geometric and kinematic models for detachment folds with fixed and variable detachment depths abstract detachment folds are defined by competent rock units and are cored by incompetent units deformed internally above a detachment horizon we have developed two geometric models to constrain possible geometries and kinematic paths for ideal detachment folds the models each independently relate fold geometry to shortening and to detachment depth model assumptions include plane strain constant competent bedlength constant cross sectional area chevron fold geometry and no bed parallel shear outside the fold detachment depth is constant in one model but may vary in the other thus allowing evaluation of the implications for fold geometry and kinematics of fixed vs variable detachment depth detachment folds formed above a detachment unit of constant thickness constant detachment depth must be initially symmetrical and cannot grow with fixed hinges fixed arc length or a self similar geometry detachment folds formed above a detachment unit of variable thickness variable detachment depth must also be initially symmetrical but any one fold geometry can have a range of possible initial and final detachment depths kinematic paths for folds with fixed hinges fixed arc lengths migrating hinges variable arc lengths and selfsimilar geometries are all possible if detachment depth varies the change in detachment depth during deformation can be determined using the variable detachment depth model if either initial or final detachment depth is known the models demonstrate a wider range of variability in the geometry and kinematics of ideal detachment folds particularly for the variable depth model than is the case for ideal fault bend and fault propagation folds this variability limits the usefulness of simple geometric models for reconstructing the geometry of natural detachment folds balancing cross sections over a sufficient area and evaluating strain may compensate for these limitations

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

co2 mineral reaction in a natural analogue for co2 storage implications for modeling geochemical models of co2 injection into reservoir sandstones often predict the growth of minerals that will permanently store the co2 in solid form and injection experiments record significant fluctuations in porewater chemistry on a short time scale yet the proportion of co2 reaction may be small even over geological time scales a southern north sea uk gas accumulation with a high natural co2 content c 50 forms a natural analogue to engineered storage and provides a calibration point for geochemical models of co2 rock reaction in the analogue site the carbonate mineral dawsonite has formed in only trace amounts 0 4 0 3 solid volume despite exposure to high levels of co2 for 50 myr or more it is calculated that only 2 4 0 9 of the co2 present within the structure is currently locked up as dawsonite and a similar quantity in solution in the porewaters comparison of stable o and c isotopes with a neighboring field with low co2 content gas suggests that up to 0 7 2 solid volume dolomite cement is associated with the co2 charge equivalent to 0 25 of the total co2 the remaining 70 95 of the co2 is present as a free phase after tens of millions of years consequently geological storage of anthropogenic co2 in reservoirs similar to the rotliegend group must rely on physical containment and not mineral sequestration the rotliegend group is still an excellent candidate for a co2 storage reservoir though using physical trapping mechanisms and not chemical ones

the impact of cover rock rheology on the style of folding in the zagros fold thrust belt abstract the present day morphology of the zagros fold thrust belt is dominated by magnificent exposures of nw se trending folds these folds differ in their size and geometry and these differences are related mainly to the rheological profile of the cover rock the cover rock succession of the zagros consists of a sequence of competent and incompetent units which vary both along and across the belt field based study combined with the use of satellite images reveals that the thickness and facies distribution of the cover rock succession has a significant impact on the style of deformation during the shortening linked to the current convergence of the arabian and iranian plates the incompetent units act as detachment horizons which localise thrusting and which act as decollement above which detachment folds form in addition where these incompetent units are thick e g 1 km they allow the deformation above and below them to become completely decoupled enabling disharmonic folding to occur as a result the folds above and below the incompetent units in the central part of the zagros folded belt have significantly different geometries and wavelengths as the zagros folds host the majority of the hydrocarbon reserves in iran and iraq an understanding of the processes that influence their geometry and spatial organization at different levels in the cover rock is crucial for the future exploration in the region

influence of pre tectonic carbonate facies architecture on deformation patterns of syntectonic turbidites an example from the central mexican fold thrust belt abstract the mexican fold thrust belt in central mexico excellently exposes relatively well preserved syntectonic deposits that overlay rocks with lateral lithostratigraphic changes across the belt we consider the deformational effects of these changes by investigating the geometry kinematics and strain distribution within syntectonic turbidites which are deposited on top of albian cenomanian shallow and deep water carbonate layers field observations and detailed structural analysis at different stratigraphic and structural levels of the late cretaceous syntectonic formation are compared with the deformation as a function of lithological and structural variations in the underlying carbonate units to better understand the effect of these lithostratigraphic variations on deformation kinematics strain distribution and propagation of deformation from our kinematic analyses we conclude that the syntectonic strata are pervasively affected by folding in all areas and that deformation partitioning localized shear zones at the boundaries of this unit particularly along the contact with massive carbonates at the boundaries with massive platformal carbonates the turbidites are strongly deformed by isoclinal folding with a pervasive sub horizontal axial plane cleavage and 70 60 shortening in contrast contacts with thinly bedded carbonate layers basinal facies do not show strain localization and have horizontal shortening of 50 40 that is accommodated by buckle folds with a less pervasive steeply dipping cleavage the mechanical properties variations in the underlying pre tectonic units as a function of changes in lithostratigraphy fundamentally control the deformation in the overlying syntectonic strata which is an effect that could be expected to occur in any deformed sedimentary sequence with such variations

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

a unified kinematic model for the evolution of detachment folds abstract detachment folds represent a major structural element in a number of fold belts they are common in the jura mountains the zagros fold belt the central appalachian fold belt the wyoming fold belt the brooks range the parry islands fold belt and parts of the subandean belt these structures form in stratigraphic packages with high competency contrasts among units the competent upper units exhibit parallel fold geometries whereas the weak lower unit displays disharmonic folding and significant penetrative deformation two distinct geometric types disharmonic detachment folds and lift off folds have been recognized however these structures commonly represent different stages in the progressive evolution of detachment folds the structures first form by symmetric or asymmetric folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require sinking of units in the synclines and movement of the ductile unit from the synclines to the anticlines continuing deformation results in increasing fold amplitudes and tighter geometries resulting from both limb segment rotation and hinge migration initially limb rotation occurs primarily by flexural slip folding but in the late stages of deformation the rotation may involve significant internal deformation of units between locked hinges the folds eventually assume tight isoclinal geometries resembling lift off folds variations in the geometry of detachment fold geometry such as fold asymmetry significant faulting and fold associated with multiple detachments are related to variations in the mechanical stratigraphy and pre existing structure

syn tectonic magmatism and the development of compositional layering ungava orogen northern quebec canada abstract layer and foliation parallel emplacement of granitic veins was an important process in the regional development of compositional layering in now exhumed middle crustal sections of both archean and paleoproterozoic age in the northern ungava peninsula quebec canada in the archean superior province diorite and tonalite plutons were penetratively deformed and metamorphosed at granulite facies conditions coeval with voluminous granitic magmatism the paleoproterozoic narsajuaq arc contains evidence for contemporaneous magmatism transpressional deformation and granulite facies metamorphism prior to its collision with the superior province basement in both plutonic domains regional compositional layering is defined by 1 metre to kilometre scale alternation of generally well foliated tonalite and quartz diorite bodies and 2 centimetre to kilometre scale variably deformed granitic veins and sheets that lie parallel to layering tectonic foliation in the host rocks syn tectonic intrusion of a substantial portion of the veins along extension fractures sub parallel to layering foliation i e at high angle to the regional shortening direction is interpreted to have occurred due to the combination of a strong anisotropy and high magma pressures compositional layering generated and or enhanced by this process may contribute to the overall seismic reflectivity of the middle and lower crust

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

bacterial methane in the atzbach schwanenstadt gas field upper austrian molasse basin part ii retracing gas generation and filling history by mass balancing of organic carbon conversion applying hydrogeochemical modelling abstract in the austrian molasse basin bacterial methane gas accumulations occur in upper oligocene to early miocene deepwater clastic sediments gas is produced from the upper puchkirchen formation aquitanian in the atzbach schwanenstadt gas field the diagenetic pathway of the reservoir cements was controlled by the conversion of metabolizable organic carbon incorporated in the fine grained sediments these pathways have been retraced by hydrogeochemical modelling the redox conversion of metabolizable organic carbon this approach unravels the relative timing of the coupled processes gas generation and precipitation dissolution of cements the labile organic material was decomposed by fermentation and subsequent co 2 reduction co 2 released via these reactions was nearly completely fixed as carbonate cement methane generated during early diagenesis 10 s to max 100 m sediment depth was dissolved in pore water until saturation after exsolution as a free gas phase methane could have been fixed as hydrate within pore space due to the prevailing paleoceanographic conditions sediment water interface 1000 mbsl 4 c the temperature increase in consequence of the rapid basin subsidence and high sedimentation rates led to the decomposition of the hydrates and to charging of the reservoir by methane still during the aquitanian a further consequence of hydrate decomposition was dilution of pore water salinity according to the results the presented approach offers a a tool to retrace the bacterial methane potential by analysis of diagenetic cement as a quantitative indicator and b to predict the interaction between porosity development and reservoir charging by methane additionally c gas field water salinity and hydrochemistry may be applied in similar architectural elements of deepwater channels as tracers for fossil gas hydrate formation as low chloride concentrations are result of sediment compaction and dilution by pure h 2 o due to gas hydrate dissociation

accommodation of the different structural styles in the foreland fold and thrust belts northern dezful embayment in the zagros belt iran structural styles in the zagros foreland fold and thrust belt vary spatially differential lateral propagation of folds causes to create tear faults in this belt in this research tear faults are studied in northern dezful embayment tear faults have been accommodated the different structural styles in sedimentary cover during the compressional regime in the zagros fold and thrust belt different structural styles indicate a difference in intensity deformation these faults originated as the pre existing inverted reactive deep seated faults or which activate in the sedimentary strata during the compressional regime investigation of the structural style of folds in the sedimentary cover is a key point to recognize tear faults in this research the structural style of the kabood qale nar bala rud and lab e safid subsurface anticlines in the northern dezful embayment has been studied the interpretation of seismic profiles balanced cross sections restoration and 3d structural modeling is investigated to study the structural style of mentioned anticlines the area of the studied region is 92 20 km2 two tear faults with nne trending have been separated qale nar and bala rud anticlines in the central part from lab e safid and kabood anticlines in eastern and western parts respectively the intensity of deformation in the lab e safid anticline is less than the qale nar and bala rud anticlines on its western side displacement and deformation of the kabood anticline are more than the qale nar anticline in its eastern side kabood anticline is multi bend fault bend fold qale nar and bala rud are fault bend folds and lab e safid is detachment fold tear faults have been accommodated by these different structural styles in this region

biodegradation of oil in uplifted basins prevented by deep burial sterilization biodegradation of crude oil by bacterial activity which has occurred in the majority of the earth s oil reserves is known to reduce greatly the quality of petroleum in reservoirs for economically successful prospecting for oil it is therefore important to understand the processes and conditions in geological formations that lead to oil biodegradation although recent studies speculate that bacterial activity can potentially occur up to temperatures as high as 150 degrees c refs 3 4 it is generally accepted that effective petroleum biodegradation over geological timescales generally occurs in reservoirs with temperatures below 80 degrees c ref 2 this appears however to be at odds with the observation that non degraded oils can still be found in reservoirs below this temperature here we compile data regarding the extent of oil biodegradation in several oil reservoirs and find that the extensive occurrence of non biodegraded oil in shallow cool basins is restricted to those that have been uplifted from deeper hotter regions of the earth we suggest that these petroleum reservoirs were sterilized by heating to a temperature around 80 90 degrees c during deep burial inactivating hydrocarbon degrading organisms that occur in the deep biosphere even when such reservoirs are subsequently uplifted to much cooler regions and filled with oil degradation does not occur implying that the sterilized sediments are not recolonized by hydrocarbon degrading bacteria

nano crystal formation of tio2 polymorphs brookite and anatase due to organic inorganic rock fluid interactions the occurrence of the titania polymorphs brookite and anatase as nano crystals in organic matter rich sediments of differing age and thermal maturity has been investigated by means of a multidisciplinary analytical approach fib tem organic geochemistry and petrography it was the aim of the study to analyze the formation mechanisms fate and behavior of the titania nano crystals as a result of organic inorganic rock fluid interactions brookite nano crystals have been detected in immature mediterranean sapropels of quaternary age but anatase also occurs in deeper and older black shales furongian alum shale sweden devonian to carboniferous bakken shale williston basin usa whereas anatase prevails as single crystals brookite nano crystals often are agglomerated single brookite nano crystals from posidonia shale lower jurassic northern germany have increasing crystal diameters with increasing thermal maturity exclusively anatase nano crystals both as single crystals or as agglomerates have been detected at oil water contacts in oilfields and along fractures with fluid flow enriched in dissolved organic carbon titania nano crystal precipitation growth and agglomeration takes place in the pore water of micro environments at low to high temperatures and where low ph is coupled to the occurrence of dissolved organic components low sedimentation rates preserving a critical geochemical environment or higher temperatures seem major controls for the precipitation of anatase and its tendency not to agglomerate

the origin of changes in structural style across the bandar abbas syntaxis se zagros iran abstract the bandar abbas syntaxis marks the transition between the zagros collisional belt and the makran subduction related prism and constitutes a major structural feature within the alpine himalayan mountain belt within the foreland part of the zagros the zagros fold thrust belt zftb the transition is marked by a sudden change in structural trends and style and a rapid decrease in seismicity and salt diapirism from west to east of the syntaxis the depth to decollement and lithology affect the geometry and size of the folds on each side of the syntaxis while different mechanical coupling along the basal decollement affects the degree of internal rock deformation thus the short and broad folds of the western side of the syntaxis are decoupled along the 8 km deep hormuz evaporites visible at surface in numerous salt diapirs strong seismicity in this area suggests that the basement is involved in the deformation by contrast the long and narrow folds of the eastern side of the syntaxis appear to be controlled by frictional slip along a 6 km deep detachment the absence of seismicity suggests that the basement is not involved in the deformation in this area we propose that the basal decollement for these structures corresponds to the eroded top of the nne ssw trending oman mesozoic nappes resulting from late cretaceous obduction of tethys on the arabian margin these structures are visible onshore in the northern tip of the oman peninsula and seen in offshore seismic profiles continuing northward beneath the strait of hormuz finally map view observations show that the main zagros thrust and the zendan fault separating the zftb from the internal zones of the orogen are shallow low angle thrust faults rather than steeply dipping faults

structural framework of the zagros fold thrust belt iran abstract data gleaned from the literature on the zagros have been compiled and used in conjunction with new interpretations to provide a better picture of the structures sedimentation history and deformation of this hydrocarbon rich mountain belt the belt parallel mountain front the n s trending kazerun izeh and e w trending bala rud fault zones are defined as the master structural elements of the belt these fault zones divide the zagros basin into zones with different stratigraphic successions and different rheological profiles this resulted in different structural styles developing along the belt during the subsequent collision the kazerun and izeh fault zones acted as the depositional system transition zone between the lurestan and fars regions in jurassic cretaceous time and partly controlled the distribution of the kazhdumi formation one of the major source rocks by the end of the cretaceous the nw se trending mountain front fault divided the present folded belt of the zagros into a major foreland basin to the southwest and a piggyback basin to the northeast activity along other major transfer fault zones including the izeh kazerun and bala rud fault zones occurred at this time and controlled the sedimentation and subsidence of the dezful embayment the main target region for hydrocarbon exploration these fault zones controlled the thickness of the asmari formation one of the main reservoirs and also the considerable thickness and facies changes of the gachsaran formation the major seal to the asmari formation the present morphology of the mountain belt is interpreted as being mainly related to the pinning of the mountain front fault to the northwest of the dezful embayment and to the north of the strait of hormuz

seismicity patterns associated with the september 10th 2008 qeshm earthquake south iran the b value of the gutenberg richter relation and the standard deviate z were calculated to investigate the temporal and spatial variations in seismicity patterns associated with the september 10th 2008 mw 6 1 qeshm earthquake the temporal variations of b value illustrate a distinct dramatic drop preceding the qeshm earthquake and the spatial changes in b value highlight a zone with an abnormally low b value around the epicenter of this event the cumulative number and z value as a function of time show a precursory seismic quiescence preceding the 2008 qeshm earthquake that observed for 1 year in a circle with r 50 km around its epicenter the spatial distribution map of the standard deviate z also exhibits an obvious precursory seismic quiescence region before the 2008 qeshm event around the epicenter of this event interestingly the precursory seismic quiescence region is approximately consistent with low b value anomaly region and both have e w to ne sw trend these two precursory anomalies took place in relatively large regions which were possibly relevant to the preparation zone of the 2008 qeshm event

zagros phantom earthquakes reassessed the interplay of seismicity and deep salt flow in the simply folded belt unraveling the contributions of main shock slip aftershocks aseismic afterslip and postseismic relaxation to the deformation observed in earthquake sequences heightens our understanding of crustal rheology triggering phenomena and seismic hazard here we revisit two recent earthquakes in the zagros mountains iran which exhibited unusual and contentious aftereffects the mw 6 earthquakes at qeshm 2005 and fin 2006 are both associated with large interferometric synthetic aperture radar insar signals consistent with slip on steep reverse faults in carbonate rocks of the middle sedimentary cover but small aftershocks detected with local seismic networks were concentrated at significantly greater depths this discrepancy can be interpreted in one of two ways either 1 there is a genuine vertical separation between main shock and aftershocks reflecting a complex stress state near the basement cover interface or 2 the aftershocks delimit the main shock slip and the insar signals were caused by shallow updip afterslip phantom earthquakes with very similar magnitudes mechanisms and geographical positions as the original earthquakes here we show that main shock centroid depths obtained from body waveform modeling which in this instance is the only method that can reveal for certain the depth at which seismic slip was centered strongly support the first interpretation at qeshm microseismic aftershock depths are centered at the level of the hormuz formation an infracambrian sequence of intercalated evaporitic and nonevaporitic sediments these aftershocks may reflect the breaking up of harder hormuz sediments and adjacent strata as the salt flows in response to main shock strain at the base of the cover this work bolsters recent suggestions that most large earthquakes in the zagros are contained within carbonate rocks in the midlower sedimentary cover and that the crystalline basement shortens mostly aseismically

variation of structural style and basin evolution in the central zagros izeh zone and dezful embayment iran abstract structural style and its relationship to sedimentary facies and the evolution of sedimentary depocenters since late cretaceous times have been studied on the basis of one regional balanced transect and several updated isopach maps in the izeh zone and the dezful embayment central zagros this study relies on fieldwork data existing geological maps seismic data and well information a new structural classification for part of the zagros sedimentary cover is presented to highlight the different mechanical behavior of the formations in the stratigraphic column it shows the existence of several local decollement levels activated during folding these decollement levels separate lithotectonic units which accommodate shortening in different ways the lower paleozoic is the basal decollement level throughout the studied area triassic evaporites albian shales eocene marls and miocene evaporites can act as intermediate decollement levels and present variable facies in the central zagros lateral facies and thickness variations the sedimentary overburden and the close relationship with inherited fault patterns influenced the wavelength amplitude and style of folding in the study area furthermore surface structures do not necessarily coincide with deeper objectives where these disharmonic levels are involved in folding the evolution of sedimentary depocenters from the late cretaceous obduction episode until early miocene collision is described based on updated isopach maps and tectonic subsidence curves this analysis shows continuous compression and movements along n s and nw se trending faults in the zagros basement which predate the neogene zagros folding and influence sedimentation history it also indicates a southwestward migration of the depocenters through time in addition to the basement involvement below some folds during the zagros orogeny

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

quantification of co2 generation in sedimentary basins through carbonate clays reactions with uncertain thermodynamic parameters abstract we develop a methodological framework and mathematical formulation which yields estimates of the uncertainty associated with the amounts of co 2 generated by carbonate clays reactions ccr in large scale subsurface systems to assist characterization of the main features of this geochemical process our approach couples a one dimensional compaction model providing the dynamics of the evolution of porosity temperature and pressure along the vertical direction with a chemical model able to quantify the partial pressure of co 2 resulting from minerals and pore water interaction the modeling framework we propose allows i estimating the depth at which the source of gases is located and ii quantifying the amount of co 2 generated based on the mineralogy of the sediments involved in the basin formation process a distinctive objective of the study is the quantification of the way the uncertainty affecting chemical equilibrium constants propagates to model outputs i e the flux of co 2 these parameters are considered as key sources of uncertainty in our modeling approach because temperature and pressure distributions associated with deep burial depths typically fall outside the range of validity of commonly employed geochemical databases and typically used geochemical software we also analyze the impact of the relative abundancy of primary phases in the sediments on the activation of ccr processes as a test bed we consider a computational study where pressure and temperature conditions are representative of those observed in real sedimentary formation our results are conducive to the probabilistic assessment of i the characteristic pressure and temperature at which ccr leads to generation of co 2 in sedimentary systems ii the order of magnitude of the co 2 generation rate that can be associated with ccr processes

quantitative structural analysis using remote sensing data kurdistan northeast iraq the use of remote sensing data increases the efficiency of field mapping especially in areas with difficult access or where geologic fieldwork is expensive or hazardous this study presents a newly developed software tool for interactively mapping and measuring the spatial orientation i e dip angle and dip direction of finite planar geologic structure from digital elevation models dems the orientations of planar data e g sedimentary bedding or fault planes are derived by approximating a virtual plane to the intersection of the planar feature with the dem topography to increase the informative value of the dem satellite images can be draped onto the topographic data set the software tool was tested in the zagros fold and thrust belt northeast of erbil kurdistan northeast iraq where the stratigraphy has been deformed into subcylindrical fold trains computed orientations have been compared with actual dip angles and directions measured in the field under favorable conditions moderately dipping planes strong competence contrast between stratigraphic boundaries intersection with a rugged topography low vegetation statistical comparison of computed data with the field measurements demonstrates that the spatial data set can be reproduced from the dem within an average error of approximately 10 the strength of the method is demonstrated by integrating field data with computed values from inaccessible areas resulting in a reasonably well constrained balanced geologic cross section

a quantitative model of biological petroleum degradation within the brent group reservoir in the gullfaks field norwegian north sea abstract it has been documented that the degree of biological degradation of the petroleum in the brent group reservoir in the gullfaks field quadrant 34 10 norwegian north sea varies laterally the most severe degradation has taken place in the western part of the field where the brent group sediments are not eroded lack of erosion in the west suggests that this part of the reservoir has always been buried at greater depths than the eastern part of the field the geochemical description with the most severe biodegradation in the west seems therefore to conflict with the most obvious geological model with easiest access for bacteria with meteoric water from the east this suggests that we either do not understand the geology of the gullfaks field area or we do not understand the biological degradation process or perhaps both it is possible to give a reasonably good approximation of the amount of carbon that has been removed from the reservoired petroleum by bacterial degradation by comparing degraded and non degraded petroleum with a fill spill relationship in the area by assuming that the supply of an oxygenating agent is the rate limiting factor in biological degradation of petroleum within a reservoir it is possible to simplify the very complex processes and mechanisms involved in petroleum degradation and to reduce the number of variables to three these are the thickness of the supply zone below the reservoir from which an oxygenating agent can be supplied the flow of water within this supply zone below the oil water contact o w c and the time available to degrade the petroleum in the reservoir geochemical and geological observations and modelling have demonstrated that it is unlikely that the degradation involves sulphate reducing bacteria but that degradation is probably aerobic bacterially mediated and a supply of oxygen rich water with nutrients or is related to a yet unidentified process this mass balance based on the supply and demand of oxygen dissolved in meteoric water indicates that several thousand reservoir volumes are required to degrade the petroleum within the brent group to its present stage this is difficult to explain with the current geological model of the field however the biological degradation must be accounted for when establishing a realistic geological model in the gullfaks area the main advantage of our model is that it is quantitative and although some inaccuracies are inevitable it gives an order of magnitude estimate of the amount of water which must have been supplied into the reservoir

dawsonite cement in the triassic lam formation shabwa basin yemen a natural analogue for a potential mineral product of subsurface co2 storage for greenhouse gas reduction abstract the origin and permeability effects of carbonate cement blamed for poor reservoir quality in the upper triassic turbidite sandstones of the lam formation in yemen have been investigated using petrography x ray diffraction stable isotopes fluid inclusions and thermodynamic modelling in order of growth in the sandstone the carbonate cements include ferroan calcite dawsonite naalco3 oh 2 ferroan dolomite and siderite ferroan dolomite is the most abundant cement there is an inverse correlation between permeability and total carbonate cement volume supporting the earlier assertion that carbonate cements are the main control on reservoir quality in these sandstones ferroan calcite replaced and was sourced by marine limestone rock fragments that are abundant in the turbidite sandstone the later cements were probably also at least partly sourced from the marine limestone rock fragments stable isotope data from ferroan calcite ferroan dolomite and siderite show that diagenesis occurred in formation water with oxygen isotopes typical of closed system diagenesis and that only minor organic derived carbon dioxide was involved in diagenesis dawsonite while not common as a diagenetic mineral in sandstones has recently been suspected of being a routine consequence of co2 storage in the subsurface for greenhouse gas reduction in the lam formation dawsonite found at concentrations of up to 8 vol of the rock grew at the expense of detrital feldspar minerals under conditions of elevated partial pressure of carbon dioxide isotopic data show that dawsonite grew in the presence of carbon dioxide with a 13c value of about 4 to 2 this is distinctly different from the carbon isotope ratio of the gas phase carbon dioxide now present in the sandstone 27 which had an organic source rock origin the dawsonite 13c data probably represent a mixture between carbonate from detrital marine limestone rock fragments and carbon dioxide from a moderately negative source possibly of magmatic or basement origins dawsonite may thus be the result of a mass influx of deep e g magmatic carbon dioxide that pushed the lam formation into the dawsonite stability field at the expense of albite

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

bacterial methane in the atzbach schwanenstadt gas field upper austrian molasse basin part i geology abstract bacterial methane gas accumulations occur in upper oligocene to early miocene clastic deepwater sediments in the austrian molasse basin methane gas is produced from the upper puchkirchen fm aquitanian in the atzbach schwanenstadt gas field which is one of the largest gas fields in this basin the bacterial gas is composed of 97 vol methane 13 c 62 d 200 connate pore water below the gas water contact is characterized by low salinity ccl ca 0 25 mol kgw or 8900 mg kgw the top of the main reservoir zone a4 is approximately 1600 m subsurface thickness of reservoir intervals in the a4 sands the main reservoir is variable and ranges from 8 to 30 m with decreasing thickness to the north the porosity of the sand ranges from 13 to 20 permeability from 6 md to 70 md the reservoir temperature is 63 c reservoir rocks of this field wedge out to the north and represent dam break through splay sediment this reservoir architecture enabled early gas accumulation in a stratigraphic trap the source rocks and reservoir rocks are intimately connected claystone layers intercalate and seal the reservoir sediments these fine grained sediments with potential source rock characteristics contain immature organic matter of kerogen types ii iii the toc contents of these fine grained sediments vary from 0 34 to 0 94 wt the cement inventory of the source and reservoir rocks is characteristic for diagenetic pathways of organic rich sediments pyrite is preserved in the sediments as the first precipitation product due to rapidly developing anoxic pore water conditions a following dolomite precipitation dissolution phase was replaced by precipitation of calcite ankerite and siderite a last cement phase is chlorite the about 700 m thick upper puchkirchen fm was deposited during a time interval of about 2 6 ma aquitanian in a deep sea fan environment water depth 1000 m bottom water temperature of about 4 c free gas phases may have been trapped as gas hydrate due to basin subsidence and high sedimentation rates hydrates have been decomposed below the base of the gas hydrate stability zone 200 40 mbsf still during the aquitanian and thus still during or shortly after deposition of the upper puchkirchen fm

geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding this paper presents geometric arguments for modifying the conventional concept for the evolution of concentric fold trains above nonductile detachment zones the common geometric model for concentric folding above a detachment invokes a wave train with fixed fold axes regularly spaced along the fold panel limb lengths from crest to trough remain constant as the limb dips increase to uplift the anticlinal crests while the synclinal troughs slide parallel to the detachment plane the basic depth to detachment calculation which derives from the law of conservation of volume requires that the area of uplift above regional for a concentric anticline be equal to the arithmetic product of the shortening and the depth to detachment this imposes a geometric constraint with which a constant limb length anticline growing by increasing limb dip above a fixed detachment plane cannot comply unless in the early stages mobile material in the detachment zone flows from the synclinal troughs to the anticlinal crests and then in the later stages the flow direction reverses relatively few detachment zones contain a significant amount of mobile salt or shale therefore in most concentric detachment fold trains a basic geometric incompatibility exists between the conventional geometric model and themore law of conservation of volume the conflict can be resolved by an evolutionary fold model wherein the anticlinal fold limbs are short at the inception of folding and grow longer as dips increase and the fold grows in this model the anticlinal axes generally are fixed and the synclinal axes active which has structural and economic implications for the distribution of permeability and syntectonic sediments as well as for the migration and entrapment of hydrocarbons 18 figs less

structural style variation and its impact on hydrocarbon traps in central fars southern zagros folded belt iran abstract the fars area is the main target for permian gas exploration in the zagros fold belt it contains approximately 15 percent of the world s proven gas reserves the geometrical characteristics of the folded structures change dramatically across the n s trending gavbandi high we used seismic profiles well data magnetic survey information and field observations to show that thickness variation of the sedimentary pile inherited from basement geometry is the main reason behind structural style variation in this area which occurred during the zagros folding differences in thickness were more significant in early middle paleozoic time and decreased considerably upward in time the total thickness of the lower paleozoic succession in the eastern side of the gavbandi high is approximately 40 50 thicker than on the summit of this basement high sedimentary pinch outs through cretaceous and tertiary times indicate that the activity of the basement faults decreased but did not stop the impact on hydrocarbon traps of the pre folding basin architecture and the differences in the behavior of the sedimentary cover after miocene folding is discussed and documented

temperature dependence of organic matter remineralization in deeply buried marine sediments abstract assuming that the temperature dependence of sediment organic matter remineralization can be described by the arrhenius equation organic matter that is highly refractory at seafloor temperatures 2 3 c should become more reactive at sediment depths of several hundred meters due to burial and heating by the natural geothermal gradient results obtained using a coupled non linear reactive transport model support this suggestion for deeply buried marine sediments i e those found 100s of meters below the seafloor model results predict the occurrence of a deep zone of methanogenesis that is separated by a relatively thick region in which methane diffuses upwards to be oxidized by downward diffusing sulfate this depth zonation of biogeochemical processes in deeply buried sediments is in sharp contrast to that observed in nearshore marine sediments where sulfate reduction and methanogenesis generally occur in much closer vertical proximity model results presented here also provide a simple mechanistic explanation for the occurrence of linear pore water sulfate profiles that are common in many continental margin sediments linear sulfate gradients are often taken as an indirect indicator of gas hydrate occurrence although results presented here suggest that this does not necessarily always have to be the case application of the model to gas hydrate containing sediments on the blake ridge yields results that are in good agreement with sediment and pore water data and microbial rate studies in these sediments model results also suggest that in situ methanogenesis in and or near the gas hydrate stability zone may play an important role in supplying the methane found in blake ridge gas hydrates

a mineral water gas interaction model of pco2 as a function of temperature in sedimentary basins abstract accurate prediction of co2 partial pressure pco2 in sedimentary basins is important for reducing risk in natural gas exploration predicting non hydrocarbon gas in geological formations improving reservoir quality prediction optimizing production and reservoir management operations and understanding geological storage of co2 it has been proposed for some time now that pco2 in sedimentary basins is buffered by water mineral gas interactions and is primarily related to the temperature however the pco2 values predicted from thermodynamic calculations do not always match field observations here we developed a new and general geochemical model to predict pco2 in sedimentary basins by treating each component of the geochemical model of co2 water rock reactions rigorously our model is able to match observed pco2 in a number of sedimentary basins around the world the thermodynamic treatments introduced in the model include a a gas mixture including ch4 g co2 g h2s g and h2o g rather than a single gas in previous models b the peng robinson equation of state to calculate the fugacity coefficients in the gas mixture rather than assuming ideal gas c taking into account of the hydrostatic pressure of the system and make pressure corrections on equilibrium constants of gas aqueous species and minerals reactions for sedimentary basins with complicated uplift and subsidence history we introduced reaction path modeling to account for the p t history the geochemical model allows the input of basin specific conditions and serves as a tool to identify the key processes that control pco2 in sedimentary basins

structural models of faulted detachment folds faulted detachment folds represent a common structural style in several hydrocarbon producing fold and thrust belts including the zagros idaho wyoming utah carpathian and albanide belts and several deep water fold belts including the mississippi fan and per dido belts these structures form in units with high competency contrasts and display a transition in deformational behavior from detachment folding to progressive fault propagation with increasing shortening the structures first form by symmetric or asymmetric detachment folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require the movement of material from the synclines to the anticlines contin ued shortening results in tighter folds with limb rotation by hinge migration limb segment rotation and internal shear rotation of limb segments between locked hinges results in thrust faults which propagate through deformation zones on the frontlimb and possibly the backlimb the faults may terminate both up and down section within brittle or ductile deformation zones eventually a through going fault connects one of the major faults with the basal detach ment variations in the structural geometry are related to the rela tive thickness and competency of the units and the mechanisms of deformation because faulted detachment folds superficially resem ble fault propagation folds their geometry can be misinterpreted in areas of poor data quality characteristic features for distinguish ing these structures include 1 smaller variations in anticlinal length during fold evolution 2 a more open and rounded fold geometry 3 complex and nonuniform variations in fault slip 4 a significant variation in deformational behavior among different units and 5 fold fault relationships indicating transition from folding to faulting such as footwall synclines and decapitated fold geometries

supraglacial forcing of subglacial drainage in the ablation zone of the greenland ice sheet 1 we measure hydrological parameters in meltwater draining from an outlet glacier in west greenland to investigate seasonal changes in the structure and behaviour of the hydrological system of a large catchment in the greenland ice sheet gris our data reveal seasonal upglacier expansion and increase in hydraulic efficiency of the subglacial drainage system across a catchment 600 km2 to distances 50 km from the ice sheet margin this expansion occurs episodically in response to the drainage of surface meltwaters into a hitherto inefficient subglacial drainage system as new input locations become active progressively further upglacier this system is similar to alpine glaciers these observations provide the first synopsis of seasonal hydrological behaviour in the ablation zone of the gris

late miocene deformation kinematics along the nw zagros fold thrust belt kurdistan region of iraq constraints from apatite u th he thermochronometry and balanced cross sections

petrography fluid inclusion isotope and trace element constraints on the origin of quartz cementation and feldspar dissolution and the associated fluid evolution in arkosic sandstones feldspar dissolution quartz cementation and clay cementation are significant diagenetic processes in deep water fan feldspar rich sandstones in the shengtuo area dongying sag east china the timing and origin of these water rock interactions as well as the paleofluids in which relevant chemical reactions occurred were deduced using data from microscopy fluid inclusion microthermometry oxygen isotope microanalysis and trace element microanalysis three distinct separate episodes of quartz overgrowths referred to as q1 q2 and q3 were distinguished by cathodoluminescence microscopy the q1 quartz identified in all porous sandstones from 2500 to 3600 m 8200 to 11 800 ft was formed at approximately 100 c 115 c 212 f 239 f before oil filled the reservoirs the q2 quartz was mainly precipitated at 115 c 130 c 239 f 275 f accompanying or slightly postdating the main phase of oil filling and was identified in samples from 2800 to 3600 m 9200 to 11 800 ft the q3 quartz was only identified in sandstones buried deeper than 3500 m 11 400 ft and was likely precipitated in the quaternary when temperature exceeded 130 c 135 c 266 f 275 f secondary ion mass spectrometry oxygen isotope microanalyses yielded 18ovsmow vienna standard mean ocean water values ranging from 21 42 to 24 35 for q1 quartz from 22 03 to 24 99 for q2 quartz and from 21 72 to 22 91 for q3 quartz a mass balance calculation and quantitative petrography data of the amount of leached feldspars and associated secondary minerals suggest that the internal feldspar dissolution is likely the primary source for the authigenic clays and quartz cements in these sandstones positive 18o water values 0 5 to 4 5 vsmow of quartz forming waters indicate that quartz cementation and feldspar dissolution occurred in a geochemical system with a limited volume of diagenetically modified connate water the variations of 18o cements and trace element compositions from q1 quartz to q2 quartz in individual overgrowth suggest that hydrocarbon filling changed the chemistry of the pore fluid significantly further 18o water values of the pore water increased by approximately 2 vsmow after oil filling meteoric freshwater did not contribute to quartz cementation and simultaneous feldspar dissolution the detected co2 and hydrocarbons in fluid inclusions in the quartz cements the existence of co2 in hydrocarbon rich natural gas and the pyrobitumen in the feldspar hosted pores suggest that acids derived from organic matter kerogen in source rocks and hydrocarbons in reservoirs probably have promoted the extensive subsurface leaching reactions of feldspars in these sandstones the ongoing development of q2 and q3 quartz suggests that quartz precipitation did not cease after oil filling further diagenetic reactions likely have proceeded from water rock interactions to hydrocarbon water rock interactions

stratigraphy and sedimentary petrology of an archean volcanic sedimentary succession at mt goldsworthy in the pilbara block western australia implications of evaporite nahcolite and barite deposition abstract a approximately 3 3 ga sedimentary succession at mt goldsworthy in the northeastern pilbara block australia contains beds composed of silicified pseudomorphs of nahcolite nahco3 or barite baso4 this sedimentary succession correlates with the corboy formation and consists of lower middle and upper sedimentary units which conformably overlie mafic to ultramafic volcanic and volcaniclastic rocks the lower and middle units are predominantly siliciclastic whereas the upper unit is characterized by ferruginous cherts and banded iron formations with minor proportions of intercalated mature sandstone the succession defines an overall upward fining and deepening trend the detrital materials were derived from older greenstone successions volcaniclastics and reworked precipitative beds silicified pseudomorphs of nahcolite crystals up to 40 cm in length occur in a 20 m thick bed in the upper portion of the lower unit the formation of this unit was initiated by deposition of immature terrigenous clastic sediments and followed by the precipitation of nahcolite from na hco3 brines in a closed or semi closed evaporitic basin bladed barite deposits occur mainly in the middle unit which was deposited in a sub aerial to shallow marine environment barite may have precipitated as a result of mixing of so42 rich seawater and ba2 rich hydrothermal fluids the mt goldsworthy sedimentary succession records an archean shallow to sub aerial sedimentary environment that probably developed in a continental margin setting

petrology and isotopic geochemistry of dawsonite bearing sandstones in hailaer basin northeastern china abstract the co2 gas reservoir sandstones in the hailaer basin contain abundant dawsonite and provide an ideal laboratory to study whether any genetic relationship exists between dawsonite and the modern gas phase of co2 the origins of dawsonite and co2 in these sandstones were studied by petrographic and isotopic analysis according to the paragenetic sequence of the sandstones dawsonite grew later than co2 charging at 110 85 ma the dawsonite 18o value is 7 4 smow and the calculated 18o values of the water present during dawsonite growth are from 11 4 to 9 2 smow this combined with the nahco3 dominated water linked to dawsonite growth suggests meteoric water being responsible for dawsonite growth the 13c values of gas phase co2 and the ratios of 3he 4he of the associated he suggest a mantle magmatic origin of co2 rich natural gas in hailaer basin dawsonite 13c values are 5 3 to 1 5 average 3 4 and the calculated 13c values of co2 gas in isotopic equilibrium with dawsonite are 11 4 to 7 3 these c isotopic values are ambiguous for the dawsonite c source from the geological context the timing of events together with formation water conditions for dawsonite growth dawsonite possibly grew in meteoric derived water atmospherically derived co2 maybe or at least the dominant c source for dawsonite it seems that there are few relationships between dawsonite and the modern gas phase of co2 in the hailaer basin

continental scale magmatic carbon dioxide seepage recorded by dawsonite in the bowen gunnedah sydney basin system eastern australia abstract dawsonite naalco3 oh 2 is widespread as a cement replacement and cavity filling in permo triassic sedimentary rocks of the bowen gunnedah sydney basin system eastern australia the origin of dawsonite in these rocks was studied by petrographic and stable isotope analysis dawsonite d13c pdb values range from 4 0 to 4 1 and are remarkably consistent throughout the bowen gunnedah sydney basin system these values indicate either a marine carbonate or magmatic source for carbon in the dawsonite a magmatic carbon source is considered more likely on the basis that 1 evidence of and the cause for widespread marine carbonate dissolution in the sedimentary successions are not apparen 2 dawsonite is widespread in both marine and nonmarine facies 3 the region has been the site of major igneous activity 4 other dawsonite deposits of similar carbon isotopic composition are linked to igneous activity and 5 magmatic co2 accumulations are known in parts of the bowen gunnedah sydney basin system the timing of igneous activity in the bowen basin constrains the timing of dawsonite formation in the bowen gunnedah sydney basin system to the tertiary consistent with textural relationships which indicate that dawsonite formed late during the burial history of the permo triassic sequences the distribution and interpreted origin of dawsonite implies magmatic co2 seepage in the bowen gunnedah sydney basin system on a continental scale

from shale oil to biogenic shale gas retracing organic inorganic interactions in the alum shale furongian lower ordovician in southern sweden methane rich gas occurs in the total organic carbon rich alum shale furongian to lower ordovician in southern sweden the lower part of the thermally immature alum shale was impregnated by bitumen locally generated by heating from magmatic intrusions from the carboniferous to the permian organic geochemical data indicate that the migrated bitumen is slightly degraded in the upper alum shale where methane is the main hydrocarbon in thermovaporization experiments centimeter size calcite crystals occur that contain fluid inclusions filled with oil gas or water the alum shale is thus considered a mixed shale oil biogenic shale gas play the presented working hypothesis to explain the biogenic methane occurrence considers that water soluble bitumen components of the alum shale were converted to methane a hydrogeochemical modeling approach allows the quantitative retracing of inorganic reactions triggered by oil degradation the modeling results reproduce the present day gas and mineralogical composition the conceptual model applied to explain the methane occurrence in the alum shale in southern sweden resembles the formation of biogenic methane in the antrim shale michigan basin united states in both models melting water after the pleistocene glaciation and modern meteoric water may have diluted the contents of total dissolved solids tds in basinal brines such pore waters with low tds contents create a subsurface aqueous environment favorable for microbes that have the potential to form biogenic methane today biogenic methane production rates with shale as the substrate using different hydrocarbon degrading microbial enrichment cultures in incubation experiments range from 10 to 620 nmol per gram and per day

berthierine formation in reservoir rocks from the siri oilfield danish north sea as result of fluid rock interactions part ii deciphering organic inorganic processes by hydrogeochemical modeling abstract berthierine formation reduces the permeability of the glauconitic reservoir sandstones in the siri oilfield danish north sea and is therefore a considerable production factor a new hydrogeochemical batch model that is based on thermodynamics of chemical equilibrium was developed to identify the processes which activated and controlled berthierine formation a good match has been achieved between the mineralogical alteration features observed in the siri field and the results of the batch modeling this match points to the validity of the modeling mechanisms for berthierine formation based on the identified mechanisms the modeling enables to quantify the mass conversion of hydrogeochemical processes in glauconite bearing and berthierine forming water rock gas systems the modeling results reveal that intense berthierine formation in the siri field resulted from in situ glauconite alteration within a more or less closed system due to hydrocarbon degradation driven water rock gas interactions this process is accompanied by formation of secondary sio2 s and potassium mica precipitation of iron bearing carbonates is prevented by berthierine formation although the glauconitic sandstones are rich in iron and carbonate species moreover such systems are brought to disequilibrium by the release of reducing and acidic agents originating from oil degradation and undergo long term diffusion dominated mass fluxes instead of advective mass fluxes

decollement folding as a mechanism for thrust ramp spacing the hypothesis that early formed decollement folds localize thrust ramps explaining the regular spacing of major thrust ramps observed in many mountain belts is examined the model for folding instability consists of a rigid basement a weak decollement zone and a stiff thrust sheet the model incorporates the effects of topographic stresses and syntectonic erosion and redeposition and uses a linearized power law rheology for the thrust sheet this approximation is valid for small angles of fold limb dip 15 and is appropriate for analysis of the wave length selection of folds at the onset of deformation the spacing of major thrust ramps and the stratigraphic thicknesses of the decollement zone and thrust sheet from the wyoming portion of the sevier fold and thrust belt are used to test the model the ratio of the fold dominant wavelength to thrust sheet thickness ld h2 increases with the ratio r of the viscosity of the stiff layer to that of the decollement zone and decreases with the power law stress exponent n2 the fold amplification factor increases with both n2 and r as the topographic decay ratio d increases ld h2 increases at fixed n2 and r acceptable models for the absaroka and darby thrust sheets have n2 3 only when r 1000 and significant erosion and redeposition of sediments accompany the folding of the thrust sheet d 103 does the required r fall below a reasonable limit thus a model in which decollement folding is accompanied by syntectonic erosion and redeposition precedes thrusting is consistent with the available observational constraints

controls on co2 fate and behavior in the gullfaks oil field norway how hydrogeochemical modeling can help decipher organic inorganic interactions oil degradation in the gullfaks field led to hydrogeochemical processes that caused high co2 partial pressure and a massive release of sodium into the formation water hydrogeochemical modeling of the inorganic equilibrium reactions of water rock gas interactions allows us to quantitatively analyze the pathways and consequences of these complex interconnected reactions this approach considers interactions among mineral assemblages anorthite albite k feldspar quartz kaolinite goethite calcite dolomite siderite dawsonite and nahcolite various aqueous solutions and a multicomponent fixed pressure gas phase co2 ch4 and h2 at 4496 psi 31 mpa reservoir pressure the modeling concept is based on the anoxic degradation of crude oil irreversible conversion of n alkanes to co2 ch4 h2 and acetic acid at oil water contacts these water soluble degradation products are the driving forces for inorganic reactions among mineral assemblages components dissolved in the formation water and a coexisting gas at equilibrium conditions the modeling results quantitatively reproduce the proven alteration of mineral assemblages in the reservoir triggered by oil degradation showing 1 nearly complete dissolution of plagioclase 2 stability of k feldspar 3 massive precipitation of kaolinite and to a lesser degree of ca mg fe carbonate and 4 observed uncommonly high co2 partial pressure 61 psi 0 42 mpa at maximum the evolving composition of coexisting formation water is strongly influenced by the uptake of carbonate carbon from oil degradation and sodium released from dissolving albitic plagioclase this causes supersaturation with regard to thermodynamically stable dawsonite the modeling results also indicate that nahcolite may form as a co2 sequestering sodium carbonate instead of dawsonite likely controlling co2 partial pressure

effect of spatial distribution of hormuz salt on deformation style in the zagros fold and thrust belt an analogue modelling approach scaled analogue models of thin skinned simultaneous shortening above adjacent viscous and frictional decollements simulate the effect of hormuz salt on the shortening in the zagros fold and thrust belt the models consisted of sand layers that partly overlay a viscous layer of silicone and were shortened from one end spatial distribution of the viscous decollement varied along strike and dip as occurs in part of the zagros fold and thrust belt in this belt phanerozoic sedimentary cover was shortened partly above the hormuz salt lying on the precambrian crystalline basement behaving as a basal viscous decollement model results display how the nature of the decollement affects the evolution of an orogenic belt using model results we explain the development of deflection zones and discuss strain partitioning formation of different topographic wedges and differential sedimentation along the zagros fold and thrust belt model results suggest the formation of a gentle taper consisting of both foreward and backward thrusts above a viscous decollement and a relatively steeper taper consisting only of forward vergent imbricates above a frictional decollement however in our models the steepest wedge with the highest topography formed where the viscous substrate had a limited extent with a transitional boundary pinch out perpendicular to the shortening direction shortening of this boundary led to development of frontal ramps associated with significant uplift of the area behind the deformation front

oilfield waters and sandstone diagenesis abstract the evolution of the organic geochemistry and carbonate alkalinity of oilfield waters is apparently regular and predictable this evolution can be typified by five generalizations 1 at or near 80 c there appears to be an exponential rise in the concentration of organic acid anions 2 the maximum concentration of organic acid anions occurs over approximately the 80 100 c temperature interval 3 the highest concentrations of difunctional acid anions are associated with the other organic species maxima 4 difunctional acid anions are the first to be decarboxylated typically at temperatures of 100 110 c 5 with increasing temperature 110 130 c monofunctional acid anions begin to become decarboxylated resulting in a fluid alkalinity dominated by bicarbonate dissolution experiments using artificial and natural oilfield waters demonstrate that mono and difunctional carboxylic acid anions and hydroxybenzoic acid anions present in both oilfield waters and the aqueous phase of hydrous pyrolysates are capable of greatly enhancing al si fe and ca concentrations in solutions from dissolution of minerals by organometallic complexation this enhancement of mineral solubility has been called upon to explain aluminosilicate dissolution porosity which is quantitatively important in many subsurface reservoirs certainly no other viable mechanism has been proposed to explain aluminum transport in the subsurface when integrated into basin models the regular evolution of organic and carbonate alkalinity in oilfield waters and the changing mineral stabilities that accompany that evolution help explain commonly observed diagenetic sequences in clastic systems

mineralogical and geochemical consequences of the long term presence of co2 in natural reservoirs an example from the springerville st johns field arizona and new mexico u s a abstract the springerville st johns co2 field in eastern arizona and western new mexico is one of more than a dozen gas fields developed within the colorado plateau and southern rocky mountain region extensive travertine caco3 deposits record a long history of co2 migration and leakage to the atmosphere the oldest travertine deposits may have formed during the initial filling of the co2 reservoir when groundwaters exsolved co2 upon reaching the surface the youngest travertine deposits are associated with springs on the floor of the little colorado river valley but travertine deposition appears to be insignificant today older deposits occur up to 325 m above the valley floor geologic relationships suggest travertine deposition began in the late pleistocene after volcanic activity ended at 0 3 ma most of the caco3 could have been derived from dissolution of the underlying limestones and dolomites interactions between the reservoir fluids and rocks were observed in core samples from one of the intervals that produced dry gas these reactions resulted in the dissolution of carbonate cements and detrital feldspars and the formation of dawsonite and kaolinite geochemical simulations suggest that the dawsonite could have been deposited when the co2 fugacity reached 20 bars and that the kaolinite formed as the co2 fugacity decreased corrosion of drill pipe by acidic waters and a pronounced hco3 anomaly above the co2 reservoir provide evidence of a continuing flux of co2 from depth co2 storage occurs primarily as dissolved carbonate species and as gas accumulations only a small percentage of the co2 was sequestered in secondary minerals

detachment folding in the central and eastern zagros fold belt iran salt mobility multiple detachments and late basement control abstract detachment folding has been studied on the basis of field and subsurface examples from the central and eastern zagros iran we discuss different aspects of detachment folding well illustrated in the studied area in particular we focus on salt mobility multiple decollements and late basement control salt mobility concerns the hormuz basal detachment and the gachsaran upper detachment for the latter it is shown that mobility results not only from folding related diapirism but also from early gravity driven migration from growing anticlines towards intervening synclines concentric folding between two detachment levels is directly observed in the izeh zone central zagros where it is shown that the wave length depends on the distance between the two active decollements and that the fold shape is a function of the level of erosion throughout the zagros detachment folds mainly developed during an initial thin skinned phase of deformation which was followed by the current thick skinned stage this succession is particularly well expressed in the eastern zagros where basement faults cut early detachment folds obliquely

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

hydrogen sulfide formation fate and behavior in anhydrite sealed carbonate gas reservoirs a three dimensional reactive mass transport modeling approach a novel hydrogeochemical modeling approach is developed to unravel thermochemical sulfate reduction tsr in hydrocarbon reservoirs our numerical model couples a web of interconnected hydrogeochemical reactions to three dimensional 3 d and reservoir wide diffusive mass transport our modeling approach simulates a semigeneric gas reservoir sealed by anhydrite the calculated diagenetic processes fit the observations in reservoirs affected by tsr formation of water precipitation of calcite metal di sulfides and elemental sulfur as replacements of dissolved anhydrite at the expense of ch4 g as well as formation of hydrogen sulfide h2s by varying input parameters the crucial factors controlling tsr have been identified our results highlight that reservoir wide diffusive mass transport is one prerequisite for tsr an increase in the rate constant of abiotic sulfate reduction asr and in diffusive mass fluxes as well as lack of precursor minerals for metal di sulfide precipitation can increase the souring intensity and accelerate h2s outgassing in contrast precipitation of elemental sulfur which is stable according to the chemical thermodynamics weakens h2s formation our modeling shows that tsr is complex and cannot be represented by the single reaction asr and by simple correlations between the rate constant of asr and the h2s gas content the application of 3 d reactive transport modeling presented here despite its semigeneric nature provides a good example of how such an approach can be used ahead of drilling our modeling helps to investigate tsr in time and space to quantify the mass conversion of all reactants involved within this web and to predict the souring level

petrological record of co 2 influx in the dongying sag bohai bay basin ne china abstract dawsonite occurs in sandstones of the fourth member of the shahejie formation dongying sag bohai bay basin northeastern china the paragenesis sequence formation temperatures carbon dioxide co2 and aqueous medium origin of dawsonite from the binnan area were studied to understand the formation of dawsonite as a possible mechanism for mineral trapping of co2 in carbon capture and storage ccs programs the petrological and geochemical characteristics of the dawsonite bearing sandstones were identified using polarizing microscope examination scanning electron microscope x ray fluorescence x ray diffraction and stable isotopic analyses the paragenesis sequence of the authigenic minerals are mainly quartz overgrowth early stage calcite a ferrocalcite dawsonite late stage calcite b ankerite siderite the carbon and oxygen isotope compositions of dawsonite reveal that 13c values of dawsonite range from 2 27 to 3 50 indicating inorganic co2 the calculated 13c values of co2 gas in isotopic equilibrium with dawsonite range from 7 2 to 1 6 suggesting that co2 originated mainly from degassing of mantle derived magmas and partly from thermal decomposition of carbonate rocks as supported by regional magmatic activities rifting and observation of carbonate during drilling in well bin76 the 18o values of dawsonite vary from 17 2 to 19 8 and the calculated 18o values of h2o in isotopic equilibrium with dawsonite range from 2 1 to 0 4 the mixed aqueous medium was mainly connate water influenced by magmatic activities and meteoric water influx during the formation of dawsonite according to oxygen isotope data the formation temperatures of dawsonite in the binnan area range from 77 c to 95 c which are consistent with the estimated paleo temperatures 79 c to 85 c indicating that the dawsonite formed at the late stage of the diagenetic phase

structure of the mountain front flexure along the anaran anticline in the pusht e kuh arc nw zagros iran insights from sand box models this is a contribution of the group of dynamics of the lithosphere gdl financed by a collaborative project between the institute of earth sciences jaume almera csic of barcelona spain and statoilhydro tehran and statoilhydro research centre with the partial support of project team consolider ingenio 2010 no csd 2006 00041

role of the kazerun fault zone in the formation and deformation of the zagros fold thrust belt iran 1 the kazerun fault is a n s trending fault zone which obliquely truncates the nw se trending zagros fold thrust belt this active fault zone is an ancient structural lineament which has controlled the structure sedimentation and subsidence of the central part of the zagros since the early cambrian and has had an influence on the formation of the hydrocarbon system of the belt the kazerun fault limited the distribution of the cambrian hormuz salt the major decollement horizon that separates the precambrian basement from the thick sedimentary cover to the west its later reactivation with other n s trending fault zones e g the izeh fault zone during the cretaceous resulted in major sedimentary thickness and facies variations along the belt this study presents a new interpretation for the evolution of the kazerun fault zone based on field evidence and a review of various published and unpublished data it is argued that at the surface the fault zone is delineated by four north south trending segments and that marked differences occur in the distribution of deformation on either side of the fault segments in the late tertiary during this time these segments acted as transfer faults lateral ramps linking different segments of the zagros deformation fronts

the 2006 march 25 fin earthquakes iran insights into the vertical extents of faulting in the zagros simply folded belt summary we investigate the depth of faulting and its connection with surface folding in the zagros simply folded belt of iran our focus is a sequence of earthquakes mw 5 7 5 5 5 2 5 0 4 9 that struck the fin region in the south eastern simply folded belt on 2006 march 25 modelling ground displacements measured with radar interferometry we find that either n or s dipping model reverse faults can reproduce the observed fringe patterns despite the uncertainty in fault orientation we can constrain the vertical extents of rupture to between a top depth of 5 6 km and a bottom depth of 9 10 km consistent with the 8 km centroid depth of the largest earthquake we suggest that the faulting ruptured the thick competent group of paleozoic and mesozoic conglomerates and platform carbonates which makes up the lower part of the sedimentary cover the rupture probably terminated within the precambrian hormuz salt at its base and the cretaceous gurpi marls at its top these mechanically weak layers act as barriers to rupture separating faulting within the competent group from deformation in the layers above and below the pattern of coseismic surface uplift is centred on the common limb of the fin syncline and guniz anticline but is oblique by 20 to the trend of these open symmetric whaleback folds and also overlaps a section of the fin syncline axis these observations suggest that locally surface folding is decoupled from the underlying reverse faulting although the fin syncline and guniz anticline are symmetric structures some other nearby folds show a strong asymmetry with steep or overturned southern limbs consistent with growth above n dipping reverse faults this suggests that the simply folded belt contains a combination of forced folds and detachment folds we also investigate the distribution of locally recorded aftershocks in the weeks following the main earthquakes most of these occurred at depths of 10 30 km with a particularly high concentration of events at 20 25 km these aftershocks therefore lie within the crystalline basement rather than the sedimentary cover and are vertically separated from the main rupture this study confirms earlier suggestions that earthquakes of mw 5 6 are capable of being generated within the thick competent group of paleozoic and mesozoic sediments as well as in the basement below the hormuz salt formation

the controls on the composition of biodegraded oils in the deep subsurface part ii geological controls on subsurface biodegradation fluxes and constraints on reservoir fluid property prediction the principal controls on the fluid properties of biodegraded oil systems have been determined by a combination of petroleum geochemistry numerical modeling of oil biodegradation in reservoirs and analysis of oil property data sets from a variety of geological settings petroleum biodegradation proceeds under anaerobic conditions in any reservoir that has a water leg and has not been heated to temperatures more than 80c in most reservoirs with low concentrations of aqueous sulfate methanogenic degradation is a primary mechanism of petroleum degradation whereas in waters containing abundant sulfate sulfate reduction and sulfide production may dominate net degradation of petroleum fractions in reservoirs is primarily controlled by the reservoir temperature the chemical compounds being degraded and relationships between the oil water contact owc area and oil volume the relative volumes of water leg to oil leg prior level of oil biodegradation and reservoir water salinity act as second order controls on the process typically degradation fluxes kilograms of petroleum destroyed per square meter of oil water contact area per year or kg petroleum m2 owc yr1 for fresh petroleum in clastic reservoirs are in the range of 103 104 kg petroleum m2 owc yr1 and increase with decreasing reservoir temperature from zero near 80c to a maximum flux at the owc of less than 103 kg petroleum m2 owc yr1 at a temperature less than 40c at very low reservoir temperatures and with severely degraded oils such as are seen in the near surface canadian tar sands at the present day the net degradation fluxes are much less than maximum values nutrient supply from the aquifer and adjacent shales mostly buffered by mineral dissolution probably provides the ultimate control on the range of degradation flux values oil compositional gradients and resulting oil viscosity variations are common on both reservoir thickness and field scales in biodegraded oil reservoirs and are a defining characteristic of heavy oil fields produced by crude oil biodegradation continuous vertical gradients in the oil columns document episodic degradation for many millions of years suggesting that the time scales of oil field degradation and petroleum charging are similar the flux temperature relationship we have derived coupled with typical reservoir charge histories defines the range of variation of fluid properties seen in many biodegraded oil provinces and identifies oil charge mixing of biodegraded and fresh oils and reservoir temperature history as the primary controls on fluid properties these flux temperature relationships are easily integrated into prospect charge modeling procedures sensitivity analyses show that the limiting factor in fluid property predictions using even this first level approach are ultimately constrained by the accuracy of current oil charge modeling estimates the absence today of any functional geochemical proxies for assessing oil residence time in oil fields and the substantial uncertainty in petroleum charging times estimated by forward basin modeling is a major obstacle to more accurate fluid property predictions that needs to be addressed