aragonite relic preservation in jurassic calcite replaced bivalves shells of the aragonite bivalve neomiodon great estuarine group jurassic scotland replaced by coarse neomorphic calcite contain oriented relics of the original aragonite ultrastructure the presence of these relics in such old altered shells as well as the high sr content of the replacement calcite indicate that the process of calcite replacement of aragonite is not a cumulative slow process involving repeated alteration events but rather a rapid one step process aragonite relics once encased in neomorphic spar will survive as unequivocal evidence of original aragonite mineralogy barring total remobilization of the enclosing stable calcite a generally unlikely event the retention of this residual aragonite and high sr calcite supports recent isotopic studies which suggest that the multiple phases of alteration recrystallization invoked in earlier literature are unlikely events in the diagenesis of most undolomitized limestones retention of aragonite relics appears to be independent of whether alteration occurs in shallow meteoric or as in the case of our neomiodon material deeper burial environments pseudopleochroism of the replaced neomiodon shells appears to be due to organic largely graphitic relics not to the aragonite relics

neomorphic spar versus cement in some jurassic grainstones significance for evaluation of porosity evolution and compaction thinly bedded upper bathonian grainstones with shales in wiltshire uk have intergranular spar of 2 kinds a primary calcite cement and a neomorphic spar that has replaced an earlier fibrous cement the earlier cemented grainstones have been less compacted than those cemented by a late calcite spar fewer broken grains fewer grain contacts more intergranular spar the crystals in the neomorphic intergranular spar are mostly subequant have irregular intercrystalline boundaries patchy extinction some dusty relics of earlier cement fringes and with cathodoluminescence show bright orange needle like relics of earlier cement fabric most of this subequant neomorphic spar is indistinguishable from the neomorphic spar that has replaced the aragonite of molluscan shells it is concluded that calcitization of an early cement and of the aragonite shells along with the precipitation of the true cement spar were delayed until after the carbonate sands had undergone some compactive fracture and grain grain pressure solution

geodynamic control on carbonate diagenesis petrographic and isotopic investigation of the upper jurassic formations of the paris basin france abstract the oxfordian and kimmeridgian carbonates of the eastern edge of the paris basin display poor reservoir properties stable isotope investigation of these non recrystallized cements through both microdrilling sampling and in situ sims secondary ion mass spectrometry analysis shows that they originated from slightly buffered meteoric fluids 3 smow to 8 smow flowing through the malm carbonate aquifers of the eastern edge of the paris basin after a review of the post upper jurassic history of the paris basin it appears that meteoric water supplies leading to such cementations were associated with the evolution of the basin s geodynamic setting and notably with the lcu late cimmerian unconformity major event which corresponds to the uplift of the london brabant massif denudation of the oxfordian and kimmeridgian carbonates on the southern flank of the london brabant massif to the north of the study area then lead to lateral recharging of the associated aquifers with meteoric fluids this scenario is similar to the one proposed to explain cementations of the jurassic carbonates in the wessex weald basins which emphasizes the main role played by the cretaceous unconformities over carbonate diagenesis at the scale of the northwestern tethys margin

geochemical comparison of fluid inclusion and present day oil accumulations in the papuan foreland evidence for previously unrecognised petroleum source rocks abstract petroleum production in papua new guinea is limited to the papuan fold belt present day oil accumulations in fields such as iagifu hedinia and gobe are thought to be mainly derived from clay rich jurassic marine source rocks containing terrestrially derived organic matter that were deposited under oxic conditions in this study other generative source rocks in the papuan foreland are indicated using fluid inclusion fi oil data from three wildcat wells koko 1 bujon 1 and kimu 1 which were drilled on the bosavi arch detailed organic geochemistry of these fi oils and associated free oils or oil stains suggests that none of these were generated from the aforementioned jurassic source rocks instead at least three different generative source rocks are indicated firstly a marine probably late cretaceous or younger source rock deposited under reducing conditions is indicated by the bujon 1 fi oil this source rock had a moderate contribution from higher plant organic matter including oleanane and or lupane the bujon 1 fi oil has similarities with fi oils from the iagifu 7x and p nyang 2x wells in the papuan fold belt secondly an algal dominated lacustrine source rock is indicated by the biodegraded koko 1 rft crude oil the unbiodegraded fi oil from koko 1 and the bujon 1 oil stains from the toro and imburu formations these lacustrine oils have high abundances of tricyclic terpanes pregnane homopregnane and gammacerane contain carotane and have high c26 c25 tricyclic terpane ratios the source of the lacustrine oils is inferred to contain moderate amounts of terrestrial organic matter indicated by a dominance of c29 steranes and abundant aromatic higher plant biomarkers and could be gypsiferous shales embedded in oligocene miocene carbonates or triassic age sediments deposited on igneous basement during early rifting associated with the break up of gondwana the kimu 1 fi oil was generated from a mature marine suboxic source rock but has a different geochemical composition to free oil from a similar interval which was derived from a carbonate rich source rock none of the fi oils correlate well with oil families previously described in papua new guinea accordingly the oils recovered from fis in this part of the papuan basin support the presence of laterally varying source rock compositions and qualities and indicate that there are opportunities to develop new charge models for features across the papuan foreland furthermore koko 1 bujon 1 and kimu 1 fi oils have different geochemical compositions compared to the associated free oils or oil stains indicating that each of these localities has a multi phase charge history further work to lower exploration risk in the papuan foreland should be directed to understanding the distribution maturity and expulsion history of these newly recognised potential source rocks

charging of the penglai 9 1 oil field bohai bay basin china functions of the delta on accumulating petroleum abstract the penglai 9 1 pl9 1 oil field which contains china s third largest offshore oil accumulation in place reserves greater than 2 28 10 8 ton or 1 49 10 9 bbl was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl9 1 field contains two oil bearing series the granite intrusions in mesozoic mz and both the sandstone reservoirs in neogene guantao ng and neogene minghuazhen nm formation the origins of the pl9 1 field both in terms of source rock intervals and generative kitchens were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples the mesozoic granite intrusions which hold more than 80 of the oil reserves in the field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression the neogene reservoirs of the pl9 1 field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression and in the south by oil generated from the first member es 1 of the shahejie formation in the miaoxibei depression interactive contact between the large fan delta and the mature source rocks residing in the es 3 formation of the bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the pl9 1 field which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east china

lower middle jurassic nonmarine source rocks and petroleum systems of the northern qaidam basin northwest china the qaidam basin is a nonmarine petroliferous basin on the northeastern margin of the tibet plateau potential source rocks are reported from tertiary saline lacustrine deposits and jurassic freshwater lacustrine or terrestrial strata the jurassic source rock is similar in terms of depositional system lithology age and organic geochemistry to nonmarine jurassic rocks that are thought to be potentially significant hydrocarbon sources in many basins of central asia including the tarim junggar and other important petroleum producing basins these jurassic source rocks were deposited in freshwater lacustrine systems in intracontinental foreland style basins during the early and middle jurassic these lacustrine strata are associated with coals and coaly mudstones with possible secondary importance as hydrocarbon source rocks oils from the northern qaidam basin can be divided into two groups based on molecular indicators of depositional environment and age diagnostic biomarkers those derived from this jurassic freshwater lacustrine source rock and those derived from a tertiary hypersaline lacustrine source rock the correlation of some qaidam oils to a jurassic source establishes a petroleum system involving these nonmarine jurassic source rocks oils of this petroleum system have been produced from tertiary and mesozoic reservoirs in anticlinal and thrust related traps in northeastern qaidam maturation modeling of the jurassic source rock indicates that these oils were generated and expelled during the miocene pliocene in much of northern qaidam the geological context of the basin suggests that drainage within the basin primarily was vertical probably mainly along faults until evaporite or overpressured shale seals were encountered in the overlying cenozoic section documentation of this petroleum system suggests other exploration targets remain underevaluated in northern and southwestern qaidam furthermore the northern qaidam petroleum system is a useful analog to interpret the role of similar jurassic source rocks in other sparsely documented basins of central asia

loss of primary texture and geochemical signatures in speleothems due to diagenesis evidences from castanar cave spain geochemical signals from speleothems are commonly used in the investigation of palaeoenvironments in most cases however little attention is paid to whether or not these signals are primary or altered by diagenesis the speleothems of the castanar cave caceres spain which are initially formed of calcite or aragonite have undergone a variety of meteoric diagenetic processes such as micritization and neomorphism inversion that collectively modify their primary features textures mineralogy geochemical signals the mean 13c and 18o values of the aragonites in the cave are 8 66 and 4 64 respectively whereas the primary calcites have mean 13c and 18o values of 9 99 and 5 77 respectively following the diagenetic process of micritization the aragonite isotopic signals averaged 7 63 13c and 4 74 18o and the calcite micrite signals 9 53 13c and 5 21 18o where inversion took place some secondary calcites after the aragonite show preserved aragonite whereas others do not the secondary calcites without aragonite relics show isotopic values slightly higher than those of the primary calcite due to the inheritance of the aragonite signal where aragonite relics are preserved the isotopic signatures are very similar to those of the aragonite micrite in addition the stable isotopic values and sr and mg contents of the speleothems became also modified by micritization and or inversion these diagenetic processes were driven by the changes in composition of the cave waters over time and space but also in the case of aragonite by its initial unstable mineralogy the present results highlight how important diagenesis is in caves and how the initial features of cave minerals may be lost these changes alter the geochemical signals shown by speleothems which may have an impact on the interpretation of the results obtained in palaeoenvironmental studies

characterization of various stages of calcitization in porites sp corals from uplifted reefs case studies from new caledonia vanuatu and futuna south west pacific abstract this study focuses on the processes of calcitization under meteoric conditions based on observations and analyses of a series of subaerial fossil corals of the genus porites collected from emerged holocene and pleistocene reefs in the pacific ocean we can establish two types of low magnesian calcite lmc precipitates according to their textural characteristics after their transformation from the initial aragonitic skeleton to the calcitized corals in the first variety lmc1 the calcite contains remnants of the original exoskeleton structure in situ insoluble organic tissues pieces of aragonite needles while in the second variety lmc2 filling the primary inter skeletal macro pores such relicts are not present such textural segregation is faithfully reflected in the elemental data on some parts of calcitized corals lmc1 is characterized by mg2 sr2 and mn2 compositions inherited from the aragonite precursor indicating a formation in a semi closed intra skeleton diagenetic environment in disequilibrium with the meteoric bulk aquifer water lmc2 has a chemistry indicative of equilibrium with ambient bulk meteoric water these chemical characteristics can be likened to a two fold mechanism a fine scale process neomorphism typified by the concomitant dissolution of intra fabric aragonite and re precipitation of the lmc1 resulting from the biogenic skeleton and marine waters followed by the cementation of the inter fabric macro voids by an allochthonous subaerial and meteoric lmc2 in the other parts of calcitized corals lmc1 and lmc2 have similar trace element contents in mg2 and sr2 the chemical data are consistent with formation by partial skeletal dissolution followed eventually by cementation of primary voids lmc2 and secondary voids lmc1 by calcite in equilibrium with meteoric bulk aquifer water these two mechanisms of the calcitization of skeletal aragonite mainly differ in the space and time length scales of the intervening transport step and are commonly found juxtaposed in the same thin section taking into account such a heterogeneity is a real challenge for the development of predictive models assessing the effects of diagenetic products on paleoclimatic reconstructions

the role of skeletal porosity in aragonite neomorphism strombus and montastrea from the pleistocene key largo limestone florida abstract the neomorphism of aragonite to calcite involves complex textural and chemical alterations that are in part controlled by the degree of communication between diagenetic and ambient formation fluids two taxa montastrea annularis and strombus gigas from the vadose zone of the pleistocene key largo formation in southern florida were examined in order to evaluate the effect of initial skeletal porosity on system closure during neomorphism fabrics of replacement calcite in both taxa are similar consisting of blocky crystals largely restricted to areas of former skeletal aragonite oriented aragonite and organic inclusions result in the preservation of relic fabrics in both taxa the chemical signatures of coralline and molluscan aragonite and calcite are strongly dependent on initial skeletal porosity compared to original aragonite montastrea calcite is enriched in magnesium 1 151 64 ppm versus 2 114 619 ppm and depleted in strontium 7 397 376 ppm versus 2 510 43 ppm these data in conjunction with large calcite oxygen depletions 3 8 0 2 versus 5 7 0 3 and variable calcite carbon depletions 0 6 0 6 versus 1 3 to 7 3 demonstrate significant exchange between neomorphic front and formational fluids in contrast strombus calcite composition is largely inherited from original aragonite and is only slightly enriched in strontium and magnesium 2 299 316 ppm versus 2 519 759 ppm and 96 23 ppm versus 173 79 ppm while carbon exhibits a small depletion 5 3 0 5 versus 4 4 0 8 similarity of str mbus aragonite and calcite compositions reflects high rock water ratios in relatively closed diagenetic systems calcite oxygen depletion 0 5 0 5 versus 3 6 0 4 observed in strombus however requires some exchange between formation and neomorphic front fluids differences in the thickness of replacement calcite rims between taxa reflect variable skeletal porosities and rates of migration of neomorphic fronts neomorphism was six times faster by volume in porous montastrea than in dense strombus skeletal structures thus skeletal porosity influences degrees of system openness during aragonite neomorphism

expulsion of petroleum hydrocarbons from shale source rocks there is compelling evidence that movement of petroleum from organic rich shales into sandstones and limestones occurs in the subsurface1 this expulsion of material must occur if crude oil accumulations are to form and it is termed primary migration2 earlier studies3 4 suggested that this movement occurs with chemical fractionation some components are more mobile than others one of the agents of expulsion at early maturity stages is compaction which is not only capable of forcing water but also organic components out of the pore network of a source rock2 5 6 because the fractionation effects associated with expulsion provide clues to the transport mechanisms involved we have made detailed quantitative comparisons of the hydrocarbons of shales of different thicknesses the centre and edges of thick shales and sandstones adjacent to shales from two cored interbedded shale and sandstone sequences from spitsbergen island svalbard norway these observations confirm considerable movement of hydrocarbons in the subsurface with lower molecular weight components being more mobile up to 90 the original amount of n pentadecane may be lost from very thin shales sandwiched between sandstone horizons and from shales close to a lithological boundary with sandstone

aragonite calcite relationships in speleothems grotte de clamouse france environment fabrics and carbonate geochemistry abstract in grotte de clamouse france aragonite forms in a variety of crystal habits whose properties reflect the conditions of formation prolonged degassing and evaporation yield needle aragonite which is more enriched in 18o and 13c than aragonite ray crystals which form near isotopic equilibrium at present aragonite ray crystals form at the tops of stalagmites at very low discharge 0 00035 ml min and when fluid mg ca ratio is 1 1 temperature and evaporation do not seem to have a significant role in their formation the presence of aragonite in stalagmites should be indicative of a decrease in drip rate related to either dry climate conditions or local hydrology fossil aragonite was in part replaced by calcite in a time frame 13c signal and u content and preserved aragonite relicts up to 16 weight the isotope signal of different aragonite habits may reflect conditions of formation rather than climate parameters the real extent of aragonite to calcite transformation may be underestimated when replacement calcite inherits both textural and chemical properties of the precursor

stable isotope composition alteration produced by the aragonite to calcite transformation in speleothems and implications for paleoclimate reconstructions abstract aragonite a mineralogical constituent of speleothems in cave environments is unstable and susceptible to inversion to calcite a diagenetic process that involves changes in the mineralogy texture and geochemistry of speleothems however the exact alterations of stable isotope compositions during such diagenesis have not been fully investigated in this study two aragonite stalagmites sn3 and sn15 from the shennong cave southeast china were found partially inverted to calcite as determined by x ray diffraction xrd and scanning electron microscopy sem analyses and thin section inspections under microscope the fiber relics and textural ghosts of aragonite preserved in coarse and equant mosaic calcite crystals clearly indicate that the calcite in these two stalagmites were inverted from aragonite the stable isotope compositions 13 c and 18 o given in per mil versus vpdb standard of primary aragonite and secondary calcite were analyzed and compared along both growth layers and growth axes the results show that along growth layers differences of 13 c values between aragonite and calcite are negligible 0 1 0 2 whereas differences of 18 o values between aragonite and calcite are significant 0 63 0 87 comparisons along growth axes show similar results i e differences of 13 c values are negligible 0 06 0 22 whereas differences of 18 o values are significant 0 85 0 29 most likely the aragonite in sn3 and sn15 were internally inverted by interactions of trace calcite crystallites and pore water within intercrystalline pore spaces by a dissolution reprecipitation process occurring in trapped pore water in the case of the inversion of aragonite to calcite in speleothems such as that observed in sn3 and sn15 the 13 c values could be used in paleoclimate and paleoenvironment reconstructions because they are inherited from those of primary aragonite although the 18 o values might be cross calibrated to those of primary aragonite if the aragonite calcite fractionation offset is known e g 0 85 0 29 in this study however the 18 o values of secondary calcite should be used with caution in such reconstructions as the 18 o offset value is not consistently invariable

thin ice and storms sea ice deformation from buoy arrays deployed during n ice2015 arctic sea ice has displayed significant thinning as well as an increase in drift speed in recent years taken together this suggests an associated rise in sea ice deformation rate a winter and spring expedition to the sea ice covered region north of svalbard the norwegian young sea ice2015 expedition n ice2015 gave an opportunity to deploy extensive buoy arrays and to monitor the deformation of the first year and second year ice now common in the majority of the arctic basin during the 5 month long expedition the ice cover underwent several strong deformation events including a powerful storm in early february that damaged the ice cover irreversibly the values of total deformation measured during n ice2015 exceed previously measured values in the arctic basin at similar scales at 100 km scale n ice2015 values averaged above 0 1 d 1 compared to rates of 0 08 d 1 or less for previous buoy arrays the exponent of the power law between the deformation length scale and total deformation developed over the season from 0 37 to 0 54 with an abrupt increase immediately after the early february storm indicating a weakened ice cover with more free drift of the sea ice floes our results point to a general increase in deformation associated with the younger and thinner arctic sea ice and to a potentially destructive role of winter storms

diagenetic replacement controlled by force of crystallization many diagenetic replacements in sedimentary rocks occur along thin solution films between the authigenic and host phases rather than conventionally invoking bulk pore water undersaturation for host phase dissolution we propose that many diagenetic replacements occur by a force of crystallization controlled replacement mechanism whereby nonhydrostatic stresses resulting from authigenic crystal growth are principally responsible for host phase dissolution this model explains diagenetic features such as the restriction of host phase dissolution to authigenic host crystal contacts and euhedral authigenic crystal faces in planar contact with unreplaced host phases as well as the relative replacement tendencies of some common authigenic minerals

the organic geochemistry of petroleum reservoirs abstract the organic constituents of petroleum reservoirs frequently show measurable compositional variations both laterally between wells and vertically within a single well the pattern of variation is controlled by the geological setting of the reservoir which influences the way in which migrating petroleum fills the reservoir from one or more source kitchens having achieved a high petroleum pore saturation the reservoir fluids may then redistribute themselves at rates are often comparable to geological time periods mass transfer by diffusion and density driven convection must be considered and their timescales compared with the elapsed time since the accumulation was filled in many cases the compositional variations inherited from the filling process persist to the current day this paper outlines the mechanisms by which reservoirs fill and mix and describes how this can lead to observable lateral differences in composition the relationship between certain engineering parameters particularly the gas oil ratio and reservoir fluid density reservoir rock description and geochemical parameters will be stressed the goal being to improve the characterisation of petroleum reservoirs by combining geochemical and engineering data into a scientifically consistent framework many aspects of the geochemistry of petroleum reservoirs have only recently begun to be researched it is hoped that the recent advances in the geochemical characterisation of oils and gases will be increasingly applied to the problems of reservoir and petroleum engineering this should lead to improvements in the efficiency with which petroleum is recovered from the subsurface

subsynoptic scale spatial variability of sea ice deformation in the western weddell sea during early summer 1 ice station polarstern ispol deployed in the western weddell sea from november 2004 to january 2005 included a study of subsynoptic scale variability in sea ice velocity and deformation using an array of 24 buoys upon deployment the ispol buoy array measured 70 km in both zonal and meridional extent and consisted of subarrays that resolved sea ice deformation on scales from 10 to 70 km across the ispol array divergence varied and did not show a distinct coherent length scale spectral analysis of divergence and shear of subarrays revealed that deformation did not vary smoothly across the array this indicates variability of internal ice stress on the scale of 10 km ice conditions within the ispol array encompassed two distinct regimes separated by shear along the continental shelf break differences in spectral power of the tidal and inertial bands across the two regions do not mirror expected differences due to spatial variability of tide induced deformation on the shelf break instead they indicate that the pack ice s internal stress behaved anisotropically on the scale of the shear zone across the buoy array 70 km

mg isotopic systematics during early diagenetic aragonite calcite transition insights from the key largo limestone abstract the seawater magnesium mg isotopic composition 26mgsw can be applied to quantify marine mg cycle in earth s history however reconstruction of 26mgsw by using marine carbonate has been challenged by the large range of variation in mg isotopic composition of carbonate 26mgcarb such variation on the one hand reflects e g the mineralogy temperature and precipitation rate dependent isotopic fractionation during ca carbonate precipitation on the other hand the pristine seawater record could be modified in carbonate diagenesis during which less stable carbonate minerals would spontaneously convert to more stable mineral phases in the modern ocean with high mg ca molar ratio 5 aragonite precipitation is favored however aragonite is thermodynamically less stable than low mg calcite at ambient surface environment resulting in the spontaneous transition from aragonite to low mg calcite in the earliest stage of diagenesis i e the aragonite calcite transition as a common process in the modern ocean mg isotopic fractionation in aragonite calcite transition may provide valuable constraints on the variation of 26mgcarb in this study we measured mg isotopic compositions of pleistocene key largo limestone florida which has been experiencing the aragonite calcite transition during early diagenesis the key largo limestone samples consist of a mixture of calcite and aragonite 26mg of aragonite 26mgarag shows higher and more stable values while calcite has lower yet more variable mg isotopes 26mgcal we suggest a model conceptualizing a water film attached to the mineral surface in which the aragonite calcite transition initiates with aragonite dissolution and the mg exchange with external fluid can be variable followed by mg isotopes fractionate during low mg calcite precipitation in this model 26mgcal is controlled by 1 the chemical composition of water film which is dependent on the mineralogical composition of aragonite i e mg content and 26mgarag the composition of external fluid i e fresh water seawater or mixed fresh water and seawater and the mixing ratio between dissolved aragonite and external fluid and 2 the isotopic fractionation during calcite precipitation because the isotopic fractionation in calcite is sensitive to the rate of calcite precipitation that is dependent on the calcite saturation state of solution therefore 26mgcal could be highly heterogeneous depending on the aragonite dissolution and calcite precipitation processes further complicating the interpretation of carbonate data thus the process controlled mg isotopic fractionation should be taken into consideration when reconstructing 26mgsw by using carbonate sediments rocks

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

mechanisms of petroleum accumulation in the bozhong sub basin bohai bay basin china part 1 origin and occurrence of crude oils the origin of the fourteen major oil fields in the bozhong sub basin bohai bay basin was studied based on the results of rock eval pyrolysis on more than 700 samples and biomarker analysis on 61 source rock samples and 87 oil samples the three possible source rock intervals have different biomarker assemblages and were deposited in different environments the third member of the oligocene dongying formation e3d3 32 8 30 3 ma in age is characterized mainly by high c19 c23 tricyclic terpane 0 75 high c24 tetracyclic terpane c26 tricyclic terpane 2 5 low gammacerane c30 hopane 0 15 and low 4 methyl steranes c29 steranes 0 15 ratios and was deposited in sub oxic to anoxic environments with significant terrigenous organic matter input the first e2s1 35 8 32 8 ma and third e2s3 43 0 38 0 ma members of the eocene shahejie formation have low c19 c23 tricyclic terpane and low c24 tetracyclic terpane c26 tricyclic terpane ratios and were deposited in anoxic environments with minor terrestrial organic matter input but have different abundances of 4 methyl steranes and gammacerane the hydrocarbon generating potential and biomarker associations of these three source rock intervals were controlled by tectonic evolution of the sub basin and climate changes three oil families derived from e2s3 e2s1 and e3d respectively and three types of mixed oils have been identified all large oil fields in the bozhong sub basin display considerable heterogeneities in biomarker compositions and originated from more than one source rock interval which suggests that mixing of oils derived from multiple source rock intervals or multiple generative kitchens and or focusing of oils originated from a large area of a generative kitchen is essential for the formation of large oil fields in the bozhong sub basin e2s3 and e2s1 derived oils experienced relatively long distance lateral migration and accumulated in traps away from the generative kitchen e3d3 derived oils had migrated short distances and accumulated in traps closer to the generative kitchen such a petroleum distribution pattern has important implications for future exploration there is considerable exploration potential for dongying derived oils in the bozhong sub basin and traps close to or within the generative kitchens have better chance to contain oils generated from the dongying formation

diagenetic evolution of the eocene ramp carbonates a paradigm from the nile valley egypt petrographical and geochemical attributes abstract carbonate rocks of east nile valley in egypt have been investigated as a paradigm for revealing the diagenetic evolution of the eocene ramp carbonates the integration of petrographical elemental geochemical and stable isotopic data revealed that the studied carbonates have been influenced by a sequence of diagenetic processes which are included in three diagenetic episodes i e eogenesis mesogenesis and telogenesis and are related to four diagenetic environments i e marine phreatic meteoric phreatic burial and uplifting environments the paragenetic sequence of the studied carbonates commences with the eodiagenetic episode which includes the marine and meteoric phreatic diagenetic environments the marine phreatic diagenetic environment comprises micritization glauconitization pyritization marine cementation fibrous calcite and syntaxial overgrowth rim cements early dolomitization formation of fine crystalline matrix replacive dolomites and early stages of mechanical compaction before significant burial the meteoric phreatic diagenetic environment includes the neomorphism dissolution meteoric cementation earlier phases of sparry calcite cements and precipitation of megaquartz in the void spaces of the peritidal carbonates during the mesogenesis episode the studied carbonates were exposed to burial diagenesis the shallow burial diagenesis resulted in the creation of point tangenetial contacts between the allochemical constituents and the precipitation of a medium coarse crystalline dolomite cement filling the dissolved fossils and dissolution pores the deep burial diagenetic processes embody the chemical compaction condensed fitted interpeneteration and pressure dissolution fabrics fracturing and burial cementation the telodiagenesis represents the last episode in the diagenetic history of the studied carbonates it witnessed the fracturing meteoric vadose cementation and hematitization processes

spatial and temporal characterization of sea ice deformation in late march 2007 an array of gps ice drifters was deployed in the beaufort sea as part of the sea ice experiment dynamic nature of the arctic sedna the drifters were deployed in an array designed to resolve four nested spatial scales of sea ice deformation from 10 to 140 km with the arrays maintaining appropriate shape for strain rate calculation until mid june in this paper we test whether sea ice deformation displays fractal properties in the vicinity of sedna we identify that deformation time series have different spectral properties depending on the spatial scale at the scales around 100 km deformation is a red noise process indicating the importance of the ice pack surface forcing in determining the deformation rate of sea ice at this scale at smaller scales the deformation becomes an increasingly whiter process it has pink noise properties which suggests an increasing role of dissipative processes at smaller scales at spatial scales of 10 100 km and sub daily scales there is no deformation coherence across scales coherence only becomes apparent at longer scales greater than 100 km the lack of coherence at small scales aids in understanding previous observations where correlation between 10km regions adjacent to each other varied widely with correlation coefficients between 0 3 and 1 this suggests it is not appropriate to think of sea ice as having a decorrelation length scale for deformation we find that lead scale observations of deformation are required when estimating ice growth in leads and ridging time series for the two sedna arrays we find coherence between 140 and 20 km scale deformation up to periods of 16 days this suggests sea ice deformation displays coherent deformation between 100 km scale and the scale of the beaufort sea of order 1000 km over synoptic time periods daily to weekly timescales organization of leads at synoptic and larger scales is an emergent feature of the deformation field that is caused by the smooth variation of surface forcing wind on the ice pack

heterogeneity of oil composition within a reservoir as a reflection of accumulation history abstract the unaltered petroleums of a small oil field in the f r germany reveal pronounced spatial heterogeneities in bulk and molecular composition over most of the field area the oil in high porosity high permeability sand intervals bears a higher proportion of saturated hydrocarbons and has a higher maturity chemical signature as compared to oils occupying lower porosity lower permeability zones for all sands with less than about 13 porosity a regular relationship was observed between oil composition and porosity permeability with a decrease of the latter petrophysical properties increasingly lower chemical maturities and increasingly different bulk chemical compositions lower proportions of saturated hydrocarbons and higher proportions of nso compounds were recorded maximum contrasts measured for chemical maturities are e g 0 63 versus 0 82 vitrinite reflectance equivalents rc values calculated on the basis of the methylphenanthrene index according to radke and welte 1983 0 31 versus 0 84 for the ratio of triaromatic to mono plus triaromatic steroid hydrocarbons and 0 38 versus 0 47 for the 20s 20s 20r ratio of c29 5 h 14 h 17 h steranes these spatial heterogeneities in the composition of the oils are interpreted to reflect 1 i successive stages of trap filling due to episodes of increasing burial and maturation of the relevant source rocks in combination with 2 ii low rates of in reservoir mixing of these individual oil charges by convection or diffusion recognition of compositional heterogeneities within the oil column of individual fields may not only provide a basis for the reconstruction of reservoir filling history but may also have important implications for improving petroleum production

diversity of neomorphic fabrics in new zealand plio pleistocene cool water limestones insights into aragonite alteration pathways and controls abstract many ancient cool water carbonates include little or no evidence for aragonite being present in their primary sediment composition and consequently that they inherited a low diagenetic potential however despite differences in skeletal assemblages age and depositional settings plio pleistocene cool water limestones from eastern north island of new zealand are characterized by locally abundant aragonite remains typically c 20 range 60 either directly as variably altered skeletons or indirectly as biomolds oversized pores and detrital material resulting from collapse of dissolved shells specifically five types of aragonite preservation are evident a skeletons with original aragonite b skeletons with original aragonite but with leaching cavities c skeletons with aragonite relics encased in either dirty or pale brown neomorphic calcite spar d skeletons neomorphically altered to calcite preserving relic shell structures and e dissolved out skeletons leaving an empty or calcite cement filled cavity all these types of preservation including transitions between them can occur within the same sample these observations motivate a conceptual model for the timing and complex pathways of neomorphism in these plio pleistocene cool water limestones related to their diagenetic evolution from shallow marine to burial to uplift related meteoric environments in this the aragonite alteration pathways suggest that the different neomorphic fabrics formed at any stage during the diagenetic history of the host carbonates and are likely not unequivocal indicators of specific diagenetic environments instead differing alteration pathways can potentially produce similar fabrics the observations are consistent with the interpretation that shell microstructures controlling the nature of the intraskeletal neomorphic front and the degree of openness of the diagenetic system were of greater importance in determining the neomorphic fabrics and relic preservation of aragonite than was the general diagenetic environment be it marine meteoric or burial also important were external controls linked to the types of depositional settings that dictated the composition of carbonate factories the morpho tectonic evolution of the host basin and the influence of relative sea level fluctuations on sediment production accumulation and condensation these results illustrate that factors controlling ultimate preservation of carbonate biofacies are multifarious and complex moreover they suggest that the importance of aragonitic components could be underestimated for many ancient cool water carbonate deposits thereby compromising estimation of original skeletal assemblages depositional environments and sediment budgets

meteorological conditions in a thinner arctic sea ice regime from winter to summer during the norwegian young sea ice expedition n ice2015 atmospheric measurements were made over arctic sea ice north of svalbard from winter to early summer january june 2015 during the norwegian young sea ice n ice2015 expedition these measurements which are available publicly represent a comprehensive meteorological data set covering the seasonal transition in the arctic basin over the new thinner sea ice regime winter was characterized by a succession of storms that produced short lived less than 48 h temperature increases of 20 to 30 k at the surface these storms were driven by the hemispheric scale circulation pattern with a large meridional component of the polar jet stream steering north atlantic storms into the high arctic nonstorm periods during winter were characterized by strong surface temperature inversions due to strong radiative cooling radiatively clear state the strength and depth of these inversions were similar to those during the surface heat budget of the arctic ocean sheba campaign in contrast atmospheric profiles during the opaquely cloudy state were different to those from sheba due to differences in the synoptic conditions and location within the ice pack storm events observed during spring summer were the result of synoptic systems located in the barents sea and the arctic basin rather than passing directly over n ice2015 these synoptic systems were driven by a large scale circulation pattern typical of recent years with an arctic dipole pattern developing during june surface temperatures became near constant 0 c on 1 june marking the beginning of summer atmospheric profiles during the spring and early summer show persistent lifted temperature and moisture inversions that are indicative of clouds and cloud processes

the mechanism of skeletal aragonite neomorphism evidence from neomorphosed mollusks from the upper purbeck formation late jurassic early cretaceous southern england abstract the trace element geochemistry and microtextures of neomorphosed mollusks from the upper purbeck formation late jurassic early cretaceous of southern england suggest that calcite replacement of aragonite occurs by a force of crystallization driven mechanism similar to that of non polymorphic skeletal carbonate replacement reactions such as silicification the purbeck neomorphic calcites are substantially enriched in mg mn and fe and depleted in sr compared to skeletal aragonite indicating that the neomorphic reaction zones were not chemically isolated from the bulk pore waters to a significant degree neomorphic calcite microtextures are fundamentally similar to the replacement microtextures of silicified and celestite replaced fossils in terms of the degree and style of preservation of traces of skeletal microtextures in authigenic crystals and the relationships of authigenic crystal morphology and crystallographic orientation to shell microtexture the neomorphic replacement of aragonite by calcite differs from most non polymorphic replacement reactions in that the calcite cannibalizes aragonite decreases in the intraskeletal pore water calcium carbonate ion activity product caused by calcite precipitation results in aragonite dissolution adjacent to aragonite calcite contacts i e chalkification in some fossils chalkification does not occur in non polymorphic replacements of skeletal carbonate

variability of arctic sea ice thickness and volume from cryosat 2 we present our estimates of the thickness and volume of the arctic ocean ice cover from cryosat 2 data acquired between october 2010 and may 2014 average ice thickness and draft differences are within 0 16 m of measurements from other sources moorings submarine electromagnetic sensors icebridge the choice of parameters that affect the conversion of ice freeboard to thickness is discussed estimates between 2011 and 2013 suggest moderate decreases in volume followed by a notable increase of more than 2500 km 3 or 0 34 m of thickness over the basin in 2014 which could be attributed to not only a cooler summer in 2013 but also to large scale ice convergence just west of the canadian arctic archipelago due to wind driven onshore drift variability of volume and thickness in the multiyear ice zone underscores the importance of dynamics in maintaining the thickness of the arctic ice cover volume estimates are compared with those from icesat as well as the trends in ice thickness derived from submarine ice draft between 1980 and 2004 the combined icesat and cryosat 2 record yields reduced trends in volume loss compared with the 5 year icesat record which was weighted by the record setting ice extent after the summer of 2007

thermal history and tectonic subsidence of the bohai basin northern china a cenozoic rifted and local pull apart basin the bohai basin is a part of the larger bohai bay basin a cenozoic rifted intraplate basin heat flow measurements show that the bohai basin is characterized by present day heat flow varying between 53 and 74 mw m 2 with a mean of 63 mw m 2 however thermal history analyses derived from vitrinite reflectance vr and apatite fission track aft data indicate that tertiary cooling took place following a period of much higher paleo heat flow 70 90 mw m 2 prior to 25 million years to the present furthermore tectonic subsidence analysis reveals that the bohai basin experienced episodic sub rifting processes from the eocene to the end of the oligocene the post rift thermal subsidence was superimposed by intensified subsidence from the late miocene 12 million years in the bozhong depression and from the early quaternary 2 4 million years in the east liao bay indicating a rejuvenation of sedimentation related likely to transpressional structures developed locally on strike slip faults the present results indicate that there is good agreement between the reconstructed thermal history and the timing of the tectonic subsidence stages within the bohai basin the bohai basin is an early cenozoic rifted and local pull apart sub basin of the larger bohai bay basin 2001 elsevier science b v all rights reserved

carbonate diagenesis in a high transmissivity coastal aquifer biscayne aquifer southeastern florida usa abstract cores collected through the biscayne aquifer plio pleistocene in hollywood southeastern florida as part of the hollywood coastal salinity barrier project provided an opportunity to examine the diagenesis of limestones and sandstones at the meteoric to marine water transition of one of the most transmissive aquifers in the world the saline water front and thus coastal mixing zone has migrated landward approximately 1 km in the hollywood area as the result of wellfield withdrawals no changes in mineralogy such as dolomitization cement types and abundances paragenetic sequence or porosity are evident that can be correlated with the current or likely pre development wellfield withdrawals location of the mixing zone an approximately 2 downhole increase in calcite 18 o values is present in a core hmw 6d that penetrates the pre development mixing zone which may be related to either a down hole increase in salinity or to the interaction of meteoric waters with marine carbonate sediments during calcite cementation the biscayne aquifer in hollywood is currently a relatively quiescent diagenetic environment the limited current diagenesis appears to consist of the dissolution of trace skeletal aragonite remaining in the aquifer as suggested by a meteoric water sr ca ratio similar to that of molluscan aragonite it is proposed that a punctuated equilibria model may be applicable to diagenesis in the biscayne and other aquifers in which limestones and sandstones entered a long period of diagenetic stasis after a period of relatively rapid textural and mineralogical stabilization

geology compositional heterogeneities and geochemical origin of the yacheng gas field qiongdongnan basin south china sea the yacheng gas field is located in the footwall of the no 1 fault the boundary fault between the yinggehai and qiongdongnan basins the main reservoir is the fan delta sandstones in the lingshui formation the seals are meishan for m ation shales near the no 1 fault and lingshui formation shales away from the no 1 fault all strata are normally pressured in the gas field except for the meishan formation the meishan formation is overpressured near the no 1 fault in the gas field and in the adjacent yinggehai basin away from this fault into the qiongdongnan basin the overpressure diminishes an obvious thermal anomaly occurs below 3600 m in the gas field this anomaly characterized by an abrupt increase in drill stem test and fluid inclusion homogenization temperatures vitrinite reflectance ro and rock eval tmax and by an abnormally low temperature ro tmax gradient diminishes away from the yinggehai basin the gases and condensates have abnormally high aromatic hydrocarbon contents and show obvious heterogeneities away from the no 1 fault the c2 hydrocarbon content and c2 scn increase carbon dioxide content decreases d13c values for methane ethane and carbon dioxide become lighter the heptane and isoheptane values decrease and the relative contents of aromatic hydrocarbons both in c6 c7 light hydrocarbons and in the condensates decrease such heterogeneities reflect the reservoir filling process and origin of the gas field the gas field was charged from both the qiongdongnan and the yinggehai basins hydrocarbons sourced from the qiongdongnan basin have relatively low maturities whereas hydrocarbons from the yinggehai basin have relatively higher maturities and seem to have been in association with hydrothermal fluids the hydro thermal fluids from the yinggehai basin in which methane ethane carbon dioxide and especially aromatic hydrocarbons dissolved under the high temperature and high pressure subsurface conditions migrated along the no 1 fault and caused the abnormally high concentration of aromatic hydrocarbons as well as the thermal anomalies in the gas field especially near the no 1 fault

thinning of arctic sea ice observed in fram strait 1990 2011 1 time series 1990 2011 of sea ice thickness observed by moored sonars in the transpolar drift in fram strait are examined contrasting the post 2007 years against the 1990s three remarkable changes in the monthly ice thickness distributions are highlighted 1 the thickness of old level ice modal thickness is reduced by 32 2 the old ice modal peak width is reduced by 25 and 3 the fraction of ridged ice thicker than 5 m is reduced by 50 the combined effect on the mean ice thickness is a reduction from an annual average of 3 0 m during the 1990s to 2 2 m during 2008 2011 most of the thinning took place after 2005 2006 while the old ice modal thickness and peak width show signs of recovery after 2008 the decreasing trend in fraction of ridged ice and mean ice thickness persists until the end of the record in 2011 the ice observed in fram strait carries an integrated signal of arctic change due to the advection of ice from many sites in the arctic based on concurrence in timing we conclude that much of the thinning quantified here is reflecting recent change in the age composition of the arctic ice cover toward younger ice the old level ice remains thin and as such the ice cover remains preconditioned for new summers of very low sea ice extent

oxygen and stable carbon isotopes from a nautiloid from the middle pennsylvanian late carboniferous impregnation lagerstatte buckhorn asphalt quarry primary paleo environmental signals versus diagenesis abstract two shell fragments one of an undetermined cephalopod and one of an orthoconic nautiloid pseudorthoceratidae gen et sp indet from the pennsylvanian buckhorn asphalt lagerstatte oklahoma were studied to reconstruct paleotemperatures and to explore possible diagenetic alterations for the first time not only parts of the shell of an orthoconic nautiloid but also its cameral deposits were sampled in high resolution the mineralogy geochemistry and microstructure of both shell remains the pseudorthoceratid and the undetermined cephalopod were investigated in detail before high resolution transects for oxygen and stable carbon isotopes were sampled the shell fragment of the undetermined cephalopod showed no or very little diagenetic alteration therefore the measured 18o variation 18o range of 0 68 and the inferred temperature range of 28 to 31 c are interpreted to represent an original signal the temperatures indicate that the specimen lived in shallow warm tropical waters the 13c signal with a 13c range of 3 43 is interpreted to be the consequence of a strong metabolic effect a septum of the phragmocone of the pseudorthoceratid nautiloid was only slightly altered by diagenesis and a largely original 18o signal could be obtained the 18o values exhibit an inferred temperature range of 14 to 15 c indicating that this species lived in deeper and cooler waters the cameral deposits were investigated in detail by energy dispersive x ray edx and by xrd gadds x ray diffraction general area detector diffraction system analyses part of the cameral deposits in the orthoconic nautiloid turned out to originally consist of high mg calcite hmc instead of the estimated aragonite anyhow the massive cameral deposits show signs of strong small scale alteration resulting in a distinct spreading of oxygen values the oxygen and carbon isotope plots show a linear trend for the oxygen carbon correlation this is interpreted as the mixing of two end members with the lightest end members suggesting a meteoric diagenesis with a diagenetic fractionation of the aragonite to low mg calcite lmc respectively the hmc to lmc and dolomite the calculated temperatures of the pseudorthoceratid specimen and the undetermined cephalopod indicate two different paleoenvironments additionally the pseudorthoceratid nautiloid displays the narrow range of temperatures in the deeper parts of the sea and the undetermined cephalopod the more fluctuating temperatures in the shallow areas it is also shown how important a detailed investigation of microstructures and mineralogy of samples with an according cautious interpretation of the achieved dataset is the importance of an intensive examination of samples is pointed out to avoid small scale alterations to be overlooked since this would lead to a misinterpretation of the results

hydrocarbon habitat of the offshore bohai basin china the bohai basin is a major continental petroliferous basin located in eastern china of which the offshore part of the basin contains more than one third of the total petroleum resources in the basin although the basin has been explored for nearly 40 years the offshore part of the basin is just reaching a moderately mature stage of exploration and its petroleum geological features are gradually becoming known the subduction of the pacific plate to the eurasia plate resulted in the convective upwelling of the mantle in the bohai area and triggered the development of nne and ne striking extensional faults along the mesozoic structures in the late paleocene causing the formation of the rift basin during the oligocene the depocenters and subsidence centers of the greater bohai basin migrated from west to east and from south to north and finally concentrated in the offshore part of the basin since the oligocene especially during the neogene due to the indentation of the india block to the eurasia plate the right lateral strike slip movement of the tan lu fault was relatively intense in the offshore part of the basin these characteristics led to the differences between the offshore and onshore sectors in sedimentation structural features and petroleum geology during the deposition of the dongying formation the offshore sector became the depocenter and subsidence center of the basin resulting in the deposition of the lower dongying formation mudstone source rocks while these mudstones are immature in the onshore part of the basin in the offshore bohai most major discoveries have been made in the drape anticlines on the rises in the upper tertiary reservoirs while the lower tertiary reservoirs within the half grabens only serve as secondary reservoirs as the neogene depocenter of the basin the offshore part accommodated some fine grained shallow lacustrine clastics of the lower minghuazhen formation serving as important regional seals for the neogene reservoirs a set of shallow faults and a central faulted anticlinal belt in the shallow upper tertiary sequences were formed during the neogene in the offshore sector under the influence of right lateral strike slip faulting of the tan lu fault these shallow faults networked with deep extensional faults serving as hydrocarbon conduits the central faulted anticline belt along the tan lu fault system also provides significant traps

relationships between colour and diagenesis in the aragonite calcite speleothems in basajaun etxea cave spain abstract basajaun etxea cave north spain contains a wide morphological and colour variety of speleothems most of them are composed of aragonite but calcite speleothems are also found their most common colour is white but there are also pink green and turquoise speleothems in different areas of the cave mg rich dissolution waters from the cave s crystalline dolostone and magnesite host rock favour aragonite precipitation and drive important diagenetic changes in this paper we will discuss how diagenesis modifies speleothem texture mineralogy and geochemistry causing significant changes in the colour we also discuss how speleothems that have undergone diagenesis may also be useful indictors of paleoclimatic conditions our work shows that diagenesis changes the colour of the speleothems because of the mobility of the chromophore elements during this process along with this elemental alteration comes the loss of the primary isotopic signals of speleothems detailed petrological studies of speleothems should precede their analysis for palaeoclimatic reconstruction so that influence of areas affected by diagenesis can be eliminated in addition diagenetic signals also contain valuable information on the changes of the waters within the cave and the overall evolution of speleothems and the cave itself

positive trend in the mean speed and deformation rate of arctic sea ice 1979 2007 using buoy data from the international arctic buoy program we found that the sea ice mean speed has substantially increased over the last 29 years 17 per decade for winter and 8 5 for summer a strong seasonal dependence of the mean speed is also revealed with a maximum in october and a minimum in april the sea ice mean strain rate also increased significantly over the period 51 per decade for winter and 52 for summer we check that these increases in both sea ice mean speed and deformation rate are unlikely to be consequences of a stronger atmospheric forcing instead they suggest that sea ice kinematics play a fundamental role in the albedo feedback loop and sea ice decline increasing deformation means stronger fracturing hence more lead opening and therefore a decreasing albedo this accelerates sea ice thinning in summer and delays refreezing in early winter therefore decreasing the mechanical strength of the cover and allowing even more fracturing larger drifting speed and deformation and possibly a faster export of sea ice through the fram strait the september minimum sea ice extent of 2007 might be a good illustration of this interplay between sea ice deformation and sea ice shrinking as we found that for both winter 2007 and summer 2007 exceptionally large deformation rates affected the arctic sea ice cover

contributions of growth and deformation to monthly variability in sea ice thickness north of the coasts of greenland and the canadian arctic archipelago regional variability in monthly cryosat 2 sea ice thickness is partitioned into contributions from dynamics and thermodynamics using ice deformation calculated from large scale ice drift for five winters december to april 2011 2015 over a region of persistent convergence north of the coasts of greenland and the canadian arctic archipelago deformation explains 34 of the overall variance up to 69 in 2014 2015 in monthly thickness changes approximately 42 56 or 0 6 m of the seasonal changes in mean regional ice thickness can be attributed to divergence and shear the estimated area averaged growth of 0 12 0 03 m month compares favorably with measurements from ice mass balance buoys examination of the time variable thickness distributions shows areas covered by ice 3 m increased albeit at fairly coarse resolution this coupled analysis of thickness changes and deformation offered a first look at the character of the regional thickness redistribution process

influence of a major exposure surface on the development of microporous micritic limestones example of the upper mishrif formation cenomanian of the middle east microporous platform top limestones of the cenomanian mishrif formation offshore qatar were studied in order to investigate the diagenetic processes associated with the top mishrif subaerial unconformity and its influence on the development of microporosity in underlying carbonates petrographical and stable isotope results indicate that complex diagenetic changes occurred during subaerial exposure of the mishrif formation including pervasive dissolution and meteoric cementation as well as neomorphism of the micritic matrix micrites at the top of the mishrif formation are coarse i e 2 m sub rounded and very dull luminescent under cathodoluminescence in this uppermost part of the studied interval the limestone matrix first underwent dissolution of unstable grains in the vadose zone with subsequent precipitation of low magnesium calcite lmc overgrowths within an oxidising phreatic setting this process explains the poor luminescence of the micrite crystals and their relatively coarse crystallometry which results in the present day in relatively good reservoir properties 13c ratios within the microporous limestones are negative up to 4 v pdb due to the incorporation of isotopically light carbon derived from palaeosols which developed during exposure by contrast fine i e 2 m polyhedral and bright luminescent micritic matrix with higher 13c values up to 4 v pdb and lower permeability are dominant within the underlying carbonate interval these fine micrites are likely to be the product of early neomorphic recrystallisation in the lowermost part of the palaeo aquifer associated with the top mishrif unconformity and were precipitated from meteoric or mixed dysoxic waters which were slightly supersaturated with respect to calcite

origin of micropores in late jurassic oxfordian micrites of the eastern paris basin france porous micritic facies either primary chalks or resulting from secondary destructive micritization can constitute important hydrocarbon or water reservoirs characterization of reservoir properties and the understanding of factors which controlled the distribution of porosity are of primary interest to evaluate the prospective reserves middle and late oxfordian limestones of the eastern paris basin show several horizons with porosities higher than 20 the porosity is mainly microporous and located either within secondary micritized grains or in the micritic matrix using sem cathodoluminescence as well as confocal microscopy stable oxygen and carbon isotope ratios and petrophysical measurements a scenario for the evolution of the micropores is proposed lime mudstones to packstones constitute the majority of the high porosity facies hpfs inner lagoonal deposits are more micritized and thus more porous than grainstones and facies rich in leiolitic oncoids and echinoid clasts are less impacted by micritization micritization was responsible for an increase of the intragranular porosity in most grain types during both eogenesis and shallow burial mineralogical stabilization dissolved aragonitic particles and allowed precipitation of calcite rhombs this process was probably enhanced below surfaces of subaerial exposure during burial ostwald ripening allowed the growth of larger micrite crystals at the expense of smaller ones during early berriasian and late aptian recharges of deep aquifers when the northern margin of the basin was exposed overgrowths on micrite crystals were more important in intervals strongly affected by chemical compaction which favored oversaturation of waters with respect to calcite in low porosity horizons lpfs the dense micritic texture of oncoids and the monocrystalline architecture of echinoid clasts prevented an intense micritization while the strong chemical compaction enhanced poronecrosis telogenetic fracturing created new fluid pathways that favored inputs of meteoric fluid in porous micrite and allowed the continuation of ostwald ripening during cenozoic times as a whole mesogenetic inputs of waters undersaturated with respect to calcite in deep aquifers during exposure of basin margins are a more efficient process than early subaerial exposure for enhancing aggrading neomorphism and appearance of microporous micrites initial mineralogical heterogeneities also impact the intensity of chemical compaction and thus the stratigraphical distribution of microporous limestones

skeletal aragonite neomorphism in plio pleistocene sandy limestones and sandstones hollywood florida usa abstract the basic mechanics of the neomorphism of aragonitic shells to calcite are generally understood but fundamental questions remain concerning the details of the process completely and partially neomorphosed aragonitic skeletal fragments recovered in cores of plio pleistocene limestones and sandstones from hollywood florida provide some insights into the process skeletal aragonite neomorphism occurred in a volume for volume manner across solution films which resulted in the preservation of ghosts of fine scale microstructures neomorphic calcite crystals that replaced skeletal aragonite in at least some instances inherited their crystallographic orientation from adjoining calcite cement crystals rather than from the host shell microstructure some neomorphic calcite crystals inherited the optical orientation of nearby echinoderm ossicles however host shell microstructure commonly controlled the direction of migration of the neomorphic replacement front anisotropies in shell solubility influenced the directional rates of growth of neomorphic calcite crystals as evidenced by the strong tendency for the boundaries between neomorphic calcite and aragonite to parallel or coinicide with shell microstructural features no examples were observed where neomorphic calcite replaced aragonite along euhedral crystal faces such as commonly occurs during dolomitization and the replacement of limestone by megaquartz

small scale sea ice deformation during n ice2015 from compact pack ice to marginal ice zone we studied small scale 50 m to 5 km sea ice deformation from ship radar images recorded during the n ice2015 campaign the campaign consisted of 4 consecutive drifting ice stations floes 1 to 4 north of svalbard with a total duration of nearly 5 months deformation was calculated using 5 different time intervals from 10 min to 24 h and the deformation rate was found to depend strongly on the time scale floes 1 to 3 had a mean deformation rate within the range of 0 06 to 0 07 h 1 with the interval of 10 min and 0 03 to 0 04 h 1 with the interval of 1 h floe 4 represented marginal ice zone miz with very high deformation rate 0 14 0 08 h 1 with the interval of 10 min 1 h deep in the ice pack high deformation rates occurred only with high wind and drift speed while in miz they were found also during calm conditions the deformation rates were found to follow power law scaling with respect to length and time scale even on this small scales and in small domain 15 km 15 km the length scale dependence of deformation rate depends on the time scale the power law scaling exponent of the whole study period decreases from 0 82 to 0 52 with the time interval increasing from 10 min to 24 h ship radar images reveal the importance of the deformation history of the ice pack since the deformation events were initialized along the lines of previous damages

two stage neomorphism of jurassic aragonitic bivalves implications for early diagenesis abstract aragonitic bivalves in middle jurassic paralic limestones from lincolnshire eastern england have been neomorphically replaced by inclusion rich calcite spar textural features of neomorphic spar are analogous to examples from other calcitized jurassic molluscs but lincolnshire bivalves show evidence for two distinct stages of replacement staining cathodoluminescence and backscatter scanning electron microscopy reveal an initial volumetrically minor and frequently fabric selective replacement by nonferroan calcite with most of the remaining skeletal aragonite subsequently replaced by ferroan calcite spar stable isotope data from individual bivalves define a negative covariant mixing trend ranging from early relatively 13c depleted and 18o enriched nonferroan calcite d13c 2 pdb to ferroan calcite with composition similar to associated late pore filling cements d13c 2 pdb d1 o 7 pdb the early diagenetic end member precipitated from depositional pore fluids with bicarbonate supplied both from dissolution of skeletal aragonite and bacterial oxidation of organic material in contrast ferroan neomorphic spar precipitated during burial diagenesis and dewatering of shales surrounding the limestone bulk trace element signatures of the bivalves are dominated by late ferroan calcite but electron probe microanalysis and intrinsic blue cathodoluminescence shows that early neomorphic calcite contains negligible amounts of fe mn and mg together with isotopic and fabric data this indicates that early neomorphism occurred at shallow depths and may even have begun at the sediment water interface in the absence of through flowing meteoric waters early replacement did not proceed via an inward migrating neomorphic front instead calcitization was initiated at numerous individual reaction centers throughout the shells and was principally controlled by the distribution of the skeletal organic matrix this contrasts strongly with most previous reports of aragonite neomorphism during arly diagenesis

charging of oil fields surrounding the northern end of liaoxi uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract the liaoxi uplift one of the most petroliferous uplifts in the bohai bay basin is sandwiched by two sags containing multiple mature source rocks the origins of oil located on the northern end of this uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions from 75 source rock extracts and 15 oils two oil families have been identified using 4 biomarker parameters and could be linked to the source rocks of the first and second members of the shehejie formation e 2 s 1 2 and the third member of the dongying formation e 3 d 3 respectively e 2 s 1 2 derived oils were found in the liaoxi sag and on the liaoxi uplift and were interpreted to originate primarily from the liaoxi sag e 3 d 3 derived oils were found in the liaozhong sag and originated from the liaozhong sag the liaoxi uplift have not been charged by e 2 s 3 drived oils from the liaoxi sag mainly because it departed from the dominant migration direction of e 2 s 3 drived oils the liaoxi uplift have not been charged by e 2 s 3 e 2 s 1 2 and e 3 d 3 drived oils from the liaozhong sag mainly because there were no delta sandstones developed on the slope between the liaoxi uplift and the liaozhong sag to serve as migration channels from source rocks to uplift in all three formations the sandstone up dip pinch out traps in e 2 s 3 formation in the liaoxi sag traps within the liaozhong sag and traps on the slope between the liaozhong sag and the liaodong uplift have a better chance to accumulating petroleum

geochemical characteristics of tertiary saline lacustrine oils in the western qaidam basin northwest china abstract based on the systematic analyses of light hydrocarbon saturate aromatic fractions and c isotopes of over 40 oil samples along with related tertiary source rocks collected from the western qaidam basin the geochemical characteristics of the tertiary saline lacustrine oils in this region was investigated the oils are characterized by bimodal n alkane distributions with odd to even c11 c17 and even to odd c18 c28 predominance low pr ph mostly lower than 0 6 high concentration of gammacerane c35 hopane and methylated mttcs reflecting the high salinity and anoxic setting typical of a saline lacustrine depositional environment mango s k1 values in the saline oils are highly variable 0 99 1 63 and could be associated with the facies dependent parameters such as pr ph and gammacerane indexes compared with other tertiary oils the studied tertiary saline oils are marked by enhanced c28 sterane abundance 30 or more of c27 c29 homologues possibly derived from halophilic algae it is noted that the geochemical parameters of the oils in various oilfields exhibit regular spatial changes which are consistent with the depositional phase variations of the source rocks the oils have uncommon heavy c isotopic ratios 24 to 26 and a flat shape of the individual n alkane isotope profile and show isotopic characteristics similar to marine organic matter the appearance of oleanane and high 24 24 27 norcholestane ratios 0 57 0 87 in the saline oils and source rocks confirm a tertiary organic source

dating and characterization of polymorphic transformation of aragonite to calcite in pleistocene bivalves from rhodes greece by combined shell microstructure stable isotope and electron spin resonance study absolute dating of diagenesis is a challenging yet significant problem reconstructing the depositional and diagenetic history of a late pleistocene coralligene type red algal reef and overlying maerl red algal sand from the plimiri coastal cliff se island of rhodes greece is enabled using a combination of microstructure stable isotope analyses and electron spin resonance of large bivalve shells partially altered by diagenesis these shells consisting of both original shell aragonite and polymorphic transformed rims now consisting of neomorphic spar provide the opportunity to date the primary age when the shells were precipitated as well as the age of their polymorphic transformation the contamination of samples presented a significant problem for interpreting ages based on data from electron spin resonance esr alone however sample contamination was evaluated with quantitative xrd providing the opportunity to apply corrections which increased reliability of the ages the carbon and oxygen stable isotope values and the neomorphic spar microtexture suggested that the polymorphic transformation at plimiri took place in a meteoric environment with a high and increasing fluid rock ratio the electron spin resonance dates combined with the vertical sedimentary evolution allowed to assign the formation of the red algal reef to the marine isotope stages 6 to 5e transgressive event ca 135 to 120 ka and to identify meteoric diagenetic phases during possibly the marine isotope stage 5d and the upper marine isotope stage 5c to lower 3 the use of electron spin resonance dating of neomorphic spar and age correction for sample contamination is presented herein for the first time and the results suggest that it might provide a useful tool to date late pleistocene diagenesis

oil source correlation in the fulin basin shengli petroleum province east china the fulin basin is located within the giant shengli petroleum province in east china the source rock in the basin is mainly the lower part of the third member es3 of the eocene portion of the shahejie formation it is composed of organic rich dark mudstone and oil shale of lacustrine origin and contains good quality type i ii kerogen these strata reach the oil generative stage at ro 0 4 0 8 the first member es1 of the oligocene portion of the shahejie formation has excellent oil potential in the nearby gunan basin but is immature in the fulin basin and is not an effective source rock the oil and rock samples from both basins can be grouped into three major families based on biomarkers the first family shows low prph 0 3 and notable carotane typical of carbonate evaporite environments this family exists in es1 rocks and the related oils and is early mature 0 2 0 3 and s r s 0 10 0 20 the second family shows high prph 1 a low gammacerane index 0 2 and abundant 4 methyl steranes indicative of freshwater lacustrine conditions like those in es3 this family shows higher maturation 0 30 0 50 and s r s 0 35 0 55 and notable diasteranes the third family is transitional has source and maturity ratios between the above families and occurs in the es3 unit samples from the basin interior based on biomarker similarities between oils and rock extracts all oils in the fulin basin originated from es3 source rocks slight maturation differences indicate that these oils have been derived from different source areas no oil from es1 is found in the fulin basin suggesting es1 source rocks are too immature to generate commercial oil although the nearby gunan basin has much oil generated from es1 source rocks no migrated oil from es1 in this basin reached the kenli faulted zone because of intervening faults which disrupt migration

skeletal aragonite neomorphism quantitative modelling of a two water diagenetic system abstract the neomorphism of skeletal aragonite occurs by the simultaneous dissolution of aragonite and precipitation of calcite along thin solution films which may have an associated zone of partly dissolved aragonite chalky zone it has been proposed that pore waters at neomorphic calcite aragonite contact zones neomorphic fronts may be partly isolated from bulk pore waters and thus retain primary geochemical signatures to varying degrees iterative computer programs were developed that simulate aragonite neomorphism in two water diagenetic systems using stable isotope and trace element data neomorphism of aragonitic mollusks from the purbeck group of southern england late jurassic to early cretaceous was associated with a decrease in strontium concentration from approximately 5100 ppm to 500 ppm modelling results indicate a high bulk water rock ratio and minimal if any isolation of the neomorphic front waters for the purbeck group mollusks and also for some pleistocene corals partial isolation of neomorphic front waters from bulk pore waters is uncommon based on published data on the geochemistry of neomorphic calcites however partial isolation does occur in some thick low porosity shells such as the gastropod strombus gigas pleistocene process based modelling of fluid rock interaction provides a means for better interpreting trace element and stable isotope data in diagenetic carbonates sensitivity analysis results indicate that water rock ratios cannot be determined at much better than order of magnitude accuracies because of uncertainties over initial pore water composition fractionation factors and distribution coefficients

migration of hydrocarbons in the tampen spur area norwegian north sea a reservoir geochemical evaluation abstract this paper describes the application of reservoir geochemical protocols to a study of oil field and regional petroleum compositional variations in the major fields in the tampen spur area the tampen spur high is located in the middle of several oil mature to gas mature source rock kitchens and most of the structures might receive petroleum from several different directions based on the definition of several different petroleum populations within the tampen spur area we define five major petroleum charging systems correlating the petroleum population variations with geological information allows us to derive likely migration fill scenarios for many of the oil fields and requires us to invoke a new upper jurassic carrier system in parts of the area connecting brent group reservoirs across major faults based on this hypothesis two exploration wells were drilled on structures to test this carrier and petroleum was found in one of the structures an understanding of the migration pathways and petroleum drainage efficiency of the basins is of great economic interest because most of the smaller substructures are marginally economic thus it is important to provide an effective risk analysis and ranking of the satellite prospects prior to drilling this study has demonstrated that filling and migration in a geological province are controlled by a series of complex processes and that the filling history of the structures within the tampen spur is more complicated than suggested earlier