paleomagnetic evidence for the paleoposition of sumba island indonesia abstract jurassic paleomagnetic directions have been obtained for the sedimentary rocks in sumba the mean direction is 59 2 in declination and 44 2 in inclination the reliability of the direction is ascertained through thermal demagnetization and the presence of normal and reversed polarities comparison with the permian paleomagnetic direction of timor indicates that sumba was subjected to a clockwise rotation through 79 4 relative to timor since the jurassic when sumba is restored by a counter clockwise rotation the sumba pole is gradually approaching the jurassic pole of australia as well as the timor permian pole this implies that at least until the jurassic sumba and timor were situated at the australian continental margin and that sumba rotated clockwise during or after the jurassic

importance of clay in iron transport and sediment reddening evidence from reduction features of the abo formation new mexico u s a abstract petrographic and geochemical data from reduction features in the abo formation permian of central new mexico provide insight into the source of iron for hematite precipitation in red beds reduction features in the abo formation include isolated reduction spots as well as zones of reduction associated with fractures and coarser grained beds the reduction features contain less iron and more copper than the host rock mean values in ppm host rock fe 6456 cu 9 reduced fe 3730 cu 113 hematite relics are present in reduced areas associated with fractures and reduced bedding but are absent in reduction spots hematite apparently never formed in the reduction spots because of localized reducing conditions present at the time of pervasive reddening reduced fractures and bedding most likely result from migration of reducing pore fluids flowing through more permeable areas and postdate hematite precipitation iron bearing sand and silt grains which are typically regarded to be the principal source of iron for hematite precipitation in red beds are uncommon average 1 in the abo formation where present these grains are not significantly altered in either red host rock or in the white reduction features therefore detrital iron bearing clay size material is the primary source of iron in the abo formation although compositionally variable the clay rich areas contain a mean of 8 4 feo total in the host rock and a mean of 4 6 feo total in reduction spots chemical and mineralogical data from clay rich areas suggest that ferric oxyhydroxides associated with the clays are a more important iron source than iron from the clay crystal structure low whole rock iron content of the abo formation relative to other red bed units is consistent with clay and associated ferric oxyhydroxides being the principal iron source the abo formation may represent a clay dominated end member in a continuum of red beds in which the iron needed for reddening is derived from clays and coarser iron bearing framework grains

a tectonostratigraphic framework for the mid norway region abstract the tectonostratigraphic analysis presented here aims to establish a broad stratigraphic framework within which the likely distribution of both reservoir and source rock intervals within the deep water voering and more basins can be evaluated in terms of hydrocarbon potential the devonian to triassic interval can be effectively discounted by its extreme depth of burial across most of the study area the middle jurassic is interpreted to provide a potential reservoir target in the gjallar ridge area the cretaceous is seismically mappable across the region and has been divided into five tectonostratigraphic sequences late cretaceous reservoirs are considered to offer targets in the nyk high area six tectonostratigraphic sequences are described within the cenozoic succession paleocene reservoirs are interpreted to offer targets over both the ytterskallen and ormen lange areas of the more basin source rock maturity is critical for exploration success mapping shows the late jurassic earliest cretaceous spekk formation to be overmature over most of the area though the presence of possible dhis indicates the probable presence of major gas accumulations in the region only on the western flank of the vigrid syncline does the spekk shallow sufficiently to lie within the potential oil window it is concluded that the region has the potential to become a significant new hydrocarbon province for the 21st century

influence of rotation on the metal rain in a hadean magma ocean 1 today it is widely accepted that during its early evolution the earth experienced a magma ocean that covered most of its surface the separation of metal from silicate was much facilitated in the environment of such a magma ocean the differentiation mechanism is known as the metal rain scenario our study will focus on the settling dynamics of these metal droplets because of the low viscosity of molten silicate and a higher rotation period of the earth at that time the rotation has a potentially strong influence on the dynamics of the magma ocean we use numerical 3d fluid simulations to analyze the combined effects of strong rotation and convection on the settling of the iron droplets we show that the influence of rotation on the settling depends on the latitude at the poles the influence of rotation is only marginal at the equator three different scenarios can be distinguished first at low rotation rates the particles form a dense layer at the bottom second for strong rotation the particles stay mostly suspended and layers form in the temperature field third at higher rotation rates the particles form a ribbon like structure in the middle of the box the influence of rotation on the iron droplets may lead to a scenario where part of the iron is kept in the mantle instead of transported to the core this would have a strong influence on the later states of the differentiation process and the amount of siderophile elements in the mantle

cementation and porosity evolution of tight sandstone reservoirs in the permian sulige gas field ordos basin central china abstract tight sandstone gas reservoirs constitute an important type of unconventional gas resources and may be of crucial significance as environment friendly source of energy in the world however the dynamics of densification and evolution of the low porosity and low permeability sandstone reservoirs are intensively debated in literature recently the question of sequence of reservoir densification and hydrocarbon accumulation has arisen a typical tight sandstone reservoir the first member of the shanxi formation and the eighth member of shihezi formation in the permian sulige gas field in central china provides an excellent case study to probe these questions by using a variety of different methodologies such as scanning electron microscopy sem x ray diffraction xrd cathodoluminescence fluid inclusion analysis and confocal raman spectrometer analysis we identified different authigenic minerals such as illite kaolinite dickite chlorite and smectite illitization coexisting with siliceous and calcitic cements these authigenic minerals precipitated at different diagenetic stages related to the changing conditions during compaction and lithification and therefore changed the porosities of the host rocks during each of these stages the types of pores in the sulige gas field are dominated by illite and kaolinite intercrystalline pores matrix solution pores and primary intergranular pores the results of this study suggest that compaction and cementation are the reasons for the most distinct loss in porosity on the other hand kaolinite and illite preserve their intercrystalline pores which could be identified as the main reserve space of the tight gas reservoirs therefore the secondary porosity of the sandstone reservoirs forms the most important contributor to the gas reservoir potential in the sulige gas field in addition it could be inferred that the tight gas accumulation took place during the densification of the reservoirs the implications of the presented results may also help to understand the formation of other tight reservoirs world wide

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

reservoir quality controls on rotliegend fluvio aeolian wells in germany and the netherlands southern permian basin impact of grain coatings and cements abstract reservoir quality in sandstones can be a function of temperature pressure and chemical alterations over time some intrinsic properties of sandstones can additionally impact the evolution of reservoir quality the detrital composition depositional environment and properties controlled thereby dictate some of the diagenetic changes extrinsic processes like external fluids e g from hydrothermal events or dewatering of clay minerals can additionally result in changes of reservoir quality one of these properties are grain coatings on quartz grains which can strongly affect pore cementation by quartz overgrowths to predict and infer the quality of undrilled reservoirs constraints are needed to predict their occurrence we analyse two reservoir settings in the southern permian basin and delineate the impact of depositional systems lithologies detrital and authigenic composition on reservoir quality and with regard to grain coatings results highlight the importance of diagenetic alterations and the source area in regards to burial development in different parts of the southern permian basin samples from the rotliegend bahnsen sandstone member from germany and the slochteren sandstone formation from the netherlands have been petrographically and petrophysically analysed and linked to depositional environments our data shows that the emplacement and presence of grain coating minerals cannot be simply linked to the depositional environment or processes controlled thereby e g grain size and sorting neither on a reservoir nor on a basin scale the dissolution of alumosilicates additionally has no consistent impact on the authigenesis of chloritic grain coatings on the reservoir or basin scale in this study this implies the necessity of sample specific analyses and importance of the assessment of diagenetic alterations when analysing modelling or predicting reservoir quality in similar settings worldwide

facies related diagenesis and multiphase siderite cementation and dissolution in the reservoir sandstones of the khatatba formation egypt s western desert in the fluvio deltaic quartz arenitic sandstones of the jurassic khatatba formation in the salam field egypt9s western desert diagenesis and sedimentary facies control reservoir quality fluvial channel sandstones have the highest porosities 10 15 and permeabilities 100 600 md in part because of siderite cementation which 1 inhibited compaction and quartz cement and 2 was later dissolved creating intergranular secondary porosity 1 4 of total porosity fluvial crevasse splay and marine sandstones have the lowest reservoir quality because of an abundance of depositional kaolin matrix and pervasive shallow burial fe dolomite cement respectively siderite precipitation was multiphase and separated by distinct dissolution events the earliest siderite precipitated near surface within suboxic tropical coastal swamps containing predominantly meteoric waters some influence of marine waters is indicated by local enrichments in mg and ca the next major siderite generation shows a trend to decreasing mn and ca contents and is of shallow burial origin the last major siderite phase is mg rich and interpreted as deeper burial in origin some dissolution occurred during shallow burial related to climatically controlled meteoric water fluxing under unconformities the most important dissolution however occurred during deep burial resulting in 1 a major corrosion surface predating the last mg rich zone 2 selective dissolution of some earlier zones and 3 secondary porosity this burial dissolution is interpreted to have been caused by cooling of compactional waters expelled from the basin along major faults other diagenetic phases observed include early diagenetic pyrite kaolin quartz bitumen and late diagenetic barite and illite kaolinite precipitated at shallow depths 130 c during and or after rapid late cretaceous burial quartz developed in two phases separated by oil migration this paper illustrates that in fluvio deltaic quartz arenites deposited under the influence of humid tropical climate reservoir quality can be largely controlled by the contrasting pathways of carbonate diagenesis followed by the different sedimentary facies this paper also documents a case in which siderite dissolution generated significant secondary porosity in reservoir sandstones and where both siderite cementation and dissolution took place in multiple phases during different diagenetic stages including early shallow burial and deep burial diagenesis the present study also shows that in multiphase siderite cements the earlier growth zones can be selectively dissolved and replaced by later siderite zones i e recrystallized during burial diagenesis these findings contrast with the general thought that siderite cements are not susceptible to generation of significant secondary porosity by dissolution and that earlier formed siderites are essentially stable during diagenesis

sedimentary heterogeneity and petrophysical characterization of barremian tsunami and barrier island inlet deposits the aliaga outcrop as a reservoir analogue galve sub basin eastern spain abstract the present study examined two sandstone deposits in the aliaga outcrop as a reservoir analogue over a distance of 200 m long and attempted to establish a correlation between sand facies and the petrophysical properties of the sandstones in order to investigate the reservoir heterogeneity the aliaga reservoir analogue represents the upper part of camarillas fm deposited during the barremian synrift phase of the galve sub basin iberian basin spain it is characterized by a transitional sedimentary interval from sandy dominant deposits to carbonate dominant deposits which were deposited under the same palaeoenvironmental conditions in relation to systems of back barrier sedimentation the description of the aliaga outcrop provided here consists of lithological descriptions of two sandstone deposits a tsunami and a barrier island inlet at both mesoscopic decimetres to tens of metres and microscopic scales millimetres to centimetres both deposits recognized at the basin scale were described in terms of sand grain size sand sorting and cementation further cores were drilled along outcrop to collect samples for porosity and permeability measurements both sandstone reservoirs are the result of different sedimentary processes that determined facies characteristics as the different petrophysical properties observed in these deposits consequently the sedimentary process controls the heterogeneity of the sandstones facies and thus the sand heterogeneity controls the distribution of the petrophysical properties the classification of sand facies in terms of sand sorting seems to be more appropriate for describing sand heterogeneity accordingly petrophysical parameters in both deposits were also influenced by sand sorting the sand facies and petrophysics heterogeneity of the described deposits can be hierarchically ordered first order heterogeneity is related to the basin scale second order heterogeneity is related to genesis and the conditions of sediment deposition and third order heterogeneity is related to synsedimentary faults and or post sedimentation events

impact of sequence stratigraphy depositional facies diagenesis and co2 charge on reservoir quality of the lower cretaceous quantou formation southern songliao basin china abstract the fourth member of the lower cretaceous quantou formation in southern fuxin uplift zone of the southern songliao basin is typical tight oil reservoir which has recently been explored and produced for effective exploration and development the evaluation and control factors of the reservoir quality of the k1q4 sandstones should be thoroughly studied the study focused on the control of the combination of sequence stratigraphy depositional facies and diagenesis on the reservoir quality and identified the impact of co2 charging based on the core and thin section observation xrd sem fluid inclusion and isotope testing and analysis the fourth member of the lower cretaceous quantou formation consists of lowstand system tracts lst transgressive system tracts tst and highstand system tracts hst the k1q4 sandstones were mostly deposited in distributary channels and crevasse splays of a delta plain within the lst and tst and underwater distributary channels and sheet sands of a delta front within the hst the k1q4 sandstones mostly silt to medium grained medium to well sorted and are mostly lithic arkoses and feldspathic litharenites have undergone significantly diagenetic alterations such as compaction quartz cementation unstable grains feldspar and volcanic fragments dissolution carbonate cementation and clay minerals cementation the reservoir quality of the k1q4 sandstones are poor with low porosity and permeability showing variations among the different system tracts and depositional facies and are influenced by the charging of co2 and controlled by the combination of sequence stratigraphy depositional facies and diagenesis the sandstones with high reservoir quality are mostly deposited in high energy environments including the underwater distributary channel sandstones especially the lst distributary channel sandstones with the best reservoir quality among the lst tst and hst sandstones which can be ascribed to larger grain size and better sorting resulting in larger intergranular pore space after compaction and less content of carbonate cements illite and mixed layer i s and more pore lining chlorite and more effectively dissolution the poor reservoir quality of sandstones from crevasse splay and sheet sand is due to the small grain size and bad sorting which resulted in extensive compaction and the resulting weak dissolution the charging of co2 has dual impact on the reservoir quality of the k1q4 sandstones the co2 charging can induce the dissolution of unstable detrital grains and the precipitation of dawsonite the former create new secondary pore space while the latter occupy the intergranular pore space the co2 charging is harmful to the reservoir quality when the dawsonite content exceeds a threshold of 5

connectivity of molten fe alloy in peridotite based on in situ electrical conductivity measurements implications for core formation in terrestrial planets abstract the connectivity of molten fe s in peridotite has been experimentally investigated by means of in situ electrical conductivity measurements at high temperatures and 1 gpa starting materials were powdered mixtures of peridotite klb 1 with various amounts 0 3 6 13 19 24 vol of the 1 gpa eutectic composition in the fe fes binary system at temperatures above the eutectic point in the fe fes system 980 c and below the solidus of klb1 1200 c molten fe s in a solid silicate matrix interconnects when the volume fraction is over 5 conductivity temperature paths indicate that in the presence of partial silicate melting the connectivity of molten fe s in a peridotite matrix is inhibited based on observations of retrieved samples the percolation threshold of fe s melts in the presence of low to moderate degrees of silicate melt is estimated at 13 2 vol these results indicate that if the volume fraction of fe alloy in a planetesimal was initially greater than 5 and if early heating by decay of radionuclides raised the temperature of the interior above the fe alloy melting point initial metal segregation was controlled by permeable flow of molten iron alloy in a solid silicate matrix these conditions were likely met by many terrestrial objects in the early solar nebula efficient removal of residual fe alloy 5 vol from silicate requires high degree melting of silicate so that metal can segregate as droplets giant impacts during the final stage of accretion of large planetary objects could supply the energy required for high degrees of melting alternatively if initial metal segregation were delayed until a planetary object grew to large size 1000 km in diameter release of gravitational potential energy due to metal segregation could contribute enough heat to form a magma ocean

magmatism in western indonesia the trapping of the sumba block and the gateways to the east of sundaland abstract the western sulawesi magmatic belt and the sunda banda arc define the eastern and south eastern margins of sundaland which is part of the relatively stable eurasian plate the eastern margin is bounded by the makassar strait which separates western sulawesi from kalimantan the initial opening of the makassar strait took place in the late cretaceous early tertiary leading to the opening of the pacific indian ocean gateway during neogene time recent studies indicate similarities in the late cretaceous paleogene stratigraphic sequence and calc alkali magmatism between sumba south sulawesi and south east kalimantan suggesting a sundaland origin for all of these areas the southward migration of sumba to the present frontal arc position of the sunda banda arc has occurred since late cretaceous paleocene time

slumping and sliding in miocene and recent developing arc basins onshore and offshore sumba indonesia abstract neogene slidemasses in eastern sumba are discussed and compared to neogene and quaternary analogues in seismic profiles from the offshore lombok and savu basins the onshore examples were deposited in deep marine base of slope environments within the reach of large amounts of clastics derived from a volcanic arc i e in a setting comparable to that of the recent slides onshore three types of slides are distinguished ranging from mud clast rich debris flows type 1 their possible seismic origin is discussed elongate lenticular slumps type 2 to over 100 m thick slide masses of intimately mixed and folded strata together with rafts of less deformed sediments type 3 the offshore analogues may be twice as thick both in the field and in the seismic profiles such slides are found at various superimposed levels five superimposed units can be distinguished in a seismic profile in the savu basin near the westernmost extension of the offshore sumba ridge a giant blocky slide occurs all slide masses are located on slopes with increasing gradients due to differential vertical movements tectonically induced oversteepening is therefore considered a main cause of failure in outcrops the upper surfaces of the slides are almost flat this contrasts with a hummocky topography seen in some of the offshore examples

coupled core mantle thermal evolution of early mars 1 several arguments point out that at the end of planetary accretion the core of mars was likely to be much hotter than its mantle resulting in the formation of a completely or partially molten thermal boundary layer at the base of the mantle here we address the following questions how did the superheated core cool and what role did it play in the early mantle dynamics of mars we divide the coupled core mantle evolution of early mars into two stages during the first stage vigorous convection within the molten boundary layer removes the heat from the core so that the boundary layer expands up as the boundary layer gets thicker the temperature of the layer decreases eventually the temperature of the molten boundary layer drops down to the temperature for the rheological transition melt fraction 40 within 100 years this stage is described by a parameterized convection approach the second stage is modeled in spherical shell geometry using the fully three dimensional finite element code citcoms a single plume superplume forms by the instability of the thermal boundary layer the superplume stage lasts much longer on the scale of millions to hundreds of millions of years depending on the mantle viscosity during both stages of evolution the heat flux can easily satisfy the requirements for the dynamo

magnitude and timing of peat to coal compaction the peat to coal transition is commonly assumed to be accompanied by compaction that decreases the thickness of the organic deposit to values of 10 or less of the original peat thickness decompaction modeling using such values for coal seams in contact with penecontemporaneous channel sandstones leads to impossible depositional geometries for the sandstones which have a final thickness that is 90 of their original thickness similarly decompaction modeling of the fragments of organic material within channel lags using the assumed large peat compaction value results in the destruction of the associated sedimentary structures such as trough cross beds dinosaur tracks in the roofs of coal mines show a shallow depth of penetration and a preservation of foot morphology that is not possible unless the peat the animals walked upon was very firm these data confirm the macroscopic observations from coal balls that the compaction associated with the peat to coal transformation is minimal equally important the data also show that most of the compaction occurs essentially at the surface and not at the depths where coalification takes place

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

the role of fluid pressure and diagenetic cements for porosity preservation in triassic fluvial reservoirs of the central graben north sea anomalously high porosities and permeabilities are commonly found in the fluvial channel sandstone facies of the triassic skagerrak formation in the central north sea at burial depths greater than 3200 m 10 499 ft from which hydrocarbons are currently being produced the aim of our study was to improve understanding of sandstone diagenesis in the skagerrak formation to help predict whether the facies with high porosity may be found at even greater depths the skagerrak sandstones comprise fine to medium grained arkosic to lithic arkosic arenites we have used scanning electron microscopy petrographic analysis pressure history modeling and core analysis to assess the timing of growth and origin of mineral cements with generation and the impact of high fluid pressure on reservoir quality our interpretation is that the anomalously high porosities in the skagerrak sandstones were maintained by a history of overpressure generation and maintenance from the late triassic onward in combination with early microquartz cementation and subsequent precipitation of robust chlorite grain coats increasing salinity of pore fluids during burial diagenesis led to pore filling halite cements in sustained phreatic conditions the halite pore filling cements removed most of the remaining porosity and limited the precipitation of other diagenetic phases fluid flow associated with the migration of hydrocarbons during the neogene is inferred to have dissolved the halite locally dissolution of halite cements in the channel sands has given rise to megapores and porosities of as much as 35 at current production depths

neogene basin history and paleomagnetism of a rifted and inverted forearc region on and offshore sumba eastern indonesia the island of sumba is located in the arc trench gap at the junction of the sunda and banda arcs to elucidate its enigmatic forearc position stratigraphic and paleomagnetic data were collected along three transects in central and east sumba sumba represents the emerged part of a terrane of se asian origin results of stratigraphic and paleomagnetic investigations on central and east sumba are presented and discussed in order to identify patterns of horizontal and vertical crustal movements a synthetic seismogram of the onshore record enables correlation with the offshore neogene e of sumba in order to interpret the data in a regional context the neogene basin history of sumba started when overall subsidence took place around the transition from early to middle miocene on east sumba above a basal condensed interval up to 600 m of middle late miocene volcaniclastic submarine fan deposits occur the sediments reflect island arc volcanism and are interpreted as parts of a prograding submarine fan system on a north dipping paleoslope fed by a volcanic source to the south of sumba biostratigraphic data indicate a high volcanic supply during the middle miocene and early middle tortonian a waning supply during the late tortonian and renewed supply during the messinian these patterns probably reflect variation in volcanic activity during the messinian calcilutites and foraminiferal chalks became dominant and deposition of these pelagic sediments continued into the early pliocene using the pattern of magnetic polarity changes in a selected interval the position of the mioceneepliocene boundary is better constrained seismic studies in the offshore area e of sumba van der werff 1995a b indicate the presence of an extensive tract of n prograding turbidites on sumba ridge savu basin the proposed correlation with the onshore record suggests lateral continuity from the island into the offshore area where the volcaniclastic submarine fan system presumably had its largest development subsidence proceeded so fast i m ka on east sumba that before the beginning of the late miocene sediments were deposited below the ccd this pattern suggests that the sumba region underwent strong crustal attenuation due to rifting as this was coupled with the arrival of volcaniclastics we envisage intra arc rifting coupled with the growth of a short lived volcanic arc further south its initiation at the transition of middle late miocene suggests interaction with the then approaching banda arc subduction system the paleomagnetic data indicate that during this process sumba was at a paleolatitude of 12 south and underwent a counter clockw ise rotation of 5 the reappearance of planktonic foraminiferal assemblages during the latest miocene and their present elevation above sea level suggest an average rate of post miocene uplift of 0 7 mm a emergence of sumba probably did not take place before 3 ma this inverted motion of the sumba terrane is probably coupled with the change to the present tectonic situation in which volcanic activity was resumed in the present inner arc after a non volcanic interval during the spreading stage 1 1997 elsevier science ltd

quantitative integration of 3d and 4d seismic impedance into reservoir simulation model updating in the norne field the ultimate goal of reservoir simulation in reservoir surveillance technology is to estimate long term production forecasting and to plan development and management of petroleum fields however maintaining reliable reservoir models which honour available static and dynamic data involve inherent risks due to the uncertainties in space and time of the distribution of hydrocarbons inside reservoirs recent applications have shown that these uncertainties can be reduced by quantitative integration of seismic data into the reservoir modelling workflows to identify which areas and reservoir attributes of the model should be updated this work aims using seismic data to reduce ambiguity in calibrating reservoir flow simulation model with an uncertain petro elastic model proposing a circular workflow of inverted seismic impedance 3d and 4d and engineering studies with emphasis on the interface between static and dynamic models the main contribution is to develop an updating procedure for adjusting reservoir simulation response before using it in the production forecasting and enhance the interpretive capability of reservoir properties accordingly the workflow evaluates consistency of reservoir simulation model and inverted seismic impedance assisted by production history data to close the loop between reservoir engineering and seismic domains the methodology is evaluated in a complex faulted sandstone reservoir the norne benchmark field where a significant reservoir behaviour understanding about the static and dynamic reservoir properties is obtained towards the quantitative integration of seismic impedance data this leads to diagnosis of the reservoir flow simulation reliability and generation of an updated simulation model consistent with observed seismic and well production history data as well as a calibrated petro elastic model furthermore as norne field is a benchmark case this study can be considered to enrich the discussions over deterministic or probabilistic history matching studies

dynamics of core formation and equilibration by negative diapirism 1 we investigate dynamically the timing and metal silicate equilibration processes during core formation by negative diapirism using numerical modeling in 3 d axisymmetric geometry we follow the sinking of iron rich diapirs through a viscous silicate mantle we carried out a parameter study in which shear heating as well as several viscous rheologies are considered and systematically varied general scaling laws are derived for the diapir sinking velocity as well as for the silicate melt generation and distribution around the diapir using these scaling laws we show that metal diapirs of a radius 1 100 m sinking through a partially molten silicate mantle can chemically equilibrate within the timescales suggested by geochemical constraints therefore negative diapirism can contribute significantly to metal silicate equilibration processes during core formation

turbulent mixing of metal and silicate during planet accretion and interpretation of the hf w chronometer in the current view of planet formation the final assembly of the earth involved giant collisions between proto planets 1000 km radius with the moon formed as a result of one such impact at this stage the colliding bodies had likely differentiated into a metallic core surrounded by a silicate mantle during the moon forming impact nearly all metal sank into the earth s core we investigate to what extent large self gravitating iron cores can mix with surrounding silicate and how this influences the short lived chronometer hf w used to infer the age of the moon we present fluid dynamical models of turbulent mixing in fully liquid systems attempting to place constraints on the degree of mixing erosion of sinking cores driven by rayleigh taylor instability does lead to intimate mixing and equilibration but large blobs 10 km diameter do not emulsify entirely emulsification is enhanced if most of the accreting metal cores deform into thin structures during descent through the earth s mantle yet only 1 20 of earth s core would equilibrate with silicate during earth s accretion the initial speed of the impactor is of little importance we proceed to evaluate the mixing potential for shear instabilities where silicate entrainment across vertical walls causes mixing the turbulent structure indicates that vortices remain at the largest scale and do not mix to centimeter length scale where diffusion operates and isotopes can equilibrate thus incomplete emulsification and equilibration of accreting iron cores is likely to occur the extent of metal silicate equilibration provides key information for interpretation of siderophile budgets and the timing of core formation using the hf w chronometer the time scale of core formation derived from the hf w chronometer is usually tied to the last major metal silicate re equilibration believed to coincide with time of the moon forming impact however we show that large cores have limited ability to reset the hf w system in the silicate earth excess 182 w in bulk silicate earth is more sensitive to early core formation processes than to radiogenic ingrowth after the last giant impact

factors controlling reservoir properties and hydrocarbon accumulation of the eocene lacustrine beach bar sandstones in the dongying depression bohai bay basin china abstract lacustrine beach bar sandstone reservoirs are economical important exploration targets in the dongying depression bohai bay basin the factors that controls reservoir quality and hydrocarbon accumulation in lacustrine beach bar sandstones were systematically investigated through an integrated petrographic petrophysical and diagenesis analysis the reservoir properties of the beach bar sandstones are mainly affected by compaction carbonate cementation and dissolution significant negative relationships exist between both the porosity and permeability and the volume of carbonate cement carbonate cement is mainly distributed along the sandstone mudstone contacts sandstones with thicknesses less than 1 m are generally tightly cemented to form zones with low petrophysical properties the material source of the carbonate cement in the tightly cemented zone was highly likely from the interbedded mudstone content of carbonate cements in the center of the thick sandstones is low whereas compaction is the dominant diagenetic process with some dissolution there is a positive correlation between the petrophysical properties of the beach bar sandstones and the content of kaolinite the petrophysical properties have an inverse correlation with the contents of illite and illite smectite mixed layer clays reservoir petrophysical property largely controls hydrocarbon accumulation in the beach bar sandstones compared with non oil bearing sandstones oil bearing sandstones have higher porosity and a larger pore throat size sandstones with a porosity of less than 8 5 and or low permeability of less than 1 02 10 3 m2 are mostly incapable of accumulating oil

compaction behavior of argillaceous sediments as function of diagenesis the paper presents the results of laboratory compaction tests on samples of kimmeridge clay taken from two different locations in the uk the main objective of the laboratory tests is to determine how diagenesis affects the hydro mechanical properties and compaction behavior of argillaceous sediments the two kimmeridge clays used in the tests are essentially from the same parent material but have undergone different degrees of mechanical and chemical diagenesis the laboratory tests are designed to determine the effects of mechanical loading and chemical processes on changes in porosity permeability compressibility strength and effective horizontal stress in argillaceous materials another objective of the study is to investigate the adequacy of soil mechanical constitutive models in predicting the response of argillaceous materials to conditions corresponding to burial depths in sedimentary basins the tests on kimmeridge clay are carried out to as high as 150 mpa effective vertical stress corresponding to about 9 km in burial the results indicate that mechanical compaction and burial depth cannot explain the differences in the hydro mechanical behavior of the tested materials the differences in hydro mechanical response are attributed to chemical diagenesis by precipitation of minerals in the pores of the sediment other observed effects of chemical diagenesis on hydro mechanical behavior of lithified sediments are 1 increase in apparent pre consolidation stress 2 decrease in compressibility 3 decrease in permeability and 4 decrease in effective horizontal stress implications of the results to fluid flow and overpressure development in sedimentary basins are discussed

history of quartz cementation in the lower cretaceous travis peak formation east texas abstract quartz is the most abundant authigenic mineral in sandstones of the travis peak formation in east texas but the extent of quartz cementation varies widely to determine major controls on quartz cement distribution this study used 431 thin sections from 1 100 m of core from 26 wells volume of detrital clay matrix is the main textural control on quartz cement in sandstones lacking detrital clay no significant correlation exists between quartz cement and grain size sorting bed thickness or sedimentary structure depositional facies was an indirect control on quartz cement distribution because facies controlled detrital matrix content but no significant difference exists between average quartz cement volume in matrix free paralic 16 7 and matrix free fluvial 17 1 sandstones quartz cement increases significantly with present depth from an average of 14 6 at 1 825 m to 20 0 at 3 050 m this trend of increasing quartz cement is interpreted to be the result of 1 an early episode of quartz cementation by meteoric water that resulted in relatively uniform distribution of quartz within the formation and 2 a later episode related to the development of stylolites that preferentially added quartz cement in the deepest sandstones approximately 10 to 20 of the authigenic silica in travis peak sandstones was derived internally from intergranular pressure solution and stylolitization the remaining 80 was imported from unknown sources outside the sandstones

the geology of heidrun a giant oil and gas field on the mid norwegian shelf the heidrum field is located in the haltenbanken region on the mid norwegian continental shelf 165 mi from shore in water depths of approximately 1 150 ft the field is a giant cimmerian structure with hydrocarbons trapped in jurassic sandstone reservoirs the field has 750 mm bbl recoverable oil reserves with associated gas reserves of 0 45 tcf and free gas reserves of 1 3 tcf the accumulation extends over 14 4 mi and was unitized in 1989 with 75 of the field in block 6507 7 and 25 of the field in block 6507 8 the 6507 7 block was acquired by conoco norway and partners in 1984 in the eighth round of licenses offered by the norwegian government the acquisition was based on extensive in house exploration regional studies which identified a jurassic rift element in haltenbanken and the potential for the generation of liquid hydrocarbons the heidrun structure is a large southwesterly plunging horst block on the southwestern flank of the nordland ridge and was formed during the cimmerian extensional tectonic phase in the late jurassic early cretaceous the heidrun reservoirs are severely truncated at the northern edge of the structure and are sealed by cretaceous shales the heidrun jurassic reservoir rock the fangst group and themore tilje and are formations were deposited on the southeastern flank of the developing northeastern atlantic rift domain the shallow burial depth 8 100 ft has limited compaction effects and reservoir quality therefore is enhanced with permeabilities up to 10 d and porosities in excess of 30 in the cleaner sands of the fangst the primary sources for the petroleum is the upper jurassic spekk formation which is mature in the downdip areas 3 10 mi southwest and west of heidrun therefore fairly long petroleum migration paths are inferred a 5 000 km high resolution three dimensional seismic survey was acquired in 1986 the three dimensional data set forms the basis for detailed geologic and reservoir models less

quaternary raised coral reef terraces on sumba island indonesia a spectacular sequence of coral reef terraces six steps broader than 500 meters and many minor substeps is developed near cape laundi sumba island between an ancient patch reef 475 meters high and sea level several raised reefs have been dated with the electron spin resonance and the uranium series dating methods the uplift trend deduced from these reefs is 0 5 millimeter per year most terraces although polycyclic in origin appear to correspond to specific interglacial stages with the oldest terrace formed 1 million years ago this puts them among the longest and most complete mid quaternary terrace sequences

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

collision rotation and the initiation of subduction in the evolution of sulawesi indonesia the island of sulawesi indonesia has been shaped and deformed as a result of collision with the sula platform a sliver of continental material from the northern margin of australia new guinea the collision has resulted in rotation of the north volcanic arm of sulawesi and the development of the accretionary wedge of the north sulawesi trench the north sulawesi trench changes laterally from a zone of no active deformation in the eastern part to a wide accretionary wedge in the west early stages of thrusting produce a steep frontal slope 8 16 indicative of relatively high basal shear stress whereas the more advanced western zone of thrusting produces a gentle 2 slope consistent with low basal shear stress reported paleomagnetic data suggest post late eocene counter clockwise rotation of the north arm and the offshore geophysics are explained by a pivot of the north arm with respect to the celebes basin about the eastern end of the arc convergence between the north banda basin and southeast sulawesi is documented by the presence of the tolo thrust its outcrop is strongly arcuate and its accretionary wedge varies in width from a minimum of a few kilometers at each end to a maximum of 30 40 km in the central part the northern end transforms to the leftlateral matano fault with a reported offset of 20 km the southern end of the thrust projects toward the deformed rocks of buton but the structural relations there are not clear the matano fault zone appears to connect westward with the palu fault which forms the western transform of the north sulawesi trench the palu matano fault system acts as a trench trench transform between the north sulawesi trench and the tolo thrust and this system is described by the same rotation pole as that for the sulawesi north arm

dynamics of metal silicate separation in a terrestrial magma ocean in a terrestrial magma ocean the metal silicate separation involved small metal droplets our goal is to better understand the dynamics of the metal droplet scenario the mechanism of sedimentation in a vigorously convecting and strongly rotating magma ocean may differ significantly from settling droplets in a still fluid in order to systematically study the parameter dependence on the style of motion we utilize two dimensional and three dimensional numerical convection models combined with a tracer based sedimentation method we investigate the characteristic flow patterns resulting from the competing effects of convection and droplet settling and find three styles of motion a temperature dominated style where most droplets remain suspended a droplet dominated style where the droplets separate from the fluid and a style of repetitive motion we find that the droplet dominated style is relevant to the magma ocean in this scenario the droplets settle and form a dense bottom layer one of the key findings of this work is that the formation of the dense bottom layer and therefore the separation of metal droplets from the liquid silicate occurs on a characteristic timescale which is identical with the stokes settling time finally we study the chemical interaction of settling metal droplets and liquid silicate and discuss how accurately a simple parameterized model can describe the chemical equilibration in the metal rain scenario of a terrestrial magma ocean we find agreement between the parameterized model and our two dimensional model our simulations which include thermal convection into the metal rain model confirm the fundamental observation that metal droplets are not permanently suspended in the convecting silicate melt but that they sink and rapidly form a dense layer at the base of the magma ocean

a multi phase model of runaway core mantle segregation in planetary embryos abstract a classic scenario of core formation suggests that growing proto planets are heated by the impacts of accreting planetesimals at their surface until their shallow layers reach the melting temperature of their metallic components or even of the silicates in this partially molten shell metal and silicates differentiate and the metallic phase ponds on top of the still undifferentiated inner planet later a gravitational instability brings dense metallic diapirs to the center of the planet we test this multi phase scenario by using a formalism that self consistently accounts for the presence of solid silicates solid and liquid iron at each point of the mixture an average velocity and a separation velocity of the solid and liquid phases are defined the energy balance accounts from the changes in potential energy associated with the segregation we show that core formation starts before a significant melting of the silicates as soon as impact heating is large enough to reach the melting temperature of the metallic component segregation proceeds in a few thousand years by a runaway process due to the conversion of gravitational energy into heat that occurs necessarily in all undifferentiated embryos of moon to mars sizes the first metallic diapirs leave behind them a trailing conduit along which most of the further melting occurs the cores of large planets do not form at the end of accretion but must result from the merging of the already differentiated hot cores of embryos

melt flow in a variable viscosity matrix it is often assumed that the molten regions of planetary interiors can be modeled as a compacting viscous matrix permeated by a less viscous melt phase in order to assess the true behaviour it is important to test as many different aspects of these models as possible in the calculations presented here the matrix viscosity is made to decrease as the proportion of melt increases new results in two dimensions show that if only gravity drives the flow pockets of melt travel upwards as solitary waves and the behaviour is similar to the well known constant viscosity case however when an external shear strain is applied an instability occurs and melt flows into elongated pockets or veins perpendicular to the least compressive stress whilst veins much greater than a compaction length in width are suppressed their minimum width is not clearly constrained the growth rate of veins is directly proportional to the applied strain rate so that their degree of development is proportional to the total strain it is suggested that under mid ocean ridges the total strain may be enough for such veins to be important

a late triassic lake system in east greenland facies depositional cycles and palaeoclimate abstract the upper triassic fleming fjord formation of the jameson land basin in east greenland contains a well exposed succession 200 300 m thick of lake deposits the malmros klint member 100 130 m thick is composed of cyclically bedded intraformational conglomerates red siltstones and fine grained sandstones and disrupted dolomitic sediments paleosols the cyclicity is composite with cycles having mean thicknesses of 25 5 9 and 1 6 m the overlying carlsberg fjord beds of the orsted dal member 80 115 m thick are composed of structureless red mudstones rhythmically broken by thin greyish siltstones this unit also has a composite cyclicity with cycles having mean thicknesses of 5 0 and 1 0 m the uppermost tait bjerg beds of the orsted dal member 50 65 m thick can be divided into two units a lower unit is composed of cyclically bedded intraformational conglomerates or thin sandstones red mudstones greenish mudstones and yellowish marlstones an upper unit is composed of relatively simple cycles of grey mudstones and yellowish marlstones recognized cycles have mean thicknesses of 5 6 and 1 6 m the lake deposits contain evidence of seasonal orbital and long term climatic change seasonal change is documented by numerous desiccation surfaces especially in the malmros klint member and carlsberg fjord beds orbital change is suggested by the composite cyclicity and long term climatic change is indicated by the systematic upwards change in sedimentary characteristics of the lake deposits the sedimentary features of the malmros klint member suggest lacustrine deposition in a dry climate that fluctuated between desert and steppe conditions the carlsberg fjord beds probably record lacustrine lake deposition in a rather constant dry steppe climate while the tait bjerg beds record lake sedimentation in a climate that fluctuated between dry steppe and warm moist temperate in the tait bjerg beds the upward change in cycle characteristics indicates a shift towards more humid conditions climatic deductions from sedimentary facies are in good agreement with climate maps of laurasia as simulated by numerical climate models palaeomagnetic data indicate a northward drift of east greenland of about 10 from ca 25 n to ca 35 n in the middle to late triassic the fleming fjord formation which represents ca 5 m y of the late triassic interval was deposited during latitudinal drift of 1 2 it is possible that the observed long term upward shift in climatic indicators within the formation can be ascribed to plate drift but southward shift of climatic belts could also have been of importance

deformation induced metal melt networks in silicates implications for core mantle interactions in planetary bodies abstract previous analyses of texturally equilibrated hydrostatically annealed olivine rocks containing metal and metal sulfide melts have determined that these melts do not form interconnected networks at low volume fractions to characterize the change in connectivity of metal melt in response to deformation we used optical microscopy and electron microprobe analyses to investigate the microstructures of samples of olivine gold sheared to shear strains of 200 deformation causes the development of a strong melt preferred orientation 13 15 to the shear plane and antithetic to the shear direction this melt preferred orientation consists of previously isolated pockets of gold melt that have connected into networks extending for many grain lengths as well as linear trails of isolated pockets melt was observed to have migrated 125 200 m in response to pressure gradients induced by serrations in the pistons in contact with the sample proving that finite permeability exists during deformation well below the critical melt fraction for connectivity consideration of the balance between differential and interfacial stresses on melt pockets indicates that melt channels formed in response to deformation can drain rocks to a very small melt fraction in a direction subparallel to the shear direction stranding less melt than drainage under hydrostatic conditions therefore core formation by percolative flow of non wetting melt in actively deforming planets and planetesimals may be accomplished more efficiently than previously believed in addition core material entrained in the mantle at the core mantle boundary will be strongly aligned sub horizontally in regions of horizontal shear and have little to no permeability in the vertical direction providing a mechanism to trap core material in d

diagenesis and evolution of the lower eocene red bed sandstone reservoirs in the dongying depression china abstract the diagenetic evolution of the lower eocene red bed high quality reservoirs in the dongying depression was systematically investigated through an integrated petrographic petrophysical fluid evolution and thermal history analysis the reservoirs experienced several phases of diagenesis including compaction carbonate cementation gypsum and ankerite cementation feldspar and carbonate dissolution quartz overgrowth cementation and clay mineral cementation and transformation an early alkaline diagenetic environment caused significant cementation of calcite and gypsum in the reservoir sandstone units near the sandstone mudstone contacts acidic formation fluids caused widespread dissolution of the feldspar and carbonate cements leading to synchronous occurrences of primary intergranular pores and acidic dissolution pores from the middle parts of the reservoir sandstone units to the sandstone mudstone contacts dissolution wanes gradually with ferro carbonate progressively diminishing migration of exogenetic thermal fluid along faults may have contributed to the gradual decrease in dissolution and the gradual increase in cementation from the lower part to the upper part of fault blocks the alternating alkaline and acidic diagenetic environments and the distribution of diagenetic products caused the development of the high quality red bed reservoirs in the middle part of the thick layered sandstone units in the lower part of fault blocks because of the spatial and temporal relationships between the diagenetic stages and their products lithological traps of a diagenetic origin were developed in the red bed reservoirs

origin and diagenetic evolution of ca mg fe carbonates in some coalfields of japan carbonate concretions lenses and bands in the pleistocene palaeogene and upper triassic coalfields of japan consist of various carbonate minerals with varied chemical compositions authigenic carbonates in freshwater sediments are siderite calcite ankerite dolomite ferroan magnesite in brackish water to marine sediments in the coal measures calcite dolomite ankerite siderite ferroan magnesite and in the overlying marine deposits calcite dolomite siderite most carbonates were formed progressively during burial within a range of depths between the sediment water interface and approximately 3 km the mineral species and the chemical composition of the carbonates are controlled primarily by the initial sedimentary facies of the host sediments and secondarily by the diagenetic evolution of pore water during burial based on the regular sequence and burial depth of precipitation of authigenic carbonates in a specific sedimentary facies three diagenetic stages of carbonates are proposed carbonates formed during stage i 2000 m are fe calcite and extremely high ca mg siderite the latter is exclusively in marine mudstones the supply of ca is partly from the alteration of silicates in the sediments at elevated burial temperatures after uplift calcite with low mg content precipitates from percolating groundwater and fills extensional cracks

pore characteristic responses to categories of depositional microfacies of delta lacustrine tight reservoirs in the upper triassic yanchang formation ordos basin nw china abstract primary depositional variations interact with diagenetic modifications to exert strong control on pore networks in tight hydrocarbon reservoirs however the linkage between pore characteristics and depositional microfacies remains enigmatic which restricts the prediction of high quality reservoir distributions the continental tight reservoirs of the yanchang formation in the ordos basin are targeted to clarify and estimate the sensitivity of pore characteristics to depositional microfacies a multi methodical approach utilizing petrographic assessments logging evaluations digital imaging analyses and high pressure mercury intrusion experiments enables us to reveal the high microheterogeneity of pore types pore size distribution and pore fractal features the results identified the microfacies including distributary channels dcs mouth bars mbs interdistributary bays ibs sheet sands sss turbidite fans tfs shallow lacustrine mudstones slms and semi deep lacustrine mudstones sdlms from the chang 8 to chang 6 members dominated by residual intergranular pores and microfractures the main storage spaces of the dc and mb microfacies are within mesopores which provide 62 92 and 81 of the total pore volume respectively however the micropores that are mainly composed of clay intercrystalline pores and feldspar dissolved pores provide 55 70 52 62 and 53 80 of the total pore volume for the ib slm and sdlm microfacies respectively in addition the pore fractal dimension results indicate that the mesoporous structure of the argillaceous microfacies ib slm and sdlm is more heterogeneous than that of the arenaceous microfacies dc mb and tf therefore the dominant reservoir spaces of the different depositional microfacies are distributed over diverse pore radius ranges and the varying degrees of mesoporous development are a crucial factor affecting the reservoir capacity moreover the fractal dimensions have a significant negative correlation with pore volume in the meso micropore range characterized by lower pore sorting coefficients broader skewness and more abundant rigid siliceous grains the arenaceous microfacies with lower fractal dimensions and higher pore volume have better reservoir capacity than argillaceous microfacies that are rich in ductile minerals microscopic observations show that the muddier reservoirs of interdistributary bays and lacustrine mudstones are more susceptible to pore filling chlorite and illite which can deteriorate the reservoir quality these results indicate that the controlling effect of depositional microfacies on pore characteristics is fundamentally caused by differences in mineralogical composition and depositional texture and these results could provide new insights into the mechanisms of microfacies controls on reservoir quality

the tectonic emplacement of sumba in the sunda banda arc paleomagnetic and geochemical evidence from the early miocene jawila volcanics the island of sumba is a continental fragment in the fore arc region near the transition between the sunda arc and banda arc in southeastern indonesia paleomagnetic and geochemical evidence from the early miocene volcanics of the jawila formation in western sumba constrain the final drift stage and tectonic emplacement of the island the lavas range from predominantly andesites to dacites and display textural evidence for a weak metamorphism rock magnetic and mineral chemical data point to pseudo single to multi domain titanojmagnetite fe ti o with grain sizes up to 10 pm as the main carrier of remanence the jawila formation reveals a chrm direction with declination 4 6 inclination 19 2 c 9 9 and a paleolatitude of 9 9 s which corroborates earlier results chamalaun and sunata 1982 taking paleomagnetic evidence from other formations on the island into account we conclude that the sumba fragment has occupied approximately its present position since the miocene the talc alkaline affinity and trace element signatures of the lavas point to an origin in an arc environment this occurrence of subduction related volcanic activity in the early miocene on sumba implies that a volcanic arc existed south of the present day east sunda arc or that the island was located within the latter arc between sumbawa and eastern flores and still had a minor southward drift to cover

earth s core formation aided by flow channelling instabilities induced by iron diapirs abstract the core formation mechanism remains poorly known an unstable gravitational configuration of a dense molten metallic layer overlying a cold chondritic protocore is predicted by most studies which leads to the formation of a rayleigh taylor rt instability recent results dahl t w 2005 turbulent mixing during planet accretion and core formation interpretation of the hf w chronometer and implications for the age of the moon m sc thesis university of copenhagen indicate that additionally iron cores of predifferentiated planetesimals are also able to plunge mostly intact into the cold protocore and create large iron diapirs for both scenarios we propose the application of the stress induced melt channelling mechanism stevenson d j 1989 spontaneous small scale melt segregation in partial melts undergoing deformation geophys res lett 16 1 067 1 070 in the region surrounding an incipient iron diapir we therefore perform numerical experiments solving the two phase two composition flow equations within a 2d rectangular box with symmetrical boundary conditions we apply the compaction boussinesq approximation cba and include a depth dependent gravity for simplicity we use a constant viscosity for the solid phase and a melt fraction dependent rheology for the partially molten region around the diapir we investigate the physical conditions under which the melt channels can form and whether they are applicable to the early earth as a result for sufficiently small melt retention numbers iron rich melt channels develop within a region of approximately twice the diapir s size this could lead to effective draining of the surrounding region and might initiate cascading daughter diapirs the region of the protocore drained by this cascading mechanism is expected to significantly increase with depth and thus indicates an effective mechanism to also extract iron melt from deeper parts of the initially chondritic protocore this mechanism could effectively accelerate the process of core formation

habitat of hydrocarbons on the norwegian continental shelf eds a m spenceret al norwegian petroleum society graham and trotman 1986 isbn 0 86010 833 3 price 65 00

how to make a planet an introduction the special collection building planets the dynamics and geochemistry of core formation aims to combine cutting edge experimental analytical and modeling results with review articles defining the state of the science and current challenges to our understanding of the origin geophysics and geochemistry of planetary cores our goal is to highlight novel and interdisciplinary approaches that address aspects of core formation and evolution at the atomic grain and planetary scales

sedimentary evolution of overlapped sand bodies in terrestrial faulted lacustrine basin insights from 3d stratigraphic forward modeling abstract terrestrial faulted lacustrine basins usually have large variabilities in structural subsidence and multiple river sources the facies in such basins are thus characterised by frequently changed facies and complex relationship of overlapped sand bodies e g liaoxi depression of liaodong bay bohai sea china therefore it s a great challenge to quantitatively describe evolution of sand bodies and their overlap relationship in this study a three dimensional stratigraphic forward model is used to solve this problem which is corrected according to well log data after the parameter optimization was verified against borehole strata thickness and lithology this model had a thickness error within 8 and the lithology distribution agreed with the well data as a whole four evolution phases of the shahejie 3 formation were recognised through the modeling in the first phase the lake level rose and the eastern fan delta sand developed in the second phase the fan delta sand scaled up and the braided river delta front sand developed at a small scale in the third phase the lake level shifted from falling to rising the fan delta sand further expanded the scale and the braided river delta developed at a large scale sands on both sides overlapped at a large scale in the fourth phase the lake level rose the lake basin expanded and lake shale was the main lithology in the study area from the sedimentary evolution of es3 formation sand overlapped in the third stage in 39 75 ma two parts of the sand body began to overlap and reached largest scale in 39 6 ma which was approximately 10 km 2 both then retrograded to a separation in 39 ma when the overlap ended coupling stratigraphic forward simulation with uncertainty quantification allowed us to estimate the influence of each stratigraphic parameter on sand overlap fluvial discharge appears to be the most influential parameter while the initial bathymetry and lake level variations exert a minor to moderate impact

seismic stratigraphy and cenozoic evolution of the lombok forearc basin eastern sunda arc abstract on the basis of single and multi channel seismic reflection data the stratigraphic framework and geologic history of the lombok forearc basin is discussed the lombok basin is built on the southeast sunda shelf continental margin and probably underlain by basement of thinned rifted continental crust it represents a broad ridged residual forearc basin which is still in an early stage of evolution five seismo stratigraphic sequences reflecting the cenozoic history and development of the forearc basin south of the islands of bali and lombok were identified the lowermost sequence 1 probably is composed of synrift deposits of paleogene age which predate the initiation of the present convergent margin sequences 2 and 3 reflect two major phases of tectonic evolution of the accretionary prism between the late oligocene and mid miocene sequences 4 and 5 represent slope front fill deposits and reflect both volcanic activity as well as tectonic uplift of the magmatic arc from mid miocene times onwards by the late miocene increased convergence between the subducting indian and overlying asian plates resulted in a stronger mechanical coupling between both plates this was expressed in the southern forearc basin by folding of the oldest basin fill deposits the present tectonic activity in the lombok basin is governed by the late pliocene collision of the accretionary prism with the scott marginal and roo rise oceanic plateaus this resulted in uplift of both the outer arc ridge and the southern part of the forearc basement

polydiapirs multiwavelength gravity structures polydiapirs domes in domes result from the evolution of a multiwavelength rayleigh taylor gravitational instability the present work investigates the initiation and development of polydiapirs by means of two dimensional finite difference models of gravitationally unstable triple layered sequences of newtonian fluids the values of viscosities thicknesses and densities were systematically varied for selected examples in triple layered sequences only two types of density stratification are likely to result in multiwavelength instabilities that will eventually develop into polydiapiric structures the limiting factors and evolution of such structures were studied for both these types of density stratifications finite difference calculations on models with physical parameters appropriate to evaporitic sequences and covered by a viscous clastic overburden showed that a very small downward density decrease in the evaporitic source may cause an internal overturn that will compete with the main overturn between source and overburden this may lead to the development of sequential or simultaneous polydiapirs the mature polydiapirs in the models exhibit spines curtain folds pendant repetitions of the source layers inside the large diapirs and anomalous interdiapiric distances all these features are known in natural salt diapirs suggesting that polydiapirs may be far more common in nature than hitherto recognized

two dimensional stokes flow around a heated cylinder a possible application for diapirs in the mantle 1 it is widely assumed that the separation of metal and silicates in a homogeneously accreted protoplanet occurred rather rapidly the process of core formation through the descent of large hot iron rich bodies through a cold silicate protoplanet is discussed if iron diapirs sink toward the planet center with the stokes velocity they would require more than 800 ma to form a core in the case of a planet similar to the earth we therefore implement a temperature dependent rheology for the silicate material surrounding the diapir which leads to a reduction of the drag force exerted on the iron drop we compare the drag force for different sinking velocities to the body force on the diapir and find that the terminal velocity in the temperature dependent viscosity model is a factor of 30 higher than that in an isoviscous medium on the basis of these results the core formation time for the earth could be as little as 30 ma

impact of sequence stratigraphy depositional facies and diagenesis on reservoir quality a case study on the pennsylvanian taiyuan sandstones northeastern ordos basin china abstract the pennsylvanian taiyuan formation of the shenmu field in the northeastern ordos basin of china contains tight sandstone reservoirs that have recently been commercially produced an evaluation of the reservoir quality of the taiyuan sandstones will play a critical role in the development of the field an investigation was conducted to explore possible effects of the sequence stratigraphy depositional facies and diagenetic alterations on the reservoir quality of the taiyuan sandstones based on core descriptions the examination of thin sections and core plug and scanning electron microscope analyses the taiyuan formation consists of lowstand system tracts lst transgressive system tracts tst and highstand system tracts hst the lst sandstones are principally medium to coarse grained and are interpreted to have been deposited in the dominant distributary channels of a delta plain the early tst fine to coarse grained sandstones were largely deposited in the underwater distributary channel and mouth bar of a delta front and the middle tst fine to medium grained sandstones were deposited in the shoreface to foreshore environment the hst silt to medium grained sandstones were mostly deposited in the mouth bar of a delta front and shoreface to foreshore the taiyuan sandstones which are composed of sublitharenites quartzarenites and litharenites suffered from extensive compaction that resulted in a large loss of intergranular porosity before the sandstones were further cemented severely the sandstone cements are mostly composed of illite ankerite calcite and quartz the taiyuan sandstones have a particularly low average core plug porosity of 7 41 and horizontal permeability of 0 916 md which results from that most of the pores of the sandstones are micropores and secondary pores with poor connectivity the lst dominant distributary channel early tst underwater distributary channel and proximal mouth bar and hst shoreface to foreshore sandstones with relatively coarser grain sizes mostly medium to coarse grained have relatively higher porosities and permeabilities than the sandstones with relatively finer grain size which is ascribed to a widespread early dissolution by meteor water leaching and lower content of cements within the coarser grained sandstones however the lst dominant distributary channel sandstones had undergone a more effectively early dissolution and less carbonate cementation than the tst underwater distributary channel and proximal mouth bar and hst shoreface and foreshore sandstones had which lead to the relatively best reservoir quality of the lst dominant distributary channel sandstones among the taiyuan sandstones the study revealed that the reservoir quality of the tight taiyuan sandstones was controlled by sequence stratigraphy framework depositional facies grain size and diagenetic alterations together the sequence stratigraphy framework played a key role in controlling the reservoir quality of the taiyuan sandstones by governing the depositional facies and corresponding diagenetic products while the grain size affected the reservoir quality of the sandstones by controlling the content of cement within the sandstones

tertiary tectonic and magmatic evolution of western sulawesi and the makassar strait indonesia evidence for a miocene continent continent collision

mesozoic and late tertiary submarine fan sequences and their tectonic significance sumba indonesia abstract the indonesian island of sumba occupies a critical zone which separates a normal subduction complex java trench system from a continent island arc collision zone banda arc sumba is considered by some authors to be a microcontinental fragment although in this context its pre fragmentation origin is uncertain detailed studies of the stratigraphy of sumba however throw light on the origin and subsequent geological history of the island and surrounding areas on available evidence the oldest outcropping rocks are of cretaceous age and locally contain a tropical tethyan marine fauna they comprise dark coloured sometimes carbonaceous and often volcanogenic mudstones sandstones gravels and diamictites pervasively intruded by andesitic and dacitic dykes and locally intruded by granodiorite plutons these sediments are siliclastic and appear to have had a continental provenance the cretaceous rocks in many areas compromise part of a major submarine fan complex which at least in south central sumba prograded towards the southwest and south shallow marine and non marine paleogene sediments and volcanic agglomerates lie unconformably above the uplifted tilted and eroded cretaceous strata these are overlain in turn by the widely outcropping miocene sumba formation an oceanic sequence with island arc affinities accessible outcrops of the sumba formation comprise platform carbonates with abundant reef developments in west sumba and a major submarine fan pelagic chalk complex in east sumba the fan complex which extends beneath the southern savu sea north of sumba is dominated by large scale slumps olistostromes and thin and thick bedded turbidites turbidite sands and gravels invariably are volcaniclastic containing components derived from a typical inner volcanic arc complex paleocurrent indicators are difficult to find in the sumba formation thus it is uncertain at this stage whether the volcaniclastic turbidites were derived from the present volcanic arc or from an undetermined source which may since have subsided the portion of the fan complex which underlies east sumba however has undergone vertical uplift since its emplacement of between one and several kilometres uplift is actively in progress at present possibly due to underthrusting by northward moving australian continental crust in this context the island of sumba comprises an uplifted north tilted and subaerially exposed part of the forearc basin of the indonesian arc this uplift can be related to initial stages of continental collision

a dual porosity model for evaluating petroleum resource potential in unconventional tight shale plays with application to utica shale quebec canada unconventional tight to shale reservoirs vary from tight sandstone siltstone to organic rich mudstone shale commonly with mixed lithologies in such reservoir systems matrix pores and organic pores with different origins and distinct physical and chemical properties co exist for hydrocarbon storage traditional resource assessment methods designed for conventional reservoirs cannot handle the two pore systems properly this study proposes a dual porosity model to respond to the need for a new method in assessing hydrocarbon resource potential in such reservoir systems the dual porosity model treats the two types of pores separately and derives the resource estimates from different sources of data thus better characterizing unconventional reservoirs with complicated pore systems the new method also has the flexibility of assessing resource potential for the entire spectrum of mixed lithologies ranging from a complete tight to a pure source rock organic rich shale mudstone reservoir the proposed method is illustrated through the assessment of the in place petroleum resource potential in the upper ordovician utica shale of southern quebec canada the results of the application suggest that the proposed approach effectively handles the two pore systems in tight shale reservoirs effectively and provides a useful tool for estimating resource potential in unconventional plays

direct numerical simulation of an iron rain in the magma ocean core formation in terrestrial planets is a complex process possibly involving several mechanisms this paper presents a direct numerical simulation of one of these the separation of an emulsion of metal in a magma ocean the model using a fully lagrangian approach called the moving particle semi implicit method solves the equations of fluid dynamics including a proper treatment of surface tension it allows investigation of the balances controlling the distribution of drop size and velocity in both two and three dimensional situations a scaling analysis where buoyancy is balanced by both surface tension and inertia correctly predicts the average values in these quantities the full calculation gives an average drop radius of 1 5 cm falling at a velocity of about 30 cm s 1 analysis of the full distribution remains interesting and shows that a significant part of the smallest droplets is entrained upward by the return flow in molten silicate and might be entrained by succeeding thermal convection in addition we investigate the conversion of gravitational energy into viscous heating and the thermal equilibration between both phases we find that viscous heating is essentially produced at the surface of iron drops and that thermal equilibration is dominated by advection scaling thermal diffusion to chemical diffusion leads to the estimation that the latter would happen in less than 100 m in the magma ocean

formation of a solid inner core during the accretion of earth the formation of an inner core during the accretion of earth is investigated using self gravitating and compressible earth models formed by accreting a total of 25 or 50 moon to mars size planetary embryos the impact of an embryo heats the proto earth s interior differentially more below the impact site than elsewhere the rotating core dynamically overturns and stratifies shortly after each impact creating a spherically symmetric and radially increasing temperature distribution relative to an adiabatic profile merging of an embryo to the proto earth increases the lithostatic pressure that results in compressional temperature increase while further enhances the melting temperature of the core causing solidification a total of 36 thermal evolution models of the growing proto earth s core are calculated to investigate effects of major physical parameters no solidification is considered in the first 21 models where modified two body escape velocities are used as the impact velocities of the embryos at the end of accretion temperatures in the upper part of the core are significantly different among these models whereas temperatures in the deeper parts are similar the core solidification considered in the remaining 15 models where impact velocities higher than the modified two body escape velocities are adopted drastically changes the temperature distribution in the deeper parts of the core all of the models produce partially solidified stiff inner cores 1000 2100 km in radius at the end of accretion where the solid fraction is larger than 50 the innermost of the stiff inner cores are completely solidified to radii 250 1500 km

evolution of microstructures and of macroscopic properties of some clays during experimental compaction abstract in order to understand the evolution of clay sediments during their burial to three or four kilometers depth remoulded and non remoulded clay samples were oedometrically consolidated under loads ranging from 0 1 50 mpa and their microstructural mechanical and transport properties were studied for this study four clays were selected on mineralogical grounds a kaolinite st austell clay two illitic clays la bouzule clay and salins 14 clay and an illite smectite mixed clay marais poitevin clay among those materials two are almost pure clays st austell clay and salins 14 clay and were compacted in a remoulded state the other two have a clay fraction about 60 and were studied in non remoulded state for marais poitevin clay and both remoulded and non remoulded for la bouzule clay the oedometric tests have been performed in classical oedometers and in a new oedometric cell specially designed to measure lateral stresses and to perform hydraulic conductivity measurements under compaction load the two pure clays show an evolution of their void ratio differing from what is expected considering their liquid limits the behaviour seems to be governed by the size of the clay particles around 1 m for st austell clay and around 0 1 m for salins 14 clay marais poitevin clay very slightly compacted in its natural state and remoulded la bouzule clay have consolidation coefficients cc and void ratios consistent with their liquid limits a relationship reported in soil mechanics literature skempton 1944 burland 1990 nagaraj et al 1994 the natural la bouzule clay shows very low void ratios and cc due to overconsolidation the microstructure observed by tem showed that clay particles are platy and made of aggregates of individual crystals except for salins 14 clay where individual crystals do not aggregate the evolution of the microstructure with applied stress shows no change in the particles structure but a progressive reorientation of the particles perpendicular to the load axis these microstructural observations explain the transport properties measured and their evolution the thermal conductivity of kaolinite measured in the axial and radial direction reflects the evolution of anisotropy with compaction observed on particles orientation the different hydraulic conductivities observed on the various samples are compared to those obtained with the kozeny carman formula using two types of specific surface determination this comparison emphasizes the importance of inter and intraparticule pore size and of their intimate organisation

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

segregation of core melts by permeable flow in the lower mantle we measured the dihedral angle of molten iron in mg fe sio3 perovskite aggregate with increasing pressure and temperature using laser heated diamond anvil cell results demonstrate that it decreases from 94 at 27 gpa and 2400 k to 51 at 47 gpa and 3000 k this value is smaller than the critical angle of 60 thus allowing iron melt to wet the grain boundaries of silicate perovskite and develop an interconnected melt network within the perovskite dominant matrix even at very small melt fractions the quenched liquid iron contained substantial amounts of oxygen and silicon as pressure and temperature increase such a decrease in the dihedral angle is likely due to a reduction in the iron perovskite interfacial energy by dissolving oxygen and silicon into the liquid iron from coexisting silicate perovskite these suggest that a wetting behaviour of core melts in the solid silicate mantle changes above 40 gpa corresponding to 1000 km depth in the present earth and efficient metal segregation may have proceeded by permeable flow in a late stage of accretion oxygen and silicon incorporated during core formation and later by core mantle boundary process may be important light elements in the earth s core

k ar dating young rhyolitic rocks a case study of the sierra la primavera jalisco mexico this study demonstrates the feasibility of dating by the k ar method an eruptive sequence of silicic volcanic rocks with ages close to the limits of conventional 14 c dating forty six conventional k ar analyses of sanidine and glass from rhyolites of the sierra la primavera mexico yielded dates of 5 to 150 ka thousand years one sigma errors range from 3 to 39 ka although the samples contain small amounts of extraneous argon most of the dates are consistent with relative ages determined in the field the exceptions are dates on immediately postcaldera eruptive units which are older than the dates for the caldera producing ash flow tuff a similar result has been obtained on dating tuffs and lavas of some other pleistocene calderas this effect is attributed to incomplete outgassing of the larger amount of extraneous argon dissolved in magma that occupied a position deeper in the chamber than the ash flow tuff magma and that erupted immediately after caldera collapse we present two new error equations one a simple extension of the commonly used equation demonstrates the importance of including a term for the uncertainty in the spectrometer mass discrimination factor in the error equation the second equation is a more rigorous formulation of the propagation of errors in the calculation of the age it yields meaningful error estimates for all proportions of radiogenic 40 ar and because it expresses the error in absolute rather than relative terms it can be used to put an upper limit on the age of a sample when no radiogenic 40 ar has been resolved

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

facies controls on the distribution of diagenesis and compaction in fluvial deltaic deposits abstract the upper triassic lower jurassic are formation comprising the deeper reservoir in the heidrun field offshore mid norway consists of fluvial channel sandstones fch floodplain fines ff and sandy and muddy bay fill sediments sbf mbf deposited in an overall transgressive fluvial to lower delta plain regime the formation has been investigated to examine possible sedimentary facies controls on the distribution of cementation and compaction based on petrography and sem micro probe analyses of core samples related to facies associations and key stratigraphic surfaces the most significant authigenic minerals are kaolinite calcite and siderite kaolinite and secondary porosity from dissolution of feldspar and biotite are in particular abundant in the fluvial sandstones the carbonate minerals show complex compositional and micro structural variation of pure siderite sid i mg siderite sid ii fe dolomite ankerite and calcite displaying decreasing fe from early to late diagenetic carbonate cements an early diagenetic origin for siderite and kaolinite is inferred from micro structural relations whereas pore filling calcite and ankerite formed during later diagenesis the fe dolomite probably related to mixing zone dolomitization from increasing marine influences and a regional correlatable calcite cemented layer has been related to a flooding event porosity values in non cemented sandstone samples are generally high in both fch and sbf facies associations averaging 27 differential compaction between sandstone and mudstone has a ratio of up to 1 2 and with lower values for mbf we emphasize the role of eogenetic siderite cementation in reducing compactability in the fine grained coal bearing sediments most prominent in mbf facies this has implications for modeling of differential compaction between sandstone and mudstones deposited in fluvial deltaic environments

origin of the sumba forearc basement abstract an interpretation of acoustic basement structures in the eastern sunda western banda forearc region suggests structural continuity between sumba and northern timor the area between sumba and timor is delineated as a zone of continuous structures without major strike slip offsets these structures trend east west in the west but gradually change towards the east into ne sw trending structures a major ne sw trending discontinuity west of sumba between 117 30 and 118 30 e marks the transition between an intraoceanic volcanic arc system in the west and a volcanic arc continent collision zone in the east the extent of the sumba basement suggests either a common late jurassic rift drift history for both sumba and northern timor or an early miocene magmatic welding of two continental fragments of different origin resulting in structural continuity between two microplates the first explanation implies that sumba originated from the north west australian continental margin south of tethys from which it drifted away in the late jurassic the second hypothesis which is favoured proposes a northern provenance of sumba the island would then originate from the south east asian continent north of tethys from which it was detached in the eocene

the evolution of sumba island indonesia revisited in the light of new data on the geochronology and geochemistry of the magmatic rocks abstract the island of sumba presently located in the southern row of islands of the eastern nusa tenggara province of eastern indonesia has a unique position being part of the sunda banda magmatic arc and subduction system it represents a continental crustal fragment located at the boundary between the sunda oceanic subduction system and the australian arc continent collision system separating the savu basin from the lombok basin new data on magmatic rocks collected from sumba are presented in this paper including bulk rock major and trace element chemistry petrography and whole rock and mineral 40k 40ar ages three distinct calc alkaline magmatic episodes have been recorded during cretaceous paleogene all of them characterized by similar rock assemblages i e pyroclastic rocks basaltic andesitic lava flows and granodioritic intrusions they are i the santonian campanian episode 86 77 ma represented by volcanic and plutonic rock exposures in the masu complex in eastern sumba ii the maastrichtian thanetian episode 71 56 ma represented by the volcanic and plutonic units of sendikari bay tengairi bay and the tanadaro complex in central sumba and iii the lutetian rupelian episode 42 31 ma of which the products are exposed at lamboya and jawila in the western part of sumba no neogene magmatic activity has been recorded

sequence stratigraphy sedimentary facies and reservoir quality of es4s southern slope of dongying depression bohai bay basin east china abstract thin bedded beach bar sandstone reservoirs are common in the eocene shahejie formation es4s of niuzhuang sag along the southern gentle slope of the dongying depression here we report on the link between sequence stratigraphy sedimentary facies and diagenetic effects on reservoir quality seismic data wireline logs core observations and analyses are used to interpret depositional settings and sequence stratigraphic framework petrographic study based on microscopic observation of optical cathodoluminescence cl confocal laser scanning lscm and scanning electron microscope sem and x ray diffraction xrd analyses were used to describe the fabric texture allogenic and authigenic mineralogy of these highly heterogeneous sandstone reservoirs the es4s interval is interpreted as third order sequence composed of a lowstand systems tract lst a transgressive systems tract tst and a highstand systems tract hst on the fourth order twenty nine parasequences and seven parasequence sets have been identified sand bodies were deposited mainly in the shoreface shallow lake beach bar clastic beach bar semi deep lake carbonate beach bar and the fluvial channels the depositional and diagenetic heterogeneities were mainly due to the following factors 1 fine grain size poor sorting and continuous thin inter bedded mud layers with siltstone fine sandstone having argillaceous layers in regular intervals 2 immature sediment composition and 3 even with the dissolution of grains and several fractures destruction of porosity by cementation and compaction secondary pores from feldspar dissolution are better developed in sandstones with increased cementation grain coating smectite clays preserved the primary porosity at places while dominating pore filling authigenic illite and illite smectite clays reduced permeability with little impact on porosity due to the high degree of heterogeneity in the es4s beach bar interval it is recognized as middle to low permeable reservoir the aforementioned study reflects significant insight into the understanding of the properties of the beach bar sands and valuable for the comprehensive reservoir characterization and overall reservoir bed quality

a thermal model for the differentiation of asteroid 4 vesta based on radiogenic heating a finite element code has been developed to model the thermal history of asteroid 4 vesta this is the first attempt to model the thermal history of a differentiated asteroid through core and crust formation and subsequent cooling until geochemical closure is attained the results of the simulation are consistent with chronological measurements and other constraints provided by cumulate and noncumulate eucrites believed to have been derived from vesta the work solves two major problems with the hypothesis of heating by decay of26al an extinct radionuclide postulated to be a plausible heat source in the early solar system first the model demonstrates that it is possible to keep the mantle of vesta hot for 100 ma thereby explaining the observed difference in ages between cumulate and noncumulate eucrites second the simulation offers a possible explanation of why detectable excesses of26mg the decay product of26al are not observed in noncumulate eucrites the simulation draws a model chronology of vesta and predicts times relative to cai formation for accretion at 2 85 myr core formation at 4 58 myr crust formation at 6 58 myr and geochemical closure at 100 myr for a h chondrite asteroidal bulk composition decay of60fe is found to cause no perceptible difference in the thermal history of vesta even when sequestered into a central core although chondritic xenoliths have not been described in hed igneous lithologies the thermal model suggests the possibility that a veneer of unmelted near surface material should remain

a model of metal silicate separation on growing planets abstract the thermal evolution of planets during their accretionary growth is strongly influenced by impact heating the temperature increase following a collision takes place mostly below the impact location in a volume a few times larger than that of the impactor impact heating depends essentially on the radius of the impacted planet when this radius exceeds 1000 km the metal phase melts and forms a shallow and dense pool that penetrates the deep mantle as a diapir to study the evolution of a metal diapir we propose a model of thermo chemical readjustment that we compare to numerical simulations in axisymmetric spherical geometry and with variable viscosity we show that the metallic phase sinks with a velocity of order of a stokes velocity the thermal energy released by the segregation of metal is smaller but comparable to the thermal energy buried during the impact however as the latter is distributed in a large undifferentiated volume and the former potentially liberated into a much smaller volume the diapir and its close surroundings a significant heating of the metal can occur raising its temperature excess by at most a factor of 2 or 3 when the viscosity of the hot differentiated material decreases the proportion of thermal energy transferred to the undifferentiated material increases and a protocore is formed at a temperature close to that of the impact zone

heat partitioning in terrestrial planets during core formation by negative diapirism article i nfo we investigate the gravitational heat partitioning between silicate and metallic phases during core formation by negative diapirism in terrestrial planets we model the dynamic evolution of an iron diapir sinking through a solid silicate proto mantle our calculations include viscous heating and strong temperature and composition dependence of viscosity we show that the diapir mean temperature evolves towards an asymptotic value td which depends on the efficiency of viscous heating and heat transfer between the diapir and its surroundings and on the viscous rheology we derived a simple analytic model that captures the thermal evolution observed in our numerical experiments this model can be applied to determine the heat distribution within terrestrial planets with a large number of diapirs during their growth and early differentiation we show that the partitioning of core formation heating during negative diapirism depends strongly on the size distribution of the iron diapirs a large number of small sinking iron diapirs favors metal silicate heat exchange and leads to a relatively hot core which allows a sustainable dynamo as on earth a small number of large diapirs have the opposite effect and could correspond to a mars like planet with an early dynamo that is no longer active in all cases negative diapirism tends to leave the lowermost mantle significantly hotter than its upper part which could trigger large amounts of melting in the early deep mantle

modal distribution of pore throat size in sandy conglomerates from an alluvial fan environment lower karamay formation junggar basin west china abstract alluvial fan exhibits various modal distribution of pore throat size which effectively control the oil displacement efficiency and fluid movement however the genetic mechanism of the modal distribution of the pore throat size and its macroscopic distribution within alluvial fan is poorly understood based on core analysis this paper which take the sandy conglomerate reservoir within the alluvial fan in junggar basin as an example aims to study the variations in modal distribution of pore throat size and controlling mechanisms the results reveal that 1 the modal distribution types of the pore throat size are complicated and can be classified into six subtypes including unimodal type uni unimodal type uni unimodal type uni bimodal type bi bimodal type bi and multimodal type multi uni uni and uni is dominated by intergranular pores intragranular dissolved pores and micropores respectively bi bi and multi are characterized by the combination of several pore types 2 diagenesis including compaction cementation and dissolution rock composition the mudstone fragment content and rock texture the clay content control the volume of each pore throat type which significantly influences the modal distribution of the pore throat size lithofacies with low mudstone fragment and clay content and great grain sorting tend to have experienced weak compaction thereby retaining a large volume of intergranular pores and have been subjected to strong dissolution when adequate acidic ions occur in the porewater resulting in a large volume of intragranular dissolved pores strong dissolution reduced the rock compressive strength and further enhanced the degree of mechanical compaction during the burial process cementation occurred later than compaction and dissolution and its intensity is controlled by the supply of co2 and ca2 and compaction intensity thus reducing the volume of intergranular pores the content of mudstone fragment and clay varies among different lithofacies of different origins for traction current deposits lithofacies with smaller median grain size contain fewer mudstone fragments resulting in fewer micropores the clay content decreased first and then increased with decreasing median grain size and lithofacies with lower clay content cause less volume of micropores 3 lithofacies types combined with porewater condition for dissolution and lithofacies location affect the diagenetic intensity rock composition and rock texture variations thus resulting in various modal distribution of pore throat size within the alluvial fan moreover the rock texture especially grain sorting is very important for compaction and facilitates percolation of meteoric water and dissolution

tectonic development of the mid norway continental margin abstract the area reviewed covers the mid norway continental margin between latitudes 62 n and 68 n main structural elements as defined at the base cretaceous level are the trondelag platform underlying the inner shelf the more and voring basins located beneath the outer shelf and slope and the more platform and the outer voring plateau forming a base of slope trend of highs sediments contained in the mid norway basin range in age from late palaeozoic to cenozoic the basement was consolidated during the caledonian orogenic cycle devonian and early carboniferous wrench movements along the axis of the arctic north atlantic caledonides are thought to have preceded the namurian onset of crustal extension rifting processes were intermittently active for some 270 my until crustal separation between greenland and fennoscandia was achieved during the early eocene during the evolution of the norwegian greenland sea rift system a stepwise concentration of tectonic activities to its axial zone the area of subsequent continental separation is observed during the late palaeozoic to mid jurassic a broad zone was affected by tensional faulting during the late jurassic and cretaceous the trondelag platform was little affected by faulting whilst major rift systems in the more and voring basins subsided rapidly and their shoulders became concomitantly upwarped during the latest cretaceous and early palaeogene terminal rifting phase only the western more and voring basins were affected by intrusive and extrusive igneous activity following the early eocene crustal separation and the onset of sea floor spreading in the norwegian greenland sea the voring segment of the mid norway marginal basin subsided less rapidly than the more segment during the early and mid tertiary minor compressional deformations affected the voring basin and to a lesser degree the more basin tensional forces dominated the late palaeozoic to early cenozoic evolution of the mid norway basin and effected strain mainly in the area where the crust was weakened by the previous lateral displacements the lithosphere thinned progressively and the effects of the passively upwelling hot asthenospheric material became more pronounced massive dyke invasion of the thinned crust preceded its rupture

porosity depth trends in reservoir sandstones theoretical models related to jurassic sandstones offshore norway abstract theoretical models of compaction and porosity modification in sandstones during burial are discussed theory predicts that mechanical compaction is the dominant porosity reducing mechanism during burial from 0 to 2 5 3 km porosity depth trends are at this stage mainly controlled by the stability of the grain framework and the effective stress time and temperature also influence the porosity depth gradients at shallow to moderate depths but are probably less important than effective stress and framework grain composition at greater burial depths below 2 5 3 km chemical compaction including pressure solution can explain most of the porosity reduction in well sorted clean arenites theoretical modelling of the intergranular pressure solution suggests that sandstones may lose porosity rapidly by this mechanism below 2 5 3 km and that factors capable of retarding pressure solution and quartz cementation are required to maintain prospective porosities below 4 km this theory and comparisons with empirical data from jurassic sandstones from offshore norway indicate that high porosity is favoured by 1 overpressures approaching the lithostatic pressure gradient 2 a short residence time below 3 km burial 3 coatings on grains of clay or microcrystalline quartz which prevent quartz dissolution and precipitation and 4 a high content of feldspar and early diagenetic secondary pores early hydrocarbon emplacement may retard quartz cementation and preserve porosity but chemical compaction probably continues after oil emplacement except at very high hydrocarbon saturations

stratigraphic control on laterally persistent cementation book cliffs utah field data from the upper cretaceous blackhawk formation in the book clitfs utah colorado demonstrate the presence of laterally extensive carbonate cements beneath major marine flooding surfaces the occurrence of firmgrounds compaction around concretions and high minus cement porosities indicate that cementation occurred during early diagenesis it is proposed that the early cementation associated with these marine flooding surfaces occurred as a result of reduced sediment accumulation rates or non depositional hiatuses linked to abrupt deepening during marine flooding these reduced sediment accumulation rates extended sediment residence time within early diagenetic zones leading to enhanced early cementation in shallow marine sandstones and mudstones