ground ice and slope sediments archiving late quaternary paleoenvironment and paleoclimate signals at the margins of el gygytgyn impact crater ne siberia an accumulation terrace close to the el gygytgyn impact crater in northeastern siberia contains stratigraphic and periglacial evidence of the paleoenvironmental and paleoclimatic history and permafrost dynamics during late quaternary time a succession of paleo active layer deposits that mirror environmental changes records periods favorable for the establishment and growth of ice wedge polygonal networks and sediment variations these two elements of the periglacial landscape serve as complementary paleoenvironmental archives that can be traced back to 14 000 cal yr bp the slope sediments and the ground ice contained therein have prominent relative maxima and minima in properties grain size total organic content oxygen isotopes they document a regional early holocene thermal maximum at about 9000 cal yr bp followed by a transition to slightly cooler conditions and a subsequent transition to slightly warmer conditions after about 4000 cal yr bp results from sedimentary analysis resemble morphological and geochemical oxygen and hydrogen isotopes results from ice wedge studies in which successive generations of ice wedge polygonal networks record warmer winters in late holocene time moreover peaks of light soluble cation contents and quartz grain surface textures reveal distinct traces of cryogenic weathering we propose a conclusive sedimentation model illustrating terrace formation in a permafrost terrain

episodic petroleum fluid migration in fault zones of the northwestern junggar basin northwest china evidence from hydrocarbon bearing zoned calcite cement hydrocarbon bearing zoned calcite cements occur widely in jurassic cretaceous fault zone cores and sandstone outcrops of the northwestern junggar basin northwest china hydrocarbon bearing bands alternate with nearly hydrocarbon free bands at a micron scale analytical results from biomarker organic geochemistry fourier transform infrared microspectroscopy and trace element geochemistry on these zoned cements suggest that at least three different types of fluids have participated in their formation the first fluid type is probably primary unmodified lacustrine formation water from which the hydrocarbon poor bands are formed and are characterized by mg rich calcite the other two types of fluids include basinal fluids e g hot hydrocarbon bearing fluids and meteoric water the hydrocarbon rich bands in which the hydrocarbons have been biodegraded and the mn content is relatively high suggest a mixture of hydrocarbon bearing basinal fluid and meteoric water the alternating growth of hydrocarbon bearing and hydrocarbon free bands of calcite cements implies that the cement formation is episodic it is related to alternating episodes of mixed petroleum bearing fluid and unmodified primary formation waters respectively the fault appears to have been a mixing zone where seismic pumping during the movement of associated regional faults occurred thus in the northwestern junggar basin the micron scale hydrocarbon bearing zoned structure of the calcite cements is likely a reflection of episodic petroleum fluid migration in fault zones

charging of the neogene penglai 19 3 field bohai bay basin china oil accumulation in a young trap in an active fault zone the penglai 19 3 pl19 3 oil field the largest offshore oil field in china was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl19 3 anticline was not finally formed until about 2 0 ma and is cut by densely distributed faults source rock and crude oil samples from the pl19 3 field were analyzed to determine the origin and formation mechanisms of this large oil field three organic rich oil prone source rock intervals exist in the bozhong subbasin each of which has a distinct biomarker assemblage oil samples from different wells have different biomarker associations and three source related oil classes were identified within the pl19 3 field based on biomarker compositions and multivariate analysis of the data the pl19 3 field displays considerable compositional heterogeneity the compositional heterogeneity within the field and comparison between oil samples from the pl19 3 field and those from nearby structures suggest three field filling directions which is consistent with the results of migration pathway modeling the pl19 3 field was charged in the north by oil generated from dongying formation source rocks in the eastern bozhong depression and bodong depression in the southeast by oil generated from shahejie formation source rocks in the miaoxi depression and in the northwest by oil generated from shahejie formation source rocks in the central bozhong depression oil charge from multiple source rock intervals and multiple generative kitchens and focusing of oil originating from a large area of the bozhong depression into the same trap resulted in rapid oil accumulation in the pl19 3 structure and the formation of this large oil field in a very young trap within an active fault zone

petrophysics of lower silurian sandstones and integration with the tectonic stratigraphic framework appalachian basin united states petrophysical properties were determined for six facies in lower silurian sandstones of the appalachian basin fluvial estuarine upper shoreface lower shoreface tidal channel and tidal flat fluvial sandstones have the highest permeability for a given porosity and exhibit a wide range of porosity 2 18 and permeability 0 002 450 md with a transition zone thickness of only 1 6 m 3 20 ft fluvial sandstones with permeability greater than 5 md have irreducible water saturation siw less than 20 typical of many gas reservoirs upper shoreface sandstones exhibit good reservoir properties with high porosity 10 21 high permeability 3 250 md and low siw 20 lower shoreface sandstones which are finer grained have lower porosity 4 12 lower permeability 0 0007 4 md thicker transition zones 6 180 m 20 600 ft and higher siw in the tidal channel tidal flat and estuarine facies low porosity average 6 low permeability average 0 02 md and small pore throats result in large transition zones 30 200 m 100 650 ft and high water saturations the most favorable reservoir petrophysical properties and the best estimated production from the lower silurian sandstones are associated with fluvial and upper shoreface facies of incised valley fills which we interpret to have formed predominantly in areas of structural recesses that evolved from promontories along a collisional margin during the taconic orogeny although the total thickness of the sandstone may not be as great in these areas reservoir quality is better than in adjacent structural salients which is attributed to higher energy depositional processes and shallower maximum burial depth in the recesses than in the salients

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

single crystal 40ar 39ar dating of the olorgesailie formation southern kenya rift single crystal laser fusion sup 40 ar sup 39 ar analyses and several conventional bulk fusion sup 40 k sup 40 ar dates have been used to determine the age of volcaniclastic strata within the olorgesailie formation and of associated volcanic and sedimentary units of the southern kenya rift in the principal exposures along the southern edge of the legemunge plain the formation spans the interval from approximately 500 to 1 000 ka deposition continued to the east along the ol keju nyiro river where a tuff near the top of the formation has been dated at 215 ka in these exposures the formation is unconformably overlain by sediments dated at 49 ka a possible source for the olorgesailie tephra the ol doinyo nyokie volcanic complex contains as ash flow dated at approximately 1 ma extending the known age range of this complex to encompass that of virtually the entire olorgesailie formation in the legemunge plain these geologic examples illustrate the importance of the single crystal sup 40 ar sup 39 ar dating technique whereby contaminant altered or otherwise aberrant grains can be identified and eliminated from the determination of eruptive ages for reworked or altered pyroclastic deposits the authors have presented a computer modeling procedure based on an inverse isochron analysis thatmore promotes a more objective approach to trimming sup 40 ar sup 39 ar isotope data sets of this type less

on the use of combined geophysical methods to assess water content and water conductivity of near surface formations abstract we propose to deepen the interpretation of combined geophysical methods georadar seismic and electric to assess physical properties characterizing the near surface porous formations especially the influence of water velocity analysis of multioffset georadar data are used together with seismic methods to estimate lateral and vertical ground water fluctuations this enables us to identify transitions from non saturated to fully saturated porous layers with certainty furthermore the accurate knowledge of seismic velocities helps to estimate the porosity of the ground water formations finally we show how the radar technique may be useful in solving the problem of trade off between bulk resistivity which is deduced from electrical measurements and that of water ionic conductivity and water content these theoretical considerations are illustrated using various measurements conducted at the same test site our interpretation is compared with a few laboratory measurements on water and soil samples this study displays the impact of combined geophysical approaches for providing models of water and ionic transfers down to a depth of several metres

evolution of fracture and fault controlled fluid pathways in carbonates of the albanides fold thrust belt the process of fracture and fault formation in carbonates of the albanides fold thrust belt has been systematically documented using hierarchical development of structural elements from hand sample outcrop and geologic map scales the function of fractures and faults in fluid migration was elucidated using calcite cement and bitumen in these structures as a paleoflow indicator two prefolding pressure solution and vein assemblages were identified an overburden assemblage and a remote tectonic stress assemblage sheared layer parallel pressure solution surfaces of the overburden assemblage define mechanical layers shearing of mechanical layers associated with folding resulted in the formation of a series of folding assemblage fractures at different orientations depending on the slip direction of individual mechanical layers prefolding and folding related fracture assemblages together formed fragmentation zones in mechanical layers and are the sites of incipient fault localization further deformation along these sites was accommodated by rotation and translation of fragmented rock which formed breccia and facilitated fault offset across multiple mechanical layers strike slip faults formed by this process are organized in two sets in an apparent conjugate pattern calcite cement and bitumen that accumulated along fractures and faults are evidence of localized fluid flow along fault zones by systematic identification of fractures and faults their evolution and their fluid and bitumen contents along with subsurface core and well log data we identify northeast southwest trending strike slip faults and the associated structures as dominant fluid pathways in the albanides fold thrust belt

a coupled fluid fracture approach to propagation of clastic dikes during earthquakes abstract the propagation of clastic dikes was studied in ami az plain where hundreds of clastic dikes cross cut the soft rock of the late pleistocene lacustrine lisan formation within the seismically active dead sea basin two analytic models were established to estimate the dike propagation velocities the dike emplacement duration and the driving pressures that were associated with dike propagation either under laminar or turbulent flow conditions these models depend on the host rock and fluid properties dike width and length based on these properties and field limitations the results indicate that the dikes were propagated under turbulent flow conditions and propagation velocities of 4 65 m s the emplacement duration of the clastic dikes is between 0 8 and 2 s which is similar to the order of the acoustic wave duration that passes through the soft rock during an earthquake event this implies that the propagation of dikes could form during the passing acoustic waves and may thus be considered as an earthquake induced impact structures the calculated driving pressures that were generated during the earthquake events near the surface are 1 2 mpa one order of magnitude larger than the pressure due to the overburden on the source layer

transverse versus longitudinal extension in the foredeep peripheral bulge system role of cretaceous structural inheritances during early miocene extensional faulting in inner central apennines belt this study reports on the rocca di cave extensional fault system which is located in the prenestini mountains central italy of the apennines fold and thrust belt and presently represents the oldest exposure of early orogenic foreland fault system of the apennines this fault system was oriented perpendicular to the strike of the foredeep peripheral bulge system indicating that the onset of convergence was marked by a foredeep parallel extension instead of the commonly observed foredeep perpendicular stretching associated with lithosphere flexuring the studied fault system is formed by a 10 km long and 2 km wide e w elongated area that includes two mutually orthogonal sets of faults oriented about e w and n s respectively e w and mainly n s striking faults developed during a preorogenic santonian to campanian in age e w oriented extension kinematics which caused first uplift and erosion and then drowning of the cretaceous carbonate platform and the onset of a pelagic environment both fault sets were later reactivated in the early miocene when the area was forming part of the foreland region ahead of the eastward migrating apennines fold and thrust belt and was undergoing local n s oriented i e foredeep parallel stretching this extensional stage implied the sedimentation of hundreds of meters of synkinematic strata in the northern block of the rocca di cave fault system coevally with episodes of subaerial erosion in areas of the southern block further extensional and right lateral reactivation of inherited faults occurred in the late miocene during the progressive incorporation of the area into the apennines belt

multiple dolomitization events along the pozalagua fault pozalagua quarry basque cantabrian basin northern spain the pozalagua quarry in the basque cantabrian basin of northern spain exposes a unique set of fault associated dolomites that can be studied on a decametre scale the dolomites developed along the pozalagua fault system in slope deposited limestones of albian age following marine phreatic diagenesis the limestones were subject to meteoric karst formation the resulting cavities were filled either by angular limestone fragments in a black clay rich matrix or by cave floor pond now dolomitized sediments the subsequent diagenetic history reflects repeated periods of fracturing fluid expulsion dissolution and cementation contrasting fluid pulses resulted in the formation of a network of hydrothermal karst and the subsequent development of coarse crystalline calcite cement zebra dolomite recrystallized coarse crystalline dolomite elongated blue grey coarse crystalline dolomite cement in the open fault and finally coarse crystalline saddle dolomite decimetre size reworked host rock fragments present in the latter two dolomite phases probably reflect roof collapse fragments of a cave system that developed along the pozalagua fault system however there are also metre scale host rock fragments that apparently float in the coarse crystalline saddle dolomites implying that either fragment assimilation was a widespread process or violent expulsion of fluids occurred along the pozalagua fault system the presence of pre dolomite and post dolomite stylolites parallel to bedding supports a linkage between the diagenetic events and the late albian tectonism that affected the region

styles of positive inversion tectonics in the central apennines and in the adriatic foreland implications for the evolution of the apennine chain italy abstract integration of new field structural and geophysical data with existing information from the apennines chain in italy and its adjacent adriatic foreland indicates that the styles of positive inversion tectonics and the modes of interaction between the extensional and the subsequent compressive structures vary starting from the cretaceous the contractional deformation induced by the mainly north directed convergence of africa adria with respect to the european plate promoted the closure of various arms of the atlantic and the neo tethys oceans which opened in different times and with distinct orientations the mosaic of continental blocks carbonate platforms rift basins and oceanic domains with several geometries and orientations with respect to the axis of the subsequent compression and the resulting heterogeneities within the shallow sedimentary cover and the overall lithosphere strongly influenced both the structural evolution of the apennine orogenic belt and the intra continental deformation within the adriatic foreland field observations reveal that the steeply e and w dipping mesozoic cenozoic normal faults are systematically decapitated by sub horizontal or gently west dipping thrusts propagating with short cut trajectories pre thrusting normal faults were commonly deformed by later thrusts but little evidence seems to support their entire reactivation as high angle reverse faults this suggests that these shallow and steeply dipping discontinuities were not suitable to be reutilized by the superficial thin skinned thrust faults propagating within the sedimentary cover in contrast presumably late paleozoic and mesozoic w dipping normal faults appear moderately reactivated in the adriatic foreland and strong positive inversion tectonics affect the deeper and buried structural levels of the apennine chain within the latter the syn rift sediments in the hangingwall blocks of the fault bounded basins were totally extruded and generated the strong uplift of the thinned adria continental crust finally the contrasting styles of interactions of the pre existing normal faults with later thrusts i e passive truncation or positive reactivation strictly result from the different evolution of the apennine chain and the combined thin and thick skinned modes of deformation of the stretched lithosphere of the adria plate

mineralogy of the tumanny au ag te hg epithermal veins western chukchi peninsula russia abstract the tumanny au ag te hg epithermal prospect chukchi peninsula russia is located in the near contact zone of the large vuknei pluton part of the early cretaceous egdykgych complex which is related to the peschanka porphyry copper deposit and the nakhodka porphyry epithermal ore district located 45 km north of tumanny mineralization at tumanny is characterized by an early carbonate base metal and a late gold silver sulfosalt mineral assemblage pyrite of the first assemblage is unzoned and as poor and tennantite tetrahedrite solid solutions ttrs are characterized by a weak oscillatory zoning caused by variable contents of sb and as low ag content and the widely variable sb sb as values pyrite of the second assemblage is zoned and as rich up to 5 2 wt and ttrs is weakly zoned and ag rich up to 10 35 apfu and has a comparatively narrow range of sb sb as value electrum au ag alloy kustelite au ag s phases hessite polybasite and imiterite recognized at the prospect belong to the second mineral assemblage the homogenization temperature of primary fluid inclusions in quartz ranges from 340 to 210 c and decreased during the mineralizing process fluid salinity varying from 0 8 to 5 2 wt nacl equiv is not evolved during the process cores of quartz crystals formed from a boiling fluid whereas crystal rims appear to have formed from a lower temperature non boiling liquid logfs2 decreased from 8 at the formation of carbonate base metal assemblage to 16 at the deposition of gold silver sulfosalt assemblage as temperature decreased from 340 to 200 c bulk icp oes analysis of mineralized samples indicated up to 38 ppm au 908 ppm ag 154 ppm mo 106 ppm te 53 ppm se 9246 ppm as 1284 ppm sb and 23 ppm bi cluster analysis of the data obtained identified three geochemical associations corresponding the carbonate base metal the gold silver sulfosalt and to the overlapped mineral assemblages the whole ore composition is controlled by mineralogy of these assemblages taking into account the geological setting mineralogy composition of minerals and fluid inclusion data the tumanny au ag te hg prospect is characterized as intermediate sulfidation epithermal style

petroleum migration pathways and charge concentration a three dimensional model petroleum migration pathways through a basin are determined by the three dimensional distribution of discontinuous sealing surfaces which are usually parallel to bedding the petroleum migrates below the sealing surface taking the structurally most advantageous route the three dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper application of the model to the paris and williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models pathways form a dense network overlying generating areas in the central parts of basins toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing surface morphologies eventually these pathways may reach the surface as seepages it is important to integrate surface outcrops of migration routes surface seepages into migration modeling deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal fault juxtaposition or cross formational seals such as salt intrusions deflection of pathways also occurs where there are hydrodynamic conditions in response to topography driven groundwater flow zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies or juxtaposition to nonsealing strata by faults vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool it assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion

late quaternary lake level changes of lake el gygytgyn ne siberia abstract lake el gygytgyn is situated in a 3 6 ma old impact crater in northeastern siberia presented here is a reconstruction of the quaternary lake level history as derived from sediment cores from the southern lake shelf there a cliff like bench 10 m below the modern water level has been investigated deep water sediments on the shelf indicate high lake levels during a warm mid pleistocene period one period with low lake level prior to marine oxygen isotope stage mis 3 has been identified followed by a period of high lake level 10 m above present in the course of mis 2 the lake level dropped to 10 m at the end of mis 2 the bench was formed and coarse beach sedimentation occurred subsequently the lake level rose rapidly to the holocene level changes in water level are likely linked to climate variability during relatively temperate periods the lake becomes free of ice in summer strong wave actions transport sediment parallel to the coast and towards the outlet where the material tends to accumulate resulting in lake level rise during cold periods the perennial lake ice cover hampers any wave activity and pebble transport keeping the outlet open and causing the lake level to drop

a 48 m y history of fracture opening temperature and fluid pressure cretaceous travis peak formation east texas basin quartz cement bridges across opening mode fractures of the cretaceous travis peak formation provide a textural and fluid inclusion record of incremental fracture opening during the burial evolution of this low porosity sandstone incremental crack seal fracture opening is inferred based on the banded structure of quartz cement bridges consisting of up to 700 cement bands averaging 5 m in thickness as observed with scanning electron microscope cathodoluminescence crack seal layers contain assemblages of aqueous two phase fluid inclusions based on fluid inclusion microthermometry and raman microprobe analyses we determined that these inclusions contain methane saturated brine trapped over temperatures ranging from 130 c to 154 c using textural crosscutting relations of quartz growth increments to infer the sequence of cement growth we reconstructed the fluid temperature and pore fluid pressure evolution during fracture opening in combination with published burial evolution models this reconstruction indicates that fracture opening started at ca 48 ma and above hydrostatic pore fluid pressure conditions and continued under steadily declining pore fluid pressure during partial exhumation until present times individual fractures opened over an 48 m y time span at rates of 16 23 m m y these rates suggest that fractures can remain hydraulically active over geologically long times in deep basinal settings

hydrocarbon accumulation model for neogene traps in the chengdao area bohai bay basin china abstract chengdao is an offshore area in the bohai bay basin that contains approximately 25 7 10 8 bbl of oil and gas reserves within the sandstone reservoirs in neogene strata however previous predictions of hydrocarbon accumulation in neogene traps are inaccurate resulting in a current failure rate of 50 when drilling for hydrocarbons in this area to build an improved exploration model for neogene traps we select 92 traps from neogene strata in the chengdao area to quantify the filling degree which is an indicator of hydrocarbon accumulation efficiency the quantified filling degree is based on actual geological and exploration data and differs significantly among various trap types the filling degree of traps also varies significantly with their structural locations and decreases generally from the northwest to the southeast along the chengbei fault zone vertically the filling degree is highly heterogeneous initially increasing from the bottom to the middle of neogene strata and then decreasing towards the top of the strata these neogene hydrocarbon reservoirs are sourced from the paleogene and as they lay vertically away from the source rocks their hydrocarbon enrichment is constrained largely by hydrocarbon migration distance and vertical migration pathways the sealing capacity of faults and cap rocks sandbody orientation and reservoir sedimentary facies determine the maximum column height which in turn affects the amount of hydrocarbon accumulation within these traps a scatter plot analysis of individual controls and volumetric filling for each trap type is compiled using multivariate linear regression analysis to quantify controls and the dominant control of hydrocarbon accumulation is determined

flexural isostasy and uplift of the sierra nevada of california the sierra nevada of california has experienced several kilometers of uplift in the last 10 m y but its present elevation is isostatically compensated by a crustal root that has probably existed since late cretaceous flexural isostasy can reconcile these observations basin and range faulting and extension starting 10 m y ago allowed rapid uplift of an eroded and regionally compensated magmatic arc underlain by an excess crustal root a quantitative model of an unbroken elastic plate buoyed up by the excess root provides an explanation for the estimated 10 m y paleotopography of the range the same model fits the present topography when broken shear and fiber stresses not transmitted at the location of the owens valley fault zone the broken plate model predicts the appropriate amount of westward tilt of the sierra nevada and can explain the pronounced eastward tilt of the white and inyo mountains the position where paleo and present drainages in the sierra cross over in elevation is the most sensitive indicator of the elastic thickness required of the lithosphere an effective elastic thickness of 50 km best fits the observed crossover distances and is consistent with the amount of post 10 m y uplift calculated fiber and shear stresses suggest that actual extension of the crust is more important in permitting the uplift than the mere presence of normal faults part of the residual isostatic gravity anomaly pattern high gravity over the eastern great valley and western sierra nevada low residual gravity over the high sierra may be explained by the continuing flexural support of departure from local isostatic equilibrium the model implies that before 10 m y ago the sierra should have been marked by a negative isostatic gravity anomaly of more than 100 m gal flanked by isostatic gravity highs such large isostatic anomalies have not been observed to date over eroded arcs but the sierra has uniquely low heat flow and presumably therefore high lithospheric strength and the sierran root is at the upper limit of size that could be isostatically suppressed

key factors controlling hydrocarbon accumulations in ordovician carbonate reservoirs in the tazhong area tarim basin western china abstract the tazhong area at the center of the tarim basin western china contains abundant hydrocarbon resources principally in ordovician carbonate reservoirs the geological conditions for hydrocarbon accumulation in the area are quite complicated and are characterized by multiple stages of hydrocarbon generation accumulation adjustment and alteration despite decades of exploration and production in the region the mechanisms of hydrocarbon accumulation and their controlling factors are still not well established the geological setting and the distribution characteristics of the reservoir have been used to investigate the mechanisms of accumulation to quantitatively describe the main controlling factors and to predict potential favorable hydrocarbon accumulation zones in ordovician carbonate rocks of tazhong our results show that the hydrocarbons in the ordovician reservoirs came from mixed sources including middle lower cambrian and middle upper ordovician source rocks within the majiaer sag four stages of accumulation are recognized and hydrocarbons migrated into the tazhong area along six intersections of ne and nw fault sets principally from the northeast to the southwest but then locally from the northwest to the southeast the ordovician carbonate reservoirs are typically lithologically defined and the dynamic force of hydrocarbon accumulation is primarily reflects differential capillary forces the accumulation and distribution of hydrocarbons was controlled by the petrophysical properties of the reservoir and by hydrocarbon supply charge energy the petrophysical properties of the reservoir controlled the hydrocarbon accumulation threshold with the maximum differential capillary pressure force on average approximately 13 mpa the supply or charge energy of the hydrocarbons controls the accumulation distribution range the daily production of individual wells decreases with increasing distance from the fault intersections and the maximum hydrocarbon migration distance is about 35 km reservoir properties and the hydrocarbon supply charge energy coupling index rei appear to control hydrocarbon accumulation and distribution accumulation does not occur when the value of rei is 0 6 but is favored when values are higher

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

geochemical and sedimentological responses of arctic glacial lake ilirney chukotka far east russia to palaeoenvironmental change since 51 8 ka bp abstract palaeoenvironmental reconstructions with temporal coverages extending beyond marine isotope stage mis three are scarce within the data sparse region of chukotka far east russia the objective of this paper is to infer palaeoenvironmental variability from a 10 76 m long osl and 14c dated sediment core from lake ilirney chukotka 67 21 n 168 19 e we analysed high resolution sediment geochemistry xrf sedimentology tc tn toc grain size mineralogy xrd and preliminary micropalaeontological data diatoms and pollen from the core as well as acoustic sub bottom profiling data from the lake basin our results affirm the application of xrf based sediment geochemical proxies as effective tracers of palaeoenvironmental variability within arctic lake systems our study reveals that a lake formed during mis3 from 51 8 4 1 ka bp following extensive mis4 glaciation catchment palaeoenvironmental conditions during this time remained harsh associated with the continued presence of a catchment glacier until 36 2 2 6 ka bp partial amelioration reflected by increased diatom catchment vegetation and lake organic productivity and clastic sediment input from mixed sources from 36 2 2 6 ka bp resulted in a lake high stand 15 m above present and is interpreted as evidence of a more productive palaeoenvironment coincident with the mis3 interstadial optimum a transitional period of deteriorating palaeoenvironmental conditions occurred 30 27 9 ka bp and was superseded by periglacial glacial conditions from 27 9 0 8 ka bp during the last glacial maximum deglaciation as marked by sediment geochemical proxies commenced at 20 2 0 8 ka bp our findings are compared with lacustrine yedoma and river bluff records from across beringia and potentially yield limited support for a marked younger dryas cooling in the study area

natural hydraulic fracturing of tight gas sandstone reservoirs piceance basin colorado natural fractures form preferred pathways for basinal fluid flow and associated heat and mass transport in gas sandstone reservoirs with low matrix permeability fractures provide flow pathways between organic rich source and reservoir layers during gas charge and between matrix pores hydraulic fractures and the well bore during production while the formation of natural fractures has previously been associated with gas generation and pore fluid pressure increase through a process referred to as natural hydraulic fracturing other driving mechanisms such as stress changes by tectonic or exhumation processes remained viable alternatives to test whether these mechanisms contributed to fracture development we investigated the spatial and temporal distribution of fracture formation and its relationship to gas generation migration and charge in sandstone of the cretaceous mesaverde group across the entire production interval on a basinwide scale using fluid inclusion microthermometry of crack seal fracture cement formed concurrently with fracture opening we observed temperature trends that when compared with temperature evolution models of the formation date fracture formation between 41 and 6 ma in the northern and between 39 and 6 ma in the southern piceance basin the onset of fracture formation 20 30 m y prior to maximum burial eliminates changes in stress state associated with exhumation as a mechanism for triggering the onset of fracture formation instead calculated paleo pore fluid pressures of 40 90 mpa 5800 13 000 psi during fracture opening and the presence of methane rich inclusions in fracture cement suggest that fracture formation was aided by high pore fluid pressures during gas generation in organic rich shales and coals and associated charging of adjacent and interlayered sandstone reservoirs a 10 20 m y age progression in the onset of fracture formation from deeper to shallower horizons of the mesaverde group is consistent with gas generation and onset of fracture formation activated by burial temperature with limited upward migration of gas at this stage of reservoir evolution this age progression with depth is inconsistent with fracture formation triggered by changes in stress conditions associated with tectonic or structural processes expected to affect the entire formation synchronously our observations are thus most consistent with fracture formation by natural hydraulic fracturing in response to gas generation in interbedded source layers and reservoir charge based on widespread observations of fractures with similar structural and diagenetic attributes we consider natural hydraulic fracture formation in response to thermocatalytic gas generation to be a fundamental mode of brittle failure in otherwise structurally quiescent basins

modelling the effect of physical and chemical characteristics of shallow aquifers on water and nitrate transport in small agricultural catchments the aim of this study is threefold 1 to evaluate the effect of the physical properties of weathered granitic material geometry and spatial distribution of hydraulic conductivity on water fluxes at the outlets of two small and nearby agricultural catchments kerbemez and kerrien 0 12 and 0 095 km 2 underlain by granite bedrock 2 to explain the variations of nitrate concentration in streamwater in relation to the spatial distribution of dissolved nitrate in the groundwater 3 to investigate the origin of the groundwater nitrate by analysing the reaction times of groundwater to variations of nitrate concentration in water recharge these objectives were attained by developing a flow and nitrate transport model for the two catchments from geophysical measurements on the geometry and hydraulic conductivity of the weathered granite layer and using data collected from soil surveys the models were calibrated and validated from spatial and temporal observations of hydraulic heads and nitrate concentrations in groundwater and stream water the flow models appeared to be less sensitive to the geometry of the weathered granite layer than the spatial distribution of hydraulic conductivity model results show that seasonal patterns of nitrate concentrations in streamwater result partly from the spatial distribution of nitrate concentration in the groundwater the horizontal distribution of nitrate concentrations in groundwater derives from denitrification in the downslope domain an analysis of the groundwater reaction times for both catchments shows that following a variation in the recharge nitrate concentration the time to reach equilibrium in the whole groundwater body is more than 14 years in the kerbemez catchment the vertical distribution observed in groundwater nitrate concentrations appears to be caused by a temporal decrease of the nitrate concentration in the water recharge over the last 15 years

new 40ar 39ar ages of cretaceous continental volcanics from central chukotka implications for initiation and duration of volcanism within the northern part of the okhotsk chukotka volcanic belt northeastern eurasia abstract we used the single crystal sanidine laser fusion 40ar 39ar method to date five samples of volcanic rocks from the northern chukotka part of the cretaceous okhotsk chukotka volcanic belt northeastern eurasia ages of four samples from lowermost stratigraphic units range from 87 94 to 87 08 ma and one sample from the top of the section shows the age of 87 55 ma new results combined with previously published 40ar 39ar data indicate that volcanism within the northern part of the belt started in coniacian time at ca 88 ma and was very short lived ca 1 6 m yr

testing the basin centered gas accumulation model using fluid inclusion observations southern piceance basin colorado the upper cretaceous mesaverde group in the piceance basin colorado is considered a continuous basin centered gas accumulation in which gas charge of the low permeability sandstone occurs under high pore fluid pressure in response to gas generation high gas pressure favors formation of pervasive systems of opening mode fractures this view contrasts with thatofothermodelsoflow permeabilitygasreservoirsinwhich gas migrates by buoyant drive and accumulates in conventional traps with fractures an incidental attribute of these reservoirs we tested the aspects of the basin centered gas accumulation model as it applies to the piceance basin by determining the timing of fracturegrowth and associated temperature pressure and fluid composition conditions using microthermometry and raman microspectrometry of fluid inclusions trapped in fracture cement that formed during fracture growth trapping temperatures of methane saturated aqueous fluid inclusions record systematic temperature trends that increase from approximately 140 to 185 c and then decrease to approximately 158 c over time which indicates fracture growth during maximum burial conditions calculated pore fluid pressures for methanerich aqueous inclusions of 55 to 110 mpa 7977 15 954 psi indicate fracture growth under near lithostatic pressure conditions consistent with fracture growth during active gas maturation and charge lack of systematic pore fluid pressure trends

contrasting tectonic and sedimentary history of the central and eastern parts of the polish carpathian foredeep basin results of seismic data interpretation polish carpathian foredeep basin pcfb is located at the junction between western and eastern european platforms such location caused different evolution of various parts of this basin in the central part of the pcfb growth fault propagation folds related to latest badenian stages of thrusting in this segment of the carpathians developed only minor normal faulting related to miocene reactivation of older basement faults was detected paleovalleys mapped within the mesozoic basement were interpreted as palaeogene tectonically controlled erosional features developed after inversion of the polish trough in the central pcfb post evaporitic sediments were supplied into the foredeep basin from south from the eroded carpathians in the eastern part of the pcfb a system of large normal faults related to miocene flexure induced reactivation of inherited mesozoic faults was identified within the hangingwall of this system reverse faults rotated blocks and basement pop up structures were described their formation was related to combined effect of compressional stresses transferred from the carpathian collision zone and reactivation of older large scale fault caused by both flexural extension and strike slip movements during deposition of the miocene foredeep sediments differential compaction also played an important role gentle onlap of the middle badenian evaporites by post evaporitic sediments towards the nw was interpreted as a result of tectonically driven relative sea level rise and re establishment of marine connections with eastern paratethys

structural characterization of the fracture systems in the porcelanites comparing data from the monterey formation in california usa and the sap bon formation in central thailand abstract the fractures in the porcelanites from the monterey formation in california usa and the sap bon formation in central thailand were documented for a comparative study of their modes distribution and their relationship to other structures such as folds and bedding planes both formations consist in thinly bedded stiff units that are prone to folding flexural slip and cross bedding brittle fracturing under compression there are two assemblages in the porcelanites the first assemblage includes commonly vertical high angle opening mode fractures left lateral strike slip faults normal faults and thrust faults the second one is sub horizontal fractures which are associated with folds bedding slip and thrusts faults in both monterey and sap bon formations the structural architectures of these rocks and the associated groups of structures are remarkably similar in terms of both opening and shearing modes and their relationships with the bedding due to their depositional architecture and the compressional tectonic regimes in spite of the fact that the two locations are more than ten thousand kilometers apart and have very different ages of deformation

an integrated geophysical investigation of the hydrogeology of an anisotropic unconfined aquifer abstract the predictive capability of groundwater flow models is frequently restricted by insufficient characterisation of a typically heterogeneous and anisotropic subsurface trace levels of volatile organic compounds have been detected at municipal water supply wells in gray maine groundwater flow modelling based on available hydrogeologic data defines a dominant w e transport vector that is inconsistent with the apparent n40e transport of a plume emanating from a road salt storage facility as mapped with a terrain conductivity instrument a local scale geophysical study at an undisturbed site in the glacial marine delta deposit aquifer was conducted to investigate the possible influence of anisotropy on flow through these unconsolidated sediments ground penetrating radar and terrain conductivity measurements reveal evidence for structural features that are likely to promote preferential transport paths orientated in a general ne sw direction two conductive tracers one deep and one surficial were injected and monitored for direct evaluation of the groundwater flow vector using resistivity and self potential methods although interpretation was limited by an incomplete resistivity dataset the results and modelling of both methods supports a general n30e n40e flow vector furthermore consistent flow velocity estimates 0 15 m day are obtained from the two methods analysis of this integrated dataset suggests that anisotropy exerts a significant control on flow in this unconsolidated aquifer predictions of sources of groundwater contamination at municipal wells based on flow models not accounting for this anisotropy will likely be in error this study illustrates the potential value of an integrated geophysical study which will aid the development of accurate flow models for unconsolidated aquifers

a coupled fluid inclusion and stable isotope record of paleofluids in the monterey formation california determining the history of fossil hydrologic systems that is recorded in vein minerals can be complicated by heterogeneity in the oxygen and carbon isotope compositions at millimeter and smaller scales several samples of diagenetic dolomite from two location in the miocene monterey formation california have 18o and 13c values that vary over a few millimeters by 28 and 6 5 respectively relative to the pee dee belemnite isotope standard these variations reflect episodic flow and mixing of waters from different sources with distinct diagenetic histories on the other hand isotopic conpositions of dolomite in samples with gradual shifts in isotopic compositions and correlated 18o and 13c values may have been controlled by mass diffusion and thermal conduction between episodic flow events primary fluid inclusion assemblages from samples collected at one location yielded homogenization temperatures of 87 8 3 6 c 2 these temperatures were combined with measured 18o values very nearly collocated in each dolomite sample to show that 18owater values ranged between 0 8 and 2 5 relative to standard mean ocean water the samples from this monterey formation dolomite thus indicate their precipitation from water more enriched in 18o than late miocene and younger seawater and must reflect modification of the 18o values of the involved waters by mineral dehydration reactions prior to dolomite precipitation samples from the other location contain no primary fluid inclusion assemblages and few abrupt shifts in isotopic compositions perhaps reflecting recrystallization small scale variations in isotopic compositions of vein minerals could be interpreted as the result of a changing regional hydrologic pattern but we think such an interpretation for the monterey formation samples would be incorrect instead we infer that these variations provide important information about localized effects on the ancient hydrologic system and that these effects bear on the origins of the paleofluids responsible for the mineral precipitation

seismic characteristics and identification of negative flower structures positive flower structures and positive structural inversion negative and positive flower structures and positive inverted structures imply specific modes of formation and their distinctive characteristics make them important criteria for the identification of certain structural styles a negative flower structure from the andaman sea consists of a shallow synform bounded by upward spreading strands of a wrench fault that have mostly normal separations paralleling monoclines and oblique en echelon normal faults flank the divergent wrench fault a positive flower structure from the ardmore basin oklahoma consists of a shallow antiform displaced by the upward diverging strands of a wrench fault that have mostly reverse separations en echelon folds are present on either side of this convergent wrench fault flower structures may resemble extensional or contractional fault blocks on individual seismic profiles flower structures are identified by their unique internal fault and fold architecture by their association with a straight and throughgoing zone of deformation and by their lack of a consistent sense of separation or regional upthrown side positive structural inversion at the rambutan oil field south sumatra basin has formed a shallow anticlinorium and has partly uplifted the underlying graben deeper fault segments bounding the graben have retained their normal fault profiles but at shallow levels some of these faults have reverse separations similar changes of separation with depth may be produced by strike slip but sets of faults with listric profiles and nearby blocklike trend patterns identify the inversion as a dip slip event where correlation of reflections is uncertain or deep control is unobtainable positive inverted structures may also resemble contrational fault blocks detached normal fault assemblages and certain negative inverted structures

role of a ductile decollement in the development of pull apart basins experimental results and natural examples abstract traditional models describe pull apart basins as graben or half graben basins with normal or normal oblique slip master faults analogous to death valley california yet many pull aparts are characterized by asymmetric basins with strike slip master faults indicating that not all pull apart basins conform to the simple death valley models we present analogue modelling results that show developmental sequences and structural styles of pull aparts are dramatically different when overburden rides over a ductile horizon and that thickness of the ductile horizon exerts control on basin development in our models synthetic and antithetic strike slip faults control basin geometries while localized normal faulting and local oblique slip on strike slip faults accommodate basin subsidence faults evolve from initial strike slip to normal oblique and normal dip slip to form a system of either isolated sub basins in the case of thick ductile layers or coalescing sub basins in the case of thin ductile layers these results demonstrate distinct differences between non ductile and ductile decollement pull apart structures basin boundaries dominated by normal faults suggest a decollement within or at the base of a non ductile layer similar to death valley california basin bounding faults dominated by strike slip and oblique slip faults indicate basin formation over a ductile layer similar to the gulf of elat aqaba or gulf of paria venezuela and trinidad

structural evolution of horst and half graben structures proximal to a transtensional fault system determined using 3d seismic data from the shipwreck trough offshore otway basin australia abstract using a three dimensional 3d seismic reflection dataset from the shipwreck trough offshore otway basin southern australia we aim to characterise and understand the structural evolution of the shipwreck fault zone sfz and associated extensional structures the sfz is a key structural element of the otway basin which is a nw striking upper jurassic cenozoic rift to passive margin basin that formed due to the breakup of australia and antarctica the sfz marks the transition from the major southern margin rift system to the west and the oceanic continental transform margin to the se the sfz formed and bounds the shipwreck trough on the eastern side and is interpreted as a n s striking transtensional fault zone representing the northern en echelon extension of the transform margin to the south the shipwreck trough is the downward thrown western side of the sfz and is host to an array of horst and half graben structures two of which contain the producing geographe and thylacine gas fields the shipwreck trough and sfz are imaged by the investigator 3d seismic dataset which has previously been studied to conduct 2d restorations and interpret the timing magnitude orientation and nature of the structural events of the shipwreck trough our study adds to this previous research by using spectral decomposition and coherence volumes to further characterise the sfz and associated igneous features basement structural elements and late cretaceous horst and half graben structures we have identified examples of releasing bend releasing jog and restraining jog structures along the sfz that are indicative of sinistral transtensional deformation and have highlighted areas of increased basement fault block relief which have driven extensional faulting in the cover we have also conducted throw distance and throw depth analysis on four horst and half graben structures and shown that the associated normal faults have had continuous late cretaceous growth with the structures being formed through incidental linkage of normal fault segments finally our two way time twt and isochronal mapping of the entire 3d survey shows the development of the late cretaceous rifting event in the shipwreck trough and highlights numerous other structural closures similar to and with close vicinity of the thylacine and geographe gas fields providing implications for prospectivity

fault growth mechanisms and scaling properties in foreland basin system the case study of monte alpi southern apennines italy abstract the present work focuses on the comprehension of the growth mechanisms and dimensional properties of the pre pliocene monte alpi fault network by mean of integrated field and laboratory analyses after this multidisciplinary approach detailed throw profiles are computed for each fault belonging to the monte alpi network subsequently the dimensional properties of the individual faults are calculated data obtained from this work are discussed in terms of fault growth mechanisms and timing of deformation and reported in a conceptual tectonic evolution model of the messinian foreland basin system data suggest that originally isolated fault segments developed during the earliest stages of foreland basin formation by re activation of a pre existing early cretaceous fault set and formation of an orthogonal one these two fault sets formed a scale independent network differently the same fault sets were also active during its subsequent development forming a scale dependent fault network characterized by t and y shaped fault intersections this deformation controlled the half graben depocenters evolution filled by up to ca 600 meters of terrigenous deposits during the late messinian time

geothermometry and geobarometry of overpressured lower paleozoic gas shales in the jiaoshiba field central china insight from fluid inclusions in fracture cements the wufeng longmaxi organic rich shales host the largest shale gas fields of china this study examines sealed fractures within core samples of the wufeng longmaxi shales in the jiaoshiba shale gas field in order to understand the development of overpressures in terms of magnitude timing and burial in wufeng longmaxi shales and thus the causes of present day overpressure in these paleozoic shale formations as well as in all gas shales quartz and calcite fracture cements from the wufeng longmaxi shale intervals in four wells at depth intervals between 2253 89 m and 3046 60 m were investigated and the fluid composition temperature and pressure during natural fracture cementation determined using an integrated approach consisting of petrography raman spectroscopy and microthermometry many crystals in fracture cements were found to contain methane inclusions only and aqueous two phase inclusions were consistently observed alongside methane inclusions in all cement samples indicating that fluid inclusions trapped during fracture cementation are saturated with a methane hydrocarbon fluid homogenization temperatures of methane saturated aqueous inclusions provide trends in trapping temperatures that th values concentrate in the range of 198 5 c 229 9 c 196 2 c 221 7 c for quartz and calcite respectively pore fluid pressures of 91 8 139 4 mpa for methane inclusions calculated using the raman shift of c h symmetric stretching v1 band of methane and equations of state for supercritical methane indicate fluid inclusions trapped at near lithostatic pressures high trapping temperature and overpressure conditions in fluid inclusions represent a state of temperature and overpressure of wufeng longmaxi shales at maximum burial and the early stage of the yanshanian uplift which can provide a key evidence for understanding the formation and evolution of overpressure our results demonstrate that the main cause of present day overpressure in shale gas deposits is actually the preservation of moderate high overpressure developed as a result of gas generation at maximum burial depths

an overview of the petroleum system of maracaibo basin the geologically complex maracaibo basin in northwestern venezuela is one of the most prolific hydrocarbon basins in the world having a basinal area of 50 000 km2 19 300 mi2 the basin has produced more than 30 billion bbl of oil with estimated recoverable oil reserves of more than 44 billion bbl the central elements of the petroleum system of the basin include 1 a world class source rock upper cretaceous la luna formation deposited on a shelf to slope environment under anoxic conditions and modified by intermittent oxygenated periods and tectonic events 2 high quality clastic reservoir rocks deposited in eocene and miocene fluviodeltaic settings 3 two main periods of rapid tectonic subsidence responsible for two pulses of voluminous hydrocarbon generation first during paleogene caribbean south american oblique plate collision and second during the neogene uplift of the sierra de perij mrida andes and 4 lateral and vertical migration of oil along strike slip normal and inverted faults as well as a regional unconformity of late eocene oligocene age the maturation migration and trapping of hydrocarbons were closely controlled by the tectonic evolution of the maracaibo basin during the paleogene the development of a foredeep along the northeastern margin of the basin and the strike slip reactivation of the rift related jurassic faults on the maracaibo platform controlled the early structural setting of the source and reservoir rocks hydrocarbons migrated updip from source rocks beneath the north northeastern margin of the basin along north south strike slip faults and into overlying eocene clastic reservoirs in the south central parts of the basin the second period of the maracaibo basin petroleum system developed during subaerial exposure of most of the maracaibo basin during oligocene miocene uplift of the adjacent sierra de perij and mrida andes uplift of mountain ranges surrounding the basin folded and depressed the interior of the basin to form the extensive maracaibo syncline because of the formation of the maracaibo syncline oil generation began in the central and southern parts of the synclinal basin and migrated northward hydrocarbons migrated up the flanks of the maracaibo syncline along reactivated strike slip faults and into miocene rocks adjacent to the uplifted mountain ranges escaping oil has formed numerous surface seeps along the edges of the maracaibo basin

mechanisms and controls on the formation of sand intrusions sandstone intrusions are found in all sedimentary environments but have been reported most commonly from deep water settings they also appear to be more frequently developed in tectonically active settings where applied tectonic stresses facilitate development of high fluid pressures within the sediments a variety of mechanisms have been cited as triggers for clastic intrusions these include seismicity induced liquefaction application of tectonic stresses excess pore fluid pressures generated by deposition related processes and the influx of an overpressured fluid from deeper within the basin into a shallow sand body the formation of sandstone dykes and sills is investigated here by considering them as natural hydraulic fractures when the seal on an unconsolidated overpressured sand body fails the resulting steep hydraulic gradient may cause the sand to fluidize the fluidized slurry can then inject along pre existing or new fractures to form clastic intrusions the scale and the geometry of an intrusive complex is governed by the stress state depth and pre existing joints or faults within the sedimentary succession as well as the nature of the host sediments for the simplest tectonic setting where the maximum stress in a basin is vertical gravitational loading small irregular intrusions commonly result in the formation of sills at shallow depths within a few metres of the surface whereas at greater depth dykes and sills forming clastic intrusion networks are more typical a simple relationship is derived to calculate the maximum burial depth at which a dyke sill complex forms as a function of the source bed to sill height the bulk density of the surrounding sediments and the ratio of the vertical to horizontal effective stresses k 0 when applied to three examples of large scale dyke sill complexes developed within paleocene and eocene deep water reservoir sand bodies of the north sea maximum burial depths in a range of 375 to c 500 m 450 700 m and 550 850 m are estimated for intrusion of each of the three complexes

structural interpretation of hydrocarbon traps sealed by basement normal block faults at stable flank of foredeep basins and at rift basins closures sealed by basement normal block faults are most commonly formed by a grid of faults with multiple orientations and by a favorable dip of the reservoir strata hydrocarbons are trapped updip by structural upturns along the edge of the downdropped blocks or at the upthrown or downthrown edge of blocks where block tilt is away from the sealing faults closure parallel with reservoir strike is provided by 1 updip junction of primary oblique or oblique and longitudinal block bounding faults 2 internal secondary faults that trend transverse or oblique to the block boundaries 3 positive bend of reservoir strata 4 plunge of block edge folds and or 5 stratigraphic terminations of the reservoir fault seal upward along the faults is most likely where a thick section of impervious strata above the reservoir is in contact with itself across the fault or where the fault does not extend upward into shallower permeable zones seal across the fault surface is most certain where impermeable rocks are laterally juxtaposed against the reservoir impervious material within the fault zone such as shaly smear gouge cataclastic gouge mineral deposits and asphalt or tar impregnations can be effective barriers where reservoir facies are juxtaposed across the fault the traps can form a major hydrocarbon play on the stable shelves of foredeep or foreland basins as demonstrated by the san joaquin valley and eastern venezuela basins the traps provide secondary prospects in rift basins uch as the viking graben and vienna basin

fracturing and fluid flow in a sub decollement sandstone or a leak in the basement crack seal texture within fracture cements in the triassic el alamar formation ne mexico shows that the fractures opened during precipitation of quartz cements later overlapping calcite cements further occluded pore space previous workers defined four systematic fracture sets a oldest to d youngest with relative timing constrained by crosscutting relationships quartz fluid inclusion homogenization temperatures are higher within set b 148 20 c than in set c 105 12 c these data and previous burial history modelling are consistent with set c forming during exhumation fluid inclusions in set c quartz have higher salinity than those in set b 22 9 v 14 2 wt nacl equivalent respectively and set c quartz cement is more enriched in 18 o 20 2 v 18 7 vsmow under most assumptions about the true temperature during fracture opening the burial duration the amount of cement precipitated and fluid flow patterns it appears that the fracture fluid became depleted in 18 o and enriched in 13 c this isotopic evolution combined with increasing salinity suggests that throughout fracture opening there was a gravity driven influx of fluid from upsection jurassic evaporites which form a regional decollement fracture opening amid downward fluid motion suggests that fracturing was driven by external stresses such as tectonic stretching or unloading rather than increases in fluid pressure

soil resistivity a non invasive tool to map soil structure horizonation abstract since geophysical methods are non invasive they can be of great help in soil studies because they disturb neither the structure nor the dynamics of the soil moreover data are acquired with reliable spatial sampling the usual ways of investigation like augering and excavation disturb the soil and are totally incompatible with a spatially dense sampling strategy which would destroy the object of the study both approaches are complementary when excavations have a limited extent and are distributed according to the information conveyed by the geophysical investigation a basic principle of applied geophysics is to measure different physical parameters without direct access to the studied volume horizontal and or vertical variations of the parameter s can be recorded possible soil parameters should be restricted to measurements which do not alter the medium reversible effect to be significant the variations of the parameter s should exhibit a wide dynamic range over different soil types and should be correlated in some way to soil parameters such as particle size or hydraulic conductivity after summarising the soil properties two examples are shown whereby electrical resistivity was used the first example is a specific soil so called hardpan sandy soil in arid area in lagadge north cameroon using resistivity surveys the three dimensional extension of a very coherent horizon was mapped this horizon is delineated by low resistivities 10 ms m because of the disposition of clay particles around the quartz grains in a second example a homogeneous area ought to be found delimit the extent of a surface where a pesticide transfer experiment is to take place accurate mapping of soil horizons was not feasible by augering resistivity data have clearly shown the three dimensional extension of clayey horizons in the complex delta context

carbonate cements indicate channeled fluid flow along a zone of vertical faults at the deformation front of the cascadia accretionary wedge northwest u s coast to understand the relation between fluid seeps and structures sedimentary rocks were collected with the dsrv alvin from a vertical fault zone that transects the deformation front of the cascadia accretionary wedge the rocks contained diagenetic carbonate cement that was precipitated from fluids expelled during accretion carbon oxygen and strontium isotope data are consistent with a fluid source at 2 km depth most carbon isotopes range from 1 to 25 pdb peedee belemnitel standard consistent with a thermogenic methane source oxygen isotopes show extreme 18 o depletions 4 to 13 pdb that are consistent with precipitation from fluids with temperatures as high as 100 c 87 sr 86 sr values of 0 70975 to 0 71279 may be due to strontium in fluids derived from clay rich parts of the stratigraphic section the ubiquity of carbonate precipitates and the isotope data indicate that the vertical fault zone is an efficient conduit for fluid dewatering from deep levels of the accretionary wedge

evaluation of geological factors in characterizing fault connectivity during hydrocarbon migration application to the bohai bay basin faults play an intricate role in hydrocarbon migration and accumulation since they can serve either as a conduit or a seal quantitative evaluation of fault opening sealing properties requires the selection of valid and optimal parameters among numerous geological factors to characterize the hydraulic behaviors of faults the present study focuses on the chengbei step fault area in the qikou depression bohai bay basin ne china because hydrocarbon migration and accumulation in this area occurred in a relatively short period so that accumulated hydrocarbons can be used as an indicator to deduce hydraulic connectivity of a fault zone between two sites various geological parameters pertinent to a fault such as burial depth dip angle throw strike percentage of sandstone of faulted intervals fluid pressure in faulted mudstone stress normal to the fault plane and shale gouge ratio are analyzed to assess their effectiveness in characterizing fault connectivity an index the fault connectivity probability np is proposed to evaluate the possibility that a fault has been once serving as a migration pathway the statistical relationship between np and any a geological parameter may be used to indicate the effectiveness of this parameter in characterizing the connectivity of a fault during hydrocarbon migration the correlation coefficient of a relationship is a good indicator of the effectiveness and the results are generally in agreement with qualitative assessments parameters representing a single geological factor are generally ineffective whereas those representing implicitly or explicitly two or more factors such as shale gouge ratio stress normal to the fault plane and fault opening index are more effective

kilometer scale chemical reaction boundary patterns and deformation in sedimentary rocks abstract we use three dimensional 3d seismic data to image patterns developed by kilometer scale chemical reaction boundaries to demonstrate that chemical patterns are scaleable phenomena the patterns develop in biosiliceous marine successions due to the dissolution of opal a biogenic silica and reprecipitation as opal ct crystobalite and tridymite during burial the reaction boundary patterns comprise roughly circular regions where the reaction boundary has preferentially advanced these regions are up to 2 7 km wide and c 50 200 m in height and are termed cells the cells form by amalgamation with adjacent juvenile cells they also form by the incorporation of much smaller regions surrounding the cells where the chemical change has already occurred that we term satellites 50 m wide the reaction results in enhanced rates of sediment compaction hence differential advancement of reaction boundaries causes differential subsidence of the overburden inducing folding and faulting of the overburden above the cellular promontories we propose three potential mechanisms for the development of kilometer scale reaction boundary patterns a mass transport of silica by advection b perturbation of isotherms as a result of convective or conductive heat transport or c establishment of a positive feedback loop between fluid production due to the reaction hydraulic fracturing and the upward and lateral transport of fluids this study provides the first insights into how strongly patterned diagenetic reaction boundaries evolve at a basin scale an initial conceptualization of the potential range of reaction boundary morphologies that could exist in this diagenetic system and the likely mechanisms that could control them furthermore it demonstrates that the discipline of seismic diagenesis could represent a completely new approach for the study of chemical diagenetic processes in sedimentary rocks

lithostratigraphy of the impactite and bedrock section of icdp drill core d1c from the el gygytgyn impact crater russia in 2008 2009 the international continental scientific drilling program icdp obtained drill cores from the el gygytgyn impact structure located on the chukotka peninsula russia these cores provide the most complete geological section ever obtained from an impact structure in siliceous volcanic rock the lithostratigraphy comprises a thick sequence of lacustrine sediments overlying impact breccias and deformed target rock the interval from 316 m below lake floor blf to the end of the core at 517 m depth can be subdivided into four lithological sequences at 316 m depth the first mesoscopic clasts of shocked target rock occur in lacustrine sediments the growing abundance of target rock clasts with increasing depth and corresponding decrease of lacustrine sediment components indicate the extent of this transition zone to 328 m depth it constitutes a zone of mixed reworked impact breccia and lacustrine sediments volcanic clasts in this reworked suevite section show all stages of shock metamorphism up to melting the underlying unit 328 390 m depth represents a suevite package a polymict impact breccia with considerable evidence of shock deformation in a wide variety of volcanic clasts this includes fragments with quartz that exhibit planar fractures and planar deformation features pdf in addition at three depths several centimeter sized clasts with shatter cones were detected due to microanalytical identification of relatively rare microscopic impact melt particles in the matrix of this breccia this material can be confidently labeled a suevite also in this sequence three unshocked 1 m thick intersections of volcanic blocks occur at 333 83 351 52 and 383 00 m depths the upper bedrock unit begins at 390 74 m depth has a thickness of 30 15 m and represents a sequence of different volcanic rocks an upper part with basaltic composition from 390 74 to 391 79 m depth overlying a lower rhyodacitic part from 391 79 to 420 27 m depth this parautochthonous basement unit is only very weakly affected by the impact only one shocked quartz grain with two sets of pdf was recorded at 391 33 m depth the lower bedrock unit 420 89 517 09 m depth end of core is a brittly deformed rather homogeneous welded ignimbrite that in part can be considered a cataclasite the top three meters of this section are sheared which could represent pre impact tectonic deformation a 54 cm thick injection of polymict impact breccia occurs at 471 42 471 96 m depth

cockade breccia product of mineralisation along dilational faults cockade breccias are fault fills in which individual clasts are completely surrounded by concentric layers of cement they occur particularly in low temperature near surface hydrothermal veins at least six mechanisms have been proposed for the formation of cockade breccia like textures but only two repeated rotation accretion and partial metasomatic replacement of clast minerals have been supported by detailed evidence a typical example of cockade breccia from the gower peninsula south wales shows clear evidence for the rotation accretion mechanism in particular overgrown breakage points in cement layers where cockades were previously touching each other and rotated geopetal infills of haematitic sediment based on the available evidence it is proposed that cockade textures result from low rates of cement growth compared to high rates of dilational fault slip seven criteria are given for the correct identification of cockade breccias

mineral precipitation as a mechanism of fault core growth abstract faults vary in structural style from simple planes to complex systems composed of fault cores and damage zones increased fault complexity results from the interaction of mechanical and chemical processes including fracture growth shear and linkage and mineral dissolution and precipitation although water rock interaction is traditionally associated with fault rock weakening and shear localization we investigate processes of fault core widening by water rock interactions that resulted in quartz precipitation we combine field and petrographic observations with prior mechanical characterization to assess the impact of alteration and cementation on fault architecture at the dixie comstock epithermal gold deposit nevada usa mineralized portions of the fault contain strong thick silicified fault cores and wide weak damage zones with evidence for widening of the core through entrainment of damage zone material and repeated cycles of embrittlement dilation and cementation we present a model of fault zone evolution in which the hydrothermal regimes favoring either alteration weakening or precipitation strengthening result in distinct fault zone architecture and mechanical and flow properties of fault systems alteration weakening favors localization of the fault into thinner clay rich low permeability fault cores precipitation strengthening promotes thick strong and low permeability fault cores with mineralization embrittlement enhancing transient permeability following coseismic failure

origin characteristics and distribution of fault related and fracture related dolomitization insights from mississippian carbonates isle of man abstract the southwest davis zinc field sdzf is among the westernmost mvt districts associated with the allegheny ouachita orogeny in the midcontinent u s it consists of a series of small zinc sulfide deposits and associated dolomitization covering an area of 16 km2 6 mi2 adjacent to the arbuckle anticline in southern oklahoma mineralization occurs within the royer dolomite upper cambrian and the butterly dolomite lower ordovician of the arbuckle group and is associated with faults and breccia bodies that parallel the trend of the anticline mining activity in the sdzf was restricted to the early part of the 20th century ore mineralization consists chiefly of sphalerite and subordinate smithsonite with minor galena chalcopyrite and pyrite as well as supergene alterations of these minerals homogenization temperatures th of fluid inclusions in gangue dolomite cement range from 88 to 101 c and have salinities of 6 5 to 20 9 wt nacl equivalent rarer fluid inclusions in sphalerite have an average th value of 105 c and average salinity of 19 2 wt nacl equivalent gangue dolomite cements have 18o values of 6 9 to 9 1 vpdb and 13c values of 0 2 to 1 1 vpdb the 87sr 86sr ratios for these dolomites range from 0 7088 to 0 7105 mineralization likely occurred from a flow system in which basement influenced brines entered the host formations through faults and circulated through the brecciated zones as the ore hydrothermal system waned the relative importance of local brines within the carbonate section increased and resulted in precipitation of late dolomite cements

recognizing the seismic cycle along ancient faults co2 induced fluidization of breccias in the footwall of a sealing low angle normal fault abstract the zuccale low angle normal fault exposed on the island of elba italy is a crustal scale structure which contains a strongly foliated fault core in the immediate footwall of the zuccale fault cohesive fault related breccias which were initially deformed by typical frictional deformation mechanisms experienced fluidization over areas of at least 10 2 10 3 km 2 three internal variants of fluidized breccia are recognized with each related to a separate fluidization event characteristics of the fluidized breccias include 1 a highly irregular intrusive boundary with the overlying fault core 2 no grain scale evidence for typical frictional deformation mechanisms 3 an association with carbonate cements indicating that fluids contained co 2 and 4 a clast preferred orientation suggesting that fluids were moving vertically and spreading laterally as they encountered the foliated fault core our observations suggest that the fluidized breccias are representative of the interseismic period along the zuccale low angle fault and developed across small fault patches during build ups in fluid overpressure attainment of a critical fluid overpressure triggered embrittlement and the formation of low angle slip surfaces and sub vertical tensile veins within the overlying fault core which may account for the presence and the dimensions 10 1 10 3 km 2 of rupture surfaces which produce microseismicity along active low angle normal faults in central italy

distinct element modeling of structures formed in sedimentary overburden by extensional reactivation of basement normal faults fault and fold patterns in sedimentary rocks have been modeled using a computer code based on the distinct element method dem this numerical method considers the relative motion of disconnected elastic elements governed by newton s laws and frictional sliding criteria forces are transmitted between elements at contact points by changing element size ratios assemblages of elements can simulate different kinematic behavior from localized faulting to distributed flow as an application of the method we investigate folding and faulting patterns that develop in the sedimentary overburden above basement normal faults the number position orientation and sense of slip on faults as well as the fold geometry depend on the basement fault dip and basement rotation the dem model results have practical implications for predicting the evolving characteristics of structural traps and their petroleum potential

the 2011 expedition to the el gygytgyn impact structure northeast russia toward a new geological map for the crater area el gygytgyn is a 3 6 ma 18 km diameter impact crater formed in an approximately 88 ma old volcanic target in northeast siberia the structure has been the subject of a recent icdp drilling project in parallel to those efforts a russian german expedition was undertaken in summer 2011 to investigate the permafrost soil lake terraces and the volcanic rocks of the southern and eastern crater rim this provided the unique opportunity for mapping and sampling of the volcanic target rocks around a large part of this complex impact structure samples from 43 outcrops were collected and analyzed petrographically and geochemically the results were combined with earlier mapping outcomes to create a new geological map of this impact structure and its immediate environs at the scale of 1 50 000 compositions of our rock suites are compared with the lithologies of the 2009 icdp drill core the ignimbrite described as lower bedrock in the icdp drill core shows petrographically and chemically strong similarities to the rhyolitic and rhyodacitic ignimbrites observed on surface the suevite sequence exposed in the icdp drill core is a mixture of all observed target rocks at their respective proportions in the area in contrast to previous studies the calculated average target composition of el gygytgyn takes the contribution of the basic target rocks into consideration mafic and intermediate rocks approximately 7 5 and felsic rocks approximately 92 5

origin of low δ18o pre compactional ferroan carbonates in the marine sto formation middle jurassic offshore nw norway siderite delta 18 o pdb 9 3 to 5 7 parts per thousand and fe dolomite ankerite delta 18 o pdb 13 7 to 7 7 parts per thousand occur as texturally early diagenetic pre compactional ce

textural evidence for recent co seismic circulation of fluids in the nojima fault zone awaji island japan abstract the hirabayashi borehole awaji island japan was drilled by the geological survey of japan gsj 1 year after the hyogo ken nanbu kobe earthquake 1995 mjma 7 2 this has enabled scientists to study the complete sequence of deformation across the active nojima fault from undeformed granodiorite to the fault core in the fault core different types of gouge and fractures have been observed and can be interpreted in terms of a complex history of faulting and fluid circulation above the fault core and within the hanging wall compacted cataclasites and gouge are cut by fractures which show high apparent porosity and are filled by 5 50 m euhedral and zoned siderite and ankerite crystals these carbonate filled fractures have been observed within a 5 5 m wide zone above the fault but are especially abundant in the vicinity 1 m of the fault the log normal crystal size distributions of the siderite and ankerite suggest that they originated by decaying rate nucleation accompanied by surface controlled growth in a fluid saturated with respect to these carbonates these carbonate filled fractures are interpreted as the result of co seismic hydraulic fracturing and upward circulation of fluids in the hanging wall of the fault with the fast nucleation of carbonates attributed to a sudden fluid or co2 partial pressure drop due to fracturing the fractures cut almost all visible structures at a thin section scale although in some places the original idiomorphic shape of carbonates is modified by a pressure solution mechanism or the carbonate filled fractures are cut and brecciated by very thin gouge zones these features are attributed to low and high strain rate mechanisms respectively the composition of the present day groundwater is at near equilibrium or slightly oversaturated with respect to the siderite calcite dolomite and rhodochrosite taken together this suggests that these fractures formed very late in the evolution of the fault zone and may be induced by co seismic hydraulic fracturing and circulation of a fluid with a similar composition to the present day groundwater they are therefore potentially related to recent earthquake activity

high chemical weathering rates in first order granitic catchments induced by agricultural stress chemical erosion rates have been determined on two upland granitic catchments under agricultural pressure in brittany france intensive agriculture has been carried out for at least 30 years in this region the influence of geochemical processes related to agriculture on the chemistry of streamwaters is determined through a geochemical mass balance the elemental export fluxes from these two agricultural catchments are then compared with other catchments around the world the volume and concentrations of the precipitation are taken into account as well as the inputs of organic and chemical fertilizers groundwaters and streamwaters to estimate the relative influence on export fluxes and then evaluate the elemental fluxes released by weathering the relatively high si flux of about 1 8 0 9 kmol ha 1 yr 1 is directly attributed to the chemical weathering of soil and rock in the catchment system however the si flux remains comparable to values found in both small and large sized catchments under temperate and tropical conditions on the other hand extremely high fluxes of major cations ca na and mg are observed ranging from 4 2 2 6 to 8 0 4 9 kmol ha 1 yr 1 which can be attributed to chemical weathering these fluxes remain dramatically higher than those found in granitic catchments worldwide despite an integrated agriculture the soil acidification induced by fertilizer application leads mainly to a release of major cations from the system by processes of soil ion exchange leaching as well as weathering of soil and rock

how precisely can the temperature of a fluid event be constrained using fluid inclusions u s national science foundation ear 1624589 chemical sciences geosciences and biosciences division office of basic energy sciences office of science u s department of energy de fg02 03er15430 bureau of economic geology jackson school of geosciences university of texas austin

seasonal and spatial variation in groundwater quality along the hillslope of an agricultural research catchment western france shallow groundwater that develops on hillslopes is the main compartment in headwater catchments for flow and solute transport to rivers although spatial and temporal variations in its chemical composition are reported in the literature there is no coherent description of the way these variations are organized nor is there an accepted conceptual model for the mechanism involved on the basis of the results from an experimental hillslope we propose a description of the variation in spatial and temporal patterns of groundwater chemical composition and discuss the mechanisms involved we instrumented a headwater catchment with a network of 42 nested piezometers along a 200 m hillslope and monitored major anion composition frequently over a 2 year period the results demonstrated that i the anionic composition in water table fluctuation zone varied significantly compared to deeper portions of the aquifer on the hillslope confirming that this layer constitutes a main compartment for the mixing of new recharge water and old groundwater ii deeper parts of the aquifer exhibited seasonal variations with structured hysteretic patterns suggesting that mixing processes also occurred at greater depths and iii these hysteretic patterns were dampered from upslope to downslope indicating an increased influence of lateral flow downslope we recommend that the generality of these observations be assessed in different environments as they can constitute a new set of processes to include in hydrological models copyright 2010 john wiley sons ltd

graben hydrocarbon occurrences and structural style major hydrocarbon occurrences types of traps and structural styles have been synthesized from the sirte basin the suez and viking grabens and from other normal faulted regions hydrocarbons occur in a stacked succession of one or more basins pregraben graben fill and interior sag preservation of pregraben accumulations depends on late initiation of crustal arching and limitation of uplift to the graben shoulders furthermore a stable pregraben tectonic environment is required to ensure internal continuity of subsequent fault block closures hydrocarbon traps in the pregraben and graben fill sediments are primarily dependent on the multidirectional orientation of normal faults tilting of fault blocks and in many cases flexing or erosion parallel with block edges the fault pattern is dominated by longitudinal faults subparallel with the graben axis and secondarily by oblique faults the direction and degree of block rotation are influenced by fault profile planar or listric degree of extension fault pattern doglegs junctions terminations downwarping of the subsequent sag basin and isostatic adjustments between large blocks fold closures result from the upward termination of faults into forced folds which may be accentuated by drag during renewed faulting passive drape and differential compaction extend he folds to shallower depths because they form along block edges the flexures have trends that mimic the multidirectional fault patterns truncation traps are usually developed from the erosional retreat of fault scarps and they can also mimic the fault patterns where the sedimentary succession is complete an interior sag basin is superimposed across the graben its lower part is structured mostly by drape and differential compaction across the underlying graben fault blocks and fault block topography the upper part is usually an unsegmented syncline and hydrocarbon traps at this level include depositional buildups reefs turbidite mounds and salt diapirs or other structures caused by superimposed deformation unrelated to graben tectonics

akaso field nigeria use of integrated 3 d seismic fault slicing clay smearing and rft pressure data on fault trapping and dynamic leakage the akaso field stoiip 78 106 m3 401 million stb of the eastern niger delta is separated from the large cawthorne channel field stoiip 208 106 m3 1307 million stb by a major antithetic counterregional normal fault in 1989 three dimensional 3 d seismic data acquired and interpreted over the field revealed a subtle splinter or backsplit fault off this major antithetic fault west of the main akaso field behind this backsplit fault we observed stacked amplitude anomalies these anomalies extended to the structural spillpoint defined against the akaso backsplit fault fault slicing and clay smear studies of the backsplit and main antithetic fault indicated strong seal potential with possible leak windows along the fault planes in 1989 the sealing potentials of the western end of the akaso boundary fault were fully confirmed by a deviated appraisal well which found a stoiip of 29 106 m3 183 million stb in a series of stacked footwall closures the initial trapping potential of this major antithetic normal fault can be contrasted with its subsequent behavior during depletion by using rft data acquired in a series of development wells drilled in 1990 in the main akaso structure at the eastern end of the antithetic fault here major stacked columns of oil and gas are trapped and sealed by the antithetic fault but we identified evidence of subsequent leakage due to production effects from the adjacent cawthorne channel field depletion of the unproduced akaso g sands was found to be due to production from the juxtaposed e sands of the adjacent cawthorne channel field thus we inferred dynamic fault leakage we observed a dynamic pressure drop of 400 2144 kpa 58 311 psi between the juxtaposed akaso and cawthorne channel sand due to active crossflow the akaso field therefore represents a prime example of the trapping potential of a clay smeared fault and its subsequent leakage during differential depletion our observations methodology and implications described herein may have an important bearing on reservoir management philosophies in similar structural settings

natural fractures in carbonate rich tight oil reservoirs from the permian lucaogou formation southern junggar basin nw china insights from fluid inclusion microthermometry and isotopic geochemistry abstract natural fractures within tight reservoirs form preferred pathways for hydrocarbon charge and provide space for hydrocarbon preservation however the mechanism that controls the formation of natural fractures in tight reservoirs remains controversial this study investigates natural fractures within carbonate rich tight oil reservoirs from the permian lucaogou formation in the jimsar sag southern junggar basin drill core and image log observations show that fractures in the lucaogou formation can be categorized into two types bedding parallel fractures and inclined fractures the carbon and oxygen isotopic compositions of calcite cements in the bedding parallel fractures range from 0 6 to 6 0 13cpdb and from 15 5 to 8 9 18opdb respectively which are similar to those of the organic rich host rock this suggests that the bedding parallel fractures likely formed in a closed fluid system fluid inclusion analyses of the aqueous inclusions in calcite cements from the bedding parallel fractures record homogenization temperatures of 91 5 c 130 4 c indicating that they formed at the cretaceous to cenozoic during when the lucaogou formation reached peak oil generation stage therefore the bedding parallel fractures were most likely generated by hydrocarbon generation overpressure the presence of hydrocarbon inclusions in bedding parallel fracture cements supports natural fracturing by high pore fluid pressure the 13cpdb and 18opdb of calcite cements within the inclined fractures vary from 3 6 to 9 6 and from 11 0 to 2 9 respectively which are close to those of the carbonate rich parent rock this also supports a closed fluid system scenario the relatively lower fluid inclusion trapping temperatures 70 5 c 109 7 c suggest that they were likely generated by decrease of confining stress during uplift processes therefore both an increase in pore fluid pressure and a decrease in confining stress contribute to the formation of natural fractures in the lucaogou formation tight oil reservoirs

oil migration through preferential petroleum migration pathway ppmp and polycyclic faults a case study from the shijiutuo uplift bohai bay basin china abstract the shijiutuo uplift is an oil enriched uplift in the offshore bohai bay basin petroleum migration is a key factor for oil enrichment in neogene reservoirs far away from the hydrocarbon kitchen in this article an integration of geological geophysical and geochemical analyses are employed to investigate the petroleum migration and accumulation on the shijiutuo uplift hydrocarbons in the qhd32 6 and qhd33 oilfields are mainly originated from the third e 2 s 3 and first e 2 s 1 member of the shahejie formation the shallow traps have significant contributions of late stage e 2 s 1 derived oil lateral petroleum migration is a major mechanism forming large oilfields on the shijiutuo uplift the large oilfields have multiple hydrocarbon kitchens multiple source rocks and numerous preferential petroleum migration pathways ppmps once petroleum arrives at the structural highs on the shijiutuo uplift through the guantao formation n 1 g carrier beds neotectonic faults cutting through guantao n 1 g and minghuazhen n 1 m l formations could serve as effective conduits for vertical petroleum migration neotectonic faults have experienced polycyclic fault activities fluid inclusions indicate episodic hydrocarbon charging crude oils display duplex properties of biodegradation and non biodegradation which is strong evidence for multiple and episodic oil charging on the shijiutuo uplift finally episodic petroleum charging along polycyclic neotectonic faults causes the late stage e 2 s 1 derived oils to occur in the shallow reservoirs

zebra and boxwork fabrics in hydrothermal dolomites of northern canada indicators for dilational fracturing dissolution or in situ replacement zebra and boxwork fabrics in manetoe and presqu ile hydrothermal dolomites provide critical data for discrimination between hypotheses for their origin in a unique occurrence sets of weakly imbricated decimetre sized curvilinear lenticles of white dolospar are developed within sub metre sized tongues of greyish white dolomitized crinoidal packstone and grainstone this nascent zebra fabric has developed along wavy to nodular intra bed sedimentary partings primary bedding can be traced through dolomitized masses containing these fabrics into the surrounding undolomitized limestone all zebra and boxwork fabrics are confined within single beds consistent with an early burial time of origin no change in bed thickness occurs across zebra or boxwork fabrics within beds this indicates a dissolutional rather than a dilational origin for the creation of pore space partly cemented with white dolospar the dolomitized groundmass displays an abruptly gradational or sharp transition to centripetal saddle dolomite cement which partially to nearly completely occludes vugs circulation of geothermally heated hypersaline devonian elk point basinal sea water brines led to dissolution and replacive dolomitization of limestone adjacent to vugs and near contemporaneous precipitation of white dolospar within dissolutional vugs consistent with geochemical simulations the presence of downward extending galleries of white dolospar cemented solution collapse breccia provides further support for an interpretation of regional thermally driven convection of hydrothermal evaporative sea water brines across a broad area of northern canada the absence of gases under pressure in vacuoles within fluid inclusions from manetoe and presqu ile dolospars is also more consistent with a dissolutional and contemporaneous dolomitization origin for these fabrics rather than an origin involving dilational fracturing for space creation and dolospar precipitation the ubiquitous presence of zebra and boxwork fabrics in hydrothermal dolomite reservoirs indicates that they are not confined fault zones and instead occur wherever precursor limestones had relatively greater porosity and permeability prior to dolomitization

breccia formation by particle fluidization in fault zones implications for transitory rupture controlled fluid flow regimes in hydrothermal systems breccias in the rusey fault cornwall uk and the roamane fault porgera gold deposit papua new guinea provide insights about the dynamics of fluid flow and flow velocities when fault ruptures breach overpressured reservoirs of hydrothermal fluid these faults contain cockade like breccias in which rock fragments are mantled by spheroidal overgrowths of hydrothermal minerals at rusey the overgrowths are quartz dominant whereas in the roamane fault overgrowths are composed of calcite quartz or gold rich pyrite although none of the rock fragment cores of accretionary spheroids are in contact with their neighbours the spheroidal overgrowths do contact each other and are at least partially cemented together the hydrothermal overgrowths mostly comprise either outwards coarsening crystals that radiate from the surface of the core rock fragment or finer grained inequigranular to mesh like intergrowths concentric textural banding and oscillatory growth zones are present in some hydrothermal mantles the breccias occur as fault parallel layers and lenses each up to several tens of centimeters thick adjacent layers are characterized by texturally distinct ranges of clast sizes and different proportions of clasts to hydrothermal overgrowths in the rusey fault many texturally distinct breccia layers are present within a 3m wide fault core some layers truncate others and many breccia layers exhibit grainsize grading or banding clasts in the breccias include fragments of wall rock veins and various fault damage products including fragments of earlier generations of cemented breccia brecciation was episodic and separated by periods of cementation the distinctive textures of the breccias are interpreted to have formed by fluidization of fault damage products in a high fluid flux regime hydrothermal coatings developed while clasts were in a suspended state during fluid ascent through dilatant fault segments layered breccias record multiple episodes of particle fluidization and indicate that the faults provided conduits for repeated transitory fluid upflow particle size distributions indicate that fluid velocities during fluidization were in the range 0 1 ms 1 to 1 ms 1 the maximum flow rates correspond to fluid fluxes of 10 to 100 l s 1 per meter strike length of fault through dilatant fault apertures up to several tens of centimeters wide such high flow rates characteristically induce intense swarm seismicity rather than mainshock aftershock seismicity and have implications for the dynamics and rates of formation of fault related hydrothermal ore deposits

on palaeozoic mesozoic brittle normal faults along the sw barents sea margin fault processes and implications for basement permeability and margin evolution palaeozoic mesozoic brittle normal faults onshore along the sw barents sea passive margin off northern norway give valuable insight into fault and fluid flow processes from the lower brittle crust microstructural evidence suggests that late permian early triassic faulting took place during multiple phases with initial fault movement at minimum p t conditions of c 300 c and c 240 mpa c 10 km depth followed by later fault movement at minimum p t conditions of c 275 c and c 220 mpa c 8 5 km depth the study shows that pore pressures locally reached lithostatic levels 240 mpa during faulting and that faulting came to a halt during early deep stages of rifting along the margin fault permeability has been controlled by healing and precipitation processes through time which have sealed off the core zone and eventually the damage zones after faulting a minimum average exhumation rate of c 40 m ma 1 since the late permian is estimated it implies that the debated late cenozoic uplift of the margin may be explained by increased erosion rates in the coastal regions owing to climate detoriation which caused subsequent isostatic recalibration and uplift of the marginal crust the studied faults may be used as analogues of basement involved fault complexes offshore revealing details about the offshore nature of faulting including past and present basement and fault zone permeability

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk