geochemical characteristics and hydrocarbon generation modeling of the jurassic source rocks in the shoushan basin north western desert egypt abstract the shoushan basin is an important hydrocarbon province in the western desert egypt but the origin of the hydrocarbons is not fully understood in this study organic matter content type and maturity of the jurassic source rocks exposed in the shoushan basin have been evaluated and integrated with the results of basin modeling to improve our understanding of burial history and timing of hydrocarbon generation the jurassic source rock succession comprises the ras qattara and khatatba formations which are composed mainly of shales and sandstones with coal seams the toc contents are high and reached a maximum up to 50 the toc values of the ras qattara formation range from 2 to 54 wt while khatatba formation has toc values in the range 1 47 wt the ras qattara and khatatba formations have hi values ranging from 90 to 261 mghc gtoc suggesting types ii iii and iii kerogen vitrinite reflectance values range between 0 79 and 1 12 vrr rock eval t max values in the range 438 458 c indicate a thermal maturity level sufficient for hydrocarbon generation thermal and burial history models indicate that the jurassic source rocks entered the mature to late mature stage for hydrocarbon generation in the late cretaceous to tertiary hydrocarbon generation began in the late cretaceous and maximum rates of oil with significant gas have been generated during the early tertiary paleogene the peak gas generation occurred during the late tertiary neogene

evolution characteristics of transtensional faults and their impacts on hydrocarbon migration and accumulation a case study from the huimin depression bohai bay basin eastern china abstract the study of transtensional faults is significantly important for analysing migration and accumulation of hydrocarbons in petroliferous basins the purpose of this study is to present disparities in the temporal and spatial evolution of two boundary transtensional faults northern linshang fault and southern xiakou fault in the huimin depression by 2d structural restoration and quantitative calculations of fault activity this paper also reveals the controls of transtensional faults on the migration and accumulation of hydrocarbons by considering the stress normal to the fault plane p the shale gouge ratio sgr of the fault zone and models of migration pathways the results show that the transtensional systems within the huimin depression were generated from the reactivation of basement faults under an oblique extensional stress field the linshang fault linked two initially separated segments and then behaved as a single fault since the ek period whereas the xiakou fault retained significant three segment growth properties during the paleogene during the hydrocarbon charging period the weak activity and strong vertical sealing restricted the occurrence of vertical migration around the xiakou fault while the relatively strong movement and weak vertical sealing resulted in multilayer hydrocarbon accumulations around the linshang fault meanwhile the vertically closed fault with high sgr 0 6 acted as barriers and trapped hydrocarbons on the lateral migration pathways whereas the vertically closed fault with low sgr

petroleum origin and accumulation in basin evolution a quantitative model basin data geologic geophysical geochemical hydrodynamic and thermodynamic can be combined for quantified hydrocarbon prediction a three dimensional deterministic dynamic basin model can be constructed to calculate all the measurable values with the help of mass and energy transport equations and equations describing the physical and or physicochemical changes in organic matter as a function of temperature input data consist of heat flux initial physical and thermal properties of sediments paleobathymetric estimates sedimentation rate and amount and type of organic matter subsequently the model computes pressure temperature physical and thermal properties of sediments maturity of organic matter and the hydrocarbon potential of any source rock as a func ion of space and time thus the complex dynamic processes of petroleum formation and occurrence in a given sedimentary basin can be quantified for example hydrocarbon potential maps for any given source rock and any geologic time slice of the basin evolution can be provided as computer printouts the computer model can be applied to any stage of an exploration campaign and updated as more information becomes available

a p t t d discontinuity in east central nepal implications for the evolution of the himalayan mid crust abstract rock specimens collected from lower middle and upper portions of the exhumed himalayan mid crust in the upper tama kosi region of east central nepal yield pressure temperature time deformation p t t d paths that demonstrate the presence of a structural metamorphic and geochronologic discontinuity a p t t d path from below the discontinuity defines a loading path with deformation at staurolite grade metamorphic conditions occurring at 10 8 ma p t t d paths from above the discontinuity in contrast record an earlier and protracted metamorphic history that includes decompressional heating monazite ages from specimens collected above the discontinuity constrain prograde garnet growth to be 21 ma with decompression related garnet breakdown initiating at c 19 ma and likely continuing until c 15 ma these contrasting p t t d histories separated by a tectonometamorphic discontinuity are consistent with an evolutionary model for the himalaya in which rocks above the discontinuity were metamorphosed in the deep hinterland of the orogen and deformed during lateral extrusion from beneath tibet while rocks below the discontinuity were deformed and metamorphosed later within the shallower foreland of the orogen these results demonstrate the spatial and temporal relationships and compatibility between lateral midcrustal extrusive flow and wedge taper processes within an evolving orogen

kinematic analyses of brittle roto translational planar and listric faults based on various rotational to translational velocities of the faulted blocks abstract research on rotational roto translational faults have been relatively less than translational faults this is despite perfect translational faults seldom occur in mega scale this work models slickenside lineation patterns on planar and listric fault planes for different ratios of rates of rotation to the uniform speed towards a specific geographic direction v of faulted blocks curves simulated for the planar fault planes are fitted with natural examples of such roto translational faults in our 10 chosen examples the v ratio ranges between 0 2 fault at san miguelito range central mexico and as high as 2 4 fault at hyogoken nambu japan knowing the v ratios from terrains can better interpret its tectonics for example if v and the total time of duration of the deformation are known from some other studies even the total amount of rotation can be estimated the far reaching implication of this study is that as several hydrocarbon reserves and terrains with landslides are related to roto translational faults this work will be a stepping stone in petroleum geosciences e g stability of hydercarbon reserve and engineering geology e g stability of slope

syn to post rift fault evolution in a failed rift a reflection seismic study in central cambay basin gujarat india the barmer and cambay basins india formed as rifts during the cretaceous to paleocene prior to seychelles india separation during late cretaceous both of the rifts failed subsequently and the seychelles separated from india along the current saurashtra mumbai continental margin we study the fault kinematics i e fault growth and linkages in the cambay tarapur block and comment on the fault evolution from syn to post rift stages we use fault plane topography throw length and throw depth plots to understand the kinematics of the fault planes throw length plots show the along strike linkage of faults the throw depth plots are used to understand the down and up dip linkage of the fault planes faults originating at the deccan traps level and faults confined only to post rift progressed as single fault planes along strike throughout their deformation history faults initiating within the syn rift started as multiple along strike segments and joined together as they grew along dip faults can be classified as i faults originating at deccan traps and reaching post rift ii faults originating within syn rift sediments and reaching post rift iii faults confined only within syn rift and iv faults confined only within post rift some of the syn rift faults also show spatially and temporally limited compression indicating their possible oblique slip nature the faults were normal slip or oblique slip during syn rift and thereafter they propagated as normal dip slip faults as analysed from fault plane topography showing strike perpendicular ridges such ridges may indicate only the last movement on the fault plane due to the presence of thick shale horizons in the syn rift many faults show soft linked segments along dip hydrocarbon occurrences in the shallow 1200 1600 m miocene sands can possibly be attributed to the normal faults controlling fluid flow into the reservoirs 282 words

thermal maturity history and petroleum generation modelling for the lower cretaceous abu gabra formation in the fula sub basin muglad basin sudan abstract two petroleum source rock intervals of the lower cretaceous abu gabra formation at six locations within the fula sub basin muglad basin sudan were selected for comprehensive modelling of burial history petroleum maturation and expulsion of the generated hydrocarbons throughout the fula sub basin locations of wells selected include three in the deepest parts of the area keyi oilfield and three at relatively shallow locations moga oilfield the chosen wells were drilled to depths that penetrated a significant part of the geological section of interest where samples were available for geochemical and source rock analysis vitrinite reflectances ro were measured to aid in calibrating the developed maturation models the abu gabra formation of the muglad basin is stratigraphically subdivided into three units abu gabra lower abu gabra middle and abu gabra upper from the oldest to youngest the lower and upper abu gabra are believed to be the major source rocks in the province and generally contain more than 2 0 wt toc thus indicating a very good to excellent hydrocarbon generative potential they mainly contain type i kerogen vitrinite reflectance values range from 0 59 to 0 76 ro indicating the oil window has just been reached in general the thermal maturity of the abu gabra source rocks is highest in the abu gabra lower deep western part of the keyi area and decreases to the east toward the moga oilfied at the fula sub basin maturity and hydrocarbon generation modelling indicates that in the abu gabra lower early oil generation began from the middle late cretaceous to late paleocene time 82 0 58ma main oil generation started about 58 ma ago and continues until the present day in the abu gabra upper oil generation began from the end of the cretaceous to early eocene time 66 0 52ma only in one location keyi n1 well did the abu gabra upper reach the main oil stage oil expulsion has occurred only from the abu gabra lower unit at keyi n1 during the early miocene 50 transformation ratio tr continuing to present day 20 0 0 0 ma neither unit has generated gas oil generation and expulsion from the abu gabra source rocks occurred after the deposition of seal rocks of the aradeiba formation

pervasive granitoid magma transfer through the lower middle crust during non coaxial compressional deformation granitic magmas migrated through early proterozoic middle lower crust at mt hay central australia via a diverse network of narrow structurally controlled channelways during a period of progressive w sw directed thrusting d1a d1d they utilized existing folds boudins and shear zones or created new channels by magmatic fracture either parallel to layering or rarely in irregular arrays the magmas rose obliquely parallel to the plunging 50 60 regional elongation direction which was defined by coaxial folds boudin necks and a strong mineral elongation lineation megacrystic charnockitic magmas migrated through metre scale conduits during d1a d1b but leucosomes were generally restricted to smaller centimetre scale structures that existed throughout the entire deformation history thus d1a d1b leucosomes were potential feeders of in situ partial melts to the adjacent larger conduits of charnockite magma thereby providing a pervasive interconnected network that allowed efficient migration of all magma types during the early stages of thrusting the upper middle crust of the anmatjira reynolds range area contains abundant megacrystic granitoid sheets that are of similar age and geochemistry to those at mt hay they are considered to have formed as syntectonic intrusions emplaced during w sw directed thrusting as at mt hay suggesting that granitic magmas formed near the base of the continental crust passed through the mid lower crustal level 25 30 km exposed at mt hay and accumulated in batholithic proportions at shallower crustal levels 12 20 km such as the anmatjira reynolds range area the observations imply that granitoid magmas in the deep crust are capable of pervasive migration through the crust during major compressive noncoaxial shear deformation localization of magmas by sequentially developed narrow compressive structures suggests that dilatancy followed successive foliation forming events a situation that can occur during steady state deformation if the effective confining pressures are low which would be a result of high and possibly variable rates of magma influx the inferred rapid melt segregation and migration during deformation suggest that large chambers do not form until magma reaches neutral buoyancy in the middle to upper continental crust

geothermal history and petroleum generation in the norwegian south viking graben revealed by pseudo 3d basin modelling abstract hydrocarbon exploration in the norwegian south viking graben 57 45 60 15 n began in the late 1960s and has now entered a mature phase a map based pseudo three dimensional 3d basin modelling study is performed in order to unravel regional trends in hydrocarbon generation and expulsion and to evaluate the remaining potential of this mature petroleum province generation and expulsion from all major source rock horizons in the area the draupne heather hugin and sleipner formations is simulated using a pseudo 3d model comprising 36 isochronous geological events the map based pseudo 3d model is built from 1d models combined with subsurface and source rock quality maps hydrocarbon expulsion from the middle and upper jurassic source rocks in the area occurred in two major phases the first phase lasted from palaeocene to middle miocene with peak oil and gas expulsion during the early miocene the second quaternary phase of expulsion which supplied 11 and 13 of all oil and gas respectively is related to increased subsidence rates during this period a total of 74 109 sm3 oil and 8 2 1012 sm3 gas has been expelled in the area the frigg area in the north is with 2 9 1012 sm3 gas expelled the most gas prone area and the greater balder area seems to be the most oil prone area with 17 109 sm3 oil expelled the lower syn rift section of the upper jurassic draupne formation dominated oil expulsion 54 of all expelled oil whilst the heather formation dominated gas expulsion with 37 of all gas expelled model predictions were successfully applied to explain the fill and secondary alteration history of the greater balder area norway the modelling supports the draupne formation origin of the oils in the greater balder area as well as the presence of oils deriving from multiple charge phases found in correlation studies based on the modelled cumulative volumes expelled and estimates for in place volumes in the area generation accumulation efficiencies gaes of 1 01 1 05 for oil and 9 67 12 89 for gas have been estimated for the south viking graben in light of comparisons with other petroleum systems and critical evaluation of the elements of the petroleum systems the estimated gaes should be regarded as encouraging for further exploration of the area

evolution of the stress fields in the zagros foreland folded belt using focal mechanisms and kinematic analyses the case of the fars salient iran the nw se trending zagros orogenic belt was initiated during the convergence of the afro arabian continent and the iranian microcontinent in the late cretaceous ongoing convergence is confirmed by intense seismicity related to compressional stresses collision related in the zagros orogenic belt by reactivation of an early extensional faulting to latter compressional segmented strike slip and dip slip faulting these activities are strongly related either to the deep seated basement fault activities deep seated earthquakes underlies the sedimentary cover or gently dipping shallow seated decollement horizon of the rheological weak rocks of the infra cambrian hormuz salt the compressional stress regimes in the different units play an important role in controlling the stress conditions between the different units within the sedimentary cover and basement a significant set of nearly n s trending right lateral strike slip faults exists throughout the study area in the fars area in the zagros foreland folded belt fault slip and focal mechanism data were analyzed using the stress inversion method to reconstruct the paleo and recent stress conditions the results suggest that the current direction of maximum principal stress averages n19 e with n38 e that for the past from cretaceous to tertiary although a few sites on the kar e bass fault yield a different direction the results are consistent with the collision of the afro arabian continent and the iranian microcontinent the difference between the current and paleo stress directions indicates an anticlockwise rotation in the maximum principle stress direction over time this difference resulted from changes in the continental convergence path but was also influenced by the local structural evolution including the lateral propagation of folds and the presence of several local decollement horizons that facilitated decoupling of the deformation between the basement and the sedimentary cover the obliquity of the maximum compressional stress into the fault trends reveals a typical stress partitioning of thrust and strike slip motion in the kazerun kar e bass sabz pushan and sarvestan fault zones that caused these fault zones behave as segmented strike slip and dip slip faults

deformation induced polymorphic transformation experimental deformation of kyanite andalusite and sillimanite abstract torsion experiments were performed on the al 2 sio 5 polymorphs in the sillimanite stability field to determine basic rheological characteristics and the effect of deformation on polymorphic transformation the experiments resulted in extensive transformation of andalusite and kyanite to sillimanite no transformation occurred during the hot press no deformation stage of sample preparation which was carried out at similar p t conditions and duration as the torsion experiments experiments were conducted on fine grained 4 s to a maximum shear strain of 400 electron back scattered diffraction ebsd analysis of the experiments revealed development of lattice preferred orientations with alignment of sillimanite and andalusite 001 slightly oblique to the shear plane the kyanite experiment could not be analyzed using ebsd because of near complete transformation to sillimanite very little strain 30 is required to produce widespread transformation in kyanite and andalusite polymorphic transformation in andalusite and kyanite experiments occurred primarily along 500 m wide shear bands oriented slightly oblique and antithetic to the shear plane and dominated by sub m 100 150 nm fibrolitic sillimanite shear bands are observed across the entire strain field preserved in the torsion samples scanning transmission electron microscope imaging shows evidence for transformation away from shear bands e g fibrolitic rims on relict andalusite or kyanite relict grains typically have an asymmetry that is consistent with shear direction these experimental results show that sillimanite is by far the weakest of the polymorphs but no distinction can yet be made on the relative strengths of kyanite and andalusite these observations also suggest that attaining high bulk strain energy in strong materials such as the al 2 sio 5 polymorphs is not necessary for triggering transformation strain energy is concentrated along grain boundaries and transformation occurs by a dynamic recrystallization type process these experiments also illustrate the importance of grain size sensitive creep at high strains in a system with simultaneous reaction and deformation

geochemistry and organic petrology study of kimmeridgian organic rich shales in the marib shabowah basin yemen origin and implication for depositional environments and oil generation potential kimmeridgian organic rich shales of the madbi formation from the marib shabowah basin in western yemen were analysed to evaluate the type of organic matter origin and depositional environments as well as their oil generation potential results of the current study establishes the organic geochemical characteristics of the kimmeridgian organic rich shales and identifies the kerogen type based on their organic petrographic characteristics as observed under reflected white light and blue light excitation kerogen microscopy shows that the kimmeridgian organic rich shales contain a large amount of organic matter consisting predominantly of yellow fluorescing alginite and amorphous organic matter with marine microfossils e g dinoflagellate cysts and micro foraminiferal linings terrigenous organic matters e g vitrinite spores and pollen are also present in low quantities the high contributions of marine organic matter with minor terrigenous organic matter are also confirmed by carbon isotopic values the organic richness of the kimmeridgian shales is mainly due to good preservation under suboxic to relatively anoxic conditions as indicated by the percent of numerous pyritized fragments associated with the organic matter the biomarker parameters obtained from mass spectrometer data on m z 191 and m z 217 also indicate that these organic rich shales contain mixed organic matter that were deposited in a marine environment and preserved under suboxic to relatively anoxic conditions the kimmeridgian organic rich shales thus have high oil and low gas generation potential due to oil window maturities and the nature of the organic matter with high content of hydrogen rich type ii and mixed type ii iii kerogens with minor contributions of type iii kerogen

a new evaluation of palaeo heat flows and eroded thicknesses for the carboniferous ruhr basin western germany palaeo heat flows and thicknesses of eroded carboniferous overburden in the coal bearing ruhr basin western germany were estimated using one dimensional basin modelling techniques thermal and burial histories for 11 localities were calibrated by comparing measured and calculated vitrinite reflectance data based on the assumption of pre tectonic maturation in contrast to former studies the kinetic easy r0 approach applied for the calculation of vitrinite reflectance lopatin s tti algorithm was used in addition for one well in order to demonstrate the impact of the selection of the algorithm for vitrinite reflectance calculation on the simulation results simulated palaeo heat flows for the time of maximum burial most probably in the stephanian range from 64 to 83 mw m2 and decrease towards the south these heat flows are lower than values computed during earlier studies but are still relatively high in comparison to recent foreland basins the regional distribution of palaeo heat flows indicates that the crust beneath the ruhr basin was relatively thin and thickened towards the south at the end of the carboniferous after the stephanian 2200 3500 m of carboniferous overburden were eroded an observed southward increase in eroded thicknesses is caused by an uplift of the area studied which decreased towards the north at the end of the variscan folding large thicknesses of deposited and later eroded carboniferous sediments have to be postulated to explain the maturity data even along the present southern margin of the ruhr basin this indicates that the late carboniferous sediments originally extended far to the south geological arguments suggest that the deposition of carboniferous sediments in the entire ruhr basin continued until the stephanian

assessment of mesozoic and upper paleozoic source rocks in the south yellow sea basin based on the continuous borehole csdp 2 abstract being lack of core data and measured data although the marine oil gas exploration in the south yellow sea basin has been going on for 57 years no commercial hydrocarbon reservoirs have been found so far the quantitative source rocks evaluation based on geochemical data and fluid inclusions containing hydrocarbon benefits from the completion of borehole csdp 2 in 2016 a continuous coring well of the chinese continental shelf drilling program csdp which indicates that the marine origin oil gas exploration in the south yellow sea basin enters into a new stage as revealed by the well csdp 2 three sets of effective hydrocarbon source rocks in the mesozoic and upper paleozoic have been identified which are distributed in the lower triassic qinglong formation t1q upper permian longtan dalong formation p3l d and middle permian gufeng qixia formation p2g q respectively among them organic rich source rocks mainly concentrate in the lower part of the p3l d and the middle upper part of the p2g q and the p3d mudstone also works as good source rock the p3l d mudstone with high organic abundance is the chief source rock in the south yellow sea basin whose maximum hydrocarbon generating intensity may reaches up to 795 09 104 t km2 and hydrocarbon expulsing intensity remains at the level of 165 03 104 t km2 a noteworthy feature of the p2g q source rocks is the strong vertical heterogeneity with the hydrocarbon expulsing intensity of the upper part being 34 14 104 t km2 while that of the lower part being 18 07 104 t km2 in contrast the organic abundance of argillaceous limestone in the t1q is mainly poor to medium and its hydrocarbon expulsing intensity is the weakest one in the three sets of hydrocarbon source rocks only about 12 7 104 t km2 taking into consideration the joint influence of depositional environment organic matter parent source and biological productivity the overall quality of source rocks in the south yellow sea basin is at the similar level to the lower yangtze subei basin but lower than that of the upper yangtze sichuan basin the most significant oil gas information is that multiple direct oil indications and high value abnormalities of gas logging have been discovered in the well csdp 2 moreover the mesozoic and upper paleozoic marine strata in the south yellow sea basin have experienced three hydrocarbon charging stages indicating a broad prospect of marine oil gas exploration

basin modeling of the late miocene zeit source rock in the sudanese portion of red sea basin implication for hydrocarbon generation and expulsion history abstract the late miocene zeit formation is exposed in the red sea basin of sudan and represents an important oil source rock in this study five 5 exploratory wells along red sea basin of sudan are used to model the petroleum generation and expulsion history of the zeit formation burial thermal models illustrate that the red sea is an extensional rift basin and initially developed during the late eocene to oligocene heat flow models show that the present day heat flow values in the area are between 60 and 109 mw m2 the variation in values of the heat flow can be linked to the raise in the geothermal gradient from margins of the basin towards offshore basin the offshore basin is an axial area with thick burial depth which is the principal heat flow source the paleo heat flow values of the basin are approximately from 95 to 260 mw m2 increased from oligocene to early pliocene and then decreased exponentially prior to late pliocene this high paleo heat flow had a considerable effect on the source rock maturation and cooking of the organic matter the maturity history models indicate that the zeit formation source rock passed the late oil window and converted the oil generated to gas during the late miocene the basin models also indicate that the petroleum was expelled from the zeit source rock during the late miocene 7 ma and it continues to present day with transformation ratio of more than 50 therefore the zeit formation acts as an effective source rock where significant amounts of petroleum are expected to be generated in the red sea basin

paleo heat flow evolution of the tabei uplift in tarim basin northwest china abstract the paleo heat flow evolution of the tabei uplift in the tarim basin is investigated based on burial and thermal history reconstruction of 14 wells and using basin modeling numerous geological parameters such as temperature data and missing sediment thickness by erosion were used in the modeling the basin model was calibrated using 460 measured vitrinite reflectance vr o and vitrinite like maceral reflectance vlmr o values to constrain the validity of the maturity model the heat flow history of the tabei uplift tarim basin shows the following characteristics 1 the highest paleo heat flow was predicted to have occurred in the early ordovician as 65 5 mw m 2 and gradually decreased to 55 5 mw m 2 during the late carboniferous 2 a thermal kick was modeled to have occurred in the permian as suggested by an abrupt rise in the heat flow 3 the heat flow gradually decreased since the triassic 4 the present day heat flow was predicted to be as low as 38 mw m 2 this heat flow history honors the geologic and tectonic evolution history of the tabei uplift and is suggested as the best case heat flow model

remagnetization of lower silurian black shale and insights into shale gas in the sichuan basin south china the organic rich lower silurian shale of the longmaxi formation in the sichuan basin is the most important target for shale gas exploration in china most paleozoic rocks of the sichuan basin have experienced extraordinarily pervasive remagnetizations to test a hypothesized connection between hydrocarbon generation and remagnetization and contribute to shale gas exploration in the region we undertook an integrated magnetic geochemical and petrographic study of 160 specimens from the shale the results suggest that the shale contains a reliable remanent magnetization dec 41 4 inc 40 8 and 95 6 8 the magnetization predates tilting and the paleopole plots close to the late triassic segment of the south china apparent polar wander path the rock magnetic data and scanning electron microscope sem observations confirm that framboidal magnetites carry the bulk of the magnetization which suggest a late triassic chemical remanent magnetization in the shale 87sr 86sr and magnetic analyses indicate that the amount of magnetite was unaffected by fluid alterations around the veins but is strongly covariant with the amount of total organic matter moreover sem observations reveal possible evidence of the replacement of pyrite framboids by magnetite probably in the presence of organic acids these analyses therefore suggest that the remagnetization was caused by organic maturation rather than orogenic fluids and that the maturation occurred in the late triassic this timing of organic maturation has been validated by independent modeling studies and provides important constraints on the complex thermal history of the longmaxi shale as well as contributing to shale gas exploration efforts

facies analysis of tuffaceous volcaniclastics and felsic volcanics of tadpatri formation cuddapah basin andhra pradesh india the felsic volcanics tuff and volcaniclastic rocks within the tadpatri formation of proterozoic cuddapah basin are not extensively studied so far it is necessary to evaluate the extrusive environment of felsic lavas with associated ash fall tuffs and define the resedimented volcaniclastic components the spatial and temporal bimodal association were addressed but geochemical and petrographic studies of mafic volcanics are paid more attention so far the limited exposures of eroded felsic volcanics and tuffaceous volcaniclastic components in this terrain are highly altered and that is the challenge of the present facies analysis based on field observation and mapping of different lithounits a number of facies are categorized unbiased lithogeochemical sampling have provided major and selective trace element data to characterize facies types thin section studies are also carried out to interpret different syn and post volcanic features the facies analysis are used to prepare a representative facies model to visualize the entire phenomenon with reference to the basin evolution different devitrification features and other textural as well as structural attributes typical of flow surge and ash fall deposits are manifested in the middle lower and upper stratigraphic levels spatial and temporal correlation of lithologs are also supportive of bimodal volcanism felsic and mafic lavas are interpreted to have erupted through the n s trending rift associated fissures due to lithospheric stretching during late palaeoproterozoic it is also established from the facies model that the volcaniclastics were deposited in the deeper part of the basin in the east the rifting and associated pressure release must have provided suitable condition of decompression melting at shallow depth with high geothermal gradient and this partial melting of mantle derived material at lower crust must have produced mafic magmas such upwelling into cold crust also caused partial heat transfer and associated melting of the surrounding shallow crustal rocks to generate felsic magmas

the dinevar transtensional pull apart basin nw zagros mountains iran a geological study and comparison to 2d finite element elastic models the dinevar transtensional pull apart basin is a nw se trending basin located in the northwest part of the zagros mountains sanandaj sirjan tectonic zone iran this basin was formed by oblique extension in a strike slip fault system which was controlled by the pre existing sahneh and the mianrahan faults in addition to a field study we constructed a 2d finite element elastic model based on the major fault segments according to the field study various geological structures are formed around the pre existing fault segments including pencil structures with 13 aspect ratio 19 tight to open asymmetric folds oblique normal faults synthetic and antithetic faults normal and reverse fault drags and negative and hybrid type flower structure fe model results show that around the fault step is a zone of displacement gradient that indicates extension transtension within the overlapping zone consequently subsidence is predicted over the releasing fault step the modelled stress distributions within the fault step and around the fault segment tips are asymmetric elastic modelling shows that the mean normal stress within the step is tensional which would impede plastic yield while the region outside the step is characterised by compressive mean normal stress the mean normal stress pattern is characterised by a regional minimum localised inside the extensional step transtension zone and two local maximum and minimum couples formed at the advancing and retreating sides respectively in the fault segment tips the results show that two main subsidence regions depocentres or sub basins form along and in the proximity of the fault segment tips the imposed relative motion is entirely accommodated by creep on the faults which causes plastic strain to accumulate outside the faults mostly localised within the fault step this localised strain between fault segments could initiate connecting faults or reactivate earlier faults generally at high angles relative to the master fault segments as suggested by the stress and strain patterns the rotation and magnitude variation in the stress and strain trajectories reflects heterogeneous deformation in general the dinevar transtensional pull apart basin is characterised by an elongate rhomboidal to trapezoidal shaped geometry the modelled stress distribution and strain localisations within the basin are in general agreement with the locations of fault segments within the dinevar transtensional pull apart basin

geochemical characteristics of some crude oils from alif field in the marib shabowah basin and source related types the marib shabowah basin is an important hydrocarbon province in western yemen but the origin of hydrocarbons is not fully understood in this regard geochemical characteristics are used to provide information on source organic matter input depositional environment and the correlation between crude oils from different pay zones two oil families are present within the study area and classified based on biomarker and non biomarker parameters the family i oils are characterized by low api gravity high sulfur and trace metal ni v contents and low ph ph ratio 1 0 these oils were derived from an alga organic matter that was deposited in a highly anoxic hypersaline marine depositional environment and generated at low maturity family ii oils have medium to high api gravity low sulfur and trace metal contents and relatively high pr ph ratios 1 09e1 59 the family ii oils were derived from mixed marine and terrigenous organic matter and deposited under sub oxic conditions these oils were generated from source rocks with a wide range of thermal maturity ranging from early to peak oil window the oil characteristics suggest that family i oils may be derived from the tithonian age safer calcareous shales and family ii oils from the deeper kimmeridgian madbi shales

brittle shear tectonics in a narrow continental rift asymmetric nonvolcanic barmer basin rajasthan india abstractour field studies emphasizing brittle shear p and y planes along the margins of the barmer basin rajasthan india support its two phase nw se followed by ne sw extension during early cretaceous and late cretaceous paleocene periods we also document nearly ne trending megascale transfer zones along the northern margin of the barmer basin preexisting brittle planes in the malani basement rocks guided the relay structures here structures at the western basin shoulder margin indicate ne sw extension and the crosscut relation connotes the relative timing of the two extension phases the crosscutting conjugate fault sets are non andersonian the nw trending faults produced by the second phase extension and the inherited nnw trending brittle features are dominantly dip slip prior fractures of the malani rocks at 45 to the ne sw principal extension direction extended the barmer basin obliquely during the late cretaceous paleocene period the asymmetric nature of the rift too connotes its ob

modeling petroleum generation in the paleozoic of the carnarvon basin western australia implications for prospectivity maturity and petroleum generation modeling of the paleozoic succession in the carnarvon basin shows that most potential source rock intervals reached their maximum generation migration during the carboniferous permian and could have charged traps developed during rifting in the middle carboniferous to early permian except for the peedamullah shelf where generation peaked during the cretaceous however identification of such traps is challenging because it is difficult to differentiate between the deformation associated with middle carboniferous early permian rifting and that of the early cretaceous breakup rifting given the presence of suitable reservoir and sealing units in most of the paleozoic the prime risks for this section are the volume of available source rock trap integrity because of the long period of preservation required and relative timing of generation vs trap formation such that charging of younger traps requires secondary migration the best paleozoic oil prone source beds identified in the carnarvon basin are thin beds in carbonate dominated silurian and devonian units on the gascoyne platform but devonian source beds are restricted to the northern parts of the platform the maturity of these units progressively increases from immature in the south southeast to mature in the north northwest following increasing depth of burial in that direction the best gas prone source beds lie within the lower permian of the merlinleigh subbasin and their maturity ranges from immature along the margins of the subbasin to overmature toward the center within the upper permian the best source beds for oil and gas are in the peedamullah shelf where they range from immature in the southeast to mature in the northwest commercial paleozoic petroleum has yet to be discovered in the paleozoic of the carnarvon basin but the assessment of this part of the basin is limited because few if any of the exploration wells drilled to date were valid tests of these objectives

thermal maturity history and petroleum generation modelling for the upper jurassic madbi source rocks in the marib shabowah basin western yemen abstract widely exposed in the marib shabowah basin the early upper jurassic madbi formation is divided into two units lam and meem youngest to oldest believed to be major source rocks the madbi source rocks are characterized by relatively high total organic carbon contents toc ranging from 0 5 to 10 0 wt meeting the standard as a fair to excellent source rock generative potential they contain type ii kerogen grading to mixed type ii iii kerogens and type iii kerogen with hi values between 40 and 620 mg hc g toc vitrinite reflectance values range from 0 41 to 2 61 r o indicating sufficient thermal maturity for both oil and gas generation burial thermal history models indicate that the upper jurassic madbi source rocks passed the peak of oil generation stage and convert the oil to dry gas in the late jurassic to late cretaceous time oil generation began immediately after deposition in the late jurassic time 150 145 ma and maximum rates of oil with significant gas have been generated during late cretaceous time 110 65 ma the peak gas generation occurred during the early tertiary the modelled hydrocarbon expulsion evolution suggests that the timing of hydrocarbon expulsion from the madbi source rocks began in the early cretaceous 140 ma persisted to present day the modelling results also indicate that the peak hydrocarbon generation and expulsion from madbi source rocks in the studied area occurs well after deposition of the seal rock and formation of traps ensuring entrapment and preservation of migrated hydrocarbons

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

organic geochemistry and basin modeling of late cretaceous harshiyat formation in the onshore and offshore basins in yemen implications for effective source rock potential and hydrocarbon generation abstract the purpose of this study is to present the source rock characteristics of late cretaceous harshiyat formation source rock in the onshore and offshore basins of yemen i e mukalla sayhut sayun masilah and jiza qamar source rock geochemical characterizations were completed and integrated to perform 1 d basin modeling to back predict source rock thermal maturation oil generation and expulsion the geochemical findings revealed that mudstone intervals within the harshiyat formation comprised favorable source rocks with total organic carbon toc content between 0 50 and 35 10 wt the organic matter intervals in the harshiyat mudstones are mainly types ii iii and iii kerogens with certain amount of type ii and i kerogens based on rock eval hi values ranging from 40 to 923 mg hc g toc mixed kerogen types were consistent with vitrinite and sapropelic organic matters as observed by visual kerogen examination and the distribution of biomarker fingerprints the existence of mixed types i ii and iii organic matter suggests that the harshiyat mudstones could contribute to oil and gas at sufficient thermal maturity levels the biomarker data of the organic matter in the harshiyat mudstones show that the source rock contains a mix marine phytoplanktonic bacteria terrestrial land plant enthronement and were deposited in suboxic anoxic conditions results of chemical and optical maturity indicators led to the conclusion of varying maturity stages from immature to late oil window levels for the mudstones of the harshiyat formation thermal maturation distributions inferred from the analyzed samples indicate that mudstone intervals in the offshore mukalla sayhut basin are extremely mature compatible with the late mature oil window and may have generated significant amounts of oil this interpretation was supported by strong geochemical similarity between the organic matter in the mudstones and those of the oils found in the offshore mukalla sayhut basin and demonstrated by the concentrations of n alkanes and isoprenoids as well as carbon isotopes in the offshore ras ghashwah 1x well burial and thermal models were constructed and used to address the effect of tectonic events in triggering oil generation and expulsion from mature harshiyat source rock in the offshore area kinetic database models for type ii and iii kerogen mixtures indicate that the initial conversion of kerogen to oil occurred since the late oligocene with transformation ratios tr that span between 10 and 50 furthermore the oil was expelled from organic matter intervals in the harshiyat source rock starting from late oligocene and continuing until late miocene with trs of 50 72 from that period up to the present the retained oil was cracked into wet gas in the gas window with an easy ro greater than 1 30 and with peak tr ratios greater than 72

particle tracking in ideal faulted blocks using 3d co ordinate geometry abstract this article performs particle material point tracking for ideal brittle faults with translational and rotational slip components the fault planes are considered to be planar and step like in separate cases in the latter case the hangingwall block is considered to behave ductilely for a specific choice of the three cartesian co ordinate axes dip slip fault will change two out of the three ordinates of any point in the faulted block that moves a strike slip faulting can change one out of the three ordinates on the other hand whatever be the orientation of the orthogonal co ordinate axes an oblique slip fault of any dip amount and a purely rotational fault with dip 0 90 alter all the three ordinates except the pivot point in the latter case as expected oblique slip faulting modifies the co ordinates of the shifted material points depending on both i the pitch of stretching lineation and ii the dip of the fault plane

mechanical evolution of transpression zones affected by fault interactions insights from 3d elasto plastic finite element models abstract the mechanical evolution of transpression zones affected by fault interactions is investigated by a 3d elasto plastic mechanical model solved with the finite element method ductile transpression between non rigid walls implies an upward and lateral extrusion the model results demonstrate that a transpression zone evolves in a 3d strain field along non coaxial strain paths distributed plastic strain slip transfer and maximum plastic strain occur within the transpression zone outside the transpression zone fault slip is reduced because deformation is accommodated by distributed plastic shear with progressive deformation the 3 axis the minimum compressive stress rotates within the transpression zone to form an oblique angle to the regional transport direction 9 10 the magnitude of displacement increases faster within the transpression zone than outside it rotation of the displacement vectors of oblique convergence with time suggests that transpression zone evolves toward an overall non plane strain deformation the slip decreases along fault segments and with increasing depth this can be attributed to the accommodation of bulk shortening over adjacent fault segments the model result shows an almost symmetrical domal uplift due to off fault deformation generating a doubly plunging fold and a positive flower structure outside the overlap zone expanding asymmetric basins subside to negative flower structures on both sides of the transpression zone and are called transpressional basins deflection at fault segments causes the fault dip fall to less than 90 86 89 near the surface 1 5 km this results in a pure shear dominated triclinic and discontinuous heterogeneous flow of the transpression zone

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

origin of organic matter and paleoenvironment conditions of the late jurassic organic rich shales from shabwah sub basin western yemen constraints from petrology and biological markers abstract late jurassic organic rich shales from shabwah sub basin of western yemen were analysed based on a combined investigations of organic geochemistry and petrology to define the origin type of organic matter and the paleoenvironment conditions during deposition the organic rich shales have high total sulphur content values in the range of 1 49 4 92 wt and excellent source rock potential is expected based on the high values of toc 7 high extractable organic matter content and hydrocarbon yield exceeding 7000 ppm the high total sulphur content and its relation with high organic carbon content indicate that the late jurassic organic rich shales of the shabwah sub basin were deposited in a marine environment under suboxic anoxic conditions this has been evidenced from kerogen microscopy and their biomarker distributions the kerogen microscopy investigation indicated that the late jurassic organic rich shales contain an abundant liptinitic organic matter i e alginite structureless amorphous organic matters the presence of alginite with morphology similar to the lamalginite alga and amorphous organic matter in these shale samples further suggests a marine origin the biomarker distributions also provide evidence for a major contribution by aquatic algae and microorganisms with a minor terrigenous organic matter input the biomarkers are characterized by unimodal distribution of n alkanes low acyclic isoprenoids compared to normal alkanes relatively high tricyclic terpanes compared to tetracyclic terpanes and high proportion of c27 and c29 regular steranes compared to c28 regular sterane moreover the suboxic to anoxic bottom water conditions as evidenced in these late jurassic shales is also supported based on relatively low pristane phytane pr ph ratios in the range of 0 80 1 14 therefore it is envisaged here that the high content of organic matter toc 7 wt in the analysed late jurassic shales is attributed to good organic matter om preservation under suboxic to anoxic bottom water conditions during deposition

basin modelling a new comprehensive method in petroleum geology abstract integrated basin modelling is used to understand and reconstruct the geological and thermal evolution of a sedimentary basin to quantify this information and hence to derive among other results the history of generation migration and accumulation of petroleum this new methodical approach is rapidly gaining world wide recognition throughout the geo scientific community because it offers two distinct advantages when addressing geological problems firstly it enables a logical quantitative treatment of very complex interrelated geological processes and secondly it permits these processes to be examined on the basis of an absolute geological time scale the prerequisites for basin modelling are 1 the translation of logical and consistent geological concepts into numerical form and then into suitable computer programs and 2 the application of these programs using high speed computers with large memories using such an approach is an important part of modern petroleum exploration because 1 1 provision is made for total coverage of the basin by allowing extrapolation to non drilled often deeper parts of the basin accessible only by using seismic data 2 2 a three dimensional view of the basin can be constructed and followed through geological time 3 3 an internal logic is utilised which is consistent with physical and chemical laws 4 4 geological geophysical and geochemical data are integrated and modelled iteratively and therefore control each other this paper shows the rapidly widening scope of basin modelling and points out some of the present day limitations and necessary research directions for the future it describes concepts for modelling of tectonic processes and for simulating expulsion of liquid petroleum

petroleum generation modeling of the organic rich shales of late jurassic early cretaceous succession from mintaq 01 well in the wadi hajar sub basin yemen late jurassic early cretaceous shales of the naifa safer and madbi formations were studied to evaluate source rock characterization the results of the source rock were then incorporated into basin modeling to understand the timing of hydrocarbon hc generation and expulsion the late jurassic early cretaceous shales have low to high organic matter with total organic carbon toc values in the range of 0 50 28 01 indicating fair to excellent source rock potential main oil and gas are anticipated to be generated from the naifa safer and lam shale samples with types i and or ii and types ii iii kerogens in contrast the meem samples are dominated by type iii kerogen hydrogen index hi 200 mg hc g toc and are thus considered to be gas prone the late jurassic early cretaceous shale samples have temperatures of maximum pyrolysis yield tmax in the range of 337 515 c consistent with immature to post mature stages the tmax data also indicate that the safer and madbi shale samples h

structural controls on jurassic gold mineralization and cretaceous tertiary exhumation in the foreland of the southern patagonian andes new constraints from la paloma area deseado massif argentina abstract fluid rock interaction occurring within high permeability conduits represented by fault fracture meshes is well known to control the development of hydrothermal ore deposits in this study we document the fundamental role of four sets of precursor joints reactivated as dilational faults displaying variable normal dip slip and strike slip components of motion in the formation of epithermal au ag deposits of economic interest paleostress analysis unravels how all the resulting four sets of hybrid extension shear fractures are kinematically compatible with an extensional stress field characterized by multiple permutations between the 3 and the 2 axes such permutations are interpreted to be associated with dominantly normal fault reactivation of suitably oriented early joint sets as a result of continued regional extension and by orthogonal stretching produced by differential downthrow of the hanging wall blocks of laterally terminating jurassic normal faults later fault reactivation appears to be associated with far field propagation of andean stresses marked by superposed strike slip and reverse fault slip components recording roughly e w horizontal compression this late fault reactivation could be related with a late early cretaceous shortening event known to have affected the studied sector of the deseado massif the subsequent tectonic evolution of the study area occurred within the general framework of a slow cretaceous to tertiary exhumation recorded by apatite fission track cooling ages our new thermochronometric results recording steady state cooling at a rate of c 1 c ma during the last 90 ma shed new light onto the post jurassic geodynamic evolution of the foreland of the southern patagonian andes

source rock characteristics and hydrocarbon expulsion potential of the middle eocene wenchang formation in the huizhou depression pearl river mouth basin south china sea abstract the middle eocene wenchang wc formation in the huizhou depression of the pearl river mouth basin is an important geological element for petroleum exploration in the south china sea in this study the geological and geochemical characteristics of the wc source rocks including the distribution sedimentary environment organic matter type hydrocarbon generation potential and thermal maturity were investigated hydrocarbon generation history and hydrocarbon expulsion intensity and quantities were evaluated through one dimensional basin modelling and an improved hydrocarbon generation potential methodology the wc source rocks are widely distributed and have an elevated thickness mostly thicker than 200 m with a maximum thickness greater than 1000 m they were deposited in a lacustrine weak oxidation weak reduction sedimentary environment with low salinity the source rocks have low to high organic matter abundance toc mainly ranges from 0 27 to 3 59 wt with an average of 1 39 wt dominated by ii 1 type and ii 2 type kerogen resulting in significant hydrocarbon generating potential under moderate high thermal evolution r o mainly ranges from 0 65 to 1 2 on the margins of sags and greater than 1 2 in the centre of sags the source rocks became mature r o 0 5 in the early miocene and began to generate hydrocarbons they reached the hydrocarbon expulsion threshold at 0 8 r o and the hydrocarbon expulsion rate became greatest at 1 1 r o the expulsion intensities in the h26 sag h21 sag x24 sag and x23 sag are relatively large with their greatest expulsion intensities being 104 10 6 71 10 6 62 10 6 and 53 10 6 t km 2 respectively the comprehensive hydrocarbon expulsion efficiency was approximately 75 about 690 1 10 8 t of hydrocarbons were expulsed from the wc source rocks in the huizhou depression

modeling of gas generation from the alam el bueib formation in the shoushan basin northern western desert of egypt the shoushan basin is an important hydrocarbon province in the northern western desert egypt but the burial thermal histories for most of the source rocks in the basin have not been assigned yet in this study subsurface samples from selected wells were collected to characterize the source rocks of alam el bueib formation and to study thermal history in the shoushan basin the lower cretaceous alam el bueib formation is widespread in the shoushan basin which is composed mainly of shales and sandstones with minor carbonate rocks deposited in a marine environment the gas generative potential of the lower cretaceous alam el bueib formation in the shoushan basin was evaluated by rock eval pyrolysis most samples contain sufficient type iii organic matter to be considered gas prone vitrinite reflectance was measured at eight stratigraphic levels jurassic cretaceous vitrinite reflectance profiles show a general increase of vitrinite reflectance with depth vitrinite reflectance values of alam el bueib formation range between 0 70 and 0 87 vrr indicating a thermal maturity level sufficient for hydrocarbon generation thermal maturity and burial histories models predict that the alam el bueib source rock entered the mid mature stage for hydrocarbon generation in the tertiary these models indicate that the onset of gas generation from the alam el bueib source rock began in the paleocene 60 ma and the maximum volume of gas generation occurred during the pliocene 3 2 ma

controls on cu mineralization in central part of the kerman porphyry copper belt se iran constraints from structural and spatial pattern analysis abstract the sarduiyeh area in the central part of the kerman porphyry copper belt kpcb se iran contains numerous cu deposits and prospects this area is bound by e w trending major faults which show the northern and southern borders of fault duplex minor faults first second or third orders were identified in three trends of nw n s and ne analysis of the fault kinematics data revealed an extensional fault duplex pattern for this area in this fault zone cu deposits are associated with faults that have a special trend this proposed kinematic model for evolution of sarduiyeh extensional fault duplex emphasizes that the main cu deposits in the sarduiyeh area are located within the dilatational zones related to nw se trending normal faults in this study the spatial pattern analysis conducted by fry fractal fracture density and buffer zones methods support the conceptual model of district scale mechanism of structural controls on final emplacement of cu deposits this investigation of sarduiyeh cu mineralization revealed that the nw se trending faults are effective in localization of cu mineralization in the central part of kpcb

organic geochemical characteristics and oil generating potential of the upper jurassic safer shale sediments in the marib shabowah basin western yemen the organic rich safer shales exposed in the north central part of onshore marib shabowah basin are evaluated and their depositional environments are interpreted total organic carbon contents toc of the shales range from 1 02 16 8 wt and yield hydrogen index hi values ranging from 130 to 820 mg hc g toc consistent with mainly type ii with minor contributions from type i and mixed types ii iii kerogens the safer shale samples have vitrinite reflectance values in the range of 0 5 1 0 ro indicating early mature to peak mature stage for oil generation tmax values range from 429 438 c which are in reasonably good agreement with vitrinite reflectance data kerogen microscopy shows that the safer shales are characterized by high amounts of organic matter consisting predominantly of yellow fluorescing amorphous organic matter and alginite of marine origin this is supported by their high content of hydrogen rich type ii and i oil prone kerogen the biomarker distributions of the upper jurassic safer extracts are characterized by dominant low to medium molecular weight compounds n c14 to n c20 low pr ph ratio 1 0 high phytane n c18 ratios 0 82 2 68 and predominant regular sterane c27 all biomarker parameters clearly indicate that the organic matter was derived from marine algal inputs and deposited under anoxic reducing conditions hypersaline conditions also prevailed during deposition of these sediments as indicated by the presence of gammacerane

the interpretation of inverted metamorphic isograds using simple physical calculations several zones of major thrust faulting exhibit a juxtaposition of rocks of higher metamorphic grade over rocks of lower grade this configuration may indicate but does not require that temperature gradients were temporarily inverted near the fault we examine the physical conditions under which such a temperature inversion could occur the overthrusting of hotter rock on colder rock can cause a temporarily inverted gradient both above and below the fault only if the time taken to underthrust rock from the land surface to a given depth z on the fault is less than times the characteristic time for diffusion of heat through the block above the fault where is thermal diffusivity an inverted gradient cannot form without heat generation in the fault zone unless v z sin 100 where v is the rate of underthrusting in millimeters per year z is in kilometers and is the dip of the fault this simple criterion is sufficient to demonstrate that several examples of inverted metamorphic gradients cannot be explained simply by the thrusting of hot on cold rock without heat sources in the fault zone dissipative heating accompanying deformation can cause an inverted temperature gradient within and beneath the thrust zone but whereas the overthrusting of hot upon cold rocks cools the fault zone dissipation heats it thus the overthrusting of hot on cold rock and dissipative heating affect the temperature gradient and the maximum temperatures differently we show that the magnitudes of the inverted temperature gradient and of the maximum temperature above the inverted gradient yield independent estimates of the rate of dissipative heating discrepancy between these estimates implies that some additional process must have occurred such as the post thrusting disruption of the isograds if there is such a discrepancy the maximum temperature probably provides the more reliable estimate of the rate of heating at the fault we illustrate this analysis by applying it to reported inverted metamorphic zonation in the pelona schist the st anthony complex the mt everest region of the main central thrust and the olympos thrust petrological inferences of maximum temperatures depths of metamorphism and magnitudes of apparent inverted gradients imply that shear stresses of about 100 mpa accompanied thrust faulting in some of these regions and that some zones of inverted metamorphism have been tectonically thinned after the metamorphism occured

numerical simulation of present day tectonic stress across the indian subcontinent in situ measurements of maximum horizontal stress shmax in the indian subcontinent are limited and do not present regional trends of intraplate stress orientation the observed orientations of shmax vary considerably and often differ from the plate velocity direction we have simulated orientation and magnitude of shmax through finite element modeling incorporating heterogeneities in elastic property of the indian continent and plain stress approximation to understand the variability of shmax four different scenarios are tested in simulation 1 homogeneous plate with fixed plate boundary 2 homogeneous plate with boundary forces 3 heterogeneous plate with fixed boundary 4 heterogeneous plate with boundary forces the estimated orientation and magnitude of shmax with a heterogeneous plate with boundary forces in the himalayan region and an eastern plate boundary comprising the indo burmese arc and andaman subduction zone are consistent with measured maximum horizontal stress this study suggests that plate boundary force varies along the northern indian plate margin and also provides a constraint on the intraplate stress field in the indian subcontinent

linking metamorphic textures to u pb monazite in situ geochronology to determine the age and nature of aluminosilicate forming reactions in the northern monashee mountains british columbia abstract the monashee mountains of the canadian cordillera are thought to expose a classic barrovian facies series of isograds the timing of aluminosilicate growth in the region was determined for four pelitic schist samples by combining textural relationships with monazite compositional zoning and monazite u pb geochronology conducted directly on thin sections by the laser ablation method three distinct phases of kyanite growth are recorded in the kyanite zone at c 153 ma between 122 and 94 ma and between 76 and 58 ma for each phase monazite and garnet grew synchronously with kyanite probably by a reaction involving the breakdown of staurolite in contrast sillimanite growth by muscovite dehydration melting occurred at or before c 104 ma in the sillimanite zone and retrograde sillimanite grew in schists previously metamorphosed at the kyanite grade during the first two phases by the influx of hot acidic fluids during top to the east shearing at ca 71 ma these results indicate that rocks metamorphosed at different places and different times in the orogen were juxtaposed prior to being overprinted at the sillimanite grade in the late cretaceous early paleocene during the influx of hot fluids in a structurally coherent body deforming by easterly directed shearing this study also provides new insight into monazite petrogenesis and suggests that at least in some circumstances monazite formation is linked to the staurolite out reaction that produces kyanite

modeling petroleum generation in the southern muglad rift basin sudan maturity and petroleum generation have been modeled in a 120 km long northeast southwest cross section of the southern muglad basin sudan the section passes close to the unity and kaikang areas which provide well control on the structure interpreted from gravity and seismic reflection profiles modeling of geotherms from corrected bottom hole temperatures indicates present heat flows around 60 mw m2 in the well control areas using measured vitrinite data as calibrant maturity can be modeled equally well with a constant paleoheat flow similar to the present day or with a complex heat flow pattern related to rifting a geologically realistic complex heat flow model was employed to calculate the timing of generation and expulsion from the lower cretaceous lacustrine source rocks of the abu gabra and sharaf formations kinetic easy ro calculation of vitrinite maturity indicates a projected oil preservation depth limit around 4000 m shallowing to around 3500 m northeast of unity near the basin margin

heat flow and thermal maturity modelling in the northern carnarvon basin north west shelf australia abstract the northern carnarvon basin is located at the southern end of the north west shelf of australia it was developed by rifting during the jurassic earliest cretaceous heat flow and thermal maturity in seven wells from three sub basins rankin platform and exmouth plateau of the northern carnarvon basin were modelled using basinmod 1d program multiple thermal maturity parameters were used to constrain the influence of anomalously low vitrinite reflectance those t max data with reliable quality can be applied to correlate with vitrinite reflectance establish thermal maturity and calibrate the modelled results the modelled results indicated that the measured maturity data in some wells were consistent with the rift heat flow model jarvis mckenzie associated with the jurassic rift and the earliest cretaceous seafloor spreading events the maximum values of heat flow were in the range from 67 mw m 2 jurabi 1 to 105 mw m 2 bowers 1 in the exmouth and barrow sub basins on the exmouth plateau the maximum values of heat flow were modelled to be 72 mw m 2 in the jupiter 1 well and 78 mw m 2 in the investigator 1 well these maximum values were modelled to occur during syn rift phase which were 29 88 and 33 37 greater than their current heat flow values in the sub basins and on the exmouth plateau respectively this study suggests that maturity indicators are less diagnostic of rifting thermal histories if the maximum thermal effect is associated with cretaceous and cainozoic burial in this basin

geochemical characteristics of crude oil from a tight oil reservoir in the lucaogou formation jimusar sag junggar basin jimusar sag which lies in the junggar basin is an important tight oil study area in china however the properties and origin of the crude oil and the geochemical characteristics of the tight oil from the lucaogou formation have not yet been studied in the present study 23 crude oil samples from the lucaogou formation were collected for analysis including physical properties density and viscosity bulk composition saturated hydrocarbon gas chromatography mass spectrometry and calculation of various biomarker parameters source rock evaluation and porosity permeability analysis were applied to the mudstones and siltstones to analyze the hydrocarbon generation history of the lucaogou source rocks one dimensional basin modeling was performed the oil filling history was also investigated by means of basin modeling and microthermometry biomarkers of suitable source rocks total organic carbon content is 1 summation of the free and volatile hydrocarbon and remaining hydrocarbon generative potential is 6 mg hc g rock and vitrinite reflectance is between 0 7 and 1 were analyzed for oil source correlation the results indicate that low maturity to mature crude oils originated from the source rocks containing terrigenous organic matter which were deposited in a saline lake the source rocks are of mainly type ii kerogen oil in the lower section of the lucaogou formation is relatively dense and viscous and has elevated nonhydrocarbon content in addition a higher proportion of bacteria and algae is shown to have contributed to the formation of crude oil in the lower section when compared with the upper section of the lucaogou formation oil source correlations demonstrate that not all mudstones within the lucaogou formation contribute to oil accumulation thin section observation indicates organic macerals surround the grains of some siltstones within the porous and permeable subsections which proves the siltstones contribute to hydrocarbon generation crude oils from the upper and lower sections mainly originate from thin bedded mudstones interbedded and siltstones within the porous and permeable subsections the mudstones over or beneath the porous and permeable subsections consist of seals and prevent the vertical movement of oil by capillary forces despite being thicker mudstones between the two porous and permeable subsections make no obvious contribution to the oil accumulation because of their low permeability and distance from the porous and permeable subsections which is consistent with the principle of near source charging for tight oil accumulations lucaogou oil has been charged twice once from 235 to 210 ma and again from 180 to 150 ma coinciding with oil generation time

shear heat model for gouge free dip slip listric normal faults abstract shear heating due to brittle faulting is important in petroleum geosciences tectonics and seismic studies temporal variation of shear heat in a listric normal fault with a circular arc shaped fault plane is simulated in this work which was not done so far the work is expected to have a far reaching implication in tectonics and petroleum geosciences since listric faults can be closely associated with hydrocarbon reserves e g valdiya and sanwal 2017 for such a fault plane devoid of gouge and any secondary faulting shear heat is proportional to the mass of the hanging wall block the coefficient of friction acting between the hanging wall and the footwall block and radius of the circular arc shear heating intensifies temporally as the hanging wall block slides down and reaches progressively gentler fault dip

organic geochemistry characterization of the paleogene to neogene source rocks in the sayhut subbasin gulf of aden basin with emphasis on organic matter input and petroleum generation potential paleogene umm er radhuma and ghaydah and neogene sarar source rocks from sayhut subbasin in the gulf of aden basin were studied to provide information such as organic matter types paleoenvironmental conditions and petroleum generation potential this study is based on whole rock organic geochemical analyses and organic petrology the total organic carbon toc contents of the paleogene to neogene source rocks range from 0 43 to 6 11 with an average toc value of 1 00 indicating fair to very good source rock potential the paleogene ghaydah and umm er radhuma source rocks are relatively higher in genetic petroleum potential than neogene sarar source rocks mainly oil and gas are anticipated from the ghaydah and umm er radhuma source rocks with hydrogen index hi values ranging from 95 to 715 mg hydrocarbon hc g toc this is supported by the presence of significant amounts of liptinite macerals in the ghaydah and umm er radhuma source rocks the sarar source rocks are dominated by vitrinitic type iii kerogen hi 200 mg hc g toc and are thus considered to be gas source rocks the paleogene to neogene source rocks have vitrinite reflectance r o values in the range between 0 30 and 0 77 r o and pyrolysis maximum temperature values range from 412 c to 444 c 774 f to 831 f consistent with the immature to early mature oil window therefore the present day kerogen type in the paleogene to neogene source rocks is original and should not have been altered by thermal maturity the biomarker of organic matter suggests that the paleogene to neogene source rocks were deposited in a marine environment under suboxic to anoxic conditions the biomarkers also indicate that the paleogene to neogene source rocks contain a mixture of aquatic organic matter planktonic and bacterial and terrigenous organic matter with increasing terrigenous influence to sarar source rock samples highly hypersaline reducing conditions are also evidenced in ghaydah and umm er radhuma source rocks as indicated by the presence of the gammacerane biomarker low pristane to phytane ratios and homohopane distribution patterns

stress regime changes in the main boundary thrust zone eastern himalaya decoded from fault slip analysis abstract the main boundary thrust mbt zone in the darjeeling foothills eastern himalaya exhibits northerly dipping fault splays named here as mbt 1 and mbt 2 with proterozoic daling group in the mbt 1 hanging wall upper paleozoic gondwana rocks between the mbt 1 and the mbt 2 and neogene siwalik group in the footwall of the mbt 2 on the basis of reduced stress tensors from fault slip analysis and their grouping relative to different stratigraphic units in the mbt zone that crops out over a strike length of 20 km the following successive stress regimes have been interpreted the earliest brittle deformation recorded only in the basal part of the gondwana succession was controlled by a pre himalayan nw se extensional regime the himalayan deformation under sustained n s compressive regime developed in three stages a thrust displacement along the mbt 1 juxtaposing folded daling rocks against the lower gondwana rocks b tilting and fracturing of lower gondwana succession and thrust transport over the siwalik rocks along the mbt 2 c strike slip regime with nw and ne trending faults affecting both the lower gondwana and siwalik strata developed possibly due to increased tectonic loading the tensor solutions under n s compressional regime are consistent with the modern plate convergence supporting a foreland propagating thrust system in the eastern himalaya in addition an e w extensional regime led to apparent orogen parallel extension