organic geochemistry of oils and condensates in the kekeya field southwest depression of the tarim basin china this study shows that the oils and condensates in the kekeya field in the tarim basin nw china belong to a single family most likely derived from marine shale source rocks deposited under oxic suboxic conditions with mixed terrigenous and algal bacterial organic inputs the maturity data clearly indicate that the paraffinic condensates were not formed by thermal cracking of oil during late catagenesis ro 1 2 both the oils and condensates were generated within the normal oil window whereas addition of gaseous hydrocarbons from a separate source resulted in migration fractionation and hence spuriously high heptane indices age specific biomarkers show that the oils and condensates were not generated from the mesozoic cenozoic strata but from the carboniferous permian sections 1d basin modeling results are consistent with this interpretation suggesting that the mesozoic eocene strata are currently immature with respect to hydrocarbon generation and expulsion deep seated faults may have provided routes for upward fluid migration at the time of active deformation during several pulses of the himalayan orogeny the favored targets for further petroleum exploration in front of the kunlun mountains include the deep structures within the carboniferous permian strata for indigenous petroleum accumulations and anticlines and stratigraphic traps within the mesozoic cenozoic sections that are cut by deep seated thrust faults where secondary petroleum accumulations most likely occurred

influence of maturity on carbazole and benzocarbazole distributions in crude oils and source rocks from the sonda de campeche gulf of mexico abstract carbazole geochemistry has been studied for a petroleum system in which vertical migration is prominent and where reservoirs are locally sourced an essentially uniform organofacies of organicrich tithonian source rocks from the sonda de campeche gulf of mexico covering a well defined maturity sequence 0 36 1 29 rr and associated crude oils 0 49 0 92 rc from palaeocene reservoirs formed the sampling base comparison of the distribution of alkylcarbazoles and benzocarbazoles in rock bitumens and oils revealed that fractionation due to primary expulsion had no effect on the distribution of shielded exposed carbazoles within crude oils perhaps more importantly the benzocarbazole ratio in both rock extracts and crude oils increased with maturity indicating that this parameter cannot be directly used as a migration indicator in petroleum systems where vertical migration through faults and fissures represents the main avenues of oil migration

dynamics of shallow late variscan gold mineralization the le châtelet au arsenopyrite quartz veins massif central france the le ch telet gold deposit is unique among the mined deposits of the french variscan basement in that the gold is not free but caught up in the arsenopyrite crystal lattice microstructural analysis shows that the au arsenopyrite quartz veins are hosted by north trending dextral strike slip faults resulting from nne ssw compression during the early stephanian around 300 ma textural study indicates that vein emplacement was due to sequential dynamics related to spasmodic strike slip movements along these brittle structures seismic regime the classic sequence begins with the slow crystallization of sulphide free comb quartz followed by a co deposition of microcrystalline quartz and needles of au arsenopyrite the rapid crystallization of the au arsenopyrite bearing microcrystalline quartz was due to a sudden drop in fluid pressure the veins correspond to dilational jogs formed by a suction pump mechanism during a late phase of the variscan orogeny they were trapped in migmatite about 1 km below surface

mixing of metamorphic and surficial fluids during the uplift of the hercynian upper crust consequences for gold deposition a detailed geochemical study of fluids from representative quartz sealed faults hosting late hercynian gold concentrations shows that fluids percolating the mineralised faults had two main distinct reservoirs one was a quite shallow and the other rather deep seated both fluids have lost a great part of their original geochemical signature through interactions with host metamorphic formations early fluids present during the primary sealing of the faults by quartz are considered to have effectively equilibrated with the metamorphic pile and then predominantly flowed upwards along the faults they are characterised by ch4 co2 h2o ratios rather typical of fluids equilibrated with graphite and moderate to medium chlorinities with a high br cl ratio the striking feature of the gold bearing quartz is that gold is not synchronous within any quartz deposition and appears located in late microfractures and associated with pb bi sb sulphosalts and sulphides these late stages are characterised by fluids whose salinities decrease to very low values indicating their progressive dilution by waters of more surficial origin in the fault system the long lived activity of the fault favoured the connection between two distinct fluid reservoirs at a critical time during the basement uplift the fluids evolved through two main driving mechanisms which were responsible for the au deposition i decrease in temperature accompanying decompression from supra lithostatic to hydrostatic conditions which yielded in some instances volatile unmixing in the faulted systems ii mixing of the resulting fluids with waters entering the hydrological systems from shallower reservoirs in addition to dilution and fluid mixing which are favourable factors for decreasing the gold solubility the presence of microfractured sulphides could have enhanced gold precipitation through electrochemical processes d 2002 elsevier science b v all rights reserved

geochemical characterisation of middle devonian oils in nw alberta canada possible source and maturity effect on pyrrolic nitrogen compounds abstract molecular geochemical compositions of a suite of middle devonian sourced and reservoired oils from the rainbow zama shekilie sub basins in n w alberta canada reveal the presence of at least two oil families in the study area the distribution of each oil family is geographically restricted to a single sub basin consistent with the oils being sourced locally within a series of closed generation migration trapping systems the diversity in the biomarker distributions of the oils indicates the wide range of depositional environments and source materials existing in each sub basin rather than mixing of end member oils across different sub basins clear maturity differences are observed between the oils from the rainbow and zama subbasins pre cretaceous thermal anomalies along the reactivated regional precambrian basement faults are proposed as one of the major causes for the relatively high maturity levels for the middle devonian source rocks in the study area we infer that depositional environment and thermal maturity have had a strong impact on the geochemical characteristics of the saturated and aromatic hydrocarbons in the rainbow shekilie zama oils but may not influence the pyrrolic nitrogen compounds to a significant extent however recognition of possible source and maturity effects on pyrrolic nitrogen compounds in other studies suggests that these factors should be considered before the pyrrolic nitrogen compounds are used to characterize petroleum migration

orientation of in situ stresses in the oceanic crust two in situ measurements of principal stress directions have been made in dsdp holes 504b south of the costa rica rift on the nazca plate and 597c west of the east pacific rise on the pacific plate in both cases the orientations of in situ principal stresses determined from borehole breakouts are consistent with the stress directions inferred from intraplate earthquakes located near the sites

fluid rock interaction processes related to hydrothermal vein type mineralization in the siegerland district germany implications from inorganic and organic alteration patterns altered wallrocks of vein type pb zn sb mineralization siegerland district rheinisches schiefergebirge have been investigated by a combination of inorganic and organic geochemical methods including major and trace element analysis vitrinite reflectance measurements c isotope and elemental analysis of kerogen alteration features of the siliciclastic pelitic psammitic lower devonian wallrocks are increased k na ratios significant desilicification and relative immobility of a number of elements notably al ti zr cr v wallrock kerogens display elevated vitrinite reflectance values decrease in h c atomic ratios coupled with increase in s c atomic ratios and heavier c isotope compositions compared to the unaltered precursor sedimentary rocks interaction processes between the hydrothermal fluids and the respective wallrocks related to injection of high temperature silica undersaturated solutions are dominated by quartz dissolution coupled with sericitization reactions heat transfer due to fluid infiltration convection and wallrock reactions caused fluid cooling which promoted the sequential deposition of quartz and stibnite sulphosalts within the vein systems hydrocarbons detected in ore assemblages of pb zn and sb mineralization were most probably derived from the lower devonian very low grade meta sedimentary rocks high maturity levels and pronounced typical organic alteration patterns indicate that thermochemical so2 4 reduction tsr played an important role in precipitation of metal sulphides the present study demonstrates that a combination of inorganic and organic investigations on fluid rock interaction processes is particularly useful for deciphering precipitation mechanisms of base metal sulphides

a review of the biogeochemical controls on the occurrence and distribution of polycyclic aromatic compounds pacs in coals abstract the organic matter in coal contains polycyclic aromatic compounds pacs of varying quantities in diverse soluble and insoluble forms pacs in coal are of special interest for organic geochemical studies because they have been successfully used as biological marker compounds biomarkers and indicators of thermal maturity in addition they could provide critical information to understand the structural and compositional evolution of the coal organic matters during coalification and to predict pac releasing characteristics during coal utilization the main purpose of this paper is to provide a critical review on the current state of knowledge on the potential use of pac composition to understand the underlying biogeochemical factors that control pac occurrence and distribution in coal the published pac data of world coal are first compiled according to their ranks natural coke anthracite semi anthracite bituminous coal low volatile bituminous coal medium volatile bituminous coal high volatile bituminous coal sub bituminous coal lignite countries brazil canada china france germany japan usa formation periods carboniferous permian jurassic cretaceous early middle cenozoic then the biogeochemical factors affecting the occurrence and distribution of pacs in coal including biogenic precursor materials coal rank maceral composition depositional environment and geological settings are comprehensively reviewed the results show that the geochemical parameters of pacs in coal are robust tools to trace the coalification processes from the molecular perspectives and to understand the corresponding biogeochemical process e g depositional environment geological settings igneous intrusion occurring during coal formation

correlation and migration studies of north central sumatra oils the central sumatra basin csb is a prolific petroleum producing basin and its petroleum systems have been extensively studied the widely occurring tertiary lacustrine shale brown shale has long been recognized as the main source rock for tens of billions of barrels of oil in place the oils produced from different fields display significant variation in source characteristics that have been attributed to variation in source facies despite this generalized recognition of the oil source the links between major oil accumulations and many possible source kitchens throughout the basin have not been established as detailed oil source correlation and oil migration routes are not well defined for continued exploration in the region detailed genetic grouping and migration routes of the oils were evaluated through geochemical characterization of numerous oils from various fields in the northern part of central sumatra biomarker and carbon isotopic data indicate that the oils are quite similar geochemically but form several genetic groups on the basis of subtle but persistent differences in source facies the groupings appear geographically meaningful and show association of the different oil groups with various troughs carbazole distributions show consistency in suggesting differences in relative migration distance among the oils within each genetic group by combining the oil grouping and carbazole distributions with geological data models of migration directions and pathways for oils in north central sumatra have been constructed

an example of intraplate neotectonic activity vilarica basin northeast portugal the vilarica tectonic basin nw iberian peninsula is presented as an example of intraplate neotectonic activity the regional geological setting is first introduced then followed by a brief view on the neotectonic activity in portugal the basin consists of an elongated depression approximately 20 km long and 2 to 3 km wide trending nne ssw it is located astride a late variscan strike slip fault the manteigas braganca fault suggesting that it might correspond to a structural depression related to reactivation movements on that fault mapping of neogene and quaternary cover deposits preserved in the basin and its vicinity was accomplished and numerous evidence of tectonic deformation tilting and faulting affecting the sediments were found other geomorphological criteria are discussed showing the structural origin of the vilarica basin and its neotectonic activity attending to its location on the manteigas braganca fault the vilarica depression is interpreted as a pull apart basin resulting from left lateral strike slip displacement on that fault in the quaternary average fault slip rates are estimated with values comprised between 0 2 mm yr and 0 5 mm yr these slip rates are typical of moderate to moderately high degrees of fault activity and are compatible with the regional faulting geomorphic expression and the relatively important historical and instrumental seismicity affecting the vilarica region finally a geodynamical model is proposed and the studied area is presented in the geodynamic framework

on the tectonic origin of iberian topography the present day topography of the iberian peninsula can be considered as the result of the mesozoiccenozo ic tectonic evolution of the iberian plate including rifting and basin formation during the mesozoic and compression and mountain building processes at the borders and inner part of the plate during the tertiary followed by neogene rifting on the mediterranean side and surface processes acting during the quaternary the northern central part of iberia corresponding to the geological units of the duero basin the iberian chain and the central system shows a mean elevation close to one thousand meters above sea level in average some hundreds of meters higher than the southern half of the iberian plate this elevated area corresponds to i the top of sedimentation in tertiary terrestrial endorheic sedimentary basins paleogene and neogene and ii planation surfaces developed on paleozoic and mesozoic rocks of the mountain chains surrounding the tertiary sedimentary basins both types of surfaces can be found in continuity along the margins of some of the tertiary basins the bouguer anomaly map of the iberian peninsula indicates negative anomalies related to thickening of the continental crust correlations of elevation to crustal thickness and elevation to bouguer anomalies indicate that the dierent landscape units within the iberian plate can be ascribed to dierent patterns 1 the negative bouguer anomaly in the iberian plate shows a rough correlation with elevation the most important gravity anomalies being linked to the iberian chain 2 most part of the so called iberian meseta is linked to intermediate elevation areas with crustal thickening this pattern can be applied to the two main intraplate mountain chains iberian chain and central system 3 the main mountain chains pyrenees and betics show a direct correlation between crustal thickness and elevation with higher elevation crustal thickness ratio for the central systemvs the betics and the pyrenees other features of the iberian topography namely the longitudinal pro le of the main rivers in the iberian peninsula and the distribution of present day endorheic areas are consistent with the tertiary tectonic evolution and the change from an endorheic to an exorheic regime during the late neogene and the quaternary some of the problems involving the timing and development of the iberian meseta can be analysed considering the youngest reference level constituted by the shallow marine upper cretaceous limestones that indicates strong dierences induced by i the overall tertiary and recent compression in the iberian plate responsible for dierences in elevation of the reference level of more than 6 km between the mountain chains and the endorheic basins and ii the eect of neogene extension in the mediterranean margin responsible for lowering several thousands of meters toward the east and uplift of rift shoulders a part of the recent uplift within the iberian plate can be attributed o sostatic uplift in zones of crustal thickening

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

influence of maturity on distributions of benzo and dibenzothiophenes in tithonian source rocks and crude oils sonda de campeche mexico abstract the sureste basin is the most prolific oil producing area of mexico extending from the mainland into the sonda de campeche offshore region the tithonian sedimentary sequence is the most important source of hydrocarbons it contains sulphur rich kerogen which progressively cracks to form petroleum beginning at 0 53 rr maturity increases from northeast to southwest across the region sulphur compounds in the tithonian source rocks and in the petroleums they have generated have been studied by gas chromatography alkylbenzothiophenes are present in highest abundance at low maturity whereas the alkyldibenzothiophenes are most abundant at higher stages of maturity the relative abundance of specific c3 benzothiophene isomers are especially sensitive to changes in maturity of sulphur rich type ii organic matter a novel maturity parameter the c3 benzothiophene index c3bti shows a very good correlation to vitrinite reflectance values r2 0 96 n 10 the methyldibenzothiophene ratio mdr also has a wide dynamic range application of c3bti and mdr to the study area strongly supports a model involving localised vertical migration avenues though several possible scenarios may explain the filling history of reservoirs in the southwest part of the sonda de campeche

carbazole distributions in rocks from non marine depositional environments abstract pyrrolic nitrogen compounds have been studied from extracts of the rocks collected from the tertiary saline lacustrine strata in the qaidam basin and the middle lower jurassic coal bearing strata in the turpan basin nw china biomarker signatures revealed the presence of three sample groups related to saline lacustrine conditions in the qaidam basin and freshwater lake and swamp depositional settings in the turpan basin significant differences in carbazole distributions were observed among the sample groups from different depositional environments generally a strong predominance of 1 4 1 5 dimethylcarbazoles over 1 3 1 6 dimethylcarbazoles was found for the qaidam rocks from the saline lacustrine settings with a ratio of 1 3 1 6 1 4 1 5 dimethylcarbazole ranging from 0 35 to 0 66 while enhanced amounts of 1 3 1 6 dimethylcarbazoles relative to 1 4 1 5 dimethylcarbazoles were detected for the turpan samples from the swamp environments with the 1 3 1 6 1 4 1 5 dimethylcarbazole ratio 0 8 samples from the freshwater lake environments in the turpan basin showed intermediate values for the 1 3 1 6 1 4 1 5 dimethylcarbazole ratio in addition a predominance of 2 4 dimethylcarbazole over 2 6 dimethylcarbazole was observed for the qaidam samples whereas most turpan samples showed elevated amounts of 2 6 dimethylcarbazole relative to 2 4 dimethylcarbazole moreover 3 methylcarbazole occurred as the least abundant c 1 carbazole isomer for most qaidam rocks while the turpan samples from swamp settings often showed an enhanced abundance of 3 methylcarbazole the 1 3 1 6 1 4 1 5 dimethylcarbazole ratio was observed to have a positive correlation with 3 4 methylcarbazole 2 6 2 4 dimethylcarbazole and pr ph respectively these observations may indicate that c 1 and c 2 carbazoles with a methyl group at c 3 c 6 prevailed for swamp settings whereas isomers with a methyl at c 4 c 5 were dominant for the freshwater or saline lacustrine environments although variations in benzocarbazoles were detected in the bitumens an obvious correlation was not observed for the different depositional environments

fractionation of azaarenes during oil migration abstract a comparative study of alkylbenzoquinolines in crude oils and rock extracts bitumens from japan and sumatra shows that the ratios of nitrogen masked isomers nmis to nitrogen exposed isomers neis and the ratio of higher homologs to lower homologs is higher in crude oils than in corresponding bitumens also a regular increase in the ratios of nmis to neis with increasing migration distance is observed for a series of crude oils from the sarukawa oil field northeastern japan these results are attributed to the preferential migration of nmis caused by their weak adsorption on clay minerals and or their low solubility in interstitial water and the selective removal of lower honologs caused by their irreversible adsorption onto clays during oil migration which are regarded as geochromatographic phenomena it is suggested that those ratios can be used to estimate the degree of fractionation of oils during primary and secondary migration

stress pattern in portugal mainland and the adjacent atlantic region west iberia the portuguese mainland territory is located close to the azores gibraltar plate boundary in a tectonic setting responsible for significant neotectonic and seismic activities however few data concerning the present regional lithospheric stress field were available as testified by recently published maps of stress indicators for the europe and mediterranean regions one of the authors already presented a synthesis on this subject cabral 1993 where geological and geophysical stress indicators were considered in this paper we introduce new information mainly a considerable amount of borehole breakout data the updated data set comprises 32 reliable stress indicators showing a mean azimuth of 145 standard deviation 21 for the maximum horizontal stress direction shmax on the average the geological data are rotated clockwise and the focal mechanism data deviated anticlockwise to that azimuth while the borehole elongation results are consistent with the mean shmax trend these differences in stress trend suggest a regional progressive rotation of the shmax direction from nnw sse to wnw ese since the upper pliocene to estimate stress trajectories new and published stress indicators in the adjacent atlantic area and northern africa were also investigated showing a very uniform nw se shmax trend in west iberia a high level of horizontal compressive stress acting oblique to the western portuguese continental margin is inferred and interpreted in view of a proposed regional geodynamical model of activation of this passive margin with the nucleation of a subduction zone in the atlantic sw of iberia at the gorringe submarine bank which is propagating northward along the base of the continental slope at the transition between thinned and normal continental crust

mesozoic exhumation history and palaeolandscape of the iberian massif in eastern galicia from apatite fission track and u th he data apatite fission track aft and u th he ahe data combined with time temperature inverse modelling reveal the cooling and exhumation history of the iberian massif in eastern galicia since the mesozoic the continuous cooling at various rates correlates with variation of tectonic boundary conditions in the adjacent continental margins the data provide constraints on the 107 timescale longevity of a relict paleolandscape aft ages range from 68 to 174 ma with mean track lengths of 10 7 2 6 to 12 6 1 8 m and ahe ages range from 73 to 147 ma fastest exhumation 0 25 km ma occurred during the late jurassic to early cretaceous main episode of rifting in the adjacent western and northern margins exhumation rates have decreased since then and have been approximately one order of magnitude lower across inland galicia the aft data are consistent with early cretaceous movement on post variscan ne trending faults this is coeval with an extensional episode offshore the ahe data in this region indicate less than 1 7 km of denudation in the last 100 ma this low exhumation suggests the attainment of a mature landscape during late cretaceous post rift tectonic stability whose remains are still preserved the low and steady rate of denudation prevailed across inland galicia despite minor n s shortening in the northern margin since 45 ma ago in north galicia rock uplift in response to nw strike slip faulting since early oligocene to early miocene has caused insufficient exhumation 3 km to remove the mesozoic cooling signal recorded by the aft data

the influence of facies and depositional environment on the occurrence and distribution of carbazoles and benzocarbazoles in crude oils a case study from the gulf of suez egypt abstract two major hinge zones separate the gulf of suez gos of egypt into three tectonic sub provinces namely the northern central and southern sectors based on bulk and molecular parameters the crude oils from the gos can be subdivided into three groups according to their geographical origin from the three sectors the geochemical characteristics of the oils are consistent with inferred depositional environments of anoxic marine carbonate facies in the central sector compared to a more oxic environment that has received an increased proportion of clastic input in the southern sector while the northern is intermediate in character most of the oils cover a relatively narrow maturity range 0 86 0 98 r c in the peak oil window the biomarker parameter ts ts tm is controlled by variations of facies and depositional environment but not by maturity concentrations of pyrrolic nitrogen compounds in the gos crude oils are in general relatively low but show a large range of variability in crude oils of the northern sector a strong predominance of c 4 and c 5 carbazoles over the lower homologues is observed towards the south the relative abundance of carbazole and the methylcarbazoles increases successively variations within the methylcarbazoles and c 2 carbazoles are rather small and therefore are not useful for a straightforward classification of oil families however atypical patterns in some of the oils particularly from the northern sector give evidence for contributions from yet unidentified local sources which might not be of general importance in the gos petroleum province benzo b carbazole is near or even below detection limit in the gos crude oils the benzocarbazole a a c ratio shows a consistently positive correlation with api gravity pr ph and ts ts tm and a negative correlation with the sulphur content based on these observations it is inferred that facies and depositional environment of the relevant source rocks are the major factors influencing the benzocarbazole distributions in the central sector of the gos in which oils are predominantly sourced from carbonates deposited under strongly reducing conditions a a c values are mainly below 0 5 in the southern sector where source rocks were deposited under less reducing conditions and received significant clastic input as well as in the northern sector the a a c values are mainly above 0 5

migration features of crude oil in fluvial deposits of maling oilfield in ordos basin china abstract oils in the maling oil field ordos basin are produced from fluvial deposits within the yan 9 and yan 10 subsections of the yanan formation through the analysis of pyrrolic nitrogen compounds and fluid inclusions the oil charging site migration direction and pathway and timing were interpreted in relationship with the sedimentary features and the high pressure observed in the mesozoic sequence the spatial distribution pattern of the fractionation of neutral nitrogen compounds in the crude oils suggested two possible charging positions in the studied area the ratios of the isomeric nitrogen compounds increase toward the center of the study area from both northwest and southeast directions of the region indicating that the lateral charging directions were likely from both the southeast and the northwest toward the center of the oil field the isomeric ratios of pyrrolic nitrogen compounds in the oils from different area of the maling oilfield increase with the decrease of depth from yan 10 to yan 4 5 subsections showing vertical migration of oil to the reservoirs the homogenization temperature of fluid inclusions in the reservoir rocks exhibited two peaks reflecting the two stages of oil migration and accumulation the migration pathways include fluvial sand bodies and unconformity surfaces the migration driving force was likely the capillary pressure and the abnormally high strata pressure in the mesozoic sequences

effect of artificial maturation on carbazole distributions as revealed by the hydrous pyrolysis of an organic sulphur rich source rock ghareb formation jordan abstract hydrous pyrolysis experiments were performed on the ghareb formation upper cretaceous jordan a carbonate and organic rich toc 19 6 source rock using a temperature range of 200 to 360 c 72 h the original sediment contains only low amounts of carbazoles maximum 2 2 g g bitumen for 1 methylcarbazole with increasing thermal maturation intense generation begins at temperatures only in excess of 300 c reaching a maximum at 360 c likewise during natural maturation generation occurs at later stages of maturity e g for tithonian source rocks at 0 81 rr and for posidonia shale at 0 88 rr some isomeric changes during hydrous pyrolysis do not resemble those in nature whereas others do the relative abundances of selected c1 and c2 alkylcarbazoles on ternary diagrams reveal differences whereas the benzo a carbazole benzo a carbazole benzo c carbazole ratio is closely similar the latter result supports the contention that maturation plays a key role in controlling carbazole distributions in source rocks however the results for alkylcarbazoles especially the c2 carbazoles are not easy to interpret

oil origin and secondary migration pathway in the bonan sag bohai bay basin china abstract the oil origin and secondary migration pathways were investigated in the bonan sag using basin modeling and petroleum geochemical data including biomarker assemblages of saturated hydrocarbons and pyrrolic nitrogen compounds the modeling of secondary oil migration pathway was performed based on the reconstruction of burial thermal maturity and oil generation histories modeling results are calibrated by the distribution of oil wells and oil fields as well as traced secondary oil migration pathways inferred from pyrrolic nitrogen compounds carbazole parameters were selected to trace the secondary oil migration pathway based on the investigation of oil origin three groups of oils sourced from source rocks of the third and fourth members of shahejie formation es3 and es4 have been identified in this study group oils from es3 source rocks mainly occurred in the center of sag group oils from es4 source rocks occurred in the margin regions group oils were interpreted to be the mixed sources from es3 and es4 source rocks three oil migration pathways can be traced by pyrrolic nitrogen compounds based on varied carbazole parameters the major stages of oil generation of es3 and es4 source rocks occurred at about 30 20 ma and 5 0 ma which coincided with oil charge periods secondary oil migration pathways have been predicted successfully by the oil migration modeling in the bonan sag based on the calibration with oil wells oil fields and the traced oil migration pathways by pyrrolic nitrogen compounds favorable zones located on the primary secondary oil migration pathways at the periods of oil charge may be the prospective regions for oil exploration in the bonan sag

effect of maturity and petroleum expulsion on pyrrolic nitrogen compound yields and distributions in duvernay formation petroleum source rocks in central alberta canada abstract a quantitative study of pyrrolic nitrogen compounds was conducted on a series of marine carbonate petroleum source rock extracts taken from the upper devonian duvernay formation in the central alberta portion of the western canada sedimentary basin with increasing thermal maturity concentrations of various pyrrolic nitrogen compounds in the rock extracts increase drastically together with significant compositional variations related to alkyl substitution position the study provides circumstantial evidence for adsorptive interactions operating between organic nitrogen compounds and solid organic mineral phases in subsurface sedimentary rocks during petroleum generation and expulsion the absolute concentrations and relative distributions of pyrrolic nitrogen compounds in the extracts of different maturity ranges provide background information for the calibration of such data in migrated petroleums as an independent measurement of secondary oil migration range of duvernaysourced oils in the basin

geochemical effects of petroleum migration and expulsion from toarcian source rocks in the hils syncline area nw germany for mature oil prone source rocks of toarcian age in the hils syncline area nw germany the geochemical effects of primary migration of petroleum are shown expulsion has occurred at high efficiencies primarily via a network of macro and micro fractures the effects of this fracture controlled expulsion with respect to gross and molecular composition of c15 soluble organic matter are documented samples from fractured intervals have expelled total c15 soluble organic matter more efficiently than adjacent unfractured intervals a systematic comparison of samples taken at cm intervals away from macro fractures reveals compositional gradients which are interpreted to reflect preferential depletion of saturated and aromatic hydrocarbons from the source rock shale into the fractures extracts of shale samples directly at fracture walls are enriched in nso compounds and highly polar asphaltene like fractions the composition of residual petroleum fluids extracted from the fracture fill materials is variable in some cases there is a close match with that of the shale at some distance away from the fractures in other cases there is geochemical evidence to suggest that petroleum fluids were chemically altered during lateral flow along the fractures based on available geological and geochemical evidence a conceptual model is proposed to explain fracture development and fluid flow processes rapid heating by a nearby intrusive body at shallow depths when the toarcian sediments still contained about 15 20 pore water has played an important role overpressuring of aqueous pore fluids with abundant dissolved carbonate caused intense fracturing of the rich intervals in the mature toarcian sections finally the closely interdependent relationships between petroleum generation and petroleum migration processes are documented especially the evolution of these relationships with maturity progress from immature 0 48 rm to mature 0 68 and 0 88 rm and overmature 1 45 rm stages is shown for example in the maturity interval from 0 68 to 0 88 rm most of the measured shale compaction and porosity decrease is achieved by expulsion of petroleum for some samples there is an inverse relationship between kerogen quality and extractable hydrocarbon yields suggesting that expulsion efficiencies were higher from the better quality intervals because the petroleum achieved higher saturations and hence higher relative permeabilities

maturity effect on carbazole distributions in source rocks from the saline lacustrine settings the western qaidam basin nw china abstract carbazole distributions and biomarker compositions have been investigated in a series of source rocks from the tertiary strata in the western qaidam basin nw china typical biomarker signatures high gammacerane high c 35 hopane and low pr ph indicate a saline lacustrine environment maturity parameter c 29 sterane s s r ranges from 0 06 to 0 58 indicating immature ca 0 35 stages significant variations were observed for carbazole distributions with maturation as for c 1 carbazoles the relative amounts of 1 mc methylcarbazole show a decrease trend in the immature stage and an increase trend in the mature stage while the other three isomers 2 3 and 4 mcs show a generally opposite change indicating a two stage variation as for c 2 carbazole isomers complex variations were observed for their relative amounts an overall increase for 1 7 dmc dimethylcarbazole a slight two stage change for 1 8 and 1 3 dmcs and a marked two stage variation for 2 4 2 5 and 2 6 dmcs comparison of the distributions of carbazole and benzocarbazoles revealed a preferential generation for benzocarbazoles at high maturity levels benzocarbazole ratio a a c varies only in a narrow range 0 52 0 61 in the entire maturity range suggesting limited maturity dependence the results here support the idea that carbazole distributions have strong maturity effect in a wide maturity range and the two stage variations for some pyrrolic nitrogen isomers may indicate their different geochemical controls between the immature and mature stages

antithetic behaviour of gold in the volcanogenic massive sulphide deposits of the iberian pyrite belt detailed mineralogical and geochemical studies of the volcanogenic sulphide mineralization in the spanish part of the iberian pyrite belt ipb define two geochemical mineralogical and spatial gold associations 1 the tharsis sotiel migollas type in which the gold is enriched with co bi in the stockworks and interaction zones at the base of the massive sulphide mound and 2 the rio tinto aznalcollar la zarza type in which the gold is enriched in facies with a polymetallic zn ag as tl hg signature in a distal position or blocked beneath the massive sulphides the first type is localized within a domain covering the southern half of the belt which is characterized by an abundance of sedimentary facies the paragenesis shows that the gold association formed at high temperature 300 c during the initial phases of massive sulphide genesis the gold which occurs in patches of very auriferous electrum au 75 wt was transported by chloride complexes the second type is found in the northern domain of the belt where volcanic facies are predominant the paragenesis shows that the gold association formed at lower temperature 280 c late in the massive sulphide genesis this gold was transported by bisulphide complexes au hs 2 and is contained in ag and hg rich electrum up to 61 0 and 30 5 wt respectively and or auriferous arsenopyrite mean of 280 ppm au two mineral expressions that are able to coexist it would appear that sulphur activity and oxygen fugacity were important factors in controlling the distribution of gold between the two host minerals and also in determining the ag content of the electrum this antithetic behaviour of the gold in the ipb reflects differences in the gold mineralizing fluids that may be due to the geologic environment i e either dominantly sedimentary and acting as a mechanical barrier for gold bearing fluids or dominantly volcanic and more open to seawater circulation the fact that possible complications can occur during massive sulphide genesis in response to the source and evolution of the fluids raises the question of whether one or two gold influxes are involved for example the two gold associations could derive from a single gold influx with remobilization and redistribution of the gold from the early co bi facies giving rise to the later gold paragenesis of the zn ag as tl hg facies this would not have occurred or would have been limited at the tharsis sotiel migollas type orebodies alternatively the two gold associations could reflect two separate evolutionary processes distinguished by the gold appearing either early or late in the hydrothermal fluids knowing the gold association of a massive sulphide deposit is an advantage when exploring for potential host facies

africa eurasia kinematics main constraints and uncertainties abstract it is widely believed that the africa eurasian relative motion in the mediterranean region is oriented se nw to s n this result has been deduced from the analysis of north atlantic kinematic data by assuming that eurasia is a unique coherent plate from the north atlantic ridges to the pacific trenches however this assumption cannot easily account for the not negligible tectonic activity inside and around western europe rhine graben system pyrenees and off shore portugal this paper shows that if one allows western europe to move independently from main eurasia the kinematic indicators in the north atlantic do not exclude other kinematic solutions which are significantly different from those currently accepted in particular it is demonstrated that a ssw nne to sw ne trending africa eurasia convergence beside allowing plausible explanations of major post tortonian deformation events in the central mediterranean region can fit north atlantic data within experimental errors

variation in alkylphenol distributions in a homogenous oil suite from the dhahaban petroleum system of oman as part of a study to determine the effect of migration processes on the abundance and distribution of alkylphenols in crude oils we have analysed a homogeneous suite of 15 oils from the dhahaban petroleum system in oman that lies along a secondary migration pathway in a foreland basin setting geochemical parameters based on aliphatic hydrocarbon biomarkers and aromatic hydrocarbon concentrations and ratios suggest a similar maturity and source facies for the oils despite the wide variation in relative petroleum migration distance up to c 260 km given the similarity in source facies and maturity characteristics of the oils we conclude that the observed variations in alkylphenol concentrations in this sample suite are controlled mainly by secondary migration processes the majority of the oils are not degraded and in these samples we observe a significant decrease in total alkylphenol concentration within the first c 50 km relative migration distance supporting similar studies on north sea petroleum systems and suggesting that alkylphenols may be useful as geotracers over shorter migration distances there is little evidence of systematic migration distance related variation in the relative abundance of individual alkylphenol isomers or homologue groups the alkylphenol distributions in two biodegraded oils in the sample suite both from relatively shallow reservoirs were dominated almost completely by phenol and this is discussed in the context of the microbial production and alteration of phenols and the influence of water washing on the content and distribution of phenols in crude oils

geochemical characteristics and significance of heteroatom compounds in lacustrine oils of the dongpu depression bohai bay basin china by negative ion fourier transform ion cyclotron resonance mass spectrometry abstract saline and freshwater lacustrine oils from the dongpu depression bohai bay basin were characterized by negative ion electrospray ionization esi fourier transform ion cyclotron resonance mass spectrometry ft icr ms esi ft icr ms detected a large range of nitrogen and oxygen compounds in the oils mostly comprising n1 o1 o2 and n1o1 species the low mature oils are dominated by o1 species with double bond equivalent of 4 dbe 4 mainly alkylphenols o2 species with dbe 5 6 i e hopanoid secohopanoic and steroid acids and dbe 1 i e fatty acids indicating a genetic relationship between oxygen compounds and their precursors the nitrogen and oxygen compounds were significantly influenced by maturity with the lower maturity oils analyzed enriched in o2 species particularly fatty acids and 4 5 ring naphthenes with biologically sourced hydrocarbon skeletons ratios of o2 n1 0 7 c20 30 c15 45 dbe1 o2 0 4 and dbe5 6 dbe12 22 o2 6 0 may be useful indicators of low maturity with increasing maturity the condensation degree of the compounds increased and the carbon number decreased the relative abundances of n1 and o1 species with the following specific dbe carbon number ranges were particularly sensitive to maturity dbe9 12 dbe15 18 n1 c20 28 c29 40 dbe12 n1 c20 30 c31 50 dbe15 n1 dbe9 12 dbe4 20 o1 and c20 30 c31 50 dbe8 o1 in some instances the ft icr ms proxies provided a more reliable indication of high maturity levels than traditional sterane based maturity parameters however several of these species were also responsive to other influences namely c20 28 c29 40 dbe12 n1 and c20 30 c31 50 dbe15 n1 ratios reflected an organofacies control and dbe9 12 dbe4 20 o1 and c20 30 c31 50 dbe8 o1 ratios changed with thermochemical sulfate reduction tsr confirmed by 34s variances of oscs in light of the multiple controls on the nitrogen and oxygen compounds dbe9 12 dbe15 18 n1 ratio seems unaffected by organofacies or tsr and was considered the most reliable maturity proxy displaying a similar or better maturity relationship than ts ts tm aside from secondary alteration effects the freshwater samples showed several compositional differences to the saline samples albeit from a limited data set including generally higher o2 and n1 particularly low mw product abundances lower abundances and quite different distribution of o1 products these distinctions suggest esi ft icr ms analysis has potential for distinguishing these sample types

fractionation of benzocarbazoles between source rocks and petroleums the concentrations of the a and c isomers of benzocarbazoles in a number of crude oils and source rock bitumens were obtained by in house methods and from reported published data the changes in benzocarbazole concentrations and the benzocarbazole a a c ratio relating to source maturity facies and migration are described with increasing source maturity in north sea oils and source rocks up to 0 85 vitrinite reflectance equivalent benzocarbazole concentrations increase due to generation followed by a decrease above 0 85 vitrinite reflectance equivalent due to expulsion dilution by newly generated hydrocarbons comparison of benzocarbazole concentrations between reservoired petroleum and related source petroleum revealed a concentration bias in favour of source petroleum where concentrations of benzocarbazoles reached up to 10 times that found in equivalent reservoired petroleum the differences in benzocarbazole concentrations between related oils and source rocks indicate that the major fractionation is introduced during primary migration and expulsion because when secondary migration is limited as in the miller field we see extensive benzocarbazole fractionation between reservoired petroleum and associated source petroleum the relationships between source rock toc content and petroleum benzocarbazole concentrations and a a c ratios indicate that source organic matter exerts a strong influence on benzocarbazole distributions the introduction of a reservoir source fractionation parameter rsfp defined as the ratio between the concentrations of benzo a benzo c carbazole in reservoired petroleum versus the concentration of benzo a benzo c carbazole in source petroleum enables description of the relationship between reservoired petroleum and source petroleum from different petroleum systems petroleum deriving from clastic source rocks demonstrated high levels of benzocarbazole fractionation between reservoired petroleum and source petroleum during primary and secondary migration compared to petroleum deriving from carbonate systems the rsfp parameter may also be used to examine fractionation effects during migration between different compound types the more polar benzocarbazoles are fractionated more strongly than dibenzothiophene and phenanthrene between reservoired petroleum and source petroleum whereas sometimes source maturity signals do dominate the benzocarbazole signals in migrated oils in other circumstances often associated with clastic source rocks no clear maturity signal is transferred to migrated oils

integrated gravity and topography analysis in analog models intraplate deformation in iberia in the western part of the iberian microplate the main topographic highs trend e w to ne sw and are periodically spaced with wavelengths of 250 km conversely in the northeastern part the region of the iberian chain topography is more irregular and strike directions vary from nw se to e w and ne sw we relate this phenomenon to shortening of a continental lithosphere which contains two different well defined domains of lithospheric strength our hypothesis is supported by physical analog models a new processing method has been developed to assist the interpretation of the model results it utilizes spectral analysis of gravity and topography data derived from the experiments folding of the crust and mantle lithosphere yields periodic gravity fluctuations while thickening processes lead to localized gravity lows in this way gravity data can be used to distinguish between the two forms of lithosphere deformation and to correlate areas that underwent the same type of deformation gravity modeling has been performed under full in depth control of the experimental lithosphere structure as such gravity signals from the models may be compared to field gravity data for better understanding the underlying deformation mechanism

the late variscan fault network in central northern portugal nw iberia a re evaluation abstract the fault network in central northern portugal especially the fault system with mean strike n25 has been used to help deduce the late palaeozoic dynamics of western europe on the other hand the n80 strike slip fault system was recognized in previous works as late variscan and left lateral but was scarcely mapped and its importance neglected this study shows that the n25 faults were dextral in the late stages of the variscan orogeny and sinistral during the alpine cycle due to pervasive reactivation fault rocks and intrusions are clearly different according to age mostly high temperature quartz infillings but locally muscovite tourmaline and aplite dykes in late variscan times and low temperature cataclasites fault gouges and mesozoic mafic dykes in younger alpine times we dated dextral n45 segments of the n25 fault system because they are less prone to reactivation by the nnw sse alpine compression and can thus preserve the variscan record we used k ar in muscovite concentrates and obtained a minimum age of the analysed faults of ca 312 ma which sets a lower limit to the so called late variscan wrench faulting period the present study shows that the n80 fault set is pervasive and sinistral in central northern portugal and therefore that it only admits one brittle dextral conjugate the n25 fault system both were generated by a maximum compressive stress bearing between n50 and n55 in azimuth we did not find evidence of a variscan sinistral strike slip movement in the n25 fault system and therefore this kinematics is believed to represent only the displacements accommodated during the alpine cycle

influence of migration distance maturity and facies on the stable isotopic composition of alkanes and on carbazole distributions in oils and source rocks of the alpine foreland basin of austria abstract the austrian part of the alpine foreland basin has been studied previously by organic geochemical methods to establish oil oil and oil source rock correlations the lateral distance of oil fields to the position of mature source rocks lower oligocene schoneck and eggerding formations beneath the alpine nappes in the south suggests long distance migration up to 50 km minor compositional trends in w e direction were obtained reflecting differences in depositional environment facies and maturity of potential source rocks therefore the oil and source rock samples are thought to provide valuable insights into carbazole distributions in relation to migration distance maturity and facies compound specific carbon isotope analyses on n alkanes and isoprenoids reflect the w e trend already seen within the total hydrocarbon fractions the observed trend toward lighter 13 c values of alkanes from oil fields in a w e direction are consistent with lower 13 c values of organic matter in unit c and similar differences obtained from sediments of the schoneck formation at wells oberhofen 1 w and molln 1 e the 13 c patterns of n alkanes and isoprenoids are in agreement with data obtained from the potential marine source rocks schoneck formation of the oils the hydrogen isotopic composition of short chain n alkanes c 15 19 of most oil samples are lower than the data obtained from the extracts of the marine permian kupferschiefer of the polish zechstein basin at similar maturation stages only the oils from the western oil fields yield d values of n alkanes comparable to those obtained from marine source rocks the data imply brackish water conditions during deposition of unit c of the schoneck formation differences in the position of d of isoprenoids in relation to the respective maturation trend line are most probably related to calibration errors alkylated carbazoles and benzocarbazoles are only present in sufficient amounts for quantification in oils sampled from the eastern fields rock extracts of the schoneck formation from drill cores molln 1 5200 m depth 0 92 rr and from the marginally mature ca 0 6 rr samples from well oberhofen 1 4300 m depth obtained sufficient amounts of carbazoles the significantly different concentrations of benzocarbazoles in the extracts around 10 g g at oberhofen 1 50 g g at molln 1 are related to maturity differences whereas the predominance of 1 methylcarbazole in the oberhofen samples is inferred to reflect differences in source rock facies in the oils from the eastern deposits neither the concentration ratios of methylcarbazoles nor the benzocarbazole ratio show indications for the influence of facies differences maturity of oil expulsion is estimated on the basis of mpi 1 rc 0 76 0 88 confirmed by sterane isomerization parameters the results argue for a minor influence of maturity differences on the benzocarbazole ratios of the oil samples the obtained ratios and the reservoir source fractionation parameters calculated from the data of molln 1 source rocks and the respective oils show a systematic decrease with the estimated migration distance the results argue for the applicability of benzocarbazoles for the assessment of relative differences in migration distances in oil plays characterized by minor differences in source rock facies and maturity during oil expulsion

carbazole distributions in carbonate and clastic source rocks abstract carbazole the benzocarbazoles and their alkyl derivatives have been studied from rock extracts to assess the contribution of facies and maturity in controlling their distribution carbonates from the keg river formation elk point group middle devonian western canada consisting of two different facies reflecting deposition under trangressive and regressive events were used to assess facies influences to study maturation a uniform organo facies of organic rich posidonia shale lower toarcian jurassic northern germany from 0 48 to 1 45 r r was used the organic rich lower keg member deposited under photic zone anoxia contained predominantly c 4 c 5 carbazoles by contrast the upper keg river member deposited under regressive higher salinity environment contains predominantly carbazole itself 1 methylcarbazole and a high abundance of benzo c carbazole relative to benzo a carbazole the distribution of the c 1 to c 3 carbazoles was seen to vary with facies an examination of the carbazole derivatives within the posidonia shale reveals that maturation strongly influences the distribution of carbazole methylcarbazoles 1 8 dimethylcarbazole 1 ethylcarbazole benzo a carbazole and benzo c carbazole quantitative determination of these compounds indicates a maximum yield at 0 88 r r for all derivatives with the exception of carbazole which displays as a maximum at 0 53 r r a systematic variation of compound ratios with maturity to 0 88 r r suggests that selective isomerisation destruction generation of carbazole derivatives may occur in contrast to earlier publications which stress the importance of carbazoles as migration markers in migrated oils the results presented here indicate that facies and maturation do play a significant role in controlling the distribution of carbazole derivatives in source rocks and other sediments

hydrocarbon migration in the multiple sourced petroleum system in the northwestern junggar basin northwestern china constraint from geochemical and phase fractionation analysis oil mixing and absence of source rock samples make it difficult to identify the hydrocarbon migration routes in a petroleum system we provide a case study in the northwestern junggar basin to show that combined geochemical and phase fractionation analyses are robust tools to unravel the complex hydrocarbon migration processes the study rebuilds a migration history that multiple sourced hydrocarbons migrated mixed accumulated and fractionated along the evolution of regional tectonics in detail the shawan and mahu sags expelled the early stage hydrocarbons during the late triassic and late jurassic respectively because of their variable subsidence these hydrocarbons charged the entire area based on the evidence from bitumen and oil inclusions during the early cretaceous both sags subsided rapidly and expelled their late stage hydrocarbons these hydrocarbons first mixed along unconformities in the sags which generated mixed source oils and induced gas washing subsequently they further mixed with or displaced the encountered early stage oils during migration along the basal unconformity of the upper permian into the area causing a horizontal distribution of oil maturity zones in addition gases flowing through the early stage oils induced gas washing again creating heavy oils condensate oils and mixed gases after the late stage oils finally accumulated in fractured volcanics migration fractionation caused the remigration of light end compositions this study also shows the strong control of structures on hydrocarbon migration the unconformity network provided opportunities for long distance migration and widespread mixing of multiple sourced hydrocarbons whereas the paleoridge line of the zhongguai high defined the boundary of regional migration

zoned hydrothermal alteration and genesis of the gold deposit at le chatelet french massif central hydrothermal alteration envelopes in the walls of the le chatelet au arsenopyrite deposit are superimposed on a regional chlorite phengite assemblage the outer parts of the envelopes consist of a kaolinite li bearing tosudite siderite alteration facies whereas the inner parts comprise an illite siderite and or pyrite pyrrhotite alteration facies accompanied by quartz near the feeder conduit transition between the two facies is gradational the economic gold bearing arsenopyrite associated with rare pyrrhotite loellingite pyrite and marcasite is concentrated in siliceous veins and disseminated in illitized and silicified wall rock analyses of fluid inclusions in quartz show two distinct fluid generations early primary to secondary volatile rich co 2 ch 4 fluids mainly in metasomatic quartz and migmatite quartz included in the mineralized veins and late secondary aqueous and slightly saline 5 4 wt nacl equiv solutions distributed widely throughout the hydrothermal facies spatial relationships between the volatile rich fluids and the hydrothermal facies indicate that the fluids were contemporaneous with the first stages of hydrothermal activity their presence as primary inclusions within arsenopyrite bearing metasomatic quartz suggests that they were also involved at a later stage with arsenopyrite deposition the variable co 2 ch 4 ratios of these early fluids reflect possible effervescence and trapping at a temperature lower than or equal to 270 degrees c the stability of the alteration minerals and fluid inclusions indicates that the temperature of hydrothermal activity at le chatelet ranged between 280 degrees and 180 degrees c the arsenopyrite association with pyrrhotite and loellingite or pyrite indicates that oxygen fugacities during sulfide deposition were very low log fo 2 45 to 39 at 250 degrees c compatible with the estimate made from the co 2 ch 4 ratio of the early inclusions logf sub o 2 38 5 the presence of illite reflects neutral to slightly alkaline ph conditions thermodynamic modeling carried out between 100 degrees and 250 degrees c shows that a single stage zoned alteration in both the outer and inner parts of the envelopes facies 2 o and 2 i would result from differential dissolution of the protolith minerals in particular a rapid dissolution of plagioclase due to temperature variations in the hydrothermal system and flow gradient comparison between the deduced age of mineralization stephanian a b and that of the regional silico albitic to albitic and lithium rich granite magmatism suggests the latter as a possible heat and fluid source indicated by abundant li at le chatelet nonequilibrium deposition of the au arsenopyrite mineralization during an abrupt opening phase along brittle faults is supported by well developed breccia in conduits cemented by fine grained arsenopyrite bearing quartz and a well developed patchy zoning of the au arsenopyrite the new data obtained from fluid inclusions suggest two possibilities for the hydrothermal activity at le chatelet single fluid evolution with a late overprint of the hydrothermal alteration by aqueous fluids or two fluid evolution with introduction of the aqueous fluid during a phase of opening

probabilistic seismic hazard assessment for portugal the probabilistic seismic hazard of portugal is analyzed with a logic tree approach a critical part of the work was the review of the seismic catalog and the moment magnitude m estimation for historical earthquakes to produce a cat alog with a uniform magnitude scale the instrumental magnitudes were converted to m through empirical relations two seismic zonations were considered each in cluding two broad tectonic zones and a set of smaller seismicity zones catalog completeness and the b value for the truncated exponential recurrence model were calculated for the broad sources defined by tectonic criteria the smaller seismicity sources were used to calculate the a value using the fixed b value of the correspond ing tectonic zone this approach allows for a larger amount of data to estimate the most critical parameters by statistical methods without compromising the spatial detail of hazard results three published attenuation relations were used in the logic tree with weights that were based on tectonic considerations and on the comparison with macroseismic data converted to horizontal peak ground acceleration pga the ambraseys et al 1996 attenuation model for pga used by most previous hazard studies of the region seems to underestimate considerably the ground motion for mainland portugal a total of 96 hazard curves were calculated with seisrisk iii for each point of the map the resulting mean hazard map for 10 exceedence probability in 50 years displays pga values that range from 0 05g to 0 20g these mean values are slightly higher than in previous pga studies the hazard patterns obtained display a maximum related to intraplate onshore seismicity whereas pre vious studies using intensities highlighted the southwest offshore contribution fur ther work on ground motion attenuation in western iberia is necessary to improve the seismic hazard assessment

molecular distributions and geochemical implications of pyrrolic nitrogen compounds in the permian phosphoria formation derived oils of wyoming abstract crude oils from the laramide structures of wyoming were studied with respect to their geochemical compositions the sampling areas include the greater green river wind river and big horn basins and the casper arch region based on pristane phytane ratio and various hopane and sterane parameters the permian phosphoria formation derived oils can be readily differentiated from oils with different origins within the phosphoria formation derived oils three subgroups can be identified using ts ts tm and diasterane regular sterane ratios corresponding to sources with subtle variation in organic facies and or thermal maturity of the phosphoria formation differences in source organic input depositional environments and thermal maturity were observed to greatly influence the saturated hydrocarbon compositions of the permian phosphoria formation derived oils however the distributions of pyrrolic nitrogen compounds in these oils do not appear as diagnostic as the conventional hydrocarbon parameters commonly used as indicators of these geological factors this fact may be related to the more significant role of oil migration in the modification of pyrrolic nitrogen compound distributions in foreland basins as compared to that in rift basins the recognition of possible source and maturity effects on pyrrolic nitrogen compounds suggests that all of these factors should be taken into proper consideration before the pyrrolic nitrogen compounds are used as indicators for any specific geological process

seismotectonics of portugal and its adjacent area in the atlantic abstract new elements on the seismicity of portugal and new focal mechanism solutions of earthquakes with epicentres situated off the coast of the portuguese mainland and in the azores region are presented historical seismicity data show that in the territory of the portuguese mainland there are active faults that are responsible for earthquakes that have caused important damage and many casualties however most of the intraplate earthquakes with epicentres situated in the portuguese mainland or near the shore are normally of small magnitude and this renders difficult their interpretation in the light of focal mechanisms a solution for one earthquake with magnitude 5 and epicentre at the nazare submarine canyon is presented southwestwards of cape st vincent there is an important seismic zone responsible for high magnitude earthquakes such as that of 1 november 1755 this zone is situated in the region where the extension of the messejana fault into the ocean joins with the azores gibraltar fault the seismicity of the area situated between the western coast of the portuguese mainland and the azores increases approximately along the 15 w meridian from the latitude of the azores gibraltar fault up to 44 n focal mechanisms of earthquakes with epicentres situated along this line show very similar solutions the interpretation of the focal mechanism solutions of the earthquakes with epicentres situated in the studied area shows that the stress field trends approximately nw se it is assumed that this stress field results from the interaction of the eurasian and african plates however this direction is not maintained in the azores region

unravelling maturity and migration related carbazole and phenol distributions in central graben crude oils abstract in this contribution we present the results of an integrated investigation of selected nitrogen and oxygen bearing compounds in norwegian central graben crude oils we first provide an interpretation framework built on hydrocarbon biomarkers and then use this framework to relate polar compound geochemistry to the influences of source facies farsund versus mandal formations maturity migration and reservoir lithology oil maturity could be assessed using established changes in carbazole annelation n1 dbe 9 vs 12 vs 15 classes as well as hydrocarbon biomarkers 29ts 29ts nh correlated best with the polar compound maturity data secondary migration fractionation appears nevertheless to have played a role as seen by increased dbe 9 and 12 carbazole and benzocarbazole proportions and a loss of c2 3 dbe 12 homologues within carbonate reservoirs as compared to intraformational upper jurassic siliciclastic reservoirs thus migration distances pathways and wettability of carrier systems ostensibly play a significant role in carbazole distributions of the central graben oils manifesting itself as apparent maturity retardation in an attempt to eliminate the migration component from maturity assessment we here present a novel ternary diagram including dibenzocarbazoles n1 dbe 15 and phenolic species o1 dbe 4 and 5 based on a single measurement using the ft icr ms however the integration of such results into 3d modelling software must be conducted to clarify source kitchen migration pathways and distances

geochemical study of crude oils from the xifeng oilfield of the ordos basin china abstract the xifeng oilfield is the largest newly discovered oilfield in the ordos basin in order to determine the possible source crude oils collected systematically from the oilfield and an adjacent oilfield have been examined isotopically and molecularly the predominance of long chain n alkanes high abundance of c29 sterane lower ratios of c25 c26 tricyclic terpane and c25 tricyclic terpane c24 tetracyclic terpane and high c24 tetracyclic terpane c24 tetracyclic terpane c26 tricyclic terpanes ratio in the studied oils suggest generation from a source with mixed terrigenous and algal bacterial organic matter the presence of diterpenoid hydrocarbon with abietane skeletons is characteristic of the main contribution of higher land plants to the oils the biomarker distributions in the oils show that they were formed under a weakly reducing freshwater environment molecular maturity parameters indicate that the crude oils are mature the oil source rock correlation and oil migration investigation suggest that the oils in the xifeng oilfield originated from the source rocks of the yanchang formation deposited in a shallow to deep freshwater lacustrine environment especially chang 7 source rocks the data from the distribution of pyrrolic nitrogen compounds indicate that the charging direction of the chang 8 crude oils is mainly from the zhuang 12 well northeast of the oilfield toward the southwest this direction of oil migration is consistent with that indicated by regional geological data

5 late variscan mineralizing systems related to orogenic processes the french massif central abstract the french massif central constitutes an exceptional study area due to the diversity of its metallic deposits its internal position in the variscan belt and the abundance of available geological geophysical and metallogenic data obtained within the geofrance 3d programme the deposits formed towards the end of the orogenic evolution represent the economic products of two distinct mineralizing systems a au sb hydrothermal system and a w sn and rare metals magmatic hydrothermal system which were simultaneously active during a short time span between ca 310 and 300 ma two types of gold deposit can be distinguished on the basis of their depth of emplacement deep seated gold deposits developed under lithostatic to hydrostatic pressure during rapid exhumation and shallow gold deposits emplaced under hydrostatic pressure with no significant uplift deposits of w sn and rare metals were emplaced in the upper crust during final crystallization of specialized magmas after their rapid ascent perhaps enhanced by simultaneous regional uplift the gold bearing systems are associated with a complex network of re activated crustal scale faults initially active during the period between 335 and 315 ma normal motion along the faults coeval with 335 to 315 ma granite migmatite domes played a major role in the 3d distribution of the hydrothermal plumbing system gold and related metals were carried within huge hydrothermal cells which reached ca 100 km by 10 km in area and 30 km in depth in contrast granites rich in magmatophile elements w sn rare metals generated smaller hydrothermal cells 10 km by 10 km in area and

aromatic biomarkers as indicators of source depositional environment maturity and secondary migration in the oils of cambay basin india abstract aromatic biomarkers have been analysed for source depositional environment maturity and secondary migration in crude oils from different formations of paleocene to eocene age in the ahmedabad mehsana block of north cambay basin and the broach block of south cambay basin north cambay basin oils are characterized by a high abundance of 1 2 5 and 1 2 7 trimethylnaphthalenes tmn and low to medium ratio of dibenzothiophene phenanthrene and low ratio of pristane phytane indicates that these oils have been derived from a source containing predominantly higher plants and that the organic matter was deposited in restricted marine or lacustrine environments in anoxic to suboxic conditions the relative abundance of 1 2 7 tmn suggests that it was derived from the structural degradation of oleanane type triterpenoids present in angiosperms south cambay basin oils are less abundant in 1 2 5 and 1 2 7 tmns and low ratio of dibenzothiophene phenanthrene and high ratio of pristane phytane indicating that the oils were derived from higher plant source organic matter deposited under marine or fluvial deltaic environment in oxic conditions maturity sensitive ratios based on phenanthrene naphthalene dibenzothiophene and their alkyl substituted isomers have been used to calculate the equivalent vitrinite reflectance these parameters indicate a wide range of thermal maturity of the oils ranging from 0 60 to 0 93 vrc methylphenanthrene index and methyldibenzothiophene ratios indicate that the maturity of north and south cambay basin oils are different the north cambay basin oils are less mature than south cambay basin oils pyrrolic nitrogen distribution indicates that the alkylated carbazoles and benzocarbazoles are more abundant in south cambay basin oils as compared to north cambay basin oils these data indicate that north cambay basin oils are less migrated compared to south cambay basin oils this systematic investigation of the aromatic biomarkers in oils of cambay basin has resulted in a new generation migration and entrapment model that has led to the development of new exploration leads

migration and accumulation of crude oils from permian lacustrine source rocks to triassic reservoirs in the mahu depression of junggar basin nw china constraints from pyrrolic nitrogen compounds and fluid inclusion analysis abstract the geochemical compositions of crude oils and permian source rocks from the mahu depression of the junggar basin were analyzed in this study based on tricyclic terpanes and isoprenoid biomarkers three oil groups i ii and iii can be identified that correspond to different source rock formations and organic facies after examination of the influence of source facies and thermal maturity and selected biomarker ratios based on carbazole isomers such as 1 mc 4 mc 1 8 dmc 2 7 dmc and a a c bc ratios in different oil groups allowed us to determine the direction of hydrocarbon migration in different reservoirs in addition abundant oil inclusions are present with fluorescence colors ranging from yellow to blue white these were analyzed by ftir to distinguish between different sources for the oils fluid inclusion petrography and microthermometry were also used to prove two stages of oil migration and their different sources taking into consideration possible migration pathways and likely driving forces we conclude that abnormally high pressure in the permian sequence acted as the main driving force for oil migration the major migration pathways were vertical faults in the fault belts and slope areas and sand bodies in the deeper areas group i1 oils from p1f carbonate source rocks in the fault belts mainly migrated vertically through the faults and accumulated in t1b reservoirs in the late triassic and were driven by excess formation pressure and buoyancy group i2 oils in the slope areas first migrated vertically within thrust faults from p1f mudstone source rock in the late triassic after which they migrated laterally over short distances to accumulate in t1b sand bodies group ii oils from adjacent p2w source rocks in the center of the depression migrated mainly in the late jurassic due to abnormally high pressure and accumulated in nearby t1b traps some reservoir rocks in the slope area contain two generations of fluid inclusions implying oil mixing from early stage p1f oils and late stage p2w oils resulting in the group iii oils combining these data from biomarkers pyrrolic nitrogen compounds and fluid inclusions allowed us to construct models of migration and accumulation for oils in the mahu depression

the effect of sea level changes on fault reactivation potential in portugal abstract the aim of this study is to assess the impact of sea level changes on both the stress field and the potential of fault reactivation in west iberia the analysis is applied to a set of five active faults distributed across portugal selected for representing predominant fault directions and for being seismically active the results show that the rise of sea level since the last glacial maximum has produced flexural effects with distinct impacts on different faults the coulomb stress changes induced by the sea level rise along the s marcos quarteira south portugal and the horseshoe offshore sw iberia faults are found to be extremely small independently of the elastic plate thickness these faults are thus unaffected by flexural effects related to ocean loading and are unlikely to possess any paleoseismic record of this phenomenon in contrast the eustatic sea level rise during the late pleistocene could have raised the coulomb stress by 0 5 1 mpa along the manteigas vilarica braganca north portugal and lower tagus valley lisbon area fault systems such stress perturbations are probably sufficient to impact the seismic cycle of the manteigas vilarica braganca fault bringing it closer to failure and possibly triggering the earthquake clusters that have been observed in previous paleoseismologic studies