the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

impact of the kuroshio current on the south china sea based on a 115 000 year diatom record we used the tropical oceanic planktonic diatom species nitzschia marina rhizosolenia bergonii and azpeitia africana azpeitia neocrenulata most commonly found in the surface sediments of the northeastern most south china sea scs where the kuroshio current enters the scs through the bashi strait north of luzon to analyse the influence of the the kuroshio current on the scs the impact of the kuroshio current seems to be relatively strong during major warm periods and to a lesser degree in minor warm periods during the last 115 000 years the strongest influence took place during the main part of the holocene and during the very late phase of marine isotope stage mis 5e it is possible to distinguish two magnitudes of change in the impact of the kuroshio current on the scs large changes occurred at shifts between glacial and interglacial conditions while smaller changes seem to have recurred in both glacial and interglacial episodes as well as during the holocene climatic oceanographic changes and sea level variations were possibly the two most important mechanisms for the varying influences of the kuroshio current on the scs the interaction between the kuroshio current and monsoon related processes may also have played a role however because of restricted knowledge of the present day kuroshio current and the absence of a modern analogue to the ancient scs due to the marked changes in palaeogeography this relationship is difficult to establish copyright c 2006 john wiley sons ltd less

an amoeboid olivine inclusion aoi in ck3 nwa 1559 comparison to aois in cv3 allende and the origin of aois in ck and cv chondrites an amoeboid olivine inclusion in ck3 nwa 1559 0 54 1 3 mm consists of a diopside rich interior approximately 35 vol and an olivine rich rim approximately 65 vol it is the first aoi to be described in ck chondrites the apparent paucity of these inclusions is due to extensive parent body recrystallization the aoi interior contains irregular 3 15 m sized al bearing diopside grains approximately 70 vol 2 20 m sized pores approximately 30 vol and traces of approximately 2 m plagioclase grains the 75 160 m thick rim contains 20 130 m sized ferroan olivine grains some with 120o triple junctions a few coarse 25 50 m sized patches of plagioclase with 2 18 m thick diopside rinds occur in several places just beneath the rim the occurrence of olivine rims around aoi 1 and around many aois in cv3 allende suggests that ck and cv aois formed by the acquisition of porous forsteritic rims around fine grained rimless cais that consisted of diopside anorthite melilite and spinel individual aois in carbonaceous chondrites may have formed after transient heating events melted their olivine rims as well as portions of the underlying interiors in aoi 1 coarse plagioclase grains with diopside rinds crystallized immediately below the olivine rim secondary parent body alteration transformed forsterite in the rims of cv and ck aois into more ferroan olivine some of the abundant pores in the interior of aoi 1 may have formed during aqueous alteration after fine grained melilite and anorthite were leached out chondrite groups with large chondrules tend to have large aois aois that formed in dust rich nebular regions where cv and ck chondrites later accreted tend to be larger than aois from less dusty regions

linear coupling of carbon and strontium isotopes in rotliegend sandstone north sea evidence for cross formational fluid flow isotopic analyses of carbon and strontium in diagenetic dolomite and ankerite present in the eolian lower permian rotliegend sandstone southern north sea show an excellent linear correlation between delta sup 13 c and sup 87 sr sup 86 sr r 0 93 suggesting that the sources of these elements were interlinked the isotopic data indicate that late permian zechstein seas flooded the basin and displaced the interstitial meteoric rotliegent pore fluids producing early dolomite with predominantly marine bicarbonate delta sup 13 c minus 15 per thousand and strontium sup 87 sr sup 86 sr 0 7076 isotopic signatures the isotopic values of this dolomite form a trend to merge with the diagenetically later ankerite which has lower sup 13 c sup 12 c delta sup 13 c minus 4 per thousand and more radiogenic strontium sup 87 sr sup 86 sr 0 7112 the obvious source of low delta sup 13 c carbon was thermal decarboxylation of organic matter in the underlying upper carboniferous mudstones the authors also suggest that the increasing quantities of radiogenic strontium sup 87 sr sup 86 sr 0 720 were released when organic acids dissolved silicates feldspar in the same underlying mudstones the upward movement of fluid or diffusion of ions across formation boundaries therefore progressively became the dominant control on carbonate precipitation in the rotliegend sandstone

kinetic constraints on illitization reactions and the effects of organic diagenesis in sandstone shale sequences abstract based on water rock interaction modelling and kinetic considerations the present study is aimed at testing the impact of organic matter maturation on two kinds of diagenetic reactions leading to the alteration of the petrophysical properties of sandstones 1 clay mineral conversion to illite with k feldspar being a local potential source of k and 2 dissolution precipitation processes produced in sandstones by the action of water soluble organic species derived from adjacent shales assuming firstly that the chemical reactions take place in closed systems the nature and timing of diagenetic reactions in marine sandstone shale formations were modelled for a 50 120 c temperature range in order to improve understanding of the factors that control the illitization reaction with k feldspar coexisting with aluminous clay illite is modelled here as a muscovite type mineral we tested the effects of an energy barrier on illite growth by allowing or preventing the muscovite illite precipitation reaction to occur while using several illitization reaction rates we also compared the stable mineral parageneses predicted for organic material free systems with those predicted in the case of organic diagenesis release of co 2 ch 4 acetic and oxalic acids similarities and discrepancies between numerical results and natural mineral assemblages suggest that the illitization reaction depends on the nature of the reacting clays kaolinite conversion to end member illite involves high energy conditions 2 kcal mol 1 which are not met when the pore water equilibrates with the mineral matrix from undersaturated conditions in a closed system to overcome this barrier the fluid should be oversaturated with respect to k feldspar an external source of k or a ph increase in an open system is necessary for this reaction no particular effect of organic diagenesis on this reaction was found in the present study on the other hand smectite to illite conversion involves a lower energy barrier and can operate in closed systems where k feldspars are the source of k the maturation of organic matter may speed up the smectite to illite conversion rate by increasing the gibbs free energy of illite growth interactions between sandstone and shale were examined by modelling the transfer of aqueous species of organic origin from shale to sandstone fluid expulsion from shale had little or no effect on diagenesis in adjacent sandstones during each flushing cycle mainly because organic protons and ligands were neutralized in the source rock however the diffusion of shale derived cations through sandstone as organometallic complexes mg ca fe al appears to be an efficient process during carbonate cementation in sandstones where oxidizing conditions enhance the decomposition of such complexes

evidence for episodic cementation and diagenetic recording of seismic pumping events north coles levee california u s a abstract bands of calcite and dolomite cements alternating with zones of nearly carbonate free sand occur in the stevens sandston aat north coles levee san joaquin valley california temperatures calculated from o isotopes suggest that the calcite cement bands were emplaced episodically as a result of repeated injections of hot water from deeper in the section burial analysis suggests that these cements precipitated from 7 ma to the present over the temperature range of 45 to 95 c carbon isotope data suggest that the c in the cements is a mixture derived from two sources detrital shell material 13c pdb and co2 liberated from maturing kerogen 13c 24 plots of 13c vs time and depth of crystallization show that the cementation sequence was 1 dolomite cements possibly concretionary precipitated at depths a log of 13c vs calculated depth of crystallization correlates with the stratigraphic column at north coles levee if the correlation is valid the light 13 in each cement sample can be tied to its source a model based on this interpretation suggests that the early light c was derived from maturing kerogen in the kreyenhagen formation eocene as it passed through the oil window between 4 and 5 ma the subsequent passage of younger sediments with less organic material produced correspondingly smaller amounts of light co2 which was reflected in the relatively heavier c isotopes in the later cements it is suggested that the epidsodic injections of hot water carried dissolved gases and minerals principally calcite upward from rocks as deep as 2 3 km below the stevens sandstone and reprecipitated the calcite in more permeable zones in the rock degassing of co2 from rising pore waters likely triggered the precipitation and accounts for the relatively large volumes of cement the sibson model for seismic pumping of pore fluids is considered a likely explanation for the observed cementation

mass transfer and problems of secondary porosity creation in deeply buried hydrocarbon reservoirs abstract secondary porosity created by the post depositional leaching of detrital grains and cements can be of great economic importance the term secondary porosity is only descriptive and does not give any information on whether the porosity of the rock has been enhanced in reality there are two end member volumetric outcomes to the leaching process firstly the mineral can be completely dissolved and its components transported out of the system in such an instance the porosity of the rock will be enhanced secondly it is possible that a mineral will decompose and by product minerals will be precipitated which will occupy approximately the same volume as the original mineral the latter case is more likely where the pore waters are close to equilibrium with the majority of the minerals of the rock this will occur at elevated temperatures and or where the pore waters have been in contact with the rock for a long time these conditions are commonly met during intermediate to deep burial many metastable minerals such as high temperature feldspars probably decompose in this way a consequence of the decomposition of such metastable minerals is that primary porosity will be swapped for secondary and that older and more deeply buried rocks will contain a higher proportion of secondary porosity the mass transport equation may be used to examine the physico chemical environment where enhanced porosities most likely occur during leaching by using a simple non equilibrium mass transport model based on the silica system it is possible to demonstrate the relative importance of flow rate reaction rates specific surfaces and temperature in controlling the areal extent of leaching wide leaching zones are related to high flow rates which in turn promote a high throughput of undersaturated fluid and dispersion leaching over a wide area is also favoured by low reaction rates which will occur at low temperatures although it is true to say that less of a given silicate mineral can be dissolved by an undersaturated pore water at low temperature than at high temperature it is probable that pore fluids from deeply buried sediments are more likely to be close to equilibrium with a given mineral than for instance meteoric water thus the most likely environment for the production of widespread enhanced porosity is in the shallow subsurface the lower flow rates and higher temperatures that are encountered during deep burial diagenesis will result in far narrower more intense leaching zones as a result providing sufficient reactive mineral is present any undersaturated pore water will approach equilibrium in a short distance in order to transport undersaturated pore waters appreciable distances in the deep subsurface it is necessary to minimize their interaction with the host rock this could occur if the pore fluid were to move through a fracture system where it would interact with a far smaller surface area of reactive mineral than if it moved through the pore network

simulation of potassium feldspar dissolution and illitization in the statfjord formation north sea prior work has suggested that potassium mobility is an important control on the formation of late stage illite in deep reservoirs of the north sea we developed a one dimensional finite difference reactive transport model to simulate the concurrent dissolution of k feldspar and illitization of kaolinite in statfjord formation reservoirs the kinetics of k feldspar dissolution is set to be faster than diffusion consistent with the observed behavior and the proposition that the reaction was transport limited k feldspar dissolution produced dissolved potassium and silica that diffused and then precipitated to form illite and quartz areas that had higher initial reactant k feldspar produced higher solute concentrations and formed chemical gradients having areas that had lower initial feldspar content in typical north sea cases this means mass transfer would be from sandstone to shale the diffusive transport moved significant amounts of potassium and silica over distances of several meters and created observable diagenetic alteration simulations of an oil filled reservoir showed that oil emplacement did not stop illitization but did limit potassium mobility and maximized illite formation within the sandstone preservation of preillitization permeability was favored in water filled reservoirs that had slower illite formation where diffusion could export potassium from the sandstone before precipitation similar patterns of transport and precipitation were predicted for silica from k feldspar dissolution the results of the model showed good agreement with field data from other north sea reservoirs

relationship between diagenesis and reservoir quality in sandstones of the garn formation haltenbanken mid norwegian continental shelf a quantitative model is proposed for the dependence of porosity and permeability on diagenesis in subarkosic arenites of the middle jurassic garn formation porosity variation is controlled by the combined effects of compaction and quartz cementation in general more porosity has been lost by compaction than by quartz cementation but compactional porosity loss appears to have occurred relatively early in the burial history before burial below 2 km below the sea floor thus progressive reduction of the total porosity with increasing burial below 2 km results mainly from quartz cementation permeability is a function of the abundance of intergranular macroporosity which is interpreted to be a measure of effective porosity at depths less than 3 5 km below the sea fl or intergranular macroporosity generally comprises more than 50 percent of the total porosity but at greater depth as total porosity decreases below about 16 percent the ratio of effective to ineffective porosity drops below one this depth corresponds to the onset of extensive illitization and grain dissolution which results in major reorganization of the pore system generation of secondary porosity by feldspar dissolution appears not to have been beneficial to reservoir quality in the garn formation but it is regarded as an intrinsic part of the overall process of porosity destruction with increasing diagenesis

on the kuroshio branch in the taiwan strait during wintertime abstract past investigations reported that warm and saline waters originating from the kuroshio region occupied the northern south china sea nscs during wintertime these waters were called a branch of the kuroshio and an offshoot of them was long believed to flow persistently along the west coast of taiwan contrary to the winter ne monsson however these descriptions are not completely consistent with recent evidence field measurements in the eastern taiwan strait now available display a quasi stationary oceanic front whose alignment is roughly normal to the transverse of the strait which separates the warmer more saline water to the south from the colder fresher china coastal water in the north during most of the winter this feature implies the further northward movement of southeasterly kuroshio water having been stagnated by cold waters to the north of the front therefore the intruded kuroshio water driven by the ne monsoon tends to accumulate in the nscs and eventually establishes an anti cyclonic warm core eddy there the first event of the intrusion of warm waters from the eddy into or even through the taiwan strait usually appears when the ne wind weakens from a strong cold air outbreak in winter or early spring we believe the inception of the kuroshio branch in the strait starts from such an intrusion event

diatoms from the surface sediments of the south china sea and their relationships to modern hydrography abstract a principal components analysis of diatoms in surface sediment samples from the south china sea scs shows a clear relationship between the spatial distributions of diatoms and the current pattern of the region six diatom assemblages are distinguished representing environments with different hydrological characteristics the neritic planktonic species thalassionema nitzschioides is the dominant component in the surface sediment diatoms with relatively small changes throughout the scs suggesting that the water mass exchanges between the scs and the pacific and indian oceans are relatively small the strongest impact of the warm oceanic water occurs in the northeasternmost part of the scs where assemblage v is located with nitzschia marina azpeitia nodulifera azpeitia neocrenulata rhizosolenia bergonii and thalassionema frauenfeldii as main taxa warm oceanic planktonic species n marina r bergonii and a neocrenulata can be used as indicators of warm oceanic waters flowing into the scs in paleoceanographic reconstructions of the area in particular in tracking the water from the western pacific including the kuroshio current it may however be problematic to use another tropical oceanic planktonic species a nodulifera as an environmental indicator because of its strong resistance to dissolution thus possibly further transport

upper ocean currents around taiwan abstract current velocity measured by shipboard acoustic doppler current profiler sb adcp during 1991 2000 was used to study the upper ocean the composite and moored currents revealed a branch of the kuroshio that intruded steadily and persistently into the south china sea part of the intruded kuroshio flowed out of the south china sea through the northern luzon strait and re united with the main stream kuroshio the kuroshio had two velocity maximum cores southeast of taiwan but gradually combined into one as the kuroshio flowed north the kuroshio was deflected by the i lan ridge east of taiwan and the zonal running shelf break northeast of taiwan at the shelf break the kuroshio split with one branch intruding onto the shelf west of the luzon strait the kuroshio intruded into the south china sea some water flowed northward into the taiwan strait and re joined the kuroshio currents in the taiwan strait flowed primarily in a northward direction except for the southward current near the coast of mainland china north of the taiwan strait a branch of the northward flow followed the northern coast of taiwan to join the kuroshio the composite current varied consistently from season to season there was generally poor correlation between currents and local winds especially in the deep water regime remote forces were important in the currents around taiwan

coarse grained chondrule rims in type 3 chondrites abstract relatively coarse grained rims occur around all types of chondrules in type 3 carbonaceous and ordinary chondrites those in h l ll3 chondrites are composed primarily of olivine and low ca pyroxene those in cv3 chondrites contain much less low ca pyroxene average grain sizes range from 4 m in h l ll3 chondrites to 10 m in cv3 chondrites such rims surround 50 10 and 1 of chondrules in cv3 h l ll3 and co3 chondrites respectively but are rare 1 around cv3 ca al rich inclusions rim thicknesses average 150 m in h l ll3 chondrites and 400 m in cv3 chondrites the rims in h l ll3 chondrites are composed of material very similar to that which comprises darkzoned chondrules and recrysiallized matrix dark zoned chondrules and coarse grained rims probably formed in the solar nebula from clumps of opaque matrix material heated to sub solidus to sub liquidus temperatures during chondrule formation mechanisms capable of completely melting some material while only sintering other material require steep thermal gradients suitable processes are lightning reconnecting magnetic field lines and possibly aerodynamic drag heating cv chondrites may have formed in a region where the chondrule formation mechanism was less efficient probably at greater solar distances than the ordinary chondrites the lesser efficiency of heating could be responsible for the greater abundance of coarse grained rims around cv chondrules alternatively cv chondrules may have suffered fewer particle collisions prior to agglomeration

thermoluminescence and compositional zoning in the mesostasis of a semarkona group a1 chondrule and new insights into the chondrule forming process a large group a1 porphyritic olivine chondrule in the semarkona ll3 0 chondrite with induced thermoluminescence tl and compositional zoning in its mesostasis has been discovered the chondrule has ca rich and fe poor olivine cao 0 36 0 40 wt fa0 3 0 5 and its mesostasis is highly anorthite normative 52 5 wt the chondrule shows an intense induced tl peak at 300 c with a half width of 180 c the induced tl in the 40 440 c range increases monotonically by a factor of 6 from center to rim while sio2 na2o and mno increase by factors of 1 1 3 6 and 6 respectively the spectrum of the induced tl over the 200 350 c range i e a dominant peak at 570 nm with a half width of about 100 nm and the mn tl correlation suggest mn activated plagioclase is an important constituent of the refractory mesostases in group a1 chondrules the zoning may reflect fractional crystallization soret diffusion transport of volatiles into the chondrule by aqueous alteration a zoned precursor reduction of precursor dust aggregate or recondensation of volatiles lost during chondrule formation the first four possibilities seem unlikely explanations for the zoning of the mesostasis but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning reducing conditions at high temperatures are suggested to have prevailed during the formation of group a1 chondrules

role of microbial processes in linking sandstone diagenesis with organic rich clays abstract numerous chemical reactions within clay sequences have been proposed to produce dissolved material for diagenesis of deeply buried sands however reactions responsible for solubilizing inorganic and organic constituents in clays at intermediate depths and their importance to sandstone diagenesis have not been evaluated results from this study show that the processes of microbial organic acid production via fermentation in clays and microbial organic acid consumption via sulfate reduction in sands effectively link organic rich clays to sandstone diagenesis in the black creek formation of south carolina diagenetic processes have resulted in the formation of 10 volume percent calcite cement 0 1 volume percent authigenic pyrite and 1 5 volume percent secondary porosity in black creek sands however the distribution of these diagenetic processes is not uniform resulting in net destruction of porosity in some parts of the sand and net porosity enhancement in other parts mass balance derived rates of microbial organic acid production 10 5 mmole carbon 1 1 yr 1 and microbial co2 production 4 10 5 mmole l 1 yr 1 show that microbial processes can account for all organic carbon in the calcite cements at least 11 of carbonate carbon based on isotope balance calculations all observed authigenic pyrite and all observed secondary porosity these findings show that microbial processes can serve to link organic rich clays with sandsto e diagenesis at intermediate depths

constraints on the development of secondary porosity in the subsurface re evaluation of processes abstract secondary porosity formed by the dissolution of grains and cements is of great economic importance in both clastic and carbonate reservoirs a review of the commonly proposed mechanisms for the production of secondary porosity indicates that meteoric water penetration and mixing corrosion may be able to create significant volumes of secondary porosity in the shallow subsurface leaching by acidic fluids generated by solution of co 2 or monocarboxylic acids both derived during the thermal maturation of organic matter or by acidic fluids created by clay mineral reactions in shales are the most commonly proposed mechanisms by which secondary porosity is said to form in the deep subsurface however these mechanisms suffer from great difficulties in producing significant volumes of secondary porosity once mass balance and fluid migration problems are taken into account it is highly likely that the correct mechanism for the creation of economically significant amounts of secondary porosity in the deep subsurface is yet to be found

illite smectite formation and potassium mass transfer during burial diagenesis of mudrocks a study from the texas gulf coast paleocene eocene abstract mudrock samples from a well penetrating eocene and paleocene strata 1235 4455 m of the texas gulf coast have been studied to assess geochemical redistribution in mudrocks during burial diagenesis and the mechanism by which detrital smectitic illite smectite i s is transformed into diagenetic illitic i s idealized smectite and illite end member compositions for interstratified i s are estimated to be k0 00x 10 56mg0 39fe0 57al1 13si3 90o10 oh 2 and k0 53x 10 18mg0 17fe0 16al2 28 si3 40o10 oh 2 respectively there is no obvious difference in the amount of k addition to i s in random and ordered interstratified i s aluminum substitution into both tetrahedral and octahedral sites suggests that the smectite to illite reaction is a complete dissolution precipitation reaction rather than a solid state k 1 al 3 for si 4 substitution reaction depth relat d mineral trends and mass balance calculations suggest that illitic i s may form from kaolinite and possibly illite or mica as well as from smectitic i s although most whole rock element abundances are invariant over the sampled depth interval k2o content increases from ca 2 0 weight percent at 1500 m of burial to ca 3 8 weight percent at 4000 m some of this increase is probably caused by import of k into the shale via fluids derived from interbedded sandstones implying that gulf coast mudrocks behave as open chemical systems during burial diagenesis if this is the case a minimum of 103 pore volumes of fluid must have passed through the most k enriched shales to have introduced the added potassium provided that the k content of present day formation water is representative of that of ancient formation water

a numerical model for porosity modification at a sandstone mudstone boundary by quartz pressure dissolution and diffusive mass transfer in many sandstones quartz cements significantly reduce porosity the origin of these cements is often unclear this paper investigates a possible mechanism for the generation of silica for quartz cement by pressure dissolution in interbedded mudstones theoretical models of quartz pressure dissolution including the effects of silica precipitation kinetics show that the concentration of dissolved silica in the pore fluids of a compacting sediment increases with decreasing grain size and silica precipitation constant quartz precipitation is strongly inhibited by the presence of small amounts of clay within a sediment suggesting that siltstones and quartz rich mudstones which are undergoing pressure dissolution may act as a source of dissolved silica for export to nearby coarser sediments a computational model for the diagenetic modification of a sandstone mudstone interface due to pressure dissolution is described both sandstone and mudstone layers are assumed to be actively compacting by pressure dissolution and mass transport by molecular diffusion is considered as quartz precipitation in the mudstone layer is relatively slow compared to that in the sandstone significant amounts of dissolved silica become available in the mudstone and may be exported into the adjacent sandstone in the absence of pore fluid advection this may result in the formation of extensive secondary quartz within the sandstone close to the interface the volume of silica exported from the mudstone is limited by the length scale over which diffusion through the mudstone is effective this is typically 3 5 m the volume of silica available therefore suggests that extensive porosity modification within the adjacent sandstone can only occur close to the mudstone thus it is possible that thin sandstones could become cemented by slow diffusive transfer of silica but that in thicker sandstones the silica may become dispersed by pore fluid advection

potassium leached zones at the contacts of the garn formation mid norwegian continental shelf evidence for the role of shale in sandstone diagenesis abstract

nepheline and sodalite in the matrix of the ningqiang carbonaceous chondrite implications for formation through parent body processes abstract ningqiang is an ungrouped carbonaceous chondrite that chemically and petrologically resembles cv3 chondrites the matrix of ningqiang shows much higher abundances of na k and al by factors of 4 4 2 7 and 1 6 respectively than in cv3 chondrites our scanning and transmission electron microscope observations and synchrotron radiation x ray diffraction measurements reveal that the major proportions of these elements can be attributed to the presence of nepheline and sodalite rietveld refinement of x ray diffraction data shows that the feldspathoids constitute 7 7 vol of all crystalline phases in the matrix nepheline and sodalite occur mostly as discrete equidimensional grains 2 5 m in diameter that are dispersed homogeneously in the matrix most of the grains contain inclusions of fe rich olivine and minor ca pyroxene magnetite troilite and pentlandite despite the high abundances of na k and al in the matrix of ningqiang the bulk meteorite abundances of these elements are comparable to those of the cv group e g rubin et al 1988 this means that the chondrules which constitute a major proportion of the volume other than the matrix in ningqiang are depleted in na k and al in fact our analyses and observations show that the chondrules in ningqiang overall contain very small amounts of these elements our interpretation of these findings suggests that nepheline and sodalite in the ningqiang matrix were originally formed by na metasomatism of the chondrules and ca al rich inclusions in the meteorite parent body afterward they were likely disaggregated and scattered into the matrix however it is difficult to envisage that the disaggregation and scattering occurred in situ in the present setting of the meteorite hence we suggest that the ningqiang meteorite underwent these processes before final lithification

reservoir characterization and diagenesis of the oligocene 64 zone sandstone north belridge field kern county california the oligocene zemorrian 64 zone sandstone is an important oil and gas reservoir in north belridge field kern county california the 64 zone is a submarine fan deposit that ranges from 83 to 137 m in thickness although diagenesis has played an important role in modifying porosity and permeability the overall variations in reservoir quality reflect an upward increase in grain size associated with depositional processes three diagenetic events have had a significant impact on reservoir quality 1 compaction which has reduced intergranular volume to an average of 20 2 quartz cement which has reduced porosity by an average of 6 2 and 3 feldspar dissolution although an average of 2 7 porosity is directly associated with leached feldspar grains mass balance calculations indicate that secondary porosity is roughly balanced by formation of authigenic kaolinite resulting in little or no net gain in porosity three episodes of calcite cementation reflect various stages of burial history petrographic and isotopic data demonstrate that calcite i formed at shallow depths in the zone of bacterial sulfate reduction fluid inclusion data indicate that calcite ii precipitated at temperatures of 92 to 167 c from fluids less saline than seawater fracture filling calcite iii postdates calcite ii but formed at lower temperatures 85 to 125 c the results of isotopic modeling indicate that calcite ii precipitated in equilibrium with waters expelled by shales during i s diagenesis dgr18osmow 2 to 8 pmil and that calcite iii precipitated during tectonic uplift from a mixture of shale derived and meteoric waters dgr18osmow 0 to 4 pmil most fluid inclusions in calcite ii yield temperatures greater than present bottom hole values sim110 c assuming that fluid inclusions in calcite ii record maximum burial and a geothermal gradient of 33 c km tectonic uplift of 0 6 to 1 7 km sim2000 5700 ft would be required to explain the fluid inclusion data

diagenetic destruction of reservoir potential in shallow marine sandstones of the broadford beds lower jurassic north west scotland depositional versus burial and thermal history controls on porosity destruction abstract the broadford beds are a shallow marine mixed siliciclastic carbonate unit up to 140 m thick that crops out in the northern inner hebrides adjacent to a major tertiary igneous centre the formation can be divided into three lithological units a lower limestone dominated unit a middle unit of muddy calcareous sandstones and an upper unit of cleaner sandstones the limestones underwent early meteoric diagenesis and early diagenetic processes in the overlying sandstones included the precipitation of berthierine corrensite phosphate and a small amount of mg calcite the most abundant burial cement is ferroan calcite most of which precipitated during mesozoic burial at depths of about 1 km these cements were sourced through the chemical compaction of depositional carbonate within interbedded muddier horizons later calcite cements were precipitated in fractures from meteoric fluids during late jurassic early cretaceous inversion and early tertiary uplift and a final stage of calcite cementation was associated with tertiary hydrothermal activity other burial diagenetic phases include quartz overgrowths and chlorite quartz cementation was initiated before the main phase of calcite cementation but the most significant quartz cementation accompanied the formation of chlorite during tertiary hydrothermal activity overall the most significant factor leading to porosity loss in the broadford beds was the abundance of detrital clays and depositional carbonate in the original sediment this led to extensive calcite cementation that both occuluded primary pores and inhibited the formation of secondary porosity

problem of secondary porosity frio formation oligocene texas gulf coast secondary porosity formed by the dissolution of both carbonate and silicate minerals especially k feldspars is widely developed in sandstones of the frio formation oligocene in the texas gulf coast co 2 produced by decarboxylation of organic matter is commonly suggested as the acid required for dissolution material balance calculations indicate that co 2 produced by decarboxylation of organic matter in frio formation shales can account for a regional average of only 1 or 2 secondary porosity in frio formation sandstones yet point count data indicate an average of 10 secondary porosity long distance fluid transport many kilometres and or other mechanisms of acid generation should therefore be considered carbon isotopic data on dissolved inorganic carbon in formation water co 2 in produced natural gas and carbonate cements indicate that co 2 produced by decarboxylation had a minor impact on these carbon reservoirs the reaction kerogen water methane carbon dioxide can explain the isotopic data but alone it is insufficient to account for all the secondary porosity unless long distance material transport is involved

burial diagenesis of argillaceous sediment south texas gulf of mexico sedimentary basin a reexamination cuttings from a well through a thick section of miocene oligocene mudrocks from kenedy county texas spanning a depth range of 2130 to 5490 m 7000 to 18 000 ft have been studied petrographically and geochemically on the basis of whole rock chemical analyses the deepest samples have lost 18 wt and approximately vol mostly as caco3 mineral bound h2o and sio2 but including additional ca as well as sr light rare earth elements ree la ce nd sm fe and li k2o and rb have been added to the deeper rocks the large chemical changes are accompanied mineralogically by loss of detrital calcite kaolinite k feldspar ca plagioclase and muscovite gain of chlorite and albite and continued reaction of smectitic illite smectite i s to more illitic and k rich compositions throughout the entire depth interval of the well the large chemical changes in this thick mud rich interval almost certainly require advection of water free convection to accomplish the mass transfer initial variation in sediment composition is ruled out as a cause of the observed compositional changes with increasing depth because 1 a variety of immobile elements al2o3 tio2 zr hf heavy ree er yb th and sc remain constant relative to each other despite their uneven distribution across various particle size fractions in the sediments 2 deep frio shales are unlike quaternary gulf of mexico sediments or average shales and 3 unreasonable primary mineralogic compositions would be necessary to explain the chemical composition of the deep samples these results indicate that burial diagenesis of argillaceous sediment can be a considerably more open chemical process than is conventionally assumed that it can account for the two major chemical cements calcite and quartz in associated sandstones and that it mirrors secular changes in shales throughout geologic time

physical properties of chondrules in different chondrite groups implications for multiple melting events in dusty environments chondrite groups cv ck cr with large average chondrule sizes have low proportions of rp plus c chondrules high proportions of enveloping compound chondrules high proportions of chondrules with thick igneous rims and relatively low proportions of type i chondrules containing sulfide in contrast chondrite groups cm co oc r eh el with smaller average chondrule sizes have the opposite properties equilibrated ck chondrites have plagioclase with relatively low na equilibrated oc r eh and el chondrites have more sodic plagioclase enveloping compound chondrules and chondrules with igneous rims formed during a remelting event after the primary chondrule was incorporated into a dustball repeated episodes of remelting after chondrules were surrounded by dust would tend to produce large chondrules rp and c chondrules formed by complete melting of their precursor assemblages remelting of rp and c chondrules surrounded by dust would tend to produce porphyritic chondrules as small dust particles mixed with the melt providing nuclei for crystallizing phenocrysts this process would tend to diminish the numbers of rp and c chondrules correlations among these chondrule physical properties suggest that chondrite groups with large chondrules were typically surrounded by thick dust rich mantles that formed in locally dusty nebular environments chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away slow cooling led to enhanced migration of sulfide to chondrule surfaces and more extensive sulfide evaporation these chondrules also lost na the plagioclase that formed from equilibrated ck chondrites was thus depleted in na

thermochemical stability of low iron manganese enriched olivine in astrophysical environments low iron manganese enriched lime olivine grains are found in cometary samples returned by the stardust mission from comet 81p wild 2 similar grains are found in primitive meteoritic clasts and unequilibrated meteorite matrix lime olivine is thermodynamically stable in a vapor of solar composition at high temperature at total pressures of a millibar to a microbar but enrichment of solar composition vapor in a dust of chondritic composition causes the feo mno ratio of olivine to increase the compositions of lime olivines in primitive materials indicate oxygen fugacities close to those of a very reducing vapor of solar composition the compositional zoning of lime olivines in amoeboid olivine aggregates is consistent with equilibration with nebular vapor in the stability field of olivine without re equilibration at lower temperatures a similar history is likely for lime olivines found in comet samples and in interplanetary dust particles lime olivine is not likely to persist in nebular conditions in which silicate liquids are stable

transports and tidal current estimates in the taiwan strait from shipboard adcp observations 1999 2001 tidal and mean flows in the taiwan strait are obtained from analysis of 2 5 years 1999 2001 of shipboard adcp data using a spatial least squares technique the average tidal current amplitude is 0 46 ms 1 the maximum amplitude is 0 80 ms 1 at the northeast and southeast entrances and the minimum amplitude is 0 20 ms 1 in the middle of the strait the tidal current ellipses derived from the shipboard adcp data compare well with the predictions of a high resolution regional tidal model for the mean currents the average velocity is about 0 40 ms 1 the mean transport through the strait is northward into the east china sea at 1 8 sv the transport is related to the along strait wind by a simple regression transport sv 2 42 0 12 wind ms 1 using this empirical formula the maximum seasonal transport is in summer about 2 7 sv the minimum transport is in winter at 0 9 sv and the mean transport is 1 8 sv for comparison this result indicates that the seasonal amplitude is almost identical to the classical estimate by wyrtki physical oceanography of the southeast asian waters scientific results of marine investigations of the south china sea and gulf of thailand 1959 1961 naga report 2 scripps institute of oceanography 195 pp based on the mass balance in the south china sea while the mean is close to the recent estimate by isobe continental shelf research 19 1999 195 based on the mass balance in the east china sea 2003 elsevier science b v all rights reserved

kaolinized potassium leached zones at the contacts of the garn formation haltenbanken mid norwegian continental shelf abstract the middle jurassic garn formation consists mainly of subarkosic arenite in which potassium feldspar is several times as abundant as plagioclase in cores from eight wells the top of the formation upper 6 12 m appears to have undergone relatively intense alteration of potassium feldspar to kaolinite with the resulting loss of bulk postassium content this could be explained as a result of subaerial weathering of the top of the sandstone body except for the fact that in two of the wells the same pattern of alteration is observed at the base of the formation an alternative explanation is that alteration resulted from the introduction of acid released by the maturation of organic matter in adjacent shales in all instances the altered zones display a gradual increase in kaolinite content and a decrease in the ratio of bulk rock potassium aluminium over a distance of several metres approaching the formation boundary this pattern indicates that the active species responsible for the alteration entered vertically from the formation contacts rather than being introduced by lateral flow along the sandstone bed the cores studied are tentatively interpreted as recording different stages in the following depth related sequence of diagenetic events 1 early kaolinization throughout the formation by meteoric water flushing 2 formation of additional kaolinite near the formation contacts by the influx of acid from surrounding shales at approximately 2 7 km depth below the sea floor and 3 extensive alteration of kaolinite to illite at approximately 3 7 km depth illitization has been impeded in the leached zones near the formation contacts due to a local deficiency in reactive potassium here kaolinite survives unaltered whereas kaolinite throughout the rest of the formation has been extensively replaced by illite this implies that the illitization of sandstone can occur by short range diffusion in a chemically closed system solely in response to increasing thermal exposure at greater depth

chondrules matrix and coarse grained chondrule rims in the allende meteorite origin interrelationships and possible precursor components bulk compositions of 20 chondrules 13 coarse grained chondrule rims and two composite samples of matrix material from cv3 allende were determined by instrumental neutron activation analysis three rare nonporphyritic cv chondrules from allende leoville and vigarano were analyzed by broad beam electron microprobe analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 refractory and semi refractory lithophiles with low feo 2 common siderophiles and chalcophiles 3 common to slightly volatile lithophiles si cr mn and modal pyroxene with moderately high feo feo mgo 4 moderately volatile siderophiles and 5 alkalies these precursor components can be explained by plausible processes occurring in the solar nebula the precursor components of coarsegrained rims are apparently the same as those of chondrules these components differ from those inferred previously for oc eh or cm co chondrules in general the compositions of coarse grained rims are more similar to the mean chondrule composition than to those of the chondrules they enclose rim siderophile contents are generally 2 5x greater than those in the chondrules and 0 5 to 2x those in bulk allende rims as a group are more homogeneous than chondrules suggesting that rims formed from finer grained precursors several chondrules and rims have fractionated rare earth patterns and may have been affected by metamorphism the enclosure of some coarse grained rims by fine grained matrix like rims that are almost certainly of nebular origin indicates that coarse grained rims were also formed in the nebula two matrix samples are similar in composition to some coarse grained rims suggesting that matrix was derived from similar compositional reservoirs of nebular dust chondrules with coarse grained rims were reheated in space following the accretion of dusty coatings this restricts plausible chondrule forming mechanisms to those that allow multiple nebular heating events

lagrangian observations of surface flow patterns in the vicinity of taiwan two satellite tracked surface drifters were launched off the southwestern coast of taiwan on october 7 1997 both traveled northward along the taiwan strait ts and into the seas north of taiwan lasting 20 and 53 days respectively from the drifter trajectories their rotary spectra and satellite infrared imagery several oceanic features have been detected and are discussed in this paper our results indicate that in the southern and central portions of the ts the floats followed a northward flow with a mean speed of 30 50 cm s upon reaching the northwestern taiwan coast the trajectories were strongly affected by the semidiurnal tides and interacted with the kuroshio water in the southern east china sea the onset of the strong northeastern winter monsoon in early november decelerated the northward movement and eventually reversed the direction this process was accompanied by wind generated near inertial motion one drifter was then captured by a counterclockwise circulation of a cold dome at the continental shelf break northeast of taiwan finally the drifter was entrained by the mainstream of the kuroshio and flowed towards the northeast

correlation of carbon dioxide abundance with temperature in clastic hydrocarbon reservoirs relationship to inorganic chemical equilibrium the mol co2 of gas reservoired in sandstones tends to increase with increasing temperature along both the us gulf coast and the norwegian continental shelf each of these provinces displays identical linear correlations between temperature and the log of the partial pressure of co2 i e pco2 in the reservoir fluid that is the product of the mol co2 the reservoir pressure this correlation is the same both in gulf coast reservoirs younger than 17 ma and in norwegian reservoirs of jurassic to triassic age 144 245 ma indicating that it is not dependent on reaction kinetics norwegian shelf data indicate that the same correlation also applies for gas condensate and oil reservoirs we suggest that the log pco2versus temperature correlation is the result of inorganic chemical equilibria between feldspar clay and carbonate minerals a trend of decreasing ph with increasing temperature is fixed by equilibria between aluminosilicate minerals feldspar kaolinite at lower temperatures followed by various reactions between kaolinite illite chlorite and feldspar as temperatures exceed 110 140 c responding to the ph set by the aluminosilicate system co2 activity in the formation water and thereby co2 partial pressure in any gas phase present is controlled by equilibrium with carbonate minerals this model predicts that co2 released by organic maturation will in general result in precipitation of carbonate minerals below 100 120 c and that there should be widespread carbonate dissolution at higher temperatures

depositional and diagenetic controls on reservoir quality and gas composition in a mixed siliciclastic carbonate setting thomasville field mississippi abstract the smackover formation in central mississippi is sour gas productive from siliciclastics interbedded with tight carbonates the sandstones have low reservoir quality porosity and permeability of 7 0 and 0 35 md respectively but wells are capable of producing at high rates and with large volumes because of the extremely large geopressures and locally thick continuous sandstone packages production is from a hostile subsurface environment which includes high temperatures 365 degree f high pressures 0 88 psi ft great depths 20 000 ft and variable and corrosive sour gas mixtures ch sub 4 55 h sub 2 s 36 co sub 2 9 five fields are productive in this trend thomasville the largest field is used to illustrate the depositional and diagenetic controls on productivity deposition occurred as an upward shoaling sequence of outer ramp to nearshore and sabkha environments the lower sandstones are bioturbated low quality reservoirs interbedded with carbonate mudstones and packstones the middle interval consists of the thickest and most continuous sandstones that are interpreted to be amalgamated inner ramp shoal and ridge deposits the upper interval consists of the common but tight smackover ooid grainstone shoals that are interbedded with continuous but thin shoal and shoreface sandstone the middle interval has the best reservoir quality and contains more 75 of the hydrocarbons seismic may be used to map the sandstone packages but not the individual sandstones in addition to the larger net gross and more continuous sandstones in the middle zone two postdepositional controls also govern the reservoir quality these include small scale faulting but more importantly diagenetic events which strongly overprint but do not obscure the original depositional control at least 15 different diagenetic events have occurred in the sour gas fields that have generally decreased reservoir quality less

seasonal variability of thermal fronts in the northern south china sea from satellite data the 8 year 1991 1998 pathfinder sea surface temperature data have been applied here to produce the objectively derived seasonality of the oceanic thermal fronts in the northern south china sea from 17 degreesn to 25 degreesn several fronts have been clearly distinguished namely fujian and guangdong coastal water pear river estuary coastal taiwan bank kuroshio intrusion hainan island east coast and tonkin gulf coastal fronts the frontal patterns in winter spring and summer are quite similar whereas individual fronts display different modes of seasonal variability due to different mechanisms favoring those fronts

carbon dioxide in clastic rocks and silicate hydrolysis the amount of carbon dioxide in clastic rocks in sedimentary basins increases with depth organic matter dissolved organic species and dissolution of carbonate minerals have been suggested as sources of co sub 2 which increases in abundance with depth and temperature isotopic compositions of aqueous hco sub 3 sup minus gaseous co sub 2 and calcite from conventional hydrocarbon wells and steam assisted recovery of heavy oil suggest that calcite or other carbonate minerals are the source of co sub 2 particularly at higher temperatures detailed examination of the stability of diagenetic minerals such as kaolinite smectite and analcime among others relative to the coexisting waters indicates that silicate hydrolysis is the driving force for dissolution of carbonate minerals and the ultimate source of abundant co sub 2 in clastic rocks in diagenetic environments at temperatures over approximately 100 c

burial diagenesis of illite smectite in shales and the origins of authigenic quartz and secondary porosity in sandstones several gram size samples of 0 1 mu m nearly monomineralic mixed layer illite smectite i s were isolated from nineteen whole cores of shale of the frio formation from the texas gulf coast between approximately 7 000 ft 2133 m and approximately 15 000 ft 4572 m burial depth i s changes from random interstratification r 0 with low 1 to ordered interstratification r 3 with high i the accompanying chemical changes are loss of si mg and fe sup 3 gain of k al and fe sup 2 and a shift in the ree content of the mineral there is no chemical or mineralogical evidence for a cessation of i s reaction at approximately 80 i as is commonly accepted both chemical and mineralogical changes occur throughout burial continuous change in the oxygen isotopic composition of i s implies that the conversion of smectite layers to illite layers is a dissolution and reprecipitation process mass balance calculations indicate that burial diagenesis of frio formation shales is an open system process that requires addition of k sub 2 o and al sub 2 o sub 3 and results in loss of sio sub 2 the amount of sio sub 2 made available by shale diagenesis is sufficient to be the source of the quartz overgrowth cements in the associated frio sandstones iron reduction in i s is amore significant source of the acid required for the diagenesis of both frio shales and sandstones 68 refs 12 figs 4 tabs less

spring of no kuroshio intrusion in the southern taiwan strait 1 the taiwan strait connects the east china sea ecs to the south china sea scs typically in spring the water in the scs and a branch of the kuroshio occupy the eastern part of the strait while the china coastal waters including a large contribution from the changjiang yangtze river occupy the western part during spring 2008 when the taiwan strait was under the influence of la nina and according to field observations the kuroshio branch did not contribute much to the waters in the southern taiwan strait a numerical model verifies this observation the china coastal waters also seem to have had less effect than in typical years since the scs waters contain more nutrients than the kuroshio branch more nutrients may be transported from the scs to the ecs in a la nina spring than at other times

a simple three dimensional model of diffusion with precipitation applied to localised pyrite formation in framboids fossils and detrital iron minerals a three dimensional diffusion with precipitation model is constructed to estimate radial variations in the amounts of pyrite which precipitate where a spherical mass of organic matter producing h2s by sulphate reduction is enveloped in a dissolved iron bearing porewater the model indicates that higher rates of sulphate reduction more readily metabolisable organic matter and larger organic masses require increasingly high dissolved iron concentrations in order to confine pyrite or iron sulphide precipitation to the decay site the maximum size sphere of exceedingly metabolisable organic matter equivalent to fresh planktonic material which can be pyritised is about 50 m radius where decay occurs in porewaters with typical dissolved iron levels this radius is close to the maximum radius of framboidal pyrite the formation of which could involve model type processes fossil carcases although mainly composed of less readily metabolisable organic matter may be orders of magnitude larger and the model demonstrates that their pyritisation requires unusually high porewater dissolved iron concentrations these inferred chemical conditions are consistent with sedimentological observations of pyritisation in beecher s trilobite bed new york state at greater depths within the sediment pyritisation is controlled by the kinetics of iron mineral reactivity towards h2s sediments vary widely in their exposure times to h2s which can range at least from 50 to 106 years at low exposure times only iron oxides are pyritised whereas at high exposure times even the most refractory iron silicates can become pyritised

seasonal circulation patterns of the yellow and east china seas derived from satellite tracked drifter trajectories and hydrographic observations abstract we investigated seasonal circulation patterns of the yellow and east china seas yecs by reviewing previous works on the circulation and its dominant currents and taking into account newly compiled trajectories of satellite tracked drifters collected between the 1980s and 2000s the circulation patterns suggested before the 1990s can be categorized into two groups depending on the identified origin of the tsushima warm current in the korea tsushima straits i branching from the kuroshio southwest of kyushu or ii northeastward continuation of the taiwan strait throughflow the branching of the kuroshio southwest of kyushu and northeast of taiwan was clearly evidenced by current measurements and concurrent hydrographic surveys however there is still no clear evidence for the northeastward pathway of taiwan strait throughflow across the mid shelf area of the east china sea target oriented surveys in the 1990s and 2000s employing advanced instruments such as drifter tracking and acoustic doppler current profiler measurements now provide decisive proof of the clockwise rounding of the cheju warm current around jeju do throughout the year of the northeastward extension of changjiang discharge in summer and of the presence of the yellow sea warm current only in winter thus both coastal currents in shallow water and secondary branch currents of the kuroshio such as the yellow sea warm current are found to significantly change from winter to summer to better present the basic pattern of yecs circulation and its seasonality we have constructed seasonal circulations patterns based on review results on the newly compiled drifter trajectories and on hydrographic observations further investigations should be carried out in future with support of comprehensive current measurements on shelf areas and through elaborate numerical modeling

water mass and throughflow transport variability in the taiwan strait 1 variability of water mass and throughflow transport in the taiwan strait are analyzed using strait wide conductivity temperature depth 1985 2003 and sectional acoustic doppler current profiler 1999 2001 data results from a cluster analysis temperature salinity diagrams and direct transport calculations indicate that the strong northeast monsoon drives the brackish mixed china coastal water into the northern strait and hinders the northward intruded saline kuroshio branch water kbw in the southeastern strait from december to january the mean throughflow transport across the central strait is about 0 1 sv southward during this period thus supporting previous observations that there is no persistent northward flowing current throughout the strait in winter the weakening of the northeast monsoon in february march however emancipates the kbw to intrude northward into the east china sea ecs in june the increase in this northward transport accompanied by the decrease in the westward intrusion of kuroshio through the luzon strait leads to the replacement of the kbw by the less saline south china sea water scsw the northward transports ranging from 1 16 to 2 34 sv between march and august yield 0 131 0 238 1015 w and 53 33 81 74 106 kg s of temperature and salt transports respectively toward the ecs the inception of the northeast monsoon in october marks both the change of water mass from fall to winter patterns and the decrease of the northward throughflow transport our results also reveal that the subsurface kbw and scsw remain consistent throughout the observation periods between 100 and 200 m and below 200 m depths respectively in the southeastern strait

the influence of variations in illite morphology on the permeability of middle jurassic brent group sandstones cormorant field uk north sea abstract sem examination of core samples from brent group sandstones in the cormorant field reveals that critical point drying preserves delicate illite morphologies that are damaged during air drying this damage may lead to an increase in permeability as defined by the drying effect air permeability air dried air permeability critical point dried the cormorant reservoir sandstones contain four illite morphologies early diagenetic pore lining illite formed before hydrocarbon emplacement and occurs ubiquitously pore bridging illite blooming illite and illite that replaces kaolinite all formed later and occur preferentially at or below the oil water contact damage to these late illites causes an average drying effect of 3 5 and explains why measured permeabilities predict higher water injection rates than occur in the field comparison with data from other reservoirs reveals that the drying effect is influenced by variations in illite particle dimensions as well as illite morphology tem shadowing techniques reveal that illite particle sizes describe a trend from small particles in reservoirs with large drying effects to large particles in reservoirs with small drying effects these size variations probably reflect differing illite growth rates permeability in illite bearing sandstones thus reflects not only the amount of illite present but also the size of the individual particles and their morphology

seasonal variation of volume transport in the major inflow region of the taiwan strait the penghu channel abstract eight cruises of current measurements along a zonal transect 31 84 km across the major inflow region of the taiwan strait the penghu channel were carried out using the shipboard acoustic doppler current profiler during 1999 2001 on each cruise the measurement was repeated twice along the transect with a time lag of 6 h and 12 min and the repeated data were averaged to eliminate the dominant semidiurnal tidal currents velocities after removing semidiurnal tides suggest a strong northward flow in the channel with a speed of about 100 cm s in the upper 50 m in summer the northward flow becomes much weaker in winter the calculated throughflow transports vary seasonally and are correlated with the change of the east asia monsoon the estimated transport is around 0 during the peak northeast monsoon in winter increases from 0 5 to 1 sv 1 sv 106 m3 s as the northeast monsoon weakens in spring peaks to 1 5 sv at the end of southwest monsoon in summer and decreases rapidly from 1 5 to 0 sv when the northeast monsoon intensifies in fall the error mostly induced by unfiltered diurnal tidal currents is estimated to be 0 20 sv in the transport calculation

experimental studies of silicate carbonate reactions i applications to diagenesis abstract the formation of clays and co2 from silicate carbonate reactions and the effect of these products on reservoir quality and fluid chemistry have been well recognized in the study of sediment diagenesis the phase relationships for the reaction of kaolinite dolomite quartz to calcite chlorite smectite co2 reactions were chemographically examined and experimentally evaluated the phase boundary of this reaction on a t xco2 diagram was interpolated between high temperature experimental data and low temperature field data the results can be applied to predict the amounts type and timing of clay and co2 formation during sediment diagenesis the variation of pore fluid composition e g ca2 and mg2 caused by these reactions was also evaluated using a geochemical modeling program the major conclusions and implications are the following 1 the concentration of co2 in the reaction fluid controls the reaction temperature as well as the clay type chlorite vs smectite formed the equilibrium boundary provides a guideline for estimating the co2 contents the sealing integrity and temperatures of a diagenetic system based on the observed mineral assemblages 2 the silicate carbonate reactions can occur in diagenetic environments that are open to co2 and can therefore be an important inorganic source of co2 which can lead to the formation of co2 rich gas fields and secondary porosity the diagenetic reactions however are significantly suppressed in a closed system e g overpressure zone and therefore cannot significantly contribute to overpressure formation nore generate enough pressure to create fractures and 3 the formation of smectite of chlorite which can serve as a sink for mg2 and to a lesser extent for ca2 the pore fluid released from these reactions during shale diagenesis in general contains much less mg2 than ca2 the reactions in shales are likely sources of ca2 for carbonate cements but not of mg2 for dolomitization

high resolution palynological record of holocene climatic and oceanographic changes in the northern south china sea abstract for the first time palynological records of terrestrial palynomorphs and dinoflagellate cysts are investigated in a sediment core from the northern south china sea scs covering the last 12 500 years both terrestrial and marine palynomorph records show strong signals of the sea level change during the studied interval the highest herb pollen content was associated with extensive grasslands on the exposed shelf at the low sea level stand during the younger dryas and early holocene the increase in fern spores and decrease in concentrations of dinoflagellate cysts and terrestrial palynomorphs was observed during the sea level rise interval from 12 500 to 6800 or 6000 cal yr bp then the sea level became stabilized and consistently low dinoflagellate cyst abundances and high abundances of fern spores were recorded a high abundance of impagidinium in the period 12 000 10 400 cal yr bp possibly resulted from increased input of western philippine sea waters into the scs and the branching of the kuroshio current a short term decrease of impagidinium at 11 700 11 000 cal yr bp corresponding to the mwp 1b event might be associated with input of the east china sea waters through the taiwan strait the relationship between the sedimentation rates and the concentrations of terrestrial palynomorphs indicates a water dominant transport for pollen and spore dispersal prior to 6300 cal yr bp whereas wind transport became more prominent thereafter the timing of this change corresponds to the highest sea level stand at 6800 6000 cal yr bp when the present oceanographic setting was formed the mid holocene optimum can be seen by the highest abundance of subtropical tropical broad leaved arboreal pollen and by the highest abundances of dapsilidinium pastielsii three strengthened winter monsoon intervals at 5500 cal yr bp 4000 cal yr bp and 2500 cal yr bp are reflected by increases in pinus pollen content after the present oceanographic condition formed

sandstone diagenesis in mixed siliciclastic carbonate sequences quadrant and tensleep formations pennsylvanian northern rocky mountains abstract sandstones in the quadrant and tensleep formations are well to extremely well sorted and compositionally mature mean q98 out of 9 cements 4 have special significance 1 anhydrite earliest 2 dolomite 3 quartz and 4 calcite latest the distribution of major cement types was strongly influenced by vertical location within sandstone units early anhydrite and dolomite are principally responsible for pore space reduction near sandstone carbonate contacts these cements were precipitated from pore fluids with compositions controlled by depositional setting and proximity to enclosing carbonate sediments the later precipitation of quartz overgrowths preferentially occluded pore space toward the middle of sandstone beds calcite sporadically distributed throughout sandstones represents a late stage passive pore filling event the middle 50 thickness of sandstone bodies exhibits porosities averaging about two times greater than lower and upper portions of sandstone units hence quadrant and tensleep sandstones are highly stratified on a relatively small scale as to cement and porosity distribution estimates of starting porosity and measurements of intergranular volume show that regardless of the location within sandstone bodies of the quadrant cementation dominates over compaction in terms of intergranular porosity destruction this relation also holds for the base and top of sandstone units in the tensleep only within the middle portion of sandstones of the tensleep does compaction equal or dominate over cementation in destruction of pore space

chondrules in ck carbonaceous chondrites and thermal history of the cv ck parent body ck chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6 it is commonly reported than 15 vol of ck4 6 samples are composed of chondrules the modal abundance of chondrules estimated here for 18 ck3 6 including 5 ck3s ranges from zero totally recrystallized to 50 5 although almost all chemically re equilibrated with the host matrix we recognized in ck3s and tanezrouft tnz 057 ck4 up to 85 of chondrules as former type i chondrules mean diameters of chondrules range from 0 22 to 1 05 mm for karoonda ck4 and tnz 057 ck4 respectively up to 60 of chondrules in ck3 4 are surrounded by igneous rims from 20 m to 2 mm width zoned olivines were found in unequilibrated chondrules from dag 431 ck3 an nwa 4724 ck3 8 nwa 4423 ck3 9 and tnz 057 ck4 we modeled fe mg interdiffusion profiles measured in zoned olivines to evaluate the peak metamorphic temperatures and time scales of the ck parent body metamorphism and proposed a two stage diffusion process in order to account for the position of inflection points situated within chondrules time scales inferred from fe mg interdiffusion in olivine from unequilibrated chondrules are on the order of tens to a hundred of thousand years from 50 to 70 000 years for peak metamorphic temperatures of 1140 and 920 k respectively these durations are longer than what is commonly accepted for shock metamorphism and shorter than what is required for nuclide decay using the concept of a continuous cv ck metamorphic series which is reinforced by this study we estimated peak metamorphic temperatures 850 k for cv 850 920 k for ck3 and 920 1140 k for ck4 6 chondrites considering a duration of 70 000 years

diagenesis of the safaniya sandstone member mid cretaceous in saudi arabia abstract safaniya member of the mid cretaceous wasia formation was deposited as fluvio marine deltaic sediments in northeastern saudi arabia and the northwestern arabian gulf after its deposition and initial burial the mid cretaceous sequence was uplifted during late cretaceous structural movements structural traps in the region also started forming at this time but structural growth continued during the eocene and new structures developed during the plio pleistocene the diagenetic mineral assemblage in the safaniya sandstones includes kaolinite illite glauconite pyrite quartz and carbonate cements kaolinite and illite occur both as authigenic and detrital minerals authigenic kaolinite exists as skeletal and euhedral plates forming vermicules and aggregates of booklets infilling the pore spaces authigenic illite occurs as overgrowths of projecting laths quartz cement is present as syntaxial overgrowths and as microcrystalline quartz carbonates occur as patches and show replacement textures early diagenetic events include the formation of calcite siderite glauconite and pyrite at or close to the sediment water interface vermicular kaolinite and microcrystalline quartz probably formed by meteoric water diagenesis during the late cretaceous uplift quartz overgrowths and the bulk of the euhedral kaolinite may have formed during the late cretaceous early tertiary burial illite and ankerite were precipitated during deep burial probably from fluids expelled from the basinal kazhdumi shales to the east and northeast the precipitation of authigenic minerals in the clean quartz sandstones has reduced the primary interparticle porosity by an average of about 9 of the rocks because the clays occur mainly as pore filling cements their precipitation has caused only a small reduction in the permeability of these rocks

the seasonal variation of the intrusion of the philippine sea water into the south china sea the seasonal variation of the intrusion of the philippine sea water into the south china sea was studied by analyzing the historical hydrographic station data in the northern south china sea and the philippine sea water masses at 150 200 and 250 m were classified by discriminant analysis according to their temperature salinity characteristics at each depth most water in the study region was classified into two groups representing the philippine sea water and the south china sea water respectively the geographic distribution of water masses in the south china sea shows that the philippine sea water was present along the continental margin south of china between october and january a westward current in the northern south china sea in winter was inferred from the distribution of the intrusion water

geochemical evidence of the indirect pathway of terrestrial particulate material transport to the okinawa trough the major source of particulate matter in the east china sea ecs is the changjiang yangtze river sediment types the geochemical indices of terrigenous and biogenic inputs toc caco3 and sc and biomarker indices such as the carbon preference index cpi of long chain n alkanes and the cinnamyli vanillyl ratio c v in surface sediments all reveal that the influence of terrestrial material initially declines away from the mouth of the changjiang river across the ecs continental shelf however the influence then strengthens from the middle ecs shelf toward the continental slope and the okinawa trough because when the northeast winds prevail from september to april the changjiang river plume flows southwestward along the coast of china part of this flow turns eastward in the northern taiwan strait and then joins the northeastwardly flowing kuroshio to reach the okinawa trough as the central ecs is bypassed the sediments accumulated there are geologically older carbonate rich and organic poor than those found off the coast of china and in the okinawa trough

on the origin of the tsushima warm current the origin of the tsushima warm current referred to as twc was investigated by surface drifter experiments and conductivity temperature and depth ctd surveys in the northeastern east china sea ecs at three different times july 1991 and april and november 1992 trajectories of 10 satellite tracked drifters provide direct information for the first time on the surface flow patterns in each season and ctd observations allow identification of warm and saline twc waters the results of the experiments argue against two historical concepts of twc origins i e 1 a northward flow transporting warm and saline water through the deep trough southwest of kyushu toward the korea strait after separation from the kuroshio and 2 a northeastward continuation of the taiwan current tc on the shelf of ecs after passing through the taiwan strait a persistent northward current was found to exist both on the shelf west of the trough and on the western flank of the trough the northward flow seems to bifurcate around the northwestern corner of the trough splitting into a northward continuing flow on the shelf of 100 150 m and an eastward flow along the northern wall of the trough the northward flow on the shelf which might be the shore fringe of the kuroshio corresponds to the origin of twc entering the korea strait the eastward flow on the northern slope turned back to the south along the west coast of kyushu and eventually joined the kuroshio this structure was accompanied by an anticyclonic eddy in the northern trough the second concept that of twc originating from tc contradicts the observed differences in physical properties between twc and tc waters the saline water in the taiwan strait flows out intermittently only during late winter early spring and its salinity during other seasons is lower than that of the twc water in the korea strait experiments also indicated a seasonal shift of drifter paths in the northeastern ecs and coexistence of cyclonic and anticyclonic eddies in the trough during the cold season

diagenesis of sandstones at shale contacts and diagenetic heterogeneity frio formation texas diagenetic trends near sandstone shale contacts were studied in 12 cored sequences from four wells between depths of 5200 and 15 700 ft 1585 and 4785 m to evaluate the heterogeneity of diagenetic processes on a local scale and to evaluate the hypothesis that reactive aqueous fluids and components for cements in sandstones were derived from adjacent shales the only evidence suggesting that diagenetic components in sandstones were derived from immediately adjacent shales is an increase in chlorite cement in sandstones toward contacts with shale beds for two of three contacts appropriate for study secondary pores and cements of quartz carbonate and kaolinite do not correlate with proximity to shale beds but have a preference for sandstones that had relatively high ini ial porosities and permeabilities thus the flux of formation water and probably long distance transportation of diagenetic components were more important influences on reservoir quality of sandstones than was the local availability of components multiple regression of 22 independent variables indicates that the best predictors of secondary porosity are kaolinite cement and intergranular porosity sandstone sequences are extremely heterogeneous in the distribution of total thin section porosity secondary porosity and quartz and carbonate cements in addition they have significant variations in the abundance of kaolinite and chlorite cements mass balance calculations for silica and aluminum indicate silica was imported to and aluminum was exported from the sandstones

a model for diagenetic mass transfer between adjacent sandstone and shale abstract there are numerous suggestions that mass transfer between sandstone and shale is an important factor in the diagenesis of sandstone reservoirs however advective transport models for mass transport have not produced results that support these proposals a model is developed that overcomes the problems of advective transport models by assuming that diffusive mass transfer is the principle transport mechanism the process occurs when the rate of dissolution of reactive detrital components exceeds the local rate of diffusive transport at that point in the burial history units with greater amounts of a reactive component will generate more solute per unit time than units with less reactive component the process forms chemical gradients that can rapidly transfer mass equivalent to several vol of rock over distances of at least 5 m the observed transport of potassium and silica between adjacent sandstone and shale in the north sea during late stage illitization was correctly predicted using this conceptual approach the conceptual framework from the illite model can be extended to other diagenetic reactions and suggests that the burial of adjacent sandstone shale units could produce episodic diffusion gradients that transfer mass and form multiple generations of cement in sandstone reservoirs

diagenetic history of eocene wilcox sandstones south central texas abstract sandstones and shales of the lower eocene wilcox group extend from outcrop to depths greater than 5 km where temperatures exceed 200 c eight authigenic minerals have been identified quartz kaolinite calcite ankerite and albitized plagioclase are volumetrically significant whereas chlorite illite albite overgrowths and dolomite are present only in trace amounts quartz kaolinite and ankerite cements are present over the entire depth range sampled 1528 to 4446 m calcite cement occurs only in sandstones shallower than 3300 m albitized plagioclase is the predominant feldspar in samples deeper than 2600 m whereas detrital potassium feldspar has been completely dissolved out of sandstones deeper than about 3200 m no systematic variations in the chemical composition of calcite with depth no zoning within calcite or ankerite and no compositional differences between pore filling and grain replacing calcite or ankerite were found calcite cements have 87 sr 86 sr ratios generally less than 0 708 whereas ankerite cements are significantly enriched in 87sr the oxygen isotopic composition of carbonate cement ranges between 9 and 14 pdb for calcite and between 8 and 12 for ankerite with no systematic variation with depth calculated 18o values for authigenic quartz and kaolinite range from 22 to 31 smow and from 14 to 17 respectively volumetrically important amounts of authigenic quartz and kaolinite precipitated during early burial before calcite cementation secondary porosity generation or smectite to illite transformation in encasing shales the isotopic composition of strontium in calcite cement shows most of it to be of eocene or older marine carbonate origin ankerite cementation followed the generation of secondary porosity and occurred after the products of organic maturation and shale diagenesis plagioclase albitization or potassium feldspar dissolution significantly affected the sandstone pore water system

effect of a lower layer current on wind driven upwelling the conventional two layered alongshore independent wind driven upwelling model is extended to incorporate an initial subsurface current through the advective term involving cross stream shear under the condition that the thickness of the upper layer and the equilibrium displacement of the interface are both much smaller than the thickness of the second layer explicit solutions are obtainable for cases of exponential and parabolic profiles of the initial interface in the presence of the initial current in the lower layer the upwelling is reduced near the coast and increased offshore compared to a case without the initial current the modification is achieved through an abatement and an enhancement in divergence near the coast and offshore respectively as a result of the net effect from the continuity condition and the advection of the offshore velocity in terms of the cross stream shear the mechanism provides one of the possible explanations for an exceptionally wide cold water zone observed in an upwelling system influenced by an ambient large scale ocean current

characterizing surface circulation in the taiwan strait during ne monsoon from geostationary ocean color imager abstract the taiwan strait is the only channel connecting the south china sea scs and the east china sea ecs and plays a key role in the material exchanges between scs and ecs the region however is poorly sampled during the northeast ne monsoon when severe weather hinders shipboard measurements in this study the surface circulations in the taiwan strait and the adjacent east china sea are derived from the geostationary ocean color imager goci with a high spatiotemporal resolution the satellite observations are limited by cloud over nevertheless they provide the only surface flow observations useful in hypothesis testing it is demonstrated that the transient surface currents can be classified into three regimes a southwestward flow for strong winds a northeastward flow for weak winds and a cross strait flow for moderate winds the satellite observations are also valuable in validating model currents two high resolution global ocean reanalysis products the hybrid coordinate ocean model hycom and the copernicus marine environment monitoring service cmems are examined the reanalysis products are generally consistent with the satellite observations the cmems moreover shows a superior performance this study illustrates the unique capability of the geostationary ocean color satellite in providing spatially extensive surface flow observations in broad shelf regions where current meter data are sparse or non existent

multiple melting in a four layered barred olivine chondrule with compositionally heterogeneous glass from ll3 0 semarkona chondrule k7p from ll3 0 semarkona consists of four nested barred olivine bo chondrules the innermost bo chondrule chondrule 1 formed by complete melting of an olivine rich dustball after formation the chondrule was incorporated into another olivine rich dustball a second heating event caused this second dustball to melt the mesostasis and some of the olivine in chondrule 1 were probably also melted at this time but the chondrule 1 structure remained largely intact at this stage the object was an enveloping compound bo chondrule this two step process of melting and dustball enshrouding repeated two more times the different proportions of olivine and glass in chondrules 1 4 suggest that the individual precursor dustballs differed in the amounts of chondrule fragments they contained and the mineral proportions in those fragments the final dustball which ultimately formed chondrule 4 was somewhat more ferroan after melting crystallizing and quenching chondrule 4 contained olivine and glass with higher feo and mno contents than those of the earlier formed chondrules subsequent aqueous alteration on the ll parent body transformed the abundant metal blebs and stringers at the chondrule surface into carbide iron oxide and minor ni rich metal portions of the mesostasis underwent dissolution producing holes and adjacent blades of more resistant material much of the glass in the chondrule remained isotropic even after minor hydration and leaching the sharp moderately lobate boundary between the extensively altered mesostasis and the isotropic glass represents the reaction front beyond which there was little or no glass dissolution

the origin of authigenic ankerite from the ninian field uk north sea the carbonate minerals ankerite and ferroan dolomite are widely reported in studies of concretions1 2 and of sandstone hydrocarbon reservoirs3 8 these minerals are often thought to have formed relatively late in the sandstones diagenetic history and in the gulf coast their occurrence has been linked to clay mineral diagenesis in the surrounding shales9 i describe here authigenic ankerite from the ninian field10 ankerite formation was probably synchronous with hydrocarbon emplacement and is related to clay mineral diagenesis in the hydrocarbon source rocks of the viking graben it occurs throughout the reservoir sandstones but is particularly abundant below the oil water contact this distribution reflects hydrocarbon emplacement arresting diagenesis at progressively deeper levels of the reservoir the resulting preferential cementation may adversely affect transmissibility between the aquifer and the oil column and consequently could reduce hydrocarbon recovery

oxygen isotopes in chondrules and coarse grained chondrule rims from the allende meteorite abstract the oxygen isotopic compositions of porphyritic chondrules and coarse grained chondrule rims from the allende cv chondrite form a 16 o mixing trend situated near the carbonaceous chondrite anhydrous minerals ccam mixing line lying 0 1 0 7 higher in 17 o coarse grained rims are depleted in 16 o relative to their enclosed chondrules chondrules and rims exhibit significant correlations between their oxygen isotopic and chemical compositions objects rich in 16 o tend to have higher contents of refractory lithophiles and alkalies objects poor in 16 o tend to have higher contents of feo and volatile siderophiles cv chondrite matrix material is chemically and isotopically similar to some coarse grained chondrule rims previous work showed that o isotope data for cv barred olivine bo chondrules plot just below the terrestrial fractionation tf line near 18 o 4 well off the ccam line the allende data suggest that three solid precursor components are required to account for the o isotopic compositions of cv chondrules and rims 1 a high temperature refractory alkali and 16 o rich component perhaps near 18 o 40 17 o 42 relative to smow 2 a low temperature feo rich refractory and 16 o poor component lying near the ccam line perhaps near its intersection with the tf line at 18 o 10 and 3 an additional component required to explain the composition of bo chondrules

evidence for fractional condensation and reprocessing at high temperatures in ch chondrites we performed a detailed study of silica rich components src in the paired ch chondrites acfer 182 and 207 these srcs appear either as chondrules or fragments and they contribute 0 1 vol to the bulk meteorite they usually contain a silica and a silicate portion both portions are in most cases cryptocrystalline and have bulk sio2 concentrations between 65 and 85 wt the silicate generally has a pyroxene normative composition the silica often appears as blebs within the silicate matrix or vice versa if there are no blebs silica and silicate still form rounded interfaces the srcs are depleted in refractory elements like ca al and ti relative to ci a few src like objects are extremely rich in mn and show no depletion in refractory elements we conducted micro raman studies on the silica portions of the srcs to determine their structure and we identified several silica phases quartz cristobalite glass and a yet unidentified polymorph the silicate portion is glass when the silica is glass and crystalline when the silica is crystalline the low contents of al and ca make an igneous origin of the srcs very unlikely and the absence of metal excludes the formation by reduction of pyroxene we suggest instead a fractional condensation origin of the srcs from a si enriched gas after removal of gaseous mg by forsterite condensation additional evidence for fractional condensation is provided by a unique layered object with olivine in the core pyroxene and metal at the rim and silica at the outermost border these layers record the condensation sequence two chondrules were found with several percent of mn and high cr na and k contents providing further evidence for condensation from a fractionated gas the texture of the srcs and the occurrence of cristobalite and silica glass however require formation by liquid immiscibility at high temperatures above 1968 k and subsequent fast cooling therefore we propose a 2 stage model for the formation of srcs in ch chondrites 1 fractional condensation of forsterite enstatite and sio2 rich phases and 2 reheating of sio2 rich components to temperatures above 1968 k followed by rapid cooling all other phases identified in ch chondrites can be understood within the framework of this model thus the extremely unequilibrated ch chondrites provide a wealth of evidence for fractional condensation processes in the early solar nebula in metals meibom et al 1999 and in silicates

diagenetic mass transport in the southern san joaquin basin california u s a implications from the strontium isotopic composition of modern pore fluids abstract three types of chemically and isotopically distinct pore fluids from the southern san joaquin basin previously recognized by j b fisher and j r boles also have distinctive 87 sr 86 sr ratios and sr concentrations meteoric fluids have stable isotopic compositions which lie on or near the meteoric water line and low chlorinities sr concentrations are between 0 01 and 2 6 mg l 1 and 87 sr 86 sr ratios range from 0 7061 to 0 7078 diagenetically modified connate marine fluids have d and 18o values more positive than 35 and 0 respectively and have chlorinities generally comparable to seawater sr concentration are much higher than the meteoric group 16 198 mg l 1 although the 87 sr 86 sr ratios 0 7070 0 7081 are not distinctive mixed meteoric modified connate fluids have d 18o and chlorinity intermediate between the meteoric and modified connate groups sr concentrations are also intermediate between 16 and 22 mg l 1 but 87 sr 86 sr ratios 0 7080 0 7087 are generally more radiogenic than either the meteoric or modified connate groups all of the fluids have 87 sr 86 sr ratios comparable to or lower than tertiary seawater alteration of detrital plagioclase is the probable origin of the low isotopic ratios mass balance calculations based on the sr data suggest that essentially no transport of sr occurred during diagenesis of sandstones containing modified connate pore fluids while large amounts of sr have been transported out of meteoric reservoirs by fluid flow the chemically anomalous mixed meteoric modified connate fluids contain the most radiogenic strontium in the basin these fluids are spatially associated with major faults and may represent clay mineral dehydration waters which have been transported upward from greater depth these results suggest that the three types of fluids identified by fisher and boles represent three distinct mass transport regimes a largely stagnant deep basin system containing modified connate pore fluids an actively recharging meteoric system along the basin flanks and a third system restricted to the southern basin which may be characterized by largescale cross formational fluid flow rather than dilution by meteoric waters

modelling of thermal convection in sedimentary basins and its relevance to diagenetic reactions abstract mathematical calculations of thermal convection have been carried out using a porous three player model to simulate pore water flow in a sedimentary basin with layers of different permeabilities the calculated flow lines demonstrate that even very thin layers eg around salt domes and igneous or hydrothermal intrusions analyses of formation waters from sedimentary basins like the north sea often show evidence of a crude stratification of the pore water with respect to salinity and isotopic composition this is evidence suggesting that large scale convection or other types of mixing does not take place and positive salinity depth gradient may help to physically stabilize the formation water the fact that many of the shallow reservoir rocks from the north sea have formation water with low salinity and negative 18 o values suggest that this is modified meteoric water and that migration of petroleum from deeper parts of the basin occurred as a separate phase along restricted migration pathways and was not associated with a high flux of pore water in the absence of thermal convection the total pore water flux through sandstones will be rather small except locally where we may have focused compactional flow through small cross sections diagenetic reactions will therefore normally be relatively isochemical during deeper burial

a numerical study on the changjiang diluted water in the yellow and east china seas 1 a numerical simulation is performed using the princeton ocean model pom to investigate the behavior of the changjiang diluted water cdw and to evaluate the freshwater budget in the yellow and east china seas in addition the major process controlling the behavior of the cdw is discussed the simulated cdw distributions are fairly consistent with the observed distributions showing a remarkable seasonal variation the cdw extends to the northeast toward the tsushima korea straits during summer while it hugs the chinese coast to the southwest within a narrow band in winter tracer experiment is carried out to track the freshwater originating only from the changjiang and to evaluate the freshwater budget in the yellow and east china seas the result shows that about 68 percent of the changjiang discharge is transported through the tsushima korea straits and that about 27 percent is transported through the taiwan strait in autumn and winter to investigate the main process controlling the behavior of the cdw mentioned above another experiment is carried out without wind forcing it is found that the eastward extension of the cdw is strongly constrained by the taiwan tsushima warm current system over the shelf regime the wind is however responsible for the northeastward extension of the cdw in summer in addition the southwestward extension at the taiwan strait during winter is done by strong northeasterly monsoon the experiment without wind forcing shows that freshwater transport through the tsushima korea straits increases to 90 percent of the total changjiang discharge