impacts of various toc distributions on hydrocarbon generation abstract this study used numerical basin modeling methods to examine how various total organic carbon content toc distributions in formations with a fixed average toc impact the overall oil and gas generation ability different geological and geochemical conditions such as thickness and burial depth of the source formation thermal gradient organic richness degree of spread and types of kerogen are considered in this investigation the results show that there is a significant impact on the overall oil and gas generation capability especially when the source rocks are in the peak generation windows the magnitudes of oil and gas generation rates can vary by up to 5 10 times in some cases the general rules are that the more dispersion of toc in the formation or the thicker the formation and the greater the thermal gradient the larger the difference of generation rates between the distributions which favor hydrocarbon generation therefore in addition to the average toc richness the toc distribution in a source rock formation must also be considered when the petroleum potential of a basin is evaluated

integrated computer aided basin modeling applied to analysis of hydrocarbon generation history in a northern italian oil field abstract the application of reaction kinetics to the analysis of hydrocarbon hc generation processes requires a detailed temperature history of potential source rocks in order to obtain optimum results the necessary accuracy can be obtained by employing integrated computer aided basin modeling techniques to simulate the depositional history resulting in a continuous record of temperatures throughout the study area the technique has been applied to the analysis of an on off structure hc generation problem in a northern italian oil field the simulation of the geologic processes shows that low sedimentation rates and more importantly the high thermal conductivities of the carbonate rocks resulted in low temperatures throughout most of the geologic history of the study area which were followed by a sudden rapid temperature increase in the off structure area during the last 6 5 ma the calculated temperature history enables an accurate determination of the hc generation history using a kinetic approach which shows how hc generation is closely controlled by the sedimentation history and structural development and which also describes its relation to trap formation it also shows why hcs are generated at very low vitrinite reflectance levels i e peak oil generation at approximately 0 6 r o determination of the hc generation rate gives additional critical information as even source rocks located in apparently good potential zones at present i e in the on structure area can be of minor importance for a trap due to slow generation rates and consequent low expulsion efficiencies

hydrocarbon potential and depositional environment of the lower cretaceous black mudstones and shales in the coastal guangdong province china abstract the mesozoic especially the cretaceous sequences in the northern south china sea scs are important potential targets of oil and gas exploration however they are currently poorly understood we use organic petrology and geochemistry to evaluate the hydrocarbon potential and study depositional environment of the cretaceous black mudstones and shales from the dayawan section in the guangdong province china these mudstones and shales yield total organic carbon toc contents of 0 63 2 76 and most samples meet the requirement for higher toc source rocks organic matters in the mudstones and shales were sourced mainly from higher plants as well as subordinate benthic macroalgae organic petrology and geochemical data suggested that the organic matters were dominated by type iii and minor type ii and generally have low thermal maturity thus we evaluated the black mudstones and shales have a potential for hydrocarbon generation especially gas prone pr ph trace elements and mixture source of organic matter suggested that these black mudstones and shales formed in a coastal lacustrine environment characterized by weakly oxidizing weakly reducing conditions and low salinity a marine transgression developing in the middle part of the section was recognized generally the northern scs which exhibits the more marine influence likely contains source rocks with higher toc contents and better organic matter types the cretaceous source rocks with higher liquid hydrocarbon generation potential may occur locally in the pearl river mouth basin

sub surface structure of la soufriere of guadeloupe lava dome deduced from a ground based magnetic survey abstract in this study we present the analysis and interpretation of a new ground magnetic survey acquired at the soufriere volcano on guadeloupe island observed short wavelength magnetic anomalies are compared to those predicted assuming a constant magnetization within the sub surface the good correlation between modeled and observed data over the summit of the dome indicates that the shallow sub surface displays relatively constant and high magnetization intensity in contrast the poor correlation at the base of the dome suggests that the underlying material is non to weakly magnetic consistent with what is expected for a talus comprised of randomly oriented and highly altered and weathered boulders the new survey also reveals a dipole anomaly that is not accounted for by a constant magnetization in the sub surface and suggests the existence of material with decreased magnetization beneath the soufriere lava dome we construct simple models to constrain its dimensions and propose that this body corresponds to hydrothermally altered material within and below the dome the very large inferred volume for such material may have implications on the stability of the dome

geochemistry of the sunnfjord melange sediment mixing from different sources during obduction of the solund stavfjord ophiolite complex norwegian caledonides

ultramafic rocks of a fracture zone ophiolite north cascades washington abstract the ingalls complex was deformed in a late jurassic oceanic fracture zone an unusually diverse group of ultramafic tectonites comprise three units in this ophiolite unit 1 consists mostly of poorly to moderately foliated harzburgite and dunite characterized by porphyroclastic textures irregular shaped and tabular dunite bodies probably represent intrusive bodies or residues of partial melting voluminous unit 2 consists mostly of poorly to strongly foliated iherzolite and clinopyroxene bearing harzburgite plagioclase peridotite is present locally olivine and enstatite generally define equigranular mosaics or weakly porphyroclastic textures clinopyroxene however in some samples displays only weak deformation compositional zoning simple growth twins and interstitial commonly poikilitic texture clinopyroxene and plagioclase in these samples probably formed from a melt after recrystallization of olivine and enstatite indicating that these iherzolites are impregnated peridotites other iherzolites and clinopyroxene bearing harzburgites may represent weakly depleted mantle pods of metagabbroic gneiss within unit 2 probably are small intrusions that were deformed as they cooled unit 3 represents a major high temperature 700 900 c shear zone that separates units 1 and 2 and consists of strongly foliated commonly mylonitic iherzolites and hornblende peridotites the latter are the most strongly foliated ultramafites and olivine in them records stresses as high as 275 mpa the abundance of hornblende implies a genetic relationship between mylonitization and the hydration and metasomatism necessary to form such rocks from iherzolites mineral chemistry and geothermometry are typical of mantle tectonites in many ophiolites and oceanic fracture zones there is a particularly strong similarity between the spinels in the ingalls complex and the spinels from the owen and vema fracture zones hornblende in unit 3 ranges from edenite to edenitic hornblende calculated temperatures from cpx opx pairs in unit 2 range from 950 to 1000 c these data are best explained by horizontal and vertical displacements in oceanic fracture zones which may juxtapose lithosphere formed at different structural levels and with different petrologic histories unit 1 represents a block of upper mantle which probably experienced convective upwelling and partial melting beneath a spreading ridge near its intersection with a fracture zone during convective upwelling at least parts of the upper mantle represented by unit 2 were impregnated by a melt the impregnated iherzolite may be accounted for by the edge effect at a fracture zone or reduced melt production at a fracture zone due to ribbon spreading the mylonite zone of unit 3 reworks iherzolites and harzburgites which were originally part of the block represented by unit 2 and probably records deformation in the active segment of the fracture zone these observations document the complexities that may occur in ultramafic rocks within oceanic fracture zones they also suggest that impregnation metasomatism and high stresses are important in these zones

the thermal history of the bowen basin queensland australia vitrinite reflectance and clay mineralogy of late permian coal measures abstract the thermal history of the bowen basin queensland australia has been investigated using vitrinite reflectance data and clay mineralogy vitrinite reflectance data combined with a study of clay mineral reactions indicates that the maximum temperatures which induced organic maturation of the bowen basin coals and extensive clay mineralisation are not related to deep burial metamorphism during the latest middle triassic earliest late triassic as previously believed the results of the present study indicate that the development of a zone of high heat flow in the latest late triassic had a major control on the thermal history of the bowen basin high palaeogeothermal gradients estimated in the northern bowen basin are interpreted to result from convective heat transfer during a hydrothermal event variable heat distributions due to localised fracture enhanced permeable zones acting as hot reservoirs in the deeper part of the basin may have been responsible for some significant local thermal anomalies in the lower coal measures the estimated palaeogeothermal gradients in the southern bowen basin also indicate high heat flow in the lower sections of the stratigraphy sections in the southern bowen basin however are believed to reflect a rock dominated semi closed system with low water rock ratio where rocks are impervious to circulating fluids and thus heat transfer may have occurred by conduction the correlation between vitrinite reflectance and clay mineralogy shows a delay in illitisation reaction relative to organic maturity for many illite smectite i s mixed layer clays in the northern bowen basin this phenomenon can be explained as a result of insufficient time for the completion of mineral reactions and a variable potassium supply in relatively impermeable rocks the relationship between i s expandability and vitrinite reflectance for the bowen basin data compared to basins with known tectonic regimes suggests a thermal history in a rift setting for the bowen basin the effect of thin igneous intrusions on clay mineral reactions is very limited intensive illitisation due to heating of intrusions can only be observed in narrow zones immediately adjacent to intrusive bodies this further demonstrates that mineral reactions are too slow to record the effect of extremely short heating duration in contrast to organic maturity indicators these differences between mineral and organic parameters aid in the identification of local contact metamorphic effects

development of microporosity in a micritic limestone reservoir lower cretaceous middle east abstract abundant intercrystalline microporosity is developed within the matrix of micritic limestones over several hundreds of meters of section in the thamama group lower cretaceous at sajaa field eastern u a e sediments in the upper shuaiba formation uppermost tamama group include muddy rudist algal coralgal and orbitolina dominated lithofacies matrix is composed of euhedral to subhedral micro rhombic low mg calcite crystals with average diameters of about 5 m microporosity development was not related to leaching chalkification of lithified micrite during post depositional emergence of the shuaiba formation features diagnostic of emergence are lacking in core below the upper contact of the unit matrix microporosity is believed to have been an early developed property of micritic limestones trace element compositions of matrix reflect a diagenetic process that involved conversion of a calcitic lime mud into micro rhombic micrite and microspar using a closed system geochemical model the observed matrix oxygen isotope compositions 18 o of 4 to 5 pdb are compatible with dissolution of aptian lime mud 18 o of 2 pdb and reprecipitation of calcite in fluids of marine composition under conditions corresponding to burial depths of 550 800 m porosity of 30 50 at 40 50 c closed system conditions are consistent with textural constraints for limited or arrested cementation in the matrix chemical compaction was responsible for partial occlusion of matrix microporosity as microporosity is decreased in zones of intense stylolitization slight corrosion of matrix crystals and leaching of peloids and orbitolina postdated cementation and chemical compaction during deep burial

coalification in the northern wildhorn nappe and adjacent units western switzerland implications for tectonic burial histories abstract vitrinite reflectance of fourteen eocene coal samples from the northern wildhorn nappe in the kander valley have been analyzed and compared to nine agewise similar coals from adjacent tectonic units the degree of coalification decreases regularly from semi anthracite in the kander valley to lignite in the plateau molasse the degree of coalification in the tertiary coals appears to be solely dependent on their tectonic history and indicates and estimated 6 km of burial by higher pennine nappes for the kander valley the rank at this locality low volatile bituminous to semi anthracite is significantly higher than in the border chain at beatenberg high volatile a bituminous the latter locality therefore was never buried deeper than about 4 km a further decrease in rank is found in the subalpine flysch and molasse high volatile b bituminous which in turn is significantly more mature than lignites from the folded plateau molasse at linden two samples of dogger coal from the pennine prealpes medianes are medium to low volatile bituminous that is intermediate between the kander valley and beatenberg their rank however was achieved before their final emplacement north of the wildhorn nappe by comparing calculated tti time temperature indices values for time depth burial curves with measured vitrinite reflectances maximum burial temperatures were estimated for the various tectonic units for the wildhorn nappe 160 180 c were obtained in the kander valley and 100 130 c in the border chain as a result of tectonic burial due to the thrusting by the pennine prealps sedimentary burial led to temperatures of 100 120 c in the subalpine molasse below the border chain prior to its thrusting

uplift of deep crust during orogenic extensional collapse a model based on field studies in the sogn sunnfjord region of western norway the western gneiss region wgr in norway experienced high pressure metamorphism during silurian devonian continent continent collision the eclogite bearing lower crust is separated from the middle and upper crust by major detachment zones formed during extensional collapse of the orogen formation of the devonian basins is related to the extension the footwall of the detachment zones comprises three structural and metamorphic zones the upper zone zone 1 is characterized by penetrative homogeneous down to the west simple shear developed under retrograde greenschist facies metamorphism zone 2 suffered inhomogeneous simple shear of the same polarity petrography and mineral chemistry data from the lower zone zone 3 show a record of initial eclogite facies metamorphism at 600 c and 16 kbar which was decompressed almost isothermally to amphibolite facies conditions at 550 c and 10 12 kbar both the eclogite and amphibolite facies metamorphism developed in a regime of pure shear with vertical shortening the rapid decompression records an approach of approximately 20 km to the surface related to uplift that was probably the result of the removal of a thickened thermal boundary layer in the mantle lithosphere the pure shear regime which developed initially in the lower crust was truncated by zones of simple shear as the lower crust was uplifted to middle and upper crustal levels extension by simple shear in the upper crust was rooted in the lower crust where extension occurred by pure shear the shear zones in zones 1 and 2 did not penetrate the pure shear regime of the lower crust a considerable amount of tectonic stripping of the orogenic welt predates deposition of the devonian sedimentary basins

magmatic development and tectonomagmatic models for the solund stavfjord ophiolite complex west norwegian caledonides abstract geochemical variation and different extrusion rates of the late ordovician solund stavfjord ophiolite complex ssoc suggest both open and closed magma chambers closed chambers existed off axis and within a transform fault and are indicated by dykes and pillow lavas that evolved from high mgo basalt to ferrobasalt by fractional crystallization of olivine plagioclase and clinopyroxene hybrid magmas with ferrobasaltic composition represent open magmatic systems and are characterized by frequent eruptions of sheet flows the ssoc is interpreted as representing either a normal or a propagating ridge transform intersection rti the propagating rti model is favoured as it explains both the high frequency of ferrobasalt and uplift of ultramafic rocks to above the sea level which is suggested by detrital ultramafics occurring in an ophiolitic melange

gravity terrain corrections calculated using digital elevation models corrections for terrain effects are required for virtually all gravity measurements acquired in mountainous areas as well as for high precision surveys even in areas of low relief terrain corrections are normally divided into two parts one part being the correction for terrain relatively close to the gravity station the inner zone correction and the other part being the correction for more distant say 2 km terrain the latter correction is normally calculated using a machine procedure that accesses a digital terrain data set the corrections for terrain very close to the gravity station are done manually using hammer s 1939 procedures or a similar method are guessed in the field or simply are neglected occasionally special correction procedures are used for the inner zone terrain corrections e g lafehr et al 1988 but such instances are uncommon

lithic volcanic sandstones derived from oceanic crust in the franciscan complex of california sedimental memories of source rock geochemistry the permanente terrane part of the franciscan accretionary complex of california contains an unusual fault bounded packet bearing lithic volcanic sandstones and conglomerates based on petrographical sedimentological stratigraphical and geochemical studies it is concluded that these rocks were deposited on the flank of an oceanic rise or plateau by sediment gravity flows probably below the carbonate compensation depth the bulk geochemistry of the sandstones is similar to the chemistry of greenstones in the permanente terrane suggesting that the greenstones or rocks similar to them represent the source of the lithic volcanic sandstones and that the sandstones geochemically remember the chemistry of their source rocks this sedimental memory is impressive geochemical variation in the sandstones is co linear with presumable magmatic variation trends in the greenstones sandstone geochemistry plotted on zr y vs y and v vs ti diagrams shows that compositions occupy similar fields as greenstones in the permanente terrane and oceanic crustal compositions in general because oceanic crustal sequences can become accreted to continental margins oceanic crust should be considered a potential source of sediment especially in continental margin settings however differentiating sandstones derived from oceanic arcs and from oceanic crust is extremely difficult unless discriminating geochemical criteria are used

the antarctic margin and its possible hydrocarbon potential abstract geological and geophysical data over the antarctic margin are reviewed to define those areas where thick sedimentary sequences occur which may have potential to source hydrocarbons where possible the waples lopatin model has been used to calculate whether the degree of maturation of the sediments is sufficient for hydrocarbons to have been generated significant sedimentary sequences occur along the continental margins of wilkes land western dronning maud land antarctic peninsula and ellsworth land and as basins or troughs on the continental shelf of prydz bay weddell sea and ross sea maturation assessments are possible for western dronning maud land eastern weddell sea western antarctic peninsula ellsworth land and ross sea regions within the great limitations of the data only western weddell sea and ross sea basins have maturation values sufficient for the generation of hydrocarbons

post alleghanian unroofing history of the appalachian basin pennsylvania from apatite fission track analysis and thermal models results of apatite fission track analyses on 29 ordovician through permian sandstones from the appalachian basin in pennsylvania are presented ages range from 111 17 to 184 10 ma mean track lengths of 10 71 0 29 to 13 10 0 17 m with unimodal negatively skewed length distributions are indicative of slow cooling the data separate into two groups on an age versus mean length plot the younger group 111 144 ma is found in the structural depressions of the anthracite basin and the broad top basin and adjacent appalachian plateau the older group 144 184 ma is found in the structurally higher southwestern appalachian plateau and juniata culmination and adjacent central plateau fission track data suggest that the basin cooled slowly after the alleghanian orogeny with culminations cooling earlier than depressions cooling histories modeled from apatite fission track data with maximum temperatures constrained by vitrinite reflectance indicate cooling beginning soon after the alleghanian orogeny except in the juniata culmination which apparently experienced synorogenic cooling and unroofing during formation of the underlying duplex model cooling histories and available geologic information indicate that the foreland basin did not experience mesozoic reheating unroofing histories were modeled from fission track cooling histories using heat flow estimates and burial depths derived from vitrinite reflectance profiles the models suggest that the unroofing history of the appalachian basin in pennsylvania can be divided into three episodes an initial episode of relatively rapid cooling and unroofing late permian early jurassic is attributed to flexural rebound of the foreland in response to erosional removal of alleghanian topographic load initial unroofing rates are higher in eastern pennsylvania than in the west consistent with a flexural model an episode of little to no unroofing middle jurassic late oligocene began contemporaneously with the inception of drift at the atlantic continental margin at this time unloading of the orogen was replaced by subsidence and sedimentation on the new margin without flexural rebound the driving force for unroofing of the basin was removed and unroofing slowed greatly an episode of rapid unroofing over the full width of the basin occurred from the miocene to the present although the driving mechanism for unroofing at this time has not been identified it is consistent with increased sedimentation rates in the middle atlantic offshore basins for the same period

a common source rock for egyptian and saudi hydrocarbons in the red sea the northern red sea area hosts a classic triple junction of the red sea gulf of aqaba and gulf of suez rifted basins the sedimentary succession here can be divided into prerift pre miocene and synrift miocene and post miocene megasequences the prerift section has been penetrated in only a few wells drilled on the western egyptian side of the red sea whereas the synrift section is known on both the egyptian and the saudi sides of the red sea although the synrift units on both sides of the water are similar in facies thicknesses and depositional environments they have different stratigraphic nomenclatures the northern red sea consists of elongated troughs separated by elongated structural highs both of which trend northwest southeast gulf of suez trend these highs are dissected by cross elements trending northeast southwest gulf of aqaba trend and east northeast west southwest and are looked upon as strike slip faults dislocating these highs identified rich source rocks are present in the upper senonian carbonates the sudr and duwi formations on the western side of the sea the early miocene rudeis formation burqan group and the middle miocene kareem and belayim formations maqna group the pre miocene and the early miocene source rocks host oil prone kerogen whereas the middle and late miocene source rocks contain oil and gas prone kerogen all of these source rocks are sufficiently mature copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received january 18 1996 revised manuscript received october 11 1996 final acceptance march 21 1997 2faculty of science uae university p o box 17551 al ain united arab emirates we are especially grateful to the egyptian general petroleum corporation for supplying the materials and the necessary data on which the present work is based and the permission to publish it we also thank c g st c kendall and a e m nairn who read the early draft of this paper and offered valuable comments thanks to aapg reviewers d waples r j murris w maze and an anonymous reviewer for their constructive comments which we have used to improve our paper we acknowledge g cole bhp petroleum for granting permission to use some of his previous work

migration of orogenic fluids through the siluro devonian helderberg group during late paleozoic deformation constraints on fluid sources and implications for thermal histories of sedimentary basins abstract fluid inclusion data and fracture filling cement fabrics in deformed but non overthrusted carbonate and siliciclastic rocks of the siluro devonian helderberg group central appalachians indicate post cementation late paleozoic migration of high pressure high temperature fluids void filling quartz and calcite cements contain secondary two phase fluid inclusions liquid vapor which occur in annealed microfractures most melting temperatures last occurrence of ice are 20 to 25 c which correspond to salinities of greater than 22 equivalent wt nacl pressure corrected liquid vapor homogenization temperatures are 200 to 300 c and greatly exceed maximum paleotemperatures 150 c given by conodont cai values vitrinite reflectance illite crystallinity or temperatures calculated from known sedimentary overburden completely cemented sandstone and limestone also have multiple crosscutting trains of secondary hydrocarbon inclusions hydrocarbon inclusions occur along deformation microstructures in cements some hydrocarbon inclusion trains crosscut cement filled fractures the nature of occurrence of the secondary inclusions suggests that fluids moved along intracrystalline deformation microstructures either during or after late paleozoic deformation rare fractures contain transported skeletal grains exotic clasts lithologies different from wall rock recemented clasts of fracture filling cement and mud cement clasts contain solid inclusions of mud and skeletal fragments and indicate several episodes of particle transport cementation and refracturing prior to final fracture filling and cementation these fracture fills locally crosscut stylolites coarse grained poorly sorted clastic fracture fills suggest migration of rapidly moving fluids which were capable of transporting clasts through fracture conduits under deep burial conditions conduction calculations place upper limits on size and duration of thermal anomalies which were caused by extrabasinal fluids these calculations indicate that hot fluid migration events most likely were short lived heat transfer by extraformational fluids moving along faults and fractures may have been the mechanism by which thermal anomalies developed in the helderberg group stratigraphic constraints suggest that likely sources for the hot brines are overthrusted terranes to the east of the study area possible stratigraphic horizons which were sources for the overpressured hot fluids may have been thick cambrian shales which are important detachment horizons for major late paleozoic thrust sheets in the eastern valley and ridge province east of the study area fluids may have migrated during thrusting along thrust faults which ramp upwards from east to west into stratigraphically higher units thrust faults ultimately die out in devonian units some of the dissolved ions in the secondary two phase inclusions may have been incorporated when shale derived fluids moved through silurian evaporites or cambro ordovician carbonates which contain evidence of cryptic evaporites potential source rocks for secondary hydrocarbon inclusions may have been lower silurian through lower devonian strata based on lopatin modeling and assuming that migration occurred during late paleozoic deformation this study may help to explain many apparently anomalous geologic phenomena in deformed foreland basin sediments it also has implications for tracking migration pathways for fluids which facilitate regional scale deformation in fold and thrust belts and how tectonic fluids may affect the rocks through which they move

oxygen and carbon isotope compositions of carbonates in a prominent lithologically mixed unit in the central south norwegian caledonides a prominent pre scandian lithologically mixed unit in the central south norwegian caledonides contains more than 100 partly carbonated and hydrated metaperidotite bodies and locally fossiliferous detrital serpentinites the lateral consistency of this mixed unit was not fully appreciated in the past therefore parts of the mixed unit along strike were interpreted to belong to several different tectonostratigraphic levels here we present new carbonate stable isotope data that suggest that the carbonates of the mixed unit between bergen and otta re equilibrated at unit wide similar peak metamorphic conditions the isotope compositions are characteristic for this unit and indicate that it represented one single tectonic unit during the scandian orogeny the carbonates in the melange are characterized by a narrow range of 18o smow values between 11 and 15 5 and three groups of 13c pdb values i 1 6 to 0 3 ii 1 8 to 3 9 and iii 6 to 8 6 carbonates of group iii probably were affected by decarbonation or by a fluid containing organic carbon whereas carbonates of group i and ii overlap with 13c values typical for ediacaran silurian marine carbonates and may have retained their initial 13c imprint we suggest that the 18o values re equilibrated with unit wide released metamorphic fluids during scandian metamorphism an outcrop scale homogenisation of the 13c values reflects the local carbon isotope signature of the released metamorphic fluids that circulated channelized through the melange unit

zabargad st john s island an uplifted fragment of sub red sea lithosphere zabargad is a small island located in the red sea about 50 km w of its axis between 23o and 24on the island is not volcanic but probably represents an uplifted block of upper mantle and crustal rocks and yields information on the nature of the underlying lithosphere peridotites are the main rock type consisting of exceptionally fresh spinel lherzolites which equilibrated last at a depth 30 km in the mantle other ultramafic facies some representing rocks which mixed with a basaltic melt fraction and some which underwent metasomatic exchange at depth are also present the peridotite bodies are in tectonic contact with a metamorphic formation consisting of gneissic and amphibolitic rocks similar to those outcropping in the pan african metamorphic basement of eastern egypt peridotites and metamorphic rocks are both crossed by several generations of basaltic dykes the sedimentary zabargad formation of probable cretaceous or palaeocene age consists of alternations of silicified limestones sandstones black shales and phosphoritic lenses and is overlain by evaporites probably of miocene age and by reef limestone units one probably of early pleistocene age the other probably deposited during the last interglacial various formations are affected by localized metasomatic mineralizations recrystallized large gem quality olivine cancrinite scapolite garnierite the uplift of upper mantle ultramafic bodies with fragments of crust which created the island might have occurred in connection with the early stages of development of the rift which preceded the formation of the red sea an alternative explanation that the zabargad peridotites are remnants of a pan african palaeozoic ophiolitic complex is possible but less likely

a sloping wedge technique for calculating gravity terrain corrections gravity terrain corrections account for the upward pull of topographic features which are higher than a gravity station hills and the lack of downward pull from open space which is lower than the station valleys in areas of rugged topography or in high precision surveys the magnitude of the terrain corrections can be comparable to the anomalies being sought and the uncertainties in the terrain corrections can limit the accuracy of the survey also calculating the corrections can require more time and effort than gathering the original field data even if terrain corrections are not made it is necessary to show that their omission does not compromise the integrity of the survey

determination of critical parameters for evaluating coal measure shale gas in china abstract coal measure shale is one of the most abundant types of marine continental shales in china two sets of typical coal measure shales in china are developed in the shanxi formation ordos basin and in the longtan formation guizhou province in this study thermal simulation rock pyrolysis and x ray diffraction experiments were used to analyze four coal measure shale samples collected from typical areas of china based on the study of hydrocarbon generation process of the samples the lower limits of thermal maturity ro of favorable and target areas for coal measure shale were 1 8 and 2 5 respectively the threshold ro value of oil generation in coal measure shale was preliminarily inferred to be 0 6 the gaseous hydrocarbon production per unit of s1 s2 after the gas generation threshold was linearly and positively correlated with ro the lower limits of total organic carbon toc corresponding to the favorable and target areas were 2 45 wt and 2 84 wt respectively combined with x ray diffraction experiments the diagenetic stage and the hydrocarbon generation model of coal measure shale were established and could be divided into four evolutionary stages the results of this study have direct scientific and practical significance for the evaluation of gas content and selection of areas in china for the extraction of coal measure shale

cyclic volcanic stratigraphy in a late ordovician marginal basin west norwegian caledonides the well preserved extrusive sequence of the solund stavfjord ophiolite complex ssoc in the west norwegian caledonides enables reconstruction of the uppermost oceanic crust that developed in a marginal basin basaltic sheet flows pillow lavas and volcanic breccias are the main components of the extrusive sequence and show stratigraphic and structural evidence for a cyclic development the first stage in a volcanic cycle is characterized by high extrusion rates yielding sheet flows commonly with the thickest flow units at the base sequences of sheet flows can be correlated laterally for at least 6 5 km pillow lavas succeed the sheet flows later in a volcanic cycle with progressively smaller pillows forming at decreasing extrusion rates volcanic breccias occur towards the end of a volcanic cycle but may also occur at lower stratigraphie levels they are made generally of pillow breccias and hyaloclastites the extrusive sequence of the ssoc oceanic crust was constructed through seven volcanic cycles that resulted in stratigraphic units with thicknesses ranging from 40 to 225 m this architecture is comparable to sequences in in situ oceanic crust developed along slow to intermediate spreading ridges

seismic stratigraphic analysis of the punta del este basin offshore uruguay south america the punta del este basin of offshore uruguay is one of a series of mesozoic sedimentary basins along the eastern seaboard of south america the basin resulted from continental rifting of an older gondwana landmass this rifting led to the initiation of the south atlantic ocean the tectonic and stratigraphic history of the basin can be characterized by a three phase evolution with each phase involving a separate and distinct basin geometry style of faulting and lithostratigraphic succession the rift phase deposited predominantly continental siliciclastics of neocomian age arranged in a number of syndepositional assymetric trap door grabens this phase is overlain by a largely unfaulted succession of continental to marine rocks of the sag basin phase of aptian to maastrichtian age these rocks record an overall marine transgression the passive margin phase is represented by a thick sequence of tertiary sediments that postdate rift related tectonism and correspond to sedimentation along the margin of the newly opened south atlantic ocean the punta del este part of the greater salado basin is relatively unexplored with only two wells having been drilled both in the updip part of the basin these two wells have contributed some understanding of the stratigraphic succession but have failed to adequately assess the basin s true hydrocarbon potential this paper constitutes one of the first detailed comprehensive published accounts of this basin and is a prerequisite for future exploration in the area

evidence for a fossil transform fault in the solund stavfjord ophiolite complex west norwegian caledonides on the island of tviberg west norway a sheeted dike complex is rotated anticlockwise into parallelism with a zone of strong deformation hosting screens of sheared meta ultramafite incompatible element enriched high level plutonic rocks and two swarms of mafic dikes are intruded into sheared and unsheared meta ultramafites intrusion and sinistral shearing of the high level plutonic rocks and an old swarm of mafic dikes took place contemporaneously with sinistral shearing of the meta ultrabasites these field relationships are interpreted to reflect magmatism within a transform fault and the dike rotation is explained as fault drag along a strike slip zone in the transform a younger swarm of mafic dikes striking at a high angle to the shear zones transects all tectonic structures and may reflect a second phase of magmatism within the transform in fault contact with the transform fault related plutonic rocks and dikes lenses of serpentine diatreme breccias and lenses of sediments composed of mafic and ultramafic detritus are hosted in a phyllonitic matrix comprising basic ultrabasic and continent derived detritus this rock unit is interpreted as an ophiolitic melange and it probably started to form when obduction of the ophiolite nucleated on the transform

petroleum geology of southern iraq subsurface relations of the albian rocks in southern iraq are postulated from the study of lithofacies electrical well logs petroleum occurrences geothermal source rocks maturation and hydrogeologic mapping from these studies an evaluation of the commercial potential for oil in the nahr umr formation became feasible it appears that a petroliferous belt exists in the marine marginal facies of the lower albian nahr umr sandstone the oil in the nahr umr reservoirs has probably been generated in deep lower cretaceous source rocks and may have started to generate as early as paleocene time the upper shale beds of the nahr umr formation supersedes the ahmadi shale formation which acts as a cap rock to the albian reservoirs in kuwait and neutral zone hitherto no economic oil trap has been discovered in the upper albian mauddud formation that overlies the nahr umr and underlies the ahmadi in southern iraq

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

the solund stavfjord ophiolite complex and associated rocks west norwegian caledonides geology geochemistry and tectonic environment

the role of fracture zones during early red sea rifting structural analysis using space shuttle radar and landsat imagery the structural pattern of the red sea region an area where continental lithosphere is cut by a young oceanic rift was studied by means of satellite and space shuttle radar imagery the space shuttle mission 2 made two passes over the red sea bracketing a region transitional between the southern red sea where true seafloor spreading started about 5 ma bp and the northern red sea where crust is probably continental though thinned and stretched structures on these passes define bands of shearing in the african and arabian margins parallel to the dead sea fracture zone 000 020 combinations of these data with landsat information reveal four shear bands along the margins of the red sea and one oblique to the gulf of suez we have named the northern three red sea shear zones detected on the sir a data the brothers dead sea fracture zone the zabargad fracture zone and the shagara fracture zone two sets of normal faults were also detected trending 330 340 parallel to the northern red sea coastline and 310 320 parallel to the axial deeps in the red sea a map of the 310 320 faults bordering the red sea resembles a v shaped wedge narrowing to the north near the gulf of suez these faults may have formed as a result of the most recent push of seafloor spreading if this is so then there may be a propagating tectonic wedge moving from south to north which thins the continental crust up to distances of 300 km from the axis of spreading following continental deformation oceanic crust may be emplaced in 9hot points9 along the rift axis these 9punctiform9 oceanic spreading centres should propagate in the same direction as continental rifting during this episode palaeo shear zones probably act as barriers 9locked zones9 to the axial propagation one such case is at the zabargad fracture zone where the oblique impact of the propagating rift against the palaeo shear may have placed the red sea9s western side under compression and uplift while the eastern side may have been subject to oblique extension with the formation of pull apart basins the space shuttle imagery allows integration of some of the northern red sea morphotectonic features with structures on the continent

palynofacies analysis of sediments from the cote d ivoire ghana transform margin preliminary correlation with some regional events in the equatorial atlantic abstract analyses of the palynofacies and sporomorph thermal alteration indices tai of sediments from ocean drilling program odp sites 959 to 962 in the cote d ivoire ghana transform margin west africa were undertaken to 1 determine the source and depositional conditions of the organic matter in the sediments 2 refine a paleobathymetric curve derived from other data for site 959 which drilled the most continuous sedimentary sequence from pleistocene to albian and 3 interpret the paleothermal history of the area twelve types of dispersed organic matter were identified amorphous organic matter aom marine palynomorphs algae resins black debris yellow brown fragments black brown fragments cuticles plant tissue wood sporomorphs and fungi the relative abundances of these organic matter components at each site were analyzed using cluster analysis resulting in the identification of seven palynofacies assemblages at site 959 five each at sites 960 and 961 and four at site 962 amorphous organic matter which is chiefly marine derived black debris and wood have played the most significant role in defining palynofacies assemblages the palynofacies assemblages show some correlation with lithologic units sediment sources and depositional environments previous palynofacies studies in passive margins have demonstrated that changes in the ratio of aom to terrestrial organic matter are related primarily to proximal distal positions of depositional environments relative to the shoreline however this assumption does not always hold true for a transform margin where tectonic factors play an important role in the organic matter distribution at least in the early stages of evolution lithofacies ccd paleodepths for the north atlantic trace fossil association benthic foraminifera and palynofacies data were the criteria used for reconstructing a paleobathymetric curve for site 959 a cyclicity in the organic matter distribution of the upper miocene to lower pliocene pelagic sediments could be related to fluctuations in productivity of biosiliceous and calcareous organisms and sedimentation rates a drastic increase in the amount of aom and a decrease in black debris and wood in the carbonate and clastic rocks lithologic unit iv overlying the tectonized albian sediments lithologic unit v at sites 959 and 960 coincide with the presence of an unconformity qualitative color analysis of palynomorphs was undertaken for all sites although the main focus was on site 959 where detailed organic geochemical data were available at site 959 tai values indicate an immature stage of organic maturation 2 except for the claystone samples between 1012 52 and 1036 5 mbsf and one limestone sample at 1043 4 mbsf reaching peak levels of 2 58 to 3 0 in the tectonized albian sediments below the unconformity these tai values show a positive correlation with the tmax values derived from rock eval pyrolysis data the highest values recorded in the basal tectonized units at all the sites sites 960 962 have mean values between 2 25 and 3 13 may be related to high heat flow during the intracontinental to syntransform basin stage in the region

ordovician faunas island arcs and ophiolites in the scandinavian caledonides ordovician faunal data from the scandinavian caledonides is tested with new geochemical information from zircons to give u pb ages and source origins of volcanic arc and ophiolite sequences early ordovician arenig llanvirn low latitude toquima table head faunas from the upper upper allochthon are associated with an island arc system formed adjacent to laurentia contemporaneous mafic magmas were contaminated by crustal material during subduction and associated granites contain inherited zircons of archaean age the nearest source for such rocks is on the laurentian rather than the baltic side higher latitude celtic province faunas from the upper upper allochthon are from one insular site accessible to forms from both laurentia and baltica the late ordovician low latitude holorhynchus and subtropical hirnantia faunas occur in overstep sequences above deeply eroded early ordovician arc complexes the transgression appears to be coeval with a second generation of spreading related complexes single detrital zircons from sediments show sources from archaean proterozoic and early ordovician terranes this suggests that deposition was in a basin situated along the same continental margin laurentia to which the early ordovician ophiolite arc sequences had already become accreted the late ordovician faunas link both laurentia and baltica at a time of narrowing of lapetus the new geochemical data together with the faunal information is supported by recent palaeomagnetic studies

volcanic evolution of oceanic crust in a late ordovician back arc basin the solund stavfjord ophiolite complex west norway 1 the stratigraphy of the well preserved solund stavfjord ophiolite complex in the west norwegian caledonides documents the volcanic evolution of a spreading center in a late ordovician back arc basin basaltic sheet flows pillow lavas and volcanic breccias are the main components of the 470 800 m thick extrusive sequence and are organized stratigraphically in a cyclic manner cyclic units vary in thickness from 5 m to 225 m and are typically composed of basal sheet flows or lava flows with large pillows that are succeeded by flows with progressively smaller pillows and volcanic breccias thick independent breccia units also occur in the stratigraphy in sheet flow dominated parts of the sequence the cyclic units are thicker average 85 m than in pillow dominated parts average 20 m detailed logging of closely spaced profiles 1 km or less apart shows that the proportions of sheet flows pillow lavas and volcanic breccias varies laterally along an axial segment of less than 10 km the volcanic products change from predominantly sheet flows reflecting robust volcanic centers to pillow lavas to volcanic breccias sheet flow dominated volcanic centers seem to be spaced at intervals of 25 30 km and we tentatively interpret their regularity as an expression of volcanic segmentation at an intermediate to fast spreading center observations of modern ocean crust suggest that sheet flows dominate at fast spreading ridges while pillow lavas dominate at slow spreading ridges volcanic breccias are apparently rare in both of these environments these features contrast with the stratigraphy of the solund stavfjord ophiolite complex where the proportion of different volcanic products varies laterally and volcanic breccias are common we emphasize the importance of detailed studies of the volcanic stratigraphy of ophiolites as complements to those of in situ oceanic crust in order to provide a more complete picture of volcanic evolution of oceanic crust in different spreading regimes

bed thickness and grain size of turbidites in measured sequences of limestone and greywacke turbidites the bed thickness is found to vary proportionally with the fall velocity of the maximum grain size found at the base of the bed a simple theoretical model based on the decay of isotropic turbulence suggests that bed thickness should be a function not only of this fall velocity but also of bottom slope flow depth and the concentration and grain size distribution of the sediment in the turbidity current the field data do show some influence of these additional factors nevertheless for many natural sequences of turbidites the flows must have carried very poorly sorted sediments and the inferred flow volumes and densities must cluster tightly about modal values thus grain size remains the primary variable and the modal regression curve of bed thickness on maximum grain size is well defined and resembles a fall velocity curve relatively steep basin floors near to source can theoretically cause these modal regressions for distal and very proximal parts of a turbidite to diverge introducing a crudely parabolic appearance in the form of the total regression curve the form of this parabolic curve predicts the deposition of thin but relatively coarse proximal beds such beds do occur they are different from the thin but relatively fine proximal beds that have been interpreted as the result of a fractionation of a turbidity current during levee forming processes

the sunnfjord melange evidence of silurian ophiolite accretion in the west norwegian caledonides a major composite terrane the sunnfjord melange has been identified in the west norwegian caledonides the rocks of the melange provide a terrane link between the allochthonous continental rocks of the dalsfjord suite with its cover of continental margin deposits and the oceanic terrane of the solund stavfjord ophiolite complex the melange was formed as the ophiolite was emplaced on the the fossiliferous lower to middle silurian continental margin deposits of the herland group this group unconformably overlies older metasedimentary rocks of the hoyvik group and the crystalline basement of the dalsfjord suite a structural style characteristic of thin skinned thrust foldbelts is locally preserved within the herland group on atloy and the thrust foldbelt was developed in the foreland of the continental margin during the ophiolite accretion a u pb zircon age of 443 3 ma from the ophiolite the silurian fossils in the herland group and the identification of the sunnfjord melange as an obduction melange provide the basis for a well constrained model of ophiolite accretion in the scandinavian caledonides

role of diffusion in primary migration of hydrocarbons the following effective diffusion coefficients d cm2 sec were determined for the diffusion of light hydrocarbons through the water saturated pore space of shales methane 2 12 10 6 ethane 1 11 10 6 propane 5 55 10 7 iso butane 3 75 10 7 n butane 3 01 10 7 n pentane 1 57 10 7 n hexane 8 20 10 8 n heptane 4 31 10 8 and n decane 6 08 10 9 on the basis of these new data a deterministic dynamic model was set up to simulate the diffusive transport of light hydrocarbons c1 to c10 from source rocks for eight documented source rock units representing a wid range of geologic conditions maturities of 0 40 to 1 35 mean vitrinite reflectance oil to gas prone kerogens the cumulative amounts of hydrocarbons escaping with time were calculated thus it was shown that diffusion represents an effective process for primary migration of gas but not for oil the rate of mass transport for gas from source rocks with geologic time can be sufficiently high to account for the origin of commercial size gas fields for example a cumulative amount of 109 kg of methane 1 5 109 std m3 or 5 3 1010 scf has escaped by diffusion in 540 000 years from a certain volume 1 000 km2 by 200 m thick of a high mature gas prone mesozoic source rock in western canada the origin of hydrocarbon accumulations with high gas to oil ratios in low mature sediments in geologically young basins early gases and condensates can be explained by an early phase of primary migration predominantly based on diffusion during the initial stages of the accumulation history of those fields extending up to millions of years under certain conditions the reservoir gas changes with geologic time from a methane rich to a wet gas composition at low maturity levels below about 0 6 rm even oil prone source rocks yield methane rich light hydrocarbon mixtures by migration through diffusion compositional trends among reservoir gases of several multiple pay gas fields in louisiana represent evidence for diffusive transport of hydrocarbons the variation in gas composition between the individual pay zones is controlled by increasing distances of diffusive transport of the hydrocarbons from a uniform source rock at depth to their present accumulation sites in the shallow pay zones compounds of high diffusivity are enriched for example in the sligo gas field of louisiana the methane ethane and the iso butane n butane ratios increase from 10 2 to 36 0 and from 0 86 to 1 13 respectively from the deepest to the shallowest of the five productive reservoir sands which are spread over a a depth interval of 5 500 ft 1 676 m diffusion of light hydrocarbons in the subsurface can also have economically adverse effects for example existing gas accumulations can be destroyed by dissipation the rate of this destruction was calculated for the harlingen gas field holland by diffusive loss through 400 m of shale cap rock the initial amount of methane in place of 1 93 109 std m3 6 8 1010 scf is reduced by one half over a period of 4 5 million years this leads us to propose the concept that large gas accumulations can persist through extended periods of geologic time only as dynamic systems reaching some kind of steady state equilibrium between diffusive loss through the cap rock and continuous replenishment from the source rock

u pb ages of ophiolites and arc related plutons of the norwegian caledonides implications for the development of iapetus u pb zircon ages are reported for four ophiolites and three crosscutting arc related plutons from the norwegian caledonides plagiogranite differentiated from gabbro of the karmoy ophiolite is dated at 493 7 4 ma whereas arc related trondhjemite cutting this ophiolite crystallized at 485 2 ma a crosscutting clinopyroxene phyric gabbro intrusion is dated at 470 9 5 ma by near concordant magmatic titanite sphene and discordant u rich 2903 6677 ppm zircon lower intercepts of 247 68 and 191 70 ma defined by the plagiogranite and clinopyroxene phyric gabbro best fit lines may reflect a real low t alteration rift related event

ophiolitic source rocks for taconic age flysch trace element evidence flysch generated along the appalachian orogen during the ordovician taconic orogeny ranges in age from late arenig to early caradoc allochthonous flysch and from late llanvirn to ashgill autochthonous flysch sandstones in these units are dominantly lithic arenites with a heavy mineral suite containing common to abundant mg rich chromite north of the canada united states border the only reasonable sources for the chromite were the lower ultramafic units of obducted ophiolites trace element analyses cr ni v cu ti zr y of flysch sandstones indicate a striking increase in cr and ni concentrations from the united states appalachians to the canadian appalachians in the united states units cr is in the range of 10 to 50 ppm canadian flysch units average an order of magnitude more cr these results suggest that ophiolite obduction either did not occur or was of minor importance during the taconic orogeny in the united states appalachians the difference in ophiolite abundance between the canadian and united states appalachians suggests a fundamental difference in tectonic style along the orogen a feature that must be accommodated by plate tectonic models new models will probably need to consider both obliquity of subduction and geological complexity of the ordovician collision zone in order to explain the spatial distribution of obducted ophiolite sheets

archean metavolcanics from the rouyn noranda district abitibi greenstone belt quebec 2 mobility of trace elements and petrogenetic constraints qualitative evaluation of altered mafic pillows from the rouyn noranda district of the abitibi metavolcanic belt reveals that for low grade metamorphism the high field strength elements hfs zr y ti and the rare earth elements ree are immobile however where alteration is extreme the ree elements are leached and redeposited by carbonate rich and k rich metasomatic fluids whilst zr y and zr ti remain unchanged rubidium ba and to a lesser extent sr are mobile at all levels of alteration however provided certain filters are applied the original geochemical values of the lavas for the alkaline elements the hfs elements and the ree can be defined the geochemical variations thus identified for the volcanic series of the rouyn noranda district are ascribed to a combination of contamination and fractional crystallization of a primitive tholeiitic magma

basin analysis predictions of known hydrocarbon occurrences the north sea viking graben as a test case abstract basin analysis can assimilate structural burial and thermal histories to predict hydrocarbon prone zones in speculative areas the validity of the modelling approach was field tested in the north sea viking graben an area for which good data are available a recent birps deep seismic reflection profile across tectonic strike of the graben was interpreted and depth converted with good well control the burial and structural histories were determined by backstripping the chronostratigraphic layers using a one dimensional fluid flow compaction model on pseudo wells after removal of each sequence the section was manually reconstructed the thermal history was examined using thermal indicator tomography extensional models and calculations of depth to detachment lack of resolution required that three different paleo heat flow trends be tested to encompass the range in variability a gradual warming trend a constant heat flow through time and a low heat flow until the cretaceous tertiary boundary where a heat pulse occurred basement subsidence extension depth to detachment calculations and thermal indicator inversions all suggest that the uk side of the graben has developed differently to the norwegian section the generation modelling predicts the position of the oil window in the cross section the areas where this window enveloped the draupne formation kimmeridge clay source rock broadly correlate with the positions of the gullfaks statfjord and thistle oilfields of the uk sector however in the norwegian sector the draupne formation was generally overmature except in the area around the troll oilfield predicted middle to late cretaceous generation in the rift axis may have caused updip oil migration towards the horda platform the correct prediction of oil prone zones validates the use of quantitative basin analysis as a tool for evaluating frontier areas where data are limited

oil generation and migration in the gifhorn trough nw germany abstract the origin and migration of oils from selected oil fields in the gifhorn trough nw germany was investigated by geochemical analysis of crude oils and possible lower and middle jurassic source rocks productive reservoir sandstones in the gifhorn trough occur in the dogger beta zone of the middle jurassic bajocian and are interbedded with shales that contain 1 2 toc mostly type iii kerogen in the lower jurassic toarcian organic matter rich shales 9 12 toc whose kerogen has a type ii composition form the best quality oil prone source rocks biomarker and stable isotope analyses of oils and source rock extracts reveal that all oils analysed are derived from the lower toarcian shales lias epsilon the timing of oil generation and migration was investigated by reconstructing the geothermal history of the source rock in specific drainage areas and determining the availability of migration pathways through geological time hydrocarbon generation started in the central part of the gifhorn trough in upper cretaceous time differences in the maturity of the oils display separate small drainage areas close to the reservoirs variations in oil composition within deep buried reservoirs indicate the preservation of different migration phases

coalification and thermal histories of tertiary basins in relation to late alpidic evolution of the eastern alps the thermal histories of tertiary basins situated around and within the eastern alps are examined using coalification data waples method is used to estimate paleogeothermal conditions the data suggest that the basins thermal histories are intimately related to late alpidic geodynamics of the eastern alps

hydrocarbon prospects across narmada tapti rift in deccan trap central india inferences from integrated interpretation of magnetotelluric and geochemical prospecting studies abstract as the mesozoic sediments contribute most of the oil and gas reserves of the world we present an integrated interpretation approach using magnetotellurics mt and surface geochemical prospecting studies to demarcate hydrocarbon prospective gondwana mesozoic formations underneath the deccan flood basalts of late cretaceous age across narmada tapti rift between bhusawal and barwah in central india the mt interpretation shows deep 5 km basement structure between southern and central part of the mt profile however it gradually becomes shallower to either ends of the profile with a predominant basement depth reduction in the northern end compared to the southern end the geophysical results suggest thick 2 3 5 km mesozoic sediments in the area characterized by deep basement structure the geochemical analysis of the near surface soil samples indicate higher concentrations of light gaseous hydrocarbons constituents over the area marked with thick sub basalt mesozoic formations analyses of the geochemical data imply that these hydrocarbons are genetically related generated from a thermogenic source and these samples fall in the oil producing zone the temperature depth estimations in the region supports favorable temperature conditions 80 120 c for oil generation at basement depths

effects of smectite on the oil expulsion efficiency of the kreyenhagen shale san joaquin basin california based on hydrous pyrolysis experiments the amount of oil that maturing source rocks expel is expressed as their expulsion efficiency which is usually stated in milligrams of expelled oil per gram of original total organic carbon oil expulsion efficiency can be determined by heating thermally immature source rocks in the presence of liquid water i e hydrous pyrolysis at temperatures between 350 c and 365 c for 72 hr this pyrolysis method generates oil that is compositionally similar to natural crude oil and expels it by processes operative in the subsurface consequently hydrous pyrolysis provides a means to determine oil expulsion efficiencies and the rock properties that influence them smectite in source rocks has previously been considered to promote oil generation and expulsion and is the focus of this hydrous pyrolysis study involving a representative sample of smectite rich source rock from the eocene kreyenhagen shale in the san joaquin basin of california smectite is the major clay mineral 31 wt in this thermally immature sample which contains 9 4 wt total organic carbon toc comprised of type ii kerogen compared to other immature source rocks that lack smectite as their major clay mineral the expulsion efficiency of the kreyenhagen shale was significantly lower the expulsion efficiency of the kreyenhagen whole rock was reduced 88 compared to that of its isolated kerogen this significant reduction is attributed to bitumen impregnating the smectite interlayers in addition to the rock matrix within the interlayers much of the bitumen is converted to pyrobitumen through crosslinking instead of oil through thermal cracking as a result smectite does not promote oil generation but inhibits it bitumen impregnation of the rock matrix and smectite interlayers results in the rock pore system changing from water wet to bitumen wet this change prevents potassium ion transfer and dissolution and precipitation reactions needed for the conversion of smectite to illite as a result illitization only reaches 35 to 40 at 310 c for 72 hr and remains unchanged to 365 c for 72 hr bitumen generation before or during early illitization in these experiments emphasizes the importance of knowing when and to what degree illitization occurs in natural maturation of a smectite rich source rock to determine its expulsion efficiency complete illitization prior to bitumen generation is common for paleozoic source rocks e g woodford shale and retort phosphatic shale member of the phosphoria formation and expulsion efficiencies can be determined on immature samples by hydrous pyrolysis conversely smectite is more common in cenozoic source rocks like the kreyenhagen shale and expulsion efficiencies determined by hydrous pyrolysis need to be made on samples that reflect the level of illitization at or near bitumen generation in the subsurface

oscillatory spreading explanation of anomalously old uplifted crust near oceanic transforms rocks significantly older than their theoretically predicted age have been recovered in the vicinity of some atlantic transform zones rocks of palaeocene 55 58 myr and possibly even of cretaceous age are found near the vema transform on tectonically uplifted crust which should not be older than 30 myr we present here a model which might explain the presence of uplifted anomalously old crust near the vema transform zone tz the proposed model involves axial rift propagation and reorientation and migration of the transform as a result of a change in the regional stress field during transform migration a crustal wedge formerly part of the african plate is transferred to the south american plate the ensuing oscillatory spreading can explain the anomalous age of the uplifted crustal block compression resulting from rift propagation and transform migration provides a mechanism for crustal uplift

review of drones photogrammetry and emerging sensor technology for the study of dykes best practises and future potential abstract dykes play a major role in transporting magma through the crust to subsurface storage reservoirs or eruption sites at the surface the geometry connectivity and internal textures of dykes preserve an important record of dyke emplacement linkage and magma flow dynamics unravelling these facets of dyke evolution is critical to interpreting signals of magma migration in active volcanoes as well as tectonic processes including crust formation and continental break up during hazard assessment unfortunately our ability to develop new insights is limited by the continuity of high precision data that can be extracted from the field the emergence of unmanned aerial vehicles uavs a k a drones photogrammetry and other sensor techniques are set to greatly improve our field capabilities by collecting data at higher density and with greater precision here we present a workflow emphasising best practise in uav survey design the construction of photogrammetric models and standardised reporting of those models emphasis is given to the factors that should be considered in order to resolve the geological features of interest in any study e g wall rock fractures chilled margins magmatic breccias dyke apertures etc a point to raster technique is documented that measures spatial error in the rasters that are derived from photogrammetric models e g orthomosaics and digital elevation models using three case studies we show how dyke swarms can be mapped accurately over areas approaching 1 km2 at sub centimetre resolution the data illustrate how questions about dyke induced deformation host rock controls on segmentation and aperture variation may be addressed and we present a method for the high density high precision measurement of dyke apertures in 3d we also review semi automated mapping tools and emerging uav sensing techniques including hyperspectral and aeromagnetic sensors and the potentially important contributions they will make to the study of intrusive systems and volcanology more broadly

effects of subduction parameters on geothermal gradients in forearcs with an application to franciscan subduction in california geothermal gradients in forearcs are often suppressed below normal values because of the cooling effect of the relatively cold downgoing plate in this paper finite difference thermal modeling is used to evaluate the influence on forearc gradients of variations in six potentially important subduction zone parameters variations in forearc radiogenic heat production over the general range likely in forearc rocks 0 to 1 5 10 6 w m 3 cause only minor changes in temperatures at the base of the forearc about 2 to 35 depending on other parameters and thus have relatively little effect on pressure temperature pt conditions of metamorphism however their effect on gradients at shallow levels and thus on surface heat flows may be greater up to about 100 likely variations in forearc thermal conductivity 1 5 to 3 5 w m 1 c 1 similarly change temperatures at the base of the forearc only modestly 10 25 but change surface heat flows more substantially 1 45 1 75 times decreasing the subduction angle from 27 to 3 6 increases gradients by about a factor of 2 at both deep and shallow levels decreasing the subduction rate by a factor of 8 160 to 20 km m y increases gradients by about a factor of 2 when frictional heating at the plate contact is excluded and less when modest amounts of frictional heating are included forearc gradients increase virtually linearly with the presubduction geothermal gradient in the subducting slab and thus are higher above a younger slab when frictional heating is excluded forearc gradients are 2 0 2 8 times higher above a 10 m y old slab than above a 150 m y old slab again the relative effect is lessened when frictional heating is incorporated the amount of frictional heating at the plate contact potentially has the greatest influence on forearc gradients the frictional heat production h is given by h vs where is the shear stress along the plate contact and vs is the subduction rate the modeling shows that forearc gradients increase linearly with unless plate contact shear stresses are only a small fraction of those expected with frictional sliding of dry rocks outer parts of forearcs would be the sites of pervasive low p t metamorphism greenschist facies rather than high p t metamorphism blueschist facies very high fluid pressures along the plate contact are probably the way shear stresses are reduced pressure temperature conditions of blueschist facies metamorphism in the franciscan subduction complex of california are easily explained with typical subduction rates and slab ages with plate contact shear stresses of the order of 10 mpa equivalent to around 3 of lithostatic pressure but stresses within the range zero to a few tens of megapascals are probably permitted by the thermal constraints speculative application of the modeling results assuming a shear stress of 4 of lithostatic pressure to plate motion reconstructions for the franciscan forearc suggests that forearc gradients were about 8 c km around 85 ma when the subducting slab was perhaps 145 m y old and the subduction rate was perhaps 95 km m y gradients increased moderately through the latest cretaceous to middle tertiary as subduction became slower and the subducting slab became younger reaching about 16 c km at 28 ma when the slab age was about 11 m y and the subduction rate was about 48 km m y the slab age subduction rate and forearc gradient then remained fairly constant until 5 ma when subduction slowed to about 32 km m y and the slab age decreased to about 8 m y causing gradients to rise to about 20 c km

documented international enquiry on solid sedimentary fossil fuels coal definitions classifications reserves resources and energy potential abstract this paper deals with all solid sedimentary fossil fuels i e coal the main one for geological reserves and resources peat and oil shales definitions of coal the 50 ash limit already adopted by un ece for coal definition allows the creation of a new category the organic shales 50 75 ash comprising energetic materials still valuable for thermal use coal shales or to be retorted for oil production oil shales geological relations between coals oil shales solid bitumen liquid hydrocarbons natural gas and coalbed methane are also examined together with environmental problems as a final synthesis of all topics the paper discusses the problems related with a modern geological classification of all solid sedimentary fuels based on various rank parameters moisture content calorific value reflectance maceral composition and mineral matter content and washability finally it should be pointed out that the paper is presented as series of problems some of them old ones but never resolved until now in order to facilitate the next generation of coal geologists to resolve these problems on the basis of international agreements all sections begin with documented introductions for further questions opening an international enquiry the authors hope that the answers will be abundant enough and pertinent to permit synthetic international solutions valuable for the new millennium with the help of interested consulted authorities international pertinent organisations and regional experts

thermal history of michigan basin the elevated organic maturity observed in shallowly buried units from the michigan basin implies that higher temperatures and thicker overburdens once existed in the basin evidence from sediment accumulation rates regional dips and maturity of pennsylvanian age coals suggests that up to 1 000 m 3 280 ft of sediment were removed by erosion prior to the late jurassic when the basin became stable geothermal gradients during paleozoic basin subsidence probably ranged from 35 to 45 c km 19 to 25 f 1 000 ft in contrast to the average present value of 25 c km 14 f 1 000 ft depths to the top of the oil window ranged from 1 900 to 2 300 m 6 230 to 7 540 ft during the paleozoic post pennsylvanian erosional uplift and further thermal m turation of the basin have combined to raise the top of the oil window to its present level of 500 m 1 640 ft

the use of free radicals of organic matter to determine paleogeothermal gradient abstract free radicals in 60 kerogen samples from 5 wells in the qiongdongnan tarim and liaohe basins in china were analyzed by electron spin resonance esr for use in geothermometry based on esr data for 44 kerogen samples from the tertiary qiongdongnan basin a regression curve was shown to fit free radical densities n g with burial depth of samples for use in geothermal gradient estimation using this curve the highest geothermal gradients experienced by carboniferous permian strata well tmc1 in the tarim basin and oligocene eocene strata well lr16 in the liaohe basin were estimated concurrently five samples from liaohe basin were examined by apatite fission track analysis to assess the reliability of the esr kerogen method for geothermal gradient determination results of esr analyses match those of vitrinite reflectance and apatite fission track analysis indicating that maximum geothermal gradients obtained from the esr curve are reliable this paper presents a useful esr kerogen method for estimating paleogeothermal gradients which is especially useful where vitrinite and apatite are not present

trace element geochemistry and sedimentary provinces a study from the tasman geosyncline australia abstract the abundances of la th u and hf have been determined in flysch sequences of the tasman geosyncline australia the arc derived graywackes differ from those of rifted continental margins and marginal basins in containing low abundances of la th u and hf la 9 2 1 7 ppm th 1 4 0 6 ppm u 0 52 0 2 ppm hf 2 1 0 6 ppm reflecting similar low abundances in the andesitic source rocks graywackes of rifted continental margins and marginal basins in contrast are mature and characterised by high abundances of la th u and hf la 39 9 9 ppm th 16 0 6 ppm u 3 40 0 5 ppm hf 7 9 ppm mirroring increased abundances in the granitic and sedimentary source rocks sedimentary rocks deposited in inter arc basins show wide dispersion but have characteristics intermediate between these two types the th u ratio for magmatic arc sediments is 2 7 for most other sedimentary rocks it remains uniform at 4 5 0 3 for sediments having andesitic and dacitic rocks as provenance the la th ratios are 6 7 and 4 5 respectively this ratio remains constant at 2 6 for most quartzose sedimentary rocks

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

provenance of turbiditic cover to the caledonian solund stavfjord ophiolite from u pb single zircon dating u pb dating has been carried out on single zircon and titanite grains in greywacke intercalated with lavas of the late ordovician 443 3 ma solund stavfjord ophiolite the ages range from 2495 ma to 462 ma indicating that detritus was provided by a precambrian continental region as well as an ordovician caledonian terrane the caledonian component of the detritus was probably derived from the early ordovician ophiolitic terrane of west norway and the data therefore link two generations of caledonian ophiolites the mapped relationships of the ophiolitic terranes suggest that the late ordovician early silurian evolution of the caledonides was dominated by rifting and the formation of marginal basin s

propagating rift tectonics of a caledonian marginal basin multi stage seafloor spreading history of the solund stavfjord ophiolite in western norway abstract the late ordovician solund stavfjord ophiolite in western norway represents a remnant of the iapetus oceanic lithosphere that developed in a caledonian marginal basin the ophiolite contains three structural domains that display distinctively different crustal architecture that reflects the mode and nature of magmatic and tectonic processes operated during the multi stage seafloor spreading evolution of this marginal basin domain i includes from top to bottom an extensive extrusive sequence a transition zone consisting of dike swarms with screens of pillow breccias a sheeted dike complex and plutonic rocks composed mainly of isotropic gabbro and microgabbro extrusive rocks include pillow lavas pillow breccias and massive sheet flows and are locally sheared and mineralized containing epidosites sulfide sulfate deposits fe oxides and anhydrite veins reminiscent of hydrothermal alteration zones on the seafloor along modern mid ocean ridges a fossil lava lake in the northern part of the ophiolite consists of a 65 m thick volcanic sequence composed of a number of separate massive lava units interlayered with pillow lavas and pillow breccia horizons the ne trending sheeted dike complex contains multiple intrusions of metabasaltic dikes with one and two sided chilled margins and displays a network of both dike parallel normal and dike perpendicular oblique slip faults of oceanic origin the dike gabbro boundary is mutually intrusive and represents the root zone of the sheeted dike complex the internal architecture and rock types of domain i are analogous to those of intermediate spreading oceanic crust at modern mid ocean ridge environments the ophiolitic units in domain ii include mainly sheeted dikes and plutonic rocks with a general nw structural grain and are commonly faulted against each other although primary intrusive relations between the sheeted dikes and the gabbros are locally well preserved the exposures of this domain occur only in the northern and southern parts of the ophiolite complex and are separated by the ene trending domain iii in which isotropic to pegmatitic gabbros and dike swarms are plastically deformed along ene striking sinistral shear zones these shear zones which locally include fault slivers of serpentinite intrusions are crosscut by n20 e striking undeformed basaltic dike swarms that contain xenoliths of gabbroic material the nw trending sheeted dike complex in the northern part of domain ii curves into an ene orientation approaching domain iii in the south the anomalous nature of deformed crust in domain iii is interpreted to have developed within an oceanic fracture zone or transform fault boundary ree chemistry of representative extrusive and dike rocks from all three domains indicates n to e morb affinities of their magmas with high th ta ratios that are characteristic of subduction zone environments the magmatic evolution of domain i encompasses closed system fractional crystallization of high mg basaltic magmas in small ephemeral chambers which gradually interconnected to form large chambers in which mixing of primary magmas with more evolved and fractionated magma caused resetting of magma compositions through time the compositional range from high mg basalts to ferrobasalts within domain i is reminiscent of modern propagating rift basalts we interpret the ne trending domain i as a remnant of an intermediate spread rift system that propagated northeastwards in present coordinate system into a pre existing oceanic crust which was developed along the nw trending doomed rift domain ii in the marginal basin the n20 e dikes laterally intruding into the anomalous oceanic crust in domain iii represent the tip of the rift propagator the inferred propagating rift tectonics of the solund stavfjord ophiolite is similar to the evolutionary history of the modern lau back arc basin in the sw pacific and suggests a complex magmatic evolution of the caledonian marginal basin via multi stage seafloor spreading tectonics

the gabbro dyke transition zone demonstrated on tviberg solund stavfjord ophiolite complex the transition zone between 100 dykes and high level plutonic rocks of the solund stavfjord ophiolite complex is complex due to the existence of many lithologies with different and variable contact relationships the rocks of the plutonic complex vary in composition from feti basaltic to quartz dioritic and the grain sizes vary from fine to pegmatitic felsic varieties are produced by fractional crystallization of basaltic magma as demonstrated by geochemical evolution and by gradual transition from gabbro to quartz diorite patches of fractionated dioritic rocks may show both gradual and intrusive relationships with the surrounding host gabbro this demonstrates that late stage liquids commonly left the source region and locally intruded the surrounding parent rocks the high level plutonic rocks are thoroughly epidotized and are cut by dykes consisting of granoblastic epidote and quartz the high level plutonic complex is associated with irregular bodies of fine to medium grained plagioclase porphyritic diabase of high mgo content these diabase bodies are intruded by dykes that become progressively more regular in shape the plutonic complex locally shows intrusive relationships with the overlying 100 dyke complex but is itself cut by two dyke swarms the dykes of the first swarm formed while the plutonic complex experienced sinistral shear strain and the dykes are generally less regular and thinner than the dykes of the second swarm this indicates that the dykes of the first swarm intruded while the rocks of the plutonic complex were still hot while the next dyke swarm intruded later when the rock complex was colder dykes of both swarms range in composition from slightly to strongly fractionated suggesting that the magma chambers they were expelled from underwent significant fractionation in between magma replenishment numerous dykes of both swarms carry large quantities of glomeroporphyritic aggregates of plagioclase and altered clinopyroxene indicating that the source area to the dykes very often was a crystal mush

the chemical discrimination of clastic sedimentary components abstract the detrital composition of siliciclastic rocks from six localities in the taconic and acadian sections of new york and quebec can be described as mixtures of two or more differentiable sedimentary components a sedimentary component is defined as a mineral or group of minerals that sort independently of other sedimentary constituents because of grain morphology phyllosilicates usually dominate the finer grained component and quartz or mixtures of quartz and feldspar dominate the coarser grained components the chemical composition of a sedimentary component is distinctive and the differentiation of sedimentary components usually results in the concomitant separation of associated elements typical separations include the enrichment of k2o and al2o3 in the finer grained phyllosilicate rich fraction and the enrichment of sio2 and na2o in the coarser grained tectosilicate rich fraction fe2o3 and mgo are also enriched in the fine fraction if they are abundant constituents in the phyllosilicates the chemical composition of the graywackes from north america was compared to the chemical composition of unlithified turbidite sediments from the black sea the chemical variation trends found in the deeply buried sedimentary rocks are similar to the trends found in the suite of slightly buried and unlithified deep sea sediments this indicates that burial alteration does not necessarily result in large scale redistribution of the constituent elements it is possible therefore to use the chemical variations observed in a suite of deeply buried and mineralogically altered sedimentary rock to infer the original clastic assemblage and to help clarify the processes that produced the sediment

petrochemistry and origin of sub ophiolitic metamorphic and related rocks in the oman mountains the semail ophiolite complex of the northern oman mountains was obducted during cenomanian to campanian upper cretaceous times onto the arabian continental margin during this time span schistose metamorphic rocks of amphibolite and greenschist facies exhibiting polyphase deformation were formed and accreted below the ophiolite slice whole rock and mineral analyses confirm that the amphibolites were originally tholeiitic basalts comparable to present day occurrences at mid ocean ridges a comparison of trace element geochemistries however suggests that the protoliths were not equivalent to the haybi alkaline and transitional tholeiites found in the underlying structural slice or to the semail ophiolite volcanic rocks which lie structurally higher in the sequence it is therefore suggested that the amphibolites may have been derived from jurassic or lower cretaceous oceanic basalts not recognized elsewhere in the oman mountains structurally beneath the amphibolites within the metamorphic sheet greenschist facies metasedimentary rocks including quartzites and marbles are interbanded with metabasite horizons containing actinolite and less commonly blue crossitic amphiboles it is suggested that the sedimentary and volcanic protoliths were metamorphosed in a subduction zone environment during initial ophiolite displacement and were accreted to the base of the ophiolite during progressive underthrusting