solid bitumen reflectance and rock eval tmax as maturation indices an example from the nordegg member western canada sedimentary basin abstract marine organic rich rock units commonly contain little for vitrinite reflectance v r 0 measurement the most commoly used method of assessing thermal maturity this is true of the lower jurassic nordegg member a type i ii sulphur rich source rock from the western canada sedimentary basin this study examines the advantages and pitfalls associated with the use of rock eval t max and solid bitumen reflectance b r 0 to determined maturity in the nordegg vitrinite reflectance data from cretaceous coals and known coalification gradients in the study area are used to extrapolate v r 0 values for the nordegg t max increases non linearly with respect to both b r 0 and extrapolated v r 0 values a sharp increase in the reflectaance of both solid bitumen and vitrinite occurs between t max 440 450 c and is coincident with a pronounced decrease in hydrogen index values and the loss of solid bitumen and telalginite fluorescence over the same narrow t max interval this t max range is interpreted as the main zone of hydrocarbon generation in the nordegg and corresponds to extrapolated v r 0 values of 0 55 0 85 the moderate to high sulphur contents in the kerogen played a significant role in determining the boundaries of the nordegg oil window a linear relationship between b r 0 and extrapolated v r 0 as proposed elsewhere is not true for the nordegg b r 0 increases with respect to extrapolated v r 0 according to jacob s 1985 formula v r 0 0 618 b r 0 0 40 up to v r 0 0 72 b r 0 0 52 beyond this point b r 0 increases sharply relative to extrapolated v r 0 according to the relatioship v r 0 0 277 b r 0 0 57 r 2 0 91 the break in the b r 0 v r 0 curve at 0 72 v r 0 is thought to signifiy the peak of hydrocarbon generation and represents a previously unrecognized coalification jump in the solid bitumen analogous to the first coalification jump of liptinites

foraminiferal inventory and lithologic description of the lower cretaceous albian hulcross shale monkman area northeastern british columbia correlation of an arenaceous microfauna of 41 species 44 subspecies from the hulcross formation of the monkman pass area with that found in the hulcross shale on the peace river has a further corroboration in matching spectra of volcanic ash beds at both localities the monkman pass equivalents of both the basalmost portion and the upper part of the hulcross beds on the peace river are in sandy to continental facies diatoms are plentiful in the monkman pass section in the shaly facies the foraminiferal genera include bathysiphon thuramminoides psammosphaera hippocrepina saccammina reophax glomospira ammodiscus psamminopelta haplophragmoides ammobaculites trochammina textulariopsis pseudobolivina verneuilinoides uvigerinammina gaudryina eggerella and dorothia only thuramminoides haplophragmoides and trochammina occur in abundance indicating water of depth around 100 m at time of deposition and of salinity close to that of normal seawater the low degree of bioturbation and the pres

thermal basin modelling of the arauco forearc basin south central chile heat flow and active margin tectonics abstract the arauco basin is part of the coastal forearc domain in south central chile during its evolution since the late cretaceous it was subject to multiple deposition cycles and the erosion of lower bathyal to beach and lagoon sediments these different environments were established in alternating accretional and erosive subduction tectonic settings along the south andean active margin whereas the general development is well understood inconsistencies arise regarding the origin of the high thermal maturity of eocene coals and the estimates of vertical movements of the whole area during the cenozoic thermal modelling of this forearc basin provides new insights regarding its thermal evolution and evaluation of the magnitudes of subsidence and inversion results are based on the analysis of coal samples from surface outcrops mines and drill cores of ten onshore wells from enap sipetrol newly derived vitrinite reflectance vr r measurements indicated a temperature in the range of 135 150 c for the oldest sediment unit of the arauco basin which was reached in post eocene times furthermore 1d basin modelling techniques indicate scenarios that could explain the coalification values in the basin s sediments the models were calibrated against vr r data from drill core samples supplied by enap sipetrol a miocene and an oligocene subsidence inversion scenario were considered while neither could be securely discarded based on the modelling results furthermore it can be shown that the current thermal maturity was not reached by an increased heat flow hf or a deep subsidence only consequently a structural inversion accompanied by the erosion of 3 0 0 4 km depending on the locality in combination with a high hf of 64 4 mw m 2 is the best explanation of the available data the hf which is high for a forearc setting can be attributed to the increased temperature of the relatively young subducted nazca plate and an additional influence of ascending hot fluids from the subduction zone the maximum temperature gradient inferred is

some mass balance and geological constraints on migration mechanisms oil and gas are not at rest in the sedimentary mantle of the earth they are not in equilibrium whether they are finely dispersed in a potential source rock or whether they are concentrated in a trap in a reservoir rock a wide variety of possible escape mechanisms exists these include diffusion continuous single phase flow solution of oil in gas or gas in oil and solution in water derived from compaction clay diagenesis or meteoric sources the problem is to quantify the possible mechanisms and to rank their relative importance under a given set of physical chemical and geologic conditions the quantitative importance of the various proposed mechanisms can vary by orders of magnitude depending on the physical chemical and geologic conditions during the past decade oil to source correlations have become reliable and the timing of peak generation and concomitant migration has been sufficiently quantified to allow the geologist geochemist to make estimates of when and how much petroleum moved from one location to another combined with a knowledge of the physical chemical and geologic conditions at the time of migration such quantitative descriptions of subsurface petroleum transfer permit an empirical test of the applicability of the various proposed migration mechanisms the application of this technique to selected areas suggests that most of the major commercial oil accumulations of the world left their source rock in a continuous oil phase when bitumen concentrations in the rock are too low for continuous phase flo to exist other migration mechanisms which always are operative will increase in both absolute and relative intensity solution of oil in gas may become significant in thick tertiary delta systems and meteoric water may be a surprising asset in some very specific geologic settings however it is unlikely that solution of oil in water derived from compaction or from dehydration of clay has much to do with the origin of many of the major oil accumulations of the world

coal rank and burial history of cretaceous tertiary strata in the grande cache and hinton areas alberta canada implications for fossil fuel exploration the present study discusses coal rank and burial histories for cretaceous tertiary coal measures and thermal maturity of associated source rocks coal rank ranges from subbituminous to semianthracite coalification maps for selected coal zones indicate a broad coalification maximum east of the deformed belt in the pocahontas brule and hinton areas rank levels appear to be elevated locally due to geothermal anomalies thermal modelling indicates that the westward decrease of coal rank in lower cretaceous strata is related to a westward decrease in the duration of burial beneath maastrichtian eocene foreland basin deposits upper cretaceous tertiary strata were subjected to relatively low geothermal gradients 20 c km whereas lower cretaceous strata were exposed to much higher gradients up to 46 c km tectonic loading in the foothills had only a minor impact on coalification at obed marsh alberta syncline thermal modelling suggests that deformation in the thrust belt continued for at least

light volatile liquid and gas shale reservoir potential of the cretaceous shaftesbury formation in northeastern british columbia canada the geologic controls on reservoir properties and potential hydrocarbon volatile low molecular weight liquid and gas resources of the cretaceous shaftesbury formation in northeastern british columbia have been investigated maturity varies from the oil to dry gas window tmax 429 486c with increasing maturity and depth of burial toward the south the tmax in degrees celsius is the oven temperature at the peak generation of s2 during pyrolysis total organic carbon toc content ranges between 0 64 and 8 0 wt with an average of 2 2 wt the toc content distribution mirrors the trends in maturity with lower toc content in areas of high maturity kerogen is characterized as either type ii iii or type iii the quartz content ranges between 33 and 66 with higher quartz content in areas with lower toc content and greater maturities porosity ranges between 4 5 and 14 6 with higher porosities observed within shallower wells low quartz content or maturities or a combination of all three the porosity is reduced in high maturity samples by mechanical compaction and silica cementation total gas capacities range between 4 5 and 24 8 cm3 g and gas in place gip estimates are between 0 98 and 3 39 bcf section meter the calculated hydrocarbon generation is less than 3 6 bcf section meter with light liquid generation between 3 7 and 516 2 mmbo present day depths and organic maturity have strong influences on the hydrocarbon capacity more so than toc content deeper higher maturity samples in the south have the largest total gas capacity and gip estimates 0 98 3 39 bcf section meter maturity is within the dry gas window in the southern one third of the study area highest volumes of light liquid hydrocarbons are found within the less mature northern part of the study area

the timing of coalification in relation to structural events in the grande cache area alberta canada lower cretaceous coals from the inner foothills of the rocky mountains were sampled for a study of the relationships between coal rank and folding and faulting the coals were collected from laterally continuous seams in a highly folded and faulted area near grande cache alberta rank of the coals as determined by measuring mean maximum vitrinite reflectances ranges from medium to low volatile bituminous the results indicate that the degree of coalification was established during burial from albian to late paleocene times before folding and faulting started isoreflectance lines run parallel to the bedding of the folded strata and there are no significant changes in reflectances in the same seam from one thrust sheet to the other however in the footwall of the mason thrust the mean maximum reflectances and bireflectances are locally increased above regional values regionally there appears to be a trend to slightly lower reflectances in the southeast of the study area it is suggested that the low

comparison of isotopic and geochemical characteristics of sediments from a gas and liquids prone wells in marcellus shale from appalachian basin west virginia abstract the middle devonian age marcellus shale contains one of the largest shale gas plays in north america hydrocarbon production in the eastern part of the play is mostly dry gas consisting of essentially pure methane production of natural gas liquids condensate increases toward the west which is the area currently being targeted by developers two marcellus shale cores from west virginia were analyzed to compare the isotopic and geochemical characteristics of a liquids prone well wv 7 in wetzel county with a gas prone well wv 6 in monongalia county the contrasts between the cores indicate that the conditions of the marcellus shale deposition were different between the two sites the dominant organic matter preserved in each core is isotopically different 13corg values are lighter on average in wv 6 compared with wv 7 a possible explanation is that a larger fraction of terrestrial organic matter was preserved in the wv 6 core whereas wv 7 may contain a greater percentage of marine organic matter clastic influx proxies e g ti al ca al and mg al also suggest that the wv 6 core site received a higher siliciclastic input compared to wv 7 consistent with a more proximal location to dry land and the delivery of greater amounts of terrestrial organic matter depleted 13ccarb values low concentrations of redox sensitive elements e g v cr ni and u and high variability 15n values in the wv 6 core all suggest the presence of higher dissolved oxygen concentration and short term shifts in an oxic anoxic boundary near the sediment water interface during deposition these lines of evidence indicate that the depositional conditions were favorable for the accumulation of predominantly gas prone type iii kerogen in the marcellus shale at the wv 6 site in contrast the marcellus shale at the wv 7 site was deposited in a more distal area that received a low terrestrial sediment supply organic matter primarily derived from marine algae and bottom water conditions that were dominantly anoxic such conditions were favorable for the accumulation of type ii kerogen that has a greater capacity to generate liquid hydrocarbons differences between the liquids prone and gas prone parts of the marcellus shale play have been largely ascribed to depth of burial and thermal maturation history this study indicates that depositional environment and sedimentary facies may have played significant roles as well

pedogenic and diagenetic influences on void coating formation in lower cretaceous paleosols of the mill creek formation southwestern alberta canada abstract pedogenic and diagenetic influences on void coating formation were studied in two paleosols from the lower cretaceous albian mill creek formation in southwestern alberta canada using detailed micromorphological mineralogical and geochemical methods the paleosols consist of alternating decimetre scale beds of red grey green and variegated mudstone intermediate horizons red and grey green variegated mudstones contain associations of pale yellow clay coatings dark red clay coatings fe depletion hypo coatings and fe oxide quasi coatings sem edx ray analyses indicate that the dark reddish coatings are dominated by si al and fe with subordinate amounts of k na ca mg and ti pale yellow clay coatings have a higher si content and lower al k na ca and fe contents relative to reddish coatings within the paleosol profiles the distribution of clay minerals indicates 1 an increase in discrete clay minerals downward 2 a decrease in mixed layer illite smectite downward and 3 an increase in chlorite upward x ray diffraction indicates that the pale yellow and dark red clay void coatings are polymineralic pale yellow clay coatings have a higher proportion of mixed layer illite smectite and kaolinite less chlorite and are less crystalline than dark reddish coatings despite a diagenetic overprint including development of diffusion gleyans degradation of organic matter burial reddening and probably some smectite illitization both compositional and morphological gradients exist in the paleosol profiles and void coatings these gradients are most likely related to depositional variations and to pedogenic development in the original soils under variable eh ph conditions in the presence of organic matter therefore although the void coatings are altered diagenetic features their morphology mineralogy and perhaps even some of their microchemistry is attributable to the presence of pedogenic precursors initially formed in soils similar to modern temperate alfisols and glossic soils

the rock mechanics of kimberlite volcanic pipe excavation abstract the rock mechanics theory for deformation of open pit and underground mining excavations can be used to better understand aspects of the growth and geometry of kimberlite volcanic pipes large scale rock mass behaviour around an excavation such as a volcanic pipe is dependent on the rock mass strength the in situ rock stress conditions and the excavation geometry rock mass strength is empirically derived from the intact rock strength and quantification of the shear strength frequency and orientation of rock discontinuities tensile slope or sidewall failure typically occurs in shallow level 0 1000 m conditions in which pre existing structures shear due to gravity driven forces the orientation of the pre existing structures provides an important control on the size shape and position of the rock mass failure slope failures are shown to influence the development of many kimberlite volcanic craters and the distribution of layered volcaniclastic facies in the crater explosions or removal of key blocks in a pipe sidewall can cause undercutting and collapse of the sidewall with the rock unravelling along pre existing structures towards surface many lithic rich breccias commonly found on the margins of kimberlite pipes are interpreted to form in this way at intermediate 1000 m to deep 2500 m depths the increasing compressive stress can cause fractures to develop around an excavation stress induced fractures should cause scaling of a volcanic pipe s sidewalls and expansion perpendicular to the maximum component of compressive stress a larger horizontal tectonic stress ratio and a lower internal pipe pressure will promote pipe sidewall fracturing volcanic pipe expansion will also be increased in rate by i mechanical sidewall erosion by flowing magma and or pyroclasts ii by failure on large intersecting fault or dyke structures and iii by reduction in the country rock mass strength by volcanic explosions the final pipe shape and distribution of some internal facies is therefore a consequence of the dominant rock mechanical failure processes in the pipe sidewalls the type of failure is dependant on the rock mass strength geological structures stress and depth below surface

source rock potential and paleoenvironment of the miocene rudeis and kareem formations gulf of suez egypt an integrated palynofacies and organic geochemical approach abstract a study on source rock characterization and paleoenvironmental interpretation has been carried out on a relatively thick miocene sedimentary succession from three wells gh 404 2a gh 420 1 sa e6a in the southern gulf of suez egypt the compilation of detailed optical investigations including palynofacies analysis spore coloration index sci vitrinite reflectance vrr and source rock geochemical data enables a detailed evaluation of organic matter om richness kerogen type and thermal maturation level despite their high content of calcium carbonate up to 52 the studied sediments yielded sufficient palynologic residue for a detailed palynofacies and organic petrographic study the palynomorph content comprises mainly marine components essentially dinoflagellate cysts and accessorily microforaminiferal linings while terrestrial derived material is relatively rare persistent occurrence of amorphous organic matter aom indicates that dysoxic to anoxic conditions prevailed throughout the deposition of the investigated sediments the main objective of this study is to combine organic geochemical and palynological data in an attempt to assess the source rock potential of the rudeis and kareem formations in the gulf of suez these data in addition also allow for the reconstruction of the depositional environment the present investigation employs multimode microscopic methods using transmitted white light along with incident light fluorescence microscopy for the first time geochemical and petrographic analyses performed on bulk rock samples and palynological residues demonstrate that both the rudeis formation and the kareem formation are mainly of kerogen type iii or mixed type ii iii independent thermal maturation specific parameters such as rock eval tmax vrr and sci indicate an immature to early mature stage palynofacies analyses combined with organic geochemical data indicate that the rudeis formation was deposited under shallow to open marine conditions whereas the overlying kareem formation was formed mainly in an open marine setting

organic maturity in the western canada sedimentary basin abstract organic maturity of strata in the western canada sedimentary basin has been investigated in numerous studies using petrological chemical and physical methods compilation of these data has facilitated a regional analysis of the maturity patterns and maturation history variation in maturity patterns can be divided into three levels basin wide 1st order regional 2nd order and local 3rd order first order variations are manifested by an overall increase in maturity of strata of the same age from east to west from the plains to the rocky mountain foothills and front ranges in response to progressively deeper burial and higher paleo geothermal gradients superimposed on this first order basinal scale variation in maturity are second and third order variations which reflect local differences in depth of burial conductive and advective heat transport or effects of thrust faulting maturity gradients in the axis of the basin are low averaging 0 10 log r omax km whereas in the front ranges and foothills the gradients are substantially greater average 0 25 log r omax km variations in maturity gradients reflect lower paleo geothermal gradients resulting from rapid sediment loading and subsequent unloading in the plains and higher conductive heat transport in the deformed belt the main component of maturity of most phanerozoic strata occurred during deep burial under upper cretaceous and or paleogene molasse in foredeeps developed in response to crustal loading during the easterly migration of the foreland fold and thrust belt as a result of the west to east propagation of deformation during the laramide orogeny deep burial maturation hydrocarbon generation and uplift occurred earlier in the foreland belt late cretaceous than in the plains to the east where the main component of maturity and hydrocarbon generation occurred as late as eocene in the plains because of the low maturity gradients a thick succession of strata currently is within the oil window in the deformed belt however higher maturity gradients have resulted in a thinner succession of strata within the oil window in response to higher paleo geothermal gradients strata in the deformed belt matured more quickly leading to more rapid hydrocarbon generation and migration than areas to the east in the southern part of the cordillera a significant component of maturation post dates structural deformation of the strata whereas in northeastern british columbia and adjacent parts of alberta maturity primarily pre dates structural deformation data from some deep bore holes and surface samples in the southern part of the cordillera provide evidence for maturity post dating or accompanying emplacement of major overthrust sheets tectonic burial in most areas however there is no clear evidence for the timing of maturity relative to faulting or evidence of frictional heating the maturity gradients and levels of maturity of surface and near surface strata in the western plains and rocky mountain foothills indicate that a succession several kilometres of paleogene strata were deposited in these regions foredeep and subsequently eroded in response to post laramide uplift

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

influence of geochemical organo petrographical and palynofacies assemblages on hydrocarbon generation a study from upper oligocene coal and shale of the makum coal basin assam india abstract the makum coal basin of northeast india comprises important coal and shale reserves of upper oligocene age a total of twenty samples were collected to evaluate the kerogen type hydrocarbon generation potential and thermal maturity through geochemically organo petrographically and palynofacies analyses the samples are characterized by high toc total organic carbon and large s2 remaining heavier hydrocarbons meet the required standards as good to excellent generation potential the coal and shale are marked by mixed type iii ii kerogen with minor occurrence of type i kerogen moderate to high hydrogen index hi values and are considered to generate thermogenic gas with some condensate oil the reflectance values indicate samples are mostly immature and close to the oil birth line the amount of vt60 grains also suggests that the samples can produce some condensate oil along with thermogenic gas the rock eval pyrolysis rep data stands with the interpretation through petrographic palynofacies and fourier transform infrared spectroscopy ftir in determining kerogen type and generation potential the generation potential is also controlled by the degree of organic matters reactivity the estimated reactivity indicates that besides vitrinite and liptinite up to 70 vol of the inertinite macerals have the potential to generate hydrocarbon the occurrence of a substantial amount of reactive macerals i e collotelinite vitrodetrinite collodetrinte corpogelinite alginite resinite and bituminite within the samples makes them more potential to generate hydrocarbons the diagram proposed based on our data of macerals and palynofacies assemblages may also be a convenient tool in detecting kerogen type s and nature of hydrocarbons

quantitative evaluation of lower cretaceous mannville group as source rock for alberta s oil sands the western canada sedimentary basin hosts about 12 billion bbl of conventional oil in devonian to cretaceous reservoirs lower cretaceous oil sands contain an additional 1 3 trillion bbl in place the oil sands represent the biodegraded remnants of supergiant conventional oil deposits the source for which has been thought to be mature rocks of the equivalent age mannville group this work shows however that the known mannville rocks alone are incapable of generating the required volume of hydrocarbons the volume of hydrocarbons generated in the mannville beneath central alberta was calculated by combining measured geochemical and geologic data with lopatin s method for thermal maturation original hydrocarbon generative capacity of the mannville rocks was calculated from geochemical analyses of immature samples using average values for total organic carbon toc 1 3 and rock eval hydrogen index 100 mg hc g toc maximum hydrocarbon generation per unit volume of source rock was calculated the maturation model was then employed to estimate the extent to which maximum yield has actually been achieved total volume of source rock in the basin was obtained from isopach maps of mannville shale multiplication of actual oil generation per unit volume by source rock volume gave a generated volume of 450 billion bbl these calculated values are exceedingly optimistic however because they ignore inefficiencies in expulsion and migration inclusion of oil generated in mannville equivalent source rock in the foothills belt would less than double this quantity assuming that source potential there is similar to that of the central alberta rocks it is clear that the mannville group of the western canada sedimentary basin cannot be the major source of alberta s oil sand hydrocarbons either the hydrocarbons were generated in as yet undocumented very organic rich mannville equivalent rocks in the foothills or they are derived from multiple sources throughout the basin

use of micromorphology for palaeoenvironmental interpretation of complex alluvial palaeosols an example from the mill creek formation albian southwestern alberta canada abstract field observations are often not sufficient for process based interpretations of palaeosols particularly where they form parts of thick aggradational pedocomplexes within alluvial successions under such conditions micromorphology provides genetic temporal and spatial information on soil forming processes that is critical to an understanding of past environmental conditions thick alluvial successions of the albian mill creek formation contain abundant evidence of pedogenesis but few well developed palaeosol profiles and therefore provide an ideal case study in which to demonstrate the usefulness of micromorphological data for palaeoenvironmental interpretation the micromorphological features of greatest interpretive value are types of clay coatings and ferruginous segregations structure and fabric papules evidence of bioactivity and ferruginous concretions provide information on geomorphic surface stability and assist in reconstructing temporal changes in drainage conditions while individual features can provide some palaeoenvironmental information the relationships of features to one another and assemblages of features provides additional information when analysed hierarchically to establish a sequence of sedimentologic and pedogenic events a common recurring sequence of palaeoenvironmental events subject to local variations can be recognized throughout the mill creek formation the presence of illuvial clay requires that water percolated through the soil and that the soil periodically dried out so that the translocated clay was retained dark reddish clay coatings indicate clay illuviation under freely drained conditions while pale yellow and silty clay coatings suggest that phases of free drainage alternated with phases of poorly drained or saturated soil conditions the presence of iron depletion coatings iron nodules and quasiferrans indicates that these units were at least periodically saturated and the occurrence of multiple overlapping phases within single thin sections demonstrates that redox conditions fluctuated strongly suggesting development in the vadose zone recent soils containing similar assemblages of features develop under warm temperate seasonal climates alternating phases of well drained and saturated conditions on the mill creek floodplains are attributed to changing sediment supply and local palaeogeomorphology rather than to any major regional climate change this type of process based micromorphological analysis should have broad application in other complex pedogenically modified alluvial successions and similar studies would lead to a more detailed understanding of ancient palaeoenvironments

source rock potential of lower to middle jurassic black clastic sequences of the intermontane belt1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia lower to middle jurassic clastic sequences are widespread within the interior of the canadian cordillera these successions cap waning jurassic volcanism in many cordilleran arc terranes and are succeeded by clastic sequences of the intermontane basins fine grained carbonaceous lithologies which locally contain elevated levels of organic carbon characterize these clastic successions these include sections of the spatsizi formation abou member and smithers formation in northern and western bowser basin respectively ashcroft formation and equivalent strata in central quesnellia and last creek formation and junction creek rocks below the tyaughton methow basin these rocks locally contain metre thick sections with total organic carbon toc levels 5 wt and others have thicknesses approaching 100 m with toc between 3 and 5 wt thermal maturation levels are high in many sections suggesting original organic contents were greater and that these rocks may have been excellent source beds associate

regional coalification pattern of lower cretaceous coal bearing strata rocky mountain foothills and foreland canada implications for future exploration abstract the regional coalification pattern of lower cretaceous strata in parts of the canadian foothills belt and adjacent foreland has been determined by vitrinite reflectance measurements the present study focusses on two coal bearing sequences bluesky gething and gates formation both of which contain coal resources of economic interest the vitrinite reflectances r max in the bluesky gething formation range from 0 76 high volatile a bituminous to 2 55 semianthracite rank changes from top to the base of bluesky gething formation follow 1st order regression lines factors influencing the rate of increase of r max per depth interval coalification gradient include paleogeothermal gradients the rank level under investigation conductivities of host rocks and thicknesses of coal seams time depth burial curves for the lower cretaceous bluesky gething formation suggest that the regional coalification pattern for the top of the formation results largerly from variations in the depth and or duration of burial beneath maastrichtian tertiary foredeep deposits coalification largerly predates deformation the coalification pattern is more complicated for the base of the bluesky gething formation because thickness changes in the lower cretaceous bluesky gething interval locally have a greater effect on the rank than does the regional change in the thickness of maastrichtian tertiary sedimentary wedge detailed rank studies on laterally continuous coal seams of the gates formation showed that coalification levels were largerly established before folding and thrusting started isoreflectance lines of the beds run parallel to the bedding of the folded strata seams collected from various thrust sheets exposed at surface do not in general show significant changes in vitrinite reflectances from one thrust sheet to another many of the coals of the gates formation were found to have biaxial negative reflectance in dicatrices orientation of r max is in all cases parallel of subparallel to the mactroscopic fold axes indicating preferential orientation of the aromatic lamellae in the coals in the direction of minimum compressive stress it is suggested that the occurrence of biaxial negative coals is related to a tectonic stress field that existed during the later stages of burial and subsequent deformation

organic petrography and petroleum source rock evaluation of the cretaceous mamfe formation mamfe basin southwest cameroon abstract the mamfe basin is thought to be a rift splay segment of the southern benue trough and is genetically link to the abakaliki and anambra sub basins in nigeria in the mamfe basin very little studies have been done on maceral characterization and hydrocarbon generative potential of the cretaceous black shale organic petrography and rock eval pyrolysis studies were done on the black shale outcropping in the basin the objectives were to determine the types of macerals present and their relative abundance as well as their hydrocarbon generation potential to assess the black shale s source rocks richness and quality and to evaluate the source rock thermal maturity and the relationship between maturity and hydrocarbon generation the results of this investigation indicated that the maceral content include relatively low percentages of vitrinite 4 9 inertinite 3 4 and scare liptinite 0 5 the total organic carbon of the samples vary from 0 17 to 4 53 wt mean 1 11 wt indicating poor to good source rocks generative potential while the s1 values ranges from 0 04 1 25 mg hc g rock mean 0 23 mg hc g rock indicating poor fair source rocks generation potential most of the samples are mature peak mature for gaseous hydrocarbon generation based on the organic petrography and geochemical analyses performed on the black shale samples of the mamfe formation they are described as mainly humic type iii reworked oxidized type iv kerogen the genetic potential of these source rocks is low and free hydrocarbon are absent given the prevalence of type iii iv kerogen thermal maturity levels and hydrocarbon yield it can be concluded that the source rocks of the mamfe formation have some moderate to fair potential for gaseous hydrocarbon which have not yet been generated at the present outcrop levels

rates controls and sand body geometries of transgressive regressive cycles cretaceous moosebar and gates formations british columbia the moosebar and gates formations lower cretaceous in northeastern british columbia consist of seven transgressive regressive sequence nonmarine sediments are thickest in the south and pinch out northward the sequences are laterally persistent extending east from the foothills for 240 km 150 mi the orientation of maximum transgressive and regressive limits in five cycles occurs within an east west trending zone 30 40 km 19 25 mi wide a recurring northward bulging sediment depocenter near the alberta british columbia border was fed by a series of stacked northerly flowing rivers the rivers were a major source of sediment for gravel beaches to the north and east isopach maps of marine sandstone and conglomerate show a series of west northwest east southeast o iented sand bodies 60 70 km 37 43 mi wide parallel with the shorelines each coastline prograded northward as a shoreline attached strand plain and a series of arcuate or cuspate deltas gates formation marine nonmarine cyclicity is a series of fourth order cycles superimposed on a major third order cycle the cyclicity and lateral extent of the sequences can be explained as a result of tectonic thrusting and loading superimposed on the trend of the peace river arch the influence of eustatic sea level variations and sedimentologic switching of point sources had minimal effect coastal retreat ranged from 437 to 875 m 1 000 years 1 433 to 2 780 ft 1 000 years coastal progradation ranged from 218 to 437 m 1 000 years 175 to 1 433 ft 1 000 years the duration of several transgressive regressive cycles was 103 000 275 000 years

burial history and thermal maturity rocky mountain front ranges foothills and foreland east central british columbia and adjacent alberta canada the regional pattern of maturation of cretaceous strata in the study area was determined from vitrinite reflectance measurements maturation increases from west to east across the foothills to a maximum near the eastern limit of foothills deformation and decreases farther east maturation along the eastern limit of deformation also decreases northward significantly reflectance measurements from carboniferous strata exposed in the front ranges are much lower than values from the lower cretaceous near the eastern limit of deformation modeling using burial history curves indicates the regional maturation pattern largely reflects variations in the depth and or duration of burial beneath maastrichtian eocene foredeep deposits however differential vertical movements associa ed with the peace river arch embayment in the carboniferous triassic early cretaceous and maastrichtian eocene had an important effect on the maturation pattern determined and estimated maturation levels for reservoir strata are consistent with the known occurrences of gas fields and oil pools except along the relatively unexplored western margin of the study area there moderate maturation levels indicate a potential for wet gas or oil preservation in shallow structures containing triassic and lower carboniferous carbonates in the south in the north structures in the western foothills deforming triassic strata with lower levels of maturation are breached

maturation history and thermal evolution of cretaceous source rocks of bighorn basin wyoming and montana abstract the laramide basins of the rocky mountain region are deep asymmetric structural depressions containing thick sequences of upper cretaceous and tertiary sandstone strata the combined effects of tectonics and sedimentation have contributed to the thermal evolution of the basins and to the maturation history of the source rocks in the bighorn basin of wyoming and montana total organic carbon toc values for samples from a 2 000 ft 610 m thick interval including the thermopolis mowry frontier and cody formations average 1 wt the hydrogen indices and elemental analyses suggest that most of the samples presently contain kerogen between types ii and iii the genetic potential of these samples suggests that they are moderately good source rocks vitrinite reflectan e values production indices elemental analyses and the distribution of extractable hydrocarbons suggest that these cretaceous source rocks can be within the liquid hydrocarbon window from a present day depth of 2 000 3 000 ft 610 914 m down to 11 000 12 000 ft 3 353 3 658 m on the basis of these observations plus graphical and numerical thermal models for the bighorn basin it is suggested that 1 the cretaceous section has generated hydrocarbons and could have produced the hydrocarbon production in the bighorn basin particularly from cretaceous reservoirs 2 migration distances for hydrocarbons into cretaceous reservoirs could be short 3 the stratigraphic and lateral distribution of marine sandstones intercalated within the cretaceous source rocks provide ample opportunity for stratigraphic and or diagenetic traps over a wide depth interval in this basin and 4 owing to variations in thermal gradients within this basin or similar laramide type basins the hydrocarbon liquid window is expanded over a particular stratigraphic interval with dept end of article last page 937

the organic matter distribution and methane capacity of the lower cretaceous strata of northeastern british columbia canada abstract the methane sorption capacity of a succession of sandstone siltstone shale and coal from the lower cretaceous fort st john group of northeastern british columbia was investigated average organic matter om content for all formations is 2 3 wt with a minimum of 0 6 wt and maximum of 10 1 wt the methane sorption capacity ranges between 0 19 and 2 74 cm3 g at 6 mpa and at 30 c total gas capacity free and sorbed gas ranges between 2 2 and 16 6 cm3 g at 6 mpa micropore volumes range between 0 43 and 1 69 cm3 100 g a positive correlation exists between the om content micropore volume and the methane capacity of shales shales with high methane capacities have either high contents of inertodetrinite or vitrinite moisture content shows a positive relationship with om content micropore volume and methane capacity the negative relationship between moisture and surface area derived from n2 adsorption suggests the moisture is located within the microporosity of the om and also explains the positive relationship between methane capacity and moisture the high inertodetrinite and vitrinite contents correlate with sea level regressions that delivered terrestrial om from coastal plains located south of the study area into the basin

effect of mineral matrix and seam thickness on reflectance of vitrinite in high to low volatile bituminous coals an enigma abstract the variation of vitrinite reflectance with respect to mineral matrix lithology the thickness of coal seams and coal lenses and the type of organic matter was studied from two cores in a 550 m sedimentary succession from the upper jurassic to lower cretaceous kootenay group the data obtained indicate that reflectance in high to low volatile bituminous coals ro max 0 8 1 35 with depth of burial is affected by the percentage of organic matter in the samples a positive correlation between the vitrinite reflectance and the percentage of organic matter and a negative correlation with the percentage of mineral matter exist and the thicker the coal interval the higher the vitrinite reflectance thick coal seams 1 m with a mineral content 20 vitrinite dispersed in sandstone and to a lesser extent siltstone and carbonaceous shale has the lowest reflectance variations in vitrinite reflectance may be attributed to chemical differences in the organic matter possibly induced by degradation and diagenesis syn or post depositionally and to the effect of some clay minerals present in the sediments which may act as catalysts differences in the thermal conductivity of the strata have demonstratably not accounted for the observed variations in reflectance with lithology the differences in the vitrinite reflectance of organic matter between lithotypes is substantial and is thus an important consideration in resolving the time temperature history and generation of hydrocarbons from a sedimentary succession

source rock potential and thermal maturity of lower cretaceous strata monkman pass area british columbia shale and coals from 1 2 km of core through most of the preserved lower cretaceous in western canada were analyzed for source rock potential and maturation level although much of the core lies within the oil window none of the formations are notably oil prone oxidizing bottom conditions and the large predominance of terrestrial organic matter om in the relatively nearshore depositional setting of the marine sediments have led to the dominance of terrestrial om throughout this sequence of rocks including the marine shales as such mostly gas will be or has been generated the nonmarine minnes group and gething and gates formations average 2 7 6 3 and 5 2 total organic carbon toc respectively with fair to very good gas source potential the nonmarine boulder creek formation contains 1 1 toc and has poor source rock potential due to the presence of several thick paleosols the marine moosebar hulcross and basal shaftesbury formations contain 1 5 1 7 and 1 5 average toc contents respectively and have poor to fair source rock potential these marine sediments which may have generated limited amounts of oil show a progressive decrease of hydrogen index hi with depth due to thermal degradation with increased burial hi for nonmarine sediments remains constant with depth the marine sediments contain mostly type iii kerogen with lesser amounts of thermally degraded type ii kerogen vitrinite reflectance increases systematically with depth from 0 94 to 1 5 romax tmax values correspond well with vitr nite reflectance although tmax values for marine sediments increase more slowly with increasing maturation than nonmarine sediments

recent advances in the geology of koffiefontein mine free state province south africa abstract the complex internal geology of the koffiefontein pipe has contributed to the marginal nature of the mine the key to this is the presence of a large zone dominated by down rafted country rock karoo sediment and dolerite xenoliths recent work indicates that the kimberlite pipe at koffiefontein consists of precursor dykes the west and east fissures and the main pipe in which two main eruptive phases have been recognized groundmass spinel compositions have been used to provide a chemical fingerprint of each lithology there is evidence for at least three magma batches each with its own chemical signature cross cutting contact relationships were used to determine the emplacement sequence the characterization of the different internal geological units permitted the development of a three dimensional 3d model of the pipe both main eruptive phases viz the speckled west kimberlite and the speckled east kimberlite comprise volcaniclastic kimberlite they are separated by a large irregular mass of kimberlite that contains abundant country rock xenoliths comprising varying proportions of karoo mudstone and dolerite as well as probable bedded crater facies fragments this zone of contamination dilutes the grade of the kimberlites affects the geotechnical stability and adversely affects the economics of the mine

tertiary metallogenesis in the eastern alps the waldenstein hematite deposit austria the specularite deposit at waldenstein is an epigenetic replacement vein type hematite mineralization with distinct alteration zones it is situated in highly metamorphosed schists and gneisses of the koralm crystalline complex sericitization and chloritization are strictly bound to this alteration and occur within a few meters of the hematite veins radiometric dating of the sericitization and the implicity of the mineralization yield a middle eocene age petrographic evidence proves an early relatively reduced paragenesis magnetite ilmenite being partly replaced by hematite and chlorite during the main phase of ore formation fluid inclusion and stable isotope investigations indicate that formation temperatures were approximately 300 c during the main stage and decreased to 200 c in the latest stage of the hydrothermal event the h isotope compositions of chlorites and of fluid inclusions in quartz indicate the influence of seawater this also explains the high salinities determined by fluid inclusion studies 20 30 nacl equiv according to the genetic model presented in this paper the hydrothermal activity started when the deformation accompanying the uplift of the koralm crystalline complex passed from a ductile to brittle regime middle eocene the brittle faults acted as channelways for rising deep fluids probably of metamorphic origin temperature differences between the different uplifting crustal segments supported fluid circulation precipitation of the ore occurred at shallow crustal levels where the hydraulic regime was dominated by seawater and oxidation of the original reducing fluids took place

geochemical characteristics of lower cretaceous lacustrine organic matter in the southern sag of the wuliyasitai depression erlian basin china abstract the wuliyasitai southern sag is an oil rich area in the erlian basin the geochemical characteristics of the organic matter were comprehensively analyzed by a combined investigation of rock eval pyrolysis molecular geochemistry vitrinite reflectance and thin section observation the studied samples have vitrinite reflectance ro values of 0 33 1 22 and pyrolysis parameter tmax values of 424 456 c suggesting that organic matter is mainly present in the low mature to mature stage the values of the abundance indicators including total organic carbon toc chloroform bitumen a potential hydrocarbon generation amount pg hydrogen index hi and total hydrocarbon hc suggest a good to very good hydrocarbon generation potential the pyrolysis parameter tmax and hi obtained imply that the samples are dominated by the type 1 2 organic matter the composition characteristics of n alkanes steranes and terpanes confirm that the organic matter has mixed input sources the aershan formation k1ba in the southeastern part of the sag show higher contributions of algae and bacteria due to fertilization by volcanic ash the hydrocarbon generation threshold was determined from the hydrocarbon index hci production index pi chloroform bitumen a toc and hc toc by analyzing the relationships between toc and pyrolysis parameter hci chloroform bitumen a toc the lower limits of the toc values for effective source rocks were established to be 2 5 wt in the k1bt1 and 1 5 wt in the k1ba the pristane phytane pr ph gammacerane c31 22r hopane c35 c34 homohopane and trace element ratios suggest that the source rocks are primarily deposited in a freshwater sub oxidizing environment the toc and hi are negatively correlated with pr ph indicating that redox conditions play an important role in source rock preservation most molecular maturity parameters are not recommended owing to their poor correlations with ro

an anoxic event at the albian cenomanian boundary the fish scale marker bed northern alberta canada abstract the fish scale marker bed fsmb of the shaftesbury formation which marks the albian cenomanian boundary is a regional stratigraphic marker in the western interior of canada at the outcrop studied on the smoky river in northwestern alberta three major shale units can be distinguished in the fsmb and contiguous strata the lowermost shale unit 1 is bioturbated and contains high diversity dinoflagellate and moderate diversity foraminiferal assemblages it has dominantly type iii terrestrial organic matter om and low total organic carbon content toc the unit was deposited in an open marine neritic environment of normal salinity the fsmb unit 2 represents a zone of condensed bioclastic accumulation composed of abundant fish remains the dinoflagellate species diversity is drastically reduced in this unit and it lacks benthonic foraminifera and bioturbation unit 2 is characterized by mainly type ii marine om and high toc values unit 2a contains rippled sandstone related to either a shallowing or to deeper water currents a fish hash conglomerate making up unit 2b can alternatively be interpreted as a bioclastic condensed and winnowed deposit or as a transgressive lag unit 2c consists of black platy shale with abundant fish remains and represents a minor marine trangression during the deposition of fsmb when the bottom waters were dominantly anoxic collectively the features of unit 2 suggest deposition under a stratified water column with moderate productivity of planktonic and nektonic organisms in the upper oxygenated layers but with anoxic bottom waters unit 3 overlying the fsmb consists of blocky shale with reduced concentration of fish remains due to increased rate sedimentation during its deposition the organic rich sediment of unit 3 was progressively diluted by clastic material and there was an increase in the dissolved oxygen content of the bottom waters the anoxic event at the fsmb is related to a relative rise in sea level and possibly to the mixing of waters different salinities and temperatures from the arctic ocean and the gulf of mexico in the western interior seaway