to source rock correlations 13c values of bitumens extracted from the pyrolyzed rock showed an initial decrease during the incipient oil generation stage followed by depletion during the primary and post oil generation stages this reversal is not favorable for geochemical correlation or maturity evaluation saturated and polar components of the bitumen show the greatest 13c variations with increasing thermal maturation the difference between the 13c of these two components gives a unidirectional trend that serves as a general indicator of thermal maturation and is referred to as the bitumen isotope index bii 13c values of the expelled pyrolysates show a unidirectional increase with increasing thermal maturation the constancy and similarity of 13c values of the aromatic components in the expelled pyrolysates and bitumens with increasing thermal maturation encourages their use in oil to oil and oil to source rock correlations isotopic type curves for expelled pyrolysates indicate that they may be useful in oil to oil correlations but have a limited use in oil to source rock correlations

normal fault growth and its function on the control of sedimentation during basin formation a case study from field exposures of the upper cambrian owen conglomerate west coast range western tasmania australia the evolution of a complex ancient segmented basin margin fault system was examined using integrated structural relationships lithostratigraphic architecture facies architecture and paleoflow trends to define the control on synrift development during the deposition of the upper cambrian owen conglomerate west coast range western tasmania australia four distinct stages are recognized during the evolution of the normal fault array the rift initiation stage defined early fault nucleation and isolated growth before fault interaction led to strain localization and the abandonment of antithetic faults renewed fault initiation led to further fault growth prior to the transition to rift climax stage with the development of a throughgoing linked array boundary faults propagated to near maximum length prior to significant basin formation whereas segment interaction clearly exerted a primary control on synrift distribution and paleogeography temporal fault evolution is marked by highly varied displacement patterns and pronounced lateral shifts in maximum synrift thickness accumulations the case study presented here is compared with existing models of fault growth and provides a field example for the assessment of basin formation particularly in polydeformed terranes which can offer crucial high resolution temporal data on fault system evolution associated stratal architectures and sediment dispersal patterns

radioactive production and diffusional loss of radiogenic 40ar in clays in relation to its flux to the atmosphere abstract this paper addresses the release mechanisms of radiogenic 40 ar from clays for the purpose of estimating the 40 ar flux from the sedimentary crust to the atmosphere clays from sedimentary sequences of cambrian to neogene age show discrepancies between their depositional stratigraphic ages and the k ar apparent ages or dates of the different size fractions the possible geochemical mechanisms that may be responsible for the k ar dates being either higher or lower than the stratigraphic age are discussed in general the known observation of a decrease in the k ar apparent age of clays with decreasing particle size is interpreted as due to a faster escape of radiogenic 40 ar from the smaller particles in the younger neogene clays the mass fractions of 40 ar lost are in a range from 13 to 34 in the fine size particles that are smaller by a factor of 10 in their linear dimension than the bigger particles in the older formation samples cambrian to triassic the 40 ar loss is smaller from 7 to 19 for the same particle size range this smaller decrease in the 40 ar 40 k ratio in the stratigraphically older samples may be at least in part accounted for by the closure of the mineral system after the process of 40 ar escape went on for some time in all sediments a lowering of the k ar apparent age of the different size fractions mainly in the smaller is possibly due to authigenesis of mixed layered illite smectite and illite as a new generation of particles that result from and are therefore better adapted to the new diagenetic environment in a neogene basin sediments of depositional age as an overall model we present a mechanism that explains the lowering of the 40 ar 40 k ratio and k ar apparent age in fine clay size fractions based on the production of 40 ar in a closed system for some period of time followed subsequently by the diffusional escape of 40 ar with its continuing production from 40 k in the particles this analysis gives 40 ar diffusion coefficients consistently in a range from 10 28 to 10 27 cm 2 s from the results in this paper the flux of radiogenic 40 ar from the sedimentary crust to the atmosphere is estimated as 5 to 13 10 6 mol year which is about 15 to 40 of the flux from the whole continental crust as reported by other investigators