reflectance of dispersed vitrinite in palaeozoic rocks with and without cleavage implications for burial and thermal history modeling in the devonian of rursee area northern rhenish massif germany abstract vitrinite reflectance is used as coalification parameter in coals and as maturity and palaeotemperature indicator in sedimentary rocks in high grade diagenetic rocks i e rocks at the boundary between diagenesis and metamorphism vitrinites become increasingly anisotropic therefore it has been suggested to study maximum minimum reflectance instead of mean reflectance for rocks which reached this stage in the present study vitrinite reflectance data from a folded sequence of the northern rhenish massif germany are combined with microtectonic study of thin sections in samples in which both bedding and cleavage are present we show that vitrinites in different microtectonic domains cleavage domains and microlithons show significant differences in both maximum vitrinite reflectance and vitrinite reflectance anisotropy this behaviour is due to a strong partitioning of deformation in cleavage domains as compared to microlithons so that vitrinite reflectance is controlled by the thermal and deformation history accordingly estimation of maximum palaeotemperatures during burial should be based on vitrinite reflectance measurements in microlithons unaffected by deformation after maximum burial based on this finding burial and temperature history of the rursee area in the eastern rhenish massif is reconstructed numerical simulations indicate a maximum burial at the siegen ems boundary of about 5000 m and a maximum burial temperature of about 220 c

release fault a variety of cross fault in linked extensional fault systems in the sergipe alagoas basin ne brazil abstract two types of cross faults are herein recognized transfer faults and the newly termed release faults transfer faults form where cross faults connect distinct normal faults and horizontal displacements predominate over vertical ones in contrast release faults form where cross faults associated with individual normal faults die out within the hangingwall before connecting to other normal faults and have predominantly vertical displacements release faults are geometrically required to accommodate variable displacements along the strike of a normal fault thus they form to release the bending stresses in the hangingwall and do not cut normal fault planes nor detachment surfaces at depth release faults have maximum throws adjacent to normal faults and may be nearly perpendicular or obliquely oriented to the strike of the latter such geometry appears not to depend upon pre existing weaknesses but such variable orientation to normal faults is an inherent property of release faults release faults commonly appear as simple normal faults in seismic sections without implying extension along the strike of rift and basins three dimensional strain deformation occurs in the hangingwall only between the terminations of an individual normal fault but regionally release faulting is associated with plane strain deformation in linked extensional fault systems

the characteristics of cenozoic sedimentary basins in the north china platform abstract in the cenozoic a series of faulted downwarped basins developed in the north china platform the large depressions located in the eastern part of china are the north china depression and the northern jiangsu depression the depressions are comprised of a series of parallel grabens mainly single fault grabens and uplifts in the central part and along western and northwestern margins of the north china platform there is a series of smaller en echelon grabens these depressions and grabens formed during late cretaceous early paleogene and early neogene formation and development of the grabens was controlled by tensional normal faults characterized by steep dip in the upper parts and gentle dip in the lower parts of the fault planes the cenozoic sedimentary fill of the large depressions differs from the smaller grabens the large depressions are filled mainly by paralic lake sediments which are the most important oil producing beds in the cenozoic of the eastern part of china as sea water intermittently invaded the depressions many so called abnormal marine beds were deposited the sedimentary sequences were intruded by alkali basalts and tholeiites in contrast in the smaller grabens mainly lake river sediments were deposited the cenozoic paleoclimate record for the north china platform shows that a sub tropical warm humid climate prevailed in the paleogene followed by a warm dry climate in the neogene and by temperate cold dry to cold humid climate in the quaternary the tectonic evolution of the two large depressions can be subdivided into two stages 1 the faulting stage of late cretaceous to paleogene when series of parallel grabens and uplifts were formed and 2 the downwarping stage neogene to quaternary when two large depressions were formed the formation and evolution of the cenozoic depressions and grabens of the north china platform was influenced by extension and faulting of the crust resulting from uplift of the upper mantle

lower cretaceous lacustrine source rocks in northern gabon effect of organic facies and thermal maturity on crude oil quality abstract organic facies variation which is a key factor affecting the quality of hydrocarbon accumulations is characterized for the pre salt freshwater lacustrine source rocks in the interior basin and n komi rift areas in northern gabon by integrating geochemical and geological data the kissenda shales have 0 59 2 23 total organic carbon toc and hydrogen indices hi from 458 93 mghc goc pyrolysis of isolated kerogen and gas chromatography on rock extracts indicate that these samples are overall more waxy than those from the overlying melania shales which have 0 77 4 79 toc and hi from 896 212 in addition hopane sterane ratios and c30 4 methyl sterane indices increase systematically with depth it is proposed that the early cretaceous lacustrine system in northern gabon was initially oligotrophic and contained primarily bacteria and cyanobacteria with a small population of dinoflagellates and botryococcus as trophic level increased through time the food chain length increased eukaryotic organisms became more abundant and diversified steroids increased relative to hopanoids in the sediment and the preserved organic matter became less waxy burial history modeling shows that the onal 1 structure is charged primarily by waxy oils generated from the lower kissenda shales lower wax better quality oils are expected to the southwest where the kissenda shales are more mature and the less waxy melania shales also become effective source rocks thus variation in organic facies and thermal maturity in the cretaceous pre salt source rocks result in commercial production from the rabi field vs the subcommercial discovery in the onal 1 structure

40ar 39ar dating of the jurassic volcanic province of patagonia migrating magmatism related to gondwana break up and subduction abstract the mesozoic large igneous province lip of patagonia southern south america which is one of the largest silicic provinces on earth has been investigated by the 40ar 39ar method twenty seven ages considered as valid including twenty plateau ages show that the volcanic activity ranging from 187 to 144 ma occurred between and contemporaneously with the initial break up of gondwana starting with the karoo antarctic tasmanian kat flood basalt province in the east and a subduction in the west the data display a regular decreasing of ages from the ene 187 ma to the wsw 144 ma along about 650 km apparently related to the tectonic structure in half grabens oriented nnw sse the good fitting of this trend with the opening of the rocas verdes sarmiento marginal basin favors a space time evolution of this continental volcanism culminating towards the ssw in a continental disruption behind the magmatic arc the observed age progression of volcanism may be the result of the variations of the physical characteristics of the subduction the spreading and thermal effect of the kat plume may have an additional effect and also could account for the unusually large volume of magma

upper permian lacustrine oil shales southern junggar basin northwest china upper permian organic rich lacustrine mudstones oil shales that crop out in the southern junggar basin rank among the richest and thickest petroleum source rock intervals in the world with maximum toc values reaching 34 and rock eval pyrolytic yields s 2 up to 200 kg hc t rock lacustrine sedimentary facies define an overall transgressive regressive cycle of approximately 2000 m gross thickness which includes approximately 800 m of source rocks averaging 4 1 toc and 26 2 kg hc t rock basinal facies comprise silicic organic rich laminated lacustrine mudstones and interbedded siltstones organic matter contained in the mudstones ranges in composition from type i to type iii basinal facies were deposited in a deep oxygen deficient stratified lake lake margi facies consist of nonlaminated siliciclastic mudstones rippled dolomitic siltstones and sandstones and minor limestones maximum toc values are approximately 6 desiccation cracks are common in the marginal facies but evaporite minerals are rare or absent biomarker correlation parameters measured from rock extracts exhibit significant stratigraphic variability but strongly support the hypothesis that upper permian lacustrine oil shales charge the giant karamay field in the northwestern junggar basin karamay oils are characterized by high relative abundances of beta carotane this characteristic is restricted to desiccated facies in the outcrop sections however we therefore propose that an abundance of beta carotane indicates elevated environmental salinities during deposition of the oil shales orographic precipitation induced by a paleo tian shan range may have provided fresh water to the southern areas of the basin while more evaporative conditions prevailed to the north outcrop oil seeps confirm that the outcrop sections have attained sufficient thermal maturity to generate oil t max values range from 431 to 451 degrees c vitrinite reflectances range from 0 73 to 0 88 and sterane isomerization ratios range from 0 30 to 0 48 20s 20s 20r matoil registered trademark computer modeling of burial history and thermal maturity of the outcrop sections indicates that approximately 4 5 km of triassic jurassic cover was needed to bring the oil shales to their current maturity the major phase of hydrocarbon generation in this area appears to have preceded the creation of traps by neogene thrusting which may account for the lack of discoveries in the southern junggar basin most of the oil discovered so far is trapped in structures which originated duri g the late paleozoic or mesozoic

pacific subduction coeval with the karoo mantle plume the early jurasssic subcordilleran belt of northwestern patagonia the early mesozoic magmatism of southwestern gondwana is reviewed in the light of new u pb shrimp zircon ages 181 2 ma 181 3 ma 185 2 ma and 182 2 ma that establish an early jurassic age for the granites of the subcordilleran plutonic belt in northwestern argentine patagonia new geochemical and isotopic data confirm that this belt represents an early subduction related magmatic arc along the proto pacific margin of gondwana thus subduction was synchronous with the initial phase of chon aike rhyolite volcanism ascribed to the thermal effects of the karoo mantle plume and heralding rifting of this part of the supercontinent overall there is clear evidence that successive episodes of calc alkaline arc magmatism from late triassic times until establishment of the andean patagonian batholith in the late jurassic involved westerly migration and clockwise rotation of the arc this indicates a changing geodynamic regime during gondwana break up and suggests differential rollback of the subducted slab with accretion of new crustal material and or asymmetrical scissor like opening of back arc basins this almost certainly entailed dextral displacement of continental domains in patagonia

origin of epithermal ag au cu pb zn mineralization in guanajuato mexico the guanajuato epithermal district is one of the largest silver producers in mexico mineralization occurs along three main vein systems trending dominantly northwest southeast the central veta madre the la luz system to the northwest and the sierra system to the east mineralization consists dominantly of silver sulfides and sulfosalts base metal sulfides mostly chalcopyrite galena sphalerite and pyrite and electrum there is a broad zonation of metal distribution with up to 10 cu pb zn in the deeper mines along the northern and central portions of the veta madre ore occurs in banded veins and breccias and as stockworks with gangue composed dominantly of quartz and calcite host rocks are mesozoic sedimentary and intrusive igneous rocks and tertiary volcanic rocks most fluid inclusion homogenization temperatures are between 200 and 300 c with salinities below 4 wt nacl equivalent fluid temperature and salinity decreased with time from 290 to 240 c and from 2 5 to 1 1 wt nacl equivalent relatively constant fluid inclusion liquid to vapor ratios and a trend of decreasing salinity with decreasing temperature and with increasing time suggest dilution of the hydrothermal solutions however evidence of boiling such as quartz and calcite textures and the presence of adularia is noted along the veta madre particularly at higher elevations fluid inclusion and mineralogical evidence for boiling of metal bearing solutions is found in gold rich portions of the eastern sierra system this part of the system is interpreted as the least eroded part of the district oxygen carbon and sulfur isotope analysis of host rocks ore and gangue minerals and fluid inclusion contents indicate a hydrothermal fluid with an initial magmatic component that mixed over time with infiltrating meteoric water and underwent exchange with host rocks mineral deposition was a result of decreasing activities of sulfur and oxygen decreasing temperature increasing ph and in places boiling

drill hole design for dilational ore shoot targets in fault fill veins ore along fault fill veins typically has an uneven distribution with semilinear high grade ore shoots separated by lower grade zones or barren fault segments therefore a successful drill campaign must be optimally designed for intersection of ore shoots and not the intervening zones however the typical drill hole design for fault fill veins which targets the vein directly downdip from the highest grade outcrops will miss most ore shoots that rake less than 80 to 90 in the structure dilational ore shoots form along pre or synmineralization faults in localized elongated structural openings perpendicular to the slip vector the rake of such ore shoots in fault fill veins can be predicted using models of stress controlled fault fracture kinematics equations are presented that use fault kinematic data to design drill holes for optimal success in targeting such ore shoots the equations calculate the universal transverse mercator utm coordinates of the drill target given fault fill vein orientation slip vector rake usually determined from slickenlines vertical depth to intersect the ore shoot and the utm coordinates of geochemically anomalous outcrops along the fault vein although the method assumes that fault kinematics control ore shoot orientation and is not applicable to all fault vein ore shoots such as those formed at intersections of faults or shear zones with permeable beds other faults or dikes the method increases the probability of success for drill testing ore shoots through optimal drill hole design

organic geochemistry and petrography of lower cretaceous wealden black shales of the lower saxony basin the transition from lacustrine oil shales to gas shales abstract ninety seven wealden black shale samples from three wells in the lower saxony basin have been studied by organic geochemical and organic petrographical methods to determine their maturity organic facies and depositional environment the maturities of the three wells range from early mature ex a late to postmature ex c to overmature ex b as determined by vitrinite reflectance measurements diamondoid ratios and other geochemical maturity parameters ex c and ex b show distinct petrographic features related to oil generation and migration in particular the occurrence of dispersed solid bitumen replacing initial type i kerogen suggests a formerly active petroleum system structural and textural differences between early mature alginites and solid bitumen in postmature to overmature samples show an alteration of the pore system with increasing maturity a freshwater depositional environment is indicated by widespread occurrence of botryococcus algae and other small alginite particles predominating in the immature well these alginites are absent in the more mature gas shales of wells ex c and ex b geochemical evidence of algae and phytoplankton in general is provided by numerous biomarker parameters while the occurrence of carotane in some samples indicates events of increased salinity although no hypersaline conditions are inferred due to very low gammacerane indices increased amounts of vitrinite and inertinite in samples of ex b suggest locally significant terrigenous input of organic matter for some periods during wealden shale deposition high sulfur organic carbon ratios provide evidence for sulfate rich waters and partly anoxic bottom water conditions while the lower mature lacustrine source rocks generate paraffinic waxy oils gas and condensates are produced at post mature stages furthermore maturity distribution maps from 3d numerical petroleum systems modeling reveal substantial differences in respect to petroleum generation

geochemical investigation of oils and source rocks from qianjiang depression of jianghan basin a terrigenous saline basin china abstract six oils and seven suspected source rocks from the jianghan saline basin in the central eastern part of china have been examined using a variety of geochemical techniques the results from this study show that oils from the third and fourth sections of the qianjiang formation eocene are derived from similar source materials but have a different source from the oils of xingouzui formation eocene in the same basin the oils of the xingouzui formation eocene are more mature and probably have a greater input of terrigenous source material and in all probability have migrated greater distances than the qianjiang oils oils from these sections are derived from an environment characterized as being extremely anoxic strongly reducing and highly saline the suspected source rocks examined in the study were from the qianjiang formation and were generally mature except for the shallowest sample the biomarker distributions in the suspected source rocks examined from the qianjiang formation were very different from those of the oils present in the same sections it is proposed that oils from the qianjiang formation have sources in addition to or exclusive of the suspected source rocks examined in this study

the multiple inverse method a new technique to separate stresses from heterogeneous fault slip data abstract a new inverse technique is presented here to separate stresses from heterogeneous fault slip data without a priori information on the stresses or on the classification of faults according to the stresses four parameters are determined by the inversion one for the shape of the stress ellipsoid and three for the direction of the stress axes accordingly the inversion is equivalent to the projection of the fault slip data to a point in four dimensional parameter space the data are divided into k element subsets to which the inverse technique is applied where k 4 or 5 is the optimal choice for the stability of solutions and for the reduction of computation significant solutions are identified as clusters in parameter space the technique is demonstrated first by simulated fault slip data as an example field data obtained from miocene fore arc sediments in western japan were processed by the method

petroleum systems in the jiangling dangyang area jianghan basin china source related geochemical data define at least four petroleum systems in the jiangling dangyang area of the jianghan basin eocene paleocene anoxic evaporitic lacustrine source rocks generated most of the crude oils in the area eocene qianjiang rock from the sha 13 well 1322 m contains fast reacting sulfur rich type is organic matter and its extract is most similar to the sha 13 oil sand bitumen qianjiang reservoir lower eocene paleocene xingouzhui rocks from the xin 73 well 842 and 862 m contain slow reacting low sulfur type i organic matter and their extracts are most similar to the sha 26 oil sand bitumen eocene jinsha reservoir and the ling 2 sha 24 and tuo 3 oils xingouzhui reservoirs two unidentified middle triassic or older marine carbonate evaporite source rocks or different facies of the same source rock generated the daxiakou oil triassic jialingjiang formation outcrop xingshan county and the moderately biodegraded tianwan seep oil permian changxing outcrop chengxi county respectively one or more unidentified marine source rocks which could include the lower permian qixia or the upper sinian doushantuo formations generated the miaoshi and yanmenkuo seep oils permian qixia outcrops the jingshan seep oil ordovician baota outcrop probably is related to these oils but could represent another petroleum system different kinetics for hydrocarbon generation among eocene qianjiang and lower eocene paleocene xingouzhui formation source rocks and chemical differences among the related oils are caused by organic facies variations high salinity and low eh enhanced the preservation of oil prone organic matter in these lacustrine settings and facilitated incorporation of sulfur into the organic matter anoxia and the unusual presence of abundant sulfate as gypsum resulted in the microbial reduction of sulfate to sulfide and incorporation of this sulfur into the kerogen for example biomarkers show that source rock in the sha 13 well 1322 m was deposited under more saline lower eh conditions than that in the ling 80 well 1808 m although both are from the qianjiang formation the sha 13 rock sample is more organic rich 6 62 vs 1 27 wt toc and has a higher hydrogen index 794 vs 501 mg hc g toc and faster reaction kinetics than the ling 80 sample kerogen from the sha 13 sample is type is because it has a high hydrogen index and an atomic s c ratio 0 074 in the range of sulfur rich fast reacting kerogens of the monterey formation s c 0 040 organic rich lower jurassic coaly rocks from outcrops at daxiakou contain immature to mature gas prone organic matter that is not related to any oils in the study several organic rich upper sinian to permian samples could have been source rocks in the past but are now highly mature based on high tmax 464 540 c and estimated vitrinite reflectance ro values mass balance calculations were used to estimate the original toc toc c in these samples prior to maturation these samples could not be correlated with the oils using biomarkers because of high maturities and low extract yields however stable carbon isotope type curves suggest that the miaoshi yanmenkuo permian qixia formation and the jingshan ordovician baota formation seep oils originated from source rocks in the lower permian qixia 3 00 wt toc or upper sinian doushantuo formations 5 96 wt toc lack of triaromatic dinosteroids in the miaoshi and yanmenkuo seep oils supports but does not prove a permian source rock very negative stable carbon isotope ratios for kerogens from the lower cambrian shuijintuo formation 33 5 to 33 6 8 85 16 64 wt toc show that they are not related to any of the analyzed oils

un coupled thrust belt foreland deformation in the northern patagonian andes new insights from the esquel gastre sector 41 30 43 s the patagonian andes represent a unique natural laboratory to study surface deformation in relation to deep slab dynamics in the sector comprised between latitudes 41 30 and 43 s new apatite u th he ages indicate a markedly different unroofing pattern between the broken foreland area characterized by late cretaceous to paleogene exhumation and the adjacent andean sector to the west which is dominated by miocene pliocene exhumation these unroofing stages can be confidently ascribed to inversion tectonics involving reverse fault related uplift and concomitant erosion late cretaceous paleogene shortening and exhumation are well known to have affected also the thrust belt sector of the study area during a prolonged stage of flat slab subduction therefore the different ages of near surface unroofing documented in this study suggest coupling of the deformation between the thrust belt and its foreland during periods of flat slab subduction e g during late cretaceous paleogene times and dominant uncoupling during periods of steep slab subduction and rollback even when these are associated with high convergence rates i e 4 cm year as those documented in miocene times for the patagonian andes

mesozoic rifting in the basque cantabrian basin spain inherited faults transversal structures and stress perturbation terra nova 24 70 76 2012 abstract in the basque cantabrian basin northern iberian margin inherited wnw ese striking faults were reactivated during the mesozoic extensional stage associated with the opening of the bay of biscay syn rift structures in the area include different sets apparently indicating multiple extensional stages in particular abundant ne sw striking extensional elements have been interpreted in the past as having developed during a late rifting left lateral transtensional stage however the development of these structures also fits well with an analytical model of ridge perpendicular extension along strike stretching imposed by displacement variations along inherited faults locally produced an additional stress field oriented obliquely to the regional one this caused rotation of the local minimum stress and development of anomalously oriented transversal structures a single extensional stage is thus inferred during mesozoic rifting with a stretching direction oriented approximately perpendicular to the trend of the bay of biscay oceanic ridge

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

shale oil potential and thermal maturity of the lower toarcian posidonia shale in nw europe a suite of drilling cores and outcrop samples of the lower toarcian posidonia shale ps were collected from multiple locations including the swabian alb and franconian alb of southwest germany runswick bay of uk and loon op zand well loz 1 of the west netherlands basin in order to assess the thermal maturity and quantify the petroleum generation potential of the rocks elemental analysis rock eval pyrolysis organic petrographic investigations and molecular hydrocarbon analyses were performed available literature data of the posidonia shale from luxembourg and northwest germany were used for comparison in the discussion the lower toarcian shale is more carbonate rich about 30 on average in sw germany nw germany and luxembourg and is instead more silicate rich in uk and nl with carbonate contents of about 15 on average this coincides with the relative distances of the depositional settings to the clastic source areas on the continents during the early jurassic however hi values are similar approx 500 700 mg hc g toc on average at all sampling localities exhibiting typical type ii kerogen with excellent hydrocarbon generation potential differences in relative abundance of terrigenous organic matter input are deduced from molecular indicators rock eval data and organic petrography the highest abundance of terrigenous organic matter is evident for runswick bay uk samples from outcrops of the lower toarcian shale from runswick bay uk have reached the early stage of the oil window with quite uniform t max values 425 438 c avg 433 c and a narrow range of pi production index values 0 10 0 19 substantiated by mature fluorescing characteristics of telalginite and lamalginite and vitrinite reflectance values of 0 6 0 7 wider ranges of t max values 421 443 c avg 427 c vitrinite reflectance 0 4 0 8 and production indices 0 06 0 29 suggest more variable thermal maturation ranging from immature to almost peak oil generation at the loz 1 well nl although only some intervals indicate advanced thermal maturity there in contrast the lower toarcian marlstones from the swabian and franconian alb of sw germany are clearly immature similar to the samples from luxembourg in nw germany the posidonia shale covers a wide spectrum of maturity ranging from immature to overmature source potential index spi indicates the highest value in the loz 1 nl followed by wickensen nw germany and esch sur alzette lu mainly due to differences in thickness of the studied sections the lowest value was observed in sw germany the lower toarcian jet rock in runswick bay uk is assumed to have a high shale oil potential because of its advanced thermal maturity although its spi is not high due to the limited thickness of the section studied the ps in sw germany has low shale oil potential due to low thermal maturity and limited thickness 2015 elsevier b v

andean flat slab subduction through time the analysis of magmatic distribution basin formation tectonic evolution and structural styles of different segments of the andes shows that most of the andes have experienced a stage of flat subduction evidence is presented here for a wide range of regions throughout the andes including the three present flat slab segments pampean peruvian bucaramanga three incipient flat slab segments carnegie guanacos tehuantepec three older and no longer active cenozoic flat slab segments altiplano puna payenia and an inferred palaeozoic flatslab segment early permian san rafael based on the present characteristics of the pampean flat slab combined with the peruvian and bucaramanga segments a pattern of geological processes can be attributed to slab shallowing and steepening this pattern permits recognition of other older cenozoic subhorizontal subduction zones throughout the andes based on crustal thickness two different settings of slab steepening are proposed slab steepening under thick crust leads to delamination basaltic underplating lower crustal melting extension and widespread rhyolitic volcanism as seen in the caldera formation and huge ignimbritic fields of the altiplano and puna segments on the other hand when steepening affects thin crust extension and extensive within plate basaltic flows reach the surface forming large volcanic provinces such as payenia in the southern andes this last case has very limited crustal melt along the axial part of the andean roots which shows incipient delamination based on these cases a palaeozoic flat slab is proposed with its subsequent steepening and widespread rhyolitic volcanism the geological evolution of the andes indicates that shallowing and steepening of the subduction zone are thus frequent processes which can be recognized throughout the entire system

rifted margin source rock deposition a carbon isotope and biomarker study of a west african lower cretaceous lacustrine section lower cretaceous passive margin sections penetrated in wells peripheral to the deep basinal development of pre salt sediments of the liawenda ponta vermelha troughs in the lower congo coastal basin revealed sustained source potential kerogen type kinetic ea a and carbon isotopic data plus rock extract biomarker signatures confirmed large systematic organofacies variations within these rift phase sediments an inverse correlation between 25 28 30 trisnorhopane and gammacerane abundances suggested three major depositional regimes reflecting salinity and water depth control 13c depleted basal sediments showing strong gammacerane 4 methyl sterane signatures were segregated by a major isotopic excursion this event represented the transition between saline playa lake to deeper water stratified conditions supporting a high level of anoxia for these intermediate sediments sterane and tricyclic diterpane abundances plus sterane hopane ratios had marine connotations and could be interpreted as the result of intermittent marine incursions fore shadowing irreversible oceanic ingression a resurgence of gammacerane abundance in the uppermost sediments typified littoral shallow marine depositional conditions recognition of a possible non ubiquity in lacustrine depositional conditions during the opening of a rifted margin provides further insight into the complexity and attendant controls on hydrocarbon generation in such habitats

kinetic study of marine and lacustrine shale grains using rock eval pyrolysis implications to hydrocarbon generation retention and expulsion abstract the kinetic parameters of marine and lacustrine shale grains 4 mm were retrieved by using rock eval pyrolysis in comparison with finely ground powder

the character and origin of lacustrine source rocks in the lower cretaceous synrift section congo basin west africa lower cretaceous synrift lacustrine shales from the congo basin west africa have been analyzed with sedimentological and geochemical techniques to characterize source rock quality and identify triggers for deposition of intervals richest in organic carbon the sequence includes a lower active rift section deposited during active faulting and subsidence overlain by an upper late rift section deposited during reduced faulting and subsidence total organic carbon toc averages 2 3 wt throughout the active rift siliciclastic shale section 6 in marls in the lower part of the late rift section and 1 2 in deltaic shales in the upper part of the late rift section organic matter consists of mixed types i and iii kerogen in the active rift shales pure type i kerogen in the late rift marls and a type i and iii mixture in the late rift deltaic shales redox proxies indicate that the deep lake was relatively reducing throughout deposition of the active rift and lower late rift sections therefore enhanced anoxia did not trigger deposition of the richest source rocks decreased sedimentation rates in the late rift do not account for the full increase in toc nor the shift on organic matter type the richest source rocks are associated with high rates of organic productivity and chemical sedimentation indicating that flux of dissolved components to the rift lake including nutrients for algae growth was critical we propose that reduced topography associated with the late rift was necessary for efficient cycling of plant derived carbon into soil carbonate and ultimately the rift lake and for enhancing chemical weathering and nutrient flux

peculiarities of salt lake sediments as potential source rocks in china abstract hypersaline lake sediments are widely distributed in china and can be good sources for petroleum the palaeogene sediments of the jianghan basin in eastern china are a typical example composed of salt lake evaporite clastic facies in fault subsided basins their organic matter is variable but is dominated by type ii kerogen the biological marker characteristics of core extracts and oils from the jianghan basin include i low oep values for n alkanes and occasionally an even odd predominance ii a high concentration of phytane iii a relatively high gammacerane 17 h 21 h hopane ratio and iv abundant mainly nickel porphyrins sample guang 33 k 33 is typical of the immature oils found in the jianghan basin geological and geochemical data both indicate that it was generated from source rocks in the maturity range r 0 0 45 0 55 its characteristics are similar to those of immature source rocks with high concentrations of phytane steranes triterpanes and nickel porphyrins and for an oil extremely low values for molecular parameters of maturity such as c 29 20s 20s 20r 14 h 17 h steranes c 32 22s 22s 22r 17 h 21 h hopanes and dpep dpep etio porphyrins

seismic interpretation and structural restoration of the heligoland glaciotectonic thrust fault complex implications for multiple deformation during pre elsterian to warthian ice advances into the southern north sea basin abstract despite a long history of research the locations of former ice margins in the north sea basin are still uncertain in this study we present new palaeogeographic reconstructions of pre elsterian and warthian ice margins in the southeastern north sea basin which were previously unknown the reconstructions are based on the integration of palaeo ice flow data derived from glaciotectonic thrusts tunnel valleys and mega scale glacial lineations we focus on a huge glaciotectonic thrust complex located about 10 km north of heligoland and 50 km west of the north frisian coast of schleswig holstein northern germany multi channel high resolution 2d seismic reflection data show a thrust fault complex in the upper 300 ms twt ca 240 m of seismic data this thrust fault complex consists of mainly neogene delta sediments covers an area of 350 km2 and forms part of a large belt of glaciotectonic complexes that stretches from offshore denmark via northern germany to poland the deformation front of the heligoland glaciotectonic complex trends approximately nne ssw the total length of the glaciotectonic thrust complex is approximately 15 km the thrust faults share a common detachment surface located at a depth of 250 300 ms twt 200 240 m below sea level the detachment surface most probably formed at a pronounced rheological boundary between upper miocene fine grained pro delta deposits and coarser grained delta front deposits although we cannot rule out that deep permafrost in the glacier foreland played a role for the location of this detachment surface restored cross sections reveal the shortening of the complex along the detachment to have been on average 23 ranging from ca 16 50 the determined ice movement direction from east southeast to southeast suggests deformation by an ice advance from the baltic region the chronospatial relationship of the thrust fault complex and adjacent northwest southeast to northeast southwest trending elsterian tunnel valleys implies a pre elsterian mis 16 age of the glaciotectonic complex however the age of these elsterian tunnel valleys is poorly constrained and the glaciotectonic complex of heligoland may also have been formed during an early elsterian ice advance into the southeastern north sea basin the glaciotectonic complex underwent further shortening and the elsterian tunnel valley fills that were incised into the glaciotectonic complex were partly deformed during the saalian drenthe and warthe 1 ice advances

structural localization and origin of compartmentalized fluid flow comstock lode virginia city nevada bonanza grade orebodies in epithermal style mineral deposits characteristically occur as discrete zones within spatially more extensive fault and or fracture systems empirically the segregation of such systems into compartments of higher and lower permeability appears to be a key process necessary for high grade ore formation and most commonly it is such concentrations of metals that make an epithermal vein district world class in the world class silver and gold producing comstock mining district nevada several lines of evidence lead to the conclusion that the comstock lode is localized in an extensional stepover between right lateral fault zones this evidence includes fault geometries kinematic indicators of slip the hydraulic connectivity of faults as demonstrated by veins and dikes along faults and the opening of a normal fault bounded asymmetric basin between two parallel and overlapping northwest striking lateral to lateral oblique slip fault zones during basin opening thick generally subeconomic banded quartz adularia veins were deposited in the normal fault zone the comstock fault and along one of the bounding lateral fault zones the silver city fault as deformation continued the intrusion of dikes and small plugs into the hanging wall of the comstock fault zone may have impeded the ability of the stepover to accommodate displacement on the bounding strike slip faults through extension within the stepover a transient period of transpressional deformation of the comstock fault zone ensued and the early stage veins were deformed through boudinaging and hydraulic fragmentation fault motion inversion and high and low angle axial rotations of segments of the fault planes and some fault bounded wedges this deformation led to the formation of spatially restricted compartments of high vertical permeability and hydraulic connectivity and low lateral hydraulic connectivity bonanza orebodies were formed in the compartmentalized zones of high permeability and hydraulic connectivity as heat flow and related hydrothermal activity waned along the comstock fault zone extension was reactivated in the stepover along the occidental zone of normal faults east of the comstock fault zone volcanic and related intrusive activity in this part of the stepover led to a new episode of hydrothermal activity and formation of the occidental lodes

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

polyphase thermal evolution in the infra cambrian ara group south oman salt basin as deduced by maturity of solid reservoir bitumen petrographic and organic geochemical analyses on solid reservoir bitumen from the late precambrian to early cambrian ara group indicate polyphase thermal evolution in the south oman salt basin sosb the ara group constitutes a complex petroleum system in the deep subsurface 3 5 km of interior oman salt diapirs encase isolated partly highly overpressured carbonate bodies intra salt stringers which represent a predominantly self charging hydrocarbon system a large number of stringer cores show that reservoir quality is decreased by the presence of solid reservoir bitumen by using different microscopy techniques this solid reservoir bitumen has been identified within pores pore throats and microfractures of the carbonates solid bitumen reflectance measurements brr were converted to vitrinite reflectance vrr using a new improved calibration vitrinite reflectance geothermometry shows that maximum paleo temperatures have a highly heterogeneous distribution paleo temperatures of 380 c were obtained from coke like solid reservoir bitumen which most likely formed from thermal cracking of oil in our model this process is related to hydrothermal fluids deriving from deeper pre salt strata of the sosb which entered the intra salt carbonate stringers during times of basement tectonic activity via hydrofractures this caused the formation of high maturities pyrobitumens in close vicinity to the fractures and precipitation of migrabitumens with increasing distance to the ht source which is supported by the geochemical composition of the solid reservoir bitumens the influx of these fluids into the carbonate stringers is considered to represent a major contribution to their strong overpressures 2007 elsevier ltd all rights reserved

patterns of organic carbon enrichment in a lacustrine system across the k t boundary insight from a multi proxy analysis of the yacoraite formation salta rift basin argentina abstract in this study an integrated approach was applied using available sedimentary geochronology geochemical and isotopic datasets to better understand the complex interactions between production destruction and dilution processes that characterize the organic rich sediments dynamic across the k t boundary in a lacustrine system this approach was tested here on the late cretaceous to early cenozoic yacoraite formation a typical lacustrine source rock from the salta rift basin nw argentina the yacoraite formation corresponds to a mixed carbonate siliciclastic lacustrine sedimentary system deposited during the sag phase post rift we demonstrated here that new ashes u pb dating tie the k t boundary during the deposition of the yacoraite formation the yacoraite formation recorded major climate changes that can be documented in terms of catchment dynamic erosion processes carbonate accumulation trends lacustrine dynamic and source rock quality the pattern of organic carbon enrichment in the yacoraite formation illustrates how a biological pump came across a major climatic change the background organic matter correspond to type i dominated by algal growth mean hi 600 800 mghc gtoc toc0 1 2 wt the k t boundary was the climax of a climate change initiated ca 0 3 myr before and induced a major change in the catchment weathering processes which temporally corresponds to the accumulation of poor quality source rock intervals toc0 0 2 wt and hi

artificial thermal maturation of source rocks at different thermal maturity levels application to the triassic montney and doig formations in the western canada sedimentary basin abstract artificial thermal maturation of petroleum source rocks is widely performed by either open or closed system pyrolysis these experiments are performed usually on immature source rock or isolated kerogen samples to quantify petroleum generation potential and to calculate kinetic parameters here we characterize a maturation series from the triassic montney and doig formations in the western canada sedimentary basin wcsb in order to investigate the evolution of the source rock properties and their corresponding kerogen kinetic parameters as a function of the thermal maturity organic petrography determined the thermal maturity and the spatial distribution of organic matter particles rock eval shale play analyses were then applied to assess the presence of both free and sorbed hydrocarbons still contained in the sample as well as the hydrocarbon generation potential based on vitrinite reflectance values three kerogen samples from the doig formation and one kerogen sample from the montney formation at different thermal maturity levels were selected for analysis of bulk kinetic parameters e g activation energy distribution frequency factor using programmed open system pyrolysis additionally we evaluated the type of hydrocarbons and determined the molecular composition of organic compounds that comprise the first two rock eval peaks sh0 and sh1 obtained during the improved thermovaporization td gc ms fid analyses were carried out on rock samples sequentially from 100 c to 200 c and then from 200 c to 350 c in order to characterize the composition of hydrocarbons represented by each rock eval shale play peak free and sorbed low to medium molecular weight aliphatic and aromatic hydrocarbons 20 are the main hydrocarbon components released in the temperature range corresponding to the rock eval shale play sh0 parameter medium and high molecular weight hydrocarbons c 10 c 30 aromatics and saturates are predominant components thermally released in the temperature range corresponding to the rock eval shale play sh1 parameter results show both an increasing activation energy and loss of petroleum generation potential as thermal degradation proceeds the shale play method has been developed to better discriminate the generated fluids sh0 sh1 from the residual kerogen sh2 providing a more accurate rock eval t max sh0 and sh1 parameters also offer a practical way for an early estimate of oil in place

elastic stress control on the pattern of tensile fracturing around a small fault network at nash point uk abstract complex trajectories of fault related opening mode fractures at nash point in south wales uk are consistent with elastic stress fields computed for the observed fault network subject to north south compression the linear elasticity theory is used to calculate local stress increments produced by slip on the fault network faults are assumed to be free of shear stress and to slip in response to some remote stress load brittle failure of rock within this stress field is determined according to a combined griffith coulomb criterion discrete fracture networks are simulated according to simple growth rules where fractures initiate according to the state of brittle failure and propagate along a surface normal to the direction of most tensile local stress results demonstrate the dominant opening mode fracture were caused by a uniform body force e g unloading and are just locally perturbed by the pre existing fault network fault heights of 2 3 times the mean fault block width and regional contraction along an azimuth of 180 10 are required to reproduce the observed fracture pattern independent kinematic analysis of nearby faults yield estimates of the azimuth of regional contraction of 170 180 some features in the observed fracture pattern are not well reproduced but these are small scale and related to small scale irregularities on the fault planes

evaluation of the petroleum composition and quality with increasing thermal maturity as simulated by hydrous pyrolysis a case study using a brazilian source rock with type i kerogen abstract hydrous pyrolysis hp experiments were used to investigate the petroleum composition and quality of petroleum generated from a brazilian lacustrine source rock containing type i kerogen with increasing thermal maturity the tested sample was of aptian age from the araripe basin ne brazil the temperatures 280 360 c and times 12 132 h employed in the experiments simulated petroleum generation and expulsion i e oil window prior to secondary gas generation from the cracking of oil results show that similar to other oil prone source rocks kerogen initially decomposes in part to a polar rich bitumen which decomposes in part to hydrocarbon rich oil these two overall reactions overlap with one another and have been recognized in oil shale retorting and natural petroleum generation during bitumen decomposition to oil some of the bitumen is converted to pyrobitumen which results in an increase in the apparent kerogen i e insoluble carbon content with increasing maturation the petroleum composition and its quality i e api gravity gas oil ratio c 15 fractions alkane distribution and sulfur content are affected by thermal maturation within the oil window api gravity c 15 fractions and gas oil ratios generated by hp are similar to those of natural petroleum considered to be sourced from similar brazilian lacustrine source rocks with type i kerogen of lower cretaceous age api gravity of the hp expelled oils shows a complex relationship with increasing thermal maturation that is most influenced by the expulsion of asphaltenes c 15 fractions i e saturates aromatics resins and asphaltenes show that expelled oils and bitumen are compositionally separate organic phases with no overlap in composition gas oil ratios gor initially decrease from 508 131 m 3 m 3 during bitumen generation and remain essentially constant 81 84 m 3 m 3 to the end of oil generation this constancy in gor is different from the continuous increase through the oil window observed in anhydrous pyrolysis experiments alkane distributions of the hp expelled oils are similar to those of natural crude oils considered to be sourced from similar brazilian lacustrine source rocks with type i kerogen of lower cretaceous age isoprenoid and n alkane ratios i e pristane n c 17 and phytane n c 18 decrease with increasing thermal maturity as observed in natural crude oils pristane phytane ratios remain constant with increasing thermal maturity through the oil window with ratios being slightly higher in the expelled oils relative to those in the bitumen generated hydrocarbon gases are similar to natural gases associated with crude oils considered to be sourced from similar brazilian lacustrine source rocks with type i kerogen of lower cretaceous with the exception of elevated ethane contents the general overall agreement in composition of natural and hydrous pyrolysis petroleum of lacustrine source rocks observed in this study supports the utility of hp to better characterize petroleum systems and the effects of maturation and expulsion on petroleum composition and quality

paleostress states at the south western margin of the central european basin system application of fault slip analysis to unravel a polyphase deformation pattern abstract we analyse the deformation pattern along the south western margin of the central european basin system cebs where upper carboniferous mesozoic rocks are uplifted due to the late cretaceous basin inversion the geometry of mesoscale faults and associated striae are used to calculate the stress state s responsible for the observed deformation each reduced stress tensor obtained comprises i the directions of the principal stress axes 1 2 and 3 1 2 3 and ii the ratio of principal stress differences r 2 3 1 3 we present a stress inversion technique that allows each stress state inherent in a heterogeneous fault population to be identified by integrating the results of the pbt method turner f j 1953 nature and dynamic interpretation of deformation lamellae in calcite of three marbles american journal of sciences 251 4 276 298 sperner b ratschbacher l and ott r 1993 fault striae analysis a turbo pascal program package for graphical presentation and reduced stress tensor calculation computers geosciences 19 1361 1388 and the multiple inverse method yamaji a 2000 the multiple inverse method a new technique to separate stresses from heterogeneous fault slip data journal of structural geology 22 4 441 452 this comprehensive approach not only facilitates the separation of complex data sets into homogeneous subsets but also guarantees that each stress state derived fulfils both the criteria of low misfit angles wallace bott hypothesis and high shear to normal stress ratios mohr coulomb criterion the reliability of our technique is confirmed by the fact that irrespective of i the number of fault slip data from an outcrop ii the number of subsets they represent and iii the proportion of newly formed and reactivated faults we obtain consistent results from outcrops of variously aged rocks this consistency concerns both calculated stress states as well as locally observed deformation sequences such local chronologies are derived from cross cutting relationships and superimposition of different fault slip data which individually are assigned to a consistent stress state a synthesis of results from different locations of the study area argues for the superposition of two main deformation events most prominently the area was affected by a stress state with a horizontal n s to ne sw directed maximum compression 1 and a low stress ratio which induced reverse and strike slip faulting a pure strike slip regime of e w to nw se directed compression with moderate stress ratios is less prevalent and probably younger the age of the youngest rocks documenting these two phases proves the stress fields to correspond to the polyphase late cretaceous tertiary basin inversion of the cebs during post cenomanian times the youngest tectonic imprints detected in the study area correspond to locally appearing extensional stress states with varying directions of 3 at many sites the youngest derived paleostress state coincides with the present day stress field in terms of the direction of the maximum horizontal stress axis s hmax the only stress state detected which pre dates the basin inversion corresponds to an extensional regime with an wnw ese to nw se directed 3 axis observed only locally in the n s striking leine graben and its prolongation to the north the fact that the majority of variously aged rocks exhibit only the traces of the latest deformation phases indicates a high degree of fault plane reactivation in the study area

geochemical distribution and supergene behavior of indium at the pinguino epithermal polymetallic vein system patagonia argentina abstract the pinguino deposit located in the low sulfidation epithermal metallogenic province of the deseado massif patagonia argentina represents a distinct deposit type for this region it evolved through two different mineralization events an early in bearing polymetallic event that introduced in zn pb ag cd au as cu sn w and bi represented by a complex sulfide assemblage and late ag au quartz rich veining that crosscut and overprinted the early polymetallic mineralization three in bearing mineralization stages were identified within the polymetallic event iron rich sphalerite of the second stage is the major in carrier in the deposit the spatial distribution of in within the veins shows its maximum mean values in the marta centro and ivonne norte veins in a pattern similar to the zn distribution showing a close spatial relation with the unexposed kasia intrusive complex at the vein scale and in the hypogene zone the in distribution is associated with variations in the temperature of mineralizing fluids the vertical distribution of in within the veins exhibits consistent values both below and above the oxidation level resembling the behavior of pb and sn and therefore suggesting that in behaves as an immobile element during vein weathering

organic geochemistry of freshwater and alkaline lacustrine sediments in the green river formation of the washakie basin wyoming u s a abstract two members of the green river formation in the washakie basin have been analysed by organic geochemical and organic petrographic techniques and the results placed in a sequence stratigraphic framework one of these members the laney shale was deposited in a hydrologically closed alkaline lake under an arid climate and was characterized by high concentrations of alginite rich organic matter whereas the other the luman tongue was deposited in a hydrologically open freshwater lake under a humid climate and consisted of organic poor profundal lake mudstones and coaly lake margin sediments potential source rocks in both lake types have the potential for generating high wax oil at high subsurface temperatures 150 175 c at a heating rate of 5 k ma but the alkaline system is clearly more prolific the most abundant biological marker hydrocarbons were the 4 methylsteranes in both lake types though dinosteranes were found only in the laney shale oleanane was absent from the luman tongue despite an abundance of angiosperm palynomorphs intraformational heterogeneities were best documented for the laney shale where molecular differences in kerogen type occur at the parasequence level with early transgression maximum transgression and rejuvenation stages of lake history having its own kerogen type and distinctive high wax oil fingerprint thermal lability was shown to be linked to kerogen structure in particular the presence of alicyclic and oxygen containing moieties and these in turn are correlated with total organic carbon content and thence productivity degree of preservation some kerogen components appear to have originated via selective preservation whereas others may have been formed by diagenetic condensation reactions

la josefina au ag deposit patagonia argentina a jurassic epithermal deposit formed in a hot spring environment abstract the la josefina jurassic epithermal au ag deposit located in patagonia argentina developed in an extensional setting of a back arc environment associated with a widespread middle late jurassic calc alkaline volcanism block faulting has juxtaposed shallow level features evidenced by hot spring manifestations hydrothermal eruption breccias and au rich veins which suggest that mineralization in these veins could extend far below the depths already tested by core drilling veins are filled by quartz chalcedony opal and minor adularia and barite with massive comb cockade colloform crustiform bandings and lattice bladed textures ore minerals include electrum ag rich sulfosalts freibergite pyrite galena sphalerite chalcopyrite and specular hematite with minor arsenopyrite marcasite tetrahedrite and bornite four mineralizing stages have been identified the first two s1 and s2 are au and ag rich with temperatures ranging from 225 to 290 and salinities from up to 15 wt in s1 decreasing to 1 wt nacl in s2 the third stage s3 displays higher base metal contents at lower temperatures 200 c finally the last stage s4 is barren with temperatures lower than 100 c veins are surrounded by a proximal alteration halo of quartz pyrite adularia illite followed outwards by illite smectite interstratified clays and smectites with less chlorite to a propylitic zone stable isotope values calculated for the fluids show a mostly meteoric origin for mineralization fluids such distinct features place the la josefina deposits in a hot spring environment with evidences of being formed at a proximal position of the jurassic paleosurface and paleowater level

new insights on the green river petroleum system in the uinta basin from hydrous pyrolysis experiments the tertiary green river petroleum system in the uinta basin generated about 500 million bbl of recoverable high pour point paraffinic crude oil from lacustrine source rocks a prolific complex of marginal and open lacustrine source rocks dominated by carbonate oil shales containing up to 60 wt type i kerogen occur within distinct stratigraphic units in the basin petroleum generation is interpreted to originate from source pods in the basal green river formation buried to depths greater than 3000 m along the steeply dipping northern margin of the basin producing fields in the altamont bluebell trend have elevated pore fluid pressures approaching 80 of lithostatic pressure and are completed in strata where open fractures provide permeability active hydrocarbon generation is one explanation for the origin of the overpressured reservoirs in this study experiments were undertaken to examine the mechanisms of hydrocarbon generation and accumulation in the uinta basin we combined analyses of representative source rocks from the entire green river stratigraphic section with detailed laboratory simulation experiments using both open and closed system pyrolysis this information provides new insights on lacustrine source rock lithofacies gas oil source rock correlations hydrocarbon generation kinetics and basin modeling the results show that the basal green river formation contains a unique type i source facies responsible for generation of paraffinic crude oils the classic type i oil shales in the upper green river formation correlate well with low maturity aromatic asphaltic samples we determined kinetic parameters for the source rocks and used them to develop basin models for hydrocarbon generation the models show that hydrous pyrolysis kinetic parameters are more consistent with the natural data in terms of predicted timing and extent of oil generation as compared to models using rock eval kinetics begin page 1334

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

structural evolution of the golden cross epithermal au ag deposit new zealand golden cross located in the hauraki goldfield of new zealand is a classic example of a fault fracture hosted epithermal vein system gold silver mineralization was mined in two areas the open pit stock work veins and the underground empire vein system which are collectively referred to as the empire zone open pit stockwork veins are either parallel or subperpendicular to northeast striking moderately southeast dipping bedding bedding perpendicular veins are mostly pure extensional structures whereas bedding parallel veins open in an extensional regime with a minor component of shear vein frequency across strike is typically 15 m and most veins are 0 01 to 0 2 m thick the underground empire vein system consists of the steeply west dipping empire vein and a complex array of footwall veins the 2 to 10 m thick empire vein strikes northeast dips steeply 65 85 northwest has a mineralized strike length of about 500 m and a vertical extent of 250 m it is localized in a deflection of the empire fault where the dip of the fault decreases the footwall veins are low angle gently west dipping veins up to 100 m long hosted in extensional shear and pure extension fractures they splay off the empire vein at an average angle of 30 up to seven vein types record the multiple fault fracture openings that provided highly permeable pathways for hydrothermal fluids in the empire zone the empire zone was initially characterized by a pervasive network of thin barren sulfide veins followed by two to five stages of electrum bearing quartz veins the most voluminous of these stages were quartz adularia veins with well developed colloform and crustiform bands and breccia textures the final stage was massive coarsely crystalline calcite veins similarities in vein type orientation and crosscutting relationships between the empire vein system and stockwork veins suggest that they formed under similar stress regimes and that mineralization in the two areas overlapped in time at least in part host rocks at golden cross dip 50 to the southeast if the vein system and bedding are rotated so that bedding is restored to horizontal the empire fault and empire vein reflect a steeply southeast dipping normal fault after rotation the former footwall veins form a network of subvertical veins in the hanging wall of the empire fault they form an en echelonlike array similar to horse tail extensional fracture networks that commonly develop in normal faults in the near surface therefore we infer that before tilting empire zone fractures and veins formed in an extensional regime with 1 subvertical 2 subhorizontal oriented northeast south west and 3 subhorizontal oriented northwest southeast consistent with the interpreted rift tectonics of the coromandel volcanic zone during the late miocene time of mineralization

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

textural evidence for remobilization in metamorphic environments remobilization of stratabound massive sulphide deposits involves both dislocation flow mechanical remobilization and fluid state processes chemical remobilization textural support for such remobilization is presented at micro meso and macroscales microscale evidence establishes the degree the amount of a deposit affected of remobilization likewise mesoscale textures establish the degree and may provide mesoscale models of macroscale remobilization processes but still do not establish the extent the distance over which translocation may have occurred of remobilization where macrotexture indicates a departure from an original conformable relationship gross remobilization is suggested and may be the consequence of mechanical and or chemical processes the case for gross mechanical and or chemical remobilization is often difficult to sustain because alternative hypotheses e g hydrothermal replacement may be compatible with the observed relationships remobilization of a conformable ore layer may involve internal redistribution during which sulphides have been modified by dislocation flow and or fluid state processes within the layer constraints or external where the layer constraints have been substantially transgressed during dislocation flow and or fluid phase remobilization if mesoscale textures indicate remobilization of the external type then macroscale gross remobilization remains a possibility subject to substantiation

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

curving cross joints and the lithospheric stress field in eastern north america cross joints are late formed nonsystematic fractures that extend across intervals between systematic joints traces of such cross joints are seen on bedding plane surfaces of devonian catskill clastic sedimentary rocks of the appalachian plateau of western new york state where the maximum horizontal principal stress s h is oriented n65 e as indicated by in situ stress measurements between pairs of closely spaced systematic joints traces of cross joints are commonly planar and orthogonal to the preexisting joints however in the mid region between some widely spaced systematic joints in western new york cross joints strike parallel to the s h of the present lithospheric stress field but then curve to abut the preexisting joints at right angles a curving trace reflects a local perturbation of the regional stress field in the vicinity of preexisting joints and the perpendicular termination indicates that the preexisting joints were open depending on their age the strike of the mid region of curving cross joints denotes the orientation of either the neotectonic stress field or its tertiary predecessor in the north american lithosphere

high grade ore shoots at the martha epithermal vein system deseado massif argentina the interplay of tectonic hydrothermal and supergene processes in ore genesis abstract the complexity of high grade ore shoot formation is addressed through a detailed study of the martha mine epithermal deposit deseado massif patagonia argentina the mine was active from 2002 to 2012 producing over 21 million oz of silver from an intermediate sulfidation vein system hosted in a pyroclastic sequence erupted during upper jurassic times 40ar 39ar age 157 6 1 ma the martha deposit is composed of more than 15 different veins 8 of which show high grade ore shoots locally up to 45 000 g t ag veins are hosted in a sinistral transtensive horst structure delimited by two nw se trending first order veins up to 600 m long and 5 m thick inside this horst a series of e w trending veins up to 450 m long and 2 5 m thick developed as second order structures in response to growth and linkage of the two overlapping first order vein structures ore is characterized by a complex paragenetic sequence of ag as sb sulfosalts and cu pb zn sulfides with an adularia quartz illite gangue hydrothermal alteration is zoned outward and rarely extends for more than 15 m away from the vein walls five alteration zones were defined an adularia zone close to the veins an intermediate halo characterized by illite and illite smectite zones and a distal smectite zone additionally a late and supergene kaolinite zone can be found near the surface in close association with the mineralized structures high grade bonanza ore shoots are the result of the interplay of a series of structural hydrothermal mostly physicochemical and supergene processes the mineralization evolved through three main phases a main hydrothermal tectonically controlled phase a late tectonic hydrothermal phase and a post mineral supergene phase the main hydrothermal phase was the result of mineral deposition from low salinity 0 5 to 3 5 wt nacl eq near neutral to weakly alkaline chloride aqueous hydrothermal solutions with estimated temperatures ranging from 215 5 c to 316 5 c and isotopic composition suggesting high proportions of meteoric waters 18oh2o from 8 1 to 2 7 relatively constant fluid inclusion liquid to vapor ratios and a trend of decreasing th and 18oh2o with increasing time suggest that cooling and dilution were the main mechanisms controlling ore deposition these physicochemical conditions combined with an efficient network of structural conduits vein intersections jogs and step over zones were the first step in the construction of the high grade ore shoots that characterize the vein system 40ar 39ar dating in adularia crystals constrains the hydrothermal activity to the upper jurassic 156 5 0 9 ma afterwards a late tectonic hydrothermal phase occurred through the development of irregularly shaped bodies of massive fault breccias and foliated cataclasites related to tectonic reactivations of the vein system in synchronism with the waning stages of the hydrothermal system the interplay between deformation and fluid circulation resulted in mechanical and chemical remobilization of the previously deposited ag rich sulfosalts by lower temperature 138 c to 168 c and higher salinity fluids 7 7 and 9 9 wt nacl eq possibly reflecting a late magmatic input into the waning system this late tectonic hydrothermal phase strongly contributes to increase the grades in some veins and therefore is considered an essential process in order to build the highest grade portions of the ore shoots found at the mine finally a post mineral supergene phase defined a 20 m thick oxidized zone close to the surface followed by a 20 30 m thick secondary enrichment zone below it developed in response to the circulation of descending cold meteoric waters despite its small size and vertical extension the secondary enrichment level at martha mine constitutes an important economic factor for the mining operations as it helped to increase the silver grades in the shallower portion of the vein system the martha mine vein system constitutes an excellent example of how the interplay of hydrothermal processes controlling mineral deposition structural factors building up an efficient plumbing system tectonic ore remobilization and late supergene secondary enrichment processes are combined in order to build bonanza grade ore shoots in the epithermal environment

diffuse faulting in the machu picchu granitoid pluton eastern cordillera peru abstract a series of batholiths forming part of the roots of a permo liassic rift system are exposed in the high eastern cordillera of central peru as a result of tectonic inversion shortening of the machu picchu granitoid pluton was accommodated by widespread shear reactivation of primary joints by a process termed here diffuse faulting fault like reactivation of precursor joint surfaces marked by chlorite epidote and quartz shear fibres is locally evidenced by few centimetres offsets within apparently undeformed granite analysis of fault slip data indicates that shear reactivation of different joint sets was kinematically consistent with ene oriented shortening less frequent mylonitic shear zones appear to have evolved from the common brittle precursors apart from rare phyllonitic shear zones fluid rock interaction along the brittle precursors was generally limited and pluton deformation appears to be mainly controlled by the geometry and distribution of primary joints three main sets of reactivated joints can be recognized characterized by oblique slip kinematics with variable reverse and strike slip components of motion theoretical modelling based on quantitative fracture analysis scan line data and different displacement length relationships applied to the main reactivated joint sets yield first order estimates of pluton finite strain the results suggest that bulk finite strain is oblate and essentially coaxial and is characterized by horizontal shortening not exceeding 10 relatively small finite strains integrated over the size of the pluton still result in a few kilometres of crustal shortening

adularia in epithermal veins queensland morphology structural state and origin four types of adularia i e sub rhombic rhombic tabular and pseudo acicular are recognised from examination of samples from ten epithermal vein deposits and prospects in queensland based on morphology of the individual crystals further investigation of the structural state of adularia reveals that each group has some specific features in terms of the degree of al si disordering which can be related to various crystallisation conditions and the thermal history sub rhombic adularia is commonly 2 4 mm in size and subhedral with more or less rhombic outlines and has a relatively ordered al si distribution 2t1 0 84 reflecting slow crystallisation conditions adularia of this type in association with coarse grained quartz is predominant at deep levels of epithermal systems where boiling is initiated in an environment of low permeability and the fluid is slightly supersaturated with respect to adularia and quartz tabular adularia characterised by its lath shape and disordered structure 2t1 values ranging from 0 64 to 0 74 is likely to have formed when the fluid moves up to a more permeable environment and starts boiling violently relatively high temperatures and rapidly changing conditions account for its special morphology and disordered structure rhombic adularia showing very small crystal size 0 2 mm with euhedral rhombic form has an intermediate degree of al si ordering pseudo acicular adularia is interpreted as pseudomorphs after carbonate and its high al si ordered structure is attributed to the presence of a carbonate precursor these two types of adularia commonly occur within crustiform and colloform bands in association with high grade ore and chalcedony or fine grained quartz which often displays various recrystallisation textures it is most likely that adularias of these two types are formed when extensive boiling is protracted microprobe analyses indicate the composition of all adularia types close to pure kalsi3o8 sericite and or carbonate altered adularias consistently display more ordered structures suggesting that the post crystallisation thermal regime affects the structural state of altered adularia even at temperatures as low as in epithermal environments

upper permian lacustrine organic facies evolution southern junggar basin nw china abstract the jingjingzigou lucaogou and hongyanchi formations of the southern junggar basin together comprise over 1000 m of organic rich lacustrine facies they record an overall evolution from relatively shallow evaporative lakes to freshwater lakes associated with fluvial systems the jingjingzigou formation is characterized by low toc and hi and biomarker features such as abundant carotane consistent with a specialized saline or hypersaline biota biomarker distributions in jingjingzigou formation extracts most closely resemble oils from the giant karamay oilfield the lucaogou formation represents one of the richest and thickest lacustrine source rock intervals in the world yet it contradicts conventional lacustrine source rock models in at least two important aspects first deposition occurred at middle paleolatitudes 39 43 n rather than in the tropics second limited nutrient supply in a drainage basin dominated by intermediate volcanic rocks appears to have caused low to moderate primary productivities stable salinity stratification and low inorganic sedimentation rates in a deep lake nonetheless resulted in deposits with up to 20 toc and hi near 800 the overlying hongyanchi formation has 1 5 toc but low hi and was deposited in freshwater oxic to sub oxic lakes

hydrothermal breccias in vein type ore deposits a review of mechanisms morphology and size distribution abstract breccias are among the most widely distributed rock textures found in hydrothermal vein type deposits previous studies have mainly been interested in developing qualitative descriptive approaches leading to a confusing profusion of terms brecciation originates in numerous ways resulting in highly complex classification systems and frequent misinterpretations of facies field observations are difficult to reconcile with physical theories of fragmentation partly due to the fact that few satisfactory quantitative tools have been developed a review of the main brecciation processes occurring in hydrothermal vein type deposits allows for the discrimination between chemical and physical mechanisms including tectonic comminution wear abrasion two types of fluid assisted brecciation hydraulic and critical volume expansion or reduction impact and collapse each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry including fragment morphology size distribution of the fragments fabric and dilation ratio the first two parameters are especially important because 1 the morphology of the fragments allows chemical and physical mechanical breccias to be distinguished and 2 the particle size distribution psd is a function of the energy input during breccia formation the slope of the cumulative psd fractal dimension ranges from high values for high energy brecciation processes to low values for low energy processes indicated by an isometric distribution the evolution of a vein system can be divided into three stages propagation wear and dilation these stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity these two thresholds also mark the transition between different types of brecciation mineralization occurs during all three stages and may display different textures due to pressure variations the use of quantitative parameters in fault related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment including structural setting and crustal level as well as fluid rock interactions recognition of the different breccia types could also be important during the early stages of mineral exploration

lacustrine type i kerogen characterization at different thermal maturity levels application to the late cretaceous yacoraite formation in the salta basin argentina abstract a maturation series from the late cretaceous to danian yacoraite formation in the salta basin argentina was selected to investigate the evolution of organic matter properties from source rock samples mainly containing lacustrine type i kerogen organic petrography determined the thermal maturity and the spatial distribution of organic matter particles rock eval analyses and kerogen isolation procedures were then applied to assess the hydrocarbon generation potential of the investigated intervals biomarker ratios as well as the molecular composition of organic compounds present in four immature to early mature rock samples and their corresponding aliphatic and aromatic fractions were investigated to complete the lacustrine organic matter characterization based on petrographic results immature to early mature yacoraite samples have a large content of yellow brownish liptinites alginites whereas mature samples are characterized by abundant solid bitumen three kerogen samples from the yacoraite formation at different thermal maturity levels were also selected for analysis of bulk kinetic parameters e g activation energy distribution frequency factor using programmed open system pyrolysis in this way bulk kinetic parameters were calculated as a function of the thermal maturity for these three lacustrine kerogen samples bulk kinetic results show both an increasing activation energy and loss of petroleum generation potential as thermal degradation proceeds the investigated yacoraite kerogen samples show single activation energy distributions which are typical for a type i kerogen of lacustrine origin finally it was demonstrated that the organic matter om characteristics from the yacoraite formation argentina could be compared to the typical type i kerogen from the green river formation usa showing similar om characteristics petroleum potential and activation energy distributions the novelty of the geological and geochemical information brought in this article about yacaroite system in argentina provides premises for further investigation

a review of deformation pattern templates in foreland basin systems and fold and thrust belts implications for the state of stress in the frontal regions of thrust wedges aesthetically appealing thrust systems and related large scale anticlines in both active and fossil foreland fold and thrust belts and the economic potential associated with the m have captured the interest of structural geologists for many decades as a consequence a large amount of data on sub seismic deformation patterns from thrust related an ticlines is available in the literature we provide a review of deformation pattern templates from fi eld data in foreland fold and thrust belts and show that the most frequent tre nds of sub seismic syn orogenic deformation structures hosted in km scale thrust related folds frequently and pa radoxically indicate a syn th rusting strike slip stress fi eld con fi guration with a near vertical 2 and a sub horizontal 3 rather than a contractional one where the latter is expected to be the vertical principal axis of the stress ellipsoid this a pparent inconsistency between sub seismic syn orogenic deformation structures and stress fi eld orientation is here named the 2 paradox field data support a possible expla nation of the paradox provided by the major role played by i nherited early orogenic extensional deformation struc tures on thrust fault nucleation nucleation of major thru sts and their propagation is facilitated and driven by the positive inversion and linkage of the early orogenic sub s eismic extensional inheritance developed in the foreland basin this process eventually leads to the development of l argereversefaultzonesandcanoccurbothincontractional and strike slip stress fi eld con fi gurations

age of supergene oxidation and enrichment in the chilean porphyry copper province twenty five samples of supergene alunite collected from deeply developed supergene profiles in porphyry copper deposits and prospects between latitudes 20 degrees and 27 degrees s in northern chile yield k ar ages ranging from about 34 to 14 ma therefore supergene oxidation and enrichment processes were active from the early oligocene to the middle miocene a minimum of 20 m y supergene activity at individual deposits lasted for at least 0 4 to 6 2 m y the early oligocene supergene activity affected deposits in the paleocene porphyry copper belt whereas early and middle miocene supergene processes are documented in the early cretaceous paleocene and late eocene to early oligocene porphyry copper belts middle miocene oxidation also affected the oldest epithermal gold silver deposits in the maricunga belt farther east supergene activity commenced no less than 11 m y after generation of each porphyry copper deposit because of the time required to unroof the copper bearing parts of the system supergene activity throughout northern chile ceased at approximately 14 ma the geologic features of deposits and prospects and their morphotectonic positions present latitudes and present elevations display no obvious correlations with the supergene chronology exploration for major cumulative enrichment blankets should not be carried out either beneath thick sequences of piedmont gravels or ignimbrites of oligocene through middle miocene age unless their accumulation is demonstrably late in the documented history of supergene activity or in porphyry copper provinces such as those of central chile and northwestern argentina which formed after approximately 14 ma the uplift responsible for efficient cumulative copper enrichment is difficult to correlate convincingly with the brief pulses of compressive tectonism postulated for northern chile and contiguous areas unless their effects were much more prolonged intensifying aridity is confirmed as the likely reason for the cessation of supergene activity in northern chile and tectonic uplift was its most probable cause however more fundamental global controls producing a period of chemical weathering followed by worldwide dessication also may have played a role

major environmental changes recorded by lacustrine sedimentary organic matter since the last glacial maximum near the equator lagoa do caco ne brazil sediment samples collected along a 6 m core drilled in the deepest part of the lagoa do caco ne brazil have been investigated in order to determine source s and degradation conditions of the organic matter om with special emphasis on paleoenvironmental implications bulk organic geochemistry rock eval pyrolysis c n determination 13c and 15n measurement and petrography combined with sedimentological evidence and radiocarbon dates allowed to identify four major intervals documenting major environmental changes that occurred during the last 20 000 years the first interval dating back to the end of the last glacial maximum lgm contains well preserved om derived from higher plants this material was most probably produced in an ephemeral palustrine system and rapidly buried by sands this level is thought to have been deposited under relatively arid climate conditions associated with strong but episodic rainfalls between 19 240 and 17 250 cal years bp the climate appears to have been more humid and seasonality more pronounced as suggested by the presence of a permanent lake after a drastic environmental change dating back to 17 250 cal years bp the sediment became truly lacustrine with restricted mineral input and highly degraded higher plant derived organic matter after that a stepwise improvement in the preservation of om occurred as revealed by several pronounced shifts in the rock eval tps2 signal these changes could document abrupt climatically driven changes during the late glacial finally around 5610 cal years bp environmental conditions approaching those prevailing today were established minor climatic changes during the holocene were probably buffered by a high water table which might explain the lack of paleoenvironmental fluctuations

kinematic and analog modeling of 3 d extensional ramps observations and a new 3 d deformation model abstract we present results of kinematic and dry sand analog models of hanging wall folding over an extensional ramp flat system containing complementary strike bends the kinematic models illustrate that differential structural relief is controlled by changes in apparent fault dip in the displacement direction variation in inclined shear angle modifies the magnitude but not the sign of this differential relief in a novel analog modeling method we create a weak fault zone by coating the entire rigid footwall ramps and flat with a thin layer of silicone putty below a dry sand hanging wall at low strain rates the silicone polymer is weaker than the dry sand and thus provides a good fault zone analog a 3 tilt is sufficient to induce displacement and all deformation is driven by gravity in the models we observe that hanging wall displacements near the oblique segment of the ramp are deflected toward the ramp strike oblique inclined shear a new quantitative geometric model explains the bending of displacement paths towards the strike rather than the dip of oblique ramp segments the model is conceptually equivalent to 2 d inclined shear models in which the hanging wall is imagined to pull rigidly away from and then collapse against the footwall because gravity is the driving force antithetic collapse is directed normal to the incipient void which introduces a component of slip normal to the fault strike vector sum of the normal component with the regional component results in the observed displacement

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

determination of gross kinetic parameters for petroleum formation from jurassic source rocks of different maturity levels by means of laboratory experiments abstract solvent extracted core samples of lower toarcian carbonate rich shales posidonia shale lias of the hils syncline area lower saxony basin northern germany covering a wide maturity range vitrinite reflectance rr 0 48 0 88 and 1 45 and a kimmeridge mudstone rr 0 45 are pyrolyzed at three different heating rates 0 1 0 7 and 5 0 k min by application of non isothermal first order reaction kinetics to the resulting hydrocarbon evolution curves activation energy distributions between 46 and 70 kcal mol and pre exponential arrhenius factors are obtained by an iteration method hypothetical hydrocarbon generation curves are calculated for the lias assuming three geological heating rates 0 5 5 and 50 k 106a peak hydrocarbon generation temperatures range from 135 to 165 c

organic and isotope geochemistry of the early cretaceous rift sequence in the camamu basin brazil paleolimnological inferences and source rock models abstract the camamu basin located at the eastern brazilian continental margin is characterized by a thick early cretaceous organic rich rift sequence the integration of bulk geochemical isotopic and biomarker data with paleontological and geological information provided the basis for a better assessment of rift lake evolution hydrological regime redox potential salinity etc and its impact on source rock development pyrolysis and visual kerogen analyses reveal the dominance of lipid rich algal bacterial type i kerogen through the entire rift sequence paleolimnological reconstruction suggests that the lower rift sequence morro do barro formation neocomian was deposited in a fault bounded deep lake with fresh to brackish water stable water column stratification and water bottom anoxia high hydrogen indices 700 900 mg hc gtoc and 13c depleted carbon isotopic composition of the organic matter 13c values around 30 might reflect enhanced organic preservation the recycling of light ch4 generated by methanogenesis and the incorporation of isotopically light lipid rich bacterial biomass on the other hand the upper rift sequence rio de contas formation barremian was probably deposited within a broader shallower lake with a higher frequency of water column overturn and a deeper thermocline high organic carbon contents and strong 13c enrichment of the organic matter 13c excursions of up to 23 are interpreted to have resulted from enhanced primary productivity triggered by an increased input recycling of nutrients favored by lake morphology and humid climate

hydrocarbon exploration potential within intraplate shear related depocenters deseado and san julian basins southern argentina the deseado and san julian late paleozoic mesozoic rift basins occupy sizable parts of central patagonia and offshore southern argentina respectively the basins record a similar linked tectonostratigraphic evolution since their inception in the late paleozoic both evolved as continental intracratonic rifts developed above a basement comprising devonian low grade metasediments overlying older continental crust in response to regional tectonic extension that preceded late disaggregation of gondwana this late permian rifting was followed by continuous filling of the basin during triassic thermal subsidence jurassic extension produced a framework of grabens and half grabens filled with mafic and felsic proximal volcanics and volcaniclastics the east west orientation of these jurassic rift features in sharp contrast to the north south trend of the permian triassic rift systems suggests that the jurassic depocenters shifted in response to oblique extension development of a transtensional pull apart basin in the upper valanginian aptian a strong compressive event marked by a prominent angular unconformity affected the deseado and san julian basins wrenching associated with this compressive event produced transpressive structures in both basins a period of relative tectonic stability was observed during the upper cretaceous and tertiary the only interruption being a mild transpressive reactivation along major preexisting faults during the miocene andean orogeny the first marine incursion occurred in the paleocene as the seas transgressed over an extensive peneplained terrain the deseado and san julian basins remain virtually unexplored only three wells having been drilled oil seeps in neocomian strata in the deseado basin indicate that this frontier basin has petroleum potential source quality intervals were encountered in the neocomian bajo grande formation of the san julian basin begin page 1796 distal lacustrine facies of the neocomian la matilde formation are expected to be potential source rocks in the deseado basin the permian triassic section is also thought to contain well developed source rocks however the section has yet to be penetrated reservoir quality rocks occur in clastics of the upper cretaceous neocomian triassic and permian formations possible play types include paleozoic reservoirs in positive transpressive features lateral updip pinch outs of neocomian sandstones and fractured jurassic volcanics adjacent to fault zones

organic geochemistry and petrology of posidonia shale lower toarcian western europe the evolution from immature oil prone to overmature dry gas producing kerogen abstract kerogen concentrates as well as whole rock samples of the lower jurassic posidonia shale representing a complete maturity series from immature to highly overmature were analyzed using organic petrography palynology bulk geochemical analysis ft ir and curie point pyrolysis gc ms cp py gc ms in order to investigate changes in kerogen composition with increasing maturation vitrinite reflectance vrr ranges from 0 5 to 3 hi values reflect the maturity trend very well with little scatter in contrast tmax oi and pi values show more scatter and greater differences between kerogen concentrates and whole rock samples ft ir spectra show a decrease in functional group bands with increasing maturation which has been quantified cp py gc ms analyses indicate an increase in hydrocarbons especially for short and medium length n alkanes with a strong predominance of short length alkanes at highest maturities about 3 vrr this effect however depends also on the applied pyrolysis temperature where higher temperatures 920 c as compared to 650 c favor generation of short length n alkanes especially for samples at high levels of maturation ratios of aromatic over aliphatic hydrocarbons or alkenes over alkanes show a non steady evolution depending also on the applied pyrolysis temperatures indicating that higher pyrolysis temperatures are needed for pyrolytic alkene formation with a maximum alkene formation for samples within early overmature maturities 1 4 vrr aromaticity first decreases but increases at high levels of maturation finally weathering of the highly overmature sample 3 vrr resulted in strong oxidation of organic matter with impact on rock eval ftir and curie point pyrolysis data

jurassic hot spring deposits of the deseado massif patagonia argentina characteristics and controls on regional distribution abstract the deseado massif santa cruz province argentinean patagonia hosts numerous middle to late jurassic age geothermal and epithermal features represented by siliceous and calcareous chemical precipitates from hot springs sinters and travertines respectively hydrothermal breccias quartz veins and widespread hydrothermal silicification they indicate pauses in explosive volcanic activity marking the final stages in the evolution of an extensive jurassic ca 178 151 ma volcanic complex set in a diffuse extensional back arc setting heralding the opening of the atlantic ocean published paleo hot spring sites for the deseado massif plus additional sites identified during our recent field studies reveal a total of 23 locations five of which were studied in detail to determine their geologic and facies associations they show structural lithologic textural and biotic similarities with miocene to recent hot spring systems from the taupo and coromandel volcanic zones new zealand as well as with modern examples from yellowstone national park u s a these comparisons aid in the definition of facies assemblages for deseado massif deposits proximal middle apron and distal siliceous sinter and travertine terraces and mounds with preservation of many types of stromatolitic fabrics that likely were controlled by formation temperature ph hydrodynamics and fluid compositions locally the mapped hot spring deposits largely occur in association with reworked volcaniclastic lacustrine and or fluvial sediments silicic to intermediate lava domes and hydrothermal mineralization all of which are related to local and regional structural lineaments moreover the numerous geothermal and significant epithermal those with published minable resources deposits of the deseado massif geological province mostly occur in four regional nnw and wnw hydrothermal structural belts northwestern northern central and southern defined here by alignment of five or more hot spring deposits and confirmed as structurally controlled by aeromagnetic data the northern and northwestern belts in particular concentrate most of the geothermal and epithermal occurrences hence jurassic hydrothermal fluid flow was strongly influenced by the most dominant and long active geological boundaries in the region the outer limits of the deseado massif horst itself

organic geochemistry of the lower toarcian posidonia shale in nw europe abstract a suite of core and outcrop samples of the lower toarcian posidonia shale and time equivalent deposits was collected from multiple locations including southern germany swabian alb and franconian alb northern germany the east coast of great britain the netherlands and luxembourg in order to study major differences and similarities with respect to depositional environment and redox potential based on molecular geochemical data all samples are immature or in the early oil window with the highest thermal maturity occurring in the profile from great britain about 0 7 vitrinite reflectance molecular geochemical maturity parameters were used to quantify maturation in detail during shale deposition in the west cleveland basin great britain h 2 s was immediately consumed in the water column by terrigenous input supplying abundant reactive iron to form pyrite these samples are characterized by low dibenzothiophene phenanthrene ratios 95 of 2 and h 2 s in contrast sulfidic euxinic bottom waters possibly with enhanced salinity and stratified water column prevailed due to a more restricted iron supply in luxembourg northern germany and the franconian alb of southern germany a more oxygenated dysoxic bottom water column associated with anoxic sediments i e anoxic dysoxic boundary close to the sediment water interface prevailed in the swabian alb of southern germany despite observed changes within each vertical profile at each site large scale regional trends in depositional conditions can be clearly identified for the early toarcian

depositional history source rock quality and thermal maturity of upper ordovician lower silurian organic rich sedimentary rocks in the central part of the baltic basin lithuania abstract this study provides a comprehensive geochemical and mineralogical characterisation of the fine grained organic matter rich sedimentary rocks of the lower palaeozoic in the central part of the baltic basin western lithuania the primary objective was to deduce environmental conditions for the lower palaeozoic succession which is very well preserved in the baltic basin while the secondary goal was to obtain information on maturation and thermal history of the rocks the sample set covers different stratigraphic units of the ordovician lower silurian succession and was analysed with a wide range of different methods including elemental analysis organic petrography rock eval pyrolysis molecular geochemical analysis of saturated and aromatic hydrocarbon fractions inorganic geochemistry mineralogy xrf xrd analysis and magnetic susceptibility ms of rock samples their integration allowed a determination of the redox conditions paleoproductivity and clastic input during sediment deposition the fine grained sediments are dominated by clay minerals and quartz and to a lesser extent carbonate pyrite and feldspar microscopic analysis revealed abundant solid bitumen and zooclasts biomarker data indicate a marine origin for the precursor organic matter maturity parameters revealed the presence of a thermal maturity anomaly in the southwestern part of lithuania where the late phase of oil generation and possibly beginning of condensate wet gas generation with corresponding maximum paleotemperatures of 140 180 c has been reached bottom water conditions varied from oxic to anoxic euxinic during deposition driven by interaction of climate states water mass circulation and stratification water geochemistry and sea bottom bathymetry four shaly horizons at the upper ordovician fjacka and mossen fms silurian dobele fm and near llandovery wenlock boundary levels were recognized as being formed in oxygen depleted benthic settings as indicated by high toc and ts contents sedimentation features high metal enrichment or degree of piritization the deposition of highly organic matter rich silurian dobele fm might have coincided with oceanic anoxia and late aeronian bioevent accompanied by an upwelling regime with increased paleoproductivity the interpreted coarsening upward trend at the early silurian adavere regional stage terminates with fall in relative sea level at the llandovery wenlock boundary the geochemical proxies near llandovery wenlock boundary may reflect the perturbations in oceanic water geochemistry which in turn may have eventually led to ireviken mass extinction event

neogene patagonian plateau lavas continental magmas associated with ridge collision at the chile triple junction extensive neogene patagonian plateau lavas 46 5 to 49 5 s southeast of the modern chile triple junction can be related to opening of asthenospheric slab windows associated with collisions of chile rise segments with the chile trench at 12 ma and 6 ma support comes from 26 new total fusion whole rock 40ar 39ar ages and geochemical data from back arc plateau lavas in most localities plateau lava sequences consist of voluminous tholeiitic main plateau flows overlain by less voluminous 2 to 5 million year younger alkalic postplateau flows northeast of where the ridge collided at 12 ma most lavas are syncollisional or postcollisional in age with eruptions of both sequences migrating northeastward at 50 to 70 km ma plateau lavas have ages from 12 to 7 ma in the western back arc and from 5 to 2 ma farther to the northeast trace element and isotopic data indicate main plateau lavas formed as larger percentage melts of a garnet bearing oceanic island basalt oib like mantle than postplateau lavas the highest percentage melts erupted in the western and central plateaus in a migrating slab window model main plateau lavas can be explained as melts that formed as upwelling subslab asthenosphere which flowed around the trailing edge of the descending nazca plate and then interacted with subduction altered asthenospheric wedge and continental lithosphere alkaline postplateau lavas can be explained as melts generated by weaker upwelling of subslab asthenosphere through the open slab window thermal problems of high pressure melt generation of anhydrous mantle can be explained by volatiles h2o and co2 introduced by the subduction process into slab window source region s an oib like rather than a mid ocean ridge basalt morb like source region and the lack of magmatism northeast of where ridge collision occurred at 13 to 14 ma can be explained by entrainment of weak plume s or regional variations in an ambient oib like asthenosphere

neogene uplift of central eastern patagonia dynamic response to active spreading ridge subduction the chile triple junction ctj episodically migrated northward during the past 14 ma from 54 s to its present day position at 46 30 s as different almost trench parallel spreading segments entered in subduction this migration resulted in the opening of an asthenospheric window below patagonia inducing a disturbance in the regional mantle convection on the overriding plate the middle miocene time corresponds to a major change in the central patagonian basin dynamics with a transition from subsidence to generalized uplift the detailed mapping and the morphological study of post middle miocene terraces evidence regional scale trench parallel tilt histories that differ depending on latitude south of 46 30 s the slopes of the fluvial terraces indicate a change from northward to southward tilt during late miocene terraces younger than the early pliocene do not show any trench parallel tilt north of 46 30 s in contrast only northward tilt active until the pleistocene is recorded we use a semianalytical model of dynamic topography which suggests that the northward migration of the chile triple junction should be accompanied by a dynamic uplift of the central patagonian basin uplift would cause both north directed and south directed tilt north and south of the triple junction respectively with values of 0 1 0 2 500 km east of the trench tilt measured in the southeastern part of the central patagonian basin 0 1 is comparable to values predicted using the semianalytical model the dynamic topography associated to the chile ridge subduction may have exerted a major control on the neogene dynamics of patagonia

pinguino in bearing polymetallic vein deposit deseado massif patagonia argentina characteristics of mineralization and ore forming fluids the pinguino deposit located in the low sulfidation epithermal metallogenetical province of the deseado massif patagonia argentina represents a distinct deposit type in the region it evolved through two different mineralization events an early in bearing polymetallic event that introduced in zn pb ag cd au as cu sn w and bi represented by complex sulfide mineralogy and a late ag au quartz rich vein type that crosscut and overprints the early polymetallic mineralization the indium bearing polymetallic mineralization developed in three stages an early cu au in as sn w bi stage ps1 a zn pb ag in cd sb stage ps2 and a late zn in cd ps3 indium concentrations in the polymetallic veins show a wide range 3 4 to 1 184 ppm in the highest indium values up to 1 184 ppm relate to the ps2 mineralization stage and are associated with fe rich sphalerites although significant in enrichment up to 159 ppm is also present in the ps1 paragenesis associated with sn minerals ferrokesterite and cassiterite the hydrothermal alteration associated with the polymetallic mineralization is characterized by advanced argillic alteration within the immediate vein zone and sericitic alteration enveloping the vein zone fluid inclusion studies indicate homogenisation temperatures of 308 2 327 c for ps1 and 255 312 4 c for ps2 and low to moderate salinities 2 to 5 eq wt nacl and 4 to 9 eq wt nacl respectively 34s values of sulfide minerals 0 76 to 3 61 indicate a possible magmatic source for the sulfur in the polymetallic mineralization while pb isotope ratios for the sulfides and magmatic rocks 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 17 379 to 18 502 15 588 to 15 730 and 38 234 to 38 756 respectively are consistent with the possibility that the pb reservoirs for both had the same crustal source spatial relationships hydrothermal alteration styles s and pb isotopic data suggest a probable genetic relation between the polymetallic mineralization and dioritic intrusions that could have been the source of metals and hydrothermal fluids mineralization paragenesis alteration mineralogy geochemical signatures fluid inclusion data and isotopic data confirm that the in bearing polymetallic mineralization from pinguino deposit is a distinct type in comparison with the well known epithermal low sulfidation mineralization from the deseado massif

jurassic epithermal au ag deposits of patagonia argentina abstract important precious metal deposits have been discovered during the last 10 years in the deseado massif region of patagonia argentina this region is a plateau consisting of middle to upper jurassic volcanic rocks that host fracture controlled epithermal au ag mineralization these mineral deposits represent low sulfidation type hydrothermal systems and formed following the main period of volcanism probably during the late jurassic period the presence of silica sinters and veins interpreted to be feeder structures indicates that the tops of some deposits have been preserved with erosion of younger sedimentary and volcanic rocks now exposing these systems these deposits represent diverse erosional levels ranging from sinter formed at the paleosurface to intermediate au ag rich quartz veins to base metal bearing au ag veins that represent deeper levels of the epithermal systems the best known deposits are in the cerro vanguardia district where vein systems occur over a 350 km 2 area and veins can be traced for more than 14 km geological mapping of the district has resulted in the definition of over 140 km of veins current reserves are over 3 2 million ounces au equivalent with grades of 10 g t au and 120 g t ag the geologic characteristics of the region and the presence of major au ag deposits provide targets for continuing exploration in the deseado massif

role of water in hydrocarbon generation from type i kerogen in mahogany oil shale of the green river formation abstract hydrous and anhydrous closed system pyrolysis experiments were conducted on a sample of mahogany oil shale eocene green river formation containing type i kerogen to determine whether the role of water had the same effect on petroleum generation as reported for type ii kerogen in the woodford shale the experiments were conducted at 330 and 350 c for 72 h to determine the effects of water during kerogen decomposition to polar rich bitumen and subsequent bitumen decomposition to hydrocarbon rich oil the results showed that the role of water was more significant in bitumen decomposition to oil at 350 c than in kerogen decomposition to bitumen at 330 c at 350 c the hydrous experiment generated 29 more total hydrocarbon product and 33 more c 15 hydrocarbons than the anhydrous experiment this is attributed to water dissolved in the bitumen serving as a source of hydrogen to enhance thermal cracking and facilitate the expulsion of immiscible oil in the absence of water cross linking is enhanced in the confines of the rock resulting in formation of pyrobitumen and molecular hydrogen these differences are also reflected in the color and texture of the recovered rock despite confining liquid water pressure being 7 9 times greater in the hydrous experiments than the confining vapor pressure in the anhydrous experiments recovered rock from the former had a lighter color and expansion fractures parallel to the bedding fabric of the rock the absence of these open tensile fractures in the recovered rock from the anhydrous experiments indicates that water promotes net volume increase reactions like thermal cracking over net volume decrease reactions like cross linking which results in pyrobitumen the results indicate the role of water in hydrocarbon and petroleum formation from type i kerogen is significant as reported for type ii kerogen

the marianas san marcos vein system characteristics of a shallow low sulfidation epithermal au ag deposit in the cerro negro district deseado massif patagonia argentina the cerro negro district within the argentinian deseado massif province has become one of the most significant recent epithermal discoveries with estimated reserves plus resources of 6 7 moz au equivalent the marianas san marcos vein system contains about 70 of the au ag resources in the district mineralization consists of upper jurassic 155 ma epithermal au and ag rich veins of low to intermediate sulfidation style hosted in and genetically related to jurassic intermediate composition volcanic rocks 159 156 ma veins have a complex infill history represented by ten stages with clear crosscutting relationships that can be summarized in four main episodes a low volume metal rich initial episode e1 an extended banded quartz episode with minor mineralization e2 a barren waning stage episode e3 and a silver rich late tectonic hydrothermal episode e4 the first three episodes are interpreted to have formed at the same time and probably from fluids of similar composition a 290 230 c fluid dominated by meteoric and volcanic waters 3 to 0 18owater with 3 nacl equivalent salinity and with a magmatic source of sulfur 1 to 2 34swater metal was mainly precipitated at the beginning of vein formation episode 1 due to a combination of boiling at 600 to 800 m below the paleowater table and associated mixing cooling processes as evidenced by sulfide rich bands showing crustiform colloform quartz adularia and chlorite smectite banding during episodes 2 and 3 metal contents progressively decrease during continuing boiling conditions and veins were filled by quartz and calcite during waning stages of the hydrothermal system and the influx of bicarbonate waters 6 to 8 5 18owater hydrothermal alteration is characterized by proximal illite adularia and silica zone with chlorite and minor epidote intermediate interlayered illite smectite and a distal chlorite halo this assemblage is in agreement with measured fluid inclusion temperatures a striking aspect of the marianas san marcos vein system is that the high grade high temperature veins are partially covered by breccia and volcaniclastic deposits of acidic composition and are spatially associated with hot spring related deposits and an advanced argillic alteration blanket a telescoped model is therefore proposed for the marianas san marcos area where deeper veins were uplifted and eroded and then partially covered by non explosive post mineral rhyolitic domes and reworked volcaniclastic deposits together with shallow geothermal features the last tectonic hydrothermal mineralization episode e4 interpreted to have formed at lower temperatures could be related to this late tectonic and hydrothermal activity

gold in magmatic hydrothermal solutions and the rapid formation of a giant ore deposit the ladolam hydrothermal system on lihir island papua new guinea hosts one of the youngest and largest gold deposits in the world several deep more than 1 kilometer geothermal wells were drilled beneath the ore bodies to extract water at 275 c and to facilitate open pit mining using a titanium down hole sampler we determined that the deep geothermal brine of magmatic origin contains 15 parts per billion gold at the current gold flux of 24 kilograms per year this deposit could have formed within 55 000 years the combination of sustained metal flux and efficient metal precipitation led to the formation of a giant hydrothermal gold deposit in a short period

the chon aike province of patagonia and related rocks in west antarctica a silicic large igneous province the field occurrence age classification and geochemistry of the mesozoic volcanic rocks of patagonia and west antarctica are reviewed using published and new information dominated by rhyolitic ignimbrites which form a bimodal association with minor mafic and intermediate lavas these constitute one of the largest silicic igneous provinces known equivalent in size to many mafic lips diachronism is recognized between the early middle jurassic volcanism of eastern patagonia marifil and chon aike formations and the middle jurassic earliest cretaceous volcanism of the andean cordillera el quemado ibanez and tobifera formations this is accompanied by a change in geochemical characteristics from relatively high zr and nb types in the east to subalkaline arc related rocks in the west although the predominance of rhyolites remains a constant factor all of the associated mafic rocks are well fractionated compared to direct mantle derivatives petrogenetic models favour partial melting of immature lower crust as a result of the intrusion of basaltic magmas possibly with some hybridisation of the liquids and subsequent fractionation by crystal settling or solidification and remelting the formation of large amounts of intracrustal silicic melt acted as a density barrier against the further rise of mafic magmas which are thus rare in the province

geochemical and petrophysical source rock characterization of the vaca muerta formation argentina implications for unconventional petroleum resource estimations abstract the vaca muerta formation is currently regarded as the most prolific source rock interval for unconventional petroleum exploration in argentina in this study we integrate recent ct scanner nuclear magnetic resonance nmr t1 t2 and rock eval shale play analytical techniques combined with classical geochemical petrological and petrophysical methods to characterize vaca muerta source rocks along a vertical profile the proposed analytical workflow was tested here on 4 samples derived from one core the lje 1010 borehole drilled in the lowermost jurassic vaca muerta member neuquen basin argentina to evaluate the unconventional hydrocarbon potential and pore network attributes first entire rock samples were analyzed by dual energy ct scanner to evaluate possible heterogeneities this also helped in the selection of representative samples then the organic matter properties were investigated by open system pyrolysis techniques organic petrography and biomarker analyses as a function of the core depth a comparative approach between open system pyrolysis methods e g rock eval basic bulk rock shale play methods vs source rock analyzer is also illustrated in this work finally petrophysical characteristics and pore network attributes in shale were estimated by gas permeability steady state method corrected for klinkenberg effect porosity and nmr methods the investigated samples have oil window maturity and are characterized by a network of solid bitumen based on new rock eval shale play data the potentially producible oil present in the rock samples was estimated using the modified oil saturation index osi sh0 sh1 peaks 100 toc results indicate that the oil crossover effect and potential productive oils occur within intervals showing higher toc values 3 to 8 wt we also illustrated here that for unconventional shale play perspectives rock eval shale play parameters sh0 sh1 allow to obtain both a better quantification of free and retained hydrocarbons in source reservoir rock samples and correct original oil in place ooip estimations in early exploration campaign for shale oil and shale gas assessment for vaca muerta rock samples ooip estimations range from 60 to 160 bbl oil acre ft approximately we also demonstrated that the solid bitumen oil and organic matter are clearly distinguished in the studied samples using advanced nmr t1 t2 maps obtained at different temperatures the solid bitumen was clearly evidenced as a peak with t1 t2 ratio 14 on nmr t1 t2 maps concerning the matrix bulk rock permeability the obtained results showed that the most deep sample is characterized by a permeability of about 140 nanodarcy nd whereas the shallower sample containing also higher amounts of organic matter is more permeable 213 nd indicating that toc values play a main control on vaca muerta poromechanical characteristics the maximum total porosity values range between 6 5 and 21 8 and were calculated in this work integrating nmr and helium porosity values finally global interpretations of these obtained results suggest that the vaca muerta formation could be considered as a prolific shale play interval for unconventional petroleum exploration in the near future

basin evolution and oil shale deposition during upper cretaceous in the songliao basin ne china implications from sequence stratigraphy and geochemistry abstract the controlling factors of oil shale formation within the upper cretaceous qingshankou and nenjiang formations of the songliao basin are investigated by petrological and geochemical methods sediment deposition was balanced by basin subsidence resulting in the accumulation of cretaceous strata of high thickness global sea level fluctuations have been related to periods of oil shale deposition within the basin the results indicate a comparable depositional environment during oil shale formation within the two upper cretaceous strata with respect to palaeotectonic and palaeoclimate but differences in the accommodation space during accumulation of the two formations the larger accommodation space during deposition of the nenjiang formation resulted in the higher thickness and wider distribution of the oil shale members total thickness 11 2 32 m distribution area 4 48 103 km2 within the basin as compared to the oil shale of the qingshankou formation total thickness 2 19 3 m distribution area 1 3 103 km2 further differences exist with regard to the palaeoenvironment of oil shale formation and primary productivity deposition of the qingshankou formation 1st member and nenjiang formation 1st member took place within a saline brackish lake under anoxic conditions in the bottom water preservation of organic matter is suggested to have been less favorable during deposition of the nenjiang formation 2nd member higher primary productivity is believed to be the responsible factor for the accumulation of organic rich sediments in the qingshankou formation 1st member the interplay of these two factors i e preservation productivity leads to the formation of oil shale in the qingshankou formation average toc 8 32 tocmax 13 52 average oil yield 5 57 with better hydrocarbon source rock potential and slightly higher oil yield during pyrolysis as in the nenjiang formation average toc 7 76 tocmax 9 7 average oil yield 5 54 primary productivity is suggested as the main controlling factor on differences in oil shale quality and source rock potential between the two formations whereas the variations in quality within each formation mainly depend on the preservation of organic matter the high thickness wide spatial distribution and excellent hydrocarbon potential of the upper cretaceous oil shales in the songliao basin are suggested to have been the result of large accommodation space stable palaeoenvironmental conditions and high primary productivity

self ordering and complexity in epizonal mineral deposits epizonal base and precious metal deposits makeup a range of familiar deposit styles including porphyry copper gold epithermal veins and stockworks carbonate replacement deposits and polymetallic volcanic rock hosted vhms deposits they occur along convergent plate margins and are invariably associated directly with active faults and volcanism they are complex in form variable in their characteristics at all scales and highly localized in the earth s crust more than a century of detailed research has provided an extensive base of obser vational data characterizing these deposits from their regional setting to the fluid and isotope chemistry of mineral deposition this has led to a broad understanding of the large scale hydrothermal systems within which they form low salinity vapor released by magma crystallization and dispersed into vigorously convecting ground water systems is recognized as a principal source of metals and the gases that control redox conditions within systems the temperature and pressure of the ambient fluid anywhere within these systems is close to its vapor liquid phase boundary and mineral deposition is a consequence of short timescale perturbations generated by localized release of crustal stress however a review of occurrence data raises questions about ore formation that are not addressed by traditional genetic models for example what are the origins of banding in epithermal veins and what controls the frequency of oscillatory lamina tion what controls where the phenomenon of mineralization occurs and why are some porphyry deposits for example so much larger than others the distinctive self organized characteristics of epizonal deposits are shown to be the result of repetitive coupling of fracture dilation consequent on brittle failure phase separation boiling and heat transfer between fluid and host rock process cou pling substantially increases solute concentrations and triggers fast far from equilib rium depositional processes since these coupled processes lead to localized transient changes in fluid characteristics paragenetic isotope and fluid inclusion data relate to conditions at the site of deposition and only indirectly to the characteristics of the larger scale hydrothermal system and its longer term behavior the metal concentra 1 the us government has the right to retain a nonexclusive royalty free license in and to any copyright covering this paper

organic accumulation in lacustrine rift basin constraints from mineralogical and multiple geochemical proxies the lunpola basin in the central tibet is the highest petroliferous basin in the world the basin is a cenozoic lacustrine rift basin with widespread oil shale depositions which provide a valuable example for understanding the mechanisms of organic accumulation thirty five samples of oil shale and mudstone were collected from one of the organic rich oil shale intervals in the lunpola basin to discuss the controlling factors of organic enrichment in the investigated oil shale interval many redox proxies including v v ni ratios mo u covariations and pyrite framboid size distribution suggest anoxic conditions however the almost consistent variation patterns of toc p and mo contents indicate that organic matter accumulation was controlled mainly by primary productivity the relatively low sr ba average 0 74 and sr cu ratios average 4 75 suggest a warm humid climate during the oil shale deposition these conditions are suitable for living of organisms which would raise the initial productivity of lake and in turn could have led to the oxygen depleted conditions the detrital input together with fast sedimentary rate during the oil shale deposition would result in dilution of organic matter

a plea for more caution in fault slip analysis abstract the analysis of fault slip data is a widely used tool in structural geology this method consists of three major steps a data acquisition by measurements in outcrops b data separation into homogeneous subsets and calculation of the principal stress or strain axes with one of several available methods and c data interpretation in a regional tectonic context which includes the assignment of ages and the derivation of regional patterns each one of these three steps may introduce artefacts and misinterpretations the major problem during step a is sampling bias due to unfavourable outcrop geometry or due to neglecting faults with subtle slip sense indicators step b contains numerous possibilities to influence the calculation results e g by arbitrary separation of data into subsets choice of the analysis method and uncritical use of software age assignment in step c can in most cases be made only indirectly e g by the assumption that measured outcrop scale faults have the same age as parallel map scale faults or by the inference that subsets from different sites with parallel oriented principal axes are syngenetic neither assumption is necessarily valid with this paper we want to sharpen researchers awareness of the problems related to fault slip analysis

seismic reflection patterns associated with continental convergent margins through time abstract the important role of tectonic wedging in accommodating horizontal shortening strain is increasingly recognized to occur at all scales within continental convergence zones wedge structures appear most common in accretionary orogens involving former passive margins with large volume turbidite sedimentary fans or accretionary prisms relatively small scale wedges can be recognized in outcrop but crustal scale wedge geometries must be observed and analysed using seismic reflection methods reflection profiles now exist across a large number of accretionary orogen settings of diverse ages and continents similarities in seismic patterns within the major eras enable creation of a series of stylised continental margin transects for each major time period relatively low rock strength found in turbidite sediments rich in micas especially when contrasted with strengths of igneous volcanic arc rocks plays a major role because it localizes thrust faults within weaker horizons schematic cross sections across accretionary margins that span five geological eras summarize the principal features interpreted on numerous seismic reflection sections important details vary such as the depths where tectonic wedging initiates but tectonic wedges of diverse scales are observed in all cross sections the percentage and degree of consolidation or metamorphism of turbiditic greywackes apparently controls the degree depth and scale of the crustal wedging